publicationDate,title,abstract,id
2010-07-28,Current-induced torques in the presence of spin-orbit coupling,"In systems with strong spin-orbit coupling, the relationship between
spin-transfer torque and the divergence of the spin current is generalized to a
relation between spin transfer torques, total angular momentum current, and
mechanical torques. In ferromagnetic semiconductors, where the spin-orbit
coupling is large, these considerations modify the behavior of the spin
transfer torques. One example is a persistent spin transfer torque in a spin
valve: the spin transfer torque does not decay away from the interface, but
approaches a constant value. A second example is a mechanical torque at single
ferromagnetic-nonmagnetic interface.",1007.5037v1
2022-08-20,Field theoretical approach to spin torques: Slonczewski torques,"The quantum field theoretical approach with the Kubo formula has successfully
captured spin torques, such as spin-transfer torques and spin-orbit torques,
for continuum systems. We examine the field theoretical approach to
current-induced spin-transfer torques in a magnetic junction system. We first
give a brief overview of the field theoretical approach to spin torques. Then,
we consider a five-layers system consisting of three nonmagnetic metal layers
separated by two ferromagnetic metal layers and apply an electric field
perpendicular to the layers. We demonstrate that the Slonczewski-type
spin-transfer torque, or shortly the Slonczewski torque, on the magnetizations
in ferromagnetic layers is obtained by evaluating nonequilibrium electron spin
density, based on the linear response theory with the Green function method.
The obtained coefficient of the Slonczewski torque has a quantum oscillation at
absolute zero temperature, which has not been mentioned before. A field-like
torque accompanied by the Slonczewski torque is also evaluated.",2208.09581v1
2009-02-24,Theory of spin accumulation and spin transfer torque in a magnetic domain wall,"We study spin accumulation and spin transfer torque in a domain wall by
solving the Boltzmann equation with a diffusion approximation. We obtained the
analytical expressions of spin accumulation and spin transfer torque. Both the
adiabatic and the non-adiabatic components of the spin transfer torque
oscillate with the thickness of the domain wall. We show that the oscillation
plays a dominant role in the non-adiabatic torque when the domain wall
thickness is less than the spin-flip length, which is defined by the product of
the Fermi velocity and the spin-flip scattering time.",0902.4094v2
2008-12-13,Spin-Transfer Torque in Helical Spin-Density Waves,"The current driven magnetisation dynamics of a helical spin-density wave is
investigated. Expressions for calculating the spin-transfer torque of real
systems from first principles density functional theory are presented. These
expressions are used for calculating the spin-transfer torque for the spin
spirals of Er and fcc Fe at two different lattice volumes. It is shown that the
calculated torque induces a rigid rotation of the order parameter with respect
to the spin spiral axis. The torque is found to depend on the wave vector of
the spin spiral and the spin-polarisation of the Fermi surface states. The
resulting dynamics of the spin spiral is also discussed.",0812.2509v1
2018-08-25,Resonance spin transfer torque in ferromagnetic/normal/ferromagnetic spin-valve structure of topological insulators,"We theoretically study the spin current and spin-transfer torque generation
in a conventional spin- valve hybrid structure of type ferromagnetic/normal
metal/ferromagnetic (FM/NM/FM) made of the topological insulator (TI), in which
a gate voltage is attached to the normal layer. We demonstrate the penetration
of the spin-transfer torque into the right ferromagnetic layer and show that,
unlike graphene spin-valve junction, the spin-transfer torque in TI is very
sensitive to the chemical potential of the NM region. As an important result,
by changing the chemical potential of the NM spacer and magnetization
directions, one can control all components of the STT. Interestingly, both the
resonance spin current and the resonance spin-transfer torque appear for
energies determined from a resonance equation. By increasing the chemical
potential of the NM spacer, the amplitude of the STTs decreases while at large
chemical potentials of $\mu_N$ there are intervals of chemical potential in
which both the spin current and the spin-transfer torque become zero. These
findings could open new perspectives for applications in spin-transfer torque
magnetic random access memory (STT-MRAM) devices based on TI.",1808.08379v1
2017-02-16,Microscopic theory of electrically induced spin torques in magnetic Weyl semimetals,"We theoretically study electrical responses of magnetization in Weyl
semimetals. The Weyl semimetal is a new class of topological semimetals,
possessing hedgehog type spin textures in momentum space. Because of this
peculiar spin texture, an interplay of electron transport and spin dynamics
might provide new method to electrical control of magnetization. In this paper,
we consider the magnetically doped Weyl semimetals, and systematically study
current- and charge-induced spin torque exerted on the local magnetization in
three-dimensional Dirac-Weyl metals. We determine all current-induced spin
torques including spin-orbit torque, spin-transfer torque, and the so-called
$\beta$-term, up to first order with respect to spatial and temporal derivation
and electrical currents. We find that spin-transfer torque and $\beta$-term are
absent while spin-orbit torque is proportional to the axial current density. We
also calculate the charge-induced spin torque microscopically. We find the
charge-induced spin torque originates from the chiral anomaly due to the
correspondence between spin operators and axial current operators in our model.",1702.04918v1
2017-01-12,Optical spin transfer and spin-orbit torques in thin film ferromagnets,"We study the optically induced torques in thin film ferromagnetic layers
under excitation by circularly polarized light. We study cases both with and
without Rashba spin-orbit coupling using a 4-band model. In the absence of
Rashba spin-orbit coupling, we derive an analytic expression for the optical
torques, revealing the conditions under which the torque is mostly derived from
optical spin transfer torque (i.e. when the torque is along the direction of
optical angular momentum), versus when the torque is derived from the inverse
Faraday effect (i.e. when the torque is perpendicular to the optical angular
momentum). We find the optical spin transfer torque dominates provided that the
excitation energy is far away from band edge transitions, and the magnetic
exchange splitting is much greater than the lifetime broadening. For the case
with large Rashba spin-orbit coupling and out-of-plane magnetization, we find
the torque is generally perpendicular to the photon angular momentum and is
ascribed to an optical Edelstein effect.",1701.03495v2
2022-07-25,Spin-transfer and spin-orbit torques in the Landau-Lifshitz-Gilbert equation,"Dynamic simulations of spin-transfer and spin-orbit torques are increasingly
important for a wide range of spintronic devices including magnetic random
access memory, spin-torque nano-oscillators and electrical switching of
antiferromagnets. Here we present a computationally efficient method for the
implementation of spin-transfer and spin-orbit torques within the
Landau-Lifshitz-Gilbert equation used in micromagnetic and atomistic
simulations. We consolidate and simplify the varying terminology of different
kinds of torques into a physical action and physical origin that clearly shows
the common action of spin torques while separating their different physical
origins. Our formalism introduces the spin torque as an effective magnetic
field, greatly simplifying the numerical implementation and aiding the
interpretation of results. The strength of the effective spin torque field
unifies the action of the spin torque and subsumes the details of experimental
effects such as interface resistance and spin Hall angle into a simple
transferable number between numerical simulations. We present a series of
numerical tests demonstrating the mechanics of generalised spin torques in a
range of spintronic devices. This revised approach to modelling spin-torque
effects in numerical simulations enables faster simulations and a more direct
way of interpreting the results, and thus it is also suitable to be used in
direct comparisons with experimental measurements or in a modelling tool that
takes experimental values as input.",2207.12071v2
2004-10-20,Spin-Transfer Torque and Electron-Magnon Scattering,"According to the spin-torque model, current-driven magnetic dynamics in
ferromagnetic multilayers is determined by the transfer of electron spin
perpendicular to the layers' magnetizations. By separating the largest
contributions to the magnetic dynamics, we demonstrate that the dominant effect
of spin-torque is rather due to the electron spin parallel to the field. We
show that this effect can be equivalently described as stimulated
current-driven excitation of spin-waves, and discuss four specifically
quantum-mechanical aspects of spin-transfer, not described by the spin-torque.",0410520v1
2012-06-17,Spin Transfer Torque in Fully Insulating Magnetic Tunnel Junctions,"Voltage-driven spin transfer torque in a magnetic tunnel junction comprising
magnetic insulating electrodes is studied theoretically. In contrast with the
conventional magnetic tunnel junctions comprising transition metal
ferromagnets, the spin transfer torque presents unconventional bias
dependencies, related to the presence of spin-dependent Fowler-Nordheim
tunneling processes. In particular, we find that (i) the out-of-plane torque
generally dominates the in-plane torque, (ii) out-of-plane torque and in-plane
torque are symmetric and asymmetric at low bias voltage, respectively, and
(iii) both of torques show a dramatic enhancement at large bias voltage.
Materials consideration are discussed and we show that due to the low damping
parameter expected in magnetic insulators a spin transfer torque can be
experimentally observed in such systems.",1206.3743v1
2013-11-13,A new route to spin-orbit torque engineering via oxygen manipulation,"Spin transfer torques allow for electrical manipulation of magnetization at
room temperature, which is utilized to build future electronic devices such as
spin transfer torque memories. Recent experiments have discovered that the
combination of the spin transfer torque with the spin Hall effect enables more
efficient manipulation. A versatile control mechanism of such spin-orbit
torques is beneficial to envision device applications with competitive
advantages over the existing schemes. Here we report that the oxidation
manipulation of spin-orbit torque devices triggers a new mechanism, and the
resulting torques are estimated to be about two times stronger than that of the
spin Hall effect. Our result introduces an entirely new way to engineer the
spin-orbit torques for device operation via oxygen manipulation. Combined with
electrical gating for the control of the oxygen content, our finding may also
pave the way for towards reconfigurable logic devices.",1311.3032v1
2015-11-23,Nonlocal spin torques in Rashba quantum wires with steep magnetic textures,"We provide a general procedure to calculate the current-induced spin-transfer
torque which acts on a general steep magnetic texture due to the exchange
interaction with an applied spin-polarized current. As an example, we consider
a one-dimensional ferromagnetic quantum wire and also include a Rashba
spin-orbit interaction. The spin-transfer torque becomes generally spatially
non-local. Likewise, the Rashba spin-orbit interaction induces a spatially
nonlocal field-like nonequilibrium spin-transfer torque. We also find a
spatially varying nonadiabaticity parameter and markedly different domain wall
dynamics for very steep textures as compared to wide domain walls.",1511.07264v1
2023-11-18,Thermal Spin Orbit Torque with Dresselhaus Spin Orbit Coupling,"Based on the spinor Boltzmann equation, we obtain a temperature dependent
thermal spin-orbit torque in terms of the local equilibrium distribution
function in a two dimensional ferromagnet with Dresselhaus spin-orbit coupling.
We also derive the continuity equation of spin accumulation and spin current,
the spin diffusion equation in Dresselhaus ferromagnet, which contains the
thermal spin orbit torque under local equilibrium assumption. This temperature
dependent thermal spin-orbit torque originates from the temperature gradient
applied to the system. it is also sensitive to temperature due to the local
equilibrium distribution function therein. In the spin diffusion equation, we
can single out the usual spin-orbit torque as well as the spin transfer torque,
which is conceded to our previous results. Finally, we illustrate them by an
example of spin-polarized transport through a ferromagnet with Dresselhaus
spin-orbit coupling driven by temperature gradient, those torques including
thermal spin-orbit torque are demonstrated numerically.",2311.14719v1
2015-11-28,Spin-orbit torque engineering via oxygen manipulation,"Spin transfer torques allow the electrical manipulation of the magnetization
at room temperature, which is desirable in spintronic devices such as spin
transfer torque memories. When combined with spin-orbit coupling, they give
rise to spin-orbit torques which are a more powerful tool for magnetization
control and can enrich device functionalities. The engineering of spin-orbit
torques, based mostly on the spin Hall effect, is being intensely pursued. Here
we report that the oxidation of spin-orbit torque devices triggers a new
mechanism of spin-orbit torque, which is about two times stronger than that
based on the spin Hall effect. We thus introduce a way to engineer spin-orbit
torques via oxygen manipulation. Combined with electrical gating of the oxygen
level, our findings may also pave the way towards reconfigurable logic devices.",1511.08868v1
2017-09-01,Scaling of the Rashba spin-orbit torque in magnetic domain walls,"Spin-orbit torque in magnetic domain walls was investigated by solving the
Pauli-Schr\""{o}dinger equation for the itinerant electrons. The Rashba
interaction considered is derived from the violation of inversion symmetry at
interfaces between ferromagnets and heavy metals. In equilibrium, the Rashba
spin-orbit interaction gives rise to a torque corresponding to the
Dzyaloshinskii-Moriya interaction. When there is a current flowing, the
spin-orbit torque experienced by the itinerant electrons in short domain walls
has both field-like and damping-like components. However, when the domain wall
width is increased, the damping-like component, which is the counterpart of the
non-adiabatic spin transfer torque, decreases rapidly at the domain wall
center. In contrast to the non-adiabatic spin transfer torque, the damping-like
spin-orbit torque does not approach to zero far away from the domain wall
center, even in the adiabatic limit. The scattering of spin-up and spin-down
wave functions, which is caused by the Rashba spin-orbit interaction and the
spatial variation of magnetization profile in the domain wall, gives rise to
the finite damping-like spin-orbit torque.",1709.00187v3
2020-09-06,Adiabatic and Nonadiabatic Spin-transfer Torques in Antiferromagnets,"Electron transport in magnetic orders and the magnetic orders dynamics have a
mutual dependence, which provides the key mechanisms in spin-dependent
phenomena. Recently, antiferromagnetic orders are focused on as the magnetic
order, where current-induced spin-transfer torques, a typical effect of
electron transport on the magnetic order, have been debatable mainly because of
the lack of an analytic derivation based on quantum field theory. Here, we
construct the microscopic theory of spin-transfer torques on the slowly-varying
staggered magnetization in antiferromagnets with weak canting. In our theory,
the electron is captured by bonding/antibonding states, each of which is the
eigenstate of the system, doubly degenerates, and spatially spreads to
sublattices because of electron hopping. The spin of the eigenstates depends on
the momentum in general, and a nontrivial spin-momentum locking arises for the
case with no site inversion symmetry, without considering any spin-orbit
couplings. The spin current of the eigenstates includes an anomalous component
proportional to a kind of gauge field defined by derivatives in momentum space
and induces the adiabatic spin-transfer torques on the magnetization.
Unexpectedly, we find that one of the nonadiabatic torques has the same form as
the adiabatic spin-transfer torque, while the obtained forms for the adiabatic
and nonadiabatic spin-transfer torques agree with the phenomenological
derivation based on the symmetry consideration. This finding suggests that the
conventional explanation for the spin-transfer torques in antiferromagnets
should be changed. Our microscopic theory provides a fundamental understanding
of spin-related physics in antiferromagnets.",2009.02686v1
2011-06-06,Metastable state in a shape-anisotropic single-domain nanomagnet subjected to spin-transfer-torque,"We predict the existence of a new metastable magnetization state in a
single-domain nanomagnet with uniaxial shape anisotropy. It emerges when a
spin-polarized current, delivering a spin-transfer-torque, is injected into the
nanomagnet. It can trap the magnetization vector and prevent
spin-transfer-torque from switching the magnetization from one stable state
along the easy axis to the other. Above a certain threshold current, the
metastable state no longer appears. This has important technological
consequences for spin-transfer-torque based magnetic memory and logic systems.",1106.1215v2
2021-09-03,Robust spin-transfer torque and magnetoresistance in non-collinear antiferromagnetic junctions,"Ferromagnetic spin-valves and tunneling junctions are crucial for spintronics
applications and are one of the most fundamental spintronics devices. Motivated
by the potential unique advantages of antiferromagnets for spintronics, we
theoretically study here junctions built out of non-collinear antiferromagnets.
We demonstrate a large and robust magnetoresistance and spin-transfer torque
capable of ultrafast switching between parallel and anti-parallel states of the
junction. In addition, we show that the non-collinear order results in a
spin-transfer torque that is in several key aspects different from the
spin-transfer torque in ferromagnetic junctions.",2109.01399v1
2012-04-23,Spin Transfer Torque with Spin Diffusion in Magnetic Tunnel Junctions,"Spin transport in magnetic tunnel junctions in the presence of spin diffusion
is considered theoretically. Combining ballistic tunneling across the barrier
and diffusive transport in the electrodes, we solve the spin dynamics equation
in the metallic layers. We show that spin diffusion mixes the transverse spin
current components and dramatically modifies the bias dependence of the
effective spin transfer torque. This leads to a significant linear bias
dependence of the out-of-plane torque, as well as a non-conventional thickness
dependence of both spin torque components.",1204.5000v2
2007-12-01,Description of current-driven torques in magnetic tunnel junctions,"A free electron description of spin-dependent tranport in magnetic tunnel
junctions with non collinear magnetizations is presented. We investigate the
origin of transverse spin density in tunnelling transport and the quantum
interferences which give rise to oscillatory torques on the local
magnetization. Spin transfer torque is also analyzed and an important bias
asymmetry is found as well as a damped oscillatory behaviour. Furthermore, we
investigate the influence of the s-d exchange coupling on torque in particular
in the case of half-metallic MTJ in which the spin transfer torque is due to
interfacial spin-dependent reflections.",0712.0055v1
2009-02-12,Correlation of the angular dependence of spin-transfer torque and giant magnetoresistance in the limit of diffusive transport in spin valves,"Angular variation of giant magnetoresistance and spin-transfer torque in
metallic spin-valve heterostructures is analyzed theoretically in the limit of
diffusive transport. It is shown that the spin-transfer torque in asymmetric
spin valves can vanish in non-collinear magnetic configurations, and such a
non-standard behavior of the torque is generally associated with a
non-monotonic angular dependence of the giant magnetoresistance, with a global
minimum at a non-collinear magnetic configuration.",0902.2208v1
2014-09-19,Angular dependence of spin-orbit spin transfer torques,"In ferromagnet/heavy metal bilayers, an in-plane current gives rise to
spin-orbit spin transfer torque which is usually decomposed into field-like and
damping-like torques. For two-dimensional free-electron and tight-binding
models with Rashba spin-orbit coupling, the field-like torque acquires
nontrivial dependence on the magnetization direction when the Rashba spin-orbit
coupling becomes comparable to the exchange interaction. This nontrivial
angular dependence of the field-like torque is related to the Fermi surface
distortion, determined by the ratio of the Rashba spin-orbit coupling to the
exchange interaction. On the other hand, the damping-like torque acquires
nontrivial angular dependence when the Rashba spin-orbit coupling is comparable
to or stronger than the exchange interaction. It is related to the combined
effects of the Fermi surface distortion and the Fermi sea contribution. The
angular dependence is consistent with experimental observations and can be
important to understand magnetization dynamics induced by spin-orbit spin
transfer torques",1409.5600v1
2010-10-08,Time-resolved detection of spin-transfer-driven ferromagnetic resonance and spin torque measurement in magnetic tunnel junctions,"Several experimental techniques have been introduced in recent years in
attempts to measure spin transfer torque in magnetic tunnel junctions (MTJs).
The dependence of spin torque on bias is important for understanding
fundamental spin physics in magnetic devices and for applications. However,
previous techniques have provided only indirect measures of the torque and
their results to date for the bias dependence are qualitatively and
quantitatively inconsistent. Here we demonstrate that spin torque in MTJs can
be measured directly by using time-domain techniques to detect resonant
magnetic precession in response to an oscillating spin torque. The technique is
accurate in the high-bias regime relevant for applications, and because it
detects directly small-angle linear-response magnetic dynamics caused by spin
torque it is relatively immune to artifacts affecting competing techniques. At
high bias we find that the spin torque vector differs markedly from the simple
lowest-order Taylor series approximations commonly assumed.",1010.1777v1
2012-07-22,Manipulating the Voltage Dependence of Tunneling Spin Torques,"Voltage-driven spin transfer torques in magnetic tunnel junctions provide an
outstanding tool to design advanced spin-based devices for memory and
reprogrammable logic applications. The non-linear voltage dependence of the
torque has a direct impact on current-driven magnetization dynamics and on
devices performances. After a brief overview of the progress made to date in
the theoretical description of the spin torque in tunnel junctions, I present
different ways to alter and control the bias dependence of both components of
the spin torque. Engineering the junction (barrier and electrodes) structural
asymmetries or controlling the spin accumulation profile in the free layer
offer promising tools to design efficient spin devices.",1207.5231v1
2010-07-29,Magnetic domain walls displacement : automotion vs. spin-transfer torque,"The magnetization dynamics equation predicts that a domain wall that changes
structure should undergo a displacement by itself - automotion - due to the
relaxation of the linear momentum that is associated with the wall structure.
We experimentally demonstrate this effect in soft nanostrips,transforming under
spin transfer torque a metastable asymmetric transverse wall into a vortex
wall. Displacements more than three times as large as under spin transfer
torque only are measured for 1~ns pulses. The results are explained by
analytical and numerical micromagnetics. Their relevance to domain wall motion
under spin transfer torque is emphasized.",1007.5233v1
2005-01-08,A Spin-Mechanical Device for Detection and Control of Spin Current by Nanomechanical Torque,"We propose a spin-mechanical device to control and detect spin currents by
mechanical torque. Our hybrid nano-electro-mechanical device, which contains a
nanowire with a ferromagnetic-nonmagnetic interface, is designed to measure or
induce spin polarized currents. Since spin carries angular momentum, a spin
flip or spin transfer process involves a change in angular momentum--and hence,
a torque--which enables mechanical measurement of spin flips. Conversely, an
applied torque can result in spin polarization and spin current.",0501162v1
2018-10-17,Unified theory of magnetization dynamics with relativistic and nonrelativistic spin torques,"Spin torques play a crucial role in operative properties of modern spintronic
devices. To study current-driven magnetization dynamics, spin-torque terms
providing the action of spin-polarized currents have previously often been
added in a phenomenological way to the Landau-Lifshitz-Gilbert equation
describing the local spin dynamics, yet without derivation from fundamental
principles. Here, starting from the Dirac-Kohn-Sham theory and incorporating
nonlocal spin transport we rigorously derive the various spin-torque terms that
appear in current-driven magnetization dynamics. In particular we obtain an
extended magnetization dynamics equation that precisely contains the
nonrelativistic adiabatic and relativistic nonadiabatic spin-transfer torques
(STTs) of the Berger and Zhang-Li forms as well as relativistic spin-orbit
torques (SOTs). We derive in addition a previously unnoticed relativistic
spin-torque term and moreover show that the various obtained spin-torque terms
do not appear in the same mathematical form in both the Landau-Lifshitz and
Landau-Lifshitz-Gilbert equations of spin dynamics.",1810.07438v1
2009-12-18,Stochastic resonance of a nanomagnet excited by spin transfer torque,"Spin transfer torque from spin-polarized electrical current can excite
large-amplitude magnetization dynamics in metallic ferromagnets of nanoscale
dimensions. Since magnetic anisotropy energies of nanomagnets are comparable to
the thermal energy scale, temperature can have a profound effect on the
dynamics of a nanomagnet driven by spin transfer torque. Here we report the
observation of unusual types of microwave-frequency nonlinear magnetization
dynamics co-excited by alternating spin transfer torque and thermal
fluctuations. In these dynamics, temperature amplifies the amplitude of
GHz-range precession of magnetization and enables excitation of highly
nonlinear dynamical states of magnetization by weak alternating spin transfer
torque. We explain these thermally activated dynamics in terms of non-adiabatic
stochastic resonance of magnetization driven by spin transfer torque. This type
of magnetic stochastic resonance may find use in sensitive nanometer-scale
microwave signal detectors.",0912.3842v1
2021-06-15,Collective skyrmion motion under the influence of an additional interfacial spin-transfer torque,"Here we study the effect of an additional interfacial spin-transfer torque,
as well as the well established spin-orbit torque and bulk spin-transfer
torque, on skyrmion collections - group of skyrmions dense enough that they are
not isolated from on another - in ultrathin heavy metal / ferromagnetic
multilayers, by comparing modelling with experimental results. Using a skyrmion
collection with a range of skyrmion diameters and landscape disorder, we study
the dependence of the skyrmion Hall angle on diameter and velocity, as well as
the velocity as a function of diameter. We show the experimental results are in
good agreement with modelling when including the interfacial spin-transfer
torque, and cannot be reproduced by using the spin-orbit torque alone. We also
show that for skyrmion collections the velocity is approximately independent of
diameter, in marked contrast to the motion of isolated skyrmions, as the group
of skyrmions move together at an average group velocity. Moreover, the
calculated skyrmion velocities are comparable to those obtained in experiments
when the interfacial spin-transfer torque in included, whilst modelling using
the spin-orbit torque alone shows large discrepancies with the experimental
data. Our results thus show the significance of the interfacial spin-transfer
torque in ultrathin magnetic multilayers, which is of similar strength to the
spin-orbit torque, and both significantly larger than the bulk spin-transfer
torque. Due to the good agreement with experiments, we conclude that the
interfacial spin-transfer torque should be included in numerical modelling for
correct reproduction of experimental results.",2106.08046v3
2018-06-16,Field-free switching of perpendicular magnetic tunnel junction by the interplay of spin orbit and spin transfer torques,"Spin-orbit torque and spin-transfer torque are leading the pathway to the
future of spintronic memories. However, both of the mechanisms are suffering
from intrinsic limitations. In particular, an external magnetic field is
required for spin-orbit torque to execute deterministic switching in
perpendicular magnetic tunnel junctions; the demand for reduced spin-transfer
torque switching current to realize ultralow power is still remaining. Thus, a
more advanced switching mechanism is urgently needed to move forward
spintronics for wide applications. Here, we experimentally demonstrate the
field-free switching of three-terminal perpendicular-anisotropy nanopillar
devices through the interaction between spin-orbit and spin-transfer torques.
The threshold current density of spin-transfer torque switching is reduced to
0.94 MA.cm-2, which is a significant decrease compared to that in other
current-induced magnetization switching mechanisms. In addition, thanks to the
interplay of spin-orbit and spin-transfer torques, lower current-induced
switching in the conventional two-terminal perpendicular magnetic tunnel
junctions is also achieved.",1806.06174v1
2012-02-04,Non-equilibrium spatial distribution of Rashba spin torque in ferromagnetic metal layer,"We study the spatial distribution of spin torque induced by a strong Rashba
spin-orbit coupling (RSOC) in a ferromagnetic (FM) metal layer, using the
Keldysh non-equilibrium Green's function method. In the presence of the s-d
interaction between the non-equilibrium conduction electrons and the local
magnetic moments, the RSOC effect induces a torque on the moments, which we
term as the Rashba spin torque.
  A correlation between the Rashba spin torque and the spatial spin current is
presented in this work, clearly mapping the spatial distribution of Rashba Spin
torque in a nano-sized ferromagnetic device. When local magnetism is turned on,
the out-of-plane (Sz) Spin Hall effect (SHE) is disrupted, but rather
unexpectedly an in-plane (Sy) SHE is detected. We also study the effect of
Rashba strength (\alpha_R) and splitting exchange (\Delta) on the
non-equilibrium Rashba spin torque averaged over the device. Rashba spin torque
allows an efficient transfer of spin momentum such that a typical switching
field of 20 mT can be attained with a low current density of less than 10^6
A/cm^2.",1202.0890v2
2018-02-28,Effect of exchange-correlation spin-torque on spin dynamics,"A recently proposed exchange-correlation functional (Dewhurst et al.
10.1021/acs.jctc.7b01049) with in density functional theory, which ensures that
the exchange-correlation magnetic field is source-free, is shown to give
non-zero internal spin-torque. This spin-torque is identically zero for all
conventional local and semi-local functionals. Extension of this source-free
functional to the time domain is used to study the effect of the internal
spin-torque on the laser induced spin-dynamics in bulk Co, Ni and interfaces of
these metals with Pt. It is shown that the internal spin-torque contribute
significantly to spin-dynamics only when the magneto crystalline anisotropy
energy is small, as in the case of cubic bulk materials. For surfaces or
interfaces, where the anisotropy energy is large, these torques are too small
to cause any significant precession of spins in early times ($<$ 100fs).
Further more it is shown that the spin-dynamics caused by the internal
spin-torque is slow compared to the inter-site spin transfer and spin-orbit
mediated spin-flips.",1802.10382v1
2019-03-03,Theory for spin torque in Weyl semimetal with magnetic texture,"The spin-transfer torque is a fundamental physical quantity to operate the
spintronics devices such as racetrack memory. We theoretically study the
spin-transfer torque and analyze the dynamics of the magnetic domain walls in
magnetic Weyl semimetals. Owing to the strong spin-orbit coupling in Weyl
semimetals, the spin-transfer torque can be significantly enhanced, because of
which they can provide a more efficient means of controlling magnetic textures.
We derive the analytical expression of the spin-transfer torque and find that
the velocity of the domain wall is one order of magnitude greater than that of
conventional ferromagnetic metals. Furthermore, due to the suppression of
longitudinal conductivity in the thin domain-wall configuration, the
dissipation due to Joule heating for the spin-transfer torque becomes much
smaller than that in bulk metallic ferromagnets. Consequently, the fast-control
of the domain wall can be achieved with smaller dissipation from Joule heating
in the Weyl semimetals as required for application to low-energy-consumption
spintronics devices.",1903.00849v1
2020-05-06,Sub-Nanosecond Spin-Transfer Torque in an Ensemble of Superparamagnetic-Like Nanomagnets,"Spin currents can exert spin-transfer torques on magnetic systems even in the
limit of vanishingly small net magnetization, as is the case for
antiferromagnets. Here, we experimentally show that a spin-transfer torque is
operative in a material with weak, short-range magnetic order -- namely, a
macroscopic ensemble of superparamagnetic-like Co nanomagnets. We employ
element- and time-resolved X-ray ferromagnetic resonance (XFMR) spectroscopy to
directly detect sub-ns dynamics of the Co nanomagnets, excited into precession
with cone angle $\geq$0.003$^{\circ}$ by an oscillating spin current. XFMR
measurements reveal that as the net moment of the ensemble decreases, the
strength of the spin-transfer torque increases relative to those of magnetic
field torques. Our findings point to spin-transfer torque as an effective way
to manipulate the state of nanomagnet ensembles at sub-ns timescales.",2005.03081v1
2014-03-24,Spin Transfer Torque in Antiferromagnetic Spin-Valves: From Clean to Disordered Regimes,"Current-driven spin torques in metallic spin-valves composed of
antiferromagnets are theoretically studied using the non-equilibrium Green's
function method implemented on a tight-binding model. We focus our attention on
G-type and L-type antiferromagnets in both clean and disordered regimes. In
such structures, spin torques can either rotate the magnetic order parameter
coherently (coherent torque) or compete with the internal antiferromagnetic
exchange (exchange torque). We show that, depending on the symmetry of the
spin-valve, the coherent and exchange torques can be either in the plane,
{\alpha} n\times(q \times n) or out of the plane {\alpha} n \times q, where q
and n are the directions of the order parameter of the polarizer and the free
antiferromagnetic layers, respectively. Although disorder conserves the
symmetry of the torques, it strongly reduces the torque magnitude, pointing out
the need for momentum conservation to ensure strong spin torque in
antiferromagnetic spin-valves",1403.6383v2
2020-05-03,Unconventional spin-orbit torque in transition metal dichalcogenide/ferromagnet bilayers from first-principles calculations,"Motivated by recent observations of unconventional out-of-plane dampinglike
torque in \ch{WTe2}/Permalloy bilayer systems, we calculate the spin-orbit
torque generated in two-dimensional transition metal dichalcogenide
(TMD)-ferromagnet heterostructures using first-principles methods and linear
response theory. Our numerical calculation of spin-orbit torques in
\ch{WTe2}/Co and \ch{MoTe2}/Co heterostructures shows both conventional and
novel dampinglike torkances (torque per electric field) with comparable
magnitude, around $100~\hbar/2e~(\rm \Omega\cdot cm)^{-1}$, for an electric
field applied perpendicular to the mirror plane of the TMD layer. To gain
further insight into the source of dampinglike torque, we compute the spin
current flux between the TMD and Co layers and find good agreement between the
two quantities. This indicates that the conventional picture of dampinglike
spin-orbit torque, whereby the torque results from the spin Hall effect plus
spin transfer torque, largely applies to TMD/Co bilayer systems.",2005.01109v2
2009-05-28,Spin Hall Current and Spin-transfer Torque in Ferromagnetic Metal,"We theoretically examine the spin-transfer torque in the presence of
spin-orbit interaction (SOI) at impurities in a ferromagnetic metal on the
basis of linear response theory. We obtained, in addition to the usual
spin-transfer torque, a new contributioin $\sim {\bm j}_{\rm
SH}^{\phantom{\dagger}} \cdot \nabla {\bm n}$ in the first order in SOI, where
${\bm j}_{\rm SH}^{\phantom{\dagger}}$ is the spin Hall current driven by an
external electric field. This is a reaction to inverse spin Hall effect driven
by spin motive force in a ferromagnet.",0905.4561v1
2017-10-27,Spin transfer and spin pumping in disordered normal metal-antiferromagnetic insulator systems,"We consider an antiferromagnetic insulator that is in contact with a metal.
Spin accumulation in the metal can induce spin-transfer torques on the
staggered field and on the magnetization in the antiferromagnet. These torques
relate to spin pumping: the emission of spin currents into the metal by a
precessing antiferromagnet. We investigate how the various components of the
spin-transfer torque are affected by spin-independent disorder and spin-flip
scattering in the metal. Spin-conserving disorder reduces the coupling between
the spins in the antiferromagnet and the itinerant spins in the metal in a
manner similar to Ohm's law. Spin-flip scattering leads to spin-memory loss
with a reduced spin-transfer torque. We discuss the concept of a staggered spin
current and argue that it is not a conserved quantity. Away from the interface,
the staggered spin current varies around a zero mean in an irregular manner. A
network model explains the rapid decay of the staggered spin current.",1710.10250v1
2013-11-07,Spin-Orbit Torques and Anisotropic Magnetization Damping in Skyrmion Crystals,"The length scale of the magnetization gradients in chiral magnets is
determined by the relativistic Dzyaloshinskii-Moriya interaction. Thus, even
conventional spin-transfer torques are controlled by the relativistic
spin-orbit coupling in these systems, and additional relativistic corrections
to the current-induced torques and magnetization damping become important for a
complete understanding of the current-driven magnetization dynamics. We
theoretically study the effects of reactive and dissipative homogeneous
spin-orbit torques and anisotropic damping on the current-driven skyrmion
dynamics in cubic chiral magnets. Our results demonstrate that spin-orbit
torques play a significant role in the current-induced skyrmion velocity. The
dissipative spin-orbit torque generates a relativistic Magnus force on the
skyrmions, whereas the reactive spin-orbit torque yields a correction to both
the drift velocity along the current direction and the transverse velocity
associated with the Magnus force. The spin-orbit torque corrections to the
velocity scale linearly with the skyrmion size, which is inversely proportional
to the spin-orbit coupling. Consequently, the reactive spin-orbit torque
correction can be the same order of magnitude as the non-relativistic
contribution. More importantly, the dissipative spin-orbit torque can be the
dominant force that causes a deflected motion of the skyrmions if the torque
exhibits a linear or quadratic relationship with the spin-orbit coupling. In
addition, we demonstrate that the skyrmion velocity is determined by
anisotropic magnetization damping parameters governed by the skyrmion size.",1311.1778v1
2012-09-19,Spin-Transfer and Exchange Torques in Ferromagnetic Superconductors,"We consider how superconducting correlations influence spin-transfer torques
in ferromagnetic superconductors. It is demonstrated that there is a novel
torque arising from particle-hole interference that depends on the U(1) phase
associated with the superconducting order parameter. We also show that there is
an equilibrium exchange torque between two ferromagnetic superconductors in
contact via a normal metal mediated by Andreev states. The latter equilibrium
magnetic torque is also sensitive to spin-resolved phase differences in the
superconducting order parameters as well as to an externally applied phase
difference.",1209.4356v2
2007-05-29,Measurement of the Spin-Transfer-Torque Vector in Magnetic Tunnel Junctions,"Spin-polarized currents can transfer spin angular momentum to a ferromagnet,
generating a torque that can efficiently reorient its magnetization. Achieving
quantitative measurements of the spin-transfer-torque vector in magnetic tunnel
junctions (MTJs) is important for understanding fundamental mechanisms
affecting spin-dependent tunneling, and for developing magnetic memories and
nanoscale microwave oscillators. Here we present direct measurements of both
the magnitude and direction of the spin torque in Co60Fe20B20/MgO/Co60Fe20B20
MTJs. At low bias V, the differential torque vector d{tau}/dV lies in the plane
defined by the electrode magnetizations, and its magnitude is in excellent
agreement with a prediction for highly-spin-polarized tunneling. With
increasing bias, the in-plane component d{tau}_{parallel}/dV remains large, in
striking contrast to the decreasing magnetoresistance ratio. The differential
torque vector also rotates out of the plane under bias; we measure a
perpendicular component tau_{perp}(V) with bias dependence proportional to V^2
for low V, that becomes as large as 30% of the in-plane torque.",0705.4207v1
2016-12-01,Field- and damping-like spin-transfer torque in magnetic multilayers,"We investigate the spin-transfer torque in a magnetic multilayer structure by
means of a spin-diffusion model. The torque in the considered system,
consisting of two magnetic layers separated by a conducting layer, is caused by
a perpendicular-to-plane current. We compute the strength of the field-like and
the damping-like torque for different material parameters and geometries. Our
studies suggest that the field-like torque highly depends on the exchange
coupling strength of the itinerant electrons with the magnetization both in the
pinned and the free layer. While a low coupling leads to very high field-like
torques, a high coupling leads to low or even negative field-like torques. The
dependence of the different torque terms on system parameters is considered
very important for the development of applications such as STT MRAM and
spin-torque oscillators.",1612.00194v1
2011-08-12,Spin Transfer Torques induced by Spin Hall Effect,"Spin accumulation and spin transfer torques induced by Spin Hall Effect in
bi-layer structures comprising ferromagnetic and paramagnetic materials are
theoretically investigated. The charge and spin diffusion equations taking into
account spin-flip and spin Hall effect are formulated and solved analytically
and numerically for in structures with simplified and complex geometry,
respectively. It is demonstrated that spin torques could be efficiently
produced by means of Spin Hall effect which may be further enhanced by
modifying structure geometry.",1108.2589v1
2007-11-28,Spin Transfer Torques,"This tutorial article introduces the physics of spin transfer torques in
magnetic devices. We provide an elementary discussion of the mechanism of spin
transfer torque, and review the theoretical and experimental progress in this
field. Our intention is to be accessible to beginning graduate students. This
is the introductory paper for a cluster of ""Current Perspectives"" articles on
spin transfer torques published in volume 320 of the Journal of Magnetism and
Magnetic Materials. This article is meant to set the stage for the others which
follow it in this cluster; they focus in more depth on particularly interesting
aspects of spin-torque physics and highlight unanswered questions that might be
productive topics for future research.",0711.4608v3
2022-06-20,Spin transfer torques due to the bulk states of topological insulators,"Spin torques at topological insulator (TI)/ferromagnet interfaces have
received considerable attention in recent years with a view towards achieving
full electrical manipulation of magnetic degrees of freedom. The most important
question in this field concerns the relative contributions of bulk and surface
states to the spin torque, a matter that remains incompletely understood.
Whereas the surface state contribution has been extensively studied, the
contribution due to the bulk states has received comparatively little
attention. Here we study spin torques due to TI bulk states and show that: (i)
There is no spin-orbit torque due to the bulk states on a homogeneous
magnetisation, in contrast to the surface states, which give rise to a
spin-orbit torque via the well-known Edelstein effect. (ii) The bulk states
give rise to a spin transfer torque (STT) due to the inhomogeneity of the
magnetisation in the vicinity of the interface. This spin transfer torque,
which has not been considered in TIs in the past, is somewhat unconventional
since it arises from the interplay of the bulk TI spin-orbit coupling and the
gradient of the monotonically decaying magnetisation inside the TI. Whereas we
consider an idealised model in which the magnetisation gradient is small and
the spin transfer torque is correspondingly small, we argue that in real
samples the spin transfer torque should be sizable and may provide the dominant
contribution due to the bulk states. We show that an experimental smoking gun
for identifying the bulk states is the fact that the field-like component of
the spin transfer torque generates a spin density with the same size but
opposite sign for in-plane and out-of-plane magnetisations. This distinguishes
them from the surface states, which are expected to give a spin density of a
similar size and the same sign for both an in-plane and out-of-plane
magnetisations.",2206.09939v2
2008-03-17,Spin transfer torques in nonlocal lateral spin valve,"We report a theoretical study on the spin and electron transport in the
nonlocal lateral spin valve with non-collinear magnetic configuration. The
nonlocal magnetoresistance, defined as the voltage difference on the detection
lead over the injected current, is derived analytically. The spin transfer
torques on the detection lead are calculated. It is found that spin transfer
torques are symmetrical for parallel and antiparallel magnetic configurations,
which is different from that in conventional sandwiched spin valve.",0803.2440v2
2016-08-06,Spin Transfer Torque in the Semiconductor/Ferromagnetic Structure in the Presence of Rashba Effect,"Spin transfer torque in magnetic structures occurs when the transverse
component of the spin current that flows from the nonmagnetic medium to
ferromagnetic medium are absorbed by the interface. In this paper, considering
the Rashba effect on semiconductor region, we have discussed the spin transfer
torque in semiconductor/ferromagnetic structure and obtained the components of
spin-current density for two models: (I)-single electron and (II)- the
distribution of electrons. We have shown that whatever the difference between
Fermi surfaces in semiconductor and Fermi spheres for the up and down spins in
ferromagnetic increase, the transmission probability decreases. The obtained
results for the values used in this article illustrate that Rashba effect
increases the difference between a Fermi sphere in semiconductors and Fermi
sphere for the up and down spins in ferromagnetic. The results also show that
the Rashba effect, brings an additional contribution to the components of spin
transfer torque, which is not exist in the absence of the Rashba interaction.
Moreover, the Rashba term has also different effects on the transverse
components of the spin torque transfer.",1608.02129v1
2013-07-01,Phenomenology of Current-Induced Spin-Orbit Torques,"Currents induce magnetization torques via spin-transfer when the spin angular
momentum is conserved or via relativistic spin-orbit coupling. Beyond simple
models, the relationship between material properties and spin-orbit torques is
not known. Here, we present a novel phenomenology of current-induced torques
that is valid for any strength of intrinsic spin-orbit coupling. In $\rm
Pt|Co|AlO_x$, we demonstrate that the domain walls move in response to a novel
relativistic dissipative torque that is dependent on the domain wall structure
and that can be controlled via the Dzyaloshinskii-Moriya interaction. Unlike
the non-relativistic spin-transfer torque, the new torque can, together with
the spin-Hall effect in the Pt-layer, move domain walls by means of electric
currents parallel to the walls.",1307.0395v3
2017-07-10,Theory of in-plane current induced spin torque in metal/ferromagnet bilayers,"Using a semiclassical approach that simultaneously incorporates the spin Hall
effect (SHE), spin diffusion, quantum well states, and interface spin-orbit
coupling (SOC), we address the interplay of these mechanisms as the origin of
the in-plane current induced spin torque observed in the normal
metal/ferromagnetic metal bilayer thin films. Focusing on the bilayers with a
ferromagnet much thinner than its spin diffusion length, such as Pt/Co with
$\sim 10$nm thickness, our approach addresses simultaneously the two
contributions to the spin torque, namely the spin-transfer torque (SHE-STT) due
to SHE induced spin injection, and the spin-orbit torque (SOT) due to SOC
induced spin accumulation. The SOC produces an effective magnetic field at the
interface, hence it modifies the angular momentum conservation expected for the
SHE-STT. The SHE induced spin voltage and the interface spin current are
mutually dependent, hence are solved in a self-consistent manner. In addition,
the spin transport mediated by the quantum well states may be responsible for
the experimentally observed rapid variation of the spin torque with respect to
the thickness of the ferromagnet.",1707.02771v1
2005-07-19,Nonequilibrium spin-transfer torque in SFNFS junctions,"We report theoretical results for the nonequilibrium spin current and
spin-transfer torque in voltage-biased SFNFS Josephson structures. The
subharmonic gap structures and high voltage asymptotic behaviors of the dc and
ac components of the spin current are analyzed and related to the
spin-dependent inelastic scattering of quasiparticles at both F layers.",0507449v2
2014-08-20,Microscopic calculation of thermally-induced spin-transfer torques,"Spin-transfer torques induced by temperature gradients in conducting
ferromagnets are calculated microscopically for smooth magnetization textures.
Temperature gradients are treated a la Luttinger by introducing a fictitious
gravitational field that couples to the energy density. The thermal torque
coefficients obtained by the Kubo formula contain divergences caused by
equilibrium components that should be subtracted before applying the
Einstein-Luttinger relation. Only by following this procedure a familiar
Mott-like formula is obtained for the dissipative spin-transfer torque. The
result indicates that a fictitious field coupled to the entropy rather than
energy would solve the issue from the outset.",1408.4562v1
2010-06-21,Spin transfer torque enhancement in dual spin valve in the ballistic regime,"The spin transfer torque in all-metal dual spin valve, in which two
antiparallelly aligned pinned ferromagnetic layers are on the two sides of a
free ferromagnetic layer with two thin nonmagnetic spacers in between, is
studied in the ballistic regime. It is argued that, similar to the results in
the diffusion regime, the spin transfer torque is dramatically enhanced in
comparison to that in a conventional spin valve although no spin accumulation
exists at the magnetic-nonmagnetic interfaces. Within the Slonczewski's
approach, an analytical expression of the torque on the free magnetic layer is
obtained, which may serve as a theoretical model for the micromagnetic
simulation of the spin dynamics in dual spin valve. Depending on the
orientation of free layer and the degree of electron polarization, the spin
transfer torque enhancement could be tens times. The general cases when
transmission and reflection probabilities of free layer are different from zero
or one are also numerically calculated.",1006.4003v3
2018-04-05,Dynamics of macrospin under periodic field and spin transfer torque,"The dynamics of a macrospin model for a single magnetic domain is
investigated in two cases: (i) under the action of a periodic magnetic field
and (ii) under the external field plus a spin transfer torque from
spin-polarized current or spin current. It has been proved that (i) without
spin transfer torque, the trajectory of magnetization (hysteresis) is always a
closed curve oscillating between two stable points and following the same path
each time; (ii) under the action of a constant field (or with small periodic
perturbation) and a constant spin transfer torque, the spin would always turn
to the stable solution finally, which is independent of the parameters or
initial conditions; (iii) considering a periodic oscillating field plus a spin
transfer torque, the system can also have a stable solution around a limit
circle, but on some special points on the attractor, the system may be
sensitive to the initial conditions and have no limit circle.",1804.01667v1
2009-10-13,Voltage Asymmetry of Spin-Transfer Torques,"We present a Non-Equilibrium Green's Function based model for spin torque
transfer (STT) devices which provides quantitative agreement with
experimentally measured (1) differential resistances, (2) Magnetoresistance
(MR), (3) In-plane torque and (4) out-of-plane torque over a range of bias
voltages, using a single set of three adjustable parameters. We believe this is
the first theoretical model that is able to cover this diverse range of
experiments and a key aspect of our model is the inclusion of multiple
transverse modes. We also provide a simple explanation for the asymmetric bias
dependence of the in-plane torque, based on the polarization of the two
contacts in energy range of transport.",0910.2489v1
2019-06-03,Impact of spin transfer torque on the write error rate of a voltage-torque-based magnetoresistive random access memory,"Impact of spin transfer torque (STT) on the write error rate of a
voltage-torque-based magnetoresistive random access memory is theoretically
analyzed by using the macrospin model. During the voltage pulse the STT assists
or suppresses the precessional motion of the magnetization depending on the
initial magnetization direction. The characteristic value of the current
density is derived by balancing the STT and the external-field torque, which is
about 5$\times$ 10$^{11}$ A/m$^{2}$. The results show that the write error rate
is insensitive to the STT below the current density of $10^{10}$ A/m$^{2}$.",1906.00593v1
2017-06-22,Observation of anomalous spin-torque generated by a ferromagnet,"In this work we report observation of in-plane current induced out-of-plane
magnetic field driven torque in spin valve structure. Since ferromagnet has
high spin orbit coupling it is expected to be the source of spin-orbit-torque
as it possesses anomalous-Hall-effect (AHE: equivalent to spin Hall effect in
heavy metal). So we have carried out spin-torque ferromagnetic resonance
(ST-FMR) experiment in a spin valve (consists of a fixed magnet and a free
magnet which are separated by Cu spacer), passing in-plane radio frequency
current and measuring DC voltage. Our experimental results eventually indicate
that spin torque exerted on the free magnet is not caused due to the spin
current injection by the fixed magnet owing to its AHE, but it is originated
from in-plane current driven out-of plane effective magnetic field. This is new
class of spin torque which is completely different from Slonczewski-spin
transfer torque and Rashba like field like torque. The effective out-of plane
magnetic field depends on the direction of current (in-plane) and magnetization
(in-plane) of the pinned layer. One possible mechanism behind this
unconventional torque could be intefacial spin-scattering which is also origin
of current in-plane GMR effect. Most importantly this effective out-of plane
torque can be useful to switch out-of plane magnetic bits in spintronic memory
application.",1706.07245v1
2020-01-21,Numerical Computation of Spin-Transfer Torques for Antiferromagnetic Domain walls,"We numerically compute current-induced spin-transfer torques for
antiferromagnetic domain walls, based on a linear response theory in a
tight-binding model. We find that, unlike for ferromagnetic domain wall motion,
the contribution of adiabatic spin torque to antiferromagnetic domain wall
motion is negligible, consistent with previous theories. As a result, the
non-adiabatic spin-transfer torque is a main driving torque for
antiferromagnetic domain wall motion. Moreover, the non-adiabatic spin-transfer
torque for narrower antiferromagnetic domain walls increases more rapidly than
that for ferromagnetic domain walls, which is attributed to the enhanced spin
mistracking process for antiferromagnetic domain walls.",2001.07351v2
2021-11-26,Thermal Spin-Orbit Torque in Spintronics,"Within the spinor Boltzmann equation (SBE) formalism, we derived a
temperature dependent thermal spin-orbit torque based on local equilibrium
assumption in a system with Rashba spin-orbit interaction. If we expand the
distribution function of spinor Boltzmann equation around local equilibrium
distribution, we can obtain the spin diffusion equation from SBE, then the spin
transfer torque, spin orbit torque as well as thermal spin-orbit torque we seek
to can be read out from this equation. It exhibits that this thermal spin-orbit
torque originates from the temperature gradient of local equilibrium
distribution function, which is explicit and straightforward than previous
works. Finally, we illustrate them by an example of spin-polarized transport
through a ferromagnet with Rashba spin-orbit coupling, in which those torques
driven whatever by temperature gradient or bias are manifested quantitatively.",2112.01370v1
2012-12-21,Shot noise of spin current and spin transfer torque,"We report the theoretical investigation of noise spectrum of spin current and
spin transfer torque for non-colinear spin polarized transport in a spin-valve
device which consists of normal scattering region connected by two
ferromagnetic electrodes. Our theory was developed using non-equilibrium
Green's function method and general non-linear $S^\sigma-V$ and $S^\tau-V$
relations were derived as a function of angle $\theta$ between magnetization of
two leads. We have applied our theory to a quantum dot system with a resonant
level coupled with two ferromagnetic electrodes. It was found that for the MNM
system, the auto-correlation of spin current is enough to characterize the
fluctuation of spin current. For a system with three ferromagnetic layers,
however, both auto-correlation and cross-correlation of spin current are needed
to characterize the noise spectrum of spin current. Furthermore, the spin
transfer torque and the torque noise were studied for the MNM system. For a
quantum dot with a resonant level, the derivative of spin torque with respect
to bias voltage is proportional to $\sin\theta$ when the system is far away
from the resonance. When the system is near the resonance, the spin transfer
torque becomes non-sinusoidal function of $\theta$. The derivative of noise
spectrum of spin transfer torque with respect to the bias voltage $N_\tau$
behaves differently when the system is near or far away from the resonance.
Specifically, the differential shot noise of spin transfer torque $N_\tau$ is a
concave function of $\theta$ near the resonance while it becomes convex
function of $\theta$ far away from resonance. For certain bias voltages, the
period $N_\tau(\theta)$ becomes $\pi$ instead of $2\pi$. For small $\theta$, it
was found that the differential shot noise of spin transfer torque is very
sensitive to the bias voltage and the other system parameters.",1212.5474v1
2003-03-12,Spin-Flip Scattering Effect on the Current-Induced Spin Torque in Ferromagnet-Insulator-Ferromagnet Tunnel Junctions,"We have investigated the current-induced spin transfer torque of a
ferromagnet-insulator-ferromagnet tunnel junction by taking the spin-flip
scatterings into account. It is found that the spin-flip scattering can induce
an additional spin torque, enhancing the maximum of the spin torque and giving
rise to an angular shift compared to the case when the spin-flip scatterings
are neglected. The effects of the molecular fields of the left and right
ferromagnets on the spin torque are also studied. It is found that $\tau
^{Rx}/I_{e}$ ($\tau ^{Rx}$ is the spin-transfer torque acting on the right
ferromagnet and $I_{e}$ is the tunneling elcetrical current) does vary with the
molecular fields. At two certain angles, $\tau ^{Rx}/I_{e}$ is independent of
the molecular field of the right ferromagnet, resulting in two crossing points
in the curve of $\tau ^{Rx}/I_{e}$ versus the relevant orientation for
different molecular fields.",0303215v1
2021-08-05,Spin-transfer torque driven localized spin excitations in the presence of field-like torque,"We study the existence of localized one-spin excitation in the Heisenberg
one-dimensional ferromagnetic spin chain in the presence of perpendicular and
parallel external magnetic fields and current with spin-transfer torque and
field-like torque. The Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation is
exactly solved for the one spin excitation in the absence of onsite anisotropy
for the excitations of spin with fields perpendicular and parallel to the
chain. We show the removal of damping in the spin excitations by appropriately
introducing current and also the enhancement of angular frequency of the
oscillations due to field-like torque in the case of both perpendicular and
parallel field. The exactness of the analytical results is verified by matching
with numerical counterparts. Further, we numerically confirm the existence of
in-phase and anti-phase stable synchronized oscillations for two
spin-excitations in the presence of current with perpendicular field and
field-like torque. We also show that the one-spin excitation is stable against
thermal noise and gets only slightly modified against thermal fluctuations.",2108.02380v1
2023-05-21,Spin-orbit torque on nuclear spins exerted by a spin accumulation via hyperfine interactions,"Spin-transfer and spin-orbit torques allow controlling magnetic degrees of
freedom in various materials and devices. However, while the transfer of
angular momenta between electrons has been widely studied, the contribution of
nuclear spins has yet to be explored further. This article demonstrates that
the hyperfine coupling, which consists of Fermi contact and dipolar
interactions, can mediate the application of spin-orbit torques acting on
nuclear spins. Our starting point is a sizable nuclear spin in a metal with
electronic spin accumulation. Then, via the hyperfine interactions, the nuclear
spin modifies the an electronic spin density. The reactions to the equilibrium
and nonequilibrium components of the spin density is a torque on the nucleus
with field-like and damping-like components, respectively. This nuclear
spin-orbit torque is a step toward stabilizing and controlling nuclear magnetic
momenta, in magnitude and direction, and realizing nuclear spintronics.",2305.12390v2
2008-01-21,First principles study on the spin transfer torques,"An efficient first principles method was developed to calculate spin transfer
torques in layered system with noncollinear magnetization. The complete
scattering wave function is determined by matching the wave function in the
scattering region with the Bloch states in the leads. The spin transfer torques
are obtained with aid of the scattering wave function. We applied our method to
the ferromagnetic spin valve and found that the material (Co, Ni and Ni80Fe20)
dependence of the spin transfer torques could be well understood by the Fermi
surface. Ni has much longer spin injection penetration length than Co.
Interfacial disorder is also considered. It is found that the spin transfer
torques could be enhanced by the interfacial disorder in some system.",0801.3135v1
2019-08-19,Enhancement of Thermal Spin Transfer Torque via Bandpass Energy Filtering,"We propose the use of energy bandpass filtering approach in the magnetic
tunnel junction device as a route to enhance the thermal spin transfer torque.
Using the spin-resolved non-equilibrium Green's function formalism, we harness
the optical analog of anti-reflective coating in a heterostructure MTJ device,
that reports a huge spin torque in the linear regime of temperature bias. In
particular, we discuss the position of transmission function with respect to
the Fermi energy that caters the maximum thermal effect. The boxcar
transmission feature of anti-reflective configuration enhances the charge and
spin transport through the structure in comparison to the normal superlattice
configurations. The thermally excited spin transfer torque is enhanced by
almost five times more with our device design. Although, the thermally driven
spin torque is much smaller than the potential driven torque, this technique
provides an energy-efficient way to switch the magnetization. This opens up a
new viable area in the spintronics applications. With the existing advanced
thin-film growth technology, the optimized superlattice configurations can be
achieved.",1908.06614v1
2016-06-18,Spin Transport at Interfaces with Spin-Orbit Coupling: Formalism,"We generalize magnetoelectronic circuit theory to account for spin transfer
to and from the atomic lattice via interfacial spin-orbit coupling. This
enables a proper treatment of spin transport at interfaces between a
ferromagnet and a heavy-metal non-magnet. This generalized approach describes
spin transport in terms of drops in spin and charge accumulations across the
interface (as in the standard approach), but additionally includes the
responses from in-plane electric fields and offsets in spin accumulations. A
key finding is that in-plane electric fields give rise to spin accumulations
and spin currents that can be polarized in any direction, generalizing the
Rashba-Edelstein and spin Hall effects. The spin accumulations exert torques on
the magnetization at the interface when they are misaligned from the
magnetization. The additional out-of-plane spin currents exert torques via the
spin-transfer mechanism on the ferromagnetic layer. To account for these
phenomena we also describe spin torques within the generalized circuit theory.
The additional effects included in this generalized circuit theory suggest
modifications in the interpretations of experiments involving spin orbit
torques, spin pumping, spin memory loss, the Rashba-Edelstein effect, and the
spin Hall magnetoresistance.",1606.05758v1
2020-03-24,Spin-transfer torque driven intrinsic localized spin excitations in the presence of field-like torque,"We study the existence of intrinsic localized one-spin excitation in the
Heisenberg one-dimensional ferromagnetic spin chain in the presence of
perpendicular and parallel external magnetic fields and current with
spin-transfer torque and field-like torque. The
Landau-Lifshitz-Gilbert-Slonczewski(LLGS) equation is exactly solved for the
one spin excitation in the absence of onsite anisotropy for the excitations of
spin with fields perpendicular and parallel to the chain. We show the removal
of damping in the spin excitations by appropriately introducing current and
also the enhancement of angular frequency of the oscillations due to field-like
torque in the case of both perpendicular and parallel field. The exactness of
the analytical results is verified by matching with numerical counterparts.
Further, we numerically confirm the existence of in-phase and anti-phase stable
synchronized oscillations for two spin-excitations in the presence of current
with perpendicular field and field-like torque.",2003.11023v2
2024-02-07,Quantum Theory of Spin-Transfer and Spin-Pumping in Collinear Antiferromagnets and Ferrimagnets,"Antiferromagnets are promising candidates as active components in spintronic
applications. They share features with ferrimagnets in that opposing spin
orientations exist in two or more sublattices. Spin transfer torque and spin
pumping are essential ingredients in antiferromagnetic and ferrimagnet
spintronics. This paper develops an out-of-equilibrium quantum theory of the
spin dynamics of collinear magnets containing many spins coupled to normal
metal reservoirs. At equilibrium, the spins are parallel or antiparallel to the
easy axis. The theory, therefore, covers collinear antiferromagnets and
ferrimagnets. We focus on the resulting semi-classical spin dynamics. The
dissipation in the spin dynamics is enhanced due to spin-pumping. Spin
accumulations in the normal metals induce deterministic spin-transfer torques
on the magnet. Additionally, each electron's discrete spin angular momentum
causes stochastic fluctuating torques on the antiferromagnet or ferrimagnet. We
derive these fluctuating torques. The fluctuation-dissipation theorem holds at
high temperatures, including the effects of spin-pumping. At low temperatures,
we derive shot noise contributions to the fluctuations.",2402.04719v2
2008-11-28,Effect of Nonlocal Spin-Transfer Torque on Current-Induced Magnetization Dynamics,"Using the self-consistent model, we present nonlocal spin-transfer effects
caused by the feedback between inhomogeneous magnetization and spin-transfer
torque on the current-induced magnetization dynamics in nanomagnets. The
nonlocal effects can substantially improve the coherence time of precession in
nanomagnets and thus reduce the linewidth of power spectrum. This narrow
linewidth results from the nonlinear damping of spin-waves due to the nonlocal
spin torque which is inherent and thus should be considered in future
experiments.",0811.4649v1
2009-09-15,Critical current density for spin transfer torque switching with composite free layer structure,"Critical current density of composite free layer (CFL) in magnetic tunneling
junction is investigated. CFL consists of two exchange coupled ferromagnetic
layers, where the coupling is parallel or anti-parallel. Instability condition
of the CFL under the spin transfer torque, which is related with critical
current density, is obtained by analytic spin wave excitation model and
confirmed by macro-spin Landau-Lifshitz-Gilbert equation. The critical current
densities for the coupled two identical layers are investigated with various
coupling strengths, and spin transfer torque efficiencies.",0909.2711v1
2010-10-24,Feedback control of noise in spin valves by the spin-transfer torque,"The miniaturisation of magnetic read heads and random access memory elements
makes them vulnerable to thermal fluctuations. We demonstrate how
current-induced spin-transfer torques can be used to suppress the effects of
thermal fluctuations. This enhances the fidelity of perpendicular magnetic spin
valves. The simplest realization is a dc current to stabilize the free magnetic
layers. The power can be significantly reduced without losing fidelity by
simple control schemes, in which the stabilizing current-induced spin-transfer
torque is controlled by the instantaneous resistance.",1010.4954v1
2011-09-28,Angular momentum transfer torques in spin valves with perpendicular magnetization,"Spin valves incorporating perpendicularly magnetized materials are promising
structures for memory elements and high-frequency generators. We report the
angular dependence of the spin-transfer torque in spin valves with
perpendicular equilibrium magnetization computed by first-principles circuit
theory and compare results with experiments by W.H. Rippard c.s. [Phys. Rev. B
81, 014426 (2010)] on the CoFe|Cu|CoNi system. Furthermore, we predict a
non-monotonous (""wavy"") spin-transfer torque when the Cu spacer is replaced by
a Ru layer.",1109.6074v1
2020-02-06,Spin-orbit torque switching of perpendicular magnetization in ferromagnetic trilayers,"In ferromagnetic trilayers, a spin-orbit-induced spin current can have a spin
polarization of which direction is deviated from that for the spin Hall effect.
Recently, magnetization switching in ferromagnetic trilayers has been proposed
and confirmed by the experiments. In this work, we theoretically and
numerically investigate the switching current required for perpendicular
magnetization switching in ferromagnetic trilayers. We confirm that the tilted
spin polarization enables field-free deterministic switching at a lower current
than conventional spin-orbit torque or spin-transfer torque switching, offering
a possibility for high-density and low-power spin-orbit torque devices.
Moreover, we provide analytical expressions of the switching current for an
arbitrary spin polarization direction, which will be useful to design
spin-orbit torque devices and to interpret spin-orbit torque switching
experiments.",2002.02132v1
2004-06-21,Basic considerations for magnetization dynamics in the combined presence of spin-transfer torques and thermal fluctuations,"This article reviews basic theoretical features of Gilbert magnetization
dynamics of a single domain magnetic film in the presence of Slonczewski
spin-transfer torques, with and without thermal fluctuations taken into
account. Rather than showing results of detailed numerical calculations, the
discussion here is restricted to basic analytical results and conclusions which
can mostly be derived from simply the form of the equations of motion, as well
as elementary considerations based on classical stability analysis and the
fluctuation-dissipation theorem. The presents work describes how interesting
features of spin-transfer may be viewed as arising from non-equilibrium
thermodynamics that are a direct consequence of the nonreciprocal nature of
spin-transfer torques. The present article discusses fairly general results for
spin-torque induced instability without thermal fluctuations, as well as the
case of thermally activated magnetization reversal in uniaxial devices in the
combined presence of external fields, thermal fluctuations, and spin-transfer
torques. The results will be discussed and briefly compared and contrasted with
that of prior work.",0406486v1
2013-05-06,Spin-Torque Generation in Topological-Insulator-Based Heterostructures,"Heterostructures utilizing topological insulators exhibit a remarkable
spin-torque efficiency. However, the exact origin of the strong torque, in
particular whether it stems from the spin-momentum locking of the topological
surface states or rather from spin-Hall physics of the topological-insulator
bulk remains unclear. Here, we explore a mechanism of spin-torque generation
purely based on the topological surface states. We consider
topological-insulator-based bilayers involving ferromagnetic metal (TI/FM) and
magnetically doped topological insulators (TI/mdTI), respectively. By ascribing
the key theoretical differences between the two setups to location and number
of active surface states, we describe both setups within the same framework of
spin diffusion of the non-equilibrium spin density of the topological surface
states. For the TI/FM bilayer, we find large spin-torque efficiencies of
roughly equal magnitude for both in-plane and out-of-plane spin torques. For
the TI/mdTI bilayer, we elucidate the dominance of the spin-transfer-like
torque. However, we cannot explain the orders of magnitude enhancement
reported. Nevertheless, our model gives an intuitive picture of spin-torque
generation in topological-insulator-based bilayers and provides theoretical
constraints on spin-torque generation due to topological surface states.",1305.1328v3
2003-02-17,Magnetization dynamics with a spin-transfer torque,"The magnetization reversal and dynamics of a spin valve pillar, whose lateral
size is 64$\times$64 nm$^2$, are studied by using micromagnetic simulation in
the presence of spin transfer torque. Spin torques display both characteristics
of magnetic damping (or anti-damping) and of an effective magnetic field. For a
steady-state current, both M-I and M-H hysteresis loops show unique features,
including multiple jumps, unusual plateaus and precessional states. These
states originate from the competition between the energy dissipation due to
Gilbert damping and the energy accumulation due to the spin torque supplied by
the spin current. The magnetic energy oscillates as a function of time even for
a steady-state current. For a pulsed current, the minimum width and amplitude
of the spin torque for achieving current-driven magnetization reversal are
quantitatively determined. The spin torque also shows very interesting thermal
activation that is fundamentally different from an ordinary damping effect.",0302337v1
2015-08-17,Magnetization dynamics driven by angle-dependent spin-orbit spin transfer torque,"Spin-orbit spin transfer torque allows an efficient control of magnetization
by an in-plane current. Recent experiments found that the spin-orbit torque has
strong dependence on the magnetization angle [Garello et al., Nature
Nanotechnol. 8, 587 (2013); Qiu et al., Sci. Rep. 4, 4491 (2014)]. We
theoretically investigate magnetization switching and domain wall motion in a
perpendicularly magnetized layer, induced by angle-dependent spin-orbit torque.
We obtain analytic expressions of the switching current and domain wall
velocity, in agreement with numerical results. Based on the expressions, we
find that the spin-orbit torque increasing with the polar angle of
magnetization is beneficial for both switching and domain wall motion. Our
result will serve as a guideline to design and interpret switching and domain
wall experiments based on spin-orbit torque.",1508.04067v2
2016-07-06,Robust spin transfer torque in antiferromagnetic tunnel junctions,"We theoretically study the current-induced spin torque in antiferromagnetic
tunnel junctions, composed of two semi-infinite antiferromagnetic layers
separated by a tunnel barrier, in both clean and disordered regimes. We find
that the torque enabling the electrical manipulation of the N\'eel
antiferromagnetic order parameter is out of plane $\sim {\bf n}\times{\bf p}$,
while the torque competing with the antiferromagnetic exchange is in-plane
$\sim {\bf n}\times({\bf p}\times{\bf n})$. Here, ${\bf { p}}$ and ${\bf { n}}$
are the N\'eel order parameter direction of the reference and free layers,
respectively. Their bias dependence shows similar behavior as in ferromagnetic
tunnel junctions, the in-plane torque being mostly linear in bias while the
out-of-plane torque is quadratic. Most importantly, we find that the spin
transfer torque in antiferromagnetic tunnel junctions is much more robust
against disorder than in antiferromagnetic metallic spin-valves due to the
tunneling nature of spin transport.",1607.01523v2
2018-01-17,First-principles quantum transport modeling of spin-transfer and spin-orbit torques in magnetic multilayers,"We review a unified approach for computing: (i) spin-transfer torque in
magnetic trilayers like spin-valves and magnetic tunnel junction, where
injected charge current flows perpendicularly to interfaces; and (ii)
spin-orbit torque in magnetic bilayers of the type
ferromagnet/spin-orbit-coupled-material, where injected charge current flows
parallel to the interface. Our approach requires to construct the torque
operator for a given Hamiltonian of the device and the steady-state
nonequilibrium density matrix, where the latter is expressed in terms of the
nonequilibrium Green's functions and split into three contributions. Tracing
these contributions with the torque operator automatically yields field-like
and damping-like components of spin-transfer torque or spin-orbit torque
vector, which is particularly advantageous for spin-orbit torque where the
direction of these components depends on the unknown-in-advance orientation of
the current-driven nonequilibrium spin density in the presence of spin-orbit
coupling. We provide illustrative examples by computing spin-transfer torque in
a one-dimensional toy model of a magnetic tunnel junction and realistic
Co/Cu/Co spin-valve, both of which are described by first-principles
Hamiltonians obtained from noncollinear density functional theory calculations;
as well as spin-orbit torque in a ferromagnetic layer described by a
tight-binding Hamiltonian which includes spin-orbit proximity effect within
ferromagnetic monolayers assumed to be generated by the adjacent monolayer
transition metal dichalcogenide.",1801.05793v2
2019-10-03,Alternating Current-induced Interfacial Spin-transfer Torque,"We investigate an interfacial spin-transfer torque and $\beta$-term torque
with alternating current (AC) parallel to a magnetic interface. We find that
both torques are resonantly enhanced as the AC frequency approaches to the
exchange splitting energy. We show that this resonance allows us to estimate
directly the interfacial exchange interaction strength from the domain wall
motion. We also find that the $\beta$-term includes an unconventional
contribution which is proportional to the time derivative of the current and
exists even in absence of any spin relaxation processes.",1910.01306v1
2015-06-03,"Synchronization of spin-transfer torque oscillators by spin pumping, inverse spin Hall, and spin Hall effects","We have proposed a method to synchronize multiple spin-transfer torque
oscillators based on spin pumping, inverse spin Hall, and spin Hall effects.
The proposed oscillator system consists of a series of nano-magnets in junction
with a normal metal with high spin-orbit coupling, and an accumulative feedback
loop. We conduct simulations to demonstrate the effect of modulated charge
currents in the normal metal due to spin pumping from each nano-magnet. We show
that the interplay between the spin Hall effect and inverse spin Hall effect
results in synchronization of the nano-magnets.",1506.01357v1
2013-12-27,Spin Transfer Torque and Electric Current in Helical Edge States in Quantum Spin Hall Devices,"We study the dynamics of a quantum spin Hall edge coupled to a magnet with
its own dynamics. Using spin transfer torque principles, we analyze the
interplay between spin currents in the edge state and dynamics of the axis of
the magnet, and draw parallels with circuit analogies. As a highlighting
feature, we show that while coupling to a magnet typically renders the edge
state insulating by opening a gap, in the presence of a small potential bias,
spin-transfer torque can restore perfect conductance by transferring angular
momentum to the magnet. In the presence of interactions within the edge state,
we employ a Luttinger liquid treatment to show that the edge, when subject to a
small voltage bias, tends to form a unique dynamic rotating spin wave state
that naturally couples into the dynamics of the magnet. We briefly discuss
realistic physical parameters and constraints for observing this interplay
between quantum spin Hall and spin-transfer torque physics.",1312.7303v1
2010-02-01,Spin relaxation torque in metallic ferromagnets,"Spin relaxation torque ${\cal T}$ in uniform metallic ferromagnets with the
spin-orbit interaction arising from random impurities is calculated
microscopically. ${\cal T}$ is shown to be written by spatial derivatives of
the electric field, but is not always given as a divergence of a torque dipole
density. The result is due to the fast dissipation of the orbital angular
momentum, and thus a conserving spin current cannot be defined. It is discussed
that the $\beta$ term in the spin transfer torque can also be asymmetric.",1002.0207v2
2017-08-11,Gradient expansion formalism for generic spin torques,"We propose a new quantum-mechanical formalism to calculate spin torques based
on the gradient expansion, which naturally involves spacetime gradients of the
magnetization and electromagnetic fields. We have no assumption in the
small-amplitude formalism or no difficulty in the SU($2$) gauge transformation
formalism. As a representative, we calculate the spin renormalization, Gilbert
damping, spin-transfer torque, and $\beta$-term in a three-dimensional
ferromagnetic metal with nonmagnetic and magnetic impurities being taken into
account within the self-consistent Born approximation. Our results serve as a
first-principles formalism for spin torques.",1708.03424v1
2015-02-10,Disentangling relativistic spin torques in a ferromagnet/semiconductor bilayer,"Recently discovered relativistic spin torques induced by a lateral current at
a ferromagnet/paramagnet interface are a candidate spintronic technology for a
new generation of electrically-controlled magnetic memory devices.
Phenomenologically, the torques have field-like and antidamping-like components
with distinct symmetries. Microscopically, they are considered to have two
possible origins. In one picture, a spin-current generated in the paramagnet
via the relativistic spin Hall effect (SHE) is absorbed in the ferromagnet and
induces the spin transfer torque (STT). In the other picture, a non-equilibrium
spin-density is generated via the relativistic inverse spin galvanic effect
(ISGE) and induces the spin-orbit torque (SOT) in the ferromagnet. From the
early observations in paramagnetic semiconductors, SHE and ISGE are known as
companion phenomena that can both allow for electrically aligning spins in the
same structure. It is essential for our basic physical understanding of the
spin torques at the ferromagnet/paramagnet interface to experimentally
disentangle the SHE and ISGE contributions. To achieve this we prepared an
epitaxial transition-metal-ferromagnet/semiconductor-paramagnet single-crystal
structure and performed a room-temperature vector analysis of the relativistic
spin torques by means of the all-electrical ferromagnetic resonance (FMR)
technique. By design, the field-like torque is governed by the ISGE-based
mechanism in our structure while the antidamping-like torque is due to the
SHE-based mechanism",1502.02870v1
2020-04-13,Theory of Current-Induced Angular Momentum Transfer Dynamics in Spin-Orbit Coupled Systems,"Motivated by the importance of understanding competing mechanisms to
current-induced spin-orbit torque in complex magnets, we develop a unified
theory of current-induced spin-orbital coupled dynamics. The theory describes
angular momentum transfer between different degrees of freedom in solids, e.g.,
the electron orbital and spin, the crystal lattice, and the magnetic order
parameter. Based on the continuity equations for the spin and orbital angular
momenta, we derive equations of motion that relate spin and orbital current
fluxes and torques describing the transfer of angular momentum between
different degrees of freedom. We then propose a classification scheme for the
mechanisms of the current-induced torque in magnetic bilayers. Based on our
first-principles implementation, we apply our formalism to two different
magnetic bilayers, Fe/W(110) and Ni/W(110), which are chosen such that the
orbital and spin Hall effects in W have opposite sign and the resulting spin-
and orbital-mediated torques can compete with each other. We find that while
the spin torque arising from the spin Hall effect of W is the dominant
mechanism of the current-induced torque in Fe/W(110), the dominant mechanism in
Ni/W(110) is the orbital torque originating in the orbital Hall effect of W. It
leads to negative and positive effective spin Hall angles, respectively, which
can be directly identified in experiments. This clearly demonstrates that our
formalism is ideal for studying the angular momentum transfer dynamics in
spin-orbit coupled systems as it goes beyond the ""spin current picture"" by
naturally incorporating the spin and orbital degrees of freedom on an equal
footing. Our calculations reveal that, in addition to the spin and orbital
torque, other contributions such as the interfacial torque and self-induced
anomalous torque within the ferromagnet are not negligible in both material
systems.",2004.05945v2
2016-02-22,Spin-orbit-coupling induced torque in ballistic domain walls: equivalence of charge-pumping and nonequilibrium magnetization formalisms,"To study the effect of spin-orbit coupling (SOC) on spin-transfer torque in
magnetic materials, we have implemented two theoretical formalisms that can
accommodate SOC. Using the ""charge-pumping"" formalism, we find two
contributions to the out-of-plane spin-transfer torque parameter $\beta$ in
ballistic Ni domain walls (DWs). For short DWs, the nonadiabatic reflection of
conduction electrons caused by the rapid spatial variation of the exchange
potential results in an out-of-plane torque that increases rapidly with
decreasing DW length. For long DWs, the Fermi level conduction channel
anisotropy that gives rise to an intrinsic DW resistance in the presence of SOC
leads to a linear dependence of $\beta$ on the DW length. To understand this
counterintuitive divergence of $\beta$ in the long DW limit, we use the
""nonequilibrium magnetization"" formalism to examine the spatially resolved
spin-transfer torque. The SOC-induced out-of-plane torque in ballistic DWs is
found to be quantitatively consistent with the values obtained using the
charge-pumping calculations indicating the equivalence of the two theoretical
methods.",1602.06676v1
2007-11-13,Implementation of a non-equilibrium Green's function method to calculate spin transfer torque,"We present an implementation of the steady state Keldysh approach in a
Green's function multiple scattering scheme to calculate the non-equilibrium
spin density. This density is used to obtain the spin transfer torque in
junctions showing the magnetoresistance effect. We use our implementation to
study the spin transfer torque in metallic Co/Cu/Co junctions.",0711.2082v2
2013-03-24,Spin-Transfer Torques in Helimagnets,"We theoretically investigate current-induced magnetization dynamics in
chiral-lattice helimagnets. Spin-orbit coupling in non-centrosymmetric crystals
induces a reactive spin-transfer torque that has not been previously
considered. We demonstrate how the torque is governed by the crystal symmetry
and acts as an effective magnetic field along the current direction in cubic
B20-type crystals. The effects of the new torque are computed for
current-induced dynamics of spin-spirals and the Doppler shift of spin waves.
In current-induced spin-spiral motion, the new torque tilts the spiral
structure. The spin waves of the spiral structure are initially displaced by
the new torque, while the dispersion relation is unaffected.",1303.5921v2
2017-06-07,Adiabatic and nonadiabatic spin torques induced by spin-triplet supercurrent,"We study spin transfer torques induced by a spin-triplet supercurrent in a
magnet with the superconducting proximity effect. By a perturbative approach,
we show that spin-triplet correlations realize new types of torques, which are
analogous to the adiabatic and non-adiabatic ($\beta$) torques, without
extrinsic spin-flip scattering. Remarkable advantages compared to conventional
spin-transfer torques are highlighted in domain wall manipulation. Oscillatory
motions of a domain wall do not occur for a small Gilbert damping, and the
threshold current density to drive its motion becomes zero in the absence of
extrinsic pinning potentials due to the nonadiabatic torque controlled by the
triplet correlations.",1706.02296v2
2021-09-13,Observation of spin splitting torque in a collinear antiferromagnet RuO2,"Current-induced spin torques provide efficient data writing approaches for
magnetic memories. Recently, the spin splitting torque (SST) was theoretically
predicted (R. Gonz\'alez-Hern\'andez et al. Phys. Rev. Lett. 126, 127701
(2021)), which combines advantages of conventional spin transfer torque (STT)
and spin-orbit torque (SOT) as well as enables controllable spin polarization.
Here we provide the experimental evidence of SST in collinear antiferromagnet
RuO2 films. The spin current direction is found to be correlated to the crystal
orientation of RuO2 and the spin polarization direction is dependent on
(parallel to) the N\'eel vector. These features are quite characteristic for
the predicted SST. Our finding not only present a new member for the spin
torques besides traditional STT and SOT, but also proposes a promising spin
source RuO2 for spintronics.",2109.05933v2
2017-04-25,Unified Treatment of Spin Torques using a Coupled Magnetisation Dynamics and Three-Dimensional Spin Current Solver,"A three-dimensional spin current solver based on a generalised spin
drift-diffusion description, including the spin Hall effect, is integrated with
a magnetisation dynamics solver. The resulting model is shown to simultaneously
reproduce the spin-orbit torques generated using the spin Hall effect, spin
pumping torques generated by magnetisation dynamics in multilayers, as well as
the spin transfer torques acting on magnetisation regions with spatial
gradients, whilst field-like and spin-like torques are reproduced in a spin
valve geometry. Two approaches to modelling interfaces are analysed, one based
on the spin mixing conductance and the other based on continuity of spin
currents where the spin dephasing length governs the absorption of transverse
spin components. In both cases analytical formulas are derived for the
spin-orbit torques in a heavy metal / ferromagnet bilayer geometry, showing in
general both field-like and damping-like torques are generated. The limitations
of the analytical approach are discussed, showing that even in a simple bilayer
geometry, due to the non-uniformity of the spin currents, a full
three-dimensional treatment is required. Finally the model is applied to the
quantitative analysis of the spin Hall angle in Pt by reproducing published
experimental data on the ferromagnetic resonance linewidth in the bilayer
geometry.",1704.07758v2
2014-10-16,Spin-transfer torque switching in nanopillar superconducting-magnetic hybrid Josephson junctions,"The combination of superconducting and magnetic materials to create novel
superconducting devices has been motivated by the discovery of Josephson
critical current (Ics) oscillations as a function of magnetic layer thickness
and the demonstration of devices with switchable critical currents. However,
none of the hybrid devices have shown any spintronic effects, such as
spin-transfer torque, which are currently used in room-temperature magnetic
devices, including spin-transfer torque random-access memory and spin-torque
nano-oscillators. We have developed nanopillar Josephson junctions with a
minimum feature size of 50 nm and magnetic barriers exhibiting magnetic
pseudo-spin-valve behavior at 4 K. These devices allow current-induced
magnetization switching that results in 20-fold changes in Ics. The
current-induced magnetic switching is consistent with spin-transfer torque
models for room-temperature magnetic devices. Our work demonstrates that
devices that combine superconducting and spintronic functions show promise for
the development of a nanoscale, nonvolatile, cryogenic memory technology.",1410.4529v1
2008-06-02,Voltage Dependence of Spin Transfer Torque in Magnetic Tunnel Junctions,"Theoretical investigations of spin transfer torque in magnetic tunnel
junctions using the tight-binding model in the framework of non-equilibrium
Green functions formalism are presented. We show that the behavior of the spin
transfer torque as a function of applied voltage can vary over a wide range
depending on the band parameters of the ferromagnetic electrodes and the
insulator that comprise the magnetic tunnel junction. The behavior of both the
parallel and perpendicular components of the spin torque is addressed. This
behavior is explained in terms of the spin and charge current dependence and on
the interplay between evanescent states in the insulator and the Fermi surfaces
of ferromagnetic electrodes comprising the junction. The origin of the
perpendicular (field-like) component of spin transfer torque at zero bias, i.e.
exchange coupling through the barrier between ferromagnetic electrodes is
discussed.",0806.0396v1
2012-01-06,Experimental observation of the optical spin transfer torque,"The spin transfer torque is a phenomenon in which angular momentum of a spin
polarized electrical current entering a ferromagnet is transferred to the
magnetization. The effect has opened a new research field of electrically
driven magnetization dynamics in magnetic nanostructures and plays an important
role in the development of a new generation of memory devices and tunable
oscillators. Optical excitations of magnetic systems by laser pulses have been
a separate research field whose aim is to explore magnetization dynamics at
short time scales and enable ultrafast spintronic devices. We report the
experimental observation of the optical spin transfer torque, predicted
theoretically several years ago building the bridge between these two fields of
spintronics research. In a pump-and-probe optical experiment we measure
coherent spin precession in a (Ga,Mn)As ferromagnetic semiconductor excited by
circularly polarized laser pulses. During the pump pulse, the spin angular
momentum of photo-carriers generated by the absorbed light is transferred to
the collective magnetization of the ferromagnet. We interpret the observed
optical spin transfer torque and the magnetization precession it triggers on a
quantitative microscopic level. Bringing the spin transfer physics into optics
introduces a fundamentally distinct mechanism from the previously reported
thermal and non-thermal laser excitations of magnets. Bringing optics into the
field of spin transfer torques decreases by several orders of magnitude the
timescales at which these phenomena are explored and utilized.",1201.1436v1
2019-10-21,High-frequency magnon excitation due to femtosecond spin-transfer torques,"Femtosecond laser pulses can induce ultrafast demagnetization as well as
generate bursts of hot electron spin currents. In trilayer spin valves
consisting of two metallic ferromagnetic layers separated by a nonmagnetic one,
hot electron spin currents excited by an ultrashort laser pulse propagate from
the first ferromagnetic layer through the spacer reaching the second magnetic
layer. When the magnetizations of the two magnetic layers are noncollinear,
this spin current exerts a torque on magnetic moments in the second
ferromagnet. Since this torque is acting only within the sub-ps timescale, it
excites coherent high-frequency magnons as recently demonstrated in
experiments. Here, we calculate the temporal shape of the hot electron spin
currents using the superdiffusive transport model and simulate the response of
the magnetic system to the resulting ultrashort spin-transfer torque pulse by
means of atomistic spin-dynamics simulations. Our results confirm that the
acting spin-current pulse is short enough to excite magnons with frequencies
beyond 1 THz, a frequency range out of reach for current induced spin-transfer
torques. We demonstrate the formation of thickness dependent standing spin
waves during the first picoseconds after laser excitation. In addition, we vary
the penetration depth of the spin-transfer torque to reveal its influence on
the excited magnons. Our simulations clearly show a suppression effect of
magnons with short wavelengths already for penetration depths in the range of 1
nm confirming experimental findings reporting penetration depths below $2\,
{\rm nm}$.",1910.09412v1
2011-06-22,All-magnonic spin-transfer torque and domain wall propagation,"The spin wave transportation through a transverse magnetic domain wall (DW)
in a magnetic nanowire is studied. It is found that spin wave passes through a
DW without reflection. A magnon, the quantum of the spin wave, carries opposite
spins on the two sides of the DW. As a result, there is a spin angular momentum
transfer from the propagating magnons to the DW. This magnonic spin-transfer
torque can efficiently drive a DW to propagate in the opposite direction to
that of the spin wave.",1106.4382v2
2014-11-15,Spin-transfer-torque through antiferromagnetic IrMn,"Spin-transfer-torque, a transfer of angular momentum between the electron
spin and the local magnetic moments, is a promising and key mechanism to
control ferromagnetic materials in modern spintronic devices . However, much
less attention has been paid to the same effect in antiferromagnets. For the
sake of investigating how the spin current interacts with the magnetic moments
in antiferromagnets, we perform spin-torque ferromagnetic resonance
measurements on Co20Fe60B20 4nm/Ir25Mn75 tIrMn nm/Pt 4 nm multilayers under a
spin Hall effect of Pt. The effective magnetic damping in Co20Fe60B20 is
modified by the spin current injected from the Pt layer via the IrMn layer. The
results indicate that the spin current interacts with IrMn magnetic moments and
exerts the anti-damping torque on the magnetic moments of Co20Fe60B20 through
the IrMn. It is also found that the reduction of the exchange bias in the
IrMn/Pt interface degrades the anti-damping torque exerted on the Co20Fe60B20
layer, suggesting the transmission of the spin torque becomes less efficient as
the interface exchange coupling degrades. Our work infers that the magnetic
moments in IrMn can be manipulated by spin torque similarly to the one in a
ferromagnetic layer.",1411.4100v4
2015-11-12,Thermally-driven spin torques in layered magnetic insulators,"Thermally-driven spin-transfer torques have recently been reported in
electrically insulating ferromagnet$|$normal-metal heterostructures. In this
paper, we propose two physically distinct mechanisms for such torques. The
first is a local effect: out-of-equilibrium, thermally-activated magnons in the
ferromagnet, driven by a spin Seebeck effect, exert a torque on the
magnetization via magnon-magnon scattering with coherent dynamics. The second
is a nonlocal effect which requires an additional magnetic layer to provide the
symmetry breaking necessary to realize a thermal torque. The simplest structure
in which to induce a nonlocal thermal torque is a spin valve composed of two
insulating magnets separated by a normal metal spacer; there, a thermal flux
generates a pure spin current through the spin valve, which results in a torque
when the magnetizations of the layers are misaligned.",1511.04104v1
2016-06-14,Spin orbit torque in disordered antiferromagnets,"We investigate the current-induced spin-orbit torque in antiferromangnetic
materials in the presence of Rashba spin orbit coupling using both the linear
response theory and the non-equilibrium Green's function technique implemented
on a tight-binding model. We show that a staggered spin density arises from
interband contributions. The effect of the disorder is restricted to the
diminution of the torque magnitude and does not bring any anomalous behavior to
the dependences of the torque on the spin orbit strength and the exchange
interaction between the antiferromagnetic local moments and the itinerant
electrons spins. We prove that the spin orbit torque is robust against the
application of the disorder compared to the case of the antiferromagnetic
spin-valve spin transfer torque.",1606.04261v1
2021-07-08,Torque field and skyrmion movement by spin transfer torque in a quasi-2d interface in presence of strong spin-orbit interaction,"We investigate the torque field and skyrmion movement at an interface between
a ferromagnet hosting a skyrmion and a material with strong spin-orbit
interaction. We analyze both semiconductor materials and topological insulators
using a Hamiltonian model that includes a linear term. The spin torque inducing
current is considered to flow in the single band limit therefore a quantum
model of current is used. Skyrmion movement due spin transfer torque proves to
be more difficult in presence of spin orbit interaction in the case where only
interface in-plane currents are present. However, edge effects in narrow
nanowires can be used to drive the skyrmion movement and to exert a limited
control on its movement direction. We also show the differences and
similarities between torque fields due to electric current in the many and in
the single band limits.",2107.03879v1
2023-12-16,Spin-torque nano-oscillator based on two in-plane magnetized synthetic ferrimagnets,"We report the dynamic characterization of the spin-torque-driven in-plane
precession modes of a spin-torque nano-oscillator based on two different
synthetic ferrimagnets: a pinned one characterized by a strong RKKY interaction
which is exchange coupled to an antiferromagnetic layer; and a second one,
non-pinned characterized by weak RKKY coupling. The microwave properties
associated with the steady-state precession of both SyFs are characterized by
high spectral purity and power spectral density. However, frequency dispersion
diagrams of the damped and spin transfer torque modes reveal drastically
different dynamical behavior and microwave emission properties in both SyFs. In
particular, the weak coupling between the magnetic layers of the non-pinned SyF
raises discontinuous dispersion diagrams suggesting a strong influence of mode
crossing. An interpretation of the different dynamical features observed in the
damped and spin torque modes of both SyF systems was obtained by solving
simultaneously, in a macrospin approach, a linearized version of the
Landau-Lifshitz-Gilbert equation including the spin transfer torque term.",2312.10451v2
2008-04-30,Spin-transfer torque in magnetic tunnel junctions: Scattering theory,"We study the bias-dependent spin-transfer torque in magnetic tunnel junctions
in the Stoner model by scattering theory. We show that the in-plane
(Slonczewski type) torque vanishes and subsequently reverses its direction when
the bias voltage becomes larger or the barrier wider than material and
device-dependent critical values. We are able to reproduce the magnitude and
the bias dependence of measured in-plane and out-of-plane torques using
realistic parameters. The condition for the vanishing torque is summarized by a
phase diagram depending on the applied bias and barrier width, which is
explained in terms of an interface spin polarization and the electron focusing
by the barrier. Quantum size effects in the spin-transfer torque are predicted
as a function of the thickness of a normal metal layer inserted between the
ferromagnet and tunnel barrier.",0804.4736v2
2019-08-01,Theory of current-driven dynamics of spin textures on a surface of topological insulators,"Spin-transfer torque is one of the important physical quantities to
understand for successful application of topological insulators to spintronics.
In this paper, we present analytical expressions of the spin-transfer torques
on a surface of a magnetic topological insulator by including the higher-order
contributions of momentum, $k^2$-term and the hexagonal warping. We obtain six
different types of the spin-transfer torque including both the field-like and
the damping-like torques; the four of them appear only when the higher-order
momentum contributions are included. In addition, we discuss the dynamics of
magnetic skyrmions driven by the spin-transfer torques on the surface of the
topological insulator. Unlike the skyrmion dynamics in conventional metals, we
find that the dynamics significantly depends on the internal structure of
magnetic textures.",1908.00152v1
2019-02-12,Domain-wall motion induced by spin transfer torque delivered by helicity-dependent femtosecond laser,"In magnetic wires with perpendicular anisotropy, moving domain with only
current or only circularly polarized light requires a high power. Here, we
propose to reduce it by using both short current pulses and femtosecond laser
pulses simultaneously. The wires were made out of perpendicularly magnetized
film of Pt/Co/Ni/Co/Pt. The displacement of the domain wall is found to be
dependent on the laser helicity. Based on a quantitative analysis of the
current-induced domain wall motion, the spin orbit torque contribution can be
neglected when compared to the spin transfer torque contribution. The effective
field of the spin transfer torque is extracted from the pulsed field domain
wall measurements. Finally, our result can be described using the
Fatuzzo-Labrune model and considering the effective field due to the polarized
laser beam, the effective field due to spin transfer torque, and the Gaussian
temperature distribution of the laser spot.",1902.04348v1
2011-04-05,Magnetic domain wall motion in a nanowire: depinning and creep,"The domain wall motion in a magnetic nanowire is examined theoretically in
the regime where the domain wall driving force is weak and its competition
against disorders is assisted by thermal agitations. Two types of driving
forces are considered; magnetic field and current. While the field induces the
domain wall motion through the Zeeman energy, the current induces the domain
wall motion by generating the spin transfer torque, of which effects in this
regime remain controversial. The spin transfer torque has two mutually
orthogonal vector components, the adiabatic spin transfer torque and the
nonadiabatic spin transfer torque. We investigate separate effects of the two
components on the domain wall depinning rate in one-dimensional systems and on
the domain wall creep velocity in two-dimensional systems, both below the
Walker breakdown threshold. In addition to the leading order contribution
coming from the field and/or the nonadiabatic spin transfer torque, we find
that the adiabatic spin transfer torque generates corrections, which can be of
relevance for an unambiguous analysis of experimental results. For instance, it
is demonstrated that the neglect of the corrections in experimental analysis
may lead to incorrect evaluation of the nonadiabaticity parameter. Effects of
the Rashba spin-orbit coupling on the domain wall motion are also analyzed.",1104.0744v2
2009-07-21,Electric breakdown in ultra-thin MgO tunnel barrier junctions for spin-transfer torque switching,"Magnetic tunnel junctions for spin-transfer torque switching were prepared to
investigate the dielectric breakdown. The breakdown occurs typically at
voltages not much higher than the switching voltages, a bottleneck for the
implementation of spin-transfer torque Magnetic Random Access Memory. Intact
and broken tunnel junctions are characterized by transport measurements and
then prepared for transmission electron microscopy and energy dispersive x-ray
spectrometry by focussed ion beam. The comparison to our previous model of the
electric breakdown for thicker MgO tunnel barriers reveals significant
differences arising from the high current densities.",0907.3579v1
2011-08-23,Controllable Spin-Transfer Torque on an Antiferromagnet in a Dual Spin-Valve,"We consider current-induced spin-transfer torque on an antiferromagnet in a
dual spin-valve setup. It is demonstrated that a net magnetization may be
induced in the AFM by partially or completely aligning the sublattice
magnetizations via a current-induced spin-transfer torque. This effect occurs
for current densities ranging below 10$^6$ A/cm$^2$. The direction of the
induced magnetization in the AFM is shown to be efficiently controlled by means
of the magnetic configuration of the spin-valve setup, with the anti-parallell
configuration yielding the largest spin-transfer torque. Interestingly, the
magnetization switching time-scale $\tau_\text{switch}$ itself has a strong,
non-monotonic dependence on the spin-valve configuration. These results may
point toward new ways to incorporate AFMs in spintronic devices in order to
obtain novel types of functionality.",1108.4685v1
2013-01-18,Current induced torques and interfacial spin-orbit coupling: Semiclassical Modeling,"In bilayer nanowires consisting of a ferromagnetic layer and a non-magnetic
layer with strong spin-orbit coupling, currents create torques on the
magnetization beyond those found in simple ferromagnetic nanowires. The
resulting magnetic dynamics appear to require torques that can be separated
into two terms, damping-like and field-like. The damping-like torque is
typically derived from models describing the bulk spin Hall effect and the spin
transfer torque, and the field-like torque is typically derived from a Rashba
model describing interfacial spin-orbit coupling. We derive a model based on
the Boltzmann equation that unifies these approaches. We also consider an
approximation to the Boltzmann equation, the drift-diffusion model, that
qualitatively reproduces the behavior, but quantitatively fails to reproduce
the results. We show that the Boltzmann equation with physically reasonable
parameters can match the torques for any particular sample, but in some cases,
it fails to describe the experimentally observed thickness dependences.",1301.4513v1
2016-08-08,Laser-induced torques in metallic ferromagnets,"We study laser-induced torques in bcc Fe, hcp Co and $L1_0$ FePt based on
first-principles electronic structure calculations and the Keldysh
nonequilibrium formalism. We find that the torques have two contributions, one
from the inverse Faraday effect (IFE) and one from the optical spin-transfer
torque (OSTT). Depending on the ferromagnet at hand and on the quasiparticle
broadening the two contributions may be of similar magnitude or one
contribution may dominate over the other. Additionally, we determine the
nonequilibrium spin polarization in order to investigate its relation to the
torque. We find the torques and the perpendicular component of the
nonequilibrium spin polarization to be odd in the helicity of the laser light,
while the spin polarization that is induced parallel to the magnetization is
helicity-independent. The parallel component of the nonequilibrium spin
polarization is orders of magnitude larger than the perpendicular component. In
the case of hcp Co we find good agreement between the calculated laser-induced
torque and a recent experiment.",1608.02656v1
2019-10-24,Algebraic decay of the nonadiabaticity arising through chiral spin transfer torque in magnetic domain walls with Rashba spin-orbit interaction,"Spin transfer torque in a two dimensional electron gas system without space
inversion symmetry was theoretically investigated by solving the
Pauli-Schr\""{o}dinger equation for the itinerant electrons inside magnetic
domain walls. Due to the presence of the Rashba spin-orbit coupling induced by
the broken inversion symmetry, the spin transfer torque is chiral and the
nonadiabaticity, which is defined to measure the relative importance of the
nonadiabatic, field-like torque to the adiabatic, damping-like torque, exhibits
an inverse power law decay as the domain wall width is increased. This
algebraic decay is much slower than the exponential decay observed for systems
without the Rashba spin-orbit coupling, and may find applications in innovative
design of spintronic devices utilising magnetic topological textures such as
magnetic domain walls and skyrmions.",1910.11031v3
2014-09-18,Spin-transfer torque induced spin waves in antiferromagnetic insulators,"We explore the possibility of exciting spin waves in insulating
antiferromagnetic films by injecting spin current at the surface. We analyze
both magnetically compensated and uncompensated interfaces. We find that the
spin current induced spin-transfer torque can excite spin waves in insulating
antiferromagnetic materials and that the chirality of the excited spin wave is
determined by the polarization of the injected spin current. Furthermore, the
presence of magnetic surface anisotropy can greatly increase the accessibility
of these excitations.",1409.5460v2
2022-09-10,Self-Consistent Computation of Spin Torques and Magneto-Resistance in Tunnel Junctions and Magnetic Read-Heads with Metallic Pinhole Defects,"A three-dimensional self-consistent spin transport model is developed, which
includes both tunnelling transport, as well as metallic transport. Using the
spin accumulation computed either side of a tunnel barrier, spin torques are
obtained, and it is shown the model reproduces both damping-like and field-like
spin-transfer torques, with the expected sinusoidal angular dependence, and
inverse ferromagnetic layer thickness dependence. An explicit solution to the
drift-diffusion model is derived, which allows analysing the effect of both the
reference and free layer thickness on the spin-transfer torque polarization and
field-like coefficient. In particular, when the layers are thin, additional
spin-dependent scattering contributions due to incomplete absorption of
transverse spin components reduce both the damping-like and field-like spin
torques. It is shown the model developed here can be used to compute the
signal-to-noise ratio in realistic magnetic read-heads, where spin
torque-induced fluctuations and instabilities limit the maximum operating
voltage. The effect of metallic pinhole defects in the insulator layer is also
analysed, which results in a mixture of metallic and tunnelling transport, and
highly non-uniform charge and spin currents, requiring the full spin transport
model to compute the resulting magneto-resistance and spin torques. Increasing
the area covered by pinholes results in a rapid degradation of the
magneto-resistance, following an inverse dependence. Moreover, the spin torque
angular dependence becomes skewed, and the spin-transfer torque polarization
decreases. The same results are obtained when considering tunnel junctions with
a single pinhole defect, but decreasing cross-sectional area, showing that even
a single pinhole defect can significantly degrade the performance of tunnel
junctions and magnetic read-heads below the 40 nm node.",2209.04613v1
2007-11-28,Ab initio studies of the spin-transfer torque in tunnel junctions,"We calculate the spin-transfer torque in Fe/MgO/Fe tunnel junctions and
compare the results to those for all-metallic junctions. We show that the
spin-transfer torque is interfacial in the ferromagnetic layer to a greater
degree than in all-metallic junctions. This result originates in the half
metallic behavior of Fe for the $\Delta_1$ states at the Brillouin zone center;
in contrast to all-metallic structures, dephasing does not play an important
role. We further show that it is possible to get a component of the torque that
is out of the plane of the magnetizations and that is linear in the bias.
However, observation of such a torque requires highly ideal samples. In samples
with typical interfacial roughness, the torque is similar to that in
all-metallic multilayers, although for different reasons.",0711.4560v1
2016-12-30,Derivation of Spin Torques of the Magnetic System in Broken Inversion Symmetry,"We propose a new approach to derive spin torque in systems of broken
inversion symmetry. It uses the concepts of asymmetric and directional
spin-spin interactions to obtain their effective fields. We applied the
effective fields into the Landau-Lifshitz equation and obtained spin torques.
The model offers a new and general approach for spin dynamics, one that
effectively merges the Dzyaloshinskii-Moriya interaction, spin transfer
torques, and spin-orbit torque into the spin dynamics equation. We discussed
how our model is imposed on the spin dynamics and compared our approach with
the traditional discussions on spin dynamics.",1612.09405v3
2007-02-15,Theory of Nonequilibrium Spin Transport and Spin Transfer Torque in Superconducting-Ferromagnetic Nanostructures,"Spin transport currents and the spin-transfer torques in voltage-biased
superconducting-ferromagnetic nanopillars (SFNFS point contacts) are computed.
We develop and implement an algorithm based on the Ricatti formulation of the
quasiclassical theory of superconductivity to solve the time-dependent boundary
conditions for the nonequilibrium Green's functions for spin transport through
the ferromagnetic interfaces. A signature of the nonequilibrium torque is a
component perpendicular to the plane spanned by the two ferromagnetic moments.
The perpendicular component is absent in normal-metal-ferromagnetic nanopillars
(NFNFN) contacts, but is shown to have the same order of magnitude as the
in-plane torque for non-equilibrium SFNFS contacts. The out-of-plane torque is
due to the rotation of quasiparticle spin by the exchange fields of the
ferromagnetic layers. In the ballistic limit the equilibrium torque is related
to the spectrum of spin-polarized Andreev bound states, while the {\sl ac}
component, for small bias voltages, is determined by the nearly adiabatic
dynamics of the Andreev bound states. The nonlinear voltage dependence of the
non-equilibrium torque, including the subharmonic gap structure and the
high-voltage asymptotics, is attributed to the interplay between multiple
Andreev reflections, spin filtering and spin mixing. These properties of spin
angular momentum transport may be exploited to control the state of
nanomagnets.",0702371v3
2009-08-21,Giant adiabatic spin torque in magnetic tunnel junctions with a hybrid free layer structure,"The discovery of spin torque transfer (STT) has lead to a significant advance
in the development of spintronic devices. Novel structures and materials have
been studied in order to improve the performance of the magnetic tunnel
junctions (MTJs) performances and understand the fundamental physics in spin
torque transfer. The adiabatic spin torque effect, which is due to the spatial
non-uniformity of magnetic properties, has been predicted in theory and
demonstrated experimentally in magnetic nanowires. However, this important spin
torque has been rarely concerned in the magnetic tunnel junctions (MTJ) because
of its extremely weak effect in conventional MTJs. This paper reports for the
first time a giant adiabatic spin torque in MTJ devices with a hybrid free
layer structure. The generation of the giant adiabatic spin torque was realized
through the introduction of a spatial magnetic non-uniformity in a hybrid free
layer along the current direction. It is observed that the giant adiabatic spin
torque can substantially promote the current-induced switching process in the
MTJ devices: the adiabatic spin torque can be larger than the in-plane spin
torque, which allows for the switching with a single-polar current under
different bias fields. Moreover, the adiabatic spin torque, which is
proportional to the level of spatial non-uniformity, increases during the
switching process. The observed effects are confirmed by numerical simulations.
These results have far-reaching implications for the future of high-density
STT-MRAM devices.",0908.3050v1
2009-12-18,Magnetic Domain Wall Pumping by Spin Transfer Torque,"We show that spin transfer torque from direct spin-polarized current applied
parallel to a magnetic domain wall (DW) induces DW motion in a direction
independent of the current polarity. This unidirectional response of the DW to
spin torque enables DW pumping: long-range DW displacement driven by
alternating current. Our numerical simulations reveal that DW pumping can be
resonantly amplified through excitation of internal degrees of freedom of the
DW by the current.",0912.3789v1
2013-03-27,Influence of Quantum and Thermal Noise on Spin-Torque-Driven Magnetization Switching,"We apply a recently developed quantum theory of spin transfer torque to study
the effect of the quantum noise in spin transfer process on the magnetization
switching in spin-torque-driven devices. The quantum noise induces considerable
fluctuation of the switching time at zero temperature. By including the thermal
noise, the temperature dependence of the expectation value and standard
deviation of the switching time are obtained in the Monte Carlo simulations,
and the results are fitted to an effective first passage model. We expect that
the predictions here are observable in the single-shot measurement experiments.",1303.6754v1
2016-10-31,Strong non-equilibrium effects in spin torque systems,"We consider a problem of persistent magnetization precession in a single
domain ferromagnetic nano particle under the driving by the spin-transfer
torque. We find that the adjustment of the electronic distribution function in
the particle renders this state unstable. Instead, abrupt switching of the spin
orientation is predicted upon increase of the spin-transfer torque current. On
the technical level, we derive an effective action of the type of
Ambegaokar-Eckern-Sch\""on action for the coupled dynamics of magnetization
(gauge group $SU(2)$) and voltage (gauge group $U(1)$).",1610.09944v2
2012-03-15,Resonance Measurement of Nonlocal Spin Torque in a Three-Terminal Magnetic Device,"A pure spin current generated within a nonlocal spin valve can exert a spin
transfer torque on a nanomagnet. This nonlocal torque enables new design
schemes for magnetic memory devices that do not require the application of
large voltages across tunnel barriers that can suffer electrical breakdown.
Here we report a quantitative measurement of this nonlocal spin torque using
spin-torque-driven ferromagnetic resonance. Our measurement agrees well with
the prediction of an effective circuit model for spin transport. Based on this
model, we suggest strategies for optimizing the strength of nonlocal torque.",1203.3266v2
2008-09-17,Spin-transfer torque induced reversal in magnetic domains,"Using the complex stereographic variable representation for the macrospin,
from a study of the nonlinear dynamics underlying the generalized
Landau-Lifshitz(LL) equation with Gilbert damping, we show that the
spin-transfer torque is effectively equivalent to an applied magnetic field. We
study the macrospin switching on a Stoner particle due to spin-transfer torque
on application of a spin polarized current. We find that the switching due to
spin-transfer torque is a more effective alternative to switching by an applied
external field in the presence of damping. We demonstrate numerically that a
spin-polarized current in the form of a short pulse can be effectively employed
to achieve the desired macro-spin switching.",0809.2910v1
2010-12-25,Screw-pitch effect and velocity oscillation of domain-wall in ferromagnetic nanowire driven by spin-polarized current,"We investigate the dynamics of domain wall in ferromagnetic nanowire with
spin-transfer torque. The critical current condition is obtained analytically.
Below the critical current, we get the static domain wall solution which shows
that the spin-polarized current can't drive domain wall moving continuously. In
this case, the spin-transfer torque plays both the anti-precession and
anti-damping roles, which counteracts not only the spin-precession driven by
the effective field but also Gilbert damping to the moment. Above the critical
value, the dynamics of domain wall exhibits the novel screw-pitch effect
characterized by the temporal oscillation of domain wall velocity and width,
respectively. Both the theoretical analysis and numerical simulation
demonstrate that this novel phenomenon arise from the conjunctive action of
Gilbert-damping and spin-transfer torque. We also find that the roles of
spin-transfer torque are entirely contrary for the cases of below and above the
critical current.",1012.5473v1
2016-04-18,Spin-transfer torques in antiferromagnets: efficiency and quantification method,"We formulate a theory of spin-transfer torques in antiferromagnets, which
covers the small to large limits of the exchange coupling energy relative to
the kinetic energy of the inter-sublattice electron dynamics. Our theory
suggests a natural definition of the efficiency of spin-transfer torques in
antiferromagnets in terms of well-defined material parameters, revealing that
the charge current couples predominantly to the antiferromagnetic order
parameter and the sublattice-canting moment in, respectively, the limits of
large and small exchange coupling. The effects can be quantified by analyzing
the antiferromagnetic spin-wave dispersions in the presence of charge current:
in the limit of large exchange coupling the spin-wave Doppler shift always
occurs, whereas, in the opposite limit, the only spin-wave modes to react to
the charge current are ones that carry a pronounced sublattice-canting moment.
The findings offer a framework for understanding and designing spin-transfer
torques in antiferromagnets belonging to different classes of sublattice
structures such as, e.g., bipartite and layered antiferromagnets.",1604.05277v2
2016-10-02,Spin-transfer torque in ferromagnetic bilayers generated by anomalous Hall effect and anisotropic magnetoresistance,"We propose an experimental scheme to determine the spin-transfer torque
efficiency excited by the spin-orbit interaction in ferromagnetic bilayers from
the measurement of the longitudinal magnetoresistace. Solving a diffusive
spin-transport theory with appropriate boundary conditions gives an analytical
formula of the longitudinal charge current density. The longitudinal charge
current has a term that is proportional to the square of the spin-transfer
torque efficiency and that also depends on the ratio of the film thickness to
the spin diffusion length of the ferromagnet. Extracting this contribution from
measurements of the longitudinal resistivity as a function of the thickness can
give the spin-transfer torque efficiency.",1610.00222v1
2022-05-29,"Quantum Scattering Theory of Spin Transfer Torque, Spin Pumping and Fluctuations","Spin transfer torque and spin pumping are central reciprocal phenomena in
spintronics. These phenomena occur in hybrid systems of normal metals and
magnets. Spin transfer is the conversion of spin currents in metals to a torque
on the magnetization of magnets. Spin pumping is the emission of spin currents
from precessing magnets. Here, we demonstrate a general way to understand these
effects within a quantum out-of-equilibrium path-integral model. Our results
agree with known expressions for spin transfer and spin pumping in terms of
transverse (mixing) conductances when there are no fluctuations. However, at a
finite temperature, frequency or spin accumulation, the magnet also experiences
fluctuating torques. In the classical regime, when the thermal energy is larger
than the bias voltage and precession frequency, we reproduce the classical
Brownian-Langevin forces associated with spin transfer and spin pumping. At low
temperatures, in the quantum regime, we demonstrate that magnetization
fluctuations differ in the elastic and inelastic electron transport regimes.
Furthermore, we show how additional transport coefficients beyond the mixing
conductance govern the fluctuations. Some of these coefficients are related to
electron shot noise because of the discrete spin angular momentum of electrons.
We estimate the fluctuation coefficients of clean, tunnel, and disordered
junctions and in the case of an insulating magnet. Our results open a path for
exploring low-temperature magnetization dynamics and spin caloritronics.",2205.14672v2
2007-03-02,Quantum mechanics of spin transfer in coupled electron-spin chains,"The manner in which spin-polarized electrons interact with a magnetized thin
film is currently described by a semi-classical approach. This in turn provides
our present understanding of the spin transfer, or spin torque phenomenon.
However, spin is an intrinsically quantum mechanical quantity. Here, we make
the first strides towards a fully quantum mechanical description of spin
transfer through spin currents interacting with a Heisenberg-coupled spin
chain. Because of quantum entanglement, this requires a formalism based on the
density matrix approach. Our description illustrates how individual spins in
the chain time-evolve as a result of spin transfer.",0703068v1
2020-04-16,Facilitating domain wall injection in magnetic nanowires by electrical means,"We investigate how to facilitate the injection of domain walls in chiral
ferromagnetic nanowires by electrical means. We calculate the critical current
density above which domain walls are injected into the nanowire depending on
the material parameters and the source of interaction including spin-transfer
torques as well as spin-orbit torques. We demonstrate that the
Dzyaloshinskii-Moriya interaction can significantly reduce the required
critical current to inject the types of domain walls favored by the
Dzyaloshinskii-Moriya interaction. We find that in chiral magnets it is only
possible to shed a single domain wall by means of spin-orbit torques, as they
modify the ground state orientation of the system. In contrast, for
spin-transfer-torque induced shedding of domain walls, we show that there exist
two different critical current densities for the two different domain wall
chiralities, respectively.
  Additionally, for the consecutive creation of domain walls by means of
spin-transfer torques, we find that the interaction between the domain walls
cannot be neglected and even may lead to the pairwise annihilation of
consecutive domain walls with opposite chiralities.",2004.07546v1
2016-03-29,Optomechanical measurement of photon spin angular momentum and optical torque in integrated photonic devices,"Photons carry linear momentum, and spin angular momentum when circularly or
elliptically polarized. During light-matter interaction, transfer of linear
momentum leads to optical forces, while angular momentum transfer induces
optical torque. Optical forces including radiation pressure and gradient forces
have long been utilized in optical tweezers and laser cooling. In nanophotonic
devices optical forces can be significantly enhanced, leading to unprecedented
optomechanical effects in both classical and quantum regimes. In contrast, to
date, the angular momentum of light and the optical torque effect remain
unexplored in integrated photonics. Here, we demonstrate the measurement of the
spin angular momentum of photons propagating in a birefringent waveguide and
the use of optical torque to actuate rotational motion of an optomechanical
device. We show that the sign and magnitude of the optical torque are
determined by the photon polarization states that are synthesized on the chip.
Our study reveals the mechanical effect of photon's polarization degree of
freedom and demonstrates its control in integrated photonic devices. Exploiting
optical torque and optomechanical interaction with photon angular momentum can
lead to torsional cavity optomechanics and optomechanical photon spin-orbit
coupling, as well as applications such as optomechanical gyroscope and
torsional magnetometry.",1603.08950v1
2022-02-07,Spin-transfer-assisted parametric pumping of magnons in yttrium iron garnet,"The combination of parametric pumping and spin-transfer torque is a powerful
approach that enables high-level control over magnetic excitations in thin-film
ferromagnets. The excitation parameters, such as pumping power and external
field strength, affect the instabilities of individual magnon modes. We
theoretically explore how the simultaneous effects of parametric pumping and
spin transfer torque influence these magnetic instabilities in a thin-film
ferromagnet. Within the Landau-Lifshitz-Gilbert framework, we perform
micromagnetic simulations of magnon excitations in yttrium iron garnet by
pumping, spin transfer torque, and a combination of the two. We find that
consistent with experimental results, the magnitude and direction of the
spin-transfer torque tune the parametric instability thresholds.",2202.03247v2
2021-05-31,Intrinsic torques emerging from anomalous velocity in magnetic textures,"Momentum-space topology of electrons under strong spin-orbit coupling
contributes to the electrically induced torques exerting on magnetic textures
insensitively to disorder or thermal fluctuation. We present a direct
connection between band topology and the torques by classifying the whole
torques phenomenologically. As well as the intrinsic anomalous Hall effect, the
torques also emerge intrinsically from the anomalous velocity of electrons
regardless of a nonequilibrium transport current. We especially point out the
intrinsic contribution arising exclusively in magnetic textures, which we call
the ""topological Hall torque (THT)."" The THT emerges in bulk crystals without
any interface or surface structures. We numerically demonstrate the enhancement
of the THT in comparison with the conventional spin-transfer torque in the bulk
metallic ferromagnet, which accounts for the giant current-induced torque
measured in ferromagnetic SrRuO3.",2105.14922v2
2011-03-24,Spin wave assisted current induced magnetic domain wall motion,"The interaction between the propagating spin waves and the current driven
motion of a transverse domain wall in magnetic nanowires is studied by
micromagnetic simulations. If the speed of domain walls due to current induced
spin transfer torque is comparable to the velocity driven by spin waves, the
speed of domain wall is improved by applying spin waves. The domain wall
velocity can be manipulated by the frequency and amplitude of spin waves. The
effect of spin waves is suppressed in the high current density regime in which
the domain wall is mostly driven by current induced spin transfer torque.",1103.4673v1
2002-12-03,A self-consistent treatment of non-equilibrium spin torques in magnetic multilayers,"It is known that the transfer of spin angular momenta between current
carriers and local moments occurs near the interface of magnetic layers when
their moments are non-collinear. However, to determine the magnitude of the
transfer, one should calculate the spin transport properties far beyond the
interface regions. Based on the spin diffusion equation, we present a
self-consistent approach to evaluate the spin torque for a number of layered
structures. One of the salient features is that the longitudinal and transverse
components of spin accumulations are inter-twined from one layer to the next,
and thus, the spin torque could be significantly amplified with respect to
treatments which concentrate solely on the transport at the interface due to
the presence of the much longer longitudinal spin diffusion length. We conclude
that bare spin currents do not properly estimate the spin angular momentum
transferred between to the magnetic background; the spin transfer that occurs
at interfaces should be self-consistently determined by embedding it in our
globally diffuse transport calculations.",0212045v1
2004-06-11,Time-Dependent Spintronic Transport and Current-Induced Spin Transfer Torque in Magnetic Tunnel Junctions,"The responses of the electrical current and the current-induced spin transfer
torque (CISTT) to an ac bias in addition to a dc bias in a magnetic tunnel
junction are investigated by means of the time-dependent nonquilibrium Green
function technique. The time-averaged current (time-averaged CISTT) is
formulated in the form of a summation of dc current (dc CISTT) multiplied by
products of Bessel functions with the energy levels shifted by $m\hbar \omega
_{0}$. The tunneling current can be viewed as to happen between the photonic
sidebands of the two ferromagnets. The electrons can pass through the barrier
easily under high frequencies but difficultly under low frequencies. The tunnel
magnetoresistance almost does not vary with an ac field. It is found that the
spin transfer torque, still being proportional to the electrical current under
an ac bias, can be changed by varying frequency. Low frequencies could yield a
rapid decrease of the spin transfer torque, while a large ac signal leads to
both decrease of the electrical current and the spin torque. If only an ac bias
is present, the spin transfer torque is sharply enhanced at the particular
amplitude and frequency of the ac bias. A nearly linear relation between such
an amplitude and frequency is observed.",0406257v1
2019-07-14,Current-Induced magnetization switching by the high spin Hall conductivity $α$-W,"The spin Hall effect originating from 5d heavy transition metal thin films
such as Pt, Ta, and W is able to generate efficient spin-orbit torques that can
switch adjacent magnetic layers. This mechanism can serve as an alternative to
conventional spin-transfer torque for controlling next-generation magnetic
memories. Among all 5d transition metals, W in its resistive amorphous phase
typically shows the largest spin-orbit torque efficiency ~ 0.20-0.50. In
contrast, its conductive and crystalline $\alpha$ phase possesses a
significantly smaller efficiency ~ 0.03 and no spin-orbit torque switching has
yet been realized using $\alpha$-W thin films as the spin Hall source. In this
work, through a comprehensive study of high quality W/CoFeB/MgO and the
reversed MgO/CoFeB/W magnetic heterostructures, we show that although
amorphous-W has a greater spin-orbit torque efficiency, the spin Hall
conductivity of $\alpha$-W
($|\sigma_{\operatorname{SH}}^{\alpha\operatorname{-W}}|=3.71\times10^{5}\operatorname{\Omega}^{-1}\operatorname{m}^{-1}$)
is ~3.5 times larger than that of amorphous-W
($|\sigma_{\operatorname{SH}}^{\operatorname{amorphous-W}}|=1.05\times10^{5}\operatorname{\Omega}^{-1}\operatorname{m}^{-1}$).
Moreover, we demonstrate spin-orbit torque driven magnetization switching using
a MgO/CoFeB/$\alpha$-W heterostructure. Our findings suggest that the
conductive and high spin Hall conductivity $\alpha$-W can be a potential
candidate for future low power consumption spin-orbit torque memory
applications.",1907.06192v1
2012-03-30,Network analyzer measurements of spin transfer torques in magnetic tunnel junctions,"We demonstrate a simple network-analyzer technique to make quantitative
measurements of the bias dependence of spin torque in a magnetic tunnel
junction. We apply a microwave current to exert an oscillating spin torque near
the ferromagnetic resonance frequency of the tunnel junction's free layer. This
produces an oscillating resistance that, together with an applied direct
current, generates a microwave signal that we measure with the network
analyzer. An analysis of the resonant response yields the strength and
direction of the spin torque at non-zero bias. We compare to measurements of
the spin torque vector by time-domain spin-torque ferromagnetic resonance.",1204.0038v2
2016-08-17,Current-induced instability of domain walls in cylindrical nanowires,"We study the current-driven domain wall (DW) motion in cylindrical nanowires
using micromagnetic simulations by implementing the Landau-Lifshitz-Gilbert
equation with nonlocal spin-transfer torque in a finite difference
micromagnetic package. We find that in the presence of DW Gaussian wave packets
(spin waves) will be generated when the charge current is applied to the system
suddenly. And this effect is excluded when using the local spin-transfer
torque. The existence of spin waves emission indicates that transverse domain
walls can not move arbitrarily fast in cylindrical nanowires although they are
free from the Walker limit. We establish an upper-velocity limit for the DW
motion by analyzing the stability of Gaussian wave packets using the local
spin-transfer torque. Micromagnetic simulations show that the stable region
obtained by using nonlocal spin-transfer torque is smaller than that by using
its local counterpart. This limitation is essential for multiple domain walls
since the instability of Gaussian wave packets will break the structure of
multiple domain walls.",1608.04876v2
2018-07-31,Terahertz Spin Transfer Torque Oscillator Based on a Synthetic Antiferromagnet,"Bloch-Bloembergen-Slonczewski equation is adopted to simulate magnetization
dynamics in spin-valve based spin-transfer torque oscillator with synthetic
antiferromagnet acting as a free magnetic layer. High frequency up to the
terahertz scale is predicted in synthetic antiferromagnet spin-transfer torque
oscillator with no external magnetic field if the following requirements are
fulfilled: antiferromagnetic coupling between synthetic antiferromagnetic
layers is sufficiently strong, and the thickness of top (bottom) layer of
synthetic antiferromagnet is sufficiently thick (thin) to achieve a wide
current density window for the high oscillation frequency. Additionally, the
transverse relaxation time of the free magnetic layer should be sufficiently
larger compared with the longitudinal relaxation time. Otherwise, stable
oscillation cannot be sustained or scenarios similar to regular spin
valve-based spin-transfer torque oscillator with relatively low frequency will
occur. Our calculations pave a new way for exploring THz spintronics devices.",1807.11633v1
2014-11-18,Spin transfer torques generated by the anomalous Hall effect and anisotropic magnetoresistance,"Spin-orbit coupling in ferromagnets gives rise to the anomalous Hall effect
and the anisotropic magnetoresistance, both of which can be used to create
spin-transfer torques in a similar manner as the spin Hall effect. In this
paper we show how these effects can be used to reliably switch perpendicularly
magnetized layers and to move domain walls. A drift-diffusion treatment of the
anomalous Hall effect and the anisotropic magnetoresistance describes the spin
currents that flow in directions perpendicular to the electric field. In
systems with two ferromagnetic layers separated by a spacer layer, an in-plane
electric field cause spin currents to be injected from one layer into the
other, creating spin transfer torques. Unlike the related spin Hall effect in
non-magnetic materials, the anomalous Hall effect and the anisotropic
magnetoresistance allow control of the orientation of the injected spins, and
hence torques, by changing the direction of the magnetization in the injecting
layer. The torques on one layer show a rich angular dependence as a function of
the orientation of the magnetization in the other layer. The control of the
torques afforded by changing the orientation of the magnetization in a fixed
layer makes it possible to reliably switch a perpendicularly magnetized free
layer. Our calculated critical current densities for a representative
CoFe/Cu/FePt structure show that the switching can be efficient for appropriate
material choices. Similarly, control of the magnetization direction can drive
domain wall motion, as shown for NiFe/Cu/NiFe structures.",1411.4863v1
2018-03-27,Spin flip scattering engendered quantum spin torque in a Josephson junction,"We examine a Josephson junction with two Ferromagnets and a spin flipper
sandwiched between two superconductors. In such Ferromagnetic Josephson
junctions, equilibrium spin torque exists only when Ferromagnets are
misaligned. This is explained via the ""conventional"" mechanism of spin transfer
torque, which owes its origin to the misalignment of two Ferromagnets. However,
we see surprisingly when the magnetic moments of the Ferromagnets are aligned
parallel or antiparallel, there is a finite equilibrium spin torque due to the
quantum mechanism of spin-flip scattering. We explore the properties of this
unique spin-flip scattering induced equilibrium quantum spin torque, especially
its tunability via exchange coupling and phase difference across the
superconductors.",1803.10105v2
2018-09-09,Spin transfer torques and spin-dependent transport in a metallic F/AF/N tunneling junction,"We study spin-dependent electron transport through a
ferromagnetic-antiferromagnetic-normal metal tunneling junction subject to a
voltage or temperature bias, in the absence of spin-orbit coupling. We derive
microscopic formulas for various types of spin torque acting on the
antiferromagnet as well as for charge and spin currents flowing through the
junction. The obtained results are applicable in the limit of slow
magnetization dynamics. We identify a parameter regime in which an
unconventional damping-like torque can become comparable in magnitude to the
equivalent of the conventional Slonczewski's torque generalized to
antiferromagnets. Moreover, we show that the antiferromagnetic sublattice
structure opens up a channel of electron transport which does not have a
ferromagnetic analogue and that this mechanism leads to a pronounced field-like
torque. Both charge conductance and spin current transmission through the
junction depend on the relative orientation of the ferromagnetic and the
antiferromagnetic vectors (order parameters). The obtained formulas for charge
and spin currents allow us to identify the microscopic mechanisms responsible
for this angular dependence and to assess the efficiency of an
antiferromagnetic metal acting as a spin current polarizer.",1809.02950v1
2019-03-22,Effect of inter-layer spin diffusion on skyrmion motion in magnetic multilayers,"It is well known that skyrmions can be driven using spin-orbit torques due to
the spin-Hall effect. Here we show an additional contribution in multilayered
stacks arises from vertical spin currents due to inter-layer diffusion of a
spin accumulation generated at a skyrmion. This additional interfacial spin
torque is similar in form to the in-plane spin transfer torque, but is
significantly enhanced in ultra-thin films and acts in the opposite direction
to the electron flow. The combination of this diffusive spin torque and the
spin-orbit torque results in skyrmion motion which helps to explain the
observation of small skyrmion Hall angles even with moderate magnetisation
damping values. Further, the effect of material imperfections on threshold
currents and skyrmion Hall angle is also investigated. Topographical surface
roughness, as small as a single monolayer variation, is shown to be an
important contributing factor in ultra-thin films, resulting in good agreement
with experimental observations.",1903.09398v1
2007-08-16,Spin-transfer torques in anti-ferromagnetic metals from first principles,"In spite of the absence of a macroscopic magnetic moment, an anti-ferromagnet
is spin-polarized on an atomic scale. The electric current passing through a
conducting anti-ferromagnet is polarized as well, leading to spin-transfer
torques when the order parameter is textured, such as in anti-ferromagnetic
non-collinear spin valves and domain walls. We report a first principles study
on the electronic transport properties of anti-ferromagnetic systems. The
current-induced spin torques acting on the magnetic moments are comparable with
those in conventional ferromagnetic materials, leading to measurable angular
resistances and current-induced magnetization dynamics. In contrast to
ferromagnets, spin torques in anti-ferromagnets are very nonlocal. The torques
acting far away from the center of an anti-ferromagnetic domain wall should
facilitate current-induced domain wall motion.",0708.2143v2
2011-03-24,Effect of nonadiabatic spin transfer torque on domain wall resonance frequency and mass,"The dynamics of a magnetic domain wall in a semi circular nanowire loop is
studied by an analytical model and micromagnetic simulations. We find a damped
sinusoidal oscillation of the domain wall for small displacement angles around
its equilibrium position under an external magnetic field in the absence of
currents. By studying the effect of current induced nonadiabatic spin transfer
torque on the magnetic domain wall resonance frequency and mass, a red shift is
found in the resonance frequency and domain wall mass increases by increasing
the ratio of nonadiabatic spin torque to adiabatic contribution above 1.",1103.4670v1
2006-06-05,Phenomenological theory of current driven exchange switching in ferromagnetic nanojunctions,"Phenomenological approach is developed in the theory of spin-valve type
ferromagnetic junctions to describe exchange switching by current flowing
perpendicular to interfaces. Forward and backward current switching effects are
described and they may be principally different in nature. Mobile electron
spins are considered as being free in all the contacting ferromagnetic layers.
Joint action of the following two current effects is investigated: the
nonequilibrium longitudinal spin-injection effective field and the transverse
spin-transfer surface torque. Dispersion relation for fluctuations is derived
and solved for a junction model having spatially localized spin transfer
torque: depth of the torque penetration into the free layer is assumed much
smaller than the total free layer thickness. Some critical value of the well
known Gilbert damping constant is established for the first time. Spin transfer
torque dominates in the instability threshold determination for small enough
damping constants, while the spin-injection effective field dominates for high
damping. Fine interplay between spin transfer torque and spin injection is
necessary to provide a hysteretic behavior of the resistance versus current
dependence. The state diagram building up shows the possibility of
non-stationary (time dependent) nonlinear states arising due to instability
development. Calculations lead to the instability rise time values of the order
of 0.1 ns. Spin wave resonance frequency spectrum softening occurs under the
current growing to the instability threshold. Magnetization fluctuations above
the threshold rise oscillating with time for low damping, but rise
aperiodically and much more rapid for high damping.",0606102v2
2009-02-06,Spin torque from tunneling through impurities in a magnetic tunnel junction,"We calculate the contribution to the spin transfer torque from sequential
tunneling through impurities in a magnetic tunnel junction. For a junction with
weakly polarized ferromagnetic contacts, the torque is found to be in the plane
spanned by the magnetizations of the ferromagnetic contacts and proportional to
$\sin \theta$, where $\theta$ is the angle between the magnetic moments. If the
polarization is larger, the torque acquires a significant out-of-plane
component and a different dependence on $\theta$.",0902.1150v2
2020-03-27,Generalized magnetoelectronic circuit theory and spin relaxation at interfaces in magnetic multilayers,"Spin transport at metallic interfaces is an essential ingredient of various
spintronic device concepts, such as giant magnetoresistance, spin-transfer
torque, and spin pumping. Spin-orbit coupling plays an important role in many
such devices. In particular, spin current is partially absorbed at the
interface due to spin-orbit coupling. We develop a general magnetoelectronic
circuit theory and generalize the concept of the spin mixing conductance,
accounting for various mechanisms responsible for spin-flip scattering. For the
special case when exchange interactions dominate, we give a simple expression
for the spin mixing conductance in terms of the contributions responsible for
spin relaxation (i.e., spin memory loss), spin torque, and spin precession. The
spin-memory loss parameter $\delta$ is related to spin-flip transmission and
reflection probabilities. There is no straightforward relation between spin
torque and spin memory loss. We calculate the spin-flip scattering rates for
N|N, F|N, F|F interfaces using the Landauer-B\""uttiker method within the linear
muffin-tin orbital method and determine the values of $\delta$ using circuit
theory.",2003.12221v1
2016-10-31,Driven energy transfer between coupled modes in spin-torque oscillators,"The mutual interaction between the different eigenmodes of a spin-torque
oscillator can lead to a large variety of physical mechanisms from mode hopping
to multi-mode generation, that usually reduce their performances as
radio-frequency devices. To tackle this issue for the future applications, we
investigate the properties of a model spin-torque oscillator that is composed
of two coupled vortices with one vortex in each of the two magnetic layers of
the oscillator. In such double-vortex system, the remarkable properties of
energy transfer between the coupled modes, one being excited by spin transfer
torque while the second one being damped, result into an alteration of the
damping parameters. As a consequence, the oscillator nonlinear behavior is
concomitantly drastically impacted. This efficient coupling mechanism, driven
mainly by the dynamic dipolar field generated by the spin transfer torque
induced motion of the vortices, gives rise to an unexpected dynamical regime of
self-resonance excitation. These results show that mode coupling can be
leveraged for controlling the synchronization process as well as the frequency
tunability of spin-torque oscillators.",1610.10007v1
2010-09-19,Effect of spin transfer torque on the magnetic domain wall ferromagnetic resonance frequency in the nanowires,"We investigate the influence of the domain wall ferromagnetic resonance
frequency on the spin transfer torque in a ferromagnetic nanowire. By employing
micromagnetic simulations with the spin transfer torque, we find that the
domain wall resonance frequency decreases with increasing spin polarized
current density, when there is no change in the resonance frequency of the
domain itself. Surprisingly, the variation of the resonance frequency is
remarkable (> 1.6 GHz) with the spin transfer torque even though the domain
wall is pinned. Since the presented domain wall ferromagnetic resonance study
has been performed for the pinned domain wall, the contributions of extrinsic
defects are excluded. It is strong advantages of the present study, since the
effects of extrinsic pinning sites are inevitable in the imaging or transport
measurements.",1009.3618v1
2018-04-02,Spin torques and magnetic texture dynamics driven by the supercurrent in superconductor/ferromagnet structures,"We introduce the general formalism to describe spin torques induced by the
supercurrents injected from the adjacent superconducting electrodes into the
spin-textured ferromagnets. By considering the adiabatic limit for the
equal-spin superconducting correlations in the ferromagnet we show that the
supercurrent can generate both the field-like spin transfer torque and the
spin-orbital torque. These dissipationless spin torques are expressed through
the current-induced corrections to the effective field derived from the system
energy. The general formalism is applied to show that the supercurrent can
either shift or move the magnetic domain walls depending on their structure and
the type of spin-orbital interaction in the system. These results can be used
for the prediction and interpretation of the experiments studying magnetic
texture dynamics in superconductor/ferromagnet/superconductor Josephson
junctions and other hybrid structures.",1804.00718v2
2004-07-27,Domain wall dynamics driven by adiabatic spin transfer torques,"In a first approximation, known as the adiabatic process, the direction of
the spin polarization of currents is parallel to the local magnetization vector
in a domain wall. Thus the spatial variation of the direction of the spin
current inside the domain wall results in an adiabatical spin transfer torque
on the magnetization. We show that domain wall motion driven by this spin
torque has many unique features that do not exist in the conventional wall
motion driven by a magnetic field. By analytically and numerically solving the
Landau-Lifshitz-Gilbert equation along with the adiabatic spin torque in
magnetic nanowires, we find the domain wall has its maximum velocity at the
initial application of the current but the velocity decreases to zero as the
domain wall begins to deform during its motion. We have computed domain wall
displacement and domain wall deformation of nanowires, and concluded that the
spin torque based on the adiabatic propagation of the spin current in the
domain wall is unable to maintain wall movement. We also introduce a novel
concept of domain wall inductance to characterize the capacity of the
spin-torque induced magnetic energy stored in a domain wall. In the presence of
domain wall pinning centers, we construct a phase diagram for the domain wall
depinning by the combined action of the magnetic field and the spin current.",0407064v1
2014-07-23,Deterministic Domain Wall Motion Orthogonal To Current Flow Due To Spin Orbit Torque,"Deterministic control of domain walls orthogonal to the direction of current
flow is demonstrated by exploiting spin orbit torque in a perpendicularly
polarized Ta/CoFeB/MgO multilayer in presence of an in-plane magnetic field.
Notably, such orthogonal motion with respect to current flow is not possible
from traditional spin transfer torque driven domain wall propagation even in
presence of an external magnetic field. Reversing the polarity of either the
current flow or the in-plane field is found to reverse the direction of the
domain wall motion. From these measurements, which are unaffected by any
conventional spin transfer torque by symmetry, we estimate the spin orbit
torque efficiency of Ta to be 0.08.",1407.6137v1
2018-07-05,Bridging magnonics and spin-orbitronics,"The emerging field of nano-magnonics utilizes high-frequency waves of
magnetization - the spin waves - for the transmission and processing of
information on the nanoscale. The advent of spin-transfer torque has spurred
significant advances in nano-magnonics, by enabling highly efficient local
spin-wave generation in magnonic nanodevices. Furthermore, the recent emergence
of spin-orbitronics, which utilizes spin-orbit interaction as the source of
spin torque, has provided a unique ability to exert spin torque over spatially
extended areas of magnonic structures, enabling enhanced spin-wave
transmission. Here, we experimentally demonstrate that these advances can be
efficiently combined. We utilize the same spin-orbit torque mechanism for the
generation of propagating spin waves, and for the long-range enhancement of
their propagation, in a single integrated nano-magnonic device. The
demonstrated system exhibits a controllable directional asymmetry of spin wave
emission, which is highly beneficial for applications in non-reciprocal
magnonic logic and neuromorphic computing.",1807.02050v1
2005-11-09,Current driven magnetization dynamics in helical spin density waves,"A mechanism is proposed for manipulating the magnetic state of a helical spin
density wave using a current. In this paper, we show that a current through a
bulk system with a helical spin density wave induces a spin transfer torque,
giving rise to a rotation of the order parameter.The use of spin transfer
torque to manipulate the magnetization in bulk systems does not suffer from the
obstacles seen for magnetization reversal using interface spin transfer torque
in multilayered systems. We demonstrate the effect by a quantitative
calculation of the current induced magnetization dynamics of Erbium. Finally we
propose a setup for experimental verification.",0511224v2
2015-05-20,Josephson Currents and Spin Transfer Torques in Ballistic SFSFS Nanojunctions,"Utilizing a full microscopic Bogoliubov-de Gennes (BdG) approach, we study
the equilibrium charge and spin currents in ballistic $SFSFS$ Josephson
systems, where $F$ is a uniformly magnetized ferromagnet and $S$ is a
conventional $s$-wave superconductor. From the spatially varying spin currents,
we also calculate the associated equilibrium spin transfer torques. Through
variations in the relative phase differences between the three $S$ regions, and
magnetization orientations of the ferromagnets, our study demonstrates
tunability and controllability of the spin and charge supercurrents. The spin
transfer torques are shown to reveal details of the proximity effects that play
a crucial role in these types of hybrid systems. The proposed $SFSFS$
nanostructure is discussed within the context of a superconducting magnetic
torque transistor.",1505.05520v1
2017-10-04,Possible evidence for spin-transfer torque induced by spin-triplet supercurrent,"Cooper pairs in superconductors are normally spin singlet. Nevertheless,
recent studies suggest that spin-triplet Cooper pairs can be created at
carefully engineered superconductor-ferromagnet interfaces. If Cooper pairs are
spin-polarized they would transport not only charge but also a net spin
component, but without dissipation, and therefore minimize the heating effects
associated with spintronic devices. Although it is now established that triplet
supercurrents exist, their most interesting property - spin - is only inferred
indirectly from transport measurements. In conventional spintronics, it is well
known that spin currents generate spin-transfer torques that alter
magnetization dynamics and switch magnetic moments. The observation of similar
effects due to spin-triplet supercurrents would not only confirm the net spin
of triplet pairs but also pave the way for applications of superconducting
spintronics. Here, we present a possible evidence for spin-transfer torques
induced by triplet supercurrents in superconductor/ferromagnet/superconductor
(S/F/S) Josephson junctions. Below the superconducting transition temperature
T_c, the ferromagnetic resonance (FMR) field at X-band (~ 9.0 GHz) shifts
rapidly to a lower field with decreasing temperature due to the spin-transfer
torques induced by triplet supercurrents. In contrast, this phenomenon is
absent in ferromagnet/superconductor (F/S) bilayers and
superconductor/insulator/ferromagnet/superconductor (S/I/F/S) multilayers where
no supercurrents pass through the ferromagnetic layer. These experimental
observations are discussed with theoretical predictions for ferromagnetic
Josephson junctions with precessing magnetization.",1710.01534v1
2013-06-27,Influence of the magnetic material on tunneling magnetoresistance and spin-transfer torque in tunnel junctions: Ab initio studies,"The dependence of tunneling magnetoresistance and spin-transfer torque in
FeCo/MgO/FeCo tunnel junctions on the Co concentration and the bias voltage are
investigated ab initio. We find that the tunneling magnetoresistance decreases
with the Co concentration in contradiction with previous calculations but in
agreement with recent experiments. This dependence is explained from bulk
properties of the alloys. By using a realistic description of the disorder in
the alloys we can show that even small amounts of disorder lead to a drastic
drop in the tunneling magnetoresistance. This provides a quantitative
explanation of the difference between calculated and measured values.
  The spin-transfer torque shows a linear voltage dependence for the in-plane
component and a quadratic for the out-of-plane component for all concentrations
at small bias voltages. In particular, the linear slope of the in-plane torque
is independent of the concentration. For high bias voltages the in-plane torque
shows a strong nonlinear deviation from the linear slope for high Co
concentrations. This is explained from the same effects which govern the
tunneling magnetoresistance.",1306.6447v1
2005-08-25,Current-induced Vortex Motion by Spin-Transfer Torque,"We investigate the dynamics of a magnetic vortex driven by spin-transfer
torque due to spin current in the adiabatic case. The vortex core represented
by collective coordinate experiences a transverse force proportional to the
product of spin current and gyrovector, which can be interpreted as the
geometric force determined by topological charges. We show that this force is
just a reaction force of Lorentz-type force from the spin current of conduction
electrons. Based on our analyses, we propose analytically and numerically a
possible experiment to check the vortex displacement by spin current in the
case of single magnetic nanodot.",0508599v1
2006-03-09,Spin Current and Current-Induced Spin Transfer Torque in Ferromagnet-Quantum Dot-Ferromagnet Coupled Systems,"Based on Keldysh's nonequilibrium Green function method, the spin-dependent
transport properties in a ferromagnet-quantum dot (QD)-ferromagnet coupled
system are investigated. It is shown the spin current shows quite different
characteristics from its electrical counterpart, and by changing the relative
orientation of both magnetizations, it can change its magnitude even sign. The
current-induced spin transfer torque (CISTT) is uncovered to be greatly
enhanced when the bias voltage meets with the discrete levels of the QD at
resonant positions. The relationship between the CISTT, the electrical current
and the spin current is also addressed.",0603235v1
2007-01-09,Thermal Spin-Transfer Torques in Magnetoelectronic Devices,"We predict that the magnetization direction of a ferromagnet can be reversed
by the spin-transfer torque accompanying spin-polarized thermoelectric heat
currents. We illustrate the concept by applying a finite-element theory of
thermoelectric transport in disordered magnetoelectronic circuits and devices
to metallic spin valves. When thermalization is not complete, a spin heat
accumulation vector is found in the normal metal spacer, i.e., a directional
imbalance in the temperature of majority and minority spins.",0701163v2
2012-11-16,Dependence of the Switching Current Density on the Junction Sizes in Spin Transfer Torque,"We investigate the dependence of switching current density on the junction
sizes in the spin transfer torque nanopillar structures by using micromagnetic
simulations. While the macro spin model predicts weak dependence of switching
current density on the junction sizes, we find that the switching current
density is a sensitive function of the junction sizes. It can be explained with
the complicated spin configurations and dynamics during the switching process.
The detail spin configurations and dynamics are determined by spin wave
excitation with the finite wave vector, which is related with the exchange
coupling energy and junction shape.",1211.3785v1
2013-05-04,Role of the Non-Collinear Polarizer Layer in Spin Transfer Torque Switching Processes,"We have recently reported that the spin transfer torque switching current
density is very sensitive to not only the junction sizes but also the exchange
stiffness constants of the free layer according to the micromagnetic
simulations. The results are very complicate and far from the macro-spin model
because of the non-coherent spin switching processes. The dependence of the
switching current density on the junction sizes and the exchange stiffness
constants becomes systematic when we employ the non-collinear polarizer layer.
It is found that the non-collinear polarizer layer enhances the coherency of
the spin dynamics by breaking symmetric spin configurations.",1305.0869v1
2022-08-26,Unified theory of spin and charge in a ferromagnet,"We derive a unified theory of spin and charge degrees of freedom in a
ferromagnet. The spin-transfer torque and spin electromotive force are examined
from the coarse-grained perspective of collective coordinates. The resulting
equations of motion reflect a balance of conservative, gyroscopic
(Berry-phase), and dissipative forces. We then expand the space of collective
coordinates by adding the electric charge. The adiabatic spin-transfer torque
and spin emf turn out to be a gyroscopic force; their nonadiabatic counterparts
are a dissipative force.",2208.12800v2
2023-05-20,Absence of cross-sublattice spin pumping and spin-transfer torques in collinear antiferromagnets,"We resolve the debate over the existence and magnitude of cross-sublattice
(CS) contributions to spin pumping and spin-transfer torques in a
two-sublattice antiferromagnet connected to a non-magnetic metal. Guided by
symmetry considerations, we first relate the controversial CS terms to specific
components in the spin conductance matrix. Then we quantify these components by
studying the spin-dependent electron scattering on a fully compensated
interface. We ascertain the absence of all CS contributions in the collinear
regime. Even in the non-collinear regime, the CS contributions only constitute
a higher-order correction to the existing theory.",2305.13334v2
2008-02-26,Spin transfer torques in magnetic tunnel junctions,"This chapter presents a review on spin transfer torque in magnetic tunnel
junctions. In the first part, we propose an overview of experimental and
theoretical studies addressing current-induced magnetization excitations in
magnetic tunnel junctions. The most significant results are presented and the
main observable characteristics are discussed. A description of the mechanism
of spin transfer in ferromagnets is finally proposed. In the second part, a
quantum description of spin transport in magnetic tunnel junctions with
amorphous barrier is developed. The role of spin-dependent reflections as well
as electron incidence and spin-filtering by the barrier are described. We show
that these mechanisms give rise to specific properties of spin transfer in
tunnel junctions, very different from the case of metallic spin-valves. In the
third part, the theoretical observable features of spin transfer in magnetic
tunnel junctions are derived and the validity of these results is discussed and
compared to recent experiments. To conclude this chapter, we study the
mechanism of spin transfer in half-metallic tunnel junctions, expected to mimic
MgO-based magnetic tunnel junctions.",0802.3754v1
2008-08-14,Co-resonant enhancement of spin-torque critical currents in spin-valves with synthetic-ferrimagnet free-layer,"It is experimentally shown that the critical current for onset of spin-torque
instability in current-perpendicular-to-plane spin-valves can be strongly
enhanced using ""synthetic ferrimagnet"" free-layers of form FM1/Ru/FM2
(FM=ferrromagnet). However, this enhancement occurs for only one polarity of
bias current. A two-macrospin model is shown to reproduce the observations. The
model suggests that this phenomenon is related to a polarity-dependent,
spin-torque induced co-resonance between the two natural dynamic modes of the
FM1/FM2 couple. The resonance condition facilitates energy transfer out of the
spin-torque destabilized mode into the other stable mode whose effective
damping is actually enhanced by spin-torques, thereby delaying the onset of
instability of this coupled system to larger critical currents.",0808.2015v2
2013-08-12,Analytical description of ballistic spin currents and torques in magnetic tunnel junctions,"In this work we demonstrate explicit analytical expressions for both charge
and spin currents which constitute the 2x2 spinor in magnetic tunnel junctions
with noncollinear magnetizations under applied voltage. The calculations have
been performed within the free electron model in the framework of the Keldysh
formalism and WKB approximation. We demonstrate that spin/charge currents and
spin transfer torques are all explicitly expressed through only three
irreducible quantities, without further approximations. The conditions and
mechanisms of deviation from the conventional sine angular dependence of both
spin currents and torques are shown and discussed. It is shown in the thick
barrier approximation that all tunneling transport quantities can be expressed
in an extremely simplified form via Slonczewski spin polarizations and our
effective spin averaged interfacial transmission probabilities and effective
out-of-plane polarizations at both interfaces. It is proven that the latter
plays a key role in the emergence of perpendicular spin torque as well as in
the angular dependence character of all spin and charge transport considered.
It is demonstrated directly also that for any applied voltage, the parallel
component of spin current at the FM/I interface is expressed via collinear
longitudinal spin current components. Finally, spin transfer torque behavior is
analyzed in a view of transverse characteristic length scales for spin
transport.",1308.2619v2
2018-07-19,Spin-wave amplification and lasing driven by inhomogeneous spin transfer torques,"We show that an inhomogeneity in the spin-transfer torques in a metallic
ferromagnet under suitable conditions strongly amplifies incoming spin waves.
Moreover, at nonzero temperatures the incoming thermally occupied spin waves
will be amplified such that the region with inhomogeneous spin transfer torques
emits spin waves spontaneously, thus constituting a spin-wave laser. We
determine the spin-wave scattering amplitudes for a simplified model and
set-up, and show under which conditions the amplification and lasing occurs.
Our results are interpreted in terms of a so-called black-hole laser, and could
facilitate the field of magnonics, that aims to utilize spin waves in logic and
data-processing devices.",1807.07312v1
2020-05-27,Effects of the Zhang-Li Torque on Spin Torque nano Oscillators,"Spin-torque nano-oscillators (STNO) are microwave auto-oscillators based on
magnetic resonances having a nonlinear response with the oscillating amplitude,
which provides them with a large frequency tunability including the possibility
of mutual synchronization. The magnetization dynamics in STNO are induced by
spin transfer torque (STT) from spin currents and can be detected by changes in
electrical resistance due to giant magnetoresistance or tunneling
magnetoresistance. The STT effect is usually treated as a damping-like term
that reduces magnetic dissipation and promotes excitation of magnetic modes.
However, an additional term, known as Zhang-Li term has an effect on
magnetization gradients such as domain walls, and could have an effect on
localized magnetic modes in STNO. Here we study the effect of Zhang-Li torques
in magnetic excitations produced in STNO with a nanocontact geometry. Using
micromagnetic simulations we find that Zhang-Li torque modify threshold
currents of magnetic modes and their effective sizes. Additionally we show that
effects can be controlled by changing the ratio between nanocontact size and
layer thickness.",2005.13364v1
2021-05-13,Characterization of a double torsion pendulum used to detect spin-induced torque based on Beth's experiment,"We characterized a double torsion pendulum system, including measurements of
the photon-spin-induced torque. Our experimental strategy was similar to that
used in Beth's experiment, which was performed in 1936 to measure
photon-spin-induced torque using forced oscillation caused by polarization
modulation of light incident on a suspended object. Through simple passive
isolation of the suspended object from external vibration noise, the achieved
torque sensitivity was 2 x 10^{-17} N m in a measurement time of 10^4 s, which
is close to the thermal noise limit and one order smaller than the minimum
torque measured in Beth's experiment. The observed spin-induced torque exerted
on the light-absorbing optics is consistent with the angular momentum transfer
of hbar per photon.",2105.06181v2
2007-04-03,Shaped angular dependence of the spin transfer torque and microwave generation without magnetic field,"The generation of oscillations in the microwave frequency range is one of the
most important applications expected from spintronics devices exploiting the
spin transfer phenomenon. We report transport and microwave power measurements
on specially designed nanopillars for which a non-standard angular dependence
of the spin transfer torque (wavy variation) is predicted by theoretical
models. We observe a new kind of current-induced dynamics that is characterized
by large angle precessions in the absence of any applied field, as this is also
predicted by simulation with such a wavy angular dependence of the torque. This
type of non-standard nanopillars can represent an interesting way for the
implementation of spin transfer oscillators since they are able to generate
microwave oscillations without applied magnetic field. We also emphasize the
theoretical implications of our results on the angular dependence of the
torque.",0704.0370v1
2010-06-23,Proposal of a spin torque majority gate logic,"A new spin based logic device is proposed. It is comprised of a common free
ferromagnetic layer separated by a tunnel junction from three inputs and one
output with separate fixed layers. It has the functionality of a majority gate
and is switched by spin transfer torque. Validity of its logic operation is
demonstrated by micromagnetic simulation. A version of such devices with
perpendicular magnetization is examined. Switching encompasses moving domain
walls. The device reuses most of the materials and structures from spin torque
RAM, and is entirely compatible with CMOS technology.",1006.4663v1
2013-06-12,Anomalous domain wall velocity and Walker breakdown in hybrid systems with anisotropic exchange,"It has recently been proposed that spin-transfer torques in magnetic systems
with anisotropic exchange can be strongly enhanced, reducing the characteristic
current density with up to four orders of magnitude compared to conventional
setups. Motivated by this, we analytically solve the equations of motion in a
collective-coordinate framework for this type of anisotropic exchange system,
to investigate the domain wall dynamics in detail. In particular, we obtain
analytical expressions for the maximum attainable domain wall velocity of such
a setup and also for the occurrence of Walker breakdown. Surprisingly, we find
that, in contrast to the standard case with domain wall motion driven by the
nonadiabatic torque, the maximum velocity obtained via the anisotropic exchange
torque is completely independent of the nonadiabaticity parameter beta, in
spite of the torque itself being very large for small beta. Moreover, the
Walker breakdown threshold has an opposite dependence on beta in these two
cases; i.e., for the anisotropic exchange torque scenario, the threshold value
decreases monotonically with beta. These findings are of importance to any
practical application of the proposed giant spin-transfer torque in anisotropic
exchange systems.",1306.2957v1
2008-10-19,Macrospin model of incubation delay due to the field-like spin transfer torque,"We show that the absence of pre-switching oscillations (""incubation delay"")
in magnetic tunnel junctions can be explained within the macrospin model by a
sizable field-like component of the spin-transfer torque. It is further
suggested that measurements of the voltage dependence of tunnel junction
switching time in the presence of external easy axis magnetic fields can be
used to determine the magnitude and voltage dependence of the field-like
torque.",0810.3421v1
2011-10-16,Signatures of asymmetric and inelastic tunneling on the spin torque bias dependence,"The influence of structural asymmetries (barrier height and exchange
splitting), as well as inelastic scattering (magnons and phonons) on the bias
dependence of the spin transfer torque in a magnetic tunnel junction is studied
theoretically using the free electron model. We show that they modify the
""conventional"" bias dependence of the spin transfer torque, together with the
bias dependence of the conductance. In particular, both structural asymmetries
and bulk (inelastic) scattering add {\em antisymmetric} terms to the
perpendicular torque ($\propto V$ and $\propto j_e|V|$), while the interfacial
inelastic scattering conserves the junction symmetry and only produces {\em
symmetric} terms ($\propto |V|^n$, $n\in\mathbb{N}$). The analysis of spin
torque and conductance measurements displays a signature revealing the origin
(asymmetry or inelastic scattering) of the discrepancy.",1110.3492v1
2013-06-29,First-principles calculations of current-induced spin-transfer torques in magnetic domain walls,"Current-induced spin-transfer torques (STTs) have been studied in Fe, Co and
Ni domain walls (DWs) by the method based on the first-principles noncollinear
calculations of scattering wave functions expanded in the tight-binding
linearized muffin-tin orbital (TB-LMTO) basis. The results show that the
out-of-plane component of nonadiabatic STT in Fe DW has localized form, which
is in contrast to the typical nonlocal oscillating nonadiabatic torques
obtained in Co and Ni DWs. Meanwhile, the degree of nonadiabaticity in STT is
also much greater for Fe DW. Further, our results demonstrate that compared to
the well-known first-order nonadiabatic STT, the torque in the third-order
spatial derivative of local spin can better describe the distribution of
localized nonadiabatic STT in Fe DW. The dynamics of local spin driven by this
third-order torques in Fe DW have been investigated by the
Landau-Lifshitz-Gilbert (LLG) equation. The calculated results show that with
the same amplitude of STTs the DW velocity induced by this third-order term is
about half of the wall speed for the case of the first-order nonadiabatic STT.",1307.0062v1
2015-11-27,Universal relationships between optical force/torque and orbital versus spin momentum/angular momentum of light,"We establish universal relationships between optical force/torque on a
general particle and different parts of linear and angular momentum (AM) of
generic monochromatic optical field. It is rigorously proved that the optical
force comes about by the transfer of orbital (canonical) optical momentum from
light to matter, while the other part of optical momentum, known as spin
momentum, does not generate optical force on matter but, instead, stays
conserved even when the translational invariance is broken by putting particles
into the optical fields. On the other hand, based on a generic multipole theory
of optical torque, we demonstrate that the optical torque stems from the
transfer of the total optical AM, including both orbital and spin AM,
clarifying in generic case the long-standing confusion about whether the
orbital AM can induce a spinning torque on a general particle in generic
optical fields.",1511.08546v3
2005-12-29,Current-induced magnetization dynamics in disordered itinerant ferromagnets,"Current-driven magnetization dynamics in ferromagnetic metals are studied in
a self-consistent adiabatic local-density approximation in the presence of
spin-conserving and spin-dephasing impurity scattering. Based on a quantum
kinetic equation, we derive Gilbert damping and spin-transfer torques entering
the Landau-Lifshitz equation to linear order in frequency and wave vector.
Gilbert damping and a current-driven dissipative torque scale identically and
compete, with the result that a steady current-driven domain-wall motion is
insensitive to spin dephasing in the limit of weak ferromagnetism. A uniform
magnetization is found to be much more stable against spin torques in the
itinerant than in the \textit{s}-\textit{d} model for ferromagnetism. A dynamic
spin-transfer torque reminiscent of the spin pumping in multilayers is
identified and shown to govern the current-induced domain-wall distortion.",0512715v4
2014-04-15,Spin pumping and spin-transfer torques in antiferromagnets,"Spin pumping and spin-transfer torques are two reciprocal phenomena widely
studied in ferromagnetic materials. However, pumping from antiferromagnets and
its relation to current-induced torques have not been explored. By calculating
how electrons scatter off a normal metal-antiferromagnetic interface, we derive
pumped spin and staggered spin currents in terms of the staggered field, the
magnetization, and their rates of change. For both compensated and
uncompensated interfaces, spin pumping is of a similar magnitude as in
ferromagnets with a direction controlled by the polarization of the driving
microwave. The pumped currents are connected to current-induced torques via
Onsager reciprocity relations.",1404.4023v3
2017-10-02,Multi-scale modelling of current-induced switching in magnetic tunnel junctions using ab initio spin transfer torques,"There exists a significant challenge in developing efficient magnetic tunnel
junctions with low write currents for non-volatile memory devices. With the aim
of analysing potential materials for efficient current-operated magnetic
junctions we have developed a multi-scale methodology combining the ab initio
calculations of spin-transfer torque with large-scale time-dependent
simulations using atomistic spin dynamics. In this work we introduce our
multi-scale approach including a discussion on a number of possible mapping
schemes the ab initio spin torques into the spin dynamics. We demonstrate this
methodology on a prototype Co/MgO/Co/Cu tunnel junction showing that the spin
torques are primarily acting at the interface between the Co free layer and
MgO. Using spin dynamics we then calculate the reversal switching times for the
free layer and the critical voltages and currents required for such switching.
Our work provides an efficient, accurate and versatile framework for designing
novel current-operated magnetic devices, where all the materials details are
take into account.",1710.00574v1
2003-10-16,Spin Torque and its Relation to Spin Filtering,"The spin torque exerted on a magnetic moment is a reaction to spin filtering
when spin-polarized electrons interact with a thin ferromagnetic film. We show
that, for certain conditions, a spin transmission resonance (STR) gives rise to
a failure of spin filtering. As a consequence, no spin is transfered to the
ferromagnet. The condition for STR depends on the incoming energy of electrons
and the thickness of the film. For a simple model we find that when the STR
condition is satisfied, the ferromagnetic film is transparent to the incoming
electrons.",0310392v1
2015-10-16,Voltage-Driven Spin-Transfer Torque in a Magnetic Particle,"We discuss a spin-transfer torque device, where the role of the soft
ferromagnetic layer is played by a magnetic particle or a magnetic molecule, in
weak tunnel contact with two spin polarized leads. We investigate if the
magnetization of the particle can be manipulated electronically, in the regime
where the critical current for magnetization switching is negligibly weak,
which could be due to the reduced particle dimensions. Using master equation
simulations to evaluate the effects of spin-orbit anisotropy energy
fluctuations on spin-transfer, we obtain reliable reading and writing of the
magnetization state of such magnetic particle, and find that the device relies
on a critical voltage rather than a critical current. The critical voltage is
governed by the spin-orbit energy shifts of discrete levels in the particle.
This finding opens a possibility to significantly reduce the power dissipation
involved in spin-transfer torque switching, by using very small magnetic
particles or molecules.",1510.04769v1
2020-01-21,Nonresonant amplification of coherent spin waves through voltage-induced interface magnetoelectric effect and spin-transfer torque,"We present new mechanism for manipulation of the spin-wave amplitude through
the use of the dynamic charge-mediated magnetoelectric effect in ultrathin
multilayers composed of dielectric thin-film capacitors separated by a
ferromagnetic bilayer. Propagating spin waves can be amplified and attenuated
with rising and decreasing slopes of the oscillating voltage, respectively,
locally applied to the sample. The way the spin accumulation is generated makes
the interaction of the spin-transfer torque with the magnetization dynamics
mode-selective and restricted to some range of spin-wave frequencies, which is
in contrary to known types of the spin-transfer torque effects. The interfacial
nature of spin-dependent screening allows to reduce the thickness of the fixed
magnetization layer to a few nanometers, thus the proposed effect significantly
contributes toward realization of the magnonic devices and also miniaturization
of the spintronic devices.",2001.07474v1
2023-02-20,Néel-Vector Switching and THz Spin-Wave Excitation in Mn$_2$Au due to Femtosecond Spin-Transfer Torques,"Efficient and fast manipulation of antiferromagnets has to date remained a
challenging task, hindering their application in spintronic devices. For
ultrafast operation of such devices, it is highly desirable to be able to
control the antiferromagnetic order within picoseconds - a timescale that is
difficult to achieve with electrical circuits. Here, we demonstrate that bursts
of spin-polarized hot-electron currents emerging due to laser-induced ultrafast
demagnetization are able to efficiently excite spin dynamics in
antiferromagnetic Mn$_2$Au by exerting a spin-transfer torque on femtosecond
timescales. We combine quantitative superdiffusive transport and atomistic
spin-model calculations to describe a spin-valve-type trilayer consisting of
Fe$|$Cu$|$Mn$_2$Au. Our results demonstrate that femtosecond spin-transfer
torques can switch the Mn$_2$Au layer within a few picoseconds. In addition, we
find that spin waves with high frequencies up to several THz can be excited in
Mn$_2$Au.",2302.09822v1
2019-01-21,"Edelstein effects, spin-transfer torque, and spin pumping caused by pristine surface states of topological insulators","The Edelstein effect caused by the pristine surface states of
three-dimensional topological insulators is investigated by means of a
semiclassical approach. The combined effect of random impurity scattering and
the spin-momentum locking of the gapless Dirac cone yields a current-induced
surface spin accumulation independent from chemical potential and temperature.
In a nearby ferromagnet that does not make direct contact with the topological
insulator, the bound state nature of the pristine surface state causes a
spin-transfer torque that is entirely field-like, whose magnitude is highly
influenced by the interface cleanliness and the quantum well state of the
ferromagnet. Through incorporating quantum tunneling into Bloch equation, the
spin pumping mediated by the pristine surface state is shown to be described by
the same spin mixing conductance as the spin-transfer torque, and a
semiclassical approach is proposed to explain the inverse Edelstein effect that
converts the spin pumping spin current into a charge current. Consistency of
these results with various experiments will be elaborated in detail.",1901.06953v2
2011-10-31,Magnetic switching by spin torque from the spin Hall effect,"The spin Hall effect (SHE) generates spin currents within nonmagnetic
materials. Previously, studies of the SHE have been motivated primarily to
understand its fundamental origin and magnitude. Here we demonstrate, using
measurement and modeling, that in a Pt/Co bilayer with perpendicular magnetic
anisotropy the SHE can produce a spin transfer torque that is strong enough to
efficiently rotate and reversibly switch the Co magnetization, thereby
providing a new strategy both to understand the SHE and to manipulate magnets.
We suggest that the SHE torque can have a similarly strong influence on
current-driven magnetic domain wall motion in Pt/ferromagnet multilayers. We
estimate that in optimized devices the SHE torque can switch magnetic moments
using currents comparable to those in magnetic tunnel junctions operated by
conventional spin-torque switching, meaning that the SHE can enable magnetic
memory and logic devices with similar performance but simpler architecture than
the current state of the art.",1110.6846v2
2016-05-06,Negative optical spin torque wrench of a nondiffracting non-paraxial fractional Bessel vortex beam,"An absorptive Rayleigh dielectric sphere in a non-diffracting non-paraxial
fractional Bessel vortex beam experiences a spin torque. The axial and
transverse radiation spin torque components are evaluated in the dipole
approximation using the radiative correction of the electric field. Particular
emphasis is given on the polarization as well as changing the topological
charge and the beam's half-cone angle. When the beam order is zero, the axial
spin torque component vanishes. However, when the beam order becomes a real
positive number, the vortex beam induces left-handed (negative) axial spin
torque as the sphere shifts off-axially from the center of the beam. The
results show that a non-diffracting non-paraxial fractional Bessel vortex beam
is capable to induce a spin reversal of an absorptive Rayleigh sphere placed
arbitrarily in its path. Potential applications are yet to be explored in
particle manipulation, rotation in optical tweezers, optical tractor beams, the
design of optically-engineered metamaterials to name a few areas.",1605.03432v2
2022-11-30,"Universal Relations of Energy Flow, Acoustic Spin and Torque for Near-Field Acoustic Tweezers","Acoustic spin, radiation torque, energy flow, and reactive power are of
significant importance from both fundamental and practical aspects, responsible
for flexible tweezer manipulations and near-field sound directionality.
Nevertheless, the intrinsic relations among these physical quantities are far
from clear. Here, we prove the universal geometric relations among them in
acoustics, independent on wave structure details. Particularly, we connect
acoustic spin and torque to the cross product of time-averaged energy flow and
reactive power, as well as to the local vorticity of energy flow. These
relations are universally valid, verified in a variety of different acoustic
systems. We also demonstrate the multipole mechanical torques and forces
generated in three acoustic near-field sources: Janus, Huygens and Spin
sources, applying on small lossy particles. These universal geometric relations
uncover hidden locking relations beyond simple spin-momentum locking of
near-field waves, and show the basic principles between the acoustic spin,
radiation torque, and energy flow, reactive power.",2212.00028v1
2005-05-11,Surface spin-transfer torque and spin-injection effective field in ferromagnetic junctions: Unified theory,"We consider theoretically a current flowing perpendicular to interfaces of a
spin-valve type ferromagnetic metallic junction. For the first time an
effective approach is investigated to calculate a simultaneous action of the
two current effects, namely, the nonequilibrium longitudinal spin injection and
the transversal spin-transfer surface torque. Dispersion relation for
fluctuations is derived and solved. Nonlinear problem is solved about steady
state arising due to instability for a thick enough free layer.",0505268v2
2007-10-11,Direct current voltage induced by microwave signal in a ferromagnetic wire,"Experimental results of rectification of a constant wave radio frequency (RF)
current flowing in a single-layered ferromagnetic wire are presented. We show
that a detailed external magnetic field dependence of the RF current induced a
direct-current voltage spectrum. The mechanism of the rectification is
discussed in a term of the spin transfer torque, and the rectification is
closely related to resonant spin wave excitation with the assistant of the
spin-polarized RF current. The micromagnetic simulation taking into account the
spin transfer torque provides strong evidence which supports the generation of
spin wave excitation by the RF current.",0710.2172v1
2011-03-19,Spin transfer torque on magnetic insulators,"Recent experimental and theoretical studies focus on spin-mediated heat
currents at interfaces between normal metals and magnetic insulators. We
resolve conflicting estimates for the order of magnitude of the spin transfer
torque by first-principles calculations. The spin mixing conductance
G^\uparrow\downarrow of the interface between silver and the insulating
ferrimagnet Yttrium Iron Garnet (YIG) is dominated by its real part and of the
order of 10^14 \Omega^-1m^-2, i.e. close to the value for intermetallic
interface, which can be explained by a local spin model.",1103.3764v2
2012-01-17,Spin wave excitation in magnetic insulators by spin-transfer torque,"We study the excitation of spin waves in magnetic insulators by the
current-induced spin-transfer torque. We predict preferential excitation of
surface spin waves induced by an easy-axis surface anisotropy with critical
current inversely proportional to the penetration depth and surface anisotropy.
The surface modes strongly reduce the critical current and enhance the
excitation power of the current-induced magnetization dynamics.",1201.3442v1
2022-12-02,Interplay between spin wave and magnetic vortex,"In this paper, the interplay between spin wave and magnetic vortex is
studied. We find three types of magnon scatterings: skew scattering, symmetric
side deflection and back reflection, which associate with respectively magnetic
topology, energy density distribution and linear momentum transfer torque
within vortex. The vortex core exhibits two translational modes: the intrinsic
circular mode and a coercive elliptical mode, which can be excited based on
permanent and periodic magnon spin-transfer torque effects of spin wave.
Lastly, we propose a vortex-based spin wave valve in which via inhomogeneity
modulation we access arbitrary control of the phase shift.",2212.01172v1
2008-06-11,Critical current of spin transfer torque-driven magnetization dynamics in magnetic multilayers,"The critical current of the spin transfer torque-driven magnetization
dynamics was studied by taking into account both spin pumping and the finite
penetration depth of the transverse spin current. We successfully reproduced
the recent experimental results obtained by Chen et al. [Phys. Rev. B {\bf 74},
144408 (2006)] and found that the critical current remains finite even in the
zero-thickness limit of the free layer. We showed that the remaining value of
the critical current is determined mainly by spin pumping.",0806.1822v2
2022-02-16,Orbit-transfer torque driven field-free switching of perpendicular magnetization,"The reversal of perpendicular magnetization (PM) by electric control is
crucial for high-density integration of low-power magnetic random-access memory
(MRAM). Although the spin-transfer torque (STT) and spin-orbit torque (SOT)
technologies have been used to switch the magnetization of a free layer with
perpendicular magnetic anisotropy, the former has limited endurance because of
the high current density directly through the junction, while the latter
requires an external magnetic field or unconventional configuration to break
the symmetry. Here we propose and realize the orbit-transfer torque (OTT), that
is, exerting torque on the magnetization using the orbital magnetic moments,
and thus demonstrate a new strategy for current-driven PM reversal without
external magnetic field. The perpendicular polarization of orbital magnetic
moments is generated by a direct current in a few-layer WTe2 due to the
existence of nonzero Berry curvature dipole, and the polarization direction can
be switched by changing the current polarity. Guided by this principle, we
construct the WTe2/Fe3GeTe2 heterostructures, where the OTT driven field-free
deterministic switching of PM is achieved.",2202.07840v1
2009-07-17,Current-induced dynamics in non-collinear dual spin-valves,"Spin-transfer torque and current induced spin dynamics in spin-valve
nanopillars with the free magnetic layer located between two magnetic films of
fixed magnetic moments is considered theoretically. The spin-transfer torque in
the limit of diffusive spin transport is calculated as a function of magnetic
configuration. It is shown that non-collinear magnetic configuration of the
outermost magnetic layers has a strong influence on the spin torque and spin
dynamics of the central free layer. Employing macrospin simulations we make
some predictions on the free layer spin dynamics in spin valves composed of
various magnetic layers. We also present a formula for critical current in
non-collinear magnetic configurations, which shows that the magnitude of
critical current can be several times smaller than that in typical single spin
valves.",0907.3094v2
2019-09-16,Spin current pumped by resonant skyrmion,"Spin pumping is a widely recognized method to generate the spin current in
the spintronics, which is acknowledged as a fundamentally dynamic process
equivalent to the spin-transfer torque. In this work, we theoretically verify
that the oscillating spin current can be pumped from the microwave-motivated
breathing skyrmion. The skyrmion spin pumping can be excited by a relatively
low frequency compared with the ferromagnetic resonance (FMR) and the current
density is larger than the ordinary FMR spin pumping. Based on the skyrmion
spin pumping, we build a high reading-speed racetrack memory model whose
reading speed is an order of magnitude higher than the SOT (spin-orbit torque)
/STT (spin-transfer torque) skyrmion racetrack. Our work explored the spin
pumping phenomenon in the skyrmion, and it may contribute to the applications
of the skyrmion-based device.",1909.07077v1
2020-10-23,Maximizing spin-orbit torque efficiency of Ta(O)/Py via modulating oxygen-induced interface orbital hybridization,"Spin-orbit torques due to interfacial Rashba and spin Hall effects have been
widely considered as a potentially more efficient approach than the
conventional spin-transfer torque to control the magnetization of ferromagnets.
We report a comprehensive study of spin-orbit torque efficiency in
Ta(O)/Ni81Fe19 bilayers by tuning low-oxidation of \b{eta}-phase tantalum, and
find that the spin Hall angle {\theta}DL increases from ~ -0.18 of the pure
Ta/Py to the maximum value ~ -0.30 of Ta(O)/Py with 7.8% oxidation.
Furthermore, we distinguish the efficiency of the spin-orbit torque generated
by the bulk spin Hall effect and by interfacial Rashba effect, respectively,
via a series of Py/Cu(0-2 nm)/Ta(O) control experiments. The latter has more
than twofold enhancement, and even more significant than that of the former at
the optimum oxidation level. Our results indicate that 65% enhancement of the
efficiency should be related to the modulation of the interfacial Rashba-like
spin-orbit torque due to oxygen-induced orbital hybridization cross the
interface. Our results suggest that the modulation of interfacial coupling via
oxygen-induced orbital hybridization can be an alternative method to boost the
change-spin conversion rate.",2010.12253v1
2012-08-20,Reversal and Termination of Current-Induced Domain Wall Motion via Magnonic Spin-Transfer Torque,"We investigate the domain wall dynamics of a ferromagnetic wire under the
combined influence of a spin-polarized current and magnonic spin-transfer
torque generated by an external field, taking also into account Rashba
spin-orbit coupling interactions. It is demonstrated that current-induced
motion of the domain wall may be completely reversed in an oscillatory fashion
by applying a magnonic spin-transfer torque as long as the spin-wave velocity
is sufficiently high. Moreover, we show that the motion of the domain wall may
be fully terminated by means of the generation of spin-waves, suggesting the
possibility to pin the domain-walls to predetermined locations. We also discuss
how strong spin-orbit interactions modify these results.",1208.4108v1
2007-09-25,Current-Induced Torques in Magnetic Metals: Beyond Spin Transfer,"Current-induced torques on ferromagnetic nanoparticles and on domain walls in
ferromagnetic nanowires are normally understood in terms of transfer of
conserved spin angular momentum between spin-polarized currents and the
magnetic condensate. In a series of recent articles we have discussed a
microscopic picture of current-induced torques in which they are viewed as
following from exchange fields produced by the misaligned spins of current
carrying quasiparticles. This picture has the advantage that it can be applied
to systems in which spin is not approximately conserved. More importantly, this
point of view makes it clear that current-induced torques can also act on the
order parameter of an antiferromagnetic metal, even though this quantity is not
related to total spin. In this informal and intentionally provocative review we
explain this picture and discuss its application to antiferromagnets.",0709.3862v1
2012-02-29,Spin-transfer torque and spin-polarization in topological-insulator/ferromagnet vertical heterostructures,"We predict an unconventional spin-transfer torque (STT) acting on the
magnetization of a free ferromagnetic (F) layer within N/TI/F vertical
heterostructures which originates from strong spin-orbit coupling (SOC) on the
surface of a three-dimensional topological insulator (TI), as well as from
charge current becoming spin-polarized in the direction of transport as it
flows from the normal metal (N) across the bulk of the TI slab. Unlike
conventional STT in symmetric F'/I/F magnetic tunnel junctions, where only the
in-plane STT component is non-zero in the linear response, both the in-plane
and perpendicular torque are sizable in N/TI/F junctions while not requiring
fixed F' layer as spin-polarizer which is advantageous for spintronic
applications. Using the nonequilibrium Born-Oppenheimer treatment of
interaction between fast conduction electrons and slow magnetization, we derive
a general Keldysh Green function-based STT formula which makes it possible to
analyze torque in the presence of SOC either in the bulk or at the interface of
the free F layer.",1202.6602v1
2012-09-05,Gate voltage modulation of spin-Hall-torque-driven magnetic switching,"Two promising strategies for achieving efficient control of magnetization in
future magnetic memory and non-volatile spin logic devices are spin transfer
torque from spin polarized currents and voltage-controlled magnetic anisotropy
(VCMA). Spin transfer torque is in widespread development as the write
mechanism for next-generation magnetic memory, while VCMA offers the potential
of even better energy performance due to smaller Ohmic losses. Here we
introduce a 3-terminal magnetic tunnel junction (MTJ) device that combines both
of these mechanisms to achieve new functionality: gate-voltage-modulated spin
torque switching. This gating makes possible both more energy-efficient
switching and also improved architectures for memory and logic applications,
including a simple approach for making magnetic memories with a maximum-density
cross-point geometry that does not require a control transistor for every MTJ.",1209.0962v1
2013-12-03,Dynamical properties of three terminal magnetic tunnel junctions: spintronics meets spin-orbitronics,"This letter introduces a micromagnetic model able to characterize the
magnetization dynamics in three terminal magnetic tunnel junctions, where the
effects of spin-transfer torque and spin-orbit torque are taken into account.
Our results predict that the possibility to separate electrically those two
torque sources is very promising from a technological point of view for both
next generation of nanoscale spintronic oscillators and microwave detectors. A
scalable synchronization scheme based on the parallel connection of those three
terminal devices is also proposed.",1312.0806v1
2021-10-13,Nonzero Skyrmion Hall Effect in Topologically Trivial Structures,"It is widely believed that the skyrmion Hall effect, often disruptive for
device applications, vanishes for overall topologically trivial structures such
as (synthetic) antiferromagnetic skyrmions and skyrmioniums due to a
compensation of Magnus forces. In this manuscript, however, we report that in
contrast to the case of spin-transfer torque driven skyrmion motion, this
notion is generally false for spin-orbit torque driven objects. We show that
the skyrmion Hall angle is directly related to their helicity and imposes an
unexpected roadblock for developing faster and lower input racetrack memories
based on spin-orbit torques.",2110.07063v1
2022-09-14,Magnetization switching in polycrystalline Mn3Sn thin film induced by self-generated spin-polarized current,"Electrical manipulation of spins is essential to design state-of-the-art
spintronic devices and commonly relies on the spin current injected from a
second heavy-metal material. The fact that chiral antiferromagnets produce spin
current inspires us to explore the magnetization switching of chiral spins
using self-generated spin torque. Here, we demonstrate the electric switching
of noncollinear antiferromagnetic state in Mn3Sn by observing a crossover from
conventional spin-orbit torque to the self-generated spin torque when
increasing the MgO thickness in Ta/MgO/Mn3Sn polycrystalline films. The spin
current injection from the Ta layer can be controlled and even blocked by
varying the MgO thickness, but the switching sustains even at a large MgO
thickness. Furthermore, the switching polarity reverses when the MgO thickness
exceeds around 3 nm, which cannot be explained by the spin-orbit torque
scenario due to spin current injection from the Ta layer. Evident
current-induced switching is also observed in MgO/Mn3Sn and Ti/Mn3Sn bilayers,
where external injection of spin Hall current to Mn3Sn is negligible. The
inter-grain spin-transfer torque induced by spin-polarized current explains the
experimental observations. Our findings provide an alternative pathway for
electrical manipulation of non-collinear antiferromagnetic state without
resorting to the conventional bilayer structure.",2209.06503v1
2003-02-17,Thermally assisted magnetization reversal in the presence of a spin-transfer torque,"We propose a generalized stochastic Landau-Lifshitz equation and its
corresponding Fokker-Planck equation for the magnetization dynamics in the
presence of spin transfer torques. Since the spin transfer torque can pump a
magnetic energy into the magnetic system, the equilibrium temperature of the
magnetic system is ill-defined. We introduce an effective temperature based on
a stationary solution of the Fokker-Planck equation. In the limit of high
energy barriers, the law of thermal agitation is derived. We find that the
N\'{e}el-Brown relaxation formula remains valid as long as we replace the
temperature by an effective one that is linearly dependent of the spin torque.
We carry out the numerical integration of the stochastic Landau-Lifshitz
equation to support our theory. Our results agree with existing experimental
data.",0302339v2
2008-03-14,Magnetoresistance and spin-transfer torque in magnetic tunnel junctions,"We comment on both recent progress and lingering puzzles related to research
on magnetic tunnel junctions (MTJs). MTJs are already being used in
applications such as magnetic-field sensors in the read heads of disk drives,
and they may also be the first device geometry in which spin-torque effects are
applied to manipulate magnetic dynamics, in order to make nonvolatile magnetic
random access memory. However, there remain many unanswered questions about
such basic properties as the magnetoresistance of MTJs, how their properties
change as a function of tunnel-barrier thickness and applied bias, and what are
the magnitude and direction of the spin-transfer-torque vector induced by a
tunnel current.",0803.2254v1
2013-01-30,Influence of MgO tunnel barrier thickness on spin-transfer ferromagnetic resonance and torque in magnetic tunnel junctions,"Spin-transfer ferromagnetic resonance (ST-FMR) in symmetric magnetic tunnel
junctions (MTJs) with a varied thickness of the MgO tunnel barrier (0.75 nm <
$t_{MgO}$ < 1.05 nm) is studied using the spin-torque diode effect. The
application of an RF current into nanosized MTJs generates a DC mixing voltage
across the device when the frequency is in resonance with the resistance
oscillations arising from the spin transfer torque. Magnetization precession in
the free and reference layers of the MTJs is analyzed by comparing ST-FMR
signals with macrospin and micromagnetic simulations. From ST-FMR spectra at
different DC bias voltage, the in-plane and perpendicular torkances are
derived. The experiments and free-electron model calculations show that the
absolute torque values are independent of tunnel barrier thickness. The
influence of coupling between the free and reference layer of the MTJs on the
ST-FMR signals and the derived torkances are discussed.",1301.7186v1
2011-07-06,Spin Seebeck Effect: Amplification of Spin Waves by Thermal Torque,"We observe amplification of spin-wave packets propagating along a film of
yttrium iron garnet (YIG) subject to a transverse temperature gradient. The
amplification is attributed to a spin-transfer thermal torque created by spin
currents generated by means of the spin Seebeck effect that acts on the
magnetization and opposes the relaxation. The experimental data are interpreted
with a simple theoretical model using spin-wave theory that gives an
amplification gain in very good agreement with measurements.",1107.1271v2
2014-12-23,Current-induced spin torque resonance of a magnetic insulator,"Pure spin currents transport angular momentum without an associated charge
flow. This unique property makes them attractive for spintronics applications,
such as torque induced magnetization control in nanodevices that can be used
for sensing, data storage, interconnects and logics. Up to now, however, most
spin transfer torque studies focused on metallic ferromagnets, while magnetic
insulators were largely ignored, in spite of superior magnetic quality factors.
Here, we report the observation of spin torque-induced magnetization dynamics
in a magnetic insulator. Our experiments show that in ultrathin magnetic
insulators the spin torque induced magnetization dynamics can be substantially
larger than those generated by the Oersted field. This opens new perspectives
for the efficient integration of ferro-, ferri-, and antiferromagnetic
insulators into electronic devices.",1412.7460v1
2016-01-06,Mutual synchronization of spin torque nano-oscillators through a non-local and tunable electrical coupling,"The concept of spin torque driven high frequency magnetization dynamics has
opened up the field of spintronics to non-linear physics, potentially in
complex networks of dynamical systems. In the scarce demonstrations of
synchronized spin-torque oscillators, the local nature of the magnetic coupling
that is used have largely hampered a good understanding and thus the control of
the synchronization process. Here we take advantage of the non-local nature of
an electrical coupling to mutually synchronize spin-torque oscillators through
their self-emitted microwave currents. The control of the synchronized state is
achieved at the nanoscale through two active components of spin transfer
torques, but also externally through an electrical delay line. These additional
levels of control of the synchronization capability provide new approaches to
underlie a large variety of nanoscale collective dynamics in complex networks.",1601.01247v1
2023-11-11,Spin transfer exchange torque in ferromagnet/ferromagnet structures made of half metals with large exchange gaps,"Spin torques in magnetic multilayers are produced by spin polarization $P$ of
ferromagnetic (F) layers, and increase with growing $P$. The latter, however,
cannot exceed the $P=1$ value found in half metals. We study the $P=1$ case to
find what other parameters still influence spin torques in this extreme limit.
It is found that the ratio of exchange gap to Fermi energy strongly affects the
properties of the torque. For large values of the gap the magnitude of exchange
spin torque exhibits a sharp peak at very small misalignment angles between
magnetizations. This behavior is found to be linked to a transition between
Ohmic and tunneling transport regimes through the F/F boundary.",2311.06626v1
2018-10-24,Long spin coherence length and bulk-like spin-orbit torque in ferrimagnetic multilayers,"Ferromagnetic spintronics has been a main focus as it offers non-volatile
memory and logic applications through current-induced spin-transfer torques.
Enabling wider applications of such magnetic devices requires a lower switching
current for a smaller cell while keeping the thermal stability of magnetic
cells for non-volatility. As the cell size reduces, however, it becomes
extremely difficult to meet this requirement with ferromagnets because
spin-transfer torque for ferromagnets is a surface torque due to rapid spin
dephasing, leading to the 1/ferromagnet-thickness dependence of the spin-torque
efficiency. Requirement of a larger switching current for a thicker and thus
more thermally stable ferromagnetic cell is the fundamental obstacle for
high-density non-volatile applications with ferromagnets. Theories predicted
that antiferromagnets have a long spin coherence length due to the staggered
spin order on an atomic scale, thereby resolving the above fundamental
limitation. Despite several spin-torque experiments on antiferromagnets and
ferrimagnetic alloys, this prediction has remained unexplored. Here we report a
long spin coherence length and associated bulk-like-torque characteristic in an
antiferromagnetically coupled ferrimagnetic multilayer. We find that a
transverse spin current can pass through > 10 nm-thick ferrimagnetic Co/Tb
multilayers whereas it is entirely absorbed by 1 nm-thick ferromagnetic Co/Ni
multilayer. We also find that the switching efficiency of Co/Tb multilayers
partially reflects a bulk-like-torque characteristic as it increases with the
ferrimagnet-thickness up to 8 nm and then decreases, in clear contrast to
1/thickness-dependence of Co/Ni multilayers. Our results on
antiferromagnetically coupled systems will invigorate researches towards
energy-efficient spintronic technologies.",1810.10404v1
2020-07-20,Sizable spin-transfer torque in Bi/Ni80Fe20 bilayer film,"The search for efficient spin conversion in Bi has attracted great attention
in spin-orbitronics. In the present work, we employ spin-torque ferromagnetic
resonance to investigate spin conversion in Bi/Ni80Fe20(Py) bilayer films with
continuously varying Bi thickness. In contrast with previous studies, sizable
spin-transfer torque (i.e., a sizable spin-conversion effect) is observed in
Bi/Py bilayer film. Considering the absence of spin conversion in
Bi/yttrium-iron-garnet bilayers and the enhancement of spin conversion in
Bi-doped Cu, the present results indicate the importance of material
combinations to generate substantial spin-conversion effects in Bi.",2007.09830v1
2015-05-04,Landau-Lifshitz theory of the thermomagnonic torque,"We derive the thermomagnonic torque associated with smooth magnetic textures
subjected to a temperature gradient, in the framework of the stochastic
Landau-Lifshitz-Gilbert equation. Our approach captures on equal footing two
distinct contributions: (1) A local entropic torque that is caused by a
temperature dependence of the effective exchange field, the existence of which
had been previously suggested based on numerics and (2) the well-known
spin-transfer torque induced by thermally-induced magnon flow. The dissipative
components of two torques have the same structure, following a common
phenomenology, but opposite signs, with the twice larger entropic torque
leading to a domain-wall motion toward the hotter region. We compare the
efficiency of the torque-driven domain-wall motion with the recently proposed
Brownian thermophoresis.",1505.00818v1
2018-09-13,Spin-current driven spontaneous coupling of ferromagnets,"A theoretical framework is proposed for the spin-current driven synchronized
self-oscillations in ferromagnets in the spin Hall geometry. The spin current
generated by the spin Hall effect in a bottom nonmagnetic heavy metal excites a
self-oscillation of the magnetization in an attached ferromagnet through
spin-transfer effect. The spin current simultaneously creates spin accumulation
inside the ferromagnet. Therefore, when the top surfaces of two ferromagnets
are connected by a nonmagnetic material having a long spin diffusion length,
another spin current flows according to the gradient of the spin accumulations
between the ferromagnets. This additional spin current excites an additional
spin torque leading to a coupled motion of the magnetizations. This coupling
mechanism comes purely from spin degree of freedom in the system without using
electric and/or magnetic interactions. The additional spin torque acts as a
repulsive force between the magnetizations, and prefers an antiphase
synchronization between the oscillators. The phase difference in a synchronized
state is determined by the competition between this additional spin torque and
spin pumping. Eventually, either an in-phase or antiphase synchronization is
spontaneously excited in the individual ferromagnets, depending on the current
magnitude. These conclusions are obtained by deriving the theoretical formula
of the additional spin torque from the diffusive spin transport theory and
solving the equation of motion of the magnetizations both numerically and
analytically.",1809.05195v1
2020-09-08,Role of an additional interfacial spin-transfer torque for current-driven skyrmion dynamics in chiral magnetic layers,"Skyrmions can be driven by spin-orbit torques as a result of the spin Hall
effect. Here we model an additional contribution in ultra-thin multilayers,
arising from the spin accumulation at heavy metal / ferromagnetic interfaces
and observe the effects on a large range of skyrmion diameters. The combination
of the interfacial spin-transfer torque and the spin-orbit torque results in
skyrmion motion which helps to explain the observation of small skyrmion Hall
angles for skyrmion diameters less than 100 nm. We show that this additional
term has a significant effect on the skyrmion dynamics and leads to rapidly
decreasing skyrmion Hall angles for small skyrmion diameters, as well as a
skyrmion Hall angle versus skyrmion velocity dependence nearly independent of
the surface roughness characteristics. Also, the effect of various disordered
energy landscapes, in the form of surface roughness, on the skyrmion Hall angle
and velocity is shown to be largely drive-dependent. Our results show good
agreement with those found in experiments thus concluding that the interfacial
spin-transfer torque should be included in micromagnetics simulations for the
reproduction of experimental results.",2009.03751v2
2018-10-09,Non-trivial spatial dependence of the spin torques in L1$_0$ FePt-based tunnelling junctions,"We present an {\it ab-initio} study of the spin-transfer torque in a
Fe/MgO/FePt/Fe magnetic tunnel junctions. We consider a FePt film with a
thickness up to six unit cells, either in direct contact with the MgO spacer or
with an intercalated ultra-thin Fe seed layer. We find that in the FePt layer
the torque is not attenuated as strongly as in the case of pure Fe. Moreover,
in FePt the torque alternates sign at the Fe and Pt atomic planes throughout
the stack for all FePt thicknesses considered. Finally, when Fe is intercalated
between MgO and L$1_0$-FePt, the torque is sharply attenuated and it is
transferred to FePt only for a Fe seed layer that is less than
two-atomic-planes thick. We attribute these features to the different spatial
profiles of the exchange and correlation field and the induced non-equilibrium
spin accumulation. The calculated tunnelling magneto-resistance of the
Fe/MgO/FePt/Fe junctions studied is enhanced with respect to the one of
Fe/MgO/Fe, while it is reduced with Fe intercalation. Our work shows that
L$1_0$-FePt junctions can be promising candidates for current-operated magnetic
devices and that the magnetic texture at the atomic scale has an important
effect on the spin transfer torque.",1810.04136v1
2009-02-03,Dependence of critical current of spin transfer torque-driven magnetization dynamics on free layer thickness,"The dependence of the critical current of spin transfer torque-driven
magnetization dynamics on the free-layer thickness was studied by taking into
account both the finite penetration depth of the transverse spin current and
spin pumping. We showed that the critical current remains finite in the
zero-thickness limit of the free layer for both parallel and anti-parallel
alignments. We also showed that the remaining value of the critical current of
parallel to anti-parallel switching is larger than that of anti-parallel to
parallel switching.",0902.0420v1
2012-11-18,Controlling the Spin Torque Efficiency with Ferroelectric Barriers,"Non-equilibrium spin-dependent transport in magnetic tunnel junctions
comprising a ferroelectric barrier is theoretically investigated. The exact
solutions of the free electron Schr\""odinger equation for electron tunneling in
the presence of interfacial screening are obtained by combining Bessel and Airy
functions. We demonstrate that the spin transfer torque efficiency, and more
generally the bias-dependence of tunneling magneto- and electroresistance, can
be controlled by switching the ferroelectric polarization of the barrier. This
effect provides a supplementary way to electrically control the current-driven
dynamic states of the magnetization and related magnetic noise in spin transfer
devices.",1211.4196v1
2006-01-09,Spin Transfer Torque for Continuously Variable Magnetization,"We report quantum and semi-classical calculations of spin current and
spin-transfer torque in a free-electron Stoner model for systems where the
magnetization varies continuously in one dimension.Analytic results are
obtained for an infinite spin spiral and numerical results are obtained for
realistic domain wall profiles. The adiabatic limit describes conduction
electron spins that follow the sum of the exchange field and an effective,
velocity-dependent field produced by the gradient of the magnetization in the
wall. Non-adiabatic effects arise for short domain walls but their magnitude
decreases exponentially as the wall width increases. Our results cast doubt on
the existence of a recently proposed non-adiabatic contribution to the
spin-transfer torque due to spin flip scattering.",0601172v2
2006-04-27,Current-driven destabilization of both collinear configurations in asymmetric spin-valves,"Spin transfer torque in spin valves usually destabilizes one of the collinear
configurations (either parallel or antiparallel) and stabilizes the second one.
Apart from this, balance of the spin-transfer and damping torques can lead to
steady precessional modes. In this letter we show that in some asymmetric
nanopillars spin current can destabilize both parallel and antiparallel
configurations. As a result, stationary precessional modes can occur at zero
magnetic field. The corresponding phase diagram as well as frequencies of the
precessional modes have been calculated in the framework of macrospin model.
The relevant spin transfer torque has been calculated in terms of the
macroscopic model based on spin diffusion equations.",0604641v2
2021-03-04,Effects of screened Coulomb interaction on spin transfer torque,"In a magnetic multilayer, magnetizations can be manipulated by spin transfer
torque. Both spin transfer torque and its reciprocal effect, spin pumping, are
governed by spin mixing conductance. The magnitude of spin mixing conductance
at the interface of nearly magnetic metal has been theoretically shown to be
enhanced by electron-electron interaction. However, experiments show both
increasing and decreasing values of spin mixing conductance for metals with
larger electron-electron interaction. Here we take into account the effect of
electron-electron interaction on the screening of the Coulomb interaction at
the magnetic interface to correctly describe the experiment.",2103.02929v2
2013-01-10,Parameter space for thermal spin-transfer torque,"Thermal spin-transfer torque describes the manipulation of the magnetization
by the application of a heat flow. The effect has been calculated theoretically
by Jia et al. in 2011. It is found to require large temperature gradients in
the order of Kelvins across an ultra thin MgO barrier. In this paper, we
present results on the fabrication and the characterization of magnetic tunnel
junctions with 3 monolayer thin MgO barriers. The quality of the interfaces at
different growth conditions is studied quantitatively via high-resolution
transmission electron microscopy imaging. We demonstrate tunneling magneto
resistance ratios of up to 55% to 64% for 3 to 4 monolayer barrier thickness.
Magnetic tunnel junctions with perpendicular magnetization anisotropy show
spin-transfer torque switching with a critical current of 0.2 MA/cm$^2$. The
thermally generated torque is calculated ab initio using the
Korringa-Kohn-Rostoker and non-equilibrium Green's function method. Temperature
gradients generated from femtosecond laser pulses were simulated using COMSOL,
revealing gradients of 20 K enabling thermal spin-transfer-torque switching.",1301.2042v2
2015-12-10,Drastic emergence of huge negative spin-transfer torque in atomically thin Co layers,"Current-induced domain wall (DW) motion has drawn great attention in the last
decades as the key operational principle of emerging magnetic memory devices.
As the major driving force of the current-induced DW motion, the spin-orbit
torque (SOT) on chiral DWs has been proposed and extensively studied nowadays.
However, we demonstrate here that there exists another driving force, which is
larger than the SOT in ultra-thin Co films. Moreover, the direction of the
present force is found to be opposite to the prediction of the spin-transfer
torque (STT), resulting in the DW motion along the current direction. The
symmetry of the force and its peculiar dependence on the DW structure suggest
that the present force is, most likely, attributed to considerable enhancement
of the nonadiabatic STT with a negative spin polarization in atomically thin Co
layers. These findings open a new pathway to enhance the overall spin torque
efficiency-the critical parameter in emerging spintronic devices.",1512.03405v2
2007-08-07,Spin Pumping of Current in Non-Uniform Conducting Magnets,"Using irreversible thermodynamics we show that current-induced spin transfer
torque within a magnetic domain implies spin pumping of current within that
domain. This has experimental implications for samples both with conducting
leads and that are electrically isolated. These results are obtained by
deriving the dynamical equations for two models of non-uniform conducting
magnets: (1) a generic conducting magnet, with net conduction electron density
n and net magnetization $\vec{M}$; and (2) a two-band magnet, with up and down
spins each providing conduction and magnetism. For both models, in regions
where the equilibrium magnetization is non-uniform, voltage gradients can drive
adiabatic and non-adiabatic bulk spin torques. Onsager relations then ensure
that magnetic torques likewise drive adiabatic and non-adiabatic currents --
what we call bulk spin pumping. For a given amount of adiabatic and
non-adiabatic spin torque, the two models yield similar but distinct results
for the bulk spin pumping, thus distinguishing the two models. As in the recent
spin-Berry phase study by Barnes and Maekawa, we find that within a domain wall
the ratio of the effective emf to the magnetic field is approximately given by
$P(2\mu_{B}/e)$, where P is the spin polarization. The adiabatic spin torque
and spin pumping terms are shown to be dissipative in nature.",0708.0997v1
2017-07-19,Hybridization-induced interface states in a topological insulator-magnetic metal heterostructure,"Recent experiments demonstrating large spin-transfer torques in topological
insulator (TI)-ferromagnetic metal (FM) bilayers have generated a great deal of
excitement due to their potential applications in spintronics. The source of
the observed spin-transfer torque, however, remains unclear. This is because
the large charge transfer from the FM to TI layer would prevent the Dirac cone
at the interface from being anywhere near the Fermi level to contribute to the
observed spin-transfer torque. Moreover, there is yet little understanding of
the impact on the Dirac cone at the interface from the metallic bands
overlapping in energy and momentum, where strong hybridization could take
place. Here, we build a simple microscopic model and perform
first-principles-based simulations for such a TI-FM heterostructure,
considering the strong hybridization and charge transfer effects. We find that
the original Dirac cone is destroyed by the hybridization as expected. Instead,
we find a new interface state which we dub 'descendent state' to form near the
Fermi level due to the strong hybridization with the FM states at the same
momentum. Such a `descendent state' carries a sizable weight of the original
Dirac interface state, and thus inherits the localization at the interface and
the same Rashba-type spin-momentum locking. We propose that the `descendent
state' may be an important source of the experimentally observed large
spin-transfer torque in the TI-FM heterostructure.",1707.06319v2
2021-07-16,Large Unidirectional Magnetoresistance in Metallic Heterostructures in the Spin Transfer Torque Regime,"A large unidirectional magnetoresistance (UMR) ratio of UMR/$R_{xx}\sim$
$0.36\%$ is found in W/CoFeB metallic bilayer heterostructures at room
temperature. Three different regimes in terms of the current dependence of UMR
ratio are identified: A spin-dependent-scattering mechanism regime at small
current densities $J \sim$ $10$$^{9}$A/m$^{2}$ (UMR ratio $\propto$ $J$), a
spin-magnon-interaction mechanism regime at intermediate $J \sim$
$10$$^{10}$A/m$^{2}$ (UMR ratio $\propto$ $J$$^{3}$), and a spin-transfer
torque (STT) regime at $J \sim$ $10$$^{11}$A/m$^{2}$ (UMR ratio independent of
$J$). We verify the direct correlation between this large UMR and the transfer
of spin angular momentum from the W layer to the CoFeB layer by both
field-dependent and current-dependent UMR characterizations. Numerical
simulations further confirm that the large STT-UMR stems from the tilting of
the magnetization affected by the spin Hall effect-induced spin-transfer
torques. An alternative approach to estimate damping-like spin-torque
efficiencies from magnetic heterostructures is also proposed.",2107.07780v1
2009-12-23,Current-induced torques in continuous antiferromagnetic textures,"We study the influence of an electric current on a continuous non-collinear
antiferromagnetic texture. Despite the lack of a net magnetic moment we find
that the exchange interaction between conduction electrons and local
magnetization generally results in current-induced torques that are similar in
phenomenology to spin transfer torques in ferromagnets. We present the
generalization of the non-linear sigma model equation of motion for the
N\'{e}\`{e}l vector that includes these current-induced torques, and briefly
discuss the resulting current-induced antiferromagnetic domain wall motion and
spin-wave Doppler shift. We give an interpretation of our results using a
unifying picture of current-induced torques in ferromagnets and
antiferromagnets in which they are viewed as due to the current-induced spin
polarization resulting from an effective spin-orbit coupling.",0912.4519v1
2020-06-03,Skyrmion spin transfer torque due to current confined in a nanowire,"In this work we compute the torque field present in a ferromagnet in contact
with a metallic nanowire when a skyrmion is present. If the nanowire is narrow
enough the current is carried by a single conduction band. In this regime the
classical torque model breaks down and we show that a skyrmion driven by spin
transfer torque moves in a different direction than predicted by the classical
model. However, the amount of charge current required to move a skyrmion with a
certain velocity in the single band regime is similar to a classical model of
torque where it is implicitly assumed current transport by many conduction
bands. The single band regime is more efficient creating spin current from
charge current because of the perfect polarization of the single band but is
less efficient creating torque from spin current. Nevertheless, it is possible
to take profit of the single band regime to move skyrmions even with no net
charge or spin current flowing between the device contacts. We have also been
able to recover the classical limit considering an ensemble of only a few
electronic states. In this limit we have discovered that electron diffusion
needs to be considered even in ballistic nanowires due the effect of the
skyrmion structure on the electron current.",2006.02311v2
2004-07-21,Boltzmann Test of Slonczewski's Theory of Spin Transfer Torque,"We use a matrix Boltzmann equation formalism to test the accuracy of
Slonczewski's theory of spin-transfer torque in thin-film heterostructures
where a non-magnetic spacer layer separates two non-collinear ferromagnetic
layers connected to non-magnetic leads. When applicable, the model predictions
for the torque as a function of the angle between the two ferromagnets agree
extremely well with the torques computed from a Boltzmann equation calculation.
We focus on asymmetric structures (where the two ferromagnets and two leads are
not identical) where the agreement pertains to a new analytic formula for the
torque derived by us using Slonczewski's theory. In almost all cases, we can
predict the correct value of the model parameters directly from the geometric
and transport properties of the multilayer. For some asymmetric geometries, we
predict a new mode of stable precession that does not occur for the symmetric
case studied by Slonczewski.",0407569v1
2011-11-14,New mechanism for generating spin transfer torque without charge current,"A new physical mechanism for generating spin-transfer torque is proposed. It
is due to interference of bias driven nonequilibrium electrons incident on a
switching junction with the electrons reflected from an insulating barrier
inserted in the junction after the switching magnet. It is shown using the
rigorous Keldysh formalism that this new out-of-plane torque $T_{\perp}$ is
proportional to an applied bias and is as large as the torque in a conventional
junction generated by a strong charge current. However, the charge current and
the in-plane torque $T_{\parallel}$ are almost completely suppressed by the
insulating barrier. This new junction thus offers the highly applicable
possibility of bias-induced switching of magnetization without charge current.",1111.3196v2
2013-03-14,Spin-torque effects in thermally assisted magnetization reversal: Method of statistical moments,"Thermal fluctuations of nanomagnets driven by spin-polarized currents are
treated via the Landau-Lifshitz-Gilbert equation generalized to include both
the random thermal noise field and the Slonczewski spin-transfer torque term.
By averaging this stochastic (Langevin) equation over its realizations, the
explicit infinite hierarchy of differential-recurrence relations for
statistical moments (averaged spherical harmonics) is derived for arbitrary
demagnetizing factors and magnetocrystalline anisotropy for the generic
nanopillar model of a spin-torque device comprising two ferromagnetic strata
representing the free and fixed layers and a nonmagnetic conducting spacer all
sandwiched between two ohmic contacts. The influence of thermal fluctuations
and spin-transfer torques on relevant switching characteristics, such as the
stationary magnetization, the magnetization reversal time, etc., is calculated
by solving the hierarchy for wide ranges of temperature, damping, external
magnetic field, and spin-polarized current indicating new spin-torque effects
in the thermally assisted magnetization reversal comprising several orders of
magnitude. In particular, a pronounced dependence of the switching
characteristics on the directions of the external magnetic field and the spin
polarization exists.",1303.3476v4
2011-10-16,Spin Torque in Anisotropic Tunneling Junctions,"Spin transport in magnetic tunnel junctions comprising a single magnetic
layer in the presence of interfacial spin-orbit interaction (SOI) is
investigated theoretically. Due to the presence of interfacial SOI, a
current-driven spin torque can be generated at the second order in SOI, even in
the absence of an external spin polarizer. This torque possesses two
components, in-plane and perpendicular to the plane of rotation, that can
induce either current-driven {\em magnetization switching} from in-plane to
out-of-plane configuration or {\em magnetization precessions}, similarly to
Spin Transfer Torque in spin-valves. Consequently, it appears that it is
possible to control the magnetization steady state and dynamics by either
varying the bias voltage or electrically modifying the SOI at the interface.",1110.3488v1
2013-08-08,Interface control of the magnetic chirality in TaN|CoFeB|MgO heterosctructures,"Recent advances in the understanding of spin orbital effects in ultrathin
magnetic heterostructures have opened new paradigms to control magnetic moments
electrically. The Dzyaloshinskii-Moriya interaction (DMI) is said to play a key
role in forming a Neel-type domain wall that can be driven by the spin Hall
torque, a torque resulting from the spin current generated in a neighboring
non-magnetic layer via the spin Hall effect. Here we show that the sign of the
DMI, which determines the direction to which a domain wall moves with current,
can be changed by modifying the adjacent non-magnetic layer. We find that the
sense of rotation of a domain wall spiral is reversed when the Ta underlayer is
doped with nitrogen in Ta|CoFeB|MgO heterostructures. The spin Hall angle of
the Ta and nitrogen doped Ta underlayers carry the same sign, suggesting that
the sign of the DMI is defined at the interface. Depending on the sense of
rotation, spin transfer torque and spin Hall torque can either compete or
assist each other, thus influencing the efficiency of moving domain walls with
current.",1308.1751v1
2015-02-05,Nonlinear analysis of magnetization dynamics excited by spin Hall effect,"We investigate the possibility of exciting self-oscillation in a
perpendicular ferromagnet by the spin Hall effect on the basis of a nonlinear
analysis of the Landau-Lifshitz-Gilbert (LLG) equation. In the self-oscillation
state, the energy supplied by the spin torque during a precession on a constant
energy curve should equal the dissipation due to damping. Also, the current to
balance the spin torque and the damping torque in the self-oscillation state
should be larger than the critical current to destabilize the initial state. We
find that the second condition in the spin Hall system is not satisfied by
deriving analytical solutions of the energy supplied by the spin transfer
effect and the dissipation due to the damping from the nonlinear LLG equation.
This indicates that the self-oscillation of a perpendicular ferromagnet cannot
be excited solely by the spin Hall torque.",1502.01420v2
2018-02-19,Spin current and spin transfer torque in ferromagnet/superconductor spin valves,"Using fully self consistent methods, we study spin transport in realistic,
fabricable experimental spin valve systems consisting of two magnetic layers, a
superconducting layer, and a spacer normal layer between the ferromagnets. Our
methods ensure that the proper relations between spin current gradients and
spin transfer torques are satisfied. We present results as a function of
geometrical parameters, interfacial barrier values, misalignment angle between
the ferromagnets, and bias voltage. Our main results are for the spin current
and spin accumulation as functions of position within the spin valve structure.
We see precession of the spin current about the exchange fields within the
ferromagnets, and penetration of the spin current into the superconductor for
biases greater than the critical bias, defined in the text. The spin
accumulation exhibits oscillating behavior in the normal metal, with a strong
dependence on the physical parameters both as to the structure and formation of
the peaks. We also study the bias dependence of the spatially averaged spin
transfer torque and spin accumulation. We examine the critical bias effect of
these quantities, and their dependence on the physical parameters. Our results
are predictive of the outcome of future experiments, as they take into account
imperfect interfaces and a realistic geometry.",1802.06834v1
2004-07-14,Quantum Mechanics of Spin Transfer in Ferromagnetic Multilayers,"We use a quantum mechanical treatment of a ballistic spin current to describe
novel aspects of spin transfer to a ferromagnetic multilayer. We demonstrate
quantum phenomena from spin transmission resonance (STR) to magnetoelectric
spin echo (MESE), depending on the coupling between the magnetic moments in the
ferromagnetic thin films. Our calculation reveals new channels through which
the zero spin transfer occurs in multilayers: the STR and MESE. We also
illustrate that counter-intuitively, a negative spin torque can act initially
on the second moment in a bilayer system.",0407365v1
2003-12-18,Spin momentum transfer in current perpendicular to the plane spin valves,"We present experimental and numerical micromagnetic data on the effect of
spin momentum transfer in current perpendicular to the plane spin valves.
Starting from a configuration with orthogonal free and pinned layer
magnetizations, the free layer magnetization exhibits abrupt current induced
switching that is qualitatively consistent with the spin torque model. When
operating the spin valve as a field sensor, spin transfer can produce a change
in resistance that mimics an effective magnetic field and induce magnetic
instability that requires a larger bias field in order to stabilize the device.",0312505v1
2002-02-22,Anatomy of Spin-Transfer Torque,"Spin-transfer torques occur in magnetic heterostructures because the
transverse component of a spin current that flows from a non-magnet into a
ferromagnet is absorbed at the interface. We demonstrate this fact explicitly
using free electron models and first principles electronic structure
calculations for real material interfaces. Three distinct processes contribute
to the absorption: (1) spin-dependent reflection and transmission; (2) rotation
of reflected and transmitted spins; and (3) spatial precession of spins in the
ferromagnet. When summed over all Fermi surface electrons, these processes
reduce the transverse component of the transmitted and reflected spin currents
to nearly zero for most systems of interest. Therefore, to a good
approximation, the torque on the magnetization is proportional to the
transverse piece of the incoming spin current.",0202397v1
2006-09-15,Relativistic treatment of spin-currents and spin-transfer torque,"It is shown that a useful relativistic generalization of the conventional
spin density for the case of moving electrons is the expectation value of the
four-component Bargmann-Wigner polarization operator. An exact equation of
motion for this quantity is derived, using the one-particle Dirac equation, and
the relativistic analogues of the non-relativistic concepts of spin-currents
and spin-transfer torques are identified. In the classical limit the time
evolution is governed by the equation of motion first proposed by Bargmann,
Michel and Telegdi generalized to the case of inhomogeneous systems. In the
non-relativistic limit it is found that the spin-current has an intrinsic Hall
contribution and to order 1/c^2 a spin-orbit coupling related torque appears in
the equation of motion. The relevance of these results to the theory of the
intrinsic spin Hall effect and current-induced switching are briefly discussed.",0609376v2
2019-07-03,Anisotropy of spin-transfer torques and Gilbert damping induced by Rashba coupling,"Spin-transfer torques (STT), Gilbert damping (GD), and effective spin
renormalization (ESR) are investigated microscopically in a 2D Rashba
ferromagnet with spin-independent Gaussian white-noise disorder. Rashba
spin-orbit coupling induced anisotropy of these phenomena is thoroughly
analysed. For the case of two partly filled spin subbands, a remarkable
relation between the anisotropic STT, GD, and ESR is established. In the
absence of magnetic field and other torques on magnetization, this relation
corresponds to a current-induced motion of a magnetic texture with the
classical drift velocity of conduction electrons. Finally, we compute spin
susceptibility of the system and generalize the notion of spin-polarized
current.",1907.02041v3
2017-10-05,Transport theory for femtosecond laser-induced spin-transfer torques,"Ultrafast demagnetization of magnetic layers pumped by a femtosecond laser
pulse is accompanied by a nonthermal spin-polarized current of hot electrons.
These spin currents are studied here theoretically in a spin valve with
noncollinear magnetizations. To this end, we introduce an extended model of
superdiffusive spin transport that enables to treat noncollinear magnetic
configurations, and apply it to the perpendicular spin valve geometry. We show
how spin-transfer torques arise due to this mechanism and calculate their
action on the magnetization present, as well as how the latter depends on the
thicknesses of the layers and other transport parameters. We demonstrate that
there exists a certain optimum thickness of the out-of-plane magnetized
spin-current polarizer such that the torque acting on the second magnetic layer
is maximal. Moreover, we study the magnetization dynamics excited by the
superdiffusive spin-transfer torque due to the flow of hot electrons employing
the Landau-Lifshitz-Gilbert equation. Thereby we show that a femtosecond laser
pulse applied to one magnetic layer can excite small-angle precessions of the
magnetization in the second magnetic layer. We compare our calculations with
recent experimental results.",1710.02083v2
2015-08-11,Detrimental Effect of Interfacial Dzyaloshinskii-Moriya Interaction on Perpendicular Spin-Transfer-Torque Magnetic Random Access Memory,"Interfacial Dzyaloshinskii-Moriya interaction in ferromagnet/heavy metal
bilayers is recently of considerable interest as it offers an efficient control
of domain walls and the stabilization of magnetic skyrmions. However, its
effect on the performance of perpendicular spin transfer torque memory has not
been explored yet. We show based on numerical studies that the interfacial
Dzyaloshinskii-Moriya interaction decreases the thermal energy barrier while
increases the switching current. As high thermal energy barrier as well as low
switching current is required for the commercialization of spin torque memory,
our results suggest that the interfacial Dzyaloshinskii-Moriya interaction
should be minimized for spin torque memory applications.",1508.02587v2
2020-11-17,Single-shot dynamics of spin-orbit torque and spin transfer torque switching in three-terminal magnetic tunnel junctions,"Current-induced spin-transfer torques (STT) and spin-orbit torques (SOT)
enable the electrical switching of magnetic tunnel junctions (MTJs) in
nonvolatile magnetic random access memories. In order to develop faster memory
devices, an improvement of the timescales underlying the current driven
magnetization dynamics is required. Here we report all-electrical time-resolved
measurements of magnetization reversal driven by SOT in a three-terminal MTJ
device. Single-shot measurements of the MTJ resistance during current injection
reveal that SOT switching involves a stochastic two-step process consisting of
a domain nucleation time and propagation time, which have different genesis,
timescales, and statistical distributions compared to STT switching. We further
show that the combination of SOT, STT, and voltage control of magnetic
anisotropy (VCMA) leads to reproducible sub-ns switching with a spread of the
cumulative switching time smaller than 0.2 ns. Our measurements unravel the
combined impact of SOT, STT, and VCMA in determining the switching speed and
efficiency of MTJ devices.",2011.08709v1
2013-04-08,Correlations between spin accumulation and degree of time-inverse breaking for electron gas in solid,"It is shown that the electron spin may not be conserved after a
spin-independent scattering. This fact strongly limits the validity of the
classical model of spin-up/spin-down bands, which has been used for description
of magnetic properties of conduction electrons. It is shown that it is possible
to divide all conduction electrons into two group distinguished by their
symmetry for time reversal. The number of electrons in each group is conserved
after a spin-independent scattering. This makes it convenient to use these
groups for describing of the magnetic properties of conduction electrons. The
energy distribution of spins, the Pauli paramagnetism and the spin distribution
in the ferromagnetic metals are described within the presented model. The
effects of spin torque and spin-torque current are described. The origin of
spin-transfer torque is explained within presented model.",1304.2150v1
2013-05-21,Spin-orbit torques in Co/Pt(111) and Mn/W(001) magnetic bilayers from first principles,"An applied electric current through a space-inversion asymmetric magnet
induces spin-orbit torques (SOTs) on the magnetic moments, which holds much
promise for future memory devices. We discuss general Green's function
expressions suitable to compute the linear-response SOT in disordered
ferromagnets. The SOT can be decomposed into an even and an odd component with
respect to magnetization reversal, where in the limit of vanishing disorder the
even SOT is given by the constant Berry curvature of the occupied states, while
the odd part exhibits a divergence with respect to disorder strength. Within
this formalism, we perform first principles density-functional theory
calculations of the SOT in Co/Pt(111) and Mn/W(001) magnetic bilayers. We find
the even and odd torque components to be of comparable magnitude. Moreover, the
odd torque depends strongly on an additional capping layer, while the even
torque is less sensitive. We show that the even torque is nearly entirely
mediated by spin currents in contrast to the odd torque, which can contain an
important contribution not due to spin transfer. Our results are in agreement
with experiments, showing that our linear response theory is well-suited for
the description of SOTs in complex ferromagnets.",1305.4873v3
2021-06-02,"Interplay of voltage control of magnetic anisotropy, spin transfer torque, and heat in the spin-orbit torque switching in three-terminal magnetic tunnel junctions","We use three-terminal magnetic tunnel junctions (MTJs) designed for
field-free switching by spin-orbit torques (SOTs) to systematically study the
impact of dual voltage pulses on the switching performances. We show that the
concurrent action of an SOT pulse and an MTJ bias pulse allows for reducing the
critical switching energy below the level typical of spin transfer torque while
preserving the ability to switch the MTJ on the sub-ns time scale. By
performing dc and real-time electrical measurements, we discriminate and
quantify three effects arising from the MTJ bias: the voltage-controlled change
of the perpendicular magnetic anisotropy, current-induced heating, and the spin
transfer torque. The experimental results are supported by micromagnetic
modeling. We observe that, depending on the pulse duration and the MTJ
diameter, different effects take a lead in assisting the SOTs in the
magnetization reversal process. Finally, we present a compact model that allows
for evaluating the impact of each effect due to the MTJ bias on the critical
switching parameters. Our results provide input to optimize the switching of
three-terminal devices as a function of time, size, and material parameters.",2106.01054v1
2006-08-25,Critical current under an optimal time-dependent polarization direction for Stoner particles in spin-transfer torque induced fast magnetization reversal,"Fast magnetization reversal of uniaxial Stoner particles by spin-transfer
torque due to the spin-polarized electric current is investigated. It is found
that a current with a properly designed time-dependent polarization direction
can dramatically reduce the critical current density required to reverse a
magnetization. Under the condition that the magnitude and the polarization
degree of the current do not vary with time, the shape of the optimal
time-dependent polarization direction is obtained such that the magnetization
reversal is the fastest.",0608563v1
2007-03-22,Current-Induced Magnetic Domain-Wall Motion by Spin Transfer Torque: Collective Coordinate Approach with Domain-Wall Width Variation,"The spin transfer torque generated by a spin-polarized current can induce the
shift of the magnetic domain-wall position. In this work, we study
theoretically the current-induced domain-wall motion by using the collective
coordinate approach [Gen Tatara and Hiroshi Kohno, Phys. Rev. Lett. 92, 86601
(2004)]. The approach is extended to include not only the domain-wall position
and the polarization angle changes but also the domain-wall width variation. It
is demonstrated that the width variation affects the critical current.",0703569v1
2018-08-03,A thermally driven spin-transfer-torque system far from equilibrium: enhancement of the thermoelectric current via pumping current,"We consider a small itinerant ferromagnet exposed to an external magnetic
field and strongly driven by a thermally induced spin current. For this model,
we derive the quasi-classical equations of motion for the magnetization where
the effects of a dynamical non-equilibrium distribution function are taken into
account self-consistently. We obtain the Landau-Lifshitz-Gilbert equation
supplemented by a spin-transfer torque term of Slonczewski form. We identify a
regime of persistent precessions in which we find an enhancement of the
thermoelectric current by the pumping current.",1808.01192v1
2019-09-10,Thermally induced spin-transfer torques in superconductor/ferromagnet bilayers,"Thermally induced magnetization dynamics is currently a flourishing field of
research due to its potential application in information technology. We study
the paradigmatic system of a magnetic domain wall in a thermal gradient which
is interacting with an adjacent superconductor. The spin-transfer torques
arising in this system due to the combined action of the giant thermoelectric
effect and the creation of equal-spin pairs in the superconductor are large
enough to give rise to high domain wall velocities $10^3$ times larger than
previously predicted.",1909.04418v2
2005-10-28,"Spin torque, tunnel-current spin polarization and magnetoresistance in MgO magnetic tunnel junctions","We examine the spin torque (ST) response of magnetic tunnel junctions (MTJs)
with ultra-thin MgO tunnel barrier layers to investigate the relationship
between the spin-transfer torque and the tunnel magnetoresistance (TMR) under
finite bias. We find that the spin torque per unit current exerted on the free
layer decreases by less than 10% over a bias range where the TMR decreases by
over 40%. We examine the implications of this result for various spin-polarized
tunneling models and find that it is consistent with magnetic-state-dependent
effective tunnel decay lengths.",0510786v1
2012-10-10,Matching domain wall configuration and spin-orbit torques for very efficient domain-wall motion,"In our numerical study, we identify the best conditions for efficient domain
wall motion by spin-orbit torques originating from the Spin Hall effect or
Rashba effect. We demonstrate that the effect depends critically on the domain
wall configuration, the current injection scheme and the symmetry of the
spin-orbit torque. The best identified configuration corresponds to a N\'eel
wall driven by spin Hall Effect in a narrow strip with perpendicular magnetic
anisotropy. In this case, the domain wall velocity can be a factor of 10 larger
than that for the conventional current-in-plane spin-transfer torque.",1210.3049v1
2015-03-06,Spin-Motive Forces and Current-Induced Torques in Ferromagnets,"In metallic ferromagnets, the spin-transfer torque and spin-motive force are
known to exhibit a reciprocal relationship. Recent experiments on ferromagnets
with strong spin-orbit coupling have revealed a rich complexity in the
interaction between itinerant charge carriers and magnetization, but a full
understanding of this coupled dynamics is lacking. Here, we develop a general
phenomenology of the two reciprocal processes of charge pumping by spin-motive
forces and current-driven magnetization dynamics. The formalism is valid for
spin-orbit coupling of any strength and presents a systematic scheme for
deriving all possible torque and charge-pumping terms that obey the symmetry
requirements imposed by the point group of the system. We demonstrate how the
different charge pumping and torque contributions are connected via the Onsager
reciprocal relations. The formalism is applied to two important classes of
systems: isotropic ferromagnets with non-uniform magnetization and homogeneous
ferromagnets described by the point group $C_{2v}$.",1503.01899v2
2016-06-08,Current driven spin-orbit torque oscillator: ferromagnetic and antiferromagnetic coupling,"We consider theoretically the impact of Rashba spin-orbit coupling on spin
torque oscillators (STOs) in synthetic ferromagnets and antiferromagnets that
have either a bulk multilayer or a thin film structure. The synthetic magnets
consist of a fixed polarizing layer and two free magnetic layers that interact
through the Ruderman-Kittel-Kasuya-Yosida interaction. We determine
analytically which collinear states along the easy axis that are stable, and
establish numerically the phase diagram for when the system is in the STO mode
and when collinear configurations are stable, respectively. It is found that
the Rashba spin-orbit coupling can induce anti-damping in the vicinity of the
collinear states, which assists the spin transfer torque in generating
self-sustained oscillations, and that it can substantially increase the STO
part of the phase diagram. Moreover, we find that the STO phase can extend deep
into the antiferromagnetic regime in the presence of spin-orbit torques.",1606.02720v2
2019-11-28,Spin-torque memristors based on perpendicular magnetic tunnel junctions with a hybrid chiral texture,"Spin-torque memristors were proposed in 2009, which could provide fast,
low-power and infinite memristive behavior for large-density non-volatile
memory and neuromorphic computing. However, the strict requirements of
combining high magnetoresistance, stable intermediate states and spin-polarized
current switching in a single device pose difficulties in physical
implementation. Here, we experimentally demonstrate a nanoscale spin-torque
memristor based on a perpendicular-anisotropy magnetic tunnel junction with a
CoFeB/W/CoFeB composite free layer structure. Its tunneling magnetoresistance
is higher than 200%, and memristive behavior can be realized by spin-transfer
torque switching. Memristive states are maintained by robust domain wall
pinning around clusters of W atoms, where nanoscale vertical chiral spin
textures could be formed through the competition between opposing
Dzyaloshinskii-Moriya interactions and the fluctuating interlayer coupling
caused by the Ruderman-Kittel-Kasuya-Yosida interaction between the two CoFeB
free layers. Spike-timing-dependent plasticity is also demonstrated in this
device.",1911.12784v1
2019-06-17,Electronic structure and Magneto-transport in MoS$_2$/Phosphorene van der Waals heterostructure,"The time-dependent spin current mediated spin transfer torque behaviour has
been investigated via scattering formalism within density functional theory
framework supported by Green's function. Quantum magnetotransport
characteristics have been revealed in a model semiconducting
MoS$_2$/phosphorene van der Waals heterostructure. The dynamics of spin current
channelized heterolayer transport has been studied with rotational variation in
magnetization angle. It is observed that the time-dependent spin transport
torque remains invariant irrespective of magnetization angle direction. The
polarized spin-current is persistent with the external magnetic field for
potential applicability towards spintronics.",1906.09187v1
2017-12-01,Spin-resolved electron waiting times in a quantum dot spin valve,"We study the electronic waiting time distributions (WTDs) in a
non-interacting quantum dot spin valve by varying spin polarization and the
noncollinear angle between the magnetizations of the leads using scattering
matrix approach. Since the quantum dot spin valve involves two channels (spin
up and down) in both the incoming and outgoing channels, we study three
different kinds of WTDs, which are two-channel WTD, spin-resolved
single-channel WTD and cross-channel WTD. We analyze the behaviors of WTDs in
short times, correlated with the current behaviors for different spin
polarizations and noncollinear angles. Cross-channel WTD reflects the
correlation between two spin channels and can be used to characterize the spin
transfer torque process. We study the influence of the earlier detection on the
subsequent detection from the perspective of cross-channel WTD, and define the
influence degree quantity as the cumulative absolute difference between
cross-channel WTDs and first passage time distributions to quantitatively
characterize the spin flip process. The influence degree shows a similar
behavior with spin transfer torque and can be a new pathway to characterize
spin correlation in spintronics system.",1712.00215v2
2007-12-04,Microwave excitations associated with a wavy angular dependence of the spin transfer torque : model and experiments,"The spin transfer torque (STT) can lead to steady precession of magnetization
without any external applied field in magnetic spin valve where the magnetic
layer have very different spin diffusion length. This effect is associated with
an unusual angular dependence of the STT, called ""wavy"" (WAD-STT), predicted in
the frame of diffusive models of spin transfer. In this article, we present a
complete experimental characterization of the magnetization dynamics in the
presence of a WAD-STT. The results are compared to the prediction of the
magnetization dynamics obtained by single domain magnetic simulations
(macrospin approximation). The macrospin simulations well reproduced the main
static and dynamical experimental features (phase diagram, R(I) curves,
dependence of frequency with current and field) and suggest that the dynamical
excitations observed experimentally are associated with a large angle
out-of-plane precession mode. The present work validates the diffusive models
of the spin transfer and underlines the role of the spin accumulation and the
spin relaxation effects on the STT.",0712.0548v1
2016-09-27,Steady State and Dynamics of Joule Heating in Magnetic Tunnel Junctions Observed via the Temperature Dependence of RKKY Coupling,"Understanding quantitatively the heating dynamics in magnetic tunnel
junctions (MTJ) submitted to current pulses is very important in the context of
spin-transfer-torque magnetic random access memory development. Here we provide
a method to probe the heating of MTJ using the RKKY coupling of a synthetic
ferrimagnetic storage layer as a thermal sensor. The temperature increase
versus applied bias voltage is measured thanks to the decrease of the spin-flop
field with temperature. This method allows distinguishing spin transfer torque
(STT) effects from the influence of temperature on the switching field. The
heating dynamics is then studied in real-time by probing the conductance
variation due to spin-flop rotation during heating. This approach provides a
new method for measuring fast heating in spintronic devices, particularly
magnetic random access memory (MRAM) using thermally assisted or spin transfer
torque writing.",1609.08385v1
2017-11-27,Characterization of Spin-Transfer-Torque effect induced magnetization dynamics driven by short current pulses,"We present a time-resolved study of the magnetization dynamics in a
microstructured Cr$|$Heusler$|$Pt waveguide driven by the Spin-Hall-Effect and
the Spin-Transfer-Torque effect via short current pulses. In particular, we
focus on the determination of the threshold current at which the spin-wave
damping is compensated. We have developed a novel method based on the temporal
evolution of the magnon density at the beginning of an applied current pulse at
which the magnon density deviates from the thermal level. Since this method
does not depend on the signal-to-noise ratio, it allows for a robust and
reliable determination of the threshold current which is important for the
characterization of any future application based on the Spin-Transfer-Torque
effect.",1711.09647v1
2019-02-25,Steering of the Skyrmion Hall Angle By Gate Voltage,"Magnetic skyrmions can be driven by an applied spin-polarized electron
current which exerts a spin-transfer torque on the localized spins constituting
the skyrmion. However, the longitudinal dynamics is plagued by the skyrmion
Hall effect which causes the skyrmions to acquire a transverse velocity
component. We show how to use spin-orbit interaction to control the skyrmion
Hall angle and how the interplay of spin-transfer and spin-orbit torques can
lead to a complete suppression of the transverse motion. Since the spin-orbit
torques can be controlled all-electronically by a gate voltage, the skyrmion
motion can be steered all-electronically on a broad racetrack at high speed and
conceptually new writing and gating operations can be realized.",1902.09521v2
2016-06-10,Nanoscale confinement of ultrafast spin transfer torque exciting non-uniform spin dynamics by femtosecond spin current pulses,"Spintronics had a widespread impact over the past decades due to transferring
information by spin rather than electric currents. Its further development
requires miniaturization and reduction of characteristic timescales of spin
dynamics combining the sub-nanometer spatial and femtosecond temporal ranges.
These demands shift the focus of interest towards the fundamental open question
of the interaction of femtosecond spin current (SC) pulses with a ferromagnet
(FM). The spatio-temporal properties of the impulsive spin transfer torque
exerted by ultrashort SC pulses on the FM open the time domain for probing
non-uniform magnetization dynamics. Here we employ laser-generated ultrashort
SC pulses for driving ultrafast spin dynamics in FM and analyzing its transient
local source. Transverse spins injected into FM excite inhomogeneous
high-frequency spin dynamics up to 0.6 THz, indicating that the perturbation of
the FM magnetization is confined to 2 nm.",1606.03403v1
2017-08-19,Current induced multi-mode propagating spin waves in a spin transfer torque nano-contact with strong perpendicular magnetic anisotropy,"Current induced spin wave excitations in spin transfer torque nano-contacts
are known as a promising way to generate exchange-dominated spin waves at the
nano-scale. It has been shown that when these systems are magnetized in the
film plane, broken spatial symmetry of the field around the nano-contact
induced by the Oersted field opens the possibility for spin wave mode
co-existence including a non-linear self-localized spin-wave bullet and a
propagating mode. By means of micromagnetic simulations, here we show that in
systems with strong perpendicular magnetic anisotropy (PMA) in the free layer,
two propagating spin wave modes with different frequency and spatial
distribution can be excited simultaneously. Our results indicate that in-plane
magnetized spin transfer nano-contacts in PMA materials do not host a solitonic
self-localized spin-wave bullet, which is different from previous studies for
systems with in plane magnetic anisotropy. This feature renders them
interesting for nano-scale magnonic waveguides and crystals since magnon
transport can be configured by tuning the applied current.",1708.05886v1
2017-09-22,A conductive topological insulator with colossal spin Hall effect for ultra-low power spin-orbit-torque switching,"Spin-orbit-torque (SOT) switching using the spin Hall effect (SHE) in heavy
metals and topological insulators (TIs) has great potential for ultra-low power
magnetoresistive random-access memory (MRAM). To be competitive with
conventional spin-transfer-torque (STT) switching, a pure spin current source
with large spin Hall angle (${\theta}_{SH}$ > 1) and high electrical
conductivity (${\sigma} > 10^5 {\Omega}^{-1}m^{-1}$) is required. Here, we
demonstrate such a pure spin current source: BiSb thin films with
${\sigma}{\sim}2.5*10^5 {\Omega}^{-1}m^{-1}$, ${\theta}_{SH}{\sim}52$, and spin
Hall conductivity ${\sigma}_{SH}{\sim}1.3*10^7 {\hbar}/2e{\Omega}^{-1}m^{-1}$
at room temperature. We show that BiSb thin films can generate a colossal
spin-orbit field of 2770 Oe/(MA/cm$^2$) and a critical switching current
density as low as 1.5 MA/cm$^2$ in Bi$_{0.9}$Sb$_{0.1}$ / MnGa bi-layers. BiSb
is the best candidate for the first industrial application of topological
insulators.",1709.07684v2
2014-09-25,Interfacial Spin and Heat Transfer between Metals and Magnetic Insulators,"We study the role of thermal magnons in the spin and heat transport across a
normal-metal/insulating-ferromagnet interface, which is beyond an elastic
electronic spin transfer. Using an interfacial exchange Hamiltonian, which
couples spins of itinerant and localized orbitals, we calculate spin and energy
currents for an arbitrary interfacial temperature difference and misalignment
of spin accumulation in the normal metal relative to the ferromagnetic order.
The magnonic contribution to spin current leads to a temperature-dependent
torque on the magnetic order parameter; reciprocally, the coherent precession
of the magnetization pumps spin current into the normal metal, the magnitude of
which is affected by the presence of thermal magnons.",1409.7128v1
2008-05-21,Non-equilibrium thermodynamic study of magnetization dynamics in the presence of spin-transfer torque,"The dynamics of magnetization in the presence of spin-transfer torque was
studied. We derived the equation for the motion of magnetization in the
presence of a spin current by using the local equilibrium assumption in
non-equilibrium thermodynamics. We show that, in the resultant equation, the
ratio of the Gilbert damping constant, $\alpha$, and the coefficient, $\beta$,
of the current-induced torque, called non-adiabatic torque, depends on the
relaxation time of the fluctuating field $\tau_{c}$. The equality
$\alpha=\beta$ holds when $\tau_c$ is very short compared to the time scale of
magnetization dynamics. We apply our theory to current-induced magnetization
reversal in magnetic multilayers and show that the switching time is a
decreasing function of $\tau_{c}$.",0805.3306v1
2008-11-21,Spin Transfer Torque as a Non-Conservative Pseudo-Field,"In this paper we show that the spin transfer torque can be described by a
pseudo magnetic field, proportional to the magnetic moment of the itinerant
electrons that enters the Landau-Lifshitz-Gilbert equation in the same way as
other external or internal magnetic fields. However, unlike an ordinary
magnetic field, which is always conservative in nature, the spin torque induced
pseudo field may have both conservative and non-conservative components. We
further show that the magnetic moment of itinerant electrons develops an
out-of-plane component only at non-equilibrium and this component is
responsible for the Slonczewski type switching that acts against the damping
and is always non-conservative. On the other hand, the in-plane components of
the pseudo field exist both at equilibrium and out-of-equilibrium, and are
responsible for the field like term. For tunnel based devices, this term
results in lower switching current for anti-parallel (AP) to parallel (P)
switching compared to P to AP, even when the torque magnitudes are completely
symmetric with voltage.",0811.3472v1
2013-07-29,Current-induced spin wave excitation in Pt|YIG bilayer,"We develop a self-consistent theory for current-induced spin wave excitations
in normal metal-magnetic insulator bilayer systems, thereby establishing the
relation between spin wave excitation and the experimentally controlled
parameters. We fully take into account the complex spin wave spectrum including
dipolar interactions and surface anisotropy as well as the spin-pumping at the
interface. Our results focus on the mode-dependent power close to the critical
currents for spin wave excitation. The major findings are (a) the spin transfer
torque can excite different spin-wave modes simultaneously; (b) spin pumping
counterbalances spin-transfer torque and affects the surface modes more than
the bulk modes; (c) spin pumping inhibits high frequency spin-wave modes,
thereby redshifting the excitation spectrum. We can get agreement with
experiments on yttrium iron garnet|platinum bilayers by postulating the
existence of surface anisotropy modes.",1307.7607v2
2018-01-03,Effect of spin relaxations on the spin mixing conductances for a bilayer structure,"The spin current can result in a spin-transfer torque in the
normal-metal(NM)|ferromagnetic-insulator(FMI) or
normal-metal(NM)|ferromagnetic-metal(FMM) bilayer. In the earlier study on this
issue, the spin relaxations were ignored or introduced phenomenologically. In
this paper, considering the FMM or FMI with spin relaxations described by a
non-Hermitian Hamiltonian, we derive an effective spin-transfer torque and an
effective spin mixing conductance in the non-Hermitian bilayer. The dependence
of the effective spin mixing conductance on the system parameters (such as
insulating gap, \textit{s-d} coupling, and layer thickness) as well as the
relations between the real part and the imaginary part of the effective spin
mixing conductance are given and discussed. We find that the effective spin
mixing conductance can be enhanced in the non-Hermitian system. This provides
us with the possibility to enhance the spin mixing conductance.",1802.02058v1
2021-06-29,Spin pumping in noncollinear antiferromagnets,"The ac spin pumping of noncollinear antiferromagnets is theoretically
investigated. Starting from an effective action description of the spin system,
we derive the Onsager coefficients connecting the spin pumping and
spin-transfer torque associated with the dynamics of the SO(3)-valued
antiferromagnetic order parameter. Our theory is applied to a kagome
antiferromagnet resonantly driven by a uniform external magnetic field. We
demonstrate that the reactive (dissipative) spin-transfer torque parameter can
be extracted from the pumped ac spin current in-phase (in quadrature) with the
driving field. Furthermore, we find that the three spin-wave bands of the
kagome AF generate spin currents with mutually orthogonal polarization
directions. This offers a unique way of controlling the spin orientation of the
pumped spin current by exciting different spin-wave modes.",2106.15187v2
2019-04-02,Spin pumping and spin torque in interfacial tailored Co2FeAl/\b{eta}-Ta layers,"The Heusler ferromagnetic (FM) compound Co2FeAl interfaced with a high-spin
orbit coupling non-magnetic (NM) layer is a promising candidate for energy
efficient spin logic circuits. The circuit potential depends on the strength of
angular momentum transfer across the FM/NM interface; hence, requiring low spin
memory loss and high spin-mixing conductance. To highlight this issue, spin
pumping and spin-transfer torque ferromagnetic resonance measurements have been
performed on Co_2FeAl/\beta-Ta heterostructures tailored with Cu interfacial
layers. The interface tailored structure yields an enhancement of the effective
spin-mixing conductance. The interface transparency and spin memory loss
corrected values of the spin-mixing conductance, spin Hall angle and spin
diffusion length are found to be 3.40 \pm 0.01 \times 10^{19} m^{-2}, 0.029 \pm
0.003, and 2.3 \pm 0.5 nm, respectively. Furthermore, a high current modulation
of the effective damping of around 2.1 % has been achieved at an applied
current density of 1 \times 10^9 A/m^2 , which clearly indicates the potential
of using this heterostructure for energy efficient control in spin devices",1904.01506v3
2020-09-15,Giant spin transfer torque in atomically thin magnetic bilayers,"In cavity quantum electrodynamics, the multiple reflections of a photon
between two mirrors defining a cavity is exploited to enhance the
light-coupling of an intra-cavity atom. We show that this paradigm for
enhancing the interaction of a flying particle with a localized object can be
generalized to spintronics based on van der Waals 2D magnets. Upon tunneling
through a magnetic bilayer, we find the spin transfer torques per electron
incidence can become orders of magnitude larger than $\hbar/2$, made possible
by electron's multi-reflection path through the ferromagnetic monolayers as an
intermediate of their angular momentum transfer. Over a broad energy range
around the tunneling resonances, the damping-like spin transfer torque per
electron tunneling features a universal value of $\frac{\hbar}{2}
\tan{\frac{\theta}{2}}$, depending only on the angle $\theta$ between the
magnetizations. These findings expand the scope of magnetization manipulations
for high-performance and high-density storage based on van der Waals magnets.",2009.06849v2
2010-09-29,Spin quadrupoletronics: moving spin anisotropy around,"We show that spin anisotropy can be transferred to an isotropic system by
transport of spin quadrupole moment. We derive the quadrupole moment current
and continuity equation and study a high-spin valve structure consisting of two
ferromagnets coupled to a quantum dot probing an impurity spin. The quadrupole
back-action on their coupled spin results in spin torques and anisotropic spin
relaxation which do not follow from standard spin current considerations. We
demonstrate the detection of the impurity spin by charge transport and its
manipulation by electric fields.",1009.5874v2
2014-02-19,Sustained RF oscillations from thermally induced spin-transfer torque,"We investigate the angular dependence of the spin torque generated when
applying a temperature difference across a spin-valve. Our study shows the
presence of a non-trivial fixed point in this angular dependence, i.e. the
possibility for a temperature gradient to stabilize radio frequency
oscillations without the need for an external magnetic field. This so called
""wavy"" behavior can already be found upon applying a voltage difference across
a spin-valve but we find that this effect is much more pronounced with a
temperature difference. Our semi-classical theory is parametrized with
experimentally measured parameters and allows one to predict the amplitude of
the torque with good precision. Although thermal spin torque is by nature less
effective than its voltage counterpart, we find that in certain geometries,
temperature differences as low as a few degrees should be sufficient to trigger
the switching of the magnetization.",1402.4725v1
2016-01-30,A skyrmion-based spin-torque nano-oscillator,"A model for a spin-torque nano-oscillator based on the self-sustained
oscillation of a magnetic skyrmion is presented. The system involves a circular
nanopillar geometry comprising an ultrathin film free magnetic layer with a
strong Dzyaloshinkii-Moriya interaction and a polariser layer with a
vortex-like spin configuration. It is shown that spin-transfer torques due to
current flow perpendicular to the film plane leads to skyrmion gyration that
arises from a competition between geometric confinement due to boundary edges
and the vortex-like polarisation of the spin torques. A phenomenology for such
oscillations is developed and quantitative analysis using micromagnetics
simulations is presented. It is also shown that weak disorder due to random
anisotropy variations does not influence the main characteristics of the
steady-state gyration.",1602.00118v1
2016-05-31,Spin-Orbit Torques in ferrimagnetic GdFeCo Alloys,"The spin-orbit torque switching of ferrimagnetic
Gd$_x$(Fe$_{90}$Co$_{10}$)$_{100-x}$ films was studied for both transition
metal (TM)-rich and rare earth (RE)-rich configurations. The spin-orbit torque
driven magnetization switching follows the same handedness in TM-rich and
RE-rich samples with respect to the total magnetization, but the handedness of
the switching is reversed with respect to the TM magnetization. This indicates
that the sign of the spin-orbit-torque-driven magnetic switching follows the
total magnetization, although transport based techniques such as anomalous Hall
effect are only sensitive to the transition metal magnetization. These results
provide important insight into the physics of spin angular momentum transfer in
materials with antiferromagnetically coupled sublattices.",1605.09498v1
2017-07-25,3D MOKE spin-orbit torque magnetometer,"We demonstrate simultaneous detection of current driven antidamping-like and
field-like spin-orbit torques in heavy metal/ferromagnetic metal bilayers by
measuring all three magnetization components m_(x,) m_y, and m_z using the
vector magneto-optic Kerr effect. We have also implemented a self-calibration
method to accurately determine the effective fields of spin-orbit torques. With
this technique, we investigate the magnitude and direction of spin-orbit
torques in a series of platinum/permalloy samples. The values found are in
excellent agreement with results obtained via quadratic magneto-optic Kerr
effect, planar Hall effect, and spin transfer ferromagnetic resonance
measurements.",1707.08565v1
2009-06-12,Magnetic dynamics with spin transfer torques near the Curie temperature,"We use atomistic stochastic Landau-Lifshitz-Slonczewski simulations to study
the interaction between large thermal fluctuations and spin transfer torques in
the magnetic layers of spin valves. At temperatures near the Curie temperature
$T_{\rm C}$, spin currents measurably change the size of the magnetization
(i.e. there is a {\it longitudinal} spin transfer effect). The change in
magnetization of the free magnetic layer in a spin valve modifies the
temperature dependence of the applied field-applied current phase diagram for
temperatures near $T_{\rm C}$. These atomistic simulations can be accurately
described by a Landau-Lifshitz-Bloch + Slonczewski equation, which is a
thermally averaged mean field theory. Both the simulation and the mean field
theory show that a longitudinal spin transfer effect can be a substantial
fraction of the magnetization close to $T_{\rm C}$.",0906.2423v1
2016-07-30,Spin diffusion and torques in disordered antiferromagnets,"We have developed a drift-diffusion equation of spin transport in collinear
bipartite metallic antiferromagnets. Starting from a model tight-binding
Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism
and expand it to the lowest order in spatial gradient using Wigner expansion
method. In the diffusive limit, these equations track the spatio-temporal
evolution of the spin accumulations and spin currents on each sublattice of the
antiferromagnet. We use these equations to address the nature of spin transfer
torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet,
(ii) a metallic bilayer consisting in an antiferromagnet adjacent to a heavy
metal possessing spin Hall effect, and in (ii) a single antiferromagnet
possessing spin Hall effect. We show that the latter can experience a
self-torque thanks to the non-vanishing spin Hall effect in the
antiferromagnet.",1608.00140v1
2018-01-29,Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems,"Spin-orbit coupling in inversion-asymmetric magnetic crystals and structures
has emerged as a powerful tool to generate complex magnetic textures,
interconvert charge and spin under applied current, and control magnetization
dynamics. Current-induced spin-orbit torques mediate the transfer of angular
momentum from the lattice to the spin system, leading to sustained magnetic
oscillations or switching of ferromagnetic as well as antiferromagnetic
structures. The manipulation of magnetic order, domain walls and skyrmions by
spin-orbit torques provides evidence of the microscopic interactions between
charge and spin in a variety of materials and opens novel strategies to design
spintronic devices with potentially high impact in data storage, nonvolatile
logic, and magnonic applications. This paper reviews recent progress in the
field of spin-orbitronics, focusing on theoretical models, material properties,
and experimental results obtained on bulk noncentrosymmetric conductors and
multilayer heterostructures, including metals, semiconductors, and topological
insulator systems. Relevant aspects for improving the understanding and
optimizing the efficiency of nonequilibrium spin-orbit phenomena in future
nanoscale devices are also discussed.",1801.09636v2
2008-11-02,Micromagnetic simulations of persistent oscillatory modes excited by spin-polarized current in nanoscale exchange-biased spin valves,"We perform 3D micromagnetic simulations of current-driven magnetization
dynamics in nanoscale exchange biased spin-valves that take account of (i) back
action of spin-transfer torque on the pinned layer, (ii) non-linear damping and
(iii) random thermal torques. Our simulations demonstrate that all these
factors significantly impact the current-driven dynamics and lead to a better
agreement between theoretical predictions and experimental results. In
particular, we observe that, at a non-zero temperature and a sub-critical
current, the magnetization dynamics exhibits nonstationary behaviour in which
two independent persistent oscillatory modes are excited which compete for the
angular momentum supplied by spin-polarized current. Our results show that this
multi-mode behaviour can be induced by combined action of thermal and spin
transfer torques.",0811.0173v1
2020-03-28,Acoustic spin transfer to a subwavelength spheroidal particle,"We demonstrate that the acoustic spin of a first-order Bessel beam can be
transferred to a subwavelength (prolate) spheroidal particle at the beam axis
in a viscous fluid. The induced radiation torque is proportional to the
acoustic spin, which scales with the beam energy density. The analysis of the
particle rotational dynamics in a Stokes' flow regime reveals that its angular
velocity varies linearly with the acoustic spin. Asymptotic expressions of the
radiation torque and angular velocity are obtained for a quasispherical and
infinitely thin particle. Excellent agreement is found between the theoretical
results of radiation torque and finite element simulations. The induced
particle spin is predicted and analyzed using the typical parameter values of
the acoustical vortex tweezer and levitation devices. We discuss how the beam
energy density and fluid viscosity can be assessed by measuring the induced
spin of the particle.",2003.12784v1
2008-10-09,Electrical rectification effect in single domain magnetic microstrips: a micromagnetics-based analysis,"Upon passing an a.c. electrical current along magnetic micro- or nanostrips,
the measurement of a d.c. voltage that depends sensitively on current frequency
and applied field has been recently reported by A. Yamaguchi and coworkers. It
was attributed to the excitation of spin waves by the spin transfer torque,
leading to a time-varying anisotropic magnetoresistance and, by mixing of a.c.
current and resistance, to a d.c. voltage. We have performed a quantitative
analysis by micromagnetics, including the spin transfer torque terms considered
usually, of this situation. The signals found from the spin transfer torque
effect are several orders of magnitude below the experimental values, even if a
static inhomogeneity of magnetization (the so-called ripple) is taken into
account. On the other hand, the presence of a small non-zero average Oersted
field is shown to be consistent with the full set of experimental results, both
qualitatively and quantitatively. We examine, quantitatively, several sources
for this average field and point to the contacts to the sample as a likely
origin.",0810.1588v1
2011-08-11,Thermoelectric Spin-Transfer Torque MRAM with Sub-Nanosecond Bi-Directional Writing using Magnonic Current,"A new genre of Spin-Transfer Torque (STT) MRAM is proposed, in which
bi-directional writing is achieved using thermoelectrically controlled magnonic
current as an alternative to conventional electric current. The device uses a
magnetic tunnel junction (MTJ), which is adjacent to a non-magnetic metallic
and a ferrite film. This film stack is heated or cooled by a Peltier element
which creates a bi-directional magnonic pulse in the ferrite film. Conversion
of magnons to spin current occurs at the ferrite-metal interface, and the
resulting spin-transfer torque is used to achieve sub-nanosecond precessional
switching of the ferromagnetic free layer in the MTJ. Compared to electric
current driven STT-MRAM with perpendicular magnetic anisotropy (PMA),
thermoelectric STT-MRAM reduces the overall magnetization switching energy by
more than 40% for nano-second switching, combined with a write error rate (WER)
of less than 10-9 and a lifetime of 10 years or higher. The combination of
higher thermal activation energy, sub-nanosecond read/write speed, improved
tunneling magneto-resistance (TMR) and tunnel barrier reliability make
thermoelectric STT-MRAM a promising choice for future non-volatile memory
applications.",1108.2386v1
2011-10-02,Metastable magnetic domain wall dynamics,"The dynamics of metastable magnetic domain walls in straight ferromagnetic
nanowires under spin waves, external magnetic fields, and current induced spin
transfer torque are studied by micromagnetic simulations. It is found that in
contrast to a stable wall, it is possible to displace a metastable domain wall
in the absence of any external excitation. In addition, independent of the
domain wall excitation method, the velocity of a metastable wall is much
smaller than a stable wall and their displacement direction could be different
from the stable wall depending on the structure of metastable walls. Under the
current induced spin transfer torque excitation, the direction of domain wall
displacement is directly related to the intensity of nonadiabatic spin transfer
torque. In a rough nanowire, it is found that the displacement of a metastable
wall could happen much below the critical excitation of a stable wall.
Furthermore, we show that it is possible to have either a forward or backward
displacement of a metastable domain wall by changing the pulse width of the
excitation.",1110.0175v1
2013-03-07,Theory of atomistic simulation of spin-transfer torque in nanomagnets,"In spin-transfer torque (STT) for technological applications, the
miniaturization of the magnet may reach the stage of requiring a fully
quantum-mechanical treatment. We present an STT theory which uses the quantum
macrospin ground and excited (magnon) states of the nanomagnet. This allows for
energy and angular momentum exchanges between the current electron and the
nano-magnet. We develop a method of magnetization dynamics simulation which
captures the heating effect on the magnet by the spin-polarized current and the
temperature-dependence in STT. We also discuss the magnetostatics effect on
magnon scattering for ferromagnetic relaxation in a thin film. Our work
demonstrates a realistic step towards simulation of quantum spin-transfer
torque physics in nano-scale magnets.",1303.1775v1
2016-10-04,Effect of temperature on spin-transfer torque induced magnetic solitons,"Spin-transfer torques in a nanocontact to an extended magnetic film can
create spin waves that condense to form dissipative droplet solitons. Here we
report an experimental study of the temperature dependence of the current and
applied field thresholds for droplet soliton formation, as well as the
nanocontact's electrical characteristics associated with droplet dynamics.
Nucleation of droplet solitons requires higher current densities at higher
temperatures, in contrast to typical spin-transfer torque induced switching
between static magnetic states. Magnetoresistance and electrical noise
measurements show that soliton instabilities become more pronounced with
increasing temperature. These results are of fundamental interest in
understanding the influence of thermal noise on droplet solitons, and in
controlling their dynamics.",1610.00931v1
2020-09-28,Determination of spin-orbit torques by thickness-dependent spin-orbit torque FMR measurement,"Current induced spin-orbit torques (SOTs) in Fe/Pt bilayers have been
investigated utilizing the spin-orbit torque ferromagnetic resonance (SOT-FMR)
measurement. Characterization of thin films with different thicknesses
indicates existence of a sizable field-like spin-orbit torque competing with
the Oersted field induced torque (Oersted torque). The field-like torque is
neglected in the standard SOT-FMR method and the presence of a strong
field-like torque makes estimation of the spin Hall angle (SHA) problematic.
Also, it is challenging to differentiate the field-like torque from the Oersted
torque in a radiofrequency measurement. Based on the thickness dependence of
field-like torque, anti-damping torque, and Oersted torque, the
thickness-dependent SOT-FMR measurement is proposed as a more reliable,
self-calibrated approach for characterization of spin-orbit torques.",2009.13162v2
2016-08-22,"Thermally induced magnonic spin current, thermomagnonic torques and domain wall dynamics in the presence of Dzyaloshinskii-Moriya interaction","Thermally activated domain wall (DW) motion in magnetic insulators has been
considered theoretically, with a particular focus on the role of
Dzyaloshinskii-Moriya Interaction (DMI) and thermomagnonic torques. The
thermally assisted DW motion is a consequence of the magnonic spin current due
to the applied thermal bias. In addition to the exchange magnonic spin current
and the exchange adiabatic and the entropic spin transfer torques, we also
consider the DMI-induced magnonic spin current, thermomagnonic DMI field-like
torque and the DMI entropic torque. Analytical estimations are supported by
numerical calculations. We found that the DMI has a substantial influence on
the size and the geometry of DWs, and that the DWs become oriented parallel to
the long axis of the nanostrip. Increasing the temperature smoothes the DWs.
Moreover, the thermallyinduced magnonic current generates a torque on the DWs,
which is responsible for their motion. From our analysis it follows that for a
large enough DMI the influence of DMI-induced field-like torque is much
stronger than that of the DMI and the exchange entropic torques. By
manipulating the strength of the DMI constant, one can control the speed of the
DW motion, and the direction of the DW motion can be switched, as well. We also
found that DMI not only contributes to the total magnonic current, but also it
modifies the exchange magnonic spin current, and this modification depends on
the orientation of the steady state magnetization. The observed phenomenon can
be utilized in spin caloritronics devices, for example in the DMI based thermal
diodes. By switching the magnetization direction, one can rectify the total
magnonic spin current.",1608.06179v1
2016-06-30,Skyrmion dynamics in a chiral magnet driven by periodically varying spin currents,"In this work, we investigated the spin dynamics in a slab of chiral magnets
induced by an alternating (ac) spin current. Periodic trajectories of the
skyrmion in real space are discovered under the ac current as a result of the
Magnus and viscous forces, which originate from the Gilbert damping, the spin
transfer torque, and the $ \beta $-nonadiabatic torque effects. The results are
obtained by numerically solving the Landau-Lifshitz-Gilbert equation and can be
explained by the Thiele equation characterizing the skyrmion core motion.",1606.09326v2
2018-02-05,Realization of a spin wave switch based on the Spin-Transfer-Torque effect,"We investigate the amplification of externally excited spin waves via the
Spin-Transfer-Torque (STT) effect in combination with the Spin-Hall-Effect
(SHE) employing short current pulses. The results reveal that, in the case of
an overcompensation of the spin wave damping, a strong nonlinear shift of the
spin wave frequency spectrum occurs. In particular, this shift affects the spin
wave amplification using the SHE-STT effect. In contrast, this effect allows
for the realization of a spin wave switch. By determining the corresponding
working point, an efficient spin wave excitation is only possible in the
presence of the SHE-STT effect yielding an increased spin wave intensity of a
factor of 20 compared to the absence of the SHE-STT effect.",1802.01294v1
2012-01-10,Quantum spin pumping mediated by magnon,"We theoretically propose quantum spin pumping mediated by magnons, under a
time-dependent transverse magnetic field, at the interface between a
ferromagnetic insulator and a non-magnetic metal. The generation of a spin
current under a thermal equilibrium condition is discussed by calculating the
spin transfer torque, which breaks the spin conservation law for conduction
electrons and operates the coherent magnon state. Localized spins lose spin
angular momentum by emitting magnons and conduction electrons flip from down to
up by absorbing the momentum. The spin transfer torque has a resonance
structure as a function of the angular frequency of the applied transverse
field. This fact is useful to enhance the spin pumping effect induced by
quantum fluctuations. We also discuss the distinction between our quantum spin
pumping theory and the one proposed by Tserkovnyak et al.",1201.1947v3
2009-06-24,Anomalous stabilization in a spin-transfer system at high spin polarization,"Switching diagrams of nanoscale ferromagnets driven by a spin-transfer torque
are studied in the macrospin approximation. We consider a disk-shaped free
layer with in-plane easy axis and external magnetic field directed in-plane at
90 degrees to that axis. It is shown that this configuration is sensitive to
the angular dependence of the spin-transfer efficiency factor and can be used
to experimentally distinguish between different forms of $g(\theta)$, in
particular between the original Slonczewski form and the constant $g$
approximation. The difference in switching diagrams is especially pronounced at
large spin polarizations, with the Slonczewski case exhibiting an anomalous
region.",0906.4566v1
2009-06-12,Analytic expression of the temperature increment in a spin transfer torque nanopillar structure,"The temperature increment due to the Joule heating in a nanopillar spin
transfer torque system is investigated. We obtain a time dependent analytic
solution of the heat conduction equation in nanopillar geometry by using the
Green's function method after some simplifications of the problem. While Holm's
equation is applicable only to steady states in metallic systems, our solution
describes the time dependence and is also applicable to a nanopillar-shaped
magnetic tunneling junction with an insulator barrier layer. The validity of
the analytic solution is confirmed by numerical finite element method
simulations and by the comparison with Holm's equation.",0906.2248v1
2011-01-17,Digital logic using 3-terminal spin transfer torque devices,"We demonstrate for the first time that functionally complete digital logic
can be created by using three terminal devices each consisting of a magnetic
tunnel junction (MTJ) and spin transfer torque (STT) element with a shared free
magnetic layer. Rather than the output of devices being high or low voltage
levels, logical states are represented as output resistances which retain their
state when unpowered. By cascading and clocking devices using a multi-phase
clock, threshold logic can be used to implement functionally complete digital
logic. Using this approach, a single device can act as an AND, NAND, OR, or NOR
gate without the need for external circuitry. Required device parameters and
tolerances are discussed.",1101.3222v1
2011-10-03,Spin transfer torque oscillator based on asymmetric magnetic tunnel junctions,"We present a study of the spin transfer torque oscillator based on
CoFeB/MgO/CoFeB asymmetric magnetic tunnel junctions. We observe microwave
precession in junctions with different thickness of the free magnetization
layer. Taking advantage of the ferromagnetic interlayer exchange coupling
between the free and reference layer in the MTJ and perpendicular interface
anisotropy in thin CoFeB electrode we demonstrate the nanometer scale device
that can generate high frequency signal without external magnetic field
applied. The amplitude of the oscillation exceeds 10 nV/Hz^0.5 at 1.5 GHz.",1110.0295v1
2012-01-23,Micromagnetic Simulations for Spin Transfer Torque in Magnetic Multilayers,"We investigate the spin transfer torque (STT) in the magnetic multilayer
structures with micromagnetic simulations. We implement the STT contribution
for the magnetic multilayer structures in addition to the
Landau-Lifshitz-Gilbert (LLG) micromagnetic simulators. Not only the Sloncewski
STT term, the zero, first, and second order field- like terms are also
considered, and the effects of the Oersted field by the current are addressed.
We determine the switching current densities of the free layer with the
exchange biased synthetic ferrimagnetic reference layers for various cases.",1201.4707v1
2014-09-03,Current Induced Fingering Instability in Magnetic Domain Walls,"The shape instability of magnetic domain walls under current is investigated
in a ferromagnetic (Ga,Mn)(As,P) film with perpendicular anisotropy. Domain
wall motion is driven by the spin transfer torque mechanism. A current density
gradient is found either to stabilize domains with walls perpendicular to
current lines or to produce finger-like patterns, depending on the domain wall
motion direction. The instability mechanism is shown to result from the
non-adiabatic contribution of the spin transfer torque mechanism.",1409.1007v3
2015-04-08,Skyrmion-number dependence of spin-transfer torque on magnetic bubbles,"We theoretically study the skyrmion-number dependence of spin-transfer torque
acting on magnetic bubbles. The skymrion number of magnetic bubbles can take
any integer value depending on the magnetic profile on its circumference and
the size of the bubble. We find that the transverse motion of a bubble with
respect to the charge current is greatly suppressed as the absolute value of
skyrmion number departs from unity, whereas the longitudinal motion is less
sensitive.",1504.01795v5
2008-02-12,Dynamical Coupling Between Ferromagnets Due to Spin Transfer Torque,"We use a combination of analytic calculations and numerical simulations to
demonstrate that electrical current flowing through a magnetic bilayer induces
dynamical coupling between the layers. The coupling originates from the
dependence of the spin transfer torque exerted on the layers on the relative
orientations of their magnetic moments. We demonstrate that such coupling
modifies the behaviors of both layers, significantly affecting the the
stability of the current-induced dynamical regimes and the efficiency of
current-induced magnetic reversal.",0802.1560v1
2014-01-24,Performance Analysis of Spin Transfer Torque Random Access Memory with cross shaped free layer using Heusler Alloys by using micromagnetic studies,"We investigated the performance of spin transfer torque random access memory
(STT-RAM) cell with cross shaped Heusler compound based free layer using
micromagnetic simulations. We designed the free layer using Cobalt based
Heusler compounds. Here in this paper, simulation results predict that
switching time from one state to other state is reduced. Also it is examined
that critical switching current density to switch the magnetization of free
layer of STT RAM cell is reduced.",1401.6971v1
2015-07-19,Spin-transfer-torque efficiency enhanced by edge-damage of perpendicular magnetic random access memories,"We numerically investigate the effect of magnetic and electrical damages at
the edge of a perpendicular magnetic random access memory (MRAM) cell on the
spin-transfer-torque (STT) efficiency that is defined by the ratio of thermal
stability factor to switching current. We find that the switching mode of an
edge-damaged cell is different from that of an undamaged cell, which results in
a sizable reduction in the switching current. Together with a marginal
reduction of the thermal stability factor of an edge-damaged cell, this feature
makes the STT efficiency large. Our results suggest that a precise edge control
is viable for the optimization of STT-MRAM.",1507.05276v1
2020-04-30,Local spin transfer torque and magnetoresistance in domain walls with variable width,"Use of a spin polarized current for the manipulation of magnetic domain walls
in ferromagnetic nanowires has been the subject of intensive research for many
years. Recently, due to technological advancements, creating nano-contacts with
special characteristics is becoming more and more prevalent. We now present a
full quantum investigation of the magnetoresistance and the spin transfer
torque in a domain wall, which is embedded in a nano-contact of Ni$_{80}$Fe$_
{20}$, where the size of the domain wall becomes a relevant tunable parameter.
The dependence on the domain wall width as well as the spatial dependence of
the torque along the domain wall can be analyzed in complete detail. The
magnetoresistance drops with increasing domain wall width as expected, but also
shows characteristic modulations and points of resonant spin-flip transmission.
The spin transfer torque has both significant in-plane and out-of-plane
contributions even without considering relaxation. A closer inspection
identifies contributions from the misalignment of the spin density for short
domain walls as well as an effective gauge field for longer domain walls, both
of which oscillate along the domain wall.",2005.00011v1
2023-12-03,Room-temperature orbit-transfer torque enabling van der Waals magnetoresistive memories,"The nonvolatile magnetoresistive random access memory (MRAM) is believed to
facilitate emerging applications, such as in memory computing, neuromorphic
computing and stochastic computing. Two dimensional (2D) materials and their
van der Waals heterostructures promote the development of MRAM technology, due
to their atomically smooth interfaces and tunable physical properties. Here we
report the all-2D magnetoresistive memories featuring all electrical data
reading and writing at room temperature based on WTe2/Fe3GaTe2/BN/Fe3GaTe2
heterostructures. The data reading process relies on the tunnel
magnetoresistance of Fe3GaTe2/BN/Fe3GaTe2. The data writing is achieved through
current induced polarization of orbital magnetic moments in WTe2, which exert
torques on Fe3GaTe2, known as the orbit transfer torque (OTT) effect. In
contrast to the conventional reliance on spin moments in spin transfer torque
and spin orbit torque, the OTT effect leverages the natural out of plane
orbital moments, facilitating field-free perpendicular magnetization switching
through interface currents. Our results indicate that the emerging OTT MRAM is
promising for low power, high performance memory applications.",2312.01269v1
2013-06-08,Observation of a Berry phase anti-damping spin-orbit torque,"Recent observations of current-induced magnetization switching at
ferromagnet/normal-conductor interfaces have important consequences for future
magnetic memory technology. In one interpretation, the switching originates
from carriers with spin-dependent scattering giving rise to a relativistic
anti-damping spin-orbit torque (SOT) in structures with broken space-inversion
symmetry. The alternative interpretation combines the relativistic spin Hall
effect (SHE), making the normal-conductor an injector of a spin-current, with
the non-relativistic spin-transfer torque (STT) in the ferromagnet. Remarkably,
the SHE in these experiments originates from the Berry phase effect in the band
structure of a clean crystal and the anti-damping STT is also based on a
disorder-independent transfer of spin from carriers to magnetization. Here we
report the observation of an anti-damping SOT stemming from an analogous Berry
phase effect to the SHE. The SOT alone can therefore induce magnetization
dynamics based on a scattering-independent principle. The ferromagnetic
semiconductor (Ga,Mn)As we use has a broken space-inversion symmetry in the
crystal. This allows us to consider a bare ferromagnetic element which
eliminates by design any SHE related contribution to the spin torque. We
provide an intuitive picture of the Berry phase origin of the anti-damping SOT
and a microscopic modeling of measured data.",1306.1893v1
2004-07-21,A selfconsistent theory of current-induced switching of magnetization,"A selfconsistent theory of the current-induced switching of magnetization
using nonequilibrium Keldysh formalism is developed for a junction of two
ferromagnets separated by a nonmagnetic spacer. It is shown that the
spin-transfer torques responsible for current-induced switching of
magnetization can be calculated from first principles in a steady state when
the magnetization of the switching magnet is stationary. The spin-transfer
torque is expressed in terms of one-electron surface Green functions for the
junction cut into two independent parts by a cleavage plane immediately to the
left and right of the switching magnet. The surface Green functions are
calculated using a tight-binding Hamiltonian with parameters determined from a
fit to an {\it ab initio} band structure.This treatment yields the spin
transfer torques taking into account rigorously contributions from all the
parts of the junction. To calculate the hysteresis loops of resistance versus
current, and hence to determine the critical current for switching, the
microscopically calculated spin-transfer torques are used as an input into the
phenomenological Landau-Lifshitz equation with Gilbert damping. The present
calculations for Co/Cu/Co(111) show that the critical current for switching is
$\approx 10^7A/cm^2$, which is in good agreement with experiment.",0407562v2
2008-01-30,Time-Resolved X-ray Microscopy of Spin-Torque-Induced Magnetic Vortex Gyration,"Time-resolved X-ray microscopy is used to image the influence of alternating
high-density currents on the magnetization dynamics of ferromagnetic vortices.
Spin-torque induced vortex gyration is observed in micrometer-sized permalloy
squares. The phases of the gyration in structures with different chirality are
compared to an analytical model and micromagnetic simulations, considering both
alternating spinpolarized currents and the current's Oersted field. In our case
the driving force due to spin-transfer torque is about 70% of the total
excitation while the remainder originates from the current's Oersted field.
This finding has implications to magnetic storage devices using spin-torque
driven magnetization switching and domain-wall motion.",0801.4719v1
2010-07-22,Theory of the power spectrum of spin-torque nanocontact vortex oscillators,"Spin-transfer torques in magnetic nanocontacts can lead to self-sustained
magnetization oscillations that involve large-amplitude gyrotropic vortex
motion. This dynamics consists of a steady state orbit around the nanocontact,
which is made possible because the intrinsic magnetic damping is compensated by
spin torques. In this article, we present an analytical theory of the power
spectrum of these oscillations based on a rigid-vortex model. The appearance of
vortex oscillations in nanocontacts is not associated with a Hopf bifurcation:
there is no critical current and the only precondition for steady-state
oscillations at finite currents is the existence of a vortex in the system, in
contrast with conventional spin-torque oscillators that involve large-angle
magnetization precession. The oscillation frequency is found to depend linearly
on the applied current and inversely proportional to the orbital radius. By
solving the associated Langevin problem for the vortex dynamics, the lineshape
and linewidth for the power spectrum are also obtained. Under typical
experimental conditions, a Lorentzian lineshape with a current-independent
linewidth is predicted. Good quantitative agreement between the theory and
recent experiments is shown.",1007.3859v1
2018-09-10,Torque of guided light on an atom near an optical nanofiber,"We calculate analytically and numerically the axial orbital and spin torques
of guided light on a two-level atom near an optical nanofiber. We show that the
generation of these torques is governed by the angular momentum conservation
law in the Minkowski formulation. The orbital torque on the atom near the fiber
has a contribution from the average recoil of spontaneously emitted photons.
Photon angular momentum and atomic spin angular momentum can be converted into
atomic orbital angular momentum. The orbital and spin angular momenta of the
guided field are not transferred separately to the orbital and spin angular
momenta of the atom.",1809.03121v2
2006-09-11,"Current-driven ferromagnetic resonance, mechanical torques and rotary motion in magnetic nanostructures","We study theoretically the detection and possible utilization of electric
current-induced mechanical torques in ferromagnetic-normal metal
heterostructures that are generated by spin-flip scattering or the absorption
of transverse spin currents by a ferromagnet. To this end, we analyze the DC
voltage signals over a spin valve that is driven by an AC current. In agreement
with recent studies, this ""rectification"", measured as a function of AC
frequency and applied magnetic field, contains important information on the
magnetostatics and --dynamics. Subsequently, we show that the vibrations
excited by spin-transfer to the lattice can be detected as a splitting of the
DC voltage resonance. Finally, we propose a concept for a spin-transfer-driven
electric nanomotor based on integrating metallic nanowires with carbon
nanotubes, in which the current-induced torques generate a rotary motion.",0609258v2
2014-05-04,Spin Torque Oscillators with Thermal Noise: A Constant Energy Orbit Approach,"We consider a biaxial macrospin with an easy and hard axis, and study its
dynamical evolution under the combined effects of thermal noise and spin
transfer torque. The spin-torque is associated with both a perpendicularly
magnetized polarizer and an in-plane magnetized reference layer, leading to an
effective tilt between the easy and spin polarization axes. Using techniques
based on energy averaging over the relevant dynamical trajectories, we analyze
the effects of tilt on the dynamics and derive the conditions for the
occurrence of stable out-of-plane precessionary states. The presence of these
states and their predicted stability boundaries can be tested in experiments on
orthogonal spin-transfer devices, and may also serve as a test of the
applicability of the macrospin model to real devices, which have internal
magnetic degrees of freedom.",1405.0731v3
2020-06-09,Back-hopping in Spin-Transfer-Torque switching of perpendicularly magnetized tunnel junctions,"We analyse the phenomenon of back-hopping in spin-torque induced switching of
the magnetization in perpendicularly magnetized tunnel junctions. The analysis
is based on single-shot time-resolved conductance measurements of the
pulse-induced back-hopping. Studying several material variants reveals that the
back-hopping is a feature of the nominally fixed system of the tunnel junction.
The back-hopping is found to proceed by two sequential switching events that
lead to a final state P' of conductance close to --but distinct from-- that of
the conventional parallel state. The P' state does not exist at remanence. It
generally relaxes to the conventional antiparallel state if the current is
removed. The P' state involves a switching of the sole spin-polarizing part of
the fixed layers. The analysis of literature indicates that back-hopping occurs
only when the spin-polarizing layer is too weakly coupled to the rest of the
fixed system, which justifies a posteriori the mitigation strategies of
back-hopping that were implemented empirically in spin-transfer-torque magnetic
random access memories.",2006.05108v1
2009-05-19,Spin-Transfer Torque and Magnetoresistance in Superconducting Spin-Valves,"We study the spin-transfer torque and magnetoresistance of a
ferromagnet$\mid$superconductor$\mid$ferromagnet spin-valve, allowing for an
arbitrary magnetization misorientation and treating both s-wave and d-wave
symmetries of the superconductor. We take fully into account Andreev reflection
and also the spin-triplet correlations that are generated when the
magnetizations are non-collinear. It is found that the torque and
magnetoresistance are both strongly enhanced when topological zero-energy
states are present at the interfaces, which is the case for d-wave
superconductors with a crystallographic orientation of [110] relative to the
interface ($d_{xy}$-wave symmetry). Moreover, we find that the
magnetoresistance displays a strong oscillatory and non-monotonous behavior as
a function of $d_S/\xi$ where $d_S$ and $\xi$ are the interlayer width of the
superconducting region and the superconducting coherence length, respectively.
This feature is also attributed to the crossover from layers of size $d_S\sim
2\xi$ to layers of size $d_S\gg 2\xi$, where the contribution to transport from
zero-energy states gradually vanishes.",0905.3171v1
2015-07-23,Minimal Model of Spin-Transfer Torque and Spin Pumping caused by Spin Hall Effect,"In the normal metal/ferromagnetic insulator bilayer (such as
Pt/Y$_{3}$Fe$_{5}$O$_{12}$) and the normal metal/ferromagnetic metal/oxide
trilayer (such as Pt/Co/AlO$_{x}$) where spin injection and ejection are
achieved by the spin Hall effect in the normal metal, we propose a minimal
model based on quantum tunneling of spins to explain the spin-transfer torque
and spin pumping caused by the spin Hall effect. The ratio of their
damping-like to field-like component depends on the tunneling wave function
that is strongly influenced by generic material properties such as interface
$s-d$ coupling, insulating gap, and layer thickness, yet the spin relaxation
plays a minor role. The quantified result renders our minimal model an
inexpensive tool for searching for appropriate materials.",1507.06447v2
2018-12-09,Manipulating Quantum Spins by a Spin-Polarized Current: An Approach Based Upon PT-Symmetric Quantum Mechanics,"We propose a quantum processor based upon single-molecule magnets and spin
transfer torque described by PT-symmetric quantum mechanics. In recent years
PT-symmetric Hamiltonians have been used to obtain stability thresholds of
various systems out of equilibrium. One such problem is the magnetization
reversal due to the spin transfer torque generated by a spin-polarized current.
So far the studies of this problem have mostly focused on a classical limit of
a large spin. In this work we are discussing spin tunneling and quantum
dynamics of a small spin induced by a spin polarized current within a
PT-symmetric theory. This description can be used for manipulating spin qubits
by electric currents.",1812.03481v1
2022-10-20,Strong variation of spin-orbit torques with relative spin relaxation rates in ferrimagnets,"Spin-orbit torques (SOTs) have been widely understood as an interfacial
transfer of spin that is independent of the bulk properties of the magnetic
layer. Here, we report that SOTs acting on ferrimagnetic FexTb1-x layers
decrease and vanish upon approaching the magnetic compensation point because
the rate of spin transfer to the magnetization becomes slower than the rate of
spin relaxation into the crystal lattice due to spin-orbit scattering. These
results indicate that the relative rates of competing spin relaxation processes
within magnetic layers play a critical role in determining the strength of
SOTs, which provides a unified understanding for the diverse and even seemingly
puzzling SOT phenomena in ferromagnetic and compensated systems. Our work
indicates that spin-orbit scattering within the magnet should be minimized for
efficient SOT devices. We also find that the interfacial spin-mixing
conductance of interfaces of ferrimagnetic alloys (such as FexTb1-x) is as
large as that of 3d ferromagnets and insensitive to the degree of magnetic
compensation.",2210.11042v1
2014-03-20,"Current-induced switching of magnetic tunnel junctions: Effects of field-like spin-transfer torque, pinned-layer magnetization orientation and temperature","We study current-induced switching in magnetic tunnel junctions (MTJs) in the
presence of a field-like spin-transfer torque and titled pinned-layer
magnetization in the high current limit at finite temperature. We consider both
the Slonczewski and field-like torques with coefficients $a_J$ and $b_J $,
respectively. At finite temperatures, $\sigma= b_J/a_J = \pm1$ leads to a
smaller mean switching time compared that with $\sigma = 0$. The reduction of
switching time in the presence of the field-like term is due to the alignment
effect (for $\sigma > 0$) and the initial torque effect.",1403.5033v1
2016-07-01,Role of spin-transfer torques on synchronization and resonance phenomena in stochastic magnetic oscillators,"A theoretical study on how synchronization and resonance-like phenomena in
superparamagnetic tunnel junctions can be driven by spin-transfer torques is
presented. We examine the magnetization of a superparamagnetic free layer that
reverses randomly between two well-defined orientations due to thermal
fluctuations, acting as a stochastic oscillator. When subject to an external ac
forcing this system can present stochastic resonance and noise-enhanced
synchronization. We focus on the roles of the mutually perpendicular
damping-like and field-like torques, showing that the response of the system is
very different at low and high-frequencies. We also demonstrate that the
field-like torque can increase the efficiency of the current-driven forcing,
specially at sub-threshold electric currents. These results can be useful for
possible low-power, more energy efficient, applications.",1607.00341v2
2017-05-07,Enhancing the spin transfer torque in magnetic tunnel junctions by ac modulation,"The phenomenon of spin transfer torque (STT) has attracted a great deal of
interests due to its promising prospects in practical spintronic devices. In
this paper, we report a theoretical investigation of STT in a noncollinear
magnetic tunnel junction under ac modulation based on the nonequilibrium
Green's function formalism, and derive a closed-formulation for predicting the
time-averaged STT. Using this formulation, the ac STT of a
carbon-nanotube-based magnetic tunnel junction is analyzed. Under ac
modulation, the low-bias linear (quadratic) dependence of the in-plane
(out-of-plane) torque on bias still holds, and the $\sin\theta$ dependence on
the noncollinear angle is maintained. By photon-assisted tunneling, the
bias-induced components of the in-plane and out-of-plane torques can be
enhanced significantly, about 12 and 75 times, respectively. Our analysis
reveals the condition for achieving optimized STT enhancement and suggests that
ac modulation is a very effective way for electrical manipulation of STT.",1705.02579v1
2001-07-09,Tidal interaction in binary black hole inspiral,"In rotating viscous fluid stars, tidal torque leads to an exchange of spin
and orbital angular momentum. The horizon of a black hole has an effective
viscosity that is large compared to that of stellar fluids, and an effective
tidal torque may lead to important effects in the strong field interaction at
the endpoint of the inspiral of two rapidly rotating holes. In the most
interesting case both holes are maximally rotating and all angular momenta
(orbital and spins) are aligned. We point out here that in such a case (i) the
transfer of angular momentum may have an important effect in modifying the
gravitational wave ``chirp'' at the endpoint of inspiral. (ii) The tidal
transfer of spin energy to orbital energy may increase the amount of energy
being radiated. (iii) Tidal transfer in such systems may provide a mechanism
for shedding excess angular momentum. We argue that numerical relativity, the
only tool for determining the importance of tidal torque, should be more
specifically focused on binary configurations with aligned, large, angular
momenta.",0107029v1
2010-10-28,Thermally assisted spin transfer torque switching in synthetic free layers,"We studied the magnetization reversal rates of thermally assisted spin
transfer torque switching in a ferromagnetically coupled synthetic free layer
theoretically. By solving the Fokker-Planck equation, we obtained the
analytical expression of the switching probability for both the weak and the
strong coupling limit. We found that the thermal stability is proportional to
Delta_{0}(1-I/I_{c})^{2}, not Delta_{0}(1-I/I_{c}) argued by Koch et al. [Phys.
Rev. Lett. 92, 088302 (2004)], where I and I_{c} are the electric current and
the critical current of spin transfer torque switching at absolute zero
temperature. The difference in the exponent of (1-I/I_{c}) leads to a
significant underestimation of the thermal stability Delta_{0}. We also found
that fast switching is achieved by choosing the appropriate direction of the
applied field.",1010.5845v3
2011-05-27,"Magnonic spin-transfer torque MRAM with low power, high speed, and error-free switching","A new class of spin-transfer torque magnetic random access memory (STT-MRAM)
is discussed, in which writing is achieved using thermally initiated magnonic
current pulses as an alternative to conventional electric current pulses. The
magnonic pulses are used to destabilize the magnetic free layer from its
initial direction, and are followed immediately by a bipolar electric current
exerting conventional spin-transfer torque on the free layer. The combination
of thermal and electric currents greatly reduces switching errors, and
simultaneously reduces the electric switching current density by more than an
order of magnitude as compared to conventional STT-MRAM. The energy efficiency
of several possible electro-thermal circuit designs have been analyzed
numerically. As compared to STT-MRAM with perpendicular magnetic anisotropy,
magnonic STT-MRAM reduces the overall switching energy by almost 80%.
Furthermore, the lower electric current density allows the use of thicker
tunnel barriers, which should result in higher tunneling magneto-resistance and
improved tunnel barrier reliability. The combination of lower power, improved
reliability, higher integration density, and larger read margin make magnonic
STT-MRAM a promising choice for future non-volatile storage.",1105.5473v1
2013-09-13,Spin-transfer torque switching below 20 kA/cm$^2$ in perpendicular magnetic tunnel junctions,"We demonstrate the reduction of critical spin-transfer torque (STT) switching
currents in Co-Fe-B/MgO based magnetic tunnel junctions (MTJ) with
perpendicular magnetization anisotropy (PMA). The junctions yield tunnel
magnetoresistance (TMR) ratios of up to 64% at 4 monolayer (ML) tunnel barrier
thickness. In this paper, the reduction of the critical switching current
density is studied. By optimizing the applied bias field during DC-STT
measurements, ultra low critical switching current densities of less than 20
kA/cm$^2$, even down to 9 kA/cm$^2$, are found. With the reduced switching
currents, our samples are ideal candidates for further experimental studies
such as the theoretical predicted thermally driven spin-transfer torque effect.",1309.3397v1
2013-11-06,Thermal spin-transfer torque in magnetic tunnel junctions,"The thermal spin-transfer torque (TSTT) is an effect to switch the magnetic
free layer in a magnetic tunnel junction by a temperature gradient only. We
present ab initio calculations of the TSTT. In particular, we discuss the
influence of magnetic layer composition by considering
$\text{Fe}_\text{x}\text{Co}_{\text{1-x}}$ alloys. Further, we compare the TSTT
to the bias voltage driven STT and discuss the requirements for a possible
thermal switching. For example, only for very thin barriers of 3 monolayers MgO
a thermal switching is imaginable. However, even for such a thin barrier the
TSTT is still too small for switching at the moment and further optimization is
needed. In particular, the TSTT strongly depends on the composition of the
ferromagentic layer. In our current study it turns out that at the chosen
thickness of the ferromagnetic layer pure Fe gives the highest thermal
spin-transfer torque.",1311.1457v1
2014-11-18,Towards wafer scale inductive characterization of spin transfer torque critical current density of magnetic tunnel junction stacks,"We explore the prospects of wafer scale inductive probing of the critical
current density $j^{c0}$ for spin transfer torque switching of a
CoFeB/MgO/CoFeB magnetic tunnel junction with varying MgO thickness. From
inductive measurements magnetostatic parameters and the effective damping are
derived and $j^{c0}$ is calculated based on spin transfer torque equations. The
inductive values compare well to the values derived from current induced
switching measurements on individual nanopillars. Using a wafer scale inductive
probe head could in the future enable wafer probe station based metrology of
$j^{c0}$.",1411.4868v1
2014-11-24,Enhancement of Spin-transfer torque switching via resonant tunneling,"We propose the use of resonant tunneling as a route to enhance the
spin-transfer torque switching characteristics of magnetic tunnel junctions.
The proposed device structure is a resonant tunneling magnetic tunnel junction
based on a MgO-semiconductor heterostructure sandwiched between a fixed magnet
and a free magnet. Using the non-equilibrium Green's function formalism coupled
self consistently with the Landau-Lifshitz-Gilbert-Slonczewski equation, we
demonstrate enhanced tunnel magneto-resistance characteristics as well as lower
switching voltages in comparison with traditional trilayer devices. Two device
designs based on MgO based heterostructures are presented, where the physics of
resonant tunneling leads to an enhanced spin transfer torque thereby reducing
the critical switching voltage by up to 44%. It is envisioned that the
proof-of-concept presented here may lead to practical device designs via
rigorous materials and interface studies.",1411.6454v1
2015-02-28,Ultrafast Switching of Antiferromagnets via Spin-transfer Torque,"Picosecond switching of the staggered antiferromagnetic order is shown to be
realizable through spin-transfer torques from a short current pulse. The
coupled dynamics of sublattice magnetization is mapped onto a classical
pendulum subject to gravity and a driving pulse, where switching occurs if the
pendulum acquires sufficient kinetic energy during the pulse to overcome the
maximum of the effective gravity potential. The optimal switching scheme is
explored through the dependence of switch angle and magnetic loss on the
duration and strength of the current pulse. The physics discussed here provides
a general route towards multi-functional THz applications via the spin-transfer
torque in antiferromagnetic materials.",1503.00076v1
2019-02-21,Stochastic ejection of nanocontact droplet solitons via drift instability,"The magnetic droplet soliton is a large amplitude, coherently precessing wave
state that exists in ferromagnetic thin films with perpendicular magnetic
anisotropy. To effectively sustain a droplet, magnetic damping can be locally
compensated in a nanocontact region that imparts spin-transfer torque; this has
been successfully deployed in experiment to directly image the droplet and
probe its dynamics electrically. However, theory predicts and experiments
indicate the existence of a drift instability whereby the droplet is ejected
from the spin-transfer-torque-active region and subsequently decays, an effect
that may be enhanced or possibly induced by thermal fluctuations. Using soliton
perturbation theory and large deviation theory, this work determines the
soliton ejection rate and the most likely path an ejected soliton tracks in the
presence of thermal fields. These results lead to an effective lower bound on
the stability of magnetic droplet solitons in spin-transfer torque nanocontact
devices operating at finite temperature and point to ways in which droplets can
be made more robust.",1902.09310v1
2019-07-04,Resonant Acoustic Wave Assisted Spin-Transfer-Torque Switching of Nanomagnets,"We report the possibility of achieving an order of magnitude reduction in the
energy dissipation needed to write bits in perpendicular magnetic tunnel
junctions (p-MTJs) by simulating the magnetization dynamics under a combination
of resonant surface acoustic waves (r-SAW) and spin-transfer-torque (STT). The
magnetization dynamics were simulated using the Landau-Lifshitz-Gilbert
equation under macrospin assumption with the inclusion of thermal noise. The
resonant magnetization dynamics in the magnetostrictive nanomagnet build over
few 10s of cycles of SAW application that drives the magnetization to precess
in a cone with a deflection of ~45 degrees from the perpendicular direction.
This reduces the STT current density required to switch the magnetization
direction without increasing the STT application time or degrading the
switching probability in the presence of room temperature thermal noise. This
could lead to a pathway to achieve energy efficient switching of spin transfer
torque random access memory (STTRAM) whose lateral dimensions can be scaled
aggressively despite using materials with low magnetostriction by employing
resonant excitation.",1907.02255v1
2020-10-05,"Theoretical study of current-induced domain wall motion in magnetic nanotubes with azimuthal domains, including Œrsted field and spin-transfer torques","We report a theoretical overview of the magnetic domain wall behavior under
an electric current in infinitely-long nanotubes with azimuthal magnetization,
combining the $1$D analytic model and micromagnetic simulations. We highlight
effects that, besides spin-transfer torques already largely understood in flat
strips, arise specifically in the tubular geometry: the \OErsted field and
curvature-induced magnetic anisotropy resulting both from exchange and material
growth. Depending on both the geometry of the tube and the strength of the
azimuthal anisotropy, Bloch or N\'eel walls arise at rest, resulting in two
regimes of motion largely dominated by either spin-transfer torques or the
\OErsted field. We determine the Walker breakdown current in all cases, and
highlight the most suitable parameters to achieve high domain wall speed.",2010.01966v1
2006-10-27,Charge and spin transport in spin valves with anisotropic spin relaxation,"We investigate effects of spin-orbit splitting on electronic transport in a
spin valve consisting of a large quantum dot defined on a two-dimensional
electron gas with two ferromagnetic contacts. In the presence of both structure
inversion asymmetry (SIA) and bulk inversion asymmetry (BIA) a giant anisotropy
in the spin-relaxation times has been predicted. We show how such an anisotropy
affects the electronic transport properties such as the angular
magnetoresistance and the spin-transfer torque. Counterintuitively, anisotropic
spin-relaxation processes sometimes enhance the spin accumulation.",0610770v1
2012-03-13,Spin torque switching with the giant spin Hall effect of tantalum,"We report a giant spin Hall effect (SHE) in {\beta}-Ta that generates spin
currents intense enough to induce efficient spin-transfer-torque switching of
ferromagnets, thereby providing a new approach for controlling magnetic devices
that can be superior to existing technologies. We quantify this SHE by three
independent methods and demonstrate spin-torque (ST) switching of both
out-of-plane and in-plane magnetized layers. We implement a three-terminal
device that utilizes current passing through a low impedance Ta-ferromagnet
bilayer to effect switching of a nanomagnet, with a higher-impedance magnetic
tunnel junction for read-out. The efficiency and reliability of this device,
together with its simplicity of fabrication, suggest that this three-terminal
SHE-ST design can eliminate the main obstacles currently impeding the
development of magnetic memory and non-volatile spin logic technologies.",1203.2875v1
2020-09-17,Control of spin-orbit torques by interface engineering in topological insulator heterostructures,"(Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ topological insulators (TIs) are gathering
increasing attention owing to their large charge-to-spin conversion efficiency
and the ensuing spin-orbit torques (SOTs) that can be used to manipulate the
magnetization of a ferromagnet (FM). The origin of the torques, however,
remains elusive, while the implications of hybridized states and the strong
material intermixing at the TI/FM interface are essentially unexplored. By
combining interface chemical analysis and spin-transfer ferromagnetic resonance
(ST-FMR) measurements, we demonstrate that intermixing plays a critical role in
the generation of SOTs. By inserting a suitable normal metal spacer, material
intermixing is reduced and the TI properties at the interface are largely
improved, resulting in strong variations in the nature of the SOTs. A dramatic
enhancement of a field-like torque, opposing and surpassing the Oersted-field
torque, is observed, which can be attributed to the non-equilibrium spin
density in Rashba-split surface bands and to the suppression of spin memory
loss.",2009.08215v1
2007-09-05,Time-Domain Studies of Very-Large-Angle Magnetization Dynamics Excited by Spin Transfer Torques,"We describe time-domain measurements which provide new information about the
large-angle nonlinear dynamics of nanomagnets excited by spin-transfer torque
from a spin-polarized current. Sampling-oscilloscope measurements, which
average over thousands of experimental time traces, show that the mean reversal
time for spin-transfer-driven magnetic switching has a step-like dependence on
magnetic field, because an integer number of precession cycles is required for
reversal. Storage-oscilloscope measurements of individual experimental traces
reveal non-periodic large-amplitude resistance variations at values of magnetic
field and current in a crossover region between the regimes of
spin-transfer-driven switching and steady-state precession. We also observe
directly the existence of time-dependent switching, on the nanosecond scale,
between different precessional modes and between a precessional mode and a
static state, at particular values of magnetic field and current bias.",0709.0560v1
2001-10-12,Non-collinear spin transfer in Co/Cu/Co multilayers,"This paper has two parts. The first part uses a single point of view to
discuss the reflection and averaging mechanisms of spin-transfer between
current-carrying electrons and the ferromagnetic layers of
magnetic/non-magnetic heterostructures. The second part incorporates both
effects into a matrix Boltzmann equation and reports numerical results for
current polarization, spin accumulation, magnetoresistance, and spin-transfer
torques for Co/Cu/Co multilayers. When possible, the results are compared
quantitatively with relevant experiments.",0110275v1
2007-06-04,Generation of microwave radiation in planar spin-transfer devices,"Current induced precession states in spin-transfer devices are studied in the
case of large easy plane anisotropy (present in most experimental setups). It
is shown that the effective one-dimensional planar description provides a
simple qualitative understanding of the emergence and evolution of such states.
Switching boundaries are found analytically for the collinear device and the
spin-flip transistor. The latter can generate microwave oscillations at zero
external magnetic field without either special functional form of spin-transfer
torque, or ``field-like'' terms, if Gilbert constant corresponds to the
overdamped planar regime.",0706.0529v1
2009-08-21,Spin-transfer torque in disordered weak ferromagnets,"We study theoretically the spin transfer effect on a domain wall in
disordered weak ferromagnets. We have identified the adiabatic condition for
the disordered case as $\lambda \gg \lambda_{\rm D}\equiv \sqrt{{\hbar
D}/{\spol}}$, where $D$ and $\spol$ are the diffusion constant and the spin
splitting energy due to the $s$-$d$ type exchange interaction, respectively,
and found out that perfect spin-transfer effect occurs even in weak
ferromagnets as long as this condition is satisfied. The effective $\beta$ term
arising from the force turns out to govern the wall dynamics, and therefore,
the wall motion can be as efficient as in strong ferromagnets even if $\spol$
is small.",0908.3048v1
2022-03-26,Nonequilibrium dynamics in a spin valve with noncollinear magnetization,"We utilize a hybrid quantum-classical equation of motion approach to
investigate the spin dynamics and spin-transfer torque in a spin valve under
bias voltage. We show that the interplay between localized classical magnetic
moments and conduction electrons induces a complex effective exchange coupling
between the magnetic layers. This leads to a declination of magnetizations from
layers anisotropy axes even in equilibrium. Introducing a finite bias voltage
triggers spin currents and related spin-transfer torques which further tilt the
magnetizations and govern the relaxation processes of the spin dynamics.
Analyzing different scenarios of the applied bias voltage, we show that
symmetric and asymmetric voltage drops can lead to relaxation times of the spin
dynamics that differ by several orders of magnitude at comparable charge
currents. In both cases we observe resonant features, where the relaxation is
boosted whenever the chemical potential of the leads matches the maxima in the
density of the states of the spin-valve electrons.",2203.14068v2
2010-09-15,Spin-wave interference patterns created by spin-torque nano-oscillators for memory and computation,"Magnetization dynamics in nanomagnets has attracted broad interest since it
was predicted that a dc-current flowing through a thin magnetic layer can
create spin-wave excitations. These excitations are due to spin-momentum
transfer, a transfer of spin angular momentum between conduction electrons and
the background magnetization, that enables new types of information processing.
Here we show how arrays of spin-torque nano-oscillators (STNO) can create
propagating spin-wave interference patterns of use for memory and computation.
Memristic transponders distributed on the thin film respond to threshold tunnel
magnetoresistance (TMR) values thereby detecting the spin-waves and creating
new excitation patterns. We show how groups of transponders create resonant
(reverberating) spin-wave interference patterns that may be used for
polychronous wave computation of arithmetic and boolean functions and
information storage.",1009.4116v1
2008-03-14,Spin-torque shot noise in magnetic tunnel junctions,"Spin polarized current may transfer angular momentum to a ferromagnet,
resulting in a spin-torque phenomenon. At the same time the shot noise,
associated with the current, leads to a non-equilibrium stochastic force acting
on the ferromagnet. We derive stochastic version of Landau-Lifshitz-Gilbert
equation for a magnetization of a ''free'' ferromagnetic layer in contact with
a ''fixed'' ferromagnet. We solve the corresponding Fokker-Planck equation and
show that the non-equilibrium noise yields to a non-monotonous dependence of
the precession spectrum linewidth on the current.",0803.2101v1
2016-12-19,Thickness dependence study of current-driven ferromagnetic resonance in Y3Fe5O12/heavy metal bilayers,"We use ferromagnetic resonance to study the current-induced torques in
YIG/heavy metal bilayers. YIG samples with thickness varying from 14.8 nm to 80
nm, with Pt or Ta thin film on top, are measured by applying a microwave
current into the heavy metals and measuring the longitudinal DC voltage
generated by both spin rectification and spin pumping. From a symmetry analysis
of the FMR lineshape and its dependence on YIG thickness, we deduce that the
Oersted field dominates over spin-transfer torque in driving magnetization
dynamics.",1612.06111v1
2019-07-29,"Spin-polarized current, spin-transfer torque and spin Hall effect in presence of an electromagnetic non-minimal coupling","In this contribution, we start off from a fully relativistic description of a
single electron non-minimally coupled to an external electromagnetic field.
Making direct use of the field equation, instead of canonically deriving from
the Lagrangian density, the relativistic total angular momentum is attained,
where the effect of the relativistic torque due to the external sources is also
taken into account. Both the spin density and the orbital angular momentum
tensors are identified in the relativistic-covariant approach. Furthermore, the
symmetric and gauge invariant energy-momentum tensor is derived as well. In
addition, to inspect the non-relativistic regime, a perturbative expansion of
the field equation up to the leading order in $\left(v/c\right)$ is carried
out, where spin-orbit interaction terms naturally emerge in the
non-relativistic Hamiltonian as a consequence of the non-minimal coupling.
Features related to the spin currents, the spin-transfer torque and their
dependence on both magnetic and electric external fields are then calculated
and discussed. Considering that spin-orbit coupled systems are of particular
interest in the study of spin Hall effect, a two-dimensional (planar) scenario
of the system is contemplated, where the contributions to the Landau levels are
re-assessed. As a consequence of the planar regime and the non-minimal
coupling, a peculiar sort of fractionalization of the spin-up and -down
components emerges with the different spin components localized in distinct
positions.",1907.12196v2
2020-12-06,Thermal equilibrium spin torque: Near-field radiative angular momentum transfer in magneto-optical media,"Spin and orbital angular momentum of light plays a central role in quantum
nanophotonics as well as topological electrodynamics. Here, we show that the
thermal radiation from finite-sized bodies comprising of nonreciprocal
magneto-optical materials can exert a spin torque even in global thermal
equilibrium. Moving beyond the paradigm of near-field heat transfer, we
calculate near-field radiative angular momentum transfer between finite-sized
nonreciprocal objects by combining Rytov's fluctuational electrodynamics with
the theory of optical angular momentum. We prove that a single magneto-optical
cubic particle in non-equilibrium with its surroundings experiences a torque in
the presence of an applied magnetic field (T-symmetry breaking). Furthermore,
even in global thermal equilibrium, two particles with misaligned gyrotropic
axes experience equal magnitude torques with opposite signs which tend to align
their gyrotropic axes parallel to each other. Our results are universally
applicable to semiconductors like InSb (magneto-plasmas) as well as Weyl
semi-metals which exhibit the anomalous Hall effect (gyrotropy) at infrared
frequencies. Our work paves the way towards near-field angular momentum
transfer mediated by thermal fluctuations for nanoscale devices.",2012.03193v3
2006-06-05,Anomalous Bias Dependence of Spin Torque in Magnetic Tunnel Junctions,"We predict an anomalous bias dependence of the spin transfer torque parallel
to interface, $T_{||}$, in magnetic tunnel junctions (MTJ), which can be
selectively tuned by the exchange splitting. It may exhibit a sign reversal
{\it without} a corresponding sign reversal of the bias or even a quadratic
bias dependence. We demonstrate that the underlying mechanism is the interplay
of spin currents for the ferromagnetic (antiferromagnetic) configurations,
which vary linearly (quadratically) with bias, respectively, due to the
symmetric (asymmetric) nature of the barrier. The spin transfer torque
perpendicular to interface exhibits a quadratic bias dependence.",0606080v3
2006-10-31,Spin-transfer torque in magnetic multilayer nanopillars,"We consider a quasi one-dimensional configuration consisting of two small
pieces of ferromagnetic material separated by a metallic one and contacted by
two metallic leads. A spin-polarized current is injected from one lead. Our
goal is to investigate the correlation induced between the magnetizations of
the two ferromagnets by spin-transfer torque. This torque results from the
interaction between the magnetizations and the spin polarization of the
current. We discuss the dynamics of a single ferromagnet, the extension to the
case of two ferromagnets, and give some estimates for the parameters based on
experiments.",0610878v1
2006-12-12,Spin torque and force due to current for general spin textures,"Non-adiabatic correction to spin transfer torque arising from fast-varying
spin texture is calculated treating conduction electron fully quantum
mechanically. The torque is non-local in space, and is shown to equivalent to a
force (due to momentum transfer) acting on the center of mass of the texture.
Another kind of force exists in the adiabatic regime, and is identified to be
of topological origin. These forces are shown to be the counter reaction of
electric transport properties, resistivity and Hall effect, respectively.",0612275v3
2014-07-23,Modulating spin transfer torque switching dynamics with two orthogonal spin-polarizers by varying the cell aspect ratio,"We study in-plane magnetic tunnel junctions with additional perpendicular
polarizer for subnanosecond-current-induced switching memories. The
spin-transfer-torque switching dynamics was studied as a function of the cell
aspect ratio both experimentally and by numerical simulations using the
macrospin model. We show that the anisotropy field plays a significant role in
the dynamics, along with the relative amplitude of the two spin-torque
contributions. This was confirmed by micromagnetic simulations. Real-time
measurements of the reversal were performed with samples of low and high aspect
ratio. For low aspect ratios, a precessional motion of the magnetization was
observed and the effect of temperature on the precession coherence was studied.
For high aspect ratios, we observed magnetization reversals in less than 1 ns
for high enough current densities, the final state being controlled by the
current direction in the magnetic tunnel junction cell.",1407.6240v2
2015-04-09,Spin-transfer torque effects in the dynamic forced response of the magnetization of nanoscale ferromagnets in superimposed ac and dc bias fields in the presence of thermal agitation,"Spin-transfer torque (STT) effects on the stationary forced response of
nanoscale ferromagnets subject to thermal fluctuations and driven by an ac
magnetic field of arbitrary strength and direction are investigated via a
generic nanopillar model of a spin-torque device comprising two ferromagnetic
strata representing the free and fixed layers and a nonmagnetic conducting
spacer all sandwiched between two ohmic contacts. The STT effects are treated
via the Brown magnetic Langevin equation generalized to include the Slonczewski
STT term thereby extending the statistical moment method [Y. P. Kalmykov et
al., Phys. Rev. B 88, 144406 (2013)] to the forced response of the most general
version of the nanopillar model. The dynamic susceptibility, nonlinear
frequency-dependent dc magnetization, dynamic magnetic hysteresis loops, etc.
are then evaluated highlighting STT effects on both the low-frequency thermal
relaxation processes and the high-frequency ferromagnetic resonance, etc.,
demonstrating a pronounced dependence of these on the spin polarization current
and facilitating interpretation of STT experiments.",1504.02319v2
2016-09-15,Spin pumping and torque statistics in the quantum noise limit,"We analyze the statistics of charge and energy currents and spin torque in a
metallic nanomagnet coupled to a large magnetic metal via a tunnel contact. We
derive a Keldysh action for the tunnel barrier, describing the stochastic
currents in the presence of a magnetization precessing with the rate $\Omega$.
In contrast to some earlier approaches, we include the geometric phases that
affect the counting statistics. We illustrate the use of the action by deriving
spintronic fluctuation relations, the quantum limit of pumped current noise,
and consider the fluctuations in two specific cases: the situation with a
stable precession of magnetization driven by spin transfer torque, and the
torque-induced switching between the minima of a magnetic anisotropy. The
quantum corrections are relevant when the precession rate exceeds the
temperature $T$, i.e., for $\hbar \Omega \gtrsim k_B T$.",1609.04619v1
2017-06-21,Time-domain stability of parametric synchronization in a spin-torque nano-oscillator based on a magnetic tunnel junction,"We report on a time-domain study of parametric synchronization in a magnetic
tunnel junction based spin torque nano-oscillator (STNO). Time-domain
measurements of the instantaneous frequency ($f_{i}$) of a parametrically
synchronized STNO show random short-term unlocking of the STNO signal for low
injected radio-frequency (RF) power, which cannot be revealed in time-averaged
frequency domain measurements. Macrospin simulations reproduce the experimental
results and reveal that the random unlocking during synchronization is driven
by thermal fluctuations. We show that by using a high injected RF power, random
unlocking of the STNO can be avoided. However, a perfect synchronization
characterized by complete suppression of phase noise, so-called phase noise
squeezing, can be obtained only at a significantly higher RF power. Our
macrospin simulations suggest that a lower temperature and a higher positive
ratio of the field-like torque to the spin transfer torque reduce the threshold
RF power required for phase noise squeezing under parametric synchronization.",1706.06736v2
2017-03-09,Dynamics and inertia of a skyrmion in chiral magnets and interfaces: A linear response approach based on magnon excitations,"Taking all the magnon modes into account, we derive the skyrmion dynamics in
response to a weak external drive. A skyrmion has rotational symmetry and the
magnon modes can be characterized by an angular momentum. For a weak distortion
of a skyrmion, only the magnon modes with an angular momentum $|m|=1$ govern
the dynamics of skyrmion topological center. The skyrmion inertia is determined
by the magnon modes in the continuum spectrum. For a skyrmion driven by a
magnetic field gradient or by a spin transfer torque generated by a current,
the dynamical response is practically instantaneous. This justifies the rigid
skyrmion approximation used in Thiele's collective coordinate approach. For a
skyrmion driven by a spin Hall torque, the torque couples to the skyrmion
motion through the magnons in the continuum and damping, therefore the skyrmion
dynamics shows sizable inertia in this case. The trajectory of a skyrmion is an
ellipse for an ac drive of spin Hall torque.",1703.03099v2
2021-03-13,Microscopic Calculation of Spin Torques in Textured Antiferromagnets,"A microscopic calculation is presented for the spin-transfer torques (STT)
and damping torques in metallic antiferromagnets (AF). It is found that the
sign of the STT is opposite to that in ferromagnets because of the AF transport
character, and the current-to-STT conversion factor is enhanced near the AF gap
edge. The dissipative torque parameter $\beta_n$ and the damping parameter
$\alpha_n$ for the N\'eel vector arise from spin relaxation of electrons.
Physical consequences are demonstrated for the AF domain wall motion using
collective coordinates, and some similarities to the ferromagnetic case are
pointed out such as intrinsic pinning and the specialty of $\alpha_n =
\beta_n$. A recent experiment on a ferrimagnetic GdFeCo near its
angular-momentum compensation temperature is discussed.",2103.07634v1
2014-02-05,Spin Transfer Torque Generated by the Topological Insulator Bi_2Se_3,"Magnetic devices are a leading contender for implementing memory and logic
technologies that are nonvolatile, that can scale to high density and high
speed, and that do not suffer wear-out. However, widespread applications of
magnetic memory and logic devices will require the development of efficient
mechanisms for reorienting their magnetization using the least possible current
and power. There has been considerable recent progress in this effort, in
particular discoveries that spin-orbit interactions in heavy metal/ferromagnet
bilayers can yield strong current-driven torques on the magnetic layer, via the
spin Hall effect in the heavy metal or the Rashba-Edelstein effect in the
ferromagnet. As part of the search for materials to provide even more efficient
spin-orbit-induced torques, some proposals have suggested topological
insulators (TIs), which possess a surface state in which the effects of
spin-orbit coupling are maximal in the sense that an electron's spin
orientation is locked relative to its propagation direction. Here we report
experiments showing that charge current flowing in-plane in a thin film of the
TI Bi_2Se_3 at room temperature can indeed apply a strong spin-transfer torque
to an adjacent ferromagnetic permalloy (Py = Ni81Fe19) thin film, with a
direction consistent with that expected from the topological surface state. We
find that the strength of the torque per unit charge current density in the
Bi_2Se_3 is greater than for any other spin-torque source material measured to
date, even for non-ideal TI films wherein the surface states coexist with bulk
conduction. Our data suggest that TIs have potential to enable very efficient
electrical manipulation of magnetic materials at room temperature for memory
and logic applications.",1402.1124v1
2011-05-16,Spin down of protostars through gravitational torques,"Young protostars embedded in circumstellar discs accrete from an angular
momentum-rich mass reservoir. Without some braking mechanism, all stars should
be spinning at or near break-up velocity. In this paper, we perform simulations
of the self-gravitational collapse of an isothermal cloud using the ORION
adaptive mesh refinement code and investigate the role that gravitational
torques might play in the spin-down of the dense central object. While magnetic
effects likely dominate for low mass stars, high mass and Population III stars
might be less well magnetised. We find that gravitational torques alone prevent
the central object from spinning up to more than half of its breakup velocity,
because higher rotation rates lead to bar-like deformations that enable
efficient angular momentum transfer to the surrounding medium. We also find
that the long-term spin evolution of the central object is dictated by the
properties of the surrounding disc. In particular, spiral modes with azimuthal
wavenumber $m=2$ couple more effectively to its spin than the lopsided $m=1$
mode, which was found to inhibit spin evolution. We suggest that even in the
absence of magnetic fields, gravitational torques may provide an upper limit on
stellar spin, and that moderately massive circumstellar discs can cause
long-term spin down.",1105.3205v2
2017-05-03,Current driven second harmonic domain wall resonance in ferromagnetic metal/ nonmagnetic metal bilayer: a field-free method for spin Hall angle measurements,"We study the ac current-driven domain wall motion in bilayer ferromagnetic
metal (FM)/nonmagnetic metal (NM) nanowire. The solution of the modified
Landau-Lifshitz-Gilbert equation including all the spin transfer torques is
used to describe motion of the domain wall in presence of the spin Hall effect.
We show that the domain wall center has second harmonic frequency response in
addition to the known first harmonic excitation. In contrast to the
experimentally observed second harmonic response in harmonic Hall measurements
of spin-orbit torque in magnetic thin films, this second harmonic response
directly originates from spin-orbit torque driven domain wall dynamics. Based
on the spin current generated by domain wall dynamics, the longitudinal spin
motive force generated voltage across the length of the nanowire is determined.
The second harmonic response introduces additionally a new practical field-free
and all-electrical method to probe the effective spin Hall angle for FM/NM
bilayer structures that could be applied in experiments. Our results also
demonstrate the capability of utilizing FM/NM bilayer structure in domain wall
based spin torque signal generators and resonators.",1705.01355v5
2009-06-09,Magnetically Torqued Neutrino-Dominated Accretion Flows for Gamma-ray Bursts,"Recent observations and theoretical work on gamma-ray bursts (GRBs) favor the
central engine model of a Kerr black hole (BH) surrounded by a magnetized
neutrino-dominated accretion flow (NDAF). The magnetic coupling between the BH
and disk through a large-scale closed magnetic field exerts a torque on the
disk, and transports the rotational energy from the BH to the disk. We
investigate the properties of the NDAF with this magnetic torque. For a rapid
spinning BH, the magnetic torque transfers enormous rotational energy from BH
into the inner disk. There are two consequences: (i) the luminosity of neutrino
annihilation is greatly augmented; (ii) the disk becomes thermally and
viscously unstable in the inner region, and behaves S-Shape of the surface
density versus accretion rate. It turns out that magnetically torqued NDAF can
be invoked to interpret the variability of gamma-ray luminosity. In addition,
we discuss the possibility of restarting the central engine to produce the
X-ray flares with required energy.",0906.1635v1
2016-03-14,Spin Hall Effect Induced Spin Transfer Through an Insulator,"When charge current passes through a normal metal that exhibits spin Hall
effect, spin accumulates at the edge of the sample in the transverse direction.
We predict that this spin accumulation, or spin voltage, enables quantum
tunneling of spin through an insulator or vacuum to reach a ferromagnet without
transferring charge. In a normal metal/insulator/ferromagnetic insulator
trilayer (such as Pt/oxide/YIG), the quantum tunneling explains the
spin-transfer torque and spin pumping that exponentially decay with the
thickness of the insulator. In a normal metal/insulator/ferromagnetic metal
trilayer (such as Pt/oxide/Co), the spin transfer in general does not decay
monotonically with the thickness of the insulator. Combining with the spin Hall
magnetoresistance, this tunneling mechanism points to the possibility of a new
type of tunneling spectroscopy that can probe the magnon density of states of a
ferromagnetic insulator in an all-electrical and noninvasive manner.",1603.04240v2
2007-10-31,Spin-Torque Driven Magnetization Dynamics: Micromagnetic Modelling,"In this paper we present an overview of recent progress made in the
understanding of the spin-torque induced magnetization dynamics in nanodevices
using mesoscopic micromagnetic simulations. We first specify how a spin-torque
term may be added to the usual Landau-Lifshitz-Gilbert equation of
magnetization motion and detail its physical meaning. After a brief description
of spin-torque driven dynamics in the macrospin approximation, we discuss the
validity of this approximation for various experimentally relevant geometries.
Next, we perform a detailed comparison between accurate experimental data
obtained from nanopillar devices and corresponding numerical modelling. We show
that, on the one hand, many qualitatively important features of the observed
magnetization dynamics (e.g., non-linear frequency shift and frequency jumps
with increasing current) can be satisfactory explained by sophisticated
micromagnetic models, but on the other hand, understanding of these experiments
is still far from being complete. We proceed with the numerical analysis of
point-contact experiments, where an even more complicated magnetization
dynamics is observed. Simulations reveal that such a rich behaviour is due to
the formation of several strongly non-linear oscillation modes. In the last
part of the paper we emphasize the importance of sample characterization and
conclude with some important remarks concerning the relation between
micromagnetic modelling and real experiments.",0710.5924v1
2018-05-02,Spatial Mapping of Torques within a Spin Hall Nano-oscillator,"Time-resolved scanning Kerr microscopy (TRSKM) was used to study precessional
magnetization dynamics induced by a radio frequency (RF) current within a
Al$_2$O$_3$/Py(5 nm)/Pt(6 nm)/Au(150 nm) spin Hall nano-oscillator structure.
The Au layer was formed into two needle-shaped electrical contacts that
concentrated the current in the centre of a Py/Pt mesa of 4 $\mu$m diameter.
Due to the spin Hall effect, current within the Pt layer drives a spin current
into the Py layer, exerting a spin transfer torque (STT). By injecting RF
current, and exploiting the phase-sensitivity of TRSKM and the symmetry of the
device structure, the STT and Oersted field torques have been separated and
spatially mapped. The STT and torque due to the in-plane Oersted field are
observed to exhibit minima at the device centre that is ascribed to spreading
of RF current that is not observed for DC current. Torques associated with the
RF current may destabilise the position of the self-localised bullet mode
excited by the DC current, and inhibit injection locking. The present study
demonstrates the need to characterise both DC and RF current distributions
carefully.",1805.00999v3
2009-07-20,Computational study of microwave oscillations in absence of external field in nonstandard spin valves in the diffusive transport limit,"An anomalous (inverse) spin accumulation in the nonmagnetic spacer may build
up when the spin valve consists of magnetic films having different spin
symmetries. This leads to wavy-like dependence of spin-transfer torque on the
angle between magnetizations, as predicted by spin-dependent diffusive
transport model, and also confirmed experimentally. Making use of these
predictions, we have numerically studied the magnetization dynamics in presence
of such a wavy-torque in Co(8 nm)/Cu(10 nm)/Py(8 nm) nanopillar, considering
geometry with extended and etched Co layer. In both cases we specify conditions
for the out-of-plane precession to appear in absence of external magnetic field
and neglecting thermal fluctuations. We prove the assumption of wavy-like
torque angular dependence to be fully consistent with experimental
observations. We also show that some features reported experimentally, like
nonlinear slope of frequency vs. current behavior, are beyond the applicability
range of macrospin approximation and can be explained only by means of full
micromagnetic analysis.",0907.3384v1
2013-08-22,Magnetization oscillations by vortex-antivortex dipoles,"A vortex-antivortex dipole can be generated due to current with in-plane
spin-polarization, flowing into a magnetic element, which then behaves as a
spin transfer oscillator. Its dynamics is analyzed using the Landau-Lifshitz
equation including a Slonczewski spin-torque term. We establish that the vortex
dipole is set in steady state rotational motion due to the interaction between
the vortices, while an external in-plane magnetic field can tune the frequency
of rotation. The rotational motion is linked to the nonzero skyrmion number of
the dipole. The spin-torque acts to stabilize the vortex dipole at a definite
vortex-antivortex separation distance. In contrast to a free vortex dipole, the
rotating pair under spin-polarized current is an attractor of the motion,
therefore a stable state. Three types of vortex-antivortex pairs are obtained
as we vary the external field and spin-torque strength. We give a guide for the
frequency of rotation based on analytical relations.",1308.4805v1
2015-06-11,Giant thermal spin torque assisted magnetic tunnel junction switching,"Spin-polarized charge-currents induce magnetic tunnel junction (MTJ)
switching by virtue of spin-transfer-torque (STT). Recently, by taking
advantage of the spin dependent thermoelectric properties of magnetic
materials, novel means of generating spin-currents from temperature gradients,
and their associated thermal spin torques (TSTs) have been proposed, but so far
these TSTs have not been large enough to influence MTJ switching. Here we
demonstrate significant TSTs in MTJs by generating large temperature gradients
across ultrathin MgO tunnel barriers that considerably affect the switching
fields of the MTJ. We attribute the origin of the TST to an asymmetry of the
tunneling conductance across the zero-bias voltage of the MTJ. Remarkably, we
estimate through magneto-Seebeck voltage measurements that the charge-currents
that would be generated due to the temperature gradient would give rise to STT
that is a thousand times too small to account for the changes in switching
fields that we observe.",1506.03854v1
2021-08-24,Spin-orbit torque: Moving towards two-dimensional van der Waals heterostructures,"The manipulation of magnetic properties using either electrical currents or
gate bias is the key of future high-impact nanospintronics applications such as
spin-valve read heads, non-volatile logic, and random-access memories. The
current technology for magnetic switching with spin-transfer torque requires
high current densities, whereas gate-tunable magnetic materials such as
ferromagnetic semiconductors and multiferroic materials are still far from
practical applications. Recently, magnetic switching induced by pure spin
currents using the spin Hall and Rashba effects in heavy metals, called
spin-orbit torque (SOT), has emerged as a candidate for designing
next-generation magnetic memory with low current densities. The recent
discovery of topological materials and two-dimensional (2D) van der Waals (vdW)
materials provides opportunities to explore versatile 3D-2D and 2D-2D
heterostructures with interesting characteristics. In this review, we introduce
the emerging approaches to realizing SOT nanodevices including techniques to
evaluate the SOT efficiency as well as the opportunities and challenges of
using 2D topological materials and vdW materials in such applications.",2108.10622v1
2010-11-11,Spin Torque Ferromagnetic Resonance Induced by the Spin Hall Effect,"We demonstrate that the spin Hall effect in a thin film with strong
spin-orbit scattering can excite magnetic precession in an adjacent
ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer
generates an oscillating transverse spin current in the Pt, and the resultant
transfer of spin angular momentum to the NiFe induces ferromagnetic resonance
(FMR) dynamics. The Oersted field from the current also generates an FMR signal
but with a different symmetry. The ratio of these two signals allows a
quantitative determination of the spin current and the spin Hall angle.",1011.2788v1
2013-05-07,Spin Wave Excitation in Magnetic Insulator Thin Films by Spin-Transfer Torque,"We describe excitation of dipole-exchange spin waves in insulating magnetic
thin films by spin current injection at the surface of the film. An easy-axis
magnetic surface anisotropy can induce a non-chiral surface spin wave mode with
penetration depth inversely proportional to the strength of the surface
anisotropy, which strongly reduces the critical current and enhances the
excitation power. The importance of the interface spin wave modes on the
excitation spectrum is reduced by spin pumping, which depends on the quality of
the interface as expressed by the spin mixing conductance.",1305.1364v2
2010-01-29,Spin-current vortices in current-perpendicular-to-plane nanoconstricted spin-valves,"The charge and spin diffusion equations taking into account spin-flip and
spin-transfer torque were numerically solved using a finite element method in
complex non-collinear geometry with strongly inhomogeneous current flow. As an
illustration, spin-dependent transport through a non-magnetic nanoconstriction
separating two magnetic layers was investigated. Unexpected results such as
vortices of spin-currents in the vicinity of the nanoconstriction were
obtained. The angular variations of magnetoresistance and spin-transfer torque
are strongly influenced by the structure geometry.",1001.5367v2
2020-08-17,Terahertz spin dynamics driven by an optical spin-orbit torque,"Spin torques are at the heart of spin manipulations in spintronic devices.
Here, we examine the existence of an optical spin-orbit torque, a relativistic
spin torque originating from the spin-orbit coupling of an oscillating applied
field with the spins. We compare the effect of the nonrelativistic Zeeman
torque with the relativistic optical spin-orbit torque for ferromagnetic
systems excited by a circularly polarised laser pulse. The latter torque
depends on the helicity of the light and scales with the intensity, while being
inversely proportional to the frequency. Our results show that the optical
spin-orbit torque can provide a torque on the spins, which is quantitatively
equivalent to the Zeeman torque. Moreover, temperature dependent calculations
show that the effect of optical spin-orbit torque decreases with increasing
temperature. However, the effect does not vanish in a ferromagnetic system,
even above its Curie temperature.",2008.07308v2
2013-03-06,A Quantum Approach of Meso-Magnet Dynamics with Spin Transfer Torque,"We present a theory of magnetization dynamics driven by spin-polarized
current in terms of the quantum master equation. In the spin coherent state
representation, the master equation becomes a Fokker-Planck equation, which
naturally includes the spin transfer and quantum fluctuation. The current
electron scattering state is correlated to the magnet quantum states, giving
rise to quantum correction to the electron transport properties in the usual
semiclassical theory. In the large spin limit, the magnetization dynamics is
shown to obey the Hamilton-Jacobi equation or the Hamiltonian canonical
equations.",1303.1250v2
2014-08-16,Two-Dimensional TaSe2 Metallic Crystals: Spin-Orbit Scattering Length and Breakdown Current Density,"We have determined the spin-orbit scattering length of two-dimensional
layered 2H-TaSe2 metallic crystals by detailed characterization of the weak
anti-localization phenomena in this strong spin-orbit interaction material. By
fitting the observed magneto-conductivity, the spin-orbit scattering length for
2H-TaSe2 is determined to be 17 nm in the few-layer films. This small
spin-orbit scattering length is comparable to that of Pt, which is widely used
to study the spin Hall effect, and indicates the potential of TaSe2 for use in
spin Hall effect devices. In addition to strong spin-orbit coupling, a material
must also support large charge currents to achieve spin-transfer-torque via the
spin Hall effect. Therefore, we have characterized the room temperature
breakdown current density of TaSe2 in air, where the best breakdown current
density reaches 3.7$\times$10$^7$ A/cm$^2$. This large breakdown current
further indicates the potential of TaSe2 for use in spin-torque devices and
two-dimensional device interconnect applications.",1408.3753v1
2017-02-07,Resonant spin transfer torque nano-oscillators,"Spin transfer torque nano-oscillators are potential candidates for replacing
the traditional inductor based voltage controlled oscillators in modern
communication devices. Typical oscillator designs are based on trilayer
magnetic tunnel junctions which are disadvantaged by low power outputs and poor
conversion efficiencies. In this letter, we theoretically propose to use
resonant spin filtering in pentalayer magnetic tunnel junctions as a possible
route to alleviate these issues and present device designs geared toward a high
microwave output power and an efficient conversion of the d.c. input power. We
attribute these robust qualities to the resulting non-trivial spin current
profiles and the ultra high tunnel magnetoresistance, both arising from
resonant spin filtering. The device designs are based on the nonequilibrium
Green's function spin transport formalism self-consistently coupled with the
stochastic Landau-Lifshitz-Gilbert-Slonczewski's equation and the Poisson's
equation. We demonstrate that the proposed structures facilitate oscillator
designs featuring a large enhancement in microwave power of around $775\%$ and
an efficiency enhancement of over $1300\%$ in comparison with typical trilayer
designs. We also rationalize the optimum operating regions via an analysis of
the dynamic and static device resistances. This work sets stage for pentalyer
spin transfer torque nano-oscillator device designs that extenuate most of the
issues faced by the typical trilayer designs.",1702.01869v1
2021-01-29,Dynamically stable negative-energy states induced by spin-transfer torques,"We investigate instabilities of the magnetic ground state in ferromagnetic
metals that are induced by uniform electrical currents, and, in particular, go
beyond previous analyses by including dipolar interactions. These instabilities
arise from spin-transfer torques that lead to Doppler shifted spin waves. For
sufficiently large electrical currents, spin-wave excitations have negative
energy with respect to the uniform magnetic ground state, while remaining
dynamically stable due to dissipative spin-transfer torques. Hence, the uniform
magnetic ground state is energetically unstable, but is not able to dynamically
reach the new ground state. We estimate this to happen for current densities $
j\gtrsim (1-D/D_c)10^{13} \mathrm{A/m^2} $ in typical thin film experiments,
with $ D $ the Dzyaloshinskii-Moriya interaction constant, and $ D_c $ the
Dzyaloshinskii-Moriya interaction that is required for spontaneous formation of
spirals or skyrmions. These current densities can be made arbitrarily small for
ultrathin film thicknesses at the order of nanometers, due to surface- and
interlayer effects. From an analogue gravity perspective, the stable negative
energy states are an essential ingredient to implement event horizons for
magnons -- the quanta of spin waves -- giving rise to e.g. Hawking radiation
and can be used to significantly amplify spin waves in a so-called black-hole
laser.",2101.12544v1
2017-03-11,Generalized Boundary Conditions for Spin Transfer,"We develop a comprehensive description of static and dynamic spin-transfer
torque at interfaces between a normal metal and a magnetic material. Specific
examples of the latter include ferromagnets, collinear and noncollinear
antiferromagnets, general ferrimagnets, and spin glasses. We study the limit of
the exchange-dominated interactions, so that the full system is isotropic in
spin space, apart from a possible symmetry-breaking order. A general such
interface yields three coefficients (corresponding to three independent
generators of rotations) generalizing the well-established notion of the
spin-mixing conductance, which pertains to the collinear case. We develop a
nonequilibrium thermodynamic description of the emerging interfacial spin
transfer and its effect on the collective spin dynamics, while circumventing
the usual discussion of spin currents and net spin dynamics. Instead, our focus
is on the dissipation and work effectuated by the interface. Microscopic
scattering-matrix based expressions are derived for the generalized
spin-transfer coefficients.",1703.04020v2
2010-10-22,Spin-Transfer Torque Induced Vortex Dynamics in Fe/Ag/Fe Nanopillars,"We report experimental and analytical work on spin-transfer torque induced
vortex dynamics in metallic nanopillars with in-plane magnetized layers. We
study nanopillars with a diameter of 150 nm, containing two Fe layers with a
thickness of 15 nm and 30 nm respectively, separated by a 6 nm Ag spacer. The
sample geometry is such that it allows for the formation of magnetic vortices
in the Fe disks. As confirmed by micromagnetic simulations, we are able to
prepare states where one magnetic layer is homogeneously magnetized while the
other contains a vortex. We experimentally show that in this configuration
spin-transfer torque can excite vortex dynamics and analyze their dependence on
a magnetic field applied in the sample plane. The center of gyration is
continuously dislocated from the disk center, and the potential changes its
shape with field strength. The latter is reflected in the field dependence of
the excitation frequency. In the second part we propose a novel mechanism for
the excitation of the gyrotropic mode in nanopillars with a perfectly
homogeneously magnetized in-plane polarizing layer. We analytically show that
in this configuration the vortex can absorb energy from the spin-polarized
electric current if the angular spin-transfer efficiency function is
asymmetric. This effect is supported by micromagnetic simulations.",1010.4791v2
2023-10-31,Antiferromagnetic Switching in Mn$_2$Au Using a Novel Laser Induced Optical Torque on Ultrafast Timescales,"Efficient manipulation of the N\'eel vector in antiferromagnets can be
induced by generation of spin orbit (SOT) or spin-transfer (STT) torques. Here
we predict another possibility for antiferromagnetic domain switching by using
a non-zero staggered field induced from optical laser excitation. We present
results on the atomistic scale dynamic simulations from the application of a
novel laser induced torque using optical frequencies for all-optical switching
(AOS) of the N\'eel vector in the antiferromagnet Mn$_2$Au. The driving
mechanism takes advantage of the sizeable 'exchange enhancement' characteristic
of antiferromagnets, allowing for small picosecond 90 and 180 degree
precessional switching with laser fluences on the order of mJ/cm$^2$. The
symmetry of these novel torques are highly dependent on the time-varying
magnetisation direction, creating a sign change in the torque which greatly
minimises the ""over-shooting problem"" common to SOT and STT. Lastly, we
demonstrate the opportunity for this laser optical torque to deterministically
switch single magnetic domains.",2311.00155v2
2011-07-02,Energy dissipation and switching delay in spin-transfer torque switching of nanomagnets with low-saturation magnetization in the presence of thermal fluctuations,"A common ploy to reduce the switching current and energy dissipation in
spin-transfer-torque driven magnetization switching of shape-anisotropic
single-domain nanomagnets is to employ magnets with low saturation
magnetization $M_s$ and high shape-anisotropy. The high shape-anisotropy
compensates for low $M_s$ to keep the static switching error rate constant.
However, this ploy increases the switching delay, its variance in the presence
of thermal noise, and the dynamic switching error rate. Using the stochastic
Landau-Lifshitz-Gilbert equation with a random torque emulating thermal noise,
we show that pumping some excess spin-polarized current into the nanomagnet
during switching will keep the mean switching delay and its variance constant
as we reduce $M_s$, while still reducing the energy dissipation significantly.",1107.0387v2
2013-08-21,Possible charge analogues of spin transfer torques in bulk superconductors,"Spin transfer torques (STT) occur when electric currents travel through
inhomogeneously magnetized systems and are important for the motion of magnetic
textures such as domain walls. Since superconductors are easy-plane
ferromagnets in particle-hole (charge) space, it is natural to ask whether any
charge duals of STT phenomena exist therein. We find that the superconducting
analogue of the adiabatic STT vanishes in a bulk superconductor with a
momentum-independent order parameter, while the superconducting counterpart of
the nonadiabatic STT does not vanish. This nonvanishing superconducting torque
is induced by heat (rather than charge) currents and acts on the charge (rather
than spin) degree of freedom. It can become significant in the vicinity of the
superconducting transition temperature, where it generates a net quasiparticle
charge and alters the dispersion and linewidth of low-frequency collective
modes.",1308.4622v1
2019-08-25,Controlled spin-torque driven domain wall motion using staggered magnetic nanowires,"The growing demand for storage, due to big data applications, cannot be met
by hard disk drives. Domain wall (DW) memory devices such as racetrack memory
offer an alternative route to achieve high capacity storage. In DW memory,
control of domain wall positions and their motion using spin-transfer torque
are important challenges. In this paper, we demonstrate controlled domain wall
motion using spin-transfer torque in staggered magnetic nanowires. The devices,
fabricated using electron-beam lithography, were tested using a magneto-optical
Kerr microscopy and electrical transport measurements. The depinning current,
pinning potential and thermal stability were found to depend on the device
dimensions of the staggering nanowires. Thus, the proposed staggering
configuration helps to fine-tune the properties of domain wall devices for
memory applications.",1908.09304v1
2020-05-07,Thermal Activation Barriers for Creation and Annihilation of Magnetic Droplet Solitons in the Presence of Spin Transfer Torque,"We study noise-induced creation and annihilation of magnetic droplet solitons
in experimental parameter regions in which they are linearly stable against
drift. Exploiting the rotational symmetry of the problem, we transform to the
reference frame rotating with the droplet soliton and introduce an effective
potential energy that accounts for the work done against spin-transfer torque
to rotate the magnetization between two different orientations. We use this
function to compute the activation barrier in both directions between the
uniform magnetization state and the droplet soliton state for a variety of
nanocontact radii and currents. We investigate droplet soliton structures with
both zero and nonzero spin-torque asymmetry parameter. Our approach can be
applied to estimate activation barriers for dynamical systems where
non-gradient terms can be absorbed by changes of reference frames, and suggests
a technique applicable to extended systems that may not be uniformly
magnetized.",2005.03416v1
2011-09-12,Spin-transfer mechanism for magnon-drag thermopower,"We point out a relation between the dissipative spin-transfer-torque
parameter $\beta$ and the contribution of magnon drag to the thermoelectric
power in conducting ferromagnets. Using this result we estimate $\beta$ in iron
at low temperatures, where magnon drag is believed to be the dominant
contribution to the thermopower. Our results may be used to determine $\beta$
from magnon-drag-thermopower experiments, or, conversely, to infer the strength
of magnon drag via experiments on spin transfer.",1109.2414v1
2008-03-19,Resonant Spin-Transfer-Driven Switching of Magnetic Devices Assisted by Microwave Current Pulses,"The torque generated by the transfer of spin angular momentum from a
spin-polarized current to a nanoscale ferromagnet can switch the orientation of
the nanomagnet much more efficiently than a current-generated magnetic field,
and is therefore in development for use in next-generation magnetic random
access memory (MRAM). Up to now, only DC currents and square-wave current
pulses have been investigated in spin-torque switching experiments. Here we
present measurements showing that spin transfer from a microwave-frequency
pulse can produce a resonant excitation of a nanomagnet and lead to improved
switching characteristics in combination with a square current pulse. With the
assistance of a microwave-frequency pulse, the switching time is reduced and
achieves a narrower distribution than when driven by a square current pulse
alone, and this can permit significant reductions in the integrated power
required for switching. Resonantly excited switching may also enable
alternative, more compact MRAM circuit architectures.",0803.2880v1
2018-02-21,Magnonic Spin-Transfer Torque in Ferromagnet/Antiferromagnet/Ferromagnet Trilayer,"In an antiferromagnet (AF) with uniaxial anisotropy, spin-up and spin-down
magnons coexist and form an intrinsic degree of freedom resembling electrons.
When polarized by an adjacent ferromagnet (F), a magnonic pure spin current can
be thermally generated in an AF. We explore thermal magnon transport in an
insulating F/AF/F trilayer where propagating magnons inside the AF spacer can
transfer angular momenta between the two Fs. We find that a sufficiently large
temperature gradient can switch the downstream F via magnonic spin-transfer
torque if it is initially antiparallel with the upstream F. A reciprocal
switching is achievable by reversing the temperature gradient. Using typical
material parameters, we estimate the threshold to be less than 1 K/nm at room
temperature, which can be reduced by raising temperature and enhancing the
interfacial exchange coupling.",1802.07709v2
2004-06-25,Excitations of incoherent spin-waves due to spin-transfer torque,"As predicted by Slonczewski and Berger, the possibility of exciting microwave
oscillations in a nanomagnet by a spin-polarized current has been recently
demonstrated. This observation opens very important perspectives of
applications in RF components. However, some unresolved inconsistencies are
found when interpreting the magnetization dynamics results within the coherent
spin-torque model (CSM). In some cases, the telegraph noise caused by
spin-currents could not be described quantitatively by the CSM. This led to
controversies about the need of an effective magnetic temperature model (ETM).
Here we interpret the experimental results of Kiselev et al. [Nature 425, 380
(2003)] using micromagnetic simulations. We point out the key role played by
incoherent spin-waves excitation due to spin-transfer effects. The incoherence
is caused by the spatial inhomogeneities of the local fields, generating a
distribution of local precession frequencies. It results in telegraph noise at
zero temperature associated with transitions between attraction wells in phase
space.",0406628v3
2008-09-26,Current-pulse-induced magnetic switching in standard and nonstandard spin-valves,"Magnetization switching due to a current-pulse in symmetric and asymmetric
spin valves is studied theoretically within the macrospin model. The switching
process and the corresponding switching parameters are shown to depend
significantly on the pulse duration and also on the interplay of the torques
due to spin transfer and external magnetic field. This interplay leads to
peculiar features in the corresponding phase diagram. These features in
standard spin valves, where the spin transfer torque stabilizes one of the
magnetic configurations (either parallel or antiparallel) and destabilizes the
opposite one, differ from those in nonstandard (asymmetric) spin valves, where
both collinear configurations are stable for one current orientation and
unstable for the opposite one. Following this we propose a scheme of ultrafast
current-induced switching in nonstandard spin valves, based on a sequence of
two current pulses.",0809.4584v3
2010-09-22,Optimal control of magnetization dynamics in ferromagnetic heterostructures by spin--polarized currents,"We study the switching-process of the magnetization in a
ferromagnetic-normal-metal multilayer system by a spin polarized electrical
current via the spin transfer torque. We use a spin drift-diffusion equation
(SDDE) and the Landau-Lifshitz-Gilbert equation (LLGE) to capture the coupled
dynamics of the spin density and the magnetization dynamic of the
heterostructure. Deriving a fully analytic solution of the stationary SDDE we
obtain an accurate, robust, and fast self-consistent model for the
spin-distribution and spin transfer torque inside general ferromagnetic/normal
metal heterostructures. Using optimal control theory we explore the switching
and back-switching process of the analyzer magnetization in a seven-layer
system. Starting from a Gaussian, we identify a unified current pulse profile
which accomplishes both processes within a specified switching time.",1009.4296v2
2013-11-01,Domain wall displacement by remote spin-current injection,"We demonstrate numerically the ability to displace a magnetic domain wall by
a remote spin current injection. We consider a long and narrow magnetic
nanostripe with a single domain wall (DW). The spin-polarized current is
injected perpendicularly to the plane of the film (CPP) through a small
nanocontact which is located at certain distance from the domain wall initial
position. We show theoretically that the DW motion can be initiated not only by
conventional spin-transfer torque but also by indirect spin-torque, created by
a remote spin-current injection and then transferred to the DW by the
exchange-spring mechanism. An analytical description of this effect is
proposed. This finding may lead to a solution of bottleneck problems of DW
motion-based spintronic and neuromorphic devices with perpendicular
spin-current injection.",1311.0229v2
2014-08-19,Bipolar switching in an orthogonal spin transfer spin valve device,"We demonstrate current-induced bipolar switching in in-plane magnetized
spin-valve devices that incorporate a perpendicularly magnetized spin
polarizing layer. Further, hysteretic transitions into a state with
intermediate resistance occur at high currents, again for both current
polarities. These transitions are shown to be consistent with a macrospin model
that considers a spin-polarized current that is tilted with respect to the free
layer plane, due to the presence of spin-transfer torque from the polarizing
layer. These unique switching characteristics, which have their origin in the
noncollinear layer magnetizations, are of interest for magnetic random access
memory and spin-torque oscillator devices.",1408.4494v1
2015-05-20,Effect of Transverse Magnetic Field on Dynamics of Current Driven Domain Wall Motion in the Presence of Spin-Hall Effect,"Theoretically, we study the dynamics of a current induced domain wall in the
bi-layer structure consists of a ferromagnetic layer and a non-magnetic metal
layer with strong spin-orbit coupling in the presence of spin-Hall effect. The
analytical expressions for the velocity and width of the domain wall interms of
excitation angle are obtained by solving the Landau-Lifshitz-Gilbert equation
with adiabatic, nonadiabatic and spin Hall effect-spin transfer torques using
Schryers and Walker's method. Numerical results show that the occurance of
polarity switching in the domain wall is observed only above the threshold
current density. The presence of transverse magnetic field along with spin Hall
effect-spin transfer torque enchances the value of the threshold current
density, and the corresponding saturated velocity at the threshold current
density is also increased.",1505.05249v1
2015-10-16,Exceptionally Strong Spin-Transfer in Single Ni Nanoparticles,"This letter presents studies of spin-transfer efficiency in electron
transport via discrete electron-in- a-box levels in individual nanometer-scale
Ni particles at 0.06K temperature. In a strong magnetic field, the
spin-transfer rates are estimated by measuring the amplitudes of the Zeeman
splitting of the levels. We find that the spin- and the charge-transfer rates
are comparable, demonstrating significant enhancement of the spin-transfer
efficiency compared to that in larger magnets. In a low magnetic field, we find
an additional energy splitting as evidence that the spin-transfer rate is far
higher than the charge-transfer rate. The effect is explained in terms of the
strong mesoscopic spin- orbit torques, which are exerted on the magnetization
in response to sequential electron tunneling.",1510.05042v2
2016-03-29,Current-induced asymmetric magnetoresistance due to energy transfer via quantum spin-flip process,"Current-induced magnetization excitation is a core phenomenon for
next-generation magnetic nanodevices, and has been attributed to the
spin-transfer torque (STT) that originates from the transfer of the spin
angular momentum between a conduction electron and a local magnetic moment
through the exchange coupling. However, the same coupling can transfer not only
spin but also energy, though the latter transfer mechanism has been largely
ignored. Here we report on experimental evidence concerning the energy transfer
in ferromagnet/heavy metal bilayers. The magnetoresistance (MR) is found to
depend significantly on the current direction down to low in-plane currents,
for which STT cannot play any significant role. Instead we find that the
observed MR is consistent with the energy transfer mechanism through the
quantum spin-flip process, which predicts short wavelength,
current-direction-dependent magnon excitations in the THz frequency range. Our
results unveil another aspect of current-induced magnetic excitation, and open
a channel for the dc-current-induced generation of THz magnons.",1603.08746v1
2016-10-07,Local thermomagnonic torques in two-fluid spin dynamics,"We develop a general phenomenology describing the interplay between coherent
and incoherent dynamics in ferromagnetic insulators. Using the Onsager
reciprocity and Neumann's principle, we derive expressions for the local
thermomagnonic torques exerted by thermal magnons on the order-parameter
dynamics and the reciprocal pumping processes, which are in close analogy to
the spin-transfer torque and spin pumping at metallic interfaces. Our formalism
is applicable to general long-wavelength dynamics and, although here we
explicitly focus on ferromagnetic insulators possessing U(1) symmetry, our
approach can be easily extended to other classes of magnetic materials. As an
illustrative example, we apply our theory to investigate a domain wall floating
over a spin superfluid, whose dynamics is triggered thermally at the system's
edge. Our results demonstrate that the local pumping of coherent spin dynamics
by a thermal magnon gas offers an alternative route - with no need for
conducting components and thus devoid of Ohmic losses - for the control and
manipulation of topological solitons.",1610.02224v1
2017-09-05,Newton's second law in spin-orbit torque,"Spin-orbit torque (SOT) refers to the excitation of magnetization dynamics
via spin-orbit coupling under the application of a charged current. In this
work, we introduce a simple and intuitive description of the SOT in terms of
spin force. In Rashba spin-orbit coupling system, the damping-like SOT can be
expressed as ${\mathbf T}^\mathrm{so}={\mathbf R}_c\times {\mathbf F}^{{\mathrm
{so}}}$, in analogy to the classical torque-force relation, where $R_c$ is the
effective radius characterizing the Rashba splitting in the momentum space. As
a consequence, the magnetic energy is transferred to the conduction electrons,
which dissipates through Joule heating at a rate of $({\mathbf j}_e\cdot
{\mathbf F}^{\mathrm {so}})$, with $j_e$ being the applied current. Finally, we
propose an experimental verification of our findings via measurement of the
anisotropic magnetoresistance effect.",1709.01302v2
2017-02-08,Non-local field-like spin-orbit torques in Rashba systems: an ab-initio study of Ag$_{2}$Bi/Ag/Fe film,"We investigate from first principles the field-like spin-orbit torques (SOTs)
in a Ag$_{2}$Bi-terminated Ag(111) film grown on ferromagnetic Fe(110). We find
that a large part of the SOT arises from the spin-orbit interaction (SOI) in
the Ag$_{2}$Bi layer far away from the Fe layers. These results clearly hint at
a long range spin transfer in the direction perpendicular to the film that does
not originate in the spin Hall effect. In order to bring evidence of the
non-local character of the computed SOT, we show that the torque acting on the
Fe layers can be engineered by the introduction of Bi vacancies in the
Ag$_{2}$Bi layer. Overall, we find a drastic dependence of the SOT on the
disorder type, which we explain by a complex interplay of different
contributions to the SOT in the Brillouin zone.",1702.02518v1
2007-09-26,Spin-polarized Current-induced Instability in Spin-Valve with Antiferromagnetic Layer,"In the framework of phenomenological model we consider dynamics of a
compensated collinear antiferromagnet (AFM) in the presence of spin-polarised
current. The model is based on the assumption that AFM spins are localised and
spin torque is transferred to each magnetic sublattice independently. It is
shown that in AFM spin current i) can be a source of the ""negative friction"";
and ii) modifies spin-wave frequencies. Equilibrium state of AFM can be
destabilized by the current polarized in parallel to AFM vector. Threshold
current at which the loss of stability takes place depends upon the magnetic
anisotropy of AFM.",0709.4172v1
2011-07-01,Current induced magnetization reversal on the surface of a topological insulator,"We study dynamics of the magnetization coupled to the surface Dirac fermions
of a three di- mensional topological insulator. By solving the
Landau-Lifshitz-Gilbert equation in the presence of charge current, we find
current induced magnetization dynamics and discuss the possibility of mag-
netization reversal. The torque from the current injection depends on the
transmission probability through the ferromagnet and shows nontrivial
dependence on the exchange coupling. The mag- netization dynamics is a direct
manifestation of the inverse spin-galvanic effect and hence another ferromagnet
is unnecessary to induce spin transfer torque in contrast to the conventional
setup.",1107.0116v1
2013-05-25,Thermally-Assisted Spin-Transfer Torque Dynamics in Energy Space,"We consider the general Landau-Lifshitz-Gilbert theory underlying the
magnetization dynamics of a macrospin magnet subject to spin-torque effects and
thermal fluctuations. Thermally activated dynamical properties are analyzed by
averaging the full magnetization equations over constant- energy orbits. After
averaging, all the relevant dynamical scenarios are a function of the ratio
between hard and easy axis anisotropies. We derive analytically the range of
currents for which limit cycles exist and discuss the regimes in which the
constant energy orbit averaging technique is applicable.",1305.5945v2
2015-09-24,Skyrmion based microwave detectors and harvesting,"Magnetic skyrmions are topologically protected states that are very promising
for the design of the next generation of ultralow-power electronic devices. In
this letter, we propose a magnetic tunnel junction based spin-transfer torque
diode with a magnetic skyrmion as ground state and a perpendicular polarizer
patterned as nanocontact for a local injection of the current. The key result
is the possibility to achieve sensitivities (i.e. detection voltage over input
microwave power) larger than 2000V/W for optimized contact diameters. Our
results can be very useful for the identification of a new class of spin-torque
diodes with a non-uniform ground state.",1510.03841v1
2006-10-10,Nanofabrication of spin-transfer torque devices by a PMMA mask one step process: GMR versus single layer devices,"We present a method to prepare magnetic spin torque devices of low specific
resistance in a one step lithography process. The quality of the pillar devices
is demonstrated for a standard magnetic double layer device. For single layer
devices, we found hysteretic switching and a more complex dynamical excitation
pattern in higher fields. A simple model to explain the resistance spikes is
presented.",0610277v1
2023-12-16,Predicted Multiple Walker Breakdowns for Current-Driven Domain-Wall Motion in Antiferromagnets,"We theoretically discover possible emergence of reentrant Walker breakdowns
for current-driven domain walls in layered antiferromagnets in striking
contrast to the unique Walker breakdown in ferromagnets. We reveal that the
Lorentz contraction of domain-wall width in antiferromagnets gives rise to
nonlinear current-dependence of the wall velocity and the predicted multiple
Walker breakdowns. The dominant efficiency of the current-induced staggered
spin-orbit torque over the spin-transfer torque to drive the domain-wall motion
is also demonstrated. These findings are expected to be observed in synthetic
antiferromagnets experimentally and provide an important contribution to the
growing research field of antiferromagnetic spintronics.",2312.10337v1
2016-05-06,Nanosecond-timescale low error switching of in-plane magnetic tunnel junctions through dynamic Oersted-field assisted spin-Hall effect,"We investigate fast-pulse switching of in-plane-magnetized magnetic tunnel
junctions (MTJs) within 3-terminal devices in which spin-transfer torque is
applied to the MTJ by the giant spin Hall effect. We measure reliable
switching, with write error rates down to $10^{-5}$, using current pulses as
short as just 2 ns in duration. This represents the fastest reliable switching
reported to date for any spin-torque-driven magnetic memory geometry, and
corresponds to a characteristic time scale that is significantly shorter than
predicted possible within a macrospin model for in-plane MTJs subject to
thermal fluctuations at room temperature. Using micromagnetic simulations, we
show that in the 3-terminal spin-Hall devices the Oersted magnetic field
generated by the pulse current strongly modifies the magnetic dynamics excited
by the spin-Hall torque, enabling this unanticipated performance improvement.
Our results suggest that in-plane MTJs controlled by Oersted-field-assisted
spin-Hall torque are a promising candidate for both cache memory applications
requiring high speed and for cryogenic memories requiring low write energies.",1605.02104v2
2017-12-07,Narrow-band tunable THz detector in antiferromagnets via Néel spin-orbit torque and spin-transfer torque,"We study dynamics of antiferromagnets induced by simultaneous application of
dc spin current and ac charge current, motivated by the requirement of
all-electrically controlled devices in THz gap (0.1-30 THz). We show that ac
electric current, via N\'eel spin orbit torques, can lock the phase of a steady
rotating N\'eel vector whose precession is controlled by a dc spin current. In
the phase-locking regime the frequency of the incoming ac signal coincides with
the frequency of autooscillations which for typical antiferromagnets fall into
the THz range. The frequency of autooscillations is proportional to the
precession-induced tilting of the magnetic sublattices related to the so-called
dynamical magnetization. We show how the incoming ac signal can be detected
from the measurement of the dc-current dependencies of the constant dynamical
magnetization. We formulate the conditions of phase-locking based on relations
between parameters of an antiferromagnet and the characteristics of the
incoming signal (frequency, amplitude, bandwidth, duration). We also show that
the rotating N\'eel vector can generate ac electrical current via inverse
N\'eel spin-orbit torque. Hence, antiferromagnets driven by dc spin current can
be used as tunable detectors and emitters of narrow-band signals operating in
the THz range.",1712.02686v1
2013-05-14,How to construct the proper gauge-invariant density matrix in steady-state nonequilibrium: Applications to spin-transfer and spin-orbit torques,"Experiments observing spin density and spin currents (responsible for, e.g.,
spin-transfer torque) in spintronic devices measure only the nonequilibrium
contributions to these quantities, typically driven by injecting unpolarized
charge current or by applying external time-dependent fields. On the other
hand, theoretical approaches to calculate them operate with both the
nonequilibrium (carried by electrons around the Fermi surface) and the
equilibrium (carried by the Fermi sea electrons) contributions. Thus, an
unambiguous procedure should remove the equilibrium contributions, thereby
rendering the nonequilibrium ones which are measurable and satisfy the
gauge-invariant condition according to which expectation values of physical
quantities should not change when electric potential everywhere is shifted by a
constant amount. Using the framework of nonequilibrium Green functions, we
delineate such procedure which yields the proper gauge-invariant nonequilibrium
density matrix in the linear-response and elastic transport regime for
current-carrying steady state of an open quantum system connected to two
macroscopic reservoirs. Its usage is illustrated by computing: (i) conventional
spin-transfer torque (STT) in asymmetric F/I/F magnetic tunnel junctions
(MTJs); (ii) unconventional STT in asymmetric N/I/F semi-MTJs with the strong
Rashba spin-orbit coupling (SOC) at the I/F interface and injected current
perpendicular to that plane; and (iii) current-driven spin density within a
clean ferromagnetic Rashba spin-split two-dimensional electron gas (2DEG) which
generates SO torque in laterally patterned N/F/I heterostructures when such
2DEG is located at the N/F interface and injected charge current flows parallel
to the plane.",1305.3180v2
2013-01-16,Symmetry and magnitude of spin-orbit torques in ferromagnetic heterostructures,"Current-induced spin torques are of great interest to manipulate the
orientation of nanomagnets without applying external magnetic fields. They find
direct application in non-volatile data storage and logic devices, and provide
insight into fundamental processes related to the interdependence between
charge and spin transport. Recent demonstrations of magnetization switching
induced by in-plane current injection in ferromagnetic heterostructures have
drawn attention to a class of spin torques based on orbital-to-spin momentum
transfer, which is alternative to pure spin transfer torque (STT) between
noncollinear magnetic layers and amenable to more diversified device functions.
Due to the limited number of studies, however, there is still no consensus on
the symmetry, magnitude, and origin of spin-orbit torques (SOTs). Here we
report on the quantitative vector measurement of SOTs in Pt/Co/AlO trilayers
using harmonic analysis of the anomalous and planar Hall effects as a function
of the applied current and magnetization direction. We provide an all-purpose
scheme to measure the amplitude and direction of SOTs for any arbitrary
orientation of the magnetization, including corrections due to the interplay of
Hall and thermoelectric effects. Based on general space and time inversion
symmetry arguments, we show that asymmetric heterostructures allow for two
different SOTs having odd and even behavior with respect to magnetization
reversal. Our results reveal a scenario that goes beyond established models of
the Rashba and spin Hall contributions to SOTs. The even SOT is STT-like but
stronger than expected from the spin Hall effect in Pt. The odd SOT is composed
of a constant field-like term and an additional component, which is strongly
anisotropic and does not correspond to a simple Rashba field.",1301.3573v2
2018-09-24,Quantum spin-transfer torque induced nonclassical magnetization dynamics and electron-magnetization entanglement,"The standard spin-transfer torque (STT)---where spin-polarized current drives
dynamics of magnetization viewed as a classical vector---requires
noncollinearity between electron spins carried by the current and magnetization
of a ferromagnetic layer. However, recent experiments [A. Zholud et al., Phys.
Rev. Lett. 119, 257201 (2017)] observing magnetization dynamics in spin valves
at cryogenic temperatures, even when electron spin is collinear to
magnetization, point at overlooked quantum effects in STT which can lead to
highly nonclassical magnetization states. Using fully quantum many-body
treatment, where an electron injected as spin-polarized wave packet interacts
with local spins comprising the anisotropic quantum Heisenberg ferromagnetic
chain, we define quantum STT as any time evolution of local spins due to
initial many-body state not being an eigenstate of electron+local-spins system.
For time evolution caused by injected spin-down electron scattering off local
up-spins, entanglement between electron subsystem and local spins subsystem
takes place leading to decoherence and, therefore, shrinking of the total
magnetization but without rotation from its initial orientation which explains
the experiments. Furthermore, the same processes---entanglement and thereby
induced decoherence---are present also in standard noncollinear geometry,
together with the usual magnetization rotation. This is because STT in quantum
many-body picture is caused only by electron spin-down factor state, and the
only difference between collinear and noncollinear geometries is in relative
size of the contribution of initial many-body state containing such factor
state to superpositions of separable many-body quantum states generated during
time evolution.",1809.09090v1
2015-05-05,Large spin Hall magnetoresistance and its correlation to the spin-orbit torque in W/CoFeB/MgO structures,"The spin-orbit interaction in heavy metal/ferromagnet/oxide structures has
been extensively investigated because it can be employed in manipulation of the
magnetization direction by in-plane current. This implies the existence of an
inverse effect, in which the conductivity in such structures should depend on
the magnetization orientation. In this work, we report a systematic study of
the magnetoresistance (MR) of the W/CoFeB/MgO structures and its correlation to
the current-induced torque to the magnetization. We observe that the MR is
independent of the angle between magnetization and current direction, but is
determined by the relative magnetization orientation with respect to the spin
direction accumulated by spin Hall effect, which is the same symmetry of
so-called spin Hall magnetoresistance. The MR of ~1% in W/CoFeB/MgO samples is
considerably larger than those in other structures of Ta/CoFeB/MgO or
Pt/Co/AlOx, which indicates a larger spin Hall angle of W. Moreover, the
similar W thickness dependence of the MR and the current-induced magnetization
switching efficiency demonstrates that they share the same underlying physics,
which allows one to utilize the MR in non-magnet/ferromagnet structure in order
to understand closely related other spin-orbit coupling effects such as inverse
spin Hall effect, spin-orbit spin transfer torques, etc.",1505.00899v1
2017-03-16,Spin Angular Momentum Transfer and Plasmogalvanic Phenomena,"We introduce the continuity equation for the electromagnetic spin angular
momentum (SAM) in matter and discuss the torque associated with the SAM
transfer in terms of effective spin forces acting in a material. In plasmonic
metal, these spin forces result in plasmogalvanic phenomenon which is pinning
the plasmon-induced electromotive force to atomically-thin layer at the metal
interface.",1703.05628v2
2006-10-16,Inelastic scattering in ferromagnetic and antiferromagnetic metal spintronics,"We use a ferromagnetic voltage probe model to study the influence of
inelastic scattering on giant magnetoresistance and current-induced torques in
ferromagnetic and antiferromagnetic metal spin valves. The model is based on
the Green's function formulation of transport theory and represents
spin-dependent and spin-independent inelastic scatterers by interior voltage
probes that are constrained to carry respectively no charge current and no spin
or charge current. We find that giant magnetoresistance and spin transfer
torques in ferromagnetic metal spin valve structures survive arbitrarily strong
spin-independent inelastic scattering, while the recently predicted analogous
phenomena in antiferromagnetic metal spin valves are partially suppressed. We
use toy-model numerical calculations to estimate spacer layer thickness
requirements for room temperature operation of antiferromagnetic metal spin
valves.",0610417v1
2015-06-18,Ultra-low-energy computing paradigm using giant spin Hall devices,"Spin Hall effect converts charge current to spin current, which can exert
spin-torque to switch the magnetization of a nanomagnet. Recently, it is shown
that the ratio of spin current to charge current using spin Hall effect can be
made more than unity by using the areal geometry judiciously, unlike the case
of conventional spin-transfer-torque switching of nanomagnets. This can enable
energy-efficient means to write a bit of information in nanomagnets. Here, we
study the energy dissipation in such spin Hall devices. By solving stochastic
Landau-Lifshitz-Gilbert equation of magnetization dynamics in the presence of
room temperature thermal fluctuations, we show a methodology to simultaneously
reduce switching delay, its variance and energy dissipation, while lateral
dimensions of the spin Hall devices are scaled down.",1506.07863v1
2007-01-16,A numerical method to solve the Boltzmann equation for a spin valve,"We present a numerical algorithm to solve the Boltzmann equation for the
electron distribution function in magnetic multilayer heterostructures with
non-collinear magnetizations. The solution is based on a scattering matrix
formalism for layers that are translationally invariant in plane so that
properties only vary perpendicular to the planes. Physical quantities like spin
density, spin current, and spin-transfer torque are calculated directly from
the distribution function. We illustrate our solution method with a systematic
study of the spin-transfer torque in a spin valve as a function of its
geometry. The results agree with a hybrid circuit theory developed by
Slonczewski for geometries typical of those measured experimentally.",0701385v1
2008-01-09,Impact of in-plane currents on magnetoresistance properties of an exchange-biased spin-valve with insulating antiferromagnetic layer,"The impact of in-plane alternating currents on the exchange bias, resistance,
and magnetoresistance of a CoFe/NiCoO/CoFe/Cu/CoFe spin-valve is studied. With
increasing current, the resistance is increased while the maximum
magnetoresistance ratio decreases. Noticeably, the reversal of the pinned layer
is systematically suppressed in both field sweeping directions. Since the NiCoO
oxide is a good insulator, it is expected that the ac current flows only in the
CoFe/Cu/CoFe top layers, thus ruling out any presence of spin-transfer torque
acting on the spins in the antiferromagnetic layer. Instead, our measurements
show clear evidences for the influence of Joule heating caused by the current.
Moreover, results from temperature-dependent measurements very much resemble
those of the current dependence, indicating that the effect of Joule heating
plays a major role in the current-in-plane spin-valve configurations. The
results also suggest that spin-transfer torques between ferromagnetic layers
might still exist and compete with the exchange bias at sufficiently high
currents.",0801.1515v1
2009-11-20,Spin Transfer Dynamics in Spin Valves with Out-of-plane Magnetized CoNi Free Layers,"We have measured spin transfer-induced dynamics in magnetic nanocontact
devices having a perpendicularly magnetized Co/Ni free layer and an in-plane
magnetized CoFe fixed layer. The frequencies and powers of the excitations
agree well with the predictions of the single-domain model and indicate that
the excited dynamics correspond to precessional orbits with angles ranging from
zero to 90 degrees as the applied current is increased at a fixed field. From
measurements of the onset current as a function of applied field strength we
estimate the magnitude of the spin torque asymmetry parameter lambda ~ 1.5. By
combining these with spin torque ferromagnetic resonance measurements, we also
estimate the spin wave radiation loss in these devices.",0911.4077v1
2010-07-05,Laser-induced Spin Dynamics in Metallic Multilayers,"Electronic excitations in a ferromagnet can trigger ultrafast spin dynamics
with potential applications in a speed increase in magnetic recording. The
project investigates ultrafast magnetization dynamics, which is driven in
metallic layers by ballistic hot electrons. In a ferromagnet these electrons
induce a change in the absolute value of the magnetization M through
spin-dependent scattering. If the electrons are spin-polarized, scattering at
the interface of a noble metal and a ferromagnet results in spin-transfer
torque and hence modifies the direction of M. To reveal the underlying
mechanisms, we study model systems, which are realized by layers of Au with its
large ballistic mean free path and Fe as an itinerant ferromagnet. We aim at
understanding ultrafast demagnetization and femtosecond all-optical generation
of spin transfer torque effects (excitation of hot electrons with a femtosecond
laser). The launched dynamics are probed by magneto-optics in a time-resolved
experiment.",1007.0726v1
2013-08-30,First-principles study of spin-transfer torque in Co2MnSi/Al/Co2MnSi spin-valve,"The spin-transfer torque (STT) in Co2MnSi(CMS)/Al/Co2MnSi spin-valve system
with and without interfacial disorder is studied by a first-principles
noncollinear wave-function-matching method. It is shown that in the case of
clean interface the angular dependence of STT for CoCo/Al (the asymmetry
parameter Lambda approx. 4.5) is more skewed than that for MnSi/Al (Lambda
approx. 2.9), which suggests the clean CoCo/Al architecture is much more
efficient for the application on radio frequency oscillation. We also find that
even with interfacial disorder the spin-valve of half-metallic CMS still has a
relatively large parameter Lambda compared to that of conventional ferromagnet.
In addition, for clean interface the in-plane torkance of MnSi/Al is about
twice as large as that of CoCo/Al. However, as long as the degree of
interfacial disorder is sufficiently large, the CoCo/Al and MnSi/Al will show
approximately the same magnitude of in-plane torkance. Furthermore, our results
demonstrate that CMS/Al/CMS system has very high efficiency of STT to switch
the magnetic layer of spin-valve.",1308.6703v1
2014-01-03,Spin-Transfer-Torque Driven Magneto-Logic Gates Using Nano Spin-Valve Pillars,"We propose model magneto-logic NOR and NAND gates using a spin valve pillar,
wherein the logical operation is induced by spin-polarized currents which also
form the logical inputs. The operation is facilitated by the simultaneous
presence of a constant controlling magnetic field. The same spin-valve assembly
can also be used as a magnetic memory unit. We identify regions in the
parameter space of the system where the logical operations can be effectively
performed. The proposed gates retain the non-volatility of a magnetic random
access memory,(MRAM). We verify the functioning of the gate by numerically
simulating its dynamics, governed by the appropriate Landau-Lifshitz-Gilbert
equation with the spin-transfer torque term. The flipping time for the logical
states is estimated to be within nano seconds.",1401.0723v1
2021-04-19,Spin transfer torque and anisotropic conductance in spin orbit coupled graphene,"We theoretically study spin-transfer torque (STT) in a graphene system with
spin-orbit coupling (SOC). We consider a graphene-based junction where the
spin-orbit coupled region is sandwiched between two ferromagnetic (F) segments.
The magnetization in each ferromagnetic segment can possess arbitrary
orientations. Our results show that the presence of SOC results in
anisotropically modified STT, magnetoresistance, and charge conductance as a
function of relative magnetization misalignment in the F regions. We have found
that within the Klein regime, where particles hit the interfaces
perpendicularly, the spin-polarized Dirac fermions transmit perfectly through
the boundaries of an F-F junction (i.e., with zero reflection), regardless of
the relative magnetization misalignment and exert zero STT. In the presence of
SOC, however, due to band structure modification, a nonzero STT reappears. Our
findings can be exploited for experimentally examining proximity-induced SOC
into a graphene system",2104.09039v1
2019-07-02,Enhanced spin transfer torque in platinum/ferromagnetic-metal structures by optimizing the platinum thickness,"Spin transfer torque (STT) driven by a charge current plays a key role in
magnetization switching in heavy-metal/ferromagnetic-metal structures. The STT
efficiency defined by the ratio between the effective field due to STT and the
current density, is required to be improved to reduce energy compulsions in the
STT-based spintronic devices. In this work, using the harmonic Hall measurement
method, we experimentally studied the STT efficiency in platinum(Pt)/FM
structures as a function of the Pt thickness. We found that the STT efficiency
strongly depends on the Pt thickness and reaches a maximum value of 4.259
mT/($10^6$A/$cm^{2}$) for the 1.8-nm-thickness Pt sample. This result indicates
that competition between spin Hall effect (SHE) and Rashba effect as well as
spin diffusion process across the Pt layer determines the Pt thickness for the
maximum STT efficiency. We demonstrated the role played by the spin diffusion
besides the spin current generation mechanisms in improvement of the STT
efficiency, which is helpful in designing STT-based devices.",1907.01278v2
2019-08-17,Band-pass Magnetic Tunnel Junction based Magnetoresistive Random Access Memory,"We propose spin transfer torque--magnetoresistive random access memory
(STT-MRAM) based on magneto-resistance and spin transfer torque physics of
band-pass spin filtering. Utilizing the electronic analogs of optical phenomena
such as anti-reflection coating and resonance for spintronic devices, we
present the design of an STT-MRAM device with improved features when compared
with a traditional trilayer device. The device consists of a superlattice
heterostructure terminated with the anti-reflective regions sandwiched between
the fixed and free ferromagnetic layers. Employing the Green's function spin
transport formalism coupled self-consistently with the stochastic
Landau-Lifshitz-Gilbert-Slonczewski equation, we present the design of an
STT-MRAM based on the band-pass filtering having an ultra-high TMR (3.5*10e4)
and large spin current. We demonstrate that the STT-MRAM design having
band-pass spin filtering are nearly 1100% more energy efficient than
traditional trilayer magnetic tunnel junction (MTJ) based STT-MRAM. We also
present detailed probabilistic switching and energy analysis for a trilayer MTJ
and band-pass filtering based STT-MRAM. Our predictions serve as a template to
consider the heterostructures for next-generation spintronic device
applications.",1908.06279v1
2021-09-17,Current-Induced Spin-Wave Doppler Shift in Antiferromagnets,"We theoretically study the spin dynamics in antiferromagnets (AFs)under the
influence of an electric current. We identify two different sources of
spin-transfer torques that stem from uniform (${\boldsymbol v}_n$) and
staggered (${\boldsymbol v}_\ell$) electron spin densities. While the former is
well recognized, the latter is often overlooked. We show that both
${\boldsymbol v}_n$ and ${\boldsymbol v}_\ell$ contribute equally to the
spin-wave Doppler shift. Microscopic calculations are presented for electrons
on a two-dimensional square lattice with nearest-neighbor ($t$) and
next-nearest-neighbor ($t'$) hopping, which interpolate two opposite transport
regimes of strongly-coupled AF ($t'/t \ll 1$) and two weakly coupled
ferromagnets ($t'/t \gg 1$). In the AF transport regime ($t'/t \ll 1$),
${\boldsymbol v}_n$ and ${\boldsymbol v}_\ell$ have opposite signs, and the
sign of the Doppler shift depends on band filling; ${\boldsymbol v}_n$
(${\boldsymbol v}_\ell$) is dominant near the AF gap (near the band bottom or
the top). As $t'/t$ is increased, ${\boldsymbol v}_n$ undergoes a sign change
whereas ${\boldsymbol v}_\ell$ does not. In the limit of vanishing $t$,
${\boldsymbol v}_n$ and ${\boldsymbol v}_\ell$ coincide and the spin-transfer
torque reduces to that of ferromagnets.",2109.08432v1
2010-01-26,Strategies and tolerances of spin transfer torque switching,"Schemes of switching nanomagnetic memories via the effect of spin torque with
various polarizations of injected electrons are studied. Simulations based on
macrospin and micromagnetic theories are performed and compared. We demonstrate
that switching with perpendicularly polarized current by short pulses and free
precession requires smaller time and energy than spin torque switching with
collinear in plane spin polarization; it is also found to be superior to other
kinds of memories. We study the tolerances of switching to the magnitude of
current and pulse duration. An increased Gilbert damping is found to improve
tolerances of perpendicular switching without increasing the threshold current,
unlike in plane switching.",1001.4578v1
2014-10-28,Generalized analysis of thermally activated domain-wall motion in Co/Pt multilayers,"Thermally activated domain-wall (DW) motion driven by magnetic field and
electric current is investigated experimentally in out-of-plane magnetized
Pt(Co/Pt)$_3$ multilayers. We directly extract the thermal activation energy
barrier for DW motion and observe the dynamic regimes of creep, depinning, and
viscous flow. Further analysis reveals that the activation energy must be
corrected with a factor dependent on the Curie temperature, and we derive a
generalized Arrhenius-like equation governing thermally activated motion. By
using this generalized equation, we quantify the efficiency of current-induced
spin torque in assisting DW motion. Current produces no effect aside from Joule
heating in the multilayer with 7-\AA\ thick Co layers, whereas it generates a
finite spin torque on DWs in the multilayer with atomically thin 3-\AA\ Co
layers. These findings suggest that conventional spin-transfer torques from
in-plane spin-polarized current do not drive DWs in ultrathin Co/Pt
multilayers.",1410.7685v1
2014-11-12,Electric-Field Control over Spin-Wave and Current Induced Domain Wall Motion and Magnonic Torques in Multiferroics,"We discover that the way spin-waves exert magnetic torques in multiferroic
materials can cause not only domain wall motion, but also magnetization
dynamics for homogeneous magnetization textures. Interestingly, the domain wall
motion can be controlled via purely electrical means with the spin-waves being
generated by an ac electric field $E$ while the direction of the wall motion
also is sensitive to an applied dc $E$ field. Moreover, we determine the
interaction between spin-transfer torque from an electric current and a
magnetic domain wall in multiferroics and show that the Walker breakdown
threshold scales with the magnitude of a perpendicular electric field, offering
a way to control the properties of domain wall propagation via electric gating.",1411.3327v2
2017-09-13,Chaotic dynamics in a macrospin spin-torque nano-oscillator with delayed feedback,"A theoretical study of delayed feedback in spin-torque nano-oscillators is
presented. A macrospin geometry is considered, where self-sustained
oscillations are made possible by spin transfer torques associated with spin
currents flowing perpendicular to the film plane. By tuning the delay and
amplification of the self-injected signal, we identify dynamical regimes in
this system such as chaos, switching between precession modes with complex
transients, and oscillator death. Such delayed feedback schemes open up a new
field of exploration for such oscillators, where the complex transient states
might find important applications in information processing.",1709.04310v2
2020-04-02,Stable solitons in a nearly PT-symmetric ferromagnet with spin-transfer torque,"We consider the Landau-Lifshitz equation for the spin torque oscillator - a
uniaxial ferromagnet in an external magnetic field with polarised spin current
driven through it. In the absence of the Gilbert damping, the equation turns
out to be PT-symmetric. We interpret the PT-symmetry as a balance between gain
and loss - and identify the gaining and losing modes. In the vicinity of the
bifurcation point of a uniform static state of magnetisation, the PT-symmetric
Landau-Lifshitz equation with a small dissipative perturbation reduces to a
nonlinear Schr\""odinger equation with a quadratic nonlinearity. The analysis of
the Schr\""odinger dynamics demonstrates that the spin torque oscillator
supports stable magnetic solitons. The PT near-symmetry is crucial for the
soliton stability: the addition of a finite dissipative term to the
Landau-Lifshitz equation destabilises all solitons that we have found.",2004.01245v2
2016-03-14,Merging droplets in double nano-contact spin torque oscillators,"We demonstrate how magnetic droplet soliton pairs, nucleated by two separated
nano-contact (NC) spin torque oscillators, can merge into a single droplet
soliton. A detailed description of the magnetization dynamics of this merger
process is obtained by micromagnetic simulations: A droplet pair with a
steady-state in-phase spin precession is generated through the spin-transfer
torque effect underneath two separate NCs, followed by a gradual expansion of
the droplets volume and the out phase of magnetization on the inner side of the
two droplets, resulting in the droplets merging into a larger droplet. This
merger occurs only when the NC separation is smaller than a critical value. A
transient breathing mode is observed before the merged droplet stabilizes into
a steady precession state. The precession frequency of the merged droplet is
lower than that of the droplet pair, consistent with its larger size. Merged
droplets can again break up into droplet pairs at high enough magnetic field
with a strong hysteretic response.",1603.04133v1
2021-12-29,Dzyaloshinskii-Moriya Induced Spin-Transfer Torques in Kagome Antiferromagnets,"In recent years antiferromagnets (AFMs) have become very promising for
nanoscale spintronic applications due to their unique properties such as THz
dynamics and absence of stray fields. Manipulating antiferromagnetic textures
is currently, however, limited to very few exceptional material symmetry
classes allowing for staggered torques on the magnetic sublattices. In this
work, we predict for kagome AFMs with broken mirror symmetry a new coupling
mechanism between antiferromagnetic domain walls (DWs) and spin currents,
produced by the relativistic Dzyaloshinskii-Moriya interaction (DMI). We
microscopically derive the DMI's free energy contribution for the kagome AFMs.
Unlike ferromagnets and collinear AFMs, the DMI does not lead to terms linear
in the spatial derivatives but instead renormalizes the spin-wave stiffness and
anisotropy energies. Importantly, we show that the DMI induces a highly
nontrivial twisted DW profile that is controllable via two linearly independent
components of the spin accumulation. This texture manipulation mechanism goes
beyond the concept of staggered torques and implies a higher degree of
tunability for the current-driven DW motion compared to conventional
ferromagnets and collinear AFMs.",2112.14504v2
2020-03-01,Spin-orbit interaction and spin selectivity for tunneling electron transfer in DNA,"Electron transfer (ET) in biological molecules such as peptides and proteins
consists of electrons moving between well defined localized states (donors to
acceptors) through a tunneling process. Here we present an analytical model for
ET by tunneling in DNA, in the presence of Spin-Orbit (SO) interaction, to
produce a strong spin asymmetry with the intrinsic atomic SO strength in meV
range. We obtain a Hamiltonian consistent with charge transport through $\pi$
orbitals on the DNA bases and derive the behavior of ET as a function of the
injection state momentum, the spin-orbit coupling and barrier length and
strength. A highly consistent scenario arises where two concomitant mechanisms
for spin selection arises; spin interference and differential spin amplitude
decay. High spin filtering can take place at the cost of reduced amplitude
transmission assuming realistic values for the spin-orbit coupling. The spin
filtering scenario is completed by addressing the spin dependent torque under
the barrier, with a consistent conserved definition for the spin current.",2003.00582v2
2008-06-24,Spin dynamics in point contacts to single ferromagnetic films,"Excitation of magnons or spin-waves driven by nominally unpolarized transport
currents in point contacts of normal and ferromagnetic metals is probed by
irradiating the contacts with microwaves. Two characteristic dynamic effects
are observed: a rectification of off-resonance microwave current by spin-wave
nonlinearities in the point contact conductance, and a resonant stimulation of
spin-wave modes in the nano-contact core by the microwave field. These
observations provide a direct evidence that the magnetoconductance effects
observed are due to GHz spin dynamics at the ferromagnetic interface driven by
the spin transfer torque effect of the transport current.",0806.3805v1
2010-02-02,Finite Element Modeling of Charge and Spin-currents in Magnetoresistive Pillars with Current Crowding Effects,"The charge and spin diffusion equations taking into account spin-flip and
spin-transfer torque were numerically solved using a finite element method in
complex non-collinear geometry. This approach was used to study the
spin-dependent transport in giant magnetoresistance metallic pillars sandwiched
between extended electrodes as in magnetoresistive heads for hard disk drives.
The charge current crowding around the boundaries between the electrodes and
the pillar has a quite significant influence on the spin current.",1002.0545v1
2013-03-26,Current-driven domain wall motion with spin Hall effect: Reduction of threshold current density,"We theoretically study the current-driven domain wall motion in the presence
of both the spin Hall effect and an extrinsic pinning potential. The spin Hall
effect mainly affects the damping ratio of the domain wall precession in the
pinning potential. When the pinning potential is not too strong, this results
in a significant reduction of a threshold current density for the depinning of
a domain wall with certain polarity. We also propose one way to distinguish the
spin Hall effect induced spin-transfer torque from the one induced by the
Rashba spin-orbit coupling experimentally.",1303.6458v1
2018-10-17,Out-of-plane auto-oscillation in spin Hall oscillator with additional polarizer,"The theoretical investigation on magnetization dynamics excited by the spin
Hall effect in metallic multilayers having two ferromagnets is discussed. The
relaxation of the transverse spin in one ferromagnet enables us to manipulate
the direction of the spin-transfer torque excited in another ferromagnet,
although the spin-polarization originally generated by the spin Hall effect is
geometrically fixed. Solving the Landau-Lifshitz-Gilbert-Slonczewski equation,
the possibility to excite an out-of-plane auto-oscillation of an in-plane
magnetized ferromagnet is presented. An application to magnetic recording using
microwave-assisted magnetization reversal is also discussed.",1810.07831v1
2011-08-01,Spin Pumping and Spin Transfer,"Spin pumping is the emission of a spin current by a magnetization dynamics
while spin transfer stands for the excitation of magnetization by spin
currents. Using Onsager's reciprocity relations we prove that spin pumping and
spin-transfer torques are two fundamentally equivalent dynamic processes in
magnetic structures with itinerant electrons. We review the theory of the
coupled motion of the magnetization order parameter and electron for textured
bulk ferromagnets (e.g. containing domain walls) and heterostructures (such as
spin valves). We present first-principles calculations for the
material-dependent damping parameters of magnetic alloys. Theoretical and
experimental results agree in general well.",1108.0385v3
2010-06-07,Roles of adiabatic and nonadiabatic spin transfer torques on magnetic domain wall motion,"Electric current exerts torques-so-called spin transfer torques (STTs)-on
magnetic domain walls (DWs), resulting in DW motion. At low current densities,
the STTs should compete against disorders in ferromagnetic nanowires but the
nature of the competition remains poorly understood. By achieving
two-dimensional contour maps of DW speed with respect to current density and
magnetic field, here we visualize unambiguously distinct roles of the two
STTs-adiabatic and nonadiabatic-in scaling behaviour of DW dynamics arising
from the competition. The contour maps are in excellent agreement with
predictions of a generalized scaling theory, and all experimental data collapse
onto a single curve. This result indicates that the adiabatic STT becomes
dominant for large current densities, whereas the nonadiabatic STT-playing the
same role as a magnetic field-subsists at low current densities required to
make emerging magnetic nanodevices practical.",1006.1216v1
2016-11-22,First-principles spin-transfer torque in CuMnAs$|$GaP$|$CuMnAs junctions,"We demonstrate that an all-antiferromagnetic tunnel junction with current
perpendicular to the plane geometry can be used as an efficient spintronics
device with potential high frequency operation. By using state-of-the-art
density functional theory combined with quantum transport, we show that the
N\'eel vector of the electrodes can be manipulated by spin-transfer torque.
This is staggered over the two different magnetic sublattices and can generate
dynamics and switching. At the same time the different magnetization states of
the junction can be read by standard tunnelling magnetoresistance. Calculations
are performed for CuMnAs$|$GaP$|$CuMnAs junctions with different surface
terminations between the anti-ferromagnetic CuMnAs electrodes and the
insulating GaP spacer. In particular we find that the torque remains staggered
regardless of the termination, while the magnetoresistance depends on the
microscopic details of the interface.",1611.07445v1
2016-07-18,Magnetic Skyrmion Transport in a Nanotrack With Spatially Varying Damping and Non-adiabatic Torque,"Reliable transport of magnetic skyrmions is required for any future
skyrmion-based information processing devices. Here we present a micromagnetic
study of the in-plane current-driven motion of a skyrmion in a ferromagnetic
nanotrack with spatially sinusoidally varying Gilbert damping and/or
non-adiabatic spin-transfer torque coefficients. It is found that the skyrmion
moves in a sinusoidal pattern as a result of the spatially varying Gilbert
damping and/or non-adiabatic spin-transfer torque in the nanotrack, which could
prevent the destruction of the skyrmion caused by the skyrmion Hall effect. The
results provide a guide for designing and developing the skyrmion transport
channel in skyrmion-based spintronic applications.",1607.04983v3
2017-02-22,Domain wall motion by localized temperature gradients,"Magnetic domain wall (DW) motion induced by a localized Gaussian temperature
profile is studied in a Permalloy nanostrip within the framework of the
stochastic Landau-Lifshitz-Bloch equation. The different contributions to
thermally induced DW motion, entropic torque and magnonic spin transfer torque,
are isolated and compared. The analysis of magnonic spin transfer torque
includes a description of thermally excited magnons in the sample. A third
driving force due to a thermally induced dipolar field is found and described.
Finally, thermally induced DW motion is studied under realistic conditions by
taking into account the edge roughness. The results give quantitative insights
into the different mechanisms responsible for domain wall motion in temperature
gradients and allow for comparison with experimental results.",1702.06725v1
2019-03-25,Detection of radiation torque exerted on an alkali-metal vapor cell,"We have developed a torsion balance to detect the rotation of a cell
containing spin-polarized gaseous atoms to study angular momentum transfer from
gaseous atoms to solid. A cesium vapor cell was hung from a thin wire in a
vacuum chamber, and irradiated from the bottom with circularly polarized light
tuned to the $D_2$ transition to polarize cesium atoms in the cell. By varying
the light helicity at the resonance frequency of the torsion balance, we
induced forced rotational oscillation of the cell and detected radiation torque
exerted on the cesium vapor cell through the cesium atoms inside. The torque
was particularly large when both hyperfine levels of cesium atoms were
optically pumped with application of a longitudinal magnetic field. Further
detailed study will provide new insights into spin-transfer processes at the
gas-solid interface.",1903.10123v2
2012-11-02,Effect of Spin Torque on Magnetization Switching Speed Having Nonuniform Spin Distribution,"We study the influence of the spin torque, which depends on the space and
time derivative of magnetization, on magnetization reversal time in a
ferromagnetic fine particle. The spin torque operates to dissipate the angular
momentum of the magnetization precession, and the torque increases in a spin
vortex structure. We calculate the magnetization reversal time under a DC
magnetic field using the Landau-Lifshitz-Gilbert equation containing a spin
torque term. We found that the spin torque changes the magnetization switching
speed significantly during the reversal process by maintaining a spin vortex in
an intermediate state.",1211.0360v1
2009-10-20,Bifurcation and chaos in spin-valve pillars in a periodic applied magnetic field,"We study the bifurcation and chaos scenario of the macro-magnetization vector
in a homogeneous nanoscale-ferromagnetic thin film of the type used in
spin-valve pillars. The underlying dynamics is described by a generalized
Landau-Lifshitz-Gilbert (LLG) equation. The LLG equation has an especially
appealing form under a complex stereographic projection, wherein the
qualitative equivalence of an applied field and a spin-current induced torque
is transparent. Recently chaotic behavior of such a spin vector has been
identified by Zhang and Li using a spin polarized current passing through the
pillar of constant polarization direction and periodically varying magnitude,
owing to the spin-transfer torque effect. In this paper we show that the same
dynamical behavior can be achieved using a periodically varying applied
magnetic field, in the presence of a constant DC magnetic field and constant
spin current, which is technically much more feasible, and demonstrate
numerically the chaotic dynamics in the system for an infinitely thin film.
Further, it is noted that in the presence of a nonzero crystal anisotropy field
chaotic dynamics occurs at much lower magnitudes of the spin-current and DC
applied field.",0910.3776v1
2013-10-22,Control of Majorana Edge Modes by a g-factor Engineered Nanowire Spin Transistor,"We propose the manipulation of Majorana edge states via hybridization and
spin currents in a nanowire spin transistor. The spin transistor is based on a
heterostructure nanowire comprising of semiconductors with large and small
g-factors that form the topological and non-topological regions respectively.
The hybridization of bound edge states results in spin currents and
$4\pi$-periodic torques, as a function of the relative magnetic field angle --
an effect which is dual to the fractional Josephson effect. We establish
relation between torques and spin-currents in the non-topological region where
the magnetic field is almost zero and spin is conserved along the spin-orbit
field direction. The angular momentum transfer could be detected by sensitive
magnetic resonance force microscopy techniques.",1310.5847v1
2020-07-30,Electron-magnon spin conversion and magnonic spin pumping in antiferromagnet/heavy metal heterostructure,"We study the exchange between electron and magnon spins at the interface of
an antiferromagnet and a heavy metal at finite temperatures. The underlying
physical mechanism is based on spin torque associated with the
creation/annihilation of thermal magnons with right-hand and left-hand
polarization. The creation/annihilation process depends strongly on the
relative orientation between the polarization of the electron and the magnon
spins. For a sufficiently strong spin transfer torque (STT), the conversion
process becomes nonlinear, generating a nonzero net spin pumping current in the
AFM that can detected in the neighboring metal layer. Applying an external
magnetic field renders possible the manipulation of the STT driving thermal
spin pumping. Our theoretical results are experimentally feasible and are of a
direct relevance to antiferromagnet-based spintronic devices.",2007.15512v1
2023-05-07,Lectures on spintronics and magnonincs,"In this series of lectures, we discuss the basic theoretical concepts of
magnonics and spintronics. We first briefly recall the relevant topics from
quantum mechanics, electrodynamics of continuous media, and basic theory of
magnetism. We then discuss the classical theory of magnetic dynamics:
ferromagnetic and antiferromagnetic resonance, dynamic susceptibilities, and
spin waves. We open the main discussion with phenomena of spin and exchange
spin currents, spin torques, the spin Hall effect, and the spin Hall and Hanle
magnetoresistance. Special emphasis is given to the effects of spin transfer
torque and spin pumping, where we follow the celebrated derivation utilizing
Landauer quantum multi-channel scattering matrix approach. Finally, we outline
the most important features distinguishing antiferromagnetic dynamics from
ferromagnetic one, which make antiferromagnets particularly promising material
candidates for spintronics and magnonics.",2305.04385v1
2007-03-15,Functional Keldysh Theory of Spin Torques,"We present a microscopic treatment of current-induced torques and thermal
fluctuations in itinerant ferromagnets based on a functional formulation of the
Keldysh formalism. We find that the nonequilibrium magnetization dynamics is
governed by a stochastic Landau-Lifschitz-Gilbert equation with spin transfer
torques. We calculate the Gilbert damping parameter $\alpha$ and the
non-adiabatic spin transfer torque parameter $\beta$ for a model ferromagnet.
We find that $\beta \neq \alpha$, in agreement with the results obtained using
imaginary-time methods of Kohno, Tatara and Shibata [J. Phys. Soc. Japan 75,
113706 (2006)]. We comment on the relationship between $s-d$ and
isotropic-Stoner toy models of ferromagnetism and more realistic
density-functional-theory models, and on the implications of these
relationships for predictions of the $\beta/\alpha$ ratio which plays a central
role in domain wall motion. Only for a single-parabolic-band isotropic-Stoner
model with an exchange splitting that is small compared to the Fermi energy
does $\beta/\alpha$ approach one. In addition, our microscopic formalism
incorporates naturally the fluctuations needed in a nonzero-temperature
description of the magnetization. We find that to first order in the applied
electric field, the usual form of thermal fluctuations via a phenomenological
stochastic magnetic field holds.",0703414v2
2020-07-24,"Determination of the spin Hall angle, spin mixing conductance and spin diffusion length in Ir/CoFeB for spin-orbitronic devices","Iridium is a very promising material for spintronic applications due to its
interesting magnetic properties such as large RKKY exchange coupling as well as
its large spin-orbit coupling value. Ir is for instance used as a spacer layer
for perpendicular synthetic antiferromagnetic or ferrimagnet systems. However,
only a few studies of the spintronic parameters of this material have been
reported. In this paper, we present inverse spin Hall effect - spin pumping
ferromagnetic resonance measurements on CoFeB/Ir based bilayers to estimate the
values of the effective spin Hall angle, the spin diffusion length within
iridium, and the spin mixing conductance in the CoFeB/Ir bilayer. In order to
have reliable results, we performed the same experiments on CoFeB/Pt bilayers,
which behavior is well known due to numerous reported studies. Our experimental
results show that the spin diffusion length within iridium is 1.3 nm for
resistivity of 250 n$\Omega$.m, the spin mixing conductance $g_{eff}^{\uparrow
\downarrow}$ of the CoFeB/Ir interface is 30 nm$^{-2}$, and the spin Hall angle
of iridium has the same sign than the one of platinum and is evaluated at 26%
of the one of platinum. The value of the spin Hall angle found is 7.7% for Pt
and 2% for Ir. These relevant parameters shall be useful to consider Ir in new
concepts and devices combining spin-orbit torque and spin-transfer torque.",2007.12413v1
2017-03-06,Computing in Memory with Spin-Transfer Torque Magnetic RAM,"In-memory computing is a promising approach to addressing the
processor-memory data transfer bottleneck in computing systems. We propose
Spin-Transfer Torque Compute-in-Memory (STT-CiM), a design for in-memory
computing with Spin-Transfer Torque Magnetic RAM (STT-MRAM). The unique
properties of spintronic memory allow multiple wordlines within an array to be
simultaneously enabled, opening up the possibility of directly sensing
functions of the values stored in multiple rows using a single access. We
propose modifications to STT-MRAM peripheral circuits that leverage this
principle to perform logic, arithmetic, and complex vector operations. We
address the challenge of reliable in-memory computing under process variations
by extending ECC schemes to detect and correct errors that occur during CiM
operations. We also address the question of how STT-CiM should be integrated
within a general-purpose computing system. To this end, we propose
architectural enhancements to processor instruction sets and on-chip buses that
enable STT-CiM to be utilized as a scratchpad memory. Finally, we present data
mapping techniques to increase the effectiveness of STT-CiM. We evaluate
STT-CiM using a device-to-architecture modeling framework, and integrate
cycle-accurate models of STT-CiM with a commercial processor and on-chip bus
(Nios II and Avalon from Intel). Our system-level evaluation shows that STT-CiM
provides system-level performance improvements of 3.93x on average (upto
10.4x), and concurrently reduces memory system energy by 3.83x on average (upto
12.4x).",1703.02118v4
2014-10-28,Current driven asymmetric magnetization switching in perpendicularly magnetized CoFeB/MgO heterostructures,"The flow of in-plane current through ultrathin magnetic heterostructures can
cause magnetization switching or domain wall nucleation owing to bulk and
interfacial effects. Within the magnetic layer, the current can create magnetic
instabilities via spin transfer torques (STT). At interface(s), spin current
generated from the spin Hall effect in a neighboring layer can exert torques,
referred to as the spin Hall torques, on the magnetic moments. Here, we study
current induced magnetization switching in perpendicularly magnetized CoFeB/MgO
heterostructures with a heavy metal (HM) underlayer. Depending on the thickness
of the HM underlayer, we find distinct differences in the inplane field
dependence of the threshold switching current. The STT is likely responsible
for the magnetization reversal for the thinner underlayer films whereas the
spin Hall torques cause the switching for thicker underlayer films. For the
latter, we find differences in the switching current for positive and negative
currents and initial magnetization directions. We find that the growth process
during the film deposition introduces an anisotropy that breaks the symmetry of
the system and causes the asymmetric switching. The presence of such symmetry
breaking anisotropy enables deterministic magnetization switching at zero
external fields.",1410.7473v2
2004-01-24,Reduction of spin transfer by synthetic antiferromagnets,"Synthetic antiferromagnetic layers (SAF) are incorporated into spin transfer
nanopillars giving a layer composition [Co(bottom)/Ru/Co(fixed)]/Cu/Co(free),
where square brackets indicate the SAF. The Co(bottom) and Co(fixed) layers are
aligned antiparallel (AP) by strong indirect exchange coupling through the Ru
spacer. All three magnetic layers are patterned, so this AP alignment reduces
undesirable dipole fields on the Co(free) layer. Adding the Co(bottom)/Ru
layers reduces the spin polarization of the electron current passing through
the nanopillar, leading to a decreased spin-torque per unit current incident on
the Co(free) layer. This may be advantageous for device applications requiring
a reduction of the effects of a spin-torque, such as nanoscale CPP-GMR read
heads.",0401483v1
2004-06-03,A Circuit Model for Domain Walls in Ferromagnetic Nanowires: Application to Conductance and Spin Transfer Torques,"We present a circuit model to describe the electron transport through a
domain wall in a ferromagnetic nanowire. The domain wall is treated as a
coherent 4-terminal device with incoming and outgoing channels of spin up and
down and the spin-dependent scattering in the vicinity of the wall is modelled
using classical resistances. We derive the conductance of the circuit in terms
of general conductance parameters for a domain wall. We then calculate these
conductance parameters for the case of ballistic transport through the domain
wall, and obtain a simple formula for the domain wall magnetoresistance which
gives a result consistent with recent experiments. The spin transfer torque
exerted on a domain wall by a spin-polarized current is calculated using the
circuit model and an estimate of the speed of the resulting wall motion is
made.",0406076v1
2010-03-15,Evidence for thermal spin transfer torque,"Large heat currents are obtained in Co/Cu/Co spin valves positioned at the
middle of Cu nanowires. The second harmonic voltage response to an applied
current is used to investigate the effect of the heat current on the switching
of the spin valves. Both the switching field and the magnitude of the voltage
response are found to be dependent on the heat current. These effects are
evidence for a thermal spin transfer torque acting on the magnetization and are
accounted for by a thermodynamic model in which heat, charge and spin currents
are linked by Onsager reciprocity relations.",1003.3042v2
2012-06-02,Dependence of the Spin Transfer Torque Switching Current Density on the Exchange Stiffness Constant,"We investigate the dependence of the switching current density on the
exchange stiffness constant in the spin transfer torque magnetic tunneling
junction structure with micromagnetic simulations. Since the widely accepted
analytic expression of the switching current density is based on the macro-spin
model, there is no dependence of the exchange stiffness constant. When the
switching is occurred, however, the spin configuration forms C-, S-type, or
complicated domain structures. Since the spin configuration is determined by
the shape anisotropy and the exchange stiffness constant, the switching current
density is very sensitive on their variations. It implies that there are more
rooms for the optimization of the switching current density with by controlling
the exchange stiffness constant, which is determined by composition and the
detail fabrication processes.",1206.0343v1
2015-12-16,Parity-time symmetry breaking in magnetic systems,"The understanding of out-of-equilibrium physics, especially dynamic
instabilities and dynamic phase transitions, is one of the major challenges of
contemporary science, spanning the broadest wealth of research areas that range
from quantum optics to living organisms. Focusing on nonequilibrium dynamics of
an open dissipative spin system, we introduce a non-Hermitian Hamiltonian
approach, in which non-Hermiticity reflects dissipation and deviation from
equilibrium. The imaginary part of the proposed spin Hamiltonian describes the
effects of Gilbert damping and applied Slonczewski spin-transfer torque. In the
classical limit, our approach reproduces Landau-Lifshitz-Gilbert-Slonczewski
dynamics of a large macrospin. We reveal the spin-transfer torque-driven
parity-time symmetry-breaking phase transition corresponding to a transition
from precessional to exponentially damped spin dynamics. Micromagnetic
simulations for nanoscale ferromagnetic disks demonstrate the predicted effect.
Our findings can pave the way to a general quantitative description of
out-of-equilibrium phase transitions driven by spontaneous parity-time symmetry
breaking.",1512.05408v2
2018-08-02,Quantum kinetic theory of spin-transfer torque and magnon-assisted transport in nanostructures,"We theoretically investigate the role of spin fluctuations in charge
transport through a magnetic junction. Motivated by recent experiments that
measure a nonlinear dependence of the current on electrical bias, we develop a
systematic understanding of the interplay of charge and spin dynamics in
nanoscale magnetic junctions. Our model captures two distinct features arising
from these fluctuations: magnon-assisted transport and the effect of
spin-transfer torque on the magnetoconductance. The latter stems from magnetic
misalignment in the junction induced by spin-current fluctuations. As the
temperature is lowered, inelastic quantum scattering takes over thermal
fluctuations, exhibiting signatures that make it readily distinguishable from
magnon-assisted transport.",1808.00777v2
2020-04-21,Ultrafast antiferromagnetic switching in NiO induced by spin transfer torques,"NiO is a prototypical antiferromagnet with a characteristic resonance
frequency in the THz range. From atomistic spin dynamics simulations that take
into account the crystallographic structure of NiO, and in particular a
magnetic anisotropy respecting its symmetry, we describe antiferromagnetic
switching at THz frequency by a spin transfer torque mechanism. Sub-picosecond
S-state switching between the six allowed stable spin directions is found for
reasonably achievable spin currents, like those generated by laser induced
ultrafast demagnetization. A simple procedure for picosecond writing of a
six-state memory is described, thus opening the possibility to speed up current
logic of electronic devices by several orders of magnitude.",2004.09822v3
2017-06-04,Field- and temperature-modulated spin-diode effect in a GMR nanowire with dipolar coupling,"An analytical model of the spin-diode effect induced by resonant
spin-transfer torque in a ferromagnetic bilayer with strong dipolar coupling
provides the resonance frequencies and the lineshapes of the magnetic field
spectra obtained under field or laser-light modulation. The effect of laser
irradiation is accounted for by introducing the temperature dependence of the
saturation magnetization and anisotropy, as well as thermal spin-transfer
torques. The predictions of the model are compared with experimental data
obtained with single Co/Cu/Co spin valves, embedded in nanowires and produced
by electrodeposition. Temperature modulation provides excellent signal-to-noise
ratio. High temperature-modulation frequency is possible because these
nanostructures have a very small heat capacity and are only weakly heat-sunk.
The two forms of modulation give rise to qualitative differences in the spectra
that are accounted for by the model.",1706.01036v1
2022-08-02,Response of the chiral soliton lattice to spin polarized currents,"Spin polarized currents originate a spin-transfer torque that enables the
manipulation of magnetic textures. Here we theoretically study the effect of a
spin-polarized current on the magnetic texture corresponding to a chiral
soliton lattice in a monoaxial helimagnet under a transverse magnetic field. At
sufficiently small current density the chiral soliton lattice reaches a steady
motion state with a velocity proportional to the intensity of the applied
current, the mobility being independent of the density of solitons and the
magnetic field. This motion is accompanied with a small conical distortion of
the chiral soliton lattice. At large current density the spin-transfer torque
destabilizes the chiral soliton lattice, driving the system to a ferromagnetic
state parallel to the magnetic field. We analyze how the deformation of the
chiral soliton lattice depends on the applied current density. The destruction
of the chiral soliton lattice under current could serve as a possible erasure
mechanisms for spintronic applications.",2208.01768v1
2007-03-29,Enhancing the spin-transfer torque through proximity of quantum well states,"We predict that the spin-transfer, $T_{i,||}$, and field-like, $T_{i,\bot}$,
components of the {\it local} spin torque are dramatically enhanced in
double-barrier magnetic tunnel junctions. The {\it spin-mixing} enhancement is
due to the energetic proximity of majority and minority quantum well states
(QWS) of different quantum numbers within the bias window. $T_{i,||}$ exhibits
a switch-on and switch-off step-like bias behavior when spin polarized QWS
enter the bias window or exit the energy band, while $T_{i,\bot}$, changes sign
between switch-on biases. The {\it net} $T_{\bot}$ exhibits an anomalous
angular behavior due to the bias interplay of the bilinear and biquadratic
effective exchange couplings.",0703789v2
2011-03-13,Micromagnetic understanding of stochastic resonance driven by spin-transfertorque,"In this paper, we employ micromagnetic simulations to study non-adiabatic
stochastic resonance (NASR) excited by spin-transfer torque in a
super-paramagnetic free layer nanomagnet of a nanoscale spin valve. We find
that NASR dynamics involves thermally activated transitions among two static
states and a single dynamic state of the nanomagnet and can be well understood
in the framework of Markov chain rate theory. Our simulations show that a
direct voltage generated by the spin valve at the NASR frequency is at least
one order of magnitude greater than the dc voltage generated off the NASR
frequency. Our computations also reproduce the main experimentally observed
features of NASR such as the resonance frequency, the temperature dependence
and the current bias dependence of the resonance amplitude. We propose a simple
design of a microwave signal detector based on NASR driven by spin transfer
torque.",1103.2536v1
2016-10-27,Spin transfer driven resonant expulsion of a magnetic vortex core for efficient rf detector,"Spin transfer magnetization dynamics have led to considerable advances in
Spintronics, including opportunities for new nanoscale radiofrequency devices.
Among the new functionalities is the radiofrequency(rf) detection using the
spin diode rectification effect in spin torque nano-oscillators (STNOs). In
this study, we focus on a new phenomenon, the resonant expulsion of a magnetic
vortex in STNOs. This effect is observed when the excitation vortex radius, due
to spin torques associated to rf currents, becomes larger than the actual
radius of the STNO. This vortex expulsion is leading to a sharp variation of
the voltage at the resonant frequency. Here we show that the detected frequency
can be tuned by different parameters; furthermore, a simultaneous detection of
different rf signals can be achieved by real time measurements with several
STNOs having different diameters. This result constitutes a first
proof-of-principle towards the development of a new kind of nanoscale rf
threshold detector.",1610.08660v1
2018-06-21,Spin transfer torque induced paramagnetic resonance,"We show how the spin-transfer torque generated by an ac voltage may be used
to excite a paramagnetic resonance of an atomic spin deposited on a metallic
surface. This mechanism is independent of the environment of the atom and may
explain the ubiquity of the paramagnetic resonance reported by Baumann
$\textit{et al.}$ [$\href{http://dx.doi.org/10.1126/science.aac8703}{Science
\textbf{350}, 417 (2015)}$]. The current and spin dynamics are modeled by a
time-dependent Redfield master equation generalized to account for the periodic
driven voltage. Our approach shows that the resonance effect is a consequence
of the nonlinearity of the coupling between the magnetic moment and the
spin-polarized current which generates a large second-harmonic amplitude that
can be measured in the current signal.",1806.08260v2
2016-11-18,Temporal evolution of auto-oscillations in a YIG/Pt microdisc driven by pulsed spin Hall effect-induced spin-transfer torque,"The temporal evolution of pulsed Spin Hall Effect - Spin Transfer Torque
(SHE-STT) driven auto-oscillations in a Yttrium Iron Garnet (YIG) / platinum
(Pt) microdisc is studied experimentally using time-resolved Brillouin Light
Scattering (BLS) spectroscopy. It is demonstrated that the frequency of the
auto-oscillations is different in the center and at the edge of the
investigated disc that is related to the simultaneous STT excitation of a
bullet and a non-localized spin-wave mode. Furthermore, the magnetization
precession intensity is found to saturate on a time scale of 20 ns or longer,
depending on the current density. For this reason, our findings suggest that a
proper ratio between the current and the pulse duration is of crucial
importance for future STT-based devices.",1611.06054v1
2012-02-20,Stress in Spin-Valve Nanopillars due to Spin Transfer,"We report a mechanical effect in spin-valve nanopillars due to spin transfer.
A polarized current carrying electron spins transfers torque to local
magnetization and leads to a magnetic switching of free layer. Like classical
Einstein-de Haas effect, the conservation of angular momentum needs the free
layer to offset the change of angular momentum and then a mechanical rotation
occurs. The free layer is not free standing, so the mechanical angular momentum
will be revealed as stress and strain. We study the effect of a spin induced
stress in a nanopillar device with in-plane magnetization. Our calculations
show that the tress in as device is dependent on frequency and the ratio of
length/thickness and about 1 MPa at GHz. It is concluded that the stress owing
to spin transfer is much less than the internal stress of film and does not
introduce damage to the device.",1202.4218v1
2005-11-22,Magnetomechanical Torques in Small Magnetic Cantilevers,"We study the dnamics of small magnetic cantilevers, either made from Si
covered by a magnetic film or entirely ferromagnetic ones. The
magnetomechanical torques are found to cause line splittings in ferromagnetic
resonance spectra and magnetization reversal facilitated by mechanical degrees
of freedom. We show that the magnetomechanical torques can extend the limits of
detecting and exciting motion at the nanoscale. A ""nanomotor"" described here
effectively transforms rf magnetic fields into mechanical oscillations. We
furthermore propose to integrate mechanical oscillators into magnetoelectronic
devices that make use of current-induced spin-transfer torques. This opens new
possibilities for electric transducers of nanomechanical motion.",0511548v1
2018-06-16,Recent Advances in Mechanical Torque Studies of Small-scale Magnetism,"There is a storied scientific history in the role of mechanical instruments
for the measurement of fundamental physical interactions. Among these include
the detection of magnetic torques via a displacement of a compliant mechanical
sensor as a result of angular momentum transfer. Modern nanofabrication methods
have enabled the coupling of mechanical structures to single, miniature
magnetic specimens. This has allowed for strikingly sensitive detection of
magnetic hysteresis and other quasi-static effects, as well as spin resonances,
in materials confined to nanoscale geometries. The extraordinary sensitivities
achieved in mechanical transduction through recent breakthroughs in cavity
optomechanics, where a high-finesse optical cavity is used for readout of
motion, are now being harnessed for torque magnetometry. In this article, we
review the recent progress in mechanical detection of magnetic torques,
highlight current applications, and speculate on possible future developments
in the technology and science. Guidelines for designing and implementing the
measurements are also included.",1806.06288v1
2008-08-28,Bias and angular dependence of spin-transfer torque in magnetic tunnel junctions,"We use spin-transfer-driven ferromagnetic resonance (ST-FMR) to measure the
spin-transfer torque vector T in MgO-based magnetic tunnel junctions as a
function of the offset angle between the magnetic moments of the electrodes and
as a function of bias, V. We explain the conflicting conclusions of two
previous experiments by accounting for additional terms that contribute to the
ST-FMR signal at large |V|. Including the additional terms gives us improved
precision in the determination of T(V), allowing us to distinguish among
competing predictions. We determine that the in-plane component of has a weak
but non-zero dependence on bias, varying by 30-35% over the bias range where
the measurements are accurate, and that the perpendicular component can be
large enough to be technologically significant. We also make comparisons to
other experimental techniques that have been used to try to measure T(V).",0808.3810v2
2012-03-02,Investigation of Optical Spin Transfer Torque in Ferromagnetic Semiconductor GaMnAs by Magneto-Optical Pump-and-Probe Method,"We report on magnetization precession induced in (Ga,Mn)As by an optical spin
transfer torque (OSTT). This phenomenon, which corresponds to a transfer of
angular momentum from optically-injected spin-polarized electrons to
magnetization, was predicted theoretically in 2004 and observed experimentally
by our group in 2012. In this paper we provide experimental details about the
observation of OSTT by a time-resolved pump-and-probe magneto-optical
technique. In particular, we show that the precession of magnetization due to
OSTT can be experimentally separated from that induced by the well known
magnetic-anisotropy-related mechanism in a hybrid structure
piezo-stressor/(Ga,Mn)As with an in situ electrical control of the magnetic
anisotropy. We also illustrate that OSTT is clearly apparent in the measured
dynamical magneto-optical signal in a large variety of (Ga,Mn)As samples with a
Mn concentration from 3% to 9%.",1203.0483v1
2009-06-24,Invariant form of spin-transfer switching condition,"We derive an invariant form of the current-induced switching condition in
spin-transfer devices and show that for energy minima and maxima the ""switching
ability"" of the current is determined by the spin torque divergence. In
contrast, energy saddle points are normally stabilized by current-induced
merging with other equilibria. Our approach provides new predictions for
several experimental setups and shows the limitations of some frequently used
approximations.",0906.4416v1
2009-09-01,Spin transfer and current-induced switching in antiferromagnets,"We present theoretical description of the precessional switching processes
induced by simultaneous application of spin-polarized current and external
magnetic field to antiferromagnetic component of the ""pinned"" layer. We found
stability ranges of different static and dynamic regimes. We showed the
possibility of steady current-induced precession of antiferromagnetic vector
with frequency that linearly depends on the bias current. Furthermore, we found
an optimal duration of current pulse required for switching between different
orientations of antiferromagnetic vector and current and field dependence of
switching time. Our results reveal the difference between dynamics of ferro-
and antiferromagnets subjected to spin transfer torques.",0909.0234v2
2019-11-27,Interstellar Asteroid Rotation with the Mechanical Torque Produced by Interstellar Medium,"The first interstellar object 'Oumuamua is discovered in 2017. When 'Oumuamua
travels in interstellar space, it keeps colliding with interstellar medium
(ISM). Given a sufficiently long interaction time, its rotation state may
change significantly because of the angular momentum transfer with interstellar
medium. Using generated Gaussian random spheres with the dimension ratios 6:1:1
and 5:5:1, this paper explores the ISM torque curve and proposes that ISM
collision may account for 'Oumuamua's tumbling with the simple constant-torque
analytical method. The statistic results show that the asymptotic obliquities
distribute mostly at 0 and 180 degree and most cases spin down at the
asymptotic obliquity, indicating the ISM collision effect is similar to the
YORP effect with zero heat conductivity assumed. Given a long time of
deceleration of the spin rate, an initial major-axis rotation may evolve into
tumbling motion under ISM torque. Using a constant-torque analytical model, the
timescales of evolving into tumbling for the sample of 200 shapes are found to
range from several Gyrs to ens of Gyrs, highly dependent on the chosen shape.
The mean value is about 8.5 Gyrs for prolate shapes and 7.3 Gyrs for oblate
shapes. Rotation of asteroids in the Oort cloud might be also dominated by the
ISM collision effect since the YORP effect is quite weak at such a long
distance from the Sun. Although this paper assumes an ideal mirror reflection
and a constant relative velocity of 'Oumuamua, the results still show the
importance of the ISM collision effect.",1911.12228v3
2015-11-18,Spin-orbit torque switching without external field with a ferromagnetic exchange-biased coupling layer,"Magnetization reversal of a perpendicular ferromagnetic free layer by
spin-orbit torque (SOT) is an attractive alternative to spin-transfer torque
(STT) switching in magnetic random-access memory (MRAM) where the write process
involves passing a high current across an ultrathin tunnel barrier. A small
symmetry-breaking bias field is usually needed for deterministic SOT switching
but it is impractical to generate the field externally for spintronic
applications. Here, we demonstrate robust zero-field SOT switching of a
perpendicular Co90Fe10 (CoFe) free layer where the symmetry is broken by
magnetic coupling to a second in-plane exchange-biased CoFe layer via a
nonmagnetic Ru spacer. The preferred magnetic state of the free layer is
determined by the current polarity and the nature of the interlayer exchange
coupling (IEC). Our strategy offers a scalable solution to realize
bias-field-free SOT switching that can lead to a generation of SOT-based
devices, that combine high storage density and endurance with potentially low
power consumption.",1511.05773v1
2017-08-10,Interplay between the d- and pi-electron systems in magnetic torque of the layered organic conductor \k{appa}-(BETS)2Mn[N(CN)2]3,"In the organic charge transfer salt k-(BETS)2Mn[N(CN)2]3 the metallic
conductivity is provided by itinerant pi-electrons in the layers of BETS
molecules, whereas magnetization is largely dominated by the localized
d-electrons of the Mn2+ ions in the insulating anionic layers. We study
magnetic properties of the compound in its low-temperature, Mott-insulating
state by means of magnetic torque technique. The complex behavior of the torque
can be qualitatively explained by the coexistence of two weakly interacting
magnetic subsystems associated with paramagnetic d-electron spins and
antiferromagnetically ordered pi-electron spins, respectively. Based on the
experimental data, we determine the principal axes of magnetization of the Mn2+
sublattice and propose a qualitative model for the pi-electron spin
arrangement, implying an important role of the Dzyaloshinskii-Moriya
interaction.",1708.03595v1
2018-04-30,Modular Compact Modeling of Magnetic Tunnel Junction Devices,"This paper describes a robust, modular, and physics- based circuit framework
to model conventional and emerging Magnetic Tunnel Junction (MTJ) devices.
Magnetization dynamics are described by the stochastic Landau-Lifshitz-Gilbert
(sLLG) equation whose results are rigorously benchmarked with a Fokker-Planck
Equation (FPE) description of magnet dynamics. We then show how sLLG is coupled
to transport equations of MTJ-based devices in a unified circuit platform. Step
by step, we illustrate how the physics-based MTJ model can be extended to
include different spintronics phenomena, including spin-transfer-torque (STT),
voltage-control of magnetic anisotropy (VCMA) and spin-orbit torque (SOT)
phenomena by experimentally benchmarked examples. To demonstrate how our
approach can be used in the exploration of novel MTJ-based devices, we also
present a recently proposed MEMS resonator- driven spin-torque nano oscillator
(STNO) that can reduce the phase noise of STNOs. We briefly elaborate on the
use of our framework beyond conventional devices.",1805.00066v2
2014-06-26,Spin-torque diode radio-frequency detector with voltage tuned resonance,"We report on a voltage tunable radio-frequency (RF) detector based on a
magnetic tunnel junction (MTJ). The spin-torque diode effect is used to excite
and/or detect RF oscillations in the magnetic free layer of the MTJ. In order
to reduce the overall in-plane magnetic anisotropy of the free layer, we take
advantage of the perpendicular magnetic anisotropy at the interface between
ferromagnetic and insulating layers. The applied bias voltage is shown to have
a significant influence on the magnetic anisotropy, and thus on the resonance
frequency of the device. This influence also depends on the voltage polarity.
The obtained results are accounted for in terms of the interplay of
spin-transfer-torque and voltage-controlled magnetic anisotropy effects.",1406.6935v1
2018-08-04,Chiral skyrmion auto-oscillations in a ferromagnet under spin transfer torque,"A skyrmion can be stabilized in a nanodisc geometry in a ferromagnetic
material with Dzyaloshinskii-Moriya (DM) interaction. We apply spin torque
uniform in space and time and observe numerically that the skyrmion is set in
steady rotational motion around a point off the nanodisc center. We give a
theoretical description of the emerging auto-oscillation dynamics based on the
coupling of the rotational motion to the breathing mode of the skyrmion and to
the associated oscillations of the in-plane magnetization. The analysis shows
that the achievement of auto-oscillations in this simple set-up is due to the
chiral symmetry breaking. Thus, we argue that the system is turned into a
spin-torque oscillator due to the chiral DM interaction.",1808.01436v1
2020-03-31,Spin-torque switching mechanisms of perpendicular magnetic tunnel junctions nanopillars,"Understanding the magnetization dynamics induced by spin transfer torques in
perpendicularly magnetized magnetic tunnel junction nanopillars and its
dependence on material parameters is critical to optimizing device performance.
Here we present a micromagnetic study of spin-torque switching in a disk-shaped
element as a function of the free layer's exchange constant and disk diameter.
The switching is shown to generally occur by 1) growth of the magnetization
precession amplitude in the element center; 2) an instability in which the
reversing region moves to the disk edge, forming a magnetic domain wall; and 3)
the motion of the domain wall across the element. For large diameters and small
exchange, step 1 leads to a droplet with a fully reversed core that experiences
a drift instability (step 2). While in the opposite case (small diameters and
large exchange), the central region of the disk is not fully reversed before
step 2 occurs. The origin of the micromagnetic structure is shown to be the
disk's non-uniform demagnetization field. Faster, more coherence and energy
efficient switching occur with larger exchange and smaller disk diameters,
showing routes to increase device performance.",2003.13875v1
2021-10-13,Eigenvalue-based micromagnetic analysis of switching in spin-torque-driven structures,"We present an eigenvalue-based approach for studying the magnetization
dynamics in magnetic nanostructures driven by spintronic excitations, such as
spin transfer torque and spin orbit torque. The approach represents the system
dynamics in terms of normal oscillation modes (eigenstates) with corresponding
complex eigenfrequencies. The dynamics is driven by a small number of active
eigenstates and often considering just a single eigenstate is sufficient. We
develop a perturbation theory that provides semi-analytical dynamic solutions
by using eigenstates for the case in the absence of damping and spintronic
excitations as a basis. The approach provides important insights into dynamics
in such systems and allows solving several difficulties in their modeling, such
as extracting the switching current in magnetic random access memories (MRAM)
and understanding switching mechanisms. We show that the presented approach
directly predicts the critical switching current, i.e., switching current for
an infinite time. The approach also provides solutions for the switching
dynamics allowing obtaining the switching current for a finite switching time,
provided that the system symmetry is broken, e.g., by tilting the polarizer, so
that switching by a finite pulse is possible.",2110.07085v2
2021-10-23,Write asymmetry of spin-orbit torque memory induced by in-plane magnetic fields,"Write asymmetry, the significantly different write current for high-to-low
and low-to-high resistance switching because of natural stochastic behaviors of
magnetization, is a fundamental issue in magnetic random-access memory (MRAM).
For high-performance spin transfer torque (STT) MRAM, it can be eliminated by
precisely controlling atomically thin magnetic multilayers or by introducing
compensation techniques in circuit-level designs, while for spin-orbit torque
(SOT) MRAM, it has not been addressed. Here we systematically investigated the
write asymmetry of SOT-MRAM as a function of applied magnetic fields (H) and
demonstrated that the write currents are intrinsically asymmetric due to
different SOT efficiencies for high-to-low and low-to-high switching.
Furthermore, we found that the SOT efficiency is very sensitive to the tilt
angle between H and write current, which can be tuned through H to achieve
symmetric SOT switching. These results provide an additional guideline for
designing SOT devices and suggest that the write asymmetry can be eliminated by
adjusting the introduced effective magnetic fields within a field-free SOT-MRAM
architecture.",2110.12116v1
2019-07-24,Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions,"We demonstrate field and current controlled magnetodynamics in nanocontact
spin-torque nano-oscillators (STNOs) based on orthogonal magnetic tunnel
junctions (MTJs). We systematically analyze the microwave properties (frequency
$f$, linewidth $\Delta f$, power $P$, and frequency tunability $df/dI$) with
their physical origins---perpendicular magnetic anisotropy (PMA), damping-like
and field-like spin transfer torque (STT), and voltage-controlled magnetic
anisotropy (VCMA). These devices present several advantageous characteristics:
high emission frequencies ($f> 20$ GHz), high frequency tunability
($df/dI=0.25$~GHz/mA), and zero-field operation ($f\sim 4$ GHz). Furthermore, a
detailed investigation of $f(H, I)$ reveals that $df/dI$ is mostly governed by
the large VCMA (287~fJ/(V$\cdot$m)), while STT plays a negligible role.",1907.10427v2
2019-12-24,Synchronization and chaos in a spin-torque oscillator with a perpendicularly magnetized free layer,"Synchronization and chaos caused by alternating current and microwave field
in a spin torque oscillator consisting of a perpendicularly magnetized free
layer and an in-plane magnetized reference layer is comprehensively studied
theoretically. A forced synchronization by the alternating current is observed
in numerical simulation over wide ranges of its amplitude and frequency. An
analytical theory clarifies that the nonlinear frequency shift, as well as the
spin-transfer torque asymmetry, plays a key role in determining locking range
and phase difference between the oscillator and current. Chaos caused by the
alternating current is identified for a region of large alternating current by
evaluating the Lyapunov exponent. Similar results are also obtained for
microwave field, although the parameter regions causing chaos are narrower than
those by the alternating current.",1912.11179v1
2020-07-09,Domain wall propagation by spin-orbit torques in in-plane magnetized systems,"The effect of damping-like spin-orbit torque (DL SOT) on magnetic domain
walls (DWs) in in-plane magnetised soft tracks is studied analytically and with
micromagnetic simulations. We find that DL SOT drives vortex DWs, whereas
transverse DWs, the other typical DW structure in soft tracks, propagate only
if the Dzyaloshinskii-Moriya interaction (DMI) is present. The SOT drive can
add to, and be more efficient than, spin-transfer torque (STT), and so may
greatly benefit applications that require in-plane DWs. Our analysis based on
the Thiele equation shows that the driving force arises from a cycloidal
distortion of the DW structure caused by geometrical confinement or DMI. This
distortion is higher, and the SOT more efficient, in narrower, thinner tracks.
These results show that the effects of SOT cannot be understood by simply
considering the effective field at the center of the structure, an ill-founded
but often-used estimation. We also show that the relative magnitude of STT and
DL SOT can be determined by comparing the motion of different vortex DW
structures in the same track.",2007.04891v1
2024-01-10,Self-generated spin-orbit torque driven by anomalous Hall current,"Spin-orbit torques enable energy-efficient manipulation of magnetization by
electric current and hold promise for applications ranging from nonvolatile
memory to neuromorphic computing. Here we report the discovery of a giant
spin-orbit torque induced by anomalous Hall current in ferromagnetic
conductors. This anomalous Hall torque is self-generated as it acts on
magnetization of the ferromagnet that engenders the torque. The magnitude of
the anomalous Hall torque is sufficiently large to fully negate magnetic
damping of the ferromagnet, which allows us to implement a microwave spin
torque nano-oscillator driven by this torque. The peculiar angular symmetry of
the anomalous Hall torque favors its use over the conventional spin Hall torque
in coupled nano-oscillator arrays. The universal character of the anomalous
Hall torque makes it an integral part of the description of coupled spin
transport and magnetization dynamics in magnetic nanostructures.",2401.05006v1
2016-03-30,Low-damping transmission of spin waves through YIG/Pt-based layered structures for spin-orbit-torque applications,"We show that in YIG-Pt bi-layers, which are widely used in experiments on the
spin transfer torque and spin Hall effects, the spin-wave amplitude
significantly decreases in comparison to a single YIG film due to the
excitation of microwave eddy currents in a Pt coat. By introducing a novel
excitation geometry, where the Pt layer faces the ground plane of a microstrip
line structure, we suppressed the excitation of the eddy currents in the Pt
layer and, thus, achieved a large increase in the transmission of the
Damon-Eshbach surface spin wave. At the same time, no visible influence of an
external dc current applied to the Pt layer on the spin-wave amplitude in the
YIG-Pt bi-layer was observed in our experiments with YIG films of micrometer
thickness.",1603.09201v1
2005-01-13,Magnetization noise in magnetoelectronic nanostructures,"By scattering theory we show that spin current noise in normal electric
conductors in contact with nanoscale ferromagnets increases the magnetization
noise by means of a fluctuating spin-transfer torque. Johnson-Nyquist noise in
the spin current is related to the increased Gilbert damping due to spin
pumping, in accordance with the fluctuation-dissipation theorem. Spin current
shot noise in the presence of an applied bias is the dominant contribution to
the magnetization noise at low temperatures.",0501318v1
2012-09-07,Self-sustained current oscillations in spin-blockaded quantum dots,"Self-sustained current oscillation observed in spin-blockaded double quantum
dots is explained as a consequence of periodic motion of dynamically polarized
nuclear spins (along a limit cycle) in the spin-blockaded regime under an
external magnetic field and a spin-transfer torque. It is shown, based on the
Landau-Lifshtz-Gilbert equation, that a sequence of semistable limit cycle,
Hopf and homoclinic bifurcations occurs as the external field is tuned. The
divergent period near the homoclinic bifurcation explains well why the period
in the experiment is so long and varies by many orders of magnitudes.",1209.1548v1
1999-08-16,Current-driven Magnetization Reversal and Spin Wave Excitations in Co/Cu/Co Pillars,"Using thin film pillars ~100 nm in diameter, containing two ferromagnetic Co
layers of different thicknesses separated by a paramagnetic Cu spacer, we
examine effects of torques due to spin-polarized currents flowing perpendicular
to the layers. In accordance with spin-transfer theory, spin-polarized
electrons flowing from the thin to the thick Co layer can switch the magnetic
moments of the layers antiparallel, while a reversed electron flow causes
switching to a parallel state. When large magnetic fields are applied, the
current no longer fully reverses the magnetic moment, but instead stimulates
spin-wave excitations.",9908231v1
2006-01-11,Relaxing-Precessional Magnetization Switching,"A new way of magnetization switching employing both the spin-transfer torque
and the torque by a magnetic field is proposed. The solution of the
Landau-Lifshitz-Gilbert equation shows that the dynamics of the magnetization
in the initial stage of the switching is similar to that in the precessional
switching, while that in the final stage is rather similar to the relaxing
switching. We call the present method the relaxing-precessional switching. It
offers a faster and lower-power-consuming way of switching than the relaxing
switching and a more controllable way than the precessional switching.",0601227v1
2021-01-06,Magnetic skyrmion binning,"When spin polarised electrons flow through a magnetic texture a transfer
torque is generated. We examine the effect of this torque on skyrmions and
skyrmion bags, skyrmionic structures of arbitrary integer topological degree,
in thin ferromagnetic films. Using micromagnetic simulations and analysis from
the well known Thiele equation we explore the potential for sorting or binning
skyrmions of varying degrees mechanically. We investigate the applicability of
the Thiele equation to problems of this nature and derive a theory of skyrmion
deflection ordered by topological degree.",2101.02045v1
2019-03-11,Giant spin-orbit torque in a single ferrimagnetic metal layer,"Antiferromagnets and compensated ferrimagnets offer opportunities to
investigate spin dynamics in the 'terahertz gap' because their resonance modes
lie in the 0.3 THz to 3 THz range. Despite some inherent advantages when
compared to ferromagnets, these materials have not been extensively studied due
to difficulties in exciting and detecting the high-frequency spin dynamics,
especially in thin films. Here we show that spin-obit torque in a single layer
of the highly spin-polarized compensated ferrimagnet Mn2RuxGa is remarkably
efficient at generating spin-orbit fields \mu_0H_eff, which approach 0.1x10-10
T m2/A in the low-current density limit -- almost a thousand times the Oersted
field, and one to two orders of magnitude greater than the effective fields in
heavy metal/ferromagnet bilayers. From an analysis of the harmonic Hall effect
which takes account of the thermal contributions from the anomalous Nernst
effect, we show that the antidamping component of the spin-orbit torque is
sufficient to sustain self-oscillation. Our study demonstrates that spin
electronics has the potential to underpin energy-frugal, chip-based solutions
to the problem of ultra high-speed information transfer.",1903.04432v3
2017-01-12,Dynamic coupling of ferromagnets via spin Hall magnetoresistance,"The synchronized magnetization dynamics in ferromagnets on a nonmagnetic
heavy metal caused by the spin Hall effect is investigated theoretically. The
direct and inverse spin Hall effects near the ferromagnetic/nonmagnetic
interface generate longitudinal and transverse electric currents. The
phenomenon is known as the spin Hall magnetoresistance effect, whose magnitude
depends on the magnetization direction in the ferromagnet due to the spin
transfer effect. When another ferromagnet is placed onto the same nonmagnet,
these currents are again converted to the spin current by the spin Hall effect
and excite the spin torque to this additional ferromagnet, resulting in the
excitation of the coupled motions of the magnetizations. The in-phase or
antiphase synchronization of the magnetization oscillations, depending on the
value of the Gilbert damping constant and the field-like torque strength, is
found in the transverse geometry by solving the Landau-Lifshitz-Gilbert
equation numerically. On the other hand, in addition to these synchronizations,
the synchronization having a phase difference of a quarter of a period is also
found in the longitudinal geometry. The analytical theory clarifying the
relation among the current, frequency, and phase difference is also developed,
where it is shown that the phase differences observed in the numerical
simulations correspond to that giving the fixed points of the energy supplied
by the coupling torque.",1701.03201v2
2014-11-11,Magnonic Charge Pumping via Spin-Orbit Coupling,"The interplay between spin, charge, and orbital degrees of freedom has led to
the development of spintronic devices like spin-torque oscillators, spin-logic
devices, and spin-transfer torque magnetic random-access memories. In this
development spin pumping, the process where pure spin-currents are generated
from magnetisation precession, has proved to be a powerful method for probing
spin physics and magnetisation dynamics. The effect originates from direct
conversion of low energy quantised spin-waves in the magnet, known as magnons,
into a flow of spins from the precessing magnet to adjacent normal metal leads.
The spin-pumping phenomenon represents a convenient way to electrically detect
magnetisation dynamics, however, precessing magnets have been limited so far to
pump pure spin currents, which require a secondary spin-charge conversion
element such as heavy metals with large spin Hall angle or multi-layer layouts
to be detectable. Here, we report the experimental observation of charge
pumping in which a precessing ferromagnet pumps a charge current, demonstrating
direct conversion of magnons into high-frequency currents via the relativistic
spin-orbit interaction. The generated electric current, differently from spin
currents generated by spin-pumping, can be directly detected without the need
of any additional spin to charge conversion mechanism and amplitude and phase
information about the relativistic current-driven magnetisation dynamics. The
charge-pumping phenomenon is generic and gives a deeper understanding of the
recently observed spin-orbit torques, of which it is the reciprocal effect and
which currently attract interest for their potential in manipulating magnetic
information. Furthermore, charge pumping provides a novel link between
magnetism and electricity and may find application in sourcing alternating
electric currents.",1411.2779v1
2019-10-25,Energy-efficient ultrafast SOT-MRAMs based on low-resistivity spin Hall metal Au0.25Pt0.75,"Many key electronic technologies (e.g., large-scale computing, machine
learning, and superconducting electronics) require new memories that are fast,
reliable, energy-efficient, and of low-impedance at the same time, which has
remained a challenge. Non-volatile magnetoresistive random access memories
(MRAMs) driven by spin-orbit torques (SOTs) have promise to be faster and more
energy-efficient than conventional semiconductor and spin-transfer-torque
magnetic memories. This work reports that the spin Hall effect of
low-resistivity Au0.25Pt0.75 thin films enables ultrafast antidamping-torque
switching of SOT-MRAM devices for current pulse widths as short as 200 ps. If
combined with industrial-quality lithography and already-demonstrated
interfacial engineering, our results show that an optimized MRAM cell based on
Au0.25Pt0.75 can have energy-efficient, ultrafast, and reliable switching, e.g.
a write energy of < 1 fJ (< 50 fJ) for write error rate of 50% (<1e-5) for 1 ns
pulses. The antidamping torque switching of the Au0.25Pt0.75 devices is 10
times faster than expected from a rigid macrospin model, most likely because of
the fast micromagnetics due to the enhanced non-uniformity within the free
layer. These results demonstrate the feasibility of Au0.25Pt0.75-based
SOT-MRAMs as a candidate for ultrafast, reliable, energy-efficient,
low-impedance, and unlimited-endurance memory.",1910.11896v2
2012-11-05,Tailoring spin-orbit torque in diluted magnetic semiconductors,"We study the spin orbit torque arising from an intrinsic linear Dresselhaus
spin-orbit coupling in a single layer III-V diluted magnetic semiconductor. We
investigate the transport properties and spin torque using the linear response
theory and we report here : (1) a strong correlation exists between the angular
dependence of the torque and the anisotropy of the Fermi surface; (2) the spin
orbit torque depends nonlinearly on the exchange coupling. Our findings suggest
the possibility to tailor the spin orbit torque magnitude and angular
dependence by structural design.",1211.0867v2
2020-01-25,Phase estimation of spin-torque oscillator by nonlinear spin-torque diode effect,"A theoretical analysis is developed on spin-torque diode effect in nonlinear
region. An analytical solution of the diode voltage generated from spin-torque
oscillator by the rectification of an alternating current is derived. The diode
voltage is revealed to depend nonlinearly on the phase difference between the
oscillator and the alternating current. The validity of the analytical
prediction is confirmed by numerical simulation of the Landau-Lifshitz-Gilbert
equation. The results indicate that the spin-torque diode effect is useful to
evaluate the phase of a spin-torque oscillator in forced synchronization state.",2001.09247v1
2022-12-25,Theory of superdiffusive spin transport in noncollinear magnetic multilayers,"Ultrafast demagnetization induced by femtosecond laser pulses in thin
metallic layers is caused by the outflow of spin-polarized hot electron
currents describable by the superdiffusive transport model. These
laser-generated spin currents can cross the interface into another magnetic
layer and give rise to magnetization dynamics in magnetic spin valves with
noncollinear magnetizations. To describe ultrafast transport and spin dynamics
in such nanostructures we develop here the superdiffusive theory for general
noncollinear magnetic multilayers. Specifically, we introduce an Al/Ni/Ru/Fe/Ru
multilayer system with noncollinear Ni and Fe magnetic moments and analyze how
the ultrafast demagnetization and spin-transfer torque depend on the
noncollinearity. We employ ab initio calculations to compute the spin- and
energy-dependent transmissions of hot electrons at the interfaces of the
multilayer. Taking into account multiple electron scattering at interfaces and
spin mixing in the spacer layer we find that the laser-induced demagnetization
of the Ni layer and magnetization change of the Fe layer strongly depend on the
angle between their magnetizations. Similarly, the spin-transfer torques on the
Ni and Fe layers and the total spin momentum absorbed in the Ni and Fe layer
are found to vary markedly with the amount of noncollinearity.
  These results suggest that changing the amount of noncollinearity in magnetic
multilayers one can efficiently control the hot electron spin transport, which
may open a way toward achieving fast, laser-driven spintronic devices.",2212.12961v1
2005-01-24,Macroscopic description of current induced switching due to spin-transfer,"We develop a macroscopic description of the current-induced torque due to
spin transfer in a layered system consisting of two ferromagnetic layers
separated by a nonmagnetic layer. The description is based on i) the classical
spin diffusion equations for the distribution functions used in the theory of
CPP-GMR, ii) the relevant boundary conditions for the longitudinal and
transverse components of the spin current in the situation of quasi-interfacial
absorption of the transverse components in a magnetic layer. The torque is
expressed as a function of the usual parameters derived from CPP-GMR
experiments and two additional parameters involved in the transverse boundary
conditions. Our model is used to describe qualitatively normal and inverse
switching phenomena studied in recent experiments. We also present a structure
for which we predict only states of steady precession above a certain critical
current. We finally discuss the limits of a small angle between magnetic
moments of the ferromagnetic layers and of vanishing imaginary part of the
mixing conductance.",0501570v1
2006-11-13,Spin transfer torque in continuous textures: semiclassical Boltzmann approach,"We consider a microscopic model of itinerant electrons coupled via
ferromagnetic exchange to a local magnetization whose direction vector n(r,t)
varies in space and time. We assume that to first order in the spatial gradient
and time derivative of n(r,t) the magnetization distribution function f(p,r,t)
of itinerant electrons has the Ansatz form: f(p,r,t)=f_{parallel}(p)n(r,t)+
f_{1 r}(p) n ^ nabla_{r} n+f_{2 r}(p) nabla_{r} n+ f_{1 t}(p) n ^ partial_t
n+f_{2 t}(p) partial_t n. Using then the Landau-Sillin equations of motion
approach we derive explicit forms for the components f_{parallel}(p), f_{1
r}(p), f_{2 r}(p), f_{1 t}(p) and f_{2 t}(p) in ""equilibrum"" and in out of
equilibrum situations for: (i) no scattering by impurities, (ii) spin
conserving scattering and (iii) spin non-conserving scattering. The back action
on the localized electron magnetization from the out of equilibrum part of the
two components f_{1 r}, f_{2 r} constitutes the two spin transfer torque terms.",0611320v3
2009-06-04,Thermoelectric spin transfer in textured magnets,"We study charge and energy transport in a quasi-1D magnetic wire in the
presence of magnetic textures. The energy flows can be expressed in a fashion
similar to charge currents, leading to new energy-current induced spin torques.
In analogy to charge currents, we can identify two reciprocal effects:
spin-transfer torque on the magnetic order parameter induced by energy current
and the Berry-phase gauge field induced energy flow. In addition, we
phenomenologically introduce new $\beta-$like viscous coupling between magnetic
dynamics and energy current into the LLG equation, which originates from spin
mistracking of the magnetic order. We conclude that the new viscous term should
be important for the thermally induced domain wall motion. We study the
interplay between charge and energy currents and find that many of the effects
of texture motion on the charge currents can be replicated with respect to
energy currents. For example, the moving texture can lead to energy flows which
is an analogue of the electromotive force in case of charge currents. We
suggest a realization of cooling effect by magnetic texture dynamics.",0906.1002v2
2009-11-24,Origin of adiabatic and non-adiabatic spin transfer torques in current-driven magnetic domain wall motion,"A consistent theory to describe the correlated dynamics of quantum mechanical
itinerant spins and semiclassical local magnetization is given. We consider the
itinerant spins as quantum mechanical operators, whereas local moments are
considered within classical Lagrangian formalism. By appropriately treating
fluctuation space spanned by basis functions, including a zero-mode wave
function, we construct coupled equations of motion for the collective
coordinate of the center-of-mass motion and the localized zero-mode coordinate
perpendicular to the domain wall plane. By solving them, we demonstrate that
the correlated dynamics is understood through a hierarchy of two time scales:
Boltzmann relaxation time when a non-adiabatic part of the spin-transfer torque
appears, and Gilbert damping time when adiabatic part comes up.",0911.4628v1
2011-08-16,Magnetic rogue wave in a perpendicular anisotropic ferromagnetic nanowire with spin-transfer torque,"We present the current controlled motion of dynamic soliton embedded in spin
wave background in ferromagnetic nanowire. With the stronger breather character
we get the novel magnetic rogue wave and clarify its formation mechanism. The
generation of magnetic rogue wave is mainly arose from the accumulation of
energy and magnons toward to its central part. We also observe that the
spin-polarized current can control the exchange rate of magnons between
envelope soliton and background, and the critical current condition is obtained
analytically. Even more interesting is that the spin-transfer torque plays the
completely opposite role for the cases of below and above the critical value.",1108.3252v2
2012-10-29,Thermally-Assisted Spin-Transfer Torque Magnetization Reversal of Uniaxial Nanomagnets in Energy Space,"The asymptotic behavior of switching time as a function of current for a
uniaxial macrospin under the effects of both spin-torque and thermal noise is
explored analytically by focusing on its diffusive energy space dynamics. The
scaling dependence ($I\rightarrow 0$, $<\tau\propto\exp(-\xi(1-I)^2)$) is shown
to confirm recent literature results. The analysis shows the mean switching
time to be functionally independent of the angle between the spin current and
magnet's uniaxial axes. These results have important implications for modeling
the energetics of thermally assisted magnetization reversal of spin transfer
magnetic random access memory bit cells.",1210.7682v2
2015-08-19,Skyrmion dynamics in chiral ferromagnets under spin-transfer torque,"We study the dynamics of skyrmions under spin-transfer torque in
Dzyaloshinskii-Moriya materials with easy-axis anisotropy. In particular, we
study the motion of a topological skyrmion with skyrmion number $Q=1$ and a
non-topological skyrmionium with $Q=0$ using their linear momentum, virial
relations, and numerical simulations. The non-topological $Q=0$ skyrmionium is
accelerated in the direction of the current flow and it either reaches a steady
state with constant velocity, or it is elongated to infinity. The steady-state
velocity is given by a balance between current and dissipation and has an upper
limit. In contrast, the topological $Q=1$ skyrmion converges to a steady-state
with constant velocity at an angle to the current flow. When the spin current
stops the $Q=1$ skyrmion is spontaneously pinned whereas the $Q=0$ skyrmionium
continues propagation. Exact solutions for the propagating skyrmionium are
identified as solutions of equations given numerically in a previous work.
Further exact results for propagating skyrmions are given in the case of the
pure exchange model. The traveling solutions provide arguments that a
spin-polarized current will cause rigid motion of a skyrmion or a skyrmionium.",1508.04821v1
2014-06-23,Magnon-Driven Domain-Wall Motion with the Dzyaloshinskii-Moriya Interaction,"We study domain wall (DW) motion induced by spin waves (magnons) in the
presence of Dzyaloshinskii-Moriya interaction (DMI). The DMI exerts a torque on
the DW when spin waves pass through the DW, and this torque represents a linear
momentum exchange between the spin wave and the DW. Unlike angular momentum
exchange between the DW and spin waves, linear momentum exchange leads to a
rotation of the DW plane rather than a linear motion. In the presence of an
effective easy plane anisotropy, this DMI induced linear momentum transfer
mechanism is significantly more efficient than angular momentum transfer in
moving the DW.",1406.5997v2
2019-04-19,Sub-terahertz ferrimagnetic spin-transfer torque oscillator,"A theory of magnetization dynamics in ferrimagnetic materials with
antiparallel aligned spin sub-lattices under action of spin-transfer torques
(STT) is developed. We consider magnetization dynamics in GdFeCo layers in two
cases of magnetic anisotropy: easy plane and easy axis. We demonstrate that,
(i) for the easy plane anisotropy the precession of the N\'{e}el vector is
conical and the cone angle depends on the STT strength and the value of spin
non-compensation, while the frequency of precession can reach sub-THz
frequencies; (ii) for the easy axis anisotropy two regimes are possible:
deterministic switching of the net magnetization and a conical sub-THz
precession depending on the STT strength.",1904.09341v1
2020-01-02,Three-dimensional dynamics of magnetic hopfion driven by spin transfer torque,"Magnetic hopfion is three-dimensional (3D) topological soliton with novel
spin structure that would enable exotic dynamics. Here we study the current
driven 3D dynamics of a magnetic hopfion with unit Hopf index in a frustrated
magnet. Attributed to spin Berry phase and symmetry of the hopfion, the phase
space entangles multiple collective coordinates, thus the hopfion exhibits rich
dynamics including longitudinal motion along the current direction, transverse
motion perpendicular to the current direction, rotational motion and dilation.
Furthermore, the characteristics of hopfion dynamics is determined by the ratio
between the non-adiabatic spin transfer torque parameter and the damping
parameter. Such peculiar 3D dynamics of magnetic hopfion could shed light on
understanding the universal physics of hopfions in different systems and boost
the prosperous development of 3D spintronics.",2001.00417v1
2020-09-30,Switching induced by spin Hall effect in an in-plane magnetized ferromagnet with the easy axis parallel to the current,"Magnetization switching in a fine-structured ferromagnet of nanoscale by the
spin-transfer torque excited via the spin Hall effect has attracted much
attention because it enables us to manipulate the magnetization without
directly applying current to the ferromagnet. However, the switching mechanism
is still unclear in regard to the ferromagnet having an in-plane easy axis
parallel to the current. Here, we develop an analytical theory of the
magnetization switching in this type of ferromagnet, and reveal the threshold
current formulas for a deterministic switching. It is clarified that the
current should be in between a certain range determined by two threshold
currents because the spin-transfer torque due to a large current outside the
range brings the magnetization in an energetically unstable state, and causes
magnetization precession around the hard axis.",2010.00136v1
2023-08-18,Chiral spin-transfer torque induced by curvature gradient,"This work analyzes the propagation of a transverse domain wall (DW) motion
under the action of an electric current along a nanowire (NW) with a curvature
gradient. Our results evidence that the curvature gradient induces a chiral
spin-transfer torque (CSTT) whose effect on the DW motion depends on the
direction along which the DW points. The origin of the CSTT is explained in
terms of a position and phase-dependent effective field associated with the DW
profile and the electric current direction. Finally, our results reveal that
this chiral mechanism can also affect the behavior of other magnetization
collective modes, such as spin waves. This work shows the emergence of
curvature-induced chiral spin transport and highlights a new phenomenon to be
considered for designing spintronic devices.",2308.09276v1
2009-02-13,Distortion of the Stoner-Wohlfarth astroid by a spin-polarized current,"The Stoner-Wohlfarth astroid is a fundamental object in magnetism. It
separates regions of the magnetic field space with two stable magnetization
equilibria from those with only one stable equilibrium and it characterizes the
magnetization reversal of nano-magnets induced by applied magnetic fields. On
the other hand, it was recently demonstrated that transfer of spin angular
momentum from a spin-polarized current provides an alternative way of switching
the magnetization. Here, we examine the astroid of a nano-magnet with uniaxial
magnetic anisotropy under the combined influence of applied fields and
spin-transfer torques. We find that spin-transfer is most efficient at
modifying the astroid when the external field is applied along the easy-axis of
magnetization. On departing from this situation, a threshold current appears
below which spin-transfer becomes ineffective yielding a current-induced dip in
the astroid along the easy-axis direction. An extension of the Stoner-Wohlfarth
model is outlined which accounts for this phenomenon.",0902.2337v2
2010-11-12,"Magnetization Dynamics, Bennett Clocking and Associated Energy Dissipation in Multiferroic Logic","It has been recently shown that multiferroic logic - where logic bits are
encoded in the magnetization orientation of a nanoscale magnetostrictive layer
elastically coupled to a piezoelectric layer - can be Bennett clocked with
small electrostatic potentials of few tens of mV applied to the piezoelectric
layer. The potential generates stress in the magnetostrictive layer and rotates
its magnetization by a large angle to carry out Bennett clocking. This method
of clocking is far more energy-efficient than using spin transfer torque. In
order to assess if such a clocking scheme can be also reasonably fast, we have
studied the magnetization dynamics of a multiferroic logic array with nearest
neighbor dipole coupling using the Landau-Lifshitz-Gilbert (LLG) equation. We
find that switching delays of ~ 3 ns (clock rates of 0.33 GHz) can be achieved
with proper design provided we clock non-adiabatically and dissipate ~48,000 kT
(at room temperature) of energy per clock cycle per bit flip in the clocking
circuit. This dissipation far exceeds the energy barrier separating the two
logic states, which we assumed to be 32 kT to yield a bit error probability of
. Had we used spin transfer torque to switch with the same ~ 3 ns delay, the
energy dissipation would have been much larger (~ $6 \times 106$ kT). This
shows that spin transfer torque, widely used in magnetic random access memory,
is an inefficient way to switch a magnet, and multiferroic logic clocked with
voltage-induced stress is a superior nanomagnetic logic scheme.",1011.2914v2
2015-03-16,Dynamics of Current and Field Driven Domain Wall Motion under the Influence of Transverse Magnetic Field,"The dynamics of transverse Neel domain wall in a ferromagnetic nanostrip in
the presence of driving field, current and transverse magnetic field is
investigated by the Landau-Lifshitz-Gilbert(LLG) equation with the adiabatic
and non-adiabatic spin-transfer torques both analytically and numerically. The
analytical expressions for the velocity, width, excitation angle and
displacement for the domain wall are obtained by using small angle
approximation along with Walkers trial function. The results show that the
initial velocity of the domain wall can be controlled by the adiabatic
spin-transfer torque and the saturated velocity can be controlled by the
non-adiabatic spin-transfer torque and driving field. The large increase in the
saturated velocity of the domain wall driven by current and field due to the
transverse magnetic field is identified through the presence of driving field.
There is no impact in the saturated velocity of the domain wall driven by
current from the transverse magnetic field. For the domain wall driven by the
current in the presence of the transverse magnetic field, the saturated
velocity remains constant. The transverse magnetic field along with current and
driving field is more advantageous that the transverse magnetic field along
with current for increasing the saturated velocity of the domain wall. The
numerical results showed that the saturated velocity is increased by the
transverse magnetic field with the irrespective of the directions of the
driving field and current further it is higher and lower when the directions of
driving field and current are antiparallel and parallel respectively. The
obtained analytical solutions are closely coincided with the computed numerical
results.",1503.04560v2
2014-07-06,From Spin Torque Nano-Oscillators to Memristors: Multi-Functional Nanodevices for Advanced Computing,"This Habilitation Thesis written in 2013 reviews my research work on spin
torque nano-oscillators (from zero-field oscillations, to synchronization and
vortex oscillators) and memristive devices (spin Torque and ferroelectric
memristors).",1407.1494v1
2020-10-26,Spin Insulatronics,"Spin insulatronics covers efforts to generate, detect, control, and utilize
high-fidelity pure spin currents and excitations inside magnetic insulators.
Ultimately, the new findings may open doors for pure spin-based information and
communication technologies. The aim is to replace moving charges with dynamical
entities that utilize low-dissipation coherent and incoherent spin excitations
in antiferromagnetic and ferromagnetic insulators. The ambition is that the new
pure spin-based system will suffer reduced energy losses and operate at high
frequencies. In magnetic insulators, there are no mobile charge carriers that
can dissipate energy. Integration with conventional electronics is possible via
interface exchange interactions and spin-orbit couplings. In this way, the free
electrons in the metals couple to the localized spins in the magnetic
insulators. In turn, these links facilitate spin-transfer torques and
spin-orbit torques across metal-insulator interfaces and the associated
phenomena of spin-pumping and charge-pumping. The interface couplings also
connect the electron motion inside the metals with the spin fluctuations inside
the magnetic insulators. These features imply that the system can enable
unprecedented control of correlations resulting from the electron-magnon
interactions. We review recent developments to realize electric and thermal
generation, manipulation, detection, and control of pure spin information in
insulators.",2010.13512v1
2013-12-09,Spin-orbit torque opposing the Oersted torque in ultrathin Co/Pt bilayers,"Current-induced torques in ultrathin Co/Pt bilayers were investigated using
an electrically driven FMR technique. The angle dependence of the resonances,
detected by a rectification effect as a voltage, were analysed to determine the
symmetries and relative magnitudes of the spin-orbit torques. Both anti-damping
(Slonczewski) and field-like torques were observed. As the ferromagnet
thickness was reduced from 3 to 1 nm, the sign of the field-like torque
reversed. This observation is consistent with the emergence of a Rashba spin
orbit torque in ultra-thin bilayers.",1312.2409v1
2012-07-02,Experimental observation of the optical spin-orbit torque,"Spin polarized carriers electrically injected into a magnet from an external
polarizer can exert a spin transfer torque (STT) on the magnetization. The phe-
nomenon belongs to the area of spintronics research focusing on manipulating
magnetic moments by electric fields and is the basis of the emerging
technologies for scalable magnetoresistive random access memories. In our
previous work we have reported experimental observation of the optical
counterpart of STT in which a circularly polarized pump laser pulse acts as the
external polarizer, allowing to study and utilize the phenomenon on several
orders of magnitude shorter timescales than in the electric current induced
STT. Recently it has been theoretically proposed and experimentally
demonstrated that in the absence of an external polarizer, carriers in a magnet
under applied electric field can develop a non-equilibrium spin polarization
due to the relativistic spin-orbit coupling, resulting in a current induced
spin-orbit torque (SOT) acting on the magnetization. In this paper we report
the observation of the optical counterpart of SOT. At picosecond time-scales,
we detect excitations of magnetization of a ferromagnetic semiconductor
(Ga,Mn)As which are independent of the polarization of the pump laser pulses
and are induced by non-equilibrium spin-orbit coupled photo-holes.",1207.0307v1
2007-02-09,Magnetic vortex oscillator driven by dc spin-polarized current,"Transfer of angular momentum from a spin-polarized current to a ferromagnet
provides an efficient means to control the dynamics of nanomagnets. A peculiar
consequence of this spin-torque, the ability to induce persistent oscillations
of a nanomagnet by applying a dc current, has previously been reported only for
spatially uniform nanomagnets. Here we demonstrate that a quintessentially
nonuniform magnetic structure, a magnetic vortex, isolated within a nanoscale
spin valve structure, can be excited into persistent microwave-frequency
oscillations by a spin-polarized dc current. Comparison to micromagnetic
simulations leads to identification of the oscillations with a precession of
the vortex core. The oscillations, which can be obtained in essentially zero
magnetic field, exhibit linewidths that can be narrower than 300 kHz, making
these highly compact spin-torque vortex oscillator devices potential candidates
for microwave signal-processing applications, and a powerful new tool for
fundamental studies of vortex dynamics in magnetic nanostructures.",0702253v1
2012-08-08,Spin transfer torque devices utilizing the giant spin Hall effect of tungsten,"We report a giant spin Hall effect (SHE) in {\beta}-W thin films. Using spin
torque induced ferromagnetic resonance with a {\beta}-W/CoFeB bilayer
microstrip we determine the spin Hall angle to be |\theta|=0.30\pm0.02, large
enough for an in-plane current to efficiently reverse the orientation of an
in-plane magnetized CoFeB free layer of a nanoscale magnetic tunnel junction
adjacent to a thin {\beta}-W layer. From switching data obtained with such
3-terminal devices we independently determine |\theta|=0.33\pm0.06. We also
report variation of the spin Hall switching efficiency with W layers of
different resistivities and hence of variable ({\alpha} and {\beta}) phase
composition.",1208.1711v1
2018-03-07,Ultra-Fast Ferrimagnetic All Spin Logic Device,"All spin logic device (ASLD) blazes an alternative path for realizing
ultra-low power computing in the Post-Moore era. However, initial device
structure relying on ferromagnetic input/output and spin transfer torque (STT)
driven magnetization switching degrades its performance and even hinders its
realization. In this paper, we propose an ASLD based on rare-earth
(RE)-transition-metal (TM) ferromagnetic alloy that can achieve an ultra-high
frequency up to terahertz. The spin orbit torque (SOT) induced fast precession
near the spin angular momentum compensated point is investigated through the
macrospin model. Combining the non-local spin current diffusing from the input
to the output, a deterministic picosecond switching can be realized without any
external magnetic field. Our results show that ASLD has the potential to exceed
the performance of mainstream computing.",1803.02552v1
2023-11-20,Electrical control of magnetism by electric field and current-induced torques,"While early magnetic memory designs relied on magnetization switching by
locally generated magnetic fields, key insights in condensed matter physics
later suggested the possibility to do it electrically. In the 1990s,
Slonczewzki and Berger formulated the concept of current-induced spin torques
in magnetic multilayers through which a spin-polarized current may switch the
magnetization of a ferromagnet. This discovery drove the development of
spin-transfer-torque magnetic random-access memories (STT-MRAMs). More recent
research unveiled spin-orbit-torques (SOTs) and will lead to a new generation
of devices including SOT-MRAMs. Parallel to these advances, multiferroics and
their magnetoelectric coupling experienced a renaissance, leading to novel
device concepts for information and communication technology such as the MESO
transistor. The story of the electrical control of magnetization is that of a
dance between fundamental research (in spintronics, condensed matter physics,
and materials science) and technology (MRAMs, MESO, microwave emitters,
spin-diodes, skyrmion-based devices, components for neuromorphics, etc). This
pas de deux led to major breakthroughs over the last decades (pure spin
currents, magnetic skyrmions, spin-charge interconversion, etc). As a result,
this field has propelled MRAMs into consumer electronics products but also
fueled discoveries in adjacent research areas such as ferroelectrics or
magnonics. Here, we cover recent advances in the control of magnetism by
electric fields and by current-induced torques. We first review fundamental
concepts in these two directions, then discuss their combination, and finally
present various families of devices harnessing the electrical control of
magnetic properties for various application fields. We conclude by giving
perspectives in terms of both emerging fundamental physics concepts and new
directions in materials science.",2311.11724v1
2011-05-02,Design scheme of new multifunctional Heusler compounds for spin-transfer torque applications,This paper has been withdrawn.,1105.0337v2
2015-03-13,"Reply to Comment on ""Acoustically assisted spin-transfer-torque switching of nanomagnets: An energy-efficient hybrid writing scheme for non-volatile memory"" [Appl. Phys. Lett., 103, 232401 (2013)]","This is a reply to a comment on our work recently posted in arXiv. To our
knowledge, this comment has not been published anywhere else. We show that the
points raised in the comment are invalid",1503.04174v1
2009-03-03,Spin Transfer Torque in Domain Wall Structures by Keldysh Green Functions,"This paper has been withdrawn by the author due to a serious errors in the
calculations.",0903.0613v2
2015-08-30,Spin-transfer torque based damping control of parametrically excited spin waves in a magnetic insulator,"The damping of spin waves parametrically excited in the magnetic insulator
Yttrium Iron Garnet (YIG) is controlled by a dc current passed through an
adjacent normal-metal film. The experiment is performed on a macroscopically
sized YIG(100nm)/Pt(10nm) bilayer of 4x2 mm^2 lateral dimensions. The spin-wave
relaxation frequency is determined via the threshold of the parametric
instability measured by Brillouin light scattering (BLS) spectroscopy. The
application of a dc current to the Pt film leads to the formation of a
spin-polarized electron current normal to the film plane due to the spin Hall
effect (SHE). This spin current exerts a spin transfer torque (STT) in the YIG
film and, thus, changes the spin-wave damping. Depending on the polarity of the
applied dc current with respect to the magnetization direction, the damping can
be increased or decreased. The magnitude of its variation is proportional to
the applied current. A variation in the relaxation frequency of +/-7.5% is
achieved for an applied dc current density of 5*10^10 A/m^2.",1508.07517v1
2006-06-16,Spin transfer in an antiferromagnet,"An electrical current can transfer spin angular momentum to a ferromagnet.
This novel physical phenomenon, called spin transfer, offers unprecedented
spatial and temporal control over the magnetic state of a ferromagnet and has
tremendous potential in a broad range of technologies, including magnetic
memory and recording. Recently, it has been predicted that spin transfer is not
limited to ferromagnets, but can also occur in antiferromagnetic materials and
even be stronger under some conditions. In this paper we demonstrate transfer
of spin angular momentum across an interface between ferromagnetic and
antiferromagnetic metals. The spin transfer is mediated by an electrical
current of high density (~10^12 A/m^2) and revealed by variation in the
exchange bias at the ferromagnet/antiferromagnet interface. We find that,
depending on the polarity of the electrical current flowing across the
interface, the strength of the exchange bias can either increase or decrease.
This finding is explained by the theoretical prediction that a spin polarized
current generates a torque on magnetic moments in the antiferromagnet.
Current-mediated variation of exchange bias can be used to control the magnetic
state of spin-valve devices, e.g., in magnetic memory applications.",0606462v1
2015-02-12,Anti-damping spin transfer torque through epitaxial Nickel oxide,"We prepare the high quality epitaxial
MgO(001)[100]/Pt(001)[100]/NiO(001)[100]/FeNi/SiO2 films to investigate the
spin transport in the NiO antiferromagnetic insulator. The ferromagnetic
resonance measurements of the FeNi under a spin current injection from the Pt
by the spin Hall effect revealed the change of the ferromagnetic resonance
linewidth depending on the amount of the spin current injection. The results
can be interpreted that there is an angular momentum transfer through the NiO.
A high efficient angular momentum transfer we observed in the epitaxial NiO can
be attributed to the well-defined orientation of the antiferromagnetic moments
and the spin quantization axis of the injected spin current.",1502.03855v1
2023-07-27,Electrical coupling of superparamagnetic tunnel junctions mediated by spin-transfer-torques,"In this work, the effect of electrical coupling on stochastic switching of
two in-plane superparamagnetic tunnel junctions (SMTJs) is studied, using
experimental measurements as well as simulations. The coupling mechanism relies
on the spin-transfer-torque (STT) effect, which enables the manipulation of the
state probability of an SMTJ. Through the investigation of time-lagged
cross-correlation, the strength and direction of the coupling are determined.
In particular, the characteristic state probability transfer curve of each SMTJ
leads to the emergence of a similarity or dissimilarity effect. The
cross-correlation as a function of applied source voltage reveals that the
strongest coupling occurs for high positive voltages for our SMTJs. In
addition, we show state tuneability as well as coupling control by the applied
voltage. The experimental findings of the cross-correlation are in agreement
with our simulation results.",2307.15165v1
2021-06-21,Resonant Measurement of Non-Reorientable Spin-Orbit Torque from a Ferromagnetic Source Layer Accounting for Dynamic Spin Pumping,"Using a multilayer structure containing (cobalt detector layer)/(copper
spacer)/(Permalloy source layer), we show experimentally how the
non-reorientable spin-orbit torque generated by the Permalloy source layer (the
component of spin-orbit torque that does not change when the Permalloy
magnetization is rotated) can be measured using spin-torque ferromagnetic
resonance (ST-FMR) with lineshape analysis. We find that dynamic spin pumping
between the magnetic layers exerts torques on the magnetic layers as large or
larger than the spin-orbit torques, so that if dynamic spin pumping is
neglected the result would be a large overestimate of the spin-orbit torque.
Nevertheless, the two effects can be separated by performing ST-FMR as a
function of frequency. We measure a non-reorientable spin torque ratio
$\xi_{\text{Py}} = 0.04 \pm 0.01$ for spin current flow from Permalloy through
an 8 nm Cu spacer to the Co, and a strength of dynamic spin pumping that is
consistent with previous measurements by conventional ferromagnetic resonance.",2106.11127v1
2019-09-24,Spin-transfer dynamics in MgO-based magnetic tunnel junctions with an out-of-plane magnetized free layer and an in-plane polarizer,"Here, we present an analytical and numerical model describing the
magnetization dynamics in MgO-based spin-torque nano-oscillators with an
in-plane magnetized polarizer and an out-of-plane free layer. We introduce the
spin-transfer torque asymmetry by considering the cosine angular dependence of
the resistance between the two magnetic layers in the stack. For the analytical
solution, dynamics are determined by assuming a circular precession trajectory
around the direction perpendicular to the plane, as set by the effective field,
and calculating the energy integral over a single precession period. In a more
realistic approach, we include the bias dependence of the tunnel
magnetoresistance, which is assumed empirically to be a piecewise linear
function of the applied voltage. The dynamical states are found by solving the
stability condition for the Jacobian matrix for out-of-plane static states. We
find that the bias dependence of the tunnel magnetoresistance, which is an
inseparable effect in every tunnel junction, exhibits drastic impact on the
spin-torque nano-oscillator phase diagram, mainly by increasing the critical
current for dynamics and quenching the oscillations at high currents. The
results are in good agreement with our experimental data published elsewhere.",1909.10983v1
2018-11-23,All-Optical Generation and Tuning of Ultrafast Spin-Hall Current via Optical Vortices,"Spin Hall effect, one of the cornerstones in spintronics refers to the
emergence of an imbalance in the spin density transverse to a charge flow in a
sample under voltage bias. This study points to a novel way for an ultrafast
generation and tuning of a unidirectional nonlinear spin Hall current by means
of subpicosecond laser pulses of optical vortices. When interacting with
matter, the optical orbital angular momentum (OAM) carried by the vortex and
quantified by its topological charge is transferred to the charge carriers. The
residual spin-orbital coupling in the sample together with confinement effects
allow exploiting the absorbed optical OAM for spatio-temporally controlling the
spin channels. Both the non-linear spin Hall current and the dynamical spin
Hall angle increase for a higher optical topological charge. The reason is the
transfer of a higher amount of OAM and the enhancement of the effective
spin-orbit interaction strength. No bias voltage is needed. We demonstrate that
the spin Hall current can be all-optically generated in an open circuit
geometry for ring-structured samples. These results follow from a full-fledged
propagation of the spin-dependent quantum dynamics on a time-space grid coupled
to the phononic environment. The findings point to a versatile and controllable
tool for the ultrafast generation of spin accumulations with a variety of
applications such as a source for ultrafast spin transfer torque and charge and
spin current pulse emitter.",1811.09519v1
2007-09-18,Theory of current-driven magnetization dynamics in inhomogeneous ferromagnets,"We give a brief account of recent developments in the theoretical
understanding of the interaction between electric currents and inhomogeneous
ferromagnetic order parameters. We start by discussing the physical origin of
the spin torques responsible for this interaction and construct a
phenomenological description. We then consider the electric current-induced
ferromagnetic instability and domain-wall motion. Finally, we present a
microscopic justification of the phenomenological description of current-driven
magnetization dynamics, with particular emphasis on the dissipative terms, the
so-called Gilbert damping $\alpha$ and the $\beta$ component of the adiabatic
current-driven torque.",0709.2937v2
2011-07-25,Thermal Relaxation Rates of Magnetic Nanoparticles in the Presence of Magnetic Fields and Spin-Transfer Effects,"We have measured the relaxation time of a thermally unstable ferromagnetic
nanoparticle incorporated into a magnetic tunnel junction (MTJ) as a function
of applied magnetic field, voltage V (-0.38 V < V < +0.26 V), and temperatures
(283 K< T< 363 K) . By analyzing the results within the framework of a modified
N\'eel-Brown formalism we determine the effective attempt time of the
nanoparticle and also the bias dependences of the in-plane and out-of-plane
spin torques. There is a significant linear modification of the effective
temperature with voltage due to the in-plane torque and a significant
contribution of a ""field like"" torque that is quadratic with voltage. The
methods presented here do not require complicated models for device heating or
calibration procedures, but instead directly measure how temperature, field,
and voltage influence the energy landscape and thermal fluctuations of a
two-state system. These results should have significant implications for
designs of future nanometer-scale magnetic random access memory elements and
provide a straightforward methodology to determine these parameters in other
MTJ device structures.",1107.5007v1
2018-06-25,Two-terminal spin-orbit torque magnetoresistive random access memory,"Spin-transfer torque magnetoresistive random access memory (STT-MRAM) is an
attractive alternative to current random access memory technologies due to its
non-volatility, fast operation and high endurance. STT-MRAM does though have
limitations including the stochastic nature of the STT-switching and a high
critical switching current, which makes it unsuitable for ultrafast operation
at nanosecond and sub-nanosecond regimes. Spin-orbit torque (SOT) switching,
which relies on the torque generated by an in-plane current, has the potential
to overcome these limitations. However, SOT-MRAM cells studied so far use a
three-terminal structure in order to apply the in-plane current, which
increases the size of the cells. Here we report a two-terminal SOT-MRAM cell
based on a CoFeB/MgO magnetic tunnel junction pillar on an ultrathin and narrow
Ta underlayer. In this device, an in-plane and out-of-plane current are
simultaneously generated upon application of a voltage, and we demonstrate that
the switching mechanism is dominated by SOT. We also compare our device to a
STT-MRAM cell built with the same architecture and show that critical write
current in the SOT-MRAM cell is reduced by more than 70%.",1806.09713v2
2009-11-18,Spin-transfer torque on a single magnetic adatom,"We theoretically show how the spin orientation of a single magnetic adatom
can be controlled by spin polarized electrons in a scanning tunneling
microscope configuration. The underlying physical mechanism is spin assisted
inelastic tunneling. By changing the direction of the applied current, the
orientation of the magnetic adatom can be completely reversed on a time scale
that ranges from a few nanoseconds to microseconds, depending on bias and
temperature. The changes in the adatom magnetization direction are, in turn,
reflected in the tunneling conductance.",0911.3478v1
2011-06-13,Quantum Dynamics of a Nanomagnet driven by Spin-Polarized Current,"A quantum theory of magnetization dynamics of a nanomagnet as a sequence of
scatterings of each electron spin with the macrospin state of the magnetization
results in each encounter a probability distribution of the magnetization
recoil state associated with each outgoing state of the electron. The quantum
trajectory of the magnetization contains the average motion tending in the
large spin limit to the semi-classical results of spin transfer torque and the
fluctuations giving rise to a quantum magnetization noise and an additional
noise traceable to the current noise.",1106.2359v1
2016-02-22,Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators,"We investigate magnetization dynamics in a spin-Hall oscillator using a
direct current measurement as well as conventional microwave spectrum analysis.
When the current applies an anti-damping spin-transfer torque, we observe a
change in resistance which we ascribe to the excitation of incoherent exchange
magnons. A simple model is developed based on the reduction of the effective
saturation magnetization, quantitatively explaining the data. The observed
phenomena highlight the importance of exchange magnons on the operation of
spin-Hall oscillators.",1602.06710v1
2018-08-08,Quantum magnetization fluctuations via spin shot noise,"Recent measurements in current-driven spin valves demonstrate magnetization
fluctuations that deviate from semiclassical predictions. We posit that the
origin of this deviation is spin shot noise. On this basis, our theory predicts
that magnetization fluctuations asymmetrically increase in biased junctions
irrespective of the current direction. At low temperatures, the fluctuations
are proportional to the bias, but at different rates for opposite current
directions. Quantum effects control fluctuations even at higher temperatures.
Our results are in semiquantitative agreement with recent experiments and are
in contradiction to semiclassical theories of spin-transfer torque.",1808.02907v2
2002-10-04,Current-induced spin-wave excitations in a single ferromagnetic layer,"A new current induced spin-torque transfer effect has been observed in a
single ferromagnetic layer without resorting to multilayers. At a specific
current density of one polarity injected from a point contact, abrupt
resistance changes due to current-induced spin wave excitations have been
observed. The critical current at the onset of spin-wave excitations depends
linearly on the external field applied perpendicular to the layer. The observed
effect is due to current-driven heterogeneity in an otherwise uniform
ferromagnetic layer.",0210116v1
2005-04-06,Non-collinear single-electron spin-valve transistors,"We study interaction effects on transport through a small metallic cluster
connected to two ferromagnetic leads (a single-electron spin-valve transistor)
in the ""orthodox model"" for the Coulomb blockade. The non-local exchange
between the spin accumulation on the island and the ferromagnetic leads is
shown to affect the transport properties such as the electric current and
spin-transfer torque as a function of the magnetic configuration, gate voltage,
and applied magnetic field.",0504137v1
2006-06-07,Detection of current-induced spins by ferromagnetic contacts,"Detection of current-induced spin accumulation via ferromagnetic contacts is
discussed. Onsager's relations forbid that in a two-probe configuration spins
excited by currents in time-reversal symmetric systems can be detected by
switching the magnetization of a ferromangetic detector contact. Nevertheless,
current-induced spins can be transferred as a torque to a contact magnetization
and affect the charge currents in many-terminal configurations. We demonstrate
the general concepts by solving the microscopic transport equations for the
diffuse Rashba system with magnetic contacts.",0606193v2
2013-06-10,Spin Transfer of Quantum Information between Majorana Modes and a Resonator,"We show that resonant coupling and entanglement between a mechanical
resonator and majorana bound states can be achieved via spin currents in a 1D
quantum wire with strong spin-orbit interactions. The bound states induced by
vibrating and stationary magnets can hybridize thus resulting in spin-current
induced $4\pi$-periodic torque, as a function of the relative field angle,
acting on the resonator. We study the feasibility of detecting and manipulating
majorana bound states with the use of magnetic resonance force microscopy
techniques.",1306.2339v1
2014-10-15,Micromagnetic Study of Spin Transfer driven Vortex Dipole and Vortex Quadrupole Dynamics,"Vortices and antivortices are typical non uniform magnetization
configurations that can be achieved in spin-torque oscillators with in-plane
materials. Dynamics of a vortex-antivortex pair, namely vortex dipole, were
predicted and already observed. In this paper, we present a systematic
micromagnetic study on that kind of dynamics in different spin-valves where the
current is injected through a nano-aperture. Rotation and translation of vortex
dipoles and rotation of vortex quadrupoles are shown depending on the shape and
the size of the spin-valve. The origin of the different behaviors is explained
within a micromagnetic framework.",1410.3957v1
2015-04-29,Role of transparency of platinum-ferromagnet interface in determining intrinsic magnitude of spin Hall effect,"The spin Hall effect (SHE) converts charge current to pure spin currents in
orthogonal directions in materials that have significant spin-orbit
coupling.The efficiency of the conversion is described by the spin Hall Angle
(SHA). The SHA can most readily be inferred by using the generated spin
currents to excite or rotate the magnetization of ferromagnetic films or
nano-elements via spin-transfer torques.Some of the largest spin torque derived
spin Hall angles (ST-SHA) have been reported in platinum. Here we show, using
spin torque ferromagnetic resonance (ST-FMR) measurements, that the
transparency of the Pt-ferromagnet interface to the spin current plays a
central role in determining the magnitude of the ST-SHA. We measure a much
larger ST-SHA in Pt/cobalt (~0.11) compared to Pt/permalloy (~0.05) bilayers
when the interfaces are assumed to be completely transparent. Taking into
account the transparency of these interfaces, as derived from spin-mixing
conductances, we find that the intrinsic SHA in platinum has a much higher
value of 0.19 +- 0.04 as compared to the ST-SHA. The importance of the
interface transparency is further exemplified by the insertion of atomically
thin magnetic layers at the Pt/permalloy interface that we show strongly
modulates the magnitude of the ST-SHA.",1504.07929v1
2007-02-17,"Low Field, Current-Hysteretic Oscillations in Spin Transfer Nanocontacts","We have measured spin-transfer-driven, large amplitude, current hysteretic,
low frequency (< 500 MHz), narrowband oscillations in nanocontacts made to spin
valve structures. The oscillations occur in zero field, persist up to 5 mT for
in plane applied fields, and to beyond 400 mT for out of plane fields. Unlike
previous measurements, the oscillation frequency is well below that for
uniform-mode ferromagnetic resonance, is only a weak function of applied field,
and is highly anharmonic. The oscillations are hysteretic with applied dc
current, appearing at high currents but persisting to lower currents upon
decrease of the current. We suggest that these observations are consistent with
the dynamics of a nonuniform magnetic state in the vicinity of the contact
nucleated by both the spin transfer torque and dc current-generated Oersted
fields, with the dynamics driven by spin transfer. The electrical oscillation
amplitudes are large and narrowband, with the largest amplitudes on the order
of 1 mV and the narrowest linewidths below 1 MHz.",0702416v1
2023-12-13,"Current-induced near-field radiative energy, linear-momentum, and angular-momentum transfer","In this paper, we study the near-field radiative energy, linear-momentum, and
angular-momentum transfer from a current-biased graphene to nanoparticles. The
electric current through the graphene sheet induces nonequilibrium
fluctuations, causing energy and momentum transfer even in the absence of a
temperature difference. The inherent spin-momentum locking of graphene surface
plasmons leads to an in-plane torque perpendicular to the direction of the
electric current. In the presence of a temperature difference, the energy
transfer is greatly enhanced while the lateral force and torque remain within
the same order. Our work explores the potential of utilizing current-biased
graphene to manipulate nanoparticles.",2312.07954v3
2022-06-19,Enhancement of spin mixing conductance by $s$-$d$ orbital hybridization in heavy metals,"In a magnetic multilayer, the spin transfer between localized magnetization
dynamics and itinerant conduction spin arises from the interaction between a
normal metal and an adjacent ferromagnetic layer. The spin-mixing conductance
then governs the spin-transfer torques and spin pumping at the magnetic
interface. Theoretical description of spin-mixing conductance at the magnetic
interface often employs a single conduction-band model. However, there is
orbital hybridization between conduction $s$ electron and localized $d$
electron of the heavy transition metal, in which the single conduction-band
model is insufficient to describe the $s$-$d$ orbital hybridization. In this
work, using the generalized Anderson model, we estimate the spin-mixing
conductance that arises from the $s$-$d$ orbital hybridization. We find that
the orbital hybridization increases the magnitude of the spin-mixing
conductance.",2206.09347v2
2013-04-04,Dynamics of Antiferromagnets Driven by Spin Current,"When a spin-polarized current flows through a ferromagnetic (FM) metal,
angular momentum is transferred to the background magnetization via
spin-transfer torques. In antiferromagnetic (AFM) materials, however, the
corresponding problem is unsolved. We derive microscopically the dynamics of an
AFM system driven by spin current generated by an attached FM polarizer, and
find that the spin current exerts a driving force on the local staggered order
parameter. The mechanism does not rely on the conservation of spin angular
momentum, nor does it depend on the induced FM moments on top the AFM
background. Two examples are studied: (i) A domain wall is accelerated to a
terminal velocity by purely adiabatic effect where the Walker's break-down is
avoided; and (ii) Spin injection modifies the AFM resonance frequency, and spin
current injection triggers spin wave instability of local moments above a
threshold.",1304.1284v5
2022-01-31,Tuning spin-orbit torques across the phase transition in VO$_2$/NiFe heterostructure,"The emergence of spin-orbit torques as a promising approach to
energy-efficient magnetic switching has generated large interest in material
systems with easily and fully tunable spin-orbit torques. Here, current-induced
spin-orbit torques in VO$_2$/NiFe heterostructures were investigated using
spin-torque ferromagnetic resonance, where the VO$_2$ layer undergoes a
prominent insulator-metal transition. A roughly two-fold increase in the
Gilbert damping parameter, $\alpha$, with temperature was attributed to the
change in the VO$_2$/NiFe interface spin absorption across the VO$_2$ phase
transition. More remarkably, a large modulation ($\pm$100%) and a sign change
of the current-induced spin-orbit torque across the VO$_2$ phase transition
suggest two competing spin-orbit torque generating mechanisms. The bulk spin
Hall effect in metallic VO$_2$, corroborated by our first-principles
calculation of spin Hall conductivity, $\sigma_{SH} \approx 10^4
\frac{\hbar}{e} \Omega^{-1} m^{-1}$, is verified as the main source of the
spin-orbit torque in the metallic phase. The self-induced/anomalous torque in
NiFe, of the opposite sign and a similar magnitude to the bulk spin Hall effect
in metallic VO$_2$, could be the other competing mechanism that dominates as
temperature decreases. For applications, the strong tunability of the torque
strength and direction opens a new route to tailor spin-orbit torques of
materials which undergo phase transitions for new device functionalities.",2201.12984v1
2003-10-30,Magnetization reversal by injection and transfer of spin: experiments and theory,"Reversing the magnetization of a ferromagnet by spin transfer from a current,
rather than by applying a magnetic field, is the central idea of an extensive
current research. After a review of our experiments of current-induced
magnetization reversal in Co/Cu/Co trilayered pillars, we present the model we
have worked out for the calculation of the current-induced torque and the
interpretation of the experiments.",0310737v1
2006-02-04,Spin-transfer-driven ferromagnetic resonance of individual nanomagnets,"We demonstrate a technique that enables ferromagnetic resonance (FMR)
measurements of the normal modes for magnetic excitations in individual
nanoscale ferromagnets, smaller in volume by a factor of 1000 than can be
probed by other methods. The measured peak shapes indicate two regimes of
response: simple FMR and phase locking. Studies of the resonance frequencies,
amplitudes, and linewidths as a function of microwave power, DC current, and
magnetic field provide detailed new information about the exchange, damping,
and spin-transfer torques that govern the dynamics in magnetic nanostructures.",0602105v1
2011-06-08,Thermal spin-transfer in Fe-MgO-Fe tunnel junctions,"We compute thermal spin transfer torques (TST) in Fe-MgO-Fe tunnel junctions
using a first principles wave function-matching method. At room temperature,
the TST in a junction with 3 MgO monolayers amounts to 10^-7J/m^2/K, which is
estimated to cause magnetization reversal for temperature differences over the
barrier of the order of 10 K. The large TST can be explained by multiple
scattering between interface states through ultrathin barriers. The angular
dependence of the TST can be very skewed, possibly leading to thermally induced
high-frequency generation.",1106.1572v2
2011-12-12,Temperature dependence of microwave voltage emission associated to spin-transfer induced vortex oscillation in magnetic tunnel junction,"The temperature dependence of a vortex-based nano-oscillator induced by spin
transfer torque (STVO) in magnetic tunnel junctions (MTJ) is considered. We
obtain emitted signals with large output power and good signal coherence. Due
to the reduced non-linearities compared to the uniform magnetization case, we
first observe a linear decrease of linewidth with decreasing temperature.
However, this expected behavior no longer applies at lower temperature and a
bottom limit of the linewidth is measured.",1112.2643v1
2021-06-09,Maximizing Spin-Orbit Torque Generated by the Spin Hall Effect of Pt,"Efficient generation of spin-orbit torques (SOTs) is central for the exciting
field of spin-orbitronics. Platinum, the archetypal spin Hall material, has the
potential to be an outstanding provider for spin-orbit torques due to its giant
spin Hall conductivity, low resistivity, high stabilities, and the ability to
be compatible with CMOS circuits. However, pure clean-limit Pt with low
resistivity still provides a low damping-like spin-orbit torque efficiency,
which limits its practical applications. The efficiency of spin-orbit torque in
Pt-based magnetic heterostructures can be improved considerably by increasing
the spin Hall ratio of Pt and spin transmissivity of the interfaces. Here we
reviews recent advances in understanding the physics of spin current
generation, interfacial spin transport, and the metrology of spin-orbit
torques, and summarize progress towards the goal of Pt-based spin-orbit torque
memories and logic that are fast, efficient, reliable, scalable, and
non-volatile.",2106.04992v2
2019-07-17,Topical Review on Skyrmions and Hall Transport,"We review recent progresses towards an understanding of the Skyrmion Hall
transport in insulating as well as conducting materials. First, we consider a
theoretical breakthrough based on the quantum field theory Ward identity, a
first principle analysis, relying on symmetries and conservation laws. Broken
parity (inversion) symmetry plays a crucial role in Skyrmion Hall transport. In
addition to the well known thermal and electric Hall conductivities, our
analysis has led us to the discovery of a new and unforeseen physical quantity,
Hall viscosity - an anti-symmetric part of the viscosity tensor. We propose a
simple way to confirm the existence of Hall viscosity in the measurements of
Hall conductivity as a function of momentum. We provide various background
materials to assist the readers to understand the quantum field theory Ward
identity.
  In the second part, we review recent theoretical and experimental
advancements of the Skyrmion Hall effects and the topological (Magnon) Hall
effects for conducting (insulting) magnets. For this purpose, we consider two
enveloping themes: spin torque and thermo-electromagnetic effect. First, we
overview various spin torques, such as spin transfer torque, spin-orbit torque,
and spin Hall torque, and generalized Landau-Lifshitz-Gilbert equations and
Thiele equations using a phenomenological approach. Second, we consider
irreversible thermodynamics to survey possible thermo-electromagnetic effects,
such as Seebeck, Peltier and Thompson effects in the presence of the electric
currents, along with the Hall effects in the presence of a background magnetic
field. Recently developed spin Seebeck effects are also a significant part of
the survey. We also accommodate extensive background materials to make this
review self-contained. Finally, we revisit the Skyrmion Hall transport from the
Ward identity view point.",1907.07696v1
2012-07-21,Spin-torque efficiency enhanced by Rashba spin splitting in three dimensions,"We examine a spin torque induced by the Rashba spin-orbit coupling in three
dimensions within the Boltzmann transport theory. We analytically calculate the
spin torque and show how its behavior is related with the spin topology in the
Fermi surfaces by studying the Fermi-energy dependence of the spin torque.
Moreover we discuss the spin-torque efficiency which is the spin torque divided
by the applied electric current in association with the current-induced
magnetization reversal. It is found that high spin-torque efficiency is
achieved when the Fermi energy lies on only the lower band and there exists an
optimal value for the Rashba parameter, where the spin-torque efficiency
becomes maximum.",1207.5094v1
2008-12-13,Non-Adiabatic Spin Transfer Torque in Real Materials,"The motion of simple domain walls and of more complex magnetic textures in
the presence of a transport current is described by the
Landau-Lifshitz-Slonczewski (LLS) equations. Predictions of the LLS equations
depend sensitively on the ratio between the dimensionless material parameter
$\beta$ which characterizes non-adiabatic spin-transfer torques and the Gilbert
damping parameter $\alpha$. This ratio has been variously estimated to be close
to 0, close to 1, and large compared to 1. By identifying $\beta$ as the
influence of a transport current on $\alpha$, we derive a concise, explicit and
relatively simple expression which relates $\beta$ to the band structure and
Bloch state lifetimes of a magnetic metal. Using this expression we demonstrate
that intrinsic spin-orbit interactions lead to intra-band contributions to
$\beta$ which are often dominant and can be (i) estimated with some confidence
and (ii) interpreted using the ""breathing Fermi surface"" model.",0812.2570v1
2010-10-26,Off-centered immobile magnetic vortex under influence of spin-transfer torque,"Equilibrium magnetization distribution of the vortex state magnetic
nanoparticle is affected by the influence of the spin-transfer torque: an
off-center out--of--plane vortex appears in the case of the disk shape particle
and pure planar vortex in the case of asymmetric ring shape particle. The spin
current causes extra out-of-plane magnetization structures identical to well
known dip structures for the moving vortex. The shape of the dip structure
depends on the current strength and value of the off-center displacement and it
does not depend on the vortex polarity. The critical current depends on the
nanodot thickness.",1010.5446v2
2012-12-10,Microscopic derivation of Spin-transfer torques in ferromagnets,"Spin-transfer torque (STT) provides key mechanisms for current-induced
phenomena in ferromagnets. While it is widely accepted that STT involves both
adiabatic and non-adiabatic contributions, their underlying physics and range
of validity are quite controversial. By computing microscopically the response
of conduction electron spins to a time varying and spatially inhomogeneous
magnetic background, we derive the adiabatic and non-adiabatic STT in a unified
fashion. Our result confirms the macroscopic theory [Phys. Rev. Lett.
\textbf{93},~127204 (2004)] with all coefficients matched exactly. Our
derivation also reveals a benchmark on the validity of the result, which is
used to explain three recent measurements of the non-adiabatic STT in quite
different settings.",1212.1964v3
2014-09-22,Optical spin transfer torque driven domain wall motion in ferromagnetic semiconductor,"We demonstrate optical manipulation of the position of a domain wall in a
dilute magnetic semiconductor, GaMnAsP. Two main contributions are identified.
Firstly, photocarrier spin exerts a spin transfer torque on the magnetization
via the exchange interaction. The direction of the domain wall motion can be
controlled using the helicity of the laser. Secondly, the domain wall is
attracted to the hot-spot generated by the focused laser. Unlike magnetic field
driven domain wall depinning, these mechanisms directly drive domain wall
motion, providing an optical tweezer like ability to position and locally probe
domain walls.",1409.6223v2
2017-11-21,Coupling magneto-elastic Lagrangians to spin transfer torque sources,"The consequences of coupling magnetic and elastic degrees of freedom, where
spins and deformations are carried by point-like objects subject to local
interactions, are studied, theoretically and by detailed numerical simulations.
From the constrained Lagrangians we derive consistent equations of motion for
the coupled dynamical variables. In order to probe the dynamics of such a
system, we consider external perturbations, such as spin transfer torques for
the magnetic part, and homogeneous stresses for the elastic part, associated to
their corresponding damping. This approach is applied to the study of ultrafast
switching processes in anti-ferromagnetic systems, which have recently
attracted attention as candidates for anti-ferromagnetic spintronic devices.
Our strategy is then checked in simple, but instructive, situations. We carried
out numerical experiments to study, in particular, how the magnetostrictive
coupling and external stresses affect the nature of the switching processes in
a prototype anti-ferromagnetic material.",1711.08062v2
2020-04-01,"Spin-transfer torque-driven motion, deformation, and instabilities of magnetic skyrmions at high currents","In chiral magnets, localized topological magnetic whirls, magnetic skyrmions,
can be moved by spin polarized electric currents. Upon increasing the current
strength, with prospects for high-speed skyrmion motion for spintronics
applications in mind, isolated skyrmions deform away from their typical
circular shape. We analyze the influence of spin-transfer torques on the shape
of a single skyrmion, including its stability upon adiabatically increasing the
strength of the applied electric current. For rather compact skyrmions at
uniaxial anisotropies well above the critical anisotropy for domain wall
formation, we find for high current densities that the skyrmion assumes a
non-circular shape with a tail, reminiscent of a shooting star. For larger and
hence softer skyrmions close to the critical anisotropy, in turn, we observe a
critical current density above which skyrmions become unstable. We show that
above a second critical current density the shooting star solution can be
recovered also for these skyrmions.",2004.00450v2
2023-12-24,Domain-wall Magnetic-texture dependent Creep Motion driven by Spin-transfer Torques,"We explore the contributions of adiabatic and non-adiabatic spin-transfer
torques (STT) of a spin-polarized current to the thermally activated creep
motion of domain-walls in a thin (Ga,Mn)(As,P) film with perpendicular
anisotropy. For a domain-wall transverse to current, the non-adiabatic STT is
found to act as an external magnetic field. Close to the compensation between
these two terms, the adiabatic contribution is strongly enhanced. The
domain-wall velocity may be both increased or reduced by the adiabatic STT,
which we associate to variations of creep pinning energy barrier with
domain-wall magnetic texture. Far from compensation, the contribution of
adiabatic STT is negligible. Field and current driven domain-wall motion
present common universal behaviors described by the quenched Edwards Wilkinson
universality class.",2312.15512v1
2007-05-03,Effective attraction induced by repulsive interaction in a spin-transfer system,"In magnetic systems with dominating easy-plane anisotropy the magnetization
can be described by an effective one dimensional equation for the in-plane
angle. Re-deriving this equation in the presence of spin-transfer torques, we
obtain a description that allows for a more intuitive understanding of
spintronic devices' operation and can serve as a tool for finding new dynamic
regimes. A surprising prediction is obtained for a planar ``spin-flip
transistor'': an unstable equilibrium point can be stabilized by a current
induced torque that further repels the system from that point. Stabilization by
repulsion happens due to the presence of dissipative environment and requires a
Gilbert damping constant that is large enough to ensure overdamped dynamics at
zero current.",0705.0508v1
2017-06-02,Experimental investigation of the temperature-dependent magnon density and its influence on studies of spin-transfer-torque-driven systems,"We present the temperature dependence of the thermal magnon density in a thin
ferromagnetic layer. By employing Brillouin light scattering and varying the
temperature, an increase of the magnon density accompanied by a lowering of the
spin-wave frequency is observed with increasing temperature. The magnon density
follows the temperature according to the Bose-Einstein distribution function
which leads to an approximately linear dependency. In addition, the influence
of this effect in spin-transfer-torque-driven systems is presented. In
particular, the increase in the magnon density with temperature sets the limit
for a suppression of magnons in charge current-driven systems. Hence, the
maximum possible suppression of thermal magnons occurs at a finite current.",1706.00619v1
2017-01-09,Spin-Wave versus Joule Heating in Spin-Hall-Effect/Spin-Transfer-Torque Driven Cr/Heusler/Pt Waveguides,"We present a time-resolved study of the DC-current driven magnetization
dynamics in a microstructured Cr/Heusler/Pt waveguide by means of Brillouin
light scattering. A reduction of the effective spin-wave damping via the
spin-transfer-torque effect leads to a strong increase in the magnon density.
This is accompanied by a decrease of the spin-wave frequencies. By evaluating
the time scales of these effects, the origin of this frequency shift can be
identified. However, recently, we found that the experimental setup partially
influences the decay of the spin-wave intensity after the current pulse is
switched off. Thus, further investigations on the presented effect are needed
to allow for a more detailed analysis. For this reason, we need to withdraw the
manuscript at this point and might publish an updated version later.",1701.02094v2
2014-07-08,Comparison between thermal and current driven spin-transfer torque in nanopillar metallic spin valves,"We investigate the relation between thermal spin-transfer torque (TSTT) and
the spin-dependent Seebeck effect (SDSE), which produces a spin current when a
temperature gradient is applied across a metallic ferromagnet, in nanopillar
metallic spin valves. Comparing its angular dependence (aSDSE) with the angle
dependent magnetoresistance (aMR) measurements on the same device, we are able
to verify that a small spin heat accumulation builds up in our devices. From
the SDSE measurement and the observed current driven STT switching current of
0.8 mA in our spin valve devices, it was estimated that a temperature
difference of 230 K is needed to produce an equal amount of TSTT. Experiments
specifically focused on investigating TSTT show a response that is dominated by
overall heating of the magnetic layer. Comparing it to the current driven STT
experiments we estimate that only ~10% of the response is due to TSTT. This
leads us to conclude that switching dominated by TSTT requires a direct
coupling to a perfect heat sink to minimize the effect of overall heating.
Nevertheless the combined effect of heating, STT and TSTT could prove useful
for inducing magnetization switching when further investigated and optimized.",1407.2046v1
2016-09-20,Low-power Spin Valve Logic using Spin-transfer Torque with Automotion of Domain Walls,"A novel scheme for non-volatile digital computation is proposed using
spin-transfer torque (STT) and automotion of magnetic domain walls (DWs). The
basic computing element is composed of a lateral spin valve (SV) with two
ferromagnetic (FM) wires served as interconnects, where DW automotion is used
to propagate the information from one device to another. The non-reciprocity of
both device and interconnect is realized by sizing different contact areas at
the input and the output as well as enhancing the local damping mechanism. The
proposed logic is suitable for scaling due to a high energy barrier provided by
a long FM wire. Compared to the scheme based on non-local spin valves (NLSVs)
in the previous proposal, the devices can be operated at lower current density
due to utilizing all injected spins for local magnetization reversals, and thus
improve both energy efficiency and resistance to electromigration. This device
concept is justified by simulating a buffer, an inverter, and a 3-input
majority gate with comprehensive numerical simulations, including spin
transport through the FM/non-magnetic (NM) interfaces as well as the NM channel
and stochastic magnetization dynamics inside FM wires. In addition to digital
computing, the proposed framework can also be used as a transducer between DWs
and spin currents for higher wiring flexibility in the interconnect network.",1609.06281v1
2016-07-15,Optically induced spin-dependent diffusive transport in the presence of spin-orbit interaction for all-optical magnetization reversal,"We have considered the effect of different spin-orbit interaction mechanisms
on the process of demagnetization under the influence of short-pulse lasers.
All-optical magnetization reversal of perpendicularly magnetized thin films can
occur if there are sufficient strong spin-Hall, skew scattering, and Rashba
interactions. In the presence of spin-orbit interactions, the transient charge
currents provide the generation of transverse-spin currents and accumulations,
which eventually exert spin-transfer torque on the magnetization. By combining
the optically excited spin-dependent diffusive transport with the spin and
charge currents due to skew scattering, spin-Hall, inverse spin-Hall and Rashba
interactions, into a numerical model, we demonstrate a possibility of
ultra-fast all-optical magnetization reversal. This understanding provokes
intriguing, more in-depth experimental studies on the role of spin-orbit
interaction mechanisms in optimizing structures for all-optical magnetization
reversal.",1607.04432v1
2015-01-28,Spin Amplification by Controlled Symmetry Breaking for Spin-Based Logic,"Spin amplification is one of the most critical challenges for spintronics and
spin-based logic in order to achieve spintronic circuits with fan-out. We
propose a new concept for spin amplification that will allow a small spin
current in a non-magnetic spin channel to control the magnetization of an
attached ferromagnet. The key step is to bring the ferromagnet into an unstable
symmetric state (USS), so that a small spin transfer torque from a small spin
current can provide a magnetic bias to control the spontaneous symmetry
breaking and select the final magnetization direction of the ferromagnet. Two
proposed methods for achieving the USS configuration are voltage-controlled
Curie temperature (VC-TC) and voltage-controlled magnetic anisotropy (VC-MA).
We believe the development of new 2D magnetic materials with greater tunability
of VC-TC and VC-MA will be needed for practical applications. A successful
realization of spin amplification by controlled symmetry breaking will be
important for the implementation of existing spin-logic proposals (e.g. ""All
Spin Logic"") and could inspire alternative ideas for spintronic circuits and
devices.",1501.07125v2
2017-12-10,Effective gauge field theory of spintronics,"The aim of this paper is to present a comprehensive theory of spintronics
phenomena based on the concept of effective gauge field, the spin gauge field.
An effective gauge field generally arises when we change a basis to describe
system and describes low energy properties of the system. In the case of
ferromagnetic metals we consider, it arises from structures of localized spin
(magnetization) and couples to spin current of conduction electron. The first
half of the paper is devoted to quantum mechanical arguments and phenomenology.
We show that the spin gauge field has adiabatic and nonadiabatic (off-diagonal)
components, consisting an SU(2) gauge field. The adiabatic component gives rise
to spin Berry's phase, topological Hall effect and spin motive force, while
nonadiabatic components are essential for spin-transfer torque and spin pumping
effects by inducing nonequilibrium spin accumulation. In the latter part of the
paper, field theoretic approaches are described. Dynamics of localized spins in
the presence of applied spin-polarized current is studied in a microscopic
viewpoint, and current-driven domain wall motion is discussed. Recent
developments on interface spin-orbit interaction is also mentioned.",1712.03489v2
2018-01-25,Theory of high-resolution tunneling spin transport on a magnetic skyrmion,"Tunneling spin transport characteristics of a magnetic skyrmion are described
theoretically in magnetic scanning tunneling microscopy (STM). The
spin-polarized charge current in STM (SP-STM) and tunneling spin transport
vector quantities, the longitudinal spin current and the spin transfer torque,
are calculated in high spatial resolution within the same theoretical
framework. A connection between the conventional charge current SP-STM image
contrasts and the magnitudes of the spin transport vectors is demonstrated that
enables the estimation of tunneling spin transport properties based on
experimentally measured SP-STM images. A considerable tunability of the spin
transport vectors by the involved spin polarizations is also highlighted. These
possibilities and the combined theory of tunneling charge and vector spin
transport pave the way for gaining deep insight into electric-current-induced
tunneling spin transport properties in SP-STM and to the related dynamics of
complex magnetic textures at surfaces.",1801.08375v2
2012-10-09,On the connection between accreting X-ray and radio millisecond pulsars,"For many years it has been recognized that the terminal stages of mass
transfer in a low-mass X-ray binary (LMXB) should cause the magnetosphere of
the accreting neutron star to expand, leading to a braking torque acting on the
spinning pulsar. After the discovery of radio millisecond pulsars (MSPs) it was
therefore somewhat a paradox (e.g. Ruderman et al. 1989) how these pulsars
could retain their fast spins following the Roche-lobe decoupling phase, RLDP.
Here I present a solution to this so-called ""turn-off problem"" which was
recently found by combining binary stellar evolution models with torque
computations (Tauris 2012). The solution is that during the RLDP the spin
equilibrium of the pulsar is broken and therefore it remains a fast spinning
object. I briefly discuss these findings in view of the two observed spin
distributions in the populations of accreting X-ray millisecond pulsars
(AXMSPs) and radio MSPs.",1210.2598v1
2014-02-23,Light-induced spin polarizations in quantum rings,"Non-resonant circularly polarized electromagnetic radiation can exert torques
on magnetization by the Inverse Faraday Effect (IFE). Here we discuss the
enhancement of IFE by spin-orbit interactions (SOI). We illustrate the
principle by studying a simple generic model system, i.e. the quasi-1D ring in
the presence of linear/cubic Rashba and Dresselhaus interactions. We combine
the classical IFE in electron plasmas that is known to cause persistent
currents in the plane perpendicular to the direction of the propagation of
light with the concept of current and spin-orbit-induced spin transfer torques.
We calculate light-induced spin polarization that in ferromagnets might give
rise to magnetization switching.",1402.5590v1
2015-09-29,Field-free magnetization reversal by spin-Hall effect and exchange bias,"Magnetic random-access memory (MRAM) driven by spin-transfer torque (STT) is
a major contender for future memory applications. The energy dissipation
involved in writing remains problematic, even with the advent of more efficient
perpendicular magnetic anisotropy (PMA) devices. A promising alternative
switching mechanism employs spin-orbit torques and the spin-Hall effect (SHE)
in particular, but additional symmetry breaking is required to achieve
deterministic switching in PMA devices. Currently used methods rely on in-plane
magnetic fields or anisotropy gradients, which are not suitable for practical
applications. Here, we interface the magnetic layer with an anti-ferromagnetic
material. An in-plane exchange bias (EB) is created, and shown to enable
field-free SHE-driven magnetization reversal of a perpendicularly magnetized
Pt/Co/IrMn structure. Aside from the potential technological implications, our
experiment provides additional insight into the local spin structure at the
ferromagnetic/anti-ferromagnetic interface.",1509.08752v2
2018-07-19,Anomalous direction for skyrmion bubble motion,"Magnetic skyrmions are localized topological excitations that behave as
particles and can be mobile, with great potential for novel data storage
devices. In this work, the current-induced dynamics of large skyrmion bubbles
is studied. When skyrmion motion in the direction opposite to the electron flow
is observed, this is usually interpreted as a perpendicular spin current
generated by the spin Hall effect exerting a torque on the chiral N\'{e}el
skyrmion. By designing samples in which the direction of the net generated spin
current can be carefully controlled, we surprisingly show that skyrmion motion
is always against the electron flow, irrespective of the net vertical
spin-current direction. We find that a negative bulk spin-transfer torque is
the most plausible explanation for the observed results, which is qualitatively
justified by a simple model that captures the essential behaviour. These
findings demonstrate that claims about the skyrmion chirality based on their
current-induced motion should be taken with great caution.",1807.07365v1
2019-04-15,Spin-Orbit-Torque Driven Propagating Spin Waves,"Spin-orbit torque (SOT) can drive sustained spin wave (SW) auto-oscillations
in a class of emerging microwave devices known as spin Hall nano-oscillators
(SHNOs), which have highly non-linear properties governing robust mutual
synchronization at frequencies directly amenable to high-speed neuromorphic
computing. However, all demonstrations have relied on localized SW modes
interacting through dipolar coupling and/or direct exchange. As nanomagnonics
requires propagating SWs for data transfer, and additional computational
functionality can be achieved using SW interference, SOT driven propagating SWs
would be highly advantageous. Here, we demonstrate how perpendicular magnetic
anisotropy can raise the frequency of SOT driven auto-oscillations in magnetic
nano-constrictions well above the SW gap, resulting in the efficient generation
of field and current tunable propagating SWs. Our demonstration greatly extends
the functionality and design freedom of SHNOs enabling long range SOT driven SW
propagation for nanomagnonics, SW logic, and neuro-morphic computing, directly
compatible with CMOS technology.",1904.06945v1
2019-12-15,Erase-hidden and Drivability-improved Magnetic Non-Volatile Flip-Flops with NAND-SPIN Devices,"Non-volatile flip-flops (NVFFs) using power gating techniques promise to
overcome the soaring leakage power consumption issue with the scaling of CMOS
technology. Magnetic tunnel junction (MTJ) is a good candidate for constructing
the NVFF thanks to its low power, high speed, good CMOS compatibility, etc. In
this paper, we propose a novel magnetic NVFF based on an emerging memory device
called NAND-SPIN. The data writing of NAND-SPIN is achieved by successively
applying two unidirectional currents, which respectively generate the spin
orbit torque (SOT) and spin transfer torque (STT) for erase and programming
operations. This characteristic allows us to design an erase-hidden and
drivability-improved magnetic NVFF. Furthermore, more design flexibility could
be obtained since the backup operation of the proposed NVFF is not limited by
the inherent slave latch. Simulation results show that our proposed NVFF
achieves performance improvement in terms of power, delay and area, compared
with conventional slave-latch-driven SOT-NVFF designs.",1912.06986v2
2022-10-13,Electron-mediated entanglement of two distant macroscopic ferromagnets within a nonequilibrium spintronic device,"Using the nascent concept of quantum spin-transfer torque [A. Zholud et al.,
Phys. Rev. Lett. {\bf 119}, 257201 (2017); M. D. Petrovi\'{c} {\em et al.},
Phys. Rev. X {\bf 11}, 021062 (2021)], we demonstrate that a current pulse can
be harnessed to entangle quantum localized spins of two spatially separated
ferromagnets (FMs) which are initially unentangled. The envisaged setup
comprises a spin-polarizer (FM$_p$) and a spin-analyzer (FM$_a$) FM layers
separated by normal metal (NM) spacer. The injection of a current pulse into
the device leads to a time-dependent superposition of many-body states
characterized by a high degree of entanglement between the spin degrees of
freedom of the two distant FM layers. The non-equilibrium dynamics are due to
the transfer of spin angular momentum from itinerant electrons to the localized
spins via a quantum spin-torque mechanism that remains active even for {\em
collinear but antiparallel} arrangements of the FM$_p$ and FM$_a$
magnetizations (a situation in which the conventional spin-torque is absent).
We quantify the mixed-state entanglement generated between the FM layers by
tracking the time-evolution of the full density matrix and analyzing the
build-up of the mutual logarithmic negativity over time. The effect of
decoherence and dissipation in the FM layers due to coupling to bosonic baths
at finite temperature, the use of multi-electron current pulses and the
dependence on the number of spins are also considered in an effort to ascertain
the robustness of our predictions under realistic conditions. Finally, we
propose a ``current-pump/X-ray-probe'' scheme, utilizing ultrafast X-ray
spectroscopy, that can witness nonequilibrium and transient entanglement of the
FM layers by extracting its time-dependent quantum Fisher information.",2210.06634v2
2021-10-28,On the torque reversals of 4U 1626--67,"We have investigated the detailed torque-reversal behavior of 4U 1626--67 in
the framework of the recently developed comprehensive model of the inner disk
radius and torque calculations for neutron stars accreting from geometrically
thin disks. The model can reproduce the torque -- X-ray luminosity relation
across the torque reversals of 4U 1626--67. Our results imply that: (1)
rotational equilibrium is reached when the inner disk radius equals the
co-rotation radius, $r_\mathrm{co}$, while the conventional Alfven radius is
greater than and close to $r_\mathrm{co}$, (2) both spin-up and spin-down
torques are operating on either side of torque reversal, (3) with increasing
accretion rate the spin-up torque associated with accretion onto the star
gradually dominates the spin-down torque exerted by the disk. The torque
reversals are the natural outcome of transitions between the well-defined
weak-propeller and spin-up phases of the star with a stable geometrically thin
accretion disk.",2110.15392v1
2022-06-21,Spin transfer from dark matter to gas during halo formation,"In the protogalactic density field, diffuse gas and collision-less cold dark
matter (DM) are often assumed sufficiently mixed that both components
experience identical tidal torques. However, haloes in cosmological simulations
consistently end up with a higher specific angular momentum (sAM) in gas, even
in simulations without radiative cooling and galaxy formation physics. We
refine this result by analysing the spin distributions of gas and DM in
$\sim$50,000 well-resolved haloes in a non-radiative cosmological simulation
from the SURFS suite. The sAM of the halo gas on average ends up $\sim$40\%
above that of the DM. This can be pinned down to an excess AM in the inner halo
($<$50\% virial radius), paralleled by a more coherent rotation pattern in the
gas. We uncover the leading driver for this AM difference through a series of
control simulations of a collapsing ellipsoidal top-hat, where gas and DM are
initially well mixed. These runs reveal that the pressurised inner gas shells
collapse more slowly, causing the DM ellipsoid to spin ahead of the gas
ellipsoid. The arising torque generally transfers AM from the DM to the gas.
The amount of AM transferred via this mode depends on the initial spin, the
initial axes ratios and the collapse factor. These quantities can be combined
in a single dimensionless parameter, which robustly predicts the AM transfer of
the ellipsoidal collapse. This simplistic model can quantitatively explain the
average AM excess of the gas found in the more complex non-radiative
cosmological simulation.",2206.10079v1
2016-09-22,Magnetization oscillations and waves driven by pure spin currents,"Recent advances in the studies of pure spin currents - flows of angular
momentum (spin) not accompanied by the electric currents - have opened new
horizons for the emerging technologies based on the electron's spin degree of
freedom, such as spintronics and magnonics. The main advantage of pure spin
current, as compared to the spin-polarized electric current, is the possibility
to exert spin transfer torque on the magnetization in thin magnetic films
without electrical current flow through the material. In addition to minimizing
Joule heating and electromigration effects, this characteristic enables the
implementation of spin torque devices based on the low-loss insulating magnetic
materials, and offers an unprecedented geometric flexibility. Here we review
the recent experimental achievements in investigations of magnetization
oscillations excited by pure spin currents in different magnetic nanosystems
based on metallic and insulating magnetic materials. We discuss the spectral
properties of spin-current nano-oscillators, and relate them to the spatial
characteristics of the excited dynamic magnetic modes determined by the
spatially-resolved measurements. We also show that these systems support
locking of the oscillations to external microwave signals, as well as their
mutual synchronization, and can be used as efficient nanoscale sources of
propagating spin waves.",1609.06899v1
2015-09-27,Valley-dependent spin-orbit torques in two dimensional hexagonal crystals,"We study spin-orbit torques in two dimensional hexagonal crystals such as
graphene, silicene, germanene and stanene. The torque possesses two components,
a field-like term due to inverse spin galvanic effect and an antidamping torque
originating from Berry curvature in mixed spin-$k$ space. In the presence of
staggered potential and exchange field, the valley degeneracy can be lifted and
we obtain a valley-dependent Berry curvature, leading to a tunable antidamping
torque by controlling the valley degree of freedom. The valley imbalance can be
as high as 100\% by tuning the bias voltage or magnetization angle. These
findings open new venues for the development of current-driven spin-orbit
torques by structural design.",1509.08060v1
2010-04-26,Spin transfer in a ferromagnet-quantum dot and tunnel barrier coupled Aharonov-Bohm ring system with Rashba spin-orbit interactions,"The spin transfer effect in ferromagnet-quantum dot (insulator)-ferromagnet
Aharonov-Bohm (AB) ring system with Rashba spin-orbit (SO) interactions is
investigated by means of Keldysh nonequilibrium Green function method. It is
found that both the magnitude and direction of the spin transfer torque (STT)
acting on the right ferromagnet electrode can be effectively controlled by
changing the magnetic flux threading the AB ring or the gate voltage on the
quantum dot. The STT can be greatly augmented by matching a proper magnetic
flux and an SO interaction at a cost of low electrical current. The STT,
electrical current, and spin current are uncovered to oscillate with the
magnetic flux. The present results are expected to be useful for information
storage in nanospintronics.",1004.4507v1
2011-02-10,Vertical current induced domain wall motion in MgO-based magnetic tunnel junction with low current densities,"Shifting electrically a magnetic domain wall (DW) by the spin transfer
mechanism is one of the future ways foreseen for the switching of spintronic
memories or registers. The classical geometries where the current is injected
in the plane of the magnetic layers suffer from a poor efficiency of the
intrinsic torques acting on the DWs. A way to circumvent this problem is to use
vertical current injection. In that case, theoretical calculations attribute
the microscopic origin of DW displacements to the out-of-plane (field-like)
spin transfer torque. Here we report experiments in which we controllably
displace a DW in the planar electrode of a magnetic tunnel junction by vertical
current injection. Our measurements confirm the major role of the out-of-plane
spin torque for DW motion, and allow to quantify this term precisely. The
involved current densities are about 100 times smaller than the one commonly
observed with in-plane currents. Step by step resistance switching of the
magnetic tunnel junction opens a new way for the realization of spintronic
memristive devices.",1102.2106v1
2014-12-08,Voltage Controlled Magnetic Anisotropy Based Low Energy Switching of a Ferromagnet on a Topological Insulator,"We present a novel memory device that consists of a thin ferromagnetic layer
of Fe deposited on topological insulator thin film, Bi2Se3. The ferromagnetic
layer has perpendicular anisotropy, due to MgO deposited on the top surface of
Fe. When current is passed on the surface of Bi2Se3, the surface of the Bi2Se3
becomes spin polarized and strong exchange interaction occurs between the d
electrons in the ferromagnet and the electrons conducting the current on the
surface of the Bi2Se3. Part of the current is shunted through the ferromagnet
which generates spin transfer torque in the ferromagnet. The combination of the
spin transfer torque and exchange interaction torque along with
voltage-controlled magnetic anisotropy (VCMA) allows ultralow-energy switching
of the ferromagnet. We perform micromagnetic simulations and predict switching
time of the order of 2.5 ns and switching energy of the order of 0.45fJ for a
ferromagnetic bit with thermal stability of 43kBT. Such ultralow-energy and
high-speed VCMA-induced switching of a perpendicular anisotropy ferromagnet on
a topological insulator could be utilized for energy-efficient memory design.",1412.2434v3
2015-11-11,Magnetization switching by current and microwaves,"We propose a theoretical model of magnetization switching in a ferromagnetic
multilayer by both electric current and microwaves. The electric current gives
a spin transfer torque on the magnetization, while the microwaves induce a
precession of the magnetization around the initial state. Based on numerical
simulation of the Landau-Lifshitz-Gilbert (LLG) equation, it is found that the
switching current is significantly reduced compared with the switching caused
solely by the spin transfer torque when the microwave frequency is in a certain
range. We develop a theory of switching from the LLG equation averaged over a
constant energy curve. It was found that the switching current should be
classified into four regions, depending on the values of the microwave
frequency. Based on the analysis, we derive an analytical formula of the
optimized frequency minimizing the switching current, which is smaller than the
ferromagnetic resonance frequency. We also derive an analytical formula of the
minimized switching current. Both the optimized frequency and the minimized
switching current decrease with increasing the amplitude of the microwave
field. The results will be useful to achieve high thermal stability and low
switching current in spin torque systems simultaneously.",1511.03366v2
2016-01-27,Asymmetric angular dependence of spin-transfer torques in CoFe/Mg-B-O/CoFe magnetic tunnel junctions,"Using a first-principles noncollinear wave-function-matching method, we
studied the spin-transfer torques (STTs) in CoFe/Mg-B-O/CoFe(001) magnetic
tunnel junctions (MTJs), where three different types of B-doped MgO in the
spacer are considered, including B atoms replacing Mg atoms (Mg$_3$BO$_4$), B
atoms replacing O atoms (Mg$_4$BO$_3$), and B atoms occupying interstitial
positions (Mg$_4$BO$_4$) in MgO. A strong asymmetric angular dependence of STT
can be obtained both in ballistic CoFe/Mg$_3$BO$_4$ and CoFe/Mg$_4$BO$_4$ based
MTJs, whereas a nearly symmetric STT curve is observed in the junctions based
on CoFe/Mg$_4$BO$_3$. Furthermore, the asymmetry of the angular dependence of
STT can be suppressed significantly by the disorder of B distribution. Such
skewness of STTs in the CoFe/Mg-B-O/CoFe MTJs could be attributed to the
interfacial resonance states induced by the B diffusion into MgO spacer. The
present investigation demonstrates the feasibility of effectively enhancing
microwave output power in MgO based spin torque oscillator (STO) by doping the
B atoms into MgO spacer.",1601.07286v2
2019-12-21,Bipolar electric field switching of perpendicular magnetic tunnel junctions through voltage controlled exchange coupling,"Perpendicular magnetic tunnel junctions (p-MTJs) switched utilizing bipolar
electric fields have extensive applications in energy-efficient memory and
logic devices. Voltage-controlled magnetic anisotropy linearly lowers the
energy barrier of ferromagnetic layer via electric field effect and efficiently
switches p-MTJs only with a unipolar behavior. Here we demonstrate a bipolar
electric field effect switching of 100-nm p-MTJs with a synthetic
antiferromagnetic free layer through voltage-controlled exchange coupling
(VCEC). The switching current density, ~1.1x10^5 A/cm^2, is one order of
magnitude lower than that of the best-reported spin-transfer torque devices.
Theoretical results suggest that electric field induces a
ferromagnetic-antiferromagnetic exchange coupling transition of the synthetic
antiferromagnetic free layer and generates a field-like interlayer exchange
coupling torque, which cause the bidirectional magnetization switching of
p-MTJs. A preliminary benchmarking simulation estimates that VCEC dissipates an
order of magnitude lower writing energy compared to spin-transfer torque at the
15-nm technology node. These results could eliminate the major obstacle in the
development of spin memory devices beyond their embedded applications.",1912.10289v2
2020-10-05,Terrestrial Orbit-Spin Coupling Torque Episodes in Late 2020,"Orbit-spin coupling torques on the Earth in November 2020 are larger than at
any other time between 2000 and 2050. This affords an opportunity to observe
the terrestrial atmospheric response to the putative torque in near real time.",2010.02289v1
2015-03-13,Comparison of spin-orbit torques and spin pumping across NiFe/Pt and NiFe/Cu/Pt interfaces,"We experimentally investigate spin-orbit torques and spin pumping in NiFe/Pt
bilayers with direct and interrupted interfaces. The damping-like and
field-like torques are simultaneously measured with spin-torque ferromagnetic
resonance tuned by a dc bias current, whereas spin pumping is measured
electrically through the inverse spin Hall effect using a microwave cavity.
Insertion of an atomically thin Cu dusting layer at the interface reduces the
damping-like torque, field-like torque, and spin pumping by nearly the same
factor of ~1.4. This finding confirms that the observed spin-orbit torques
predominantly arise from diffusive transport of spin current generated by the
spin Hall effect. We also find that spin-current scattering at the NiFe/Pt
interface contributes to additional enhancement in magnetization damping that
is distinct from spin pumping.",1503.04104v3
2015-07-22,Theory of spin Hall magnetoresistance (SMR) and related phenomena,"We review the recently discovered spin Hall magnetoresistance (SMR) and
related effects from a theoretical point of view. The SMR is observed in
bilayers of a magnetic insulator and a metal, in which spin currents
aregenerated in the normal metal due to the spin Hall effect. The associated
angular momentum transfer to the ferromagnetic layer and thereby the electrical
resistance is modulated by the angle between the applied current and the
magnetization direction. The SMR provides a convenient tool to non-invasively
measure the magnetization direction and spin-transfer torque to an insulator.
We introduce the minimal theoretical instruments to calculate the SMR, i.e.
spin diffusion theory and quantum mechanical boundary conditions. This leads to
a small set of parameters that can be fitted to experiments. We discuss the
limitations of the theory as well as alternative mechanisms such as the
ferromagnetic proximity effect and Rashba spin-orbit torques, and point out new
developments related to the SMR.",1507.06054v2
2023-03-15,Efficient domain wall motion driven by the out-of-plane spin polarization,"Fast domain wall motion in systems with perpendicular magnetization is
necessary for many novel applications such as the racetrack memory, domain wall
logic devices and artificial synapses. The domain wall speed has been greatly
improved after the demonstration of current driven domain wall motion using the
spin transfer torque, and later achieved another leap due to the combined
effect of spin-Hall effect and Dzyaloshinskii-Moriya interaction (DMI).
However, only Neel wall can be effectively driven in the latter system. In this
paper, we show that both Bloch and Neel domain walls can be effectively moved
by exploiting the field-like torque with the out-of-plane spin polarization,
which can be generated in materials with reduced symmetry. In addition, we find
that the Neel wall and Bloch walls stabilized by the magnetostatic energy are
easily distorted by the spin-orbit torque and they then enter the Walker
breakdown region. External magnetic field and DMI are introduced to stabilize
the domain wall, and a very high domain wall velocity over 500 m/s is obtained
at a moderate current density of $2\times 10^{11} A/m^2$. In principle, this
mechanism can be used to drive any types of domain walls. This work thus
provides new degrees of freedom in the control of domain wall motion.",2303.08378v1
2015-07-31,Topological spin transport by Brownian diffusion of domain walls,"We propose thermally-populated domain walls (DWs) in an easy-plane
ferromagnetic insulator as robust spin carriers between two metals. The
chirality of a DW, which serves as a topological charge, couples to the metal
spin accumulation via spin-transfer torque and results in the
chirality-dependent thermal nucleation rates of DWs at the interface. After
overpopulated DWs of a particular (net) chirality diffuse and leave the
ferromagnet at the other interface, they reemit the spin current by spin
pumping. The conservation of the topological charge supports an algebraic decay
of spin transport as the length of the ferromagnet increases; this is analogous
to the decaying behavior of superfluid spin transport but contrasts with the
exponential decay of magnon spin transport. We envision that similar spin
transport with algebraic decay may be implemented in materials with exotic spin
phases by exploiting topological characteristics and the associated conserved
quantities of their excitations.",1507.08767v2
2019-09-11,Determining key spin-orbitronic parameters by means of propagating spin waves,"We characterize spin wave propagation and its modification by an electrical
current in Permalloy(Py)/Pt bilayers with Py thickness between 4 and 20 nm.
First, we analyze the frequency non-reciprocity of surface spin waves and
extract from it the interfacial Dzyaloshinskii-Moriya interaction constant
$D_s$ accounting for an additional contribution due to asymmetric surface
anisotropies. Second, we measure the spin-wave relaxation rate and deduce from
it the Py/Pt spin mixing conductance $g^{\uparrow\downarrow}_{eff}$. Last,
applying a \textit{dc} electrical current, we extract the spin Hall
conductivity $\sigma_{SH}$ from the change of spin wave relaxation rate due to
the spin-Hall spin transfer torque. We obtain a consistent picture of the spin
wave propagation data for different film thicknesses using a single set of
parameters $D_s=0.25$ pJ/m, $g^{\uparrow\downarrow}_{eff} = 3.2\times 10^{19}$
m$^{-2}$ and $\sigma_{SH}=4\times10^{5}$ S/m.",1909.04935v1
2022-10-05,Torque reversals and wind variations of X-ray pulsar Vela X-1,"The erratic spin history of Vela X-1 shows some continuous spin-up/spin-down
trend over tens of days. We study the orbital profile and spectral property of
Vela X-1 in these spin-up/spin-down intervals, using the spin history monitored
by Fermi/GBM and light curve from Swift/BAT and MAXI/GSC. The BAT fluxes in the
spin-up intervals are about 1.6 times those of the spin-down intervals for
out-of-eclipse orbital phases. The spin-up intervals also show a higher column
density than the spin-down intervals, indicating there are more material on the
orbital scale for the spin-up intervals. It could be due to the variation of
the stellar wind of the optical star (HD 77581) on tens of days. The varying
wind could lead to alternating prograde/retrograde accreting flow to the
neutron star, which dominates the transfer of the angular momentum to Vela X-1,
but not the total observed luminosity.",2210.02032v1
2020-08-06,Paramagnetic spin Hall magnetoresistance,"Spin Hall magnetoresistance (SMR) refers to a resistance change in a metallic
film reflecting the magnetization direction of a magnet attached to the film.
The mechanism of this phenomenon is spin exchange between conduction-electron
spins and magnetization at the interface. SMR has been used to read out
information written in a small magnet and to detect magnetization dynamics, but
it has been limited to magnets; magnetic ordered phases or instability of
magnetic phase transition has been believed to be indispensable. Here, we
report the observation of SMR in a paramagnetic insulator
Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG) without spontaneous magnetization combined with
a Pt film. The paramagnetic SMR can be attributed to spin-transfer torque
acting on localized spins in GGG. We determine the efficiencies of spin torque
and spin-flip scattering at the Pt/GGG interface, and demonstrate these
quantities can be tuned with external magnetic fields. The results clarify the
mechanism of spin-transport at a metal/paramagnetic insulator interface, which
gives new insight into the spintronic manipulation of spin states in
paramagnetic systems.",2008.02446v2
2014-04-29,Nanowire Spin Torque Oscillator Driven by Spin Orbit Torques,"Spin torque from spin current applied to a nanoscale region of a ferromagnet
can act as negative magnetic damping and thereby excite self-oscillations of
its magnetization. In contrast, spin torque uniformly applied to the
magnetization of an extended ferromagnetic film does not generate
self-oscillatory magnetic dynamics but leads to reduction of the saturation
magnetization. Here we report studies of the effect of spin torque on a system
of intermediate dimensionality - a ferromagnetic nanowire. We observe coherent
self-oscillations of magnetization in a ferromagnetic nanowire serving as the
active region of a spin torque oscillator driven by spin orbit torques. Our
work demonstrates that magnetization self-oscillations can be excited in a
one-dimensional magnetic system and that dimensions of the active region of
spin torque oscillators can be extended beyond the nanometer length scale.",1404.7262v2
2016-03-25,Microscopic theory of spin-orbit torques and skyrmion dynamics,"We formulate a general microscopic approach to spin-orbit torques in thin
ferromagnet/heavy-metal bilayers in linear response to electric current or
electric field. The microscopic theory we develop avoids the notion of spin
currents and spin-Hall effect. Instead, the torques are directly related to a
local spin polarization of conduction electrons, which is computed from
generalized Kubo-St\v{r}eda formulas. A symmetry analysis provides a one-to-one
correspondence between polarization susceptibility tensor components and
different torque terms in the Landau-Lifshitz-Gilbert equation for
magnetization dynamics. The spin-orbit torques arising from Rashba or
Dresselhaus type of spin-orbit interaction are shown to have different
symmetries. We analyze these spin-orbit torques microscopically for a generic
electron model in the presence of an arbitrary smooth magnetic texture. For a
model with spin-independent disorder we find a major cancelation of the
torques. In this case the only remaining torque corresponds to the
magnetization-independent Edelstein effect. Furthermore, our results are
applied to analyze the dynamics of a Skyrmion under the action of electric
current.",1603.07994v2
2020-12-23,Parity-controlled spin-wave excitations in synthetic antiferromagnets,"We report in this study the current-induced-torque excitation of acoustic and
optical modes in Ta/NiFe/Ru/NiFe/Ta synthetic antiferromagnet stacks grown on
SiO2/Si substrates. The two Ta layers serve as spin torque sources with the
opposite polarisations both in spin currents and Oersted fields acting on their
adjacent NiFe layers. This can create the odd symmetry of spatial spin torque
distribution across the growth direction, allowing us to observe different
spin-wave excitation efficiency from synthetic antiferromagnets excited by
homogeneous torques. We analyse the torque symmetry by in-plane angular
dependence of symmetric and anti-symmetric lineshape amplitudes for their
resonance and confirm that the parallel (perpendicular) pumping nature for the
acoustic (optical) modes in our devices, which is in stark difference from the
modes excited by spatially homogeneous torques. We also present our macrospin
model for this particular spin-torque excitation geometry, which excellently
supports our experimental observation. Our results offer capability of
controlling spin-wave excitations by local spin-torque sources and we can
explore further spin-wave control schemes based on this concept.",2012.12999v2
2023-07-12,Quasi-static magnetization dynamics in a compensated ferrimagnetic half-metal -- Mn$_2$Ru$_x$Ga,"Exploring anisotropy and diverse magnetization dynamics in specimens with
vanishing magnetic moments presents a significant challenge using traditional
magnetometry, as the low resolution of existing techniques hinders the ability
to obtain accurate results. In this study, we delve deeper into the examination
of magnetic anisotropy and quasi-static magnetization dynamics in \mrg\,(MRG)
thin films, as an example of a compensated ferrimagnetic half-metal, by
employing anomalous Hall effect measurements within a tetragonal crystal
lattice system. Our research proposes an innovative approach to accurately
determine the complete set of anisotropy constants of these MRG thin films. To
achieve this, we perform anomalous Hall voltage curve fitting, using torque
models under the macrospin approximation, which allow us to obtain out-of-plane
anisotropy constants $K_1=4.0\times10^4$ J m$^{-3}$ ($K_1/M=0.655$\,T) and
$K_2=2.54\times10^4$ J m$^{-3}$ ($K_2/M=0.416$\,T), along with a weaker
in-plane anisotropy constant $K_3=3.48\times10^3$ J m$^{-3}$
($K_3/M=0.057$\,T). By additionally employing first-order reversal curves
(FORC) and classical Preisach hysteresis (hysterons) models, we are able to
validate the efficacy of the macrospin model in capturing the magnetic behavior
of MRG thin films. Furthermore, our investigation substantiates that the
complex quasi-static magnetization dynamics of MRG thin films can be
effectively modelled using a combination of hysteronic and torque models. This
approach facilitates the exploration of both linear and non-linear quasi-static
magnetization dynamics, in the presence of external magnetic field and/or
current-induced effective fields, generated by the spin-orbit torque and spin
transfer torque mechanisms.",2307.06403v1
2020-04-20,Current-induced torque originating from orbital current,"The electrical manipulation of magnetization by current-induced spin torques
has given access to realize a plethora of ultralow power and fast spintronic
devices such as non-volatile magnetic memories, spin-torque nano-oscillators,
and neuromorphic computing devices. Recent advances have led to the notion that
relativistic spin-orbit coupling is an efficient source for current-induced
torques, opening the field of spin-orbitronics. Despite the significant
progress, however, the fundamental mechanism of magnetization manipulation, the
requirement of spin currents in generating current-induced torques, has
remained unchanged. Here, we demonstrate the generation of current-induced
torques without the use of spin currents. By measuring the current-induced
torque for naturally-oxidized-Cu/ferromagnetic-metal bilayers, we observed an
exceptionally high effective spin Hall conductivity at low temperatures despite
the absence of strong spin-orbit coupling. Furthermore, we found that the
direction of the torque depends on the choice of the ferromagnetic layer, which
counters the conventional understanding of the current-induced torque. These
unconventional features are best interpreted in terms of an orbital counterpart
of the spin torque, an orbital torque, which arises from the orbital Rashba
effect and orbital current. These findings will shed light on the underlying
physics of current-induced magnetization manipulation, potentially altering the
landscape of spin-orbitronics.",2004.09165v1
2015-03-23,Spin-Orbit Torques in Two-Dimensional Rashba Ferromagnets,"Magnetization dynamics in single-domain ferromagnets can be triggered by
charge current if spin-orbit coupling is sufficiently strong. We apply
functional Keldysh theory to investigate Rashba spin-orbit torques in metallic
two-dimensional ferromagnets. A reactive, anti-damping-like spin-orbit torque
as well as a dissipative, field-like torque are calculated microscopically, to
the leading order in the spin-orbit interaction strength. By calculating the
first vertex correction we show that the intrinsic anti-damping-like torque
vanishes unless the scattering rates are spin-dependent.",1503.06872v2
2016-03-05,Enhancement of the spin transfer torque efficiency in magnetic STM junctions,"We introduce a method for a combined calculation of charge and vector spin
transport of elastically tunneling electrons in magnetic scanning tunneling
microscopy (STM). The method is based on the three-dimensional
Wentzel-Kramers-Brillouin (3D-WKB) approach combined with electronic structure
calculations using first principles density functional theory. As an
application, we analyze the STM contrast inversion of the charge current above
the Fe/W(110) surface depending on the bias voltage, tip-sample distance and
relative magnetization orientation between the sample and an iron tip. For the
spin transfer torque (STT) vector we find that its in-plane component is
generally larger than the out-of-plane component, and we identify a
longitudinal spin current component, which, however, does not contribute to the
torque. Our results suggest that the torque-current relationship in magnetic
STM junctions follows the power law rather than a linear function.
Consequently, we show that the ratio between the STT and the spin-polarized
charge current is not constant, and more importantly, it can be tuned by the
bias voltage, tip-sample distance and magnetization rotation. We find that the
STT efficiency can be enhanced by about a factor of seven by selecting a proper
bias voltage. Thus, we demonstrate the possible enhancement of the STT
efficiency in magnetic STM junctions, which can be exploited in technological
applications. We discuss our results in view of the indirect measurement of the
STT above the Fe/W(110) surface reported by Krause et al. in Phys. Rev. Lett.
107, 186601 (2011).",1603.01714v3
2003-04-02,Current-induced transverse spin wave instability in a thin nanomagnet,"We show that an unpolarized electric current incident perpendicular to the
plane of a thin ferromagnet can excite a spin-wave instability transverse to
the current direction if source and drain contacts are not symmetric. The
instability, which is driven by the current-induced ``spin-transfer torque'',
exists for one current direction only.",0304069v2
2004-03-15,Current Induced Excitations in Cu/Co/Cu Single Ferromagnetic Layer Nanopillars,"Current-induced magnetic excitations in Cu/Co/Cu single layer nanopillars
(~50 nm in diameter) have been studied experimentally as a function of Co layer
thickness at low temperatures for large applied fields perpendicular to the
layers. For asymmetric junctions current induced excitations are observed at
high current densities for only one polarity of the current and are absent at
the same current densities in symmetric junctions. These observations confirm
recent predictions of spin-transfer torque induced spin wave excitations in
single layer junctions with a strong asymmetry in the spin accumulation in the
leads.",0403367v1
2007-09-01,Thermally Assisted Current-Driven Bistable Precessional Regimes in Asymmetric Spin Valves,"Spin-transfer torque in asymmetric spin valves can destabilize both parallel
and antiparallel configurations and can lead to precessional modes also in the
absence of an external magnetic field. We find a bistable precessional regime
in such systems and show that thermal fluctuations can excite transitions
(telegraph noise) between the corresponding oscillatory regimes that are well
separated by irreversible paths at low temperatures. Because of the thermally
induced transitions, the frequency of the resulting current-driven oscillations
is different from that obtained at very low temperatures. We also show that the
power spectrum in the bistable region is dominated by the out-of-plane
oscillatory mode.",0709.0039v1
2008-01-23,Theory of Domain Wall Dynamics under Current,"Microscopic theory of domain wall dynamics under electric current is
reviewed. Domain wall is treated as rigid and planar. The spin-transfer torque
and forces on the wall are derived based on the $s$-$d$ exchange interaction
between localized spins and conduction electrons, treating non-adiabaticity
expressed by the gauge field perturbatively. Effect of spin relaxation is also
studied.",0801.3517v1
2008-07-11,Probing the spin polarization of current by soft X-ray imaging of current-induced magnetic vortex dynamics,"Time-resolved soft X-ray transmission microscopy is applied to image the
current-induced resonant dynamics of the magnetic vortex core realized in a
micronsized Permalloy disk. The high spatial resolution better than 25 nm
enables us to observe the resonant motion of the vortex core. The result also
provides the spin polarization of the current to be 0.67 +/-0.16 for Permalloy
by fitting the experimental results with an analytical model in the framework
of the spin-transfer torque.",0807.1782v1
2010-10-23,High spin polarization in epitaxial films of ferrimagnetic Mn3Ga,"Ferrimagnetic Mn3Ga exhibits a unique combination of low saturation
magnetization (Ms = 0.11 MA m-1) and high perpendicular anisotropy with a
uniaxial anisotropy constant of Ku = 0.89 MJ m-3. Epitaxial c-axis films
exhibit spin polarization as high as 58%, measured using point contact Andreev
reflection. These epitaxial films will be able to support thermally stable
sub-10 nm bits for spin transfer torque memories.",1010.4872v1
2013-02-27,Injection locking at zero field in two free layer spin-valves,"This paper predicts the possibility to achieve synchronization (via injection
locking to a microwave current) of spin-transfer torque oscillators based on
hybrid spin-valves composed by two free layers and two perpendicular polarizers
at zero bias field. The locking regions are attained for microwave frequency
near 0.5f0, f0, and 2f0 where f0 is the input oscillator frequency. Those
properties make this system promising for applications, such as high-speed
frequency dividers and multipliers, and phase-locked-loop demodulators.",1302.6744v1
2013-05-21,Switching of a single ferromagnetic layer driven by spin Hall effect,"The magnetization switching of a thin ferromagnetic layer placed on top of a
heavy metal (such as Pt, Ta or W) driven by an in-plane current has been
observed in recent experiments. The magnetization dynamics of these processes
is studied in a full micromagnetic framework which takes into account the
transfer-torque from spin Hall effect due to the spin-orbit coupling.
Simulations indicate that the reversal occurs via nucleation of complex
magnetization patterns. In particular, magnetic bubbles appear during the
reversal of the magnetization in the perpendicular configuration while for the
in-plane configuration, nucleation of vortexes are observed.",1305.4806v1
2017-03-06,Controlling topological superconductivity by magnetization dynamics,"We study theoretically a chain of precessing classical magnetic impurities in
an $s$-wave superconductor. Utilizing a rotating wave description, we derive an
effective Hamiltonian that describes the emergent Shiba band. We find that this
Hamiltonian shows non-trivial topological properties, and we obtain the
corresponding topological phase diagrams both numerically and analytically. We
show that changing the precession frequency offers a control over topological
phase transitions and the emergence of Majorana bound states. We propose
driving the magnetic impurities or magnetic texture into precession by means of
spin-transfer torque in a spin-Hall setup, and manipulate it using spin
superfluidity in the case of planar magnetic order.",1703.01870v1
2019-04-28,Quantum noise in the spin transfer torque effect,"Describing the microscopic details of the interaction of magnets and
spin-polarized currents is key to achieve control of such systems at the
microscopic level. Here we discuss a description based on the Keldysh
technique, casting the problem in the language of open quantum systems. We
reveal the origin of noise in the presence of both field-like and damping like
terms in the equation of motion arising from spin conductance.",1904.12372v1
2021-03-28,"Skyrmion elongation, duplication and rotation by spin-transfer torque under spatially varying spin current","The effect of the spatially varying spin current on a skyrmion is numerically
investigated. It is shown that an inhomogeneous current density induces an
elongation of the skyrmion. This elongation can be controlled using current
pulses of different strength and duration. Long current pulses lead to a
splitting that forms two replicas of the initial skyrmion while for short
pulses the elongated skyrmion relaxes back to its initial circular state
through rotation in the MHz-GHz frequency range. The frequency is dependent on
the strength of the damping coefficient.",2103.15094v1
2008-03-13,Bias-driven large power microwave emission from MgO-based tunnel magnetoresistance devices,"Spin-momentum transfer between a spin-polarized current and a ferromagnetic
layer can induce steady-state magnetization precession, and has recently been
proposed as a working principle for ubiquitous radio-frequency devices for
radar and telecommunication applications. However, to-date, the development of
industrially attractive prototypes has been hampered by the inability to
identify systems which can provide enough power. Here, we demonstrate that
microwave signals with device-compatible output power levels can be generated
from a single magnetic tunnel junction with a lateral size of 100 nm, seven
orders of magnitude smaller than conventional radio-frequency oscillators. We
find that in MgO magnetic tunnel junctions the perpendicular torque induced by
the spin-polarized current on the local magnetization can reach 25% of the
in-plane spin-torque term, while exhibiting a different bias-dependence. Both
findings contrast with the results obtained on all-metallic structures -
previously investigated -, reflecting the fundamentally different transport
mechanisms in the two types of structures.",0803.2013v2
2009-03-16,Non-stationary magnetization dynamics driven by spin transfer torque,"This paper shows that the presence of two dynamical regimes, characterized by
different precessional-axis, is the origin of the non-monotonic behavior of the
output integrated power for large-amplitude magnetization precession driven by
spin-polarized current in nanoscale exchange biased spin-valves. In particular,
at the transition current between those two regimes exists an abruptly loss in
the integrated output power. After the introduction of a time-frequency
analysis of magnetization dynamics based on the wavelet transform, we performed
a numerical experiment by means of micromagnetic simulations. Our results
predicted that, together with a modulation of the frequency of the main excited
mode of the magnetization precession, at high non-linear dynamical regime the
instantaneous output power of the spin-torque oscillator can disappear and then
reappear at nanosecond scale.",0903.2751v1
2011-09-16,Mesoscopic Current-In-Plane Giant Magneto-Resistance,"We develop a three dimensional semiclassical theory which generalizes the
Valet-Fert model in order to account for non-collinear systems with magnetic
texture, including e.g. domain walls or magnetic vortices. The theory allows
for spin transverse to the magnetization to penetrate inside the ferromagnet
over a finite length and properly accounts for the Sharvin resistances. For
ferromagnetic-normal-ferromagnetic multilayers where the current is injected in
the plane of the layers (CIP), we predict the existence of a non zero
mesoscopic CIP Giant Magneto-Resistance (GMR) at the diffusive level. This
mesoscopic CIP-GMR, which adds to the usual ballistic contributions, has a non
monotonic spatial variation and is reminiscent of conductance quantization in
the layers. Furthermore, we study the spin transfer torque in spin valve
nanopillars. We find that when the magnetization direction is non uniform
inside the free layer, the spin torque changes very significantly and simple
one-dimensional calculations cease to be reliable.",1109.3602v1
2013-01-15,Single spin-torque vortex oscillator using combined bottom-up approach and e-beam lithography,"A combined bottom-up assembly of electrodeposited nanowires and electron beam
lithography technique has been developed to investigate the spin transfer
torque and microwave emission on specially designed nanowires containing a
single Co/Cu/Co pseudo spin valve. Microwave signals have been obtained even at
zero magnetic field. Interestingly, high frequency vs. magnetic field
tunability was demonstrated, in the range 0.4 - 2 MHz/Oe, depending on the
orientation of the applied magnetic field relative to the magnetic layers of
the pseudo spin valve. The frequency values and the emitted signal frequency as
a function of the external magnetic field are in good quantitative agreement
with the analytical vortex model as well as with micromagnetic simulations.",1301.3431v2
2013-04-03,Synchronization of an array of spin torque nano oscillators in periodic applied external magnetic field,"Considering an array of spin torque transfer nano oscillators (STNOs), we
have investigated the synchronization property of the system under the action
of a common periodically driven applied external magnetic field by numerically
analyzing the underlying system of Landau-Lifshitz-Gilbert-Slonczewski (LLGS)
equations for the macro-spin variables. We find the novel result that the
applied external magnetic field can act as a medium to induce synchronization
of periodic oscillations, both in-phase and anti-phase, even without coupling
through spin current, thereby leading to the exciting possibility of
enhancement of microwave power in a straightforward way.",1304.0875v1
2014-01-03,"Spin-Transfer-Torque Driven Magneto-Logic OR, AND and NOT Gates","We show that current induced magneto-logic gates like AND, OR and NOT can be
designed with the simple architecture involving a single nano spin-valve
pillar, as an extension of our recent work on spin-torque-driven magneto-logic
universal gates, NAND and NOR. Here the logical operation is induced by
spin-polarized currents which also form the logical inputs. The operation is
facilitated by the simultaneous presence of a constant controlling magnetic
field, in the absence of which the same element operates as a magnetoresistive
memory element. We construct the relevant phase space diagrams for the free
layer magnetization dynamics in the monodomain approximation and show the
rationale and functioning of the proposed gates. The flipping time for the
logical states of these non-universal gates is estimated to be within nano
seconds, just like their universal counter parts.",1401.0627v1
2019-05-24,The microscopic Einstein-de Haas effect,"The Einstein-de Haas (EdH) effect, where the spin angular momentum of
electrons is transferred to the mechanical angular momentum of atoms, was
established experimentally in 1915. While a semi-classical explanation of the
effect exists, modern electronic structure methods have not yet been applied to
modelling the phenomenon. In this paper we investigate its microscopic origins
by means of a non-collinear tight-binding model of an $\textrm{O}_2$ dimer,
which includes the effects of spin-orbit coupling, coupling to an external
magnetic field, and vector Stoner exchange. By varying an external magnetic
field in the presence of spin-orbit coupling, a torque can be generated on the
dimer, validating the presence of the EdH effect. Avoided energy level
crossings and the rate of change of magnetic field determine the evolution of
the spin. We find also that the torque exerted on the nuclei by the electrons
in a time-varying $B$ field is not only due to the EdH effect. Other
contributions arise from field-induced changes in the electronic orbital
angular momentum and from the direct action of the Faraday electric field
associated with the time-varying magnetic field.",1905.10449v1
2020-11-06,Picosecond Switching of Optomagnetic Tunnel Junctions,"Perpendicular magnetic tunnel junctions are one of the building blocks for
spintronic memories, which allow fast nonvolatile data access, offering
substantial potentials to revolutionize the mainstream computing architecture.
However, conventional switching mechanisms of such devices are fundamentally
hindered by spin polarized currents4, either spin transfer torque or spin orbit
torque with spin precession time limitation and excessive power dissipation.
These physical constraints significantly stimulate the advancement of modern
spintronics. Here, we report an optomagnetic tunnel junction using a
spintronic-photonic combination. This composite device incorporates an
all-optically switchable Co/Gd bilayer coupled to a CoFeB/MgO-based
perpendicular magnetic tunnel junction by the Ruderman-Kittel-Kasuya-Yosida
interaction. A picosecond all-optical operation of the optomagnetic tunnel
junction is explicitly confirmed by time-resolved measurements. Moreover, the
device shows a considerable tunnel magnetoresistance and thermal stability.
This proof-of-concept device represents an essential step towards ultrafast
spintronic memories with THz data access, as well as ultralow power
consumption.",2011.03612v1
2017-01-26,Antiferromagnetic textures and dynamics on the surface of a heavy metal,"We investigate the formation and dynamics of spin textures in
antiferromagnetic insulators adjacent to a heavy-metal substrate with strong
spin-orbit interactions. Exchange coupling to conduction electrons engenders an
effective anisotropy, Dzyaloshinskii-Moriya interactions, and a magnetoelectric
effect for the N\'{e}el order, which can conspire to produce nontrivial
antiferromagnetic textures. Current-driven spin transfer enabled by the heavy
metal, furthermore, triggers ultrafast (THz) oscillations of the N\'{e}el order
for dc currents exceeding a critical threshold, opening up the possibility of
Terahertz spin-torque self-oscillators. For a commonly invoked
antidamping-torque geometry, however, the instability current scales with the
energy gap of the antiferromagnetic insulator and, therefore, may be
challenging to reach experimentally. We propose an alternative generic geometry
for inducing ultrafast autonomous antiferromagnetic dynamics.",1701.07863v2
2019-01-21,Mn4N ferrimagnetic thin films for sustainable spintronics,"Spintronics, which is the basis of a low-power, beyond-CMOS technology for
computational and memory devices, remains up to now entirely based on critical
materials such as Co, heavy metals and rare-earths. Here, we show that Mn4N, a
rare-earth free ferrimagnet made of abundant elements, is an exciting candidate
for the development of sustainable spintronics devices. Mn4N thin films grown
epitaxially on SrTiO3 substrates possess remarkable properties, such as a
perpendicular magnetisation, a very high extraordinary Hall angle (2%) and
smooth domain walls, at the millimeter scale. Moreover, domain walls can be
moved at record speeds by spin polarised currents, in absence of spin-orbit
torques. This can be explained by the large efficiency of the adiabatic spin
transfer torque, due to the conjunction of a reduced magnetisation and a large
spin polarisation. Finally, we show that the application of gate voltages
through the SrTiO3 substrates allows modulating the Mn4N coercive field with a
large efficiency.",1901.06868v2
2022-09-06,Current-driven magnetization dynamics and their correlation with magnetization configurations in perpendicularly magnetized tunnel junctions,"We study spin-transfer-torque driven magnetization dynamics of a
perpendicular magnetic tunnel junction (MTJ) nanopillar. Based on the
combination of spin-torque ferromagnetic resonance and microwave spectroscopy
techniques, we demonstrate that the free layer (FL) and the weak pinned
reference layer (RL) exhibit distinct dynamic behaviors with opposite frequency
vs. field dispersion relations. The FL can support a single coherent spin-wave
(SW) mode for both parallel and antiparallel configurations, while the RL
exhibits spin-wave excitation only for the antiparallel state. These two SW
modes corresponding to the FL and RL coexist at an antiparallel state and
exhibit a crossover phenomenon of oscillation frequency with increasing the
external magnetic field, which could be helpful in the mutual synchronization
of auto-oscillations for SW-based neuromorphic computing.",2209.02271v1
2023-06-08,XNOR-VSH: A Valley-Spin Hall Effect-based Compact and Energy-Efficient Synaptic Crossbar Array for Binary Neural Networks,"Binary neural networks (BNNs) have shown an immense promise for
resource-constrained edge artificial intelligence (AI) platforms as their
binarized weights and inputs can significantly reduce the compute, storage and
communication costs. Several works have explored XNOR-based BNNs using SRAMs
and nonvolatile memories (NVMs). However, these designs typically need two
bit-cells to encode signed weights leading to an area overhead. In this paper,
we address this issue by proposing a compact and low power in-memory computing
(IMC) of XNOR-based dot products featuring signed weight encoding in a single
bit-cell. Our approach utilizes valley-spin Hall (VSH) effect in monolayer
tungsten di-selenide to design an XNOR bit-cell (named 'XNOR-VSH') with
differential storage and access-transistor-less topology. We co-optimize the
proposed VSH device and a memory array to enable robust in-memory dot product
computations between signed binary inputs and signed binary weights with sense
margin (SM) > 1 micro-amps. Our results show that the proposed XNOR-VSH array
achieves 4.8% ~ 9.0% and 37% ~ 63% lower IMC latency and energy, respectively,
with 4 % ~ 64% smaller area compared to spin-transfer-torque (STT)-MRAM and
spin-orbit-torque (SOT)-MRAM based XNOR-arrays.",2306.05219v1
2012-05-29,Thermally-Assisted Spin-Transfer Torque Magnetization Reversal in Uniaxial Nanomagnets,"We simulate the stochastic Landau-Lifshitz-Gilbert (LLG) dynamics of a
uniaxial nanomagnet out to sub-millisecond timescales using a graphical
processing unit based micromagnetic code and determine the effect of
geometrical tilts between the spin-current and uniaxial anisotropy axes on the
thermally assisted reversal dynamics. The asymptotic behavior of the switching
time ($I\rightarrow 0$, $<\tau>\propto\exp(-\xi(1-I)^2)$) is approached
gradually, indicating a broad crossover regime between ballistic and thermally
assisted spin transfer reversal. Interestingly, the mean switching time is
shown to be nearly independent of the angle between the spin current and
magnet's uniaxial axes. These results have important implications for modeling
the energetics of thermally assisted magnetization reversal of spin transfer
magnetic random access memory bit cells.",1205.6509v1
2018-12-03,Microscopic theory of magnon-drag electron flow in ferromagnetic metals,"A temperature gradient applied to a ferromagnetic metal induces not only
independent flows of electrons and magnons but also drag currents because of
their mutual interaction. In this paper, we present a microscopic study of the
electron flow induced by the drag due to magnons. The analysis is based on the
$s$-$d$ model, which describes conduction electrons and magnons coupled via the
$s$-$d$ exchange interaction. Magnetic impurities are introduced in the
electron subsystem as a source of spin relaxation. The obtained magnon-drag
electron current is proportional to the entropy of magnons and to $\alpha -
\beta$ (more precisely, to $1 - \beta/\alpha$), where $\alpha$ is the Gilbert
damping constant and $\beta$ is the dissipative spin-transfer torque parameter.
This result almost coincides with the previous phenomenological result based on
the magnonic spin-motive forces, and consists of spin-transfer and
momentum-transfer contributions, but with a slight disagreement in the former.
The result is interpreted in terms of the nonequilibrium spin chemical
potential generated by nonequilibrium magnons.",1812.00720v1
2015-02-09,Large amplitude oscillation of magnetization in spin-torque oscillator stabilized by field-like torque,"Oscillation frequency of spin torque oscillator with a perpendicularly
magnetized free layer and an in-plane magnetized pinned layer is theoretically
investigated by taking into account the field-like torque. It is shown that the
field-like torque plays an important role in finding the balance between the
energy supplied by the spin torque and the dissipation due to the damping,
which results in a steady precession. The validity of the developed theory is
confirmed by performing numerical simulations based on the
Landau-Lifshitz-Gilbert equation.",1502.02699v1
2023-10-10,Emerging Spin-Orbit Torques in Low Dimensional Dirac Materials,"We report a theoretical description of novel spin-orbit torque components
emerging in two-dimensional Dirac materials with broken inversion symmetry. In
contrast to usual metallic interfaces where field-like and damping-like torque
components are competing, we find that an intrinsic damping-like torque which
derives from all Fermi-sea electrons can be simultaneously enhanced along with
the field-like component. Additionally, hitherto overlooked torque components
unique to Dirac materials, emerge from the coupling between spin and pseudospin
degrees of freedom. These torques are found to be resilient to disorder and
could enhance the magnetic switching performance of nearby magnets.",2310.06447v1
2005-12-13,Focused-ion-beam milling based nanostencil mask fabrication for spin transfer torque studies,"Focused-ion-beam milling is used to fabricate nanostencil masks suitable for
the fabrication of magnetic nanostructures relevant for spin transfer torque
studies. Nanostencil masks are used to define the device dimensions prior to
the growth of the thin film stack. They consist of a wet etch resistant top
layer and an insulator on top of a pre-patterned bottom electrode. The
insulator supports a hard mask and gives rise to an undercut by its selective
etching. The approach is demonstrated by fabricating current perpendicular to
the plane Co/Cu/Co nanopillar junctions, which exhibit current-induced
magnetization dynamics.",0512283v1
2007-07-23,"Magnetocrystalline anisotropy controlled local magnetic configurations in (Ga,Mn)As spin-transfer-torque microdevices","The large saturation magnetization in conventional dense moment ferromagnets
offers flexible means of manipulating the ordered state through demagnetizing
shape anisotropy fields but these dipolar fields, in turn, limit the
integrability of magnetic elements in information storage devices. We show that
in a (Ga,Mn)As dilute moment ferromagnet, with comparatively weaker magnetic
dipole interactions, locally tunable magnetocrystalline anisotropy can take the
role of the internal field which determines the magnetic configuration.
Experiments and theoretical modeling are presented for lithographically
patterned microchannels and the phenomenon is attributed to lattice relaxations
across the channels. The utility of locally controlled magnetic anisotropies is
demonstrated in current induced switching experiments. We report structure
sensitive, current induced in-plane magnetization switchings well below the
Curie temperature at critical current densities 10^5 Acm^-2. The observed
phenomenology shows signatures of a contribution from domain-wall
spin-transfer-torque effects.",0707.3329v1
2009-04-06,Origin of the spectral linewidth in non linear oscillators based on MgO tunnel junctions,"We demonstrate the strong impact of the oscillator agility on the line
broadening by studying spin transfer induced microwave emission in MgO-based
tunnel junctions with current. The linewidth is almost not affected by
decreasing the temperature. At very low currents, a strong enhancement of the
linewidth at low temperature is attributed to an increase of the non linearity,
probably due to the field-like torque. Finally we evidence that the noise is
not dominated by thermal fluctuations but rather by the chaotization of the
magnetization system induced by the spin transfer torque.",0904.0880v2
2011-01-27,Anomalous magnetic transport in ferromagnetic graphene junctions,"We investigate magnetotransport in a ferromagnetic/normal/ferromagnetic
graphene junction where a gate electrode is attached to the normal segment. It
is shown that the charge conductance can be maximal at an antiparallel
configuration of the magnetizations. Moreover, we demonstrate that both the
magnitude and the sign of the spin-transfer torque can be controlled by means
of the gate voltage in the normal segment. In this way, the present system
constitutes a spin-transfer torque transistor. These anomalous phenomena are
attributed to the combined effect of the exchange field and the Dirac
dispersion of graphene. Our prediction opens up the possibility of moving
domain walls parallel or antiparallel to the current in a controllable fashion
by means of a local gate voltage.",1101.5236v1
2011-05-20,Nonlinear bias dependence of spin-transfer torque from atomic first principles,"We report first-principles analysis on the bias dependence of spin-transfer
torque (STT) in Fe/MgO/Fe magnetic tunnel junctions. The in-plane STT changes
from linear to nonlinear dependence as the bias voltage is increased from zero.
The angle dependence of STT is symmetric at low bias but asymmetric at high
bias. The nonlinear behavior is marked by a threshold point in the STT versus
bias curve. The high-bias nonlinear STT is found to be controlled by a resonant
transmission channel in the anti-parallel configuration of the magnetic
moments. Disorder scattering due to oxygen vacancies in MgO significantly
changes the STT threshold bias.",1105.4051v2
2011-10-24,CoB/Ni-Based Multilayer Nanowire with High-Speed Domain Wall Motion under Low Current Control,"The spin-transfer torque motion of magnetic domain walls (DWs) in a
CoB/Ni-based nanowire driven by a low current density of
(1.12\pm0.8)\times10^{11} A m^{-2} has been observed indirectly by
magnetotransport measurements. A high DW velocity of 85\pm4 m/s at zero field
was measured at the threshold current density. Upon increasing the current
density to 2.6\times10^{11} A m^{-2}, the DW velocity increases to 197\pm16 m/s
before decreasing quickly in the high-current-density regime attributed to
nonadiabatic spin-transfer torque at a low damping factor and weak pinning. The
addition of B atoms to the Co layers decreased the magnitude of saturation
magnetization, Gilbert damping factor, and density of pinning sites, making the
CoB/Ni multilayer nanowire favorable for practical applications.",1110.5112v3
2014-04-12,Dynamical magnetic skyrmions,"Spin transfer torque (STT) affords magnetic nanodevices the potential to act
as memory, computing, and microwave elements operating at ultra-low currents
and at a low energy cost. Spin transfer torque is not only effective in
manipulating well-known magnetic structures, such as domain walls and vortices,
but can also nucleate previously unattainable nano-magnetic objects, such as
magnetic droplets and skyrmions. While the droplet and the skyrmion are both
solitons, the former is inherently dynamic and non-topological, whereas the
latter is static but topologically protected. Here we show that it is possible
to combine these properties into a novel topologically protected dynamical
skyrmion, which adds additional degrees of freedom, and functionality, to both
droplet and skyrmion based applications. Unlike static skyrmions, the dynamical
skyrmion can be nucleated and sustained without Dzyaloshinskii-Moriya
interaction (DMI) or dipole-dipole interaction (DDI), and is a generic soliton
solution independent of STT and damping once nucleated. In the presence of
large DMI, the dynamical skyrmion experiences strong breathing with particular
promise for skyrmion-based memory and microwave applications.",1404.3281v2
2016-04-02,Influence of Joule heating on current-induced domain wall depinning,"The domain wall depinning from a notch in a Permalloy nanostrip on top of a
${\rm SiO_2/Si}$ substrate is studied theoretically under application of static
magnetic fields and the injection of short current pulses. The influence of
Joule heating on current-induced domain wall depinning is explored
self-consistently by coupling the magnetization dynamics in the ferromagnetic
strip to the heat transport throughout the system. Our results indicate that
Joule heating plays a remarkable role in these processes, resulting in a
reduction in the critical depinning field and/or in a temporary destruction of
the ferromagnetic order for typically injected current pulses. In agreement
with experimental observations, similar pinning-depinning phase diagrams can be
deduced for both current polarities when the Joule heating is taken into
account. These observations, which are incompatible with the sole contribution
of spin transfer torques, provide a deeper understanding of the physics
underlying these processes and establish the real scope of the spin transfer
torque. They are also relevant for technological applications based on
current-induced domain-wall motion along soft strips.",1604.00522v2
2016-03-24,Anomalous tunnel magnetoresistance and spin transfer torque in magnetic tunnel junctions with embedded nanoparticles,"The tunnel magnetoresistance (TMR) in the magnetic tunnel junction (MTJ) with
embedded nanoparticles (NPs) was calculated in range of the quantum-ballistic
model. The simulation was performed for electron tunneling through the
insulating layer with embedded magnetic and nonmagnetic NPs within the approach
of the double barrier subsystem connected in parallel to the single barrier
one. This model can be applied for both MTJs with in-plane magnetization and
perpendicular one. We also calculated the in-plane component of the spin
transfer torque (STT) versus the applied voltage in MTJs with magnetic NPs and
determined that its value can be much larger than in single barrier system
(SBS) for the same tunneling thickness. The reported simulation reproduces
experimental data of the TMR suppression and peak-like TMR anomalies at low
voltages available in literature.",1603.07447v1
2019-05-07,Origin of the resistance-area product dependence of spin transfer torque switching in perpendicular magnetic random access memory cells,"We report on an experimental study of current induced switching in
perpendicular magnetic random access memory (MRAM) cells with variable
resistance-area products (RAs). Our results show that in addition to spin
transfer torque (STT), current induced self-heating and voltage controlled
magnetic anisotropy also contribute to switching and can explain the RA
dependencies of switching current density and STT efficiency. Our findings
suggest that thermal optimization of perpendicular MRAM cells can result in
significant reduction of switching currents.",1905.02673v1
2019-05-16,Magnetization dynamics modulated by Dzyaloshinskii-Moriya interaction in the double-interface spin transfer torque magnetic tunnel junction,"Currently double-interface MTJs have been developed for enhancing the thermal
stability barrier in small technology node. Dzyaloshinskii-Moriya interaction
(DMI) inevitably exists in such devices due to the use of the
heavy-metal/ferromagnet structures. Previous studies have demonstrated the
detrimental effect of DMI on the conventional single-interface spin transfer
torque (STT) MTJs. Here in this work we will prove that the detrimental effect
of the DMI could be almost eliminated in the double-interface STT-MTJ. This
conclusion is attributed to the suppressing effect of the
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction on the DMI. Detailed
mechanisms are analyzed based on the theoretical models and micromagnetic
simulation results. Our work highlights the importance of appropriately
controlling the DMI in two free layers of the double-interface STT-MTJ.",1905.06848v2
2019-09-11,Chaos in nanomagnet via feedback current,"Nonlinear magnetization dynamics excited by spin-transfer effect with
feedback current is studied both numerically and analytically. The numerical
simulation of the Landau-Lifshitz-Gilbert equation indicates the positive
Lyapunov exponent for a certain range of the feedback rate, which identifies
the existence of chaos in a nanostructured ferromagnet. Transient behavior from
chaotic to steady oscillation is also observed in another range of the feedback
parameter. An analytical theory is also developed, which indicates the
appearance of multiple attractors in a phase space due to the feedback current.
An instantaneous imbalance between the spin-transfer torque and damping torque
causes a transition between the attractors, and results in the complex
dynamics.",1909.05315v2
2022-02-14,Tuning the Hall response of a noncollinear antiferromagnet via spin-transfer torques and oscillating magnetic fields,"The kagome lattice antiferromagnets Mn$_3$X(= Sn, Ge) have a noncollinear
120$^\circ$ ordered ground state, which engenders a strong anomalous Hall
response. It has been shown that this response is linked to the magnetic order
and can be manipulated through it. Here we use a combination of strain and
spin-transfer torques to control the magnetic order and hence switch
deterministically between states of different chirality. Each of these chiral
ground states has an anomalous Hall conductivity tensor in a different
direction. Furthermore, we show that a similar manipulation of the strained
sample can be obtained through oscillating magnetic fields, potentially opening
a pathway to optical switching in these materials.",2202.06882v3
2022-10-26,"Perpendicular magnetic anisotropy, tunneling magnetoresistance and spin-transfer torque effect in magnetic tunnel junctions with Nb layers","Nb and its compounds are widely used in quantum computing due to their high
superconducting transition temperatures and high critical fields. Devices that
combine superconducting performance and spintronic non-volatility could deliver
unique functionality. Here we report the study of magnetic tunnel junctions
with Nb as the heavy metal layers. An interfacial perpendicular magnetic
anisotropy energy density of 1.85 mJ/m2 was obtained in Nb/CoFeB/MgO
heterostructures. The tunneling magnetoresistance was evaluated in junctions
with different thickness combinations and different annealing conditions. An
optimized magnetoresistance of 120% was obtained at room temperature, with a
damping parameter of 0.011 determined by ferromagnetic resonance. In addition,
spin-transfer torque switching has also been successfully observed in these
junctions with a quasistatic switching current density of 7.3*10^5 A/cm2.",2210.14969v1
2005-11-04,Synchronized Magnetization Oscillations in F/N/F Nanopillars,"Current-induced magnetization dynamics in a trilayer structure composed of
two ferromagnetic free layers and a nonmagnetic spacer is examined. Both free
layers are treated as a monodomain magnetic body with an uniform agnetization.
The dynamics of the two magnetizations is modeled by modified
Landau-Lifshitz-Gilbert equations with spin-transfer torque terms. By solving
the equations simultaneously, we discuss their various solutions in detail. We
show that there exists the synchronous motion of two magnetizations among the
various solutions; the magnetizations are resonantly coupled via spin-transfer
torques and perform precessional motions with the same period. The condition to
excite the synchronous motion depends on the difference between the intrinsic
frequencies of the two ferromagnetic free layers as well as the magnitude of
current.",0511095v1
2003-08-29,Optical alignment and spinning of laser-trapped microscopic particles,"Light-induced rotation of absorbing microscopic particles by transfer of
angular momentum from light to the material raises the possibility of optically
driven micromachines. The phenomenon has been observed using elliptically
polarized laser beams or beams with helical phase structure. But it is
difficult to develop high power in such experiments because of overheating and
unwanted axial forces, limiting the achievable rotation rates to a few hertz.
This problem can in principle be overcome by using transparent particles,
transferring angular momentum by a mechanism first observed by Beth in 1936,
when he reported a tiny torque developed in a quartz waveplate due to the
change in polarization of transmitted light. Here we show that an optical
torque can be induced on microscopic birefringent particles of calcite held by
optical tweezers. Depending on the polarization of the incident beam, the
particles either become aligned with the plane of polarization (and thus can be
rotated through specified angles) or spin with constant rotation frequency.
Because these microscopic particles are transparent, they can be held in
three-dimensional optical traps at very high power without heating. We have
observed rotation rates in excess of 350 Hz.",0308113v1
2010-11-30,Spin Transfer Torque and Tunneling Magnetoresistance Dependences on the Finite Bias Voltages and Insulator Barrier Energy,"We investigate the dependence of perpendicular and parallel spin transfer
torque (STT) and tunneling magnetoresistance (TMR) on the insulator barrier
energy in the magnetic tunnel junction (MTJ). We employed single orbit tight
binding model combined with the Keldysh non-equilibrium Green's function method
in order to calculate the perpendicular and parallel STT, and TMR in MTJ with
the finite bias voltages. The dependences of STT and TMR on the insulator
barrier energy are calculated for the semi-infinite half metallic ferromagnetic
electrodes. We find that perfect linear relation between the parallel STT and
the tunneling current for the wide range of the insulator barrier energy.
Furthermore, the TMR also depends on the insulator barrier energy, which
contradicts to the Julliere's simple model.",1011.6456v1
2012-11-14,Reversal process of a magnetic vortex core under the combined action of a perpendicular field and spin transfer torque,"In a nanopillar with dipolarly coupled vortices, we present an experimental
and simulation study to understand how the interplay between the bias field and
spin transfer torque impacts reversal of the vortex cores. We find that,
depending on the current values, vortex cores might experience different
physical mechanisms for their reversal, namely a static or a dynamic switching.
We believe that our results might be useful in the context of vortex based non
volatile memories, as a current controlled selective core switching is
proposed.",1211.3276v1
2015-07-29,Observation of droplet soliton drift resonances in a spin-transfer-torque nanocontact to a ferromagnetic thin film,"Magnetic droplet solitons are non-linear dynamical modes that can be excited
in a thin film with perpendicular magnetic anisotropy with a
spin-transfer-torque. Although droplet solitons have been proved to be stable
with a hysteretic response to applied currents and magnetic fields at low
temperature, measurements at room temperature indicate less stability and
reduced hysteresis width. Here, we report evidence of droplet soliton drift
instabilities, leading to drift resonances, at room temperature that explains
their lower stability. Micromagnetic simulations show that the drift
instability is produced by an effective field asymmetry in the nanocontact
region that can have different origins.",1507.08218v1
2017-02-09,Spin Transfer Torque Driven Coupled Oscillators for Self-Oscillating RF Mixers,"Spin transfer torque oscillators (STOs) based on magnetic tunnel junction
(MTJ) devices are emerging as a possible replacement for complementary
metal-oxide semiconductors for radio-frequency (RF) signal generation.
Advantages include low power consumption, small device area, and large
frequency tunability. But such a single device cannot achieve the necessary
noise performance for RF applications. It has been reported lately that a
network of globally coupled STOs achieves significant improvement in phase
noise. The study here is to propose use of such coupled STOs as
self-oscillating RF mixers. Critical mixer performance parameters, including
conversion gain, output power, and linearity, are discussed.",1702.02746v5
2017-01-14,Giant magnetoresistance and anomalous transport in phosphorene-based multilayers with noncollinear magnetization,"We theoretically investigate the unusual features of the magnetotransport in
a monolayer phosphorene ferromagnetic/normal/ferromagnetic (F/N/F) hybrid
structure. We find that the charge conductance can feature a minimum at
parallel (P) configuration and a maximum near the antiparallel (AP)
configuration of magnetization in the F/N/F structure with $n$-doped F and
$p$-doped N regions and also a finite conductance in the AP configuration with
the N region of $n$-type doping. In particular, the proposed structure exhibits
giant magnetoresistance, which can be tuned to unity. This perfect switching is
found to show strong robustness with respect to increasing the contact length
and tuning the chemical potential of the N region with a gate voltage. We also
explore the oscillatory behavior of the charge conductance or magnetoresistance
in terms of the size of the N region. We further demonstrate the penetration of
the spin-transfer torque into the right F region and show that, unlike graphene
structure, the spin-transfer torque is very sensitive to the chemical potential
of the N region as well as the exchange field of the F region.",1701.03887v2
2022-09-28,Distribution of write error rate of spin-transfer-torque magnetoreistive random access memory caused by a distribution of junction parameters,"Distribution of write error rate (WER) of spin-transfer-torque
magnetoreistive random access memory (STT MRAM) caused by a distribution of
resistance area product and anisotropy constant is theoretically studied.
Assuming that WER is much smaller than unity, and junction parameters obey a
normal distribution, we show that the WER obeys a logarithmic normal
distribution. We derive analytical expressions for the probability density
function and statistical measures. We find that the coefficient of variation of
WER can be reduced by decreasing the pulse width. We also perform numerical
simulations based on the Fokker-Planck equation and confirm the validity of the
analytical expressions. The results are useful for designing reliable STT
MRAMs.",2209.13828v2
2022-11-15,Nonlinear chiral photocurrent in parity-violating magnetic Weyl semimetals,"The strong correlation between the non-trivial band topology and the magnetic
texture makes magnetic Weyl semimetals excellent candidates for the
manipulation and detection of magnetization dynamics. The parity violation
together with the Pauli blocking cause only one Weyl node to contribute to the
photocurrent response, which in turn affects the magnetic texture due to the
spin transfer torque. Utilizing the Landau-Lifshitz-Gilbert equation and the
spin-transfer torque in non-centrosymmetric Weyl magnets, we show that the
chiral photocurrent rotates the magnetization from the easy c axis to the a or
b axis, which leads to an exotic current next to the photocurrent response. The
chiral photocurrent is calculated in the context of quantum kinetic theory and
it has a strong resonance on the order of mA/W near the Weyl nodes, the
magnitude of which is controlled by the momentum relaxation time. Remarkably,
we study the influence of magnetic texture dynamics on the topological
nonlinear photocurrent response, including shift and injection currents along
with the new chiral photocurrent, and show that both the magnitude and the
in-plane orientation of the chiral photocurrent are strongly correlated with
the direction of the magnetic moments.",2211.08521v1
2008-04-30,Biased quasi ballistic spin torque magnetization reversal,"We explore the fundamental time limit of ultra fast spin torque induced
magnetization reversal of a magnetic memory cell. Spin torque precession during
a spin torque current pulse and free precessional magnetization ringing after
spin torque pulse excitation is detected by time resolved magneto transport.
Adapting the duration of the spin torque excitation pulse to the spin torque
precession period allows suppression of the magnetization ringing and thus
coherent control of the final orientation of the magnetization. In the presence
of a hard axis bias field such coherent control enables an optimum ultra fast,
quasi ballistic spin torque magnetization reversal by a single precessional
turn directly from the initial to the reversed equilibrium state.",0804.4840v1
2013-09-05,Current-induced torques and interfacial spin-orbit coupling,"In bilayer systems consisting of an ultrathin ferromagnetic layer adjacent to
a metal with strong spin-orbit coupling, an applied in-plane current induces
torques on the magnetization. The torques that arise from spin-orbit coupling
are of particular interest. Here, we calculate the current-induced torque in a
Pt-Co bilayer to help determine the underlying mechanism using first principles
methods. We focus exclusively on the analogue to the Rashba torque, and do not
consider the spin Hall effect. The details of the torque depend strongly on the
layer thicknesses and the interface structure, providing an explanation for the
wide variation in results found by different groups. The torque depends on the
magnetization direction in a way similar to that found for a simple Rashba
model. Artificially turning off the exchange spin splitting and separately the
spin-orbit coupling potential in the Pt shows that the primary source of the
""field-like"" torque is a proximate spin-orbit effect on the Co layer induced by
the strong spin-orbit coupling in the Pt.",1309.1356v1
2018-08-21,Recent advances in spin-orbit torques: Moving towards device applications,"The ability of spintronic devices to utilize an electric current for
manipulating the magnetization has resulted in large-scale developments, such
as, magnetic random access memories and boosted the spintronic research area.
In this regard, over the last decade, magnetization manipulation using
spin-orbit torque has been devoted a lot of research attention as it shows a
great promise for future ultrafast and power efficient magnetic memories. In
this review, we summarize the latest advancements in spin-orbit torque research
and highlight some of the technical challenges for practical spin-orbit torque
devices. We will first introduce the basic concepts and highlight the latest
material choices for spin-orbit torque devices. Then, we will summarize the
important advancements in the study of magnetization switching dynamics using
spin-orbit torque, which are important from scientific as well as technological
aspect. The final major section focuses on the concept of external assist field
free spin-orbit torque switching which is a requirement for practical
spin-orbit torque devices.",1808.06829v1
2021-05-06,Interfacial and bulk spin Hall contributions to field-like spin-orbit torque generated by Iridium,"We present measurements of spin orbit torques generated by Ir as a function
of film thickness in sputtered Ir/CoFeB and Ir/Co samples. We find that Ir
provides a damping-like component of spin orbit torque with a maximum spin
torque conductivity 1.4e5 in SI unit and a maximum spin-torque efficiency of
0.04, which is sufficient to drive switching in an 0.8 nm film of CoFeB with
perpendicular magnetic anisotropy. We also observe a surprisingly large field
like spin orbit torque. Measurements as a function of Ir thickness indicate a
substantial contribution to the FLT from an interface mechanism so that in the
ultrathin limit there is a non-zero FLT with a maximum torque conductivity
-5.0E4 in the SI unit. When the Ir film thickness becomes comparable to or
greater than its spin diffusion length, 1.6 nm, there is also a smaller bulk
contribution to the fieldlike torque.",2105.02787v1
2012-05-13,Voltage-Induced Ferromagnetic Resonance in Magnetic Tunnel Junctions,"We demonstrate excitation of ferromagnetic resonance in CoFeB/MgO/CoFeB
magnetic tunnel junctions (MTJs) by the combined action of voltage-controlled
magnetic anisotropy (VCMA) and spin transfer torque (ST). Our measurements
reveal that GHz-frequency VCMA torque and ST in low-resistance MTJs have
similar magnitudes, and thus that both torques are equally important for
understanding high-frequency voltage-driven magnetization dynamics in MTJs. As
an example, we show that VCMA can increase the sensitivity of an MTJ-based
microwave signal detector to the sensitivity level of semiconductor Schottky
diodes.",1205.2835v2
2012-02-07,Prediction of Giant Spin Motive Force due to Rashba Spin-Orbit Coupling,"Magnetization dynamics in a ferromagnet can induce a spin-dependent electric
field through spin motive force. Spin current generated by the spin-dependent
electric field can in turn modify the magnetization dynamics through
spin-transfer torque. While this feedback effect is usually weak and thus
ignored, we predict that in Rashba spin-orbit coupling systems with large
Rashba parameter $\alpha_{\rm R}$, the coupling generates the spin-dependent
electric field [$\pm(\alpha_{\rm R}m_e/e\hbar) (\vhat{z}\times \partial
\vec{m}/\partial t)]$, which can be large enough to modify the magnetization
dynamics significantly. This effect should be relevant for device applications
based on ultrathin magnetic layers with strong Rashba spin-orbit coupling.",1202.1406v2
2013-02-06,Theory of spin Hall magnetoresistance,"We present a theory of the spin Hall magnetoresistance (SMR) in multilayers
made from an insulating ferromagnet F, such as yttrium iron garnet (YIG), and a
normal metal N with spin-orbit interactions, such as platinum (Pt). The SMR is
induced by the simultaneous action of spin Hall and inverse spin Hall effects
and therefore a non-equilibrium proximity phenomenon. We compute the SMR in
F$|$N and F$|$N$|$F layered systems, treating N by spin-diffusion theory with
quantum mechanical boundary conditions at the interfaces in terms of the
spin-mixing conductance. Our results explain the experimentally observed spin
Hall magnetoresistance in N$|$F bilayers. For F$|$N$|$F spin valves we predict
an enhanced SMR amplitude when magnetizations are collinear. The SMR and the
spin-transfer torques in these trilayers can be controlled by the magnetic
configuration.",1302.1352v1
2018-11-14,Spin-dependent Seebeck effect in non-local spin valve devices,"We performed measurements of Py/Cu and Py/Ag lateral spin valves as function
of injection current direction and magnitude. Above a 'critical' current, there
is an unexpected dependence of spin injection on current direction. Positive
currents show higher polarization of spin injection than negative. This implies
that in addition to current-induced spin injection, there is a thermally
induced injection from a spin-dependent Seebeck effect. A temperature gradient
in the Py electrode, caused by Joule heating, is responsible for injecting
excess spins into the non-magnetic channel. This effect has important
consequences for understanding high-current spin-based devices, such as spin
transfer torque devices.",1811.06112v1
2016-03-17,Spin wave amplification using the spin Hall effect in permalloy/platinum bilayers,"We investigate the effect of an electrical current on the attenuation length
of a 900 nm wavelength spin-wave in a permalloy/Pt bilayer using propagating
spin-wave spectroscopy. The modification of the spin-wave relaxation rate is
linear in current density, reaching up to 14% for a current density of
2.3$\times10^{11} $A/m$^2$ in Pt. This change is attributed to the spin
transfer torque induced by the spin Hall effect and corresponds to an effective
spin Hall angle of 0.13, which is among the highest values reported so far. The
spin Hall effect thus appears as an efficient way of amplifying/attenuating
propagating spin waves.",1603.05478v1
2022-08-15,Absorption of Transverse Spin Current in Ferromagnetic NiCu: Dominance of Bulk Dephasing over Spin-Flip Scattering,"In ferromagnetic metals, transverse spin currents are thought to be absorbed
via dephasing -- i.e., destructive interference of spins precessing about the
strong exchange field. Yet, due to the ultrashort coherence length of
$\approx$1 nm in typical ferromagnetic thin films, it is difficult to
distinguish dephasing in the bulk from spin-flip scattering at the interface.
Here, to assess which mechanism dominates, we examine transverse spin-current
absorption in ferromagnetic NiCu alloy films with reduced exchange fields. We
observe that the coherence length increases with decreasing Curie temperature,
as weaker dephasing in the film bulk slows down spin absorption. Moreover,
nonmagnetic Cu impurities do not diminish the efficiency of spin-transfer
torque from the absorbed spin current. Our findings affirm that transverse spin
current is predominantly absorbed by dephasing inside the nanometer-thick
ferromagnetic metals, even with high impurity contents.",2208.07294v1
2008-12-17,Theory of Spin-Transfer Torque in the Current-in-Plane Geometries,"Two alternative current-induced switching geometries, in which the current
flows parallel to the magnet/nonmagnet interface, are investigated
theoretically using the nonequilibrium Keldysh theory. In the first geometry,
the current is perpendicular to the polarizing magnet/nonmagnet interface but
parallel to the nonmagnet/switching magnet interface (CPIP). In the second
geometry, the current is parallel to both the polarizing magnet/nonmagnet and
nonmagnet/switching magnet interfaces (CIP). Calculations for a single-orbital
tight binding model indicate that the spin current flowing parallel to the
switching magnet/nonmagnet interface can be absorbed by a lateral switching
magnet as efficiently as in the traditional current-perpendicular-to-plane
(CPP) geometry. The results of the model calculations are shown to be valid
also for experimentally relevant Co/Cu CPIP system described by fully realistic
tight binding bands fitted to an ab initio band structure. It is shown that
almost complete absorption of the incident spin current by a lateral switching
magnet occurs when the lateral dimensions of the switching magnet are of the
order of 50-100 interatomic distances, i.e., about 20nm and its height as small
as a few atomic planes. It is also demonstratedthat strong spin current
absorption in the CPIP/CIP geometry is not spoilt by the presence of a rough
interface between the switching magnet and nonmagnetic spacer. Polarization
achieved using a lateral magnet in the CIP geometry is found to be about 25% of
that in the traditional CPP geometry. The present CPIP calculations of the spin
transfer torque are also relevant to the so called pure-spin-current-induced
magnetization switching that had been recently observed.",0812.3346v1
2020-01-22,The dynamics of a domain wall in ferrimagnets driven by spin-transfer torque,"The spin-transfer-torque-driven (STT-driven) dynamics of a domain wall in an
easy-axis rare-earth transition-metal ferrimagnet is investigated theoretically
and numerically in the vicinity of the angular momentum compensation point
$T_A$, where the net spin density vanishes. The particular focus is given on
the unusual interaction of the antiferromagnetic dynamics of a ferrimagnetic
domain wall and the adiabatic component of STT, which is absent in
antiferromagnets but exists in the ferrimagnets due to the dominant coupling of
conduction electrons to transition-metal spins. Specifically, we first show
that the STT-induced domain-wall velocity changes its sign across $T_A$ due to
the sign change of the net spin density, giving rise to a phenomenon unique to
ferrimagnets that can be used to characterize $T_A$ electrically. It is also
shown that the frequency of the STT-induced domain-wall precession exhibits its
maximum at $T_A$ and it can approach the spin-wave gap at sufficiently high
currents. Lastly, we report a numerical observation that, as the current
density increases, the domain-wall velocity starts to deviate from the
linear-response result, calling for a more comprehensive theory for the
domain-wall dynamics in ferrimagnets driven by a strong current.",2001.08037v1
2019-03-08,Spin-transfer torques for domain walls in antiferromagnetically coupled ferrimagnets,"Antiferromagnetic materials are outstanding candidates for next generation
spintronic applications, because their ultrafast spin dynamics makes it
possible to realize several orders of magnitude higher-speed devices than
conventional ferromagnetic materials1. Though spin-transfer torque (STT) is a
key for electrical control of spins as successfully demonstrated in
ferromagnetic spintronics, experimental understanding of STT in
antiferromagnets has been still lacking despite a number of pertinent
theoretical studies2-5. Here, we report experimental results on the effects of
STT on domain-wall (DW) motion in antiferromagnetically-coupled ferrimagnets.
We find that non-adiabatic STT acts like a staggered magnetic field and thus
can drive DWs effectively. Moreover, the non-adiabaticity parameter {\beta} of
STT is found to be significantly larger than the Gilbert damping parameter
{\alpha}, challenging our conventional understanding of the non-adiabatic STT
based on ferromagnets as well as leading to fast current-induced
antiferromagnetic DW motion. Our study will lead to further vigorous
exploration of STT for antiferromagnetic spin textures for fundamental physics
on spin-charge interaction as wells for efficient electrical control of
antiferromagnetic devices.",1903.03251v1
2017-12-08,Impact of intergrain spin transfer torques due to huge thermal gradients on the performance of heat assisted magnetic recording,"Heat assisted magnetic recording (HAMR) is a new technology which uses
temporary near field laser heating of the media during write to increase hard
disk drive storage density. By using plasmonic antenna embedded in the write
head, extremely high thermal gradient are created in the recording media (up to
10K/nm). State of the art HAMR media consists of grains of FePtX ordered alloys
exhibiting high perpendicular anisotropy separated by insulating grain
boundaries. Nearby the plasmonic antenna, the difference of temperature between
two 8nm wide neighboring grains in the media can reach 80K, representing a
gigantic thermal gradient of ~40K/nm across the grain boundary. Such situations
with much weaker thermal gradient (~1K/nm, already considered as very large)
have already been studied in the field of spincaloritronics. There, it was
shown that very large spin transfer torques due to thermal gradients can arise
in magnetic tunnel junctions which can even yield magnetization switching.
Considering that two neighboring grains separated by an insulating grain
boundary in a HAMR media can be viewed as a magnetic tunnel junction and that
the thermal gradients in HAMR are one to two orders of magnitude larger than
those existing in conventional spincaloritronics, one may expect a major impact
from these thermal torques on magnetization switching dynamics and therefore on
HAMR recording performances. This paper combines theory, experiments aiming at
determining the polarization of tunneling electrons across the media grain
boundaries, and micromagnetic simulations of recording process. It is shown
that the thermal in-plane torque can have a detrimental impact on the recording
performances by favoring antiparallel magnetic alignment between neighboring
grains during the media cooling. Implications on media design are discussed in
order to limit the impact of these thermal torques.",1712.03302v1
2018-01-22,Spin-orbit torques in NbSe$_2$/Permalloy bilayers,"We present measurements of current-induced spin-orbit torques generated by
NbSe$_2$, a fully-metallic transition-metal dichalcogenide material, made using
the spin-torque ferromagnetic resonance (ST-FMR) technique with
NbSe$_{2}$/Permalloy bilayers. In addition to the out-of-plane Oersted torque
expected from current flow in the metallic NbSe$_{2}$ layer, we also observe an
in-plane antidamping torque with torque conductivity $\sigma_{S} \approx 10^{3}
(\hbar / 2e)$($\Omega$m)$^{-1}$ and indications of a weak field-like
contribution to the out-of-plane torque oriented opposite to the Oersted
torque. Furthermore, in some samples we also measure an in-plane field-like
torque with the form $\hat{m} \times \hat{z}$, where $\hat{m}$ is the Permalloy
magnetization direction and $\hat{z}$ is perpendicular to the sample plane. The
size of this component varies strongly between samples and is not correlated
with the NbSe$_{2}$ thickness. A torque of this form is not allowed by the bulk
symmetries of NbSe$_{2}$, but is consistent with symmetry breaking by a
uniaxial strain that might result during device fabrication.",1801.07281v1
2012-10-29,Spin-Transfer Torque Magnetization Reversal in Uniaxial Nanomagnets with Thermal Noise,"We consider the general Landau-Lifshitz-Gilbert (LLG) dynamical theory
underlying the magnetization switching rates of a thin film uniaxial magnet
subject to spin-torque effects and thermal fluctuations (thermal noise). After
discussing the various dynamical regimes governing the switching phenomena, we
present analytical results for the mean switching time behavior. Our approach,
based on explicitly solving the first passage time problem, allows for a
straightforward analysis of the thermally assisted, low spin-torque, switching
asymptotics of thin film magnets. To verify our theory, we have developed an
efficient GPU-based micromagnetic code to simulate the stochastic LLG dynamics
out to millisecond timescales. We explore the effects of geometrical tilts
between the spin-current and uniaxial anisotropy axes on the thermally assisted
dynamics. We find that even in the absence of axial symmetry, the switching
times can be functionally described in a form virtually identical to the
collinear case. We further verify that asymptotic behavior is reached fairly
slowly, thus quantifying the role of thermal noise in the crossover regime
linking deterministic to thermally assisted magnetization reversal.",1210.7675v3
2020-04-14,Materials Requirements of High-Speed and Low-Power Spin-Orbit-Torque Magnetic Random-Access Memory,"As spin-orbit-torque magnetic random-access memory (SOT-MRAM) is gathering
great interest as the next-generation low-power and high-speed on-chip cache
memory applications, it is critical to analyze the magnetic tunnel junction
(MTJ) properties needed to achieve sub-ns, and ~fJ write operation when
integrated with CMOS access transistors. In this paper, a 2T-1MTJ cell-level
modeling framework for in-plane type Y SOT-MRAM suggests that high spin Hall
conductivity and moderate SOT material sheet resistance are preferred. We
benchmark write energy and speed performances of type Y SOT cells based on
various SOT materials experimentally reported in the literature, including
heavy metals, topological insulators and semimetals. We then carry out detailed
benchmarking of SOT material Pt, beta-W, and BixSe(1-x) with different
thickness and resistivity. We further discuss how our 2T-1MTJ model can be
expanded to analyze other variations of SOT-MRAM, including perpendicular (type
Z) and type X SOT-MRAM, two-terminal SOT-MRAM, as well as spin-transfer-torque
(STT) and voltage-controlled magnetic anisotropy (VCMA)-assisted SOT-MRAM. This
work will provide essential guidelines for SOT-MRAM materials, devices, and
circuits research in the future.",2004.06268v2
2019-10-08,Correlated fluctuations in spin orbit torque-coupled perpendicular nanomagnets,"Low barrier nanomagnets have attracted a lot of research interest for their
use as sources of high quality true random number generation. More recently,
low barrier nanomagnets with tunable output have been shown to be a natural
hardware platform for unconventional computing paradigms such as probabilistic
spin logic. Efficient generation and tunability of high quality random bits is
critical for these novel applications. However, current spintronic random
number generators are based on superparamagnetic tunnel junctions (SMTJs) with
tunability obtained through spin transfer torque (STT), which unavoidably leads
to challenges in designing concatenated networks using these two terminal
devices. The more recent development of utilizing spin orbit torque (SOT)
allows for a three terminal device design, but can only tune in-plane
magnetization freely, which is not very energy efficient due to the needs of
overcoming a large demagnetization field. In this work, we experimentally
demonstrate for the first time, a stochastic device with perpendicular magnetic
anisotropy (PMA) that is completely tunable by SOT without the aid of any
external magnetic field. Our measurements lead us to hypothesize that a tilted
anisotropy might be responsible for the observed tunability. We carry out
stochastic Landau-Lifshitz-Gilbert (sLLG) simulations to confirm our
experimental observation. Finally, we build an electrically coupled network of
two such stochastic nanomagnet based devices and demonstrate that finite
correlation or anti-correlation can be established between their output
fluctuations by a weak interconnection, despite having a large difference in
their natural fluctuation time scale. Simulations based on a newly developed
dynamical model for autonomous circuits composed of low barrier nanomagnets
show close agreement with the experimental results.",1910.03184v1
2022-05-13,Field-free spin-orbit torque switching enabled by interlayer Dzyaloshinskii-Moriya interaction,"Perpendicularly magnetized structures that are switchable using a spin
current under field-free conditions can potentially be applied in spin-orbit
torque magnetic random-access memory(SOT-MRAM).Several structures have been
developed;however,new structures with a simple stack structure and MRAM
compatibility are urgently needed.Herein,a typical structure in a perpendicular
spin-transfer torque MRAM,the Pt/Co multilayer and its synthetic
antiferromagnetic counterpart with perpendicular magnetic anisotropy, was
observed to possess an intrinsic interlayer chiral interaction between
neighboring magnetic layers,namely the interlayer Dzyaloshinskii-Moriya
interaction (DMI) effect. Furthermore, using a current parallel to the
eigenvector of the interlayer DMI, we switched the perpendicular magnetization
of both structures without a magnetic field, owing to the additional
symmetry-breaking introduced by the interlayer DMI. This SOT switching scheme
realized in the Pt/Co multilayer and its synthetic antiferromagnet structure
may open a new avenue toward practical perpendicular SOT-MRAM and other SOT
devices.",2205.06706v1
2023-10-03,Controlled Quasi-Latitudinal Solutions for ultra-fast Spin-Torque Precessional Magnetization Switching,"The aim of the paper is to present a novel class of time-dependent controls
to realize ultra-fast magnetization switching in nanomagnets driven by
spin-torques produced by spin-polarized electric currents. Magnetization
dynamics in such systems is governed by the Landau-Lifshitz-Slonczewski
equation which describes the precessional motion of (dimensionless)
magnetization vector on the unit-sphere. The relevant case of nanoparticles
with uniaxial anisotropy having in-plane easy and intermediate axes and
out-of-plane hard axis is considered. By exploiting the characteristic
smallness of damping and spin-torque intensity, the aforementioned controls are
constructed via suitable perturbative tools in a way to realise approximate
\emph{latitudinal solutions} (i.e. motions on a sphere in which the
out-of-plane magnetization component stays constant) with the effect to fast
``switch'' the system from one stationary state to another. The possibility to
keep a (``small'') bounded value of the out-of-plane coordinate throughout this
process of ``transfer'', turns out to be advantageous in the applications as it
sensibly reduces the post-switching relaxation oscillations that may cause the
failure of switching in real samples. Further relevant quantitative results on
the behaviour of the solutions during the pre- and post-switching stages
(termed ``expulsion'' and ``attraction'', respectively), are given as a
byproduct. A selection of validating numerical experiments is presented
alongside the corresponding theoretical results.",2310.02070v1
2024-02-05,Circular motion of non-collinear spin textures in Corbino disks: Dynamics of Néel- versus Bloch-type skyrmions and skyrmioniums,"Magnetic skyrmions are nano-scale magnetic whirls that can be driven by
currents via spin torques. They are promising candidates for spintronic devices
such as the racetrack memory, where a motion along the uniform current is
typically desired. However, in Corbino disks, the goal is to achieve a circular
motion, perpendicular to the radially applied current. As we show, based on
analytical calculations and micromagnetic simulations, Bloch skyrmions engage
in a circular motion with frequencies in the MHz range when driven by
spin-orbit torques. In contrast, N\'eel skyrmions get stuck at the edges of the
disk. Our analysis reveals that the antagonistic dynamics between Bloch- and
N\'eel-type magnetic textures arise from their helicity. Furthermore, we find
that skyrmioniums, which are topologically trivial variations of skyrmions,
move even faster and allow an increase in the current density without being
pushed toward the edges of the disk. When driven by spin-transfer torques
instead, Bloch and N\'eel skyrmions no longer exhibit different dynamics.
Instead, they move along a circular trajectory due to the skyrmion Hall effect
caused by their topological charge. Consequently, the topologically trivial
skyrmioniums inevitably become trapped at the disk edge in this scenario. To
provide a comprehensive understanding, our study also examines currents applied
tangentially, further enriching our insights into skyrmion dynamics and
appropriate current injection methods for skyrmion-based devices.",2402.03023v1
2017-05-03,Surface-plasmon opto-magnetic field enhancement for all-optical magnetization switching,"The demand for faster magnetization switching speeds and lower energy
consumption has driven the field of spintronics in recent years. The magnetic
tunnel junction is the most developed spintronic memory device in which the
magnetization of the storage layer is switched by spin-transfer-torque or
spin-orbit torque interactions. Whereas these novel spin-torque interactions
exemplify the potential of electron-spin-based devices and memory, the
switching speed is limited to the ns regime by the precessional motion of the
magnetization. All-optical magnetization switching, based on the inverse
Faraday effect, has been shown to be an attractive method for achieving
magnetization switching at ps speeds. Successful magnetization reversal in thin
films has been demonstrated by using circularly polarized light. However, a
method for all-optical switching of on-chip nanomagnets in high density memory
modules has not been described. In this work we propose to use plasmonics, with
CMOS compatible plasmonic materials, to achieve on-chip magnetization reversal
in nanomagnets. Plasmonics allows light to be confined in dimensions much
smaller than the diffraction limit of light. This in turn, yields higher
localized electromagnetic field intensities. In this work, through simulations,
we show that using localized surface plasmon resonances, it is possible to
couple light to nanomagnets and achieve significantly higher opto-magnetic
field values in comparison to free space light excitation.",1705.01311v1
2018-03-31,Understanding current-driven dynamics of magnetic Néel walls in heavy metal/ferromagnetic metal/oxide trilayers,"We consider analytically current-driven dynamics of magnetic N\'{e}el walls
in heavy metal/ferromagnetic metal/oxide trilayers where strong spin-orbit
coupling and interfacial Dzyaloshinskii-Moriya interaction (i-DMI) coexist. We
show that field-like spin-orbit torque (FL-SOT) with effective field along
$\mathbf{n}\times\hat{\mathbf{J}}$ ($\mathbf{n}$ being the interface normal and
$\hat{\mathbf{J}}$ being the charge current direction) and i-DMI induced torque
can both lead to Walker breakdown suppression meanwhile leaving the wall
mobility (velocity versus current density) unchanged. However, i-DMI itself can
not induce the ""universal absence of Walker breakdown"" (UAWB) while FL-SOT
exceeding a certain threshold can. Finitely-enlarged Walker limits before UAWB
are theoretically calculated and well explain existing data. In addition,
change in wall mobility and even its sign-inversion can be understood only if
the anti-damping-like (ADL) SOT is appended. For N\'{e}el walls in
ferromagnetic-metal layer with both perpendicular and in-plane anisotropies, we
have calculated the respective modifications of wall mobility under the
coexistence of spin-transfer torque, SOTs and i-DMI. Analytics shows that in
trilayers with perpendicular anisotropy strong enough spin Hall angle and
appropriate sign of i-DMI parameter can lead to sign-inversion in wall mobility
even under small enough current density, while in those with in-plane
anisotropy this only occurs for current density in a specific range.",1804.00127v4
2008-06-13,Coherent control of nanomagnet dynamics via ultrafast spin torque pulses,"The magnetization orientation of a nanoscale ferromagnet can be manipulated
using an electric current via the spin transfer effect. Time domain
measurements of nanopillar devices at low temperatures have directly shown that
magnetization dynamics and reversal occur coherently over a timescale of
nanoseconds. By adjusting the shape of a spin torque waveform over a timescale
comparable to the free precession period (100-400 ps), control of the
magnetization dynamics in nanopillar devices should be possible. Here we report
coherent control of the free layer magnetization in nanopillar devices using a
pair of current pulses as narrow as 30 ps with adjustable amplitudes and delay.
We show that the switching probability can be tuned over a broad range by
timing the current pulses with the underlying free-precession orbits, and that
the magnetization evolution remains coherent for more than 1 ns even at room
temperature. Furthermore, we can selectively induce transitions along
free-precession orbits and thereby manipulate the free magnetic moment motion.
We expect this technique will be adopted for further elucidating the dynamics
and dissipation processes in nanomagnets, and will provide an alternative for
spin torque driven spintronic devices, such as resonantly pumping microwave
oscillators, and ultimately, for efficient reversal of memory bits in magnetic
random access memory (MRAM).",0806.2297v1
2023-11-13,Origin of reduced dynamical friction by dark matter halos with net prograde rotation,"We provide an explanation for the reduced dynamical friction on galactic bars
in spinning dark matter halos. Earlier work based on linear theory predicted an
increase in dynamical friction when dark halos have a net forward rotation,
because prograde orbits couple to bars with greater strength than retrograde
orbits. Subsequent numerical studies, however, found the opposite trend:
dynamical friction weakens with increasing spin of the halo. We revisit this
problem and demonstrate that linear theory in fact correctly predicts a reduced
torque in forward-rotating halos. We show that shifting the halo mass from
retrograde to prograde phase space generates a positive gradient in the
distribution function near the origin of the z-angular momentum (Lz=0), which
results in a resonant transfer of Lz to the bar, making the net dynamical
friction weaker. While this effect is subdominant for the major resonances,
including the corotation resonance, it leads to a significant positive torque
on the bar for the series of direct radial resonances, as these resonances are
strongest at Lz=0. The overall dynamical friction from spinning halos is shown
to decrease with the halo's spin, in agreement with the secular behavior of
N-body simulations. We validate our linear calculation by computing the
nonlinear torque from individual resonances using the angle-averaged
Hamiltonian.",2311.07640v2
2020-12-08,Transferring Orbital Angular Momentum to an Electron Beam Reveals Toroidal and Chiral Order,"Orbital angular momentum and torque transfer play central roles in a wide
range of magnetic textures and devices including skyrmions and spin-torque
electronics(1-4). Analogous topological structures are now also being explored
in ferroelectrics, including polarization vortex arrays in
ferroelectric/dielectric superlattices(5). Unlike magnetic toroidal order,
electric toroidal order does not couple directly to linear external fields. To
develop a mechanism that can control switching in polarization vortices, we
utilize a high-energy electron beam and show that transverse currents are
generated by polar order in the ballistic limit. We find that the presence of
an electric toroidal moment in a ferro-rotational phase transfers a measurable
torque and orbital angular momentum to the electron beam. Furthermore, we find
that the complex polarization patterns, observed in these heterostructures, are
microscopically chiral with a non-trivial axial component of the polarization.
This chirality opens the door for the coupling of ferroelectric and optical
properties.",2012.04134v2
2020-08-03,Interfacial spin-orbit torques,"Spin-orbit torques offer a promising mechanism for electrically controlling
magnetization dynamics in nanoscale heterostructures. While spin-orbit torques
occur predominately at interfaces, the physical mechanisms underlying these
torques can originate in both the bulk layers and at interfaces. Classifying
spin-orbit torques based on the region that they originate in provides clues as
to how to optimize the effect. While most bulk spin-orbit torque contributions
are well studied, many of the interfacial contributions allowed by symmetry
have yet to be fully explored theoretically and experimentally. To facilitate
progress, we review interfacial spin-orbit torques from a semiclassical
viewpoint and relate these contributions to recent experimental results. Within
the same model, we show the relationship between different interface transport
parameters. For charges and spins flowing perpendicular to the interface,
interfacial spin-orbit coupling both modifies the mixing conductance of
magnetoelectronic circuit theory and gives rise to spin memory loss. For
in-plane electric fields, interfacial spin-orbit coupling gives rise to torques
described by spin-orbit filtering, spin swapping and precession. In addition,
these same interfacial processes generate spin currents that flow into the
non-magnetic layer. For in-plane electric fields in trilayer structures, the
spin currents generated at the interface between one ferromagnetic layer and
the non-magnetic spacer layer can propagate through the non-magnetic layer to
produce novel torques on the other ferromagnetic layer.",2008.01182v1
2015-06-02,Respective influence of in-plane and out-of-plane spin-transfer torques in magnetization switching of perpendicular magnetic tunnel junctions,"The relative contributions of in-plane (damping-like) and out-of-plane
(field-like) spin-transfer-torques in the magnetization switching of
out-of-plane magnetized magnetic tunnel junctions (pMTJ) has been theoretically
analyzed using the transformed Landau-Lifshitz (LL) equation with the STT
terms. It is demonstrated that in a pMTJ structure obeying macrospin dynamics,
the out-of-plane torque influences the precession frequency but it does not
contribute significantly to the STT switching process (in particular to the
switching time and switching current density), which is mostly determined by
the in-plane STT contribution. This conclusion is confirmed by finite
temperature and finite writing pulse macrospin simulations of the current-field
switching diagrams. It contrasts with the case of STT-switching in in-plane
magnetized MTJ in which the field-like term also influences the switching
critical current. This theoretical analysis was successfully applied to the
interpretation of voltage-field STT switching diagrams experimentally measured
on perpendicular MTJ pillars 36 nm in diameter, which exhibit macrospin-like
behavior. The physical nonequivalence of Landau and Gilbert dissipation terms
in presence of STT-induced dynamics is also discussed.",1506.00780v2
2023-11-10,Observation of the out-of-plane orbital antidamping-like torque,"The out-of-plane antidamping-like orbital torque fosters great hope for
high-efficiency spintronic devices. Here we report experimentally the
observation of out-of-plane antidamping-like torque that could be generated by
z-polarized orbital current in ferromagnetic-metal/oxidized Cu bilayers, which
is presented unambiguously by the magnetic field angle dependence of
spin-torque ferromagnetic resonance signal. The oxidized Cu thickness
dependence of orbital torque ratios highlights the interfacial effect would be
responsible for the generation of orbital current. Besides that, the oxidized
Cu thickness dependence of damping parameter further proves the observation of
antidamping-like torque. This result contributes to enriching the
orbital-related theory of the generation mechanism of the orbital torque.",2311.05868v1
2019-11-13,Impact of the crystal orientation on spin-orbit torques in Fe/Pd bilayers,"Spin-orbit torques in ferromagnetic (FM)/non-magnetic (NM) heterostructures
offer more energy-efficient means to realize spin-logic devices; however, their
strengths are determined by the heterostructure interface. This work examines
crystal orientation impact on the spin-orbit torque efficiency in different
Fe/Pd bilayer systems. Spin torque ferromagnetic measurements evidence that the
damping-like torque efficiency is higher in epitaxial than in polycrystalline
bilayer structures while the field-like torque is negligible in all bilayer
structures. The strength of the damping-like torque decreases with
deterioration of the bilayer epitaxial quality. The present finding provides
fresh insight for the enhancement of spin-orbit torques in magnetic
heterostructures.",1911.05487v1
2022-04-27,Hidden interplay of current-induced spin and orbital torques in bulk Fe$_3$GeTe$_2$,"Low crystal symmetry of magnetic van der Waals materials naturally promotes
spin-orbital complexity unachievable in common magnetic materials used for
spin-orbit torque switching. Here, using first-principles methods, we
demonstrate that an interplay of spin and orbital degrees of freedom has a
profound impact on spin-orbit torques in a prototype van der Waals ferromagnet:
Fe$_3$GeTe$_2$ (FGT). While we show that bulk FGT hosts strong ""hidden""
current-induced torques harvested by each of its layers, we uncover that their
origin alternates between the conventional spin flux torque and the so-called
orbital torque as the magnetization direction is varied. A drastic difference
in the behavior of the two types of torques results in a non-trivial evolution
of switching properties with doping. Our findings promote the design of
non-equilibrium orbital properties as the guiding mechanism for crafting the
properties of spin-orbit torques in layered van der Waals materials.",2204.13052v3
2020-10-26,Domain Wall-Magnetic Tunnel Junction Spin Orbit Torque Devices and Circuits for In-Memory Computing,"There are pressing problems with traditional computing, especially for
accomplishing data-intensive and real-time tasks, that motivate the development
of in-memory computing devices to both store information and perform
computation. Magnetic tunnel junction (MTJ) memory elements can be used for
computation by manipulating a domain wall (DW), a transition region between
magnetic domains. But, these devices have suffered from challenges: spin
transfer torque (STT) switching of a DW requires high current, and the multiple
etch steps needed to create an MTJ pillar on top of a DW track has led to
reduced tunnel magnetoresistance (TMR). These issues have limited experimental
study of devices and circuits. Here, we study prototypes of three-terminal
domain wall-magnetic tunnel junction (DW-MTJ) in-memory computing devices that
can address data processing bottlenecks and resolve these challenges by using
perpendicular magnetic anisotropy (PMA), spin-orbit torque (SOT) switching, and
an optimized lithography process to produce average device tunnel
magnetoresistance TMR = 164%, resistance-area product RA = 31
{\Omega}-{\mu}m^2, close to the RA of the unpatterned film, and lower switching
current density compared to using spin transfer torque. A two-device circuit
shows bit propagation between devices. Device initialization variation in
switching voltage is shown to be curtailed to 7% by controlling the DW initial
position, which we show corresponds to 96% accuracy in a DW-MTJ full adder
simulation. These results make strides in using MTJs and DWs for in-memory and
neuromorphic computing applications.",2010.13879v1
2009-05-14,Maximum Spin of Black Holes Driving Jets,"Unbounded outflows in the form of highly collimated jets and broad winds
appear to be a ubiquitous feature of accreting black hole systems. The most
powerful jets are thought to derive a significant fraction, if not the
majority, of their power from the rotational energy of the black hole. Whatever
the precise mechanism that causes them, these jets must therefore exert a
braking torque on the black hole. We calculate the spin-up function for an
accreting black hole, accounting for this braking torque. We find that the
predicted black hole spin-up function depends only on the black hole spin and
dimensionless parameters describing the accretion flow. Using recent
relativistic magnetohydrodynamical numerical simulation results to calibrate
the efficiency of angular momentum transfer in the flow, we find that an ADAF
flow will spin a black hole up (or down) to an equilibrium value of about 96%
of the maximal spin value in the absence of jets. Combining our ADAF system
with a simple model for jet power, we demonstrate that an equilibrium is
reached at approximately 93% of the maximal spin value, as found in the
numerical simulation studies of the spin-up of accreting black holes, at which
point the spin-up of the hole by accreted material is balanced by the braking
torque arising from jet production. Our model also yields a relationship
between jet efficiency and black hole spin that is in surprisingly good
agreement with that seen in the simulation studies, indicating that our simple
model is a useful and convenient description of ADAF inflow - jet outflow about
a spinning black hole for incorporation in models of the formation and
evolution of galaxies, groups and clusters of galaxies.",0905.2378v2
2020-05-27,High-resolution tunneling spin transport characteristics of topologically distinct magnetic skyrmionic textures from theoretical calculations,"High-resolution tunneling electron spin transport properties (longitudinal
spin current (LSC) and spin transfer torque (STT) maps) of topologically
distinct real-space magnetic skyrmionic textures are reported by employing a
3D-WKB combined scalar charge and vector spin transport theory in the framework
of spin-polarized scanning tunneling microscopy (SP-STM). For our theoretical
investigation metastable skyrmionic spin structures with various topological
charges ($Q=-3,-2,-1,0,1,2$) in the (Pt$_{0.95}$Ir$_{0.05}$)/Fe/Pd(111)
ultrathin magnetic film are considered. Using an out-of-plane magnetized SP-STM
tip it is found that the maps of the LSC vectors acting on the spins of the
magnetic textures and all STT vector components exhibit the same topology as
the skyrmionic objects. In contrast, an in-plane magnetized tip generally does
not result in spin transport vector maps that are topologically equivalent to
the underlying spin structure, except for the LSC vectors acting on the spins
of the skyrmionic textures at a specific relation between the spin
polarizations of the sample and the tip. The magnitudes of the spin transport
vector quantities exhibit close relations to charge current SP-STM images
irrespectively of the skyrmionic topologies. Moreover, we find that the STT
efficiency (torque/current ratio) acting on the spins of the skyrmions can
reach large values up to $\sim$25 meV/$\mu$A ($\sim$0.97 $h/e$) above the rim
of the magnetic objects, but it considerably varies between large and small
values depending on the lateral position of the SP-STM tip above the
topological spin textures. A simple expression for the STT efficiency is
introduced to explain its variation. Our calculated spin transport vectors can
be used for the investigation of spin-polarized tunneling-current-induced spin
dynamics of topologically distinct surface magnetic skyrmionic textures.",2005.13266v2
2018-05-22,FMR-related phenomena in spintronic devices,"Spintronic devices, such as non-volatile magnetic random access memories and
logic devices, have attracted considerable attention as potential candidates
for future high efficient data storage and computing technology. In a heavy
metal or other emerging material with strong spin-orbit coupling (SOC), the
charge currents induce spin currents or spin accumulations via SOC. The
generated spin currents can exert spin-orbit torques (SOTs) on an adjacent
ferromagnet, which opens up a new way to realize magnetization dynamics and
switching of the ferromagnetic layer for spintronic devices. In the SOT scheme,
the charge-to-spin interconversion efficiency (SOT efficiency) is an important
figure of merit for applications. For the effective characterization of this
efficiency, the ferromagnetic resonance (FMR) based methods, such as the spin
transfer torque ferromagnetic resonance (ST-FMR) and the spin pumping, are
common utilized in addition to low frequency harmonic or dc measurements. In
this review, we focus on the ST-FMR measurements for the evaluation of the SOT
efficiency. We provide a brief summary of the different ST-FMR setups and data
analysis methods. We then discuss ST-FMR and SOT studies in various materials,
including heavy metals and alloys, topological insulators, two dimensional (2D)
materials, interfaces with strong Rashba effect, antiferromagnetic materials,
two dimensional electron gas (2DEG) in oxide materials and oxidized nonmagnetic
materials.",1805.08496v1
2023-05-23,Topological nature of the proper spin current and the spin-Hall torque,"Spin currents are key to spin torque devices, but determining the proper spin
current is non-trivial. Here we derive a general quantum-mechanical formula for
the intrinsic proper spin current showing that it is topological and can be
finite in the gap. For topological insulators with an out of plane
magnetization and the chemical potential in the surface state gap, the net spin
torque is determined by the competition between the topological spin-Hall
torque due to the bulk and the topological Edelstein effect due to the surface
states. We also discuss spin-3/2 hole quantum wells.",2305.14108v2
2012-11-15,Spin transport and tunable Gilbert damping in a single-molecule magnet junction,"We study time-dependent electronic and spin transport through an electronic
level connected to two leads and coupled with a single-molecule magnet via
exchange interaction. The molecular spin is treated as a classical variable and
precesses around an external magnetic field. We derive expressions for charge
and spin currents by means of the Keldysh non-equilibrium Green's functions
technique in linear order with respect to the time-dependent magnetic field
created by this precession. The coupling between the electronic spins and the
magnetization dynamics of the molecule creates inelastic tunneling processes
which contribute to the spin currents. The inelastic spin currents, in turn,
generate a spin-transfer torque acting on the molecular spin. This back-action
includes a contribution to the Gilbert damping and a modification of the
precession frequency. The Gilbert damping coefficient can be controlled by the
bias and gate voltages or via the external magnetic field and has a
non-monotonic dependence on the tunneling rates.",1211.3611v2
2018-05-25,Quasiclassical theory of the spin-orbit magnetoresistance of three-dimensional Rashba metals,"The magnetoresistance of a three-dimensional Rashba material placed on top of
a ferromagnetic insulator is theoretically investigated. In addition to the
intrinsic Rashba spin-orbit interaction, we also consider extrinsic spin-orbit
coupling via side-jump and skew scattering, and the Elliott-Yafet spin
relaxation mechanism. The latter is anisotropic due to the mass anisotropy
which reflects the noncentrosymmetric crystal structure of three-dimensional
Rashba metals. A quasiclassical approach is employed to derive a set of coupled
spin-diffusion equations, which are supplemented by boundary conditions that
account for the spin-transfer torque at the interface of the bilayer. The
magnetoresistance is fully determined by the current-induced spin polarization,
i.e., it cannot in general be ascribed to a single (bulk) spin Hall angle. Our
theoretical results reproduce several features of the experiments, at least
qualitatively, and contain established phenomenological results in the relevant
limiting cases. In particular, the anisotropy of the Elliott-Yafet spin
relaxation mechanism plays a major role for the interpretation of the observed
magnetoresistance.",1805.10245v1
2019-03-07,Investigating optically-excited THz standing spin waves using noncollinear magnetic bilayers,"We investigate optically excited THz standing spin waves in noncollinear
magnetic bilayers. Using femtosecond laser-pulse excitation, a spin current is
generated in the first ferromagnetic (FM) layer, and flows through a conductive
spacer layer to be injected into the second (transverse) FM layer, where it
exerts a spin-transfer torque on the magnetization and excites higher-order
standing spin waves. We show that the noncollinear magnetic bilayer is a
convenient tool that allows easy excitation of THz spin waves, and can be used
to investigate the dispersion and thereby the spin wave stiffness parameter in
the thin-film regime. This is experimentally demonstrated using wedge-shaped Co
and CoB (absorption) layers. Furthermore, the damping of these THz spin waves
is investigated, showing a strong increase of the damping with decreasing
absorption layer thickness, much stronger than expected from interface spin
pumping effects. Additionally, a previously unseen sudden decrease in the
damping for the thinnest films is observed. A model for the additional damping
contribution incorporating both these observations is proposed.",1903.02802v1
2019-07-04,Domain wall dynamics due to femtosecond laser-induced superdiffusive spin transport,"Manipulation of magnetic domain walls via a helicity-independent laser pulse
has recently been experimentally demonstrated and various physical mechanisms
leading to domain wall dynamics have been discussed. Spin-dependent
superdiffusive transport of hot electrons has been identified as one of the
possible ways how to affect a magnetic domain wall. Here, we develop a model
based on superdiffusive spin-dependent transport to study the laser-induced
transport of hot electrons through a smooth magnetic domain wall. We show that
the spin transfer between neighboring domains can enhance ultrafast
demagnetization in the domain wall. More importantly, our calculations reveal
that when the laser pulse is properly focused on to the vicinity of the domain
wall, it can excite sufficiently strong spin currents to generate a
spin-transfer torque that can rapidly move the magnetic domain wall by several
nanometers in several hundreds of femtoseconds, leading to a huge
nonequilibrium domain wall velocity.",1907.02419v1
2022-02-10,Did bio-homochirality arise from spin-polarized electron?,"The origin of bio-homochirality is a subject of much debate. The emergence of
chirality and life on earth is a break of symmetry to be compared with the
breaks of symmetry in the evolution of the universe. Based on a perspective of
asymmetry transfer, the chirality at molecular level might stem from electron
spin at subatomic level. Accordingly, in this paper a spin-induced chiral
selectivity (SICS) mechanism and its outreach are introduced and discussed. The
stress force or spin torque derived from quantum electrodynamics (QED) might be
the driving force for the transfer of asymmetry and the formation of molecular
chirality. Some recent experimental results seem to support the SICS
conjecture. If spin-polarized electrons (SPEs) did cause life to become
chirally selective, a magnetic half-metal material such as greigite (Fe3S4), a
mineral present in a primordial site where life could have emerged, might act
as a spin filter to produce SPEs, which then induced the asymmetric synthesis
of chiral molecules via the SICS mechanism. All these tentative thoughts may
help explain how homochirality and life could have arisen on the early Earth.",2202.04808v2
2017-06-22,Sign reversal of field like spin-orbit torque in ultrathin Chromium/Nickel bilayer,"In this work report unconventional sign change of field like spin orbit
torque in ultra-thin Chromium(1.5nm-5nm)/Nickel(8nm) bi-layer. We performed
standard spin-torque ferromagnetic resonance (ST-FMR) experiment in Cr/Ni
bi-layer by passing radio frequency current and measuring DC voltage. We
observe that when thickness of Cr layer is critically low (<6nm) spin orbit
torque by Cr on Ni significantly increases. Most importantly the sign of field
like torque is opposite to the Oersted field generated torque. To verify
interracial nature of this torque, 2 nm thin Cu is inserted between Cr and Ni
and field like torque behaves same as Oersted field induced torque. Hence
possible origin of such unconventional sign change of field like torque could
be inter-facial Rashba like spin orbit interaction which is present between Cr
and Ni but vanishes in Cr/Cu/Ni hetero-structure. From our experiment we can
estimate that approximately 35 Oe of effective Rashba like magnetic field is
created on 8 nm thicker Ni layer, when 1E12 A/m^2 current flows through Cr
layer. All experiments are done at room temperature. So Cr thin film is
expected to behave like paramagnet (Neel temperature of bulk Cr is 311K). Hence
Cr can be a good choice as a heavy metal to employ large spin orbit torque
combining bulk spin Hall effect and inter-facial Rashba interaction.",1706.07260v1
2018-01-29,Band-pass superlattice magnetic tunnel junctions,"Significant scientific and technological progress in the field of spintronics
is based on trilayer magnetic tunnel junction devices which principally rely on
the physics of single barrier tunneling. While technologically relevant devices
have been prototyped, the physics of single barrier tunneling poses ultimate
limitations on the performance of magnetic tunnel junction devices. Here, we
propose a fresh route toward high performance magnetic tunnel junctions by
making electronic analogs of optical phenomena such as anti-reflections and
Fabry-P\`erot resonances. The devices we propose feature anti-reflection
enabled superlattice heterostructures sandwiched between the fixed and the free
ferromagnets of the magnetic tunnel junction structure. Our predictions are
based on the non-equilibrium Green's function spin transport formalism coupled
self-consistently with the Landau-Lifshitz-Gilbert-Slonczewski equation. Owing
to the physics of bandpass spin filtering in the bandpass superlattice magnetic
tunnel junction device, we demonstrate an ultra-high boost in the tunnel
magneto-resistance (TMR$\approx5\times10^4\%$) and nearly 92% suppression of
spin transfer torque switching bias in comparison to a traditional trilayer
magnetic tunnel junction device. We rationalize improvised spin transfer torque
switching via analysis of the Slonczewski spin current transmission spectra.
The proof of concepts presented here can lead to next-generation spintronics
device design harvesting the rich physics of superlattice heterostructures and
exploiting spintronic analogs of optical phenomena.",1801.09409v2
2018-01-23,The dominancy of damping like torque for the current induced magnetization switching in Pt/Co/W multilayers,"Two classes of spin-orbit coupling (SOC) mechanisms have been considered as
candidate sources for the spin orbit torque (SOT): the spin Hall Effect (SHE)
in heavy metals with strong SOC and the Rashba effect arising from broken
inversion symmetry at material surfaces and interfaces. In this work, we have
investigated the SOT in perpendicularly magnetized Pt/Co/W films, which is
compared with the results in Pt/Co/AlOx films. Theoretically, in the case of
the asymmetric structure of trilayers with opposite sign of spin Hall angle,
both damping like torque and field like torque due to the SHE and the Rashba
effect will be enhanced. Using the harmonic measurements, we have characterized
the effective fields corresponding to the damping like torque and the field
like torque, but we have found the dominancy of damping like torque in the
Pt/Co/W films. It is much different from the results in the Pt/Co/AlOx films,
in which both the damping like torque and the field like torque are strong.",1801.07408v1
2006-02-07,Spin-transfer in bilayer magnetic nanopillars at high fields as a function of free layer thickness,"Spin transfer in asymmetric Co/Cu/Co bilayer magnetic nanopillars junctions
has been studied at low temperature as a function of free-layer thickness. The
phase diagram for current-induced magnetic excitations has been determined for
magnetic fields up to 7.5 T applied perpendicular to the junction surface and
free-layers thicknesses from 2 to 5 nm. The junction magnetoresistance is
independent of thickness. The critical current for magnetic excitations
decreases linearly with decreasing free-layer thickness, but extrapolates to a
finite critical current in the limit of zero thickness. The limiting current is
in quantitative agreement with that expected due to a spin-pumping contribution
to the magnetization damping. It may also be indicative of a decrease in the
spin-transfer torque efficiency in ultrathin magnetic layers.",0602159v3
2015-01-30,Improved spectral stability in spin transfer nano-oscillators: single vortex versus coupled vortices dynamics,"We perform a comparative study of spin transfer induced excitation of the
gyrotropic motion of a vortex core with either uniform or vortex spin
polarizers. The microwave output voltage associated with the vortex dynamics,
detected in both cases, displays a strong reduction of phase fluctuations in
the case of the vortex polarizer, with a decrease of the peak linewidth by one
order of magnitude down to 200kHz at zero field. A thorough study of rf
emission features for the different accessible vortex configurations shows that
this improvement is related to the excitation of coupled vortex dynamics by
spin transfer torques.",1501.07839v1
2015-02-11,Understanding of phase noise squeezing under fractional synchronization of non-linear spin transfer vortex oscillator,"We investigate experimentally the synchronization of a vortex based spin
transfer oscillator to an external rf current whose frequency is at multiple
integers, as well as half integer, of the oscillator frequency. Through a
theoretical study of the locking process, we highlight both the crucial role of
the symmetries of the spin torques acting on the magnetic vortex and the
nonlinear properties of the oscillator on the phase locking process. Through
the achievement of a perfect injection locking state, we report a record phase
noise reduction down to -90dBc/Hz at 1 kHz offset frequency. The phase noise of
these nanoscale oscillators is demonstrating as being low and controllable
which is of significant importance for real applications using spin transfer
devices.",1502.03485v1
2016-05-10,Topological spin-transfer drag driven by skyrmion diffusion,"We study the spin-transfer drag mediated by the Brownian motion of skyrmions.
The essential idea is illustrated in a two-terminal geometry, in which a thin
film of a magnetic insulator is placed in between two metallic reservoirs. An
electric current in one of the terminals pumps topological charge into the
magnet via a spin-transfer torque. The charge diffuses over the bulk of the
system as stable skyrmion textures. By Onsager's reciprocity, the topological
charge leaving the magnet produces an electromotive force in the second
terminal. The voltage signal decays algebraically with the separation between
contacts, in contrast to the exponential suppression of the spin drag driven by
non-protected excitations like magnons. We show how this topological effect can
be used as a tool to characterize the phase diagram of chiral magnets and thin
films with interfacial Dzyaloshinskii-Moriya interactions.",1605.02857v2
2019-10-01,Sub-nanosecond spin-torque switching of perpendicular magnetic tunnel junction nanopillars at cryogenic temperatures,"Spin-transfer magnetic random access memory is of significant interest for
cryogenic applications where a persistent, fast, low-energy consumption and
high device density is needed. Here we report the low-temperature nanosecond
duration spin-transfer switching characteristics of perpendicular magnetic
tunnel junction (pMTJ) nanopillar devices (40 to 60 nm in diameter) and
contrast them to their room temperature properties. Interestingly, at fixed
pulse voltage overdrive the characteristic switching time decreases with
temperature, in contrast to macrospin model predictions, with the largest
reduction in switching time occurring between room temperature and 150 K. The
switching energy increases with decreasing temperature, but still compares very
favorably to other types of spin-transfer devices at 4 K, with < 300 fJ
required per switch. Write error rate (WER) measurements show highly reliable
(WER <= 5x10^-5 with 4 ns pulses at 4 K) demonstrating the promise of pMTJ
devices for cryogenic applications and routes to further device optimization.",1910.00625v1
2021-07-28,Transport theory and spin-transfer physics for frustrated magnets,"We study the electron dynamics in magnetic conductors with frustrated
interactions dominated by isotropic exchange. We present a transport theory for
itinerant carriers built upon the (single-band) doped Hubbard model and the
slave-boson formalism, which incorporates the spin-exchange with the
magnetically frustrated background into the representation of electron
operators in a clear and controllable way. We also formulate hydrodynamic
equations for the itinerant charge and spin degrees of freedom, whose currents
contain new contributions that depend on the spatiotemporal variations of the
order parameter of the frustrated magnet, which are described by Yang-Mills
fields. Furthermore, we elucidate the transfer of angular momentum from the
itinerant charge fluid to the magnet (i.e., the spin-transfer torque) via
reciprocity arguments. A detailed microscopic derivation of our effective
theory is also provided for one of the simplest models of frustrated magnetism,
namely the Heisenberg antiferromagnet on a triangular lattice. Our findings
point towards the possibility of previously unanticipated Hall physics in these
frustrated platforms.",2107.13330v2
2006-11-20,Current Induced Order Parameter Dynamics: Microscopic Theory Applied to Co/Cu/Co spin valves,"Transport currents can alter alter order parameter dynamics and change steady
states in superconductors, in ferromagnets, and in hybrid systems. In this
article we present a scheme for fully microscopic evaluation of order parameter
dynamics that is intended for application to nanoscale systems. The approach
relies on time-dependent mean-field-theory, on an adiabatic approximation, and
on the use of non-equilibrium Greens function (NEGF) theory to calculate the
influence of a bias voltage across a system on its steady-state density matrix.
We apply this scheme to examine the spin-transfer torques which drive
magnetization dynamics in Co/Cu/Co spin-valve structures. Our microscopic
torques are peaked near Co/Cu interfaces, in agreement with most previous
pictures, but suprisingly act mainly on Co transition metal $d$-orbitals rather
than on $s$-orbitals as generally supposed.",0611534v1
2008-03-26,Effects of rf Current on Spin Transfer Torque Induced Dynamics,"The impact of radiofrequency (rf) currents on the direct current (dc) driven
switching dynamics in current-perpendicular-to-plane nanoscale spin valves is
demonstrated. The rf currents dramatically alter the dc driven free layer
magnetization reversal dynamics as well as the dc switching level. This occurs
when the frequency of the rf current is tuned to a frequency range around the
dc driven magnetization precession frequencies. For these frequencies,
interactions between the dc driven precession and the injected rf induce
frequency locking and frequency pulling effects that lead to a measurable
dependence of the critical switching current on the frequency of the injected
rf. Based on macrospin simulations, including dc as well as rf spin torque
currents, we explain the origin of the observed effects.",0803.3791v2
2008-07-18,Microscopic approach to current-driven domain wall dynamics,"This review describes in detail the essential techniques used in microscopic
theories on spintronics. We have investigated the domain wall dynamics induced
by electric current based on the $s$-$d$ exchange model. The domain wall is
treated as rigid and planar and is described by two collective coordinates: the
position and angle of wall magnetization. The effect of conduction electrons on
the domain wall dynamics is calculated in the case of slowly varying spin
structure (close to the adiabatic limit) by use of a gauge transformation. The
spin-transfer torque and force on the wall are expressed by Feynman diagrams
and calculated systematically using non-equilibrium Green's functions, treating
electrons fully quantum mechanically. The wall dynamics is discussed based on
two coupled equations of motion derived for two collective coordinates. The
force is related to electron transport properties, resistivity, and the Hall
effect. Effect of conduction electron spin relaxation on the torque and wall
dynamics is also studied.",0807.2894v2
2010-04-22,Optimal time-dependent polarized current pattern for fast domain wall propagation in nanowires: Exact solutions for biaxial and uniaxial anisotropies,"One of the important issues in nanomagnetism is to lower the current needed
for a technologically useful domain wall (DW) propagation speed. Based on the
modified Landau-Lifshitz-Gilbert (LLG) equation with both Slonczewski
spin-transfer torque and the field-like torque, we derive the optimal spin
current pattern for fast DW propagation along nanowires. Under such conditions,
the DW velocity in biaxial wires can be enhanced as much as ten times compared
to the velocities achieved in experiments so far. Moreover, the fast variation
of spin polarization can help DW depinning. Possible experimental realizations
are discussed.",1004.3840v1
2011-02-17,Long-Term evolution of Discs around Magnetic Stars,"We investigate the evolution of a thin viscous disc surrounding magnetic
star, including the spindown of the star by the magnetic torques it exerts on
the disc. The transition from an accreting to a non-accreting state, and the
change of the magnetic torque across the corotation radius are included in a
generic way, the widths of the transition taken in the range suggested by
numerical simulations. In addition to the standard accreting state, two more
are found. An accreting state can develop into a 'dead' disc state, with inner
edge well outside corotation. More often, a 'trapped' state develops, in which
the inner disc edge stays close to corotation even at very low accretion rates.
The long-term evolution of these two states is different. In the dead state the
star spins down incompletely, retaining much of its initial spin. In the
trapped state the star asymptotically can spin down to arbitarily low rates,
its angular momentum transferred to the disc. We identify these outcomes with
respectively the rapidly rotating and the very slowly rotating classes of Ap
stars and magnetic white dwarfs.",1102.3697v2
2012-01-13,Intermediate state switching dynamics in magnetic double layer nanopillars grown by molecular beam epitaxy,"We observe a stable intermediate resistance switching state in the current
perpendicular to plane geometry for all Co/Cu/Co double layer nanopillar
junctions grown by molecular beam epitaxy. This novel state has a resistance
between the resistances of the parallel and antiparallel alignment of both
Co-layer magnetizations. The state, which originates from an additional
in-plane magnetic easy axis, can be reached by spin transfer torque switching
or by an external magnetic field. In addition to spin torque-induced coherent
small-angle spin wave modes we observe a broad microwave emission spectrum. The
latter is attributed to incoherent magnetic excitations that lead to a
switching between the intermediate state and the parallel or antiparallel
alignment of both ferromagnetic layers. We conclude that the additional
magnetic easy axis suppresses a stable trajectory of coherent large-angle
precession, which is not observed in our samples.",1201.2752v1
2015-07-23,Nanomagnet coupled to quantum spin Hall edge: An adiabatic quantum motor,"The precessing magnetization of a magnetic islands coupled to a quantum spin
Hall edge pumps charge along the edge. Conversely, a bias voltage applied to
the edge makes the magnetization precess. We point out that this device
realizes an adiabatic quantum motor and discuss the efficiency of its operation
based on a scattering matrix approach akin to Landauer-B""uttiker theory.
Scattering theory provides a microscopic derivation of the
Landau-Lifshitz-Gilbert equation for the magnetization dynamics of the device,
including spin-transfer torque, Gilbert damping, and Langevin torque. We find
that the device can be viewed as a Thouless motor, attaining unit efficiency
when the chemical potential of the edge states falls into the
magnetization-induced gap. For more general parameters, we characterize the
device by means of a figure of merit analogous to the ZT value in
thermoelectrics.",1507.06505v2
2017-05-03,Synthetic ferrimagnet spin transfer torque oscillator: model and non-linear properties,"The non-linear parameters of spin-torque oscillators based on a synthetic
ferrimagnet free layer (two coupled layers) are computed. The analytical
expressions are compared to macrospin simulations in the case of a synthetic
ferrimagnet excited by a current spin-polarized by an external fixed layer. It
is shown that, of the two linear modes, acoustic and optical, only one is
excited at a time, and therefore the self-sustained oscillations are similar to
the dynamics of a single layer. However, the non-linear parameters values can
be controlled by the parameters of the synthetic ferrimagnet. With a strong
coupling between the two layers and asymmetric layers (different thicknesses),
it is demonstrated that the non-linear frequency shift can be reduced, which
results in the reduction of the linewidth of the power spectral density. For a
particular applied field, the non-linear parameter can even vanish; this
corresponds to a transition between a red-shift and a blue-shift frequency
dependence on the current and a linewidth reduction to the linear linewidth
value.",1705.01335v1
2019-06-14,Electrically-driven domain wall motion in a ferromagnetic Kagome lattice,"We theoretically study domain wall motion induced by an electric field in the
quantum anomalous Hall states on a two-dimensional Kagome lattice with
ferromagnetic order and spin-orbit coupling. We show that an electric charge is
accumulated near the domain wall which indicates that the electric field drives
both the accumulated charge and the domain wall with small energy dissipation.
Using the linear response theory we compute the non-equilibrium spin density
which exerts a non-adiabatic spin transfer torque on textures of the local
magnetization. This torque emerges even when the bulk is insulating and does
not require the longitudinal electric current. Finally, we estimate the
velocity of domain wall motion in this system, which is faster than that in
conventional metals.",1906.05980v1
2017-03-06,Damping dependence of spin-torque effects in thermally assisted magnetization reversal,"Thermal fluctuations of nanomagnets driven by spin-polarized currents are
treated via the Landau-Lifshitz-Gilbert equation as generalized to include both
the random thermal noise field and Slonczewski spin-transfer torque terms. The
magnetization reversal time of such a nanomagnet is then evaluated for wide
ranges of damping by using a method which generalizes the solution of the
so-called Kramers turnover problem for mechanical Brownian particles, thereby
bridging the very low damping and intermediate damping Kramers escape rates, to
the analogous magnetic turnover problem. The reversal time is then evaluated
for a nanomagnet with the free energy density given in the standard form of
superimposed easy-plane and in-plane easy-axis anisotropies with the dc bias
field along the easy axis.",1703.01879v5
2019-01-12,Importance sampling for thermally induced switching and non-switching probabilities in spin-torque magnetic nanodevices,"Spin-transfer torque magnetoresistive random access memory is a potentially
transformative technology in the non-volatile memory market. Its viability
depends, in part, on one's ability to predictably induce or prevent switching;
however, thermal fluctuations cause small but important errors in both the
writing and reading processes. Computing these very small probabilities for
magnetic nanodevices using naive Monte Carlo simulations is essentially
impossible due to their slow statistical convergence, but variance reduction
techniques can offer an effective way to improve their efficiency. Here, we
provide an illustration of how importance sampling can be efficiently used to
estimate low read and write soft error rates of macrospin and coupled-spin
systems.",1901.03890v1
2021-12-24,Skyrmion nucleation on the surface of a topological insulator,"Skyrmion nucleation induced by spin-transfer torques at an interface of a
topological insulator and a ferromagnetic insulator is investigated. Due to
strong spin-orbit coupling on a surface of topological insulators, which
enhances the effect of spin torques, efficient manipulation of skyrmions is
expected, and therefore, topological insulators could provide the ideal
platform to achieve high-performance skyrmionic devices. Using micromagnetic
simulations and energetics, we evaluate properties of the skyrmion nucleation
on a surface of topological insulators, such as nucleation time, critical
electric field, and skyrmion numbers. We show that the nucleation time is
inversely proportional to the applied electric field. We also identify the
Gilbert damping and temperature dependencies of the critical field.
Furthermore, we analytically evaluate the effect of the Dzyaloshinskii-Moriya
interaction and demonstrate that the temperature dependence can be explained by
the reduction of a magnon excitation gap due to the self-energy corrections.",2112.12967v2
2022-11-09,Alternative understanding of the skyrmion Hall effect based on one-dimensional domain wall motion,"A moving magnetic skyrmion exhibits transverse deflection. This so-called
skyrmion Hall effect has been explained by the Thiele equation. Here, we
provide an alternative interpretation of the skyrmion Hall effect based on the
dynamics of domain walls enclosing the skyrmion. We relate the
spin-torque-induced local rotation of the domain wall segments to the shift of
the skyrmion core, explaining the skyrmion Hall effect at the micromagnetic
level. Bases on our intuitive interpretation, we also show that the skyrmion
Hall effect can be suppressed by combining the spin-transfer and spin-orbit
torques, whereby removing the major obstacle to utilizing skyrmions in devices.",2211.04949v2
2021-12-16,"Optical multipolar torque in structured electromagnetic fields: on `helicity gradient' torque, quadrupolar torque and the spin of field gradient","Structured light mechanically interacts with matter via optical forces and
torques. The optical torque is traditionally calculated via the flux of total
angular momentum (AM) into a volume enclosing an object. In [Phys. Rev. A 92,
043843 (2015)] a powerful method was suggested to calculate optical torque
separately from the flux of the spin and the orbital parts of optical AM,
providing useful physical insight. However, the method predicted a new type of
dipolar torque dependent on the gradient of the helicity density of the optical
beam, inconsistent with prior torque calculations. In this work we intend to
clarify this discrepancy and clear up the confusion. We re-derive, from first
principles and with detailed derivations, both the traditional dipolar total
torque using total AM flux, and the spin and orbital torque components based on
the corresponding AM contributions, ensuring that their sum agrees with the
total torque. We also test our derived analytical expressions against numerical
integration, with exact agreement. We find that `helicity gradient' torque
terms indeed exist in the spin and orbital components separately, but we
present corrected prefactors, such that upon adding them, they cancel out, and
the `helicity gradient' term vanishes from the total dipolar torque,
reconciling literature results. We also derive the analytical expression of the
quadrupolar torque, showing that it is proportional to the spin of the EM field
gradient, rather than the local EM field spin, as sometimes wrongly assumed in
the literature. We provide examples of counter-intuitive situations where the
spin of the EM field gradient behaves very differently to the local EM spin.
Naively using the local EM field spin leads to wrong predictions of the torque
on large particles with strong contributions of quadrupole and higher-order
multipoles, especially in a structured incident field.",2112.09256v1
2014-11-12,Dependence of the Efficiency of Spin Hall Torque on the Transparency of Pt-Ferromagnetic Layer Interfaces,"We report that spin current transport across Pt-ferromagnet (FM) interfaces
is strongly dependent on the type and the thickness of the FM layer and on
post-deposition processing protocols. By employing both harmonic voltage
measurements and spin-torque ferromagnetic resonance measurements, we find that
the efficiency of the Pt spin Hall effect in exerting a damping-like spin
torque on the FM ranges from < 0.05 to > 0.10 under different interfacial
conditions. We also show that the temperature dependence of the spin torque
efficiencies for both the damping-like torque and field-like torque is
dependent upon the details of the Pt-FM interface. The ""internal"" spin Hall
angle of the Pt thin films used in this study, after taking the interfacial
spin transmission factor into account, is estimated to be ~ 0.20. This suggests
that a careful engineering of Pt-FM interfaces can improve the spin-Hall-torque
efficiency of Pt-based spintronic devices.",1411.3379v1
2004-05-26,Current-Induced Effective Magnetic Fields in Co/Cu/Co Nanopillars,"We present a method to measure the effective field contribution to
spin-transfer-induced interactions between the magnetic layers in a trilayer
nanostructure, which enables spin-current effects to be distinguished from the
usual charge-current-induced magnetic fields. This technique is demonstrated on
submicron Co/Cu/Co nanopillars. The hysteresis loop of one of the magnetic
layers in the trilayer is measured as a function of current while the direction
of magnetization of the other layer is kept fixed, first in one direction and
then in the opposite direction. These measurements show a current-dependent
shift of the hysteresis loop which, based on the symmetry of the magnetic
response, we associate with spin-transfer. The observed loop-shift with applied
current at room temperature is reduced in measurements at 4.2 K. We interprete
these results both in terms of a spin-current dependent effective activation
barrier for magnetization reversal and a spin-current dependent effective
magnetic field. From data at 4.2 K we estimate the magnitude of the
spin-transfer induced effective field to be $\sim 1.5 \times 10^{-7} $ Oe
cm$^2$/A, about a factor of 5 less than the spin-transfer torque.",0405617v1
2023-04-28,Dynamical friction and feedback on galactic bars in the general fast-slow regime,"Current theories of dynamical friction on galactic bars are based either on
linear perturbation theory, which is valid only in the fast limit where the bar
changes its pattern speed rapidly, or on adiabatic theory, which is applicable
only in the slow limit where the bar's pattern speed is near-constant. In this
paper, we study dynamical friction on galactic bars spinning down at an
arbitrary speed, seamlessly connecting the fast and slow limits. We treat the
bar-halo interaction as a restricted $N$-body problem and solve the
collisionless Boltzmann equation using the fast-angle-averaged Hamiltonian. The
phase-space distribution and density wakes predicted by our averaged model are
in excellent agreement with full 3D simulations. In the slow regime where
resonant trapping occurs, we show that, in addition to the frictional torque,
angular momentum is transferred directly due to the migration of the trapped
phase-space: trapped orbits comoving with the resonance typically gain angular
momentum, while untrapped orbits leaping over the trapped island lose angular
momentum. Due to the negative gradient in the distribution function, gainers
typically outnumber the losers, resulting in a net negative torque on the
perturber. Part of this torque due to the untrapped orbits was already
identified by Tremaine & Weinberg who named the phenomenon dynamical feedback.
Here, we derive the complete formula for dynamical feedback, accounting for
both trapped and untrapped orbits. Using our revised formula, we show that
dynamical feedback can account for up to $30\%$ of the total torque on the
Milky Way's bar.",2305.00022v2
2021-09-23,Large Exotic Spin Torques in Antiferromagnetic Iron Rhodium,"Spin torque is a promising tool for driving magnetization dynamics for novel
computing technologies. These torques can be easily produced by spin-orbit
effects, but for most conventional spin source materials, a high degree of
crystal symmetry limits the geometry of the spin torques produced. Magnetic
ordering is one way to reduce the symmetry of a material and allow exotic
torques, and antiferromagnets are particularly promising because they are
robust against external fields. We present spin torque ferromagnetic resonance
measurements and second harmonic Hall measurements characterizing the spin
torques in antiferromagnetic iron rhodium alloy. We report extremely large,
strongly temperature-dependent exotic spin torques with a geometry apparently
defined by the magnetic ordering direction. We find the spin torque efficiency
of iron rhodium to be (330$\pm$150) % at 170 K and (91$\pm$32) % at room
temperature. We support our conclusions with theoretical calculations showing
how the antiferromagnetic ordering in iron rhodium gives rise to such exotic
torques.",2109.11108v1
2013-08-05,Magnonic momentum transfer force on domain walls confined in space,"Momentum transfer from incoming magnons to a Bloch domain wall is calculated
using one dimensional continuum micromagnetic analysis. Due to the confinement
of the wall in space, the dispersion relation of magnons is different from that
of a single domain. This mismatch of dispersion relations can result in
reflection of magnons upon incidence on the domain wall, whose direct
consequence is a transfer of momentum between magnons and the domain wall. The
corresponding counteraction force exerted on the wall can be used for the
control of domain wall motion through magnonic linear momentum transfer, in
analogy with the spin transfer torque induced by magnonic angular momentum
transfer.",1308.0965v1
2021-11-23,Effect of interfacial intermixing on spin-orbit torque in Co/Pt bilayers,"Using the first-principles non-equilibrium Green's function technique with
supercell disorder averaging, we study the influence of interfacial intermixing
on the spin-orbit torque in Co$\mid$Pt bilayers. Intermixing is modeled by
inserting one or more monolayers of a disordered CoPt alloy between Co and Pt.
Dampinglike torque is moderately enhanced by interfacial intermixing, while the
fieldlike torque, which is small for abrupt interfaces, is strongly enhanced
and becomes comparable to the dampinglike torque. The enhancement of the
fieldlike torque is attributed to the interface between Co and the intermixed
region. The planar Hall-like torque increases with intermixing but remains
relatively small. The behavior of the torques is similar for bilayers with
(111) and (001)-oriented interfaces. Strong dependence of the fieldlike torque
on intermixing could provide a way to tune the fieldlike-to-dampinglike torque
ratio by interface engineering.",2111.12178v2
2014-05-04,Magnetic braking of Ap/Bp stars: an alternative formation mechanism of compact intermediate-mass binary pulsars,"It is difficult for the intermediate-mass X-ray binaries (IMXBs) evolutionary
channel to form intermediate-mass binary pulsars (IMBPs) with a short orbital
period (less than 3 d) via stable mass transfer. The main reason is that the
magnetic braking mechanisms are generally thought not to work for donor stars
with a mass of greater than 1.5 $\rm M_{\odot}$ in the canonical model.
However, some intermediate-mass stars have anomalously strong magnetic fields
(about 100 -- 10000 G), i. e. so-called Ap or Bp stars. With the coupling
between the magnetic field and the irradiation-driven wind from the surface of
Ap/Bp stars, a plausible magnetic braking mechanism should be expected. In this
work, we attempt to investigate if IMXBs with Ap/Bp stars can produce IMBPs
with a short orbital period (less than 3 d) by such an anomalous magnetic
braking mechanism. Using a stellar evolution code, we have simulated the
evolution of a large number of IMXBs consisting of a NS and an Ap/Bp star. For
the spin evolution of the NS, we consider the accretion torque, the propeller
torque, and the spin-down torque caused by the interaction between the magnetic
field and the accretion disc. The calculated results show that, employing
anomalous magnetic braking of Ap/Bp stars, IMXBs can evolve into compact IMBPs
with short orbital periods of less than 3 d. However, there exists significant
discrepancy between the spin periods of IMBPs in our simulated results and
those observed.",1405.0691v1
2018-03-06,Exoplanets Torqued by the Combined Tides of a Moon and Parent Star,"In recent years, there has been interest in Earth-like exoplanets in the
habitable zones of low mass stars ($\sim0.1-0.6\,M_\odot$). Furthermore, it has
been argued that a large moon may be important for stabilizing conditions on a
planet for life. If these two features are combined, then an exoplanet can feel
a similar tidal influence from both its moon and parent star, leading to
potentially interesting dynamics. The moon's orbital evolution depends on the
exoplanet's initial spin period $P_0$. When $P_0$ is small, transfer of the
exoplanet's angular momentum to the moon's orbit can cause the moon to migrate
outward sufficiently to be stripped by the star. When $P_0$ is large, the moon
migrates less and the star's tidal torques spin down the exoplanet. Tidal
interactions then cause the moon to migrate inward until it is likely tidally
disrupted by the exoplanet and potentially produces rings. While one may think
that these findings preclude the presence of moons for the exoplanets of low
mass stars, in fact a wide range of timescales are found for the loss or
destruction of the moon; it can take $\sim10^6-10^{10}\,{\rm yrs}$ depending on
the system parameters. When the moon is still present, the combined tidal
torques force the exoplanet to spin asynchronously with respect to both its
moon and parent star, which tidally heats the exoplanet. This can produce heat
fluxes comparable to those currently coming through the Earth, arguing that
combined tides may be a method for driving tectonic activity in exoplanets.",1803.01971v2
2016-11-16,Switching based Spin Transfer Torque Oscillator with zero-bias field and large tuning-ratio,"We propose a novel concept of obtaining oscillations with frequencies in
very-high frequency (VHF) and ultra-high frequency (UHF) bands. A traditional
spin torque nano-oscillator (STNO) consists of at least one pinned layer (PL)
and one free layer (FL) which precesses in a fixed orbit, defined by a
precession angle, which results in magneto-resistance (MR) oscillations. In
STNO, with aligned or even orthogonal easy-axis of the magnetic layers and with
or without external bias magnetic field, it is not possible to attain full MR
swing. The constringed MR swing jeopardizes the extracted output power.
Furthermore, the orbit is strongly disturbed by the thermal fluctuations
resulting in strong magnetic noise. In stark contrast to the operation
principle of a STNO, we theoretically demonstrate, with the practical
parameters from the experiments, that with a unidirectional current in a dual
asymmetric free-layers (with no pinned layer) based perpendicular magnetic
tunnel junction (pMTJ), both of the free layers can attain a complete and
out-of-phase self-sustained switching without the aid of any external magnetic
field. This design facilitates a switching based spin torque oscillator
(SW-STO) with a full MR swing, and hence a larger output power, for stable and
more thermally robust free-running oscillations. Furthermore, the integration
with the n-type metal-oxide-semiconductor (NMOS) field-effect transistors at
130, 65 and 14 nm node is appraised to expound its effect on the oscillator
performance, controllability with DC bias and the design constraints, to
demonstrate the viability of the design as a dynamically controllable
oscillator for practical on-chip implementation.",1611.05169v3
2022-07-25,Spin-orbit torque switching of magnetic tunnel junctions for memory application,"Spin-orbit torques (SOT) provide a versatile tool to manipulate the
magnetization of diverse classes of materials and devices using electric
currents, leading to novel spintronic memory and computing approaches. In
parallel to spin transfer torques (STT), which have emerged as a leading
non-volatile memory technologie, SOT broaden the scope of current-induced
magnetic switching to applications that run close to the clock speed of the
central processing unit and unconventional computing architectures. In this
paper, we review the fundamental characteristics of SOT and their use to switch
magnetic tunnel junction (MTJ) devices, the elementary unit of the
magnetoresistive random access memory (MRAM). In the first part, we illustrate
the physical mechanisms that drive the SOT and magnetization reversal in
nanoscale structures. In the second part, we focus on the SOT-MTJ cell. We
discuss the anatomy of the MTJ in terms of materials and stack development,
summarize the figures of merit for SOT switching, review the field-free
operation of perpendicularly magnetized MTJs, and present options to combine
SOT, STT and voltage-gate assisted switching. In the third part, we consider
SOT-MRAMs in the perspective of circuit integration processes, introducing
considerations on scaling and performance, as well as macro-design
architectures. We thus bridge the fundamental description of SOT-driven
magnetization dynamics with an application-oriented perspective, including
device and system-level considerations, goals, and challenges.",2207.11974v1
2022-11-29,Spin Torque Oscillator and Magnetization Switching in double barrier Rashba Zeeman Magnetic Tunnel Junction,"In this letter, we have studied the spin torque based magnetization
oscillations and switching in presence of Rashba - Zeeman (RZ), Ruderman -
Kittel - Kasuya - Yoside (RKKY) and Dzyaloshinskii - Moriya (DM) interactions
in a double barrier RZ$|$Heavy Metal (HM)$|$RZ magnetic tunnel junction (MTJ).
The system has stable magnetization oscillations and can work as an oscillator
or a switcher for a significant difference in the strength of RKKY and DM
interaction under suitable spin transfer torque (STT). For the proposed system
with same order of RKKY and DM interaction, a nonlinear characteristic of the
magnetization oscillation is observed. However, this nonlinearity of
oscillations can be reduced by an external magnetic field or considering a
material with suitable RZ interaction. In addition to this, our study reveals
the magnetization switching can be tuned by using suitable STT. A dependence of
switching time on layer thickness is also observed. Also, the switching speed
increases with the thickness for systems having either same order of RKKY and
DM interaction or dominated by RKKY interaction. An opposite characteristic is
seen when DM interaction dominates over RKKY interaction.",2211.16127v2
2015-11-11,Spin Swapping Transport and Torques in Ultrathin Magnetic Bilayers,"Planar spin transport in disordered ultrathin magnetic bilayers comprising a
ferromagnet and a normal metal (typically used for spin pumping, spin Seebeck
and spin-orbit torque experiments) is investigated theoretically. Using a
tight-binding model that treats extrinsic spin Hall effect, spin swapping and
spin relaxation on equal footing, we show that the nature of spin-orbit coupled
transport dramatically depends on ratio between the layers thickness $d$ and
the mean free path $\lambda$. While spin Hall effect dominates in the diffusive
limit ($d\gg\lambda$), spin swapping dominates in Knudsen regime
($d\lesssim\lambda$). A remarkable consequence is that the symmetry of the
spin-orbit torque exerted on the ferromagnet is entirely different in these two
regimes.",1511.03454v1
2011-06-17,Gate-dependent spin-torque in a nanoconductor-based spin-valve,"This article discusses the spin-torque effect in a spin-valve made out of two
ferromagnetic leads connected through a coherent nanoconductor (NC), in the
limit where a single channel of the NC lies near the Fermi energy of the leads.
Due to quantum interferences inside the NC, the spin-torque presents clear
qualitative differences with respect to the case of a multichannel disordered
spin-valve. In particular, it can be modulated with the NC gate voltage. In
principle, this modulation can be observed experimentally, assuming that the
spin-torque affects a ferromagnetic nano-domain in direct contact with the NC.",1106.3540v1
2010-04-09,Thermally driven spin injection from a ferromagnet into a non-magnetic metal,"Creating, manipulating and detecting spin polarized carriers are the key
elements of spin based electronics. Most practical devices use a perpendicular
geometry in which the spin currents, describing the transport of spin angular
momentum, are accompanied by charge currents. In recent years, new sources of
pure spin currents, i.e., without charge currents, have been demonstrated and
applied. In this paper, we demonstrate a conceptually new source of pure spin
current driven by the flow of heat across a ferromagnetic/non-magnetic metal
(FM/NM) interface. This spin current is generated because the Seebeck
coefficient, which describes the generation of a voltage as a result of a
temperature gradient, is spin dependent in a ferromagnet. For a detailed study
of this new source of spins, it is measured in a non-local lateral geometry. We
developed a 3D model that describes the heat, charge and spin transport in this
geometry which allows us to quantify this process. We obtain a spin Seebeck
coefficient for Permalloy of -3.8 microvolt/Kelvin demonstrating that thermally
driven spin injection is a feasible alternative for electrical spin injection
in, for example, spin transfer torque experiments.",1004.1566v1
2020-02-11,Spintronics meets density matrix renormalization group: Quantum spin torque driven nonclassical magnetization reversal and dynamical buildup of long-range entanglement,"We introduce time-dependent density matrix renormalization group (tDMRG) as a
solution to long standing problem in spintronics -- how to describe
spin-transfer torque (STT) between flowing spins of conduction electrons and
localized spins within a magnetic material by treating the dynamics of both
spin species fully quantum-mechanically. In contrast to conventional
Slonczewski-Berger STT, where the localized spins are viewed as classical
vectors obeying the Landau-Lifshitz-Gilbert equation and where their STT-driven
dynamics is initiated only when the spin-polarization of flowing electrons and
localized spins are noncollinear, quantum STT can occur when these vectors are
collinear but antiparallel. Using tDMRG, we simulate the time evolution of a
many-body quantum state of electrons and localized spins, where the former are
injected as a spin-polarized current pulse while the latter comprise a quantum
Heisenberg ferromagnetic metallic (FM) spin-$\frac{1}{2}$ XXZ chain initially
in the ground state with spin-polarization antiparallel to that of injected
electrons. The quantum STT reverses the direction of localized spins, but
without rotation from the initial orientation, when the number of injected
electrons exceeds the number of localized spins. Such nonclassical reversal,
which is absent from LLG dynamics, is strikingly inhomogeneous across the FM
chain and it can be accompanied by reduction of the magnetization associated
with localized spins, even to zero at specific locations. This is because
quantum STT generates a highly entangled nonequilibrium many-body state of all
flowing and localized spins, despite starting from the initially unentangled
ground state of a mundane FM. Furthermore, the mutual information between
localized spins at the FM edges remains nonzero even at infinite separation as
the signature of dynamical buildup of long-range entanglement.",2002.04655v4
2004-03-03,Current-Induced Nanomagnet Dynamics for Magnetic Fields Perpendicular to the Sample Plane,"We present electrical measurements of high-frequency magnetic dynamics
excited by spin-polarized currents in Co/Cu/Ni80Fe20 nanopillar devices, with a
magnetic field applied perpendicular to the sample layers. As a function of
current and magnetic field, the dynamical phase diagram contains several
distinguishable precessional modes and also static magnetic states. Using
detailed comparisons with numerical simulations, we provide rigorous tests of
the theory of spin-transfer torques.",0403100v1
2007-01-25,Current-induced vortex-vortex switching in a nanopillar comprising two Co nano-rings,"We fabricated a current-perpendicular-to-plane pseudo-spin-valve nanopillar
comprising a thick and a thin Co rings with deep submicron lateral sizes. The
dc current can effectively induce the flux-closure vortex states in the rings
with desired chiralities. Abrupt transitions between the vortex states are also
realized by the dc current and detected with the giant magnetoresistance
effect. Both Oersted field and spin-transfer torque are found important to the
magnetic transitions, but the former is dominant. They can be designed to
cooperate with each other in the vortex-to-vortex transitions by carefully
setting the chirality of the vortex state in the thick Co ring.",0701618v1
2008-03-14,Current-induced noise and damping in non-uniform ferromagnets,"In the presence of spatial variation of the magnetization direction, electric
current noise causes a fluctuating spin-transfer torque that increases the
fluctuations of the ferromagnetic order parameter. By the
fluctuation-dissipation theorem, the equilibrium fluctuations are related to
the magnetization damping, which in non-uniform ferromagnets acquires a
nonlocal tensor structure. In biased ferromagnets, shot noise can become the
dominant contribution to the magnetization noise at low temperatures.
Considering spin spirals as a simple example, we show that the current-induced
noise and damping is significant.",0803.2175v1
2009-03-06,Simulation of current-induced microwave oscillation in geometrically confined domain wall,"We studied magnetization dynamics of a geometrically confined domain wall
under dc current by solving simultaneously the Landau-Lifshitz-Gilbert equation
and diffusion equation for spin accumulation. We showed that the oscillation
motion of the domain wall is driven by the spin-transfer torque and the dc
current is converted to the ac voltage signal. The results means that the
geometrically confined domain wall is applicable as a source of microwave
oscillator.",0903.1151v1
2009-12-30,Voltage induced control and magnetoresistance of noncollinear frustrated magnets,"Noncollinear frustrated magnets are proposed as a new class of spintronic
materials with high magnetoresistance which can be controlled with relatively
small applied voltages. It is demonstrated that their magnetic configuration
strongly depends on position of the Fermi energy and applied voltage. The
voltage induced control of noncollinear frustrated materials (VCFM) can be seen
as a way to intrinsic control of colossal magnetoresistance (CMR) and is the
bulk material counterpart of spin transfer torque concept used to control giant
magnetoresistance in layered spin-valve structures.",0912.5487v1
2010-03-19,Dynamics of magnetization on the topological surface,"We investigate theoretically the dynamics of magnetization coupled to the
surface Dirac fermions of a three dimensional topological insulator, by
deriving the Landau-Lifshitz-Gilbert (LLG) equation in the presence of charge
current. Both the inverse spin-Galvanic effect and the Gilbert damping
coefficient $\alpha$ are related to the two-dimensional diagonal conductivity
$\sigma_{xx}$ of the Dirac fermion, while the Berry phase of the ferromagnetic
moment to the Hall conductivity $\sigma_{xy}$. The spin transfer torque and the
so-called $\beta$-terms are shown to be negligibly small. Anomalous behaviors
in various phenomena including the ferromagnetic resonance are predicted in
terms of this LLG equation.",1003.3769v1
2012-01-11,Frequency domain studies of current-induced magnetization dynamics in single magnetic-layer nanopillars,"Spin transfer torque-induced high-frequency dynamics of single thin
cobalt-layer nanopillars of circular and elliptical shape have been observed
directly. Two types of precessional modes can be identified as a function of
magnetic field perpendicular to the layer plane, excited for negative current
polarity only. They are assigned to vortex-core and transverse spin-wave
excitations, which corroborate recent model predictions. The observed narrow
linewidth of 4 MHz at room temperature indicates the high coherence of the
magnetic excitations.",1201.2268v1
2006-01-23,"Velocity of domain-wall motion induced by electrical current in a ferromagnetic semiconductor (Ga,Mn)As","Current-induced domain-wall motion with velocity spanning over five orders of
magnitude up to 22 m/s has been observed by magneto-optical Kerr effect in
(Ga,Mn)As with perpendicular magnetic anisotropy. The data are employed to
verify theories of spin-transfer by the Slonczewski-like mechanism as well as
by the torque resulting from spin-flip transitions in the domain-wall region.
Evidence for domain-wall creep at low currents is found.",0601515v1
2006-04-05,Current-driven resonant excitation of magnetic vortex,"A magnetic vortex core in a ferromagnetic circular nanodot has a resonance
frequency originating from the confinement of the vortex core. By the
micromagnetic simulation including the spin-transfer torque, we show that the
vortex core can be resonantly excited by an AC (spin-polarized) current through
the dot and that the resonance frequency can be tuned by the dot shape. The
resistance measurement under the AC current successfully detects the resonance
at the frequency consistent with the simulation.",0604123v1
2010-12-03,Energy-efficient mixed mode switching of a multiferroic nanomagnet for logic and memory,"In magnetic memory and logic devices, a magnet's magnetization is usually
flipped with a spin polarized current delivering a spin transfer torque (STT).
This mode of switching consumes too much energy and considerable energy saving
can accrue from using a multiferroic nanomagnet switched with a combination of
STT and mechanical stress generated with a voltage (VGS). The VGS mode consumes
less energy than STT, but cannot rotate magnetization by more than 90?, so that
a combination of the two modes is needed for energy-efficient switching.",1012.0819v1
2016-06-16,Crossover between fast and slow excitation of magnetization by spin torque,"A crossover between two mechanisms destabilizing the magnetization in
equilibrium by the spin transfer effect is found in a ferromagnetic multilayer
consisting of an in-plane magnetized free layer and a perpendicularly
magnetized pinned layer, where an in-plane magnetic field is applied, and
electric current flows from the pinned to the free layer. A fast transition
from the in-plane to the out-of-plane state occurs in the low-field region,
whereas a slow transition with small-amplitude oscillation becomes dominant in
the high-field region. On the other hand, only the fast transition mechanism
appears for the opposite current direction.",1606.05375v1
2018-10-04,Domain wall dynamics in easy-cone magnets,"We theoretically and numerically investigate magnetic domain wall dynamics in
a nanowire of easy-cone magnet. The easy-cone domain wall exhibits several
distinguishing dynamic features in comparison to the easy-axis domain wall. The
features of easy-cone domain wall are related to the generation of additional
chiral spin textures due to the domain wall precession, which is common for
various driving sources such as magnetic fields and spin-transfer torques. The
unique easy-cone domain wall dynamics could enrich magnetic domain wall study
and find use in device applications based on easy-cone domain walls.",1810.02216v1
2020-09-02,Skyrmion-antiskyrmion droplets in a chiral ferromagnet,"We find numerically skyrmionic textures with skyrmion number Q=0 in
ferromagnets with the Dzyaloshinskii-Moriya interaction and perpendicular
anisotropy. These have the form of a skyrmion-antiskyrmion pair and may be
called chiral droplets. They are stable in an infinite film as well as in
disc-shaped magnetic elements. Droplets are found for values of the parameters
close to the transition from the ferromagnetic to the spiral phase. We study
their motion under spin-transfer torque. They move in the direction of the spin
flow and, thus, their dynamics are drastically different than the Hall dynamics
of the standard Q=0 skyrmion.",2009.00890v1
2019-01-04,Hydrodynamics of three-dimensional skyrmions in frustrated magnets,"We study the nucleation and collective dynamics of Shankar skyrmions [R.
Shankar, Journal de Physique 38, 1405 (1977)] in the class of frustrated
magnetic systems described by an SO(3) order parameter, including multi-lattice
antiferromagnets and amorphous magnets. We infer the expression for the
spin-transfer torque that injects skyrmion charge into the system and the
Onsager-reciprocal pumping force that enables its detection by electrical
means. The thermally-assisted flow of topological charge gives rise to an
algebraically decaying drag signal in nonlocal transport measurements. We
contrast our findings to analogous effects mediated by spin supercurrents.",1901.01208v1
2019-07-29,Magnetization Dynamics in Holographic Ferromagnets: Landau-Lifshitz Equation from Yang-Mills Fields,"We introduce a new approach to understand magnetization dynamics in
ferromagnets based on the holographic realization of ferromagnets. A
Landau-Lifshitz equation describing the magnetization dynamics is derived from
a Yang-Mills equation in the dual gravitational theory, and temperature
dependences of the spin-wave stiffness and spin transfer torque appearing in
the holographic Landau-Lifshitz equation are investigated by the holographic
approach. The results are consistent with the known properties of magnetization
dynamics in ferromagnets with conduction electrons.",1907.12306v1
2023-06-28,Stochastic Landau-Lifshitz-Gilbert equations for frustrated magnets under fluctuating currents,"We examine a stochastic Landau-Lifshitz-Gilbert equation for a frustrated
ferromagnet with competing first and second order exchange interactions exposed
to deterministic and random spin transfer torques in form of transport noise.
We prove the existence and pathwise uniqueness of weak martingale solutions in
the energy space. The result ensures the persistence of topological patterns,
occurring in such magnetic systems, under the influence of a fluctuating spin
current.",2306.15843v1
2022-03-01,Magnetic Braking of Accreting T Tauri Stars II: Torque Formulation Spanning Spin-Up and Spin-Down Regimes,"The magnetic interaction between a classical T Tauri star and its surrounding
accretion disk is thought to influence its rotational evolution. We use 2.5D
magnetohydrodynamic, axisymmetric simulations of star-disk interaction,
computed via the PLUTO code, to calculate the net torque acting on these stars.
We divide the net torque into three contributions: accretion (spin-up), stellar
winds (spin-down), and magnetospheric ejections (MEs) (spin-up or down). In
Paper I, we explored interaction regimes in which the stellar magnetosphere
truncates the inner disk at a location spinning faster than the star, resulting
in a strong net spin-up contribution from accretion and MEs (""steady accretion""
regime). In this paper, we investigate interaction regimes in which the
truncation radius gets closer to and even exceeds corotation, where it is
possible for the disk material to gain angular momentum and be periodically
ejected by the centrifugal barrier (""propeller"" regime). This reduces the
accretion torque, can change the sign of the ME torque, and can result in a net
stellar spin-down configuration. These results suggest it is possible to have a
net spin-down stellar torque even for truncation radii within the corotation
radius ($R_\text{t} \gtrsim 0.7 R_\text{co}$). We fit semi-analytic functions
for the truncation radius, and the torque associated with star-disk interaction
(i.e., the sum of accretion and ME torques) and stellar wind, allowing for the
prediction of the net stellar torque for a parameter regime covering both net
spin-up and spin-down configurations, as well as the possibility of
investigating rotational evolution via 1D stellar evolution codes.",2203.00326v1
2015-06-07,Experimental observation of the interaction of propagating spin waves with Néel domain walls in a Landau domain structure,"The interaction of propagating dipolar spin waves with magnetic domain walls
is investigated in square-shaped microstructures patterned from the Heusler
compound Co$_2$Mn$_{0.6}$Fe$_{0.4}$Si. Using magnetic force microscopy, the
reversible preparation of a Landau state with four magnetic domains separated
by N\'eel domain walls is confirmed. A local spin-wave excitation using a
microstructured antenna is realized in one of the domains. It is shown by
Brillouin light scattering microscopy (BLS) that the domain structure in the
remanence state has a strong influence on the spin-wave excitation and
propagation. The domain walls strongly reflect the spin waves and can be used
as spin-wave reflectors. A comparison with micromagnetic simulations shows that
the strong reflection is due to the long-range dipolar interaction which has
important implications for the use of these spin waves for exerting an
all-magnonic spin-transfer torque.",1506.02303v1
2016-01-07,Dynamic Feedback in Ferromagnet/Spin Hall Metal Heterostructures,"In ferromagnet/normal metal heterostructures, spin pumping and spin-transfer
torques are two reciprocal processes that occur concomitantly. Their interplay
introduces a dynamic feedback effect interconnecting energy dissipation
channels of both magnetization and current. By solving the spin diffusion
process in the presence of the spin Hall effect in the normal metal, we show
that the dynamic feedback gives rise to: (i) a nonlinear magnetic damping that
is crucial to sustain uniform steady-state oscillations of a spin Hall
oscillator at large angles. (ii) a frequency dependent spin Hall
magnetoimpedance that reduces to the spin Hall magnetoresistance in the dc
limit.",1601.01618v3
2017-12-04,"Faster, farther, stronger: spin transfer torque driven high order propagating spin waves in nano-contact magnetic tunnel junctions","Short wave-length exchange-dominated propagating spin waves will enable
magnonic devices to operate at higher frequencies and higher data transmission
rates.1 While GMR based magnetic nano-contacts are highly efficient injectors
of propagating spin waves2,3, the generated wave lengths are 2.6 times the
nano-contact diameter4, and the electrical signal strength remains much too
weak for practical applications. Here we demonstrate nano-contact based spin
wave generation in magnetic tunnel junction stacks, and observe large discrete
frequency steps consistent with the hitherto ignored possibility of second and
third order propagating spin waves with wave lengths of 120 and 74 nm, i.e.
much smaller than the 150 nm nano-contact. These higher-order propagating spin
waves will not only enable magnonic devices to operate at much higher
frequencies, but also greatly increase their transmission rates and spin wave
propagating lengths, both proportional to the much higher group velocity.",1712.00954v2
2018-07-25,Left-handed polarized spin waves in ferromagnets induced by spin-transfer torque,"Polarization is a fundamental property of waves that refers to the
orientation of the oscillations. It has been widely used to encode information
in photonics and phononics. However, the polarization of spin waves is rarely
used yet in magnonics. The reason for this is that only the right-handed
polarized spin waves can be accommodated in ferromagnets. Here, we report that
stable left-handed polarized spin waves can be introduced into ferromagnets if
a spin-polarized electrical current is presented. The right-handed and
left-handed polarized spin waves coexist when the current density is larger
than a critical value while the system keeps stable. The results are confirmed
by micromagnetic simulations. This work provides new playgrounds to study spin
waves and points to new findings for future experimental studies.",1807.09456v2
2021-04-13,Theory of spin-Hall magnetoresistance in the AC (terahertz) regime,"In bilayers consisting of a normal metal (N) with spin-orbit coupling and a
ferromagnet (F), the combination of the spin-Hall effect, the spin-transfer
torque, and the inverse spin-Hall effect gives a small correction to the
in-plane conductivity of N, which is referred to as spin-Hall magnetoresistance
(SMR). We here present a theory of the SMR and the associated off-diagonal
conductivity corrections for frequencies up to the terahertz regime. We show
that the SMR signal has pronounced singularities at the spin-wave frequencies
of F, which identifies it as a potential tool for all-electric spectroscopy of
magnon modes. A systematic change of the magnitude of the SMR at lower
frequencies is associated with the onset of a longitudinal magnonic
contribution to spin transport across the F-N interface.",2104.06518v2
2020-05-03,Subterahertz spin pumping from an insulating antiferromagnet,"Spin-transfer torque and spin Hall effects combined with their reciprocal
phenomena, spin-pumping and inverse spin Hall (ISHE) effects, enable the
reading and control of magnetic moments in spintronics. The direct observation
of these effects remains elusive in antiferromagnetic-based devices. We report
sub-terahertz spin-pumping at the interface of a uniaxial insulating
antiferromagnet MnF2 and platinum. The measured ISHE voltage arising from
spin-charge conversion in the platinum layer depends on the chirality of the
dynamical modes of the antiferromagnet, which is selectively excited and
modulated by the handedness of the circularly polarized sub-THz irradiation.
Our results open the door to the controlled generation of coherent pure spin
currents at THz frequencies.",2005.01203v1
2019-06-03,Layer-dependent spin-orbit torques generated by the centrosymmetric transition metal dichalcogenide $β$-MoTe$_2$,"Single-crystal materials with sufficiently low crystal symmetry and strong
spin-orbit interactions can be used to generate novel forms of spin-orbit
torques on adjacent ferromagnets, such as the out-of-plane antidamping torque
previously observed in WTe$_2$/ferromagnet heterostructures. Here, we present
measurements of spin-orbit torques produced by the low-symmetry material
$\beta$-MoTe$_2$, which unlike WTe$_2$ retains bulk inversion symmetry. We
measure spin-orbit torques on $\beta$-MoTe$_2$/Permalloy heterostructures using
spin-torque ferromagnetic resonance as a function of crystallographic alignment
and MoTe$_2$ thickness down to the monolayer limit. We observe an out-of-plane
antidamping torque with a spin torque conductivity as strong as 1/3 of that of
WTe$_2$, demonstrating that the breaking of bulk inversion symmetry in the
spin-generation material is not a necessary requirement for producing an
out-of-plane antidamping torque. We also measure an unexpected dependence on
the thickness of the $\beta$-MoTe$_2$ -- the out-of-plane antidamping torque is
present in MoTe$_2$/Permalloy heterostructures when the $\beta$-MoTe$_2$ is a
monolayer or trilayer thick, but goes to zero for devices with bilayer
$\beta$-MoTe$_2$.",1906.01068v1
2020-03-16,Spin-orbit torques originating from bulk and interface in Pt-based structures,"We investigated spin-orbit torques in prototypical Pt-based spintronic
devices. We found that, in Pt/Ni and Pt/Fe bilayers, the damping-like torque
efficiency depends on the thickness of the Pt layer. We also found that the
damping-like torque efficiency is almost identical in the Pt/Ni and Pt/Fe
bilayers despite the stronger spin memory loss at the Pt/Fe interface. These
results suggest that although the dominant source of the damping-like torque is
the bulk spin Hall effect in the Pt layer, a sizable damping-like torque is
generated by the interface in the Pt/Fe bilayer due to the stronger interfacial
spin-orbit coupling. In contrast to the damping-like torque, whose magnitude
and sign are almost identical in the Pt/Ni and Pt/Fe bilayers, the field-like
torque strongly depends on the choice of the ferromagnetic layer. The sign of
the field-like torque originating from the bulk spin Hall effect in the Pt
layer is opposite between the Pt/Ni and Pt/Fe bilayers, which can be attributed
to the opposite sign of the imaginary part of the spin-mixing conductance.
These results demonstrate that the spin-orbit torques are quite sensitive to
the electronic structure of the FM layer.",2003.07271v2
2005-04-06,Macrospin Models of Spin Transfer Dynamics,"The current-induced magnetization dynamics of a spin valve are studied using
a macrospin (single domain) approximation and numerical solutions of a
generalized Landau-Lifshitz-Gilbert equation. For the purpose of quantitative
comparison with experiment [Kiselev {\it et al.} Nature {\bf 425}, 380 (2003)],
we calculate the resistance and microwave power as a function of current and
external field including the effects of anisotropies, damping, spin-transfer
torque, thermal fluctuations, spin-pumping, and incomplete absorption of
transverse spin current. While many features of experiment appear in the
simulations, there are two significant discrepancies: the current dependence of
the precession frequency and the presence/absence of a microwave quiet magnetic
phase with a distinct magnetoresistance signature. Comparison is made with
micromagnetic simulations designed to model the same experiment.",0504142v1
2008-02-07,Spin-transfer switching and low-field precession in exchange-biased spin valve nano-pillars,"Using a three-dimensional focused-ion beam lithography process we have
fabricated nanopillar devices which show spin transfer torque switching at zero
external magnetic fields. Under a small in-plane external bias field, a
field-dependent peak in the differential resistance versus current is observed
similar to that reported in asymmetrical nanopillar devices. This is
interpreted as evidence for the low-field excitation of spin waves which in our
case is attributed to a spin-scattering asymmetry enhanced by the IrMn exchange
bias layer coupled to a relatively thin CoFe fixed layer.",0802.1003v1
2011-06-14,All Spin Logic device with inbuilt Non-Reciprocity,"The need for low power alternatives to digital electronic circuits has led to
increasing interest in logic devices where information is stored in
nanomagnets. This includes both nanomagnetic logic (NML) where information is
communicated through magnetic fields of nanomagnets and all-spin logic (ASL)
where information is communicated through spin currents. A key feature needed
for logic implementation is non-reciprocity, whereby the output is switched
according to the input but not the other way around, thus providing directed
information transfer. The objective of this paper is to draw attention to
possible ASL-based schemes that utilize the physics of spin-torque to build in
non-reciprocity similar to transistors that could allow logic implementation
without the need for special clocking schemes. We use an experimentally
benchmarked coupled spin-transport/ magnetization-dynamics model to show that a
suitably engineered single ASL unit indeed switches in a non-reciprocal manner.
We then present heuristic arguments explaining the origin of this directed
information transfer. Finally we present simulations showing that individual
ASL devices with inbuilt directionality can be cascaded to construct circuits.",1106.2789v1
2010-01-18,Critical Tunneling Currents in Quantum Hall Superfluids: Pseudospin-Transfer Torque Theory,"At total filling factor $\nu=1$ quantum Hall bilayers can have an ordered
ground state with spontaneous interlayer phase coherence. The ordered state is
signaled experimentally by dramatically enhanced interlayer tunnel conductances
at low bias voltages; at larger bias voltages inter-layer currents are similar
to those of the disordered state. We associate this change in behavior with the
existence of a critical current beyond which static inter-layer phase
differences cannot be maintained, and examine the dependence of this critical
current on sample geometry, phase stiffness, and the coherent tunneling energy
density. Our analysis is based in part on analogies between coherent bilayer
behavior and spin-transfer torque physics in metallic ferromagnets. Comparison
with recent experiments suggests that disorder can dramatically suppress
critical currents.",1001.2923v1
2010-08-27,Spin-transfer-torque resonant switching and injection locking in presence of a weak external microwave field for spin valves with perpendicular materials,"The effects of a weak microwave field in the magnetization dynamics driven by
spin-transfer-torque in spin-valves with perpendicular materials have been
systematically studied by means of full micromagnetic simulations. In the
system we studied, depending on the working point (bias field and current) in
the dynamical stability diagram, we observe either resonant switching and
injection locking. The resonant switching, observed in the switching region,
occurs when the field frequency is approaching the frequency of the main
pre-switching mode giving rise to an asymmetric power distribution of that mode
in the sectional area of the free layer. At the resonant frequency, the
switching time is weakly dependent on the relative phase between the instant
when the current pulse is applied and the microwave field. The injection
locking, observed in the dynamical region, is characterized by the following
properties: (i) a locking bandwidth which is linearly dependent on the force
locking, and (ii) a locking for integer harmonics of the self-oscillation
frequency. We compare our numerical results with analytical theory for
non-autonomous non-linear system obtaining a good agreement in the current
region where the oscillation frequency and output power are characterized from
a linear relationship.",1008.4746v1
2023-10-19,Detailed and high-throughput measurement of composition dependence of magnetoresistance and spin-transfer torque using a composition-gradient film: application to Co$_{x}$Fe$_{1-x}$ (0 $\le$ $\textit{x}$ $\le$ 1) system,"We develop a high-throughput method for measuring the composition dependence
of magnetoresistance (MR) and spin-transfer-torque (STT) effects in
current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices and
report its application to the CoFe system. The method is based on the use of
composition-gradient films deposited by combinatorial sputtering. This
structure allows the fabrication of devices with different compositions on a
single substrate, drastically enhancing the throughput in investigating
composition dependence. We fabricated CPP-GMR devices on a single GMR film
consisting of a Co$_{x}$Fe$_{1-x}$ (0 $\le$ $\textit{x}$ $\le$ 1)
composition-gradient layer, a Cu spacer layer, and a NiFe layer. The MR ratio
obtained from resistance-field measurements exhibited the maximum in the broad
Co concentration range of 0.3 $\le$ $\textit{x}$ $\le$ 0.65. In addition, the
STT efficiency was estimated from the current to induce magnetization reversal
of the NiFe layer by spin injection from the Co$_{x}$Fe$_{1-x}$ layer. The STT
efficiency was also the highest around the same Co concentration range as for
the MR ratio, and this correlation was theoretically explained by the change in
the spin polarization of the Co$_{x}$Fe$_{1-x}$ layer. The results revealed the
Co$_{x}$Fe$_{1-x}$ composition range suitable for spintronic applications,
demonstrating the advantages of the developed method.",2310.12434v1
2018-03-16,Intrinsic spin-orbit torque in an antiferromagnet with a weakly noncollinear spin configuration,"An antiferromagnet is a promising material for spin-orbit torque generation.
Earlier studies of the spin-orbit torque in an antiferromagnet are limited to
collinear spin configurations. We calculate the spin-orbit torque in an
antiferromagnet whose spin ordering is weakly noncollinear. Such
noncollinearity may be induced spontaneously during the magnetization dynamics
even when the equilibrium spin configuration is perfectly collinear. It is
shown that deviation from perfect collinearity can modify properties of the
spin-orbit torque since noncollinearity generates extra Berry phase
contributions to the spin-orbit torque, which are forbidden for collinear spin
configurations. In sufficiently clean antiferromagnets, this modification can
be significant. We estimate this effect to be of relevance for fast
antiferromagnetic domain wall motion.",1803.06428v2
2018-06-06,Control of magnetization dynamics by spin Nernst torque,"Control of magnetization dynamics is one of the primary goals in spintronics.
It has been demonstrated using spin Hall effect i.e charge current to spin
current conversion in non-magnetic metal which has large spin-orbit coupling
such as Pt, W etc. Recently different groups have shown generation of spin
current in Pt, W while thermal gradient is created by virtue of spin Nernst
effect. In this work we show the evidence of magnetization control by spin
Nernst torque in Pt/Py bi-layer. We compared relative strength of spin Nernst
Torque and spin Hall torque by measuring the systematic variation of magnetic
linewidth on application of constant heat or charge current. Spin-torque
ferromagnetic resonance (ST-FMR) technique is adopted to excite the magnet and
to measure line-width precisely from the symmetric and anti-symmetric voltage
component. Control of magnetization dynamics by spin Nernst torque will emerge
as an alternative way to manipulate nano-magnets.",1806.01978v1
2020-02-21,Spin pumping and large field-like torque at room temperature in sputtered amorphous WTe$_{2-x}$ films,"We studied the spin-to-charge and charge-to-spin conversion at room
temperature in sputtered WTe2-x (x=0.8)(t)/Co20Fe60B20(6 nm) heterostructures.
Spin pumping measurements were used to characterize the spin-to-charge
efficiency and the spin efficiency was calculated to be larger than ~0.035.
Second harmonic Hall measurements were carried out to estimate the
charge-to-spin conversion ratio. We found that the system exhibits a large
field-like-torque (spin torque efficiency ~ 0.1) and small damping-like-torque
(spin torque efficiency ~0.001) compared to that reported for heavy metals.
High-resolution transmission electron microscopy images show that the WTe2-x
layer is amorphous, which may enhance the spin swapping effect by inducing
large interfacial spin orbit scattering, thus contributing to a large field
like torque.",2002.09510v1
2003-12-22,Mass Transfer between Double White Dwarfs,"Three periodically variable stars have recently been discovered (V407 Vul,
P=9.5 min; ES Cet, P=10.3 min; RX J0806.3+1527, P=5.3 min) with properties that
suggest that their photometric periods are also their orbital periods, making
them the most compact binary stars known. If true, this might indicate that
close, detached, double white dwarfs are able to survive the onset of mass
transfer caused by gravitational wave radiation and emerge as the
semi-detached, hydrogen-deficient stars known as the AM CVn stars. The
accreting white dwarfs in such systems are large compared to the orbital
separations. This has two effects: first it makes it likely that the mass
transfer stream can hit the accretor directly, and second it causes a loss of
angular momentum from the orbit which can destabilise the mass transfer unless
the angular momentum lost to the accretor can be transferred back to the orbit.
The effect of the destabilisation is to reduce the number of systems which
survive mass transfer by as much as one hundred-fold. In this paper we analyse
this destabilisation and the stabilising effect of a dissipative torque between
the accretor and the binary orbit. We obtain analytic criteria for the
stability of both disc-fed and direct impact accretion, and carry out numerical
integrations to assess the importance of secondary effects, the chief one being
that otherwise stable systems can exceed the Eddington accretion rate. We show
that to have any effect upon survival rates, the synchronising torque must act
on a timescale of order 1000 years or less. If synchronisation torques are this
strong, then they will play a significant role in the spin rates of white
dwarfs in cataclysmic variable stars as well.",0312577v1
2017-06-21,Constraints on the disc-magnetosphere interaction in accreting pulsar 4U 1626--67,"Using the spin and flux evolution of the accreting pulsar 4U 1626$-$67 across
the 2008 torque reversal, we determine the fastness parameter dependence of the
dimensionless torque acting on the pulsar. We find that the dimensionless
torque is qualitatively different from the existing models: it is concave-up
across the torque equilibrium whereas the existing torque models predict a
concave-down (convex) relation with the fastness parameter. We show that the
dimensionless torque has a cubic dependence on the fastness parameter near the
torque equilibrium. We also find that the torque can not attain large values
away from the equilibrium, either in the positive or the negative side, but
saturates at limited values. The spin-down torque can attain a 2.5 times larger
magnitude at the saturation limit than the spin-up torque. From the evolution
of the frequency of quasi-periodic oscillations of 4U 1626$-$67 across the
torque reversal of 1990, we determine the critical fastness parameter
corresponding to torque equilibrium to be $\omega_{\rm c} \simeq 0.75$ within
the framework of the beat frequency model and boundary region model for
reasonable values of the model parameters. We find that the disc magnetosphere
interaction becomes unstable when the inner radius approaches the corotation
radius as predicted by some models, though with a longer timescale. We also
find that there is an unstable regime that is triggered when the fastness
parameter is 0.8 times the critical fastness parameter ($\omega=0.6$ for
$\omega_{\rm c} \simeq 0.75$) possibly associated with an instability observed
in numerical simulations.",1706.06800v1
2015-03-04,Critical current destabilizing perpendicular magnetization by the spin Hall effect,"The critical current needed to destabilize the magnetization of a
perpendicular ferromagnet via the spin Hall effect is studied. Both the
dampinglike and fieldlike torques associated with the spin current generated by
the spin Hall effect is included in the Landau-Lifshitz-Gilbert equation to
model the system. In the absence of the fieldlike torque, the critical current
is independent of the damping constant and is much larger than that of
conventional spin torque switching of collinear magnetic systems, as in
magnetic tunnel junctions. With the fieldlike torque included, we find that the
critical current scales with the damping constant as $\alpha^{0}$ (i.e.,
damping independent),$\alpha$, and $\alpha^{1/2}$ depending on the sign of the
fieldlike torque and other parameters such as the external field. Numerical and
analytical results show that the critical current can be significantly reduced
when the fieldlike torque possesses the appropriate sign, i.e. when the
effective field associated with the fieldlike torque is pointing opposite to
the spin direction of the incoming electrons. These results provide a pathway
to reducing the current needed to switch magnetization using the spin Hall
effect.",1503.01478v2
2016-05-17,Self-current induced spin-orbit torque in FeMn/Pt multilayers,"Extensive efforts have been devoted to the study of spin-orbit torque in
ferromagnetic metal/heavy metal bilayers and exploitation of it for
magnetization switching using an in-plane current. As the spin-orbit torque is
inversely proportional to the thickness of the ferromagnetic layer, sizable
effect has only been realized in bilayers with an ultrathin ferromagnetic
layer. Here we demonstrate that, by stacking ultrathin Pt and FeMn alternately,
both ferromagnetic properties and current induced spin-orbit torque can be
achieved in FeMn/Pt multilayers without any constraint on its total thickness.
The critical behavior of these multilayers follows closely three-dimensional
Heisenberg model with a finite Curie temperature distribution. The spin torque
effective field is about 4 times larger than that of NiFe/Pt bilayer with a
same equivalent NiFe thickness. The self-current generated spin torque is able
to switch the magnetization reversibly without the need for an external field
or a thick heavy metal layer. The removal of both thickness constraint and
necessity of using an adjacent heavy metal layer opens new possibilities for
exploiting spin-orbit torque for practical applications.",1605.05135v1
2017-08-23,Spin-orbit torques induced by interface-generated spin currents,"Magnetic torques generated through spin-orbit coupling promise
energy-efficient spintronic devices. It is important for applications to
control these torques so that they switch films with perpendicular
magnetizations without an external magnetic field. One suggested approach uses
magnetic trilayers in which the torque on the top magnetic layer can be
manipulated by changing the magnetization of the bottom layer. Spin currents
generated in the bottom magnetic layer or its interfaces transit the spacer
layer and exert a torque on the top magnetization. Here we demonstrate
field-free switching in such structures and attribute it to a novel spin
current generated at the interface between the bottom layer and the spacer
layer. The measured torque has a distinct dependence on the bottom layer
magnetization which is consistent with this interface-generated spin current
but not the anticipated bulk effects. This other interface-generated spin-orbit
torque will enable energy-efficient control of spintronic devices.",1708.06864v1
2007-05-03,Planar spin-transfer device with a dynamic polarizer,"In planar nano-magnetic devices magnetization direction is kept close to a
given plane by the large easy-plane magnetic anisotropy, for example by the
shape anisotropy in a thin film. In this case magnetization shows effectively
in-plane dynamics with only one angle required for its description. Moreover,
the motion can become overdamped even for small values of Gilbert damping. We
derive the equations of effective in-plane dynamics in the presence of
spin-transfer torques. The simplifications achieved in the overdamped regime
allow to study systems with several dynamic magnetic pieces (``free layers'').
A transition from a spin-transfer device with a static polarizer to a device
with two equivalent magnets is observed. When the size difference between the
magnets is less than critical, the device does not exhibit switching, but goes
directly into the ``windmill'' precession state.",0705.0406v1
2004-11-10,Universality of thermally assisted magnetic domain wall motion under spin torque,"Thermally assisted motion of magnetic domain wall under spin torque is
studied theoretically. It is shown that the wall velocity $v$ depends
exponentially on the spin current,
  $\Is$, below the threshold value, in the same way as in a thermally activated
motion driven by a force. A novel property of the spin torque driven case at
low temperature is that the linear term in spin current is universal, i.e.,
$\ln v \sim \frac{\pi\hbar}{2e}(\Is/\kB T)$. This behavior, which is
independent of pinning and material constants, could be used to confirm
experimentally the spin torque as the driving mechanism.",0411250v1
2008-08-11,Calculation of current-induced torque from spin continuity equation,"Current-induced torque is formulated based on the spin continuity equation.
The formulation does not rely on the assumption of separation of local spin and
charge degrees of freedom, in contrast to approaches based on the $s$-$d$ model
or mean-field approximation of itinerant ferromagnetism. This new method would
be thus useful for the estimation of torques in actual materials by
first-principles calculations. As an example, the formalism is applied to the
adiabatic limit of the $s$-$d$ model in order to obtain the analytical
expression for torques and corresponding $\beta$ terms arising from spin
relaxation due to spin-flip scattering and spin-orbit interaction.",0808.1445v1
2016-06-24,Current-Induced Instability of a Perpendicular Ferromagnet in Spin Hall Geometry,"We develop a theoretical formula of spin Hall torque in the presence of two
ferromagnets. While the direction of the conventional spin Hall torque always
points to the in-plane direction, the present system enables to manipulate the
torque direction acting on one magnetization by changing the direction of
another magnetization. Based on the diffusion equation of the spin accumulation
and the Landauer formula, we derive analytical formula of the spin Hall torque.
The present model provides a solution to switch a perpendicular ferromagnet
deterministically at zero field using the spin Hall effect.",1606.07540v1
2017-05-11,Synchronization of spin torque oscillators through spin Hall magnetoresistance,"Spin torque oscillators placed onto a nonmagnetic heavy metal show
synchronized auto-oscillations due to the coupling originating from spin Hall
magnetoresistance effect. Here, we study a system having two spin torque
oscillators under the effect of the spin Hall torque, and show that switching
the external current direction enables us to control the phase difference of
the synchronization between in-phase and antiphase.",1705.04386v2
2023-07-27,Spin-orbit torque emerging from orbital textures in centrosymmetric materials,"We unveil a hitherto concealed spin-orbit torque mechanism driven by orbital
degrees of freedom in centrosymmetric two-dimensional transition metal
dichalcogenides (focusing on PtSe${}_2$ ). Using first-principles simulations,
tight-binding models and large-scale quantum transport calculations, we show
that such a mechanism fundamentally stems from a spatial localization of
orbital textures at opposite sides of the material, which imprints their
symmetries onto spin-orbit coupling effects, further producing efficient and
tunable spin-orbit torque. Our study suggests that orbital-spin entanglement at
play in centrosymmetric materials can be harnessed as a resource for
outperforming conventional spin-orbit torques generated by the Rashba-type
effects.",2307.14673v1
2008-01-02,Accretion-Powered Stellar Winds III: Spin Equilibrium Solutions,"We compare the stellar wind torque calculated in a previous work (Paper II)
to the spin-up and spin-down torques expected to arise from the magnetic
interaction between a slowly rotating ($\sim 10$% of breakup) pre-main-sequence
star and its accretion disk. This analysis demonstrates that stellar winds can
carry off orders of magnitude more angular momentum than can be transferred to
the disk, provided that the mass outflow rates are greater than the solar wind.
Thus, the equilibrium spin state is simply characterized by a balance between
the angular momentum deposited by accretion and that extracted by a stellar
wind. We derive a semi-analytic formula for predicting the equilibrium spin
rate as a function only of the ratio of $\dot M_{\rm w} / \dot M_{\rm a}$ and a
dimensionless magnetization parameter, $\Psi \equiv B_*^2 R_*^2 (\dot M_{\rm a}
v_{\rm esc})^{-1}$, where $\dot M_{\rm w}$ is the stellar wind mass outflow
rate, $\dot M_{\rm a}$ the accretion rate, $B_*$ the stellar surface magnetic
field strength, $R_*$ the stellar radius, and $v_{\rm esc}$ the surface escape
speed. For parameters typical of accreting pre-main-sequence stars, this
explains spin rates of $\sim 10$% of breakup speed for $\dot M_{\rm w} / \dot
M_{\rm a} \sim 0.1$. Finally, the assumption that the stellar wind is driven by
a fraction of the accretion power leads to an upper limit to the mass flow
ratio of $\dot M_{\rm w} / \dot M_{\rm a} \la 0.6$.",0801.0440v2
2015-06-17,Charge and Spin Currents in Ferromagnetic Josephson junctions,"We determine, using a self consistent method, the charge and spin currents in
ballistic Josephson junctions consisting of ferromagnetic ($F$) layers
sandwiched between superconducting ($S$) electrodes ($SFS$-type junctions).
When there are two $F$ layers, we also consider the experimentally relevant
configuration where a normal ($N$) nonmagnetic spacer layer separates them. We
study the current-phase relationships as functions of geometrical parameters
that are accessible experimentally including the angles that characterize the
relative orientation of the magnetization in the $F$ layers. Our
self-consistent method ensures that the proper charge conservation laws are
satisfied. As we vary the phase difference $\Delta\varphi$ between the two
outer $S$ electrodes, multiple harmonics in the current phase relations emerge,
their extent depends on the interface scattering strength and the relative $F$
layer widths and magnetization orientations. By manipulating the relative $F$
layer magnetization orientations, we find that the charge supercurrent can
reverse directions or vanish altogether. These findings are discussed in the
context of the generation and long-range nature of triplet pair correlation. We
also investigate the spin currents and associated spin transfer torques
throughout the junction. For noncollinear relative magnetizations, the
non-conserved spin currents in a given $F$ region gives rise to net torques
that can switch directions at particular magnetic configurations or
$\Delta\varphi$ values. The details of the spin current behavior are shown to
depend strongly on the degree of magnetic inhomogeneity in the system.",1506.05489v1
2017-11-09,Fabrication of magnetic tunnel junctions connected through a continuous free layer to enable spin logic devices,"Magnetic tunnel junctions (MTJs) interconnected via a continuous
ferromagnetic free layer were fabricated for Spin Torque Majority Gate (STMG)
logic. The MTJs are biased independently and show magnetoelectric response
under spin transfer torque. The electrical control of these devices paves the
way to future spin logic devices based on domain wall (DW) motion. In
particular, it is a significant step toward the realization of a majority gate,
even though further downscaling may be required. To our knowledge, this is the
first fabrication of a cross-shaped free layer shared by several perpendicular
MTJs. The fabrication process can be generalized to any geometry and any number
of MTJs. Thus, this framework can be applied to other spin logic concepts based
on magnetic interconnect. Moreover, it allows exploration of spin dynamics for
logic applications",1711.03609v2
2005-08-30,Spin-Polarized Current Induced Torque in Magnetic Tunnel Junctions,"We present tight-binding calculations of the spin torque in non-collinear
magnetic tunnel junctions based on the non-equilibrium Green functions
approach. We have calculated the spin torque via the effective local magnetic
moment approach and the divergence of the spin current. We show that both
methods are equivalent, i.e. the absorption of the spin current at the
interface is equivalent to the exchange interaction between the electron spins
and the local magnetization. The transverse components of the spin torque
parallel and perpendicular to the interface oscillate with different phase and
decay in the ferromagnetic layer (FM) as a function of the distance from the
interface. The period of oscillations is inversely proportional to the
difference between the Fermi-momentum of the majority and minority electrons.
The phase difference between the two transverse components of the spin torque
is due to the precession of the electron spins around the exchange field in the
FM layer. In absence of applied bias and for a relatively thin barrier the
perpendicular component of the spin torque to the interface is non-zero due to
the exchange coupling between the FM layers across the barrier.",0508713v1
2015-03-11,Spin-wave-induced spin torque in Rashba spin-orbit coupling system,"We study the effects of Rashba spin-orbit coupling on the spin torque induced
by spin waves, which are the plane wave dynamics of magnetization. The spin
torque is derived from linear response theory, and we calculate the dynamic
spin torque by considering the impurity-ladder-sum vertex corrections. This
dynamic spin torque is divided into three terms: a damping term, a $distortion$
term, and a correction term for the equation of motion. The $distorting$ torque
describes a phenomenon unique to the Rashba spin-orbit coupling system, where
the distorted motion of magnetization precession is subjected to the
anisotropic force from the Rashba coupling. The oscillation mode of the
precession exhibits an elliptical trajectory, and the ellipticity depends on
the strength of the nesting effects, which could be reduced by decreasing the
electron lifetime.",1503.03171v2
2015-05-29,Topological Surface States Originated Spin-Orbit Torques in Bi2Se3,"Three dimensional topological insulator bismuth selenide (Bi2Se3) is expected
to possess strong spin-orbit coupling and spin-textured topological surface
states, and thus exhibit a high charge to spin current conversion efficiency.
We evaluate spin-orbit torques in Bi2Se3/Co40Fe40B20 devices at different
temperatures by spin torque ferromagnetic resonance measurements. As
temperature decreases, the spin-orbit torque ratio increases from ~ 0.047 at
300 K to ~ 0.42 below 50 K. Moreover, we observe a significant out-of-plane
torque at low temperatures. Detailed analysis indicates that the origin of the
observed spin-orbit torques is topological surface states in Bi2Se3. Our
results suggest that topological insulators with strong spin-orbit coupling
could be promising candidates as highly efficient spin current sources for
exploring next generation of spintronic applications.",1505.07937v1
2018-04-19,Effect of capping layer on spin-orbit torques,"In order to enhance the magnitude of spin-orbit torque (SOT), considerable
experimental works have been devoted to studying the thickness dependence of
the different layers in multilayers consisting of heavy metal (HM), ferromagnet
(FM) and capping layers. Here we present a theoretical model based on the
spin-drift-diffusion (SDD) formalism to investigate the effect of the capping
layer properties such as its thickness on the SOT observed in experiments. It
is found that the spin Hall-induced SOT can be significantly enhanced by
incorporating a capping layer with opposite spin Hall angle to that of the HM
layer. The spin Hall torque can be maximized by tuning the capping layer
thickness. However, in the absence of the spin Hall effect (SHE) in the capping
layer, the torque decreases monotonically with capping layer thickness.
Conversely, the spin Hall torque is found to decrease monotonically with the FM
layer thickness, irrespective of the presence or absence of SHE in the capping
layer. All these trends are in correspondence with experimental observations.
Finally, our model suggests that capping layers with long spin diffusion length
and high resistivity would also enhance the spin Hall torque.",1804.07001v1
2020-06-03,Topological Hall Effect and Skyrmion-like Bubbles at a Charge-transfer Interface,"Exploring exotic interface magnetism due to charge transfer and strong
spin-orbit coupling has profound application in future development of
spintronic memory. Here, the emergence, tuning and interpretation of hump-shape
Hall Effect from a CaMnO3/CaIrO3/CaMnO3 trilayer structure are studied in
detail. The hump signal can be recognized as Topological Hall Effect suggesting
the presence of Skyrmion-like magnetic bubbles; but the debated alternative
interpretation where the signal being an artefact between two cancelling
Anomalous Hall Effect loops is also discussed. Firstly, by tilting the magnetic
field direction, the evolution of Hall signal suggests transformation of the
bubbles topology into a more trivial kind. Secondly, by varying the thickness
of CaMnO3, the optimal thicknesses for the hump signal emergence are found,
suggesting a tuning of charge transfer fraction. Using high-resolution
transmission electron microscopy, a stacking fault is also identified, which
distinguishes the top and bottom CaMnO3/CaIrO3 interfaces in terms of charge
transfer fraction and possible interfacial Dzyaloshinskii-Moriya Interaction.
Finally, a spin-transfer torque experiment revealed a low threshold current
density of ~10^9 A/m^2 for initiating the motion of bubbles. This discovery
opens a possible route for integrating Skyrmions with antiferromagnetic
spintronics.",2006.02004v1
2020-02-13,Semi-realistic tight-binding model for spin-orbit torques,"We compute the spin-orbit torque in a transition metal heterostructure using
Slater-Koster parameterization in the two-center tight-binding approximation
and accounting for d-orbitals only. In this method, the spin-orbit coupling is
modeled within Russel-Saunders scheme, which enables us to treat interfacial
and bulk spin-orbit transport on equal footing. The two components of the
spin-orbit torque, dissipative (damping-like) and reactive (field-like), are
computed within Kubo linear response theory. By systematically studying their
thickness and angular dependence, we were able to accurately characterize these
components beyond the traditional ""inverse spin galvanic"" and ""spin Hall""
effects. Whereas the conventional field-like torque is purely interfacial, we
unambiguously demonstrate that the conventional the damping-like torque
possesses both an interfacial and a bulk contribution. In addition, both
field-like and damping-like torques display substantial angular dependence with
strikingly different thickness behavior. While the planar contribution of the
field-like torque decreases smoothly with the nonmagnetic metal thickness, the
planar contribution of the damping-like torque increases dramatically with the
nonmagnetic metal thickness. Finally, we investigate the self-torque exerted on
the ferromagnet when the spin-orbit coupling of the nonmagnetic metal is turned
off. Our results suggest that the spin accumulation that builds up inside the
ferromagnet can be large enough to induce magnetic excitations.",2002.05533v1
2002-08-06,Spin pumping and magnetization dynamics in metallic multilayers,"We study the magnetization dynamics in thin ferromagnetic films and small
ferromagnetic particles in contact with paramagnetic conductors. A moving
magnetization vector causes \textquotedblleft pumping\textquotedblright of
spins into adjacent nonmagnetic layers. This spin transfer affects the
magnetization dynamics similar to the Landau-Lifshitz-Gilbert phenomenology.
The additional Gilbert damping is significant for small ferromagnets, when the
nonmagnetic layers efficiently relax the injected spins, but the effect is
reduced when a spin accumulation build-up in the normal metal opposes the spin
pumping. The damping enhancement is governed by (and, in turn, can be used to
measure) the mixing conductance or spin-torque parameter of the
ferromagnet--normal-metal interface. Our theoretical findings are confirmed by
agreement with recent experiments in a variety of multilayer systems.",0208091v2
2005-04-27,Perpendicular spin valves with ultra-thin ferromagnetic layers,"We address two finite size effects in perpendicular transport through
magnetic multilayers. When the magnetic layer thickness in spin valves becomes
of the order or smaller than the spin-flip diffusion length, structural
asymmetries affect the transport properties. A magnetic layer with thickness
approaching the magnetic coherence length becomes transparent for spin currents
polarized perpendicular to the magnetization. We use the generalized
magnetoelectronic circuit theory to investigate both effects on the angular
magnetoresistance (aMR) and spin transfer torque. We analyze recent aMR
experiments to determine the spin-flip diffusion length in the ferromagnet as
well as the interface spin-mixing conductance and propose a method to measure
the ferromagnetic coherence length.",0504705v2
2012-02-28,Spin-precession-assisted supercurrent in a superconducting quantum point contact coupled to a single-molecule magnet,"The supercurrent of a quantum point contact coupled to a nanomagnet strongly
depends on the dynamics of the nanomagnet's spin. We employ a fully microscopic
model to calculate the transport properties of a junction coupled to a spin
whose dynamics is modeled as Larmor precession brought about by an external
magnetic field and find that the dynamics affects the charge and spin currents
by inducing transitions between the continuum states below the superconducting
gap edge and the Andreev levels. This redistribution of the quasiparticles
leads to a non-equilibrium population of the Andreev levels and an enhancement
of the supercurrent which is visible as a modified current-phase relation as
well as a non-monotonous critical current as function of temperature. The
non-monotonous behavior is accompanied by a corresponding change in
spin-transfer torques acting on the precessing spin and leads to the
possibility of using temperature as a means to tune the back-action on the
spin.",1202.6197v1
2014-11-25,Computing with spins and magnets,"The possible use of spin and magnets in place of charge and capacitors to
store and process information is well known. Magnetic tunnel junctions are
being widely investigated and developed for magnetic random access memories.
These are two terminal devices that change their resistance based on switchable
magnetization of magnetic materials. They utilize the interaction between
electron spin and magnets to read information from the magnets and write onto
them. Such advances in memory devices could also translate into a new class of
logic devices that offer the advantage of nonvolatile and reconfigurable
information processing over transistors. Logic devices having a transistor-like
gain and directionality could be used to build integrated circuits without the
need for transistor-based amplifiers and clocks at every stage. We review
device characteristics and basic logic gates that compute with spins and
magnets from the mesoscopic to the atomic scale, as well as materials,
integration, and fabrication challenges and methods.",1411.6960v1
2015-01-06,Berry-phase effects and electronic dynamics in noncollinear antiferromagnetic texture,"Antiferromagnets (AFMs), in contrast to ferromagnets, show a nontrivial
magnetic structure with zero net magnetization. However, they share a number of
spintronic effects with ferromagnets, including spin-pumping and spin transfer
torques. Both phenomena stem from the coupled dynamics of free carriers and
localized magnetic moments. In the present paper I study the adiabatic dynamics
of a spin-polarized electrons in a metallic AFM exhibiting a noncollinear
120$^\circ$ magnetic structure. I show that the slowly varying AFM spin texture
produces a non-Abelian gauge potential related to the time/space gradients of
the N\'{e}el vectors. Corresponding emergent electric and magnetic fields
induce rotation of spin and influence the orbital dynamics of free electrons. I
discuss both the possibility of a topological spin Hall effect in the vicinity
of topological AFM solitons with nonzero curvature and rotation of the electron
spin traveling through the AFM domain wall.",1501.01189v2
2020-06-15,Magnetic Droplet Solitons,"Magnetic droplet solitons are dynamical magnetic textures that form due to an
attractive interaction between spin waves in thin films with perpendicular
magnetic anisotropy. Spin currents and the spin torques associated with these
currents enable their formation as they provide a means to excite
non-equilibrium spin wave populations and compensate their decay. Recent years
have seen rapid advances in experiments that realize and study magnetic
droplets. Important advances include the first direct x-ray images of droplets,
determination of their threshold and sustaining currents, measurement of their
generation and annihilation time and evidence for drift instabilities, which
can limit their lifetime in spin-transfer nanocontacts. This article reviews
these studies and contrasts these solitons to other types of spin-current
excitations such as spin-wave bullets, and static magnetic textures, including
magnetic vortices and skyrmions. Magnetic droplet solitons can also serve as
current controlled microwave frequency oscillators with potential applications
in neuromorphic chips as nonlinear oscillators with memory.",2006.08808v2
2021-03-16,All-electrical Magnon Transport Experiments in Magnetically Ordered Insulators,"Angular momentum transport is one of the cornerstones of spintronics. Spin
angular momentum is not only transported by mobile charge carriers, but also by
the quantized excitations of the magnetic lattice in magnetically ordered
systems. In this regard, magnetically ordered insulators provide a platform for
magnon spin transport experiments without additional contributions from spin
currents carried by mobile electrons. In combination with charge-to-spin
current conversion processes in conductors with finite spin-orbit coupling it
is possible to realize all-electrical magnon transport schemes in thin film
heterostructures. This review provides an insight into such experiments and
recent breakthroughs achieved. Special attention is given to charge current
based manipulation via an adjacent normal metal of magnon transport in
magnetically ordered insulators in terms of spin-transfer torque. Moreover, the
influence of two magnon modes with opposite spin in antiferromagnetic
insulators on all-electrical magnon transport experiments is discussed.",2103.08996v2
2022-02-28,Observation of long-range orbital transport and giant orbital torque,"Modern spintronics relies on the generation of spin currents through
spin-orbit coupling. The spin-current generation has been believed to be
triggered by current-induced orbital dynamics, which governs the angular
momentum transfer from the lattice to the electrons in solids. The fundamental
role of the orbital response in the angular momentum dynamics suggests the
importance of the orbital counterpart of spin currents: orbital currents.
However, evidence for its existence has been elusive. Here, we demonstrate the
generation of giant orbital currents and uncover fundamental features of the
orbital response. We experimentally and theoretically show that orbital
currents propagate over longer distances than spin currents by more than an
order of magnitude in a ferromagnet and nonmagnets. Furthermore, we find that
the orbital current enables electric manipulation of magnetization with
efficiencies significantly higher than the spin counterpart. These findings
open the door to orbitronics that exploits orbital transport and spin-orbital
coupled dynamics in solid-state devices.",2202.13896v2
2022-04-28,Field-Assisted Sub-Terahertz Spin Pumping and Auto-Oscillation in NiO,"Spin pumping converting sub-terahertz electromagnetic waves to DC spin
currents has recently been demonstrated in antiferromagnets (AFMs) with
easy-axis magnetic anisotropy. However, easy-plane AFMs such as NiO, which are
easier to prepare experimentally, are considered to be bad candidates for spin
pumping because the N\'{e}el vector oscillation is linearly polarized, placing
a major restriction on the material choice for practical applications. Through
a case study of NiO, we show that an applied magnetic field below the spin-flop
transition can substantially modify the polarization of the resonance
eigenmodes, which enables coherent sub-terahertz spin pumping as strong as that
in easy-axis AFMs. In addition, we find that an applied magnetic field can
significantly reduce the threshold of N\'{e}el vector auto-oscillation
triggered by spin-transfer torques. These prominent field-assisted effects can
greatly facilitate spintronic device engineering in the sub-terahertz frequency
regime.",2204.13283v2
2022-12-02,Coherent magnon-induced domain wall motion in a magnetic insulator channel,"Advancing the development of spin-wave devices requires high-quality
low-damping magnetic materials where magnon spin currents can propagate
efficiently and interact effectively with local magnetic textures. We show that
magnetic domain walls (DW) can modulate spin-wave transport in perpendicularly
magnetized channels of Bi-doped yttrium-iron-garnet (BiYIG). Conversely, we
demonstrate that the magnon spin current can drive DW motion in the BiYIG
channel device by means of magnon spin-transfer torque. The DW can be reliably
moved over 15 um distances at zero applied magnetic field by a magnon spin
current excited by an RF pulse as short as 1 ns. The required energy for
driving DW motion is orders of magnitude smaller than those reported for
metallic systems. These results facilitate low-switching-energy magnonic
devices and circuits where magnetic domains can be efficiently reconfigured by
magnon spin currents flowing within magnetic channels.",2212.01408v1
2023-01-12,Towards Magnonic Logic and Neuromorphic Computing: Controlling Spin-Waves by Spin-Polarized Current,"Spin-waves (magnons) are among the prime candidates for building fast yet
energy-efficient platforms for information transport and computing. We here
demonstrate theoretically and in state-of-the-art micromagnetic simulation the
effects that strategically-injected spin-polarized current can have on
controlling magnonic transport. We reveal analytically that the Zhang-Li
spin-transfer-torque induced by applied current is analogous to the
Dzyaloshinskii-Moriya interaction for scattering the magnons in the linear
regime, to then provide a generalized Snell's law that describes the spin-wave
propagation across regions with different current densities. We validate the
latter in numerical simulations of realistic systems, and exemplify how these
findings may help advance the design of spin-wave logic and neuromorphic
computing devices.",2301.04922v1
2014-12-30,Exploring Spin-Transfer-Torque Devices for Logic Applications,"As CMOS nears the end of the projected scaling roadmap, significant effort
has been devoted to the search for new materials and devices that can realize
memory and logic. Spintronics, is one of the promising directions for the
Post-CMOS era. While the potential of spintronic memories is relatively well
known, realizing logic remains an open and critical challenge. All Spin Logic
(ASL) is a recently proposed logic style that realizes Boolean logic using
spin-transfer-torque (STT) devices based on the principle of non-local spin
torque. ASL has advantages such as density, non-volatility, and low operating
voltage. However, it also suffers from drawbacks such as low speed and static
power dissipation. Recent work has shown that, in the context of simple
arithmetic circuits (adders, multipliers), the efficiency of ASL can be greatly
improved using techniques that utilize its unique characteristics. An
evaluation of ASL across a broad range of circuits, considering the known
optimization techniques, is an important next step in determining its
viability. In this work, we propose a systematic methodology for the synthesis
of ASL circuits. Our methodology performs various optimizations that benefit
ASL, such as intra-cycle power gating, stacking of ASL nanomagnets, and
fine-grained logic pipelining. We utilize the proposed methodology to evaluate
the suitability of ASL implementations for a wide range of benchmarks viz.
random combinational and sequential logic, digital signal processing circuits,
and the Leon SPARC3 general-purpose processor. Based on our evaluation, we
identify (i) the large current requirement of nanomagnets at fast switching
speeds, (ii) the static power dissipation in the all-metallic devices, and
(iii) the short spin flip length in interconnects as key bottlenecks that limit
the competitiveness of ASL.",1412.8689v2
2005-05-05,Angular Dependence of Spin-Torque Critical Currents in CPP-GMR Read Heads,"This paper derives expressions for the critical current at the onset of
spin-transfer-torque (STT) instability in CPP-GMR read heads, as a function of
the relative angle (theta) between the free and reference layer magnetizations.
Including a general angular dependent STT coefficient B(q=cos(theta)) exclusive
of the angular momentum conserving sin(theta) factor, the critical current is
found to depend on both B(q) and dB/dq in the non-collinear case |q| < 1. The
paper also details the experimental measurement of the angular dependent
critical currents on 50-nm sized CPP-GMR devices with synthetic antiferromagnet
pinned layers, and fabricated using e-beam lithography. The measurements are
consistent with prior theoretical models of the form B(q) ~ 1/[1+cnst*q], and
indicate perhaps unanticipated implications for read head operation due to the
critical current dependence on dB/dq.",0505117v1
2007-03-22,Spin-Torque Ferromagnetic Resonance Measurements of Damping in Nanomagnets,"We measure the magnetic damping parameter a in thin film CoFeB and permalloy
(Py) nanomagnets at room temperature using ferromagnetic resonance driven by
microwave frequency spin-transfer torque. We obtain $\alpha_{CoFeB} = 0.014 \pm
0.003$ and $\alpha_{Py}=0.010 \pm 0.002$, values comparable to measurements for
extended thin films, but significantly less than the effective damping
determined previously for similar nanomagnets by fits to time-domain studies of
large-angle magnetic excitations and magnetic reversal. The greater damping
found for the large amplitude nanomagnet dynamics is attributed to the
nonlinear excitation of non-uniform magnetic modes.",0703577v1
2008-05-28,"Magneto-optical and micromagnetic simulation study the current driven domain wall motion in ferromagnetic (Ga,Mn)As","We have studied current-driven domain wall motion in modified
Ga_0.95Mn_0.05As Hall bar structures with perpendicular anisotropy by using
spatially resolved Polar Magneto-Optical Kerr Effect Microscopy and
micromagnetic simulation. Regardless of the initial magnetic configuration, the
domain wall propagates in the opposite direction to the current with critical
current of 1~2x10^5A/cm^2. Considering the spin transfer torque term as well as
various effective magnetic field terms, the micromagnetic simulation results
are consistent with the experimental results. Our simulated and experimental
results suggest that the spin-torque rather than Oersted field is the reason
for current driven domain wall motion in this material.",0805.4308v1
2011-11-01,Modulation of domain wall dynamics in TbFeCo single layer nanowire,"We demonstrate the possibility to write and modulate the magnetic domain
walls in a TbFeCo single layer nanowire (300 nm width, 150 $\mu$m length). To
realize this, a tiny magnetic domain was nucleated by an Oersted field produced
by a 1.6 MHz pulse current (35 mA in amplitude, 5-40 ns in length) crossed the
wire. To write the wall to the wire, a DC current was used to drive the
nucleated domain (with two walls in two sides) to the wire in accordance with
spin-transfer torque mechanism. A critical current density of $J_c =
3.5\times10^{10} Am^{-2}$ was required to control the motion of the walls in
the wire. It was found that the size of the domain moving in the wire could be
adjusted by either external field or the length of the nucleated pulse current.
This could be considered as an important note for writing process in domain
wall spin-torque devices, especially, memory elements.",1111.0202v1
2014-10-06,Spin Orbit Torque Based Electronic Neuron,"A device based on current-induced spin-orbit torque (SOT) that functions as
an electronic neuron is proposed in this work. The SOT device implements an
artificial neuron's thresholding (transfer) function. In the first step of a
two-step switching scheme, a charge current places the magnetization of a
nano-magnet along the hard-axis i.e. an unstable point for the magnet. In the
second step, the SOT device (neuron) receives a current (from the synapses)
which moves the magnetization from the unstable point to one of the two stable
states. The polarity of the synaptic current encodes the excitatory and
inhibitory nature of the neuron input, and determines the final orientation of
the magnetization. A resistive crossbar array, functioning as synapses,
generates a bipolar current that is a weighted sum of the inputs. The
simulation of a two layer feed-forward Artificial Neural Network (ANN) based on
the SOT electronic neuron shows that it consumes ~3X lower power than a 45nm
digital CMOS implementation, while reaching ~80% accuracy in the classification
of one hundred images of handwritten digits from the MNIST dataset.",1410.1257v1
2018-05-15,Not an Oxymoron: Some X-ray Binary Pulsars with Enormous Spinup Rates Reveal Weak Magnetic Fields,"Three high-mass X-ray binaries have been discovered recently exhibiting
enormous spinup rates. Conventional accretion theory predicts extremely high
surface dipolar magnetic fields that we believe are unphysical. Instead, we
propose quite the opposite scenario: some of these pulsars exhibit weak
magnetic fields, so much so that their magnetospheres are crushed by the weight
of inflowing matter. The enormous spinup rate is achieved before inflowing
matter reaches the pulsar's surface as the penetrating inner disk transfers its
excess angular momentum to the receding magnetosphere which, in turn, applies a
powerful spinup torque to the pulsar. This mechanism also works in reverse: it
spins a pulsar down when the magnetosphere expands beyond corotation and finds
itself rotating faster than the accretion disk which then exerts a powerful
retarding torque to the magnetic field and to the pulsar itself. The above
scenaria cannot be accommodated within the context of neutron-star accretion
processes occurring near spin equilibrium, thus they constitute a step toward a
new theory of extreme (far from equilibrium) accretion phenomena.",1805.06069v1
2017-05-08,Simultaneous readout of two adjacent bit tracks with a spin-torque oscillator,"We propose a novel setup for a spin-torque oscillator reader in magnetic hard
disk drive technology. Two adjacent bit tracks are to be read simultaneously,
leading to high data transfer rate and increased resilience to noise as the
lateral size of the oscillator device is allowed to remain larger than the bit
width. We perform micromagnetic simulations of an example system and find that
the magnetization response has a clear unimodal character, which enables for
detection of two bit values at the same time. We analyze the frequency of the
device under the influence of two different external fields and conduct a
simulation of a successful dynamic readout. We estimate the signal linewidth
and signal-to-noise ratios of the setup and show that it may be potentially
beneficial for magnetic readout applications.",1705.07726v1
2020-04-28,"Current-Induced Dynamics of Chiral Magnetic Structures: Creation, Motion, and Applications","Magnetic textures can be manipulated by electric currents via the mechanisms
of spin-transfer and spin-orbit-torques. We review how these torques can be
exploited to create chiral magnetic textures in magnets with broken inversion
symmetries, including domain walls and skyrmions. These chiral textures can
also be moved by (electric) currents and obey very rich dynamics. For example,
magnetic domain walls feature the famous Walker breakdown, and magnetic whirls
are subject to the skyrmion Hall effect, which is rooted in their real-space
topology. These properties led to a variety of potential novel applications
which we briefly overview.",2004.13535v2
2019-05-22,Current-Driven Dynamics of Magnetic Hopfions,"Topological magnetic textures have attracted considerable interest since they
exhibit new properties and might be useful in information technology. Magnetic
hopfions are three-dimensional (3D) spatial variations in the magnetization
with a non-trivial Hopf index. We find that in ferromagnetic materials, two
types of hopfions, Bloch-type and N\'{e}el-type hopfions, can be excited as
metastable states in the presence of bulk and interfacial Dzyaloshinskii-Moriya
interactions, respectively. We further investigate how hopfions can be driven
by currents via spin-transfer torques (STTs) and spin-Hall torques (SHTs).
Distinct from 2D ferromagnetic skyrmions, hopfions have a vanishing gyrovector.
Consequently, there are no undesirable Hall effects. N\'{e}el-type hopfions
move along the current direction via both STT and SHT, while Bloch-type
hopfions can be moved either transverse to the current direction by SHT or
parallel to the current direction by STT. Our findings open the door to
utilizing hopfions as information carriers.",1905.09154v5
2017-04-11,CoFeAlB alloy with low damping and low magnetization for spin transfer torque switching,"We investigate the effect of Al doping on the magnetic properties of the
alloy CoFeB. Comparative measurements of the saturation magnetization, the
Gilbert damping parameter $\alpha$ and the exchange constant as a function of
the annealing temperature for CoFeB and CoFeAlB thin films are presented. Our
results reveal a strong reduction of the magnetization for CoFeAlB in
comparison to CoFeB. If the prepared CoFeAlB films are amorphous, the damping
parameter $\alpha$ is unaffected by the Al doping in comparison to the CoFeB
alloy. In contrast, in the case of a crystalline CoFeAlB film, $\alpha$ is
found to be reduced. Furthermore, the x-ray characterization and the evolution
of the exchange constant with the annealing temperature indicate a similar
crystallization process in both alloys. The data proves the suitability of
CoFeAlB for spin torque switching properties where a reduction of the switching
current in comparison with CoFeB is expected.",1704.03326v1
2023-05-05,Threshold Current for Field-free Switching of the In-plane Magnetization in the Three-terminal Magnetic Tunnel Junction,"Three-terminal magnetic tunnel junction (MTJ), where non-volatile
magnetization state can be switched via spin orbit torque (SOT), is attracting
massive research interests since it is featured by high speed, low power,
nearly unlimited endurance, etc. The threshold switching current is a key
parameter for MTJ as it determines the energy efficiency. Here, with the
Routh-Hurwitz criterion, we theoretically derive the threshold current for
switching in-plane magnetization in the three-terminal MTJ. Two devices with
field-free switching mode are investigated. The one is the Type-x device
switched by the combination of SOT and spin transfer torque (STT). The other is
the three-terminal MTJ with a canted easy-axis. To the best of our knowledge,
this is the first theoretical work on the threshold switching current for these
two devices. Our developed theoretical method shows clear physical picture,
meanwhile good agreement between theoretical derivation and numerical
simulation is achieved.",2305.03388v1
2011-12-02,The contribution of spin torque to spin Hall coefficient and spin motive force in spin-orbit coupling system,"We derive rigorously the relativistic angular momentum conservation equation
by means of quantum electrodynamics. The novel nonrelativistic spin current and
torque in the spin-orbit coupling system, up to the order of $1/c^{4}$, are
exactly investigated by using Foldy-Wouthuysen transformation. We find a
perfect spin Hall coefficient including the contribution of spin torque dipole.
A novel spin motive force, analogue to the Lorentz force, is also obtained for
understanding of the spin Hall effect.",1112.0394v1
2015-05-11,Current-induced spin polarization and spin-orbit torque in graphene,"Using the Green function formalism we calculate a current-induced spin
polarization of weakly magnetized graphene with Rashba spin-orbit interaction.
In a general case, all components of the current-induced spin polarization are
nonzero, contrary to the nonmagnetic limit, where the only nonvanishing
component of spin polarization is that in the graphene plane and normal to
electric field. When the induced spin polarization is exchange-coupled to the
magnetization, it exerts a spin-orbit torque on the latter. Using the Green
function method we have derived some analytical formulas for the spin
polarization and also determined the corresponding spin-orbit torque
components.",1505.02530v2
2018-02-02,Spin wave emission by spin-orbit torque antennas,"We study the generation of propagating spin waves in Ta/CoFeB waveguides by
spin-orbit torque antennas and compare them to conventional inductive antennas.
The spin-orbit torque was generated by a transverse microwave current across
the magnetic waveguide. The detected spin wave signals for an in-plane
magnetization across the waveguide (Damon-Eshbach configuration) exhibited the
expected phase rotation and amplitude decay upon propagation when the current
spreading was taken into account. Wavevectors up to about 6 rad/$\mu$m could be
excited by the spin-orbit torque antennas despite the current spreading,
presumably due to the non-uniformity of the microwave current. The relative
magnitude of generated anti-damping spin-Hall and Oersted fields was calculated
within an analytic model and it was found that they contribute approximately
equally to the total effective field generated by the spin-orbit torque
antenna. Due to the ellipticity of the precession in the ultrathin waveguide
and the different orientation of the anti-damping spin-Hall and Oersted fields,
the torque was however still dominated by the Oersted field. The prospects for
obtaining a pure spin-orbit torque response are discussed, as are the energy
efficiency and the scaling properties of spin-orbit torque antennas.",1802.00861v2
2018-04-06,Spin absorption by in situ deposited nanoscale magnets on graphene spin valves,"An in situ measurement of spin transport in a graphene nonlocal spin valve is
used to quantify the spin current absorbed by a small (250 nm $\times$ 750 nm)
metallic island. The experiment allows for successive depositions of either Fe
or Cu without breaking vacuum, so that the thickness of the island is the only
parameter that is varied. Furthermore, by measuring the effect of the island
using separate contacts for injection and detection, we isolate the effect of
spin absorption from any change in the spin injection and detection mechanisms.
As inferred from the thickness dependence, the effective spin current $j_e =
\frac{2e}{\hbar} j_s$ absorbed by Fe is as large as $10^8$ A/m$^2$. The maximum
value of $j_e$ is limited by the resistance-area product of the graphene/Fe
interface, which is as small as 3 $\Omega\mu$m$^2$. The spin current absorbed
by the same thickness of Cu is smaller than for Fe, as expected given the
longer spin diffusion length and larger spin resistance of Cu compared to Fe.
These results allow for a quantitative assessment of the prospects for
achieving spin transfer torque switching of a nanomagnet using a graphene-based
nonlocal spin valve.",1804.02103v1
2003-03-17,Millisecond pulsars with r-modes as steady gravitational radiators,"Millisecond pulsars (MSPs) are generally agreed to originate in low-mass
X-ray binaries (LMXBs), in which mass transfer onto the neutron stars spins
them up to their observed, fast rotation. The lack of MSPs and LMXBs rotating
near break-up and the similar rotation periods of several LMXBs have been
attributed to the accretion torque being balanced, at fast rotation, by
gravitational radiation, perhaps caused by an oscillation mode made unstable
through the so-called Chandrasekhar-Friedman-Schutz mechanism. Recently,
Wagoner has argued that internal dissipation through weak interaction processes
involving $\Lambda^0$ and $\Sigma^-$ hyperons may cause LMXBs to evolve into a
quasi-steady state, in which the neutron star has a nearly constant rotation
rate, temperature, and mode amplitude. We take this hypothesis one step
further, showing that MSPs descending from these LMXBs spend a long time in a
similar state, in which a low-amplitude r-mode turns them into extremely steady
sources of both gravitational waves and thermal X-rays, while they spin down
due to a combination of gravitational radiation and the standard magnetic
torque. Observed MSP braking torques already place meaningful constraints on
the allowed gravitational wave amplitudes and dissipation mechanisms.",0303375v2
2013-11-24,Current induced torques between ferromagnets and compensated antiferromagnets: symmetry and phase coherence effects,"It is shown that the current-induced torques between a ferromagnetic layer
and an antiferromagnetic layer with a compensated interface vanish when the
ferromagnet is aligned with an axis of spin-rotation symmetry of the
antiferromagnet. For properly chosen geometries this implies that the current
induced torque can stabilize the out-of-plane (or hard axis) orientation of the
ferromagnetic layer. This current-induced torque relies on phase coherent
transport, and we calculate the robustness of this torque to phase breaking
scattering. From this it is shown that the torque is not linearly dependent on
applied current, but has an absolute maximum.",1311.6161v1
2017-07-12,Thickness dependence of spin-orbit torques generated by WTe2,"We study current-induced torques in WTe2/permalloy bilayers as a function of
WTe2 thickness. We measure the torques using both second-harmonic Hall and
spin-torque ferromagnetic resonance measurements for samples with WTe2
thicknesses that span from 16 nm down to a single monolayer. We confirm the
existence of an out-of-plane antidamping torque, and show directly that the
sign of this torque component is reversed across a monolayer step in the WTe2.
The magnitude of the out-of-plane antidamping torque depends only weakly on
WTe2 thickness, such that even a single-monolayer WTe2 device provides a strong
torque that is comparable to much thicker samples. In contrast, the
out-of-plane field-like torque has a significant dependence on the WTe2
thickness. We demonstrate that this field-like component originates
predominantly from the Oersted field, thereby correcting a previous inference
drawn by our group based on a more limited set of samples.",1707.03757v1
2009-07-09,Annular Spin-Transfer Memory Element,"An annular magnetic memory that uses a spin-polarized current to switch the
magnetization direction or helicity of a magnetic region is proposed. The
device has magnetic materials in the shape of a ring (1 to 5 nm in thickness,
20 to 250 nm in mean radius and 8 to 100 nm in width), comprising a reference
magnetic layer with a fixed magnetic helicity and a free magnetic layer with a
changeable magnetic helicity. These are separated by a thin non-magnetic layer.
Information is written using a current flowing perpendicular to the layers,
inducing a spin-transfer torque that alters the magnetic state of the free
layer. The resistance, which depends on the magnetic state of the device, is
used to read out the stored information. This device offers several important
advantages compared to conventional spin-transfer magnetic random access memory
(MRAM) devices. First, the ring geometry offers stable magnetization states,
which are, nonetheless, easily altered with short current pulses. Second, the
ring geometry naturally solves a major challenge of spin-transfer devices:
writing requires relatively high currents and a low impedance circuit, whereas
readout demands a larger impedance and magnetoresistance. The annular device
accommodates these conflicting requirements by performing reading and writing
operations at separate read and write contacts placed at different locations on
the ring.",0907.1600v1
2012-05-03,Current-induced torques in textured Rashba ferromagnets,"In systems with small spin-orbit coupling, current-induced torques on the
magnetization require inhomogeneous magnetization textures. For large
spin-orbit coupling, such torques exist even without gradients in the
magnetization direction. Here, we consider current-induced torques in
ferromagnetic metals with both Rashba spin-orbit coupling and inhomogeneous
magnetization. We first phenomenologically construct all torques that are
allowed by the symmetries of the system, to first order in
magnetization-direction gradients and electric field. Second, we use a
Boltzmann approach to calculate the spin torques that arise to second order in
the spin-orbit coupling. We apply our results to current-driven domain walls
and find that the domain-wall mobility is strongly affected by torques that
result from the interplay between spin-orbit coupling and inhomogeneity of the
magnetization texture.",1205.0653v1
2017-12-07,Cu metal / Mn phthalocyanine organic spinterfaces atop Co with high spin polarization at room temperature,"The organic spinterface describes the spin-polarized properties that develop,
due to charge transfer, at the interface between a ferromagnetic metal (FM) and
the molecules of an organic semiconductor. Yet, if the latter is also magnetic
(e.g. molecular spin chains), the interfacial magnetic coupling can generate
complexity within magnetotransport experiments. Also, assembling this interface
may degrade the properties of its constituents (e.g. spin crossover or
non-sublimable molecules). To circumvent these issues, one can separate the
molecular and FM films using a less reactive nonmagnetic metal (NM).
Spin-resolved photoemission spectroscopy measurements on the prototypical
system Co(001)//Cu/Mnphthalocyanine (MnPc) reveal that the Cu/MnPc spinterface
atop ferromagnetic Co is highly spin-polarized at room temperature, up to Cu
spacer thicknesses of at least 10 monolayers. Ab-initio theory describes a spin
polarization of the topmost Cu layer after molecular hybridization that can be
accompanied by magnetic hardening effects. This spinterface's unexpected
robustness paves the way for 1) integrating electronically fragile molecules
within organic spinterfaces, and 2) manipulating molecular spin chains using
the well-documented spin transfer torque properties of the FM/NM bilayer.",1712.02600v1
2013-06-06,Critically-rotating accretors and non-conservative evolution in Algols,"During the mass-transfer phase in Algol systems, a large amount of mass and
angular momentum are accreted by the gainer star which can be accelerated up to
its critical Keplerian velocity. The fate of the gainer once it reaches this
critical value is unclear. We investigate the orbital and stellar spin
evolution in semi-detached binary systems, specifically for systems with
rapidly rotating accretors. Our aim is to better distinguish between the
different spin-down mechanisms proposed which can consistently explain the slow
rotation observed in Algols' final states and assess the degree of
non-conservatism due to the formation of a hotspot. We use our state-of-the-art
binary evolution code, Binstar, which incorporates a detailed treatment of the
orbital and stellar spin, including all torques due to mass transfer, the
interactions between a star and its accretion disc, tidal effects and magnetic
braking. We also present a new prescription for mass loss due to the formation
of a hotspot based on energy conservation. The coupling between the star and
the disc via the boundary layer prevents the gainer from exceeding the critical
rotation. Magnetic-field effects, although operating, are not the dominant
spin-down mechanism for sensible field strengths. Spin down owing to tides is
2-4 orders of magnitudes too weak to compensate the spinning-up torque due to
mass accretion. Moreover, we find that the final separation strongly depends on
the spin-down mechanism. The formation of a hotspot leads to a large event of
mass loss during the rapid phase of mass transfer. The degree of conservatism
strongly depends on the opacity of the impacted material. A statistical study
as well as new observational constraints are needed to find the optimal set of
parameters (magnetic-field strength, hotspot geometry,...) to reproduce Algol
evolutions.",1306.1348v2
2020-09-24,Quantum spin torque driven transmutation of antiferromagnetic Mott insulator,"The standard model of spin-transfer torque (STT) in antiferromagnetic
spintronics considers exchange of angular momentum between quantum spins of
flowing electrons and noncollinear-to-them localized spins treated as classical
vectors. These vectors are assumed to realize N\'{e}el order in equilibrium,
$\uparrow \downarrow \ldots \uparrow \downarrow$, and their STT-driven dynamics
is described by the Landau-Lifshitz-Gilbert (LLG) equation. However, many
experimentally employed materials (such as archetypal NiO) are strongly
electron-correlated antiferromagnetic Mott insulators (AFMI) where localized
spins form a ground state quite different from the unentangled N\'{e}el state
$|\!\! \uparrow \downarrow \ldots \uparrow \downarrow \rangle$. The true ground
state is entangled by quantum spin fluctuations, leading to expectation value
of all localized spins being zero, so that LLG dynamics of classical vectors of
fixed length rotating due to STT cannot even be initiated. Instead, a fully
quantum treatment of both conduction electrons and localized spins is necessary
to capture exchange of spin angular momentum between them, denoted as quantum
STT. We use a recently developed time-dependent density matrix renormalization
group approach to quantum STT to predict how injection of a spin-polarized
current pulse into a normal metal layer coupled to AFMI overlayer via exchange
interaction and possibly small interlayer hopping -- which mimics, e.g.,
topological-insulator/NiO bilayer employed experimentally -- will induce
nonzero expectation value of AFMI localized spins. This new nonequilibrium
phase is a spatially inhomogeneous ferromagnet with zigzag profile of localized
spins. The total spin absorbed by AFMI increases with electron-electron
repulsion in AFMI, as well as when the two layers do not exchange any charge.",2009.11833v3
2017-01-03,Universal Absence of Walker Breakdown and Linear Current-Velocity Relation via Spin-Orbit Torques in Coupled and Single Domain Wall Motion,"We consider theoretically domain wall motion driven by spin-orbit and spin
Hall torques. We find that it is possible to achieve universal absence of
Walker breakdown for all spin-orbit torques using experimentally relevant
spin-orbit coupling strengths. For spin-orbit torques other than the pure
Rashba spin-orbit torque, this gives a linear current-velocity relation instead
of a saturation of the velocity at high current densities. The effect is very
robust and is found in both soft and hard magnetic materials, as well as in the
presence of the Dzyaloshinskii-Moriya interaction and in coupled domain walls
in synthetic antiferromagnets, where it leads to very high domain wall
velocities. Moreover, recent experiments have demonstrated that the switching
of a synthetic antiferromagnet does not obey the usual spin Hall
angle-dependence, but that domain expansion and contraction can be selectively
controlled toggling only the applied in-plane magnetic field magnitude and not
its sign. We show for the first time that the combination of spin Hall torques
and interlayer exchange coupling produces the necessary relative velocities for
this switching to occur.",1701.00786v2
2004-02-03,First-principles study of magnetization relaxation enhancement and spin-transfer in thin magnetic films,"The interface-induced magnetization damping of thin ferromagnetic films in
contact with normal-metal layers is calculated from first principles for clean
and disordered Fe/Au and Co/Cu interfaces. Interference effects arising from
coherent scattering turn out to be very small, consistent with a very small
magnetic coherence length. Because the mixing conductances which govern the
spin transfer are to a good approximation real valued, the spin pumping can be
described by an increased Gilbert damping factor but an unmodified gyromagnetic
ratio. The results also confirm that the spin-current induced magnetization
torque is an interface effect.",0402088v2
2006-09-27,Distribution of the magnetization reversal duration in sub-ns spin-transfer switching,"We study the distribution of switching times in spin-transfer switching
induced by sub-ns current pulses in pillar-shaped spin-valves. The pulse
durations leading to switching follow a comb-like distribution, multiply-peaked
at a few most probable, regularly spaced switching durations. These durations
reflect the precessional nature of the switching, which occurs through a
fluctuating integer number of precession cycles. This can be modeled
considering the thermal variance of the initial magnetization orientations and
the occurrence of vanishing total torque in the possible magnetization
trajectories. Biasing the spin-valve with a hard axis field prevents some of
these occurrences, and can provide an almost perfect reproducibility of the
switching duration.",0609687v1
2011-05-27,Mechanisms of nonlinear spin-wave emission from a microwave driven nanocontact,"We present a micromagnetic study of linear and nonlinear spin-wave modes
excited in an extended permalloy thin film by a microwave driven nanocontact.
We show that the linear mode having the frequency equal to the excitation
frequency (f) is driven by the ac Oersted field component perpendicular to the
static external field (applied in-plane of the sample). The nonlinear mode with
the frequency f /2 is excited as an independent eigenmode within a parametric
longitudinal pumping process (due ac Oersted field component parallel to the
bias field). Spectral positions of those modes are determined both in the space
and phase domain. The results are important for the transfer of information
coded into spin-waves between nanocontacts, and for synchronization of spin
transfer torque nano-oscillators.",1105.5512v1
2012-01-30,Quantitative MRFM characterization of the autonomous and forced dynamics in a spin transfer nano-oscillator,"Using a magnetic resonance force microscope (MRFM), the power emitted by a
spin transfer nano-oscillator consisting of a normally magnetized Py$|$Cu$|$Py
circular nanopillar is measured both in the autonomous and forced regimes. From
the power behavior in the subcritical region of the autonomous dynamics, one
obtains a quantitative measurement of the threshold current and of the noise
level. Their field dependence directly yields both the spin torque efficiency
acting on the thin layer and the nature of the mode which first
auto-oscillates: the lowest energy, spatially most uniform spin-wave mode. From
the MRFM behavior in the forced dynamics, it is then demonstrated that in order
to phase-lock this auto-oscillating mode, the external source must have the
same spatial symmetry as the mode profile, i.e., a uniform microwave field must
be used rather than a microwave current flowing through the nanopillar.",1201.6344v1
2012-02-19,Magnetoelastic Coupling and Possibility of Spintronic Electromagnetomechanical Effects,"Nanoelectromangetomechanical systems (NEMMS) open up a new path for the
development of high speed autonomous nanoresonators and signal generators that
could be used as actuators, for information processing, as elements of quantum
computers etc. Those NEMMS that include ferromagnetic layers could be
controlled by the electric current due to effects related with spin transfer.
In the present paper we discuss another situation when the current-controlled
behaviour of nanorod that includes an antiferro- (instead of one of ferro-)
magnetic layer. We argue that in this case ac spin-polarized current can also
induce resonant coupled magneto-mechanical oscillations and produce an
oscillating magnetization of antiferromagnetic (AFM) layer. These effects are
caused by \emph{i}) spin-transfer torque exerted to AFM at the interface with
nonmagnetic spacer and by \emph{ii}) the effective magnetic field produced by
the spin-polarized free electrons due to $sd$-exchange.The described nanorod
with an AFM layer can find an application in magnetometry and as a
current-controlled high-frequency mechanical oscillator.",1202.4181v1
2012-07-15,Magnetic domain wall motion by spin transfer,"The discovery that a spin polarized current can exert a large torque on a
ferromagnet through a transfusion of spin angular momentum, offers a new way to
control a magnetization by simple current injection, without the help of an
applied external field. Spin transfer can be used to induce magnetization
reversals and oscillations, or to control the position of a magnetic domain
wall. In this review, we focus on this last mechanism, which is today the
subject of an extensive research, both because the microscopic details for its
origin are still debated, but also because promising applications are at stake
for non-volatile magnetic memories.",1207.3489v1
2017-11-28,Coherent spin-transfer precession switching in orthogonal spin-torque devices,"We present experimental results and macrospin simulations of the switching
characteristics of orthogonal spin-transfer devices incorporating an
out-of-plane magnetized polarizing layer and an in-plane magnetized spin valve
device at cryogenic temperatures. At $T=4$ K we demonstrate: high speed
deterministic switching at short pulse lengths - down to 100 ps - with
sufficient measurement statistics to establish a switching error rate of
$10^{-5}$; coherent precessional switching at longer times; and ensemble
decoherence effects at even longer times. Finite temperature macrospin models
capture the precessional switching well but fail to fully reproduce all the
decoherence and switching error behavior.",1711.10575v1
2018-07-09,Probing a spin transfer controlled magnetic nanowire with a single nitrogen-vacancy spin in bulk diamond,"The point-like nature and exquisite magnetic field sensitivity of the
nitrogen vacancy (NV) center in diamond can provide information about the inner
workings of magnetic nanocircuits in complement with traditional transport
techniques. Here we use a single NV in bulk diamond to probe the stray field of
a ferromagnetic nanowire controlled by spin transfer (ST) torques. We first
report an unambiguous measurement of ST tuned, parametrically driven,
large-amplitude magnetic oscillations. At the same time, we demonstrate that
such magnetic oscillations alone can directly drive NV spin transitions,
providing a potential new means of control. Finally, we use the NV as a local
noise thermometer, observing strong ST damping of the stray field noise,
consistent with magnetic cooling from room temperature to $\sim$150 K.",1807.03411v2
2020-09-09,Micromagnetic instabilities in spin-transfer switching of perpendicular magnetic tunnel junctions,"Micromagnetic instabilities and non-uniform magnetization states play a
significant role in spin transfer induced switching of nanometer scale magnetic
elements. Here we model domain wall mediated switching dynamics in
perpendicularly magnetized magnetic tunnel junction nanopillars. We show that
domain wall surface tension always leads to magnetization oscillations and
instabilities associated with the disk shape of the junction. A collective
coordinate model is developed that captures aspects of these instabilities and
illustrates their physical origin. Model results are compared to those of
micromagnetic simulations. The switching dynamics is found to be very sensitive
to the domain wall position and phase, which characterizes the angle of the
magnetization in the disk plane. This sensitivity is reduced in the presence of
spin torques and the spin current needed to displace a domain wall can be far
less than the threshold current for switching from a uniformly magnetized
state. A prediction of this model is conductance oscillations of increasing
frequency during the switching process.",2009.04376v1
2020-12-01,Nanocontact vortex oscillators based on Co$_2$MnGe pseudo-spin valves,"We present an experimental study of vortex dynamics in magnetic nanocontacts
based on pseudo spin valves comprising the Co$_2$MnGe Heusler compound. The
films were grown by molecular beam epitaxy, where precise stoichiometry control
and tailored stacking order allowed us to define the bottom ferromagnetic layer
as the reference layer, with minimal coupling between the free and reference
layers. 20-nm diameter nanocontacts were fabricated using a nano-indentation
technique, leading to self-sustained gyration of the vortex generated by
spin-transfer torques above a certain current threshold. By combining
frequency- and time-domain measurements, we show that different types of
spin-transfer induced dynamics related to different modes associated to the
magnetic vortex configuration can be observed, such as mode hopping, mode
coexistence and mode extinction appear in addition to the usual gyration mode.",2012.00522v3
2021-12-13,Spin-transfer and Topological Hall Effects as Novel Probes for Magnetic Disclinations in Frustrated Magnets,"Magnetic frustrated systems have resurged in spintronics as optimal
candidates for hosting three dimensional topological solitons, such as Shankar
skyrmions and 4$\pi$-vortices, and other singular topological defects. These
topological excitations are encoded in the order-parameter connected to the
spin-spin correlation of the system. The key challenge for their experimental
discovery is the lack of probes to observe them. We demonstrate here that
spin-transfer torque and topological Hall effect measurements can serve as
probes of magnetic disclinations and solitons in these systems, by means of a
previously unidentified contribution to them from these topological defects,
with no analog in collinear magnetism. We present a minimal low-energy
long-wavelength theory for the itinerant carriers and derive the effective
emergent electrodynamics arising from the noncoplanar magnetic background with
topological defects and solitons. This opens new avenues for the detection of
topological defects in magnetic systems with order-parameter manifolds beyond
the conventional $S^{2}$ (unit sphere) ferromagnetic paradigm.",2112.06680v1
2005-08-10,Period Changes in Ultra-compact Double White Dwarfs,"In recent years there has been much interest in the nature of two stars, V407
Vul and RXJ0806+1527, which are widely thought to be binary white dwarfs of
very short orbital period, 570 and 321 seconds respectively. As such they
should be strong sources of gravitational waves and possible ancestors of the
accreting AM CVn stars. Monitoring at X-ray and optical wavelengths has
established that the period of each star is decreasing, at rates compatible
with that expected from gravitational radiation. This has been taken to support
the ``unipolar inductor'' model in which the white dwarfs are detached and the
X-rays produced by the dissipation of magnetically-induced electric currents.
In this paper we show that this interpretation is incorrect because it ignores
associated torques which transfer angular momentum between the spin of the
magnetic white dwarf and the orbit. We show that this torque is 10^5 times
larger than the GR term in the case of V407 Vul, and 10 times larger for
RXJ0806+1527. For V407 Vul, the unipolar inductor model can only survive if the
white dwarf spins 100 times faster than the orbit. Since this could only come
about through accretion, the validity of the unipolar inductor appears
questionable for this star. We also consider whether accretion models can fit
the observed spin-up, concluding that they can, provided that a mechanism
exists for driving the mass transfer rate away from its equilibrium value.",0508233v1
2011-10-16,Voltage-driven v.s. Current-driven Spin Torque in Anisotropic Tunneling Junctions,"Non-equilibrium spin transport in a magnetic tunnel junction comprising a
single magnetic layer in the presence of interfacial spin-orbit interaction
(SOI) is studied theoretically. The interfacial SOI generates a spin torque of
the form {\bf T}=T_{||}{\bf M}x({\bf z}x{\bf M})+T_{\bot}{\bf z}x{\bf M}, even
in the absence of an external spin polarizer. For thick and large tunnel
barriers, the torque reduces to the perpendicular component, $T_{\bot}$, which
can be electrically tuned by applying a voltage across the insulator. In the
limit of thin and low tunnel barriers, the in-plane torque $T_{||}$ emerges,
proportional to the tunneling current density. Experimental implications on
magnetic devices are discussed.",1110.3491v1
2018-06-04,Current-induced four-state magnetization switching by spin-orbit torques in perpendicular ferromagnetic trilayers,"We demonstrated current-induced four-state magnetization switching in a
trilayer system using spin-orbit torques. The memory device contains two Co
layers with different perpendicular magnetic anisotropy, separated by a space
layer of Pt. Making use of the opposite spin current at the top and bottom
surface of the middle Pt layer, magnetization of both Co layers can be switched
oppositely by the spin-orbit torques with different critical switching
currents. By changing the current pulse forms through the device, the four
magnetic states memory was demonstrated. Our device provides a new idea for the
design of low power and high density spin-orbit torque devices.",1806.00964v1
2018-11-17,Optical detection of spin orbit torque and current induced heating,"We have studied spin orbit torque in heavy metal (HM)/ferromagnetic metal
(FM) bilayers using magneto-optical Kerr effect. A double modulation technique
is developed to separate signals from spin orbit torque and Joule heating. At a
current density of ~1x10$^{10}$ A/m$^2$, we observe optical signals that scale
linearly and quadratically with the current density, both in similar magnitude.
The spin orbit torque estimated using this technique is consistent with that
evaluated using spin transport measurements. We find that changes in the
refractive index of the film with temperature is the main source of the heating
induced signal.",1811.07118v1
2016-07-02,Interface-Induced Phenomena in Magnetism,"This article reviews static and dynamic interfacial effects in magnetism,
focusing on interfacially-driven magnetic effects and phenomena associated with
spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides
a historical background and literature survey, but focuses on recent progress,
identifying the most exciting new scientific results and pointing to promising
future research directions. It starts with an introduction and overview of how
basic magnetic properties are affected by interfaces, then turns to a
discussion of charge and spin transport through and near interfaces and how
these can be used to control the properties of the magnetic layer. Important
concepts include spin accumulation, spin currents, spin transfer torque, and
spin pumping. An overview is provided to the current state of knowledge and
existing review literature on interfacial effects such as exchange bias,
exchange spring magnets, spin Hall effect, oxide heterostructures, and
topological insulators. The article highlights recent discoveries of
interface-induced magnetism and non-collinear spin textures, non-linear
dynamics including spin torque transfer and magnetization reversal induced by
interfaces, and interfacial effects in ultrafast magnetization processes.",1607.00439v4
2012-04-26,Thermal spin pumping mediated by magnon in the semiclassical regime,"We microscopically analyze thermal spin pumping mediated by magnons, at the
interface between a ferromagnetic insulator and a non-magnetic metal, in the
semiclassical regime. The generation of a spin current is discussed by
calculating the thermal spin transfer torque, which breaks the spin
conservation law for conduction electrons and operates the coherent magnon
state. Inhomogeneous thermal fluctuations between conduction electrons and
magnons induce a net spin current, which is pumped into the adjacent
non-magnetic metal. The pumped spin current is proportional to the temperature
difference. When the effective temperature of magnons is lower than that of
conduction electrons, localized spins lose spin angular momentum by emitting
magnons and conduction electrons flip from down to up by absorbing all the
emitted momentum, and vice versa. Magnons at the zero mode cannot contribute to
thermal spin pumping because they are eliminated by the spin-flip condition.
Consequently thermal spin pumping does not cost any kinds of applied magnetic
fields. We have discussed the distinction from the theory proposed by Xiao et
al. [Phys. Rev. B, 81 (2010) 214418], Adachi et al. [Phys. Rev. B, 83 (2011)
094410], and Bender et al. [arXiv:1111.2382].",1204.5811v2
2020-08-31,Electrically Controlled Spin Injection from Giant Rashba Spin-Orbit Conductor BiTeBr,"Ferromagnetic materials are the widely used source of spin-polarized
electrons in spintronic devices, which are controlled by external magnetic
fields or spin-transfer torque methods. However, with increasing demand for
smaller and faster spintronic components, utilization of spin-orbit phenomena
provides promising alternatives. New materials with unique spin textures are
highly desirable since all-electric creation and control of spin polarization
is expected, where the strength, as well as an arbitrary orientation of the
polarization, can be defined without the use of a magnetic field. In this work,
we use a novel spin-orbit crystal BiTeBr for this purpose. Owning to its giant
Rashba spin splitting, bulk spin polarization is created at room temperature by
an electric current. Integrating BiTeBr crystal into graphene-based spin valve
devices, we demonstrate for the first time that it acts as a current-controlled
spin injector, opening new avenues for future spintronic applications in
integrated circuits.",2008.13764v1
2018-04-24,High-resolution combined tunneling electron charge and spin transport theory of Néel and Bloch skyrmions,"Based on a combined charge and vector spin transport theory capable of
imaging noncollinear magnetic textures on surfaces with spin-polarized scanning
tunneling microscopy (SP-STM), the high-resolution tunneling electron charge
and coupled spin transport properties of a variety of N\'eel- and Bloch-type
skyrmions are investigated. Axially symmetric skyrmions are considered within
the same topology class characterized by a vorticity value of $m=1$, and their
helicities are varied by taking $\gamma=0$ and $\pi$ values for the N\'eel
skyrmions and $\gamma=-\pi/2$ and $\pi/2$ values for the Bloch skyrmions.
Depending on the orientation of the magnetization of the STM tip as well as on
the helicity and the time-reversal of the skyrmionic spin structures, several
relationships between their spin transport vector components, the in-plane and
out-of-plane spin transfer torque and the longitudinal spin current, are
identified. The magnitudes of the spin transport vector quantities show close
relation to standard charge current SP-STM images. It is also demonstrated that
the SP-STM images can be used to determine the helicity of the skyrmions.
Moreover, the modified spin polarization vectors of the conduction electrons
due to the local chirality of the complex spin texture are incorporated into
the tunneling model. It is found that this effect modifies the apparent size of
the skyrmions. These results contribute to the proper identification of
topological surface magnetic objects imaged by SP-STM, and deliver important
parameters for current-induced spin dynamics.",1804.09096v2
2022-12-05,Néel Spin Currents in Antiferromagnets,"Ferromagnets are known to support spin-polarized currents that control
various spin-dependent transport phenomena useful for spintronics. On the
contrary, fully compensated antiferromagnets are expected to support only
globally spin-neutral currents. Here, we demonstrate that these globally
spin-neutral currents can represent the N\'eel spin currents, i.e. staggered
spin currents flowing through different magnetic sublattices. The N\'eel spin
currents emerge in antiferromagnets with strong intra-sublattice coupling
(hopping) and drive the spin-dependent transport phenomena such as tunneling
magnetoresistance (TMR) and spin-transfer torque (STT) in antiferromagnetic
tunnel junctions (AFMTJs). Using RuO$_{2}$ and Fe$_{4}$GeTe$_{2}$ as
representative antiferromagnets, we predict that the N\'eel spin currents with
a strong staggered spin-polarization produce a sizable field-like STT capable
of the deterministic switching of the N\'eel vector in the associated AFMTJs.
Our work uncovers the previously unexplored potential of fully compensated
antiferromagnets and paves a new route to realize the efficient writing and
reading of information for antiferromagnetic spintronics.",2212.02367v1
2018-06-15,Field-free Magnetization Switching by Utilizing the Spin Hall Effect and Interlayer Exchange Coupling of Iridium,"Magnetization switching by spin-orbit torque (SOT) via spin Hall effect
represents as a competitive alternative to that by spin-transfer torque (STT)
used for magnetoresistive random access memory (MRAM), as it does not require
high-density current to go through the tunnel junction. For perpendicular MRAM,
however, SOT driven switching of the free layer requires an external in-plane
field, which poses limitation for viability in practical applications. Here we
demonstrate field-free magnetization switching of a perpendicular magnet by
utilizing an Iridium (Ir) layer. The Ir layer not only provides SOTs via spin
Hall effect, but also induce interlayer exchange coupling with an in-plane
magnetic layer that eliminates the need for the external field. Such dual
functions of the Ir layer allows future build-up of magnetoresistive stacks for
memory and logic applications. Experimental observations show that the SOT
driven field-free magnetization reversal is characterized as domain nucleation
and expansion. Micromagnetic modeling is carried out to provide in-depth
understanding of the perpendicular magnetization reversal process in the
presence of an in-plane exchange coupling field.",1806.05961v4
2012-12-11,Spin torque due to diffusive spin current in magnetic texture,"We present a microscopic theory of spin torque due to diffusive spin currents
induced by spin accumulation. The obtained expression is a natural extension of
the existing one due to 'local' spin currents associated with ordinary electric
currents, and is the reciprocal of the spin motive force which induces charge
accumulation as studied recently [J. Shibata and H. Kohno, Phys. Rev. B84,
184408 (2011)]. The result is applied to a domain wall motion in a nonlocal
spin injection system, and the torque and force due to diffusive spin current
are evaluated.",1212.2363v1
2019-04-10,Enhancement of spin transparency by interfacial alloying,"We report that atomic-layer alloying (intermixing) at a Pt/Co interface can
increase, by approximately 30%, rather than degrade the interfacial spin
transparency, and thereby strengthen the efficiency of the dampinglike
spin-orbit torque arising from the spin Hall effect in the Pt. At the same
time, this interfacial alloying substantially reduces fieldlike spin-orbit
torque. Insertion of an ultrathin magnetic alloy layer at
heavy-metal/ferromagnet interfaces represents an effective approach for
improving interfacial spin transparency that may enhance not only spin-orbit
torques but also the spin detection efficiency in inverse spin Hall
experiments.",1904.05455v1
2016-11-17,Inductive detection of field-like and damping-like AC inverse spin-orbit torques in ferromagnet/normal metal bilayers,"Functional spintronic devices rely on spin-charge interconversion effects,
such as the reciprocal processes of electric field-driven spin torque and
magnetization dynamics-driven spin and charge flow. Both damping-like and
field-like spin-orbit torques have been observed in the forward process of
current-driven spin torque and damping-like inverse spin-orbit torque has been
well-studied via spin pumping into heavy metal layers. Here we demonstrate that
established microwave transmission spectroscopy of ferromagnet/normal metal
bilayers under ferromagnetic resonance can be used to inductively detect the AC
charge currents driven by the inverse spin-charge conversion processes. This
technique relies on vector network analyzer ferromagnetic resonance (VNA-FMR)
measurements. We show that in addition to the commonly-extracted spectroscopic
information, VNA-FMR measurements can be used to quantify the magnitude and
phase of all AC charge currents in the sample, including those due to spin
pumping and spin-charge conversion. Our findings reveal that
Ni$_{80}$Fe$_{20}$/Pt bilayers exhibit both damping-like and field-like inverse
spin-orbit torques. While the magnitudes of both the damping-like and
field-like inverse spin-orbit torque are of comparable scale to prior reported
values for similar material systems, we observed a significant dependence of
the damping-like magnitude on the order of deposition. This suggests interface
quality plays an important role in the overall strength of the damping-like
spin-to-charge conversion.",1611.05798v2
2023-01-03,Spin-orbit torque for field-free switching in C_{3v} crystals,"Spin-orbit torques in noncentrosymmetric polycrystalline magnetic
heterostructures are usually described in terms of field-like and damping-like
torques. However, materials with a lower symmetry point group can exhibit
torques whose behavior substantially deviates from the conventional ones. In
particular, based on symmetry arguments it was recently proposed that systems
belonging to the C_{3v} point group display spin-orbit torques that can promote
field-free switching [Liu et al. Nature Nanotechnology 16, 277 (2021)]. In the
present work, we analyze the general form of the torques expected in C3v
crystals using the Invariant Theory. We uncover several new components that
arise from the coexistence of the three-fold rotation and mirror symmetries.
Using both tight binding model and first principles simulations, we show that
these unconventional torque components arise from the onset of trigonal warping
of the Fermi surface and can be as large as the damping-like torque. In other
words, the Fermi surface warping is a key indicator to the onset of field-free
switching in low symmetry crystals.",2301.01133v2
2009-07-19,Current Driven tri-stable Resistance States in Magnetic Point Contacts,"Point contacts between normal and ferromagnetic metals are investigated using
magneto-resistance and transport spectroscopy measurements combined with
micromagnetic simulations. Pronounced hysteresis in the point-contact
resistance versus both bias current and external magnetic field are observed.
It is found that such hysteretic resistance can exhibit, in addition to
bi-stable resistance states found in ordinary spin valves, tri-stable
resistance states with a middle resistance level. We interpret these
observation in terms of surface spin-valve and spin-vortex states, originating
from a substantially modified spin structure at the ferromagnetic interface in
contact core. We argue that these surface spin states, subject to a weakened
exchange interaction, dominate the effects of spin transfer torques on the
nanometer scale.",0907.3286v1
2013-10-09,Chargeless spin current for switching and coupling of domain walls in magnetic nanowires,"The demonstration of the generation and control of a pure spin current
(without net charge flow) by electric fields and/or temperature gradient has
been an essential leap in the quest for low-power consumption electronics. The
key issue of whether and how such a current can be utilized to drive and
control information stored in magnetic domain walls (DWs) is still outstanding
and is addressed here. We demonstrate that pure spin current acts on DWs in a
magnetic stripe with an effective spin-transfer torque resulting in a mutual
DWs separation dynamics and picosecond magnetization reversal. In addition,
long-range ($\sim$ mm) antiferromagnetic DWs coupling emerges. If one DW is
pinned by geometric constriction, the spin current induces a dynamical spin
orbital interaction that triggers an internal electric field determined by
$\vec{E} \sim \hat{e}_{x} \cdot (\vec{n}_{1} \times \vec{n}_{2})$ where
$\vec{n}_{1/2}$ are the effective DWs orientations and $\hat{e}_{x} $ is their
spatial separation vector. This leads to charge accumulation or persistent
electric current in the wire. As DWs are routinely realizable and tuneable, the
predicted effects bear genuine potential for power-saving spintronics devices.",1310.2331v1
2014-04-04,Angular and temperature dependence of current induced spin-orbit effective fields in Ta/CoFeB/MgO nanowires,"Current induced spin-orbit effective magnetic fields in
metal/ferromagnet/oxide trilayers provide a new way to manipulate the
magnetization, which is an alternative to the conventional current induced spin
transfer torque arising from noncollinear magnetization. Ta/CoFeB/MgO
structures are expected to be useful for non-volatile memories and logic
devices due to its perpendicular anisotropy and large current induced
spin-orbit effective fields. However many aspects such as the angular and
temperature dependent phenomena of the effective fields are little understood.
Here, we evaluate the angular and temperature dependence of the current-induced
spin-orbit effective fields considering contributions from both the anomalous
and planar Hall effects. The longitudinal and transverse components of
effective fields are found to have strong angular dependence on the
magnetization direction at 300 K. The transverse field decreases significantly
with decreasing temperature, whereas the longitudinal field shows weaker
temperature dependence. Our results reveal important features and provide an
opportunity for a more comprehensive understanding of current induced
spin-orbit effective fields.",1404.1130v1
2018-10-31,Anisotropic and controllable Gilbert-Bloch dissipation in spin valves,"Spin valves form a key building block in a wide range of spintronic concepts
and devices from magnetoresistive read heads to spin-transfer-torque
oscillators. We elucidate the dependence of the magnetic damping in the free
layer on the angle its equilibrium magnetization makes with that in the fixed
layer. The spin pumping-mediated damping is anisotropic and tensorial, with
Gilbert- and Bloch-like terms. Our investigation reveals a mechanism for tuning
the free layer damping in-situ from negligible to a large value via the
orientation of fixed layer magnetization, especially when the magnets are
electrically insulating. Furthermore, we expect the Bloch contribution that
emerges from the longitudinal spin accumulation in the non-magnetic spacer to
play an important role in a wide range of other phenomena in spin valves.",1811.00020v2
2018-02-05,Micromagnetic view on ultrafast magnon generation by femtosecond spin current pulses,"In this Article we discuss a micromagnetic modelling approach to describe the
ultrafast spin-transfer torque excitation of coherent and incoherent magnons on
the nanoscale. Implementing the action of a femtosecond spin current pulse
entering an orthogonally magnetized thin ferromagnetic film, we reproduce
recent experimental results and reveal the factors responsible for the unequal
excitation efficiency of various spin waves. Our findings are in an excellent
agreement with the results of an analytical description of spin-wave excitation
based on classical kinetic equations. Furthermore, we suggest an experimental
design allowing for the excitation of laterally propagating spin waves beyond
the optical diffraction limit. Our findings demonstrate that the classical
micromagnetic picture retains its predictive and interpretative power on
femtosecond temporal and nanometer spatial scales.",1802.01305v1
2016-12-01,Electrically Driven Bose-Einstein Condensation of Magnons in Antiferromagnets,"We explore routes to realize electrically driven Bose-Einstein condensation
of magnons in insulating antiferromagnets. Even in insulating antiferromagnets,
the localized spins can strongly couple to itinerant spins in adjacent metals
via spin-transfer torque and spin pumping. We describe the formation of
steady-state magnon condensates controlled by a spin accumulation polarized
along the staggered field in an adjacent normal metal. Two types of magnons
exist in antiferromagnets, which carry opposite magnetic moments. Consequently,
and in contrast to ferromagnets, Bose-Einstein condensation can occur for
either sign of the spin accumulation. This condensation may occur even at room
temperature when the interaction with the normal metal is fast compared to the
relaxation processes within the antiferromagnet. In antiferromagnets, the
operating frequencies of the condensate are orders of magnitude faster than in
ferromagnets.",1612.00366v1
2021-03-23,Giant and tunneling magnetoresistance effects from anisotropic and valley-dependent spin-momentum interactions in antiferromagnets,"Giant or tunneling magnetoresistance are physical phenomena used for reading
information in commercial spintronic devices. The effects rely on a conserved
spin current passing between a reference and a sensing ferromagnetic electrode
in a multilayer structure. Recently, we have proposed that these fundamental
spintronic effects can be realized in collinear antiferromagnets with staggered
spin-momentum exchange interaction, which generates conserved spin currents in
the absence of a net equilibrium magnetization. Here we elaborate on the
proposal by presenting archetype model mechanisms for the antiferromagnetic
giant and tunneling magnetoresistance effects. The models are based,
respectively, on anisotropic and valley-dependent forms of the non-relativistic
staggered spin-momentum interaction. Using first principles calculations we
link these model mechanisms to real antiferromagnetic materials and predict a
$\sim$100\% scale for the effects. We point out that besides the GMR/TMR
detection, our models directly imply the possibility of spin-transfer-torques
excitation of the antiferromagnets.",2103.12664v1
2016-06-20,Asymmetric Pt/Co/Pt structure as a platform for extracting pure spin Hall torque,"We have quantitatively studied the spin-orbit torque purely generated by the
spin Hall effect in a wide range of temperatures by intensionally eliminating
the Rashba spin-orbit torque using Pt/Co/Pt trilayers with asymmetric
thicknesses of the top and bottom Pt layers. The vanishingly small contribution
from the Rashba effect has been confirmed through the vector measurements of
the current-induced effective fields. In order to precisely determine the value
of the spin Hall torque, the complete cancelation of the spin Hall torque has
been verified by fabricating symmetric Pt/Co/Pt structure on SiO2 and Gd3Ga5O12
(GGG) substrates. Despite of the complete cance- lation on the GGG substrate,
the spin Hall torque cannot be completely canceled out even when the top and
bottom Pt layers have same thicknesses on the SiO2 substrate, which suggests
that Pt/Co/Pt trilayers on a GGG substrate is a suitable system for precise
measurements of the spin Hall torque. The result of the vector measurements on
Pt/Co/Pt/GGG from 300 to 10 K shows that the spin Hall torque is almost
independent of temperature, which is quantitatively reproduced under the
assumption of the temperature-independent spin Hall angle of Pt.",1606.05986v1
2021-10-04,Separation of Artifacts from Spin-Torque Ferromagnetic Resonance Measurements of Spin-Orbit Torque for the Low-Symmetry van der Waals Semi-Metal ZrTe$_\textbf{3}$,"We measure spin-orbit torque generated by exfoliated layers of the
low-symmetry semi-metal ZrTe$_3$ using the spin-torque ferromagnetic resonance
(ST-FMR) technique. When the ZrTe$_3$ has a thickness greater than about 10 nm,
artifacts due to spin pumping and/or resonant heating can cause the standard
ST-FMR analysis to overestimate the true magnitude of the torque efficiency by
as much as a factor of 30, and to indicate incorrectly that the spin-orbit
torque depends strongly on the ZrTe$_3$ layer thickness. Artifact-free
measurements can still be achieved over a substantial thickness range by the
method developed recently to detect ST-FMR signals in the Hall geometry as well
as the longitudinal geometry. ZrTe$_3$/Permalloy samples generate a
conventional in-plane anti-damping spin torque efficiency
$\xi_{||}^{\text{DL}}$ = 0.014 $\pm$ 0.004, and an unconventional in-plane
field-like torque efficiency $|\xi_{||}^{\text{FL}}|$ = 0.003 $\pm$ 0.001. The
out-of-plane anti-damping torque is negligible. We suggest that artifacts
similarly interfere with the standard ST-FMR analysis for other van der Waals
samples thicker than about 10 nm.",2110.01720v2
2021-11-15,Observation of spin-splitter torque in collinear antiferromagnetic RuO$_2$,"The spin-splitter effect is theoretically predicted to generate an
unconventional spin current with $\mathit{x}$- and $\mathit{z}$- spin
polarization via the spin-split band in antiferromagnets. The generated torque,
namely spin-splitter torque, is effective for the manipulation of magnetization
in an adjacent magnetic layer without an external magnetic field for spintronic
devices such as MRAM. Here, we study the generation of torque in collinear
antiferromagnetic RuO$_2$ with (100), (101), and (001) crystal planes. Next we
find all $\mathit{x}$-, $\mathit{y}$-, and $\mathit{z}$-polarized spin currents
depending on the N\'{e}el vector direction in RuO$_2$(101). For RuO$_2$(100)
and (001), only $\mathit{y}$-polarized spin current was present, which is
independent of the N\'{e}el vector. Using the $\mathit{z}$-polarized spin
currents, we demonstrate field-free switching of the perpendicular magnetized
ferromagnet at room temperature. The spin-splitter torque generated from
RuO$_2$ is verified to be useful for the switching phenomenon and paves the way
for a further understanding of the detailed mechanism of the spin-splitter
effect and for developing antiferromagnetic spin-orbitronics.",2111.07487v1
2018-07-17,Field-free spin-orbit torque switching from geometrical domain wall pinning,"Spin-orbit torques, which utilize spin currents arising from the spin-orbit
coupling, offer a novel method to electrically switch the magnetization with
perpendicular anisotropy. However, the necessity of an external magnetic field
to achieve a deterministic switching is an obstacle for realizing practical
spin-orbit torque devices with all-electric operation. Here, we report a
field-free spin-orbit torque switching by exploiting the domain wall motion in
an anti-notched microwire with perpendicular anisotropy, which exhibits
multi-domain states stabilized by the domain wall surface tension. The
combination of spin-orbit torque, Dzyaloshinskii-Moriya interaction, and domain
wall surface tension induced geometrical pinning allows a deterministic control
of the domain wall and offers a novel method to achieve a field-free spin-orbit
torque switching. Our work demonstrates the proof of concept of a perpendicular
memory cell which can be readily adopted in a three-terminal magnetic memory.",1807.06287v1
2019-02-04,Spin-current induced mechanical torque in a chiral molecular junction,"We analyse the appearance of a mechanical torque that acts on a chiral
molecule: a single-stranded DNA, in which the spin-orbit interaction is
expected to induce a spin-selectivity effect. The mechanical torque is shown to
appear as a result of the non-conservation of the spin current in the presence
of the spin-orbit interaction. Adopting a simple microscopic model Hamiltonian
for a chiral molecule connected to source and drain leads, and accounting for
the mechanical torque acting on the chiral molecule as the back action on the
electrons traversing the molecule, we derive the spin continuity-equation. It
connects the spin current expressed by a Landauer-type formula and the
mechanical torque. Thus, by injecting a spin-polarized current from the source
electrode, it is possible to generate a torque, which will rotate the DNA
molecule.",1902.01152v1
2017-12-20,Planar Hall torque,"Spin-orbit torques in bilayers of ferromagnetic and nonmagnetic materials
hold promise for energy efficient switching of magnetization in nonvolatile
magnetic memories. Previously studied spin Hall and Rashba torques originate
from spin-orbit interactions within the nonmagnetic material and at the bilayer
interface, respectively. Here we report a spin-orbit torque that arises from
planar Hall current in the ferromagnetic material of the bilayer and acts as
either positive or negative magnetic damping. This planar Hall torque exhibits
unusual biaxial symmetry in the plane defined by the applied electric field and
the bilayer normal. The magnitude of the planar Hall torque is similar to that
of the giant spin Hall torque and is large enough to excite auto-oscillations
of the ferromagnetic layer magnetization.",1712.07335v1
2019-03-04,Orbital Torque: Torque Generation by Orbital Current Injection,"We propose a mechanism of torque generation by injection of an orbital
current, which we call $\textit{orbital torque}$. In a magnetic bilayer
consisting of a nonmagnet (NM) and a ferromagnet (FM), we consider a situation
where the spin-orbit coupling (SOC) is present only in the FM. Although the SOC
is absent in the NM, the orbital Hall effect can arise in the NM. When the
resulting orbital Hall current is injected to the FM, the SOC of the FM
converts the orbital angular momentum into spin, which exerts torque to the
magnetization of the FM. Remarkably, even for small SOC strength comparable to
that of $3d$ FMs, the orbital torque can be comparable to the spin torque
induced by the spin Hall effect of the NM with strong SOC. This provides a way
to experimentally probe the OHE and opens a new venue to achieving spin-torque
devices based on light elements that exhibit gigantic orbital response.
Experimental implications are discussed.",1903.01085v3
2020-12-04,"Growth, strain and spin orbit torques in epitaxial NiMnSb films sputtered on GaAs","We report current-induced spin torques in epitaxial NiMnSb films on a
commercially available epi-ready GaAs substrate. The NiMnSb was grown by
co-sputtering from three targets using optimised parameter. The films were
processed into micro-scale bars to perform current-induced spin-torque
measurements. Magnetic dynamics were excited by microwave currents and electric
voltages along the bars were measured to analyse the symmetry of the
current-induced torques. We found that the extracted symmetry of the spin
torques matches those expected from spin-orbit interaction in a tetragonally
distorted half-Heusler crystal. Both field-like and damping-like torques are
observed in all the samples characterised, and the efficiency of the
current-induced torques is comparable to that of ferromagnetic metal/heavy
metal bilayers.",2012.02568v4
2014-01-31,Self-Oscillation in Spin Torque Oscillator Stabilized by Field-like Torque,"The self-oscillation of the magnetization in a spin torque oscillator (STO)
with a perpendicularly magnetized free layer and an in-plane magnetized pinned
layer in the absence of an applied magnetic field was studied by numerically
solving the Landau-Lifshitz-Gilbert equation. It was pointed out that
field-like torque was necessary to realize stable self-oscillation in this type
of STO at zero field. The numerical simulation at finite temperature showed
that the presence of the field-like torque led to a high power with a
relatively high oscillation frequency.",1401.8088v2
2021-03-18,Large Amplitude Spin-Hall Oscillations due to Field-like Torque,"Large amplitude spin-Hall oscillations are identified in a ferromagnetic
layer with two perpendicular in-plane easy axis in the presence of field-like
torque without any polarizer and external field. The analytical study confirms
the possibility of oscillations in the presence of field-like torque. The
investigation shows that the oscillation frequency can be tuned from 2 GHz to
80 GHz by current and enhanced by field-like torque. Further, the enhancement
of frequency along with the Q-factor by current and field-like torque is also
observed.",2103.10037v1
2014-08-12,Spin-transfer-driven nano-oscillators are equivalent to parametric resonators,"The equivalence between different physical systems permits us to transfer
knowledge between them and to characterize the universal nature of their
dynamics. We demonstrate that a nanopillar driven by a spin-transfer torque is
equivalent to a rotating magnetic plate, which permits us to consider the
nanopillar as a macroscopic system under a time-modulated injection of energy,
that is, a simple parametric resonator. This equivalence allows us to
characterize the phases diagram and to predict magnetic states and dynamical
behaviors, such as solitons, stationary textures, and oscillatory localized
states, among others. Numerical simulations confirm these predictions.",1408.2736v2
2015-04-07,Generation of coherent spin-wave modes in Yttrium Iron Garnet microdiscs by spin-orbit torque,"Spin-orbit effects [1-4] have the potential of radically changing the field
of spintronics by allowing transfer of spin angular momentum to a whole new
class of materials. In a seminal letter to Nature [5], Kajiwara et al. showed
that by depositing Platinum (Pt, a normal metal) on top of a 1.3 $\mu$m thick
Yttrium Iron Garnet (YIG, a magnetic insulator), one could effectively transfer
spin angular momentum through the interface between these two different
materials. The outstanding feature was the detection of auto-oscillation of the
YIG when enough dc current was passed in the Pt. This finding has created a
great excitement in the community for two reasons: first, one could control
electronically the damping of insulators, which can offer improved properties
compared to metals, and here YIG has the lowest damping known in nature;
second, the damping compensation could be achieved on very large objects, a
particularly relevant point for the field of magnonics [6,7] whose aim is to
use spin-waves as carriers of information. However, the degree of coherence of
the observed auto-oscillations has not been addressed in ref. [5]. In this
work, we emphasize the key role of quasi-degenerate spin-wave modes, which
increase the threshold current. This requires to reduce both the thickness and
lateral size in order to reach full damping compensation [8] , and we show
clear evidence of coherent spin-orbit torque induced auto-oscillation in
micron-sized YIG discs of thickness 20 nm.",1504.01512v1
2020-08-06,Magnon versus electron mediated spin-transfer torque exerted by spin currents across antiferromagnetic insulator to switch magnetization of adjacent ferromagnetic metal,"The recent experiment [Y. Wang et al., Science 366, 1125 (2019)] on
magnon-mediated spin-transfer torque (MSTT) was interpreted in terms of a
picture where magnons are excited within an antiferromagnetic insulator (AFI),
by applying nonequilibrium electronic spin density at one of its surfaces, so
that their propagation across AFI deprived of conduction electrons eventually
leads to reversal of magnetization of a ferromagnetic metal (FM) attached to
the opposite surface of AFI. We employ a recently developed time-dependent
nonequilibrium Green functions combined with the Landau-Lifshitz-Gilbert
equation (TDNEGF+LLG) formalism to evolve conduction electrons
quantum-mechanically while they interact via self-consistent back-action with
localized magnetic moments described classically by atomistic spin dynamics
solving a system of LLG equations. Upon injection of square current pulse as
the initial condition, TDNEGF+LLG simulations of FM-polarizer/AFI/FM-analyzer
junctions show that reversal of localized magnetic moments within FM-analyzer
is less efficient, in the sense of requiring larger pulse height and its longer
duration, than conventional electron-mediated STT (ESTT) driving magnetization
switching in standard FM-polarizer/normal-metal/FM-analyzer spin valve. Since
both electronic, generated by spin pumping from AFI, and magnonic, generated by
direct transmission from AFI, spin currents are injected into the FM-analyzer,
its localized magnetic moments will experience combined MSTT and ESTT.
Nevertheless, by artificially turning off ESTT we demonstrate that MSTT plays a
dominant role whose understanding, therefore, paves the way for
all-magnon-driven magnetization switching devices with no electronic parts.",2008.02794v3
2014-12-23,STT-SNN: A Spin-Transfer-Torque Based Soft-Limiting Non-Linear Neuron for Low-Power Artificial Neural Networks,"Recent years have witnessed growing interest in the use of Artificial Neural
Networks (ANNs) for vision, classification, and inference problems. An
artificial neuron sums N weighted inputs and passes the result through a
non-linear transfer function. Large-scale ANNs impose very high computing
requirements for training and classification, leading to great interest in the
use of post-CMOS devices to realize them in an energy efficient manner. In this
paper, we propose a spin-transfer-torque (STT) device based on Domain Wall
Motion (DWM) magnetic strip that can efficiently implement a Soft-limiting
Non-linear Neuron (SNN) operating at ultra-low supply voltage and current. In
contrast to previous spin-based neurons that can only realize hard-limiting
transfer functions, the proposed STT-SNN displays a continuous resistance
change with varying input current, and can therefore be employed to implement a
soft-limiting neuron transfer function. Soft-limiting neurons are greatly
preferred to hard-limiting ones due to their much improved modeling capacity,
which leads to higher network accuracy and lower network complexity. We also
present an ANN hardware design employing the proposed STT-SNNs and Memristor
Crossbar Arrays (MCA) as synapses. The ultra-low voltage operation of the
magneto metallic STT-SNN enables the programmable MCA-synapses, computing
analog-domain weighted summation of input voltages, to also operate at
ultra-low voltage. We modeled the STT-SNN using micro-magnetic simulation and
evaluated them using an ANN for character recognition. Comparisons with analog
and digital CMOS neurons show that STT-SNNs can achieve more than two orders of
magnitude lower energy consumption.",1412.8648v1
2018-02-06,Magnetic oscillations Excited by Concurrent Spin Injection from a Tunneling Current and a Spin Hall Current,"In this paper, a 3-terminal spin-transfer torque nano-oscillator (STNO) is
studied using the concurrent spin injection of a spin-polarized tunneling
current and a spin Hall current exciting the free layer into dynamic regimes
beyond what is achieved by each individual mechanism. The pure spin injection
is capable of inducing oscillations in the absence of charge currents
effectively reducing the critical tunneling current to zero. This reduction of
the critical charge currents can improve the endurance of both STNOs and
non-volatile magnetic memories (MRAM) devices. It is shown that the system
response can be described in terms of an injected spin current density $J_s$
which results from the contribution of both spin injection mechanisms, with the
tunneling current polarization $p$ and the spin Hall angle $\theta$ acting as
key parameters determining the efficiency of each injection mechanism. The
experimental data exhibits an excellent agreement with this model which can be
used to quantitatively predict the critical points ($J_s = -2.26\pm 0.09 \times
10^9 \hbar/e$ A/m$^2$) and the oscillation amplitude as a function of the input
currents. In addition, the fitting of the data also allows an independent
confirmation of the values estimated for the spin Hall angle and tunneling
current polarization as well as the extraction of the damping $\alpha = 0.01$
and non-linear damping $Q = 3.8\pm 0.3$ parameters.",1802.02224v1
2019-04-01,X-ray spectroscopy of current-induced spin-orbit torques and spin accumulation in Pt/3d transition metal bilayers,"An electric current flowing in Pt, a material with strong spin-orbit
coupling, leads to spins accumulating at the interfaces by virtue of the spin
Hall effect and interfacial charge-spin conversion. We measure the influence of
these interfacial magnetic moments onto adjacent 3d transition metal layers by
x-ray absorption spectroscopy and x-ray magnetic circular dichroism in a
quantitative and element-selective way, with sensitivity below $10^{-5}~\mu_B$
per atom. In Pt(6 nm)/Co(2.5 nm), the accumulated spins cause a deviation of
the Co magnetization direction, which corresponds to an effective spin-Hall
angle of 0.08. The spin and orbital magnetic moments of Co are affected in
equal proportion by the absorption of the spin current, showing that the
transfer of orbital momentum from the recently predicted orbital Hall effect is
either below our detection limit, or not directed to the 3d states of Co. For
Pt/NM (NM = Ti, Cr, Cu), we find upper limits for the amount of injected spins
corresponding to about $3\times 10^{-6}~\mu_B$ per atom.",1904.00877v2
2011-11-23,Rashba spin torque in an ultrathin ferromagnetic metal layer,"In a two-dimensional ferromagnetic metal layer lacking inversion symmetry,
the itinerant electrons mediate the interaction between the Rashba spin-orbit
interaction and the ferromagnetic order parameter, leading to a Rashba spin
torque exerted on the magnetization. Using Keldysh technique, in the presence
of both magnetism and a spin-orbit coupling, we derive a spin diffusion
equation that provides a coherent description to the diffusive spin dynamics.
The characteristics of the spin torque and its implication on magnetization
dynamics are discussed in the limits of large and weak spin-orbit coupling.",1111.5466v1
2016-06-27,Supercurrent-Induced Spin-Orbit Torques,"We theoretically investigate the supercurrent-induced magnetization dynamics
of a two-dimensional lattice of ferromagnetically ordered spins placed on a
conventional superconductor with broken spatial inversion symmetry and strong
spin-orbit coupling. We develop a phenomenological description of the coupled
dynamics of the superconducting condensate and the spin system, and demonstrate
that supercurrents produce a reactive spin-orbit torque on the magnetization.
By performing a microscopic self-consistent calculation, we show that the
spin-orbit torque originates from a spin-polarization of the Cooper pairs due
to current-induced spin-triplet correlations. Interestingly, we find that there
exists an intrinsic limitation for the maximum achievable spin-orbit torque,
which is determined by the coupling strength between the condensate and the
spin system. In proximitized hole-doped semiconductors, the maximum achievable
spin-orbit torque field is estimated to be on the order of $0.16$ mT, which is
comparable to the critical field for current-induced magnetization switching in
ferromagnetic semiconductors.",1606.08470v1
2020-06-14,Spin-orbit torque generated by amorphous Fe$_{x}$Si$_{1-x}$,"While tremendous work has gone into spin-orbit torque and spin current
generation, charge-to-spin conversion efficiency remains weak in silicon to
date, generally stemming from the low spin-orbit coupling (low atomic number,
Z) and lack of bulk lattice inversion symmetry breaking. Here we report the
observation of spin-orbit torque in an amorphous, non-ferromagnetic
Fe$_{x}$Si$_{1-x}$ / cobalt bilayer at room temperature, using spin torque
ferromagnetic resonance and harmonic Hall measurements. Both techniques provide
a minimum spin torque efficiency of about 3 %, comparable to prototypical heavy
metals such as Pt or Ta. According to the conventional theory of the spin Hall
effect, a spin current in an amorphous material is not expected to have any
substantial contribution from the electronic bandstructure. This, combined with
the fact that Fe$_{x}$Si$_{1-x}$ does not contain any high-Z element, paves a
new avenue for understanding the underlying physics of spin-orbit interaction
and opens up a new class of material systems - silicides - that is directly
compatible with complementary metal-oxide-semiconductor (CMOS) processes for
integrated spintronics applications.",2006.07786v1
2022-07-13,Boosting spin-orbit torque efficiency in spin-current generator/magnet/oxide superlattices,"Efficient manipulation of magnetic materials is essential for spintronics. In
spin-current generator/magnet bilayers, the efficiency of spin-orbit torques
per magnetic layer thickness scales inversely with the magnetic layer
thickness, leading to considerable power increase in applications with large
magnetic layer thickness. Here, we develop a 3D spin-orbit material scheme in
which the spin torque efficiency can be remarkably boosted up by stacking
[spin-current generator/magnet/oxide]n superlattices, with the oxide layers
breaking the inversion symmetry. In contrast, the spin torque diminishes in
[spin-current generator/magnet]n superlattices lacking inversion symmetry
breaking. These results advances the understanding of spin-orbit torques in
magnetic multilayers and establishes spin-current generator/magnet/oxide
superlattices as advantageous bricks for development of high energy-efficiency,
high-endurance, and high-density spintronic memory and computing.",2207.05968v2
2009-04-01,Current-induced microwave excitation of a domain wall confined in a magnetic wire with bi-axial anisotropy,"We studied the current-induced magnetization dynamics of a domain wall
confined in a magnetic wire with bi-axial anisotropy. We showed that above the
threshold current density, breathing-mode excitation, where the thickness of
the domain wall oscillates, is induced by spin-transfer torque. We found that
the breathing-mode can be applied as a source of microwave oscillation because
the resistance of the domain wall is a function of the domain wall thickness.
In a current sweep simulation, the frequency of the breathing-mode exhibits
hysteresis because of the confinement.",0904.0044v1
2010-05-28,Bennett clocking of nanomagnetic logic using electrically induced rotation of magnetization in multiferroic single-domain nanomagnets,"The authors show that it is possible to rotate the magnetization of a
multiferroic (strain-coupled two-layer magnetostrictive-piezoelectric)
nanomagnet by a large angle with a small electrostatic potential. This can
implement Bennett clocking in nanomagnetic logic arrays resulting in
unidirectional propagation of logic bits from one stage to another. This method
of Bennett clocking is superior to using spin-transfer torque or local magnetic
fields for magnetization rotation. For realistic parameters, it is shown that a
potential of ~ 0.2 V applied to a multiferroic nanomagnet can rotate its
magnetization by nearly 900 to implement Bennett clocking.",1005.5358v1
2014-09-23,Guidelines for understanding cubic manganese-rich Heusler compounds,"Manganese-rich Heusler compounds are attracting much interest in the context
of spin transfer torque and rare-earth free hard magnets. Here we give a
comprehensive overview of the magnetic properties of non-centrosymmetric cubic
Mn$_2$-based Heusler materials, which are characterized by an antiparallel
coupling of magnetic moments on Mn atoms. Such a ferrimagnetic order leads to
the emergence of new properties that are absent in ferromagnetic
centrosymmetric Heusler structures. In terms of the band structure
calculations, we explain the formation of this magnetic order and the Curie
temperatures. This overview is intended to establish guidelines for a basic
understanding of magnetism in Mn2 -based Heusler compounds.",1409.6532v1
2015-03-12,Chirp spectroscopy applied to the characterization of Ferromagnetic Resonance in Magnetic Tunnel Junctions,"Magnetic Tunnel Junction devices find use in several applications based on
the exploitation of the Spin-Transfer Torque phenomenon. The Ferromagnetic
Resonance curve is a key characteristic of any Magnetic Tunnel Junctions. It is
usually characterized both experimentally and numerically by performing a lot
of measurements of the magnetic response to a sinusoidal field or current. Here
we propose the use of a chirp signal as excitation signal to reconstruct the
Ferromagnetic resonance curve with a single measurement/simulation. A
micromagnetic comparison of the proposed method with the traditional one is
shown.",1503.03719v1
2015-03-12,Micromagnetic study of electrical-field-assisted magnetization switching in MTJ devices,"Perpendicular MgO-based Magnetic Tunnel Junctions are optimal candidates as
building block of Spin Transfer Torque (STT) magnetoresistive memories.
However, up to now, the only STT is not enough to achieve switching current
density below 106 A/cm2. A recent work [Wang et al., Nature Mater., vol. 11, pp
64-68, Jan. 2012] has experimentally demonstrated the possibility to perform
magnetization switching assisted by an electric-field at ultra-low current
density. Theoretically, this switching has been studied by using a macrospin
approach only. Here, we show a full micromagnetic study. We found that the
switching occurs via a complex nucleation process including the nucleation of
magnetic vortexes.",1503.03721v1
2015-03-16,Impact of Current on Static and Kinetic Depinning Fields of Domain Wall in Ferromagnetic Nanostrip,"The impact of current on static and kinetic depinning fields of a domain wall
in an one dimensional ferromagnetic nanostrip is investigated by solving the
Landau-Lifshitz-Gilbert equation with adiabatic and non-adiabatic spin-transfer
torques analytically and numerically. The results show that in the absence of
current, the static depinning field is greater than the kinetic depinning field
and both the depinning fields decrease by the increase of current applied in a
direction opposite to the direction of the applied field. Both the depinning
fields can also be tuned by the current to make them equal.",1503.04553v1
2015-05-09,Large Fluctuations and Singular Behavior of Nonequilibrium Systems,"We present a general geometrical approach to the problem of escape from a
metastable state in the presence of noise. The accompanying analysis leads to a
simple condition, based on the norm of the drift field, for determining whether
caustic singularities alter the escape trajectories when detailed balance is
absent. We apply our methods to systems lacking detailed balance, including a
nanomagnet with a biaxial magnetic anisotropy and subject to a spin transfer
torque. The approach described within allows determination of the regions of
experimental parameter space that admit caustics.",1505.02285v1
2015-06-02,Current-Driven Motion of Magnetic Domain Wall with Many Bloch Lines,"The current-driven motion of a domain wall (DW) in a ferromagnet with many
Bloch lines (BLs) via the spin transfer torque is studied theoretically. It is
found that the motion of BLs changes the current-velocity ($j$-$v$)
characteristic dramatically. Especially, the critical current density to
overcome the pinning force is reduced by the factor of the Gilbert damping
coefficient $\alpha$ even compared with that of a skyrmion. This is in sharp
contrast to the case of magnetic field driven motion, where the existence of
BLs reduces the mobility of the DW.",1506.00723v1
2015-07-24,Boosting Domain Wall Propagation by Notches,"We report a counter-intuitive finding that notches in an otherwise
homogeneous magnetic nanowire can boost current-induced domain wall (DW)
propagation. DW motion in notch-modulated wires can be classified into three
phases: 1) A DW is pinned around a notch when the current density is below the
depinning current density. 2) DW propagation velocity is boosted by notches
above the depinning current density and when non-adiabatic spin-transfer torque
strength $\beta$ is smaller than the Gilbert damping constant $\alpha$. The
boost can be manyfold. 3) DW propagation velocity is hindered when $\beta >
\alpha$. The results are explained by using the Thiele equation.",1507.06748v1
2012-09-14,Skyrmion Dynamics in Multiferroic Insulator,"Recent discovery of Skyrmion crystal phase in insulating multiferroic
compound Cu$_2$OSeO$_3$ calls for new ways and ideas to manipulate the
Skyrmions in the absence of spin transfer torque from the conduction electrons.
It is shown here that the position-dependent electric field, pointed along the
direction of the average induced dipole moment of the Skyrmion, can induce the
Hall motion of Skyrmion with its velocity orthogonal to the field gradient.
Finite Gilbert damping produces longitudinal motion. We find a rich variety of
resonance modes excited by a.c. electric field.",1209.3120v1
2014-06-12,Large exchange-dominated domain wall velocities in antiferromagnetically coupled nanowires,"Magnetic nanowires supporting field- and current-driven domain wall motion
are envisioned for new methods of information storage and processing. A major
obstacle for their practical use is the domainwall velocity, which is
traditionally limited due to the Walker breakdown occurring when the forcing
field or current reaches a critical threshold value. We show through numerical
and analytical modeling that the Walker breakdown limit can be extended or
completely eliminated in antiferromagnetically coupled magnetic nanowires.
These coupled nanowires allow for giant domain-wall velocities driven by field
and/or current via spin transfer torque as compared to conventional nanowires.",1406.3253v1
2019-06-10,High Frequency Domain Wall Oscillations in Ferromagnetic Nanowire with a Nanoscale Dzyaloshinskii Moriya Interaction (DMI) Region,"The Dzyaloshinskii Moriya Interaction (DMI) has laid the foundation for many
novel chiral structures such as Skyrmions. In most of the studies so far, the
DMI is present in the whole of the magnetic layer. Here, we report our
investigations on a ferromagnetic nanowire where DMI is confined to a nanoscale
region. We observe that the local modulation of magnetic properties causes
oscillation of domain walls under the influence of spin-transfer torque. The
oscillation frequency is tunable within a few GHz, making this observation
potentially useful for applications in neuromorphic computing.",1906.03844v1
2022-05-07,Current-driven Dynamics of Skyrmion Bubbles in Achiral Uniaxial Magnets,"We report dynamics of skyrmion bubbles driven by spin-transfer torque in
achiral ferromagnetic nanostripes using micromagnetic simulations. In a
three-dimensional uniaxial ferromagnet with a quality factor that is smaller
than 1, the skyrmion bubble is forced to stay at the central nanostripe by a
repulsive force from the geometry border. The coherent motion of skyrmion
bubbles in the nanostripe can be realized by increasing the quality factor to
~3.8. Our results should propel the design for future spintronic devices such
as artificial neural computing and racetrack memory based on dipole-stabilized
skyrmion bubbles.",2205.03641v1
2023-06-06,A Reference-less Slope Detection Technique in 65nm for Robust Sensing of 1T1R Arrays,"Spin-Torque-Transfer RAM (STTRAM) is a promising technology however process
variation poses serious challenge to sensing. To eliminate bit-to-bit process
variation we propose a reference-less, destructive slope detection technique
which exploits the MTJ switching from high to low state to detect memory state.
A proof-of-concept fabricated test-chip using 96kb mimicked STTRAM bits in 65nm
technology shows that slope sensing reduces failure rate by 120X in 2.5K-5K
array@TMR=100% and 162X in 2.5K-5K@TMR=80% array compared to conventional
voltage sensing.",2306.03972v1
2011-02-20,Hybrid CMOS-MQCA Logic Architectures using Multi-Layer Spintronic Devices,"We present a novel hybrid CMOS-MQCA architecture using multi-layer Spintronic
devices as computing elements. A feasibility study is presented with 22nm CMOS
where new approaches for spin transfer torque induced clocking and read-out
scheme for variability-tolerance are introduced. A first-of-its-kind Spintronic
device model enables circuit simulation using existing CAD infrastructure.
Approximately 70% reduction in energy consumption is observed when compared
against conventional field-induced clocking scheme.",1102.4034v2
2011-04-07,Current driven defect unbinding transition in an XY ferromagnet,"A Keldysh-contour effective field theory is derived for magnetic vortices in
the presence of current flow. The effect of adiabatic and non-adiabatic spin
transfer torques on vortex motion is highlighted. Similarities to and
differences from the superconducting case are presented and explained. Current
flow across a magnetically ordered state is shown to lead to a defect-unbinding
phase transition which is intrinsically nonequilibrium in the sense of not
being driven by a variation in effective temperature. The dependence of the
density of vortices on the current density is determined.",1104.1345v2
2017-11-21,Stability of axisymmetric chiral skyrmions,"We examine topological solitons in a minimal variational model for a chiral
magnet, so-called chiral skyrmions. In the regime of large background fields,
we prove linear stability of axisymmetric chiral skyrmions under arbitrary
perturbations in the energy space, a long-standing open question in physics
literature. Moreover, we show strict local minimality of axisymmetric chiral
skyrmions and nearby existence of moving soliton solution for the
Landau-Lifshitz-Gilbert equation driven by a small spin transfer torque.",1711.07717v1
2020-01-27,Bidirectional switching assisted by interlayer exchange coupling in asymmetric magnetic tunnel junctions,"We study the combined effects of spin transfer torque, voltage modulation of
interlayer exchange coupling and magnetic anisotropy on the switching behavior
of perpendicular magnetic tunnel junctions (p-MTJs). In asymmetric p-MTJs, a
linear-in-voltage dependence of interlayer exchange coupling enables the
effective perpendicular anisotropy barrier to be lowered for both voltage
polarities. This mechanism is shown to reduce the critical switching current
and effective activation energy. Finally, we analyze the possibility of having
switching via interlayer exchange coupling only.",2001.10024v1
2021-09-10,Device geometry dependent deterministic skyrmion generation from a skyrmionium,"A magnetic skyrmionium can be perceived as an association of two magnetic
skyrmions with opposite topological charges. In this work, we have investigated
the transformation of skyrmionium into multi-skyrmionic states via domain wall
(DW) pairs in three different devices with variable geometric configurations.
The same device geometries were considered for single ferromagnetic layer as
well as synthetic antiferromagnetic (SAF) system. It is observed that by tuning
the current density, deterministic generation of skyrmions is possible via the
spin transfer torque (STT). The proposed device is efficiently adjustable to
change the number of skyrmions . The results may lead to development of
skyrmion-based devices for neuromorphic and unconventional computing.",2109.04973v1
2022-10-03,Probing domain wall dynamics in magnetic Weyl semimetals via the non-linear anomalous Hall effect,"The magnetic textures of Weyl semimetals are embedded into their topological
structure and interact dynamically with it. Here, we examine electric
field-induced structural phase transitions in domain walls mediated by the spin
transfer torque, and their footprint in charge transport. Remarkably, domain
wall dynamics lead to a transient, local, non-linear anomalous Hall effect and
non-linear anomalous drift current, which serve as direct probes of the
magnetization dynamics and of the domain wall location. We discuss experimental
observation in state-of-the-art samples.",2210.01150v1
2008-10-25,The domain wall spin torque-meter,"We report the direct measurement of the non-adiabatic component of the
spin-torque in domain walls. Our method is independent of both the pinning of
the domain wall in the wire as well as of the Gilbert damping parameter. We
demonstrate that the ratio between the non-adiabatic and the adiabatic
components can be as high as 1, and explain this high value by the importance
of the spin-flip rate to the non-adiabatic torque. Besides their fundamental
significance these results open the way for applications by demonstrating a
significant increase of the spin torque efficiency.",0810.4633v1
2010-10-03,"Adiabatic quantum pumping, magnification effects and quantum size effects of spin-torque in magnetic tunnel junctions","We study the adiabatic quantum pumping and quantum size effects of
spin-torque in a magnetic tunnel junction within a scattering matrix approach.
Quantum size effects are predicted in the presence of a dc bias as a function
of the thickness of the normal metal layer inserted between two magnetic layers
and of the fixed magnetic layer. In the presence of ac voltages, the results
for the spin-torque show a peculiar magnification effect and advantages of
spin-torque pumping in actual devices are also discussed.",1010.0381v1
2011-07-04,Minimization of the Switching Time of a Synthetic Free Layer in Thermally Assisted Spin Torque Switching,"We theoretically studied the thermally assisted spin torque switching of a
synthetic free layer and showed that the switching time is minimized if the
condition H_J=|H_s|/(2 alpha) is satisfied, where H_J, H_s and alpha are the
coupling field of two ferromagnetic layers, the amplitude of the spin torque,
and the Gilbert damping constant. We also showed that the coupling field of the
synthetic free layer can be determined from the resonance frequencies of the
spin-torque diode effect.",1107.0753v2
2013-12-02,Critical Field of Spin Torque Oscillator with Perpendicularly Magnetized Free Layer,"The oscillation properties of a spin torque oscillator consisting of a
perpendicularly magnetized free layer and an in-plane magnetized pinned layer
are studied based on an analysis of the energy balance between spin torque and
damping. The critical value of an external magnetic field applied normal to the
film plane is found, below which the controllable range of the oscillation
frequency by the current is suppressed. The value of the critical field depends
on the magnetic anisotropy, the saturation magnetization, and the spin torque
parameter.",1312.0300v1
2015-09-19,Spin torque and Nernst effects in Dzyaloshinskii-Moriya ferromagnets,"We predict that a temperature gradient can induce a magnon-mediated intrinsic
torque and a transverse spin current in systems with non-trivial magnon Berry
curvature. With the help of a microscopic linear response theory of
nonequilibrium magnon-mediated torques and spin currents we identify the
interband and intraband components that manifest in ferromagnets with
Dzyaloshinskii-Moriya interactions and magnetic textures. To illustrate and
assess the importance of such effects, we apply our theory to the
magnon-mediated spin Nernst and torque responses in a kagome lattice
ferromagnet.",1509.05847v3
2024-03-15,Chiral-stress-energy-momentum tensor for covariant description of spin and torque densities of light,"The measurement of the spin angular momentum of circularly polarized light by
Beth [Phys. Rev. 50, 115 (1936)] can be explained by using a microscopic torque
density. However, the experiment does not resolve the space- and time-dependent
evolution of the spin density of light and the wave plate and the covariant
form of the microscopic torque density. Here we focus on the covariant
description of the helicity, spin, and torque densities of light in materials
using the chiral-stress-energy-momentum tensor. We also perform simulations of
Gaussian light pulses in quarter-wave-plate geometries made of birefringent and
dielectric materials.",2403.10466v1
2009-03-11,Nanomechanical Detection of Itinerant Electron Spin Flip,"Spin is an intrinsically quantum property, characterized by angular momentum.
A change in the spin state is equivalent to a change in the angular momentum or
mechanical torque. This spin-induced torque has been invoked as the intrinsic
mechanism in experiments ranging from the measurements of angular momentum of
photons g-factor of metals and magnetic resonance to the magnetization reversal
in magnetic multi-layers A spin-polarized current introduced into a nonmagnetic
nanowire produces a torque associated with the itinerant electron spin flip.
Here, we report direct measurement of this mechanical torque and itinerant
electron spin polarization in an integrated nanoscale torsion oscillator, which
could yield new information on the itinerancy of the d-band electrons. The
unprecedented torque sensitivity of 10^{-22} N m/ \sqrt{Hz} may enable
applications for spintronics, precision measurements of CP-violating forces,
untwisting of DNA and torque generating molecules.",0903.1894v1
2012-04-22,Spin Hall effect versus Rashba torque: a Diffusive Approach,"Current-driven magnetization dynamics of single ferromagnets in heavy
metal/ferromagnet bilayers has been recently realized. In this work, spin
torque induced by so-called Rashba spin-orbit coupling and spin Hall effect are
considered within a diffusive model. The dependence of the resulting torque as
a function of the thicknesses of the ferromagnet and heavy metal is analyzed.
We show that (i) both torques are on the form ${\bf T}=T_{||}{\bf m}\times{\bf
y}+T_\bot{\bf m}\times({\bf y}\times{\bf m})$, (ii) the ratio $T_{||}/T_\bot$
strongly depends on the thickness of the layers and (iii) the thickness
dependence of the spin torque provides an indication of the origin of the
(Rashba- or spin Hall effect-induced) spin torque .",1204.4869v1
2020-07-01,Magnetic asymmetry induced anomalous spin-orbit torque in IrMn,"We demonstrate an anomalous spin-orbit torque induced by the broken magnetic
symmetry in the antiferromagnet IrMn. We study the magnetic structure of three
phases of IrMn thin films using neutron diffraction technique. The magnetic
mirror symmetry M' is broken laterally in both L10-IrMn and L12-IrMn3 but not
{\gamma}-IrMn3. We observe an out-of-plane damping-like spin-orbit torque in
both L10-IrMn/permalloy and L12-IrMn3/permalloy bilayers but not in
{\gamma}-IrMn3/permalloy. This is consistent with both the symmetry analysis on
the effects of a broken M' on spin-orbit torque and the theoretical predictions
of the spin Hall effect and the Rashba-Edelstein effect. In addition, the
measured spin-orbit torque efficiencies are 0.61+-0.01, 1.01+-0.03 and
0.80+-0.01 for the L10, L12 and {\gamma} phases, respectively. Our work
highlights the critical roles of the magnetic asymmetry in spin-orbit torque
generation.",2007.00262v1
2020-07-16,Spin torque and persistent currents caused by percolation of topological surface states,"The topological insulator/ferromagnetic metal (TI/FMM) bilayer thin films
emerged as promising topological surface state-based spintronic devices, most
notably in their efficiency of current-induced spin torque. Using a cubic
lattice model, we reveal that the surface state Dirac cone of the TI can
gradually merge into or be highly intertwined with the FMM bulk bands, and the
surface states percolate into the FMM and eventually hybridize with the quantum
well states therein. The magnetization can distort the spin-momentum locking of
the surface states and yield an asymmetric band structure, which causes a
laminar flow of room temperature persistent charge current. Moreover, the
proximity to the FMM also promotes a persistent laminar spin current. Through a
linear response theory, we elaborate that both the surface state and the FMM
bulk bands contribute to the current-induced spin torque, and their real wave
functions render the spin torque predominantly field-like, with a magnitude
highly influenced by the degree of the percolation of the surface states. On
the other hand, impurities can change the spin polarization expected from the
Edelstein effect and generate a damping-like torque, and produce a torque even
when the magnetization points in-plane and orthogonal to the current direction.",2007.08055v1
2022-06-20,Spin Torque Generated by Valley Hall Effect in WSe2,"Monolayer transition metal dichalcogenides are promising materials for
spintronics due to their robust spin-valley locked valence states, enabling
efficient charge-to-spin conversion via valley Hall effect with non-equilibrium
spins possessing long spin diffusion lengths of hundreds of nanometers. In this
work, we show that the injection of a pure valley current, induced by valley
Hall effect in a WSe2 monolayer, imparts a spin torque on the magnetization of
an overlaid Fe or CoFe in a tunneling structure. The torque efficiency is found
to be comparable to that in conventional perpendicular magnetic tunnel
junctions and can be further optimized with valley Hall angle in WSe2. The
valley nature of the spin torque gives rise to out-of-plane damping-like
torques in a current-in-plane configuration, vanishing charge transport
perpendicular-to-the-plane as well as torque efficiency tunable through gating.",2206.09998v1
2021-06-04,Efficient conversion of orbital Hall current to spin current for spin-orbit torque switching,"Spin Hall effect, an electric generation of spin current, allows for
efficient control of magnetization. Recent theory revealed that orbital Hall
effect creates orbital current, which can be much larger than spin Hall-induced
spin current. However, orbital current cannot directly exert a torque on a
ferromagnet, requiring a conversion process from orbital current to spin
current. Here, we report two effective methods of the conversion through
spin-orbit coupling engineering, which allows us to unambiguously demonstrate
orbital-current-induced spin torque, or orbital Hall torque. We find that
orbital Hall torque is greatly enhanced by introducing either a rare-earth
ferromagnet Gd or a Pt interfacial layer with strong spin-orbit coupling in
Cr/ferromagnet structures, indicating that the orbital current generated in Cr
is efficiently converted into spin current in the Gd or Pt layer. Furthermore,
we show that the orbital Hall torque can facilitate the reduction of switching
current of perpendicular magnetization in spin-orbit-torque-based spintronic
devices.",2106.02286v2
2011-09-06,Compression of matter in the center of accreting neutron stars,"To estimate the feasibility of dense-matter phase transition, we studied the
evolution of the central density as well as the baryon chemical potential of
accreting neutron stars. We compared the thin-disk accretion with and without
the magnetic field torque with the spin-down scenario for a selection of recent
equations of state. We compared the prevalent (in the recycled-pulsar context)
Keplerian thin-disk model, in which the matter is accreted from the
marginally-stable circular orbit, with the recent magnetic-torque model that
takes into account the influence of stellar magnetic field on the effective
inner boundary of the disk. Calculations were performed using a multi-domain
spectral methods code in the framework of General Relativity. We considered
three equations of state consistent with the recently measured mass of PSR
J1614-2230, 1.97 +- 0.04 M_sun (one of them softened by the appearance of
hyperons). If there is no magnetic torque and efficient angular momentum
transfer from the disk to the star, substantial central compression is limited
to the region of initial stellar masses close to the maximum mass. Outside the
maximum mass vicinity, accretion-induced central compression is significant
only if the angular momentum transfer is inefficient. Accounting for the
magnetic field effectively decreases the efficiency of angular momentum
transfer and implies a significant central compression. An efficient angular
momentum transfer from a thin disk onto a non-magnetized neutron star does not
provide a good mechanism for the central compression and possible phase
transition. Substantial central compression is possible for a broad range of
masses of slowly-rotating initial configurations for magnetized neutron stars.
Accretion-induced central compression is particularly strong for stiff equation
of state with a high-density softening.",1109.1179v2
2021-06-30,Origin of Nonlinear Damping due to Mode Coupling in Auto-Oscillatory Modes Strongly Driven by Spin-Orbit Torque,"We investigate the physical origin of nonlinear damping due to mode coupling
between several auto-oscillatory modes driven by spin-orbit torque in
constricted Py/Pt heterostructures by examining the dependence of
auto-oscillation on temperature and applied field orientation. We observe a
transition in the nonlinear damping of the auto-oscillation modes extracted
from the total oscillation power as a function of drive current, which
coincides with the onset of power redistribution amongst several modes and the
crossover from linewidth narrowing to linewidth broadening in all individual
modes. This indicates the activation of another relaxation process by nonlinear
magnon-magnon scattering within the modes. We also find that both nonlinear
damping and threshold current in the mode-interaction damping regime at high
drive current after transition are temperature independent, suggesting that the
mode coupling occurs dominantly through a non-thermal magnon scattering process
via a dipole or exchange interaction rather than thermally excited
magnon-mediated scattering. This finding presents a promising pathway to
overcome the current limitations of efficiently controlling the interaction
between two highly nonlinear magnetic oscillators to prevent mode crosstalk or
inter-mode energy transfer and deepens understanding of complex nonlinear spin
dynamics in multimode spin wave systems.",2107.00150v2
2022-05-05,Free Core Nutation and its relation to the Spin-Over Mode,"The time-varying response of the Earth's and other planets' rotation to
external gravitational torques depends strongly on their internal structure. In
particular, the existence of the mode known as the Free Core Nutation in the
fluid core, is known to amplify the forced nutations in the near-diurnal
retrograde frequency band (as measured in the planetary frame of reference).
Due to their proximity in shape and frequency, this mode is sometimes equated
with the so-called Spin-Over Mode which denotes the free oscillation of a
steadily rotating ellipsoidal fluid core. Through a careful study of the freely
rotating two-layer planetary model with a rigid mantle and an inviscid fluid
core, we show that the Spin-Over Mode frequency corresponds to that where the
sum of the external and internal torques on the mantle are balanced, causing it
to rotate steadily. The presence of dissipation at the Core-Mantle Boundary
causes the Free Core Nutation to become damped and slightly offset its
resonance frequency. We show that this offset, which is $\approx-1$ day for the
Earth, can be interpreted as the result of the proximity of the Free Core
Nutation frequency to that of the Spin-Over Mode, which now corresponds to a
minimum in the magnitude of the transfer function for nutations. We also show
how this proximity leads to a slightly lower Quality factor for the resonance
than that compute from the usual formula. We conclude by discussing possible
implications of this mechanism for Mars, the Moon, and the long-term evolution
of the Earth.",2205.02799v1
2016-08-12,Coherent microwave generation by spintronic feedback oscillator,"The transfer of spin angular momentum to a nanomagnet from a spin polarized
current provides an efficient means of controlling the magnetization direction
in nanomagnets. A unique consequence of this spin torque is that the
spontaneous oscillations of the magnetization can be induced by applying a
combination of a dc bias current and a magnetic field. Here we experimentally
demonstrate a different effect, which can drive a nanomagnet into spontaneous
oscillations without the need of external spin torque injection. For the
demonstration of this effect, we use a nano-pillar of magnetic tunnel junction
(MTJ) powered by a dc current and connected to a coplanar waveguide (CPW) lying
above the free layer of the MTJ. Any fluctuation of the free layer
magnetization is converted into oscillating voltage via the tunneling
magneto-resistance effect and is fed back into the MTJ by the CPW through
inductive coupling. As a result of this feedback, the magnetization of the free
layer can be driven into a continual precession. The combination of MTJ and CPW
behaves similar to a laser system and outputs a stable rf power with quality
factor exceeding 10,000.",1608.03708v1
2016-08-24,Emergent Geometric Frustration of Artificial Magnetic Skyrmion Crystals,"Magnetic skyrmions have been receiving growing attention as potential
information storage and magnetic logic devices since an increasing number of
materials have been identified that support skyrmion phases. Explorations of
artificial frustrated systems have led to new insights into controlling and
engineering new emergent frustration phenomena in frustrated and disordered
systems. Here, we propose a skyrmion spin ice, giving a unifying framework for
the study of geometric frustration of skyrmion crystals in a non-frustrated
artificial geometrical lattice as a consequence of the structural confinement
of skyrmions in magnetic potential wells. The emergent ice rules from the
geometrically frustrated skyrmion crystals highlight a novel phenomenon in this
skyrmion system: emergent geometrical frustration. We demonstrate how skyrmion
crystal topology transitions between a non-frustrated periodic configuration
and a frustrated ice-like ordering can also be realized reversibly. The
proposed artificial frustrated skyrmion systems can be annealed into different
ice phases with an applied current induced spin-transfer torque, including a
long range ordered ice rule obeying ground state, as-relaxed random state,
biased state and monopole state. The spin-torque reconfigurability of the
artificial skyrmion ice states, difficult to achieve in other artificial spin
ice systems, is compatible with standard spintronic device fabrication
technology, which makes the semiconductor industrial integration
straightforward.",1608.06733v1
2021-01-11,Current-driven domain wall dynamics in ferrimagnetic Ni-doped Mn4N films : very large domain wall velocities and reversal of motion direction across the magnetic compensation point,"Spin-transfer torque (STT) and spin-orbit torque (SOT) are spintronic
phenomena allowing magnetization manipulation using electrical currents. Beyond
their fundamental interest, they allow developing new classes of magnetic
memories and logic devices, in particular based on domain wall (DW) motion. In
this work, we report the study of STT driven DW motion in ferrimagnetic
manganese nickel nitride (Mn4-xNixN) films, in which a fine adjustment of the
Ni content allows setting the magnetic compensation at room temperature. The
reduced magnetization, combined with the large spin polarization of conduction
electrons, strongly enhances the STT so that domain wall velocities approaching
3000 m/s can be obtained for Ni compositions close to the compensation point.
In addition, a reversal of the domain wall motion direction is observed when
the magnetic compensation composition is crossed. This striking feature,
related to the change of direction of the spin polarization with respect to
that of the net magnetization, is clarified by ab initio band structure
calculations.",2101.04220v2
2020-01-17,Thermal spin transport and spin in thermoelectrics,"This article reviews the principles that govern the combined transport of
spin, heat, and charge. The extensive thermodynamic quantity associated with
spin transport is the magnetization; its Onsager-conjugate force is in general
the derivative of the free energy with respect to the magnetization. Spins are
carried in one of two ways: (1) by spin-polarized free electrons in magnetic
metals and doped semiconductors, or (2) by spin waves (magnons) that reside on
localized electrons on unfilled d- or f-shells of transition metal or
rare-earth elements. The paper covers both cases in separate chapters. In both
cases, it is possible to define a spin chemical potential whose gradient is the
more practical conjugate force to spin transport. The paper further describes
the anomalous Hall, spin Hall, and inverse spin Hall effects in magnetic and
non-magnetic solids with strong spin-orbit coupling because these effects are
used to generate and measure spin fluxes. Spin transport across interfaces is
described next, and includes spin pumping and spin transfer torque. The final
chapter then puts all these concepts together to describe the spin-Seebeck,
spin-Peltier, and magnon-drag effects, which exist in ferromagnetic,
antiferromagnetic, and even paramagnetic solids. Magnon-drag, in particular, is
a high-temperature effect that boosts the thermopower of metals by an order of
magnitude and that of semiconductors by a factor of 2 or 3 above the electronic
diffusion thermopower. This is the only example where a spin-driven effect is
larger than a charge-driven effect. Magnon drag leads a simple binary
paramagnetic semiconductor, MnTe, to have zT > 1 without optimization. This
shows how adding spin as an additional design parameter in thermoelectrics
research is a new and promising approach toward the quest for high-zT
materials.",2001.06366v1
2004-06-24,Thermal Effects on the Magnetic Field Dependence of Spin Transfer Induced Magnetization Reversal,"We have developed a self-aligned, high-yield process to fabricate CPP
(current perpendicular to the plane) magnetic sensors of sub 100 nm dimensions.
A pinned synthetic antiferromagnet (SAF) is used as the reference layer which
minimizes dipole coupling to the free layer and field induced rotation of the
reference layer. We find that the critical currents for spin transfer induced
magnetization reversal of the free layer vary dramatically with relatively
small changes the in-plane magnetic field, in contrast to theoretical
predictions based on stability analysis of the Gilbert equations of
magnetization dynamics including Slonczewski-type spin-torque terms. The
discrepancy is believed due to thermal fluctuations over the time scale of the
measurements. Once thermal fluctuations are taken into account, we find good
quantitative agreement between our experimental results and numerical
simulations.",0406574v1
2010-05-03,Dynamics of two coupled vortices in a spin valve nanopillar excited by spin transfer torque,"We investigate the dynamics of two coupled vortices driven by spin transfer.
We are able to independently control with current and perpendicular field, and
to detect, the respective chiralities and polarities of the two vortices. For
current densities above $J=5.7*10^7 A/cm^2$, a highly coherent signal
(linewidth down to 46 kHz) can be observed, with a strong dependence on the
relative polarities of the vortices. It demonstrates the interest of using
coupled dynamics in order to increase the coherence of the microwave signal.
Emissions exhibit a linear frequency evolution with perpendicular field, with
coherence conserved even at zero magnetic field.",1005.0290v2
2011-03-29,Current induced rotational torques in the skyrmion lattice phase of chiral magnets,"In chiral magnets without inversion symmetry, the magnetic structure can form
a lattice of magnetic whirl lines, a two-dimensional skyrmion lattice,
stabilized by spin-orbit interactions in a small range of temperatures and
magnetic fields. The twist of the magnetization within this phase gives rise to
an efficient coupling of macroscopic magnetic domains to spin currents. We
analyze the resulting spin-transfer effects, and, in particular, focus on the
current induced rotation of the magnetic texture by an angle. Such a rotation
can arise from macroscopic temperature gradients in the system as has recently
been shown experimentally and theoretically. Here we investigate an alternative
mechanism, where small distortions of the skyrmion lattice and the transfer of
angular momentum to the underlying atomic lattice play the key role. We employ
the Landau-Lifshitz-Gilbert equation and adapt the Thiele method to derive an
effective equation of motion for the rotational degree of freedom. We discuss
the dependence of the rotation angle on the orientation of the applied magnetic
field and the distance to the phase transition.",1103.5548v2
2017-06-18,Neutron star dynamics under time dependent external torques,"The two component model describes neutron star dynamics incorporating the
response of the superfluid interior. Conventional solutions and applications
involve constant external torques, as appropriate for radio pulsars on
dynamical timescales. We present the general solution of two component dynamics
under arbitrary time dependent external torques, with internal torques that are
linear in the rotation rates, or with the extremely non-linear internal torques
due to vortex creep. The two-component model incorporating the response of
linear or nonlinear internal torques can now be applied not only to radio
pulsars but also to magnetars and to neutron stars in binary systems, with
strong observed variability and noise in the spin-down or spin-up rates. Our
results allow the extraction of the time dependent external torques from the
observed spin-down (or spin-up) time series, $\dot{\Omega}(t)$. Applications
are discussed.",1706.05662v2
2023-10-10,Non-relativistic torque and Edelstein effect in noncollinear magnets,"The Edelstein effect is the origin of the spin-orbit torque: a
current-induced torque that is used for the electrical control of ferromagnetic
and antiferromagnetic materials. This effect originates from the relativistic
spin-orbit coupling, which necessitates utilizing materials with heavy
elements. Here we show that in magnetic materials with non-collinear magnetic
order, the Edelstein effect and consequently also a current-induced torque can
exist even in the absence of the spin-orbit coupling. Using group symmetry
analysis, model calculations, and realistic simulations on selected compounds,
we identify large classes of non-collinear magnet candidates and demonstrate
that the current-driven torque is of similar magnitude as the celebrated
spin-orbit torque in conventional transition metal structures. We also show
that this torque can exist in an insulating material, which could allow for
highly efficient electrical control of magnetic order.",2310.06499v1
2008-10-12,Non-equilibrium magnetism in dual spin valves,"The field of spin electronics (spintronics) was initiated by the discovery of
giant magnetoresistance (GMR) for which Fert[1] and Grunberg[2] were awarded
the 2007 Nobel Prize for Physics. GMR arises from differential scattering of
the majority and minority spin electrons by a ferromagnet (FM) so that the
resistance when the FM layers separated by non-magnetic (NM) spacers are
aligned by an applied field is different to when they are antiparallel. In 1996
Slonczewski[3] and Berger[4] predicted that a large spin-polarised current
could transfer spin-angular momentum and so exert a spin transfer torque (STT)
sufficient to switch thin FM layers between stable magnetisation states[5] and,
for even higher current densities, drive continuous precession which emits
microwaves[6]. Thus, while GMR is a purely passive phenomenon which ultimately
depends on the intrinsic band structure of the FM, STT adds an active element
to spintronics by which the direction of the magnetisation may be manipulated.
Here we show that highly non-equilibrium spin injection can modify the
scattering asymmetry and, by extension, the intrinsic magnetism of a FM. This
phenomenon is completely different to STT and provides a third ingredient which
should further expand the range of opportunities for the application of
spintronics.",0810.2093v1
2012-02-08,Cross-point architecture for spin transfer torque magnetic random access memory,"Spin transfer torque magnetic random access memory (STT-MRAM) is considered
as one of the most promising candidates to build up a true universal memory
thanks to its fast write/read speed, infinite endurance and non-volatility.
However the conventional access architecture based on 1 transistor + 1 memory
cell limits its storage density as the selection transistor should be large
enough to ensure the write current higher than the critical current for the STT
operation. This paper describes a design of cross-point architecture for
STT-MRAM. The mean area per word corresponds to only two transistors, which are
shared by a number of bits (e.g. 64). This leads to significant improvement of
data density (e.g. 1.75 F2/bit). Special techniques are also presented to
address the sneak currents and low speed issues of conventional cross-point
architecture, which are difficult to surmount and few efficient design
solutions have been reported in the literature. By using a STT-MRAM SPICE model
including precise experimental parameters and STMicroelectronics 65 nm
technology, some chip characteristic results such as cell area, data access
speed and power have been calculated or simulated to demonstrate the expected
performances of this new memory architecture.",1202.1782v1
2014-08-02,Tunnel magnetoresistance and spin-transfer-torque switching in polycrystalline Co2FeAl full-Heusler alloy magnetic tunnel junctions on Si/SiO2 amorphous substrates,"We studied polycrystalline B2-type Co2FeAl (CFA) full-Heusler alloy based
magnetic tunnel junctions (MTJs) fabricated on a Si/SiO2 amorphous substrate.
Polycrystalline CFA films with a (001) orientation, a high B2 ordering, and a
flat surface were achieved using a MgO buffer layer. A tunnel magnetoresistance
(TMR) ratio up to 175% was obtained for an MTJ with a CFA/MgO/CoFe structure on
a 7.5-nm-thick MgO buffer. Spin-transfer torque induced magnetization switching
was achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as a
switching layer. Using a thermal activation model, the intrinsic critical
current density (Jc0) was determined to be 8.2 x 10^6 A/cm^2, which is lower
than 2.9 x 10^7 A/cm^2, the value for epitaxial CFA-MTJs [Appl. Phys. Lett.
100, 182403 (2012)]. We found that the Gilbert damping constant evaluated using
ferromagnetic resonance measurements for the polycrystalline CFA film was
~0.015 and was almost independent of the CFA thickness (2~18 nm). The low Jc0
for the polycrystalline MTJ was mainly attributed to the low damping of the CFA
layer compared with the value in the epitaxial one (~0.04).",1408.0341v1
2016-06-14,Ultrafast Spin-Transfer-Torque Switching of Synthetic Ferrimagnets,"The switching speed and the write current required for spin-transfer-torque
reversal of spintronic devices such as magnetic tunnel junctions (MTJ)
currently hinder their wide implementation into memory and logic devices. This
problem is further exacerbated as the dimensions of MTJ nanostructures are
scaled down to tens of nanometers in diameter, as higher magnetic anisotropy
materials are required to meet thermal stability requirements that demand
higher switching current densities. Here, we propose a simple solution to these
issues based on synthetic ferrimagnet (SFM) structures. It is commonly assumed
that to achieve a given switching delay, the current has to exceed the critical
current by a certain factor and so a higher critical current implies a higher
switching current. We show that this is not the case for SFM structures which
can provide significantly reduced switching delay for a given current density,
even though the critical current is increased. This non-intuitive result can be
understood from the requirements of angular momentum conservation. We conclude
that a 20 nm diameter MTJ incorporating the proposed SFM free layer structure
can be switched in tens of picosecond time scales. This remarkable switching
speed can be attained by employing current perpendicular magnetic anisotropy
materials with experimentally demonstrated exchange coupling strengths.",1606.04428v2
2020-08-04,Ultrathin perpendicular free layers for lowering the switching current in STT-MRAM,"The critical current density $J_{c0}$ required for switching the
magnetization of the free layer (FL) in a spin-transfer torque magnetic random
access memory (STT-MRAM) cell is proportional to the product of the damping
parameter, saturation magnetization and thickness of the free layer, $\alpha
M_S t_F$. Conventional FLs have the structure CoFeB/nonmagnetic spacer/CoFeB.
By reducing the spacer thickness, W in our case, and also splitting the single
W layer into two layers of sub-monolayer thickness, we have reduced $t_F$ while
minimizing $\alpha$ and maximizing $M_S$, ultimately leading to lower $J_{c0}$
while maintaining high thermal stability. Bottom-pinned MRAM cells with device
diameter in the range of 55-130 nm were fabricated, and $J_{c0}$ is lowest for
the thinnest (1.2 nm) FLs, down to 4 MA/cm$^2$ for 65 nm devices, $\sim$30%
lower than 1.7 nm FLs. The thermal stability factor $\Delta_{\mathrm{dw}}$, as
high as 150 for the smallest device size, was determined using a domain wall
reversal model from field switching probability measurements. With high
$\Delta_{\mathrm{dw}}$ and lowest $J_{c0}$, the thinnest FLs have the highest
spin-transfer torque efficiency.",2008.01343v1
2016-03-28,Write error rate of spin-transfer-torque random access memory including micromagnetic effects using rare event enhancement,"Spin-transfer-torque random access memory (STT-RAM) is a promising candidate
for the next-generation of random-access-memory due to improved scalability,
read-write speeds and endurance. However, the write pulse duration must be long
enough to ensure a low write error rate (WER), the probability that a bit will
remain unswitched after the write pulse is turned off, in the presence of
stochastic thermal effects. WERs on the scale of 10$^{-9}$ or lower are
desired. Within a macrospin approximation, WERs can be calculated analytically
using the Fokker-Planck method to this point and beyond. However, dynamic
micromagnetic effects within the bit can affect and lead to faster switching.
Such micromagnetic effects can be addressed via numerical solution of the
stochastic Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. However,
determining WERs approaching 10$^{-9}$ would require well over 10$^{9}$ such
independent simulations, which is infeasible. In this work, we explore
calculation of WER using ""rare event enhancement"" (REE), an approach that has
been used for Monte Carlo simulation of other systems where rare events
nevertheless remain important. Using a prototype REE approach tailored to the
STT-RAM switching physics, we demonstrate reliable calculation of a WER to
10$^{-9}$ with sets of only approximately 10$^{3}$ ongoing stochastic LLGS
simulations, and the apparent ability to go further.",1603.08512v2
2021-05-17,On the Temperature-dependent Characteristics of Perpendicular Shape Anisotropy-Spin Transfer Torque-Magnetic Random Access Memories (PSA-STT-MRAMs),"The perpendicular shape anisotropy-spin transfer torque-magnetic random
access memories (PSASTT-MRAMs) takes advantage of the nanopillar free-layer
geometry for securing a good thermal stability factor from the shape anisotropy
of the nanomagnet. Such a concept is particularly well-suited for small
junctions down to a few nanometers. At such a volume size, the nanopillar can
be effectively modeled as a Stoner-Wohlfarth (SW) particle, and the shape
anisotropy scales with the spontaneous magnetization by ~ Ms^2. For almost all
ferromagnets, Ms is a strong function of temperature, therefore, the
temperature-dependent shape anisotropy is an important factor to be considered
in any modeling of the temperature-dependent performance of PSA-STT-MRAMs. In
this work, we summarize and discuss various possible temperature-dependent
contributions to the thermal stability factor and coercivity of the
PSA-STT-MRAMs by modeling and comparing different temperature scaling and
parameters. We reveal nontrivial corrections to the thermal stability factor by
considering both temperature-dependent shape and interfacial anisotropies. The
coercivity, blocking temperature, and electrical switching characteristics that
resulted from incorporating such a temperature dependence are also discussed,
in conjugation with the nanomagnet dimension and coherence volume.",2105.07801v1
2022-05-19,Smart Material Implication Using Spin-Transfer Torque Magnetic Tunnel Junctions for Logic-in-Memory Computing,"Smart material implication (SIMPLY) logic has been recently proposed for the
design of energy-efficient Logic-in-Memory (LIM) architectures based on
non-volatile resistive memory devices. The SIMPLY logic is enabled by adding a
comparator to the conventional IMPLY scheme. This allows performing a
preliminary READ operation and hence the SET operation only in the case it is
actually required. This work explores the SIMPLY logic scheme using nanoscale
spin-transfer torque magnetic tunnel junction (STT-MTJ) devices. The
performance of the STT-MTJ based SIMPLY architecture is analyzed by varying the
load resistor and applied voltages to implement both READ and SET operations,
while also investigating the effect of temperature on circuit operation.
Obtained results show an existing tradeoff between error rate and energy
consumption, which can be effectively managed by properly setting the values of
load resistor and applied voltages. In addition, our analysis proves that
tracking the temperature dependence of the MTJ properties through a
proportional to absolute temperature (PTAT) reference voltage at the input of
the comparator is beneficial to mitigate the reliability degradation under
temperature variations.",2205.09388v1
2023-01-13,Nanosecond True Random Number Generation with Superparamagnetic Tunnel Junctions -- Identification of Joule Heating and Spin-Transfer-Torque effects,"This work investigates nanosecond superparamagnetic switching in 50 nm
diameter in-plane magnetized magnetic tunnel junctions (MTJs). Due to the small
in-plane uniaxial anisotropy, dwell times below 10 ns and auto-correlation
times down to 5 ns are measured for circular superparamagnetic tunnel junctions
(SMTJs). SMTJs exhibit probabilistic switching of the magnetic free layer,
which can be used for the generation of true random numbers. The quality of
random bitstreams, generated by our SMTJ, is evaluated with a statistical test
suite (NIST STS, sp 800-22) and shows true randomness after three XOR
operations of four random SMTJ bitstreams. A low footprint CMOS circuit is
proposed for fast and energy-efficient random number generation. We demonstrate
that the probability of a 1 or 0 can be tuned by spin-transfer-torque (STT),
while the average bit generation rate is mainly affected by the current density
via Joule heating. Although both effects are always present in MTJs, Joule
heating most often is neglected. However, with a resistance area (RA) product
of 15 $\Omega \mu$m$^2$ and current densities of the order of 1 MA/cm$^2$, an
increasing temperature at the tunneling site results in a significant increase
in the switching rate. As Joule heating and STT scale differently with current
density, device design can be optimized based on our findings.",2301.05694v1
2023-03-22,Enhancing Spin Transfer Torque in Magnetic Tunnel Junction Devices: Exploring the Influence of Capping Layer Materials and Thickness on Device Characteristics,"We have developed and optimized two categories of spin transfer torque
magnetic tunnel junctions (STT-MTJs) that exhibit a high tunnel
magnetoresistance (TMR) ratio, low critical current, high outputpower in the
micro watt range, and auto-oscillation behavior. These characteristics
demonstrate the potential of STT-MTJs for low-power, high-speed, and reliable
spintronic applications, including magnetic memory, logic, and signal
processing. The only distinguishing factor between the two categories, denoted
as A-MTJs and B-MTJs, is the composition of their free layers, 2 CoFeB/0.21
Ta/6 CoFeSiB for A-MTJs and 2 CoFeB/0.21 Ta/7 NiFe for B-MTJs. Our study
reveals that B-MTJs exhibit lower critical currents for auto-oscillation than
A-MTJs. We found that both stacks have comparable saturation magnetization and
anisotropy field, suggesting that the difference in auto-oscillation behavior
is due to the higher damping of A-MTJs compared to B-MTJs. To verify this
hypothesis, we employed the all-optical time-resolved magneto-optical Kerr
effect (TRMOKE) technique, which confirmed that STT-MTJs with lower damping
exhibited auto-oscillation at lower critical current values. Additionally, our
study aimed to optimize the STT-MTJ performance by investigating the impact of
the capping layer on the device's response to electronic and optical stimuli.",2303.12450v2
2019-08-29,Spin-orbit torques in a Rashba honeycomb antiferromagnet,"Recent experiments on switching antiferromagnetic domains by electric current
pulses have attracted a lot of attention to spin-orbit torques in
antiferromagnets. In this work, we employ the tight-binding model solver,
kwant, to compute spin-orbit torques in a two-dimensional antiferromagnet on a
honeycomb lattice with strong spin-orbit interaction of Rashba type. Our model
combines spin-orbit interaction, local s-d-like exchange, and scattering of
conduction electrons on on-site disorder potential to provide a microscopic
mechanism for angular momentum relaxation. We consider two versions of the
model: one with preserved and one with broken sublattice symmetry. A
non-equilibrium staggered polarization, that is responsible for the so-called
Neel spin-orbit torque, is shown to vanish identically in the symmetric model
but may become finite if sublattice symmetry is broken. Similarly, anti-damping
spin-orbit torques vanish in the symmetric model but become finite and
anisotropic in a model with broken sublattice symmetry. As expected,
anti-damping torques also reveal a sizable dependence on impurity
concentration. Our numerical analysis also confirms symmetry classification of
spin-orbit torques and strong torque anisotropy due to in-plane confinement of
electron momenta.",1908.11354v2
2013-10-08,Magnetic and Gravitational Disk-Star Interactions: An Interdependence of PMS Stellar Rotation Rates and Spin-Orbit Misalignments,"The presence of giant gaseous planets that reside in close proximity to their
host stars may be a consequence of large-scale radial migration through the
proto-planetary nebulae. Within the context of this picture, significant
orbital obliquities characteristic of a substantial fraction of such planets
can be attributed to external torques that perturb the disks out of alignment
with the spin axes of their host stars. Therefore, the acquisition of orbital
obliquity exhibits sensitive dependence on the physics of disk-star
interactions. Here, we analyze the primordial excitation of spin-orbit
misalignment of Sun-like stars, in light of disk-star angular momentum
transfer. We begin by calculating the stellar pre-main sequence rotational
evolution, accounting for spin-up due to gravitational contraction and
accretion as well as spin-down due to magnetic star-disk coupling. We devote
particular attention to angular momentum transfer by accretion, and show that
while generally subdominant to gravitational contraction, this process is
largely controlled by the morphology of the stellar magnetic field (i.e.
specific angular momentum accreted by stars with octupole-dominated surface
fields is smaller than that accreted by dipole-dominated stars by an order of
magnitude). Subsequently, we examine the secular spin-axis dynamics of
disk-bearing stars, accounting for the time-evolution of stellar and disk
properties and demonstrate that misalignments are preferentially excited in
systems where stellar rotation is not overwhelmingly rapid. Moreover, we show
that the excitation of spin-orbit misalignment occurs impulsively, through an
encounter with a resonance between the stellar precession frequency and the
disk-torquing frequency. Cumulatively, the model developed herein opens up a
previously unexplored avenue towards understanding star-disk evolution and its
consequences in a unified manner.",1310.2179v1
1998-03-06,Magnetic torques between accretion discs and stars,"I show in this paper that two types of magnetic torques can appear in the
interaction between an accretion disc and a magnetic accretor. There is the
well-known torque resulting from the difference in angular velocity between the
accretion disc and the star, but in addition there is a torque coming from the
interaction between the stellar magnetic field and the disc's own magnetic
field. The latter form of magnetic torque decreases in strength more slowly
with increasing radius, and will therefore dominate at large radii. The
direction of the disc field is not determined by the difference in angular
velocity between the star and the disc as in the Ghosh & Lamb model, but is
rather a free parameter. The magnetic torque may therefore either spin up or
spin down the star, and the torque changes sign if the magnetic field in the
disc reverses. I suggest that this mechanism can explain the torque reversals
that have been observed in some disc-fed X-ray pulsars.",9803068v1
2012-06-28,Spin-orbit coupled transport and spin torque in a ferromagnetic heterostructure,"Ferromagnetic heterostructures provide an ideal platform to explore the
nature of spin-orbit torques arising from the interplay mediated by itinerant
electrons between a Rashba-type spin-orbit coupling and a ferromagnetic
exchange interaction. For such a prototypic system, we develop a set of coupled
diffusion equations to describe the diffusive spin dynamics and spin-orbit
torques. We characterize the spin torque and its two prominent--out-of-plane
and in-plane--components for a wide range of relative strength between the
Rashba coupling and ferromagnetic exchange. The symmetry and angular dependence
of the spin torque emerging from our simple Rashba model is in an agreement
with experiments. The spin diffusion equation can be generalized to incorporate
dynamic effect such as spin pumping and magnetic damping.",1206.6726v2
2018-03-19,Enhanced spin-orbit torque via interface engineering in Pt/CoFeB/MgO heterostructures,"Spin-orbit torque facilitates efficient magnetization switching via an
in-plane current in perpendicularly magnetized heavy metal/ferromagnet
heterostructures. The efficiency of spin-orbit-torque-induced switching is
determined by the charge-to-spin conversion arising from either bulk or
interfacial spin-orbit interactions, or both. Here, we demonstrate that the
spin-orbit torque and the resultant switching efficiency in Pt/CoFeB systems
are significantly enhanced by an interfacial modification involving Ti
insertion between the Pt and CoFeB layers. Spin pumping and X-ray magnetic
circular dichroism experiments reveal that this enhancement is due to an
additional interface-generated spin current of the nonmagnetic interface and/or
improved spin transparency achieved by suppressing the proximity-induced moment
in the Pt layer. Our results demonstrate that interface engineering affords an
effective approach to improve spin-orbit torque and thereby magnetization
switching efficiency.",1803.06961v1
2009-05-04,Direct current control of three magnon scattering processes in spin-valve nanocontacts,"We have investigated the generation of spin waves in the free layer of an
extended spin-valve structure with a nano-scaled point contact driven by both
microwave and direct electric current using Brillouin light scattering
microscopy. Simultaneously with the directly excited spin waves, strong
nonlinear effects are observed, namely the generation of eigenmodes with
integer multiple frequencies (2 \emph{f}, 3 \emph{f}, 4 \emph{f}) and modes
with non-integer factors (0.5 \emph{f}, 1.5 \emph{f}) with respect to the
excitation frequency \emph{f}. The origin of these nonlinear modes is traced
back to three magnon scattering processes. The direct current influence on the
generation of the fundamental mode at frequency \emph{f} can be related to the
spin-transfer torque, while the efficiency of three-magnon-scattering processes
is controlled by the Oersted field as an additional effect of the direct
current.",0905.0323v1
2010-09-28,Non-Collinear Ferromagnetic Luttinger Liquids,"The presence of electron-electron interactions in one dimension profoundly
changes the properties of a system. The separation of charge and spin degrees
of freedom is just one example. We consider what happens when a system
consisting of a ferromagnetic region of non-collinearity, i.e. a domain wall,
is coupled to interacting electrons in one-dimension (more specifically a
Luttinger liquid). The ferromagnetism breaks spin charge separation and the
presence of the domain wall introduces a spin dependent scatterer into the
problem. The absence of spin charge separation and the effects of the electron
correlations results in very different behaviour for the excitations in the
system and for spin-transfer-torque effects in this model.",1009.5509v1
2010-12-16,Spin Transfer Torques in MnSi at Ultra-low Current Densities,"Spin manipulation using electric currents is one of the most promising
directions in the field of spintronics. We used neutron scattering to observe
the influence of an electric current on the magnetic structure in a bulk
material. In the skyrmion lattice of MnSi, where the spins form a lattice of
magnetic vortices similar to the vortex lattice in type II superconductors, we
observe the rotation of the diffraction pattern in response to currents which
are over five orders of magnitude smaller than those typically applied in
experimental studies on current-driven magnetization dynamics in
nanostructures. We attribute our observations to an extremely efficient
coupling of inhomogeneous spin currents to topologically stable knots in spin
structures.",1012.3496v1
2013-08-29,Control of Propagating Spin Waves via Spin Transfer Torque in a Metallic Bilayer Waveguide,"We investigate the effect of a direct current on propagating spin waves in a
CoFeB/Ta bilayer structure. Using the micro-Brillouin light scattering
technique, we observe that the spin wave amplitude may be attenuated or
amplified depending on the direction of the current and the applied magnetic
field. Our work suggests an effective approach for electrically controlling the
propagation of spin waves in a magnetic waveguide and may be useful in a number
of applications such as phase locked nano-oscillators and hybrid information
processing devices.",1308.6357v2
2014-11-28,Topological Charge Analysis of Ultrafast Single Skyrmion Creation,"Magnetic skyrmions are topologically non-trivial spin textures of potential
interest for future information storage applications, and for such purposes,
the control and understanding of single skyrmion creation is required. A scheme
is analyzed to create single N\'{e}el-type and Bloch-type skyrmions in
helimagnetic thin films utilizing the dynamical excitations induced by the
Oersted field and the spin transfer torque given by a vertically injected
spin-polarized current. A topological charge analysis using a lattice version
of the topological charge provides insight into the locally triggered
transition from a trivial to a non-trivial topological spin texture of the
N\'{e}el or Bloch type skyrmion. The topological protection of the magnetic
skyrmion is determined by the symmetric Heisenberg exchange energy. The
critical switching current density is $\sim10^{7}\thinspace\textrm{A/cm}^{2}$,
which decreases with the easy-plane type uniaxial anisotropy and thermal
fluctuations. In-plane spin polarization of the injected current performs
better than out-of-plane polarization, and it provides ultrafast switching
times (within 100 ps) and reliable switching outcomes.",1411.7762v2
2015-04-01,Direct observation and imaging of a spin-wave soliton with $p-$like symmetry,"The prediction and realization of magnetic excitations driven by electrical
currents via the spin transfer torque effect, enables novel magnetic
nano-devices where spin-waves can be used to process and store information. The
functional control of such devices relies on understanding the properties of
non-linear spin-wave excitations. It has been demonstrated that spin waves can
show both an itinerant character, but also appear as localized solitons. So
far, it was assumed that localized solitons have essentially cylindrical,
$s-$like symmetry. Using a newly developed high-sensitivity time-resolved
magnetic x-ray microscopy, we instead observe the emergence of a novel
localized soliton excitation with a nodal line, i.e. with $p-$like symmetry.
Micromagnetic simulations identify the physical mechanism that controls the
transition from $s-$ to $p-$like solitons. Our results suggest a potential new
pathway to design artificial atoms with tunable dynamical states using
nanoscale magnetic devices.",1504.00144v1
2015-11-25,Ferromagnetic resonance phase imaging in spin Hall multilayers,"We experimentally image the magnetic precession phase of patterned spin Hall
multilayer samples to study the rf driving field vector using time-resolved
anomalous Nernst effect (TRANE) microscopy. Our ferromagnetic resonance (FMR)
measurements quantify the phase and amplitude for both the magnetic precession
and the electric current, which allows us to establish the total driving field
orientation and the strength of spin Hall effect. In a channel of uniform
width, we observe spatial variation of the FMR phase laterally across the
channel. We interpret our findings in the context of electrical measurement
using the spin-transfer torque ferromagnetic resonance technique and show that
observed phase variation introduces a systematic correction into the spin Hall
angle if spatial phase and amplitude variations are not taken into account.",1511.08126v1
2016-05-30,Spin Josephson effects in Exchange coupled Anti-ferromagnets,"The energy of exchange coupled antiferromagnetic insulators (AFMIs) is a
periodic function of the relative in-plane orientation of the N\'{e}el vector
fields. We show that this leads to oscillations in the relative magnetization
of exchange coupled AFMIs separated by a thin metallic barrier. These
oscillations pump a spin current ($I_{S}$) through the metallic spacer that is
proportional to the rate of change of the relative in-plane orientation of the
N\'{e}el vector fields. By considering spin-transfer torque induced by a spin
chemical potential ($V_{S}$) at one of the interfaces, we predict non-Ohmic
$I_{S}$-$V_{S}$ characteristics of AFMI exchange coupled hetero-structures,
which leads to a non-local voltage across a spin-orbit coupled metallic spacer.",1605.09427v1
2018-05-25,Parity-time symmetry breaking in spin chains,"We investigate nonequilibrium phase transitions in classical Heisenberg spin
chains associated with spontaneous breaking of parity-time ($\mathcal{PT}$)
symmetry of the system under the action of Slonczewski spin-transfer torque
(STT) modeled by an applied \textit{imaginary} magnetic field. We reveal the
STT-driven $\mathcal{PT}$ symmetry-breaking phase transition between the
regimes of precessional and exponentially damped spin dynamics and show that
its several properties can be derived from the distribution of zeros of the
system's partition function, the approach first introduced by Yang and Lee for
studying equilibrium phase transitions in Ising spin chains. The physical
interpretation of imaginary magnetic field as describing the action of
non-conservative forces opens the possibility of direct observations of
Lee-Yang zeros in nonequilibrium physical systems.",1805.10346v1
2018-11-13,Enhanced domain wall velocity near a ferromagnetic instability,"Assuming a Fermi liquid behavior for $s$-conduction electrons, we rewrite the
extended Landau-Lifshitz-Gilbert (LLG) equation renormalized by interactions
through the Landau parameters $F^{a}_{l}$ ($l=0,1,2 \cdots$) in an explicit
form to describe the dynamic of a domain wall (DW) due to spin transfer torque
phenomenon. The interaction between spins of the \textit{s}-conduction
electrons explains qualitatively the DW velocity experimental observations in
$\mathrm{Ni_{81}}\mathrm{Fe_{19}}$ (Permalloy) recalculated by us without
defects or impurity hypothesis. Close to Stoner ferromagnetic instability point
where $F^{a}_{0} \approx -0.99$, the DW velocity becomes high
($v^{*}_{DW}\approx 600$ $ms^{-1}$) and critical spin current density becomes
reduced ($j^{*}_{c}\approx1\times10^{12}$ $Am^{-2}$) when compared to that
calculated by nonadiabatic approach. At the critical point, the DW velocity
diverges while critical spin current density at the same point goes to zero.
Our theory also provides a prediction to looking for materials in which is
possible applies a smallest critical spin current density and observes higher
DW velocity.",1811.05380v4
2016-12-14,Transport in Ferromagnet/Superconductor spin valves,"We consider charge transport properties in realistic, fabricable,
Ferromagnet/Superconductor spin valves having a layered structure
$F_1/N/F_2/S$, where $F_1$ and $F_2$ denote the ferromagnets, $S$ the
superconductor, and $N$ the normal metal spacer usually inserted in actual
devices. Our calculation is fully self-consistent, as required to ensure that
conservation laws are satisfied. We include the effects of scattering at all
the interfaces. We obtain results for the device conductance $G$, as a function
of bias voltage, for all values of the angle $\phi$ between the magnetizations
of the $F_1$ and $F_2$ layers and a range of realistic values for the material
and geometrical parameters in the sample. We discuss, in the context of our
results for $G$, the relative influence of all parameters on the spin valve
properties. We study also the spin current and the corresponding spin transfer
torque in $F_1/F_2/S$ structures.",1612.04696v1
2020-01-10,Orbital Hall Insulating Phase in Transition Metal Dichalcogenide Monolayers,"We show that H-phase transition metal dichalcogenides (TMDs) monolayers such
as MoS$_2$ and WSe$_2$, are orbital Hall insulators. They present very large
orbital Hall conductivity plateaus in their semiconducting gap, where the spin
Hall conductivity vanishes. Our results open the possibility of using TMDs for
orbital current injection and orbital torque transfers that surpass their
spin-counterparts in spin-orbitronics devices. The orbital Hall effect (OHE) in
TMD monolayers occurs even in the absence of spin-orbit coupling. It can be
linked to exotic momentum-space Dresselhaus-like orbital textures, analogous to
the spin-momentum locking in 2D Dirac fermions that arise from a combination of
orbital attributes and lattice symmetry.",2001.03592v2
2021-03-04,Intrinsic and extrinsic tunability of Rashba spin-orbit coupled emergent inductors,"The emergent induction of spiral magnets that was proposed [Jpn. J. Appl.
Phys. 58, 120909 (2019)] and recently demonstrated [Nature 586, 232 (2020)] is
shown to be further extended by a comprehensive treatment of the Rashba
spin-orbit coupling and the electron spin relaxation that affect the underlying
processes of spin-transfer torque and spinmotive force. Within adiabatic
approximation, we show that the output voltages are widely altered
intrinsically via the Rashba effect whereas extrinsically via the nonadiabatic
correction due to the spin relaxation and sample disorder. The findings
respectively clarify the origins for the amplitude modulation and sign change
of the emergent inductance with tunability by electrical gating and careful
sample preparation.",2103.02859v1
2023-01-09,X-ray detected ferromagnetic resonance techniques for the study of magnetization dynamics,"Element-specific spectroscopies using synchrotron-radiation can provide
unique insights into materials properties. The recently developed technique of
X-ray detected ferromagnetic resonance (XFMR) allows studying the magnetization
dynamics of magnetic spin structures. Magnetic sensitivity in XFMR is obtained
from the X-ray magnetic circular dichroism (XMCD) effect, where the phase of
the magnetization precession of each magnetic layer with respect to the
exciting radio frequency is obtained using stroboscopic probing of the spin
precession. Measurement of both amplitude and phase response in the magnetic
layers as a function of bias field can give a clear signature of spin-transfer
torque (STT) coupling between ferromagnetic layers due to spin pumping. Over
the last few years, there have been new developments utilizing X-ray scattering
techniques to reveal the precessional magnetization dynamics of ordered spin
structures in the GHz frequency range. The techniques of diffraction and
reflectometry ferromagnetic resonance (DFMR and RFMR) provide novel ways for
the probing of the dynamics of chiral and multilayered magnetic materials,
thereby opening up new pathways for the development of high-density and
low-energy consumption data processing solutions.",2301.03256v1
2023-03-15,Instability of magnetic skyrmion strings induced by longitudinal spin currents,"It is well established that spin-transfer torques exerted by in-plane spin
currents give rise to a motion of magnetic skyrmions resulting in a skyrmion
Hall effect. In films of finite thickness or in three-dimensional bulk samples
the skyrmions extend in the third direction forming a string. We demonstrate
that a spin current flowing longitudinally along the skyrmion string instead
induces a Goldstone spin wave instability. Our analytical results are confirmed
by micromagnetic simulations of both a single string as well as string lattices
suggesting that the instability eventually breaks the strings. A longitudinal
current is thus able to melt the skyrmion string lattice via a dynamical phase
transition. For films of finite thickness or in the presence of disorder a
threshold current will be required, and we estimate the latter assuming weak
collective pinning.",2303.08532v1
2015-04-03,Straintronic spin-neuron,"In artificial neural networks, neurons are usually implemented with highly
dissipative CMOS-based operational amplifiers. A more energy-efficient
implementation is a 'spin-neuron' realized with a magneto-tunneling junction
(MTJ) that is switched with a spin-polarized current (representing weighted sum
of input currents) that either delivers a spin transfer torque or induces
domain wall motion in the soft layer of the MTJ. Here, we propose and analyze a
different type of spin-neuron in which the soft layer of the MTJ is switched
with mechanical strain generated by a voltage (representing weighted sum of
input voltages) and term it straintronic spin-neuron. It dissipates orders of
magnitude less energy in threshold operations than the traditional
current-driven spin neuron at 0 K temperature and may even be faster. We have
also studied the room-temperature firing behaviors of both types of spin
neurons and find that thermal noise degrades the performance of both types, but
the current-driven type is degraded much more than the straintronic type if
both are optimized for maximum energy-efficiency. On the other hand, if both
are designed to have the same level of thermal degradation, then the
current-driven version will dissipate orders of magnitude more energy than the
straintronic version. Thus, the straintronic spin neuron is superior to
current-driven spin neurons.",1504.00940v1
2021-08-21,Transport Spin Polarization of Noncollinear Antiferromagnetic Antiperovskites,"Spin-polarized currents play a key role in spintronics. Recently, it has been
found that antiferromagnets with a non-spin-degenerate band structure can
efficiently spin-polarize electric currents, even though their net
magnetization is zero. Among the antiferromagnetic metals with magnetic space
group symmetry supporting this functionality, the noncollinear
antiferromagnetic antiperovskites ANMn$_3$ (A = Ga, Ni, Sn, and Pt) are
especially promising. This is due to their high N\'eel temperatures and a good
lattice match to perovskite oxide substrates, offering possibilities of high
structural quality heterostructures based on these materials. Here, we
investigate the spin polarization of antiferromagnetic ANMn$_3$ metals using
first-principles density functional theory calculations. We find that the spin
polarization of the longitudinal currents in these materials is comparable to
that in widely used ferromagnetic metals, and thus can be exploited in magnetic
tunnel junctions and spin transfer torque devices. Moreover, for certain film
growth directions, the out-of-plane transverse spin currents with a giant
charge-to-spin conversion efficiency can be achieved, implying that the
ANMn$_3$ antiperovskites can be used as efficient spin sources. These
properties make ANMn$_3$ compounds promising for application in spintronics.",2108.09540v2
2021-10-11,Topological phonons in an inhomogeneously strained silicon-4: Large spin dependent thermoelectric response and thermal spin transfer torque due to topological electronic magnetism of phonons,"The superposition of flexoelectronic doping and topological phonons give rise
to topological electronic magnetism of phonon in an inhomogeneously strained Si
in the bilayer structure with metal. In case of ferromagnetic metal and Si
bilayer structure, the flexoelectronic doping will also give rise to larger
spin current, which will lead to large spin to charge conversion due to
topological electronic magnetism of phonon. By applying a temperature
difference to ferromagnetic metal/Si bilayer structure under an applied strain
gradient, a large thermoelectric response can be generated. In this
experimental study, we report a large spin dependent thermoelectric response at
Ni80Fe20/Si bilayer structure. The spin dependent response is found to be an
order of magnitude larger than that in Pt thin films and similar to topological
insulators surface states in spite of negligible intrinsic spin-orbit coupling
of Si. This large response is attributed to the flexoelectronic doping and
topological electronic magnetism of phonons, which was uncovered using
topological Nernst effect measurement. This alternative and novel approach of
using inhomogeneous strain engineering to address both spin current density and
spin to charge conversion can open a new window to the realization of
spintronics and spin-caloritronics devices using metal and doped-semiconductor
layered materials.",2110.04939v1
2000-04-05,Critical State Behaviour in a Low Dimensional Metal Induced by Strong Magnetic Fields,"We present the results of magnetotransport and magnetic torque measurements
on the alpha-(BEDT-TTF)2KHg(SCN)4 charge-transfer salt within the high magnetic
field phase, in magnetic fields extending to 33 T and temperatures as low as 27
mK. While the high magnetic field phase (at fields greater than ~ 23 T) is
expected, on theoretical grounds, to be either a modulated charge-density wave
phase or a charge/spin-density wave hybrid, the resistivity undergoes a
dramatic drop below ~ 3 K within the high magnetic field phase, falling in an
approximately exponential fashion at low temperatures, while the magnetic
torque exhibits pronounced hysteresis effects. This hysteresis, which occurs
over a broad range of fields, is both strongly temperature-dependent and has
several of the behavioural characteristics predicted by critical-state models
used to describe the pinning of vortices in type II superconductors in strong
magnetic fields. Thus, rather than exhibiting the usual behaviour expected for
a density wave ground state, both the transport and the magnetic properties of
alpha-(BEDT-TTF)2KHg(SCN)4, at high magnetic fields, closely resembles those of
a type II superconductor.",0004083v1
2013-05-13,Backhopping effect in magnetic tunnel junctions: comparison between theory and experiment,"We report on the magnetic switching and backhopping effects due to
spin-transfer-torque in magnetic tunnel junctions. Experimental data on the
current-induced switching in junctions with MgO tunnel barrier reveal a random
back-and-forth switching between the magnetization states, which appears when
the current direction favors the parallel magnetic configuration. The effect
depends on the barrier thickness $t_b$, and is not observed in tunnel junctions
with very thin MgO tunnel barriers, $t_b$ $<$ 0.95 nm. Switching dependence on
the bias voltage and barrier thickness is explained in terms of the macrospin
model, with the magnetization dynamics described by the modified
Landau-Lifshitz-Gilbert equation. Numerical simulations indicate that the
competition between in-plane and out-of-plane torque components can result at
high bias voltages in a non-deterministic switching behavior, in agreement with
experimental observations. When the barrier thickness is reduced, the overall
coupling between the magnetic layers across the barrier becomes ferromagnetic,
which suppresses the backhopping effect.",1305.2711v1
2018-02-15,On the timing behavior of PSR B1259-63 under the propeller torque from a transient accretion disc,"The $\gamma$-ray pulsar binary system PSR B1259-63 flares in GeV after each
periastron. The origin of those flares is still under debate. Recently,
[2017ApJ...844..114Y] proposed a mechanism that might explain the GeV flares.
In that model, a transient accretion disc is expected to be formed from the
matter which was gravity-captured by the neutron star from the main sequence
companion's circumstellar disc. The transient accretion disc exerts a spin down
torque on the neutron star (propeller effect), which might be traceable via
pulsar timing observation of PSR B1259-63. In this paper, we phenomenologically
consider the propeller effect with a parameter $\chi$, which describes the
coupling between the disc matter and the neutron star. Comparing the expected
timing residuals against the recent observation in [2014MNRAS.437.3255S], we
conclude that the angular momentum transfer is very weak (with the coupling
parameter $\chi\le10^{-4}$).",1802.05432v1
2021-04-06,Geometry and Symmetry in Skyrmion Dynamics,"The uniform motion of chiral magnetic skyrmions induced by a spin-transfer
torque displays an intricate dependence on the skyrmions' topological charge
and shape. We reveal surprising patterns in this dependence through simulations
of the Landau-Lifshitz-Gilbert equation with Zhang-Li torque and explain them
through a geometric analysis of Thiele's equation. In particular, we show that
the velocity distribution of topologically non-trivial skyrmions depends on
their symmetry: it is a single circle for skyrmions of high symmetry and a
family of circles for low-symmetry configurations. We also show that the
velocity of the topologically trivial skyrmions, previously believed to be the
fastest objects, can be surpassed, for instance, by antiskyrmions. The
generality of our approach suggests the validity of our results for exchange
frustrated magnets, bubble materials, and others.",2104.02342v1
2017-07-16,Indirect excitation of self-oscillation in perpendicular ferromagnet by spin Hall effect,"A possibility to excite a stable self-oscillation in a perpendicularly
magnetized ferromagnet by the spin Hall effect is investigated theoretically.
It had been shown that such self-oscillation cannot be stabilized solely by the
direct spin torque by the spin Hall effect. Here, we consider adding another
ferromagnet, referred to as pinned layer, on the free layer. The pinned layer
provides another spin torque through the reflection of the spin current. The
study shows that the stable self-oscillation is excited by the additional spin
torque when the magnetization in the pinned layer is tilted from the film
plane.",1707.04825v1
2022-06-29,Tailoring the switching efficiency of magnetic tunnel junctions by the fieldlike spin-orbit torque,"Current-induced spin-orbit torques provide a versatile tool for switching
magnetic devices. In perpendicular magnets, the dampinglike component of the
torque is the main driver of magnetization reversal. The degree to which the
fieldlike torque assists the switching is a matter of debate. Here we study the
switching of magnetic tunnel junctions with a CoFeB free layer and either W or
Ta underlayers, which have a ratio of fieldlike to dampinglike torque of 0.3
and 1, respectively. We show that the fieldlike torque can either assist or
hinder the switching of CoFeB when the static in-plane magnetic field required
to define the polarity of spin-orbit torque switching has a component
transverse to the current. In particular, the non-collinear alignment of the
field and current can be exploited to increase the switching efficiency and
reliability compared to the standard collinear alignment. By probing individual
switching events in real-time, we also show that the combination of transverse
magnetic field and fieldlike torque can accelerate or decelerate the reversal
onset. We validate our observations using micromagnetic simulations and
extrapolate the results to materials with different torque ratios. Finally, we
propose device geometries that leverage the fieldlike torque for density
increase in memory applications and synaptic weight generation.",2206.14587v2
2015-10-15,Extraction of the Anomalous Nernst Effect in the Electric Measurement of the Spin Orbit Torque,"Spin orbit torque has been intensively investigated because of its high
energy efficiency in manipulating a magnetization. Although various methods for
measuring the spin orbit torque have been developed so far, the measurement
results often show inconsistency among the methods, implying that an
electromotive force, such as Nernst effect, irrelevant to the spin orbit torque
may affect the measurement results as an artifact. In this letter, we developed
a unique method to distinguish the spin orbit torque and the anomalous Nernst
effect. The measurement results show that the spin orbit torque can be
underestimated up to 50% under the influence of the anomalous Nernst effect.",1510.04363v1
2019-05-28,Spin-Orbit Torque in a Single Ferromagnetic Layer with Large Spin-Orbit Coupling,"Spin-orbit torque in heavy metal/ferromagnet heterostructures with broken
spatial inversion symmetry provides an efficient mechanism for manipulating
magnetization using a charge current. Here, we report the presence of a spin
torque in a single ferromagnetic layer in both asymmetric MgO/Fe0.8Mn0.2 and
symmetric MgO/Fe0.8Mn0.2/MgO structures, which manifests itself in the form of
an effective field transverse to the charge current. The current to effective
field conversion efficiency, which is characterized using both the nonlinear
magnetoresistance and second-order planar Hall effect methods, is comparable to
the efficiency in typical heavy metal/ferromagnet bilayers. We argue that the
torque is caused by spin rotation in the vicinity of the surface via impurity
scattering in the presence of a strong spin-orbit coupling. Instead of
cancelling off with each other, the torques from the top and bottom surfaces
simply add up, leading to a fairly large net torque, which is readily observed
experimentally.",1905.11565v1
2017-03-24,Anomalous current-induced spin torques in ferrimagnets near compensation,"While current-induced spin-orbit torques (SOTs) have been extensively studied
in ferromagnets and antiferromagnets, ferrimagnets have been less studied. Here
we report the presence of enhanced spin-orbit torques resulting from negative
exchange interaction in ferrimagnets. The effective field and switching
efficiency increase substantially as CoGd approaches its compensation point,
giving rise to 9 times larger spin-orbit torques compared to that of
non-compensated one. The macrospin modelling results also support efficient
spin-orbit torques in a ferrimagnet. Our results suggest that ferrimagnets near
compensation can be a new route for spin-orbit torque applications due to their
high thermal stability and easy current-induced switching assisted by negative
exchange interaction.",1703.08263v1
2019-10-17,Planar Hall driven torque in a FM/NM/FM system,"An important goal of spintronics is to covert a charge current into a spin
current with a controlled spin polarization that can exert torques on an
adjacent magnetic layer. Here we demonstrate such torques in a two ferromagnet
system. A CoNi multilayer is used as a spin current source in a sample with
structure CoNi/Au/CoFeB. Spin torque ferromagnetic resonance is used to measure
the torque on the CoFeB layer. The response as a function of the applied field
angle and current is consistent with the symmetry expected for a torques
produced by the planar Hall effect originating in CoNi. We find the strength of
this effect to be comparable to that of the spin Hall effect in platinum,
indicating that the planar Hall effect holds potential as a spin current source
with a controllable polarization direction.",1910.08039v1
2019-10-22,In-situ study of oxygen exposure effect on spin-orbit torque in Pt/Co bilayers in ultrahigh vacuum,"Oxygen incorporation has been reported to increase the current-induced
spin-orbit torque in ferromagnetic heterostructures, but the underlying
mechanism is still under active debate. Here, we report on an in-situ study of
the oxygen exposure effect on spin-orbit torque in Pt/Co bilayers via
controlled oxygen exposure, Co and Mg deposition, and electrical measurements
in ultrahigh vacuum. We show that the oxygen exposure on Pt/Co indeed leads to
an increase of spin-orbit torque, but the enhancement is not as large as those
reported previously. Similar enhancement of spin-orbit torque is also observed
after the deposition of an MgO capping layer. The results of ab initio
calculations on the Rashba splitting of Pt/Co and Pt/Co/O suggest that the
enhancement is due to enhanced Rashba-Edelstein effect by surface-adsorbed
oxygen. Our findings shed some light on the varying roles of oxygen in
modifying the spin torque efficiency reported previously.",1910.09810v1
2020-10-09,Interface-induced field-like optical spin torque in a ferromagnet/heavy metal heterostructure,"The manipulation of magnetization in a metallic ferromagnet by using optical
helicity has been much attracted attention for future opto-spintronic devices.
The optical helicity induced torques on the magnetization, {\it optical spin
torque}, have been observed in ferromagnetic thin films recently. However, the
interfacial effect of the optical spin torque in ferromagnet/nonmagnetic heavy
metal heterostructures have not been addressed so far, which are widely
utilized to efficiently control magnetization via electrical means. Here, we
studied optical spin torque vectors in the ferromagnet/nonmagnetic heavy metal
heterostructures and observed that in-plane field-like optical spin torque was
significantly increased with decreasing ferromagnetic layer thicknesses. The
interfacial field-like optical spin torque was explained by the optical
Rashba-Edelstein effect caused by the structural inversion symmetry breaking.
This work will aid in the efficient optical manipulation of thin film
nanomagnets using optical helicity.",2010.04341v2
2021-09-28,Sagnac interferometry for high-sensitivity optical measurements of spin-orbit torque,"We adapt Sagnac interferometry for magneto-optic Kerr effect measurements of
spin-orbit-torque-induced magnetic tilting in thin-film magnetic samples. The
high sensitivity of Sagnac interferometry permits for the first time optical
quantification of spin-orbit torque from small-angle magnetic tilting of
samples with perpendicular magnetic anisotropy (PMA). We find significant
disagreement between Sagnac measurements and simultaneously-performed harmonic
Hall (HH) measurements of spin-orbit torque on Pt/Co/MgO and Pd/Co/MgO samples
with PMA. The Sagnac results for PMA samples are consistent with both HH and
Sagnac measurements for the in-plane geometry, so we conclude that the
conventional analysis framework for PMA HH measurements is flawed. We suggest
that the explanation for this discrepancy is that although magnetic-field
induced magnetic tilting in PMA samples can produce a strong planar Hall
effect, when tilting is instead generated by spin-orbit torque it produces
negligible change in the planar Hall signal. This very surprising result
demonstrates an error in the most-popular method for measuring spin-orbit
torques in PMA samples, and represents an unsolved puzzle in understanding the
planar Hall effect in magnetic thin films.",2109.13759v1
2022-07-21,Influence of nonuniform magnetization reorientation on spin-orbit torque measurements,"Measurements of spin-orbit torques in a ferromagnetic/nonmagnetic multilayer
are typically based on an assumption that the entire ferromagnetic layer
uniformly responds to the spin-orbit torque. This assumption breaks down when
the thickness of the ferromagnetic layer is comparable to the dynamic exchange
coupling length, which can be as short as a few nanometers in certain
measurement geometries. The nonuniform magnetization reorientation coupled with
nonuniform contribution of each magnetic sublayer to the magnetoresistance or
the Kerr effect may impact the accuracy in the extrapolation of spin-orbit
torque, particularly if a thick ferromagnetic layer is used. In this paper, we
use numerical models to investigate such an impact in three different
techniques: the magneto-optic-Kerr-effect method, the second-harmonic method
and the spin torque ferromagnetic resonance method. We show that the
second-harmonic and magneto-optic-Kerr-effect methods are prone to be
influenced by the nonuniform magnetization reorientation, while the spin torque
ferromagnetic resonance method is much less impacted.",2207.10349v1
2023-11-22,Discovery of torque reversal in the Be/X-ray binary pulsar GX 304-1,"We study the long-term spin period evolution of the Be/X-ray binary pulsar GX
304-1 and discover a new torque reversal after nearly three years of spinning
up. The averaged spin-up rate before the torque reversal is $\sim 1.3 \times
10^{-13}$ Hz s$^{-1}$ which changes to an averaged spin-down rate of $\sim -5
\times 10^{-14}$ Hz s$^{-1}$. The pulsar is detected at low luminosities (about
${2}\times 10^{35}$ erg s$^{-1}$) near periastron passages during the torque
reversal suggesting that accretion is not quenched during this period. The
long-term optical observations of the companion star suggest that the activity
of the companion star may have decreased compared to the period when X-ray
outbursts were earlier detected from the pulsar. The spin-up rates estimated
during regular bright outbursts of the pulsar are observed to decrease
systematically as the pulsar enters a low activity state after the outbursts
and undergoes torque reversal. We explore plausible mechanisms to explain the
torque reversal and long-term spin-down in this pulsar.",2311.13303v1
2021-07-22,Interfacial Spin-Orbit Torques and Magnetic Anisotropy in WSe$_{2}$/Permalloy Bilayers,"Transition metal dichalcogenides (TMDs) are promising materials for efficient
generation of current-induced spin-orbit torques on an adjacent ferromagnetic
layer. Numerous effects, both interfacial and bulk, have been put forward to
explain the different torques previously observed. Thus far, however, there is
no clear consensus on the microscopic origin underlying the spin-orbit torques
observed in these TMD/ferromagnet bilayers. To shine light on the microscopic
mechanisms at play, here we perform thickness dependent spin-orbit torque
measurements on the semiconducting WSe$_{2}$/permalloy bilayer with various
WSe$_{2}$ layer thickness, down to the monolayer limit. We observe a large
out-of-plane field-like torque with spin-torque conductivities up to
$1\times10^4 ({\hbar}/2e) ({\Omega}m)^{-1}$. For some devices, we also observe
a smaller in-plane antidamping-like torque, with spin-torque conductivities up
to $4\times10^{3} ({\hbar}/2e) ({\Omega}m)^{-1}$, comparable to other TMD-based
systems. Both torques show no clear dependence on the WSe$_{2}$ thickness, as
expected for a Rashba system. Unexpectedly, we observe a strong in-plane
magnetic anisotropy - up to about $6.6\times10^{4} erg/cm^{3}$ - induced in
permalloy by the underlying hexagonal WSe$_{2}$ crystal. Using scanning
transmission electron microscopy, we confirm that the easy axis of the magnetic
anisotropy is aligned to the armchair direction of the WSe$_{2}$. Our results
indicate a strong interplay between the ferromagnet and TMD, and unveil the
nature of the spin-orbit torques in TMD-based devices. These findings open new
avenues for possible methods for optimizing the torques and the interaction
with interfaced magnets, important for future non-volatile magnetic devices for
data processing and storage.",2107.10621v2
2016-05-09,Control of spin-orbit torques through crystal symmetry in WTe2/ferromagnet bilayers,"Recent discoveries regarding current-induced spin-orbit torques produced by
heavy-metal/ferromagnet and topological-insulator/ferromagnet bilayers provide
the potential for dramatically-improved efficiency in the manipulation of
magnetic devices. However, in experiments performed to date, spin-orbit torques
have an important limitation -- the component of torque that can compensate
magnetic damping is required by symmetry to lie within the device plane. This
means that spin-orbit torques can drive the most current-efficient type of
magnetic reversal (antidamping switching) only for magnetic devices with
in-plane anisotropy, not the devices with perpendicular magnetic anisotropy
that are needed for high-density applications. Here we show experimentally that
this state of affairs is not fundamental, but rather one can change the allowed
symmetries of spin-orbit torques in spin-source/ferromagnet bilayer devices by
using a spin source material with low crystalline symmetry. We use WTe2, a
transition-metal dichalcogenide whose surface crystal structure has only one
mirror plane and no two-fold rotational invariance. Consistent with these
symmetries, we generate an out-of-plane antidamping torque when current is
applied along a low-symmetry axis of WTe2/Permalloy bilayers, but not when
current is applied along a high-symmetry axis. Controlling S-O torques by
crystal symmetries in multilayer samples provides a new strategy for optimizing
future magnetic technologies.",1605.02712v1
2024-03-18,Tuning of the ultrafast demagnetization by ultrashort spin polarized currents in multi-sublattice ferrimagnets,"Femtosecond laser pulses can be used to induce ultrafast changes of the
magnetization in magnetic materials. Several microscopic mechanisms have been
proposed to explain the observations, including the transport of ultrashort
spin-polarized hot-electrons (SPHE). Such ultrafast spin currents find growing
interest because of the recent challenges in ultrafast spintronics however they
are only poorly characterized. One of the key challenges is to characterize the
spin-polarized ultrafast currents and the microscopic mechanisms behind SPHE
induced manipulation of the magnetization, especially in the case of
technologically relevant ferrimagnetic alloys. Here, we have used a combined
approach using time- and element-resolved X-ray magnetic circular dichroism and
theoretical calculations based on atomistic spin-dynamics simulations to
address the ultrafast transfer of the angular momentum from spin-polarized
currents into ferrimagnetic Fe74Gd26 films and the concomitant reduction of
sub-lattice magnetization. Our study shows that using a Co/Pt multilayer as a
polarizer in a spin-valve structure, the SPHE drives the demagnetization of the
two sub-lattices of the Fe74Gd26 film. This behaviour is explained based on two
physical mechanisms, i.e., spin transfer torque and thermal fluctuations
induced by the SPHE. We provide a quantitative description of the heat transfer
of the ultrashort SPHE pulse to the Fe74Gd26 films, as well as the degree of
spin-polarization of the SPHE current density responsible for the observed
magnetization dynamics. Our work finally characterizes the spin-polarization of
the SPHEs revealing unexpected opposite spin polarization to the Co
magnetization, explaining our experimental results.",2403.11739v2
2017-07-31,Spin-orbit torques from interfacial spin-orbit coupling for various interfaces,"We use a perturbative approach to study the effects of interfacial spin-orbit
coupling in magnetic multilayers by treating the two-dimensional Rashba model
in a fully three-dimensional description of electron transport near an
interface. This formalism provides a compact analytic expression for
current-induced spin-orbit torques in terms of unperturbed scattering
coefficients, allowing computation of spin-orbit torques for various contexts,
by simply substituting scattering coefficients into the formulas. It applies to
calculations of spin-orbit torques for magnetic bilayers with bulk magnetism,
those with interface magnetism, a normal metal/ferromagnetic insulator
junction, and a topological insulator/ferromagnet junction. It predicts a
dampinglike component of spin-orbit torque that is distinct from any intrinsic
contribution or those that arise from particular spin relaxation mechanisms. We
discuss the effects of proximity-induced magnetism and insertion of an
additional layer and provide formulas for in-plane current, which is induced by
a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in
the same formalism.",1707.09847v1
2020-04-03,Modulation of field-like spin orbit torque in heavy metal / ferromagnet heterostructure,"Recent studies rediscovered the crucial role of field-like spin orbit torque
(SOT) in nanosecond-timescale SOT dynamics. However, there is not yet an
effective way to control its relative amplitude. Here, we experimentally
modulate the field-like SOT in W/CoFeB/MgO trilayers through tuning the
interfacial spin accumulation. By performing spin Hall magnetoresistance
measurement, we find that the CoFeB with enhanced spin dephasing, either
generated from larger layer thickness or from proper annealing, can distinctly
boost the spin absorption and enhance the interfacial spin mixing conductance
G_r. While the damping-like torque efficiency increases with G_r, the
field-like torque efficiency turns out to decrease with it. The results suggest
that the interfacial spin accumulation, which largely contributes to a
field-like torque, is reduced by higher interfacial spin transparency. Our work
shows a new path to further improve the performance of SOT-based magnetic
devices.",2004.01357v1
2021-03-09,Self-induced spin-orbit torques in metallic ferromagnets,"We present a phenomenological theory of spin-orbit torques in a metallic
ferromagnet with spin-relaxing boundaries. The model is rooted in the coupled
diffusion of charge and spin in the bulk of the ferromagnet, where we account
for the anomalous Hall effects as well as the anisotropic magnetoresistance in
the corresponding constitutive relations for both charge and spin sectors. The
diffusion equations are supplemented with suitable boundary conditions
reflecting the spin-sink capacity of the environment. In inversion-asymmetric
heterostructures, the uncompensated spin accumulation exerts a dissipative
torque on the order parameter, giving rise to a current-dependent linewidth in
the ferromagnetic resonance with a characteristic angular dependence. We
compare our model to recent spin-torque ferromagnetic resonance measurements,
illustrating how rich self-induced spin-torque phenomenology can arise even in
simple magnetic structures.",2103.05743v2
2010-05-05,Spin Evolution of Accreting Young Stars. I. Effect of Magnetic Star-Disk Coupling,"We present a model for the rotational evolution of a young, solar mass star
interacting with an accretion disk. The model incorporates a description of the
angular momentum transfer between the star and disk due to a magnetic
connection, and includes changes in the star's mass and radius and a decreasing
accretion rate. The model also includes, for the first time in a spin evolution
model, the opening of the stellar magnetic field lines, as expected to arise
from twisting via star-disk differential rotation. In order to isolate the
effect that this has on the star-disk interaction torques, we neglect the
influence of torques that may arise from open field regions connected to the
star or disk. For a range of magnetic field strengths, accretion rates, and
initial spin rates, we compute the stellar spin rates of pre-main-sequence
stars as they evolve on the Hayashi track to an age of 3~Myr. How much the
field opening affects the spin depends on the strength of the coupling of the
magnetic field to the disk. For the relatively strong coupling (i.e., high
magnetic Reynolds number) expected in real systems, all models predict spin
periods of less than $\sim3$ days, in the age range of 1--3~Myr. Furthermore,
these systems typically do not reach an equilibrium spin rate within 3~Myr, so
that the spin at any given time depends upon the choice of initial spin rate.
This corroborates earlier suggestions that, in order to explain the full range
of observed rotation periods of approximately $1$--$10$ days, additional
processes, such as the angular momentum loss from powerful stellar winds, are
necessary.",1005.0863v1
2019-05-31,Imaging and writing magnetic domains in the non-collinear antiferromagnet Mn$_{\text{3}}$Sn,"Harnessing the unique properties of non-collinear antiferromagnets (AFMs)
will be essential for exploiting the full potential of antiferromagnetic
spintronics. Indeed, many of the effects enabling ferromagnetic spintronic
devices have a corresponding counterpart in materials with non-collinear spin
structure. In addition, new phenomena such as the magnetic spin Hall effect
were experimentally observed in non-collinear AFMs, and the presence of the
equivalent to the ferromagnetic spin transfer torque via spin polarized
currents was theoretically predicted. In spite of these developments, an
interpretation of the rich physical phenomena observed in non-collinear
antiferromagnets is challenging, since the microscopic spin arrangement, the
magnetic domain distribution, and the domain orientations have proven
notoriously difficult to access experimentally. This is all the more
problematic, as imaging and writing magnetic domains is of central importance
for applications. Successful imaging is a basic requirement to experimentally
confirm the spin transfer torque acting on non-collinear domain walls and
therefore of eminent interest. Here, we demonstrate that the local magnetic
structure of the non-collinear AFM Mn3Sn films can be imaged by scanning
thermal gradient microscopy (STGM). The technique is based on scanning a laser
spot over the sample's surface, and recording the ensuing thermo-voltage. We
image the magnetic structure at a series of different temperatures and show
that at room temperature, the domain structure is not affected by the
application of moderate magnetic fields. In addition to imaging, we establish a
scheme for heat-assisted magnetic recording, using local laser heating in
combination with magnetic fields to intentionally write domain patterns into
the antiferromagnet.",1905.13504v1
2020-09-29,Spin transfer torque in Mn$_3$Ga-based ferrimagnetic tunnel junctions from first principles,"We report on first-principles calculations of spin-transfer torque (STT) in
epitaxial magnetic tunnel junctions (MTJs) based on ferrimagnetic tetragonal
Mn$_3$Ga electrodes, both as analyzer in an Fe/MgO stack, and also in an
analogous stack with a second Mn$_3$Ga electrode (instead of Fe) as polarizer.
Solving the ballistic transport problem (NEGF + DFT) for the nonequilibrium
spin density in a scattering region extended to over 7.6 nm into the Mn$_3$Ga
electrode, we find long-range spatial oscillations of the STT decaying on a
length scale of a few tens of angstroms, both in the linear response regime and
for finite bias. The oscillatory behavior of the STT in Mn$_3$Ga is robust
against variations in the stack geometry and the applied bias voltage, which
may affect the phase and the amplitude of the spatial oscillation, but the wave
number is only responsive to variations in the longitudinal lattice constant of
Mn$_3$Ga (for fixed in-plane geometry) without being commensurate with the
lattice. Our interpretation of the long-range STT oscillations is based on the
bulk electronic structure of Mn$_3$Ga, taking also into account the
spin-filtering properties of the MgO barrier. Comparison to a fully
Mn$_3$Ga-based stack shows similar STT oscillations, but a significant
enhancement of both the TMR effect at the Fermi level and the STT at the
interface, due to resonant tunneling for the mirror-symmetric junction with
thinner barrier (three monoatomic layers). From the calculated energy
dependence of the spin-polarized transmissions at 0 V, we anticipate asymmetric
or symmetric TMR as a function of the applied bias voltage for the Fe-based and
the all-Mn$_3$Ga stacks, respectively, which also both exhibit a sign change
below 1 V. In the latter (symmetric) case we expect a TMR peak at zero, which
is larger for the thinner barriers because of a spin-polarized resonant
tunneling contribution.",2009.14095v2
2007-03-02,Topological Force and Torque in Spin-Orbit Coupling System,"The topological force and torque are investigated in the systems with
spin-orbit coupling. Our results show that the topological force and torque
appears as a pure relativistic quantum effect in an electromagnetic field. The
origin of both topological force and torque is the Zitterbewegung effect.
Considering nonlinear behaviors of spin-orbit coupling, we address possible
phenomena driven by the topological forces.",0703048v1
2013-07-29,Theoretical Study of Spin-Torque Oscillator with Perpendicularly Magnetized Free Layer,"The magnetization dynamics of spin torque oscillator (STO) consisting of a
perpendicularly magnetized free layer and an in-plane magnetized pinned layer
was studied by solving the Landau-Lifshitz-Gilbert equation. We derived the
analytical formula of the relation between the current and the oscillation
frequency of the STO by analyzing the energy balance between the work done by
the spin torque and the energy dissipation due to the damping. We also found
that the field-like torque breaks the energy balance, and change the
oscillation frequency.",1307.7427v1
2015-05-29,Coherent Sub-Nanosecond Switching of Perpendicular Magnetization by the Field-like Spin-Orbit Torque without an External Magnetic Field,"We theoretically study the influence of a predominant field-like spin-orbit
torque on the magnetization switching of small devices with a uniform
magnetization. We show that for a certain range of ratios (0.23-0.55) of the
Slonczewski to the field-like torques, it is possible to deterministically
switch the magnetization without requiring any external assist field. A precise
control of the pulse length is not necessary, but the pulse edge sharpness is
critical. The proposed switching scheme is numerically verified to be effective
in devices by micromagnetic simulations. Switching without any external assist
field is of great interest for the application of spin-orbit torques to
magnetic memories.",1505.07939v1
2022-11-09,Giant efficiency of long-range orbital torque in Co/Nb bilayers,"We report unambiguously experimental evidence of a strong orbital current in
Nb films with weak spin-orbit coupling via the spin-torque ferromagnetic
resonance (ST-FMR) spectrum for Fe/Nb and Co/Nb bilayers. The sign change of
the damping-like torque in Co/Nb demonstrates a large spin-orbit correlation
and thus great efficiency of orbital torque in Co/Nb. By studying the
efficiency as a function of the thickness of Nb sublayer, we reveal a long
orbital diffusion length (~3.1 nm) of Nb. Further planar Hall resistance (PHE)
measurements at positive and negative applying current confirm the nonlocal
orbital transport in ferromagnetic-metal/Nb heterostructures.",2211.04809v1
2018-04-12,Spin Transport in Half-Metallic Ferromagnet-Superconductor Junctions,"We investigate the charge and spin transport in half-metallic ferromagnet
($F$) and superconductor ($S$) nanojunctions. We utilize a self-consistent
microscopic method that can accommodate the broad range of energy scales
present, and ensures proximity effects that account for the interactions at the
interfaces are accurately determined. Two experimentally relevant half-metallic
junction types are considered: The first is a $F_1 F_2 S$ structure, where a
half-metallic ferromagnet $F_1$ adjoins a weaker conventional ferromagnet
$F_2$. The current is injected through the $F_1$ layer by means of an applied
bias voltage. The second configuration involves a $S F_1 F_2 F_3 S$ Josephson
junction whereby a phase difference $\Delta\varphi$ between the two
superconducting electrodes generates the supercurrent flow. In this case, the
central half-metallic $F_2$ layer is surrounded by two weak ferromagnets $F_1$
and $F_3$. By placing a ferromagnet with a weak exchange field adjacent to an
$S$ layer, we are able to optimize the conversion process in which
opposite-spin triplet pairs are converted into equal-spin triplet pairs that
propagate deep into the half-metallic regions in both junction types. For the
tunnel junctions, we study the bias-induced local magnetization, spin currents,
and spin transfer torques for various orientations of the relative
magnetization angle $\theta$ in the $F$ layers. We find that the bias-induced
equal-spin triplet pairs are maximized in the half-metal for
$\theta\approx90^\circ$ and as part of the conversion process, are
anticorrelated with the opposite-spin pairs. We show that the charge current
density is maximized, corresponding to the occurrence of a large amplitude of
equal-spin triplet pairs, when the exchange interaction of the weak ferromagnet
is about $0.1E_F.$",1804.04275v1
2014-07-11,Magnetic domain-wall motion twisted by nanoscale probe-induced spin transfer,"A method for deterministic control of the magnetic order parameter using an
electrical stimulus is highly desired for the new generation of spintronic and
magnetoelectronic devices. Much effort has been focused on magnetic domain-wall
motion manipulated by a successive injection of spin-polarized current into a
magnetic nanostructure. However, an integrant high-threshold current density of
107~108 A/cm2 inhibits the integration of those nanostructures with
low-energy-cost technology. In addition, a precise determination of the
location of domain walls at nanoscale seems difficult in artificially
manufactured nanostructures. Here we report an approach to manipulate a single
magnetic domain wall with a perpendicular anisotropy in a
manganite/dielectric/metal capacitor using a probe-induced spin displacement. A
spin angular momentum transfer torque occurs in the strongly correlated
manganite film during the spin injection into the capacitor from the nanoscale
magnetized tip with an ultralow voltage of 0.1 V, where the threshold
spin-polarized current density is ~104 A/cm2 at the tip/manganite interface.
The probe-voltage-controlled domain wall motion in the capacitor demonstrates a
critical framework for the fundamental understanding of the manipulation of the
nano-magnet systems with low energy consumption.",1407.3016v1
2022-03-01,Ultrafast enhancement of interfacial exchange coupling in ferromagnetic bilayer,"Fast spin manipulation in magnetic heterostructures, where magnetic
interactions between different materials often define the functionality of
devices, is a key issue in the development of ultrafast spintronics. Although
recently developed optical approaches such as ultrafast spin-transfer and
spin-orbit torques open new pathways to fast spin manipulation, these processes
do not fully utilize the unique possibilities offered by interfacial magnetic
coupling effects in ferromagnetic multilayer systems. Here, we experimentally
demonstrate ultrafast photo-enhanced interfacial exchange interactions in the
ferromagnetic Co$_2$FeAl/(Ga,Mn)As system at low laser fluence levels. The
excitation efficiency of Co$_2$FeAl with the (Ga,Mn)As layer is 30-40 times
higher than the case with the GaAs layer at 5 K due to a photo-enhanced
exchange coupling interaction via photoexcited charge transfer between the two
ferromagnetic layers. In addition, the coherent spin precessions persist to
room temperature, excluding the drive of photo-enhanced magnetization in the
(Ga,Mn)As layer and indicating a proximity-effect-related optical excitation
mechanism. The results highlight the importance of considering the range of
interfacial exchange interactions in ferromagnetic heterostructures and how
these magnetic coupling effects can be utilized for ultrafast, low-power spin
manipulation.",2203.00293v3
2014-08-08,Stable Magnetic Droplet Solitons in Spin Transfer Nanocontacts,"Magnetic thin films with perpendicular magnetic anisotropy (PMA) have
localized excitations that correspond to reversed dynamically precessing
magnetic moments, known as magnetic droplet solitons. Fundamentally, these
excitations are associated with an attractive interaction between elementary
spin-excitations (i.e., magnons) and were predicted to occur in PMA materials
in the absence of damping [1,2]. While damping, present in all magnetic
materials, suppresses these excitations, it is now possible to compensate
damping by spin transfer torques through electrical current flow in nanometer
scale contacts to ferromagnetic thin films [3,4]. A theory predicts the
appearance of magnetic droplet solitons at a threshold current in nanocontacts
[5] and, recently, experimental signatures of droplet nucleation have been
reported [6]. However, thus far, they have been observed to be nearly
reversible excitations, with only partially reversed magnetization and to be
subject to instabilities that cause them to drift away from the nanocontacts
(i.e., drift instabilities) [6]. Here we show that magnetic droplet solitons
can be stabilized in a spin transfer nanocontact. Further, they exhibit a
strong hysteretic response to fields and currents and a nearly fully reversed
magnetization in the contact. These observations, in addition to their
fundamental interest, open up new applications for magnetic droplet solitons as
multi-state high frequency current and field tunable oscillators.",1408.1902v1
2013-12-26,Synchronization and chaos in spin-transfer-torque nano-oscillators coupled via a high speed Op Amp,"We propose a system of two coupled spin-torque nano-oscillators (STNOs), one
driver and another response, and demonstrate {using numerical studies} the
synchronization of the response system to the frequency of the driver system.
To this end we use a high speed operational amplifier in the form of a voltage
follower which essentially isolates the drive system from the response system.
We find the occurrence of 1:1 as w ell as 2:1 synchronization in the system,
wherein the oscillators show limit cycle dynamics. An increase in power output
is noticed when the two oscillators are locked in 1:1 synchronization. Moreover
in the cro ssover region between these two synchronization dynamics we show the
existence of chaotic dynamics in the slave system. The coupled dynamics under
periodic forcing, using a small ac input current in addition to that of the dc
part, is also studied. The slave oscillator is seen to retain its qualitative
identity in the parameter space in spite of being fed in, at times, a chaotic
signal. Such electrically coupled STNOs will be highly useful in fabricating
commercial spin-valve oscillators with high power output, when integrated with
other spintronic devices.",1312.7092v1
2014-10-18,Giant spin-torque diode sensitivity at low input power in the absence of bias magnetic field,"Microwave detectors based on the spin-transfer torque diode effect are among
the key emerging spintronic devices. By utilizing the spin of electrons in
addition to charge, they have the potential to overcome the theoretical
performance limits of their semiconductor (Schottky) counterparts, which cannot
operate at low input power. Here, we demonstrate nanoscale microwave detectors
exhibiting record-high detection sensitivity of 75400 mV mW$^{-1}$ at room
temperature, without any external bias fields, for input microwave power down
to 10 nW. This sensitivity is 20x and 6x larger than state-of-the-art Schottky
diode detectors (3800 mV mW$^{-1}$) and existing spintronic diodes with >1000
Oe magnetic bias (12000 mV mW$^{-1}$), respectively. Micromagnetic simulations
supported by microwave emission measurements reveal the essential role of the
injection locking to achieve this sensitivity performance. The results enable
dramatic improvements in the design of low input power microwave detectors,
with wide-ranging applications in telecommunications, radars, and smart
networks.",1410.4958v1
2018-07-20,Another view on Gilbert damping in two-dimensional ferromagnets,"A keen interest towards technological implications of spin-orbit driven
magnetization dynamics requests a proper theoretical description, especially in
the context of a microscopic framework, to be developed. Indeed, magnetization
dynamics is so far approached within Landau-Lifshitz-Gilbert equation which
characterizes torques on magnetization on purely phenomenological grounds.
Particularly, spin-orbit coupling does not respect spin conservation, leading
thus to angular momentum transfer to lattice and damping as a result. This
mechanism is accounted by the Gilbert damping torque which describes relaxation
of the magnetization to equilibrium. In this study we work out a microscopic
Kubo-St\v{r}eda formula for the components of the Gilbert damping tensor and
apply the elaborated formalism to a two-dimensional Rashba ferromagnet in the
weak disorder limit. We show that an exact analytical expression corresponding
to the Gilbert damping parameter manifests linear dependence on the scattering
rate and retains the constant value up to room temperature when no vibrational
degrees of freedom are present in the system. We argue that the methodology
developed in this paper can be safely applied to bilayers made of non- and
ferromagnetic metals, e.g., CoPt.",1807.07897v2
2020-07-21,Electric-field-driven Non-volatile Multi-state Switching of Individual Skyrmions in a Multiferroic Heterostructure,"Electrical manipulation of skyrmions attracts considerable attention for its
rich physics and promising applications. To date, such a manipulation is
realized mainly via spin-polarized current based on spin-transfer torque or
spin-orbital torque effect. However, this scheme is energy-consuming and may
produce massive Joule heating. To reduce energy dissipation and risk of
heightened temperatures of skyrmion-based devices, an effective solution is to
use electric field instead of current as stimulus. Here, we realize an
electric-field manipulation of skyrmions in a nanostructured
ferromagnetic/ferroelectrical heterostructure at room temperature via an
inverse magneto-mechanical effect. Intriguingly, such a manipulation is
non-volatile and exhibits a multi-state feature. Numerical simulations indicate
that the electric-field manipulation of skyrmions originates from
strain-mediated modification of effective magnetic anisotropy and
Dzyaloshinskii-Moriya interaction. Our results open a direction for
constructing low-energy-dissipation, non-volatile, and multi-state
skyrmion-based spintronic devices.",2007.10652v1
2023-02-07,Computational capability for physical reservoir computing using a spin-torque oscillator with two free layers,"A numerical analysis on the computational capability of physical reservoir
computing utilizing a spin-torque oscillator with two free layers is reported.
Conventional spintronics devices usually consist of two ferromagnets, where the
direction of magnetization in one layer, called the free layer, can move while
that of the other, the reference layer, is fixed. Recently, however, devices
with two free layers, where the reference layer is replaced by another free
layer, have been developed for various practical applications. Adding another
free layer drastically changes the dynamical response of the device through the
couplings via the spin-transfer effect and the dipole magnetic field. A
numerical simulation of the Landau-Lifshitz-Gilbert equation and a statistical
analyses of the Lyapunov exponent and the synchronization index reveal the
appearance of an amplitude-modulated oscillation and chaos in the oscillators
with two free layers. Such complex dynamics qualitatively change the
computational capability of physical reservoir computing because the
computational resource is dynamics of the physical system. An evaluation of the
short-term memory capacity clarifies that oscillators with two free layers have
a larger capacity than those of conventional oscillators. An enhancement in
capacity near the edge of echo state property, i.e., the boundary between zero
and finite synchronization index, is also found.",2302.03769v1
2016-09-21,Ultrafast Magnetization Reversal by Picosecond Electrical Pulses,"The field of spintronics involves the study of both spin and charge transport
in solid state devices with a view toward increasing their functionality and
efficiency. Alternatively, the field of ultrafast magnetism focuses on the use
of femtosecond laser pulses to excite electrons in magnetic materials, which
allows the magnetic order to be dramatically changed on unprecedented
sub-picosecond time-scales. Here, we unite these two distinct research
activities by using picosecond electrical pulses to rapidly excite electrons in
a magnetic metal. We are able to deterministically and repetitively reverse the
magnetization of a GdFeCo film with sub-10 picosecond electrical pulses. The
magnetization reverses in ~10ps, which is more than an order of magnitude
faster than any other electrically controlled magnetic switching. We attribute
the deterministic switching of the magnetization to ultrafast excitation of the
electrons, a fundamentally different mechanism from other current driven
switching mechanisms such as spin-transfer-torque (STT) or spin-orbit-torque
(SOT). The energy density required for switching is measured and the process is
found to be efficient, projecting to only 4 fJ needed to switch a (20 nm)^3
cell, which is comparable to other state-of-the-art STT-MRAM memory devices.
This discovery will launch a new field of research into picosecond spintronic
phenomena and devices.",1609.06392v2
2023-09-11,Spin-Hall effect due to the bulk states of topological insulators: Extrinsic contribution to the conserved spin current,"The substantial amount of recent research into spin torques has been
accompanied by a revival of interest in the spin-Hall effect. This effect
contributes to the spin torque in many materials, including topological
insulator/ferromagnet devices, Weyl semimetals, and van der Waals
heterostructures. In general the relative sizes of competing spin torque
mechanisms remain poorly understood. Whereas a consensus is beginning to emerge
on the evaluation of a conserved spin current, the role of extrinsic disorder
mechanisms in the spin-Hall effect has not been clarified. In this work we
present a comprehensive calculation of the extrinsic spin Hall effect while
focussing on the bulk states of topological insulators as a prototype system
and employing a fully quantum mechanical formalism to calculate the proper spin
current. Our calculation of the proper spin current employs a 4x4 k.p
Hamiltonian describing the bulk states of topological insulators. At the same
time, we provide a qualitative explanation of the proper spin currents
calculated based on an effective $2\times2$ Hamiltonian obtained via a
Schrieffer-Wolf transformation. We find that the extrinsic contribution to the
proper spin current, driven by side jump, skew scattering and related
mechanisms, is of a comparable magnitude to the intrinsic contribution, making
it vital to take such disorder effects into account when seeking to understand
experiments. Among the scattering effects considered, side jump scattering is
the primary contributor to the extrinsic spin Hall effect. The total spin
susceptibility calculated here is too small to explain experimentally measured
spin torques, hence we expect the spin Hall effect to make a negligible
contribution to the spin torque in topological insulator structures.",2309.05723v1
2014-07-28,Full-counting statistics of charge and spin transport in the transient regime: A nonequilibrium Green's function approach,"We report the investigation of full-counting statistics (FCS) of transferred
charge and spin in the transient regime where the connection between central
scattering region (quantum dot) and leads are turned on at $t=0$. A general
theoretical formulation for the generating function (GF) is presented using a
nonequilibrium Green's function approach for the quantum dot system. In
particular, we give a detailed derivation on how to use the method of path
integral together with nonequilibrium Green's function technique to obtain the
GF of FCS in electron transport systems based on the two-time quantum
measurement scheme. The correct long-time limit of the formalism, the
Levitov-Lesovik's formula, is obtained. This formalism can be generalized to
account for spin transport for the system with noncollinear spin as well as
spin-orbit interaction. As an example, we have calculated the GF of
spin-polarized transferred charge, transferred spin, as well as the spin
transferred torque for a magnetic tunneling junction in the transient regime.
The GF is compactly expressed by a functional determinant represented by
Green's function and self-energy in the time domain. With this formalism, FCS
in spintronics in the transient regime can be studied. We also extend this
formalism to the quantum point contact system. For numerical results, we
calculate the GF and various cumulants of a double quantum dot system connected
by two leads in transient regime. The signature of universal oscillation of FCS
is identified. On top of the global oscillation, local oscillations are found
in various cumulants as a result of the Rabi oscillation. Finally, the
influence of the temperature is also examined.",1407.7362v3
2014-01-05,Magnon-Mediated Dzyaloshinskii-Moriya Torque in Homogeneous Ferromagnets,"In thin magnetic layers with structural inversion asymmetry and spin-orbit
coupling, a Dzyaloshinskii-Moriya interaction arises at the interface. When a
spin wave current ${\bf j}_m$ flows in a system with a homogeneous
magnetization {\bf m}, this interaction produces an effective field-like torque
on the form ${\bf T}_{\rm FL}\propto{\bf m}\times({\bf z}\times{\bf j}_m)$ as
well as a damping-like torque, ${\bf T}_{\rm DL}\propto{\bf m}\times[({\bf
z}\times{\bf j}_m)\times{\bf m}]$ in the presence of spin-wave relaxation
(${\bf z}$ is normal to the interface). These torques mediated by the magnon
flow can reorient the time-averaged magnetization direction and display a
number of similarities with the torques arising from the electron flow in a
magnetic two dimensional electron gas with Rashba spin-orbit coupling. This
magnon-mediated spin-orbit torque can be efficient in the case of magnons
driven by a thermal gradient.",1401.0883v2
2015-10-09,Spin-orbit torque in Pt/CoNiCo/Pt symmetric devices,"Current induced magnetization switching by spin-orbit torques offers an
energy-efficient means of writing information in heavy metal/ferromagnet (FM)
multilayer systems. The relative contributions of field-like torques and
damping-like torques to the magnetization switching induced by the electrical
current are still under debate. Here, we describe a device based on a symmetric
Pt/FM/Pt structure, in which we demonstrate a strong damping-like torque from
the spin Hall effect and unmeasurable field-like torque from Rashba effect. The
spin-orbit effective fields due to the spin Hall effect were investigated
quantitatively and were found to be consistent with the switching effective
fields after accounting for the switching current reduction due to thermal
fluctuations from the current pulse. A non-linear dependence of deterministic
switching of average Mz on the in-plane magnetic field was revealed, which
could be explained and understood by micromagnetic simulation.",1510.02555v1
2018-10-13,Spin-torque resonance due to diffusive dynamics at a surface of topological insulator,"We investigate spin-orbit torques on magnetization in an insulating
ferromagnetic (FM) layer that is brought into a close proximity to a
topological insulator (TI). In addition to the well-known field-like spin-orbit
torque, we identify an anisotropic anti-damping-like spin-orbit torque that
originates in a diffusive motion of conduction electrons. This diffusive torque
is vanishing in the limit of zero momentum (i. e. for spatially homogeneous
electric field or current), but may, nevertheless, have a strong effect on
spin-torque resonance at finite frequency provided external field is neither
parallel nor perpendicular to the TI surface. The required electric field
configuration can be created by a grated top gate.",1810.05828v3
2020-10-29,Collective spin dynamics under dissipative spin Hall torque,"Current-induced spin torques in layered magnetic heterostructures have many
commonalities across broad classes of magnetic materials. These include not
only collinear ferromagnets, ferrimagnets, and antiferromagnets, but also more
complex noncollinear spin systems. We develop a general Lagrangian-Rayleigh
approach for studying the role of dissipative torques, which can pump energy
into long-wavelength magnetic dynamics, causing dynamic instabilities. While
the Rayleigh structure of such torques is similar for different magnetic
materials, their consequences depend sensitively on the nature of the order
and, in particular, on whether there is a net magnetic moment. The latter
endows the system with a unipolar switching capability, while magnetically
compensated materials tend to evolve towards limit cycles, at large torques,
with chirality dependent on the torque sign. Apart from the ferromagnetic and
antiferromagnetic cases, we discuss ferrimagnets, which display an intricate
competition between switching and limit cycles. As a simple case for
compensated noncollinear order, we consider isotropic spin glasses, as well as
a scenario of their coexistence with a collinear magnetic order.",2010.15994v1
2021-11-15,First-principles calculations of spin-orbit torques in Mn$_2$Au/heavy-metal bilayers,"Using the non-equilibrium Green's function technique, we calculate spin-orbit
torques in a Mn$_2$Au/heavy-metal bilayer, where the heavy metal (HM) is W or
Pt. Spin-orbit coupling (SOC) in the bulk of Mn$_2$Au generates strong
fieldlike torquance, which is parallel on the two sublattices and scales
linearly with the conductivity, and a weaker dampinglike torquance that is
antiparallel on the two sublattices. Interfaces with W or Pt generate parallel
dampinglike torques of opposite signs that are similar in magnitude to those in
ferromagnetic bilayers and similarly insensitive to disorder. The dampinglike
torque efficiency depends strongly on the termination of the interface and on
the presence of spin-orbit coupling in Mn$_2$Au, suggesting that the
dampinglike torque is not due solely to the spin-Hall effect in the HM layer.
Interfaces also induce antiparallel fieldlike and dampinglike torques that can
penetrate deep into Mn$_2$Au.",2111.07532v2
2005-08-17,Spin orbit induced torque in collinear spin valve structuer and associated entropy,"We predict that due to spin-orbit(SO) interaction there is a torque even for
the parallel configuration of spin valve structure (F1/2DEG/F2). This torque
arises due to spin orbit interaction. We develop a scattering theory for spin
density matrix which allows us to study this effect quantitatively. Further we
show that the von-Neumann entropy associated with transport of polarization can
show non-linear behavior as a function of absolute angle and oscillator
behavior as a function of SO interaction strength.",0508386v1
2005-08-30,Effects of spin current on ferromagnets,"When a spin-polarized current flows through a ferromagnet, the local
magnetization receives a spin torque. Two consequences of this spin torque are
studied. First, the uniformly magnetized ferromagnet becomes unstable if a
sufficiently large current is applied. The characteristics of the instability
include spin wave generation and magnetization chaos. Second, the spin torque
has profound effects on the structure and dynamics of the magnetic domain wall.
A detail analysis on the domain wall mass, kinetic energy and wall depinning
threshold is given.",0508735v1
2007-03-27,Gauge Field Formulation of Adiabatic Spin Torques,"Previous calculation of spin torques for small-amplitude magnetization
dynamics around a uniformly magnetized state [J. Phys. Soc. Jpn. {\bf 75}
(2006) 113706] is extended here to the case of finite-amplitude dynamics. This
is achieved by introducing an `` adiabatic'' spin frame for conduction
electrons, and the associated SU(2) gauge field. In particular, the Gilbert
damping is shown to arise from the time variation of the spin-relaxation source
terms in this new frame, giving a new physical picture of the damping. The
present method will allow a `` first-principle'' derivation of spin torques
without any assumptions such as rotational symmetry in spin space.",0703705v1
2009-12-09,Microscopic Theory of Current-Spin Interaction in Ferromagnets,"Interplay between magnetization dynamics and electric current in a conducting
ferromagnet is theoretically studied based on a microscopic model calculation.
First, the effects of the current on magnetization dynamics (spin torques) are
studied with special attention to the ""dissipative"" torques arising from
spin-relaxation processes of conduction electrons. Next, an analysis is given
of the ""spin motive force"", namely, a spin-dependent 'voltage' generation due
to magnetization dynamics, which is the reaction to spin torques. Finally, an
attempt is presented of a unified description of these effects.",0912.1676v1
2012-06-25,Spin torque due to non-uniform Rashba spin orbit effect,"Following the early theoretical descriptions of the spin-orbit-induced spin
torque [S.G. Tan et al., arXiv:0705.3502 (2007); S.G.Tan et al., Ann. Phys.326,
207 (2011)], the first experimental observation of such effect was reported by
L. M. Miron et al., Nature Mater, 9, 230 (2010). We present in this article
three additional spin torque terms that arise from the non-uniformity in
magnetization space of the Rashba spin-orbit effect. We propose a simple Rashba
gradient device which could potentially lower switching current by n orders of
magnitude, where large n measures a small magnetization change.",1206.5616v1
2023-04-25,Magnetization Switching in van der Waals Systems by Spin-Orbit Torque,"Electrical switching of magnetization via spin-orbit torque (SOT) is of great
potential in fast, dense, energy-efficient nonvolatile magnetic memory and
logic technologies. Recently, enormous efforts have been stimulated to
investigate switching of perpendicular magnetization in van der Waals systems
that have unique, strong tunability and spin-orbit coupling effect compared to
conventional metals. In this review, we first give a brief, generalized
introduction to the spin-orbit torque and van der Waals materials. We will then
discuss the recent advances in magnetization switching by the spin current
generated from van der Waals materials and summary the progress in the
switching of Van der Waals magnetization by the spin current.",2304.12632v1
2016-04-26,Spin-orbit torques in locally and globally non-centrosymmetric crystals: Antiferromagnets and ferromagnets,"One of the main obstacles that prevents practical applications of
antiferromagnets is the difficulty of manipulating the magnetic order
parameter. Recently, following the theoretical prediction [J. \v{Z}elezn\'y et
al., PRL 113, 157201 (2014)], the electrical switching of magnetic moments in
an antiferromagnet has been demonstrated [P. Wadley et al., Science 351, 587
(2016)]. The switching is due to the so-called spin-orbit torque, which has
been extensively studied in ferromagnets. In this phenomena a non-equilibrium
spin-polarization exchange coupled to the ordered local moments is induced by
current, hence exerting a torque on the order parameter. Here we give a general
systematic analysis of the symmetry of the spin-orbit torque in locally and
globally non-centrosymmetric crystals. We study when the symmetry allows for a
nonzero torque, when is the torque effective, and its dependence on the applied
current direction and orientation of magnetic moments. For comparison, we
consider both antiferromagnetic and ferromagnetic orders. In two representative
model crystals we perform microscopic calculations of the spin-orbit torque to
illustrate its symmetry properties and to highlight conditions under which the
spin-orbit torque can be efficient for manipulating antiferromagnetic moments.",1604.07590v1
2019-02-12,Effective field analysis using the full angular spin-orbit torque magnetometry dependence,"Spin-orbit torques promise ultra-efficient magnetization switching used for
advanced devices based on emergent quasi-particles such as domain walls and
skyrmions. Recently, the spin structure dynamics, materials and systems with
tailored spin-orbit torques are being developed. A method, which allows one to
detect the acting torques in a given system as a function of the magnetization
direction is the torque-magnetometry method based on a higher harmonics
analysis of the anomalous Hall-effect. Here we show that the effective fields
acting on magnetic domain walls that govern the efficiency of their dynamics
require a sophisticated analysis taking into account the full angular
dependence of the torques. Using a 1-D model we compared the spin orbit torque
efficiencies by depinning measurements and spin torque magnetometry. We show
that the effective fields can be accurately determined and we find good
agreement. Thus our method allows us now to rapidly screen materials and
predict the resulting quasi-particle dynamics.",1902.04665v2
2019-10-17,Scattering-induced and highly tunable by gate damping-like spin-orbit torque in graphene doubly proximitized by two-dimensional magnet Cr$_2$Ge$_2$Te$_6$ and WS$_2$,"Graphene sandwiched between semiconducting monolayers of ferromagnet
Cr$_2$Ge$_2$Te$_6$ and transition-metal dichalcogenide WS$_2$ acquires both
spin-orbit (SO), of valley-Zeeman and Rashba types, and exchange couplings.
Using first-principles combined with quantum transport calculations, we predict
that such doubly proximitized graphene within van der Waals heterostructure
will exhibit SO torque driven by unpolarized charge current. This system
lacking spin Hall current, putatively considered to be necessary for efficient
damping-like (DL) SO torque that plays a key role in magnetization switching,
demonstrates how DL torque component can be generated solely by skew-scattering
off spin-independent potential barrier or impurities in purely two-dimensional
electronic transport due to the presence of proximity SO coupling and its spin
texture tilted out-of-plane. This leads to current-driven nonequilibrium spin
density emerging in all spatial directions, whose cross product with proximity
magnetization yields DL SO torque, unlike the ballistic regime with no
scatterers in which only field-like (FL) SO torque appears. In contrast to SO
torque on conventional metallic ferromagnets in contact with three dimensional
SO-coupled materials, the ratio of FL and DL torque can be tuned by more than
an order of magnitude via combined top and back gates.",1910.08072v3
2018-12-03,Spin transfer torque and exchange coupling in Josephson junctions with ferromagnetic superconductor reservoirs,"In this paper, the spin transfer torque (STT) and the exchange coupling of
the Josephson junctions containing interesting cases of
diffusive/ballistic-triplet/singlet ferromagnetic superconductor materials
together with diffusive Josephson junction of the form
S$_{1}$/F$_{1}$/I$_1$/N/I$_2$/F$_2$ with I being insulating barrier are
investigated. Using the Nazarov quantum circuit theory, it is found that for
the diffusive FS$_1$/N/FS$_2$ structure the only emerged torque in normal
direction to the plane of the exchange fields of F$_1$ and F$_2$ results in
antiparallel/parallel or vice versa parallel/antiparallel transition of
favorable exchange coupling depending on the considered parameters of the
system, including the nonmagnetic spacer thickness, the superconducting phase
difference, the length and the exchange field of the ferromagnets. Furthermore,
the analyze of the width of the transitions, the phase difference interval in
which an interlayer length-induced antiparallel/parallel transition can be
occurred, is performed. For instance, as the exchange field or the temperature
increases, the interval of phase difference gets larger. On the other hand,
ballistic Josephson junction containing the triplet ferromagnetic
superconductor reservoirs solving the 16$\times$16 Bogoliubov-de-Gennes
equation is studied. It is found that although the exchange fields of the FS
are laid in the z and y direction, the STT interestingly exists in all three
directions of x, y and z. This exciting finding suggests that the favorable
equilibrium configuration concerning the least exchange coupling occurs in the
relative exchange field direction different from 0 or $\pi$. To the best of our
knowledge it is for the first time that the occurrence of the in-plane STT is
reported. Moreover, the occurrence of the beat like behavior with two
oscillation period for the out-of-plane STT is interestingly acquired.",1812.02733v2
2016-01-28,Interfacial spin-orbit torque without bulk spin-orbit coupling,"An electric current in the presence of spin-orbit coupling can generate a
spin accumulation that exerts torques on a nearby magnetization. We demonstrate
that, even in the absence of materials with strong bulk spin-orbit coupling, a
torque can arise solely due to interfacial spin-orbit coupling, namely
Rashba-Eldestein effects at metal/insulator interfaces. In magnetically soft
NiFe sandwiched between a weak spin-orbit metal (Ti) and insulator
(Al$_2$O$_3$), this torque appears as an effective field, which is
significantly larger than the Oersted field and sensitive to insertion of an
additional layer between NiFe and Al$_2$O$_3$. Our findings point to new routes
for tuning spin-orbit torques by engineering interfacial electric dipoles.",1601.07687v2
2017-11-29,Spin-orbit torque in 3D topological insulator-ferromagnet heterostructure: crossover between bulk and surface transport,"Current-driven spin-orbit torques are investigated in a heterostructure
composed of a ferromagnet deposited on top of a three dimensional topological
insulator using the linear response formalism. We develop a tight-binding model
of the heterostructure adopting a minimal interfacial hybridization scheme that
promotes induced magnetic exchange on the topological surface states, as well
as induced Rashba-like spin-orbit coupling in the ferromagnet. Therefore, our
model accounts for spin Hall effect from bulk states together with inverse spin
galvanic and magnetoelectric effects at the interface on equal footing. By
varying the transport energy across the band structure, we uncover a crossover
from surface-dominated to bulk-dominated transport regimes. We show that the
spin density profile and the nature of the spin-orbit torques differ
substantially in both regimes. Our results, which compare favorably with
experimental observations, demonstrate that the large damping torque reported
recently is more likely attributed to interfacial magnetoelectric effect, while
spin Hall torque remains small even in the bulk-dominated regime.",1711.11016v2
2017-11-15,Anomalous spin-orbit torque switching due to field-like torque-assisted domain wall reflection,"Spin-orbit torques (SOT) allow the electrical control of magnetic states.
Current-induced SOT switching of the perpendicular magnetization is of
particular technological importance. The SOT consists of damping-like and
field-like torques so that the efficient SOT switching requires to understand
combined effects of the two torque-components. Previous quasi-static
measurements have reported an increased switching probability with the width of
current pulses, as predicted with considering the damping-like torque only.
Here we report a decreased switching probability at longer pulse-widths, based
on time-resolved measurements. Micromagnetic analysis reveals that this
anomalous SOT switching results from domain wall reflections at sample edges.
The domain wall reflection is found to strongly depend on the field-like torque
and its relative sign to the damping-like torque. Our result demonstrates a key
role of the field-like torque in the deterministic SOT switching and notifies
the importance of sign correlation of the two torque-components, which may shed
light on the SOT switching mechanism.",1711.05367v1
1997-02-13,Torque-luminosity correlation and possible evidence for core-crust relaxation in the X-ray pulsar GX 1+4,"We present the detection of a positive correlation between spin-down rate
$\dot{P}$ and pulsed X-ray luminosity in the BATSE archival data of the bright
hard X-ray pulsar GX 1+4. We have also seen a delay of 5.6 $\pm$ 1.2 days
between the luminosity change and the corresponding change in the spin-down
rate. The observed correlation between $\dot{P}$ and L_X is used to reproduce
the period history of GX 1+4 based on the observed luminosity alone, and it is
found that the spin period can be predicted correct to 0.026% when the
luminosity is adequately sampled. The idea that at a higher luminosity more
matter is accreted and the accretion disk extends closer to the neutron star
thereby transferring more angular momentum to the system, seems not to be the
case with GX 1+4. The observed lag between the spin-down rate and the
luminosity is reported here for the first time in any such binary X-ray pulsar,
and is found to be consistent with the time scale for the core-crust relaxation
in a neutron star.",9702113v1
2006-02-06,Non-collinear Magnetoelectronics,"The electron transport properties of hybrid ferromagnetic|normal metal
structures such as multilayers and spin valves depend on the relative
orientation of the magnetization direction of the ferromagnetic elements.
Whereas the contrast in the resistance for parallel and antiparallel
magnetizations, the so-called Giant Magnetoresistance, is relatively well
understood for quite some time, a coherent picture for non-collinear
magnetoelectronic circuits and devices has evolved only recently. We review
here such a theory for electron charge and spin transport with general
magnetization directions that is based on the semiclassical concept of a vector
spin accumulation. In conjunction with first-principles calculations of
scattering matrices many phenomena, e.g. the current-induced spin-transfer
torque, can be understood and predicted quantitatively for different material
combinations.",0602151v1
2006-06-19,"Giant current-driven domain wall mobility in (Ga,Mn)As","We study theoretically hole current-driven domain wall dynamics in (Ga,Mn)As.
We show that the spin-orbit coupling causes significant hole reflection at the
domain wall, even in the adiabatic limit when the wall is much thicker than the
Fermi wavelength, resulting in spin accumulation and mistracking between
current-carrying spins and the domain wall magnetization. This increases the
out-of-plane non-adiabatic spin transfer torque and consequently the
current-driven domain wall mobility by three to four orders of magnitude.
Trends and magnitude of the calculated domain wall current mobilities agree
with experimental findings.",0606498v3
2009-03-25,Landauer theory of ballistic torkances in non-collinear spin valves,"We present a theory of voltage-induced spin-transfer torques in ballistic
non-collinear spin valves. The torkance on one ferromagnetic layer is expressed
in terms of scattering coefficients of the whole spin valve, in analogy to the
Landauer conductance formula. The theory is applied to Co/Cu/Ni(001)-based
systems where long-range oscillations of the Ni-torkance as a function of Ni
thickness are predicted. The oscillations represent a novel quantum size effect
due to the non-collinear magnetic structure. The oscillatory behavior of the
torkance contrasts a thickness-independent trend of the conductance.",0903.4387v4
2012-05-13,Signs of magnetic accretion in X-ray pulsars,"The spin-down mechanism of accreting neutron stars is discussed with an
application to one of the best studied X-ray pulsars GX 301-2. We show that the
maximum possible spin-down torque applied to a neutron star from the accretion
flow can be evaluated as $K_{\rm sd}^{\rm (t)} = \mu^2/(r_{\rm m} r_{\rm
cor})^{3/2}$. The spin-down rate of the neutron star in GX 301-2 can be
explained provided the magnetospheric radius of the neutron star is smaller
than its canonical value. We calculate the magnetospheric radius considering
the mass-transfer in the binary system in the frame of the magnetic accretion
scenario suggested by V.F. Shvartsman. The spin-down rate of the neutron star
expected within this approach is in a good agreement with that derived from
observations of GX 301-2.",1205.2846v1
2013-01-23,Data Storage: Review of Heusler Compounds,"In the recent decade, the family of Heusler compounds has attracted
tremendous scientific and technological interest in the field of spintronics.
This is essentially due to their exceptional magnetic properties, which qualify
them as promising functional materials in various data-storage devices, such as
giant-magnetoresistance spin valves, magnetic tunnel junctions, and
spin-transfer torque devices. In this article, we provide a comprehensive
review on the applications of the Heusler family in magnetic data storage. In
addition to their important roles in the performance improvement of these
devices, we also try to point out the challenges as well as possible solutions,
of the current Heusler-based devices. We hope that this review would spark
further investigation efforts into efficient incorporation of this eminent
family of materials into data storage applications by fully arousing their
intrinsic potential.",1301.5455v2
2014-05-09,Current-induced magnetization dynamics in two magnetic insulators separated by a normal metal,"We study the dynamics of spin valves consisting of two layers of magnetic
insulators separated by a normal metal in the macrospin model. A current
through the spacer generates a spin Hall current that can actuate the
magnetization via the spin-transfer torque. We derive expressions for the
effective Gilbert damping and the critical currents for the onset of
magnetization dynamics including the effects of spin pumping that can be tested
by ferromagnetic resonance experiments. The current generates an amplitude
asymmetry between the in-phase and out-of-phase modes. We briefly discuss
superlattices of metals and magnetic insulators.",1405.2267v1
2015-03-17,"Topological, non topological and instanton droplets driven by spin-transfer torque in materials with perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya Interaction","The interfacial Dzyaloshinskii-Moriya Interaction can modify the topology of
droplets excited by a localized spin-polarized current. Here, we show that, in
addition to the stationary droplet excitations with skyrmion number either one
(topological) or zero (non-topological), there exists, for a fixed current, an
excited mode with a non-stationary time behavior. We call this mode ""instanton
droplet"", which is characterized by time domain transitions of the skyrmion
number. These transitions are coupled to an emission of incoherent spin-waves
that can be observed in the frequency domain as a source of noise. Our results
are interesting from a fundamental point of view to study spin-wave emissions
due to a topological transition in current-driven systems, and could open the
route for experiments based on magnetoresistance effect for the design of a
further generation of nanoscale microwave oscillators.",1503.05161v2
2016-10-03,Linear dynamics of classical spin as Möbius transformation,"Although the overwhelming majority of natural processes occurs far from the
equilibrium, general theoretical approaches to non-equilibrium phase
transitions remain scarce. Recent breakthroughs introducing description of open
dissipative systems in terms of non-Hermitian quantum mechanics allowed to
identify a class of non-equilibrium phase transitions associated with the loss
of combined parity (reflection) and time-reversal symmetries. Here we report
that time evolution of a single classical spin (e.g. monodomain ferromagnet)
governed by the Landau-Lifshitz-Gilbert-Slonczewski equation in absence of
higher-order anisotropy terms is described by a M\""{o}bius transformation in
complex stereographic coordinates. We identify the \textit{parity-time}
symmetry-breaking phase transition occurring in spin-transfer torque-driven
linear spin systems as a transition between hyperbolic and loxodromic classes
of M\""{o}bius transformations, with the critical point of the transition
corresponding to the parabolic transformation. This establishes the
understanding of non-equilibrium phase transitions as topological transitions
in configuration space.",1610.00762v1
2016-10-21,Spin-torque switching in large size nano-magnet with perpendicular magnetic fields,"DC current induced magnetization reversal and magnetization oscillation was
observed in 500 nm large size Co90Fe10/Cu/Ni80Fe20 pillars. A perpendicular
external field enhanced the coercive field separation between the reference
layer (Co90Fe10) and free layer (Ni80Fe20) in the pseudo spin valve, allowing a
large window of external magnetic field for exploring the free-layer reversal.
The magnetization precession was manifested in terms of the multiple peaks on
the differential resistance curves. Depending on the bias current and applied
field, the regions of magnetic switching and magnetization precession on a
dynamical stability diagram has been discussed in details. Micromagnetic
simulations are shown to be in good agreement with experimental results and
provide insight for synchronization of inhomogenieties in large sized device.
The ability to manipulate spin-dynamics on large size devices could prove
useful for increasing the output power of the spin-transfer nano-oscillators
(STNOs).",1610.06959v1
2017-12-19,Creation of Localized Skyrmion Bubbles in Co/Pt Bilayers using a Spin Valve Nanopillar,"We fabricate devices in which a magnetic nanopillar spin valve makes contact
to a Co/Pt bilayer thin film with perpendicular magnetic anisotropy, in order
to achieve local control of domains in the Co/Pt bilayer underneath the
nanopillar. The goal is to develop the ability to nucleate, detect, and
annihilate magnetic skyrmions in the Co/Pt using spin-polarized currents from
the nanopillar. We demonstrate the ability to distinguish the local behavior of
the Co/Pt film beneath the nanopillar from the extended film and show that the
two can switch independently of each other. This allows us to isolate a
localized domain under the pillar that can be controlled separately from the
rest of the Co/Pt film using applied currents and magnetic fields.
Micromagnetic simulations indicate that this localized domain has skyrmion
symmetry. Our results represent a first step toward controlling
room-temperature skyrmions using localized spin-transfer torque.",1712.07201v1
2018-05-10,Current-Modulated Magnetoplasmonic Devices,"We model the operation and readout sensitivity of two current-modulated
magnetoplasmonic devices which exploit spin Hall effect-like behavior as a
function of their device and material parameters. In both devices, current
pulses are applied to an electrically-isolated stack, containing an active
layer (either a metal with large spin orbit coupling or a topological
insulator) embedded within a plasmonic metal (Au). The first device, composed
of a ferromagnet and the active layer, illustrates a plasmonic readout scheme
for detecting magnetic reorientation driven by current-induced spin transfer
torques. The plasmonic readout of these current-modulated non-volatile states
may facilitate the development of plasmon-based memory or logic devices. The
second device, containing only the active layer, explores the magnetoplasmonic
readout conditions required to directly measure the spin accumulation in these
materials. The estimated thickness-dependent sensitivity agrees with recent
experimental magneto-optical Kerr effect observations.",1805.03926v1
2017-06-08,Equations of Motion and Frequency Dependence of Magnon-Induced Domain Wall Motion,"Spin waves can induce domain wall motion in ferromagnets. We derive the
equations of motion for a transverse domain wall driven by spin waves. Our
calculations show that the magnonic spin-transfer torque does not cause
rotation-induced Walker breakdown. The amplitude of spin waves that are excited
by a localized microwave field depends on the spatial profile of the field and
the excitation frequency. By taking this frequency dependence into account, we
show that a simple one-dimensional model may reproduce much of the puzzling
frequency dependence observed in early numerical studies.",1706.02709v2
2019-03-03,Clockless Spin-based Look-Up Tables with Wide Read Margin,"In this paper, we develop a 6-input fracturable non-volatile Clockless LUT
(C-LUT) using spin Hall effect (SHE)-based Magnetic Tunnel Junctions (MTJs) and
provide a detailed comparison between the SHE-MTJ-based C-LUT and Spin Transfer
Torque (STT)-MTJ-based C-LUT. The proposed C-LUT offers an attractive
alternative for implementing combinational logic as well as sequential logic
versus previous spin-based LUT designs in the literature. Foremost, C-LUT
eliminates the sense amplifier typically employed by using a differential
polarity dual MTJ design, as opposed to a static reference resistance MTJ. This
realizes a much wider read margin and the Monte Carlo simulation of the
proposed fracturable C-LUT indicates no read and write errors in the presence
of a variety of process variations scenarios involving MOS transistors as well
as MTJs. Additionally, simulation results indicate that the proposed C-LUT
reduces the standby power dissipation by 5.4-fold compared to the SRAM-based
LUT. Furthermore, the proposed SHE-MTJ-based C-LUT reduces the area by 1.3-fold
and 2-fold compared to the SRAM-based LUT and the STT-MTJ-based C-LUT,
respectively.",1903.00978v2
2020-03-25,Asymmetric scattering behaviors of spin wave dependent on magnetic vortex chirality,"In this letter, an asymmetric spin wave scattering behaviors caused by vortex
chirality are investigated in cross-shaped ferromagnetic system. In the system,
four scattering behaviors are found, 1) asymmetric skew scattering, depending
on the polarity of vortex core, 2) back scattering (reflection), depending on
the vortex core stiffness, 3) side deflection scattering, depending on
structural symmetry of the vortex circulation, and 4) geometrical scattering,
depending on waveguide structure. The first and second scattering behaviors are
attributed to nonlinear topological magnon spin Hall effect related to magnon
spin-transfer torque effect, which has value for magnonic exploration and
application.",2003.11193v2
2008-06-28,Theory of spin magnetohydrodynamics,"We develop a phenomenological hydrodynamic theory of coherent magnetic
precession coupled to electric currents. Exchange interaction between electron
spin and collective magnetic texture produces two reciprocal effects:
spin-transfer torque on the magnetic order parameter and the Berry-phase gauge
field experienced by the itinerant electrons. The dissipative processes are
governed by three coefficients: the ohmic resistance, Gilbert damping of the
magnetization, and the ""beta coefficient"" describing viscous coupling between
magnetic dynamics and electric current, which stems from spin mistracking of
the magnetic order. We develop general magnetohydrodynamic equations and
discuss the net dissipation produced by the coupled dynamics. The latter in
particular allows us to determine a lower bound on the magnetic-texture
resistivity.",0806.4656v2
2019-07-17,Inhomogeneous domain walls in spintronic nanowires,"In case of a spin-polarized current, the magnetization dynamics in nanowires
are governed by the classical Landau-Lifschitz equation with Gilbert damping
term, augmented by a typically non-variational Slonczewski term. Taking axial
symmetry into account, we study the existence of domain wall type coherent
structure solutions, with focus on one space dimension and spin-polarization,
but our results also apply to vanishing spin-torque term. Using methods from
bifurcation theory for arbitrary constant applied fields, we prove the
existence of domain walls with non-trivial azimuthal profile, referred to as
inhomogeneous. We present an apparently new type of domain wall, referred to as
non-flat, whose approach of the axial magnetization has a certain oscillatory
character. Additionally, we present the leading order mechanism for the
parameter selection of flat and non-flat inhomogeneous domain walls for an
applied field below a threshold, which depends on anisotropy, damping, and
spin-transfer. Moreover, numerical continuation results of all these domain
wall solutions are presented.",1907.07470v2
2021-07-12,Further Evidence for Tidal Spin-Up of Hot Jupiter Host Stars,"For most hot Jupiters around main-sequence Sun-like stars, tidal torques are
expected to transfer angular momentum from the planet's orbit to the star's
rotation. The timescale for this process is difficult to calculate, leading to
uncertainties in the history of orbital evolution of hot Jupiters. We present
evidence for tidal spin-up by taking advantage of recent advances in planet
detection and host-star characterization. We compared the projected rotation
velocities and rotation periods of Sun-like stars with hot Jupiters and
spectroscopically similar stars with (i) wider-orbiting giant planets, and (ii)
less massive planets. The hot Jupiter hosts tend to spin faster than the stars
in either of the control samples. Reinforcing earlier studies, the results
imply that hot Jupiters alter the spins of their host stars while they are on
the main sequence, and that the ages of hot-Jupiter hosts cannot be reliably
determined using gyrochronology.",2107.05759v1
2022-06-15,Giant Rashba electrical control of magnetism in band models,"It is of considerable technological importance to achieve an electrical
control of magnetism of sufficient magnitude. To overcome the in-plane shape
anisotropy, needed is the electrical control of a perpendicular magnetic
anisotropy (PMA). It is known, within a free electron model, the Rashba
spin-orbit coupling provides such a control. Surprisingly, this same Rashba PMA
is enhanced by two to three orders of magnitude when a periodic potential is
added. Usually spin Berry phase physics reflects time dependent magnetic
fields. Here it is shown, within a time independent model, such physics arises
because the Rashba effective magnetic field has texture within the unit cell.
Predicted are electrical controllable band-structure gaps, linear in the
applied electric field $E$, that can result in a truly giant linear PMA. Also
possible is a Peierls mechanism, in which the magnetisation tilts from the
vertical, shifting these gaps to the Fermi level. As a consequence there are
low dissipation electric field driven dynamics, an alternative to the more
dissipative spin torque transfer (STT) effect. The theory requires the
introduction of an intrinsic spin Berry connection $\vec A_s$, an effective
vector potential, and is incompatible with current density functional theories
(DFT).",2206.07399v1
2022-09-19,Unidirectional orbital magnetoresistance in light metal/ferromagnet bilayers,"We report the observation of a unidirectional magnetoresistance (UMR) that
originates from the nonequilibrium orbital momentum induced by an electric
current in a naturally oxidized Cu/Co bilayer. The orbital-UMR scales with the
torque efficiency due to the orbital Rashba-Edelstein effect upon changing the
Co thickness and temperature, reflecting their common origin. We attribute the
UMR to orbital-dependent electron scattering and orbital-to-spin conversion in
the ferromagnetic layer. In contrast to the spin-current induced UMR, the
magnon contribution to the orbital-UMR is absent in thin Co layers, which we
ascribe to the lack of coupling between low energy magnons and orbital current.
The magnon contribution to the UMR emerges in Co layers thicker than about 5
nm, which is comparable to the orbital-to-spin conversion length. Our results
provide insight into orbital-to-spin momentum transfer processes relevant for
the optimization of spintronic devices based on light metals and orbital
transport.",2209.09355v1
2023-04-11,Photon Chiral Memory Effect Stored on Celestial Sphere,"This work introduces the chiral memory effect on the celestial sphere that
measures the permanent change of electromagnetic fields by spin-dependent
processes in bulk. Unlike the conventional memory effect based on the permanent
soft shift in the gauge field itself, it is a permanent change in its spin
angular momentum. The concept underlying the chiral memory (conventional
memory) effect is optical spin torque (optical force) induction in bulk.
Photons and EM radiation carry angular momentum, which is conserved without
interactions. Chiral interactions with matter, medium, curvature, and theories
with parity violation, i.e., axion-QED, transfers spin angular momentum to EM
fields. In nature, such phenomena occur either on EM radiation (chiral memory)
or in the vacuum of QED (vacuum chiral memory). It can be parametrized in terms
of the photon's topological (axial) current at null infinity. To elude the
gauge ambiguity of the topological current, we use the transverse gauge and
show it is the physical part of the current suggested by its cohomology
structure.",2304.05381v1
2018-05-07,Highly efficient spin current generation by the spin Hall effect in Au$_{1-x}$Pt$_x$,"We report very efficient spin current generation by the spin Hall effect in
the alloy Au0.25Pt0.75, which, as determined by two different direct spin-orbit
torque measurements, exhibits a giant internal spin Hall ratio of > 0.58
(anti-damping spin-orbit torque efficiency of ~ 0.35 in bilayers with Co), a
relatively low resistivity of ~ 83 uOhm cm, an exceptionally large spin Hall
conductivity of > 7.0x10^5 ohm^-1 m^-1, and a spin diffusion length of 1.7 nm.
This work establishes Au0.25Pt0.75 as a milestone spin current generator that
provides greater energy efficiency than that yet obtained with other heavy
metals or with the topological insulators Bi2Se3 and (Bi,Se)2Te3. Our findings
should advance spin-orbit torque-based fundamental research and benefit the
development of new fast, efficient spin-orbit torque-driven magnetic memories,
skyrmion and chiral domain wall devices, and microwave and terahertz emitters.",1805.02329v3
2015-04-21,New memory devices based on the proton transfer process,"Memory devices operating due to the fast proton transfer (PT) process are
proposed by means of the first-principles calculations. Writing an information
is performed using the electrostatic potential of the scanning tunneling
microscopy (STM). Reading an information is based on the effect of the local
magnetization induced at the zigzag graphene nanoribbon (Z-GNR) edge -
saturated with oxygen or the hydroxy group - and can be realized with the use
of the giant magnetoresistance (GMR), magnetic tunnel junction (MTJ) or
spin-transfer torque (STT) devices. The energetic barriers for the hop-forward
and -backward processes can be tuned by the distance and potential of the STM
tip. Thus, enabling to tailor the non-volatile logic states. The proposed
system enables very dense packing of the logic cells and could be used in the
random access and flash memory devices.",1504.05607v2
2015-03-12,Current induced torques in structures with ultra-thin IrMn antiferromagnet,"Relativistic current induced torques and devices utilizing antiferromagnets
have been independently considered as two promising new directions in
spintronics research. Here we report electrical measurements of the torques in
structures comprising a $\sim1$~nm thick layer of an antiferromagnet IrMn. The
reduced N\'eel temperature and the thickness comparable to the spin-diffusion
length allow us to investigate the role of the antiferromagnetic order in the
ultra-thin IrMn films in the observed torques. In a Ta/IrMn/CoFeB structure,
IrMn in the high-temperature phase diminishes the torque in the CoFeB
ferromagnet. At low temperatures, the antidamping torque in CoFeB flips sign as
compared to the reference Ta/CoFeB structure, suggesting that IrMn in the
antiferromagnetic phase governs the net torque acting on the ferromagnet. At
low temperatures, current induced torque signatures are observed also in a
Ta/IrMn structure comprising no ferromagnetic layer.",1503.03729v2
2020-05-06,Precessional angular velocity and field strength in the complex octonion space,"The paper aims to apply the octonions to explore the precessional angular
velocities of several particles in the electromagnetic and gravitational
fields. Some scholars utilize the octonions to research the electromagnetic and
gravitational fields. One formula can be derived from the octonion torque,
calculating the precessional angular velocity generated by the gyroscopic
torque. When the octonion force is equal to zero, it is able to deduce the
force equilibrium equation and precession equilibrium equation and so forth.
From the force equilibrium equation, one can infer the angular velocity of
revolution for the particles. Meanwhile, from the precession equilibrium
equation, it is capable of ascertaining the precessional angular velocity
induced by the torque derivative, including the angular velocity of Larmor
precession. Especially, some ingredients of torque derivative are in direct
proportion to the field strengths. The study reveals that the precessional
angular velocity induced by the torque derivative is independent of that
generated by the torque. The precessional angular velocity, induced by the
torque derivative, is relevant to the torque derivative and the spatial
dimension of precessional velocity. It will be of great benefit to
understanding further the precessional angular velocity of the spin angular
momentum.",2005.04000v1
2011-07-05,Parametric oscillator based on non-linear vortex dynamics in low resistance magnetic tunnel junctions,"Radiofrequency vortex spin-transfer oscillators based on magnetic tunnel
junctions with very low resistance area product were investigated. A high power
of excitations has been obtained characterized by a power spectral density
containing a very sharp peak at the fundamental frequency and a series of
harmonics. The observed behaviour is ascribed to the combined effect of spin
transfer torque and Oersted-Amp\`ere field generated by the large applied
dc-current. We furthermore show that the synchronization of a vortex
oscillation by applying a ac bias current is mostly efficient when the external
frequency is twice the oscillator fundamental frequency. This result is
interpreted in terms of a parametric oscillator.",1107.0867v2
2020-11-30,Mechanism of current-assisted Bloch-point wall stabilization for ultra fast dynamics,"Two types of domain walls exist in magnetically soft cylindrical nanowires:
the transverse-vortex wall (TVW) and the Bloch-point wall (BPW). The latter is
expected to prevent the usual Walker breakdown, and thus enable high domain
wall speed. We showed recently [M. Sch\""obitz \etal, Phys. Rev. Lett. 123,
217201 (2019)] that the previously overlooked OErsted field associated with an
electric current is a key in experiments to stabilize the BPW and reach speed
above 600 m/s with spin-transfer. Here, we investigate in detail this situation
with micromagnetic simulations and modeling. The switching of the azimuthal
circulation of the BPW to match that of the OErsted field occurs above a
threshold current scaling with $1/R^3$ ($R$ is the wire radius), through
mechanisms that may involve the nucleation and/or annihilation of Bloch points.
The domain wall dynamics then remains of a below-Walker type, with speed
largely determined by spin-transfer torque alone.",2011.14869v1
2021-10-10,Deterministic generation of skyrmions and antiskyrmions by electric current,"Magnetic skyrmions are nanoscale spin whirlpools that promise breakthroughs
in future spintronic applications. Controlled generation of magnetic skyrmions
by electric current is crucial for this purpose. While previous studies have
demonstrated this operation, the topological charge of the generated skyrmions
is determined by the direction of the external magnetic fields, thus is fixed.
Here, we report the current-induced skyrmions creation in a chiral magnet FeGe
nanostructure by using the \emph{in-situ} Lorentz transmission electron
microscopy. We show that magnetic skyrmions or antiskyrmions can be both
transferred from the magnetic helical ground state simply by controlling the
direction of the current flow at zero magnetic field. The force analysis and
symmetry consideration, backed up by micromagnetic simulations, well explain
the experimental results, where magnetic skyrmions or antiskyrmions are created
due to the edge instability of the helical state in the presence of spin
transfer torque. The on-demand generation of skyrmions and control of their
topology by electric current without the need of magnetic field will enable
novel purely electric-controlled skyrmion devices.",2110.04713v1
2002-11-18,Field dependence of magnetization reversal by spin transfer,"We analyse the effect of the applied field (Happl) on the current-driven
magnetization reversal in pillar-shaped Co/Cu/Co trilayers, where we observe
two different types of transition between the parallel (P) and antiparallel
(AP) magnetic configurations of the Co layers. If Happl is weaker than a rather
small threshold value, the transitions between P and AP are irreversible and
relatively sharp. For Happl exceding the threshold value, the same transitions
are progressive and reversible. We show that the criteria for the stability of
the P and AP states and the experimentally observed behavior can be precisely
accounted for by introducing the current-induced torque of the spin transfer
models in a Landau-Lifschitz-Gilbert equation. This approach also provides a
good description for the field dependence of the critical currents.",0211371v1
2020-09-14,Large field-like torque in amorphous Ru2Sn3 originated from the intrinsic spin Hall effect,"We investigated temperature dependent current driven spin-orbit torques in
magnetron sputtered Ru2Sn3 (4 and 10 nm) /Co20Fe60B20 (5 nm) layered structures
with in-plane magnetic anisotropy. The room temperature damping-like and
field-like spin torque efficiencies of the amorphous Ru2Sn3 films were measured
to be 0.14 +- 0.008 (0.07 +- 0.012) and -0.03 +- 0.006 (-0.20 +- 0.009), for
the 4 (10 nm) films respectively, by utilizing the second harmonic Hall
technique. The large field-like torque in the relatively thicker Ru2Sn3 (10 nm)
thin film is unique compared to the traditional spin Hall materials interfaced
with thick magnetic layers with in-plane magnetic anisotropy which typically
have dominant damping-like and negligible field-like torques. Additionally, the
observed room temperature field-like torque efficiency in Ru2Sn3 (10 nm)/CoFeB
(5 nm) is up to three times larger than the damping-like torque (-0.20 +- 0.009
and 0.07 +- 0.012, respectively) and thirty times larger at 50 K (-0.29 +-
0.014 and 0.009 +- 0.017, respectively). The temperature dependence of the
field-like torques show dominant contributions from the intrinsic spin Hall
effect while the damping-like torques show dominate contributions from the
extrinsic spin Hall effects, skew scattering and side jump. Through macro-spin
calculations, we found that including field-like torques on the order or larger
than the damping-like torque can reduce the switching critical current and
decrease magnetization procession for a perpendicular ferromagnetic layer.",2009.06711v2
2024-02-24,Steerable current-driven emission of spin waves in magnetic vortex pairs,"The efficient excitation of spin waves is a key challenge in the realization
of magnonic devices. We demonstrate the current-driven generation of spin waves
in antiferromagnetically coupled magnetic vortices. We employ time-resolved
scanning transmission X-ray microscopy (TR-STXM) to directly image the emission
of spin waves upon the application of an alternating current flowing directly
through the magnetic stack. Micromagnetic simulations allow us to identify the
origin of the excitation to be the current-driven Oersted field, which in the
present system proves to be orders of magnitude more efficient than the
commonly used excitation via stripline antennas. Our numerical studies also
reveal that the spin-transfer torque can lead to the emission of spin waves as
well, yet only at much higher current amplitudes. By using magnetostrictive
materials, we futhermore demonstrate that the direction of the magnon
propagation can be steered by increasing the excitation amplitude, which
modifies the underlying magnetization profile through an additional anisotropy
in the magnetic layers. The demonstrated methods allow for the efficient and
tunable excitation of spin waves, marking a significant advance in the
generation and control of spin waves in magnonic devices.",2402.15831v1
2020-02-19,Ion-Irradiation-Induced Cobalt/Cobalt Oxide Heterostructures: Printing 3D Interfaces,"Interfaces separating ferromagnetic (FM) layers from non-ferromagnetic layers
offer unique properties due to spin-orbit coupling and symmetry breaking,
yielding effects such as exchange bias, perpendicular magnetic anisotropy,
spin-pumping, spin-transfer torques, conversion between charge and spin
currents and vice-versa. These interfacial phenomena play crucial roles for
magnetic data storage and transfer applications, which require forming FM
nano-structures embedded in non-ferromagnetic matrices. Here, we investigate
the possiblity of creating such nano-structures by ion-irradiation. We study
the effect of lateral confinement on the ion-irradiation-induced reduction of
non-magnetic metal oxides (e.g., antiferro- or paramagnetic) to form
ferromagnetic metals. Our findings are later exploited to form 3-dimensional
magnetic interfaces between Co, CoO and Pt by spatially-selective irradiation
of CoO/Pt multilayers. We demonstrate that the mechanical displacement of the O
atoms plays a crucial role during the reduction from insulating,
non-ferromagnetic cobalt oxides to metallic cobalt. Metallic cobalt yields both
perpendicular magnetic anisotropy in the generated Co/Pt nano-structures, and,
at low temperatures, exchange bias at vertical interfaces between Co and CoO.
If pushed to the limit of ion-irradiation technology, this approach could, in
principle, enable the creation of densely-packed, atomic scale ferromagnetic
point-contact spin-torque oscillator (STO) networks, or conductive channels for
current-confined-path based current perpendicular-to-plane giant
magnetoresistance read-heads.",2002.08090v1
2020-02-06,"Effects of transition-metal spacers on the spin-orbit torques, spin Hall magnetoresistance, and magnetic anisotropy of Pt/Co bilayers","We studied the effect of inserting 0.5 nm-thick spacer layers (Ti, V, Cr, Mo,
W) at the Pt/Co interface on the spin-orbit torques, Hall effect,
magnetoresistance, saturation magnetization, and magnetic anisotropy. We find
that the damping-like spin-orbit torque decreases substantially for all samples
with a spacer layer compared to the reference Pt/Co bilayer, consistently with
the opposite sign of the atomic spin-orbit coupling constant of the spacer
elements relative to Pt. The reduction of the damping-like torque is monotonic
with atomic number for the isoelectronic 3d, 4d, and 5d elements, with the
exception of V that has a stronger effect than Cr. The field-like spin-orbit
torque almost vanishes for all spacer layers irrespective of their composition,
suggesting that this torque predominantly originates at the Pt/Co interface.
The anomalous Hall effect, magnetoresistance, and saturation magnetization are
also all reduced substantially, whereas the sheet resistance is increased in
the presence of the spacer layer. Finally, we evidence a correlation between
the amplitude of the spin-orbit torques, the spin Hall-like magnetoresistance,
and the perpendicular magnetic anisotropy. These results highlight the
significant influence of ultrathin spacer layers on the magnetotransport
properties of heavy metal/ferromagnetic systems.",2002.02162v1
2020-10-28,On the Torque Reversals of Accreting Neutron Stars,"We have extended the analytical model proposed earlier to estimate the inner
disk radius of accreting neutron stars in the strong-propeller (SP) phase, and
the conditions for the transitions between the strong and weak propeller (WP)
phases (Ertan 2017, 2018) to the WP (accretion with spin-down) and the spin-up
(SU) phases, and the torque reversals during the WP/SU transitions. The model
can account for some basic observed properties of these systems that are not
expected in conventional models: (1) accretion on to the star at low X-ray
luminosities and the transitions to the SP phase (no accretion) at critical
accretion rates much lower than the rate required for the spin-up/spin-down
transition, (2) ongoing accretion throughout a large range of accretion rates
while the source is spinning down (WP phase), and (3) transitions between the
spin-up and spin-down phases with comparable torque magnitudes, without
substantial changes in the mass-flow rate. Our results indicate that the
magnitudes of the torques on either side of the torque reversal have a ratio
similar for different systems independently of their spin periods, magnetic
dipole moments and accretion rates during the transitions. Estimated torque
reversal properties in our model are in agreement with the observed torque
reversals of 4U 1626--67.",2010.15035v1
2011-11-16,Review and Analysis of Measurements of the Spin Hall Effect in Platinum,"Several different experimental techniques have been used in efforts to
measure the spin Hall conductivity and the spin Hall angle in Pt samples at
room temperature, with results that disagree by more than a factor of 20, with
spin Hall conductivities from 2.4 x 10^4 to 5.1 x 10^5 [hbar/(2e)] (Ohm-m)^-1
and spin Hall angles from 0.0037 to 0.08. We review this work, and analyze
possible reasons for the discrepancies. We explain that the smallest values for
the spin Hall angle that have been reported, based on measurements of lateral
permalloy/copper/platinum devices, are incorrect because the original analyses
did not properly take into account that copper layers in these devices will
shunt charge current flowing through adjacent platinum wires, thereby greatly
reducing the size of the spin-Hall-related signals. We suggest that differences
between the results for the spin Hall angle found by other experimental
techniques are primarily a consequence of different assumptions about the value
of the spin diffusion length in Pt. We present a new measurement of the spin
diffusion length in Pt within sputtered Pt/permalloy bilayer thin films at room
temperature, finding 1.4 \pm 0.3 nm, a much smaller value than has generally
been assumed previously. With this value for the spin diffusion length, the
previously-discordant results can be brought into much better agreement, with
the result that the spin Hall conductivities are (1.4 - 3.4) x 10^5 [hbar/(2e)]
(Ohm-m)^-1 and the spin Hall angles are greater than 0.05. These values are
sufficiently large that the spin Hall effect in Pt can be used to generate spin
currents and spin transfer torques strong enough for efficient manipulation of
magnetic moments in adjacent ferromagnetic layers.",1111.3702v3
2021-03-19,Systematics and Consequences of Comet Nucleus Outgassing Torques,"Anisotropic outgassing from comets exerts a torque sufficient to rapidly
change the angular momentum of the nucleus, potentially leading to rotational
instability. Here, we use empirical measures of spin changes in a sample of
comets to characterize the torques and to compare them with expectations from a
simple model. Both the data and the model show that the characteristic spin-up
timescale, $\tau_s$, is a strong function of nucleus radius, $r_n$.
Empirically, we find that the timescale for comets (most with perihelion 1 to 2
AU and eccentricity $\sim$0.5) varies as $\tau_s \sim 100 r_n^{2}$, where $r_n$
is expressed in kilometers and $\tau_s$ is in years. The fraction of the
nucleus surface that is active varies as $f_A \sim 0.1 r_n^{-2}$. We find that
the median value of the dimensionless moment arm of the torque is $k_T$ = 0.007
(i.e. $\sim$0.7\% of the escaping momentum torques the nucleus), with weak
($<$3$\sigma$) evidence for a size dependence $k_T \sim 10^{-3} r_n^2$.
Sub-kilometer nuclei have spin-up timescales comparable to their orbital
periods, confirming that outgassing torques are quickly capable of driving
small nuclei towards rotational disruption. Torque-induced rotational
instability likely accounts for the paucity of sub-kilometer short-period
cometary nuclei, and for the pre-perihelion destruction of sungrazing comets.
Torques from sustained outgassing on small active asteroids can rival YORP
torques, even for very small ($\lesssim$1 g s$^{-1}$) mass loss rates. Finally,
we highlight the important role played by observational biases in the measured
distributions of $\tau_s$, $f_A$ and $k_T$.",2103.10577v1
2014-10-20,Topological-Berry-phase-induced spin torque current in a two-dimensional system with generic $k$-linear spin-orbit interaction,"The Berry phase on the Fermi surface and its influence on the conserved spin
current in a two-dimensional system with generic $k$-linear spin-orbit
interaction are investigated. We calculate the response of the effective
conserved spin current to the applied electric field, which is composed of
conventional and spin torque currents, by using the Kubo formula. We find that
the conventional spin current is not determined by the Berry phase effect.
Remarkably, the spin torque Hall current is found to be proportional to the
Berry phase, and the longitudinal spin torque current vanishes because of the
Berry phase effect. When the $k$-linear spin-orbit interaction dominates the
system, the Berry phase on the Fermi surface maintains two invariant
properties. One is that the magnitude of the spin torque current protected by
the Berry phase is unchanged by a small fluctuation of energy dispersion. The
other one is that the change in the direction of the applied electric field
does not change the magnitude of the spin torque current even if the energy
dispersion is not spherically symmetric; i.e., the Berry phase effect has no
dependence on the two-dimensional material orientation. The spin torque current
is a universal value for all $k$-linear systems, such as Rashba, Dresselhaus,
and Rashba-Dresselhaus systems. The topological number attributed to the Berry
phase on the Fermi surface represents the phase of the orbital chirality of
spin in the $k$-linear system. The change in the topological number results in
a phase transition in which the orbital chirality of spin $s_z$ and $-s_z$ is
exchanged. We found that the spin torque current can be experimentally
measured.",1410.5289v1
2005-01-12,Current induced magnetization switching in exchange biased spin-valves for CPP-GMR heads,"In contrast to earlier studies performed on simple Co/Cu/Co sandwiches, we
have investigated spin transfer effects in complex spin-valve pillars with a
diameter of 130nm developed for current-perpendicular to the plane (CPP)
magneto-resistive heads. The structure of the samples included an exchange
biased synthetic pinned layer and a free layer both laminated by insertion of
several ultrathin Cu layers. Despite the small thickness of the polarizing
layer, our results show that the free layer can be switched between the
parallel (P) and the antiparallel (AP) states by applying current densities of
the order of 10^7 A/cm^2. A strong asymmetry is observed between the two
critical currents IcAP-P and IcP-AP, as predicted by the model of Slonczewski
model. Thanks to the use of exchange biased structures, the stability phase
diagrams could be obtained in the four quadrants of the (H, I) plan. The
critical lines derived from the magnetoresistance curves measured with
different sense currents, and from the resistance versus current curves
measured for different applied fields, match each other very well. The main
features of the phase diagrams can be reproduced by investigating the stability
of the solutions of the Landau Lifshitz Gilbert equation including spin torque
term within a macrospin model. A spin-transfer saturation effect was observed
in the positive currents range. We attribute it to a de-depolarization effect
which appears as a consequence of the asymmetric heating of the pillars, whose
top and the bottom leads are made of different materials.",0501281v1
2009-01-07,Predictions of polarized dust emission from interstellar clouds: spatial variations in the efficiency of radiative torque alignment,"Polarization carries information about the magnetic fields in interstellar
clouds. The observations of polarized dust emission are used to study the role
of magnetic fields in the evolution of molecular clouds and the initial phases
of star-formation. We study the grain alignment with realistic simulations,
assuming the radiative torques to be the main mechanism that spins the grains
up. The aim is to study the efficiency of the grain alignment as a function of
cloud position and to study the observable consequences of these spatial
variations. Our results are based on the analysis of model clouds derived from
MHD simulations. The continuum radiative transfer problem is solved with Monte
Carlo methods to estimate the 3D distribution of dust emission and the
radiation field strength affecting the grain alignment. We also examine the
effect of grain growth in cores. We are able to reproduce the results of Cho &
Lazarian using their assumptions. However, the anisotropy factor even in the 1D
case is lower than their assumption of $\gamma = 0.7$, and thus we get less
efficient radiative torques. Compared with our previous paper, the polarization
degree vs. intensity relation is steeper because of less efficient grain
alignment within dense cores. Without grain growth, the magnetic field of the
cores is poorly recovered above a few $A_{\rm V}$. If grain size is doubled in
the cores, the polarization of dust emission can trace the magnetic field lines
possibly up to $A_{\rm V} \sim 10$ magnitudes. However, many of the prestellar
cores may be too young for grain coagulation to play a major role. The
inclusion of direction dependent radiative torque efficiency weakens the
alignment. Even with doubled grain size, we would not expect to probe the
magnetic field past a few magnitudes in $A_{\rm V}$.",0901.0831v4
2009-04-27,Effect of resistance feedback on spin torque-induced switching of nanomagnets,"In large magnetoresistance devices spin torque-induced changes in resistance
can produce GHz current and voltage oscillations which can affect magnetization
reversal. In addition, capacitive shunting in large resistance devices can
further reduce the current, adversely affecting spin torque switching. Here, we
simultaneously solve the Landau-Lifshitz-Gilbert equation with spin torque and
the transmission line telegrapher's equations to study the effects of
resistance feedback and capacitance on magnetization reversal of both spin
valves and magnetic tunnel junctions. While for spin valves parallel (P) to
anti-parallel (AP) switching is adversely affected by the resistance feedback
due to saturation of the spin torque, in low resistance magnetic tunnel
junctions P-AP switching is enhanced. We study the effect of resistance
feedback on the switching time of MTJ's, and show that magnetization switching
is only affected by capacitive shunting in the pF range.",0904.4159v2
2013-04-17,Angular dependence and symmetry of Rashba spin torque in ferromagnetic heterostructures,"In a ferromagnetic heterostructure, the interplay between a Rashba spin-orbit
coupling and an exchange field gives rise to a current-driven spin torque. In a
realistic device setup, we investigate the Rashba spin torque in the diffusive
regime and report two major findings: (i) a nonvanishing torque exists at the
edges of the device even when the magnetization and effective Rashba field are
aligned; (ii) anisotropic spin relaxation rates driven by the Rashba spin-orbit
coupling assign the spin torque a general expression ${\bm
T}=T^y_{\para}(\theta){\bm m}\times(\hat{\bm y}\times{\bm
m})+T^y_{\bot}(\theta)\hat{\bm y}\times{\bm m}+T^z_{\para}(\theta){\bm
m}\times(\hat{\bm z}\times{\bm m})+T^z_{\bot}(\theta)\hat{\bm z}\times{\bm m}$,
where the coefficients $T_{\para,\bot}^{y,z}$ depend on the magnetization
direction. Our results agree with recent experiments.",1304.4823v1
2014-08-27,Fluctuation Theorem for a Small Engine and Magnetization Switching by Spin Torque,"We consider a reversal of the magnetic moment of a nano-magnet by the
fluctuating spin-torque induced by a non-equilibrium current of electron spins.
This is an example of the problem of the escape of a particle from a metastable
state subjected to a fluctuating non-conservative force. The spin-torque is the
non-conservative force and its fluctuations are beyond the description of the
fluctuation-dissipation theorem. We estimate the joint probability distribution
of work done by the spin torque and the Joule heat generated by the current,
which satisfies the fluctuation theorem for a small engine. We predict a
threshold voltage above which the spin-torque shot noise induces probabilistic
switching events and below which such events are blocked. We adopt the theory
of the full-counting statistics under the adiabatic pumping of spin angular
momentum. This enables us to account for the backaction effect, which is
crucial to maintain consistency with the fluctuation theorem.",1408.6588v1
2014-12-18,Intrinsic Spin Torque Without Spin-Orbit Coupling,"We derive an intrinsic contribution to the non-adiabatic spin torque for
non-uniform magnetic textures. It differs from previously considered
contributions in several ways and can be the dominant contribution in some
models. It does not depend on the change in occupation of the electron states
due to the current flow but rather is due to the perturbation of the electronic
states when an electric field is applied. Therefore it should be viewed as
electric-field-induced rather than current-induced. Unlike previously reported
non-adiabatic spin torques, it does not originate from extrinsic relaxation
mechanisms nor spin-orbit coupling. This intrinsic non-adiabatic spin torque is
related by a chiral connection to the intrinsic spin-orbit torque that has been
calculated from the Berry phase for Rashba systems.",1412.6123v2
2018-05-25,Accretion And Propeller Torque In The Spin-down Phase Of Neutron Stars: The Case Of Transitional Millisecond Pulsar PSR J1023+0038,"The spin-down rate of PSR J1023+0038, one of the three confirmed transitional
millisecond pulsars, was measured in both radio pulsar (RMSP) and X-ray pulsar
(LMXB) states. The spin-down rate in the LMXB state is only about 27 % greater
than in the RMSP state (Jaodand et al. 2016). The inner disk radius, r_in,
obtained recently by Ertan (2017) for the propeller phase, which is close to
the co-rotation radius, r_co, and insensitive to the mass-flow rate, can
explain the observed torques together with the X-ray luminosities, Lx . The
X-ray pulsar and radio pulsar states correspond to accretion with spin-down
(weak propeller) and strong propeller situations respectively. Several times
increase in the disk mass-flow rate takes the source from the strong propeller
with a low Lx to the weak propeller with a higher Lx powered by accretion on to
the star. The resultant decrease in r_in increases the magnetic torque
slightly, explaining the observed small increase in the spin-down rate. We have
found that the spin-up torque exerted by accreting material is much smaller
than the magnetic spin-down torque exerted by the disk in the LMXB state.",1805.10091v1
2017-02-17,Spin-orbit torque in MgO/CoFeB/Ta/CoFeB/MgO symmetric structure with interlayer antiferromagnetic coupling,"Spin current generated by spin Hall effect in the heavy metal would diffuse
up and down to adjacent ferromagnetic layers and exert torque on their
magnetization, called spin-orbit torque. Antiferromagnetically coupled
trilayers, namely the so-called synthetic antiferromagnets (SAF), are usually
employed to serve as the pinned layer of spintronic devices based on spin
valves and magnetic tunnel junctions to reduce the stray field and/or increase
the pinning field. Here we investigate the spin-orbit torque in
MgO/CoFeB/Ta/CoFeB/MgO perpendicularly magnetized multilayer with interlayer
antiferromagnetic coupling. It is found that the magnetization of two CoFeB
layers can be switched between two antiparallel states simultaneously. This
observation is replicated by the theoretical calculations by solving
Stoner-Wohlfarth model and Landau-Lifshitz-Gilbert equation. Our findings
combine spin-orbit torque and interlayer coupling, which might advance the
magnetic memories with low stray field and low power consumption.",1702.05331v1
2019-01-24,Non-equilibrium spin density and spin-orbit torque in three dimensional topological insulators - antiferromagnet heterostructure,"We study the behavior of non-equilibrium spin density and spin-orbit torque
in a topological insulator - antiferromagnet heterostructure. Unlike
ferromagnetic heterostructures where Dirac cone is gapped due to time-reversal
symmetry breaking, here the Dirac cone is preserved. We demonstrate the
existence of a staggered spin density corresponding to a damping like torque,
which is quite robust against the scalar impurity, when the transport energy is
in the topological insulator surface energy regime. We show the contribution to
the non-equilibrium spin density due to both surface and bulk topological
insulator bands. Finally, we show that the torques in topological
insulator-antiferromagnet heterostructure exhibit an angular dependence that is
consistent with the standard spin-orbit torque obtained in Rashba system with
some additional nonlinear effects arising from the interfacial coupling.",1901.08314v1
2019-08-07,Interfacial contributions to spin-orbit torque and magnetoresistance in ferromagnet/heavy-metal bilayers,"The thickness dependence of spin-orbit torque and magnetoresistance in
ferromagnet/heavy-metal bilayers is studied using the first-principles
non-equilibrium Green's function formalism combined with the Anderson disorder
model. A systematic expansion in orthogonal vector spherical harmonics is used
for the angular dependence of the torque. The damping-like torque in Co/Pt and
Co/Au bilayers can be described as a sum of the spin-Hall contribution, which
increases with thickness in agreement with the spin-diffusion model, and a
comparable interfacial contribution. The magnetoconductance in the plane
perpendicular to the current in Co/Pt bilayers is of the order of a conductance
quantum per interfacial atom, exceeding the prediction of the spin-Hall model
by more than an order of magnitude. This suggests that the ""spin-Hall
magnetoresistance,"" similarly to the damping-like torque, has a large
interfacial contribution unrelated to the spin-Hall effect.",1908.02680v2
2020-10-13,Effects of spin-orbit torque on the ferromagnetic and exchange spin wave modes in ferrimagnetic CoGd alloy,"We use micro-focus Brillouin light scattering spectroscopy to study the
effects of spin-orbit torque on thermal spin waves in almost angular-momentum
compensated ferrimagnetic CoGd alloy films. The spin-orbit torque is produced
by the electric current flowing in the Pt layer adjacent to CoGd. Both the
ferromagnetic and the exchange modes are detected in our measurements. The
intensity and the linewidth of the ferromagnetic mode are modified by the
spin-orbit torque. In contrast, the properties of the exchange mode are
unaffected by the spin-orbit torque. We also find that the frequencies and the
linewidths of both modes are significantly modified by Joule heating, due to
the strong temperature dependence of the magnetic properties of CoGd in the
vicinity of angular momentum compensation point. Our results provide insight
into the mechanisms that can enable the implementation of sub-THz magnetic
nano-oscillators based on ferrimagnetic materials, as well as related effects
in antiferromagnets.",2010.06615v1
2020-11-27,Laser-induced torques in spin spirals,"We investigate laser-induced torques in magnetically non-collinear
ferromagnets with a spin-spiral magnetic structure using \textit{ab-initio}
calculations. Since spin-spirals may be used to approximate the magnetization
gradients locally in domain walls and skyrmions, our method may be used to
obtain the laser-induced torques in such objects from a multiscale approach.
Employing the generalized Bloch-theorem we obtain the electronic structure
computationally efficiently. We employ our method to assess the laser-induced
torques in bcc Fe, hcp Co, and L$_{1}0$ FePt when a spin-spiral magnetic
structure is imposed. We find that the laser-induced torques in these
magnetically noncollinear systems may be orders of magnitude larger than those
in the corresponding magnetically collinear systems and that they exist both
for linearly and circularly polarized light. This result suggests that
laser-induced torques driven by noncollinear magnetic order or by magnetic
fluctuations may contribute significantly to processes in ultrafast magnetism.",2011.13707v2
2017-12-19,Neutron Star Dynamics under Time Dependent External Torques,"The two component model of neutron star dynamics describing the behaviour of
the observed crust coupled to the superfluid interior has so far been applied
to radio pulsars for which the external torques are constant on dynamical
timescales. We recently solved this problem under arbitrary time dependent
external torques. Our solutions pertain to internal torques that are linear in
the rotation rates, as well as to the extremely non-linear internal torques of
the vortex creep model. Two-component models with linear or nonlinear internal
torques can now be applied to magnetars and to neutron stars in binary systems,
with strong variability and timing noise. Time dependent external torques can
be obtained from the observed spin-down (or spin-up) time series,
$\dot{\Omega}(t)$.",1712.07119v1
2016-10-12,Microscopic derivation of magnon spin current in a topological insulator/ferromagnet heterostructure,"We investigate a spin-electricity conversion effect in a topological
insulator/ferromagnet heterostructure. In the spin-momentum-locked surface
state, an electric current generates nonequilibrium spin accumulation, which
causes a spin-orbit torque that acts on the ferromagnet. When spins in the
ferromagnet are completely parallel to the accumulated spin, this spin-orbit
torque is zero. In the presence of spin excitations, however, a coupling
between magnons and electrons enables us to obtain a nonvanishing torque. In
this paper, we consider a model of the heterostructure in which a
three-dimensional magnon gas is coupled with a two-dimensional massless Dirac
electron system at the interface. We calculate the torque induced by an
electric field, which can be interpreted as a magnon spin current, up to the
lowest order of the electron-magnon interaction. We derive the expressions for
high and low temperatures and estimate the order of magnitude of the induced
spin current for realistic materials at room temperature.",1610.03636v3
2020-03-17,Experimental evidence of spin-orbit torque from metallic interfaces,"Spin currents can modify the magnetic state of ferromagnetic ultrathin films
through spin-orbit torque. They may be generated by means of spin-orbit
interaction by either bulk or interfacial phenomena. Electrical transport
measurements reveal a six-fold increase of the spin-orbit torque accompanied by
a drastic reduction of the spin Hall magnetoresistance upon the introduction of
a Cu interlayer in a Pt/Cu/Co/Pt structure with perpendicular magnetic
anisotropy. We analyze the dependence of the spin Hall magnetoresistance with
the thickness of the interlayer in the frame of a drift diffusion model that
provides information on the expected spin currents and spin accumulations in
the system. The results demonstrate that the major responsible of both effects
is spin memory loss at the interface. The enhancement of the spin-orbit torque
when introducing an interlayer opens the possibility to design more effient
spintronic devices based on materials that are cheap and abundant such as
copper.",2003.07677v1
2021-09-15,Observation of unconventional spin polarization induced spin orbit torque in L1$_2$-ordered antiferromagnetic Mn$_3$Pt thin films,"Non-collinear antiferromagnets exhibits richer magneto-transport properties
due to the topologically nontrivial spin structure they possess compared to
conventional nonmagnetic materials, which allows us to manipulate the
charge-spin conversion more freely by taking advantage of the chirality. In
this work, we explore the unconventional spin orbit torque of L1$_2$-ordered
Mn$_3$Pt with a triangular spin structure. We observed an unconventional spin
orbit torque along the $\mathbf{x}$-direction for the (001)-oriented L1$_2$
Mn$_3$Pt, and found that it has a unique sign reversal behavior relative to the
crystalline orientation. This generation of unconventional spin orbit torque
for L1$_2$-ordered Mn$_3$Pt can be interpreted as stemming from the magnetic
spin Hall effect. This report help clarify the correlation between the
topologically nontrivial spin structure and charge-spin conversion in
non-collinear antiferromagnets.",2109.07256v2
2024-01-17,Spin Orbit Torque on a Curved Surface,"We provide a general formulation of the spin-orbit coupling on a 2D curved
surface. Considering the wide applicability of spin-orbit effect in
spinor-based condensed matter physics, a general spin-orbit formulation could
aid the study of spintronics, Dirac graphene, topological systems, and quantum
information on curved surfaces. Particular attention is then devoted to the
development of an important spin-orbit quantity known as the spin-orbit torque.
As devices trend smaller in dimension, the physics of local geometries on
spin-orbit torque, hence spin and magnetic dynamics shall not be neglected. We
derived the general expression of a spin-orbit anisotropy field for the curved
surfaces and provided explicit solutions in the special contexts of the
spherical, cylindrical and flat coordinates. Our expressions allow spin-orbit
anisotropy fields and hence spin-orbit torque to be computed over the entire
surfaces of devices of any geometry.",2401.08966v1
2016-07-01,Size-dependence of nanosecond-scale spin-torque switching in perpendicularly magnetized tunnel junctions,"We time-resolve the spin-transfer-torque-induced switching in perpendicularly
magnetized tunnel junctions of diameters from 50 to 250 nm in the thermally
activated regime. When the field and the spin-torque concur to favor the P to
AP transition, the reversal yields monotonic resistance ramps that can be
interpreted as a domain wall propagation through the device at velocities of 17
to 30 nm/ns; smaller cells switch hence faster. When the field hinders the P to
AP transition, the switching is preceded by repetitive switching attempts,
during which the resistance transiently increases until successful reversal
occurs. At 50 nm, the P to AP switching proceeds reproducibly in 3 ns, with a
monotonic increase of the device resistance. In the reverse transition (AP to
P), several reversal paths are possible even in the smallest junctions.
Besides, the non uniform nature of the response seems still present at
nanoscale, with sometimes electrical signatures of strong disorder during the
reversal. The AP to P transition is preceded by a strong instability of the AP
state in devices above 100 nm. The resistance becomes extremely agitated before
switching to P in a path yielding a slow (20-50 ns) irregular increase of the
conductance with variability. Unreversed bubbles of 60 nm can persist a few
microseconds in the largest junctions. The complexity of the AP to P switching
is reduced but not suppressed when the junctions are downsized below 60 nm. The
instability of the initial AP state is no longer detected but the other
features remain. In the smallest junctions (50 nm) we occasionally observe much
faster (sub-1 ns) switching events. We discuss the origin of the switching
asymmetry and its size dependence, with an emphasis on the role of the non
uniformities of the stray field emanating from the reference layers, which
affects the zones in which nucleation is favored.",1607.00260v1
2022-11-29,Random Bitstream Generation using Voltage-Controlled Magnetic Anisotropy and Spin Orbit Torque Magnetic Tunnel Junctions,"Probabilistic computing using random number generators (RNGs) can leverage
the inherent stochasticity of nanodevices for system-level benefits. The
magnetic tunnel junction (MTJ) has been studied as an RNG due to its
thermally-driven magnetization dynamics, often using spin transfer torque (STT)
current amplitude to control the random switching of the MTJ free layer
magnetization, here called the stochastic write method. There are additional
knobs to control the MTJ-RNG, including voltage-controlled magnetic anisotropy
(VCMA) and spin orbit torque (SOT), and there is need to systematically study
and compared these methods. We build an analytical model of the MTJ to
characterize using VCMA and SOT to generate random bit streams. The results
show that both methods produce high quality, uniformly distributed bitstreams.
Biasing the bitstreams using either STT current or an applied magnetic field
shows an approximately sigmoidal distribution vs. bias amplitude for both VCMA
and SOT, compared to less sigmoidal for stochastic write for the same
conditions. The energy consumption per sample is calculated to be 0.1 pJ (SOT),
1 pJ (stochastic write), and 20 pJ (VCMA), revealing the potential energy
benefit of using SOT and showing using VCMA may require higher damping
materials. The generated bitstreams are then applied to two example tasks:
generating an arbitrary probability distribution using the Hidden Correlation
Bernoulli Coins method and using the MTJ-RNGs as stochastic neurons to perform
simulated annealing in a Boltzmann machine, where both VCMA and SOT methods
show the ability to effectively minimize the system energy with small delay and
low energy. These results show the flexibility of the MTJ as a true RNG and
elucidate design parameters for optimizing the device operation for
applications.",2211.16588v1
2023-11-27,Magnetic Tunnel Junction Random Number Generators Applied to Dynamically Tuned Probability Trees Driven by Spin Orbit Torque,"Perpendicular magnetic tunnel junction (pMTJ)-based true-random number
generators (RNG) can consume orders of magnitude less energy per bit than CMOS
pseudo-RNG. Here, we numerically investigate with a macrospin
Landau-Lifshitz-Gilbert equation solver the use of pMTJs driven by spin-orbit
torque to directly sample numbers from arbitrary probability distributions with
the help of a tunable probability tree. The tree operates by dynamically
biasing sequences of pMTJ relaxation events, called 'coinflips', via an
additional applied spin-transfer-torque current. Specifically, using a single,
ideal pMTJ device we successfully draw integer samples on the interval 0,255
from an exponential distribution based on p-value distribution analysis. In
order to investigate device-to-device variations, the thermal stability of the
pMTJs are varied based on manufactured device data. It is found that while
repeatedly using a varied device inhibits ability to recover the probability
distribution, the device variations average out when considering the entire set
of devices as a 'bucket' to agnostically draw random numbers from. Further, it
is noted that the device variations most significantly impact the highest level
of the probability tree, iwth diminishing errors at lower levels. The devices
are then used to draw both uniformly and exponentially distributed numbers for
the Monte Carlo computation of a problem from particle transport, showing
excellent data fit with the analytical solution. Finally, the devices are
benchmarked against CMOS and memristor RNG, showing faster bit generation and
significantly lower energy use.",2311.16345v1
2004-07-07,Roles of non-equilibrium conduction electrons on magnetization dynamics of ferromagnets,"The mutual dependence of spin-dependent conduction and magnetization dynamics
of ferromagnets provides the key mechanisms in various spin-dependent
phenomena. We compute the response of the conduction electron spins to a
spatial and time varying magnetization ${\bf M} ({\bf r},t)$ within the
time-dependent semiclassical transport theory. We show that the induced
non-equilibrium conduction spin density in turn generates four spin torques
acting on the magnetization--with each torque playing different roles in
magnetization dynamics. By comparing with recent theoretical models, we find
that one of these torques that has not been previously identified is crucial to
consistently interpret experimental data on domain wall motion.",0407174v2
2018-12-18,Thermal gradient driven domain wall dynamics,"The issue of whether a thermal gradient acts like a magnetic field or an
electric current in the domain wall (DW) dynamics is investigated. Broadly
speaking, magnetization control knobs can be classified as energy-driving or
angular-momentum driving forces. DW propagation driven by a static magnetic
field is the best-known example of the former in which the DW speed is
proportional to the energy dissipation rate, and the current-driven DW motion
is an example of the latter. Here we show that DW propagation speed driven by a
thermal gradient can be fully explained as the angular momentum transfer
between thermally generated spin current and DW. We found DW-plane rotation
speed increases as DW width decreases. Both DW propagation speed along the wire
and DW-plane rotation speed around the wire decrease with the Gilbert damping.
These facts are consistent with the angular momentum transfer mechanism, but
are distinct from the energy dissipation mechanism. We further show that
magnonic spin-transfer torque (STT) generated by a thermal gradient has both
damping-like and field-like components. By analyzing DW propagation speed and
DW-plane rotation speed, the coefficient ( \b{eta}) of the field-like STT
arising from the non-adiabatic process, is obtained. It is found that \b{eta}
does not depend on the thermal gradient; increases with uniaxial anisotropy
K_(||) (thinner DW); and decreases with the damping, in agreement with the
physical picture that a larger damping or a thicker DW leads to a better
alignment between the spin-current polarization and the local magnetization, or
a better adiabaticity.",1812.07244v2
2022-05-25,Transfer of angular momentum of guided light to an atom with an electric quadrupole transition near an optical nanofiber,"We study the transfer of angular momentum of guided photons to a two-level
atom with an electric quadrupole transition near an optical nanofiber. We show
that the generation of the axial orbital torque of the driving guided field on
the atom is governed by the internal-state selection rules for the quadrupole
transition and by the angular momentum conservation law with the photon angular
momentum given in the Minkowski formulation. We find that the torque depends on
the photon angular momentum, the change in the angular momentum of the atomic
internal state, and the quadrupole-transition Rabi frequency. We calculate
numerically the torques for the quadrupole transitions between the sublevel
$M=2$ of the hyperfine-structure level $5S_{1/2}F=2$ and the sublevels $M'=0$,
1, 2, 3, and 4 of the hyperfine-structure level $4D_{5/2}F'=4$ of a $^{87}$Rb
atom. We show that the absolute value of the torque for the higher-order mode
HE$_{21}$ is larger than that of the torque for the fundamental mode HE$_{11}$
except for the case $M'-M=2$, where the torque for the mode HE$_{21}$ is
vanishing.",2205.12440v1
2018-06-20,Current-induced modulation of interfacial Dzyaloshinskii-Moriya interaction,"The Dzyaloshinskii-Moriya (DM) interaction is an antisymmetric exchange
interaction that is responsible for the emergence of chiral magnetism. The
origin of the DM interaction, however, remains to be identified albeit the
large number of studies reported on related effects. It has been recently
suggested that the DM interaction is equivalent to an equilibrium spin current
density originating from spin-orbit coupling, an effect referred to as the spin
Doppler effect. The model predicts that the DM interaction can be controlled by
spin current injected externally. Here we show that the DM exchange constant
($D$) in W/CoFeB based heterostructures can be modulated with external current
passed along the film plane. At higher current, $D$ decreases with increasing
current, which we infer is partly due to the adiabatic spin transfer torque. At
lower current, $D$ increases linearly with current regardless of the polarity
of current flow. The rate of increase in $D$ with the current density agrees
with that predicted by the model based on the spin Doppler effect. These
results imply that the DM interaction at the HM/FM interface partly originates
from an equilibrium interface spin (polarized) current which can be modulated
externally.",1806.07746v2
2021-07-08,"Magnetism, symmetry and spin transport in van der Waals layered systems","The discovery of an ever increasing family of atomic layered magnetic
materials, together with the already established vast catalogue of strong
spin-orbit coupling (SOC) and topological systems, calls for some guiding
principles to tailor and optimize novel spin transport and optical properties
at their interfaces. Here we focus on the latest developments in both fields
that have brought them closer together and make them ripe for future fruitful
synergy. After outlining fundamentals on van der Waals (vdW) magnetism and SOC
effects, we discuss how their coexistence, manipulation and competition could
ultimately establish new ways to engineer robust spin textures and drive the
generation and dynamics of spin current and magnetization switching in 2D
materials-based vdW heterostructures. Grounding our analysis on existing
experimental results and theoretical considerations, we draw a prospective
analysis about how intertwined magnetism and spin-orbit torque (SOT) phenomena
combine at interfaces with well-defined symmetries, and how this dictates the
nature and figures-of-merit of SOT and angular momentum transfer. This will
serve as a guiding role in designing future non-volatile memory devices that
utilize the unique properties of 2D materials with the spin degree of freedom.",2107.03763v2
2022-09-03,Controlling 3D spin textures by manipulating sign and amplitude of interlayer DMI with electrical current,"The recently discovered interlayer Dzyaloshinskii-Moriya interaction (IL-DMI)
in multilayers with perpendicular magnetic anisotropy favors the canting of
spins in the in-plane direction and could thus enable new exciting spin
textures such as Hopfions in continuous multilayer films. A key requirement is
to control the IL-DMI and so in this study, the influence of an electric
current on the IL-DMI is investigated by out-of-plane hysteresis loops of the
anomalous Hall effect under applied in-plane magnetic fields. The direction of
the in-plane field is varied to obtain a full azimuthal dependence, which
allows us to quantify the effect on the IL-DMI. We observe a shift in the
azimuthal dependence of the IL-DMI with increasing current, which can be
understood from the additional in-plane symmetry breaking introduced by the
current flow. Using an empirical model of two superimposed cosine functions we
demonstrate the presence of a current-induced term that linearly increases the
IL-DMI in the direction of current flow. With this, a new easily accessible
possibility to manipulate 3D spin textures by current is realized. As most
spintronic devices employ spin-transfer or spin-orbit torques to manipulate
spin textures, the foundation to implement current-induced IL-DMI into
thin-film devices is broadly available.",2209.01450v1
2019-02-10,Low Barrier Magnet Design for Efficient Hardware Binary Stochastic Neurons,"Binary stochastic neurons (BSN's) form an integral part of many machine
learning algorithms, motivating the development of hardware accelerators for
this complex function. It has been recognized that hardware BSN's can be
implemented using low barrier magnets (LBM's) by minimally modifying
present-day magnetoresistive random access memory (MRAM) devices. A crucial
parameter that determines the response of these LBM based BSN designs is the
\emph{correlation time} of magnetization, $\tau_c$. In this letter, we show
that for magnets with low energy barriers ($\Delta \approx k_BT$ and below),
circular disk magnets with in-plane magnetic anisotropy (IMA) lead to $\tau_c$
values that are two orders of magnitude smaller compared to $\tau_c$ for
magnets having perpendicular magnetic anisotropy (PMA) and provide analytical
descriptions. We show that this striking difference in $\tau_c$ is due to a
precession-like fluctuation mechanism that is enabled by the large
demagnetization field in IMA magnets. We provide a detailed energy-delay
performance evaluation of previously proposed BSN designs based on
Spin-Orbit-Torque (SOT) MRAM and Spin-Transfer-Torque (STT) MRAM employing low
barrier circular IMA magnets by SPICE simulations. The designs exhibit sub-ns
response times leading to energy requirements of $\sim$a few fJ to evaluate the
BSN function, orders of magnitude lower than digital CMOS implementations with
a much larger footprint. While modern MRAM technology is based on PMA magnets,
results in this paper suggest that low barrier circular IMA magnets may be more
suitable for this application.",1902.03650v2
2020-03-28,Acoustic Wave Induced FMR Assisted Spin-Torque Switching of Perpendicular MTJs with Anisotropy Variation,"We have investigated Surface Acoustic Wave (SAW) induced ferromagnetic
resonance (FMR) assisted Spin Transfer Torque (STT) switching of perpendicular
MTJ (p-MTJ) with inhomogeneities using micromagnetic simulations that include
the effect of thermal noise. With suitable frequency excitation, the SAW can
induce ferromagnetic resonance in magnetostrictive materials, and the
magnetization can precesses in a cone with high deflection from the
perpendicular direction. With incorporation of inhomogeneity via lateral
anisotropy variation as well as room temperature thermal noise, the
magnetization precession in different gains can be significantly incoherent.
Interestingly, the precession in different grains are found to be in phase,
even though the precession amplitude (angle of deflection from the
perpendicular direction) vary across grains of different anisotropy.
Nevertheless, the high mean deflection angle can complement the STT switching
by reducing the STT current significantly; even though the applied stress
induced change in anisotropy is much lower than the total anisotropy barrier.
This work indicates that SAW assisted switching can improve energy efficiency
while being scalable to very small dimensions, which is technologically
important for STT-RAM and elucidates the physical mechanism for the potential
robustness of this paradigm in realistic scenarios with thermal noise and
material inhomogeneity",2003.12903v1
2019-10-02,Stability and dynamics of in-plane skyrmions in collinear ferromagnets,"We study the emergence and dynamics of in-plane skyrmions in collinear
ferromagnetic heterostructures. We present a minimal energy model for this
class of magnetic textures, determine the crystal symmetries compatible with it
and propose material candidates, based on symmetries only, for the observation
of these topological solitons. We calculate exact solutions of the energy model
for in-plane skyrmions in the absence of dipolar interactions at critical
coupling, the latter defined by the relations $H = K$ and $D = \sqrt{AK}$ for
the strength of the external magnetic field and the Dzyaloshinskii coupling
constant, respectively, with $K$ and $A$ being the anisotropy constant and the
exchange stiffness of the material. Through micromagnetic simulations, we
demonstrate the possibility of in-plane skyrmion production via i) the motion
of domain walls through a geometrical constriction and ii) shedding from a
magnetic impurity driven both by spin-transfer torques. In-plane skyrmion
dynamics triggered by spin-orbit torques are also investigated analytically and
numerically. Our findings point towards the possibility of designing racetracks
for in-plane skyrmions, whose speed could be tuned by adjusting the angle
between the charge current and the uniform background magnetization; in
particular, the speed is maximum for currents parallel to the easy axis and
becomes zero for currents transverse to it.",1910.00987v2
2020-12-08,DeepNVM++: Cross-Layer Modeling and Optimization Framework of Non-Volatile Memories for Deep Learning,"Non-volatile memory (NVM) technologies such as spin-transfer torque magnetic
random access memory (STT-MRAM) and spin-orbit torque magnetic random access
memory (SOT-MRAM) have significant advantages compared to conventional SRAM due
to their non-volatility, higher cell density, and scalability features. While
previous work has investigated several architectural implications of NVM for
generic applications, in this work we present DeepNVM++, a framework to
characterize, model, and analyze NVM-based caches in GPU architectures for deep
learning (DL) applications by combining technology-specific circuit-level
models and the actual memory behavior of various DL workloads. We present both
iso-capacity and iso-area performance and energy analysis for systems whose
last-level caches rely on conventional SRAM and emerging STT-MRAM and SOT-MRAM
technologies. In the iso-capacity case, STT-MRAM and SOT-MRAM provide up to
3.8x and 4.7x energy-delay product (EDP) reduction and 2.4x and 2.8x area
reduction compared to conventional SRAM, respectively. Under iso-area
assumptions, STT-MRAM and SOT-MRAM provide up to 2x and 2.3x EDP reduction and
accommodate 2.3x and 3.3x cache capacity when compared to SRAM, respectively.
We also perform a scalability analysis and show that STT-MRAM and SOT-MRAM
achieve orders of magnitude EDP reduction when compared to SRAM for large cache
capacities. Our comprehensive cross-layer framework is demonstrated on
STT-/SOT-MRAM technologies and can be used for the characterization, modeling,
and analysis of any NVM technology for last-level caches in GPUs for DL
applications.",2012.04559v1
2008-02-25,Current-induced spin torques in III-V ferromagnetic semiconductors,"We formulate a theory of current-induced spin torques in inhomogeneous III-V
ferromagnetic semiconductors. The carrier spin-3/2 and large spin-orbit
interaction, leading to spin non-conservation, introduce significant conceptual
differences from spin torques in ferromagnetic metals. We determine the spin
density in an electric field in the weak momentum scattering regime,
demonstrating that the torque on the magnetization is intimately related to
spin precession under the action of both the spin-orbit interaction and the
exchange field characteristic of ferromagnetism. The spin polarization excited
by the electric field is smaller than in ferromagnetic metals and, due to lack
of angular momentum conservation, cannot be expressed in a simple closed
vectorial form. Remarkably, scalar and spin-dependent scattering do not affect
the result. We use our results to estimate the velocity of current-driven
domain walls.",0802.3717v2
2015-08-31,All electrical manipulation of magnetization dynamics in a ferromagnet by antiferromagnets with anisotropic spin Hall effects,"We investigate spin-orbit torques of metallic CuAu-I-type antiferromagnets
using spin-torque ferromagnetic resonance tuned by a dc-bias current. The
observed spin torques predominantly arise from diffusive transport of spin
current generated by the spin Hall effect. We find a growth-orientation
dependence of the spin torques by studying epitaxial samples, which may be
correlated to the anisotropy of the spin Hall effect. The observed anisotropy
is consistent with first-principles calculations on the intrinsic spin Hall
effect. Our work demonstrates large tunable spin-orbit effects in
magnetically-ordered materials.",1508.07906v2
2019-01-07,Simultaneous Optical and Electrical Spin-Torque Magnetometry with Stroboscopic Detection of Spin-Precession Phase,"Spin-based coherent information processing and encoding utilize the
precession phase of spins in magnetic materials. However, the detection and
manipulation of spin precession phases remain a major challenge for advanced
spintronic functionalities. By using simultaneous electrical and optical
detection, we demonstrate the direct measurement of the precession phase of
Permalloy ferromagnetic resonance driven by the spin-orbit torques from
adjacent heavy metals. The spin Hall angle of the heavy metals can be
independently determined from concurrent electrical and optical signals. The
stroboscopic optical detection also allows spatially measuring local
spin-torque parameters and the induced ferromagnetic resonance with
comprehensive amplitude and phase information. Our study offers a route towards
future advanced characterizations of spin-torque oscillators, magnonic
circuits, and tunnelling junctions, where measuring the current-induced spin
dynamics of individual nanomagnets are required.",1901.01923v1
2022-07-13,Strong Spin-Orbit Torque Induced by the Intrinsic Spin Hall Effect in Cr1-xPtx,"We report on a spin-orbit torque study of the spin current generation in
Cr1-xPtx alloy, using the light 3d ferromagnetic Co as the spin current
detector. We find that the dampinglike spin-orbit torque of Cr1-xPtx/Co
bilayers can be enhanced by tuning the Cr concentration in the Cr1-xPtx layer,
with a maximal value of 0.31 at the optimal composition of Cr0.2Pt0.8. We find
that the spin current generation in the Cr1-xPtx alloy can be fully understood
by the characteristic trade-off between the intrinsic spin Hall conductivity of
Pt and the carrier lifetime in the dirty limit. We find no evidence for the
spin current generation by other mechanisms in this material, revealing that
the role of Cr is found to be simply the same as other metals and oxides in
previous studies. This work also establishes the low-resistivity Cr0.2Pt0.8 as
an energy-efficient spin-orbit torque provider for magnetic memory and
computing technologies.",2207.05992v2
2005-03-15,Adjustable spin torque in magnetic tunnel junctions with two fixed layers,"We have fabricated nanoscale magnetic tunnel junctions (MTJs) with an
additional fixed magnetic layer added above the magnetic free layer of a
standard MTJ structure. This acts as a second source of spin-polarized
electrons that, depending on the relative alignment of the two fixed layers,
either augments or diminishes the net spin-torque exerted on the free layer.
The compound structure allows a quantitative comparison of spin-torque from
tunneling electrons and from electrons passing through metallic spacer layers,
as well as analysis of Joule selfheating effects. This has significance for
current-switched magnetic random access memory (MRAM), where spin torque is
exploited, and for magnetic sensing, where spin torque is detrimental.",0503376v1
2011-09-13,Interplay between non equilibrium and equilibrium spin torque using synthetic ferrimagnets,"We discuss the current induced magnetization dynamics of spin valves F0|N|SyF
where the free layer is a synthetic ferrimagnet SyF made of two ferromagnetic
layers F1 and F2 coupled by RKKY exchange coupling. In the interesting
situation where the magnetic moment of the outer layer F2 dominates the
magnetization of the ferrimagnet, we find that the sign of the effective spin
torque exerted on the free middle layer F1 is controlled by the strength of the
RKKY coupling: for weak coupling one recovers the usual situation where spin
torque tends to, say, anti-align the magnetization of F1 with respect to the
pinned layer F0. However for large coupling the situation is reversed and the
spin torque tends to align F1 with respect to F0. Careful numerical simulations
in the intermediate coupling regime reveal that the competition between these
two incompatible limits leads generically to spin torque oscillator (STO)
behavior. The STO is found in the absence of magnetic field, with very
significant amplitude of oscillations and frequencies up to 50 GHz or higher.",1109.2705v2
2013-11-13,Thermally activated in-plane magnetization rotation induced by spin torque,"We study the role of thermal fluctuations on the spin dynamics of a thin
permalloy film with a focus on the behavior of spin torque and find that the
thermally assisted spin torque results in new aspects of the magnetization
dynamics. In particular, we uncover the formation of a finite, spin
torque-induced, in-plane magnetization component. The orientation of the
in-plane magnetization vector depends on the temperature and the spin-torque
coupling. We investigate and illustrate that the variation of the temperature
leads to a thermally-induced rotation of the in-plane magnetization.",1311.3120v1
2015-09-16,Charge-Induced Spin Torque in Anomalous Hall Ferromagnets,"We demonstrate that spin-orbit coupled electrons in a magnetically doped
system exert a spin torque on the local magnetization, without a flowing
current, when the chemical potential is modulated in a magnetic field. The spin
torque is proportional to the anomalous Hall conductivity, and its effective
field strength may overcome the Zeeman field. Using this effect, the direction
of the local magnetization is switched by gate control in a thin film. This
charge-induced spin torque is essentially an equilibrium effect, in contrast to
the conventional current-induced spin-orbit torque, and, thus, devices using
this operating principle possibly have higher efficiency than the conventional
ones. In addition to a comprehensive phenomenological derivation, we present a
physical understanding based on a model of a Dirac-Weyl semimetal, possibly
realized in a magnetically doped topological insulator. The effect might be
realized also in nanoscale transition materials, complex oxide ferromagnets,
and dilute magnetic semiconductors.",1509.04799v1
2015-10-03,Engineering spin-orbit torque in Co/Pt multilayers with perpendicular magnetic anisotropy,"To address thermal stability issues for spintronic devices with a reduced
size, we investigate spin-orbit torque in Co/Pt multilayers with strong
perpendicular magnetic anisotropy. Note that the spin-orbit torque arises from
the global imbalance of the spin currents from the top and bottom interfaces
for each Co layer. By inserting Ta or Cu layers to strengthen the top-down
asymmetry, the spin-orbit torque efficiency can be greatly modified without
compromised perpendicular magnetic anisotropy. Above all, the efficiency builds
up as the number of layers increases, realizing robust thermal stability and
high spin-orbit-torque efficiency simultaneously in the multilayers structure.",1510.00836v1
2014-06-15,Direct and inverse spin-orbit torques,"In collinear magnets lacking inversion symmetry application of electric
currents induces torques on the magnetization and conversely magnetization
dynamics induces electric currents. The two effects, which both rely on
spin-orbit interaction (SOI), are reciprocal to each other and denoted direct
spin-orbit torque (SOT) and inverse spin-orbit torque (ISOT), respectively. We
derive expressions for SOT and ISOT within the Kubo linear response formalism.
We show that expressions suitable for density-functional theory calculations
can be derived either starting from a Kohn-Sham Hamiltonian with time-dependent
exchange field or by expressing general susceptibilities in terms of the
Kohn-Sham susceptibilities. For the case of magnetic bilayer systems we derive
the general form of the ISOT current induced under ferromagnetic resonance.
Using \textit{ab initio} calculations within density-functional theory we
investigate SOT and ISOT in Co/Pt(111) magnetic bilayers. We determine the
spatial distribution of spin and charge currents as well as torques in order to
expose the mechanisms underlying SOT and ISOT and to highlight their
reciprocity on the microscopic level. We find that the spin Hall effect is
position-dependent close to interfaces.",1406.3866v2
2021-04-12,Spin-orbit torque switching of Néel order in two-dimensional CrI$_3$,"Spin-orbit torque enables electrical control of the magnetic state of
ferromagnets or antiferromagnets. In this work we consider the spin-orbit
torque in the 2-d Van der Waals antiferromagnetic bilayer CrI$_3$, in the
$n$-doped regime. In the purely antiferromagnetic state, two individually
inversion-symmetry broken layers of CrI$_3$ form inversion partners, like the
well-studied CuMnAs and Mn$_2$Au. However, the exchange and anisotropy energies
are similar in magnitude, unlike previously studied antiferromagnets, which
leads to qualitatively different behaviors in this material. Using a
combination of first-principles calculations of the spin-orbit torque and an
analysis of the ensuing spin dynamics, we show that the deterministic
electrical switching of the N\'eel vector is the result of dampinglike
spin-orbit torque, which is staggered on the magnetic sublattices.",2104.05155v1
2023-05-03,"Impacts of the half-skyrmion spin topology, spin-orbit torque, and dynamic symmetry breaking on the growth of magnetic stripe domains","We have performed an experimental and modeling-based study of the spin-orbit
torque-induced growth of magnetic stripe domains in heavy metal/ferromagnet
thin-film heterostructures that possess chiral N\'eel-type domain walls due to
an interfacial Dzyaloshinskii-Moriya interaction. In agreement with previous
reports, the stripe domains stabilized in these systems exhibit a significant
transverse growth velocity relative to the applied current axis. This behavior
has previously been attributed to the Magnus force-like skyrmion Hall effect of
the stripe domain spin topology, which is analogous to that of a half-skyrmion.
However, through analytic modeling of the in-plane torques generated by
spin-orbit torque, we find that a dynamical reconfiguration of the domain wall
magnetization profile is expected to occur - promoting motion with similar
directionality and symmetry as the skyrmion Hall effect. These results further
highlight the sensitivity of spin-orbit torque to the local orientation of the
domain wall magnetization profile and its contribution to domain growth
directionality.",2305.02181v1
2023-07-10,Angular dependence of spin-orbit torque in monolayer $Fe_3GeTe_2$,"In ferromagnetic systems lacking inversion symmetry, an applied electric
field can control the ferromagnetic order parameters through the spin-orbit
torque. The prototypical example is a bilayer heterostructure composed of a
ferromagnet and a heavy metal that acts as a spin current source. In addition
to such bilayers, spin-orbit coupling can mediate spin-orbit torques in
ferromagnets that lack bulk inversion symmetry. A recently discovered example
is the two-dimensional monolayer ferromagnet $Fe_3GeTe_2$. In this work, we use
first-principles calculations to study the spin-orbit torque and ensuing
magnetic dynamics in this material. By expanding the torque versus
magnetization direction as a series of vector spherical harmonics, we find that
higher order terms (up to $\ell=4$) are significant and play important roles in
the magnetic dynamics. They give rise to deterministic, magnetic field-free
electrical switching of perpendicular magnetization.",2307.04900v2
2011-04-15,Enhanced spin transfer torque effect for transverse domain walls in cylindrical nanowires,"Recent studies have predicted extraordinary properties for transverse domain
walls in cylindrical nanowires: zero depinning current, the absence of the
Walker breakdown, and applications as domain wall oscillators. In order to
reliably control the domain wall motion, it is important to understand how they
interact with energy barriers.
  In this paper, we study the motion and depinning of transverse domain walls
through potential barriers in ferromagnetic cylindrical nanowires. We use
magnetic fields and spin-polarized currents to drive the domain walls along the
wire. Using magnetic fields, we find that the minimum and the maximum fields
required to push the domain wall through the barrier differ by 30 %. On the
contrary, using spin-polarized currents, we find variations of a factor 130
between the minimum value of the depinning current density and the maximum
value.
  We study the depinning current density as a function of the height of the
energy barrier using numerical and analytical methods. We find that, for a
barrier of 40 k_B T, a depinning current density of about 5 uA is sufficient to
depin the domain wall.
  We reveal and explain the mechanism that leads to these unusually low
depinning currents. One requirement for this new depinning mechanism is for the
domain wall to be able to rotate around its own axis. With the right barrier
design, the spin torque transfer term is acting exactly against the damping in
the micromagnetic system, and thus the low current density is sufficient to
accumulate enough energy quickly. These key insights may be crucial in
furthering the development of novel memory technologies, such as the racetrack
memory, that can be controlled through low current densities.",1104.3010v1
1998-02-09,Spin Evolution of Pulsars with Weakly Coupled Superfluid Interiors,"We discuss the spin evolution of pulsars in the case where a superfluid
component of the star is coupled to the observable crust on long, spindown
timescales. The momentum transfer from the superfluid interior results in an
apparent decay of the external torque and, after a dramatic increase, to an
asymptotic decrease of the generic value of the braking index, e.g. $n=3$, to
values $n\sim 2.5$ if the magnetic field of the star does not decay over its
lifetime. In the case where an exponential decay of the magnetic field towards
a residual value occurs, the star undergoes a spin-up phase after which it
could emerge in the millisecond sector of the $P$-$\dot P$ diagram.",9802102v1
2005-05-30,Mechanisms limiting the coherence time of spontaneous magnetic oscillations driven by DC spin-polarized currents,"The spin-transfer torque from a DC spin-polarized current can generate
highly-coherent magnetic precession in nanoscale magnetic-multilayer devices.
By measuring linewidths of spectra from the resulting resistance oscillations,
we argue that the coherence time can be limited at low temperature by thermal
deflections about the equilibrium magnetic trajectory, and at high temperature
by thermally-activated transitions between dynamical modes. Surprisingly, the
coherence time can be longer than predicted by simple macrospin simulations.",0505733v2
2005-08-11,Magnetization self-organization in a single-domain ferromagnet subject to a spin current,"The Landau-Lifshitz equation for the magnetization dynamics of a
single-domain magnetic system is solved using the methods of self-organization.
The description takes into account the torque due to spin transfer. The
potential energy of the system includes the uniaxial and easy-plane
anisotropies, and the Zeeman energy due to an external magnetic field. The
equilibrium and stationary states are investigated as a function of the spin
current and external magnetic field. The presented bifurcation diagram allows
to determine the margins of a neutral stability mode of the equilibrium and
stationary states for different values of the easy-plane anisotropy constant.
Using the power spectral density method, the trajectory tracing, Hausdorff
dimension, and maximum Lyapunov exponent, the dynamics of the phase states in
an external magnetic field is demonstrated. The analytical transcendent
equations for switching between different equilibrium states are also obtained,
proving the importance of phase averaging.",0508280v1
2008-11-25,The quantum-mechanical basis of an extended Landau-Lifshitz-Gilbert equation for a current-carrying ferromagnetic wire,"An extended Landau-Lifshitz-Gilbert (LLG) equation is introduced to describe
the dynamics of inhomogeneous magnetization in a current-carrying wire. The
coefficients of all the terms in this equation are calculated
quantum-mechanically for a simple model which includes impurity scattering.
This is done by comparing the energies and lifetimes of a spin wave calculated
from the LLG equation and from the explicit model. Two terms are of particular
importance since they describe non-adiabatic spin-transfer torque and damping
processes which do not rely on spin-orbit coupling. It is shown that these
terms may have a significant influence on the velocity of a current-driven
domain wall and they become dominant in the case of a narrow wall.",0811.4118v1
2009-07-29,The Shape of an Accretion Disc in a Misaligned Black Hole Binary,"We model the overall shape of an accretion disc in a semi-detached binary
system in which mass is transfered on to a spinning black hole the spin axis of
which is misaligned with the orbital rotation axis. We assume the disc is in a
steady state. Its outer regions are subject to differential precession caused
by tidal torques of the companion star. These tend to align the outer parts of
the disc with the orbital plane. Its inner regions are subject to differential
precession caused by the Lense-Thirring effect. These tend to align the inner
parts of the disc with the spin of the black hole. We give full numerical
solutions for the shape of the disc for some particular disc parameters. We
then show how an analytic approximation to these solutions can be obtained for
the case when the disc surface density varies as a power law with radius. These
analytic solutions for the shape of the disc are reasonably accurate even for
large misalignments and can be simply applied for general disc parameters. They
are particularly useful when the numerical solutions would be slow.",0907.5142v1
2009-10-01,Spin motive forces and current fluctuations due to Brownian motion of domain walls,"We compute the power spectrum of the noise in the current due to spin motive
forces by a fluctuating domain wall. We find that the power spectrum of the
noise in the current is colored, and depends on the Gilbert damping, the spin
transfer torque parameter $\beta$, and the domain-wall pinning potential and
magnetic anisotropy. We also determine the average current induced by the
thermally-assisted motion of a domain wall that is driven by an external
magnetic field. Our results suggest that measuring the power spectrum of the
noise in the current in the presence of a domain wall may provide a new method
for characterizing the current-to-domain-wall coupling in the system.",0910.0163v1
2010-12-03,Dissipationless mechanism of skyrmion Hall current in double-exchange ferromagnets,"We revisit a theory of skyrmion transport in ferromagnets. On a basis of an
effective U(1) gauge theory for spin-chirality fluctuations in double-exchange
ferromagnets, we derive an expression for the velocity of a skyrmion core
driven by the dc electric field. We find that mutual feedback effects between
conduction electrons and localized spins give rise to Chern-Simons terms,
suggesting a dissipationless mechanism for the skyrmion Hall current. A
conventional description of the current-induced skyrmion motion, appearing
through the spin transfer torque and scattering events, is reproduced in a
certain limit of our description, where the Chern-Simons terms are not fully
incorporated. Our theory is applicable to not only metallic but also insulating
systems, where the purely topological and dissipationless skyrmion Hall current
can be induced in the presence of an energy gap.",1012.0631v3
2012-02-02,Spin-Down of Radio Millisecond Pulsars at Genesis,"Millisecond pulsars are old neutron stars that have been spun up to high
rotational frequencies via accretion of mass from a binary companion star. An
important issue for understanding the physics of the early spin evolution of
millisecond pulsars is the impact of the expanding magnetosphere during the
terminal stages of the mass-transfer process. Here I report binary stellar
evolution calculations that show that the braking torque acting on a neutron
star, when the companion star decouples from its Roche-lobe, is able to
dissipate >50% of the rotational energy of the pulsar. This effect may explain
the apparent difference in observed spin distributions between x-ray and radio
millisecond pulsars and help account for the noticeable age discrepancy with
their young white dwarf companions.",1202.0551v2
2013-05-17,DSTT-MRAM: Differential Spin Hall MRAM for On-chip Memories,"A new device structure for spin transfer torque based magnetic random access
memory is proposed for on-chip memory applications. Our device structure
exploits spin Hall effect to create a differential memory cell that exhibits
fast and energy-efficient write operation. Moreover, due to inherently
differential device structure, fast and reliable read operation can be
performed. Our simulation study shows 10X improvement in write energy over the
standard 1T1R STT-MRAM memory cell, and 1.6X faster read operation compared to
single-ended sensing (as in standard 1T1R STT-MRAMs). The bit-cell
characteristics are promising for high performance on-chip memory applications.",1305.4085v1
2013-07-12,Angular and Linear Momentum of Excited Ferromagnets,"The angular momentum vector of a Heisenberg ferromagnet with isotropic
exchange interaction is conserved, while under uniaxial crystalline anisotropy
the projection of the total spin along the easy axis is a constant of motion.
Using Noether's theorem, we prove that these conservation laws persist in the
presence of dipole-dipole interactions. However, spin and orbital angular
momentum are not conserved separately. We also define the linear momentum of
ferromagnetic textures. We illustrate the general principles with special
reference to the spin transfer torques and identify the emergence of a
non-adiabatic effective field acting on domain walls in ferromagnetic
insulators.",1307.3432v1
2013-08-12,AC current generation in chiral magnetic insulators and skyrmion motion induced by the spin Seebeck effect,"We show that a temperature gradient induces an ac electric current in
multiferroic insulators when the sample is embedded in a circuit. We also show
that a thermal gradient can be used to move magnetic skyrmions in insulating
chiral magnets: the induced magnon flow from the hot to the cold region drives
the skyrmions in the opposite direction via a magnonic spin transfer torque.
Both results are combined to compute the effect of skyrmion motion on the ac
current generation and demonstrate that skyrmions in insulators are a promising
route for spin caloritronics applications.",1308.2634v3
2013-09-04,Time-resolved observation of fast domain-walls driven by vertical spin currents in short tracks,"We present time-resolved measurements of the displacement of magnetic
domain-walls (DWs) driven by vertical spin-polarized currents in track-shaped
magnetic tunnel junctions. In these structures we observe very high DW
velocities (600 m/s) at current densities below $10^7 A/cm^2$. We show that the
efficient spin-transfer torque combined with a short propagation distance
allows to avoid the Walker breakdown process, and achieve deterministic,
reversible and fast ($\approx$ 1 ns) DW-mediated switching of magnetic tunnel
junction elements, which is of great interest to the implementation of fast
DW-based spintronic devices.",1309.1002v2
2015-10-19,Noiseless manipulation of helical edge state transport by a quantum magnet,"The current through a helical edge state of a quantum-spin-Hall insulator may
be fully transmitted through a magnetically gapped region due to a combination
of spin-transfer torque and spin pumping [Meng {\em et al.}, Phys. Rev. B {\bf
90}, 205403 (2014)]. Using a scattering approach, we here argue that in such a
system the current is effectively carried by electrons with energies below the
magnet-induced gap and well below the Fermi energy. This has striking
consequences, such as the absence of shot noise, an exponential suppression of
thermal noise, and an obstruction of thermal transport. For two helical edges
covered by the same quantum magnet, the device can act as robust noiseless
current splitter.",1510.05670v1
2016-04-12,Voltage-driven magnetization switching and spin pumping in Weyl semimetals,"We demonstrate electrical magnetization switching and spin pumping in
magnetically doped Weyl semimetals. The Weyl semimetal is a new class of
topological semimetals, known to have nontrivial coupling between the charge
and the magnetization due to the chiral anomaly. By solving the
Landau-Lifshitz-Gilbert equation for a multilayer structure of a Weyl
semimetal, an insulator and a metal whilst taking the charge-magnetization
coupling into account, magnetization dynamics is analyzed. It is shown that the
magnetization dynamics can be driven by the electric voltage. Consequently,
switching of the magnetization with a pulsed electric voltage can be achieved,
as well as precession motion with an applied oscillating electric voltage. The
effect requires only a short voltage pulse and may therefore be more
energetically efficient for us in spintronics devices compared to conventional
spin transfer torque switching.",1604.03326v1
2016-10-21,Parametric Auto-Excitation of Magnetic Droplet Soliton Perimeter Modes,"Recent experiments performed in current-driven nano-contacts with strong
perpendicular anisotropy have shown that spin-transfer torque can drive
self-localized spin waves [1, 2] that above a certain threshold intensity can
condense into a highly nonlinear magnetodynamic and nano-sized state known as a
magnetic droplet soliton [3]. Here we demonstrate analytically, numerically,
and experimentally that at sufficiently large driving currents, and for a spin
polarization that is tilted away from the film normal, the circular droplet
soliton can become unstable to periodic excitations of its perimeter. We
furthermore show that these perimeter excitation modes (PEMs) are
parametrically excited when the fundamental droplet soliton precession
frequency is close to twice the frequency of one or more of the PEMs. As a
consequence, for increasing applied fields, progressively higher PEMs can be
excited. Quantitative agreement with experiment confirms this picture.",1610.06650v1
2017-08-18,Antiferromagnetic nano-oscillator in external magnetic fields,"We describe the dynamics of an antiferromagnetic nano-oscillator in an
external magnetic field of any given time distribution. The oscillator is
powered by a spin current originating from spin-orbit effects in a neighboring
heavy metal layer, and is capable of emitting a THz signal in the presence of
an additional easy-plane anisotropy. We derive an analytical formula describing
the interaction between such a system and an external field, which can affect
the output signal character. Interactions with magnetic pulses of different
shapes, with a sinusoidal magnetic field and with a sequence of rapidly
changing magnetic fields are discussed. We also perform numerical simulations
based on the Landau-Lifshitz-Gilbert equation with spin-transfer torque effects
to verify the obtained results and find a very good quantitative agreement
between analytical and numerical predictions.",1708.05590v2
2018-06-17,Stabilization of the skyrmion crystal phase in thin-film antiferromagnets,"We investigate the formation and stability of the skyrmion crystal phase in
antiferromagnetic thin films subjected to fieldlike torques such as, e.g.,
those induced by an electric current in CuMnAs and Mn$_{2}$Au via the inverse
spin-galvanic effect. We show that the skyrmion lattice represents the ground
state of the antiferromagnet in a substantial area of the phase diagram,
parametrized by the staggered field and the (effective) uniaxial anisotropy
constant. Skyrmion motion can be driven in the crystal phase by the spin
transfer effect. In the metallic scenario, itinerant electrons experience an
emergent SU$(2)$-electromagnetic field associated with the (N\'{e}el) skyrmion
background, leading to a topological spin-Hall response. Experimental
signatures of the skyrmion crystal phase and readout schemes based on
topological transport are discussed.",1806.06450v1
2018-10-24,Dragging of magnetic domain walls by interlayer exchange,"Magnetic domain walls can be moved by spin-polarized currents due to
spin-transfer torques. This opens the possibility to use them in spintronic
memory devices as, e.g., in racetrack storage. Naturally, in miniaturized
devices domain walls can get very close to each other and affect each others
dynamics. In this work we consider two separated domain walls in different
layers which interact via an interlayer exchange coupling. One of these walls
is moved by a spin-polarized current. Depending on several parameters as the
current density, the interlayer coupling or the pinning potential, the combined
dynamics of the two domain walls can change very strongly allowing, e.g., for a
correlated motion of the walls. In addition, more subtle effect appear as a
suppression of the Walker breakdown accompanied by an increase of the domain
wall velocity.",1810.10354v1
2018-02-19,Static properties and current-induced dynamics of pinned $90$ degree magnetic domain walls under applied fields: an analytic approach,"Magnetic domain walls are pinned strongly by abrupt changes in magnetic
anisotropy. When driven into oscillation by a spin-polarized current, locally
pinned domain walls can be exploited as tunable sources of short-wavelength
spin waves. Here, we develop an analytical framework and discrete Heisenberg
model to describe the static and dynamic properties of pinned domain walls with
a head-to-tail magnetic structure. We focus on magnetic domain walls that are
pinned by 90$^\circ$ rotations of uniaxial magnetic anisotropy. Our model
captures the domain wall response to a spin-transfer torque that is exerted by
an electric current. Model predictions of the domain wall resonance frequency
and its evolution with magnetic anisotropy strength and external magnetic field
are compared to micromagnetic simulations.",1802.06741v3
2017-10-23,Manipulating Magnetic Moments by Superconducting Currents,"We show that the interaction between a superconducting order parameter and
the magnetic moment of an atomic cluster in a two-dimensional s-wave
superconductor with Rashba spin-orbit coupling generates magnetic anisotropy
that can be stronger or comparable to the magnetic anisotropy due to the
crystal field and the shape of the cluster. Transport current through the
superconductor produces the effective magnetic field acting on the cluster's
magnetic moment. The direction of the effective field depends on the direction
of the current, thus allowing one to manipulate the magnetic moment by the
superconducting current. Due to the large density of the superconducting
current this method of magnetization reversal can be more advantageous at low
temperatures than the spin-transfer torque method that requires a large
spin-polarized current through a normal metal.",1710.08157v1
2016-11-10,Energy efficient and fast reversal of a fixed skyrmions with spin current assisted by voltage controlled magnetic anisotropy,"Recent work [1,2] suggests that ferromagnetic reversal with spin transfer
torque (STT) requires more current in a system in the presence of DMI than
switching a typical ferromagnet of the same dimensions and perpendicular
magnetic anisotropy (PMA). However, DMI promotes stabilization of skyrmions and
we report that when the perpendicular anisotropy is modulated (reduced) for
both the skyrmion and ferromagnet, it takes much smaller current to reverse the
fixed skyrmion than to reverse the ferromagnet in the same time, or the
skyrmion reverses much faster than the ferromagnet at similar levels of
current. We show with rigorous micromagnetic simulations and energy portraits
that the skyrmion switching proceeds along a different path at very low PMA
which results in a significant reduction in the spin current required or time
required for reversal. This can have potential for memory application where a
relatively simple modification of the standard STT-RAM to include a heavy metal
adjacent to the soft magnetic layer and with appropriate design of the tunnel
barrier can lead to energy efficient and fast magnetic memory device based on
the reversal of fixed skyrmions.",1611.03138v2
2019-04-08,Phase locking of spin transfer nano-oscillators using common microwave sources,"In this paper, we study typical nonlinear phenomenon of phase-locking or
synchronization in spin-torque nano oscillators (STNOs). To start with the
oscillators are considered as uncoupled but interlinked through either a common
microwave current or a microwave field. We identify the phase locking of an
array of STNOs (first for two and then for 100 oscillators) by means of
injection locking which represents locking the oscillations to a common
alternating spin current or a common microwave magnetic field. We characterize
the locking of STNOs through both first and second harmonic lockings in an
array. We find that second harmonic lockings takes lesser value of microwave
current and field when compared with the first harmonic lockings. Our results
also show that oscillating microwave current can induce integer harmonic
locking while microwave field can induce both integer and several fractional
harmonic lockings. We also extend our analysis to study locking behavior of two
STNOs by introducing time delay feedback and coupling through a current
injection and bring out the associated locking characteristics. Finally, we
have also analyzed the stability of synchronization of identical array of STNOs
with current coupling by using master stability function formalism.",1904.04910v1
2019-08-12,On a simple derivation of the very low damping escape rate for classical spins by modifying the method of Kramers,"The original perturbative Kramers' method (starting from the phase space
coordinates) (Kramers, 1940) of determining the energy-controlled-diffusion
equation for Newtonian particles with separable and additive Hamiltonians is
generalized to yield the energy-controlled diffusion equation and thus the very
low damping (VLD) escape rate including spin-transfer torque for classical
giant magnetic spins with two degrees of freedom. These have dynamics governed
by the magnetic Langevin and Fokker-Planck equations and thus are generally
based on non-separable and non-additive Hamiltonians. The derivation of the VLD
escape rate directly from the (magnetic) Fokker-Planck equation for the surface
distribution of magnetization orientations in the configuration space of the
polar and azimuthal angles $(\vartheta, \varphi)$ is much simpler than those
previously used.",1908.06747v1
2022-04-19,Role of shape anisotropy on thermal gradient-driven domain wall dynamics in magnetic nanowires,"We investigate the magnetic domain wall (DW) dynamics in uniaxial/biaxial
nanowires under a thermal gradient (TG). The findings reveal that the DW
propagates toward the hotter region in both nanowires. The main physics of such
observations is the magnonic angular momentum transfer to the DW. The hard
(shape) anisotropy exists in biaxial nanowire, which contributes an additional
torque, hence DW speed is larger than that in uniaxial nanowire. With lower
damping, the DW velocity is smaller and DW velocity increases with damping
which is opposite to usual expectation. To explain this, it is predicted that
there is a probability to form the standing spin-waves (which do not carry net
energy/momentum) together with travelling spin-waves if the propagation length
of thermally-generated spin-waves is larger than the nanowire length. For
larger-damping, DW decreases with damping since the magnon propagation length
decreases. Therefore, the above findings might be useful in realizing the
spintronic (racetrack memory) devices.",2204.09101v2
2022-12-14,Non-uniform Superlattice Magnetic Tunnel Junctions,"We propose a new class of non-uniform superlattice magnetic tunnel junctions
(Nu-SLTJs) with the Linear, Gaussian, Lorentzian, and P\""oschl-teller width and
height based profiles manifesting a sizable enhancement in the TMR($\approx
10^4-10^6\%$) with a significant suppression in the switching bias($\approx$9
folds) owing to the physics of broad-band spin filtering. By exploring the
negative differential resistance region in the current-voltage characteristics
of the various Nu-SLTJs, we predict the Nu-SLTJs offer the fastest spin
transfer torque switching in the order of a few hundred picoseconds. We
self-consistently employ the atomistic non-equilibrium Green's function
formalism coupled with the Landau-Lifshitz-Gilbert-Slonczewski equation to
evaluate the device performance of the various Nu-SLTJs. We also present the
design of minimal three-barrier Nu-SLTJs having significant TMR($\approx
10^4\%$) and large spin current for ease of device fabrication. We hope that
the class of Nu-SLTJs proposed in this work may lay the bedrock to embark on
the exhilarating voyage of exploring various non-uniform superlattices for the
next generation of spintronic devices.",2212.07202v2
2023-10-28,Einstein-de Haas torque as a discrete spectroscopic probe allows nanomechanical measurement of a magnetic resonance,"The Einstein-de Haas (EdH) effect is a fundamental, mechanical consequence of
any temporal change of magnetism in an object. EdH torque results from
conserving the object's total angular momentum: the angular momenta of all the
specimen's magnetic moments, together with its mechanical angular momentum.
Although the EdH effect is usually small and difficult to observe, it increases
in magnitude with detection frequency. We explore the frequency-dependence of
EdH torque for a thin film permalloy microstructure by employing a ladder of
flexural beam modes (with five distinct resonance frequencies spanning from 3
to 208 MHz) within a nanocavity optomechanical torque sensor via magnetic
hysteresis curves measured at mechanical resonances. At low DC fields the
gyrotropic resonance of a magnetic vortex spin texture overlaps the 208 MHz
mechanical mode. The massive EdH mechanical torques arising from this
co-resonance yield a fingerprint of vortex core pinning and depinning in the
sample. The experimental results are discussed in relation to mechanical
torques predicted from both macrospin (at high DC magnetic field) and
finite-difference solutions to the Landau-Lifshitz-Gilbert (LLG) equation. A
global fit of the LLG solutions to the frequency-dependent data reveals a
statistically significant discrepancy between the experimentally observed and
simulated torque phase behaviours at spin texture transitions that can be
reduced through the addition of a time constant to the conversion between
magnetic cross-product torque and mechanical torque, constrained by experiment
to be in the range of 0.5 - 4 ns.",2310.18546v2
2023-05-08,Interfacial origin of unconventional spin-orbit torque in Py/$γ-$IrMn$_{3}$,"Angle-resolved spin-torque ferromagnetic resonance measurements are carried
out in heterostructures consisting of Py (Ni$_{81}$Fe$_{19}$) and a
noncollinear antiferromagnetic quantum material $\gamma-$IrMn$_{3}$. The
structural characterization reveals that $\gamma-$IrMn$_{3}$ is polycrystalline
in nature. A large exchange bias of 158~Oe is found in Py/$\gamma-$IrMn$_{3}$
at room temperature, while $\gamma-$IrMn$_{3}$/Py and Py/Cu/$\gamma-$IrMn$_{3}$
exhibited no exchange bias. Regardless of the exchange bias and stacking
sequence, we observe a substantial unconventional out-of-plane anti-damping
torque when $\gamma-$IrMn$_{3}$ is in direct contact with Py. The magnitude of
the out-of-plane spin-orbit torque efficiency is found to be twice as large as
the in-plane spin-orbit torque efficiency. The unconventional spin-orbit torque
vanishes when a Cu spacer is introduced between Py and $\gamma-$IrMn$_{3}$,
indicating that the unconventional spin-orbit torque in this system originates
at the interface. These findings are important for realizing efficient
antiferromagnet-based spintronic devices via interfacial engineering.",2305.04596v1
2001-07-12,Spin torque in a magnetic trilayer coupled to a superconductor,"A ferromagnet-normal-metal-ferromagnet trilayer does not conserve spin
current and as a result, the conduction electrons can create a torque on the
magnetic moments. When the trilayer is connected to a superconducting
electrode, the spin torque created by a current flowing perpendicularly to the
trilayer can drive the system to a configuration where the two magnetic moments
are perpendicular to each other. Here we argue that in contrast to the
non-equilibrium torque, the equilibrium torque (or magnetic exchange
interaction) does not single out the perpendicular configuration. We calculate
the equilibrium torque for a one-dimensional lattice model and find that it is
sensitive to the presence of the superconductivity.",0107265v1
2009-12-18,Discovery of a New Torque Reversal of the Accreting X-ray Pulsar 4U 1626-67 by Fermi/GBM,"Recent X-ray observations by Fermi/GBM discovered a new torque reversal of 4U
1626-67 after 18 years of steady spinning down. Using Swift/BAT observations we
were able to center this new torque reversal on Feb 4 2008, lasting
approximately 150 days. From 2004 up to the end of 2007, the spin-down rate
averaged at a mean rate of ~dnu/dt=-4.8e-13 Hz s-1 until the torque reversal
reported here. Since then it has been following a steady spin-up at a mean rate
of ~dnu/dt= 4e-13 Hz s-1. The properties of this torque reversal, as well as
the lack of correlation between the X-ray flux and the torque applied to the
neutron star before this transition, challenges our understanding of the
physical mechanisms operating in this system.",0912.3809v1
2013-06-19,"Asymmetric Ferromagnetic Resonance, Universal Walker Breakdown, and Counterflow Domain Wall Motion in the Presence of Multiple Spin-Orbit Torques","We study the motion of several types of domain wall profiles in spin-orbit
coupled magnetic nanowires and also the influence of spin-orbit interaction on
the ferromagnetic resonance of uniform magnetic films. We extend previous
studies by fully considering not only the field-like contribution from the
spin-orbit torque, but also the recently derived Slonczewski-like spin-orbit
torque. We show that the latter interaction affects both the domain wall
velocity and the Walker breakdown threshold non-trivially, which suggests that
it should be accounted in experimental data analysis. We find that the presence
of multiple spin-orbit torques may render the Walker breakdown to be universal
in the sense that the threshold is completely independent on the
material-dependent Gilbert damping, non-adiabaticity, and the chirality of the
domain wall. We also find that domain wall motion against the current injection
is sustained in the presence of multiple spin-orbit torques and that the wall
profile will determine the qualitative influence of these different types of
torques (e.g. field-like and Slonczewski-like). In addition, we consider a
uniform ferromagnetic layer under a current bias, and find that the resonance
frequency becomes asymmetric against the current direction in the presence of
Slonczewski-like spin-orbit coupling. This is in contrast with those cases
where such an interaction is absent, where the frequency is found to be
symmetric with respect to the current direction. This finding shows that
spin-orbit interactions may offer additional control over pumped and absorbed
energy in a ferromagnetic resonance setup by manipulating the injected current
direction.",1306.4680v1
2014-06-23,Propulsion of a domain wall in an antiferromagnet by magnons,"We analyze the dynamics of a domain wall in an easy-axis antiferromagnet
driven by circularly polarized magnons. Magnons pass through a stationary
domain wall without reflection and thus exert no force on it. However, they
reverse their spin upon transmission, thereby transferring two quanta of
angular momentum to the domain wall and causing it to precess. A precessing
domain wall partially reflects magnons back to the source. The reflection of
spin waves creates a previously identified reactive force. We point out a
second mechanism of propulsion, which we term redshift: magnons passing through
a precessing domain wall lower their frequency by twice the angular velocity of
the domain wall; the concomitant reduction of magnons' linear momentum
indicates momentum transfer to the domain wall. We solve the equations of
motion for spin waves in the background of a uniformly precessing domain wall
with the aid of supersymmetric quantum mechanics and compute the net force and
torque applied by magnons to the domain wall. Redshift is the dominant
mechanism of propulsion at low spin-wave intensities; reflection dominates at
higher intensities. We derive a set of coupled algebraic equations to determine
the linear velocity and angular frequency of the domain wall in a steady state.
The theory agrees well with numerical micromagnetic simulations.",1406.6051v1
2021-12-15,Wide ferromagnetic domain walls can host both adiabatic reflectionless spin transport and finite nonadiabatic spin torque: A time-dependent quantum transport picture,"The key concept in spintronics of current-driven noncollinear magnetic
textures, such as magnetic domain walls (DWs), is adiabaticity, i.e., how
closely electronic spins track classical localized magnetic moments (LMMs) of
the texture. When mistracking occurs nonadiabatic effects arise, the salient of
which is nonadiabatic spin transfer torque (STT) where spin angular momentum is
exchanged between electrons and LMMs to cause their dynamics and enable DW
motion without any current threshold. The microscopic mechanisms behind
nonadiabatic STT have been debated theoretically for nearly two decades, but
with unanimous conclusion that they should be significant only in narrow DWs.
However, this contradicts sharply experiments [O. Boulle {\em et al.}, Phys.
Rev. Lett. {\bf 101}, 216601 (2008); C. Burrowes {\em et al.}, Nat. Phys. {\bf
6}, 17 (2010)] observing nonadiabatic STT in DWs much wider than putatively
relevant $\sim 1$ nm scale, as well as largely insensitive to further
increasing the DW width $w$. Here we employ time-dependent quantum transport
for electrons to obtain both nonadiabatic and adiabatic STT from the exact
nonequilibrium density matrix and its lowest order as adiabatic density matrix
defined by assuming that LMMs are infinitely slow. This allows us to
demonstrate that our microscopically, and without any simplifications of prior
derivations like effectively static DW, extracted nonadiabatic STT: (i) does
not decay, but instead saturates at a finite value, with increasing $w$ of a
moving DW ensuring entry into the adiabatic limit, which we characterize by
showing that electronic spins do not reflect from the static DW in this limit;
and (ii) it has both out-of-DW-plane, as is the case of phenomenological
expression widely used in the LLG equation, and in-plane components, where the
former remains finite with increasing $w$.",2112.08356v2
2011-11-04,Spin Currents Induced by Nonuniform Rashba-Type Spin-Orbit Field,"We study the spin relaxation torque in nonmagnetic or ferromagnetic metals
with nonuniform spin-orbit coupling within the Keldysh Green's function
formalism. In non-magnet, the relaxation torque is shown to arise when the
spin-orbit coupling is not uniform. In the absence of an external field, the
spin current induced by the relaxation torque is proportional to the vector
chirality of Rashba-type spin-orbit field (RSOF). In the presence of an
external field, on the other hand, spin relaxation torque arises from the
coupling of the external field and vector chirality of RSOF. Our result
indicates that spin-sink or source effects are controlled by designing RSOF in
junctions.",1111.1197v1
2017-07-26,Reorientable Spin Direction for Spin Current Produced by the Anomalous Hall Effect,"We show experimentally that the spin direction of the spin current generated
by spin-orbit interactions within a ferromagnetic layer can be reoriented by
turning the magnetization direction of this layer. We do this by measuring the
field-like component of spin-orbit torque generated by an exchange-biased FeGd
thin film and acting on a nearby CoFeB layer. The relative angle of the CoFeB
and FeGd magnetic moments is varied by applying an external magnetic field. We
find that the resulting torque is in good agreement with predictions that the
spin current generated by the anomalous Hall effect from the FeGd layer depends
on the FeGd magnetization direction $\hat{m}_{FeGd}$ according to
$\vec{\sigma}\propto\left ( \hat{y}\cdot \hat{m}_{FeGd} \right
)\hat{m}_{FeGd}$, where $\hat{y}$ is the in-plane direction perpendicular to
the applied charge current. Because of this angular dependence, the spin-orbit
torque arising from the anomalous Hall effect can be non-zero in a sample
geometry for which the spin Hall torque generated by non-magnetic materials is
identically zero.",1707.08631v1
2006-11-27,Microscopic Calculation of Spin Torques and Forces,"Spin torques, that is, effects of conduction electrons on magnetization
dynamics, are calculated microscopically in the first order in spatial gradient
and time derivative of magnetization. Special attention is paid to the
so-called \beta-term and the Gilbert damping, \alpha, in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
impurities. Two types of forces that the electric/spin current exerts on
magnetization are identified based on a general formula relating the force to
the torque.",0611669v1
2009-09-28,Current-induced domain wall motion including thermal effects based on Landau-Lifshitz-Bloch equation,"We employ the Landau-Lifshitz-Bloch (LLB) equation to investigate
current-induced domain wall motion at finite temperatures by numerical
micromagnetic simulations. We extend the LLB equation with spin torque terms
that account for the effect of spin-polarized currents and we find that the
velocities depend strongly on the interplay between adiabatic and non-adiabatic
spin torque terms. As a function of temperature, we find non-monotonous
behavior, which might be useful to determine the relative strengths of the spin
torque terms experimentally.",0909.5043v1
2014-08-09,Mutual Phase Locking of Very Nonidentical Spin Torque Nanooscillators via Spin Wave Interaction,"In this paper the mutual phase locking theory of very nonidentical
spin-torque nanooscillators, which is based on the Slavin-Tiberkevich model,
considering the theory of nonlinear oscillations, is developed. Using
generalized Adler equation we calculate phase-locking region of the system with
spinwave coupling in the parameter plane - distance between nanocontacts and
radii difference. We describe trajectories of such a system in the phase space
and show the effect of a broadband synchronization. We introduce a
generalization of this approach to the ensembles of spin-torque nanooscillators",1408.2141v1
2012-09-04,Magnetic oscillations driven by the spin Hall effect in 3-terminal magnetic tunnel junction devices,"We show that direct current in a tantalum microstrip can induce steady-state
magnetic oscillations in an adjacent nanomagnet through spin torque from the
spin Hall effect (SHE). The oscillations are detected electrically via a
magnetic tunnel junction (MTJ) contacting the nanomagnet. The oscillation
frequency can be controlled using the MTJ bias to tune the magnetic anisotropy.
In this 3-terminal device the SHE torque and the MTJ bias therefore provide
independent controls of the oscillation amplitude and frequency, enabling new
approaches for developing tunable spin torque nano-oscillators.",1209.0655v1
2023-02-15,Non-linear dynamics near exceptional points of synthetic antiferromagnetic spin-torque oscillators,"We consider a synthetic antiferromagnetic spin-torque oscillator with
anisotropic interlayer exchange coupling. This system exhibits exceptional
points in its linearized dynamics. We find the non-linear dynamics and the
dynamical phase diagram of the system both analytically and numerically.
Moreover, we show that, near one of the exceptional points, the power of the
oscillator depends extremely sensitively on the injected spin current. Our
findings may be useful for designing sensitive magnetometers and for other
applications of spin-torque oscillators.",2302.07607v1
2021-08-23,Hydrodynamic theory of vorticity-induced spin transport,"Electron spin transport in a disordered metal is theoretically studied from
the hydrodynamic viewpoint focusing on the role of electron vorticity. The
spin-resolved momentum flux density of electrons is calculated taking account
of the spin-orbit interaction and uniform magnetization, and the expression for
the spin motive force is obtained as the linear response to a driving electric
field. It is shown that the spin-resolved momentum flux density and motive
force are characterized by troidal moments expressed as vector products of the
applied external electric field and the spin polarization and/or magnetization.
The spin-vorticity and magnetization-vorticity couplings studied recently are
shown to arise from the toridal moments contribution to the momentum flux
density. Spin motive force turns out to have a nonconservative contribution
besides the conventional conservative one due to the spin-vorticity coupling.
Spin accumulation induced by an electric field is calculated to demonstrate the
direct relation between vorticity and induced spin, and the spin Hall effect is
interpreted as due to the spin-vorticity coupling. The spin-vorticity coupling
is shown to give rise to a vorticity-induced torque and a spin relaxation. The
vorticity-induced torque is a linear effect of the spin-orbit interaction and
is expected to be larger than the second-order torques such as nonadiabatic
($\beta$) current-induced torque due to magnetization structure. The intrinsic
inverse spin Hall effect is argued to correspond to the antisymmetric
components of the momentum flux density in the hydrodynamic context.",2108.09919v1
2019-11-13,Unveiling domain wall dynamics of ferrimagnets in thermal magnon currents: competition of angular momentum transfer and entropic torque,"Control of magnetic domain wall motion holds promise for efficient
manipulation and transfer of magnetically stored information. Thermal magnon
currents, generated by temperature gradients, can be used to move magnetic
textures, from domain walls, to magnetic vortices and skyrmions. In the last
years, theoretical studies have centered in ferro- and antiferromagnetic spin
structures, where domain walls always move towards the hotter end of the
thermal gradient. Here we perform numerical studies using atomistic spin
dynamics simulations and complementary analytical calculations to derive an
equation of motion for the domain wall velocity. We demonstrate that in
ferrimagnets, domain wall motion under thermal magnon currents shows a much
richer dynamics. Below the Walker breakdown, we find that the temperature
gradient always pulls the domain wall towards the hot end by minimizating its
free energy, in agreement with the observations for ferro- and antiferromagnets
in the same regime. Above Walker breakdown, the ferrimagnetic domain wall can
show the opposite, counterintuitive behavior of moving towards the cold end. We
show that in this case, the motion to the hotter or the colder ends is driven
by angular momentum transfer and therefore strongly related to the angular
momentum compensation temperature, a unique property of ferrimagnets where the
intrinsic angular momentum of the ferrimagnet is zero while the sublattice
angular momentum remains finite. In particular, we find that below the
compensation temperature the wall moves towards the cold end, whereas above it,
towards the hot end. Moreover, we find that for ferrimagnets, there is a torque
compensation temperature at which the domain wall dynamics shows similar
characteristics to antiferromagnets, that is, quasi-inertia-free motion and the
absence of Walker breakdown.",1911.05393v1
2005-04-07,Which Massive stars are Gamma-Ray Burst Progenitors?,"The collapsar model for gamma-ray bursts requires three essential
ingredients: a massive core, removal of the hydrogen envelope, and enough
angular momentum in the core. We study current massive star evolution models of
solar metallicity to determine which massive star physics is capable of
producing these ingredients. In particular, we investigate the role of
hydrodynamic and magnetic internal angular momentum transport and binary mass
and angular momentum transfer. We follow the evolution of rotating single stars
and of binary systems that include rotational processes for both stars.
Neglecting magnetic fields, we show that the cores of massive single stars can
maintain a high specific angular momentum when evolved with the assumption that
mean molecular weight gradients suppress rotational mixing processes. In binary
systems that undergo mass transfer during core hydrogen burning the mass
receiving star accretes large amounts of high angular momentum material,
leading to a spin-up of the core. We find, however, that this merely
compensates for the tidal angular momentum loss due to spin-orbit coupling,
which leads to synchronous rotation before the mass transfer event. Therefore
the resulting cores do not rotate faster than in single stars. We also present
models that include magnetic fields generated by differential rotation and we
consider the internal angular momentum transport by magnetic torques. We
investigate the capability of magnetic torques to efficiently pump angular
momentum into the cores of accreting stars. Despite our finding that this
mechanism works, the magnetic coupling of core and envelope after the accreting
star ends core hydrogen burning leads to slower rotation than in the
non-magnetic case.",0504175v2
2014-03-06,Influence of the Dzyaloshinskii-Moriya interaction on the spin-torque diode effect,"This paper predicts the effect of the Dzyaloshinskii-Moriya interaction (DMI)
and spin Hall effect in the spin-torque diode response of a Magnetic Tunnel
Junction built over a Tantalum strip. Our results indicate that, for a
microwave current large enough, the DMI can change qualitatively the resonant
response by splitting the ferromagnetic resonance peak. We also find out that
the two modes have a non-uniform spatial distribution.",1403.1485v1
2021-02-16,Fully Spin-transparent magnetic interfaces enabled by insertion of a paramagnetic NiO layer,"Spin backflow and spin-memory loss have been well established to considerably
lower the interfacial spin transmissivity of metallic magnetic interfaces and
thus the energy efficiency of spin-orbit torque technologies. Here we report
that spin backflow and spin-memory loss at Pt-based heavy metal/ferromagnet
interfaces can be effectively eliminated by inserting an insulating
paramagnetic NiO layer of optimum thickness. The latter enables the thermal
magnon-mediated essentially unity spin-current transmission at room temperature
due to considerably enhanced effective spin-mixing conductance of the
interface. As a result, we obtain dampinglike spin-orbit torque efficiency per
unit current density of up to 0.8 as detected by the standard technology
ferromagnet FeCoB and others, which reaches the expected upper-limit spin Hall
ratio of Pt. We establish that Pt/NiO and Pt-Hf/NiO are two energy-efficient,
integration-friendly, and high-endurance spin-current generators that provide
>100 times greater energy efficiency than sputter-deposited topological
insulators BiSb and BiSe. Our finding will benefit spin-orbitronic research and
advance spin-torque technologies.",2102.08487v1
2018-02-01,Spin Seebeck effect and thermal spin galvanic effect in Ni80Fe20/p-Si bilayers,"The development of spintronics and spin-caloritronics devices need efficient
generation, detection and manipulation of spin current. The thermal spin
current from spin-Seebeck effect has been reported to be more energy efficient
than the electrical spin injection methods. But, spin detection has been the
one of the bottlenecks since metals with large spin-orbit coupling is an
essential requirement. In this work, we report an efficient thermal generation
and interfacial detection of spin current. We measured a spin-Seebeck effect in
Ni80Fe20 (25 nm)/p-Si (50 nm) (polycrystalline) bilayers without heavy metal
spin detector. The p-Si, having the centosymmetric crystal structure, has
insignificant intrinsic spin-orbit coupling leading to negligible spin-charge
conversion. We report a giant inverse spin-Hall effect, essential for detection
of spin-Seebeck effect, in the Ni80Fe20/p-Si bilayer structure, which
originates from Rashba spin orbit coupling due to structure inversion asymmetry
at the interface. In addition, the thermal spin pumping in p-Si leads to spin
current from p-Si to Ni80Fe20 layer due to thermal spin galvanic effect and
spin-Hall effect causing spin-orbit torques. The thermal spin-orbit torques
leads to collapse of magnetic hysteresis of 25 nm thick Ni80Fe20 layer. The
thermal spin-orbit torques can be used for efficient magnetic switching for
memory applications. These scientific breakthroughs may give impetus to the
silicon spintronics and spin-caloritronics devices.",1802.00132v1
2015-09-18,Self-injection locking of a vortex spin torque oscillator by delayed feedback,"The self-synchronization of spin torque oscillators is investigated
experimentally by re-injecting its radiofrequency (rf) current after a certain
delay time. We demonstrate that the emission power and the spectral linewidth
are improved for optimal delay times. Moreover by varying the phase difference
between the emitted power and the re-injected one, we find a clear oscillatory
dependence with a 2\pi\ periodicity of the frequency of the oscillator as well
as its power and linewidth. Such periodical behavior within the self-injection
regime is well described by the general model of nonlinear auto-oscillators
including not only a delayed rf current but also all spin torque forces
responsible for the self-synchronization. Our results reveal new approaches for
controlling the non-autonomous dynamics of spin torque oscillators, a key issue
for rf spintronics applications as well as for the development of
neuro-inspired spin-torque oscillators based devices.",1509.05583v1
2017-07-06,Relaxation time and critical slowing down of a spin-torque oscillator,"The relaxation phenomena of spin-torque oscillators consisting of
nanostructured ferromagnets are interesting research targets in magnetism. A
theoretical study on the relaxation time of a spin-torque oscillator from one
self-oscillation state to another is investigated. By solving the
Landau-Lifshitz-Gilbert equation both analytically and numerically, it is shown
that the oscillator relaxes to the self-oscillation state exponentially within
a few nanoseconds, except when magnetization is close to a critical point. The
relaxation rate, which is an inverse of relaxation time, is proportional to the
current. On the other hand, a critical slowing down appears near the critical
point, where relaxation is inversely proportional to time, and the relaxation
time becomes on the order of hundreds of nanoseconds. These conclusions are
primarily obtained for a spin-torque oscillator consisting of a perpendicularly
magnetized free layer and an in-plane magnetized pinned layer, and are further
developed for application to arbitrary types of spin-torque oscillators.",1707.01960v1
2018-05-22,Spin-orbit torque in completely compensated synthetic antiferromagnet,"Synthetic antiferromagnets (SAF) have been proposed to replace ferromagnets
in magnetic memory devices to reduce the stray field, increase the storage
density and improve the thermal stability. Here we investigate the spin-orbit
torque in a perpendicularly magnetized Pt/[Co/Pd]/Ru/[Co/Pd] SAF structure,
which exhibits completely compensated magnetization and an exchange coupling
field up to 2100 Oe. The magnetizations of two Co/Pd layers can be switched
between two antiparallel states simultaneously by spin-orbit torque. The
magnetization switching can be read out due to much stronger spin-orbit
coupling at bottom Pt/[Co/Pd] interface compared to its upper counterpart
without Pt. Both experimental and theoretical analyses unravel that the torque
efficiency of antiferromagnetic coupled stacks is significantly higher than the
ferromagnetic counterpart, making the critical switching current of SAF
comparable to the conventional single ferromagnet. Besides adding an important
dimension to spin-orbit torque, the efficient switching of completely
compensated SAF might advance magnetic memory devices with high density, high
speed and low power consumption.",1805.08486v2
2018-06-08,Magnetization reversal driven by low dimensional chaos in a nanoscale ferromagnet,"Energy-efficient switching of magnetization is a central problem in
nonvolatile magnetic storage and magnetic neuromorphic computing. In the past
two decades, several efficient methods of magnetic switching were demonstrated
including spin torque, magneto-electric, and microwave-assisted switching
mechanisms. Here we report the discovery of a new mechanism giving rise to
magnetic switching. We experimentally show that low-dimensional magnetic chaos
induced by alternating spin torque can strongly increase the rate of
thermally-activated magnetic switching in a nanoscale ferromagnet. This
mechanism exhibits a well-pronounced threshold character in spin torque
amplitude and its efficiency increases with decreasing spin torque frequency.
We present analytical and numerical calculations that quantitatively explain
these experimental findings and reveal the key role played by low-dimensional
magnetic chaos near saddle equilibria in enhancement of the switching rate. Our
work unveils an important interplay between chaos and stochasticity in the
energy assisted switching of magnetic nanosystems and paves the way towards
improved energy efficiency of spin torque memory and logic.",1806.03383v1
2018-11-07,Spin torque nano-oscillators based on antiferromagnetic skyrmions,"Skyrmion-based spin torque nano-oscillators are potential next-generation
microwave signal generators. However, ferromagnetic skyrmion-based spin torque
nano-oscillators cannot reach high oscillation frequencies. In this work, we
propose to use the circular motion of an antiferromagnetic skyrmion to create
the oscillation signal in order to overcome this obstacle. Micromagnetic
simulations demonstrate that the antiferromagnetic skyrmion-based spin torque
nano-oscillators can produce high frequencies (tens of GHz). Furthermore, the
speed of the circular motion for an antiferromagnetic skyrmion in a nanodisk is
analytically derived, which agrees well with the results of numerical
simulations. Our findings are useful for the understanding of the inertial
dynamics of an antiferromagnetic skyrmion and the development of future
skyrmion-based spin torque nano-oscillators.",1811.02869v1
2017-06-06,Spin-orbit-torque MRAM: from uniaxial to unidirectional switching,"With ultra-fast writing capacity and high reliability, the spin-orbit torque
is regarded as a promising alternative to fabricate next-generation magnetic
random access memory. However, the three-terminal setup can be challenging when
scaling down the cell size. In particular, the thermal stability is an
important issue. Here we demonstrate that the current-pulse-induced
perpendicular exchange bias can significantly relieve the concern of thermal
stability. The switching of the exchange bias direction is induced by the
spin-orbit torque when passing current pulses through the Pt/Co system with an
inserted IrMn antiferromagnetic layer. Manipulating the current-pulse-induced
exchange bias, spin-orbit-torque switching at zero field between states with
unidirectional anisotropy is achieved and the thermal agitation of the magnetic
moment is strongly suppressed. The spin-orbit torque mechanism provides an
innovative method to generate and to control the exchange bias by electrical
means, which enables us to realize the new switching mechanism of highly stable
perpendicular memory cells.",1706.01639v1
2020-09-03,Thermal effects in spin torque switching of perpendicular magnetic tunnel junctions at cryogenic temperatures,"Temperature plays an important role in spin torque switching of magnetic
tunnel junctions causing magnetization fluctuations that decrease the switching
voltage but also introduce switching errors. Here we present a systematic study
of the temperature dependence of the spin torque switching probability of
state-of-the-art perpendicular magnetic tunnel junction nanopillars (40 to 60
nm in diameter) from room temperature down to 4 K, sampling up to a million
switching events. The junction temperature at the switching voltage---obtained
from the thermally assisted spin torque switching model---saturates at
temperatures below about 75 K, showing that junction heating is significant
below this temperature and that spin torque switching remains highly stochastic
down to 4 K. A model of heat flow in a nanopillar junction shows this effect is
associated with the reduced thermal conductivity and heat capacity of the
metals in the junction.",2009.01743v1
2019-08-29,Resilience of the Spin-Orbit Torque against Geometrical Backscattering,"We show in this paper that the technologically relevant field-like spin-orbit
torque shows resilience against the geometrical effect of electron
backscattering. As device grows smaller in sizes, the effect of geometry on
physical properties like spin torque, and hence switching current could place a
physical limit on the continued shrinkage of such device -- a necessary trend
of all memory devices (MRAM). The geometrical effect of curves has been shown
to impact quantum transport and topological transition of Dirac and topological
systems. In our work, we have ruled out the potential threat of line-curves
degrading the effectiveness of spin-orbit torque switching. In other words,
spin-orbit torque switching will be resilient against the influence of curves
that line the circumferences of defects in the events of electron
backscattering, which commonly happen in the channel of modern electronic
devices.",1908.11028v1
2019-08-29,Giant magnetoresistance amplifier for spin-orbit torque nano-oscillators,"Spin-orbit torque nano-oscillators based on bilayers of ferromagnetic (FM)
and nonmagnetic (NM) metals are ultra-compact current-controlled microwave
signal sources. They serve as a convenient testbed for studies of spin-orbit
torque physics and are attractive for practical applications such as microwave
assisted magnetic recording, neuromorphic computing, and chip-to-chip wireless
communications. However, a major drawback of these devices is low output
microwave power arising from the relatively small anisotropic magnetoresistance
(AMR) of the FM layer. Here we experimentally show that the output power of a
spin-orbit torque nano-oscillator can be enhanced by nearly three orders of
magnitude without compromising its structural simplicity. Addition of a FM
reference layer to the oscillator allows us to employ current-in-plane giant
magnetoresistance (CIP GMR) to boost the output power of the device. This
enhancement of the output power is a result of both large magnitude of GMR
compared to that of AMR and different angular dependences of GMR and AMR. Our
results pave the way for practical applications of spin-orbit torque
nano-oscillators.",1908.11411v1
2019-10-24,Topological damping Rashba spin orbit torque in ballistic magnetic domain walls,"Rashba spin orbit torque derived from the broken inversion symmetry at
ferromagnet/heavy metal interfaces has potential application in spintronic
devices. In conventional description of the precessional and damping components
of the Rashba spin orbit torque in magnetization textures, the decomposition
coefficients are assumed to be independent of the topology of the underlying
structure. Contrary to this common wisdom, for Schr\""{o}dinger electrons
trespassing ballistically across a magnetic domain wall, we found that the
decomposition coefficient of the damping component is determined by the
topology of the domain wall. The resultant damping Rashba spin orbit torque is
protected by the topology of the underlying magnetic domain wall and robust
against small deviations from the ideal domain wall profile. Our identification
of a topological damping Rashba spin orbit torque component in magnetic domain
walls will help to understand experiments on current driven domain wall motion
in ferromagnet/heavy metal systems with broken inversion symmetry and to
facilitate its utilization in innovative device designs.",1910.10977v2
2020-10-14,Spin torque gate magnetic field sensor,"Spin-orbit torque provides an efficient pathway to manipulate the magnetic
state and magnetization dynamics of magnetic materials, which is crucial for
energy-efficient operation of a variety of spintronic devices such as magnetic
memory, logic, oscillator, and neuromorphic computing. Here, we describe and
experimentally demonstrate a strategy for the realization of a spin torque gate
magnetic field sensor with extremely simple structure by exploiting the
longitudinal field dependence of the spin torque driven magnetization
switching. Unlike most magnetoresistance sensors which require a delicate
magnetic bias to achieve a linear response to the external field, the spin
torque gate sensor can achieve the same without any magnetic bias, which
greatly simplifies the sensor structure. Furthermore, by driving the sensor
using an ac current, the dc offset is automatically suppressed, which
eliminates the need for a bridge or compensation circuit. We verify the concept
using the newly developed WTe2/Ti/CoFeB trilayer and demonstrate that the
sensor can work linearly in the range of 3-10 Oe with negligible dc offset.",2010.07158v1
2014-02-27,Non-Equilibrium Green's Function based Circuit Models for Coherent Spin Devices,"With recent developments in spintronics, it is now possible to envision
spin-driven devices with magnets and interconnects that require a new class of
transport models using generalized Fermi functions and currents, each with four
components: one for charge and three for spin. The corresponding impedance
elements are not pure numbers but $4\times4$ matrices. Starting from the
Non-Equilibrium Green's Function (NEGF) formalism in the elastic,
phase-coherent transport regime, we develop spin generalized
Landauer-B\""uttiker formulas involving such $4\times 4$ conductances, for
multi-terminal devices in the presence of Normal-Metal (NM) leads. In addition
to usual terminal conductances describing currents at the contacts, we provide
spin-transfer torque conductances describing the spin currents absorbed by
ferromagnetic (FM) regions inside the conductor, specifying both of these
currents in terms of Fermi functions at the terminals. We derive universal sum
rules and reciprocity relations that would be obeyed by such matrix
conductances. Finally, we apply our formulation to two example Hamiltonians
describing the Rashba and the Hanle effect in 2D. Our results allows the use of
pure quantum transport models as building blocks in constructing circuit models
for complex spintronic and nano-magnetic structures and devices for simulation
in SPICE-like simulators.",1402.7055v4
2000-11-01,Spin Profile of Galactic Halos and Disk Formation,"We summarize recent developments in the study of the origin of halo spin
profiles and preliminary implications on disk formation. The specific
angular-momentum distributions within halos in N-body simulations match a
universal shape, M(<j) \propto j/(j_0+j). It is characterized by a power law
over most of the mass, and one shape parameter in addition to the spin
parameter \lambda. The angular momentum tends to be aligned throughout the halo
and of cylindrical symmetry. Even if angular momentum is conserved during
baryonic infall, the resultant disk density profile is predicted to deviate
from exponential, with a denser core and an extended tail. A slightly corrected
version of the scaling relation due to linear tidal-torque theory is used to
explain the origin of a typical power-law profile in shells, j(M) \propto M^s
with s \gsim 1. While linear theory crudely predicts the amplitudes of halo
spins, it is not a good predictor of their directions. Independently, mergers
of halos are found to produce a similar profile due to j transfer from the
orbit to the product halo via dynamical friction and tidal stripping. The halo
spin is correlated with having a recent major merger, though this correlation
is weakened by mass loss. These two effects are due to a correlation between
the spins of neighboring halos and their orbit, leading to prograde mergers.",0011002v1
2004-09-09,Nonlocal magnetization dynamics in ferromagnetic heterostructures,"Two complementary effects modify the GHz magnetization dynamics of nanoscale
heterostructures of ferromagnetic and normal materials relative to those of the
isolated magnetic constituents: On the one hand, a time-dependent ferromagnetic
magnetization pumps a spin angular-momentum flow into adjacent materials and,
on the other hand, spin angular momentum is transferred between ferromagnets by
an applied bias, causing mutual torques on the magnetizations. These phenomena
are manifestly nonlocal: they are governed by the entire spin-coherent region
that is limited in size by spin-flip relaxation processes. We review recent
progress in understanding the magnetization dynamics in ferromagnetic
heterostructures from first principles, focusing on the role of spin pumping in
layered structures. The main body of the theory is semiclassical and based on a
mean-field Stoner or spin-density--functional picture, but quantum-size effects
and the role of electron-electron correlations are also discussed. A growing
number of experiments support the theoretical predictions. The formalism should
be useful to understand the physics and to engineer the characteristics of
small devices such as magnetic random-access memory elements.",0409242v3
2012-10-30,Mode- and size-dependent Landau-Lifshitz damping in magnetic nanostructures: Evidence for non-local damping,"We demonstrate a strong dependence of the effective damping on the nanomagnet
size and the particular spin-wave mode that can be explained by the theory of
intralayer transverse-spin-pumping. The effective Landau-Lifshitz damping is
measured optically in individual, isolated nanomagnets as small as 100 nm. The
measurements are accomplished by use of a novel heterodyne magneto-optical
microwave microscope with unprecedented sensitivity. Experimental data reveal
multiple standing spin-wave modes that we identify by use of micromagnetic
modeling as having either localized or delocalized character, described
generically as end- and center-modes. The damping parameter of the two modes
depends on both the size of the nanomagnet as well as the particular spin-wave
mode that is excited, with values that are enhanced by as much as 40% relative
to that measured for an extended film. Contrary to expectations based on the ad
hoc consideration of lithography-induced edge damage, the damping for the
end-mode decreases as the size of the nanomagnet decreases. The data agree with
the theory for damping caused by the flow of intralayer transverse
spin-currents driven by the magnetization curvature. These results have serious
implications for the performance of nanoscale spintronic devices such as
spin-torque-transfer magnetic random access memory.",1210.8118v3
2020-08-30,Microwave and spin transfer torque driven coherent control in ferromagnets,"Coherent control is a method used to manipulate the state of matter using
oscillatory electromagnetic radiation which relies on the non-adiabatic
interaction. It is commonly applied in quantum processing applications. This
technique is interesting in the context of ferromagnetic materials because of
the ability to combine it with spintronics for the purpose of fundamental spin
transport research, low-power information processing, and potentially future
quantum bit (Qubit) applications. In this work we address the theoretical
grounds of coherent manipulation in practical ferromagnetic systems. We study
electromagnetic radiation driven interaction that is enhanced in the presence
of spin polarized currents and map the conditions that allow coherent
manipulation for which Rabi oscillations take place. The role of the magnetic
anisotropy field is shown to act as an additional oscillatory driving field. We
discuss the Gilbert losses in the context of effective coherence decay rates
and show that it is possible to control these rates by application of a static
spin current. The case of coherent manipulation using oscillatory spin currents
that is free of radiation is discussed as well. Our work paves the way towards
spin current amplification as well as radiation-free coherent control schemes
that may potentially lead to novel Qubits that are robust and scalable.",2008.13139v3
2020-09-01,Spin coherence on the ferromagnetic spherical surface,"Spintronics on flat surfaces has been studied over the years, and the
scenario is relatively well-known; however, there is a lack of information when
we consider non-flat surfaces. In this paper, we are concerned about the spin
dynamics of the ferromagnetic model on the spherical surface. We use the
Schwinger bosonic formalism for describing the thermodynamics of spin operators
in terms of spinon operators. Opposite to the flat two-dimensional model, which
is disordered at finite temperature, the curvature of the spherical surface
provides non-zero critical temperature for Schwinger boson condensation, which
characterizes order at finite temperature even in the absence of external
magnetic fields. The thermodynamics is then analyzed in the low-temperature
regime. In addition, we consider the presence of both static and oscillating
magnetic fields, the necessary condition for inducing the ferromagnetic
resonance, and we show systematically that the studied model is well-described
by $SU(2)$ coherent states, which provides the correct dynamics of the
magnetization. The archived results can be applied for describing a diversity
of experiments such as spin superfluidity, angular momentum injection by spin
pumping and spin-transfer torque in non-conventional junctions, magnon
dissipation, and magnetoelectronics on the spherical surface.",2009.00636v2
2022-08-21,Efficient generation of spin currents by the Orbital Hall effect in pure Cu and Al and their measurement by a Ferris-wheel ferromagnetic resonance technique at the wafer level,"We present a new ferromagnetic resonance (FMR) method that we term the Ferris
FMR. It is wideband, has significantly higher sensitivity as compared to
conventional FMR systems, and measures the absorption line rather than its
derivative. It is based on large-amplitude modulation of the externally applied
magnetic field that effectively magnifies signatures of the spin-transfer
torque making its measurement possible even at the wafer-level. Using the
Ferris FMR, we report on the generation of spin currents from the orbital Hall
effect taking place in pure Cu and Al. To this end, we use the spin-orbit
coupling of a thin Pt layer introduced at the interface that converts the
orbital current to a measurable spin current. While Cu reveals a large
effective spin Hall angle exceeding that of Pt, Al possesses an orbital Hall
effect of opposite polarity in agreement with the theoretical predictions. Our
results demonstrate additional spin- and orbit- functionality for two important
metals in the semiconductor industry beyond their primary use as interconnects
with all the advantages in power, scaling, and cost.",2208.09802v1
2004-09-28,The spin of accreting stars: dependence on magnetic coupling to the disc,"We formulate a general, steady-state model for the torque on a magnetized
star from a surrounding accretion disc. For the first time, we include the
opening of dipolar magnetic field lines due to the differential rotation
between the star and disc, so the magnetic topology then depends on the
strength of the magnetic coupling to the disc. This coupling is determined by
the effective slip rate of magnetic field lines that penetrate the diffusive
disc. Stronger coupling (i.e., lower slip rate) leads to a more open topology
and thus to a weaker magnetic torque on the star from the disc. In the expected
strong coupling regime, we find that the spin-down torque on the star is more
than an order of magnitude smaller than calculated by previous models. We also
use our general approach to examine the equilibrium (`disc-locked') state, in
which the net torque on the star is zero. In this state, we show that the
stellar spin rate is roughly an order of magnitude faster than predicted by
previous models. This challenges the idea that slowly-rotating, accreting
protostars are disc locked. Furthermore, when the field is sufficiently open
(e.g., for mass accretion rates > 5 x 10^{-9} M_sun / yr, for typical accreting
protostars), the star will receive no magnetic spin-down torque from the disc
at all. We therefore conclude that protostars must experience a spin-down
torque from a source that has not yet been considered in the star-disc torque
models--possibly from a stellar wind along the open field lines.",0409701v2
2014-08-18,Tunneling Conductance and Spin Transport in Clean Ferromagnet-Ferromagnet-Superconductor Heterostructures,"We present a transfer matrix approach that combines the
Blonder-Tinkham-Klapwijk (BTK) formalism and self-consistent solutions to the
Bogolibuov-de Gennes (BdG) equations and use it to study the tunneling
conductance and spin transport in ferromagnet (${\rm F}$)-superconductor (${\rm
S}$) trilayers (${\rm F_1F_2 S}$) as functions of bias voltage. The
self-consistency ensures that the spin and charge conservation laws are
properly satisfied. We consider forward and angularly averaged conductances
over a broad range of the strength of the exchange fields and ${\rm F}$
thicknesses, as the relative in-plane magnetization angle, $\phi$, between the
two ferromagnets varies. The $\phi$-dependence of the self-consistent
conductance curves in the trilayers can differ substantially from that obtained
via a non-self-consistent approach. The zero bias forward conductance peak
exhibits, as $\phi$ varies, resonance effects intricately associated with
particular combinations of the geometrical and material parameters. We find,
when the magnetizations are non-collinear, signatures of the anomalous Andreev
reflections in the subgap regions of the angularly averaged conductances. When
${\rm F_1}$ is half-metallic, the angularly averaged subgap conductance chiefly
arises from anomalous Andreev reflection. The in-plane components of the spin
current are strongly bias dependent, while the out-of-plane spin current
component is only weakly dependent upon voltage. The components of the spin
current aligned with the local exchange field of one of the F layers are
conserved in that layer and in the S region, while they oscillate in the other
layer. We compute the spin transfer torques, in connection with the oscillatory
behavior of spin currents, and verify that the spin continuity equation is
strictly obeyed in our method.",1408.4172v2
2005-08-14,Consistency in Formulation of Spin Current and Torque Associated with a Variance of Angular Momentum,"Stimulated generally by recent interest in the novel spin Hall effect, the
nonrelativistic quantum mechanical conserved currents, taken into account of
spin-orbit coupling, are rigorously formulated based on the symmetries of
system and Noether' theorem. The quantum mechanical force on the spin as well
as the torque associated with the variance of angular momentum are obtained.
Consequently, the kinetic interpretation of the variances of spin and orbit
angular momentum currents implies a torque on the ""electric dipole"" associated
with the moving spin. The bearing of the force and the torque on the properties
of spin current in a two-dimensional electron gas with the Rashba spin-orbit
interaction is discussed.",0508340v1
2007-08-13,Current-induced non-adiabatic spin torques and domain wall motion with spin relaxation in a ferromagnetic metallic wire,"Within the s-d model description, we derive the current-driven spin torque in
a ferromagnet, taking explicitly into account a spin-relaxing Caldeira-Leggett
bath coupling to the s-electrons. We derive Bloch-Redfield equations of motion
for the s-electron spin dynamics, and formulate a systematic gradient expansion
to obtain non-adiabatic (higher-order) corrections to the well-known adiabatic
(first-order) spin torque. We provide simple analytical expressions for the
second-order spin torque. The theory is applied to current-driven domain wall
motion. Second-order contributions imply a deformation of a transverse
tail-to-tail domain wall. The wall center still moves with a constant velocity
that now depends on the spin-polarized current in a non-trivial manner.",0708.1684v2
2018-08-28,An Intrinsic Spin Orbit Torque Nano-Oscillator,"Spin torque and spin Hall effect nanooscillators generate high intensity spin
wave auto oscillations on the nanoscale enabling novel microwave applications
in spintronics, magnonics, and neuromorphic computing. For their operation,
these devices require externally generated spin currents either from an
additional ferromagnetic layer or a material with a high spin Hall angle. Here
we demonstrate highly coherent field and current tunable microwave signals from
nanoconstrictions in single 15 and 20 nm thick permalloy layers. Using a
combination of spin torque ferromagnetic resonance measurements, scanning
microBrillouin light scattering microscopy, and micromagnetic simulations, we
identify the autooscillations as emanating from a localized edge mode of the
nanoconstriction driven by spin orbit torques. Our results pave the way for
greatly simplified designs of auto oscillating nanomagnetic systems only
requiring a single ferromagnetic layer.",1808.09330v1
2006-07-24,Measurement of the total optical angular momentum transfer in optical tweezers,"We describe a way to determine the total angular momentum, both spin and
orbital, transferred to a particle trapped in optical tweezers. As an example
an LG02 mode of a laser beam with varying degrees of circular polarisation is
used to trap and rotate an elongated particle with a well defined geometry. The
method successfully estimates the total optical torque applied to the particle.
For this technique, there is no need to measure the viscous drag on the
particle, as it is an optical measurement. Therefore, knowledge of the
particle's size and shape, as well as the fluid's viscosity, is not required.",0607216v1
2021-03-31,A magnetic domain wall Mackey-Glass oscillator,"We propose a time-delay oscillator with Mackey-Glass nonlinearity based on a
pinned magnetic domain wall in a thin film nanostrip. Through spin transfer
torques, electric currents applied along the strip cause the domain wall to
deform and displace away from a geometrical pinning site, which can be
converted into a nonlinear transfer function through a suitable choice of a
readout. This readout serves as a delay signal, which is subsequently fed back
into the applied current with amplification. With micromagnetics simulations,
we study the role of the readout position, time delay, and feedback gain on the
dynamics of this domain wall. In particular, we highlight regimes in which
self-sustained oscillations and complex transients are possible.",2104.00080v2
2021-10-22,Dynamical Tides in Eccentric Binaries Containing Massive Main-Sequence Stars: Analytical Expressions,"Tidal evolution of eccentric binary systems containing at least one massive
main-sequence (MS) star plays an important role in the formation scenarios of
merging compact-object binaries. The dominant dissipation mechanism in such
systems involves tidal excitation of outgoing internal gravity waves at the
convective-radiative boundary and dissipation of the waves at the stellar
envelope/surface. We have derived analytical expressions for the tidal torque
and tidal energy transfer rate in such binaries for arbitrary orbital
eccentricities and stellar rotation rates. These expressions can be used to
study the spin and orbital evolution of eccentric binaries containing massive
MS stars, such as the progenitors of merging neutron star binaries. Applying
our results to the PSR J0045-7319 system, which has a massive B-star companion
and an observed, rapidly decaying orbit, we find that for the standard radius
of convective core based on non-rotating stellar models, the B-star must have a
significant retrograde and differential rotation in order to explain the
observed orbital decay rate. Alternatively, we suggest that the convective core
may be larger as a result of rapid stellar rotation and/or mass transfer to the
B-star in the recent past during the post-MS evolution of the pulsar
progenitor.",2110.12030v1
2017-12-08,Spin Hall and spin swapping torques in diffusive ferromagnets,"A complete set of the generalized drift-diffusion equations for a coupled
charge and spin dynamics in ferromagnets in the presence of extrinsic
spin-orbit coupling is derived from the quantum kinetic approach, covering
major transport phenomena, such as the spin and anomalous Hall effects, spin
swapping, spin precession and relaxation processes. We argue that the spin
swapping effect in ferromagnets is enhanced due to spin polarization, while the
overall spin texture induced by the interplay of spin-orbital and spin
precessional effects displays a complex spatial dependence that can be
exploited to generate torques and nucleate/propagate domain walls in
centrosymmetric geometries without use of external polarizers, as opposed to
the conventional understanding of spin-orbit mediated torques.",1712.03009v1
2019-04-23,Spin injection and pumping generated by a direct current flowing through a magnetic tunnel junction,"A charge flow through a magnetic tunnel junction (MTJ) leads to the
generation of a spin-polarized current which exerts a spin-transfer torque
(STT) on the magnetization. When the density of applied direct current exceeds
some critical value, the STT excites high-frequency magnetization precession in
the ""free"" electrode of MTJ. Such precession gives rise to microwave output
voltage and, furthermore, can be employed for spin pumping into adjacent normal
metal or semiconductor. Here we describe theoretically the spin dynamics and
charge transport in the CoFeB/MgO/CoFeB/Au tunneling heterostructure connected
to a constant-current source. The magnetization dynamics in the free CoFeB
layer with weak perpendicular anisotropy is calculated by numerical integration
of the Landau-Lifshitz-Gilbert-Slonczewski equation accounting for both STT and
voltage controlled magnetic anisotropy associated with the CoFeB|MgO interface.
It is shown that a large-angle magnetization precession, resulting from
electrically induced dynamic spin reorientation transition, can be generated in
a certain range of relatively low current densities. An oscillating spin
current, which is pumped into the Au overlayer owing to such precession, is
then evaluated together with the injected spin current. Considering both the
driving spin-polarized charge current and the pumped spin current, we also
describe the charge transport in the CoFeB/Au bilayer with the account of
anomalous and inverse spin Hall effects. An electric potential difference
between the lateral sides of the CoFeB/Au bilayer is calculated as a function
of distance from the CoFeB|MgO interface. It is found that this transverse
voltage signal in Au is large enough for experimental detection, which
indicates significant efficiency of the proposed current-driven spin injector.",1904.10361v1
2019-03-16,Dzyaloshinskii-Moriya interaction and spin-orbit torque at the Ir/Co interface,"We studied the spin torque efficiency and the Dzyaloshinskii-Moriya
interaction (DMI) of heterostructures that contain interface(s) of Ir and Co.
The current-induced shifts of the anomalous Hall loops were used to determine
the spin torque efficiency and DMI of [Pt/Co/X] multilayers (X=Ir, Cu) as well
as Ir/Co and Pt/Ir/Co reference films. We find the effective spin Hall angle
and the spin diffusion length of Ir to be ~0.01 and less than ~1 nm,
respectively. The short spin diffusion length and the high conductivity make Ir
an efficient spin sink layer. Such spin sink layer can be used to control the
flow of spin current in heterostructures and to induce sufficient spin-orbit
torque on the magnetic layer. The DMI of Ir and Co interface is found to be in
the range of ~1.4 to ~2.2 mJ/m2, similar in magnitude to that of the Pt and Co
interface. The Ir/Co and Pt/Co interfaces possess the same sign of DMI,
resulting in a reduced DMI for the [Pt/Co/Ir] multilayers compared to that of
the [Pt/Co/Cu] multilayers. These results show the unique role the Ir layer
plays in defining spin-orbit torque and chiral magnetism in thin film
heterostructures.",1903.06913v1
2019-05-26,Influence of field-like torque in synchronization of spin torque oscillators,"The magnetization dynamics of two parallelly coupled spin torque oscillators,
destabilization of steady states and removal of multistability, are
investigated by taking into account the influence of field-like torque. It is
shown that the existence of such torque can cancel the effect of damping and
can, therefore, cause the oscillators to exhibit synchronized oscillations in
response to direct current. Further, our results show that the presence of
field-like torque enhances the power and Q-factor of the synchronized
oscillations. The validity of the above results is confirmed by numerical and
analytical studies based on the stochastic Landau-Lifshitz-Gilbert-Slonczewski
equation.",1905.10804v2
2021-03-29,Laser-induced torques in metallic antiferromagnets,"We study the laser-induced torques in the antiferromagnet (AFM) Mn$_2$Au. We
find that even linearly polarized light may induce laser-induced torques in
Mn$_2$Au, i.e., the light does not have to be circularly polarized. The
laser-induced torques in Mn$_2$Au are comparable in magnitude to those in the
ferromagnets Fe, Co and FePt at optical frequencies. We also compute the
laser-induced torques at terahertz (THz) frequencies and compare them to the
spin-orbit torques (SOTs) excited by THz laser-pulses. We find the SOTs to be
dominant at THz frequencies for the laser-field strengths used in experiments.
Additionally, we show that the matrix elements of the spin-orbit interaction
(SOI) can be used to add SOI only during the Wannier interpolation, which we
call Wannier interpolation of SOI (WISOI). This technique allows us to perform
the Wannier interpolation conveniently for many magnetization directions from a
single set of Wannier functions.",2103.15657v2
2022-10-05,Detection of long-range orbital-Hall torques,"We report and quantify a large orbital-Hall torque generated by Nb and Ru,
which we identify from a strong dependence of torques on the ferromagnets. This
is manifested as a sign reversal and strong enhancement in the damping-like
torques measured in Nb (or Ru)/Ni bilayers as compared to Nb (or Ru)/FeCoB
bilayers. The long-range nature of orbital transport in the ferromagnet is
revealed by the thickness dependences of Ni in Nb (or Ru)/Ni bilayers which are
markedly different from the regular spin absorption in the ferromagnet that
takes place within a few angstroms and thus it uniquely distinguishes the
orbital Hall torque from the spin Hall torque.",2210.02283v2
2023-07-11,Charge conservation in spin torque oscillators leads to a self-induced torque,"Spin torque oscillators are conventionally described by the
Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. However, at the onset of
oscillations, the predictions of the conventional LLGS equation differ
qualitatively from experimental results and thus appear to be incomplete. In
this work we show that taking charge conservation into account leads to a
previously-overlooked self-induced torque, which modifies the LLGS equation. We
show that the self-induced torque originates from the pumping current that a
precessing magnetization drives through a magnetic tunnel junction. To
illustrate the importance of the self-induced torque, we consider an in-plane
magnetized nanopillar, where it gives clear qualitative corrections to the
conventional LLGS description.",2307.05105v3
1997-10-14,Constraints on Torque-Reversing Accretion-Powered X-ray Pulsars,"The observed abrupt torque reversals in X-ray pulsars, 4U 1626-67, GX 1+4,
and OAO 1657-415, can be explained by transition in accretion flow rotation
from Keplerian to sub-Keplerian, which takes place at a critical accretion
rate, $\sim 10^{16}-10^{17}g/s$. When a pulsar system spins up near equilibrium
spin before the transition, the system goes into spin-down after transition to
sub-Keplerian. If a system is well into the spin-up regime, the transition can
cause a sharp decrease in spin-up rate but not a sudden spin-down. These
observable types of abrupt torque change are distinguished from the smooth
torque variation caused by change of ${\dot M}$ in the Keplerian flow. The
observed abrupt torque reversal is expected when the pulsar magnetic field
$B_*\sim 5\times 10^{11}b_p^{-1/2}L_{x,36}^{1/2}P_{*,10}^{1/2}G$ where the
magnetic pitch parameter $b_p\sim$ a few, $L_{x,36}$ is the X-ray luminosity in
$10^{36} erg/s$, and $P_{*,10}$ is the pulsar spin period in 10s. Observed
quasi-periodic oscillation (QPO) periods tightly constrain the model. For 4U
1626-67, ${\dot M}\approx 2.7\times 10^{16}g/s$ with $b_p^{1/2} B_*\approx
2\times 10^{12}G$. We estimate ${\dot M}\sim 6\times 10^{16} g/s$ and
$b_p^{1/2}B_*\sim 5\times 10^{13}G$ for GX 1+4, and ${\dot M} \sim 1\times
10^{17} g/s$ and $b_p^{1/2}B_*\sim 2\times 10^{13}G$ for OAO 1657-415. Reliable
detection of QPOs before and after torque reversal could directly test the
model.",9710148v1
2009-03-05,Extreme Sensitivity of the YORP Effect to Small-Scale Topography,"Radiation recoil (YORP) torques are shown to be extremely sensitive to
small-scale surface topography. Starting from simulated objects representative
of the near-Earth object population, random realizations of three types of
small-scale topography are added: Gaussian surface fluctuations, craters, and
boulders. For each, the resulting expected relative errors in the spin and
obliquity components of the YORP torque are computed. Gaussian power produces
errors of order 100% if observations constrain the surface to a spherical
harmonic order l < 10. A single crater with diameter roughly half the object's
mean radius, placed at random locations, results in errors of several tens of
percent. Boulders create torque errors roughly 3 times larger than do craters
of the same diameter. A single boulder comparable to Yoshinodai on 25143
Itokawa, moved by as little as twice its own diameter, can alter the magnitude
of the torque by factors of several, and change the sign of its spin component
at all obliquities. A YORP torque prediction derived from groundbased data can
be expected to be in error by of order 100% due to unresolved topography. Small
surface changes caused by slow spin-up or spin-down may have significant
stochastic effects on the spin evolution of small bodies. For rotation periods
between roughly 2 and 10 hours, these unpredictable changes may reverse the
sign of the YORP torque. Objects in this spin regime may random-walk up and
down in spin rate before the rubble-pile limit is exceeded and fissioning or
loss of surface objects occurs. Similar behavior may be expected at rotation
rates approaching the limiting values for tensile-strength dominated objects.",0903.1119v1
1999-03-02,Conserved Ordering Dynamics of Heisenberg Spins with Torque,"We show that a torque induced by the local molecular field drives the
zero-temperature ordering dynamics of a conserved Heisenberg magnet to a new
fixed point, characterised by exponents z=2 and $\lambda \approx 5.15$.
Numerical solutions of the Langevin equation indicate that theories using a
Gaussian closure are inconsistent even when the torque is absent. The torque is
relevant even for quenches to T_c, with exponents $z=4-\epsilon/2$ and $\lambda
= d$ (where $\epsilon = 6-d$). Indeed $\lambda$ is always equal to d for
quenches to T_c whenever the order parameter is conserved.",9903041v1
2020-03-14,Rotational Disruption of Nonspherical Cometary Dust Particles by Radiative Torques,"Rigorous statistical numerical analysis of the response of a nonspherical
dust particle ensemble composed of aggregates of astronomical silicate is
presented. It is found that the rotational disruption mechanism is not only
likely to occur but to be a key element in explaining many separate
observations of cometary dust. Namely, radiative torques are shown to spin-up
and align cometary dust within the timescales of cometary activity.
Additionally, the radiative torque alignment and disruption mechanisms within
certain conditions are shown to be consistent with observations of rapid
polarization of dust and spectral bluing of dust. The results indicate that
radiative torques should be taken into account nearly universally when
considering the evolution of cometary dust.",2003.06577v1
2018-03-29,Giant resonant nonlinear damping in nanoscale ferromagnets,"Magnetic damping is a key metric for emerging technologies based on magnetic
nanoparticles, such as spin torque memory and high-resolution biomagnetic
imaging. Despite its importance, understanding of magnetic dissipation in
nanoscale ferromagnets remains elusive, and the damping is often treated as a
phenomenological constant. Here we report the discovery of a giant
frequency-dependent nonlinear damping that strongly alters the response of a
nanoscale ferromagnet to spin torque and microwave magnetic field. This novel
damping mechanism originates from three-magnon scattering that is strongly
enhanced by geometric confinement of magnons in the nanomagnet. We show that
the giant nonlinear damping can invert the effect of spin torque on a
nanomagnet leading to a surprising current-induced enhancement of damping by an
antidamping torque. Our work advances understanding of magnetic dynamics in
nanoscale ferromagnets and spin torque devices.",1803.10925v1
2019-04-26,Terahertz spin dynamics driven by a field-derivative torque,"Efficient manipulation of magnetization at ultrashort time scales is of
particular interest for future technology. Here, we numerically investigate the
influence of the so-called field-derivative torque, which was derived earlier
based on relativistic Dirac theory [Mondal et al., Phys. Rev. B 94, 144419
(2016)], on the spin dynamics triggered by ultrashort laser pulses. We find
that only considering the THz Zeeman field can underestimate the spin
excitation in antiferromagnetic oxide systems as, e.g., NiO and CoO. However,
accounting for both, the THz Zeeman torque and the field-derivative torque, the
amplitude of the spin excitation increases significantly. Studying the damping
dependence of field-derivative torque we observe larger effects for materials
having larger damping constants.",1904.11768v2
2021-03-06,Resolving Discrepancies in Spin-Torque Ferromagnetic Resonance Measurements: Lineshape vs. Linewidth Analyses,"When spin-orbit torques are measured using spin-torque ferromagnetic
resonance (ST-FMR), two alternative ways of analyzing the results to extract
the torque efficiencies -- lineshape analysis and analysis of the change in
linewidth versus DC current -- often give inconsistent results. We identify a
source for these inconsistencies. We show that fits of ST-FMR data to the
standard analysis framework leave significant residuals that we identify as due
to (i) current-induced excitations of a small volume of magnetic material with
magnetic damping much larger than the bulk of the magnetic layer, that we
speculate is associated with the heavy-metal/magnet interface and (ii)
oscillations of the sample magnetization at the modulation frequency due to
heating. The dependence of the residual signals on DC current can interfere
with an accurate extraction of spin-torque efficiencies by the linewidth
method. We show that the discrepancies between the two types of analysis can be
largely eliminated by extrapolating the window of magnetic fields used in the
linewidth fits to small values so as to minimize the influence of the residual
signals.",2103.04172v1
2021-12-22,Quantifying Spin-Orbit Torques in Antiferromagnet/Heavy Metal Heterostructures,"The effect of spin currents on the magnetic order of insulating
antiferromagnets (AFMs) is of fundamental interest and can enable new
applications. Toward this goal, characterizing the spin-orbit torques (SOT)
associated with AFM/heavy metal (HM) interfaces is important. Here we report
the full angular dependence of the harmonic Hall voltages in a predominantly
easy-plane AFM, epitaxial c-axis oriented $\alpha$-Fe$_2$O$_3$ films, with an
interface to Pt. By modeling the harmonic Hall signals together with the
$\alpha$-Fe$_2$O$_3$ magnetic parameters, we determine the amplitudes of
field-like and damping-like SOT. Out-of-plane field scans are shown to be
essential to determining the damping-like component of the torques. In contrast
to ferromagnetic/heavy metal heterostructures, our results demonstrate that the
field-like torques are significantly larger than the damping-like torques,
which we correlate with the presence of a large imaginary component of the
interface spin-mixing conductance. Our work demonstrates a direct way of
characterizing SOT in AFM/HM heterostructures.",2112.12238v1
2023-10-18,Neel tensor torque at the ferromagnet/antiferromagnet interface,"Antiferromagnets (AFMs) exhibit spin arrangements with no net magnetization,
positioning them as promising candidates for spintronics applications. While
electrical manipulation of the single-crystal AFMs, composed of periodic spin
configurations, is achieved recently, it remains a daunting challenge to
characterize and to manipulate polycrystalline AFMs. Utilizing statistical
analysis in data science, we demonstrate that polycrystalline AFMs can be
described using a real, symmetric, positive semi-definite, rank-two tensor,
which we term the Neel tensor. This tensor introduces a unique spin torque,
diverging from the conventional field-like and Slonczewski torques in
spintronics devices. Remarkably, Neel tensors can be trained to retain a
specific orientation, functioning as a form of working memory. This attribute
enables zero-field spin-orbit-torque switching in trilayer devices featuring a
heavy-metal/ferromagnet/AFM structure and is also consistent with the X-ray
magnetic linear dichroism measurements. Our findings uncover hidden statistical
patterns in polycrystalline AFMs and establishes the presence of Neel tensor
torque, highlighting its potential to drive future spintronics innovations.",2310.11839v1
2023-11-23,Effect of multi-layering and crystal orientation on spin-orbit torque efficiency in Ni/Pt layer stacking,"We study spin-orbit torques (SOTs) in Ni/Pt bi-layers and multi-layers by
ferromagnetic resonance (FMR) and harmonic-Hall measurements. The effect of
multi-layering and crystal orientation on field-like (FL) and damping-like (DL)
torque efficiencies is examined by exploiting the samples with different
crystal orientations: epitaxial and poly-crystalline structures on Sapphire and
SiO$_2$ substrates, respectively.
  We find that both DL and FL torque efficiencies are larger in multi-layer
samples and there is no complete cancellation of torque efficiencies that is
generally expected for ideal symmetric stacking structures. The results of
SOT-FMR indicate that the epitaxial samples show higher efficiency for SOT
generation compared to the poly-crystalline samples, suggesting that SOT
generation is modified depending on the interfacial contribution. In addition,
the spin Hall conductivity of the epitaxial multi-layer is the largest among
the samples. The present results signify the importance of crystal orientation,
multi-layering and interface-quality in improving the efficiency of SOTs
generation combined with larger spin hall angle for developing future
spintronic devices.",2311.13835v1
2013-05-22,Self-consistent calculation of spin transport and magnetization dynamics,"A spin-polarized current transfers its spin-angular momentum to a local
magnetization, exciting current-induced magnetization dynamics. So far, most
studies in this field have focused on the direct effect of spin transport on
magnetization dynamics, but ignored the feedback from the magnetization
dynamics to the spin transport and back to the magnetization dynamics. Although
the feedback is usually weak, there are situations when it can play an
important role in the dynamics. In such situations, self-consistent
calculations of the magnetization dynamics and the spin transport can
accurately describe the feedback. This review describes in detail the feedback
mechanisms, and presents recent progress in self-consistent calculations of the
coupled dynamics. We pay special attention to three representative examples,
where the feedback generates non-local effective interactions for the
magnetization. Possibly the most dramatic feedback example is the dynamic
instability in magnetic nanopillars with a single magnetic layer. This
instability does not occur without non-local feedback. We demonstrate that full
self-consistent calculations generate simulation results in much better
agreement with experiments than previous calculations that addressed the
feedback effect approximately. The next example is for more typical spin valve
nanopillars. Although the effect of feedback is less dramatic because even
without feedback the current can induce magnetization oscillation, the feedback
can still have important consequences. For instance, we show that the feedback
can reduce the linewidth of oscillations, in agreement with experimental
observations. Finally, we consider nonadiabatic electron transport in narrow
domain walls. The non-local feedback in these systems leads to a significant
renormalization of the effective nonadiabatic spin transfer torque.",1305.5087v1
2020-12-17,Spin-torque Dynamics for Noise Reduction in Vortex-based Sensors,"Performance of magnetoresistive sensors is today mainly limited by their 1/f
low-frequency noise. Here, we study this noise component in vortex-based TMR
sensors. We compare the noise level in different magnetization configurations
of the device, i.e vortex state or uniform parallel or antiparallel states. We
find that the vortex state is at least an order of magnitude noisier than the
uniform states. Nevertheless, by activating the spin-transfer induced dynamics
of the vortex configuration, we observe a reduction of the 1/f noise, close to
the values measured in the AP state, as the vortex core has a lower probability
of pinning into defect sites. Additionally, by driving the dynamics of the
vortex core by a non-resonant rf field or current we demonstrate that the 1/f
noise can be further decreased. The ability to reduce the 1/f low-frequency
noise in vortex-based devices by leveraging their spin-transfer dynamics thus
enhances their applicability in the magnetic sensors' landscape.",2012.09616v1
2000-01-24,"Ordering Dynamics of Heisenberg Spins with Torque: Crossover, Spinwaves and Defects","We study the effect of a torque induced by the local molecular field on the
phase ordering dynamics of the Heisenberg model when the total magnetization is
conserved. The torque drives the zero-temperature ordering dynamics to a new
fixed point, characterized by exponents $z=2$ and $\lambda \approx 5$. This
`torque-driven' fixed point is approached at times such that $g^2 t\gg 1$,
where $g$ is the strength of the torque. All physical quantities, like the
domain size $L(t)$ and the equal and unequal time correlation functions obey a
crossover scaling form over the entire range of $g$. An attempt to understand
this crossover behavior from the approximate Gaussian Closure Scheme fails
completely, implying that the dynamics at late times cannot be understood from
the dynamics of defects alone. We provide convincing arguments that the spin
configurations can be decomposed in terms of defects and spin-waves which
interact with each other even at late times. In the absence of the torque term,
the spin waves decay faster, but even so we find that the Gaussian closure
scheme is inconsistent. In the latter case the inconsistency may be remedied by
including corrections to a simple gaussian distribution. For completeness we
include a discussion of the ordering dynamics at $T_c$, where the torque is
shown to be relevant, with exponents $z=4-\epsilon/2$ and $\lambda = d$ (where
$\epsilon = 6-d$). We show to all orders in perturbation theory that
$\lambda=d$ as a consequence of the conservation law.",0001340v1
2015-06-19,The optical torque: Electromagnetic spin and orbital angular momenta conservation laws and their significance,"The physics involved in the fundamental conservation equations of the spin
and orbital angular momenta leads to new laws and phenomena that I disclose. To
this end, I analyse the scattering of an electromagnetic wavefield by the
canonical system constituted by a small particle, which I assume dipolar in the
wide sense. Specifically, under quite general conditions these laws lead to
understanding how is the contribution and weight of each of those angular
momenta to the electromagnetic torque exerted by the field on the object, which
is shown to consist of an extinction and a scattering, or recoil, part. This
leads to an interpretation of its effect different to that taken up till now by
many theoretical and experimental works, and implies that a part of the recoil
torque cancels the usually called intrinsic torque which was often considered
responsible of the particle spinning. In addition, I obtain the contribution of
the spatial structure of the wave to this torque, unknown to this date, showing
its effect in the orbiting of the object, and demonstrating that it often leads
to a negative torque on a single particle, i.e. opposite to the incident
helicity, producing an orbital motion contrary to its spinning. Furthermore, I
establish a decomposition of the electromagnetic torque into conservative and
non-conservative components in which the helicity and its flow play a role
analogous to the energy and its flux for electromagnetic forces. I illustrate
these phenomena with examples of beams, also showing the difficulties of some
paraxial formulations whose fields do not hold the transversality condition.",1506.06016v2
2022-03-27,Giant bulk spin-orbit torque and efficient electrical switching in single ferrimagnetic FeTb layers with strong perpendicular magnetic anisotropy,"Efficient manipulation of antiferromagnetically coupled materials that are
integration-friendly and have strong perpendicular magnetic anisotropy (PMA) is
of great interest for low-power, fast, dense magnetic storage and computing.
Here, we report a distinct, giant bulk damping-like spin-orbit torque in
strong-PMA ferrimagnetic Fe100-xTbx single layers that are integration-friendly
(composition-uniform, amorphous, sputter-deposited). For sufficiently-thick
layers, this bulk torque is constant in the efficiency per unit layer
thickness, {\xi}_DL^j/t, with a record-high value of 0.036nm-1, and the
dampinglike torque efficiency {\xi}_DL^j achieves very large values for thick
layers, up to 300% for 90 nm layers. This giant bulk torque by itself switches
tens of nm thick Fe100-xTbx layers that have very strong PMA and high
coercivity at current densities as low as a few MA/cm2. Surprisingly, for a
given layer thickness, {\xi}_DL^j shows strong composition dependence and
becomes negative for composition where the total angular momentum is oriented
parallel to the magnetization rather than antiparallel. Our findings of giant
bulk spin torque efficiency and intriguing torque-compensation correlation will
stimulate study of such unique spin-orbit phenomena in a variety of
ferrimagnetic hosts. This work paves a promising avenue for developing
ultralow-power, fast, dense ferrimagnetic storage and computing devices.",2203.14193v1
2014-04-08,Reconstructing the intermittent dynamics of the torque in wind turbines,"We apply a framework introduced in the late nineties to analyze load
measurements in off-shore wind energy converters (WEC). The framework is
borrowed from statistical physics and properly adapted to the analysis of
multivariate data comprising wind velocity, power production and torque
measurements, taken at one single WEC. In particular, we assume that wind
statistics drives the fluctuations of the torque produced in the wind turbine
and show how to extract an evolution equation of the Langevin type for the
torque driven by the wind velocity. It is known that the intermittent nature of
the atmosphere, i.e. of the wind field, is transferred to the power production
of a wind energy converter and consequently to the shaft torque. We show that
the derived stochastic differential equation quantifies the dynamical coupling
of the measured fluctuating properties as well as it reproduces the
intermittency observed in the data. Finally, we discuss our approach in the
light of turbine monitoring, a particular important issue in off-shore wind
farms.",1404.2063v1
2014-05-01,Optical Torque from Enhanced Scattering by Multipolar Plasmonic Resonance,"We present a theoretical study of the optical angular momentum transfer from
a circularly polarized plane wave to thin metal nanoparticles of different
rotational symmetries. While absorption has been regarded as the predominant
mechanism of torque generation on the nanoscale, we demonstrate numerically how
the contribution from scattering can be enhanced by using multipolar plasmon
resonance. The multipolar modes in non-circular particles can convert the
angular momentum carried by the scattered field, thereby producing
scattering-dominant optical torque, while a circularly symmetric particle
cannot. Our results show that the optical torque induced by resonant scattering
can contribute to 80% of the total optical torque in gold particles. This
scattering-dominant torque generation is extremely mode-specific, and deserves
to be distinguished from the absorption-dominant mechanism. Our findings might
have applications in optical manipulation on the nanoscale as well as new
designs in plasmonics and metamaterials.",1405.0239v1
2014-09-29,Royal Observatory of Belgium Gravitational balance,"An astatized symmetrical vertical pendulum is monitoring torque {\Gamma}(M)
resulting of gravitational attractions exerted by two external masses M moving
up down. Local gravity field g produce the main pendulum restoring torque
combined with a very weak variable torque {\Gamma}(c) induced by rotation of
watch needles fixed to the pendulum. Transfer of fundamental units to calibrate
the {\Gamma}(c) torques is obtained by a reference torque {\Gamma}({\mu})
resulting of precise displacements of a well known mass {\mu}. We permanently
monitored ratio between the gravitational effect {\Gamma}(M) and calibrated
{\Gamma}(c) to determine G. Position of the pendulum is measured with a
capacitive bridge. Bias voltages sent to two electrodes set-up at the bottom of
the pendulum allows to feedback pendulum with a controlled electrostatic
torque. We discuss potential interest of our prototype to design a multi
pendulum system to check systematic effects for different geometries and
various kinds of materials.",1409.8016v1
2022-01-03,Evaluation and comparison of SEA torque controllers in a unified framework,"Series elastic actuators (SEA) with their inherent compliance offer a safe
torque source for robots that are interacting with various environments,
including humans. These applications have high requirements for the SEA torque
controllers, both in the torque response as well as interaction behavior with
its the environment. To differentiate state of the art torque controllers, this
work is introducing a unifying theoretical and experimental framework that
compares controllers based on their torque transfer behavior, their apparent
impedance behavior, and especially the passivity of the apparent impedance,
i.e. their interaction stability, as well as their sensitivity to sensor noise.
We compare classical SEA control approaches such as cascaded PID controllers
and full state feedback controllers with advanced controllers using disturbance
observers, acceleration feedback and adaptation rules. Simulations and
experiments demonstrate the trade-off between stable interactions, high
bandwidths and low noise levels. Based on these tradeoffs, an application
specific controller can be designed and tuned, based on desired interaction
with the respective environment.",2201.00583v1
2001-11-08,Ordering in Heisenberg Spin Glasses,"For five different Heisenberg spin glass systems, torque experiments were
performed in applied magnetic fields up to $4 T$. The Dzyaloshinski-Moriya
random anisotropy strengths, the in-field torque onset temperatures, and the
torque relaxation were measured. Critical exponents were estimated
independently using a standard protocol. The data are strong evidence for a
true spin glass ordered state which survives under high applied magnetic
fields; they can be interpreted consistently in terms of a chiral ordering
model with replica symmetry breaking as proposed by Kawamura and coworkers.",0111129v2
2003-08-15,Current-Driven Magnetization Dynamics in Magnetic Multilayers,"We develop a quantum analog of the classical spin-torque model for
current-driven magnetic dynamics. The current-driven magnetic excitation at
finite field becomes significantly incoherent. This excitation is described by
an effective magnetic temperature rather than a coherent precession as in the
spin-torque model. However, both the spin-torque and effective temperature
approximations give qualitatively similar switching diagrams in the
current-field coordinates, showing the need for detailed experiments to
establish the proper physical model for current-driven dynamics.",0308320v2
2005-09-15,Spectroscopy of phonons and spin torques in magnetic point contacts,"Phonon spectroscopy is used to investigate the mechanism of current-induced
spin torques in nonmagnetic/ferromagnetic (N/F) point contacts. Magnetization
excitations observed in the magneto-conductance of the point contacts are
pronounced for diffusive and thermal contacts, where the electrons experience
significant scattering in the contact region. We find no magnetic excitations
in highly ballistic contacts. Our results show that impurity scattering at the
N/F interface is the origin of the new single-interface spin torque effect.",0509396v1
2007-06-12,Gilbert and Landau-Lifshitz damping in the presense of spin-torque,"A recent article by Stiles et al. (cond-mat/0702020) argued in favor of the
Landau-Lifshitz damping term in the micromagnetic equations of motion over that
of the more commonly accepted Gilbert damping form. Much of their argument
revolved around spin-torque driven domain wall motion in narrow magnetic wires,
since the presence of spin-torques can more acutely draw a distinction between
the two forms of damping. In this article, the author uses simple arguments and
examples to offer an alternative point of view favoring Gilbert.",0706.1736v1
2008-11-04,Amplitude-Phase Coupling in a Spin-Torque Nano-Oscillator,"The spin-torque nano-oscillator in the presence of thermal fluctuation is
described by the normal form of the Hopf bifurcation with an additive white
noise. By the application of the reduction method, the amplitude-phase coupling
factor, which has a significant effect on the power spectrum of the spin-torque
nano-oscillator, is calculated from the Landau-Lifshitz-Gilbert-Slonczewski
equation with the nonlinear Gilbert damping. The amplitude-phase coupling
factor exhibits a large variation depending on in-plane anisotropy under the
practical external fields.",0811.0425v1
2009-05-19,Proposal of a robust measurement scheme for the non-adiabatic spin torque using the displacement of magnetic vortices,"The strength of the non-adiabatic spin torque is currently under strong
debate, as its value differs by orders of magnitude as well in theoretical
predictions as in measurements. Here, a measurement scheme is presented that
allows to determine the strength of the non-adiabatic spin torque accurately
and directly. Analytical and numerical calculations show that the scheme allows
to separate the displacement due to the Oersted field and is robust against
uncertainties of the exact current direction.",0905.3141v1
2009-09-02,Spin-torque generation by dc or ac voltages in magnetic layered structures,"A general expression of the current induced spin torque in a magnetic layered
structure in the presence of external dc or ac voltages is derived in the
framework of the scattering matrix approach. A detailed analysis is performed
for a magnetic-nonmagnetic-magnetic trilayer connected to external leads in the
presence of dc voltage bias in the ballistic regime. Alternatively, the
possibility of producing spin torque by means of the adiabatic ac modulation of
external gate voltages (quantum pumping) is proposed and discussed.",0909.0374v1
2011-12-14,Quenched Slonczewski-Windmill in Spin-Torque Vortex-Oscillators,"We present a combined analytical and numerical study on double-vortex
spin-torque nano-oscillators and describe a mechanism that suppresses the
windmill modes. The magnetization dynamics is dominated by the gyrotropic
precession of the vortex in one of the ferromagnetic layers. In the other layer
the vortex gyration is strongly damped. The dominating layer for the
magnetization dynamics is determined by the current polarity. Measurements on
Fe/Ag/Fe nano-pillars support these findings. The results open up a new
perspective for building high quality-factor spin-torque oscillators operating
at selectable, well-separated frequency bands.",1112.3163v1
2013-06-09,Force and torque on an electric dipole by spinning light fields,"We calculate the optical force and torque applied to an electric dipole by a
spinning light field. We find that the dissipative part of the force depends on
the orbital energy flow of the field only, because the latter is related to the
phase gradient generalized for such a light field. As for the remaining spin
energy flow, it gives rise to an optical torque. The resulting change in the
optical force is detailed for different experimentally relevant configurations,
and we show in particular how this change is critical when surface plasmon
modes are involved.",1306.2050v2
2013-06-19,A quasi-linear spin-torque nano-oscillator via enhanced negative feedback of power fluctuations,"We report an approach to improving the performance of spin torque
nano-oscillators (STNOs) that utilizes power-dependent negative feedback to
achieve a significantly enhanced dynamic damping. In combination with a
sufficiently slow variation of frequency with power this can result in a
quasi-linear STNO, with very weak non-linear coupling of power and phase
fluctuations over a range of bias current and field. An implementation of this
approach that utilizes a non-uniform spin-torque demonstrates that highly
coherent room temperature STNOs can be achieved while retaining a significant
tunability.",1306.4668v1
2014-03-24,Skyrmionic spin Seebeck effect via dissipative thermomagnonic torques,"We derive thermomagnonic torque and its ""$\beta$-type"" dissipative correction
from the stochastic Landau-Lifshitz-Gilbert equation. The ""$\beta$-type""
dissipative correction describes viscous coupling between magnetic dynamics and
magnonic current and it stems from spin mistracking of the magnetic order. We
show that thermomagnonic torque is important for describing temperature
gradient induced motion of skyrmions in helical magnets while dissipative
correction plays an essential role in generating transverse Magnus force. We
propose to detect such skyrmionic motion by employing the transverse spin
Seebeck effect geometry.",1403.6160v2
2015-05-15,Critical current and linewidth reduction in spin-torque nano-oscillators by delayed self-injection,"Based on theoretical models, the dynamics of spin-torque nano-oscillators can
be substantially modified by re-injecting the emitted signal to the input of
the oscillator after some delay. Numerical simulations for vortex magnetic
tunnel junctions show that with reasonable parameters this approach can
decrease critical currents as much as 25 % and linewidths by a factor of 4.
Analytical calculations, which agree well with simulations, demonstrate that
these results can be generalized to any kind of spin-torque oscillator.",1505.04102v1
2017-12-13,Mutual synchronization of spin-torque oscillators consisting of perpendicularly magnetized free layers and in-plane magnetized pinned layers,"A mutual synchronization of spin-torque oscillators coupled through current
injection is studied theoretically. Models of electrical coupling in parallel
and series circuits are proposed. Solving the Landau-Lifshitz-Gilbert equation,
excitation of in-phase or antiphase synchronization, depending on the ways the
oscillators are connected, is found. It is also found from both analytical and
numerical calculations that the current-frequency relations for both parallel
and series circuits are the same as that for a single spin-torque oscillator.",1712.04591v1
2018-07-26,Emission of coherent propagating magnons by insulator-based spin-orbit torque oscillators,"We experimentally demonstrate generation of coherent propagating magnons in
ultra-thin magnetic-insulator films by spin-orbit torque induced by dc electric
current. We show that this challenging task can be accomplished by utilizing
magnetic-insulator films with large perpendicular magnetic anisotropy. We
demonstrate simple and flexible spin-orbit torque devices, which can be used as
highly efficient nanoscale sources of coherent propagating magnons for
insulator-based spintronic applications.",1807.09976v1
2019-06-27,Spin-orbit torques and magnetization switching in perpendicularly magnetized epitaxial Pd/Co2FeAl/MgO structures,"We demonstrate efficient current induced spin orbit torque switching in
perpendicularly magnetized epitaxial MgO(001)//Pd/Co2FeAl/MgO heterostructures
grown by magnetron sputtering. The advantage of such heterostructures for spin
orbit torque MRAM devices is that they allow a unique combination of critical
ingredients: i) low resistivity required for reduced electric energy
consumption during writing, ii) high TMR ratio required for efficient reading
and iii) strong perpendicular magnetic anisotropy for increased thermal
stability.",1906.11917v1
2016-12-21,Critical current density of a spin-torque oscillator with an in-plane magnetized free layer and an out-of-plane magnetized polarizer,"Spin-torque induced magnetization dynamics in a spin-torque oscillator with
an in-plane (IP) magnetized free layer and an out-of-plane (OP) magnetized
polarizer under IP shape-anisotropy field ($H_{\rm k}$) and applied IP magnetic
field ($H_{\rm a}$) was theoretically studied based on the macrospin model. The
rigorous analytical expression of the critical current density ($J_{\rm c1}$)
for the OP precession was obtained. The obtained expression successfully
reproduces the experimentally obtained $H_{\rm a}$-dependence of $J_{\rm c1}$
reported in [D. Houssameddine $et$ $al$., Nat. Mater. 6, 447 (2007)].",1612.06951v1
2017-01-31,Controlling the synchronization properties of two dipolarly coupled vortex based spin-torque nano-oscillators by the intermediate of a third one,"In this paper, we propose to control the strength of phase-locking between
two dipolarly coupled vortex based spin-torque nano-oscillators by placing an
intermediate oscillator between them. We show through micromagnetic simulations
that the strength of phase-locking can be largely tuned by a slight variation
of current in the intermediate oscillator. We develop simplified numerical
simulations based on analytical expressions of the vortex core trajectories
that will be useful for investigating large arrays of densely packed
spin-torque oscillators interacting through their stray fields.",1701.09101v1
2019-04-01,Synchrony breakdown and noise-induced oscillation death in ensembles of serially connected spin-torque oscillators,"We consider collective dynamics in the ensemble of serially connected
spin-torque oscillators governed by the Landau-Lifshitz-Gilbert-Slonczewski
magnetization equation. Proximity to homoclinicity hampers synchronization of
spin-torque oscillators: when the synchronous ensemble experiences the
homoclinic bifurcation, the Floquet multiplier, responsible for the temporal
evolution of small deviations from the ensemble mean, diverges. Depending on
the configuration of the contour, sufficiently strong common noise, exemplified
by stochastic oscillations of the current through the circuit, may suppress
precession of the magnetic field for all oscillators. We derive the explicit
expression for the threshold amplitude of noise, enabling this suppression.",1904.00897v1
2020-02-11,Geometric phase-control of a spin-torque oscillator,"We show that the phase of a spin-torque oscillator generically acquires a
geometric contribution upon slow and cyclic variation of the parameters that
govern its dynamics. As an example, we compute the geometric phase that results
from a cyclic excursion of the magnitude of the external field and the current.
We consider thermal phase fluctuations and conclude that the geometric phase
should be experimentally observable at room temperature with current setups. We
briefly comment on arrays of spin-torque oscillators and possible applications.",2002.04492v1
2020-05-16,Multiple modes of a single spin torque oscillator under the non-linear region,"A numerical investigation is conducted for a single spin-torque oscillator
under the non-linear region. A large angle precession triggers the generation
of multiple modes without any feedbacked circuits and/or magnetic couplings
with neighboring oscillators. Our simulations show that a single eigenmode of a
given spin-torque oscillator can trigger up to six discrete modes as the
sideband modes. These findings will offer the new functionality to the STO for
developing the spintronic logic circuits.",2005.07836v2
2020-10-02,Dynamic Phase Diagram of an Orthogonal Spin Torque device: Topological Category,"The magnetization evolution of the free layer in an orthogonal spin-torque
device is studied based on a macrospin model. The trajectory of magnetization
vector under various conditions has shown rich nonlinear properties. The phase
diagram is obtained in the parameter spaces of current density and the
polarization distribution (the ratio of in-plane and out-of-plane polarizers).
These dynamic phases can be classified according to their nonlinear behaviors
which are topologically different, namely limit point and/or limit cycle. The
topological classification is meaningful to design the ultra-fast spin-torque
devices under different dynamic conditions towards various applications such as
memory and oscillators.",2010.00749v1
2021-12-13,Magnon frequency renormalization by the electronic geometrical spin torque in itinerant magnets,"We investigate non-adiabatic effects on the magnon frequency in an
interacting system of localized spins and itinerant electrons. Including the
lowest order corrections to the adiabatic dynamics in an analytically solvable
model, applicable to simple ferromagnets like Fe, Co and Ni, we find that the
magnon frequency is renormalized by a geometrical torque arising from the
electronic spin Berry curvature. Comparison to exact numerical simulations
reveals that our analytical solution captures essential low-energy features,
and provides a mechanism for the magnon frequency hardening observed in recent
first principles calculations for Fe, provided the geometrical torque is taken
into account.",2112.06547v1
2022-08-16,Exchange torque in noncollinear spin density functional theory with a semilocal exchange functional,"We present a semilocal exchange-correlation energy functional for
noncollinear spin density functional theory based on short-range expansions of
the spin-resolved exchange hole and the two-body density matrix. Our functional
is explicitly derived for noncollinear magnetism, U(1) and SU(2) gauge
invariant, and gives rise to nonvanishing exchange-correlation torques. Testing
the functional for frustrated antiferromagnetic chromium clusters, the exchange
part is shown to perform favorably compared to the far more expensive Slater
and optimized effective potentials, and a delicate interplay between exchange
and correlation torques is uncovered.",2208.07729v2
2024-03-18,Current-induced magnon trapping in spin torque oscillation,"Spin torque nano-oscillators realized by magnetization dynamics trapped in a
current-induced potential are reported. We fabricated Ni$_{81}$Fe$_{19}$/Pt
nanostructures and measured current-induced microwave emission from the
structures. The result shows an increase in the magnitude and spectral
narrowing of the microwave emission. We demonstrate that the current-induced
magnetic field suppresses magnon radiation loss and significantly reduces the
linewidth and the threshold current required for the spin torque oscillation.",2403.11618v1
2015-06-30,Experimental Demonstration of Efficient Spin-Orbit Torque Switching of an MTJ with sub-100 ns Pulses,"Efficient generation of spin currents from charge currents is of high
importance for memory and logic applications of spintronics. In particular,
generation of spin currents from charge currents in high spin-orbit coupling
metals has the potential to provide a scalable solution for embedded memory. We
demonstrate a net reduction in critical charge current for spin torque driven
magnetization reversal via using spin-orbit mediated spin current generation.
We scaled the dimensions of the spin-orbit electrode to 400 nm and the
nanomagnet to 270 nm x 68 nm in a three terminal spin-orbit torque, magnetic
tunnel junction (SOT-MTJ) geometry. Our estimated effective spin Hall angle is
0.15-0.20 using the ratio of zero temperature critical current from spin Hall
switching and estimated spin current density for switching the magnet. We show
bidirectional transient switching using spin-orbit generated spin torque at 100
ns switching pulses reliably followed by transient read operations. We finally
compare the static and dynamic response of the SOT-MTJ with transient spin
circuit modeling showing the performance of scaled SOT-MTJs to enable
nanosecond class non-volatile MTJs.",1506.09177v4
2018-10-02,Nanoscale transfer of angular momentum mediated by the Casimir torque,"Casimir interactions play an important role in the dynamics of nanoscale
objects. Here, we investigate the noncontact transfer of angular momentum at
the nanoscale through the analysis of the Casimir torque acting on a chain of
rotating nanoparticles. We show that this interaction, which arises from the
vacuum and thermal fluctuations of the electromagnetic field, enables an
efficient transfer of angular momentum between the elements of the chain.
Working within the framework of fluctuational electrodynamics, we derive
analytical expressions for the Casimir torque acting on each nanoparticle in
the chain, which we use to study the synchronization of chains with different
geometries and to predict unexpected dynamics, including a rattleback-like
behavior. Our results provide new insights into the Casimir torque and how it
can be exploited to achieve efficient noncontact transfer of angular momentum
at the nanoscale, and therefore have important implications for the control and
manipulation of nanomechanical devices.",1810.01342v2
2001-08-29,Current and Spin-Torque in Double Tunnel Barrier Ferromagnet - Superconductor - Ferromagnet Systems,"We calculate the current and the spin-torque in small symmetric double tunnel
barrier ferromagnet - superconductor - ferromagnet (F-S-F) systems.
Spin-accumulation on the superconductor governs the transport properties when
the spin-flip relaxation time is longer than the transport dwell time. In the
elastic transport regime, it is demonstrated that the relative change in the
current (spin-torque) for F-S-F systems equals the relative change in the
current (spin-torque) for F-N-F systems upon changing the relative
magnetization direction of the two ferromagnets. This differs from the results
in the inelastic transport regime where spin-accumulation suppresses the
superconducting gap and dramatically changes the magnetoresistance [S.
Takahashi, H. Imamura, and S. Maekawa, Phys. Rev. Lett. 82, 3911 (1999)]. The
experimental relevance of the elastic and inelastic transport regimes,
respectively, as well as the reasons for the change in the transport properties
are discussed.",0108490v2
2014-01-10,Thermally activated switching of perpendicular magnet by spin-orbit spin torque,"We theoretically investigate the threshold current for thermally activated
switching of a perpendicular magnet by spin-orbit spin torque. Based on the
Fokker-Planck equation, we obtain an analytic expression of the switching
current, in agreement with numerical result. We find that thermal energy
barrier exhibits a quasi-linear dependence on the current, resulting in an
almost linear dependence of switching current on the log-scaled current
pulse-width even below 10 ns. This is in stark contrast to standard spin torque
switching, where thermal energy barrier has a quadratic dependence on the
current and the switching current rapidly increases at short pulses. Our
results will serve as a guideline to design and interpret switching experiments
based on spin-orbit spin torque",1401.2266v1
2014-09-30,Current-induced spin torque resonance of magnetic insulators affected by field-like spin-orbit torques and out-of-plane magnetizations,"The spin-torque ferromagnetic resonance (ST-FMR) in a bilayer system
consisting of a magnetic insulator such as Y3Fe5O12 and a normal metal with
spin-orbit interaction such as Pt is addressed theoretically. We model the
ST-FMR for all magnetization directions and in the presence of field-like
spin-orbit torques based on the drift-diffusion spin model and quantum
mechanical boundary conditions. ST-FMR experiments may expose crucial
information about the spin-orbit coupling between currents and magnetization in
the bilayers.",1409.8406v2
2015-03-12,Gate-control of spin-motive force and spin-torque in Rashba SOC systems,"The introduction of a strong Rashba spin orbit coupling (SOC) had been
predicted to enhance the spin motive force (SMF) [see Phys. Rev. Lett. {\bf
108}, 217202 (2012)]. In this work, we predict further enhancement of the SMF
by time modulation of the Rashba coupling $\alpha_R$, which induces an
additional electric field $E^R_d={\dot \alpha_R} m_e/e\hbar({\hat z}\times
{\mathbf m})$. When the modulation frequency is higher than the magnetization
precessing frequency, the amplitude of this field is significantly larger than
previously predicted results. Correspondingly, the spin torque on the
magnetization is also effectively enhanced. Additionally, the nature of SOC
induced spin torque in the system can be transformed from damping to
antidamping-like by modulating ${\dot \alpha_R}$. We also suggest a biasing
scheme to achieve rectification of SMF, {\it i.e.}, by application of a square
wave voltage at the resonant frequency. Finally, we numerically estimate the
resulting spin torque field arising from a Gaussian pulse time modulation of
$\alpha_R$.",1503.03651v2
2016-04-06,Antiferromagnetic domain wall motion driven by spin-orbit torques,"We theoretically investigate dynamics of antiferromagnetic domain walls
driven by spin-orbit torques in antiferromagnet/heavy metal bilayers. We show
that spin-orbit torques drive antiferromagnetic domain walls much faster than
ferromagnetic domain walls. As the domain wall velocity approaches the maximum
spin-wave group velocity, the domain wall undergoes Lorentz contraction and
emits spin-waves in the terahertz frequency range. The interplay between spin
orbit torques and the relativistic dynamics of antiferromagnetic domain walls
leads to the efficient manipulation of antiferromagnetic spin textures and
paves the way for the generation of high frequency signals in antiferromagnets.",1604.01473v1
2016-12-06,Spin-Hall Torques Generated by Rare-Earth (Lanthanide) Thin Films,"We report an initial experimental survey of spin-Hall torques generated by
the rare-earth metals Gd, Dy, Ho, and Lu, along with comparisons to
first-principles calculations of their spin Hall conductivities. Using spin
torque ferromagnetic resonance (ST-FMR) measurements and DC-biased ST-FMR, we
estimate lower bounds for the spin-Hall torque ratio, $\xi_{SH}$, of $\approx$
0.04 for Gd, $\approx$ 0.05 for Dy, $\approx$ 0.14 for Ho, and $\approx$ 0.014
for Lu. The variations among these elements are qualitatively consistent with
results from first principles (density functional theory, DFT, in the local
density approximation with a Hubbard-U correction). The DFT calculations
indicate that the spin Hall conductivity is enhanced by the presence of the
partially-filled $f$ orbitals in Dy and Ho, which suggests a strategy to
further strengthen the contribution of the $f$ orbitals to the spin Hall effect
by shifting the electron chemical potential.",1612.01927v1
2017-03-14,A Novel Spin-Orbit Torque due to Conduction Electrons,"The anomalous Hall effect is mainly used to probe the magnetization
orientation in ferromagnetic materials. A less explored aspect is the torque
acting back on magnetization, an effect that can be important at high currents.
The spin-orbit coupling of the conduction electrons causes spin-up and
spin-down electrons to scatter to opposite sides when a charge current flows in
the sample. This is equivalent to a spin current with orientation and flow
perpendicular to the driving charge current, leading to a non-equilibrium spin
accumulation that exerts a torque on the bulk magnetization through the s-d
exchange interaction. The symmetry of this toque is that of an uniaxial
anisotropy along the driving current. The large screening currents generated
with laser pulses in all-optical magnetic switching experiments make for
practical uses of this torque.",1703.04724v2
2020-02-21,Determination of spin-orbit torque efficiencies in heterostructures with in-plane magnetic anisotropy,"It has been shown that the spin Hall effect from heavy transition metals can
generate sufficient spin-orbit torque and further produce current-induced
magnetization switching in the adjacent ferromagnetic layer. However, if the
ferromagnetic layer has in-plane magnetic anisotropy, probing such switching
phenomenon typically relies on tunneling magnetoresistance measurement of
nano-sized magnetic tunnel junctions, differential planar Hall voltage
measurement, or Kerr imaging approaches. We show that in magnetic
heterostructures with spin Hall metals, there exist current-induced in-plane
spin Hall effective fields and unidirectional magnetoresistance that will
modify their anisotropic magnetoresistance behavior. We also demonstrate that
by analyzing the response of anisotropic magnetoresistance under such
influences, one can directly and electrically probe magnetization switching
driven by the spin-orbit torque, even in micron-sized devices. This pump-probe
method allows for efficient and direct determination of key parameters from
spin-orbit torque switching events without lengthy device fabrication
processes.",2002.09104v1
2023-04-04,Geometrical torque on magnetic moments coupled to a correlated antiferromagnet,"The geometrical spin torque mediates an indirect interaction of magnetic
moments, which are weakly exchange coupled to a system of itinerant electrons.
It originates from a finite spin-Berry curvature and leads to a non-Hamiltonian
magnetic-moment dynamics. We demonstrate that there is an unprecedentedly
strong geometrical spin torque in case of an electron system, where
correlations cause antiferromagnetic long-range order. The key observation is
that the anomalous torque is strongly boosted by low-energy magnon modes
emerging in the two-electron spin-excitation spectrum due to spontaneous
breaking of SU(2) spin-rotation symmetry. As long as single-electron
excitations are gapped out, the effect is largely universal, i.e., essentially
independent of the details of the electronic structure, but decisively
dependent on the lattice dimension and spatial and spin anisotropies. Analogous
to the reasoning that leads to the Mermin-Wagner theorem, there is a lower
critical dimension at and below which the spin-Berry curvature diverges.",2304.02071v1
2016-02-10,Spin-orbit torques and spin accumulation in FePt/Pt and Co/Cu thin films from first principles: the role of impurities,"Using the Boltzmann formalism based on the first principles electronic
structure and scattering rates, we investigate the current-induced spin
accumulation and spin-orbit torques in FePt/Pt and Co/Cu bilayers in the
presence of substitutional impurities. In FePt/Pt bilayers we consider the
effect of intermixing of Fe and Pt atoms in the FePt layer, and find a crucial
dependence of spin accumulation and spin-orbit torques on the details of the
distribution of these defects. In Co/Cu bilayers we predict that the magnitude
and sign of the spin-orbit torque and spin accumulation depend very sensitively
on the type of the impurities used to dope the Cu substrate. Moreover,
simultaneously with impurity-driven scattering we consider the effect of an
additional constant quasiparticle broadening of the states at the Fermi surface
to simulate phonon scattering at room temperature, and discover that even a
small broadening of the order of 25 meV can drastically influence the magnitude
of the considered effects. We explain our findings based on the analysis of the
complex interplay of several competing Fermi surface contributions to the spin
accumulation and spin-orbit torques in these structurally and chemically
non-uniform systems.",1602.03417v1
2019-11-01,Impact of inherent energy barrier on spin-orbit torques in magnetic-metal/semimetal heterojunctions,"Spintronic devices are based on heterojunctions of two materials with
different magnetic and electronic properties. Although an energy barrier is
naturally formed even at the interface of metallic heterojunctions, its impact
on spin transport has been overlooked. Here, using diffusive spin Hall
currents, we provide evidence that the inherent energy barrier governs the spin
transport even in metallic systems. We find a sizable field-like torque, much
larger than the damping-like counterpart, in
Ni$_{81}$Fe$_{19}$/Bi$_{0.1}$Sb$_{0.9}$ bilayers. This is a distinct signature
of barrier-mediated spin-orbit torques, which is consistent with our theory
that predicts a strong modification of the spin mixing conductance induced by
the energy barrier. Our results suggest that the spin mixing conductance and
the corresponding spin-orbit torques are strongly altered by minimizing the
work function difference in the heterostructure. These findings provide a new
mechanism to control spin transport and spin torque phenomena by interfacial
engineering of metallic heterostructures.",1911.00413v3
2011-06-20,Spin-dependent transport for armchair-edge graphene nanoribbons between ferromagnetic leads,"We theoretically investigate the spin-dependent transport for the system of
an armchair-edge graphene nanoribbon (AGNR) between two ferromagnetic (FM)
leads with arbitrary polarization directions at low temperatures, where a
magnetic insulator is deposited on the AGNR to induce an exchange splitting
between spin-up and -down carriers. By using the standard nonequilibrium
Green's function (NGF) technique, it is demonstrated that, the spin-resolved
transport property for the system depends sensitively on both the width of AGNR
and the polarization strength of FM leads. The tunneling magnetoresistance
(TMR) around zero bias voltage possesses a pronounced plateau structure for
system with semiconducting 7-AGNR or metallic 8-AGNR in the absence of exchange
splitting, but this plateau structure for 8-AGNR system is remarkably broader
than that for 7-AGNR one. Interestingly, the increase of exchange splitting
$\Delta$ suppresses the amplitude of the structure for 7-AGNR system. However,
the TMR is enhanced much for 8-AGNR system under the bias amplitude comparable
to splitting strength. Further, the current-induced spin transfer torque (STT)
for 7-AGNR system is systematically larger than that for 8-AGNR one. The
findings here suggest the design of GNR-based spintronic devices by using a
metallic AGNR, but it is more favorable to fabricate a current-controlled
magnetic memory element by using a semiconducting AGNR.",1106.3843v1
2011-11-28,Spin Evolution of Accreting Young Stars. II. Effect of Accretion-Powered Stellar Winds,"We present a model for the rotational evolution of a young, solar-mass star
interacting magnetically with an accretion disk. As in a previous paper (Paper
I), the model includes changes in the star's mass and radius as it descends the
Hayashi track, a decreasing accretion rate, and a prescription for the angular
momentum transfer between the star and disk. Paper I concluded that, for the
relatively strong magnetic coupling expected in real systems, additional
processes are necessary to explain the existence of slowly rotating
pre-main-sequence stars. In the present paper, we extend the stellar spin model
to include the effect of a spin-down torque that arises from an
accretion-powered stellar wind. For a range of magnetic field strengths,
accretion rates, initial spin rates, and mass outflow rates, the modeled stars
exhibit rotation periods within the range of 1--10 days in the age range of
1--3 Myr. This range coincides with the bulk of the observed rotation periods,
with the slow rotators corresponding to stars with the lowest accretion rates,
strongest magnetic fields, and/or highest stellar wind mass outflow rates. We
also make a direct, quantitative comparison between the accretion-powered
stellar wind scenario and the two types of disk-locking models (namely the
X-wind and Ghosh & Lamb type models) and identify some remaining theoretical
issues for understanding young star spins.",1111.6407v1
2014-02-26,Anomalous temperature dependence of current induced torques in CoFeB|MgO heterostructures with Ta based underlayers,"We have studied the underlayer thickness and temperature dependences of the
current induced effective field in CoFeB|MgO heterostructures with Ta based
underlayers. The underlayer thickness at which the effective field saturates is
found to be different between the two orthogonal components of the effective
field, i.e. the damping-like term tends to saturate at smaller underlayer
thickness than the field-like term. For large underlayer thickness films in
which the effective field saturates, we find that the temperature significantly
influences the size of the effective field. A striking difference is found in
the temperature dependence of the two components: the damping-like term
decreases whereas the field-like term increases with increasing temperature.
Using a simple spin diffusion-spin transfer model, we find that all of these
results can be accounted for provided the real and imaginary parts of an
effective spin mixing conductance are negative. These results imply that either
spin transport in this system is different from conventional metallic
interfaces or effects other spin diffusion into the magnetic layer need to be
taken account in order to model the system accurately.",1402.6388v1
2017-07-14,Symmetry-broken dissipative exchange flows in thin-film ferromagnets with in-plane anisotropy,"Planar ferromagnetic channels have been shown to theoretically support a
long-range ordered and coherently precessing state where the balance between
local spin injection at one edge and damping along the channel establishes a
dissipative exchange flow, sometimes referred to as a spin superfluid. However,
realistic materials exhibit in-plane anisotropy, which breaks the axial
symmetry assumed in current theoretical models. Here, we study dissipative
exchange flows in a ferromagnet with in-plane anisotropy from a dispersive
hydrodynamic perspective. Through the analysis of a boundary value problem for
a damped sine-Gordon equation, dissipative exchange flows in a ferromagnetic
channel can be excited above a spin current threshold that depends on material
parameters and the length of the channel. Symmetry-broken dissipative exchange
flows display harmonic overtones that redshift the fundamental precessional
frequency and lead to a reduced spin pumping efficiency when compared to their
symmetric counterpart. Micromagnetic simulations are used to verify that the
analytical results are qualitatively accurate, even in the presence of nonlocal
dipole fields. Simulations also confirm that dissipative exchange flows can be
driven by spin transfer torque in a finite-sized region. These results
delineate the important material parameters that must be optimized for the
excitation of dissipative exchange flows in realistic systems.",1707.04664v3
2019-12-31,The 2020 Skyrmionics Roadmap,"The notion of non-trivial topological winding in condensed matter systems
represents a major area of present-day theoretical and experimental research.
Magnetic materials offer a versatile platform that is particularly amenable for
the exploration of topological spin solitons in real space such as skyrmions.
First identified in non-centrosymmetric bulk materials, the rapidly growing
zoology of materials systems hosting skyrmions and related topological spin
solitons includes bulk compounds, surfaces, thin films, heterostructures,
nano-wires and nano-dots. This underscores an exceptional potential for major
breakthroughs ranging from fundamental questions to applications as driven by
an interdisciplinary exchange of ideas between areas in magnetism which
traditionally have been pursued rather independently. The skyrmionics roadmap
provides a review of the present state of the art and the wide range of
research directions and strategies currently under way. These are, for
instance, motivated by the identification of the fundamental structural
properties of skyrmions and related textures, processes of nucleation and
annihilation in the presence of non-trivial topological winding, an
exceptionally efficient coupling to spin currents generating spin transfer
torques at tiny current densities, as well as the capability to purpose-design
broad-band spin dynamic and logic devices.",2001.00026v3
2023-08-04,First-principle study of spin transport property in $L1_0$-FePd(001)/graphene heterojunction,"In our previous work, we synthesized a metal/2D material heterointerface
consisting of $L1_0$-ordered iron-palladium (FePd) and graphene (Gr) called
FePd(001)/Gr. This system has been explored by both experimental measurements
and theoretical calculations. In this study, we focus on a heterojunction
composed of FePd and multilayer graphene referred to as
FePd(001)/$m$-Gr/FePd(001), where $m$ represents the number of graphene layers.
We perform first-principles calculations to predict their spin-dependent
transport properties. The quantitative calculations of spin-resolved
conductance and magnetoresistance (MR) ratio (150-200%) suggest that the
proposed structure can function as a magnetic tunnel junction in spintronics
applications. We also find that an increase in $m$ not only reduces conductance
but also changes transport properties from the tunneling behavior to the
graphite $\pi$-band-like behavior. Additionally, we investigate the
spin-transfer torque-induced magnetization switching behavior of our
\color{blue} junction structures \color{black} using micromagnetic simulations.
Furthermore, we examine the impact of lateral displacements (``sliding'') at
the interface and find that the spin transport properties remain robust despite
these changes; this is the advantage of two-dimensional material
hetero-interfaces over traditional insulating barrier layers such as MgO.",2308.02171v5
2020-05-08,Nanoscale Spin Injector Driven by a Microwave Voltage,"We propose an electrically driven spin injector into normal metals and
semiconductors, which is based on a magnetic tunnel junction (MTJ) subjected to
a microwave voltage. Efficient functioning of such an injector is provided by
electrically induced magnetization precession in the ""free"" layer of MTJ, which
generates the spin pumping into a metallic or semiconducting overlayer. We
theoretically describe the spin and charge dynamics in the
CoFeB/MgO/CoFeB/Au(GaAs) heterostructures. First, the magnedynamics in the free
CoFeB layer is quantified with the account of a spin-transfer torque and a
voltage-controlled magnetic anisotropy. By numerically solving the
magnetodynamics equation, we determine dependences of the precession amplitude
on the frequency $f$ and magnitude $V_\mathrm{max}$ of the ac voltage applied
to the MTJ. It is found that the frequency dependence changes drastically above
the threshold amplitude $V_\mathrm{max} \approx 200$mV, exhibiting a break at
the resonance frequency $f_\mathrm{res}$ due to nonlinear effects. The results
obtained for the magnetization dynamics are used to describe the spin injection
and pumping into the Au and GaAs overlayers. Since the generated spin current
creates additional charge current owing to the inverse spin Hall effect, we
also calculate distribution of the electric potential in the thick Au
overlayer. The calculations show that the arising transverse voltage becomes
experimentally measurable at $f = f_\mathrm{res}$. Finally, we evaluate the
spin accumulation in a long n$^+$-GaAs bar coupled to the MTJ and determine its
temporal variation and spatial distribution along the bar. It is found that the
spin accumulation under resonant excitation is large enough for experimental
detection even at micrometer distances from the MTJ. This result demonstrates
high efficiency of the described nanoscale spin injector.",2005.03896v1
1999-01-08,Disk Accretion onto Magnetized Neutron Stars: The Inner Disk Radius and Fastness Parameter,"It is well known that the accretion disk around a magnetized compact star can
penetrate inside the magnetospheric boundary, so the magnetospheric radius
$\ro$ does not represent the true inner edge $\rin$ of the disk; but
controversies exist in the literature concerning the relation between $\ro$ and
$\rin$. In the model of Ghosh & Lamb, the width of the boundary layer is given
by $\delta=\ro-\rin\ll\ro$, or $\rin\simeq\ro$, while Li & Wickramasinghe
recently argued that $\rin$ could be significantly smaller than $\ro$ in the
case of a slow rotator. Here we show that if the star is able to absorb the
angular momentum of disk plasma at $\ro$, appropriate for binary X-ray pulsars,
the inner disk radius can be constrained by $0.8\lsim \rin/\ro\lsim 1$, and the
star reaches spin equilibrium with a relatively large value of the fastness
parameter ($\sim 0.7-0.95$). For accreting neutron stars in low-mass X-ray
binaries (LMXBs), $\ro$ is generally close to the stellar radius $\rs$ so that
the toroidal field cannot transfer the spin-up torque efficiently to the star.
In this case the critical fastness parameter becomes smaller, but $\rin$ is
still near $\ro$.",9901083v1
2000-09-04,Current Induced Magnetization Switching in Small Domains of Different Anisotropies,"Several recent experimental studies have confirmed the possibility of
switching the magnetization direction in the small magnetic domains by pumping
large spin-polarized currents through them. On the basis of equations proposed
by J.Slonczewski for the case when magnetization of the domains is almost
uniform, we analyze the stability and switching for two types of magnetic and
shape anisotropies of a magnetic domain in a nanowire and find qualitatively
different behavior, including different shapes of bistable regions. Our study
is analytic as opposed to recent numeric work. Assumed anisotropies can be
realized in experiments and our predictions can be used to experimentally test
the theory of spin-transfer torques. Such test would be especially interesting
since alternative approaches are discussed in the literature.",0009034v1
2005-04-16,Spin-Transfer Excitations of Permalloy Nanopillars for Large Applied Currents,"Using measurements of the spectra of microwave-frequency resistance
oscillations, we determine the phase diagram of magnetic excitations caused by
torques from DC spin-polarized currents in (thin permalloy)/copper/(thick
permalloy) multilayer samples. We extend the measurements to larger values of
current than have been reported previously. We find several additional modes
that we are able to identify with motion of the thick magnetic layer as well as
the thin one. Peaks in the microwave spectra at multiple frequencies suggest
that spatially non-uniform dynamical states can be important in some
circumstances. We compare the experimental phase diagram with simple
theoretical models and achieve a good qualitative agreement.",0504402v1
2007-06-21,Spin pumping by a field-driven domain wall,"We calculate the charge current in a metallic ferromagnet to first order in
the time derivative of the magnetization direction. Irrespective of the
microscopic details, the result can be expressed in terms of the conductivities
of the majority and minority electrons and the non-adiabatic spin transfer
torque parameter $\beta$. The general expression is evaluated for the specific
case of a field-driven domain wall and for that case depends strongly on the
ratio of $\beta$ and the Gilbert damping constant. These results may provide an
experimental method to determine this ratio, which plays a crucial role for
current-driven domain-wall motion.",0706.3160v3
2008-11-13,"Intrinsic Coupling between Current and Domain Wall Motion in (Ga,Mn)As","We consider current-induced domain wall motion and, the reciprocal process,
moving domain wall-induced current. The associated Onsager coefficients are
expressed in terms of scattering matrices. Uncommonly, in (Ga,Mn)As, the
effective Gilbert damping coefficient $\alpha_w$ and the effective out-of-plane
spin transfer torque parameter $\beta_w$ are dominated by spin-orbit
interaction in combination with scattering off the domain wall, and not
scattering off extrinsic impurities. Numerical calculations give $\alpha_w \sim
0.01$ and $\beta_w \sim 1$ in dirty (Ga,Mn)As. The extraordinary large
$\beta_w$ parameter allows experimental detection of current or voltage induced
by domain wall motion in (Ga,Mn)As.",0811.2235v2
2009-05-27,Magnetization switching driven by spin-transfer-torque in high-TMR magnetic tunnel junctions,"This paper describes a numerical experiment of magnetization switching driven
by spin-polarized current in high-TMR magnetic tunnel junctions (TMR>100%).
Differently from other works, the current density distribution throughout the
cross-sectional area of the free-layer is here computed dinamically, by
modeling the ferromagnet/insulator/ferromagnet trilayer as a series of parallel
resistances. The validity of the main postulated hypothesis, which states that
the current density vector is perpendicular to the sample plane, has been
verified by numerically solving the Poisson equation. Our results show that the
nonuniform current density distribution is a source of asymmetry for the
switching. Furthermore, we found out that the switching processes are
characterized by well defined localized pre-switching oscillation modes.",0905.4437v1
2010-05-06,"Current-driven domain wall motion across a wide temperature range in a (Ga,Mn)(As,P) device","Current-driven magnetic domain wall motion is demonstrated in the quaternary
ferromagnetic semiconductor (Ga,Mn)(As,P) at temperatures well below the
ferromagnetic transition temperature, with critical currents of the order
10^5Acm^-2. This is enabled by a much weaker domain wall pinning compared to
(Ga,Mn)As layers grown on a strain-relaxed buffer layer. The critical current
is shown to be comparable with theoretical predictions. The wide temperature
range over which domain wall motion can be achieved indicates that this is a
promising system for developing an improved understanding of spin-transfer
torque in systems with strong spin-orbit interaction.",1005.0946v2
2011-04-13,Current induced vortex superlattices in nanomagnets,"Influence of the spin-transfer torque on the vortex state magnetic nanodisk
is studied numerically via Slonczewski-Berger mechanism. The existence of a
critical current is determined for the case of same-directed electrical
current, its spin polarization and polarity of the vortex. The critical current
separates two regimes: (i) deformed but static vortex state and (ii)
essentially dynamic state under which the spatio-temporal periodic structures
can appear. The structure is a stable vortex-antivortex lattice. Symmetry of
the lattice depends on the applied current value and for high currents (close
to saturation) only square lattices are observed. General relations for sizes
of the stable lattice is obtained analytically.",1104.2483v1
2011-12-13,Temperature dependence of the emission linewidth in MgO-based spin torque nano-oscillators,"Spin transfer driven excitations in magnetic nanostructures are characterized
by a relatively large microwave emission linewidth (10 -100 MHz). Here we
investigate the role of thermal fluctuations as well as of the non-linear
amplitude-phase coupling parameter and the amplitude relaxation rate to explain
the linewidth broadening of in-plane precession modes induced in planar
nanostructures. Experiments on the linewidth broadening performed on MgO based
magnetic tunnel junctions are compared to the linewidth obtained from macrospin
simulations and from evaluation of the phase variance. In all cases we find
that the linewidth varies linearly with temperature when the amplitude
relaxation rate is of the same order as the linewidth and when the
amplitude-phase coupling parameter is relatively small. The small
amplitude-phase coupling parameter means that the linewidth is dominated by
direct phase fluctuations and not by amplitude fluctuations, explaining thus
its linear dependence as a function of temperature.",1112.2833v1
2013-06-24,Tunability versus deviation sensitivity in a non-linear vortex oscillator,"Frequency modulation experiments were performed on a spin torque vortex
oscillator for a wide range of modulation frequency, up to 10 % of the
oscillator frequency. A thorough analysis of the intermodulation products shows
that the key parameter that describes these experiments is the deviation
sensitivity, which is the dynamical frequency-current dependence. It differs
significantly from the oscillator tunability discussed so far in the context of
spin-transfer oscillators. The essential difference between these two concepts
is related to the response time of the vortex oscillator, driven either in
quasi-steady state or in a transient regime.",1306.5552v1
2014-03-14,Investigation on Mn$_{3-δ}$Ga/MgO interface for magnetic tunneling junctions,"The Mn$_3$Ga Heusler compound and related alloys are the most promising
materials for the realization of spin-transfer-torque switching in magneto
tunneling junctions. Improved performance can be achieved by high quality
interfaces in these multilayered structured devices. In this context, the
interface between Mn$_{1.63}$Ga and MgO is of particular interest because of
its spin polarization properties in tunneling junctions. We performed a
chemical characterization of the MgO/Mn$_{1.63}$Ga junction by hard x-ray
photoelectron spectroscopy (HAXPES). The experiment indicated the formation of
Ga-O bonds at the interface and evidenced changes in the local environment of
Mn atoms in the proximity of the MgO film. In addition, we show that the
insertion of a metallic Mg-layer interfacing the MgO and Mn--Ga film strongly
suppresses the oxidation of gallium.",1403.3556v4
2014-04-11,Experimental Clocking of Nanomagnets with Strain for Ultra Low Power Boolean Logic,"Nanomagnetic implementations of Boolean logic [1,2] have garnered attention
because of their non-volatility and the potential for unprecedented
energy-efficiency. Unfortunately, the large dissipative losses that take place
when nanomagnets are switched with a magnetic field [3], or
spin-transfer-torque [4] inhibit the promised energy-efficiency. Recently,
there have been experimental reports of utilizing the Spin Hall effect for
switching magnets [5-7], and theoretical proposals for strain induced switching
of single-domain magnetostrictive nanomagnets [8-12], that might reduce the
dissipative losses significantly. Here, we demonstrate, for the first time,
that strain-induced switching of single-domain magnetostrictive nanomagnets of
lateral dimensions ~200 nm fabricated on a piezoelectric substrate can
implement a nanomagnetic Boolean NOT gate and unidirectional bit information
propagation in dipole-coupled nanomagnets chains. This portends
ultra-low-energy logic processors and mobile electronics that may be able to
operate solely by harvesting energy from the environment without ever requiring
a battery.",1404.2980v2
2014-09-05,Electric field-induced Skyrmion distortion and giant lattice rotation in the magnetoelectric insulator Cu2OSeO3,"Uniquely in Cu2OSeO3, the Skyrmions, which are topologically protected
magnetic spin vortex-like objects, display a magnetoelectric coupling and can
be manipulated by externally applied electric (E) fields. Here, we explore the
E-field coupling to the magnetoelectric Skyrmion lattice phase, and study the
response using neutron scattering. Giant E-field induced rotations of the
Skyrmion lattice are achieved that span a range of $\sim$25$^{\circ}$.
Supporting calculations show that an E-field-induced Skyrmion distortion lies
behind the lattice rotation. Overall, we present a new approach to Skyrmion
control that makes no use of spin-transfer torques due to currents of either
electrons or magnons.",1409.1756v1
2015-08-24,Origin of robust interaction of spin waves with a single skyrmion in perpendicularly magnetized nanostripes,"We studied interactions between propagating spin waves (SWs) and a single
skyrmion in a perpendicularly magnetized CoFeB nanostripe where the magnetic
layer is interfaced with W and MgO. Micromagnetic numerical calculations
revealed that robust interactions between the incident SWs and the skyrmion
give rise to considerable forward skyrmion motions for specific SW frequencies
(e.g., here: fsw = 12 - 19 GHz). Additionally, it was found that there exists a
sufficiently low threshold field amplitude, e.g., 0.1 kOe for the fsw = 15 GHz
SWs. This frequency-dependent interaction originated from the robust coupling
of the SWs with the internal modes of the skyrmion, through the SWs' linear
momentum transfer torque acting on the skyrmion. This work provides for
all-magnetic control of skyrmion motions without electronic currents, and
facilitates further understanding of the interactions between magnons and
topological solitons in constricted geometries.",1508.05682v1
2016-01-11,Reliable spin-transfer torque driven precessional magnetization reversal with an adiabatically decaying pulse,"We show that a slowly decaying current pulse can lead to nearly deterministic
precessional switching in the presence of noise. We consider a biaxial
macrospin, with an easy axis in the plane and a hard axis out-of-the plane,
typical of thin film nanomagnets patterned into asymmetric shapes. Out-of-plane
precessional magnetization orbits are excited with a current pulse with a
component of spin polarization normal to the film plane. By numerically
integrating the stochastic Landau-Lifshitz-Gilbert-Slonczewski equation we show
that thermal noise leads to strong dephasing of the magnetization orbits.
However, an adiabatically decreasing pulse amplitude overwhelmingly leads to
magnetization reversal, with a final state that {\em only} depends on the pulse
polarity, not on the pulse amplitude. We develop an analytic model to explain
this phenomena and to determine the pulse decay time necessary for adiabatic
magnetization relaxation and thus precessional magnetization switching.",1601.02336v1
2016-01-30,Magnetic radial vortex stabilization and efficient manipulation driven by the Dzyaloshinskii Moriya Interaction and the spin-transfer torque,"Solitons are very promising for the design of next generation of ultralow
power devices for storage and computation. The key ingredient to achieve this
goal is the fundamental understanding of their stabilization and manipulation.
Here, we show how the interfacial Dzyaloshinskii Moriya Interaction (i DMI) is
able to lift the energy degeneracy of a magnetic vortex state by stabilizing a
topological soliton with radial chirality, hereafter called radial vortex. It
has a non-integer skyrmion number S (0.5<|S|<1) due to both the vortex core
polarity and the magnetization tilting induced by the i DMI boundary
conditions. Micromagnetic simulations predict that a magnetoresistive memory
based on the radial vortex state in both free and polarizer layers can be
efficiently switched by a threshold current density smaller than 106 A/cm2. The
switching processes occur via the nucleation of topologically connected
vortices and vortex antivortex pairs, followed by spin wave emissions due to
vortex antivortex annihilations.",1602.00153v2
2016-06-16,Inertial displacement of a domain wall excited by ultra-short circularly polarized laser pulses,"Domain wall motion driven by ultra-short laser pulses is a prerequisite for
envisaged low-power spintronics combining storage of information in magneto
electronic devices with high speed and long distance transmission of
information encoded in circularly polarized light. Here we demonstrate the
conversion of the circular polarization of incident femtosecond laser pulses
into inertial displacement of a domain wall in a ferromagnetic semiconductor.
In our study we combine electrical measurements and magneto-optical imaging of
the domain wall displacement with micromagnetic simulations. The optical spin
transfer torque acts over a picosecond recombination time of the spin polarized
photo-carriers which only leads to a deformation of the internal domain wall
structure. We show that subsequent depinning and micro-meter distance
displacement without an applied magnetic field or any other external stimuli
can only occur due to the inertia of the domain wall.",1606.05212v1
2016-10-17,Designing compensated magnetic states in tetragonal Mn3Ge-based alloys,"Magnetic compensated state attracted much interests due to the observed large
exchange bias and large coercivity, and its potential applications in the
antiferromagnetic spintronics with merit of no stray field. In this work, by ab
initio calculations with KKR-CPA for the treatment of random substitution, we
obtain the complete compensated states in the Ni (Pd, Pt) doped Mn3Ge-based
D022-type tetragonal Heusler alloys. We find the total moment change is
asymmetric across the compensation point (at ~ x = 0.3) in Mn3-xYxGe (Y = Ni,
Pd, Pt), which is highly conforming to that experimentally observed in Mn3Ga.
In addition, an uncommon discontinuous jump is observed across the critical
zero-moment point, indicating that some non-trivial properties can emerge at
this point. Further electronic analysis for the three compensation compositions
reveals large spin polarizations, together with the high Curie temperature of
the host Mn3Ge, making them promising candidates for spin transfer torque
applications.",1610.04971v1
2016-10-30,Time-Resolved Studies of the Spin-Transfer Reversal Mechanism in Perpendicularly Magnetized Magnetic Tunnel Junctions,"Pulsed spin-torque switching has been studied using single-shot time-resolved
electrical measurements in perpendicularly magnetized magnetic tunnel junctions
as a function of pulse amplitude and junction size in 50 to 100 nm diameter
circular junctions. The mean switching time depends inversely on pulse
amplitude for all junctions studied. However, the switching dynamics is found
to be strongly dependent on junction size and pulse amplitude. In 50 nm
diameter junctions the switching onset is stochastic but the switching once
started, is fast; after being initiated it takes less than 2 ns to switch. In
larger diameter junctions the time needed for complete switching is strongly
dependent on the pulse amplitude, reaching times less than 2 ns at large pulse
amplitudes. Anomalies in the switching rate versus pulse amplitude are shown to
be associated with the long lived (> 2 ns) intermediate junction resistance
states.",1610.09710v1
2017-08-02,"Emergence, evolution, and control of multistability in a hybrid topological quantum/classical system","We present a novel class of nonlinear dynamical systems - a hybrid of
relativistic quantum and classical systems, and demonstrate that multistability
is ubiquitous. A representative setting is coupled systems of a topological
insulator and an insulating ferromagnet, where the former possesses an
insulating bulk with topologically protected, dissipationless, and conducting
surface electronic states governed by the relativistic quantum Dirac
Hamiltonian and latter is described by the nonlinear classical evolution of its
magnetization vector. The interactions between the two are essentially the spin
transfer torque from the topological insulator to the ferromagnet and the local
proximity induced exchange coupling in the opposite direction. The hybrid
system exhibits a rich variety of nonlinear dynamical phenomena besides
multistability such as bifurcations, chaos, and phase synchronization. The
degree of multistability can be controlled by an external voltage. In the case
of two coexisting states, the system is effectively binary, opening a door to
exploitation for developing spintronic memory devices. Because of the
dissipationless and spin-momentum locking nature of the surface currents of the
topological insulator, little power is needed for generating a significant
current, making the system appealing for potential applications in next
generation of low power memory devices.",1708.09413v1
2017-12-12,Scaling Projections on Spin Transfer Torque Magnetic Tunnel Junctions,"We investigate scaling of technologically relevant magnetic tunnel junction
devices in the trilayer and pentalayer configurations by varying the
cross-sectional area along the transverse direction using the non-equilibrium
Green's function spin transport formalism. We study the geometry dependence by
considering square and circular cross-sections. As the transverse dimension in
each case reduces, we demonstrate that the transverse mode energy profile plays
a major role in the resistance-area product. Both types of devices show
constant tunnel magnetoresistance at larger cross-sectional areas but achieve
ultra-high magnetoresistance at small cross-sectional areas, while maintaining
low resistance-area products. We notice that although the critical switching
voltage for switching the magnetization of the free layer nanomagnet in the
trilayer case remains constant at larger areas, it needs more energy to switch
at smaller areas. In the pentalayer case, we observe an oscillatory behavior at
smaller areas as a result of double barrier tunneling. We also describe how
switching characteristics of both kinds of devices are affected by the scaling.",1712.04235v1
2018-01-08,Systematic motion of magnetic domain walls in notched nanowires under ultra-short current pulses,"The precise manipulation of transverse magnetic domain walls in
finite/infinite nanowires with artificial defects under the influence of very
short spin-polarized current pulses is investigated. We show that for a
classical $3d$ ferromagnet material like Nickel, the exact positioning of the
domain walls at room temperature is possible only for pulses with very short
rise and fall time that move the domain wall reliably to nearest neighboring
pinning position. The influence of the shape of the current pulse and of the
transient effects on the phase diagram current-pulse length are discussed. We
show that large transient effects appear even when $\alpha$=$\beta$, below a
critical value, due to the domain wall distortion caused by the current pulse
shape and the presence of the notches. The transient effects can oppose or
amplify the spin-transfer torque (STT), depending on the ratio $\beta/\alpha$.
This enlarges the physical comprehension of the DW motion under STT and opens
the route to the DW displacement in both directions with unipolar currents.",1801.02345v1
2012-09-24,The effect of disorder on transverse domain wall dynamics in magnetic nanostrips,"We study the effect of disorder on the dynamics of a transverse domain wall
in ferromagnetic nanostrips, driven either by magnetic fields or spin-polarized
currents, by performing a large ensemble of GPU-accelerated micromagnetic
simulations. Disorder is modeled by including small, randomly distributed
non-magnetic voids in the system. Studying the domain wall velocity as a
function of the applied field and current density reveals fundamental
differences in the domain wall dynamics induced by these two modes of driving:
For the field-driven case, we identify two different domain wall pinning
mechanisms, operating below and above the Walker breakdown, respectively,
whereas for the current-driven case pinning is absent above the Walker
breakdown. Increasing the disorder strength induces a larger Walker breakdown
field and current, and leads to decreased and increased domain wall velocities
at the breakdown field and current, respectively. Furthermore, for adiabatic
spin transfer torque, the intrinsic pinning mechanism is found to be suppressed
by disorder. We explain these findings within the one-dimensional model in
terms of an effective damping parameter $\alpha^*$ increasing with the disorder
strength.",1209.5274v1
2018-12-06,Damping and Anti-Damping Phenomena in Metallic Antiferromagnets: An ab-initio Study,"We report on a first principles study of anti-ferromagnetic resonance (AFMR)
phenomena in metallic systems [MnX (X=Ir,Pt,Pd,Rh) and FeRh] under an external
electric field. We demonstrate that the AFMR linewidth can be separated into a
relativistic component originating from the angular momentum transfer between
the collinear AFM subsystem and the crystal through the spin orbit coupling
(SOC), and an exchange component that originates from the spin exchange between
the two sublattices. The calculations reveal that the latter component becomes
significant in the low temperature regime. Furthermore, we present results for
the current-induced intersublattice torque which can be separated into the
Field-Like (FL) and Damping-Like (DL) components, affecting the intersublattice
exchange coupling and AFMR linewidth, respectively.",1812.02844v2
2016-12-03,Impurity-limited quantum transport variability in magnetic tunnel junctions,"We report an extensive first-principles investigation of impurity-induced
device-to-device variability of spin-polarized quantum tunneling through
Fe/MgO/Fe magnetic tunnel junctions (MTJ). In particular, we calculated the
tunnel magnetoresistance ratio (TMR) and the average values and variances of
the currents and spin transfer torque (STT) of an interfacially doped Fe/MgO/Fe
MTJ. Further, we predicted that N-doped MgO can improve the performance of a
doped Fe/MgO/Fe MTJ. Our first-principles calculations of the fluctuations of
the on/off currents and STT provide vital information for future predictions of
the long-term reliability of spintronic devices, which is imperative for
high-volume production.",1612.00972v1
2017-02-21,"Back hopping in spin-transfer-torque devices, possible origin and counter measures","The effect of undesirable high-frequency free-layer switching in magnetic
multilayer systems, referred to as back hopping, is investigated by means of
the spin-diffusion model. A possible origin of the back-hopping effect is found
to be the destabilization of the pinned layer which leads to perpetual
switching of both layers. The influence of different material parameters on the
critical switching currents for the free and pinned layer is obtained by
micromagnetic simulations. It is found that the choice of a free-layer material
with low polarization $\beta$ and saturation magnetization $M_s$, and a
pinned-layer material with high $\beta$ and $M_s$ leads to a low free-layer
critical current and a high pinned-layer critical current and hence reduces the
likelihood of back hopping. While back hopping was observed in various types of
devices, there are only few experiments that exhibit this effect in
perpendicularly magnetized systems. However, our simulations suggest, that this
is likely to change due to loss of pinned-layer anisotropy when decreasing
device sizes.",1702.06604v3
2018-04-04,Anomalous nonlinearity of the magnonic edge mode,"Nonlinearity of magneto-dynamics is typically described by a single constant,
$\mathcal{N}$, with positive and negative values indicating repulsion and
attraction of magnons, respectively. In thin magnetic films with easy-plane
magnetic anisotropy, magnon attraction is typically achieved for an in-plane
magnetization. At sufficient stimulus, e.g. via application of spin transfer
torque, the attraction can give rise to self-localized magnetic solitons, such
as spin wave bullets, which shrink as their amplitude increases. In contrast,
for an oblique magnetization above a certain critical angle, the repulsion of
magnons only allows for propagating modes, which expand when pumped more
strongly. Here we demonstrate, both analytically and using micromagnetic
simulations, that such a dichotomic description is inadequate for magnonic edge
modes, which naturally appear in confined magnetic systems. In particular, we
demonstrate that the confinement potential of such modes is nonlinear in nature
and its contribution makes $\mathcal{N}$ non-monotonically dependent on their
amplitude. As a prominent example, edge modes show compression and expansion
for negative and positive $\mathcal{N}$, yet remain localized. In striking
contrast to the extended geometries, edge magnons might also repeal even for an
in-plane magnetization.",1804.01585v1
2019-05-22,Reduced Exchange Interactions in Magnetic Tunnel Junction Free Layers with Insertion Layers,"Perpendicularly magnetized CoFeB layers with ultra-thin non-magnetic
insertion layers are very widely used as the electrodes in magnetic tunnel
junctions for spin transfer magnetic random access memory devices. Exchange
interactions play a critical role in determining the thermal stability of
magnetic states in such devices and their spin torque switching efficiency.
Here the exchange constant of free layers incorporated in full magnetic tunnel
junction layer stacks, specifically CoFeB free layers with W insertion layers
is determined by magnetization measurements in a broad temperature range. A
significant finding is that the exchange constant decreases significantly and
abruptly with W insertion layer thickness. The perpendicular magnetic
anisotropy shows the opposite trend; it initially increases with W insertion
layer thickness and shows a broad maximum for approximately one monolayer (0.3
nm) of W. These results highlight the interdependencies of magnetic
characteristics required to optimize the performance of magnetic tunnel
junction devices.",1905.09329v1
2019-07-12,Voltage control of domain walls in magnetic nanowires for energy efficient neuromorphic devices,"An energy-efficient voltage controlled domain wall device for implementing an
artificial neuron and synapse is analyzed using micromagnetic modeling in the
presence of room temperature thermal noise. By controlling the domain wall
motion utilizing spin transfer or spin orbit torques in association with
voltage generated strain control of perpendicular magnetic anisotropy in the
presence of Dzyaloshinskii-Moriya interaction, different positions of the
domain wall are realized in the free layer of a magnetic tunnel junction to
program different synaptic weights. The feasibility of scaling of such devices
is assessed in the presence of thermal perturbations that compromise
controllability. Additionally, an artificial neuron can be realized by
combining this DW device with a CMOS buffer. This provides a possible pathway
to realize energy efficient voltage controlled nanomagnetic deep neural
networks that can learn in real time.",1907.05843v2
2019-10-03,Current driven domain wall dynamics in ferrimagnetic strips explained by means of a two interacting sublattices model,"The current-driven domain wall dynamics along ferrimagnetic systems are here
theoretically analyzed as a function of the temperature by means of
micromagnetic simulations and a one dimensional model. Contrarily to
conventional effective approaches, our model takes into account the two coupled
ferromagnetic sublattices forming the ferrimagnetic system. Although the model
is suitable for systems with asymmetric exchange interaction and spin-orbit
coupling effects due to adjacent heavy metal layers, we here focus our
attention on the case of single-layer ferrimagnetic strips where domain walls
adopt achiral Bloch configurations at rest. Such domain walls can be driven by
either out-of-plane fields or spin transfer torques upon bulk current
injection. Our results indicate that the domain wall velocity is optimized at
the angular compensation temperature for both field-driven and current-driven
cases. Our advanced models allow us to infer that the precession of the
internal domain wall moments is suppressed at such compensation temperature,
and they will be useful to interpret state-of-the art experiments on these
systems.",1910.01405v2
2020-01-13,High Frequency Microwave Emission of a Tri-layer Magnetic Tunnel Junction in the Absence of External Bias-Magnetic Field,"We perform an experimental study of DC current induced microwave emission in
a magnetic tunnel junction (MTJ) consisting of three active magnetic layers.
For this tri-layer structure, in addition to a conventional bilayer orthogonal
MTJ containing a perpendicular free layer and an in-plane fixed layer, a second
perpendicular layer has been introduced. We found that the microwave emission
frequency induced by spin-transfer torque (STT) can reach as high as 6 GHz in
the absence of any applied magnetic field. Moreover, microwave emission is
observed for both current polarizations where a redshift is seen with increase
in magnitude of current. We discuss spin-dynamics of the observed
bi-directional high-frequency emission and the physical origin of the
red-shift. The distinct microwave emission properties exhibited in this
tri-layer MTJ structure could potentially be useful for future applications in
nanoscale spintronics devices such as microwave communication and neuromorphic
computing.",2001.04539v1
2021-03-27,Zeeman term for the Néel vector in a two sublattice antiferromagnet using Dzyaloshinsky-Moriya interaction and magnetic field,"We theoretically investigate the dynamics of solitons in two sublattice
antiferromagnets under external perturbations, focusing on the effect of
Dzyaloshinsky-Moriya (DM) interactions. To this end, we construct a
micromagnetic field theory for the antiferromagnet in the presence of the
external magnetic field, DM interaction, and spin-transfer torque. In
particular, we show external magnetic field and spin current couple to N\'eel
vector in a Zeeman-like manner when DM interactions present, which can be used
to efficiently drive antiferromagnetic solitons of different dimensions.
Besides, we study the effect of straining the local lattice. It can serve as an
external handle on the N\'eel field inertia and thus dynamical properties. Our
findings may find applications in antiferromagnetic spintronics.",2103.14982v2
2021-11-06,Photon spin molasses for laser cooling molecular rotation,"Laser cooling of translational motion of small molecules is performed by
addressing transitions that ensure spontaneous emission cannot cause net
rotational excitation. This will not be possible once the rotational splitting
becomes comparable to the operational excitation linewidth, as will occur for
large molecules or wide bandwidth lasers. We show theoretically that in this
regime, angular momentum transfer from red-detuned Doppler cooling light can
also exert a damping torque on linear molecules, cooling rotation to the same
Doppler limit (typically $\approx$ 500 $\mu$K for molecules with $\approx$ 10
ns excited-state lifetimes). This cooling process is derived from photon spin,
and indicates that standard optical molasses can also cool molecular rotation
with no additional experimental resources.",2111.03763v1
2022-11-07,When Plasmonic Colloids Meet Optical Vortices -- A Brief Review,"Structured light has emerged as an important tool to interrogate and
manipulate matter at micron and sub-micron scale. One form of structured light
is an optical vortex beam. The helical wavefront of these vortices carry
orbital angular momentum which can be transferred to a Brownian colloid. When
the colloid is made of metallic nanostructures, such as silver and gold,
resonant optical effects play a vital role, and the interaction leads to
complex dynamics and assembly. This brief review aims to discuss some recent
work on trapping plasmonic colloids with optical vortices and their lattices.
The role of optical scattering and absorption has important implications on the
underlying forces and torques, which is specifically enunciated. The effect of
spin and orbital angular momentum in an optical vortex can lead to spin-orbit
coupling dynamics, and these effects are highlighted with examples from the
literature. In addition to assembly and dynamics, enhanced Brownian motion of
plasmonic colloids under the influence of a vortex-lattice is discussed. The
pedagogical aspects to understand the interaction between optical vortex and
plasmonic colloids is emphasized.",2211.03547v1
2022-12-18,Experimental observation of one-dimensional motion of interstitial skyrmion in FeGe,"The interplay between dimensionality and topology manifests in magnetism via
both exotic texture morphology and novel dynamics. A free magnetic skyrmion
exhibits the skyrmion Hall effect under electric currents. Once it is confined
in one-dimensional (1D) channels, the skyrmion Hall effect would be suppressed,
and the current-driven skyrmion speed should be boosted by the non-adiabatic
spin transfer torque \b{eta}. Here, we experimentally demonstrate that stripes
of a spatially modulated spin helix serve as natural 1D channels to restrict
skyrmion. Using FeGe as a benchmark, an interstitial skyrmion is created by
geometry notch and further moves steadily without the skyrmion Hall effect. The
slope of the current-velocity curve for 1D skyrmion is enhanced almost by an
order of magnitude owing to a large \b{eta} in FeGe. This feature is also
observed in other topological defects. Utilizing the 1D skyrmion dynamics would
be a highly promising route to implement topological spintronic devices.",2212.08991v1
2023-05-25,A tunable and versatile 28nm FD-SOI crossbar output circuit for low power analog SNN inference with eNVM synapses,"In this work we report a study and a co-design methodology of an analog SNN
crossbar output circuit designed in a 28nm FD-SOI technology node that
comprises a tunable current attenuator and a leak-integrate and fire neurons
that would enable the integration of emerging non-volatile memories (eNVMs) for
synaptic arrays based on various technologies including phase change (PCRAM),
oxide-based (OxRAM), spin transfer and spin orbit torque magnetic memories
(STT, SOT-MRAM). Circuit SPICE simulation results and eNVM experimental data
are used to showcase and estimate the neurons fan-in for each type of eNVM
considering the technology constraints and design trade-offs that set its
limits such as membrane capacitance and supply voltage, etc.",2305.16187v1
2023-07-26,Symmetry of the emergent inductance tensor exhibited by magnetic textures,"Metals hosting gradually varying spatial magnetic textures are attracting
attention as a new class of inductor. Under the application of an alternating
current, the spin-transfer-torque effect induces oscillating dynamics of the
magnetic texture, which subsequently yields the spin-motive force as a back
action, resulting in an inductive voltage response. In general, a second-order
tensor representing a material's response can have an off-diagonal component.
However, it is unclear what symmetries the emergent inductance tensor has and
also which magnetic textures can exhibit a transverse inductance response. Here
we reveal both analytically and numerically that the emergent inductance tensor
should be a symmetric tensor in the so-called adiabatic limit. By considering
this symmetric tensor in terms of symmetry operations that a magnetic texture
has, we further characterize the magnetic textures in which the transverse
inductance response can appear. This finding provides a basis for exploring the
transverse response of emergent inductors, which has yet to be discovered.",2307.14542v2
2024-03-04,Current-driven dynamics of antiferromagnetic skyrmions: from skyrmion Hall effects to hybrid inter-skyrmion scattering,"Antiferromagnetic (AFM) skyrmions have emerged as a highly promising avenue
in the realm of spintronics, particularly for the development of advanced
racetrack memory devices. A distinguishing feature of AFM skyrmions is their
zero topological charge and hence anticipated zero skyrmion Hall effect (SkHE).
Here, we unveil that the latter is surprisingly finite under the influence of
spin-transfer torque, depending on the direction of the injected current
impinging on intrinsic AFM skyrmions emerging in CrPdFe trilayer on Ir(111)
surface. Hinging on first-principles combined with atomistic spin dynamics
simulations, we identify the origin of the SkHE and uncover that FM skyrmions
in the underlying Fe layer act as effective traps for AFM skyrmions, confining
them and reducing their velocity. These findings hold significant promise for
spintronic applications, the design of multi-purpose skyrmion-tracks, advancing
our understanding of AFM-FM skyrmion interactions and hybrid soliton dynamics
in heterostructures.",2403.01987v1
2022-11-22,Spatially Nonuniform Oscillations in Ferrimagnets Based on an Atomistic Model,"The ferrimagnets, such as GdxFeCo(1-x), can produce ultrafast magnetic
switching and oscillation due to the strong exchange field. The two-sublattices
macrospin model has been widely used to explain the experimental results.
However, it fails in describing the spatial nonuniform magnetic dynamics which
gives rises to many important phenomenons such as the domain walls and
skyrmions. Here we develop the two-dimensional atomistic model and provide a
torque analysis method to study the ferrimagnetic oscillation. Under the
spin-transfer torque, the magnetization oscillates in the exchange mode or the
flipped exchange mode. When the Gd composition is increased, the exchange mode
firstly disappears, and then appears again as the magnetization compensation
point is reached. We show that these results can only be explained by analyzing
the spatial distribution of magnetization and effective fields. In particular,
when the sample is small, a spatial nonuniform oscillation is also observed in
the square film. Our work reveals the importance of spatial magnetic
distributions in understanding the ferrimagnetic dynamics. The method developed
in this paper provides an important tool to gain a deeper understanding of
ferrimagnets and antiferromagnets. The observed ultrafast dynamics can also
stimulate the development of THz oscillators.",2211.12247v1
2016-04-29,Tunable spin-charge conversion through topological phase transitions in zigzag nanoribbons,"We study spin-orbit torques and charge pumping in magnetic quasi-one
dimensional zigzag nanoribbons with hexagonal lattice, in the presence of large
intrinsic spin-orbit coupling. Such a system experiences topological phase
transition from a trivial band insulator to a quantum spin Hall insulator
either by tuning the magnetization direction or the intrinsic spin-orbit
coupling. We find that spin-charge conversion efficiency (i.e. spin-orbit
torque and charge pumping) is dramatically enhanced at the topological
transition, displaying a substantial angular anisotropy.",1604.08782v1
2023-04-19,Torque-based Deep Reinforcement Learning for Task-and-Robot Agnostic Learning on Bipedal Robots Using Sim-to-Real Transfer,"In this paper, we review the question of which action space is best suited
for controlling a real biped robot in combination with Sim2Real training.
Position control has been popular as it has been shown to be more sample
efficient and intuitive to combine with other planning algorithms. However, for
position control gain tuning is required to achieve the best possible policy
performance. We show that instead, using a torque-based action space enables
task-and-robot agnostic learning with less parameter tuning and mitigates the
sim-to-reality gap by taking advantage of torque control's inherent compliance.
Also, we accelerate the torque-based-policy training process by pre-training
the policy to remain upright by compensating for gravity. The paper showcases
the first successful sim-to-real transfer of a torque-based deep reinforcement
learning policy on a real human-sized biped robot. The video is available at
https://youtu.be/CR6pTS39VRE.",2304.09434v1
2016-05-24,Inside the perpendicular spin-torque memristor,"Memristors are non-volatile nano-resistors. Their resistance can be tuned by
applied currents or voltages and set to a large number of levels between two
limit values. Thanks to these properties, memristors are ideal building blocks
for a number of applications such as multilevel non-volatile memories and
artificial nano-synapses, which are the focus of this work. A key point towards
the development of large scale memristive neuromorphic hardware is to build
these neural networks with a memristor technology compatible with the best
candidates for the future mainstream non-volatile memories. Here we show the
first experimental achievement of a memristor compatible with Spin-Torque
Magnetic Random Access Memory. The resistive switching in our spin-torque
memristor is linked to the displacement of a magnetic domain wall by
spin-torques in a perpendicularly magnetized magnetic tunnel junction. We
demonstrate that our magnetic synapse has a large number of intermediate
resistance states, sufficient for neural computation. Moreover, we show that
engineering the device geometry allows leveraging the most efficient spin
torque to displace the magnetic domain wall at low current densities and thus
to minimize the energy cost of our memristor. Our results pave the way for
spin-torque based analog magnetic neural computation.",1605.07460v1
2017-01-07,Interface enhanced spin-orbit torques and current-induced magnetization switching of Pd/Co/AlO$_x$ layers,"Magnetic heterostructures that combine large spin-orbit torque efficiency,
perpendicular magnetic anisotropy, and low resistivity are key to develop
electrically-controlled memory and logic devices. Here we report on vector
measurements of the current-induced spin orbit torques and magnetization
switching in perpendicularly magnetized Pd/Co/AlO$_x$ layers as a function of
Pd thickness. We find sizeable damping-like (DL) and field-like (FL) torques,
of the order of 1~mT per $10^7$~A/cm$^2$, which have different thickness and
magnetization angle dependence. The analysis of the DL torque efficiency per
unit current density and electric field using drift-diffusion theory leads to
an effective spin Hall angle and spin diffusion length of Pd larger than 0.03
and 7~nm, respectively. The FL SOT includes a significant interface
contribution, is larger than estimated using drift-diffusion parameters, and is
further strongly enhanced upon rotation of the magnetization from the
out-of-plane to the in-plane direction. Finally, taking advantage of the large
spin-orbit torques in this system, we demonstrate bipolar magnetization
switching of Pd/Co/AlO$_x$ layers with similar current density as used for
Pt/Co layers with comparable perpendicular magnetic anisotropy.",1701.01843v1
2020-06-25,Strong Spin-Orbit Torque effect on magnetic defects due to topological surface state electrons in Bi$_{2}$Te$_{3}$,"We investigate the spin-orbit torque exerted on the magnetic moments of the
transition-metal impurities Cr, Mn, Fe and Co, embedded in the surface of the
topological insulator Bi$_{2}$Te$ _{3} $, in response to an electric field and
a consequent electrical current flow in the surface. The multiple scattering
problem of electrons off impurity atoms is solved by first-principles
calculations within the full-potential relativistic Korringa-Kohn-Rostoker
(KKR) Green function method, while the spin-orbit torque calculations are
carried out by combining the KKR method with the semiclassical Boltzmann
transport equation. We analyze the correlation of the spin-orbit torque to the
spin accumulation and spin flux in the defects. We compare the torque on
different magnetic impurities and unveil the effect of resonant scattering. In
addition, we calculate the resistivity and the Joule heat as a function of the
torque in these systems. We predict that the Mn/Bi$_{2}$Te$_{3}$ is optimal
among the studied systems.",2006.14555v1
2021-12-03,Torque reversal and orbital profile of X-ray pulsar OAO 1657-415,"OAO 1657-415 is an atypical supergiant X-ray binary among wind-fed and
disk-fed systems, showing alternate spin-up/spin-down intervals lasting on the
order of tens of days. We study different torque states of OAO 1657-415 based
on the spin history monitored by {\it Fermi}/GBM, together with fluxes from
{\it Swift}/BAT and {\it MAXI}/GSC. Its spin frequency derivatives are well
correlated with {\it Swift}/BAT fluxes during rapid spin-up episodes,
anti-correlated with {\it Swift}/BAT fluxes during rapid spin-down episodes,
and not correlated in between. The orbital profile of spin-down episodes is
reduced by a factor of 2 around orbital phases of 0.2 and 0.8 compared to that
of spin-up episodes. The orbital hardness ratio profile of spin-down episodes
is also lower than that of spin-up episodes around phases close to the
mid-eclipse, implying that there is more material between the neutron star and
the observer for spin-down episodes than for spin-up episodes around these
phases. These results indicate that the torque state of the neutron star is
connected with the material flow on orbital scale and support the
retrograde/prograde disk accretion scenario for spin-down/spin-up torque
reversal.",2112.01993v1
2017-08-25,Role of dimensional crossover on spin-orbit torque efficiency in magnetic insulator thin films,"Magnetic insulators (MIs) attract tremendous interest for spintronic
applications due to low Gilbert damping and absence of Ohmic loss. Magnetic
order of MIs can be manipulated and even switched by spin-orbit torques (SOTs)
generated through spin Hall effect and Rashba-Edelstein effect in heavy
metal/MI bilayers. SOTs on MIs are more intriguing than magnetic metals since
SOTs cannot be transferred to MIs through direct injection of electron spins.
Understanding of SOTs on MIs remains elusive, especially how SOTs scale with
the film thickness. Here, we observe the critical role of dimensionality on the
SOT efficiency by systematically studying the MI layer thickness dependent SOT
efficiency in tungsten/thulium iron garnet (W/TmIG) bilayers. We first show
that the TmIG thin film evolves from two-dimensional to three-dimensional
magnetic phase transitions as the thickness increases, due to the suppression
of long-wavelength thermal fluctuation. Then, we report the significant
enhancement of the measured SOT efficiency as the thickness increases. We
attribute this effect to the increase of the magnetic moment density in concert
with the suppression of thermal fluctuations. At last, we demonstrate the
current-induced SOT switching in the W/TmIG bilayers with a TmIG thickness up
to 15 nm. The switching current density is comparable with those of heavy
metal/ferromagnetic metal cases. Our findings shed light on the understanding
of SOTs in MIs, which is important for the future development of ultrathin
MI-based low-power spintronics.",1708.07584v2
2020-05-04,Spin-orbit-torque magnonics,"The field of magnonics, which utilizes propagating spin waves for nano-scale
transmission and processing of information, has been significantly advanced by
the advent of the spin-orbit torque. The latter phenomenon can allow one to
overcome two main drawbacks of magnonic devices - low energy efficiency of
conversion of electrical signals into spin wave signals, and fast spatial decay
of spin waves in thin-film waveguiding structures. At first glance, the
excitation and amplification of spin waves by spin-orbit torques can seem to be
straightforward. Recent research indicates, however, that the lack of the
mode-selectivity in the interaction of spin currents with dynamic magnetic
modes and the onset of dynamic nonlinear phenomena represent significant
obstacles. Here, we discuss the possible route to overcoming these limitations,
based on the suppression of nonlinear spin-wave interactions in magnetic
systems with perpendicular magnetic anisotropy. We show that this approach
enables efficient excitation of coherent magnetization dynamics and propagating
spin waves in extended spatial regions, and is expected to enable practical
implementation of complete compensation of spin-wave propagation losses.",2005.01391v1
2024-03-11,Impact of spin torques and spin pumping phenomena on magnon-plasmon polaritons in antiferromagnetic insulator-semiconductor heterostructures,"We investigate the impact of spin torque and spin pumping on the surface
magnon polariton dispersion in a antiferromagnetic insulator-semiconductor
heterostructure. In the bilayer system, the surface magnon polaritons
conventionally couple to the plasma-oscillations in the semiconductor via
electromagnetic fields. Additionally, magnons in the antiferromagnetic
insulator layer may interact with the semiconductor layer via spin torques and
their reciprocal phenomena of spin pumping. Due to the spin-to-charge
conversion from the spin Hall and inverse spin Hall effects in the
semiconductor layer with a strong spin-orbit coupling, this can couple the
magnons to the plasmons in the semiconductor layer. Our research reveals that
modifications in the mode frequency and the hybridization gap induced by these
phenomena depend on the thickness of the antiferromagnetic layer. In thick
layers, the spin-pumping contribution to the frequency shift and damping is
inversely proportional to the wavelength, while in thin layers it is inversely
proportional to the thickness. Furthermore, hybridization of the surface magnon
polariton and dispersive magnons in the antiferromagnet is shown to depend on
both the thickness and wavelength of the modes.",2403.06934v1
2024-03-19,Unraveling the dynamics of magnetization in topological insulator-ferromagnet heterostructures via spin-orbit torque,"Spin-orbit coupling stands as a pivotal determinant in the realm of condensed
matter physics. In recent, its profound influence on spin dynamics opens up a
captivating arena with promising applications. Notably, the topological
insulator-ferromagnet heterostructure has been recognized for inducing spin
dynamics through applied current, driven by spin-orbit torque. Building upon
recent observations revealing spin flip signals within this heterostructure,
our study elucidates the conditions governing spin flips by studying the
magnetization dynamics. We establish that the interplay between spin-anisotropy
and spin-orbit torque plays a crucial role in shaping the physics of
magnetization dynamics within the heterostructure. Furthermore, we categorize
various modes of magnetization dynamics, constructing a comprehensive phase
diagram across distinct energy scales, damping constants, and applied
frequencies. This research not only offers insights into controlling spin
direction but also charts a new pathway to the practical application of
spin-orbit coupled systems.",2403.12701v1
2021-05-03,Magnetic angle evolution in accreting neutron stars,"The rotation of a magnetised accreting neutron star (NS) in a binary system
is described by its spin period and two angles: spin inclination $\alpha$ with
respect to the orbital momentum and magnetic angle $\chi$ between the spin and
the magnetic moment. Magnetospheric accretion spins the NS up and adjusts its
rotation axis, decreasing $\alpha$ to nearly perfect alignment. Its effect upon
the magnetic angle is more subtle and relatively unstudied. In this work, we
model the magnetic angle evolution of a rigid spherical accreting NS. We find
that the torque spinning the NS up may affect the magnetic angle while both
$\alpha$ and $\chi$ significantly deviate from zero, and the spin-up torque
varies with the phase of the spin period. As the rotation axis of the NS is
being aligned with the spin-up torque, the magnetic axis becomes misaligned
with the rotation axis. Under favourable conditions, magnetic angle may
increase by $\Delta \chi \sim 15^\circ-20^\circ$. This orthogonalisation may be
an important factor in the evolution of millisecond pulsars, as it partially
compensates the $\chi$ decrease potentially caused by pulsar torques. If the
direction of the spin-up torque changes randomly with time, as in wind-fed
high-mass X-ray binaries, both the rotation axis of the NS and its magnetic
axis become involved in a non-linear random-walk evolution. The ultimate
attractor of this process is a bimodal distribution in $\chi$ peaking at $\chi
=0^\circ$ and $\chi = 90^\circ$.",2105.00754v1
2022-05-05,Intrinsic spin Hall torque in a moire Chern magnet,"In spin torque magnetic memories, electrically actuated spin currents are
used to switch a magnetic bit. Typically, these require a multilayer geometry
including both a free ferromagnetic layer and a second layer providing spin
injection. For example, spin may be injected by a nonmagnetic layer exhibiting
a large spin Hall effect, a phenomenon known as spin-orbit torque. Here, we
demonstrate a spin-orbit torque magnetic bit in a single two-dimensional system
with intrinsic magnetism and strong Berry curvature. We study AB-stacked
MoTe2/WSe2, which hosts a magnetic Chern insulator at a carrier density of one
hole per moire superlattice site. We observe hysteretic switching of the
resistivity as a function of applied current. Magnetic imaging using a
superconducting quantum interference device reveals that current switches
correspond to reversals of individual magnetic domains. The real space pattern
of domain reversals aligns precisely with spin accumulation measured near the
high-Berry curvature Hubbard band edges. This suggests that intrinsic spin- or
valley-Hall torques drive the observed current-driven magnetic switching in
both MoTe2/WSe2 and other moire materials. The switching current density of
10^3 Amps per square centimeter is significantly less than reported in other
platforms paving the way for efficient control of magnetic order.",2205.02823v1
2023-12-07,Direct and indirect spin current generation and spin-orbit torques in ferromagnet/nonmagnet/ferromagnet trilayers,"Spin-orbit torques in ferromagnet/nonmagnet/ferromagnet trilayers are studied
using a combination of symmetry analysis, circuit theory, semiclassical
simulations, and first-principles calculations using the non-equilibrium
Green's function method with supercell disorder averaging. We focus on
unconventional processes involving the interplay between the two ferromagnetic
layers, which are classified into direct and indirect mechanisms. The direct
mechanism involves spin current generation by one ferromagnetic layer and its
subsequent absorption by the other. In the indirect mechanism, the in-plane
spin-polarized current from one ferromagnetic layer ``leaks'' into the other
layer, where it is converted into an out-of-plane spin current and reabsorbed
by the original layer. The direct mechanism results in a predominantly
dampinglike torque, which damps the magnetization towards a certain direction
$\mathbf{s}_d$. The indirect mechanism results in a predominantly fieldlike
torque with respect to a generally different direction $\mathbf{s}_f$. Similar
to the current-in-plane giant magnetoresistance, the indirect mechanism is only
active if the thickness of the nonmagnetic spacer is smaller than or comparable
to the mean-free path. Numerical calculations for a semiclassical model based
on the Boltzmann equation confirm the presence of both direct and indirect
mechanisms of spin current generation. First-principles calculations reveal
sizeable unconventional spin-orbit torques in Co/Cu/Co, Py/Cu/Py, and Co/Pt/Co
trilayers and provide strong evidence of indirect spin current generation.",2312.04538v1
2020-05-12,Magnetization reversal driven by spin-transfer-torque in perpendicular shape anisotropy magnetic tunnel junctions,"The concept of perpendicular shape anisotropy spin-transfer torque magnetic
random-access memory (PSA-STT-MRAM) consists in increasing the storage layer
thickness to values comparable to the cell diameter, to induce a perpendicular
shape anisotropy in the magnetic storage layer. Making use of that
contribution, the downsize scalability of the STT-MRAM may be extended towards
sub-20 nm technological nodes, thanks to a reinforcement of the thermal
stability factor $\Delta$. Although the larger storage layer thickness improves
$\Delta$, it is expected to negatively impact the writing current and switching
time. Hence, optimization of the cell dimensions (diameter, thickness) is of
utmost importance for attaining a sufficiently high $\Delta$ while keeping a
moderate writing current. Micromagnetic simulations were carried out for
different pillar thicknesses of fixed lateral size 20 nm. The switching time
and the reversal mechanism were analysed as a function of the applied voltage
and aspect-ratio (AR) of the storage layer. For AR $<$ 1, the magnetization
reversal resembles a macrospin-like mechanism, while for AR $>$ 1 a
non-coherent reversal is observed, characterized by the nucleation of a
transverse domain wall at the ferromagnet/insulator interface which then
propagates along the vertical axis of the pillar. It was further observed that
the inverse of the switching time is linearly dependent on the applied voltage.
This study was extended to sub-20 nm width with a value of $\Delta$ around 80.
It was observed that the voltage necessary to reverse the magnetic layer
increases as the lateral size is reduced, accompanied with a transition from
macrospin-reversal to a buckling-like reversal at high aspect-ratios.",2005.06024v2
2023-10-26,Period bouncers as detached magnetic cataclysmic variables,"The general prediction that more than half of all CVs have evolved past the
period minimum is in strong disagreement with observational surveys, which show
that the relative number of these objects is just a few per cent. Here, we
investigate whether a large number of post-period minimum CVs could detach
because of the appearance of a strong white dwarf magnetic field potentially
generated by a rotation- and crystallization-driven dynamo. We used the MESA
code to calculate evolutionary tracks of CVs incorporating the spin evolution
and cooling as well as compressional heating of the white dwarf. If the
conditions for the dynamo were met, we assumed that the emerging magnetic field
of the white dwarf connects to that of the companion star and incorporated the
corresponding synchronization torque, which transfers spin angular momentum to
the orbit. We find that for CVs with donor masses exceeding 0.04 Msun, magnetic
fields are generated mostly if the white dwarfs start to crystallize before the
onset of mass transfer. It is possible that a few white dwarf magnetic fields
are generated in the period gap. For the remaining CVs, the conditions for the
dynamo to work are met beyond the period minimum, when the accretion rate
decreased significantly. Synchronization torques cause these systems to detach
for several Gyrs even if the magnetic field strength of the white dwarf is just
one MG. If the rotation- and crystallization-driven dynamo - which is currently
the only mechanism that can explain several observational facts related to
magnetism in CVs and their progenitors - or a similar temperature-dependent
mechanism is responsible for the generation of magnetic field in white dwarfs,
most CVs that have evolved beyond the period minimum must detach for several
Gyrs at some point. This reduces the predicted number of semi-detached period
bouncers by up to 60-80 per cent.",2310.17276v1
2014-06-26,"Spin Supercurrent, Magnetization Dynamics, and Phi-State in Spin-Textured Josephson Junctions","The prospect of combining the dissipationless nature of superconducting
currents with the spin-polarization of magnetic materials is interesting with
respect to exploring superconducting analogues of topics in spintronics. In
order to accomplish this aim, it is pivotal to understand how
spin-supercurrents interact dynamically with magnetization textures. We
investigate the appearance of a spin-supercurrent and the resulting
magnetization dynamics in a textured magnetic Josephson current by using three
experimentally relevant models: i) a S/F/S junction with spin-active
interfaces, ii) a S/F1/F2/F3/S Josephson junction with a ferromagnetic
trilayer, and iii) a Josephson junction containing a domain wall. In all of
these cases, the supercurrent is spin-polarized and exerts a spin-transfer
torque on the ferromagnetic interlayers which causes magnetization dynamics.
Using a scattering matrix formalism in the clean limit, we compute the
Andreev-bound states and free energy of the system which is used to solve the
Landau-Lifshiftz-Gilbert equation. We compute both how the inhomogeneous
magnetism influences the phase-dependence of the charge supercurrent as well as
the magnetization dynamics caused by the spin-supercurrent. Using a realistic
experimental parameter set, we find that the supercurrent can induce
magnetization switching that is controlled by the superconducting phase
difference. Moreover, we demonstrate that the combined effect of chiral spin
symmetry breaking and interface scattering causes the system to act as a phase
battery that may supply any superconducting phase difference phi in the ground
state. Such a phi junction is accompanied by an anomalous supercurrent
appearing even at zero phase difference, and we demonstrate that the flow
direction of this current is controlled by the chirality of the magnetization
configuration.",1406.7016v1
2011-10-16,Spin Hall Effect-driven Spin Torque in Magnetic Texture,"Current-induced spin torque and magnetization dynamics in the presence of
spin Hall effect in magnetic textures is studied theoretically. The local
deviation of the charge current gives rise to a current-induced spin torque of
the form (1-\beta{\bf M})x[({\bf u}_0+\alpha_H{\bf u}_0x\bf M})\cdot{\bm
\nabla}]{\bf M}, where {\bf u}_0 is the direction of the injected current,
\alpha_H is the Hall angle and \beta is the non-adiabaticity parameter due to
spin relaxation. Since \alpha_H and \beta can have a comparable order of
magnitude, we show that this torque can significantly modify the
current-induced dynamics of both transverse and vortex walls.",1110.3485v1
2015-01-30,Phase diagram and optimal switching induced by spin Hall effect in a perpendicular magnetic layer,"In a ferromagnet/heavy-metal bilayer device with strong spin Hall effect an
in-plane current excites magnetic dynamics through spin torque. We analyze
bilayers with perpendicular magnetization and calculate three-dimensional phase
diagrams describing switching by external magnetic field at a fixed current. We
then concentrate on the case of a field applied in the plane formed by the film
normal and the current direction. Here we analytically study the evolution of
both the conventional ""up""/""down"" magnetic equilibria and the additional
equilibria created by the spin torque. Expressions for the stability regions of
all equilibria are derived, and the nature of switching at each critical
boundary is discussed. The qualitative picture obtained this way predicts
complex hysteresis patterns that should occur in bilayers. By analyzing the
phase portraits of the system we show that when the spin torque induced
equilibrium exists, switching between ""up"" and ""down"" states proceeds through
it as an intermediate state. Using numeric simulations we analyze the switching
time and compare it to that of a conventional spin torque device with collinear
magnetizations of the polarizer and the free layer.",1501.07787v1
2016-08-16,On the origin of field-like spin-orbit torques in heavy metal-ferromagnet-oxide thin film heterostructures,"We report measurements of the thickness and temperature (T) dependencies of
current-induced spin-orbit torques, especially the field-like (FL) component,
in various heavy metal (HM)/normal metal (NM) spacer/ferromagnet (FM)/Oxide
(MgO and HfOx/MgO) heterostructures. The FL torque in these samples originates
from spin current generated by the spin Hall effect (SHE) in the HM. For a FM
layer sufficiently thin that a substantial portion of this spin current can
reach the FM/Oxide interface, T-dependent spin scattering there can yield a
strong FL torque that is, in some cases, opposite in sign to that exerted at
the NM/FM interface.",1608.04443v1
2018-05-31,Spin-orbit torque induced dipole skyrmion motion at room temperature,"We demonstrate deterministic control of dipole-field-stabilized skyrmions by
means of spin-orbit torques arising from heavy transition-metal seed layers.
Experiments are performed on amorphous Fe/Gd multilayers that are patterned
into wires and exhibit stripe domains and dipole skyrmions at room temperature.
We show that while the domain walls and skyrmions are achiral on average due to
lack of Dzyaloshinskii-Moriya interactions, the N\'eel-like closure domain
walls at each surface are chiral and can couple to spin-orbit torques. The
current-induced domain evolutions are reported for different magnetic phases,
including disordered stripe domains, coexisting stripes and dipole skyrmions
and a closed packed dipole skyrmion lattice. The magnetic textures exhibit
motion under current excitations with a current density ~10^8 A/m2. By
comparing the motion resulting from magnetic spin textures in Fe/Gd films with
different heavy transition-metal interfaces, we confirm spin currents can be
used to manipulate achiral dipole skyrmions via spin-orbit torques.",1805.12517v1
2017-10-17,"Fast, low-current spin-orbit torque switching of magnetic tunnel junctions through atomic modifications of the free layer interfaces","Future applications of spin-orbit torque will require new mechanisms to
improve the efficiency for switching nanoscale magnetic tunnel junctions
(MTJs), while also controlling the magnetic dynamics to achieve fast,
nanosecond scale performance with low write error rates. Here we demonstrate a
strategy to simultaneously enhance the interfacial magnetic anisotropy energy
and suppress interfacial spin memory loss by introducing sub-atomic and
monatomic layers of Hf at the top and bottom interfaces of the ferromagnetic
free layer of an in-plane magnetized three-terminal MTJ device. When combined
with a beta-W spin Hall channel that generates spin-orbit torque, the
cumulative effect is a switching current density of 5.4 x 106 A/cm2, more than
a factor of 3 lower than demonstrated in any other spin-orbit-torque magnetic
memory device at room temperature, and highly reliable switching with current
pulses only 2 ns long.",1710.06391v1
2004-05-13,Spin-torque switching: Fokker-Planck rate calculation,"We describe a new approach to understanding and calculating magnetization
switching rates and noise in the recently observed phenomenon of ""spin-torque
switching"". In this phenomenon, which has possible applications to information
storage, a large current passing from a pinned ferromagnetic (FM) layer to a
free FM layer switches the free layer. Our main result is that the spin-torque
effect increases the Arrhenius factor $\exp(-E/kT)$ in the switching rate, not
by lowering the barrier $E$, but by raising the effective spin temperature $T$.
To calculate this effect quantitatively, we extend Kramers' 1940 treatment of
reaction rates, deriving and solving a Fokker-Planck equation for the energy
distribution including a current-induced spin torque of the Slonczewski type.
This method can be used to calculate slow switching rates without long-time
simulations; in this Letter we calculate rates for telegraph noise that are in
good qualitative agreement with recent experiments. The method also allows the
calculation of current-induced magnetic noise in CPP (current perpendicular to
plane) spin valve read heads.",0405305v2
2019-04-16,Enhancing spin-orbit torque by strong interfacial scattering from ultra-thin insertion layers,"Increasing dampinglike spin-orbit torque (SOT) is both of fundamental
importance for enabling new research into spintronics phenomena and also
technologically urgent for advancing low-power spin-torque memory, logic, and
oscillator devices. Here, we demonstrate that enhancing interfacial scattering
by inserting ultra-thin layers within a spin Hall metals with intrinsic or
side-jump mechanisms can significantly enhance the spin Hall ratio. The
dampinglike SOT was enhanced by a factor of 2 via sub-monolayer Hf insertion,
as evidenced by both harmonic response measurements and current-induced
switching of in-plane magnetized magnetic memory devices with the record low
critical switching current of ~73 uA (switching current density of 3.6x10^6
A/cm^2). This work demonstrates a very effective strategy for maximizing
dampinglike SOT for low-power spin-torque devices.",1904.07800v1
2013-11-13,Spin-orbit torques in Co/Pd multilayer nanowires,"Current induced spin-orbit torques have been studied in ferromagnetic
nanowires made of 20 nm thick Co/Pd multilayers with perpendicular magnetic
anisotropy. Using Hall voltage and lock-in measurements, it is found that upon
injection of an electric current both in-plane (Slonczewski-like) and
perpendicular (field-like) torques build up in the nanowire. The torque
efficiencies are found to be as large as 1.17 kOe and 5 kOe at 108 A/cm2 for
the in-plane and perpendicular components, respectively, which is surprisingly
comparable to previous studies in ultrathin (~ 1 nm) magnetic bilayers. We show
that this result cannot be explained solely by spin Hall effect induced torque
at the outer interfaces, indicating a probable contribution of the bulk of the
Co/Pd multilayer.",1311.3033v1
2015-01-14,Intraband and interband spin-orbit torques in non-centrosymmetric ferromagnets,"Intraband and interband contributions to the current-driven spin-orbit torque
in magnetic materials lacking inversion symmetry are theoretically studied
using Kubo formula. In addition to the current-driven field-like torque ${\bf
T}_{\rm FL}= \tau_{\rm FL}{\bf m}\times{\bf u}_{\rm so}$ (${\bf u}_{\rm so}$
being a unit vector determined by the symmetry of the spin-orbit coupling), we
explore the intrinsic contribution arising from impurity-independent interband
transitions and producing an anti-damping-like torque of the form ${\bf T}_{\rm
DL}= \tau_{\rm DL}{\bf m}\times({\bf u}_{\rm so}\times{\bf m})$. Analytical
expressions are obtained in the model case of a magnetic Rashba two-dimensional
electron gas, while numerical calculations have been performed on a dilute
magnetic semiconductor (Ga,Mn)As modeled by the Kohn-Luttinger Hamiltonian
exchanged coupled to the Mn moments. Parametric dependences of the different
torque components and similarities to the analytical results of the Rashba
two-dimensional electron gas in the weak disorder limit are described.",1501.03292v1
2018-10-25,First-principles calculation of spin-orbit torque in a Co/Pt bilayer,"The angular dependence of spin-orbit torque in a disordered Co/Pt bilayer is
calculated using a first-principles non-equilibrium Green's function formalism
with an explicit supercell averaging over Anderson disorder. In addition to the
usual dampinglike and fieldlike terms, the odd torque contains a sizeable
planar Hall-like term $(\mathbf{m\cdot
E})\mathbf{m}\times(\mathbf{z}\times\mathbf{m})$ whose contribution to
current-induced damping is consistent with experimental observations. The
dampinglike and planar Hall-like torquances depend weakly on disorder strength,
while the fieldlike torquance declines with increasing disorder. The torques
that contribute to damping are almost entirely due to spin-orbit coupling on
the Pt atoms, but the fieldlike torque does not require it.",1810.11003v2
2017-02-23,Spin-Orbit Coupling of Conduction Electrons in Magnetization Switching,"Strong magnetic field pulses associated with a relativistic electron bunch
can imprint switching patterns in magnetic thin films that have uniaxial
in-plane anisotropy. In experiments with Fe and FeCo alloy films the pattern
shape reveals an additional torque acting on magnetization during the short (in
the 100fs time scale) magnetic field pulse. The magnitude of the torque is as
high as 15% of the torque from the magnetic field. The torque symmetry is that
of a uniaxial anisotropy along the direction of the eddy current screening the
magnetic field. Spin-orbit interaction acting on the conduction electrons can
produce such a torque with the required symmetry and magnitude. The same
interaction causes the anomalous Hall current to be spin-polarized, exerting a
back reaction on magnetization direction. Such a mechanism may be at work in
all-optical laser switching of magnetic materials.",1702.07153v1
2019-05-29,Acoustic Radiation Force and Torque on Small Particles as Measures of the Canonical Momentum and Spin Densities,"We examine acoustic radiation force and torque on a small (subwavelength)
absorbing isotropic particle immersed in a monochromatic (but generally
inhomogeneous) sound-wave field. We show that by introducing the monopole and
dipole polarizabilities of the particle, the problem can be treated in a way
similar to the well-studied optical forces and torques on dipole Rayleigh
particles. We derive simple analytical expressions for the acoustic force
(including both the gradient and scattering forces) and torque. Importantly,
these expressions reveal intimate relations to the fundamental field properties
introduced recently for acoustic fields: the canonical momentum and spin
angular momentum densities. We compare our analytical results with previous
calculations and exact numerical simulations. We also consider an important
example of a particle in an evanescent acoustic wave, which exhibits the
mutually-orthogonal scattering (radiation-pressure) force, gradient force, and
torque from the transverse spin of the field.",1905.12216v2
2019-07-01,Electrically driven spin torque and dynamical Dzyaloshinskii-Moriya interaction in magnetic bilayer systems,"Efficient control of magnetism with electric means is a central issue of
current spintronics research, which opens an opportunity to design integrated
spintronic devices. However, recent well-studied methods are mostly based on
electric-current injection, and they are inevitably accompanied by considerable
energy losses through Joule heating. Here we theoretically propose a way to
exert spin torques into magnetic bilayer systems by application of electric
voltages through taking advantage of the Rashba spin-orbit interaction. The
torques resemble the well-known electric-current-induced torques, providing
similar controllability of magnetism but without Joule-heating energy losses.
The torques also turn out to work as an interfacial Dzyaloshinskii-Moriya
interaction which enables us to activate and create noncollinear magnetism like
skyrmions by electric-voltage application. Our proposal offers an efficient
technique to manipulate magnetizations in spintronics devices without
Joule-heating energy losses.",1907.00601v2
2024-02-01,Quantum Metric Nonlinear Spin-Orbit Torque Enhanced by Topological Bands,"Effects manifesting quantum geometry have been a focus of physics research.
Here, we reveal that quantum metric plays a crucial role in nonlinear electric
spin response, leading to a quantum metric spin-orbit torque. We argue that
enhanced quantum metric can occur at band (anti)crossings, so the nonlinear
torque could be amplified in topological metals with nodal features close to
Fermi level. By applying our theory to magnetic Kane-Mele model and monolayer
CrSBr, which feature nodal lines and Weyl points, we demonstrate that the
quantum metric torque dominates the response, and its magnitude is
significantly enhanced by topological band structures, which even surpasses the
previously reported linear torques and is sufficient to drive magnetic
switching by itself.",2402.00532v1
2023-03-07,The Role of Self-Torques in Transition Metal Dichalcogenide/Ferromagnet Bilayers,"Recently, transition metal dichalcogenides (TMDs) have been extensively
studied for their efficient spin-orbit torque generation in TMD/ferromagnetic
bilayers, owing to their large spin-orbit coupling, variety in crystal
symmetries, and pristine interfaces. Although the TMD layer was considered
essential for the generation of the observed SOTs, recent reports show the
presence of a self-torque in single-layer ferromagnetic devices with magnitudes
comparable to TMD/ferromagnetic devices. Here, we perform second-harmonic Hall
SOT measurements on metal-organic chemical vapor deposition (MOCVD) grown
MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ devices and compare them to a single-layer
permalloy/Al$_{2}$O$_{3}$ device to accurately disentangle the role of
self-torques from contributions from the TMD layer. We report a damping-like
self-torque conductivity of opposite sign in our single-layer
permalloy/Al$_{2}$O$_{3}$ device compared to one
MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ device, and find no significant one for all
other MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ devices. This indicates a competition
between the self-torque and the torque arising from the TMD layer, which would
reduce the observed torque in these bilayers. In addition, we find a field-like
spin-torque conductivity of comparable magnitude to control
MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ devices, indicating only a minor role of
the MoS$_{2}$ layer. Finally, we find a linear dependence of the SOT
conductivity on the Hall bar leg/channel width ratio of our devices, indicating
that the Hall bar dimensions are of significant importance for the reported SOT
strength. Our results accentuate the importance of delicate details, like
device asymmetry, Hall bar dimensions, and self-torque generation, for the
correct disentanglement of the microscopic origins underlying the SOTs,
essential for future energy-efficient spintronic applications.",2303.03892v2
2023-12-13,Exploration of field-like torque and field-angle tunability in coupled spin-torque nano oscillators for synchronization,"We investigate the influence of field-like torque and the direction of the
external magnetic field on a one-dimensional array of serially connected
spin-torque nano oscillators, having free layers with perpendicular anisotropy,
to achieve complete synchronization between them by analyzing the associated
Landau-Lifshitz-Gilbert-Slonczewski equation. The obtained results for
synchronization are discussed for the cases of 2, 10 and 100 oscillators
separately. The roles of the field-like torque and the direction of the
external field on the synchronization of the STNOs are explored through the
Kuramoto order parameter. While the field-like torque alone is sufficient to
bring out global synchronization in the system made up of a small number of
STNOs, the direction of the external field is also needed to be slightly tuned
to synchronize the one-dimensional array of a large number of STNOs. The
formation of complete synchronization through the construction of clusters
within the system is identified for the 100 oscillators. The large amplitude
synchronized oscillations are obtained for small to large numbers of
oscillators. Moreover, the tunability in frequency for a wide range of currents
is shown for the synchronized oscillations up to 100 spin-torque oscillators.
In addition to achieving synchronization, the field-like torque increases the
frequency of the synchronized oscillations. The transverse Lyapunov exponents
are deduced to confirm the stable synchronization in coupled STNOs due to the
field-like torque and to validate the results obtained in the numerical
simulations. The output power of the array is estimated to be enhanced
substantially due to complete synchronization by the combined effect of
field-like torque and tunability of the field angle.",2312.16175v1
2021-12-03,Solar System Dynamics and Multiyear Droughts of the Western USA,"The recent addition of orbit-spin coupling torques to atmospheric global
circulation models has enabled successful years-in-advance forecasts of global
and regional-scale dust storms on Mars. Here we explore the applicability of
the orbit-spin coupling mechanism for understanding and forecasting anomalous
weather and climate events on Earth. We calculate the time history of
orbit-spin coupling torques on the Earth system for the interval from
1860-2040. The torque exhibits substantial variability on decadal to bidecadal
timescales. Deep minima recur at intervals from 15-26 years; eight such
episodes are documented within the study period prior to 2020. Each of the
identified torque minima corresponds in time to an episode of widespread
drought in the Western USA extending over several years. The multiyear droughts
of the 1930s, the 1950s, the mid-1970s, the early 1990s, and of 2011-2015 were
each coincident in time with orbit-spin coupling torque minima. The upcoming
torque minimum of 2030 is the deepest such minimum of the 180-yr study
interval. A multiyear episode of widespread drought in the Western USA is
likely to be underway by 2028 plus or minus 4 years (2 standard deviations).
The potential benefits to societies of improved drought predictions justify an
immediate high-priority effort to include forcing by orbit-spin coupling within
state-of-the-art Earth system GCMs. Future targeted numerical modeling
investigations are likely to yield forecasts with considerably lower
uncertainties and with much improved temporal resolution in comparison to that
obtained here.",2112.02186v1
2007-06-12,Magnetic fingerprint in a ferromagnetic wire: Spin torque diode effect and induction of the DC voltage spectrum inherent in the wire under application for RF current,"We report the rectifying effect of a constant-wave radio frequency (RF)
current by a magnetic domain wall (DW) on a single-layered ferromagnetic wire.
A direct-current (DC) voltage is generated by the spin torque diode effect,
which is a consequence of magnetoresistance oscillation due to the resonant
spin wave excitation induced by the spin-polarized RF current. The DC voltage
spectrum strongly depends on the internal spin structure in the DW, which
corresponds to the magnetic fingerprint of the spin structure in the
ferromagnetic wire.",0706.1733v1
2020-06-21,Understanding spintronics in F/N/F structures through a mechanical analogy,"A mechanical equivalent system is introduced to mimic the behavior of
multilayer structures with diffusive spin transport. The analogy allows one to
use existing mechanical intuition to predict the influence of various
parameters on spin torques and spin-dependent magnetoresistance. In particular,
it provides an understanding of the sign-changing behavior of spin torque in
asymmetric F/N/F spin valves. It further helps to uncover the physical reason
behind the singular behavior of spin magnetoresistance in devices with
ultra-thin N-layers.",2006.11900v1
2018-02-12,Spin-orbit torque and spin pumping in YIG/Pt with interfacial insertion layers,"We experimentally investigate spin-orbit torque and spin pumping in
Y$_3$Fe$_5$O$_{12}$(YIG)/Pt bilayers with ultrathin insertion layers at the
interface. An insertion layer of Cu suppresses both spin-orbit torque and spin
pumping, whereas an insertion layer of Ni$_{80}$Fe$_{20}$ (permalloy, Py)
enhances them, in a quantitatively consistent manner with the reciprocity of
the two spin transmission processes. However, we observe a large enhancement of
Gilbert damping with the insertion of Py that cannot be accounted for solely by
spin pumping, suggesting significant spin-memory loss due to the interfacial
magnetic layer. Our findings indicate that the magnetization at the YIG-metal
interface strongly influences the transmission and depolarization of pure spin
current.",1802.03865v3
2019-03-08,"Extraordinary efficient spin-orbit torque switching in (W, Ta)/epitaxial-Co60Fe40/TiN heterostructures","The giant spin Hall effect in magnetic heterostructures along with low spin
memory loss and high interfacial spin mixing conductance are prerequisites to
realize energy efficient spin torque based logic devices. We report giant spin
Hall angle (SHA) of 28.67 (5.09) for W (Ta) interfaced epi- Co60Fe40/TiN
structures. The spin-orbit torque switching current density (J_Crit) is as low
as 1.82 (8.21) MA/cm2 in W (Ta)/Co60Fe40(t_CoFe)/TiN structures whose origin
lies in the epitaxial interfaces. These structures also exhibit very low spin
memory loss and high spin mixing conductance. These extraordinary values of SHA
and therefore ultra-low J_Crit in semiconducting industry compatible epitaxial
materials combinations open up a new direction for the realization of energy
efficient spin logic devices by utilizing epitaxial interfaces.",1903.03480v3
2019-12-03,Spin-orbit torque-mediated spin-wave excitation as an alternative paradigm for femtomagnetism,"Laser-induced femtosecond demagnetization, femtomagnetism, offers a potential
route to develop faster magnetic storage devices. It is generally believed that
the traditional spin-wave theory, which is developed for thermally driven slow
demagnetization, can not explain this rapid demagnetization by design. Here we
show that this traditional spin-wave theory, once augmented by laser-induced
spin-orbit torque, provides a highly efficient paradigm for demagnetization, by
capturing low-energy spin-wave excitation that is absent in existing
mechanisms. Our paradigm is different from existing ones, but does not exclude
them. Microscopically, we find that optical spin-orbit torque generates massive
spin waves across several hundred lattice sites, collapsing the long-range
spin-spin correlation within 20 fs. Our finding does not only explain new
experiments, but also establishes an alternative paradigm for femtomagnetism.
It is expected to have far-reaching impacts on future research.",1912.01736v1
2017-05-24,Deficiency of the Bulk Spin Hall Effect Model for Spin-Orbit Torques in Magnetic Insulator/Heavy Metal Heterostructures,"Electrical currents in a magnetic insulator/heavy metal heterostructure can
induce two simultaneous effects, namely, spin Hall magnetoresistance (SMR) on
the heavy metal side and spin-orbit torques (SOTs) on the magnetic insulator
side. Within the framework of the pure spin current model based on the bulk
spin Hall effect (SHE), the ratio of the spin Hall-induced anomalous Hall
effect (SH-AHE) to SMR should be equal to the ratio of the field-like torque
(FLT) to damping-like torque (DLT). We perform a quantitative study of SMR,
SH-AHE, and SOTs in a series of thulium iron garnet/platinum or Tm3Fe5O12/Pt
heterostructures with different Tm3Fe5O12 thicknesses, where Tm3Fe5O12 is a
ferrimagnetic insulator with perpendicular magnetic anisotropy. We find the
ratio between measured effective fields of FLT and DLT is at least 2 times
larger than the ratio of the SH-AHE to SMR. In addition, the bulk SHE model
grossly underestimates the spin torque efficiency of FLT. Our results reveal
deficiencies of the bulk SHE model and also address the importance of
interfacial effects such as the Rashba and magnetic proximity effects in
magnetic insulator/heavy metal heterostructures.",1705.08919v1
2015-10-13,Nonlocal torque operators in ab initio theory of the Gilbert damping in random ferromagnetic alloys,"We present an ab initio theory of the Gilbert damping in substitutionally
disordered ferromagnetic alloys. The theory rests on introduced nonlocal
torques which replace traditional local torque operators in the well-known
torque-correlation formula and which can be formulated within the atomic-sphere
approximation. The formalism is sketched in a simple tight-binding model and
worked out in detail in the relativistic tight-binding linear muffin-tin
orbital (TB-LMTO) method and the coherent potential approximation (CPA). The
resulting nonlocal torques are represented by nonrandom, non-site-diagonal and
spin-independent matrices, which simplifies the configuration averaging. The
CPA-vertex corrections play a crucial role for the internal consistency of the
theory and for its exact equivalence to other first-principles approaches based
on the random local torques. This equivalence is also illustrated by the
calculated Gilbert damping parameters for binary NiFe and FeCo random alloys,
for pure iron with a model atomic-level disorder, and for stoichiometric FePt
alloys with a varying degree of L10 atomic long-range order.",1510.03571v2
2022-02-18,Generally applicable holographic torque measurement for optically trapped particles,"We present a method to measure the optical torque applied to particles of
arbitrary shape held in an optical trap, inferred from the change of angular
momentum of light induced by the particle. All torque components can be
determined from a single interference pattern recorded by a camera in the back
focal plane of a high-NA condenser collecting all forward scattered light. We
derive explicit expressions mapping the measured complex field in this plane to
the torque components. The required phase is retrieved by an iterative
algorithm, using the known position of the optical traps as constraints. The
torque pertaining to individual particles is accessible, as well as separate
spin or orbital parts of the total torque.",2202.09051v2
2024-01-01,Calculation of Gilbert damping and magnetic moment of inertia using torque-torque correlation model within ab initio Wannier framework,"Magnetization dynamics in magnetic materials are well described by the
modified semiclassical Landau-Lifshitz-Gilbert (LLG) equation, which includes
the magnetic damping $\alpha$ and the magnetic moment of inertia $\mathrm{I}$
tensors as key parameters. Both parameters are material-specific and physically
represent the time scales of damping of precession and nutation in
magnetization dynamics. $\alpha$ and $\mathrm{I}$ can be calculated quantum
mechanically within the framework of the torque-torque correlation model. The
quantities required for the calculation are torque matrix elements, the real
and imaginary parts of the Green's function and its derivatives. Here, we
calculate these parameters for the elemental magnets such as Fe, Co and Ni in
an ab initio framework using density functional theory and Wannier functions.
We also propose a method to calculate the torque matrix elements within the
Wannier framework. We demonstrate the effectiveness of the method by comparing
it with the experiments and the previous ab initio and empirical studies and
show its potential to improve our understanding of spin dynamics and to
facilitate the design of spintronic devices.",2401.00714v1
2016-07-15,Picosecond all-optical switching of magnetic tunnel junctions,"Control of magnetism without using magnetic fields enables large-scale
integration of spintronic devices for memory, computation and communication in
the beyond-CMOS era. Mechanisms including spin torque transfer, spin Hall
effect, and electric field or strain assisted switching have been implemented
to switch magnetization in various spintronic devices. Their operation speed,
however, is fundamentally limited by the spin precession time to be longer than
10-100 picoseconds. Overcoming such a speed constraint is critical for the
prospective development of spintronics. Here we report the demonstration of
picosecond all-optical switching of a magnetic tunnel junction (MTJ)- the
building block of spintronic logic and memory -only using single telecom-band,
infrared laser pulses. This first optically switchable MTJ uses ferrimagnetic
GdFeCo as the free layer, and its switching is directly readout by measuring
its tunneling magnetoresistance with a DR/R ratio of 0.6%. An instrument
limited switching repetition rate at MHz has been demonstrated, but the
fundamental limit should be higher than tens of GHz. This result represents an
important step toward integrated opto-spintronic devices that combines
spintronics and photonics technologies to enable ultrafast conversion between
fundamental information carriers of electron spins and photons.",1607.04615v1
2011-07-01,The role of gauge symmetry in spintronics,"In this work we employ a field theoretical approach to explain the nature of
the non-conserved spin current in spintronics. In particular, we consider the
usual U(1) gauge theory for the electromagnetism at classical level in order to
obtain the broken continuity equation involving the spin current and
spin-transfer torque. Inspired in the recent work of A. Vernes, B. L. Gyorffy
and P. Weinberger where they obtain such equation in terms of relativistic
quantum mechanics, we formalize their result in terms of the well known
currents of field theory such as the Bargmann-Wigner current and the chiral
current. Thus, an interpretation of spintronics is provided in terms of Noether
currents (conserved or not) and symmetries of the electromagnetism. In fact,
the main result of the present work is that the non-conservation of the spin
current is associated to the gauge invariance of physical observables where the
breaking term is proportional to the chiral current. Moreover, we generalize
their result by including the electromagnetic field as a dynamical field
instead of an external one.",1107.0332v2
2015-04-04,Brillouin zone spin filtering mechanism of enhanced TMR and correlation effects in Co(0001)/h-BN/Co(0001) magnetic tunnel junction,"The 'Brillouin zone spin filtering' mechanism of enhanced tunneling
magnetoresistance (TMR) is described for magnetic tunnel junctions (MTJ) and
studied on an example of the MTJ with hcp Co electrodes and hexagonal BN (h-BN)
spacer. Our calculations based on local density approximation of density
functional theory (LDA-DFT) for Co(0001)/h-BN/Co(0001) MTJ predict high TMR in
this device due to Brillouin zone filtering mechanism. Owning to the specific
complex band structure of the h-BN the spin-dependent tunneling conductance of
the system is ultra-sensitive to small variations of the Fermi energy position
inside the BN band gap. Doping of the BN and, consequentially, changing the
Fermi energy position could lead to variation of the TMR by several orders of
magnitude. We show also that taking into account correlation effects on beyond
DFT level is required to accurately describe position of the Fermi level and
thus transport propertied of the system. Our study suggests that new MTJ based
on hcp Co-Pt or Co-Pd disordered alloy electrodes and p-doped hexagonal BN
spacer is a promising candidate for the spin-transfer torque magnetoresistive
random-access memory (STT-MRAM).",1504.01017v1
2017-11-07,Encoding Neural and Synaptic Functionalities in Electron Spin: A Pathway to Efficient Neuromorphic Computing,"Present day computers expend orders of magnitude more computational resources
to perform various cognitive and perception related tasks that humans routinely
perform everyday. This has recently resulted in a seismic shift in the field of
computation where research efforts are being directed to develop a
neurocomputer that attempts to mimic the human brain by nanoelectronic
components and thereby harness its efficiency in recognition problems. Bridging
the gap between neuroscience and nanoelectronics, this paper attempts to
provide a review of the recent developments in the field of spintronic device
based neuromorphic computing. Description of various spin-transfer torque
mechanisms that can be potentially utilized for realizing device structures
mimicking neural and synaptic functionalities is provided. A cross-layer
perspective extending from the device to the circuit and system level is
presented to envision the design of an All-Spin neuromorphic processor enabled
with on-chip learning functionalities. Device-circuit-algorithm co-simulation
framework calibrated to experimental results suggest that such All-Spin
neuromorphic systems can potentially achieve almost two orders of magnitude
energy improvement in comparison to state-of-the-art CMOS implementations.",1711.02235v4
2023-01-19,Ab initio comparison of spin-transport properties in MgO-spaced ferrimagnetic tunnel junctions based on Mn$_3$Ga and Mn$_3$Al,"We report on first-principles spin-polarised quantum transport calculations
(from NEGF+DFT) in MgO-spaced magnetic tunnel junctions (MTJs) based on two
different Mn-based Heusler ferrimagnetic metals, namely Mn$_3$Al and Mn$_3$Ga
in their tetragonal DO$_{22}$ phase. The former is a fully compensated
half-metallic ferrimagnet, while the latter is a low-moment
high-spin-polarisation ferrimagnet, both with a small lattice mismatch from
MgO. In identical symmetric and asymmetric interface reconstructions across a
3-monolayer thick MgO barrier for both ferrimagets, the linear response
(low-voltage) spin-transfer torque (STT) and tunneling magneto-resistance (TMR)
effects are evaluated. A larger staggered in-plane STT is found in the Mn$_3$Ga
case, while the STT in Mn$_3$Al vanishes quickly away from the interface
(similarly to STT in ferromagnetic MTJs). The roles are reversed for the TMR,
which is practically 100\% in the half-metallic Mn$_3$Al-based MTJs (using the
conservative definition) as opposed to 60\% in the Mn$_3$Ga case. The weak
dependence on the exact interface reconstruction would suggest
Mn$_3$Ga-Mn$_3$Al solid solutions as a possible route towards optimal trade-off
of STT and TMR in the low-bias, low-temperature transport regime.",2301.08300v1
2023-08-06,The Einstein-de Haas Effect in an $\textrm{Fe}_{15}$ Cluster,"Classical models of spin-lattice coupling are at present unable to accurately
reproduce results for numerous properties of ferromagnetic materials, such as
heat transport coefficients or the sudden collapse of the magnetic moment in
hcp-Fe under pressure. This inability has been attributed to the absence of a
proper treatment of effects that are inherently quantum mechanical in nature,
notably spin-orbit coupling. This paper introduces a time-dependent,
non-collinear tight binding model, complete with spin-orbit coupling and vector
Stoner exchange terms, that is capable of simulating the Einstein-de Haas
effect in a ferromagnetic $\textrm{Fe}_{15}$ cluster. The tight binding model
is used to investigate the adiabaticity timescales that determine the response
of the orbital and spin angular momenta to a rotating, externally applied $B$
field, and we show that the qualitative behaviours of our simulations can be
extrapolated to realistic timescales by use of the adiabatic theorem. An
analysis of the trends in the torque contributions with respect to the field
strength demonstrates that SOC is necessary to observe a transfer of angular
momentum from the electrons to the nuclei at experimentally realistic $B$
fields. The simulations presented in this paper demonstrate the Einstein-de
Haas effect from first principles using a Fe cluster.",2308.03130v2
2023-10-05,Exotic rare earth-based materials for emerging spintronic technology,"The progress in materials science has always been associated with the
development of functional materials systems, which enables us to design
proof-of-concept devices. To advance further, theoretical predictions of new
novel materials and their experimental realization is very important. This
chapter reviews the intriguing properties of rare earth-based materials and
their applications in spintronics. Spintronics is an emerging technology, which
exploits spin degree of freedom of an electron along with its charge property.
Discovery of various physical phenomena and their industrial applications in
the field of magnetic sensors, magnetic recording and non-volatile memories
such as magnetic random access memory (MRAM) and spin-transfer torque (STT)
MRAM opens several new directions in this field. Materials with large spin
polarization, strong spin-orbit coupling, and tunable electronic and magnetic
properties offer an excellent platform for the spintronics technology.
Combination of rare earths with other elements such as transition metals show
broad range of structural, electronic, and magnetic properties which make them
excellent candidates for various spintronic applications. This chapter
discusses many such materials ranging from Heusler alloys, topological
insulators to two-dimensional ferromagnets and their potential applications.
The review gives an insight of how rare-earth materials can play a key role in
emerging future technology and have great potential in many new spintronic
related applications.",2310.03541v1
2023-10-27,Effect of interfacial Dzyaloshinskii-Moriya interaction in spin dynamics of an Antiferromagnet coupled Ferromagnetic double-barrier Magnetic Tunnel Junction,"In this work, we have studied the spin dynamics of a synthethic
Antiferromagnet (SAFM)$|$Heavy Metal (HM)$|$Ferromagnet (FM) double barrier
magnetic tunnel junction (MTJ) in presence of Ruderman-Kittel-Kasuya-Yoside
interaction (RKKYI), interfacial Dzyaloshinskii-Moriya interaction (iDMI),
N\'eel field and Spin-Orbit Coupling (SOC) with different Spin Transfer Torque
(STT). We employ Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation to
investigate the AFM dynamics of the proposed system. We found that the system
exhibits a transition from regular to damped oscillations with the increase in
strength of STT for systems with weaker iDMI than RKKYI while display sustained
oscillatons for system having same order of iDMI and RKKYI. On the other hand
the iDMI dominating system exhibits self-similar but aperiodic patterns in
absence of N\'eel field. In the presence of N\'eel field, the RKKYI dominating
systems exhibit chaotic oscillations for low STT but display sustained
oscillation under moderate STT. Our results suggest that the decay time of
oscillations can be controlled via SOC. The system can works as an oscillator
for low SOC but display nonlinear characteristics with the rise in SOC for
systems having weaker iDMI than RKKYI while an opposite characteristic are
noticed for iDMI dominating systems. We found periodic oscillations under low
external magnetic field in RKKYI dominating systems while moderate field are
necessary for sustained oscillation in iDMI dominating systems. Moreover, the
system exhibits saddle-node bifurcation and chaos under moderate N\'eel field
and SOC with suitable iDMI and RKKYI. In addition, our results indicate that
the magnon lifetime can be enhanced by increasing the strength of iDMI for both
optical and acoustic modes.",2310.18175v1
2023-09-27,Quantifying the large contribution from orbital Rashba effect to the effective damping-like torque on magnetization,"The generation of large spin currents, and the associated spin torques, which
are at the heart of modern spintronics, have long been achieved by
charge-to-spin conversion mechanisms, i.e. the spin Hall effect and/or the
Rashba effect, intrinsically linked to a strong spin-orbit coupling. Recently,
a novel path has been predicted and observed for achieving significant
current-induced torques originating from light elements, hence possessing a
weak spin-orbit interaction. These findings point out to the potential
involvement of the orbital counterpart of electrons, namely the orbital Hall
and orbital Rashba effects. In this study, we aim at quantifying these
orbital-related contributions to the effective torques acting on a thin Co
layer in different systems. First, in Pt|Co|Cu|AlOx stacking, we demonstrate a
comparable torque strength coming from the conversion due to the orbital Rashba
effect at the Cu|AlOx interface and the one from the effective spin Hall effect
in bottom Pt|Co system. Secondly, in order to amplify the orbital-to-spin
conversion, we investigate the impact of an intermediate Pt layer in
Co|Pt|Cu|CuOx. From the Pt thickness dependence of the effective torques
determined by harmonic Hall measurements complemented by spin Hall
magneto-resistance and THz spectroscopy experiments, we demonstrate that a
large orbital Rashba effect is present at the Cu|CuOx interface, leading to a
twofold enhancement of the net torques on Co for the optimal Pt thickness. Our
findings not only demonstrate the crucial role that orbital currents can play
in low-dimensional systems with weak spin-orbit coupling, but also reveal that
they enable more energy efficient manipulation of magnetization in spintronic
devices.",2309.15987v2
2012-07-09,The torque transfer coefficient in DNA under torsional stress,"In recent years, significant progress in understanding the properties of
supercoiled DNA has been obtained due to nanotechniques that made stretching
and twisting of single molecules possible. Quantitative interpretation of such
experiments requires accurate knowledge of torques inside manipulated DNA. This
paper argues that it is not possible to transfer the entire magnitudes of
external torques to the twisting stress of the double helix, and that a
reducing torque transfer coefficient (TTC<1) should always be assumed. This
assertion agrees with simple physical intuition and is supported by the results
of all-atom molecular dynamics (MD) simulations. According to MD, the TTCs
around 0.8 are observed in nearly optimal conditions. Reaching higher values
requires special efforts and it should be difficult in practice. The TTC can be
partially responsible for the persistent discrepancies between the twisting
rigidity of DNA measured by different methods.",1207.2018v1
2016-02-01,Facet-dependent giant spin orbit torque in single crystalline antiferromagnetic Ir-Mn / ferromagnetic permalloy bilayers,"There has been considerable interest in spin-orbit torques for the purpose of
manipulating the magnetization of ferromagnetic (FM) films or nano-elements for
spintronic technologies. Spin-orbit torques are derived from spin currents
created from charge currents in materials with significant spin-orbit coupling
that diffuse into an adjacent FM material. There have been intensive efforts to
search for candidate materials that exhibit large spin Hall angles, i.e.
efficient charge to spin current conversion. Here we report, using spin torque
ferromagnetic resonance, the observation of a giant spin Hall angle of up to
~0.35 in (100) oriented single crystalline antiferromagnetic (AF) IrMn3 thin
films, coupled to ferromagnetic permalloy layers, and a spin Hall angle that is
about three times smaller in (111) oriented films. For the (100) oriented
samples we show that the magnitude of the spin Hall angle can be significantly
changed by manipulating the populations of the various AF domains through field
annealing. Using ab-initio calculations we show that the triangular AF
structure of IrMn3 gives rise to a substantial intrinsic spin Hall conductivity
that is three times larger for the (100) than for the (111) orientations,
consistent with our experimental findings.",1602.00670v1
2019-02-14,Anomalous Spin-Orbit Torques in Magnetic Single-Layer Films,"Spin-orbit interaction (SOI) couples charge and spin transport, enabling
electrical control of magnetization. A quintessential example of SOI-induced
transport is the anomalous Hall effect (AHE), first observed in 1880, in which
an electric current perpendicular to the magnetization in a magnetic film
generates charge accumulation on the surfaces. Here we report the observation
of a counterpart of the AHE that we term the anomalous spin-orbit torque
(ASOT), wherein an electric current parallel to the magnetization generates
opposite spin-orbit torques on the surfaces of the magnetic film. We interpret
the ASOT as due to a spin-Hall-like current generated with an efficiency of
0.053+/-0.003 in Ni80Fe20, comparable to the spin Hall angle of Pt. Similar
effects are also observed in other common ferromagnetic metals, including Co,
Ni, and Fe. First principles calculations corroborate the order of magnitude of
the measured values. This work suggests that a strong spin current with spin
polarization transverse to magnetization can exist in a ferromagnet, despite
spin dephasing. It challenges the current understanding of spin-orbit torque in
magnetic/nonmagnetic bilayers, in which the charge-spin conversion in the
magnetic layer has been largely neglected.",1902.05490v1
2016-06-14,Torques and angular momentum: Counter-rotation in galaxies and ring galaxies,"We present an alternate origin scenario to explain the observed phenomena of
(1) counter-rotation between different galaxy components and (2) the formation
of ring galaxies. We suggest that these are direct consequences of the galaxy
being acted upon by a torque which causes a change in its primordial spin
angular momentum first observed as changes in the gas kinematics or
distribution. We suggest that this torque is exerted by the gravitational force
between nearby galaxies. This origin requires the presence of at least one
companion galaxy in the vicinity - we find a companion galaxy within 750 kpc
for 51/57 counter-rotating galaxies and literature indicates that all ring
galaxies have a companion galaxy thus giving observable credence to this
origin. Moreover in these 51 galaxies, we find a kinematic offset between
stellar and gas heliocentric velocities $>50$ kms$^{-1}$ for several galaxies
if the separation between the galaxies $<$ 100 kpc. This, we suggest, indicates
a change in the orbital angular momentum of the torqued galaxies. A major
difference between the torque origin suggested here and the existing model of
gas accretion/galaxy collision, generally used to explain the above two
phenomena, is that the torque acts on the matter of the same galaxy whereas in
the latter case gas, with different properties, is brought in from outside. An
important implication of our study is that mutual gravity torques acting on the
galaxy can explain the formation of warps, polar ring galaxies and lenticular
galaxies. We conclude that mutual gravity torques play an important role in the
dynamical evolution of galaxies and that they naturally explain several galaxy
observables.",1606.04242v1
2021-10-11,Gravitational torques dominate the dynamics of accreted gas at $z>2$,"Galaxies form from the accretion of cosmological infall of gas. In the high
redshift Universe, most of this gas infall is expected to be dominated by cold
filamentary flows which connect deep down inside halos, and, hence, to the
vicinity of galaxies. Such cold flows are important since they dominate the
mass and angular momentum acquisition that can make up rotationally-supported
disks at high-redshifts. We study the angular momentum acquisition of gas into
galaxies, and in particular, the torques acting on the accretion flows, using
hydrodynamical cosmological simulations of high-resolution zoomed-in halos of a
few $10^{11}\,\rm M_\odot$ at $z=2$. Torques can be separated into those of
gravitational origin, and hydrodynamical ones driven by pressure gradients. We
find that coherent gravitational torques dominate over pressure torques in the
cold phase, and are hence responsible for the spin-down and realignment of this
gas. Pressure torques display small-scale fluctuations of significant
amplitude, but with very little coherence on the relevant galaxy or halo-scale
that would otherwise allow them to effectively re-orientate the gas flows. Dark
matter torques dominate gravitational torques outside the galaxy, while within
the galaxy, the baryonic component dominates. The circum-galactic medium
emerges as the transition region for angular momentum re-orientation of the
cold component towards the central galaxy's mid-plane.",2110.05384v2
2020-05-18,The Einstein - de Haas effect at radio frequencies in and near magnetic equilibrium,"The Einstein-de Haas (EdH) effect and its reciprocal the Barnett effect are
fundamental to magnetism and uniquely yield measures of the ratio of magnetic
moment to total angular momentum. These effects, small and generally difficult
to observe, are enjoying a resurgence of interest as contemporary techniques
enable new approaches to their study. The high mechanical resonance frequencies
in nanomechanical systems offer a tremendous advantage for the observation of
EdH torques in particular. At radio frequencies, the EdH effect can become
comparable to or even exceed in magnitude conventional cross-product magnetic
torques. In addition, the RF-EdH torque is expected to be phase-shifted by 90
degrees relative to cross-product torques, provided the magnetic system remains
in quasi-static equilibrium, enabling separation in quadratures when both
sources of torque are operative. Radio frequency EdH measurements are
demonstrated through the full hysteresis range of micrometer scale,
monocrystalline yttrium iron garnet (YIG) disks. Equilibrium behavior is
observed in the vortex state at low bias field. Barkhausen-like features emerge
in the in-plane EdH torque at higher fields in the vortex state, revealing
magnetic disorder too weak to be visible through the in-plane cross-product
torque. Beyond vortex annihilation, peaks arise in the EdH torque versus bias
field, and these together with their phase signatures indicate additional
utility of the Einstein-de Haas effect for the study of RF-driven spin
dynamics.",2005.08406v1
2001-04-25,Equilibrium and stability of supermassive stars in binary systems,"We investigate the equilibrium and stability of supermassive stars of mass $M
\agt 10^5M_{\odot}$ in binary systems. We find that corotating binaries are
secularly unstable for close, circular orbits with $r \alt
4R(M/10^6M_{\odot})^{1/6}$ where $r$ is the orbital separation and $R$ the
stellar radius. We also show that corotation cannot be achieved for distant
orbits with $r \agt 12 R (M/10^6M_{\odot})^{-11/24}$, since the timescale for
viscous angular momentum transfer associated with tidal torques is longer than
the evolution timescale due to emission of thermal radiation. These facts
suggest that the allowed mass range and orbital separation for corotating
supermassive binary stars is severely restricted. In particular, for
supermassive binary stars of large mass $M \agt 6\times 10^6M_{\odot}$,
corotation cannot be achieved, as viscosity is not adequate to mediate the
transfer between orbital and spin angular momentum. One possible outcome for
binary supermassive stars is the onset of quasi-radial, relativistic
instability which drives each star to collapse prior to merger: We discuss
alternative outcomes of collapse and possible spin states of the resulting
black holes. We estimate the frequency and amplitude of gravitational waves
emitted during several inspiral and collapse scenarios.",0104408v1
2017-12-07,What Makes the Family of Barred Disc Galaxies So Rich: Damping Stellar Bars in Spinning Haloes,"We model and analyse the secular evolution of stellar bars in spinning dark
matter (DM) haloes with the cosmological spin lambda ~ 0 -- 0.09. Using
high-resolution stellar and DM numerical simulations, we focus on angular
momentum exchange between stellar discs and DM haloes of various axisymmetric
shapes --- spherical, oblate and prolate. We find that stellar bars experience
a diverse evolution which is guided by the ability of parent haloes to absorb
angular momentum lost by the disc through the action of gravitational torques,
resonant and non-resonant. We confirm the previous claim that dynamical bar
instability is accelerated via resonant angular momentum transfer to the halo.
Our main findings relate to the long-term, secular evolution of disc-halo
systems: with an increasing lambda, bars experience less growth and dissolve
after they pass through the vertical buckling instability. Specifically, with
an increasing halo spin, (1) The vertical buckling instability in stellar bars
colludes with inability of the inner halo to absorb angular momentum --- this
emerges as the main factor weakening or destroying bars in spinning haloes; (2)
Bars lose progressively less angular momentum, and their pattern speeds level
off; (3) Bars are smaller, and for lambda >= 0.06 cease their growth completely
following buckling; (4) Bars in lambda > 0.03 haloes have ratio of
corotation-to-bar radii, R_CR / R_b > 2, and represent so-called slow bars
which do not show offset dust lanes. We provide a quantitative analysis of
angular momentum transfer in disc-halo systems, and explain the reasons for
absence of growth in fast spinning haloes and its observational corollaries. We
conclude that stellar bar evolution is substantially more complex than
anticipated, and bars are not as resilient as has been considered so far.",1712.02802v2
2000-05-15,The Role of Spin-Dependent Interface Scattering in Generating Current-Induced Torques in Magnetic Multilayers,"We present a calculation of current-induced torques in metallic magnetic
multilayers derived from the spin-dependent transmission and reflection
properties of the magnetic layers. A scattering formalism is employed to
calculate the torques in a magnetic-nonmagnetic-magnetic trilayer, for currents
perpendicular to the layers, in both the ballistic and diffusive regimes.",0005251v2
2013-07-22,Analytical expression for the harmonic Hall voltages in evaluating spin orbit torques,"Solid understanding of current induced torques is key to the development of
current and voltage controlled magnetization dynamics in ultrathin magnetic
heterostructures. A versatile technique is needed to evaluate such torques in
various systems. Here we examine the adiabatic (low frequency) harmonic Hall
voltage measurement that has been recently developed to study current induced
effective field that originate from the spin orbit effects. We analytically
derive a form that can be used to evaluate the harmonic Hall voltages and
extract relevant parameters in two representative systems, i.e. out of plane
and in-plane magnetized systems. Contributions from the anomalous Hall and
planar Hall effects are considered.",1307.5603v1
2013-11-29,Transverse spinning of a sphere in a plasmonic field,"We evaluate optical forces and torques induced by a surface plasmon to a
sphere of arbitrary size, i.e. beyond the point-like dipolar limit. Through a
multipolar decomposition of the plasmonic field, we demonstrate that the
induced torque is purely transverse to the plasmon propagation direction. Our
approach removes the inherent ambiguities of the dipolar regime with respect to
rotations and emphasizes the crucial role played by dissipation in the onset of
the plasmonic torque. We also give realistic estimates of such plasmon-induced
spinning of gold spheres immersed in water or air.",1311.7481v2
2021-01-28,Voltage Controlled Spin-Orbit Torque Switching in W/CoFeB/MgO,"Voltage control of magnetism and spintronics have been highly desirable, but
rarely realized. In this work, we show voltage-controlled spin-orbit torque
(SOT) switching in W/CoFeB/MgO films with perpendicular magnetic anisotropy
(PMA) with voltage administered through SrTiO3 with a high dielectric constant.
We show that a DC voltage can significantly lower PMA by 45%, reduce switching
current by 23%, and increase the damping-like torque as revealed by the first
and second-harmonic measurements. These are characteristics that are
prerequisites for voltage-controlled and voltage-select SOT switching
spintronic devices.",2101.12281v1
2011-05-30,Bodily tides near spin-orbit resonances,"Spin-orbit coupling can be described in two approaches. The method known as
""the MacDonald torque"" is often combined with an assumption that the quality
factor Q is frequency-independent. This makes the method inconsistent, because
the MacDonald theory tacitly fixes the rheology by making Q scale as the
inverse tidal frequency.
  Spin-orbit coupling can be treated also in an approach called ""the Darwin
torque"". While this theory is general enough to accommodate an arbitrary
frequency-dependence of Q, this advantage has not yet been exploited in the
literature, where Q is assumed constant or is set to scale as inverse tidal
frequency, the latter assertion making the Darwin torque equivalent to a
corrected version of the MacDonald torque.
  However neither a constant nor an inverse-frequency Q reflect the properties
of realistic mantles and crusts, because the actual frequency-dependence is
more complex. Hence the necessity to enrich the theory of spin-orbit
interaction with the right frequency-dependence. We accomplish this programme
for the Darwin-torque-based model near resonances. We derive the
frequency-dependence of the tidal torque from the first principles, i.e., from
the expression for the mantle's compliance in the time domain. We also explain
that the tidal torque includes not only the secular part, but also an
oscillating part.
  We demonstrate that the lmpq term of the Darwin-Kaula expansion for the tidal
torque smoothly goes through zero, when the secondary traverses the lmpq
resonance (e.g., the principal tidal torque smoothly goes through nil as the
secondary crosses the synchronous orbit).
  We also offer a possible explanation for the unexpected frequency-dependence
of the tidal dissipation rate in the Moon, discovered by LLR.",1105.6086v9
2013-03-28,Spin Torque on Magnetic Textures Coupled to the Surface of a Three-Dimensional Topological Insulator,"We investigate theoretically the spin torque and magnetization dynamic in a
thin ferromagnetic (FM) layer with spatially varying magnetization. The FM
layer is deposited on the surface of a topological insulator (TI). In the limit
of the adiabatic relaxation of electron spin along the magnetization, the
interaction between the exchange interaction and the Rashba-like surface
texture of a TI yields a topological gauge field. Under the gauge field and an
applied current, spin torque is induced according to the direction of the
current. We derived the corresponding effective anisotropy field and hence the
modified Landau-Lifshitz-Gilbert equation, which describes the spin torque and
the magnetization dynamic. In addition, we study the effective field for
exemplary magnetic textures, such as domain wall, skyrmion, and vortex
configurations. The estimated strength of the effective field is comparable to
the switching fields of typical FM materials, and hence can significantly
influence the dynamics of the FM layer.",1303.7031v1
2013-05-29,Hydrodynamic theory of coupled current and magnetization dynamics in spin-textured antiferromagnets,"Antiferromagnets with vanishingly small (or zero) magnetization are
interesting candidates for spintronics applications. In the present paper we
propose two models for description of the current-induced phenomena in
antiferromagnetic textures. We show that the magnetization that originates from
rotation or oscillations of antiferromagnetic vector can, via $sd$-exchange
coupling, polarize the current and give rise to adiabatic and nonadiabatic spin
torques. Due to the Lorentz-type dynamics of antiferromagnetic moments (unlike
the Galilenian-like dynamics in ferromagnets), the adiabatic spin torque
affects the characteristic lengthscale of the moving texture. Nonadiabatic spin
torque contributes to the energy pumping and can induce the stable motion of
antiferromagnetic texture, but, in contrast to ferromagnets, has pure dynamic
origin. We also consider the current-induced phenomena in artificial
antiferromagnets where the current maps the staggered magnetization of the
structure. In this case the effect of nonadiabatic spin torque is similar to
that in ferromagnetic constituents of the structure. In particular, the current
can remove degeneracy of the translational antiferromagnetic domains
indistinguishable in the external magnetic field and thus can set into motion
the 180$^\circ$ domain wall.",1305.6734v2
2016-09-05,Spin Orbit Torque in two dimensional Antiferromagnetic Topological Insulators,"We investigate spin transport in two dimensional ferromagnetic (FTI) and
antiferromagnetic (AFTI) topological insulators. In presence of an in plane
magnetization AFTI supports zero energy modes, which enables topologically
protected edge conduction at low energy. We address the nature of
current-driven spin torque in these structures and study the impact of
spin-independent disorder. Interestingly, upon strong disorder the spin torque
develops an antidamping component (i.e. {\em even} upon magnetization reversal)
along the edges, which could enable current-driven manipulation of the
antiferromagnetic order parameter. This antidamping torque decreases when
increasing the system size and when the system enters the trivial insulator
regime.",1609.01174v3
2018-02-26,Role of phonon skew scattering in the spin Hall effect of platinum,"We measure and analyze the effective spin Hall angle of platinum in the low
residual resistivity regime by second harmonic measurements of the spin-orbit
torques for a multilayer of Pt/Co/AlO$_x$. An angular dependent study of the
torques allows us to extract the effective spin Hall angle responsible for the
damping-like torque in the system. We observe a strikingly non-monotonic and
reproducible temperature dependence of the torques. This behavior is compatible
with recent theoretical predictions which include both intrinsic and extrinsic
(impurities and phonons) contributions to the spin Hall effect at finite
temperature.",1802.09438v1
2019-06-30,"Non-linear spin torque, pumping and cooling in superconductor/ferromagnet systems","We study the effects of the coupling between magnetization dynamics and the
electronic degrees of freedom in a heterostructure of a metallic nanomagnet
with dynamic magnetization coupled with a superconductor containing a steady
spin-splitting field. We predict how this system exhibits a non-linear spin
torque, which can be driven either with a temperature difference or a voltage
across the interface. We generalize this notion to arbitrary magnetization
precession by deriving a Keldysh action for the interface, describing the
coupled charge, heat and spin transport in the presence of a precessing
magnetization. We characterize the effect of superconductivity on the
precession damping and the anti-damping torques. We also predict the full
non-linear characteristic of the Onsager counterparts of the torque, showing up
via pumped charge and heat currents. For the latter, we predict a spin-pumping
cooling effect, where the magnetization dynamics can cool either the nanomagnet
or the superconductor.",1907.00424v2
2021-07-21,Spin orbit torque switching of antiferromagnet through the Neel reorientation in rare-earth ferrite,"We suggest coherent switching of canted antiferromagnetic (AFM) spins using
spin-orbit torque (SOT) in small magnet. The magnetic system of orthoferrite
features biaxial easy anisotropy and the Dzyaloshinskii Moriya interaction,
which is perpendicular to the easy axes and therefore creates weak
magnetization (m). A damping-like component of the SOT induces N\'eel
reorientation along one of the easy axes and then exerts torque on m, leading
to tilting of the N\'eel order l. The torque on the magnetization becomes
stronger due to coupling with the induced Oersted field or the field-like
component of the SOT, enhancing the tilting of l. Therefore, l is found to
experience deterministic switching after the SOT is turned off. Based upon both
numerical and analytical analysis of the coherent switching, XOR logic gates
are also found to be implemented in a single magnetic layer. In addition, we
investigate how magnetic parameters affect the critical reorientation angle and
current density in a simple layered structure of platinum and a canted AFM. Our
findings are expected to provide an alternative spin-switching mechanism for
ultrafast applications such as spin logic and electronic devices.",2107.10156v1
2022-11-19,Anomalous sign inversion of spin-orbit torque in ferromagnetic/nonmagnetic bilayer systems due to self-induced spin-orbit torque,"Self-induced spin-orbit torques (SI-SOTs) in ferromagnetic (FM) layers have
been overlooked when estimating the spin Hall angle (SHA) of adjacent
nonmagnetic (NM) layers. In this work, we observe anomalous sign inversion of
the total SOT in the spin-torque ferromagnetic resonance due to the enhanced
SI-SOT, and successfully rationalize the sign inversion through a theoretical
calculation considering the SHE in both the NM and FM layers. The findings show
that using an FM layer whose SHA sign is the same as that of the NM achieves
efficient SOT-magnetization switching with the assistance of the SI-SOT. The
contribution of the SI-SOT becomes salient for a weakly conductive NM layer,
and conventional analyses that do not consider the SI-SOT can overestimate the
SHA of the NM layer by a factor of more than 150.",2211.10692v1
2022-11-23,Anatomy of spin wave driven magnetic texture motion via magnonic torques,"The interplay between spin wave and magnetic texture represents the
information exchange between the fast and slow dynamical parts of magnetic
systems. Here we formulate a set of magnonic torques acting on background
magnetic texture, by extracting time-invariant information from the fast
precessing spin waves. Under the frame of magnonic torques, we use theoretical
formulations and micromagnetic simulations to investigate the spin wave driven
domain wall motion in two typical symmetry-breaking situations: the rotational
symmetry broken by the Dzyaloshinkii-Moriya interaction, and the translational
symmetry broken by magnetic damping. The torque-based microscopic analyses
provide compact yet quantitative tools to reinterpret the magnetic texture
dynamics induced by spin wave, beyond the conventional framework of global
momentum conservation.",2211.12958v1
2023-12-29,Spin-orbit torques and magnetization switching in Gd/Fe multilayers generated by current injection in NiCu alloys,"Light transition metals have recently emerged as a sustainable material class
for efficient spin-charge interconversion. We report measurements of
current-induced spin-orbit torques generated by Ni$_{1-x}$Cu$_{x}$ alloys in
perpendicularly magnetized ferrimagnetic Gd/Fe multilayers. We show that the
spin-orbit torque efficiency of Ni$_{1-x}$Cu$_{x}$ increases with the Ni/Cu
atomic ratio, reaching values comparable to those of Pt for Ni$_{55}$Cu$_{45}$.
Furthermore, we demonstrate magnetization switching of a 20-nm-thick Gd/Fe
multilayer with a threshold current that decreases with increasing Ni
concentration, similar to the spin-orbit torque efficiency. Our findings show
that Ni$_{1-x}$Cu$_{x}$$-$based magnetic heterostructures allow for efficient
control of the magnetization by electric currents.",2312.17652v1
2017-01-05,Excitation and detection of short-waved spin waves in ultrathin Ta/CoFeB/MgO-layer system suitable for spin-orbit-torque magnonics,"We report on the excitation and detection of short-waved spin waves with wave
vectors up to about $40\,\mathrm{rad}\,\mu\mathrm{m}^{-1}$ in spin-wave
waveguides made from ultrathin, in-plane magnetized Co$_{8}$Fe$_{72}$B$_{20}$
(CoFeB). The CoFeB is incorporated in a layer stack of Ta/CoFeB/Mgo, a layer
system featuring large spin orbit torques and a large perpendicular magnetic
anisotropy constant. The short-waved spin waves are excited by nanometric
coplanar waveguides and are detected via spin rectification and microfocussed
Brillouin light scattering spectroscopy. We show that the large perpendicular
magnetic anisotropy benefits the spin-wave lifetime greatly, resulting in a
lifetime comparable to bulk systems without interfacial damping. The presented
results pave the way for the successful extension of magnonics to ultrathin
asymmetric layer stacks featuring large spin orbit torques.",1701.01399v1
2020-06-30,Spin-orbit torque magnetization switching in MoTe2/permalloy heterostructures,"The ability to switch magnetic elements by spin-orbit-induced torques has
recently attracted much attention for a path towards high-performance,
non-volatile memories with low power consumption. Realizing efficient
spin-orbit-based switching requires harnessing both new materials and novel
physics to obtain high charge-to-spin conversion efficiencies, thus making the
choice of spin source crucial. Here we report the observation of spin-orbit
torque switching in bilayers consisting of a semimetallic film of 1T'-MoTe2
adjacent to permalloy. Deterministic switching is achieved without external
magnetic fields at room temperature, and the switching occurs with currents one
order of magnitude smaller than those typical in devices using the
best-performing heavy metals. The thickness dependence can be understood if the
interfacial spin-orbit contribution is considered in addition to the bulk spin
Hall effect. Further threefold reduction in the switching current is
demonstrated with resort to dumbbell-shaped magnetic elements. These findings
foretell exciting prospects of using MoTe2 for low-power semimetal material
based spin devices.",2006.16618v1
2021-03-16,Efficient field-free perpendicular magnetization switching by a magnetic spin Hall effect,"Current induced spin-orbit torques driven by the conventional spin Hall
effect are widely used to manipulate the magnetization. This approach, however,
is nondeterministic and inefficient for the switching of magnets with
perpendicular magnetic anisotropy that are demanded by the high-density
magnetic storage and memory devices. Here, we demonstrate that this limitation
can be overcome by exploiting a magnetic spin Hall effect in noncollinear
antiferromagnets, such as Mn3Sn. The magnetic group symmetry of Mn3Sn allows
generation of the out-of-plane spin current carrying spin polarization induced
by an in-plane charge current. This spin current drives an out-of-plane
anti-damping torque providing deterministic switching of perpendicular
magnetization of an adjacent Ni/Co multilayer. Compared to the conventional
spin-orbit torque devices, the observed switching does not need any external
magnetic field and requires much lower current density. Our results demonstrate
great prospects of exploiting the magnetic spin Hall effect in noncollinear
antiferromagnets for low-power spintronics.",2103.09011v1
2022-04-04,Inverse Orbital Torque via Spin-Orbital Entangled States,"While current-induced torque by orbital current has been experimentally found
in various structures, evidence for its reciprocity has been missing so far.
Here, we report experimental evidence of strong inverse orbital torque in
YIG/Pt/CuOx (YIG = Y3Fe5O12) mediated by spin-orbital entangled electronic
states in Pt. By injecting spin current from YIG to Pt by the spin pumping via
ferromagnetic resonance and by the spin Seebeck effect, we find a pronounced
inverse spin Hall effect-like signal. While a part of the signal is explained
as due to the inverse spin-orbital Hall effect in Pt, we also find substantial
increase of the signal in YIG/Pt/CuOx structures compared to the signal in
YIG/Pt. We attribute this to the inverse orbital Rashba-Edelstein effect at
Pt/CuOx interface mediated by the spin-orbital entangled states in Pt. Our work
paves the way toward understanding of spin-orbital entangled physics in
nonequilibrium and provides a way for electrical detection of the orbital
current in orbitronic device applications.",2204.01825v2
2009-09-30,Elastic ice shells of synchronous moons: Implications for cracks on Europa and non-synchronous rotation of Titan,"A number of synchronous moons are thought to harbor water oceans beneath
their outer ice shells. A subsurface ocean frictionally decouples the shell
from the interior. This has led to proposals that a weak tidal or atmospheric
torque might cause the shell to rotate differentially with respect to the
synchronously rotating interior. As a result of centrifugal and tidal forces,
the ocean would assume an ellipsoidal shape with its long axis aligned toward
the parent planet. Any displacement of the shell away from its equilibrium
position would induce strains thereby increasing its elastic energy and giving
rise to an elastic restoring torque. We compare the elastic torque with the
tidal torque acting on Europa and the atmospheric torque acting on Titan. For
Europa, the tidal torque is far too weak to produce stresses that could
fracture the ice shell, thus refuting a widely advocated idea. Instead, we
suggest that cracks arise from time-dependent stresses due to non-hydrostatic
gravity anomalies from tidally driven, episodic convection in the interior. Two
years of Cassini RADAR observations of Titan's surface are interpreted as
implying an angular displacement of ~0.24 degrees relative to synchroneity.
Compatibility of the amplitude and phase of the observed non-synchronous
rotation with estimates of the atmospheric torque requires that Titan's shell
be decoupled from its interior. We find that the elastic torque balances the
atmospheric torque at an angular displacement <0.05 degrees, thus coupling the
shell to the interior. Moreover, if Titan's surface were spinning faster than
synchronous, the tidal torque tending to restore synchronous rotation would
certainly be larger than the atmospheric torque. There must either be a problem
with the interpretation of the radar observations, or with our understanding of
Titan's atmosphere and/or interior.",0910.0032v3
2010-12-15,Observational limits on the spin-down torque of Accretion Powered Stellar Winds,"The rotation period of classical T Tauri stars (CTTS) represents a
longstanding puzzle. While young low-mass stars show a wide range of rotation
periods, many CTTS are slow rotators, spinning at a small fraction of break-up,
and their rotation period does not seem to shorten, despite the fact that they
are actively accreting and contracting. Matt & Pudritz (2005) proposed that the
spin-down torque of a stellar wind powered by a fraction of the accretion
energy would be strong enough to balance the spin-up torque due to accretion.
Since this model establishes a direct relation between accretion and ejection,
the observable stellar parameters (mass, radius, rotation period, magnetic
field) and the accretion diagnostics (accretion shock luminosity), can be used
to constraint the wind characteristics. In particular, since the accretion
energy powers both the stellar wind and the shock emission, we show in this
letter how the accretion shock luminosity L_UV can provide upper limits to the
spin-down efficiency of the stellar wind. It is found that luminous sources
with L_UV > 0.1 L_Sun and typical dipolar field components < 1 kG do not allow
spin equilibrium solutions. Lower luminosity stars (L_UV < 0.1 L_Sun) are
compatible with a zero-torque condition, but the corresponding stellar winds
are still very demanding in terms of mass and energy flux. We therefore
conclude that accretion powered stellar winds are unlikely to be the sole
mechanism to provide an efficient spin-down torque for accreting classical T
Tauri stars.",1012.3333v1
2018-01-11,A rapid decrease in the rotation rate of comet 41P/Tuttle-Giacobini-Kresák,"Cometary outgassing can produce torques that change the spin state of the
nucleus, influencing the evolution and lifetimes of comets (1,2). If these
torques spin up the rotation to the point that centripetal forces exceed the
material strength of the nucleus, the comet may fragment (3). Torques that slow
down the rotation can cause the spin state to become unstable, but if the
torques persist, the nucleus may eventually reorient itself and start to spin
up again (4). Simulations predict that most comets will go through a short
phase of changing spin states, after which changes occur gradually over long
times (5). We report on observations of comet 41P/Tuttle-Giacobini-Kres\'ak
during its highly favourable close approach to Earth (0.142 au on April 1,
2017) that reveal a dramatic spin-down. Between March and May 2017, the
nucleus' apparent rotation period increased from 20 hours to over 46 hours,
reflecting a rate of change more than an order of magnitude larger than has
ever been measured before. This phenomenon must be caused by a fortuitous
alignment of the comet's gas emission in such a way as to produce an
anomalously strong torque that is slowing the nucleus' spin rate. The behaviour
of 41P suggests that it is in a distinct evolutionary state and that its
rotation may be approaching the point of instability.",1801.03870v1
2021-04-19,Giant spin-orbit torque efficiency in all-epitaxial heterostructures,"A large anti-damping spin-obit torque (SOT) efficiency in magnetic
heterostructures is a prerequisite to realize energy efficient spin torque
based magnetic memories and logic devices. The efficiency can be characterized
in terms of the spin-orbit fields generated by anti-damping torques when an
electric current is passed through the non-magnetic layer. We report a giant
spin-orbit field of 48.96 (27.50) mT at an applied current density of 1 MAcm-2
in beta-W interfaced Co60Fe40 (Ni81Fe19)/TiN epitaxial structures due to an
anti-damping like torque, which results in a magnetization auto-oscillation
current density as low as 1.68(3.27) MAcm-2. The spin-orbit field value
increases with decrease of beta-W layer thickness, which affirms that epitaxial
surface states are responsible for the extraordinary large efficiency. SOT
induced energy efficient in-plane magnetization switching in large 20x100 um2
structures has been demonstrated by Kerr microscopy and the findings are
supported by results from micromagnetic simulations. The observed giant SOT
efficiencies in the studied all-epitaxial heterostructures are comparable to
values reported for topological insulators. These results confirm that by
utilizing epitaxial material combinations an extraordinary large SOT efficiency
can be achieved using semiconducting industry compatible 5d heavy metals, which
provides immediate solutions for the realization of energy efficient spin-logic
devices.",2104.09168v1
2021-03-12,Magnetoelectric torque and edge currents in spin-orbit coupled graphene nanoribbons,"For graphene nanoribbons with Rashba spin-orbit coupling, the peculiar
magnetic response due to the presence of a magnetization and geometric
confinement are analyzed within a tight-binding model. We observe a sizable
transverse susceptibility that can be considered as a gate voltage-induced
magnetoelectric torque without the need of a bias voltage, with different
directions for zigzag and armchair ribbons. The local torque generates
non-collinear spin polarization between the two edges and/or along the ribbon,
and the net torque averages to zero if the magnetization is homogeneous.
Nevertheless, a nonzero net torque can appear in partially magnetized
nanoribbons or in nanoflakes of irregular shapes. The equilibrium spin current
produced by the spin-orbit coupling also appears in nanoribbons, but the
component flowing in the direction of confinement is strongly suppressed. Even
without the magnetization, an out-of-plane polarized chiral edge spin current
is produced, resembling that in the quantum spin Hall effect. Moreover, a
magnetization pointing perpendicular to the edge produces a laminar flow of
edge charge currents, whose flow direction is symmetric (non chiral) or
antisymmetric (chiral) between the two edges depends on whether the
magnetization points in-plane or out-of-plane.",2103.07426v1
2021-06-29,Spin-orbit torques and magnetotransport properties of $α$-Sn and $β$-Sn heterostructures,"Topological insulators have emerged as an important material class for
efficient spin-charge interconversion. Most topological insulators considered
to date are binary or ternary compounds, with the exception of $\alpha$-Sn.
Here we report a comprehensive characterization of the growth, magnetotransport
properties, and current-induced spin-orbit torques of $\alpha$-Sn and
$\beta$-Sn-based ferromagnetic heterostructures. We show that $\alpha$-Sn grown
with a Bi surfactant on CdTe(001) promotes large spin-orbit torques in a
ferromagnetic FeCo layer at room temperature, comparable to Pt, whereas
$\alpha$-Sn grown without Bi surfactant and the non-topological phase,
$\beta$-Sn, induce lower torques. The dampinglike and fieldlike spin-orbit
torque efficiency in $\alpha$-Sn with Bi are 0.12 and 0.18, respectively.
Further, we show that $\alpha$-Sn grown with and without Bi presents a spin
Hall-like magnetoresistance comparable to that found in heavy metal/ferromagnet
bilayers. Our work demonstrates direct and efficient charge-to-spin conversion
in $\alpha$-Sn ferromagnetic heterostructures, showing that $\alpha$-Sn is a
promising material for current-induced magnetization control in spintronic
devices.",2106.15386v1
2014-08-19,Binary evolution using the theory of osculating orbits: conservative Algol evolution,"Our aim is to calculate the evolution of Algol binaries within the framework
of the osculating orbital theory, which considers the perturbing forces acting
on the orbit of each star arising from mass exchange via Roche lobe overflow
(RLOF). The scheme is compared to results calculated from a `classical'
prescription. Using our stellar binary evolution code BINSTAR, we calculate the
orbital evolution of Algol binaries undergoing case A and case B mass transfer,
by applying the osculating scheme. The velocities of the ejected and accreted
material are evaluated by solving the restricted three-body equations of
motion, within the ballistic approximation. This allows us to determine the
change of linear momentum of each star, and the gravitational force applied by
the mass transfer stream. Torques applied on the stellar spins by tides and
mass transfer are also considered. Using the osculating formalism gives shorter
post-mass transfer orbital periods typically by a factor of 4 compared to the
classical scheme, owing to the gravitational force applied onto the stars by
the mass transfer stream. Additionally, during the rapid phase of mass
exchange, the donor star is spun down on a timescale shorter than the tidal
synchronization timescale, leading to sub-synchronous rotation. Consequently,
between 15 and 20 per cent of the material leaving the inner-Lagrangian point
is accreted back onto the donor (so-called `self-accretion'), further enhancing
orbital shrinkage. Self-accretion, and the sink of orbital angular momentum
which mass transfer provides, may potentially lead to more contact binaries.
Even though Algols are mainly considered, the osculating prescription is
applicable to all types of interacting binaries, including those with eccentric
orbits.",1408.4303v2
2019-11-05,Zero-field spin-orbit-torque switching driven by magnetic spin Hall effect,"Spin Hall effect plays an essential role in generating spin current from the
injected charge current, following the Dyakonov-Perel rule that the directions
of charge flow, spin flow and spin polarization are mutually perpendicular to
each other. Recently, its generalization from an antiferromagnet, so-called
magnetic spin Hall effect, has been studied and verified by measuring anomalous
spin accumulations. Here, we investigate the magnetic spin Hall effect in
bilayer materials made of a heavy metal and an antiferromagnet. The spin
current generated by the magnetic spin Hall effect accomplishes
spin-orbit-torque switching for ferromagnetic magnetization and exchange bias
concurrently without any external magnetic field. The switching mechanism
crucially relies on the non-collinear spin texture in the antiferromagnet,
capable of generating symmetry-breaking components in the spin-current tensor
so that the external magnetic field is no longer necessary. The zero-field
concurrent switching of magnetization and exchange bias is a significant
technological breakthrough. Furthermore, our findings pave the way to explore
the magnetic spin Hall effects in various spin textures through
spin-orbit-torque switching.",1911.01785v1
2021-09-04,A mechanistic model for the asymmetric torque-speed relationships of a bacterial flagellar motor,"A tiny bacterial flagellar motor rotates in both counter-clockwise (CCW) and
clockwise (CW) rotational directions. The most important measurable
characteristic of the flagellar motor is its torque versus angular speed
relationship in CCW or CW modes, which is found to be non-symmetrical with each
other, and still, such a phenomenon is not clearly understood.Here, we explain
this asymmetry through a mechanistic model based on the detailed torque
analysis for the rotation of the motor and the revolutionary as well as
spinning motion of the filament and bead. We find out that the asymmetry
results from the conformational changing of the hook due to rotational
switching, rather than any non-symmetric changes in the potential of mean force
generated by the stator-rotor interactions. In CCW mode, when the hook remains
bend and flexible, the revolution motion predominates and the restoring torque
in this motion, originated due to drag, governs the shape of the torque-speed
curve. However, in CW mode, spinning motion dominates as the hook becomes
straight and rigid, and the linear torque-speed relation arises due to the
restoring torque for the drag corresponding to this motion. Our study indicates
the significant role of the hook's conformational change upon the biological
functions of the motor and paves the way for further experimental exploration
on the structural origin of such asymmetry.",2109.01813v1
2018-01-04,Spin Force and Torque in Non-relativistic Dirac Oscillator on a Sphere,"The spin force operator on a non-relativistic Dirac oscillator ( in the
non-relativistic limit the Dirac oscillator is a spin one-half 3D harmonic
oscillator with strong spin-orbit interaction) is derived using the Heisenberg
equations of motion and is seen to be formally similar to the force by the
electromagnetic field on a moving charged particle . When confined to a sphere
of radius R, it is shown that the Hamiltonian of this non-relativistic
oscillator can be expressed as a mere kinetic energy operator with an anomalous
part. As a result, the power by the spin force and torque operators in this
case are seen to vanish. The spin force operator on the sphere is calculated
explicitly and its torque is shown to be equal to the rate of change of the
kinetic orbital angular momentum operator, again with an anomalous part. This,
along with the conservation of the total angular momentum, suggest that the
spin force exerts a spin-dependent torque on the kinetic orbital angular
momentum operator in order to conserve total angular momentum. The presence of
an anomalous spin part in the kinetic orbital angular momentum operator gives
rise to an oscillatory behavior similar to the \textit{Zitterbewegung}. It is
suggested that the underlying physics that gives rise to the spin force and the
\textit{Zitterbewegung} is one and the same in NRDO and in systems that
manifest spin Hall effect.",1801.01348v1
2008-12-10,Symmetry and the generation and measurement of optical torque,"A key element in the generation of optical torque in optical traps, which
occurs when electromagnetic angular momentum is transferred from the trapping
beam to the trapped particle by scattering, is the symmetries of the scattering
particle and the trapping beam. We discuss the effect of such symmetries on the
generation and measurement of optical torque in optical tweezers, and some
consequent general principles for the design of optically-driven micromachines.",0812.2039v1
2012-12-18,Thermoelectric spin accumulation and long-time spin precession in a non-collinear quantum dot spin valve,"We explore thermoelectric spin transport and spin dependent phenomena in a
non-collinear quantum dot spin valve set up. Using this set up, we demonstrate
the possibility of a thermoelectric excitation of single spin dynamics inside
the quantum dot. Many-body exchange fields generated on the single spins in
this set up manifest as effective magnetic fields acting on the net spin
accumulation in the quantum dot. We first identify generic conditions by which
a zero bias spin accumulation in the dot may be created in the thermoelectric
regime. The resulting spin accumulation is then shown to be subject to a
field-like spin torque due to the effective magnetic field associated with
either contact. This spin torque that is generated may yield long-time
precession effects due to the prevailing blockade conditions. The implications
of these phenomena in connection with single spin manipulation and pure spin
current generation are then discussed.",1212.4353v2
2021-04-12,Controllable Spin Current in van der Waals Ferromagnet Fe3GeTe2,"The control of spin current is pivotal for spintronic applications,
especially for spin-orbit torque devices. Spin Hall effect (SHE) is a prevalent
method to generate spin current. However, it is difficult to manipulate its
spin polarization in nonmagnet. Recently, the discovery of spin current in
ferromagnet offers opportunity to realize the manipulation. In the present
work, the spin current in van der Waals ferromagnet Fe3GeTe2 (FGT) with varying
magnetization is theoretically investigated. It has been observed that the spin
current in FGT presents the nonlinear behavior with respect to magnetization.
The in-plane and out-of-plane spin polarization emerges simultaneously, and the
bilayer FGT can even exhibit arbitrary spin polarization thanks to the reduced
symmetry. More intriguingly, the correlation between anomalous Hall effect
(AHE) and spin anomalous Hall effect (SAHE) has been interpreted from the
aspect of Berry curvature. This work illustrates that the interplay of symmetry
and magnetism can effectively control the magnitude and spin polarization of
the spin current, providing a practical method to realize exotic spin-orbit
torques.",2104.05308v2
1996-11-19,Radiative Torques on Interstellar Grains: II. Grain Alignment,"Radiative torques on irregular dust grains, in addition to producing
superthermal rotation, play a direct dynamical role in the alignment of
interstellar dust with the local magnetic field. The equations governing the
orientation of spinning, precessing grains are derived; H_2 formation torques
and paramagnetic dissipation are included in the dynamics. Stationary solutions
(constant alignment angle and spin rate) are found; these solutions may be
stable (""attractors"") or unstable (""repellors""). The equations of motion are
numerically integrated for three exemplary irregular grain geometries, exposed
to anisotropic radiation with the spectrum of interstellar starlight. The
resulting ""trajectory maps"" are classified as ""noncyclic"", ""semicyclic"", or
""cyclic"", with examples of each given.
  We find that radiative torques result in rapid grain alignment, even in the
absence of paramagnetic dissipation. It appears that radiative torques due to
starlight can account for the observed alignment of interstellar grains with
the Galactic magnetic field.",9611149v1
2013-10-15,Current induced domain wall dynamics in the presence of spin orbit torques,"Current induced domain wall (DW) motion in perpendicularly magnetized
nanostripes in the presence of spin orbit torques is studied. We show using
micromagnetic simulations that the direction of the current induced DW motion
and the associated DW velocity depend on the relative values of the field like
torque (FLT) and the Slonczewski like torques (SLT). The results are well
explained by a collective coordinate model which is used to draw a phase
diagram of the DW dynamics as a function of the FLT and the SLT. We show that a
large increase in the DW velocity can be reached by a proper tuning of both
torques.",1310.3998v3
2013-10-18,Quantitative characterization of the spin orbit torque using harmonic Hall voltage measurements,"Solid understanding of current induced torques is key to the development of
current and voltage controlled magnetization dynamics in ultrathin magnetic
heterostructures. To evaluate the size and direction of such torques, or
effective fields, a number of methods have been employed. Here we examine the
adiabatic (low frequency) harmonic Hall voltage measurement that has been used
to study the effective field. We derive an analytical formula for the harmonic
Hall voltages to evaluate the effective field for both out of plane and
in-plane magnetized systems. The formula agrees with numerical calculations
based on a macrospin model. Two different in-plane magnetized films,
Pt|CoFeB|MgO and CuIr|CoFeB|MgO are studied using the formula developed. The
effective field obtained for the latter system shows relatively good agreement
with that estimated using a spin torque switching phase diagram measurements
reported previously. Our results illustrate the versatile applicability of
harmonic Hall voltage measurement for studying current induced torques in
magnetic heterostructures.",1310.4879v1
2021-07-13,Implementing Multiple Modes of the Perpendicular Magnetization Switching within a Single Spin Orbit Torque Device,"Spin orbit torque (SOT) has been considered as one of the promising
technologies for the next-generation magnetic random access memory (MRAM). So
far, SOT has been widely utilized for inducing various modes of magnetization
switching. However, it is challenging to integrate multiple modes of
magnetization switching together. In this work we propose a method for
implementing both unipolar and bipolar switching of the perpendicular
magnetization within a single SOT device. The mode of switching could be easily
altered by tuning the amplitude of the applied current. We show that the
field-like torque plays an important role in the switching process. The
field-like torque induces the precession of the magnetization in the case of
unipolar switching, whereas it helps to generate an effective z-component
torque in the case of bipolar switching. In addition, the influence of key
parameters on the mode of switching is discussed. Our proposal could be used to
design novel reconfigurable logic circuits in the near future.",2107.05999v1
2021-12-30,Spin Torque Oscillations Triggered by In-plane Field,"We study the dynamics of a spin torque nano oscillator that consists of
parallelly magnetized free and pinned layers by numerically solving the
associated Landau-Lifshitz-Gilbert-Slonczewski equation in the presence of a
field-like torque. We observe that an in-plane magnetic field which is applied
for a short interval of time ($<$1ns) triggers the magnetization to exhibit
self-oscillations from low energy initial magnetization state. Also, we confirm
that the frequency of oscillations can be tuned over the range $\sim$25 GHz to
$\sim$72 GHz by current, even in the absence of field-like torque. We find the
frequency enhancement up to 10 GHz by the presence of field-like torque. We
determine the Q-factor for different frequencies and show that it increases
with frequency. Our analysis with thermal noise confirms that the system is
stable against thermal noise and the dynamics is not altered appreciably by it.",2112.15004v1
2007-07-15,Mechanical measurement of equilibrium spin currents in the Rashba medium,"We demonstrate that an equilibrium spin current in a 2D electron gas with
Rashba spin-orbit interaction (Rashba medium) results in a mechanical torque on
a substrate near an edge of the medium. If the substrate is a cantilever, the
mechanical torque displaces the free end of the cantilever. The effect can be
enhanced and tuned by a magnetic field. Observation of this displacement would
be an effective method to prove existence of equilibrium spin currents. The
analysis of edges of the Rashba medium demonstrates the existence of localized
edge states. They form a 1D continuum of states. This suggests a new type of
quantum wire: spin-orbit quantum wire.",0707.2197v1
2010-06-18,Theory of spin transport induced by the temperature gradient,"Spin transport driven by the temperature gradient in ferromagnetic metals is
studied based on a microscopic theory. It is shown that the temperature
gradient works as an effective field equivalent to the electric field as for
both the spin current generation and the spin relaxation torque. The thermally
driven contribution of the spin current and the relaxation torque are thus
proportional to $\nabla T$ and $\nabla^2 T$, respectively.",1006.3628v1
2011-07-05,Scattering theory of magnetic/superconducting junctions with spin active interfaces,"We formulate a generalized scattering field theory a la Buttiker describing
particles transport in magnetic/superconducting heterostructures. The proposed
formalism, characterized by a four- component spinorial wavefunction of the
Bogoliubov de Gennes theory, allows to describe the spin flipping phenomena
induced by noncollinear magnetizations in the scattering region. As a specific
application of the theory, we analyze the conductance, the magnetoresistance
and the generation of spin-torque produced by an applied voltage in a
spin-valve system. Quantum size effects and quantum beating patterns both in
the conductance and in the spin-torque are carefully described.",1107.0819v1
2013-10-30,Spin torque ferromagnetic resonance with magnetic field modulation,"We demonstrate a technique of broadband spin torque ferromagnetic resonance
(ST-FMR) with magnetic field modulation for measurements of spin wave
properties in magnetic nanostructures. This technique gives great improvement
in sensitivity over the conventional ST-FMR measurements, and application of
this technique to nanoscale magnetic tunnel junctions (MTJs) reveals a rich
spectrum of standing spin wave eigenmodes. Comparison of the ST-FMR
measurements with micromagnetic simulations of the spin wave spectrum allows us
to explain the character of low-frequency magnetic excitations in nanoscale
MTJs.",1310.7996v1
2014-04-09,Current-induced spin torque resonance of magnetic insulators,"We formulate a theory of the AC spin Hall magnetoresistance (SMR) in a
bilayer system consisting of a magnetic insulator such as yttrium iron garnet
(YIG) and a heavy metal such as platinum (Pt). We derive expressions for the DC
voltage generation based on the drift-diffusion spin model and quantum
mechanical boundary condition at the interface that reveal a spin torque
ferromagnetic resonance (ST-FMR). We predict that ST-FMR experiments will
reveal valuable information on the current-induced magnetization dynamics of
magnetic insulators and AC spin Hall effect.",1404.2360v2
2017-05-03,Anomalous spin precession under a geometrical torque,"Precession and relaxation predominantly characterize the real-time dynamics
of a spin driven by a magnetic field and coupled to a large Fermi sea of
conduction electrons. We demonstrate an anomalous precession with frequency
higher than the Larmor frequency or with inverted orientation in the limit
where the electronic motion adiabatically follows the spin dynamics. For a
classical spin, the effect is traced back to a geometrical torque resulting
from a finite spin Berry curvature.",1705.01313v2
2015-06-26,Modeling and Simulation of Spin Transfer Torque Generated at Topological Insulator/Ferromagnetic Heterostructure,"Topological Insulator (TI) has recently emerged as an attractive candidate
for possible application to spintronic circuits because of its strong spin
orbit coupling. TIs are unique materials that have an insulating bulk but
conducting surface states due to band inversion and these surface states are
protected by time reversal symmetry. In this paper, we propose a physics-based
spin dynamics simulation framework for TI/Ferromagnet (TI/FM) bilayer
heterostructures that is able to capture the electronic band structure of a TI
while calculating the electron and spin transport properties. Our model differs
from TI/FM models proposed in the literature in that it is able to account for
the 3D band structure of TIs and the effect of exchange coupling and external
magnetic field on the band structure. Our proposed approach uses 2D surface
Hamiltonian for TIs that includes all necessary features for spin transport
calculations so as to properly model the characteristics of a TI/FM
heterostructure. Using this Hamiltonian and appropriate parameters, we show
that the effect of quantum confinement and exchange coupling are successfully
captured in the calculated surface band structure compared with the quantum
well band diagram of a 3D TI, and matches well with experimental data reported
in the literature. We then show how this calibrated Hamiltonian is used with
the self-consistent non equilibrium Green's functions (NEGF) formalism to
determine the charge and spin transport in TI/FM bilayer heterostructures. Our
calculations agree well with experimental data and capture the unique features
of a TI/FM heterostructure such as high spin Hall angle, high spin conductivity
etc. Finally, we show how the results obtained from NEGF calculations may be
incorporated into the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) formulation to
simulate the magnetization dynamics of an FM layer sitting on top of a TI.",1506.07932v2
2005-03-29,Spin-Forster transfer in optically excited quantum dots,"The mechanisms of energy and spin transfer in quantum dot pairs coupled via
the Coulomb interaction are studied. Exciton transfer can be resonant or
phonon-assisted. In both cases, the transfer rates strongly depend on the
resonance conditions. The spin selection rules in the transfer process come
from the exchange and spin-orbit interactions. The character of energy
dissipation in spin transfer is different than that in the traditional spin
currents. The spin-dependent photon cross-correlation functions reflect the
exciton transfer process. In addition, a mathematical method to calculate
F\""orster transfer in crystalline nanostructures beyond the dipole-dipole
approximation is described.",0503688v1
2002-03-14,Interaction Of Electrons With Spin Waves In The Bulk And In Multilayers,"The exchange interaction between electrons and magnetic spins is considerably
enhanced near interfaces, in magnetic multilayers. As a result, a dc current
can be used to generate spin oscillations. We review theory and experimental
evidence. The s-d exchange interaction causes a rapid precession of itinerant
conduction-electron spins s around the localized spins S of magnetic electrons.
Because of the precession, the time-averaged interaction torque between s and S
vanishes. An interface between a magnetic layer and a spacer causes a local
coherence between the precession phases of differnt electrons, within 10 nm
from the interface, and restores the torque. Also, a second magnetic layer with
pinned S is used to prepare s in a specific direction. the current-induced
drive torque of s on S in the active layer may be calculated from the spin
current (Slonczewski) or from the spin imbalance Delta-mu (Berger). Spin
current and Delta-mu are proportional to each other, and can arise from
Fermi-surface translation, as well as from expansion/contraction.",0203314v1
2004-12-20,Current induced spin injection and surface torque in ferromagnetic metallic junctions,"Joint influence of two effects, namely, nonequilibrium spin injection by
current, and current induced surface torque, on spin-valve type ferromagnetic
metallic junctions is considered theoretically. The CPP configuration is
assumed. The consideration is based on solving a coupled set of equations of
motion for the mobile electron and lattice magnetizations. Boundary conditions
are derived from the total magnetization flux continuity condition. A
dispersion relation is derived for current dependent spin-wave fluctuations.
The fluctuations become unstable under current density exceeding some threshold
value. Joint action of the longitudinal spin injection and the torque lowers
the instability threshold. The spin injection softens spin wave frequency near
the threshold and can pin magnetization at the injecting contact. The pinning
rises under the current increasing, so that the appearance of new spin-wave
resonance lines can be observed.",0412523v1
2014-11-03,Experimental Demonstration of the Co-existence of the Spin Hall and Rashba Effects in beta-Tantalum/Ferromagnet Bilayers,"We have measured the spin torques of beta-Tantalum / Co20Fe60B20 bilayers
versus Ta thickness at room temperature using an FMR technique. The spin Hall
coefficient was calculated both from the observed change in damping coefficient
of the ferromagnet with Ta thickness, and from the ratio of the symmetric and
anti-symmetric components of the FMR signal. Results from these two methods
yielded values for the spin Hall coefficient of -0.090+/-0.005 and
-0.11+/-0.01, respectively. We have also identified a significant out-of-plane
spin torque originating from Ta, which is constant with Ta thickness. We
ascribe this to an interface spin orbit coupling, or Rashba effect, due to the
strength and constancy of the torque with Ta thickness. From fitting measured
data to a model including interface spin orbit coupling, we have determined the
spin diffusion length for beta-Tantalum to be ~2.5 nm.",1411.0601v1
2015-11-13,Magnified Damping under Rashba Spin Orbit Coupling,"The spin orbit coupling spin torque consists of the field-like [REF: S.G. Tan
et al., arXiv:0705.3502, (2007).] and the damping-like terms [REF: H.
Kurebayashi et al., Nature Nanotechnology 9, 211 (2014).] that have been widely
studied for applications in magnetic memory. We focus, in this article, not on
the spin orbit effect producing the above spin torques, but on its magnifying
the damping constant of all field like spin torques. As first order precession
leads to second order damping, the Rashba constant is naturally co-opted,
producing a magnified field-like damping effect. The Landau-Liftshitz-Gilbert
equations are written separately for the local magnetization and the itinerant
spin, allowing the progression of magnetization to be self-consistently locked
to the spin.",1511.04227v1
2015-12-22,Spin torque study of the spin Hall conductivity and spin diffusion length in platinum thin films with varying resistivity,"We report measurements of the spin torque efficiencies in
perpendicularly-magnetized Pt/Co bilayers where the Pt resistivity $\rho_{Pt}$
is strongly dependent on thickness $t_{Pt}$ . The damping-like spin Hall torque
efficiency per unit current density, $\xi^j_{DL}$ , varies significantly with
$t_{Pt}$, exhibiting a peak value $\xi^j_{DL}=0.12$ at $t_{Pt} = 2.8 - 3.9$ nm.
In contrast, $\xi^j_{DL}/\rho_{Pt}$ increases monotonically with $t_{Pt}$ and
saturates for $t_{Pt} > 5$ nm, consistent with an intrinsic spin Hall effect
mechanism, in which $\xi^j_{DL}$ is enhanced by an increase in $\rho_{Pt}$ .
Assuming the Elliott-Yafet spin scattering mechanism dominates we estimate that
the spin diffusion length $\lambda_s = (0.77 \pm 0.08) \times 10^{-15} \Omega
m^2 /\rho_{Pt}$.",1512.06931v1
2019-03-10,Electrical generation and propagation of spin waves in antiferromagnetic thin films,"Electrical generation of THz spin waves is theoretically explored in an
antiferromangetic nanostrip via the current-induced spin-orbit torque. The
analysis based on micromagnetic simulations clearly illustrates that the
Neel-vector oscillations excited at one end of the magnetic strip can propagate
in the form of a traveling wave when the nanostrip axis aligns with the
magnetic easy-axis. A sizable threshold is observed in the driving current
density or the torque to overcome the unfavorable anisotropy as expected. The
generated spin waves are found to travel over a long distance while the angle
of rotation undergoes continuous decay in the presence of non-zero damping. The
oscillation frequency is tunable via the strength of the spin-orbit torque,
reaching the THz regime. Other key characteristics of the spin waves such as
the phase and the chirality can also be modulated actively. The simulation
results further indicate the possibility of wave-like superposition between the
excited spin oscillations, illustrating its application as an efficient source
of spin-wave signals for information processing.",1903.04068v2
2019-10-19,Current-induced spin-orbit field in permalloy interfaced with ultrathin Ti and Cu,"How spin-orbit torques emerge from materials with weak spin-orbit coupling
(e.g., light metals) is an open question in spintronics. Here, we report on a
field-like spin-orbit torque (i.e., in-plane spin-orbit field transverse to the
current axis) in SiO$_2$-sandwiched permalloy (Py), with the top Py-SiO$_2$
interface incorporating ultrathin Ti or Cu. In both SiO$_2$/Py/Ti/SiO$_2$ and
SiO$_2$/Py/Cu/SiO$_2$, this spin-orbit field opposes the classical Oersted
field. While the magnitude of the spin-orbit field is at least a factor of 3
greater than the Oersted field, we do not observe evidence for a significant
damping-like torque in SiO$_2$/Py/Ti/SiO$_2$ or SiO$_2$/Py/Cu/SiO$_2$. Our
findings point to contributions from a Rashba-Edelstein effect or spin-orbit
precession at the (Ti, Cu)-inserted interface.",1910.08669v2
2020-02-05,Topological spin torque emerging in classical-spin systems with different time scales,"In classical spin systems with two largely different inherent time scales,
the configuration of the fast spins almost instantaneously follows the
slow-spin dynamics. We develop the emergent effective theory for the slow-spin
degrees of freedom and demonstrate that this generally includes a topological
spin torque. This torque gives rise to anomalous real-time dynamics. It derives
from the holonomic constraints defining the fast-spin configuration space and
is given in terms of a topological charge density which becomes a quantized
homotopy invariant when integrated.",2002.01914v2
2020-02-05,Microscopic Origin of Spin-Orbit Torque in Ferromagnetic Heterostructures: A First Principles Approach,"We present an {\it ab initio}-based theoretical framework which elucidates
the origin of the spin-orbit torque (SOT) in Normal-Metal(NM)/Ferromagnet(FM)
heterostructures. The SOT is decomposed into two contributions, namely, {\it
spin-Hall} and the {\it spin-orbital} components. We find that {\it (i)} the
Field-Like (FL) SOT is dominated by the spin-orbital component and {\it (ii)}
both components contribute to the damping-like torque with comparable magnitude
in the limit of thick Pt film. The contribution of the spin-orbital component
to the DL-SOT is present only for NMs with strong SOC coupling strength. We
demonstrate that the FL-SOT can be expressed in terms of the non-equilibrium
spin-resolved orbital moment accumulation. The calculations reveal that the
experimentally reported oxygen-induced sign-reversal of the FL-SOT in Pt/Co
bilayers is due to the significant reduction of the majority-spin orbital
moment accumulation on the interfacial NM atoms.",2002.01983v1
2021-03-29,Spin Dynamics of Extrasolar Giant Planets in Planet-Planet Scattering,"Planet-planet scattering best explains the eccentricity distribution of
extrasolar giant planets. Past literature showed that the orbits of planets
evolve due to planet-planet scattering. This work studies the spin evolution of
planets in planet-planet scattering in 2-planet systems. Spin can evolve
dramatically due to spin-orbit coupling made possible by the evolving spin and
orbital precession during the planet-planet scattering phase. The main source
of torque to planet spin is the stellar torque, and the total planet-plane
torque contribution is negligible. As a consequence of the evolution of the
spin, planets can end up with significant obliquity (the angle between a
planet's own orbit normal and spin axis) like planets in our Solar System.",2103.15902v1
2022-11-02,Spin wave excitations in a nanowire spin-torque oscillator with perpendicular magnetic anisotropy,"Spin torque oscillators (STOs) are emerging microwave devices that can
potentially be used in spin-logic devices and the next-generation high-speed
computing architecture. Thanks to their non-linear nature, STOs are easily
tunable by the magnetic field and the dc current. Spin Hall nano-oscillators
(SHNOs) are promising types of STOs and most of the current studies focus on
localized modes that can be easily excited. Here, we study using micromagnetic
simulations, the nature of the spin-torque-induced excitations in nanowire
devices made of perpendicular magnetic anisotropy (PMA) material. Our results
showed that upon including PMA the excitation of localized and propagating spin
wave modes is feasible. We study the nature of the mode excitations as a
function of the PMA strength (\text{K}$_u$), and the current. Indeed, we
estimate a critical value of \text{K}$_u$ to allow for the excitation of the
propagating spin wave. We attribute this mode selectivity between localized and
propagating modes to a switch in the sign of the nonlinearity of the system
from negative to positive at a non-zero \text{K}$_u$ which is supported by
analytical calculations. Our results provide deep insight into engineering
reconfigurable microwave devices for future magnonic and computational
applications.",2211.01078v1
2022-11-07,Determining Perpendicular Magnetic Anisotropy in Fe/MgO/Fe Magnetic Tunnel Junction: A DFT-Based Spin-Orbit Torque Method,"In our JunPy package, we have combined the first-principles calculated
self-consistent Hamiltonian with divide-and-conquer technique to successfully
determine the magnetic anisotropy (MA) in an Fe/MgO/Fe magnetic tunnel junction
(MTJ). We propose a comprehensive analytical derivation to clarify the crucial
roles of spin-orbit coupling that mediates the exchange and spin-orbit
components of spin torque, and the kinetic and spin-orbit components of spin
current accumulation. The angular dependence of cumulative spin-orbit torque
(SOT) indicates a uniaxial MA corresponding to the out-of-plane rotations of
magnetic moments of the free Fe layers. Different from the conventional MA
energy calculation and the phenomenological theory for a whole MTJ, our results
provide insight into the orbital-resolved SOT for atomistic spin dynamics
simulation in emergency complex magnetic heterojunctions.",2211.03603v3
2024-02-02,Seamless Capture and Stabilization of Spinning Satellites By Space Robots with Spinning Base,"This paper introduces an innovative guidance and control method for
simultaneously capturing and stabilizing a fast-spinning target satellite, such
as a spin-stabilized satellite, using a spinning-base servicing satellite
equipped with a robotic manipulator, joint locks, and reaction wheels (RWs).
The method involves controlling the RWs of the servicing satellite to replicate
the spinning motion of the target satellite, while locking the manipulator's
joints to achieve spin-matching. This maneuver makes the target stationary with
respect to the rotating frame of the servicing satellite located at its
center-of-mass (CoM), simplifying the robot capture trajectory planning and
eliminating post-capture trajectory planning entirely. In the next phase, the
joints are unlocked, and a coordination controller drives the robotic
manipulator to capture the target satellite while maintaining zero relative
rotation between the servicing and target satellites. The spin stabilization
phase begins after completing the capture phase, where the joints are locked to
form a single tumbling rigid body consisting of the rigidly connected servicing
and target satellites. An optimal controller applies negative control torques
to the RWs to dampen out the tumbling motion of the interconnected satellites
as quickly as possible, subject to the actuation torque limit of the RWs and
the maximum torque exerted by the manipulator's end-effector.",2402.01959v1
2021-06-10,Spin-Orbit Torque Engineering in β-W/CoFeB Heterostructures via Ta and V Alloying at Interfaces,"Spin-orbit torque manifested as an accumulated spin-polarized moment at
nonmagnetic normal metal, and ferromagnet interfaces is a promising
magnetization switching mechanism for spintronic devices. To fully exploit this
in practice, materials with a high spin Hall angle, i.e., a charge-to-spin
conversion efficiency, are indispensable. To date, very few approaches have
been made to devise new nonmagnetic metal alloys. Moreover, new materials need
to be compatible with semiconductor processing. Here we introduce W-Ta and W-V
alloys and deploy them at the interface between $\beta$-W/CoFeB layers. First,
spin Hall conductivities of W-Ta and W-V structures with various compositions
are carried out by first-principles band calculations, which predict the spin
Hall conductivity of the W-V alloy is improved from $-0.82 \times 10^3$ S/cm
that of W to $-1.98 \times 10^3$ S/cm. Subsequently, heterostructure
fabrication and spin-orbit torque properties are characterized experimentally.
By alloying $\beta$-W with V at a concentration of 20 at%, we observe a large
enhancement of the absolute value of spin Hall conductivity of up to $-(2.77
\pm 0.31) \times 10^3$ S/cm. By employing X-ray diffraction and scanning
transmission electron microscopy, we further explain the enhancement of
spin-orbit torque efficiency is stemmed from W-V alloy between W and CoFeB.",2106.05460v1
2023-10-10,Large out-of-plane spin-orbit torque in topological Weyl semimetal candidate TaIrTe4,"Topological quantum materials, with novel spin textures and broken crystal
symmetries are suitable candidates for spintronic memory technologies. Their
unique electronic properties, such as protected surface states and exotic
quasiparticles, can provide an out-of-plane spin polarized current needed for
external field free magnetization switching of magnets with perpendicular
magnetic anisotropy. Conventional spin-orbit torque materials, such as heavy
metals and topological insulators, provide only an in-plane spin polarized
current, and recently explored materials with lower crystal symmetries provide
very low out-of-plane spin polarized current components, which is not suitable
for energy-efficient spin-orbit torque (SOT) applications. Here, we demonstrate
a large out-of-plane damping-like SOT at room temperature using a topological
Weyl semimetal candidate TaIrTe4 with a lower crystal symmetry. We performed
spin-orbit torque ferromagnetic resonance (STFMR) experiments in a
TaIrTe4/Ni80Fe20 heterostructure and observed a large out-of-plane damping-like
SOT efficiency. The out-of-plane spin Hall conductivity is estimated to be an
order of magnitude higher than the reported values in other materials. These
findings of high spin Hall conductivity and large out-of-plane SOT efficiency
are suitable for the development of energy efficient and external field-free
spintronic devices.",2310.06395v1
1997-04-28,Torque Reversal in Accretion-Powered X-ray Pulsars,"Accretion-powered X-ray pulsars 4U 1626-67, GX 1+4, and OAO 1657-415 have
recently shown puzzling torque reversals. These reversals are characterized by
short time scales, on the order of days, nearly identical spin-up and spin-down
rates, and very small changes in X-ray luminosity. We propose that this
phenomenon is the result of sudden dynamical changes in the accretion disks
triggered by a gradual variation of mass accretion rates. These sudden torque
reversals may occur at a critical accretion rate $\sim$
$10^{15}-10^{16}g~s^{-1}$ when the system makes a transition from (to) a
primarily Keplerian flow to (from) a substantially sub-Keplerian, radial
advective flow in the inner disk. For systems near spin equilibrium, the
spin-up torques in the Keplerian state are slightly larger than the spin-down
torques in the advective state, in agreement with observation. The abrupt
reversals could be a signature of pulsar systems near spin equilibrium with the
mass accretion rates modulated on a time scale of a year or longer near the
critical accretion rate. It is interesting that cataclysmic variables and black
hole soft X-ray transients change their X-ray emission properties at accretion
rates similar to the pulsars' critical rate. We speculate that the dynamical
change in pulsar systems shares a common physical origin with white dwarf and
black hole accretion disk systems.",9704269v2
2015-07-30,"Torque Enhancement, Spin Equilibrium, and Jet Power from Disk-Induced Opening of Pulsar Magnetic Fields","The interaction of a rotating star's magnetic field with a surrounding plasma
disk lies at the heart of many questions posed by neutron stars in X-ray
binaries. We consider the opening of stellar magnetic flux due to differential
rotation along field lines coupling the star and disk, using a simple model for
the disk-opened flux, the torques exerted on the star by the magnetosphere, and
the power extracted by the electromagnetic wind. We examine the conditions
under which the system enters an equilibrium spin state, in which the accretion
torque is instantaneously balanced by the pulsar wind torque alone. For
magnetic moments, spin frequencies, and accretion rates relevant to accreting
millisecond pulsars, the spin-down torque from this enhanced pulsar wind can be
substantially larger than that predicted by existing models of the
disk-magnetosphere interaction, and is in principle capable of maintaining spin
equilibrium at frequencies less than 1 kHz. We speculate that this mechanism
may account for the non-detection of frequency increases during outbursts of
SAX J1808.4-3658 and XTE J1814-338, and may be generally responsible for
preventing spin-up to sub-millisecond periods. If the pulsar wind is collimated
by the surrounding environment, the resulting jet can satisfy the power
requirements of the highly relativistic outflows from Cir X-1 and Sco X-1. In
this framework, the jet power scales relatively weakly with accretion rate, L_j
~ Mdot^{4/7}, and would be suppressed at high accretion rates only if the
stellar magnetic moment is sufficiently low.",1507.08627v2
2020-06-25,Temperature-Dependent Anisotropic Magnetoresistance and Spin-Torque-Driven Vortex Dynamics in a Single Microdisk,"Spin-orbit-torque-driven dynamics have recently gained interest in the field
of magnetism due to the reduced requirement of current densities and an
increase in efficiency, as well as the ease of implementation of different
devices and materials. From a practical point of view, the low-frequency
dynamics below 1 GHz is particularly interesting since dynamics associated with
magnetic domains lie in this frequency range. While spin-torque excitation of
high-frequency modes has been extensively studied, the intermediate
low-frequency dynamics have received less attention, although spin torques
could potentially be used for both manipulation of the spin texture, as well as
the excitation of dynamics. In this work, we demonstrate that it is possible to
drive magnetic vortex dynamics in a single microdisk by spin-Hall torque at
varying temperatures, and relate the results to transport properties. We find
that the gyrotropic mode of the core couples to the low-frequency microwave
signal and produces a measurable voltage. The dynamic measurements are in
agreement with magnetic transport measurements and are supported by
micromagnetic simulations. Our results open the door for integrating magnetic
vortex devices in spintronic applications.",2006.14454v1
2022-02-22,Giant spin torque efficiency in naturally oxidized polycrystalline TaAs thin films,"We report the measurement of efficient charge-to-spin conversion at room
temperature in Weyl semimetal/ferromagnet heterostructures with both oxidized
and pristine interfaces. Polycrystalline films of the Weyl semimetal, TaAs, are
grown by molecular beam epitaxy on (001) GaAs and interfaced with a metallic
ferromagnet (Ni$_{0.8}$Fe$_{0.2}$). Spin torque ferromagnetic resonance
(ST-FMR) measurements in samples with an oxidized interface yield a spin torque
efficiency as large as $\xi_{\mathrm{FMR}}=0.45\pm 0.25$ for a 8 nm
Ni$_{0.8}$Fe$_{0.2}$ layer thickness. By studying ST-FMR in these samples with
varying Ni$_{0.8}$Fe$_{0.2}$ layer thickness, we extract a damping-like torque
efficiency as high as $\xi_{\mathrm{DL}}=1.36\pm 0.66$. In samples with a
pristine (unoxidized) interface, the spin torque efficiency has opposite sign
to that observed in oxidized samples ($\xi_{\mathrm{FMR}}=-0.27\pm 0.14$ for a
5 nm Ni$_{0.8}$Fe$_{0.2}$ layer thickness). We also find a lower bound on the
spin Hall conductivity ($424 \pm 110 \frac{\hbar}{e}$ S/cm) which is
surprisingly consistent with theoretical predictions for the single crystal
Weyl semimetal state of TaAs.",2202.10656v1
2005-01-25,Where Are All The Fallback Disks? Constraints on Propeller Systems,"Fallback disks are expected to form around new-born neutron stars following a
supernova explosion. In almost all cases, the disk will pass through a
propeller stage. If the neutron star is spinning rapidly (initial period $\sim
10$ ms) and has an ordinary magnetic moment ($\sim 10^{30}$ G cm$^3$), the
rotational power transferred to the disk by the magnetic field of the neutron
star will exceed the Eddington limit by many orders of magnitude, and the disk
will be rapidly disrupted. Fallback disks can thus survive only around
slow-born neutron stars and around black holes, assuming the latter do not
torque their surrounding disks as strongly as do neutron stars. This might
explain the apparent rarity of fallback disks around young compact objects.",0501551v1
2003-01-17,Current-Induced Magnetization Reversal in High Magnetic Fields in Co/Cu/Co Nanopillars,"Current-induced magnetization dynamics in Co/Cu/Co trilayer nanopillars
(~100nm in diameter) has been studied experimentally for large applied fields
perpendicular to the layers. An abrupt and hysteretic increase in dynamic
resistance is observed at high current densities for one polarity of the
current, comparable to the giant magnetoresistance effect observed at low
fields. A micromagnetic model, that includes a spin-transfer torque, suggests
that the current induces a complete reversal of the thin Co layer to alignment
antiparallel to the applied field-that is, to a state of maximum magnetic
energy.",0301324v4
2004-07-23,Micromagnetic understanding of current-driven domain wall motion in patterned nanowires,"In order to explain recent experiments reporting a motion of magnetic domain
walls (DW) in nanowires carrying a current, we propose a modification of the
spin transfer torque term in the Landau-Lifchitz-Gilbert equation. We show that
it explains, with reasonable parameters, the measured DW velocities as well as
the variation of DW propagation field under current. We also introduce
coercivity by considering rough wires. This leads to a finite DW propagation
field and finite threshold current for DW propagation, hence we conclude that
threshold currents are extrinsic. Some possible models that support this new
term are discussed.",0407628v2
2007-02-01,Adiabatic Domain Wall Motion and Landau-Lifshitz Damping,"Recent theory and measurements of the velocity of current-driven domain walls
in magnetic nanowires have re-opened the unresolved question of whether
Landau-Lifshitz damping or Gilbert damping provides the more natural
description of dissipative magnetization dynamics. In this paper, we argue that
(as in the past) experiment cannot distinguish the two, but that
Landau-Lifshitz damping nevertheless provides the most physically sensible
interpretation of the equation of motion. From this perspective, (i) adiabatic
spin-transfer torque dominates the dynamics with small corrections from
non-adiabatic effects; (ii) the damping always decreases the magnetic free
energy, and (iii) microscopic calculations of damping become consistent with
general statistical and thermodynamic considerations.",0702020v3
2007-08-23,Ballistic vs Diffusive Transport in Current-Induced Magnetization Switching,"We test whether current-induced magnetization switching due to
spin-transfer-torque in ferromagnetic/non-magnetic/ferromagnetic (F/N/F)
trilayers changes significantly when scattering within the N-metal layers is
changed from ballistic to diffusive. Here ballistic corresponds to a ratio r =
lambda/t greater than or equal to 3 for a Cu spacer layer, and diffusive to r =
lambda/t less than or equal to 0.4 for a CuGe alloy spacer layer, where lambda
is the mean-free-path in the N-layer of fixed thickness t = 10 nm. The average
switching currents for the alloy spacer layer are only modestly larger than
those for Cu. The best available model predicts a much greater sensitivity of
the switching currents to diffuse scattering in the spacer layer than we see.",0708.3229v2
2007-11-26,Creep of current-driven domain-wall lines: intrinsic versus extrinsic pinning,"We present a model for current-driven motion of a magnetic domain-wall line,
in which the dynamics of the domain wall is equivalent to that of an overdamped
vortex line in an anisotropic pinning potential. This potential has both
extrinsic contributions due to, e.g., sample inhomogeneities, and an intrinsic
contribution due to magnetic anisotropy. We obtain results for the domain-wall
velocity as a function of current for various regimes of pinning. In
particular, we find that the exponent characterizing the creep regime depends
strongly on the presence of a dissipative spin transfer torque. We discuss our
results in the light of recent experiments on current-driven domain-wall creep
in ferromagnetic semiconductors, and suggest further experiments to corroborate
our model.",0711.4058v3
2008-07-16,Current-induced domain-wall motion in synthetic antiferromagnets,"Domain-wall magnetoresistance and low-frequency noise have been studied in
epitaxial antiferromagnetically-coupled [Fe/Cr(001)]_10 multilayers and
ferromagnetic Co line structures as a function of DC current intensity. In
[Fe/Cr(001)]_10 multilayers a transition from excess to suppressed domain-wall
induced 1/f noise above current densities of j_c ~ 2*10^5 A/cm^2 has been
observed. In ferromagnetic Co line structures the domain wall related noise
remains qualitatively unchanged up to current densities exceeding 10^6A/cm^2.
Theoretical estimates of the critical current density for a synthetic Fe/Cr
antiferromagnet suggest that this effect may be attributed to current-induced
domain-wall motion that occurs via spin transfer torques.",0807.2519v1
2009-01-22,Diurnal Thermal Tides in a Non-synchronized Hot Jupiter,"We perform a linear analysis to investigate the dynamical response of a
non-synchronized hot Jupiter to stellar irradiation. In this work, we consider
the diurnal Fourier harmonic of the stellar irradiation acting at the top of a
radiative layer of a hot Jupiter with no clouds and winds. In the absence of
the Coriolis force, the diurnal thermal forcing can excite internal waves
propagating into the planet's interior when the thermal forcing period is
longer than the sound crossing time of the planet's surface. When the Coriolis
effect is taken into consideration, the latitude-dependent stellar heating can
excite weak internal waves (g modes) and/or strong baroclinic Rossby waves
(buoyant r modes) depending on the asynchrony of the planet. When the planet
spins faster than its orbital motion (i.e. retrograde thermal forcing), these
waves carry negative angular momentum and are damped by radiative loss as they
propagate downwards from the upper layer of the radiative zone. As a result,
angular momentum is transferred from the lower layer of the radiative zone to
the upper layer and generates a vertical shear. We estimate the resulting
internal torques for different rotation periods based on the parameters of HD
209458b.",0901.3401v1
2009-07-23,Frequency converter based on nanoscale MgO magnetic tunnel junctions,"We observe both dc voltage rectification and frequency conversion that occur
when a reference microwave current is injected to a MgO based magnetic tunnel
junction (MTJ). The rectification that is spin-transfer torque dependent is
observed when the frequency of the input microwave current coincides with the
resonance frequency of the magnetization of the active layer. In addition, we
demonstrate that frequency conversion is the result of amplitude modulation
between the reference signal and the resistance of the MTJ that is fluctuating
at the resonance frequency of the magnetization of the active layer.",0907.3992v1
2009-11-09,"Thermopower and Thermally Induced Domain Wall Motion in (Ga,Mn)As","We study two reciprocal thermal effects in the ferromagnetic semiconductor
(Ga,Mn)As by scattering theory: domain wall motion induced by a temperature
gradient as well as heat currents pumped by a moving domain wall. The effective
out-of-plane thermal spin transfer torque parameter $P_Q \beta_{Q}$, which
governs the coupling between heat currents and a magnetic texture, is found to
be of the order of unity. Unpinned domain walls are predicted to move at speed
10 m/s in temperature gradients of the order 10 ${\rm K/ \mu m}$. The cooling
power of a moving domain wall only compensates the heating due to friction
losses at ultra-low domain wall velocities of about 0.07 m/s. The Seebeck
coefficient is found to be of the order 100-500 ${\rm \mu V / K}$ at T=10 K, in
good agreement with recent experiment.",0911.1758v2
2010-03-12,White Dwarfs in Ultrashort Binary Systems,"This contribution summarizes, as of early 2008, the observational and
theoretical understanding of the physics, and emission properties of two Double
Degenerate Binaries with the shortest orbital period known to date. In
particular, the Unipolar Inductor Model and its coupling to GW emission have
been introduced to explain a number of puzzling features that these two sources
have in common and that are thought difficult to reconcile with models of mass
transfer in such systems. Emphasis was put on the relevant new physical
features that characterize the model. The role of spin-orbit coupling through
the Lorentz torque and the role of GW emission in keeping the electric
interaction active at all times has been thoroughly discussed in all their
implications. Application of the model to both HM Cnc and V407 Vul accounts in
a natural way for their main observational properties. Constraints on physical
parameters are derived in order for the model to work, and can be verified by
future observations.",1003.2636v1
2010-10-07,Power optimization for domain wall motion in ferromagnetic nanowires,"The current mediated domain-wall dynamics in a thin ferromagnetic wire is
investigated. We derive the effective equations of motion of the domain wall.
They are used to study the possibility to optimize the power supplied by
electric current for the motion of domain walls in a nanowire. We show that a
certain resonant time-dependent current moving a domain wall can significantly
reduce the Joule heating in the wire, and thus it can lead to a novel proposal
for the most energy efficient memory devices. We discuss how Gilbert damping,
non-adiabatic spin transfer torque, and the presence of Dzyaloshinskii-Moriya
interaction can effect this power optimization.",1010.1537v1
2011-02-15,MuMax: a new high-performance micromagnetic simulation tool,"We present MuMax, a general-purpose micromagnetic simulation tool running on
Graphical Processing Units (GPUs). MuMax is designed for high performance
computations and specifically targets large simulations. In that case speedups
of over a factor 100x can easily be obtained compared to the CPU-based OOMMF
program developed at NIST. MuMax aims to be general and broadly applicable. It
solves the classical Landau-Lifshitz equation taking into account the
magnetostatic, exchange and anisotropy interactions, thermal effects and
spin-transfer torque. Periodic boundary conditions can optionally be imposed. A
spatial discretization using finite differences in 2 or 3 dimensions can be
employed. MuMax is publicly available as open source software. It can thus be
freely used and extended by community. Due to its high computational
performance, MuMax should open up the possibility of running extensive
simulations that would be nearly inaccessible with typical CPU-based
simulators.",1102.3069v2
2011-11-06,Quasi-spherical accretion in X-ray pulsars,"Quasi-spherical accretion in wind-fed X-ray pulsars is discussed. At X-ray
luminosities <4 10^{36} erg/s, a hot convective shell is formed around the
neutron star magnetosphere, and subsonic settling accretion regime sets in. In
this regime, accretion rate onto neutron star is determined by the ability of
plasma to enter magnetosphere via Rayleigh-Taylor instability. A gas-dynamic
theory of settling accretion is constructed taking into account anisotropic
turbulence. The angular momentum can be transferred through the quasi-static
shell via large-scale convective motions initiating turbulence cascade. The
angular velocity distribution in the shell is found depending on the turbulent
viscosity prescription. Comparison with observations of long-period X-ray
wind-fed pulsars shows that an almost iso-angular-momentum distribution is most
likely realized in their shells. The theory explains long-term spin-down in
wind- fed accreting pulsars (e.g. GX 1+4) and properties of short-term
torque-luminosity correlations. The theory can be applied to slowly rotating
low-luminosity X-ray pulsars and non-stationary accretion phenomena observed in
some SFXTs.",1111.1382v1
2013-03-19,X-ray absorption spectroscopy and magnetic circular dichroism studies of L1_0-Mn-Ga thin films,"Tetragonally distorted \(\rm{Mn}_{3-x}\rm{Ga}_x\) thin films with \(0.1< x <
2\) show a strong perpendicular magnetic anisotropy and low magnetization and
thus have the potential to serve as electrodes in spin transfer torque magnetic
random access memory. Because a direct capping of these films with MgO is
problematic due to oxide formation, we examined the influence of a CoFeB
interlayer, and of two different deposition methods for the MgO barrier on the
formation of interfacial MnO for \(\rm{Mn}_{62}\rm{Ga}_{38}\) by element
specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism
(XMCD). A highly textured L1\(_0\) crystal structure of the Mn-Ga films was
verified by X-ray diffraction (XRD) measurements. For samples with e-beam
evaporated MgO barrier no evidence for MnO was found, whereas in samples with
magnetron sputtered MgO MnO was detected, even for the thickest interlayer
thickness. Both XAS and XMCD measurements showed an increasing interfacial MnO
amount with decreasing CoFeB interlayer thickness. Additional element specific
full hysteresis loops determined an out-of-plane magnetization axis for the Mn
and Co, respectively.",1303.4648v2
2013-06-04,Influence of material defects on current-driven vortex domain wall mobility,"Many future concepts for spintronic devices are based on the current-driven
motion of magnetic domain walls through nanowires. Consequently a thorough
understanding of the domain wall mobility is required. However, the magnitude
of the nonadiabatic component of the spin-transfer torque driving the domain
wall is still debated today as various experimental methods give rise to a
large range of values for the degree of nonadiabaticity. Strikingly,
experiments based on vortex domain wall motion in magnetic nanowires
consistently result in lower values compared to other methods. Based on the
micromagnetic simulations presented in this contribution we can attribute this
discrepancy to the influence of distributed disorder which vastly affects the
vortex domain wall mobility, but is most often not taken into account in the
models adopted to extract the degree of nonadiabaticity.",1306.0681v2
2013-10-29,Switching probability investigation of electric field-induced precessional magnetization switching,"We report theoretical investigation of the switching probability of electric
field-induced precessional magnetization switching by solving the Fokker-Planck
equation numerically with finite difference method. The switching probability
is determined by the net magnetic field induced by the deviation of precession
angle from its equilibrium position after precession process. The error rate
has the lowest value under an appropriate applied external field for the
voltage pulse duration ${\tau}_{pulse}$ a little longer than the half
precession period. The calculated results show that ultra-low error rate down
to the order of $10^{-12}$ can be achieved for thermal stability factor
{\Delta} = 50 and low damping factor material should be used for free layer to
improve the switching probability. For parallel (anti-parallel) magnetization
to anti-parallel (parallel) magnetization switching process, the spin transfer
torque tends to decrease (increase) the error rate when the ${\tau}_{pulse}$ is
shorter than the half precession period, and increase (decrease) the error rate
when ${\tau}_{pulse}$ is longer than the half-period. These results exhibit
potential of electric field-induced precessional magnetization switching for
ultra-low power, high speed magnetic random access memory (MRAM) application.",1310.7685v3
2013-10-31,Using Cache-coloring to Mitigate Inter-set Write Variation in Non-volatile Caches,"In recent years, researchers have explored use of non-volatile devices such
as STT-RAM (spin torque transfer RAM) for designing on-chip caches, since they
provide high density and consume low leakage power. A common limitation of all
non-volatile devices is their limited write endurance. Further, since existing
cache management policies are write-variation unaware, excessive writes to a
few blocks may lead to a quick failure of the whole cache. We propose an
architectural technique for wear-leveling of non-volatile last level caches
(LLCs). Our technique uses cache-coloring approach which adds a
software-controlled mapping layer between groups of physical pages and cache
sets. Periodically the mapping is altered to ensure that write-traffic can be
spread uniformly to different sets of the cache to achieve wear-leveling.
Simulations performed with an x86-64 simulator and SPEC2006 benchmarks show
that our technique reduces the worst-case writes to cache blocks and thus
improves the cache lifetime by 4.07X.",1310.8494v1
2013-12-08,A Cache Energy Optimization Technique for STT-RAM Last Level Cache,"Last level caches (LLCs) occupy a large chip-area and there size is expected
to grow further to offset the limitations of memory bandwidth and speed. Due to
high leakage consumption of SRAM device, caches designed with SRAM consume
large amount of energy. To address this, use of emerging technologies such as
spin torque transfer RAM (STT-RAM) has been investigated which have lower
leakage power dissipation. However, the high write latency and power of it may
lead to large energy consumption which present challenges in its use. In this
report, we propose a cache reconfiguration based technique for improving the
energy efficiency of STT-RAM based LLCs. Our technique dynamically adjusts the
active cache size to reduce the cache leakage energy consumption with minimum
performance loss. We choose a suitable value of STT-RAM retention time for
avoiding refresh overhead and gaining performance. Single-core simulations have
been performed using SPEC2006 benchmarks and Sniper x86-64 simulator. The
results show that while, compared to an STT-RAM LLC of similar area, an SRAM
LLC incurs nearly 100% loss in energy and 7.3% loss in performance; our
technique using STT-RAM cache saves 21.8% energy and incurs only 1.7% loss in
performance.",1312.2207v2
2014-02-18,Switching Properties in Magnetic Tunnel Junctions with Interfacial Perpendicular Anisotropy: Micromagnetic Study,"The role of universal memory can be successfully satisfied by magnetic tunnel
junctions (MTJs) where the writing mechanism is based on spin-transfer torque
(STT). An improvement in the switching properties (lower switching current
density maintaining the thermal stability) has been achieved in MTJs with
interfacial perpendicular anisotropy (IPA) at the interface between CoFeB and
MgO. In this paper, micromagnetic simulations point out the influence of IPA
and saturation magnetization (MS) on the properties of fast magnetization
reversal achieved in 5, 10 and 20 ns. Both cases of in-plane and out-of-plane
free layer are considered. In addition, the thermal effect is included for the
in-plane switching at 20 ns and a complete analysis of energy dissipation
during the switching is illustrated. This study can provide useful information
for the design of STT-based memories.",1402.4352v1
2014-05-16,Spin-transfer torque switching at ultra low current densities,"The influence of the tantalum buffer layer on the magnetic anisotropy of
perpendicular Co-Fe-B/MgO based magnetic tunnel junctions is studied using
magneto-optical Kerr-spectroscopy. Samples without a tantalum buffer are found
to exhibit no perpendicular magnetization. The transport of Boron into the
tantalum buffer is considered to play an important role on the switching
currents of those devices. With the optimized layer stack of a perpendicular
tunnel junction, a minimal critical switching current density of only 9.2
kA/cm$^2$ is observed. As of today, this value is the lowest reported value for
current-induced magnetization reversal.",1405.4172v2
2014-05-28,Domain wall motions in perpendicularly magnetized CoFe/Pd multilayer nanowire,"Current induced domain wall (DW) motion has been investigated in a 600-nm
wide nanowire using multilayer film with a structure of Ta(5 nm)/Pd(5
nm)/[CoFe(0.4 nm)/Pd(1.2 nm)]$_{15}$/Ta(5 nm)in terms of anomalous Hall effect
measurements. It is found that motion of DWs can be driven by a current density
as low as 1.44$\times$10$^{11}$ A.m$^{-2}$. The effect of the Oersted field
($H_{Oe}$) and spin transfer torque field ($H_{ST}$), which are considered as
effective fields for DW motion, has been quantitatively separated from the
dependence of depinning fields on the current. The results show that the motion
of the walls was essentially dominated by the non-adiabaticity with a high
non-adiabatic factor $\beta$ up to 0.4.",1405.7164v1
2014-07-17,Current-Driven Domain Wall Depinning and Propagation in Notched Nanowires,"Adiabatic spin transfer torque induced domain wall (DW) depinning from a
notch and DW propagation in a nanowire with a series of notches is
investigated. Surprisingly, notches help a current to depin a DW and make a DW
easier to propagate along a wire. Following fascinating results on DW dynamics
are found. 1) The depinning current density of a DW in a notch is substantially
lower than the intrinsic threshold value below which a sustainable DW
propagation doesn't exist in a homogeneous wire. 2) The DW displacement from a
notch is insensitive to notch geometry and current density when it is between
the depinning and the intrinsic threshold current density. 3) A current density
below the intrinsic threshold value can induce a sustainable DW propagation
along notched nanowires. These findings not only reveal interesting and
complicated interaction between a current and a DW, but also have profound
implications in our current understanding of current-driven DW dynamics as well
as in the design of spintronic devices.",1407.4559v1
2014-10-27,Calculation of energy-barrier lowering by incoherent switching in STT-MRAM,"To make a useful STT-MRAM (spin-transfer torque magnetoresistive
random-access memory) device, it is necessary to be able to calculate switching
rates, which determine the error rates of the device. In a single-macrospin
model, one can use a Fokker-Planck equation to obtain a low-current thermally
activated rate $\propto \exp(-E_{eff}/k_B T)$. Here the effective energy
barrier $E_{eff}$ scales with the single-macrospin energy barrier $KV$, where
$K$ is the effective anisotropy energy density and $V$ the volume. A
long-standing paradox in this field is that the actual energy barrier appears
to be much smaller than this. It has been suggested that incoherent motions may
lower the barrier, but this has proved difficult to quantify. In the present
paper, we show that the coherent precession has a magnetostatic instability,
which allows quantitative estimation of the energy barrier and may resolve the
paradox.",1410.7361v1
2015-01-21,Perturbation Theory for Propagating Magnetic Droplet Solitons,"Droplet solitons are a strongly nonlinear, inherently dynamic structure in
the magnetization of ferromagnets, balancing dispersion (exchange energy) with
focusing nonlinearity (strong perpendicular anisotropy). Large droplet solitons
have the approximate form of a circular domain wall sustained by precession
and, in contrast to single magnetic vortices, are predicted to propagate in an
extended, homogeneous magnetic medium. In this work, multiscale perturbation
theory is utilized to develop an analytical framework for investigating the
impact of additional physical effects on the behavior of a propagating droplet.
After first developing soliton perturbation theory in the general context of
Hamiltonian systems, a number of physical phenomena of current interest are
investigated. These include droplet-droplet and droplet-boundary interactions,
spatial magnetic field inhomogeneities, spin transfer torque induced forcing in
a nanocontact device, and damping. Their combined effects demonstrate the
fundamental mechanisms for a previously observed droplet drift instability and
under what conditions a slowly propagating droplet can be supported by the
nanocontact, important considerations for applications. This framework
emphasizes the particle-like dynamics of the droplet, providing analytically
tractable and practical predictions for modern experimental configurations.",1501.05276v1
2015-06-04,High Curie temperature and perpendicular magnetic anisotropy in homoepitaxial InMnAs films,"We have prepared the dilute magnetic semiconductor (DMS) InMnAs with
different Mn concentrations by ion implantation and pulsed laser melting. The
Curie temperature of the In1-xMnxAs epilayer depends on the Mn concentration x,
reaching 82 K for x=0.105. The substitution of Mn ions at the Indium sites
induces a compressive strain perpendicular to the InMnAs layer and a tensile
strain along the in-plane direction. This gives rise to a large perpendicular
magnetic anisotropy, which is often needed for the demonstration of electrical
control of magnetization and for spin-transfer-torque induced magnetization
reversal.",1506.01537v1
2015-06-11,Magnetism in tetragonal manganese-rich Heusler compounds,"A comprehensive study of the total energy of manganese-rich Heusler compounds
using density functional theory is presented. Starting from a large set of
cubic parent systems, the response to tetragonal distortions is studied in
detail. We single out the systems that remain cubic from those that most likely
become tetragonal. The driving force of the tetragonal distortion and its
effect on the magnetic properties, especially where they deviate from the
Slater--Pauling rule, as well as the trends in the Curie temperatures, are
highlighted. By means of partial densities of states, the electronic structural
changes reveal the microscopic origin of the observed trends. We focus our
attention on the magnetocrystalline anisotropy and find astonishingly high
values for tetragonal Heusler compounds containing heavy transition metals
accompanied by low magnetic moments, which indicates that these materials are
promising candidates for spin-transfer torque magnetization-switching
applications.",1506.03735v1
2015-10-26,Edge instability in a chiral stripe domain under an electric current and skyrmion generation,"Motivated by the recent experimental observations on the skyrmion creation by
cutting chiral stripe domains under a current drive [Jiang {\emph{et al.}},
Science {\bf{349}}, 283 (2015)], we study the mechanism of skyrmion generation
by simulating the dynamics of stripe domains. Our theory for skyrmion
generation is based on the fact that there are two half skyrmions attached to
the ends of a stripe domain. These half skyrmions move due to the coupling
between the skyrmion topological charge and current. As a consequence, the
stripe domain is bent or stretched depending on the direction of motion of the
half skyrmions. For a large current, skyrmions are created by chopping the
stripe domains via strong bending or stretching. Our theory provides an
explanation to the experiments and is supported by the new experiments.
Furthermore, we predict that skyrmions can also be generated using a Bloch
stripe domain under a spin transfer torque which can be realized in B20
compounds.",1510.07353v3
2015-11-11,Electric-field Controlled Magnetization Switching in Co/Pt thin-Film Ferromagnets,"A study of dynamic and reversible voltage controlled magnetization switching
in ferromagnetic Co/Pt thin film with perpendicular magnetic anisotropy at room
temperature is presented. The change in the magnetic properties of the system
is observed in a relatively thick film of 15 nm. A surface charge is induced by
the formation of electrochemical double layer between the metallic thin film
and non-aqueous lithium LiClO4 electrolyte to manipulate the magnetism. The
change in the magnetic properties occurred by the application of an external
electric field. As the negative voltage was increased, the coercivity and the
switching magnetic field decreased thus activating magnetization switching. The
results are envisaged to lead to faster and ultra-low power magnetization
switching as compared to spin-transfer torque (STT) switching in spintronic
devices.",1511.03717v1
2016-01-01,Effects of thermal perturbations on magnetic dissipative droplet solitons,"The magnetic dissipative droplet is a strongly nonlinear wave structure that
can be stabilized in a thin film ferromagnet exhibiting perpendicular magnetic
anisotropy by use of spin transfer torque. These structures have been observed
experimentally at room temperature, showcasing their robustness against noise.
Here, we quantify the effects of thermal noise by deriving the stochastic
equations of motion for a droplet based on soliton perturbation theory. First,
it is found that deterministic droplets are linearly unstable at large bias
currents, subject to a drift instability. When the droplet is linearly stable,
our framework allows us to analytically compute the droplet's generation
linewidth and center variance. Additionally, we study the influence of
non-local and Oersted fields with micromagnetic simulations, providing insight
into their effect on the generation linewidth. These results motivate detailed
experiments on the current and temperature-dependent linewidth as well as drift
instability statistics of droplets, which are important figures-of-merit in the
prospect of droplet-based applications.",1601.00048v1
2016-04-13,Instability Mechanism for STT-MRAM switching,"To optimize the design of STT-MRAM (spin-transfer torque magnetic random
access memory), it is necessary to be able to predict switching (error) rates.
For small elements, this can be done using a single-macrospin theory since the
element will switch quasi-uniformly. Experimental results on switching rates
suggest that elements large enough to be thermally stable switch by some
mechanism with a lower energy barrier. It has been suggested that this
mechanism is local nucleation, but we have also previously reported a global
magnetostatic instability, which is consistent with the lower experimental
energy barriers. In this paper, we try to determine which of these mechanisms
is most important by visualizing the switching in a ""U-NU"" (uniform -
nonuniform) phase diagram. We find that switching trajectories follow the
horizontal U axis (i.e., quasi-uniform precession) until they reach a critical
amplitude, at which the magnetostatic instability grows exponentially and a
domain wall forms at the center, whose motion completes the switching. We have
tried unsuccessfully to induce local nucleation (a domain wall at the edge). We
conclude that the dominant switching mechanism is not edge nucleation, but the
magnetostatic instability.",1604.03992v1
2016-06-01,Multi-Bit Read and Write Methodologies for Diode-STTRAM Crossbar Array,"Crossbar arrays using emerging non-volatile memory technologies such as
Resistive RAM (ReRAM) offer high density, fast access speed and low-power.
However the bandwidth of the crossbar is limited to single-bit read/write per
access to avoid selection of undesirable bits. We propose a technique to
perform multi-bit read and write in a diode-STTRAM (Spin Transfer Torque RAM)
crossbar array. Simulation shows that the biasing voltage of half-selected
cells can be adjusted to improve the sense margin during read and thus reduce
the sneak path through the half-selected cells. In write operation, the
half-selected cells are biased with a pulse voltage source which increases the
write latency of these cells and enables to write 2-bits while keeping the
half-selected bits undisturbed. Simulation results indicate biasing the
half-selected cells by 700mV can enable reading as much as 512-bits while
sustaining 512x512 crossbar with 2.04 years retention. The 2-bit writing
requires pulsing by 50mV to optimize energy.",1606.00470v1
2016-07-15,A versatile rotary-stage high frequency probe station for studying magnetic films and devices,"We present a rotary-stage microwave probe station suitable for magnetic films
and spintronic devices. Two stages, one for field rotation from parallel to
perpendicular to the sample plane (Out-of-Plane) and the other intended for
field rotation within the sample plane (In-Plane) have been designed. The
sample, probes and micro positioners are rotated simultaneously with the
stages, which allows the field orientation to cover $\theta$ from 0 to
$90^{\circ}$ and $\varphi$ from 0 to $360^{\circ}$. $\theta$ and $\varphi$
being the angle between the direction of current flow and field in a
Out-of-Plane and an In-Plane rotation, respectively. The operation frequency is
up to 40 GHz and the magnetic field up to 1 T. The sample holder, vision system
and probe assembly are compactly designed for the probes to land on a wafer
with diameter up to 3$\,$cm. Using homemade multi-pin probes and commercially
available high frequency probes, several applications including 4-probe DC
measurements, the determination of domain wall velocity and spin transfer
torque ferromagnetic resonance are demonstrated.",1607.04356v1
2016-07-28,The Study of Transient Faults Propagation in Multithread Applications,"Whereas contemporary Error Correcting Codes (ECC) designs occupy a
significant fraction of total die area in chip-multiprocessors (CMPs),
approaches to deal with the vulnerability increase of CMP architecture against
Single Event Upsets (SEUs) and Multi-Bit Upsets (MBUs) are sought. In this
paper, we focus on reliability assessment of multithreaded applications running
on CMPs to propose an adaptive application-relevant architecture design to
accommodate the impact of both SEUs and MBUs in the entire CMP architecture.
This work concentrates on leveraging the intrinsic soft-error-immunity feature
of Spin-Transfer Torque RAM (STT-RAM) as an alternative for SRAM-based storage
and operation components. We target a specific portion of working set for
reallocation to improve the reliability level of the CMP architecture design. A
selected portion of instructions in multithreaded program which experience high
rate of referencing with the lowest memory modification are ideal candidate to
be stored and executed in STT-RAM based components. We argue about why we
cannot use STT-RAM for the global storage and operation counterparts and
describe the obtained resiliency compared to the baseline setup. In addition, a
detail study of the impact of SEUs and MBUs on multithreaded programs will be
presented in the Appendix.",1607.08523v1
2016-08-02,Intrinsic optimization using stochastic nanomagnets,"This paper draws attention to a hardware system which can be engineered so
that its intrinsic physics is described by the generalized Ising model and can
encode the solution to many important NP-hard problems as its ground state. The
basic constituents are stochastic nanomagnets which switch randomly between the
$\pm 1$ Ising states and can be monitored continuously with standard
electronics. Their mutual interactions can be short or long range, and their
strengths can be reconfigured as needed to solve specific problems and to
anneal the system at room temperature. The natural laws of statistical
mechanics guide the network of stochastic nanomagnets at GHz speeds through the
collective states with an emphasis on the low energy states that represent
optimal solutions. As proof-of-concept, we present simulation results for
standard NP-complete examples including a 16-city traveling salesman problem
using experimentally benchmarked models for spin-transfer torque driven
stochastic nanomagnets.",1608.00679v2
2016-08-10,Kinetic small angle neutron scattering of the Skyrmion lattice in MnSi,"We report a kinetic small angle neutron scattering study of the skyrmion
lattice (SL) in MnSi. Induced by an oscillatory tilting of the magnetic field
direction, the elasticity and relaxation of the SL along the magnetic field
direction have been measured with microsecond resolution. For the excitation
frequency of 325 Hz the SL begins to track the tilting motion of the applied
magnetic field under tilting angles exceeding $\alpha_c$ > 0.4{\deg}.
Empirically the associated angular velocity of the tilting connects
quantitatively with the critical charge carrier velocity of approx. 0.1mm/s
under current driven spin transfer torques, for which the SL unpins. In
addition, a pronounced temperature dependence of the skyrmion motion is
attributed to the variation of the skyrmion stiffness. Taken together our study
highlights the power of kinetic small angle neutron scattering as a new
experimental tool to explore, in a rather general manner, the elasticity and
impurity pinning of magnetic textures across a wide parameter space without
parasitic signal interferences due to ohmic heating or Oersted magnetic fields.",1608.03156v1
2016-10-31,Amplicification of Voltage Controlled Magnetic Anisotropy Effect with Negative Capacitance,"The high current density required by Magnetic Tunneling Junction (MTJ)
switching driven by Spin Transfer Torque (STT) effect leads to large power
consumption and severe reliability issues therefore hinder the timetable for
STT Magnetic Random Access Memory (STT-MRAM) to mass market. By utilizing
Voltage Controlled Magnetic Anisotropy (VCMA) effect, the MTJ can be switched
by voltage effect and is postulated to achieve ultra-low power (fJ). However,
the VCMA coefficient measured in experiments is far too small for MTJ dimension
below 100 nm. Here in this work, a novel approach for the amplification of VCMA
effect which borrow ideas from negative capacitance is proposed. The
feasibility of the proposal is proved by physical simulation and in-depth
analysis.",1610.09831v1
2017-07-25,Skyrmion mediated voltage controlled switching of ferromagnets for reliable and energy efficient 2-terminal memory,"We propose a two terminal nanomagnetic memory element based on magnetization
reversal of a perpendicularly magnetized nanomagnet employing a unipolar
voltage pulse that modifies the perpendicular anisotropy of the system. Our
work demonstrates that the presence of Dzyaloshinskii-Moriya Interaction (DMI)
can create alternative route for magnetization reversal that obviates the need
for utilizing precessional magnetization dynamics as well as a bias magnetic
field that are employed in traditional voltage control of magnetic anisotropy
(VCMA) based switching of perpendicular magnetization. We show with extensive
micromagnetic simulation, in the presence of thermal noise, that the proposed
skyrmion mediated VCMA switching mechanism is robust at room temperature
leading to extremely low error switching while also being potentially 1-2
orders of magnitude more energy efficient than state of the art spin transfer
torque (STT) based switching.",1707.07777v1
2017-11-02,"Integer, fractional and side band injection locking of spintronic feedback nano-oscillator to microwave signal","In this article we demonstrate the injection locking of recently demonstrated
spintronic feedback nano oscillator to microwave magnetic fields at integers as
well fractional multiples of its auto oscillation frequency. Feedback
oscillators have delay as a new degree of freedom which is absent for
spin-transfer torque based oscillators, which gives rise to side peaks along
with a main peak. We show that it is also possible to lock the oscillator on
its side band peaks, which opens a new avenue to phase locked oscillators with
large frequency differences. We observe that for low driving fields, side band
locking improves the quality factor of the main peak, whereas for higher
driving fields the main peak is suppressed. Further, measurements at two field
angles provide some insight into the role of symmetry of oscillation orbit in
determining the fractional locking.",1711.00691v1
2017-11-18,Mitigating Read-disturbance Errors in STT-RAM Caches by Using Data Compression,"Due to its high density and close-to-SRAM read latency, spin transfer torque
RAM (STT-RAM) is considered one of the most-promising emerging memory
technologies for designing large last level caches (LLCs). However, in deep
sub-micron region, STT-RAM shows read-disturbance error (RDE) whereby a read
operation may modify the stored data value and this presents a severe threat to
performance and reliability of STT-RAM caches. In this paper, we present a
technique, named SHIELD, to mitigate RDE in STT-RAM LLCs. SHIELD uses data
compression to reduce number of read operations from STT-RAM blocks to avoid
RDE and also to reduce the number of bits written to cache during both write
and restore operations. Experimental results have shown that SHIELD provides
significant improvement in performance and energy efficiency. SHIELD consumes
smaller energy than two previous RDE-mitigation techniques, namely high-current
restore required read (HCRR, also called restore-after-read) and low-current
long latency read (LCLL) and even an ideal RDE-free STT-RAM cache.",1711.06790v1
2017-12-23,Shape anisotropy revisited in single-digit nanometer magnetic tunnel junctions,"Nanoscale magnetic tunnel junction plays a pivotal role in magnetoresistive
random access memories. Successful implementation depends on a simultaneous
achievement of low switching current for the magnetization switching by
spin-transfer torque and high thermal stability, along with a continuous
reduction of junction size. Perpendicular-easy-axis CoFeB/MgO stacks possessing
interfacial anisotropy have paved the way down to 20-nm scale, below which a
new approach needs to be explored. Here we show magnetic tunnel junctions that
satisfy the requirements at ultrafine scale by revisiting shape anisotropy,
which is a classical part of magnetic anisotropy but has not been fully
utilized in the current perpendicular systems. Magnetization switching solely
driven by current is achieved for junctions smaller than 10 nm where sufficient
thermal stability is provided by shape anisotropy without adopting new material
systems. This work is expected to push forward the development of magnetic
tunnel junctions towards single-digit-nm-scale nano-magnetics/spintronics.",1712.08774v1
2018-01-09,Influence of image forces on the interlayer exchange interaction in magnetic tunnel junctions with ferroelectric barrier,"We study interlayer exchange interaction in magnetic tunnel junctions with
ferroelectric barrier. We focus on the influence of image forces on the voltage
dependence of the interlayer magnetic interaction (magneto-electric effect).
The influence of the image forces is twofold: 1) they significantly enforce
magneto-electric effect occurring due to the surface charges at the interface
between ferroelectric and ferromagnets; 2) in combination with voltage
dependent dielectric constant of the ferroelectric barrier image forces cause
an additional contribution to the magneto-electric effect in magnetic tunnel
junctions. This contribution can exceed the one coming from surface charges. We
compare the interlayer exchange coupling voltage variation with spin transfer
torque effect and show that for half-metallic electrodes the interlayer
exchange coupling variation is dominant and defines the magnetic state and
dynamics of magnetization in the tunnel junction.",1801.03113v1
2018-03-29,Three-Dimensional Magnetic Page Memory,"The increasing need to store large amounts of information with an
ultra-dense, reliable, low power and low cost memory device is driving
aggressive efforts to improve upon current perpendicular magnetic recording
technology. However, the difficulties in fabricating small grain recording
media while maintaining thermal stability and a high signal-to-noise ratio
motivate development of alternative methods, such as the patterning of magnetic
nano-islands and utilizing energy-assist for future applications. In addition,
both from sensor and memory perspective three-dimensional spintronic devices
are highly desirable to overcome the restrictions on the functionality in the
planar structures. Here we demonstrate a three-dimensional magnetic-memory
(magnetic page memory) based on thermally assisted and stray-field induced
transfer of domains in a vertical stack of magnetic nanowires with
perpendicular anisotropy. Using spin-torque induced domain shifting in such a
device with periodic pinning sites provides additional degrees of freedom by
allowing lateral information flow to realize truly three-dimensional
integration.",1803.11146v1
2018-05-01,Localized charge in various configurations of magnetic domain wall in Weyl semimetal,"We numerically investigate the electronic properties of magnetic domain walls
formed in a Weyl semimetal. Electric charge distribution is computed from the
electron wave functions, by numerically diagonalizing the Hamiltonian under
several types of domain walls. We find a certain amount of electric charge
localized around the domain wall, depending on the texture of the domain wall.
This localized charge stems from the degeneracy of Landau states under the
axial magnetic field, which corresponds to the curl in the magnetic texture.
The localized charge enables one to drive the domain wall motion by applying an
external electric field without injecting an electric current, which is
distinct from the ordinary spin-transfer torque and is free from Joule heating.",1805.00383v1
2018-11-09,Information Theoretic Bounds Based Channel Quantization Design for Emerging Memories,"Channel output quantization plays a vital role in high-speed emerging
memories such as the spin-torque transfer magnetic random access memory
(STT-MRAM), where high-precision analog-to-digital converters (ADCs) are not
applicable. In this paper, we investigate the design of the 1-bit quantizer
which is highly suitable for practical applications. We first propose a
quantized channel model for STT-MRAM. We then analyze various information
theoretic bounds for the quantized channel, including the channel capacity,
cutoff rate, and the Polyanskiy-Poor-Verd\'{u} (PPV) finite-length performance
bound. By using these channel measurements as criteria, we design and optimize
the 1-bit quantizer numerically for the STT-MRAM channel. Simulation results
show that the proposed quantizers significantly outperform the conventional
minimum mean-squared error (MMSE) based Lloyd-Max quantizer, and can approach
the performance of the 1-bit quantizer optimized by error rate simulations.",1811.03832v1
2018-02-28,Ultra-fast artificial neuron: generation of picosecond-duration spikes in a current-driven antiferromagnetic auto-oscillator,"We demonstrate analytically and numerically, that a thin film of an
antiferromagnetic (AFM) material, having biaxial magnetic anisotropy and being
driven by an external spin-transfer torque signal, can be used for the
generation of ultra-short ""Dirac-delta-like"" spikes. The duration of the
generated spikes is several picoseconds for typical AFM materials and is
determined by the in-plane magnetic anisotropy and the effective damping of the
AFM material. The generated output signal can consist of a single spike or a
discrete group of spikes (""bursting""), which depends on the repetition (clock)
rate, amplitude, and shape of the external control signal. The spike generation
occurs only when the amplitude of the control signal exceeds a certain
threshold, similar to the action of a biological neuron in response to an
external stimulus. The ""threshold"" behavior of the proposed AFM spike generator
makes possible its application not only in the traditional microwave signal
processing but also in the future neuromorphic signal processing circuits
working at clock frequencies of tens of gigahertz.",1802.10236v1
2018-08-11,Walker solution for Dzyaloshinskii domain wall in ultrathin ferromagnetic films,"We analyze the electric current and magnetic field driven domain wall motion
in perpendicularly magnetized ultrathin ferromagnetic films in the presence of
interfacial Dzyaloshinskii-Moriya interaction and both out-of-plane and
in-plane uniaxial anisotropies. We obtain exact analytical Walker-type
solutions in the form of one-dimensional domain walls moving with constant
velocity due to both spin-transfer torques and out-of-plane magnetic field.
These solutions are embedded into a larger family of propagating solutions
found numerically. Within the considered model, we find the dependencies of the
domain wall velocity on the material parameters and demonstrate that adding
in-plane anisotropy may produce domain walls moving with velocities in excess
of 500 m/s in realistic materials under moderate fields and currents.",1808.03772v2
2018-12-03,"Mn2V0.5Co0.5Z (Z= Ga, Al) Heusler alloys: Fully compensated ferrimagnets with high Tc and compensation temperature","High TC fully compensated ferrimagnets are potential candidates for spin
transfer torque based spintronic devices. We report the structural and magnetic
properties of high TC fully compensated ferrimagnets Mn2V0.5Co0.5Z where Z is
Ga, Al, in the melt spun ribbon and arc melted bulk form. While the parent
alloys Mn2YZ where Y is V, Co and Z is Ga, Al exhibits a magnetic moment value
around 2 muB per f.u, the Mn2V0.5Co0.5Ga alloy exhibits room temperature nearly
fully compensated moment value of 0.09 and 0.13 muB per f.u. in the bulk and
ribbon form respectively. For Mn2V0.5Co0.5Al this turned out to be 0.04 and
0.08 muB per f.u. In Contrast to the bulk sample's Neel P type ferrimagnetic
behaviour, ribbon samples exhibit Neel N type ferrimagnetic characteristic with
a high compensation temperature of 420 K for Ga alloy and 275 K for Al alloy.
The observed TC values are more than 640 K for all samples. The differences in
the magnetic properties of arc melted and melt spun alloys indicates that even
a slight variation in stoichiometry and sample preparation method can influence
the physical properties of a compensated system.",1812.00714v1
2019-02-08,A Microwave Oscillator Based on a Single Straintronic Magneto-tunneling Junction,"There is growing interest in exploring nanomagnetic devices as potential
replacements for electronic devices (e.g. transistors) in digital switching
circuits and systems. A special class of nanomagnetic devices are switched with
electrically generated mechanical strain leading to electrical control of
magnetism. Straintronic magneto-tunneling junctions (s-MTJ) belong to this
category. Their soft layers are composed of two-phase multiferroics comprising
a magnetostrictive layer elastically coupled to a piezoelectric layer. Here, we
show that a single straintronic magneto-tunneling junction with a passive
resistor can act as a microwave oscillator whose traditional implementation
would have required microwave operational amplifiers, capacitors and resistors.
This reduces device footprint and cost, while improving device reliability.
This is an analog application of magnetic devices where magnetic interactions
(interaction between the shape anisotropy, strain anisotropy, dipolar coupling
field and spin transfer torque in the soft layer of the s-MTJ) are exploited to
implement an oscillator with reduced footprint.",1902.03307v2
2019-06-16,Tunable Magnetic Domain Walls for Therapeutic Neuromodulation at Cellular Level: Stimulating Neurons Through Magnetic Nanowires,"Cellular-level neuron stimulation has attracted much attention in the areas
of prevention, diagnosis and treatment of neurological disorders. Herein, we
propose a spintronic neurostimulator based on the domain wall movement inside
stationary magnetic nanowires driven by the spin transfer torque. The
electromotive forces generated by the domain wall motion can serve as highly
localized stimulation signals for neuron cells. Our simulation results show
that the induced electric field from the domain wall motion in permalloy
nanowires can reach up to 14 V/m, which is well above the reported threshold
stimulation signal for clinical applications. The proposed device operates on a
current range of several uA which is 10^3 times lower compared to magnetic
stimulation by microcoils. The duration and amplitude of the stimulating signal
can be controlled by adjusting the applied current density, the geometry of the
nanowire, and the magnetic properties of the nanowire material.",1906.08701v1
2016-03-18,Voltage-Controlled Low-Energy Switching of Nanomagnets through Ruderman-Kittel-Kasuya-Yosida Interactions for Magnetoelectric Device Applications,"In this letter, we consider through simulation Ruderman-Kittel-Kasuya-Yosida
(RKKY) interactions between nanomagnets sitting on a conductive surface, and
voltage-controlled gating thereof for low-energy switching of nanomagnets for
possible memory and nonvolatile logic applications. For specificity, we
consider nanomagnets with perpendicular anisotropy on a three-dimensional
topological insulator. We model the possibility and dynamics of RKKY-based
switching of one nanomagnet by coupling to one or more nanomagnets of set
orientation. Applications for both memory and nonvolatile logic are considered,
with follower, inverter and majority gate functionality shown. Sub-attojoule
switching energies, far below conventional spin transfer torque (STT)-based
memories and even below CMOS logic appear possible. Switching times on the
order of a few nanoseconds, comparable to times for STT switching, are
estimated for ferromagnetic nanomagnets.",1603.05779v1
2016-03-22,Side Channel Attacks on STTRAM and Low-Overhead Countermeasures,"Spin Transfer Torque RAM (STTRAM) is a promising candidate for Last Level
Cache (LLC) due to high endurance, high density and low leakage. One of the
major disadvantages of STTRAM is high write latency and write current.
Additionally, the latency and current depends on the polarity of the data being
written. These features introduce major security vulnerabilities and expose the
cache memory to side channel attacks. In this paper we propose a novel side
channel attack model where the adversary can monitor the supply current of the
memory array to partially identify the sensitive cache data that is being read
or written. We propose several low cost solutions such as short retention
STTRAM, 1-bit parity, multi-bit random write and constant current write driver
to mitigate the attack. 1-bit parity reduces the number of distinct write
current states by 30% for 32-bit word and the current signature is further
obfuscated by multi-bit random writes. The constant current write makes it more
challenging for the attacker to extract the entire word using a single supply
current signature.",1603.06675v1
2017-10-17,Current-driven thermo-magnetic switching in magnetic tunnel junctions,"We investigate switching of magnetic tunnel junctions (MTJs) driven by the
thermal effect of the transport current through the junctions. The switching
occurs in a specially designed composite free layer, which acts as one of the
MTJ electrodes, and is due to a current-driven ferro-to-paramagnetic Curie
transition with the associated exchange decoupling within the free layer
leading to magnetic reversal. We simulate the current and heat propagation
through the device and show how heat focusing can be used to improve the power
efficiency. The Curie-switch MTJ demonstrated in this work has the advantage of
being highly tunable in terms of its operating temperature range, conveniently
to or just above room temperature, which can be of technological significance
and competitive with the known switching methods using spin-transfer torques.",1710.06311v1
2019-03-05,FUSE: Fusing STT-MRAM into GPUs to Alleviate Off-Chip Memory Access Overheads,"In this work, we propose FUSE, a novel GPU cache system that integrates
spin-transfer torque magnetic random-access memory (STT-MRAM) into the on-chip
L1D cache. FUSE can minimize the number of outgoing memory accesses over the
interconnection network of GPU's multiprocessors, which in turn can
considerably improve the level of massive computing parallelism in GPUs.
Specifically, FUSE predicts a read-level of GPU memory accesses by extracting
GPU runtime information and places write-once-read-multiple (WORM) data blocks
into the STT-MRAM, while accommodating write-multiple data blocks over a small
portion of SRAM in the L1D cache. To further reduce the off-chip memory
accesses, FUSE also allows WORM data blocks to be allocated anywhere in the
STT-MRAM by approximating the associativity with the limited number of tag
comparators and I/O peripherals. Our evaluation results show that, in
comparison to a traditional GPU cache, our proposed heterogeneous cache reduces
the number of outgoing memory references by 32% across the interconnection
network, thereby improving the overall performance by 217% and reducing energy
cost by 53%.",1903.01776v2
2019-03-08,MFM and FORC+ study of switching mechanism in Co$_{25}$Pd$_{75}$ films,"Recent research on CoPd alloys with perpendicular magnetic anisotropy (PMA)
has suggested that they might be useful as the pinning layer in CoFeB/MgO-based
perpendicular magnetic tunnel junctions (pMTJ's) for various spintronic
applications such as spin-torque transfer random access memory (STT-RAM). We
have previously studied the effect of seed layer and composition on the
structure (by XRD, SEM, AFM and TEM) and performance (coercivity) of these CoPd
films. These films do not switch coherently, so the coercivity is determined by
the details of the switching mechanism, which was not studied in our previous
paper. In the present paper, we show that information can be obtained about the
switching mechanism from magnetic force microscopy (MFM) together with first
order reversal curves (FORC), despite the fact that MFM can only be used at
zero field. We find that these films switch by a mechanism of domain nucleation
and dendritic growth into a labyrinthine structure, after which the unreversed
domains gradually shrink to small dots and then disappear.",1903.03568v2
2019-05-30,Interface moment dynamics and its contribution to spin-transfer torque switching process in magnetic tunnel junctions,"A practical problem for memory applications involving perpendicularly
magnetized magnetic tunnel junctions is the reliability of switching
characteristics at high-bias voltage. Often it has been observed that at
high-bias, additional error processes are present that cause a decrease in
switching probability upon further increase of bias voltage. We identify the
main cause of such error-rise process through examination of switching
statistics as a function of bias voltage and applied field, and the junction
switching dynamics in real time. These experiments show a coincidental onset of
error-rise and the presence of a new low-frequency microwave emission well
below that dictated by the anisotropy field. We show that in a few-macrospin
coupled numerical model, this is consistent with an interface region with
concentrated perpendicular anisotropy, and where the magnetic moment has
limited exchange coupling to the rest of the layers. These results point to the
important role high-frequency interface magnetic moment dynamics play in
determining the switching characteristics of these tunnel junction devices.",1905.13253v1
2020-03-26,Energy storage in magnetic textures driven by vorticity flow,"An experimentally feasible energy-storage concept is formulated based on
vorticity (hydro)dynamics within an easy-plane insulating magnet. The free
energy, associated with the magnetic winding texture, is built up in a circular
easy-plane magnetic structure by injecting a vorticity flow in the radial
direction. The latter is accomplished by electrically induced spin-transfer
torque, which pumps energy into the magnetic system in proportion to the vortex
flux. The resultant magnetic metastable state with a finite winding number can
be maintained for a long time because the process of its relaxation via phase
slips is exponentially suppressed when the temperature is well below the Curie
temperature. We propose to characterize the vorticity-current interaction
underlying the energy-loading mechanism through its contribution to the
effective electric inductance in the rf response. Our proposal may open an
avenue for naturally powering spintronic circuits and nontraditional
magnet-based neuromorphic networks.",2003.12121v1
2020-11-11,Role of impurity clusters for the current-driven motion of magnetic Skyrmions,"We study how impurities influence the current-induced dynamics of magnetic
Skyrmions moving in a racetrack geometry. For this, we solve numerically the
generalized Landau-Lifshitz-Gilbert equation extended by the current-induced
spin transfer torque. In particular, we investigate two classes of impurities,
non-conducting and magnetic impurities. The former are magnetically rigid
objects and yield to an inhomogeneous current density over the racetrack which
we determine separately by solving the fundamental electrostatic equations. In
contrast, magnetic impurities leave the applied current density homogeneous
throughout the stripe. Depending on parameters, we observe four different
scenarios of Skyrmion motions in the presence of disorder, the Skyrmion decay,
the pinning, the creation of additional Skyrmions, and ordinary Skyrmion
passage. We calculate and discuss phase diagrams in dependence of the impurity
concentration and radii of the impurities.",2011.06027v1
2020-11-17,Ultra-efficient magnetism modulation in a Weyl ferromagnet by current-assisted domain wall motion,"Flexible and efficient manipulation of magnetic configurations can be
challenging. In the design of practical devices, achieving a high effective
magnetic field with a low working current is under tight demand. Here, we
report a unique method for efficient magnetism modulation by direct current
injection in magnetic Weyl semimetal Co3Sn2S2. We demonstrate that the
modulation process stems from current-assisted domain wall motion. Through two
independent methods, we reveal that the spin-transfer torque efficiency of
Co3Sn2S2 reaches as high as 2.4-5.6 kOe MA^(-1) cm^2, and the threshold current
density for driving the magnetic domain walls is as low as <5.1*10^5 A/cm^2
without an external field, and <1.5*10^5 A/cm^2 with a moderate external field.
Our findings manifest a new and powerful approach for sub-micron magnetism
manipulation, and also open the door towards a new paradigm of spintronics that
combines magnetism, topology, and metallicity for low-energy consumption memory
and computing.",2011.08391v2
2021-10-12,Magnetization dynamics in the density matrix formalism,"Magnetization dynamics described by the Landau-Lifshitz-Gilbert-Slonczewski
(LLGS) equation can be formulated to have the form of the well-known
two-level-system (TLS) equations. Recently, we showed that a DC spin-transfer
torque (STT) term in the LLGS equation can be mapped to a modulation of the
carrier relaxation rates in the analogous TLS equations. Here, we extend the
analogy to the TLS dynamics by including the AC magnetic field, AC
demagnetization field, and AC STT excitation that we show constitute the
interaction term in the analogous TLS picture. Interestingly, we find that the
carrier injection rate in the TLS equations that is responsible for transitions
between the excited and ground states of the system naturally translates to an
intense short magnetic pulse that reverses the magnetization state.
Furthermore, we also show that the two helicities of circularly polarized
magnetic pulses correspond to the two carrier injection rates in the analogous
TLS picture. In the context of the highly debated all-optical helicity
dependent switching experiment, it offers a new explanation of the
magnetization reversal from first principles.",2110.06138v3
2016-11-07,Compactness results for static and dynamic chiral skyrmions near the conformal limit,"We examine lower order perturbations of the harmonic map prob- lem from
$\mathbb{R}^2$ to $\mathbb{S}^2$ including chiral interaction in form of a
helicity term that prefers modulation, and a potential term that enables decay
to a uniform background state. Energy functionals of this type arise in the
context of magnetic systems without inversion symmetry. In the almost conformal
regime, where these perturbations are weighted with a small parameter, we
examine the existence of relative minimizers in a non-trivial homotopy class,
so-called chiral skyrmions, strong compactness of almost minimizers, and their
asymptotic limit. Finally we examine dynamic stability and compactness of
almost minimizers in the context of the Landau-Lifshitz-Gilbert equation
including spin-transfer torques arising from the interaction with an external
current.",1611.01984v1
2017-01-23,Understanding stability diagram of perpendicular magnetic tunnel junctions,"Perpendicular magnetic tunnel junctions (MTJ) with a bottom pinned reference
layer and a composite free layer (FL) are investigated. Different thicknesses
of the FL were tested to obtain an optimal balance between tunneling
magnetoresistance (TMR) ratio and perpendicular magnetic anisotropy. After
annealing at 400 $^\circ$C, the TMR ratio for 1.5 nm thick CoFeB sublayer
reached 180 % at room temperature and 280 % at 20 K with an MgO tunnel barrier
thickness corresponding to the resistance area product RA = 10
Ohm$\mathrm{\mu}$m$^2$. The voltage vs. magnetic field stability diagrams
measured in pillar-shaped MTJs with 130 nm diameter indicate the competition
between spin transfer torque (STT), voltage controlled magnetic anisotropy
(VCMA) and temperature effects in the switching process. An extended stability
phase diagram model that takes into account all three parameters and the
effective damping measured independently using broadband ferromagnetic
resonance technique enabled the determination of both STT and VCMA coefficients
that are responsible for the FL magnetization switching.",1701.06411v1
2017-04-17,A Study on Performance and Power Efficiency of Dense Non-Volatile Caches in Multi-Core Systems,"In this paper, we present a novel cache design based on Multi-Level Cell
Spin-Transfer Torque RAM (MLC STTRAM) that can dynamically adapt the set
capacity and associativity to use efficiently the full potential of MLC STTRAM.
We exploit the asymmetric nature of the MLC storage scheme to build cache lines
featuring heterogeneous performances, that is, half of the cache lines are
read-friendly, while the other is write-friendly. Furthermore, we propose to
opportunistically deactivate ways in underutilized sets to convert MLC to
Single-Level Cell (SLC) mode, which features overall better performance and
lifetime. Our ultimate goal is to build a cache architecture that combines the
capacity advantages of MLC and performance/energy advantages of SLC. Our
experiments show an improvement of 43% in total numbers of conflict misses, 27%
in memory access latency, 12% in system performance, and 26% in LLC access
energy, with a slight degradation in cache lifetime (about 7%) compared to an
SLC cache.",1704.05044v1
2019-04-19,Energy-Efficient Runtime Adaptable L1 STT-RAM Cache Design,"Much research has shown that applications have variable runtime cache
requirements. In the context of the increasingly popular Spin-Transfer Torque
RAM (STT-RAM) cache, the retention time, which defines how long the cache can
retain a cache block in the absence of power, is one of the most important
cache requirements that may vary for different applications. In this paper, we
propose a Logically Adaptable Retention Time STT-RAM (LARS) cache that allows
the retention time to be dynamically adapted to applications' runtime
requirements. LARS cache comprises of multiple STT-RAM units with different
retention times, with only one unit being used at a given time. LARS
dynamically determines which STT-RAM unit to use during runtime, based on
executing applications' needs. As an integral part of LARS, we also explore
different algorithms to dynamically determine the best retention time based on
different cache design tradeoffs. Our experiments show that by adapting the
retention time to different applications' requirements, LARS cache can reduce
the average cache energy by 25.31%, compared to prior work, with minimal
overheads.",1904.09363v1
2019-07-08,Skyrmion Racetrack memory with an antidot,"Skyrmion racetrack memory has a lots of potential in future non-volatile
solid state devices. In general such devices require current to nucleate
skyrmions via spin transfer torque (STT) effect. Further the current is also
required to drive the skyrmions in the nanowire device. However the current
applied during nucleation of successive skyrmions may have unwanted
perturbation \emph{viz.} Joule heating and skyrmion Hall effect, on the
propagation of previously generated skyrmions. Therefore new methodology is
required to decouple the generation and propagation of skyrmions. Here we
present a novel route via micromagnetic simulation for generation of skyrmions
from triangular antidot structure in a ferromagnetic nanotrack using local
oersted field. Antidots are holes in a magnetic nanoelement. Controlled
skyrmion injection can be achieved by tuning the dimensions of the antidots
that are placed at either end of the nanotrack. Multiple skyrmions can be
simultaneously generated by incorporating more number of antidots. Here we
propose a novel design to realise skyrmionic racetrcak memory where one can
individually generate and manipulate the skyrmions within the nanotrack.",1907.03449v2
2019-07-23,Intrinsic Picosecond Magnetic Switching Mechanism Assisted by an Electric Field in a Synthetic Antiferromagnetic Structure,"The processional switching mechanism governs magnetic switching in magnetic
tunnel junctions (MTJs) in the sub-nanosecond range, which limits the
application of spin transfer torque magnetic random access memory (STT-MRAM) in
the ultrafast region. In this paper, we propose a new picosecond magnetic
switching mechanism in a synthetic antiferromagnetic (SAF) structure using the
adjustable Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction controlled by an
external electric field (E-field). It is shown that along with the sign change
of the RKKY interaction in the SAF structure with an external E-field, the
critical switching current density can be significantly reduced by one order of
magnitude compared to that of a normal MTJ design at 100 ps; thus, this novel
STT-MRAM can be written with a very low switching current density to avoid the
MTJ breakdown problem and reduce the writing energy. To understand the physical
origin of this abnormal phenomenon, a toy model is proposed in which the
external-E-field-controlled sign change of the RKKY interaction in the SAF
structure provides an extra contribution to the total energy that helps
thespins overcome the energy barrier and break the processional switching
mechanism.",1907.09861v1
2019-08-06,Superparamagnetic dwell times and tuning of switching rates in perpendicular CoFeB/MgO/CoFeB tunnel junctions,"Thin electrodes of magnetic tunnel junctions can show superparamagnetism at
surprisingly low temperature. We analysed their thermally induced switching for
varying temperature, magnetic and electric field. Although the dwell times
follow an Arrhenius law, they are orders of magnitude too small compared to a
model of single domain activation. Including entropic effects removes this
inconsistency and leads to a magnetic activation volume much smaller than that
of the electrode. Comparing data for varying barrier thickness then allows to
separate the impact of Zeman energy, spin-transfer-torque and voltage induced
anisotropy change on the dwell times. Based on these results, we demonstrate a
tuning of the switching rates by combining magnetic and electric fields, which
opens a path for their application in noisy neural networks.",1908.02139v3
2019-08-08,Energy and Performance Analysis of STTRAM Caches for Mobile Applications,"Spin-Transfer Torque RAMs (STTRAMs) have been shown to offer much promise for
implementing emerging cache architectures. This paper studies the viability of
STTRAM caches for mobile workloads from the perspective of energy and latency.
Specifically, we explore the benefits of reduced retention STTRAM caches for
mobile applications. We analyze the characteristics of mobile applications'
cache blocks and how those characteristics dictate the appropriate retention
time for mobile device caches. We show that due to their inherently interactive
nature, mobile applications' execution characteristics---and hence, STTRAM
cache design requirements---differ from other kinds of applications. We also
explore various STTRAM cache designs in both single and multicore systems, and
at different cache levels, that can efficiently satisfy mobile applications'
execution requirements, in order to maximize energy savings without introducing
substantial latency overhead.",1908.04744v1
2019-09-26,"Storage Class Memory: Principles, Problems, and Possibilities","Storage Class Memory (SCM) is a class of memory technology which has recently
become viable for use. Their namearises from the fact that they exhibit
non-volatility of data, similar to secondary storage while also having
latencies comparable toprimary memory and byte-addressibility. In this area,
Phase Change Memory (PCM), Spin-Transfer-Torque Random Access Memory(STT-RAM),
and Resistive RAM (ReRAM) have emerged as the major contenders for commercial
and industrial use. In this paper, wedescribe how these memory types function,
while highlighting the problems of endurance and performance that these memory
typesface. We also discuss the future possibilities of Multi-Level Cells
(MLCs), as well as how SCM can be used to construct accelerators.",1909.12221v1
2019-10-01,A Novel Low Power Non-Volatile SRAM Cell with Self Write Termination,"A non-volatile SRAM cell is proposed for low power applications using Spin
Transfer Torque-Magnetic Tunnel Junction (STT-MTJ) devices. This novel cell
offers non-volatile storage, thus allowing selected blocks of SRAM to be
switched off during standby operation. To further increase the power savings, a
write termination circuit is designed which detects completion of MTJ write and
closes the bidirectional current path for the MTJ. A reduction of 25.81% in the
number of transistors and a reduction of 2.95% in the power consumption is
achieved in comparison to prior work on write termination circuits.",1910.04683v1
2020-01-15,"Survey on STT-MRAM Testing: Failure Mechanisms, Fault Models, and Tests","As one of the most promising emerging non-volatile memory (NVM) technologies,
spin-transfer torque magnetic random access memory (STT-MRAM) has attracted
significant research attention due to several features such as high density,
zero standby leakage, and nearly unlimited endurance. However, a high-quality
test solution is required prior to the commercialization of STT-MRAM. In this
paper, we present all STT-MRAM failure mechanisms: manufacturing defects,
extreme process variations, magnetic coupling, STT-switching stochasticity, and
thermal fluctuation. The resultant fault models including permanent faults and
transient faults are classified and discussed. Moreover, the limited test
algorithms and design-for-testability (DfT) designs proposed in the literature
are also covered. It is clear that test solutions for STT-MRAMs are far from
well established yet, especially when considering a defective part per billion
(DPPB) level requirement. We present the main challenges on the STT-MRAM
testing topic at three levels: failure mechanisms, fault modeling, and test/DfT
designs.",2001.05463v1
2020-06-24,Periodic structure of memory function in spintronics reservoir with feedback current,"The role of the feedback effect on physical reservoir computing is studied
theoretically by solving the vortex-core dynamics in a nanostructured
ferromagnet. Although the spin-transfer torque due to the feedback current
makes the vortex dynamics complex, it is clarified that the feedback effect
does not always contribute to the enhancement of the memory function in a
physical reservoir. The memory function, characterized by the correlation
coefficient between the input data and the dynamical response of the vortex
core, becomes large when the delay time of the feedback current is not an
integral multiple of the pulse width. On the other hand, the memory function
remains small when the delay time is an integral multiple of the pulse width.
As a result, a periodic behavior for the short-term memory capacity is observed
with respect to the delay time, the phenomenon of which can be attributed to
correlations between the virtual neurons via the feedback current.",2006.13404v1
2020-07-07,Combing the helical phase of chiral magnets with electric currents,"The competition between the ferromagnetic exchange interaction and
anti-symmetric Dzyaloshinskii-Moriya interaction can stabilize a helical phase
or support the formation of skyrmions. In thin films of chiral magnets, the
current density can be large enough to unpin the helical phase and reveal its
nontrivial dynamics. We theoretically study the dynamics of the helical phase
under spin-transfer torques that reveal distinct orientation processes, driven
by topological defects in the bulk or induced by edges, limited by
instabilities at higher currents. Our experiments confirm the possibility of
on-demand switching the helical orientation by current pulses. This helical
orientation might serve as a novel order parameter in future spintronics
applications.",2007.03414v3
2020-07-14,Dynamics of chiral solitons driven by polarized currents in monoaxial helimagnets,"Chiral solitons are one dimensional localized magnetic structures that are
metastable in some ferromagnetic systems with Dzyaloshinskii-Moriya
interactions and/or uniaxial magnetic anisotropy. Though topological textures
in general provide a very interesting playground for new spintronics phenomena,
how to properly create and control single chiral solitons is still unclear. We
show here that chiral solitons in monoaxial helimagnets, characterized by a
uniaxial Dzyaloshinskii-Moriya interaction, can be stabilized with external
magnetic fields. Once created, the soliton moves steadily in response to a
polarized electric current, provided the induced spin-transfer torque has a
dissipative (nonadiabatic) component. The structure of the soliton depends on
the applied current density in such a way that steady motion exists only if the
applied current density is lower than a critical value, beyond which the
soliton is no longer stable.",2007.07123v2
2021-03-30,Nematic and smectic stripe phases and stripe-SkX transformations,"Based on the findings of stripe skyrmions and the metastability of a state of
an arbitrary number of skyrmions, precisely controlled manipulation of stripe
skyrmions in pre-designed structures and mutual transformation between helical
states and skyrmion crystals (SkXs) are demonstrated in chiral magnetic films.
As a proof of the concept, we show how to use patterned magnetic fields and
spin-transfer torques (STTs) to generate nematic and smectic stripe phases, as
well as ""UST"" mosaic from three curved stripe skyrmions. Cutting one stripe
into many pieces and coalescing several skyrmions into one by various external
fields are good ways to transform helical states and SkXs from each other.",2103.16052v2
2021-05-08,A Fokker-Planck Approach for Modeling the Stochastic Phenomena in Magnetic and Resistive Random Access Memory Devices,"Embedded non-volatile memory technologies such as resistive random access
memory (RRAM) and spin-transfer torque magnetic RAM (STT MRAM) are increasingly
being researched for application in neuromorphic computing and hardware
accelerators for AI. However, the stochastic write processes in these memory
technologies affect their yield and need to be studied alongside process
variations, which drastically increase the complexity of yield analysis using
the Monte Carlo approach. Therefore, we propose an approach based on the
Fokker-Planck equation for modeling the stochastic write processes in STT MRAM
and RRAM devices. Moreover, we show that our proposed approach can reproduce
the experimental results for both STT-MRAM and RRAM devices.",2105.03691v3
2021-06-09,A Compact Model for Scalable MTJ Simulation,"This paper presents a physics-based modeling framework for the analysis and
transient simulation of circuits containing Spin-Transfer Torque (STT) Magnetic
Tunnel Junction (MTJ) devices. The framework provides the tools to analyze the
stochastic behavior of MTJs and to generate Verilog-A compact models for their
simulation in large VLSI designs, addressing the need for an industry-ready
model accounting for real-world reliability and scalability requirements.
Device dynamics are described by the Landau-Lifshitz-Gilbert-Slonczewsky
(s-LLGS ) stochastic magnetization considering Voltage-Controlled Magnetic
Anisotropy (VCMA) and the non-negligible statistical effects caused by thermal
noise. Model behavior is validated against the OOMMF magnetic simulator and its
performance is characterized on a 1-Mb 28 nm Magnetoresistive-RAM (MRAM) memory
product.",2106.04976v1
2021-12-10,Synchronous Unsupervised STDP Learning with Stochastic STT-MRAM Switching,"The use of analog resistance states for storing weights in neuromorphic
systems is impeded by fabrication imprecision and device stochasticity that
limit the precision of synapse weights. This challenge can be resolved by
emulating analog behavior with the stochastic switching of the binary states of
spin-transfer torque magnetoresistive random-access memory (STT-MRAM). However,
previous approaches based on STT-MRAM operate in an asynchronous manner that is
difficult to implement experimentally. This paper proposes a synchronous
spiking neural network system with clocked circuits that perform unsupervised
learning leveraging the stochastic switching of STT-MRAM. The proposed system
enables a single-layer network to achieve 90% inference accuracy on the MNIST
dataset.",2112.05707v1
2022-05-25,Current-Controlled Topological Magnetic Transformations in a Nanostructured Kagome Magnet,"Topological magnetic charge Q is a fundamental parameter that describes the
magnetic domains and determines their intriguing electromagnetic properties.
The ability to switch Q in a controlled way by electrical methods allows for
flexible manipulation of electromagnetic behavior in future spintronic devices.
Here we report the room-temperature current-controlled topological magnetic
transformations between Q = -1 skyrmions and Q = 0 stripes or type-II bubbles
in a kagome crystal Fe$_3$Sn$_2$. We show that the reproducible and reversible
skyrmion-bubble and skyrmion-stripe transformations can be achieved by tuning
the density of nanosecond pulsed current of the order of ~10$^{10}$ A$^{-2}$.
Further numerical simulations suggest that spin-transfer torque combined with
Joule thermal heating effects determine the current-induced topological
magnetic transformations.",2205.12426v1
2022-08-16,EXTENT: Enabling Approximation-Oriented Energy Efficient STT-RAM Write Circuit,"Spin Transfer Torque Random Access Memory (STT-RAM) has garnered interest due
to its various characteristics such as non-volatility, low leakage power, high
density. Its magnetic properties have a vital role in STT switching operations
through thermal effectiveness. A key challenge for STT-RAM in industrial
adaptation is the high write energy and latency. In this paper, we overcome
this challenge by exploiting the stochastic switching activity of STT-RAM cells
and, in tandem, with circuit-level approximation. We enforce the robustness of
our technique by analyzing the vulnerability of write operation against
radiation-induced soft errors and applying a low-cost improvement. Due to
serious reliability challenges in nanometer-scale technology, the robustness of
the proposed circuit is also analyzed in the presence of CMOS and magnetic
tunnel junction (MTJ) process variation. Compared to the state-of-the-art, we
achieved 33.04% and 5.47% lower STT-RAM write energy and latency, respectively,
with a 3.7% area overhead, for memory-centric applications.",2208.07838v1
2022-09-13,Skyrmion Echo in a system of interacting Skyrmions,"We consider helical rotation of skyrmions confined in the potentials formed
by nano-disks. Based on numerical and analytical calculations we propose the
skyrmion echo phenomenon. The physical mechanism of the skyrmion echo formation
is also proposed. Due to the distortion of the lattice, impurities, or pinning
effect, confined skyrmions experience slightly different local fields, which
leads to dephasing of the initial signal. The interaction between skyrmions
also can contribute to the dephasing process. However, switching the
magnetization direction in the nanodiscs (e.g. by spin transfer torque) also
switches the helical rotation of the skyrmions from clockwise to anticlockwise
(or vice-versa), and this restores the initial signal (which is the essence of
skyrmion echo).",2209.05925v1
2022-12-22,The role of damping rate amplitude in the synchronization of two coupled oscillators,"We investigate the synchronization phenomenon between two Spin-transfer
Torque Nano-Oscillators (STNOs) of different frequencies in two pillar systems
under vortex configuration detunings or driving frequencies. The oscillators'
mutual synchronization occurs through magnetic dipolar interaction. Our
micromagnetic simulations show that an amplitude fluctuation referred to as
$\Gamma_p$ has a significant impact on determining the synchronization
frequency. The evolution of frequency and amplitude fluctuation rate in two
different oscillator sizes versus external perpendicular field are compared and
discussed. Our results reveal that the oscillator with lower $\Gamma_p$,
referred to as the ""Leader"" oscillator, leads the synchronization process. As
such, the ""follower"" oscillator adjusts its frequency as to that of the
""Leader"", thus achieving synchronization. We believe that taking $\Gamma_p$
into consideration can help in controlling synchronization frequencies in
future building blocks of any network multi-array spintronics' devices.",2212.11521v1
2023-01-15,Anisotropic angle-dependent Andreev reflection at the ferromagnet/superconductor junction on the surface of topological insulators,"We theoretically demonstrate that a ferromagnetic/superconductor junction on
the surface of three-dimensional topological insulators (3D TIs) has an
anisotropic angle-dependent Andreev reflection when the in-plane magnetization
has a component perpendicular to the junction. In the presence of in-plane
magnetization, the Dirac cone's location adjusts in the $k$-space, whereas its
out-of-plane component induces a gap. This movement leads to the anisotropic
angle-dependent Andreev reflection and creates transverse conductance flows
parallel to the interface. Also, an indirect gap induces in the junction, which
removes the transport signatures of Majorana bound states. Because of the full
spin-momentum locking of Dirac fermions on the surface of 3DTIs, a torque that
called \textit{Andreev Transfer Torque} (ATT) imposes on the junction.
Moreover, we propose a setup to detect them experimentally.",2301.06137v1
2023-02-08,Stabilizing skyrmions in stepped magnetic devices for multistate memory,"The dynamics and stability of magnetic skyrmions within a nano-track with
multiple confinements are investigated. Firstly, the motion of a single
skyrmion under spin transfer torque (STT) is studied. By accurately adjusting
the current pulse magnitude and width, the study reveals the possibility to pin
and stabilize the skyrmion in each confinement. Due to the Hall angle, the
depining of the skyrmion from the top confinement requires two pulses with
adjustable time delay while a single pulse is enough to depin it for the case
of bottom confinement. In the case of two skyrmions, once one is pinned in one
confinement, the second one stabilizes in the nearest available empty state and
no more than one skyrmion could be seen in single confinement. Finally and for
further confirmation of this behavior, the motion of a large number of
skyrmions is investigated under the same conditions. The results show that a
multistate device could be obtained with still the existence of only one
skyrmion per state. The skyrmions could be displaced along the nano-track until
their annihilation at the end of the device.",2302.04131v1
2023-03-08,Dextrous Tactile In-Hand Manipulation Using a Modular Reinforcement Learning Architecture,"Dextrous in-hand manipulation with a multi-fingered robotic hand is a
challenging task, esp. when performed with the hand oriented upside down,
demanding permanent force-closure, and when no external sensors are used. For
the task of reorienting an object to a given goal orientation (vs. infinitely
spinning it around an axis), the lack of external sensors is an additional
fundamental challenge as the state of the object has to be estimated all the
time, e.g., to detect when the goal is reached. In this paper, we show that the
task of reorienting a cube to any of the 24 possible goal orientations in a
${\pi}$/2-raster using the torque-controlled DLR-Hand II is possible. The task
is learned in simulation using a modular deep reinforcement learning
architecture: the actual policy has only a small observation time window of
0.5s but gets the cube state as an explicit input which is estimated via a deep
differentiable particle filter trained on data generated by running the policy.
In simulation, we reach a success rate of 92% while applying significant domain
randomization. Via zero-shot Sim2Real-transfer on the real robotic system, all
24 goal orientations can be reached with a high success rate.",2303.04705v1
2023-05-25,Energetic perspective on emergent inductance exhibited by magnetic textures in the pinned regime,"Spatially varying magnetic textures can exhibit electric-current-induced
dynamics as a result of the spin-transfer torque effect. When such a magnetic
system is electrically driven, an electric field is generated, which is called
the emergent electric field. In particular, when magnetic-texture dynamics are
induced under the application of an AC electric current, the emergent electric
field also appears in an AC manner, notably, with an out-of-phase time profile,
thus exhibiting inductor behaviour, often called an emergent inductor. Here we
show that the emergent inductance exhibited by magnetic textures in the pinned
regime can be explained in terms of the current-induced energy stored in the
magnetic system. We numerically find that the inductance values defined from
the emergent electric field and the current-induced magnetization-distortion
energy, respectively, are in quantitative agreement in the so-called adiabatic
limit. Our findings indicate that emergent inductors retain the basic concept
of conventional inductors; that is, the energy is stored under the application
of electric current.",2305.16123v2
2023-07-19,Controlling stable Bloch points with electric currents,"The Bloch point is a point singularity in the magnetisation configuration,
where the magnetisation vanishes. It can exist as an equilibrium configuration
and plays an important role in many magnetisation reversal processes. In the
present work, we focus on manipulating Bloch points in a system that can host
stable Bloch points - a two-layer FeGe nanostrip with opposite chirality of the
two layers. We drive Bloch points using spin-transfer torques and find that
Bloch points can move collectively without any Hall effect and report that
Bloch points are repelled from the sample boundaries and each other. We study
pinning of Bloch points at wedge-shaped constrictions (notches) in the
nanostrip and demonstrate that arrays of Bloch points can be moved past a
series of notches in a controlled manner by applying consecutive current pulses
of different strength. Finally, we simulate a T-shaped geometry and demonstrate
that a Bloch point can be moved along different paths by applying current
between suitable strip ends.",2307.10170v1
2023-07-26,An Asynchronous and Low-Power True Random Number Generator using STT-MTJ,"The emerging Spin Transfer Torque Magnetic Tunnel Junction (STT-MTJ)
technology exhibits interesting stochastic behavior combined with small area
and low operation energy. It is, therefore, a promising technology for security
applications, specifically the generation of random numbers. In this paper,
STT-MTJ is used to construct an asynchronous true random number generator
(TRNG) with low power and a high entropy rate. The asynchronous design enables
decoupling of the random number generation from the system clock, allowing it
to be embedded in low-power devices. The proposed TRNG is evaluated by a
numerical simulation, using the Landau-Lifshitz-Gilbert (LLG) equation as the
model of the STT-MTJ devices. Design considerations, attack analysis, and
process variation are discussed and evaluated. We show that our design is
robust to process variation, achieving an entropy generating rate between
99.7Mbps and 127.8Mbps with 6-7.7 pJ per bit for 90% of the instances.",2307.14476v1
2023-09-12,Anisotropy-assisted magnon condensation in ferromagnetic thin films,"We theoretically demonstrate that adding an easy-axis magnetic anisotropy
facilitates magnon condensation in thin yttrium iron garnet (YIG) films.
Dipolar interactions in a quasi-equilibrium state stabilize room-temperature
magnon condensation in YIG. Even though the out-of-plane easy-axis anisotropy
generally competes with the dipolar interactions, we show that adding such
magnetic anisotropy may even assist the generation of the magnon condensate
electrically via the spin transfer torque mechanism. We use analytical
calculations and micromagnetic simulations to illustrate this effect. Our
results may explain the recent experiment on Bi-doped YIG and open a pathway
toward applying current-driven magnon condensation in quantum spintronics.",2309.05982v3
2023-12-08,Dipolar coupled core-shell perpendicular shape anisotropy MTJ with enhanced write speed and reduced cross-talk,"The concept of Perpendicular Shape-Anisotropy Spin-Transfer-Torque Magnetic
Random-Access Memory tackles the downsize scalability limit of conventional
ultrathin magnetic tunnel junctions (MTJ) below sub-20 nm technological nodes.
This concept uses a thicker storage layer with a vertical aspect ratio,
enhancing the thermal stability factor thanks to the favorable contribution of
the shape anisotropy. However, the increased aspect ratio comes with an
increase in switching time under applied voltage and the cross-over to
non-uniform reversal mechanism at higher aspect ratio, limiting the gain in
scalability. Additionally, the larger volume of the magnetic cell significantly
increases the stray field acting on the neighboring devices compared to thin
MTJs. In this work, we propose the use of a dipolar-coupled core-shell system
as a storage layer. This improves both bottlenecks, as predicted by
micromagnetic simulations for magnetisation reversal, and a macrospin model to
estimate the stray field in a dense array.",2312.05245v1
2024-01-26,HOPE: Holistic STT-RAM Architecture Exploration Framework for Future Cross-Platform Analysis,"Spin Transfer Torque Random Access Memory (STT-RAM) is an emerging
Non-Volatile Memory (NVM) technology that has garnered attention to overcome
the drawbacks of conventional CMOS-based technologies. However, such
technologies must be evaluated before deployment under real workloads and
architecture. But there is a lack of available open-source STT-RAM-based system
evaluation framework, which hampers research and experimentation and impacts
the adoption of STT- RAM in a system. This paper proposes a novel, extendable
STT-RAM memory controller design integrated inside the gem5 simulator. Our
framework enables understanding various aspects of STT-RAM, i.e., power, delay,
clock cycles, energy, and system throughput. We will open-source our HOPE
framework, which will fuel research and aid in accelerating the development of
future system architectures based on STT-RAM. It will also facilitate the user
for further tool enhancement.",2401.14888v1
2024-02-25,Effect of Magnetic Anisotropy Constants on Skyrmion Formation in Co/Pt,"Skyrmions, which are topologically stable magnetic structures, have
manifested promising features to be used as an information carrier in new-age,
non-volatile data storage devices. In this article, we show how the creation
and stability of skyrmion can be manipulated by external stimuli (here,
nano-second current pulse). Co/Pt square nano-structure with Co free layer
thickness in the range 1 nm to 5 nm and first and second-order anisotropy
constants are taken to study the controlled creation of skyrmions. The
magnetization dynamics controlled by the current-induced spin transfer torque
help to nucleate skyrmions by transformation from perpendicularly magnetized
ground state to a stable state of isolated skyrmions via complex transformation
of Neel wall following its image inversion. Compared with the first-order
anisotropy alone, how the higher-order anisotropy constants (up to second
order) impact the relaxed state of a system has been discussed.",2402.16060v1
2024-03-12,Ferrimagnetic Heusler tunnel junctions with fast spin-transfer torque switching enabled by low magnetization,"Magnetic random access memory that uses magnetic tunnel junction memory cells
is a high performance, non-volatile memory technology that goes beyond
traditional charge-based memories. Today its speed is limited by the high
magnetization of the memory storage layer. Here we show that fast and highly
reliable switching is possible using a very low magnetization ferrimagnetic
Heusler alloy, Mn3Ge. Moreover, the tunneling magnetoresistance is the highest
yet achieved for a ferrimagnetic material at ambient temperature. Furthermore,
the devices were prepared on technologically relevant amorphous substrates
using a novel combination of a nitride seed layer and a chemical templating
layer. These results show a clear path to the lowering of switching currents
using ferrimagnetic Heusler materials and, therefore, to the scaling of high
performance magnetic random access memories beyond those nodes possible with
ferromagnetic devices.",2403.08112v1
2010-08-11,Theory for a dissipative droplet soliton excited by a spin torque nanocontact,"A novel type of solitary wave is predicted to form in spin torque oscillators
when the free layer has a sufficiently large perpendicular anisotropy. In this
structure, which is a dissipative version of the conservative droplet soliton
originally studied in 1977 by Ivanov and Kosevich, spin torque counteracts the
damping that would otherwise destroy the mode. Asymptotic methods are used to
derive conditions on perpendicular anisotropy strength and applied current
under which a dissipative droplet can be nucleated and sustained. Numerical
methods are used to confirm the stability of the droplet against various
perturbations that are likely in experiments, including tilting of the applied
field, non-zero spin torque asymmetry, and non-trivial Oersted fields. Under
certain conditions, the droplet experiences a drift instability in which it
propagates away from the nanocontact and is then destroyed by damping.",1008.1898v1
2012-01-19,What Sets the Initial Rotation Rates of Massive Stars?,"The physical mechanisms that set the initial rotation rates in massive stars
are a crucial unknown in current star formation theory. Observations of young,
massive stars provide evidence that they form in a similar fashion to their
low-mass counterparts. The magnetic coupling between a star and its accretion
disk may be sufficient to spin down low-mass pre-main sequence (PMS) stars to
well below breakup at the end stage of their formation when the accretion rate
is low. However, we show that these magnetic torques are insufficient to spin
down massive PMS stars due to their short formation times and high accretion
rates. We develop a model for the angular momentum evolution of stars over a
wide range in mass, considering both magnetic and gravitational torques. We
find that magnetic torques are unable to spin down either low or high mass
stars during the main accretion phase, and that massive stars cannot be spun
down significantly by magnetic torques during the end stage of their formation
either. Spin-down occurs only if massive stars' disk lifetimes are
substantially longer or their magnetic fields are much stronger than current
observations suggest.",1201.4186v1
2014-01-05,Spin torque building blocks,"The discovery of the spin torque effect has made magnetic nanodevices
realistic candidates for active elements of memory devices and applications.
Magnetoresistive effects allow the read-out of increasingly small magnetic
bits, and the spin torque provides an efficient tool to manipulate - precisely,
rapidly and at low energy cost - the magnetic state, which is in turn the
central information medium of spintronic devices. By keeping the same magnetic
stack, but by tuning a device's shape and bias conditions, the spin torque can
be engineered to build a variety of advanced magnetic nanodevices. Here we show
that by assembling these nanodevices as building blocks with different
functionalities, novel types of computing architectures can be envisisaged. We
focus in particular on recent concepts such as magnonics and spintronic neural
networks.",1401.0874v1
2015-01-09,Spin Hall Switching of the Magnetization in Ta/TbFeCo Structures with Bulk Perpendicular Anisotropy,"Spin-orbit torques are studied in Ta/TbFeCo patterned structures with a bulk
perpendicular magnetic anisotropy (bulk-PMA) for the first time. The
current-induced magnetization switching is investigated in the presence of a
perpendicular, longitudinal, or transverse field. In order to rule out Joule
heating effect, switching of the magnetization is also demonstrated using
current pulses. It is found that the anti-damping torque correlated with spin
Hall effect is very strong, and a spin Hall angle of about 0.12 is obtained.
The field-like torque related with Rashba effect is negligible in this
structure suggesting that the interface play a significant role in Rashba-like
torque.",1501.02294v1
2015-09-03,All-Optical Vector Measurement of Spin-Orbit-Induced Torques Using Both Polar and Quadratic Magneto-Optic Kerr Effects,"We demonstrate that the magneto-optic-Kerr effect with normal light incidence
can be used to obtain quantitative optical measurements of both components of
spin-orbit-induced torque (both the antidamping and effective-field components)
in heavy-metal/ferromagnet bilayers. This is achieved by analyzing the
quadratic Kerr effect as well as the polar Kerr effect. The two effects can be
distinguished by properly selecting the polarization of the incident light. We
use this all-optical technique to determine the spin-orbit torques generated by
a series of Pt/Permalloy samples, finding values in excellent agreement with
spin-torque ferromagnetic resonance measurements.",1509.01266v1
2016-10-28,Spin-Orbit Torque Efficiency in Compensated Ferrimagnetic Cobalt-Terbium Alloys,"Despite the potential advantages of information storage in
antiferromagnetically coupled materials, it remains unclear whether one can
control the magnetic moment orientation efficiently because of the cancelled
magnetic moment. Here, we report spin-orbit torque induced magnetization
switching of ferrimagnetic Co1-xTbx films with perpendicular magnetic
anisotropy. Current induced switching is demonstrated in all of the studied
film compositions, including those near the magnetization compensation point.
The spin-orbit torque induced effective field is further quantified in the
domain wall motion regime. A divergent behavior that scales with the inverse of
magnetic moment is confirmed close to the compensation point, which is
consistent with angular momentum conservation. Moreover, we also quantify the
Dzyaloshinskii-Moriya interaction energy in the Ta/Co1-xTbx system and we find
that the energy density increases as a function of the Tb concentration. The
demonstrated spin-orbit torque switching, in combination with the fast magnetic
dynamics and minimal net magnetization of ferrimagnetic alloys, promises
spintronic devices that are faster and with higher density than traditional
ferromagnetic systems.",1610.09200v1
2018-07-06,Spin-torque-induced magnetization dynamics in ferrimagnets based on Landau-Lifshitz-Bloch Equation,"A theoretical model based on the Landau-Lifshitz-Bloch equation is developed
to study the spin-torque effect in ferrimagnets. Experimental findings, such as
the temperature dependence, the peak in spin torque, and the angular-momentum
compensation, can be well captured. In contrast to the ferromagnet system, the
switching trajectory in ferrimagnets is found to be precession free. The two
sublattices are not always collinear, which produces large exchange field
affecting the magnetization dynamics. The study of material composition shows
the existence of an oscillation region at intermediate current density, induced
by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert
model, our developed model based on the Landau-Lifshitz-Bloch equation enables
the systematic study of spin-torque effect and the evaluation of
ferrimagnet-based devices.",1807.02445v1
2018-10-12,Energy-efficient domain wall motion governed by the interplay of helicity-dependent optical effect and spin-orbit torque,"Spin-orbit torque provides a powerful means of manipulating domain walls
along magnetic wires. However, the current density required for domain wall
motion is still too high to realize low power devices. Here we experimentally
demonstrate helicity-dependent domain wall motion by combining synchronized
femtosecond laser pulses and short current pulses in Co/Ni/Co ultra-thin film
wires with perpendicular magnetization. Domain wall can remain pinned under one
laser circular helicity while depinned by the opposite circular helicity.
Thanks to the all-optical helicity-dependent effect, the threshold current
density due to spin-orbit torque can be reduced by more than 50%. Based on this
joint effect combining spin-orbit torque and helicity-dependent laser pulses,
an optoelectronic logic-in-memory device has been experimentally demonstrated.
This work enables a new class of low power spintronic-photonic devices beyond
the conventional approach of all-optical switching or all-current switching for
data storage.",1810.05375v2
2018-08-30,Antiferromagnetic Single-layer Spin-Orbit Torque Oscillators,"We show how a charge current through a single antiferromagnetic layer can
excite and control self-oscillations. Sustained oscillations with tunable
amplitudes and frequencies are possible in a variety of geometries using
certain classes of non-centrosymmetric materials that exhibit finite
dissipative spin-orbit torque. We compute the steady-state phase diagram as a
function of the current and spin-orbit torque magnitude. The anisotropic
magnetoresistance causes the conversion of the resulting AF oscillations to a
terahertz AC output voltage. These findings provide an attractive and novel
route to design terahertz antiferromagnetic spin-orbit torque oscillators in
simple single-layer structures.",1808.10182v2
2018-12-14,Current Control of Magnetism in Two-Dimensional Fe3GeTe2,"The recent discovery of magnetism in two-dimensional van der Waals systems
opens the door to discovering exciting physics. We investigate how a current
can control the ferromagnetic properties of such materials. Using symmetry
arguments, we identify a recently realized system in which the current-induced
spin torque is particularly simple and powerful. In Fe3GeTe2, a single
parameter determines the strength of the spin-orbit torque for a uniform
magnetization. The spin-orbit torque acts as an effective out-of-equilibrium
free energy. The contribution of the spin-orbit torque to the effective free
energy introduces new in-plane magnetic anisotropies to the system. Therefore,
we can tune the system from an easy-axis ferromagnet via an easy-plane
ferromagnet to another easy-axis ferromagnet with increasing current density.
This finding enables unprecedented control and provides the possibility to
study the Berezinskii-Kosterlitz-Thouless phase transition in the 2D XY model
and its associated critical exponents.",1812.06096v2
2020-04-08,Benchmarking of spin-orbit torque switching efficiency in Pt alloys,"We systematically survey on Pt$_{x}$Cu$_{1-x}$/Co/MgO magnetic
heterostructure with perpendicular magnetic anisotropy and report a significant
improvement on spin-orbit torque switching efficiency in Pt-Cu alloy system.
The largest damping-like spin-orbit torque efficiency determined by hysteresis
loop shift measurement is about 0.44 for Pt$_{0.57}$Cu$_{0.43}$, which is
originated from the higher resistivity tuned by alloying. Moreover, from the
results of current-induced switching measurements, a lower critical switching
current density is achieved by proper alloying due to the simultaneous
enhancement of spin-orbit torque efficiency and reduction of coercivity of the
Co layer. Finally, the ability to lower power consumption and preserve good
thermal stability using Pt$_{x}$Cu$_{1-x}$ alloy is demonstrated, which
suggests that Pt$_{x}$Cu$_{1-x}$ is an attractive candidate for future SOT-MRAM
applications.",2004.03962v2
2021-04-08,Out-of-plane magnetization oscillation in spin Hall device assisted by field-like torque,"An excitation of a large-amplitude out-of-plane magnetization oscillation in
a ferromagnet by the spin Hall effect is of great interest for practical
applications such as microwave generator and neuromorphic computing. However,
both experimental and theoretical works have revealed that only small-amplitude
oscillation around an in-plane easy axis can be excited via the spin Hall
effect. Here, we propose that an out-of-plane oscillation can be excited due to
an assistance of field-like torque. We focus on an in-plane magnetized
ferromagnet with an easy axis parallel to current direction. We notice that the
field-like torque with an appropriate sign provides an additional field
modifying the dynamic trajectory of the magnetization and drives the
auto-oscillation. The condition on the sign of the field-like torque is
satisfied for typical nonmagnet used in spin Hall devices such as tungsten.",2104.04057v1
2017-01-27,Mixed Weyl semimetals and dissipationless magnetization control in insulators by spin-orbit torques,"Reliable and energy efficient magnetization switching by electrically-induced
spin-orbit torques is of crucial technological relevance for spintronic devices
implementing memory and logic functionality. Here we predict that the strength
of spin-orbit torques and the related Dzyaloshinskii-Moriya interaction in
topologically non-trivial magnetic insulators can exceed by far that of
conventional metallic magnets. In analogy to the quantum anomalous Hall effect,
we explain this extraordinary response in absence of longitudinal currents as a
hallmark of magnetic monopoles in the electronic structure of systems that are
interpreted most naturally within the framework of mixed Weyl semimetals. We
thereby launch the effect of spin-orbit torque into the field of topology and
reveal its crucial role in mediating the topological phase transitions arising
due to the complex interplay between magnetization direction and momentum-space
topology. The concepts presented here may be exploited to understand and
utilize magneto-electric coupling phenomena in insulating ferromagnets and
antiferromagnets.",1701.08050v2
2019-08-26,Designing large arrays of interacting spin-torque nano-oscillators for microwave information processing,"Arrays of spin-torque nano-oscillators are promising for broadband microwave
signal detection and processing, as well as for neuromorphic computing. In many
of these applications, the oscillators should be engineered to have
equally-spaced frequencies and equal sensitivity to microwave inputs. Here we
design spin-torque nano-oscillator arrays with these rules and estimate their
optimum size for a given sensitivity, as well as the frequency range that they
cover. For this purpose, we explore analytically and numerically conditions to
obtain vortex spin-torque nano-oscillators with equally-spaced gyrotropic
oscillation frequencies and having all similar synchronization bandwidths to
input microwave signals. We show that arrays of hundreds of oscillators
covering ranges of several hundred MHz can be built taking into account
nanofabrication constraints.",1908.09908v2
2019-12-25,Materials Relevant to Realizing a Field-Effect Transistor based on Spin-Orbit Torques,"Spin-orbit torque is a promising mechanism for writing magnetic memories,
while field-effect transistors are the gold-standard device for logic
operation. The spin-orbit torque field effect transistor (SOTFET) is a proposed
device that couples a spin-orbit-torque-controlled ferromagnet to a
semiconducting transistor channel via the transduction in a magnetoelectric
multiferroic. This allows the SOTFET to operate as both a memory and a logic
device, but its realization depends on the choice of appropriate materials. In
this report, we discuss and parametrize the types of materials that can lead to
a SOTFET heterostructure.",1912.11715v1
2020-05-21,Magnetar outburst and spin-down glitch,"The outburst and spin-down glitch of magnetars are modeled from the
magnetospheric point of view. We try to discuss the following four questions:
(1) Which pulsar on the period and peirod-derivative diagram are more likely to
show magnetar outburst? (2) Which outburst will make the glitch that triggered
the outburst to become a spin-down glitch? (3) Can we model the outburst and
spin-down glitch in PSR J1119$-$6127 simultaneously? (4) Why the torque
variation is delayed compared with the peak of the X-ray luminosity in 1E
1048.1$-$5937 and PSR J1119$-$6127? It is found that both the global and local
twisted magnetic field will affect the radiation and timing behaviors of
magnetars. Especially, the delay of torque variations may due to the combined
effect of increasing twist in the j-bundle and untwisting of the global
magnetosphere. A toy model is build for magnetar outburst and torque
variations. It can catch the general trend of magnetar outburst: decaying flux,
shrinking hot spot, and torque variations.",2005.11281v2
2024-04-15,Using ZDI maps to determine magnetic forces and torques at the photospheres of Early-type stars,"We use the magnetic field components measured by Zeeman Doppler imaging (ZDI)
to calculate the stellar surface force and torque due to magnetic stresses for
the fast rotators $\sigma$ Ori E, 36 Lyn and CU Vir, and the slow rotator
$\tau$ Sco. If we assume the stars have spherical photospheres, the estimated
torques give spin down time scales no larger than $7 \times 10^5$ yr. For
$\sigma$ Ori E, the predicted spin down time scale, $\simeq 6000$ yr, is much
less than the observationally measured time scale of $\simeq 10^6$ yr. However,
for CU Vir, we find that the spin down time scale from its ZDI map is $7 \times
10^5$ yr in good agreement with its average rate of spin down from 1960 to
2010.
  With the exception of $\tau$ Sco, the net force due to magnetic stresses at
the stellar surface are large compared to the surface-integrated pressure. We
discuss possible reasons for the large values of the forces (and torques), and
suggest that the likely explanation is that rotation and the magnetic stresses
create significant departures from spherical symmetry.",2404.10161v1
2017-02-15,Room-temperature current-induced generation and motion of sub-100nm skyrmions,"Magnetic skyrmions are nanoscale windings of the spin configuration that hold
great promise for technology due to their topology-related properties and
extremely reduced sizes. After the recent observation at room temperature of
sub-100 nm skyrmions stabilized by interfacial chiral interaction in magnetic
multilayers, several pending questions remain to be solved, notably about the
means to nucleate individual compact skyrmions or the exact nature of their
motion. In this study, a method leading to the formation of magnetic skyrmions
in a micrometer-sized nanotrack using homogeneous current injection is
evidenced. Spin-transfer-induced motion of these small
electricalcurrent-generated skyrmions is then demonstrated and the role of the
out-of-plane magnetic field in the stabilization of the moving skyrmions is
also analysed. The results of these experimental observations of spin torque
induced motion are compared to micromagnetic simulations reproducing a granular
type, non-uniform magnetic multilayer, in order to address the particularly
important role of the magnetic inhomogeneities on the current-induced motion of
sub-100 nm skyrmions, for which the material grains size is comparable to the
skyrmion diameter.",1702.04616v1
2002-06-27,Discovery of a High-Latitude Accreting Millisecond Pulsar in an Ultracompact Binary,"We have identified the third known accretion-powered millisecond pulsar, XTE
J0929-314, with the Rossi X-Ray Timing Explorer. The source is a faint,
high-Galactic-latitude X-ray transient (d >~ 5 kpc) that was in outburst during
2002 April-June. The 185 Hz (5.4 ms) pulsation had a fractional rms amplitude
of 3-7% and was generally broad and sinusoidal, although occasionally
double-peaked. The hard X-ray pulses arrived up to 770 microseconds earlier
than the soft X-ray pulses. The pulsar was spinning down at an average rate of
-(9.2 +/- 0.4) * 10^-14 Hz/s; the spin-down torque may arise from magnetic
coupling to the accretion disk, a magnetohydrodynamic wind, or gravitational
radiation from the rapidly spinning pulsar. The pulsations were modulated by a
43.6 min ultracompact binary orbit, yielding the smallest measured mass
function (2.7 * 10^-7 M_sun) of any stellar binary. The binary parameters imply
an approximately 0.01 M_sun white dwarf donor and a moderately high
inclination. We note that all three known accreting millisecond pulsars are
X-ray transients in very close binaries with extremely low mass transfer rates.
This is an important clue to the physics governing whether or not persistent
millisecond pulsations are detected in low-mass X-ray binaries.",0206493v3
2006-08-02,Magnetocatalytic Adiabatic Spin Torque Orbital Transformations for Novel Chemical and Catalytic Reaction Dynamics: The Little Effect,"In this manuscript the theory and phenomena associated with the Little Effect
are introduced as the spin induced orbital dynamics of confined fermions under
strong magnetic and thermal environments. This Little Effect is considered in
details for the electron transfer reactions associated with redox processes of
Cu-Ag alloy within deionized water and for the orbital dynamics during the iron
catalyzed covalent bond rearrangements associated with amorphous carbon
conversion to diamond. Furthermore, prolong extreme conditions of 74,000 amps,
403 V, strong Lorentz compression, and thermal stresses upon this Cu-Ag- H2O
system on the basis of the Little Effect of high spin, thermally induced
orbital dynamics are predicted and demonstrated to cause the magnetically
organized reverse beta, electron capture, proton capture and neutron capture
processes for various infrequent pycnonuclear transmutations within the Cu-Ag
coil. The general experimental verification and the broad implications of this
Little Effect on chemistry are demonstrated within these two ideal systems: an
ionic case and a molecular case. The Little Effect is contrasted with the
Hedvall Effect as a dynamical phenomenon causing the kinematics of the Hedvall
Effect. The compatibility of the Little Effect with the Woodward-Hoffmann Rule
is demonstrated. The Little Effect provides greater understanding of order in
systems far from equilibrium. The implications of the Little Effect for other
interesting phenomena such as ferromagnetism, unconventional magnetism,
superparamagnetism, superconductivity, and pycnonuclear effects are concluded.",0608071v1
2017-02-14,On the origin of magnetization auto-oscillations in constriction-based spin Hall nano-oscillators,"We use micromagnetic simulations to map out and compare, the linear and
auto-oscillating modes in constriction-based spin Hall nano-oscillators as a
function of applied magnetic field with varying magnitude and out-of-plane
angle. We demonstrate that for all possible applied field configurations the
auto-oscillations emerge from the localized linear modes of the constriction.
For field directions tending towards the plane, these modes are of the
so-called ""edge"" type, i.e. localized at the opposite sides of the
constriction. When the magnetization direction instead approaches the film
normal, the modes transform to the so-called ""bulk"" type, i.e. localized inside
the constriction with substantially increased precession volume, consistent
with the re-distribution of the magnetic charges from the sides to the top and
bottom surfaces of the constriction. In general, the threshold current of the
corresponding auto-oscillations increases with the applied field strength and
decreases with its out-of-plane angle, consistent with the behavior of the
internal field and in good agreement with a macrospin model. A quantitative
agreement is then achieved by taking into account the strongly non-uniform
character of the system via a mean-field approximation. Both the Oe field and
the spin transfer torque from the drive current increase the localization and
decrease the frequency of the observed mode. Furthermore, the anti-symmetric Oe
field breaks the lateral symmetry, favoring the localized mode at one of the
two constriction edges, in particular for large out-of-plane field angles where
the threshold current is significantly increased and the edge demagnetization
is suppressed.",1702.04155v1
2019-07-03,Electric current control of spin helicity in an itinerant helimagnet,"Chirality is breaking of mirror symmetry in matter. In the fields of biology
and chemistry, this is particularly important because some of the essential
molecules in life such as amino acids and DNA have chirality. It is a
long-standing mystery how one of the enantiomers was chosen at the beginning
stage of life. The understanding of the emergence of homochirality under some
conditions is indispensable for the study of the origin of life as well as
pharmaceutical science. The chirality is also emergent in magnetic structures.
The longitudinal helical magnetic structure is the chiral object composed of
magnetic moments, in which the ordered direction of the magnetic moment
spatially rotates in the plane perpendicular to the propagation vector (Fig.
1a). Since the sense of rotation, which is denoted as helicity, is reversed by
any mirror operation, it is corresponding to the chirality. Here we show that
the chirality of a longitudinal helical structure can be controlled by the
magnetic field and electric current owing to the spin-transfer torque
irrelevant to the spin-orbit interaction and probed by electrical magnetochiral
effect, which is sensitive to the chiral symmetry breaking, in an itinerant
helimagnet MnP. This phenomenon is distinct from the multiferroicity in
transverse-type insulating helical magnets, in which the helical plane is
parallel to the propagation vector, because the magnetic structure has polar
symmetry not chiral one. While the combination of the magnetic field and
electric current satisfies the symmetrical rule of external stimulus for the
chirality control, the control with them was not reported for any chiral object
previously. The present result may pave a new route to the control of
chiralities originating from magnetic and atomical arrangements.",1907.01798v1
1999-04-09,"Magnetically Driven Warping, Precession and Resonances in Accretion Disks","The inner region of the accretion disk onto a rotating magnetized central
star (neutron star, white dwarf or T Tauri star) is subjected to magnetic
torques which induce warping and precession of the disk. The origin of these
torques lies in the interaction between the (induced) surface current on the
disk and the horizontal magnetic field (parallel to the disk) produced by the
inclined magnetic dipole. Under quite general conditions, there exists a
magnetic warping instability in which the magnetic torque drives the disk plane
away from the equatorial plane of the star toward a state where the disk normal
vector is perpendicular to the spin axis. Viscous stress tends to suppress the
warping instability at large radii, but the magnetic torque always dominates as
the disk approaches the magnetosphere boundary. The magnetic torque also drives
the tilted inner disk into retrograde precession around the stellar spin axis.
Moreover, resonant magnetic forcing on the disk can occur which may affect the
dynamics of the disk. The magnetically driven warping instability and
precession may be related to a number observational puzzles, including: (1)
Spin evolution (torque reversal) of accreting X-ray pulsars; (2) Quasi-periodic
oscillations in low-mass X-ray binaries; (3) Super-orbital periods in X-ray
binaries; (4) Photometric period variations of T Tauri stars.",9904110v3
2020-04-27,Nonlinear interaction of acoustic waves with a spheroidal particle: radiation force and torque effects,"The nonlinear interaction of a time-harmonic acoustic wave with an
anisotropic particle gives rise to the radiation force and torque effects.
These phenomena are at the heart of the acoustofluidics technology, where
microparticles such as cells and microorganisms are acoustically manipulated.
We present a theoretical model considering a generic acoustic beam interacting
with a subwavelength spheroidal particle in a nonviscous fluid. Concise
analytical expressions of the radiation force and torque are obtained in the
scattering dipole approximation. The radiation force is given in terms of a
gradient and scattering force; while the radiation torque has two fundamental
contributions, namely, the momentum arm and acoustic spin (spin-torque effect).
As a practical example, we use the theory to describe the interaction of two
crossed plane waves and a prolate spheroidal particle. The results reveal the
particle is transversely trapped in a pressure node and is axially pushed by
the radiation force. Also, the momentum arm aligns the particle in the axial
direction. At certain specific positions, only the spin-torque occurs. Our
findings are remarkably consistent with finite-element simulations. The success
of our model enables its use as an investigation tool for the manipulation of
anisotropic microparticles in acoustofluidics.",2004.12980v1
2020-05-28,Spintronics meets nonadiabatic molecular dynamics: Geometric spin torque and damping on noncollinear classical magnetism due to electronic open quantum system,"We analyze a quantum-classical hybrid system of steadily precessing slow
classical localized magnetic moments, forming a head-to-head domain wall,
embedded into an open quantum system of fast nonequilibrium electrons. The
electrons reside within a metallic wire connected to macroscopic reservoirs.
The model captures the essence of dynamical noncollinear and noncoplanar
magnetic textures in spintronics, while making it possible to obtain the exact
time-dependent nonequilibrium density matrix of electronic system and split it
into four contributions. The Fermi surface contribution generates dissipative
(or damping-like in spintronics terminology) spin torque on the moments, and
one of the two Fermi sea contributions generates geometric torque dominating in
the adiabatic regime. When the coupling to the reservoirs is reduced, the
geometric torque is the only nonzero contribution. Locally it has both
nondissipative (or field-like in spintronics terminology) and damping-like
components, but with the sum of latter being zero, which act as the
counterparts of geometric magnetism force and electronic friction in
nonadiabatic molecular dynamics. Such current-independent geometric torque is
absent from widely used micromagnetics or atomistic spin dynamics modeling of
magnetization dynamics based on the Landau-Lifshitz-Gilbert equation, where
previous analysis of Fermi surface-type torque has severely underestimated its
magnitude.",2005.14153v2
1997-08-21,On the Dramatic Spin-up/Spin-down Torque Reversals in Accreting Pulsars,"Dramatic torque reversals between spin up and spin down have been observed in
half of the persistent X-ray pulsars monitored by the BATSE all-sky monitor on
CGRO. Theoretical models developed to explain early pulsar timing data can
explain spin down torques via a disk-magnetosphere interaction if the star
nearly corotates with the inner accretion disk. To produce the observed BATSE
torque reversals, however, these equilibrium models require the disk to
alternate between two mass accretion rates, with $\dot M_{\pm}$ producing
accretion torques of similar magnitude, but always of opposite sign. Moreover,
in at least one pulsar (GX 1+4) undergoing secular spin down the neutron star
spins down faster during brief ($\sim 20$ day) hard X-ray flares -- this is
opposite the correlation expected from standard theory, assuming BATSE pulsed
flux increases with mass accretion rate. The $10$ day to 10 yr intervals
between torque reversals in these systems are much longer than any
characteristic magnetic or viscous time scale near the inner disk boundary and
are more suggestive of a global disk phenomenon.
  We discuss possible explanations of the observed torque behavior. Despite the
preferred sense of rotation defined by the binary orbit, the BATSE observations
are surprisingly consistent with an earlier suggestion by Makishima \etal
(1988) for GX~1+4: the disks in these systems somehow alternate between
episodes of prograde and retrograde rotation. We are unaware of any mechanism
that could produce a stable retrograde disk in a binary undergoing Roche-lobe
overflow, but such flip-flop behavior does occur in numerical simulations of
wind-fed systems. One possibility is that the disks in some of these binaries
are fed by an X-ray excited wind.",9708193v1
2020-04-07,"Strong, Temperature-Dependent Spin-Orbit Torques in Heavy Fermion YbAl$_3$","The use of current-generated spin-orbit torques[1] to drive magnetization
dynamics is under investigation to enable a new generation of non-volatile,
low-power magnetic memory. Previous research has focused on spin-orbit torques
generated by heavy metals[2-8], interfaces with strong Rashba
interactions[9,10] and topological insulators [11-14]. These families of
materials can all be well-described using models with noninteracting-electron
bandstructures. Here, we show that electronic interactions within a strongly
correlated heavy fermion material, the Kondo lattice system YbAl$_{3}$, can
provide a large enhancement in spin-orbit torque. The spin-torque conductivity
increases by approximately a factor of 4 as a function of decreasing
temperature from room temperature to the coherence temperature of YbAl$_{3}$
($T^* \approx 37$ K), with a saturation at lower temperatures, achieving a
maximum value greater than any heavy metal element. This temperature dependence
mimics the increase and saturation at $T^*$ of the density of states at the
Fermi level arising from the ytterbium 4$f$-derived heavy bands in the Kondo
regime, as measured by angle-resolved photoemission spectroscopy[15]. We
therefore identify the many-body Kondo resonance as the source of the large
enhancement of spin-orbit torque in YbAl$_{3}$. Our observation reveals new
opportunities in spin-orbit torque manipulation of magnetic memories by
engineering quantum many-body states.",2004.03678v2
2017-01-24,Influence of interlayer coupling on the spin torque driven excitations in a spin torque oscillator,"The influence of dynamic interlayer interactions on the spin torque driven
and damped excitations are illustrated for a three layer macrospin model system
that corresponds to a standard spin-torque oscillator. The free layer and a
synthetic antiferromagnetic (SyF) pinned layer of the spin-torque oscillator
are in-plane magnetized. In order to understand experimental results, numerical
simulations have been performed considering three types of interlayer
interactions: exchange interaction between the two magnetic layers of the SyF,
mutual spin torque between the top layer of the SyF and the free layer and
dipolar interaction between all three magnetic layers. It will be shown that
the dynamic dipolar coupling plays a predominant role. First, it leads to a
hybridization of the free layer and the SyF linear modes and through this gives
rise to a strong field dependence of the critical current. In particular, there
is a field range of enhanced damping in which much higher current is required
to drive the modes into steady state. This results in a gap in the excitation
spectrum. Second, the dynamic dipolar interaction is also responsible for the
non-linear interaction between the current driven steady state mode and the
damped modes of the system. Here one can distinguish: (i) a resonant
interaction that leads to a kink in the frequency-field and frequency-current
dispersions accompanied by a small hysteresis and a reduction of the linewidth
of the steady state mode and (ii) a non-resonant interaction that leads to a
strong frequency redshift of the damped mode. The results underline the strong
impact of interlayer coupling on the excitation spectra of spin-torque
oscillators and illustrate in a simple three mode model system how in the
non-linear regime the steady state and damped modes influence each other.",1701.06787v1
2024-03-25,The interacting double white dwarf population with LISA; stochastic foreground and resolved sources,"In this work, we investigate the impact of tidal torques and mass transfer on
the population of double white dwarfs (DWDs) that will be observed with LISA.
Starting from a distribution of DWDs at formation predicted by numerical
simulations, we use a semi-analytical model to evolve DWDs under different
hypotheses for the efficiency of tidal coupling and the birth spins of white
dwarfs. We then estimate the stochastic foreground and the population of
resolvable binaries for LISA in each scenario. Our predicted DWD binary
distribution can differ substantially from the distribution expected if only
gravitational waves (GWs) are considered. If white dwarfs spin slowly, then we
predict an excess of systems around a few mHz, due to binaries that outspiral
after the onset of mass transfer. This excess of systems leads to differences
in the confusion noise, which are most pronounced for strong tidal coupling. In
that case, we find a significantly higher number of resolvable binaries than in
the GW-only scenario. If instead white dwarfs spin rapidly and tidal coupling
is weak, then we find no excess around a few mHz, and the confusion noise due
to DWDs is very small. In that scenario, we also predict a subpopulation of
outspiralling binaries below 0.1 mHz. Using the Fisher matrix approximation, we
estimate the uncertainty on the GW-frequency derivative of resolvable systems.
We estimate that, even for non-accreting systems, the mismodelling error due to
neglect of effects other than GWs is larger than the statistical uncertainty,
and thus this neglect would lead to biased estimates for mass and distance. Our
results highlight the need for flexible tools in LISA data analysis. Because
our semi-analytical model hinges upon a simplistic approach to determining the
stability of mass accretion it will be important to deepen our comprehension of
stability in mass-transferring DWD binaries.",2403.16867v1
2020-10-18,Current-induced spin torques on single GdFeCo magnetic layers,"Spintronics exploits spin-orbit coupling (SOC) to generate spin currents,
spin torques, and, in the absence of inversion symmetry, Rashba, and
Dzyaloshinskii-Moriya interactions (DMI). The widely used magnetic materials,
based on 3d metals such as Fe and Co, possess a small SOC. To circumvent this
shortcoming, the common practice has been to utilize the large SOC of
nonmagnetic layers of 5d heavy metals (HMs), such as Pt, to generate spin
currents by Spin Hall Effect (SHE) and, in turn, exert spin torques on the
magnetic layers. Here, we introduce a new class of material architectures,
excluding nonmagnetic 5d HMs, for high-performance spintronics operations. We
demonstrate very strong current-induced torques exerted on single GdFeCo layers
due to the combination of large SOC of the Gd 5d states, and inversion symmetry
breaking mainly engineered by interfaces. These ""self-torques"" are enhanced
around the magnetization compensation temperature (close to room temperature)
and can be tuned by adjusting the spin absorption outside the GdFeCo layer. In
other measurements, we determine the very large emission of spin current from
GdFeCo. This material platform opens new perspectives to exert ""self-torques""
on single magnetic layers as well as to generate spin currents from a magnetic
layer.",2010.09137v1
2010-06-04,The Accreting Millisecond X-ray Pulsar IGR J00291+5934: Evidence for a Long Timescale Spin Evolution,"Accreting Millisecond X-ray Pulsars like IGR J00291+5934 are important
because it is possible to test theories of pulsar formation and evolution. They
give also the possibility to constrain gravitational wave emission theories and
the equation of state of ultra dense matter. Particularly crucial to our
understanding is the measurement of the long term spin evolution of the
accreting neutron star. An open question is whether these accreting pulsars are
spinning up during an outburst and spinning down in quiescence as predicted by
the recycling scenario. Until now it has been very difficult to measure
torques, due to the presence of fluctuations in the pulse phases that
compromise their measurements with standard coherent timing techniques. By
applying a new method, I am now able to measure a spin up during an outburst
and a spin down during quiescence. I ascribe the spin up
(Fdot=5.1(3)x10^{-13}\Hz/s) to accretion torques and the spin down
(Fdot=-3.0(8)x10^{-15} Hz/s) to magneto dipole torques, as those observed in
radio pulsars. Both values nicely fit in the recycling scenario and I infer the
existence of a magnetic field for the pulsar of B~2x10^{8} G. No evidence for
an enhanced spin down due to gravitational wave emission is found. The
accretion torques are smaller than previously reported and there is strong
evidence for an ordered process that is present in all outbursts that might be
connected with a motion of the hot spot on the neutron star surface.",1006.0815v2
2013-08-13,Exploring Boolean and Non-Boolean Computing Applications of Spin Torque Devices,"In this paper we discuss the potential of emerging spintorque devices for
computing applications. Recent proposals for spinbased computing schemes may be
differentiated as all-spin vs. hybrid, programmable vs. fixed, and, Boolean vs.
non-Boolean. All spin logic-styles may offer high area-density due to small
form-factor of nano-magnetic devices. However, circuit and system-level design
techniques need to be explored that leverage the specific spin-device
characteristics to achieve energy-efficiency, performance and reliability
comparable to those of CMOS. The non-volatility of nanomagnets can be exploited
in the design of energy and area-efficient programmable logic. In such
logic-styles, spin-devices may play the dual-role of computing as well as
memory-elements that provide field-programmability. Spin-based threshold logic
design is presented as an example (dynamic resisitve threshold logic and
magnetic threshold logic). Emerging spintronic phenomena may lead to ultralow-
voltage, current-mode, spin-torque switches that can offer attractive computing
capabilities, beyond digital switches. Such devices may be suitable for
non-Boolean data-processing applications which involve analog processing.
Integration of such spin-torque devices with charge-based devices like CMOS and
resistive memory can lead to highly energy-efficient information processing
hardware for applications like pattern-matching, neuromorphic-computing,
image-processing and data-conversion. Towards the end, we discuss the
possibility of applying emerging spin-torque switches in the design of
energy-efficient global interconnects, for future chip multiprocessors.",1308.2745v2
2016-08-09,"Creation,transport and detection of imprinted magnetic solitons stabilized by spin-polarized current","With the recent proposition of skyrmion utilization in racetrack memories at
room temperature, skyrmionics has become a very attractive field. However, for
the stability of skyrmions, it is essential to incorporate the
Dzyaloshinskii-Moriya interaction (DMI) and the out-of-plane magnetic field
into the system. In this work, we explore a system without these interactions.
First, we propose a controlled way for the creation of magnetic skyrmions and
skyrmioniums imprinted on a ferromagnetic nanotrack via a nanopatterned
nanodisk with the magnetic vortex state. Then we investigate the detachment of
the imprinted spin textures from the underneath of the nanodisk, as well as its
transport by the spin-transfer torque imposed by spin-polarized current pulses
applied in the nanotrack. A prominent feature of the moving imprinted spin
texture is that its topological number Q is oscillating around the averaged
value of Q=0 as if it is a resonant state between the skyrmions with Q= +/- 1
and the bubble with Q=0. We may call it a resonant magnetic soliton (RMS). A
RMS moves along a straight line since it is free from the skyrmion Hall effect.
In our studied device, the same electrodes are employed to realize the
imprinted spin texture detachment and its transport. In addition, we have
investigated the interaction between the RMS and a magnetic tunnel junction
sensor, where the passing of the RMS in the nanotrack can be well detected. Our
results would be useful for the development of novel spintronic devices based
on moveable spin textures.",1608.02915v2
2017-03-15,A Comprehensive Library of X-ray Pulsars in the Small Magellanic Cloud: Time Evolution of their Luminosities and Spin Periods,"We have collected and analyzed the complete archive of {\itshape XMM-Newton\}
(116), {\itshape Chandra\} (151), and {\itshape RXTE\} (952) observations of
the Small Magellanic Cloud (SMC), spanning 1997-2014. The resulting
observational library provides a comprehensive view of the physical, temporal
and statistical properties of the SMC pulsar population across the luminosity
range of $L_X= 10^{31.2}$--$10^{38}$~erg~s$^{-1}$. From a sample of 67 pulsars
we report $\sim$1654 individual pulsar detections, yielding $\sim$1260 pulse
period measurements. Our pipeline generates a suite of products for each pulsar
detection: spin period, flux, event list, high time-resolution light-curve,
pulse-profile, periodogram, and spectrum. Combining all three satellites, we
generated complete histories of the spin periods, pulse amplitudes, pulsed
fractions and X-ray luminosities. Some pulsars show variations in pulse period
due to the combination of orbital motion and accretion torques. Long-term
spin-up/down trends are seen in 12/11 pulsars respectively, pointing to
sustained transfer of mass and angular momentum to the neutron star on decadal
timescales. Of the sample 30 pulsars have relatively very small spin period
derivative and may be close to equilibrium spin. The distributions of
pulse-detection and flux as functions of spin-period provide interesting
findings: mapping boundaries of accretion-driven X-ray luminosity, and showing
that fast pulsars ($P<$10 s) are rarely detected, which yet are more prone to
giant outbursts. Accompanying this paper is an initial public release of the
library so that it can be used by other researchers. We intend the library to
be useful in driving improved models of neutron star magnetospheres and
accretion physics.",1703.05196v1
2019-11-30,Transferable Force-Torque Dynamics Model for Peg-in-hole Task,"We present a learning-based force-torque dynamics to achieve model-based
control for contact-rich peg-in-hole task using force-only inputs. Learning the
force-torque dynamics is challenging because of the ambiguity of the
low-dimensional 6-d force signal and the requirement of excessive training
data. To tackle these problems, we propose a multi-pose force-torque state
representation, based on which a dynamics model is learned with the data
generated in a sample-efficient offline fashion. In addition, by training the
dynamics model with peg-and-holes of various shapes, scales, and elasticities,
the model could quickly transfer to new peg-and-holes after a small number of
trials. Extensive experiments show that our dynamics model could adapt to
unseen peg-and-holes with 70% fewer samples required compared to learning from
scratch. Along with the learned dynamics, model predictive control and
model-based reinforcement learning policies achieve over 80% insertion success
rate. Our video is available at https://youtu.be/ZAqldpVZgm4.",1912.00260v1
2017-03-09,Material developments and domain wall based nanosecond-scale switching process in perpendicularly magnetized STT-MRAM cells,"We investigate the Gilbert damping and the magnetization switching of
perpendicularly magnetized FeCoB-based free layers embedded in tunnel junctions
adequate for spin-torque operated memories. We study the influence of the boron
content in MgO / FeCoB /Ta systems alloys on their Gilbert damping after
crystallization annealing. Increasing the boron content from 20 to 30\%
increases the crystallization temperature, thereby postponing the onset of
elemental diffusion within the free layer. This reduction of the interdiffusion
of the Ta atoms helps maintaining the Gilbert damping at a low level of 0.009
without any penalty on the anisotropy and the magneto-transport properties up
to the 400$^\circ$C annealing required in CMOS back-end of line processing. In
addition, we show that dual MgO free layers of composition
MgO/FeCoB/Ta/FeCoB/MgO have a substantially lower damping than their
MgO/FeCoB/Ta counterparts, reaching damping parameters as low as 0.0039 for a 3
\r{A} thick Tantalum spacer. This confirms that the dominant channel of damping
is the presence of Ta impurities within the FeCoB alloy. On optimized tunnel
junctions, we then study the duration of the switching events induced by
spin-transfer-torque. We focus on the sub-threshold thermally activated
switching in optimal applied field conditions. From the electrical signatures
of the switching, we infer that once the nucleation has occurred, the reversal
proceeds by a domain wall sweeping though the device at a few 10 m/s. The
smaller the device, the faster its switching. We present an analytical model to
account for our findings. The domain wall velocity is predicted to scale
linearly with the current for devices much larger than the wall width. The wall
velocity depends on the Bloch domain wall width, such that the devices with the
lowest exchange stiffness will be the ones that host the domain walls with the
slowest mobilities.",1703.03198v3
2024-01-11,Volume Transfer: A New Design Concept for Fabric-Based Pneumatic Exosuits,"The fabric-based pneumatic exosuit is now a hot research topic because it is
lighter and softer than traditional exoskeletons. Existing research focused
more on the mechanical properties of the exosuit (e.g., torque and speed), but
less on its wearability (e.g., appearance and comfort). This work presents a
new design concept for fabric-based pneumatic exosuits Volume Transfer, which
means transferring the volume of pneumatic actuators beyond the garments
profile to the inside. This allows for a concealed appearance and a larger
stress area while maintaining adequate torques. In order to verify this
concept, we develop a fabric-based pneumatic exosuit for knee extension
assistance. Its profile is only 26mm and its stress area wraps around almost
half of the leg. We use a mathematical model and simulation to determine the
parameters of the exosuit, avoiding multiple iterations of the prototype.
Experiment results show that the exosuit can generate a torque of 7.6Nm at a
pressure of 90kPa and produce a significant reduction in the electromyography
activity of the knee extensor muscles. We believe that Volume Transfer could be
utilized prevalently in future fabric-based pneumatic exosuit designs to
achieve a significant improvement in wearability.",2401.05881v1
2013-04-19,Boolean and Non-Boolean Computation With Spin Devices,"Recently several device and circuit design techniques have been explored for
applying nano-magnets and spin torque devices like spin valves and domain wall
magnets in computational hardware. However, most of them have been focused on
digital logic, and, their benefits over robust and high performance CMOS
remains debatable. Ultra-low voltage, current-switching operation of
magneto-metallic spin torque devices can potentially be more suitable for
non-Boolean computation schemes that can exploit current-mode analog
processing. Device circuit co-design for different classes of
non-Boolean-architectures using spin-torque based neuron models in spin-CMOS
hybrid circuits show that the spin-based non-Boolean designs can achieve
15X-100X lower computation energy for applications like, image-processing,
data-conversion, cognitive-computing, pattern matching and programmable-logic,
as compared to state of art CMOS designs.",1304.5291v2
2013-06-20,Pseudo spin torque induced by strain field of Dirac fermions in graphene,"In contrast to recent description [Phys. Rev. Lett. 106 (2011)116803], we
show that pseudo spin in graphene is not completely a real angular momentum.
The pseudo spin only in the direction perpendicular to graphene sheet is real
angular momentum, while the pseudo spin parallel to graphene plane is still not
real angular momentum. Interestingly, it is also shown that the Newtonian-like
force and pseudo spin torque of massive Dirac electrons in graphene under
strain field mimic gravitomagnetic force and gravitomagnetic spin torque,
respectively. This is due to the equivalence of pseudo spin and velocity
operators of 2+1 dimensional massive electrons in graphene, different from that
in real 3+1 dimensional Dirac fields. This work reveals new physical property
of graphene as a pseudo gravitomagnetic material.",1306.4804v2
2015-12-22,Magnetic Torque in k-(BETS)2Mn[N(CN)2]3,"Peculiarities observed in the field dependencies of the magnetic torque in
k-(BETS)2Mn[N(CN)2]3 measured at T=1.5K, H=0-150kOe, have been explained from
the viewpoint of the two interacting spin subsystems, one associated with
d-electron spins of Mn2+ residing in the anion layer, and the other with the
spins of pi-electrons which localize below the metal-insulator transition
temperature, T_MI=25K, forming a long-range antiferromagnetic structure. The
principal axes of the Mn2+ spin subsystem have been defined. A model of
antiferromagnetic pi-spin arrangement has been suggested that associates the
observed kinks in the torque H-dependencies with a spin-reorientation
transition. One of the observed effects is ascribed to the pi-d interaction
between the two spin subsystems.",1512.07013v3
2017-08-30,Current induced magnetization switching in PtCoCr structures with enhanced perpendicular magnetic anisotropy and spin-orbit torques,"Magnetic trilayers having large perpendicular magnetic anisotropy (PMA) and
high spin-orbit torques (SOTs) efficiency are the key to fabricate nonvolatile
magnetic memory and logic devices. In this work, PMA and SOTs are
systematically studied in Pt/Co/Cr stacks as a function of Cr thickness. An
enhanced perpendicular anisotropy field around 10189 Oe is obtained and is
related to the interface between Co and Cr layers. In addition, an effective
spin Hall angle up to 0.19 is observed due to the improved antidamping-like
torque by employing dissimilar metals Pt and Cr with opposite signs of spin
Hall angles on opposite sides of Co layer. Finally, we observed a nearly linear
dependence between spin Hall angle and longitudinal resistivity from their
temperature dependent properties, suggesting that the spin Hall effect may
arise from extrinsic skew scattering mechanism. Our results indicate that 3d
transition metal Cr with a large negative spin Hall angle could be used to
engineer the interfaces of trilayers to enhance PMA and SOTs.",1708.09174v1
2018-01-03,Negative spin-Hall angle and anisotropic spin-orbit torques in epitaxial IrMn,"A spin-torque ferromagnetic resonance study is performed in epitaxial
$\mathrm{Fe / Ir_{15}Mn_{85}}$ bilayers with different Fe thicknesses. We
measure a negative spin-Hall angle of a few percent in the antiferromagnetic
IrMn in contrast to previously reported positive values. A large spin-orbit
field with Rashba symmetry opposing the Oersted field is also present.
Magnitudes of measured spin-orbit torques depend on the crystallographic
direction of current and are correlated with the exchange bias direction set
during growth. We suggest that the uncompensated moments at the Fe / IrMn
interface are responsible for the observed anisotropy. Our findings highlight
the importance of crystalline and magnetic structures for the spin-Hall effect
in antiferromagnets.",1801.01065v1
2019-05-27,Spin-Cooling of the Motion of a Trapped Diamond,"Observing and controlling macroscopic quantum systems has long been a driving
force in research on quantum physics. In this endeavor, strong coupling between
individual quantum systems and mechanical oscillators is being actively
pursued. While both read-out of mechanical motion using coherent control of
spin systems and single spin read-out using pristine oscillators have been
demonstrated, temperature control of the motion of a macroscopic object using
long-lived electronic spins has not been reported. Here, we observe both a
spin-dependent torque and spin-cooling of the motion of a trapped microdiamond.
Using a combination of microwave and laser excitation enables the spin of
nitrogen-vacancy centers to act on the diamond orientation and to cool the
diamond libration via a dynamical back-action. Further, driving the system in
the non-linear regime, we demonstrate bistability and self-sustained coherent
oscillations stimulated by the spin-mechanical coupling, which offers prospects
for spin-driven generation of non-classical states of motion. Such a levitating
diamond operated as a compass with controlled dissipation has implications in
high-precision torque sensing, emulation of the spin-boson problem and probing
of quantum phase transitions. In the single spin limit and employing ultra-pure
nano-diamonds, it will allow quantum non-demolition read-out of the spin of
nitrogen-vacancy centers under ambient conditions, deterministic entanglement
between distant individual spins and matter-wave interferometry.",1905.11509v2
2014-09-05,Spin-orbit torques in L1$_0$-FePt/Pt thin films driven by electrical and thermal currents,"Using the linear response formalism for the spin-orbit torque (SOT) we
compute from first principles the SOT in a system of two layers of
L1$_0$-FePt(001) deposited on an fcc Pt(001) substrate of varying thickness. We
find that at room temperature the values of the SOTs that are even and odd with
respect to magnetization generally lie in the range of values measured and
computed for Co/Pt bilayers. We also observe that the even SOT is much more
robust with respect to changing the number of layers in the substrate, and as a
function of energy it follows the general trend of the even SOT exerted by the
spin Hall current in fcc Pt. The odd torque, on the other hand, is strongly
affected by modification of the electronic structure for a specific energy
window in the limit of very thin films. Moreover, taking the system at hand as
an example, we compute the values of the thermal spin-orbit torque (T-SOT). We
predict that the gradients of temperature which can be experimentally created
in this type of systems will cause a detectable torque on the magnetization. We
also underline the correlation between the even T-SOT and the spin Nernst
effect, thus motivating a more intensive experimental effort aimed at
observation of both phenomena.",1409.1767v1
2020-01-29,Influence of flicker noise and nonlinearity on the frequency spectrum of spin torque nano-oscillators,"The correlation of phase fluctuations in any type of oscillator fundamentally
defines its spectral shape. However, in nonlinear oscillators, such as spin
torque nano oscillators, the frequency spectrum can become particularly
complex. This is specifically true when not only considering thermal but also
colored $1/f$ flicker noise processes, which are crucial in the context of the
oscillator's long term stability. In this study, we address the frequency
spectrum of spin torque oscillators in the regime of large-amplitude steady
oscillations experimentally and as well theoretically. We particularly take
both thermal and flicker noise into account. We perform a series of
measurements of the phase noise and the spectrum on spin torque vortex
oscillators, notably varying the measurement time duration. Furthermore, we
develop the modelling of thermal and flicker noise in Thiele equation based
simulations. We also derive the complete phase variance in the framework of the
nonlinear auto-oscillator theory and deduce the actual frequency spectrum. We
investigate its dependence on the measurement time duration and compare with
the experimental results. Long term stability is important in several of the
recent applicative developments of spin torque oscillators. This study brings
some insights on how to better address this issue.",2001.10984v1
2022-06-29,Deep Learning for Spin-Orbit Torque Characterizations with a Projected Vector Field Magnet,"Spin-orbit torque characterizations on magnetic heterostructures with
perpendicular anisotropy are demonstrated on a projected vector field magnet
via hysteresis loop shift measurement and harmonic Hall measurement with planar
Hall correction. Accurate magnetic field calibration of the vector magnet is
realized with the help of deep learning models, which are able to capture the
nonlinear behavior between the generated magnetic field and the currents
applied to the magnet. The trained models can successfully predict the applied
current combinations under the circumstances of magnetic field scans, angle
scans, and hysteresis loop shift measurements. The validity of the models is
further verified, complemented by the comparison of the spin-orbit torque
characterization results obtained from the deep-learning-trained vector magnet
system with those obtained from a conventional setup comprised of two separated
electromagnets. The damping-like spin-orbit torque (DL-SOT) efficiencies
(|$\xi_{DL}$|) extracted from the vector magnet and the traditional measurement
configuration are consistent, where |$\xi_{DL}$| $\approx$ 0.22 for amorphous W
and |$\xi_{DL}$| $\approx$ 0.02 for $\alpha$-W. Our work provides an advanced
method to meticulously control a vector magnet and to conveniently perform
various spin-orbit torque characterizations.",2206.14670v1
1999-10-22,Ordering in a spin glass under applied magnetic field,"Torque, torque relaxation, and magnetization measurements on a AuFe spin
glass sample are reported. The experiments carried out up to 7 T show a
transverse irreversibility line in the (H,T) plane up to high applied fields,
and a distinct strong longitudinal irreversibility line at lower fields. The
data demonstrate for that this type of sample, a Heisenberg spin glass with
moderately strong anisotropy, the spin glass ordered state survives under high
applied fields in contrast to predictions of certain ""droplet"" type scaling
models. The overall phase diagram closely ressembles those of mean field or
chiral models, which both have replica symmetry breaking transitions.",9910353v1
2002-05-22,Universal angular magnetoresistance and spin torque in ferromagnetic/normal metal hybrids,"The electrical resistance of ferromagnetic/normal-metal (F/N)
heterostructures depends on the nature of the junctions which may be tunnel
barriers, point contacts, or intermetallic interfaces. For all junction types,
the resistance of disordered F/N/F perpendicular spin valves as a function of
the angle between magnetization vectors is shown to obey a simple universal
law. The spin-current induced magnetization torque can be measured by the
angular magnetoresistance of these spin valves. The results are generalized to
arbitrary magnetoelectronic circuits.",0205453v1
2003-04-24,The spin-torque transistor,"A magnetoelectronic thin-film transistor is proposed that can display
negative differential resistance and gain. The working principle is the
modulation of the soure-drain current in a spin valve by the magnetization of a
third electrode, which is rotated by the spin-torque created by a control
spin-valve. The device can operate at room temperature, but in order to be
useful, ferromagnetic materials with polarizations close to unity are required.",0304550v1
2006-05-08,Microscopic Calculation of Spin Torques in Disordered Ferromagnets,"Effects of conduction electrons on magnetization dynamics, represented by
spin torques, are calculated microscopically in the first order in spatial
gradient and time derivative of magnetization. Special attention is paid to the
so-called $\beta$-term and the Gilbert damping, $\alpha$, in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
(and spin-orbit) impurities. The obtained results such as $\alpha \ne \beta$
hold for localized as well as itinerant ferromagnetism.",0605186v1
2008-08-14,Suppression of spin-torque in current perpendicular to the plane spin-valves by addition of Dy cap layers,"We demonstrate that the addition of Dy capping layers in current
perpendicular to the plane giant magneto-resistive spin-valves can increase the
critical current density beyond which spin-torque induced instabilities are
observed by about a factor of three. Current densities as high as 5e7 A/cm2 are
measured provided that the electron current flows from the free to the
reference layer. While Dy capped samples exhibit nonmagnetic 1/f noise, it is
sufficiently small to be unimportant for read head operation at practical data
rates.",0808.2030v1
2018-04-04,Independence of spin-orbit torques from the exchange bias direction in Ni$_{81}$Fe$_{19}$/IrMn bilayers,"We investigated a possible correlation between spin Hall angles and exchange
bias in Ni$_{81}$Fe$_{19}$/IrMn samples by performing spin torque ferromagnetic
resonance measurements. This correlation is probed by patterning of
Ni$_{81}$Fe$_{19}$/IrMn bilayers in different relative orientations with
respect to the exchange bias direction. The measured voltage spectra allow a
quantitative determination of spin Hall angles, which are independent of the
orientation around 2.8\pm0.3%.",1804.01612v1
2021-03-01,Magnetic-Torque Enhanced by Tunable Dipolar interactions,"We use tunable dipolar-interactions between the spins of nitrogen-vacancy
(NV) centers in diamond to rotate a diamond crystal. Specifically, we employ
cross-relaxation between the electronic spin of pairs of NV centers in a
trapped diamond to enhance the anisotropic NV paramagnetism and thus to
increase the associated spin torque. Our observations open a path towards the
use of mechanical oscillators to detect paramagnetic defects that lack optical
transitions, to investigation of angular momentum conservation in spin
relaxation processes and to novel means of cooling the motion of mechanical
oscillators.",2103.00836v1
2021-09-21,Torque-free manipulation of nanoparticle rotations via embedded spins,"Spin angular momentum and mechanical rotation both contribute to the total
angular momentum of rigid bodies, leading to spin-rotational coupling via the
Einstein-de Haas and Barnett effects. Here we show that the revolutions of
symmetric nanorotors can be strongly affected by a small number of intrinsic
spins. The resulting dynamics are observable with freely rotating nanodiamonds
with embedded nitrogen-vacancy centers and persist for realistically-shaped
near-symmetric particles, opening the door to torque-free schemes to control
their rotations at the quantum level.",2109.10340v2
2020-12-16,Observation of anti-damping spin-orbit torques generated by in-plane and out-of-plane spin polarizations in MnPd3,"High spin-orbit torques (SOTs) generated by topological materials and heavy
metals interfaced with a ferromagnetic layer show promise for next generation
magnetic memory and logic devices. SOTs generated from the in-plane spin
polarization along y-axis originated by the spin Hall and Edelstein effects can
switch magnetization collinear with the spin polarization in the absence of
external magnetic fields. However, an external magnetic field is required to
switch the magnetization along x and z-axes via SOT generated by y-spin
polarization. Here, we present that the above limitation can be circumvented by
unconventional SOT in magnetron-sputtered thin film MnPd3. In addition to the
conventional in-plane anti-damping-like torque due to the y-spin polarization,
out-of-plane and in-plane anti-damping-like torques originating from z-spin and
x-spin polarizations, respectively have been observed at room temperature. The
spin torque efficiency corresponding to the y-spin polarization from MnPd3 thin
films grown on thermally oxidized silicon substrate and post annealed at 400
Deg C is 0.34 - 0.44. Remarkably, we have demonstrated complete external
magnetic field-free switching of perpendicular Co layer via unconventional
out-of-plane anti-damping-like torque from z-spin polarization. Based on the
density functional theory calculations, we determine that the observed x- and
z- spin polarizations with the in-plane charge current are due to the low
symmetry of the (114) oriented MnPd3 thin films. Taken together, the new
material reported here provides a path to realize a practical spin channel in
ultrafast magnetic memory and logic devices.",2012.09315v1
2013-03-20,Domain walls in spin valve nanotracks: characterisation and applications,"Magnetic systems based on the manipulation of domain walls (DWs) in
nano-tracks have been shown to store data at high density, perform complex
logic operations, and mechanically manipulate magnetic beads. The magnetic
track has been a model system to study magnetic and magneto-electronic
phenomena, such as field induced DW propagation and spin-transfer torque. This
thesis focuses on DW manipulation and DW-based devices in spin-valve (SV)
tracks. In comparison to monolayer tracks, the SV track enables more sensitive
and versatile measurements, as well as an electronic output of DW-based
devices, of crucial interest to applications. However, these multi-layered
tracks add new, potentially disruptive magnetic interactions, as well as
fabrication challenges. In this thesis, the DW propagation in SV tracks of
different compositions was studied, and a system with DW propagation properties
comparable to the state-of-the-art in monolayer tracks was demonstrated, down
to an unprecedented lateral size of 33nm. Several logic devices were
demonstrated and studied, namely a turn-counting DW spiral, a DW gate, DW logic
NOT gates, and a DW-DW interactor. It was found that the magnetic behaviour of
these devices was analogous to that of monolayer structures, and the device
performance, as defined by the range of field wherein they function desirably,
was found to be comparable to that of monolayer systems. The interaction
between DWs in adjacent tracks was studied and new phenomena were
characterised, such as DW depinning induced by a static or travelling adjacent
DW. The contribution of different mechanisms to electrical current induced
depinning were quantified, and it was found that the Oersted field, negligible
in monolayer tracks, was responsible for large variations in depinning field in
SV tracks, and that the strength of spin-transfer effect was similar to that
reported in monolayer tracks.",1303.5018v1
2002-01-08,Field dependent anisotropy change in a supramolecular Mn(II)-[3x3] grid,"The magnetic anisotropy of a novel Mn(II)-[3x3] grid complex was investigated
by means of high-field torque magnetometry. Torque vs. field curves at low
temperatures demonstrate a ground state with S > 0 and exhibit a torque step
due to a field induced level-crossing at B* \approx 7.5 T, accompanied by an
abrupt change of magnetic anisotropy from easy-axis to hard-axis type. These
observations are discussed in terms of a spin Hamiltonian formalism.",0201090v1
2008-09-26,New Calculations of Stellar Wind Torques,"Using numerical simulations of magnetized stellar winds, we carry out a
parameter study to find the dependence of the stellar wind torque on observable
parameters. We find that the power-law dependencies of the torque on parameters
is significantly different than what has been used in all spin evolution models
to date.",0809.4718v1
2010-04-30,A diagnosis on torque reversals in 4U 1626-67,"Several X-ray pulsars have been observed to experience torque reversals,
which provide important observational clues to the interaction between the
neutron star magnetic field and the accretion disk. We review the current
models proposed for the torque reversals and discuss their viability based on
the observations of the quasi-periodic oscillations (QPOs) in 4U 1626-67. Most
of these models seem to be incompatible with the evolution of the QPO
frequencies if they are interpreted in terms of the beat frequency model. We
suggest that winds or outflows from the neutron star and the accretion disk may
play an important role in accounting for the spin-down in disk-fed neutron
stars.",1004.5520v1
1999-05-17,Spectral Transition and Torque Reversal in X-ray Pulsar 4U 1626-67,"The accretion-powered, X-ray pulsar 4U 1626-67 has recently shown an abrupt
torque reversal accompanied by a dramatic spectral transition and a relatively
small luminosity change. The time-averaged X-ray spectrum during spin-down is
considerably harder than during spin-up. The observed torque reversal can be
explained by an accretion flow transition triggered by a gradual change in the
mass accretion rate. The sudden transition to spin-down is caused by a change
in the accretion flow rotation from Keplerian to sub-Keplerian. 4U 1626-67 is
estimated to be near spin equilibrium with a mass accretion rate Mdot~2x10**16
g/s, Mdot decreasing at a rate ~6x10**14 g/s/yr, and a polar surface magnetic
field of ~2b_p**{-1/2} 10^**12G where b_p is the magnetic pitch. During
spin-up, the Keplerian flow remains geometrically thin and cool. During
spin-down, the sub-Keplerian flow becomes geometrically thick and hot. Soft
photons from near the stellar surface are Compton up-scattered by the hot
accretion flow during spin-down while during spin-up such scattering is
unlikely due to the small scale-height and low temperature of the flow. This
mechanism accounts for the observed spectral hardening and small luminosity
change. The scattering occurs in a hot radially falling column of material with
a scattering depth ~0.3 and a temperature ~10^9K. The X-ray luminosity at
energies >5keV could be a poor indicator of the mass accretion rate. We briefly
discuss the possible application of this mechanism to GX 1+4, although there
are indications that this system is significantly different from other
torque-reversal systems.",9905214v1
2008-08-27,Torque and conventional spin-Hall currents in two-dimensional spin-orbit coupled systems: Universal relation and hyper-selection rule,"We investigate torque and also conventionally defined spin-Hall currents in
two-dimensional (2D) spin-orbit coupled systems of spin-1/2 particles within
the linear response Kubo formalism. We obtain some interesting relations
between the conventional and torque spin-Hall conductivities for the generic
effective Hamiltonian $H_0=\epsilon_k^0+A(k)\sigma_x-B(k)\sigma_y$, where
$A(k)=\eta^A_ik_i+\eta^A_{ij}k_ik_j+\eta^A_{ijl}k_ik_jk_l+...$,
$B(k)=\eta^B_ik_i+\eta^B_{ij}k_ik_j+\eta^B_{ijl}k_ik_jk_l+...$, and $\eta$'s
are the specific system-dependent coefficients. Specifically, we find that in
the intrinsic case the magnitude of torque spin-Hall conductivity
$\sigma^{\tau_z}_{xy}(0)$ is always twice larger than the conventional
spin-Hall conductivity $\sigma^{s_z}_{xy}(0)$, and the two conductivities have
the opposite signs, i.e., $\sigma^{\tau_z}_{xy}(0)=-2\sigma^{s_z}_{xy}(0)$.
This universal relation also holds in the presence of an uniform in-plane
magnetic field. We also find that if the energy dispersion is rotationally
invariant, there exists a hyper-angular momentum $I_z = (k\times
\partial\theta/\partial k)_z s_z + L_z$ which is conserved. Furthermore, the
hyper-angular momentum current $<{1/2}\{I_z,v_x\}>$ vanishes, and this leads to
a hyper selection rule for the conventional spin-Hall current.",0808.3625v2
2016-10-28,Insulating nanomagnets driven by spin torque,"Magnetic insulators, such as yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$), are
ideal materials for ultra-low power spintronics applications due to their low
energy dissipation and efficient spin current generation and transmission.
Recently, it has been realized that spin dynamics can be driven very
effectively in micrometer-sized Y$_3$Fe$_5$O$_{12}$/Pt heterostructures by
spin-Hall effects. We demonstrate here the excitation and detection of spin
dynamics in Y$_3$Fe$_5$O$_{12}$/Pt nanowires by spin-torque ferromagnetic
resonance. The nanowires defined via electron-beam lithography are fabricated
by conventional room temperature sputtering deposition on Gd$_3$Ga$_5$O$_{12 }$
substrates and lift-off. We observe field-like and anti-damping-like torques
acting on the magnetization precession, which are due to simultaneous
excitation by Oersted fields and spin-Hall torques. The Y$_3$Fe$_5$O$_{12}$/Pt
nanowires are thoroughly examined over a wide frequency and power range. We
observe a large change in the resonance field at high microwave powers, which
is attributed to a decreasing effective magnetization due to microwave
absorption. These heating effects are much more pronounced in the investigated
nanostructures than in comparable micron-sized samples. By comparing different
nanowire widths, the importance of geometrical confinements for magnetization
dynamics becomes evident: quantized spin-wave modes across the width of the
wires are observed in the spectra. Our results are the first stepping stones
toward the realization of integrated magnonic logic devices based on
insulators, where nanomagnets play an essential role.",1610.09360v1
2019-12-05,Deterministic magnetization switching using lateral spin-orbit torque,"Current-induced magnetization switching by spin-orbit torque (SOT) holds
considerable promise for next generation ultralow-power memory and logic
applications. In most cases, generation of spin-orbit torques has relied on an
external injection of out-of-plane spin currents into the magnetic layer, while
an external magnetic field along the electric current direction is generally
required for realizing deterministic switching by SOT. Here, we report
deterministic current-induced SOT full magnetization switching by lateral
spin-orbit torque in zero external magnetic field. The Pt/Co/Pt magnetic
structure was locally annealed by a laser track along the in-plane current
direction, resulting in a lateral Pt gradient within the ferromagnetic layer,
as confirmed by microstructure and chemical composition analysis. In zero
magnetic field, the direction of the deterministic current-induced
magnetization switching depends on the location of the laser track, but shows
no dependence on the net polarization of external out-of-plane spin currents.
From the behavior under external magnetic fields, we identify two independent
mechanisms giving rise to SOT, i.e. the lateral Pt-Co asymmetry as well as
out-of-plane injected spin currents, where the polarization and the magnitude
of the SOT in the former case depends on the relative location and the laser
power of the annealing track. Our results demonstrate an efficient field-free
deterministic full magnetization switching scheme, without requiring
out-of-plane spin current injection or complex external stack structures.",1912.02388v1
2023-02-09,Spin torques and anomalous velocity in spin textures induced by fast electron injection from topological ferromagnets: The role of gauge fields,"A new method for analysing magnetization dynamics in spin textures under the
influence of fast electron injection from topological ferromagnetic sources
such as Dirac half metals has been proposed. These electrons, traveling at a
velocity $v$ with a non-negligible value of $v/c$ (where c is the speed of
light), generate a non-equilibrium magnetization density in the spin-texture
region, which is related to an electric dipole moment via relativistic
interactions. When this resulting dipole moment interacts with gauge fields in
the spin-texture region, an effective field is created that produces spin
torques. These torques, like spin-orbit torques that occur when electrons are
injected from a heavy metal into a ferromagnet, can display both damping-like
and anti-damping-like properties. Finally, we demonstrate that such an
interaction between the dipole moment and the gauge field introduces an
anomalous velocity that can contribute to transverse electrical conductivity in
the spin texture in a way comparable to the topological Hall effect.",2302.04551v7
2011-10-12,Roche Accretion of stars close to massive black holes,"In this paper we consider Roche accretion in an Extreme Mass-Ratio Inspiral
(EMRI) binary system formed by a star orbiting a massive black hole. The
ultimate goal is to detect the mass and spin of the black hole and provide a
test of general relativity in the strong-field regime from the resultant
quasi-periodic signals. Before accretion starts, the stellar orbit is presumed
to be circular and equatorial, and shrinks due to gravitational radiation. New
fitting formulae are presented for the inspiral time and the radiation-reaction
torque in the relativistic regime. If the inspiralling star fills its Roche
lobe outside the Innermost Stable Circular Orbit (ISCO) of the hole, gas will
flow through the inner Lagrange point (L1) to the hole. We give new
relativistic interpolation formulae for the volume enclosed by the Roche lobe.
If this mass-transfer happens on a time scale faster than the thermal time
scale but slower than the dynamical time scale, the star will evolve
adiabatically, and, in most cases, will recede from the hole while filling its
Roche lobe. We calculate how the stellar orbital period and mass-transfer rate
will change through the ""Roche evolution"" for various types of stars in the
relativistic regime. We envisage that the mass stream eventually hits the
accretion disc, where it forms a hot spot orbiting the hole and may ultimately
modulate the luminosity with the stellar orbital frequency. The observability
of such a modulation is discussed along with a possible interpretation of an
intermittent 1 hour period in the X-ray emission of RE J1034+396.",1110.2614v2
2016-12-22,Frequency control and coherent excitation transfer in a nanostring resonator network,"Coupling, synchronization, and non-linear dynamics of resonator modes are
omnipresent in nature and highly relevant for a multitude of applications
ranging from lasers to Josephson arrays and spin torque oscillators.
Nanomechanical resonators are ideal candidates to study these effects on a
fundamental level and to realize all-mechanical platforms for information
processing and storage. For larger resonator networks, however, this requires
the ability to tune the mode frequencies selectively and to operate the
resonators in the strong coupling regime. Here, we present a proof-of-principle
realization of a resonator network consisting of two high-quality nanostring
resonators, coupled mechanically by a shared support. First, we demonstrate
that we can control the fundamental mode frequencies of both nanostrings
independently by a strong drive tone resonant with one of the higher harmonics
of the network, rendering local control gates redundant. The tuning mechanism
relies on an effective increase of the pre-stress in a highly excited
nanostring, known as geometric nonlinearity. Using this selective frequency
control of the individual nanomechanical resonators, we investigate the
coherent dynamics of the resonator network, which is a classical model system
showing several of the characteristic features of strongly coupled quantum
systems. In particular, we demonstrate mode splitting, classical Rabi
oscillations, as well as adiabatic and diabatic transitions between the coupled
states representing the classical analog of Landau-Zener tunneling. Therefore,
this coupling and tuning concept opens the path to a selective phonon transfer
between two spatially separated mechanical resonators.",1612.07511v1
2020-07-21,TCIM: Triangle Counting Acceleration With Processing-In-MRAM Architecture,"Triangle counting (TC) is a fundamental problem in graph analysis and has
found numerous applications, which motivates many TC acceleration solutions in
the traditional computing platforms like GPU and FPGA. However, these
approaches suffer from the bandwidth bottleneck because TC calculation involves
a large amount of data transfers. In this paper, we propose to overcome this
challenge by designing a TC accelerator utilizing the emerging
processing-in-MRAM (PIM) architecture. The true innovation behind our approach
is a novel method to perform TC with bitwise logic operations (such as
\texttt{AND}), instead of the traditional approaches such as matrix
computations. This enables the efficient in-memory implementations of TC
computation, which we demonstrate in this paper with computational
Spin-Transfer Torque Magnetic RAM (STT-MRAM) arrays. Furthermore, we develop
customized graph slicing and mapping techniques to speed up the computation and
reduce the energy consumption. We use a device-to-architecture co-simulation
framework to validate our proposed TC accelerator. The results show that our
data mapping strategy could reduce $99.99\%$ of the computation and $72\%$ of
the memory \texttt{WRITE} operations. Compared with the existing GPU or FPGA
accelerators, our in-memory accelerator achieves speedups of $9\times$ and
$23.4\times$, respectively, and a $20.6\times$ energy efficiency improvement
over the FPGA accelerator.",2007.10702v1
2021-12-01,Triangle Counting Accelerations: From Algorithm to In-Memory Computing Architecture,"Triangles are the basic substructure of networks and triangle counting (TC)
has been a fundamental graph computing problem in numerous fields such as
social network analysis. Nevertheless, like other graph computing problems, due
to the high memory-computation ratio and random memory access pattern, TC
involves a large amount of data transfers thus suffers from the bandwidth
bottleneck in the traditional Von-Neumann architecture. To overcome this
challenge, in this paper, we propose to accelerate TC with the emerging
processing-in-memory (PIM) architecture through an algorithm-architecture
co-optimization manner. To enable the efficient in-memory implementations, we
come up to reformulate TC with bitwise logic operations (such as AND), and
develop customized graph compression and mapping techniques for efficient data
flow management. With the emerging computational Spin-Transfer Torque Magnetic
RAM (STT-MRAM) array, which is one of the most promising PIM enabling
techniques, the device-to-architecture co-simulation results demonstrate that
the proposed TC in-memory accelerator outperforms the state-of-the-art GPU and
FPGA accelerations by 12.2x and 31.8x, respectively, and achieves a 34x energy
efficiency improvement over the FPGA accelerator.",2112.00471v1
2022-04-21,Off-axis electron holography for the direct visualization of perpendicular shape anisotropy in nano-scale 3D magnetic random-access-memory devices,"Perpendicular shape anisotropy (PSA) and double magnetic tunnel junctions
(DMTJ) offer practical solutions to downscale spin-transfer-torque Magnetic
Random-Access Memory (STT-MRAM) beyond 20 nm technology nodes, whilst retaining
their thermal stability and reducing critical currents applied. However, as
these modern devices become smaller and three-dimensionally (3D) complex, our
understanding of their functional magnetic behavior is often indirect, relying
on magnetoresistance measurements and micromagnetic modelling. In this paper,
we review recent work that was performed on these structures using a range of
advanced electron microscopy techniques, focusing on aspects specific to the 3D
and nanoscale nature of such elements. We present the methodology for the
systematic transfer of individual SST-MRAM nano-pillars from large-scale arrays
to image their magnetic configurations directly using off-axis electron
holography. We show that improved phase sensitivity through stacking of
electron holograms can be used to image subtle variations in DMTJs and the
thermal stability of < 20 nm PSA-STT-MRAM nano-pillars during in-situ heating.
The experimental practicalities, benefits and limits of using electron
holography for analysis of MRAM devices are discussed, unlocking practical
pathways for direct imaging of the functional magnetic performance of these
systems with high spatial resolution and sensitivity.",2204.10220v1
2023-08-21,Neuromorphic Hebbian learning with magnetic tunnel junction synapses,"Neuromorphic computing aims to mimic both the function and structure of
biological neural networks to provide artificial intelligence with extreme
efficiency. Conventional approaches store synaptic weights in non-volatile
memory devices with analog resistance states, permitting in-memory computation
of neural network operations while avoiding the costs associated with
transferring synaptic weights from a memory array. However, the use of analog
resistance states for storing weights in neuromorphic systems is impeded by
stochastic writing, weights drifting over time through stochastic processes,
and limited endurance that reduces the precision of synapse weights. Here we
propose and experimentally demonstrate neuromorphic networks that provide
high-accuracy inference thanks to the binary resistance states of magnetic
tunnel junctions (MTJs), while leveraging the analog nature of their stochastic
spin-transfer torque (STT) switching for unsupervised Hebbian learning. We
performed the first experimental demonstration of a neuromorphic network
directly implemented with MTJ synapses, for both inference and
spike-timing-dependent plasticity learning. We also demonstrated through
simulation that the proposed system for unsupervised Hebbian learning with
stochastic STT-MTJ synapses can achieve competitive accuracies for MNIST
handwritten digit recognition. By appropriately applying neuromorphic
principles through hardware-aware design, the proposed STT-MTJ neuromorphic
learning networks provide a pathway toward artificial intelligence hardware
that learns autonomously with extreme efficiency.",2308.11011v1
2020-09-29,Migration of gap-opening planets in 3D stellar-irradiated accretion disks,"Context. The origin of giant planets at moderate separations
$\simeq$$1$$-$$10$ au is still not fully understood because numerical studies
of Type II migration in protoplanetary disks often predict a decay of the
semi-major axis that is too fast. According to recent 2D simulations, inward
migration of a gap-opening planet can be slowed down or even reversed if the
outer gap edge becomes heated by irradiation from the central star, and puffed
up.
  Aims. Here we study how stellar irradiation reduces the disk-driven torque
and affects migration in more realistic 3D disks.
  Methods. Using 3D hydrodynamic simulations with radiation transfer, we
investigated the static torque acting on a single gap-opening planet embedded
in a passively heated accretion disk.
  Results. Our simulations confirm that a temperature inversion is established
at the irradiated outer gap edge and the local increase of the scale height
reduces the magnitude of the negative outer Lindblad torque. However, the
temperature excess is smaller than assumed in 2D simulations and the torque
reduction only becomes prominent for specific parameters. For the viscosity
$\alpha=10^{-3}$, the total torque is reduced for planetary masses ranging from
$0.1$ to $0.7$ Jupiter mass, with the strongest reduction being by a factor of
$-0.17$ (implying outward migration) for a Saturn-mass planet. For a
Jupiter-mass planet, the torque reduction becomes stronger with increasing
$\alpha$ (the torque is halved when $\alpha=5\times10^{-3}$).
  Conclusions. We conclude that planets that open moderately wide and deep gaps
are subject to the largest torque modifications and their Type II migration can
be stalled due to gap edge illumination. We then argue that the torque
reduction can help to stabilize the orbits of giant planets forming at
$\gtrsim$$1$ au.",2009.14142v1
2006-01-10,Accretion torque on magnetized neutron stars,"The conventional picture of disk accretion onto magnetized neutron stars has
been challenged by the spin changes observed in a few X-ray pulsars, and by
theoretical results from numerical simulations of disk-magnetized star
interactions. These indicate possible accretion during the propeller regime and
the spin-down torque increasing with the accretion rate. Here we present a
model for the accretion torque exerted by the disk on a magnetized neutron
star, assuming accretion continues even for rapid rotators. The accretion
torque is shown to have some different characteristics from that in the
conventional model, but in accord with observations and numerical calculations
of accretion-powered magnetized neutron stars. We also discuss its possible
applications to the spin evolution in X-ray pulsars.",0601211v1
2009-09-21,Spin torque and charge resistance of ferromagnetic semiconductor $2π$ and $π$ domain walls,"Charge resistance and spin torque are generated by coherent carrier transport
through ferromagnetic 360 degree domain walls, although they follow
qualitatively different trends than for 180 degree domain walls. The charge
resistance of 360 degree domain walls reaches a maximum at an intermediate wall
thickness, unlike 180 degree domain walls, whose resistance decreases
monotonically with wall thickness. The peak amplitude of the spin torque and
the optimal thickness of the domain wall to maximize torque for a 360 degree
wall are more than twice as large as found for a 180 degree domain wall in the
same material, producing a larger domain wall velocity for the 360 degree wall
and suggesting unexpected nonlinearities in magnetoelectronic devices
incorporating domain wall motion.",0909.3831v1
2014-11-22,Large voltage-induced modification of spin-orbit torques in Pt/Co/GdOx,"We report on large modifications of current-induced spin-orbit torques in a
gated Pt/Co/Gd-oxide microstrip due to voltage-driven O$^{2-}$ migration. The
Slonczewski-like and field-like torques are quantified using a low-frequency
harmonic technique based on the polar magneto-optical Kerr effect.
Voltage-induced oxidation of Co enhances the Slonczewski-like torque by as much
as an order of magnitude, and simultaneously reduces the anisotropy energy
barrier by a factor of ~5. Such magneto-ionic tuning of interfacial spin-orbit
effects may significantly enhance the efficiency of magnetization switching and
provide additional degrees of freedom in spintronic devices.",1411.6153v1
2015-09-23,Dirac Spin-Orbit Torques at the Surface of Topological Insulators,"We address the nature of spin-orbit torques at the magnetic surfaces of
topological insulators, using both Kubo formula and Keldysh formalism. Through
the analysis of the derived spin-charge equations, we find that the so-called
Dirac torques possess a different symmetry compared to their Rashba
counterpart, as well as a high anisotropy as a function of the magnetization
direction. In particular, the damping torque vanishes when the magnetization
lies in the plane of the topological insulator surface. This peculiarity has
important consequences in terms of magnetization dynamics and switching, as
demonstrated numerically via a macrospin model.",1509.06929v2
2018-11-09,Switching of biaxial synthetic antiferromagnets: a micromagentic study,"We simulate the switching behavior of nanoscale synthetic antiferromagnets
(SAFs), inspired by recent experimental progress in spin-orbit-torque switching
of crystal antiferromagnets. The SAF consists of two ferromagnetic thin films
with in-plane biaxial anisotropy and interlayer exchange coupling. Staggered
field-like Rashba spin-orbit torques from the opposite surfaces of the SAF
induce a canted net magnetization, which triggers an orthogonal torque that
drives 90$^\circ$ switching of the N\'eel vector. Such dynamics driven by the
field-like spin-orbit torque allows for faster switching with increased Gilbert
damping, without a significant detrimental increase of the threshold switching
current density. Our results point to the potential of SAFs as model systems,
based on simple ferromagnetic metals, to mimic antiferromagnetic device
physics.",1811.04094v2
2017-05-31,Rashba torque beyond the Boltzmann regime,"We study spin torques induced by Rashba spin-orbit coupling in
two-dimensional ferromagnets under the good-metal condition
$\epsilon_{F}\tau/\hbar\gg1$ ($\epsilon_{F}$ the Fermi energy, $\tau$ the
electron lifetime) by employing the Kubo formula. We find that, in the presence
of spin-dependent disorder the Rashba torque changes greatly as the system
evolves out of the weak disorder limit where $\hbar/\tau$ is much smaller than
any intrinsic energy scale characterizing the multiband structure. The
antidamping-like component of Rashba torque can be comparable to and larger
than the field-like one out of the weak disorder limit. The semiclassical
Boltzmann theory produces the same results as microscopic linear response
calculations only in the weak disorder limit. Our analysis indicates that rich
behaviors of various nonequilibrium phenomena beyond the Boltzmann theory may
also be present even when $\epsilon_{F}\tau/\hbar\gg1$ in multiband systems
where $\epsilon_{F}$ is not the unique intrinsic energy scale.",1706.00049v2
2017-06-08,Writing and Reading antiferromagnetic Mn$_2$Au: Néel spin-orbit torques and large anisotropic magnetoresistance,"Antiferromagnets are magnetically ordered materials which exhibit no net
moment and thus are insensitive to magnetic fields. Antiferromagnetic
spintronics aims to take advantage of this insensitivity for enhanced
stability, while at the same time active manipulation up to the natural THz
dynamic speeds of antiferromagnets is possible, thus combining exceptional
storage density and ultra-fast switching. However, the active manipulation and
read-out of the N\'eel vector (staggered moment) orientation is challenging.
Recent predictions have opened up a path based on a new spin-orbit torque,
which couples directly to the N\'eel order parameter. This N\'eel spin-orbit
torque was first experimentally demonstrated in a pioneering work using
semimetallic CuMnAs. Here we demonstrate for Mn$_2$Au, a good conductor with a
high ordering temperature suitable for applications, reliable and reproducible
switching using current pulses and readout by magnetoresistance measurements.
The symmetry of the torques agrees with theoretical predictions and a large
read-out magnetoresistance effect of more than $\simeq 6$~$\%$ is reproduced by
ab initio transport calculations.",1706.02482v1
2019-05-02,Direct Evidence of Torque-mediated Optical Magnetism,"We report experimental evidence of a mechanism that supports and intensifies
induced magnetization at optical frequencies without the intervention of
spin-orbit or spin-spin interactions. Energy-resolved spectra of scattered
light, recorded at moderate intensities (108 W/cm2) and short timescales (<150
fs) in a series of non-magnetic molecular liquids, reveal the signature of
torque dynamics driven jointly by the electric and magnetic field components of
light at the molecular level. While past experiments have recorded radiant
magnetization from magneto-electric interactions of this type, no evidence has
been provided to date of the inelastic librational features expected in
cross-polarized light scattering spectra due to the Lorentz force acting in
combination with optical magnetic torque. Here, torque is shown to account for
inelastic components in the magnetic scattering spectrum under conditions that
produce no such features in electric dipole scattering, in excellent agreement
with quantum theoretical predictions",1905.00552v1
2016-11-24,Effect of surface state hybridization on current-induced spin-orbit torque in thin topological insulator films,"We investigate the current-induced spin-orbit torque in thin topological
insulator (TI) films in the presence of hybridization between the top and
bottom surface states. We formulate the relation between spin torque and TI
thickness, from which we derived the optimal value of the thickness to maximize
the torque. We show numerically that in typical TI thin films made of
$\mathrm{Bi_2Se_3}$, the optimal thickness is about 3-5 nm.",1611.08116v2
2019-10-11,Investigation of spin orbit torque driven dynamics in ferromagnetic heterostructures,"We use time-resolved (TR) measurements based on the polar magneto-optical
Kerr effect (MOKE) to study the magnetization dynamics excited by spin orbit
torques in Py (Permalloy)/Pt and Ta/CoFeB bilayers. The analysis reveals that
the field-like (FL) spin orbit torque (SOT) dominates the amplitude of the
first oscillation cycle of the magnetization precession and the damping-like
(DL) torque determines the final steady-state magnetization. In our bilayer
samples, we have extracted the effective fields, hFL and hDL, of the two SOTs
from the time-resolved magnetization oscillation spectrum. The extracted values
are in good agreement with those extracted from time-integrated DCMOKE
measurements, suggesting that the SOTs do not change at high frequencies. We
also find that the amplitude ratio of the first oscillation to steady state is
linearly proportional to the ratio hFL/hDL. The first oscillation amplitude is
inversely proportional to, whereas the steady state value is independent of,
the applied external field along the current direction.",1910.04945v1
2023-09-10,Deterministic and non-volatile switching of all-van der Waals spin-orbit torque system above room temperature without external magnetic fields,"Two-dimensional van der Waals (vdW) magnetic materials hold promise for the
development of high-density, energy-efficient spintronic devices for memory and
computation. Recent breakthroughs in material discoveries and spin-orbit torque
(SOT) control of vdW ferromagnets have opened a path for integration of vdW
magnets in commercial spintronic devices. However, a solution for field-free
electric control of perpendicular magnetic anisotropy (PMA) vdW magnets at room
temperatures, essential for building compact and thermally stable spintronic
devices, is still missing. Here, we report the first demonstration of
field-free deterministic and non-volatile switching of a PMA vdW ferromagnet,
Fe$_3$GaTe$_2$ above room temperature (up to 320 K). We use the unconventional
out-of-plane anti-damping torque from an adjacent WTe$_2$ layer to enable such
switching with a low current density of $2.23 \times 10^6$ A/cm$^2$. This study
exemplifies the efficacy of low-symmetry vdW materials for spin-orbit torque
control of vdW ferromagnets and provides an all-vdW solution for the next
generation of scalable and energy-efficient spintronic devices.",2309.04930v1
2017-08-04,Quantification of spin accumulation causing spin-orbit torque in Pt/Co/Ta stack,"Spin accumulation induced by spin-orbit coupling is experimentally quantified
in stack with in-plane magnetic anisotropy via the contribution of spin
accumulation to Hall resistances. Using a biasing direct current the spin
accumulation within the structure can be tuned, enabling quantification.
Quantification shows the spin accumulation can be more than ten percentage of
local magnetization, when the electric current is 1E11 A/m*m. The spin
accumulation is dependent of the thickness of Ta layer, the trend agrees with
that of spin Hall angle indicating the capability of Ta and Pt in generating
spins.",1709.07948v1
2016-09-19,Switching ferromagnetic spins by an ultrafast laser pulse: Emergence of giant optical spin-orbit torque,"Faster magnetic recording technology is indispensable to massive data storage
and big data sciences. {All-optical spin switching offers a possible solution},
but at present it is limited to a handful of expensive and complex rare-earth
ferrimagnets. The spin switching in more abundant ferromagnets may
significantly expand the scope of all-optical spin switching. Here by studying
40,000 ferromagnetic spins, we show that it is the optical spin-orbit torque
that determines the course of spin switching in both ferromagnets and
ferrimagnets. Spin switching occurs only if the effective spin angular momentum
of each constituent in an alloy exceeds a critical value. Because of the strong
exchange coupling, the spin switches much faster in ferromagnets than
weakly-coupled ferrimagnets. This establishes a paradigm for all-optical spin
switching. The resultant magnetic field (65 T) is so big that it will
significantly reduce high current in spintronics, thus representing the
beginning of photospintronics.",1609.05855v1
2019-02-12,Spin transparency for an interface of an ultrathin magnet within the spin dephasing length,"We examine a modified drift-diffusion formalism to describe spin transport
near an ultrathin magnet whose thickness is similar to or less than the spin
dephasing length. Most of the previous theories on spin torque assume the
transverse component of a injected spin current dephases perfectly thus are
fully absorbed into the ferromagnet. However, in the state-of-art multilayer
systems under consideration of recent studies, the thicknesses of ferromagnets
are on the order of or less than a nanometer, thus one cannot safely assume the
spin dephasing to be perfect. To describe the effects of a finite dephasing
rate, we adopt the concept of transmitted mixing conductance, whose application
to the drift-diffusion formalism has been limited. For a concise description of
physical consequences, we introduce an effective spin transparency.
Interestingly, for an ultrathin magnet with a finite dephasing rate, the spin
transparency can be even enhanced and there arises a non-negligible field-like
spin-orbit torque even in the absence of the imaginary part of the spin mixing
conductance. The effective spin transparency provides a simple extension of the
drift-diffusion formalism, which is accessible to experimentalists analyzing
their results.",1902.04239v2
2023-07-22,Dense plasma irradiated platinum with improved spin Hall effect,"The impurity incorporation in host high-spin orbit coupling materials like
platinum has shown improved charge-to-spin conversion by modifying the up-spin
and down-spin electron trajectories by bending or skewing them in opposite
directions. This enables efficient generation, manipulation, and transport of
spin currents. In this study, we irradiate the platinum with non-focus dense
plasma to incorporate the oxygen ion species. We systematically analyze the
spin Hall angle of the oxygen plasma irradiated Pt films using spin torque
ferromagnetic resonance. Our results demonstrate a 2.4 times enhancement in the
spin Hall effect after plasma treatment of Pt as compared to pristine Pt. This
improvement is attributed to the introduction of disorder and defects in the Pt
lattice, which enhances the spin-orbit coupling and leads to more efficient
charge-to-spin conversion without breaking the spin-orbit torque symmetries.
Our findings offer a new method of dense plasma-based modification of material
for the development of advanced spintronic devices based on Pt and other heavy
metals.",2307.12139v1
2017-12-31,Proper dissipative torques in antiferromagnetic dynamics,"There is little doubt that the magnetization dynamics of ferromagnetic
systems is governed by the Landau-Lifshitz-Gilbert equation or its
generalization with various spin torques. In contrast, there are several sets
of dynamic equations for two-sublattice antiferromagnets (AFMs) in literature
that have different forms of dissipative torques and no proper dynamic
equations for multi-sublattice AFMs and ferrimagnets in general. Here we
introduce the general Rayleigh dissipation functional into the Lagrange
equation and derive the proper form of the dissipative torques in the
phenomenological equations for the AFMs with multiple sublattices. A new type
of dissipative torque arising from inter-sublattice drag effect is discovered
that has important influences on magnon lifetime and domain wall motion. In
particular, our theory unifies different dynamic equations of AFMs in
literature.",1801.00217v1
2021-03-09,Current-induced torques in magnetic Weyl semimetal tunnel junctions,"We study the current-induced torques in asymmetric magnetic tunnel junctions
containing a conventional ferromagnet and a magnetic Weyl semimetal contact.
The Weyl semimetal hosts chiral bulk states and topologically protected Fermi
arc surface states which were found to govern the voltage behavior and
efficiency of current-induced torques. We report how bulk chirality dictates
the sign of the non-equilibrium torques acting on the ferromagnet and discuss
the existence of large field-like torques acting on the magnetic Weyl semimetal
which exceeds the theoretical maximum of conventional magnetic tunnel
junctions. The latter are derived from the Fermi arc spin texture and display a
counter-intuitive dependence on the Weyl nodes separation. Our results shed
light on the new physics of multilayered spintronic devices comprising of
magnetic Weyl semimetals, which might open doors for new energy efficient
spintronic devices.",2103.05512v1
2021-12-23,Theory of Harmonic Hall Responses of Spin-Torque Driven Antiferromagnets,"Harmonic analysis is a powerful tool to characterize and quantify
current-induced torques acting on magnetic materials, but so far it remains an
open question in studying antiferromagnets. Here we formulate a general theory
of harmonic Hall responses of collinear antiferromagnets driven by
current-induced torques including both field-like and damping-like components.
By scanning a magnetic field of variable strength in three orthogonal planes,
we are able to distinguish the contributions from field-like torque,
damping-like torque, and concomitant thermal effects by analyzing the second
harmonic signals in the Hall voltage. The analytical expressions of the first
and second harmonics as functions of the magnetic field direction and strength
are confirmed by numerical simulations with good agreement. We demonstrate our
predictions in two prototype antiferromagnets, $\alpha-$Fe$_{2}$O$_{3}$ and
NiO, providing direct and general guidance to current and future experiments.",2112.12772v2
2023-05-26,Multipolar Pseudochirality Induced Optical Torque,"It has been observed that achiral nano-particles, such as flat helices, may
be subjected to an optical torque even when illuminated by normally incident
linearly polarized light. However, the origin of this fascinating phenomenon
has so far remained mostly unexplained. We therefore propose an exhaustive
discussion that provides a clear and rigorous explanation for the existence of
such a torque. Using multipolar theory, and taking into account nonlocal
interactions, we find that this torque stems from multipolar pseudochiral
responses that generate both spin and orbital angular momenta. We also show
that the nature of these peculiar responses makes them particularly dependent
on the asymmetry of the particles. By elucidating the origin of this type of
torque, this work may prove instrumental for the design of high-performance
nano-rotors.",2305.16942v1
2018-05-01,Self-torque and angular momentum balance for a spinning charged sphere,"Angular momentum balance is examined in the context of the electrodynamics of
a spinning charged sphere, which is allowed to possess any variable angular
velocity. We calculate the electric and magnetic fields of the (hollow) sphere,
and express them as expansions in powers of $\tau/t_c \ll 1$, the ratio of the
light-travel time $\tau$ across the sphere and the characteristic time scale
$t_c$ of variation of the angular velocity. From the fields we compute the
self-torque exerted by the fields on the sphere, and argue that only a piece of
this self-torque can be associated with radiation reaction. Then we obtain the
rate at which angular momentum is radiated away by the shell, and the total
angular momentum contained in the electromagnetic field. With these results we
demonstrate explicitly that the field angular momentum is lost in part to
radiation and in part to the self-torque; angular momentum balance is thereby
established. Finally, we examine the angular motion of the sphere under the
combined action of the self-torque and an additional torque supplied by an
external agent.",1805.01372v2
2021-11-15,Probing magnetic anisotropy in Kagome antiferromagnetic Mn$_3$Ge with torque magnetometry,"We investigate the magnetic symmetry of the topological antiferromagnetic
material Mn$_3$Ge by using torque measurements. Below the Neel temperature,
detailed angle-dependent torque measurements were performed on Mn$_3$Ge single
crystals in directions parallel and perpendicular to the Kagome basal plane.
The out-of plane torque data exhibit $\pm\sin\theta$ and $\sin2\theta$
behaviors, of which the former results from the spontaneous ferromagnetism
within the basal plane and the latter from the in- and out-of-plane
susceptibility anisotropy. The reversible component of the in-plane torque
exhibits $\sin6\varphi$ behavior, revealing the six-fold symmetry of the
in-plane magnetic free energy. Moreover, we find that the free energy minima
are pinned to the direction of spontaneous ferromagnetism, which correspond to
the maxima of the irreversible component of the in-plane torque. We provide an
effective spin model to describe the in-plane magnetic anisotropy. Our results
demonstrate that the ground state of Mn$_3$Ge is described by the coexistence
of a strong six-fold antichiral order and a weak ferromagnetic order induced by
second-order spin anisotropy.",2111.07587v2
2024-04-03,Harnessing Orbital Hall Effect in Spin-Orbit Torque MRAM,"Spin-Orbit Torque (SOT) Magnetic Random-Access Memory (MRAM) devices offer
improved power efficiency, nonvolatility, and performance compared to static
RAM, making them ideal, for instance, for cache memory applications. Efficient
magnetization switching, long data retention, and high-density integration in
SOT MRAM require ferromagnets (FM) with perpendicular magnetic anisotropy (PMA)
combined with large torques enhanced by Orbital Hall Effect (OHE). We have
engineered PMA [Co/Ni]$_3$ FM on selected OHE layers (Ru, Nb, Cr) and
investigated the potential of theoretically predicted larger orbital Hall
conductivity (OHC) to quantify the torque and switching current in
OHE/[Co/Ni]$_3$ stacks. Our results demonstrate a $\sim$30\% enhancement in
damping-like torque efficiency with a positive sign for the Ru OHE layer
compared to a pure Pt, accompanied by a $\sim$20\% reduction in switching
current for Ru compared to pure Pt across more than 250 devices, leading to
more than a 60\% reduction in switching power. These findings validate the
application of Ru in devices relevant to industrial contexts, supporting
theoretical predictions regarding its superior OHC. This investigation
highlights the potential of enhanced orbital torques to improve the performance
of orbital-assisted SOT-MRAM, paving the way for next-generation memory
technology.",2404.02821v1
2008-01-02,Accretion-Powered Stellar Winds II: Numerical Solutions for Stellar Wind Torques,"[Abridged] In order to explain the slow rotation observed in a large fraction
of accreting pre-main-sequence stars (CTTSs), we explore the role of stellar
winds in torquing down the stars. For this mechanism to be effective, the
stellar winds need to have relatively high outflow rates, and thus would likely
be powered by the accretion process itself. Here, we use numerical
magnetohydrodynamical simulations to compute detailed 2-dimensional
(axisymmetric) stellar wind solutions, in order to determine the spin down
torque on the star. We explore a range of parameters relevant for CTTSs,
including variations in the stellar mass, radius, spin rate, surface magnetic
field strength, the mass loss rate, and wind acceleration rate. We also
consider both dipole and quadrupole magnetic field geometries.
  Our simulations indicate that the stellar wind torque is of sufficient
magnitude to be important for spinning down a ``typical'' CTTS, for a mass loss
rate of $\sim 10^{-9} M_\odot$ yr$^{-1}$. The winds are wide-angle,
self-collimated flows, as expected of magnetic rotator winds with moderately
fast rotation. The cases with quadrupolar field produce a much weaker torque
than for a dipole with the same surface field strength, demonstrating that
magnetic geometry plays a fundamental role in determining the torque. Cases
with varying wind acceleration rate show much smaller variations in the torque
suggesting that the details of the wind driving are less important. We use our
computed results to fit a semi-analytic formula for the effective Alfv\'en
radius in the wind, as well as the torque. This allows for considerable
predictive power, and is an improvement over existing approximations.",0801.0436v3
2012-07-21,Swing switching of spin-torque valves,"We propose a method for inducing magnetization reversal using an AC spin
current polarized perpendicular to the equilibrium magnetization of the free
magnetic layer. We show that the critical AC spin current is significantly
smaller than the corresponding DC one. The effect is understood as a
consequence of the underdamped nature of the spin-torque oscillators. It allows
to use the kinetic inertia to overcome the residual energy barrier, rather than
suppressing the latter by a large spin current. The effect is similar to a
swing which may be set into high amplitude motion by a weak near-resonant push.
The optimal AC frequency is identified as the upper bifurcation frequency of
the corresponding driven nonlinear oscillator. Together with fast switching
times it makes the perpendicular AC method to be the most efficient way to
realize spin-torque memory valve.",1207.5171v3
2013-03-19,Spin torque transistor revisited,"This paper reports on the improvement of the differential current gain in the
spin-torque transistor based on two independent innovations, viz.the use of
magnetic insulators and the spin Hall effect. Since, except for a few examples,
spin transistors lack the current gain that is essential for many applications,
spintronics and magnetic information technology lack an essential functionality
compared to CMOS devices. Here, we show that negative differential resistance
and large differential gain is possible in a large region of parameter space of
the spin torque transistor. We also demonstrate that functionality is preserved
when the control part is replaced by a normal metal film with a large spin Hall
angle.",1303.4493v1
2013-09-12,Spin Neurons: A Possible Path to Energy-Efficient Neuromorphic Computers,"Recent years have witnessed growing interest in the field of brain-inspired
computing based on neural-network architectures. In order to translate the
related algorithmic models into powerful, yet energy-efficient
cognitive-computing hardware, computing-devices beyond CMOS may need to be
explored. The suitability of such devices to this field of computing would
strongly depend upon how closely their physical characteristics match with the
essential computing primitives employed in such models. In this work we discuss
the rationale of applying emerging spin-torque devices for bio-inspired
computing. Recent spin-torque experiments have shown the path to low-current,
low-voltage and high-speed magnetization switching in nano-scale magnetic
devices. Such magneto-metallic, current-mode spin-torque switches can mimic the
analog summing and thresholding operation of an artificial neuron with high
energy-efficiency. Comparison with CMOS-based analog circuit-model of neuron
shows that spin neurons can achieve more than two orders of magnitude lower
energy and beyond three orders of magnitude reduction in energy-delay product.
The application of spin neurons can therefore be an attractive option for
neuromorphic computers of future.",1309.3303v1
2014-03-20,Frequent Spin Reorientation of Galaxies due to Local Interactions,"We study the evolution of angular momenta of ($M_*=10^{10}-10^{12}\msun$)
galaxies utilizing large-scale ultra-high resolution cosmological hydrodynamic
simulations and find that spin of the stellar component changes direction
frequently, caused by major mergers, minor mergers, significant gas inflows and
torques by nearby systems. The rate and nature of change of spin direction can
not be accounted for by large-scale tidal torques, because the latter fall
short in rates by orders of magnitude and because the apparent random swings of
the spin direction are inconsistent with alignment by linear density field. The
implications for galaxy formation as well as intrinsic alignment of galaxies
are profound. Assuming the large-scale tidal field is the sole alignment agent,
a new picture emerging is that intrinsic alignment of galaxies would be a
balance between slow large-scale coherent torquing and fast spin reorientation
by local interactions. What is still open is whether other processes, such as
feeding galaxies with gas and stars along filaments or sheets, introduce
coherence for spin directions of galaxies along the respective structures.",1403.5274v1
2017-09-21,Current-induced magnetization switching using electrically-insulating spin-torque generator,"Current-induced magnetization switching through spin-orbit torques (SOTs) is
the fundamental building block of spin-orbitronics. The SOTs generally arise
from the spin-orbit coupling of heavy metals. However, even in a
heterostructure where a metallic magnet is sandwiched by two different
insulators, a nonzero current-induced SOT is expected because of the broken
inversion symmetry; an electrical insulator can be a spin-torque generator.
Here, we demonstrate current-induced magnetization switching using an
insulator. We show that oxygen incorporation into the most widely used
spintronic material, Pt, turns the heavy metal into an electrically-insulating
generator of the SOTs, enabling the electrical switching of perpendicular
magnetization in a ferrimagnet sandwiched by electrically-insulating oxides. We
further found that the SOTs generated from the Pt oxide can be controlled
electrically through voltage-driven oxygen migration. These findings open a
route towards energy-efficient, voltage-programmable spin-orbit devices based
on solid-state switching of heavy metal oxidation.",1709.07127v1
2019-11-12,Iridium Enabled Field-free Spin-orbit Torque Switching of Perpendicular Magnetic Tunnel Junction Device,"Writing magnetic bits by spin-orbit torques (SOTs) arising from spin Hall
effect creates new possibilities for ultrafast and low-power magnetoresistive
random access memory (MRAM). For perpendicular MRAM, an extra in-plane field is
required to break the symmetry for the deterministic SOT writing of the
perpendicular storage layer. Although schemes have been demonstrated in
external-field-free SOT switching of a perpendicular layer, practically
integrating them with perpendicular MTJs still appears to be challenging. Here,
we present experimental demonstration of spin-orbit torques (SOTs) switching a
perpendicular magnetic tunnel junction (MTJ) device without applying an
external magnetic field. An Ir layer is used to serve dual-purpose of both
injecting the pure spin current via spin Hall effect and mediating an in-plane
exchange field to the perpendicular free layer of the MTJ. Robust field-free
SOT switching with pulsed write path current is demonstrated for various MTJ
sizes ranging from 50 nm to 500 nm. The effect of MTJ size and pulse width on
the critical switching current is studied. Combined micromagnetic simulations
are carried out to provide in-depth analysis of the switching dynamics as well
as the thermal effect on the switching.",1911.05007v1
2020-04-08,Charge-to-spin conversion efficiency in ferromagnetic nanowires by spin torque ferromagnetic resonance: Reconciling lineshape and linewidth analysis methods,"Spin orbit torques are of great interest for switching the magnetization
direction in nanostructures, moving skyrmions and exciting spin waves. The
standard method of determining their efficiency is by spin torque ferromagnetic
resonance (ST-FMR), a technique that involves analyzing the resonance linewidth
or lineshape. On microstuctures these two analysis methods are quite
consistent. Here we present ST-FMR results on permalloy (Ni$_{80}$Fe$_{20}$)
nanowires -- with widths varying from $150$ to 800 nm -- that show that the
standard model used to analyze the resonance linewidth and lineshape give
different results; the efficiency appears greatly enhanced in nanowires when
the lineshape method is used. A ST-FMR model that properly accounts for the
sample shape is presented and shows much better consistency between the two
methods. Micromagnetic simulations are used to verify the model. These results
and the more accurate nanowire model presented are of importance for
characterizing and optimizing charge-to-spin conversion efficiencies in
nanostructures.",2004.03784v1
2019-03-08,Field-free spin-orbit torque switching in Co/Pt/Co multilayer with mixed magnetic anisotropies,"Spin-orbit-torque (SOT) induced magnetization switching in Co/Pt/Co trilayer,
with two Co layers exhibiting magnetization easy axes orthogonal to each other
is investigated. Pt layer is used as a source of spin-polarized current as it
is characterized by relatively high spin-orbit coupling. The spin Hall angle of
Pt, $\theta = 0.08$ is quantitatively determined using spin-orbit torque
ferromagnetic resonance technique. In addition, Pt serves as a spacer between
two Co layers and depending on it's thickness, different interlayer exchange
coupling (IEC) energy between ferromagnets is induced. Intermediate IEC
energies, resulting in a top Co magnetization tilted from the perpendicular
direction, allows for SOT-induced feld-free switching of the top Co layer. The
switching process is discussed in more detail, showing the potential of the
system for neuromorphic applications.",1903.03368v1
2021-01-26,Lack of simple correlation between switching current density and spin-orbit torque efficiency of perpendicularly magnetized spin-current generator/ferromagnet heterostructures,"Spin-orbit torque can drive electrical switching of magnetic layers. Here, we
report that at least for micrometer-sized samples there is no simple
correlation between the efficiency of dampinglike spin-orbit torque
({\xi}_DL^j) and the critical switching current density of perpendicularly
magnetized spin-current generator/ferromagnet heterostructures. We find that
the values of {\xi}_DL^j based on switching current densities can either under-
or over-estimated {\xi}_DL^j by up to tens of times in a domain-wall depinning
analysis, while in the macrospin analysis based on the switching current
density {\xi}_DL^j can be overestimated by up to thousands of times. When
comparing the relative strengths of {\xi}_DL^j of spin-current generators, the
critical switching current densities by themselves are a poor predictor.",2101.10521v1
2023-03-13,Intrinsic spin-orbit torque mechanism for deterministic all-electric switching of noncollinear antiferromagnets,"Using a pure electric current to control kagome noncollinear antiferromagnets
is promising in information storage and processing, but a full description is
still lacking, in particular, on intrinsic (i.e., no external magnetic fields
or external spin currents) spin-orbit torques. In this work, we
self-consistently describe the relations among the electronic structure,
magnetic structure, spin accumulations, and intrinsic spin-orbit torques, in
the magnetic dynamics of a noncollinear antiferromagnet driven by a pure
electric current. Our calculation can yield a critical current density
comparable with those in the experiments, when considering the boost from the
out-of-plane magnetic dynamics induced by the current-driven spin accumulation
on individual magnetic moments. We stress the parity symmetry breaking in
deterministic switching among magnetic structures. This work will be helpful
for future applications of noncollinear antiferromagnets.",2303.06929v2
2012-01-26,Pseudospin Transfer Torques in Semiconductor Electron Bilayers,"We use self-consistent quantum transport theory to investigate the influence
of electron-electron interactions on interlayer transport in semiconductor
electron bilayers in the absence of an external magnetic field. We conclude
that, even though spontaneous pseudospin order does not occur at zero field,
interaction-enhanced quasiparticle tunneling amplitudes and pseudospin transfer
torques do alter tunneling I-V characteristics, and can lead to time-dependent
response to a dc bias voltage.",1201.5569v2
2022-09-06,Enhancement of spin-orbit torque efficiency by tailoring interfacial spin-orbit coupling in Pt-based magnetic multilayers,"We study inserting Co layer thickness-dependent spin transport and spin-orbit
torques (SOTs) in the Pt/Co/Py trilayers by spin-torque ferromagnetic
resonance. The interfacial perpendicular magnetic anisotropy energy density
($K_s = 2.7~erg/cm^2$), which is dominated by interfacial spin-orbit coupling
(ISOC) in the Pt/Co interface, total effective spin-mixing conductance
($G_{eff,tot} = 0.42 {\times} 10^{15}~{\Omega}^{-1} m^{-2}$) and two-magnon
scattering (${\beta}_{TMS} = 0.46~nm^2$) are first characterized, and the
damping-like torque (${\xi}_{DL}$ = 0.103) and field-like torque (${\xi}_{FL}$
= -0.017) efficiencies are also calculated quantitatively by varying the
thickness of the inserting Co layer. The significant enhancement of
${\xi}_{DL}$ and ${\xi}_{FL}$ in Pt/Co/Py than Pt/Py bilayer system originates
from the interfacial Rashba-Edelstein effect due to the strong ISOC between
Co-3d and Pt-5d orbitals at the Pt/Co interface. Additionally, we find a
considerable out-of-plane spin polarization SOT, which is ascribed to the spin
anomalous Hall effect and possible spin precession effect due to IPMA-induced
perpendicular magnetization at the Pt/Co interface. Our results demonstrate
that the ISOC of the Pt/Co interface plays a vital role in spin transport and
SOTs-generation. Our finds offer an alternative approach to improve the
conventional SOTs efficiencies and generate unconventional SOTs with
out-of-plane spin polarization to develop low power Pt-based spintronic via
tailoring the Pt/FM interface.",2209.02282v1
2009-06-23,New Torque Reversal and Spin-Up of 4u 1626- 67 Observed by Fermi/GBM and Swift/BAT,"After about 18 years of steadily spinning down, the accretion-powered pulsar
4U 1626-67, experienced a torque reversal at the beginning of 2008. For the
present study we have used all available Fermi/GBM data since its launch in
2008 June 11 and over 5 yr of hard X-ray Swift/BAT observations (starting from
2004 October up to the present time). This second detected torque reversal is
centered near MJD 54500 (2008 Feb 4) and it lasts approximately 150 days. From
2004 up to the end of 2007 4U 1626-67 the spin-down rate decreased at a mean
rate of ~ -5.5E-13 Hz s-1 until the source reversed torque again. Since then it
has been following a steady spin-up at a mean rate of ~ 5E-13 Hz s-1. In
addition, 4U 1626-67 increased its flux simultaneously (a ~2.5 factor). We
present detailed long-term timing analysis of this source and a long term
spectral hardness ratio study in order to see whether there are spectral
changes around this new observed torque reversal.",0906.4224v2
2022-11-15,On torque reversal during delayed spin up glitch of SGR 1935+2154,"Ge et al. reported a peculiar large glitch observed from SGR 1935
recently~\citep{2022arXiv221103246G}. % Interestingly, this glitch occurred
about $3.1\pm 2.5~\rm{days}$ before FRB 200428, accompanied by a delayed spin
up (DSU) process with a timescale of $8\pm 1~\rm{days}$. % This DSU is the
first one detected from magnetars unambiguously, previously, DSU has only been
detected from large glitches of the young Crab pulsar. % Strikingly, this DSU
even resulted in torque reversal, i.e., the spin down state of SGR 1935 was
turned into a spin up one within $8\pm 1~\rm{days}$, the first case observed
from isolated neutron stars as far as we know. % What's more, the average
positive torque is consistent in value and order of magnitude with those
deduced from DSUs observed from the Crab pulsar. % The coincidences of DSU
appearance and consistent positive torque in the Crab pulsar and SGR 1935
suggest that, these DSUs have the same physical origin and should be analyzed
simultaneously. % Joint analysis on DSUs from the Crab pulsar and SGR 1935
suggests a physical origin independent of (at least not directly dependent on)
rotational parameters. % If this new DSU and torque reversal phenomena be
further confirmed and accretion be excluded convincingly, nearly all models
regarding DSU phenomenon under the framework of vortex motion should be
reconsidered, new physics will be required. % We stress that, joint analysis on
DSUs from different pulsars with different rotational parameters may provide
pivotal clue to reveal their physical origin, even neutron star equation of
state and the triggering mechanism(s) of (galactic) fast radio bursts
ultimately.",2211.08151v1
2022-10-16,Design and Modeling of a Smart Torque-Adjustable Rotary Electroadhesive Clutch for Application in Human-Robot Interaction,"The increasing need for sharing workspace and interactive physical tasks
between robots and humans has raised concerns regarding safety of such
operations. In this regard, controllable clutches have shown great potential
for addressing important safety concerns at the hardware level by separating
the high-impedance actuator from the end effector by providing the power
transfer from electromagnetic source to the human. However, the existing
clutches suffer from high power consumption and large-weight, which make them
undesirable from the design point of view. In this paper, for the first time,
the design and development of a novel, lightweight, and low-power
torque-adjustable rotary clutch using electroadhesive materials is presented.
The performance of three different pairs of clutch plates is investigated in
the context of the smoothness and quality of output torque. The performance
degradation issue due to the polarization of the insulator is addressed through
the utilization of an alternating current waveform activation signal. Moreover,
the effect of the activation frequency on the output torque and power
consumption of the clutch is investigated. Finally, a time-dependent model for
the output torque of the clutch is presented, and the performance of the clutch
was evaluated through experiments, including physical human-robot interaction.
The proposed clutch offers a torque to power consumption ratio that is six
times better than commercial magnetic particle clutches. The proposed clutch
presents great potential for developing safe, lightweight, and low-power
physical human-robot interaction systems, such as exoskeletons and robotic
walkers.",2210.08664v1
2007-08-14,Spin torque contribution to the a.c. spin Hall conductivity,"Using the recently proposed definition of a conserved spin-current operator
[J. Shi et al., Phys. Rev. Lett. 96, 076604 (2006)] we explore the frequency
dependent spin Hall conductivity for a two-dimensional electron gas with Rashba
and Dresselhaus spin-orbit interaction in response to an oscillating electric
field. We show that the optical spectrum of the spin Hall conductivity exhibit
remarkable changes when the new definition of spin current is applied. Such
behavior is mainly due to a significant contribution of the spin torque term
which is absent in the conventional form of the spin current. In addition, it
is observed that the magnitude and direction of the dynamic spin Hall current
strongly depends on the electric field frequency as with the interplay of the
spin-orbit coupling strengths.",0708.1957v2
2020-10-09,Staggered spin Hall conductivity,"The intrinsic spin Hall effect plays an important role in spintronics
applications, such as spin-orbit torque-based memory. The bulk space group
symmetry determines the form of the bulk spin current conductivity tensor. This
paper considers materials for which the local point group symmetry of
individual atoms is lower than the global (bulk) symmetry. This enables a
position-dependent spin current response, with additional tensor components
allowed relative to the bulk response. We present a general method to compute
the position-dependent intrinsic spin Hall conductivity, with similar
computational effort relative to computing the bulk spin Hall conductivity. We
also present the general symmetry-constrained form of the position-dependent
spin current response. We apply this method to 1T'-WTe$_2$, which exhibits a
conventional spin Hall conductivity tensor component $\sigma^y_{xz}$ and a
staggered unconventional component $\sigma^z_{xz}$. The magnitude of these two
components, around 100 and 20 $(\rm \Omega\cdot cm)^{-1}$, respectively, are
comparable to the spin-orbit torque exerted on adjacent ferromagnets in
experiments. We then consider orthorhombic PbTe, in which both uniform and
staggered spin current conductivity are one order of magnitude larger.",2010.04772v2
2022-02-10,Amplifying spin waves along Néel domain wall by spin-orbit torque,"Traveling spin waves in magnonic waveguides undergo severe attenuation, which
tends to result in a finite propagation length of spin waves, even in magnetic
materials with the accessible lowest damping constant, heavily restricting the
development of magnonic devices. Compared with the spin waves in traditional
waveguides, propagating spin waves along strip domain wall are expected to
exhibit enhanced transmission. Here, we demonstrate, theoretically and through
micromagnetic simulations, that spin-orbit torque associated with a
ferromagnet/heavy metal bilayer can efficiently control the attenuation of spin
waves along a N\'eel-type strip domain wall, despite the complexity in the
ground-state magnetization configuration. The direction of the electric current
applied to the heavy-metal layer determines whether these spin waves are
amplified or further attenuated otherwise. Remarkably, our simulations reveal
that the effective current densities required to efficiently tune the decay of
such spin waves are just ~10^10 Am-2, roughly an order smaller than those
required in conventional spin waveguides. Our results will enrich the toolset
for magnonic technologies.",2202.05181v1
2024-01-17,Torque-dependent orbital modulation of X-ray pulsar Cen X-3,"Cen X-3 shows alternate spin-up/spin-down episodes lasting for tens of days.
We study the orbital profiles and spectra of Cen X-3 during these
spin-up/spin-down intervals, using long-term data monitored by Fermi/GBM,
Swift/BAT and MAXI/GSC. In spin-up intervals, its orbital profile in 2-10 keV
is symmetrically peaked around orbital phase 0.42, while in spin-down intervals
of similar fluxes and similar magnitudes of spin change rate, its profile
reaches a peak around orbital phase 0.22 and then declines gradually. Such a
distinct orbital difference between spin-up and spin-down states of similar
flux is hard to explain in the standard disk model and indicates that its
torque reversals are related to processes on the orbital scale. The durations
of continuous spin-up/spin-down trend (tens of days) also point to a
superorbital variation. One possible scenario is the irradiation-driven warping
disk instability, which may produce a flipped inner disk for tens of days.",2401.09197v1
2005-12-20,Theory of Spin Torque in a nanomagnet,"We present a complete theory of the spin torque phenomena in a ultrasmall
nanomagnet coupled to non-collinear ferromagnetic electrodes through tunnelling
junctions. This model system can be described by a simple microscopic model
which captures many physical effects characteristic of spintronics: tunneling
magneto resistance, intrinsic and transport induced magnetic relaxation,
current induced magnetization reversal and spin accumulation. Treating on the
same footing the magnetic and transport degrees of freedom, we arrive at a
closed equation for the time evolution of the magnetization. This equation is
very close to the Landau-Lifshitz-Gilbert equation used in spin valves
structures. We discuss how the presence of the Coulomb blockade phenomena and
the discretization of the one-body spectrum gives some additional features to
the current induced spin torque. Depending on the regime, the dynamic induced
by the coupling to electrode can be viewed either as a spin torque or as a
relaxation process. In addition to the possibility of stabilizing uniform spin
precession states, we find that the system is highly hysteretic: up to three
different magnetic states can be simultaneously stable in one region of the
parameter space (magnetic field and bias voltage).We also discuss how the
magneto-resistance can be used to provide additional information on the
non-equilibrium peaks present in the nanomagnet spectroscopy experiments.",0512508v1
2017-08-08,Spin-orbit-torque driven magnetoimpedance in Pt-layer/magnetic-ribbon heterostructures,"When a flow of electron passes through a paramagnetic layer with strong
spin-orbit-coupling such as platinum (Pt), a net spin current is produced via
spin Hall effect (SHE). This spin current can exert a torque on the
magnetization of an adjacent ferromagnetic layer which can be probed via
magnetization dynamic response, e.g. spin-torque ferromagnetic resonance
(ST-FMR). Nevertheless, that effect in lower frequency magnetization dynamic
regime (MHz) where skin effect occurs in high permeability ferromagnetic
conductors namely the magneto-impedance (MI) effect can be fundamentally
important which has not been studied so far. Here, by utilizing the MI effect
in magnetic-ribbon/Pt heterostructure with high magnetic permeability that
allows the ac current effectively confined at the skin depth of ~100 nm
thickness, the effect of spin-orbit-torque (SOT) induced by the SHE probed via
MI measurement is investigated. We observed a systematic MI frequency shift
that increases by increasing the applied current amplitude and thickness of the
Pt layer (varying from 0 nm to 20 nm). In addition, the role of Pt layer in
ribbon/Pt heterostructure is evaluated with ferromagnetic resonance (FMR)
effect representing standard Gilbert damping increase as the result of presence
of the SHE. Our results unveil the role of SOT in dynamic control of the
transverse magnetic permeability probed with impedance spectroscopy as useful
and valuable technique for detection of future SHE devices.",1708.02402v2
2018-06-04,Site-Specific Spin Reorientation in Antiferromagnetic State of Quantum System SeCuO$_3$,"We report on the magnetocrystalline anisotropy energy (MAE) and spin
reorientation in antiferromagnetic state of spin $S=1/2$ tetramer system
SeCuO$_3$ observed in torque magnetometry measurements in magnetic fields
$H<5$~T and simulated using density functional calculations. We employ simple
phenomenological model of spin reorientation in finite magnetic field to
describe our experimental torque data. Our results strongly support collinear
model for magnetic structure in zero field with possibility of only very weak
canting. Torque measurements also indicate that, contrary to what is expected
for uniaxial antiferromagnet, in SeCuO$_3$ only part of the spins exhibit spin
flop instead all of them, allowing us to conclude that AFM state of SeCuO$_3$
is unconventional and comprised of two decoupled subsystems. Taking into
account previously proposed site-selective correlations and dimer singlet state
formation in this system, our results offer further proof that AFM state in
SeCuO$_3$ is composed of a subsystem of AFM dimers forming singlets immersed in
antiferromagnetically long-range ordered spins, where both states coexist on
atomic scale. Furthermore, we show, using an ab-initio approach, that both
subsystems contribute differently to the MAE, corroborating the existence of
decoupled subnetworks in SeCuO$_3$. Combination of torque magnetometry,
phenomenological approach and DFT simulations to magnetic anisotropy presented
here represents a unique and original way to study site-specific reorientation
phenomena in quantum magnets.",1806.01233v2
2020-01-06,Highly efficient spin orbit torque in Pt/Co/Ir multilayers with antiferromagnetic interlayer exchange coupling,"We have studied the spin orbit torque (SOT) in Pt/Co/Ir multilayers with 3
repeats of the unit structure. As the system exhibits oscillatory interlayer
exchange coupling (IEC) with varying Ir layer thickness, we compare the SOT of
films when the Co layers are coupled ferromagnetically and
antiferromagnetically. SOT is evaluated using current induced shift of the
anomalous Hall resistance hysteresis loops. A relatively thick Pt layer,
serving as a seed layer to the multilayer, is used to generate spin current via
the spin Hall effect. In the absence of antiferromagnetic coupling, the SOT is
constant against the applied current density and the corresponding spin torque
efficiency (i.e. the effective spin Hall angle) is $\sim$0.09, in agreement
with previous reports. In contrast, for films with antiferromagnetic coupling,
the SOT increases with the applied current density and eventually saturates.
The SOT at saturation is a factor of $\sim$15 larger than that without the
antiferromagnetic coupling. The spin torque efficiency is $\sim$5 times larger
if we assume the net total magnetization is reduced by a factor of 3 due to the
antiferromagnetic coupling. Model calculations based on the Landau Lifshitz
Gilbert equation show that the presence of antiferromagnetic coupling can
increase the SOT but the degree of enhancement is limited, in this case, to a
factor of 1.2-1.4. We thus consider there are other sources of SOT, possibly at
the interfaces, which may account for the highly efficient SOT in the
uncompensated synthetic anti-ferromagnet (SAF) multilayers.",2001.01454v1
2020-07-06,Transverse and Longitudinal Spin-Torque Ferromagnetic Resonance for Improved Measurements of Spin-Orbit Torques,"Spin-torque ferromagnetic resonance (ST-FMR) is a common method used to
measure spin-orbit torques (SOTs) in heavy metal/ferromagnet bilayer
structures. In the course of a measurement, other resonant processes such as
spin pumping (SP) and heating can cause spin current or heat flows between the
layers, inducing additional resonant voltage signals via the inverse spin Hall
effect (ISHE) and Nernst effects (NE). In the standard ST-FMR geometry, these
extra artifacts exhibit a dependence on the angle of an in-plane magnetic field
that is identical to the rectification signal from the SOTs. We show
experimentally that the rectification and artifact voltages can be quantified
separately by measuring the ST-FMR signal transverse to the applied current
(i.e., in a Hall geometry) in addition to the usual longitudinal geometry. We
find that in Pt (6 nm)/CoFeB samples the contribution from the artifacts is
small compared to the SOT rectification signal for CoFeB layers thinner than 6
nm, but can be significant for thicker magnetic layers. We observe a sign
change in the artifact voltage as a function of CoFeB thickness that we suggest
may be due to a competition between a resonant heating effect and the SP/ISHE
contribution.",2007.02850v1
2022-01-12,Efficient Spin-Orbit Torques in an Antiferromagnetic Insulator with Tilted Easy Plane,"Electrical manipulation of spin textures inside antiferromagnets represents a
new opportunity for developing spintronics with superior speed and high device
density. Injecting spin currents into antiferromagnets and realizing efficient
spin-orbit-torque-induced switching is however still challenging due to the
complicated interactions from different sublattices. Meanwhile, because of the
diminishing magnetic susceptibility, the nature and the magnitude of
current-induced magnetic dynamics remain poorly characterized in
antiferromagnets, whereas spurious effects further complicate experimental
interpretations. In this work, by growing a thin film antiferromagnetic
insulator, {\alpha}-Fe2O3, along its non-basal plane orientation, we realize a
configuration where an injected spin current can robustly rotate the N\'eel
vector within the tilted easy plane, with an efficiency comparable to that of
classical ferromagnets. The spin-orbit torque effect stands out among other
competing mechanisms and leads to clear switching dynamics. Thanks to this new
mechanism, in contrast to the usually employed orthogonal switching geometry,
we achieve bipolar antiferromagnetic switching by applying positive and
negative currents along the same channel, a geometry that is more practical for
device applications. By enabling efficient spin-orbit torque control on the
antiferromagnetic ordering, the tilted easy plane geometry introduces a new
platform for quantitatively understanding switching and oscillation dynamics in
antiferromagnets.",2201.04732v1
2022-08-15,Nonperturbative approach to interfacial spin-orbit torques induced by Rashba effect,"Current-induced spin-orbit torque (SOT) in normal metal/ferromagnet (NM/FM)
bilayers bears great promise for technological applications, but the
microscopic origin of purely interfacial SOTs in ultra-thin systems is not yet
fully understood. Here, we show that a linear response theory with a
nonperturbative treatment of spin-dependent interactions and impurity
scattering potential predicts damping-like SOTs that are strictly absent in
perturbative approaches. The technique is applied to a two-dimensional
Rashba-coupled ferromagnet (the paradigmatic model of a NM/FM interface), where
higher-order scattering processes encoding skew scattering from nonmagnetic
impurities allow for current-induced spin polarization with nonzero components
along all spatial directions. This is in stark contrast to previous results of
perturbative methods (neglecting skew scattering), which predict a coplanar
spin-polarization locked perpendicular to the charge current as a result of
conventional Rashba-Edelstein effect. Furthermore, the angular dependence of
ensuing SOTs and their dependence upon the scattering potential strength is
analysed numerically. Simple analytic expressions for the
spin-density--charge-current response function, and related SOT efficiencies,
are obtained in the weak scattering limit. We find that the extrinsic
damping-like torques driven by impurity scattering reaches efficiencies of up
to 7% of the field-like (Rashba-Edelstein) torque. Our microscopic theory shows
that bulk phenomena, such as the spin Hall effect, are not a necessity in the
generation of the damping-like SOTs of the type observed in experiments on
ultra-thin systems.",2208.07296v1
2023-12-07,Unusual Sign Reversal of Field-like Spin-Orbit Torque in Pt/Ni/Py with an Ultrathin Ni Spacer,"The magnetization manipulation by spin-orbit torques (SOTs) in
nonmagnetic-metal (NM)/ferromagnet (FM) heterostructures has provided great
opportunities for spin devices. Besides the conventional spin Hall effect (SHE)
in heavy metals with strong spin-orbit coupling, the orbital currents have been
proposed to be another promising approach to generate strong SOTs. Here, we
systematically study the SOTs efficiency and its dependence on the FM thickness
and different NM/FM interfaces in two prototypical Pt/Py and Ta/Py systems by
inserting an ultrathin magnetic layer (0.4 nm thick ML = Co, Fe, Gd, and Ni).
The dampinglike (DL) torque efficiency $\xi_{DL}$ is significantly enhanced by
inserting ultrathin Co, Fe, and Ni layers and is noticeably suppressed for the
Gd insertion. Moreover, the Ni insertion results in a sign change of the
field-like (FL) torque in Pt/Py and substantially reduces $\xi_{DL}$ in Ta/Py.
These results are likely related to the additional spin currents generated by
combining the orbital Hall effect (OHE) in the NM and orbital-to-spin
conversion in the ML insertion layer and/or their interfaces, especially for
the Ni insertion. Our results demonstrate that inserting ultrathin ML can
effectively manipulate the strength and sign of the SOTs, which would be
helpful for spintronics applications.",2312.04276v2
1999-09-24,Angular Momentum Transfer in the Binary X-ray Pulsar GX 1+4,"We describe three presentations relating to the X-ray pulsar GX 1+4 at a
workshop on magnetic fields and accretion at the Astrophysical Theory Centre,
Australian National University on 1998, November 12-13. Optical and X-ray
spectroscopy indicate that GX 1+4 is seen through a cloud of gravitationaly
bound matter. We discuss an unstable negative feedback mechanism (originally
proposed by Kotani et al, 1999), based on X-ray heating of this matter which
controls the accretion rate when the source is in a low X-ray luminosity state.
A deep minimum lasting ~6 hours occurred during observations with the RXTE
satellite over 1996, July 19-21. The shape of the X-ray pulses changed
remarkably from before to after the minimum. These changes may be related to
the transition from neutron star spin-down to spin-up which occurred at about
the same time. Smoothed particle hydrodynamic simulations of the effect of
adding matter with opposite angular momentum to an existing disc, show that it
is possible for a number of concentric rings with alternating senses of
rotation to co-exist in a disc. This could provide an explanation for the
step-like changes in Pdot which are observed in GX 1+4. Changes at the inner
boundary of the disc occur at the same timescale as that imposed at the outer
boundary. Reversals of material torque on the neutron star occur at a minimum
in L_X.",9909413v1
2006-02-22,Energy extremals and Nonlinear Stability in a Variational theory of Barotropic Fluid - Rotating Sphere System,"A new variational principle - extremizing the fixed frame kinetic energy
under constant relative enstrophy - for a coupled barotropic flow - rotating
solid sphere system is introduced with the following consequences. In
particular, angular momentum is transfered between the fluid and the solid
sphere through a modelled torque mechanism. The fluid's angular momentum is
therefore not fixed but only bounded by the relative enstrophy, as is required
of any model that supports super-rotation.
  The main results are: At any rate of spin $\Omega $ and relative enstrophy,
the unique global energy maximizer for fixed relative enstrophy corresponds to
solid-body super-rotation; the counter-rotating solid-body flow state is a
constrained energy minimum provided the relative enstrophy is small enough,
otherwise, it is a saddle point.
  For all energy below a threshold value which depends on the relative
enstrophy and solid spin $\Omega $, the constrained energy extremals consist of
only minimizers and saddles in the form of counter-rotating states$.$ Only when
the energy exceeds this threshold value can pro-rotating states arise as global
maximizers.
  Unlike the standard barotropic vorticity model which conserves angular
momentum of the fluid, the counter-rotating state is rigorously shown to be
nonlinearly stable only when it is a local constrained minima. The global
constrained maximizer corresponding to super-rotation is always nonlinearly
stable.",0602056v2
2008-01-09,Current-induced magnetization switching in MgO barrier magnetic tunnel junctions with CoFeB based synthetic ferrimagnetic free layers,"We investigated the effect of using a synthetic ferrimagnetic (SyF) free
layer in MgO-based magnetic tunnel junctions (MTJs) on current-induced
magnetization switching (CIMS), particularly for application to spin-transfer
torque random access memory (SPRAM). The employed SyF free layer had a
Co40Fe40B20/ Ru/ Co40Fe40B20 and Co20Fe60B20/Ru/Co20Fe60B20 structures, and the
MTJs(100x(150-300) nm^2) were annealed at 300oC. The use of SyF free layer
resulted in low intrinsic critical current density (Jc0) without degrading the
thermal-stability factor (E/kBT, where E, kB, and T are the energy potential,
the Boltzmann constant, and temperature,respectively). When the two CoFeB
layers of a strongly antiferromagnetically coupled SyF free layer had the same
thickness, Jc0 was reduced to 2-4x10^6 A/cm^2. This low Jc0 may be due to the
decreased effective volume under the large spin accumulation at the CoFeB/Ru.
The E/kBT was over 60, resulting in a retention time of over ten years and
suppression of the write current dispersion for SPRAM. The use of the SyF free
layer also resulted in a bistable (parallel/antiparallel) magnetization
configuration at zero field, enabling the realization of CIMS without the need
to apply external fields to compensate for the offset field.",0801.1355v1
2013-02-26,Magnetic white dwarfs with debris discs,"It has long been accepted that a possible mechanism for explaining the
existence of magnetic white dwarfs is the merger of a binary white dwarf
system, as there are viable mechanisms for producing sustainable magnetic
fields within the merger product. However, the lack of rapid rotators in the
magnetic white dwarf population has been always considered a problematic issue
of this scenario. Smoothed Particle Hydrodynamics simulations show that in
mergers in which the two white dwarfs have different masses a disc around the
central compact object is formed. If the central object is magnetized it can
interact with the disc through its magnetosphere. The torque applied by the
disc changes the spin of the star, whereas the transferred angular momentum
from the star to the disc determines the properties of the disc. In this work
we build a model for the disc evolution under the effect of magnetic accretion,
and for the angular momentum evolution of the star, which can be compared with
the observations. Our model predicts that the magnetospheric interaction of
magnetic white dwarfs with their discs results in a significant spin down, and
we show that for magnetic white dwarfs with relatively strong fields (larger
than 10 MG) the observed rotation periods of the magnetic white dwarf
population can be reproduced. We also investigate whether turbulence can be
sustained during the late phases of the evolution of the system. When a
critical temperature below which turbulence is not sustained is introduced into
the model, the periods of the three fast rotating, strongly magnetic, massive
white dwarfs in the solar neighborhood are recovered.",1302.6468v1
2015-03-24,Spin dynamics and frequency dependence of magnetic damping study in soft ferromagnetic FeTaC film with a stripe domain structure,"Perpendicular magnetic anisotropy (PMA) and low magnetic damping are the key
factors for the free layer magnetization switching by spin transfer torque
technique in magnetic tunnel junction devices. The magnetization precessional
dynamics in soft ferromagnetic FeTaC thin film with a stripe domain structure
was explored in broad band frequency range by employing micro-strip
ferromagnetic resonance technique. The polar angular variation of resonance
field and linewidth at different frequencies have been analyzed numerically
using Landau-Lifshitz-Gilbert equation by taking into account the total free
energy density of the film. The numerically estimated parameters Land\'{e}
$g$-factor, PMA constant, and effective magnetization are found to be 2.1,
2$\times10^{5}$ erg/cm$^{3}$ and 7145 Oe, respectively. The frequency
dependence of Gilbert damping parameter ($\alpha$) is evaluated by considering
both intrinsic and extrinsic effects into the total linewidth analysis. The
value of $\alpha$ is found to be 0.006 at 10 GHz and it increases with
decreasing precessional frequency.",1503.07043v5
2015-06-12,Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures,"Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts
extensive attentions due to its non-volatility, high density and low power
consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel
junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well
as a large value of perpendicular magnetic anisotropy (PMA). It has been
experimentally proven that a capping layer coating on CoFeB layer is essential
to obtain a strong PMA. However, the physical mechanism of such effect remains
unclear. In this paper, we investigate the origin of the PMA in
MgO/CoFe/metallic capping layer structures by using a first-principles
computation scheme. The trend of PMA variation with different capping materials
agrees well with experimental results. We find that interfacial PMA in the
three-layer structures comes from both the MgO/CoFe and CoFe/capping layer
interfaces, which can be analyzed separately. Furthermore, the PMAs in the
CoFe/capping layer interfaces are analyzed through resolving the magnetic
anisotropy energy by layer and orbital. The variation of PMA with different
capping materials is attributed to the different hybridizations of both d and p
orbitals via spin-orbital coupling. This work can significantly benefit the
research and development of nanoscale STT-MRAM.",1506.04078v4
2017-11-15,Hole transport across MgO-based magnetic tunnel junctions with high resistance-area product due to oxygen vacancies,"The quantum mechanical tunnelling process conserves the quantum properties of
the particle considered. As applied to solid-state tunnelling (SST), this
physical law was verified, within the field of spintronics, regarding the
electron spin in early experiments across Ge tunnel barriers, and in the 90s
across Al2O3 barriers. The conservation of the quantum parameter of orbital
occupancy, as grouped into electronic symmetries, was observed in the '00s
across MgO barriers, followed by SrTiO3 (STO). Barrier defects, such as oxygen
vacancies, partly conserve this electronic symmetry. In the solid-state, an
additional subtlety is the sign of the charge carrier: are holes or electrons
involved in transport? We demonstrate that SST across MgO magnetic tunnel
junctions (MTJs) with a large resistance-area (RA) product involves holes by
examining how shifting the MTJ's Fermi level alters the ensuing barrier heights
defined by the barrier's oxygen vacancies. In the process, we consolidate the
description of tunnel barrier heights induced by specific oxygen-vacancy
induced localized states. Our work opens prospects to understand the concurrent
observation of high TMR and spin transfer torque across MgO-based nanopillars.",1711.05643v2
2018-09-12,Are There Pre-Main-Sequence/Black Hole X-ray Binaries?,"A large fraction of black hole low-mass X-ray binaries (BHLMXBs) are in short
period orbits, which require strong orbital angular momentum loss during the
previous evolutionary stage. Ivanova (2006) put forward the possibility that
some of the BHLMXBs may harbour pre-main-sequence (MS) donor stars, in order to
explain the Li-overabundances in three BHLMXBs. In this work we investigate the
evolution of low-mass pre-MS stars in binaries with a BH companion. We
calculate the evolution of the spin and orbital periods, the stellar radius and
the Roche-lobe radius during the pre-MS stage with the stellar evolution code
MESA. We find that, because of the relatively slow rotation of the pre-MS star
after the common envelope evolution and the long turnover time in the pre-MS
stars, tidal torque is not always able to synchronize the pre-MS star, so the
spin periods are generally longer than the orbital periods. Mass transfer can
occur only for stars with mass larger than $\sim 1.2M_\odot$, which experience
expansion due to nuclear reaction after the Hayashi contraction phase. The
effective temperatures and orbital periods of these systems do not match the
observations of BHLMXBs. Our results show that the observed BHLMXBs with
lithium overabundances are unlikely to host pre-main sequence donor stars.",1809.04269v2
2019-03-07,InMRAM: Introductory course on Magnetic Random Access Memories for microelectronics students and engIneers,"Magnetic Random Access Memories (MRAM) interest is growing fast in the
microelectronics industry. Commercial MRAM products already exist and all major
industrial players have launched large R\&D efforts to bring Spin Transfer
Torque MRAM to production. The principle goal is to replace part of the memory
hierarchy (in particular DRAM) by MRAM below the 20nm node. Interest in
bringing non-volatile elements closer to the logic is also growing, in order to
improve the performance of electronic circuits by increasing the bandwidth
between logic and memory and reducing the power consumption. Despite this nsmg
interest, very few microelectronics engineers have a background in magnetism
and even more in spinelectronics so that it is very difficult for them to get
into this emerging field. Magnetism and microelectronics communities have
worked separately so far. We are convinced it is time to develop more
relationships between these two communities through joint symposia, workshops,
conferences, as well as to introduce some courses in magnetism and spin
electronics in the education of young microelectronics engineers. In this
context, SPINTEC, a French lab associated to CEA/CNRS/Grenoble University,
started organizing last year an annual Introductory Course on MRAM (InMRAM) for
students, engineers and researchers having no or little background in
magnetism. The second edition will take place in Grenoble from 2nd to 4th July
2014.",1906.10206v1
2021-08-02,PIRM: Processing In Racetrack Memories,"The growth in data needs of modern applications has created significant
challenges for modern systems leading a ""memory wall."" Spintronic Domain Wall
Memory (DWM), related to Spin-Transfer Torque Memory (STT-MRAM), provides
near-SRAM read/write performance, energy savings and nonvolatility, potential
for extremely high storage density, and does not have significant endurance
limitations. However, DWM's benefits cannot address data access latency and
throughput limitations of memory bus bandwidth. We propose PIRM, a DWM-based
in-memory computing solution that leverages the properties of DWM nanowires and
allows them to serve as polymorphic gates. While normally DWM is accessed by
applying spin polarized currents orthogonal to the nanowire at access points to
read individual bits, transverse access along the DWM nanowire allows the
differentiation of the aggregate resistance of multiple bits in the nanowire,
akin to a multilevel cell. PIRM leverages this transverse reading to directly
provide bulk-bitwise logic of multiple adjacent operands in the nanowire,
simultaneously. Based on this in-memory logic, PIRM provides a technique to
conduct multi-operand addition and two operand multiplication using transverse
access. PIRM provides a 1.6x speedup compared to the leading DRAM PIM technique
for query applications that leverage bulk bitwise operations. Compared to the
leading PIM technique for DWM, PIRM improves performance by 6.9x, 2.3x and
energy by 5.5x, 3.4x for 8-bit addition and multiplication, respectively. For
arithmetic heavy benchmarks, PIRM reduces access latency by 2.1x, while
decreasing energy consumption by 25.2x for a reasonable 10% area overhead
versus non-PIM DWM.",2108.01202v2
2020-07-31,Giant perpendicular magnetic anisotropy enhancement in MgO-based magnetic tunnel junction by using Co/Fe composite layer,"Magnetic tunnel junctions with perpendicular anisotropy form the basis of the
spin-transfer torque magnetic random-access memory (STT-MRAM), which is
non-volatile, fast, dense, and has quasi-infinite write endurance and low power
consumption. Based on density functional theory (DFT) calculations, we propose
an alternative design of magnetic tunnel junctions comprising
Fe(n)Co(m)Fe(n)/MgO storage layers with greatly enhanced perpendicular magnetic
anisotropy (PMA) up to several mJ/m2, leveraging the interfacial perpendicular
anisotropy of Fe/MgO along with a stress-induced bulk PMA discovered within bcc
Co. This giant enhancement dominates the demagnetizing energy when increasing
the film thickness. The tunneling magnetoresistance (TMR) estimated from the
Julliere model is comparable with that of the pure Fe/MgO case. We discuss the
advantages and pitfalls of a real-life fabrication of the structure and propose
the Fe(3ML)Co(4ML)Fe(3ML) as a storage layer for MgO-based STT-MRAM cells. The
large PMA in strained bcc Co is explained in the framework of Bruno's model by
the MgO-imposed strain and consequent changes in the energies of dyz and dz2
minority-spin bands.",2007.15940v1
2020-10-29,Domain wall dynamics in antiferromagnetically-coupled double-lattice systems,"In ferromagnetic materials, the rich dynamics of magnetic domain walls (DWs)
under magnetic field or current have been successfully described using the
well-known q-{\phi} analytical model. We demonstrate here that this simple
unidimensional model holds for multiple-sublattice materials such as
ferrimagnetic alloys or synthetic antiferromagnets (SAF) by using effective
parameters, and is in excellent agreement with double-lattice micromagnetic
simulations. We obtain analytical laws for the DW velocity and internal
precession angle as a function of net magnetisation for different driving
forces (magnetic field, spin transfer and spin-orbit torques) and different
propagation regimes in ferrimagnetic alloys and SAFs. The model predicts that
several distinctive dynamical features occur near or at the magnetic and the
angular compensation points when the net magnetization or the net angular
momentum of the system vanishes, and we discuss the experimental observations
that have been reported for some of them. Using a higher degree-of-freedom
analytical model that accounts for inter-sublattice distortions, we give
analytical expressions for these distortions that agree with the micromagnetic
simulations. This model shows that the DW velocity and precession rate are
independent of the strength of the inter-sublattice exchange coupling, and
justifies the use of the simpler effective parameters model.",2010.15443v1
2023-05-24,Field-free all-optical switching and electrical read-out of Tb/Co-based magnetic tunnel junctions,"Switching of magnetic tunnel junction using femto-second laser enables a
possible path for THz frequency memory operation, which means writing speeds 2
orders of magnitude faster than alternative electrical approaches based on spin
transfer or spin orbit torque. In this work we demonstrate successful
field-free 50fs single laser pulse driven magnetization reversal of [Tb/Co]
based storage layer in a perpendicular magnetic tunnel junction. The
nanofabricated magnetic tunnel junction devices have an optimized bottom
reference electrode and show Tunnel Magnetoresistance Ratio values (TMR) up to
74\% after patterning down to sub-100nm lateral dimensions. Experiments on
continuous films reveal peculiar reversal patterns of concentric rings with
opposite magnetic directions, above certain threshold fluence. These rings have
been correlated to patterned device switching probability as a function of the
applied laser fluence. Moreover, the magnetization reversal is independent on
the duration of the laser pulse. According to our macrospin model, the
underlying magnetization reversal mechanism can be attributed to an in-plane
reorientation of the magnetization due to a fast reduction of the out-of-plane
uniaxial anisotropy. These aspects are of great interest both for the physical
understanding of the switching phenomenon and their consequences for
all-optical-switching memory devices, since they allow for a large fluence
operation window with high resilience to pulse length variability.",2305.15135v1
2022-07-18,Room temperature spin-orbit torque efficiency in sputtered low-temperature superconductor delta-TaN,"In the course of searching for promising topological materials for
applications in future topological electronics, we evaluated spin-orbit torques
(SOTs) in high-quality sputtered ${\delta}-$TaN/Co20Fe60B20 devices through
spin-torque ferromagnetic resonance ST-FMR and spin pumping measurements. From
the ST-FMR characterization we observed a significant linewidth modulation in
the magnetic Co20Fe60B20 layer attributed to the charge-to-spin conversion
generated from the ${\delta}-$TaN layer. Remarkably, the spin-torque efficiency
determined from ST-FMR and spin pumping measurements is as large as ${\Theta}
=$ 0.034 and 0.031, respectively. These values are over two times larger than
for ${\alpha}-$Ta, but almost five times lower than for ${\beta}-$Ta, which can
be attributed to the low room temperature electrical resistivity $\sim
74{\mu}{\Omega}$ cm in ${\delta}-$TaN. A large spin diffusion length of at
least $\sim8$ nm is estimated, which is comparable to the spin diffusion length
in pure Ta. Comprehensive experimental analysis, together with density
functional theory calculations, indicates that the origin of the pronounced SOT
effect in ${\delta}-$TaN can be mostly related to a significant contribution
from the Berry curvature associated with the presence of a topically nontrivial
electronic band structure in the vicinity of the Fermi level (EF). Through
additional detailed theoretical analysis, we also found that an isostructural
allotrope of the superconducting ${\delta}-$TaN phase, the simple hexagonal
structure, ${\theta}-$TaN, has larger Berry curvature, and that, together with
expected reasonable charge conductivity, it can also be a promising candidate
for exploring a generation of spin-orbit torque magnetic random access memory
as cheap, temperature stable, and highly efficient spin current sources.",2207.08872v2
2002-02-21,Mechanisms of spin-polarized current-driven magnetization switching,"The mechanisms of the magnetization switching of magnetic multilayers driven
by a current are studied by including exchange interaction between local
moments and spin accumulation of conduction electrons. It is found that this
exchange interaction leads to two additional terms in the
Landau-Lifshitz-Gilbert equation: an effective field and a spin torque. Both
terms are proportional to the transverse spin accumulation and have comparable
magnitudes.",0202363v1
2013-04-02,Modeling Multi-Magnet Networks Interacting Via Spin Currents,"The significant experimental advances of the last few decades in dealing with
the interaction of spin currents and nanomagnets, at the device level, has
allowed envisioning a broad class of devices that propose to implement
information processing using spin currents and nanomagnets. To analyze such
spin-magnet logic circuits, in general, we have developed a coupled
spin-transport/ magnetization-dynamics simulation framework that could be
broadly applicable to various classes of spin-valve/ spin-torque devices.
Indeed, the primary purpose of this chapter is to describe in detail, the
overall approach we have developed to include a description of spin transport
coupled with magnetization dynamics and to show how it was benchmarked against
available data on experiments.
  We address non-collinear spin-transport in Section-2 using a lumped
""4-component spin-circuit formalism"" that describes the interaction of
non-collinear magnets (required for modeling spin torque), by computing
4-component currents and voltages at every node of a ""circuit"". For modeling
the magnetization dynamics, we use the standard Landau-Lifshitz-Gilbert (LLG)
equation with the Slonczewski and the field-like terms included for spin
torque. Section-3 describes how this LLG model is coupled with the spin
transport model to analyze spin-torque experiments and spin-magnet circuits in
general.
  We include MATLAB codes in the Appendix to facilitate a ""hands-on""
understanding of our model and hope it will enable interested readers to
conveniently analyze their own experiments, develop a deeper insight into
spin-magnet circuits or come up with their own creative designs.",1304.0742v3
2012-03-15,Tidal torque induced by orbital decay in compact object binaries,"As we observe in the moon-earth system, tidal interactions in binary systems
can lead to angular momentum exchange. The presence of viscosity is generally
regarded as the condition for such transfer to happen. In this paper, we show
how the orbital evolution can cause a persistent torque between the binary
components, even for inviscid bodies. This preferentially occurs at the final
stage of coalescence of compact binaries, when the orbit shrinks successively
by gravitational waves and plunging on a timescale shorter than the viscous
timescale. The total orbital energy transferred to the secondary by this torque
is ~0.01 of its binding energy. We further show that this persistent torque
induces a differentially rotating quadrupole perturbation. Specializing to the
case of a secondary neutron star, we find that this non equilibrium state has
an associated free energy of 10^47-10^48 erg, just prior to coalescence. This
energy is likely stored in internal fluid motions, with a sizable amount of
differential rotation. By tapping this free energy reservoir, a preexisting
weak magnetic field could be amplified up to a strength of ~10^15 Gauss. Such a
dynamically driven tidal torque can thus recycle an old neutron star into a
highly magnetized neutron star, with possible observational consequences at
merger.",1203.3440v2
2002-10-07,Frictional coupling between sliding and spinning motion,"We show that the friction force and torque, acting at a dry contact of two
objects moving and rotating relative to each other, are inherently coupled. As
a simple test system, a sliding and spinning disk on a horizontal flat surface
is considered. We calculate, and also measure, how the disk is slowing down,
and find that it always stops its sliding and spinning motion at the same
moment. We discuss the impact of this coupling between friction force and
torque on the physics of granular materials.",0210024v1
2008-04-26,Spin-torque oscillator based on tilted magnetization of the fixed layer,"The spin torque oscillator (STO), where the magnetization of the fixed layer
is tilted out of the film plane, is capable of strong microwave signal
generation in zero magnetic field. Through numerical simulations of the
Landau-Lifshitz-Gilbert-Slonczewski equations, within a macro-spin
approximation, we study the microwave signal generation as a function of drive
current for two realistic tilt angles. The tilt magnetization of the fixed
layer can be achieved by using a material with high out-of-plane
magnetocrystalline anisotropy, such as L10 FePt.",0804.4213v1
2009-07-16,Influence of magnetic viscosity on domain wall dynamics under spin-polarized currents,"We present a theoretical study of the influence of magnetic viscosity on
current-driven domain wall dynamics. In particular we examine how domain wall
depinning transitions, driven by thermal activation, are influenced by the
adiabatic and nonadiabatic spin-torques. We find the Arrhenius law that
describes the transition rate for activation over a single energy barrier
remains applicable under currents but with a current-dependent barrier height.
We show that the effective energy barrier is dominated by a linear current
dependence under usual experimental conditions, with a variation that depends
only on the nonadiabatic spin torque coefficient beta.",0907.2867v1
2011-02-09,Optimization of the current pulse for spin-torque switches,"We address optimization of the spin current intensity profile needed to
achieve spin torque switching of a nanomagnet. For systems with Ohmic
dissipation we prove that the optimal current drives the magnetization along
the trajectory, which is exact time-reversed replica of the relaxation
trajectory towards the equilibrium. In practice it means that the optimal
current is very nearly {\em twice} the minimal critical current needed to
switch the magnet. Pulse duration of such an optimal current is a slow
logarithmic function of temperature and the required probability of switching.",1102.1904v3
2012-01-04,Quantum Kinetic Theory of Current-Induced Torques in Rashba Ferromagnets,"Motivated by recent experimental studies of thin-film devices containing a
single ferromagnetic layer, we develop a quantum kinetic theory of
current-induced magnetic torques in Rashba-model ferromagnets. We find that
current-induced spin-densities that are responsible for the switching behavior
are due most essentially to spin-dependent quasiparticle lifetimes and derive
analytic expressions for relevant limits of a simple model. Quantitative model
parameter estimates suggest that spin-orbit coupling in the adjacent metal
normal magnetic layer plays an essential role in the strength of the switching
effect.",1201.0990v1
2013-10-10,Asymmetry in effective fields of spin-orbit torques in Pt/Co/Pt stacks,"Measurements of switching via spin-orbit coupling (SOC) mechanisms are
discussed for a pair of inverted Pt/Co/Pt stacks with asymmetrical Pt
thicknesses. Taking into account the planar Hall effect contribution, effective
fields of spin-orbit torques (SOT) are evaluated using lock-in measurements of
the first and second harmonics of the Hall voltage. Reversing the stack
structure leads to significant asymmetries in the switching behavior, including
clear evidence of a nonlinear current dependence of the transverse effective
field. Our results demonstrate potentially complex interplay in devices with
all-metallic interfaces utilizing SOT.",1310.2771v1
2015-03-12,Control of current-induced spin-orbit effects in a ferromagnetic heterostructure by electric field,"We study the effects of electrostatic gating on the current-induced phenomena
in ultrathin ferromagnet/heavy metal heterostructures. We utilize heterodyne
detection and analysis of symmetry with respect to the direction of the
magnetic field to separate electric field contributions to the magnetic
anisotropy, current-induced field-like torque, and damping torque. Analysis of
the electric field effects allows us to estimate the Rashba and the spin Hall
contributions to the current-induced phenomena. Electrostatic gating can
provide insight into the spin-orbit phenomena, and enable new functionalities
in spintronic devices.",1503.03882v1
2016-10-29,Near-periodical spin period evolution in the binary system LMC X-4,"In this paper we investigated the long-term evolution of the pulse-period in
the high-mass X-ray binary LMC X-4 by taking advantage of more than 43~yrs of
measurements in the X-ray domain. Our analysis revealed for the first time that
the source is displaying near-periodical variations of its spin period on a
time scale of roughly 6.8~yrs, making LMC X-4 one of the known binary systems
showing remarkable long term spin torque reversals. We discuss different
scenarios to interpret the origin of these torque reversals.",1610.09561v1
2020-06-14,Ideal memristor based on viscous magnetization dynamics driven by spin torque,"We show that ideal memristors - devices whose resistance is proportional to
the charge that flows through them - can be realized using spin torque-driven
viscous magnetization dynamics. The latter can be accomplished in the spin
liquid state of thin-film heterostructures with frustrated exchange, where
memristive response is tunable by proximity to the glass transition, while
current-induced Joule heating facilitates nonvolatile operation and
second-order memristive functionality beneficial for neuromorphic applications.
Ideal memristive behaviors can be achieved in other systems characterized by
viscous dynamics of physical, electronic, or magnetic degrees of freedom.",2006.07996v1
2022-10-28,Field-free-switching state diagram of perpendicular magnetization subjected to conventional and unconventional spin-orbit torques,"The lack of certain crystalline symmetries in strong spin-orbit-coupled
non-magnetic materials allows for the existence of uncoventional spin Hall
responses, with electrically generated transverse spin currents possessing
collinear flow and spin directions. The injection of such spin currents into an
adjacent ferromagnetic layer can excite magnetization dynamics via
unconventional spin-orbit torques, leading to deterministic switching in
ferromagnets with perpendicular magnetic anisotropy. We study the interplay
between conventional and unconventional spin-orbit torques on the magnetization
dynamics of a perpendicular ferromagnet in the small intrinsic damping limit,
and identify a rich set of dynamical regimes that includes deterministic and
probabilistic switching, precessional and pinning states. Contrary to common
belief, we found that there exists a critical conventional spin Hall angle,
beyond which deterministic magnetization switching transitions to a
precessional or pinned state. Conversely, we showed that larger unconventional
spin Hall angle is generally beneficial for deterministic switching. We derive
an approximate expression that qualitatively describes the state diagram
boundary between the full deterministic switching and precessional states and
discuss a criterion for searching symmetry-broken spin Hall materials in order
to maximize switching efficiency. Our work offers a roadmap towards energy
efficient spintronic devices, which might opens doors for applications in
advanced in-memory computing technologies.",2210.16344v1
2017-09-25,Is perpendicular magnetic anisotropy essential to all-optical ultrafast spin reversal in ferromagnets?,"All-optical spin reversal presents a new opportunity for spin manipulations,
free of a magnetic field. Most of all-optical-spin-reversal ferromagnets are
found to have a perpendicular magnetic anisotropy (PMA), but it has been
unknown whether PMA is necessary for the spin reversal. Here we theoretically
investigate magnetic thin films with either PMA or in-plane magnetic anisotropy
(IMA). Our results show that the spin reversal in IMA systems is possible, but
only with a longer laser pulse and within a narrow laser parameter region. The
spin reversal does not show a strong helicity dependence where the left- and
right-circularly polarized light lead to the identical results. By contrast,
the spin reversal in PMA systems is robust, provided both the spin angular
momentum and laser field are strong enough while the magnetic anisotropy itself
is not too strong. This explains why experimentally the majority of all-optical
spin-reversal samples are found to have strong PMA and why spins in Fe
nanoparticles only cant out of plane. It is the laser-induced spin-orbit torque
that plays a key role in the spin reversal. Surprisingly, the same spin-orbit
torque results in laser-induced spin rectification in spin-mixed configuration,
a prediction that can be tested experimentally. Our results clearly point out
that PMA is essential to the spin reversal, though there is an opportunity for
in-plane spin reversal.",1709.08690v1
2006-05-23,Dynamics of a trapped domain wall in a current perpendicular to the plane spin valve nano-structure,"A study of transverse tail-to-tail magnetic domain walls (DW) in novel
current perpendicular to the plane (CPP) spin valves (SV) of various dimensions
is presented. For films with dimensions larger than the DW width, we find that
DW motion can give rise to a substantial low frequency noise. For dimensions
comparable to the DW width, we show that the DW can be controlled by an
external field or by a spin momentum torque as opposed to the case of CPP-SV
with uniform magnetization. It is shown that in a single domain biased CPP-SV,
the spin torque can give rise to 1/f-type noise. The dipolar field, the spin
torque and the Oersted field are all accounted for in this work. Our proposed
SV requires low current densities to move DW and can simulate devices for
logical operation or magnetic sensing without having to switch the
magnetization in the free layer.",0605586v1
2010-02-15,Spin-torque driven magnetic vortex self-oscillations in perpendicular magnetic fields,"We have employed complete micromagnetic simulations to analyze dc current
driven self-oscillations of a vortex core in a spin-valve nanopillar in a
perpendicular field by including the coupled effect of the spin-torque and the
magnetostatic field computed self-consistently for the entire spin-valve. The
vortex in the thicker nanomagnet moves along a quasi-elliptical trajectory that
expands with applied current, resulting in blue-shifting of the frequency,
while the magnetization of the thinner nanomagnet is non-uniform due to the
bias current. The simulations explain the experimental magnetoresistance-field
hysteresis loop and yield good agreement with the measured frequency vs.
current behavior of this spin-torque vortex oscillator.",1002.2841v1
2011-11-04,Diffusive spin dynamics in ferromagnetic thin films with a Rashba interaction,"In a ferromagnetic metal layer, the coupled charge and spin diffusion
equations are obtained in the presence of both Rashba spin-orbit interaction
and magnetism. The mis-alignment between the magnetization and the
non-equilibrium spin density induced by the Rashba field gives rise to Rashba
spin torque acting on the ferromagnetic order parameter. In a general form, we
find that the Rashba torque consists of both in-plane and out-of-plane
components, ie $\bm{T}=T_{\bot}\hat{\bm{y}}\times{\hat{\bm
m}}+T_{\parallel}{\hat{\bm m}}\times({\hat{\bm y}}\times{\hat{\bm m}})$.
Numerical simulations on a two dimensional nano-wire discuss the impact of
diffusion on the Rashba torque, which reveals a large enhancement to the ratio
$T_{\parallel}/T_{\bot}$ for thin wires. Our theory provides an explanation to
the mechanism that drives the magnetization switching in a single ferromagnet
as observed in the recent experiments.",1111.1216v2
2013-12-27,Central role of domain wall depinning for perpendicular magnetization switching driven by spin torque from the spin Hall effect,"We study deterministic magnetic reversal of a perpendicularly magnetized Co
layer in a Co/MgO/Ta nano-square driven by spin Hall torque from an in-plane
current flowing in an underlying Pt layer. The rate-limiting step of the
switching process is domain-wall (DW) depinning by spin Hall torque via a
thermally-assisted mechanism that eventually produces full reversal by domain
expansion. An in-plane applied magnetic field collinear with the current is
required, with the necessary field scale set by the need to overcome DW
chirality imposed by the Dzyaloshinskii-Moriya interaction. Once Joule heating
is taken into account the switching current density is quantitatively
consistent with a spin Hall angle {\theta}$_{SH}$ ${\approx}$ 0.07 for 4 nm of
Pt.",1312.7301v1
2017-12-07,Spin waves in coupled YIG/Co heterostructures,"We investigate yttrium iron garnet (YIG)/cobalt (Co) heterostructures using
broadband ferromagnetic resonance (FMR). We observe an efficient excitation of
perpendicular standing spin waves (PSSWs) in the YIG layer when the resonance
frequencies of the YIG PSSWs and the Co FMR line coincide. Avoided crossings of
YIG PSSWs and the Co FMR line are found and modeled using mutual spin pumping
and exchange torques. The excitation of PSSWs is suppressed by a thin aluminum
oxide (AlOx) interlayer but persists with a copper (Cu) interlayer, in
agreement with the proposed model.",1712.02561v1
2018-03-01,Trochoidal motion and pair generation in skyrmion and antiskyrmion dynamics under spin-orbit torques,"Skyrmions and antiskyrmions in magnetic ultrathin films are characterised by
a topological charge describing how the spins wind around their core. This
topology governs their response to forces in the rigid core limit. However,
when internal core excitations are relevant, the dynamics become far richer. We
show that current-induced spin-orbit torques can lead to phenomena such as
trochoidal motion and skyrmion-antiskyrmion pair generation that only occurs
for either the skyrmion or antiskyrmion, depending on the symmetry of the
underlying Dzyaloshinskii-Moriya interaction. Such dynamics are induced by core
deformations, leading to a time-dependent helicity that governs the motion of
the skyrmion and antiskyrmion core. We compute the dynamical phase diagram
through a combination of atomistic spin simulations, reduced-variable
modelling, and machine learning algorithms. It predicts how spin-orbit torques
can control the type of motion and the possibility to generate skyrmion
lattices by antiskyrmion seeding.",1803.00534v2
2018-07-17,Chiral spin-order in some purported Kitaev spin-liquid compounds,"We examine recent magnetic torque measurements in two compounds,
$\gamma$-Li$_2$IrO$_3$ and RuCl$_3$, which have been discussed as possible
realizations of the Kitaev model. The analysis of the reported discontinuity in
torque, as an external magnetic field is rotated across the $c-$axis in both
crystals, suggests that they have a translationally-invariant chiral spin-order
of the from $<{\bf S}_i. ({\bf S}_j ~\times ~ {\bf S}_k)> \ne 0$ in the ground
state and persisting over a very wide range of magnetic field and temperature.
An extra-ordinary $|B|B^2$ dependence of the torque for small fields, beside
the usual $B^2$ part, is predicted due to the chiral spin-order, and found to
be consistent with experiments upon further analysis of the data. Other
experiments such as inelastic scattering and thermal Hall effect and several
questions raised by the discovery of chiral spin-order, including its
topological consequences are discussed.",1807.06637v2
2018-10-12,Spin-Orbit Torque and Nernst Effect in Bi-Sb/Co Heterostructures,"Harmonic measurements of the longitudinal and transverse voltages in Bi-Sb/Co
bilayers are presented. A large second harmonic voltage signal due to the
ordinary Nernst effect is observed. In experiments where a magnetic field is
rotated in the film plane, the ordinary Nernst effect shows the same angular
dependence in the transverse voltage as the damping-like spin-orbit torque and
in the longitudinal voltage as the unidirectional spin-Hall magneto-resistance
respectively. Therefore, the ordinary Nernst effect can be a spurious signal in
spin-orbit torque measurements, leading to an overestimation of the spin-Hall
angle in topological insulators or semimetals.",1810.05674v1
2018-10-21,Dirac nodal line metal for topological antiferromagnetic spintronics,"Topological antiferromagnetic (AFM) spintronics is an emerging field of
research, which exploits the N\'eel vector to control the topological
electronic states and the associated spin-dependent transport properties. A
recently discovered N\'eel spin-orbit torque has been proposed to electrically
manipulate Dirac band crossings in antiferromagnets; however, a reliable AFM
material to realize these properties in practice is missing. Here, we predict
that room temperature AFM metal MnPd$_{2}$ allows the electrical control of the
Dirac nodal line by the N\'eel spin-orbit torque. Based on first-principles
density functional theory calculations, we show that reorientation of the
N\'eel vector leads to switching between the symmetry-protected degenerate
state and the gapped state associated with the dispersive Dirac nodal line at
the Fermi energy. The calculated spin Hall conductivity strongly depends on the
N\'eel vector orientation and can be used to experimentally detect the
predicted effect using a proposed spin-orbit torque device. Our results
indicate that AFM Dirac nodal line metal MnPd$_{2}$ represents a promising
material for topological AFM spintronics.",1810.09033v2
2020-02-28,Disorder dependent spin-orbit torques in L10 FePt single layer,"We report spin-orbit torques (SOT) in L10-ordered perpendicularly magnetized
FePt single layer, which is significantly influenced by disorder. Recently,
self-induced SOT in L10-FePt single layer has been investigated, which is
ascribed to the composition gradient along the film normal direction. However,
the determined mechanisms for magnetization switching have not been fully
studied. With varying growth temperatures, we have prepared FePt single layers
with same thickness (3 nm) but with different disordering. We have found that
nearly full magnetization switching only happens in more disordered films, and
the magnetization switching ratio becomes smaller as increasing L10 ordering.
The method for deriving effective spin torque fields in the previous studies
cannot fully explain the spin current generation and self-induced SOT in
L10-FePt single layer. Combined with Magneto-Optical Kerr Effect microscopy and
anomalous Hall effect measurements, we concluded that the disorder should
determine the formation of domain walls, as well as the spin current
generation.",2003.00905v2
2019-10-23,Spin Hall magnetoresistance sensor using Au$_x$Pt$_{1-x}$ as the spin-orbit torque biasing layer,"We report on investigation of spin Hall magnetoresistance sensor based on
NiFe/AuxPt1-x bilayers. Compared to NiFe/Pt, the NiFe/AuxPt1-x sensor exhibits
a much lower power consumption (reduced by about 57%), due to 80% enhancement
of spin-orbit torque efficiency of AuxPt1-x at an optimum composition of x =
0.19 as compared to pure Pt. The enhanced spin-orbit torque efficiency allows
to increase the thickness of NiFe from 1.8 nm to 2.5 nm without significantly
increasing the power consumption. We show that, by increasing the NiFe
thickness, we were able to improve the working field range (0.86 Oe), operation
temperature range (150 degree C) and detectivity (0.71 nT/sqrt(Hz) at 1 Hz) of
the sensor, which is important for practical applications.",1910.10401v1
2020-02-16,Electric-field control of spin-orbit torques in perpendicularly magnetized W/CoFeB/MgO films,"Controlling magnetism by electric fields offers a highly attractive
perspective for designing future generations of energy-efficient information
technologies. Here, we demonstrate that the magnitude of current-induced
spin-orbit torques in thin perpendicularly magnetized CoFeB films can be tuned
and even increased by electric field generated piezoelectric strain. Using
theoretical calculations, we uncover that the subtle interplay of spin-orbit
coupling, crystal symmetry, and orbital polarization is at the core of the
observed strain dependence of spin-orbit torques. Our results open a path to
integrating two energy efficient spin manipulation approaches, the electric
field-induced strain and the current-induced magnetization switching, thereby
enabling novel device concepts.",2002.06578v1
2020-07-15,Janus Monolayers of Magnetic Transition Metal Dichalcogenides as an All-in-One Platform for Spin-Orbit Torque,"We theoretically predict that vanadium-based Janus dichalcogenide monolayers
constitute an ideal platform for spin-orbit-torque memories. Using first
principles calculations, we demonstrate that magnetic exchange and magnetic
anisotropy energies are higher for heavier chalcogen atoms, while the broken
inversion symmetry in the Janus form leads to the emergence of Rashba-like
spin-orbit coupling. The spin-orbit torque efficiency is evaluated using
optimized quantum transport methodology and found to be comparable to heavy
nonmagnetic metals. The coexistence of magnetism and spin-orbit coupling in
such materials with tunable Fermi-level opens new possibilities for monitoring
magnetization dynamics in the perspective of non-volatile magnetic random
access memories.",2007.07579v1
2020-10-09,Inplane spin orbit torque magnetization switching and its detection using the spin rectification effect at sub-GHz frequencies,"Inplane magnetization reversal of a permalloy/platinum bilayer was detected
using the spin rectification effect. Using a sub GHz microwave frequency to
excite spin torque ferromagnetic resonance (ST FMR) in the bilayer induces two
discrete DC voltages around an external static magnetic field of 0 mT. These
discrete voltages depend on the magnetization directions of the permalloy and
enable detection of the inplane magnetization reversal. The threshold current
density for the magnetization reversal is from 10 to 20 MA/cm^2, the same order
as for known spin orbit torque (SOT) switching with in-plane magnetization
materials. The magnitude of the signal is the same or larger than that of the
typical ST FMR signal; that is, detection of magnetization switching is highly
sensitive in spite of deviation from the optimal ST-FMR condition. The proposed
method is applicable to a simple device structure even for a small
ferromagnetic electrode with a width of 100 nm.",2010.04435v1
2021-03-19,Spin-orbit torque characterization in a nutshell,"Spin current and spin torque generation through the spin-orbit interactions
in solids, of bulk or interfacial origin, is at the heart of spintronics
research. The realization of spin-orbit torque (SOT) driven magnetic dynamics
and switching in diverse magnetic heterostructures also pave the way for
developing SOT magnetoresistive random access memory and other novel SOT memory
and logic devices. Of scientific and technological importance are accurate and
efficient SOT quantification techniques, which have been abundantly developed
in the last decade. In this article, we summarize popular techniques to
experimentally quantify SOTs in magnetic heterostructures at micro- and
nano-scale. For each technique, we give an overview of its principle,
variations, strengths, shortcomings, error sources, and any cautions in usage.
Finally, we discuss the remaining challenges in understanding and quantifying
the SOTs in heterostructures.",2103.10634v1
2021-07-22,Spin-Orbit Torque Switching of Noncollinear Antiferromagnetic Antiperovskite Manganese Nitride Mn$_3$GaN,"Noncollinear antiferromagnets have promising potential to replace
ferromagnets in the field of spintronics as high-density devices with ultrafast
operation. To take full advantage of noncollinear antiferromagnets in
spintronics applications, it is important to achieve efficient manipulation of
noncollinear antiferromagnetic spin. Here, using the anomalous Hall effect as
an electrical signal of the triangular magnetic configuration, spin-orbit
torque switching with no external magnetic field is demonstrated in
noncollinear antiferromagnetic antiperovskite manganese nitride Mn$_3$GaN at
room temperature. The pulse-width dependence and subsequent relaxation of Hall
signal behavior indicate that the spin-orbit torque plays a more important role
than the thermal contribution due to pulse injection. In addition, multistate
memristive switching with respect to pulse current density was observed. The
findings advance the effective control of noncollinear antiferromagnetic spin,
facilitating the use of such materials in antiferromagnetic spintronics and
neuromorphic computing applications.",2107.10426v1
2023-04-03,Switching of Perpendicular Magnetization by Spin-Orbit Torque,"Magnetic materials with strong perpendicular magnetic anisotropy are of great
interest for the development of nonvolatile magnetic memory and computing
technologies due to their high stabilities at the nanoscale. However,
electrical switching of such perpendicular magnetization in an
energy-efficient, deterministic, scalable manner has remained a big challenge.
This problem has recently attracted enormous efforts in the field of
spintronics. Here, I review recent advances and challenges in the understanding
of the electrical generation of spin currents, the switching mechanisms and the
switching strategies of perpendicular magnetization, the switching current
density by spin-orbit torque of transverse spins, the choice of perpendicular
magnetic materials, and summarize the progress in prototype perpendicular SOT
memory and logic devices toward the goal of energy-efficient, dense, fast
perpendicular spin-orbit torque applications.",2304.00683v1
2024-02-28,Coherent control of terahertz-scale spin resonances using optical spin-orbit torques,"Using optically generated spin-orbit torques generated by the heavy metal Pt
we demonstrate coherent control of GHz ferromagnetic resonances in Pt/Co/Pt
multilayers as well as sub-THz exchange resonances in [Gd/Co]$_2$ multilayers.
Employing a double-pump setup, we show that depending on the helicities of the
pump pulses, spin resonances can either be coherently amplified or suppressed
if the time delay between the arrival of the pump beams is chosen
appropriately. Furthermore, investigating phase and amplitude of the
exchange-driven modes, we identify features that challenge the current
understanding of optically generated spin-orbit torques, and we discuss
possible explanations.",2402.18671v1
2003-09-19,Semiclassical theory of spin transport in spin-orbit coupled systems,"Motivated by recent interest in novel spintronics effects, we develop a
semiclassical theory of spin transport that is valid for spin-orbit coupled
bands. Aside from the obvious convective term in which the average spin is
transported at the wavepacket group velocity, the spin current has additional
contributions from the wavepacket's spin and torque dipole moments. Electric
field corrections to the group velocity and carrier spin contribute to the
convective term. Summing all terms we obtain an expression for the intrinsic
spin-Hall conductivity of a hole-doped semiconductor, which agrees with the
Kubo formula prediction for the same quantity. We discuss the calculation of
spin accumulation, which illustrates the importance of the torque dipole near
the boundary of the system.",0309475v4
2010-11-23,Spin Period Evolution of Recycled Pulsar in Accreting Binary,"We investigate the spin-period evolutions of recycled pulsars in binary
accreting systems. Taking both the accretion induced field decay and spin-up
into consideration, we calculate their spin-period evolutions influenced by the
initial magnetic-field strengths, initial spin-periods and accretion rates,
respectively. The results indicate that the minimum spin-period (or maximum
spin frequency) of millisecond pulsar (MSP) is independent of the initial
conditions and accretion rate when the neutron star (NS) accretes $\sim>
0.2\ms$. The accretion torque with the fastness parameter and gravitational
wave (GW) radiation torque may be responsible for the formation of the minimum
spin-period (maximum spin frequency). The fastest spin frequency (716 Hz) of
MSP can be inferred to associate with a critical fastness parameter about
$\omega_{c}=0.55$. Furthermore, the comparisons with the observational data are
presented in the field-period ($B-P$) diagram.",1011.5013v1
2015-05-06,Reexamination of the Elliott-Yafet spin-relaxation mechanism,"We analyze spin-dependent carrier dynamics due to incoherent electron-phonon
scattering, which is commonly referred to as Elliott-Yafet (EY) spin-relaxation
mechanism. For this mechanism one usually distinguishes two contributions: (1)
from the electrostatic interaction together with spin-mixing in the wave
functions, which is often called the Elliott contribution, and (2) the
phonon-modulated spin-orbit interaction, which is often called the Yafet or
Overhauser contribution. By computing the reduced electronic density matrix, we
improve Yafet's original calculation, which is not valid for pronounced spin
mixing as it equates the pseudo-spin polarization with the spin polarization.
The important novel quantity in our calculation is a torque operator that
determines the spin dynamics. The contribution (1) to this torque vanishes
exactly. From this general result, we derive a modified expression for the
Elliott-Yafet spin relaxation time.",1505.01432v2
2015-09-03,Nanomechanical detection of the spin Hall effect,"The spin Hall effect creates a spin current in response to a charge current
in a material that has strong spin-orbit coupling. The size of the spin Hall
effect in many materials is disputed, requiring independent measurements of the
effect. We develop a novel mechanical method to measure the size of the spin
Hall effect, relying on the equivalence between spin and angular momentum. The
spin current carries angular momentum, so the flow of angular momentum will
result in a mechanical torque on the material. We determine the size and
geometry of this torque and demonstrate that it can be measured using a
nanomechanical device. Our results show that measurement of the spin Hall
effect in this manner is possible and also opens possibilities for actuating
nanomechanical systems with spin currents.",1509.01269v3
2019-10-28,Tuning interfacial spins in antiferromagnetic / ferromagnetic / heavy metal heterostructures via spin-orbit torque,"Antiferromagnets are outstanding candidates for the next generation of
spintronic applications, with great potential for downscaling and decreasing
power consumption. Recently, the manipulation of bulk properties of
antiferromagnets has been realized by several different approaches. However,
the interfacial spin order of antiferromagnets is an important integral part of
spintronic devices, thus the successful control of interfacial
antiferromagnetic spins is urgently desired. Here, we report the high
controllability of interfacial spins in antiferromagnetic / ferromagnetic /
heavy metal heterostructure devices using spin-orbit torque (SOT) assisted by
perpendicular or longitudinal magnetic fields. Switching of the interfacial
spins from one to another direction through multiple intermediate states is
demonstrated. The field-free SOT-induced switching of antiferromagnetic
interfacial spins is also observed, which we attribute to the effective
built-in out-of-plane field due to unequal upward and downward interfacial spin
populations. Our work provides a precise way to modulate the interfacial spins
at an antiferromagnet / ferromagnet interface via SOT, which will greatly
promote innovative designs for next generation spintronic devices.",1910.12445v1
2020-02-28,Spin-orbit torques driven by the interface-generated spin currents,"The spin currents generated by spin-orbit coupling (SOC) in the nonmagnetic
metal layer or at the interface with broken inversion symmetry are of
particular interest and importance. Here, we have explored the spin current
generation mechanisms through the spin-orbit torques (SOTs) measurements in the
Ru/Fe heterostructures with weak perpendicular magnetic anisotropy (PMA).
Although the spin Hall angle (SHA) of Ru is smaller than that in Pt, Ta or W,
reversible SOT in Ru/Fe heterostructures can still be realized. Through
non-adiabatic harmonic Hall voltage measurements and macrospin simulation, the
effective SHA in Ru/Fe heterostructures is compared with Pt. Moreover, we also
explore that the spin current driven by interface strongly depends on the
electrical conductivities. Our results suggest a new method for efficiently
generating finite spin currents in ferromagnet/nonmagnetic metal bilayers,
which establishes new opportunities for fundamental study of spin dynamics and
transport in ferromagnetic systems.",2002.12545v1
2020-12-25,Spin-circuit representation of spin-torque ferromagnetic resonance,"Spin-torque ferromagnetic resonance (ST-FMR) particularly using magnetic
insulators and heavy metals possessing a giant spin Hall effect (SHE) has
gotten a lot of attention for the development of spintronic devices. To devise
complex functional devices, it is necessary to construct the equivalent
spin-circuit representations of different phenomena. Such representation is
useful to translate physical equations into circuit elements, benchmarking
experiments, and then proposing creative and efficient designs. We utilize the
superposition principle in circuit theory to separate the spin Hall
magnetoresistance and spin pumping contributions in the ST-FMR experiments. We
show that the proposed spin-circuit representation reproduces the standard
results in literature. We further consider multilayers like a spin-valve
structure with an SHE layer sandwiched by two magnetic layers and show how the
corresponding spin-circuit representation can be constructed by simply writing
a vector netlist and solved using circuit theory.",2012.13591v1
2019-07-31,Chiral active matter: microscopic `torque dipoles' have more than one hydrodynamic description,"Many biological systems, such as bacterial suspensions and actomyosin
networks, form polar liquid crystals. These systems are `active' or
far-from-equilibrium, due to local forcing of the solvent by the constituent
particles. In many cases the source of activity is chiral; since forcing is
internally generated, some sort of `torque dipole' is then present locally. But
it is not obvious how `torque dipoles' should be encoded in the hydrodynamic
equations that describe the system at continuum level: different authors have
arrived at contradictory conclusions on this issue. In this work, we resolve
the paradox by presenting a careful derivation, from linear irreversible
thermodynamics, of the general equations of motion of a single-component chiral
active fluid with spin degrees of freedom. We find that there is no unique
hydrodynamic description for such a fluid in the presence of torque dipoles of
a given strength. Instead, at least three different hydrodynamic descriptions
emerge, depending on whether we decompose each torque dipole as two point
torques, two force pairs, or one point torque and one force pair -- where point
torques create internal angular momenta of the chiral bodies (spin), whereas
force pairs impart centre of mass motion that contributes to fluid velocity. By
considering a general expansion of the Onsager coefficients, we also derive a
new shear-elongation parameter and cross-coupling viscosity, which can lead to
unpredicted phenomena even in passive polar liquid crystals. Finally,
elimination of the angular variables gives an effective polar hydrodynamics
with renormalized active stresses, viscosities and kinetic coefficients.
Remarkably, this can include a direct contribution of chiral activity to the
equation of motion for the polar order parameter, which survives even in `dry'
active systems where the fluid velocity is set to zero.",1908.00079v1
2011-03-16,Spin-Torque Diode Measurements of MgO-Based Magnetic Tunnel Junctions with Asymmetric Electrodes,"We present a detailed study of the spin-torque diode effect in
CoFeB/MgO/CoFe/NiFe magnetic tunnel junctions. From the evolution of the
resonance frequency with magnetic field at different angles, we clearly
identify the free-layer mode and find an excellent agreement with simulations
by taking into account several terms for magnetic anisotropy. Moreover, we
demonstrate the large contribution of the out-of-plane torque in our junctions
with asymmetric electrodes compared to the in-plane torque. Consequently, we
provide a way to enhance the sensitivity of these devices for the detection of
microwave frequency.",1103.3207v1
2017-11-21,Suppression of the fieldlike spin-orbit torque efficiency due to the magnetic proximity effect in ferromagnet/platinum bilayers,"Current-induced spin-orbit torques in Co$_2$FeAl/Pt ultrathin bilayers are
studied using a magnetoresistive harmonic response technique, which
distinguishes the dampinglike and fieldlike contributions. The presence of a
temperature-dependent magnetic proximity effect is observed through the
anomalous Hall and anisotropic magnetoresistances, which are enhanced at low
temperatures for thin platinum thicknesses. The fieldlike torque efficiency
decreases steadily as the temperature is lowered for all Pt thicknesses
studied, which we propose is related to the influence of the magnetic proximity
effect on the fieldlike torque mechanism.",1711.07969v2
2019-06-26,Spin-orbit torques and their associated effective fields from gigahertz to terahertz,"Terahertz spintronics offers the prospect of devices which are both faster
and more energy-efficient. A promising route to achieve this goal is to exploit
current-induced spin-orbit torques. However, the high-frequency properties of
these quantities remain unexplored both experimentally and theoretically,
within a realistic material-specific approach. Here we investigate the
dynamical transverse components of the torques and uncover contributions
longitudinal to the magnetic moment capable of changing its magnitude. We show
that, while the torques can be drastically altered in the dynamical regime, the
effective magnetic fields that accompany them present a frequency-independent
behaviour, ranging from the static limit up to the terahertz domain - including
the ferromagnetic resonance of the system. The outcomes of this work point to
new ways to control magnetic units in next-generation spintronic devices.",1906.11314v2
2020-09-15,"On the torque exerted by a warped, magnetically threaded accretion disk","Most astrophysical accretion disks are likely to be warped. In X-ray binaries
the spin evolution of an accreting neutron star is critically dependent on the
interaction between the neutron star magnetic field and the accretion disk.
There have been extensive investigations on the accretion torque exerted by a
coplanar disk that is magnetically threaded by the magnetic field lines from
the neutron stars, but relevant works on warped/tilted accretion disks are
still lacking. In this paper we develop a simplified two-component model, in
which the disk is comprised of an inner coplanar part and an outer, tilted
part. Based on standard assumption on the formation and evolution of the
toroidal magnetic field component, we derive the dimensionless torque and show
that a warped/titled disk is more likely to spin up the neutron star compared
with a coplanar disk.We also discuss the possible influence of various initial
parameters on the torque.",2009.07019v1
2020-11-25,Non-tidal Coupling of the Orbital and Rotational Motions of Extended Bodies,"The orbital motions and spin-axis rotations of extended bodies are
traditionally considered to be coupled only by tidal mechanisms. The orbit-spin
coupling hypothesis supplies an additional mechanism. A reversing torque on
rotating extended bodies is identified. The torque effects an exchange of
angular momentum between the reservoirs of the orbital and rotational motions.
The axis of the torque is constrained to lie within the equatorial plane of the
subject body. Hypothesis testing to date has focused on the response to the
putative torque of the Martian atmosphere. Atmospheric global circulation model
simulations reveal that an episodic strengthening and weakening of meridional
overturning circulations should be observable and is diagnostic in connection
with the triggering of Martian planet-encircling dust storms. Spacecraft
observations obtained during the earliest days of the 2018 Martian global dust
storm document a strong intensification of atmospheric meridional motions as
predicted under this hypothesis. We review implications for atmospheric
physics, for investigations of planetary orbital evolution with rotational
energy dissipation, and for theories of gravitation.",2011.13053v1
2019-09-04,Two-axis cavity optomechanical torque characterization of magnetic microstructures,"Significant new functionality is reported for torsion mechanical tools aimed
at full magnetic characterizations of both spin statics and dynamics in micro-
and nanostructures. Specifically, two orthogonal torque directions are
monitored and the results co-analyzed to separate magnetic moment and magnetic
susceptibility contributions to torque, as is desired for characterization of
anisotropic three-dimensional structures. The approach is demonstrated through
application to shape and microstructural disorder-induced magnetic anisotropies
in lithographically patterned permalloy, and will have utility for the
determination of important magnetic thin-film and multilayer properties
including interface anisotropy and exchange bias. The results reflect
remarkable sensitivity of the out-of-plane magnetic torque to the nature of
small edge domains perpendicular to the applied field direction, and also
contain tantalizing indications of direct coupling to spin dynamics at the
frequency of the mechanics.",1909.01949v1
2022-12-14,Field-free spin-orbit torque switching of an antiferromagnet with perpendicular Néel vector,"The field-free spin-orbit torque induced 180{\deg} reorientation of
perpendicular magnetization is beneficial for the high performance magnetic
memory. The antiferromagnetic material (AFM) can provide higher operation speed
than the ferromagnetic counterpart. In this paper, we propose a trilayer
AFM/Insulator/Heavy Metal structure as the AFM memory device. We show that the
field-free switching of the AFM with perpendicular N\'eel vector can be
achieved by using two orthogonal currents, which provide the uniform
damping-like torque and stagger field-like torque, respectively. The reversible
switching can be obtained by reversing either current. A current density of
1.79 10^11A/m^2 is sufficient to induce the switching. In addition, the two
magnetic moments become noncollinear during the switching. This enables an
ultrafast switching within 40 picoseconds. The device and switching mechanism
proposed in this work offer a promising approach to deterministically switch
the AFM with perpendicular N\'eel vector. It can also stimulate the development
of ultrafast AFM-based MRAM.",2212.07166v1
2022-02-26,On the pulsar spin frequency derivatives and the glitch activity,"The number of sudden spin-ups in radio pulsars known as pulsar glitches has
increased over the years. Though a consensus has not been reached with regards
to the actual cause of the phenomenon, the electromagnetic braking torque on
the crust quantified via the magnitude of pulsar spin frequency first
derivative, $ \dot{\nu} $ is a key factor in mechanisms put across toward the
understanding of the underlying principles involved. The glitch size has been
used to establish a quantity used to constrain the mean possible change in
pulsar spin frequency $ (\nu) $ per year due to a glitch known as the `glitch
activity'. Traditionally, the glitch activity parameter $ A_{g} $ is calculated
from the cumulative glitch sizes in a pulsar at a certain observational time
span. In this analysis, we test the possibility of of quantifying the $ A_{g} $
with the pulsars main spin frequency derivatives (i.e. $ \dot{\nu} $ and
$\ddot{\nu} $). In this approach, the ratio of the frequency derivatives, i.e.
$ |\ddot{\nu}|/\dot{\nu}^{2} $ is seen to constrains the glitch activity in
radio pulsars. The glitch size is found to be independent of the magnitude of
the ratio, however, based on the recorded glitch events, the lower end of $
|\ddot{\nu}|/\dot{\nu}^{2} $ distribution appear to have more glitches. The
minimum inter-glitch time interval in the ensemble of pulsars scale with the
ratio as $t_{g} \sim 3.35(|\ddot{\nu}|/\dot{\nu}^{2})^{0.23} $. The $ A_{g} $
quantified in this analysis supports the idea of neutron star inner-crust
superfluid being the reservoir of momentum transferred during glitches. It
suggests that the moment of inertia of the inner-crust to be at most 10 % of
the entire neutron star moment of inertia.",2202.13136v1
2014-10-05,Spin Alignment in Analogues of The Local Sheet,"Tidal torque theory and simulations of large scale structure predict spin
vectors of massive galaxies should be coplanar with sheets in the cosmic web.
Recently demonstrated, the giants (K$_{s}$ $\leq$ -22.5 mag) in the Local
Volume beyond the Local Sheet have spin vectors directed close to the plane of
the Local Supercluster, supporting the predictions of Tidal Torque Theory.
However, the giants in the Local Sheet encircling the Local Group display a
distinctly different arrangement, suggesting that the mass asymmetry of the
Local Group or its progenitor torqued them from their primordial spin
directions. To investigate the origin of the spin alignment of giants locally,
analogues of the Local Sheet were identified in the SDSS DR9. Similar to the
Local Sheet, analogues have an interacting pair of disk galaxies isolated from
the remaining sheet members. Modified sheets in which there is no interacting
pair of disk galaxies were identified as a control sample.
  Galaxies in face-on control sheets do not display axis ratios predominantly
weighted toward low values, contrary to the expectation of tidal torque theory.
For face-on and edge-on sheets, the distribution of axis ratios for galaxies in
analogues is distinct from that in controls with a confidence of 97.6 $\%$ $\&$
96.9$\%$, respectively. This corroborates the hypothesis that an interacting
pair can affect spin directions of neighbouring galaxies.",1410.1192v2
2017-12-21,Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films,"Spin waves in ferrimagnetic yttrium iron garnet (YIG) films with ultralow
magnetic damping are relevant for magnon-based spintronics and low-power
wave-like computing. The excitation frequency of spin waves in YIG is rather
low in weak external magnetic fields because of its small saturation
magnetization, which limits the potential of YIG films for high-frequency
applications. Here, we demonstrate how exchange-coupling to a CoFeB film
enables efficient excitation of high-frequency perpendicular standing spin
waves (PSSWs) in nanometer-thick (80 nm and 295 nm) YIG films using uniform
microwave magnetic fields. In the 295-nm-thick YIG film, we measure intense
PSSW modes up to 10th order. Strong hybridization between the PSSW modes and
the ferromagnetic resonance mode of CoFeB leads to characteristic anti-crossing
behavior in broadband spin-wave spectra. A dynamic exchange torque at the
YIG/CoFeB interface explains the excitation of PSSWs. The localized torque
originates from exchange coupling between two dissimilar magnetization
precessions in the YIG and CoFeB layers. As a consequence, spin waves are
emitted from the YIG/CoFeB interface and PSSWs form when their wave vector
matches the perpendicular confinement condition. PSSWs are not excited when the
exchange coupling between YIG and CoFeB is suppressed by a Ta spacer layer.
Micromagnetic simulations confirm the exchange-torque mechanism.",1712.08204v1
2016-03-08,Spin-wave thermal population as temperature probe in Magnetic Tunnel Junctions,"We study whether a direct measurement of the absolute temperature of a
Magnetic Tunnel Junction (MTJ) can be performed using the high frequency
electrical noise that it delivers under a finite voltage bias. Our method
includes quasi-static hysteresis loop measurements of the MTJ, together with
the field-dependence of its spin wave noise spectra. We rely on an analytical
modeling of the spectra by assuming independent fluctuations of the different
sub-systems of the tunnel junction that are described as macrospin fluctuators.
We illustrate our method on perpendicularly magnetized MgO-based MTJs patterned
in 50*100 nm2 nanopillars. We apply hard axis (in-plane) fields to let the
magnetic thermal fluctuations yield finite conductance fluctuations of the MTJ.
Instead of the free layer fluctuations that are observed to be affected by both
spin-torque and temperature, we use the magnetization fluctuations of the sole
reference layers. Their much stronger anisotropy and their much heavier damping
render them essentially immune to spin-torque. We illustrate our method by
determining current-induced heating of the perpendicularly magnetized tunnel
junction at voltages similar to those used in spin-torque memory applications.
The absolute temperature can be deduced with a precision of +/- 60 K and we can
exclude any substantial heating at the spin-torque switching voltage.",1603.02591v1
2020-03-02,Non-Hermitian topology of one-dimensional spin-torque oscillator arrays,"Magnetic systems have been extensively studied both from a fundamental
physics perspective and as building blocks for a variety of applications. Their
topological properties, in particular those of excitations, remain relatively
unexplored due to their inherently dissipative nature. The recent introduction
of non-Hermitian topological classifications opens up new opportunities for
engineering topological phases in dissipative systems. Here, we propose a
magnonic realization of a non-Hermitian topological system. A crucial
ingredient of our proposal is the injection of spin current into the magnetic
system, which alters and can even change the sign of terms describing
dissipation. We show that the magnetic dynamics of an array of spin-torque
oscillators can be mapped onto a non-Hermitian Su-Schrieffer-Heeger model
exhibiting topologically protected edge states. Using exact diagonalization of
the linearized dynamics and numerical solutions of the non-linear equations of
motion, we find that a topological magnonic phase can be accessed by tuning the
spin current injected into the array. In the topologically nontrivial regime, a
single spin-torque oscillator on the edge of the array is driven into
auto-oscillation and emits a microwave signal, while the bulk oscillators
remain inactive. Our findings have practical utility for memory devices and
spintronics neural networks relying on spin-torque oscillators as constituent
units.",2003.01152v1
2020-07-30,Temperature-dependent spin-transport and current-induced torques in superconductor/ferromagnet heterostructures,"We investigate the injection of quasiparticle spin currents into a
superconductor via spin pumping from an adjacent FM layer.$\;$To this end, we
use NbN/\ch{Ni80Fe20}(Py)-heterostructures with a Pt spin sink layer and excite
ferromagnetic resonance in the Py-layer by placing the samples onto a coplanar
waveguide (CPW). A phase sensitive detection of the microwave transmission
signal is used to quantitatively extract the inductive coupling strength
between sample and CPW, interpreted in terms of inverse current-induced
torques, in our heterostructures as a function of temperature. Below the
superconducting transition temperature $T_{\mathrm{c}}$, we observe a
suppression of the damping-like torque generated in the Pt layer by the inverse
spin Hall effect (iSHE), which can be understood by the changes in spin current
transport in the superconducting NbN-layer. Moreover, below $T_{\mathrm{c}}$ we
find a large field-like current-induced torque.",2007.15569v1
2019-09-06,Macrospin analysis of RF excitations within fully perpendicular magnetic tunnel junctions with second order easy-axis magnetic anisotropy contribution,"The conditions of field and voltage for inducing steady state excitations in
fully perpendicular magnetic tunnel junctions (pMTJs), adapted for memory
applications, were numerically investigated by the resolution of the
Landau-Lifshitz-Gilbert equation in the macrospin approach. Both damping-like
and the field-like spin transfer torque terms were taken into account in the
simulations, as well as the contribution of the second order uniaxial
anisotropy term (K2), which has been recently revealed in MgO-based pMTJs. An
in-plane applied magnetic field balances the out of plane symmetry of the pMTJ
and allows the signal detection. Using this model, we assessed the states of
the free layer magnetization as a function of strength of K2 and polar theta_H
angle of the applied field (varied from 90 to 60 deg.). There are two stable
states, with the magnetization in-plane or out of plane of the layer, and two
dynamic states with self-sustained oscillations, called in-plane precession
state (IPP) or out of plane precession state (OPP). The IPP mode, with
oscillation frequencies up to 7 GHz, appears only for positive voltages if
theta_H = 90 deg. However, it shows a more complex distribution when the field
is slightly tilted out of plane. The OPP mode is excited only if K2 is
considered and reaches a maximum oscillation frequency of 15 GHz. Large areas
of dynamic states with high frequencies are obtained for strong values of the
field-like torque and K2, when applying a slightly tilted external field toward
the out of plane direction. The non-zero temperature does not modify the phase
diagrams, but reduces drastically the power spectral density peak amplitudes.",1909.02926v1
2014-02-05,Fieldlike and antidamping spin-orbit torques in as-grown and annealed Ta/CoFeB/MgO layers,"We present a comprehensive study of the current-induced spin-orbit torques in
perpendicularly magnetized Ta/CoFeB/MgO layers. The samples were annealed in
steps up to 300 degrees C and characterized using x-ray absorption
spectroscopy, transmission electron microscopy, resistivity, and Hall effect
measurements. By performing adiabatic harmonic Hall voltage measurements, we
show that the transverse (field-like) and longitudinal (antidamping-like)
spin-orbit torques are composed of constant and magnetization-dependent
contributions, both of which vary strongly with annealing. Such variations
correlate with changes of the saturation magnetization and magnetic anisotropy
and are assigned to chemical and structural modifications of the layers. The
relative variation of the constant and anisotropic torque terms as a function
of annealing temperature is opposite for the field-like and antidamping
torques. Measurements of the switching probability using sub-{\mu}s current
pulses show that the critical current increases with the magnetic anisotropy of
the layers, whereas the switching efficiency, measured as the ratio of magnetic
anisotropy energy and pulse energy, decreases. The optimal annealing
temperature to achieve maximum magnetic anisotropy, saturation magnetization,
and switching efficiency is determined to be between 240 degrees and 270
degrees C.",1402.0986v2
2018-01-23,"The Effect of Combined Magnetic Geometries on Thermally Driven Winds II: Dipolar, Quadrupolar and Octupolar Topologies","During the lifetime of sun-like or low mass stars a significant amount of
angular momentum is removed through magnetised stellar winds. This process is
often assumed to be governed by the dipolar component of the magnetic field.
However, observed magnetic fields can host strong quadrupolar and/or octupolar
components, which may influence the resulting spin-down torque on the star. In
Paper I, we used the MHD code PLUTO to compute steady state solutions for
stellar winds containing a mixture of dipole and quadrupole geometries. We
showed the combined winds to be more complex than a simple sum of winds with
these individual components. This work follows the same method as Paper I,
including the octupole geometry which increases the field complexity but also,
more fundamentally, looks for the first time at combining the same symmetry
family of fields, with the field polarity of the dipole and octupole geometries
reversing over the equator (unlike the symmetric quadrupole). We show, as in
Paper I, that the lowest order component typically dominates the spin down
torque. Specifically, the dipole component is the most significant in governing
the spin down torque for mixed geometries and under most conditions for real
stars. We present a general torque formulation that includes the effects of
complex, mixed fields, which predicts the torque for all the simulations to
within 20% precision, and the majority to within ~5%. This can be used as an
input for rotational evolution calculations in cases where the individual
magnetic components are known.",1801.07662v2
2020-11-02,"Magnetic braking of accreting T Tauri stars: Effects of mass accretion rate, rotation, and dipolar field strength","The rotational evolution of accreting pre-main-sequence stars is influenced
by its magnetic interaction with its surrounding circumstellar disk. Using the
PLUTO code, we perform 2.5D magnetohydrodynamic, axisymmetric, time-dependent
simulations of star-disk interaction---with an initial dipolar magnetic field
structure, and a viscous and resistive accretion disk---in order to model the
three mechanisms that contribute to the net stellar torque: accretion flow,
stellar wind, and magnetospheric ejections (periodic inflation and reconnection
events). We investigate how changes in the stellar magnetic field strength,
rotation rate, and mass accretion rate (changing the initial disk density)
affect the net stellar torque. All simulations are in a net spin-up regime. We
fit semi-analytic functions for the three stellar torque contributions,
allowing for the prediction of the net stellar torque for our parameter regime,
and the possibility of investigating spin-evolution using 1D stellar evolution
codes. The presence of an accretion disk appears to increase the efficiency of
stellar torques compared to isolated stars, for cases with outflow rates much
smaller than accretion rates, because the star-disk interaction opens more of
the stellar magnetic flux compared to that from isolated stars. In our
parameter regime, a stellar wind with a mass loss rate of $\approx 1 \%$ of the
mass accretion rate is capable of extracting $\lesssim 50 \%$ of the accreting
angular momentum. These simulations suggest that achieving spin-equilibrium in
a representative T Tauri case within our parameter regime, e.g., BP Tau, would
require a wind mass loss rate of $\approx 25\%$ of the mass accretion rate.",2011.01087v1
2018-01-21,Topological-charge dependence of radiation torque for an acoustic-vortex spanner,"Based on the analyses of the wave front and the wave vector of an
acoustic-vortex (AV) spanner generated by a circular array of point source, the
principle of object rotation is investigated through the calculation of the
orbital angular momentum (OAM) and the radiation torque for AVs with various
topological charges. It is demonstrated theoretically that the rotation of the
axisymmetric disk centered on an AV spanner is mainly driven by the exerted
radiation torque without the contribution of the OAM transfer. The radiation
torque on a small-radius object is inversely associated with the topological
charge in the center of the AV spanner, and it is enhanced significantly for a
larger AV with a higher topological charge. The special case of the radiation
torque proportional to the topological charge might be realized when the disk
radius is much larger than the wavelength, in which case the acoustic power of
the AV spanner can be absorbed as much as possible. With the established
sixteen-source experimental setup, the radial pressure distributions of AVs
with different topological charges measured at the frequency of 1.3 kHz in air
agree well with the simulations. The topological-charge dependence of the
radiation torque for AVs is also verified by the quantitative
laser-displacement (angle) measurements for disks with different radii. The
favorable results demonstrate that, for the object covering the vortex center
of an AV spanner, the total OAM transfer might be 0 and the object rotation is
contributed by the acting moments. Thus, the radiation torque of an AV spanner
is more applicable than the OAM for describing the driving capability of object
rotation, and it can be used as an effective tool in clinical applications to
noninvasively manipulate objects with a feature size at the wavelength-scale
(e.g. kidney stone in lithotripsy) inside body.",1801.06780v1
2018-10-09,Spin Seebeck imaging of spin-torque switching in antiferromagnetic Pt/NiO heterostructures,"As electrical control of N\'eel order opens the door to reliable
antiferromagnetic spintronic devices, understanding the microscopic mechanisms
of antiferromagnetic switching is crucial. Spatially-resolved studies are
necessary to distinguish multiple nonuniform switching mechanisms; however,
progress has been hindered by the lack of tabletop techniques to image the
N\'eel order. We demonstrate spin Seebeck microscopy as a sensitive, table-top
method for imaging antiferromagnetic order in thin films, and apply this
technique to study spin-torque switching in NiO/Pt and Pt/NiO/Pt
heterostructures. We establish the interfacial antiferromagnetic spin Seebeck
effect in NiO as a probe of surface N\'eel order, resolving antiferromagnetic
spin domains within crystalline twin domains. By imaging before and after
applying current-induced spin torque, we resolve spin domain rotation and
domain wall motion, acting simultaneously. We correlate the changes in spin
Seebeck images with electrical measurements of the average N\'eel orientation
through the spin Hall magnetoresistance, confirming that we image
antiferromagnetic order.",1810.03997v2
2019-01-28,Strong damping-like spin-orbit torque and tunable Dzyaloshinskii-Moriya interaction generated by low-resistivity Pd$_{1-x}$Pt$_x$ alloys,"Despite their great promise for providing a pathway for very efficient and
fast manipulation of magnetization at the nanoscale, spin-orbit torque (SOT)
operations are currently energy inefficient due to a low damping-like SOT
efficiency per unit current bias, and/or the very high resistivity of the spin
Hall materials. Here, we report an advantageous spin Hall material, Pd1-xPtx,
which combines a low resistivity with a giant spin Hall effect as evidenced
through the use of three independent SOT ferromagnetic detectors. The optimal
Pd0.25Pt0.75 alloy has a giant internal spin Hall ratio of >0.47 (damping-like
SOT efficiency of ~ 0.26 for all three ferromagnets) and a low resistivity of
~57.5 {\mu}{\Omega} cm at 4 nm thickness. Moreover, we find the
Dzyaloshinskii-Moriya interaction (DMI), the key ingredient for the
manipulation of chiral spin arrangements (e.g. magnetic skyrmions and chiral
domain walls), is considerably strong at the Pd1-xPtx/Fe0.6Co0.2B0.2 interface
when compared to that at Ta/Fe0.6Co0.2B0.2 or W/Fe0.6Co0.2B0.2 interfaces and
can be tuned by a factor of 5 through control of the interfacial spin-orbital
coupling via the heavy metal composition. This work establishes a very
effective spin current generator that combines a notably high energy efficiency
with a very strong and tunable DMI for advanced chiral spintronics and spin
torque applications.",1901.09954v1
2019-08-18,Maximizing the spin-orbit torque efficiency of Pt/Ti multilayers by optimization of the tradeoff between the intrinsic spin Hall conductivity and carrier lifetime,"We report a comprehensive study of the maximization of the spin Hall ratio
({\theta}SH) in Pt thin films by the insertion of sub-monolayer layers of Ti to
decrease carrier lifetime while minimizing the concurrent reduction in the spin
Hall conductivity. We establish that the intrinsic spin Hall conductivity of
Pt, while robust against the strain and the moderate interruption of crystal
order caused by these insertions, begins to decrease rapidly at high
resistivity level because of the shortening carrier lifetime. The unavoidable
trade-off between the intrinsic spin Hall conductivity and carrier lifetime
sets a practical upper bound of {\theta}SH >=0.8 for heterogeneous materials
where the crystalline Pt component is the source of the spin Hall effect and
the resistivity is increased by shortening carrier lifetime. This work also
establishes a very promising spin-Hall metal of [Pt 0.75 nm/Ti 0.2 nm]7/Pt 0.75
nm for energy-efficient, high-endurance spin-orbit torque technologies (e.g.,
memories, oscillators, and logic) due to its combination of a giant {\theta}SH
of 0.8, or equivalently a dampinglike spin torque efficiency per unit current
density of 0.35, with a relatively low resistivity (90 uOhm cm) and high
suitability for practical technology integration.",1908.06528v1
2023-04-05,Observation of charge-to-spin conversion with giant efficiency at Ni$_{0.8}$Fe$_{0.2}$/Bi$_{2}$WO$_{6}$ interface,"Magnetization switching using spin-orbit torque offers a promising route to
developing non-volatile memory technologies. The prerequisite, however, is the
charge-to-spin current conversion, which has been achieved traditionally by
harnessing the spin-orbit interaction in heavy metals, topological insulators,
and heterointerfaces hosting a high-mobility two-dimensional electron gas.
Here, we report the observation of charge-to-spin current conversion at the
interface between ferromagnetic Ni$_{0.8}$Fe$_{0.2}$ and ferroelectric
Bi$_{2}$WO$_{6}$ thin films. The resulting spin-orbit torque consists of
damping-like and field-like components, and the estimated efficiency amounts to
about 0.48 $\pm$ 0.02, which translates to 0.96 $\pm$ 0.04 nm$^{-1}$ in terms
of interfacial efficiency. These numbers are comparable to contemporary
spintronic materials exhibiting giant spin-orbit torque efficiency. We suggest
that the Rashba Edelstein effect underpins the charge-to-spin current
conversion on the interface side of Ni$_{0.8}$Fe$_{0.2}$. Further, we provide
an intuitive explanation for the giant efficiency in terms of the spin-orbit
proximity effect, which is enabled by orbital hybridization between W and Ni
(Fe) atoms across the interface. Our work highlights that Aurivillius compounds
are a potential addition to the emerging transition metal oxide-based
spin-orbit materials.",2304.02751v1
2005-09-06,The life-time of galactic bars: central mass concentrations and gravity torques,"Bars in gas-rich spiral galaxies are short-lived. They drive gas inflows
through their gravity torques, and at the same time self-regulate their
strength. Their robustness has been subject of debate, since it was thought
that only the resulting central mass concentrations (CMCs) were weakening bars,
and only relatively rare massive CMCs were able to completely destroy them.
Through numerical simulations including gas dynamics, we find that with the gas
parameters of normal spiral galaxies, the CMC is not sufficient to fully
dissolve the bar. But another overlooked mechanism, the transfer of angular
momentum from the infalling gas to the stellar bar, can also strongly weaken
the bar. In addition, we show that gravity torques are correctly reproduced in
simulations, and conclude that bars are transient features, with life-time of
1-2 Gyr in typical Sb-Sc galaxies, because of the combined effects of CMCs and
gravity torques, while most existing works had focussed on the CMC effects
alone.",0509126v1
2007-08-07,Electromagnetic forces and torques in nanoparticles irradiated by a plane wave,"Optical tweezers and optical lattices are making it possible to control small
particles by means of electromagnetic forces and torques. In this context, a
method is presented in this work to calculate electromagnetic forces and
torques for arbitrarily-shaped objects in the presence of other objects
illuminated by a plane wave. The method is based upon an expansion of the
electromagnetic field in terms of multipoles around each object, which are in
turn used to derive forces and torques analytically. The calculation of
multipole coefficients are obtained numerically by means of the boundary
element method. Results are presented for both spherical and non-spherical
objects.",0708.1006v1
2020-11-25,Redundancy Resolution and Disturbance Rejection via Torque Optimization in Hybrid Cable-Driven Robots,"This paper presents redundancy resolution and disturbance rejection via
torque optimization in Hybrid Cable-Driven Robots (HCDRs). To begin with, we
initiate a redundant HCDR for nonlinear whole-body system modeling and model
reduction. Based on the reduced dynamic model, two new methods are proposed to
solve the redundancy resolution problem: joint-space torque optimization for
actuated joints (TOAJ) and joint-space torque optimization for actuated and
unactuated joints (TOAUJ), and they can be extended to other HCDRs. Compared to
the existing approaches, this paper provides the first solution (TOAUJ-based
method) for HCDRs that can solve the redundancy resolution problem as well as
disturbance rejection. Additionally, this paper develops detailed algorithms
targeting TOAJ and TOAUJ implementation. A simple yet effective controller is
designed for generated data analysis and validation. Case studies are conducted
to evaluate the performance of TOAJ and TOAUJ, and the results suggest the
effectiveness of the aforementioned approaches.",2011.12457v1
2004-06-18,Charge-Hall effect driven by spin force: reciprocal of the spin-Hall effect,"A new kind of charge-Hall effect is shown. Unlike in the usual Hall effect,
the driving force in the longitudinal direction is a spin force, which may
originate from the gradient of a Zeeman field or a spin-dependent chemical
potential. The transverse force is provided by a Berry curvature in a mixed
position-momentum space. We can establish an Onsager relation between this
effect and the spin-Hall effect provided the spin current in the latter is
modified by a torque dipole contribution. This remarkable relation leads to new
ways for experimental detection of spin accumulation predicted by the spin Hall
effect.",0406436v1
2008-02-28,Current driven spin-wave instability triggered by the anomalous Hall effect,"We studied the effect of strong electric current on spin waves interacting
relativistically with the current. The spin-wave spectrum is calculated at
arbitrary direction of the wave vector. It is shown that the alternating Hall
current generated by the alternating magnetic moment of the spin waves, reduces
the spin-wave damping. At strong enough unpolarized dc current the damping
changes sign, and the spin-wave amplitude starts to increase exponentially fast
with time. The critical current for the spin-wave instability is determined
mainly by the anomalous Hall effect, and can be much smaller than that for the
spin-torque mechanism of instability.",0802.4150v1
2010-12-16,Magnetic dynamics driven by the spin-current generated via spin-Seebeck effect,"We consider the spin-current driven dynamics of a magnetic nanostructure in a
conductive magnetic wire under a heat gradient in an open circuit, spin Seebeck
effect geometry. It is shown that the spin-current scattering results in a
spin-current torque acting on the nanostructure and leading to precession and
displacement. The scattering leads also to a redistribution of the spin
electrochemical potential along the wire resulting in a break of the
polarity-reversal symmetry of the inverse spin Hall effect voltage with respect
to the heat gradient inversion.",1012.3552v2
2004-04-08,"Currents, Torques, and Polarization Factors in Magnetic Tunnel Junctions","Application of Bardeen's tunneling theory to magnetic tunnel junctions having
a general degree of atomic disorder reveals the close relationship between
magneto-conduction and voltage-driven pseudo-torque, as well as the thickness
dependence of tunnel-polarization factors. Among the results: 1) The torque
generally varies as sin theta at constant applied voltage. 2) Whenever
polarization factors are well defined, the voltage-driven torque on each moment
is uniquely proportional to the polarization factor of the other magnet. 3) At
finite applied voltage, this relation predicts significant voltage-asymmetry in
the torque. For one sign of voltage the torque remains substantial even when
the magnetoconductance is greatly diminished. 4) A broadly defined junction
model, called ideal middle, allows for atomic disorder within the magnets and
F/I interface regions. In this model, the spin dependence of a state-weighting
factor proportional to the sum over general state index of evaluated within the
(e.g. vacuum) barrier generalizes the local state density in previous theories
of the tunnel-polarization factor. 5) For small applied voltage,
tunnel-polarization factors remain legitimate up to first order in the inverse
thickness of the ideal middle. An algebraic formula describes the first-order
corrections to polarization factors in terms of newly defined lateral
auto-correllation scales.",0404210v3
2013-04-22,Accretion Disks Around Binary Black Holes: A Simple GR-Hybrid Evolution Model,"We consider a geometrically thin, Keplerian disk in the orbital plane of a
binary black hole (BHBH) consisting of a spinning primary and low-mass
secondary (mass ratio q < 1). To account for the principle effects of general
relativity (GR), we propose a modification of the standard Newtonian evolution
equation for the (orbit-averaged) time-varying disk surface density. In our
modified equation the viscous torque in the disk is treated in full GR, while
the tidal torque is handled in the Newtonian limit. Our GR-hybrid treatment is
reasonable because the tidal torque is concentrated near the orbital radius of
the secondary and is most important prior to binary-disk decoupling, when the
orbital separation is large and resides in the weak-field regime. The tidal
torque on the disk diminishes during late merger and vanishes altogether
following merger. By contrast, the viscous torque drives the flow into the
strong-field region and onto the primary during all epochs. Following binary
coalescence, the viscous torque alone governs the time-dependent accretion onto
the remnant, as well as the temporal behavior, strength and spectrum of the
aftermath electromagnetic radiation from the disk. We solve our GR-hybrid
equation for a representative BHBH-disk system, identify several observable EM
signatures of the merger, and compare results obtained for the gas and EM
radiation with those found with the Newtonian prescription.",1304.6090v2
2012-09-07,Tidal Friction and Tidal Lagging. Applicability Limitations of a Popular Formula for the Tidal Torque,"Tidal torques play a key role in rotational dynamics of celestial bodies.
They govern these bodies' tidal despinning, and also participate in the subtle
process of entrapment of these bodies into spin-orbit resonances. This makes
tidal torques directly relevant to the studies of habitability of planets and
their moons.
  Our work begins with an explanation of how friction and lagging should be
built into the theory of bodily tides. Although much of this material can be
found in various publications, a short but self-consistent summary on the topic
has been lacking in the hitherto literature, and we are filling the gap.
  After these preparations, we address a popular concise formula for the tidal
torque, which is often used in the literature, for planets or stars.We explain
why the derivation of this expression, offered in the paper by Goldreich (1966;
AJ 71, 1 - 7) and in the books by Kaula (1968, eqn. 4.5.29), and Murray &
Dermott (1999, eqn. 4.159), implicitly sets the time lag to be frequency
independent. Accordingly, the ensuing expression for the torque can be applied
only to bodies having a very special (and very hypothetical) rheology which
makes the time lag frequency independent, i.e, the same for all Fourier modes
in the spectrum of tide. This expression for the torque should not be used for
bodies of other rheologies. Specifically, the expression cannot be combined
with an extra assertion of the geometric lag (or the phase lag) being constant,
because at finite eccentricities the said assumption is incompatible with the
constant-time-lag condition.",1209.1615v3
2017-04-22,Observation of Spin Nernst effect in Platinum,"Central focus of spintronics is concentrated on generation of pure spin
current and associated spin torque. Pure spin current can be generated by spin
Hall effect in heavy metals by passing charge current. By spin Seebeck effect
pure spin current can also be generated in ferromagnet. In this work we
experimentally demonstrate that if heavy metals like Platinum with high spin
orbit coupling carry heat current it can convert it into spin current due to
relativistic spin orbit interaction. This conversion of heat current into spin
current in non magnet is equivalent of thermally driven spin Hall effect or it
is known as spin Nernst effect. We observed spin Nernst effect in Ni/Pt
bi-layer experimentally and we confirm that when Pt is replaced by low spin
orbit material like Al spin Nernst effect significantly reduces. So we have
detected spin Nernst effect unambiguously and compare its strength with
electrical spin Hall effect.",1704.06788v1
2012-06-20,"A unified drift-diffusion theory for transverse spin currents in spin valves, domain walls and other textured magnets","Spins transverse to the magnetization of a ferromagnet only survives over a
short distance. We develop a drift-diffusion approach that captures the main
features of transverse spin effects in systems with arbitrary spin textures
(vortices, domain walls) and generalizes the Valet-Fert theory. In addition to
the standard characteristic lengths (mean free path for majority and manority
electrons, spin diffusion length), the theory introduces two lengths scales,
the transverse spin coherence length and the (Larmor) spin precession length.
We show how those lengths can be extracted from ab-initio calculations or
measured with giant magneto-resistance experiments. In long (adiabatic) domain
walls, we provide an analytic formula that expresses the so called
""non-adiabatic"" (or field like) torque in term of those lengths scales.
However, this ""non adiabatic"" torque is no longer a simple material parameter
and depends on the actual spin texture: in thin (< 10nm) domain walls, we
observe very significant deviations from the adiabatic limit.",1206.4470v1
2013-09-10,Spin wave excitation patterns generated by spin torque oscillators,"Spin torque nano oscillators (STNO) are nano-scale devices that can convert a
direct current into short wave-length spin-wave excitations in a ferromagnetic
layer. We show that arrays of STNO can be used to create directional spin-wave
radiation similar to electromagnetic antennas. Combining STNO excitations with
planar spin waves also creates interference patterns. We show that these
interference patterns are static and have information on the wavelength and
phase of the spin waves emitted from the STNO.We describe means of actively
controlling spin-wave radiation patterns with the direct current owing through
STNO, which is useful in on-chip communication and information processing and
could be a promising technique for studying short wave-length spin waves in
different materials.",1309.2436v1
2016-04-21,Spin Transport at Interfaces with Spin-Orbit Coupling: Phenomenology,"This paper presents the boundary conditions needed for drift-diffusion models
to treat interfaces with spin-orbit coupling. Using these boundary conditions
for heavy metal/ferromagnet bilayers, solutions of the drift-diffusion
equations agree with solutions of the spin-dependent Boltzmann equation and
allow for a much simpler interpretation of the results. A key feature of these
boundary conditions is their ability to capture the role that in-plane electric
fields have on the generation of spin currents that flow perpendicularly to the
interface. The generation of these spin currents is a direct consequence of the
effect of interfacial spin-orbit coupling on interfacial scattering. In heavy
metal/ferromagnet bilayers, these spin currents provide an important mechanism
for the creation of damping-like and field-like torques; they also lead to
possible reinterpretations of experiments in which interfacial contributions to
spin torques are thought to be suppressed.",1604.06502v2
2016-09-24,Field-like spin orbit torque in ultra-thin polycrystalline FeMn films,"Field-like spin orbit torque in FeMn/Pt bilayers with ultra-thin
polycrystalline FeMn has been characterized through planar Hall effect
measurements. A large effective field is obtained for FeMn in the thickness
range of 2 to 5 nm. The experimental observations can be reasonably accounted
for by using a macro-spin model under the assumption that the FeMn layer is
composed of two spin sublattices with unequal magnetizations. The large
effective field corroborates the spin Hall origin of the effective field
considering the much smaller uncompensated net moments in FeMn as compared to
NiFe. The effective absorption of spin current by FeMn is further confirmed by
the fact that spin current generated by Pt in NiFe/FeMn/Pt trilayers can only
travel through the FeMn layer with a thickness of 1 to 4 nm. By quantifying the
field-like effective field induced in NiFe, a spin diffusion length of 2 nm is
estimated in FeMn, in consistence with values reported in literature by
ferromagnetic resonance and spin-pumping experiments.",1609.07564v1
2016-10-22,Enhanced spin-orbit torque via modulation of spin current absorption,"The magnitude of spin-orbit torque (SOT), exerted to a ferromagnet (FM) from
an adjacent heavy metal (HM), strongly depends on the amount of spin currents
absorbed in the FM. We exploit the large spin absorption at the Ru interface to
manipulate the SOTs in HM/FM/Ru multilayers. While the FM thickness is smaller
than its spin dephasing length of 1.2 nm, the top Ru layer largely boosts the
absorption of spin currents into the FM layer and substantially enhances the
strength of SOT acting on the FM. Spin-pumping experiments induced by
ferromagnetic resonance support our conclusions that the observed increase in
the SOT efficiency can be attributed to an enhancement of the spin-current
absorption. A theoretical model that considers both reflected and transmitted
mixing conductances at the two interfaces of FM is developed to explain the
results.",1610.06989v1
2017-02-27,Current-induced spin polarization of a magnetized two-dimensional electron gas with Rashba spin-orbit interaction,"Current-induced spin polarization in a two-dimensional electron gas with
Rashba spin-orbit interaction is considered theoretically in terms of the
Matsubara Green functions. This formalism allows to describe temperature
dependence of the induced spin polarization. The electron gas is assumed to be
coupled to a magnetic substrate via exchange interaction. Analytical and
numerical results on the temperature dependence of spin polarization have been
obtained in the linear response regime. The spin polarization has been
presented as a sum of two terms - one proportional to the relaxation time and
the other related to the Berry phase corresponding to the electronic bands of
the magnetized Rashba gas. The spin-orbit torque due to Rashba interaction is
also discussed. Such a torque appears as a result of the exchange coupling
between the non-equilibrium spin polarization and magnetic moment of the
underlayer.",1702.08162v1
2019-05-09,Bidirectional spin-wave-driven domain wall motion in antiferromagnetically coupled ferrimagnets,"We investigate ferrimagnetic domain wall dynamics induced by circularly
polarized spin waves theoretically and numerically. We find that the direction
of domain wall motion depends on both the circular polarization of spin waves
and the sign of net spin density of ferrimagnet. Below the angular momentum
compensation point, left- (right-) circularly polarized spin waves push a
domain wall towards (away from) the spin-wave source. Above the angular
momentum compensation point, on the other hand, the direction of domain wall
motion is reversed. This bidirectional motion originates from the fact that the
sign of spin-wave-induced magnonic torque depends on the circular polarization
and the subsequent response of the domain wall to the magnonic torque is
governed by the net spin density. Our finding provides a way to utilize a spin
wave as a versatile driving force for bidirectional domain wall motion.",1905.03521v1
2019-01-11,Spin-orbit torques in heavy metal/ferromagnet bilayers with varying strength of interfacial spin-orbit coupling,"Despite intense efforts it has remained unresolved whether and how
interfacial spin-orbit coupling (ISOC) affects spin transport across heavy
metal (HM)/ferromagnet (FM) interfaces. Here we report conclusive experiment
evidence that the ISOC at HM/FM interfaces is the dominant mechanism for ""spin
memory loss"". An increase in ISOC significantly reduces, in a linear manner,
the dampinglike spin-orbit torque (SOT) exerted on the FM layer via degradation
of the spin transparency of the interface for spin currents generated in the
HM. In addition, the fieldlike SOT is also dominated by the spin Hall
contribution of the HM and decreases with increasing ISOC. This work reveals
that ISOC at HM/FM interfaces should be minimized to advance efficient SOT
devices through atomic layer passivation of the HM/FM interface or other means.",1901.03632v1
2019-07-24,Semi-Quantized Spin Pumping and Spin-Orbit Torques in Topological Dirac Semimetals,"We study the time-development processes of spin and charge transport
phenomena in a topological Dirac semimetal attached to a ferromagnetic
insulator with a precessing magnetization. Compared to conventional normal
metals, topological Dirac semimetals manifest a large inverse spin Hall effect
when a spin current is pumped from the attached ferromagnetic insulator. It is
shown that the induced charge current is semi-quantized, i.e., it depends only
on the distance between the two Dirac points in momentum space and hardly
depends on the disorder strength when the system remains in the topological
Dirac semimetal phase. As an inverse effect, we show that the electric field
applied to the topological Dirac semimetal exerts a spin torque on the local
magnetization in the ferromagnetic insulator via the exchange interaction and
the semi-quantized spin Hall effect. Our study demonstrates that the
topological Dirac semimetal offers a less-dissipative platform for spin-charge
conversion and spin switching.",1907.10459v2
2022-07-25,Spin-orbit torques from topological insulator surface states: Effect of extrinsic spin-orbit scattering on an out-of-plane magnetization,"The origins of the spin-orbit torque (SOT) at ferromagnet/topological
insulator (FM/TI) interfaces are incompletely understood. Theory has
overwhelmingly focussed on the Edelstein effect due to the surface states in
the presence of a scalar scattering potential. We investigate here the
contribution to the SOT due to extrinsic spin-orbit scattering of the surface
states, focusing on the case of an out-of-plane magnetization. We show that
spin-orbit scattering brings about a sizable renormalization of the field-like
SOT, which exceeds 20$\%$ at larger strengths of the extrinsic spin-orbit
parameter. The resulting SOT exhibits a maximum as a function of the Fermi
energy, magnetization, and extrinsic spin-orbit strength. The field-like SOT
decreases with increasing disorder strength while the damping-like SOT is
independent of the impurity density. With experimental observation in mind we
also determine the role of extrinsic spin-orbit scattering on the anomalous
Hall effect. Our results suggest extrinsic spin-orbit scattering is a
significant contributor to the surface SOT stemming from the Edelstein effect
when the magnetization is out of the plane.",2207.12440v1
2011-09-25,The torquing of circumnuclear accretion disks by stars and the evolution of massive black holes,"An accreting massive black hole (MBH) in a galactic nucleus is surrounded by
a dense stellar cluster. We analyze and simulate numerically the evolution of a
thin accretion disk due to its internal viscous torques, due to the
frame-dragging torques of a spinning MBH (the Bardeen-Petterson effect) and due
to the orbit-averaged gravitational torques by the stars (Resonant Relaxation).
We show that the evolution of the MBH mass accretion rate, the MBH spin growth
rate, and the covering fraction of the disk relative to the central ionizing
continuum source, are all strongly coupled to the stochastic fluctuations of
the stellar potential via the warps that the stellar torques excite in the
disk. These lead to fluctuations by factors of up to a few in these quantities
over a wide range of timescales, with most of the power on timescales
>~(M_bh/M_d)P(R_d), where M_bh and M_d are the masses of the MBH and disk, and
P is the orbital period at the disk's mass-weighted mean radius R_d. The
response of the disk is stronger the lighter it is and the more centrally
concentrated the stellar cusp. As proof of concept, we simulate the evolution
of the low-mass maser disk in NGC4258, and show that its observed O(10 deg)
warp can be driven by the stellar torques. We also show that the frame-dragging
of a massive AGN disk couples the stochastic stellar torques to the MBH spin
and can excite a jitter of a few degrees in its direction relative to that of
the disk's outer regions.",1109.5384v2
2022-04-08,Sim-to-Real Transfer of Compliant Bipedal Locomotion on Torque Sensor-Less Gear-Driven Humanoid,"Sim-to-real is a mainstream method to cope with the large number of trials
needed by typical deep reinforcement learning methods. However, transferring a
policy trained in simulation to actual hardware remains an open challenge due
to the reality gap. In particular, the characteristics of actuators in legged
robots have a considerable influence on sim-to-real transfer. There are two
challenges: 1) High reduction ratio gears are widely used in actuators, and the
reality gap issue becomes especially pronounced when backdrivability is
considered in controlling joints compliantly. 2) The difficulty in achieving
stable bipedal locomotion causes typical system identification methods to fail
to sufficiently transfer the policy. For these two challenges, we propose 1) a
new simulation model of gears and 2) a method for system identification that
can utilize failed attempts. The method's effectiveness is verified using a
biped robot, the ROBOTIS-OP3, and the sim-to-real transferred policy can
stabilize the robot under severe disturbances and walk on uneven surfaces
without using force and torque sensors.",2204.03897v4
1998-05-08,Starquake-induced Magnetic Field and Torque Evolution in Neutron Stars,"The persistent increases in spin-down rate offsets seen to accompany glitches
in the Crab and other pulsars suggest increases in the spin-down torque. We
interpret these offsets as due to starquakes occurring as the star spins down
and the rigid crust becomes less oblate. We study the evolution of strain in
the crust, the initiation of starquakes, and possible consequences for magnetic
field and torque evolution. Crust cracking occurs as equatorial material shears
under the compressive forces arising from the star's decreasing circumference,
and matter moves to higher latitudes along a fault inclined to the equator. A
starquake is most likely to originate near one of the two points on the
rotational equator farthest from the magnetic poles. The material breaks along
a fault approximately aligned with the magnetic poles. We suggest that the
observed offsets come about when a starquake perturbs the star's mass
distribution, producing a misalignment of the angular momentum and spin axes.
Subsequently, damped precession to a new rotational state increases the angle
alpha between the rotation and magnetic axes. The resulting increase in
external torque appears as a permanent increase in the spin-down rate. Repeated
starquakes would continue to increase alpha, making the pulsar more of an
orthogonal rotator.",9805115v1
2011-10-12,How terrestrial planets traverse spin-orbit resonances: A camel goes through a needle's eye,"The dynamical evolution of terrestrial planets resembling Mercury in the
vicinity of spin-orbit resonances is investigated using comprehensive harmonic
expansions of the tidal torque taking into account the frequency-dependent
quality factors and Love numbers. The torque equations are integrated
numerically with a small step in time, includng the oscillating triaxial torque
components but neglecting the layered structure of the planet and assuming a
zero obliquity. We find that a Mercury-like planet with its current value of
orbital eccentricity (0.2056) is always captured in the 3:2 resonance. The
probability of capture in the higher 2:1 resonance is approximately 0.23. These
results are confirmed by a semi-analytical estimation of capture probabilities
as functions of eccentricity for both prograde and retrograde evolution of spin
rate. As follows from analysis of equilibrium torques, entrapment in the 3:2
resonance is inevitable at eccentricities between 0.2 and 0.41. Considering the
phase space parameters at the times of periastron, the range of spin rates and
phase angles, for which an immediate resonance passage is triggered, is very
narrow, and yet, a planet like Mercury rarely fails to align itself into this
state of unstable equilibrium before it traverses the 2:1 resonance.",1110.2658v3
2015-11-23,Electric-field control of spin-orbit torque in a magnetically doped topological insulator,"Electric-field manipulation of magnetic order has proved of both fundamental
and technological importance in spintronic devices. So far, electric-field
control of ferromagnetism, magnetization and magnetic anisotropy has been
explored in various magnetic materials, but the efficient electric-field
control of spin-orbit torque (SOT) still remains elusive. Here, we report the
effective electric-field control of a giant SOT in a Cr-doped topological
insulator (TI) thin film using a top-gate FET structure. The SOT strength can
be modulated by a factor of 4 within the accessible gate voltage range, and it
shows strong correlation with the spin-polarized surface current in the film.
Furthermore, we demonstrate the magnetization switching by scanning gate
voltage with constant current and in-plane magnetic field applied in the film.
The effective electric-field control of SOT and the giant spin-torque
efficiency in Cr-doped TI may lead to the development of energy-efficient
gate-controlled spin-torque devices compatible with modern field-effect
semiconductor technologies.",1511.07442v1
2017-05-25,Spin-orbit torque-driven skyrmion dynamics revealed by time-resolved X-ray microscopy,"Magnetic skyrmions are topologically-protected spin textures with attractive
properties suitable for high-density and low-power spintronic device
applications. Much effort has been dedicated to understanding the dynamical
behaviours of the magnetic skyrmions. However, experimental observation of the
ultrafast dynamics of this chiral magnetic texture in real space, which is the
hallmark of its quasiparticle nature, has so far remained elusive. Here, we
report nanosecond-dynamics of a 100 nm-size magnetic skyrmion during a current
pulse application, using a time-resolved pump-probe soft X-ray imaging
technique. We demonstrate that distinct dynamic excitation states of magnetic
skyrmions, triggered by current-induced spin-orbit torques, can be reliably
tuned by changing the magnitude of spin-orbit torques. Our findings show that
the dynamics of magnetic skyrmions can be controlled by the spin-orbit torque
on the nanosecond time scale, which points to exciting opportunities for
ultrafast and novel skyrmionic applications in the future.",1705.09019v1
2018-10-04,Chaos and relaxation oscillations in spin-torque windmill neurons,"Spintronic neurons which emit sharp voltage spikes are required for the
realization of hardware neural networks enabling fast data processing with
low-power consumption. In many neuroscience and computer science models,
neurons are abstracted as non-linear oscillators. Magnetic nano-oscillators
called spin-torque nano-oscillators are interesting candidates for imitating
neurons at nanoscale. These oscillators, however, emit sinusoidal waveforms
without spiking while biological neurons are relaxation oscillators that emit
sharp voltage spikes. Here we propose a simple way to imitate neuron spiking in
high-magnetoresistance nanoscale spin valves where both magnetic layers are
free and thin enough to be switched by spin torque. Our numerical-simulation
results show that the windmill motion induced by spin torque in the proposed
spintronic neurons gives rise to spikes whose shape and frequency, set by the
charging and discharging times, can be tuned through the amplitude of injected
dc current. We also found that these devices can exhibit chaotic oscillations.
Chaotic-like neuron dynamics has been observed in the brain, and it is
desirable in some neuromorphic computing applications whereas it should be
avoided in others. We demonstrate that the degree of chaos can be tuned in a
wide range by engineering the magnetic stack and anisotropies and by changing
the dc current. The proposed spintronic neuron is a promising building block
for hardware neuromorphic chips leveraging non-linear dynamics for computing.",1810.02073v1
2020-04-06,Direct determination of Spin-Orbit torque by using dc current-voltage characteristics,"Spin polarized currents are employed to efficiently manipulate the
magnetization of ferromagnetic ultrathin films by exerting a torque on it. If
the spin currents are generated by means of the spin-orbit interaction between
a ferromagnetic and a non-magnetic layer, the effect is known as spin-orbit
torque (SOT), and is quantified by measuring the effective fields produced by a
charge current injected into the device. In this work, we present a new
experimental technique to quantify directly the SOT based on the measurement of
non-linearities of the dc current-voltage (IV) characteristics in Hall bar
devices employing a simple instrumentation. Through the analysis of the IV
curves, the technique provides directly the linearity of the effective fields
with current, the detection of the current range in which the thermal effects
can be relevant, the appearance of misalignments artefacts when the symmetry
relations of SOT are not fulfilled, and the conditions for the validity of the
single domain approximations, which are not considered in switching current and
second harmonic generation state-of-the-art experiments. We have studied the
SOT induced antidamping and field-like torques in Ta/Co/Pt asymmetric stacks
with perpendicular magnetic anisotropy.",2004.02695v1
2020-09-08,Spin-Orbit Torques in Transition Metal Dichalcogenide/Ferromagnet Heterostructures,"In recent years, there has been a growing interest in spin-orbit torques
(SOTs) for manipulating the magnetization in nonvolatile magnetic memory
devices. SOTs rely on the spin-orbit coupling of a nonmagnetic material coupled
to a ferromagnetic layer to convert an applied charge current into a torque on
the magnetization of the ferromagnet (FM). Transition metal dichalcogenides
(TMDs) are promising candidates for generating these torques with both high
charge-to-spin conversion ratios, and symmetries and directions which are
efficient for magnetization manipulation. Moreover, TMDs offer a wide range of
attractive properties, such as large spin-orbit coupling, high crystalline
quality and diverse crystalline symmetries. Although numerous studies were
published on SOTs using TMD/FM heterostructures, we lack clear understanding of
the observed SOT symmetries, directions, and strengths. In order to shine some
light on the differences and similarities among the works in literature, in
this mini-review we compare the results for various TMD/FM devices,
highlighting the experimental techniques used to fabricate the devices and to
quantify the SOTs, discussing their potential effect on the interface quality
and resulting SOTs. This enables us to both identify the impact of particular
fabrication steps on the observed SOT symmetries and directions, and give
suggestions for their underlying microscopic mechanisms. Furthermore, we
highlight recent progress of the theoretical work on SOTs using TMD
heterostructures and propose future research directions.",2009.03710v2
2021-06-04,Unveiling the mechanism of bulk spin-orbit torques within chemically disordered Fe$_x$Pt$_{1-x}$ single layers,"Recent discovery of spin-orbit torques (SOTs) within magnetic single-layers
has attracted attention in the field of spintronics. However, it has remained
elusive as to how to understand and how to tune the SOTs. Here, utilizing the
single layers of chemically disordered Fe$_x$Pt$_{1-x}$, we unveil the
mechanism of the ""unexpected"" bulk SOTs by studying their dependence on the
introduction of a controlled vertical composition gradient and on temperature.
We find that the bulk damping like SOT arises from an imbalanced internal spin
current that is transversely polarized and independent of the magnetization
orientation. The torque can be strong only in the presence of a vertical
composition gradient and the SOT efficiency per electric field is insensitive
to temperature but changes sign upon reversal of the orientation of the
composition gradient, which are in analogue to behaviors of the strain. From
these characteristics we conclude that the imbalanced internal spin current
originates from a bulk spin Hall effect and that the associated inversion
asymmetry that allows for a non-zero net torque is most likely a strain
non-uniformity induced by the composition gradient. The fieldlike SOT is a
relatively small bulk effect compared to the dampinglike SOT. This work points
to the possibility of developing low-power single-layer SOT devices by strain
engineering.",2106.02428v1
2009-12-18,Diffusive versus local spin currents in dynamic spin pumping systems,"Using microscopic theory, we investigate the properties of a spin current
driven by magnetization dynamics. In the limit of smooth magnetization texture,
the dominant spin current induced by the spin pumping effect is shown to be the
diffusive spin current, i.e., the one arising from only a diffusion associated
with spin accumulation. That is to say, there is no effective field that
locally drives the spin current. We also investigate the conversion mechanism
of the pumped spin current into a charge current by spin-orbit interactions,
specifically the inverse spin Hall effect. We show that the spin-charge
conversion does not always occur and that it depends strongly on the type of
spin-orbit interaction. In a Rashba spin-orbit system, the local part of the
charge current is proportional to the spin relaxation torque, and the local
spin current, which does not arise from the spin accumulation, does not play
any role in the conversion. In contrast, the diffusive spin current contributes
to the diffusive charge current. Alternatively, for spin-orbit interactions
arising from random impurities, the local charge current is proportional to the
local spin current that constitutes only a small fraction of the total spin
current. Clearly, the dominant spin current (diffusive spin current) is not
converted into a charge current. Therefore, the nature of the spin current is
fundamentally different depending on its origin and thus the spin transport and
the spin-charge conversion behavior need to be discussed together along with
spin current generation.",0912.3607v2
2006-05-16,A strong $\ddotν - \dotν$ correlation in radio pulsars with implications for torque variations,"We present an analysis of the spin-down parameters for 131 radio pulsars for
which $\ddot\nu$ has been well determined. These pulsars have characteristic
ages ranging from $10^{3} - 10^{8}$ yr and spin periods in the range 0.4--30 s;
nearly equal numbers of pulsars have $\ddot\nu>0$ as $\ddot\nu<0$. We find a
strong correlation of $\ddot\nu$ with $\dot{\nu}$, {\em independent of the sign
of} $\ddot\nu$. We suggest that this trend can be accounted for by small,
stochastic deviations in the spin-down torque that are directly proportional
(in magnitude) to the spin-down torque.",0605380v2
2005-10-31,Time-Resolved Spin Torque Switching and Enhanced Damping in Py/Cu/Py Spin-Valve Nanopillars,"We report time-resolved measurements of current-induced reversal of a free
magnetic layer in Py/Cu/Py elliptical nanopillars at temperatures T = 4.2 K to
160 K. Comparison of the data to Landau-Lifshitz-Gilbert macrospin simulations
of the free layer switching yields numerical values for the spin torque and the
Gilbert damping parameters as functions of T. The damping is strongly
T-dependent, which we attribute to the antiferromagnetic pinning behavior of a
thin permalloy oxide layer around the perimeter of the free layer. This
adventitious antiferromagnetic pinning layer can have a major impact on spin
torque phenomena.",0510798v2
2007-06-14,Viscous spin exchange torque on precessional magnetization in $(\mathrm{LaMnO}_3)_{2n}/(\mathrm{SrMnO}_3)_{n}$ superlattices,"Photoinduced magnetization dynamics is investigated in chemically ordered
$(\mathrm{LaMnO}_3)_{2n}/(\mathrm{SrMnO}_3)_n$ superlattices using the
time-resolved magneto-optic Kerr effect. A monotonic frequency-field dependence
is observed for the $n=1$ superlattice, indicating a single spin population
consistent with a homogeneous hole distribution. In contrast, for $n\geq2$
superlattices, a large precession frequency is observed at low fields
indicating the presence of an exchange torque in the dynamic regime. We propose
a model that ascribes the emergence of exchange torque to the coupling between
two spin populations -- viscous and fast spins.",0706.2157v1
2010-03-21,Current-induced domain wall motion with adiabatic spin torque only in cylindrical nanowires,"We investigate current-driven domain wall (DW) propagation in magnetic
nanowires in the framework of the modified Landau-Lifshitz-Gilbert equation
with both adiabatic and nonadiabatic spin torque (NAST) terms. Contrary to the
common opinion that NAST is indispensable for DW motion[1,2], we point out that
adiabatic spin torque (AST) only is enough for current-driven DW motion in a
cylindrical (uniaxial) nanowire. Apart from a discussion of the rigid DW motion
from the energy and angular momentum viewpoint, we also propose an experimental
scheme to measure the spin current polarization by combining both field and
current driven DW motion in a flat (biaxial) wire.",1003.3976v1
2011-10-16,Role of Spin Diffusion in Current-Induced Domain Wall Motion,"Current-induced spin torque and magnetization dynamics in the presence of
spin diffusion in magnetic textures is studied theoretically. We uncover an
additional torque on the form \sim{\bm\nabla}^2[{\bf M}x({\bf u}\cdot{\bm
\nabla}){\bf M}], where {\bf M} is the local magnetization and {\bf u} is the
direction of injected current. This torque is inversely proportional to the
square of the domain wall width (\approx\frac{1}{W^2}) and strongly depends on
the domain wall structure. Whereas its influence remains moderate for
transverse domain walls, it can significantly increase the transverse velocity
of vortex cores. Consequently, the spin diffusion can dramatically enhance the
non-adiabaticity of vortex walls.",1110.3487v1
2013-10-21,Ultrafast magnetization switching by spin-orbit torques,"Spin-orbit torques induced by spin Hall and interfacial effects in heavy
metal/ferromagnetic bilayers allow for a switching geometry based on in-plane
current injection. Using this geometry, we demonstrate deterministic
magnetization reversal by current pulses ranging from 180~ps to ms in
Pt/Co/AlOx dots with lateral dimensions of 90~nm. We characterize the switching
probability and critical current $I_c$ as function of pulse length, amplitude,
and external field. Our data evidence two distinct regimes: a short-time
intrinsic regime, where $I_c$ scales linearly with the inverse of the pulse
length, and a long-time thermally assisted regime where $I_c$ varies weakly.
Both regimes are consistent with magnetization reversal proceeding by
nucleation and fast propagation of domains. We find that $I_c$ is a factor 3-4
smaller compared to a single domain model and that the incubation time is
negligibly small, which is a hallmark feature of spin-orbit torques.",1310.5586v2
2013-10-25,Mode coupling in spin torque oscillators,"A number of recent experimental works have shown that the dynamics of a
single spin torque oscillator can exhibit complex behavior that stems from
interactions between two or more modes of the oscillator. Examples are observed
mode-hopping or mode coexistence. There has been some intial work indicating
how the theory for a single-mode (macro-spin) spin torque oscillator should be
generalized to include several modes and the interactions between them. In the
present work, we derive such a theory starting with the Landau-Lifshitz-Gilbert
equation for magnetization dynamics. We compare our results with the
single-mode theory, and show how it is a natural extension of that theory to
include mode interactions.",1310.6791v2
2013-11-29,Generation linewidth of mode-hopping spin torque oscillators,"Experiments on spin torque oscillators commonly observe multi-mode signals.
Recent theoretical works have ascribed the multi-mode signal generation to
coupling between energy-separated spin wave modes. Here, we analyze in detail
the dynamics generated by such mode coupling. We show analytically that the
mode-hopping dynamics broaden the generation linewidth and makes it generally
well described by a Voigt lineshape. Furthermore, we show that the mode-hopping
contribution to the linewidth can dominate in which case it provides a direct
measure of the mode-hopping rate. Due to the thermal drive of mode-hopping
events, the mode-hopping rate also provides information on the energy barrier
separating modes and temperature-dependent linewidth broadening. Our results
are in good agreement with experiments, revealing the physical mechanism behind
the linewidth broadening in multi-mode spin torque oscillators.",1311.7660v1
2014-05-14,Magnetic anisotropy of spin tetramer system SeCuO$_3$ studied by torque magnetometry and ESR spectroscopy,"We present an experimental study of macroscopic and microscopic magnetic
anisotropy of a spin tetramer system SeCuO$_3$ using torque magnetometry and
ESR spectroscopy. Large rotation of macroscopic magnetic axes with temperature
observed from torque magnetometry agrees reasonably well with the rotation of
the $\textbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\textbf{g}$
tensor is temperature independent, while macroscopic magnetic axes continue to
rotate. Additionally, the susceptibility anisotropy has a temperature
dependence which cannot be reconciled with the isotropic Heisenberg model of
interactions between spins. ESR linewidth analysis shows that anisotropic
exchange interaction must be present in SeCuO$_3$. These findings strongly
support the presence of anisotropic exchange interactions in the Hamiltonian of
the studied system. Below $T_N=8$~K, the system enters a long - range
antiferromagnetically ordered state with easy axis along the $<\bar{1} 0 1>^*$
direction. Small but significant rotation of magnetic axes is also observed in
the antiferromagnetically ordered state suggesting strong spin-lattice coupling
in this system.",1405.3389v2
2015-05-27,Torque magnetometry study of magnetically ordered state and spin reorientation in the quasi-one-dimensional $S=1/2$ Heisenberg antiferromagnet CuSb$_2$O$_6$,"We present an experimental study of macroscopic and microscopic magnetic
anisotropy of a spin tetramer system \cso using torque magnetometry and ESR
spectroscopy. Large rotation of macroscopic magnetic axes with temperature
observed from torque magnetometry agrees reasonably well with the rotation of
the $\mathbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\mathbf{g}$
tensor is temperature independent, while macroscopic magnetic axes continue to
rotate. Additionally, the susceptibility anisotropy has a temperature
dependence which cannot be reconciled with the isotropic Heisenberg model of
interactions between spins. ESR linewidth analysis shows that anisotropic
exchange interaction must be present in \csos. These findings strongly support
the presence of anisotropic exchange interactions in the Hamiltonian of the
studied system. Below $T_N=8$~K, the system enters a long - range
antiferromagnetically ordered state with easy axis along the $<\bar{1} 0 1>^*$
direction. Small but significant rotation of magnetic axes is also observed in
the antiferromagnetically ordered state suggesting strong spin-lattice coupling
in this system.",1505.07405v1
2016-04-26,Intrinsic spin orbit torque in a single domain nanomagnet,"We present theoretical studies of the intrinsic spin orbit torque (SOT) in a
single domain ferromagnetic layer with Rashba spin-orbit coupling (SOC) using
the non-equilibrium Green's function formalism for a model Hamiltonian. We find
that, to the first order in SOC, the intrinsic SOT has only the field-like
torque symmetry and can be interpreted as the longitudinal spin current induced
by the charge current and Rashba field. We analyze the results in terms of the
material related parameters of the electronic structure, such as band filling,
band width, exchange splitting, as well as the Rashba SOC strength. On the
basis of these numerical and analytical results, we discuss the magnitude and
sign of SOT. Our results show that the different sign of SOT in identical
ferromagnetic layers with different supporting layers, e.g. Co/Pt and Co/Ta,
could be attributed to electrostatic doping of the ferromagnetic layer by the
support.",1604.07885v2
2016-10-25,Electric control of Dirac quasiparticles by spin-orbit torque in an antiferromagnet,"Spin-orbitronics and Dirac quasiparticles are two fields of condensed matter
physics initiated independently about a decade ago. Here we predict that Dirac
quasiparticles can be controlled by the spin-orbit torque reorientation of the
N\'{e}el vector in an antiferromagnet. Using CuMnAs as an example, we formulate
symmetry criteria allowing for the co-existence of Dirac quasiparticles and
N\'{e}el spin-orbit torques. We identify the non-symmorphic crystal symmetry
protection of Dirac band crossings whose on and off switching is mediated by
the N\'{e}el vector reorientation. We predict that this concept, verified by
minimal model and density functional calculations in the CuMnAs semimetal
antiferromagnet, can lead to a topological metal-insulator transition driven by
the N\'{e}el vector and to the corresponding topological anisotropic
magnetoresistance.",1610.08107v1
2017-08-25,Spin torque control of antiferromagnetic moments in NiO,"For a long time, there have been no efficient ways of controlling
antiferromagnets. Quite a strong magnetic field was required to manipulate the
magnetic moments because of a high molecular field and a small magnetic
susceptibility. It was also difficult to detect the orientation of the magnetic
moments since the net magnetic moment is effectively zero. For these reasons,
research on antiferromagnets has not been progressed as drastically as that on
ferromagnets which are the main materials in modern spintronic devices. Here we
show that the magnetic moments in NiO, a typical natural antiferromagnet, can
indeed be controlled by the spin torque with a relatively small electric
current density (~5 x 10^7 A/cm^2) and their orientation is detected by the
transverse resistance resulting from the spin Hall magnetoresistance . The
demonstrated techniques of controlling and detecting antiferromagnets would
outstandingly promote the methodologies in the recently emerged
""antiferromagnetic spintronics"". Furthermore, our results essentially lead to a
spin torque antiferromagnetic memory.",1708.07682v1
2018-06-13,Enhanced Spin-Orbit Torques and Magnetization Switching through Interface Engineering,"The origin of spin-orbit torques generated from the conversion of
charge-to-spin currents is of considerable debate. Solid understanding of the
physics behind is key to the development of current and voltage controlled
switching dynamics in ultrathin heterostuctures. The field free switching
observed recently (Phys. Rev. Lett. 120, 117703 (2018)) in a Pt/W/CoFeB
structure has intensified such a debate. Here we derive a formula to evaluate a
perpendicular effective field generated when the current flows through the
heterostructure, considering the large resistivity difference between the two
normal metal layers and the chemical potential gradient created at the
interface. Together with recent X-ray photoelectron spectroscopy findings at
the interface of a Pd/CoFeB structure, we conclude that a new torque generated
may play a key role in the field free switching. The model and mechanism
proposed agrees with previous reports on spin current injection and field free
switching using different interface engineering methods.",1806.05163v1
2018-09-03,Manipulation of magnetizations by spin-orbit torques,"The control of magnetization by electric current is a rapidly developing area
motivated by a strong synergy between breakthrough basic research discoveries
and industrial applications in the fields of magnetic recording, magnetic field
sensors, spintronics and nonvolatile memories. In recent years, the discovery
of the spin-orbit torque has opened a spectrum of opportunities to manipulate
the magnetization efficiently. This article presents a review of the historical
background and recent literature focusing on spin-orbit torques (SOTs),
highlighting the most exciting new scientific results and suggesting promising
future research directions. It starts with an introduction and overview of the
underlying physics of spin-orbit coupling effects in bulk and at interfaces,
then describes the use of SOTs to control ferromagnets and antiferromagnets.
Finally, we summarize the prospects for the future developments of spintronics
devices based on SOTs.",1809.00546v1
2018-02-12,Easy-Plane Magnetic Strip as a Long Josephson Junction,"Spin-torque-biased magnetic dynamics in an easy-plane ferromagnet (EPF) is
theoretically studied in the presence of a weak in-plane anisotropy. While this
anisotropy spoils U(1) symmetry thereby quenching the conventional spin
superfluidity, we show that the system instead realizes a close analog of a
long Josephson junction (LJJ) model. The traditional magnetic-field and
electric-current controls of the latter map respectively onto the symmetric and
antisymmetric combinations of the out-of-plane spin torques applied at the ends
of the magnetic strip. This suggests an alternative route towards realizations
of superfluid-like transport phenomena in insulating magnetic systems. We study
spin-torque-biased phase diagram, providing an analytical solution for static
multidomain phases in the EPF. We adapt an existing self-consistency method for
the LJJ to develop an approximate solution for the EPF dynamics. The LJJ-EPF
mapping allows us to envision superconducting circuit functionality at elevated
temperatures. The results apply equally to antiferromagnets with suitable
effective free energy in terms of the N\'{e}el order instead of magnetization.",1802.04229v1
2020-04-06,Damping-like Torque in Monolayer 1T-TaS$_2$,"A damping-like spin orbit torque (SOT) is a prerequisite for ultralow power
spin logic devices. Here, we report on the damping-like SOT in just one
monolayer of the conducting transition metal dichalcogenide (TMD) TaS$_2$
interfaced with a NiFe (Py) ferromagnetic layer. The charge-spin conversion
efficiency is found to be 0.25$\pm$0.03 and the spin Hall conductivity (2.63
$\times$ 10$^5$ $\frac{\hbar}{2e}$ $\Omega^{-1}$ m$^{-1}$) is found to be
superior to values reported for other TMDs. The origin of this large
damping-like SOT can be found in the interfacial properties of the TaS$_2$/Py
heterostructure, and the experimental findings are complemented by the results
from density functional theory calculations. The dominance of damping-like
torque demonstrated in our study provides a promising path for designing next
generation conducting TMD based low-powered quantum memory devices.",2004.02649v1
2020-11-04,Level attraction and exceptional points in a resonant spin-orbit torque system,"Level attraction can appear in driven systems where instead of repulsion two
modes coalesce in a region separated by two exceptional points. This behavior
was proposed for optomechanical and optomagnonic systems, and recently observed
for dissipative cavity magnon-polaritons. We demonstrate that such a regime
exists in a spin-orbit torque system where a magnetic oscillator is resonantly
coupled to an electron reservoir. An instability mechanism necessary for mode
attraction can be provided by applying an electric field. The field excites
interband transitions between spin-orbit split bands leading to an instability
of the magnetic oscillator. Two exceptional points then appear in the
oscillator energy spectrum and the region of instability. We discuss conditions
under which this can occur and estimate the electric field strength necessary
for reaching the attraction region for a spin-orbit torque oscillator with
Rashba coupling. A proposal for experimental detection is made using magnetic
susceptibility measurements.",2011.02520v1
2021-04-27,A two-terminal spin valve device controlled by spin-orbit torques with enhanced giant magnetoresistance,"We report on the combination of current-induced spin-orbit torques and giant
magnetoresistance in a single device to achieve all-electrical write and read
out of the magnetization. The device consists of perpendicularly magnetized
TbCo and Co layers separated by a Pt or Cu spacer. Current injection through
such layers exerts spin-orbit torques and switches the magnetization of the Co
layer while the TbCo magnetization remains fixed. Subsequent current injection
of lower amplitude senses the relative orientation of the magnetization of the
Co and TbCo layers, which results in two distinct resistance levels for
parallel and antiparallel alignment due to the current-in-plane giant
magnetoresistance effect. We further show that the giant magnetoresistance of
devices including a single TbCo/spacer/Co trilayer can be improved from 0.02%
to 6% by using a Cu spacer instead of Pt. This type of devices offers an
alternative route to a two terminal spintronic memory that can be fabricated
with moderate effort.",2104.13007v2
2017-03-01,Thickness Dependence of Spin-Orbit Torques in Ferrimagnetic GdFeCo Alloys,"So far, studies of spin-orbit torques (SOT) in ferromagnets with
perpendicular magnetic anisotropy (PMA) have been restricted to ultra thin
samples, while a systematic study of its thickness dependence is still lacking
in literature. In this article we discuss the thickness dependence of SOT in
GdFeCo samples with bulk PMA. We show that the effective SOT fields are
decreasing inversely as a function of thickness while the spin-Hall angle stays
constant, as expected from angular momentum conservation. Further we show that
even 30nm thick GdFeCo samples can be switched with SOT. This has important
technological implications as the switching efficiency does not depend on the
thickness. Finally, we investigate the composition dependence of SOT in 30nm
thick GdFeCo samples and find that the spin torque effective field diverges at
the magnetization compensation point.",1703.00146v1
2020-01-10,Switching time of spin-torque-driven magnetization in biaxial ferromagnets,"We analytically model the magnetization switching time of a biaxial
ferromagnet driven by an antidamping-like spin torque. The macrospin
magnetization dynamics is mapped to an energy-flow equation, wherein a
rational-function approximation of the elliptic integrals for moderate spin
current and small damping results in a closed-form expression of the switching
time. Randomness in the initial angle of magnetization gives the distribution
function of the switching time. The analytic model conforms to the results
obtained from Monte Carlo simulation for a broad range of material parameters.
Our results can ameliorate design and benchmarking of in-plane spin torque
magnetic memory by obviating expensive numerical computation.",2001.03300v2
2022-03-06,Elongated Skyrmion as Spin Torque Nano-Oscillator and Magnonic Waveguide,"Spin torque nano-oscillator has been extensively studied both theoretically
and experimentally in recent decades due to its potential applications in
future microwave communication technology and neuromorphic computing. In this
work, we present a skyrmion-based spin torque nano-oscillator driven by a
spatially uniform direct current, where the skyrmion is confined by two pinning
sites. Different from other skyrmion-based oscillators that arise from the
circular motion or the breathing mode of a skyrmion, the steady-state
oscillatory motions are produced by the periodic deformation of an elongated
skyrmion. Through micromagnetic simulations, we find that the oscillation
frequency depends on the driving current, the damping constant as well as the
characteristics of pinning sites. This nonlinear response to direct current
turns out to be universal and can also appear in the case of antiskyrmions,
skyrmioniums and domain walls. Furthermore, the elongated skyrmion possesses a
rectangle-like domain wall, which could also serve as a magnonic waveguide.
Utilizing the propagation of spin waves in this waveguide, we propose a device
design of logic gate and demonstrate its performance.",2203.02969v2
2022-05-17,Large interfacial Rashba interaction and giant spin-orbit torques in atomically thin metallic heterostructures,"The ability of spin-orbit interactions to convert charge current into spin
current, most often in the bulk of heavy metal thin films, has been the
hallmark of spintronics in the last decade. In this study, we demonstrate how
the insertion of light metal element interface profoundly affects both the
nature of spin-orbit torque and its efficiency in terms of damping-like
($H_{\text{DL}}$) and field-like ($H_{\text{FL}}$) effective fields in
ultrathin Co ferromagnet. Indeed, we measure unexpectedly large
$H_{\text{FL}}$/$H_{\text{DL}}$ ratio ($\sim$2.5) upon inserting a 1.4 nm thin
Al layer in Pt|Co|Al|Pt as compared to a similar stacking including Cu instead
of Al. From our modelling, these results strongly evidence the presence of
large Rashba interaction at Co|Al interface producing a giant $H_{\text{FL}}$,
which was not expected from a metallic interface. The occurrence of such
enhanced torques from an interfacial origin is further validated by
demonstrating current-induced magnetization reversal showing a significant
decrease of the critical current for switching.",2205.08486v2
2015-06-09,Universal chiral-triggered magnetization switching in confined nanodots,"Spin orbit interactions are rapidly emerging as the key for enabling
efficient current-controlled spintronic devices. Much work has focused on the
role of spin-orbit coupling at heavy metal/ferromagnet interfaces in generating
current-induced spin-orbit torques. However, the strong influence of the
spin-orbit-derived Dzyaloshinskii-Moriya interaction (DMI) on spin textures in
these materials is now becoming apparent. Recent reports suggest DMI-stabilized
homochiral domain walls (DWs) can be driven with high efficiency by spin torque
from the spin Hall effect. However, the influence of the DMI on the
current-induced magnetization switching has not been explored nor is yet
well-understood, due in part to the difficulty of disentangling spin torques
and spin textures in nano-sized confined samples. Here we study the
magnetization reversal of perpendicular magnetized ultrathin dots, and show
that the switching mechanism is strongly influenced by the DMI, which promotes
a universal chiral non-uniform reversal, even for small samples at the
nanoscale. We show that ultrafast current-induced and field-induced
magnetization switching consists on local magnetization reversal with domain
wall nucleation followed by its propagation along the sample. These findings,
not seen in conventional materials, provide essential insights for
understanding and exploiting chiral magnetism for emerging spintronics
applications.",1506.02893v1
2018-11-02,Anatomy of electrical signals and dc-voltage lineshape in spin torque ferromagnetic resonance,"The electrical detection of spin torque ferromagnetic resonance (st-FMR) is
becoming a popular method for measuring the spin-Hall angle of heavy metals
(HM). However, various sensible analysis on the same material with either the
same or different experimental setups yielded different spin-Hall angles with
large discrepancy, indicating some missing ingredients in our current
understanding of st-FMR. Here we carry out a careful analysis of electrical
signals of the st-FMR in a HM/ferromagnet (HM/FM) bilayer with an arbitrary
magnetic anisotropy. The FM magnetization is driven by two radio-frequency (rf)
forces: the rf Oersted field generated by an applied rf electric current and
the so called rf spin-orbit torque from the spin current flowing
perpendicularly from the HM to the FM due to the spin-Hall effect. By using the
universal form of the dynamic susceptibility matrix of magnetic materials at
the st-FMR, the electrical signals originated from the anisotropic
magnetoresistance, anomalous Hall effect and inverse spin-Hall effect are
analysed and dc-voltage lineshape near the st-FMR are obtained.
Angle-dependence of dc-voltage is given for two setups. A way of experimentally
extracting the spin-Hall angle of a HM is proposed.",1811.00810v1
2020-08-12,Observation of strong bulk damping-like spin-orbit torque in chemically disordered ferromagnetic single layers,"Strong damping-like spin-orbit torque ({\tau}DL) has great potential for
enabling ultrafast energy-efficient magnetic memories, oscillators, and logic.
So far, the reported {\tau}DL exerted on a thin-film magnet must result from an
externally generated spin current or from an internal non-equilibrium spin
polarization in noncentrosymmetric GaMnAs single crystals. Here, we for the
first time demonstrate a very strong, unexpected {\tau}DL from current flow
within ferromagnetic single layers of chemically disordered,
face-centered-cubic CoPt. We establish that the novel {\tau}DL is a bulk
effect, with the strength per unit current density increasing monotonically
with the CoPt thickness, and is insensitive to the presence or absence of spin
sinks at the CoPt surfaces. This {\tau}DL most likely arises from a net
transverse spin polarization associated with a strong spin Hall effect (SHE),
while there is no detectable long-range asymmetry in the material. These
results broaden the scope of spin-orbitronics and provide a novel avenue for
developing single-layer-based spin-torque memory, oscillator, and logic
technologies.",2008.05400v2
2021-05-12,Investigation of the monopole magneto-chemical potential in spin ices using capacitive torque magnetometry,"The single-ion anisotropy and magnetic interactions in spin-ice systems give
rise to unusual non-collinear spin textures, such as Pauling states and
magnetic monopoles. The effective spin correlation strength ($J_{eff}$)
determines the relative energies of the different spin-ice states. With this
work, we display the capability of capacitive torque magnetometry in
characterizing the magneto-chemical potential associated with monopole
formation. We build a magnetic phase diagram of Ho$_2$Ti$_2$O$_7$, and show
that the magneto-chemical potential depends on the spin-sublattice ($\alpha$ or
$\beta$), i.e., the Pauling state, involved in the transition. Monte-Carlo
simulations using the dipolar-spin-ice Hamiltonian support our findings of a
sublattice-dependent magneto-chemical potential, but the model underestimates
the $J_{eff}$ for the $\beta$-sublattice. Additional simulations, including
next-nearest neighbor interactions ($J_2$), show that long-range exchange terms
in the Hamiltonian are needed to describe the measurements. This demonstrates
that torque magnetometry provides a sensitive test for $J_{eff}$ and the
spin-spin interactions that contribute to it.",2105.05844v2
2022-07-13,"Giant orbital Hall effect and orbital-to-spin conversion in 3d, 5d, and 4f metallic heterostructures","The orbital Hall effect provides an alternative means to the spin Hall effect
to convert a charge current into a flow of angular momentum. Recently,
compelling signatures of orbital Hall effects have been identified in 3d
transition metals. Here, we report a systematic study of the generation,
transmission, and conversion of orbital currents in heterostructures comprising
3d, 5d, and 4f metals. We show that the orbital Hall conductivity of Cr reaches
giant values of the order of 5*10^5 Ohm^{-1} m^{-1} and that Pt presents a
strong orbital Hall effect in addition to the spin Hall effect. Measurements
performed as a function of thickness of nonmagnetic Cr, Mn, and Pt layers and
ferromagnetic Co and Ni layers reveal how the orbital and spin currents compete
or assist each other in determining the spin-orbit torques acting on the
magnetic layer. We further show how this interplay can be drastically modulated
by introducing 4 f spacers between the nonmagnetic and magnetic layers. Gd and
Tb act as very efficient orbital-to-spin current converters, boosting the
spin-orbit torques generated by Cr by a factor of 4 and reversing the sign of
the torques generated by Pt. To interpret our results, we present a generalized
drift-diffusion model that includes both spin and orbital Hall effects and
describes their interconversion mediated by spin-orbit coupling.",2207.06347v1
2012-07-27,"Nonequilibrium Multi-Band Spin Quantum Transport Equations: Spin, Pseudo-Spin, and Total Charge Coupling","Using the superfield nonequilibrium Greens function technique, we derive the
spatio-temporal spin magnetization quantum transport equations (SMQTEs) for a
two-band model of semiconductors. The relevant variables are the real
(Pauli-Dirac) spin, pseudo-spin, and the total charge. The results show that
the multi-band real SMQTEs are coupled to the pseudo-spin magnetization
transport equations by virtue of the presence of two additional discrete
quantum labels besides the up and down real-spin indices, namely, the
conduction and valence band quantum labels. The SMQTEs essentially consist of
three group of terms describing the rate of change, namely, (1) a group of
terms similar to the equation for particle quantum transport, i.e., with
spin-independent transport parameters, (2) a group of terms describing various
torques influencing the spin orientation and directional flow of spin
magnetization correlations or phase-space magnetization density, and (3) a
group of terms expressing the coupling of the real spin magnetization with the
pseudo-spin magnetization. Self-consistently, the pseudo-spin magnetization
equations incorporate the pseudo-spin/real spin coupling, as well as the
pseudo-spin coupling to the total charge.",1207.6647v1
2017-04-05,"Structure, site-specific magnetism and magneto-transport properties of epitaxial D0$_{22}$ Mn$_2$Fe$_x$Ga thin films","Ferrimagnetic Mn$_2$Fe$_x$Ga $(0.26 \leq x \leq 1.12)$ thin films have been
characterised by X-ray diffraction, SQUID magnetometry, X-ray absorption
spectroscopy, X-ray magnetic circular dichroism and M\""{o}ssbauer spectroscopy
with the aim of determining the structure and site-specific magnetism of this
tetragonal, D0$_{22}$-structure Heusler compound. High-quality epitaxial films
with low RMS surface roughness ($\sim 0.6$ nm) are grown by magnetron
co-sputtering. The tetragonal distortion induces strong perpendicular magnetic
anisotropy along the $c$-axis with a typical coercive field $\mu_0 H\sim 0.8$ T
and an anisotropy field ranging from $6$ to $8$ T. Upon increasing the Fe
content $x$, substantial uniaxial anisotropy, $K_\mathrm{u} \geq 1.0$ MJ/m$^3$
can be maintained over the full $x$ range, while the magnetisation of the
compound is reduced from $400$ to $280$ kA/m. The total magnetisation is almost
entirely given by the sum of the spin moments originating from the
ferrimagnetic Mn and Fe sublattices, with the latter being coupled
ferromagnetically to one of the former. The orbital magnetic moments are
practically quenched, and have negligible contributions to the magnetisation.
The films with $x=0.73$ exhibit a high anomalous Hall angle of $2.5$ % and a
high Fermi-level spin polarisation, above $51$ %, as measured by point contact
Andreev reflection. The Fe-substituted Mn$_2$Ga films are highly tunable with a
unique combination of high anisotropy, low magnetisation, appreciable spin
polarisation and low surface roughness, making them very strong candidates for
thermally-stable spin-transfer-torque switching nanomagnets with lateral
dimensions down to $10$ nm.",1704.01326v1
2007-01-13,Theory of conserved spin current and its application to two dimensional hole gas,"We present a detailed microscopic theory of the conserved spin current which
is introduced by us [Phys. Rev. Lett. \textbf{96}, 196602 (2006)] and satisfies
the spin continuity equation even for spin-orbit coupled systems. The spin
transport coefficients $\sigma_{\mu\nu}^{s}$ as a response to the electric
field are shown to consist of two parts, i.e., the conventional part
$\sigma_{\mu\nu}^{s0}$ and the spin torque dipole correction $\sigma_{\mu\nu
}^{s\tau}$. As one key result, an Onsager relation between $\sigma_{\mu\nu
}^{s}$ and other kinds of transport coefficients are shown. The expression for
$\sigma_{\mu\nu}^{s}$ in terms of single-particle Bloch states are derived, by
use of which we study the conserved spin Hall conductivity in the two
dimensional hole gas modeled by a combined Luttinger and SIA Rashba spin-orbit
coupling. It is shown that the two components in spin Hall conductivity usually
have the opposite contributions. While in the absence of Rashba spin splitting,
the spin Hall transport is dominated by the conventional contribution, the
presence of Rashba spin splitting stirs up a large enhancement of the spin
torque dipole correction, leading to an overall sign change for the total spin
Hall conductivity. Furthermore, an approximate two-band calculation and the
subsequent comparison with the exact four-band results are given, which reveals
that the coupling between the heavy hole and light hole bands should be taken
into account for strong Rashba spin splitting.",0701293v1
2008-05-18,Effect of spin diffusion on spin torque in magnetic nanopillars,"We present systematic magnetoelectronic measurements of magnetic nanopillars
with different structures of polarizing magnetic layers. The magnetic reversal
at small magnetic field, the onset of magnetic dynamics at larger field, and
the magnetoresistance exhibit a significant dependence on the type of the
polarizing layer. We performed detailed quantitative modeling showing that the
differences can be explained by the effects of spin-dependent electron
diffusion.",0805.2706v1
2011-08-24,Dynamical Tides in Compact White Dwarf Binaries: Tidal Synchronization and Dissipation,"In compact white dwarf (WD) binary systems (with periods ranging from minutes
to hours), dynamical tides involving the excitation and dissipation of gravity
waves play a dominant role in determining the physical conditions of the WDs
prior to mass transfer or binary merger. We calculate the amplitude of the
tidally excited gravity waves as a function of the tidal forcing frequency
\omega=2(\Omega-\Omega_s) (where \Omega is the orbital frequency and \Omega_s
is the spin frequency) for several realistic carbon-oxygen WD models, assuming
that the waves are efficiently dissipated in the outer layer of the star by
nonlinear effects or radiative damping. The mechanism of wave excitation in WDs
is complex due to the sharp features associated with composition changes inside
the WD, and in our WD models gravity waves are launched just below the
helium-carbon boundary. We find that the tidal torque on the WD and the related
tidal energy transfer rate, \dot E_{\rm tide}, depend on \omega in an erratic
way. On average, \dot E_{\rm tide} scales approximately as \Omega^5\omega^5 for
a large range of tidal frequencies. We also study the effects of dynamical
tides on the long-term evolution of WD binaries. Above a critical orbital
frequency \Omega_c, corresponding to an orbital period of order one hour
(depending on WD models), dynamical tides efficiently drive \Omega_s toward
\Omega, although a small, almost constant degree of asynchronization
(\Omega-\Omega_s\sim {\rm constant}) is maintained even at the smallest binary
periods. While the orbital decay is always dominated by gravitational
radiation, the tidal energy transfer can induce significant phase error in the
low-frequency gravitational waveforms, detectable by the planned LISA project.
Tidal dissipation may also lead to significant heating of the WD envelope and
brightening of the system long before binary merger.",1108.4910v5
2015-09-21,Super-Strong Magnetic Fields of Neutron Stars in Be X-Ray Binaries Estimated with New Torque and Magnetosphere Models,"We re-estimate the surface magnetic fields of neutron stars (NSs) in Be X-ray
binaries (BeXBs) with different models of torque, improved beyond Klus et al.
(2014). In particular, a new torque model (Dai \& Li 2006) is applied to three
models of magnetosphere radius. Unlike the previous models, the new torque
model does not lead to divergent results for any fastness parameter. The
inferred surface magnetic fields of these NSs for the two compressed
magnetosphere models are much higher than that for the uncompressed
magnetosphere model. The new torque model using the compressed-magnetosphere
radius (Shi, Zhang \& Li 2014) leads to unique solutions near spin equilibrium
in all cases, unlike other models that usually give two branches of solutions.
Although our conclusions are still affected by the simplistic assumptions about
the magnetosphere radius calculations, we show several groups of possible
surface magnetic field values with our new models when the interaction between
the magnetosphere and the infalling accretion plasma is considered. The
estimated surface magnetic fields for NSs BeXBs in the Large Magellanic Cloud,
the Small Magellanic Cloud and the Milk Way are between the quantum critical
field and the maximum ""virial"" value by the spin equilibrium condition.",1509.06126v2
2018-08-17,Tunnel magnetoresistance angular and bias dependence enabling tuneable wireless communication,"Spin-transfer torques (STTs) can be exploited in order to manipulate the
magnetic moments of nanomagnets, thus allowing for new consumer-oriented
devices to be designed. Of particular interest here are tuneable
radio-frequency (RF) oscillators for wireless communication. Currently, the
structure that maximizes the output power is an Fe/MgO/Fe-type magnetic tunnel
junction (MTJ) with a fixed layer magnetized in the plane of the layers and a
free layer magnetized perpendicular to the plane. This structure allows for
most of the tunnel magnetoresistance (TMR) to be converted into output power.
Here, we experimentally and theoretically demonstrate that the main mechanism
sustaining steady-state precession in such structures is the angular dependence
of the magnetoresistance. The TMR of such devices is known to exhibit a
broken-linear dependence versus the applied bias. Our results show that the TMR
bias dependence effectively quenches spin-transfer-driven precession and
introduces a non-monotonic frequency dependence at high applied currents. Thus
we expect the bias dependence of the TMR to have an even more dramatic effect
in MTJs with Mn-Ga-based free layers, which could be used to design wireless
oscillators extending towards the THz gap, but have been experimentally shown
to exhibit a non-trivial TMR bias dependence.",1808.10812v1
2013-08-07,Constraining white dwarf viscosity through tidal heating in detached binary systems,"Although the internal structure of white dwarfs is considered to be generally
well understood, the source and entity of viscosity is still very uncertain. We
propose here to study white dwarf viscous properties using short period (< 1
hr), detached white dwarf binaries, such as the newly discovered ~12.8 min
system. These binaries are wide enough that mass transfer has not yet started
but close enough that the least massive component is subject to a measurable
tidal deformation. The associated tidal torque transfers orbital energy, which
is partially converted into heat by the action of viscosity within the deformed
star. As a consequence, its outer non-degenerate layers expand, and the star
puffs up. We self-consistently calculate the fractional change in radius, and
the degree of asynchronism (ratio of stellar to orbital spin) as a function of
the viscous time. Specializing our calculations to J0651, we find that the
discrepancy between the measured radius of the secondary star and He white
dwarf model predictions can be interpreted as tidal inflation if the viscous
timescale is either ~2 10^5 yr or ~10^4 yr. Such values point to a
non-microscopic viscosity, possibly given by tidally induced turbulence, or by
magnetic field stresses with a magnetic field strength of 10-100 Gauss.
Fortunately, these two timescales produce very different degree of
asynchronism, with the shortest one, bringing the system much closer to
synchronisation. A measurement of the stellar spin can thus univocally
determined the mean viscosity. Extrapolating the secondary's radial expansion,
we predict that the star will fill is Roche lobe at a separation which is
1.2-1.3 smaller than the current one. Applying this method to a future sample
of systems can allow us to learn whether viscosity changes with mass and/or
nuclear composition.",1308.1664v1
2001-06-01,Spin currents and spin dynamics in time-dependent density-functional theory,"We derive and analyse the equation of motion for the spin degrees of freedom
within time-dependent spin-density-functional theory (TD-SDFT). Results are (i)
a prescription for obtaining many-body corrections to the single-particle spin
currents from the Kohn-Sham equation of TD-SDFT, (ii) the existence of an
exchange-correlation (xc) torque within TD-SDFT, (iii) a prescription for
calculating, from TD-SDFT, the torque exerted by spin currents on the spin
magnetization, (iv) a novel exact constraint on approximate xc functionals, and
(v) the discovery of serious deficiencies of popular approximations to TD-SDFT
when applied to spin dynamics.",0106021v3
2017-11-09,Room Temperature Giant Charge-to-Spin Conversion at SrTiO3/LaAlO3 Oxide Interface,"Two-dimensional electron gas (2DEG) formed at the interface between SrTiO3
(STO) and LaAlO3 (LAO) insulating layer is supposed to possess strong Rashba
spin-orbit coupling. To date, the inverse Edelstein effect (i.e. spin-to-charge
conversion) in the 2DEG layer is reported. However, the direct effect of
charge-to-spin conversion, an essential ingredient for spintronic devices in a
current induced spin-orbit torque scheme, has not been demonstrated yet. Here
we show, for the first time, a highly efficient spin generation with the
efficiency of ~6.3 in the STO/LAO/CoFeB structure at room temperature by using
spin torque ferromagnetic resonance. In addition, we suggest that the spin
transmission through the LAO layer at high temperature range is attributed to
the inelastic tunneling via localized states in the LAO band gap. Our findings
may lead to potential applications in the oxide insulator based spintronic
devices.",1711.03268v1
2018-07-18,Extrinsic Spin-Charge Coupling in Diffusive Superconducting Systems,"We present a theoretical study of diffusive superconducting systems with
extrinsic spin-orbit coupling and arbitrarily strong impurity potential. We
derive from a microscopic Hamiltonian a diffusion equation for the
quasi-classical Green function, and demonstrate that all mechanisms related to
the spin-orbit coupling are expressed in terms of three kinetic coefficients:
the spin Hall angle, the spin current swapping coefficient, and the spin
relaxation rate due to Elliott-Yafet mechanism. The derived diffusion equation
contains a hitherto unknown term describing a spin-orbit torque that appears
exclusively in the superconducting state. As an example, we provide a
qualitative description of a magnetic vortex in a superconductor with triplet
correlations, and show that the novel term describes a spin torque proportional
to the vector product between the spectral angular momentum of the condensate
and the triplet vector. Our equation opens up the possibility to explore
spintronic effects in superconductors with no counterparts in the normal
metallic state.",1807.07029v2
2017-10-26,Spin dynamics in MgO based magnetic tunnel junctions with dynamical exchange coupling,"We study the spin dynamics in Fe|MgO|Fe tunnel junction with the dynamical
exchange coupling by coupled Landau-Lifshitz-Gilbert equations. The effects of
spin pumping on the spin dynamics are investigated in detail. It is observed
that the spin pumping can stabilize a quasi-antiparallel state rather than a
quasi-parallel one. More interestingly, our work suggests that the spin pumping
torque can efficiently modulate the magnetization, similar to the
thermal-bias-driven and electricbias-driven spin torques.",1710.09666v2
2017-03-27,Micromagnetic simulations of spin-torque driven magnetisation dynamics with spatially resolved spin transport and magnetisation texture,"We present a simple and fast method to simulate spin-torque driven
magnetisation dynamics in nano-pillar spin-valve structures. The approach is
based on the coupling between a spin transport code based on random matrix
theory and a micromagnetics finite-elements software. In this way the spatial
dependence of both spin transport and magnetisation dynamics is properly taken
into account. Our results are compared with experiments. The excitation of the
spin-wave modes, in- cluding the threshold current for steady state
magnetisation precession and the nonlinear frequency shift of the modes are
reproduced correctly. The giant magneto resistance effect and the magnetisa-
tion switching also agree with experiment. The similarities with recently
described spin-caloritronics devices are also discussed.",1703.08959v2
2020-01-04,Persistent currents and spin torque caused by percolated quantum spin Hall state,"Motivated by recent experiments, we investigate the quantum spin Hall state
in 2D topological insulator/ferromagnetic metal planar junctions by means of a
tight-binding model and linear response theory. We demonstrate that whether the
edge state Dirac cone is submerged into the ferromagnetic subbands and the
direction of the magnetization dramatically affect (i) how the edge state
percolates into the ferromagnet, and (ii) the spin-momentum locking of the edge
state. Laminar flows of room temperature persistent charge and spin currents
near the interface are uncovered. In addition, the current-induced spin
polarization at the edge of the 2D topological insulator is found to be
dramatically enhanced near the impurities. The current-induced spin
polarization in the ferromagnet is mainly polarized in the out-of-plane
direction ${\hat{\bf z}}$, rendering a current-induced spin torque that is
predominantly field-like $\propto {\bf S}\times{\hat{\bf z}}$.",2001.01081v3
2020-12-14,Thermally induced spin torque and domain wall motion in superconductor/antiferromagnetic insulator bilayers,"We theoretically investigate domain wall motion in an antiferromagnetic
insulator layer caused by thermally generated spin currents in an adjacent
spin-split superconductor layer. An uncompensated antiferromagnet interface
enables the two crucial ingredients underlying the mechanism - spin splitting
in the superconductor and absorption of spin currents by the antiferromagnet.
Treating the superconductor using the quasiclassical theory and the
antiferromagnet via Landau-Lifshitz-Gilbert description, we find domain wall
propagation along the thermal gradient with relatively large velocities $\sim
100$ m/s. Our proposal exploits the giant thermal response of spin-split
superconductors in achieving large spin torques towards driving domain wall and
other spin textures in antiferromagnets.",2012.07405v1
2021-03-19,Domain wall dynamics of ferrimagnets induced by spin-current near the angular momentum compensation temperature,"We report on a theoretical study of the spin-current excited dynamics of
domain walls (DWs) in ferrimagnets in the vicinity of the angular momentum
compensation point. Effective Lagrangian and nonlinear dynamic equations are
derived for a two-sublattice ferrimagnet taking into account both spin-torques
and external magnetic field. The dynamics of the DW before and after the Walker
breakdown is calculated for any direction of the spin current polarization. It
is shown that for the in-plane polarization of the spin current, the DW
mobility reaches a maximum near the temperature of the angular momentum
compensation. For the out-of-plane spin polarization, in contrast, a spin
current with the densities below the Walker breakdown does not excite the
dynamics of the DW. After overcoming the Walker breakdown, the domain wall
velocity increases linearly with increasing the current density. In this
spin-current polarization configuration the possibility of a gigahertz
oscillation dynamics of the quasi-antiferromagnetic vector under the action of
a damping-like torque in the angular momentum compensation point is
demonstrated. Possible structures for experimental demonstration of the
considered effects are discussed.",2103.10711v1
2024-01-10,Electrical Non-Hermitian Control of Topological Magnon Spin Transport,"Magnonic topological phases realize chiral edge spin waves that are protected
against backscattering, potentially enabling highly efficient spin transport.
Here we show that the spin transport through these magnonic chiral edge states
can be electrically manipulated by non-Hermitian control. We consider the
paradigmatic magnon Haldane model and show that it is transformed into an
effective non-Hermitian magnon Chern insulator by including a
sublattice-dependent spin-orbit torque. In linear spin-wave theory, this
electrically induced torque causes a lasing of the chiral edge magnons along
certain edge directions, leading to an enhancement of the spin-wave amplitude.
This prediction is confirmed by numerical simulations based on the
Landau-Lifshitz-Gilbert equation. For a spin-wave transport setup, in which
magnons are excited by a microwave field and detected with a normal metal
conductor, we find that the magnon amplification is remarkably robust against
disorder, establishing non-Hermitian control as a promising avenue for
topological magnonics.",2401.04967v2
2014-10-07,Determination of intrinsic spin Hall angle in Pt,"The spin Hall angle in Pt is evaluated in Pt/NiFe bilayers by spin torque
ferromagnetic resonance (ST-FMR) measurements, and is found to increase with
increasing the NiFe thickness. To extract the intrinsic spin Hall angle in Pt
by estimating the total spin current injected into NiFe from Pt, the NiFe
thickness dependent measurements are performed and the spin diffusion in the
NiFe layer is taken into account. The intrinsic spin Hall angle of Pt is
determined to be 0.068 at room temperature, and is found to be almost constant
in the temperature range 13 - 300 K.",1410.1601v1
2015-01-13,Spin effects induced by thermal perturbation in a normal metal/magnetic insulator system,"Using one of the methods of quantum nonequilibrium statistical physics we
have investigated the spin transport transverse to the normal
metal/ferromagnetic insulator interface in hybrid nanostructures. An
approximation of the effective parameters, when each of the interacting
subsystems (electron spin, magnon, and phonon) is characterized by its own
effective temperature have been considered. The generalized Bloch equations
which describe the spin-wave current propagation in the dielectric have been
derived. Finally, two sides of the spin transport ""coin"" have been revealed:
the diffusive nature of the magnon motion and magnon relaxation processes,
responsible for the spin pumping and the spin-torque effect.",1501.02983v1
2003-11-19,A comment on 'Accurate spin axes and solar system dynamics',"In a recent paper, Edvardsson etal (2002) propose a new solution for the spin
evolution of the Earth and Mars. Their results differ significantly with
respect to previous studies, as they found a large contribution on the
precession of the planet axis from the tidal effects of Phobos and Deimos. In
fact, this probably results from the omission by the authors of the torques
exerted on the satellites orbits by the planet's equatorial bulge, as otherwise
the average torque exerted by the satellites on the planet is null.",0311448v1
2003-01-16,Current induced distortion of a magnetic domain wall,"We consider the spin torque induced by a current flowing ballistically
through a magnetic domain wall. In addition to a global pressure in the
direction of the electronic flow, the torque has an internal structure of
comparable magnitude due to the precession of the electrons' spins at the
""Larmor"" frequency. As a result, the profile of the domain wall is expected to
get distorted by the current and acquires a periodic sur-structure.",0301293v1
2006-06-26,Self Consistent NEGF-LLG Model for Spin-Torque Based Devices,"We present here a self consistent solution of quantum transport, using the
Non Equilibrium Green's Function (NEGF) method, and magnetization dynamics,
using the Landau-Lifshitz-Gilbert (LLG) formulation. We have applied this model
to study current induced magnetic switching due to `spin torque' in a device
where the electronic transport is ballistic and the free magnetic layer is
sandwiched between two anti-parallel ferromagnetic contacts. The device shows
clear hysteretic current-voltage characteristics, at room temperature, with a
sharp transition between the bistable states and hence can be used as a
non-volatile memory. We show that the proposed design may allow reducing the
switching current by an order of magnitude.",0606648v2
2006-09-29,A simple vision of current induced spin torque in domain walls,"The effective spin pressure induced by an electric current on a domain wall
in a ferromagnet is determined using a simple classical model, which allows us
to extend previous theories to arbitrary domain wall widths. In particular, the
role of spatially non-uniform components of the torques are analyzed in detail.
We find that the effect of the current is mainly to distort the domain wall
which should enhance de-pinning. We also find that in the limit of thin domain
walls the current-induced pressure changes sign.",0609765v1
2006-11-23,Ab-initio GMR and current-induced torques in Au/Cr multilayers,"We report on an {\em ab-initio} study of giant magnetoresistance (GMR) and
current-induced-torques (CITs) in Cr/Au multilayers that is based on
non-equilibrium Green's functions and spin density functional theory. We find
substantial GMR due primarily to a spin-dependent resonance centered at the
Cr/Au interface and predict that the CITs are strong enough to switch the
antiferromagnetic order parameter at current-densities $\sim 100$ times smaller
than typical ferromagnetic metal circuit switching densities.",0611599v1
2007-09-28,Microwave power generated by a spin-torque oscillator in the presence of noise,"An expression for the microwave power generated by a spin-torque oscillator
in the presence of thermal noise is derived. This expression, when used in a
subcritical regime, demonstrates that generated power is determined by the
noise level and provides a simple way to experimentally determine the threshold
current for microwave generation. The same expression gives a good quantitative
description of the experimentally measured dependence of the generated power on
the bias current in a moderate super-critical range of bias current variation.",0709.4553v1
2007-10-02,Lineshape distortion in a nonlinear auto-oscillator near generation threshold: Application to spin-torque nano-oscillators,"The lineshape in an auto-oscillator with a large nonlinear frequency shift in
the presence of thermal noise is calculated. Near the generation threshold,
this lineshape becomes strongly non-Lorentzian, broadened, and asymmetric. A
Lorentzian lineshape is recovered far below and far above threshold, which
suggests that lineshape distortions provide a signature of the generation
threshold. The theory developed adequately describes the observed behavior of a
strongly nonlinear spin-torque nano-oscillator.",0710.0495v2
2007-10-02,Harmonic oscillator model for current- and field-driven magnetic vortices,"In experiments the distinction between spin-torque and Oersted-field driven
magnetization dynamics is still an open problem. Here, the gyroscopic motion of
current- and field-driven magnetic vortices in small thin-film elements is
investigated by analytical calculations and by numerical simulations. It is
found that for small harmonic excitations the vortex core performs an
elliptical rotation around its equilibrium position. The global phase of the
rotation and the ratio between the semi-axes are determined by the frequency
and the amplitude of the Oersted field and the spin torque.",0710.0532v1
2008-09-23,Motion of the hot spot and spin torque in accreting millisecond pulsars,"The primary concern of this contribution is that accreting millisecond
pulsars (AMXPs) show a much larger amount of information than is commonly
believed. The three questions to be addressed are: 1. Is the apparent spin
torque observed in AMXPs real ? 2. Why do we see correlations and
anti-correlations between fractional amplitudes and timing residuals in some
AMXPs ? 3. Why the timing residuals, the lightcurve and the 1Hz QPO in SAX
J1808.4$-$3658 are related ?",0809.4021v1
2008-09-29,Internal effective field sources for spin torque nano pillar oscillators,"In this paper we numerically conduct micromagnetic modelling with an expended
micromagnetic model that includes the spin torque term and an impedance model
to investigate methods to replace external field sources with internal ones and
to investigate its tuneability on nanopillar geometries. We present results for
three methods: interlayer coupling, large perpendicular anisotropy and
magnetostatic coupling. The internal field sources are evaluated as function of
frequency shift with current, its dependency on temperature and are tested
against analytical predictions.",0809.4973v1
2008-12-02,Experimental Test of Analytic Theory of Spin Torque Oscillator Dynamics,"We make measurements of power spectral density of the microwave voltage
emitted by a spin torque nano-oscillator (STNO) and compare our experimental
results to predictions of an analytic theory of a single-mode STNO dynamics by
V. S. Tiberkevich, A. N. Slavin, J. V. Kim,[Phys. Rev. B 78, 092401 (2008)]. We
find that a complete set of the oscillator spectral properties: power,
frequency, spectral line width and line shape as functions of current are
self-consistently described by the analytic theory for moderate amplitudes of
oscillations (< 70 degrees).",0812.0541v2
2009-04-07,Time domain measurement of phase noise in a spin torque oscillator,"We measure oscillator phase from the zero crossings of the voltage vs. time
waveform of a spin torque nanocontact oscillating in a vortex mode. The power
spectrum of the phase noise varies with Fourier frequency $f$ as $1/f^2$,
consistent with frequency fluctuations driven by a thermal source. The
linewidth implied by phase noise alone is about 70 % of that measured using a
spectrum analyzer. A phase-locked loop reduces the phase noise for frequencies
within its 3 MHz bandwidth.",0904.1214v1
2009-06-13,Single-shot time-domain studies of spin-torque-driven switching in magnetic tunnel junctions,"We report single-shot measurements of resistance versus time for thermally
assisted spin-torque-driven switching in magnetic tunnel junctions. We achieve
sufficient sensitivity to resolve the resistance signals leading up to
switching, including the variations between individual switching events.
Analyses of pre-switching thermal fluctuations allow detailed measurements of
coherence times and variations in magnetization precession amplitude. We find
that with a small in-plane hard-axis magnetic field the magnetization dynamics
are more spatially coherent than for the case of zero field.",0906.2476v1
2010-04-29,Direct experimental measurement of phase-amplitude coupling in spin torque oscillators,"We study spin-torque induced oscillations of MgO magnetic tunnel junctions in
the time domain. By using the Hilbert transform on the time traces, we obtain
for the first time a direct experimental measure of the coupling between the
power and the phase fluctuations. We deduce the power restoration rate and we
obtain low values for the coupling strength, which is consistent with the weak
frequency dependence on the applied voltage.",1004.5319v2
2011-04-15,Spin-torque oscillator linewidth narrowing under current modulation,"We study the behavior of the linewidth of a nano-contact based spin torque
oscillator (STO) under application of a radio frequency (100 MHz) modulating
current. We achieve a significant (up to 85%) reduction of the STO linewidth
when it is modulated across a region of high nonlinearity. The mechanism
responsible for the linewidth reduction is the nonlinear frequency shift under
the influence of current modulation, which reduces the nonlinear amplification
of the linewidth. The reduction of the linewidth during modulation can be
quantitatively calculated from the free-running behavior of the STO.",1104.3167v1
2012-04-05,Theory of Spin Torque Assisted Thermal Switching of Single Free Layer,"The spin torque assisted thermal switching of the single free layer was
studied theoretically. Based on the rate equation, we derived the theoretical
formulas of the most likely and mean switching currents of the sweep current
assisted magnetization switching, and found that the value of the exponent $b$
in the switching rate formula significantly affects the estimation of the
retention time of magnetic random access memory. Based on the Fokker-Planck
approach, we also showed that the value of $b$ should be two, not unity as
argued in the previous works.",1204.1190v1
2012-04-25,Numerical Study on Spin Torque Switching in Thermally Activated Region,"We studied the spin torque switching of the single free layer in the
thermally activated region by numerically solving the Landau-Lifshitz-Gilbert
equation. We found that the temperature dependence of the switching time of the
in-plane magnetized system is nonlinear, which means $b \neq 1$. Here, $b$ is
the exponent of the current term in the switching rate formula and has been
widely assumed to be unity. This result enables us to evaluate the thermal
stability of spintronics devices.",1204.5596v2
2012-11-07,Spin torque switching in perpendicular films at finite temperature,"We show how the phase diagram for spin torque switching in the case of
perpendicular anisotropy is altered at nonzero temperature. The hysteresis
region in which the parallel and antiparallel states coexist shrinks, and a new
region of telegraph noise appears. In a small sample, the region of coexistence
of a precessional and parallel state can disappear entirely. We show that the
phase diagram for both zero and nonzero temperatures can be understood and
calculated by plotting an effective energy as a function of angle. A
combinatorial analysis is useful for systematically describing the phase
diagram.",1211.1665v1
2012-12-19,Nanomagnetic Logic and Magnetization Switching Dynamics in Spin Torque Majority Gates,"Spin torque majority gates are modeled and several regimes of magnetization
switching (some leading to failure) are discovered. The switching speed and
noise margins are determined for STMGs and an adder based on it. With switching
time of 3ns at current of 80uA, the adder computational throughput is
comparable to that of a CMOS adder.",1212.4547v1
2013-04-26,Maximizing Spin Torque Diode Voltage by Optimizing Magnetization Alignment,"The optimum condition of the magnetization alignment to maximize the spin
torque diode voltage is derived by solving the Landau-Lifshitz-Gilbert
equation. We show that the optimized diode voltage can be one order of
magnitude larger than that of the conventional alignment where the easy axes of
the free and the pinned layers are parallel. These analytical predictions are
confirmed by numerical simulations.",1304.7079v1
2013-06-17,Robust synchronization of spin-torque oscillators with an LCR load,"We study dynamics of a serial array of spin-torque-oscillators with a
parallel inductor-capacitor-resistor (LCR) load. In a large range of parameters
the fully synchronous regime, where all the oscillators have the same state and
the output field is maximal, is shown to be stable. However, not always such a
robust complete synchronization develops from the random initial state, in many
cases nontrivial clustering is observed, with a partial synchronization
resulting in a quasiperiodic or chaotic mean field dynamics.",1306.3803v1
2013-08-06,Dependence of spin torque diode voltage on applied field direction,"The optimum condition of an applied field direction to maximize spin torque
diode voltage was theoretically derived for a magnetic tunnel junction with a
perpendicularly magnetized free layer and an in-plane magnetized pinned layer.
We found that the diode voltage for a relatively small applied field is
maximized when the projection of the applied field to the film-plane is
parallel or anti-parallel to the magnetization of the pinned layer. However, by
increasing the applied field magnitude, the optimum applied field direction
shifts from the parallel or anti-parallel direction. These analytical
predictions were confirmed by numerical simulations.",1308.1170v1
2013-09-27,Current Dependence of Spin Torque Switching Barrier,"The current dependence of the switching barrier for spin torque switching of
an in-plane magnetized ferromagnet was studied. Two scaling currents, I_{c}$
and I_{c}^{*}(>I_{c}), were introduced to distinguish the magnetization
stability. In the low-current region I<I_{c}, the switching barrier is linear
to the current with another scaling current \tilde{I}_{c}, while such linear
scaling does not hold in the high-current region I_{c} < I < I_{c}^{*}. The
linear scaling is valid for the high temperature and the long current pulse
duration time.",1309.7116v1
2013-12-20,Thermally activated switching rate of a nanomagnet in the presence of spin torque,"The current dependence of the spin torque switching rate in a thermally
activated region of an in-plane magnetized system was studied. The logarithm of
the switching rate depended nonlinearly on current in the high-current region,
I_{c} < I < I_{c}^{*}, where I_{c} and I_{c}^{*} are critical currents
distinguishing the stability of the magnetization. We also found that the
attempt frequency had a minimum around I_{c}, and that the attempt frequency at
I_{c} was three orders of magnitude smaller than that at zero current, contrary
to the assumption in previous analyses of experiments that it remains constant.",1312.6118v1
2014-01-09,Current dependence of spin torque switching rate based on Fokker-Planck approach,"The spin torque switching rate of an in-plane magnetized system in the
presence of an applied field is derived by solving the Fokker-Planck equation.
It is found that three scaling currents are necessary to describe the current
dependence of the switching rate in the low-current limit. The dependences of
these scaling currents on the applied field strength are also studied.",1401.2182v1
2014-03-07,Transition from one- to two-mode generation regime in spin-torque nano-oscillator mediated by thermal noise,"Two-mode model of spin-torque nano-oscillator (STNO) under the action of
thermal noise is considered. Langevin equations for mode amplitudes were
derived starting from general nonlinear oscillator model. Stationary
probability distribution function describing mean mode generation powers was
obtained using Fokker-Planck equation. It was shown that thermal noise can lead
to two-mode generation in STNO. An increase of thermal noise power leads to
excitation of the second mode in a system and to a two-mode generation regime
through intermediate state when two modes coexist only in some range of the
applied currents.",1403.1688v2
2014-04-25,Linewidth of Power Spectrum Originated from Thermal Noise in Spin Torque Oscillator,"A theoretical formula of the linewidth caused by the thermal activation in a
spin torque oscillator with a perpendicularly magnetized free layer and an
in-plane magnetized pinned layer was developed by solving the stochastic
Landau-Lifshitz-Gilbert equation in the energy-phase representation. It is
shown that the linewidth can be suppressed down to 0.1 MHz by applying a large
current (10 mA for typical material parameters). A quality factor larger than
10^{4} is predicted in the large current limit, which is two orders of
magnitude larger than the recently observed experimental value.",1404.6558v1
2014-08-17,Phase Locked Loop of the Spin-Torque Nanooscillator,"We have studied the dynamics of a spin-torque nanooscillator's (STNO) phase
locked loop (PLL) generating microwave oscillations in a broad range of
frequencies under the effect of direct current and external magnetic field.
Bifurcations in the system caused by a change in the frequency detuning of
synchronized oscillations are considered. Bands of phase locking and
synchronism are determined. The existence of a phase locking band in the
filterless PLL of STNOs basically distinguishes these oscillators from other
types of microwave generators.",1408.3868v1
2014-09-15,Enhanced synchronization in an array of spin torque nano oscillators in the presence of oscillating external magnetic field,"We demonstrate that the synchronization of an array of electrically coupled
spin torque nano-oscillators (STNO) modelled by
Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation can be enhanced appreciably
in the presence of a common external microwave magnetic field. The applied
microwave magnetic field stabilizes and enhances the regions of synchronization
in the parameter space of our analysis, where the oscillators are exhibiting
synchronized oscillations thereby emitting improved microwave power. To
characterize the synchronized oscillations we have calculated the locking range
in the domain of external source frequency.",1409.4384v2
2014-12-04,Role of Magnetic Field in Self-Oscillation of Nanomagnet Excited by Spin Torque,"The critical current of the self-oscillation of spin torque oscillator (STO)
consisting of a perpendicularly magnetized free layer and an in-plane
magnetized pinned layer was studied by solving the Landau-Lifshitz-Gilbert
(LLG) equation. We found that the critical current diverged at certain field
directions, indicating that the self-oscillation does not occur at these
directions. It was also found that the sign of the critical current changed
depending on the applied field direction.",1412.1532v1
2016-07-26,Numerical Fokker-Planck study of stochastic write error slope in spin torque switching,"This paper analyzes write errors in spin torque switching due to thermal
fluctuations in a system with Perpendicular Magnetic Anisotropy (PMA). Prior
analytical and numerical methods are summarized, a physics based Fokker-Planck
Equation (FPE) chosen for its computational efficiency and broad applicability
to all switching regimes. The relation between write error slope and material
parameters is discussed in detail to enable better device engineering and
optimization. Finally a 2D FPE tool is demonstrated that extends the
applicability of FPE to write error in non PMA systems with built-in asymmetry.",1607.07523v1
2016-08-02,Ferromagnetic Damping/Anti-damping in a Periodic 2D Helical surface; A Non-Equilibrium Keldysh Green Function Approach,"In this paper, we investigate theoretically the spin-orbit torque as well as
the Gilbert damping for a two band model of a 2D helical surface state with a
Ferromagnetic (FM) exchange coupling. We decompose the density matrix into the
Fermi sea and Fermi surface components and obtain their contributions to the
electronic transport as well as the spin-orbit torque (SOT). Furthermore, we
obtain the expression for the Gilbert damping due to the surface state of a 3D
Topological Insulator (TI) and predicted its dependence on the direction of the
magnetization precession axis.",1608.00984v2
2018-09-10,Size dependence of spin-torque switching in perpendicular magnetic tunnel junctions,"We simulate the spin torque-induced reversal of the magnetization in thin
disks with perpendicular anisotropy at zero temperature. Disks typically
smaller than 20 nm in diameter exhibit coherent reversal. A domain wall is
involved in larger disks. We derive the critical diameter of this transition.
Using a proper definition of the critical voltage, a macrospin model can
account perfectly for the reversal dynamics when the reversal is coherent. The
same critical voltage appears to match with the micromagnetics switching
voltage regardless of the switching path.",1809.03353v2
2020-04-06,Frequency enhancement and power tunability in tilted polarizer spin-torque nano oscillator,"In the absence of an applied magnetic field, a spin-torque nano
oscillator(STNO) with a tilted polarizer is studied using numerical simulation
of the associated Landau-Lifshitz-Gilbert-Slonczewski equation. We find
considerable enhancement of frequency by tilting the polarizer out-of-plane
appropriately. Also, we observe improved tunability of frequency of
oscillations from 15 GHz to 75 GHz and increment in the power spectral density
by current and tilt angle. In addition, our findings and insights pave a simple
way for nanoscale level microwave generators to be implemented.",2004.02659v1
2020-11-11,Reduction of back switching by large damping ferromagnetic material,"Recent studies on magnetization dynamics induced by spin-orbit torque have
revealed a weak dependence of the critical current for magnetization switching
on the damping constant of a ferromagnetic free layer. This study, however,
reveals that the damping constant nevertheless plays a key role in
magnetization switching induced by spin-orbit torque. An undesirable switching,
returning to an initial state, named as back switching, occurs in a ferromagnet
with an easy axis parallel to the current direction. Numerical and theoretical
analyses reveal that back switching is strongly suppressed when the damping
constant of the ferromagnet is large.",2011.05566v1
2017-03-03,Spin-orbit effective fields in Pt/GdFeCo bilayers,"In the increasing interests on spin-orbit torque (SOT) with various magnetic
materials, we investigated SOT in rare earth-transition metal ferrimagnetic
alloys. The harmonic Hall measurements were performed in Pt/GdFeCo bilayers to
quantify the effective fields resulting from the SOT. It is found that the
damping-like torque rapidly increases near the magnetization compensation
temperature TM of the GdFeCo, which is attributed to the reduction of the net
magnetic moment.",1703.00995v1
2019-09-20,Microwave magnetic field modulation of spin torque oscillator based on perpendicular magnetic tunnel junctions,"Modulation of a spin-torque oscillator (STO) signal based on a magnetic
tunnel junction (MTJ) with perpendicularly magnetized free layer is
investigated. Magnetic field inductive loop was created during MTJ fabrication
process, which enables microwave field application during STO operation. The
frequency modulation by the microwave magnetic field of up to 3 GHz is
explored, showing a potential for application in high-data-rate communication
technologies. Moreover, an inductive loop is used for self-synchronization of
the STO signal, which after field-locking exhibits significant improvement of
the linewidth and oscillation power.",1909.09503v1
2019-12-06,Generation of n-qubit W states using Spin Torque,"We examine here a scheme to generate a W state of an n-qubit system with
all-to-all pairwise exchange interaction between n qubits. This relies on
sharing of superposed excitations of a smaller number of $q$ qubits among
others. We present a bound on the maximal jumps from q to n and formalize a
scheme to generate $W_n$ state in $\mathcal{O}(\log_4 n)$ stages. We
demonstrate this scheme in the context of spin torque based quantum computing
architecture that are characterized by repeated interactions between static and
flying qubits.",1912.03171v1
2022-11-14,Sub-Nanosecond Electrical Pulse Switching of an Easy Plane Antiferromagnetic Insulator,"Electrical switching of antiferromagnets (AFM) is critical for AFM
spintronics. However, there is an active debate about the mechanisms of
observed AFM switching on whether the switching is due to spin-orbit torques or
the much slower thermally-induced magnetoelastic effect. We report reliable
current-induced AFM switching in Pt/$\alpha$-Fe$_2$O$_3$ bilayers using
electrical pulses with various durations down to 0.3 ns. The dependence of
switching threshold current density on the pulse width indicates that
spin-orbit torques are the dominant mechanism responsible for electrical
switching of AFMs in the ns regime, reaffirming AFM spintronics as a promising
field for ultrafast and ultrahigh-frequency applications.",2211.07589v1
2023-12-11,Asymptotical dynamics of askew-polarized spinning top under the radiation reaction torque,"Rotary dynamics of polarized composite particles as dipole rigid bodies is
considered. It is described the Euler equations singularly perturbed by the
radiation reaction torque. The Schott term is taken into account, and the
reduction procedure lowering higher derivatives is applied. Asymptotic methods
of nonlinear mechanics are used to analyze the rotary dynamics of
askew-polarized spinning top. Numerical estimates are relevant to the
hypothetical DAST-nanocrystals that might possess a huge dipole moment.",2401.02970v1
2024-03-29,Field-free switching of perpendicular magnetic elements by using two orthogonal sub nanosecond spin orbit torque pulses,"We propose a field-free switching mechanism that utilizes two spatially
orthogonal spin-orbit torque (SOT) currents. Initially applied simultaneously,
one of the currents is subsequently switched off. The superposition of these
two currents results in an in-plane magnetization, which is not orthogonal to
the remaining SOT current after the second one is deactivated. This
symmetry-breaking procedure leads to reproducible and rapid switching, with
field pulse durations as short as 0.25 nanoseconds.",2403.20235v1
2009-06-23,Energy dissipation and angular momentum transfer within a magnetically torqued accretion disc,"We discuss transportation and redistribution of energy and angular momentum
in the magnetic connection (MC) process and Blandford-Payne (BP) process. The
MC results in readjusting the interior viscous torque, and its effects are
operative not only in but also beyond the MC region. The BP process is invoked
to transfer the ""excessive"" angular momentum from an accretion disc. In
addition, we derive a criterion for the interior viscous torque to resolve the
puzzle of the overall equilibrium of angular momentum in disc accretion. It
turns out that the BP efficiency of extracting angular momentum and the
intensity of the outflow are required to be greater than some critical values.",0906.4241v1
2021-10-30,Angular momentum transfered by the field of a moving point charge,"The flux of angular momentum of electromagnetic field of an arbitrarily
moving point charge is investigated. General equations are obtained for the
transfer of angular momentum at arbitrary distance from the charge, and
corresponding equations in the far-field approximation. An explicit expression
is obtained for the flux of angular momentum in the wave zone in terms of
coordinates, velocity, and acceleration of the charge. The torque is
calculated, that would act on an object if it absorbed all the radiation
incident on it. It is shown that this torque is proportional to the curl of the
stress tensor of the electromagnetic field; in the far field approximation the
torque is proportional to the curl of the Poynting vector.",2111.00321v1
2021-11-17,Plasmon Coupling Induced Photon Scattering Torque,"Bio-compatible Au nanoparticles exhibit great advantages in the application
of biomedical researches, such as bio-sensing, medical diagnosis, and cancer
therapy. Bio-molecules can even be manipulated by laser tweezers with the
optically trapped Au nanoparticles as handles. In this Letter, optical
scattering torque arising from the coupled Au nanoparticles driven by
circularly polarized light is theoretically presented. The coupled plasmon
resonance modes boost the angular momentum transfer from photons to the Au
nanoparticle dimers and trimers through light scattering, which does not bring
any optical-heating side effect. The generated optical torques on the
nanostructures highly depend on the plasmon coupling in the structures. The
angular momentum transfer efficiencies from scattered photons to nanostructures
can reach around 200\%. The results suggest that coupled plasmonic nanoparticle
oligomers are promising candidates to construct optically driven rotary
nanomotors that can be applied in biomedical applications.",2111.08986v1
2023-07-03,Spatiotemporal torquing of light,"We demonstrate the controlled spatiotemporal transfer of transverse orbital
angular momentum (OAM) to electromagnetic waves: the spatiotemporal torquing of
light. This is a radically different situation than OAM transfer to
longitudinal, spatially-defined OAM light by stationary or slowly varying
refractive index structures such as phase plates or air turbulence. We show
that transverse OAM can be imparted to a short light pulse only for (1)
sufficiently fast transient phase perturbations overlapped with the pulse in
spacetime, or (2) energy removal from a pulse that already has transverse OAM.
Our OAM theory for spatiotemporal optical vortex (STOV) pulses [Phys. Rev.
Lett. 127, 193901 (2021)] correctly quantifies the light-matter interaction of
this experiment, and provides a torque-based explanation for the first
measurement of STOVs [Phys. Rev. X 6, 031037 (2016)].",2307.01019v3
2018-01-16,Spin-orbit-torque and magnetic damping in tailored ferromagnetic bilayers,"We study spin-orbit-torque-driven ferromagnetic resonance (FMR) in
ferromagnetic (FM) bilayers, consisting of Co and permalloy (Py), sandwiched
between Pt and MgO layers. We find that the FM layer in contact with the Pt
layers dominantly determines that spin Hall angle, which is consistent with the
spin-transparency model. By contrast, the FMR linewidths are considerably
influenced not only by the spin-pumping effect across the Pt|FM in terface but
also by the spin relaxation such as two-magnon scattering at the FMMgO
interface.The CoMgO interface leads to notably increased FMR linewidths, while
the Py|MgO interface has less effect. This different contribution of each
interface to the spin Hall angel and dissipation parameter suggests that the
stack configuration of Pt|Co|Py|MgO requires less writing energy than
Pt|Py|Co|MgO in spin-orbit-torque-driven magnetic switching. Our approach
offers a promising method to optimize material parameters by engineering either
interfaces in contact with the heavy-metal or the oxide layer.",1801.05131v2
2021-05-19,"Determination of the spin Hall angle by the inverse spin Hall effect, device level ferromagnetic resonance, and spin torque ferromagnetic resonance: a comparison of methods","The spin torque ferromagnetic resonance (STFMR) is one of the popular methods
for measurement of the spin Hall angle (SHA). However, in order to accurately
determine SHA from STFMR measurements, the acquired data must be carefully
analyzed: The resonance linewidth should be determined to an accuracy of a
fraction of an Oe, while the dynamical interaction leading to the measured
response consists of the conventional field-induced ferromagnetic resonance
(FMR), spin-torque induced FMR, and of the inverse spin Hall effect (ISHE).
Additionally, the signal often deteriorates when DC current is passed through
the device. In this work we compare the STFMR method with two other FMR-based
methods that are used to extract SHA. The first is a device-level FMR and the
second is based on the ISHE. We identify artefacts that are caused by the noise
floor of the instrumentation that make the measurement of SHA illusive even
when the signal to noise ratio seems to be reasonable. Additionally, we
estimate a 10% error in SHA that results from neglecting the magnetic
anisotropies as in conventional measurements. Overall, we find the STFMR to be
the most robust of the three methods despite the complexity of the interaction
taking place therein. The conclusions of our work lead to a more accurate
determination of SHA and will assist in the search of novel materials for
energy efficient spin-based applications.",2105.09023v1
2021-06-18,Study of Spin-Orbit Interactions and Interlayer Ferromagnetic Coupling in Co/Pt/Co Trilayers in Wide Range of Heavy Metal Thickness,"The spin-orbit torque, a torque induced by a charge current flowing through
the heavy-metal conducting layer with strong spin-orbit interactions, provides
an efficient way to control the magnetization direction in
heavy-metal/ferromagnet nanostructures, required for applications in the
emergent magnetic technologies like random access memories, high-frequency nano
oscillators, or bio-inspired neuromorphic computations. We study the interface
properties, magnetization dynamics, magnetostatic features and spin-orbit
interactions within the multilayer system
Ti(2)/Co(1)/Pt(0-4)/Co(1)/MgO(2)/Ti(2) (thicknesses in nanometers) patterned by
optical lithography on micrometer-sized bars. In the investigated devices, Pt
is used as a source of the spin current and as a non-magnetic spacer with
variable thickness, which enables the magnitude of the interlayer ferromagnetic
exchange coupling to be effectively tuned. We also find the Pt
thickness-dependent changes in magnetic anisotropies, magnetoresistance,
effective Hall angle and, eventually, spin-orbit torque fields at interfaces.
The experimental findings are supported by the relevant interface
structure-related simulations, micromagnetic, macrospin, as well as the spin
drift-diffusion models. Finally, the contribution of the spin-orbital
Edelstein-Rashba interfacial fields is also briefly discussed in the analysis.",2106.10103v1
2023-07-31,4U 1626-67 Returns to Spin-Down: Timing features toe the line,"We present a comprehensive analysis of X-ray pulsar 4U 1626-67 during its
current spin-down (2SD) state, following a recent torque reversal. Since its
discovery, this ultra-compact binary has experienced multiple torque states,
transitioning from spin-up (1SU) during 1977-1990 to spin-down (1SD) during
1990-2008, and again spin-up (2SU) until 2023. From NuSTAR observation of May
2023, we have investigated the timing and spectral properties of this pulsar
during its 2SD phase, while also comparing them with previous spin-up-down
states. For energies upto 8 keV, a distinct bi-horned pulse profile was
observed during the spin-up phase, while several sub-structures emerged during
spin-down. Beyond 8 keV, a broad asymmetric peak was consistently observed
across all torque states. The pulse fraction during the 2SD phase was higher
than that during 2SU phase. A prominent ~46.8 mHz quasi-periodic oscillation
has been exclusively detected during the spin-down phase. The broadband
spectrum during the 2SD phase is described by empirical NPEX model, cyclotron
absorption feature and its first harmonic. The spectrum during 2SU phase
requires an additional blackbody component and asymmetry in the cyclotron
absorption line. A significant flux drop by a factor of ~3 in the 2SD was
observed.",2307.16599v1
2024-01-09,Spin current leakage and Onsager reciprocity in interfacial spin-charge interconversion,"Experimental investigations of spin-charge interconversion in magnetic
bilayers comprising a ferromagnet adjacent to a topological insulator have
reported scattered results on the spin-charge and charge-spin conversion
efficiency. Attempting to reconcile these contradicting experimental results,
we develop a phenomenological theory of spin-charge interconversion accounting
for both interfacial interconversion through the spin galvanic effect, also
called the Rashba-Edelstein effect, as well as bulk interconversion via the
spin Hall effect. We find that the spin current leakage into the nonmagnetic
metal plays a central role during the spin-to-charge and charge-to-spin
conversion, leading to dissymmetric interconversion processes. In particular,
spin-to-charge conversion is much less sensitive to the spin current absorption
in the nonmagnetic metal than charge-to-spin conversion. This suggests that
spin pumping is a more trustable technique to extract the interfacial Rashba
parameter than spin-orbit torque.",2401.04413v1
2014-02-17,An Analytic Model for Buoyancy Resonances in Protoplanetary Disks,"Zhu, Stone, and Rafikov (2012) found in 3D shearing box simulations a new
form of planet-disk interaction that they attributed to a vertical buoyancy
resonance in the disk. We describe an analytic linear model for this
interaction. We adopt a simplified model involving azimuthal forcing that
produces the resonance and permits an analytic description of its structure. We
derive an analytic expression for the buoyancy torque and show that the
vertical torque distribution agrees well with results of Athena simulations and
a Fourier method for linear numerical calculations carried out with the same
forcing. The buoyancy resonance differs from the classic Lindblad and
corotation resonances in that the resonance lies along tilted planes. Its width
depends on damping effects and is independent of the gas sound speed. The
resonance does not excite propagating waves. At a given large azimuthal
wavenumber k_y > 1/h (for disk thickness h), the buoyancy resonance exerts a
torque over a region that lies radially closer to the corotation radius than
the Lindblad resonance. Because the torque is localized to the region of
excitation, it is potentially subject to the effects of nonlinear saturation.
In addition, the torque can be reduced by the effects of radiative heat
transfer between the resonant region and its surroundings. For each azimuthal
wavenumber, the resonance establishes a large scale density wave pattern in a
plane within the disk.",1402.4162v1
2016-10-28,Planetary Torque in 3D Isentropic Disks,"Planet migration is inherently a three-dimensional (3D) problem, because
Earth-size planetary cores are deeply embedded in protoplanetary disks.
Simulations of these 3D disks remain challenging due to the steep requirement
in resolution. Using two different hydrodynamics code, FARGO3D and PEnGUIn, we
simulate disk-planet interaction for a 1 to 5 Earth-mass planet embedded in an
isentropic disk. We measure the torque on the planet and ensure that the
measurements are converged both in resolution and between the two codes. We
find that the torque is independent of the smoothing length of the planet's
potential ($r_{\rm s}$), and that it has a weak dependence on the adiabatic
index of the gaseous disk ($\gamma$). The torque values correspond to an inward
migration rate qualitatively similar to previous linear calculations. We
perform additional simulations with explicit radiative transfer using FARGOCA,
and again find agreement between 3D simulations and existing torque formulae.
We also present the flow pattern around the planets, and show that active flow
is present within the planet's Hill sphere, and meridional vortices are shed
downstream. The vertical flow speed near the planet is faster for a smaller
$r_{\rm s}$ or $\gamma$, up to supersonic speeds for the smallest $r_{\rm s}$
and $\gamma$ in our study.",1610.09375v2
2017-09-21,"Force, Torque, Linear Momentum, and Angular Momentum in Classical Electrodynamics","The classical theory of electrodynamics is built upon Maxwell's equations and
the concepts of electromagnetic (EM) field, force, energy, and momentum, which
are intimately tied together by Poynting's theorem and by the Lorentz force
law. Whereas Maxwell's equations relate the fields to their material sources,
Poynting's theorem governs the flow of EM energy and its exchange between
fields and material media, while the Lorentz law regulates the back-and-forth
transfer of momentum between the media and the fields. An alternative force
law, first proposed by Einstein and Laub, exists that is consistent with
Maxwell's equations and complies with the conservation laws as well as with the
requirements of special relativity. While the Lorentz law requires the
introduction of hidden energy and hidden momentum in situations where an
electric field acts on a magnetized medium, the Einstein-Laub (E-L) formulation
of EM force and torque does not invoke hidden entities under such
circumstances. Moreover, total force/torque exerted by EM fields on any given
object turns out to be independent of whether the density of force/torque is
evaluated using the law of Lorentz or that of Einstein and Laub. Hidden
entities aside, the two formulations differ only in their predicted force and
torque distributions inside matter. Such differences in distribution are
occasionally measurable, and could serve as a guide in deciding which
formulation, if either, corresponds to physical reality.",1709.07444v1
2021-04-20,A Learning-Based Approach for Estimating Inertial Properties of Unknown Objects from Encoder Discrepancies,"Many robots utilize commercial force/torque sensors to identify inertial
properties of unknown objects. However, such sensors can be difficult to apply
to small-sized robots due to their weight, size, and cost. In this paper, we
propose a learning-based approach for estimating the mass and center of mass
(COM) of unknown objects without using force/torque sensors at the end-effector
or on the joints. In our method, a robot arm carries an unknown object as it
moves through multiple discrete configurations. Measurements are collected when
the robot reaches each discrete configuration and stops. A neural network is
designed to estimate joint torques from encoder discrepancies. Given multiple
samples, we derive the closed-form relation between joint torques and the
object's inertial properties. Based on the derivation, the mass and COM of
object are identified by weighted least squares. In order to improve the
accuracy of inferred inertial properties, an attention model is designed to
generate weights of joints, which indicate the relative importance for each
joint. Our framework requires only encoder measurements without using any
force/torque sensors, but still maintains accurate estimation capability. The
proposed approach has been demonstrated on a 4 degree of freedom (DOF) robot
arm.",2104.09858v2
2001-09-20,Large Torque Variations in Two Soft Gamma Repeaters,"We have monitored the pulse frequencies of the two soft gamma repeaters SGR
1806-20 and SGR 1900+14 through the beginning of year 2001 using primarily
Rossi X-ray Timing Explorer Proportional Counter Array observations. In both
sources, we observe large changes in the spin-down torque up to a factor of ~4,
which persist for several months. Using long baseline phase-connected timing
solutions as well as the overall frequency histories, we construct torque noise
power spectra for each SGR. The power spectrum of each source is very red
(power-law slope ~-3.5). The torque noise power levels are consistent with some
accreting systems on time scales of ~1 year, yet the full power spectrum is
much steeper in frequency than any known accreting source. To the best of our
knowledge, torque noise power spectra with a comparably steep frequency
dependence have only been seen in young, glitching radio pulsars (e.g. Vela).
The observed changes in spin-down rate do not correlate with burst activity,
therefore, the physical mechanisms behind each phenomenon are also likely
unrelated. Within the context of the magnetar model, seismic activity cannot
account for both the bursts and the long-term torque changes unless the
seismically active regions are decoupled from one another.",0109361v2
2021-11-22,Effect of Differential Rotation on Magnetic Braking of Low-Mass and Solar-Like Stars: A Proof-of-Concept Study,"On the main sequence, low-mass and solar-like stars are observed to spin-down
over time, and magnetized stellar winds are thought to be predominantly
responsible for this significant angular momentum loss. Previous studies have
demonstrated that the wind torque can be predicted via formulations dependent
on stellar properties, such as magnetic field strength and geometry, stellar
radius and mass, wind mass-loss rate, and stellar rotation rate. Although these
stars are observed to experience surface differential rotation, torque
formulations so far have assumed solid-body rotation. Surface differential
rotation is expected to affect the rotation of the wind and thus the angular
momentum loss. To investigate how differential rotation affects the torque, we
use the PLUTO code to perform 2.5D magnetohydrodynamic, axisymmetric
simulations of stellar winds, using a colatitude-dependent surface differential
rotation profile that is solar-like (i.e., rotation is slower at the poles than
the equator). We demonstrate that the torque is determined by the average
rotation rate in the wind, so that the net torque is less than that predicted
by assuming solid-body rotation at the equatorial rate. The magnitude of the
effect is essentially proportional to the magnitude of the surface differential
rotation, for example, resulting in a torque for the Sun that is $\sim 20 \%$
smaller than predicted by the solid-body assumption. We derive and fit a
semi-analytic formulation that predicts the torque as a function of the
equatorial spin rate, magnitude of differential rotation, and wind
magnetization (depending on the dipolar magnetic field strength and mass-loss
rate, combined).",2111.11082v2
2023-09-21,Trends in torques acting on the star during a star-disk magnetospheric interaction,"We assess the modification of angular momentum transport in various
configurations of star-disk accreting systems based on numerical simulations
with different parameters. We quantify the torques exerted on a star by the
various components of the flow in our simulations of a star-disk magnetospheric
interaction. We obtained results using different stellar rotation rates, dipole
magnetic field strengths, and resistivities. We probed a part of the parameter
space with slowly rotating central objects, up to 20% of the Keplerian rotation
rate at the equator. Different components of the flow in star-disk
magnetospheric interaction were considered in the study: a magnetospheric wind
(i.e., the ``stellar wind'') ejected outwards from the stellar vicinity, matter
infalling onto the star through the accretion column, and a magnetospheric
ejection launched from the magnetosphere. We also took account of trends in the
total torque in the system and in each component individually. We find that for
all the stellar magnetic field strengths, B$_\star$, the anchoring radius of
the stellar magnetic field in the disk is extended with increasing disk
resistivity. The torque exerted on the star is independent of the stellar
rotation rate, $\Omega_\star$, in all the cases without magnetospheric
ejections. In cases where such ejections are present, there is a weak
dependence of the anchoring radius on the stellar rotation rate, with both the
total torque in the system and torque on the star from the ejection and infall
from the disk onto the star proportional to $\Omega_\star B^3$. The torque from
a magnetospheric ejection is proportional to $\Omega_\star^4$. Without the
magnetospheric ejection, the spin-up of the star switches to spin-down in cases
involving a larger stellar field and faster stellar rotation. The critical
value for this switch is about 10% of the Keplerian rotation rate.",2309.12383v1
2011-08-29,"Magnetization Dynamics, Throughput and Energy Dissipation in a Universal Multiferroic Nanomagnetic Logic Gate with Fan-in and Fan-out","The switching dynamics of a multiferroic nanomagnetic NAND gate with
fan-in/fan-out is simulated by solving the Landau-Lifshitz-Gilbert (LLG)
equation while neglecting thermal fluctuation effects. The gate and logic wires
are implemented with dipole-coupled 2-phase (magnetostrictive/piezoelectric)
multiferroic elements that are clocked with electrostatic potentials of ~50 mV
applied to the piezoelectric layer generating 10 MPa stress in the
magnetostrictive layers for switching. We show that a pipeline bit throughput
rate of ~ 0.5 GHz is achievable with proper magnet layout and sinusoidal
four-phase clocking. The gate operation is completed in 2 ns with a latency of
4 ns. The total (internal + external) energy dissipated for a single gate
operation at this throughput rate is found to be only ~ 1000 kT in the gate and
~3000 kT in the 12-magnet array comprising two input and two output wires for
fan-in and fan-out. This makes it respectively 3 and 5 orders of magnitude more
energy-efficient than complementary-metal-oxide-semiconductor-transistor (CMOS)
based and spin-transfer-torque-driven nanomagnet based NAND gates. Finally, we
show that the dissipation in the external clocking circuit can always be
reduced asymptotically to zero using increasingly slow adiabatic clocking, such
as by designing the RC time constant to be 3 orders of magnitude smaller than
the clocking period. However, the internal dissipation in the device must
remain and cannot be eliminated if we want to perform fault-tolerant classical
computing.
  Keywords: Nanomagnetic logic, multiferroics, straintronics and spintronics,
Landau-Lifshitz-Gilbert equation.",1108.5758v1
2012-10-07,Tailoring Magnetism of Perpendicularly Magnetized MnxGa Epitaxial Films on GaAs for Practical Applications,"MnxGa films with high perpendicular anisotropy, coercivity and energy product
have great application potential in ultrahigh-density perpendicular recording,
permanent magnets, spin-transfer-torque memory and oscillators,
magneto-resistance sensors and ferromagnetic metal/semiconductor
heterostructure devices. Here we present a comprehensive diagram of effective
magnetism-tailoring of perpendicularly magnetized MnxGa films grown on III-V
semiconductor GaAs by using molecular-beam epitaxy for the first time, by
systematically investigating the wide-range composition and detailed
post-growth annealing effects. We show that the (001)-orientated MnxGa films
with L10 or D022 ordering could be crystallized on GaAs in a very wide
composition range from x=0.76 to 2.6. L10-ordered MnxGa films show robust
magnetization, high remanent ratio, giant perpendicular anisotropy, high
intrinsic and extrinsic coercivity, and large energy product, which make this
kind of material favorable for perpendicular magnetic recording,
high-performance spintronic devices and permanent magnet applications. In
contrast, D022-ordered films exhibit lower perpendicular anisotropy and weaker
magnetism. Post-growth annealing MnxGa films studies reveal high
thermal-stability up to 450 oC, and effective tailoring of magnetic properties
can be realized by prolonging annealing at 450 oC. These results would be
helpful for understanding this kind of material and designing new spintronic
devices for specific practical applications.",1210.2062v3
2013-09-27,Structural and magnetic properties of Cr-diluted CoFeB,"The crystallization process and the magnetization of Cr diluted CoFeB was
investigated in both ribbon samples and thin film samples with Cr content up to
30 at. %. A primary crystallization of bcc phase from an amorphous precursor in
ribbon samples was observed when the annealing temperature rose to between 421
oC and 456 oC, followed by boron segregation at temperatures between 518 oC and
573 oC. The two onset crystallization temperatures showed strong dependences on
both Cr and B concentrations. The impact of Cr concentration on the magnetic
properties including a reduced saturation magnetization and an enhanced
coercive field was also observed. The magnetizations of both ribbon samples and
thin film samples were well fitted using the generalized Slater-Pauling curve
with modified moments for B (-0.94 {\mu}B) and Cr (-3.6 {\mu}B). Possible
origins of the enhanced coercive field were also discussed. We also achieved a
damping parameter in CoFeCrB thin films at the same level as Co40Fe40B20, much
lower than the value reported for CoFeCrB films previously. The results suggest
a possible advantage of CoFeCrB in reducing the critical switching current
density in Spin Transfer Torque Random Access Memory (STT-RAM).",1309.7331v1
2013-12-12,Post-Newtonian Conservation Laws in Rigid Quasilocal Frames,"In recent work we constructed completely general conservation laws for energy
and linear and angular momentum of extended systems in general relativity based
on the notion of a rigid quasilocal frame (RQF). We argued at a fundamental
level that these RQF conservation laws are superior to conservation laws based
on the local stress-energy-momentum tensor of matter because (1) they do not
rely on spacetime symmetries and (2) they properly account for both matter and
gravitational effects. Moreover, they provide simple, exact, operational
expressions for fluxes of gravitational energy and linear and angular momentum.
In this paper we derive the form of these laws in a general first
post-Newtonian (1PN) approximation, and then apply these approximate laws to
the problem of gravitational tidal interactions. We obtain formulas for tidal
heating and tidal torque that agree with the literature, but without resorting
to the use of pseudotensors. We describe the physical mechanism of these tidal
interactions not in the traditional terms of a Newtonian gravitational force,
but in terms of a much simpler and universal mechanism that is an exact,
quasilocal manifestation of the equivalence principle in general relativity. As
concrete examples, we look at the tidal heating of Jupiter's moon Io and
angular momentum transfer in the Earth-Moon system that causes a gradual
spin-down of the Earth and recession of the Moon. In both examples we find
agreement with observation.",1312.3617v2
2015-12-02,Dramatic pressure-driven enhancement of bulk skyrmion stability,"The recent discovery of magnetic skyrmion lattices initiated a surge of
interest in the scientific community. Several novel phenomena have been shown
to emerge from the interaction of conducting electrons with the skyrmion
lattice, such as a topological Hall-effect and a spin-transfer torque at
ultra-low current densities. In the insulating compound Cu2OSeO3,
magneto-electric coupling enables control of the skyrmion lattice via electric
fields, promising a dissipation-less route towards novel spintronic devices.
One of the outstanding fundamental issues is related to the thermodynamic
stability of the skyrmion lattice. To date, the skyrmion lattice in bulk
materials has been found only in a narrow temperature region just below the
order-disorder transition. If this narrow stability is unavoidable, it would
severely limit applications. Here we present the discovery that applying just
moderate pressure on Cu2OSeO3 substantially increases the absolute size of the
skyrmion pocket. This insight demonstrates directly that tuning the electronic
structure can lead to a significant enhancement of the skyrmion lattice
stability. We interpret the discovery by extending the previously employed
Ginzburg-Landau approach and conclude that change in the anisotropy is the main
driver for control of the size of the skyrmion pocket. This realization
provides an important guide for tuning the properties of future skyrmion
hosting materials.",1512.00633v1
2016-05-07,Giant interfacial perpendicular magnetic anisotropy in MgO/CoFe/capping layer structures,"Magnetic tunnel junction (MTJ) based on CoFeB/MgO/CoFeB structures is of
great interest due to its application in the spin-transfer-torque magnetic
random access memory (STT-MRAM). Large interfacial perpendicular magnetic
anisotropy (PMA) is required to achieve high thermal stability. Here we use
first-principles calculations to investigate the magnetic anisotropy energy
(MAE) of MgO/CoFe/capping layer structures, where the capping materials include
5d metals Hf, Ta, Re, Os, Ir, Pt, Au and 6p metals Tl, Pb, Bi. We demonstrate
that it is feasible to enhance PMA by using proper capping materials.
Relatively large PMA is found in the structures with capping materials of Hf,
Ta, Os, Ir and Pb. More importantly, the MgO/CoFe/Bi structure gives rise to
giant PMA (6.09 mJ/m2), which is about three times larger than that of the
MgO/CoFe/Ta structure. The origin of the MAE is elucidated by examining the
contributions to MAE from each atomic layer and orbital. These findings provide
a comprehensive understanding of the PMA and point towards the possibility to
achieve advanced-node STT-MRAM with high thermal stability.",1605.02247v5
2016-06-01,Attack resilient architecture to replace embedded Flash with STTRAM in homogeneous IoTs,"Spin-Transfer Torque RAM (STTRAM) is an emerging Non-Volatile Memory (NVM)
technology that provides better endurance, write energy and performance than
traditional NVM technologies such as Flash. In embedded application such as
microcontroller SoC of Internet of Things (IoT), embedded Flash (eFlash) is
widely employed. However, eFlash is also associated with cost. Therefore,
replacing eFlash with STTRAM is desirable in IoTs for power-efficiency.
Although promising, STTRAM brings several new security and privacy challenges
that pose a significant threat to sensitive data in memory. This is inevitable
due to the underlying dependency of this memory technology on environmental
parameters such as temperature and magnetic fields that can be exploited by an
adversary to tamper with the program and data. In this paper, we investigate
these attacks and propose a novel memory architecture for attack resilient IoT
network. The information redundancy present in a homogeneous peer-to-peer
connected IoT network is exploited to restore the corrupted memory of any IoT
node when under attack. We are able to build a failsafe IoT system with STTRAM
based program memory which allows guaranteed execution of all the IoT nodes
without complete shutdown of any node under attack. Experimental results using
commercial IoT boards demonstrate the latency and energy overhead of the attack
recovery process.",1606.00467v1
2016-07-27,Read-Tuned STT-RAM and eDRAM Cache Hierarchies for Throughput and Energy Enhancement,"As capacity and complexity of on-chip cache memory hierarchy increases, the
service cost to the critical loads from Last Level Cache (LLC), which are
frequently repeated, has become a major concern. The processor may stall for a
considerable interval while waiting to access the data stored in the cache
blocks in LLC, if there are no independent instructions to execute. To provide
accelerated service to the critical loads requests from LLC, this work
concentrates on leveraging the additional capacity offered by replacing
SRAM-based L2 with Spin-Transfer Torque Random Access Memory (STT-RAM) to
accommodate frequently accessed cache blocks in exclusive read mode in favor of
reducing the overall read service time. Our proposed technique partitions L2
cache into two STT-RAM arrangements with different write performance and data
retention time. The retention-relaxed STT-RAM arrays are utilized to
effectively deal with the regular L2 cache requests while the high retention
STT-RAM arrays in L2 are selected for maintaining repeatedly read accessed
cache blocks from LLC by incurring negligible energy consumption for data
retention. Our experimental results show that the proposed technique can reduce
the mean L2 read miss ratio by 51.4% and increase the IPC by 11.7% on average
across PARSEC benchmark suite while significantly decreasing the total L2
energy consumption compared to conventional SRAM-based L2 design.",1607.08086v2
2016-10-26,Skyrmion production on demand by homogeneous DC currents,"Topological magnetic textures - like skyrmions - have become a major player
in the design of next-generation magnetic storage technology due to their
stability and the control of their motion by ultra-low current densities. A
major challenge to develop this new skyrmion-based technology is to achieve the
controlled and deterministic creation of magnetic skyrmions without the need of
complex setups. We demonstrate a solution to this challenge by showing how to
create skyrmions and other magnetic textures in ferromagnetic thin films by
means of a homogeneous DC current and without requiring Dzyaloshinskii-Moriya
interactions. This is possible by exploiting a static loss of stability arising
from the interplay of current-induced spin-transfer torque and a spatially
inhomogeneous magnetization, which can be achieved, e.g., by locally
engineering the anisotropy, the magnetic field, or other magnetic interactions.
The magnetic textures are created controllably, efficiently, and periodically
with a period that can be tuned by the applied current strength. We propose
specific experimental setups realizable with simple materials, such as cobalt
based materials, to observe the periodic formation of skyrmions. We show that
adding chiral interactions will not influence the basics of the generations but
then influence the consequent dynamics with respect to the stabilization of
topological textures. Our findings allow for the production of skyrmions on
demand in simple ferromagnetic thin films by homogeneous DC currents.",1610.08313v2
2017-08-14,Current-induced magnetization switching in atom-thick tungsten engineered perpendicular magnetic tunnel junctions with large tunnel magnetoresistance,"Perpendicular magnetic tunnel junctions based on MgO/CoFeB structures are of
particular interest for magnetic random-access memories because of their
excellent thermal stability, scaling potential, and power dissipation. However,
the major challenge of current-induced switching in the nanopillars with both a
large tunnel magnetoresistance ratio and a low junction resistance is still to
be met. Here, we report spin transfer torque switching in nano-scale
perpendicular magnetic tunnel junctions with a magnetoresistance ratio up to
249% and a resistance area product as low as 7.0 {\Omega}.{\mu}m2, which
consists of atom-thick W layers and double MgO/CoFeB interfaces. The efficient
resonant tunnelling transmission induced by the atom-thick W layers could
contribute to the larger magnetoresistance ratio than conventional structures
with Ta layers, in addition to the robustness of W layers against high
temperature diffusion during annealing. The switching critical current density
could be lower than 3.0 MA.cm-2 for devices with a 45 nm radius.",1708.04111v3
2018-03-07,Highly thermally stable sub-20nm magnetic random-access memory based on perpendicular shape anisotropy,"A new approach to increase the downsize scalability of perpendicular STT-MRAM
is presented. It consists in significantly increasing the thickness of the
storage layer in out-of-plane magnetized tunnel junctions (pMTJ) as compared to
conventional pMTJ in order to induce a perpendicular shape anisotropy (PSA) in
this layer. This PSA is obtained by depositing a thick ferromagnetic (FM) layer
on top of an MgO/FeCoB based magnetic tunnel junction (MTJ) so that the
thickness of the storage layer becomes of the order or larger than the diameter
of the MTJ pillar. In contrast to conventional spin transfer torque magnetic
random access memory (STT-MRAM) wherein the demagnetizing energy opposes the
interfacial perpendicular magnetic anisotropy (iPMA), in these novel memory
cells, both PSA and iPMA contributions favor out-of-plane orientation of the
storage layer magnetization. Using thicker storage layers in these PSA-STT-MRAM
has several advantages. Thanks to the PSA, very high and easily tunable thermal
stability factors can be achieved, even down to sub-10 nm diameters. Moreover,
low damping material can be used for the thick FM material thus leading to a
reduction of the write current. The paper describes this new PSA-STT-MRAM
concept, practical realization of such memory arrays, magnetic characterization
demonstrating thermal stability factor above 200 for MTJs as small as 8nm in
diameter and possibility to maintain thermal stability factor above 60 down to
4nm diameter.",1803.02663v1
2018-12-03,Current-Driven Dynamics of Frustrated Skyrmions in a Synthetic Antiferromagnetic Bilayer,"We report the current-driven dynamics of frustrated skyrmions in an
antiferromagnetically exchange coupled bilayer system, where the bilayer
skyrmion consists of two monolayer skyrmions with opposite skyrmion numbers
$Q$. We show that the in-plane current-driven bilayer skyrmion moves in a
straight path, while the out-of-plane current-driven bilayer skyrmion moves in
a circular path. It is found that the in-plane current-driven mobility of a
bilayer skyrmion is much better than the monolayer one at a large ratio of
$\beta/\alpha$, where $\alpha$ and $\beta$ denote the damping parameter and
non-adiabatic spin transfer torque strength, respectively. Besides, the
out-of-plane current-driven mobility of a bilayer skyrmion is much better than
the monolayer one when $\alpha$ is small. We also reveal that one bilayer
skyrmion (consisting of monolayer skyrmions with $Q=\pm 2$) can be separated to
two bilayer skyrmions (consisting of monolayer skyrmions with $Q=\pm 1$) driven
by an out-of-plane current. Our results may be useful for designing skyrmionic
devices based on frustrated multilayer magnets.",1812.00520v2
2016-03-20,Cache Bypassing and Checkpointing to Circumvent Data Security Attacks on STTRAM,"Spin-Transfer Torque RAM (STTRAM) is promising for cache applications.
However, it brings new data security issues that were absent in volatile memory
counterparts such as Static RAM (SRAM) and embedded Dynamic RAM (eDRAM). This
is primarily due to the fundamental dependency of this memory technology on
ambient parameters such as magnetic field and temperature that can be exploited
to tamper with the stored data. In this paper we propose three techniques to
enable error free computation without stalling the system, (a) stalling where
the system is halted during attack; (b) cache bypass during gradually ramping
attack where the last level cache (LLC) is bypassed and the upper level caches
interact directly with the main memory; and, (c) checkpointing along with
bypass during sudden attack where the processor states are saved periodically
and the LLC is written back at regular intervals. During attack the system goes
back to the last checkpoint and the computation continues with bypassed cache.
We performed simulation for different duration and frequency of attack on
SPLASH benchmark suite and the results show an average of 8% degradation in IPC
for a one-time attack lasting for 50% of the execution time. The energy
overhead is 2% for an attack lasting for the entire duration of execution.",1603.06227v1
2019-05-18,HALLS: An Energy-Efficient Highly Adaptable Last Level STT-RAM Cache for Multicore Systems,"Spin-Transfer Torque RAM (STT-RAM) is widely considered a promising
alternative to SRAM in the memory hierarchy due to STT-RAM's non-volatility,
low leakage power, high density, and fast read speed. The STT-RAM's small
feature size is particularly desirable for the last-level cache (LLC), which
typically consumes a large area of silicon die. However, long write latency and
high write energy still remain challenges of implementing STT-RAMs in the CPU
cache. An increasingly popular method for addressing this challenge involves
trading off the non-volatility for reduced write speed and write energy by
relaxing the STT-RAM's data retention time. However, in order to maximize
energy saving potential, the cache configurations, including STT-RAM's
retention time, must be dynamically adapted to executing applications' variable
memory needs. In this paper, we propose a highly adaptable last level STT-RAM
cache (HALLS) that allows the LLC configurations and retention time to be
adapted to applications' runtime execution requirements. We also propose
low-overhead runtime tuning algorithms to dynamically determine the best
(lowest energy) cache configurations and retention times for executing
applications. Compared to prior work, HALLS reduced the average energy
consumption by 60.57% in a quad-core system, while introducing marginal latency
overhead.",1905.07511v1
2020-03-05,Angular momentum and rotational energy of meanflows in toroidal magnetic fields,"We derive the balance equation for the Favre averaged angular momentum in
toroidal not necessarily axisymmetric magnetic field equilibria. We find that
the components of angular momentum are given by the covariant poloidal and
toroidal components of ExB and parallel flow velocities and we separately
identify all relevant stress tensors, torques and source terms for each of
these components. Our results feature the Favre stress generalisations of
previously found Reynolds stresses like the diamagnetic or parallel ExB stress,
as well as the density gradient drive term. Further, we identify the magnetic
shear as a source of poloidal ExB angular momentum and discuss the mirror and
the Lorentz force. Here, we find that the geodesic transfer term, the
Stringer-Winsor spin-up term and the ion-orbit loss term are all part of the
Lorentz force and are in fact one and the same term.
  Discussing the relation to angular velocity we build the inertia tensor with
the help of the first fundamental form of a flux-surface. In turn, the inertia
tensor is used to construct a flux-surface averaged rotational energy for \ExB
surface flows of the plasma. The evolution of this rotational energy features a
correction of previous results due to the inertia tensor. In particular, this
correction suggests that density sources on the high-field side contribute much
more to zonal flow energy generation than on the low field side.",2003.02707v2
2020-09-24,A Study of Runtime Adaptive Prefetching for STTRAM L1 Caches,"Spin-Transfer Torque RAM (STTRAM) is a promising alternative to SRAM in
on-chip caches due to several advantages. These advantages include
non-volatility, low leakage, high integration density, and CMOS compatibility.
Prior studies have shown that relaxing and adapting the STTRAM retention time
to runtime application needs can substantially reduce overall cache energy
without significant latency overheads, due to the lower STTRAM write energy and
latency in shorter retention times. In this paper, as a first step towards
efficient prefetching across the STTRAM cache hierarchy, we study prefetching
in reduced retention STTRAM L1 caches. Using SPEC CPU 2017 benchmarks, we
analyze the energy and latency impact of different prefetch distances in
different STTRAM cache retention times for different applications. We show that
expired_unused_prefetches---the number of unused prefetches expired by the
reduced retention time STTRAM cache---can accurately determine the best
retention time for energy consumption and access latency. This new metric can
also provide insights into the best prefetch distance for memory bandwidth
consumption and prefetch accuracy. Based on our analysis and insights, we
propose Prefetch-Aware Retention time Tuning (PART) and Retention time-based
Prefetch Control (RPC). Compared to a base STTRAM cache, PART and RPC
collectively reduced the average cache energy and latency by 22.24% and 24.59%,
respectively. When the base architecture was augmented with the
state-of-the-art near-side prefetch throttling (NST), PART+RPC reduced the
average cache energy and latency by 3.50% and 3.59%, respectively, and reduced
the hardware overhead by 54.55%",2009.11442v1
2021-10-08,Proposal of Analog In-Memory Computing with Magnified Tunnel Magnetoresistance Ratio and Universal STT-MRAM Cell,"In-memory computing (IMC) is an effectual solution for energy-efficient
artificial intelligence applications. Analog IMC amortizes the power
consumption of multiple sensing amplifiers with analog-to-digital converter
(ADC), and simultaneously completes the calculation of multi-line data with
high parallelism degree. Based on a universal one-transistor one-magnetic
tunnel junction (MTJ) spin transfer torque magnetic RAM (STT-MRAM) cell, this
paper demonstrates a novel tunneling magnetoresistance (TMR) ratio magnifying
method to realize analog IMC. Previous concerns include low TMR ratio and
analog calculation nonlinearity are addressed using device-circuit interaction.
Peripheral circuits are minimally modified to enable in-memory matrix-vector
multiplication. A current mirror with feedback structure is implemented to
enhance analog computing linearity and calculation accuracy. The proposed
design maximumly supports 1024 2-bit input and 1-bit weight
multiply-and-accumulate (MAC) computations simultaneously. The 2-bit input is
represented by the width of the input (IN) pulses, while the 1-bit weight is
stored in STT-MRAM and the x7500 magnified TMR (m-TMR) ratio is obtained by
latching. The proposal is simulated using 28-nm CMOS process and MTJ compact
model. The integral nonlinearity is reduced by 57.6% compared with the
conventional structure. 9.47-25.4 TOPS/W is realized with 2-bit input, 1-bit
weight and 4-bit output convolution neural network (CNN).",2110.03937v1
2019-01-15,Anomalous Hall Conductivity of a Non-Collinear Magnetic Antiperovskite,"The anomalous Hall effect (AHE) is a well-known fundamental property of
ferromagnetic metals, commonly associated with the presence of a net
magnetization. Recently, an AHE has been discovered in non-collinear
antiferromagnetic (AFM) metals. Driven by non-vanishing Berry curvature of AFM
materials with certain magnetic space group symmetry, anomalous Hall
conductivity (AHC) is very sensitive to the specific type of magnetic ordering.
Here, we investigate the appearance of AHC in antiperovskite GaNMn$_{3}$ as a
representative of broader materials family ANMn$_{3}$ (A is a main group
element), where different types of non-collinear magnetic ordering can emerge.
Using symmetry analyses and first-principles density-functional theory
calculations, we show that with almost identical band structure, the nearly
degenerate non-collinear AFM $\Gamma_{5g}$ and $\Gamma_{4g}$ phases of
GaNMn$_{3}$ have zero and finite AHC, respectively. In a non-collinear
ferrimagnetic $M$-1 phase, GaNMn$_{3}$ exhibits a large AHC due to the presence
of a sizable net magnetic moment. In the non-collinear antiperovskite magnets,
transitions between different magnetic phases, exhibiting different AHC states,
can be produced by doping, strain, or spin transfer torque, which makes these
materials promising for novel spintronic applications.",1901.05040v1
2019-01-25,Gravitational waves from dynamical tides in white dwarf binaries,"We study the effect of tidal forcing on gravitational wave signals from
tidally relaxed white dwarf pairs in the LISA, DECIGO and BBO frequency band
($0.1-100\,{\rm mHz}$). We show that for stars not in hydrostatic equilibrium
(in their own rotating frames), tidal forcing will result in energy and angular
momentum exchange between the orbit and the stars, thereby deforming the orbit
and producing gravitational wave power in harmonics not excited in perfectly
circular synchronous binaries. This effect is not present in the usual
orbit-averaged treatment of the equilibrium tide, and is analogous to transit
timing variations in multiplanet systems. It should be present for all LISA
white dwarf pairs since gravitational waves carry away angular momentum faster
than tidal torques can act to synchronize the spins, and when mass transfer
occurs as it does for at least eight LISA verification binaries. With the
strain amplitudes of the excited harmonics depending directly on the density
profiles of the stars, gravitational wave astronomy offers the possibility of
studying the internal structure of white dwarfs, complimenting information
obtained from asteroseismology of pulsating white dwarfs. Since the vast
majority of white-dwarf pairs in this frequency band are expected to be in the
quasi-circular state, we focus here on these binaries, providing general
analytic expressions for the dependence of the induced eccentricity and strain
amplitudes on the stellar apsidal motion constants and their radius and mass
ratios. Tidal dissipation and gravitation wave damping will affect the results
presented here and will be considered elsewhere.",1901.09045v2
2019-07-17,A Nanomagnetic Voltage-Tunable Correlation Generator between Two Random Bit Streams for Stochastic Computing,"Graphical probabilistic circuit models of stochastic computing are more
powerful than the predominant deep learning models, but also have more
demanding requirements. For example, they require ""programmable stochasticity"",
e.g. generating two random binary bit streams with tunable amount of
correlation between the corresponding bits in the two streams. Electronic
implementation of such a system would call for several components leaving a
large footprint on a chip and dissipating excessive amount of energy. Here, we
show an elegant implementation with just two dipole-coupled magneto-tunneling
junctions (MTJ), with magnetostrictive soft layers, fabricated on a
piezoelectric film. The resistance states of the two MTJs (high or low) encode
the bits in the two streams. The first MTJ is driven to a random resistance
state via a current or voltage generating spin transfer torque and/or voltage
controlled magnetic anisotropy, while the second MTJ's resistance state is
determined solely by dipole coupling with the first. The effect of dipole
coupling can be varied with local strain applied to the second MTJ with a local
voltage (~0.2 V) and that varies the correlation between the resistance states
of the two MTJs and hence between the bits in the two streams (from 0% to
100%). This paradigm can be extended to arbitrary number of bit streams.",1907.07532v1
2019-09-25,Immunity of nanoscale magnetic tunnel junctions to ionizing radiation,"Spin transfer torque magnetic random access memory (STT-MRAM) is a promising
candidate for next generation memory as it is non-volatile, fast, and has
unlimited endurance. Another important aspect of STT-MRAM is that its core
component, the nanoscale magnetic tunneling junction (MTJ), is thought to be
radiation hard, making it attractive for space and nuclear technology
applications. However, studies of the effects of high doses of ionizing
radiation on STT-MRAM writing process are lacking. Here we report measurements
of the impact of high doses of gamma and neutron radiation on nanoscale MTJs
with perpendicular magnetic anistropy used in STT-MRAM. We characterize the
tunneling magnetoresistance, the magnetic field switching, and the
current-induced switching before and after irradiation. Our results demonstrate
that all these key properties of nanoscale MTJs relevant to STT-MRAM
applications are robust against ionizing radiation. Additionally, we perform
experiments on thermally driven stochastic switching in the gamma ray
environment. These results indicate that nanoscale MTJs are promising building
blocks for radiation-hard non-von Neumann computing.",1909.11360v1
2021-05-13,Comprehensive Study of Security and Privacy of Emerging Non-Volatile Memories,"At the end of Silicon roadmap, keeping the leakage power in tolerable limit
and bridging the bandwidth gap between processor and memory have become some of
the biggest challenges. Several promising Non-Volatile Memories (NVMs) such as,
Spin-Transfer Torque RAM (STTRAM), Magnetic RAM (MRAM), Phase Change Memory
(PCM), Resistive RAM (RRAM) and Ferroelectric RAM (FeRAM) are being
investigated to address the above issues since they offer high density and
consumes zero leakage power. On one hand, the desirable properties of emerging
NVMs make them suitable candidates for several applications including
replacement of conventional memories. On the other hand, their unique
characteristics such as, high and asymmetric read/write current and persistence
bring new threats to data security and privacy. Some of these memories are
already deployed in full systems and as discrete chips and are believed to
become ubiquitous in future computing devices. Therefore, it is of utmost
important to investigate their security and privacy issues. Note that these
NVMs can be considered for cache, main memory or storage application. They are
also suitable to implement in-memory computation which increases system
throughput and eliminates Von-Neumann Bottleneck. Compute-capable NVMs impose
new security and privacy challenges that are fundamentally different than their
storage counterpart. This work identifies NVM vulnerabilities, attack vectors
originating from device level all the way to circuits and systems considering
both storage and compute applications. We also summarize the circuit/system
level countermeasures to make the NVMs robust against security and privacy
issues.",2105.06401v1
2021-06-15,Low-Energy and CPA-Resistant Adiabatic CMOS/MTJ Logic for IoT Devices,"The tremendous growth in the number of Internet of Things (IoT) devices has
increased focus on the energy efficiency and security of an IoT device. In this
paper, we will present a design level, non-volatile adiabatic architecture for
low-energy and Correlation Power Analysis (CPA) resistant IoT devices. IoT
devices constructed with CMOS integrated circuits suffer from high dynamic
energy and leakage power. To solve this, we look at both adiabatic logic and
STT-MTJs (Spin Transfer Torque Magnetic Tunnel Junctions) to reduce both
dynamic energy and leakage power. Furthermore, CMOS integrated circuits suffer
from side-channel leakage making them insecure against power analysis attacks.
We again look to adiabatic logic to design secure circuits with uniform power
consumption, thus, defending against power analysis attacks. We have developed
a hybrid adiabatic- MTJ architecture using two-phase adiabatic logic. We show
that hybrid adiabatic-MTJ circuits are both low energy and secure when compared
with CMOS circuits. As a case study, we have constructed one round of PRESENT
and have shown energy savings of 64.29% at a frequency of 25 MHz. Furthermore,
we have performed a correlation power analysis attack on our proposed design
and determined that the key was kept hidden.",2106.07855v1
2022-01-08,A System-Level Framework for Analytical and Empirical Reliability Exploration of STT-MRAM Caches,"Spin-Transfer Torque Magnetic RAM (STT-MRAM) is known as the most promising
replacement for SRAM technology in large Last-Level Caches (LLCs). Despite its
high-density, non-volatility, near-zero leakage power, and immunity to
radiation as the major advantages, STT-MRAM-based cache suffers from high error
rates mainly due to retention failure, read disturbance, and write failure.
Existing studies are limited to estimating the rate of only one or two of these
error types for STT-MRAM cache. However, the overall vulnerability of STT-MRAM
caches, which its estimation is a must to design cost-efficient reliable
caches, has not been offered in any of previous studies. In this paper, we
propose a system-level framework for reliability exploration and
characterization of errors behavior in STT-MRAM caches. To this end, we
formulate the cache vulnerability considering the inter-correlation of the
error types including all three errors as well as the dependency of error rates
to workloads behavior and Process Variations (PVs). Our analysis reveals that
STT-MRAM cache vulnerability is highly workload-dependent and varies by orders
of magnitude in different cache access patterns. Our analytical study also
shows that this vulnerability divergence significantly increases by process
variations in STT-MRAM cells. To evaluate the framework, we implement the error
types in the gem5 full-system simulator, and the experimental results show that
the total error rate in a shared LLC varies by 32.0x for different workloads. A
further 6.5x vulnerability variation is observed when considering PVs in the
STT-MRAM cells. In addition, the contribution of each error type in total LLC
vulnerability highly varies in different cache access patterns and moreover,
error rates are differently affected by PVs.",2201.02855v1
2022-02-02,Direct observation of the perpendicular shape anisotropy and thermal stability of p-STT-MRAM nano-pillars,"Perpendicular shape anisotropy (PSA) offers a practical solution to downscale
spin-transfer torque Magnetic Random-Access Memory (STT-MRAM) beyond the sub-20
nm technology node whilst retaining thermal stability of the storage layer
magnetization. However, our understanding of the thermomagnetic behavior of
PSA-STT-MRAM is often indirect, relying on magnetoresistance measurements and
micromagnetic modelling. Here, the magnetism of a FeCoB / NiFe PSA-STT-MRAM
nano-pillar is investigated using off-axis electron holography, providing
spatially resolved magnetic information as a function of temperature, which has
been previously inaccessible. Magnetic induction maps reveal the micromagnetic
configuration of the NiFe storage layer (60 nm high, 20 nm diameter),
confirming the PSA induced by its 3:1 aspect ratio. In-situ heating
demonstrates that the PSA of the FeCoB / NiFe composite storage layer is
maintained up to at least 250 degrees centigrade, and direct quantitative
measurements reveal the very moderate decrease of magnetic induction with
temperature. Hence, this study shows explicitly that PSA provides significant
stability in STT-MRAM applications that require reliable performance over a
range of operating temperatures.",2202.01065v1
2022-03-14,Distributed On-Sensor Compute System for AR/VR Devices: A Semi-Analytical Simulation Framework for Power Estimation,"Augmented Reality/Virtual Reality (AR/VR) glasses are widely foreseen as the
next generation computing platform. AR/VR glasses are a complex ""system of
systems"" which must satisfy stringent form factor, computing-, power- and
thermal- requirements. In this paper, we will show that a novel distributed
on-sensor compute architecture, coupled with new semiconductor technologies
(such as dense 3D-IC interconnects and Spin-Transfer Torque Magneto Random
Access Memory, STT-MRAM) and, most importantly, a full hardware-software
co-optimization are the solutions to achieve attractive and socially acceptable
AR/VR glasses. To this end, we developed a semi-analytical simulation framework
to estimate the power consumption of novel AR/VR distributed on-sensor
computing architectures. The model allows the optimization of the main
technological features of the system modules, as well as the computer-vision
algorithm partition strategy across the distributed compute architecture. We
show that, in the case of the compute-intensive machine learning based Hand
Tracking algorithm, the distributed on-sensor compute architecture can reduce
the system power consumption compared to a centralized system, with the
additional benefits in terms of latency and privacy.",2203.07474v1
2022-04-20,Adjusting Thermal Stability in Double-Barrier MTJ for Energy Improvement in Cryogenic STT-MRAMs,"This paper investigates the impact of thermal stability relaxation in
double-barrier magnetic tunnel junctions (DMTJs) for energy-efficient
spin-transfer torque magnetic random access memories (STT-MRAMs) operating at
the liquid nitrogen boiling point (77K). Our study is carried out through a
macrospin-based Verilog-A compact model of DMTJ, along with a 65nm commercial
process design kit (PDK) calibrated down to 77K under silicon measurements.
Comprehensive bitcell-level electrical characterization is used to estimate the
energy/latency per operation and leakage power at the memory
architecture-level. As a main result of our analysis, we show that
energy-efficient small-to-large embedded memories can be obtained by
significantly relaxing the non-volatility requirement of DMTJ devices at room
temperature (i.e., by reducing the cross-section area), while maintaining the
typical 10-years retention time at cryogenic temperatures. This makes
DMTJ-based STT-MRAM operating at 77K more energy-efficient than six-transistors
static random-access memory (6T-SRAM) under both read and write accesses (-56%
and -37% on average, respectively). Obtained results thus prove that DMTJ-based
STT-MRAM with relaxed retention time is a promising alternative for the
realization of reliable and energy-efficient embedded memories operating at
cryogenic temperatures.",2204.09395v1
2022-11-30,A proposal for leaky integrate-and-fire neurons by domain walls in antiferromagnetic insulators,"Brain-inspired neuromorphic computing is a promising path towards next
generation analogue computers that are fundamentally different compared to the
conventional von Neumann architecture. One model for neuromorphic computing
that can mimic the human brain behavior are spiking neural networks (SNNs), of
which one of the most successful is the leaky integrate-and-fire (LIF) model.
Since conventional complementary metal-oxide-semiconductor (CMOS) devices are
not meant for modelling neural networks and are energy inefficient in network
applications, recently the focus shifted towards spintronic-based neural
networks. In this work, using the advantage of antiferromagnetic insulators, we
propose a non-volatile magnonic neuron that could be the building block of a
LIF spiking neuronal network. In our proposal, an antiferromagnetic domain wall
in the presence of a magnetic anisotropy gradient mimics a biological neuron
with leaky, integrating, and firing properties. This single neuron is
controlled by polarized antiferromagnetic magnons, activated by either a
magnetic field pulse or a spin transfer torque mechanism, and has properties
similar to biological neurons, namely latency, refraction, bursting and
inhibition. We argue that this proposed single neuron, based on
antiferromagnetic domain walls, is faster and has more functionalities compared
to previously proposed neurons based on ferromagnetic systems.",2211.16845v2
2023-01-01,Effect of Edge Roughness on resistance and switching voltage of Magnetic Tunnel Junctions,"We investigate the impact of edge roughness on the electrical transport
properties of magnetic tunnel junctions using non-equilibrium Greens function
formalism. We have modeled edge roughness as a stochastic variation in the
cross-sectional profile of magnetic tunnel junction characterized by the
stretched exponential decay of the correlation function. The stochastic
variation in the shape and size changes the transverse energy mode profile and
gives rise to the variations in the resistance and switching voltage of the
magnetic tunnel junction. We find that the variations are larger as the
magnetic tunnel junction size is scaled down due to the quantum confinement
effect. A model is proposed for the efficient calculation of edge roughness
effects by approximating the cross-sectional geometry to a circle with the same
cross-sectional area. Further improvement can be obtained by approximating the
cross-sectional area to an ellipse with an aspect ratio determined by the first
transverse eigenvalue corresponding to the 2D cross section. These results
would be useful for reliable design of the spin transfer torque-magnetic random
access memory (STT-MRAM) with ultra-small magnetic tunnel junctions.",2301.00318v1
2023-05-17,Skyrmion-mediated Nonvolatile Ternary Memory,"Multistate memory systems have the ability to store and process more data in
the same physical space as binary memory systems, making them a potential
alternative to existing binary memory systems. In the past, it has been
demonstrated that voltage-controlled magnetic anisotropy (VCMA) based writing
is highly energy-efficient compared to other writing methods used in
non-volatile nano-magnetic binary memory systems. In this study, we introduce a
new, VCMA-based and skyrmion-mediated non-volatile ternary memory system using
a perpendicular magnetic tunnel junction (p-MTJ) in the presence of room
temperature thermal perturbation. We have also shown that ternary states {-1,
0, +1} can be implemented with three magnetoresistance values obtained from a
p-MTJ corresponding to ferromagnetic up, down, and skyrmion state, with 99%
switching probability in the presence of room temperature thermal noise in an
energy-efficient way, requiring ~3 fJ energy on an average for each switching
operation. Additionally, we show that our proposed ternary memory demonstrates
an improvement in area and energy by at least 2X and ~60X respectively,
compared to state-of-the-art spin-transfer torque (STT)-based non-volatile
magnetic multistate memories. Furthermore, these three states can be
potentially utilized for energy-efficient, high-density in-memory quantized
deep neural network implementation.",2305.09950v1
2023-11-08,A Lightweight Architecture for Real-Time Neuronal-Spike Classification,"Electrophysiological recordings of neural activity in a mouse's brain are
very popular among neuroscientists for understanding brain function. One
particular area of interest is acquiring recordings from the Purkinje cells in
the cerebellum in order to understand brain injuries and the loss of motor
functions. However, current setups for such experiments do not allow the mouse
to move freely and, thus, do not capture its natural behaviour since they have
a wired connection between the animal's head stage and an acquisition device.
In this work, we propose a lightweight neuronal-spike detection and
classification architecture that leverages on the unique characteristics of the
Purkinje cells to discard unneeded information from the sparse neural data in
real time. This allows the (condensed) data to be easily stored on a removable
storage device on the head stage, alleviating the need for wires. Synthesis
results reveal a >95% overall classification accuracy while still resulting in
a small-form-factor design, which allows for the free movement of mice during
experiments. Moreover, the power-efficient nature of the design and the usage
of STT-RAM (Spin Transfer Torque Magnetic Random Access Memory) as the
removable storage allows the head stage to easily operate on a tiny battery for
up to approximately 4 days.",2311.04808v2
2023-12-29,RHS-TRNG: A Resilient High-Speed True Random Number Generator Based on STT-MTJ Device,"High-quality random numbers are very critical to many fields such as
cryptography, finance, and scientific simulation, which calls for the design of
reliable true random number generators (TRNGs). Limited by entropy source,
throughput, reliability, and system integration, existing TRNG designs are
difficult to be deployed in real computing systems to greatly accelerate target
applications. This study proposes a TRNG circuit named RHS-TRNG based on
spin-transfer torque magnetic tunnel junction (STT-MTJ). RHS-TRNG generates
resilient and high-speed random bit sequences exploiting the stochastic
switching characteristics of STT-MTJ. By circuit/system co-design, we integrate
RHS-TRNG into a RISC-V processor as an acceleration component, which is driven
by customized random number generation instructions. Our experimental results
show that a single cell of RHS-TRNG has a random bit generation speed of up to
303 Mb/s, which is the highest among existing MTJ-based TRNGs. Higher
throughput can be achieved by exploiting cell-level parallelism. RHS-TRNG also
shows strong resilience against PVT variations thanks to our designs using
bidirectional switching currents and dual generator units. In addition, our
system evaluation results using gem5 simulator suggest that the system equipped
with RHS-TRNG can achieve 3.4-12x higher performance in speeding up option
pricing programs than software implementations of random number generation.",2312.17453v1
2024-01-03,Spin-Transfer-Torque Induced Spatially Nonuniform Switching in Ferrimagnets,"Ferrimagnet (FiM), (FeCo)1-xGdx, attracts research attention due to its
ultrafast magnetic dynamics and finite net magnetization. Incorporating FiM
into the magnetic tunnel junction will be beneficial to further improve the
writing speed of magnetic random access memory (MRAM). It is commonly assumed
that the FeCo and Gd atoms are switched together due to the strong exchange
coupling, which remains valid even if one performs the two-sublattice macrospin
simulation. Interestingly, using the atomistic model developed by our group, it
is clearly seen that different atoms are not switched together. In addition,
our study reveals that the nature of switching is spatially nonuniform even in
the small sample with the dimension of 20 nm-20 nm. Furthermore, the
characteristics of nonuniformity are completely different for samples with
different Gd composition (x). When x is close to the magnetization compensation
point, successful switching cannot be obtained, but is accompanied by the
stable oscillation. The atom type that dominates the oscillation is different
from that predicted by the two-sublattice macrospin model. In addition, the
size of singular region is a non-monotonic function of current density. All
these results can only be understood by considering the spatial nonuniform
magnetization dynamics.",2401.01741v1
2024-02-24,Energy landscape of noncollinear exchange coupled magnetic multilayers,"We conduct an exploration of the energy landscape of two coupled
ferromagnetic layers with perpendicular-to-plane uniaxial anisotropy using
finite-element micromagnetic simulations. These multilayers can be used to
produce noncollinearity in spin-transfer torque magnetic random-access memory
cells, which has been shown to increase the performance of this class of
computer memory. We show that there exists a range of values of the interlayer
exchange coupling constants for which the magnetic state of these multilayers
can relax into two energy minima. The size of this region is determined by the
difference in the magnitude of the layer anisotropies and is minimized when
this difference is large. In this case, there is a wide range of experimentally
achievable coupling constants that can produce desirable and stable
noncollinear alignment. We investigate the energy barriers separating the local
and global minima using string method simulations, showing that the stabilities
of the minima increase with increasing difference in the anisotropy of the
ferromagnetic layers. We provide an analytical solution to the location of the
minima in the energy landscape of coupled macrospins, which has good agreement
with our micromagnetic results for a case involving ferromagnetic layers with
the same thickness and anisotropy, no demagnetization field, and large exchange
stiffness. These results are important to understand how best to employ
noncollinear coupling in the next generation of thin film magnetic devices.",2402.15910v1
2024-03-12,Energy versus Output Quality of Non-volatile Writes in Intermittent Computing,"We explore how to improve the energy performance of battery-less Internet of
Things (IoT) devices at the cost of a reduction in the quality of the output.
Battery-less IoT devices are extremely resource-constrained energy-harvesting
devices. Due to erratic energy patterns from the ambient, their executions
become intermittent; periods of active computation are interleaved by periods
of recharging small energy buffers. To cross periods of energy unavailability,
a device persists application and system state onto Non-Volatile Memory (NVM)
in anticipation of energy failures. We purposely control the energy invested in
these operations, representing a major energy overhead, when using
Spin-Transfer Torque Magnetic Random-Access Memory (STT-MRAM) as NVM. As a
result, we abate the corresponding overhead, yet introduce write errors. Based
on 1.9+ trillion experimental data points, we illustrate whether this is a
gamble worth taking, when, and where. We measure the energy consumption and
quality of output obtained from the execution of nine diverse benchmarks on top
of seven different platforms. Our results allow us to draw three key
observations: i) the trade-off between energy saving and reduction of output
quality is program-specific; ii) the same trade-off is a function of a
platform's specific compute efficiency and power figures; and iii) data
encoding and input size impact a program's resilience to errors. As a
paradigmatic example, we reveal cases where we achieve up to 50% reduction in
energy consumption with negligible effects on output quality, as opposed to
settings where a minimal energy gain causes drastic drops in output quality.",2403.07517v1
2016-05-14,"Comment on ""Poynting vector, orbital and spin momentum and angular momentum versus optical force and torque on arbitrary particle in generic optical fields""","We criticize the originality or correctness of some of the ideas and results
recently reported by Ng et al. in arXiv:1511.08546.",1605.06041v1
2021-04-08,Flicker and random telegraph noise between gyrotropic and dynamic C-state of a vortex based spin torque nano oscillator,"Vortex based spin torque nano oscillators (STVOs) can present more complex
dynamics than the spin torque induced gyrotropic (G) motion of the vortex core.
The respective dynamic modes and the transition between them can be controlled
by experimental parameters such as the applied dc current. An interesting
behavior is the stochastic transition from the G- to a dynamic C-state
occurring for large current densities. Moreover, the C-state oscillations
exhibit a constant active magnetic volume. We present noise measurements in the
different dynamic states that allow accessing specific properties of the
stochastic transition, such as the characteristic state transition frequency.
Furthermore,we confirm, as theoretically predicted, an increase of flicker
noise with $I_{dc}^2$ when the oscillation volume remains constant with the
current. These results bring insight into the potential optimization of noise
properties sought for many potential rf applications with spin torque
oscillators. Furthermore, the investigated stochastic characteristics open up
new potentialities, for instance in the emerging field of neuromorphic
computing schemes.",2104.03647v1
2017-03-03,Periodic and quasi-periodic attractors for the spin-orbit evolution of Mercury with a realistic tidal torque,"Mercury is entrapped in a 3:2 resonance: it rotates on its axis three times
for every two revolutions it makes around the Sun. It is generally accepted
that this is due to the large value of the eccentricity of its orbit. However,
the mathematical model originally introduced to study its spin-orbit evolution
proved not to be entirely convincing, because of the expression commonly used
for the tidal torque. Only recently, in a series of papers mainly by Efroimsky
and Makarov, a different model for the tidal torque has been proposed, which
has the advantages of being more realistic, and of providing a higher
probability of capture in the 3:2 resonance with respect to the previous
models. On the other hand, a drawback of the model is that the function
describing the tidal torque is not smooth and consists of a superposition of
kinks, so that both analytical and numerical computations turn out to be rather
delicate: indeed, standard perturbation theory based on power series expansion
cannot be applied and the implementation of a fast algorithm to integrate the
equations of motion numerically requires a high degree of care. In this paper,
we make a detailed study of the spin-orbit dynamics of Mercury, as predicted by
the realistic model: In particular, we present numerical and analytical results
about the nature of the librations of Mercury's spin in the 3:2 resonance. The
results provide evidence that the librations are quasi-periodic in time.",1703.01189v1
2022-03-14,Field free switching through bulk spin-orbit torque in L10-FePt films deposited on vicinal substrates,"L10-FePt distinguishes itself for its ultrahigh perpendicular magnetic
anisotropy (PMA), which enables memory cells with sufficient thermal stability
to scale down to 3 nm. The recently discovered ""bulk"" spin-orbit torques in
L10-FePt provide an efficient and scalable way to manipulate the L10-FePt
magnetization. However, the existence of external field during the switching
limits its practical application, and therefore field-free switching of the
L10-FePt is in highly demand. In this manuscript, we demonstrate the field-free
switching of the L10-FePt by growing it on vicinal MgO (001) substrates. This
method is different from previously established strategies, as it does not need
to add other functional layers or create asymmetry in the film structure. We
demonstrate the field-free switching is robust and can withstand strong field
disturbance up to ~1 kOe. The dependence on vicinal angle, film thickness, and
growth temperature demonstrated a wide operation window for the field-free
switching of the L10-FePt. We confirmed that the physical origin of the
field-free switching is the vicinal surface-induced the tilted anisotropy of
L10-FePt. We quantitatively characterize the spin-orbit torques in the L10-FePt
films, and found the spin-orbit torques are not significantly influenced by the
lattice strain from vicinal substrates. Our results extend beyond the
established strategies to realize field-free switching, and potentially could
be applied to other magnetic and antiferromagnetic systems.",2203.06921v1
2023-01-11,Domain Wall-Magnetic Tunnel Junction Analog Content Addressable Memory Using Current and Projected Data,"With the rise in in-memory computing architectures to reduce the
compute-memory bottleneck, a new bottleneck is present between analog and
digital conversion. Analog content-addressable memories (ACAM) are being
recently studied for in-memory computing to efficiently convert between analog
and digital signals. Magnetic memory elements such as magnetic tunnel junctions
(MTJs) could be useful for ACAM due to their low read/write energy and high
endurance, but MTJs are usually restricted to digital values. The spin orbit
torque-driven domain wall-magnetic tunnel junction (DW-MTJ) has been recently
shown to have multi-bit function. Here, an ACAM circuit is studied that uses
two domain wall-magnetic tunnel junctions (DW-MTJs) as the analog storage
elements. Prototype DW-MTJ data is input into the magnetic ACAM (MACAM) circuit
simulation, showing ternary CAM function. Device-circuit co-design is carried
out, showing that 8-10 weight bits are achievable, and that designing
asymmetrical spacing of the available DW positions in the device leads to
evenly spaced ACAM search bounds. Analyzing available spin orbit torque
materials shows platinum provides the largest MACAM search bound while still
allowing spin orbit torque domain wall motion, and that the circuit is
optimized with minimized MTJ resistance, minimized spin orbit torque material
resistance, and maximized tunnel magnetoresistance. These results show the
feasibility of using DW-MTJs for MACAM and provide design parameters.",2301.04598v1
1997-09-27,Dynamics of Ordering of Heisenberg Spins with Torque --- Nonconserved Case. I,"We study the dynamics of ordering of a nonconserved Heisenberg magnet. The
dynamics consists of two parts --- an irreversible dissipation into a heat bath
and a reversible precession induced by a torque due to the local molecular
field. For quenches to zero temperature, we provide convincing arguments, both
numerically (Langevin simulation) and analytically (approximate closure scheme
due to Mazenko), that the torque is irrelevant at late times. We subject the
Mazenko closure scheme to systematic numerical tests. Such an analysis, carried
out for the first time on a vector order parameter, shows that the closure
scheme performs respectably well. For quenches to $T_c$, we show, to ${\cal
O}(\epsilon^2)$, that the torque is irrelevant at the Wilson-Fisher fixed
point.",9709307v1
2016-09-30,Intrinsic non-adiabatic topological torque in magnetic skyrmions and vortices,"We propose that topological spin currents flowing in topologically
non-trivial magnetic textures, such as magnetic skyrmions and vortices, produce
an intrinsic non-adiabatic torque of the form ${\bf T}_t\sim [(\partial_x{\bf
m}\times\partial_y{\bf m})\cdot{\bf m}]\partial_y{\bf m}$. We show that this
torque, which is absent in one-dimensional domain walls and/or non-topological
textures, is responsible for the enhanced non-adiabaticity parameter observed
in magnetic vortices compared to one-dimensional textures. The impact of this
torque on the motion of magnetic skyrmions is expected to be crucial,
especially to determine their robustness against defects and pinning centers.",1609.09606v1
2018-09-11,On the saw-tooth torque in anisotropic $j_{\rm eff} = 1/2$ magnets: Application to $α$-RuCl$_3$,"The so-called ""Kitaev candidate"" materials based on $4d^5$ and $5d^5$ metals
have recently emerged as magnetic systems displaying strongly anisotropic
exchange interactions reminiscent of the Kitaev's honeycomb model. Recently,
these materials have been shown to commonly display a distinct saw-tooth
angular dependence of the magnetic torque over a wide range of magnetic fields.
While higher order chiral spin interactions have been considered as a source of
this observation, we show here that bilinear anisotropic interactions and/or
$g$-anisotropy are each sufficient to explain the observed torque response,
which may be distinguished on the basis of high-field measurements. These
findings unify the understanding of magnetic torque experiments in a variety of
Kitaev candidate materials.",1809.03943v3
2018-08-14,Optical forces and torques exerted on coupled silica nanospheres: unexpected effects due to the multiple scattering,"Optically coupled nanoparticles suffer the action of multiple electromagnetic
forces when they are illuminated by light. In general, two kinds of forces are
commonly assumed: binding forces that make them attract/repel each other and
scattering forces that push the system forwards. Tangential forces and orbital
torques can also be induced to align the dimer with the electric field. In this
work, new degrees of freedom are found for a dimer of silica nanospheres under
illumination with linearly-polarized plane waves. The results have a general
validity for arbitrary mesoscale systems: multiple scattering of light induces
unexpected torques and unbalanced forces. These torques include spin
contributions to the movement of the whole system.
  The results are supported by previous works and pave the way for the
engineering of nanoscale devices and nanorotators. Any application which is
based on photonics at mesoscales should take into account the new movements
predicted here.",1808.04907v1
2019-01-25,Current-Induced Torques with Dresselhaus Symmetry Due to Resistance Anisotropy in 2D Materials,"We report measurements of current-induced torques in heterostructures of
Permalloy (Py) with TaTe$_2$, a transition-metal dichalcogenide (TMD) material
possessing low crystal symmetry, and observe a torque component with
Dresselhaus symmetry. We suggest that the dominant mechanism for this
Dresselhaus component is not a spin-orbit torque, but rather the Oersted field
arising from a component of current that flows perpendicular to the applied
voltage due to resistance anisotropy within the TaTe$_2$. This type of
transverse current is not present in wires made from a single uniform layer of
a material with resistance anisotropy, but will result whenever a material with
resistance anisotropy is integrated into a heterostructure with materials
having different resistivities, thereby producing a spatially non-uniform
pattern of current flow. This effect will therefore influence measurements in a
wide variety of heterostructures incorporating 2D TMD materials and other
materials with low crystal symmetries.",1901.08908v1
2021-06-19,Nonequilibrium Casimir effects of nonreciprocal surface waves,"We show that an isotropic dipolar particle in the vicinity of a substrate
made of nonreciprocal plasmonic materials can experience a lateral Casimir
force and torque when the particle's temperature differs from that of the slab
and the environment. We connect the existence of the lateral force to the
asymmetric dispersion of nonreciprocal surface polaritons and the existence of
the lateral torque to the spin-momentum locking of such surface waves. Using
the formalism of fluctuational electrodynamics, we show that the features of
lateral force and torque should be experimentally observable using a substrate
of doped Indium Antimonide (InSb) placed in an external magnetic field, and for
a variety of dielectric particles. Interestingly, we also find that the
directions of the lateral force and the torque depend on the constituent
materials of the particles, which suggests a sorting mechanism based on lateral
nonequilibrium Casimir physics.",2106.10584v1
2017-03-27,Spin transfer due to quantum fluctuations of magnetization,"Spin transfer - the transfer of angular momentum from spin-polarized
electrical current to magnetic materials - has been extensively researched as
an efficient mechanism for the electronic manipulation of the static and
dynamic states in nanomagnetic systems, advancing our understanding of
nanomagnetism and electronic transport, and enabling the development of
energy-efficient magnetic nanodevices. Our present understanding of spin
transfer is based on the classical approximation for the magnetization, even
though the spin-polarized electrons mediating spin transfer are treated
quantum-mechanically. Here, we utilize a nanoscale magnetic spin-valve
structure to demonstrate that quantum zero-point fluctuations of magnetization,
neglected in the existing theories of spin transfer, provide the dominant
contribution to this effect at cryogenic temperatures, and remain
non-negligible even at room temperature. The demonstrated quantum spin transfer
(QST) is distinguished by a non-smooth piecewise-linear dependence of the
fluctuation intensity on current, and can be driven not only by the directional
flows of electrons, but also by their thermal motion. This effect can enhance
current-induced phenomena, overcoming the efficiency limitations that are
presently perceived as fundamental to the spin transfer mechanism.",1703.09335v2
2000-08-18,Does Pulsar B1757--24 Have a Fallback Disk?,"Radio pulsars are thought to spin-down primarily due to torque from magnetic
dipole radiation (MDR) emitted by the time-varying stellar magnetic field as
the star rotates. This assumption yields a `characteristic age' for a pulsar
which has generally been assumed to be comparable to the actual age. Recent
observational limits on the proper motion of pulsar B1757-24, however, revealed
that the actual age (>39 kyr) of this pulsar is much greater than its MDR
characteristic age (16 kyr) - calling into question the assumption of pure MDR
spin-down for this and other pulsars. To explore the possible cause of this
discrepancy, we consider a scenario in which the pulsar acquired an accretion
disk from supernova ejecta, and the subsequent spin-down occurred under the
combined action of MDR and accretion torques. A simplified model of the
accretion torque involving a constant mass inflow rate at the pulsar
magnetosphere can explain the age and period derivative of the pulsar for
reasonable values of the pulsar magnetic field and inflow rate. We discuss
testable predictions of this model.",0008300v2
2001-04-17,Pulsar Spindown by a Fall-Back Disk and the P-P_dot Diagram,"Neutron stars may be surrounded by fall-back disks formed from supernova
core-collapse. If the disk circumscribes the light-cylinder, the neutron star
will be an active radio pulsar spinning down under the propeller spin-down
torque applied by the disk as well as the usual magnetic dipole radiation
torque. Evolution across the P-P_dot diagram is very rapid when pulsar
spin-down is dominated by the propeller torque. This explains the distribution
of pulsars in the P-P_dot diagram.",0104287v3
2004-12-07,Torque bistability in the interaction between a neutron star magnetosphere and a thin accretion disc,"We present a time-dependent model of the interaction between a neutron star
magnetosphere and a thin (Shakura-Sunyaev) accretion disc, where the extent of
the magnetosphere is determined by balancing outward diffusion and inward
advection of the stellar magnetic field at the inner edge of the disc. The
nature of the equilibria available to the system is governed by the magnetic
Prandtl number Pm and the ratio \xi of the corotation radius to the Alfven
radius. For \xi > Pm^0.3, the system can occupy one of two stable states, where
the torques are of opposite signs. If the star is spinning up initially, in the
absence of extraneous perturbations, \xi decreases until the spin-up
equilibrium vanishes, the star subsequently spins down, and the torque
asymptotes to zero. Vortex-in-cell simulations of the Kelvin-Helmholtz
instability suggest that the transport speed across the mixing layer between
the disc and magnetosphere is less than the shear speed when the layer is thin,
unlike in previous models.",0412154v1
2005-07-05,Aligning spinning black holes and accretion discs,"We consider the alignment torque between a spinning black hole and an
accretion disc whose angular momenta are misaligned. This situation must hold
initially in almost all gas accretion events on to supermassive black holes,
and may occur in binaries where the black hole receives a natal supernova kick.
We show that the torque always acts to align the hole's spin with the total
angular momentum without changing its magnitude. The torque acts dissipatively
on the disc, reducing its angular momentum, and aligning it with the hole if
and only if the angle theta between the angular momenta J_d of the disc and J_h
of the hole satisfies the inequality cos theta > -J_d / 2 J_h. If this
condition fails, which requires both theta > pi/2 and J_d < 2 J_h, the disc
counteraligns.",0507098v1
2008-07-29,Spin-Torque-Induced Rotational Dynamics of a Magnetic Vortex Dipole,"We study, both experimentally and by numerical modeling, the magnetic
dynamics that can be excited in a magnetic thin-film nanopillar device using
the spin torque from a spatially localized current injected via a
10s-of-nm-diameter aperture. The current-driven magnetic dynamics can produce
large amplitude microwave emission at zero magnetic field, with a frequency
well below that of the uniform ferromagnetic resonance mode. Micromagnetic
simulations indicate that the physical origin of this efficient microwave
nano-oscillator is the nucleation and subsequent steady-state rotational
dynamics of a magnetic vortex dipole driven by the localized spin torque. These
results show this novel implementation of a spintronic nano-oscillator is a
promising candidate for microwave technology applications.",0807.4660v2
2009-06-29,Measurement of nonlinear frequency shift coefficient in spin-torque oscillators based on MgO tunnel junctions,"The nonlinear frequency shift coefficient, which represents the strength of
the transformation of amplitude fluctuations into phase fluctuations of an
oscillator, is measured for MgO-based spin-torque oscillators by analyzing the
current dependence of the power spectrum. We have observed that linewidth
against inverse normalized power plots show linear behavior below and above the
oscillation threshold as predicted by the analytical theories for spin-torque
oscillators. The magnitude of the coefficient is determined from the ratio of
the linear slopes. Small magnitude of the coefficient has been obtained for the
device exhibiting narrow linewidth at high bias current.",0906.5224v1
2011-01-12,Bias dependence of perpendicular spin torque and of free and fixed layer eigenmodes in MgO-based nanopillars,"We have measured the bias voltage and field dependence of eigenmode
frequencies in a magnetic tunnel junction with MgO barrier. We show that both
free layer (FL) and reference layer (RL) modes are excited, and that a
cross-over between these modes is observed by varying external field and bias
voltage. The bias voltage dependence of the FL and RL modes are shown to be
dramatically different. The bias dependence of the FL modes is linear in bias
voltage, whereas that of the RL mode is strongly quadratic. Using modeling and
micromagnetic simulations, we show that the linear bias dependence of FL
frequencies is primarily due to a linear dependence of the perpendicular spin
torque on bias voltage, whereas the quadratic dependence of the RL on bias
voltage is dominated by the reduction of exchange bias due to Joule heating,
and is not attributable to a quadratic dependence of the perpendicular spin
torque on bias voltage.",1101.2401v2
2011-03-22,Inductive determination of the optimum tunnel barrier thickness in magnetic tunnelling junction stacks for spin torque memory applications,"We use pulsed inductive microwave magnetometry to study the precessional
magnetization dynamics of the free layer in CoFeB/MgO/CoFeB based magnetic
tunnelling junction stacks with varying MgO barrier thickness. From the field
dependence of the precession frequency we are able to derive the uniaxial
anisotropy energy and the exchange coupling between the free and the pinned
layer. Furthermore the field dependence of the effective damping parameter is
derived. Below a certain threshold barrier thickness we observe an increased
effective damping for antiparallel orientation of free and pinned layer which
would inhibit reversible low current density spin torque magnetization
reversal. Such inductive measurements, in combination with wafer probe station
based magneto transport experiments, allow a fast determination of the optimum
tunnel barrier thickness range for spin torque memory applications in a
lithography free process.",1103.4248v1
2013-02-18,Time Domain Mapping of Spin Torque Oscillator Effective Energy,"Stochastic dynamics of spin torque oscillators (STOs) can be described in
terms of magnetization drift and diffusion over a current-dependent effective
energy surface given by the Fokker-Planck equation. Here we present a method
that directly probes this effective energy surface via time-resolved
measurements of the microwave voltage generated by a STO. We show that the
effective energy approach provides a simple recipe for predicting spectral line
widths and line shapes near the generation threshold. Our time domain technique
also accurately measures the field-like component of spin torque in a wide
range of the voltage bias values.",1302.4480v1
2013-10-30,Spin-orbit-torque magnetization switching of a three terminal perpendicular magnetic tunnel junction,"We report on the current-induced magnetization switching of a three-terminal
perpendicular magnetic tunnel junction by spin-orbit torque and the read-out
using the tunnelling magnetoresistance (TMR) effect. The device is composed of
a perpendicular Ta/FeCoB/MgO/FeCoB stack on top of a Ta current line. The
magnetization of the bottom FeCoB layer can be switched reproducibly by the
injection of current pulses with density $5\times10^{11}$ A/m$^2$ in the Ta
layer in the presence of an in-plane bias magnetic field, leading to the
full-scale change of the TMR signal. Our work demonstrates the proof of concept
of a perpendicular spin-orbit torque magnetic memory cell.",1310.8235v2
2014-05-02,Spin-orbit torque-driven magnetization switching and thermal effects studied in Ta\CoFeB\MgO nanowires,"We demonstrate magnetization switching in out-of-plane magnetized
Ta\CoFeB\MgO nanowires by current pulse injection along the nanowires, both
with and without a constant and uniform magnetic field collinear to the current
direction. We deduce that an effective torque arising from spin-orbit effects
in the multilayer drives the switching mechanism. While the generation of a
component of the magnetization along the current direction is crucial for the
switching to occur, we observe that even without a longitudinal field thermally
generated magnetization fluctuations can lead to switching. Analysis using a
generalized N\'eel-Brown model enables key parameters of the thermally induced
spin-orbit torques switching process to be estimated, such as the attempt
frequency and the effective energy barrier.",1405.0452v1
2015-10-13,Spin-flop transition and magnetic phase diagram in CaCo$_{2}$As$_{2}$ revealed by torque measurements,"The magnetic properties of CaCo$_{2}$As$_{2}$ single crystal was
systematically studied by using dc magnetization and magnetic torque
measurements. A paramagnetic to antiferromagnetic transition occurs at $T_N$ =
74 K with Co spins being aligned parallel to the c axis. For $H \parallel c$, a
field-induced spin-flop transition was observed below $T_N$ and a magnetic
transition from antiferromagnetic to paramagnetic was inferred from the
detailed analysis of magnetization and magnetic torque. Finally, we summarize
the magnetic phase diagram of CaCo$_{2}$As$_{2}$ based on our results in the
\emph{H-T} plane.",1510.03496v1
2015-11-18,Frequency locking near the gluing bifurcation: Spin-torque oscillator under periodic modulation of current,"We consider entrainment by periodic force of limit cycles which are close to
the homoclinic bifurcation. Taking as a physical example the nanoscale
spin-torque oscillator in the LC circuit, we develop the general description of
the situation in which the frequency of the stable periodic orbit in the
autonomous system is highly sensitive to minor variations of the parameter, and
derive explicit expressions for the strongly deformed borders of the resonance
regions (Arnold tongues) in the parameter space of the problem. It turns out
that proximity to homoclinic bifurcations hinders synchronization of
spin-torque oscillators.",1511.05827v3
2016-02-02,Time-resolved spin-torque switching in MgO-based perpendicularly magnetized tunnel junctions,"We study ns scale spin-torque-induced switching in perpendicularly magnetized
tunnel junctions (pMTJ). Although the switching voltages match with the
macrospin instability threshold, the electrical signatures of the reversal
indicate the presence of domain walls in junctions of various sizes. In the
antiparallel (AP) to parallel (P) switching, a nucleation phase is followed by
an irreversible flow of a wall through the sample at an average velocity of 40
m/s with back and forth oscillation movements indicating a Walker propagation
regime. A model with a single-wall locally responding to the spin-torque
reproduces the essential dynamical signatures of the reversal. The P to AP
transition has a complex dynamics with dynamical back-hopping whose probability
increases with voltage. We attribute this back-hopping to the instability of
the nominally fixed layers.",1602.00894v1
2016-02-10,The inverse thermal spin-orbit torque and the relation of the Dzyaloshinskii-Moriya interaction to ground-state energy currents,"Using the Kubo linear-response formalism we derive expressions to calculate
the heat current generated by magnetization dynamics in magnets with broken
inversion symmetry and spin-orbit interaction (SOI). The effect of producing
heat currents by magnetization dynamics constitutes the Onsager reciprocal of
the thermal spin-orbit torque (TSOT), i.e., the generation of torques on the
magnetization due to temperature gradients. We find that the energy current
driven by magnetization dynamics contains a contribution from the
Dzyaloshinskii-Moriya interaction (DMI), which needs to be subtracted from the
Kubo linear response of the energy current in order to extract the heat
current. We show that the expressions of the DMI coefficient can be derived
elegantly from the DMI energy current. Guided by formal analogies between the
Berry phase theory of DMI on the one hand and the modern theory of orbital
magnetization on the other hand we are led to an interpretation of the latter
in terms of energy currents as well. Based on \textit{ab-initio} calculations
we investigate the heat current driven by magnetization dynamics in Mn/W(001)
magnetic bilayers. We predict that fast domain walls drive strong ITSOT heat
currents.",1602.03319v1
2016-04-15,Twist in the bias-dependence of spin-torques in magnetic tunnel junctions,"The spin-torque in magnetic tunnel junctions possesses two components that
both depend on the applied voltage. Here, we develop a new method for the
accurate extraction of this bias-dependence from experiments over large voltage
ranges. We study several junctions with different magnetic layer structures of
the top electrode. Our results obtained on junctions with symmetric CoFeB
electrodes agree well with theoretical calculations. The bias-dependences of
asymmetric samples, with top electrodes containing NiFe, however, are twisted
compared to the quadratic form generally assumed. Our measurements reveal the
complexity of spin-torque mechanisms at large bias.",1604.04517v1
2016-10-19,Enhancing the injection locking range of spin torque oscillators through mutual coupling,"We investigate how the ability of the vortex oscillation mode of a
spin-torque nano-oscillator to lock to an external microwave signal is modified
when it is coupled to another oscillator. We show experimentally that mutual
electrical coupling can lead to locking range enhancements of a factor 1.64.
Furthermore, we analyze the evolution of the locking range as a function of the
coupling strength through experiments and numerical simulations. By uncovering
the mechanisms at stake in the locking range enhancement, our results will be
useful for designing spin-torque nano-oscillators arrays with high
sensitivities to external microwave stimuli.",1610.06172v2
2017-07-14,Frequency shift keying by current modulation in a MTJ-based STNO with high data rate,"Spin torque nano-oscillators are nanoscopic microwave frequency generators
which excel due to their large frequency tuning range and agility for amplitude
and frequency modulation. Due to their compactness, they are regarded as
suitable candidates for applications in wireless communications, where
cost-effective and CMOS-compatible standalone devices are required. In this
work, we study the ability of a magnetic-tunnel-junction (MTJ) based spin
torque nano-oscillator to respond to a binary input sequence encoded in a
square-shaped current pulse for its application as a frequency-shift-keying
(FSK) based emitter. We demonstrate that below the limit imposed by the spin
torque nano-oscillators intrinsic relaxation frequency, an agile variation
between discrete oscillator states is possible. For this kind of devices, we
demonstrate FSK up to data rates of 400 Mbps which is well suited for the
application of such scillators in wireless networks.",1707.04467v1
2018-03-12,Chiral skyrmions in an anisotropy gradient driven by spin-Hall effect,"A strategy to drive skyrmion motion by a combination of an anisotropy
gradient and spin Hall effect has recently been demonstrated. Here, we study
the fundamental properties of this type of motion by combining micromagnetic
simulations and a generalized Thiele equation. We find that the anisotropy
gradient drives the skyrmion mainly along the direction perpendicular to the
gradient, due to the conservative part of the torque. There is some slower
motion along the direction parallel to the anisotropy gradient due to damping
torque. When an appropriate spin Hall torque is added, the skyrmion velocity in
the direction of the anisotropy gradient can be enhanced. This motion gives
rise to acceleration of the skyrmion as this moves to regions of varying
anisotropy. This phenomenon should be taken into account in experiments for the
correct evaluation of the skyrmion velocity. We employ a Thiele like formalism
and derive expressions for the velocity and the acceleration of the skyrmion
that match very well with micromagnetic simulation results.",1803.04160v1
2018-11-01,"Reservoir computing with the frequency, phase and amplitude of spin-torque nano-oscillators","Spin-torque nano-oscillators can emulate neurons at the nanoscale. Recent
works show that the non-linearity of their oscillation amplitude can be
leveraged to achieve waveform classification for an input signal encoded in the
amplitude of the input voltage. Here we show that the frequency and the phase
of the oscillator can also be used to recognize waveforms. For this purpose, we
phase-lock the oscillator to the input waveform, which carries information in
its modulated frequency. In this way we considerably decrease amplitude, phase
and frequency noise. We show that this method allows classifying sine and
square waveforms with an accuracy above 99% when decoding the output from the
oscillator amplitude, phase or frequency. We find that recognition rates are
directly related to the noise and non-linearity of each variable. These results
prove that spin-torque nano-oscillators offer an interesting platform to
implement different computing schemes leveraging their rich dynamical features.",1811.00309v1
2019-06-07,Field-free switching of a Spin-orbit torque device aided by interlayer-coupling induced domain walls,"The spin-orbit torque device is promising as a candidate for next generation
magnetic memory, while the static in-plane field needed to induce deterministic
switching is a main obstacle for its application in highly integrated circuits.
Instead of introducing effective field into the device, in this work we present
an alternative way to achieve the field-free current-driven magnetization
switching. By adding Tb/Co multilayers at two ends of the current channel,
assisting domain wall is created by interlayer exchange coupling. The
field-free deterministic switching is achieved by the movement of the domain
wall driven by current. By loop shift measurement we find the driven force
exerted on the domain wall is determined by the direction of the in-plane
moment in the domain wall. Finally, we modify the device into a synthetic
antiferromagnetic structure to solve the problem of reading out signal. The
present work broadens the choice of field-free spin-orbit torque device design
and clearly depicts the difference between two different switching mechanism.",1906.02938v1
2019-06-24,Low offset frequency $1/f$ flicker noise in spin torque vortex oscillators,"Low frequency noise close to the carrier remains little explored in spin
torque nano oscillators. However, it is crucial to investigate as it limits the
oscillator's frequency stability. This work addresses the low offset frequency
flicker noise of a TMR-based spin-torque vortex oscillator in the regime of
large amplitude steady oscillations. We first phenomenologically expand the
nonlinear auto-oscillator theory aiming to reveal the properties of this noise.
We then present a thorough experimental study of the oscillator's $1/f$ flicker
noise and discuss the results based on the theoretical predictions. Hereby, we
connect the oscillator's nonlinear dynamics with the concept of flicker noise
and furthermore refer to the influence of a standard $1/f$ noise description
based on the Hooge formula, taking into account the non-constant magnetic
oscillation volume, which contributes to the magnetoresistance.",1906.10190v2
2016-03-01,Instability analysis of spin torque oscillator with an in-plane magnetized free layer and a perpendicularly magnetized pinned layer,"We study the theoretical conditions to excite a stable self-oscillation in a
spin torque oscillator with an in-plane magnetized free layer and a
perpendicularly magnetized pinned layer in the presence of magnetic field
pointing in an arbitrary direction. The linearized Landau-Lifshitz-Gilbert
(LLG) equation is found to be inapplicable to evaluate the threshold between
the stable and self-oscillation states because the critical current density
estimated from the linearized equation is considerably larger than that found
in the numerical simulation. We derive a theoretical formula of the threshold
current density by focusing on the energy gain of the magnetization from the
spin torque during a time shorter than a precession period. A good agreement
between the derived formula and the numerical simulation is obtained. The
condition to stabilize the out-of-plane self-oscillation above the threshold is
also discussed.",1603.00155v2
2019-03-22,Deterministic Field-free Switching of a Perpendicularly Magnetized Ferromagnetic Layer via the Joint Effects of Dzyaloshinskii-Moriya Interaction and Field-like Spin-orbit Torque: An Appraisal,"Field-free switching of perpendicularly magnetized ferromagnetic layer by
spin orbit torque (SOT) from the spin Hall effect (SHE) is of great interest in
the applications of magnetic memory devices. In this paper, we investigate the
deterministic SOT switching through the joint effects of Dzyaloshinskii-Moriya
Interaction (DMI) and field-like torque (FLT) by micromagnetic simulations. We
confirmed that within a certain range of DMI values and charge current
densities, it is possible to deterministically switch the magnetization without
the assistance external magnetic field. We show that the FLT could play an
adverse role in blocking and slowing down the magnetization switching under
certain cases of DMI and charge current-driven field-free switching. However,
in other cases, FLT can assist DMI on the deterministic field-free SOT
switching. In addition, it is found that FLT can effectively expand the current
density window for a deterministic field-free SOT switching in the presence of
DMI.",1903.09702v1
2019-03-26,Controlling spin-orbit torque by polarization field in multiferroic BiFeO3 based heterostructures,"In the last few years, some ideas of electric manipulations in ferromagnetic
heterostructures have been proposed for developing next generation spintronic
devices. Among them, the magnetization switching driven by spin-orbit torque
(SOT) is being intensely pursued. Especially, how to control the switching
current density, which is expected to enrich device functionalities, has
aroused much interest among researchers all over the world. In this paper, a
novel method to adjust the switching current is proposed, and the BiFeO3 (BFO)
based heterostructures with opposite spontaneous polarizations fields show huge
changes in both perpendicular magnetic anisotropy and the SOT-induced
magnetization switching. The damping-like torques were estimated by using
harmonic Hall voltage measurement, and the variation of effective spin Hall
angles for the heterostructures with opposite polarizations was calculated to
be 272%. At the end of this paper, we have also demonstrated the possible
applications of our structure in memory and reconfigurable logic devices.",1903.10665v1
2019-05-07,Temporal pattern recognition with delayed feedback spin-torque nano-oscillators,"The recent demonstration of neuromorphic computing with spin-torque
nano-oscillators has opened a path to energy efficient data processing. The
success of this demonstration hinged on the intrinsic short-term memory of the
oscillators. In this study, we extend the memory of the spin-torque
nano-oscillators through time-delayed feedback. We leverage this extrinsic
memory to increase the efficiency of solving pattern recognition tasks that
require memory to discriminate different inputs. The large tunability of these
non-linear oscillators allows us to control and optimize the delayed feedback
memory using different operating conditions of applied current and magnetic
field.",1905.02695v1
2021-10-12,Manipulating Ferrimagnets by Fields and Currents,"Ferrimagnets (FIMs) can function as high-frequency antiferromagnets while
being easy to detect as ferromagnets, offering unique opportunities for
ultrafast device applications. While the physical behavior of FIMs near the
compensation point has been widely studied, there lacks a generic understanding
of FIMs where the ratio of sublattice spins can vary freely between the
ferromagnetic and antiferromagnetic limits. Here we investigate the physical
properties of a model two-sublattice FIM manipulated by static magnetic fields
and current-induced torques. By continuously varying the ratio of sublattice
spins, we clarify how the dynamical chiral modes in an FIM are intrinsically
connected to their ferro- and antiferromagnetic counterparts, which reveals
unique features not visible near the compensation point. In particular, we find
that current-induced torques can trigger spontaneous oscillation of the
terahertz exchange mode. Compared with its realization in antiferromagnets, a
spin-torque oscillator using FIMs not only has a reduced threshold current
density but also can be self-stabilized, obviating the need for dynamic
feedback.",2110.06204v3
2019-07-04,Spin-orbit torque induced electrical switching of antiferromagnetic MnN,"Electrical switching and readout of antiferromagnets allows to exploit the
unique properties of antiferromagnetic materials in nanoscopic electronic
devices. Here we report experiments on the spin-orbit torque induced electrical
switching of a polycrystalline, metallic antiferromagnet with low anisotropy
and high N\'eel temperature. We demonstrate the switching in a Ta / MnN / Pt
trilayer system, deposited by (reactive) magnetron sputtering. The dependence
of switching amplitude, efficiency, and relaxation are studied with respect to
the MnN film thickness, sample temperature, and current density. Our findings
are consistent with a thermal activation model and resemble to a large extent
previous measurements on CuMnAs and Mn$_2$Au, which exhibit similar switching
characteristics due to an intrinsic spin-orbit torque.",1907.02386v2
2021-01-29,Parameter estimation of a two-component neutron star model with spin wandering,"It is an open challenge to estimate systematically the physical parameters of
neutron star interiors from pulsar timing data while separating spin wandering
intrinsic to the pulsar (achromatic timing noise) from measurement noise and
chromatic timing noise (due to propagation effects). In this paper we formulate
the classic two-component, crust-superfluid model of neutron star interiors as
a noise-driven, linear dynamical system and use a state-space-based
expectation-maximization method to estimate the system parameters using
gravitational-wave and electromagnetic timing data. Monte Carlo simulations
show that we can accurately estimate all six parameters of the two-component
model provided that electromagnetic measurements of the crust angular velocity,
and gravitational-wave measurements of the core angular velocity, are both
available. When only electromagnetic data are available we can recover the
overall relaxation time-scale, the ensemble-averaged spin-down rate, and the
strength of the white-noise torque on the crust. However, the estimates of the
secular torques on the two components and white noise torque on the superfluid
are biased significantly.",2101.12421v1
2022-03-02,Optimal protocol for spin-orbit torque switching of a perpendicular nanomagnet,"It is demonstrated by means of the optimal control theory that the energy
cost of the spin-orbit torque induced reversal of a nanomagnet with
perpendicular anisotropy can be strongly reduced by proper shaping of both
in-plane components of the current pulse. The time-dependence of the optimal
switching pulse that minimizes the energy cost associated with Joule heating is
derived analytically in terms of the required reversal time and material
properties. The optimal reversal time providing a tradeoff between the
switching speed and energy efficiency is obtained. A sweet-spot balance between
the field-like and damping-like components of the spin-orbit torque is
discovered; it permits for a particularly efficient switching by a down-chirped
rotating current pulse whose duration does not need to be adjusted precisely.",2203.01167v1
2022-06-27,Data-driven Thiele equation approach for solving the full nonlinear spin-torque vortex oscillator dynamics,"The dynamics of vortex based spin-torque nano-oscillators is investigated
theoretically. Starting from a fully analytical model based on the Thiele
equation approach, fine-tuned data-driven corrections are carried out to the
gyrotropic and damping terms. These adjustments, based on micromagnetic
simulation results, allow to quantitatively model the response of such
oscillators to any dc current within the range of the vortex stability. Both,
the transient and the steady-state regimes are accurately predicted under the
proposed data-driven Thiele equation approach. Furthermore, the computation
time required to solve the dynamics of such system is reduced by about six
orders of magnitude compared to the most powerful micromagnetic simulations.
This major breakthrough opens the path for unprecedented high-throughput
simulations of spin-torque vortex oscillators submitted to long-duration input
signals, for example in neuromorphic computing applications.",2206.13596v1
2022-09-15,Field-free high-frequency exchange-spring spin-torque nano-oscillators,"Spin-torque nano-oscillators (STNOs) are a type of nanoscale microwave
auto-oscillators utilizing spin-torque to generate magnetodynamics with great
promise for applications in microwaves, magnetic memory, and neuromorphic
computing. Here, we report the first demonstration of exchange-spring STNOs,
with an exchange-spring ([Co/Pd]-Co) reference layer and a perpendicular
([Co/Ni]) free layer. This magnetic configuration results in high-frequency
(>10 GHz) microwave emission at a zero magnetic field and exchange-spring
dynamics in the reference layer and the observation of magnetic droplet
solitons in the free layer at different current polarities. Our demonstration
of bipolar and field-free exchange-spring-based STNOs operating over a 20 GHz
frequency range greatly extends the design freedom and functionality of the
current STNO technology for energy-efficient high-frequency spintronic and
neuromorphic applications.",2209.06996v1
2023-01-04,Magnetization dynamics with time-dependent spin-density functional theory: significance of exchange-correlation torques,"In spin-density-functional theory (SDFT) for noncollinear magnetic materials,
the Kohn-Sham system features exchange-correlation (xc) scalar potentials and
magnetic fields. The significance of the xc magnetic fields is not very well
explored; in particular, they can give rise to local torques on the
magnetization, which are absent in standard local and semilocal approximations.
Exact benchmark solutions for a five-site extended Hubbard lattice at half
filling and in the presence of spin-orbit coupling are compared with SDFT
results obtained using orbital-dependent exchange-only approximations. The
magnetization dynamics following short-pulse excitations is found to be
reasonably well described in the exchange-only approximation for weak to
moderate interactions. For stronger interactions and near transitions between
magnetically ordered and frustrated phases, exchange and correlation torques
tend to compensate each other and must both be accounted for.",2301.01509v1
2023-03-07,Dynamics of bistable Néel domain walls under spin-orbit torque,"N\'eel magnetic domain walls that are stabilized by achiral energy terms
instead of the usual Dzyaloshinskii-Moriya interaction will be bistable, with
the two possible chiral forms being degenerate. Here we focus on the
theoretical study of the spin-orbit torque driven dynamics of such bistable
N\'eel domain walls. We find that, for a given domain wall, two propagation
directions along a nanowire are possible, depending on its initial state. These
dynamics also exhibit complex dependence on the spin-orbit torque magnitude,
leading to important transient regimes. Finally, a few ways are proposed for
controlled or random reversal of the domain wall propagation direction. A
robust analytical model which handles all the observed behaviors of such domain
walls is developed and validated by comparing with numerical simulations. The
obtained new dynamics open the way for new uses of domain walls in information
storage and processing devices.",2303.06142v2
2023-06-05,Spin-orbit torque generation in bilayers composed of CoFeB and epitaxial SrIrO$_{3}$ grown on an orthorhombic DyScO$_{3}$ substrate,"We report on the highly efficient spin-orbit torque (SOT) generation in
epitaxial SrIrO$_{3}$(SIO), which is grown on an orthorhombic DyScO$_{3}$(110)
substrate. By conducting harmonic Hall measurement in
Co$_{20}$Fe$_{60}$B$_{20}$ (CoFeB)/SIO bilayers, we characterize two kinds of
the SOTs, i.e., dampinglike (DL) and fieldlike ones to find that the former is
much larger than the latter. By comparison with the Pt control sample with the
same CoFeB thickness, the observed DL SOT efficiency $\xi$$_{DL}$ of SIO
($\sim$0.32) is three times higher than that of Pt ($\sim$0.093). The
$\xi$$_{DL}$ is nearly constant as a function of the CoFeB thickness,
suggesting that the SIO plays a crucial role in the large SOT generation. These
results on the CoFeB/SIO bilayers highlight that the epitaxial SIO is promising
for low-current and reliable spin-orbit torque-controlled devices.",2306.02567v1
2023-07-09,Dzyaloshinskii-Moriya torque-driven resonance in antiferromagnetic α-Fe2O3,"We examine the high-frequency optical mode of {\alpha}-Fe2O3 and report that
Dzyaloshinskii-Moriya (DM) interaction generates a new type of torque on the
magnetic resonance. Using a continuous-wave terahertz interferometer, we
measure the optical mode spectra, where the asymmetric absorption with a large
amplitude and broad linewidth is observed near the magnetic transition point,
Morin temperature (TM ~ 254.3 K). Based on the spin wave model, the spectral
anomaly is attributed to the DM interaction-induced torque, enabling to extract
the strength of DM interaction field of 4 T. Our work opens a new avenue to
characterize the spin resonance behaviors at an antiferromagnetic singular
point for next-generation and high-frequency spin-based information
technologies.",2307.04135v1
2023-07-21,Sagnac interferometry for high-sensitivity optical measurements of spin-orbit torque,"Sagnac interferometry can provide a significant improvement in
signal-to-noise ratio compared to conventional magnetic imaging based on the
magneto-optical Kerr effect (MOKE). We show that this improvement is sufficient
to allow quantitative measurements of current-induced magnetic deflections due
to spin-orbit torque even in thin-film magnetic samples with perpendicular
magnetic anisotropy for which the Kerr rotation is second-order in the magnetic
deflection. Sagnac interfermometry can also be applied beneficially for samples
with in-plane anisotropy, for which the Kerr rotation is first order in the
deflection angle. Optical measurements based on Sagnac interferometry can
therefore provide a cross-check on electrical techniques for measuring
spin-orbit torque. Different electrical techniques commonly give quantitatively
inconsistent results, so that Sagnac interferometry can help to identify which
techniques are affected by unidentified artifacts.",2307.11624v1
2000-12-18,New Origin For Spin Current And Current-Induced Spin Precession In Magnetic Multilayers,"In metallic ferromagnets, an electric current is accompanied by a flux of
angula r momentum, also called spin current. In multilayers, spatial variations
of the spin current correspond to drive torques exerted on a magnetic layer.
These torq ues result in spin precession above a certain current threshold. The
usual kind of spin current is associated with translation of the spin-up and
spin-down Ferm i surfaces in momentum space. We discuss a different kind of
spin current, assoc iated with expansion and contraction of the Fermi surfaces.
It is more nonlocal in nature, and may exist even in locations where the
electrical current density is zero. It is larger than the usual spin current,
in a ratio of 10 or 100, and is dominant in most cases. The new spin current is
proportional to the differenc e Delta-mu = 0.001 eV between spin-up and
spin-down Fermi levels, averaged over the entire Fermi surface. Conduction
processes, spin relaxation, and spin-wave emission in the multilayer can be
described by an equivalent electrical circuit resembling an unbalanced dc
Wheatstone bridge. And Delta-mu corresponds to the output voltage of the
bridge.",0012337v2
2003-07-25,Dynamics of a magnetic moment induced by a spin-polarized current,"Effects of an incoming spin-polarized current on a magnetic moment are
explored. We found that the spin torque occurs only when the incoming spin
changes as a function of time inside of the magnetic film. This implies that
some modifications are necessary in a phenomenological model where the
coefficient of the spin torque term is a constant, and the coefficient is
determined by dynamics instead of geometrical details. The precession of the
magnetization reversal depends on the incoming energy of electrons in the
spin-polarized current. If the incoming energy is smaller than the interaction
energy, the magnetization does not precess while reversing its direction. We
also found that the relaxation time associated with the reversal depends on the
incoming energy. The coupling between an incoming spin and a magnetic moment
can be estimated by measuring the relaxation time.",0307633v1
2007-10-15,"Model for a collimated spin wave beam generated by a single layer, spin torque nanocontact","A model of spin torque induced magnetization dynamics based upon
semi-classical spin diffusion theory for a single layer nanocontact is
presented. The model incorporates effects due to the current induced Oersted
field and predicts the generation of a variety of spatially dependent,
coherent, precessional magnetic wave structures. Directionally controllable
collimated spin wave beams, vortex spiral waves, and localized standing waves
are found to be excited by the interplay of the Oersted field and the
orientation of an applied field. These fields act as a spin wave ``corral''
around the nanocontact that controls the propagation of spin waves in certain
directions.",0710.2890v3
2013-01-23,Voltage and Energy-Delay Performance of Giant Spin Hall Effect Switching for Magnetic Memory and Logic,"In this letter, we show that Giant Spin Hall Effect (GSHE) MRAM can enable
better energy- delay and voltage performance than traditional MTJ based spin
torque devices at scaled nanomagnet dimensions (10-30 nm). Firstly, we derive
the effect of dimensional scaling on spin injection efficiency, voltage-delay
and energy-delay of spin torque switching using MTJs and GSHE and identify the
optimum electrode geometry for low operating voltage (<0.1 V), high speed (>10
GHz) operation. We show that effective spin injection efficiency >100 % can be
obtained using optimum spin hall electrode thickness for 30 nm nanomagnet
widths. Finally, we derive the energy-delay trajectory of GSHE and MTJ devices
to calculate the energy-delay product of GSHE and MTJ devices with an energy
minimum at the characteristic time of the magnets. Optimized GSHE devices when
combined with PMA can enable MRAM with scaled nanomagnets (30 nm X 60 nm),
ultra-low voltage operation (< 0.1 V), fast switching times (10 ps) and
switching energy as low as 100 aJ/bit.",1301.5374v1
2013-05-14,Exchange magnetic field torques in YIG/Pt bilayers observed by the spin-Hall magnetoresistance,"The effective field torque of an yttrium-iron-garnet film on the spin
accumulation in an attached Pt film is measured by the spin-Hall
magnetoresistance (SMR). As a result, the magnetization direction of a
ferromagnetic insulating layer can be measured electrically. Experimental
transverse and longitudinal resistances are well described by the theoretical
model of SMR in terms of the direct and inverse spin-Hall effect, for different
Pt thicknesses [3, 4, 8 and 35nm]. Adopting a spin-Hall angle of Pt
$\theta_{SH}=0.08$, we obtain the spin diffusion length of Pt
($\lambda=1.1\pm0.3$nm) as well as the real
($G_r=(7\pm3)\times10^{14}\Omega^{-1}$m$^{-2}$) and imaginary part
($G_i=(5\pm3)\times10^{13}\Omega^{-1}$m$^{-2}$) of the spin-mixing conductance
and their ratio ($G_r/G_i=16\pm4$).",1305.3117v2
2014-01-13,Torque reversals and pulse profile of the pulsar 4U 1626-67,"We review the pulse profile evolution of the unique accretion powered X-ray
pulsar 4U 1626-67 over the last 40 years since its discovery. This pulsar
showed two distinct eras of steady spin-up separated by a steady spin-down
episode for about 18 years. In the present work, using data from different
observatories active during each phase of spin-up and spin-down we establish a
clear correlation between the accretion torque acting on this pulsar and its
pulse profile. The energy resolved pulse profiles are identical in both the
spin-up eras and quite different in the spin-down era, especially in the low
energy band. This correlation, along with the already known feature of strong
Quasi Periodic Oscillations (QPO) that was present only in the spin-down era,
clearly establish two different accretion modes onto the neutron star which
produce different pulse profiles and only one of which produces the QPOs.",1401.2936v1
2015-04-23,Spin alignments within the cosmic web: a theory of constrained tidal torques near filaments,"The geometry of the cosmic web drives in part the spin acquisition of
galaxies. This can be explained in a Lagrangian framework, by identifying the
specific long-wavelength correlations within the primordial Gaussian random
field which are relevant to spin acquisition. Tidal Torque Theory is revisited
in the context of such anisotropic environments, biased by the presence of a
filament within a wall. The point process of filament-type saddles represents
it most efficiently. The constrained misalignment between the tidal and the
inertia tensors in the vicinity of filament-type saddles simply explains the
distribution of spin directions. This misalignment implies in particular an
azimuthal orientation for the spins of more massive galaxies and a spin
alignment with the filament for less massive galaxies. This prediction is found
to be in qualitative agreement with measurements in Gaussian random fields and
N-body simulations. It relates the transition mass to the geometry of the
saddle, and accordingly predicts its measured scaling with the mass of
non-linearity. Implications for galaxy formation and weak lensing are briefly
discussed, as is the dual theory of spin alignments in walls.",1504.06073v2
2015-08-06,Interface-driven spin-torque ferromagnetic resonance by Rashba coupling at the interface between non-magnetic materials,"The Rashba-Edelstein effect stems from the interaction between the electron's
spin and its momentum induced by spin-orbit interaction at an interface or a
surface. It was shown that the inverse Rashba-Edelstein effect can be used to
convert a spin- into a charge current. Here, we demonstrate that a Bi/Ag Rashba
interface can even drive an adjacent ferromagnet to resonance. We employ a
spin-torque ferromagnetic resonance excitation/detection scheme which was
developed originally for a bulk spin-orbital effect, the spin Hall effect. In
our experiment, the direct Rashba-Edelstein effect generates an oscillating
spin current from an alternating charge current driving the magnetization
precession in a neighboring permalloy (Py, Ni80Fe20) layer. Electrical
detection of the magnetization dynamics is achieved by a rectification
mechanism of the time dependent multilayer resistance arising from the
anisotropic magnetoresistance.",1508.01410v1
2016-06-02,Band structure and spin texture of Bi$_2$Se$_3$/3d ferromagnetic metal interface,"The spin-helical surface states in three-dimensional topological insulator
(TI), such as Bi2Se3, are predicted to have superior efficiency in converting
charge current into spin polarization. This property is said to be responsible
for the giant spin-orbit torques observed in ferromagnetic metal/TI structures.
In this work, using first-principles and model tight-binding calculations, we
investigate the interface between the topological insulator Bi2Se3 and
3d-transition ferromagnetic metals Ni and Co. We find that the difference in
the work functions of the topological insulator and the ferromagnetic metals
shift the topological surface states down about 0.5 eV below the Fermi energy
where the hybridization of these surface states with the metal bands destroys
their helical spin structure. The band alignment of Bi2Se3 and Ni (Co) places
the Fermi energy far in the conduction band of bulk Bi2Se3, where the spin of
the carriers is aligned with the magnetization in the metal. Our results
indicate that the topological surface states are unlikely to be responsible for
the huge spin-orbit torque effect observed experimentally in these systems.",1606.00763v1
2020-04-21,Surface Rashba-Edelstein Spin-Orbit Torque Revealed by Molecular Self-Assembly,"We report the observation of a spin-orbit torque (SOT) originating from the
surface Rashba-Edelstein effect. We found that the SOT in a prototypical
spin-orbitronic system, a Pt/Co bilayer, can be manipulated by molecular
self-assembly on the Pt surface. This evidences that the Rashba spin-orbit
coupling at the Pt surface generates a sizable SOT, which has been hidden by
the strong bulk and interface spin-orbit coupling. We show that the molecular
tuning of the surface Rashba-Edelstein SOT is consistent with density
functional theory calculations. These results illustrate the crucial role of
the surface spin-orbit coupling in the SOT generation, which alters the
landscape of metallic spin-orbitronic devices.",2004.09852v1
2016-12-09,Influence of intermixing at the Ta/CoFeB interface on spin Hall angle in Ta/CoFeB/MgO heterostructures,"We investigate the spin Hall effect in perpendicularly magnetized
Ta/Co40Fe40B20/MgO trilayers with Ta underlayers thicker than the spin
diffusion length. The crystallographic structures of the Ta layer and Ta/CoFeB
interface are examined in detail using X-ray diffraction and transmission
electron microscopy. The thinnest Ta underlayer is amorphous, whereas for
thicker Ta layers a disoriented tetragonal beta-phase appears. Effective
spin-orbit torques are calculated based on harmonic Hall voltage measurements
performed in a temperature range between 15 and 300 K. To account for the
temperature dependence of damping-like and field-like torques, we extend the
spin diffusion model by including an additional contribution from the Ta/CoFeB
interface. Based on this approach, the temperature dependence of the spin Hall
angle in the Ta underlayer and at Ta/CoFeB interface are determined separately.
The results indicate an almost temperature-independent spin Hall angle of
theta_SH-N = -0.2 in Ta and a strongly temperature-dependent theta_SH-I for the
intermixed Ta/CoFeB interface.",1612.03020v1
2017-01-14,Paving Spin-Wave Fibers in Magnonic Nanocircuits Using Spin-Orbit Torque,"Recent studies have revealed that domain walls in magnetic nanostructures can
serve as compact, energy-efficient spin-wave waveguides for building magnonic
devices that are considered promising candidates for overcoming the challenges
and bottlenecks of today's CMOS technologies. However, imprinting long
strip-domain walls into magnetic nanowires remains a challenge, especially in
curved geometries. Here, through micromagnetic simulations, we present a method
for writing strip-domain walls into curved magnetic nanowires using spin-orbit
torque. We employ Y-shaped magnetic nanostructures as well as an S-shaped
magnetic nanowire to demonstrate the injection process. In addition, we verify
that the Y-shaped nanostructures that incorporate strip-domain walls can
function as superior spin-wave multiplexers, and that spin-wave propagation
along each conduit can be controllably manipulated. This spin-wave multiplexer
based on strip-domain walls is expected to become a key signal-processing
component in magnon spintronics.",1701.03886v1
2019-07-16,Current-driven Rashba Field in a Magnetic Quantum Well,"In materials lacking inversion symmetry, the spin-orbit coupling enables the
direct connection between the electron's spin and its linear momentum, a
phenomenon called inverse spin galvanic effect. In magnetic materials, this
effect promotes current-driven torques that can be used to control the
magnetization direction electrically. In this work, we investigate the
current-driven inverse spin galvanic effect in a quantum well consisting in a
magnetic material embedded between dissimilar insulators. Assuming the presence
of Rashba spin-orbit coupling at the interfaces, we investigate the nature of
the non-equilibrium spin density and the influence of the quantum well
parameters. We find that the torque is governed by the interplay between the
number of states participating to the transport and their spin chirality, the
penetration of the wave function into the tunnel barriers, and the strength of
the Rashba term.",1907.07116v1
2020-01-12,Controlling vertical magnetization shift by spin-orbit torque in ferromagnetic/antiferromagnetic/ferromagnetic heterostructure,"We report the control of vertical magnetization shift (VMS) and exchange bias
through spin-orbit torque (SOT) in Pt/Co/Ir25Mn75/Co heterostructure device.
The exchange bias accompanying with a large relative VMS of about 30 % is
observed after applying a single pulse 40 mA in perpendicular field of 2 kOe.
Furthermore, the field-free SOT-induced variations of VMS and exchange bias is
also observed, which would be related to the effective built-in out-of-plane
field due to unequal upward and downward interfacial spin populations. The
SOT-induced switched fraction of out-of-plane interfacial spins shows a linear
dependence on relative VMS, indicating the number of uncompensated pinned spins
are proportional to the switched interfacial spins. Our finding offers a
comprehensive understanding for electrically manipulating interfacial spins of
AFM materials.",2001.03846v1
2022-02-03,Element Doping Enhanced Charge-to-Spin Conversion Efficiency in Amorphous PtSn4 Dirac Semimetal,"Topological semimetals (TSs) are promising candidates for low-power
spin-orbit torque (SOT) devices due to their large charge-to-spin conversion
efficiency. Here, we investigated the charge-to-spin conversion efficiency of
amorphous PtSn4 (5 nm)/CoFeB (2.5-12.5 nm) layered structures prepared by a
magnetron sputtering method at room temperature. The charge-to-spin ratio of
PtSn4/CoFeB bilayers was 0.08, characterized by a spin torque ferromagnetic
resonance (ST-FMR) technique. This ratio can further increase to 0.14 by
inducing dopants, like Al and CoSi, into PtSn4. The dopants can also decrease
(Al doping) or increase (CoSi doping) the resistivity of PtSn4. The work
proposed a way to enhance the spin-orbit coupling (SOC) in amorphous TSs with
dopants.",2202.01384v1
2022-03-15,From charge to spin: analogies and differences in quantum transport coefficients,"We review some recent results from the mathematical theory of transport of
charge and spin in gapped crystalline quantum systems. The emphasis will be in
transport coefficients like conductivities and conductances. As for the former,
those are computed as appropriate expectations of current operators in a
non-equilibrium almost-stationary state (NEASS), which arises from the
perturbation of an equilibrium state by an external electric field. While for
charge transport the usual double-commutator Kubo formula is recovered (also
beyond linear response), we obtain formulas for appropriately-defined spin
conductivities which are still explicit but more involved. Certain ""Kubo-like""
terms in these formulas are also shown to agree with corresponding
contributions to the spin conductance. In addition to that, we employ similar
techniques to show a new result, namely that even in systems with non-conserved
spin there is no generation of spin torque, that is the spin torque operator
has an expectation in the NEASS which vanishes faster than any power of the
intensity of the perturbing field.",2203.08044v2
2023-07-23,Unconventional spin polarization at Argon ion milled SrTiO3 Interfaces,"Interfacial two-dimensional electron gas (2DEG) formed at the perovskite-type
oxide, such as SrTiO3, has attracted significant attention due to its
properties of ferromagnetism, superconductivity, and its potential application
in oxide-based low-power consumption electronics. Recent studies have
investigated spin-to-charge conversion at the STO interface with different
materials, which could affect the efficiency of this 2DEG interface. In this
report, we presented an Ar^+ ion milling method to create a 2DEG at STO
directly by inducing oxygen vacancies. To quantify the spin-to-charge
conversion of this interface, we measured the angular-dependent spin-torque
ferromagnetic resonance (ST-FMR) spectra, revealing an unconventional spin
polarization at the interface of Argon ion-milled STO and NiFe. Furthermore, a
micromagnetic simulation for angular-dependent spin-torque ferromagnetic
resonance (ST-FMR) has been performed, confirming the large unconventional spin
polarization at the interface.",2307.12390v1
2003-08-29,Calculation and optical measurement of laser trapping forces on non-spherical particles,"Optical trapping, where microscopic particles are trapped and manipulated by
light is a powerful and widespread technique, with the single-beam gradient
trap (also known as optical tweezers) in use for a large number of biological
and other applications.
  The forces and torques acting on a trapped particle result from the transfer
of momentum and angular momentum from the trapping beam to the particle.
  Despite the apparent simplicity of a laser trap, with a single particle in a
single beam, exact calculation of the optical forces and torques acting on
particles is difficult. Calculations can be performed using approximate
methods, but are only applicable within their ranges of validity, such as for
particles much larger than, or much smaller than, the trapping wavelength, and
for spherical isotropic particles.
  This leaves unfortunate gaps, since wavelength-scale particles are of great
practical interest because they are readily and strongly trapped and are used
to probe interesting microscopic and macroscopic phenomena, and non-spherical
or anisotropic particles, biological, crystalline, or other, due to their
frequent occurance in nature, and the possibility of rotating such objects or
controlling or sensing their orientation.
  The systematic application of electromagnetic scattering theory can provide a
general theory of laser trapping, and render results missing from existing
theory. We present here calculations of force and torque on a trapped particle
obtained from this theory and discuss the possible applications, including the
optical measurement of the force and torque.",0308110v1
2019-03-06,Using Torque to Understand Barred Galaxy Models,"We track the angular momentum transfer in n-body simulations of barred
galaxies by measuring torques to understand the dynamical mechanisms
responsible for the evolution of the bar-disc-dark matter halo system. We find
evidence for three distinct phases of barred galaxy evolution: assembly,
secular growth, and steady-state equilibrium. Using a decomposition of the disc
into orbital families, we track bar mass and angular momentum through time and
correlate the quantities with the phases of evolution. We follow the angular
momentum transfer between particles and identify the dominant torque channels.
We find that the halo model mediates the assembly and growth of the bar for a
high central density halo, and the outer disc mediates the assembly and growth
of the bar in a low central density halo model. Both galaxies exhibit a
steady-state equilibrium phase where the bar is neither lengthening nor
slowing. The steady-state equilibrium results from the balance of torque
between particles that are gaining and losing angular momentum. We propose
observational metrics for barred galaxies that can be used to help determine
the evolutionary phase of a barred galaxy, and discuss the implications of the
phases for galaxy evolution as a whole.",1903.02566v2
2016-03-03,Non-equilibrium charge and spin transport in SFS point contacts,"The conventional Josephson effect may be modified by introducing spin-active
scattering in the interface-layer of the junction. Here, we discuss a Josephson
junction consisting of two s-wave superconducting leads coupled over a
classical spin that precesses with the Larmor frequency due to an external
magnetic field. This magnetically active interface results in a time-dependent
boundary condition with different tunnelling amplitudes for spin-up and -down
quasiparticles and where the precession produces spin-flip scattering
processes. As a result, the Andreev states develop sidebands and a
non-equilibrium population that depend on the details of the spin precession.
The Andreev states carry a steady-state Josephson charge current and a
time-dependent spin current, whose current-phase relations could be used for
characterising the precessing spin. The spin current is supported by
spin-triplet correlations induced by the spin precession and creates a
feed-back effect on the classical spin in the form of a torque that shifts the
precession frequency.
  By applying a bias voltage, the Josephson frequency adds another complexity
to the situation and may create resonances together with the Larmor frequency.
These Shapiro resonances are manifested as torques and are, under suitable
conditions, able to reverse the direction of the classical spin in
sub-nanosecond time. Another characteristic feature is the subharmonic gap
structure in the dc charge current displaying an even-odd effect that is
attributable to precession-assisted multiple Andreev reflections.",1603.01299v1
2022-09-27,Spin Berry curvature of the Haldane model,"The feedback of the geometrical Berry phase, accumulated in an electron
system, on the slow dynamics of classical degrees of freedom is governed by the
Berry curvature. Here, we study local magnetic moments, modelled as classical
spins, which are locally exchange coupled to the (spinful) Haldane model for a
Chern insulator. In the emergent equations of motion for the slow
classical-spin dynamics there is a an additional anomalous geometrical spin
torque, which originates from the corresponding spin-Berry curvature. Due to
the explicitly broken time-reversal symmetry, this is nonzero but usually small
in a condensed-matter system. We develop the general theory and compute the
spin-Berry curvature, mainly in the limit of weak exchange coupling, in various
parameter regimes of the Haldane model, particularly close to a topological
phase transition and for spins coupled to sites at the zigzag edge of the model
in a ribbon geometry. The spatial structure of the spin-Berry curvature tensor,
its symmetry properties, the distance dependence of its nonlocal elements and
further properties are discussed in detail. For the case of two classical
spins, the effect of the geometrical spin torque leads to an anomalous
non-Hamiltonian spin dynamics. It is demonstrated that the magnitude of the
spin-Berry curvature is decisively controlled by the size of the insulating
gap, the system size and the strength of local exchange coupling.",2209.13629v2
2021-02-25,Unidirectional magnetoresistance and spin-orbit torque in NiMnSb,"Spin-dependent transport phenomena due to relativistic spin-orbit coupling
and broken space-inversion symmetry are often difficult to interpret
microscopically, in particular when occurring at surfaces or interfaces. Here
we present a theoretical and experimental study of spin-orbit torque and
unidirectional magnetoresistance in a model room-temperature ferromagnet NiMnSb
with inversion asymmetry in the bulk of this half-heusler crystal. Besides the
angular dependence on magnetization, the competition of Rashba and
Dresselhaus-like spin-orbit couplings results in the dependence of these
effects on the crystal direction of the applied electric field. The
phenomenology that we observe highlights potential inapplicability of commonly
considered approaches for interpreting experiments. We point out that, in
general, there is no direct link between the current-induced non-equilibrium
spin polarization inferred from the measured spin-orbit torque and the
unidirectional magnetiresistance. We also emphasize that the unidirectional
magnetoresistance has not only longitudinal but also transverse components in
the electric field -- current indices which complicates its separation from the
thermoelectric contributions to the detected signals in common experimental
techniques. We use the theoretical results to analyze our measurements of the
on-resonance and off-resonance mixing signals in microbar devices fabricated
from an epitaxial NiMnSb film along different crystal directions. Based on the
analysis we extract an experimental estimate of the unidirectional
magnetoresistance in NiMnSb.",2102.12838v1
2023-09-13,Towards a holistic magnetic braking model from the evolution of cataclysmic variables to stellar spin-down -- I: the spin-down of fully convective M-dwarfs,"We extend a magnetic braking (MB) model, which has been used earlier to
address the evolution of cataclysmic variables, to address the spin period
$P_\mathrm{spin}$ evolution of fully convective M dwarf (FCMD) stars. The MB
mechanism is an $\alpha-\Omega$ dynamo, which leads to stellar winds that carry
away angular momentum. We model our MB torque such that the FCMDs experience a
MB torque, approximately scaling as $P_\mathrm{spin}^{-1}$ at shorter periods,
before transitioning into a Skumanich-type MB torque, scaling as
$P_\mathrm{spin}^{-3}$. We also implement a parametrized reduction in the wind
mass loss owing to the entrapment of winds in dead zones. We choose a set of
initial conditions and vary the two free parameters in our model to find a good
match of our spin trajectories with open clusters containing FCMDs such as
NGC2547, Pleiades, NGC2516 and Praesepe. We find that our model can explain the
long spin periods of field stars and that a spread in spin distribution
persists till over 3 Gyr. An advantage of our model is in relating physically
motivated estimations of the magnetic field strength and stellar wind to
properties of the stellar dynamo, which other models often remain agnostic
about. We track the spin dependence of the wind mass losses, Alfv\'en radii and
surface magnetic fields and find good agreement with observations. We discuss
the implications of our results on the effect of the host FCMD on any orbiting
exoplanets and our plans to extend this model to explain solar-like stars in
the future.",2309.06893v1
2022-07-01,The Periodic Signals of Nova V1674 Herculis (2021),"We present time-series photometry during eruption of the extremely fast nova
V1674 Herculis (Nova Her 2021). The 2021 light curve showed periodic signals at
0.152921(3) d and 501.486(5) s, which we interpret as respectively the orbital
and white dwarf spin-periods in the underlying binary. We also detected a
sideband signal at the /difference/ frequency between these two clocks. During
the first 15 days of outburst, the spin-period appears to have increased by
0.014(1)%. This increase probably arose from the sudden loss of
high-angular-momentum gas (""the nova explosion"") from the rotating, magnetic
white dwarf. Both periodic signals appeared remarkably early in the outburst,
which we attribute to the extreme speed with which the nova evolved (and became
transparent to radiation from the inner binary). After that very fast initial
increase of ~71 ms, the spin-period commenced a steady decrease of ~160 ms/year
-- about 100x faster than usually seen in intermediate polars. This is probably
due to high accretion torques from very high mass-transfer rates, which might
be common when low-mass donor stars are strongly irradiated by a nova outburst.",2207.00181v1
2011-06-07,"Spectral Energy Distributions of Young Stars in IC 348: The Role of Disks in Angular Momentum Evolution of Young, Low-Mass Stars","Theoretical work suggests that a young star's angular momentum and rotation
rate may be strongly influenced by magnetic interactions with its circumstellar
disk. A generic prediction of these 'disk-locking' (DL) theories is that a
disk-locked star will be forced to co-rotate with the Keplerian angular
velocity of the inner edge of the disk. These theories have also been
interpreted to suggest a correlation between young stars' rotation periods and
the structural properties of their disks, such that slowly rotating stars
possess close-in disks that enforce the star's slow rotation, whereas rapidly
rotating stars possess anemic or evacuated inner disks that are unable to brake
the stars and they spin up as they contract. To test these expectations, we
model the SEDs of 33 young stars in IC 348 with known rotation periods and
infrared excesses indicating the presence of disks. For each star, we match the
observed spectral energy distribution, typically sampling 0.6-8.0 \mum, to a
grid of 200,000 pre-computed star+disk radiative transfer models, from which we
infer the disk's inner-truncation radius (R_trunc). We then compare this
R_trunc to the disk's co-rotation radius (R_co), calculated from the star's
rotation period. We do not find obvious differences in the disk R_trunc of slow
vs. rapid rotators. This holds true both at the level of whether close-in disk
material is present at all, and in analyzing the precise location of the inner
disk edge relative to the R_co amongst the subset of stars with close-in disk
material. One interpretation is that DL is unimportant for the IC 348 stars in
our sample. Alternatively, if DL does operate, then it must operate on both the
slow and rapid rotators, potentially producing both spin-up and spin-down
torques, and the transition from the disk-locked state to the disk-released
state must occur more rapidly than the stellar contraction timescale.",1106.1468v2
2019-05-14,Spectral and Timing Analysis of the accretion-powered pulsar 4U 1626-67 observed with Suzaku and NuSTAR,"We present an analysis of the spectral shape and pulse profile of the
accretion-powered pulsar 4U 1626-67 observed with Suzaku and NuSTAR during a
spin-up state. The pulsar, which experienced a torque reversal to spin-up in
2008, has a spin period of 7.7 s. Comparing the phase-averaged spectra obtained
with Suzaku in 2010 and with NuSTAR in 2015, we find that the spectral shape
changed between the two observations: the 3-10 keV flux increased by 5% while
the 30-60 keV flux decreased significantly by 35%. Phase-averaged and
phase-resolved spectral analysis shows that the continuum spectrum observed by
NuSTAR is well described by an empirical NPEX continuum with an added broad
Gaussian emission component around the spectral peak at 20 keV. Taken together
with the observed Pdot value obtained from Fermi/GBM, we conclude that the
spectral change between the Suzaku and NuSTAR observations was likely caused by
an increase of the accretion rate. We also report the possible detection of
asymmetry in the profile of the fundamental cyclotron line. Furthermore, we
present a study of the energy-resolved pulse profiles using a new relativistic
ray tracing code, where we perform a simultaneous fit to the pulse profiles
assuming a two-column geometry with a mixed pencil- and fan-beam emission
pattern. The resulting pulse profile decompositions enable us to obtain
geometrical parameters of accretion columns (inclination, azimuthal and polar
angles) and a fiducial set of beam patterns. This information is important to
validate the theoretical predictions from radiation transfer in a strong
magnetic field.",1905.05356v1
2005-01-27,Current-induced macrospin vs spin-wave excitations in spin valves,"The mode dependence of current-induced magnetic excitations in spin valves is
studied theoretically. The torque exerted on the magnetization by transverse
spin currents as well as the Gilbert damping constant are found to depend
strongly on the wave length of the excitation (spin wave). Analytic expressions
are presented for the critical currents that excite a selected spin wave. The
onset of macrospin (zero wavelength) vs finite wavelength instabilities depends
on the device parameters and the current direction, in agreement with recent
experimental findings.",0501672v3
2014-07-29,Spin-Hall Nano-oscillator: a micromagnetic study,"This letter studies the dynamical behavior of spin-Hall nanoscillators from a
micromagnetic point of view. The model parameters have been identified by
reproducing recent experimental data quantitatively. Our results indicate that
a strongly localized mode is observed for in-plane bias fields such as in the
experiments, while predict the excitation of an asymmetric propagating mode for
large enough out-of plane bias field similarly to what observed in spin-torque
nanocontact oscillators. Our findings show that spin-Hall nanoscillators can
find application as spin-wave emitters for magnonic applications where spin
waves are used for transmission and processing information on nanoscale.",1407.7655v1
2023-07-17,Visualization of out-of-plane spin generation in mirror symmetry broken Co,"Generating out-of-plane spins in sputtered materials holds immense potential
for achieving field-free spin-orbit torque switching in practical applications
and mass production. In this work, we present the detection of out-of-plane
spins from single-layer ferromagnetic Co layers, which are visualized through
helicity-dependent photomapping techniques. Our experiments have shown that
out-of-plane spin generation is dependent on the magnetization direction,
current density, and Co thickness. Our findings indicate that amorphous
sputtered Co can be a promising candidate as an out-of-plane spin source
material for industrial massive production.",2307.08273v1
2011-07-28,Quantum information transfer between topological and spin qubit systems,"We propose a method to coherently transfer quantum information, and to create
entanglement, between topological qubits and conventional spin qubits. Our
suggestion uses gated control to transfer an electron (spin qubit) between a
quantum dot and edge Majorana modes in adjacent topological superconductors.
Because of the spin polarization of the Majorana modes, the electron transfer
translates spin superposition states into superposition states of the Majorana
system, and vice versa. Furthermore, we show how a topological superconductor
can be used to facilitate long-distance quantum information transfer and
entanglement between spatially separated spin qubits.",1107.5703v2
2020-05-04,Large interfacial spin-orbit torques in layered antiferromagnetic insulator NiPS$_3$/ferromagnet bilayers,"Finding efficient ways of manipulating magnetic bits is one of the core goals
in spintronic research. Electrically-generated spin-orbit torques (SOTs) are
good candidates for this and the search for materials capable of generating
highly-efficient SOTs has gained a lot of traction in the recent years. While
antiferromagnet/ferromagnet bilayer structures have been employed extensively
for passive applications, e.g. by using exchange bias fields, their active
properties are not yet widely employed. Here we show the presence of large
interfacial SOTs in bilayer of a ferromagnet and the two-dimensional layered
antiferromagnetic insulator NiPS$_3$. We observe a large in-plane damping-like
interfacial torque, showing a torque conductivity of $\sigma_\mathrm{DL}
\approx 1 \times 10^{5} \mathrm{(\frac{\hbar}{2e}) /(\Omega m)}$ even at room
temperature, comparable to the best devices reported in the literature for
standard heavy-metal-based and topological insulators-based devices.
Additionally, our devices also show an out-of-plane field-like torque arising
from the NiPS$_3$/ferromagnet interface, further indicating the presence of an
interfacial spin-orbit coupling in our structures. Temperature-dependent
measurements reveal an increase of the SOTs with a decreasing temperature below
the N\'eel temperature of NiPS$_3$ ($T_N \approx 170 \mathrm{K}$), pointing to
a possible effect of the magnetic ordering on our measured SOTs. Our findings
show the potential of antiferromagnetic insulators and two-dimensional
materials for future spintronic applications.",2005.01368v3
2015-11-01,Reciprocal spin Hall effects in conductors with strong spin-orbit coupling: a review,"Spin Hall effect and its inverse provide essential means to convert charge to
spin currents and vice versa, which serve as a primary function for spintronic
phenomena such as the spin-torque ferromagnetic resonance and the spin Seebeck
effect. These effects can oscillate magnetization or detect a thermally
generated spin splitting in the chemical potential. Importantly this conversion
process occurs via the spin-orbit interaction, and requires neither magnetic
materials nor external magnetic fields. However, the spin Hall angle, i.e., the
conversion yield between the charge and spin currents, depends severely on the
experimental methods. Here we discuss the spin Hall angle and the spin
diffusion length for a variety of materials including pure metals such as Pt
and Ta, alloys and oxides determined by the spin absorption method in a lateral
spin valve structure.",1511.00332v1
2018-05-29,Efficient injection and detection of out-of-plane spins via the anomalous spin Hall effect in permalloy nanowires,"We report a novel mechanism for the electrical injection and detection of
out-of-plane spin accumulation via the anomalous spin Hall effect (ASHE), where
the direction of the spin accumulation can be controlled by manipulating the
magnetization of the ferromagnet. This mechanism is distinct from the spin Hall
effect (SHE), where the spin accumulation is created along a fixed direction
parallel to an interface. We demonstrate this unique property of the ASHE in
nanowires made of permalloy (Py), to inject and detect out-of-plane spin
accumulation in a magnetic insulator, yttrium iron garnet (YIG). We show that
the efficiency for the injection/detection of out-of-plane spins can be up to
50% of that of in-plane spins. We further report the possibility to detect spin
currents parallel to the Py/YIG interface for spins fully oriented in the
out-of-plane direction, resulting in a sign reversal of the non-local magnon
spin signal. The new mechanisms that we have demonstrated are highly relevant
for spin torque devices and applications.",1805.11575v1
2018-02-19,Strong enhancement of the spin Hall effect by spin fluctuations near the Curie point of FexPt1-x alloys,"Robust spin Hall effects (SHE) have recently been observed in non-magnetic
heavy metal systems with strong spin-orbit interactions. These SHE are either
attributed to an intrinsic band-structure effect or to extrinsic spin-dependent
scattering from impurities, namely side-jump or skew scattering. Here we report
on an extraordinarily strong spin Hall effect, attributable to spin
fluctuations, in ferromagnetic FexPt1-x alloys near their Curie point, tunable
with x. This results in a damping-like spin-orbit torque being exerted on an
adjacent ferromagnetic layer that is strongly temperature dependent in this
transition region, with a peak value that indicates a lower bound 0.34 (+-)
0.02 for the peak spin Hall ratio within the FePt. We also observe a pronounced
peak in the effective spin-mixing conductance of the FM/FePt interface, and
determine the spin diffusion length in these FexPt1-x alloys. These results
establish new opportunities for fundamental studies of spin dynamics and
transport in ferromagnetic systems with strong spin fluctuations, and a new
pathway for efficiently generating strong spin currents for applications.",1802.06911v1
2022-03-02,Atomic-Scale Spin-Wave Polarizer Based on a Sharp Antiferromagnetic Domain Wall,"We theoretically study the scattering of spin waves from a sharp domain wall
in an antiferromagnetic spin chain. While the continuum model for an
antiferromagnetic material yields the well-known result that spin waves can
pass through a wide domain wall with no reflection, here we show that, based on
the discrete spin Hamiltonian, spin waves are generally reflected by a domain
wall with a reflection coefficient that increases as the domain-wall width
decreases. Remarkably, we find that, in the interesting case of an atomically
sharp domain wall, the reflection of spin waves exhibits strong dependence on
the state of circular polarization of the spin waves, leading to mainly
reflection for one polarization while permitting partial transmission for the
other, thus realizing an atomic-scale spin-wave polarizer. The polarization of
the transmitted spin wave depends on the orientation of the spin in the sharp
domain wall, which can be controlled by an external field or spin torque. Our
utilization of a sharp antiferromagnetic domain wall as an atomic-scale
spin-wave polarizer leads us to envision that ultra-small magnetic solitons
such as domain walls and skyrmions may enable realizations of atomic-scale
spin-wave scatterers with useful functionalities.",2203.01453v1
1998-02-12,Warped Disks as a Possible Origin of Torque Reversals in Accretion-Powered Pulsars,"Enigmatic transitions between spin-up and spin-down have been observed in
several X-ray pulsars accreting matter via an accretion disk. In these
transitions, the torque changes sign but remains at nearly the same magnitude.
It has been noted previously that alternating prograde and retrograde disk
flows would explain many features of the torque reversals, although it has been
unclear how a stable retrograde disk could be formed. We suggest that the
reversals may be related to the disk at times being warped to such an extent
that the inner region becomes tilted by more than 90 degrees. This region would
thus become retrograde, leading to a negative torque. Accretion disk models can
show such behavior, if account is taken of a warping instability due to
irradiation. The resulting `flip-overs' of the inner parts of the disk can
reproduce most characteristics of the observations, although it remains unclear
what sets the timescale on which the phenomenon occurs. If this model were
correct, it would have a number of ramifications, for instance that in the
spin-down state the X-ray source would mostly be observed through the accretion
disk.",9802162v2
2000-03-13,Accretion disc-stellar magnetosphere interaction: field line inflation and the effect on the spin-down torque,"We calculate the structure of a force-free magnetosphere which is assumed to
corotate with a central star and which interacts with an embedded
differentially rotating accretion disc. The magnetic and rotation axes are
aligned and the stellar field is assumed to be a dipole. We concentrate on the
case when the amount of field line twisting through the disc-magnetosphere
interaction is large and consider different outer boundary conditions. In
general the field line twisting produces field line inflation (eg. Bardou &
Heyvaerts 1996) and in some cases with large twisting many field lines can
become open. We calculate the spin-down torque acting between the star and the
disc and we find that it decreases significantly for cases with large field
line twisting. This suggests that the oscillating torques observed for some
accreting neutron stars could be due to the magnetosphere varying between
states with low and high field line inflation. Calculations of the spin
evolution of T Tauri stars may also have to be revised in light of the
significant effect that field line twisting has on the magnetic torque
resulting from star-disc interactions.",0003186v1
2011-11-18,4U 1626-67 as seen by Suzaku before and after the 2008 torque reversal,"Aims. The accretion-powered pulsar 4U 1626-67 experienced a new torque
reversal at the beginning of 2008, after about 18 years of steadily spinning
down. The main goal of the present work is to study this recent torque reversal
that occurred in 2008 February.
  Methods. We present a spectral analysis of this source using two pointed
observations performed by Suzaku in 2006 March and in 2010 September.
  Results. We confirm with Suzaku the presence of a strong emission-line
complex centered on 1 keV, with the strongest line being the hydrogen-like Ne
Ly-alpha at 1.025(3) keV. We were able to resolve this complex with up to seven
emission lines. A dramatic increase of the intensity of the Ne Ly-alpha line
after the 2008 torque reversal occurred, with the equivalent width of this line
reaching almost the same value measured by ASCA in 1993. We also report on the
detection of a cyclotron line feature centered at ~37 keV. In spite of the fact
that an increase of the X-ray luminosity (0.5-100 keV) of a factor of ~2.8
occurred between these two observations, no significant change in the energy of
the cyclotron line feature was observed. However, the intensity of the ~1 keV
line complex increased by an overall factor of ~8.
  Conclusions. Our results favor a scenario in which the neutron star in 4U
1626-67 accretes material from a geometrically thin disk during both the
spin-up and spin-down phases.",1111.4514v2
2015-07-09,Spin-orbit torques for current parallel and perpendicular to a domain wall,"We report field- and current-induced domain wall (DW) depinning experiments
in Ta/Co20Fe60B20/MgO nanowires through a Hall cross geometry. While purely
field-induced depinning shows no angular dependence on in-plane fields, the
effect of the current depends crucially on the internal DW structure, which we
manipulate by an external magnetic in-plane field. We show for the first time
depinning measurements for a current sent parallel to the DW and compare its
depinning efficiency with the conventional case of current flowing
perpendicularly to the DW. We find that the maximum efficiency is similar for
both current directions within the error bars, which is in line with a
dominating damping-like spin-orbit torque (SOT) and indicates that no large
additional torques arise for currents parallel to the DW. Finally, we find a
varying dependence of the maximum depinning efficiency angle for different DWs
and pinning levels. This emphasizes the importance of our full angular scans
compared to previously used measurements for just two field directions
(parallel and perpendicular to the DW) and shows the sensitivity of the
spin-orbit torque to the precise DW structure and pinning sites.",1507.02435v1
2016-04-11,A fully relativistic description of spin-orbit torques by means of linear response theory,"Symmetry and magnitude of spin-orbit torques (SOT), i.e., current-induced
torques on the magnetization of systems lacking inversion symmetry, are
investigated in a fully relativistic linear response framework based on the
Kubo formalism. By applying all space-time symmetry operations contained in the
magnetic point group of a solid to the relevant response coefficient, the
torkance expressed as torque-current correlation function, restrictions to the
shape of the direct and inverse response tensors are obtained. These are shown
to apply to the corresponding thermal analogues as well, namely the direct and
inverse thermal SOT in response to a temperature gradient or heat current.
Using an implementation of the Kubo-Bastin formula for the torkance into a
first-principles multiple-scattering Green's function framework and accounting
for disorder effects via the so-called coherent potential approximation (CPA),
all contributions to the SOT in pure systems, dilute as well as concentrated
alloys can be treated on equal footing. This way, material specific values for
all torkance tensor elements in the fcc (111) trilayer alloy system Pt |
Fe$_x$Co$_{1-x}$ | Cu are obtained over a wide concentration range and
discussed in comparison to results for electrical and spin conductivity, as
well as to previous work - in particular concerning symmetry w.r.t.
magnetization reversal and the nature of the various contributions.",1604.02798v1
2020-02-02,Static and dynamic properties of bimerons in a frustrated ferromagnetic monolayer,"Magnetic bimeron is a topological counterpart of skyrmions in in-plane
magnets, which can be used as a spintronic information carrier. We report the
static properties of bimerons with different topological structures in a
frustrated ferromagnetic monolayer, where the bimeron structure is
characterized by the vorticity $Q_{\text{v}}$ and helicity $\eta$. It is found
that the bimeron energy increases with $Q_{\text{v}}$, and the energy of an
isolated bimeron with $Q_{\text{v}}=\pm 1$ depends on $\eta$. We also report
the dynamics of frustrated bimerons driven by the spin-orbit torques, which
depend on the strength of the dampinglike and fieldlike torques. We find that
the isolated bimeron with $Q_{\text{v}}=\pm 1$ can be driven into linear or
elliptical motion when the spin polarization is perpendicular to the easy axis.
We numerically reveal the damping dependence of the bimeron Hall angle driven
by the dampinglike torque. Besides, the isolated bimeron with $Q_{\text{v}}=\pm
1$ can be driven into rotation by the dampinglike torque when the spin
polarization is parallel to the easy axis. The rotation frequency is
proportional to the driving current density. In addition, we numerically
demonstrate the possibility of creating a bimeron state with a higher or lower
topological charge by the current-driven collision and merging of bimeron
states with different $Q_{\text{v}}$. Our results could be useful for
understanding the bimeron physics in frustrated magnets.",2002.00312v3
2020-12-22,Field-free deterministic switching of a perpendicularly polarized magnet using unconventional spin-orbit torques in WTe2,"Spin-orbit torque (SOT) driven deterministic control of the magnetization
state of a magnet with perpendicular magnetic anisotropy (PMA) is key to next
generation spintronic applications including non-volatile, ultrafast, and
energy efficient data storage devices. But, field-free deterministic switching
of perpendicular magnetization remains a challenge because it requires an
out-of-plane anti-damping torque, which is not allowed in conventional spin
source materials such as heavy metals (HM) and topological insulators due to
the system's symmetry. The exploitation of low-crystal symmetries in emergent
quantum materials offers a unique approach to achieve SOTs with unconventional
forms. Here, we report the first experimental realization of field-free
deterministic magnetic switching of a perpendicularly polarized van der Waals
(vdW) magnet employing an out-of-plane anti-damping SOT generated in layered
WTe2 which is a low-crystal symmetry quantum material. The numerical
simulations confirm that out-of-plane antidamping torque in WTe2 is responsible
for the observed magnetization switching in the perpendicular direction.",2012.12388v1
2023-02-21,On the minimum spin period of accreting pulsars,"The distribution of the spin frequencies of neutron stars in low-mass X-ray
binaries exhibits a cut-off at 730 Hz, below the break-up frequency
(mass-shedding limit) of neutron stars. The absence of the sub-millisecond
pulsars presents a problem, given that these systems are older than the spin-up
timescale. We confront models of disc-magnetosphere interaction near torque
equilibrium balanced by the torque due to gravitational wave emission. We note
that field lines penetrating the disc beyond the inner radius reduce the
maximum rotation frequency of the star, a result well-known since the seminal
work of Ghosh & Lamb. We show that the polar cap area corresponds to about half
the neutron star surface area at the cut-off frequency if the inner radius is
slightly smaller than the corotation radius. We then include the change in the
moment of inertia of the star due to the accretion of mass and find that this
effect further reduces the maximum rotation frequency of the star. Finally, we
include the torque due to gravitational wave emission and calculate its
contribution to the torque equilibrium. Our results suggest that all three
processes are significant at the cut-off frequency, and all of them must be
considered in addressing the absence of sub-millisecond pulsars.",2302.10649v3
2023-10-05,Spin-orbit torques and spin Hall magnetoresistance generated by twin-free and amorphous Bi0.9Sb0.1 topological insulator films,"Topological insulators have attracted great interest as generators of
spin-orbit torques (SOTs) in spintronic devices.
Bi\textsubscript{1-x}Sb\textsubscript{x} is a prominent topological insulator
that has a high charge-to-spin conversion efficiency. However, the origin and
magnitude of the SOTs induced by current-injection in
Bi\textsubscript{1-x}Sb\textsubscript{x} remain controversial. Here we report
the investigation of the SOTs and spin Hall magnetoresistance resulting from
charge-to-spin conversion in twin-free epitaxial layers of
Bi\textsubscript{0.9}Sb\textsubscript{0.1}(0001) coupled to FeCo, and compare
it with that of amorphous Bi\textsubscript{0.9}Sb\textsubscript{0.1}. We find a
large charge-to-spin conversion efficiency of 1 in the first case and less than
0.1 in the second, confirming crystalline
Bi\textsubscript{0.9}Sb\textsubscript{0.1} as a strong spin injector material.
The SOTs and spin Hall magnetoresistance are independent of the direction of
the electric current, indicating that charge-to-spin conversion in
single-crystal Bi\textsubscript{0.9}Sb\textsubscript{0.1}(0001) is isotropic
despite the strong anisotropy of the topological surface states. Further, we
find that the damping-like SOT has a non-monotonic temperature dependence with
a minimum at 20~K. By correlating the SOT with resistivity and weak
antilocalization measurements, we conclude that charge-spin conversion occurs
via thermally-excited holes from the bulk states above 20~K, and conduction
through the isotropic surface states with increasing spin polarization due to
decreasing electron-electron scattering below 20~K.",2310.03487v1
2020-06-19,"Spin-orbit-proximitized ferromagnetic metal by monolayer transition metal dichalcogenide: Atlas of spectral functions, spin textures and spin-orbit torques in Co/MoSe$_2$, Co/WSe$_2$ and Co/TaSe$_2$ heterostructures","The bilayer heterostructures composed of an ultrathin ferromagnetic metal
(FM) and a material hosting strong spin-orbit (SO) coupling are principal
resource for SO torque and spin-to-charge conversion nonequilibrium effects in
spintronics. We demonstrate how hybridization of wavefunctions of Co layer and
a monolayer of transition metal dichalcogenides (TMDs)---such as semiconducting
MoSe$_2$ and WSe$_2$ or metallic TaSe$_2$---can lead to dramatic transmutation
of electronic and spin structure of Co within some distance away from its
interface with TMD, when compared to the bulk of Co or its surface in contact
with vacuum. This is due to proximity induced SO splitting of Co bands encoded
in the spectral functions and spin textures on its monolayers, which we obtain
using noncollinear density functional theory (ncDFT) combined with equilibrium
Green function (GF) calculations. In fact, SO splitting is present due to
structural inversion asymmetry of the bilayer even if SO coupling within TMD
monolayer is artificially switched off in ncDFT calculations, but switching it
on makes the effects associated with proximity SO coupling within Co layer
about five times larger. Injecting spin-unpolarized charge current through
SO-proximitized monolayers of Co generates nonequilibrium spin density over
them, so that its cross product with the magnetization of Co determines SO
torque. The SO torque computed via first-principles quantum transport
methodology, which combines ncDFT with nonequilibrium GF calculations, can be
used as the screening parameter to identify optimal combination of materials
and their interfaces for applications in spintronics. In particular, we
identify heterostructure two-monolayer-Co/monolayer-WSe$_2$ as the most
optimal.",2006.11335v1
2017-08-07,Photon Torpedoes and Rytov Pinwheels: Integral-Equation Modeling of Non-Equilibrium Fluctuation-Induced Forces and Torques on Nanoparticles,"We present new theoretical tools, based on fluctuational electrodynamics and
the integral-equation approach to computational electromagnetism, for numerical
modeling of forces and torques on bodies of complex shapes and materials due to
emission of thermal radiation out of thermal equilibrium. This extends our
recently-developed fluctuating-surface-current (FSC) and
fluctuating-volume-current (FVC) techniques for radiative heat transfer to the
computation of non-equilibrium fluctuation-induced forces and torques; as we
show, the extension is non-trivial due to the greater computational cost of
modeling radiative momentum transfer, including new singularities that must be
carefully neutralized. We introduce a new analytical cancellation technique
that addresses these challenges and allows, for the first time, accurate and
efficient prediction of non-equilibrium forces and torques on bodies of
essentially arbitrary shapes---including asymmetric and chiral particles---and
complex material properties, including continuously-varying and anisotropic
dielectrics. We validate our approach by showing that it reproduces known
results, then present new numerical predictions of non-equilibrium
self-propulsion, self-rotation, and momentum-transfer phenomena in complex
geometries that would be difficult or impossible to study with existing
methods. Our findings indicate that the fluctuation-induced dynamics of
micron-size room-temperature bodies in cold environments involve microscopic
length scales but macroscopic time scales, with typical linear and angular
velocities on the order of microns/second and radians/second; For a
micron-scale gear driven by thermal radiation from a nearby chiral emitter, we
find a strong and non-monotonic dependence of the magnitude and even the
\textit{sign} of the induced torque on the temperature of the emitter.",1708.01985v1
2017-02-23,Tides in a body librating about a spin-orbit resonance. Generalisation of the Darwin-Kaula theory,"The Darwin-Kaula theory of bodily tides is intended for celestial bodies
rotating without libration. We demonstrate that this theory, in its customary
form, is inapplicable to a librating body. Specifically, in the presence of
libration in longitude, the actual spectrum of Fourier tidal modes differs from
the conventional spectrum rendered by the Darwin-Kaula theory for a
non-librating celestial object. This necessitates derivation of formulae for
the tidal torque and the tidal heating rate, that are applicable under
libration.
  We derive the tidal spectrum for longitudinal forced libration with one and
two main frequencies, generalisation to more main frequencies being
straightforward. (By main frequencies we understand those emerging due to the
triaxiality of the librating body.) Separately, we consider a case of free
libration at one frequency (once again, generalisation to more frequencies
being straightforward).
  We also calculate the tidal torque. This torque provides correction to the
triaxiality-caused physical libration. Our theory is not self-consistent: we
assume that the tidal torque is much smaller than the
permanent-triaxiality-caused torque; so the additional libration due to tides
is much weaker than the main libration due to the permanent triaxiality.
  Finally, we calculate the tidal dissipation rate in a body experiencing
forced libration at the main mode, or free libration at one frequency, or
superimposed forced and free librations.",1702.07376v7
2017-10-19,Repercussions of thermal atmospheric tides on the rotation of terrestrial planets in the habitable zone,"Semidiurnal atmospheric thermal tides are important for terrestrial
exoplanets in the habitable zone of their host stars. With solid tides, they
torque these planets, thus contributing to determine their rotation states as
well as their climate. Given the complex dynamics of thermal tides, analytical
models are essential to understand its dependence on the structure and rotation
of planetary atmospheres and the tidal frequency. In this context, the state of
the art model proposed in the 60's by Lindzen and Chapman explains well the
properties of thermal tides in the asymptotic regime of Earth-like rapid
rotators but predicts a non-physical diverging tidal torque in the vicinity of
the spin-orbit synchronization. In this work, we present a new model that
addresses this issue by taking into account dissipative processes through a
Newtonian cooling. First, we recover the tidal torque recently obtained with
numerical simulations using General Circulation Models (GCM). Second, we show
that the tidal response is very sensitive to the atmospheric structure,
particularly to the stability with respect to convection. A strong stable
stratification is able to annihilate the atmospheric tidal torque, leading to
synchronization, while a convective atmosphere will be submitted to a strong
torque, leading to a non-synchronized rotation state.",1710.07222v1
2019-09-09,All-optical spin switching under different spin configurations,"We employ an atomic spin model and present a systematic investigation from a
single spin to a large system of over a million spins. To have an efficient
spin switching, the electron initial momentum direction must closely follow the
spin's orientation, so the orbital angular momentum is transverse to the spin
and consequently the spin-orbit torque lies in the same direction as the spin.
The module of the spin-orbit torque is $\lambda |{\bf S}||{\bf r}||{\bf P}|
\sqrt{\cos^2\alpha+\cos^2\beta-2\cos\alpha \cos\beta \cos\gamma} $, where
$\alpha(\beta)$ is the angle between spin {\bf S} and position {\bf r}(momentum
{ \bf P}) and $\gamma$ is the angle between {\bf r} and {\bf P}. These findings
are manifested in a much larger system. The spin response depends on underlying
spin structures. A linearly polarized laser pulse creates a dip in a uniform
inplane-magnetized thin film, but has little effects on \neel and Bloch walls.
Both right- and left- circularly polarized light ($\sigma^+$ and $\sigma^-$)
have stronger but different effects in both uniform spin domains and Neel
walls. While $\sigma^+$ light creates a basin of spins pointing down,
$\sigma^-$ light creates a mound of spins pointing up. In the vicinity of the
structure spins are reversed, similar to the experimental observation.
$\sigma^+$ light has a dramatic effect, disrupting spins in Bloch walls. By
contrast, $\sigma^-$ light has a small effect on Bloch walls because $\sigma^-$
only switches down spins up and once the spins already point up, there is no
major effect.",1909.04186v2
2012-11-20,MHD simulations of accretion onto a dipolar magnetosphere. II. Magnetospheric ejections and stellar spin-down,"This paper examines the outflows associated with the interaction of a stellar
magnetosphere with an accretion disk. In particular, we investigate the
magnetospheric ejections (MEs) due to the expansion and reconnection of the
field lines connecting the star with the disk. Our aim is to study the
dynamical properties of the outflows and evaluate their impact on the angular
momentum evolution of young protostars. Our models are based on axisymmetric
time-dependent magneto-hydrodynamic simulations of the interaction of the
dipolar magnetosphere of a rotating protostar with a viscous and resistive
disk, using alpha prescriptions for the transport coefficients. Our simulations
are designed in order to model: the accretion process and the formation of
accretion funnels; the periodic inflation/reconnection of the magnetosphere and
the associated MEs; the stellar wind. Similarly to a magnetic slingshot, MEs
can be powered by the rotation of both the disk and the star so that they can
efficiently remove angular momentum from both. Depending on the accretion rate,
MEs can extract a relevant fraction of the accretion torque and, together with
a weak but non-negligible stellar wind torque, can balance the spin-up due to
accretion. When the disk truncation approaches the corotation radius, the
system enters a ""propeller"" regime, where the torques exerted by the disk and
the MEs can even balance the spin-up due to the stellar contraction. The MEs
spin-down efficiency can be compared to other scenarios, such as the Ghosh &
Lamb, X-wind or stellar wind models. Nevertheless, for all scenarios, an
efficient spin-down torque requires a rather strong dipolar component, which
has been seldom observed in classical T Tauri stars. A better analysis of the
torques acting on the protostar must take into account non-axisymmetric and
multipolar magnetic components consistent with observations.",1211.4844v1
2020-12-16,Spin Change of Asteroid 2012 TC4 probably by Radiation Torques,"Asteroid 2012 TC4 is a small ($\sim$10 m) near-Earth object that was observed
during its Earth close approaches in 2012 and 2017. Earlier analyses of light
curves revealed its excited rotation state. We collected all available
photometric data from the two apparitions to reconstruct its rotation state and
convex shape model. We show that light curves from 2012 and 2017 cannot be
fitted with a single set of model parameters -- the rotation and precession
periods are significantly different for these two data sets and they must have
changed between or during the two apparitions. Nevertheless, we could fit all
light curves with a dynamically self-consistent model assuming that the spin
states of 2012 TC4 in 2012 and 2017 were different. To interpret our results,
we developed a numerical model of its spin evolution in which we included two
potentially relevant perturbations: (i) gravitational torque due to the Sun and
Earth, and (ii) radiation torque known as the
Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. Despite our model
simplicity, we found that the role of gravitational torques is negligible.
Instead, we argue that the observed change of its spin state may be plausibly
explained as a result of the YORP torque. To strengthen this interpretation we
verify that (i) the internal energy dissipation due to material inelasticity,
and (ii) an impact with a sufficiently large interplanetary particle are both
highly unlikely causes its observed spin state change. If true, this is the
first case when the YORP effect has been detected for a tumbling body.",2012.08771v1
2007-11-15,Enhancement in spin-torque efficiency by nonuniform spin current generated within a tapered nanopillar spin valve,"We examine the effect a spatially non-uniform spin current with a component
polarized partially out of the plane has on a low saturation magnetization
nanomagnet free layer. Micromagnetic simulations indicate that the spin torque
efficiency acting upon the reversing nanomagnet can be enhanced through this
process, resulting in faster switching with smaller currents. In doing so, we
determine that micromagnetic structure within the nanomagnets can be beneficial
for reversal processes. We verify this enhancement experimentally in devices
with a tapered nanopillar geometry that generates a spin current polarized
partly out of plane. Finally, to take even better advantage of these effects,
we examine micromagnetically the benefits of a tapered three-magnetic-layer
structure that further reduces reversal times while maintaining the thermal
stability of the free layer.",0711.2479v1
2010-05-14,Spin Torque Dynamics with Noise in Magnetic Nano-System,"We investigate the role of equilibrium and nonequilibrium noise in the
magnetization dynamics on mono-domain ferromagnets. Starting from a microscopic
model we present a detailed derivation of the spin shot noise correlator. We
investigate the ramifications of the nonequilibrium noise on the spin torque
dynamics, both in the steady state precessional regime and the spin switching
regime. In the latter case we apply a generalized Fokker-Planck approach to
spin switching, which models the switching by an Arrhenius law with an
effective elevated temperature. We calculate the renormalization of the
effective temperature due to spin shot noise and show that the nonequilibrium
noise leads to the creation of cold and hot spot with respect to the noise
intensity.",1005.2439v3
2011-07-17,Spin current induced magnetization oscillations in a paramagnetic disc,"When electron spins are injected uniformly into a paramagnetic disc, they can
precess along the demagnetizing field induced by the resulting magnetic moment.
Normally this precession damps out by virtue of the spin relaxation which is
present in paramagnetic materials. We propose a new mechanism to excite a
steady-state form of this dynamics by injecting a constant spin current into
this paramagnetic disc. We show that the rotating magnetic field generated by
the eddy currents provide a torque which makes this possible. Unlike the
ferromagnetic equivalent, the spin-torque-oscillator, the oscillation frequency
is fixed and determined by the dimensions and intrinsic parameters of the
paramagnet. The system possesses an intrinsic threshold for spin injection
which needs to be overcome before steady-state precession is possible. The
additional application of a magnetic field lowers this threshold. We discuss
the feasibility of this effect in modern materials. Transient analysis using
pump-probe techniques should give insight in the physical processes which
accompany this effect.",1107.3288v1
2013-02-19,Optimization of spin-torque switching using AC and DC pulses,"We explore spin-torque induced magnetic reversal in magnetic tunnel junctions
using combined AC and DC spin-current pulses. We calculate the optimal pulse
times and current strengths for both AC and DC pulses as well as the optimal AC
signal frequency, needed to minimize the Joule heat lost during the switching
process. The results of this optimization are compared against numeric
simulations. Finally we show how this optimization leads to different dynamic
regimes, where switching is optimized by either a purely AC or DC spin-current,
or a combination AC/DC spin-current, depending on the anisotropy energies and
the spin-current polarization.",1302.4770v4
2013-12-11,Interpreting the Spin-down Evolutions of Isolated Neutron Stars with Hall Effects,"The observed long-term spin-down evolution of isolated radio pulsars cannot
be explained by the standard magnetic dipole radiation with a constant braking
torque. However, how and why the torque varies still remains controversial,
which is a major issue in understanding neutron stars. Many pulsars have been
observed with significant long-term changes of their spin-down rates modulated
by quasi-periodic oscillations. Applying the phenomenological model of pulsar
timing noise we developed recently to the observed precise pulsar timing data
of isolated neutron stars, here we show that the observed long-term evolutions
of their spin-down rates and quasi-periodic modulations can be explained by
Hall effects in their crusts. Therefore the evolution of their crustal magnetic
fields, rather than that in their cores, dominates the observed long term
spin-down evolution of these young pulsars. Understanding of the nature of
pulsar timing noise not only reveals the interior physics of neutron stars, but
also allows physical modeling of pulsar spin-down and thus improves the
sensitivity of gravitational wave detections with pulsars.",1312.3049v2
2014-01-18,Enhancement of Perpendicular Magnetic Anisotropy and Transmission of Spin-Hall-Effect-Induced Spin Currents by a Hf Spacer Layer in W/Hf/CoFeB/MgO Layer,"We report that strong perpendicular magnetic anisotropy of the ferromagnetic
layer in a W/CoFeB/MgO multilayer structure can be established by inserting a
Hf layer as thin as 0.25 nm between the W and CoFeB layers. The Hf spacer also
allows transmission of spin currents generated by an in-plane charge current in
the W layer to apply strong spin torque on the CoFeB, thereby enabling
current-driven magnetic switching. The antidamping-like and field-like
components of the spin torque exerted on a 1 nm CoFeB layer are of comparable
magnitudes in this geometry. Both components originate from the spin Hall
effect in the underlying W layer.",1401.4617v1
2014-09-09,Why do galactic spins flip in the cosmic web? A Theory of Tidal Torques near saddles,"Filaments of the cosmic web drive spin acquisition of disc galaxies. The
point process of filament-type saddle represent best this environment and can
be used to revisit the Tidal Torque Theory in the context of an anisotropic
peak (saddle) background split. The constrained misalignment between the tidal
tensor and the Hessian of the density field generated in the vicinity of
filament saddle points simply explains the corresponding transverse and
longitudinal point-reflection symmetric geometry of spin distribution. It
predicts in particular an azimuthal orientation of the spins of more massive
galaxies and spin alignment with the filament for less massive galaxies. Its
scale dependence also allows us to relate the transition mass corresponding to
the alignment of dark matter halos spin relative to the direction of their
neighboring filament to this geometry, and to predict accordingly it s scaling
with the mass of non linearity, as was measured in simulations.",1409.2608v1
2015-04-10,Enhancement of the Anti-Damping Spin Torque Efficacy of Platinum by Interface Modification,"We report a strong enhancement of the efficacy of the spin Hall effect (SHE)
of Pt for exerting anti-damping spin torque on an adjacent ferromagnetic layer
by the insertion of $\approx$ 0.5 nm layer of Hf between a Pt film and a thin,
< 2 nm, Fe$_{60}$Co$_{20}$B$_{20}$ ferromagnetic layer. This enhancement is
quantified by measurement of the switching current density when the
ferromagnetic layer is the free electrode in a magnetic tunnel junction. The
results are explained as the suppression of spin pumping through a substantial
decrease in the effective spin-mixing conductance of the interface, but without
a concomitant reduction of the ferromagnet\' s absorption of the SHE generated
spin current.",1504.02806v1
2016-07-08,Supercurrent-induced Skyrmion dynamics and Tunable Weyl points in Chiral Magnet with Superconductivity,"Recent studies show superconductivity provides new perspectives on
spintronics. We study a heterostructure composed of an s-wave superconductor
and a cubic chiral-magnet that can stabilize a topological spin texture, a
skyrmion. We propose a supercurrent-induced spin torque that originates from
the spin-orbit coupling, and we show that the spin torque can drive a skyrmion
in an efficient way that reduces Joule heating. We also study the band
structure of Bogoliubov quasiparticles and show the existence of Weyl points,
whose positions can be controlled by the direction of the magnetization. This
results in an effective magnetic field acting on the quasiparticles in the
presence spin textures. Furthermore, the tilt of the Weyl cones can also be
tuned by the strength of the spin-orbit coupling, and we propose a possible
realization of type-II Weyl points.",1607.02336v4
2017-11-17,Shot noise of charge and spin transport in a junction with a precessing molecular spin,"Magnetic molecules and nanomagnets can be used to influence the electronic
transport in mesoscopic junction. In a magnetic field the precessional motion
leads to resonances in the dc- and ac-transport properties of a nanocontact, in
which the electrons are coupled to the precession. Quantities like the
dc-conductance or the ac-response provide valuable information like the level
structure and the coupling parameters. Here, we address the current noise
properties of such contacts. This encompasses the charge current and
spin-torque shot noise, which both show a step-like behavior as functions of
bias voltage and magnetic field. The charge current noise shows pronounced dips
around the steps, which we trace back to interference effects of electron in
quasienergy levels coupled by the molecular spin precession. We show that some
components of the noise of the spin-torque currents are directly related to the
Gilbert damping and, hence, are experimentally accessible. Our results show
that the noise characteristics allow to investigate in more detail the
coherence of spin transport in contacts containing magnetic molecules.",1711.06759v2
2018-09-08,Irrelevance of magnetic proximity effect to spin-orbit torques in heavy metal/ferromagnet bilayers,"The magnetic proximity effect (MPE) is a well-established magnetic phenomenon
that occurs at certain heavy metal (HM)/ferromagnet (FM) interfaces. However,
there is still an active debate as to whether the presence of a MPE affects
spin transport through such a HM/FM interface. Here we demonstrate that the MPE
at Pt/Co and Au0.25Pt0.75/Co interfaces can be enhanced substantially by
thermal annealing protocols. From this ability, we show that the MPE has no
discernable influence on either the damping-like or the field-like spin-orbit
torques exerted on the FM layer due to the spin Hall effect of the HM layer,
indicating a minimal role of the MPE compared to other interfacial effects,
e.g. spin memory loss and spin backflow.",1809.02828v2
2018-10-01,Energy-momentum tensor of a ferromagnet,"The energy-momentum tensor of a ferromagnet derived according to the standard
prescription of Noether's theorem has a major flaw: the term originating from
the spin Berry phase is gauge-dependent. As a consequence, some physical
quantities computed from the tensor show unphysical behavior. For example, the
presence of a spin-polarized current does not affect the energy of the domain
wall in the commonly accepted gauge, which implies-incorrectly-the absence of
the adiabatic spin torque. In other gauges, the spin torque shows unphysical
glitches occurring when the plane of magnetization crosses the Dirac string
associated with a magnetic monopole in spin space. We derive a gauge-invariant
energy-momentum tensor that is free from these artifacts but requires the
addition of an extra spatial dimension, with the ferromagnet living on its
boundary. It can be obtained most directly from the Wess-Zumino action for
spins, which relies on the same extra dimension.",1810.01006v2
2016-03-26,Strong Spin Hall Effect in the Antiferromagnet PtMn,"Effectively manipulating magnetism in ferromagnet (FM) thin film
nanostructures with an in-plane current has become feasible since the
determination of a 'giant' spin Hall effect (SHE) in certain heavy metal
(HM)/FM system. Recently, both theoretical and experimental reports indicate
that the non-collinear and collinear metallic antiferromagnet (AF) materials
can have both a large anomalous Hall effect (AHE) and a strong SHE. Here we
report a systematic study of the SHE in PtMn with several PtMn/FM systems. By
using interface engineering to reduce the 'spin memory loss' we obtain a spin
torque efficiency as large as 0.24. This is more than twice the previously
reported spin torque efficiency for PtMn. We also find that the apparent spin
diffusion length in PtMn is surprisingly long (about 2.3nm).",1603.08068v1
2020-09-25,Conserved current of nonconserved quantities,"We provide a unified semiclassical theory for the conserved current of
nonconserved quantities, and manifest it in two physical contexts: the spin
current of Bloch electrons and the charge current of mean-field Bogoliubov
quasiparticles. Several longstanding problems that limit the playground of the
conserved spin current of electrons are solved. We reveal that the hitherto
overlooked torque quadrupole density and Berry phase correction to the torque
dipole density are essential to assure a circulating spin current with
vanishing net flow at equilibrium. The band geometric origin of bulk spin
transport is ascertained to be the momentum space spin texture and Berry
curvature instead of the spin Berry curvature, paving the way for material
related studies. In superconductors the attained conserved charge current
corresponds to the quasiparticle charge current renormalized by the condensate
backflow. Its circulation at equilibrium gives an orbital magnetization, which
involves the characteristics of superconductivity, such as the Berry curvature
arising from unconventional pairing and an orbital magnetic moment induced by
the charge dipole of moving quasiparticles.",2009.12058v3
2021-04-22,Spin orbit torque nano-oscillators by dipole field-localized spin wave modes,"We demonstrate a high-quality spin orbit torque nano-oscillator comprised of
spin wave modes confined by the magnetic field by the strongly inhomogeneous
dipole field of a nearby micromagnet. This approach enables variable spatial
confinement and systematic tuning of magnon spectrum and spectral separations
for studying the impact of multi-mode interactions on auto-oscillations. We
find these dipole field-localized spin wave modes exhibit good characteristic
properties as auto-oscillators--narrow linewidth and large amplitude--while
persisting up to room temperature. We find that the linewidth of the
lowest-lying localized mode is approximately proportional to temperature in
good agreement with theoretical analysis of the impact of thermal fluctuations.
This demonstration of a clean oscillator with tunable properties provides a
powerful tool for understanding the fundamental limitations and linewidth
contributions to improve future spin-Hall oscillators.",2104.10838v3
2019-09-18,Micromagnetic Modeling of Telegraphic Mode Jumping in Microwave Spin Torque Oscillators,"The time domain stability of microwave spin torque oscillators (STOs) has
been investigated by systematic micromagnetic simulations. A model based on
internal spin wave reflection at grain boundaries with reduced exchange
coupling was implemented and used to study the oscillator under quasi-stable
operating conditions. Telegraphic mode jumping between two operating
frequencies (23.3 and 24.1 GHz) was observed in the time domain with
characteristic dwell times in the range of 10-100 ns. The oscillating volume
was shown to have a different shape at the distinct operating frequencies. The
shape difference is governed by spin wave reflections at the grain boundaries.
The resulting non-linear behavior of the oscillator was shown to be a
collective effect of spin wave scattering at different locations within a few
spin wavelengths from the nano-contact.",1909.08431v1
2020-05-15,Generation of Multipeak Spectrum of Spin Torque Oscillator in Non-linear Regime,"We investigate the spectral characteristics of spin torque oscillator (STO)
excited by the spin Hall-induced spin current. We observe that the modest spin
current injection triggers the conventional single peak oscillating behavior of
STO. As the spin current is further increased to enter the non-linear regime,
we find the transition of the spectrum from a single peak to multipeak
structure whose frequency spacing is constant. This behavior can be primarily
explained by the extremely broadened peak of the STO, which is accompanied by
the frequency-dependent filtering by the transmission line. To explain the
observation more quantitatively, we also discuss that the multipeak may reflect
the characteristics of the intrinsic dynamics of STO in the non-linear regime.",2005.07434v1
2021-01-18,Magnetization switching induced by spin-orbit torque from Co2MnGa magnetic Weyl semimetal thin films,"This study reports the magnetization switching induced by spin-orbit torque
(SOT) from the spin current generated in Co2MnGa magnetic Weyl semimetal (WSM)
thin films. We deposited epitaxial Co2MnGa thin films with highly B2-ordered
structure on MgO(001) substrates. The SOT was characterized by harmonic Hall
measurements in a Co2MnGa/Ti/CoFeB heterostructure and a relatively large spin
Hall efficiency of -7.8% was obtained.The SOT-induced magnetization switching
of the perpendicularly magnetized CoFeB layer was further demonstrated using
the structure. The symmetry of second harmonic signals, thickness dependence of
spin Hall efficiency, and shift of anomalous Hall loops under applied currents
were also investigated. This study not only contributes to the understanding of
the mechanisms of spin-current generation from magnetic-WSM-based
heterostructures, but also paves a way for the applications of magnetic WSMs in
spintronic devices.",2101.06881v1
2021-11-16,Unidirectional spin Hall magnetoresistance and spin-orbit torques in HM$_1$/Co/HM$_2$ trilayer systems,"We present a detailed analysis of harmonic longitudinal and Hall voltage
measurements for in-plane magnetized Pt/Co/Ta and Ta/Co/Pt trilayers in
reference to Pt/Co and Ta/Co bilayers. Enhancement of spin-orbit torques (SOTs)
and unidirectional spin Hall magnetoresistance (USMR) is achieved by
introducing the second heavy metal (HM) with the opposite sign of the spin Hall
angle. The extracted SOT efficiencies are larger for the trilayers as compared
to the bilayers, confirming the enhanced values reported for the trilayers with
perpendicularly magnetized Co. The maximum effective spin Hall angle found for
the Pt/Co/Ta trilayer reaches $\theta_{SH}$ = 20%. The USMR of the trilayer
yields up to 27% higher effect as for the respective bilayers with the largest
effective USMR amplitude of -0.32 $\times$ 10$^{-5}$ for the Pt/Co/Ta trilayer
at a charge current density of 10$^{7}$ A/cm$^2$.",2111.08307v1
2018-03-05,Electric-field modification of interfacial spin-orbit field-vector,"Current induced spin-orbit magnetic fields (iSOFs), arising either in
single-crystalline ferromagnets with broken inversion symmetry1,2 or in
non-magnetic metal/ferromagnetic metal bilayers3,4, can produce spin-orbit
torques which act on a ferromagnet's magnetization,thus offering an efficient
way for its manipulation.To further reduce power consumption in spin-orbit
torque devices, it is highly desirable to control iSOFs by the field-effect,
where power consumption is determined by charging/discharging a capacitor5,6.
In particular, efficient electric-field control of iSOFs acting on
ferromagnetic metals is of vital importance for practical applications. It is
known that in single crystalline Fe/GaAs (001) heterostructures with C2v
symmetry, interfacial SOFs emerge at the Fe/GaAs (001) interface due to the
lack of inversion symmetry7,8. Here, we show that by applying a gate-voltage
across the Fe/GaAs interface, interfacial SOFs acting on Fe can be robustly
modulated via the change of the magnitude of the interfacial spin-orbit
interaction. Our results show that, for the first time, the electric-field in a
Schottky barrier is capable of modifying SOFs, which can be exploited for the
development of low-power-consumption spin-orbit torque devices.",1803.01656v2
2018-12-13,Experimental Evidence of Non-Negligible Imaginary Part of Spin Mixing Conductance and Its Impact on Magnetization Dynamics in Heavy-Metal|Ferromagnet Bilayers,"The paper concerns experimental verification of the magnitude of imaginary
part of spin mixing conductance in bilayers comprising heavy metals. We present
results of broadband ferromagnetic resonance studies on heterostructures
consisting of Finemet thin films covered by Pt and Ta wedge layers with the aim
to observe spin pumping effects and to evaluate both the real and imaginary
parts of the spin mixing conductance. The experimental results are analyzed in
the framework of a recent microscopic theory which allows us to estimate the
value of the interfacial spin-orbit interaction and confirm its important role.
In particular, we show that the imaginary part of spin mixing conductance
cannot be regarded as negligible and we discuss its influence on magnetization
dynamics. For Finemet|Ta bilayers, the ratio
$\mathrm{Re}[g_{eff}^{\uparrow\downarrow}]/\mathrm{Im}[g_{eff}^{\uparrow\downarrow}]=$
0.38, that is, the field-like torque dominates over the damping-like torque in
such system. Consequently, relatively small enhancement of precession damping
with respect to significant total torque exerted on the magnetization in
Finemet|Ta system offers an attractive perspective for an application in the
next-generation magnetic random-access memory cells.",1812.05235v2
2019-06-28,Spin Logic Devices via Electric Field Controlled Magnetization Reversal by Spin-Orbit Torque,"We describe a spin logic device with controllable magnetization switching of
perpendicularly magnetized ferromagnet / heavy metal structures on a
ferroelectric (1-x)[Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] (PMN-PT) substrate using
current-induced spin-orbit torque. The devices were operated without an
external magnetic field and controlled by voltages as low as 10 V applied
across the PMN-PT substrate, which is much lower compared to previous reports
(500 V). The deterministic switching with smaller voltage was realized from the
virgin state of the PMN-PT. Ferroelectric simulation shows the unsaturated
minor loop exhibits obvious asymmetries in the polarizations. Larger
polarization can be induced from the initial ferroelectric state, while it is
difficult for opposite polarization. The XNOR, AND, NAND and NOT logic
functions were demonstrated by the deterministic magnetization switching from
the interaction between the spin-orbit torque and electric field at the
PMN-PT/Pt interface. The nonvolatile spin logic scheme in this work is simple,
scalable, programmable, which are favorable in the logic-in-memory design with
low energy consumption.",1906.12096v1
2020-04-21,Role of interfacial oxidation in generation of spin-orbit torques,"We report that current-induced spin-orbit torques (SOTs) in
heavy-metal/ferromagnetic-metal bilayers are strongly altered by the oxidation
of the ferromagnetic layer near the interface. We measured damping-like (DL)
and field-like (FL) SOTs for Pt/Co and Pt/Ni$_{81}$Fe$_{19}$ (Pt/Py) films
using spin-torque ferromagnetic resonance. In the Pt/Co film, we found that the
oxidation of the Co layer near the interface enhances both DL and FL SOTs in
spite of the insulating nature of the CoO$_x$ layer. The enhancement of the
SOTs disappears by inserting a thin Ti layer at the Pt/CoO$_x$ interface,
indicating that the dominant source of the SOTs in the Pt/CoO$_x$/Co film is
the spin-orbit coupling at the Pt/CoO$_x$ interface. In contrast to the
Pt/CoO$_x$/Co film, the SOTs in the Pt/PyO$_x$/Py film are dominated by the
bulk spin-orbit coupling. Our result shows that the interfacial oxidation of
the Pt/Py film suppresses the DL-SOT and reverses the sign of the FL-SOT. The
change of the SOTs can be attributed to the change of the real and imaginary
parts of the spin mixing conductance induced by the insertion of the insulating
PyO$_x$ layer. These results show that the interfacial oxidation provides an
effective way to manipulate the strength and sign of the SOTs.",2004.09837v1
2020-08-06,Constraining the ellipticity of millisecond pulsars with observed spin-down rates,"A spinning neutron star (NS) that is asymmetric with respect to its spin axis
can emit continuous gravitational wave (GW) signals. The spin frequencies and
their distribution of radio millisecond pulsars (MSPs) and accreting MSPs
provide some evidences of GW radiation, and MSPs are ideal probes detecting
high frequency GW signals. It is generally thought that MSPs originate from the
recycled process, in which the NS accretes the material and angular momentum
from the donor star. The accreted matter would be confined at the polar cap
zone by an equatorial belt of compressed magnetic field fixed in the deep crust
of the NS, and yields ""magnetic mountain"". Based on an assumption that the
spin-down rates of three transitional MSPs including PSR J1023+0038 are the
combinational contribution of the accretion torque, the propeller torque, and
the GW radiation torque, in this work we attempt to constrain the ellipticities
of MSPs with observed spin-down rates. Assuming some canonical parameters of
NSs, the ellipticities of three transitional MSPs and ten redbacks are
estimated to be $\epsilon=(0.9-23.4)\times 10^{-9}$. The electrical
resistivities of three transitional MSPs are also derived to be in the range
$\eta=(1.2-15.3)\times 10^{-31}~\rm s$, which display an ideal power law
relation with the accretion rate. The characteristic strains ($h_{\rm
c}=(0.6-2.5)\times10^{-27}$) of GW signals emitting by these sources are
obviously beyond the sensitivity scope of the aLIGO. We expect that the
third-generation GW detectors like the Einstein Telescope can seize the GW
signals from these sources in the future.",2008.02444v2
2017-03-18,Spin Based Biosensor with Hard Axis Assist for Enhanced Sensitivity,"We demonstrate the influence of hard axis assist on an in-plane polarized
nanomagnet layer to greatly enhance the sensitivity of a magnetic nano particle
(MNP) based MTJ biosensor. The hard axis assist has been provided to the
sensing layer in the forms of spin Hall Effect (SHE) induced spin injected
torque and stress based effective magnetic field induced torque separately.
Present work mainly focuses on the efficient and qualitative detection of a
single magnetic bead with the aim of detecting a single bimolecular recognition
event at an extremely low analyte concentration. Interfacial spin current
arising from spin orbit metal is expected to impose a torque on the free layer
along sensitive direction improving the signal strength by a factor of ~ 6.5
for a 100 nm bead at a height of 500 nm above the sensor surface. Furthermore,
the potentiality of a multiferroic composite consisting of a piezoelectric
layer coupled with magnetostrictive CoFeB based MTJ has been investigated in
the Biosensing applications. An external stress voltage of 500 mV has been
observed to be sufficient to enhance the sensitivity (~ 6 times). The use of
nanoscaled spin devices and the absence of external magnetic field operated
magnetization rotation facilitates in achieving highly compact and extremely
low power designs. This establishes the possibility of utilizing the present
schemes for advanced, highly sensitive, miniaturized and low power bioassaying
system-on-chip applications. Numerical results were compared with some earlier
reported experimental results to validate our proposed model.",1704.01555v1
2020-07-13,Spin Wave Generation via Localized Spin-Orbit Torque in an Antiferromagnet-Topological Insulator Heterostructure,"The spin-orbit torque induced by a topological insulator (TI) is
theoretically examined for spin wave generation in a neighboring
antiferromagnetic thin film. The investigation is based on the micromagnetic
simulation of N\'{e}el vector dynamics and the analysis of transport properties
in the TI. The results clearly illustrate that propagating spin waves can be
achieved in the antiferromagnetic thin-film strip through localized excitation,
traveling over a long distance. The oscillation amplitude gradually decays due
to the non-zero damping as the N\'{e}el vector precesses around the magnetic
easy axis with a fixed frequency. The frequency is also found to be tunable via
the strength of the driving electrical current density. While both the bulk and
the surface states of the TI contribute to induce the effective torque, the
calculation indicates that the surface current plays a dominant role over the
bulk counterpart except in the heavily degenerate cases. Compared to the more
commonly applied heavy metals, the use of a TI can substantially reduce the
threshold current density to overcome the magnetic anisotropy, making it an
efficient choice for spin wave generation. The N\'{e}el vector dynamics in the
nano-oscillator geometry are examined as well.",2007.06663v1
2022-05-24,Emission of coherent THz magnons in an antiferromagnetic insulator triggered by ultrafast spin-phonon interactions,"Antiferromagnetic materials have been proposed as new types of narrowband THz
spintronic devices owing to their ultrafast spin dynamics. Manipulating
coherently their spin dynamics, however, remains a key challenge that is
envisioned to be accomplished by spin-orbit torques or direct optical
excitations. Here, we demonstrate the combined generation of broadband THz
(incoherent) magnons and narrowband (coherent) magnons at 1 THz in low damping
thin films of NiO/Pt. We evidence, experimentally and through modelling, two
excitation processes of magnetization dynamics in NiO, an off-resonant
instantaneous optical spin torque and a strain-wave-induced THz torque induced
by ultrafast Pt excitation. Both phenomena lead to the emission of a THz signal
through the inverse spin Hall effect in the adjacent heavy metal layer. We
unravel the characteristic timescales of the two excitation processes found to
be < 50 fs and > 300 fs, respectively, and thus open new routes towards the
development of fast opto-spintronic devices based on antiferromagnetic
materials.",2205.11965v1
2023-10-06,Antiferromagnetic magnonic charge current generation via ultrafast optical excitation,"N\'eel spin-orbit torque allows a charge current pulse to efficiently
manipulate the N\'eel vector in antiferromagnets, which offers a unique
opportunity for ultrahigh density information storage with high speed. However,
the reciprocal process of N\'eel spin-orbit torque, the generation of ultrafast
charge current in antiferromagnets has not been demonstrated. Here, we report
the experimental observation of charge current generation in antiferromagnetic
metallic Mn2Au thin films using ultrafast optical excitation. The ultrafast
laser pulse excites antiferromagnetic magnons, resulting in instantaneous
non-equilibrium spin polarization at the antiferromagnetic spin sublattices
with broken spatial symmetry. Then the charge current is generated directly via
spin-orbit fields at the two sublattices, which is termed as the reciprocal
phenomenon of N\'eel spin-orbit torque, and the associated THz emission can be
detected at room temperature. Besides the fundamental significance on the
Onsager reciprocity, the observed magnonic charge current generation in
antiferromagnet would advance the development of antiferromagnetic THz emitter.",2310.03987v1
2024-03-11,Bulk and interface spin-orbit torques in Pt/Co/MgO thin film structures,"We investigate the origin of spin-orbit torques (SOTs) in archetypical
Pt/Co/MgO thin films structures by performing harmonic Hall measurements. The
behaviour of the damping like (DL) effective field ($h_{DL}$) with varying the
Pt layer thickness and the Co layer thickness indicates that bulk spin-Hall
effect (SHE) in Pt is mainly responsible for DL-SOT. The insertion of a Pd
ultrathin layer at the Pt/Co interface leads to a step decrease in $h_{DL}$,
attributed to the modification of interfacial spin transparency. Further
increase in Pd thickness led to a reduction of the interfacial spin-orbit
coupling (iSOC) quantified by the decrease in the surface magnetic anisotropy.
The consistent insensitivity of $h_{DL}$ to variations in iSOC at the bottom
Pt/Co interface and oxidation at the top Co/MgO interface provides additional
evidence for the bulk SHE origin of DL-SOT. The strong reduction in the
field-like (FL) torque effective field ($h_{FL}$) with decreasing iSOC at the
Pt/Co interface points to the interfacial nature of FL-SOT, either due to iSOC
induced interfacial spin-currents or to the Rashba-Edelstein effect at the
Pt/Co interface. Furthermore, we demonstrate that a FL-SOT develops at the top
Co/MgO interface opposing the one generated at the bottom Pt/Co interface,
whose strength increases with Co/MgO interfacial oxidation, and attributed to
the Rashba-Edelstein effect.",2403.06627v1
2015-09-15,The Formation of Striae within Cometary Dust Tails by a Sublimation-Driven YORP-like Effect,"Sublimating gas molecules scatter off of the surface of an icy body in the
same manner as photons. This means that for every photon-driven body force,
there should be a sublimation-driven analogue that affects icy bodies. Thermal
photons emitted from the surfaces of asymmetrically shaped bodies in the Solar
System generate net torques that change the spin rates of these bodies over
time. The long-term averaging of this torque is called the YORP effect. Here we
propose a sublimation-driven analogue to the YORP effect (SYORP), in which
sublimating gas molecules emitted from the surfaces of icy bodies also generate
net torques on the bodies. However, sublimating molecules carry momentum away
from the body at a rate ~10^4-10^5 greater than thermal photons, resulting in
much greater body torques. While previous studies of sublimative torques
focused on emissions from highly localized sources on the surfaces of Jupiter
Family Comet nuclei, SYORP applies to non-localized emissions across the entire
body, which likely dominates sublimation-drive torques on small icy chunks and
Dynamically Young Comets, and can therefore be applied without high-resolution
spacecraft observations of their surfaces. Instead, we repurpose the equations
of the YORP effect to account for sublimation-driven torques. We show how an
SYORP-driven mechanism best matches observations of the Sun-oriented lineaments
(striae) of comet tails, whose formation mechanism has remained enigmatic for
decades. The SYORP effect explains why striae are observed between
near-perihelion and ~1 AU from the Sun for comets with perihelia less than 0.6
AU, and solves longstanding problems with moving enough material into the
cometary tail to form visible striae. We show that SYORP can form striae that
match those of Comet West, and produce a power-law size frequency distribution
of their parent chunks with an index of -1.4 (-1.1- 2).",1509.04756v1
2022-10-27,The crater-induced YORP effect,"The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect plays an important
role in the rotational properties and evolution of asteroids. While the YORP
effect induced by the macroscopic shape of the asteroid and by the presence of
surface boulders has been well studied, no investigation has been performed yet
regarding how craters with given properties influence this effect.
  We introduce and estimate the crater-induced YORP effect (CYORP), which
arises from the concave structure of the crater, to investigate the magnitude
of the resulting torques as a function of varying properties of the crater and
the asteroid by a semi-analytical method.
  The CYORP torque can be comparable to the normal YORP torque when the size of
the crater is about one-tenth of the size of the asteroid, or equivalently when
the crater/roughness covers one-tenth of the asteroid's surface. Although the
torque decreases with the crater size, the combined contribution of all small
craters can become non-negligible due to their large number when the commonly
used power-law crater size distribution is considered. The CYORP torque of
small concave structures, usually considered as surface roughness, is essential
to the accurate calculation of the complete YORP torque. Under the CYORP effect
that is produced by collisions, asteroids go through a random walk in spin rate
and obliquity, with a YORP reset timescale typically of 0.4 Myr. This has
strong implications for the rotational evolution and orbital evolution of
asteroids.
  Craters and roughness on asteroid surfaces can influence the YORP torques and
therefore the rotational properties and evolution of asteroids. We suggest that
the CYORP effect should be considered in the future investigation of the YORP
effect on asteroids.",2210.15802v1
2024-02-20,The Santa Barbara Binary-Disk Code Comparison,"We have performed numerical calculations of a binary interacting with a gas
disk, using eleven different numerical methods and a standard binary-disk
setup. The goal of this study is to determine whether all codes agree on a
numerically converged solution, and to determine the necessary resolution for
convergence and the number of binary orbits that must be computed to reach an
agreed-upon relaxed state of the binary-disk system. We find that all codes can
agree on a converged solution (depending on the diagnostic being measured). The
zone spacing required for most codes to reach a converged measurement of the
torques applied to the binary by the disk is roughly 1% of the binary
separation in the vicinity of the binary components. For our disk model to
reach a relaxed state, codes must be run for at least 200 binary orbits,
corresponding to about a viscous time for our parameters, $0.2 (a^2 \Omega_B
/\nu)$ binary orbits, where $\nu$ is the kinematic viscosity. We did not
investigate dependence on binary mass ratio, eccentricity, disk temperature, or
disk viscosity; therefore, these benchmarks may act as guides towards expanding
converged solutions to the wider parameter space but might need to be updated
in a future study that investigates dependence on system parameters. We find
the most major discrepancies between codes resulted from the dimensionality of
the setup (3D vs 2D disks). Beyond this, we find good agreement in the total
torque on the binary between codes, although the partition of this torque
between the gravitational torque, orbital accretion torque, and spin accretion
torque depends sensitively on the sink prescriptions employed. In agreement
with previous studies, we find a modest difference in torques and accretion
variability between 2D and 3D disk models. We find cavity precession rates to
be appreciably faster in 3D than in 2D.",2402.13039v2
2002-07-18,Spin-transfer in diffusive ferromagnet-normal metal systems with spin-flip scattering,"The spin-transfer in biased disordered ferromagnet (F) - normal metal (N)
systems is calculated by the diffusion equation. For F1-N2-F2 and
N1-F1-N2-F2-N3 spin valves, the effect of spin-flip processes in the normal
metal and ferromagnet parts are obtained analytically. Spin-flip in the center
metal N2 reduces the spin-transfer, whereas spin-flip in the outer normal
metals N1 and N3 can increase it by effectively enhancing the spin polarization
of the device.",0207458v1
2007-04-10,Quantum State Transfer with Spin Chains,"The thesis covers various aspects of quantum state transfer in permanently
coupled spin systems.",0704.1309v1
2011-09-22,Hole spin relaxation and coefficients in Landau-Lifshitz-Gilbert equation in ferromagnetic GaMnAs,"We investigate the temperature dependence of the coefficients in the
Landau-Lifshitz-Gilbert equation in ferromagnetic GaMnAs by employing the Zener
model. We first calculate the hole spin relaxation time based on the
microscopic kinetic equation. We find that the hole spin relaxation time is
typically several tens femtoseconds and can present a nonmonotonic temperature
dependence due to the variation of the interband spin mixing, influenced by the
temperature related Zeeman splitting. With the hole spin relaxation time, we
are able to calculate the coefficients in the Landau-Lifshitz-Gilbert equation,
such as the Gilbert damping, nonadiabatic spin torque, spin stiffness and
vertical spin stiffness coefficients. We find that the nonadiabatic spin torque
coefficient $\beta$ is around $0.1\sim 0.3$ at low temperature, which is
consistent with the experiment [Adam {\em et al.}, Phys. Rev. B {\bf 80},
193204 (2009)]. As the temperature increases, $\beta$ monotonically increases
and can exceed one in the vicinity of the Curie temperature. In the low
temperature regime with $\beta<1$, the Gilbert damping coefficient $\alpha$
increases with temperature, showing good agreement with the experiments [Sinova
{\em et al.}, Phys. Rev. B {\bf 69}, 085209 (2004); Khazen {\em et al.}, {\em
ibid.} {\bf 78}, 195210 (2008)]. Furthermore, we predict that $\alpha$
decreases with increasing temperature once $\beta>1$ near the Curie
temperature. We also find that the spin stiffness decreases with increasing
temperature, especially near the Curie temperature due to the modification of
the finite $\beta$. Similar to the Gilbert damping, the vertical spin stiffness
coefficient is also found to be nonmonotonically dependent on the temperature.",1109.4964v1
2020-09-14,Non-Hamiltonian dynamics of indirectly coupled classical impurity spins,"We discuss the emergence of an effective low-energy theory for the real-time
dynamics of two classical impurity spins within the framework of a prototypical
and purely classical model of indirect magnetic exchange: Two classical
impurity spins are embedded in a host system which consists of a finite number
of classical spins localized on the sites of a lattice and interacting via a
nearest-neighbor Heisenberg exchange. An effective low-energy theory for the
slow impurity-spin dynamics is derived for the regime, where the local exchange
coupling between impurity and host spins is weak. To this end we apply the
recently developed adiabatic spin dynamics (ASD) theory. Besides the
Hamiltonian-like classical spin torques, the ASD additionally accounts for a
novel topological spin torque that originates as a holonomy effect in the
close-to-adiabatic-dynamics regime. It is shown that the effective low-energy
precession dynamics cannot be derived from an effective Hamilton function and
is characterized by a non-vanishing precession frequency even if the initial
state deviates only slightly from a ground state. The effective theory is
compared to the fully numerical solution of the equations of motion for the
whole system of impurity and host spins to identify the parameter regime where
the adiabatic effective theory applies. Effective theories beyond the adiabatic
approximation must necessarily include dynamic host degrees of freedom and go
beyond the idea of a simple indirect magnetic exchange. We discuss an example
of a generalized constrained spin dynamics which does improve the description
but also fails for certain geometrical setups.",2009.06296v2
2019-12-29,Controlling spin current polarization through non-collinear antiferromagnetism,"The spin-Hall effect describes the interconversion of charge currents and
spin currents, enabling highly efficient manipulation of magnetization for
spintronics. Symmetry conditions generally restrict polarizations of these spin
currents to be orthogonal to both the charge and spin flows. Spin polarizations
can deviate from such direction in nonmagnetic materials only when the
crystalline symmetry is reduced11. Here we experimentally show control of the
spin polarization direction by using a non-collinear antiferromagnet
Mn$_{3}$GaN, in which the triangular spin structure creates a low magnetic
symmetry state while maintaining a high crystalline symmetry. We demonstrate
that epitaxial Mn3GaN/Permalloy heterostructures can generate unique types of
spinHall torques at room temperature corresponding to unconventional spin
polarizations collinear to spin currents or charge currents which are forbidden
in any sample with two-fold rotational symmetry. Our results demonstrate an
approach based on spin-structure design for controlling spinorbit torque,
paving the way for further progress in the emergent field of antiferromagnetic
spintronics.",1912.12586v1
2020-03-27,Spin-polarized Current-driven Ferromagnetic Domain Wall Motion with a Skyrmion Building Block,"The purpose of the research is the construction of the analytical model for
description of spin-polarized current-driven ferromagnetic domain wall motion
with a skyrmion building block. The dependence of velocity of ferromagnetic
domain wall motion with a skyrmion building block is found as a function of
driving torques and an external magnetic field strength.",2003.12270v1
2021-08-02,"Dynamics of Colombo's Top: Tidal Dissipation and Resonance Capture, With Applications to Oblique Super-Earths, Ultra-Short-Period Planets and Inspiraling Hot Jupiters","We present a comprehensive theoretical study on the spin evolution of a
planet under the combined effects of tidal dissipation and gravitational
perturbation from an external companion. Such a ""spin + companion"" system
(called Colombo's top) appears in many [exo]planetary contexts. The competition
between the tidal torque (which drives spin-orbit alignment and
synchronization) and the gravitational torque from the companion (which drives
orbital precession of the planet) gives rise to two possible spin equilibria
(""Tidal Cassini Equilibria"", tCE) that are stable and attracting: the ""simple""
tCE1, which typically has a low spin obliquity, and the ""resonant"" tCE2, which
can have a significant obliquity. The latter arises from a spin-orbit resonance
and can be broken when the tidal alignment torque is stronger than the
precessional torque from the companion. We characterize the long-term evolution
of the planetary spin (both magnitude and obliquity) for an arbitrary initial
spin orientation, and develop a new theoretical method to analytically obtain
the probability of resonance capture driven by tidal dissipation. Applying our
general theoretical results to exoplanetary systems, we find that a super-Earth
(SE) with an exterior companion can have a substantial probability of being
trapped in the high-obliquity tCE2, assuming that SEs have a wide range of
primordial obliquities. We also evaluate the recently proposed ""obliquity tide""
scenarios for the formation of ultra-short-period Earth-mass planets and for
the orbital decay of hot Jupiter WASP-12b. We find in both cases that the
probability of resonant capture into tCE2 is generally low and that such a
high-obliquity state can be easily broken by the required orbital decay.",2108.01082v2
2023-12-11,Experimental demonstration of a robust training method for strongly defective neuromorphic hardware,"The increasing scale of neural networks needed to support more complex
applications has led to an increasing requirement for area- and
energy-efficient hardware. One route to meeting the budget for these
applications is to circumvent the von Neumann bottleneck by performing
computation in or near memory. An inevitability of transferring neural networks
onto hardware is that non-idealities such as device-to-device variations or
poor device yield impact performance. Methods such as hardware-aware training,
where substrate non-idealities are incorporated during network training, are
one way to recover performance at the cost of solution generality. In this
work, we demonstrate inference on hardware neural networks consisting of 20,000
magnetic tunnel junction arrays integrated on a complementary
metal-oxide-semiconductor chips that closely resembles market-ready spin
transfer-torque magnetoresistive random access memory technology. Using 36
dies, each containing a crossbar array with its own non-idealities, we show
that even a small number of defects in physically mapped networks significantly
degrades the performance of networks trained without defects and show that, at
the cost of generality, hardware-aware training accounting for specific defects
on each die can recover to comparable performance with ideal networks. We then
demonstrate a robust training method that extends hardware-aware training to
statistics-aware training, producing network weights that perform well on most
defective dies regardless of their specific defect locations. When evaluated on
the 36 physical dies, statistics-aware trained solutions can achieve a mean
misclassification error on the MNIST dataset that differs from the
software-baseline by only 2 %. This statistics-aware training method could be
generalized to networks with many layers that are mapped to hardware suited for
industry-ready applications.",2312.06446v1
2014-01-16,Effect of core--mantle and tidal torques on Mercury's spin axis orientation,"The rotational evolution of Mercury's mantle and its core under conservative
and dissipative torques is important for understanding the planet's spin state.
Dissipation results from tides and viscous, magnetic and topographic
core--mantle interactions. The dissipative core--mantle torques take the system
to an equilibrium state wherein both spins are fixed in the frame precessing
with the orbit, and in which the mantle and core are differentially rotating.
This equilibrium exhibits a mantle spin axis that is offset from the Cassini
state by larger amounts for weaker core--mantle coupling for all three
dissipative core--mantle coupling mechanisms, and the spin axis of the core is
separated farther from that of the mantle, leading to larger differential
rotation. The relatively strong core--mantle coupling necessary to bring the
mantle spin axis to its observed position close to the Cassini state is not
obtained by any of the three dissipative core--mantle coupling mechanisms. For
a hydrostatic ellipsoidal core--mantle boundary, pressure coupling dominates
the dissipative effects on the mantle and core positions, and dissipation
together with pressure coupling brings the mantle spin solidly to the Cassini
state. The core spin goes to a position displaced from that of the mantle by
about 3.55 arcmin nearly in the plane containing the Cassini state. With the
maximum viscosity considered of $\nu\sim 15.0\,{\rm cm^2/s}$ if the coupling is
by the circulation through an Ekman boundary layer or $\nu\sim 8.75\times
10^5\,{\rm cm^2/s}$ for purely viscous coupling, the core spin lags the
precessing Cassini plane by 23 arcsec, whereas the mantle spin lags by only
0.055 arcsec. Larger, non hydrostatic values of the CMB ellipticity also result
in the mantle spin at the Cassini state, but the core spin is moved closer to
the mantle spin.",1401.4131v1
2000-10-22,Hyper- and suspended-accretion states of rotating black holes and the durations of gamma-ray bursts,"We analyze the temporal evolution of accretion onto rotating black holes
subject to large-scale magnetic torques. Wind torques alone drive a disk
towards collapse in a finite time $\sim t_{ff} E_k/E_B$, where $t_{ff}$ is the
initial free-fall time and $E_k/E_B$ is the ratio of kinetic-to-poloidal
magnetic energy. Additional spin-up torques from a rapidly rotating black hole
can arrest the disk's inflow. We associate short/long gamma-ray bursts with
hyperaccretion/suspended-accretion onto slowly/rapidly spinning black holes.
This model predicts afterglow emission from short bursts, and may be tested by
HETE-II.",0010440v2
2005-09-08,Timing an Accreting Millisecond Pulsar: Measuring the Accretion Torque in IGR J00291+5934,"We present here a timing analysis of the fastest accreting millisecond pulsar
IGR J00291+5934 using RXTE data taken during the outburst of December 2004. We
corrected the arrival times of all the events for the orbital (Doppler) effects
and performed a timing analysis of the resulting phase delays. In this way we
find a clear parabolic trend of the pulse phase delays showing that the pulsar
is spinning up as a consequence of accretion torques during the X-ray outburst.
The accretion torque gives us for the first time an independent estimate of the
mass accretion rate onto the neutron star, which can be compared with the
observed X-ray luminosity. We also report a revised value of the spin period of
the pulsar.",0509224v1
2005-10-22,Locking of the Rotation of Disk-Accreting Magnetized Stars,"We investigate the rotational equilibrium state of a disk accreting
magnetized stars using axisymmetric magnetohydrodynamic (MHD) simulations. In
this ``locked'' state, the spin-up torque balances the spin-down torque so that
the net average torque on the star is zero. We investigated two types of
initial conditions, one with a relatively weak stellar magnetic field and a
high coronal density, and the other with a stronger stellar field and a lower
coronal density. We observed that for both initial conditions the rotation of
the star is locked to the rotation of the disk. In the second case, the radial
field lines carry significant angular momentum out of the star. However, this
did not appreciably change the condition for locking of the rotation of the
star. We find that in the equilibrium state the corotation radius $r_{co}$ is
related to the magnetospheric radius $r_A$ as $r_{co}/r_A\approx 1.2-1.3$ for
case (1) and $r_{co}/r_A\approx 1.4-1.5$ for case (2). We estimated periods of
rotation in the equilibrium state for classical T Tauri stars, dwarf novae and
X-ray millisecond pulsars.",0510659v1
2006-11-07,Timing an Accreting Millisecond Pulsar: Measuring the Accretion Torque in IGR J00291+5934,"We performed a timing analysis of the fastest accreting millisecond pulsar
IGR J00291+5934 using RXTE data taken during the outburst of December 2004. We
corrected the arrival times of all the events for the orbital (Doppler) effects
and performed a timing analysis of the resulting phase delays. In this way we
have the possibility to study, for the first time in this class of sources, the
spin-up of a millisecond pulsar as a consequence of accretion torques during
the X-ray outburst. The accretion torque gives us for the first time an
independent estimate of the mass accretion rate onto the neutron star, which
can be compared with the observed X-ray luminosity. We also report a revised
value of the spin period of the pulsar.",0611222v2
2011-12-19,Optical forces and torques in non-uniform beams of light,"The spin angular momentum in an elliptically polarized beam of light plays
several noteworthy roles in optical traps. It contributes to the linear
momentum density in a non-uniform beam, and thus to the radiation pressure
exerted on illuminated objects. It can be converted into orbital angular
momentum, and thus can exert torques even on optically isotropic objects. Its
curl, moreover, contributes to both forces and torques without spin-to-orbit
conversion. We demonstrate these effects experimentally by tracking colloidal
spheres diffusing in elliptically polarized optical tweezers. Clusters of
spheres circulate deterministically about the beam's axis. A single sphere, by
contrast, undergoes stochastic Brownian vortex circulation that maps out the
optical force field.",1112.4429v1
2012-10-16,Giant spin torque in systems with anisotropic exchange interaction,"Control of magnetic domain wall movement by the spin-polarized current looks
promising for creation of a new generation of magnetic memory devices. A
necessary condition for this is the domain wall shift by a low-density current.
Here I show that a strongly anisotropic exchange interaction between mobile
heavy holes and localized magnetic moments enormously increases the
current-induced torque on the domain wall as compared to systems with isotropic
exchange. This enables one to control the domain wall motion by current density
10^4 A/cm^2 in ferromagnet/semiconductor hybrids. The experimental observation
of the anisotropic torque will facilitate the integration of ferromagnetism
into semiconductor electronics",1210.4306v4
2014-02-26,Improved Domain Wall Dynamics and Magnonic Torques using Topological Insulators,"We investigate the magnetization dynamics that arise when a thin-film
ferromagnet is deposited on a topological insulator (TI), focusing in
particular on domain-wall motion via current and the possibility of a spin-wave
torque acting on the magnetization. We show analytically that the coupling
between the magnetic domain wall and the TI removes the degeneracy of the wall
profile with respect to its chirality and topological charge. Moreover, we find
that the threshold for Walker breakdown of domain wall motion is substantially
increased and determined by the interaction with the TI, allowing for higher
attainable wall velocities than in the conventional case where the hard axis
anisotropy determines the Walker threshold. Finally, we show that the allowed
modes of spin-wave excitations and the ensuing magnetization dynamics in the
presence of a TI coupling enable a magnonic torque acting even on homogeneous
magnetization textures. Our results indicate that the TI-ferromagnet
interaction has a similar effect on the magnetization dynamics as an intrinsic
Dzyaloshinskii-Moriya interaction in ferromagnets.",1402.6701v2
2016-05-18,Electrical control over perpendicular magnetization switching driven by spin-orbit torques,"Flexible control of magnetization switching by electrical manners is crucial
for applications of spin-orbitronics. Besides of a switching current that is
parallel to an applied field, a bias current that is normal to the switching
current is introduced to tune the magnitude of effective damping-like and
field-like torques and further to electrically control magnetization switching.
Symmetrical and asymmetrical control over the critical switching current by the
bias current with opposite polarities is both realized in Pt/Co/MgO and
$\alpha$-Ta/CoFeB/MgO systems, respectively. This research not only identifies
the influences of field-like and damping-like torques on switching process but
also demonstrates an electrical method to control it.",1605.05569v1
2017-09-09,Theory of Topological Spin Hall Effect in Antiferromagnetic Skyrmion: Impact on Current-induced Motion,"We demonstrate that the nontrivial magnetic texture of antiferromagnetic
skyrmions (AFM-Sks) promotes a non-vanishing topological spin Hall effect
(TSHE) on the flowing electrons. This results in a substantial enhancement of
the non-adiabatic torque and hence improves the skyrmion mobility. This
non-adiabatic torque increases when decreasing the skyrmion size, and therefore
scaling down results in a much higher torque efficiency. In clean AFM-Sks, we
find a significant boost of the TSHE close to van Hove singularity.
Interestingly, this effect is enhanced away from the band gap in the presence
of non-magnetic interstitial defects. Furthermore, unlike their ferromagnetic
counterpart, TSHE in AFM-Sks increases with increase in disorder strength thus
opening promising avenues for materials engineering of this effect.",1709.02931v1
2017-11-15,Oscillatory spin-orbit torque switching induced by field-like torques,"Deterministic magnetization switching using spin-orbit torque (SOT) has
recently emerged as an efficient means to electrically control the magnetic
state of ultrathin magnets. The SOT switching still lacks in oscillatory
switching characteristics over time, therefore, it is limited to bipolar
operation where a change in polarity of the applied current or field is
required for bistable switching. The coherent rotation based oscillatory
switching schemes cannot be applied to SOT because the SOT switching occurs
through expansion of magnetic domains. Here, we experimentally achieve
oscillatory switching in incoherent SOT process by controlling domain wall
dynamics. We find that a large field-like component can dynamically influence
the domain wall chirality which determines the direction of SOT switching.
Consequently, under nanosecond current pulses, the magnetization switches
alternatively between the two stable states. By utilizing this oscillatory
switching behavior we demonstrate a unipolar deterministic SOT switching scheme
by controlling the current pulse duration.",1711.05369v1
2018-10-20,Dynamics of a Ferromagnetic Particle Levitated Over a Superconductor,"Under conditions where the angular momentum of a ferromagnetic particle is
dominated by intrinsic spin, applied torque is predicted to cause gyroscopic
precession of the particle. If the particle is sufficiently isolated from the
environment, a measurement of spin precession can potentially yield sensitivity
to torque beyond the standard quantum limit. Levitation of a micron-scale
ferromagnetic particle above a superconductor is a possible method of near
frictionless suspension enabling observation of ferromagnetic particle
precession and ultrasensitive torque measurements. We experimentally
investigate the dynamics of a micron-scale ferromagnetic particle levitated
above a superconducting niobium surface. We find that the levitating particles
are trapped in potential minima associated with residual magnetic flux pinned
by the superconductor and, using an optical technique, characterize the
quasiperiodic motion of the particles in these traps.",1810.08748v5
2012-09-07,No pseudosynchronous rotation for terrestrial planets and moons,"We reexamine the popular belief that a telluric planet or satellite on an
eccentric orbit can, outside a spin-orbit resonance, be captured in a
quasi-static tidal equilibrium called pseudosynchronous rotation. The existence
of such configurations was deduced from oversimplified tidal models assuming
either a constant tidal torque or a torque linear in the tidal frequency. A
more accurate treatment requires that the torque be decomposed into the
Darwin-Kaula series over the tidal modes, and that this decomposition be
combined with a realistic choice of rheological properties of the mantle. This
development demonstrates that there exist no stable equilibrium states for
solid planets and moons, other than spin-orbit resonances.",1209.1616v3
2021-02-21,Direct and inverse spin-orbit torques in antiferromagnetic and ferromagnetic FeRh/W(001),"We use \textit{ab-initio} calculations to investigate spin-orbit torques
(SOTs) in FeRh(001) deposited on W(100). Since FeRh undergoes a
ferromagnetic-antiferromagnetic phase transition close to room temperature, we
consider both phases of FeRh. In the antiferromagnetic case we find that the
effective magnetic field of the even torque is staggered and therefore ideal to
induce magnetization dynamics or to switch the antiferromagnet (AFM). At the
antiferromagnetic resonance the inverse SOT induces a current density, which
can be determined from the SOT. In the ferromagnetic case our calculations
predict both even and odd components of the SOT, which can also be used to
describe the ac and dc currents induced at the ferromagnetic resonance. For
comparison we compute the SOTs in the c($2\times 2$) AFM state of Fe/W(001).",2102.10598v1
2017-04-21,Time resolved measurements of the switching trajectory of Pt/Co elements induced by spin-orbit torques,"We report the experimental observation of spin-orbit torque induced switching
of perpendicularly magnetized Pt/Co elements in a time resolved stroboscopic
experiment based on high resolution Kerr microscopy. Magnetization dynamics is
induced by injecting sub-nanosecond current pulses into the bilayer while
simultaneously applying static in-plane magnetic bias fields. Highly
reproducible homogeneous switching on time scales of several tens of
nanoseconds is observed. Our findings can be corroborated using micromagnetic
modelling only when including a field-like torque term as well as the
Dzyaloshinskii-Moriya interaction mediated by finite temperature.",1704.06418v1
2020-07-02,Field-free Deterministic Magnetization Switching Induced by Interlaced Spin-Orbit Torques,"Spin-orbit torque (SOT) based magnetic random access memory (MRAM) is
envisioned as an emerging non-volatile memory due to its ultra-high speed and
low power consumption. The field-free switching schema in SOT devices is of
great interest to both academia and industry. Here we propose a novel
field-free deterministic magnetization switching in a regular magnetic tunnel
junction (MTJ) by using two currents sequentially passing interlaced paths,
with less requirements of manufacturing process or additional physical effects.
The switching is bipolar since the final magnetization state depends on the
combination of current paths. The functionality and robustness of the proposed
schema is validated through both macrospin and micromagnetic simulation. The
influences of field-like torque and Dzyaloshinskii-Moriya interaction (DMI)
effect are further researched. Our proposed schema shows good scalability and
is expected to realize novel digital logic and even computing-in-memory
platform.",2007.01075v1
2020-07-30,Dynamical torques from Shiba states in $s$-wave superconductors,"Magnetic impurities inserted in a $s$-wave superconductor give rise to
spin-polarized in-gap states called Shiba states. We study the back-action of
these induced states on the dynamics of the classical moments. We show that the
Shiba state pertains to both reactive and dissipative torques acting on the
precessing classical spin that can be detected through ferromagnetic resonance
measurements. Moreover, we highlight the influence of the bulk states as well
as the effect of the finite linewidth of the Shiba state on the magnetization
dynamics. Finally, we demonstrate that the torques are a direct measure of the
even and odd frequency triplet pairings generated by the dynamics of the
magnetic impurity. Our approach offers non-invasive alternative to the STM
techniques used to probe the Shiba states.",2007.15392v2
2020-12-10,Ultrafast reorientation of the Néel vector in antiferromagnetic Dirac semimetals,"Antiferromagnets exhibit distinctive characteristics such as ultrafast
dynamics and robustness against perturbative fields, thereby attracting
considerable interest in fundamental physics and technological applications.
Recently, it was revealed that the N\'eel vector can be switched by a
current-induced staggered (N\'eel) spin-orbit torque in antiferromagnets with
the parity-time symmetry, and furthermore, a nonsymmorphic symmetry enables the
control of Dirac fermions. However, the real-time dynamics of the magnetic and
electronic structures remain largely unexplored. Here, we propose a theory of
the ultrafast dynamics in antiferromagnetic Dirac semimetals and show that the
N\'eel vector is rotated in the picosecond timescale by the
terahertz-pulse-induced N\'eel spin-orbit torque and other torques originating
from magnetic anisotropies. This reorientation accompanies the modulation of
the mass of Dirac fermions and can be observed in real time by the
magneto-optical effects. Our results provide a theoretical basis for emerging
ultrafast antiferromagnetic spintronics combined with the topological aspects
of materials.",2012.05902v2
2021-07-20,Strong bulk spin-orbit torques quantified in the van der Waals ferromagnet Fe3GeTe2,"The recent emergence of magnetic van der Waals materials allows for the
investigation of current induced magnetization manipulation in two dimensional
materials. Uniquely, Fe3GeTe2 has a crystalline structure that allows for the
presence of bulk spin-orbit torques (SOTs), that we quantify in a Fe3GeTe2
flake. From the symmetry of the measured torques, we identify the current
induced effective fields using harmonic analysis and find dominant bulk SOTs,
which arise from the symmetry in the crystal structure. Our results show that
Fe3GeTe2 uniquely can exhibit bulk SOTs in addition to the conventional
interfacial SOTs enabling magnetization manipulation even in thick single
layers without the need for complex multilayer engineering.",2107.09420v1
2023-03-05,Lossless Spin-Orbit Torque in Antiferromagnetic Topological Insulator MnBi$_2$Te$_4$,"We formulate and quantify the spin-orbit torque (SOT) in intrinsic
antiferromagnetic topological insulator $\rm MnBi_2Te_4$ of a few
septuple-layer thick, which exhibits conspicuous layer-resolved
characteristics. Contrary to known current-induced torques, the SOT in
insulating $\rm MnBi_2Te_4$ is driven by an electric field (or voltage). We
further study the SOT-induced magnetic resonances, where in the
tri-septuple-layer case we identify a peculiar exchange mode that is blind to
microwaves but can be exclusively driven by the predicted SOT. As an inverse
effect of the SOT, topological charge pumping generates an adiabatic current
devoid of Joule heating, which occurs concomitantly with the SOT and gives rise
to an overall magneto-reactance for $\rm MnBi_2Te_4$, enabling a lossless
conversion of electric power into magnetic dynamics.",2303.06181v3
2024-02-14,Spin-orbit torque in single-molecule junctions from ab initio,"The use of electric fields applied across magnetic heterojunctions that lack
spatial inversion symmetry has been previously proposed as a non-magnetic mean
of controlling localized magnetic moments through spin-orbit torques (SOT). The
implementation of this concept at the single-molecule level has remained a
challenge, however. Here, we present first-principle calculations of SOT in a
single-molecule junction under bias and beyond linear response. Employing a
self-consistency scheme invoking density functional theory and non-equilibrium
Green's function theory, we compute the current-induced SOT. Responding to this
torque, a localized magnetic moment can tilt. Within the linear regime our
quantitative estimates for the SOT in single-molecule junctions yield values
similar to those known for magnetic interfaces. Our findings contribute to an
improved microscopic understanding of SOT in single molecules.",2402.09610v1
2024-03-11,Tidal synchronization trapping in stars and planets with convective envelopes,"Tidal torques can alter the spins of tidally interacting stars and planets,
usually over shorter timescales than the tidal damping of orbital separations
or eccentricities. Simple tidal models predict that in eccentric binary or
planetary systems, rotation periods will evolve toward a ""pseudosynchronous""
ratio with the orbital period. However, this prediction does not account for
""inertial"" waves that are present in stars or gaseous planets with (i)
convective envelopes, and (ii) even very slow rotation. We demonstrate that
tidal driving of inertial oscillations in eccentric systems generically
produces a network of stable ""synchronization traps"" at ratios of orbital to
rotation period that are simple to predict, but can deviate significantly from
pseudosynchronization. The mechanism underlying spin synchronization trapping
is similar to tidal resonance locking, involving a balance between torques that
is maintained automatically by the scaling of inertial mode frequencies with
the rotation rate. In contrast with many resonance locking scenarios, however,
the torque balance required for synchronization trapping need not drive mode
amplitudes to nonlinearity. Synchronization traps may provide an explanation
for low-mass stars and hot Jupiters with observed rotation rates that deviate
from pseudosynchronous or synchronous expectations.",2403.06979v2
2020-09-02,Magnetic torques on T Tauri stars: accreting vs. non-accreting systems,"Classical T Tauri stars (CTTs) magnetically interact with their surrounding
disks, a process that is thought to regulate their rotational evolution. In
this work, we compute torques acting onto the stellar surface of CTTs arising
from different accreting (accretion funnels) and ejecting (stellar winds and
magnetospheric ejections) flow components. Furthermore, we compare the magnetic
braking due to stellar winds in two different systems: isolated and accreting
stars. 2.5D magnetohydrodynamic, time-dependent, axisymmetric simulations are
employed. For both systems the stellar wind is thermally driven. In the
star-disk-interaction (SDI) simulations the accretion disk is Keplerian,
viscous, and resistive. Two series of simulations are presented, one for each
system. We find that in classical T Tauri systems the presence of
magnetospheric ejections confines the stellar-wind expansion, resulting in an
hourglass-shaped geometry of the outflow. In addition, the formation of the
accretion columns modifies the amount of open magnetic flux exploited by the
stellar wind. These effects have a strong impact on the stellar wind properties
and we show that the stellar-wind braking is more efficient in the
star-disk-interacting systems than in the isolated ones. We also derive torque
scalings, over a wide range of magnetic field strengths, for each flow
component in a SDI system that directly applies a torque on the stellar
surface. In all the performed SDI simulations the stellar wind extracts less
than 2% of the mass accretion rate and the disk is truncated up to 66% of the
corotation radius. All the simulations show a net spin-up torque. In order to
achieve a stellar-spin equilibrium we need either more massive stellar winds or
disks being truncated closer to the corotation radius, which increases the
torque efficiency by the magnetospheric ejections.",2009.00940v1
2002-12-08,Exact solutions and elementary excitations in the XXZ spin chain with unparallel boundary fields,"By using a set of gauge transformations, the exact solutions of the XXZ spin
chain with unparallel boundary magnetic fields are derived in the framework of
the algebraic Bethe ansatz. In the easy-plane case, we show the elementary
excitations are some kind of spinons without definite spin because the U(1)
symmetry is broken, while in the easy-axis ferromagnetic case a spiral state is
realized in the ground state. The correlation functions, the spin torque as
well as the spin voltage for the later case are also derived.",0212163v1
2009-02-19,Spin-orbit induced non-collinear spin structure in deposited transition metal clusters,"The influence of the spin-orbit coupling on the magnetic structure of
deposited transition metal nanostructure systems has been studied by fully
relativistic electronic structure calculations. The interplay of exchange
coupling and magnetic anisotropy was monitored by studying the corresponding
magnetic torque calculated within ab-initio and model approaches. It is found
that a spin-orbit induced Dzyaloshinski-Moriya interaction can stabilise a
non-collinear spin structure even if there is a pronounced isotropic
ferromagnetic exchange interaction between the magnetic atoms.",0902.3336v1
2012-08-17,Spin-torque effect on spin wave modes in magnetic nanowires,"The interaction between a spin polarized dc electrical current and spin wave
modes of a cylindrical nanowire is investigated in this report. We found that
close to the critical current, the uniform mode is suppressed, while the edge
mode starts to propagate into the sample. When the current exceeds the critical
value, this phenomenon is even more accentuated. The edge mode becomes the
uniform mode of the nanowire. The higher spin wave modes are slowly pushed away
by the current until the propagating mode remains.",1208.3661v1
2012-11-01,Renormalization of spin-rotation coupling,"We predict the enhancement of the spin-rotation coupling due to the interband
mixing. The Bloch wavefunctions in the presence of mechanical rotation are
constructed with the generalized crystal momentum which includes a gauge
potential arising from the rotation. Using the eight- band Kane model, the
renormalized spin-rotation coupling is explicitly obtained. As a result of the
renormalization, the rotational Doppler shift in electron spin resonance and
the mechanical torque on an electron spin will be strongly modulated.",1211.0127v2
2016-10-24,Spin orbit effects in CoFeB/MgO hetereostructures with heavy metal underlayers,"We study effects originating from the strong spin orbit coupling in CoFeB/MgO
heterostructures with heavy metal (HM) underlayers. The perpendicular magnetic
anisotropy at the CoFeB/MgO interface, the spin Hall angle of the heavy metal
layer, current induced torques and the Dzyaloshinskii-Moriya interaction at the
HM/CoFeB interfaces are studied for films in which the early 5d transition
metals are used as the HM underlayer. We show how the choice of the HM layer
influences these intricate spin orbit effects that emerge within the bulk and
at interfaces of the heterostructures.",1610.07473v1
2018-11-06,Nonlinear dynamic interpretation of quantum spin,"In an effort to provide an alternative method to represent a quantum spin, a
precise nonlinear dynamics semi-classical model is used to show that standard
quantum spin analysis can be obtained. The model includes a multi-body,
anti-ferromagnetic ordering, highly coupled quantum spin and a semi-classical
interpretation of the torque on a spin magnetic moment in the presence of a
magnetic field. The deterministic nonlinear differential coupling equation is
used to introduce chaos, which is necessary to reproduce the correct
statistical quantum results.",1811.02624v1
2019-01-23,Coupled dynamics of magnetizations in spin-Hall oscillators via spin current injection,"An array of spin torque oscillators (STOs) for practical applications such as
pattern recognition was recently proposed, where several STOs are connected by
a common nonmagnet. In this structure, in addition to the electric and/or
magnetic interactions proposed in previous works, the STOs are spontaneously
coupled to each other through the nonmagnetic connector, due to the injection
of spin current. Solving the Landau-Lifshitz-Gilbert equation numerically for
such system consisting of three STOs driven by the spin Hall effect, it is
found that both in-phase and antiphase synchronization of the STOs can be
achieved by adjusting the current density and appropriate distance between the
oscillators.",1901.07669v1
2021-05-01,Induced Quantized Spin Current in Vacuum,"We uncover a fundamental effect of the QED vacuum in an external
electromagnetic (EM) field. We show that the quantized vacuum of electrons is
spin polarized by the EM field and manifests as a vacuum spin current. An
experiment is proposed to measure the spin torque exerted by the spin current
by measuring the twisted angle of the director axis of a nematic liquid
crystal.",2105.00148v2
2021-05-07,Non-linear extension of the dynamical linear response of spins; extended Heisenberg model,"We introduce a new extended Heisenberg model. The model contains the
orbital-dependent spins together with the retarded effects of spin torque. The
model is directly derived from the dynamical linear response functions on the
transversal spin fluctuation. Our model allows us to address effects which are
not accessible via the usual Heisenberg model. With the model, we can describe
not only the relaxation effects due to the Landau damping caused by the Stoner
excitations, but also the nesting effects of the Fermi surface. We discuss
possibilities of the extended Heisenberg model based on the high-resolution
plots of the spin susceptibility for Fe.",2105.03035v2
2021-06-30,Wave-Driven Torques to Drive Current and Rotation,"In the classic Landau damping initial value problem, where a planar
electrostatic wave transfers energy and momentum to resonant electrons, a
recoil reaction occurs in the nonresonant particles to ensure momentum
conservation. To explain how net current can be driven in spite of this
conservation, the literature often appeals to mechanisms that transfer this
nonresonant recoil momentum to ions, which carry negligible current. However,
this explanation does not allow the transport of net charge across magnetic
field lines, precluding ExB rotation drive. Here, we show that in steady state,
this picture of current drive is incomplete. Using a simple Fresnel model of
the plasma, we show that for lower hybrid waves, the electromagnetic energy
flux (Poynting vector) and momentum flux (Maxwell stress tensor) associated
with the evanescent vacuum wave, become the Minkowski energy flux and momentum
flux in the plasma, and are ultimately transferred to resonant particles. Thus,
the torque delivered to the resonant particles is ultimately supplied by the
electromagnetic torque from the antenna, allowing the nonresonant recoil
response to vanish and rotation to be driven. We present a warm fluid model
that explains how this momentum conservation works out locally, via a Reynolds
stress that does not appear in the 1D initial value problem. This model is the
simplest that can capture both the nonresonant recoil reaction in the
initial-value problem, and the absence of a nonresonant recoil in the
steady-state boundary value problem, thus forbidding rotation drive in the
former while allowing it in the latter.",2107.00148v1
2005-09-22,Current-induced motion of a domain wall in magnetic nanowires,"The dynamics of current-induced motion of a magnetic domain wall in a
quasi-one-dimensional ferromagnet with both easy-axis and easy-plane
anisotropy, is studied. We pay a special attention to the case of a sharp
domain wall, and calculate the spin torque created by the electric current. The
torque has two components, one of which is acting as a driving force for the
motion of the domain wall while the other distorts its shape, forcing thus the
magnetic moments to deviate from the easy plane.",0509574v1
2007-02-21,Magnetic Anisotropy of Deposited Transition Metal Clusters,"We present results of magnetic torque calculations using the fully
relativistic spin-polarized Korringa-Kohn-Rostoker approach applied to small Co
and Fe clusters deposited on the Pt(111) surface. From the magnetic torque one
can derive among others the magnetic anisotropy energy (MAE). It was found that
this approach is numerically much more stable and also computationally less
demanding than using the magnetic force theorem that allows to calculate the
MAE directly. Although structural relaxation effects were not included our
results correspond reasonably well to recent experimental data.",0702483v1
2009-05-22,Current-induced interactions of multiple domain walls in magnetic quantum wires,"We show that an applied charge current in a magnetic nanowire containing
domain walls (DWs) results in an interaction between DWs mediated by
spin-dependent interferences of the scattered carriers. The energy and torque
associated with this interaction show an oscillatory behaviour as a function of
the mutual DWs orientations and separations, thus affecting the DWs'
arrangements and shapes. Based on the derived DWs interaction energy and torque
we calculate DW dynamics and uncover potential applications of interacting DWs
as a tunable nano-mechanical oscillator. We also discuss the effect of
impurities on the DW interaction.",0905.3644v1
2013-04-15,Relationship Between Thermal Tides and Radius Excess,"Close-in extrasolar gas giants -- the hot Jupiters -- display departures in
radius above the zero-temperature solution, the radius excess, that are
anomalously high. The radius excess of hot Jupiters follows a relatively close
relation with thermal tidal tidal torques and holds for ~ 4-5 orders of
magnitude in a characteristic thermal tidal power in such a way that is
consistent with basic theoretical expectations. The relation suggests that
thermal tidal torques determine the global thermodynamic and spin state of the
hot Jupiters. On empirical grounds, it is shown that theories of hot Jupiter
inflation that invoke a constant fraction of the stellar flux to be deposited
at great depth are, essentially, falsified.",1304.4121v1
2017-01-16,Episodic Torque-Luminosity Correlations and Anticorrelations of GX 1+4,"We analyse archival CGRO-BATSE X-ray flux and spin frequency measurements of
GX 1+4 over a time span of 3000 days. We systematically search for time
dependent variations of torque luminosity correlation. Our preliminary results
indicate that the correlation shifts from being positive to negative on time
scales of few 100 days.",1701.04717v1
2023-02-17,Control of magnon-photon coupling by spin torque,"We demonstrate the influence of damping and field-like torques in the
magnon-photon coupling process by classically integrating the generalized
Landau-Lifshitz-Gilbert equation with RLC equation in which a phase correlation
between dynamic magnetization and microwave current through combined Amp\`ere
and Faraday effects are considered. We show that the gap between two hybridized
modes can be controlled in samples with damping parameter in the order of
$10^{-3}$ by changing the direction of the dc current density $J$ if a certain
threshold is reached. Our results suggest that an experimental realization of
the proposed magnon-photon coupling control mechanism is feasible in yttrium
iron garnet/Pt hybrid structures.",2302.08910v1
2005-06-24,Precession of the Isolated Neutron Star PSR B1828-11,"Stairs, Lyne & Shemar have found that arrival time residuals from PSR
B1828-11 vary periodically with a period of 500 days. This behavior can be
accounted for by precession of the radiopulsar, an interpretation that is
reinforced by the detection of variations in its pulse profile on the same
timescale. Here, we model the period residuals from PSR B1828-11 in terms of
precession of a triaxial rigid body. We include two contributions to the
residuals: (i) the geometric effect, which arises because the times at which
the pulsar emission beam points toward the observer varies with precession
phase; (ii) the spindown contribution, which arises from any dependence of the
spindown torque acting on the pulsar on the angle between its spin and magnetic
axes. We use the data to probe numerous properties of the pulsar, most notably
its shape, and the dependence of its spindown torque on the angle between its
spin and magnetic axes, for which we assume a sum of a spin-aligned component
(with a weight 1-a) and a dipolar component perpendicular to the magnetic beam
axis (weight a), rather than the vacuum dipole torque (a=1). We find that a
variety of shapes are consistent with the residuals, with a slight statistical
preference for a prolate star. Moreover, a range of torque possibilities fit
the data equally well, with no strong preference for the vacuum model. In the
case of a prolate star we find evidence for an angle-dependent spindown torque.
Our results show that the combination of geometrical and spin-down effects
associated with precession can account for the principal features of PSR
B1828-11's timing behavior, without fine tuning of the parameters.",0506606v2
2019-11-16,"On the position representation of mechanical power, force and torque operators","Quantizing the transfer of energy and momentum between interacting particles,
we obtain a quantum impulse equation and relations that the corresponding
mechanical power, force and torque satisfy. In addition to the energy-frequency
and momentum-wavelength relations, we introduce the power-frequency and
force-wavelength analogs, respectively. Further, we obtain an operator
representation for the mechanical power and impact force in the position space
and discuss their correspondence with the relevant momentum operator. The
position representation of the torque operator and its relation to the orbital
angular momentum operator is also considered. The results are grounded by the
presence of a constant that appears as fundamental as the Planck's constant to
all obtained relations.",1911.07044v3
2017-02-08,"Anomalous Doppler Effect Singularities in the Radiative Heat Generation, Interaction Force and Frictional Torque for two Rotating Nanoparticles","We calculate the quantum heat generation, the interaction force and the
frictional torque for two rotating spherical nanoparticles with a radius $R$.
In contrast to the static case, when there is an upper limit in the radiative
heat transfer between the particles, for two rotating nanoparticles the quantum
heat generation rate diverges when the angular velocity becomes equal to the
poles in the photon emission rate. These poles arise for the separation $d
<d_0= R(3/\varepsilon''(\omega_0))^{1/3}$ (where $\varepsilon''(\omega_0)$ is
the imaginary part of the dielectric function for the particle material at the
surface phonon or plasmon polariton frequency $\omega_0$ ) due to the anomalous
Doppler effect and the mutual polarization of the particles and they exist even
for the particles with losses. Similar singularities exist also for the
interaction force and the frictional torque. The obtained results can be
important for biomedical applications.",1702.02491v2
2020-11-11,A Data-Driven Reinforcement Learning Solution Framework for Optimal and Adaptive Personalization of a Hip Exoskeleton,"Robotic exoskeletons are exciting technologies for augmenting human mobility.
However, designing such a device for seamless integration with the human user
and to assist human movement still is a major challenge. This paper aims at
developing a novel data-driven solution framework based on reinforcement
learning (RL), without first modeling the human-robot dynamics, to provide
optimal and adaptive personalized torque assistance for reducing human efforts
during walking. Our automatic personalization solution framework includes the
assistive torque profile with two control timing parameters (peak and offset
timings), the least square policy iteration (LSPI) for learning the parameter
tuning policy, and a cost function based on transferred work ratio. The
proposed controller was successfully validated on a healthy human subject to
assist unilateral hip extension in walking. The results showed that the optimal
and adaptive RL controller as a new approach was feasible for tuning assistive
torque profile of the hip exoskeleton that coordinated with human actions and
reduced activation level of hip extensor muscle in human.",2011.06116v1
2021-02-16,Orbital angular momentum and current-induced motion of a Skyrmion-textured domain wall in a ferromagnetic nanotube,"We theoretically study the current-induced dynamics of a domain wall in a
ferromagnetic nanotube by developing a theory for the orbital angular momentum
of a domain wall and the current-induced torque on it. Specifically, a domain
wall with nontrivial magnetization winding along the circumference is shown to
possess finite orbital angular momentum, which is proportional to the product
of its Skyrmion charge and position, and the current is shown to exert a torque
changing the orbital angular momentum of the domain wall and thereby drives it.
The current-induced torque is interpreted as the transfer of orbital angular
momentum from electrons to the domain wall, which occurs due to the emergent
magnetic field associated with the Skyrmion charge. Our results reveal a
hitherto unrecognized utility of the orbital degree of freedom of magnetic
solitons.",2102.08405v1
2022-04-07,Learning Purely Tactile In-Hand Manipulation with a Torque-Controlled Hand,"We show that a purely tactile dextrous in-hand manipulation task with
continuous regrasping, requiring permanent force closure, can be learned from
scratch and executed robustly on a torque-controlled humanoid robotic hand. The
task is rotating a cube without dropping it, but in contrast to OpenAI's
seminal cube manipulation task, the palm faces downwards and no cameras but
only the hand's position and torque sensing are used. Although the task seems
simple, it combines for the first time all the challenges in execution as well
as learning that are important for using in-hand manipulation in real-world
applications. We efficiently train in a precisely modeled and identified rigid
body simulation with off-policy deep reinforcement learning, significantly sped
up by a domain adapted curriculum, leading to a moderate 600 CPU hours of
training time. The resulting policy is robustly transferred to the real
humanoid DLR Hand-II, e.g., reaching more than 46 full 2${\pi}$ rotations of
the cube in a single run and allowing for disturbances like different cube
sizes, hand orientation, or pulling a finger.",2204.03698v2
2022-10-08,Nonlinearity-induced optical torque,"Optically-induced mechanical torque leading to the rotation of small objects
requires the presence of absorption or breaking cylindrical symmetry of a
scatterer. A spherical non-absorbing particle cannot rotate due to the
conservation of the angular momentum of light upon scattering. Here, we suggest
a novel physical mechanism for the angular momentum transfer to non-absorbing
particles via nonlinear light scattering. The breaking of symmetry occurs at
the microscopic level manifested in nonlinear negative optical torque due to
the excitation of resonant states at the harmonic frequency with higher
projection of angular momentum. The proposed physical mechanism can be verified
with resonant dielectric nanostructures, and we suggest some specific
realizations.",2210.04021v1
2005-11-09,On the spin-up/spin-down transitions in accreting X-ray binaries,"Accreting X-Ray Binaries display a wide range of behaviours. Some of them are
observed to spin up steadily, others to alternate between spin-up and spin-down
states, sometimes superimposed on a longer trend of either spin up or spin
down. Here we interpret this rich phenomenology within a new model of the
disk-magnetosphere interaction. Our model, based on the simplest version of a
purely material torque, accounts for the fact that, when a neutron star is in
the propeller regime, a fraction of the ejected material does not receive
enough energy to completely unbind, and hence falls back into the disk. We show
that the presence of this feedback mass component causes the occurrence of
multiple states available to the system, for a given, constant value of the
mass accretion rate dot{M}_* from the companion star. If the angle chi of the
magnetic dipole axis with respect to the perpendicular to the disk is larger
than a critical value chi_crit, the system eventually settles in a cycle of
spin-up/spin-down transitions for a constant value of dot{M}_* and independent
of the initial conditions. No external perturbations are required to induce the
torque reversals. The transition from spin up to spin down is often accompanied
by a large drop in luminosity. The frequency range spanned in each cycle and
the timescale for torque reversals depend on dot{M}_*, the magnetic field of
the star, the magnetic colatitude chi, and the degree of elasticity regulating
the magnetosphere-disk interaction. The critical angle chi_crit ranges from
\~25-30 deg for a completely elastic interaction to ~40-45 deg for a totally
anelastic one. For chi ~< chi_crit, cycles are no longer possible and the
long-term evolution of the system is a pure spin up. We specifically illustrate
our model in the cases of the X-ray binaries GX 1+4 and 4U 1626-67.",0511285v1
2018-08-20,Anisotropic spin-orbit torque generation in epitaxial SrIrO3 by symmetry design,"Spin-orbit coupling (SOC), the interaction between the electron spin and the
orbital angular momentum, can unlock rich phenomena at interfaces, in
particular interconverting spin and charge currents. Conventional heavy metals
have been extensively explored due to their strong SOC of conduction electrons.
However, spin-orbit effects in classes of materials such as epitaxial
5d-electron transition metal complex oxides, which also host strong SOC, remain
largely unreported. In addition to strong SOC, these complex oxides can also
provide the additional tuning knob of epitaxy to control the electronic
structure and the engineering of spin-to-charge conversion by crystalline
symmetry. Here, we demonstrate room-temperature generation of spin-orbit torque
on a ferromagnet with extremely high efficiency via the spin-Hall effect in
epitaxial metastable perovskite SrIrO3. We first predict a large intrinsic
spin-Hall conductivity in orthorhombic bulk SrIrO3 arising from the Berry
curvature in the electronic band structure. By manipulating the intricate
interplay between SOC and crystalline symmetry, we control the spin-Hall torque
ratio by engineering the tilt of the corner-sharing oxygen octahedra in
perovskite SrIrO3 through epitaxial strain. This allows the presence of an
anisotropic spin-Hall effect due to a characteristic structural anisotropy in
SrIrO3 with orthorhombic symmetry. Our experimental findings demonstrate the
heteroepitaxial symmetry design approach to engineer spin-orbit effects. We
therefore anticipate that these epitaxial 5d transition-metal oxide thin films
can be an ideal building block for low-power spintronics.",1808.06650v1
1997-03-07,On the Correlation of Torque and Luminosity in GX 1+4,"Over five years of daily hard X-ray (>20 keV) monitoring of the 2-min
accretion-powered pulsar GX 1+4 with the Compton Gamma Ray Observatory/BATSE
large-area detectors has found nearly continuous rapid spin-down, interrupted
by a bright 200-d spin-up episode. During spin-down, the torque becomes more
negative as the luminosity increases (assuming that the 20-60 keV pulsed flux
traces bolometric luminosity), the opposite of what is predicted by standard
accretion torque theory. No changes in the shape of the 20-100 keV pulsed
energy spectrum were detected, so that a very drastic change in the spectrum
below 20 keV or the pulsed fraction would be required to make the 20-60 keV
pulsed flux a poor luminosity tracer. These are the first observations which
flatly contradict standard magnetic disk accretion theory, and they may have
important implications for understanding the spin evolution of X-ray binaries,
cataclysmic variables, and protostars. We briefly discuss the possibility that
GX 1+4 may be accreting from a retrograde disk during spin-down, as previously
suggested.",9703047v1
2015-12-25,Electromagnetic vs. Lense-Thirring alignment of black hole accretion discs,"Accretion discs and black holes (BHs) have angular momenta that are generally
misaligned with respect to each other, which can lead to warps in the discs and
bends in any jets produced. We consider a disc that is misaligned at large
radii and torqued by Lense-Thirring (LT) precession and a Blandford-Znajek (BZ)
jet torque. We consider a variety of disc states that include radiatively
inefficient thick discs, radiatively efficient thin discs, and super-Eddington
accretion discs. The magnetic field strength of the BZ jet is chosen as either
from standard equipartition arguments or from magnetically arrested disc (MAD)
simulations. We show that standard thin accretion discs can reach spin-disc
alignment out to large radii long before LT would play a role, as caused by the
slow infall time that gives even a weak BZ jet time to align the disc. We show
that geometrically thick radiatively inefficient discs and super-Eddington
discs in the MAD state reach disc-spin alignment near the black hole when
density profiles are shallow as in magnetohydrodynamical simulations, while the
BZ jet aligns discs with steep density profiles (as in advection-dominated
accretion flows) with the BH spin out to larger radii. Our results imply that
the BZ jet torque should affect the cosmological evolution of BH spin magnitude
and direction, BH spin measurements in active galactic nuclei and X-ray
binaries, and the interpretations for Event Horizon Telescope observations of
discs or jets in strong-field gravity regimes.",1512.07969v1
2016-09-07,Ferromagnetic layer thickness dependence of the Dzyaloshinskii-Moriya interaction and spin-orbit torques in Pt\Co\AlOx,"We report the thickness dependence of Dzyaloshinskii-Moriya interaction (DMI)
and spin-orbit torques (SOTs) in Pt\Co(t)\AlOx, studied by current-induced
domain wall (DW) motion and second-harmonic experiments. From the DW motion
study, a monotonous decay of the effective DMI strength with an increasing Co
thickness is observed, in agreement with a DMI originating at the Pt\Co
interface. The study of the ferromagnetic thickness dependence of spin-orbit
torques reveals a more complex behavior. The effective SOT-field driving the DW
motion is found to initially increase and then saturate with an increasing
ferromagnetic thickness, while the effective SOT-fields acting on a saturated
magnetic state exhibit a non-monotonic behavior with increasing Co-thickness.
The observed thickness dependence suggests the spin-Hall effect in Pt as the
main origin of the SOTs, with the measured SOT amplitudes resulting from the
interplay between the varying thickness and the transverse spin diffusion
length of the Co layer.",1609.02078v1
2018-02-02,Macroscopic direct observation of optical spin-dependent lateral forces and left-handed torques,"Observing and taming unusual effects arising from non-trivial light-matter
interaction has always triggered scientists to better understand Nature and
develop technological tools towards implementing novel applications. Recently,
several unusual optomechanical effects have been unveiled when subtle
spin-orbit interactions come at play to build up optical forces and torques
that are hardly seen in everyday life, such as negative optical radiation
pressure, transverse optical forces, or left-handed optical torques. To date,
there are only a few experimental proposals to reveal these effects despite
tremendous conceptual advances. In particular, spin-dependent lateral forces
and their angular analog are done either at the expense of direct observations
or at the cost of specific instrumental complexity. Here we report on naked-eye
identification of light-induced spin-dependent lateral displacements of
centimeter-sized objects endowed with structured birefringence. Its angular
counterpart is also discussed and the observation of left-handed macroscopic
rotational motion is reported. The unveiled effects are ultimately driven by
lateral optical force fields that are five orders of magnitude larger than
those reported so far. These results allow structured light-matter interaction
to move from a scientific curiosity to a new asset for the existing
multidisciplinary optical manipulation toolbox across length scales. In
addition, this highlights the spin-orbit optomechanics of anisotropic and
inhomogeneous media, which is just beginning to be explored.",1802.00607v1
2019-03-07,Spin-orbit Torque and Spin Hall Effect-based Cellular Level Therapeutic Neuromodulators: Modulating Neuron Activities through Spintronic Nanodevices,"Artificial modulation of a neuronal subset through ion channels activation
can initiate firing patterns of an entire neural circuit in vivo. As nanovalves
in the cell membrane, voltage-gated ion channels can be artificially controlled
by the electric field gradient that caused by externally applied time varying
magnetic fields. Herein, we theoretically investigate the feasibility of
modulating neural activities by using magnetic spintronic nanostructures. An
antiferromagnet/ferromagnet (AFM/FM) structure is explored as neuromodulator.
For FM layer with perpendicular magnetization, stable bidirectional
magnetization switching can be achieved by applying in-plane currents through
AFM layer to induce the spin-orbit torque (SOT) due to the spin Hall effect
(SHE). This Spin-orbit Torque Neurostimulator (SOTNS) utilizes in-plane charge
current pulses to switch the magnetization in FM layer. The time changing
magnetic stray field induces electric field that modulates the surrounding
neurons. The Object Oriented Micromagnetic Framework (OOMMF) is used to
calculate space and time dependent magnetic dynamics of SOTNS structure. The
current driven magnetization dynamics in SOTNS has no mechanically moving
parts. Furthermore, the size of SOTNS can be down to tens of nanometers, thus,
arrays of SOTNSs could be fabricated, integrated together and patterned on a
flexible substrate, which gives us much more flexible control of the
neuromodulation with cellular resolution.",1903.02726v1
2020-10-27,Gravitational waves from mountains in newly born millisecond magnetars,"In this paper we study the spin-evolution and gravitational-wave luminosity
of a newly born millisecond magnetar, formed either after the collapse of a
massive star or after the merger of two neutron stars. In both cases we
consider the effect of fallback accretion, and consider the evolution of the
system due to the different torques acting on the star, namely the spin up
torque due to accretion and spin-down torques due to magnetic dipole radiation,
neutrino emission, and gravitational wave emission linked to the formation of a
`mountain' on the accretion poles. Initially the spin period is mostly affected
by the dipole radiation, but at later times accretion spin the star up rapidly.
We find that a magnetar formed after the collapse of a massive star can accrete
up to 1 M_{\odot} , and survive on the order of 50 s before collapsing to a
black hole. The gravitational wave strain, for an object located at 1 Mpc, is
h_c \sim 10^{-23} at kHz frequencies, making this a potential target for next
generation ground based detectors. A magnetar formed after a binary neutron
star merger, on the other hand, accretes at the most 0.2 M_{\odot}, and emits
gravitational waves with a lower maximum strain of the order of h_c \sim
10^{-24} , but also survives for much longer times, and may possibly be
associated with the X-ray plateau observed in the light curve of a number of
short gamma-ray burst.",2010.15574v2
2021-06-15,Long-Range Orbital Magnetoelectric Torque in Ferromagnets,"While it is often assumed that the orbital response is suppressed and
short-ranged due to strong crystal field potential and orbital quenching, we
show that the orbital magnetoelectric response can be remarkably long-ranged in
ferromagnets. In a bilayer consisting of a nonmagnet and a ferromagnet, spin
injection from the interface results in spin accumulation and torque in the
ferromagnet, which rapidly oscillate and decay by spin dephasing. In contrast,
we find that even when an external electric field is applied only on the
nonmagnet, we find substantially long-ranged orbital magnetoelectric response
in the FM, which can go far beyond the spin dephasing length. This unusual
feature is attributed to nearly degenerate orbital characters imposed by the
crystal symmetry, which form hotspots for the intrinsic orbital response.
Because only the states near the hotspots contribute dominantly, the induced
orbital angular momentum does not exhibit destructive interference among states
with different momentum as in the case of the spin dephasing. This gives rise
to a distinct type of orbital torque on the magnetization, increasing with the
thickness of the ferromagnet. Such behavior may serve as critical long-sought
evidence of orbital transport to be directly tested in experiments. Our
findings open the possibility of using long-range orbital magnetoelectric
effect in orbitronic device applications.",2106.07928v2
2021-09-13,"Semiclassical equations of motion for disordered conductors: extrinsic interband velocity, corrected collision integral and spin-orbit torques","The semiclassical equations of motion are widely used to describe carrier
transport in conducting materials. Nevertheless, the substantial challenge of
incorporating disorder systematically into the semiclassical model persists,
leading to quantitative inaccuracies and occasionally erroneous predictions for
the expectation values of physical observables. In the present work we provide
a general prescription for reformulating the semiclassical equations of motion
for carriers in disordered conductors by taking the quantum mechanical density
matrix as the starting point. We focus on external electric fields, without
magnetic fields, and spin-independent disorder. The density matrix approach
allows averaging over impurity configurations, and the trace of the velocity
operator with the disorder-averaged density matrix can be reinterpreted as the
semiclassical velocity weighted by the Boltzmann distribution function. Through
this rationale the well-known intrinsic group and anomalous velocities are
trivially recovered, while we demonstrate the existence of an extrinsic
interband velocity, namely a disorder correction to the semiclassical velocity
of Bloch electrons, mediated by the interband matrix elements of the Berry
connection. A similar correction is present in the non-equilibrium expectation
value of the spin operator, contributing to spin-orbit torques. To obtain
agreement with diagrammatic approaches the scattering term in the Boltzmann
equation is corrected to first order in the electric field, and the Boltzmann
equation is solved up to sub-leading order in the disorder potential. Our
prescription ensures all vertex corrections present in diagrammatic treatments
are taken into account, and to illustrate this we discuss model cases in
topological insulators, including the anomalous Hall effect as well as
spin-orbit torques.",2109.06214v1
2021-09-16,Modelling spin-up episodes in accreting millisecond X-ray pulsars,"Accreting millisecond X-ray pulsars are known to provide a wealth of physical
information during their successive states of outburst and quiescence. Based on
the observed spin-up and spin-down rates of these objects it is possible, among
other things, to infer the stellar magnetic field strength and test models of
accretion disc flow. In this paper we consider the three accreting X-ray
pulsars (XTE J1751-305, IGR J00291+5934, and SAX J1808.4-3658) with the best
available timing data, and model their observed spin-up rates with the help of
a collection of standard torque models that describe a magnetically-threaded
accretion disc truncated at the magnetospheric radius. Whilst none of these
models are able to explain the observational data, we find that the inclusion
of the physically motivated phenomenological parameter $\xi$, which controls
the uncertainty in the location of the magnetospheric radius, leads to an
enhanced disc-integrated accretion torque. These 'new' torque models are
compatible with the observed spin-up rates as well as the inferred magnetic
fields of these objects provided that $\xi \approx 0.1-0.5$. Our results are
supplemented with a discussion of the relevance of additional physics effects
that include the presence of a multipolar magnetic field and
general-relativistic gravity.",2109.07657v1
2021-09-21,Spin Alignment of Dark Matter Halos: Mad Halos,"We investigate the spin alignment of the dark matter halos by considering a
mechanism somewhat similar to tidal locking. We dubbed it Tidal Locking Theory
(TLT). While Tidal Torque Theory is responsible for the initial angular
momentum of the dark matter halos, the Tidal locking Theory explains the
angular momentum evolution during non-linear ages. Our previous work showed
that close encounters between haloes could drastically change their angular
momentum. The current manuscript argues that the tidal locking theory predicts
partial alignment between speed and the spin direction for the large high-speed
halos. To examine this prediction, we use the IllustrisTNG simulation and look
for the alignment of the halos' rotation axis. We find that the excess
probability of alignment between spin and speed is about 10 percent at $z=0$
for fast haloes; with velocities larger than twice the median. We show that
tidal torque theory predicts that the spin of a halo tends to be aligned with
the middle eigendirection of the tidal tensor. Moreover, we find that the halos
at $z=10$ are preferentially aligned with the middle eigendirection of the
tidal tensor with an excess probability of 15 percent. We show that tidal
torque theory fails to predict correct alignment at $z=0$ while it works almost
flawlessly at $z=10$.",2109.09981v1
2013-11-29,Gate Tunable In- and Out-Of-Plane Spin-Orbit Coupling and Spin Splitting Anisotropy at LaAlO3/SrTiO3 (110) Interface,"Manipulating spin-orbit coupling (SOC) is important for devices such as
spin-orbit torque based memory and its understanding is neccessary to answer
several fundamental open questions in triplet state superconductivity,
topological insulators and Majorana fermions. Here we report spin splitting of
25 meV at the LaAlO3/SrTiO3 (110) interface for in-plane spins at a current
density of 1.4x104 A/cm2, which is large compared to that found in
semiconductor heterostructures or the LaAlO3/SrTiO3 (100) interface, and in
addition it is anisotropic. The anisotropy arises from the difference in
electron effective mass along the [001] and [1-10] directions. Our study
predicts a spin splitting energy > 1000 meV at a current density of 107 A/cm2,
which is enormous compared to metallic systems and will be an ideal spin
polarized source. In addition to the in-plane effect, there is an unexpected
gate-tunable out-of-plane SOC at the LaAlO3/SrTiO3 (110) interface when the
spins lie out-of-plane due to broken symmetry in the plane of the interface. We
demonstrate that this can be manipulated by varying the LaAlO3 thickness
showing that this interface can be engineered for spin-orbit torque devices.",1311.7532v3
2021-02-28,Spin and charge interconversion in Dirac semimetal thin films,"We report spin-to-charge and charge-to-spin conversion at room temperature in
heterostructure devices that interface an archetypal Dirac semimetal, Cd3As2,
with a metallic ferromagnet, Ni0.80Fe0.20 (permalloy). The spin-charge
interconversion is detected by both spin torque ferromagnetic resonance and
ferromagnetic resonance driven spin pumping. Analysis of the symmetric and
anti-symmetric components of the mixing voltage in spin torque ferromagnetic
resonance and the frequency and power dependence of the spin pumping signal
show that the behavior of these processes is consistent with previously
reported spin-charge interconversion mechanisms in heavy metals, topological
insulators, and Weyl semimetals. We find that the efficiency of spin-charge
interconversion in Cd3As2/permalloy bilayers can be comparable to that in heavy
metals. We discuss the underlying mechanisms by comparing our results with
first principles calculations.",2103.00653v1
2022-03-28,Role of the chiral spin configuration in field-free spin-orbit torque-induced magnetization switching by a locally injected spin current,"For deterministic magnetization switching by spin-orbit torque (SOT) in a
perpendicular magnetic anisotropy system, an additional in-plane direction
magnetic field is essential for deterministic switching by breaking the
magnetization symmetry. Realizing chirality in a magnetic ordering system can
be one approach for achieving asymmetry in the lateral direction for field-free
magnetization switching. However, systematic analysis of the influence of the
chiral spin system on deterministic switching is still scarce. In this report,
the achievement of field-free SOT-induced magnetization switching by using a
chiral spin configuration is investigated by experiments and micromagnetic
simulations. We designed a system in which only part of the ferromagnetic layer
overlaps with the heavy metal layer in the Pt/Co/MgO structure. Therefore, a
spin current is exerted only on a local area of the ferromagnetic layer, which
results in a N\'eel-type chiral spin configuration. The induced chiral spin
configuration can be stabilized (or destabilized) depending on the sign of the
interfacial Dzyaloshinskii-Moriya interaction of the system. The stabilized
spin configuration plays a crucial role in the deterministic switching in zero
field. We expect our findings to widen the perspective on chirality-based
all-electrical SOT device fabrication.",2203.14429v1
2023-06-03,Manipulating chiral-spin transport with ferroelectric polarization,"A collective excitation of the spin structure in a magnetic insulator can
transmit spin-angular momentum with negligible dissipation. This quantum of a
spin wave, introduced more than nine decades ago, has always been manipulated
through magnetic dipoles, (i.e., timereversal symmetry). Here, we report the
experimental observation of chiral-spin transport in multiferroic BiFeO3, where
the spin transport is controlled by reversing the ferroelectric polarization
(i.e., spatial inversion symmetry). The ferroelectrically controlled magnons
produce an unprecedented ratio of up to 18% rectification at room temperature.
The spin torque that the magnons in BiFeO3 carry can be used to efficiently
switch the magnetization of adja-cent magnets, with a spin-torque efficiency
being comparable to the spin Hall effect in heavy metals. Utilizing such a
controllable magnon generation and transmission in BiFeO3, an alloxide,
energy-scalable logic is demonstrated composed of spin-orbit injection,
detection, and magnetoelectric control. This observation opens a new chapter of
multiferroic magnons and paves an alternative pathway towards low-dissipation
nanoelectronics.",2306.02185v1
2005-12-08,High-field Magnetic Torque Measurements in (CH$_3$)$_2$CHNH$_3$CuCl$_3$,"High-field magnetic torque measurements were carried out in the spin gap
system (CH$_3$)$_2$CHNH$_3$CuCl$_3$. It was observed that the magnitude of the
magnetic torque $\tau$ is almost zero until the critical field and then
increases rapidly, which indicates the existence of the magnetic quantum phase
transition from the spin-gap phase to the field-induced magnetic ordered phase.
  From the temperature dependence of the magnetic torque $\tau$, the cusp-like
minimum indicative of the Bose-Einstein condensation (BEC) of magnons was
observed for $H \perp$ C-plane, while the kink-anomaly was observed for $H
\perp$ A-plane at the field-induced transition temperature. It was found that
this different behavior between $H \perp$ A-plane and $H \perp$ C-plane can be
interpreted as the breaking of the magnon BEC picture due to the rotational
symmetry breaking. The additional anomaly was also observed in the
field-induced magnetic ordered phase at the intermediate angle of the applied
magnetic field in the A-plane and discussed in terms of the spin-flop
transition, the spin-reorientation transition and the spin-lattice
correlations. In order to investigate the spin-lattice correlations in
(CH$_3$)$_2$CHNH$_3$CuCl$_3$, we performed the magnetostriction measurements
and observed that the magnetostriction appears by vanishing of the spin gap.",0512164v2
2006-12-01,Gilbert damping and spin Coulomb drag in a magnetized electron liquid with spin-orbit interaction,"We present a microscopic calculation of the Gilbert damping constant for the
magnetization of a two-dimensional spin-polarized electron liquid in the
presence of intrinsic spin-orbit interaction. First we show that the Gilbert
constant can be expressed in terms of the auto-correlation function of the
spin-orbit induced torque. Then we specialize to the case of the Rashba
spin-orbit interaction and we show that the Gilbert constant in this model is
related to the spin-channel conductivity. This allows us to study the Gilbert
damping constant in different physical regimes, characterized by different
orderings of the relevant energy scales -- spin-orbit coupling, Zeeman
coupling, momentum relaxation rate, spin-momentum relaxation rate, spin
precession frequency -- and to discuss its behavior in various limits.
Particular attention is paid to electron-electron interaction effects,which
enter the spin conductivity and hence the Gilbert damping constant via the spin
Coulomb drag coefficient.",0612015v1
2013-12-25,Spin structure of Graphene/Pt interface for spin current formation and induced magnetization in deposited (Ni-Fe)-nanodots,"Spin electronic structure of graphene pi-states and Pt 5d-states for the
Graphene/Pt interface has been investigated. Here, we report a large induced
spin-orbit splitting (~70-100 meV) of graphene pi-states with formation of
non-degenerated Dirac-cone spin states at the K-point of the BZ crossed with
spin-polarized Pt 5d-states at Fermi level that opens up a possibility for
creation of new spintronics devices. We propose to use this spin structure for
formation of spin current with spin locked perpendicular to the momentum for
induced remagnetization of the (Ni-Fe)-nanodots arranged atop the interface.
Theoretical estimations of the spin current created at the Graphene/Pt
interface and the induced intrinsic effective magnetic field leading to the
in-plane remagnetization of the NiFe-nanodots due to spin-orbit torque effect
are presented. By micromagnetic modeling based on experimentally observed
spin-orbit splitting we demonstarte that the induced intrinsic magnetic field
might be effectively used for magnetization swithching of the deposited
(Ni-Fe)-nanodots.",1312.6999v1
2018-10-19,Controlling spin supercurrents via nonequilibrium spin injection,"We propose a mechanism whereby spin supercurrents can be manipulated in
superconductor/ferromagnet proximity systems via nonequilibrium spin injection.
We find that if a spin supercurrent exists in equilibrium, a nonequilibrium
spin accumulation will exert a torque on the spins transported by this current.
This interaction causes a new spin supercurrent contribution to manifest out of
equilibrium, which is proportional to and polarized perpendicularly to both the
injected spins and equilibrium spin current. This is interesting for several
reasons: as a fundamental physical effect; due to possible applications as a
way to control spin supercurrents; and timeliness in light of recent
experiments on spin injection in proximitized superconductors.",1810.08623v2
2020-11-19,Determining complex spin mixing conductance and spin diffusion length from spin pumping experiments in magnetic insulator/heavy metal bilayers,"Magnetic insulators are promising materials for the development of
energy-efficient spintronics. Unlike metallic counterparts, the magnetic
insulators are characterized by imaginary part of the interfacial spin mixing
conductance as well in a bilayer with heavy metals and it is responsible for
the field-like toque in spin-orbit torque devices. Here, we study the
underlying theoretical constructs and develop a general strategy to determine
the complex spin mixing conductance from the experimental results of
ferromagnetic resonance and spin pumping. The results show that the imaginary
part of the spin mixing conductance can be one order more than the real part
and it matches the critical trend of spin mixing conductance with thickness of
the heavy metal. The interpretation of experimental results also indicates that
at small thicknesses the interface contribution becomes significant and bulk
diffusion model cannot explain the results. A thickness-dependent spin
diffusion length is necessary too that is tantamount to Elliott-Yafet spin
relaxation mechanism in the heavy metals. Also, we effectively explain the
experimental results while inserting a copper layer with varying thicknesses in
between the magnetic insulator and the heavy metal using spin-circuit
formalism.",2011.11055v1
2022-11-28,Superfluid-like spin transport in the dynamic states of easy-axis magnets,"The existing proposals for superfluid-like spin transport have been based on
easy-plane magnets where the U(1) spin-rotational symmetry is spontaneously
broken in equilibrium, and this has been limiting material choices for
realizing superfluid-like spin transport to restricted class of magnets. In
this work, we lift this limitation by showing that superfluid-like spin
transport can also be realized based on easy-axis magnets, where the U(1)
spin-rotational symmetry is intact in equilibrium but can be broken in
non-equilibrium. Specifically, we find the condition to engender a
non-equilibrium easy-cone state by applying a spin torque to easy-axis magnets,
which dynamically induces the spontaneous breaking of the U(1) spin-rotational
symmetry and thereby can support superfluid-like spin transport. By exploiting
this dynamic easy-cone state, we show theoretically that superfluid-like spin
transport can be achieved in easy-axis magnets under suitable conditions and
confirmed the prediction by micromagnetic simulations. We envision that our
work broadens material library for realizing superfluid-like spin transport,
showing the potential utility of dynamic states of magnets as venue to look for
spin-transport phenomena that do not occur in static magnetic backgrounds.",2211.15091v1
2007-11-02,Spin-torque driven ferromagnetic resonance of Co/Ni synthetic layers in spin valves,"Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study thin
Co/Ni synthetic layers with perpendicular anisotropy confined in spin-valve
based nanojunctions. Field swept ST-FMR measurements were conducted with a
magnetic field applied perpendicular to the layer surface. The resonance lines
were measured under low amplitude rf excitation, from 1 to 20 GHz. These
results are compared with those obtained using conventional rf field driven FMR
on extended films with the same Co/Ni layer structure. The layers confined in
spin valves have a lower resonance field, a narrower resonance linewidth and
approximately the same linewidth vs frequency slope, implying the same damping
parameter. The critical current for magnetic excitations is determined from
measurements of the resonance linewidth vs dc current and is in accord with the
one determined from I-V measurements.",0711.0405v2
2009-02-25,Spin torque and waviness in magnetic multilayers: a bridge between Valet-Fert theory and quantum approaches,"We develop a simple theoretical framework for transport in magnetic
multilayers, based on Landauer-Buttiker scattering formalism and Random Matrix
Theory. A simple transformation allows one to go from the scattering point of
view to theories expressed in terms of local currents and electrochemical
potential. In particular, our theory can be mapped onto the well established
classical Valet Fert theory for collinear systems. For non collinear systems,
in the absence of spin-flip scattering, our theory can be mapped onto the
generalized circuit theory. We apply our theory to the angular dependance of
spin accumulation and spin torque in non-collinear spin valves.",0902.4360v1
2010-11-03,Existence of vertical spin stiffness in Landau-Lifshitz-Gilbert equation in ferromagnetic semiconductors,"We calculate the magnetization torque due to the spin polarization of the
itinerant electrons by deriving the kinetic spin Bloch equations based on the
$s$-$d$ model. We find that the first-order gradient of the magnetization
inhomogeneity gives rise to the current-induced torques, which are consistent
to the previous works. At the second-order gradient, we find an effective
magnetic field perpendicular to the spin stiffness filed. This field is
proportional to the nonadiabatic parameter $\beta$. We show that this vertical
spin stiffness term can significantly modify the domain-wall structure in
ferromagnetic semiconductors and hence should be included in the
Landau-Lifshitz-Gilbert equation in studying the magnetization dynamics.",1011.0871v1
2014-11-22,Quantification of the spin-Hall anti-damping torque with a resonance spectrometer,"We present a simple technique using a cavity-based resonance spectrometer to
quantify the anti-damping torque due to the spin Hall effect. Modification of
ferromagnetic resonance is observed as a function of small DC current in
sub-mm-wide strips of bilayers, consisting of magnetically soft FeGaB and
strong spin-Hall metal Ta. From the detected current-induced linewidth change,
we obtain an effective spin Hall angle of 0.08-0.09 independent of the magnetic
layer thickness. Our results demonstrate that a sensitive resonance
spectrometer can be a general tool to investigate spin Hall effects in various
material systems, even those with vanishingly low conductivity and
magnetoresistance.",1411.6166v1
2014-12-08,Magnetization Dynamics driven by Non-equilibrium Spin-Orbit Coupled Electron Gas,"The dynamics of magnetization coupled to an electron gas via s-d exchange
interaction is investigated by using density matrix technique. Our theory shows
that non-equilibrium spin accumulation induces a spin torque and the electron
bath leads to a damping of the magnetization. For the two-dimensional
magnetization thin film coupled to the electron gas with Rashba spin-orbit
coupling, the result for the spin-orbit torques is consistent with the previous
semi-classical theory. Our theory predicts a damping of the magnetization,
which is absent in the semi-classical theory. The magnitude of the damping due
to the electron bath is comparable to the intrinsic Gilbert damping and may be
important in describing the magnetization dynamics of the system.",1412.2479v1
2017-07-02,Semitransparent anisotropic and spin Hall magnetoresistance sensor enabled by spin-orbit toque biasing,"We demonstrate an ultrathin and semitransparent anisotropic and spin Hall
magnetoresistance sensor based on NiFe/Pt heterostructure. The use of
spin-orbit torque effective field for transverse biasing allows to reduce the
total thickness of the sensors down to 3 - 4 nm and thereby leading to the
semitransparency. Despite the extremely simple design, the spin-orbit torque
effective field biased NiFe/Pt sensor exhibits level of linearity and
sensitivity comparable to those of sensors using more complex linearization
schemes. In a proof-of-concept design using a full Wheatstone bridge comprising
of four sensing elements, we obtained a sensitivity up to 202.9 m{\Omega}/Oe,
linearity error below 5%, and a detection limit down to 20 nT. The
transmittance of the sensor is over 50% in the visible range.",1707.00231v1
2017-08-29,Antiferromagnetic resonance excited by oscillating electric currents,"In antiferromagnetic materials the order parameter exhibits resonant modes at
frequencies that can be in the terahertz range, making them interesting
components for spintronic devices. Here, it is shown that antiferromagnetic
resonance can be excited using the inverse spin-Hall effect in a system
consisting of an antiferromagnetic insulator coupled to a normal-metal
waveguide. The time-dependent interplay between spin-torque, ac
spin-accumulation and magnetic degrees of freedom is studied. It is found that
the dynamics of the antiferromagnet effects the frequency-dependent
conductivity of the normal metal. Further, it is shown that in
antiferromagnetic insulators, the resonant excitation by ac spin-currents can
be orders of magnitude more efficient than excitation by the current-induced
Oersted field.",1708.08965v2
2017-09-14,Intrinsic Damping Phenomena from Quantum to Classical Magnets:An ab-initio Study of Gilbert Damping in Pt/Co Bilayer,"A fully quantum mechanical description of the precessional damping of Pt/Co
bilayer is presented in the framework of the Keldysh Green function approach
using {\it ab initio} electronic structure calculations. In contrast to
previous calculations of classical Gilbert damping ($\alpha_{GD}$), we
demonstrate that $\alpha_{GD}$ in the quantum case does not diverge in the
ballistic regime due to the finite size of the total spin, $S$. In the limit of
$S\rightarrow\infty$ we show that the formalism recovers the torque correlation
expression for $\alpha_{GD}$ which we decompose into spin-pumping and
spin-orbital torque correlation contributions. The formalism is generalized to
take into account a self consistently determined dephasing mechanism which
preserves the conservation laws and allows the investigation of the effect of
disorder. The dependence of $\alpha_{GD}$ on Pt thickness and disorder strength
is calculated and the spin diffusion length of Pt and spin mixing conductance
of the bilayer are determined and compared with experiments.",1709.04911v2
2017-11-30,Complementary logic operation based on electric-field controlled spin-orbit torques,"Spintronic devices as alternatives to traditional semiconductor-based
electronic devices attract considerable interest as they offer zero quiescent
power, built-in memory, scalability, and reconfigurability. To realize
spintronic logic gates for practical use, a complementary logic operation is
essential but still missing despite a recent progress in spin-based logic
devices. Here, we report the development of a complementary spin logic device
using electric-field controlled spin-orbit torque (SOT) switching. In heavy
metal/ferromagnet/oxide structures, the critical current for SOT-induced
switching of perpendicular magnetization is efficiently modulated by an
electric field via voltage-controlled magnetic anisotropy (VCMA) effect in a
non-volatile manner. Moreover, the polarity of the VCMA is tuned by the
modification of oxidation state at the ferromagnet/oxide interface. This allows
us to fabricate both n-type and p-type spin logic devices and to enable a
complementary logic operation, paving the way for the development of
non-volatile and reconfigurable logic devices.",1711.11172v1
2018-11-06,Chiral-induced switching of antiferromagnet spins in a confined nanowire,"In the development of spin-based electronic devices, a particular challenge
is the manipulation of the magnetic state with high speed and low power
consumption. Although research has focused on the current-induced spin-orbit
torque based on strong spin-orbit coupling, the charge-based and the
torque-driven devices have fundamental limitations: Joule heating, phase
mismatching and overshooting. In this work, we investigate numerically and
theoretically alternative switching scenario of antiferromagnetic insulator in
one-dimensional confined nanowire sandwiched with two electrodes. As the
electric field could break inversion symmetry and induce Dzyaloshinskii-Moriya
interaction and pseudo-dipole anisotropy, the resulting spiral texture takes
symmetric or antisymmetric configuration due to additional coupling with the
crystalline anisotropy. Therefore, by competing two spiral states, we show that
the magnetization reversal of antiferromagnets is realized, which is valid in
ferromagnetic counterpart. Our finding provides promising opportunities to
realize the rapid and energy-efficient electrical manipulation of magnetization
for future spin-based electronic devices.",1811.02200v2
2018-11-13,Spin-orbit torques acting upon a perpendicularly-magnetized Py layer,"We show that Py, a commonly-used soft ferromagnetic material with weak
anisotropy, can become perpendicularly-magnetized while depositing on Ta buffer
layer with Hf or Zr insertion layers (ILs) and MgO capping layer. By using two
different approaches, namely harmonic voltage measurement and hysteresis loop
shift measurement, the dampinglike spin-orbit torque (DL-SOT) efficiencies from
Ta/IL/Py/IL/MgO magnetic heterostructures with perpendicular magnetic
anisotropy are characterized. We find that though Ta has a significant spin
Hall effect, the DL-SOT efficiencies are small in systems with the Ta/Py
interface compared to that obtained from the control sample with the
traditional Ta/CoFeB interface. Our results indicate that the spin transparency
for the Ta/Py interface is much less than that for the Ta/CoFeB interface,
which might be related to the variation of spin mixing conductance for
different interfaces.",1811.05164v1
2019-11-05,Engineering the dynamics of topological spin textures by anisotropic spin-orbit torques,"Integrating topologically stabilized magnetic textures such as skyrmions as
nanoscale information carriers into future technologies requires the reliable
control by electric currents. Here, we uncover that the relevant skyrmion Hall
effect, which describes the deflection of moving skyrmions from the current
flow direction, acquires important corrections owing to anisotropic spin-orbit
torques that alter the dynamics of topological spin structures. Thereby, we
propose a viable means for manipulating the current-induced motion of skyrmions
and antiskyrmions. Based on these insights, we demonstrate by first-principles
calculations and symmetry arguments that the motion of spin textures can be
tailored by materials design in magnetic multilayers of Ir/Co/Pt and Au/Co/Pt.
Our work advances the understanding of the current-induced dynamics of these
magnetic textures, which underlies a plethora of memory and logic applications.",1911.01987v1
2017-05-22,Semiclassical theory of spin-orbit torques in disordered multiband electron systems,"We study spin-orbit torques (SOT) in non-degenerate multiband electron
systems in the weak disorder limit. In order to have better physical
transparency a semiclassical Boltzmann approach equivalent to the Kubo
diagrammatic approach in the non-crossing approximation is formulated. This
semiclassical framework accounts for the interband- coherence effects induced
by both the electric field and static impurity scattering. Using the
two-dimensional Rashba ferromagnet as a model system, we show that the
antidamping-like SOT arising from disorder-induced interband-coherence effects
is very sensitive to the spin structure of disorder and may have the same sign
as the intrinsic SOT in the presence of spin-dependent disorder. While the
cancellation of this SOT and the intrinsic one occurs only in the case of
spin-independent short-range disorder.",1705.07947v3
2018-08-11,Critical Spin Liquid versus Valence Bond Glass in Triangular Lattice Organic $κ$-(ET)$_2$Cu$_2$(CN)$_3$,"In the quest for materials with unconventional quantum phases, the organic
triangular-lattice antiferromagnet $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ has been
extensively discussed as a quantum spin liquid (QSL) candidate. Recently, an
intriguing quantum critical behaviour was suggested from low-temperature
magnetic torque experiments. Through microscopic analysis of all anisotropic
contributions, including Dzyaloshinskii-Moriya and multi-spin scalar chiral
interactions, we highlight significant deviations of the experimental
observations from a quantum critical scenario. Instead, we show that
disorder-induced spin defects provide a comprehensive explanation of the
low-temperature properties. These spins are attributed to valence bond defects
that emerge spontaneously as the QSL enters a valence bond glass phase at low
temperature. This theoretical treatment is applicable to a general class of
frustrated magnetic systems and has important implications for the
interpretation of magnetic torque, nuclear magnetic resonance, thermal
transport and thermodynamic experiments.",1808.03868v3
2018-12-04,Spin transport in a magnetic insulator with zero effective damping,"Applications based on spin currents strongly profit from the control and
reduction of their effective damping and their transport properties. We here
experimentally observe magnon mediated transport of spin (angular) momentum
through a 13.4 nm thin yttrium iron garnet film with full control of the
magnetic damping via spin-orbit torque. Above a critical spin-orbit torque, the
fully compensated damping manifests itself as an increase of magnon
conductivity by almost two orders of magnitude. We compare our results to
theoretical expectations based on recently predicted current induced magnon
condensates and discuss other possible origins of the observed critical
behaviour.",1812.01334v3
2020-04-28,Chiral symmetry breaking for deterministic switching of perpendicular magnetization by spin-orbit torque,"Symmetry breaking is a characteristic to determine which branch of a
bifurcation system follows upon crossing a critical point. Specifically, in
spin-orbit torque (SOT) devices, a fundamental question arises: how to break
the symmetry of the perpendicular magnetic moment by the in-plane spin
polarization? Here, we show that the chiral symmetry breaking by the DMI can
induce the deterministic SOT switching of the perpendicular magnetization. By
introducing a gradient of saturation magnetization or magnetic anisotropy,
non-collinear spin textures are formed by the gradient of effective SOT
strength, and thus the chiral symmetry of the SOT-induced spin textures is
broken by the DMI, resulting in the deterministic magnetization switching. We
introduce a strategy to induce an out-of-plane (z) gradient of magnetic
properties, as a practical solution for the wafer-scale manufacture of SOT
devices.",2004.13872v1
2017-10-20,Deterministic switching of perpendicularly magnetic layers by spin orbital torque through stray field engineering,"We proposed a novel multilayer structure to realize the deterministic
switching of perpendicularly magnetized layers by spin orbital torque from the
spin Hall effect through stray field engineering. In our design, a pinned
magnetic layer is introduced under the heave metal separated by an insulator,
generating an in-plane stray field in the perpendicularly magnetized layer. We
have confirmed the deterministic switching of perpendicularly magnetized layers
through micromagnetic simulation and theoretical analysis. The in-plane stray
field accounts for the deterministic switching exhibited in the structure and
the reversal ultimate state of the magnetic layer is predictable when the
applied spin current density is above the critical spin current density.
Moreover, the stray field is easily tunable in a wide range by adjusting the
saturation magnetization and dimensions of the pinned layer, and can
accommodate different perpendicularly magnetized materials without any external
magnetic field.",1710.08282v1
2019-05-30,Sub-nanosecond switching in a cryogenic spin-torque spin-valve memory element with a dilute permalloy free layer,"We present a study of the pulsed current switching characteristics of
spin-valve nanopillars with in-plane magnetized dilute permalloy and undiluted
permalloy free layers in the ballistic regime at low temperature. The dilute
permalloy free layer device switches much faster: the characteristic switching
time for a permalloy free (Ni0.83Fe0.17) layer device is 1.18 ns, while that
for a dilute permalloy ([Ni0.83Fe0.17]0.6Cu0.4) free layer device is 0.475 ns.
A ballistic macrospin model can capture the data trends with a reduced spin
torque asymmetry parameter, reduced spin polarization and increased Gilbert
damping for the dilute permalloy free layer relative to the permalloy devices.
Our study demonstrates that reducing the magnetization of the free layer
increases the switching speed while greatly reducing the switching energy and
shows a promising route toward even lower power magnetic memory devices
compatible with superconducting electronics.",1905.13262v1
2008-06-14,High domain wall velocities due to spin currents perpendicular to the plane,"We consider long and narrow spin valves composed of a first magnetic layer
with a single domain wall (DW), a normal metal spacer and a second magnetic
layer that is a planar or a perpendicular polarizer. For these structures, we
study numerically DW dynamics taking into account the spin torques due to the
perpendicular spin currents. We obtain high DW velocities: 50 m/s for planar
polarizer and 640 m/s for perpendicular polarizer for J = 5*10^6 A/cm^2. These
values are much larger than those predicted and observed for DW motion due to
the in-plane spin currents. The ratio of the magnitudes of the torques, which
generate the DW motion in the respective cases, is responsible for these large
differences.",0806.2369v1
2017-03-21,Room temperature spin-orbit torque switching induced by a topological insulator,"Recent studies on the magneto-transport properties of topological insulators
(TI) have attracted great attention due to the rich spin-orbit physics and
promising applications in spintronic devices. Particularly the strongly
spin-moment coupled electronic states have been extensively pursued to realize
efficient spin-orbit torque (SOT) switching. However, so far current-induced
magnetic switching with TI has only been observed at cryogenic temperatures. It
remains a controversial issue whether the topologically protected electronic
states in TI could benefit spintronic applications at room temperature. In this
work, we report full SOT switching in a TI/ferromagnet bilayer heterostructure
with perpendicular magnetic anisotropy at room temperature. The low switching
current density provides a definitive proof on the high SOT efficiency from TI.
The effective spin Hall angle of TI is determined to be several times larger
than commonly used heavy metals. Our results demonstrate the robustness of TI
as an SOT switching material and provide a direct avenue towards applicable
TI-based spintronic devices.",1703.07470v1
2017-04-17,A novel design to realize deterministic switching of perpendicularly magnetic layers by spin orbital torque through antiferromagnetic coupling,"We proposed a novel and simple multilayer structure to realize the
deterministic switching of perpendicularly magnetized layers (Co in our work)
by spin orbital torque from the spin Hall Effect in this paper. A pinned layer
is introduced, antiferromagnetically coupled to the magnetic Co layer. We have
confirmed the deterministic switching of perpendicularly magnetized layers from
perspectives of switching loops, trajectories and switching properties under
periodic spin currents through micromagnetic simulation. The antiferromagnetic
interaction accounts for the deterministic switching exhibited in the structure
and the reversal ultimate state of the magnetic layer is predictable when the
applied spin current density is above 60MA/cm2. In our design, the
antiferromagnetic coupling is easily tunable and no external magnetic field is
needed.",1704.04835v2
2019-09-17,Spin-Orbit-Torque Field-Effect Transistor (SOTFET): Proposal for a New Magnetoelectric Memory,"Spin-based memories are attractive for their non-volatility and high
durability but provide modest resistance changes, whereas semiconductor logic
transistors are capable of large resistance changes, but lack memory function
with high durability. The recent availability of multiferroic materials
provides an opportunity to directly couple the change in spin states of a
magnetic memory to a charge change in a semiconductor transistor. In this work,
we propose and analyze the spin-orbit torque field-effect transistor (SOTFET),
a device with the potential to significantly boost the energy efficiency of
spin-based memories, and to simultaneously offer a palette of new
functionalities.",1909.08133v3
2020-01-02,Wireless communication between two magnetic tunnel junctions acting as oscillator and diode,"Magnetic tunnel junctions are nanoscale spintronic devices with microwave
generation and detection capabilities. Here we use the rectification effect
called ""spin-diode"" in a magnetic tunnel junction to wirelessly detect the
microwave emission of another junction in the auto-oscillatory regime. We show
that the rectified spin-diode voltage measured at the receiving junction end
can be reconstructed from the independently measured auto-oscillation and spin
diode spectra in each junction. Finally we adapt the auto-oscillator model to
the case of spin-torque oscillator and spin-torque diode and we show that
accurately reproduces the experimentally observed features. These results will
be useful to design circuits and chips based on spintronic nanodevices
communicating through microwaves.",2001.00502v2
2020-07-05,Ultrahigh efficient spin-orbit torque magnetization switching in all-sputtered topological insulator - ferromagnet multilayers,"Spin-orbit torque (SOT) magnetization switching of ferromagnets with large
perpendicular magnetic anisotropy has a great potential for the next-generation
non-volatile magnetoresistive random-access memory (MRAM). It requires a
high-performance pure spin current source with a large spin Hall angle and high
electrical conductivity, which can be fabricated by a mass production
technique. In this work, we demonstrate ultrahigh efficient and robust SOT
magnetization switching in all-sputtered BiSb topological insulator -
perpendicularly magnetized Co/Pt multilayers. Despite fabricated by the
industry-friendly magnetron sputtering instead of the laboratory molecular beam
epitaxy, the topological insulator layer, BiSb, shows a large spin Hall angle
of $\theta$$_{SH}$ = 12.3 and high electrical conductivity of $\sigma$ =
1.5x$10^5$ $\Omega^{-1}$m$^{-1}$. Our results demonstrate the mass production
capability of BiSb topological insulator for implementation of ultralow power
SOT-MRAM and other SOT-based spintronic devices.",2007.02264v1
2020-07-15,Spin-orbit coupling in single layer ferrimagnets: direct observation of spin-orbit torques and chiral spin textures,"We demonstrate that effects of spin-orbit coupling and inversion asymmetry
exist in a single GdFeCo ferrimagnetic layer, even without a heavy metal
interface. We use electric transport measurements to quantify the spin-orbit
torques. We measure the Dzyaloshinskii-Moriya interaction using Brillouin light
scattering measurement technique, and we observe the resulting chiral magnetic
textures using x-ray PEEM microscopy. We attribute these effects to a
composition variation along the thickness, that we observed by scanning
transmission electron microscopy. We show that these effects can be optimized
by varying the GdFeCo thickness or by combining them with interfacial effects.",2007.07569v2
2020-07-19,Interfacial Dzyaloshinskii-Moriya interaction and spin-orbit torque in Au1-xPtx/Co bilayers with varying interfacial spin-orbit coupling,"The quantitative roles of the interfacial spin-orbit coupling (SOC) in
Dzyaloshinskii-Moriya interaction (DMI) and dampinglike spin-orbit torque
({\tau}DL) have remained unsettled after a decade of intensive study. Here, we
report a conclusive experiment evidence that, because of the critical role of
the interfacial orbital hybridization, the interfacial DMI is not necessarily a
linear function of the interfacial SOC, e.g. at Au1-xPtx/Co interfaces where
the interfacial SOC can be tuned significantly via strongly composition
(x)-dependent spin-orbit proximity effect without varying the bulk SOC and the
electronegativity of the Au1-xPtx layer. We also find that {\tau}DL in the
Au1-xPtx/Co bilayers varies distinctly from the interfacial SOC as a function
of x, indicating no important {\tau}DL contribution from the interfacial
Rashba-Edelstein effect.",2007.09817v2
2020-10-21,A Frustrated Bimeronium: Static Structure and Dynamics,"We show a topological spin texture called ""bimeronium"" in magnets with
in-plane magnetization. It is a topological counterpart of skyrmionium in
perpendicularly magnetized magnets and can be seen as a combination of two
bimerons with opposite topological charges. We report the static structure and
spin-orbit-torque-induced dynamics of an isolated bimeronium in a magnetic
monolayer with frustrated exchange interactions. We study the anisotropy and
magnetic field dependences of a static bimeronium. We also explore the
bimeronium dynamics driven by the damping-like spin-orbit torque. We find that
the bimeronium shows steady rotation when the spin polarization direction is
parallel to the easy axis. Moreover, we demonstrate the annihilation of the
bimeronium when the spin polarization direction is perpendicular to the easy
axis. Our results are useful for understanding fundamental properties of
bimeronium structures and may offer an approach to build bimeronium-based
spintronic devices.",2010.10822v2
2021-11-16,Energy-efficient W$_{\text{100-x}}$Ta$_{\text{x}}$/CoFeB/MgO spin Hall nano-oscillators,"We investigate a W-Ta alloying route to reduce the auto-oscillation current
densities and the power consumption of nano-constriction based spin Hall nano
oscillators. Using spin-torque ferromagnetic resonance (ST-FMR) measurements on
microbars of W$_{\text{100-x}}$Ta$_{\text{x}}$(5 nm)/CoFeB(t)/MgO stacks with t
= 1.4, 1.8, and 2.0 nm, we measure a substantial improvement in both the
spin-orbit torque efficiency and the spin Hall conductivity. We demonstrate a
34\% reduction in threshold auto-oscillation current density, which translates
into a 64\% reduction in power consumption as compared to pure W-based SHNOs.
Our work demonstrates the promising aspects of W-Ta alloying for the
energy-efficient operation of emerging spintronic devices.",2111.08627v1
2022-04-04,"Spin ice in a general applied magnetic field: Kasteleyn transition, magnetic torque and rotational magnetocaloric effect","Spin ice is a paradigmatic frustrated system famous for the emergence of
magnetic monopoles and a large magnetic entropy at low temperatures. It
exhibits unusual behavior in the presence of an external magnetic field as a
result of the competition between the spin ice entropy and the Zeeman energy.
Studies of this have generally focused on fields applied along high symmetry
directions: [111], [001], and [110]. Here we consider a model of spin ice with
external field in an arbitrary direction. We find that the Kasteleyn transition
known for $[001]$ fields, appears also for general field directions and
calculate the associated Kasteleyn temperature $T_K$ as a function of field
direction. $T_K$ is found to vanish, with a logarithmic dependence on field
angle, approaching certain lines of special field directions. We further
investigate the thermodynamic properties of spin ice for $T>T_K$, using a
Husimi cactus approximation. As the system is cooled towards $T_K$ a large
magnetic torque appears, tending to align the $[001]$ crystal axis with the
external field. The model also exhibits a rotational magnetocaloric effect:
significant temperature changes can be obtained by adabiatically rotating the
crystal relative to a fixed field.",2204.01575v1
2023-10-31,The optically thick rotating magnetic wind from a massive white dwarf merger product -- II. axisymmetric magnetohydrodynamic simulations,"We numerically construct a series of axisymmetric rotating magnetic wind
solutions, aiming at exploring the observation properties of massive white
dwarf (WD) merger remnants with a strong magnetic field, a fast spin, and an
intense mass loss, as inferred for WD J005311. We investigate the
magnetospheric structure and the resultant spin-down torque exerted to the
merger remnant with respect to the surface magnetic flux $\Phi_*$, spin angular
frequency $\Omega_*$ and the mass loss rate $\dot M$. We confirm that the wind
properties for $\sigma \equiv \Phi^2_* \Omega_*^2/\dot M v_\mathrm{esc}^3
\gtrsim 1$ significantly deviate from those of the spherical Parker wind, where
$v_\mathrm{esc}$ is the escape velocity at stellar surface. For such a rotating
magnetic wind sequence, we find: (i) quasi-periodic mass eruption triggered by
magnetic reconnection along with the equatorial plane (ii) a scaling relation
for the spin-down torque $T \approx (1/2) \times \dot{M} \Omega_* R^2_*
\sigma^{1/4}$. We apply our results to discuss the spin-down evolution and wind
anisotropy of massive WD merger remnants, the latter of which could be probed
by a successive observation of WD J005311 using Chandra.",2310.20126v1
2023-12-15,Mutual synchronization in spin torque and spin Hall nano-oscillators,"This chapter reviews the state of the art in mutually synchronized
spin-torque and spin Hall nano-oscillator (STNO and SHNO) arrays. After briefly
introducing the underlying physics, we discuss different nano-oscillator
implementations and their functional properties with respect to frequency
range, output power, phase noise, and modulation rates. We then introduce the
concepts and the theory of mutual synchronization and discuss the possible
coupling mechanisms in spintronic nano-oscillators, such as dipolar,
electrical, and spin-wave coupling. We review the experimental literature on
mutually synchronized STNOs and SHNOs in one- and two-dimensional arrays and
discuss ways to increase the number of mutually synchronized nano-oscillators.
Finally, the potential for applications ranging from microwave signal
sources/detectors and ultrafast spectrum analyzers to neuromorphic computing
elements and Ising machines is discussed together with the specific electronic
circuitry that has been designed so far to harness this potential.",2312.09656v1
2023-12-28,The long-term spin-down trend of ultra-luminous X-ray pulsar M82 X-2,"The discovery in 2014 of the pulsation from the ultra-luminous X-ray source
(ULX) M82 X-2 in 2014 has changed our view of ULXs. Because of the relatively
short baseline over which pulsations have been detected so far, M82 X-2's spin
state had been assumed to be in an equilibrium state. Using \cha and \xmm
archive data, we are able to investigate the pulsation of M82 X-2 back to 2005
and 2001. The newly determined spin frequencies clearly show a long-term
spin-down trend. If this trend is caused by magnetic threading, we infer a
dipolar magnetic field of $\sim1.2\times10^{13}$ G and that a mild beaming
factor ($\sim4$) is needed to match the braking torque with the mass accretion
torque. On the other hand, there are \nus observations showing instantaneous
spin-down behaviours, which might favour a variable prograde/retrograde flow
scenario for M82 X-2.",2312.16770v1
2010-10-05,Lindblad resonance torques in relativistic discs: II. Computation of resonance strengths,"We present a fully relativistic computation of the torques due to Lindblad
resonances from perturbers on circular, equatorial orbits on discs around
Schwarzschild and Kerr black holes. The computation proceeds by establishing a
relation between the Lindblad torques and the gravitational waveforms emitted
by the perturber and a test particle in a slightly eccentric orbit at the
radius of the Lindblad resonance. We show that our result reduces to the usual
formula when taking the nonrelativistic limit. Discs around a black hole
possess an m=1 inner Lindblad resonance with no Newtonian Keplerian analogue;
however its strength is very weak even in the moderately relativistic regime
(r/M ~ few tens), which is in part due to the partial cancellation of the two
leading contributions to the resonant amplitude (the gravitoelectric octupole
and gravitomagnetic quadrupole). For equatorial orbits around Kerr black holes,
we find that the m=1 ILR strength is enhanced for retrograde spins and
suppressed for prograde spins. We also find that the torque associated with the
m>=2 inner Lindblad resonances is enhanced relative to the nonrelativistic
case; the enhancement is a factor of 2 for the Schwarzschild hole even when the
perturber is at a radius of 25M.",1010.0759v2
2013-08-27,Berry phase theory of Dzyaloshinskii-Moriya interaction and spin-orbit torques,"Recent experiments on current-induced domain wall motion in chiral magnets
suggest important contributions both from spin-orbit torques (SOTs) and from
the Dzyaloshinskii-Moriya interaction (DMI). We derive a Berry phase expression
for the DMI and show that within this Berry phase theory DMI and SOTs are
intimately related, in a way formally analogous to the relation between orbital
magnetization (OM) and anomalous Hall effect (AHE). We introduce the concept of
the \textit{twist torque moment}, which probes the internal twist of wave
packets in chiral magnets in a similar way like the orbital moment probes the
wave packet's internal self rotation. We propose to interpret the Berry phase
theory of DMI as a theory of \textit{spiralization} in analogy to the modern
theory of OM. We show that the twist torque moment and the spiralization
together give rise to a Berry phase governing the response of the SOT to
thermal gradients, in analogy to the intrinsic anomalous Nernst effect. The
Berry phase theory of DMI is computationally very efficient because it only
needs the electronic structure of the collinear magnetic system as input. As an
application of the formalism we compute the DMI in Pt/Co, Pt/Co/O and Pt/Co/Al
magnetic trilayers and show that the DMI is highly anisotropic in these
systems.",1308.5983v1
2015-05-05,A Steady-State Alignment Front in an Accretion Disk Subjected to Lense-Thirring Torques,"Using only physical mechanisms, i.e., 3D MHD with no phenomenological
viscosity, we have simulated the dynamics of a moderately thin accretion disk
subject to torques whose radial scaling mimics those produced by lowest-order
post-Newtonian gravitomagnetism. In this simulation, we have shown how, in the
presence of MHD turbulence, a time-steady transition can be achieved between an
inner disk region aligned with the equatorial plane of the central mass's spin
and an outer region orbiting in a different plane. The position of the
equilibrium orientation transition is determined by a balance between
gravitomagnetic torque and warp-induced inward mixing of misaligned angular
momentum from the outer disk. If the mixing is interpreted in terms of
diffusive transport, the implied diffusion coefficient is
~(0.6--0.8)c_s^2/Omega for sound speed c_s and orbital frequency Omega. This
calibration permits estimation of the orientation transition's equilibrium
location given the central mass, its spin parameter, and the disk's surface
density and scaleheight profiles. However, the alignment front overshoots
before settling into an equilibrium, signaling that a diffusive model does not
fully represent the time-dependent properties of alignment fronts under these
conditions. Because the precessional torque on the disk at the alignment front
is always comparable to the rate at which misaligned angular momentum is
brought inward to the front by warp-driven radial motions, no break forms
between the inner and outer portions of the disk in our simulation. Our results
also raise questions about the applicability to MHD warped disks of the
traditional distinction between ""bending wave"" and ""diffusive"" regimes.",1505.01050v1
2017-09-28,Atmospheric thermal tides and planetary spin I. The complex interplay between stratification and rotation,"Thermal atmospheric tides can torque telluric planets away from spin-orbit
synchronous rotation, as observed in the case of Venus. They thus participate
to determine the possible climates and general circulations of the atmospheres
of these planets. In this work, we write the equations governing the dynamics
of thermal tides in a local vertically-stratified section of a rotating
planetary atmosphere by taking into account the effects of the complete
Coriolis acceleration on tidal waves. This allows us to derive analytically the
tidal torque and the tidally dissipated energy, which we use to discuss the
possible regimes of tidal dissipation and examine the key role played by
stratification.
  In agreement with early studies, we find that the frequency dependence of the
thermal atmospheric tidal torque in the vicinity of synchronization can be
approximated by a Maxwell model. This behaviour corresponds to weakly stably
stratified or convective fluid layers, as observed in ADLM2016a. A strong
stable stratification allows gravity waves to propagate, which makes the tidal
torque become negligible. The transition is continuous between these two
regimes. The traditional approximation appears to be valid in thin atmospheres
and in regimes where the rotation frequency is dominated by the forcing or the
buoyancy frequencies.
  Depending on the stability of their atmospheres with respect to convection,
observed exoplanets can be tidally driven toward synchronous or asynchronous
final rotation rates. The domain of applicability of the traditional
approximation is rigorously constrained by calculations.",1709.10148v1
2019-03-19,The Structure of a Quasi-Keplerian Accretion Disk around Magnetized Stars,"In this paper, we present the complete structure of a quasi-Keplerian thin
accretion disk with an internal dynamo around a magnetized neutron star. We
assume a full quasi-Keplerian disk with the azimuthal velocity deviating from
the Keplerian fashion by a factor of $\xi$ ($0<\xi<2$). In our approach, we
vertically integrate the radial component of the momentum equation to obtain
the radial pressure gradient equation for a thin quasi-Keplerian accretion
disk. Our results show that, at large radial distance, the accretion disk
behaves in a Keplerian fashion. However, close to the neutron star, pressure
gradient force (PGF) largely modifies the disk structure, resulting into sudden
dynamical changes in the accretion disk. The corotation radius is shifted
inward (outward) for $\xi>1$ (for $\xi<1$), and the position of the inner edge
with respect to the new corotation radius is also relocated accordingly, as
compared to the Keplerian model. The resulting PGF torque couples with viscous
torque (when $\xi<1$) to provide a spin-down torque and a spin-up torque (when
$\xi>1$) while in the advective state. Therefore, neglecting the PGF, as has
been the case in previous models, is a glaring omission. Our result has the
potential to explain the observable dynamic consequences of accretion disks
around magnetized neutron stars.",1903.07907v1
2024-03-05,Orbital torque switching in perpendicularly magnetized materials,"The orbital Hall effect in light materials has attracted considerable
attention for developing novel orbitronic devices. Here we investigate the
orbital torque efficiency and demonstrate the switching of the perpendicularly
magnetized materials through the orbital Hall material (OHM), i.e., Zirconium
(Zr). The orbital torque efficiency of approximately 0.78 is achieved in the Zr
OHM with the perpendicularly magnetized [Co/Pt]3 sample, which significantly
surpasses that of the perpendicularly magnetized CoFeB/Gd/CoFeB sample
(approximately 0.04). Such notable difference is attributed to the different
spin-orbit correlation strength between the [Co/Pt]3 sample and the
CoFeB/Gd/CoFeB sample, which has been confirmed through the theoretical
calculations. Furthermore, the full magnetization switching of the [Co/Pt]3
sample with a switching current density of approximately 2.6x106 A/cm2 has been
realized through Zr, which even outperforms that of the W spin Hall material.
Our finding provides a guideline to understand orbital torque efficiency and
paves the way to develop energy-efficient orbitronic devices.",2403.03043v1
2020-09-28,Control of skyrmion chirality in Ta/FeCoB/TaOx trilayers by TaOx oxidation and FeCoB thickness,"Skyrmions are magnetic bubbles with nontrivial topology envisioned as data
bits for ultrafast and power-efficient spintronic memory and logic devices.
They may be stabilized in heavy-metal/ferromagnetic/oxide trilayer systems. The
skyrmion chirality is then determined by the sign of the interfacial
Dzyaloshinskii-Moriya interaction (DMI). Nevertheless, for apparently identical
systems, there is some controversy about the DMI sign. Here, we show that the
degree of oxidation of the top interface and the thickness of the ferromagnetic
layer play a major role. Using Brillouin light-scattering measurements in
Ta/Fe-Co-B/TaOx trilayers, we demonstrate a sign change of the DMI with the
degree of oxidation of the Fe-Co-B/TaOx interface. Using polar magneto-optical
Kerr effect microscopy, we consistently observe a reversal of the direction of
current-induced motion of skyrmions with the oxidation level of TaOx; this is
attributed to their chirality reversal. In addition, a second chirality
reversal is observed when changing the Fe-Co-B thickness, probably due to the
proximity of the two Fe-Co-B interfaces in the ultrathin case. By properly
tuning the chirality of the skyrmion, spin-transfer and spin-orbit torques
combine constructively to enhance the skyrmion velocity. These observations
thus allow us to envision an optimization of the material parameters to produce
highly mobile skyrmions. Moreover, this chirality control enables a versatile
manipulation of skyrmions and paves the way towards multidirectional devices.",2009.13136v3
2020-12-13,Double Free-Layer Magnetic Tunnel Junctions for Probabilistic Bits,"Naturally random devices that exploit ambient thermal noise have recently
attracted attention as hardware primitives for accelerating probabilistic
computing applications. One such approach is to use a low barrier nanomagnet as
the free layer of a magnetic tunnel junction (MTJ) whose magnetic fluctuations
are converted to resistance fluctuations in the presence of a stable fixed
layer. Here, we propose and theoretically analyze a magnetic tunnel junction
with no fixed layers but two free layers that are circularly shaped disk
magnets. We use an experimentally benchmarked model that accounts for finite
temperature magnetization dynamics, bias-dependent charge and spin-polarized
currents as well as the dipolar coupling between the free layers. We obtain
analytical results for statistical averages of fluctuations that are in good
agreement with the numerical model. We find that the free layers with low
diameters fluctuate to randomize the resistance of the MTJ in an approximately
bias-independent manner. We show how such MTJs can be used to build a binary
stochastic neuron (or a p-bit) in hardware. Unlike earlier stochastic MTJs that
need to operate at a specific bias point to produce random fluctuations, the
proposed design can be random for a wide range of bias values, independent of
spin-transfer-torque pinning. Moreover, in the absence of a carefully optimized
stabled fixed layer, the symmetric double-free layer stack can be manufactured
using present day Magnetoresistive Random Access Memory (MRAM) technology by
minimal changes to the fabrication process. Such devices can be used as
hardware accelerators in energy-efficient computing schemes that require a
large throughput of tunably random bits.",2012.06950v2
2018-02-23,Generation and detection of dissipationless spin current in MgO/Si bilayer,"Spintronics is an analogue to electronics where spin of the electron rather
than its charge is functionally controlled for devices. The generation and
detection of spin current without ferromagnetic or exotic/scarce materials are
two the biggest challenges for spintronics devices. In this study, we report a
solution to the two problems of spin current generation and detection in Si.
Using non-local measurement, we experimentally demonstrate the generation of
helical dissipationless spin current using spin-Hall effect. Contrary to the
theoretical prediction, we observe the spin-Hall effect in both n-doped and
p-doped Si. The helical spin current is attributed to the site-inversion
asymmetry of the diamond cubic lattice of Si and structure inversion asymmetry
in MgO/Si bilayer. The spin to charge conversion in Si is insignificant due to
weak spin-orbit coupling. For the efficient detection of spin current, we
report spin to charge conversion at the MgO (1nm)/Si (2 um) (p-doped and
n-doped) thin film interface due to Rashba spin-orbit coupling. We detected the
spin current at a distance of >100 um, which is an order of magnitude larger
than the longest spin diffusion length measured using spin injection
techniques. The existence of spin current in Si is verified from coercivity
reduction in Co/Pd multilayer due to spin-orbit torque generated by spin
current from Si.",1802.08627v1
2021-10-18,Unconventional spin Hall effects in nonmagnetic solids,"Direct and inverse spin Hall effects lie at the heart of novel applications
that utilize spins of electrons as information carriers, allowing generation of
spin currents and detecting them via the electric voltage. In the standard
arrangement, applied electric field induces transverse spin current with
perpendicular spin polarization. Although conventional spin Hall effects are
commonly used in spin-orbit torques or spin Hall magnetoresistance experiments,
the possibilities to configure electronic devices according to specific needs
are quite limited. Here, we investigate unconventional spin Hall effects that
have the same origin as conventional ones, but manifest only in low-symmetry
crystals where spin polarization, spin current and charge current are not
enforced to be orthogonal. Based on the symmetry analysis for all 230 space
groups, we have identified crystal structures that could exhibit unusual
configurations of charge-to-spin conversion. The most relevant geometries have
been explored in more detail; in particular, we have analyzed the collinear
components yielding transverse charge and spin current with spin polarization
parallel to one of them, as well as the longitudinal ones, where charge and
spin currents are parallel. In addition, we have demonstrated that
unconventional spin Hall effect can be induced by controllable breaking the
crystal symmetries by an external electric field, which opens a perspective for
external tuning of spin injection and detection by electric fields. The results
have been confirmed by density functional theory calculations performed for
various materials relevant for spintronics. We are convinced that our findings
will stimulate further computational and experimental studies of unconventional
spin Hall effects.",2110.09242v2
2023-08-06,Anatomy of spin Hall effect in ferromagnetic metals,"The spin Hall effect in nonmagnetic materials has been intensively studied
and became one of the most crucial spin-charge conversion mechanism in
spintronics. However, the spin Hall effect in ferromagnetic metals has been
less investigated and remains unclear. In this work, we investigate the spin
Hall effect in representative ferromagnetic alloy by using first-principles
calculations. We first clarify the spin Hall effect into three different types
including conventional (CSHE), spin anomalous (SAHE) and magnetic spin Hall
effect (MSHE) and then calculate the corresponding spin Hall conductivity and
spin Hall angle for (Fe, Co, Ni)Pt, NiFe and CoFe alloy. We find the above
three spin Hall mechanisms do coexist in ferromagnetic metals. Particularly,
for Pt-based ferromagnetic alloy, a sizable conventional and magnetic spin Hall
angles comparable to that of Pt have been predicted. The remarkable
unconventional spin Hall effect in ferromagnetic metal may enrich the
spin-charge conversion phenomena. For instance, the spin current generated by
remarkable MSHE with out-of-plane spin-polarization should be helpful for
field-free switching of perpendicular magnetization through spin-orbit torque
effect. This work may stimulate future studies on the spin Hall effect in
ferromagnetic metals and pave their promising applications for spin-charge
conversion devices in spintronics.",2308.03111v1
2023-10-10,Self-induced inverse spin Hall effect in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ films,"The efficient generation of spin currents and spin torques via spin-orbit
coupling is an important goal of spintronics research. One crucial metric for
spin current generation is the spin Hall angle, which is the ratio of the spin
Hall current to the transversely flowing charge current. A typical approach to
measure the spin Hall angle in nonmagnetic materials is to generate spin
currents via spin pumping in an adjacent ferromagnetic layer and measure the
transverse voltage from the inverse spin Hall effect in the nonmagnetic layer.
However, given that the spin Hall effect also occurs in ferromagnets, single
ferromagnetic layers could generate a self-induced transverse voltage during
spin pumping as well. Here we show that manganite based
La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) films deposited by pulsed laser
deposition exhibit a significant self-induced inverse spin Hall voltage while
undergoing spin pumping. We observe efficient spin to charge conversion in the
LSMO films via the inverse spin Hall effect. A spin pumping voltage of 1.86
$\mu$V is observed in the LSMO (12 nm) film. Using density functional theory
and the Kubo formalism, we calculate the intrinsic spin current conductivities
of these films and show that they are in reasonable agreement with the
experimental measurements.",2310.06967v1
2010-01-26,Spin-wave instabilities in spin-transfer-driven magnetization dynamics,"We study the stability of magnetization precessions induced in spin-transfer
devices by the injection of spin-polarized electric currents. Instability
conditions are derived by introducing a generalized, far-from-equilibrium
interpretation of spin-waves. It is shown that instabilities are generated by
distinct groups of magnetostatically coupled spin-waves. Stability diagrams are
constructed as a function of external magnetic field and injected
spin-polarized current. These diagrams show that applying larger fields and
currents has a stabilizing effect on magnetization precessions. Analytical
results are compared with numerical simulations of spin-transfer-driven
magnetization dynamics.",1001.4806v1
2011-12-04,Effects of impurity on fidelity of quantum state transfer via spin channels,"By adopting the concept of fidelity, we investigated efficiency of quantum
state transfer with the XX chain as the quantum channel. Different from the
previous works, we concentrated on effects of spin and magnetic impurity on
fidelity of quantum state transfer. Our results revealed that the spin impurity
cannot prevent one from implementing perfect transfer of an arbitrary one-qubit
pure state across the spin channel, however, the presence of magnetic impurity
or both spin and magnetic impurities may destroy the otherwise perfect spin
channels.",1112.0738v1
2013-12-11,The Force Law of Classical Electrodynamics: Lorentz versus Einstein and Laub,"The classical theory of electrodynamics is built upon Maxwell's equations and
the concepts of electromagnetic field, force, energy, and momentum, which are
intimately tied together by Poynting's theorem and the Lorentz force law.
Whereas Maxwell's macroscopic equations relate the electric and magnetic fields
to their material sources (i.e., charge, current, polarization and
magnetization), Poynting's theorem governs the flow of electromagnetic energy
and its exchange between fields and material media, while the Lorentz law
regulates the back-and-forth transfer of momentum between the media and the
fields. As it turns out, an alternative force law, first proposed in 1908 by
Einstein and Laub, exists that is consistent with Maxwell's macroscopic
equations and complies with the conservation laws as well as with the
requirements of special relativity. While the Lorentz law requires the
introduction of hidden energy and hidden momentum in situations where an
electric field acts on a magnetic material, the Einstein-Laub formulation of
electromagnetic force and torque does not invoke hidden entities under such
circumstances. Moreover, the total force and the total torque exerted by
electromagnetic fields on any given object turn out to be independent of
whether force and torque densities are evaluated using the Lorentz law or in
accordance with the Einstein-Laub formulas. Hidden entities aside, the two
formulations differ only in their predicted force and torque distributions
throughout material media. Such differences in distribution are occasionally
measurable, and could serve as a guide in deciding which formulation, if
either, corresponds to physical reality.",1312.3262v1
2022-01-22,Magnetic Spirals in Accretion Flows Originated from Misaligned Magnetic Field,"Misalignment between rotation and magnetic field has been suggested to be one
type of physical mechanisms which can easen the effects of magnetic braking
during collapse of cloud cores leading to formation of protostellar disks.
However, its essential factors are poorly understood. Therefore, we perform a
more detailed analysis of the physics involved. We analyze existing simulation
data to measure the system torques, mass accretion rates and Toomre Q
parameters. We also examine the presence of shocks in the system. While
advective torques are generally the strongest, we find that magnetic and
gravitational torques can play substantial roles in how angular momentum is
transferred during the disk formation process. Magnetic torques can shape the
accretion flows, creating two-armed magnetized inflow spirals aligned with the
magnetic field. We find evidence of an accretion shock that is aligned
according to the spiral structure of the system. Inclusion of ambipolar
diffusion as explored in this work has shown a slight influence in the small
scale structures but not in the main morphology. We discuss potential candidate
systems where some of these phenomena could be present.",2201.08974v1
2023-07-31,End-to-End Reinforcement Learning for Torque Based Variable Height Hopping,"Legged locomotion is arguably the most suited and versatile mode to deal with
natural or unstructured terrains. Intensive research into dynamic walking and
running controllers has recently yielded great advances, both in the optimal
control and reinforcement learning (RL) literature. Hopping is a challenging
dynamic task involving a flight phase and has the potential to increase the
traversability of legged robots. Model based control for hopping typically
relies on accurate detection of different jump phases, such as lift-off or
touch down, and using different controllers for each phase. In this paper, we
present a end-to-end RL based torque controller that learns to implicitly
detect the relevant jump phases, removing the need to provide manual heuristics
for state detection. We also extend a method for simulation to reality transfer
of the learned controller to contact rich dynamic tasks, resulting in
successful deployment on the robot after training without parameter tuning.",2307.16676v2
2023-04-28,Competing signatures of intersite and interlayer spin transfer in the ultrafast magnetization dynamics,"Optically driven intersite and interlayer spin transfer are individually
known as the fastest processes for manipulating the spin order of magnetic
materials on the sub 100 fs time scale. However, their competing influence on
the ultrafast magnetization dynamics remains unexplored. In our work, we show
that optically induced intersite spin transfer (also known as OISTR) dominates
the ultrafast magnetization dynamics of ferromagnetic alloys such as Permalloy
(Ni80Fe20) only in the absence of interlayer spin transfer into a substrate.
Once interlayer spin transfer is possible, the influence of OISTR is
significantly reduced and interlayer spin transfer dominates the ultrafast
magnetization dynamics. This provides a new approach to control the
magnetization dynamics of alloys on extremely short time scales by fine-tuning
the interlayer spin transfer.",2304.14957v1
2017-04-03,Inverse spin galvanic effect in the presence of impurity spin-orbit scattering: a diagrammatic approach,"Spin-charge interconversion is currently the focus of intensive experimental
and theoretical research both for its intrinsic interest and for its potential
exploitation in the realization of new spintronic functionalities. Spin-orbit
coupling is one of the key microscopic mechanisms to couple charge currents and
spin polarizations. The Rashba spin-orbit coupling in a two-dimensional
electron gas has been shown to give rise to the inverse spin galvanic effect,
i.e. the generation of a non-equilibrium spin polarization by a charge current.
Whereas the Rashba model may be applied to the interpretation of experimental
results in many cases, in general in a given real physical system spin-orbit
coupling also occurs due other mechanisms such as Dresselhaus bulk inversion
asymmetry and scattering from impurities. In this work we consider the inverse
spin galvanic effect in the presence of Rashba, Dresselhaus and impurity
spin-orbit scattering. We find that the size and form of the inverse spin
galvanic effect is greatly modified by the presence of the various sources of
spin-orbit coupling. Indeed, spin-orbit coupling affects the spin relaxation
time by adding the Elliott-Yafet mechanism to the Dyakonov-Perel and,
furthermore, it changes the non-equilibrium value of the current-induced spin
polarization by introducing a new spin generation torque. We use a diagrammatic
Kubo formula approach to evaluate the spin polarization-charge current response
function. We finally comment about the relevance of our results for the
interpretation of experimental results.",1704.00532v1
2006-04-12,Description of spin transport and precession in spin-orbit coupling systems and a general equation of continuity,"By generalizing the usual current density to a matrix with respect to spin
variables, a general equation of continuity satisfied by the density matrix and
current density matrix has been derived. This equation holds in arbitrary
spin-orbit coupling systems as long as its Hamiltonian can be expressed in
terms of a power series in momentum. Thereby, the expressions of the current
density matrix and a torque density matrix are obtained. The current density
matrix completely describes both the usual current and spin current as well;
while the torque density matrix describes the spin precession caused by a total
effective magnetic field, which may include a realistic and an effective one
due to the spin-orbit coupling. In contrast to the conventional definition of
spin current, this expression contains an additional term if the Hamiltonian
includes nonlinear spin-orbit couplings. Moreover, if the degree of the full
Hamiltonian $\geq3$, then the particle current must also be modified in order
to satisfy the local conservation law of number.",0604320v8
2018-10-16,Spin-torque oscillation in a magnetic insulator probed by a single-spin sensor,"Coherent, self-sustained oscillation of magnetization in spin-torque
oscillators (STOs) is a promising source for on-chip, nanoscale generation of
microwave magnetic fields. Such fields could be used for local excitation of
spin-wave resonances, control of spin qubits, and studies of paramagnetic
resonance. However, local characterization of fields emitted by an STO has
remained an outstanding challenge. Here, we use the spin of a single
nitrogen-vacancy (NV) defect in diamond to probe the magnetic fields generated
by an STO in a microbar of ferromagnetic insulator yttrium-iron-garnet (YIG).
The combined spectral resolution and sensitivity of the NV sensor allows us to
resolve multiple spin-wave modes and characterize their damping. When damping
is decreased sufficiently via spin injection, the modes auto-oscillate, as
indicated by a strongly reduced linewidth, a diverging magnetic power spectral
density, and synchronization of the STO frequency to an external microwave
source. These results open the way for quantitative, nanoscale mapping of the
microwave signals generated by STOs, as well as harnessing STOs as local probes
of mesoscopic spin systems.",1810.07306v1
2017-02-16,Theory of current-induced spin polarizations in an electron gas,"We derive the Bloch equations for the spin dynamics of a two-dimensional
electron gas in the presence of spin-orbit coupling. For the latter we consider
both the intrinsic mechanisms of structure inversion asymmetry (Rashba) and
bulk inversion asymmetry (Dresselhaus), and the extrinsic ones arising from the
scattering from impurities. The derivation is based on the SU(2) gauge-field
formulation of the Rashba-Dresselhaus spin-orbit coupling. Our main result is
the identification of a new spin-generation torque arising from the
Elliot-Yafet process, which opposes a similar term arising from the
Dyakonov-Perel process. The new spin-generation torque contributes to the
current-induced spin polarization (CISP) -- also known as the Edelstein or
inverse spin-galvanic effect. As a result, the behavior of the CISP turns out
to be more complex than one would surmise from consideration of the internal
Rashba-Dresselhaus fields alone. In particular, the symmetry of the
current-induced spin polarization does not necessarily coincide with that of
the internal Rashba-Dresselhaus field, and an out-of-plane component of the
CISP is generally predicted, as observed in recent experiments. We also discuss
the extension to the three-dimensional electron gas, which may be relevant for
the interpretation of experiments in thin films.",1702.04887v1
2020-09-10,Charge-Spin Interconversion in Epitaxial Pt Probed by Spin-Orbit Torques in a Magnetic Insulator,"We measure spin-orbit torques (SOTs) in a unique model system of
all-epitaxial ferrite/Pt bilayers to gain insights into charge-spin
interconversion in Pt. With negligible electronic conduction in the insulating
ferrite, the crystalline Pt film acts as the sole source of charge-to-spin
conversion. A small field-like SOT independent of Pt thickness suggests a weak
Rashba-Edelstein effect at the ferrite/Pt interface. By contrast, we observe a
sizable damping-like SOT that depends on the Pt thickness, from which we deduce
the dominance of an extrinsic spin-Hall effect (skew scattering) and
Dyakonov-Perel spin relaxation in the crystalline Pt film. Furthermore, our
results point to a large internal spin-Hall ratio of $\approx$0.8 in epitaxial
Pt. Our experimental work takes an essential step towards understanding the
mechanisms of charge-spin interconversion and SOTs in Pt-based
heterostructures, which are crucial for power-efficient spintronic devices.",2009.04894v3
2021-10-05,Spin-orbit torque generation in NiFe/IrO2 bilayers,"The 5d transition-metal oxides have a unique electronic structure dominated
by strong spin-orbit coupling and hence they can be an intriguing platform to
explore spin-current physics. Here, we report on room-temperature generation of
spin-orbit torque (SOT) from a conductive 5d iridium oxide, IrO2. By measuring
second-harmonic Hall resistance of Ni81Fe19/IrO2 bilayers, we find both
dampinglike and fieldlike SOTs. The former is larger than the latter, enabling
easier control of magnetization. We also observe that the dampinglike SOT
efficiency has a significant dependence on IrO2 thickness, which is well
described by the drift-diffusion model based on the bulk spin Hall effect. We
deduce the effective spin Hall angle of +0.093 +- 0.003 and the spin-diffusion
length of 1.7 +- 0.2 nm. By comparison with control samples Pt and Ir, we show
that the effective spin Hall angle of IrO2 is comparable to that of Pt and
seven times higher than that of Ir. The fieldlike SOT efficiency has a negative
sign without appreciable dependence on the thickness, in contrast to the
dampinglike SOT. This suggests that the fieldlike SOT likely stems from the
interface. These experimental findings suggest that the uniqueness of the
electronic structure of 5d transition-metal oxides is crucial for highly
efficient charge to spin-current conversion.",2110.01801v1
2023-03-08,True amplification of spin waves in magnonic nano-waveguides,"Magnonic nano-devices exploit magnons -- quanta of spin waves -- to transmit
and process information within a single integrated platform that has the
potential to outperform traditional semiconductor-based electronics for low
power applications. The main missing cornerstone of this information
nanotechnology is an efficient scheme for the direct amplification of
propagating spin waves. The recent discovery of spin-orbit torque provided an
elegant mechanism for propagation losses compensation. While partial
compensation of the spin-wave damping has allowed for spin-wave signal
modulation, true amplification - the exponential increase in the spin-wave
intensity during propagation - has so far remained elusive. Here we evidence
the operating conditions to achieve unambiguous amplification using clocked
nanoseconds-long spin-orbit torque pulses in sub-micrometer wide magnonic
waveguides, where the effective magnetization has been engineered to be close
to zero to suppress the detrimental magnon-magnon scattering. As a result, we
achieve an exponential increase in the intensity of propagating spin waves up
to 500 % at a propagation distance of several micrometers. These results pave
the way towards the implementation of energy efficient, cascadable magnonic
architectures for wave-based information processing and complex on-chip
computation.",2303.04695v2
2023-06-21,Spin-orbit torques due to warped topological insulator surface states with an in-plane magnetization,"We investigate the extrinsic spin-orbit torque (SOT) on the surface of
topological insulators (TIs), which are characterized by two-dimensional warped
Dirac surface states, in the presence of an in-plane magnetization. The
interplay between extrinsic spin-orbit scattering and the in-plane
magnetization results in a net spin density leading to a SOT. Previous theory
suggested that the SOT could only be generated by an out-of-plane magnetic
field component, and any in-plane magnetic contribution could be gauged away.
However, we demonstrate theoretically that with an in-plane magnetization, the
SOT can be finite in TIs due to extrinsic spin-orbit scattering. In the case of
a TI model with a linear dispersion relation, the skew scattering term is zero,
and the extrinsic spin-orbit scattering influences the side-jump scattering,
leading to a finite SOT in TIs. However, when considering the warping term,
finite intrinsic and skew scattering terms will arise, in addition to
modifications to other scattering terms. We further show that the SOT depends
on the azimuthal angles of the magnetization and an external electric field. By
adjusting the extrinsic spin-orbit strength, Fermi energy, magnetization
strength and warping strength, the resulting SOTs can be maximized. These
findings shed light on the interplay between spin-orbit coupling and
magnetization in TIs, offering insights into the control and manipulation of
spin currents in these systems.",2306.12557v1
2024-01-29,Fluctuation-mediated spin-orbit torque enhancement in the noncollinear antiferromagnet Mn3Ni0.35Cu0.65N,"The role of spin fluctuations near magnetic phase transitions is crucial for
generating various exotic phenomena, including anomalies in the extraordinary
Hall effect, excess spin-current generation through the spin-Hall effect (SHE),
and enhanced spin-pumping, amongst others. In this study, we experimentally
investigate the temperature dependence of spin-orbit torques (SOTs) generated
by Mn3Ni0.35Cu0.65N (MNCN), a member of the noncollinear antiferromagnetic
family that exhibits unconventional magnetotransport properties. Our work
uncovers a strong and nontrivial temperature dependence of SOTs, peaking near
the N\'eel temperature of MNCN, which cannot be explained by conventional
intrinsic and extrinsic scattering mechanisms of the SHE. Notably, we measure a
maximum SOT efficiency of 30%, which is substantially larger than that of
commonly studied nonmagnetic materials such as Pt. Theoretical calculations
confirm a negligible SHE and a strong orbital Hall effect that can explain the
observed SOTs. We propose a previously unidentified mechanism wherein
fluctuating antiferromagnetic moments trigger the generation of substantial
orbital currents near the N\'eel temperature due to the emergence of scalar
spin chirality. Our findings present an approach for enhancing SOTs, which
holds promise for magnetic memory applications by leveraging antiferromagnetic
spin fluctuations to amplify both orbital and spin currents.",2401.16021v1
2014-01-24,Phase-sensitive detection of spin pumping via the ac inverse spin Hall effect,"An intriguing feature of spintronics is the use of pure spin-currents to
manipulate magnetization, e.g., spin-currents can switch magnetization in
spin-torque MRAM, a next-generation DRAM alternative. Giant spin-currents via
the spin Hall effect greatly expand the technological opportunities.
Conversely, a ferromagnet/normal metal junction emits spin-currents under
microwave excitation, i.e. spin-pumping. While such spin-currents are modulated
at the excitation frequency, there is also a non-linear, rectified component
that is commonly detected using the corresponding inverse spin Hall effect
(iSHE) dc voltage. However, the ac component should be more conducive for
quantitative analysis, as it is up to two orders of magnitude larger and
linear. But any device that uses the ac iSHE is also sensitive to inductive
signals via Faraday's Law and discrimination of the ac iSHE signal must rely on
phase-sensitive measurements. We use the inductive signal as a reference for a
quantitative measurement of the magnitude and phase of the ac iSHE.",1401.6469v1
2018-05-11,Unveiling the mechanisms of the spin Hall effect in Ta,"Spin-to-charge current interconversions are widely exploited for the
generation and detection of pure spin currents and are key ingredients for
future spintronic devices including spin-orbit torques and spin-orbit logic
circuits. In case of the spin Hall effect, different mechanisms contribute to
the phenomenon and determining the leading contribution is peremptory for
achieving the largest conversion efficiencies. Here, we experimentally
demonstrate the dominance of the intrinsic mechanism of the spin Hall effect in
highly-resistive Ta. We obtain an intrinsic spin Hall conductivity for
$\beta$-Ta of -820$\pm$120 ($\hbar$/e) $\Omega^{-1}cm^{-1}$ from spin
absorption experiments in a large set of lateral spin valve devices. The
predominance of the intrinsic mechanism in Ta allows us to linearly enhance the
spin Hall angle by tuning the resistivity of Ta, reaching up to -35$\pm$3%, the
largest reported value for a pure metal.",1805.04475v1
2014-06-04,Long-lived spin plasmons in a spin-polarized two-dimensional electron gas,"Collective charge-density modes (plasmons) of the clean two-dimensional
unpolarized electron gas are stable, for momentum conservation prevents them
from decaying into single-particle excitations. Collective spin-density modes
(spin plasmons) possess no similar protection and rapidly decay by production
of electron-hole pairs. Nevertheless, if the electron gas has a sufficiently
high degree of spin polarization ($P>1/7$, where $P$ is the ratio of the
equilibrium spin density and the total electron density, for a parabolic
single-particle spectrum) we find that a long-lived spin-plasmon---a collective
mode in which the densities of up and down spins oscillate with opposite
phases---can exist within a ""pseudo gap"" of the single-particle excitation
spectrum. The ensuing collectivization of the spin excitation spectrum is quite
remarkable and should be directly visible in Raman scattering experiments. The
predicted mode could dramatically improve the efficiency of coupling between
spin-wave-generating devices, such as spin-torque oscillators.",1406.0986v2
2017-01-19,"Spin currents, spin torques, and the concept of spin superfluidity","In magnets with non-collinear spin configuration the expectation value of the
conventionally defined spin current operator contains a contribution which
renormalizes an external magnetic field and hence affects only the precessional
motion of the spin polarization. This term, which has been named angular spin
current by Sun and Xie [Phys. Rev B 72, 245305 (2005)], does not describe the
translational motion of magnetic moments. We give a prescription how to
separate these two types of spin transport and show that the translational
movement of the spin is always polarized along the direction of the local
magnetization. We also show that at vanishing temperature the classical
magnetic order parameter in magnetic insulators cannot carry a translational
spin current, and elucidate how this affects the interpretation of spin
supercurrents.",1701.05505v1
2020-01-19,Dephasing of Transverse Spin Current in Ferrimagnetic Alloys,"It has been predicted that transverse spin current can propagate coherently
(without dephasing) over a long distance in antiferromagnetically ordered
metals. Here, we estimate the dephasing length of transverse spin current in
ferrimagnetic CoGd alloys by spin pumping measurements across the compensation
point. A modified drift-diffusion model, which accounts for spin-current
transmission through the ferrimagnet, reveals that the dephasing length is
about 4-5 times longer in nearly compensated CoGd than in ferromagnetic metals.
This finding suggests that antiferromagnetic order can mitigate spin dephasing
-- in a manner analogous to spin echo rephasing for nuclear and qubit spin
systems -- even in structurally disordered alloys at room temperature. We also
find evidence that transverse spin current interacts more strongly with the Co
sublattice than the Gd sublattice. Our results provide fundamental insights
into the interplay between spin current and antiferromagnetic order, which are
crucial for engineering spin torque effects in ferrimagnetic and
antiferromagnetic metals.",2001.06918v5
2022-05-05,Spin Manipulation by Giant Valley-Zeeman Spin-Orbit Field in Atom-Thick WSe2,"The phenomenon originating from spin-orbit coupling (SOC) provides
energy-efficient strategies for spin manipulation and device applications. The
broken inversion symmetry interface and resulting electric field induce a
Rashba-type spin-orbit field (SOF), which has been demonstrated to generate
spin-orbit torque for data storage applications. In this study, we found that
spin flipping can be achieved by the valley-Zeeman SOF in monolayer WSe2 at
room temperature, which manifests as a negative magnetoresistance in the
vertical spin valve. Quantum transmission calculations based on an effective
model near the K valley of WSe2 confirm the precessional spin transport of
carriers under the giant SOF, which is estimated to be 650 T. In particular,
the valley-Zeeman SOF-induced spin dynamics was demonstrated to be tunable with
the layer number and stacking phase of WSe2 as well as the gate voltage, which
provides a novel strategy for spin manipulation and can benefit the development
of ultralow-power spintronic devices.",2205.02876v1
2023-09-20,"Orbit-Spin Coupling, the Solar Dynamo, and the Planetary Theory of Sunspots","Orbit spin coupling is proposed as an alternative to planetary tidal models
for the excitation of solar variability as a function of time. Momentum sourced
from the orbital angular momenta of solar system bodies is deposited within the
circulating fluid envelopes of the Sun and planets in this hypothesis. A
reversing torque acts about an axis lying within the Sun's equatorial plane.
The torque gives rise to tangential differential accelerations of solar
materials as a function of longitude, latitude, depth, and time. The
accelerations pulse in amplitude, and change sign, on timescales corresponding
to the periods, beats, and harmonics of inner and outer planet orbital motions.
In contrast to planetary tidal models, no special amplification mechanism may
be required, as estimated peak accelerations are about 2 orders of magnitude
larger than the largest tidal accelerations. Organized mass motions driven by
the torque may be incorporated in dynamo simulations through the flow velocity
term of the MHD induction equation. The spatiotemporal variability of flow
velocities may then influence the variability with time of solar magnetic
activity. We provide torque values at 1 day timesteps for the years 1660 to
2220. We discuss the time variability of the torque in juxtaposition with SIDC
monthly sunspot numbers from 1750 to present. We investigate Hale cycle
synchronization, and the variability with time of the total solar irradiance,
with reference to outer and inner planet contributions respectively. We propose
a 3 component model for understanding and simulating the solar magnetic cycle,
which includes processes internal to the Sun, external forcing, due to orbit
spin coupling, and a time-delay, or system memory, component. This model
supplies a physical explanation for the observed variability with time of
Schwabe cycle periods and Hale cycle periods from 1712 to present.",2309.13076v1
2009-09-22,"Earth, Moon, Sun, and CV Accretion Disks","Net tidal torque by the secondary on a misaligned accretion disk, like the
net tidal torque by the Moon and the Sun on the equatorial bulge of the
spinning and tilted Earth, is suggested by others to be a source to retrograde
precession in non-magnetic, accreting Cataclysmic Variable (CV) Dwarf Novae
systems that show negative superhumps in their light curves. We investigate
this idea in this work. We generate a generic theoretical expression for
retrograde precession in spinning disks that are misaligned with the orbital
plane. Our generic theoretical expression matches that which describes the
retrograde precession of Earths' equinoxes. By making appropriate assumptions,
we reduce our generic theoretical expression to those generated by others, or
to those used by others, to describe retrograde precession in protostellar,
protoplanetary, X-ray binary, non-magnetic CV DN, quasar and black hole
systems. We find that differential rotation and effects on the disk by the
accretion stream must be addressed. Our analysis indicates that the best
description of a retrogradely precessing spinning, tilted, CV DN accretion disk
is a differentially rotating, tilted disk with an attached rotating, tilted
ring located near the innermost disk annuli. Our final, reduced expression for
retrograde precession agrees well with our numerical simulation results and
with selective observational systems that seem to have main sequence
secondaries. Our results suggest that tidal torques should be common to a
variety of systems where one member is spinning and tilted, regardless if
accretion disks are present or not. Our results suggest that the accretion
disk's geometric shape directly affects the disk's precession rate.",0909.4093v1
2014-09-02,Switching of Perpendicularly Polarized Nanomagnets with Spin Orbit Torque without an External Magnetic Field by Engineering a Tilted Anisotropy,"Spin orbit torque (SOT) provides an efficient way of generating spin current
that promises to significantly reduce the current required for switching
nanomagnets. However, an in-plane current generated SOT cannot
deterministically switch a perpendicularly polarized magnet due to symmetry
reasons. On the other hand, perpendicularly polarized magnets are preferred
over in-plane magnets for high-density data storage applications due to their
significantly larger thermal stability in ultra-scaled dimensions. Here we show
that it is possible switch a perpendicularly polarized magnet by SOT without
needing an external magnetic field. This is accomplished by engineering an
anisotropy in the magnets such that the magnetic easy axis slightly tilts away
from the film-normal. Such a tilted anisotropy breaks the symmetry of the
problem and makes it possible to switch the magnet deterministically. Using a
simple Ta/CoFeB/MgO/Ta heterostructure, we demonstrate reversible switching of
the magnetization by reversing the polarity of the applied current. This
demonstration presents a new approach for controlling nanomagnets with spin
orbit torque.",1409.0620v3
2015-06-03,Antidamping spin-orbit torque driven by spin-flip reflection mechanism on the surface of a topological insulator: A time-dependent nonequilibrium Green function approach,"Motivated by recent experiments observing spin-orbit torque (SOT) acting on
the magnetization $\vec{m}$ of a ferromagnetic (F) overlayer on the surface of
a three-dimensional topological insulator (TI), we investigate the origin of
the SOT and the magnetization dynamics in such systems. We predict that lateral
F/TI bilayers of finite length, sandwiched between two normal metal leads, will
generate a large antidamping-like SOT per very low charge current injected
parallel to the interface. The large values of antidamping-like SOT are {\it
spatially localized} around the transverse edges of the F overlayer. Our
analysis is based on adiabatic expansion (to first order in $\partial
\vec{m}/\partial t$) of time-dependent nonequilibrium Green functions (NEGFs),
describing electrons pushed out of equilibrium both by the applied bias voltage
and by the slow variation of a classical degree of freedom [such as
$\vec{m}(t)$]. From it we extract formulas for spin torque and charge pumping,
which show that they are reciprocal effects to each other, as well as Gilbert
damping in the presence of SO coupling. The NEGF-based formula for SOT
naturally splits into four components, determined by their behavior (even or
odd) under the time and bias voltage reversal. Their complex angular dependence
is delineated and employed within Landau-Lifshitz-Gilbert simulations of
magnetization dynamics in order to demonstrate capability of the predicted SOT
to efficiently switch $\vec{m}$ of a perpendicularly magnetized F overlayer.",1506.01303v3
2017-08-10,Magnetic anisotropy of the alkali iridate Na$_{2}$IrO$_{3}$ at high magnetic fields: evidence for strong ferromagnetic Kitaev correlations,"The magnetic field response of the Mott-insulating honeycomb iridate
Na$_{2}$IrO$_{3}$ is investigated using torque magnetometry measurements in
magnetic fields up to 60 tesla. A peak-dip structure is observed in the torque
response at magnetic fields corresponding to an energy scale close to the
zigzag ordering ($\approx 15~K$) temperature. Using exact diagonalization
calculations, we show that such a distinctive signature in the torque response
constrains the effective spin models for these classes of Kitaev materials to
ones with dominant ferromagnetic Kitaev interactions, while alternative models
with dominant antiferromagnetic Kitaev interactions are excluded. We further
show that at high magnetic fields, long range spin correlation functions decay
rapidly, signaling a transition to a long-sought-after field-induced quantum
spin liquid beyond the peak-dip structure. Kitaev systems are thus revealed to
be excellent candidates for field-induced quantum spin liquids, similar physics
having been suggested in another Kitaev material $\alpha-$RuCl$_{3}$.",1708.03235v5
2017-03-13,Study of the accretion torque during the 2014 outburst of the X-ray pulsar GRO J1744-28,"We present the spectral and timing analysis of the X-ray pulsar GRO J1744-28
during its 2014 outburst using data collected with the X-ray satellites Swift,
INTEGRAL, Chandra, and XMM-Newton. We derived, by phase-connected timing
analysis of the observed pulses, an updated set of the source ephemeris. We
were also able to investigate the spin-up of the X-ray pulsar as a consequence
of the accretion torque during the outburst. Relating the spin-up rate and the
mass accretion rate as $\dot{\nu}\propto\dot{M}^{\beta}$, we fitted the pulse
phase delays obtaining a value of $\beta=0.96(3)$. Combining the results from
the source spin-up frequency derivative and the flux estimation, we constrained
the source distance to be between 3.4-4.1 kpc, assuming a disc viscous
parameter $\alpha$ to be in the range 0.1-1. Finally, we investigated the
presence of a possible spin-down torque by adding a quadratic component to the
pulse phase delay model. The marginal statistical improvement of the updated
model does not allow us to firmly confirm the presence of this component.",1703.04449v1
2019-08-09,Experimental Demonstration of an Extreme Sub-Wavelength Nanomagnetic Acoustic Antenna Actuated by Spin-Orbit Torque from a Heavy Metal Nanostrip,"A novel on-chip extreme sub-wavelength ""acoustic antenna"" whose radiation
efficiency is ~50 times larger than the theoretical limit for a resonantly
driven antenna is demonstrated. The antenna is composed of magnetostrictive
nanomagnets deposited on a piezoelectric substrate. The nanomagnets are
partially in contact with a heavy metal (Pt) nanostrip. Passage of alternating
current through the nanostrip exerts alternating spin-orbit torque on the
nanomagnets and periodically rotates their magnetizations. During the rotation,
the magnetostrictive nanomagnets expand and contract, thereby setting up
alternating tensile and compressive strain in the piezoelectric substrate
underneath. This leads to the generation of a surface acoustic wave in the
substrate and makes the nanomagnet assembly act as an acoustic antenna. The
measured radiation efficiency of this acoustic antenna at the detected
frequency is ~1%, while the wavelength to antenna dimension ratio is ~ 67:1.
For a standard antenna driven at acoustic resonance, the efficiency would have
been limited to ~ (1/67)^2 = 0.02%. It was possible to beat that limit (by ~50
times) via actuating the antenna not by acoustic resonance, but by using a
completely different mechanism involving spin-orbit torque originating from the
giant spin Hall effect in Pt.",1908.03516v2
2021-01-13,Rotational Disruption of Porous Dust Aggregates due to Gas Flow in Protoplanetary Disks,"We introduce a possible disruption mechanism of dust grains in planet
formation by their spinning motion. This mechanism has been discussed as
rotational disruption for the interstellar dust grains. We theoretically
calculate whether porous dust aggregates can be disrupted by their spinning
motion and if it prohibits dust growth in protoplanetary disks. We assume
radiative torque and gas-flow torque as driving sources of the spinning motion,
assume that dust aggregates reach a steady-state rigid rotation, and compare
the obtained tensile stress due to the centrifugal force with their tensile
strength. We model the irregularly-shaped dust aggregates by introducing a
parameter, $\gamma_\mathrm{ft}$, that mimics the conversion efficiency from
force to torque. As a result, we find that porous dust aggregates are
rotationally disrupted by their spinning motion induced by gas flow when their
mass is larger than $\sim10^8$ g and their volume filling factor is smaller
than $\sim 0.01$ in our fiducial model, while relatively compact dust
aggregates with volume filling factor more than 0.01 do not face this problem.
If we assume the dust porosity evolution, we find that dust aggregates whose
Stokes number is $\sim0.1$ can be rotationally disrupted in their growth and
compression process. Our results suggest that the growth of dust aggregates may
be halted due to rotational disruption or that other compression mechanisms are
needed to avoid it. We also note that dust aggregates are not rotationally
disrupted when $\gamma_\mathrm{ft}\leq0.02$ in our fiducial model and the
modeling of irregularly-shaped dust aggregates is essential in future work.",2101.04910v2
2022-11-02,Three-dimensional Simulations of Magnetospheric Accretion in a T Tauri Star: Accretion and Wind Structures Just Around Star,"We perform three-dimensional magnetohydrodynamic simulations of
magnetospheric accretion in a T Tauri star to study the accretion and wind
structures in the close vicinity of the star. The gas accreting onto the star
consists of the gas from the magnetospheric boundary and the failed disk winds.
The accreting gas is commonly found as a multi-column accretion, which is
consistent with observations. A significant fraction of the angular momentum of
the accreting flows is removed by the magnetic fields of conical disk winds and
turbulent failed winds inside and near the magnetosphere. As a result, the
accretion torque is significantly reduced compared to the simple estimation
based on the mass accretion rate. The stellar spin affects the time variability
of the conical disk wind by changing the stability condition of the
magnetospheric boundary. However, the time-averaged magnetospheric radius only
weakly depends on the stellar spin, which is unlike the prediction of classical
theories that the stellar spin controls the magnetospheric radius through the
magnetic torque. The ratio of the toroidal to the poloidal field strengths at
the magnetospheric boundary, which is a key parameter for the magnetic torque,
is also insensitive to the spin; it is rather determined by the disk dynamics.
Considering newly found three-dimensional effects, we obtain a scaling relation
of the magnetospheric radius very similar to the Ghosh & Lamb relation from the
steady angular momentum transport equation.",2211.01072v1
2023-09-26,Multiferroic Magnon Spin-Torque Based Reconfigurable Logic-In-Memory,"Magnons, bosonic quasiparticles carrying angular momentum, can flow through
insulators for information transmission with minimal power dissipation.
However, it remains challenging to develop a magnon-based logic due to the lack
of efficient electrical manipulation of magnon transport. Here we present a
magnon logic-in-memory device in a spin-source/multiferroic/ferromagnet
structure, where multiferroic magnon modes can be electrically excited and
controlled. In this device, magnon information is encoded to ferromagnetic bits
by the magnon-mediated spin torque. We show that the ferroelectric polarization
can electrically modulate the magnon spin-torque by controlling the
non-collinear antiferromagnetic structure in multiferroic bismuth ferrite thin
films with coupled antiferromagnetic and ferroelectric orders. By manipulating
the two coupled non-volatile state variables (ferroelectric polarization and
magnetization), we further demonstrate reconfigurable logic-in-memory
operations in a single device. Our findings highlight the potential of
multiferroics for controlling magnon information transport and offer a pathway
towards room-temperature voltage-controlled, low-power, scalable magnonics for
in-memory computing.",2309.14614v1
2023-11-07,Revealing the ultra-fast domain wall motion in Manganese Gold through permalloy capping,"Antiferromagnets offer much faster dynamics compared to their ferromagnetic
counterparts but their order parameter is extremely difficult to detect and
control. So far, controlling the N\'eel order parameter electrically is limited
to only very few materials where N\'eel spin-orbit torques are allowed by
symmetry. In this work, we show that coupling a thin ferromagnet (permalloy)
layer on top of an antiferromagnet (Mn$_2$Au) solves a major roadblock -- the
controlled reading, writing, and manipulation of antiferromagnetic domains. We
confirm by atomistic spin dynamics simulations that the domain wall patterns in
the Mn$_2$Au are imprinted on the permalloy, therefore allowing for indirect
imaging of the N\'eel order parameter. Our simulations show that the coupled
domain wall structures in Mn$_2$Au-Py bilayers can be manipulated by either
acting on the N\'eel order parameter via N\'eel spin-orbit torques or by acting
on the magnetisation (the ferromagnetic order parameter) via magnetic fields.
In both cases, we predict ultra-high domain wall speeds on the order of 8.5
km/s. Thus, employing a thin ferromagnetic layer has the potential to easily
control the N\'eel order parameter in antiferromagnets even where N\'eel
spin-orbit torques are forbidden by symmetry. The controlled manipulation of
the antiferromagnetic order parameter provides a promising basis for the
development of high-density storage and efficient computing technologies
working in the THz regime.",2311.04305v1
2023-03-02,Control of the Radiative Heat Transfer in a Pair of Rotating Nanostructures,"The fluctuations of the electromagnetic field are at the origin of the
near-field radiative heat transfer between nanostructures, as well as the
Casimir forces and torques that they exert on each other. Here, working within
the formalism of fluctuational electrodynamics, we investigate the simultaneous
transfer of energy and angular momentum in a pair of rotating nanostructures.
We demonstrate that, due to the rotation of the nanostructures, the radiative
heat transfer between them can be increased, decreased, or even reversed with
respect to the transfer that occurs in absence of rotation, which is solely
determined by the difference in the temperature of the nanostructures. This
work unravels the unintuitive phenomena arising from the simultaneous transfer
of energy and angular momentum in pairs of rotating nanostructures.",2303.01354v1
2007-02-07,Vacuum fluctuations and the spin current in mesoscopic structures with collinear magnetic order,"We show that in magnetic nanostructures with a homogeneous magnetic order,
the equilibrium spin current can be nonzero. For example, this is the case of a
wide magnetic ring with the magnetization along the ring axis. The physical
reason of this effect is a variation of the orientation of anisotropy axis
inducing a spin torque acting on the magnetic ions. The mechanism of the spin
current generation is related to the quantum vacuum fluctuations in the
magnetic system.",0702168v2
2007-03-12,Effect of Polarized Current on the Magnetic State of Antiferromagnet,"We provide evidence for the effects of spin polarized current on a
nanofabricated antiferromagnet incorporated into a spin-valve structure.
Signatures of current-induced effects include bipolar steps in differential
resistance, current-induced changes of exchange bias correlated with these
steps, and deviations from the statistics expected for thermally activated
switching of spin valves. We explain our observations by a combination of spin
torque exerted on the interfacial antiferromagnetic moments, and
electron-magnon scattering in antiferromagnet.",0703281v2
2016-09-30,Interaction Between a Domain Wall and Spin Supercurrent in Easy-cone Magnets,"A domain wall and spin supercurrent can coexist in magnets with easy-cone
anisotropy owing to simultaneous spontaneous breaking of Z$_2$ and U(1)
symmetries. Their interaction is theoretically investigated in quasi
one-dimensional ferromagnets within the Landau-Lifshitz-Gilbert phenomenology.
Specifically, we show that spin supercurrent can exert the torque on a domain
wall and thereby drive it. We also show, as a reciprocal phenomenon, a
field-induced motion of a domain wall can generate spin supercurrent.",1610.00034v1
2018-11-06,Nonlinear Dynamics Semi-classical Model of Quantum Spin,"A nonlinear dynamics semi-classical model is used to show that standard
quantum spin analysis can be obtained. The model includes a classically driven
nonlinear differential equation with dissipation and a semi-classical
interpretation of the torque on a spin magnetic moment in the presence of a
realistic magnetic field, which will represent two equilibrium positions. The
highly complicated driven nonlinear dissipative semi-classical model is used to
introduce chaos, which is necessary to produce the correct statistical quantum
results. The resemblance between this semi-classical spin model and the
thoroughly studied classical driven-damped nonlinear pendulum are shown and
discussed.",1811.02645v1
2018-10-10,The geometro-hydrodynamical formalism of quantum spinning particle,"We present the development of the realistic geometro-hydrodynamical formalism
of quantum mechanics for the spinning particle, that involves the vortical
flows and is based on the idea, that the spinor wave represents a new type of
physical field, propagating in space-time and influencing the corpuscule
embedded in the wave. We assume that this new field created by the intrinsic
spin of the particle and can produce new intrinsic forces and torques affecting
the particle with spin. We derive and discuss physical effects of this field.",1810.04716v1
2018-10-29,Nonlinear Semi-Classical 3D Quantum Spin,"In an effort to provide an alternative method to represent a quantum spin, a
precise 3D nonlinear dynamics method is used. A two-sided torque function is
created to mimic the unique behavior of the quantum spin. A full 3D
representation of the magnetic field of a Stern-Gerlach device was used as in
the original experiment. Furthermore, the temporarily driven nonlinear damped
model exhibits chaos, but struggles to be consistent through azimuthal angles
in reproducing the quantum spin statistics.",1810.12424v1
2004-05-26,Identification of transverse spin currents in noncollinear magnetic structures,"We show that the transverse components of spin current in a ferromagnet is
linked to an off diagonal spin component of the transmission matrix at
interfaces;it has little to do with the mismatch of band structures between
dissimilar metals. When we take account of this component,not considered in
prior analyses, we find spin torque comes from a region of at lease 3 nm around
an interface.",0405610v1
2004-05-26,Different steady states for spin currents in noncollinear multilayers,"We find there are at least two different steady states for transport across
noncollinear magnetic multilayers. In the conventional one there is a
discontinuity in the spin current across the interfaces which has been
identified as the source of current induced magnetic reversal; in the one
advocated herein the spin torque arises from the spin accumulation transverse
to the magnetization of a magnetic layer. These two states have quite different
attributes which should be discerned by current experiments.",0405613v1
2023-11-30,Antiferromagnetic droplet soliton driven by spin current,"We demonstrate that a spin current flowing through a nano-contact into a
uniaxial antiferromagnet with first- and second-order anisotropy can excite a
self-localized dynamic magnetic soliton, known as a spin-wave droplet in
ferromagnets. The droplet nucleates at a certain threshold current with the
frequency of the N\'eel vector precession laying below the antiferromagnetic
resonance. The frequency exhibits nonlinear behavior with the increasing of
applied current. At the high value of applied torque, the soliton mode
transforms, and the oscillator emits spin waves propagating in the
antiferromagnetic layer.",2311.18583v1
2006-06-09,Conclusive quantum-state transfer with a single randomly coupled spin chain,"We studied the quantum state transfer in randomly coupled spin chains. By
using local memories storing the information and dividing the task into
transfer portion and decoding portion, conclusive transfer was ingeniously
achieved with just one single spin chain. In our scheme, the probability of
successful transfer can be made arbitrary close to unity. Especially, our
scheme is a good protocol to decode information from memories without adding
another spin chain. Compared with Time-reversed protocol, the average decoding
time is much less in our scheme.",0606088v1
2008-12-24,Robust and Reliable Transfer of a Quantum State Through a Spin Chain,"We present several protocols for reliable quantum state transfer through a
spin chain. We use a simple two-spin encoding to achieve a remarkably high
fidelity transfer for an arbitrary quantum state. The fidelity of the transfer
also decreases very slowly with increasing chain length. We find that we can
also increase the reliability by taking advantage of a local memory and/or
confirm transfer using a second spin-chain.",0812.4578v1
2017-07-11,Qubit(s) transfer in helical spin chains,"Qubit(s) transfer through a helical chain is studied. We consider the
transfer of a single state and Bell states across a multiferroic spin chain and
the possibility of an electric field control of the fidelity of the single
state and the Bell pairs. We analyze pure and imperfect multiferroic spin
chains. A scheme for an efficient transfer of spin states through a
multiferroic channel relies on kicking by appropriate electric field pulses at
regular interval. This electric field pulse sequence undermines the effect of
impurity on the fidelity and improves the state transfer through the helical
chain.",1707.03261v1
2021-08-23,Large spin-charge interconversion induced by interfacial spin-orbit coupling at a highly conducting all-metallic system,"Spin-charge interconversion in systems with spin-orbit coupling has provided
a new route for the generation and detection of spin currents in functional
devices for memory and logic such as spin-orbit torque switching in magnetic
memories or magnetic state reading in spin-based logic. Disentangling the bulk
(spin Hall effect) from the interfacial (inverse spin galvanic effect)
contribution has been a common issue to properly quantify the spin-charge
interconversion in these systems, being the case of Au paradigmatic. Here, we
obtain a large spin-charge interconversion at a highly conducting Au/Cu
interface which is experimentally shown to arise from the inverse spin galvanic
effect of the interface and not from the spin Hall effect of bulk Au. We use
two parameters independent of the microscopic details to properly quantify the
spin-charge interconversion and the spin losses due to the interfacial
spin-orbit coupling, providing an adequate benchmarking to compare with any
spin-charge interconversion system. The good performance of this metallic
interface, not based in Bi, opens the path to the use of much simpler
light/heavy metal systems.",2108.10409v1
2018-07-31,The Effect of Magnetic Variability on Stellar Angular Momentum Loss I: The Solar Wind Torque During Sunspot Cycles 23 & 24,"The rotational evolution of cool stars is governed by magnetised stellar
winds which slow the stellar rotation during their main sequence lifetimes.
Magnetic variability is commonly observed in Sun-like stars, and the changing
strength and topology of the global field is expected to affect the torque
exerted by the stellar wind. We present three different methods for computing
the angular momentum loss in the solar wind. Two are based on MHD simulations
from Finley & Matt (2018), with one using the open flux measured in the solar
wind, and the other using remotely-observed surface magnetograms. Both methods
agree in the variation of the solar torque seen through the solar cycle and
show a 30-40% decrease from cycle 23 to 24. The two methods calculate different
average values, $2.9\times10^{30}$erg (open flux) and $0.35\times10^{30}$erg
(surface field). This discrepancy results from the already well-known
difficulty with reconciling the magnetograms with observed open flux, which is
currently not understood, leading to an inability to discriminate between these
two calculated torques. The third method is based on the observed spin-rates of
Sun-like stars, which decrease with age, directly probing the average angular
momentum loss. This method gives $6.2\times10^{30}$erg for the solar torque,
larger than the other methods. This may be indicative of further variability in
the solar torque on timescales much longer than the magnetic cycle. We discuss
the implications for applying the formula to other Sun-like stars, where only
surface field measurements are available, and where the magnetic variations are
ill-constrained.",1808.00063v3
2004-11-28,Modelling the spin equilibrium of neutron stars in LMXBs without gravitational radiation,"In this paper we discuss the spin-equilibrium of accreting neutron stars in
LMXBs. We demonstrate that, when combined with a naive spin-up torque, the
observed data leads to inferred magnetic fields which are at variance with
those of galactic millisecond radiopulsars. This indicates the need for either
additional spin-down torques (eg. gravitational radiation) or an improved
accretion model. We show that a simple consistent accretion model can be
arrived at by accounting for radiation pressure in rapidly accreting systems
(above a few percent of the Eddington accretion rate). In our model the inner
disk region is thick and significantly sub-Keplerian, and the estimated
equilibrium periods are such that the LMXB neutron stars have properties that
accord well with the galactic millisecond radiopulsar sample. The implications
for future gravitational-wave observations are also discussed briefly.",0411747v2
2004-11-15,Current induced Spin Torque in a nanomagnet,"In a nanomagnet (whose total spin S< 1000), very small polarized currents can
lead to magnetic reversal. Treating on the same footing the transport and
magnetic properties of a nanomagnet connected to magnetic leads via tunneling
barriers, we derive a closed equation for the time evolution of the
magnetization. The interplay between Coulomb blockade phenomena and magnetism
gives some additional structure to the current induced spin torque. In addition
to the possibility of stabilizing uniform spin waves, we find that the system
is highly hysteretic: up to three different magnetic states can be
simultaneously stable in one region of the parameter (magnetic field and bias
voltage) space.",0411375v2
2007-12-03,Finite size effects on spin-torque driven ferromagnetic resonance in spin-valves with a Co/Ni synthetic free layer,"Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study magnetic
excitations in Co/Ni synthetic layers confined in nanojunctions. Field swept
ST-FMR measurements were conducted with a magnetic field applied perpendicular
to the layer surface. The resonance lines were measured under low amplitude
excitation in a linear response regime. The resulting resonance fields were
compared with those obtained using conventional rf field driven FMR on extended
films with the same Co/Ni layer structure. A lower resonance field is found in
confined structures. The effect of both dipolar fields acting on the Co/Ni
layer emanating from other magnetic layers in the device and finite size
effects on the spin wave spectrum are discussed.",0712.0404v2
2008-03-05,Micromagnetic study of a spin-torque oscillator based on a magnetic nano-contact magnetized at an arbitrary angle,"The nature of spin wave modes excited by spin-polarized direct current in a
spin-torque auto-oscillator based on a magnetic nanocontact was studied by a
micromagnetic simulation in the case when the external bias magnetic field was
rotated from the in-plane to perpendicular-to-plane orientation. In qualitative
agreement with the weakly-nonlinear analytical theory it was found, that at a
certain critical angle, an abrupt switching from the self-localized nonlinear
""bullet"" mode to a propagating quasi-linear Slonczewski mode takes place, and
is accompanied by an upward jump in generated microwave frequency. It was,
also, found that the analytical theory overestimates the magnitude of a
critical magnetization angle, corresponding to the mode switching, and that the
magnitude of the frequency jump caused by the mode switching is inversely
proportional to the nanocontact radius.",0803.0704v1
2008-04-14,Micromagnetics of single and double point contact spin torque oscillators,"In this paper we numerically conduct micromagnetic modelling to optimize
computational boundaries of magnetic thin-film elements applicable to single
and double point contact spin torque nano-oscillators. Different boundary
conditions have been introduced to compensate spin waves reflections at
boundaries that are based on extended layers, absorbing boundaries, and focal
point methods and are compared with a technique based on scattering theory. A
surface roughness boundary model is presented which is modelled according to
the Rayleigh criterion to minimize specular reflections at computational
boundaries. It is shown that the surface roughness model disperses the
reflected spin waves and improves the signal to background noise ratio. The
model is tested in comparison to conventional approaches such as extended layer
systems, variable damping constant and focal point methods for double point
contacts. The surface roughness model gives solutions that are stable in time,
in qualitative agreement with experiments and capable to reproduce phenomena
such as phase locking in double point contacts.",0804.2119v1
2011-06-30,Spin equilibrium with or without gravitational wave emission: the case of XTE J1814-338 and SAX J1808.4-3658,"In this letter we present a new analysis of the torques acting on the
accreting millisecond X-ray pulsars SAX J1808.4-365 and XTE J1814-338, and show
how our results can be used to constrain theoretical models of the spin
evolution. In particular we find upper limits on any spin-up/down phase of XTE
J1814-338 of $|\dot{\nu}|\lesssim\,1.5\times\,10^{-14}$ Hz/s at 95% confidence
level. We examine the possibility that a gravitational wave torque may be
acting in these systems and suggest that a more likely scenario is that both
systems are close to spin equilibrium, as set by the disc/magnetosphere
interaction.",1106.6264v1
2011-10-07,Nonlinear Dynamics in a Magnetic Josephson Junction,"We theoretically consider a Josephson junction formed by a ferromagnetic
spacer with a strong spin-orbit interaction or a magnetic spin valve, i.e., a
bilayer with one static and one free layer. Electron spin transport facilitates
a nonlinear dynamical coupling between the magnetic moment and charge current,
which consists of normal and superfluid components. By phenomenologically
adding reactive and dissipative interactions (guided by structural and Onsager
symmetries), we construct magnetic torques and charge pumping, whose
microscopic origins are also discussed. A stability analysis of our coupled
nonlinear systems generates a rich phase diagram with fixed points, limit
cycles, and quasiperiodic states. Our findings reduce to the known phase
diagrams for current-biased nonmagnetic Josephson junctions, on the one hand,
and spin-torque driven magnetic films, on the other, in the absence of coupling
between the magnetic and superconducting order parameters.",1110.1680v1
2011-10-17,Dynamics of nano-magnetic oscillators,"We explore how non-equilibrium noise affects spin-torque switching elements
and oscillators. To do so we first discuss the deterministic dynamics of
magnetic tunnel junctions, introducing a convenient set of slow and fast
degrees of freedom. We then derive effective Langevin equation for the slowly
varying energy of precessional orbit and introduce the corresponding energy
noise and energy diffusion coefficient. This allows for the formulation of a
Fokker-Planck equation for the energy density distribution. We use it to
analyse switching time distribution as well as the shape of the optimal
spin-current pulse, which minimizes Joule losses of a switch. Finally we derive
a generic expression for the linewidth of a spin-torque oscillator and discuss
its dependence on temperature, spin-current amplitude and other parameters.",1110.3750v1
2012-03-05,Frequency generation by a magnetic vortex-antivortex dipole in spin-polarized current,"A vortex-antivortex (VA) dipole may be generated due to a spin-polarized
current flowing through a nano-aperture in a magnetic element. We study the
vortex dipole dynamics using the Landau-Lifshitz equation in the presence of an
in-plane applied magnetic field and a Slonczewski spin-torque term with
in-plane polarization. We establish that the vortex dipole is set in steady
state rotational motion. The frequency of rotation is due to two independent
forces: the interaction between the two vortices and the external magnetic
field. The nonzero skyrmion number of the dipole is responsible for both forces
giving rise to rotational dynamics. The spin-torque acts to stabilize the
vortex dipole motion at a definite vortex-antivortex separation distance. We
give analytical and numerical results for the angular frequency of rotation and
VA dipole features as functions of the parameters.",1203.0880v1
2013-01-17,Entanglement between nitrogen vacancy spins in diamond controlled by a nanomechanical resonator,"We suggest a new type of nano-electromechanical resonator, the functionality
of which is based on a magnetic field induced deflection of an appropriate
cantilever that oscillates between nitrogen vacancy (NV) spins in daimond.
Specifically, we consider a Si(100) cantilever coated with a thin magnetic Ni
film. Magnetoelastic stress and magnetic-field induced torque are utilized to
induce a controlled cantilever deflection. It is shown that, depending on the
value of the system parameters, the induced asymmetry of the cantilever
deflection substantially modifies the characteristics of the system. In
particular, the coupling strength between the NV spins and the degree of
entanglement can be controlled through magnetoelastic stress and magnetic-field
induced torque effects. Our theoretical proposal can be implemented
experimentally with the potential of increasing several times the coupling
strength between the NV spins as compared to the maximal coupling strength
reported before in P. Rabl, et al. Phys. Rev. B 79, 041302(R) (2009).",1301.4256v1
2013-10-11,Analytical theory of modulated magnetic solitons,"Droplet solitons are coherently precessing solitary waves that have been
recently realized in thin ferromagnets with perpendicular anisotropy.In the
strongly nonlinear regime, droplets can be well approximated by a slowly
precessing, circular domain wall with a hyperbolic tangent form. Utilizing this
representation, this work develops a general droplet modulation theory and
applies it to study the long range effects of the magnetostatic field and a
nanocontact spin torque oscillator (NC-STO) where spin polarized currents act
as a gain source to counteract magnetic damping. An analysis of the dynamical
equations for the droplet's center, frequency and phase demonstrates a negative
processional frequency shift due to long range dipolar interactions, dependent
on film thickness. Further analysis also demonstrates the onset of a
saddle-node bifurcation at the minimum sustaining current for the NC-STO. The
basin of attraction associated with the stable node demonstrates that spin
torque enacts a restoring force to excursions of the droplet from the
nanocontact center, observed previously in numerical simulations. Large
excursions lead to the droplet's eventual decay into spin waves.",1310.3118v1
2013-12-03,Gravitational self-torque and spin precession in compact binaries,"We calculate the effect of self-interaction on the ""geodetic"" spin precession
of a compact body in a strong-field orbit around a black hole. Specifically, we
consider the spin precession angle $\psi$ per radian of orbital revolution for
a particle carrying mass $\mu$ and spin $s \ll (G/c) \mu^2$ in a circular orbit
around a Schwarzschild black hole of mass $M \gg \mu$. We compute $\psi$
through $O(\mu/M)$ in perturbation theory, i.e, including the correction
$\delta\psi$ (obtained numerically) due to the torque exerted by the
conservative piece of the gravitational self-field. Comparison with a
post-Newtonian (PN) expression for $\delta\psi$, derived here through 3PN
order, shows good agreement but also reveals strong-field features which are
not captured by the latter approximation. Our results can inform
semi-analytical models of the strong-field dynamics in astrophysical binaries,
important for ongoing and future gravitational-wave searches.",1312.0775v2
2014-10-30,Intrinsic synchronization of an array of spin-torque oscillators driven by the spin-Hall effect,"This paper micromagnetically studies the magnetization dynamics driven by the
spin-Hall effect in a Platinum/Permalloy bi-layer. For a certain field and
current range, the excitation of a uniform mode, characterized by a power with
a spatial distribution in the whole ferromagnetic cross section, is observed.
We suggest to use the ferromagnet of the bi-layer as basis for the realization
of an array of spin-torque oscillators (STOs): the Permalloy ferromagnet will
act as shared free layer, whereas the spacers and the polarizers are built on
top of it. Following this strategy, the frequency of the uniform mode will be
the same for the whole device, creating an intrinsic synchronization. The
synchronization of an array of parallely connected STOs will allow to increase
the output power, as necessary for technological applications.",1410.8342v1
2015-03-29,Low-non-linearity spin-torque oscillations driven by ferromagnetic nanocontacts,"Spin-torque oscillators are strong candidates as nano-scale microwave
generators and detectors. However, because of large amplitude-phase coupling
(non-linearity), phase noise is enhanced over other linear auto-oscillators.
One way to reduce nonlinearity is to use ferromagnetic layers as a resonator
and excite them at localized spots, making a resonator-excitor pair. We
investigated the excitation of oscillations in dipole-coupled ferromagnetic
layers, driven by localized current at ferromagnetic nano-contacts.
Oscillations possessed properties of optical-mode spin-waves and at low field
($\approx$200 Oe) had high frequency (15 GHz), a moderate precession amplitude
(2--3$^\circ$), and a narrow spectral linewidth ($<$3 MHz) due to localized
excitation at nano-contacts. Micromagnetic simulation showed emission of
resonator's characteristic optical-mode spin-waves from disturbances generated
by domain-wall oscillations at nano-contacts.",1503.08408v2
2015-09-30,Terahertz Antiferromagnetic Spin Hall Nano-Oscillator,"We consider the current-induced dynamics of insulating antiferromagnets in a
spin Hall geometry. Sufficiently large in-plane currents perpendicular to the
N\'{e}el order trigger spontaneous oscillations at frequencies between the
acoustic and the optical eigenmodes. The direction of the driving current
determines the chirality of the excitation. When the current exceeds a
threshold, the combined effect of spin pumping and current-induced torques
introduces a dynamic feedback that sustains steady-state oscillations with
amplitudes controllable via the applied current. The ac voltage output is
calculated numerically as a function of the dc current input for different
feedback strengths. Our findings open a route towards terahertz
antiferromagnetic spin-torque oscillators.",1509.09229v3
2015-12-10,Spin-Torque and Spin-Hall Nano-Oscillators,"This paper reviews the state of the art in spin-torque and spin Hall effect
driven nano-oscillators. After a brief introduction to the underlying physics,
the authors discuss different implementations of these oscillators, their
functional properties in terms of frequency range, output power, phase noise,
and modulation rates, and their inherent propensity for mutual synchronization.
Finally, the potential for these oscillators in a wide range of applications,
from microwave signal sources and detectors to neuromorphic computation
elements, is discussed together with the specific electronic circuitry that has
so far been designed to harness this potential.",1512.03162v1
2016-01-16,Spin-orbit torque in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO epitaxial magnetic heterostructures,"We study the spin-orbit torque (SOT) effective fields in Cr/CoFeAl/MgO and
Ru/CoFeAl/MgO magnetic heterostructures using the adiabatic harmonic Hall
measurement. High-quality perpendicular-magnetic-anisotropy CoFeAl layers were
grown on Cr and Ru layers. The magnitudes of the SOT effective fields were
found to significantly depend on the underlayer material (Cr or Ru) as well as
their thicknesses. The damping-like longitudinal effective field ({\Delta}H_L)
increases with increasing underlayer thickness for all heterostructures. In
contrast, the field-like transverse effective field ({\Delta}H_T) increases
with increasing Ru thickness while it is almost constant or slightly decreases
with increasing Cr thickness. The sign of {\Delta}H_L observed in the
Cr-underlayer devices is opposite from that in the Ru-underlayer devices while
{\Delta}H_T shows the same sign with a small magnitude. The opposite directions
of {\Delta}HL indicate that the signs of spin Hall angle in Cr and Ru are
opposite, which are in good agreement with theoretical predictions. These
results show sizable contribution from SOT even for elements with small spin
orbit coupling such as 3d Cr and 4d Ru.",1601.04164v1
2016-01-22,Determination of the Spin-Hall-Effect-Induced and the Wedged-Structure-Induced Spin Torque Efficiencies in Heterostructures with Perpendicular Magnetic Anisotropy,"We report that by measuring current-induced hysteresis loop shift versus
in-plane bias magnetic field, the spin Hall effect (SHE) contribution of the
current-induced effective field per current density, $\chi_{SHE}$, can be
estimated for Pt and Ta-based magnetic heterostructures with perpendicular
magnetic anisotropy (PMA). We apply this technique to a Pt-based sample with
its ferromagnetic (FM) layer being wedged-deposited and discover an extra
effective field contribution, $\chi_{Wedged}$, due to the asymmetric nature of
the deposited FM layer. We confirm the correlation between $\chi_{Wedged}$ and
the asymmetric depinning process in FM layer during magnetization switching by
magneto-optical Kerr (MOKE) microscopy. These results indicate the possibility
of engineering deterministic spin-orbit torque (SOT) switching by controlling
the symmetry of domain expansion through the materials growth process.",1601.05854v1
2016-02-22,Staggering antiferromagnetic domain wall velocity in a staggered spin-orbit field,"We demonstrate the possibility to drive an antiferromagnet domain-wall at
high velocities by field-like N\'{e}el spin-orbit torques. Such torques arise
from current-induced local fields that alternate their orientation on each
sub-lattice of the antiferromagnet and whose orientation depend primarily on
the current direction, giving them their field-like character. The domain-wall
velocities that can be achieved by this mechanism are two orders of magnitude
greater than the ones in ferromagnets. This arises from the efficiency of the
staggered spin-orbit fields to couple to the order parameter and from the
exchange-enhanced phenomena in antiferromagnetic texture dynamics, which leads
to a low domain-wall effective mass and the absence of a Walker break-down
limit. In addition, because of its nature, the staggered spin-orbit field can
lift the degeneracy between two 180$^\circ$ rotated states in a collinear
antiferromagnet and provides a force that can move such walls and control the
switching of the states.",1602.06766v2
2016-09-27,Anomalous Hall effect and spin orbit torques in MnGa/IrMn films: Modification from strong spin Hall effect of antiferromagnet,"We report systematic measurements of anomalous Hall effect(AHE) and spin
orbit torques(SOT) in MnGa/IrMn films,, in which a single MnGa epitaxial layer
reveals obvious orbital two-channel Kondo (2CK) effect. As increasing the
thickness of the antiferromagnet IrMn, the strong spin Hall effect(SHE)has
gradually suppressed the orbital 2CK effect and modified the AHE of MnGa.A
scaling involving multiple competing scattering mechanisms has been used to
distinguish different contributions to the modified AHE. Finally, the sizeable
SOT in the MnGa/IrMn films induced by the strong SHE of IrMn have been
investigated.The IrMn layer also supplies an in-plane exchange bias field and
enables nearly field-free magnetization reversal.",1609.08245v1
2017-08-04,Tunable Spin-Orbit Torques in Cu-Ta Binary Alloy Heterostructures,"The spin Hall effect (SHE) is found to be strong in heavy transition metals
(HM), such as Ta and W, in their amorphous and/or high resistivity form. In
this work, we show that by employing a Cu-Ta binary alloy as buffer layer in an
amorphous Cu$_{100-x}$Ta$_{x}$-based magnetic heterostructure with
perpendicular magnetic anisotropy (PMA), the SHE-induced damping-like
spin-orbit torque (DL-SOT) efficiency $|\xi_{DL}|$ can be linearly tuned by
adjusting the buffer layer resistivity. Current-induced SOT switching can also
be achieved in these Cu$_{100-x}$Ta$_{x}$-based magnetic heterostructures, and
we find the switching behavior better explained by a SOT-assisted domain wall
propagation picture. Through systematic studies on Cu$_{100-x}$Ta$_{x}$-based
samples with various compositions, we determine the lower bound of spin Hall
conductivity
$|\sigma_{SH}|\approx2.02\times10^{4}[\hbar/2e]\Omega^{-1}\cdot\operatorname{m}^{-1}$
in the Ta-rich regime. Based on the idea of resistivity tuning, we further
demonstrate that $|\xi_{DL}|$ can be enhanced from 0.087 for pure Ta to 0.152
by employing a resistive TaN buffer layer.",1708.01356v1
2017-09-07,Room temperature magnetization switching in topological insulator-ferromagnet heterostructures by spin-orbit torques,"Topological insulators (TIs) with spin momentum locked topological surface
states (TSS) are expected to exhibit a giant spin-orbit torque (SOT) in the
TI/ferromagnet systems. To date, the TI SOT driven magnetization switching is
solely reported in a Cr doped TI at 1.9 K. Here, we directly show giant SOT
driven magnetization switching in a Bi2Se3/NiFe heterostructure at room
temperature captured using a magneto-optic Kerr effect microscope. We identify
a large charge to spin conversion efficiency of ~1-1.75 in the thin TI films,
where the TSS is dominant. In addition, we find the current density required
for the magnetization switching is extremely low, ~6x10^5 A cm-2, which is one
to two orders of magnitude smaller than that with heavy metals. Our
demonstration of room temperature magnetization switching of a conventional 3d
ferromagnet using Bi2Se3 may lead to potential innovations in TI based
spintronic applications.",1709.02159v1
2017-10-31,Macro-spin Modeling and Experimental Study of Spin-orbit Torque Biased Magnetic Sensors,"We reported a systematic study of spin-orbit torque biased magnetic sensors
based on NiFe/Pt bilayers through both macro-spin modeling and experiments. The
simulation results show that it is possible to achieve a linear sensor with a
dynamic range of 0.1 - 10 Oe, power consumption of 1uW - 1 mW, and sensitivity
of 0.1-0.5 Ohm/Oe. These characteristics can be controlled by varying the
sensor dimension and current density in the Pt layer. The latter is in the
range of 1 x 10^5 - 10^7 A/cm^2. Experimental results of fabricated sensors
with selected sizes agree well with the simulation results. For a Wheatstone
bridge sensor comprising of four sensing elements, a sensitivity up to 0.548
Ohm/Oe, linearity error below 6%, and detectivity of about 2.8 nT/Sqrt(Hz) were
obtained. The simple structure and ultrathin thickness greatly facilitate the
integration of these sensors for on-chip applications. As a proof-of-concept
experiment, we demonstrate its application in detection of current flowing in
an on-chip Cu wire.",1712.02384v1
2018-05-31,The current-induced spin-orbit torque and field-free switching from Mo-based magnetic heterostructures,"Magnetic heterostructure Mo/CoFeB/MgO has strong perpendicular magnetic
anisotropy and thermal stability. Through current-induced hysteresis loop shift
measurements, we show that the dampinglike spin-orbit torque (SOT) efficiency
of Mo/CoFeB/MgO heterostructure is $\xi_{DL}\approx -0.003\pm 0.001$ and fairly
independent of the annealing temperature from 300$^\circ$C to 400$^\circ$C.
Though $|\xi_{DL}|$ is small while compare to those from Ta or W-based
heterostructures, reversible current-induced SOT switching of a
thermally-stable Mo/CoFeB/MgO heterostruture can still be achieved.
Furthermore, we observe field-free current-induced switching from a
Mo/CoFeB/MgO structure with the Mo layer being wedge-deposited. Our results
indicate that even for a weak spin-orbit interaction 4d transition metal such
as Mo, it is still possible to generate sufficient spin current for
conventional SOT switching and to realize field-free current-induced switching
by structural engineering.",1805.12322v3
2018-11-29,NGC 300 ULX1: A test case for accretion torque theory,"NGC 300 ULX1 is a newly identified ultra-luminous X-ray pulsar. The system is
associated with the supernova impostor SN 2010da that was later classified as a
possible supergiant Be X-ray binary. In this work we report on the spin period
evolution of the neutron star based on all the currently available X-ray
observations of the system. We argue that the X-ray luminosity of the system
has remained almost constant since 2010, at a level above ten times the
Eddington limit. Moreover, we find evidence that the spin period of the neutron
star evolved from ~126 s down to ~18 s within a period of about 4 years. We
explain this unprecedented spin evolution in terms of the standard accretion
torque theory. An intriguing consequence for NGC 300 ULX1 is that a neutron
star spin reversal should have occurred a few years after the SN 2010da event.",1811.11907v1
2017-05-30,"Spin-transport, spin-torque and memory in antiferromagnetic devices: Part of a collection of reviews on antiferromagnetic spintronics","Ferromagnets are key materials for sensing and memory applications. In
contrast, antiferromagnets that represent the more common form of magnetically
ordered materials, have so far found less practical application beyond their
use for establishing reference magnetic orientations via exchange bias. This
might change in the future due to the recent progress in materials research and
discoveries of antiferromagnetic spintronic phenomena suitable for device
applications. Experimental demonstrations of the electrical switching and
electrical detection of the N\'eel order open a route towards memory devices
based on antiferromagnets. Apart from the radiation and magnetic-field
hardness, memory cells fabricated in antiferromagnets are inherently multilevel
which could be used for neuromorphic computing. Switching speeds attainable in
antiferromagnets far exceed those of the ferromagnetic and semiconductor memory
technologies. Here we review the recent progress in electronic spin-transport
and spin-torque phenomena in antiferromagnets that are dominantly of the
relativistic quantum mechanics origin. We discuss their utility in pure
antiferromagnetic or hybrid ferromagnetic/antiferromagnetic memory devices",1705.10675v1
2018-02-05,Intrinsic spin-orbit torque arising from Berry curvature in metallic-magnet/Cu-oxide interface,"We report the observation of the intrinsic damping-like spin-orbit torque
(SOT) arising from the Berry curvature in metallic-magnet/CuO$_x$
heterostructures. We show that a robust damping-like SOT, an order of magnitude
larger than a field-like SOT, is generated in the heterostructure despite the
absence of the bulk spin-orbit effect in the CuO$_x$ layer. Furthermore, by
tuning the interface oxidation level, we demonstrate that the field-like SOT
changes drastically and even switches its sign, which originates from oxygen
modulated spin-dependent disorder. These results provide an important
information for fundamental understanding of the physics of the SOTs.",1802.01285v2
2018-02-15,Tunneling magnetoresistance enhancement by symmetrization in spin-orbit torque magnetic tunnel junction,"Heavy metals with strong spin-orbit coupling (SOC) have been employed to
generate spin current to control the magnetization dynamics by spin-orbit
torque (SOT). Magnetic tunnel junction based on SOT (SOT-MTJ) is a promising
application with efficient writing operation. Unfortunately, SOT-MTJ faces the
low tunneling magnetoresistance (TMR) problem. In this work, we present an ab
initio calculation on the TMR in SOT-MTJ. It is demonstrated that TMR would be
enhanced by SOT-MTJ symmetry structure. The symmetrization induces interfacial
resonant states (IRSs). When IRSs match identical resonances at the opposite
barrier interface, resonant tunneling occurs in SOT-MTJ, which significantly
contributes to the conductance in parallel configuration and improves TMR. We
demonstrate the occurrence of resonant tunneling by transmission spectra,
density of scattering states and differential density of states. We also point
out that the thickness of heavy metal has limited influence on TMR. This work
would benefit the TMR optimization in SOT-MTJ, as well as the SOT spintronics
device.",1802.05787v2
2018-12-18,Twists in Ferromagnetic Monolayers With Trigonal Prismatic Symmetry,"Two-dimensional materials such as graphene or hexagonal boron nitride are
indispensable in industry. The recently discovered 2D ferromagnetic materials
also promise to be vital for applications. In this work, we develop a
phenomenological description of non-centrosymmetric 2D ferromagnets with
trigonal prismatic crystal structure. We chose to study this special symmetry
group since these materials do break inversion symmetry and therefore, in
principle, allow for chiral spin structures such as magnetic helices and
skyrmions. However, unlike all non-centrosymmetric magnets known so far, we
show that the symmetry of magnetic trigonal prismatic monolayers neither allow
for an internal relativistic Dzyaloshinskii-Moriya interaction (DMI) nor a
reactive spin-orbit torque. We demonstrate that the DMI only becomes important
at the boundaries, where it modifies the boundary conditions of the
magnetization and leads to a helical equilibrium state with a helical
wavevector that is inherently linked to the internal spin orientation.
Furthermore, we find that the helical wavevector can be electrically
manipulated via dissipative spin-torque mechanisms. Our results reveal that 2D
magnets offer a large potential for unexplored magnetic effects.",1812.07361v1
2019-06-05,The early life of millisecond magnetars,"Some neutron stars may be born spinning fast and with strong magnetic
fields---the so-called \emph{millisecond magnetars}. It is important to
understand how a star's magnetic axis moves with respect to the spin axis in
the star's early life, as this effects both electromagnetic and gravitational
wave emission. Previous studies have highlighted the importance of viscous
dissipation within the star in this process. We advance this program by
additionally considering the effect of the electromagnetic torque. We find an
interesting interplay between the viscous dissipation, which makes the magnetic
axis orthogonalise with respect to the spin, verses magnetic torques that tend
to make the magnetic axis align with the spin axis. We present some results,
and highlight areas where our model needs to be made more realistic.",1906.02610v1
2017-02-03,Significant reduction of critical currents in MRAM designs using dual free layer with perpendicular and in-plane anisotropy,"One essential feature in MRAM cells is the spin torque efficiency, which
describes the ratio of the critical switching current to the energy barrier.
Within this paper it is reported that the spin torque efficiency can be
improved by a factor of 3.2 by the use a of dual free layer device, which
consists of one layer with perpendicular crystalline anisotropy and a second
layer with in-plane crystalline anisotropy. Detailed simulations solving the
spin transport equations simultaneously with the micromagnetics equation were
performed in order to understand the origin of the switching current reduction
by a factor of 4 for the dual layer structure compared to a single layer
structure. The main reason could be attributed to an increased spin
accumulation within the free layer due to the dynamical tilting of the
magnetization within the in-plane region of the dual free layer.",1702.00996v2
2017-02-26,Enhanced spin-orbit torques in MnAl/Ta films with improving chemical ordering,"We report the enhancement of spin-orbit torques in MnAl/Ta films with
improving chemical ordering through annealing. The switching current density is
increased due to enhanced saturation magnetization MS and effective anisotropy
field HK after annealing. Both damplinglike effective field HD and fieldlike
effective field HF have been increased in the temperature range of 50 to 300 K.
HD varies inversely with MS in both of the films, while the HF becomes liner
dependent on 1/MS in the annealed film. We infer that the improved chemical
ordering has enhanced the interfacial spin transparency and the transmitting of
the spin current in MnAl layer.",1702.07990v1
2017-06-06,Quantitative characterization of spin-orbit torques in Pt/Co/Pt /Co/Ta/BTO heterostructure on the magnetization azimuthal angle dependence,"Substantial understanding of spin-orbit interactions in heavy-metal
(HM)/ferromagnet (FM) heterostructures is crucial in developing spin-orbit
torque (SOT) spintronics devices utilizing spin Hall and Rashba effects. Though
the study of SOT effective fields dependence on the out-of-plane magnetization
angle has been relatively extensive, the understanding of in-plane
magnetization angle dependence remains unknown. Here, we analytically propose a
method to compute the SOT effective fields as a function of the in-plane
magnetization angle using harmonic Hall technique in perpendicular magnetic
anisotropy (PMA) structures. Two different samples with PMA,
Pt/Co/Pt/Co/Ta/BaTiO3 (BTO) test sample and Pt/Co/Pt/Co/Ta reference sample are
studied using the derived formula. Our measurements reveal that only the
dampinglike field of the test sample with BTO capping layer exhibits an
in-plane magnetization angle dependence while no angular dependence is found in
the reference sample. The presence of the BTO layer in the test sample, which
gives rise to a Rashba effect at the interface, is ascribed as the source of
the angular dependence of the the dampinglike field.",1706.01622v1
2018-04-16,First Principles Study of Angular Dependence of Spin-Orbit Torque in Pt/Co and Pd/Co Bilayers,"Spin-orbit torque (SOT) induced by spin Hall and interfacial effects in heavy
metal(HM)/ferromagnetic(FM) bilayers has recently been employed to switch the
magnetization direction using in-plane current injection. In this paper, using
the Keldysh Green's function approach and first principles electronic structure
calculations we determine the Field-Like (FL) and Damping-Like (DL) components
of the SOT for the HM/Co (HM = Pt, Pd) bilayers. Our approach yields the
angular dependence of both the FL- and DL-SOT on the magnetization direction
without assuming a priori their angular form. Decomposition of the SOT into the
Fermi sea and Fermi surface contributions reveals that the SOT is dominated by
the latter. Due to the large lattice mismatch between the Co and the HM we have
also determined the effect of tensile biaxial strain on both the FL- and DL-SOT
components. The calculated dependence of FL- and DL-SOT on the HM thickness is
overall in good agreement with experiment. The dependence of the SOT with the
position of the Fermi level suggests that the DL-SOT dominated by the Spin Hall
effect of the bulk HM.",1804.05947v2
2019-05-29,Kramers Weyl Semimetals as Quantum Solenoids and Their Applications in Spin-Orbit Torque Devices,"Kramers Weyl semimetals are Weyl semimetals that have Weyl points pinned at
the time reversal invariant momenta. Recently it has been discovered that all
chiral crystals host Weyl points at time reversal invariant momenta, so metals
with chiral lattice symmetry all belong to the category of Kramers Weyl
semimetals. In this work, we show that due to the chiral lattice symmetry,
Kramers Weyl semimetals have the unique longitudinal magnetoelectric effect in
which the charge current induced spin and orbital magnetization is parallel to
the direction of the current. This feature allows Kramers Weyl semimetals to
act as nanoscale quantum solenoids with both orbital and spin magnetization. As
the moving electrons of Kramers Weyl semimetal can generate longitudinal
magnetization, Kramers Weyl semimetals can be used for new designs of
spin-orbit torque devices with all electric control of magnetization switching
for magnets with perpendicular magnetic anisotropy.",1905.12575v4
2020-03-04,Highly Tunable Spin-Orbit Torque and Anisotropic Magnetoresistance in a Topological Insulator Thin Film Attached to Ferromagnetic Layer,"We investigate spin-charge conversion phenomena in hybrid structures of
topological insulator (TI) thin films and magnetic insulators. We find an
anisotropic inverse spin-galvanic effect (ISGE) that yields a highly tunable
spin-orbit torque (SOT). Concentrating on the quasiballistic limit, we also
predict a giant anisotropic magnetoresistance (AMR) at low dopings. These
effects, which have no counterparts in thick TIs, depend on the simultaneous
presence of the hybridization between the surface states and the in-plane
magnetization. Both the ISGE and AMR exhibit a strong dependence on the
magnetization and the Fermi level position and can be utilized for spintronics
and SOT-based applications at the nanoscale.",2003.02252v2
2020-03-24,A spiking neuron constructed by the skyrmion-based spin torque nano-oscillator,"Magnetic skyrmions are particle-like topological spin configurations, which
can carry binary information and thus are promising building blocks for future
spintronic devices. In this work, we investigate the relationship between the
skyrmion dynamics and the characteristics of injected current in a
skyrmion-based spin torque nano-oscillator, where the excitation source is
introduced from a point nano-contact at the center of the nanodisk. It is found
that the skyrmion will move away from the center of the nanodisk if it is
driven by a spin-polarized current; however, it will return to the initial
position in the absence of stimulus. Therefore, we propose a skyrmion-based
artificial spiking neuron, which can effectively implement the
leaky-integrate-fire operation. We study the feasibility of the skyrmion-based
spiking neuron by using micromagnetic simulations. Our results may provide
useful guidelines for building future magnetic neural networks with ultra-high
density and ultra-low energy consumption.",2003.10651v1
2021-04-19,Chaotic Antiferromagnetic Nano-Oscillator driven by Spin-Torque,"We theoretically describe the behavior of a terahertz nano-oscillator based
on an anisotropic antiferromagnetic dynamical element driven by spin torque. We
consider the situation when the polarization of the spin-current is
perpendicular to the external magnetic field applied along the anisotropy
easy-axis. We determine the domain of the parametric space (field, current)
where the oscillator demonstrates chaotic dynamics. Characteristics of the
chaotic regimes are analyzed using conventional techniques such as spectra of
the Lyapunov exponents. We show that the threshold current of the chaos
appearance is particularly low in the vicinity of the spin-flop transition. In
this regime, we consider the mechanism of the chaos appearance in detail when
the field is fixed and the current density increases. We show that the
appearance of chaos is preceded by a regime of quasiperiodic dynamics on the
surface of a two-frequency torus arising in phase space as a result of the
Neimark-Sacker bifurcation.",2104.09195v1
2019-01-17,"Influences of interfacial oxidization on surface magnetic energy, magnetic damping and spin-orbit-torques in Pt / ferromagnet / capping structures","We investigate the effect of capping layer (CAP) on the interfacial magnetic
anisotropy energy density (K_S), magnetic damping ({\alpha}), and spin-orbit
torques (SOTs) in heavy-metal (Pt) / ferromagnet (Co or Py) / CAP (MgO/Ta,
HfOx, or TaN). At room temperature (RT) the CAP materials influence the
effective magnitude of K_S, which is associated with a formation of interfacial
magnetic oxides. The dynamical dissipation parameters of Co are considerably
influenced by the CAP (especially MgO) while those of Py are not. This is
possibly due to an extra magnetic damping via spin-pumping process across the
Co/CoO interface and incoherent magnon generation (spin fluctuation) in the
interfacial CoO. It is also observed that both anti-damping and field-like SOT
efficiencies vary marginally with the CAP in the thickness ranges we examined.
Our results reveal the crucial role of interfacial oxides on the perpendicular
magnetic anisotropy, magnetic damping, and SOTs.",1901.05777v1
2019-10-31,Coherent spin pumping in a strongly coupled magnon-magnon hybrid system,"We experimentally identify coherent spin pumping in the magnon-magnon hybrid
modes of permalloy/yttrium iron garnet (Py/YIG) bilayers. Using broadband
ferromagnetic resonance, an ""avoided crossing"" is observed between the uniform
mode of Py and the spin wave mode of YIG due to the fieldlike interfacial
exchange coupling. We also identify additional linewidth suppression and
enhancement for the in-phase and out-of-phase hybrid modes, respectively,
\textcolor{black}{which can be interpreted as concerted dampinglike torque from
spin pumping}. Our analysis predicts inverse proportionality of both fieldlike
and dampinglike torques to the square root of the Py thickness, which
quantitatively agrees with experiments.",1910.14470v2
2020-05-27,Femtosecond Photocurrents at the Pt/FeRh Interface,"Femtosecond laser excitation of FeRh/Pt bilayers launches an ultrafast pulse
of electric photocurrent in the Pt-layer and thus results in emission of
electromagnetic radiation in the THz spectral range. Analysis of the THz
emission as a function of polarization of the femtosecond laser pulse, external
magnetic field, sample temperature and sample orientation shows that
photocurrent can emerge due to vertical spin pumping and photo-induced inverse
spin-orbit torque at the FeRh/Pt interface. The vertical spin pumping from FeRh
to Pt does not depend on the polarization of light and originates from
ultrafast laser-induced demagnetization of the ferromagnetic phase of FeRh. The
photo-induced inverse spin-orbit torque at the FeRh/Pt interface can be
described in terms of a helicity-dependent effect of circularly polarized light
on the magnetization of the ferromagnetic FeRh and subsequent generation of a
photocurrent.",2005.13379v1
2020-07-26,Dynamical Tidal Locking Theory: A new source of the Spin of Dark Matter Halos,"We revisit the question of what mechanism is responsible for the spins of
halos of dark matter. The answer to this question is of high importance for
modeling galaxy intrinsic alignment, which can potentially contaminate current
and future lensing data. In particular, we show that when the dark matter halos
pass nearly by each other in dense environments-- namely halo assemblies-- they
swing and spin each other via exerting mutual tidal torques. We show that this
has a significant contribution to the spin of dark matter halos comparable to
that of calculated by the so-called tidal torque theory (TTT). We use the
results of state-of-the-art simulation of Illutris to check the prediction of
this theory against the simulation data.",2007.13148v1
2021-09-30,Observation of the orbital Hall effect in a light metal Ti,"The orbital angular momentum is a core ingredient of orbital magnetism, spin
Hall effect, giant Rashba spin splitting, orbital Edelstein effect, and
spin-orbit torque. However, its experimental detection is tricky. In
particular, direct detection of the orbital Hall effect remains elusive despite
its importance for electrical control of magnetic nanodevices. Here we report
the direct observation of the orbital Hall effect in a light metal Ti. The Kerr
rotation by the accumulated orbital magnetic moment is measured at Ti surfaces,
whose result agrees with theoretical calculations semiquantitatively and is
supported by the orbital torque measurement in Ti-based magnetic
heterostructures. The results confirm the electron orbital angular momentum as
an essential dynamic degree of freedom, which may provide a novel mechanism for
the electric control of magnetism. The results may also deepen the
understanding of spin, valley, phonon, and magnon dynamics coupled with orbital
dynamics.",2109.14847v1
2022-04-14,Tuning nanosecond switching of spin-orbit torque driven magnetic tunnel junctions,"Since the discovery of the spin orbit torque (SOT) induced by spin Hall
effect in heavy metals, much effort has been devoted to understanding the
mechanism of the charge-to-spin conversion as well as to developing new schemes
for high speed, low energy magnetic recording technologies. While fast
switching has been demonstrated in three terminal magnetic tunnel junctions
(3T-MTJs) through applying short voltage pulses in the heavy metal channel,
detailed understanding of the switching mechanism is lacking due to the
complexity of the multi-layered magnetic structure and the three-terminal
geometry. We show in this letter that current-induced effective fields play a
key role in the fast switching and by tuning the applied external field we can
finely tune the symmetry of the pulse switching between two switching
polarities, namely parallel to anti-parallel (P-AP) and anti-parallel to
parallel (AP-P). These results show that the manipulation of detailed magnetic
configuration is the key to fast switching and is a useful way for future
optimization of SOT memory and further applications.",2204.07113v1
2022-05-10,Field-free spin orbit torque switching of synthetic antiferromagnet through interlayer Dzyaloshinskii-Moriya interaction,"Perpendicular synthetic antiferromagnets (SAFs) are of interest for the next
generation ultrafast, high density spintronic memory and logic devices.
However, to energy efficiently operate their magnetic order by current-induced
spin orbit torques (SOTs), an unfavored high external field is conventionally
required to break the symmetry. Here, we theoretically and experimentally
demonstrate the field-free SOT switching of a perpendicular SAF through the
introduction of interlayer Dzyaloshinskii-Moriya interaction (DMI). By
macro-spin simulation, we show that the speed of field-free switching increases
with the in-plane mirror asymmetry of injected spins. We experimentally observe
the existence of interlayer DMI in our SAF sample by an azimuthal angular
dependent anomalous Hall measurement. Field-free switching is accomplished in
such a sample and the strength of the effective switching field demonstrates
its origin from interlayer DMI. Our results provide a new strategy for SAF
based high performance SOT devices.",2205.04740v1
2022-08-25,Ultrashort spin-orbit torque generated by femtosecond laser pulses,"To realize the very objective of spintronics, namely the development of
ultra-high frequency and energy-efficient electronic devices, an ultrafast and
scalable approach to switch magnetic bits is required. Magnetization switching
with spin currents generated by the spin-orbit interaction at
ferromagnetic/non-magnetic interfaces is one of such scalable approaches, where
the ultimate switching speed is limited by the Larmor precession frequency.
Understanding the magnetization precession dynamics induced by spin-orbit
torques (SOTs) is therefore of great importance. Here we demonstrate generation
of ultrashort SOT pulses that excite Larmor precession at an epitaxial Fe/GaAs
interface by converting femtosecond laser pulses into high-amplitude current
pulses in an electrically biased p-i-n photodiode. We control the polarity,
amplitude, and duration of the current pulses and, most importantly, also their
propagation direction with respect to the crystal orientation. The SOT origin
of the excited Larmor precession was revealed by a detailed analysis of the
precession phase and amplitude at different experimental conditions.",2208.11974v1
2022-10-06,Current-induced perpendicular effective magnetic field in magnetic heterostructures,"Generation of perpendicular effective magnetic field or perpendicular spins
({\sigma}z) is central for the development of energy-efficient, scalable, and
external-magnetic-field-free spintronic memory and computing technologies.
Here, we report the first identification and the profound impacts of a
significant effective perpendicular magnetic field that can arise from
asymmetric current spreading within magnetic microstrips and Hall bars. This
effective perpendicular magnetic field can exhibit all the three
characteristics that have been widely assumed in the literature to ""signify""
the presence of a flow of {\sigma}z, i.e., external-magnetic-field-free current
switching of uniform perpendicular magnetization, a sin2{\phi}-dependent
contribution in spin-torque ferromagnetic resonance signal of in-plane
magnetization ({\phi} is the angle of the external magnetic field with respect
to the current, and a {\phi}-independent but field-dependent contribution in
the second harmonic Hall voltage of in-plane magnetization. This finding
suggests that it is critical to include current spreading effects in the
analyses of various spin polarizations and spin-orbit torques in magnetic
heterostructure. Technologically, our results provide perpendicular effective
magnetic field induced by asymmetric current spreading as a novel, universally
accessible mechanism for efficient, scalable, and external-magnetic-field-free
magnetization switching in memory and computing technologies.",2210.02916v1
2023-08-10,Some spin textures relevant to magnetic moments in the octonion spaces,"The paper aims to apply the octonions to explore the contribution of some
influence factors to magnetic moments, revealing the connection among the
influence factors and spin texture. J. C. Maxwell was the first to introduce
the quaternions to describe the electromagnetic theory. The subsequent scholars
utilize the quaternions and octonions to study the gravitational and
electromagnetic theories and so forth. The paper adopts the octonions to
research the gravitational and electromagnetic fields, including the octonion
angular momentum, torque, and force and so on. When the octonion force is equal
to zero under some circumstances, it is able to achieve eight equations
independent of each other. In particular, one of eight independent equations
reveals the interrelation between the second-torque and the divergence of
magnetic moments. One of its deductions is that the directions, magnitudes and
frequencies of some terms are capable of impacting the orientation and vortex
of magnetic moments, altering the frequency of magnetic vortex clusters. It
means that the spin textures are relevant to some external influence factors.
Some terms may have an influence on the arrangements of spin textures. The
study will be helpful for understanding the physical properties of magnetic
skyrmions and merons.",2308.13531v1
2004-03-29,Spin Transfer Without Spin Conservation,"We propose a general theory of the spin-transfer effects that occur when
current flows through inhomogeneous magnetic systems. Our theory does not rest
on an appeal to conservation of total spin, can assess whether or not
current-induced magnetization precession and switching in a particular geometry
will occur coherently, and can estimate the efficacy of spin-transfer when
spin-orbit interactions are present. We illustrate our theory by applying it to
a toy-model two-dimensional-electron-gas ferromagnet with Rashba spin-orbit
interactions.",0403710v1
2020-04-04,Energy and momentum conservation in spin transfer,"We utilize simulations of spin-polarized electron scattering by a chain of
localized quantum spins to show that energy and linear momentum conservation
laws impose strong constraints on the properties of magnetic excitations
induced by spin transfer. In turn, electron's orbital and spin dynamics depends
on the dynamical characteristics of the local spins. Our results suggest the
possibility to achieve precise control of spin transfer-driven magnetization
dynamics by tailoring the spectral characteristics of the magnetic systems and
the driving electrons.",2004.01957v1
2016-05-31,Correlation transfer in large-spin chains,"It is shown that transient spin-spin correlations in one-dimensional spin
S>>1 chain can be enhanced for initially factorized and individually squeezed
spin states. Such correlation transfer form ""internal"" to ""external"" degrees of
freedom can be well described by using a semiclassical phase-space approach.",1605.09476v1
2011-12-07,Spin Pumping Driven by Bistable Exchange Spin Waves,"Spin pumping driven by bistable exchange spin waves is demonstrated in a
Pt/Y$_3$Fe$_5$O$_{12}$ film under parametric excitation. In the
Pt/Y$_3$Fe$_5$O$_{12}$ film, the spin pumping driven by parametric excitation
selectively enhances the relaxation of short-wavelength exchange spin waves,
indicating strong coupling between the exchange spin waves and spin currents at
the interface through efficient spin transfer. The parametric spin pumping,
furthermore, allows direct access to nonlinear spin wave dynamics in
combination with the inverse spin Hall effect, revealing unconventional
bistability of the exchange spin waves.",1112.1596v2
2017-11-21,Determination of spin Hall effect and spin diffusion length of Pt from self-consistent fitting of damping enhancement and inverse spin-orbit torque measurements,"Understanding the evolution of spin-orbit torque (SOT) with increasing
heavy-metal thickness in ferromagnet/normal metal (FM/NM) bilayers is critical
for the development of magnetic memory based on SOT. However, several
experiments have revealed an apparent discrepancy between damping enhancement
and damping-like SOT regarding their dependence on NM thickness. Here, using
linewidth and phase-resolved amplitude analysis of vector network analyzer
ferromagnetic resonance (VNA-FMR) measurements, we simultaneously extract
damping enhancement and both field-like and damping-like inverse SOT in
Ni$_{80}$Fe$_{20}$/Pt bilayers as a function of Pt thickness. By enforcing an
interpretation of the data which satisfies Onsager reciprocity, we find that
both the damping enhancement and damping-like inverse SOT can be described by a
single spin diffusion length ($\approx$ 4 nm), and that we can separate the
spin pumping and spin memory loss (SML) contributions to the total damping.
This analysis indicates that less than 40% of the angular momentum pumped by
FMR through the Ni$_{80}$Fe$_{20}$/Pt interface is transported as spin current
into the Pt. On account of the SML and corresponding reduction in total spin
current available for spin-charge transduction in the Pt, we determine the Pt
spin Hall conductivity ($\sigma_\mathrm{SH} = (2.36 \pm 0.04)\times10^6
\Omega^{-1} \mathrm{m}^{-1}$) and bulk spin Hall angle
($\theta_\mathrm{SH}=0.387 \pm0.008$) to be larger than commonly-cited values.
These results suggest that Pt can be an extremely useful source of SOT if the
FM/NM interface can be engineered to minimize SML. Lastly, we find that
self-consistent fitting of the damping and SOT data is best achieved by a model
with Elliott-Yafet spin relaxation and extrinsic inverse spin Hall effect, such
that both the spin diffusion length and spin Hall conductivity are proportional
to the Pt charge conductivity.",1711.07654v2
2000-01-21,Starquake-Induced Glitches in Pulsars,"The neutron star crust is rigid material floating on a neutron-proton liquid
core. As the star's spin rate slows, the changing stellar shape stresses the
crust and causes fractures. These starquakes may trigger pulsar glitches as
well as the jumps in spin-down rate that are observed to persist after some
glitches. Earlier studies found that starquakes in spinning-down neutron stars
push matter toward the magnetic poles, causing temporary misalignment of the
star's spin and angular momentum. After the star relaxes to a new equilibrium
orientation, the magnetic poles are closer to the equator, and the magnetic
braking torque is increased. The magnitude and sign of the predicted torque
changes are in agreement with the observed persistent spin-down offsets. Here
we examine the relaxation processes by which the new equilibrium orientation is
reached. We find that the neutron superfluid in the inner crust slows as the
star's spin realigns with the angular momentum, causing the crust to spin more
rapidly. For plausible parameters the time scale and the magnitude of the
crust's spin up agree with the giant glitches in the Vela and other pulsars.",0001365v1
2001-05-08,Testing Tidal-Torque Theory: I. Spin Amplitude and Direction,"We evaluate the success of linear tidal-torque theory (TTT) in predicting
galactic-halo spin using a cosmological N-body simulation with thousands of
well-resolved haloes. The proto-haloes are identified by tracing today's haloes
back to the initial conditions. The TTT predictions for the proto-haloes match,
on average, the spin amplitudes of today's virialized haloes if linear growth
is assumed until ~t_0/3, or 55-70 per cent of the halo effective turn-around
time. This makes it a useful qualitative tool for understanding certain average
properties of galaxies, such as total spin and angular-momentum distribution
within haloes, but with a random scatter of the order of the signal itself.
Non-linear changes in spin direction cause a mean error of ~50 degrees in the
TTT prediction at t_0, such that the linear spatial correlations of spins on
scales >~ 1 Mpc/h are significantly weakened by non-linear effects. This
questions the usefulness of TTT for predicting intrinsic alignments in the
context of gravitational lensing. We find that the standard approximations made
in TTT, including a second order expansion of the Zel'dovich potential and a
smoothing of the tidal field, provide close-to-optimal results.",0105123v2
2013-11-08,Equilibrium spin pulsars unite neutron star populations,"Many pulsars are formed with a binary companion from which they can accrete
matter. Torque exerted by accreting matter can cause the pulsar spin to
increase or decrease, and over long times, an equilibrium spin rate is
achieved. Application of accretion theory to these systems provides a probe of
the pulsar magnetic field. We compare the large number of recent torque
measurements of accreting pulsars with a high-mass companion to the standard
model for how accretion affects the pulsar spin period. We find that many long
spin period (P > 100 s) pulsars must possess either extremely weak (B < 10^10
G) or extremely strong (B > 10^14 G) magnetic fields. We argue that the
strong-field solution is more compelling, in which case these pulsars are near
spin equilibrium. Our results provide evidence for a fundamental link between
pulsars with the slowest spin periods and strong magnetic fields around
high-mass companions and pulsars with the fastest spin periods and weak fields
around low-mass companions. The strong magnetic fields also connect our pulsars
to magnetars and strong-field isolated radio/X-ray pulsars. The strong field
and old age of our sources suggests their magnetic field penetrates into the
superconducting core of the neutron star.",1311.1969v1
2018-09-13,Non-Gravitational Forces and Spin Evolution of Comets,"Motion of many comets is affected by non-gravitational forces caused by
outgassing from their surfaces. Outgassing also produces reactive torques
resulting in cometary spin evolution. We propose that the two processes are
correlated and show that the change of cometary spin rate over its heliocentric
orbit scales linearly with the amplitude of its non-gravitational acceleration.
The proportionality constant depends on the comet size and orbital elements
(semi-major axis and eccentricity) and on the (dimensionless) lever arm
parameter $\zeta$ that relates the outgassing-induced torque and acceleration.
We determine $\zeta$ for 7 comets for which both non-gravitational acceleration
and change of spin period $\Delta P$ were measured and verify this relation.
This sample spanning almost 4 decades in $\Delta P$ yields $\log\zeta=-2.21\pm
0.54$, surprisingly small value and spread. We then apply our framework to 209
comets with measured non-gravitational accelerations and determine the objects
most likely to exhibit large spin period changes, $\Delta P\gtrsim 20$ min per
orbit assuming rotation period of 10 hr and $\zeta$ comparable to our control
sample. These objects should be primary targets for future studies of cometary
spin variability, further constraining distribution of $\zeta$. Lack of comets
with very high expected spin rate changes (which is not equivalent to having
the highest non-gravitational acceleration) suggests that (1) cometary fission
due to outgassing-driven spin-up must be an important process and (2) the
distribution of $\zeta$ has a lower limit $\sim 10^{-3}$.",1809.05133v1
2018-02-22,Voltage-Controlled Topological-Spin Switch for Ultra-Low-Energy Computing--Performance Modeling and Benchmarking,"A voltage-controlled topological-spin switch (vTOPSS) that uses a hybrid
topological insulator-magnetic insulator multiferroic is presented that can
implement Boolean logic operations with sub-10 aJ energy-per-bit and
energy-delay product on the order of $10^{-27}$ Js. The device uses a
topological insulator (TI), which has the highest efficiency of conversion of
electric field to spin torque yet observed at room temperature, and a
low-moment magnetic insulator (MI) that can respond rapidly to a given spin
torque. We present the theory of operation of vTOPSS, develop analytic models
of its performance metrics, elucidate performance scaling with dimensions and
voltage, and benchmark vTOPSS against existing spin-based and CMOS devices.
Compared to existing spin-based devices, such as all-spin logic and charge-spin
logic, vTOPSS offers 100$\times$ lower energy dissipation and (40-100)$\times$
lower energy-delay product. With experimental advances and improved material
properties, we show that the energy-delay product of vTOPSS can be lowered to
$10^{-29}$ Js, competitive against existing CMOS technology. Finally, we
establish that interconnect issues that dominate the performance in CMOS logic
are relatively less significant for vTOPSS, implying that highly resistive
materials can indeed be used to interconnect vTOPSS devices.",1802.07893v1
2020-03-14,Complementary lateral-spin-orbit building blocks for programmable logic and in-memory computing,"Current-driven switching of nonvolatile spintronic materials and devices
based on spin-orbit torques offer fast data processing speed, low power
consumption, and unlimited endurance for future information processing
applications. Analogous to conventional CMOS technology, it is important to
develop a pair of complementary spin-orbit devices with differentiated
magnetization switching senses as elementary building blocks for realizing
sophisticated logic functionalities. Various attempts using external magnetic
field or complicated stack/circuit designs have been proposed, however, plainer
and more feasible approaches are still strongly desired. Here we show that a
pair of two locally laser annealed perpendicular Pt/Co/Pt devices with opposite
laser track configurations and thereby inverse field-free lateral spin-orbit
torques (LSOTs) induced switching senses can be adopted as such complementary
spin-orbit building blocks. By electrically programming the initial
magnetization states (spin down/up) of each sample, four Boolean logic gates of
AND, OR, NAND and NOR, as well as a spin-orbit half adder containing an XOR
gate, were obtained. Moreover, various initialization-free, working current
intensity-programmable stateful logic operations, including the material
implication (IMP) gate, were also demonstrated by regarding the magnetization
state as a logic input. Our complementary LSOT building blocks provide an
applicable way towards future efficient spin logics and in-memory computing
architectures.",2003.06563v1
2020-03-26,Two-Dimensional Materials for Energy-Efficient Spin-Orbit Torque Devices,"Spin-orbit torques (SOTs), which rely on spin current generation from charge
current in a nonmagnetic material, promise an energy-efficient scheme for
manipulating magnetization in magnetic devices. A critical topic for spintronic
devices using SOTs is to enhance the charge to spin conversion efficiency.
Besides, the current-induced spin polarization is usually limited to in-plane,
whereas out-of-plane spin polarization could be favored for efficient
perpendicular magnetization switching. Recent advances in utilizing two
important classes of van der Waals materials$-$topological insulators and
transition-metal dichalcogenides$-$as spin sources to generate SOT shed light
on addressing these challenges. Topological insulators such as bismuth selenide
have shown a giant SOT efficiency, which is larger than those from
three-dimensional heavy metals by at least one order of magnitude.
Transition-metal dichalcogenides such as tungsten telluride have shown a
current-induced out-of-plane spin polarization, which is allowed by the reduced
symmetry. In this review, we use symmetry arguments to predict and analyze SOTs
in van der Waal material-based heterostructures. We summarize the recent
progress of SOT studies based on topological insulators and transition-metal
dichalcogenides and show how these results are in line with the symmetry
arguments. At last, we identify unsolved issues in the current studies and
suggest three potential research directions in this field.",2003.11966v2
2021-08-20,Tilted spin current generated by the collinear antiferromagnet RuO2,"We report measurements demonstrating that when the Neel vector of the
collinear antiferromagnet RuO2 is appropriately canted relative to the sample
plane, the antiferromagnet generates a substantial out of plane damping-like
torque. The measurements are in good accord with predictions that when an
electric field, E is applied to the spin split band structure of RuO2 it can
cause a strong transverse spin current even in the absence of spin-orbit
coupling. This produces characteristic changes in all three components of the E
induced torque vector as a function of the angle of E relative to the crystal
axes, corresponding to a spin current with a well defined tilted spin
orientation s approximately (but not exactly) parallel to the Neel vector,
flowing perpendicular to both E and S. This angular dependence is the signature
of an antiferromagnetic spin Hall effect with symmetries that are distinct from
other mechanisms of spin-current generation reported in antiferromagnetic or
ferromagnetic materials.",2108.09150v1
2021-10-06,"Stacking-order effect on spin-orbit torque, spin-Hall magnetoresistance, and magnetic anisotropy in Ni$_{81}$Fe$_{19}$-IrO$_2$ bilayers","The 5d transition-metal oxides have been an intriguing platform to
demonstrate efficient charge to spin current conversion due to a unique
electronic structure dominated by strong spin-orbit coupling. Here, we report
on stacking-order effect of spin-orbit torque (SOT), spin-Hall
magnetoresistance, and magnetic anisotropy in bilayer Ni$_{81}$Fe$_{19}$-5d
iridium oxide, IrO$_2$. While all the IrO$_2$ and Pt control samples exhibit
large dampinglike-SOT generation stemming from the efficient charge to spin
current conversion, the magnitude of the SOT is larger in the IrO$_2$
(Pt)-bottom sample than in the IrO$_2$ (Pt)-top one. The fieldlike-SOT has even
more significant stack order effect, resulting in an opposite sign in the
IrO$_2$ samples in contrast to the same sign in the Pt samples. Furthermore, we
observe that the magnetic anisotropy energy density and the anomalous Hall
effect are increased in the IrO$_2$ (Pt)-bottom sample, suggesting enhanced
interfacial perpendicular magnetic anisotropy. Our findings highlight the
significant influence of the stack order on spin transport and magnetotransport
properties of Ir oxide/ferromagnet systems, providing useful information on
design of SOT devices including 5d transition-metal oxides.",2110.02517v1
2022-04-20,Ferrimagnet GdFeCo characterization for spin-orbitronics: large field-like and damping-like torques,"Spintronics is showing promising results in the search for new materials and
effects to reduce energy consumption in information technology. Among these
materials, ferrimagnets are of special interest, since they can produce large
spin currents that trigger the magnetization dynamics of adjacent layers or
even their own magnetization. Here, we present a study of the generation of
spin current by GdFeCo in a GdFeCo/Cu/NiFe trilayer where the FeCo sublattice
magnetization is dominant at room temperature. Magnetic properties such as the
saturation magnetization are deduced from magnetometry measurements while
damping constant is estimated from spin-torque ferromagnetic resonance
(ST-FMR). We show that the overall damping-like (DL) and field-like (FL)
effective fields as well as the associated spin Hall angles can be reliably
obtained by performing the dependence of ST-FMR by an added dc current. The sum
of the spin Hall angles for both the spin Hall effect (SHE) and the spin
anomalous Hall effect (SAHE) symmetries are: $\theta_{DL}^{SAHE} +
\theta_{DL}^{SHE}=-0.15 \pm 0.05$ and $\theta_{FL}^{SAHE} +
\theta_{FL}^{SHE}=0.026 \pm 0.005$. From the symmetry of ST-FMR signals we find
that $\theta_{DL}^{SHE}$ is positive and dominated by the negative
$\theta_{DL}^{SAHE}$. The present study paves the way for tuning the different
symmetries in spin conversion in highly efficient ferrimagnetic systems.",2204.09776v1
2022-04-21,Tailoring neuromorphic switching by CuNx-mediated orbital currents,"Current-induced spin-orbit torque (SOT) is regarded as a promising mechanism
for driving neuromorphic behavior in spin-orbitronic devices. In principle, the
strong SOT in heavy metal-based magnetic heterostructure is attributed to the
spin-orbit coupling (SOC)-induced spin Hall effect (SHE) and/or the spin
Rashba-Edelstein effect (SREE). Recently, SOC-free mechanisms such as the
orbital angular momentum (OAM)-induced orbital Hall effect (OHE) and/or the
orbital Rashba-Edelstein effect (OREE) have been proposed to generate sizable
torques comparable to those from the conventional spin Hall mechanism. In this
work, we show that the orbital current can be effectively generated by the
nitrided light metal Cu. The overall damping-like SOT efficiency, which
consists of both the spin and the orbital current contributions, can be
tailored from ~ 0.06 to 0.4 in a Pt/Co/CuNx magnetic heterostructure by tuning
the nitrogen doping concentration. Current-induced magnetization switching
further verifies the efficacy of such orbital current with a critical switching
current density as low as Jc ~ 5 x 10^10 A/m2. Most importantly, the
orbital-current-mediated memristive switching behavior can be observed in such
heterostructures, which reveals that the gigantic SOT and efficient
magnetization switching are the tradeoffs for the applicable window of
memristive switching. Our work provides insights into the role of orbital
current might play in SOT neuromorphic devices and paves a new route for making
energy-efficient spin-orbitronic devices.",2204.09846v3
2007-10-02,Antiferromagnetic order driven by the molecular orbital order of C$_{60}$ in $α'$--tetra--$kis$--(dimethylamino)--ethylene--C$_{60}$,"We have studied the ground state of a fullerene--based magnet, the
$\alpha'$--phase tetra--$kis$--(dimethylamino)--ethylene--C$_{60}$
($\alpha'$--TDAE--C$_{60}$), by electron spin resonance (ESR) and magnetic
torque measurements. Below T$_N=7$ K, non--paramagnetic field dependent
resonances with a finite excitation gap (1.7 GHz) are observed along the
$a$--axis. Strong enhancement in their intensity as temperature is decreased is
inconsistent with excitation from a singlet state, which had been proposed for
the $\alpha'$--phase ground state. Below T$_N$, non--quadratic field dependence
of magnetic torque signal is also observed in contrast to quadratic field
dependence in the paramagnetic phase. The angle--dependent torque signals below
T$_N$ indicate the existence of an anisotropy of the bulk magnetization. From
both experiments, we propose an antiferromagnetic ground state driven by the
cooperative orientational ordering of C$_{60}$ in the
$\alpha'$--TDAE--C$_{60}$.",0710.0535v1
2007-12-06,Field dependence of the quantum ground state in the Shastry-Sutherland system SrCu$_2$(BO$_3$)$_2$,"We present magnetic torque measurements on the Shastry-Sutherland quantum
spin system SrCu$_2$(BO$_3$)$_2$ in fields up to 31 T and temperatures down to
50 mK. A new quantum phase is observed in a 1 T field range above the 1/8
plateau, in agreement with recent NMR results. Since the presence of the DM
coupling precludes the existence of a true Bose-Einstein condensation and the
formation of a supersolid phase in SrCu$_2$(BO$_3$)$_2$, the exact nature of
the new phase in the vicinity of the plateau remains to be explained.
Comparison between magnetization and torque data reveals a huge contribution of
the Dzyaloshinskii-Moriya interaction to the torque response. Finally, our
measurements demonstrate the existence of a supercooling due to adiabatic
magnetocaloric effects in pulsed field experiments.",0712.0926v1
2010-08-23,Magnetic-Torque Evidence for the Fulde-Ferrell-Larkin-Ovchinnikov State for In-Plane Magnetic Fields in the Organic Superconductor k-(BEDT-TTF)2Cu(NCS)2,"We present magnetic-torque measurements of the organic superconductor
k-(BEDT-TTF)2Cu(NCS)2 for in-plane magnetic fields up to 32 T. In this layered
two-dimensional compound the superconductivity can persist even in fields above
the Pauli limit of about 21 T. There, a pronounced upturn of the
upper-critical-field line occurs and the superconducting phase-transition line
splits and forms an additional high magnetic field phase. k-(BEDT-TTF)2Cu(NCS)2
is a spin-singlet superconductor, therefore, such a superconducting high-field
phase beyond the Pauli limit can originate only from Cooper pairing with finite
center-of-mass momentum. The measurements are discussed in connection with a
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, in accordance with earlier
specific-heat observations. The torque experiments allow us to investigate the
high magnetic-field phase diagram and the FFLO state of k-(BEDT-TTF)2Cu(NCS)2
in great detail.",1008.3747v1
2012-04-15,A Disc-Corona Model for a Rotating Black Hole,"We propose a disc-corona model in which a geometrically thin, optically thick
disc surrounds a Kerr black hole, and magnetic fields exert a time-steady
torque on the inner edge of the accretion disc. The analytical expression of
the total gravitational power is derived from the thin-disc dynamics equations
by using this new boundary condition. It is shown that the magnetic torque can
considerably enhance the amount of energy released in the disc-corona system.
Furthermore, the global solutions of this disc-corona system are obtained
numerically. We find that the fraction of the power dissipated into the corona
in the total for such disc-corona system increases with the increasing
dimensionless black hole spin parameter $a_\ast $, but is insensitive on the
$\Delta \varepsilon $ which is the additional radiative efficiency parameter
relevant to magnetic torque, for $\Delta\varepsilon > 1$. In addition, the
emerged spectra from this disc-corona system are simulated by using Monte-Carlo
method, and the effect of the different parameters on the output spectra is
discussed.",1204.3289v2
2014-12-08,"Repeated, Delayed Torque Variations Following X-ray Flux Enhancements in the Magnetar 1E$\;$1048.1$-$5937","We report on two years of flux and spin evolution monitoring of 1E
1048.1$-$5937, a 6.5-s X-ray pulsar identified as a magnetar. Using {\it Swift}
XRT data, we observed an X-ray outburst consisting of an increase in the
persistent 1--10 keV flux by a factor of 6.3$\pm$0.2, beginning on 2011
December 31 (MJD 55926). Following a delay of $\sim100$ days, the magnetar
entered a period of large torque variability, with $\dot{\nu}$ reaching a
factor of $4.55\pm0.05$ times the nominal value, before decaying in an
oscillatory manner over a time scale of months. We show by comparing to
previous outbursts from the source that this pattern of behavior may repeat
itself with a quasi-period of $\sim1800$ days. We compare this phenomenology to
periodic torque variations in radio pulsars, finding some similarities which
suggest a magnetospheric origin for the behavior of 1E 1048.1$-$5937.",1412.2780v1
2018-09-25,"Theory of damping in magnetization dynamics, dispelling a myth and pointing a way forward","There is a widely-held belief amongst theoreticians that the Gilbert damping
parameter {\alpha} in magnetization dynamics is infinite for a pure metal at
T=0. The basic error leading to this belief is pointed out explicitly and the
various methods of calculation used are viewed in a unified way based on the
Lorentzian lineshape of ferromagnetic resonance spectra. A general torque
formula for {\alpha} is proposed as a good starting-point for treating
inhomogeneous materials such as alloys, compounds and layered structures. Local
spin density functional theory provides a simple physical picture, in terms of
a non-uniform precessional cone angle in ferromagnetic resonance, of how such
inhomogeneity contributes to the damping. In a complementary many-body theory
this contribution is given by a vertex correction to the torque-torque response
function.",1809.09429v1
2018-11-22,Consequences of semidiurnal thermal tides on hot Jupiters zonal mean flows,"Hot Jupiters are submitted to an intense stellar heating. The resulting
thermal tides can torque their atmospheres into asynchronous rotation, while
these planets are usually assumed to be locked into spin-orbit synchronization
with their host star. Particularly, the thermal atmospheric torque can be
greatly enhanced by the dynamical component of the tidal response, that is the
component associated with the propagation of internal waves. Owing to the
involved complex dynamics, semi-analytical approaches are crucial to understand
the physical mechanisms that are responsible for the frequency-resonant
behavior of thermal tides, and quantify the atmospheric tidal torque. In this
work, we revisit the early works by Arras \& Socrates (2010) and present an
improved modeling of thermal tides taking into account rotation and radiative
cooling. Using this new modeling, we compute analytically the atmospheric tidal
response of hot Jupiters and show that resonances associated with low-frequency
internal gravity waves are able to drive asynchronous zonal flows in the range
1-30 days.",1811.09214v1
2018-04-03,Optical properties of coupled silicon nanowires and unusual mechanical inductions,"A recent study of the photonic coupling between metallic nanowires has
revealed new degrees of freedom in the system. Unexpected spin torques were
induced on dimers when illuminated with linearly polarized plane-waves. As
near-field observables, the spectra of torques showed more resolved resonances
than typical far-field spectra. Here the study is extended to silicon dimers.
Strong forces and torques are exerted by light under both polarizations s and
p, contrary to plasmonic systems where the resonant strong forces are found
only for p-polarization. The systems made of high-dielectric possess volume
resonances that induce the forces differently than in plasmonic systems, which
have surface resonances. The asymmetry in strong near-fields is responsible for
the unusual mechanics of the system. Some consequences of that may include the
breaking of the action-reaction principle or the appearance of pulling forces.
  The numerical study is based on an exact method. The work is thought for the
design of nanorotators and nanodetectors. It suggests a new viewpoint about
optical forces: the resultant dynamics of topological variations of
electromagnetic fields.",1804.01162v1
2018-04-16,Antidamping torque-induced switching in biaxial antiferromagnetic insulators,"We investigate the current-induced switching of the Neel order in NiO(001)/Pt
heterostructures,which is manifested electrically via the spin Hall
magnetoresistance. Significant reversible changes in the longitudinal and
transverse resistances are found at room temperature for a current threshold
lying in the range of 10^7 A/cm^2. The order-parameter switching is ascribed to
the antiferromagnetic dynamics triggered by the (current-induced) antidamping
torque, which orients the Neel order towards the direction of the writing
current. This is in stark contrast to the case of antiferromagnets such as
Mn2Au and CuMnAs, where field-like torques induced by the Edelstein effect
drive the Neel switching, therefore resulting in an orthogonal alignment
between the Neel order and the writing current. Our findings can be readily
generalized to other biaxial antiferromagnets, providing broad opportunities
for all-electrical writing and readout in antiferromagnetic spintronics.",1804.05462v1
2016-11-17,The rotation of planets hosting atmospheric tides: from Venus to habitable super-earths,"The competition between the torques induced by solid and thermal tides drives
the rotational dynamics of Venus-like planets and super-Earths orbiting in the
habitable zone of low-mass stars. The tidal responses of the atmosphere and
telluric core are related to their respective physical properties and strongly
depend on the tidal frequency. The resulting torque determines the possible
equilibrium states of the planet's spin. We compute here an analytic expression
for the total tidal torque exerted on a Venus-like planet. This expression is
used to characterize the equilibrium rotation of the body. Close to the star,
the solid tide dominates. Far from it, the thermal tide drives the rotational
dynamics of the planet. The transition regime corresponds to the habitable
zone, where prograde and retrograde equilibrium states appear. We demonstrate
the strong impact of the atmospheric properties and of the rheology of the
solid part on the rotational dynamics of Venus-like planets, highlighting the
key role played by dissipative mechanisms in the stability of equilibrium
configurations.",1611.05678v1
2019-10-24,Effects of Strong Photospheric Dissipation on the Spectra and Structure of Accretion Disks with Non-zero Inner Torque,"We present numerical calculations of spectra and structure of accretion disks
models appropriate for near-Eddington luminosity black hole X-ray binaries
(BHB). Our work incorporates non-zero torque at the ISCO as well as several
dissipation profiles based on first-principles three-dimensional disk interior
simulations. We found that significant dissipation near the photosphere can
produce steep power law-like spectra for models with moderate viewing angles
spanning a range of black hole spins while including inner torque push the
spectral peak to higher energies. Consistent with previous studies, we also
conclude that disks with stresses at the inner edge remain viable models for
high-frequency quasi-periodic oscillations (HFQPO), especially given that
increasing dissipation near the photospheres actually resulted in QPO power
spectra with higher quality factors compared to those found in recent work.",1910.10910v1
2022-04-20,A theoretical framework for the Hamiltonian of angular momentum optomechanical system,"Photon carries linear momentum and angular momentum simultaneously. Within
the light-matter interaction process, exchange of linear momentum results in
optical forces, whereas exchange of angular momentum leads to optical torques.
Use of optical forces (light pressure or damping) have been long and wide in
quantum optomechanics, however, those of optical torque and optical angular
momentum are not. Here we propose a theoretical framework based on optical
angular momentum and optical torques to derive the Hamiltonians of cavity
orbital and spin angular momentum optomechanical systems, respectively.
Moreover, based on the method, we successfully obtain the Hamiltonian of the
complex angular momentum optomechanical systems consisting of micro-cavity and
several torsional oscillators, whose reflection coefficients are non-unit. Our
results indicate the general applicability of our theoretical framework for the
Hamiltonian of angular momentum optomechanical systems and extend the research
scope of quantum optomechanics.",2204.09446v2
2018-02-05,Transfer-matrix calculations of the effects of tension and torque constraints on DNA-protein interactions,"Organization and maintenance of the chromosomal DNA in living cells strongly
depends on the DNA interactions with a plethora of DNA-binding proteins.
Single-molecule studies show that formation of nucleoprotein complexes on DNA
by such proteins is frequently subject to force and torque constraints applied
to the DNA. Although the existing experimental techniques allow to exert these
type of mechanical constraints on individual DNA biopolymers, their exact
effects in regulation of DNA-protein interactions are still not completely
understood due to the lack of systematic theoretical methods able to
efficiently interpret complex experimental observations. To fill this gap, we
have developed a general theoretical framework based on the transfer-matrix
calculations that can be used to accurately describe behaviour of DNA-protein
interactions under force and torque constraints. Potential applications of the
constructed theoretical approach are demonstrated by predicting how these
constraints affect the DNA-binding properties of different types of
architectural proteins. Obtained results provide important insights into
potential physiological functions of mechanical forces in the chromosomal DNA
organization by architectural proteins as well as into single-DNA manipulation
studies of DNA-protein interactions.",1802.01437v3
2006-06-20,Rotation of Cosmic Voids and Void-Spin Statistics,"We present a theoretical study of void spins and their correlation
properties. The concept of the spin angular momentum for an unbound void is
introduced to quantify the effect of the tidal field on the distribution of
matter that make up the void. Both the analytical and numerical approaches are
used for our study. Analytically, we adopt the linear tidal torque model to
evaluate the void spin-spin and spin-density correlations, assuming that a void
forms in the initial region where the inertia momentum and the tidal shear
tensors are maximally uncorrelated with each other. Numerically, we use the
Millennium run galaxy catalog to find voids and calculate their spin
statistics. The numerical results turn out to be in excellent agreement with
the analytic predictions, both of which consistently show that there are strong
spatial alignments between the spin axes of neighbor voids and strong
anti-alignments between the void spin axes and the directions to the nearest
voids. We expect that our work will provide a deeper insight into the origin
and properties of voids and the large scale structure.",0606477v2
2006-10-12,"Pulsar Spin, Magnetic Fields, and Glitches","In the core of a canonical spinning magnetized neutron star(NS) a nearly
uniform superfluid neutron vortex-array interacts strongly with a twisted array
of magnetic flux-tubes threading the core's superconducting protons. One
consequence is that changes in NS-spin alter both arrays and also the magnetic
field distribution on the surface of the surrounding crust. Among predicted
consequences for very young spinning-down NSs are ""spin-down indices""
increasing from 2 to 3, and a family of (Crab-like) spin-period ""glitches"" with
permanent fractional jumps in spin-down torque 10E5 times greater than those in
NS-spin. For older NSs, average spin-down indices increase to around 5, and an
additional (Vela-like) family of giant glitches develops. NS spin-up to
millesecond pulsars results in a high abundance of orthogonal and aligned
rotators, and anomolously small polar cap areas. Observations do not conflict
with these expectations. An epoch of NS magnetic field evolution between the
onset of proton superconductivity (approx. yr) and neutron superfluidity
(approx. 10E3 yrs ?) may be important for large surface magnetic field changes
and needs further study. Observations generally considered evidence for NS
precession seem to need reconsideration.",0610375v1
2012-11-06,Experimental Verification of Comparability between Spin-Orbit and Spin-Diffusion Lengths,"We experimentally confirmed that the spin-orbit lengths of noble metals
obtained from weak anti-localization measurements are comparable to the spin
diffusion lengths determined from lateral spin valve ones. Even for metals with
strong spin-orbit interactions such as Pt, we verified that the two methods
gave comparable values which were much larger than those obtained from recent
spin torque ferromagnetic resonance measurements. To give a further evidence
for the comparability between the two length scales, we measured the disorder
dependence of the spin-orbit length of copper by changing the thickness of the
wire. The obtained spin-orbit length nicely follows a linear law as a function
of the diffusion coefficient, clearly indicating that the Elliott-Yafet
mechanism is dominant as in the case of the spin diffusion length.",1211.1222v2
2018-08-08,Observation of acoustic spin,"Unlike optical waves, acoustic waves in fluids are described by scalar
pressure fields, and therefore are considered spinless. Here, we demonstrate
experimentally the existence of spin in acoustics. In the interference of two
acoustic waves propagating perpendicularly to each other, we observed the spin
angular momentum in free space as a result of the rotation of local particle
velocity. We successfully measured the acoustic spin, and spin induced torque
acting on a lossy acoustic meta-atom that results from absorption of the spin
angular momentum. The acoustic spin is also observed in the evanescent field of
a guided mode traveling along a metamaterial waveguide. We found spin-momentum
locking in acoustic waves whose propagation direction is determined by the sign
of spin. The observed acoustic spin could open a new door in acoustics and
their applications for the control of wave propagation and particle rotation.",1808.03686v1
2017-06-19,Spin Hall effect from hybridized 3$d$-4$p$ orbitals,"Electrical manipulation of magnetization by spin-orbit torque (SOT) has shown
promise for realizing reliable magnetic memories and oscillators. To date, the
generation of transverse spin current and SOT, whether it is of spin Hall
effect (SHE), Rashba-Edelstein effect or spin-momentum locking origin, relies
primarily on materials or heterostructures containing 5$d$ or 6$p$ heavy
elements with strong spin-orbit coupling. Here we show that a paramagnetic CoGa
compound possesses large enough spin Hall angle to allow robust SOT switching
of perpendicularly-magnetized ferrimagnetic MnGa films in CoGa/MnGa/Oxide
heterostructures. The spin Hall efficiency estimated via spin Hall
magnetoresistance and harmonic Hall measurements is +0.05$\pm$0.01, which is
surprisingly large for a system that does not contain any heavy metal element.
First-principles calculations corroborate our experimental observations and
suggest that the hybridized Co 3$d$ - Ga 4$p$ orbitals along R-X in the
Brillouin zone is responsible for the intrinsic SHE. Our results suggest that
efficient spin current generation can be realized in intermetallic by alloying
a transition metal with a $p$-orbital element and by Fermi level tuning.",1706.05846v1
2020-11-08,Spin Mode Reconstruction in Lagrangian Space,"Galaxy angular momentum directions (spins) are observable, well described by
the Lagrangian tidal torque theory, and proposed to probe the primordial
universe. They trace the spins of dark matter halos, and are indicators of
protohalos properties in Lagrangian space. We define a Lagrangian spin
parameter and tidal twist parameters and quantify their influence on the spin
conservation and predictability in the spin mode reconstruction in $N$-body
simulations. We conclude that protohalos in a more tidal twisting environments
are preferentially more rotation-supported, and more likely to conserve their
spin direction through the cosmic evolution. These tidal environments and spin
magnitudes are predictable by a density reconstruction in Lagrangian space, and
such predictions can improve the correlation between galaxy spins and the
initial conditions in the study of constraining the primordial universe by spin
mode reconstruction.",2011.03893v2
2016-11-22,Control and Local Measurement of the Spin Chemical Potential in a Magnetic Insulator,"The spin chemical potential characterizes the tendency of spins to diffuse.
Probing the spin chemical potential could provide insight into materials such
as magnetic insulators and spin liquids and aid optimization of spintronic
devices. Here, we introduce single-spin magnetometry as a generic platform for
non-perturbative, nanoscale characterization of spin chemical potentials. We
use this platform to investigate magnons in a magnetic insulator, surprisingly
finding that the magnon chemical potential can be efficiently controlled by
driving the system's ferromagnetic resonance. We introduce a symmetry-based
two-fluid theory describing the underlying magnon processes, realize the first
experimental determination of the local thermomagnonic torque, and illustrate
the detection sensitivity using electrically controlled spin injection. Our
results open the way for nanoscale control and imaging of spin transport in
mesoscopic spin systems.",1611.07408v1
2020-02-03,Non-trivial charge-to-spin conversion in ferromagnetic metal/Cu/Al2O3 by orbital transport,"Efficient spin/charge interconversion is desired to develop innovative
spin-based devices. So far, the interconversion has been performed by using
heavy atomic elements, strong spin-orbit interaction of which realizes the
interconversion through the spin Hall effect and the Edelstein effect. We
demonstrate highly efficient charge-to-spin conversion in a ferromagnetic
metal/Cu/Al2O3 trilayers, which do not contain any heavy element. The resulting
spin torque efficiency is higher than those of conventional spin Hall and
Rashba systems consisting of heavy elements such as Pt and Bi. Our experimental
results qualitatively deviate from typical behaviors arising from spin
transport. However, they are surprisingly consistent with the behaviors arising
from the orbital transport. Our results thus demonstrate a new direction for
efficient charge-to-spin conversion through the orbital transport.",2002.00596v2
2020-02-17,Efficient Electrical Spin-Splitter Based on Non-Relativistic Collinear Antiferromagnetism,"Electrical spin-current generation is among the core phenomena driving the
field of spintronics. Using {\em ab initio} calculations we show that a
room-temperature metallic collinear antiferromagnet RuO$_2$ allows for highly
efficient spin-current generation, arising from anisotropically-split bands
with conserved up and down spins along the N\'eel vector axis. The zero net
moment antiferromagnet acts as an electrical spin-splitter with a 34$^\circ$
propagation angle between spin-up and spin-down currents. Correspondingly, the
spin-conductivity is a factor of three larger than the record value from a
survey of 20,000 non-magnetic spin-Hall materials. We propose a versatile
spin-splitter-torque concept utilizing antiferromagnetic RuO$_2$ films
interfaced with a ferromagnet.",2002.07073v3
2021-01-09,Many-particle Quantum Hydrodynamics of Spin-1 Bose-Einstein Condensates,"We develop a novel model of the magnetized spin-1 Bose-Einstein condensate
(BEC) of neutral atoms, using the method of many-particle quantum hydrodynamic
(QHD) and propose an original derivation of the system of continual equations.
We consider bosons with a spin-spin interaction and a short range interaction
in the first order in the interaction radius, on the of basis of the
self-consistent field approximation of the QHD equations. We demonstrate that
the dynamics of the fluid velocity and magnetization is determined by a
nontrivial modification of the Euler and Landau-Lifshitz equation, and show
that a nontrivial modification of the spin density evolution equation contains
the spin torque effect that arises from the self-interactions between spins of
the bosons. The properties of the dispersion spectrum of collective excitations
are described. We obtain the new contribution of the self-interaction of spins
in the spin wave spectrum together with the influence of an external magnetic
field and spin-spin interactions between polarized particles. The anisotropic
spin wave instability is predicted.",2101.03422v1
2021-01-22,Chiral Bloch states in single layer graphene with Rashba spin-orbit coupling: Spectrum and spin current density,"We study the Bloch spectrum and spin physics of 2D massless Dirac electrons
in single layer graphene subject to a one dimensional periodic Kronig-Penney
potential and Rashba spin-orbit coupling. The Klein paradox exposes novel
features in the band dispersion and in graphene spintronics. In particular it
is shown that: (1) The Bloch energy dispersion $\veps(p)$ has unusual
structure: There are {\it two Dirac points} at Bloch momenta $\pm p \ne 0$ and
a narrow band emerges between the wide valence and conduction bands. (2) The
charge current and the spin density vector vanish. (3) Yet, all the
non-diagonal elements of the spin current density tensor are finite and their
magnitude increases linearly with the spin-orbit strength. In particular, there
is a spin density current whose polarization is perpendicular to the graphene
plane. (4) The spin density currents are space-dependent, hence their
continuity equation includes a finite spin torque density.",2101.09224v1
2022-11-09,Anomalous anisotropy of spin current in a cubic spin source with noncollinear antiferromagnetism,"Cubic materials host high crystal symmetry and hence are not expected to
support anisotropy in transport phenomena. In contrast to this common
expectation, here we report an anomalous anisotropy of spin current can emerge
in the (001) film of Mn${_3}$Pt, a noncollinear antiferromagnetic spin source
with face-centered cubic structure. Such spin current anisotropy originates
from the intertwined time reversal-odd ($T$-odd) and time reversal-even
($T$-even) spin Hall effects. Based on symmetry analyses and experimental
characterizations of the current-induced spin torques in Mn${_3}$Pt-based
heterostructures, we find that the spin current generated by Mn${_3}$Pt (001)
exhibits exotic dependences on the current direction for all the spin
components, deviating from that in conventional cubic systems. We also
demonstrate that such an anisotropic spin current can be used to realize
low-power spintronic applications such as the efficient field-free switching of
the perpendicular magnetizations.",2211.04970v1
2023-05-24,Effective model analysis of intrinsic spin Hall effect with magnetism in stacked-kagome Weyl semimetal Co3Sn2S2,"We theoretically study the spin Hall effect in a simple tight-binding model
of stacked-kagome Weyl semimetal Co3Sn2S2 with ferromagnetic ordering. We focus
on the two types of the spin Hall current: one flowing in the in-plane
direction with respect to the kagome lattice (in-plane spin Hall current), and
one flowing in the stacking direction (out-of-plane spin Hall current). We show
the spin Hall conductivities for those spin currents drastically change
depending on the direction of the magnetic moment. Especially, the out-of-plane
spin Hall current may induce surface spin accumulation, which are useful for
the perpendicular magnetization switching via spin-orbit torque.",2305.15144v1
2014-05-05,Spin-Orbit angle distribution and the origin of (mis)aligned hot Jupiters,"For 61 transiting hot Jupiters, the projection of the angle between the
orbital plane and the stellar equator (called the spin-orbit angle) has been
measured. For about half of them, a significant misalignment is detected, and
retrograde planets have been observed. This challenges scenarios of the
formation of hot Jupiters.
  In order to better constrain formation models, we relate the distribution of
the real spin-orbit angle $\Psi$ to the projected one $\beta$. Then, a
comparison with the observations is relevant.
  We analyse the geometry of the problem to link analytically the projected
angle $\beta$ to the real spin-orbit angle $\Psi$. The distribution of $\Psi$
expected in various models is taken from the literature, or derived with a
simplified model and Monte-Carlo simulations in the case of the disk-torquing
mechanism.
  An easy formula to compute the probability density function (PDF) of $\beta$
knowing the PDF of $\Psi$ is provided. All models tested here look compatible
with the observed distribution beyond 40 degrees, which is so far poorly
constrained by only 18 observations. But only the disk-torquing mechanism can
account for the excess of aligned hot Jupiters, provided that the torquing is
not always efficient. This is the case if the exciting binaries have semi-major
axes as large as 10000 AU.
  Based on comparison with the set of observations available today, scattering
models and the Kozai cycle with tidal friction models can not be solely
responsible for the production of all hot Jupiters. Conversely, the presently
observed distribution of the spin-orbit angles is compatible with most hot
Jupiters having been transported by smooth migration inside a proto-planetary
disk, itself possibly torqued by a companion.",1405.0960v2
2014-11-12,Spin Hall effect,"Spin Hall effects are a collection of relativistic spin-orbit coupling
phenomena in which electrical currents can generate transverse spin currents
and vice versa. Although first observed only a decade ago, these effects are
already ubiquitous within spintronics as standard spin-current generators and
detectors. Here we review the experimental and theoretical results that have
established this sub-field of spintronics. We focus on the results that have
converged to give us a clear understanding of the phenomena and how they have
evolved from a qualitative to a more quantitative measurement of spin-currents
and their associated spin-accumulation. Within the experimental framework, we
review optical, transport, and magnetization-dynamics based measurements and
link them to both phenomenological and microscopic theories of the effect.
Within the theoretical framework, we review the basic mechanisms in both the
extrinsic and intrinsic regime which are linked to the mechanisms present in
their closely related phenomenon in ferromagnets, the anomalous Hall effect. We
also review the connection to the phenomenological treatment based on
spin-diffusion equations applicable to certain regimes, as well as the
spin-pumping theory of spin-generation which has proven important in the
measurements of the spin Hall angle. We further connect the spin-current
generating spin Hall effect to the inverse spin galvanic effect, which often
accompanies the SHE, in which an electrical current induces a non-equilibrium
spin polarization. These effects share common microscopic origins and can
exhibit similar symmetries when present in ferromagnetic/non-magnetic
structures through their induced current-driven spin torques. Although we give
a short chronological overview, the main body is structured from a pedagogical
point of view, focusing on well-established and accepted physics.",1411.3249v1
2022-11-04,Spin and spin current -- From fundamentals to recent progress,"Along with the progress of spin science and spintronics research, the flow of
electron spins, (i.e. spin current), has attracted interest. New phenomena and
electronic states were explained in succession using the concept of spin
current. Moreover, as many of the conventionally known spintronics phenomena
became well organized based on spin current, it has rapidly been recognized as
an essential concept in a wide range of condensed matter physics. In this
article, we focus on recent developments in the physics of spin, spin current,
and their related phenomena, where the conversion between spin angular momentum
and different forms of angular momentum plays an essential role. Starting with
an introduction to spin current, we first discuss the recent progress in
spintronic phenomena driven by spin-exchange coupling: spin pumping,
topological Hall torque, and emergent inductor. We, then, extend our discussion
to the interaction/interconversion of spins with heat, lattice vibrations, and
charge current and address recent progress and perspectives on the spin Seebeck
and Peltier effects. Next, we review the interaction between mechanical motion
and electron/nuclear spins and argue the difference between the Barnett field
and rotational Doppler effect. We show that the Barnett effect reveals the
angular momentum compensation temperature, at which the net angular momentum is
quenched in ferrimagnets.",2211.02241v4
2021-01-08,Chirality Induced Spin Coherence in Electron Transfer Reactions,"Recently there has been much interest in the chirality induced spin
selectivity effect, whereby electron spin polarisation, which is dependent on
the molecular chirality, is produced in electrode-molecule electron transfer
processes. Naturally, one might consider if a similar effect can be observed in
simple molecular charge transfer reactions, for example in light-induced
electron transfer from an electron donor to an electron acceptor. In this work
we explore the effect of electron transfer on spins in chiral single radicals
and chiral radical pairs using Nakajima-Zwanzig theory. In these cases
chirality, in conjuction with spin-orbit coupling, does not lead to spin
polarisation, but instead the electron transfer generates quantum coherence
between spins states. In principle, this chirality induced spin coherence could
manifest in a range of experiments, and in particular we demonstrate that the
OOP-ESEEM pulse EPR experiment would be able to detect this effect in oriented
radical pairs.",2101.03104v1
2015-04-01,Evolution of a Binary Black Hole with a Retrograde Circumbinary Accretion Disk,"We consider the evolution of a supermassive black hole binary (SMBHB)
surrounded by a retrograde accretion disk. Assuming the disk is exactly in the
binary plane and transfers energy and angular momentum to the binary via direct
gas accretion, we calculate the time evolution of the binary's semi-major axis
$a$ and eccentricity $e$. Because the gas is predominantly transferred when the
binary is at apocenter, we find the eccentricity grows rapidly while
maintaining constant $a(1+e)$. After accreting only a fraction of the
secondary's mass, the eccentricity grows to nearly unity; from then on,
gravitational wave emission dominates the evolution, preserving constant
$a(1-e)$. The high-eccentricity waveforms redistribute the peak gravitational
wave power from the nHz to $\mu$Hz bands, substantially affecting the signal
that might be detected with pulsar timing arrays. We also estimate the torque
coupling binaries of arbitrary eccentricity with obliquely aligned circumbinary
disks. If the outer edge of the disk is not an extremely large multiple of the
binary separation, retrograde accretion can drive the binary into the
gravitational wave-dominated state before these torques align the binary with
the angular momentum of the mass supply.",1504.00311v1
2018-11-20,"Energy, linear and angular momentum of light: what do we measure?","The most commonly observed quantity related to light is its power or
equivalently its energy. It can be either measured with a bolometer, a
photodiode or estimated with the naked eye. Alternatively people can measure
the light impulse or linear momentum. However, linear momentum is characterized
by its transfer to matter, and its precise value is most of the time of little
use. Energy and linear momentum are linked and can be deduced from each other,
from a theoretical point of view. Because the linear momentum measurement is
more difficult, energy is the most often measured quantity. In every physical
process, angular momentum, like energy and linear momentum is conserved.
However, it is independent and can't be deduced from the energy or the linear
momentum. It can only be estimated via its transfer to matter using a torque
observation. Nevertheless , experimentally, the torque is found to be
proportional to the optical power. This leads to a need of a quantum
interpretation of the optical field in terms of photons. Clear experimental
evidences and consequences are presented here and debated. light temperature
rotation $\theta$ velocity energy flux light angular momentum light radiation
pressure",1811.08110v1
2019-09-17,"Torquing the Condensate: Angular Momentum Transport in Bose-Einstein Condensates by Solitonic ""Corkscrew""","When rotating classical fluid drops merge together, angular momentum can be
advected from one to another due to the viscous shear flow at the drop
interface. It remains elusive what the corresponding mechanism is in inviscid
quantum fluids such as Bose-Einstein condensates (BECs). Here we report our
theoretical study of an initially static BEC merging with a rotating BEC in
three-dimensional space along the rotational axis. We show that a soliton sheet
resembling a ""corkscrew"" spontaneously emerges at the interface. Rapid angular
momentum transfer at a constant rate universally proportional to the initial
angular momentum density is observed. Strikingly, this transfer does not
necessarily involve fluid advection or drifting of the quantized vortices. We
reveal that the solitonic corkscrew can exert a torque that directly creates
angular momentum in the static BEC and annihilates angular momentum in the
rotating BEC. Uncovering this intriguing angular momentum transport mechanism
may benefit our understanding of various coherent matter-wave systems, spanning
from atomtronics on chips to dark matter BECs at cosmic scales.",1909.08086v1
1998-01-28,Orbital Evolution and Migration of Giant Planets: Modeling Extrasolar Planets,"Giant planets in circumstellar disks can migrate inward from their initial
(formation) positions. Radial migration is caused by inward torques between the
planet and the disk; by outward torques between the planet and the spinning
star; and by outward torques due to Roche lobe overflow and consequent mass
loss from the planet. We present self-consistent numerical considerations of
the problem of migrating giant planets. Summing torques on planets for various
physical parameters, we find that Jupiter-mass planets can stably arrive and
survive at small heliocentric distances, thus reproducing observed properties
of some of the recently discovered extra-solar planets. Inward migration
timescales can be approximately equal to or less than disk lifetimes and star
spindown timescales. Therefore, the range of fates of massive planets is broad,
and generally comprises three classes: (I) planets which migrate inward too
rapidly and lose all their mass; (II) planets which migrate inward, lose some
but not all of their mass, and survive in very small orbits; and (III) planets
which do not lose any mass. Some planets in Class III do not migrate very far
from their formation locations. Our results show that there is a wide range of
possible fates for Jupiter-mass planets for both final heliocentric distance
and final mass.",9801292v1
2018-01-23,Semidiurnal thermal tides in asynchronously rotating hot Jupiters,"Thermal tides can torque the atmosphere of hot Jupiters into asynchronous
rotation, while these planets are usually assumed to be locked into spin-orbit
synchronization with their host star. In this work, our goal is to characterize
the tidal response of a rotating hot Jupiter to the tidal semidiurnal thermal
forcing of its host star, by identifying the structure of tidal waves
responsible for variation of mass distribution, their dependence on the tidal
frequency and their ability to generate strong zonal flows. We develop an ab
initio global modeling that generalizes the early approach of Arras & Socrates
(2010) to rotating and non-adiabatic planets. We derive analytically the torque
exerted on the body and the associated timescales of evolution, as well as the
equilibrium tidal response of the atmosphere in the zero-frequency limit.
Finally, we integrate numerically the equations of thermal tides for three
cases including dissipation and rotation step by step. The resonances
associated with tidally generated gravito-inertial waves amplify significantly
the resulting tidal torque in the range 1-30 days. This torque can drive
globally the atmosphere into asynchronous rotation, as its sign depends on the
tidal frequency. The resonant behaviour of the tidal response is enhanced by
rotation, which couples the forcing to several Hough modes in the general case,
while the radiative cooling tends to regularize it and diminish its amplitude.",1801.07519v1
2018-02-05,"Spinup and Disruption of Interstellar Asteroids by Mechanical Torques, and Implications for 1I/2017 U1 (`Oumuamua)","The discovery of the first interstellar asteroid, 1I/2017 U1 (`Oumuamua), has
opened a new era for research on interstellar objects. In this paper, we study
the rotational dynamics of interstellar asteroids (ISAs) of irregular shapes
moving through the interstellar gas. We find that regular mechanical torques
resulting from the bombardment of gas flow on the irregular body could be
important for the dynamics and destruction of ISAs. Mechanical torques can spin
up the ISA, resulting in the breakup of the original ISA into small binary
asteroids when the rotation rate exceeds the critical frequency. We find that
the breakup timescale is short for ISAs of highly irregular shapes and low
tensile strength. We apply our results to the first observed ISA, `Oumuamua,
and suggest that its extreme elongated shape may originate from a reassembly of
the binary fragments due to gravity along its journey in the interstellar
medium. The tumbling of `Oumuamua could have been induced by rotational
disruption due to mechanical torques. Finally, we discuss the survival
possibility of high-velocity asteroids presumably formed by tidal disruption of
planetary systems by the black hole at the Galactic center.",1802.01335v2
2020-04-07,Tidal Oscillations of Rotating Hot Jupiters,"We calculate small amplitude gravitational and thermal tides of uniformly
rotating hot Jupiters composed of a nearly isentropic convective core and a
geometrically thin radiative envelope. We treat the fluid in the convective
core as a viscous fluid and solve linearized Navier Stokes equations to obtain
tidal responses of the core, assuming that the Ekman number ${\rm Ek}$ is a
constant parameter. In the radiative envelope, we take account of the effects
of radiative dissipations on the responses. The properties of tidal responses
depend on thermal timescales $\tau_*$ in the envelope and Ekman number Ek in
the core and on weather the forcing frequency $\omega$ is in the inertial range
or not, where the inertial range is defined by $|\omega|\le2\Omega$ for the
rotation frequency $\Omega$. If ${\rm Ek}\gtrsim 10^{-7}$, the viscous
dissipation in the core is dominating the thermal contributions in the envelope
for $\tau_*\gtrsim 1$ day. If ${\rm Ek}\lesssim 10^{-7}$, however, the viscous
dissipation is comparable to or smaller than the thermal contributions and the
envelope plays an important role to determine the tidal torques. If the forcing
is in the inertial range, frequency resonance of the tidal forcing with core
inertial modes significantly affects the tidal torques, producing numerous
resonance peaks of the torque. Depending on the sign of the torque in the
peaks, we suggest that there exist cases in which the resonance with core
inertial modes hampers the process of synchronization between the spin and
orbital motion of the planets.",2004.03094v1
2018-04-30,Edge-induced radiation force and torque on a cylindrically-radiating active acoustic source near a rigid corner-space,"This work examines the physical effect of the edge-induced acoustic radiation
force and torque on an acoustically radiating circular source, located near a
rigid corner. Assuming harmonic (linear) radiating waves of the source,
vibrating in monopole or dipole radiation modes near a rigid corner-space in a
non-viscous fluid, the modal series expansion method in cylindrical
coordinates, the classical method of images and the translational addition
theorem are applied to obtain the mathematical expressions for the radiation
force and torque components in exact closed-form partial-wave series.
Computational results illustrate the theory, and examine some of the conditions
where the radiation force and torque components vanish, which has the potential
to achieve total motion suppression (i.e., translation or rotation).
Furthermore, depending on the size parameter of the source and the distances
from the rigid corner space, these physical observables take positive or
negative values, anticipating the prediction of pulling/pushing motions toward
the corner space, and possible spinning of the source clockwise or
counter-clockwise. The present analysis and its results are useful in some
applications related to the manipulation of an active carrier or ultrasound
contrast agents near a corner space or chamber walls at a right angle.",1804.11045v1
2021-04-19,Studying magnetic fields of ultraluminous X-ray pulsars using different accretion torques,"The magnetic field of ultraluminous X-ray (ULX) pulsars is the key parameter
to understand the nature and accretion physics. However, the typical magnetic
field values in these ULX pulsars are still under debate. We used six different
torque models to study the magnetic fields of ULX pulsars, to see how derived
magnetic fields change with different models, and to determine which models are
more suitable for ULX pulsars. We took the currently available period, period
derivative, and flux data of 7 confirmed ULX pulsars, M82 X-2, ULX NGC 7793
P13, ULX NGC 5907, NGC 300 ULX1, NGC 1313 X-2, M51 ULX-7, Swift J0243.6+6124,
plus one potential ULX pulsars, SMC X-3. The magnetic fields of these ULX
pulsars were constrained from two physical conditions: the spin-up process and
near equilibrium. We checked possible dependence of the magnetic field
estimations on the different torque models. The calculations suggest the
accretion torque models by Ghosh & Lamb [1], Wang [2], Kluzniak & Rappaport [3]
and Campbell [4] are more likely to support magnetar models for ULX pulsars,
while Lovelace, Romanova & Bisnovatyi-Kogan [5]'s model generally predicts the
magnetic field in normal neutron stars. Implications of our results combined
with other independent methods are also discussed, which will help us to
understand the nature and rotational behavior of these ULX pulsars.",2104.09076v1
2022-08-24,Second-order inertial forces and torques on a sphere in a viscous steady linear flow,"We compute the full set of second-order inertial corrections to the
instantaneous force and torque acting on a small spherical rigid particle
moving unsteadily in a general steady linear flow. This is achieved by using
matched asymptotic expansions and formulating the problem in a coordinate
system co-moving with the background flow. Effects of the fluid-velocity
gradients are assumed to be small, but to dominate over those of the velocity
difference between the body and fluid, which makes the results essentially
relevant to nearly neutrally buoyant particles. The outer solution (which at
first order is responsible for the Basset-Boussinesq history force at short
time and for shear-induced forces such as the Saffman lift force at long time)
is expressed via a flow-dependent tensorial kernel. The second-order inner
solution brings a number of different contributions to the force and torque.
Some are proportional to the relative translational or angular acceleration
between the particle and fluid, while others take the form of products of the
rotation/strain rate of the background flow and the relative translational or
angular velocity between the particle and fluid. Adding the outer and inner
contributions, the known added-mass force or the spin-induced lift force are
recovered, and new effects involving the rotation/strain rate of the background
flow are revealed. The resulting force and torque equations provide a rational
extension of the classical Basset-Boussinesq-Oseen equation incorporating all
first- and second-order fluid inertia effects resulting from both unsteadiness
and velocity gradients of the carrying flow.",2208.11565v2
2022-11-29,A Bayesian approach for torque modelling of BeXRB pulsars with application to super-Eddington accretors,"In this study we present a method to estimate posterior distributions for
standard accretion torque model parameters and binary orbital parameters for
X-ray binaries using a nested sampling algorithm for Bayesian Parameter
Estimation. We study the spin evolution of two Be X-ray binary systems in the
Magellanic Clouds, RX J0520.5-6932 and RX J0209-7427, during major outbursts,
in which they surpassed the Eddington-limit. Moreover, we apply our method to
the recently discovered Swift J0243.6+6124; the only known Galactic pulsating
ultra-luminous X-ray source. This is an excellent candidate for studying the
disc evolution at super-Eddington accretion rates, for its luminosity span
several orders of magnitude during its outburst, with a maximum $L_{\rm X}$
that exceeded the Eddington limit by a factor of $\sim 10$. Our method, when
applied to RX J0520.5-6932 and RX J0209-7427, is able to identify the more
favourable torque model for each system, while yielding meaningful ranges for
the NS and orbital parameters. Our analysis for Swift J0243.6+6124 illustrates
that, contrary to the standard torque model predictions, the magnetospheric
radius and the Alfv\'en radius are not proportional to each other when
surpassing the Eddington limit. Reported distance estimates of this source
range between 5 and 7 kpc. Smaller distances require non-typical neutron star
properties (i.e. mass and radius) and possibly lower radiative efficiency of
the accretion column.",2211.16079v1
2023-09-04,Fitting the Light Curve of 1I/`Oumuamua with a Nonprincipal Axis Rotational Model and Outgassing Torques,"In this paper, we investigate the nonprincipal axis (NPA) rotational state of
1I/`Oumuamua -- the first interstellar object discovered traversing the inner
Solar System -- from its photometric light curve. Building upon Mashchenko
(2019), we develop a model which incorporates NPA rotation and {Sun-induced,
time-varying} outgassing torques to generate synthetic light curves of the
object. The model neglects tidal forces, which are negligible compared to
outgassing torques over the distances that `Oumuamua was observed. We implement
an optimization scheme that incorporates the NPA rotation model to calculate
the initial rotation state of the object. We find that an NPA rotation state
with an average period of $\langle P \rangle\simeq7.34$ hr best reproduces the
photometric data. The discrepancy between this period and previous estimates is
due to continuous period modulation induced by outgassing torques in the
rotational model, {as well as different periods being used}. The best fit to
the October 2017 data does not reproduce the November 2017 data (although the
later measurements are too sparse to fit). The light curve is consistent with
no secular evolution of the angular momentum, somewhat in tension with the
empirical correlations between nuclear spin-up and cometary outgassing. The
complex rotation of `Oumuamua may be {the result of primordial rotation about
the smallest principal axis} if (i) the object experienced hypervolatile
outgassing and (ii) our idealized outgassing model is accurate.",2309.01820v1
2020-07-08,Adiabatic quantum state transfer in a semiconductor quantum-dot spin chain,"Semiconductor quantum-dot spin qubits are a promising platform for quantum
computation, because they are scalable and possess long coherence times. In
order to realize this full potential, however, high-fidelity information
transfer mechanisms are required for quantum error correction and efficient
algorithms. Here, we present evidence of adiabatic quantum-state transfer in a
chain of semiconductor quantum-dot electron spins. By adiabatically modifying
exchange couplings, we transfer single- and two-spin states between distant
electrons in less than 127 ns. We also show that this method can be cascaded
for spin-state transfer in long spin chains. Based on simulations, we estimate
that the probability to correctly transfer single-spin eigenstates and two-spin
singlet states can exceed 0.95 for the experimental parameters studied here. In
the future, state and process tomography will be required to verify the
transfer of arbitrary single qubit states with a fidelity exceeding the
classical bound. Adiabatic quantum-state transfer is robust to noise and
pulse-timing errors. This method will be useful for initialization, state
distribution, and readout in large spin-qubit arrays for gate-based quantum
computing. It also opens up the possibility of universal adiabatic quantum
computing in semiconductor quantum-dot spin qubits.",2007.03869v2
2019-04-13,Chiral transfer of angular momentum,"Suppose that viscous fluid is contained in the space between a fixed sphere
$S_2$ and an interior sphere $S_1$ which moves with time-periodic velocity
${\bf U}(t)$ and angular velocity ${\bf \Omega}(t)$, with $ \left<{\bf
U}(t)\right> = \left<{\bf \Omega}(t)\right> = 0$. It is shown that, provided
this motion is chiral in character, it can drive a flow that exerts a non-zero
torque on $S_2$. Thus angular momentum can be transferred through this
mechanism.",1904.06486v1
2023-04-05,Threshold current of field-free perpendicular magnetization switching using anomalous spin-orbit torque,"Spin-orbit torque (SOT) is a candidate technique in next generation magnetic
random-access memory (MRAM). Recently, experiments show that some material with
low-symmetric crystalline or magnetic structures can generate anomalous SOT
that has an out-of-plane component, which is crucial in switching perpendicular
magnetization of adjacent ferromagnetic (FM) layer in the field-free condition.
In this work, we analytically derive the threshold current of field-free
perpendicular magnetization switching using the anomalous SOT. And we
numerically calculate the track of the magnetic moment in a FM free layer when
an applied current is smaller and greater than the threshold current. After
that, we study the applied current dependence of the switching time and the
switching energy consumption, which shows the minimum energy consumption
decreases as out-of-plane torque proportion increases. Then we study the
dependences of the threshold current on anisotropy strength, out-of-plane
torque proportion, FM free layer thickness and Gilbert damping constant, and
the threshold current shows negative correlation with the out-of-plane torque
proportion and positive correlation with the other three parameters. Finally,
we demonstrate that when the applied current is smaller than the threshold
current, although it cannot switch the magnetization of FM free layer, it can
still equivalently add an effective exchange bias field H_{bias} on the FM free
layer. The H_{bias} is proportional to the applied current J_{SOT}, which
facilitates the determination of the anomalous SOT efficiency. This work helps
us to design new spintronic devices that favor field-free switching
perpendicular magnetization using the anomalous SOT, and provides a way to
adjust the exchange bias field, which is helpful in controlling FM layer
magnetization depinning.",2304.02248v2
2010-05-28,Non-white frequency noise in spin torque oscillators and its effect on spectral linewidth,"We measure the power spectral density of frequency fluctuations in
nanocontact spin torque oscillators over time scales up to 50 ms. We use a
mixer to convert oscillator signals ranging from 10 GHz to 40 GHz into a band
near 70 MHz before digitizing the time domain waveform. We analyze the waveform
using both zero crossing time stamps and a sliding Fourier transform, discuss
the different limitations and advantages of these two methods, and combine them
to obtain a frequency noise spectrum spanning more than five decades of Fourier
frequency $f$. For devices having a free layer consisting of either a single
Ni$_{\text{}80}$Fe$_{\text{}20}$ layer or a Co/Ni multilayer we find a
frequency noise spectrum that is white at large $f$ and varies as \emph{$1/f$}
at small $f$. The crossover frequency ranges from $\approx\unit[10^{4}]{Hz}$ to
$\approx\unit[10^{6}]{Hz}$ and the $1/f$ component is stronger in the
multilayer devices. Through actual and simulated spectrum analyzer
measurements, we show that $1/f$ frequency noise causes both broadening and a
change in shape of the oscillator's spectral line as measurement time
increases. Our results indicate that the long term stability of spin torque
oscillators cannot be accurately predicted from models based on thermal (white)
noise sources.",1005.5372v1
2015-11-19,Forced libration of tidally synchronized planets and moons,"Tidal dissipation of kinetic energy, when it is strong enough, tends to
synchronize the rotation of planets and moons with the mean orbital motion, or
drive it into long-term stable spin-orbit resonances. As the orbital motion
undergoes periodic acceleration due to a finite orbital eccentricity, the spin
rate oscillates around the equilibrium mean value too, giving rise to the
forced, or eccentricity-driven, librations. Both the shape and amplitude of
forced librations of synchronous viscoelastic planets and moons are defined by
a combination of two different types of perturbative torque, the tidal torque
and the triaxial torque. Consequently, forced librations can be tidally
dominated (e.g., Io and possibly Titan) or deformation-dominated (e.g., the
Moon) depending on a set of orbital, rheological, and other physical
parameters. With small eccentricities, for the former kind, the largest term in
the libration angle can be minus cosine of the mean anomaly, whereas for the
latter kind, it is minus sine of the mean anomaly. The shape and the amplitude
of tidal forced librations determine the rate of orbital evolution of
synchronous planets and moons, i.e., the rate of dissipative damping of
semimajor axis and eccentricity. The known super-Earth exoplanets can exhibit
both kinds of libration, or a mixture thereof, depending on, for example, the
effective Maxwell time of their rigid mantles. Our approach can be extended to
estimate the amplitudes of other libration harmonics, as well as the forced
libration in non-synchronous spin-orbit resonances.",1511.06287v1
2017-10-16,Activation of Microwave Fields in a Spin-Torque Nano-Oscillator by Neuronal Action Potentials,"Action potentials are the basic unit of information in the nervous system and
their reliable detection and decoding holds the key to understanding how the
brain generates complex thought and behavior. Transducing these signals into
microwave field oscillations can enable wireless sensors that report on brain
activity through magnetic induction. In the present work we demonstrate that
action potentials from crayfish lateral giant neuron can trigger microwave
oscillations in spin-torque nano-oscillators. These nanoscale devices take as
input small currents and convert them to microwave current oscillations that
can wirelessly broadcast neuronal activity, opening up the possibility for
compact neuro-sensors. We show that action potentials activate microwave
oscillations in spin-torque nano-oscillators with an amplitude that follows the
action potential signal, demonstrating that the device has both the sensitivity
and temporal resolution to respond to action potentials from a single neuron.
The activation of magnetic oscillations by action potentials, together with the
small footprint and the high frequency tunability, makes these devices
promising candidates for high resolution sensing of bioelectric signals from
neural tissues. These device attributes may be useful for design of
high-throughput bi-directional brain-machine interfaces.",1710.05630v1
2017-04-10,Tunable mode coupling in nano-contact spin torque oscillators,"Recent experiments on spin torque oscillators have revealed interactions
between multiple magnetodynamic modes, including mode-coexistence,
mode-hopping, and temperature-driven cross-over between modes. Initial
multimode theory has indicated that a linear coupling between several dominant
modes, arising from the interaction of the subdynamic system with a magnon
bath, plays an essential role in the generation of various multimode behaviors,
such as mode hopping and mode coexistence. In this work, we derive a set of
rate equations to describe the dynamics of coupled magnetodynamic modes in a
nano-contact spin torque oscillator. Expressions for both linear and nonlinear
coupling terms are obtained, which allow us to analyze the dependence of the
coupled dynamic behaviors of modes on external experimental conditions as well
as intrinsic magnetic properties. For a minimal two-mode system, we further map
the energy and phase difference of the two modes onto a two-dimensional phase
space, and demonstrate in the phase portraits, how the manifolds of periodic
orbits and fixed points vary with external magnetic field as well as with
temperature.",1704.03076v2
2017-04-21,Time- and spatially-resolved magnetization dynamics driven by spin-orbit torques,"Current-induced spin-orbit torques (SOTs) represent one of the most effective
ways to manipulate the magnetization in spintronic devices. The orthogonal
torque-magnetization geometry, the strong damping, and the large domain wall
velocities inherent to materials with strong spin-orbit coupling make SOTs
especially appealing for fast switching applications in nonvolatile memory and
logic units. So far, however, the timescale and evolution of the magnetization
during the switching process have remained undetected. Here, we report the
direct observation of SOT-driven magnetization dynamics in Pt/Co/AlO$_x$ dots
during current pulse injection. Time-resolved x-ray images with 25 nm spatial
and 100 ps temporal resolution reveal that switching is achieved within the
duration of a sub-ns current pulse by the fast nucleation of an inverted domain
at the edge of the dot and propagation of a tilted domain wall across the dot.
The nucleation point is deterministic and alternates between the four dot
quadrants depending on the sign of the magnetization, current, and external
field. Our measurements reveal how the magnetic symmetry is broken by the
concerted action of both damping-like and field-like SOT and show that
reproducible switching events can be obtained for over $10^{12}$ reversal
cycles.",1704.06402v1
2017-04-26,Spin Torque Efficiency and Analytic Error Rate Estimates of Skyrmion Racetrack Memory,"In this paper the thermal stability of skyrmion bubbles and the critical
currents to move them over pinning sites is investigated. For the used pinning
geometries and the used parameters, the unexpected behavior is reported that
the energy barrier to overcome the pinning site is larger than the energy
barrier of the annihilation of a skyrmion. The annihilation takes place at
boundaries by current driven motion as well as due to the excitation over
energy barriers, in the absence of currents, without forming Bloch points. It
is reported that the pinning sites, which are required to allow thermally
stable bits, significantly increase the critical current densities to move the
bits in skyrmion like structures to about $j_{crit}$ = 0.62 TA/m$^2$. These
currents are similar to those obtained experimentally to move stable skyrmions
at room temperature. By calculating the thermal stability as well as the
critical current, we can derive the spin torque efficiency $\eta$ = $\Delta/I_c
= 0.19 k_BT_{300}~/\mu$A, which is in a similar range to the simulated spin
torque efficiency of MRAM structures. Finally, it is shown that the stochastic
depinning process of any racetrack like device requires extremely narrow
depinning time distribution smaller than ~6% of the current pulse length to
reach bit error rates smaller than ${10^{ - 9}}$.",1704.08164v3
2022-10-24,Averaged Solar Torque Rotational Dynamics for Defunct Satellites,"Spin state predictions for defunct satellites in geosynchronous earth orbit
(GEO) are valuable for active debris removal and servicing missions as well as
material shedding studies and attitude-dependent solar radiation pressure (SRP)
modeling. Previous studies have shown that solar radiation torques can explain
the observed spin state evolution of some GEO objects via the
Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. These studies have focused
primarily on uniform rotation. Nevertheless, many objects are in non-principal
axis rotation (i.e. tumbling). Recent exploration of the tumbling regime for
the family of retired GOES 8-12 satellites has shown intriguing YORP-driven
behavior including spin-orbit coupling, tumbling cycles, and tumbling period
resonances. To better explore and understand the tumbling regime, we develop a
semi-analytical tumbling-averaged rotational dynamics model. The derivation
requires analytically averaging over the satellite's torque-free rotation,
defined by Jacobi elliptic functions. Averaging is facilitated by a second
order Fourier series approximation of the facet illumination function. The
averaged model is found to capture and explain the general long-term behavior
of the full dynamics while reducing computation time by roughly three orders of
magnitude. This improved computation efficiency promises to enable rapid
exploration of general long-term rotational dynamics for defunct satellites and
rocket bodies.",2210.13380v2
2023-06-10,The Central Role of Tilted Anisotropy for Field-Free Spin-Orbit Torque Switching of Perpendicular Magnetization,"The discovery of efficient magnetization switching activated by the spin Hall
effect (SHE)-induced spin-orbit torque (SOT) changed the course of magnetic
random-access memory (MRAM) research and development. However, for systems with
perpendicular magnetic anisotropy (PMA), the use of SOT is still hampered by
the necessity of a longitudinal magnetic field to break the magnetic symmetry
to achieve deterministic switching. In this work, we first demonstrate that a
robust and tunable field-free current-driven SOT switching of perpendicular
magnetization can be controlled by the growth protocol in Pt-based magnetic
heterostructures. It is further elucidated that such growth-dependent symmetry
breaking is originated from the laterally tilted magnetic anisotropy of the
ferromagnetic layer with PMA, which has been largely neglected in previous
studies and its critical role should be re-focused. We show by both experiments
and simulations that in a PMA system with tilted anisotropy, the deterministic
field-free switching possesses a conventional SHE-induced damping-like torque
feature and the resulting current-induced effective field has a non-linear
dependence on the applied current density, which could be potentially
misattributed to an unconventional SOT origin.",2306.06357v1
2023-12-22,Broken inversion symmetry in van der Waals topological ferromagnetic metal iron germanium telluride,"Inversion symmetry breaking is critical for many quantum effects and
fundamental for spin-orbit torque, which is crucial for next-generation
spintronics. Recently, a novel type of gigantic intrinsic spin-orbit torque has
been established in the topological van-der-Waals (vdW) magnet iron germanium
telluride. However, it remains a puzzle because no clear evidence exists for
interlayer inversion symmetry breaking. Here, we report the definitive evidence
of broken inversion symmetry in iron germanium telluride directly measured by
the second harmonic generation (SHG) technique. Our data show that the crystal
symmetry reduces from centrosymmetric P63/mmc to noncentrosymmetric polar P3m1
space group, giving the three-fold SHG pattern with dominant out-of-plane
polarization. Additionally, the SHG response evolves from an isotropic pattern
to a sharp three-fold symmetry upon increasing Fe deficiency, mainly due to the
transition from random defects to ordered Fe vacancies. Such SHG response is
robust against temperature, ensuring unaltered crystalline symmetries above and
below the ferromagnetic transition temperature. These findings add crucial new
information to our understanding of this interesting vdW metal, iron germanium
telluride: band topology, intrinsic spin-orbit torque and topological vdW polar
metal states.",2312.14384v1
2024-03-25,"Electrically tunable, rapid spin-orbit torque induced modulation of colossal magnetoresistance in Mn$_3$Si$_2$Te$_6$ nanoflakes","As a quasi-layered ferrimagnetic material, Mn$_3$Si$_2$Te$_6$ nanoflakes
exhibit magnetoresistance behaviour that is fundamentally different from their
bulk crystal counterparts. They offer three key properties crucial for
spintronics. Firstly, at least 10^6 times faster response comparing to that
exhibited by bulk crystals has been observed in current-controlled resistance
and magnetoresistance. Secondly, ultra-low current density is required for
resistance modulation (~ 5 A/cm$^2$). Thirdly, electrically gate-tunable
magnetoresistance has been realized. Theoretical calculations reveal that the
unique magnetoresistance behaviour in the Mn$_3$Si$_2$Te$_6$ nanoflakes arises
from a magnetic field induced band gap shift across the Fermi level. The rapid
current induced resistance variation is attributed to spin-orbit torque, an
intrinsically ultra-fast process (~nanoseconds). This study suggests promising
avenues for spintronic applications. In addition, it highlights
Mn$_3$Si$_2$Te$_6$ nanoflakes as a suitable platform for investigating the
intriguing physics underlying chiral orbital moments, magnetic field induced
band variation and spin torque.",2403.16684v1
2000-11-16,The nature of dwarf nova outbursts,"We show that if the dwarf-nova disc instability model includes the effects of
heating by stream impact and tidal torque dissipation in the outer disc, the
calculated properties of dwarf-nova outbursts change considerably, and several
notorious deficiencies of this model are repaired. In particular: (1)
outside-in outbursts occur for mass transfer rates lower than in the standard
model as required by observations; (2) the presence of long (wide) and short
(narrow) outbursts with similar peak luminosities is a natural property of the
model. Mass-transfer fluctuations by factors ~ 2 can explain the occurrence of
both long and short outbursts above the cataclysmic variable period gap,
whereas below 2 hr only short normal outbursts are expected (in addition to
superoutbursts which are not dealt with in this article). With additional
heating by the stream and tidal torques, such fluctuations can also explain the
occurrence of both outside-in and inside-out outbursts in SS Cyg and similar
systems. The occurrence of outside-in outbursts in short orbital-period, low
mass-transfer-rate systems requires the disc to be much smaller than the
tidal-truncation radius. In this case the recurrence time of both inside-out
and outside-in outbursts have a similar dependence on the mass-transfer rate.",0011312v1
2010-11-15,Source to Accretion Disk Tilt,"Many different system types retrogradely precess, and retrograde precession
could be from a tidal torque by the secondary on a misaligned accretion disk.
However, a source to cause and maintain disk tilt is unknown. In this work, we
show that accretion disks can tilt due to a force called lift. Lift results
from differing gas stream supersonic speeds over and under an accretion disk.
Because lift acts at the disk's center of pressure, a torque is applied around
a rotation axis passing through the disk's center of mass. The disk responds to
lift by pitching around the disk's line of nodes. If the gas stream flow ebbs,
then lift also ebbs and the disk attempts to return to its original
orientation.
  To first approximation, lift does not depend on magnetic fields or radiation
sources but does depend on mass and the surface area of the disk. Also, for
disk tilt to be initiated, a minimum mass transfer rate must be exceeded. For
example, a $10^{-11}M_{\odot}$ disk around a 0.8$M_{\odot}$ compact central
object requires a mass transfer rate greater than
$\sim10^{-13}$M$_{\odot}$yr$^{-1}$, a value well below known mass transfer
rates in Cataclysmic Variable Dwarf Novae systems that retrogradely precess and
that exhibit negative superhumps in their light curves and a value well below
mass transfer rates in protostellar forming systems.",1011.3282v1
2009-09-22,Spin Hall and longitudinal conductivity of a conserved spin current in two dimensional heavy-hole gases,"The spin Hall and longitudinal conductivity of a 2D heavy-hole gas with {\it
k}-cubic Rashba and Dresselhaus spin-orbit interaction is studied in the ac
frequency domain. Using Kubo linear-response theory and a recently proposed
definition for the (conserved) spin current operator suitable for spin-3/2
holes, it is shown that the spin conductivity tensor exhibit very
distinguishable features from those obtained with the standard definition of
the spin current. This is due to a significant contribution of the spin-torque
term arisen from the alternative definition of spin current which strongly
affects the magnitude and the sign of the dynamic spin current. In the dc (free
of disorder) limit, the spin Hall conductivity for only (or dominant) {\it
k}-cubic Rashba coupling is $\sigma^{s,z}_{xy}(0)=-9e/8\pi$, whereas
$\sigma^{s,z}_{xy}(0)=-3e/8\pi$ for only (or dominant) {\it k}-cubic
Dresselhaus coupling. Such anisotropic response is understood in terms of the
absence of mapping the {\it k}-cubic Rashba $\leftrightarrow$ Dresselhaus
Hamiltonians. This asymmetry is also responsible for the non-vanishing dc spin
Hall conductivity ($\sigma^{s,z}_{xy}(0)=-6e/8\pi$) when the Rashba and
Dresselhaus parameters have the same strength, in contrast with its
corresponding case for electrons. These results are of relevance to validate
the alternative definition of spin-current through measurements in the
frequency domain of the spin accumulation and/or spin currents in 2D hole
gases.",0909.4045v3
2014-11-24,Manipulating Femtosecond Spin--Orbit Torques with Laser Pulse Sequences to Control Magnetic Memory States and Ringing,"Femtosecond (fs) coherent control of collective order parameters is important
for non--equilibrium phase dynamics in correlated materials. Here we propose a
possible scheme for fs control of a ferromagnetic order parameter based on
non--adiabatic optical manipulation of electron--hole ($e$--$h$)
photoexcitations between spin--orbit--coupled bands that are exchange--split by
magnetic interaction with local spins. We photoexcite fs carrier spin--pulses
with controllable direction and time profile without using
circularly--polarized light, via time--reversal symmetry--breaking by
non--perturbative interplay between spin--orbit and magnetic exchange coupling
of coherent photocarriers. We manipulate photoexcited {\em fs spin--orbit
torques} to control complex switching pathways of the magnetization between
multiple magnetic memory states. We calculate the photoinduced fs magnetic
anisotropy in the time domain by using density matrix equations of motion
rather than the quasi--equilibrium free energy. By comparing to pump--probe
experiments, we identify a ""sudden"" magnetization canting induced by laser
excitation, which displays magnetic hysteresis absent in static
magneto--optical measurements and agrees with switchings measured by Hall
magnetoresistivity. The fs magnetization canting switches direction with
magnetic state and laser frequency, which distinguishes it from nonlinear
optical and demagnetization longitudinal effects. By shaping two--color
laser--pulse sequences analogous to multi--dimensional Nuclear Magnetic
Resonance (NMR) spectroscopy, we show that sequences of clockwise or
counter--clockwise fs spin--orbit torques can enhance or suppress magnetic
ringing and switching rotation at any desired time. We propose protocols that
can provide controlled access to four magnetic states via consequative 90$^{o}$
switchings.",1411.6662v1
2018-11-21,Strong Rashba-Edelstein Effect-Induced Spin-Orbit Torques in Monolayer Transition-Metal Dichalcogenide/Ferromagnet Bilayers,"The electronic and optoelectronic properties of two dimensional materials
have been extensively explored in graphene and layered transition metal
dichalcogenides (TMDs). Spintronics in these two-dimensional materials could
provide novel opportunities for future electronics, for example, efficient
generation of spin current, which should enable the efficient manipulation of
magnetic elements. So far, the quantitative determination of charge current
induced spin current and spin-orbit torques (SOTs) on the magnetic layer
adjacent to two-dimensional materials is still lacking. Here, we report a large
SOT generated by current-induced spin accumulation through the Rashba-Edelstein
effect in the composites of monolayer TMD (MoS$_2$ or WSe$_2$)/CoFeB bilayer.
The effective spin conductivity corresponding to the SOT turns out to be almost
temperature-independent. Our results suggest that the charge-spin conversion in
the chemical vapor deposition-grown large-scale monolayer TMDs could
potentially lead to high energy efficiency for magnetization reversal and
convenient device integration for future spintronics based on two-dimensional
materials.",1811.08583v1
2020-04-01,Interlayer exchange coupling through Ir-doped Cu spin Hall material,"Metallic superlattices where the magnetization vectors in the adjacent
ferromagnetic layers are antiferromagnetically coupled by the interlayer
exchange coupling through nonmagnetic spacer layers are systems available for
the systematic study on antiferromagnetic (AF) spintronics. As a candidate of
nonmagnetic spacer layer material exhibiting remarkable spin Hall effect, which
is essential to achieve spin-orbit torque switching, we selected the Ir-doped
Cu in this study. The AF-coupling for the Co / Cu$_{95}$Ir$_{5}$ / Co was
investigated, and was compared with those for the Co / Cu / Co and Co / Ir /
Co. The maximum magnitude of AF-coupling strength was obtained to be 0.39
mJ/m$^{2}$ at the Cu$_{95}$Ir$_{5}$ thickness of about 0.75 nm. Furthermore, we
found a large spin Hall angle of Cu$_{95}$Ir$_{5}$ in Co / Cu$_{95}$Ir$_{5}$
bilayers by carrying out spin Hall magnetoresistance and harmonic Hall voltage
measurements, which are estimated to be 3 ~ 4 %. Our experimental results
clearly indicate that Cu$_{95}$Ir$_{5}$ is a nonmagnetic spacer layer allowing
us to achieve moderately strong AF-coupling and to generate appreciable
spin-orbit torque via the spin Hall effect.",2004.00739v1
2020-04-24,Strong interfacial exchange field in a heavy metal/ferromagnetic insulator system determined by spin Hall magnetoresistance,"Spin-dependent transport at heavy metal/magnetic insulator interfaces is at
the origin of many phenomena at the forefront of spintronics research. A proper
quantification of the different interfacial spin conductances is crucial for
many applications. Here, we report the first measurement of the spin Hall
magnetoresistance (SMR) of Pt on a purely ferromagnetic insulator (EuS). We
perform SMR measurements in a wide range of temperatures and fit the results by
using a microscopic model. From this fitting procedure we obtain the
temperature dependence of the spin conductances ($G_s$, $G_r$ and $G_i$),
disentangling the contribution of field-like torque ($G_i$), damping-like
torque ($G_r$), and spin-flip scattering ($G_s$). An interfacial exchange field
of the order of 1 meV acting upon the conduction electrons of Pt can be
estimated from $G_i$, which is at least three times larger than $G_r$ below the
Curie temperature. Our work provides an easy method to quantify this
interfacial spin-splitting field, which play a key role in emerging fields such
as superconducting spintronics and caloritronics, and topological quantum
computation.",2004.12009v2
2021-07-09,Magnetoelectric torque and edge currents caused by spin-orbit coupling,"Using a tight-biding model, we elaborate that the previously discovered
out-of-plane polarized helical edge spin current caused by Rashba spin-orbit
coupling can be attributed to the fact that in a strip geometry, a positive
momentum eigenstate does not always have the same spin polarization at the edge
as the corresponding negative momentum eigenstate. In addition, in the presence
of a magnetization pointing perpendicular to the edge, an edge charge current
is produced, which can be chiral or nonchiral depending on whether the
magnetization lies in-plane or out-of-plane. The spin polarization near the
edge develops a transverse component orthogonal to the magnetization, which is
antisymmetric between the two edges and tends to cause a noncollinear magnetic
order between the two edges. If the magnetization only occupies a region near
one edge, or in an irregular shaped quantum dot, this transverse component has
a nonzero average, rendering a gate voltage-induced magnetoelectric torque
without the need of a bias voltage. We also argue that other types of
spin-orbit coupling that can be obtained from the Rashba type through a unitary
transformation, such as the Dresselhaus spin-orbit coupling, will have similar
effects too.",2107.04665v2
2021-09-07,Exploring tidal obliquity variations with SMERCURY-T,"We introduce our new code, SMERCURY-T, which is based on existing codes
SMERCURY (Lissauer et al. 2012) and Mercury-T (Bolmont et al. 2015). The result
is a mixed-variable symplectic N-body integrator that can compute the orbital
and spin evolution of a planet within a multi-planet system under the influence
of tidal spin torques from its star. We validate our implementation by
comparing our experimental results to that of a secular model. As we
demonstrate in a series of experiments, SMERCURY-T allows for the study of
secular spin-orbit resonance crossings and captures for planets within complex
multi-planet systems. These processes can drive a planet's spin state to evolve
along vastly different pathways on its road toward tidal equilibrium, as tidal
spin torques dampen the planet's spin rate and evolve its obliquity.
Additionally, we show the results of a scenario that exemplifies the crossing
of a chaotic region that exists as the overlap of two spin-orbit resonances.
The test planet experiences violent and chaotic swings in its obliquity until
its eventual escape from resonance as it tidally evolves. All of these
processes are and have been important over the obliquity evolution of many
bodies within the Solar System and beyond, and have implications for planetary
climate and habitability. SMERCURY-T is a powerful and versatile tool that
allows for further study of these phenomena.",2109.03347v1
2021-12-16,Parametric resonance of spin waves in ferromagnetic nanowires tuned by spin Hall torque,"We present a joint experimental and theoretical study of parametric resonance
of spin wave eigenmodes in Ni$_{80}$Fe$_{20}$/Pt bilayer nanowires. Using
electrically detected magnetic resonance, we measure the spectrum of spin wave
eigenmodes in transversely magnetized nanowires and study parametric excitation
of these eigenmodes by a microwave magnetic field. We also develop an
analytical theory of spin wave eigenmodes and their parametric excitation in
the nanowire geometry that takes into account magnetic dilution at the nanowire
edges. We measure tuning of the parametric resonance threshold by antidamping
spin Hall torque from a direct current for the edge and bulk eigenmodes, which
allows us to independently evaluate frequency, damping and ellipticity of the
modes. We find good agreement between theory and experiment for parametric
resonance of the bulk eigenmodes but significant discrepancies arise for the
edge modes. The data reveals that ellipticity of the edge modes is
significantly lower than expected, which can be attributed to strong
modification of magnetism at the nanowire edges. Our work demonstrates that
parametric resonance of spin wave eigenmodes is a sensitive probe of magnetic
properties at edges of thin-film nanomagnets.",2112.09222v1
2023-08-16,Deterministic Spin-Orbit Torque Switching of Mn3Sn with the Interplay between Spin Polarization and Kagome Plane,"Previous studies have demonstrated spin-orbit torque (SOT) switching of Mn3Sn
where the spin polarization lies in the kagome plane (configuration I).
However, the critical current density ($ J_{crit}$) is unrealistically large ($
J_{crit}$=$ 10^{14}$ A/$ m^2$) and independent on the external field ($
H_{ext}$). The stabilized magnetic state also depends on the initial state.
These features conflict with the ferromagnet (FM) switching scheme as claimed
in those studies, and thus call for other explanations. Alternatively, the
system with the spin polarization perpendicular to the kagome plane
(configuration II) is more like the FM based system since the spin polarization
is orthogonal to all magnetic moments. In this work, we show SOT switching of
Mn3Sn in configuration II. Similar to the FM, Jcrit and Hext are in the order
of $ 10^{10}$ A/$ m^2$ and hundreds of Oersted, respectively. The switching
result is also independent of the initial state. Interestingly, the unique spin
structure of Mn3Sn also leads to distinct features from FM systems. We
demonstrate that Jcrit increases linearly with Hext, and extrapolation gives
ultralow $ J_{crit}$ for the field-free switching system. In addition, the
switching polarity is opposite to the FM. We also provide the switching phase
diagram as a guideline for experimental demonstration. Our work provides
comprehensive understanding for the switching mechanism in both configurations.
The switching protocol proposed in this work is more advantageous in realistic
spintronic applications. We also clearly reveal the fundamental difference
between FM and noncollinear antiferromagnetic switching.",2308.08091v1
2012-10-10,Bodily tides near the 1:1 spin-orbit resonance. Correction to Goldreich's dynamical model,"Spin-orbit coupling is often described in the ""MacDonald torque"" approach
which has become the textbook standard. Within this method, a concise
expression for the additional tidal potential, derived by MacDonald (1964; Rev.
Geophys. 2, 467), is combined with an assumption that the Q factor is
frequency-independent (i.e., that the geometric lag angle is constant in time).
This makes the approach unphysical because MacDonald's derivation of the said
formula was implicitly based on keeping the time lag frequency-independent,
which is equivalent to setting Q to scale as the inverse tidal frequency. The
contradiction requires the MacDonald treatment of both non-resonant and
resonant rotation to be rewritten.
  The non-resonant case was reconsidered by Efroimsky & Williams (2009; CMDA
104, 257), in application to spin modes distant from the major
commensurabilities. We continue this work by introducing the necessary
alterations into the MacDonald-torque-based model of falling into a 1:1
resonance. (For the original version of the model, see Goldreich 1966; AJ 71,
1.)
  We also study the effect of the triaxiality on both circulating and librating
rotation near the synchronous state. Circulating rotation may evolve toward the
libration region or toward a spin rate larger than synchronous
(pseudosynchronous spin). Which behaviour depends on the eccentricity, the
triaxiality of the primary, and the mass ratio of the secondary and primary
bodies. The spin evolution will always stall for the oblate case. For
small-amplitude librations, expressions are derived for the libration
frequency, damping rate, and average orientation.
  However, the stability of pseudosynchronous spin hinges upon the dissipation
model. Makarov and Efroimsky (2012; arXiv:1209.1616) have found that a more
realistic dissipation model than the corrected MacDonald torque makes
pseudosynchronous spin unstable.",1210.2923v3
2019-04-05,Halo Spin from Primordial Inner Motions,"The standard explanation for galaxy spin starts with the tidal-torque theory
(TTT), in which an ellipsoidal dark-matter protohalo, which comes to host the
galaxy, is torqued up by the tidal gravitational field around it. We discuss a
complementary picture, using the relatively familiar velocity field, instead of
the tidal field, whose intuitive connection to the surrounding, possibly
faraway matter arrangement is more obscure. In this 'spin from primordial inner
motions' (SPIM) concept, implicit in TTT derivations but not previously
emphasized, the angular momentum from the gravity-sourced velocity field inside
a protohalo largely cancels out, but has some excess from the aspherical
outskirts. At first, the net spin scales according to linear theory, a sort of
comoving conservation of familiar angular momentum. Then, at collapse, it is
conserved in physical coordinates. Small haloes are then typically subject to
secondary exchanges of angular momentum. The TTT is useful for analytic
estimates. But a literal interpretation of the TTT is inaccurate in detail,
without some implicit concepts about smoothing of the velocity and tidal
fields. This could lead to misconceptions, for those first learning about how
galaxies come to spin. Protohaloes are not perfectly ellipsoidal and do not
uniformly torque up, as in a naive interpretation of the TTT; their inner
velocity fields retain substantial dispersion. Furthermore, quantitatively,
given initial conditions and protohalo boundaries, SPIM is more direct and
accurate than the TTT to predict halo spins. We also discuss how SPIM applies
to rotating filaments, and the relation between halo mass and spin, in which
the total spin of a halo can be thought of as a sum of random contributions.",1904.03201v3
2023-02-03,Towards Quantum Sensing of Chiral-Induced Spin Selectivity: Probing Donor-Bridge-Acceptor Molecules with NV Centers in Diamond,"Photoexcitable donor-bridge-acceptor (D-B-A) molecules that support
intramolecular charge transfer are ideal platforms to probe the influence of
chiral-induced spin selectivity (CISS) in electron transfer and resulting
radical pairs. In particular, the extent to which CISS influences spin
polarization or spin coherence in the initial state of spin-correlated radical
pairs following charge transfer through a chiral bridge remains an open
question. Here, we introduce a quantum sensing scheme to measure directly the
hypothesized spin polarization in radical pairs using shallow nitrogen-vacancy
(NV) centers in diamond at the single- to few-molecule level. Importantly, we
highlight the perturbative nature of the electron spin-spin dipolar coupling
within the radical pair, and demonstrate how Lee-Goldburg decoupling can
preserve spin polarization in D-B-A molecules for enantioselective detection by
a single NV center. The proposed measurements will provide fresh insight into
spin selectivity in electron transfer reactions.",2302.01725v1
2007-03-17,Large-amplitude coherent spin waves exited by spin-polarized current in nanoscale spin valves,"We present spectral measurements of spin-wave excitations driven by direct
spinpolarized current in the free layer of nanoscale
Ir20Mn80/Ni80Fe20/Cu/Ni80Fe20 spin valves. The measurements reveal that
large-amplitude coherent spin wave modes are excited over a wide range of bias
current. The frequency of these excitations exhibits a series of jumps as a
function of current due to transitions between different localized nonlinear
spin wave modes of the Ni80Fe20 nanomagnet. We find that micromagnetic
simulations employing the Landau-Lifshitz-Gilbert equation of motion augmented
by the Slonczewski spin torque term (LLGS) accurately describe the frequency of
the current-driven excitations including the mode transition behavior. However
LLGS simulations give qualitatively incorrect predictions for the amplitude of
excited spin waves as a function of current.",0703458v2
2007-11-14,Non-Abelian gauge field effects and its relevance to spinning particle dynamics in the technology of spintronics,"We describe formally the precession of spin vector about the k-space
effective magnetic field in condensed matter system with spin orbital effects
as constituting a local transformation of the electron wavefunction which
necessarily invokes the SU(2) transformation rule to ensure covariance. We
showed a ""no-precession"" condition as pre-requisite for the spin gauge field to
exert its influence on spin particle motion. The effects of the spin gauge
field on spin particle motion were shown to be consistent in both classical and
quantum pictures, which hence should underpin theoretical explanations for
important effects in anomalous Hall, spin Hall, spin torque, optical Magnus,
geometric quantum computation.",0711.2120v1
2008-03-25,Quantum dissipative Rashba spin ratchets,"We predict the possibility to generate a finite stationary spin current by
applying an unbiased ac driving to a quasi-one-dimensional asymmetric periodic
structure with Rashba spin-orbit interaction and strong dissipation. We show
that under a finite coupling strength between the orbital degrees of freedom
the electron dynamics at low temperatures exhibits a pure spin ratchet
behavior, {\it i.e.} a finite spin current and the absence of charge transport
in spatially asymmetric structures. It is also found that the equilibrium spin
currents are not destroyed by the presence of strong dissipation.",0803.3526v2
2012-12-15,Transverse spin gradient functional for non-collinear spin density functional theory,"We present a novel functional for spin density functional theory aiming at
the description of non-collinear magnetic structures. The construction of the
functional employs the spin-spiral-wave state of the uniform electron gas as
reference system. We show that the functional depends on transverse gradients
of the spin magnetization, i.e., in contrast to the widely used local spin
density approximation, the functional is sensitive to local changes of the
direction of the spin magnetization. As a consequence the exchange-correlation
magnetic field is not parallel to the spin magnetization and a local
spin-torque is present in the ground state of the Kohn-Sham system. As a
proof-of-principle we apply the functional to a Chromium mono-layer in the
non-collinear ${120^{\circ}}$-N{\'e}el state.",1212.3658v2
2014-07-20,Spintronic magnetic anisotropy,"An attractive feature of magnetic adatoms and molecules for nanoscale
applications is their superparamagnetism, the preferred alignment of their spin
along an easy axis preventing undesired spin reversal. The underlying magnetic
anisotropy barrier --a quadrupolar energy splitting-- is internally generated
by spin-orbit interaction and can nowadays be probed by electronic transport.
Here we predict that in a much broader class of quantum-dot systems with spin
larger than one-half, superparamagnetism may arise without spin-orbit
interaction: by attaching ferromagnets a spintronic exchange field of
quadrupolar nature is generated locally. It can be observed in conductance
measurements and surprisingly leads to enhanced spin filtering even in a state
with zero average spin. Analogously to the spintronic dipolar exchange field,
responsible for a local spin torque, the effect is susceptible to electric
control and increases with tunnel coupling as well as with spin polarization.",1407.5273v1
2015-05-01,Spin-charge transport driven by magnetization dynamics on disordered surface of doped topological insulators,"We theoretically study the spin and charge generation along with the electron
transport on a disordered surface of a doped three-dimensional topological
insulator/magnetic insulator junction by using Green's function techniques. We
find that the spin and charge current are induced by not only local but also
nonlocal magnetization dynamics through nonmagnetic impurity scattering on the
disordered surface of the doped topological insulator. We also clarify that the
spin current as well as charge density are induced by spatially inhomogeneous
magnetization dynamics, and the spin current diffusively propagates on the
disordered surface. Using these results, we discuss both local and nonlocal
spin torques before and after the spin and spin current generation on the
surface, and provide a procedure to detect the spin current.",1505.00106v1
2016-09-26,Relativistic theory of spin relaxation mechanisms in the Landau-Lifshitz-Gilbert equation of spin dynamics,"Starting from the Dirac-Kohn-Sham equation we derive the relativistic
equation of motion of spin angular momentum in a magnetic solid under an
external electromagnetic field. This equation of motion can be written in the
form of the well-known Landau-Lifshitz-Gilbert equation for a harmonic external
magnetic field, and leads to a more general magnetization dynamics equation for
a general time-dependent magnetic field. In both cases with an electronic
spin-relaxation term which stems from the spin-orbit interaction. We thus
rigorously derive, from fundamental principles, a general expression for the
anisotropic damping tensor which is shown to contain an isotropic Gilbert
contribution as well as an anisotropic Ising-like and a chiral,
Dzyaloshinskii-Moriya-like contribution. The expression for the spin relaxation
tensor comprises furthermore both electronic interband and intraband
transitions. We also show that when the externally applied electromagnetic
field possesses spin angular momentum, this will lead to an optical spin torque
exerted on the spin moment.",1609.07901v1
2018-03-01,Interface-generated spin currents,"Transport calculations based on ab-initio band structures reveal large
interface-generated spin currents at Co/Pt, Co/Cu, and Pt/Cu interfaces. These
spin currents are driven by in-plane electric fields but flow out-of-plane, and
can have similar strengths to spin currents generated by the spin Hall effect
in bulk Pt. Each interface generates spin currents with polarization along
$\bf{\hat{z}} \times \bf{E}$, where $\bf{\hat{z}}$ is the interface normal and
$\bf{E}$ denotes the electric field. The Co/Cu and Co/Pt interfaces
additionally generate spin currents with polarization along $\bf{\hat{m}}
\times (\bf{\hat{z}} \times \bf{E})$, where $\bf{\hat{m}}$ gives the
magnetization direction of Co. The latter spin polarization is controlled
by---but not aligned with---the magnetization, providing a novel mechanism for
generating spin torques in magnetic trilayers.",1803.00593v1
2018-07-03,Large spin current generation by the spin Hall effect in mixed crystalline phase Ta thin films,"Manipulation of the magnetization in heavy-metal/ferromagnetic bilayers via
the spin-orbit torque requires high spin Hall conductivity of the heavy metal.
We measure inverse spin Hall voltage using a co-planar wave-guide based
broadband ferromagnetic resonance set-up in Py/Ta system with varying
crystalline phase of Ta. We demonstrate a strong correlation between the
measured spin mixing conductance and spin Hall conductivity with the
crystalline phase of Ta thin films. We found a large spin Hall conductivity of
$-2439~(\hbar/e)~\Omega^{-1}$cm$^{-1}$ for low-resistivity (68 $\mu\Omega-$cm)
Ta film having mixed crystalline phase, which we attribute to an extrinsic
mechanism of the spin Hall effect.",1807.01127v1
2019-06-26,Fermi Level Dependent Spin Pumping from a Magnetic Insulator into a Topological Insulator,"Topological spintronics aims to exploit the spin-momentum locking in the
helical surface states of topological insulators for spin-orbit torque devices.
We address a fundamental question that still remains unresolved in this
context: does the topological surface state alone produce the largest values of
spin-charge conversion efficiency or can the strongly spin-orbit coupled bulk
states also contribute significantly? By studying the Fermi level dependence of
spin pumping in topological insulator/ferrimagnetic insulator bilayers, we show
that the spin Hall conductivity is constant when the Fermi level is tuned
across the bulk band gap, consistent with a full bulk band calculation. The
results suggest a new perspective, wherein ""bulk-surface correspondence"" allows
spin-charge conversion to be simultaneously viewed either as coming from the
full bulk band, or from spin-momentum locking of the surface state.",1906.11116v1
2021-08-12,Theory of spin-charge-coupled transport in proximitized graphene: An SO(5) algebraic approach,"Establishing the conditions under which orbital, spin and lattice-pseudospin
degrees of freedom are mutually coupled in realistic nonequilibrium conditions
is a major goal in the emergent field of graphene spintronics. Here, we use
linear-response theory to obtain a unified microscopic description of spin
dynamics and coupled spin-charge transport in graphene with an
interface-induced Bychkov-Rashba effect. Our method makes use of an SO(5)
extension of the familiar inverse-diffuson approach to obtain a quantum kinetic
equation for the single-particle density matrix that treats spin and pseudospin
on equal footing and is valid for arbitrary external perturbations. As an
application of the formalism, we derive a complete set of drift-diffusion
equations for proximitized graphene with scalar impurities in the presence of
electric and spin-injection fields which vary slowly in space and time. Our
approach is amenable to a wide variety of generalizations, including the study
of coupled spin-charge dynamics in layered materials with strong spin-valley
coupling and spin-orbit torques in van der Waals heterostructures.",2108.05559v2
2022-08-02,Finite-frequency spin conductance of a ferro-/ferrimagnetic-insulator|normal-metal interface,"The interface between a ferro-/ferrimagnetic insulator and a normal metal can
support spin currents polarized collinear with and perpendicular to the
magnetization direction. The flow of angular momentum perpendicular to the
magnetization direction (""transverse"" spin current) takes place via spin torque
and spin pumping. The flow of angular momentum collinear with the magnetization
(""longitudinal"" spin current) requires the excitation of magnons. In this
article we extend the existing theory of longitudinal spin transport [Bender
and Tserkovnyak, Phys. Rev. B 91, 140402(R) (2015)] in the zero-frequency
weak-coupling limit in two directions: We calculate the longitudinal spin
conductance non-perturbatively (but in the low-frequency limit) and at finite
frequency (but in the limit of low interface transparency). For the
paradigmatic spintronic material system YIG|Pt, we find that non-perturbative
effects lead to a longitudinal spin conductance that is ca. 40% smaller than
the perturbative limit, whereas finite-frequency corrections are relevant at
low temperatures < 100 K only, when only few magnon modes are thermally
occupied.",2208.01420v1
2023-11-14,Spin Speed and Supportedness Correlation and Evolution of Galaxy-Halo Systems,"Galaxy angular momenta (spins) contain valuable cosmological information,
complementing with their positions and velocities. The baryonic spin direction
of galaxies have been probed as a reliable tracer of their host halos and the
primordial spin modes. Here we use the TNG100 simulation of the IllustrisTNG
project to study the spin magnitude correlations between dark matter, gas and
stellar components of galaxy-halo systems, and their evolutions across the
cosmic history. We find that these components generate similar initial spin
magnitudes from the same tidal torque in Lagrangian space. At low redshifts,
the gas component still traces the spin magnitude of dark matter halo and the
primordial spin magnitude. However, the traceability of stellar component
depends on the $ex$ $situ$ stellar mass fraction, $f_{\rm acc}$. Our results
suggest that the galaxy baryonic spin magnitude can also serve as a tracer of
their host halo and the initial perturbations, and the similarity of their
evolution histories affects the galaxy-halo correlations.",2311.07969v1
2017-12-15,Acoustic radiation force and torque on a viscous fluid cylindrical particle nearby a planar rigid wall,"This work presents an analytical formalism for the modal series expansions of
the acoustic radiation force and radiation torque experienced by a fluid
viscous cylindrical object of arbitrary geometrical cross-section placed near a
planar rigid wall. A plane progressive wave field with an arbitrary angle of
incidence propagating in an inviscid fluid is assumed. Initially, an effective
field incident on the particle (including the principal incident field, the
reflected wave-field from the boundary and the scattered field from the image
object) is defined. Subsequently, the incident effective field is utilized in
conjunction with the scattered one from the object, to obtain closed-form
expansions for the longitudinal and transversal force components, in addition
to the axial torque component, based on the scattering in the far-field. The
obtained solutions involve the angle of incidence, the modal coefficients of
the scatterer and its image, and the particle-wall distance. Computations are
considered, and calculations exemplify the analysis with emphasis on changing
the particle size, the particle-wall distance and the angle of incidence. It is
found that the object experiences either an attractive or repulsive force
directed toward or away from the boundary. Moreover, it reverses its rotation
around its center of mass depending on its size, particle-wall distance and
angle of incidence. Furthermore, radiation force and torque singularities occur
(i.e., zero force and torque) such that the cylinder becomes irresponsive to
the linear and angular momenta transfer yielded by the effective field. The
exact formalism presented here using the multipole expansion method, which is
valid for any frequency range, could be used to validate other approaches using
purely numerical methods, or frequency-limiting approximate models such as the
Rayleigh and the Kirchhoff regimes.",1801.04863v1
2011-04-30,Robustness of spin-coupling distributions for perfect quantum state transfer,"The transmission of quantum information between different parts of a quantum
computer is of fundamental importance. Spin chains have been proposed as
quantum channels for transferring information. Different configurations for the
spin couplings were proposed in order to optimize the transfer. As
imperfections in the creation of these specific spin-coupling distributions can
never be completely avoided, it is important to find out which systems are
optimally suited for information transfer by assessing their robustness against
imperfections or disturbances. We analyze different spin coupling distributions
of spin chain channels designed for perfect quantum state transfer. In
particular, we study the transfer of an initial state from one end of the chain
to the other end. We quantify the robustness of different coupling
distributions against perturbations and we relate it to the properties of the
energy eigenstates and eigenvalues. We find that the localization properties of
the systems play an important role for robust quantum state transfer.",1105.0071v1
2005-07-05,Torus Formation in Neutron Star Mergers and Well-Localized Short Gamma-Ray Bursts,"Merging neutron stars (NSs) are hot candidates for the still enigmatic
sources of short gamma-ray bursts (GRBs). If the central engines of the huge
energy release are accreting relic black holes (BHs) of such mergers, it is
important to understand how the properties of the BH-torus systems, in
particular disc masses and mass and rotation rate of the compact remnant, are
linked to the characterizing parameters of the NS binaries. For this purpose we
present relativistic smoothed particle hydrodynamics simulations with
conformally flat approximation of the Einstein field equations and a physical,
non-zero temperature equation of state. Thick disc formation is highlighted as
a dynamical process caused by angular momentum transfer through tidal torques
during the merging process of asymmetric systems or in the rapidly spinning
triaxial post-merger object. Our simulations support the possibility that the
first well-localized short and hard GRBs 050509b, 050709, 050724, 050813 have
originated from NS merger events and are powered by neutrino-antineutrino
annihilation around a relic BH-torus system. Using model parameters based on
this assumption, we show that the measured GRB energies and durations lead to
estimates for the accreted masses and BH mass accretion rates which are
compatible with theoretical expectations. In particular, the low energy output
and short duration of GRB 050509b set a very strict upper limit of less than
100 ms for the time interval after the merging until the merger remnant has
collapsed to a BH, leaving an accretion torus with a small mass of only about
0.01 solar masses. This favors a (nearly) symmetric NS+NS binary with a typical
mass as progenitor system.",0507099v2
2012-04-04,Circumbinary MHD Accretion into Inspiraling Binary Black Holes,"As 2 black holes bound to each other in a close binary approach merger their
inspiral time becomes shorter than the characteristic inflow time of
surrounding orbiting matter. Using an innovative technique in which we
represent the changing spacetime in the region occupied by the orbiting matter
with a 2.5PN approximation and the binary orbital evolution with 3.5PN, we have
simulated the MHD evolution of a circumbinary disk surrounding an equal-mass
non-spinning binary. Prior to the beginning of the inspiral, the structure of
the circumbinary disk is predicted well by extrapolation from Newtonian
results. The binary opens a low-density gap whose radius is roughly two binary
separations, and matter piles up at the outer edge of this gap as inflow is
retarded by torques exerted by the binary; nonetheless, the accretion rate is
diminished relative to its value at larger radius by only about a factor of 2.
During inspiral, the inner edge of the disk at first moves inward in
coordination with the shrinking binary, but as the orbital evolution
accelerates, the rate at which the inner edge moves toward smaller radii falls
behind the rate of binary compression. In this stage, the rate of angular
momentum transfer from the binary to the disk slows substantially, but the net
accretion rate decreases by only 10-20%. When the binary separation is tens of
gravitational radii, the rest-mass efficiency of disk radiation is a few
percent, suggesting that supermassive binary black holes in galactic nuclei
could be very luminous at this stage of their evolution. If the luminosity were
optically thin, it would be modulated at a frequency that is a beat between the
orbital frequency of the disk's surface density maximum and the binary orbital
frequency. However, a disk with sufficient surface density to be luminous
should also be optically thick; as a result, the periodic modulation may be
suppressed.",1204.1073v1
2015-09-28,"Yield, Area and Energy Optimization in Stt-MRAMs using failure aware ECC","Spin Transfer Torque MRAMs are attractive due to their non-volatility, high
density and zero leakage. However, STT-MRAMs suffer from poor reliability due
to shared read and write paths. Additionally, conflicting requirements for data
retention and write-ability (both related to the energy barrier height of the
magnet) makes design more challenging. Furthermore, the energy barrier height
depends on the physical dimensions of the free layer. Any variations in the
dimensions of the free layer lead to variations in the energy barrier height.
In order to address poor reliability of STT-MRAMs, usage of Error Correcting
Codes (ECC) have been proposed. Unlike traditional CMOS memory technologies,
ECC is expected to correct both soft and hard errors in STT_MRAMs. To achieve
acceptable yield with low write power, stronger ECC is required, resulting in
increased number of encoded bits and degraded memory efficiency. In this paper,
we propose Failure aware ECC (FaECC), which masks permanent faults while
maintaining the same correction capability for soft errors without increased
encoded bits. Furthermore, we investigate the impact of process variations on
run-time reliability of STT-MRAMs. We provide an analysis on the impact of
process variations on the life-time of the free layer and retention failures.
In order to analyze the effectiveness of our methodology, we developed a
cross-layer simulation framework that consists of device, circuit and array
level analysis of STT-MRAM memory arrays. Our results show that using FaECC
relaxes the requirements on the energy barrier height, which reduces the write
energy and results in smaller access transistor size and memory array area.
Keywords: STT-MRAM, reliability, Error Correcting Codes, ECC, magnetic memory",1509.08806v2
2020-11-04,Unveiling temperature dependence mechanisms of perpendicular magnetic anisotropy at Fe/MgO interfaces,"The perpendicular magnetic anisotropy (PMA) at magnetic transition
metal/oxide interfaces is a key element in building out-of-plane magnetized
magnetic tunnel junctions for spin-transfer-torque magnetic random access
memory (STT-MRAM). Size downscaling renders magnetic properties more sensitive
to thermal effects. Thus, understanding the temperature dependence of the
magnetic anisotropy is crucial. In this work, we theoretically address the
correlation between temperature dependence of PMA and magnetization in typical
Fe/MgO-based structures. In particular, the possible mechanisms behind the
experiments reporting deviations from the Callen and Callen scaling power law
are analyzed. At ideal interfaces, first-principles calculations reveal (i)
small high-order anisotropy constants compared to first order and (ii) enhanced
exchange constants. Considering these two intrinsic effects in the atomistic
simulations, the temperature-dependence of the total and layer-resolved
anisotropy are found to follow the Callen and Callen scaling power law, thus
ruling out an intrinsic microscopic mechanism underlying deviations from this
law. Besides, two possible extrinsic macroscopic mechanisms are unveiled namely
the influence of the dead layer, often present in the storage layer of STT-MRAM
cells, and the spatial inhomogeneities of the interfacial magnetic anisotropy.
About the first mechanism, we show that the presence of a dead layer tends to
reduce the scaling exponents. In the second mechanism, increasing the
percentage of inhomogeneity in the interfacial PMA is revealed to decrease the
scaling exponent. These results allow us to explain the difference in scaling
exponents relating anisotropy and magnetization thermal variations reported in
earlier experiments. This is crucial for the understanding of the thermal
stability of the storage layer magnetization in STT-MRAM applications.",2011.02220v3
2021-04-30,Freezing and thawing magnetic droplet solitons,"Magnetic droplets are non-topological magnetodynamical solitons displaying a
wide range of complex dynamic phenomena with potential for microwave signal
generation. Bubbles, on the other hand, are internally static cylindrical
magnetic domains, stabilized by external fields and magnetostatic interactions.
In its original theory, the droplet was described as an imminently collapsing
bubble stabilized by spin transfer torque and, in its zero-frequency limit, as
equivalent to a bubble. Without nanoscale lateral confinement, pinning, or an
external applied field, such a nanobubble is unstable, and should collapse.
Here, we show that we can freeze dynamic droplets into static nanobubbles by
decreasing the magnetic field. While the bubble has virtually the same
resistance as the droplet, all signs of low-frequency microwave noise
disappear. The transition is fully reversible and the bubble can be thawed back
into a droplet if the magnetic field is increased under current. Whereas the
droplet collapses without a sustaining current, the bubble is highly stable and
remains intact for days without external drive. Electrical measurements are
complemented by direct observation using scanning transmission x-ray
microscopy, which corroborates the analysis and confirms that the bubble is
stabilized by pinning.",2104.14897v1
2019-10-31,Time-resolving magnetic scattering on rare-earth ferrimagnets with a bright soft-X-ray high-harmonic source,"We demonstrate the first time-resolved X-ray resonant magnetic scattering
(tr-XRMS) experiment at the N edge of Tb at 155 eV performed using a tabletop
high-brightness high-harmonic generation (HHG) source. In contrast to static
X-ray imaging applications, such optical-pump X-ray-probe studies pose a
different set of challenges for the ultrafast driver laser because a high
photon flux of X-rays resonant with the N edge must be attained at a low
repetition rate to avoid thermal damage of the sample. This laboratory-scale
X-ray magnetic diffractometer is enabled by directly driving HHG in helium with
terawatt-level 1 um laser fields, which are obtained through pulse compression
after a high-energy kHz-repetition-rate Yb:CaF2 amplifier. The high peak power
of the driving fields allows us to reach the fully phase-matching conditions in
helium, which yields the highest photon flux (>2x10^9 photons/s/1% bandwidth)
in the 100-220 eV spectral range, to the best of our knowledge. Our
proof-of-concept tr-XRMS measurements clearly resolve the spatio-temporal
evolution of magnetic domains in Co/Tb ferrimagnetic alloys with femtosecond
and nanometer resolution. In addition to the ultrafast demagnetization, we
observe magnetic domain expansion with a domain wall velocity similar to that
induced by spin transfer torque. The demonstrated method opens up new
opportunities for time-space-resolved magnetic scattering with elemental
specificity on various magnetic, orbital and electronic orderings in condensed
matter systems.",1910.14263v1
2021-03-14,Perpendicular magnetic anisotropy in ultra-thin Cu$_2$Sb-type (Mn-Cr)AlGe films onto thermally oxidized silicon substrates,"Perpendicularly magnetized films showing small saturation magnetization,
$M_\mathrm{s}$, are essential for spin-transfer-torque writing type
magnetoresistive random access memories, STT-MRAMs. An intermetallic compound,
{(Mn-Cr)AlGe} of the Cu$_2$Sb-type crystal structure was investigated, in this
study, as a material showing the low $M_\mathrm{s}$ ($\sim 300$ kA/m) and
high-perpendicular magnetic anisotropy, $K_\mathrm{u}$. The layer thickness
dependence of $K_\mathrm{u}$ and effects of Mg-insertion layers at top and
bottom (Mn-Cr)AlGe$|$MgO interfaces were studied in film samples fabricated
onto thermally oxidized silicon substrates to realize high-$K_\mathrm{u}$ in
the thickness range of a few nanometer. Optimum Mg-insertion thicknesses were
1.4 and 3.0 nm for the bottom and the top interfaces, respectively, which were
relatively thick compared to results in similar insertion effect investigations
on magnetic tunnel junctions reported in previous studies. The cross-sectional
transmission electron microscope images revealed that the Mg-insertion layers
acted as barriers to interdiffusion of Al-atoms as well as oxidization from the
MgO layers. The values of $K_\mathrm{u}$ were about $7 \times 10^5$ and $2
\times 10^5$ J/m$^3$ at room temperature for 5 and 3 nm-thick (Mn-Cr)AlGe
films, respectively, with the optimum Mg-insertion thicknesses. The
$K_\mathrm{u}$ at a few nanometer thicknesses is comparable or higher than
those reported in perpendicularly magnetized CoFeB films which are
conventionally used in MRAMs, while the $M_\mathrm{s}$ value is one third or
less smaller than those of the CoFeB films. The developed (Mn-Cr)AlGe films are
promising from the viewpoint of not only the magnetic properties, but also the
compatibility to the silicon process in the film fabrication.",2103.07847v2
2022-01-12,TA-LRW: A Replacement Policy for Error Rate Reduction in STT-MRAM Caches,"As technology process node scales down, on-chip SRAM caches lose their
efficiency because of their low scalability, high leakage power, and increasing
rate of soft errors. Among emerging memory technologies, Spin-Transfer Torque
Magnetic RAM (STT-MRAM) is known as the most promising replacement for
SRAM-based cache memories. The main advantages of STT-MRAM are its
non-volatility, near-zero leakage power, higher density, soft-error immunity,
and higher scalability. Despite these advantages, the high error rate in
STT-MRAM cells due to retention failure, write failure, and read disturbance
threatens the reliability of cache memories built upon STT-MRAM technology. The
error rate is significantly increased in higher temperatures, which further
affects the reliability of STT-MRAM-based cache memories. The major source of
heat generation and temperature increase in STT-MRAM cache memories is write
operations, which are managed by cache replacement policy. In this paper, we
first analyze the cache behavior in the conventional LRU replacement policy and
demonstrate that the majority of consecutive write operations (more than 66%)
are committed to adjacent cache blocks. These adjacent write operations cause
accumulated heat and increased temperature, which significantly increases the
cache error rate. To eliminate heat accumulation and the adjacency of
consecutive writes, we propose a cache replacement policy, named Thermal-Aware
Least-Recently Written (TA-LRW), to smoothly distribute the generated heat by
conducting consecutive write operations in distant cache blocks. TA-LRW
guarantees the distance of at least three blocks for each two consecutive write
operations in an 8-way associative cache. This distant write scheme reduces the
temperature-induced error rate by 94.8%, on average, compared with the
conventional LRU policy, which results in 6.9x reduction in cache error rate.",2201.04373v1
2022-08-10,Magnetic braking saturates: evidence from the orbital period distribution of low-mass detached eclipsing binaries from ZTF,"We constrain the orbital period ($P_{\rm orb}$) distribution of low-mass
detached main-sequence eclipsing binaries (EBs) with light curves from the
Zwicky Transient Facility (ZTF), which provides a well-understood selection
function and sensitivity to faint stars. At short periods ($P_{\rm orb}\lesssim
2$ days), binaries are predicted to evolve significantly due to magnetic
braking (MB), which shrinks orbits and ultimately brings detached binaries into
contact. The period distribution is thus a sensitive probe of MB. We find that
the intrinsic period distribution of low-mass ($0.1\lesssim M_1/M_{\odot} <
0.9$) binaries is basically flat (${\rm d}N/{\rm d}P_{\rm orb} \propto P_{\rm
orb}^0$), from $P_{\rm orb}=10$ days down to the contact limit. This is
strongly inconsistent with predictions of classical MB models based on the
Skumanich relation, which are widely used in binary evolution calculations and
predict ${\rm d}N/{\rm d}P_{\rm orb} \propto P_{\rm orb}^{7/3}$ at short
periods. The observed distributions are best reproduced by models in which the
magnetic field saturates at short periods, with a MB torque that scales roughly
as $\dot{J}\propto P_{\rm orb}^{-1}$, as opposed to $\dot{J} \propto P_{\rm
orb}^{-3}$ in the standard Skumanich law. We also find no significant
difference between the period distributions of binaries containing fully and
partially convective stars. Our results confirm that a saturated MB law, which
was previously found to describe the spin-down of rapidly rotating isolated M
dwarfs, also operates in tidally locked binaries. We advocate using saturated
MB models in binary evolution calculations. Our work supports previous
suggestions that MB in cataclysmic variables (CVs) is much weaker than assumed
in the standard evolutionary model, unless mass transfer leads to significant
additional angular momentum loss in CVs.",2208.05488v2
2022-12-14,The ultraluminous X-ray source M81 X-6: a weakly magnetised neutron star with a precessing accretion disc?,"We investigate the nature of the ULX M81 X-6, which has been suggested to
harbour a neutron star (NS), by studying its long-term X-ray spectral and
temporal evolution, using the rich set of available archival data from
XMM-Newton, Chandra, NuSTAR, and Swift/XRT. We tracked the evolution of the
source on the hardness-intensity diagram and find that the source oscillates
between two main states: one characterised by a hard and luminous spectrum and
the other at low hardness and luminosity. The properties of the soft component
remain constant between the two states, suggesting that changes in the
mass-transfer rate are not driving the spectral transitions. Instead, the
bi-modal behaviour of the source and the known super-orbital period would point
to the precession of the accretion disc. Here, we tested two theoretical
models: (1) Lense-Thirring precession, which can explain the super-orbital
period if the NS has a magnetic field $B$ $\lesssim10^{10}$ G, supporting the
idea of M81 X-6 as a weakly magnetised NS, and (2) precession due to the torque
of the NS magnetic field, which leads to $B \gtrsim$ 10$^{11}$ G. However, the
latter scenario, assuming M81 X-6 shares similar properties with other NS-ULXs,
is disfavoured because it would require magnetic field strengths ($B>10^{15}$
G) much higher than those known for other pulsating ULXs. We further show that
the contribution from the hard component attributed to the putative accretion
column sits just below the typical values found in pulsating ULXs, which,
together with the low value of the pulsed fraction ($\leq10$\%) found for one
XMM-Newton/pn observation, could explain the source's lack of pulsations. The
spectral properties and variability of M81 X-6 can be accounted for if the
accretor is a NS with a low magnetic field. Under the hypothesis of
Lense-Thirring precession, we predict a spin period of the NS of a few seconds.",2212.07391v1
2023-08-03,Evaluation of STT-MRAM as a Scratchpad for Training in ML Accelerators,"Progress in artificial intelligence and machine learning over the past decade
has been driven by the ability to train larger deep neural networks (DNNs),
leading to a compute demand that far exceeds the growth in hardware performance
afforded by Moore's law. Training DNNs is an extremely memory-intensive
process, requiring not just the model weights but also activations and
gradients for an entire minibatch to be stored. The need to provide
high-density and low-leakage on-chip memory motivates the exploration of
emerging non-volatile memory for training accelerators. Spin-Transfer-Torque
MRAM (STT-MRAM) offers several desirable properties for training accelerators,
including 3-4x higher density than SRAM, significantly reduced leakage power,
high endurance and reasonable access time. On the one hand, MRAM write
operations require high write energy and latency due to the need to ensure
reliable switching.
  In this study, we perform a comprehensive device-to-system evaluation and
co-optimization of STT-MRAM for efficient ML training accelerator design. We
devised a cross-layer simulation framework to evaluate the effectiveness of
STT-MRAM as a scratchpad replacing SRAM in a systolic-array-based DNN
accelerator. To address the inefficiency of writes in STT-MRAM, we propose to
reduce write voltage and duration. To evaluate the ensuing accuracy-efficiency
trade-off, we conduct a thorough analysis of the error tolerance of input
activations, weights, and errors during the training. We propose heterogeneous
memory configurations that enable training convergence with good accuracy. We
show that MRAM provide up to 15-22x improvement in system level energy across a
suite of DNN benchmarks under iso-capacity and iso-area scenarios. Further
optimizing STT-MRAM write operations can provide over 2x improvement in write
energy for minimal degradation in application-level training accuracy.",2308.02024v1
2024-02-01,Reuse Detector: Improving the Management of STT-RAM SLLCs,"Various constraints of Static Random Access Memory (SRAM) are leading to
consider new memory technologies as candidates for building on-chip shared
last-level caches (SLLCs). Spin-Transfer Torque RAM (STT-RAM) is currently
postulated as the prime contender due to its better energy efficiency, smaller
die footprint and higher scalability. However, STT-RAM also exhibits some
drawbacks, like slow and energy-hungry write operations, that need to be
mitigated. In this work we address these shortcomings by leveraging a new
management mechanism for STT-RAM SLLCs. This approach is based on the previous
observation that the stream of references arriving at the SLLC of a Chip
MultiProcessor (CMP) exhibits reuse locality, i.e., those blocks referenced
several times manifest high probability of forthcoming reuse. In this paper, we
employ a cache management mechanism that selects the contents of the SLLC aimed
to exploit reuse locality instead of temporal locality. Specifically, our
proposal consists in the inclusion of a Reuse Detector between private cache
levels and the STT-RAM SLLC to detect blocks that do not exhibit reuse, in
order to avoid their insertion in the SLLC, hence reducing the number of write
operations and the energy consumption in the STT-RAM. Our evaluation reveals
that our scheme reports on average, energy reductions in the SLLC in the range
of 37-30\%, additional energy savings in the main memory in the range of 6-8\%
and performance improvements of 3\% up to 14\% (16-core) compared to an STT-RAM
SLLC baseline where no reuse detector is employed. More importantly, our
approach outperforms DASCA, the state-of-the-art STT-RAM SLLC management,
reporting SLLC energy savings in the range of 4-11\% higher than those of
DASCA, delivering higher performance in the range of 1.5-14\%, and additional
improvements in DRAM energy consumption in the range of 2-9\% higher than
DASCA.",2402.00533v1
2019-02-20,SMART: Secure Magnetoelectric AntifeRromagnet-Based Tamper-Proof Non-Volatile Memory,"The storage industry is moving toward emerging non-volatile memories (NVMs),
including the spin-transfer torque magnetoresistive random-access memory
(STT-MRAM) and the phase-change memory (PCM), owing to their high density and
low-power operation. In this paper, we demonstrate, for the first time, circuit
models and performance benchmarking for the domain wall (DW) reversal-based
magnetoelectric-antiferromagnetic random access memory (ME-AFMRAM) at
cell-level and at array-level. We also provide perspectives for coherent
rotation-based memory switching with topological insulator-driven anomalous
Hall read-out. In the coherent rotation regime, the ultra-low power
magnetoelectric switching coupled with the terahertz-range antiferromagnetic
dynamics result in substantially lower energy-per-bit and latency metrics for
the ME-AFMRAM compared to other NVMs including STTMRAM and PCM. After
characterizing the novel ME-AFMRAM, we leverage its unique properties to build
a dense, on-chip, secure NVM platform, called SMART: A Secure Magnetoelectric
Antiferromagnet- Based Tamper-Proof Non-Volatile Memory. New NVM technologies
open up challenges and opportunities from a data-security perspective. For
example, their sensitivity to magnetic fields and temperature fluctuations, and
their data remanence after power-down make NVMs vulnerable to data theft and
tampering attacks. The proposed SMART memory is not only resilient against data
confidentiality attacks seeking to leak sensitive information but also ensures
data integrity and prevents Denial-of-Service (DoS) attacks on the memory. It
is impervious to particular power side-channel (PSC) attacks which exploit
asymmetric read/write signatures for 0 and 1 logic levels, and photonic
side-channel attacks which monitor photo-emission signatures from the chip
backside.",1902.07792v2
2020-04-22,"Impurity-dependent gyrotropic motion, deflection and pinning of current-driven ultrasmall skyrmions in PdFe/Ir(111) surface","Resting on multi-scale modelling simulations, we explore dynamical aspects
characterizing skyrmions driven by spin-transfer-torque towards repulsive and
pinning 3d and 4d single atomic defects embedded in a Pd layer deposited on the
Fe/Ir(111) surface. The latter is known to host sub-10 nm skyrmions which are
of great interest in information technology. The Landau-Lifshitz-Gilbert
equation is parametrized with magnetic exchange interactions extracted from
first-principles. Depending on the nature of the defect and the magnitude of
the applied magnetic field, the skyrmion deforms by either shrinking or
increasing in size, experiencing thereby elliptical distortions. After applying
a magnetic field of 10 Tesla, ultrasmall skyrmions are driven along a straight
line towards the various defects which permits a simple analysis of the impact
of the impurities. Independently from the nature of the skyrmion-defect complex
interaction a gyrotropic motion is observed. A repulsive force leads to a
skyrmion trajectory similar to the one induced by an attractive one. We unveil
that the circular motion is clockwise around pinning impurities but counter
clockwise around the repulsive ones, which can be used to identify the
interaction nature of the defects by observing the skyrmions trajectories.
Moreover, and as expected, the skyrmion always escapes the repulsive defects in
contrast to the pinning defects, which require a minimal depinning current to
observe impurity avoidance. This unveils the richness of the motion regimes of
skyrmions. We discuss the results of the simulations in terms of the Thiele
equation, which provides a reasonable qualitative description of the observed
phenomena. Finally, we show an example of a double track made of pinning
impurities, where the engineering of their mutual distance allows to control
the skyrmion motion with enhanced velocity.",2004.10509v1
2020-03-19,Realizing an Isotropically Coercive Magnetic Layer for Memristive Applications by Analogy to Dry Friction,"We investigate the possibility of realizing a spintronic memristive device
based on the dependence of the tunnel conductance on the relative angle between
the magnetization of the two magnetic electrodes in in-plane magnetized tunnel
junctions. For this, it is necessary to design a free layer whose magnetization
can be stabilized along several or even any in-plane direction between the
parallel and the antiparallel magnetic configurations. We experimentally show
that this can be achieved by exploiting antiferromagnet-ferromagnet exchange
interactions in a regime where the antiferromagnet is thin enough to induce
enhanced coercivity and no exchange bias. The frustration of exchange
interactions at the interfaces due to competing ferro- and antiferromagnetic
interactions is at the origin of an isotropic dissipation mechanism yielding
isotropic coercivity. From a modeling point of view, it is shown that this
isotropic dissipation can be described by a dry friction term in the
Landau-Lifshitz-Gilbert equation. The influence of this dry friction term on
the magnetization dynamics of an in-plane magnetized layer submitted to a
rotating in-plane field is investigated both analytically and numerically. The
possibility to control the free layer magnetization orientation in an in-plane
magnetized magnetic tunnel junction by using the spin transfer torque from an
additional perpendicular polarizer is also investigated through macrospin
simulation. It is shown that the memristor function can be achieved by the
injection of current pulses through the stack in the presence of an in-plane
static field transverse to the reference layer magnetization, the aim of which
is to limit the magnetization rotation between 0{\deg} and 180{\deg}.",2003.08850v1
2020-06-22,Optimizing Placement of Heap Memory Objects in Energy-Constrained Hybrid Memory Systems,"Main memory (DRAM) significantly impacts the power and energy utilization of
the overall server system. Non-Volatile Memory (NVM) devices, such as Phase
Change Memory and Spin-Transfer Torque RAM, are suitable candidates for main
memory to reduce energy consumption. But unlike DRAM, NVMs access latencies are
higher than DRAM and NVM writes are more energy sensitive than DRAM write
operations. Thus, Hybrid Main Memory Systems (HMMS) employing DRAM and NVM have
been proposed to reduce the overall energy depletion of main memory while
optimizing the performance of NVM. This paper proposes eMap, an optimal heap
memory object placement planner in HMMS. eMap considers the object-level access
patterns and energy consumption at the application level and provides an ideal
placement strategy for each object to augment performance and energy
utilization. eMap is equipped with two modules, eMPlan and eMDyn. Specifically,
eMPlan is a static placement planner which provides one time placement policies
for memory object to meet the energy budget while eMDyn is a runtime placement
planner to consider the change in energy limiting constraint during the runtime
and shuffles the memory objects by taking into account the access patterns as
well as the migration cost in terms of energy and performance. The evaluation
shows that our proposed solution satisfies both the energy limiting constraint
and the performance. We compare our methodology with the state-of-the-art
memory object classification and allocation (MOCA) framework. Our extensive
evaluation shows that our proposed solution, eMPlan meets the energy constraint
with 4.17 times less costly and reducing the energy consumption up to 14% with
the same performance. eMDyn also satisfies the performance and energy
requirement while considering the migration cost in terms of time and energy.",2006.12133v2
2007-04-17,Casimir Friction I: Friction of a vacuum on a spinning dielectric,"We introduce the concept of Casimir friction, i.e. friction due to quantum
fluctuations. In this first article we describe the calculation of a constant
torque, arising from the scattering of quantum fluctuations, on a dielectric
rotating in an electromagnetic vacuum.",0704.2194v2
2010-12-10,Angular momentum nonconservation and conservation in quasiclassical Positronium,"It is shown that due to Thomas precession, angular momentum is not generally
a constant of the motion in a quasiclassical model of the Positronium atom
consisting of circular-orbiting point charges with intrinsic spin and
associated magnetic moment. Despite absence of externally-applied torque,
angular momentum is a constant of the motion only if the electron and positron
intrinsic angular momentum vector components perpendicular to the orbital
angular momentum are antiparallel and of equal magnitude.",1012.2185v1
2019-12-03,Picosecond Spin Orbit Torque Switching,"Reducing energy dissipation while increasing speed in computation and memory
is a long-standing challenge for spintronics research. In the last 20 years,
femtosecond lasers have emerged as a tool to control the magnetization in
specific magnetic materials at the picosecond timescale. However, the use of
ultrafast optics in integrated circuits and memories would require a major
paradigm shift. An ultrafast electrical control of the magnetization is far
preferable for integrated systems. Here we demonstrate reliable and
deterministic control of the out-of-plane magnetization of a 1 nm-thick Co
layer with single 6 ps-wide electrical pulses that induce spin-orbit torques on
the magnetization. We can monitor the ultrafast magnetization dynamics due to
the spin-orbit torques on sub-picosecond timescales, thus far accessible only
by numerical simulations. Due to the short duration of our pulses, we enter a
counter-intuitive regime of switching where heat dissipation assists the
reversal. Moreover, we estimate a low energy cost to switch the magnetization,
projecting to below 1fJ for a (20 nm)^3 cell. These experiments prove that
spintronic phenomena can be exploited on picosecond time-scales for full
magnetic control and should launch a new regime of ultrafast spin torque
studies and applications.",1912.01377v4
2008-01-01,Radiative torques alignment in the presence of pinwheel torques,"We study the alignment of grains subject to both radiative torques and
pinwheel torques while accounting for thermal flipping of grains. By pinwheel
torques we refer to all systematic torques that are fixed in grain body axes,
including the radiative torques arising from scattering and absorption of
isotropic radiation. We discuss new types of pinwheel torques, which are
systematic torques arising from infrared emission and torques arising from the
interaction of grains with ions and electrons in hot plasma. We show that both
types of torques are long-lived, i.e. may exist longer than gaseous damping
time. We compare these torques with the torques introduced by E. Purcell,
namely, torques due to H$_2$ formation, the variation of accommodation
coefficient for gaseous collisions and photoelectric emission. Furthermore, we
revise the Lazarian & Draine model for grain thermal flipping. We calculate
mean flipping timescale induced by Barnett and nuclear relaxation for both
paramagnetic and superparamagnetic grains, in the presence of stochastic
torques associated with pinwheel torques, e.g. the stochastic torques arising
from H$_2$ formation, and gas bombardment. We show that the combined effect of
internal relaxation and stochastic torques can result in fast flipping for
sufficiently small grains and, because of this, they get thermally trapped,
i.e. rotate thermally in spite of the presence of pinwheel torques. For
sufficiently large grains, we show that the pinwheel torques can increase the
degree of grain alignment achievable with the radiative torques by increasing
the magnitude of the angular momentum of low attractor points and/or by driving
grains to new high attractor points.",0801.0266v2
2004-06-27,Spin transfer and coherence in coupled quantum wells,"Spin dynamics of optically excited electrons confined in asymmetric coupled
quantum wells are investigated through time resolved Faraday rotation
experiments. The inter-well coupling is shown to depend on applied electric
field and barrier thickness. We observe three coupling regimes: independent
spin precession in isolated quantum wells, incoherent spin transfer between
single-well states, and coherent spin transfer in a highly coupled system.
Relative values of the inter-well tunneling time, the electron spin lifetime,
and the Larmor precession period appear to govern this behavior.",0406668v1
2007-02-25,The magneto-optical Barnett effect and spin momentum transfer:Magnetization switching by circularly polarized light,"The interaction of polarized light with a spin in the presence of dissipation
is shown to be equivalent to a spin transfer process that can cause switching.
In plasmas, the spin transfer is dominated by a spin-spin exchange term while
at lower energy densities it is dominated by an optical Barnett-like effect.
This latter effect is used in conjunction with optical phonons to predict
femtosecond magnetization reversal believed to be recently measured in GdCoFe
thin films. Conventional approaches based on the Bloch and the Landau-Lifshitz
equations do not reproduce this ultrafast switching.",0702574v1
2006-01-08,Universal destabilization and slowing of spin transfer functions by a bath of spins,"We investigate the effect of a spin bath on the spin transfer functions of a
permanently coupled spin system. When each spin is coupled to a seperate
environment, the effect on the transfer functions in the first excitation
sector is amazingly simple: the group velocity is slowed down by a factor of
two, and the fidelity is destabilized by a modulation of |cos Gt|, where G is
the mean square coupling to the environment.",0601047v2
2000-10-10,Circumbinary disks and cataclysmic variable evolution,"The influence of a circumbinary (CB) disk on the evolution of cataclysmic
variable (CV) binary systems is investigated. We show that CB mass surface
densities sufficient to influence the evolution rate are plausibly provided by
the outflows observed in CVs, if the net effect of these winds is to deliver
$10^{-4}$--$10^{-3}$ of the mass transfer rate to the CB disk. The torque
exerted by the CB disk provides a positive feedback between mass transfer rate
and CB disk mass which can lead to mass transfer rates of $\sim 10^{-8}
-10^{-7} \mpy$. This mechanism may be responsible for causing the range of
variation of mass transfer rates in CV's. In particular, it may explain rates
inferred for the novalike variables and the supersoft X-ray binary systems
observed near the upper edge of the period gap ($P \sim 3 - 4$ hr), as well as
the spread in mass transfer rates above and below the period gap. Consquences
and the possible observability of such disks are discussed.",0010194v1
2017-03-08,Learning Invariant Feature Spaces to Transfer Skills with Reinforcement Learning,"People can learn a wide range of tasks from their own experience, but can
also learn from observing other creatures. This can accelerate acquisition of
new skills even when the observed agent differs substantially from the learning
agent in terms of morphology. In this paper, we examine how reinforcement
learning algorithms can transfer knowledge between morphologically different
agents (e.g., different robots). We introduce a problem formulation where two
agents are tasked with learning multiple skills by sharing information. Our
method uses the skills that were learned by both agents to train invariant
feature spaces that can then be used to transfer other skills from one agent to
another. The process of learning these invariant feature spaces can be viewed
as a kind of ""analogy making"", or implicit learning of partial correspondences
between two distinct domains. We evaluate our transfer learning algorithm in
two simulated robotic manipulation skills, and illustrate that we can transfer
knowledge between simulated robotic arms with different numbers of links, as
well as simulated arms with different actuation mechanisms, where one robot is
torque-driven while the other is tendon-driven.",1703.02949v1
2006-03-01,Why the braking indices of young pulsars are less than 3?,"In this letter we discuss two possible reasons which cause the observed
braking indices n of young radio pulsars to be smaller than 3: (a) the evolving
spin-down model of the magnetic field component $B_{\perp}$ increases with
time; (b) the extrinsic braking torque model in which the tidal torques exerted
on the pulsar by the fallback disk, and carries away the spin angular momentum
from the pulsar. Based on some simple assumptions, we derive the expression of
the braking indices, and calculate the spin-down evolutionary tracks of pulsars
for different input parameters.",0603012v4
2005-09-10,Theory of Magnetodynamics Induced by Spin Torque in Perpendicularly Magnetized Thin Films,"A nonlinear model of spin wave excitation using a point contact in a thin
ferromagnetic film is introduced. Large-amplitude magnetic solitary waves are
computed, which help explain recent spin-torque experiments. Numerical
simulations of the fully nonlinear model predict excitation frequencies in
excess of 0.2 THz for contact diameters smaller than 6 nm. Simulations also
predict a saturation and red shift of the frequency at currents large enough to
invert the magnetization under the point contact. The theory is approximated by
a cubic complex Ginzburg-Landau type equation. The mode's nonlinear frequency
shift is found by use of perturbation techniques, whose results agree with
those of direct numerical simulations.",0509265v1
2008-02-22,White dwarf spins from low mass stellar evolution models,"The prediction of the spins of the compact remnants is a fundamental goal of
the theory of stellar evolution. Here, we confront the predictions for white
dwarf spins from evolutionary models including rotation with observational
constraints. We perform stellar evolution calculations for stars in the mass
range 1... 3$\mso$, including the physics of rotation, from the zero age main
sequence into the TP-AGB stage. We calculate two sets of model sequences, with
and without inclusion of magnetic fields. From the final computed models of
each sequence, we deduce the angular momenta and rotational velocities of the
emerging white dwarfs. While models including magnetic torques predict white
dwarf rotational velocities between 2 and 10 km s$^{-1}$, those from the
non-magnetic sequences are found to be one to two orders of magnitude larger,
well above empirical upper limits. We find the situation analogous to that in
the neutron star progenitor mass range, and conclude that magnetic torques may
be required in order to understand the slow rotation of compact stellar
remnants in general.",0802.3286v1
2008-10-21,Spin-Peierls instabilities of antiferromagnetic rings in a magnetic field,"Motivated by the intriguing properties of magnetic molecular wheels at field
induced level crossings, we investigate the spin-Peierls instability of
antiferromagnetic rings in a field by exact diagonalizations of a microscopic
spin model coupled to the lattice via a distortion dependent
Dzyaloshinskii-Moriya interaction. We show that, beyond the unconditional
instability at level crossings for infinitesimal magnetoelastic coupling, the
model is characterized by a stronger tendency to distort at higher level
crossings, and by a dramatic angular dependence with very sharp torque
anomalies when the field is almost in the plane of the ring. These predictions
are shown to compare remarkably well with available torque and Nuclear Magnetic
Resonance data on CsFe8.",0810.3837v3
2009-10-24,Spin-torque driven ferromagnetic resonance in a nonlinear regime,"Spin-valve based nanojunctions incorporating Co|Ni multilayers with
perpendicular anisotropy were used to study spin-torque driven ferromagnetic
resonance (ST-FMR) in a nonlinear regime. Perpendicular field swept resonance
lines were measured under a large amplitude microwave current excitation, which
produces a large angle precession of the Co|Ni layer magnetization. With
increasing rf power the resonance lines broaden and become asymmetric, with
their peak shifting to lower applied field. A nonhysteretic step jump in ST-FMR
voltage signal was also observed at high powers. The results are analyzed in in
terms of the foldover effect of a forced nonlinear oscillator and compared to
macrospin simulations. The ST-FMR nonhysteretic step response may have
applications in frequency and amplitude tunable nanoscale field sensors.",0910.4678v1
2010-08-18,Parameter dependence of resonant spin torque magnetization reversal,"We numerically study ultra fast resonant spin torque (ST) magnetization
reversal in magnetic tunnelling junctions (MTJ) driven by current pulses having
a direct current (DC) and a resonant alternating current (AC) component. The
precessional ST dynamics of the single domain MTJ free layer cell are modelled
in the macro spin approximation. The energy efficiency, reversal time, and
reversal reliability are investigated under variation of pulse parameters like
direct and AC current amplitude, AC frequency and AC phase. We find a range of
AC and direct current amplitudes where robust resonant ST reversal is obtained
with faster switching time and reduced energy consumption per pulse compared to
purely direct current ST reversal. However for a certain range of AC and direct
current amplitudes a strong dependence of the reversal properties on AC
frequency and phase is found. Such regions of unreliable reversal must be
avoided for ST memory applications.",1008.3060v1
2010-09-08,Frequency shift keying in vortex-based spin torque oscillators,"Vortex-based spin-torque oscillators can be made from extended spin valves
connected to an electrical nanocontact. We study the implementation of
frequency shift keying modulation in these oscillators. Upon a square
modulation of the current in the 10 MHz range, the vortex frequency follows the
current command, with easy identification of the two swapping frequencies in
the spectral measurements. The frequency distribution of the output power can
be accounted for by convolution transformations of the dc current vortex
waveform, and the current modulation. Modeling indicates that the frequency
transitions are phase coherent and last less than 25 ns. Complementing the
multi-octave tunability and first-class agility, the capability of frequency
shift keying modulation is an additional milestone for the implementation of
vortex-based oscillators in RF circuit.",1010.4464v2
2010-11-26,Magnetic Transformations in the Organic Conductor kappa-(BETS)2Mn[N(CN)2]3 at the Metal-Insulator Transition,"A complex study of magnetic properties including dc magnetization, 1H NMR and
magnetic torque measurements has been performed for the organic conductor
kappa-(BETS)2Mn[N(CN)2]3 which undergoes a metal-insulator transition at
T_MI~25K. NMR and the magnetization data indicate a transition in the manganese
subsystem from paramagnetic to a frozen state at T_MI, which is, however, not a
simple Neel type order. Further, a magnetic field induced transition resembling
a spin flop has been detected in the torque measurements at temperatures below
T_MI. This transition is most likely related to the spins of pi-electrons
localized on the organic molecules BETS and coupled with the manganese 3d spins
via exchange interaction.",1011.5730v1
2013-02-04,Robust synchronization of an arbitrary number of spin-torque driven vortex nanooscillators,"Non-linear magnetization dynamics in ferromagnetic nanoelements excited by
the spin-polarized dc-current is one of the most intensively studied phenomena
in solid state magnetism. Despite immense efforts, synchronization of
oscillations induced in several such nanoelements (spin-torque driven
nanooscillators, or STNO) still represents a major challenge both from the
fundamental and technological points of view. In this paper we propose a system
where synchronization of any number of STNOs, represented by magnetization
vortices inside squared nanoelements, can be easily achieved. Using full-scale
micromagnetic simulations we show that synchronization of these STNOs is
extremely dynamically stable due to their very large coupling energy provided
by the magnetodipolar interaction. Finally, we demonstrate that our concept
allows robust synchronization of an arbitrary number of STNOs (arranged either
as a 1D chain or as a 2D array), even when current supplying nanocontacts have
a broad size distribution.",1302.0659v3
2013-12-30,Exploring Ultra Low-Power on-Chip Clocking Using Functionality Enhanced Spin-Torque Switches,"Emerging spin-torque (ST) phenomena may lead to ultra-low-voltage, high-speed
nano-magnetic switches. Such current-based-switches can be attractive for
designing low swing global-interconnects, like, clocking-networks and
databuses. In this work we present the basic idea of using such ST-switches for
low-power on-chip clocking. For clockingnetworks, Spin-Hall-Effect (SHE) can be
used to produce an assist-field for fast ST-switching using global-mesh-clock
with less than 100mV swing. The ST-switch acts as a compact-latch, written by
ultra-low-voltage input-pulses. The data is read using a high-resistance
tunnel-junction. The clock-driven SHE write-assist can be shared among large
number of ST-latches, thereby reducing the load-capacitance for
clock-distribution. The SHE assist can be activated by a low-swing clock
(~150mV) and hence can facilitate ultra-low voltage clock-distribution. Owing
to reduced clock-load and low-voltage operation, the proposed scheme can
achieve 97% low-power for on-chip clocking as compared to the state of the art
CMOS design. Rigorous device-circuit simulations and system-level modelling for
the proposed scheme will be addressed in future.",1401.0015v1
2015-02-16,Electrical manipulation of a ferromagnet by an antiferromagnet,"We demonstrate that an antiferromagnet can be employed for a highly efficient
electrical manipulation of a ferromagnet. In our study we use an electrical
detection technique of the ferromagnetic resonance driven by an in-plane
ac-current in a NiFe/IrMn bilayer. At room temperature, we observe
antidamping-like spin torque acting on the NiFe ferromagnet, generated by the
in-plane current driven through the IrMn antiferromagnet. A large enhancement
of the torque, characterized by an effective spin-Hall angle exceeding most
heavy transition metals, correlates with the presence of the exchange-bias
field at the NiFe/IrMn interface. It highlights that, in addition to strong
spin-orbit coupling, the antiferromagnetic order in IrMn governs the observed
phenomenon.",1502.04570v2
2015-05-20,Spin torque resonant vortex core expulsion for an efficient radio-frequency detection scheme,"Spin-polarised radio-frequency currents, whose frequency is equal to that of
the gyrotropic mode, will cause an excitation of the core of a magnetic vortex
confined in a magnetic tunnel junction. When the excitation radius of the
vortex core is greater than that of the junction radius, vortex core expulsion
is observed, leading to a large change in resistance, as the layer enters a
predominantly uniform magnetisation state. Unlike the conventional spin-torque
diode effect, this highly tunable resonant effect will generate a voltage which
does not decrease as a function of rf power, and has the potential to form the
basis of a new generation of tunable nanoscale radio-frequency detectors.",1505.05358v1
2015-07-03,Magnetization switching by spin-orbit torque in an antiferromagnet/ferromagnet bilayer system,"Spin-orbit torque (SOT)-induced magnetization switching shows promise for
realizing ultrafast and reliable spintronics devices. Bipolar switching of
perpendicular magnetization via SOT is achieved under an in-plane magnetic
field collinear with an applied current. Typical structures studied so far
comprise a nonmagnet/ferromagnet (NM/FM) bilayer, where the spin Hall effect in
the NM is responsible for the switching. Here we show that an
antiferromagnet/ferromagnet (AFM/FM) bilayer system also exhibits a SOT large
enough to switch the magnetization of FM. In this material system, thanks to
the exchange-bias effect of the AFM, we observe the switching under no applied
field by using an antiferromagnetic PtMn and ferromagnetic Co/Ni multilayer
with a perpendicular easy axis. Furthermore, tailoring the stack achieves a
memristor-like behaviour where a portion of the reversed magnetization can by
controlled in an analogue manner. The AFM/FM system is thus a promising
building block for SOT devices as well as providing an attractive pathway
towards neuromorphic computing.",1507.00888v1
2015-08-17,Increased magnetic damping of a single domain wall and adjacent magnetic domains detected by spin torque diode in a nanostripe,"We use spin-torque resonance to probe simultaneously and separately the
dynamics of a magnetic domain wall and of magnetic domains in a nanostripe
magnetic tunnel junction. Thanks to the large associated resistance variations
we are able to analyze quantitatively the resonant properties of these single
nanoscale magnetic objects. In particular, we find that the magnetic damping of
both domains and domain walls is doubled compared to the damping value of their
host magnetic layer. We estimate the contributions to damping arising from
dipolar couplings between the different layers in the junction and from the
intralayer spin pumping effect. We find that they cannot explain the large
damping enhancement that we observe. We conclude that the measured increased
damping is intrinsic to large amplitudes excitations of spatially localized
modes or solitons such as vibrating or propagating domain walls",1508.04043v1
2015-08-18,Quasistatic and Pulsed Current-Induced Switching with Spin-Orbit Torques in Ultrathin Films with Perpendicular Magnetic Anisotropy,"Spin-orbit interaction derived spin torques provide a means of reversing the
magnetization of perpendicularly magnetized ultrathin films with currents that
flow in the plane of the layers. A basic and critical question for applications
is the speed and efficiency of switching with nanosecond current pulses. Here
we investigate and contrast the quasistatic (slowly swept current) and pulsed
current-induced switching characteristics of micron scale Hall crosses
consisting of very thin ($<1$ nm) perpendicularly magnetized CoFeB layers on
$\beta$-Ta. While complete magnetization reversal is found at a threshold
current density in the quasistatic case, short duration ($\leq 10$ ns) larger
amplitude pulses ($\simeq 10 \times$ the quasistatic threshold current) lead to
only partial magnetization reversal and domain formation. We associate the
partial reversal with the limited time for reversed domain expansion during the
pulse.",1508.04336v1
2015-10-21,Magnetoresistance of heavy and light metal/ferromagnet bilayers,"We studied the magnetoresistance of normal metal (NM)/ferromagnet (FM)
bilayers in the linear and nonlinear (current-dependent) regimes and compared
it with the amplitude of the spin-orbit torques and thermally induced electric
fields. Our experiments reveal that the magnetoresistance of the heavy NM/Co
bilayers (NM = Ta, W, Pt) is phenomenologically similar to the spin Hall
magnetoresistance (SMR) of YIG/Pt, but has a much larger anisotropy, of the
order of 0.5%, which increases with the atomic number of the NM. This SMR-like
behavior is absent in light NM/Co bilayers (NM = Ti, Cu), which present the
standard AMR expected of polycrystalline FM layers. In the Ta, W, Pt/Co
bilayers we find an additional magnetoresistance, directly proportional to the
current and to the transverse component of the magnetization. This so-called
unidirectional SMR, of the order of 0.005%, is largest in W and correlates with
the amplitude of the antidamping spin-orbit torque. The unidirectional SMR is
below the accuracy of our measurements in YIG/Pt.",1510.06285v1
2015-11-29,High Sensitivity Biosensor using Injection Locked Spin Torque Nano-Oscillators,"With ever increasing research on magnetic nano systems it is shown to have
great potential in the areas of magnetic storage, biosensing, magnetoresistive
insulation etc. In the field of biosensing specifically Spin Valve sensors
coupled with Magnetic Nanolabels is showing great promise due to noise immunity
and energy efficiency [1]. In this paper we present the application of
injection locked based Spin Torque Nano Oscillator (STNO) suitable for high
resolution energy efficient labeled DNA Detection. The proposed STNO microarray
consists of 20 such devices oscillating at different frequencies making it
possible to multiplex all the signals using capacitive coupling. Frequency
Division Multiplexing can be aided with Time division multiplexing to increase
the device integration and decrease the readout time while maintaining the same
efficiency in presence of constant input referred noise.",1511.09072v1
2015-12-02,Spin-Torque Sensors for Energy Efficient High Speed Long Interconnects,"In this paper, we propose a Spin-Torque (ST) based sensing scheme that can
enable energy efficient multi-bit long distance interconnect architectures.
Current-mode interconnects have recently been proposed to overcome the
performance degradations associated with conventional voltage mode Copper (Cu)
interconnects. However, the performance of current mode interconnects are
limited by analog current sensing transceivers and equalization circuits. As a
solution, we propose the use of ST based receivers that use Magnetic Tunnel
Junctions (MTJ) and simple digital components for current-to-voltage conversion
and do not require analog transceivers. We incorporate Spin-Hall Metal (SHM) in
our design to achieve high speed sensing. We show both single and multi-bit
operations that reveal major benefits at higher speeds. Our simulation results
show that the proposed technique consumes only 3.93-4.72 fJ/bit/mm energy while
operating at 1-2 Gbits/sec; which is considerably better than existing charge
based interconnects. In addition, Voltage Controlled Magnetic Anisotropy (VCMA)
can reduce the required current at the sensor. With the inclusion of VCMA, the
energy consumption can be further reduced to 2.02-4.02 fJ/bit/mm",1512.00762v1
2016-01-29,Spin torque driven dynamics of a coupled two layer structure: interplay between conservative and dissipative coupling,"In this manuscript the general concepts of spin wave theory are adapted to
the dynamics of a self-polarized system based on two layers coupled via
interlayer exchange (conservative coupling) and mutual spin torque (dissipative
coupling). An analytical description of the non-linear dynamics is proposed and
validated through numerical simulations. In contrast to the single layer model,
the phase equation of the coupled system has a contribution coming from the
dissipative part of the LLGS equation. It is shown that this is a major
contribution to the frequency mandatory to describe well the most basic
features of the dynamics of coupled systems. Using the proposed model a
specific feature of coupled dynamics is addressed: the redshift to blueshift
transition observed in the frequency current dependence of this kind of
exchange coupled systems upon increasing the applied field. It is found that
the blueshift regime can only occur in a region of field where the two linear
eigenmodes contribute equally to the steady state mode (i.e. high mode
hybridization). Finally, a general perturbed Hamiltonian equation for the
coupled system is proposed.",1601.08150v1
2016-04-18,Temperature dependence of spin-orbit torques in W/CoFeB bilayers,"We report on the temperature and layer thickness variation of spin-orbit
torques in perpendicularly magnetized W/CoFeB bilayers. Harmonic Hall voltage
measurements reveal dissimilar temperature evolutions of longitudinal and
transverse effective magnetic field components. The transverse effective field
changes sign at 250 K for a 2 nm thick W buffer layer, indicating a much
stronger contribution from interface spin-orbit interactions compared to, for
example, Ta. Transmission electron microscopy measurements reveal that
considerable interface mixing between W and CoFeB is primarily responsible for
this effect.",1604.05204v1
2016-10-13,Giant Edelstein effect in Topological-Insulator--Graphene heterostructures,"The control of a ferromagnet's magnetization via only electric currents
requires the efficient generation of current-driven spin-torques. In magnetic
structures based on topological insulators (TIs) current-induced spin-orbit
torques can be generated. Here we show that the addition of graphene, or
bilayer graphene, to a TI-based magnetic structure greatly enhances the
current-induced spin density accumulation and significantly reduces the amount
of power dissipated. We find that this enhancement can be as high as a factor
of 100, giving rise to a giant Edelstein effect. Such a large enhancement is
due to the high mobility of graphene (bilayer graphene) and to the fact that
the graphene (bilayer graphene) sheet very effectively screens charge
impurities, the dominant source of disorder in topological insulators. Our
results show that the integration of graphene in spintronics devices can
greatly enhance their performance and functionalities.",1610.04229v3
2017-09-22,Correlation between the luminosity and spin-period changes during outbursts of 12 Be binary pulsars observed by the MAXI/GSC and the Fermi/GBM,"To observationally study spin-period changes of accreting pulsars caused by
the accretion torque, the present work analyzes X-ray light curves of 12 Be
binary pulsars obtained by the MAXI/GSC all-sky survey and their pulse periods
measured by the Fermi/GBM pulsar project, both covering more than 6 years from
2009 August to 2016 March. The 12 objects were selected because they are
accompanied by clear optical identification, and accurate measurements of
surface magnetic fields. The luminosity $L$ and the spin-frequency derivatives
$\dot{\nu}$, measured during large outbursts with $L\gtrsim 1\times 10^{37}$
erg s$^{-1}$, were found to approximately follow the theoretical relations in
the accretion torque models, represented by $\dot{\nu} \propto L^{\alpha}$
($\alpha\simeq 1$), and the coefficient of proportionality between $\dot{\nu}$
and $L^{\alpha}$, agrees, within a factor of $\sim 3$, with that proposed by
Ghosh & Lamb (1979). In the course of the present study, the orbital elements
of several sources were refined.",1709.07579v1
2018-01-01,Efficient Switching of 3-Terminal Magnetic Tunnel Junctions by the Giant Spin Hall Effect of $\rm{Pt}_{85}\rm{Hf}_{15}$ Alloy,"Recent research has indicated that introducing impurities that increase the
resistivity of Pt can enhance the efficiency of the spin Hall torque it
generates. Here we directly demonstrate the usefulness of this strategy by
fabricating prototype 3-terminal in-plane-magnetized magnetic tunnel junctions
that utilize the spin Hall torque from a $\rm{Pt}_{85}\rm{Hf}_{15}$ alloy, and
measuring the critical currents for switching. We find that
$\rm{Pt}_{85}\rm{Hf}_{15}$ reduces the switching current densities compared to
pure Pt by approximately a factor of 2 for both quasi-static ramped current
biases and nanosecond-scale current pulses, thereby proving the feasibility of
this approach to assist in the development of efficient embedded magnetic
memory technologies.",1801.00411v1
2016-12-20,Nanosecond magnetization dynamics during spin Hall switching of in-plane magnetic tunnel junctions,"We present a study of the magnetic dynamics associated with nanosecond scale
magnetic switching driven by the spin Hall effect in 3-terminal nanoscale
magnetic tunnel junctions (3T-MTJs) with in-plane magnetization. Utilizing fast
pulse measurements in a variety of material stacks and detailed micromagnetic
simulations, we demonstrate that this unexpectedly fast and reliable magnetic
reversal is facilitated by the self-generated Oersted field, and the
short-pulse energy efficiency can be substantially enhanced by micromagnetic
curvature in the magnetic free layer. The sign of the Oersted field is
essential for this enhancement --- in simulations in which we artificially
impose a field-like torque with a sign opposite to the effect of the Oersted
field, the result is a much slower and stochastic switching process that is
reminiscent of the so-called incubation delay in conventional 2-terminal
spin-torque-switched MTJs.",1612.06463v3
2017-10-03,Brownian Motion and Entropic Torque Driven Motion of Domain-Wall in Antiferromagnets,"We study the spin dynamics in antiferromagnetic nanowire under an applied
temperature gradient using micromagnetic simulations on a classical spin model
with a uniaxial anisotropy. The entropic torque driven domain-wall motion and
the Brownian motion are discussed in detail, and their competition determines
the antiferromagnetic wall motion towards the hotter or colder region.
Furthermore, the spin dynamics in an antiferromagnet can be well tuned by the
anisotropy and the temperature gradient. Thus, this paper not only strengthens
the main conclusions obtained in earlier works [Kim et al., Phys. Rev. B 92,
020402(R) (2015); Selzer et al., Phys. Rev. Lett. 117, 107201 (2016)], but more
importantly gives the concrete conditions under which these conclusions apply,
respectively. Our results may provide useful information on the
antiferromagnetic spintronics for future experiments and storage device design.",1710.01196v2
2020-03-10,Effect of magnons on the temperature dependence and anisotropy of spin-orbit torque,"We investigate the influence of magnons on the temperature-dependence and the
anisotropy of the spin-orbit torque (SOT). For this purpose we use 3rd order
perturbation theory in the framework of the Keldysh formalism in order to
derive suitable equations to compute the magnonic SOT. We find several
contributions to the magnonic SOT, which depend differently on the spin-wave
stiffness $\mathcal{A}$ and on the temperature $T$, with the dominating
contribution scaling like $T^{2}/\mathcal{A}^{2}$. Based on this formalism we
compute the magnonic SOT in the ferromagnetic Rashba model. For large Rashba
parameters the magnonic SOT is strongly anisotropic and for small quasiparticle
broadening it may become larger than the non-magnonic SOT.",2003.05028v3
2020-03-12,Efficient spin torques in antiferromagnetic CoO/Pt quantified by comparing field- and current- induced switching,"We achieve current-induced switching in collinear insulating
antiferromagnetic CoO/Pt, with fourfold in-plane magnetic anisotropy. This is
measured electrically by spin Hall magnetoresistance and confirmed by the
magnetic field-induced spin-flop transition of the CoO layer. By applying
current pulses and magnetic fields, we quantify the efficiency of the acting
current-induced torques and estimate a current-field equivalence ratio of
$4x10^{-11} T A^{-1} m^2$. The N\'eel vector final state ($n \perp j$) is in
line with a thermomagnetoelastic switching mechanism for a negative
magnetoelastic constant of the CoO.",2003.05923v3
2017-01-09,Spin-orbit torque switching of synthetic antiferromagnets,"We report that synthetic antiferromagnets (SAFs) can be efficiently switched
by spin-orbit torques (SOTs) and the switching scheme does not obey the usual
SOT switching rule. We show that both the positive and negative spin Hall angle
(SHA)-like switching can be observed in Pt/SAF structures with only positive
SHA, depending on the strength of applied in-plane fields. A new switching
mechanism directly arising from the asymmetric domain expansion is proposed to
explain the anomalous switching behaviors. Contrary to the macrospin-based
switching model that the SOT switching direction is determined by the sign of
SHA, the new switching mechanism suggests that the SOT switching direction is
dominated by the field-modulated domain wall motion and can be reversed even
with the same sign of SHA. The new switching mechanism is further confirmed by
the domain wall motion measurements. The anomalous switching behaviors provide
important insights for understanding SOT switching mechanisms and also offer
novel features for applications.",1701.02395v1
2019-12-03,"Spin-Orbit-Torque-based Devices, Circuits and Architectures","Spintronics, the use of spin of an electron instead of its charge, has
received huge attention from research communities for different applications
including memory, interconnects, logic implementation, neuromorphic computing,
and many other applications. Here, in this paper, we review the works within
spintronics, more specifically on spin-orbit torque (SOT) within different
research groups. We also provide researchers an insight into the future
potentials of the SOT-based designs. This comprehensive review paper covers
different aspects of SOT-based design from device and circuit to architecture
level as well as more ambitious and futuristic applications of such technology.",1912.01347v1
2020-06-22,Spin-orbit torque induced magnetisation dynamics and switching in CoFeB/Ta/CoFeB system with mixed magnetic anisotropy,"Spin-orbit torque (SOT) induced magnetisation switching in CoFeB/Ta/CoFeB
trilayer with two CoFeB layers exhibiting in-plane magnetic anisotropy (IPMA)
and perpendicular magnetic anisotropy (PMA) is investigated. Interlayer
exchange coupling (IEC), measured using ferromagnetic resonance technique is
modified by varying thickness of Ta spacer. The evolution of the IEC leads to
different orientation of the magnetic anisotropy axes of two CoFeB layers: for
thicker Ta layer where magnetisation prefers antiferromagnetic ordering and for
thinner Ta layer where ferromagnetic coupling exists. Magnetisation state of
the CoFeB layer exhibiting PMA is controlled by the spin-polarized current
originating from SOT in $\mu m$ sized Hall bars. The evolution of the critical
SOT current density with Ta thickness is presented, showing an increase with
decreasing $t_\mathrm{Ta}$, which coincides with the coercive field dependence.
In a narrow range of $t_\mathrm{Ta}$ corresponding to the ferromagnetic IEC,
the field-free SOT-induced switching is achieved.",2006.12068v1
2020-07-21,Asymmetric skyrmion-antiskyrmion production in ultrathin ferromagnetic films,"Ultrathin ferromagnets with frustrated exchange and the Dzyaloshinskii-Moriya
interaction can support topological solitons such as skyrmions and
antiskyrmions, which are metastable and can be considered particle-antiparticle
counterparts. When spin-orbit torques are applied, the motion of an isolated
antiskyrmion driven beyond its Walker limit can generate skyrmion-antiskyrmion
pairs. Here, we use atomistic spin dynamics simulations to shed light on the
scattering processes involved in this pair generation. Under certain conditions
a proliferation of these particles and antiparticles can appear with a growth
rate and production asymmetry that depend on the strength of the chiral
interactions and the dissipative component of the spin-orbit torques. These
features are largely determined by scattering processes between antiskyrmions,
which can be elastic or result in bound states or annihilation.",2007.10749v2
2021-06-23,Dancing Synchronization in Coupled Spin-Torque Nano-Oscillators,"We are reporting a new type of synchronization, termed dancing
synchronization, between two spin-torque nano-oscillators (STNOs) coupled
through spin waves. Different from the known synchronizations in which two
STNOs are locked with various fixed relative phases, in this new synchronized
state two STNOs have the same frequency, but their relative phase varies
periodically within the common period, resulting in a dynamic waving pattern.
The amplitude of the oscillating relative phase depends on the coupling
strength of two STNOs, as well as the driven currents. The dancing
synchronization turns out to be universal, and can exist in two nonlinear Van
der Pol oscillators coupled both reactively and dissipativly. Our findings open
doors for new functional STNO-based devices.",2106.12197v1
2021-07-30,Non-principal axis rotation in binary asteroid systems and how it weakens the BYORP effect,"Using viscoelastic mass/spring model simulations, we explore tidal evolution
and migration of compact binary asteroid systems. We find that after the
secondary is captured into a spin-synchronous state, non-principal axis
rotation in the secondary can be long-lived. The secondary's long axis can
remain approximately aligned along the vector connecting secondary to primary
while the secondary rocks back and forth about its long axis. Inward orbital
semi-major axis migration can also resonantly excite non-principal axis
rotation. By estimating solar radiation forces on triangular surface meshes, we
show that the magnitude of the BYORP effect induced torque is sensitive to the
secondary's spin state. Non-principal axis rotation within the 1:1 spin-orbit
resonance can reduce the BYORP torque or cause frequent reversals in its
direction.",2107.14789v2
2022-08-22,"Current-induced magnetization reversal in (Ga,Mn)(Bi,As) epitaxial layer with perpendicular magnetic anisotropy","Pulsed current-induced magnetization reversal is investigated in the layer of
(Ga,Mn)(Bi,As) dilute ferromagnetic semiconductor (DFS) epitaxially grown under
tensile misfit strain causing perpendicular magnetic anisotropy in the layer.
The magnetization reversal, recorded through measurements of the anomalous Hall
effect, appearing under assistance of a static magnetic field parallel to the
current, is interpreted in terms of the spin-orbit torque mechanism. Our
results demonstrate that an addition of a small fraction of heavy Bi atoms,
substituting As atoms in the prototype DFS (Ga,Mn)As and increasing the
strength of spin-orbit coupling in the DFS valence band, significantly enhances
the efficiency of current-induced magnetization reversal thus reducing
considerably the threshold current density necessary for the reversal. Our
findings are of technological importance for applications to spin-orbit
torque-driven nonvolatile memory and logic elements.",2208.10318v1
2022-12-29,Field-free spin-orbit torque-induced switching of perpendicular magnetization at room temperature in WTe2/ferromagnet heterostructures,"Spin-orbit torque (SOT) provides an efficient way to achieve charge-to-spin
conversion and can switch perpendicular magnetization, which is essential for
designing novel energy-efficient spintronic devices. An out-of-plane SOT could
directly switch perpendicular magnetization. Encouragingly, field-free
perpendicular magnetization switching of a two-dimensional (2D) material
WTe2/ferromagnet (FM) bilayer has been reported recently, but the working
temperature (200 K) is below room temperature. Here, we report the field-free
perpendicular magnetization switching carried out at room temperature on a
WTe2/Pt/Co/Pt multilayer film. Controlled experiments confirm that the
field-free switching is caused by the in-plane antidamping SOT generated in the
Pt/Co/Pt multilayer and the out-of-plane generated in the a-axis WTe2 thin
film. This work offers a potential method for using spintronic devices made of
two-dimensional materials at room temperature.",2212.14281v1
2023-01-09,Spin-Orbit Torque Flash Analog-to-Digital Converter,"Although Analog-to-digital converters (ADCs) are critical components in
mixed-signal integrated circuits (IC), their performance has not been improved
significantly over the last decade. To achieve a radical improvement (compact,
low power and reliable ADCs), spintronics can be considered as a proper
candidate due to its compatibility with CMOS and wide applications in storage,
neuromorphic computing, and so on. In this paper, a proof-of-concept of a 3-bit
spin-CMOS Flash ADC using in-plane-anisotropy magnetic tunnel junctions
(i-MTJs) with spin-orbit torque (SOT) switching mechanism is designed,
fabricated and characterized. The proposed ADC replaces the current mirrors and
power-hungry comparators in the conventional Flash ADC with seven parallel
i-MTJs with different heavy metal (HM) widths. Monte-Carlo simulations based on
the experimental measurements show the process variations/mismatch limits the
accuracy of the proposed ADC to 2 bits. Moreover, the maximum differential
nonlinearity (DNL) and integral nonlinearity (INL) are 0.739 LSB (least
significant bit) and 0.7319 LSB, respectively.",2301.03232v1
2023-04-12,Coexisting and interacting spin torque driven free and reference layer magnetic droplet solitons,"Magnetic droplets are nanoscale, non-topological, magnetodynamical solitons
that can be nucleated in spin torque nano-oscillators (STNOs) or spin Hall
nano-oscillators (SHNOs). All theoretical, numerical, and experimental droplet
studies have so far focused on the free layer (FL), and any additional dynamics
in the reference layer (RL) have been entirely ignored. Here we show, using
all-perpendicular STNOs, that there is not only significant magnetodynamics in
the RL, but the reference layer itself can host a droplet coexisting with the
FL droplet. Both droplets are observed experimentally as stepwise changes and
sharp peaks in the dc and differential resistance, respectively. Whereas the
single FL droplet is highly stable, the coexistence state exhibits high-power
broadband microwave noise. Micromagnetic simulations corroborate the
experimental results and reveal a strong interaction between the droplets. Our
demonstration of strongly interacting and closely spaced droplets offers a
unique platform for fundamental studies of highly non-linear soliton pair
dynamics.",2304.05825v1
2023-05-06,Field-Free Spin-Orbit Torque driven Switching of Perpendicular Magnetic Tunnel Junction through Bending Current,"Current-induced spin-orbit torques (SOTs) enable fast and efficient
manipulation of the magnetic state of magnetic tunnel junctions (MTJs), making
it attractive for memory, in-memory computing, and logic applications. However,
the requirement of the external magnetic field to achieve deterministic
switching in perpendicular magnetized SOT-MTJs limits its implementation for
practical applications. Here, we introduce a field-free switching (FFS)
solution for the SOT-MTJ device by shaping the SOT channel to create a ""bend""
in the SOT current. The resulting bend in the charge current creates a
spatially non-uniform spin current, which translates into inhomogeneous SOT on
an adjacent magnetic free layer enabling deterministic switching. We
demonstrate FFS experimentally on scaled SOT-MTJs at nanosecond time scales.
This proposed scheme is scalable, material-agnostic, and readily compatible
with wafer-scale manufacturing, thus creating a pathway for developing purely
current-driven SOT systems.",2305.03961v1
2023-07-26,Oscillatory Edge Modes in Two Dimensional Spin-Torque Oscillator Arrays,"Spin torque oscillators (STOs) are dissipative magnetic systems that provide
a natural platform for exploring non-Hermitian phenomena. We theoretically
study a two-dimensional (2d) array of STOs and show that its dynamics can be
mapped to a 2d, non-Hermitian Su-Schrieffer-Heeger (SSH) model. We calculate
the energy spectrum and identify the one-dimensional (1d) edge states of our
model, corresponding to auto-oscillation of STOs on the boundary of the system
while the bulk oscillators do not activate. We show that tuning the Gilbert
damping, injected spin current, and coupling between STOs allows for exploring
the edge state properties under different parameter regimes. Furthermore, this
system admits 1d edge states with non-uniform probability density, and we
explore their properties in systems of different sizes. Additional symmetry
analysis indicates that these states are not topologically protected but are
nevertheless confined to the edge of the system, as the bulk is protected by
PT-symmetry. These results indicate that 2d arrays of STOs may be useful to
explore novel edge state behavior in dissipative systems.",2307.13876v1
2023-07-29,Single-spin spectroscopy of spontaneous and phase-locked spin torque oscillator dynamics,"We employ N-$V$ magnetometry to measure the stray field dynamics of a
ferromagnetic permalloy nanowire driven by spin-orbit torques. Specifically, we
observe the optically detected magnetic resonance (ODMR) signatures of both
spontaneous DC-driven magnetic oscillations and phase-locking to a second
harmonic drive, developing a simple macrospin model that captures the salient
features. We also observe signatures of dynamics beyond the macrospin model,
including an additional ODMR feature (associated with a second SW mode) and one
mode sapping power from another. Our results provide additional insight into
N-$V$-spin wave coupling mechanisms, and represent a new modality for
sub-wavelength N-$V$ scanned probe microscopy of nanoscale magnetic
oscillators.",2307.16049v1
2024-01-17,Giant Enhancement of Vacuum Friction in Spinning YIG Nanospheres,"Experimental observations of vacuum radiation and vacuum frictional torque
are challenging due to their vanishingly small effects in practical systems.
For example, a rotating nanosphere in free space slows down due to friction
from vacuum fluctuations with a stopping time around the age of the universe.
Here, we show that a spinning yttrium iron garnet (YIG) nanosphere near
aluminum or YIG slabs exhibits vacuum radiation eight orders of magnitude
larger than other metallic or dielectric spinning nanospheres. We achieve this
giant enhancement by exploiting the large near-field magnetic local density of
states in YIG systems, which occurs in the low-frequency GHz regime comparable
to the rotation frequency. Furthermore, we propose a realistic experimental
setup for observing the effects of this large vacuum radiation and frictional
torque under experimentally accessible conditions.",2401.09563v1
2012-12-17,Spin transfer in ultrathin BiFeO3 film under external electric field,"First-principals calculations show that up-spin and down-spin carriers are
accumulating adjacent to opposite surfaces of BiFeO3(BFO) film with applying
external bias. The spin carriers are equal in magnitude and opposite in
direction, and down-spin carriers move to the direction opposing the external
electric field while up-spin ones along the field direction. This novel spin
transfer properties make BFO film an intriguing candidate for application in
spin capacitor and BFO-based multiferroic field-effect device.",1212.3985v2
2020-01-10,Long-Range Phonon Spin Transport in Ferromagnet-Nonmagnetic Insulator Heterostructures,"We investigate phonon spin transport in an insulating
ferromagnet-nonmagnet-ferromagnet heterostructure. We show that the
magnetoelastic interaction between the spins and the phonons leads to nonlocal
spin transfer between the magnets. This transfer is mediated by a local phonon
spin current and accompanied by a phonon spin accumulation. The spin
conductance depends nontrivially on the system size, and decays over millimeter
length scales for realistic material parameters, far exceeding the decay
lengths of magnonic spin currents.",2001.03462v2
2001-08-08,Angular Momentum Transfer in Protolunar Disk,"We numerically calculated angular momentum transfer processes in a dense
particulate disk within Roche limit by global $N$-body simulations, up to
$N=10^5$, for parameters corresponding to a protolunar disk generated by a
giant impact on a proto-Earth. In the simulations, both self-gravity and
inelastic physical collisions are included. We first formalized expressions for
angular momentum transfer rate including self-gravity and calculated the
transfer rate with the results of our $N$-body simulations. Spiral structure is
formed within Roche limit by self-gravity and energy dissipation of inelastic
collisions, and angular momentum is effectively transfered outward. Angular
momentum transfer is dominated by both gravitational torque due to the spiral
structure and particles' collective motion associated with the structure. Since
formation and evolution of the spiral structure is regulated by the disk
surface density, the angular momentum transfer rate depends on surface density,
but not on particle size or number, so that the time scale of evolution of a
particulate disk is independent on the number of particles ($N$) that is used
to represent the disk, if $N$ is large enough to represent the spiral
structure. With $N=10^5$, the detailed spiral structure is resolved while it is
only poorly resolved with $N=10^3$, however, we found that calculated angular
momentum transfer does not change as long as $N \gtrsim 10^3$.",0108133v1
1999-11-13,Magnetic Field Limit on SGR 1900+14,"We measured the period and spin-down rate for SGR 1900+14 during the
quiescient period two years before the recent interval of renewed burst
activity. We have shown that the spin-down age of SGR 1900+14 is consistent
with a braking index of ~1 which is appropriate for wind torques and not
magnetic dipole radiation. We have shown that a combination of dipole
radiation, and wind luminosity, coupled with estimated ages and present spin
parameters, imply that the magnetic field for SGR 1900+14 is less than 6 x
10^13 G and that the efficiency for conversion of wind luminosity to x-ray
luminosity is <2%.",9911238v1
2001-07-30,Spin Torques in Ferromagnetic/Normal Metal Structures,"Recent theories of spin-current-induced magnetization reversal are formulated
in terms of a spin-mixing conductance $G^{mix}$. We evaluate $G^{mix}$ from
first-principles for a number of (dis)ordered interfaces between magnetic and
non-magnetic materials. In multi-terminal devices, the magnetization direction
of a one side of a tunnel junction or a ferromagnetic insulator can ideally be
switched with negligible charge current dissipation.",0107589v1
2006-05-23,Suppression of telegraph noise in a CPP spin valve by an oscillating spin torque: Numerical study,"The phenomenon of stochastic resonance (SR) has been mainly studied in
one-dimensional systems with additive noise. We show that in higher dimensional
systems and in the presence of multiplicative noise, a non-linear magnetic
system with a strongly periodic current can show behavior similar to that of SR
but only for frequencies below the ferromagnetic resonance (FMR) frequency of
the system. Such a phenomena can provide an effective way to suppress low
frequency noise in spin valve magnetic sensors.",0605585v1
2008-08-09,Gilbert Damping in Conducting Ferromagnets I: Kohn-Sham Theory and Atomic-Scale Inhomogeneity,"We derive an approximate expression for the Gilbert damping coefficient
\alpha_G of itinerant electron ferromagnets which is based on their description
in terms of spin-density-functional-theory (SDFT) and Kohn-Sham quasiparticle
orbitals. We argue for an expression in which the coupling of magnetization
fluctuations to particle-hole transitions is weighted by the spin-dependent
part of the theory's exchange-correlation potential, a quantity which has large
spatial variations on an atomic length scale. Our SDFT result for \alpha_G is
closely related to the previously proposed spin-torque correlation-function
expression.",0808.1373v1
2009-01-22,Monopole and Topological Electron Dynamics in Adiabatic Spintronic and Graphene Systems,"A unified theoretical treatment is presented to describe the physics of
electron dynamics in semiconductor and graphene systems. Electron spin fast
alignment with the Zeeman magnetic field (physical or effective) is treated as
a form of adiabatic spin evolution which necessarily generates a monopole in
magnetic space. One could transform this monopole into the physical and
intuitive topological magnetic fields in the useful momentum (K) or real spaces
(R). The physics of electron dynamics related to spin Hall, torque,
oscillations and other technologically useful spinor effects can be inferred
from the topological magnetic fields in spintronic, graphene and other SU(2)
systems.",0901.3411v1
2009-09-09,Rapid Domain Wall Motion in Permalloy Nanowires Excited by Spin-Polarized Current Applied Perpendicular to the Nanowire,"We study domain wall (DW) dynamics in permalloy nanowires excited by
alternating spin-polarized current applied perpendicular to the nanowire. Spin
torque ferromagnetic resonance measurements reveal that DW oscillations at a
pinning site in the nanowire can be excited with velocities as high as 800 m/s
at current densities below 10$^7$ A/cm$^2$.",0909.1822v4
2009-10-30,Dissipative dynamics of magnetic solitons in metals,"Soliton dynamics in spin-textured metals generate electrical currents, which
produce backaction through spin torques. We modify the Landau-Lifshitz-Gilbert
equation and the corresponding solitonic equations of motion to include such
higher-order texture effects. We also find a quasistatic equation for the
induced electrochemical potential, which needs to be solved for
self-consistently, in the incompressible limit. As an example, we consider the
orbital motion of a vortex in a point-contact spin valve, and discuss
modifications of orbit radius, frequency, and dissipation power.",0910.5912v2
2010-11-18,Possibility of exchange switching ferromagnet - antiferromagnet junctions,"Current flowing is studied in magnetic junctions consisting of a
ferromagnetic metal (FM), antiferromagnetic conductor (AFM) and a nonmagnetic
metal closing the electric circuit. The FM layer with high anisotropy and
pinned spins of the magnetic atoms in the lattice acts as a spin injector
relative to the AFM layer. To obtain resulting magnetization in the AFM layer,
magnetic field is applied, which may be varied to control the magnetization.
The spin-polarized current from the FM layer creates a torque and makes it
possible to switch the magnetization. A possibility is shown to lower the
threshold current density by the orders of magnitude by means of the magnetic
field.",1011.4303v1
2014-02-05,Spin evolution of long-period X-ray pulsars,"Spin evolution of X-ray pulsars in High Mass X-ray Binaries (HMXBs) is
discussed under various assumptions about the geometry and physical parameters
of the accretion flow. The torque applied to the neutron star from the
accretion flow and equilibrium period of the pulsars are evaluated. We show
that the observed spin evolution of the pulsars can be explained in terms of a
scenario in which the neutron star accretes material from a magnetized stellar
wind.",1402.1029v3
2014-10-02,Current-driven spin orbit field in LaAlO3/SrTiO3 heterostructures,"We demonstrate a current tunable Rashba spin orbit interaction in
LaAlO3/SrTiO3 (LAO/STO) quasi two dimensional electron gas (2DEG) system.
Anisotropic magnetoresistance (AMR) measurements are employed to detect and
understand the current-induced Rashba field. The effective Rashba field scales
with the current and a value of 2.35 T is observed for a dc-current of 200 uA.
The results suggest that LAO/STO heterostructures can be considered for spin
orbit torque based magnetization switching.",1410.0456v1
2016-04-21,Non-equilibrium magnetic fields in ab initio spin dynamics,"Starting from the continuity equation for the magnetization in time-dependent
spin-density functional theory, we derive an expression for the effective
time-dependent magnetic fields driving the out-of-equilibrium spin dynamics in
magnetic systems. We evaluate these, so called, kinetic magnetic fields in the
ultrafast demagnetization response to optical pulse excitations of
ferromagnetic iron-based materials, namely Fe$_6$ cluster and bulk bcc Fe. We
identify spatial ""hot spots"" where the demagnetization is particularly enhanced
as a result of the increased kinetic torque.",1604.06262v2
2019-11-11,Domain wall motion in a diffusive weak ferromagnet,"We study the domain wall motion in a disordered weak ferromagnet, induced by
injecting a spin current from a strong ferromagnet. Starting from the spin
diffusion equation describing the spin accumulation in the weak ferromagnet, we
calculate the force and torque acting on the domain wall. We also study the
ensuing domain wall dynamics, and suggest a possible measurement method for
detecting the domain wall motion via measuring the additional resistance.",1911.04121v5
2018-07-31,Cooling of the rotation of a nanodiamond via the interaction with the electron spin of the contained NV-center,"We propose a way to cool the rotation of a nanodiamond, which contains a
NV-center and is levitated by an optical tweezer.
  Following the rotation of the particle, the NV-center electron spin
experiences varying external fields and so leads to spin-rotation coupling. By
optically pumping the electrons from a higher energy level to a lower level,
the rotation energy is dissipated. We give the analytical result for the
damping torque exerted on the nanodiamond, and evaluate the final cooling
temperature by the fluctuation-dissipation theorem. It's shown that the quantum
regime of the rotation can be reached with our scheme.",1807.11647v1
2018-08-07,Energy Storage via Topological Spin Textures,"We formulate an energy-storage concept based on the free energy associated
with metastable magnetic configurations. Despite the active, magnetic region of
the battery being electrically insulating, it can sustain effective
hydrodynamics of spin textures, whose conservation law is governed by topology.
To illustrate the key physics and potential functionality, we focus here on the
simplest quasi-one-dimensional case of planar winding of the magnetic order
parameter. The energy is stored in the metastable winding number, which can be
injected electrically by an appropriately tailored spin torque. Due to the
nonvolatility and the endurance of magnetic systems, the injected energy can be
stored essentially indefinitely, with charging/discharging cycles that do not
degrade over time.",1808.02461v1
2017-10-30,Orbit and intrinsic spin-up of the newly discovered transient X-ray pulsar Swift J0243.6+6124,"We present the orbital solution for the newly discovered transient Be X-ray
binary Swift J0243.6+6124 based on the data from gamma-ray burst monitor
onboard Fermi obtained during the Oct 2017 outburst. We model the Doppler
induced and intrinsic spin variations of the neutron star assuming that the
later is driven by accretion torque and discuss the implications of the
observed spin variations for the parameters of the neutron star and the binary.
In particular we conclude that the neutron star must be strongly magnetized,
and estimate the distance to the source at $\sim$5 kpc.",1710.10912v2
2019-07-05,Topological states,"Topological phases are characterised by a topological invariant that remains
unchanged by deformations in the Hamiltonian. Materials exhibiting topological
phases include topological insulators, superconductors exhibiting strong
spin-orbit coupling, transition metal dichalcogenides, which can be made
atomically thin and have direct band gaps, as well as high mobility Weyl and
Dirac semimetals. Devices harnessing topological electron states include
topological (spin) transistors, spin-orbit torque devices, non-linear
electrical and optical systems, and topological quantum bits.",1907.02625v1
2023-12-22,Magnetic droplet solitons,"Magnetic droplets are nanoscale, non-topological, dynamical solitons that can
be nucleated in different spintronic devices, such as spin torque
nano-oscillators (STNOs) and spin Hall nano-oscillators (SHNOs). This chapter
first briefly discusses the theory of spin current driven dissipative magnetic
droplets in ferromagnetic thin films with uniaxial anisotropy. We then
thoroughly review the research literature on magnetic droplets and their
salient features, as measured using electrical, microwave, and synchrotron
techniques, and as envisaged by micromagnetic simulations. We also touch upon a
closely related soliton, the dynamical skyrmion. Finally, we present an outlook
of new routes in droplet science.",2312.14621v1
2021-08-16,Detection of nearly periodic spin period reversals in Vela X-1 on long time-scales: inkling of solar-like cycle in the donor star?,"We explore the long-term evolution of the spin period of the High Mass X-ray
Binary (HMXB) pulsar Vela X-1 over a period of 46 yr. Our analysis indicates
nearly periodic variations in the spin period of the pulsar on time-scales of
about 5.9 yr. There is suggestion of an overall spin-down behaviour of the
pulsar though it is noticed that the source appears to stay near its
equilibrium period 283.4 s since MJD 51000, with rather erratic
spin-up/spin-down episodes around this value. Our study suggests nearly cyclic
turnover in the spin behaviour of the pulsar from spin-up to spin-down regimes
on time-scales of about 17-19 yr. To our knowledge this is the first report of
periodic variation in the spin behaviour of a wind-fed accreting pulsar. We
also observe erratic episodes of spin-up and spin-down behaviour on relatively
shorter time-scales which is a well known archetype of this wind-fed X-ray
pulsar. We investigate whether nearly periodic long-term spin period changes in
the pulsar can be explained by using known mechanisms of torque reversals in
the accretion powered neutron stars. It appears that changes in the accretion
environment of the pulsar using current ideas can probably lead to long-term
spin period changes in this X-ray pulsar.",2108.07097v1
2021-03-23,The Onset of Chaos in Permanently Deformed Binaries from Spin-Orbit and Spin-Spin Coupling,"Permanently deformed objects in binary systems can experience complex
rotation evolution, arising from the extensively studied effect of spin-orbit
coupling as well as more nuanced dynamics arising from spin-spin interactions.
The ability of an object to sustain an aspheroidal shape largely determines
whether or not it will exhibit non-trivial rotational behavior. In this work,
we adopt a simplified model of a gravitationally interacting primary and
satellite pair, where each body's quadrupole moment is approximated by two
diametrically opposed point masses. After calculating the net gravitational
torque on the satellite from the primary, and the associated equations of
motion, we employ a Hamiltonian formalism which allows for a perturbative
treatment of the spin-orbit and retrograde and prograde spin-spin coupling
states. By analyzing the resonances individually and collectively, we determine
the criteria for resonance overlap and the onset of chaos, as a function of
orbital and geometric properties of the binary. We extend the 2D planar
geometry to calculate the obliquity evolution, and find that satellites in
spin-spin resonances undergo precession when inclined out of the plane, but do
not tumble. We apply our resonance overlap criteria to the contact binary
system (216) Kleopatra, and find that its satellites, Cleoselene and
Alexhelios, may plausibly be exhibiting chaotic rotational dynamics from the
overlap of the spin-orbit and retrograde spin-spin resonances. While this model
is by construction generalizable to any binary system, it will be particularly
useful to study small bodies in the solar system, whose irregular shapes make
them ideal candidates for exotic rotational states.",2103.12484v1
2014-08-29,Transferring entangled states through spin chains by boundary-state multiplets,"Quantum spin chains may be used to transfer quantum states between elements
of a quantum information processing device. A scheme discovered recently
\cite{BFR+12} was shown to have favorable transfer properties for ingle-qubit
states even in the presence of built-in static disorder caused by manufacturing
errors. We extend that scheme in a way suggested already in \cite{BFR+12} and
study the transfer of the four Bell states which form a maximally entangled
basis in the two-qubit Hilbert space. We show that perfect transfer of all four
Bell states separately and of arbitrary linear combinations may be achieved for
chains with hundreds of spins. For simplicity we restrict ourselves to systems
without disorder.",1408.7017v1
2015-02-17,Robustness of spin-chain state-transfer schemes,"This is a shortened and slightly edited version of a chapter in the
collection ""Quantum State Transfer and Network Engineering"", edited by G.M.
Nikolopoulos and I. Jex, where we review our own research about the robustness
of spin-chain state-transfer schemes along with other approaches to the topic.
Since our own research is documented elsewhere to a large extent we here
restrict ourselves to a review of other approaches which might be useful to
other researchers in the field.",1502.04879v1
2015-10-12,Room-temperature spin-orbit torque in NiMnSb,"Materials that crystalize in diamond-related lattices, with Si and GaAs as
their prime examples, are at the foundation of modern electronics.
Simultaneoulsy, the two atomic sites in the unit cell of these crystals form
inversion partners which gives rise to relativistic non-equilibrium spin
phenomena highly relevant for magnetic memories and other spintronic devices.
When the inversion-partner sites are occupied by the same atomic species,
electrical current can generate local spin polarization with the same magnitude
and opposite sign on the two inversion-partner sites. In CuMnAs, which shares
this specific crystal symmetry of the Si lattice, the effect led to the
demonstration of electrical switching in an antiferromagnetic memory at room
temperature. When the inversion-partner sites are occupied by different atoms,
a non-zero global spin-polarization is generated by the applied current which
can switch a ferromagnet, as reported at low temperatures in the diluted
magnetic semiconductor (Ga,Mn)As. Here we demonstrate the effect of the global
current-induced spin polarization in a counterpart crystal-symmetry material
NiMnSb which is a member of the broad family of magnetic Heusler compounds. It
is an ordered high-temperature ferromagnetic metal whose other favorable
characteristics include high spin-polarization and low damping of magnetization
dynamics. Our experiments are performed on strained single-crystal epilayers of
NiMnSb grown on InGaAs. By performing all-electrical ferromagnetic resonance
measurements in microbars patterned along different crystal axes we detect
room-temperature spin-orbit torques generated by effective fields of the
Dresselhaus symmetry. The measured magnitude and symmetry of the
current-induced torques are consistent with our relativistic density-functional
theory calculations.",1510.03356v1
2015-04-14,Single photoelectron spin detection and angular momentum transfer in a gate defined quantum dot,"Recent innovations in fabricating nanoscale confined spin systems have
enabled investigation of fundamental quantum correlations between single quanta
of photons and matter states. Realization of quantum state transfer from photon
polarization to electron spin using gate defined quantum dots (QDs) may give
evidence of preserved coherence of angular momentum basis states at the
photon-spin interface. The interface would enlarge the concept of quantum
information technology, in which single photogenerated electron spins are
manipulated with the dots, but this remains a serious challenge. Here, we
report the detection of single electron spins generated by polarized single
photons via a double QD (DQD) to verify the angular momentum transfer from
single photons to single electrons. Pauli spin blockade (PSB) is used to
project the photoelectron spin state onto the up or down spin state. Our result
promises the realization of coherent quantum state transfer and development of
hybrid photon and spin quantum technology.",1504.03696v1
2010-01-14,State transfer in static and dynamic spin chains with disorder,"We examine the speed and fidelity of several protocols for state or single
excitation transfer in finite spin chains subject to diagonal and off-diagonal
disorder. We find that, for a given chain length and maximal achievable
inter-spin exchange (XY) coupling strength, the optimal static spin-coupling
protocol, implementing the fastest state transfer between the two ends of the
chain, is more susceptible to off-diagonal (XY coupling) disorder, as compared
to a much slower but robust adiabatic transfer protocol with time-dependent
coupling strengths.",1001.2444v1
2019-03-29,Adiabatic population transfer of dressed spin states with quantum optimal control,"We report theoretical studies of adiabatic population transfer using dressed
spin states. Quantum optimal control using the algorithm of Chopped Random
Basis (CRAB) has been implemented in a negatively charged diamond nitrogen
vacancy center that is coupled to a strong and resonant microwave field. We
show that the dressed spin states are highly effective in suppressing effects
of spin dephasing on adiabatic population transfer. The numerical simulation
also demonstrates that CRAB-based quantum optimal control can enable an
efficient and robust adiabatic population transfer.",1903.12651v1
1998-10-29,Runaway Heating By R-modes of Neutron Stars in Low Mass X-ray Binaries,"Recently Andersson et. al., and Bildsten have independently suggested that an
r-mode instability might be responsible for stalling the neutron-star spin-up
in strongly accreting, Low Mass X-ray Binaries (LMXBs). We show that if this
does occur, then there are two possibilities for the resulting neutron-star
evolution:
  If the r-mode damping is a decreasing function of temperature, then the star
undergoes a cyclic evolution: (i) accretional spin-up triggers the instability
near the observed maximum spin rate; (ii) the r-modes become highly excited
through gravitational-radiation reaction, and in a fraction of a year they
viscously heat the star; (iii) r-mode gravitational-radiation reaction then
spins the star down in a fraction of a year to some limiting rotational
frequency; (iv) the r-mode instability shuts off; (v) the neutron star slowly
cools and is spun up by accretion, until it once again reaches the instability
point, closing the cycle. The shortness of the epoch of r-mode activity makes
it unlikely that r-modes are currently excited in the neutron star of any
galactic LMXBs. Nevertheless, this cyclic evolution could be responsible for
keeping the rotational frequencies within the observed LMXB frequency range.
  If, on the other hand, the r-mode damping is temperature independent, then a
steady state with constant angular velocity and $T_{\rm core}\simeq 4\times
10^8$K is reached, in which r-mode viscous heating is balanced by neutrino
cooling and accretional spin-up torque is balanced by
gravitational-radiation-reaction spin-down torque. In this case the neutron
stars in LMXBs could be potential sources of periodic gravitational waves,
detectable by enhanced LIGO interferometers.",9810471v1
2018-01-11,Efficient Charge-Spin Conversion and Magnetization Switching though Rashba Effect at Topological Insulator/Ag Interface,"We report the observation of efficient charge-to-spin conversion in the
three-dimensional topological insulator (TI) Bi2Se3 and Ag bilayer by the
spin-torque ferromagnetic resonance technique. The spin orbit torque ratio in
the Bi2Se3/Ag/CoFeB heterostructure shows a significant enhancement as the Ag
thickness increases to ~2 nm and reaches a value of 0.5 for 5 nm Ag, which is
~3 times higher than that of Bi2Se3/CoFeB at room temperature. The observation
reveals the interfacial effect of Bi2Se3/Ag exceeds that of the topological
surface states (TSS) in the Bi2Se3 layer and plays a dominant role in the
charge-to-spin conversion in the Bi2Se3/Ag/CoFeB system. Based on the
first-principles calculations, we attribute our observation to the large
Rashba-splitting bands which wrap the TSS band and has the same net spin
polarization direction as TSS of Bi2Se3. Subsequently, we demonstrate for the
first time the Rashba induced magnetization switching in Bi2Se3/Ag/Py with a
low current density of 5.8 X 10^5 A/cm2.",1801.03689v1
2020-08-19,Impact of intra-grain spin wave reflections on nano-contact spin torque oscillators,"We investigate the origin of the experimentally observed varying
current-frequency nonlinearity of the propagating spin wave mode in
nano-contact spin torque oscillators. Nominally identical devices with 100 nm
diameter are characterized by electrical microwave measurements and show large
variation in the generated frequency as a function of drive current. This
quantitative and qualitative device-to-device variation is described in terms
of continuous and discontinuous nonlinear transitions between linear current
intervals. The thin film grain microstructure in our samples is determined
using atomic force and scanning electron microscopy to be on the scale of 30
nm. Micromagnetic simulations show that the reflection of spin waves against
the grain boundaries results in standing wave resonance configurations. For a
simulated device with a single artificial grain, the frequency increases
linearly with the drive current until the decreased wavelength eventually
forces another spin wave anti-node to be formed. This transition results in a
discontinuous step in the frequency versus current relation. Simulations of
complete, randomly generated grain microstructures additionally shows
continuous nonlinearity and a resulting device-to-device variation in frequency
that is similar to the experimental levels. The impact of temperature from 4 K
to 300 K on the resonance mode-transition nonlinearity and frequency noise is
investigated using simulations and it is found that the peak levels of the
spectral linewidth as a function of drive current agrees quantitatively with
typical levels found in experiments at room temperature.",2008.08357v1
2020-05-19,Skew-scattering-induced giant antidamping spin-orbit torques: Collinear and out-of-plane Edelstein effects at two-dimensional material/ferromagnet interfaces,"Heavy metal/ferromagnet interfaces feature emergent spin-orbit effects absent
in the bulk materials. Because of their inherent strong coupling between spin,
charge and orbital degrees of freedom, such systems provide a platform for
technologically sought-after spin-orbit torques (SOTs). However, the
microscopic origin of purely interfacial antidamping SOT, especially in the
ultimate atomically thin limit, has proven elusive. Here, using two-dimensional
(2D) van der Waals materials as a testbed for interfacial phenomena, we address
this problem by means of a microscopic framework accounting for band structure
effects and impurity scattering on equal footing and nonperturbatively. A
number of unconventional and measurable effects are predicted, the most
remarkable of which is a giant enhancement of antidamping SOT in the dilute
disorder limit induced by a robust skew scattering mechanism, which is
operative in realistic interfaces and does not require magnetic impurities. The
newly unveiled skew scattering mechanism activates rich semiclassical
spin-charge conversion effects that have gone unnoticed in the literature,
including a collinear Edelstein effect with nonequilibrium spin polarization
aligned with the direction of the applied current.",2005.09670v2
2022-07-04,Detection of field-free magnetization switching through thermoelectric effect in Ta/Pt/Co/Pt with significant spin-orbit torque and competing spin currents,"Application of sufficient lateral current to a heavy metal (HM) can switch
the perpendicular magnetization orientation of adjacent ferromagnetic layer
(FM) through spin-orbit torques (SOTs). The choice of the HM and its
arrangement plays a major role for the SOT induced magnetization switching in
magnetic heterostructures. Here, in asymmetric Pt/Co/Pt heterostructures,
anti-damping (AD) SOT prevails. Ta addition to this stack (Ta/Pt/Co/Pt) give
rise to several compelling effects viz. competing spin currents (due to
opposite spin-Hall angles of adjacent Ta and Pt layers), significant AD-SOT,
thermoelectric effects (particularly, anomalous Nernst effect (ANE)), and
enhanced perpendicular magnetic anisotropy. For this Ta/Pt/Co/Pt stack, the
AD-SOT values are stabilized to that of the Pt/Co/Pt stack, which is
significant than what is expected for a stack with competing spin currents.
Current-induced field-free magnetization switching was absent in uniformly
grown Ta/Pt/Co/Pt stack. It was observed that a thickness gradient is essential
to assist the field-free magnetization switching in these heterostructures.
Further, the thermoelectric effects are utilized to develop a technique to
detect the field-free magnetization switching. This technique detects the
second harmonic ANE signal as a reading mechanism. Using ANE symmetry with the
applied current, the switching can be detected in a single current sweep which
was corroborated to the conventional DC Hall method.",2207.01202v1
2022-12-23,Spin-lattice interaction parameters from first principles: theory and implementation,"A scheme is presented to calculate on a first-principles level
  the spin-lattice coupling (SLC) parameters needed to perform
  combined molecular-spin dynamics (MSD) simulations. By treating changes to
the spin configuration and atomic positions on the same level, closed
expressions for the atomic SLC parameters could be derived in a coherent way up
to any order. The properties of the SLC parameters are discussed considering
separately the symmetric and antisymmetric parts of the SLC tensor. The changes
due to atomic displacements of the spin-spin exchange coupling (SSC) parameters
estimated using the SLC parameters are compared with the SSC parameters
calculated for an embedded cluster with the central atom displaced,
demonstrating good agreement of these results. Moreover, this allows to study
the impact of different SLC contributions, linear and quadratic with respect to
displacements, on the properties of the modified SSC parameters. In addition,
we represent an approach to calculate the site-diagonal SLC parameters
characterizing local magnetic anisotropy induced by a lattice distortion, which
is a counterpart of the approach based on magnetic torque used for the
investigations of magneto-crystalline anisotropy (MCA) as well as for
calculations of the MCA constants. In particular, the dependence of the induced
magnetic torque on different types of atomic displacements is analyzed.",2212.12430v1
2002-12-11,Interaction-driven spin precession in quantum-dot spin valves,"We analyze spin-dependent transport through spin valves composed of an
interacting quantum dot coupled to two ferromagnetic leads. The spin on the
quantum dot and the linear conductance as a function of the relative angle
$\theta$ of the leads' magnetization directions is derived to lowest order in
the dot-lead coupling strength. Due to the applied bias voltage spin
accumulates on the quantum dot, which for finite charging energy experiences a
torque, resulting in spin precession. The latter leads to a non-trivial,
interaction-dependent, $\theta$-dependence of the conductance. In particular,
we find that the spin-valve effect is reduced for all $\theta \neq \pi$.",0212253v2
2006-05-22,Geometrical phase effects on the Wigner distribution of Bloch electrons,"We investigate the dynamics of Bloch electrons using a density operator
method and connect this approach with previous theories based on wave packets.
We study non-interacting systems with negligible disorder and strong spin-orbit
interactions, which have been at the forefront of recent research on
spin-related phenomena. We demonstrate that the requirement of gauge invariance
results in a shift in the position at which the Wigner function of Bloch
electrons is evaluated. The present formalism also yields the correction to the
carrier velocity arising from the Berry phase. The gauge-dependent shift in
carrier position and the Berry phase correction to the carrier velocity
naturally appear in the charge and current density distributions. In the
context of spin transport we show that the spin velocity may be defined in such
a way as to enable spin dynamics to be treated on the same footing as charge
dynamics. Aside from the gauge-dependent position shift we find additional,
gauge-covariant multipole terms in the density distributions of spin, spin
current and spin torque.",0605528v1
2007-06-01,Conserved spin Hall conductance in two dimensional electron gas in a perpendicular magnetic field,"Using the microscopic theory of the conserved spin current [Phys. Rev. Lett.
\textbf{96}, 076604 (2006)], we investigate the spin Hall effect in the two
dimensional electron gas system with a perpendicular magnetic field. The spin
Hall conductance $\sigma_{\mu\nu}^{s}$ as a response to the electric field
consists of two parts, i.e., the conventional part $\sigma_{\mu\nu}^{s0}$ and
the spin torque dipole correction $\sigma_{\mu\nu}^{s\tau}$. It is shown that
the spin-orbit coupling competes with Zeeman splitting by introducing
additional degeneracies between different Landau levels at certain values of
magnetic field. These degeneracies, if occurring at the Fermi level, turn to
give rise to resonances in both $\sigma_{\mu\nu}^{s0}$ and $\sigma_{\mu\nu
}^{s\tau}$ in spin Hall conductance. Remarkably, both of these two components
have the same sign in the wide range of variation in the magnetic field, which
result in an overall enhancement of the total spin Hall current. In particular,
the magnitude of $\sigma_{\mu\nu}^{s\tau}$ is much larger than that of
$\sigma_{\mu\nu}^{s0}$ around the resonance.",0706.0047v1
2008-12-22,Recent Torque Reversal of 4U 1907+09,"We present timing and spectral analysis of RXTE-PCA observations of the
accretion powered pulsar 4U 1907+09 between June 2007 and August 2008. 4U
1907+09 had been in a spin-down episode with a spin-down rate of
$-3.54\times10^{-14}$ Hz s$^{-1}$ before 1999. From RXTE observations after
March 2001, the source showed a $\sim 60$% decrease in spin-down magnitude and
INTEGRAL observations after March 2003 showed that source started to spin-up.
We found that the source recently entered a new spin-down episode with a
spin-down rate of $-3.59 \times 10^{-14}$ Hz s$^{-1}$. This spin-down rate is
pretty close to the previous long term spin-down rate of the source measured
before 1999. From the spectral analysis, we showed that Hydrogen column density
varies with the orbital phase.",0812.4189v2
2009-07-30,Heisenberg Spin Glass Experiments and the Chiral Ordering Scenario,"An overview is given of experimental data on Heisenberg Spin Glass materials
so as to make detailed comparisons with numerical results on model Heisenberg
spin glasses, with particular reference to the chiral driven ordering
transition scenario due to Kawamura and collaborators. On weak anisotropy
systems, experiments show critical exponents which are very similar to those
estimated numerically for the model Heisenberg chiral ordering transition but
which are quite different from those at Ising spin glass transitions. Again on
weak anisotropy Heisenberg spin glasses, experimental torque data show well
defined in-field transverse ordering transitions up to strong applied fields,
in contrast to Ising spin glasses where fields destroy ordering. When samples
with stronger anisotropies are studied, critical and in-field behavior tend
progressively towards the Ising limit. It can be concluded that the essential
physics of laboratory Heisenberg spin glasses mirrors that of model Heisenberg
spin glasses, where chiral ordering has been demonstrated numerically.",0907.5333v1
2012-10-09,Spectral Characteristics of the Microwave Emission by the Spin Hall Nano-Oscillator,"We utilized microwave spectroscopy to study the magnetization oscillations
locally induced in a Permalloy film by a pure spin current, which is generated
due to the spin Hall effect in an adjacent Pt layer. The oscillation frequency
is lower than the ferromagnetic resonance of Permalloy, indicating that the
oscillation forms a self-localized nonpropagating spin-wave soliton. At
cryogenic temperatures, the spectral characteristics are remarkably similar to
the traditional spin-torque nano-oscillators driven by spin-polarized currents.
However, the linewidth of the oscillation increases exponentially with
temperature and an additional peak appears in the spectrum below the
ferromagnetic resonance, suggesting that the spectral characteristics are
determined by interplay between two localized dynamical states.",1210.2758v2
2013-03-03,High spin polarization of the anomalous Hall current in Co-based Heusler compounds,"Based on first principles density functional calculations of the intrinsic
anomalous and spin Hall conductivities, we predict that the charge Hall current
in Co-based full Heusler compounds Co$_2$XZ (X = Cr and Mn; Z = Al, Si, Ga, Ge,
In and Sn) except Co$_2$CrGa would be almost fully spin-polarized even although
Co$_2$MnAl, Co$_2$MnGa, Co$_2$MnIn and Co$_2$MnSn do not have a half-metallic
band structure. Furthermore, the ratio of the associated spin current to the
charge Hall current is slightly larger than 1.0. This suggests that these
Co-based Heusler compounds, especially Co$_2$MnAl, Co$_2$MnGa and Co$_2$MnIn
which are found to have large anomalous and spin Hall conductivities, might be
called anomalous Hall half-metals and could have valuable applications in
spintronics such as spin valves as well as magnetoresistive and spin-torque
driven nanodevices. These interesting findings are discussed in terms of the
calculated electronic band structures, magnetic moments and also anomalous and
spin Hall conductivities as a function of the Fermi level.",1303.0509v1
2014-02-27,On the longitudinal spin current induced by a temperature gradient in a ferromagnetic insulator,"Based on the solution of the stochastic Landau-Lifshitz-Gilbert equation
discretized for a ferromagnetic chain subject to a uniform temperature
gradient, we present a detailed numerical study of the spin dynamics with a
focus particularly on finite-size effects. We calculate and analyze the net
longitudinal spin current for various temperature gradients, chain lengths, and
external static magnetic fields. In addition, we model an interface formed by a
nonuniformly magnetized finite-size ferromagnetic insulator and a normal metal
and inspect the effects of enhanced Gilbert damping on the formation of the
space-dependent spin current within the chain. A particular aim of this study
is the inspection of the spin Seebeck effect beyond the linear response regime.
We find that within our model the microscopic mechanism of the spin Seebeck
current is the magnon accumulation effect quantified in terms of the exchange
spin torque. According to our results, this effect drives the spin Seebeck
current even in the absence of a deviation between the magnon and phonon
temperature profiles. Our theoretical findings are in line with the recently
observed experimental results by M. Agrawal et al., Phys. Rev. Lett. 111,
107204 (2013).",1402.6899v1
2015-08-06,Large spin-wave bullet in a ferrimagnetic insulator driven by spin Hall effect,"Due to its transverse nature, spin Hall effects (SHE) provide the possibility
to excite and detect spin currents and magnetization dynamics even in magnetic
insulators. Magnetic insulators are outstanding materials for the investigation
of nonlinear phenomena and for novel low power spintronics applications because
of their extremely low Gilbert damping. Here, we report on the direct imaging
of electrically driven spin-torque ferromagnetic resonance (ST-FMR) in the
ferrimagnetic insulator Y$_3$Fe$_5$O$_{12}$ based on the excitation and
detection by SHEs. The driven spin dynamics in Y$_3$Fe$_5$O$_{12}$ is directly
imaged by spatially-resolved microfocused Brillouin light scattering (BLS)
spectroscopy. Previously, ST-FMR experiments assumed a uniform precession
across the sample, which is not valid in our measurements. A strong spin-wave
localization in the center of the sample is observed indicating the formation
of a nonlinear, self-localized spin-wave `bullet'.",1508.01427v1
2016-09-24,Thickness dependence of spin Hall magnetoresistance in FeMn/Pt bilayers,"We investigated spin Hall magnetoresistance in FeMn/Pt bilayers, which was
found to be one order of magnitude larger than that of heavy metal and
insulating ferromagnet or antiferromagnet bilayer systems, and comparable to
that of NiFe/Pt bilayers. The spin Hall magnetoresistance shows a non-monotonic
dependence on the thicknesses of both FeMn and Pt. The former can be accounted
for by the thickness dependence of net magnetization in FeMn thin films,
whereas the latter is mainly due to spin accumulation and diffusion in Pt.
Through analysis of the Pt thickness dependence, the spin Hall angle, spin
diffusion length of Pt and the real part of spin mixing conductance were
determined to be 0.2, 1.1 nm, and $5.5 * 10^{14} {\Omega}^{-1} m^{-2}$,
respectively. The results corroborate the spin orbit torque effect observed in
this system recently.",1609.07566v2
2017-12-15,Giant Enhancement of Intrinsic Spin Hall Conductivity in $β$ Tungsten via Substitutional Doping,"A key challenge in manipulating the magnetization in
heavy-metal/ferromagnetic bilayers via the spin-orbit torque is to identify
materials that exhibit an efficient charge-to-spin current conversion. Ab
initio electronic structure calculations reveal that the intrinsic spin Hall
conductivity (SHC) for pristine $\beta$-W is about sixty percent larger than
that of $\alpha$-W. More importantly, we demonstrate that the SHC of $\beta$-W
can be enhanced via Ta alloying. This is corroborated by spin Berry curvature
calculations of W$_{1-x}$Ta$_x$ ($x$ $\sim$ 12.5%) alloys which show a giant
enhancement of spin Hall angle of up to $\approx$ $-0.5$. The underlying
mechanism is the synergistic behavior of the SHC and longitudinal conductivity
with Fermi level position. These findings, not only pave the way for enhancing
the intrinsic spin Hall effect in $\beta$-W, but also provide new guidelines to
exploit substitutional alloying to tailor the spin Hall effect in various
materials.",1712.05516v1
2018-10-01,Determination of spin Hall angle in heavy metal/CoFeB-based heterostructures with interfacial spin-orbit fields,"Magnetization dynamics in W/CoFeB, CoFeB/Pt and W/CoFeB/Pt multilayers was
investigated using spin-orbit-torque ferromagnetic resonance (SOT-FMR)
technique. An analytical model based on magnetization dynamics due to SOT was
used to fit heavy metal (HM) thickness dependence of symmetric and
antisymmetric components of the SOT-FMR signal. The analysis resulted in a
determination of the properties of HM layers, such as spin Hall angle and spin
diffusion length. The spin Hall angle of -0.36 and 0.09 has been found in the
W/CoFeB and CoFeB/Pt bilayers, respectively, which add up in the case of
W/CoFeB/Pt trilayer. More importantly, we have determined effective interfacial
spin-orbit fields at both W/CoFeB and CoFeB/Pt interfaces, which are shown to
cancel Oersted field for particular thicknesses of the heavy metal layers,
leading to pure spin-current-induced dynamics and indicating the possibility
for a more efficient magnetization switching.",1810.00641v1
2020-08-04,Intrinsic spin Hall effect in topological insulators: A first-principles study,"The intrinsic spin Hall conductivity of typical topological insulators
Sb$_2$Se$_3$, Sb$_2$Te$_3$, Bi$_2$Se$_3$, and Bi$_2$Te$_3$ in the bulk form, is
calculated from first-principles by using density functional theory and the
linear response theory in a maximally localized Wannier basis. The results show
that there is a finite spin Hall conductivity of 100--200 ($\hbar$/2e)(S/cm) in
the vicinity of the Fermi energy. Although the resulting values are an order of
magnitude smaller than that of heavy metals, they show a comparable spin Hall
angle due to their relatively lower longitudinal conductivity. The spin Hall
angle for different compounds are then compared to that of recent experiments
on topological-insulator/ferromagnet heterostructures. The comparison suggests
that the role of the bulk in generating a spin current and consequently a spin
torque in magnetization switching applications is comparable to that of the
surface including the spin-momentum locked surface states and the
Rashba-Edelstein effect at the interface.",2008.01764v2
2017-06-05,Consistent microscopic analysis of spin pumping effects,"We present a consistent microscopic study of spin pumping effects for both
metallic and insulating ferromagnets. As for metallic case, we present a simple
quantum mechanical picture of the effect as due to the electron spin flip as a
result of a nonadiabatic (off-diagonal) spin gauge field. The effect of
interface spin-orbit interaction is briefly discussed. We also carry out
field-theoretic calculation to discuss on the equal footing the spin current
generation and torque effects such as enhanced Gilbert damping constant and
shift of precession frequency both in metallic and insulating cases. For thick
ferromagnetic metal, our study reproduces results of previous theories such as
the correspondence between the dc component of the spin current and enhancement
of the damping. For thin metal and insulator, the relation turns out to be
modified. For the insulating case, driven locally by interface $sd$ exchange
interaction due to magnetic proximity effect, physical mechanism is distinct
from the metallic case. Further study of proximity effect and interface
spin-orbit interaction would be crucial to interpret experimental results in
particular for insulators.",1706.01185v1
2019-03-22,Exceptional points in classical spin dynamics,"Non-conservative physical systems admit a special kind of spectral
degeneracy, known as exceptional point (EP), at which eigenvalues and
eigenvectors of the corresponding non-Hermitian Hamiltonian coalesce. Dynamical
parametric encircling of the EP can lead to non-adiabatic evolution associated
with a state flip, a sharp transition between the resonant modes. Physical
consequences of the dynamical encircling of EPs in open dissipative systems
have been explored in optics and photonics. Building on the recent progress in
understanding the parity-time (PT)-symmetric dynamics in spin systems, we use
topological properties of EPs to implement chiral non-reciprocal transmission
of a spin through the material with non-uniform magnetization, like helical
magnet. We consider an exemplary system, spin-torque-driven single spin
described by the time-dependent non-Hermitian Hamiltonian. We show that
encircling individual EPs in parameter space results in non-reciprocal spin
dynamics and find the range of optimal protocol parameters for high-efficiency
asymmetric spin filter based on this effect. Our findings offer a platform for
non-reciprocal spin devices for spintronics and magnonics.",1903.09729v2
2016-12-31,Spin Transport and Accumulation in 2D Weyl Fermion System,"In this work, we study the spin Hall effect and Rashba-Edelstein effect of a
2D Weyl fermion system in the clean limit using the Kubo formalism. Spin
transport is solely due to the spin-torque current in this strongly spin-orbit
coupled (SOC) system, and chiral spin-flip scattering off non-SOC scalar
impurities, with potential strength $V$ and size $a$, gives rise to a
skew-scattering mechanism for the spin Hall effect. The key result is that the
resultant spin-Hall angle has a fixed sign, with $\theta^{SH} \sim O
\left(\tfrac{V^2}{v_F^2/a^2} (k_F a)^4 \right)$ being a strongly-dependent
function of $k_F a$, with $k_F$ and $v_F$ being the Fermi wave-vector and Fermi
velocity respectively. This, therefore, allows for the possibility of tuning
the SHE by adjusting the Fermi energy or impurity size.",1701.00074v3
2019-07-01,Spin currents driven by the Higgs mode in magnetic superconductors,"Higgs mode in superconducting materials describes slowly-decaying
oscillations of the order parameter amplitude. We demonstrate that in magnetic
superconductors with built-in spin-splitting field Higgs mode is strongly
coupled to the spin degrees of freedom allowing for the generation of
time-dependent spin currents.
  Converting such spin currents to electric signals by spin-filtering elements
provides a tool for the second-harmonic generation and the electrical detection
of the Higgs mode generated by the external irradiation. The non-adiabatic spin
torques generated by these spin currents allow for the magnetic detection of
the Higgs mode by measuring the precession of magnetic moment in the adjacent
ferromagnet. We discuss also the reciprocal effect which is the generation of
the Higgs mode by the magnetic precession. Coupling the collective modes in
superconductors to light and magnetic dynamics opens the new direction of
superconducting optospintronics.",1907.00539v1
2020-12-11,Compositional effect on auto-oscillation behavior of Ni100-xFex/Pt spin Hall nano-oscillators,"We demonstrate the compositional effect on the magnetodynamic and
auto-oscillations properties of Ni100-xFex/Pt (x= 10 to 40) nanoconstriction
based spin Hall nano-oscillators. Using spin-torque ferromagnetic resonance
(ST-FMR) performed on microstrips, we measure a significant reduction in both
damping and spin Hall efficiency with increasing Fe content, which lowers the
spin pumping contribution. The strong compositional effect on spin Hall
efficiency is primarily attributed to the increased saturation magnetization in
Fe-rich devices. As a direct consequence, higher current densities are required
to drive spin-wave auto-oscillations at higher microwave frequencies in Fe-rich
nano-constriction devices. Our results establish the critical role of the
compositional effect in engineering the magnetodynamic and auto-oscillation
properties of spin Hall devices for microwav eand magnonic applications.",2012.06121v2
2023-03-14,"Inertial Spinner Swarm Experiments: Spin Pumping, Entropy Oscillations and Spin Frustration","We present here an inertial active spinning swarm consisting of mixtures of
opposite handedness torque driven spinners floating on an air bed with low
damping. Depending on the relative spin sign, spinners can act as their own
anti-particles and annihilate their spins. Rotational energy can become highly
focused, with minority fraction spinners pumped to very high levels of spin
angular momentum. Spinner handedness also matters at high spinner densities but
not low densities: oscillations in the mixing spatial entropy of spinners over
time emerge if there is a net spin imbalance from collective rotations.
Geometrically confined spinners can lock themselves into frustrated spin
states.",2303.08223v1
2023-08-22,Observation of Current-induced Nonlinear Spin Polarization in Pt-Py Bilayers,"We experimentally observe nonlinear spin polarization in metallic bilayers of
platinum and permalloy by means of spin-torque ferromagnetic resonance (ST-FMR)
with the spin-Hall effects. The ST-FMR results under massive dc current
injection contain striking features, which are not caused by extrinsic Joule
heating, but by intrinsic nonlinear spin polarization. The emergence of
nonlinear spin polarization is consistent with observation of unidirectional
spin-Hall magnetoresistance due to magnon generation/annihilation. Moreover,
the magnon generation (annihilation) leads to effective magnetization shrinkage
(expansion) revealed by the ST-FMR measurements. The present study paves a way
to spin-Hall effect based nonlinear spintronic devices as well as
6th-generation mobile communication light sources.",2308.11156v2
2024-01-25,Magnon dispersion and spin transport in CrCl$_3$ bilayers under different strain-induced magnetic states,"Atomically-thin van der Waals magnetic materials offer exceptional
opportunities to mechanically and electrically manipulate magnetic states and
spin textures. The possibility of efficient spin transport in these materials
makes them promising for the development of novel nanospintronics technology.
Using atomistic spin dynamics simulations, we investigate magnetic ground
state, magnon dispersion, critical temperature, and magnon spin transport in
CrCl$_3$ bilayers in the absence and presence of compressive and tensile
strains. We show that in the presence of mechanical strain, the magnon band gap
at the $\Gamma$ point and the critical temperature of the bilayer are
increased. Furthermore, our simulations show that the magnon diffusion length
is reduced in the presence of strain. Moreover, by exciting magnons through the
spin Seebeck effect and spin Hall-induced torque, we illustrate distinctions
between magnon spin transport in the antiferromagnetic state, under compressive
strains, and ferromagnetic states, under tensile strains or in the unstrained
case.",2401.13984v1
2024-02-19,Emergence of radial Rashba spin-orbit fields in twisted van der Waals heterostructures,"Rashba spin-orbit coupling is a quintessential spin interaction appearing in
virtually any electronic heterostructure. Its paradigmatic spin texture in the
momentum space forms a tangential vector field. Using first-principles
investigations, we demonstrate that in twisted homobilayers and
hetero-multilayers, the Rashba coupling can be predominantly radial, parallel
to the momentum. Specifically, we study four experimentally relevant
structures: twisted bilayer graphene (Gr), twisted bilayer WSe$_2$, and twisted
multilayers WSe$_2$/Gr/WSe$_2$ and WSe$_2$/Gr/Gr/WSe$_2$. We show, that the
Rashba spin-orbit field texture in such structures can be controlled by an
electric field, allowing to tune it from radial to tangential. Such spin-orbit
engineering should be useful for designing novel spin-charge conversion and
spin-orbit torque schemes, as well as for controlling correlated phases and
superconductivity in van der Waals materials.",2402.12353v1
2003-04-29,Spin and energy transfer in nanocrystals without transport of charge,"We describe a mechanism of spin transfer between individual quantum dots that
does not require tunneling. Incident circularly-polarized photons create
inter-band excitons with non-zero electron spin in the first quantum dot. When
the quantum-dot pair is properly designed, this excitation can be transferred
to the neighboring dot via the Coulomb interaction with either {\it
conservation} or {\it flipping} of the electron spin. The second dot can
radiate circularly-polarized photons at lower energy. Selection rules for spin
transfer are determined by the resonant conditions and by the strong spin-orbit
interaction in the valence band of nanocrystals. Coulomb-induced energy and
spin transfer in pairs and chains of dots can become very efficient under
resonant conditions. The electron can preserve its spin orientation even in
randomly-oriented nanocrystals.",0304663v2
2003-12-11,An exact effective two-qubit gate in a chain of three spins,"We show that an effective two-qubit gate can be obtained from the free
evolution of three spins in a chain with nearest neighbor XY coupling, without
local manipulations. This gate acts on the two remote spins and leaves the
mediating spin unchanged. It can be used to perfectly transfer an arbitrary
quantum state from the first spin to the last spin or to simultaneously
communicate one classical bit in each direction. One ebit can be generated in
half of the time for state transfer.
  For longer spin chains, we present methods to create or transfer entanglement
between the two end spins in half of the time required for quantum state
transfer, given tunable coupling strength and local magnetic field. We also
examine imperfect state transfer through a homogeneous XY chain.",0312105v1
2010-01-27,Large microwave generation from d.c. driven magnetic vortex oscillators in magnetic tunnel junctions,"Spin polarized current can excite the magnetization of a ferromagnet through
the transfer of spin angular momentum to the local spin system. This pure
spin-related transport phenomena leads to alluring possibilities for the
achievement of a nanometer scale, CMOS compatible and tunable microwave
generator operating at low bias for future wireless communications. Microwave
emission generated by the persitent motion of magnetic vortices induced by spin
transfer effect seems to be a unique manner to reach appropriate spectral
linewidth. However, in metallic systems, where such vortex oscillations have
been observed, the resulting microwave power is much too small. Here we present
experimental evidences of spin-transfer induced core vortex precessions in
MgO-based magnetic tunnel junctions with similar good spectral quality but an
emitted power at least one order of magnitude stronger. More importantly,
unlike to others spin transfer excitations, the thorough comparison between
experimental results and models provide a clear textbook illustration of the
mechanisms of vortex precessions induced by spin transfer.",1001.4933v1
2010-05-14,Perfect state transfers by selective quantum interferences within complex spin networks,"We present a method that implement directional, perfect state transfers
within a branched spin network by exploiting quantum interferences in the
time-domain. That provides a tool to isolate subsystems from a large and
complex one. Directionality is achieved by interrupting the spin-spin coupled
evolution with periods of free Zeeman evolutions, whose timing is tuned to be
commensurate with the relative phases accrued by specific spin pairs. This
leads to a resonant transfer between the chosen qubits, and to a detuning of
all remaining pathways in the network, using only global manipulations. As the
transfer is perfect when the selected pathway is mediated by 2 or 3 spins,
distant state transfers over complex networks can be achieved by successive
recouplings among specific pairs/triads of spins. These effects are illustrated
with a quantum simulator involving 13C NMR on Leucine's backbone; a six-spin
network.",1005.2593v1
2014-08-28,Interplay of spin-orbit and hyperfine interactions in dynamical nuclear polarization in semiconductor quantum dots,"We theoretically study the interplay of spin-orbit and hyperfine interactions
in dynamical nuclear polarization in two-electron semiconductor double quantum
dots near the singlet $(S)$ - triplet $(T_+)$ anticrossing. The goal of the
scheme under study is to extend the singlet $(S)$ - triplet $(T_0)$ qubit
decoherence time $T_2^{*}$ by dynamically transferring the polarization from
the electron spins to the nuclear spins. This polarization transfer is achieved
by cycling the electron spins over the $S-T_+$ anticrossing. Here, we
investigate, both quantitatively and qualitatively, how this hyperfine mediated
dynamical polarization transfer is influenced by the Rashba and Dresselhaus
spin-orbit interaction. In addition to $T_2^*$, we determine the singlet return
probability $P_s$, a quantity that can be measured in experiments. Our results
suggest that the spin-orbit interaction establishes a mechanism that can
polarize the nuclear spins in the opposite direction compared to hyperfine
mediated nuclear spin polarization. In materials with relatively strong
spin-orbit coupling, this interplay of spin-orbit and hyperfine mediated
nuclear spin polarizations prevents any notable increase of the $S-T_0$ qubit
decoherence time $T_2^{*}$.",1408.6700v1
2006-01-20,Conserved Spin and Orbital Angular Momentum Hall Current in a Two-Dimensional Electron System with Rashba and Dresselhaus Spin-orbit Coupling,"We study theoretically the spin and orbital angular momentum (OAM) Hall
effect in a high mobility two-dimensional electron system with Rashba and
Dresselhuas spin-orbit coupling by introducing both the spin and OAM torque
corrections, respectively, to the spin and OAM currents. We find that when both
bands are occupied, the spin Hall conductivity is still a constant (i.e.,
independent of the carrier density) which, however, has an opposite sign to the
previous value. The spin Hall conductivity in general would not be cancelled by
the OAM Hall conductivity. The OAM Hall conductivity is also independent of the
carrier density but depends on the strength ratio of the Rashba to Dresselhaus
spin-orbit coupling, suggesting that one can manipulate the total Hall current
through tuning the Rashba coupling by a gate voltage. We note that in a pure
Rashba system, though the spin Hall conductivity is exactly cancelled by the
OAM Hall conductivity due to the angular momentum conservation, the spin Hall
effect could still manifest itself as nonzero magnetization Hall current and
finite magnetization at the sample edges because the magnetic dipole moment
associated with the spin of an electron is twice as large as that of the OAM.
We also evaluate the electric field-induced OAM and discuss the origin of the
OAM Hall current. Finally, we find that the spin and OAM Hall conductivities
are closely related to the Berry vector (or gauge) potential.",0601466v2
2011-07-11,Spin and charge transport induced by gauge fields in a ferromagnet,"We present a microscopic theory of spin-dependent motive force (""spin motive
force"") induced by magnetization dynamics in a conducting ferromagnet, by
taking account of spin relaxation of conduction electrons. The theory is
developed by calculating spin and charge transport driven by two kinds of gauge
fields; one is the ordinary electromagnetic field $A^{\rm em}_{\mu}$, and the
other is the effective gauge field $A^{z}_{\mu}$ induced by dynamical magnetic
texture. The latter acts in the spin channel and gives rise to a spin motive
force. It is found that the current induced as a linear response to
$A^{z}_{\mu}$ is not gauge-invariant in the presence of spin-flip processes.
This fact is intimately related to the non-conservation of spin via Onsager
reciprocity, so is robust, but indicates a theoretical inconsistency. This
problem is resolved by considering the time dependence of spin-relaxation
source terms in the ""rotated frame"", as in the previous study on Gilbert
damping [J. Phys. Soc. Jpn. {\bf 76}, 063710 (2007)]. This effect restores the
gauge invariance while keeping spin non-conservation. It also gives a
dissipative spin motive force expected as a reciprocal to the dissipative spin
torque (""$\beta$-term"").",1107.2165v3
2015-10-08,Controlling superconducting spin flow with spin-flip immunity using a single homogeneous ferromagnet,"Spin transport via electrons is typically plagued by Joule heating and short
decay lengths due to spin-flip scattering. It is known that dissipationless
spin currents can arise when using conventional superconducting contacts, yet
this has only been experimentally demonstrated when using intricate
magnetically inhomogeneous multilayers, or in extreme cases such as half-metals
with interfacial magnetic disorder. Moreover, it is unknown how such spin
supercurrents decay in the presence of spin-flip scattering. Here, we present a
method for generating a spin supercurrent by using only a single homogeneous
magnetic element. Remarkably, the spin supercurrent generated in this way does
not decay spatially, in stark contrast to normal spin currents that remain
polarized only up to the spin relaxation length. We also expose the existence
of a superconductivity-mediated torque even without magnetic inhomogeneities,
showing that the different components of the spin supercurrent polarization
respond fundamentally differently to a change in the superconducting phase
difference. This establishes a mechanism for tuning dissipationless spin and
charge flow separately, and confirms the advantage that superconductors can
offer in spintronics.",1510.02488v3
2019-02-01,Photoinduced Rashba spin to charge conversion via interfacial unoccupied state,"At interfaces with inversion symmetry breaking, Rashba effect couples the
motion of electrons to their spin; as a result, spin-charge interconversion
mechanism can occur. These interconversion mechanisms commonly exploit Rashba
spin splitting at the Fermi level by spin pumping or spin torque ferromagnetic
resonance. Here, we report evidence of significant photoinduced spin to charge
conversion via Rashba spin splitting in an unoccupied state above the Fermi
level at the Cu(111)/$\alpha$-Bi$_{2}$O$_{3}$ interface. We predict an average
Rashba coefficient of $1.72\times 10^{-10}eV.m$ at 1.98 eV above the Fermi
level, by fully relativistic first-principles analysis of the interfacial
electronic structure with spin orbit interaction. We find agreement with our
observation of helicity dependent photoinduced spin to charge conversion
excited at 1.96 eV at room temperature, with spin current generation of
$J_{s}=10^{6}A/m^{2}$. The present letter shows evidence of efficient
spin-charge conversion exploiting Rashba spin splitting at excited states,
harvesting light energy without magnetic materials or external magnetic fields.",1902.00237v2
2019-08-09,Modeling the Anisotropic Tidal Effect on the Spin-Spin Correlations of Low-Mass Galactic Halos,"The halo spin-spin correlation function, $\eta(r)$, measures how rapidly the
strength of the alignments of the spin directions between the neighbor halos
change with the separation distance, $r$. The previous model based on the tidal
torque theory expresses the halo spin-spin correlation function as a power of
the linear density two-point correlation function, $\eta(r)\propto \xi^{n}(r)$,
predicting $n=2$ in the linear regime and $n=1$ in the non-linear regime. Using
a high-resolution N-body simulation, we show that the halo spin-spin
correlation function in fact drops much less rapidly with $r$ than the
prediction of the previous model, finding $\eta(r)$ to be statistically
significant even at $r\ge 10\,h^{-1}$Mpc on the dwarf galaxy scale. Claiming
that the anisotropic tidal effect is responsible for the failure of the
previous model, we propose a new formula for the halo spin-spin correlation
function expressed in terms of the integrals of $\xi(r)$. The new formula with
the best-fit parameters turns out to agree excellently with the numerical
results in a broad mass range, $0.05\le M/(10^{11}\,h^{-1}\,M_{\odot})\le 50$,
describing well the large-scale tail of $\eta(r)$. We discuss a possibility of
using the large-scale spin-spin correlations of the dwarf galactic halos as a
complementary probe of dark matter.",1908.03467v1
2019-12-16,Spin-current manipulation of photoinduced magnetization dynamics in heavy metal / ferromagnet double layer based nanostructures,"Spin currents offer a way to control static and dynamic magnetic properties,
and therefore they are crucial for next-generation MRAM devices or spin-torque
oscillators. Manipulating the dynamics is especially interesting within the
context of photo-magnonics. In typical $3d$ transition metal ferromagnets like
CoFeB, the lifetime of light-induced magnetization dynamics is restricted to
about 1 ns, which e.g. strongly limits the opportunities to exploit the wave
nature in a magnonic crystal filtering device. Here, we investigate the
potential of spin-currents to increase the spin wave lifetime in a functional
bilayer system, consisting of a heavy metal (8 nm of $\beta$-Tantalum
(Platinum)) and 5 nm CoFeB. Due to the spin Hall effect, the heavy metal layer
generates a transverse spin current when a lateral charge current passes
through the strip. Using time-resolved all-optical pump-probe spectroscopy, we
investigate how this spin current affects the magnetization dynamics in the
adjacent CoFeB layer. We observed a linear spin current manipulation of the
effective Gilbert damping parameter for the Kittel mode from which we were able
to determine the system's spin Hall angles. Furthermore, we measured a strong
influence of the spin current on a high-frequency mode. We interpret this mode
an an exchange dominated higher order spin-wave resonance. Thus we infer a
strong dependence of the exchange constant on the spin current.",1912.07728v1
2021-03-16,Large Spin-to-Charge Conversion in Ultrathin Gold-Silicon Multilayers,"Investigation of the spin Hall effect in gold has triggered increasing
interest over the past decade, since gold combines the properties of a large
bulk spin diffusion length and strong interfacial spin-orbit coupling. However,
discrepancies between the values of the spin Hall angle of gold reported in the
literature have brought into question the microscopic origin of the spin Hall
effect in Au. Here, we investigate the thickness dependence of the spin-charge
conversion efficiency in single Au films and ultrathin Au/Si multilayers by
non-local transport and spin-torque ferromagnetic resonance measurements. We
show that the spin-charge conversion efficiency is strongly enhanced in
ultrathin Au/Si multilayers, reaching exceedingly large values of 0.99 +/- 0.34
when the thickness of the individual Au layers is scaled down to 2 nm. These
findings reveal the coexistence of a strong interfacial spin-orbit coupling
effect which becomes dominant in ultrathin Au, and bulk spin Hall effect with a
relatively low bulk spin Hall angle of 0.012 +/- 0.005. Our experimental
results suggest the key role of the Rashba-Edelstein effect in the
spin-to-charge conversion in ultrathin Au.",2103.08876v1
2022-01-12,Light and microwave driven spin pumping across FeGaB-BiSb interface,"3-D topological insulators (TI) with large spin Hall conductivity have
emerged as potential candidates for spintronic applications. Here, we report
spin to charge conversion in bilayers of amorphous ferromagnet (FM)
Fe_{78}Ga_{13}B_{9} (FeGaB) and 3-D TI Bi_{85}Sb_{15} (BiSb) activated by two
complementary techniques: spin pumping and ultrafast spin-current injection. DC
magnetization measurements establish the soft magnetic character of FeGaB
films, which remains unaltered in the heterostructures of FeGaB-BiSb. Broadband
ferromagnetic resonance (FMR) studies reveal enhanced damping of precessing
magnetization and large value of spin mixing conductance (5.03 x 10^{19}
m^{-2}) as the spin angular momentum leaks into the TI layer. Magnetic field
controlled bipolar dc voltage generated across the TI layer by inverse spin
Hall effect is analyzed to extract the values of spin Hall angle and spin
diffusion length of BiSb. The spin pumping parameters derived from the
measurements of the femtosecond light-pulse-induced terahertz emission are
consistent with the result of FMR. Kubo-Bastin formula and tight-binding model
calculations shed light on the thickness-dependent spin-Hall conductivity of
the TI films, with predictions that are in remarkable agreement with the
experimental data. Our results suggest that room temperature deposited
amorphous and polycrystalline heterostructures provide a promising platform for
creating novel spin orbit torque devices.",2201.04686v1
2014-05-06,Pretty good state transfer of entangled states through quantum spin chains,"The XX model with uniform couplings represents the most natural choice for
quantum state transfer through spin chains. Given that it has long been
established that single-qubit states cannot be transferred with perfect
fidelity in this model, the notion of pretty good state transfer has been
recently introduced as a relaxation of the constraints on fidelity. In this
paper, we study the transfer of multi-qubit entangled and unentangled states
through unmodulated spin chains, and we prove that it is possible to have
pretty good state transfer of any multi-particle state. This significantly
generalizes the previous results on single-qubit state transfer, and opens way
to using uniformly coupled spin chains as quantum channels for the transfer of
arbitrary states of any dimension. Our results could be tested with current
technology.",1405.1296v3
2022-11-15,Picosecond Spin-Orbit Torque Induced Coherent Magnetization Switching in a Ferromagnet,"Electrically controllable non-volatile magnetic memories show great potential
for the replacement of semiconductor-based technologies. Recently there has
been strong interest in spin-orbit torque (SOT) induced magnetization reversal
due to the device's increased lifetime and speed of operation. However, recent
SOT switching studies reveal an incubation delay in the ~ns range due to
stochasticity in the nucleation of a magnetic domain during reversal. Here, we
experimentally demonstrate ultrafast SOT-induced magnetization switching
dynamics of a ferromagnet with no incubation delay by avoiding the nucleation
process and driving the magnetization coherently. We employ an ultrafast
photo-conducting switch and a co-planar strip line to generate and guide ~ps
current pulses into the heavy metal/ferromagnet layer stack and induce
ultrafast SOT. We use magneto-optical probing to investigate the magnetization
switching dynamics with sub-picosecond time resolution. Depending on the
relative current pulse and in-plane magnetic field polarities, we observe
either an ultrafast demagnetization and subsequent recovery along with a
SOT-induced precessional oscillation, or ultrafast SOT switching. The
magnetization zero-crossing occurs in ~70 ps, which is approximately an order
of magnitude faster than previous studies. Complete switching needs ~250 ps and
is limited by the heat diffusion to the substrate. We use a macro-magnetic
simulation coupled with an ultrafast heating model to analyze the effect of
ultrafast thermal anisotropy torque and current-induced torque in the observed
dynamics. Good agreement between our experimental results and the macro-spin
model shows that the switching dynamics are coherent and present no noticeable
incubation delay. Our work suggests a potential pathway toward dramatically
increasing the writing speed of SOT magnetic random-access memory devices.",2211.08266v1
2021-07-22,Spin-orbit torque control of spin waves in a ferromagnetic waveguide,"Spin-orbit torque (SOT) created by a spin current injected into a ferromagnet
by an adjacent heavy metal represents an efficient tool for the excitation and
manipulation of spin waves. Here we report the micromagnetic simulations
describing the influence of SOT on the propagation of spin waves in the
$\mathrm{W}/\mathrm{CoFeB}/\mathrm{MgO}$ nanostructure having
voltage-controlled magnetic anisotropy (VCMA). The simulations show that two
spin waves travelling in the opposite directions can be generated in the center
of the $\mathrm{CoFeB}$ waveguide via the modulation of VCMA induced by a
microwave voltage locally applied to the $\mathrm{MgO}$ nanolayer. The
amplitudes of these waves exponentially decrease with the propagation distance
with similar decay lengths of about 2.5 $\mu$m. In the presence of a direct
electric current injected into the $\mathrm{W}$ film beneath the waveguide
center, the decay lengths of two spin waves change in the opposite way owing to
different directions of the electric currents flowing in the underlying halves
of the $\mathrm{W}$ layer. Remarkably, above the critical current density
$J_\mathrm{W} \approx 2 \times 10^{10}$ A m$^{-2}$, SOT provides the
amplification of the spin wave propagating in one half of the waveguide and
strongly accelerates the attenuation of the wave travelling in the other half.
As a result, a long-distance spin-wave propagation takes place in a half of the
$\mathrm{CoFeB}$ waveguide only. Furthermore, by reversing the polarity of the
dc voltage applied to the heavy-metal layer one can change the propagation area
and switch the travel direction of the spin wave in the ferromagnetic
waveguide. Thus, the $\mathrm{W}/\mathrm{CoFeB}/\mathrm{MgO}$ nanostructure can
be employed as an electrically controlled magnonic device converting the
electrical input signal into a spin signal, which can be transmitted to one of
two outputs of the device.",2107.10795v2
2003-10-07,Magnetic Spin-Up of Line-Driven Winds,"We summarize recent 2D MHD simulations of line-driven stellar winds from
rotating hot-stars with a dipole magnetic field aligned to the star's rotation
axis. For moderate to strong fields, much wind outflow is initially along
closed magnetic loops that nearly corotate as a solid body with the underlying
star, thus providing a torque that results in an effective angular momentum
spin-up of the outflowing material. But instead of forming the ``magnetically
torqued disk'' (MTD) postulated in previous phenemenological analyses, the
dynamical simulations here show that material trapped near the tops of such
closed loops tends either to fall back or break out, depending on whether it is
below or above the Keplerian corotation radius. Overall the results raise
serious questions about whether magnetic torquing of a wind outflow could
naturally result in a Keplerian circumstellar disk. However, for very strong
fields, it does still seem possible to form a %``magnetically confined,
centrifugally supported, rigid-body disk'', centrifugally supported,
``magnetically rigid disk'' (MRD), in which the field not only forces material
to maintain a rigid-body rotation, but for some extended period also holds it
down against the outward centrifugal force at the loop tops. We argue that such
rigid-body disks seem ill-suited to explain the disk emission from Be stars,
but could provide a quite attractive paradigm for circumstellar emission from
the magnetically strong Bp and Ap stars.",0310179v1
2004-08-13,Intrinsic Inclination of Galaxies embedded in Cosmic Sheets and its Cosmological Implications: An Analytic Calculation,"We investigate analytically a large-scale coherence in the orientation of
galaxies embedded in two-dimensional sheet-like structures in the frame of the
tidal torque theory. Assuming that the galaxy spin and the surrounding matter
fields are intrinsically aligned in accordance with the tidal torque model, we
first derive analytically the probability distribution of the galaxy position
angles, and evaluate the degree of their inclinations relative to the plane of
the sheet. Then, we apply our analytic approach to the nearby spirals in the
Local Super Cluster, and provide theoretical explanations about why and to what
degree the nearby spirals are inclined relative to the supergalatic plane.
Finally, we conclude that the observed large-scale coherence in the orientation
of nearby spirals relative to the supergalactic plane can be quantitatively
understood in terms of galaxy intrinsic alignment predicted by the tidal torque
theory, and that the spins of luminous galaxies might be more strongly aligned
with the surrounding matter than the underlying dark halos. If applied to large
scale surveys like Sloan Digital Sky Survey (SDSS), our analytic approach will
allow us to measure accurately the strength of galaxy intrinsic alignment which
plays a role of statistical error in weak lensing searches and can be used as a
fossil record to reconstruct cosmology.",0408251v2
2011-10-10,The self-propelled Brownian spinning top: dynamics of a biaxial swimmer at low Reynolds numbers,"Recently, the Brownian dynamics of self-propelled (active) rod-like particles
was explored to model the motion of colloidal microswimmers,
catalytically-driven nanorods, and bacteria. Here, we generalize this
description to biaxial particles with arbitrary shape and derive the
corresponding Langevin equation for a self-propelled Brownian spinning top. The
biaxial swimmer is exposed to a hydrodynamic Stokes friction force at low
Reynolds numbers, to fluctuating random forces and torques as well as to an
external and an internal (effective) force and torque. The latter quantities
control its self-propulsion. Due to biaxiality and hydrodynamic
translational-rotational coupling, the Langevin equation can only be solved
numerically. In the special case of an orthotropic particle in the absence of
external forces and torques, the noise-free (zero-temperature) trajectory is
analytically found to be a circular helix. This trajectory is confirmed
numerically to be more complex in the general case involving a transient
irregular motion before ending up in a simple periodic motion. By contrast, if
the external force vanishes, no transient regime is found and the particle
moves on a superhelical trajectory. For orthotropic particles, the
noise-averaged trajectory is a generalized concho-spiral. We furthermore study
the reduction of the model to two spatial dimensions and classify the
noise-free trajectories completely finding circles, straight lines with and
without transients, as well as cycloids and arbitrary periodic trajectories.",1110.2030v1
2013-10-14,"Field-induced nematic-like magnetic transition in an iron pnictide superconductor, Ca$_{10}$(Pt$_{3}$As$_{8}$)((Fe$_{1-x}$Pt$_{x}$)$_{2}$As$_{2}$)$_{5}$","We report a high magnetic field study up to 55 T of the nearly optimally
doped iron-pnictide superconductor Ca$_{10}$(Pt$_{3}$As$_{8}$)
((Fe$_{1-x}$Pt$_{x}$)$_{2}$As$_{2}$)$_{5}$ (x=0.078(6)) with a Tc 10 K using
magnetic torque, tunnel diode oscillator technique and transport measurements.
We determine the superconducting phase diagram, revealing an anisotropy of the
irreversibility field up to a factor of 10 near Tc and signatures of multiband
superconductivity. Unexpectedly, we find a spin-flop like anomaly in magnetic
torque at 22 T, when the magnetic field is applied perpendicular to the ab
planes, which becomes significantly more pronounced as the temperature is
lowered to 0.33 K. As our superconducting sample lies well outside the
antiferromagnetic region of the phase diagram, the observed field-induced
transition in torque indicates a spin-flop transition not of long-range ordered
moments, but of nematic-like antiferromagnetic fluctuations.",1310.3728v1
2014-08-28,On planetary torque signals and sub-decadal frequencies in the discharges of large rivers,"We explore the arguments presented in the past linking changes in the angular
momentum $modulus$, $|{\bf L}|$, of the Sun's barycentric orbit, with the
discharges of Po River in Europe and Paran\'a River in South America, looking
for any evidence regarding to a possible underlying physical mechanism. We
clarify the planetary effect on solar torque presenting new analyses and
results; we also improve prior results on Paran\'a River's cycles finding
significant spectral lines around 6.5 yr, 7.6 yr, 8.7 yr, and 10.4 yr. We show
that the truly important dynamical parameter in this issue is the {\it
vectorial} planetary torque. Moreover, following the variations of ${\bf L}$
respect to the Sun's spin axis of rotation (i.e., a LS relationship), we found
virtually the same Paran\'a River discharge peaks: 6.3 yr, 7.7 yr, 8.6 yr and
9.9 yr. An analisys based on Magnitude Squared Coherence and Wavelet Coherence
between Paran\'a River discharge and our LS relationship shows significant,
although intermittently, coherence near 8-yr periodicities. Wavelet Coherence
also shows big and significant regions of coherence inside 12-19 yr band. Our
results ruled out classical tidal effects in this problem; but suggest that, if
these rivers are trully related to solar barycentric motion, the physical
origin of this connection might be related to a working solar spin-orbit
interaction.",1408.6757v2
2015-09-09,Protostellar spin-down: a planetary lift?,"When they first appear in the HR diagram, young stars rotate at a mere 10\%
of their break-up velocity. They must have lost most of the angular momentum
initially contained in the parental cloud, the so-called angular momentum
problem. We investigate here a new mechanism by which large amounts of angular
momentum might be shed from young stellar systems, thus yielding slowly
rotating young stars. Assuming that planets promptly form in circumstellar
disks and rapidly migrate close to the central star, we investigate how the
tidal and magnetic interactions between the protostar, its close-in planet(s),
and the inner circumstellar disk can efficiently remove angular momentum from
the central object. We find that neither the tidal torque nor the variety of
magnetic torques acting between the star and the embedded planet are able to
counteract the spin up torques due to accretion and contraction. Indeed, the
former are orders of magnitude weaker than the latter beyond the corotation
radius and are thus unable to prevent the young star from spinning up. We
conclude that star-planet interaction in the early phases of stellar evolution
does not appear as a viable alternative to magnetic star-disk coupling to
understand the origin of the low angular momentum content of young stars.",1509.02951v1
2018-09-04,Anomalous peak effect in iron-based superconductors Ba$_{1-x}$K$_x$Fe$_2$As$_2$ ($x \approx$ 0.69 and 0.76) for magnetic-field directions close to the $ab$ plane and its possible relation to the spin paramagnetic effect,"We report magnetic torque measurements on iron-pnictide superconductors
Ba$_{1-x}$K$_x$Fe$_2$As$_2$ ($x \approx$ 0.69 and 0.76) up to an applied field
of $B_a$ = 45 T. The peak effect is observed in torque-vs-field curves below
the irreversibility field. It is enhanced and becomes asymmetric as the field
is tilted from the $c$ axis. For field directions close to the $ab$ plane,
increasing- and decreasing-field curves peak at markedly different fields, and
exhibit a sharp jump, suggestive of a first-order phase transition, on the
high- and the low-field side of the peak, respectively. Complicated history
dependence of the torque is observed in the peak-effect region. We construct
and discuss the temperature ($T$)--applied-magnetic-field ($B_a$) phase
diagram. Since the upper critical field for the $ab$-plane direction is
comparable to the Pauli limit, we also consider possible influence of the spin
paramagnetic effect on the anomalous peak effect.",1809.00762v3
2018-09-17,Spin Evolution and Cometary Interpretation of the Interstellar Minor Object 1I/2017 'Oumuamua,"Observations of the first interstellar minor object 1I/2017 'Oumuamua did not
reveal direct signs of outgassing that would have been natural if it had
volatile-rich composition. However, a recent measurement by Micheli et al
(2018) of a substantial non-gravitational acceleration affecting the orbit of
this object has been interpreted as resulting from its cometary activity, which
must be rather vigorous. Here we critically re-assess this interpretation by
exploring the implications of measured non-gravitational acceleration for the
'Oumuamua's rotational state. We show that outgassing torques should drive
rapid evolution of 'Oumuamua's spin (on a timescale of a few days), assuming
torque asymmetry typical for the Solar System comets. However, given the highly
elongated shape of the object, its torque asymmetry is likely higher, implying
even faster evolution. This would have resulted in rapid rotational fission of
'Oumuamua during its journey through the Solar System and is clearly
incompatible with the relative stability of its rotational state inferred from
photometric variability. Based on these arguments, as well as the lack of
direct signs of outgassing, we conclude that the classification of 'Oumuamua as
a comet (invoked to explain its claimed anomalous acceleration) is
questionable.",1809.06389v3
2020-03-31,The Ups & Downs of Accreting X-Ray Pulsars: Decade-long observations with the Fermi Gamma-Ray Burst Monitor,"We review more than 10 years of continuous monitoring of accreting X-ray
pulsars with the all-sky Gamma-ray Burst Monitor (GBM) aboard the Fermi
Gamma-ray Space Telescope. Our work includes data from the start of GBM
operations in August 2008, through to November 2019. Pulsations from 39
accreting pulsars are observed over an energy range of $10-50\,$keV by GBM. The
GBM Accreting Pulsars Program (GAPP) performs data reduction and analysis for
each accreting pulsar and makes histories of the pulse frequency and pulsed
flux publicly available. We examine in detail the spin histories, outbursts and
torque behaviors of the persistent and transient X-ray pulsars observed by GBM.
The spin period evolution of each source is analyzed in the context of
disk-accretion and quasi-spherical settling accretion driven torque models.
Long-term pulse frequency histories are also analyzed over the GBM mission
lifetime and compared to those available from the previous BATSE all-sky
monitoring mission, revealing previously unnoticed episodes in some of the
analyzed sources (such as a torque reversal in 2S 1845-024). We obtain new, or
update known, orbital solutions for three sources. Our results demonstrate the
capabilities of GBM as an excellent instrument for monitoring accreting X-ray
pulsars and its important scientific contribution to this field.",2004.00051v3
2019-03-27,Field-free spin-orbit-torque switching of perpendicular magnetization aided by uniaxial shape anisotropy,"It has been demonstrated that the switching of perpendicular magnetization
can be achieved with spin orbit torque (SOT) at an ultrafast speed and low
energy consumption. However, to make the switching deterministic, an
undesirable magnetic field or unconventional device geometry is required to
break the structure inverse symmetry. Here we propose a novel scheme for
SOT-induced field-free deterministic switching of perpendicular magnetization.
The proposed scheme can be implemented in a simple magnetic tunnel junction
(MTJ) /heavy-metal system, without the need of complicated device structure.
The perpendicular-anisotropy MTJ is patterned into elliptical shape and
misaligned with the axis of the heavy metal, so that the uniaxial shape
anisotropy aids the magnetization switching. Furthermore, unlike the
conventional switching scheme where the switched final magnetization state is
dependent on the direction of the applied current, in our scheme the bipolar
switching is implemented by choosing different current paths, which offers a
new freedom for developing novel spintronics memories or logic devices. Through
the macrospin simulation, we show that a wide operation window of the applied
current pulse can be obtained in the proposed scheme. The precise control of
pulse amplitude or pulse duration is not required. The influences of key
parameters such as damping constant and field-like torque strength are
discussed as well.",1903.11487v1
2021-04-19,"The MIT Humanoid Robot: Design, Motion Planning, and Control For Acrobatic Behaviors","Demonstrating acrobatic behavior of a humanoid robot such as flips and
spinning jumps requires systematic approaches across hardware design, motion
planning, and control. In this paper, we present a new humanoid robot design,
an actuator-aware kino-dynamic motion planner, and a landing controller as part
of a practical system design for highly dynamic motion control of the humanoid
robot. To achieve the impulsive motions, we develop two new proprioceptive
actuators and experimentally evaluate their performance using our
custom-designed dynamometer. The actuator's torque, velocity, and power limits
are reflected in our kino-dynamic motion planner by approximating the
configuration-dependent reaction force limits and in our dynamics simulator by
including actuator dynamics along with the robot's full-body dynamics. For the
landing control, we effectively integrate model-predictive control and
whole-body impulse control by connecting them in a dynamically consistent way
to accomplish both the long-time horizon optimal control and high-bandwidth
full-body dynamics-based feedback. Actuators' torque output over the entire
motion are validated based on the velocity-torque model including battery
voltage droop and back-EMF voltage. With the carefully designed hardware and
control framework, we successfully demonstrate dynamic behaviors such as back
flips, front flips, and spinning jumps in our realistic dynamics simulation.",2104.09025v1
2021-08-03,Anatomy of Type-X Spin-Orbit Torque Switching,"Using type-x spin-orbit torque (SOT) switching scheme, in which the easy axis
(EA) of the ferromagnetic (FM) layer and the charge current flow direction are
collinear, is possible to realize a lower-power-consumption, higher-density,
and better-performance SOT magnetoresistive random access memory (SOT-MRAM) as
compared to the conventional type-y design. Here, we systematically investigate
type-x SOT switching properties by both macrospin and micromagnetic
simulations. The out-of-plane external field and anisotropy field dependence of
the switching current density ($J_{sw}$) is first examined in the ideal type-x
configuration. Next, we study the FM layer canting angle ($\phi_{EA}$)
dependence of $J_{sw}$ through macrospin simulations and experiments, which
show a transformation of switching dynamics from type-x to type-y with
increasing $\phi_{EA}$. By further integrating field-like torque (FLT) into the
simulated system, we find that a positive FLT can assist type-x SOT switching
while a negative one brings about complex dynamics. More crucially, with the
existence of a sizable FLT, type-x switching mode results in a lower critical
switching current than type-y at current pulse width less than ~ 10 ns,
indicating the advantage of employing type-x design for ultrafast switching
using materials systems with FLT. Our work provides a thorough examination of
type-x SOT scheme with various device/materials parameters, which can be
informative for designing next-generation SOT-MRAM.",2108.01272v1
2019-07-15,Final spin states of eccentric ocean planets,"Eccentricity tides generate a torque that can drive an ocean planet towards
asynchronous rotation states of equilibrium when enhanced by resonances
associated with the oceanic tidal modes. We investigate the impact of
eccentricity tides on the rotation of rocky planets hosting a thin uniform
ocean and orbiting cool dwarf stars such as TRAPPIST-1, with orbital periods
~1-10 days. Combining the linear theory of oceanic tides in the shallow water
approximation with the Andrade model for the solid part of the planet, we
develop a global model including the coupling effects of ocean loading,
self-attraction, and deformation of the solid regions. We derive from this
model analytic solutions for the tidal Love numbers and torque exerted on the
planet. These solutions are used with realistic values of parameters provided
by advanced models of the internal structure and tidal oscillations of solid
bodies to explore the parameter space both analytically and numerically. Our
model allows us to fully characterise the frequency-resonant tidal response of
the planet, and particularly the features of resonances associated with the
oceanic tidal modes (eigenfrequencies, resulting maxima of the tidal torque and
Love numbers) as functions of the planet parameters (mass, radius, Andrade
parameters, ocean depth and Rayleigh drag frequency). Resonances associated
with the oceanic tide decrease the critical eccentricity beyond which
asynchronous rotation states distinct from the usual spin-orbit resonances can
exist. We provide an estimation and scaling laws for this critical
eccentricity, which is found to be lowered by roughly one order of magnitude,
switching from ~0.3 to ~0.06 in typical cases and to ~0.01 in extremal ones.",1907.06451v1
2021-06-29,Breakup of the Synchronous State of Binary Asteroid Systems,"This paper continues the authors' previous work and presents a coplanar
averaged ellipsoid-ellipsoid model of synchronous binary asteroid system (BAS)
plus thermal and tidal effects. Using this model, we analyze the breakup
mechanism of the synchronous BAS. Different from the classical spin-orbit
coupling model which neglects the rotational motion's influence on the orbital
motion, our model considers simultaneously the orbital motion and the
rotational motions. Our findings are following. (1) Stable region of the
secondary's synchronous state is mainly up to the secondary's shape. The
primary's shape has little influence on it. (2) The stable region shrinks
continuously with the increasing value of the secondary's shape parameter
$a_B/b_B$. Beyond the value of $a_B/b_B=\sqrt{2}$, the planar stable region for
the secondary's synchronous rotation is small but not zero. (3) Considering the
BYORP torque, our model shows agreement with the 1-degree of freedom adiabatic
invariance theory in the outwards migration process, but an obvious difference
in the inwards migration process. In particular, our studies show that the
so-called 'long-term' stable equilibrium between the BYORP torque and the tidal
torque is never a real equilibrium state, although the binary asteroid system
can be captured in this state for quite a long time. (4) In case that the
primary's angular velocity gradually reduces due to the YORP effect, the
secondary's synchronous state may be broken when the primary's rotational
motion crosses some major spin-orbit resonances.",2106.15039v1
2022-06-03,Engineering the spin-orbit torque efficiency and magnetic properties of Tb/Co ferrimagnetic multilayers by stacking order,"We measured the spin-orbit torques (SOTs), current-induced switching, and
domain wall (DW) motion in synthetic ferrimagnets consisting of Co/Tb layers
with differing stacking order grown on a Pt underlayer. We find that the SOTs,
magnetic anisotropy, compensation temperature and SOT-induced switching are
highly sensitive to the stacking order of Co and Tb and to the element in
contact with Pt. Our study further shows that Tb is an efficient SOT generator
when in contact with Co, such that its position in the stack can be adjusted to
generate torques additive to those generated by Pt. With optimal stacking and
layer thickness, the dampinglike SOT efficiency reaches up to 0.3, which is
more than twice that expected from the Pt/Co bilayer. Moreover, the
magnetization can be easily switched by the injection of pulses with current
density of about 0.5-2*107A/cm2 despite the extremely high perpendicular
magnetic anisotropy barrier (up to 7.8 T). Efficient switching is due to the
combination of large SOTs and low saturation magnetization owing to the
ferrimagnetic character of the multilayers. We observed current-driven DW
motion in the absence of any external field, which is indicative of homochiral
N\'eel-type DWs stabilized by the interfacial Dzyaloshinkii-Moriya interaction.
These results show that the stacking order in transition metal/rare-earth
synthetic ferrimagnets plays a major role in determining the magnetotransport
properties relevant for spintronic applications.",2206.01586v1
2023-05-16,Apparent dispersion in pulsar braking index measurements caused by timing noise,"Stochastic temporal wandering of the spin frequency $\nu$ of a
rotation-powered pulsar (i.e.~the achromatic component of timing noise
unrelated to interstellar propagation) affects the accuracy with which the
secular braking torque can be measured. Observational studies confirm that
pulsars with anomalous braking indices $\vert n \vert = \vert \nu \ddot{\nu} /
\dot{\nu}^2 \vert \gg 1$ exhibit elevated levels of timing noise, where an
overdot symbolizes a derivative with respect to time. Here it is shown, through
analytic calculations and Monte Carlo simulations involving synthetic data and
modern Bayesian timing techniques, that the variance $\langle n^2 \rangle$ of
the measured $n$ scales with the square of the timing noise amplitude
$\sigma_{\ddot{\nu}}$. The anomalous regime $\langle n^2 \rangle \gg 1$
corresponds to $ \sigma_{\ddot{\nu}}^2 \gg 10^{-60}
(\gamma_{\ddot{\nu}}/10^{-6} \, {\rm s^{-1}})^2 (\dot{\nu} / 10^{-14} \, {\rm
Hz \, s^{-1}})^4 (\nu / 1 \, {\rm Hz})^{-2} (T_{\rm obs} / 10^8 \, {\rm s}) \,
{\rm Hz}^2{\rm s}^{-5 }$, where $\gamma_{\ddot{\nu}}$ is a stellar damping
time-scale, and $T_{\rm obs}$ is the total observing time. When the inequality
in the above condition is reversed, $n$ is dominated by the secular braking
torque, and timing measurements return $n\sim 3$, if the secular braking torque
is electromagnetic. The variance $\langle n^2 \rangle$ is greater, when the
stochastic process driving spin fluctuations differs from the red noise model
(e.g. power-law spectral density) assumed in the timing solution.",2305.09079v1
2023-09-29,Realistic non-collinear ground states of solids with source-free exchange correlation functional,"In this work, we extend the source-free (SF) exchange correlation (XC)
functional developed by Sangeeta Sharma and co-workers to plane-wave density
functional theory (DFT) based on the projector augmented wave (PAW) method.
This constraint is implemented by the current authors within the VASP source
code, using a fast Poisson solver that capitalizes on the parallel
three-dimensional fast Fourier transforms (FFTs) implemented in VASP. Using
this modified XC functional, we explore the improved convergence behavior that
results from applying this constraint to the GGA-PBE+$U$+$J$ functional. In the
process, we compare the non-collinear magnetic ground state computed by each
functional and their SF counterpart for a select number of magnetic materials
in order to provide a metric for comparing with experimentally determined
magnetic orderings. We observe significantly improved agreement with
experimentally measured magnetic ground state structures after applying the
source-free constraint. Furthermore, we explore the importance of considering
probability current densities in spin polarized systems, even under no applied
field. We analyze the XC torque as well, in order to provide theoretical and
computational analyses of the net XC magnetic torque induced by the source-free
constraint. Along these lines, we highlight the importance of properly
considering the real-space integral of the source-free local magnetic XC field.
Our analysis on probability currents, net torque, and constant terms draws
additional links to the rich body of previous research on spin-current density
functional theory (SCDFT), and paves the way for future extensions and
corrections to the SF corrected XC functional.",2310.00114v1
2022-07-20,Probing Accretion Physics with Gravitational Waves,"Gravitational-wave observations of extreme mass ratio inspirals (EMRIs) offer
the opportunity to probe the environments of active galactic nuclei (AGN)
through the torques that accretion disks induce on the binary. Within a
Bayesian framework, we study how well such environmental effects can be
measured using gravitational wave observations from the Laser Interferometer
Space Antenna (LISA). We focus on the torque induced by planetary-type
migration on quasicircular inspirals, and use different prescriptions for
geometrically thin and radiatively efficient disks. We find that LISA could
detect migration for a wide range of disk viscosities and accretion rates, for
both $\alpha$ and $\beta$ disk prescriptions. For a typical EMRI with masses
$50M_\odot+10^6M_\odot$, we find that LISA could distinguish between migration
in $\alpha$ and $\beta$ disks and measure the torque amplitude with $\sim 20\%$
relative precision. Provided an accurate torque model, we also show how to turn
gravitational-wave measurements of the torque into constraints on the disk
properties. Furthermore, we show that, if an electromagnetic counterpart is
identified, the multimessenger observations of the AGN EMRI system will yield
direct measurements of the disk viscosity. Finally, we investigate the impact
of neglecting environmental effects in the analysis of the gravitational-wave
signal, finding 3$\sigma$ biases in the primary mass and spin, and showing that
ignoring such effects can lead to false detection of a deviation from general
relativity. This work demonstrates the scientific potential of gravitational
observations as probes of accretion-disk physics, accessible so far through
electromagnetic observations only.",2207.10086v3
2016-04-07,Spin diffusion in p-type bilayer WSe$_2$,"We investigate the steady-state out-of-plane spin diffusion in p-type bilayer
WSe2 in the presence of the Rashba spin-orbit coupling and Hartree-Fock
effective magnetic field. The out-of-plane components of the Rashba spin-orbit
coupling serve as the opposite Zeeman-like fields in the two valleys. Together
with the identical Hartree-Fock effective magnetic fields, different total
effective magnetic field strengths in the two valleys are obtained. It is
further revealed that due to the valley-dependent total effective magnetic
field strength, similar (different) spin-diffusion lengths in the two valleys
are observed at small (large) spin injection. Nevertheless, it is shown that
the intervalley hole-phonon scattering can suppress the difference in the
spin-diffusion lengths at large spin injection due to the spin-conserving
intervalley charge transfers with the opposite transfer directions between
spin-up and -down holes. Moreover, with a fixed large pure spin injection, we
predict the build-up of a steady-state valley polarization during the spin
diffusion with the maximum along the diffusion direction being capable of
exceeding 1 %. It is revealed that the valley polarization arises from the
induced quasi hot-hole Fermi distributions with different effective hot-hole
temperatures between spin-up and -down holes during the spin diffusion, leading
to the different intervalley charge transfer rates in the opposite transfer
directions. Additionally, it is also shown that by increasing the injected spin
polarization, the hole density or the impurity density, the larger valley
polarization can be obtained.",1604.01892v2
2004-01-21,Molecular spintronics: Coherent spin transfer in coupled quantum dots,"Time-resolved Faraday rotation has recently demonstrated coherent transfer of
electron spin between quantum dots coupled by conjugated molecules. Using a
transfer Hamiltonian ansatz for the coupled quantum dots, we calculate the
Faraday rotation signal as a function of the probe frequency in a pump-probe
setup using neutral quantum dots. Additionally, we study the signal of one
spin-polarized excess electron in the coupled dots. We show that, in both
cases, the Faraday rotation angle is determined by the spin transfer
probabilities and the Heisenberg spin exchange energy. By comparison of our
results with experimental data, we find that the transfer matrix element for
electrons in the conduction band is of order 0.08 eV and the spin transfer
probabilities are of order 10%.",0401397v2
2014-07-26,Four phases of angular-momentum buildup in high-z galaxies: from cosmic-web streams through an extended ring to disc and bulge,"We study the angular-momentum (AM) buildup in high-$z$ massive galaxies using
high-resolution cosmological simulations. The AM originates in co-planar
streams of cold gas and merging galaxies tracing cosmic-web filaments, and it
undergoes four phases of evolution. (I) Outside the halo virial radius ($R_{\rm
v}\!\sim\!100\,{\rm kpc}$), the elongated streams gain AM by tidal torques with
a specific AM (sAM) $\sim\!1.7$ times the dark-matter (DM) spin due to the gas'
higher quadrupole moment. This AM is expressed as stream impact parameters,
from $\sim\!0.3R_{\rm v}$ to counter rotation. (II) In the outer halo, while
the incoming DM mixes with the existing halo of lower sAM to a spin
$\lambda_{\rm dm}\!\sim\!0.04$, the cold streams transport the AM to the inner
halo such that their spin in the halo is $\sim\!3\lambda_{\rm dm}$. (III) Near
pericenter, the streams dissipate into an irregular rotating ring extending to
$\sim\!0.3R_{\rm v}$ and tilted relative to the inner disc. Torques exerted
partly by the disc make the ring gas lose AM, spiral in, and settle into the
disc within one orbit. The ring is observable with 30\% probability as a damped
Lyman-$\alpha$ absorber. (IV) Within the disc, $<\!0.1R_{\rm v}$, torques
associated with violent disc instability drive AM out and baryons into a
central bulge, while outflows remove low-spin gas, introducing certain
sensitivity to feedback strength. Despite the different AM histories of gas and
DM, the disc spin is comparable to the DM-halo spin. Counter rotation can
strongly affect disc evolution.",1407.7129v3
2019-10-04,Do non-dipolar magnetic fields contribute to spin-down torques?,"Main sequence low-mass stars are known to spin-down as a consequence of their
magnetised stellar winds. However, estimating the precise rate of this
spin-down is an open problem. The mass-loss rate, angular momentum-loss rate
and the magnetic field properties of low-mass stars are fundamentally linked
making this a challenging task. Of particular interest is the stellar magnetic
field geometry. In this work, we consider whether non-dipolar field modes
contribute significantly to the spin-down of low-mass stars. We do this using a
sample of stars that have all been previously mapped with Zeeman-Doppler
imaging. For a given star, as long as its mass-loss rate is below some critical
mass-loss rate, only the dipolar fields contribute to its spin-down torque.
However, if it has a larger mass-loss rate, higher order modes need to be
considered. For each star, we calculate this critical mass-loss rate, which is
a simple function of the field geometry. Additionally, we use two methods of
estimating mass-loss rates for our sample of stars. In the majority of cases,
we find that the estimated mass-loss rates do not exceed the critical mass-loss
rate and hence, the dipolar magnetic field alone is sufficient to determine the
spin-down torque. However, we find some evidence that, at large Rossby numbers,
non-dipolar modes may start to contribute.",1910.02129v1
2006-08-09,Nuclear spin structure in dark matter search: The finite momentum transfer limit,"Spin-dependent elastic scattering of weakly interacting massive dark matter
particles (WIMP) off nuclei is reviewed. All available, within different
nuclear models, structure functions S(q) for finite momentum transfer (q>0) are
presented. These functions describe the recoil energy dependence of the
differential event rate due to the spin-dependent WIMP-nucleon interactions.
This paper, together with the previous paper ``Nuclear spin structure in dark
matter search: The zero momentum transfer limit'', completes our review of the
nuclear spin structure calculations involved in the problem of direct dark
matter search.",0608097v1
2001-06-17,Sub-Riemannian Geometry and Time Optimal Control of Three Spin Systems: Quantum Gates and Coherence Transfer,"Many coherence transfer experiments in Nuclear Magnetic Resonance
Spectroscopy, involving network of coupled spins, use temporary spin-decoupling
to produce desired effective Hamiltonians. In this paper, we show that
significant time can be saved in producing an effective Hamiltonian, if
spin-decoupling is avoided. We provide time optimal pulse sequences for
producing an important class of effective Hamiltonians in three spin networks.
These effective Hamiltonians are useful for coherence transfer experiments and
implementation of quantum logic gates in NMR quantum computing. It is
demonstrated that computing these time optimal pulse sequences can be reduced
to geometric problems that involve computing sub-Riemannian geodesics on
Homogeneous spaces.",0106099v1
2007-10-20,Coherent transfer of light polarization to electron spins in a semiconductor,"We demonstrate that the superposition of light polarization states is
coherently transferred to electron spins in a semiconductor quantum well. By
using time-resolved Kerr rotation we observe the initial phase of Larmor
precession of electron spins whose coherence is transferred from light. To
break the electron-hole spin entanglement, we utilized the big discrepancy
between the transverse g-factors of electrons and light holes. The result
encourages us to make a quantum media converter between flying photon qubits
and stationary electron spin qubits in semiconductors.",0710.3847v1
2009-07-24,Electrical measurement of a two-electron spin state in a double quantum dot,"We propose a scheme for electrical measurement of two-electron spin states in
a semiconductor double quantum dot. We calculated the adiabatic charge transfer
when surface gates are modulated in time. Because of spin-orbit coupling in the
semiconductor, spatial displacement of the electrons causes a total spin
rotation. It follows that the expectation value of the transferred charge
reflects the relative phase as well as the total spin population of a prepared
singlet-triplet superposition state. The precise detection of the charge
transfer serves to identify the quantum superposition.",0907.4191v1
2015-09-07,Time-optimal polarization transfer from an electron spin to a nuclear spin,"Polarization transfers from an electron spin to a nuclear spin are essential
for various physical tasks, such as dynamic nuclear polarization in nuclear
magnetic resonance and quantum state transformations on hybrid electron-nuclear
spin systems. We present time-optimal schemes for electron-nuclear polarization
transfers which improve on conventional approaches and will have wide
applications.",1509.02072v1
2022-11-17,Theory and simulations of the angular momentum transfer from swift electrons to spherical nanoparticles in STEM,"Electron beams in scanning transmission electron microscopy (STEM) exert
forces and torques on study samples, with magnitudes that allow the controlled
manipulation of nanoparticles (a technique called electron tweezers). Related
theoretical research has mostly focused on the study of forces and linear
momentum transfers from swift electrons (like those used in STEM) to
nanoparticles. However, theoretical research on the rotational aspects of the
interaction would benefit not only the development of electron tweezers, but
also other fields within electron microscopy such as electron vortices.
Starting from a classical-electrodynamics description, we present a theoretical
model, alongside an efficient numerical methodology, to calculate the angular
momentum transfer from a STEM swift electron to a spherical nanoparticle. We
show simulations of angular momentum transfers to aluminum, gold, and bismuth
nanoparticles of different sizes. We found that the transferred angular
momentum is always perpendicular to the system's plane of symmetry, displaying
a constant direction for all the cases considered. In the simulations, the
angular momentum transfer increased with the radius of the nanoparticle, but
decreased as the speed of the electron or the impact parameter increased. Also,
the electric contribution to the angular momentum transfer dominated over the
magnetic one, being comparable only for high electron's speeds (greater than
90% of the speed of light). Additionally, for nanoparticles with 1 nm radius of
the studied materials, we found validity criteria for the small-particle
approximation (in which the nanoparticle is modeled as an electric point
dipole). We believe that these findings contribute to the understanding of
rotational aspects present in STEM experiments, and might be useful for further
developments in electron tweezers and other electron microscopy related
techniques.",2211.09883v1
2005-05-15,Relaxation Optimized Transfer of Spin Order in Ising Spin Chains,"In this manuscript, we present relaxation optimized methods for transfer of
bilinear spin correlations along Ising spin chains. These relaxation optimized
methods can be used as a building block for transfer of polarization between
distant spins on a spin chain. Compared to standard techniques, significant
reduction in relaxation losses is achieved by these optimized methods when
transverse relaxation rates are much larger than the longitudinal relaxation
rates and comparable to couplings between spins. We derive an upper bound on
the efficiency of transfer of spin order along a chain of spins in the presence
of relaxation and show that this bound can be approached by relaxation
optimized pulse sequences presented in the paper.",0505116v2
2016-12-14,Directional Interlayer Spin-Valley Transfer in Two-Dimensional Heterostructures,"Van der Waals heterostructures formed by two different monolayer
semiconductors have emerged as a promising platform for new optoelectronic and
spin/valleytronic applications. In addition to its atomically thin nature, a
two-dimensional semiconductor heterostructure is distinct from its
three-dimensional counterparts due to the unique coupled spin-valley physics of
its constituent monolayers. Here, we report the direct observation that an
optically generated spin-valley polarization in one monolayer can be
transferred between layers of a two-dimensional MoSe2-WSe2 heterostructure.
Using nondegenerate optical circular dichroism spectroscopy, we show that
charge transfer between two monolayers conserves spin-valley polarization and
is only weakly dependent on the twist angle between layers. Our work points to
a new spin-valley pumping scheme in nanoscale devices, provides a fundamental
understanding of spin-valley transfer across the two-dimensional interface, and
shows the potential use of two-dimensional semiconductors as a spin-valley
generator in 2D spin/valleytronic devices for storing and processing
information.",1612.04863v1
2006-05-09,Spin dependent elastic antiproton interactions,"Relativistic formulae for spin averaged and spin dependent one photon
exchange differential cross sections are developed for spin half fermion
fermion elastic scattering. Spin transfer cross sections are important for the
Polarized Antiproton eXperiments (PAX) project at GSI Darmstadt. In particular,
cross sections for polarization transfer in antiproton electron and antiproton
proton elastic collisions are presented.",0605099v1
2019-05-29,Transverse optical pumping of spin states,"Optical pumping is an efficient method for initializing and maintaining
atomic spin ensembles in a well-defined quantum spin state. Standard
optical-pumping methods orient the spins by transferring photonic angular
momentum to spin polarization. Generally the spins are oriented along the
propagation direction of the light due to selection rules of the dipole
interaction. Here we present and experimentally demonstrate that by modulating
the light polarization, angular momentum perpendicular to the optical axis can
be transferred efficiently to cesium vapor. The transverse pumping scheme
employs transversely oriented dark states, allowing for control of the
trajectory of the spins on the Bloch sphere. This new mechanism is suitable and
potentially beneficial for diverse applications, particularly in quantum
metrology.",1905.12402v1
2004-04-08,Time-dependent secular evolution in galaxies,"Lynden-Bell & Kalnajs (1972) presented a useful formula for computing the
long-range torque between spiral arms and the disk at large. The derivation
uses second-order perturbation theory and assumes that the perturbation slowly
grows over a very long time: the time-asymptotic limit. This formula has been
widely used to predict the angular momentum transport between spiral arms and
stellar bars between disks and dark-matter halos. However, this paper shows
that the LBK time-asymptotic limit is not appropriate because the
characteristic evolution time for galaxies is too close to the relevant
dynamical times. We demonstrate that transients, not present in the
time-asymptotic formula, can play a major role in the evolution for realistic
astronomical time scales. A generalisation for arbitrary time dependence is
presented and illustrated by the bar--halo and satellite--halo interaction. The
natural time dependence in bar-driven halo evolution causes quantitative
differences in the overall torque and qualitative differences in the physical-
and phase-space location of angular momentum transfer. The time-dependent
theory predicts that four principal resonances dominate the torque at different
times and accurately predicts the results of an N-body simulation. In addition,
we show that the Inner Lindblad Resonance (ILR) is responsible for the peak
angular momentum exchange but, due to the time dependence, the changes occur
over a broad range of energies, radii and frequencies. We describe the
implication of these findings for the satellite--halo interaction using a
simple model and end with a discussion of possible impact on other aspects
secular galaxy evolution.",0404169v1
2006-07-30,Modelling optical micro-machines,"A strongly focused laser beam can be used to trap, manipulate and exert
torque on a microparticle. The torque is the result of transfer of angular
momentum by scattering of the laser beam. The laser could be used to drive a
rotor, impeller, cog wheel or some other microdevice of a few microns in size,
perhaps fabricated from a birefringent material. We review our methods of
computationally simulating the torque and force imparted by a laser beam. We
introduce a method of hybridizing the T-matrix with the Finite Difference
Frequency Domain (FDFD) method to allow the modelling of materials that are
anisotropic and inhomogeneous, and structures that have complex shapes. The
high degree of symmetry of a microrotor, such as discrete or continuous
rotational symmetry, can be exploited to reduce computational time and memory
requirements by orders of magnitude. This is achieved by performing
calculations for only a given segment or plane that is repeated across the
whole structure. This can be demonstrated by modelling the optical trapping and
rotation of a cube.",0607286v1
2014-02-18,Electromagnetic force and torque in ponderable media,"Maxwell's macroscopic equations combined with a generalized form of the
Lorentz law of force are a complete and consistent set of equations. Not only
are these five equations fully compatible with special relativity, they also
conform with conservation laws of energy, momentum, and angular momentum. We
demonstrate consistency with the conservation laws by showing that, when a beam
of light enters a magnetic dielectric, a fraction of the incident linear (or
angular) momentum pours into the medium at a rate determined by the Abraham
momentum density, ExH/c^2, and the group velocity V_g of the electromagnetic
field. The balance of the incident, reflected, and transmitted momenta is
subsequently transferred to the medium as force (or torque) at the leading edge
of the beam, which propagates through the medium with velocity V_g. Our
analysis does not require ""hidden"" momenta to comply with the conservation
laws, nor does it dissolve into ambiguities with regard to the nature of
electromagnetic momentum in ponderable media. The linear and angular momenta of
the electromagnetic field are clearly associated with the Abraham momentum, and
the phase and group refractive indices (n_p and n_g) play distinct yet
definitive roles in the expressions of force, torque, and momentum densities.",1402.7262v1
2015-11-09,Magnetic games between a planet and its host star: the key role of topology,"Magnetic interactions between a star and a close-in planet are postulated to
be a source of enhanced emissions and to play a role in the secular evolution
of the orbital system. Close-in planets generally orbit in the sub-alfv\'enic
region of the stellar wind, which leads to efficient transfers of energy and
angular momentum between the star and the planet. We model the magnetic
interactions occurring in close-in star-planet systems with three-dimensional,
global, compressible magneto-hydrodynamic numerical simulations of a planet
orbiting in a self-consistent stellar wind. We focus on the cases of magnetized
planets and explore three representative magnetic configurations. The Poynting
flux originating from the magnetic interactions is an energy source for
enhanced emissions in star-planet systems. Our results suggest a simple
geometrical explanation for ubiquitous on/off enhanced emissions associated
with close-in planets, and confirm that the Poynting fluxes can reach powers of
the order of $10^{19}$ W. Close-in planets are also showed to migrate due to
magnetic torques for sufficiently strong stellar wind magnetic fields. The
topology of the interaction significantly modifies the shape of the magnetic
obstacle that leads to magnetic torques. As a consequence, the torques can vary
by at least an order of magnitude as the magnetic topology of the interaction
varies.",1511.02837v1
2016-05-11,Van der Waals torque and force between dielectrically anisotropic layered media,"We analyse van der Waals interactions between a pair of dielectrically
anisotropic plane-layered media interacting across a dielectrically isotropic
solvent medium. We develop a general formalism based on transfer matrices to
investigate the van der Waals torque and force in the limit of weak
birefringence and dielectric matching between the ordinary axes of the
anisotropic layers and the solvent. We apply this formalism to study the
following systems: (i) a pair of single anisotropic layers, (ii) a single
anisotropic layer interacting with a multilayered slab consisting of
alternating anisotropic and isotropic layers, and (iii) a pair of multilayered
slabs each consisting of alternating anisotropic and isotropic layers, looking
at the cases where the optic axes lie parallel and/or perpendicular to the
plane of the layers. For the first case, the optic axes of the oppositely
facing anisotropic layers of the two interacting slabs generally possess an
angular mismatch, and within each multilayered slab the optic axes may either
be the same, or undergo constant angular increments across the anisotropic
layers. In particular, we examine how the behaviors of the van der Waals torque
and force can be ""tuned"" by adjusting the layer thicknesses, the relative
angular increment within each slab, and the angular mismatch between the slabs.",1605.03484v2
2018-04-04,Orbital angular momentum transfer to stably trapped elastic particles in acoustical vortex beams,"The controlled rotation of solid particles trapped in a liquid by an
ultrasonic vortex beam is observed. Single polystyrene beads, or clusters, can
be trapped against gravity while simultaneously rotated. The induced rotation
of a single particle is compared to a torque balance model accounting for the
acoustic response of the particle. The measured torque ($\sim 10$~pNm for a
driving acoustic power $\sim 40$~W/cm$^2$) suggests two dominating dissipation
mechanisms of the acoustic orbital angular momentum responsible for the
observed rotation. The first takes place in the bulk of the absorbing particle,
whilst the second arises as dissipation in the viscous boundary layer in the
surrounding fluid. Importantly, the dissipation processes affect both the
dipolar and quadrupolar particle vibration modes suggesting that the
restriction to the well-known Rayleigh scattering regime is invalid to model
the total torque even for spheres much smaller than the sound wavelength. The
findings show that a precise knowledge of the probe elastic absorption
properties is crucial to perform rheological measurements with manoeuvrable
trapped spheres in viscous liquids. Further results suggest that the external
rotational steady flow must be included in the balance and can play an
important role in other liquids.",1804.01272v3
2022-02-14,Circumbinary disk evolution in the presence of an outer companion star,"We consider a hierarchical triple system consisting of an inner eccentric
binary with an outer companion. A highly misaligned circumbinary disk around
the inner binary is subject to two competing effects: (i) nodal precession
about the inner binary eccentricity vector that leads to an increase in
misalignment (polar alignment) and (ii) Kozai-Lidov (KL) oscillations of
eccentricity and inclination driven by the outer companion that leads to a
reduction in the misalignment. The outcome depends upon the ratio of the
timescales of these effects. If the inner binary torque dominates, then the
disk aligns to a polar orientation. If the outer companion torque dominates,
then the disk undergoes KL oscillations. In that case, the highly eccentric and
misaligned disk is disrupted and accreted by the inner binary, while some mass
is transferred to the outer companion. However, when the torques are similar,
the outer parts of the circumbinary disk can undergo large eccentricity
oscillations while the inclination remains close to the polar orientation. The
range of initial disk inclinations that evolve to a polar orientation is
smaller in the presence of the outer companion. Disk breaking is also more
likely, at least temporarily, during the polar alignment process. The stellar
orbits in HD 98800 have parameters such that polar alignment of the
circumbinary disk is expected. In the absence of the gas, solid particles are
unstable at much smaller radii than the gas disk inner tidal truncation radius
because KL driven eccentricity leads to close encounters with the binary.",2202.06878v1
2021-10-11,Transition of laser-induced terahertz spin currents from torque- to conduction-electron-mediated transport,"Spin transport is crucial for future spintronic devices operating at
bandwidths up to the terahertz (THz) range. In F|N thin-film stacks made of a
ferro/ferrimagnetic layer F and a normal-metal layer N, spin transport is
mediated by (1) spin-polarized conduction electrons and/or (2) torque between
electron spins. To identify a cross-over from (1) to (2), we study laser-driven
spin currents in F|Pt stacks where F consists of model materials with different
degrees of electrical conductivity. For the magnetic insulators YIG, GIG and
maghemite, identical dynamics is observed. It arises from the THz interfacial
spin Seebeck effect (SSE), is fully determined by the relaxation of the
electrons in the metal layer and provides an estimate of the spin-mixing
conductance of the GIG/Pt interface. Remarkably, in the half-metallic
ferrimagnet Fe3O4 (magnetite), our measurements reveal two spin-current
components with opposite direction. The slower, positive component exhibits SSE
dynamics and is assigned to torque-type magnon excitation of the A- and B-spin
sublattices of Fe3O4. The faster, negative component arises from the
pyro-spintronic effect and can consistently be assigned to ultrafast
demagnetization of e-sublattice minority-spin hopping electrons. This
observation supports the magneto-electronic model of Fe3O4. In general, our
results provide a new route to the contact-free separation of torque- and
conduction-electron-mediated spin currents.",2110.05462v2
2020-12-03,Deviations from tidal torque theory: evolution of the halo spin-filament alignment,"The alignment between halo spins and the cosmic web is still poorly
understood despite being a widely studied topic. Here, we study this alignment
within the context of tidal torque theory (TTT) and deviations from it. To this
end, we analyze the evolution of the shape and spin direction of proto-haloes,
i.e. of all the volume elements associated to a $z=0$ halo, with respect to the
present-day filaments. We find that the major axis of proto-haloes undergoes a
major change, from being strongly perpendicular to the filament spine in the
initial conditions, to being preferentially aligned at the present time. In
comparison, the spin orientation shows only a mild evolution: it starts
slightly parallel to the filament spine, but the subsequent evolution, up to
$z{\sim}1$, gradually changes its orientation to preferentially perpendicular.
In order to analyze these signals in the TTT framework, we split the haloes
according to their net spin growth with respect to the median TTT expectation,
finding a clear correlation with the spin--filament alignment. At the present
time, haloes whose spin grew the most are the ones most perpendicular to the
filament spine, while haloes whose spin grew below the median TTT expectation
are typically more aligned. The dependence of spin directions on net spin
growth is already present in the initial conditions, and gets further modified
by late-time, $z<2$, evolution. Also, spin directions mildly deviate from the
TTT predictions even at high redshift, indicating the need for extensions to
the model.",2012.01638v3
2017-12-20,Magnetic field effects on a nanowire with inhomogeneous Rashba spin-orbit coupling: Spin properties at equilibrium,"By modeling a Rashba nanowire contacted to leads via an inhomogeneous
spin-orbit coupling profile, we investigate the equilibrium properties of the
spin sector when a uniform magnetic field is applied along the nanowire axis.
We find that the interplay between magnetic field and Rashba coupling generates
a spin current, polarised perpendicularly to the applied field and flowing
through the nanowire even at equilibrium. In the nanowire bulk such effect
persists far beyond the regime where the nanowire mimics the helical states of
a quantum spin Hall system, while in the leads the spin current is suppressed.
Furthermore, despite the nanowire not being proximized by superconductors, at
the interfaces with the leads we predict the appearance of localized spin
torques and spin polarizations, orthogonal to the magnetic field and partially
penetrating into the leads. This feature, due to the inhomogeneity of the
Rashba coupling, suggests to use caution in interpreting spin polarization as
signatures of Majorana fermions. When the magnetic field has a component also
along the Rashba field, its collinearity with the spin polarization and
orthogonality to the spin current are violated in the nanowire bulk too. We
analyze these quantities in terms of the magnetic field and chemical potential
for both long and short nanowires in experimentally realistic regimes.",1712.07536v2
2018-03-01,Room-temperature nanoseconds spin relaxation in WTe2 and MoTe2 thin films,"The Weyl semimetal WTe2 and MoTe2 show great potential in generating large
spin currents since they possess topologically-protected spin-polarized states
and can carry a very large current density. In addition, the intrinsic
noncentrosymmetry of WTe2 and MoTe2 endows with a unique property of crystal
symmetry-controlled spin-orbit torques. An important question to be answered
for developing spintronic devices is how spins relax in WTe2 and MoTe2. Here,
we report a room-temperature spin relaxation time of 1.2 ns (0.4 ns) in WTe2
(MoTe2) thin film using the time-resolved Kerr rotation (TRKR). Based on ab
initio calculation, we identify a mechanism of long-lived spin polarization
resulting from a large spin splitting around the bottom of the conduction band,
low electron-hole recombination rate and suppression of backscattering required
by time-reversal and lattice symmetry operation. In addition, we find the spin
polarization is firmly pinned along the strong internal out-of-plane magnetic
field induced by large spin splitting. Our work provides an insight into the
physical origin of long-lived spin polarization in Weyl semimetals which could
be useful to manipulate spins for a long time at room temperature.",1803.00305v1
2021-12-08,Edge spin transport in the disordered two-dimensional topological insulator WTe$_2$,"The spin conductance of two-dimensional topological insulators (2D TIs) is
not expected to be quantized in the presence of perturbations that break the
spin-rotational symmetry. However, the deviation from the pristine-limit
quantization has yet to be studied in detail. In this paper, we define the spin
current operator for the helical edge modes of a 2D TI and introduce a
four-terminal setup to measure spin conductances. Using the developed
formalism, we consider the effects of disorder terms that break spin-rotational
symmetry or give rise to edge-to-edge coupling. We identify a key role played
by spin torque in an out-of-equilibrium edge. We then utilize a tight-binding
model of topological monolayer WTe$_2$ and scattering matrix formalism to
numerically study spin transport in a four-terminal 2D TI device. In
particular, we calculate the spin conductances and characteristic spin decay
length in the presence of magnetic disorder. In addition, we study the effects
of inter-edge scattering in a quantum point contact geometry. We find that the
spin Hall conductance is surprisingly robust to spin symmetry-breaking
perturbations, as long as time-reversal symmetry is preserved and inter-edge
scattering is weak.",2112.04394v3
2022-08-26,Anisotropic linear and nonlinear charge-spin conversion in topological semimetal SrIrO3,"Over the past decade, utilizing spin currents in the linear response of
electric field to manipulate magnetization states via spin-orbit torques (SOTs)
is one of the core concepts for realizing a multitude of spintronic devices.
Besides the linear regime, recently, nonlinear charge-spin conversion under the
square of electric field has been recognized in a wide variety of materials
with nontrivial spin textures, opening an emerging field of nonlinear
spintronics. Here, we report the investigation of both linear and nonlinear
charge-spin conversion in one single topological semimetal SrIrO3(110) thin
film that hosts strong spin-orbit coupling and nontrivial spin textures in the
momentum space. In the nonlinear regime, the observation of crystalline
direction dependent response indicates the presence of anisotropic surface
states induced spin-momentum locking near the Fermi level. Such anisotropic
spin textures also give rise to spin currents in the linear response regime,
which mainly contributes to the fieldlike SOT component. Our work demonstrates
the power of combination of linear and nonlinear approaches in understanding
and utilizing charge-spin conversion in topological materials.",2208.12499v1
2024-02-06,Magnon mediated spin pumping by coupled ferrimagnetic garnets heterostructure,"Spin pumping has significant implications for spintronics, providing a
mechanism to manipulate and transport spins for information processing.
Understanding and harnessing spin currents through spin pumping is critical for
the development of efficient spintronic devices. The use of a magnetic
insulator with low damping, enhances the signal-to-noise ratio in crucial
experiments such as spin-torque ferromagnetic resonance (FMR) and spin pumping.
A magnetic insulator coupled with a heavy metal or quantum material offers a
more straight forward model system, especially when investigating spin-charge
interconversion processes to greater accuracy. This simplicity arises from the
absence of unwanted effects caused by conduction electrons unlike in
ferromagnetic metals. Here, we investigate the spin pumping in coupled
ferrimagnetic (FiM) Y3Fe5O12 (YIG)/Tm3Fe5O12 (TmIG) bilayers combined with
heavy-metal (Pt) using the inverse spin Hall effect (ISHE). It is observed that
magnon transmission occurs at both of the FiMs FMR positions. The enhancement
of spin pumping voltage (Vsp) in the FiM garnet heterostructures is attributed
to the strong interfacial exchange coupling between FiMs. The modulation of Vsp
is achieved by tuning the bilayer structure. Further, the spin mixing
conductance for these coupled systems is found to be 10^18 m^-2. Our findings
describe a novel coupled FiM system for the investigation of magnon coupling
providing new prospects for magnonic devices.",2402.03734v1
2012-12-06,Cosmic vorticity and the origin of halo spins,"In the standard model of cosmology, structure emerges out of non-rotational
flow and the angular momentum of collapsing halos is induced by tidal torques.
The growth of halo angular momentum in the linear and quasi-linear phases is
associated with a shear, curl-free, flow and it is well described within the
linear framework of tidal torque theory (TTT). However, TTT is rendered
irrelevant as haloes approach turn around and virialization. At that stage the
flow field around halos has non-zero vorticity. Using a cosmological
simulation, we have examined the importance of the curl of the velocity field
(vorticity) in determining halo spin, finding a strong alignment between the
two. We have also examined the alignment of vorticity with the principle axes
of the shear tensor, finding that it tends to be perpendicular to the axis
along which material is collapsing fastest (e1). This behavior is independent
of halo masses and cosmic web environment. Our results agree with previous
findings on the tendency of halo spin to be perpendicular to e1, and of the
spin of (simulated) halos and (observed) galaxies to be aligned with the
large-scale structure. Our results imply that angular momentum growth proceeds
in two distinct phases. In the first phase angular momentum emerges out of a
shear, curl-free, potential flow, as described by TTT. In the second phase, in
which haloes approach virialization, the angular momentum emerges out of a
vortical flow and halo spin becomes strongly aligned with the vorticity of the
ambient flow field.",1212.1454v1
2014-01-15,Interface control of the magnetic chirality in CoFeB|MgO heterosctructures with heavy metal underlayers,"Recent advances in the understanding of spin orbital effects in ultrathin
magnetic heterostructures have opened new paradigms to control magnetic moments
electrically. The Dzyaloshinskii-Moriya interaction (DMI) is said to play a key
role in forming a Neel-type domain wall that can be driven by the spin Hall
torque, a torque resulting from the spin current generated in a neighboring
non-magnetic layer via the spin Hall effect. Here we show that the strength and
sign of the DMI can be changed by modifying the adjacent heavy metal underlayer
(X) in perpendicularly magnetized X|CoFeB|MgO heterstructures. Albeit the same
spin Hall angle, a domain wall moves along or against the electron flow
depending on the underlayer. We find that the sense of rotation of a domain
wall spiral11 is reversed when the underlayer is changed from Hf to W and the
strength of DMI varies as the number of 5d electrons of the heavy metal layer
changes. The DMI can even be tuned by adding nitrogen to the underlayer, thus
allowing interface engineering of the magnetic texture in ultrathin magnetic
heterostructures.",1401.3568v1
2014-09-24,Angular Momentum Transport via Internal Gravity Waves in Evolving Stars,"Recent asteroseismic advances have allowed for direct measurements of the
internal rotation rates of many sub-giant and red giant stars. Unlike the
nearly rigidly rotating Sun, these evolved stars contain radiative cores that
spin faster than their overlying convective envelopes, but slower than they
would in the absence of internal angular momentum transport. We investigate the
role of internal gravity waves in angular momentum transport in evolving low
mass stars. In agreement with previous results, we find that convectively
excited gravity waves can prevent the development of strong differential
rotation in the radiative cores of Sun-like stars. As stars evolve into
sub-giants, however, low frequency gravity waves become strongly attenuated and
cannot propagate below the hydrogen burning shell, allowing the spin of the
core to decouple from the convective envelope. This decoupling occurs at the
base of the sub-giant branch when stars have surface temperatures of roughly
5500 K. However, gravity waves can still spin down the upper radiative region,
implying that the observed differential rotation is likely confined to the deep
core near the hydrogen burning shell. The torque on the upper radiative region
may also prevent the core from accreting high-angular momentum material and
slow the rate of core spin-up. The observed spin-down of cores on the red giant
branch cannot be totally attributed to gravity waves, but the waves may enhance
shear within the radiative region and thus increase the efficacy of
viscous/magnetic torques.",1409.6835v1
2015-08-10,Magnetic Origins of the Stellar Mass-Obliquity Correlation in Planetary Systems,"Detailed observational characterization of transiting exoplanet systems has
revealed that the spin-axes of massive (M > ~1.2 solar masses) stars often
exhibit substantial misalignments with respect to the orbits of the planets
they host. Conversely, lower-mass stars tend to only have limited obliquities.
A similar trend has recently emerged within the observational dataset of young
stars' magnetic field strengths: massive T-Tauri stars tend to have dipole
fields that are ~10 times weaker than their less-massive counterparts. Here we
show that the associated dependence of magnetic star-disk torques upon stellar
mass naturally explains the observed spin-orbit misalignment trend, provided
that misalignments are obtained within the disk-hosting phase. Magnetic torques
act to realign the stellar spin-axes of lower-mass stars with the disk plane on
a timescale significantly shorter than the typical disk lifetime, whereas the
same effect operates on a much longer timescale for massive stars.
Cumulatively, our results point to a primordial excitation of extrasolar
spin-orbit misalignment, signalling consistency with disk-driven migration as
the dominant transport mechanism for short-period planets. Furthermore, we
predict that spin-orbit misalignments in systems where close-in planets show
signatures of dynamical, post-nebular emplacement will not follow the observed
correlation with stellar mass.",1508.02365v1
2017-11-02,A Comparative Study on Spin-Orbit Torque Efficiencies from W/ferromagnetic and W/ferrimagnetic Heterostructures,"It has been shown that W in its resistive form possesses the largest
spin-Hall ratio among all heavy transition metals, which makes it a good
candidate for generating efficient dampinglike spin-orbit torque (DL-SOT)
acting upon adjacent ferromagnetic or ferrimagnetic (FM) layer. Here we provide
a systematic study on the spin transport properties of W/FM magnetic
heterostructures with the FM layer being ferromagnetic
Co$_{20}$Fe$_{60}$B$_{20}$ or ferrimagnetic Co$_{63}$Tb$_{37}$ with
perpendicular magnetic anisotropy. The DL-SOT efficiency $|\xi_{DL}|$, which is
characterized by a current-induced hysteresis loop shift method, is found to be
correlated to the microstructure of W buffer layer in both
W/Co$_{20}$Fe$_{60}$B$_{20}$ and W/Co$_{63}$Tb$_{37}$ systems. Maximum values
of $|\xi_{DL}|\approx 0.144$ and $|\xi_{DL}|\approx 0.116$ are achieved when
the W layer is partially amorphous in the W/Co$_{20}$Fe$_{60}$B$_{20}$ and
W/Co$_{63}$Tb$_{37}$ heterostructures, respectively. Our results suggest that
the spin Hall effect from resistive phase of W can be utilized to effectively
control both ferromagnetic and ferrimagnetic layers through a DL-SOT mechanism.",1711.00630v2
2017-11-16,Spin-orbit torques and tunable Dzyaloshinskii-Moriya interaction in Co/Cu/Co trilayers,"We study the spin-orbit torques (SOTs) in Co/Cu/Co magnetic trilayers based
on first-principles density-functional theory calculations in the case where
the applied electric field lies in-plane, i.e., parallel to the interfaces. We
assume that the bottom Co layer has a fixed in-plane magnetization, while the
top Co layer can be switched. We find that the SOT on the top ferromagnet can
be controlled by the bottom ferromagnet because of the nonlocal character of
the SOT in this system. As a consequence the SOT is anisotropic, i.e., its
magnitude varies with the direction of the applied electric field. We show that
the Dzyaloshinskii-Moriya interaction (DMI) in the top layer is anisotropic as
well, i.e., the spin-spiral wavelength of spin-spirals in the top layer depends
on their in-plane propagation direction. This effect suggests that DMI can be
tuned easily in magnetic trilayers via the magnetization direction of the
bottom layer. In order to understand the influence of the bottom ferromagnet on
the SOTs and the DMI of the top ferromagnet we study these effects in Co/Cu
magnetic bilayers for comparison. We find the SOTs and the DMI to be
surprisingly large despite the small spin-orbit interaction of Cu.",1711.06102v2
2019-11-01,Precessional spin-torque dynamics in biaxial antiferromagnets,"The N\'eel order of an antiferromagnet subject to a spin torque can undergo
precession in a circular orbit about any chosen axis. To orient and stabilize
the motion against the effects of magnetic anisotropy, the spin polarization
should have components in-plane and normal to the plane of the orbit, where the
latter must exceed a threshold. For biaxial antiferromagnets, the precessional
motion is described by the equation for a damped-driven pendulum, which has
hysteresis a function of the spin current with a critical value where the
period diverges. The fundamental frequency of the motion varies inversely with
the damping, and as $(x^p-1)^{1/p}$ with the drive-to-criticality ratio $x$ and
the parameter $p>2$. An approximate closed-form result for the threshold spin
current is presented, which depends on the minimum cutoff frequency the orbit
can support. Precession about the hard axis has zero cutoff frequency and the
lowest threshold, while the easy axis has the highest cutoff. A device setup is
proposed for electrical control and detection of the dynamics, which is
promising to demonstrate a tunable terahertz nano-oscillator.",1911.00445v4
2018-07-22,Electrical switching of perpendicular magnetization in L10 FePt single layer,"Electrical manipulation of magnetization is essential for integration of
magnetic functionalities such as magnetic memories and magnetic logic devices
into electronic circuits. The current induced spin-orbit torque (SOT) in heavy
metal/ferromagnet (HM/FM) bilayers via the spin Hall effect in the HM and/or
the Rashba effect at the interfaces provides an efficient way to switch the
magnetization. In the meantime, current induced SOT has also been used to
switch the in-plane magnetization in single layers such as ferromagnetic
semiconductor (Ga,Mn)As and antiferromagnetic metal CuMnAs with globally or
locally broken inversion symmetry. Here we demonstrate the current induced
perpendicular magnetization switching in L10 FePt single layer. The current
induced spin-orbit effective fields in L10 FePt increase with the chemical
ordering parameter (S). In 20 nm FePt films with high S, we observe a large
charge-to-spin conversion efficiency and a switching current density as low as
7.0E6 A/cm2. We anticipate our findings may stimulate the exploration of the
spin-orbit torques in bulk perpendicular magnetic anisotropic materials and the
application of high-efficient perpendicular magnetization switching in single
FM layer.",1807.08244v1
2012-09-07,Spin-orbit coupling for tidally evolving super-Earths,"We investigate the spin behavior of close-in rocky planets and the
implications for their orbital evolution. Considering that the planet rotation
evolves under simultaneous actions of the torque due to the equatorial
deformation and the tidal torque, both raised by the central star, we analyze
the possibility of temporary captures in spin-orbit resonances. The results of
the numerical simulations of the exact equations of motions indicate that,
whenever the planet rotation is trapped in a resonant motion, the orbital decay
and the eccentricity damping are faster than the ones in which the rotation
follows the so-called pseudo-synchronization. Analytical results obtained
through the averaged equations of the spin-orbit problem show a good agreement
with the numerical simulations. We apply the analysis to the cases of the
recently discovered hot super-Earths Kepler-10 b, GJ 3634 b and 55 Cnc e. The
simulated dynamical history of these systems indicates the possibility of
capture in several spin-orbit resonances; particularly, GJ 3634 b and 55 Cnc e
can currently evolve under a non-synchronous resonant motion for suitable
values of the parameters. Moreover, 55 Cnc e may avoid a chaotic rotation
behavior by evolving towards synchronization through successive temporary
resonant trappings.",1209.1580v1
2016-12-08,Complete spin and orbital evolution of close-in bodies using a Maxwell viscoelastic rheology,"In this paper, we present a formalism designed to model tidal interaction
with a viscoelastic body made of Maxwell material. Our approach remains regular
for any spin rate and orientation, and for any orbital configuration including
high eccentricities and close encounters. The method is to integrate
simultaneously the rotation and the position of the planet as well as its
deformation. We provide the equations of motion both in the body frame and in
the inertial frame. With this study, we generalize preexisting models to the
spatial case and to arbitrary multipole orders using a formalism taken from
quantum theory. We also provide the vectorial expression of the secular tidal
torque expanded in Fourier series. Applying this model to close-in exoplanets,
we observe that if the relaxation time is longer than the revolution period,
the phase space of the system is characterized by the presence of several
spin-orbit resonances, even in the circular case. As the system evolves, the
planet spin can visit different spin-orbit configurations. The obliquity is
decreasing along most of these resonances, but we observe a case where the
planet tilt is instead growing. These conclusions derived from the secular
torque are successfully tested with numerical integrations of the instantaneous
equations of motion on HD 80606b. Our formalism is also well adapted to
close-in super-Earths in multiplanet systems which are known to have non-zero
mutual inclinations.",1612.02558v1
2016-12-20,Current-nonlinear Hall effect and spin-orbit torque magnetization switching in a magnetic topological insulator,"Precise estimation of spin Hall angle as well as successful maximization of
spin-orbit torque (SOT) form a basis of electronic control of magnetic
properties with spintronic functionality. Until now, current-nonlinear Hall
effect, or second harmonic Hall voltage has been utilized as one of the methods
for estimating spin Hall angle, which is attributed to the magnetization
oscillation by SOT. Here, we argue the second harmonic Hall voltage in
magnetic/nonmagnetic topological insulator (TI) heterostructures,
Cr$_x$(Bi$_{1-y}$Sb$_y$)$_{2-x}$Te$_3$/(Bi$_{1-y}$Sb$_y$)$_2$Te$_3$. From the
angular, temperature and magnetic field dependence, it is unambiguously shown
that the large second harmonic Hall voltage in TI heterostructures is governed
not by SOT but mainly by asymmetric magnon scattering mechanism without
magnetization oscillation. Thus, this method does not allow an accurate
estimation of spin Hall angle when magnons largely contribute to electron
scattering. Instead, the SOT contribution in a TI heterostructure is
exemplified by current pulse induced non-volatile magnetization switching,
which is realized with a current density of $\sim 2.5 \times 10^{10}
\mathrm{A/m}^2$, showing its potential as spintronic materials.",1612.06862v2
2017-02-01,Continuous Tuning the Magnitude and Direction of Spin-Orbit Torque Using Bilayer Heavy Metals,"Spin-orbit torques (SOTs) have opened a new path to switch the magnetization
in perpendicularly magnetized films and are of great interest due to their
potential applications in novel data storage technology, such as the magnetic
random access memory (MRAM). The effective manipulation of SOT has thus become
an important step towards these applications. Here, current induced spin-orbit
effective fields and magnetization switching are investigated in
Pt/Ta/CoFeB/MgO structures with bilayer heavy metals. With a fixed thickness (1
nm) of the Ta layer, the magnitude and sign of current induced spin-orbit
effective fields can be continuously tuned by changing the Pt layer thickness,
consistent with the current induced magnetization switching data. The ratio of
longitudinal to transverse spin-orbit effective fields is found to be
determined by the Ta/CoFeB interface and can be continuously tuned by changing
the Pt layer thickness. The Dzyaloshinskii-Moriya interaction (DMI) is found to
be weak and shows an insignificant variation with the Pt thickness. The results
demonstrate an effective method to tune SOTs utilizing bilayer heavy metals
without affecting the DMI, a desirable feature which will be useful for the
design of SOT-based devices.",1702.00147v1
2017-03-10,Room-temperature perpendicular magnetization switching through giant spin-orbit torque from sputtered BixSe(1-x) topological insulator material,"The spin-orbit torque (SOT) arising from materials with large spin-orbit
coupling promises a path for ultra-low power and fast magnetic-based storage
and computational devices. We investigated the SOT from magnetron-sputtered
BixSe(1-x) thin films in BixSe(1-x)/CoFeB heterostructures by using a dc planar
Hall method. Remarkably, the spin Hall angle (SHA) was found to be as large as
18.83, which is the largest ever reported at room temperature (RT). Moreover,
switching of a perpendicular CoFeB multilayer using SOT from the BixSe(1-x) has
been observed with the lowest-ever switching current density reported in a
bilayer system: 2.3 * 105 A/cm2 at RT. The giant SHA, smooth surface, ease of
growth of the films on silicon substrate, successful growth and switching of a
perpendicular CoFeB multilayer on BixSe(1-x) film opens a path for use of
BixSe(1-x) topological insulator (TI) material as a spin-current generator in
SOT-based memory and logic devices.",1703.03822v1
2020-01-17,Two new outbursts and transient hard X-rays from 1E 1048.1$-$5937,"Since its discovery, 1E 1048.1$-$5937 has been one of the most active
magnetars, both in terms of radiative outbursts, and changes to its spin
properties. Here we report on a continuing monitoring campaign with the Neil
Gehrels Swift Observatory X-ray Telescope in which we observe two new outbursts
from this source. The first outburst occurred in 2016 July, and the second in
2017 December, reaching peak 0.5-10 keV absorbed fluxes of
$3.2^{+0.2}_{-0.3}\times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ and
$2.2^{+0.2}_{-0.2}\times10^{-11}$ erg s$^{-1}$ cm$^{-2}$, respectively, factors
of $\sim$5 and $\sim 4$ above the quiescent flux. Both new outbursts were
accompanied by spin-up glitches with amplitudes of $\Delta\nu=
4.47(6)\times10^{-7}$ Hz and $\Delta\nu= 4.32(5)\times10^{-7}$ Hz,
respectively. Following the 2016 July outburst, we observe, as for past
outbursts, a period of delayed torque fluctuations, which reach a peak
spin-down of $1.73\pm0.01$ times the quiescent rate, and which dominates the
spin evolution compared to the spin-up glitches. We also report an observation
near the peak of the first of these outbursts with NuSTAR in which hard X-ray
emission is detected from the source. This emission is well characterized by an
absorbed blackbody plus a broken power law, with a power-law index above
$13.4\pm0.6$ keV of $0.5_{-0.2}^{+0.3}$, similar to those observed in both
persistent and transient magnetars. The hard X-ray results are broadly
consistent with models of electron/positron cooling in twisted magnetic field
bundles in the outer magnetosphere. However the repeated outbursts and
associated torque fluctuations in this source remain puzzling.",2001.06450v1
2022-03-22,Quantum sensing and imaging of spin-orbit-torque-driven spin dynamics in noncollinear antiferromagnet Mn3Sn,"Novel noncollinear antiferromagnets with spontaneous time-reversal symmetry
breaking, nontrivial band topology, and unconventional transport properties
have received immense research interest over the past decade due to their rich
physics and enormous promise in technological applications. One of the central
focuses in this emerging field is exploring the relationship between the
microscopic magnetic structure and exotic material properties. Here, the
nanoscale imaging of both spin-orbit-torque-induced deterministic magnetic
switching and chiral spin rotation in noncollinear antiferromagnet Mn3Sn films
using nitrogen-vacancy (NV) centers is reported. Direct evidence of the
off-resonance dipole-dipole coupling between the spin dynamics in Mn3Sn and
proximate NV centers is also demonstrated with NV relaxometry measurements.
These results demonstrate the unique capabilities of NV centers in accessing
the local information of the magnetic order and dynamics in these emergent
quantum materials and suggest new opportunities for investigating the interplay
between topology and magnetism in a broad range of topological magnets.",2203.11465v1
2022-06-07,Non-volatile electric control of spin-orbit torques in an oxide two-dimensional electron gas,"Spin-orbit torques (SOTs) have opened a novel way to manipulate the
magnetization using in-plane current, with a great potential for the
development of fast and low power information technologies. It has been
recently shown that two-dimensional electron gases (2DEGs) appearing at oxide
interfaces provide a highly efficient spin-to-charge current interconversion.
The ability to manipulate 2DEGs using gate voltages could offer a degree of
freedom lacking in the classical ferromagnetic/spin Hall effect bilayers for
spin-orbitronics, in which the sign and amplitude of SOTs at a given current
are fixed by the stack structure. Here, we report the non-volatile
electric-field control of SOTs in an oxide-based Rashba-Edelstein 2DEG. We
demonstrate that the 2DEG is controlled using a back-gate electric-field,
providing two remanent and switchable states, with a large resistance contrast
of 1064%. The SOTs can then be controlled electrically in a non-volatile way,
both in amplitude and in sign. This achievement in a 2DEG-CoFeB/MgO
heterostructures with large perpendicular magnetization further validates the
compatibility of oxide 2DEGs for magnetic tunnel junction integration, paving
the way to the advent of electrically reconfigurable SOT MRAMS circuits, SOT
oscillators, skyrmion and domain-wall-based devices, and magnonic circuits.",2206.03068v1
2023-02-02,Leveraging symmetry for an accurate spin-orbit torques characterization in ferrimagnetic insulators,"Spin-orbit torques (SOTs) have emerged as an efficient means to electrically
control the magnetization in ferromagnetic heterostructures. Lately, an
increasing attention has been devoted to SOTs in heavy metal (HM)/magnetic
insulator (MI) bilayers owing to their tunable magnetic properties and
insulating nature. Quantitative characterization of SOTs in HM/MI
heterostructures are, thus, vital for fundamental understanding of charge-spin
interrelations and designing novel devices. However, the accurate determination
of SOTs in MIs have been limited so far due to small electrical signal outputs
and dominant spurious thermoelectric effects caused by Joule heating. Here, we
report a simple methodology based on harmonic Hall voltage detection and
macrospin simulations to accurately quantify the damping-like and field-like
SOTs, and thermoelectric contributions separately in MI-based systems.
Experiments on the archetypical Bi-doped YIG/Pt heterostructure using the
developed method yield precise values for the field-like and damping-like SOTs,
reaching -0.14 and -0.15 mT per 1.7x$10^{ 11}$ A/$m^2$, respectively. We
further reveal that current-induced Joule heating changes the spin transparency
at the interface, reducing the spin Hall magnetoresistance and damping-like
SOT, simultaneously. These results and the devised method can be beneficial for
fundamental understanding of SOTs in MI-based heterostructures and designing
new devices where accurate knowledge of SOTs is necessary.",2302.01141v2
2023-04-25,Torque reversal and cyclotron absorption feature in HMXB 4U 1538-522,"We present a comprehensive timing and spectral analysis of the HMXB 4U
1538-522 by using the Nuclear Spectroscopic Telescope Array (NuSTAR)
observatory data. Using three archived observations made between 2019 and 2021,
we have detected $\sim $ 526 s coherent pulsations up to 60 keV. We have found
an instantaneous spin-down rate of $\dot{P} = 6.6_{-6.0}^{+2.4} \times 10^{-6}$
s s$^{-1}$ during the first observation. The pulse profiles had a double peaked
structure consisting of a broad primary peak and an energy dependent, weak
secondary peak. We have also analysed the long-term spin-period evolution of 4U
1538-522 from data spanning more than four decades, including the data from
Fermi/GBM. Based on the recent spin trends, we have found that the third torque
reversal in 4U 1538-522 happened around MJD 58800. The source is currently
spinning up with $\dot{P} = -1.9(1) \times 10^{-9}$ s s$^{-1}$. We also report
a periodic fluctuation in the spin-period of 4U 1538-522. The broad-band
persistent spectra can be described with a blackbody component and either
powerlaw or Comptonization component along with a Fe K$_{\alpha}$ line at 6.4
keV and a cyclotron absorption feature around 22 keV. We have also found a
relatively weak absorption feature around 27 keV in the persistent spectra of
4U 1538-522 in all three observations. We have estimated a magnetic field
strength of $1.84_{-0.06}^{+0.04} (1+z) \times 10^{12}$ and
$2.33_{-0.24}^{+0.15} (1+z) \times 10^{12}$ G for the two features,
respectively.",2304.12797v1
2019-03-07,The stochastic motion of self-thermophoretic Janus particles,"Langevin equations for the self-thermophoretic dynamics of Janus motors
partially coated with an absorbing layer that is heated by a radiation field
are presented. The derivation of these equations is based on fluctuating
hydrodynamics and radiative heat transfer theory involving stochastic equations
for bulk phases and surface processes that are consistent with microscopic
reversibility. Expressions for the self-thermophoretic force and torque for
arbitrary slip boundary conditions are obtained. The overdamped Langevin
equations for the colloid displacement and radiative heat transfer provide
expressions for the self-thermophoretic velocity and its reciprocal
contribution where an external force can influence the radiative heat transfer.
A nonequilibrium fluctuation formula is also derived and shows how the
probability density of the Janus particle displacement and radiation energy
transfer during the time interval [0,t] are related to the mechanical and
thermal affinities that characterize the nonequilibrium system state.",1903.02992v1
1998-11-23,Magnetic propeller outflows,"A model is developed for magnetic `propeller'-driven outflows which cause a
rapidly rotating magnetized star accreting from a disk to spin-down. Energy and
angular momentum lost by the star goes into expelling most of the accreting
disk matter. The theory gives an expression for the effective Alfven radius
$R_A$ (where the inflowing matter is effectively stopped) which depends on the
mass accretion rate, the star's mass and magnetic moment, and the star's
rotation rate. The model points to a mechanism for `jumps' between spin-down
and spin-up evolution and for the reverse transition, which are changes between
two possible equilibrium configurations of the system. In for example the
transistion from spin-down to spin-up states the Alfven radius $R_A$ decreases
from a value larger than the corotation radius to one which is smaller. In this
transistion the `propeller' goes from being ``on'' to being ``off.'' The ratio
of the spin-down to spin-up torque (or the ratio for the reverse change) in a
jump is shown to be of order unity.",9811369v2
2008-02-14,The role of spin in the formation and evolution of galaxies,"Using the SDSS spectroscopic sample, we estimate the dark matter halo spin
parameter lambda for ~53,000 disk galaxies for which MOPED star formation
histories are available. We investigate the relationship between spin and total
stellar mass, star formation history, and environment. First, we find a clear
anti-correlation between stellar mass and spin, with low mass galaxies
generally having high dark matter spins. Second, galaxies which have formed
more than ~5% of their stars in the last 0.2 Gyr have more broadly distributed
and typically higher spins (including a significant fraction with lambda > 0.1)
than galaxies which formed a large fraction of their stars more than 10 Gyr
ago. Finally, we find little or no correlation between the value of spin of the
dark halo and environment as determined both by proximity to a new cluster
catalog and a marked correlation study. This agrees well with the predictions
from linear hierarchical torquing theory and numerical simulations.",0802.1934v2
2008-12-31,Spin Hall effect in the kagome lattice with Rashba spin-orbit interaction,"We study the spin Hall effect in the kagom\'{e} lattice with Rashba
spin-orbit coupling. The conserved spin Hall conductance $\sigma_{xy}^{s}$ (see
text) and its two components, i.e., the conventional term $\sigma_{xy}^{s0}$
and the spin-torque-dipole term $\sigma_{xy}^{s\tau}$, are numerically
calculated, which show a series of plateaus as a function of the electron Fermi
energy $\epsilon_{F}$. A consistent two-band analysis, as well as a Berry-phase
interpretation, is also given. We show that these plateaus are a consequence of
the various Fermi-surface topologies when tuning $\epsilon_{F}$. In particular,
we predict that compared to the case with the Fermi surface encircling the
$\mathbf{\Gamma}$ point in the Brillouin zone, the amplitude of the spin Hall
conductance with the Fermi surface encircling the $\mathbf{K}$ points is twice
enhanced, which makes it highly meaningful in the future to systematically
carry out studies of the $\mathbf{K}$-valley spintronics.",0901.0053v1
2010-08-16,Domain-wall depinning assisted by pure spin currents,"We study the depinning of domain walls by pure diffusive spin currents in a
nonlocal spin valve structure based on two ferromagnetic permalloy elements
with copper as the nonmagnetic spin conduit. The injected spin current is
absorbed by the second permalloy structure with a domain wall and from the
dependence of the wall depinning field on the spin current density we find an
efficiency of 6*10^{-14}T/(A/m^2), which is more than an order of magnitude
larger than for conventional current induced domain wall motion. Theoretically
we reproduce this high efficiency, which arises from the surface torques
exerted by the absorbed spin current that lead to efficient depinning.",1008.2773v1
2011-12-19,Nonequilibrium Spin Magnetization Quantum Transport Equations: Spin and Charge Coupling,"The classical Bloch equations of spin magnetization transport is extended to
fully time-dependent and highly-nonlinear nonequilibrium spin magnetization
quantum distribution function transport (SMQDFT) equations. The relevant
variables are the spinor correlation functions which separate into charge and
spin magnetization distributions that becomes highly coupled in SMQDFT equa-
tions. The leading terms consist of the Boltzmann kinetic equation with
spin-orbit coupling in a magnetic eld together with spin-dependent scattering
terms which contribute to the torque. These do not have analogue within the
classical relaxation-dephasing picture, but are inherently quantum many-body
effects. These should incorporate the spatiotemporal-dependent phase-space
dynam- ics of Elliot-Yafet and Dyakonov-Perel scatterings. The resulting SMQDFT
equations should serve as a theoretical foundation for computational spintronic
and nanomagnetic device applications, in ultrafast-switching-speed/low-power
performance and reliability analyses.",1112.4220v2
2013-11-19,Observation of the spin Peltier effect,"We report the observation of the spin Peltier effect (SPE) in the
ferrimagnetic insulator Yttrium Iron Garnet (YIG), i.e. a heat current
generated by a spin current flowing through a Platinum (Pt)|YIG interface. The
effect can be explained by the spin torque that transforms the spin current in
the Pt into a magnon current in the YIG. Via magnon-phonon interactions the
magnetic fluctuations modulate the phonon temperature that is detected by a
thermopile close to the interface. By finite-element modelling we verify the
reciprocity between the spin Peltier and spin Seebeck effect. The observed
strong coupling between thermal magnons and phonons in YIG is attractive for
nanoscale cooling techniques.",1311.4772v1
2015-05-28,Driving and detecting ferromagnetic resonance in insulators with the spin Hall effect,"We demonstrate the generation and detection of spin-torque ferromagnetic
resonance in Pt/YIG bilayers. A unique attribute of this system is that the
spin Hall effect lies at the heart of both the generation and detection
processes and no charge current is passing through the insulating magnetic
layer. When the YIG undergoes resonance, a dc voltage is detected
longitudinally along the Pt that can be described by two components. One is the
mixing of the spin Hall magnetoresistance with the microwave current. The other
results from spin pumping into the Pt being converted to a dc current through
the inverse spin Hall effect. The voltage is measured with applied magnetic
field directions that range in-plane to nearly perpendicular. We find that for
magnetic fields that are mostly out-of-plane, an imaginary component of the
spin mixing conductance is required to model our data.",1505.07791v1
2016-06-17,Phenomenological spin transport theory driven by anomalous Nernst effect,"Several experimental efforts such as material investigation and structure
improvement have been made recently to find a large anomalous Nernst effect in
ferromagnetic metals. Here, we develop a theory of spin transport driven by the
anomalous Nernst effect in a diffusive ferromagnetic/nonmagnetic multilayer.
Starting from a phenomenological formula of a spin-dependent electric current,
the theoretical formulas of electric voltage and spin torque generated by the
anomalous Nernst effect are derived. The magnitude of the electric voltage
generated from the spin current via the inverse spin Hall effect is on the
order of $0.1$ $\mu$V for currently available experimental parameter values.
The temperature gradient necessary to switch the magnetization is quite larger
than the typical experimental value. The separation of the contributions of the
Seebeck and transverse spin Seebeck effects is also discussed.",1606.05406v2
2017-09-29,Designing Magnetic Droplet Soliton Nucleation Employing Spin Polarizer,"We show by means of micromagnetic simulations that spin polarizer in
nano-contact spin torque oscillators (NC-STOs) as the representative of the
fixed layer in an orthogonal pseudo-spin valve (P-SV) can be employed to design
and to control magnetic droplet soliton nucleation and dynamics. We found that
using a tilted spin polarizer layer decreases the droplet nucleation time which
is more suitable for high speed applications. However, a tilted spin polarizer
increases the nucleation current and decreases the frequency stability of the
droplet. Additionally, by driving the magnetization inhomogenously at the
nano-contact region, it is found that a tilted spin polarizer reduces the
precession angle of the droplet and through an interplay with the Oersted field
of the DC current, it breaks the spatial symmetry of the droplet profile. Our
findings explore fundamental insight into nano-scale magnetic droplet soliton
dynamics with potential tunability parameters for future microwave electronics.",1709.10325v3
2018-01-08,Spin Conductance and Spin Conductivity in Topological Insulators: Analysis of Kubo-like terms,"We investigate spin transport in 2-dimensional insulators, with the long-term
goal of establishing whether any of the transport coefficients corresponds to
the Fu-Kane-Mele index which characterizes 2d time-reversal-symmetric
topological insulators. Inspired by the Kubo theory of charge transport, and by
using a proper definition of the spin current operator, we define the Kubo-like
spin conductance $G_K^{s_z}$ and spin conductivity $\sigma_K^{s_z}$. We prove
that for any gapped, periodic, near-sighted discrete Hamiltonian, the above
quantities are mathematically well-defined and the equality $G_K^{s_z} =
\sigma_K^{s_z}$ holds true. Moreover, we argue that the physically relevant
condition to obtain the equality above is the vanishing of the mesoscopic
average of the spin-torque response, which holds true under our hypotheses on
the Hamiltonian operator. This vanishing condition might be relevant in view of
further extensions of the result, e.g. to ergodic random discrete Hamiltonians
or to Schr\""odinger operators on the continuum. A central role in the proof is
played by the trace per unit volume and by two generalizations of the trace,
the principal value trace and it directional version.",1801.02611v1
2018-05-10,Designing Rashba-Dresselhaus effect in magnetic insulators,"One of the major strategies to control magnetism in spintronics is to utilize
the coupling between electron spin and its orbital motion. The Rashba and
Dresselhaus spin-orbit couplings induce magnetic textures of band electrons
called spin momentum locking, which produces a spin torque by the injection of
electric current. However, joule heating had been a bottleneck for device
applications. Here, we propose a theory to generate further rich spin textures
in insulating antiferromagnets with broken spatial inversion symmetry (SIS),
which is easily controlled by a small magnetic field. In antiferromagnets, the
ordered moments host two species of magnons that serve as internal degrees of
freedom in analogy with electron spins. The Dzyaloshinskii-Moriya interaction
introduced by the SIS breaking couples the two-magnon-degrees of freedom with
the magnon momentum. We present a systematic way to design such texture and to
detect it via magnonic spin current for the realization of antiferromagnetic
memory.",1805.03925v2
2019-11-03,Magnetic damping modulation in $IrMn_{3}/Ni_{80}Fe_{20}$ via the magnetic spin Hall effect,"Non-collinear antiferromagnets can have additional spin Hall effects due to
the net chirality of their magnetic spin structure, which provides for more
complex spin-transport phenomena compared to ordinary non-magnetic materials.
Here we investigated how ferromagnetic resonance of permalloy
($Ni_{80}Fe_{20}$) is modulated by spin Hall effects in adjacent epitaxial
$IrMn_{3}$ films. We observe a large dc modulation of the ferromagnetic
resonance linewidth for currents applied along the [001] $IrMn_{3}$ direction.
This very strong angular dependence of spin-orbit torques from dc currents
through the bilayers can be explained by the magnetic spin Hall effect where
$IrMn_{3}$ provides novel pathways for modulating magnetization dynamics
electrically.",1911.00943v1
2017-05-22,The Spin Distribution of Fast Spinning Neutron Stars in Low Mass X-Ray Binaries: Evidence for Two Sub-Populations,"We study the current sample of rapidly rotating neutron stars in both
accreting and non-accreting binaries in order to determine whether the spin
distribution of accreting neutron stars in low-mass X-ray binaries can be
reconciled with current accretion torque models. We perform a statistical
analysis of the spin distributions and show that there is evidence for two
sub-populations among low-mass X-ray binaries, one at relatively low spin
frequency, with an average of ~300 Hz and a broad spread, and a peaked
population at higher frequency with average spin frequency of ~575 Hz. We show
that the two sub-populations are separated by a cut-point at a frequency of
~540 Hz. We also show that the spin frequency of radio millisecond pulsars does
not follow a log-normal distribution and shows no evidence for the existence of
distinct sub-populations. We discuss the uncertainties of different accretion
models and speculate that either the accreting neutron star cut-point marks the
onset of gravitational waves as an efficient mechanism to remove angular
momentum or some of the neutron stars in the fast sub-population do not evolve
into radio millisecond pulsars.",1705.07669v1
2018-07-28,Spin-current-related magnetoresistance in epitaxial Pt/Co bilayers in the presence of spin Hall effect and Rashba-Edelstein effect,"We analyze the experimentally obtained spin-current-related magnetoresistance
in epitaxial Pt/Co bilayers by using a drift-diffusion model that incorporates
both bulk spin Hall effect and interfacial Rashba-Edelstein effect (REE). The
magnetoresistance analysis yields, for the Pt/Co interface, a
temperature-independent Rashba parameter in the order of 1e-11 eV m that agrees
with theoretical calculations, along with an effective interfacial REE
thickness of several angstroms which is in overall consistency with our
previous spin-orbit torque analysis. In particular, our results suggest that
both bulk and interface charge-spin current inter-conversions need to be taken
into account for the spin-current-related magnetoresistance analysis in
highly-conductive magnetic hetero-structures such as the epitaxial Pt/Co
bilayers.",1807.10867v2
2021-02-18,Re-estimating the Spin Parameter of the Black Hole in Cygnus X-1,"Cygnus X-1 is a well-studied persistent black hole X-ray binary. Recently,
the three parameters needed to estimate the black hole spin of this system,
namely the black hole mass $M$, the orbital inclination $i$ and the source
distance $D$, have been updated. In this work we redetermine the spin parameter
using the continuum-fitting technique for those updated parameter values. Based
on the assumption that the spin axis of the black hole is aligned with the
orbital plane, we fit the thermal disk component to a fully relativistic thin
accretion disk model. The error in the spin estimate arising from the combined
observational uncertainties is obtained via Monte Carlo (MC) simulations. We
demonstrate that, without considering the counteracting torque effect, the new
spin parameter is constrained to be a$_* > 0.9985$ (3$\sigma$), which confirms
that the spin of the black hole in Cygnus X-1 is extreme.",2102.09093v1
2017-01-18,Conversion of electronic to magnonic spin current at heavy-metal magnetic-insulator interface,"Electronic spin current is convertible to magnonic spin current via the
creation or annihilation of thermal magnons at the interface of a magnetic
insulator and a metal with a strong spin-orbital coupling. So far this
phenomenon was evidenced in the linear regime. Based on analytical and
fulledged numerical results for the non-linear regime we demonstrate that the
generated thermal magnons or magnonic spin current in the insulator is
asymmetric with respect to the charge current direction in the metal and
exhibits a nonlinear dependence on the charge current density, which is
explained by the tuning effect of the spin Hall torque and the magnetization
damping. The results are also discussed in light of and are in line with recent
experiments pointing to a new way of non-linear manipulation of spin with
electrical means.",1701.05148v1
2017-01-23,Unidirectional spin Hall magnetoresistance in topological insulator/ferromagnetic layer heterostructures,"The large spin orbit coupling in topological insulators results in helical
spin-textured Dirac surface states that are attractive for topological
spintronics. These states generate an efficient spin-orbit torque on proximal
magnetic moments at room temperature. However, memory or logic spin devices
based upon such switching require a non-optimal three terminal geometry, with
two terminals for the writing current and one for reading the state of the
device. An alternative two terminal device geometry is now possible by
exploiting the recent discovery of a unidirectional spin Hall magnetoresistance
in heavy metal/ferromagnet bilayers and (at low temperature) in magnetically
doped topological insulator heterostructures. We report the observation of
unidirectional spin Hall magnetoresistance in a technologically relevant device
geometry that combines a topological insulator with a conventional
ferromagnetic metal. Our devices show a figure-of-merit (magnetoresistance per
current density per total resistance) that is comparable to the highest
reported values in all-metal Ta/Co bilayers.",1701.06505v1
2020-05-16,Simultaneous observation of anti-damping and inverse spin Hall effect in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Pt bilayer system,"Manganites have shown potential in spintronics because they exhibit high spin
polarization. Here, by ferromagnetic resonance we have studied the damping
properties of La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Pt bilayers which are prepared by
oxide molecular beam epitaxy. The damping coefficient ($\alpha$) of
La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) single layer is found to be 0.0104.
However the LSMO/Pt bilayers exhibit decrease in $\alpha$ with increase in Pt
thickness. This decrease in the value of $\alpha$ is probably due to high
anti-damping like torque. Further, we have investigated the angle dependent
inverse spin Hall effect (ISHE) to quantify the spin pumping voltage from other
spin rectification effects such as anomalous Hall effect and anisotropic
magnetoresistance. We have observed high spin pumping voltage ($\sim$~20 $ \mu
V$). The results indicate that both anti-damping and spin pumping phenomena are
occuring simultaneously.",2005.07848v3
2020-07-02,Magnetic-field-induced reorientation in the SDW and the spin-stripe phases of the frustrated spin-1/2 chain compound $β$-TeVO$_4$,"$\beta$-TeVO$_4$ is a frustrated spin 1/2 zig-zag chain system,where
spin-density-wave (SDW), vector chiral (VC)and an exotic dynamic spin-stripe
phase compete at low temperatures. Here we use torque magnetometry to study the
anisotropy of these phases in magnetic fields of up to 5 T. Our results show
that the magnetic-field-induced spin reorientation occurs in the SDW and in the
spin stripe phases for $\mu_0 H \geq 2$~T. The observed spin reorientation is a
new element of the anisotropic phase diagram for the field directions in the
$ac$ and $a^*b$ crystallographic planes. The presented results should help
establishing the model of anisotropic magnetic interactions, which are
responsible for the formation of complex magnetic phases in $\beta$-TeVO$_4$
and similar quantum systems.",2007.00932v1
2022-05-16,Omnidirectional spin-to-charge conversion in graphene/NbSe$_2$ van der Waals heterostructures,"The conversion of spin currents polarized in different directions into charge
currents is a keystone for novel spintronic devices. Van der Waals
heterostructures with tailored symmetry are a very appealing platform for such
a goal. Here, by performing nonlocal spin precession experiments, we
demonstrate the spin-to-charge conversion (SCC) of spins oriented in all three
directions (x, y, and z). By analyzing the magnitude and temperature dependence
of the signal in different configurations, we argue that the different SCC
components measured are likely due to spin-orbit proximity and broken symmetry
at the twisted graphene/NbSe$_2$ interface. Such efficient omnidirectional SCC
opens the door to the use of new architectures in spintronic devices, from
spin-orbit torques that can switch any magnetization to the magnetic state
readout of magnetic elements pointing in any direction.",2205.07668v1
2022-09-04,Non-Hermitian dynamics of a two-spin system with PT symmetry,"A system of interacting spins that are under the influence of spin-polarized
currents can be described using a complex functional, or a non-Hermitian (NH)
Hamiltonian. We study the dynamics of two exchange-coupled spins on the Bloch
sphere. In the case of currents leading to PT symmetry, an exceptional point
that survives also in the nonlinear system is identified. The nonlinear system
is bistable for small currents and it exhibits stable oscillating motion or it
can relax to a fixed point. The oscillating motion of the two spins is akin to
synchronized spin-torque oscillators. For the full nonlinear system, we derive
two conserved quantities that furnish a geometric description of the spin
trajectories in phase space and indicate stability of the oscillating motion.
Our analytical results provide tools for the description of the dynamics of NH
systems that are defined on the Bloch sphere.",2209.01572v2
2023-01-01,Spin Hall Induced Magnetization Dynamics in Multiferroic Tunnel Junction,"The combination of spin-orbit coupling driven effects and multiferroic
tunneling properties was explored experimentally in thin Pt/Co/BTO/LSMO
multilayers. The presence of a Pt heavy metal allows for the spin
current-induced magnetization precession of Co upon radio-frequency charge
current injection. The utilization of a BTO ferroelectric tunnel barrier
separating the Co and LSMO ferromagnetic electrodes gives rise to both
tunneling-magnetoresistance and electroresistance. Using the spin-orbit torque
ferromagnetic resonance, the maganetization dynamics of the Co/Pt bilayers was
studied at room temperature. Unexpectedly the magnetization dynamics study in
the same geometry performed at low temperature reveals the existence of both Co
and LSMO resonance peaks indicating efficient spin current generation both
using the spin Hall effect in Pt and spin pumping in LSMO that tunnel via the
BTO barrier.",2301.00459v1
2023-08-06,A15 Phase Ta3Sb Thin Films: Direct Synthesis and Giant Spin-Orbit Effects,"We use co-sputtering to directly synthesize thin films of the A15 phase
intermetallic compound Ta3Sb, which has been predicted to have a giant spin
Hall conductivity. We identify a large window of Ta:Sb flux ratio that
stabilizes single-phase A15 Ta3Sb. Composition analyses of these films show a
Ta:Sb atomic ratio of 4:1, which is consistent with the known Ta-Sb phase
diagram. The spin Hall conductivity of thin film Ta3Sb is -3400+/-400 (hbar/2e)
S/cm and the spin-orbit torque efficiency is -0.6+/-0.1 at 20 K, as determined
from harmonic Hall measurements of Ta3Sb/permalloy bilayer structures. These
giant values make Ta3Sb a promising material for efficient charge-to-spin
conversion in spintronic applications. Large field-like spin-orbit effective
fields that are independent of the ferromagnetic layer thickness have also been
measured in the Ta3Sb/permalloy bilayers. We attribute the field-like
spin-orbit effective field to the Rashba effect at the interface.",2308.03220v1
2024-02-01,Spin wave-driven variable-phase mutual synchronization in spin Hall nano-oscillators,"Spin-orbit torque can drive auto-oscillations of propagating spin wave (PSW)
modes in nano-constriction spin Hall nano-oscillators (SHNOs). These modes
allow both long-range coupling and the potential of controlling its phase --
critical aspect for nano-magnonics, spin wave logic, and Ising machines. Here,
we demonstrate PSW-driven variable-phase coupling between two nano-constriction
SHNOs and study how their separation and the PSW wave vector impact their
mutual synchronization. In addition to ordinary in-phase mutual
synchronization, we observe, using both electrical measurements and
phase-resolved $\mu-$Brillouin Light Scattering microscopy, mutual
synchronization with a phase that can be tuned from 0 to $\pi$ using the drive
current or the applied field. Micromagnetic simulations corroborate the
experiments and visualize how the PSW patterns in the bridge connecting the two
nano-constrictions govern the coupling. These results advance the capabilities
of mutually synchronized SHNOs and open up new possibilities for applications
in spin wave logic, unconventional computing, and Ising Machines.",2402.00586v1
2024-02-12,Extrinsic Contribution to Nonlinear Current Induced Spin Polarization,"Nonlinear spin polarization occurring in the second order of driving electric
current is the dominant source of nonequilibrium magnetization in
centrosymmetric or weakly noncentrosymmetric nonmagnetic materials, and induces
nonlinear spin-orbit torque in magnets. Up to now, only the intrinsic mechanism
based on anomalous spin polarizability dipole, which is the spin counterpart of
Berry curvature dipole, has been studied, while disorder induced mechanisms are
still missing. Here, we derive these contributions, which include not only the
anomalous distribution function due to skew scattering and coordinate shift,
but also interband coherence effects given by disorder induced spin shift and
electric field induced anomalous scattering amplitude. We demonstrate these
terms and show their importance in a minimal model. A scaling law for nonlinear
current-induced spin polarization is constructed, which may help analyze
experimental data in the future.",2402.07756v3
2023-03-13,Towards a unified picture of polarization transfer -- pulsed DNP and chemically equivalent PHIP,"Nuclear spin hyperpolarization techniques, such as dynamic nuclear
polarization (DNP) and parahydrogen-induced polarization (PHIP), have
revolutionized nuclear magnetic resonance and magnetic resonance imaging. In
these methods, a readily available source of high spin order, either electron
spins in DNP or singlet states in hydrogen for PHIP, is brought into close
proximity with nuclear spin targets, enabling efficient transfer of spin order
under external quantum control. Despite vast disparities in energy scales and
interaction mechanisms between electron spins in DNP and nuclear singlet states
in PHIP, a pseudo-spin formalism allows us to establish an intriguing
equivalence. As a result, the important low-field polarization transfer regime
of PHIP can be mapped onto an analogous system equivalent to pulsed-DNP. This
establishes a correspondence between key polarization transfer sequences in
PHIP and DNP, facilitating the transfer of sequence development concepts. This
promises fresh insights and significant cross-pollination between DNP and PHIP
polarization sequence developers.",2303.07478v2
1997-01-15,Are We Seeing Magnetic Axis Reorientation in the Crab and Vela Pulsars?,"Variation in the angle $\alpha$ between a pulsar's rotational and magnetic
axes would change the torque and spin-down rate. We show that sudden increases
in $\alpha$, coincident with glitches, could be responsible for the persistent
increases in spin-down rate that follow glitches in the Crab pulsar. Moreover,
changes in $\alpha$ at a rate similar to that inferred for the Crab pulsar
account naturally for the very low braking index of the Vela pulsar. If
$\alpha$ increases with time, all pulsar ages obtained from the conventional
braking model are underestimates. Decoupling of the neutron star liquid
interior from the external torque cannot account for Vela's low braking index.
Variations in the Crab's pulse profile due to changes in $\alpha$ might be
measurable.",9701096v1
1997-03-03,Cosmic rays and grain alignment,"The recent detection of interstellar polarization in the solid CO feature
near 4.67 micron shows that CO-mantled grains can be aligned in cold molecular
clouds. These observations conflict with a theory of grain alignment which
attributes the polarization in molecular clouds to the effects of cosmic rays:
according to this theory, oblate spheroidal grains with H_2O and CO_2-dominated
ice mantles are spun up to suprathermal energies by molecular evaporation from
cosmic ray impact sites but spin up does not occur for CO-mantled grains.
Motivated by this conflict, we reexamine the effects of cosmic rays on the
alignment of icy grains. We show that the systematic torques produced by cosmic
rays are insufficient to cause suprathermal spin. In principle, the random
torques due to cosmic rays can enhance the efficiency of Davis-Greenstein
alignment by raising the grain rotational temperature. However, a significant
enhancement would require cosmic ray fluxes 6--7 orders of magnitude larger
than the flux in a typical cold cloud.",9703009v1
1998-01-07,The Angular Momentum of Accreting Neutron Stars,"I review the rotation measurements of accreting neutron stars. Many of the
highly magnetic accreting X-ray pulsars have been continuously observed with
the Burst and Transient Source Experiment (BATSE) aboard the Compton Gamma-Ray
Observatory (CGRO) since April 1991. These observations show that the accretion
torque exerted on many disk-fed accreting X-ray pulsars changes sign on a
monthly to yearly timescale. This results in alternating periods of spin-up and
spin-down with nearly the same torques, leading to little net angular momentum
gained by accretion. I also summarize recent discoveries with the Rossi X-Ray
Timing Explorer (RXTE) of periodicities during Type I X-ray bursts. These seem
to indicate that many of the rapidly accreting and weakly magnetic neutron
stars in our galaxy are rotating at frequencies greater than 250 Hertz. Most
remarkable is that they all rotate within a rather narrow range of frequencies.",9801043v1
2001-01-24,Precession Interpretation of the Isolated Pulsar PSR B1828-11,"Pulse timing of the isolated pulsar PSR B1882-11 shows strong Fourier power
at periods ~1000, 500 and 250 d, correlated with changes in the pulse profile
(Stairs, Lyne & Shemar 2000). We study the extent to which these data can be
explained by precession of the star's rigid crust coupled to the magnetic
dipole torque. We find that the correlated changes in the pulse duration and
spin period derivative can be explained as precession at a period of ~500 d
with a wobble angle of ~3 deg if the star's dipole moment is nearly orthogonal
to its symmetry axis. The dipole torque produces a harmonic at ~250 d.
Comparison of the predicted spin dynamics with the observed pulse durations
requires the radio beam to have a non-standard ``hour-glass'' shape. We make
predictions of variations in beam polarization and pulse profile with which to
test this interpretation. The precession interpretation of PSR B1828-11
seriously challenges the current understanding of the liquid interior of the
neutron star. In particular, if the internal liquid is in a superfluid state,
its rotational vortices cannot be significantly pinned to the crust.",0101434v1
2005-10-03,Accretion-powered Stellar Winds as a Solution to the Stellar Angular Momentum Problem,"We compare the angular momentum extracted by a wind from a pre-main-sequence
star to the torques arising from the interaction between the star and its
Keplerian accretion disk. We find that the wind alone can counteract the
spin-up torque from mass accretion, solving the mystery of why accreting
pre-main-sequence stars are observed to spin at less than 10% of break-up
speed, provided that the mass outflow rate in the stellar winds is ~10% of the
accretion rate. We suggest that such massive winds will be driven by some
fraction $\epsilon$ of the accretion power. For observationally constrained
typical parameters of classical T-Tauri stars, $\epsilon$ needs to be between a
few and a few tens of percent. In this scenario, efficient braking of the star
will terminate simultaneously with accretion, as is usually assumed to explain
the rotation velocities of stars in young clusters.",0510060v1
2007-03-12,Generation linewidth of an auto-oscillator with a nonlinear frequency shift: Spin-torque nano-oscillator,"It is shown that the generation linewidth of an auto-oscillator with a
nonlinear frequency shift (i.e. an auto-oscillator in which frequency depends
on the oscillation amplitude) is substantially larger than the linewidth of a
conventional quasi-linear auto-oscillator due to the renormalization of the
phase noise caused by the nonlinearity of the oscillation frequency. The
developed theory, when applied to a spin-torque nano-contact auto-oscillator,
predicts a minimum of the generation linewidth when the nano-contact is
magnetized at a critical angle to its plane, corresponding to the minimum
nonlinear frequency shift, in good agreement with recent experiments.",0703317v2
2007-05-03,Order in the chaos? The strange case of accreting millisecond pulsars,"We review recent results from the X-ray timing of accreting millisecond
pulsars in Low Mass X-ray Binaries. This is the first time a timing analysis is
performed on accreting millisecond pulsars, and for the first time we can
obtain information on the behavior of a very fast pulsar subject to accretion
torques. We find both spin-up and spin-down behaviors, from which, using
available models for the accretion torques, we derive information on the mass
accretion rate and magnetic field of the neutron star in these systems. We also
find that the phase delays behavior as a function of time in these sources is
sometimes quite complex and difficult to interpret, since phase shifts, most
probably driven by variations of the X-ray flux, are sometimes present.",0705.0464v2
2007-09-19,Wave Excitation in Disks Around Rotating Magnetic Stars,"The accretion disk around a rotating magnetic star (neutron star, white dwarf
or T Tauri star) is subjected to periodic vertical magnetic forces from the
star, with the forcing frequency equal to the stellar spin frequency or twice
the spin frequency. This gives rise bending waves in the disk that may
influence the variabilities of the system. We study the excitation, propagation
and dissipation of these waves using a hydrodynamical model coupled with a
generic model description of the magnetic forces. The $m=1$ bending waves are
excited at the Lindblad/vertical resonance, and propagate either to larger
radii or inward toward the corotation resonance where dissipation takes place.
While the resonant torque is negligible compared to the accretion torque, the
wave nevertheless may reach appreciable amplitude and can cause or modulate
flux variabilities from the system. We discuss applications of our result to
the observed quasi-periodic oscillations from various systems, in particular
neutron star low-mass X-ray binaries.",0709.3086v2
2008-03-19,Strong linewidth variation for spin-torque nano-oscillators as a function of in-plane magnetic field angle,"We measure the microwave signals produced by spin-torque-driven magnetization
dynamics in patterned magnetic multilayer devices at room temperature, as a
function of the angle of a magnetic field applied in the sample plane. We find
strong variations in the frequency linewidth of the signals, with a decrease by
more than a factor of 20 as the field is rotated from the magnetic easy axis to
the in-plane hard axis. Based on micromagnetic simulations, we identify these
variations as due to a transition from spatially incoherent to coherent
precession.",0803.2871v1
2008-04-24,Oersted fields and current density profiles in spin-torque driven magnetization dynamics -- Finite element modelling of realistic geometries,"The classical impact of electrical currents on magnetic nanostructures is
analyzed with numerical calculations of current-density distributions and
Oersted fields in typical contact geometries. For the Oersted field
calculation, a hybrid finite element / boundary element method (FEM/BEM)
technique is presented which can be applied to samples of arbitrary shape.
Based on the FEM/BEM analysis, it is argued that reliable micromagnetic
simulations on spin-tranfer-torque driven magnetization processes should
include precise calculations of the Oersted field, particularly in the case of
pillar contact geometries. Similarly, finite-element simulations demonstrate
that numerical calculations of current-density distributions are required,
e.g., in the case of magnetic strips with an indentation. Such strips are
frequently used for the design of devices based on current-driven domain-wall
motion. A dramatic increase of the current density is found at the apex of the
notch, which is expected to strongly affect the magnetization processes in such
strips.",0804.4010v1
2008-08-14,High-output CPP-GMR sensor with synthetic-ferrimagnet free layer and enhanced spin-torque critical currents,"It is shown that the maximum stable output of a CPP-GMR sensor is increased
significantly by using a synthetic ferrimagnet free layer, provided the
electron current flows from free layer to reference layer. This free layer
allows a larger magnetoresistance ratio for a given free layer magnetic moment,
and in addition results in a greater than three-fold increase in the critical
current above which spin-torque instability of the free layer occurs. In read
heads with net free layer moments equivalent to only 4.5nm of Ni80Fe20, this
effect is shown to result in sustainable sense current densities above 2e8
A/cm2.",0808.2001v1
2008-09-05,Current-Induced Resonant Motion of a Magnetic Vortex Core: Effect of Nonadiabatic Spin Torque,"The current-induced resonant excitation of a magnetic vortex core is
investigated by means of analytical and micromagnetic calculations. We find
that the radius and the phase shift of the resonant motion are not correctly
described by the analytical equations because of the dynamic distortion of a
vortex core. In contrast, the initial tilting angle of a vortex core is free
from the distortion and determined by the nonadiabaticity of the spin torque.
It is insensitive to experimentally uncontrollable current-induced in-plane
Oersted field. We propose that a time-resolved imaging of the very initial
trajectory of a core is essential to experimentally estimate the
nonadiabaticity.",0809.0952v1
2008-09-16,Zero Field precession and hysteretic threshold currents in spin torque oscillators with tilted polarizer,"Using non-linear system theory and numerical simulations we map out the
static and dynamic phase diagram in zero applied field of a spin torque
oscillator with a tilted polarizer (TP-STO).We find that for sufficiently large
currents, even very small tilt angles (beta>1 degree) will lead to steady free
layer precession in zero field. Within a rather large range of tilt angles, 1
degree< beta <19 degree, we find coexisting static states and hysteretic
switching between these using only current. In a more narrow window (1
degree<beta<5 degree) one of the static states turns into a limit cycle
(precession). The coexistence of static and dynamic states in zero magnetic
field is unique to the tilted polarizer and leads to large hysteresis in the
upper and lower threshold currents for TP-STO operation.",0809.2763v1
2008-10-06,"Auto-oscillation threshold, narrow spectral lines, and line jitter in spin-torque oscillators based on MgO magnetic tunnel junctions","We demonstrate spin torque induced auto-oscillation in MgO-based magnetic
tunnel junctions. At the generation threshold, we observe a strong line
narrowing down to 6 MHz at 300K and a dramatic increase in oscillator power,
yielding spectrally pure oscillations free of flicker noise. Setting the
synthetic antiferromagnet into autooscillation requires the same current
polarity as the one needed to switch the free layer magnetization. The induced
auto-oscillations are observed even at zero applied field, which is believed to
be the acoustic mode of the synthetic antiferromagnet. While the phase
coherence of the auto-oscillation is of the order of microseconds, the power
autocorrelation time is of the order of milliseconds and can be strongly
influenced by the free layer dynamics.",0810.0978v1
2008-11-01,Can disk-magnetosphere interaction models and beat frequency models for quasi-periodic oscillation in accreting X-ray pulsars be reconciled?,"In this paper we review some aspects of the theory of magnetic threaded
disks. We discuss in particular the equations that determine the position of
the inner disk boundary by using different prescriptions for the neutron
star-accretion disk interaction. We apply the results to several accretion
powered X-ray pulsars that showed both quasi-periodic oscillations in their
X-ray flux and spin-up/spin-down torque reversals. Under the hypothesis that
the beat-frequency model is applicable to the quasi-periodic oscillations, we
show that these sources provide an excellent opportunity to test models of the
disk-magnetosphere interaction. A comparison is carried out between the
magnetospheric radius obtained with all the prescriptions used in threaded disk
models; this shows that none of those prescriptions is able to reproduce the
combination of quasi-periodic oscillations and torque behaviour observed for
different X-ray luminosity levels in the X-ray pulsars in the present sample.
  This suggests that the problem of accretion disk threading by stellar
magnetic field is still lacking a comprehensive solution. We discuss briefly an
outline of possible future developments in this field.",0811.0049v1
2009-02-25,Accretion torques and motion of the hot spot on the accreting millisecond pulsar XTE J1807-294,"We present a coherent timing analysis of the 2003 outburst of the accreting
millisecond pulsar XTE J1807-294. We find an upper limit for the spin frequency
derivative of 5E-14 Hz/s. The sinusoidal fractional amplitudes of the
pulsations are the highest observed among the accreting millisecond pulsars and
can reach values of up to 27% (2.5-30 keV). The pulse arrival time residuals of
the fundamental follow a linear anti-correlation with the fractional amplitudes
that suggests hot spot motion over the surface of the neutron star both in
longitude and latitude. An anti-correlation between residuals and X-ray flux
suggests an influence of accretion rate on pulse phase, and casts doubts on the
use of standard timing techniques to measure spin frequencies and torques on
the neutron star.",0902.4323v1
2009-05-12,Sensitivity of spin-torque diodes for frequency-tunable resonant microwave detection,"We calculate the efficiency with which magnetic tunnel junctions can be used
as resonant detectors of incident microwave radiation via the spin-torque diode
effect. The expression we derive is in good agreement with the sensitivities we
measure for MgO-based magnetic tunnel junctions with an extended (unpatterned)
magnetic pinned layer. However, the measured sensitivities are reduced below
our estimate for a second set of devices in which the pinned layer is a
patterned synthetic antiferromagnet (SAF). We suggest that this reduction may
be due to an undesirable coupling between the magnetic free layer and one of
the magnetic layers within the etched SAF. Our calculations suggest that
optimized tunnel junctions should achieve sensitivities for resonant detection
exceeding 10,000 mV/mW.",0905.1912v1
2009-08-04,Time domain detection of pulsed spin torque damping reduction,"Combining multiple ultrafast spin torque impulses with a 5 nanosecond
duration pulse for damping reduction, we observe time-domain precession which
evolves from an initial 1 ns duration transient with changing precessional
amplitude to constant amplitude oscillations persisting for over 2 ns. These
results are consistent with relaxation of the transient trajectories to a
stable orbit with nearly zero damping. We find that in order to observe
complete damping cancellation and the transient behavior in a time domain
sampling measurement, a short duration, fast rise-time pulse is required to
cancel damping without significant trajectory dephasing.",0908.0481v1
2009-10-15,Non-linear frequency and amplitude modulation of a nano-contact spin torque oscillator,"We study the current controlled modulation of a nano-contact spin torque
oscillator. Three principally different cases of frequency non-linearity
($d^{2}f/dI^{2}_{dc}$ being zero, positive, and negative) are investigated.
Standard non-linear frequency modulation theory is able to accurately describe
the frequency shifts during modulation. However, the power of the modulated
sidebands only agrees with calculations based on a recent theory of combined
non-linear frequency and amplitude modulation.",0910.2819v3
2009-12-18,Oscillatory transient regime in the forced dynamics of a spin torque nano-oscillator,"We demonstrate that the transient non-autonomous dynamics of a spin torque
nano-oscillator (STNO) under a radio-frequency (rf) driving signal is
qualitatively different from the dynamics described by the Adler model. If the
external rf current $I_{rf}$ is larger than a certain critical value $I_{cr}$
(determined by the STNO bias current and damping) strong oscillations of the
STNO power and phase develop in the transient regime. The frequency of these
oscillations increases with $I_{rf}$ as $\propto\sqrt{I_{rf} - I_{cr}}$ and can
reach several GHz, whereas the damping rate of the oscillations is almost
independent of $I_{rf}$. This oscillatory transient dynamics is caused by the
strong STNO nonlinearity and should be taken into account in most STNO rf
applications.",0912.3650v1
2010-05-07,Non-adiabatic spin torque investigated using thermally activated magnetic domain wall dynamics,"Using transmission electron microscopy, we investigate the thermally
activated motion of domain walls (DWs) between two positions in permalloy
(Ni80Fe20) nanowires at room temperature. We show that this purely thermal
motion is well described by an Arrhenius law, allowing for a description of the
DW as a quasi-particle in a 1D potential landscape. By injecting small
currents, the potential is modified, allowing for the determination of the
non-adiabatic spin torque: the non-adiabatic coefficient is 0.010 +/- 0.004 for
a transverse DW and 0.073 +/- 0.026 for a vortex DW. The larger value is
attributed to the higher magnetization gradients present.",1005.1168v1
2010-07-14,Frequency modulation of spin torque oscillator pairs,"The current controlled modulation of nano-contact based spin torque
oscillator (STO) pairs is studied in both the synchronized and non-synchronized
states. The synchronized state shows a well behaved modulation and demonstrates
robust mutual locking even under strong modulation. The power distribution of
the modulation sidebands can be quantitatively described by assuming a single
oscillator model. However, in the non-synchronized state, the modulation
sidebands are not well described by the model, indicating interactions between
the two individual nano-contact STOs. These findings are promising for
potential applications requiring the modulation of large synchronized STO
arrays.",1007.2305v2
2011-02-24,Noise properties of a resonance-type spin-torque microwave detector,"We analyze performance of a resonance-type spin-torque microwave detector
(STMD) in the presence of noise and reveal two distinct regimes of STMD
operation. In the first (high-frequency) regime the minimum detectable
microwave power $P_{\rm min}$ is limited by the low-frequency Johnson-Nyquist
noise and the signal-to-noise ratio (SNR) of STMD is proportional to the input
microwave power $P_{\rm RF}$. In the second (low-frequency) regime $P_{\rm
min}$ is limited by the magnetic noise, and the SNR is proportional to
$\sqrt{P_{\rm RF}}$. The developed formalism can be used for the optimization
of the practical noise-handling parameters of a STMD.",1102.5048v1
2011-12-06,Temperature dependence of linewidth in nano-contact based spin torque oscillators: effect of multiple oscillatory modes,"We discuss the effect of mode transitions on the current (I) and temperature
(T) dependent linewidth (\Delta f) in nanocontact based spin torque oscillators
(STOs). At constant I, \Delta f exhibits an anomalous temperature dependence
near the mode transitions; \Delta f may either increase or decrease with T
depending on the position w.r.t. the mode transition. We show that the behavior
of \Delta f as a function of I can be fitted by the single mode analytical
theory of STOs, even though there are two modes present near the mode
transition, if the nonlinear amplification is determined directly from the
experiment. Using a recently developed theory of two coupled modes, we show
that the linewidth near mode transition can be described by an ""effective""
single-oscillator theory with an enhanced nonlinear amplification that carries
additional temperature dependence, which thus qualitatively explain the
experimental results.",1112.1280v2
2012-02-13,Switching Distributions for Perpendicular Spin-Torque Devices within the Macrospin Approximation,"We model ""soft"" error rates for writing (WSER) and for reading (RSER) for
perpendicular spin-torque memory devices by solving the Fokker-Planck equation
for the probability distribution of the angle that the free layer magnetization
makes with the normal to the plane of the film. We obtain: (1) an exact, closed
form, analytical expression for the zero-temperature switching time as a
function of initial angle; (2) an approximate analytical expression for the
exponential decay of the WSER as a function of the time the current is applied;
(3) comparison of the approximate analytical expression for the WSER to
numerical solutions of the Fokker-Planck equation; (4) an approximate
analytical expression for the linear increase in RSER with current applied for
reading; (5) comparison of the approximate analytical formula for the RSER to
the numerical solution of the Fokker-Planck equation; and (6) confirmation of
the accuracy of the Fokker-Planck solutions by comparison with results of
direct simulation using the single-macrospin Landau-Lifshitz-Gilbert (LLG)
equations with a random fluctuating field in the short-time regime for which
the latter is practical.",1202.2621v1
2012-02-15,Analytical investigation of modulated spin torque oscillators in the framework of coupled differential equations with variable coefficients,"Modulation of Spin Torque Oscillators (STOs) is investigated by analytically
solving the time-dependent coupled equations of an auto-oscillator. A Fourier
series solution is proposed, leading to the coefficients being determined with
a linear set of equations, from which a Nonlinear Amplitude and Frequency
Modulation (NFAM) scheme is obtained. In this framework, the NFAM features are
related to the intrinsic STO parameters, revealing a frequency-dependence of
the harmonic-dependent modulation index that allows a modulation bandwidth to
be defined for these devices. The presented results expose a rich parameter
space, where the modulation and the STO's operation conditions define the
observed modulation features. The Fourier-series representation of the time
signal is suitable for studying periodic perturbations on the auto-oscillator
equation.",1202.3429v1
2012-03-28,Decoherence and mode-hopping in a magnetic tunnel junction-based spin-torque oscillator,"We discuss the coherence of magnetic oscillations in a magnetic tunnel
junction-based spin-torque oscillator as a function of external field angle.
Time-frequency analysis shows mode-hopping between distinct oscillator modes,
which arises from linear and nonlinear couplings in the Landau-Lifshitz-Gilbert
equation, analogous to mode-hopping observed in semiconductor ring lasers.
These couplings and therefore mode-hopping are minimized near the current
threshold for antiparallel (AP) alignment of free layer with reference layer
magnetization. Away from the AP alignment, mode-hopping limits oscillator
coherence.",1203.6300v1
2012-04-09,Dependence of spin torque switching probability on electric current,"Dependence of the thermally assisted spin torque switching probability on the
sweep electric current was investigated theoretically. The analytical
expressions of the switching times for $b=1$ and $b=2$ are derived based on the
rate equation, where $b$ is the exponent of the current term in the switching
rate. The switching current is approximately proportional to the temperature
$T$ and the logarithm of the sweep rate $v$ for both $b=1$ and $b=2$ in the
experimentally performed ranges of $T$ and $v$. Experiments in very low
temperature range are required to determine the exponent $b$.",1204.2004v1
2012-07-12,Non-Adlerian phase slip and non stationary synchronization of spin-torque oscillators to a microwave source,"The non-autonomous dynamics of spin-torque oscillators in presence of both
microwave current and field at the same frequency can exhibit complex
non-isochronous effects. A non-stationary mode hopping between quasi-periodic
mode (frequency pulling) and periodic mode (phase locking), and a deterministic
phase slip characterized by an oscillatory synchronization transient
(non-Adlerian phase slip) after the phase jump of have been predicted. In the
latter effect, a wavelet based analysis reveals that in the positive and
negative phase jump the synchronization transient occurs at the frequency of
the higher and lower sideband frequency respectively. The non-Adlerian phase
slip effect, even if discovered in STOs, is a general property of
non-autonomous behavior valid to any non-isochronous auto-oscillator in regime
of moderate and large force locking.",1207.2921v1
2012-11-25,Spin torque switching of an in-plane magnetized system in a thermally activated region,"The current dependence of the exponent of the spin torque switching rate of
an in-plane magnetized system was investigated by solving the Fokker-Planck
equation with low temperature and small damping and current approximations. We
derived the analytical expressions of the critical currents, I_{c} and
I_{c}^{*}. At I_{c}, the initial state parallel to the easy axis becomes
unstable, while at I_{c}^{*} (\simeq 1.27 I_{c}) the switching occurs without
the thermal fluctuation. The current dependence of the exponent of the
switching rate is well described by (1-I/I_{c}^{*})^{b}, where the value of the
exponent b is approximately unity for I < I_{c}, while b rapidly increases up
to 2.2 with increasing current for I_{c} < I < I_{c}^{*}. The linear dependence
for I < I_{c} agrees with the other works, while the nonlinear dependence for
I_{c} < I < I_{c}^{*} was newly found by the present work. The nonlinear
dependence is important for analysis of the experimental results, because most
experiments are performed in the current region of I_{c} < I < I_{c}^{*}.",1211.5818v2
2012-12-06,Active electromagnetic metamaterial based on spin torque oscillators,"We propose theoretically an active material for electromagnetic radiation
with frequency of GHz by use of spin-torque oscillators. The origin of the
amplification is the energy supplied to the magnetization by the injected
current. We show that close to a resonance with current-driven magnetization,
the imaginary part of magnetic permeability becomes indeed negative for either
of the two circular polarizations, resulting in negative imaginary part of
refractive index. Besides, the real part of the refractive index is also
manipulated by the current. Our system thus realizes an active filter to obtain
circular polarized radiation and/or an electromagnetic metamaterial having
negative refractive index, both controlled electrically.",1212.1237v1
2013-01-28,Theoretical study of spin-torque oscillator coupled with a nano-magnet by dipole-dipole interaction,"The dynamics of a spin-torque-oscillator (STO) coupled with a nano-magnet
through dipole-dipole interaction was studied numerically by using the
macrospin model for the application of the STO as a read head sensor of hard
disk drives. We found that the current, which is required to induce the
oscillation of the free-layer (FL) of the STO, depends strongly on the distance
between the FL and the nano-magnet as well as on the relative orientation of
the magnetizations between them. To determine the dynamics of the STO it is
indispensable to consider the dynamics of the dipole-coupled nano-magnet. We
showed that we could detect the orientation of the magnetization of a
nano-magnet, or a recording-bit, by the modulation of the oscillation frequency
of the STO.",1301.6458v1
2013-08-17,Non-Adlerian synchronization of dipolar coupled vortex Spin-Torque Nano-Oscillators,"We investigate analytically and numerically the synchronization dynamics of
dipolarly coupled vortex based Spin-Torque Nano Oscillators (STNO) with
different pillar diameters. We identify the critical interpillar distances on
which synchronization occurs as a function of their diameter mismatch. We
obtain numerically a phase diagram showing the transition between
unsynchronized and synchronized states and compare it to analytical predictions
we make using Thiele approach. Our study demonstrates that for relatively small
diameters differences the synchronization dynamics can be described
qualitatively using Adler equation. However when the diameters difference
increases significantly, the system becomes strongly non-Adlerian.",1308.3811v1
2013-08-08,"Ultra-low Energy, High Performance and Programmable Magnetic Threshold Logic","We propose magnetic threshold-logic (MTL) design based on non-volatile
spin-torque switches. A threshold logic gate (TLG) performs summation of
multiple inputs multiplied by a fixed set of weights and compares the sum with
a threshold. MTL employs resistive states of magnetic tunnel junctions as
programmable input weights, while, a low-voltage domain-wall shift based
spin-torque switch is used for thresholding operation. The resulting MTL gate
acts as a low-power, configurable logic unit and can be used to build fully
pipelined, high-performance programmable computing blocks. Multiple stages in
such a MTL design can be connected using energy-efficient ultralow swing
programmable interconnect networks based on resistive switches. Owing to
memory-based compact logic and interconnect design and low-voltage, high-speed
spintorque based threshold operation, MTL can achieve more than two orders of
magnitude improvement in energy-delay product as compared to look-up table
based CMOS FPGA.",1308.4169v1
2014-12-19,Spin-Orbit Torque Induced Spike-Timing Dependent Plasticity,"Nanoelectronic devices that mimic the functionality of synapses are a crucial
requirement for performing cortical simulations of the brain. In this work we
propose a ferromagnet-heavy metal heterostructure that employs spin-orbit
torque to implement Spike-Timing Dependent Plasticity. The proposed device
offers the advantage of decoupled spike transmission and programming current
paths, thereby leading to reliable operation during online learning. Possible
arrangement of such devices in a crosspoint architecture can pave the way for
ultra-dense neural networks. Simulation studies indicate that the device has
the potential of achieving pico-Joule level energy consumption (maximum 2 pJ
per synaptic event) which is comparable to the energy consumption for synaptic
events in biological synapses.",1412.6548v1
2015-03-25,Spin Hall torque driven chiral domain walls in magnetic heterostructures,"The motion of magnetic domain walls in ultrathin magnetic heterostructures
driven by current via the spin Hall torque is described. We show results from
perpendicularly magnetized CoFeB|MgO heterostructures with various heavy metal
underlayers. The domain wall moves along or against the current flow depending
on the underlayer material. The direction to which the domain wall moves is
associated with the chirality of the domain wall spiral formed in these
heterostructures. The one-dimensional model is used to describe the
experimental results and extract parameters such as the Dzyaloshinskii-Moriya
exchange constant which is responsible for the formation of the domain wall
spiral. Fascinating effects arising from the control of interfaces in magnetic
heterostructures are described.",1503.07250v1
2015-06-02,Detection of spin torque magnetization dynamics through low frequency noise,"We present a comparative study of high frequency dynamics and low frequency
noise in elliptical magnetic tunnel junctions with lateral dimensions under 100
nm presenting current-switching phenomena. The analysis of the high frequency
oscillation modes with respect to the current reveals the onset of a
steady-state precession regime for negative bias currents above $J=10^7
A/cm^2$, when the magnetic field is applied along the easy axis of
magnetization. By the study of low frequency noise for the same samples, we
demonstrate the direct link between changes in the oscillation modes with the
applied current and the normalised low frequency (1/f) noise as a function of
the bias current. These findings prove that low frequency noise studies could
be a simple and powerful technique to investigate spin-torque based
magnetization dynamics.",1506.00901v1
2015-06-05,Optimizing magneto-dipolar interactions for synchronizing vortex based spin-torque nano-oscillators,"We report on a theoretical study about the magneto-dipolar coupling and
synchronization between two vortex-based spin-torque nano-oscillators. In this
work we study the dependence of the coupling efficiency on the relative
magnetization parameters of the vortices in the system. For that purpose, we
combine micromagnetic simulations, Thiele equation approach, and analytical
macro-dipole approximation model to identify the optimized configuration for
achieving phase-locking between neighboring oscillators. Notably, we compare
vortices configurations with parallel (P) polarities and with opposite (AP)
polarities. We demonstrate that the AP core configuration exhibits a coupling
strength about three times larger than in the P core configuration.",1506.01960v1
2015-06-10,Tunable inertia of chiral magnetic domain walls,"The time it takes to accelerate an object from zero to a given velocity
depends on the applied force and the environment. If the force ceases, it takes
exactly the same time to completely decelerate. A magnetic domain wall (DW) is
a topological object that has been observed to follow this behavior. Here we
show that acceleration and deceleration times of chiral Neel walls driven by
current are different in a system with low damping and moderate
Dzyaloshinskii-Moriya (DM) exchange constant. The time needed to accelerate a
DW with current via the spin Hall torque is much faster than the time it needs
to decelerate once the current is turned off. The deceleration time is defined
by the DM exchange constant whereas the acceleration time depends on the spin
Hall torque, enabling tunable inertia of chiral DWs. Such unique feature of
chiral DWs can be utilized to move and position DWs with lower current, key to
the development of storage class memory devices.",1506.03490v2
2015-08-03,Stable oscillation in spin torque oscillator excited by a small in-plane magnetic field,"Theoretical conditions to excite self-oscillation in a spin torque oscillator
consisting of a perpendicularly magnetized free layer and an in-plane
magnetized pinned layer are investigated by analytically solving the
Landau-Lifshitz-Gilbert equation. The analytical relation between the current
and oscillation frequency is derived. It is found that a large amplitude
oscillation can be excited by applying a small field pointing to the direction
anti-parallel to the magnetization of the pinned layer. The validity of the
analytical results is confirmed by comparing with numerical simulation, showing
good agreement especially in a low current region.",1508.00601v1
2015-09-24,Spin-orbit torque driven chiral magnetization reversal in ultrathin nanostructures,"We show that the spin-orbit torque induced magnetization switching in
nanomagnets presenting Dzyaloshinskii-Moriya (DMI) interaction is governed by a
chiral domain nucleation at the edges. The nucleation is induced by the DMI and
the applied in-plane magnetic field followed by domain wall propagation. Our
micromagnetic simulations show that the DC switching current can be defined as
the edge nucleation current, which decreases strongly with increasing amplitude
of the DMI. This description allows us to build a simple analytical model to
quantitatively predict the switching current. We find that domain nucleation
occurs down to a lateral size of 15 nm, defined by the length-scale of the DMI,
beyond which the reversal mechanism approaches a macrospin behavior. The
switching is deterministic and bipolar.",1509.07341v1
2016-04-15,Direct observation of magnetization dynamics generated by nano-contact spin-torque vortex oscillators,"Time-resolved scanning Kerr microscopy has been used to directly image the
magnetization dynamics of nano-contact (NC) spin-torque vortex oscillators
(STVOs) when phase-locked to an injected microwave (RF) current. The Kerr
images reveal free layer magnetization dynamics that extend outside the NC
footprint, where they cannot be detected electrically, but which are crucial to
phase-lock STVOs that share common magnetic layers. For a single NC, dynamics
were observed not only when the STVO frequency was fully locked to that of the
RF current, but also for a partially locked state characterized by periodic
changes in the core trajectory at the RF frequency. For a pair of NCs, images
reveal the spatial character of dynamics that electrical measurements show to
have enhanced amplitude and reduced linewidth. Insight gained from these images
may improve understanding of the conditions required for mutual phase-locking
of multiple STVOs, and hence enhanced microwave power emission.",1604.04455v1
2016-04-19,Electric field control of deterministic current-induced magnetization switching in a hybrid ferromagnetic/ferroelectric structure,"All-electrical and programmable manipulations of ferromagnetic bits are
highly pursued for the aim of high integration and low energy consumption in
modern information technology. Methods based on the spin-orbit torque switching
in heavy metal/ferromagnet structures have been proposed with magnetic field,
and recently are heading toward deterministic switching without external
magnetic field. Here we demonstrate that an in-plane effective magnetic field
can be induced by an electric field without breaking the symmetry of the
structure of the thin film, and realize the deterministic magnetization
switching in a hybrid ferromagnetic/ferroelectric structure with Pt/Co/Ni/Co/Pt
layers on PMN-PT substrate. The effective magnetic field can be reversed by
changing the direction of the applied electric field on the PMN-PT substrate,
which fully replaces the controllability function of the external magnetic
field. The electric field is found to generate an additional spin-orbit torque
on the CoNiCo magnets, which is confirmed by macrospin calculations.",1604.05561v1
2016-10-22,Spin orbit torques and Dzyaloshinskii-Moriya interaction in dual-interfaced Co-Ni multilayers,"We study the spin orbit torque (SOT) and Dzyaloshinskii-Moriya interaction
(DMI) in the dual-interfaced Co-Ni perpendicular multilayers. Through the
combination of top and bottom layer materials (Pt, Ta, MgO and Cu), SOT and DMI
are efficiently manipulated due to an enhancement or cancellation of the top
and bottom contributions. However, SOT is found to originate mostly from the
bulk of a heavy metal (HM), while DMI is more of interfacial origin. In
addition, we find that the direction of the domain wall (DW) motion can be
either along or against the electron flow depending on the DW tilting angle
when there is a large DMI. Such an abnormal DW motion induces a large assist
field required for hysteretic magnetization reversal. Our results provide
insight into the role of DMI in SOT driven magnetization switching, and
demonstrate the feasibility of achieving desirable SOT and DMI for spintronic
devices.",1610.07022v1
2017-07-15,Stochastic Spin-Orbit Torque Devices as Elements for Bayesian Inference,"Probabilistic inference from real-time input data is becoming increasingly
popular and may be one of the potential pathways at enabling cognitive
intelligence. As a matter of fact, preliminary research has revealed that
stochastic functionalities also underlie the spiking behavior of neurons in
cortical microcircuits of the human brain. In tune with such observations,
neuromorphic and other unconventional computing platforms have recently started
adopting the usage of computational units that generate outputs
probabilistically, depending on the magnitude of the input stimulus. In this
work, we experimentally demonstrate a spintronic device that offers a direct
mapping to the functionality of such a controllable stochastic switching
element. We show that the probabilistic switching of Ta/CoFeB/MgO
heterostructures in presence of spin-orbit torque and thermal noise can be
harnessed to enable probabilistic inference in a plethora of unconventional
computing scenarios. This work can potentially pave the way for hardware that
directly mimics the computational units of Bayesian inference.",1707.04687v2
2017-08-07,"Chiral damping, chiral gyromagnetism and current-induced torques in textured one-dimensional Rashba ferromagnets","We investigate Gilbert damping, spectroscopic gyromagnetic ratio and
current-induced torques in the one-dimensional Rashba model with an additional
noncollinear magnetic exchange field. We find that the Gilbert damping differs
between left-handed and right-handed N\'eel-type magnetic domain walls due to
the combination of spatial inversion asymmetry and spin-orbit interaction
(SOI), consistent with recent experimental observations of chiral damping.
Additionally, we find that also the spectroscopic $g$ factor differs between
left-handed and right-handed N\'eel-type domain walls, which we call chiral
gyromagnetism. We also investigate the gyromagnetic ratio in the Rashba model
with collinear magnetization, where we find that scattering corrections to the
$g$ factor vanish for zero SOI, become important for finite spin-orbit
coupling, and tend to stabilize the gyromagnetic ratio close to its
nonrelativistic value.",1708.02008v2
2017-11-07,Selective control of vortex polarities by microwave field in two robustly synchronized spin-torque nano-oscillators,"Manipulating operation states of coupled spin-torque nano-oscillators
(STNOs), including their synchronization, is essential for applications such as
complex oscillator networks. In this work we experimentally demonstrate
selective control of two coupled vortex STNOs through microwave-assisted
switching of their vortex core polarities. First, the two oscillators are shown
to synchronize due to dipolar interaction in a broad frequency range tuned by
external biasing field. Coherent output is demonstrated along with strong
linewidth reduction. Then, we show individual vortex polarity control of each
oscillator, which leads to synchronization/desynchronization due to accompanied
frequency shift. Our methods can be easily extended to multiple-element coupled
oscillator networks.",1711.02285v1
2017-12-11,Spin-orbit torque magnetometry by wide-field magneto-optical Kerr effect,"Magneto-optical Kerr effect (MOKE) is an efficient approach to probe surface
magnetization in thin film samples. Here we present a wide-field MOKE technique
that adopts a K$\""o$hler illumination scheme to characterize the
current-induced damping-like spin-orbit torque (DL-SOT) in micronsized and
unpatterned magnetic heterostructures with perpendicular magnetic anisotropy.
Through a current-induced hysteresis loop shift analysis, we quantify the
DL-SOT efficiency of a Ta-based heterostructure with bar-shaped geometry,
Hall-cross geometry, and unpatterned geometry to be $|\xi_{DL}|\approx$ 0.08.
The proposed wide-field MOKE approach therefore provides an instant and direct
characterization of DL-SOT, without the need of any further interpretation on
electrical signals.",1712.03810v2
2018-06-13,Staggered field driven domain walls motion in antiferromagnetic heterojunctions,"In this work, we study the antiferromagnetic (AFM) spin dynamics in
heterostructures which consist of two kinds of AFM layers. Our micromagnetic
simulations demonstrate that the AFM domain-wall (DW) can be driven by the
other one (driven by field-like Neel spin-orbit torque, Phys. Rev. Lett. 117,
017202 (2016)) through the interface couplings. Furthermore, the two DWs detach
from each other when the torque increases above a critical value. The critical
field and the highest possible velocity of the DW depending on several factors
are revealed and discussed. Bases on the calculated results, we propose a
method to modulate efficiently the multi DWs in antiferromagnet, which
definitely provides useful information for future AFM spintronics device
design.",1806.04905v1
2018-06-18,Magnetic angular position sensor enabled by spin-orbit torque,"We propose a simple scheme for magnetic angular position sensor based on
current-induced spin-orbit torque effect. A full range detection of 360o is
realized with a pair of Hall crosses made of heavy metal/ferromagnet
heterostructures. The current axes of the two Hall crosses are aligned
orthogonal to each other such that when both devices are subject to a
rotational in-plane magnetic field, the differential Hall voltage due to
current pulses of opposite polarity exhibits a sine and cosine angular
dependence on the field direction, respectively. The field rotational angle is
then calculated from the sine and cosine output signals via the arctan2
function. A linear correspondence between the calculated and actual field angle
is obtained in the field range of 500-2000 Oe, with an average angle error of
0.38-0.65o.",1806.06482v1
2018-10-05,Zero-field dynamics stabilized by in-plane shape anisotropy in MgO-based spin-torque oscillators,"Here we demonstrate numerically that shape anisotropy in MgO-based
spin-torque nano-oscillators consisting of an out-of-plane magnetized free
layer and an in-plane polarizer is necessary to stabilize out-of-plane
magnetization precession without the need of external magnetic fields. As the
in-plane anisotropy is increased, a gradual tilting of the magnetization
towards the in-plane easy direction is introduced, favouring zero-field
dynamics over static in-plane states. Above a critical value, zero-field
dynamics are no longer observed. The optimum ratio of in-plane shape to
out-of-plane uniaxial anisotropy, for which large angle out-of-plane zero-field
dynamics occur within the widest current range, is reported.",1811.00106v1
2018-11-04,Coexistence of exchange bias training effect and spin-orbit torque in IrMn-layer/ferromagnetic-ribbon heterostructures via magnetoimpedance effect,"We investigate a possible correlation between spin orbit torque (SOT) and
exchange-bias (EB) in IrMn-layer/ferromagnetic-ribbon heterostructure by
performing magnetoimpedance (MI) measurements. To uncover this correlation, we
benefit from EB training effect probed by MI effect at room temperature. A
damping-like SOT driven by ac current through the antiferromagnetic IrMn
applies to the ferromagnetic ribbon layer, determined by MI magnetic field and
frequency sweeps. Importantly, magnitude of the SOT is observed to remain
intact against EB training and decrease of EB through alternative magnetic
field sweep cycles. Our results pave the way to better elucidate the EB effect,
EB training and the SOT, useful for future spintronic elements.",1811.01352v4
2017-05-04,Field-free deterministic ultra fast creation of skyrmions by spin orbit torques,"Magnetic skyrmions are currently the most promising option to realize
current-driven magnetic shift registers. A variety of concepts to create
skyrmions were proposed and demonstrated. However, none of the reported
experiments show controlled creation of single skyrmions using integrated
designs. Here, we demonstrate that skyrmions can be generated deterministically
on subnanosecond timescales in magnetic racetracks at artificial or natural
defects using spin orbit torque (SOT) pulses. The mechanism is largely similar
to SOT-induced switching of uniformly magnetized elements, but due to the
effect of the Dzyaloshinskii-Moriya interaction (DMI), external fields are not
required. Our observations provide a simple and reliable means for skyrmion
writing that can be readily integrated into racetrack devices.",1705.01927v1
2017-05-20,The Spin-Orbit Torque from a Magnetic Heterostructure with High-Entropy Alloy,"High-entropy alloy (HEA) is a family of metallic materials with nearly equal
partitions of five or more metals, which might possess mechanical and transport
properties that are different from conventional binary or tertiary alloys. In
this work, we demonstrate current-induced spin-orbit torque (SOT) magnetization
switching in a Ta-Nb-Hf-Zr-Ti HEA-based magnetic heterostructure with
perpendicular magnetic anisotropy (PMA). The maximum damping-like SOT
efficiency from this particular HEA-based magnetic heterostructure is further
determined to be $|\zeta^{\operatorname{HEA}}_{DL}|\approx0.033$ by hysteresis
loop shift measurements, while that for the Ta control sample is
$|\zeta^{\operatorname{Ta}}_{DL}|\approx0.04$. Our results indicate that
HEA-based magnetic heterostructures can serve as a new group of potential
candidates for SOT device applications.",1705.07248v1
2017-05-29,"Contributions of Co and Fe orbitals to Perpendicular Magnetic Anisotropy of MgO/CoFeB Bilayers with Spin-Orbit-Torque-Related (Ta, W, IrMn, and Ti) Underlayers","We study the perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO
bilayers in contact with W, Ta, IrMn and Ti which has been suggested as the
spin-orbit-torque-related underlayers. The saturation magnetization of the
CoFeB depends on the underlayer materials due to formation of a dead-layer,
affecting PMA strength of each film. The x-ray magnetic circular dichroism
measurement reveals that the interfacial intermixing suppresses only the
perpendicular orbital moment of Fe, while the intermixing simultaneously
suppresses both the perpendicular and in-plane orbital moments of Co.",1705.10064v1
2012-09-24,Impact of current paths on measurement of tunneling magnetoresistance and spin torque critical current densities in GaMnAs-based magnetic tunnel junctions,"GaMnAs-based magnetic tunnel junction (MTJ) devices are characterized by
in-plane and perpendicular-toplane magnetotransport at low temperatures.
Perpendicular-to-plane transport reveals the typical tunneling magnetotransport
(TMR) signal. Interestingly, a similar TMR signature is observed in the
in-plane transport signal. Here, low-ohmic shunting of the MTJ by the top
contact results in significant perpendicular-to-plane current paths. This
effect allows the determination of TMR ratios of MTJs based on a simplified
in-plane measurement. However, the same effect can lead to an inaccurate
determination of resistance area products and spin torque critical current
densities from perpendicular-to-plane magnetotransport experiments on MTJ
pillar structures.",1209.5226v1
2017-12-08,Strain-mediated spin-orbit torque switching for magnetic memory,"Spin-orbit torque (SOT) represents an energy efficient method to control
magnetization in magnetic memory devices. However, deterministically switching
perpendicular memory bits usually requires the application of an additional
bias field for breaking lateral symmetry. Here we present a new approach of
field-free deterministic perpendicular switching using a strain-mediated SOT
switching method. The strain-induced magnetoelastic anisotropy breaks the
lateral symmetry, and the resulting symmetry-breaking is controllable. A finite
element model and a macrospin model are used to numerically simulate the
strain-mediated SOT switching mechanism. The results show that a relatively
small voltage (${\pm}0.5$ V) along with a modest current ($3.5 \times 10^{7}
A/cm^{2}$) can produce a 180{\deg} perpendicular magnetization reversal. The
switching direction (up or down) is dictated by the voltage polarity (positive
or negative) applied to the piezoelectric layer in the magnetoelastic/heavy
metal/piezoelectric heterostructure. The switching speed can be as fast as 10
GHz. More importantly, this control mechanism can be potentially implemented in
a magnetic random-access memory system with small footprint, high endurance and
high tunnel magnetoresistance (TMR) readout ratio.",1802.01647v1
2018-02-07,Breaking the current density threshold in spin-orbit-torque magnetic random access memory,"Spin-orbit-torque magnetic random access memory (SOT-MRAM) is a promising
technology for the next generation of data storage devices. The main bottleneck
of this technology is the high reversal current density threshold. This
outstanding problem of SOT-MRAM is now solved by using a current density of
constant magnitude and varying flow direction that reduces the reversal current
density threshold by a factor of more than the Gilbert damping coefficient. The
Euler-Lagrange equation for the fastest magnetization reversal path and the
optimal current pulse are derived for an arbitrary magnetic cell. The
theoretical limit of minimal reversal current density and current density for a
GHz switching rate of the new reversal strategy for CoFeB/Ta SOT-MRAMs are
respectively of the order of $10^5$ A/cm$^2$ and $10^6$ A/cm$^2$ far below
$10^7$ A/cm$^2$ and $10^8$ A/cm$^2$ in the conventional strategy. Furthermore,
no external magnetic field is needed for a deterministic reversal in the new
strategy.",1802.02415v1
2018-02-09,Néel Spin Orbit Torque driven antiferromagnetic resonance in Mn$_{2}$Au probed by time-domain THz spectroscopy,"We observe the excitation of collective modes in the THz range driven by the
recently discovered N\'{e}el spin-orbit torques (NSOT) in the metallic
antiferromagnet Mn$_{2}$Au. Temperature dependent THz spectroscopy reveals a
strong absorption mode centered near 1 THz, which upon heating from 4 K to 450
K softens and looses intensity. Comparison with the estimated eigenmode
frequencies implies that the observed mode is an in-plane antiferromagnetic
resonance (AFMR) mode. The AFMR absorption strength exceeds those found in
antiferromagnetic insulators, driven by the magnetic field of the THz
radiation, by three orders of magnitude. Based on this and the agreement with
our theory modelling, we infer that the driving mechanism for the observed mode
is the current induced NSOT. This electric manipulation of the Ne\'{e}l order
parameter at high frequencies makes Mn$_{2}$Au a prime candidate for AFM
ultrafast memory applications.",1802.03199v1
2018-12-11,Skyrmions in coupled spin torque nano-oscillator structures,"In the present work, using micromagnetic simulation, we show that the
magnetic coupling effect plays a very important role in the process of creation
of skyrmions in a coupled system of spin-torque nano-oscillators (STNO). First,
we have determined the magnetic ground state in an isolated STNO for different
values of perpendicular uniaxial anisotropy (PUA) and Dzyaloshinskii-Moriya
interaction (DMI). Next, we have applied a perpendicular pulse polarized
current density (J) and found that it is possible to create a metastable N\'eel
skyrmion from a disk whose ground state is a single magnetic domain. From these
results, we obtained a phase diagram of polarized current intensity vs. time of
application of the current pulse, for different values of parameters such as
PUA, DMI, and distance between the STNOs. Our results show that, depending on
the separation distance between the STNOs, the current density required to
create a skyrmion changes due to the magnetic interaction.",1812.04648v1
2018-12-20,Tuning spin torque nano-oscillator nonlinearity using He+ irradiation,"We use He$^+$ irradiation to tune the nonlinearity, $\mathcal{N}$, of
all-perpendicular spin-torque nano-oscillators (STNOs) using the He$^+$
fluence-dependent perpendicular magnetic anisotropy (PMA) of the [Co/Ni] free
layer. Employing fluences from 6 to 20$\times10^{14}$~He$^{+}$/cm$^{2}$, we are
able to tune $\mathcal{N}$ in an in-plane field from strongly positive to
moderately negative. As the STNO microwave signal properties are mainly
governed by $\mathcal{N}$, we can in this way directly control the threshold
current, the current tunability of the frequency, and the STNO linewidth. In
particular, we can dramatically improve the latter by more than two orders of
magnitude. Our results are in good agreement with the theory for nonlinear
auto-oscillators, confirm theoretical predictions of the role of nonlinearity,
and demonstrate a straightforward path towards improving the microwave
properties of STNOs.",1812.08873v1
2018-12-23,Asymmetric velocity and tilt angle of domain walls induced by spin-orbit torques,"We present a micromagnetic study of the current-induced domain wall motion in
perpendicularly magnetized Pt/Co/AlOx racetracks. We show that the domain wall
velocity depends critically on the tilt angle of the wall relative to the
current direction, which is determined by the combined action of the
Dzyaloshinskii-Moriya interaction, damping-like, and field-like spin-orbit
torques. The asymmetry of the domain wall velocity can be controlled by
applying a bias-field perpendicular to the current direction as well as by the
current amplitude. As the faster domain walls are expelled rapidly from the
racetrack boundaries, we argue that the domain wall velocity and tilt measured
experimentally depend on the timescale of the observations. Our findings
reconcile the discrepancy between time-resolved and quasi-static domain wall
measurements in which domain walls with opposite tilts were observed and are
relevant to tune the velocity of domain walls in racetrack structures.",1812.09719v1
2019-02-10,Skyrmion Based Spin-Torque Nano-Oscillator,"Using micromagnetic simulation, we investigate the self-sustained oscillation
of magnetic skyrmion in a ferromagnetic circular nanodot, driven by spin-torque
which is generated from a reference layer of a circular nanopillar device. We
demonstrate, by lowering the value of uniaxial anisotropy constant ($K_u$), the
velocity of the skyrmion can be increased and using this property, gyration
frequency of the skyrmion oscillator can be enhanced. Annihilation of the
skyrmion at higher current densities, limit the gyration frequency of the
oscillator, whereas by modifying the $K_u$ value at the edge of nanodot, we are
able to protect the skyrmion from being annihilated at higher current densities
which in turn, increases the gyration frequency of the skyrmion based
oscillator. By linear fitting the velocity value, obtained from the motion of
the skyrmion in a nanostrip, we also predict the gyration frequency of the
skyrmion in the nanodot which proves the validity of our idea in an intuitive
way. We have also varied the radius of the nanodisk to see its effect on
skyrmion.",1902.03668v2
2019-02-26,Controllable dispersion of domain wall movement in antiferromagnetic thin films at finite temperatures,"The dynamics of a 90$^{\circ }$ domain wall in an antiferromagnetic nanostrip
driven by the current-induced spin-orbital torque are theoretically examined in
the presence of random thermal fluctuations. A soliton-type equation of motion
is developed on the basis of energy balance between the driving forces and
dissipative processes in terms of the domain wall velocity. Comparison with
micromagnetic simulations in the deterministic conditions shows good agreement
in both the transient and steady-state transport. When the effects of random
thermal fluctuations are included via a stochastic treatment, the results
clearly indicate that the dispersion in the domain wall position can be
controlled electrically by tailoring the strength and duration of the driving
current mediating the spin orbital torque in the antiferromagnet. More
specifically, the standard deviation of the probability distribution function
for the domain wall movement can be tuned widely while maintaining the average
position unaffected. Potential applications of this unusual functionality
include the probabilistic computing such as Bayesian learning.",1902.10032v1
2020-04-07,Experimental demonstration of a rapid sweep-tuned spectrum analyzer with temporal resolution based on a spin-torque nano-oscillator,"It is demonstrated experimentally that a spin-torque nano-oscillator (STNO)
rapidly sweep-tuned by a bias voltage can be used for time-resolved spectrum
analysis of frequency-manipulated microwave signals with complicated multi-tone
spectra. The critical reduction in the time of spectrum analysis comes from the
naturally small time constants of a nano-sized STNO (1-100 ns). The
demonstration is performed on a vortex-state STNO generating in a frequency
range around 300 MHz, with frequency down-conversion and matched filtering used
for signal processing. It is shown that this STNO-based spectrum analyzer can
perform analysis of multi-tone signals, and signals with rapidly changing
frequency components with time resolution on a $\mu$s time scale and frequency
resolution limited only by the 'bandwidth' theorem. The proposed concept of
rapid time-resolved spectrum analysis can be implemented with any type of micro
and nano-scale frequency-swept oscillators having low time constants and high
oscillation frequency.",2004.03508v1
2020-08-05,Torque equilibrium spin wave theory of Raman scattering in an anisotropic triangular lattice antiferromagnet with Dzyaloshinskii-Moriya interaction,"We apply torque equilibrium spin wave theory (TESWT) to investigate an
anisotropic XXZ antiferromagnetic model with Dzyaloshinskii-Moriya (DM)
interaction in a triangular lattice. Considering the quasiparticle vacuum as
our reference, we provide an accurate analysis of the non-collinear ground
state of a frustrated triangular lattice magnet using the TESWT formalism. We
elucidate the effects of quantum fluctuations on the ordering wave vector based
on model system parameters. We study the single magnon dispersion, the
two-magnon continuum using the spectral function, and the Raman spectrum of
bimagnon and trimagnon excitations. We present our results for the $HH, VV$,
and the $HV$ polarization Raman geometry dependence of the bimagnon and the
trimagnon excitation spectrum where $H (V)$ represents horizontal (vertical)
polarization. Our calculations show that both the $HH$ and the $HV$
polarization spectrum can be used to determine the degree of anisotropy of our
system. We calculate the Raman spectra of Ba$_3$CoSb$_2$O$_9$ and
Cs$_2$CuCl$_4$.",2008.02287v2
2020-08-07,Magnetoelastic and Magnetostrictive Properties of Co$_2$XAl Heusler Compounds,"We present a comprehensive first principles electronic structure study of the
magnetoelastic and magnetostrictive properties in the Co-based Co$_2$XAl (X =
V, Ti, Cr, Mn, Fe) full Heusler compounds. In addition to the commonly used
total energy approach, we employ torque method to calculate the magnetoelastic
tensor elements. We show that the torque based methods are in general
computationally more efficient, and allow to unveil the atomic- and
orbital-contributions to the magnetoelastic constants in an exact manner, as
opposed to the conventional approaches based on second order perturbation with
respect to the spin-orbit coupling. The magnetostriction constants are in good
agreement with available experimental data. The results reveal that the main
contribution to the magnetostriction constants, $\lambda_{100}$ and
$\lambda_{111}$, arises primarily from the strained-induced modulation of the
$\langle d_{x^2-y^2}|\hat{L}_z|d_{xy}\rangle$ and $\langle
d_{z^2}|\hat{L}_x|d_{yz}\rangle$ spin orbit coupling matrix elements,
respectively, of the Co atoms.",2008.03005v1
2016-12-12,Anomalous thermal conductivity and magnetic torque response in the honeycomb magnet $α$-RuCl$_3$,"We report on the unusual behavior of the in-plane thermal conductivity
($\kappa$) and torque ($\tau$) response in the Kitaev-Heisenberg material
$\alpha$-RuCl$_3$. $\kappa$ shows a striking enhancement with linear growth
beyond H = 7 T, where magnetic order disappears, while $\tau$ for both of the
in-plane symmetry directions shows an anomaly at the same field. The
temperature- and field-dependence of $\kappa$ are far more complex than
conventional phonon and magnon contributions, and require us to invoke the
presence of unconventional spin excitations whose properties are characteristic
of a field-induced spin-liquid phase related to the enigmatic physics of the
Kitaev model in an applied magnetic field",1612.03881v3
2017-06-19,Injection locking at 2f of spin torque oscillators under influence of thermal noise,"Experiments, numerical simulations and an analytic model were developed to
elucidate the effects of noise in the synchronized state of a tunnel junction
based spin torque nano oscillator (STNO). It is demonstrated that in the in
plane magnetized structure, while the frequency is locked, much higher
reference currents are needed to reduce the noise by phase locking. Our
analysis shows that it is possible to control the phase noise by the reference
microwave current (IRF) and that it can be further reduced by increasing the
bias current (IDC) of the oscillator, keeping the reference current in feasible
limits for applications.",1706.05998v1
2017-10-09,Selective multiple domain wall injection using spin-orbit torque,"We demonstrate from both simulation and experiment a simple scheme for
selective injection of multiple domain walls in a magnetic nanowire. The
structure consists of a side-contact misaligned Hall bar made of
ferromagnet/heavy metal bilayers. The combination of current-induced spin-orbit
torque and an external magnetic field allows for the formation of localized
domains with specific magnetization direction and length, thereby creating
domain walls in predetermined locations. With the side contacts at two sides
misaligned for a distance that is comparable to the contact width, it is
possible to create densely packed domains by simply applying current between
different pairs of side contacts. Simulation results show that the proposed
scheme is scalable to a large number of domains with its dimension limited only
by the domain wall width.",1710.02930v1
2018-04-22,Spin torque oscillator for microwave assisted magnetization reversal,"A theoretical study is given for the self-oscillation excited in a spin
torque oscillator (STO) consisting of an in-plane magnetized free layer and a
perpendicularly magnetized pinned layer in the presence of a perpendicular
magnetic field. This type of STO is a potential candidate for a microwave
source of microwave assisted magnetization reversal (MAMR). It is, however,
found that the self-oscillation applicable to MAMR disappears when the
perpendicular field is larger than a critical value, which is much smaller than
a demagnetization field. This result provides a condition that the reversal
field of a magnetic recording bit by MAMR in nanopillar structure should be
smaller than the critical value. The analytical formulas of currents
determining the critical field are obtained, which indicate that a material
with a small damping is not preferable to acheive a wide range of the
self-oscillation applicable to MAMR, although such a material is preferable
from the view point of the reduction of the power consumption.",1804.08076v1
2019-03-24,"Synchronized, periodic, and chaotic dynamics in spin torque oscillator with two free layers","A phase diagram of the magnetization dynamics is studied by numerically
solving the Landau-Lifshitz-Gilbert (LLG) equation in a spin torque oscillator
consisting of asymmetric two free layers that are magnetized in in-plane
direction. We calculated the dynamics for a wide range of current density for
both low and high field cases, and found many dynamical phases such as
synchronization, auto-oscillation with different frequencies, and chaotic
dynamics. The observation of the synchronization indicates the presence of a
dynamical phase which has not been found experimentally by using the
conventional electrical detection method. The auto-oscillations with different
frequencies lead to an oscillation of magnetoresistance with a high frequency,
which can be measured experimentally. The chaotic and/or periodic behavior of
magnetoresistance in a high current region, on the other hand, leads to a
discontinuous change of the peak frequency in Fourier spectrum.",1903.09938v2
2019-05-07,Analog and digital phase modulation of spin torque nano-oscillators,"Spin torque nano-oscillators (STNO) are nanoscale devices with wide band
frequency tunability. Their multifunctional RF properties are well suited to
define novel schemes for wireless communications that use basic protocols for
data transmission such as amplitude, frequency and phase shift keying (ASK,
FSK, PSK). In contrast to ASK and FSK, implementation of PSK is more
challenging for STNOs because of their relatively high phase noise. Here we
introduce a special PSK technique by combining their modulation and injection
locking functionality. The concept is validated using magnetic tunnel junction
based vortex STNOs for injection locking at 2f and f/2 showing phase shifts up
to 2.1rad and data transmission rates up to 4Mbit/s. Quadrature phase shift
keying and analog phase modulation are also implemented, where the latter is
employed for voice transmission over a distance of 10 meters. This demonstrates
that STNO phase noise and output power meet the requested performances for
operation in existing communication schemes.",1905.02443v1
2019-05-20,Reservoir Computing on Spin-Torque Oscillator Array,"We numerically study reservoir computing on a spin-torque oscillator (STO)
array, describing the magnetization dynamics of the STO array by a nonlinear
oscillator model. The STOs exhibit synchronized oscillation due to coupling by
magnetic dipolar fields. We show that reservoir computing can be performed
using the synchronized oscillation state. The performance can be improved by
increasing the number of STOs. The performance becomes highest at the boundary
between the synchronized and disordered states. Using an STO array, we can
achieve higher performance than that of an echo-state network with similar
number of units. This result indicates that STO arrays are promising for
hardware implementation of reservoir computing.",1905.07937v2
2019-05-30,Predicting New Iron Garnet Thin Films with Perpendicular Magnetic Anisotropy,"Perpendicular magnetic anisotropy (PMA) is a necessary condition for many
spintronic applications like spin-orbit torques switching, logic and memory
devices. An important class of magnetic insulators with low Gilbert damping at
room temperature are iron garnets, which only have a few PMA types such as
terbium and samarium iron garnet. More and stable PMA garnet options are
necessary for researchers to be able to investigate new spintronic phenomena.
In this study, we predict 20 new substrate/magnetic iron garnet film pairs with
stable PMA at room temperature. The effective anisotropy energies of 10
different garnet films that are lattice-matched to 5 different commercially
available garnet substrates have been calculated using shape, magnetoelastic
and magnetocrystalline anisotropy terms. Strain type, tensile or compressive
depending on substrate choice, as well as the sign and the magnitude of the
magnetostriction constants of garnets determine if a garnet film may possess
PMA. We show the conditions in which Samarium, Gadolinium, Terbium, Holmium,
Dysprosium and Thulium garnets may possess PMA on the investigated garnet
substrate types. Guidelines for obtaining garnet films with low damping are
presented. New PMA garnet films with tunable saturation moment and field may
improve spin-orbit torque memory and compensated magnonic thin film devices.",1905.13042v1
2020-03-11,A comparison of two different mechanisms for deterministic spin orbit torque magnetization switching,"In this article we analyze by modeling two possible mechanisms for
magnetization switching using spin orbit torques, which have been reported to
cause field-free deterministic switching in experiments. Here we compare the
field-free magnetization switching due to a tilt of the anisotropy direction
against the use of an antiferromagnetic bias field. Simple results obtained
analytically show that a bias field not only causes the magnetization reversal
but also reduces the corresponding energy barrier. The critical current
required for magnetization switching is analyzed on the basis of a macrospin
model. It is shown that although the field-free deterministic switching caused
by a tilt of the anisotropy is more robust than the bias field in the
development of memory elements, a compromise between requirements has to be
adopted when selecting the parameters for specific applications.",2003.05468v1
2020-03-26,Chiral Domain Wall Injector Driven by Spin-orbit Torques,"Memory and logic devices that encode information in magnetic domains rely on
the controlled injection of domain walls to reach their full potential. In this
work, we exploit the chiral coupling induced by the Dzyaloshinskii-Moriya
interaction between in-plane and out-of-plane magnetized regions of a
Pt/Co/AlO\textsubscript{x} trilayer in combination with current-driven
spin-orbit torques to control the injection of domain walls into magnetic
conduits. We demonstrate that the current-induced domain nucleation is strongly
inhibited for magnetic configurations stabilized by the chiral coupling and
promoted for those that have the opposite chirality. These configurations allow
for efficient domain wall injection using current densities of the order of
$4\times$\SI{e11}{A m^{-2}}, which are lower than those used in other injection
schemes. Furthermore, by setting the orientation of the in-plane magnetization
using an external field, we demonstrate the use of a chiral domain wall
injector to create a controlled sequence of alternating domains in a racetrack
structure driven by a steady stream of unipolar current pulses.",2003.11805v1
2020-09-07,Dependency of high-speed write properties on external magnetic field in spin-orbit torque in-plane magnetoresistance devices,"Spin-orbit torque (SOT) magnetoresistance (MR) devices have attracted
attention for use in next-generation MR devices. The SOT devices are known to
exhibit different write properties based on the relative angle between the
magnetization direction of the free layer and the write-current direction.
However, few studies that compare the write properties of each type have been
reported. In this study, we measured the external perpendicular-magnetic field
dependence of the threshold write current density and the write current
switching probability using two types of in-plane magnetization SOT-MR devices.",2009.02887v2
2020-09-14,Voltage-driven Magnetization Switching via Dirac Magnetic Anisotropy and Spin--orbit Torque in Topological-insulator-based Magnetic Heterostructures,"Electric-field control of magnetization dynamics is fundamentally and
technologically important for future spintronic devices. Here, based on
electric-field control of both magnetic anisotropy and spin--orbit torque, two
distinct methods are presented for switching the magnetization in topological
insulator (TI)/magnetic-TI hybrid systems. The magnetic anisotropy energy in
magnetic TIs is formulated analytically as a function of the Fermi energy, and
it is confirmed that the out-of-plane magnetization is always favored for the
partially occupied surface band. Also proposed is a transistor-like device with
the functionality of a nonvolatile magnetic memory that uses voltage-driven
writing and the (quantum) anomalous Hall effect for readout. For the
magnetization reversal, by using parameters of Cr-doped
Bi_{1-x}Sb_{x})_{2}Te_{3}, the estimated source-drain current density and gate
voltage are of the orders of $10^4$--$10^5$~A/cm$^2$ and 0.1~V, respectively,
below 20~K and the writing requires no external magnetic field. Also discussed
is the possibility of magnetization switching by the proposed method in
TI/ferromagnetic-insulator bilayers with the magnetic proximity effect.",2009.06187v1
2020-09-20,Theoretical Conditions for Field-free Magnetization Switching Induced by Spin-orbit Torque and Dzyaloshinskii-Moriya Interaction,"Recently, it was demonstrated that field-free switching could be achieved by
combining spin-orbit torque (SOT) and Dzyaloshinskii-Moriya interaction (DMI).
However, this mechanism only occurs under certain conditions which have not
been well discussed. In this letter, it is found that the ratio of domain wall
width to diameter of nanodots could be utilized as a criteria for judging this
mechanism. Influences of different magnetic parameters are studied, including
exchange constant, DMI magnitude and field-like toque, etc. Besides, we reveal
the importance of the shrinkage of magnetic domain wall surface energy for
metastable states. Our work provides guidelines to the experiments on the
DMI-induced field-free magnetization switching, and also offers a new way for
the design of SOT-based memory or logic circuits.",2009.09446v1
2020-11-08,Continuous nucleation switching driven by spin-orbit torques,"Continuous switching driven by spin-orbit torque (SOT) is preferred to
realize neuromorphic computing in a spintronic manner. Here we have applied
focused ion beam (FIB) to selectively illuminate patterned regions in a
Pt/Co/MgO strip with perpendicular magnetic anisotropy (PMA), soften the
illuminated areas and realize the continuous switching by a SOT-driven
nucleation process. It is found that a large in-plane field is a benefit to
reduce the nucleation barrier, increase the number of nucleated domains and
intermediate states during the switching progress, and finally flatten the
switching curve. We proposed a phenomenological model for descripting the
current dependence of magnetization and the dependence of the number of
nucleation domains on the applied current and magnetic field. This study can
thus promote the birth of SOT devices, which are promising in neuromorphic
computing architectures.",2011.03956v1
2020-11-17,Orbital Rashba effect in surface oxidized Cu film,"Recent experimental observation of unexpectedly large current-induced
spin-orbit torque in surface oxidized Cu on top of a ferromagnet suggested a
possible role of the orbital Rashba effect (ORE). With this motivation, we
investigate the ORE from first principles by considering an oxygen monolayer on
top of a Cu(111) film. We show that surface oxidization of Cu film leads to
gigantic enhancement of the ORE for states near the Fermi surface. The
resulting chiral orbital texture in the momentum space is exceptionally strong,
reaching $\sim 0.5\hbar$ in magnitude. We find that resonant hybridization
between O $p$-states and Cu $d$-states is responsible for the emergence of the
ORE. We demonstrate that application of an external electric field generates
huge orbital Hall current, which is an order of magnitude larger than the spin
Hall current found in heavy metals. This implies that ""orbital torque""
mechanism may be significant in surface oxidized Cu/ferromagnet structures. It
also encourages experimental verification of the orbital texture in surface
oxidized Cu through optical measurements such as angle-resolved photoemission
spectroscopy.",2011.08601v1
2021-04-27,Mechanism of parametric pumping of magnetization precession in a nanomagnet. Parametric mechanism of current-induced magnetization reversal,"A mechanism of current-induced magnetization reversal based on the parametric
resonance is described. The source of the magnetization reversal is a
current-induced magnetic field, which is applied perpendicularly to the easy
axis of magnetic anisotropy of a ferromagnetic nanomagnet. The current-induced
magnetic field was measured in a FeCoB nanomagnet to be 60 Gauss at a current
density of 65 mA/um2. Two mechanisms of the magnetization reversal are
described and calculated. The first mechanism is the reversal by a RF
electrical current, which modulated at a frequency close to the precession
frequency of the nanomagnet. The second mechanism is the reversal by a DC
electrical current, in which the magneto-resistance and the current dependency
of the induced magnetic field create a positive feedback loop, which amplifies
a random tiny thermal fluctuation into a large magnetization precession leading
to the magnetization reversal. The combination of the proposed mechanism with
conventional magnetization-reversal mechanisms such as the Spin Torque and the
Spin-Orbit Torque can improve the performance of a Magnetic Random Access
Memory.",2104.13008v1
2021-04-29,Surpassing the Energy Resolution Limit with ferromagnetic torque sensors,"We discuss the fundamental noise limitations of a ferromagnetic torque sensor
based on a levitated magnet in the tipping regime. We evaluate the optimal
magnetic field resolution taking into account the thermomechanical noise and
the mechanical detection noise at the standard quantum limit (SQL). We find
that the Energy Resolution Limit (ERL), pointed out in recent literature as a
relevant benchmark for most classes of magnetometers, can be surpassed by many
orders of magnitude. Moreover, similarly to the case of a ferromagnetic
gyroscope, it is also possible to surpass the standard quantum limit for
magnetometry with independent spins, arising from spin-projection noise. Our
finding indicates that magnetomechanical systems optimized for magnetometry can
achieve a magnetic field resolution per unit volume several orders of magnitude
better than any conventional magnetometer. We discuss possible implications,
focusing on fundamental physics problems such as the search for exotic
interactions beyond the standard model.",2104.14425v2
2021-08-09,Mutual Synchronization of Spin-Torque Oscillators within a Ring Array,"An array of spin torque nano-oscillators (STNOs), coupled by dipolar
interaction and arranged on a ring, has been studied numerically and
analytically. The phase patterns and locking ranges are extracted as a function
of the number $N$, their separation, and the current density mismatch between
selected subgroups of STNOs. If $N\geq 6$ for identical current densities
through all STNOs, two degenerated modes are identified an in-phase mode (all
STNOs have the same phase) and an out-of-phase mode (the phase makes a 2$\pi$
turn along the ring). When inducing a current density mismatch between two
subgroups, additional phase shifts occur. The locking range (maximum current
density mismatch) of the in-phase mode is larger than the one for the
out-of-phase mode and depends on the number $N$ of STNOs on the ring as well as
on the separation. These results can be used for the development of magnetic
devices that are based on STNO arrays.",2108.04046v1
2021-08-20,Probing anisotropy in epitaxial Fe/Pt bilayers by spin-orbit torque ferromagnetic resonance,"We report the generation and detection of spin-orbit torque ferromagnetic
resonance (STFMR) in micropatterned epitaxial Fe/Pt bilayers grown by molecular
beam epitaxy. The magnetic field dependent measurements at an in-plane magnetic
field angle of 45 degrees with respect to the microwave-current direction
reveal the presence of two distinct voltage peaks indicative of a strong
magnetic anisotropy. We show that STFMR can be employed to probe the underlying
magnetic properties including the anisotropies in the Fe layer. We compare our
STFMR results with broadband ferromagnetic resonance spectroscopy of the
unpatterned bilayer thin films. The experimental STFMR measurements are
interpreted using an analytical formalism and further confirmed using
micromagnetic modeling, which shed light on the field-dependent magnetization
alignment in the microstructures responsible for the STFMR rectification. Our
results demonstrate a simple and efficient method for determining magnetic
anisotropies in microstructures by means of rf spectroscopy.",2108.09132v1
2021-10-06,Ultra-fast GHz-range swept-tuned spectrum analyzer with 20 ns temporal resolution based on a spin-torque nano-oscillator with a uniformly magnetized 'free' layer,"The advantage of an ultra-fast frequency-tunability of spin-torque
nano-oscillators (STNOs) that have large (> 100MHz) relaxation frequency of
amplitude fluctuations is exploited to realize ultra-fast wide-band
time-resolved spectral analysis at nanosecond time scale with the frequency
resolution limited only by the 'bandwidth' theorem. The demonstration is
performed with an STNO generating in the 9 GHz frequency range, and comprised
of a perpendicular polarizer and a perpendicularly and uniformly magnetized
'free' layer. It is shown that such a uniform-state STNO-based spectrum
analyzer can efficiently perform spectral analysis of frequency-agile signals
with rapidly varying frequency components.",2110.02618v1
2021-10-25,Stabilization of phase noise in spin torque nano oscillators by a phase locked loop,"The main limitation in order to exploit spin torque nano-oscillators (STNOs)
in various potential applications is their large phase noise. In this work, we
demonstrate its efficient reduction by a highly reconfigurable, compact,
specifically on-chip designed PLL based on custom integrated circuits. First,
we thoroughly study the parameter space of the PLL+STNO system experimentally.
Second, we present a theory which describes the locking of a STNO to an
external signal in a general sense. In our developed theory, we do not restrict
ourselves to the case of a perfect phase locking but also consider phase slips
and the corresponding low offset frequency $1/f^2$ noise, so far the main
drawback in such systems. Combining experiment and theory allows us to reveal
complex parameter dependences of the system's phase noise. The results provide
an important step for the optimization of noise properties and thus leverage
the exploitation of STNOs in prospective real applications.",2110.13073v1
2008-06-25,Temperature dependence of nonlinear auto-oscillator linewidths: Application to spin-torque nano-oscillators,"The temperature dependence of the generation linewidth for an auto-oscillator
with a nonlinear frequency shift is calculated. It is shown that the frequency
nonlinearity creates a finite correlation time, tau, for the phase
fluctuations. In the low-temperature limit in which the spectral linewidth is
smaller than 1/tau, the line shape is approximately Lorentzian and the
linewidth is linear in temperature. In the opposite high-temperature limit in
which the linewidth is larger than 1/tau, the nonlinearity leads to an apparent
""inhomogeneous broadening"" of the line, which becomes Gaussian in shape and has
a square-root dependence on temperature. The results are illustrated for the
spin-torque nano-oscillator.",0806.4116v1
2016-11-22,Probing phase coupling between two spin-torque nano-oscillators with external source,"Phase coupling between auto-oscillators is central for achieving coherent
responses such as synchronization. Here we present an experimental approach to
probe it in the case of two dipolarly coupled spin-torque vortex
nano-oscillators using an external microwave field. By phase-locking one
oscillator to the microwave field, we observe frequency pulling on the second
oscillator. From coupled Thiele equations we show analytically that this
frequency pulling results from concerted actions of dipolar and microwave
couplings. The analysis allows us to determine the amplitude of dipolar
coupling and the phase lag of each oscillator, yielding important information
for the implementation of large oscillator networks.",1611.07321v2
2017-04-12,Low Power Microwave Signal Detection With a Spin-Torque Nano-Oscillator in the Active Self-Oscillating Regime,"A spin-torque nano-oscillator (STNO) driven by a ramped bias current can
perform spectrum analysis quickly over a wide frequency bandwidth. The STNO
spectrum analyzer operates by injection locking to external microwave signals
and produces an output DC voltage $V_{\rm dc}$ that temporally encodes the
input spectrum. We found, via numerical analysis with a macrospin
approximation, that an STNO is able to scan a $10~\rm GHz$ bandwidth in less
than $100~\rm ns$ (scanning rate $R$ exceeds $100~\rm MHz/ns$). In contrast to
conventional quadratic microwave detectors, the output voltage of the STNO
analyzer is proportional to the amplitude of the input microwave signal $I_{\rm
rf}$ with sensitivity $S = dV_{\rm dc}/dI_{\rm rf} \approx 750~\rm mV/mA$. The
minimum detectable signal of the analyzer depends on the scanning rate $R$ and,
at low $R \approx 1~\rm MHz/ns$, is about $1~\rm pW$.",1704.03585v1
2019-01-10,Ultrafast magnetization dynamics in uniaxial ferrimagnets with compensation point. GdFeCo,"We derive an effective Lagrangian in the quasi-antiferromagnetic
approximation that allows to describe the magnetization dynamics for uniaxial
f-d (rare-earth - transition metal) ferrimagnet near the magnetization
compensation point in the presence of external magnetic field. We perform
calculations for the parameters of GdFeCo, a metallic ferrimagnet with
compensation point that is one of the most promising materials in ultrafast
magnetism. Using the developed approach, we find the torque that acts on the
magnetization due to ultrafast demagnetization pulse that can be caused either
by ultrashort laser or electrical current pulse. We show that the torque is
non-zero only in the non-collinear magnetic phase that can be acquired by
applying external magnetic field to the material. The coherent response of
magnetization dynamics amplitude and its timescale exhibits critical behavior
near certain values of the magnetic field corresponding to a spin-flop like
phase transition. Understanding the underlying mechanisms for these effects
opens the way to efficient control of the amplitude and the timescales of the
spin dynamics, which is one of the central problems in the field of ultrafast
magnetism.",1901.03072v2
2019-01-14,Inducing out-of-plane precession of magnetization for microwave assisted magnetic recording using an oscillating polarizer in spin torque oscillator,"We investigated the dynamics of a novel design of spin torque oscillator
(STO) for microwave assisted magnetic recording. Using Ni$_{80}$Fe$_{20}$
(NiFe) as the polarizer and Fe$_{67}$Co$_{33}$ (FeCo) as the field generating
layer, we experimentally observed the magnetization reversal of NiFe, followed
by multiple signals in the power spectra as the bias voltage increased. The
signals reflected the out-of-plane precession (OPP) mode oscillation of both
FeCo and NiFe, as well as the magnetoresistance effect of the STO device, which
had the frequency equal to the difference between the oscillation frequency of
NiFe and FeCo. Such dynamics were reproduced by micromagnetic simulation. In
addition to the merit of realizing the OPP mode oscillation with a simple and
thin structure suitable for a narrow gap recording head, the experimental
results using this design suggested that a large cone angle of $\sim$
70$^{\circ}$ for the OPP mode oscillation of FeCo was achieved, which was
estimated based on the macrospin model.",1901.04208v1
2019-04-04,Dynamics of domain walls motion driven by spin-orbit torque in antiferromagnets,"Ultrafast dynamics of antiferromagnetic materials is an appealing feature for
novel spintronic devices. Several experiments have shown that both, the static
states and the dynamical behavior of the antiferromagnetic order, are strictly
related to stabilization of domains and domain wall (DW) motion. Hence for a
quantitative understanding of statics and dynamics of multidomain states in
antiferromagnetic materials a full micromagnetic framework is necessary. Here,
we use this model to study the antiferromagnetic DW motion driven by the
spin-orbit torque. The main result is the derivation of analytical expressions
for the DW width and velocity that exhibit a very good agreement with the
numerical simulations in a wide range of parameters. We also find that a
mechanism limiting the maximum applicable current in an antiferromagnetic
racetrack memory is the continuous nucleation of the domains from the edge,
which is qualitatively different from what is observed in ferromagnetic
racetracks.",1904.02491v2
2019-04-25,Neuromorphic Computing through Time-Multiplexing with a Spin-Torque Nano-Oscillator,"Fabricating powerful neuromorphic chips the size of a thumb requires
miniaturizing their basic units: synapses and neurons. The challenge for
neurons is to scale them down to submicrometer diameters while maintaining the
properties that allow for reliable information processing: high signal to noise
ratio, endurance, stability, reproducibility. In this work, we show that
compact spin-torque nano-oscillators can naturally implement such neurons, and
quantify their ability to realize an actual cognitive task. In particular, we
show that they can naturally implement reservoir computing with high
performance and detail the recipes for this capability.",1904.11236v1
2019-07-19,Exchange-correlation magnetic fields in spin-density-functional theory,"In spin-density-functional theory for noncollinear magnetic materials, the
Kohn-Sham system features exchange-correlation (xc) scalar potentials and
magnetic fields. The significance of the xc magnetic fields is not very well
explored; in particular, they can give rise to local torques on the
magnetization, which are absent in standard local and semilocal approximations.
We obtain exact benchmark solutions for two electrons on four-site extended
Hubbard lattices over a wide range of interaction strengths, and compare exact
xc potentials and magnetic fields with approximations obtained from
orbital-dependent xc functionals. The xc magnetic fields turn out to play an
increasingly important role as systems becomes more and more correlated and the
electrons begin to localize; the effects of the xc torques, however, remain
relatively minor. The approximate xc functionals perform overall quite well,
but tend to favor symmetry-broken solutions for strong interactions.",1907.08724v1
2019-07-25,Layer-selective detection of magnetization directions from two layers of antiferromagnetically-coupled magnetizations by ferromagnetic resonance using a spin-torque oscillator,"We use micromagnetic simulation to demonstrate layer-selective detection of
magnetization directions from magnetic dots having two recording layers by
using a spin-torque oscillator (STO) as a read device. This method is based on
ferromagnetic resonance (FMR) excitation of recording-layer magnetizations by
the microwave field from the STO. The FMR excitation affects the oscillation of
the STO, which is utilized to sense the magnetization states in a recording
layer. The recording layers are designed to have different FMR frequencies so
that the FMR excitation is selectively induced by tuning the oscillation
frequency of the STO. Since all magnetic layers interact with each other
through dipolar fields, unnecessary interlayer interferences can occur, which
are suppressed by designing magnetic properties of the layers. We move the STO
over the magnetic dots, which models a read head moving over recording media,
and show that changes in the STO oscillation occur on the one-nanosecond
timescale.",1907.10877v2
2019-10-16,Walker breakdown with a twist: Dynamics of multilayer domain walls and skyrmions driven by spin-orbit torque,"Current-induced dynamics of twisted domain walls and skyrmions in
ferromagnetic perpendicularly magnetized multilayers is studied through
three-dimensional micromagnetic simulations and analytical modeling. It is
shown that such systems generally exhibit a Walker breakdown-like phenomenon in
the presence of current-induced damping-like spin-orbit torque. Above a
critical current threshold, corresponding to typical velocities of the order
tens of m/s, domain walls in some layers start to precess with frequencies in
the gigahertz regime, which leads to oscillatory motion and a significant drop
in mobility. This phenomenon originates from complex stray field interactions
and occurs for a wide range of multilayer materials and structures that include
at least three ferromagnetic layers and finite Dzyaloshinskii-Moriya
interaction. An analytical model is developed to describe the precessional
dynamics in multilayers with surface-volume stray field interactions, yielding
qualitative agreement with micromagnetic simulations.",1910.07168v1
2019-10-28,Spin-orbit torque based physical unclonable function,"This paper introduces the concept of spin-orbit-torque-MRAM (SOT-MRAM) based
physical unclonable function (PUF). The secret of the PUF is stored into a
random state of a matrix of perpendicular SOT-MRAMs. Here, we show
experimentally and with micromagnetic simulations that this random state is
driven by the intrinsic nonlinear dynamics of the free layer of the memory
excited by the SOT. In detail, a large enough current drives the magnetization
along an in-plane direction. Once the current is removed, the in-plane magnetic
state becomes unstable evolving towards one of the two perpendicular stable
configurations randomly. In addition, an hybrid CMOS/spintronics model is used
to evaluate the electrical characteristics of a PUF realized with an array of
16x16 SOT-MRAM cells. Beyond robustness against voltage and temperature
variations, hardware authentication based on this PUF scheme has additional
advantages over other PUF technologies such as non-volatility (no power
consumption in standby mode), reconfigurability (the secret can be rewritten),
and scalability. We believe that this work is a step forward the design of
spintronic devices for application in security.",1910.12464v1
2020-05-20,Stabilization of exponential number of discrete remanent states with localized spin-orbit torques,"Using bilayer films of $\beta$-Ta/Ni$_{0.8}$Fe$_{0.2}$, we fabricate
structures consisting of two, three and four crossing ellipses which exhibit
shape-induced bi-axial, tri-axial and quadro-axial magnetic anisotropy in the
crossing area, respectively. Structures consisting of N crossing ellipses can
be stabilized in 2N remanent states by applying (and removing) an external
magnetic field. However, we show that with field-free spin-orbit torques
induced by flowing currents in individual ellipses, the number of remanent
states grows to 2$^\text{N}$. Furthermore, when the current flows between the
edges of different ellipses the number of remanent states jumps to
2$^\text{2N}$, including states which exhibit a $\pi$-N\'{e}el domain wall in
the overlap area. The very large number of accessible remanent magnetic states
that are exhibited by the relatively simple magnetic structures paves the way
for intriguing spintronics applications including memory devices.",2005.10051v1
2020-06-11,Field-free switching of magnetic tunnel junctions driven by spin-orbit torques at sub-ns timescales,"We report time-resolved measurements of magnetization switching by spin-orbit
torques in the absence of an external magnetic field in perpendicularly
magnetized magnetic tunnel junctions (MTJ). Field-free switching is enabled by
the dipolar field of an in-plane magnetized layer integrated above the MTJ
stack, the orientation of which determines the switching polarity. Real-time
single-shot measurements provide direct evidence of magnetization reversal and
switching distributions. Close to the critical switching voltage we observe
stochastic reversal events due to a finite incubation delay preceding the
magnetization reversal. Upon increasing the pulse amplitude to twice the
critical voltage the reversal becomes quasi-deterministic, leading to reliable
bipolar switching at sub-ns timescales in zero external field. We further
investigate the switching probability as a function of dc bias of the MTJ and
external magnetic field, providing insight on the parameters that determine the
critical switching voltage.",2006.06390v1
2020-07-01,Emulation of Astrocyte Induced Neural Phase Synchrony in Spin-Orbit Torque Oscillator Neurons,"Astrocytes play a central role in inducing concerted phase synchronized
neural-wave patterns inside the brain. In this article, we demonstrate that
injected radio-frequency signal in underlying heavy metal layer of spin-orbit
torque oscillator neurons mimic the neuron phase synchronization effect
realized by glial cells. Potential application of such phase coupling effects
is illustrated in the context of a temporal ""binding problem"". We also present
the design of a coupled neuron-synapse-astrocyte network enabled by compact
neuromimetic devices by combining the concepts of local spike-timing dependent
plasticity and astrocyte induced neural phase synchrony.",2007.00776v6
2020-07-03,A four-state magnetic tunnel junction switchable with spin-orbit torques,"We present a magnetic tunnel junction (MTJ) where its two ferromagnetic
layers are in the form of a single ellipse (SE) and two-crossing ellipses
(TCE). The MTJ exhibits four distinct resistance states corresponding to the
four remanent states of the TCE structure. Flowing current in an underlying Ta
layer generates in the adjacent TCE structure spin-orbit torques which induce
field-free switching of the four-state MTJ between all its resistance states.
The demonstrated four-state MTJ is an important step towards fabricating
multi-level MTJs with numerous resistance states which could be important in
various spintronics applications, such as multi-level magnetic random access or
neuromorphic memory.",2007.01611v2
2020-07-24,Producing 3D Friction Loads by Tracking the Motion of the Contact Point on Bodies in Mutual Contact,"We outline a phenomenological model to assess friction at the interface
between two bodies in mutual contact. Although the approach is general, the
application inspiring the approach is the Discrete Element Method. The
kinematics of the friction process is expressed in terms of the relative 3D
motion of the contact point on the two surfaces in mutual contact. The model
produces expressions for three friction loads: slide force, roll torque, and
spin torque. The cornerstone of the methodology is the process of tracking the
evolution/path of the contact point on the surface of the two bodies in mutual
contact. The salient attribute of the model lies with its ability to
simultaneously compute, in a 3D setup, the slide, roll, and spin friction loads
for smooth bodies of arbitrary geometry while accounting for both static and
kinematic friction coefficients.",2007.12713v1
2020-10-11,Beyond the gyrotropic motion: dynamic C-state in vortex spin torque oscillators,"In the present study, we investigate a dynamical mode beyond the gyrotropic
(G) motion of a magnetic vortex core in a confined magnetic disk of a
nano-pillar spin torque nano oscillator. It is characterized by the in-plane
circular precession associated to a C-shaped magnetization distribution. We
show a transition between G and C-state mode which is found to be purely
stochastic in a current-controllable range. Supporting our experimental
findings with micromagnetic simulations, we believe that the results provide
novel opportunities for the dynamic and stochastic control of STOs, which could
be interesting to be implemented for example in neuromorphic networks.",2010.06437v1
2020-10-14,Spin-orbit torque as a method for field-free detection of in-plane magnetization switching,"We proposed and demonstrated a simple method for detection of in-plane
magnetization switching by spin-orbit torque (SOT) in bilayers of non-magnetic
/ magnetic materials. In our method, SOT is used not only for magnetization
switching but also for detection. Our method can detect arbitrary Mx and My
component without an external magnetic field, which is useful for fast
characterization of type-X, type-Y, and type-XY SOT magnetization switching.
Our SOT detection scheme can be utilized not only for fast characterization of
SOT switching in bilayers, but also for electrical detection of in-plane
magnetic domains in race-track memory.",2010.06826v2
2020-12-02,Spin orbit torque controlled stochastic oscillators with synchronization and frequency tunability,"Stochastic oscillators based on emerging nanodevices are attractive because
of their ultra-low power requirement and ability to exhibit stochastic
resonance, a phenomenon where synchronization to weak input signals is enabled
due to ambient noise. In this work, a low barrier nanomagnet based stochastic
oscillator is demonstrated, whose output jumps spontaneously between two states
by harnessing the ambient thermal noise, requiring no additional power.
Utilizing spin orbit torque in a three terminal device configuration, phase
synchronization of these oscillators to weak periodic drives of particular
frequencies is demonstrated. Experiments are performed to show the tunability
of this synchronization frequency by controlling an electrical feedback
parameter. The current required for synchronization is more than 8 times
smaller than that required for deterministic switching of similar nanomagnetic
devices. A model based on Kramers' transition rate in a symmetric double well
potential is adopted and dynamical simulations are performed to explain the
experimental results.",2012.00978v1
2020-12-14,Off-centred force-free neutron star magnetospheres,"Neutron star electromagnetic activity produces pairs that fill their
magnetosphere represented to the zeroth order by the force-free approximation.
Neither dissipation nor acceleration nor radiation from charged particles is
expected from this simplified model. So far, only centred dipole magnetic
fields have been studied in this limit. In this paper, we explore the
consequences of a rotating off-centred dipole on the force-free magnetosphere,
showing the new magnetic field geometry, its spin-down luminosity as well as
the electromagnetic kick and torque felt by the neutron star. Solutions are
obtained by time-dependent numerical simulations of the force-free regime using
our pseudo-spectral code written in spherical coordinates. Our results are also
compared to known analytical expressions found for the off-centred vacuum
dipole by an expansion to lowest order in the parameter $\epsilon = d/R$, where
$d$ is the displacement of the dipole from the stellar centre and $R$ the
neutron star radius. The presence of a force-free plasma enhances the spin-down
luminosity as well as the electromagnetic kick and torque with respect to a
centred force-free dipole. The impact on isolated and binary neutron stars is
revised in light of these new results.",2012.07709v1
2020-12-23,Electric manipulation of domain walls in magnetic Weyl semimetals via the axial anomaly,"We show how the axial (chiral) anomaly induces a spin torque on the
magnetization in magnetic Weyl semimetals. The anomaly produces an imbalance in
left- and right-handed chirality carriers when non-orthogonal electric and
magnetic fields are applied. Such imbalance generates a spin density which
exerts a torque on the magnetization, the strength of which can be controlled
by the intensity of the applied electric field. We show how this results in an
electric control of the chirality of domain walls, as well as in an improvement
of the domain wall dynamics, by delaying the onset of the Walker breakdown. The
measurement of the electric field mediated changes in the domain wall chirality
would constitute a direct proof of the axial anomaly. Additionally, we show how
quantum fluctuations of electronic Fermi arc states bound to the domain wall
naturally induce an effective magnetic anisotropy, allowing for high domain
wall velocities even if the intrinsic anisotropy of the magnetic Weyl semimetal
is small.",2012.12785v2
2021-01-10,A Thermodynamic Core using Voltage-Controlled Spin-Orbit-Torque Magnetic Tunnel Junctions,"We present a magnetic implementation of a thermodynamic computing fabric.
Magnetic devices within computing cores harness thermodynamics through its
voltage-controlled thermal stability; while the evolution of network states is
guided by the spin-orbit-torque effect. We theoretically derive the dynamics of
the cores and show that the computing fabric can successfully compute ground
states of a Boltzmann Machine. Subsequently, we demonstrate the physical
realization of these devices based on a CoFeB-MgO magnetic tunnel junction
structure. The results of this work pave the path towards the realization of
highly efficient, high-performance thermodynamic computing hardware. Finally,
this paper will also give a perspective of computing beyond thermodynamic
computing.",2101.03448v3
2021-01-15,Efficient Spin-Orbit Torque Generation in Semiconducting WTe2 with Hopping Transport,"Spin-orbit torques (SOTs) from transition metal dichalcogenides systems
(TMDs) in conjunction with ferromagnetic materials are recently attractive in
spintronics for their versatile features. However, most of the previously
studied crystalline TMDs are prepared by mechanical exfoliation, which limits
their potentials for industrial applications. Here we show that amorphous WTe2
heterostructures deposited by magnetron sputtering possess a sizable
damping-like SOT efficiency {\xi}_DL^WTe2 ~ 0.20 and low damping constant
{\alpha} = 0.009/pm0.001. Only an extremely low critical switching current
density J_c ~ 7.05\times10^9 A/m^2 is required to achieve SOT-driven
magnetization switching. The SOT efficiency is further proved to depend on the
W and Te relative compositions in the co-sputtered W_100-xTe_x samples, from
which a sign change of {\xi}_DL^WTe2 is observed. Besides, the electronic
transport in amorphous WTe2 is found to be semiconducting and is governed by a
hopping mechanism. With the above advantages and rich tunability, amorphous and
semiconducting WTe2 serves as a unique SOT source for future spintronics
applications.",2101.06047v1
2021-05-11,Effects of delayed feedback on the power spectrum of spin-torque nano-oscillators,"A theoretical study of delayed feedback in a spin-torque nano-oscillator
model is presented. The feedback acts as a modulation of the supercriticality,
which results in changes in the oscillator frequency through a strong
nonlinearity, amplitude modulations, and a rich modulation sideband structure
in the power spectrum at long delays. Modulation sidebands persist at finite
temperatures but some of the complex structure is lost through the finite
coherence time of the oscillations.",2105.04960v1
2021-11-05,Non-linear antidamping spin-orbit torque originating from intra-band transport on the warped surface of a topological insulator,"Motivated by recent experiments observing a large antidamping spin-orbit
torque (SOT) on the surface of a three-dimensional topological insulator, we
investigate the origin of the current-induced SOT beyond linear-response
theory. We find that a strong antidamping SOT arises from intraband transitions
in non-linear response, and does not require interband transitions as is the
case in linear transport mechanisms. The joint effect of warping and an
in-plane magnetization generates a non-linear antidamping SOT which can exceed
the intrinsic one by several orders of magnitude, depending on warping
parameter and the position of Fermi energy, and exhibits a complex dependence
on the azimuthal angle of the magnetization. This nonlinear SOT provides an
alternative explanation of the observed giant SOT in recent experiments.",2111.03397v1
2021-12-06,Associative Memories Using Complex-Valued Hopfield Networks Based on Spin-Torque Oscillator Arrays,"Simulations of complex-valued Hopfield networks based on spin-torque
oscillators can recover phase-encoded images. Sequences of memristor-augmented
inverters provide tunable delay elements that implement complex weights by
phase shifting the oscillatory output of the oscillators. Pseudo-inverse
training suffices to store at least 12 images in a set of 192 oscillators,
representing 16$\times$12 pixel images. The energy required to recover an image
depends on the desired error level. For the oscillators and circuitry
considered here, 5 % root mean square deviations from the ideal image require
approximately 5 $\mu$s and consume roughly 130 nJ. Simulations show that the
network functions well when the resonant frequency of the oscillators can be
tuned to have a fractional spread less than $10^{-3}$, depending on the
strength of the feedback.",2112.03358v2
2021-12-24,Third Harmonic Characterization of Antiferromagnetic Heterostructures,"Electrical switching of antiferromagnets is an exciting recent development in
spintronics, which promises active antiferromagnetic devices with high speed
and low energy cost. In this emerging field, there is an active debate about
the mechanisms of current-driven switching of antiferromagnets. Harmonic
characterization is a powerful tool to quantify current-induced spin-orbit
torques and spin Seebeck effect in heavy-metal/ferromagnet systems. However,
the harmonic measurement technique has never been verified in antiferromagnetic
heterostructures. Here, we report for the first time harmonic measurements in
Pt/$\alpha$-Fe$_2$O$_3$ bilayers, which are explained by our modeling of
higher-order harmonic voltages. As compared with ferromagnetic heterostructures
where all current-induced effects appear in the second harmonic signals, the
damping-like torque and thermally-induced magnetoelastic effect contributions
in Pt/$\alpha$-Fe$_2$O$_3$ emerge in the third harmonic voltage. Our results
provide a new path to probe the current-induced magnetization dynamics in
antiferromagnets, promoting the application of antiferromagnetic spintronic
devices.",2112.13159v1
2022-01-19,Non-linear dynamics of the non-Hermitian Su-Schrieffer-Heeger model,"We numerically determine the robustness of the lasing edge modes in a
spin-torque oscillator array that realizes the non-Hermitian
Su-Schrieffer-Heeger model. Previous studies found that the linearized dynamics
can enter a topological regime in which the edge mode is driven into
auto-oscillation, while the bulk dynamics are suppressed. Here we investigate
the full non-linear and finite-temperature dynamics, whose understanding is
essential for spin-torque oscillators-based applications. Our analysis shows
that the lasing edge mode dynamics persist in the non-linear domain for a broad
range of parameters and temperatures. We investigate the effects of
perturbations relevant to experimental implementations and discuss which ones
might be detrimental to the stability of the lasing edge mode. Finally, we map
our model onto a photonic model. Our analysis has the potential to shed light
onto the dynamics of a plethora of non-Hermitian systems with non-linearities.",2201.07678v2
2022-03-30,On the free rotation of a polarized spinning-top as a test of the correct radiation reaction torque,"The formula for dipole radiation reaction torque acting on a system of
charges, and the Larmor-like formula for the angular momentum loss by this
system, differ in the time derivative term which is the analogue of the Schott
term in the energy loss problem. In the well-known textbooks this discrepancy
is commonly avoided via neglect of the Schott term, and the Larmor-like formula
is preferred. In the present paper both formulae are used to derive two
different equations of motion of a polarized spinning-top. Both equations are
integrable for the symmetric top and lead to quite different solutions. That
one following from the Larmor-like formula is physically unplausible, in
contrast to another one. This result is accorded with the reinterpretation of
Larmor's formula discussed recently in the pedagogical literature. It is
appeared, besides, that the Schott term is of not only academic significance,
but it may determine the behavior of polarized micro- and nanoparticles in
nature or future experiments.",2204.01519v1
2022-05-11,Time-dependent multistate switching of topological antiferromagnetic order in Mn$_3$Sn,"The manipulation of antiferromagnetic order by means of spin-orbit torques
opens unprecedented opportunities to exploit the dynamics of antiferromagnets
in spintronic devices. In this work, we investigate the current-induced
switching of the magnetic octupole vector in the Weyl antiferromagnet Mn$_3$Sn
as a function of pulse shape, field, temperature, and time. We find that the
switching behavior can be either bistable or tristable depending on the
temporal structure of the current pulses. Time-resolved Hall effect
measurements reveal that Mn$_3$Sn switching proceeds via a two-step
demagnetization-remagnetization process caused by self-heating over a timescale
of tens of ns followed by cooling in the presence of spin-orbit torques. Our
results shed light on the switching dynamics of Mn$_3$Sn and prove the
existence of extrinsic limits on its switching speed.",2205.05309v4
2022-06-21,Stochastic processes for pulsar timing noise: fluctuations in the internal and external torques,"Young pulsars deviate from a perfectly regular spin-down by two
non-deterministic phenomena: impulsive glitches and timing noise. Both
phenomena are interesting per se, and may provide insights into the superfluid
properties of neutron stars, but they also act as a barrier to high-precision
pulsar timing and gravitational wave experiments. We study a minimal stochastic
model to describe the spin-down of a multicomponent neutron star, with
fluctuations in both the internal and external torques. The power spectral
density and timing noise strength of this kind of model can be obtained
analytically, and compared with known results from pulsar timing observational
campaigns. In particular, the presence of flat regions of the power spectral
density can be interpreted as a signature of the presence of internal
superfluid components. We also derive the expected scaling of the timing noise
strength with the pulsar's rotational parameters (or characteristic age).
Therefore, the present framework offers a theoretical guideline to interpret
the observed features of timing noise in both single pulsars and across pulsar
population.",2206.10416v2
2022-06-27,Quantitative and realistic description of the magnetic potential energy of spin-torque vortex oscillators,"Understanding the dynamics of magnetic vortices has emerged as an important
challenge regarding the recent development of spin-torque vortex oscillators.
Either micromagnetic simulations or the analytical Thiele equation approach are
typically used to study such systems theoretically. This work focuses on the
precise description of the restoring forces exerted on the vortex when it is
displaced from equilibrium. In particular, the stiffness parameters related to
a modification of the magnetic potential energy terms are investigated. A
method is proposed to extract exchange, magnetostatic and Zeeman stiffness
expressions from micromagnetic simulations. These expressions are then compared
to state-of-the-art analytical derivations. Furthermore, it is shown that the
stiffness parameters depend not only on the vortex core position but also on
the injected current density. This phenomenon is not predicted by commonly used
analytical ans\""atze. We show that these findings result from a deformation of
the theoretical magnetic texture caused by the current induced Amp\`ere-Oersted
field.",2206.13438v2
2022-08-01,Performing Stateful Logic Using Spin-Orbit Torque (SOT) MRAM,"Stateful logic is a promising processing-in-memory (PIM) paradigm to perform
logic operations using emerging nonvolatile memory cells. While most stateful
logic circuits to date focused on technologies such as resistive RAM, we
propose two approaches to designing stateful logic using spin orbit torque
(SOT) MRAM. The first approach utilizes the separation of read and write paths
in SOT devices to perform logic operations. In contrast to previous work, our
method utilizes a standard memory structure, and each row can be used as input
or output. The second approach uses voltage-gated SOT switching to allow
stateful logic in denser memory arrays. We present array structures to support
the two approaches and evaluate their functionality using SPICE simulations in
the presence of process variation and device mismatch.",2208.00741v1
2022-08-08,Size-dependent mobility of skyrmions beyond pinning in ferrimagnetic GdCo thin films,"Magnetic skyrmions are swirling magnetic textures that can be efficiently
driven with spin-orbit torques with a deflected trajectory. However, pinning
slows skyrmions down and alters their trajectory, which prevents a quantitative
comparison to analytical models. Here, we study skyrmions driven by spin-orbit
torques at room temperature in ferrimagnetic GdCo thin films, an amorphous
material with low pinning. Above a sharp current depinning threshold, we
observe a clearly linear velocity increase with current that extrapolates to
zero and a constant deflection angle, reaching high velocities up to 200 m/s.
The mobility increases and the depinning threshold current decreases with the
skyrmion diameter, which we vary using an external magnetic field. An
analytical model based on the Thiele equation quantitatively reproduces these
findings with a single fitting parameter. This validates the linear flow regime
description and shows, in particular, the important role of skyrmion size in
its dynamics.",2208.04384v2
2022-08-10,Effect of interlayer exchange coupling in spin-torque nano oscillator,"The dynamics of the magnetization of the free layer in a spin-torque nano
oscillator (STNO) influenced by a noncollinear alignment between the
magnetizations of the free and pinned layers due to an interlayer exchange
coupling has been investigated theoretically. The orientations of the
magnetization of the free layer with that of the pinned layer have been
computed through the macrospin model and they are found to match well with
experimental results. The bilinear and biquadratic coupling strengths make the
current to switch the magnetization between two states or oscillate steadily.
The expressions for the critical currents between which oscillations are
possible and the critical bilinear coupling strength below which oscillations
are not possible are derived. The frequency of the oscillations is shown to be
tuned and increased to or above 300 GHz by the current which is the largest to
date among nanopillar-shaped STNOs.",2208.07223v1
2022-10-31,Nematronics: Reciprocal coupling between ionic currents and nematic dynamics,"Adopting a spintronics-inspired approach, we study the reciprocal coupling
between ionic charge currents and nematic texture dynamics in a uniaxial
nematic electrolyte. Assuming quenched fluid dynamics, we develop equations of
motion analogously to spin torque and spin pumping. Based on the principle of
least dissipation of energy, we derive the adiabatic ""nematic torque"" exerted
by ionic currents on the nematic director field as well as the reciprocal
motive force on ions due to the orientational dynamics of the director. We
discuss several simple examples that illustrate the potential functionality of
this coupling. Furthermore, using our phenomenological framework, we propose a
practical means to extract the coupling strength through impedance measurements
on a nematic cell. Exploring further applications based on this physics could
foster the development of nematronics -- nematic iontronics.",2210.17116v2
2022-12-06,Dynamics of hybrid magnetic skyrmion driven by spin-orbit torque in ferrimagnets,"Magnetic skyrmions are magnetic textures with topological protection, which
are expected to be information carriers in future spintronic devices. In this
work, we propose a scheme to implement hybrid magnetic skyrmions (HMS) in
ferrimagnets, and we study theoretically and numerically the dynamics of the
HMS driven by spin-orbit torque. It is revealed that the skyrmion Hall effect
depends on the skyrmion helicity and the net angular momentum ({\delta}s),
allowing the effective modulation of the HMS motion through tuning
Dzyaloshinskii-Moriya interaction and {\delta}s. Thus, the Hall effect can be
suppressed through selecting suitable materials to better control the HMS
motion. Moreover, Magnus force for finite {\delta}s suppresses the transverse
motion and enhances the longitudinal propagation, resulting in the HMS dynamics
in ferrimagnets faster than that in antiferromagnets.",2212.02807v1
2023-03-23,Single device offset-free magnetic field sensing principle with tunable sensitivity and linear range based on spin-orbit-torques,"We propose a novel device concept using spin-orbit-torques to realize a
magnetic field sensor, where we eliminate the sensor offset using a
differential measurement concept. We derive a simple analytical formulation for
the sensor signal and demonstrate its validity with numerical investigations
using macrospin simulations. The sensitivity and the measurable linear sensing
range in the proposed concept can be tuned by either varying the effective
magnetic anisotropy or by varying the magnitude of the injected currents. We
show that undesired perturbation fields normal to the sensitive direction
preserve the zero-offset property and only slightly modulate the sensitivity of
the proposed sensor. Higher-harmonics voltage analysis on a Hall cross
experimentally confirms the linearity and tunability via current strength.
Additionally, the sensor exhibits a non-vanishing offset in the experiment
which we attribute to the anomalous Nernst effect.",2303.13261v1
2023-04-18,Stochastic spin-orbit-torque device as the STDP synapse for spiking neural networks,"Neuromorphic hardware as a non-Von Neumann architecture has better energy
efficiency and parallelism than the conventional computer. Here, with numerical
modeling spin-orbit torque (SOT) device using current-induced SOT and Joule
heating effects, we acquire its magnetization switching probability as a
function of the input current pulses and use it to mimic the
spike-timing-dependent plasticity learning behavior like actual brain working.
We further demonstrate that the artificial spiking neural network (SNN) built
by this SOT device can perform unsupervised handwritten digit recognition with
the accuracy of 80% and logic operation learning. Our work provides a new clue
to achieving SNN-based neuromorphic hardware using high-energy efficiency and
nonvolatile spintronics nanodevices",2304.08856v1
2023-04-21,Room-temperature van der Waals 2D ferromagnet switching by spin-orbit torques,"Emerging wide varieties of the two-dimensional (2D) van der Waals (vdW)
magnets with atomically thin and smooth interfaces holds great promise for
next-generation spintronic devices. However, due to the lower Curie temperature
of the vdW 2D ferromagnets than room temperature, electrically manipulating its
magnetization at room temperature has not been realized. In this work, we
demonstrate the perpendicular magnetization of 2D vdW ferromagnet Fe3GaTe2 can
be effectively switched at room temperature in Fe3GaTe2/Pt bilayer by
spin-orbit torques (SOTs) with a relatively low current density of 1.3
10^7A/cm2. Moreover, the high SOT efficiency of \xi_{DL}~0.22 is quantitatively
determined by harmonic measurements, which is higher than those in Pt-based
heavy metal/conventional ferromagnet devices. Our findings of room-temperature
vdW 2D ferromagnet switching by SOTs provide a significant basis for the
development of vdW-ferromagnet-based spintronic applications.",2304.10718v1
2023-06-03,Exchange bias between van der Waals materials: tilted magnetic states and field-free spin-orbit-torque switching,"Magnetic van der Waals heterostructures provide a unique platform to study
magnetism and spintronics device concepts in the two-dimensional limit. Here,
we report studies of exchange bias from the van der Waals antiferromagnet CrSBr
acting on the van der Waals ferromagnet Fe3GeTe2 (FGT). The orientation of the
exchange bias is along the in-plane easy axis of CrSBr, perpendicular to the
out-of-plane anisotropy of the FGT, inducing a strongly tilted magnetic
configuration in the FGT. Furthermore, the in-plane exchange bias provides
sufficient symmetry breaking to allow deterministic spin-orbit torque switching
of the FGT in CrSBr/FGT/Pt samples at zero applied magnetic field. A minimum
thickness of the CrSBr greater than 10 nm is needed to provide a non-zero
exchange bias at 30 K.",2306.02129v1
2023-06-23,Input-driven chaotic dynamics in vortex spin-torque oscillator,"A new research topic in spintronics relating to the operation principles of
brain-inspired computing is input-driven magnetization dynamics in nanomagnet.
In this paper, the magnetization dynamics in a vortex spin-torque oscillator
(STO) driven by a series of random magnetic field are studied through a
numerical simulation of the Thiele equation. It is found that input-driven
synchronization occurs in the weak perturbation limit, as found recently. As
well, chaotic behavior is newly found to occur in the vortex core dynamics for
a wide range of parameters, where synchronized behavior is disrupted by an
intermittency. Ordered and chaotic dynamical phases are examined by evaluating
the Lyapunov exponent. The relation between the dynamical phase and the
computational capability of physical reservoir computing is also studied.",2306.13278v1
2023-07-19,Oxide layer dependent orbital torque efficiency in ferromagnet/Cu/Oxide heterostructures,"The utilization of orbital transport provides a versatile and efficient spin
manipulation mechanism. As interest in orbital-mediated spin manipulation
grows, we face a new issue to identify the underlying physics that determines
the efficiency of orbital torque (OT). In this study, we systematically
investigate the variation of OT governed by orbital Rashba-Edelstein effect at
the Cu/Oxide interface, as we change the Oxide material. We find that OT varies
by a factor of ~2, depending on the Oxide. Our results suggest that the active
electronic interatomic interaction (hopping) between Cu and oxygen atom is
critical in determining OT. This also gives us an idea of what type of material
factors is critical in forming a chiral orbital Rashba texture at the Cu/Oxide
interface.",2307.09824v1
2023-08-24,Highly efficient room-temperature nonvolatile magnetic switching by current in Fe3GaTe2 thin flakes,"Effectively tuning magnetic state by using current is essential for novel
spintronic devices. Magnetic van der Waals (vdW) materials have shown superior
properties for the applications of magnetic information storage based on the
efficient spin torque effect. However, for most of known vdW ferromagnets, the
ferromagnetic transition temperatures lower than room temperature strongly
impede their applications and the room-temperature vdW spintronic device with
low energy consumption is still a long-sought goal. Here, we realize the highly
efficient room-temperature nonvolatile magnetic switching by current in a
single-material device based on vdW ferromagnet Fe3GaTe2. Moreover, the
switching current density and power dissipation are about 300 and 60000 times
smaller than conventional spin-orbit-torque devices of magnet/heavymetal
heterostructures. These findings make an important progress on the applications
of magnetic vdW materials in the fields of spintronics and magnetic information
storage.",2308.12710v1
2023-10-16,Stochastic spin-orbit-torque synapse and its application in uncertainty quantification,"Stochasticity plays a significant role in the low-power operation of a
biological neural network. In an artificial neural network (ANN), stochasticity
also contributes to critical functions such as the uncertainty quantification
(UQ) for estimating the probability for the correctness of prediction. This UQ
is vital for cutting-edge applications, including medical diagnostics,
autopilots, and large language models. Thanks to high computing velocity and
low dissipation, a spin-orbit-torque (SOT) device exhibits significant
potential for implementing the UQ. However, up until now, the application of UQ
for stochastic SOT devices remains unexplored. In this study, based on
SOT-induced stochastic magnetic domain wall (DW) motion with varying velocity,
we fabricated an SOT synapse that could emulate stochastic weight update
following the Spike-Timing-Dependent-Plasticity (STDP) rule. Furthermore, we
set up a stochastic Spiking-Neural-Network (SNN), which, when compared to its
deterministic counterpart, demonstrates a clear advantage in quantifying
uncertainty for diagnosing the type of breast tumor (benign or malignant).",2310.10317v1
2023-12-02,Virtual reservoir acceleration for CPU and GPU: Case study for coupled spin-torque oscillator reservoir,"We provide high-speed implementations for simulating reservoirs described by
$N$-coupled spin-torque oscillators. Here $N$ also corresponds to the number of
reservoir nodes. We benchmark a variety of implementations based on CPU and
GPU. Our new methods are at least 2.6 times quicker than the baseline for $N$
in range $1$ to $10^4$. More specifically, over all implementations the best
factor is 78.9 for $N=1$ which decreases to 2.6 for $N=10^3$ and finally
increases to 23.8 for $N=10^4$. GPU outperforms CPU significantly at $N=2500$.
Our results show that GPU implementations should be tested for reservoir
simulations. The implementations considered here can be used for any reservoir
with evolution that can be approximated using an explicit method.",2312.01121v1
2023-12-05,Current-controlled periodic double-polarity reversals in a spin-torque vortex oscillator,"Micromagnetic simulations are used to study a spin-torque vortex oscillator
excited by an out-of-plane dc current. The vortex core gyration amplitude is
confined between two orbits due to periodical vortex core polarity reversals.
The upper limit corresponds to the orbit where the vortex core reaches its
critical velocity triggering the first polarity reversal which is immediately
followed by a second one. After this double polarity reversal, the vortex core
is on a smaller orbit that defines the lower limit of the vortex core gyration
amplitude. This double reversal process is a periodic phenomenon and its
frequency as well as the upper and lower limits of the vortex core gyration are
controlled by the input current density while the vortex chirality determines
the onset of this confinement regime. In this non-linear regime, the vortex
core never reaches a stable orbit and thus, it may be of interest for
neuromorphic application, for example as a leaky integrate-and-fire neuron.",2312.02800v1
2024-01-10,Field-free ultrafast magnetization reversal of a nanodevice by a chirped current pulse via spin-orbit torque,"We investigated the magnetization reversal of a perpendicularly magnetized
nanodevice using a chirped current pulse (CCP) via spin-orbit torques (SOT).
Our findings demonstrate that both the field-like (FL) and damping-like (DL)
components of SOT in CCP can efficiently induce ultrafast magnetization
reversal without any symmetry-breaking means. For a wide frequency range of the
CCP, the minimal current density obtained is significantly smaller compared to
the current density of conventional SOT-reversal. This ultrafast reversal is
due to the CCP triggering enhanced energy absorption (emission) of the
magnetization from (to) the FL- and DL-components of SOT before (after)
crossing over the energy barrier. We also verified the robustness of the
CCP-driven magnetization reversal at room temperature. Moreover, this strategy
can be extended to switch the magnetic states of perpendicular synthetic
antiferromagnetic (SAF) and ferrimagnetic (SFi) nanodevices. Therefore, these
studies enrich the basic understanding of field-free SOT-reversal and provide a
novel way to realize ultrafast SOT-MRAM devices with various free layer
designs: ferromagnetic, SAF, and SFi.",2401.04882v2
2024-02-10,A spin-torque nano-oscillator based on interlayer-coupled meron-skyrmion pairs with a fixed orbit,"In recent years, magnetic skyrmion-based spin-torque nano-oscillators (STNOs)
attract considerable interest for their prospect in future-generation
communication and spintronic technologies. However, some critical issues, which
hamper their practical applications, e.g., the long start-up time and variable
skyrmion gyration orbit, remain to be resolved. Here, we numerically
demonstrate a realization of a fixed-orbit STNO, which is based on an
interlayer-coupled meron-skyrmion (MS) pair other than a magnetic skyrmion. In
this STNO, the MS pair possesses a structurally defined, fixed orbit within a
broad range of driving current, even in the presence of random defects. The
output frequency range of the STNO based on an MS pair far exceeds that of the
STNO typically based on a single skyrmion. Moreover, the output frequency of
this STNO can be further elevated if more MS pairs are incorporated. Our
results reveal the nontrivial dynamics of the interlayer-coupled MS pair,
opening perspectives for the design and optimization of fundamental spintronic
devices.",2402.06865v1
2024-03-11,"A Two-Field-Scan Harmonic Hall Voltage Analysis For Fast, Accurate Quantification Of Spin-Orbit Torques In Magnetic Heterostructures","The efficiencies of the spin-orbit torques (SOTs) play a key role in the
determination of the power consumption, integration density, and endurance of
SOT-driven devices. Accurate and time-efficient determination of the SOT
efficiencies is of great importance not only for evaluating the practical
potential of SOT devices but also for developing new mechanisms for enhancing
the SOT efficiencies. Here, we develop a ""two-field-scan"" harmonic Hall voltage
(HHV) analysis that collects the second HHV as a function of a swept in-plane
magnetic field at 45{\deg} and 0{\deg} relative to the excitation current. We
demonstrate that this two-field-scan analysis is as accurate as the
well-established but time-consuming angle-scan HHV analysis even in the
presence of considerable thermoelectric effects but takes more than a factor of
7 less measurement time. We also show that the 3-parameter fit of the HHV data
from a single field scan at 0{\deg}, which is commonly employed in the
literature, is not reliable because the employment of too many free parameters
in the fitting of the very slowly varying HHV signal allows unrealistic
pseudo-solution and thus erroneous conclusion about the SOT efficiencies.",2403.06740v1
2024-04-01,Electrical-controllable antiferromagnet-based tunnel junction,"Electrical-controllable antiferromagnet tunnel junction is a key goal in
spintronics, holding immense promise for ultra-dense and ultra-stable
antiferromagnetic memory with high processing speed for modern information
technology. Here, we have advanced towards this goal by achieving an
electrical-controllable antiferromagnet-based tunnel junction of
Pt/Co/Pt/Co/IrMn/MgO/Pt. The exchange coupling between antiferromagnetic IrMn
and Co/Pt perpendicular magnetic multilayers results in the formation of
interfacial exchange bias and exchange spring in IrMn. Encoding information
states 0 and 1 is realized through the exchange spring in IrMn, which can be
electrically written by spin-orbit torque switching with high cyclability and
electrically read by antiferromagnetic tunneling anisotropic magnetoresistance.
Combining spin-orbit torque switching of both exchange spring andexchange bias,
16 Boolean logic operation is successfully demonstrated. With both memory and
logic functionalities integrated into our electrical-controllable
antiferromagnetic-based tunnel junction, we chart the course toward
high-performance antiferromagnetic logic-in-memory.",2404.01144v1
2000-12-21,Accretion Disk Torqued by a Black Hole,"If a Kerr black hole is connected to a disk rotating around it by a magnetic
field, the rotational energy of the Kerr black hole provides an energy source
for the radiation of the disk in addition to disk accretion. The black hole
exerts a torque on the disk, which transfers energy and angular momentum
between the black hole and the disk. If the black hole rotates faster than the
disk, energy and angular momentum are extracted from the black hole and
transfered to the disk. The energy deposited into the disk is eventually
radiated away by the disk, which will increase the efficiency of the disk. If
the black hole rotates slower than the disk, energy and angular momentum are
transfered from the disk to the black hole, which will lower the efficiency of
the disk. With suitable boundary conditions, quasi-steady state solutions are
obtained for a thin Keplerian disk magnetically coupled to a Kerr black hole.
By ``quasi-steady state'' we mean that any macroscopic quantity at a given
radius in the disk slowly changes with time: the integrated change within one
rotation period of the disk is much smaller than the quantity itself. We find
that, the torque produced by the magnetic coupling propagates only outward in
the disk, the total radiation flux of the disk is a superposition of the
radiation flux produced by the magnetic coupling and that produced by
accretion. Most interestingly, a disk magnetically coupled to a rapidly
rotating black hole can radiate without accretion. Such a disk has an infinite
efficiency. For a specific example that the magnetic field touches the disk at
the inner boundary, the radial radiation profile is very different from that of
a standard accretion disk: the emissivity index is significantly bigger, most
radiation comes from a region which is closer to the center of the disk.",0012469v2
2014-02-09,Star-Disc-Binary Interactions in Protoplanetary Disc Systems and Primordial Spin-Orbit Misalignments,"We study the interactions between a protostar and its circumstellar disc
under the influence of an external binary companion to determine the evolution
of the mutual stellar spin - disc misalignment angle. The gravitational torque
on the disc from an inclined binary makes the disc precess around the binary
axis, while the star-disc interaction torque due to the rotation-induced
quadrupole makes the stellar spin and the disc angular momentum axes precess
around each other. A significant star-disc misalignment angle can be generated
from a small initial value as the star-disc system evolves in time such that
the two precession frequencies cross each other. This ``secular resonance''
behavior can be understood in a geometric way from the precession dynamics of
spin and disc angular momenta. We derive the conditions for such resonance to
occur, and find that they can be satisfied for reasonable protostar-disc-binary
parameters. The evolution of star-disc inclination is also affected by mass
accretion and by magnetic star-disc interaction torques, which can either
promote or reduce star-disc misalignment. In general, as long as the initial
binary-disc inclination is greater than a few degrees, a variety of star-disc
misalignment angles can be generated within the disc lifetimes. We discuss the
implications of our results for the stellar spin orientations in binaries, for
the alignments/misalignments of protostellar discs and debris discs, and for
the stellar obliquities in exoplanetary systems. In particular, if hot Jupiters
are produced by the Kozai effect induced by an external stellar companion, then
it is likely that ``primordial'' star-disc misalignments are already generated
by the star-disc-binary interactions. Even for systems where the Kozai effect
is suppressed, misaligned planets may still be produced during the
protoplanetary disc phase.",1402.1907v1
2018-05-29,Fundamental physics and the absence of sub-millisecond pulsars,"Observations of the spin distribution of rapidly rotating neutron stars show
evidence for a lack of stars spinning at frequencies larger than $f\approx 700$
Hz, well below the predictions of theoretical equations of state. This has
generally been taken as evidence of an additional spin-down torque operating in
these systems and it has been suggested that gravitational wave torques may be
operating and be linked to a potentially observable signal. In this paper we
aim to determine whether additional spin-down torques are necessary, or whether
the observed limit of $f\approx 700$ Hz could correspond to the mass-shedding
frequency for the observed systems and is simply a consequence of the,
currently unknown, state of matter at high densities. Given our ignorance with
regard to the true equation of state of matter above nuclear saturation
densities, we make minimal physical assumption and only demand causality in the
core. We then connect our causally-limited equation of state to a realistic
microphysical crustal equation of state for densities below nuclear saturation
density. This produces a limiting model that will give the lowest possible
maximum frequency, which we compare to observational constraints on neutron
star masses and frequencies. We also compare our findings with the constraints
on the tidal deformability obtained in the observations of the GW170817 event.
We find that the lack of pulsars spinning faster than $f\approx 700$ Hz is not
compatible with our causal limited `minimal' equation of state, for which the
breakup frequency cannot be lower than $f_{\rm max}\approx 1200$ Hz. A low
frequency cutoff, around $f\approx 800$ Hz could only be possible if we assume
that these systems do not contain neutron stars with masses above $M\approx 2
M_\odot$. This would have to be due either to selection effects, or possibly to
a phase transition in the interior of the neutron star.",1805.11277v1
2019-11-26,Collisional Ionization in the X-ray Spectrum of the Ultracompact Binary 4U 1626-67,"We report on high-resolution X-ray spectroscopy of the ultracompact X-ray
binary pulsar 4U 1626-67 with Chandra/HETGS acquired in 2010, two years after
the pulsar experienced a torque reversal. The well-known strong Ne and O
emission lines with Keplerian profiles are shown to arise at the inner edge of
the magnetically-channeled accretion disk. We exclude a photoionization model
for these lines based on the absence of sharp radiative recombination continua.
Instead, we show that the lines arise from a collisional plasma in the
inner-disk atmosphere, with $T\simeq 10^7$ K and $n_e \sim 10^{17}$ cm^(-3). We
suggest that the lines are powered by X-ray heating of the optically-thick disk
inner edge at normal incidence. Comparison of the line profiles in HETGS
observations from 2000, 2003, and 2010 show that the inner disk radius
decreased by a factor of two after the pulsar went from spin-down to spin-up,
as predicted by magnetic accretion torque theory. The inner disk is well inside
the corotation radius during spin-up, and slightly beyond the corotation radius
during spin-down. Based on the disk radius and accretion torque measured during
steady spin-up, the pulsar's X-ray luminosity is $2\times 10^{36}$ erg/s,
yielding a source distance of 3.5(+0.2-0.3) kpc. The mass accretion rate is an
order of magnitude larger than expected from gravitational radiation reaction,
possibly due to X-ray heating of the donor. The line profiles also indicate a
binary inclination of 39(+20-10) degrees, consistent with a 0.02 Msun donor
star. Our emission measure analysis favors a He white dwarf or a highly-evolved
H-poor main sequence remnant for the donor star, rather than a C-O or O-Ne
white dwarf. The measured Ne/O ratio is 0.46+-0.14 by number. In an appendix,
we show how to express the emission measure of a H-depleted collisional plasma
without reference to a H number density.",1911.11684v1
2018-10-22,Tuning a binary ferromagnet into a multi-state synapse with spin-orbit torque induced plasticity,"Inspired by ion-dominated synaptic plasticity in human brain, artificial
synapses for neuromorphic computing adopt charge-related quantities as their
weights. Despite the existing charge derived synaptic emulations, schemes of
controlling electron spins in ferromagnetic devices have also attracted
considerable interest due to their advantages of low energy consumption,
unlimited endurance, and favorable CMOS compatibility. However, a generally
applicable method of tuning a binary ferromagnet into a multi-state memory with
pure spin-dominated synaptic plasticity in the absence of an external magnetic
field is still missing. Here, we show how synaptic plasticity of a
perpendicular ferromagnetic FM1 layer can be obtained when it is
interlayer-exchange-coupled by another in-plane ferromagnetic FM2 layer, where
a magnetic-field-free current-driven multi-state magnetization switching of FM1
in the Pt/FM1/Ta/FM2 structure is induced by spin-orbit torque. We use current
pulses to set the perpendicular magnetization state which acts as the synapse
weight, and demonstrate spintronic implementation of the excitatory/inhibitory
postsynaptic potentials and spike timing-dependent plasticity. This
functionality is made possible by the action of the in-plane interlayer
exchange coupling field which leads to broadened, multi-state magnetic reversal
characteristics. Numerical simulations, combined with investigations of a
reference sample with a single perpendicular magnetized Pt/FM1/Ta structure,
reveal that the broadening is due to the in-plane field component tuning the
efficiency of the spin-orbit-torque to drive domain walls across a landscape of
varying pinning potentials. The conventionally binary FM1 inside our
Pt/FM1/Ta/FM2 structure with inherent in-plane coupling field is therefore
tuned into a multi-state perpendicular ferromagnet and represents a synaptic
emulator for neuromorphic computing.",1810.09064v1
2023-12-08,Secular change in the spin states of asteroids due to radiation and gravitation torques. New detections and updates of the YORP effect,"The rotation state of small asteroids is affected in the long term by
perturbing torques of gravitational and radiative origin (the YORP effect).
Direct observational evidence of the YORP effect is the primary goal of our
work. We carried out photometric observations of five near-Earth asteroids:
(1862) Apollo, (2100) Ra-Shalom, (85989) 1999 JD6, (138852) 2000 WN10, and
(161989) Cacus. Then we applied the light-curve inversion method to all
available data to determine the spin state and a convex shape model for each of
the five studied asteroids. In the case of (2100) Ra-Shalom, the analysis
required that the spin-axis precession due to the solar gravitational torque
also be included. We obtained two new detections of the YORP effect: (i) $(2.9
\pm 2.0)\times 10^{-9}\,\mathrm{rad\,d}^{-2}$ for (2100) Ra-Shalom, and (ii)
$(5.5\pm 0.7)\times 10^{-8}\,\mathrm{rad\,d}^{-2}$ for (138852) 2000 WN10. The
analysis of Ra-Shalom also reveals a precession of the spin axis with a
precession constant $\sim 3000''\,\mathrm{yr}^{-1}$. This is the first such
detection from Earth-bound photometric data. For the other two asteroids, we
improved the accuracy of the previously reported YORP detection: (i) $(4.94 \pm
0.09)\times 10^{-8}\,\mathrm{rad\,d}^{-2}$ for (1862) Apollo, and (ii)
$(1.86\pm 0.09)\times 10^{-8}\,\mathrm{rad\,d}^{-2}$ for (161989) Cacus.
Despite the recent report of a detected YORP effect for (85989) 1999 JD6, we
show that the model without YORP cannot be rejected statistically. Therefore,
the detection of the YORP effect for this asteroid requires future
observations. The spin-axis precession constant of Ra-Shalom determined from
observations matches the theoretically expected value. The total number of
asteroids with a YORP detection has increased to 12. In all cases, the rotation
frequency increases in time.",2312.05157v1
2016-06-06,Probabilistic Model to Treat Flexibility in Molecular Contacts,"Evaluating accessible conformational space is computationally expensive and
thermal motions are partly neglected in computer models of molecular
interactions. This produces error into the estimates of binding strength. We
introduce a method for modelling interactions so that structural flexibility is
inherently taken into account. It has a statistical model for 3D properties of
'nonlocal' contacts and a physics based description of 'local' interactions,
based on mechanical torque. The form of the torque barrier is derived using a
representation of the local electronic structure, which is presumed to improve
transferability, compared to traditional force fields. The nonlocal contacts
are more distant than 1-4 interactions and Target-atoms are represented by 3D
probability densities. Probability mass quantifies strength of contact and is
calculated as an overlap integral. Repulsion is described by negative
probability density, allowing probability mass to be used as the descriptor of
contact preference. As a result, we are able to transform the high-dimensional
problem into a simpler evaluation of three-dimensional integrals. We outline
how this scoring function gives a tool to study the enthalpy--entropy
compensation and demonstrate the feasibility of our approach by evaluating
numerical probability masses for chosen side chain to main chain contacts in a
lysine dipeptide structure.",1606.01696v1
2017-05-15,Probabilistically Safe Policy Transfer,"Although learning-based methods have great potential for robotics, one
concern is that a robot that updates its parameters might cause large amounts
of damage before it learns the optimal policy. We formalize the idea of safe
learning in a probabilistic sense by defining an optimization problem: we
desire to maximize the expected return while keeping the expected damage below
a given safety limit. We study this optimization for the case of a robot
manipulator with safety-based torque limits. We would like to ensure that the
damage constraint is maintained at every step of the optimization and not just
at convergence. To achieve this aim, we introduce a novel method which predicts
how modifying the torque limit, as well as how updating the policy parameters,
might affect the robot's safety. We show through a number of experiments that
our approach allows the robot to improve its performance while ensuring that
the expected damage constraint is not violated during the learning process.",1705.05394v1
2020-04-14,Anomalous Motion of Particle Levitated by Laguerre-Gaussian beam,"Laguerre-Gaussian (LG) beam has orbital angular momentum (OAM). A particle
trapped in an LG beam will rotate about the beam axis, due to the transfer of
OAM. The rotation of the particle is usually in the same direction as that of
the beam OAM. However, we discovere that when the LG beam is strongly focused,
the rotation of the particle and the beam OAM might be in the opposite
direction. This anomalous effect is caused by the negative torque on the
particle exerted by the focused LG beam, which is similar to the optical
pulling force in the linear case. We calculated the scattering force
distribution of a micro-particle trapped in an optical tweezers formed by the
strongly focused LG beam, and showed that there exist stable trajectories of
the particle that controlled by the negative torque. We proposed several
necessary conditions for observing the counter-intuitive trajectories. Our work
reveals that the strongly trapped micro-particle exhibits diversity of motion
patterns.",2004.06463v1
2019-07-17,Learning Variable Impedance Control for Contact Sensitive Tasks,"Reinforcement learning algorithms have shown great success in solving
different problems ranging from playing video games to robotics. However, they
struggle to solve delicate robotic problems, especially those involving contact
interactions. Though in principle a policy directly outputting joint torques
should be able to learn to perform these tasks, in practice we see that it has
difficulty to robustly solve the problem without any given structure in the
action space. In this paper, we investigate how the choice of action space can
give robust performance in presence of contact uncertainties. We propose
learning a policy giving as output impedance and desired position in joint
space and compare the performance of that approach to torque and position
control under different contact uncertainties. Furthermore, we propose an
additional reward term designed to regularize these variable impedance control
policies, giving them interpretability and facilitating their transfer to real
systems. We present extensive experiments in simulation of both floating and
fixed-base systems in tasks involving contact uncertainties, as well as results
for running the learned policies on a real system.",1907.07500v2
2023-06-16,Broadband spintronic detection of the absolute field strength of terahertz electromagnetic pulses,"We demonstrate detection of broadband intense terahertz electromagnetic
pulses by Zeeman-torque sampling (ZTS). Our approach is based on magneto-optic
probing of the Zeeman torque the terahertz magnetic field exerts on the
magnetization of a ferromagnet. Using an 8 nm thick iron film as sensor, we
detect pulses from a silicon-based spintronic terahertz emitter with bandwidth
0.1-11 THz and peak field >0.1 MV/cm. Static calibration provides access to
absolute transient THz field strengths. We show relevant added values of ZTS
compared to electro-optic sampling (EOS): an absolute and echo-free transfer
function with simple frequency dependence, linearity even at high terahertz
field amplitudes, the straightforward calibration of EOS response functions and
the modulation of the polarization-sensitive direction by an external AC
magnetic field. Consequently, ZTS has interesting applications even beyond the
accurate characterization of broadband high-field terahertz pulses for
nonlinear terahertz spectroscopy.",2306.09734v1
2023-11-24,Light--absorbed orbital angular momentum in the linear response regime,"In exploring the light-induced dynamics within the linear response regime,
this study investigates the induced orbital angular momentum on a wide variety
of electronic structures. We derive a general expression for the torque induced
by light on different electronic systems based on their characteristic
dielectric tensor. We demonstrate that this phenomenon diverges from the
inverse Faraday effect as it produces an orbital magnetization persistent
post-illumination. Indeed, our results reveal that, while isotropic
non-dissipative materials do not absorb orbital angular momentum from
circularly polarized light, any symmetry-breaking arrangement of matter, be it
spatial or temporal, introduces novel channels for the absorption of orbital
angular momentum, or magnetization. Most notably, in dissipative materials,
circularly polarized light imparts a torque corresponding to a change in
orbital angular momentum of $\hbar$ per absorbed photon. The potential of these
mechanisms to drive helicity-dependent magnetic phenomena paves the way for a
deeper understanding of light-matter interactions. Notably, the application of
pump-probe techniques in tandem with our findings allows experimentalists to
quantitatively assess the amount of orbital angular momentum transferred to
electrons in matter, thus hopefully enhancing our ability to steer ultrafast
light-induced magnetization dynamics.",2311.14774v1
2006-01-14,Spin Hall effect in two-dimensional $p$-type semiconductors in a magnetic field,"We calculate the spin Hall conductivity driven by Rashba spin-orbit
interaction in $p$-type two-dimensional semiconductors in the presence of a
perpendicular magnetic field. For a highly confined quantum well, the system is
described by a $k$-cubic Rashba term for two-dimensional heavy holes.
  The eigenstates of the system can be described by
  Landau spinor states. First we consider the conventional spin Hall
conductivity. The contribution of the interband transitions to the
Kubo-Greenwood formula gives the density dependent intrinsic spin Hall
conductivity, which approaches its universal value $\sigma^z_{xy}=9e/8\pi$ for
weak spin-orbit coupling and low Fermi energies, in agreement with previous
work.
  However two intraband contribution terms cancel this effect leading to zero
conventional spin Hall conductivity. Adding the torque dipole contribution to
the definition of spin current, we also study the {\it effective} spin
conductivity. This is shown to be proportional to the total magnetization plus
surface terms which exactly cancel it for small spin-orbit coupling. If in low
magnetic field the intraband transitions evolve to vertex corrections, the fact
that both {effective} and conventional spin Hall conductivities vanish is
unexpected. This suggests that the zero magnetic field limit of the model is
singular.",0601315v2
2015-06-29,Synchronous Spin-Exchange Optical Pumping,"We describe a new approach to precision NMR with hyperpolarized gases
designed to mitigate NMR frequency shifts due to the alkali spin exchange
field. The electronic spin polarization of optically pumped alkali atoms is
square-wave modulated at the noble-gas NMR frequency and oriented transverse to
the DC Fourier component of the NMR bias field. Noble gas NMR is driven by
spin-exchange collisions with the oscillating electron spins. On resonance, the
time-average torque from the oscillating spin-exchange field produced by the
alkali spins is zero. Implementing the NMR bias field as a sequence of alkali
2$ \pi $-pulses enables synchronization of the alkali and noble gas spins
despite a 1000-fold discrepancy in gyromagnetic ratio. We demonstrate this
method with Rb and Xe, and observe novel NMR broadening effects due to the
transverse oscillating spin exchange field. When uncompensated, the
spin-exchange field at high density broadens the NMR linewidth by an order of
magnitude, with an even more dramatic suppression (up to 70x) of the phase
shift between the precessing alkali and Xe polarizations. When we introduce a
transverse compensation field, we are able to eliminate the spin-exchange
broadening and restore the usual NMR phase sensitivity. The projected
quantum-limited sensitivity is better than 1 nHz/$\sqrt{\rm Hz}$.",1506.08797v1
2020-04-24,Quantitative comparison of electrically induced spin and orbital polarizations in heavy-metal/3d-metal bilayers,"Electrical control of magnetization is of crucial importance for integrated
spintronics devices. Spin-orbit torques (SOT) in heavy-metal/ferromagnetic
heterostructures have emerged as promising tool to achieve efficiently
current-induced magnetization reversal. However, the microscopic origin of the
SOT is being debated,with the spin Hall effect (SHE) due to nonlocal spin
currents and the spin Rashba-Edelstein effect (SREE) due to local spin
polarization at the interface being the primary candidates. We investigate the
electrically induced out-of-equilibrium spin and orbital polarizations in pure
Pt films and in Pt/3d-metal (Co, Ni, Cu) bilayer films using ab initio
electronic structure methods and linear-response theory. We compute
atom-resolved response quantities that allow us to identify the induced
spin-polarization contributions that lead to fieldlike SOTs, mostly associated
with the SREE, and dampinglike (DL) SOTs, mostly associated with the SHE, and
compare their relative magnitude, dependence on the magnetization direction, as
well as their Pt-layer thickness dependence. We find that both the FL and DL
components contribute to the resulting SOT at the Pt/Co and Pt/Ni interfaces,
with the former contributions being larger at the Pt interface layer and the
latter larger in the Co or Ni layers. Our calculations show that the
electrically-induced transverse orbital polarization is exceedingly larger than
the induced spin polarization and present even without spin-orbit coupling, in
contrast to the spin polarization.",2004.11942v5
2019-05-03,Effective spin-mixing conductance of topological-insulator/ferromagnet and heavy-metal/ferromagnet spin-orbit-coupled interfaces: A first-principles Floquet-nonequilibrium-Green-function approach,"The spin mixing conductance (SMC) is a key quantity determining efficiency of
spin transport across interfaces. Thus, knowledge of its precise value is
required for accurate measurement of parameters quantifying numerous effects in
spintronics, such as spin-orbit torque, spin Hall magnetoresistance, spin Hall
effect and spin pumping. However, the standard expression for SMC, provided by
the scattering theory in terms of the reflection probability amplitudes, is
inapplicable when strong spin-orbit coupling (SOC) is present directly at the
interface. This is the precisely the case of topological-insulator/ferromagnet
and heavy-metal/ferromagnet interfaces of great contemporary interest. We
introduce an approach where first-principles Hamiltonian of these interfaces,
obtained from noncollinear density functional theory (ncDFT) calculations, is
combined with charge conserving Floquet-nonequilibrium-Green-function formalism
to compute {\em directly} the pumped spin current $I^{S_z}$ into semi-infinite
left lead of two-terminal heterostructures Cu/X/Co/Cu or Y/Co/Cu---where
X=Bi$_2$Se$_3$ and Y=Pt or W---due to microwave-driven steadily precessing
magnetization of the Co layer. This allows us extract an effective SMC as a
prefactor in $I^{S_z}$ vs. precession cone angle $\theta$ dependence, as long
as it remains the same, $I^{S_z} \propto \sin^2 \theta$, as in the case where
SOC is absent. By comparing calculations where SOC in switched off vs. switched
on in ncDFT calculations, we find that SOC consistently reduces the pumped spin
current and, therefore, the effective SMC.",1905.01299v2
2022-11-22,Generation of out-of-plane polarized spin current by spin swapping,"The generation of spin currents and their application to the manipulation of
magnetic states is fundamental to spintronics. Of particular interest are
chiral antiferromagnets that exhibit properties typical of ferromagnetic
materials even though they have negligible magnetization. Here, we report the
generation of a robust spin current with both in-plane and out-of-plane spin
polarization in epitaxial thin films of the chiral antiferromagnet Mn3Sn in
proximity to permalloy thin layers. By employing temperature-dependent
spin-torque ferromagnetic resonance, we find that the chiral antiferromagnetic
structure of Mn3Sn is responsible for an in-plane polarized spin current that
is generated from the interior of the Mn3Sn layer and whose temperature
dependence follows that of this layer's antiferromagnetic order. On the other
hand, the out-of-plane spin polarized spin current is unrelated to the chiral
antiferromagnetic structure and is instead the result of scattering from the
Mn3Sn/permalloy interface. We substantiate the later conclusion by performing
studies with several other non-magnetic metals all of which are found to
exhibit out-of-plane polarized spin currents arising from the spin swapping
effect.",2211.12398v1
2020-12-12,Ultrafast spin-currents and charge conversion at 3d-5d interfaces probed by time-domain terahertz spectroscopy,"Spintronic structures are extensively investigated for their spin orbit
torque properties, required for magnetic commutation functionalities. Current
progress in these materials is dependent on the interface engineering for the
optimization of spin transmission. Here, we advance the analysis of ultrafast
spin-charge conversion phenomena at ferromagnetic-transition metal interfaces
due to their inverse spin-Hall effect properties. In particular the intrinsic
inverse spin Hall effect of Pt-based systems and extrinsic inverse spin-Hall
effect of Au:W and Au:Ta in NiFe/Au:(W,Ta) bilayers are investigated. The
spin-charge conversion is probed by complementary techniques -- ultrafast THz
time domain spectroscopy in the dynamic regime for THz pulse emission and
ferromagnetic resonance spin-pumping measurements in the GHz regime in the
steady state -- to determine the role played by the material properties,
resistivities, spin transmission at metallic interfaces and spin-flip rates.
These measurements show the correspondence between the THz time domain
spectroscopy and ferromagnetic spin-pumping for the different set of samples in
term of the spin mixing conductance. The latter quantity is a critical
parameter, determining the strength of the THz emission from spintronic
interfaces. This is further supported by ab-initio calculations, simulations
and analysis of the spin-diffusion and spin relaxation of carriers within the
multilayers in the time domain, permitting to determine the main trends and the
role of spin transmission at interfaces. This work illustrates that time domain
spectroscopy for spin-based THz emission is a powerful technique to probe
spin-dynamics at active spintronic interfaces and to extract key material
properties for spin-charge conversion.",2012.06900v1
2017-10-30,Spin-transfer Antiferromagnetic Resonance,"Currents can induce spin excitations in antiferromagnets, even when they are
insulating. We investigate how spin transfer can cause antiferromagnetic
resonance in bilayers and trilayers that consist of one antiferromagnetic
insulator and one or two metals. An ac voltage applied to the metal generates a
spin Hall current that drives the magnetic moments in the antiferromagnet. We
consider excitation of the macrospin mode and of transverse standing-spin-wave
modes. By solving the Landau-Lifshitz-Gilbert equation in the antiferromagnetic
insulator and the spin-diffusion equation in the normal metal, we derive
analytical expressions for the spin-Hall-magnetoresistance and spin-pumping
inverse-spin-Hall dc voltages. In bilayers, the two contributions compensate
each other and cannot easily be distinguished. We present numerical results for
a MnF$_2|$Pt bilayer. Trilayers facilitate separation of the
spin-Hall-magnetoresistance and spin-pumping voltages, thereby revealing more
information about the spin excitations. We also compute the decay of the pumped
spin current through the antiferromagnetic layer as a function of frequency and
the thickness of the antiferromagnetic layer.",1710.10909v1
2011-12-19,Exploiting boundary states of imperfect spin chains for high-fidelity state transfer,"We study transfer of a quantum state through XX spin chains with static
imperfections. We combine the two standard approaches for state transfer based
on (i) modulated couplings between neighboring spins throughout the spin chain
and (ii) weak coupling of the outermost spins to an unmodulated spin chain. The
combined approach allows us to design spin chains with modulated couplings and
localized boundary states, permitting high-fidelity state transfer in the
presence of random static imperfections of the couplings. The modulated
couplings are explicitly obtained from an exact algorithm using the close
relation between tridiagonal matrices and orthogonal polynomials [Linear
Algebr. Appl. 21, 245 (1978)]. The implemented algorithm and a graphical user
interface for constructing spin chains with boundary states (spinGUIn) are
provided as Supplemental Material.",1112.4503v2
2013-08-14,Excitation- and state-transfer through spin chains in the presence of spatially correlated noise,"We investigate the influence of environmental noise on spin networks and spin
chains. In addition to the common model of an independent bath for each spin in
the system we also consider noise with a finite spatial correlation length. We
present the emergence of new dynamics and decoherence-free subspaces with
increasing correlation length for both dephasing and dissipating environments.
This leads to relaxation blocking of one spin by uncoupled surrounding spins.
We then consider perfect state transfer through a spin chain in the presence of
decoherence and discuss the dependence of the transfer quality on spatial noise
correlation length. We identify qualitatively different features for dephasing
and dissipative environments in spin-transfer problems.",1308.3042v1
2020-07-21,Coherent transport of spin by adiabatic passage in quantum dot arrays,"We introduce an adiabatic transfer protocol for spin states in large quantum
dot arrays that is based on time-dependent modulation of the Heisenberg
exchange interaction in the presence of a magnetic field gradient. We refer to
this protocol as spin-CTAP (coherent transport by adiabatic passage) in analogy
to a related protocol developed for charge state transfer in quantum dot
arrays. The insensitivity of this adiabatic protocol to pulse imperfections has
potential advantages for reading out extended spin qubit arrays. When the
static exchange interaction varies across the array, a quantum-controlled
version of spin-CTAP is possible, where the transfer process is conditional on
the spin states in the middle of the array. This conditional operation can be
used to generate N-qubit entangled GHZ states. Using a realistic noise model,
we analyze the robustness of the spin-CTAP operations and find that
high-fidelity (>95%) spin eigenstate transfer and GHZ state preparation is
feasible in current devices.",2007.10582v2
2021-01-21,Effects of the dynamical magnetization state on spin transfer,"We utilize simulations of electron scattering by a chain of dynamical quantum
spins, to analyze the interplay between the spin transfer effect and the
magnetization dynamics. We show that the complex interactions between the
spin-polarized electrons and the dynamical states of the local spins can be
decomposed into separate processes involving electron reflection and
transmission, as well as absorption and emission of magnons - the quanta of
magnetization dynamics. Analysis shows that these processes are substantially
constrained by the energy and momentum conversation laws, resulting in a
significant dependence of spin transfer on the electron's energy and the
dynamical state of the local spins. Our results suggest that exquisite control
of spin transfer efficiency and of the resulting dynamical magnetization states
may be achievable by tailoring the spectral characteristics of the conduction
electrons and of the magnetic systems.",2101.08868v1
2022-03-30,Angular momentum transfer via relativistic spin-lattice coupling from first principles,"The transfer and control of angular momentum is a key aspect for spintronic
applications. Only recently, it was shown that it is possible to transfer
angular momentum from the spin system to the lattice on ultrashort time scales.
In an attempt to contribute to the understanding of angular momentum transfer
between spin and lattice degrees of freedom we present a scheme to calculate
fully-relativistic spin-lattice coupling parameters from first-principles. By
treating changes in the spin configuration and atomic positions at the same
level, closed expressions for the atomic spin-lattice coupling parameters can
be derived in a coherent manner up to any order. Analyzing the properties of
these parameters, in particular their dependence on spin-orbit coupling, we
find that even in bcc Fe the leading term for the angular momentum exchange
between the spin system and the lattice is a Dzyaloshiskii-Moriya-type
interaction, which is due to the symmetry breaking distortion of the lattice.",2203.16144v1
2004-12-16,Spin transfer to $Λ_{c}^{+}$ hyperons in polarized proton collisions at RHIC,"The analysis\cite{ohkuma:1} of helicity transfer to $\Lambda_{c}^{+}$ in
polarized proton collisions is extended to the proton helicity correlations
with the $\Lambda_{c}^{+}$ transverse polarization in the production plane
(parameter $D_{LS}$). The available spin transfer observables for the
collisions of {\em two} longitudinally polarized protons are evaluated. It is
shown that, in the central region at $\Lambda_{c}^{+}$ transverse momenta of a
few GeV/c, $D_{LS}$ parameters are of about the same size as the
helicity-to-helicity correlations. The methodical issue of using spin transfers
for cross-checks of systematic errors in cross-section $A_{LL}$ measurements at
polarized proton colliders is also briefly discussed.",0412244v1
2018-01-17,Action of Clifford algebra on the space of sequences of transfer operators,"We deduce from a determinant identity on quantum transfer matrices of
generalized quantum integrable spin chain model their generating functions. We
construct the isomorphism of Clifford algebra modules of sequences of transfer
matrices and the boson space of symmetric functions. As an application,
tau-functions of transfer matrices immediately arise from classical
tau-functions of symmetric functions.",1801.05514v1
2019-10-17,Pretty Good State Transfer of Multiple Qubit States on Paths,"We discuss pretty good state transfer of multiple qubit states and provide a
model for considering state transfer of arbitrary states on unmodulated XX-type
spin chains. We then provide families of paths and initial states for which we
can determine whether there is pretty good state transfer based on the
eigenvalue support of the initial state.",1910.08154v1
1999-09-09,On the Possible Enhancement of the Magnetic Field by Neutrino Reemission Processes in the Mantle of a Supernova,"URCA neutrino reemission processes under the conditions in the mantle of a
supernova with a strong toroidal magnetic field are investigated. It is shown
that parity violation in these processes can be manifested macroscopically as a
torque that rapidly spins up the region of the mantle occupied by such a field.
Neutrino spin-up of the mantle can strongly affect the mechanism of further
generation of the toroidal field, specifically, it can enhance the field in a
small neighborhood of the rigid-body-rotating core of the supernova remnant.",9909154v1
2000-01-08,Gravitational Waves from Low-Mass X-ray Binaries: a Status Report,"We summarize the observations of the spin periods of rapidly accreting
neutron stars. If gravitational radiation is responsible for balancing the
accretion torque at the observed spin frequencies of ~300 Hz, then the
brightest of these systems make excellent gravitational wave sources for
LIGO-II and beyond. We review the recent theoretical progress on two mechanisms
for gravitational wave emission: mass quadrupole radiation from deformed
neutron star crusts and current quadrupole radiation from r-mode pulsations in
neutron star cores.",0001129v1
2007-03-19,Quark core formation in spinning-down pulsars,"Pulsars spin-down due to magnetic torque reducing its radius and increasing
the central energy density. Some pulsar which are born with central densities
close to the critical value of quark deconfinement may undergo a phase
transition and structural re-arrengement. This process may excite oscillation
modes and emmit gravitational waves. We determine the rate of quark core
formation in neutron stars using a realistic population synthesis code.",0703507v1
2004-01-29,Magnetic Determination of $H_{c2}$ under Accurate Alignment in (TMTSF)$_2$ClO$_4$,"Cantilever magnetometry has been used to measure the upper critical magnetic
field $H_{c2}$ of the quasi-one dimensional molecular organic superconductor
(TMTSF)$_2$ClO$_4$. From simultaneous resistivity and torque magnetization
experiments conducted under precise field alignment, $H_{c2}$ at low
temperature is shown to reach 5T, nearly twice the Pauli paramagnetic limit
imposed on spin singlet superconductors. These results constitute the first
thermodynamic evidence for a large $H_{c2}$ in this system and provide support
for spin triplet pairing in this unconventional superconductor",0401611v1
2004-08-27,Transition from the macrospin to chaotic behaviour by a spin-torque driven magnetization precession of a square nanoelement,"We demonstrate (using full-scale micromagnetic simulations) that the spin
injection driven steady-state precession of a thin magnetic nanoelement exhibit
a complicate transition from the quasi-macrospin to the chaotic behaviour with
the increasing element size. For nanoelement parameters typical for those used
experimentally we have found that the macrospin approximation becomes invalid
already for very small nanoelement sizes (~ 30 nm), in contrast to the
previously reported results (Li and Zhang, Phys. Rev. B, vol. B68, 024404-1
(2003))",0408615v1
2005-11-02,Current-induced vortex displacement and annihilation in a single Permalloy disk,"The induced motion of a magnetic vortex in a micron-sized ferromagnetic disk
due to the DC current injection is studied by measuring planar Hall effect. The
DC current injection is found to induce the spin torque that sweeps the vortex
out of the disk at the critical current while bias magnetic field are applied.
The current-induced vortex core displacement deduced from the change in planar
Hall resistance is quantitatively consistent with theoretical prediction. Peak
structures similar to those originated from spin wave excitations are observed
in the differential planar Hall resistance curve.",0511040v1
2006-06-13,Rectification of radio frequency current in ferromagnetic nanowire,"We report the rectification of a constant wave radio frequency (RF) current
by using a single-layer magnetic nanowire; a direct-current voltage is
resonantly generated when the RF current flows through the nanowire. The
mechanism of the rectification is discussed in terms of the spin torque diode
effect reported for magnetic tunnel junction devices and the rectification is
shown to be direct attributable to resonant spin wave excitation by the RF
current.",0606305v2
2006-12-13,Switching speed distribution of spin-torque-induced magnetic reversal,"The switching probability of a single-domain ferromagnet under spin-current
excitation is evaluated using the Fokker-Planck equation(FPE). In the case of
uniaxial anisotropy, the FPE reduces to an ordinary differential equation in
which the lowest eigenvalue $\lambda_1$ determines the slowest switching
events. We have calculated $\lambda_1$ by using both analytical and numerical
methods. It is found that the previous model based on thermally distributed
initial magnetization states \cite{Sun1} can be accurately justified in some
useful limiting conditions.",0612334v1
2007-09-06,Brownian dynamics of a microswimmer,"We report on dynamic properties of a simple model microswimmer composed of
three spheres and propelling itself in a viscous fluid by spinning motion of
the spheres under zero net torque constraint. At a fixed temperature and
increasing the spinning frequency, the swimmer demonstrates a transition from
dissipation-dominated to a pumping-dominated motion regime characterized by
negative effective friction coefficient. In the limit of high frequencies, the
diffusion of the swimmer can be described by a model of an active particle with
constant velocity.",0709.0792v1
2008-08-28,Gilbert Damping in Conducting Ferromagnets II: Model Tests of the Torque-Correlation Formula,"We report on a study of Gilbert damping due to particle-hole pair excitations
in conducting ferromagnets. We focus on a toy two-band model and on a four-band
spherical model which provides an approximate description of ferromagnetic
(Ga,Mn)As. These models are sufficiently simple that disorder-ladder-sum vertex
corrections to the long-wavelength spin-spin response function can be summed to
all orders. An important objective of this study is to assess the reliability
of practical approximate expressions which can be combined with electronic
structure calculations to estimate Gilbert damping in more complex systems.",0808.3923v1
2008-11-20,Enhanced Domain Wall Motion in the Spin Valve Nanowires,"According to the recent experiment by the Fert group, the velocity of domain
wall motion in the spin valve ferromagnetic nanowires was almost doubly
enhanced compared to the old value. In this work, we propose an additional
torque model, arising from the interlayer exchange interaction, which can
enhance or suppress the domain wall velocity depending on the sign of the
exchange constant or the wall motion direction relative to the magnetization
orientation of the fixed layer.",0811.3309v2
2011-06-22,Electric spectroscopy of vortex states and dynamics in magnetic disks,"Spin-polarized radio frequency (RF) currents and RF-Oersted fields resonantly
excite a magnetic vortex core confined in a micron-scale soft magnetic disk. In
this study, we measured the rectifying voltage spectra caused by the
anisotropic magnetoresistance oscillation due to the gyration of the vortex
with different polarity and chirality. The measured spectra are presented such
that we can determine the vortex properties and strength of the spin torques
and Oersted field accurately and directly through analytical calculation.",1106.4516v2
2013-01-18,Field-Free Synthetic-Ferromagnet Spin Torque Oscillator,"We study the magnetization dynamics of spin valve structures with a free
composite synthetic ferromagnet (SyF) that consists of two ferromagnetic layers
coupled through a normal metal spacer. A ferromagnetically coupled SyF can be
excited into dynamical precessional states by an applied current without
external magnetic fields. We analytically determine the stability of these
states in the space spanned by the current density and SyF interlayer exchange
coupling. Numerical simulations confirm our analytical results.",1301.4294v1
2016-10-04,Transverse Force on Transversely Polarized Quarks in Longitudinally Polarized Nucleons,"We study the semi-classical interpretation of the $x^3$ and $x^4$ moments of
twist-3 parton distribution functions (PDFs). While no semi-classical
interpretation for the higher moments of $g_T(x)$ and $e(x)$ was find, the
$x^3$ moment of the chirally odd spin-dependent twist-3 PDF $h_L^3(x)$ can be
related to the longitudinal gradient of the transverse force on transversely
polarized quarks in longitudinally polarized nucleons in a DIS experiment. We
discuss how this result relates to the torque acting on a quark in the same
experiment. This has further implications for comparisons between tha
Jaffe-Manohar and the Ji decompositions of the nucleon spin.",1610.01166v1
2017-09-05,Voltage control of interface rare-earth magnetic moments,"The large spin orbit interaction in rare earth atoms implies a strong
coupling between their charge and spin degrees of freedom. We formulate the
coupling between voltage and the local magnetic moments of rare earth atoms
with partially filled 4f shell at the interface between an insulator and a
metal. The rare earth-mediated torques allow power-efficient control of
spintronic devices by electric field-induced ferromagnetic resonance and
magnetization switching.",1709.01271v1
2017-05-29,"Part of a collection of reviews on antiferromagnetic spintronics. Antiferromagnetic dynamics, spin-texures, and nanostructures","Antiferromagnets as active elements of spintronics can be faster than their
ferromagnetic counterparts and more robust to magnetic noise. Owing to the
strongly exchange-coupled magnetic sublattice structure, antiferromagnetic
order parameter dynamics are qualitatively different and thus capable of
engendering novel device functionalities. In this review, we discuss
antiferromagnetic textures -- nanoparticles, domain walls, and skyrmions, --
under the action of different spin torques. We contrast the antiferromagnetic
and ferromagnetic dynamics, with a focus on the features that can be relevant
for applications.",1705.10377v1
2012-09-05,Spin-torque ac impedance in magnetic tunnel junctions,"Subjecting a magnetic tunnel junction (MTJ) to a spin current and/or electric
voltage induces magnetic precession, which can reciprocally pump current
through the circuit. This results in an ac impedance, which is sensitive to the
magnetic field applied to the MTJ. Measuring this impedance can be used to
characterize the coupling between the magnetic free layer and the electric
current as well as a read-out of the magnetic configuration of the MTJ.",1209.1072v1
2016-03-24,Hydrodynamics with spin in bacterial suspensions,"We describe a new kind of self-propelling motion of bacteria based on the
cooperative action of rotating flagella on the surface of bacteria. Describing
the ensemble of rotating flagella in the framework of the hydrodynamics with
spin the reciprocal theorem of Stokesian hydrodynamics is generalized
accordingly. The velocity of the self-propulsion is expressed in terms of the
characteristics of the vector field of flagella orientation and it is shown
that unusually high velocities of \textit{Thiovulum majus} bacteria may be
explained by the cooperative action of the rotating flagella. The expressions
obtained enable us to estimate the torque created by the rotary motors of the
bacterium and show quantitative agreement with the existing experimental data.",1603.07627v1
2019-03-06,Cluster multipole dynamics in non-collinear antiferromagnets,"A systematic framework to investigate spin dynamics in non-collinear
antiferromagnet is proposed. Taking Mn$_3$Sn as a representative example, we
derive an effective low energy model based on the multipole expansion of the
magnetic structure, and investigate the uniform precession and the domain wall
dynamics. We show that the solution for the effective model accurately
reproduces the numerical calculation of the Landau-Lifshitz-Gilbert equations.
Our results indicate that Mn$_3$Sn has preferable properties for applications
to a racetrack memory and a spin torque oscillator, and thus, is a promising
candidate for new devices by using the multipole degrees of freedom.",1903.02259v1
2004-05-27,Excitation of magnetostatic spin waves in ferromagnetic films,"The torque equation of nonlinear spin dynamics is considered in the
magnetostatic approximation. In this framework, exact expressions for
propagator of linear magnetostatic waves in ferromagnetic film between two
antennas and corresponding mutual impedance of the antennas are derived, under
conditions of uniform but arbitrarily oriented static magnetization and
arbitrary anisotropy. The results imply also full description of spectrum of
the waves.",0405640v1
2019-10-31,Valence bond phases of herbertsmithite and related copper kagome materials,"Recent evidence from magnetic torque, electron spin resonance, and second
harmonic generation indicate that the prototypical quantum spin liquid
candidate, herbertsmithite, has a symmetry lower than its x-ray refined
trigonal space group. Here, we consider known and possible distortions of this
mineral class, along with related copper kagome oxides and fluorides, relate
these to possible valence bond patterns, and comment on their relevance to the
physics of these interesting materials.",1910.14196v2
2020-06-05,Harnessing non-local orbital-to-spin conversion of interfacial orbital currents for efficient spin-orbit torques,"The system generates two errors of ""Bad character(s) in field Abstract"" for
no reason. Please refer to the manuscript for the full abstract.",2006.03649v1
2023-05-28,"Magnetic domain walls : Types, processes and applications","Domain walls (DWs) in magnetic nanowires are promising candidates for a
variety of applications including Boolean/unconventional logic, memories,
in-memory computing as well as magnetic sensors and biomagnetic
implementations. They show rich physical behaviour and are controllable using a
number of methods including magnetic fields, charge and spin currents and
spin-orbit torques. In this review, we detail types of domain walls in
ferromagnetic nanowires and describe processes of manipulating their state. We
look at the state of the art of DW applications and give our take on the their
current status, technological feasibility and challenges.",2305.17800v1
2023-12-24,A Novel Field-Free SOT Magnetic Tunnel Junction With Local VCMA-Induced Switching,"By integrating the local voltage-controlled magnetic anisotropy (VCMA)
effect, Dzyaloshinskii-Moriya interaction (DMI) effect, and spin-orbit torque
(SOT) effect, we propose a novel device structure for field-free magnetic
tunnel junction (MTJ). Micromagnetic simulation shows that the device utilizes
the chiral symmetry breaking caused by the DMI effect to induce a non-collinear
spin texture under the influence of SOT current. This, combined with the
perpendicular magnetic anisotropy (PMA) gradient generated by the local VCMA
effect, enables deterministic switching of the MTJ state without an external
field. The impact of variations in DMI strength and PMA gradient on the
magnetization dynamics is analyzed.",2312.15481v1
2023-12-27,Ultrafast inertia-free switching of double magnetic tunnel junctions,"We investigate the switching of a magnetic nanoparticle comprising the middle
free layer of a memory cell based on a double magnetic tunnel junction under
the combined effect of spin-polarized current and weak on-chip magnetic field.
We obtain the timing and amplitude parameters for the current and field pulses
needed to achieve 100 ps range \emph{inertia-free} switching under
\emph{least-power} dissipation. The considered method does not rely on the
stochastics of thermal agitation of the magnetic nanoparticle typically
accompanying spin-torque switching. The regime of ultimate switching
speed-efficiency found in this work is promising for applications in
high-performance nonvolatile memory.",2312.16540v1
2007-02-08,Efficient quantum state transfer in spin chains via adiabatic passage,"We propose a method for quantum state transfer in spin chains using an
adiabatic passage technique. Modifying even and odd nearest-neighbour couplings
in time allows to achieve transfer fidelities arbitrarily close to one, without
the need for a precise control of coupling strengths and timing. We study in
detail transfer by adiabatic passage in a spin-1 chain governed by a
generalized Heisenberg Hamiltonian. We consider optimization of the transfer
process applying optimal control techniques. We discuss a realistic
experimental implementation using cold atomic gases confined in deep optical
lattices.",0702082v2
2021-06-17,Population transfer under local dephasing,"Stimulated Raman adiabatic passage is a well-known technique for quantum
population transfer due to its robustness again various sources of noises. Here
we consider quantum population transfer from one spin to another via an
intermediate spin which subjects to dephasing noise. We obtain an analytic
expression for the transfer efficiency under a specific driving protocol,
showing that dephasing could reduce the transfer efficiency, but the effect of
dephasing could also be suppressed with a stronger laser coupling or a longer
laser duration. We also consider another commonly used driving protocol, which
shows that this analytic picture is still qualitatively correct.",2106.09214v1
2015-07-24,Influence of the fluid density on the statistics of power fluctuations in von Kármán swirling flows,"Here we report experimental results on the fluctuations of injected power in
confined turbulence. Specifically, we have studied a von K\'arm\'an swirling
flow with constant external torque applied to the stirrers. Two experiments
were performed at nearly equal Reynolds numbers, in geometrically similar
experimental setups. Air was utilized in one of them and water in the other.
With air, it was found that the probability density function of power
fluctuations is strongly asymmetric, while with water, it is nearly Gaussian.
This suggests that the outcome of a big change of the fluid density in the
flow-stirrer interaction is not simply a change in the amplitude of stirrers'
response. In the case of water, with a density roughly 830 times greater than
air density, the coupling between the flow and the stirrers is stronger, so
that they follow more closely the fluctuations of the average rotation of the
nearby flow. When the fluid is air, the coupling is much weaker. The result is
not just a smaller response of the stirrers to the torque exerted by the flow;
the PDF of the injected power becomes strongly asymmetric and its spectrum
acquires a broad region that scales as $f^{-2}$. Thus, the asymmetry of the
probability density functions of torque or angular speed could be related to
the inability of the stirrers to respond to flow stresses. This happens, for
instance, when the torque exerted by the flow is weak, due to small fluid
density, or when the stirrers' moment of inertia is large. Moreover, a
correlation analysis reveals that the features of the energy transfer dynamics
with water are qualitatively and quantitatively different to what is observed
with air as working fluid.",1507.07029v2
2020-08-17,Accretion discs with non-zero central torque,"We present analytical and numerical solutions for accretion discs subject to
a non-zero central torque. We express this in terms of a single parameter, $f$,
which is the ratio of outward viscous flux of angular momentum from the inner
boundary to the inward advected flux of angular momentum there. The standard
""accretion"" disc, where the central boundary condition is zero-torque, is
represented by $f=0$. A ""decretion"" disc, where the radial velocity at the
inner boundary is zero, is represented by $f\rightarrow\infty$. For $f > 0$ a
torque is applied to the disc at the inner boundary, which feeds both angular
momentum and energy into the disc. This can arise, for example, in the case of
a circumbinary disc where resonances transfer energy and angular momentum from
the binary to the disc orbits, or where the disc is around a rotating magnetic
star which can allow the disc orbits to be accelerated outwards at the
magnetospheric radius. We present steady-state solutions to the disc structure
as a function of $f$, and for arbitrary kinematic viscosity $\nu$. For
time-dependent discs, we solve the equations using a Green's function approach
for the specific case of $\nu \propto R$ and provide an example numerical
solution to the equations for the case of $\nu \propto R^{3/2}$. We find that
for values of $f\lesssim 0.1$ the disc solutions closely resemble ""accretion""
discs. For values of $f \gtrsim 10$ the solutions initially resemble
""decretion"" discs, but at sufficiently late times exhibit the properties of
""accretion"" discs. We discuss the application of this theory to different
astrophysical systems, and in particular the values of the $f$ parameter that
are expected in different cases.",2008.07565v1
2021-08-18,Resilience of Planetesimal Formation in Weakly-Reinforced Pressure Bumps,"The discovery that axisymmetric dust rings are ubiquitous in protoplanetary
disks has provoked a flurry of research on the role of pressure bumps in planet
formation. High-resolution simulations by our group have shown that even a
modest bump can collect enough dust to trigger planetesimal formation by the
streaming instability. In this work, we probe the limits of planetesimal
formation when the external source of pressure bump reinforcement is extremely
weak. We conduct simulations of radially elongated shearing boxes to capture
the entire bump, which is generated and maintained over some timescale $t_{\rm
reinf}$ by a Newtonian relaxation scheme. We find that planetesimal formation
is extremely resilient for cm-sized grains. We reduced the strength of
reinforcement by up to a factor of 100 and the location and initial masses of
planetesimals were essentially unaffected. However, we do find that strong
reinforcement causes much faster pebble drift compared to the the standard
pebble drift rates. The resulting larger pebble flux enhances the planetesimal
growth rate by pebble accretion. We hypothesize that to sustain the bump, our
code has to extract angular momentum (the strength of this negative torque
depends on $t_{\rm reinf}$), and some of this torque is transferred to the
particles, causing them to drift faster for a stronger torque (i.e., smaller
$t_{\rm reinf}$). Since any physical process that sustains a pressure bump must
do so by torquing the gas, we conjecture that the effect on pebble drift is a
real phenomenon, motivating further work with physically realistic sources to
generate the bump.",2108.08315v3
1999-12-06,Constraints on the Steady-State R-mode Amplitude in Neutron Star Transients,"Recent observations suggest that neutron stars in low-mass X-ray binaries
rotate within a narrow range of spin frequencies clustered around 300 Hz. A
proposed explanation for this remarkable fact is that gravitational radiation
from a steady-state r-mode oscillation in the neutron star's core halts the
spin-up due to accretion. For the neutron star transients, balancing the
time-averaged accretion torque with gravitational wave emission from
steady-state, constant amplitude r-mode pulsations implies a quiescent
luminosity too bright to be consistent with observations (in particular of Aql
X-1). The viscous dissipation (roughly 10 MeV per accreted nucleon for a spin
of 300 Hz) from such an r-mode makes the core sufficiently hot to power a
thermal luminosity of order 1e34 erg/s when accretion halts. This is the
minimum quiescent luminosity that the neutron star must emit when viscous
heating in the core is balanced by radiative cooling from the surface, as is
the case when the core of the star is superfluid. We therefore conclude that
either the accretion torque is much less than (dM/dt)(GMR)^{1/2}, or that a
steady-state r-mode does not limit the spin rate of the neutron star
transients. Future observations with AXAF and XMM promise to further constrain
the amount of viscous dissipation in the neutron star core.",9912113v1
2007-03-13,Online Supplementary Material: Low temperature vortex liquid in $\rm La_{2-x}Sr_xCuO_4$,"We report here the supplementary material for Ref. [1]. Using torque
magnetometry, we measured the magnetization anisotropy of 7 crystals of $\rm
La_{2-x}Sr_xCuO_4$ (LSCO). In optimally-doped cuprates, the bulk susceptibility
is dominated by the paramagnetic van-Vleck orbital term $\chi_{orb}$ which has
a significant anisotropy ($\chi^{orb}_c>\chi^{orb}_{ab}$) that changes weakly
with $T$ (subscripts $c$ and ${ab}$ identify quantities measured with $\bf
H||c$ and $\bf H\perp c$, respectively). Moreover, in the lightly-doped regime,
the paramagnetic spin susceptibilities $\chi^s_c$ and $\chi^s_{ab}$ become
significantly large below the interval 40-60 K. However, the spin
susceptibility is very nearly isotropic (except below 10 K where its anisotropy
becomes measurable). Against the large orbital and spin terms, the weak
diamagnetic signal is very difficult to resolve using standard bulk
magnetometry in lightly-doped cuprates. By contrast, torque magnetometry
selectively detects the orbital diamagnetism generated by supercurrents
confined to the CuO$_2$ layers while ignoring the large spin contribution when
it is isotropic. The orbital van-Vleck contribution is also detected, but as a
``background'' that is $H$-linear to intense fields and only mildly $T$
dependent.",0703348v1
2002-04-08,The Dynamics of Test Particles and Pointlike Gyroscopes in the Brane World and Other 5D Models,"We study the dynamics of test particles and pointlike gyroscopes in 5D
manifolds like those used in the Randall-Sundrum brane world and non-compact
Kaluza-Klein models. Our analysis is based on a covariant foliation of the
manifold using 3+1 dimensional spacetime slices orthogonal to the extra
dimension, and is hence similar to the ADM 3+1 split in ordinary general
relativity. We derive gauge invariant equations of motion for freely-falling
test particles in the 5D and 4D affine parameterizations and contrast these
results with previous work concerning the so-called ``fifth force''. Motivated
by the conjectured localization of matter fields on a 3-brane, we derive the
form of the classical non-gravitational force required to confine particles to
a 4D hypersurface and show that the resulting trajectories are geometrically
identical to the spacetime geodesics of Einstein's theory. We then discuss the
issue of determining the 5D dynamics of a torque-free spinning body in the
point-dipole approximation, and then perform a covariant (3+1)+1 decomposition
of the relevant formulae (i.e. the 5D Fermi-Walker transport equation) for the
cases of freely-falling and hypersurface-confined point gyroscopes. In both
cases, the 4D spin tensor is seen to be subject to an anomalous torque. We
solve the spin equations for a gyroscope confined to a single spacetime section
in a simple 5D cosmological model and observe a cosmological variation of the
magnitude and orientation of the 4D spin.",0204032v1
2014-12-02,Interplay of spin-orbit torque and thermoelectric effects in ferromagnet/normal metal bilayers,"We present harmonic transverse voltage measurements of current-induced
thermoelectric and spin-orbit torque (SOT) effects in ferromagnet/normal metal
bilayers, in which thermal gradients produced by Joule heating and SOT coexist
and give rise to ac transverse signals with comparable symmetry and magnitude.
Based on the symmetry and field-dependence of the transverse resistance, we
develop a consistent method to separate thermoelectric and SOT measurements. By
addressing first ferromagnet/light metal bilayers with negligible spin-orbit
coupling, we show that in-plane current injection induces a vertical thermal
gradient whose sign and magnitude are determined by the resistivity difference
and stacking order of the magnetic and nonmagnetic layers. We then study
ferromagnet/heavy metal bilayers with strong spin-orbit coupling, showing that
second harmonic thermoelectric contributions to the transverse voltage may lead
to a significant overestimation of the antidamping SOT. We find that
thermoelectric effects are very strong in Ta(6nm)/Co(2.5nm) and negligible in
Pt(6nm)/Co(2.5nm) bilayers. After including these effects in the analysis of
the transverse voltage, we find that the antidamping SOTs in these bilayers,
after normalization to the magnetization volume, are comparable to those found
in thinner Co layers with perpendicular magnetization, whereas the field-like
SOTs are about an order of magnitude smaller.",1412.0865v1
2016-08-14,Simulations of the magnetospheres of accreting millisecond pulsars,"Accreting pulsars power relativistic jets, and display a complex spin
phenomenology. These behaviours may be closely related to the large-scale
configuration of the star's magnetic field, shaped by its interaction with the
surrounding accretion disc. Here we present the first relativistic simulations
of the interaction of a pulsar magnetosphere with an accretion flow. Our
axisymmetric simulations treat the magnetospheric, or coronal, regions using a
resistive extension of force-free electrodynamics. The magnetic field is also
evolved inside the disc, which is a defined volume with a specified velocity
field and conductivity profile, found using an alpha-disc model. We study a
range of disc alpha-parameters, thicknesses, magnetic Prandtl numbers, and
inner truncation radii. We find that a large fraction of the magnetic flux in
the pulsar's closed zone is opened by the intrusion of the disc, leading to an
enhancement of the power extracted by the pulsar wind and the spin-down torque
applied to the pulsar. In our simulations, most of the spin-down contribution
to the stellar torque acts on open field lines. The efficiency of field-line
opening is high in the simulations' long-term quasi-steady states, which
implies that a millisecond pulsar's electromagnetic wind could be strong enough
to power the observed neutron-star radio jets, and may significantly affect the
pulsar's spin evolution.",1608.04159v2
2012-09-28,Mass loss in pre-main sequence stars via coronal mass ejections and implications for angular momentum loss,"We develop an empirical model to estimate mass-loss rates via coronal mass
ejections (CMEs) for solar-type pre-main-sequence (PMS) stars. Our method
estimates the CME mass-loss rate from the observed energies of PMS X-ray
flares, using our empirically determined relationship between solar X-ray flare
energy and CME mass: log(M_CME [g]) = 0.63 x log(E_flare [erg]) - 2.57. Using
masses determined for the largest flaring magnetic structures observed on PMS
stars, we suggest that this solar-calibrated relationship may hold over 10
orders of magnitude in flare energy and 7 orders of magnitude in CME mass. The
total CME mass-loss rate we calculate for typical solar-type PMS stars is in
the range 1e-12 to 1e-9 M_sun/yr. We then use these CME mass-loss rate
estimates to infer the attendant angular momentum loss leading up to the main
sequence. Assuming the CME outflow rate for a typical ~1 M_sun T Tauri star is
< 1e-10 M_sun/yr, the resulting spin-down torque is too small during the first
~1 Myr to counteract the stellar spin-up due to contraction and accretion.
However, if the CME mass-loss rate is >1e-10 M_sun/yr, as permitted by our
calculations, the CME spin-down torque may influence the stellar spin evolution
after an age of a few Myr.",1209.6410v1
2018-02-20,Asymmetric skyrmion Hall effect in systems with a hybrid Dzyaloshinskii-Moriya interaction,"We examine the current-induced dynamics of a skyrmion that is subject to both
structural and bulk inversion asymmetry. There arises a hybrid type of
Dzyaloshinskii-Moriya interaction (DMI) which is in the form of a mixture of
interfacial and bulk DMIs. Examples include crystals with symmetry classes
C$_n$ as well as magnetic multilayers composed of a ferromagnet with a
noncentrosymmetric crystal and a nonmagnet with strong spin-orbit coupling. As
a striking result, we find that, in systems with a hybrid DMI, the
spin-orbit-torque-induced skyrmion Hall angle is asymmetric for the two
different skyrmion polarities ($\pm 1$ given by out-of-plane core
magnetization), even allowing one of them to be tuned to zero. We propose
several experimental ways to achieve the necessary straight skyrmion motion
(with zero Hall angle) for racetrack memories, even without antiferromagnetic
interactions or any interaction with another magnet. Our results can be
understood within a simple picture by using a global spin rotation which maps
the hybrid DMI model to an effective model containing purely interfacial DMI.
The formalism directly reveals the effective spin torque and effective current
that result in qualitatively different dynamics. Our work provides a way to
utilize symmetry breaking to eliminate detrimental phenomena as hybrid DMI
eliminates the skyrmion Hall angle.",1802.07327v2
2019-06-17,Interfacial Dzyaloshinskii-Moriya interaction and chiral magnetic textures in a ferrimagnetic insulator,"The interfacial Dzyaloshinskii-Moriya interaction (DMI) in multilayers of
heavy metal and ferromagnetic metals enables the stabilization of novel chiral
spin structures such as skyrmions. Magnetic insulators, on the other hand can
exhibit enhanced dynamics and properties such as lower magnetic damping and
therefore it is of interest to combine the properties enabled by interfacial
DMI with insulating systems. Here, we demonstrate the presence of interfacial
DMI in heterostructures that include insulating magnetic layers. We use a
bilayer of perpendicularly magnetized insulating thulium iron garnet (TmIG) and
the heavy metal platinum, and find a surprisingly strong interfacial DMI that,
combined with spin-orbit torque results, in efficient switching. The
interfacial origin is confirmed through thickness dependence measurements of
the DMI, revealing the characteristic 1/thickness dependence with one order of
magnitude longer decay length compared to metallic layers. We combine chiral
spin structures and spin-orbit torques for efficient switching and identify
skyrmions that allow us to establish the GGG/TmIG interface as the origin of
the DMI.",1906.07142v3
2017-06-19,Investigation of the Dzyaloshinskii-Moriya interaction and room temperature skyrmions in W/CoFeB/MgO thin films and microwires,"Recent studies have shown that material structures, which lack structural
inversion symmetry and have high spin-orbit coupling can exhibit chiral
magnetic textures and skyrmions which could be a key component for next
generation storage devices. The Dzyaloshinskii-Moriya Interaction (DMI) that
stabilizes skyrmions is an anti-symmetric exchange interaction favoring
non-collinear orientation of neighboring spins. It has been shown that material
systems with high DMI can lead to very efficient domain wall and skyrmion
motion by spin-orbit torques. To engineer such devices, it is important to
quantify the DMI for a given material system. Here we extract the DMI at the
Heavy Metal (HM) /Ferromagnet (FM) interface using two complementary
measurement schemes namely asymmetric domain wall motion and the magnetic
stripe annihilation. By using the two different measurement schemes, we find
for W(5 nm)/Co20Fe60B20(0.6 nm)/MgO(2 nm) the DMI to be 0.68 +/- 0.05 mJ/m2 and
0.73 +/- 0.5 mJ/m2, respectively. Furthermore, we show that this DMI stabilizes
skyrmions at room temperature and that there is a strong dependence of the DMI
on the relative composition of the CoFeB alloy. Finally we optimize the layers
and the interfaces using different growth conditions and demonstrate that a
higher deposition rate leads to a more uniform film with reduced pinning and
skyrmions that can be manipulated by Spin-Orbit Torques.",1706.05987v1
2019-05-12,On the dynamics of non-rigid asteroid rotation,"We have presented in this communication a new solving procedure for the
dynamics of non-rigid asteroid rotation, considering the final spin state of
rotation for a small celestial body (asteroid). The last condition means the
ultimate absence of the applied external torques (including short-term effect
from torques during collisions, long-term YORP effect, etc.). Fundamental law
of angular momentum conservation has been used for the aforementioned solving
procedure. The system of Euler equations for dynamics of non-rigid asteroid
rotation has been explored with regard to the existence of an analytic way of
presentation of the approximated solution. Despite of various perturbations
(such as collisions, YORP effect) which destabilize the rotation of asteroid
via deviating from the current spin state, the inelastic (mainly, tidal)
dissipation reduces kinetic energy of asteroid. So, evolution of the spinning
asteroid should be resulting by the rotation about maximal-inertia axis with
the proper spin state corresponding to minimal energy with a fixed angular
momentum. Basing on the aforesaid assumption (component K_1 is supposed to be
fluctuating near the given appropriate constant of the fixed angular momentum),
we have obtained that 2-nd component K_2 is the solution of appropriate Riccati
ordinary differential equation of 1-st order, whereas component K_3 should be
determined via expression for K_2.",1905.06842v4
2020-11-09,Quantum-torque-induced breaking of magnetic interfaces in ultracold gases,"A rich variety of physical effects in spin dynamics arises at the interface
between different magnetic materials. Engineered systems with interlaced
magnetic structures have been used to implement spin transistors, memories and
other spintronic devices. However, experiments in solid state systems can be
difficult to interpret because of disorder and losses. Here, we realize
analogues of magnetic junctions using a coherently-coupled mixture of ultracold
bosonic gases. The spatial inhomogeneity of the atomic gas makes the system
change its behavior from regions with oscillating magnetization -- resembling a
magnetic material in the presence of an external transverse field -- to regions
with a defined magnetization, as in magnetic materials with a ferromagnetic
anisotropy stronger than external fields. Starting from a far-from-equilibrium
fully polarized state, magnetic interfaces rapidly form. At the interfaces, we
observe the formation of short-wavelength magnetic waves. They are generated by
a quantum torque contribution to the spin current and produce strong spatial
anticorrelations in the magnetization. Our results establish ultracold gases as
a platform for the study of far-from-equilibrium spin dynamics in regimes that
are not easily accessible in solid-state systems.",2011.04271v2
2021-02-18,Spin-orbit Torque Switching in an All-Van der Waals Heterostructure,"Current-induced control of magnetization in ferromagnets using spin-orbit
torque (SOT) has drawn attention as a new mechanism for fast and energy
efficient magnetic memory devices. Energy-efficient spintronic devices require
a spin-current source with a large SOT efficiency (${\xi}$) and electrical
conductivity (${\sigma}$), and an efficient spin injection across a transparent
interface. Herein, we use single crystals of the van der Waals (vdW)
topological semimetal WTe$_2$ and vdW ferromagnet Fe$_3$GeTe$_2$ to satisfy the
requirements in their all-vdW-heterostructure with an atomically sharp
interface. The results exhibit values of ${\xi}{\approx}4.6$ and
${\sigma}{\approx}2.25{\times}10^5 {\Omega}^{-1} m^{-1}$ for WTe$_2$. Moreover,
we obtain the significantly reduced switching current density of
$3.90{\times}10^6 A/cm^2$ at 150 K, which is an order of magnitude smaller than
those of conventional heavy-metal/ ferromagnet thin films. These findings
highlight that engineering vdW-type topological materials and magnets offers a
promising route to energy-efficient magnetization control in SOT-based
spintronics.",2102.09300v1
2021-08-03,Dynamic transformation between a skyrmion string and a bimeron string in a layered frustrated system,"Frustrated topological spin textures have unique properties that may enable
novel spintronic applications, such as helicity-based information storage and
computing. Here, we report the statics and current-induced dynamics of
two-dimensional (2D) pancake skyrmions in a stack of weakly coupled frustrated
magnetic monolayers, which form a three-dimensional (3D) skyrmion string. The
Bloch-type skyrmion string is energetically more stable than its N\'eel-type
counterpart. It can be driven into translational motion by the dampinglike
spin-orbit torque and shows the damping-dependent skyrmion Hall effect. Most
notably, the skyrmion string can be transformed to a dynamically stable bimeron
string by the dampinglike spin-orbit torque. The current-induced bimeron string
rotates stably with respect to its center, which can spontaneously transform
back to a skyrmion string when the current is switched off. Our results reveal
unusual physical properties of 3D frustrated spin textures, and may open up
different possibilities for spintronic applications based on skyrmion and
bimeron strings.",2108.01365v2
2019-09-19,Angular characterization of spin-orbit torque and thermoelectric effects,"Arising from the interplay between charge, spin and orbital of electrons,
spin-orbit torque (SOT) has attracted immense interest in the past decade.
Despite vast progress, the existing quantification methods of SOT still have
their respective restrictions on the magnetic anisotropy, the entanglement
between SOT effective fields, and the artifacts from the thermal gradient and
the planar Hall effect, etc. Thus, accurately characterizing SOT across diverse
samples remains as a critical need. In this work, with the aim of removing the
afore-mentioned restrictions, thus enabling the universal SOT quantification,
we report the characterization of the sign and amplitude of SOT by angular
measurements. We first validate the applicability of our angular
characterization in a perpendicularly magnetized Pt/Co-Ni heterostructure by
showing excellent agreements to the results of conventional quantification
methods. Remarkably, the thermoelectric effects, i.e., the anomalous Nernst
effect (ANE) arising from the temperature gradient can be self-consistently
disentangled and quantified from the field dependence of the angular
characterization. The superiority of this angular characterization has been
further demonstrated in a Cu/CoTb/Cu sample with large ANE but negligible SOT,
and in a Pt/Co-Ni sample with weak perpendicular magnetic anisotropy (PMA), for
which the conventional quantification methods are not applicable and even yield
fatal error. By providing a comprehensive and versatile way to characterize SOT
and thermoelectric effects in diverse heterostructures, our results pave the
important foundation for the spin-orbitronic study as well as the
interdisciplinary research of thermal spintronic.",1909.09012v2
2020-05-25,Dynamics of ferromagnetic bimerons driven by spin currents and magnetic fields,"Magnetic bimeron composed of two merons is a topological counterpart of
magnetic skyrmion in in-plane magnets, which can be used as the nonvolatile
information carrier in spintronic devices. Here we analytically and numerically
study the dynamics of ferromagnetic bimerons driven by spin currents and
magnetic fields. Numerical simulations demonstrate that two bimerons with
opposite signs of topological numbers can be created simultaneously in a
ferromagnetic thin film via current-induced spin torques. The current-induced
spin torques can also drive the bimeron and its speed is analytically derived,
which agrees with the numerical results. Since the bimerons with opposite
topological numbers can coexist and have opposite drift directions, two-lane
racetracks can be built in order to accurately encode the data bits. In
addition, the dynamics of bimerons induced by magnetic field gradients and
alternating magnetic fields are investigated. It is found that the bimeron
driven by alternating magnetic fields can propagate along a certain direction.
Moreover, combining a suitable magnetic field gradient, the
Magnus-force-induced transverse motion can be completely suppressed, which
implies that there is no skyrmion Hall effect. Our results are useful for
understanding of the bimeron dynamics and may provide guidelines for building
future bimeron-based spintronic devices.",2005.11924v2
2020-06-18,Current-induced in-plane magnetization switching in biaxial ferrimagnetic insulator,"Ferrimagnetic insulators (FiMI) have been intensively used in microwave and
magneto-optical devices as well as spin caloritronics, where their
magnetization direction plays a fundamental role on the device performance. The
magnetization is generally switched by applying external magnetic fields. Here
we investigate current-induced spin-orbit torque (SOT) switching of the
magnetization in Y3Fe5O12 (YIG)/Pt bilayers with in-plane magnetic anisotropy,
where the switching is detected by spin Hall magnetoresistance. Reversible
switching is found at room temperature for a threshold current density of 10^7
A cm^-2. The YIG sublattices with antiparallel and unequal magnetic moments are
aligned parallel or antiparallel to the direction of current pulses, which is
consistent to the Neel order switching in antiferromagnetic system. It is
proposed that such a switching behavior may be triggered by the
antidamping-torque acting on the two antiparallel sublattices of FiMI. Our
finding not only broadens the magnetization switching by electrical means and
promotes the understanding of magnetization switching, but also paves the way
for all-electrically modulated microwave devices and spin caloritronics with
low power consumption.",2006.10313v1
2020-07-04,Current-induced magnetization switching of exchange-biased NiO heterostructures characterized by spin-orbit torque,"In this work, we study magnetization switching induced by spin-orbit torque
in W(Pt)/Co/NiO heterostructures with variable thickness of heavy-metal layers
W and Pt, perpendicularly magnetized Co layer and an antiferromagnetic NiO
layer. Using current-driven switching, magnetoresistance and anomalous Hall
effect measurements, perpendicular and in-plane exchange bias field were
determined. Several Hall-bar devices possessing in-plane exchange bias from
both systems were selected and analyzed in relation to our analytical switching
model of critical current density as a function of Pt and W thickness,
resulting in estimation of effective spin Hall angle and perpendicular
effective magnetic anisotropy. We demonstrate in both the Pt/Co/NiO and the
W/Co/NiO systems the deterministic Co magnetization switching without external
magnetic field which was replaced by in-plane exchange bias field. Moreover, we
show that due to a higher effective spin Hall angle in W than in Pt-systems the
relative difference between the resistance states in the magnetization current
switching to difference between the resistance states in magnetic field
switching determined by anomalous Hall effect ($\Delta R/\Delta
R_{\text{AHE}}$) is about twice higher in W than Pt, while critical switching
current density in W is one order lower than in Pt-devices. The current
switching stability and training process is discussed in detail.",2007.02116v2
2021-01-18,The future large obliquity of Jupiter,"Aims: We aim to determine whether Jupiter's obliquity is bound to remain
exceptionally small in the Solar System, or if it could grow in the future and
reach values comparable to those of the other giant planets.
  Methods: The spin axis of Jupiter is subject to the gravitational torques
from its regular satellites and from the Sun. These torques evolve over time
due to the long-term variations of its orbit and to the migration of its
satellites. With numerical simulations, we explore the future evolution of
Jupiter's spin axis for different values of its moment of inertia and for
different migration rates of its satellites. Analytical formulas show the
location and properties of all relevant resonances.
  Results: Because of the migration of the Galilean satellites, Jupiter's
obliquity is currently increasing, as it adiabatically follows the drift of a
secular spin-orbit resonance with the nodal precession mode of Uranus. Using
the current estimates of the migration rate of the satellites, the obliquity of
Jupiter can reach values ranging from 6{\deg} to 37{\deg} after 5 Gyrs from
now, according to the precise value of its polar moment of inertia. A faster
migration for the satellites would produce a larger increase in obliquity, as
long as the drift remains adiabatic.
  Conclusions: Despite its peculiarly small current value, the obliquity of
Jupiter is no different from other obliquities in the Solar System: It is
equally sensitive to secular spin-orbit resonances and it will probably reach
comparable values in the future.",2101.06997v1
2021-11-23,Dynamics of ferrimagnetic skyrmionium driven by spin-orbit torque,"Magnetic skyrmionium is a skyrmion-like spin texture with nanoscale size and
high mobility. It is a topologically trivial but dynamically stable structure,
which can be used as a non-volatile information carrier for next-generation
spintronic storage and computing devices. Here, we study the dynamics of a
skyrmionium driven by the spin torque in a ferrimagnetic nanotrack. It is found
that the direction of motion is jointly determined by the internal
configuration of a skyrmionium and the spin polarization vector. Besides, the
deformation of a skyrmionium induced by the intrinsic skyrmion Hall effect
depends on both the magnitude of the driving force and the net angular
momentum. The ferrimagnetic skyrmionium is most robust at the angular momentum
compensation point, whose dynamics is quite similar to the skyrmionium in
antiferromagnet. The skyrmion Hall effect is perfectly prohibited, where it is
possible to observe the position of the skyrmionium by measuring the
magnetization. Furthermore, the current-induced dynamics of a ferrimagnetic
skyrmionium is compared with that of a ferromagnetic and antiferromagnetic
skyrmionium. We also make a comparison between the motion of a ferrimagnetic
skyrmionium and a skyrmion. Our results will open a new field of ferrimagnetic
skyrmioniums for future development of ferrimagnetic spintronics devices.",2111.11603v1
2022-05-13,Large-Area Intercalated 2D-Pb/Graphene Heterostructure as a Platform for Generating Spin-Orbit Torque,"A scalable platform to synthesize ultrathin heavy metals may enable high
efficiency charge-to-spin conversion for next-generation spintronics. Here we
report centimeter-scale synthesis of air-stable, epitaxially registered
monolayer Pb underneath bilayer graphene on SiC (0001) by confinement
heteroepitaxy (CHet). Diffraction, spectroscopy, and microscopy reveal
CHet-based Pb intercalation predominantly exhibits a mottled hexagonal
superstructure due to an ordered network of Frenkel-Kontorova-like domain
walls. The system's air stability enables ex-situ spin torque ferromagnetic
resonance (ST-FMR) measurements that demonstrate charge-to-spin conversion in
graphene/Pb/ferromagnet heterostructures with a 1.5x increase in the effective
field ratio compared to control samples.",2205.06859v3
2022-10-17,Does the gamma-ray binary LS I +61°303 harbor a magnetar?,"The high-mass X-ray binary LS I +61{\deg}303 is also cataloged as a gamma-ray
binary as a result of frequent outbursts at TeV photon energies. The system has
released two soft-gamma flares in the past, suggesting a magnetar
interpretation for the compact primary. This inference has recently gained
significant traction following the discovery of transient radio pulses,
detected in some orbital phases from the system, as the measured rotation and
tentative spin-down rates imply a polar magnetic field strength of $B_p \gtrsim
10^{14}\,\mbox{G}$ if the star is decelerating via magnetic dipole braking. In
this paper, we scrutinize magnetic field estimates for the primary in LS I
+61{\deg}303 by analyzing the compatibility of available data with the system's
accretion dynamics, spin evolution, age limits, gamma-ray emissions, and radio
pulsar activation. We find that the neutron star's age and spin evolution are
theoretically difficult to reconcile unless a strong propeller torque is in
operation. This torque could be responsible for the bulk of even the maximum
allowed spin-down, potentially weakening the inferred magnetic field by more
than an order of magnitude.",2210.09471v2
2023-04-19,Deep Learning Illuminates Spin and Lattice Interaction in Magnetic Materials,"Atomistic simulations hold significant value in clarifying crucial phenomena
such as phase transitions and energy transport in materials science. Their
success stems from the presence of potential energy functions capable of
accurately depicting the relationship between system energy and lattice
changes. In magnetic materials, two atomic scale degrees of freedom come into
play: the lattice and the spin. However, accurately tracing the simultaneous
evolution of both lattice and spin in magnetic materials at an atomic scale is
a substantial challenge. This is largely due to the complexity involved in
depicting the interaction energy precisely, and its influence on lattice and
spin-driving forces, such as atomic force and magnetic torque, which continues
to be a daunting task in computational science. Addressing this deficit, we
present DeepSPIN, a versatile approach that generates high-precision predictive
models of energy, atomic forces, and magnetic torque in magnetic systems. This
is achieved by integrating first-principles calculations of magnetic excited
states with deep learning techniques via active learning. We thoroughly explore
the methodology, accuracy, and scalability of our proposed model in this paper.
Our technique adeptly connects first-principles computations and atomic-scale
simulations of magnetic materials. This synergy presents opportunities to
utilize these calculations in devising and tackling theoretical and practical
obstacles concerning magnetic materials.",2304.09606v3
2023-05-29,Spin current generation from an epitaxial tungsten dioxide WO$_{2}$,"We report on efficient spin current generation at room temperature in rutile
type WO$_{2}$ grown on Al$_{2}$O$_{3}$(0001) substrate. The optimal WO$_{2}$
film has (010)-oriented monoclinically distorted rutile structure with metallic
conductivity due to 5$\it{d}$$^2$ electrons, as characterized by x-ray
diffraction, electronic transport, and x-ray photoelectron spectroscopy. By
conducting harmonic Hall measurement in Ni$_{81}$Fe$_{19}$/WO$_{2}$ bilayer, we
estimate two symmetries of the spin-orbit torque (SOT), i.e., dampinglike (DL)
and fieldlike ones to find that the former is larger than the latter. By
comparison with the Ni$_{81}$Fe$_{19}$/W control sample, the observed DL SOT
efficiency $\xi$$_{DL}$ of WO$_{2}$ (+0.174) is about two thirds of that of W
(-0.281) in magnitude, with a striking difference in their signs. The magnitude
of the $\xi$$_{DL}$ of WO$_{2}$ exhibits comparable value to those of widely
reported Pt and Ta, and Ir oxide IrO$_{2}$. The positive sign of the
$\xi$$_{DL}$ of WO$_{2}$ can be explained by the preceding theoretical study
based on the 4$\it{d}$ oxides. These results highlight that the epitaxial
WO$_{2}$ offers a great opportunity of rutile oxides with spintronic
functionalities, leading to future spin-orbit torque-controlled devices.",2305.17887v3
2023-06-09,Giant Hall Switching by Surface-State-Mediated Spin-Orbit Torque in a Hard Ferromagnetic Topological Insulator,"Topological insulators (TI) and magnetic topological insulators (MTI) can
apply highly efficient spin-orbit torque (SOT) and manipulate the magnetization
with their unique topological surface states with ultra-high efficiency. Here,
we demonstrate efficient SOT switching of a hard MTI, V-doped (Bi,Sb)2Te3
(VBST) with a large coercive field that can prevent the influence of an
external magnetic field. A giant switched anomalous Hall resistance of 9.2
$k\Omega$ is realized, among the largest of all SOT systems. The SOT switching
current density can be reduced to $2.8\times10^5 A/cm^2$. Moreover, as the
Fermi level is moved away from the Dirac point by both gate and composition
tuning, VBST exhibits a transition from edge-state-mediated to
surface-state-mediated transport, thus enhancing the SOT effective field to
$1.56\pm 0.12 T/ (10^6 A/cm^2)$ and the interfacial charge-to-spin conversion
efficiency to $3.9\pm 0.3 nm^{-1}$ (nominal spin Hall angle to $23.2\pm 1.8$).
The findings establish VBST as an extraordinary candidate for energy-efficient
magnetic memory devices.",2306.05603v2
2023-12-01,Large enhancement of spin-orbit torques under a MHz modulation due to phonon-magnon coupling,"The discovery of spin-orbit torques (SOTs) generated through the spin Hall or
Rashba effects provides an alternative write approach for magnetic
random-access memory (MRAM), igniting the development of spin-orbitronics in
recent years. Quantitative characterization of SOTs highly relies on the
SOT-driven ferromagnetic resonance (ST-FMR), where a modulated microwave
current is used to generate ac SOTs and the modulation-frequency is usually
less than 100 kHz (the limit of conventional lock-in amplifiers). Here we have
investigated the SOT of typical SOT material/ferromagnet bilayers in an
extended modulation-frequency range, up to MHz, by developing the ST-FMR
measurement. Remarkably, we found that the measured SOTs are enhanced about
three times in the MHz range, which cannot be explained according to present
SOT theory. We attribute the enhancement of SOT to additional magnon
excitations due to phonon-magnon coupling, which is also reflected in the
slight changes of resonant field and linewidth in the acquired ST-FMR spectra,
corresponding to the modifications of effective magnetization and damping
constant, respectively. Our results indicate that the write current of SOT-MRAM
may be reduced with the assistant of phonon-magnon coupling.",2401.02967v1
2006-04-13,The White Dwarf in AE Aqr Brakes Harder,"Taking advantage of the very precise de Jager et al. optical white dwarf
orbit and spin ephemerides; ASCA, XMMN, and Chandra X-ray observations spread
over 10 yrs; and a cumulative 27 yr baseline, we have found that in recent
years the white dwarf in AE Aqr is spinning down at a rate that is slightly
faster than predicted by the de Jager et al. spin ephemeris. At the present
time, the observed period evolution is consistent with either a cubic term in
the spin ephemeris with Pdouble_dot = 3.46(56)E-19 per d, which is inconsistent
in sign and magnitude with magnetic-dipole radiation losses, or an additional
quadratic term with Pdot = 2.0(1.0)E-15 d/d, which is consistent with a modest
increase in the accretion torques spinning down the white dwarf. Regular
monitoring, in the optical, ultraviolet, and/or X-rays, is required to track
the evolution of the spin period of the white dwarf in AE Aqr.",0604314v1
2004-08-02,Electric generation of spin in crystals with reduced symmetry,"We propose a simple way of evaluating the bulk spin generation of an
arbitrary crystal with a known band structure in the strong spin-orbit coupling
limit. We show that, in the presence of an electric field, there exists an
intrinsic torque term which gives rise to a nonzero spin generation rate. Using
methods similar to those of recent experiments which measure spin polarization
in semiconductors, this spin generation rate should be experimentally
observable. The wide applicability of this effect is emphasized by explicit
consideration of a range of examples: bulk wurtzite and strained zincblende
(n-GaAs) lattices, as well as quantum well heterojunction systems.",0408020v2
2001-02-26,True energy-momentum tensors are unique. Electrodynamics spin tensor is not zero,"A true energy-momentum tensor is unique and does not admit an addition of a
term. The true electrodynamics' energy-momentum tensor is the Maxwell-Minkowski
tensor. It cannot be got with the Lagrange formalism. The canonical
energy-momentum and spin tensors are out of all relation to the physical
reality. The true electrodynamics' spin tensor is not equal to a zero. So,
electrodynamics' ponderomotive action comprises a force from the Maxwell stress
tensor and a torque from the spin tensor. A gauge non-invariant expression for
the spin tensor is presented and is used for a consideration of a circularly
polarized standing wave. A circularly polarized light beam carries a spin
angular momentum and an orbital angular momentum. So, we double the beams
angular momentum. The Beths experiment is considered.",0102084v2
2009-05-28,Hydrodynamic theory of coupled current and magnetization dynamics in spin-textured ferromagnets,"We develop the hydrodynamical theory of collinear spin currents coupled to
magnetization dynamics in metallic ferromagnets. The collective spin density
couples to the spin current through a U(1) Berry-phase gauge field determined
by the local texture and dynamics of the magnetization. We determine
phenomenologically the dissipative corrections to the equation of motion for
the electronic current, which consist of a dissipative spin-motive force
generated by magnetization dynamics and a magnetic texture-dependent
resistivity tensor. The reciprocal dissipative, adiabatic spin torque on the
magnetic texture follows from the Onsager principle. We investigate the effects
of thermal fluctuations and find that electronic dynamics contribute to a
nonlocal Gilbert damping tensor in the Landau-Lifshitz-Gilbert equation for the
magnetization. Several simple examples, including magnetic vortices, helices,
and spirals, are analyzed in detail to demonstrate general principles.",0905.4544v2
2009-05-28,Resonant Nonlinear Damping of Quantized Spin Waves in Ferromagnetic Nanowires,"We use spin torque ferromagnetic resonance to measure the spectral properties
of dipole-exchange spin waves in permalloy nanowires. Our measurements reveal
that geometric confinement has a profound effect on the damping of spin waves
in the nanowire geometry. The damping parameter of the lowest-energy quantized
spin wave mode depends on applied magnetic field in a resonant way and exhibits
a maximum at a field that increases with decreasing nanowire width. This
enhancement of damping originates from a nonlinear resonant three-magnon
confluence process allowed at a particular bias field value determined by
quantization of the spin wave spectrum in the nanowire geometry.",0905.4699v2
2009-09-17,Experimental evidence of self-localized and propagating spin wave modes in obliquely magnetized current-driven nanocontacts,"Through detailed experimental studies of the angular dependence of spin wave
excitations in nanocontact-based spin-torque oscillators, we demonstrate that
two distinct spin wave modes can be excited, with different frequency,
threshold currents and frequency tuneability. Using analytical theory and
micromagnetic simulations we identify one mode as an exchange-dominated
propagating spin wave, and the other as a self-localized nonlinear spin wave
bullet. Wavelet-based analysis of the simulations indicates that the apparent
simultaneous excitation of both modes results from rapid mode hopping induced
by the Oersted field.",0909.3331v2
2011-04-27,Spin Density Waves and Domain Wall Interactions in Nanowires,"We investigated how the dynamics of a domain wall are affected by the
presence of spin density waves in a ferromagnetic wire. Domain walls and other
scattering centres can cause coherent spin density waves to propagate through a
wire when a current is applied. In some cases the spin torque due to these
scattered electrons can be enhanced such that it is on a par with the exchange
and anisotropy energies controlling the shape and dynamics of the domain wall.
In such a case we find that the spin density waves enhance the current induced
domain wall motion, allowing for domain wall motion with smaller current
pulses. Here we consider a system involving two domain walls and focus on how
the motion of the second domain wall is modified by the spin density waves
caused by the presence of the first domain wall.",1104.5175v1
2012-04-23,Signs of Magnetic Accretion in the X-ray Pulsar Binary GX 301-2,"Observations of the cyclotron resonance scattering feature in the X-ray
spectrum of GX 301-2 suggest that the surface field of the neutron star is
B_CRSF ~ 4 x 10^{12}G. The same value has been derived in modelling the rapid
spin-up episodes in terms of the Keplerian disk accretion scenario. However,
the spin-down rate observed during the spin-down trends significantly exceeds
the value expected in currently used spin-evolution scenarios. This indicates
that either the surface field of the star exceeds 50 x B_CRSF, or a currently
used accretion scenario is incomplete. We show that the above discrepancy can
be avoided if the accreting material is magnetized. The magnetic pressure in
the accretion flow increases more rapidly than its ram pressure and, under
certain conditions, significantly affects the accretion picture. The spin-down
torque applied to the neutron star in this case is larger than that evaluated
within a non-magnetized accretion scenario. We find that the observed spin
evolution of the pulsar can be explained in terms of the magnetically
controlled accretion flow scenario provided the surface field of the neutron
star is ~ B_CRSF.",1204.4975v1
2013-02-09,Current-driven dynamics of chiral ferromagnetic domain walls,"In most ferromagnets the magnetization rotates from one domain to the next
with no preferred handedness. However, broken inversion symmetry can lift the
chiral degeneracy, leading to topologically-rich spin textures such as
spin-spirals and skyrmions via the Dzyaloshinskii-Moriya interaction (DMI).
Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy
metal and an oxide, the DMI stabilizes chiral domain walls (DWs) whose spin
texture enables extremely efficient current-driven motion. We show that spin
torque from the spin Hall effect drives DWs in opposite directions in
Pt/CoFe/MgO and Ta/CoFe/MgO, which can be explained only if the DWs assume a
N\'eel configuration with left-handed chirality. We directly confirm the DW
chirality and rigidity by examining current-driven DW dynamics with magnetic
fields applied perpendicular and parallel to the spin spiral. This work
resolves the origin of controversial experimental results and highlights a new
path towards interfacial design of spintronic devices.",1302.2257v1
2013-02-19,Chirality Sensitive Domain Wall Motion in Spin-Orbit Coupled Ferromagnets,"Using the Lagrangian formalism, we solve analytically the equations of motion
for current-induced domain-wall dynamics in a ferromagnet with Rashba
spin-orbit coupling. An exact solution for the domain wall velocity is
provided, including the effect of non-equilibrium conduction electron
spin-density, Gilbert damping, and the Rashba interaction parameter. We
demonstrate explicitly that the influence of spin-orbit interaction can be
qualitatively different from the role of non-adiabatic spin-torque in the sense
that the former is sensitive to the chirality of the domain wall whereas the
latter is not: the domain wall velocity shows a reentrant behavior upon
changing the chirality of the domain wall. This could be used to experimentally
distinguish between the spin-orbit and non-adiabatic contribution to the wall
speed. A quantitative estimate for the attainable domain wall velocity is
given, based on an experimentally relevant set of parameters for the system.",1302.4744v1
2013-08-06,Chirality from interfacial spin-orbit coupling effects in magnetic bilayers,"As nanomagnetic devices scale to smaller sizes, spin-orbit coupling due to
the broken structural inversion symmetry at interfaces becomes increasingly
important. Here we study interfacial spin-orbit coupling effects in magnetic
bilayers using a simple Rashba model. The spin-orbit coupling introduces
chirality into the behavior of the electrons and through them into the
energetics of the magnetization. In the derived form of the magnetization
dynamics, all of the contributions that are linear in the spin-orbit coupling
follow from this chirality, considerably simplifying the analysis. For these
systems, an important consequence is a correlation between the
Dzyaloshinskii-Moriya interaction and the spin-orbit torque. We use this
correlation to analyze recent experiments.",1308.1198v2
2014-01-24,Wavenumber-dependent Gilbert damping in metallic ferromagnets,"New terms to the dynamical equation of magnetization motion, associated with
spin transport, have been reported over the past several years. Each newly
identified term is thought to possess both a real and an imaginary effective
field leading to fieldlike and dampinglike torques on magnetization. Here we
show that three metallic ferromagnets possess an imaginary effective-field term
which mirrors the well-known real effective-field term associated with exchange
in spin waves. Using perpendicular standing spin wave resonance between 2-26
GHz, we evaluate the magnitude of the finite-wavenumber ($k$) dependent Gilbert
damping $\alpha$ in three typical device ferromagnets, Ni$_{79}$Fe$_{21}$, Co,
and Co$_{40}$Fe$_{40}$B$_{20}$, and demonstrate for the first time the presence
of a $k^2$ term as $\Delta\alpha=\Delta\alpha_0+A_{k}\cdot k^2$ in all three
metals. We interpret the new term as the continuum analog of spin pumping,
predicted recently, and show that its magnitude, $A_{k}$=0.07-0.1 nm$^2$, is
consistent with transverse spin relaxation lengths as measured by conventional
(interlayer) spin pumping.",1401.6467v2
2015-11-25,Theory of Magnetic-Field-Induced Polarization Flop in Spin-Spiral Multiferroics,"The magnetic-field-induced 90-degree flop of ferroelectric polarization P in
a spin-spiral multiferroic material TbMnO3 is theoretically studied based on a
microscopic spin model. We find that the direction of the P-flop or the choice
of +Pa or -Pa after the flop is governed by magnetic torques produced by the
applied magnetic field H acting on the Mn spins and thus is selected in a
deterministic way, in contradistinction to the naively anticipated
probabilistic flop. This mechanism resolves a puzzle of the previously reported
memory effect in the P direction depending on the history of the magnetic-field
sweep, and enables controlled switching of multiferroic domains by externally
applied magnetic fields. Our Monte-Carlo analysis also uncovers that the
magnetic structure in the P||a phase under H||b is not a so-far anticipated
simple ab-plane spin cycloid but a conical spin structure.",1511.07960v1
2016-04-14,THz-driven ultrafast spin-lattice scattering in amorphous metallic ferromagnets,"We use single-cycle THz fields and the femtosecond magneto-optical Kerr
effect to respectively excite and probe the magnetization dynamics in two
thin-film ferromagnets with different lattice structure: crystalline Fe and
amorphous CoFeB. We observe Landau-Lifshitz-torque magnetization dynamics of
comparable magnitude in both systems, but only the amorphous sample shows
ultrafast demagnetization caused by the spin-lattice depolarization of the
THz-induced ultrafast spin current. Quantitative modelling shows that such
spin-lattice scattering events occur on similar time scales than the
conventional spin conserving electronic scattering ($\sim30$ fs). This is
significantly faster that optical laser-induced demagnetization. THz
conductivity measurements point towards the influence of lattice disorder in
amorphous CoFeB as the driving force for enhanced spin-lattice scattering.",1604.04077v1
2016-08-16,Exchange anisotropy as mechanism for spin-stripe formation in frustrated spin chains,"We investigate the spin-stripe mechanism responsible for the peculiar
nanometer modulation of the incommensurate magnetic order that emerges between
the vector-chiral and the spin-density-wave phase in the frustrated zigzag
spin-1/2 chain compound $\beta$-TeVO$_4$. A combination of magnetic-torque,
neutron-diffraction and spherical-neutron-polarimetry measurements is employed
to determine the complex magnetic structures of all three ordered phases. Based
on these results, we develop a simple phenomenological model, which exposes the
exchange anisotropy as the key ingredient for the spin-stripe formation in
frustrated spin systems.",1608.04495v2
2017-07-29,Experimental study of extrinsic spin Hall effect in CuPt alloy,"We have experimentally studied the effects on the spin Hall angle due to
systematic addition of Pt into the light metal Cu. We perform spin torque
ferromagnetic resonance measurements on Py/CuPt bilayer and find that as the Pt
concentration increases, the spin Hall angle of CuPt alloy increases. Moreover,
only 28% Pt in CuPt alloy can give rise to a spin Hall angle close to that of
Pt. We further extract the spin Hall resistivity of CuPt alloy for different Pt
concentrations and find that the contribution of skew scattering is larger for
lower Pt concentrations, while the side-jump contribution is larger for higher
Pt concentrations. From technological perspective, since the CuPt alloy can
sustain high processing temperatures and Cu is the most common metallization
element in the Si platform, it would be easier to integrate the CuPt alloy
based spintronic devices into existing Si fabrication technology.",1707.09525v1
2018-03-04,Spin hydrodynamics in amorphous magnets,"Spin superfluidity, i.e., coherent spin transport mediated by topologically
stable textures, is limited by parasitic anisotropies rooted in relativistic
interactions and spatial inhomogeneities. Since structural disorder in
amorphous magnets can average out the effect of these undesired couplings, we
propose this class of materials as platforms for superfluid spin transport. We
establish nonlinear equations describing the hydrodynamics of spin in
insulating amorphous magnets, where the currents are defined in terms of
coherent rotations of a noncollinear texture. Our theory includes dissipation
and nonequilibrium torques at the interface with metallic reservoirs. This
framework allows us to determine different regimes of coherent dynamics and
their salient features in nonlocal magneto-transport measurements. Our work
paves the way for future studies on macroscopic spin dynamics in materials with
frustrated interactions.",1803.01309v2
2018-09-27,Spin wave radiation from vortices in $^3$He-B,"We consider a vortex line in the B phase of superfluid $^3$He under uniformly
precessing magnetization. The magnetization exerts torque on the vortex,
causing its order parameter to oscillate. These oscillations generate spin
waves, which is analogous to an oscillating charge generating electromagnetic
radiation. The spin waves carry energy, causing dissipation in the system.
Solving the equations of spin dynamics, we calculate the energy dissipation
caused by spin wave radiation for arbitrary tipping angles of the magnetization
and directions of the magnetic field, and for both vortex types of $^3$He-B.
For the double-core vortex we also consider the anisotropy of the radiation and
the dependence of the dissipation on twisting of the half cores. The radiated
energy is compared with experiments in the mid-temperature range $T \sim 0.5
T_c$. The dependence of the calculated dissipation on several parameters is in
good agreement with the experiments. Combined with numerically calculated
vortex structure, the radiation theory produces the order of magnitude of the
experimental dissipation. The agreement with the experiments indicates that
spin wave radiation is the dominant dissipation mechanism for vortices in
superfluid $^3$He-B in the mid-temperature range.",1809.10484v1
2018-11-22,Magnetoelectric effects in superconductor/ferromagnet bilayers,"We demonstrate that the hybrid structures consisting of a superconducting
layer with an adjacent spin-textured ferromagnet demonstrate the variety of
equilibrium magnetoelectric effects originating from coupling between the
conduction electron spin and superconducting current. By deriving and solving
the generalized Usadel equation which takes into account the spin-filtering
effect we find that a supercurrent generates spin polarization in the
superconducting film which is non-coplanar with the local ferromagnetic moment.
The inverse magnetoelectric effect in such structures is shown to result in the
spontaneous phase difference across the magnetic topological defects such as a
domain wall and helical spin texture. The possibilities to obtain
dissipationless spin torques and detect domain wall motion through the
superconducting phase difference are discussed.",1811.09304v2
2017-05-26,Static and Dynamic Magnetic Properties of FeMn/Pt Multilayers,"Recently we have demonstrated the presence of spin-orbit toque in FeMn/Pt
multilayers which, in combination with the anisotropy field, is able to rotate
its magnetization consecutively from 0o to 360o without any external field.
Here, we report on an investigation of static and dynamic magnetic properties
of FeMn/Pt multilayers using combined techniques of magnetometry, ferromagnetic
resonance, inverse spin Hall effect and spin Hall magnetoresistance
measurements. The FeMn/Pt multilayer was found to exhibit ferromagnetic
properties, and its temperature dependence of saturation magnetization can be
fitted well using a phenomenological model by including a finite distribution
in Curie temperature due to subtle thickness variations across the multilayer
samples. The non-uniformity in static magnetic properties is also manifested in
the ferromagnetic resonance spectra, which typically exhibit a broad resonance
peak. A damping parameter of around 0.106 is derived from the frequency
dependence of ferromagnetic resonance linewidth, which is comparable to the
reported values for other types of Pt-based multilayers. Clear inverse spin
Hall signals and spin Hall magnetoresistance have been observed in all samples
below the Curie temperature, which corroborate the strong spin-orbit torque
effect observed previously.",1705.09423v1
2019-06-18,Anomalous spin-orbit field via Rashba-Edelstein effect at W/Pt interface,"We have studied spin-orbit (SO) field in Ni$_{80}$Fe$_{20}$(Py)/W/Pt trilayer
by means of spin-torque ferromagnetic resonance, and demonstrated that the W/Pt
interface generates an extra SO field acting on the Py layer. This
unprecedented field originates from the following three processes, 1) spin
accumulation at W/Pt interface via the Rashba-Edelstein effect, 2) diffusive
spin transport in the W layer, and 3) spin absorption into the Py layer through
accumulation at the Py/W interface. Our result means that we can create extra
SO field away from the ferromagnet/ metal interface and control its strength by
a combination of two different metals.",1906.07314v2
2018-04-20,Influence of the Hall-bar geometry on harmonic Hall voltage measurements of spin-orbit torques,"Harmonic Hall voltage measurements are a wide-spread quantitative technique
for the measurement of spin-orbit induced effective fields in heavy-metal /
ferromagnet heterostructures. In the vicinity of the voltage pickup lines in
the Hall bar, the current is inhomogeneous, which leads to a hitherto not
quantified reduction of the effective fields and derived quantities, such as
the spin Hall angle or the spin Hall conductivity. Here we present a thorough
analysis of the influence of the aspect ratio of the voltage pickup lines to
current channel widths on the apparent spin Hall angle. Experiments were
performed with Hall bars with a broad range of aspect ratios and a substantial
reduction of the apparent spin Hall angle is already seen in Hall crosses with
an aspect ratio of 1:1. Our experimental results are confirmed by
finite-element simulations of the current flow.",1804.07577v1
2019-03-06,Honeycomb rare-earth magnets with anisotropic exchange interactions,"We study the rare-earth magnets on a honeycomb lattice, and are particularly
interested in the experimental consequences of the highly anisotropic spin
interaction due to the spin-orbit entanglement. We perform a high-temperature
series expansion using a generic nearest-neighbor Hamiltonian with anisotropic
interactions, and obtain the heat capacity, the parallel and perpendicular spin
susceptibilities, and the magnetic torque coefficients. We further examine the
electron spin resonance linewidth as an important signature of the anisotropic
spin interactions. Due to the small interaction energy scale of the rare-earth
moments, it is experimentally feasible to realize the strong-field regime.
Therefore, we perform the spin-wave analysis and study the possibility of
topological magnons when a strong field is applied to the system. The
application and relevance to the rare-earth Kitaev materials are discussed.",1903.02530v3
2021-10-06,Anatomy of nanomagnetic switching at a 3D Topological Insulator PN junction,"A P-N junction engineered within a Dirac cone system acts as a gate tunable
angular filter based on Klein tunneling. For a 3D topological insulator with
substantial bandgap, such a filter can produce a charge-to-spin conversion due
to the dual effects of spin-momentum locking and momentum filtering. We analyze
how spins filtered at an in-plane topological insulator PN junction (TIPNJ)
interact with a nanomagnet, and argue that the intrinsic charge-to-spin
conversion does not translate to an external gain if the nanomagnet also acts
as the source contact. Regardless of the nanomagnet's position, the spin torque
generated on the TIPNJ is limited by the surface current density, which in turn
is limited by bulk band gap. {Using quantum kinetic models, we calculate the
spatially varying spin potential and quantify the localization of the current
vs applied bias}. Additionally, with the magnetodynamic simulation of a soft
nanomagnet, we show that the PN junction can offer a critical gate tunability
in the switching probability of the nanomagnet, with potential applications in
probabilistic neuromorphic computing.",2110.02641v2
2020-06-22,Absence of Spin Hall Magnetoresistance in Pt/(CoNi)n multilayers,"We systematically studied the magnetoresistance effect in a Pt/(CoNi)n
multilayer system with perpendicular magnetic anisotropy and the fcc (111)
texture. The angular dependence of magnetoresistance, including high-order
cosine terms, was observed in a plane perpendicular to the electrical current;
this was attributed to the geometrical-size effects caused by crystal symmetry,
the ordered arrangement of grains, and the anisotropic interface
magnetoresistance effect caused by the breaking of the symmetry at interfaces.
Based on the accuracy of our experimental results, the magnitude of spin Hall
magnetoresistance (SMR) in Pt/(CoNi)n was expected to be below
$1\times10^{-4}$. However, on evaluating the spin Hall angle of $\geq$ 0.07 for
Pt using spin-torque ferromagnetic resonance measurements, the theoretical
magnitude of SMR in our samples was estimated to exceed $7\times10^{-4}$. This
absence of SMR in the experimental results can be explained by the
Elliott-Yafet spin relaxation of itinerant electrons in the ferromagnetic
metal, which indicates that the boundary conditions of the spin current in the
heavy metal/ferromagnetic insulator may not be applicable to all-metallic
heterostructures.",2006.12029v1
2021-06-15,First-principles calculations on the spin anomalous Hall effect of ferromagnetic alloys,"The spin anomalous Hall effect (SAHE) in ferromagnetic metals, which can
generate spin-orbit torque to rotate the magnetization of another ferromagnetic
layer through a non-magnetic spacer in magnetic junctions, has attracted much
attention. We theoretically investigated the spin anomalous Hall conductivity
(SAHC) of the L1$_0$-type alloys $X$Pt($X$=Fe,Co,Ni) on the basis of
first-principles density functional theory and linear response theory. We found
that the SAHC of FePt is much smaller than the anomalous Hall conductivity
(AHC), leading to very small polarization for the anomalous Hall effect
$\zeta$=SAHC/AHC of around 0.1. On the other hand, the SAHC increases with
increasing number of valence electrons($N_{\rm v}$), and CoPt and NiPt show
relatively large values of $|\zeta|$, greater than 1. The negative contribution
of the spin-down-down component of AHC is the origin of the large SAHC and
$\zeta$ in CoPt and NiPt, which is due to the anti-bonding states of Pt around
the Fermi level in the minority-spin states.",2106.07993v2
2022-01-11,Giant Valley-Polarized Spin Splittings in Magnetized Janus Pt Dichalcogenides,"We reveal giant proximity-induced magnetism and valley-polarization effects
in Janus Pt dichalcogenides (such as SPtSe), when bound to the Europium oxide
(EuO) substrate. Using first-principles simulations, it is surprisingly found
that the charge redistribution, resulting from proximity with EuO, leads to the
formation of two K and K$^{'}$valleys in the conduction bands. Each of these
valleys displays its own spin polarization and a specific spin-texture dictated
by broken inversion and time-reversal symmetries, and valley-exchange and
Rashba splittings as large as hundreds of meV. This provides a platform for
exploring novel spin-valley physics in low-dimensional semiconductors, with
potential spin transport mechanisms such as spin-orbit torques much more
resilient to disorder and temperature effects.",2201.04106v1
2022-03-11,Rotational viscosity in spin resonance of hydrodynamic electrons,"In novel ultra-pure materials electrons can form a viscous fluid, which is
fundamentally different by its dynamics from the electron gas in ordinary
conductors with significant density of defects. The shape of the non-stationary
flow of such electron fluid is similar to the alternating flow of blood in
large-radius arteries [J. R. Womersley, J. Physiol. 127, 552 (1955)]. The
rotational viscosity effect is responsible for interconnection between the
dynamics of electron spins and flow inhomogeneities. In particular, it induces
the spin polarization of electrons in a curled flow via an internal spin-orbit
torque acting on electron spins. Here we show that this effect in an electron
fluid placed in a magnetic field leads to a correction to the ac sample
impedance, which has a resonance at the Larmor frequency of electrons. In this
way, via the electrically detected spin resonance the Womersley flow of an
electron fluid can be visualized and the rotational viscosity can be measured.",2203.06070v4
2022-06-01,Exceptional spin wave dynamics in an antiferromagnetic honeycomb lattice,"We theoretically investigate possible effects of electric current on the spin
wave dynamics for the N\'{e}el-type antiferromagnetic order in a honeycomb
lattice. Based on a general vector decomposition of the spin polarization of
conduction electrons, we find that there can exist reciprocal and nonreciprocal
terms in the current-induced torque acting on the local spins in the system.
Furthermore, we show that the reciprocal terms will cause the spin wave Doppler
effect, while the nonreciprocal terms can induce rich non-Hermitian topological
phenomena in the spin wave dynamics, including exceptional points, bulk Fermi
arc, non-Hermitian skin effect, etc. Our results indicate the capability to
manipulate non-Hermitian magnons in magnetic materials by electric current,
which could be important for both fundamental physics and technology
applications.",2206.00723v1
2022-09-17,Time-Reversal-Even Nonlinear Current Induced Spin Polarization,"We propose a time-reversal-even spin generation in second order of electric
fields, which dominates the current induced spin polarization in a wide class
of centrosymmetric nonmagnetic materials, and leads to a novel nonlinear
spin-orbit torque in magnets. We reveal a quantum origin of this effect from
the momentum space dipole of the anomalous spin polarizability.
First-principles calculations predict sizable spin generations in several
nonmagnetic hcp metals, in monolayer TiTe$_{2}$, and in ferromagnetic monolayer
MnSe$_{2}$, which can be detected in experiment. Our work opens up the broad
vista of nonlinear spintronics in both nonmagnetic and magnetic systems.",2209.08364v1
2022-11-07,Interaction of gapless spin waves and a domain wall in an easy-cone ferromagnet,"We theoretically study the interaction of spin waves and a domain wall in a
quasi-one-dimensional easy-cone ferromagnet. The gapless spin waves on top of a
domain wall are found to exhibit finite reflection in contrast to the
well-known perfect transmission of gapful spin waves in easy-axis magnets.
Based on the obtained scattering properties, we study the thermal-magnon-driven
dynamics of a domain wall subjected to a thermal bias within the
Landau-B\""uttiker formalism, where transmitted magnons are shown to exert the
magnonic torque on the domain wall and thereby drive it with the velocity
linear to the applied thermal bias. The peculiar gapless nature of spin waves
in easy-cone magnets enables the thermally-driven domain-wall motion even at
low temperatures, differing from the easy-axis case where the domain-wall
velocity is exponentially suppressed at low temperatures. Our work suggests
that easy-cone magnets can serve as a useful platform to study the interaction
of gapless spin waves and nonlinear excitations and thereby realize
low-temperature magnon-related phenomena.",2211.03331v1
2023-02-20,Motion of a spinning particle under the conservative piece of the self-force is Hamiltonian to first order in mass and spin,"We consider the motion of a point particle with spin in a stationary
spacetime. We define, following Witzany (2019) and later Ramond (2022), a
twelve dimensional Hamiltonian dynamical system whose orbits coincide with the
solutions of the Mathisson-Papapetrou-Dixon equations of motion with the
Tulczyjew-Dixon spin supplementary condition, to linear order in spin. We then
perturb this system by adding the conservative pieces of the leading order
gravitational self-force and self-torque sourced by the particle's mass and
spin. We show that this perturbed system is Hamiltonian and derive expressions
for the Hamiltonian function and symplectic form. This result extends our
previous result for spinless point particles.",2302.10233v2
2023-04-05,Control of 4-magnon-scattering in a magnonic waveguide by pure spin current,"We use a pure spin current originating from the spin Hall effect to generate
a spin-orbit torque (SOT) strongly reducing the effective damping in an
adjacent ferromagnet. Due to additional microwave excitation, large spin-wave
amplitudes are achieved exceeding the threshold for 4-magnon scattering, thus
resulting in additional spin-wave signals at discrete frequencies. Two or more
modes are generated below and above the directly pumped mode with equal
frequency spacing. It is shown how this nonlinear process can be controlled in
magnonic waveguides by the applied dc current and the microwave pumping power.
The sudden onset of the nonlinear effect after exceeding the thresholds can be
interpreted as spiking phenomenom which makes the effect potentially
interesting for neuromorphic computing applications. Moreover, we investigated
this effect under microwave frequency and external field variation. The
appearance of the additional modes was investigated in the time-domain
revealing a time delay between the directly excited and the simultaneously
generated nonlinear modes. Furthermore, spatially resolved measurements show
different spatial decay lengths of the directly pumped mode and nonlinear
modes.",2304.02708v1
2023-05-05,A new microscopic representation of the spin dynamics in quantum systems with the Coulomb exchange interactions,"There is a version of the Landau-Lifshitz equation that takes into account
the Coulomb exchange interactions between atoms, expressed by the term
$\sim\bm{s}\times\triangle\bm{s}$. On the other hand, ions in the magnetic
materials have several valence electrons on the $d$-shell, and therefore the
Hamiltonian of many-electron atoms with spins $S>1$ should include a
biquadratic exchange interaction. We first propose a new fundamental
microscopic derivation of the spin density evolution equation with an explicit
form of biquadratic exchange interaction using the method of many-particle
quantum hydrodynamics. The equation for the evolution of the spin density is
obtained from the many-particle Schrodinger-Pauli equation and contains the
contributions of the usual Coulomb exchange interaction and the biquadratic
exchange. Furthermore, the derived biquadratic exchange torque in the spin
density evolution equation is proportional to the nematic tensor for the medium
of atoms with spin $\textit{S = 1}$. Our method may be very attractive for
further studies of the magnetoelectric effect in multiferroics.",2305.03826v3
1999-11-13,Measurement of Longitudinal Spin Transfer to Lambda Hyperons in Deep-Inelastic Lepton Scattering,"Spin transfer in deep-inelastic Lambda electroproduction has been studied
with the HERMES detector using the 27.6 GeV polarized positron beam in the HERA
storage ring. For an average fractional energy transfer <z> = 0.45, the
longitudinal spin transfer from the virtual photon to the Lambda has been
extracted. The spin transfer along the Lambda momentum direction is found to be
0.11 +/- 0.17 (stat) +/- 0.03 (sys); similar values are found for other
possible choices for the longitudinal spin direction of the Lambda. This result
is the most precise value obtained to date from deep-inelastic scattering with
charged lepton beams, and is sensitive to polarized up quark fragmentation to
hyperon states. The experimental result is found to be in general agreement
with various models of the Lambda spin content, and is consistent with the
assumption of helicity conservation in the fragmentation process.",9911017v3
2017-09-05,Dry-transferred CVD graphene for inverted spin valve devices,"Integrating high-mobility graphene grown by chemical vapor deposition (CVD)
into spin transport devices is one of the key tasks in graphene spintronics. We
use a van der Waals pickup technique to transfer CVD graphene by hexagonal
boron nitride (hBN) from the copper growth substrate onto predefined Co/MgO
electrodes to build inverted spin valve devices. Two approaches are presented:
(i) a process where the CVD-graphene/hBN stack is first patterned into a bar
and then transferred by a second larger hBN crystal onto spin valve electrodes
and (ii) a direct transfer of a CVD-graphene/hBN stack. We report record high
spin lifetimes in CVD graphene of up to 1.75 ns at room temperature. Overall,
the performances of our devices are comparable to devices fabricated from
exfoliated graphene also revealing nanosecond spin lifetimes. We expect that
our dry transfer methods pave the way towards more advanced device geometries
not only for spintronic applications but also for CVD-graphene-based
nanoelectronic devices in general where patterning of the CVD graphene is
required prior to the assembly of final van der Waals heterostructures.",1709.01364v1
2020-09-20,Non-classical spin transfer effects in an antiferromagnet,"We simulate scattering of electrons by a chain of antiferromagnetically
coupled quantum Heisenberg spins, to analyze spin-transfer effects not
described by the classical models of magnetism. Our simulations demonstrate
efficient excitation of dynamical states that would be forbidden by the
semiclassical symmetries, such as generation of multiple magnetic excitation
quanta by a single electron. Furthermore, quantum interference of spin
wavefunctions enables generation of magnetization dynamics with amplitudes
exceeding the transferred magnetic moment. The efficiency of excitation is
almost independent of the electron spin polarization, and is governed mainly by
the transfer of energy. Non-classical spin transfer may thus enable efficient
electronic control of antiferromagnets not limited by the classical
constraints.",2009.09540v2
1994-08-19,Spin dynamics of the doped t-J model,"We present a new method for studying the low energy excitations in finite
cluster systems and apply it to clarify the nature of the low energy spin
excitations in the moderately doped t-J model.
  We find that the character of the low energy spin excitations changes within
the Brillouin zone, with the dominant excitation for momentum transfer (pi,pi)
being a spin wave-like collective mode.
  Spin excitations with momentum transfer different from (pi,pi) have
particle-hole character. We give an explicit construction of a low energy
collective spin mode in a system with `almost broken symmetry' and demonstrate
its validity by explicit numerical check.",9408057v1
2003-07-31,Transfer of magnetization by spin injection between both interfaces of a Ni nanowire,"Magnetization switching provoked by spin-injection is studied in Ni nanowires
of various size and morphology. The response of the magnetization to the
spin-injection is studied as a function of the amplitude of the current, the
temperature, and the symmetry of the interfaces. The amplitude of the response
of the magnetization to spin-injection is a decreasing function of the
temperature, does not depend on the current sign, and occurs only in the case
of asymmetric interfaces. It is shown that the spin-injection does not act on
small magnetic inhomogeneities inside the layer. Some consequences in terms of
longitudinal spin-transfer are discussed.",0307763v1
2003-08-13,Nuclear spin relaxation probed by a single quantum dot,"We present measurements on nuclear spin relaxation probed by a single quantum
dot in a high-mobility electron gas. Current passing through the dot leads to a
spin transfer from the electronic to the nuclear spin system. Applying electron
spin resonance the transfer mechanism can directly be tuned. Additionally, the
dependence of nuclear spin relaxation on the dot gate voltage is observed. We
find electron-nuclear relaxation times of the order of 10 minutes.",0308243v1
2015-04-02,Direct Observation of Large Amplitude Spin Excitations Localized in a Spin-Transfer Nanocontact,"We report the direct observation of large amplitude spin-excitations
localized in a spin-transfer nanocontact using scanning transmission x-ray
microscopy. Experiments were conducted using a nanocontact to an ultrathin
ferromagnetic multilayer with perpendicular magnetic anisotropy. Element
resolved x-ray magnetic circular dichroism images show an abrupt onset of spin
excitations at a threshold current that are localized beneath the nanocontact,
with average spin precession cone angles of 25{\deg} at the contact center. The
results strongly suggest that we have observed a localized magnetic soliton.",1504.00488v1
2015-12-08,Spin-Directed Momentum Transfers in SIDIS Baryon Production,"The measurement of transverse single-spin asymmetries for baryon production
in the target fragmentation region of semi-inclusive deep-inelastic scattering
(SIDIS), can produce important insight into those nonperturbative aspects of
QCD directly associated with confinement and with the dynamical breaking of
chiral symmetry. We discuss here, interns of spin-directed momentum transfers,
the powerful quantum field-theoretical constraints on the spin-orbit dynamics
underlying these transverse spin observables. The spin-directed momentum
shifts, originating either in the target nucleon or in the QCD jets produced in
the deep inelastic scattering process, represent significant quantum
entanglement effects connecting information from current fragmentation with
observables in target fragmentation.",1512.02557v1
2022-06-17,Wrapping corrections for long range spin chains,"The long range spin chains play an important role in the gauge/string
duality. The aim of this paper is to generalize the recently introduced
transfer matrices of integrable medium range spin chains to long range models.
These transfer matrices define a large set of conserved charges for every
length of the spin chain. These charges agree with the original definition of
long range spin chains for infinite length. However, our construction works for
every length, providing the definition of integrable finite size long range
spin chains whose spectrum already contains the wrapping corrections.",2206.08679v3
2010-09-16,Evolution of Spin Direction of Accreting Magnetic Protostars and Spin-Orbit Misalignment in Exoplanetary Systems: II. Warped Discs,"Magnetic interactions between a protostar and its accretion disc tend to
induce warping in the disc and produce secular changes in the stellar spin
direction, so that the spin axis may not always be perpendicular to the disc.
This may help explain the recently observed spin-orbit misalignment in a number
of exoplanetary systems. We study the dynamics of warped protoplanetary discs
under the combined effects of magnetic warping/precession torques and internal
stresses in the disc, including viscous damping of warps and propagation of
bending waves. We show that when the outer disc axis is misaligned with the
stellar spin axis, the disc evolves towards a warped steady-state on a
timescale that depends on the disc viscosity or the bending wave propagation
speed, but in all cases is much shorter than the timescale for the spin
evolution (of order of a million years). Moreover, for the most likely physical
parameters characterizing magnetic protostars, circumstellar discs and their
interactions, the steady-state disc has a rather small warp, such that the
whole disc lies approximately in a single plane determined by the outer disc
boundary conditions, although more extreme parameters may give rise to larger
disc warps. In agreement with our recent analysis (Lai et al. 2010) based on
flat discs, we find that the back-reaction magnetic torques of the slightly
warped disc on the star can either align the stellar spin axis with the disc
axis or push it towards misalignment, depending on the parameters of the
star-disc system. This implies that newly formed planetary systems may have a
range of inclination angles between the stellar spin axis and the symmetry axis
of the planetary orbits.",1009.3233v2
2022-08-10,Enhancement of Spin-Charge Conversion Efficiency for Co$_{3}$Sn$_{2}$S$_{2}$ across Transition from Paramagnetic to Ferromagnetic Phase,"Co$_{3}$Sn$_{2}$S$_{2}$ (CSS) is one of the shandite compounds and becomes a
magnetic Weyl semimetal candidate below the ferromagnetic phase transition
temperature ($\textit{T}_\textrm{C}$). In this paper, we investigate the
temperature ($\textit{T}$) dependence of conversion between charge current and
spin current for the CSS thin film by measuring the spin-torque ferromagnetic
resonance (ST-FMR) for the trilayer consisting of CSS / Cu / CoFeB. Above
$\textit{T}_\textrm{C}$ ~ 170 K, the CSS / Cu / CoFeB trilayer exhibits the
clear ST-FMR signal coming from the spin Hall effect in the paramagnetic CSS
and the anisotropic magnetoresistance (AMR) of CoFeB. Below
$\textit{T}_\textrm{C}$, on the other hand, it is found that the ST-FMR signal
involves the dc voltages ($\textit{V}_\textrm{dc}$) not only through the AMR
but also through the giant magnetoresistance (GMR). Thus, the resistance
changes coming from both AMR and GMR should be taken into account to correctly
understand the characteristic field angular dependence of
$\textit{V}_\textrm{dc}$. The spin Hall torque generated from the ferromagnetic
CSS, which possesses the same symmetry as that for spin Hall effect, dominantly
acts on the magnetization of CoFeB. A definite increase in the spin-charge
conversion efficiency ($\xi$) is observed at $\textit{T}$ <
$\textit{T}_\textrm{C}$, indicating that the phase transition to the
ferromagnetic CSS promotes the highly efficient spin-charge conversion. In
addition, our theoretical calculation shows the increase in spin Hall
conductivity with the emergence of magnetic moment at $\textit{T}$ <
$\textit{T}_\textrm{C}$, which is consistent with the experimental observation.",2208.05394v1
2008-10-05,Current-Induced Dynamics in Almost Symmetric Magnetic Nanopillars,"Magnetic nanodevices usually include a free layer whose configuration can be
changed by spin-polarized current via the spin transfer effect, and a fixed
reference layer. Here, we demonstrate that the roles of the free and the
reference layers interchange over a small range of their relative thicknesses.
Precession of both layers can be induced by spin transfer in symmetric devices,
but the dynamics of one of the layers is rapidly suppressed in asymmetric
devices. We interpret our results in terms of the dynamical coupling between
magnetic layers due to spin transfer.",0810.0863v1
2009-02-14,Quantum-state transfer on spin-chain channels with random imperfection,"We investigate the quantum-state transfer on spin-chian channels with random
imperfections.Through combining the advantages of two known schemes, the
dual-rail spin-chain channels[9] and the particular ihhomogenous spin-chain
channel[10], we propose a protocol that can avoid the quantum noises introduced
by many unnecessary measurements and can enhance the anti-decoherence ability.
The results show that our protocol is more efficient to transfer an arbitrary
quantum state than the original one. In particular, we discuss the effects of
couplings fluctuations and imperfect initialization on both of the improved
scheme and original one.",0902.2432v3
2015-09-08,Probing Scalar Coupling Differences via Long-Lived Singlet States,"We probe small scalar coupling differences via the coherent interactions
between two nuclear spin singlet states in organic molecules. We show that the
spin-lock induced crossing (SLIC) technique enables the coherent transfer of
singlet order between one spin pair and another. The transfer is mediated by
the difference in cis and trans vicinal J couplings among the spins. By
measuring the transfer rate, we calculate a J coupling difference of $8 \pm 2$
mHz in phenylalanine-glycine-glycine and $2.57 \pm 0.04$ Hz in glutamate. We
also characterize a coherence between two singlet states in glutamate, which
may enable the creation of a long-lived quantum memory.",1509.02240v1
2003-03-06,Iron K alpha line profiles and the inner boundary condition of accretion flows,"Recent X-ray observations have shown evidence for exceptionally broad and
skewed iron K alpha emission lines from several accreting black hole systems.
The lines are assumed to be due to fluorescence of the accretion disk
illuminated by a surrounding corona and require a steep emissivity profile
increasing in to the innermost radius. This appears to question both standard
accretion disc theory and the zero torque assumption for the inner boundary
condition, both of which predict a much less extreme profile. Instead it argues
that a torque may be present due to magnetic coupling with matter in the
plunging region or even to the spinning black hole itself. Discussion so far
has centered on the torque acting on the disc. However the crucial determinant
of the iron line profile is the radial variation of the power radiated in the
corona. Here we study the effects of different inner boundary conditions on the
coronal emissivity and on the profiles of the observable Fe K alpha lines. We
argue that in the extreme case where a prominent highly redshifted component of
the iron line is detected, requiring a steep emissivity profile in the
innermost part and a flatter one outside, energy from the gas plunging into the
black hole is being fed directly to the corona.",0303143v1
2007-09-14,Magnetically Torqued Thin Accretion Disks,"We compute the properties of a geometrically thin, steady accretion disk
surrounding a central rotating, magnetized star. The magnetosphere is assumed
to entrain the disk over a wide range of radii. The model is simplified in that
we adopt two (alternate) ad hoc, but plausible, expressions for the azimuthal
component of the magnetic field as a function of radial distance. We find a
solution for the angular velocity profile tending to corotation close to the
central star, and smoothly matching a Keplerian curve at a radius where the
viscous stress vanishes. The value of this ''transition'' radius is nearly the
same for both of our adopted B-field models. We then solve analytically for the
torques on the central star and for the disk luminosity due to gravity and
magnetic torques. When expressed in a dimensionless form, the resulting
quantities depend on one parameter alone, the ratio of the transition radius to
the corotation radius. For rapid rotators, the accretion disk may be powered
mostly by spin-down of the central star. These results are independent of the
viscosity prescription in the disk. We also solve for the disk structure for
the special case of an optically thick alpha disk. Our results are applicable
to a range of astrophysical systems including accreting neutron stars,
intermediate polar cataclysmic variables, and T Tauri systems.",0709.2361v2
2011-03-02,Mechanics of extended masses in general relativity,"The ""external"" or ""bulk"" motion of extended bodies is studied in general
relativity. Compact material objects of essentially arbitrary shape, spin,
internal composition, and velocity are allowed as long as there is no direct
(non-gravitational) contact with other sources of stress-energy. Physically
reasonable linear and angular momenta are proposed for such bodies and exact
equations describing their evolution are derived. Changes in the momenta depend
on a certain ""effective metric"" that is closely related to a non-perturbative
generalization of the Detweiler-Whiting R-field originally introduced in the
self-force literature. If the effective metric inside a self-gravitating body
can be adequately approximated by an appropriate power series, the
instantaneous gravitational force and torque exerted on it is shown to be
identical to the force and torque exerted on an appropriate test body moving in
the effective metric. This result holds to all multipole orders. The only
instantaneous effect of a body's self-field is to finitely renormalize the
""bare"" multipole moments of its stress-energy tensor. The MiSaTaQuWa expression
for the gravitational self-force is recovered as a simple application. A
gravitational self-torque is obtained as well. Lastly, it is shown that the
effective metric in which objects appear to move is approximately a solution to
the vacuum Einstein equation if the physical metric is an approximate solution
to Einstein's equation linearized about a vacuum background.",1103.0543v4
2011-06-14,Tidal Warping of Be Star Decretion Discs,"Rapidly rotating Be stars are observed as shell stars when the decretion disc
is viewed edge on. Transitions between the two implies that the discs may be
warped and precessing. Type II X-ray outbursts are thought to occur when the
warped disc interacts with the fast stellar wind. We suggest that tides from a
misaligned companion neutron star can cause the observed effects. We make
numerical models of a Be star decretion disc in which the spin of the Be star
is misaligned with the orbital axis of a neutron star companion. Tidal torques
from the neutron star truncate the disc at a radius small enough that the
neutron star orbit does not intersect the disc unless the eccentricity or
misalignment is very large. A magnetic torque from the Be star that is largest
at the equator, where the rotation is fastest, is approximated by an inner
boundary condition. There are large oscillations in the mass and inclination of
the disc as it moves towards a steady state. These large variations may explain
the observed changes from Be star to Be shell star and vice-versa and also the
Type II X-ray outbursts. We find the tidal timescale on which the disc warps,
precesses and reaches a steady state to be around a year up to a few hundred
years. If present, the oscillations in mass and disc inclination occur on a
fraction of this timescale depending on the orbital parameters of the binary.
The timescales associated with the tidal torque for observed Be star binaries
suggest that these effects are important in all but the longest period
binaries.",1106.2591v1
2014-10-31,The effect of magnetic topology on thermally-driven winds: towards a general formulation of the braking law,"Stellar winds are thought to be the main process responsible for the spin
down of main-sequence stars. The extraction of angular momentum by a magnetized
wind has been studied for decades, leading to several formulations for the
resulting torque. However, previous studies generally consider simple dipole or
split monopole stellar magnetic topologies. Here we consider in addition to a
dipolar stellar magnetic field, both quadrupolar and octupolar configurations,
while also varying the rotation rate and the magnetic field strength. 60
simulations made with a 2.5D, cylindrical and axisymmetric set-up and computed
with the PLUTO code were used to find torque formulations for each topology. We
further succeed to give a unique law that fits the data for every topology by
formulating the torque in terms of the amount of open magnetic flux in the
wind. We also show that our formulation can be applied to even more realistic
magnetic topologies, with examples of the Sun in its minimum and maximum phase
as observed at the Wilcox Solar Observatory, and of a young K-star (TYC-0486-
4943-1) whose topology has been obtained by Zeeman-Doppler Imaging (ZDI).",1410.8746v2
2014-10-31,The influence of the magnetic topology on the braking of sun-like stars,"Stellar winds are thought to be the main process responsible for the spin
down of main-sequence stars. The extraction of angular momentum by a magnetized
wind has been studied for decades, leading to several formulations for the
resulting torque. However, previous studies generally consider simple dipole or
split monopole stellar magnetic topologies. Here we consider in addition to a
dipolar stellar magnetic field, both quadrupolar and octupolar configurations,
while also varying the rotation rate and the magnetic field strength. 60
simulations made with a 2.5D, cylindrical and axisymmetric set-up and computed
with the PLUTO code were used to find torque formulations for each topology. We
further succeed to give a unique law that fits the data for every topology by
formulating the torque in terms of the amount of open magnetic flux in the
wind. We also show that our formulation can be applied to even more realistic
magnetic topologies, with examples of the Sun in its minimum and maximum phase
as observed at the Wilcox Solar Observatory, and of a young K-star
(TYC-0486-4943-1) whose topology has been obtained by Zeeman-Doppler Imaging
(ZDI). Ideas about how to compute the open flux from ZDI Maps are discussed.",1410.8759v1
2017-07-13,The Effect of Combined Magnetic Geometries on Thermally Driven Winds I: Interaction of Dipolar and Quadrupolar Fields,"Cool stars with outer convective envelopes are observed to have magnetic
fields with a variety of geometries, which on large scales are dominated by a
combination of the lowest order fields such as the dipole, quadrupole and
octupole modes. Magnetised stellar wind outflows are primarily responsible for
the loss of angular momentum from these objects during the main sequence.
Previous works have shown the reduced effectiveness of the stellar wind braking
mechanism with increasingly complex, but singular, magnetic field geometries.
In this paper, we quantify the impact of mixed dipolar and quadrupolar fields
on the spin-down torque using 50 MHD simulations with mixed field, along with
10 of each pure geometries. The simulated winds include a wide range of
magnetic field strength and reside in the slow-rotator regime. We find that the
stellar wind braking torque from our combined geometry cases are well described
by a broken power law behaviour, where the torque scaling with field strength
can be predicted by the dipole component alone or the quadrupolar scaling
utilising the total field strength. The simulation results can be scaled and
apply to all main-sequence cool stars. For Solar parameters, the lowest order
component of the field (dipole in this paper) is the most significant in
determining the angular momentum loss.",1707.04078v1
2019-11-01,Electric-Field Control of the Interlayer Exchange Coupling for Magnetization Switching,"We propose an electric-field-controlled mechanism for magnetization switching
assisted solely by the interlayer-exchange coupling (IEC) between the fixed and
the free magnets, which are separated by two oxide barriers sandwiching a
spacer material known for exhibiting large IEC. The basic idea relies on the
formation of a quantum-well (QW) within the spacer material and controlling the
transmission coefficient across the structure with an electric-field via the
resonant tunneling phenomena. Using non-equilibrium Green's function (NEGF)
method, we show that the structure can exhibit a bias-dependent oscillatory IEC
that can switch the free magnet to have either a parallel or an antiparallel
configuration with respect to the fixed magnet, depending on the sign of the
IEC. Such bi-directional switching can be achieved with the same voltage
polarity but different magnitudes. With proper choice of the spacer material,
the current in the structure can be significantly reduced. Due to the
conservative nature of the exerted torque by the IEC, the switching threshold
of the proposed mechanism is decoupled from the switching speed, while the
conventional spin-torque devices exhibit a trade-off due to the
non-conservative nature of the exerted torque.",1911.00183v1
2018-12-22,"Electrically Driven, Optically Levitated Microscopic Rotors","We report on the electrically driven rotation of $2.4~\mu$m-radius, optically
levitated dielectric microspheres. Electric fields are used to apply torques to
a microsphere's permanent electric dipole moment, while angular displacement is
measured by detecting the change in polarization state of light transmitted
through the microsphere (MS). This technique enables greater control than
previously achieved with purely optical means because the direction and
magnitude of the electric torque can be set arbitrarily. We measure the
spin-down of a microsphere released from a rotating electric field, the
harmonic motion of the dipole relative to the instantaneous direction of the
field, and the phase lag between the driving electric field and the dipole
moment of the MS due to drag from residual gas. We also observe the gyroscopic
precession of the MS when the axis of rotation of the driving field and the
angular momentum of the microsphere are orthogonal. These observations are in
quantitative agreement with the equation of motion. The control offered by the
electrical drive enables precise measurements of microsphere properties and
torque as well as a method for addressing the direction of angular momentum for
an optically levitated particle.",1812.09625v3
2020-11-09,Search for Continuous Gravitational Waves from Scorpius X-1 in LIGO O2 Data,"We present the results of a search in LIGO O2 public data for continuous
gravitational waves from the neutron star in the low-mass X-ray binary Scorpius
X-1. We search for signals with $\approx$ constant frequency in the range
40-180 Hz. Thanks to the efficiency of our search pipeline we can use a long
coherence time and achieve unprecedented sensitivity, significantly improving
on existing results. This is the first search that has been able to probe
gravitational wave amplitudes that could balance the accretion torque at the
neutron star radius. Our search excludes emission at this level between 67.5 Hz
and 131.5 Hz, for an inclination angle $44^\circ \pm 6^\circ$ derived from
radio observations (Fomalont et al. 2001), and assuming that the spin axis is
perpendicular to the orbital plane. If the torque arm is $\approx $ 26 km -- a
conservative estimate of the \alfven\ radius -- our results are more
constraining than the indirect limit across the band. This allows us to exclude
certain mass-radius combinations and to place upper limits on the strength of
the star's magnetic field. We also correct a mistake that appears in the
literature in the equation that gives the gravitational wave amplitude at the
torque balance (Abbott et al. 2017b, 2019a) and we re-interpret the associated
latest LIGO/Virgo results in light of this.",2011.04414v1
2020-10-29,Alignment and rotational disruption of dust,"We reveal a deep connection between alignment of dust grains by RAdiative
torques (RATs) and MEchanical Torques (METs) and rotational disruption of
grains introduced by Hoang et al. (2019). The disruption of grains happens if
they have attractor points corresponding to high angular momentum (high-J). We
introduce {\it fast disruption} for grains that are directly driven to the
high-J attractor on a timescale of spin-up, and {\it slow disruption} for
grains that are first moved to the low-J attractor and gradually transported to
the high-J attractor by gas collisions. The enhancement of grain magnetic
susceptibility via iron inclusions expands the parameter space for high-J
attractors and increases percentage of grains experiencing the disruption. The
increase in the magnitude of RATs or METs can increase the efficiency of fast
disruption, but counter-intuitively, decreases the effect of slow disruption by
forcing grains towards low-J attractors, whereas the increase in gas density
accelerates disruption by faster transporting grains to the high-J attractor.
We also show that disruption induced by RATs and METs depends on the angle
between the magnetic field and the anisotropic flow. We find that pinwheel
torques can increase the efficiency of {\it fast disruption} but may decrease
the efficiency of {\it slow disruption} by delaying the transport of grains
from the low-J to high-J attractors via gas collisions. The selective nature of
the rotational disruption opens a possibility of observational testing of grain
composition as well as physical processes of grain alignment.",2010.15301v2
2021-03-11,The alignment of interstellar dust grains: thermal flipping and the Davis-Greenstein mechanism,"Interstellar dust grains are non-spherical and, in some environments,
partially aligned along the direction of the interstellar magnetic field.
Numerous alignment theories have been proposed, all of which examine the grain
rotational dynamics. In 1999, Lazarian & Draine introduced the important
concept of thermal flipping, in which internal relaxation processes induce the
grain body to flip while its angular momentum remains fixed. Through detailed
numerical simulations, we study the role of thermal flipping on the grain
dynamics during periods of relatively slow rotation, known as `crossovers', for
the special case of a spheroidal grain with a non-uniform mass distribution.
Lazarian & Draine proposed that rapid flipping during a crossover would lead to
`thermal trapping', in which a systematic torque, fixed relative to the grain
body, would time average to zero, delaying spin-up to larger rotational speeds.
We find that the time-averaged systematic torque is not zero during the
crossover and that thermal trapping is not prevalent. As an application, we
examine whether the classic Davis-Greenstein alignment mechanism is viable, for
grains residing in the cold neutral medium and lacking superparamagnetic
inclusions. We find that Davis-Greenstein alignment is not hindered by thermal
trapping, but argue that it is, nevertheless, too inefficient to yield the
alignment of large grains responsible for optical and infrared starlight
polarization. Davis-Greenstein alignment of small grains could potentially
contribute to the observed ultraviolet polarization. The theoretical and
computational tools developed here can also be applied to analyses of alignment
via radiative torques and rotational disruption of grains.",2103.06951v1
2021-06-24,Reduction of turbulent skin-friction drag by passively rotating discs,"A turbulent channel flow modified by the motion of discs that are free to
rotate under the action of wall turbulence is studied numerically. The
Navier-Stokes equations are coupled nonlinearly with the dynamical equation of
the disc motion, which synthesizes the fluid-flow boundary conditions and is
driven by the torque exerted by the wall-shear stress. We consider discs that
are fully exposed to the fluid and discs for which only half of the surface
interfaces the fluid. The disc motion is thwarted by the fluid torque in the
housing cavity and by the torque of the ball bearing that supports the disc.
For the full discs, no drag reduction occurs because of the small angular
velocities. The most energetic disc response occurs for disc diameters that are
comparable with the spanwise spacing of the low-speed streaks. A perturbation
analysis for small disc-tip velocities reveals that the two-way nonlinear
coupling has an intense attenuating effect on the disc response. The
reduced-order results show excellent agreement with the nonlinear results for
large diameters. The half discs rotate with a finite angular velocity, leading
to large reduction of the turbulence activity and of the skin-friction drag
over the spinning portion of the discs, while the maximum drag reduction over
the entire walls is 5.6%. The dependence of the drag reduction on the wall-slip
velocity and the spatial distribution of the wall-shear stress qualitatively
match results based on the only available experimental data.",2106.12824v1
2022-04-26,GRMHD simulations of accreting neutron stars I: nonrotating dipoles,"We study the general-relativistic dynamics of matter being accreted onto and
ejected by a magnetised and nonrotating neutron star. The dynamics is followed
in the framework of fully general relativistic magnetohydrodynamics (GRMHD)
within the ideal-MHD limit and in two spatial dimensions. More specifically,
making use of the numerical code BHAC, we follow the evolution of a
geometrically thick matter torus driven into accretion by the development of a
magnetorotational instability. By making use of a number of simulations in
which we vary the strength of the stellar dipolar magnetic field, we can
determine self-consistently the location of the magnetospheric (or Alfv\'en)
radius $r_{\rm msph}$ and study how it depends on the magnetic moment $\mu$ and
on the accretion rate. Overall, we recover the analytic Newtonian scaling
relation, i.e. $r_{\rm msph} \propto B^{4/7}$, but also find that the
dependence on the accretion rate is very weak. Furthermore, we find that the
material torque correlates linearly with the mass-accretion rate, although both
of them exhibit rapid fluctuations. Interestingly, the total torque fluctuates
drastically in strong magnetic field simulations and these unsteady torques
observed in the simulations could be associated with the spin fluctuations
observed in X-ray pulsars.",2204.12275v2
2005-11-14,The proximity of Mercury's spin to Cassini state 1,"In determining Mercury's core structure from its rotational properties, the
value of the normalized moment of inertia, $C/MR^2$, from the location of
Cassini 1 is crucial. If Mercury's spin axis occupies Cassini state 1, its
position defines the location of the state. The spin might be displaced from
the Cassini state if the spin is unable to follow the changes in the state
position induced by the variations in the orbital parameters and the geometry
of the solar system. The spin axis is expected to follow the Cassini state for
orbit variations with time scales long compared to the 1000 year precession
period of the spin about the Cassini state because the solid angle swept out by
the spin axis as it precesses is an adiabatic invariant. Short period
variations in the orbital elements of small amplitude should cause
displacements that are commensurate with the amplitudes of the short period
terms. By following simultaneously the spin position and the Cassini state
position during long time scale orbital variations over past 3 million years
(Quinn {\it et al.}, 1991) and short time scale variations from JPL Ephemeris
DE 408 (Standish, 2005) we show that the spin axis will remain within one
arcsec of the Cassini state after it is brought there by dissipative torques.
We thus expect Mercury's spin to occupy Cassini state 1 well within the
uncertainties for both radar and spacecraft measurements, with correspondingly
tight constraints on $C/MR^2$.",0511419v1
2005-02-09,"SU(2)xU(1) unified theory for charge, orbit and spin currents","Spin and charge currents in systems with Rashba or Dresselhaus spin-orbit
couplings are formulated in a unified version of four-dimensional
SU(2)$\times$U(1) gauge theory, with U(1) the Maxwell field and SU(2) the
Yang-Mills field. While the bare spin current is non-conserved, it is
compensated by a contribution from the SU(2) gauge field, which gives rise to a
spin torque in the spin transport, consistent with the semi-classical theory of
Culcer et al. Orbit current is shown to be non-conserved in the presence of
electromagnetic fields. Similar to the Maxwell field inducing forces on charge
and charge current, we derive forces acting on spin and spin current induced by
the Yang Mills fields such as the Rashba and Dresselhaus fields and the sheer
strain field. The spin density and spin current may be considered as a source
generating Yang-Mills field in certain condensed matter systems.",0502231v4
2018-10-18,Generalized Nonequilibrium Quantum Transport of Spin and Pseudospins: Entanglements and Topological Phases,"General nonequilibrium quantum transport equations are derived for a coupled
system of charge carriers, Dirac spin, isospin (or valley spin), and
pseudospin, such as either one of the band, layer, impurity, and boundary
pseudospins. Limiting cases are obtained for one, two or three different kinds
of spin ocurring in a system. We show that a characteristic integer number
$N_{s}$ determines the formal form of spin quantum transport equations,
irrespective of the type of spins or pseudospins, as well as the maximal
entanglement entropy. The results may shed a new perspective on the mechanism
leading to zero modes and chiral/helical edge states in topological insulators,
integer quantum Hall effect topological insulator (QHE-TI), quantum spin Hall
effect topological insulator (QSHE-TI) and Kondo topological insulator
(Kondo-TI). It also shed new light in the observed competing weak localization
and antilocalization in spin-dependent quantum transport measurements. In
particular, a novel mechanism of localization and delocalization, as well as
the new mechanism leading to the onset of superconductivity in bilayer systems
seems to emerge naturally from torque entanglements in nonequilibrium quantum
transport equations of spin and pseudospins. Moreover, the general results may
serve as a foundation for engineering approximations of the quantum transport
simulations of spintronic devices based on graphene and other 2-D materials
such as the transition metal dichalcogenides (TMDs), as well as based on
topological materials exhibiting quantum spin Hall effects. The extension of
the formalism to spincaloritronics and pseudo-spincaloritronics is
straightforward.",1810.08121v3
2019-06-04,And yet it flips: connecting galactic spin and the cosmic web,"We study the spin alignment of galaxies and halos with respect to filaments
and walls of the cosmic web, identified with DisPerSE, using the SIMBA
simulation from z=0-2. Massive halos' spins are oriented perpendicularly to
their closest filament's axis and walls, while low mass halos tend to have
their spins parallel to filaments and in the plane of walls. A similar
mass-dependent spin flip is found for galaxies, albeit with a weaker signal
particularly at low mass and low-z, suggesting that galaxies' spins retain
memory of their larger-scale environment. Low-z star-forming and
rotation-dominated galaxies tend to have spins parallel to nearby filaments,
while quiescent and dispersion-dominated galaxies show preferentially
perpendicular orientation; the star formation trend can be fully explained by
the stellar mass correlation, but the morphology trend cannot. There is a
strong dependence on HI mass, such that high-HI galaxies tend to have parallel
spins while low-HI galaxies are perpendicular, which persists even when
matching samples in stellar mass, suggesting that HI content traces anisotropic
infall more faithfully than the stellar component. Finally, at fixed stellar
mass, the strength of spin alignments correlates with the filament's density,
with parallel alignment for galaxies in high density environments. These
findings are consistent with conditional tidal torque theory, and highlight a
significant correlation between galactic spin and the larger scale tides that
are important e.g. for interpreting weak lensing studies. SIMBA allows us to
rule out numerical grid locking as the cause of previously-seen low mass
alignment.",1906.01623v1
2021-08-14,Dissipation-relaxation dynamics of a spin-1/2 particle with a Rashba-type spin-orbit coupling in an ohmic heat bath,"Spin-orbit coupling (SOC), which is inherent to a Dirac particle that moves
under the influence of electromagnetic fields, manifests itself in a variety of
physical systems including non-relativistic ones. For instance, it plays an
essential role in spintronics developed in the past few decades, particularly
by controlling spin current generation and relaxation. In the present work, by
using an extended Caldeira-Leggett model, we elucidate how the interplay
between spin relaxation and momentum dissipation of an open system of a single
spin-$1/2$ particle with a Rashba type SOC is induced by the interactions with
a spinless, three-dimensional environment. Staring from the path integral
formulation for the reduced density matrix of the system, we have derived a set
of coupled nonlinear equations that consists of a quasi-classical Langevin
equation for the momentum with a frictional term and a spin precession
equation. The spin precesses around the effective magnetic field generated by
both the SOC and the frictional term. It is found from analytical and numerical
solutions to these equations that a spin torque effect included in the
effective magnetic field causes a spin relaxation and that the spin and
momentum orientations after a long time evolution are largely controlled by the
Rashba coupling strength. Such a spin relaxation mechanism is qualitatively
different from, e.g., the one encountered in semiconductors where essentially
no momentum dissipation occurs due to the Pauli blocking.",2108.06465v1
2019-08-21,Tunable room-temperature spin galvanic and spin Hall effects in van der Waals heterostructures,"Spin-orbit coupling stands as a powerful tool to interconvert charge and spin
currents and to manipulate the magnetization of magnetic materials through the
spin torque phenomena. However, despite the diversity of existing bulk
materials and the recent advent of interfacial and low-dimensional effects,
control of the interconvertion at room-temperature remains elusive. Here, we
unequivocally demonstrate strongly enhanced room-temperature spin-to-charge
(StC) conversion in graphene driven by the proximity of a semiconducting
transition metal dichalcogenide(WS2). By performing spin precession experiments
in properly designed Hall bars, we separate the contributions of the spin Hall
and the spin galvanic effects. Remarkably, their corresponding conversion
effiencies can be tailored by electrostatic gating in magnitude and sign,
peaking nearby the charge neutrality point with a magnitude that is comparable
to the largest efficiencies reported to date. Such an unprecedented
electric-field tunability provides a new building block for spin generation
free from magnetic materials and for ultra-compact magnetic memory
technologies.",1908.07868v1
2020-05-12,"Origin and Large Enhancement of Large Spin Hall Angle in Weyl Semimetals LaAl$X$ ($X$=Si, Ge)","We study the origin of the strong spin Hall effect (SHE) in a recently
discovered family of Weyl semimetals, LaAl$X$ ($X$=Si, Ge) via a
first-principles approach with maximally localized Wannier functions. We show
that the strong intrinsic SHE in LaAl$X$ originates from the multiple slight
anticrossings of nodal lines and points near $E_F$ due to their high mirror
symmetry and large spin-orbit interaction. It is further found that both
electrical and thermal means can enhance the spin Hall conductivity
($\sigma_{SH}$). However, the former also increases the electrical conductivity
($\sigma_{c}$), while the latter decreases it. As a result, the independent
tuning of $\sigma_{SH}$ and $\sigma_{c}$ by thermal means can enhance the spin
Hall angle (proportional to $\frac{\sigma_{SH}}{\sigma_{c}}$), a figure of
merit of charge-to-spin current interconversion of spin-orbit torque devices.
The underlying physics of such independent changes of the spin Hall and
electrical conductivity by thermal means is revealed through the band-resolved
and $k$-resolved spin Berry curvature. Our finding offers a new way in the
search of high SHA materials for room-temperature spin-orbitronics
applications.",2005.05560v3
2020-10-07,High-throughput techniques for measuring the spin Hall effect,"The spin Hall effect in heavy-metal thin films is routinely employed to
convert charge currents into transverse spin currents and can be used to exert
torque on adjacent ferromagnets. Conversely, the inverse spin Hall effect is
frequently used to detect spin currents by charge currents in spintronic
devices up to the terahertz frequency range. Numerous techniques to measure the
spin Hall effect or its inverse were introduced, most of which require
extensive sample preparation by multi-step lithography. To enable rapid
screening of materials in terms of charge-to-spin conversion, suitable
high-throughput methods for measuring the spin Hall angle are required. Here,
we compare two lithography-free techniques, terahertz emission spectroscopy and
broadband ferromagnetic resonance, to standard harmonic Hall measurements and
theoretical predictions using the binary-alloy series Au$_x$Pt$_{1-x}$ as
benchmark system. Despite being highly complementary, we find that all three
techniques yield a spin Hall angle with approximately the same $x$~dependence,
which is also consistent with first-principles calculations. Quantitative
discrepancies are discussed in terms of magnetization orientation and
interfacial spin-memory loss.",2010.03543v1
2023-07-10,Spin transport properties of spinel vanadate-based heterostructures,"Spin-orbit coupling and breaking of inversion symmetry are necessary
ingredients to enable a pure spin current-based manipulation of the
magnetization via the spin-orbit torque effect. Currently, magnetic insulator
oxides with non-dissipative characteristics are being explored. When combined
with non-magnetic heavy metals, known for their large spin-orbit coupling, they
offer promising potential for energy-efficient spin-orbitronics applications.
The intrinsic electronic correlations characterizing those strongly correlated
oxides hold the promises to add extra control-knobs to the desired efficient
spin-wave propagation and abrupt magnetization switching phenomena. Spinel
vanadate FeV2O4 (FVO) exhibits several structural phase transitions which are
accompanied by an intricate interplay of magnetic, charge and orbital
orderings. When grown as a thin film onto SrTiO3, the compressive strain state
induces a perpendicular magnetic anisotropy, making FVO-based heterostructures
desirable for spin-orbitronics applications. In this study, we have optimised
the deposition of stoichiometric and epitaxial Pt/FVO heterostructures by
Pulsed Laser Deposition and examined their spin-related phenomena. From
angle-dependent magnetotransport measurements, we observed both Anisotropic
Magnetoresistance (AMR) and Spin Hall Magnetoresistance (SMR) effects. Our
findings show the SMR component as the primary contributor to the overall
magnetoresistance, whose high value of 0.12% is only comparable to properly
optimized oxide-based systems.",2307.04389v1
1997-12-11,Mixing and Transfer of Elements by Interactions and Mergers,"Galaxy interactions produce strong torques that generate radial gas flows.
There are two opposite tendencies of these flows, regarding abundance
gradients: homogeneization and gradient flattening, and enhanced star formation
in the center, and gradient steepening. Mechanisms to create abundance
gradients are discussed, and comparison with observations is detailed,
concerning spirals (such as collisional rings, starbursts..) or ellipticals
(formed or not in mergers). A review of N-body simulations predictions, taken
into account star formation, is also presented.",9712147v1
2000-06-23,Outflow from YSO and Angular Momentum Transfer,"Dynamical contraction of a slowly-rotating magnetized cloud is studied using
the magnetohydrodynamical (MHD) simulations. In the isothermal stage ($n \la
n_{\rm A} \sim 10^{10}{\rm cm}^{-3}$), the cloud evolves similarly to that
expected from Larson-Penston self-similar solution and experiences the run-away
collapse. However, after the central density exceeds $\sim n_{\rm A}$, an
accretion disk is formed around the adiabatic core. Just outside the core,
outflow is ejected by the effect of magnetic torque (magnetocentrifugal wind).
Since $\sim$ 10% of the mass is ejected with almost all the angular momentum,
the specific angular momentum of the protostellar core reduces to that observed
in main-sequence stars.",0006329v1
2012-10-25,Fluctuation-Electromagnetic Interaction between Rotating Nanoparticles. 2.Relativistic Theory,"We study the fluctuation electromagnetic interaction in a system of two
rotating electrically neutral nonmagnetic particles with allowance for
relativistic retardation effect. The particles are assumed to have different
temperatures being embedded into a heated vacuum background (photon gas).
Closed expressions for the free energy, frictional torque and the rate of heat
transfer are derived and compared to the known static results and those in the
electrostatic limit without retardation.",1210.6957v1
2020-02-29,"Atomic cluster expansion of scalar, vectorial and tensorial properties and including magnetism and charge transfer","The atomic cluster expansion (Drautz, Phys. Rev. B 99, 014104 (2019)) is
extended in two ways, the modelling of vectorial and tensorial atomic
properties and the inclusion of atomic degrees of freedom in addition to the
positions of the atoms. In particular, atomic species, magnetic moments and
charges are attached to the atomic positions and an atomic cluster expansion
that includes the different degrees of freedom on equal footing is derived.
Expressions for the efficient evaluation of forces and torques are given.
Relations to other methods are discussed.",2003.00221v1
2004-05-18,Thermal ratchet effects in ferrofluids,"Rotational Brownian motion of colloidal magnetic particles in ferrofluids
under the influence of an oscillating external magnetic field is investigated.
It is shown that for a suitable time dependence of the magnetic field, a noise
induced rotation of the ferromagnetic particles due to rectification of thermal
fluctuations takes place. Via viscous coupling, the associated angular momentum
is transferred from the magnetic nano-particles to the carrier liquid and can
then be measured as macroscopic torque on the fluid sample. A thorough
theoretical analysis of the effect in terms of symmetry considerations,
analytical approximations, and numerical solutions is given which is in
accordance with recent experimental findings.",0405393v1
2023-09-20,Rotating Alfvén waves in rotating plasmas,"Angular momentum coupling between a rotating magnetized plasma and torsional
Alfv\'en waves carrying orbital angular momentum (OAM) is examined. It is not
only demonstrated that rotation is the source of Fresnel-Faraday rotation - or
orbital Faraday rotation effects - for OAM carrying Alfv\'en waves, but also
that angular momentum from an OAM carrying Alfv\'en wave can be transferred to
a rotating plasma through the inverse process. For the direct process, the
transverse structure angular rotation frequency is derived by considering the
dispersion relation for modes with opposite OAM content. For the inverse
process, the torque exerted on the plasma is derived as a function of wave and
plasma parameters.",2309.11200v1
2023-11-27,Cavity optomechanics in ultrastrong light matter coupling regime: Self-alignment and collective rotation mediated by Casimir torque,"We theoretically consider an ensemble of quantum dimers placed inside an
optical cavity. We predict two effects: first, an exchange of angular momentum
between the dimers mediated by the emission and re-absorption of the cavity
photons leads to the alignment of dimers. Furthermore, the optical angular
momentum of the vacuum state of the chiral cavity is transferred to the
ensemble of dimers which leads to the synchronous rotation of the dimers at
certain levels of light-matter coupling strength.",2311.15969v2
2019-06-04,Torque equilibrium spin wave theory study of anisotropy and Dzyaloshinskii-Moriya interaction effects on the indirect K$-$ edge RIXS spectrum of a triangular lattice antiferromagnet,"We apply the recently formulated torque equilibrium spin wave theory (TESWT)
to compute the $1/S$-order interacting $K$ -edge bimagnon resonant inelastic
x-ray scattering (RIXS) spectra of an anisotropic triangular lattice
antiferromagnet with Dzyaloshinskii-Moriya (DM) interaction. We extend the
interacting torque equilibrium formalism, incorporating the effects of DM
interaction, to appropriately account for the zero-point quantum fluctuation
that manifests as the emergence of spin Casimir effect in a noncollinear spin
spiral state. Using inelastic neutron scattering data from Cs$_2$CuCl$_4$ we
fit the 1/S corrected TESWT dispersion to extract exchange and DM interaction
parameters. We use these new fit coefficients alongside other relevant model
parameters to investigate, compare, and contrast the effects of spatial
anisotropy and DM interaction on the RIXS spectra at various points across the
magnetic Brillouin zone. We highlight the key features of the bi- and trimagnon
RIXS spectrum at the two inequivalent rotonlike points, $M(0,2 \pi/\sqrt{3})$
and $M^{\prime}(\pi,\pi/\sqrt{3})$, whose behavior is quite different from an
isotropic triangular lattice system. While the roton RIXS spectrum at the $M$
point undergoes a spectral downshift with increasing anisotropy, the peak at
the $M^\prime$ location loses its spectral strength without any shift. With the
inclusion of DM interaction the spiral phase is more stable and the peak at
both $M$ and $M^\prime$ point exhibits a spectral upshift. Our calculation
offers a practical example of how to calculate interacting RIXS spectra in a
non-collinear quantum magnet using TESWT. Our findings provide an opportunity
to experimentally test the predictions of interacting TESWT formalism using
RIXS, a spectroscopic method currently in vogue.",1906.01619v3
2001-02-13,Resonant electron transmission through a finite quantum spin chain,"Electron transport in a finite one dimensional quantum spin chain (with
ferromagnetic exchange) is studied within an $s-d$ exchange Hamiltonian. Spin
transfer coefficients strongly depend on the sign of the $s-d$ exchange
constant. For a ferromagnetic coupling, they exhibit a novel resonant pattern,
reflecting the salient features of the combined electron-spin system. Spin-flip
processes are inelastic and feasible at finite voltage or at finite
temperature.",0102236v1
2023-03-08,Spin selective charge recombination in chiral donor-bridge-acceptor triads,"In this paper we outline a physically motivated framework for describing
spin-selective recombination processes in chiral systems, from which we derive
spin-selective reaction operators for recombination reactions of
donor-bridge-acceptor molecules, where the electron transfer is mediated by
chirality and spin-orbit coupling. In general the recombination process is
selective only for spin-coherence between singlet and triplet states, and it is
not in general selective for spin polarisation. We find that spin polarisation
selectivity only arises in hopping mediated electron transfer. We describe how
this effective spin-polarisation selectivity is a consequence of
spin-polarisation generated transiently in the intermediate state. The
recombination process also augments the coherent spin dynamics of the charge
separated state, which is found to have a significant effect on recombination
dynamics and to destroy any long-lived spin polarisation. Although we only
consider a simple donor-bridge-acceptor system, the framework we present here
can be straightforwardly extended to describe spin-selective recombination
processes in more complex systems.",2303.04742v1
2014-09-18,On the diversity of magnetic interactions in close-in star-planet systems,"Magnetic interactions between close-in planets and their host star can play
an important role in the secular orbital evolution of the planets, as well as
the rotational evolution of their host. As long as the planet orbits inside the
Alfv\'en surface of the stellar wind, the magnetic interaction between the star
and the planet can modify the wind properties and also lead to direct angular
momentum transfers between the two. We model these star-planet interactions
using compressible magneto-hydrodynamic (MHD) simulations, and quantify the
angular momentum transfers between the star, the planet, and the stellar wind.
We study the cases of magnetized and non-magnetized planets and vary the
orbital radius inside the Alfv\'en surface of the stellar wind. Based on a grid
of numerical simulations, we propose general scaling laws for the modification
of the stellar wind torque, for the torque between the star and the planet, and
for the planet migration associated with the star-planet magnetic interactions.
We show that when the coronal magnetic field is large enough and the star is
rotating sufficiently slowly, the effect of the magnetic star-planet
interaction is comparable to tidal effects and can lead to a rapid orbital
decay.",1409.5268v1
2007-02-21,Longitudinal Polarization of Lambda and anti-Lambda Hyperons in Lepton-Nucleon Deep-Inelastic Scattering,"We consider models for the spin transfers to $\Lambda$ and $\bar{\Lambda}$
hyperons produced in lepton-nucleon deep-inelastic scattering. We make
predictions for longitudinal $\Lambda$ and $\bar{\Lambda}$ spin transfers for
the COMPASS experiment and for HERA, and for the spin transfer to $\Lambda$
hyperons produced at JLAB. We demonstrate that accurate measurements of the
spin transfers to $\Lambda$ and $\bar{\Lambda}$ hyperons with COMPASS
kinematics have the potential to probe the intrinsic strangeness in the
nucleon. We show that a measurement of $\bar{\Lambda}$ polarisation could
provide a clean probe of the spin transfer from $\bar{s}$ quarks and provides a
new possibility to measure the antistrange quark distribution function. COMPASS
data in a domain of x that has not been studied previously will provide
valuable extra information to fix models for the nucleon spin structure. The
spin transfer to $\bar{\Lambda}$ hyperons, which could be measured by the
COMPASS experiment, would provide a new tool to distinguish between the SU(6)
and Burkardt-Jaffe (BJ) models for baryon spin structure. In the case of the
HERA electron-proton collider experiments with longitudinally-polarised
electrons, the separation between the target and current fragmentation
mechanisms is more clear. It provides a complementary probe of the strange
quark distribution and helps distinguish between the SU(6) and BJ models for
the $\Lambda$ and $\bar{\Lambda}$ spin structure. Finally, we show that the
spin transfer to $\Lambda$ hyperons measured in a JLAB experiment would be
dominated by the spin transfer of the intrinsic polarised-strangeness in the
remnant nucleon, providing an independent way to check our model predictions.",0702222v2
2015-06-22,Heat transport between antiferromagnetic insulators and normal metals,"Antiferromagnetic insulators can become active spintronics components by
controlling and detecting their dynamics via spin currents in adjacent metals.
This cross-talk occurs via spin-transfer and spin-pumping, phenomena that have
been predicted to be as strong in antiferromagnets as in ferromagnets. Here, we
demonstrate that a temperature gradient drives a significant heat flow from
magnons in antiferromagnetic insulators to electrons in adjacent normal metals.
The same coefficients as in the spin-transfer and spin-pumping processes also
determine the thermal conductance. However, in contrast to ferromagnets, the
heat is not transferred via a spin Seebeck effect which is absent in
antiferromagnetic insulator-normal metal systems. Instead, the heat is
transferred via a large staggered spin Seebeck effect.",1506.06705v1
2018-03-08,Competing spin transfer and dissipation at Co/Cu(001) interfaces on femtosecond timescales,"By combining interface-sensitive non-linear magneto-optical experiments with
femtosecond time resolution and ab-initio time-dependent density functional
theory, we show that optically excited spin dynamics at Co/Cu(001) interfaces
proceeds via spin-dependent charge transfer and backtransfer between Co and Cu.
This ultrafast spin transfer competes with dissipation of spin angular momentum
mediated by spin-orbit coupling already on sub 100 fs timescales. We thereby
identify the fundamental microscopic processes during laser-induced spin
transfer at a model interface for technologically relevant ferromagnetic
heterostructures.",1803.03090v3
2023-10-12,Optimising motion-induced spin transfer,"In this paper, the spin transfer between two ferromagnetic insulators is
studied. There is a narrow gap between the ferromagnetic insulators so that
they are weakly interacting with each other. One of the ferromagnetic
insulators is moving at a constant speed while the other is at rest; hence, the
system is out of equilibrium. In the presence of the shearing motion, the
interaction amplitude is periodically modulated at the Doppler frequency. A
unitary transformation allows us to regard the periodic modulation of the
interaction amplitude as an effective potential, which drives the spin
transfer. The amount of the spin current is controlled by the spectral overlap
and the carrier population difference between the two ferromagnetic media. If
the spectra of the two ferromagnets are moderately broadened, the overlap in
the spectral domain increases, enlarging the spin current. However, too much
broadening spoils the spectral overlap and, hence, the spin current. This
implies that there is an optimal condition for maximising the spin transfer.",2310.08200v2
2008-01-07,Magnetization reversal driven by spin-injection : a mesoscopic spin-transfer effect,"A mesoscopic description of spin-transfer effect is proposed, based on the
spin-injection mechanism occurring at the junction with a ferromagnet. The
effect of spin-injection is to modify locally, in the ferromagnetic
configuration space, the density of magnetic moments. The corresponding
gradient leads to a current-dependent diffusion process of the magnetization.
In order to describe this effect, the dynamics of the magnetization of a
ferromagnetic single domain is reconsidered in the framework of the
thermokinetic theory of mesoscopic systems. Assuming an Onsager
cross-coefficient that couples the currents, it is shown that spin-dependent
electric transport leads to a correction of the Landau-Lifshitz-Gilbert
equation of the ferromagnetic order parameter with supplementary diffusion
terms. The consequence of spin-injection in terms of activation process of the
ferromagnet is deduced, and the expressions of the effective energy barrier and
of the critical current are derived. Magnetic fluctuations are calculated: the
correction to the fluctuations is similar to that predicted for the activation.
These predictions are consistent with the measurements of spin-transfer
obtained in the activation regime and for ferromagnetic resonance under
spin-injection.",0801.1019v1
2010-11-23,Coherent state transfer between an electron- and nuclear spin in 15N@C60,"Electron spin qubits in molecular systems offer high reproducibility and the
ability to self assemble into larger architectures. However, interactions
between neighbouring qubits are 'always-on' and although the electron spin
coherence times can be several hundred microseconds, these are still much
shorter than typical times for nuclear spins. Here we implement an
electron-nuclear hybrid scheme which uses coherent transfer between electron
and nuclear spin degrees of freedom in order to both controllably turn on/off
dipolar interactions between neighbouring spins and benefit from the long
nuclear spin decoherence times (T2n). We transfer qubit states between the
electron and 15N nuclear spin in 15N@C60 with a two-way process fidelity of
88%, using a series of tuned microwave and radiofrequency pulses and measure a
nuclear spin coherence lifetime of over 100 ms.",1011.5157v2
2011-06-18,Electrical control of spin dynamics in finite one-dimensional systems,"We investigate the possibility of the electrical control of spin transfer in
monoatomic chains incorporating spin-impurities. Our theoretical framework is
the mixed quantum-classical (Ehrenfest) description of the spin dynamics, in
the spirit of the s-d-model, where the itinerant electrons are described by a
tight-binding model while localized spins are treated classically. Our main
focus is on the dynamical exchange interaction between two well-separated
spins. This can be quantified by the transfer of excitations in the form of
transverse spin oscillations. We systematically study the effect of an
electrostatic gate bias V_g on the interconnecting channel and we map out the
long-range dynamical spin transfer as a function of V_g. We identify regions of
V_g giving rise to significant amplification of the spin transmission at low
frequencies and relate this to the electronic structure of the channel.",1106.3687v1
2011-11-10,Electronic Pumping of Quasiequilibrium Bose-Einstein Condensed Magnons,"We theoretically investigate spin transfer between a system of
quasiequilibrated Bose-Einstein condensed magnons in an insulator in direct
contact with a conductor. While charge transfer is prohibited across the
interface, spin transport arises from the exchange coupling between insulator
and conductor spins. In normal insulator phase, spin transport is governed
solely by the presence of thermal and spin-diffusive gradients; the presence of
Bose-Einstein condensation (BEC), meanwhile, gives rise to a
temperature-independent condensate spin current. Depending on the thermodynamic
bias of the system, spin may flow in either direction across the interface,
engendering the possibility of a dynamical phase transition of magnons. We
discuss experimental feasibility of observing a BEC steady state (fomented by a
spin Seebeck effect), which is contrasted to the more familiar spin-transfer
induced classical instabilities.",1111.2382v2
2012-11-12,Dressed-State Polarization Transfer between Bright & Dark Spins in Diamond,"Under ambient conditions, spin impurities in solid-state systems are found in
thermally-mixed states and are optically ""dark"", i.e., the spin states cannot
be optically controlled. Nitrogen-vacancy (NV) centers in diamond are an
exception in that the electronic spin states are ""bright"", i.e., they can be
polarized by optical pumping, coherently manipulated with spin-resonance
techniques, and read out optically, all at room temperature. Here we
demonstrate a dressed-state, double-resonance scheme to transfer polarization
from bright NV electronic spins to dark substitutional-Nitrogen (P1) electronic
spins in diamond. This polarization-transfer mechanism could be used to cool a
mesoscopic bath of dark spins to near-zero temperature, thus providing a
resource for quantum information and sensing, and aiding studies of quantum
effects in many-body spin systems.",1211.2749v1
2011-12-02,"SXP 1062, a young Be X-ray binary pulsar with long spin period; Implications for the neutron star birth spin","(shortened) The SMC is ideally suited to investigating the recent star
formation history from X-ray source population studies. It harbours a large
number of Be/X-ray binaries, and the supernova remnants can be easily resolved
with imaging X-ray instruments. We search for new supernova remnants in the SMC
and in particular for composite remnants with a central X-ray source. We study
the morphology of newly found candidate supernova remnants using radio, optical
and X-ray images and investigate their X-ray spectra. Here we report on the
discovery of the new supernova remnant around the recently discovered Be/X-ray
binary pulsar SXP 1062 in radio and X-ray images. The Be/X-ray binary system is
found near the centre of the supernova remnant, which is located at the outer
edge of the eastern wing of the SMC. The remnant is oxygen-rich, indicating
that it developed from a type Ib event. From XMM-Newton observations we find
that the neutron star with a spin period of 1062 s shows a very high average
spin-down rate of 0.26 s per day over the observing period of 18 days. From the
currently accepted models, our estimated age of around 10000-25000 years for
the supernova remnant is not long enough to spin down the neutron star from a
few 10 ms to its current value. Assuming an upper limit of 25000 years for the
age of the neutron star and the extreme case that the neutron star was spun
down by the accretion torque that we have measured during the XMM-Newton
observations since its birth, a lower limit of 0.5 s for the birth spin period
is inferred. For more realistic, smaller long-term average accretion torques
our results suggest that the neutron star was born with a correspondingly
longer spin period. This implies that neutron stars in Be/X-ray binaries with
long spin periods can be much younger than currently anticipated.",1112.0491v1
2023-04-11,Excitation and voltage-gated modulation of single-mode dynamics in a planar nano-gap spin Hall nano-oscillator,"We experimentally study the dynamical modes excited by current-induced
spin-orbit torque and its electrostatic gating effect in a 3-terminal planar
nano-gap spin Hall nano-oscillator (SHNO) with a moderate interfacial
perpendicular magnetic anisotropy (IPMA). Both quasilinear propagating
spin-wave and localized ""bullet"" modes are achieved and controlled by varying
the applied in-plane magnetic field and driving current. The minimum linewidth
shows a linear dependence on the actual temperature of the active area,
confirming single-mode dynamics based on the nonlinear theory of spin-torque
nano-oscillation with a single mode. The observed electrostatic gating tuning
oscillation frequency arises from voltage-controlled magnetic anisotropy and
threshold current of SHNO via modification of the nonlinear damping and/or the
interfacial spin-orbit coupling of the magnetic multilayer. In contrast to
previously observed two-mode coexistence degrading the spectral purity in
Py/Pt-based SHNOs with a negligible IPMA, a single coherent spin-wave mode with
a low driven current can be achieved by selecting the ferromagnet layer with a
suitable IPMA because the nonlinear mode coupling can be diminished by bringing
in the PMA field to compensate the easy-plane shape anisotropy. Moreover, the
simulations demonstrate that the experimentally observed current and
gate-voltage modulation of auto-oscillation modes are also closely associated
with the nonlinear damping and mode coupling, which are determined by the
ellipticity of magnetization precession. The demonstrated nonlinear mode
coupling mechanism and electrical control approach of spin-wave modes could
provide the clue to facilitate the implementation of the mutual synchronization
map for neuromorphic computing applications in SHNO array networks.",2304.05026v1
2001-01-18,Z Cam stars: a particular response to a general phenomenon,"We show that the disc instability model can reproduce all the observed
properties of Z Cam stars if the energy equation includes heating of the outer
disc by the mass-transfer stream impact and by tidal torques and if the
mass-transfer rate from the secondary varies by about 30% around the value
critical for stability. In particular the magnitude difference between outburst
maxima and standstills corresponds to observations, all outbursts are of the
inside-out type and can be divided into two classes: long (wide) and short
(narrow) outbursts, as observed. Mass transfer rate fluctuations should occur
in other dwarf novae but one can exclude variations similar to those observed
in magnetic systems (AM Her's and some DQ Her's) and some nova-like systems (VY
Scl's), in which \dot{M} become very small during low states; these would
produce mini-outburst which, although detectable, have never been observed.",0101329v1
2006-06-05,Orbital Evolution of Algol Binaries with a Circumbinary Disk,"It is generally thought that conservative mass transfer in Algol binaries
causes their orbits to be wider, in which the less massive star overflows its
Roche-lobe. The observed decrease in the orbital periods of some Algol binaries
suggests orbital angular momentum loss during the binary evolution, and the
magnetic braking mechanism is often invoked to explain the observed orbital
shrinkage. Here we suggest an alternative explanation, assuming that a small
fraction of the transferred mass forms a circumbinary disk, which extracts
orbital angular momentum from the binary through tidal torques. We also perform
numerical calculations of the evolution of Algol binaries with typical initial
masses and orbital periods. The results indicate that, for reasonable input
parameters, the circumbinary disk can significantly influence the orbital
evolution, and cause the orbit to shrink on a sufficiently long timescale.
Rapid mass transfer in Algol binaries with low mass ratios can also be
accounted for in this scenario.",0606081v2
2008-06-25,Migration and growth of giant planets in self-gravitating disks with varied thermodynamics,"We report on the results of novel global high-resolution three-dimensional
simulations of disk-planet interaction which incorporate simultaneously
realistic radiation physics and the self-gravity of the gas, as well as
allowing the planet to move. We find that thermodynamics and radiative physics
have a remarkable effect on both migration and accretion of Jupiter mass
planets. In simulations with radiative transfer adopting flux-limited
diffusion, inward migration can be decreased by about 30% relative to the
isothermal case, while in adiabatic runs migration nearly shuts off after a few
tens of orbits. Migration varies because the relative strength of the inner and
outer spiral perturbations is affected by thermodynamics, thus changing the net
torque acting on the planet. Mass accretion rates on the planet can be reduced
by more than an order of magnitude going from isothermal to radiative transfer
and adiabatic simulations. A circumplanetary disk always forms except in
adiabatic runs. With radiative transfer the disk is sub-keplerian (Vrot/Vkep ~
0.7) owing to significant pressure support. We discuss the effect of
circumplanetary disk structure on the drift of embedded dust grains and
planetesimals and thus on the formation of the rocky satellites of giant
planets.",0806.3975v1
2023-10-06,Domain Randomization for Sim2real Transfer of Automatically Generated Grasping Datasets,"Robotic grasping refers to making a robotic system pick an object by applying
forces and torques on its surface. Many recent studies use data-driven
approaches to address grasping, but the sparse reward nature of this task made
the learning process challenging to bootstrap. To avoid constraining the
operational space, an increasing number of works propose grasping datasets to
learn from. But most of them are limited to simulations. The present paper
investigates how automatically generated grasps can be exploited in the real
world. More than 7000 reach-and-grasp trajectories have been generated with
Quality-Diversity (QD) methods on 3 different arms and grippers, including
parallel fingers and a dexterous hand, and tested in the real world. Conducted
analysis on the collected measure shows correlations between several Domain
Randomization-based quality criteria and sim-to-real transferability. Key
challenges regarding the reality gap for grasping have been identified,
stressing matters on which researchers on grasping should focus in the future.
A QD approach has finally been proposed for making grasps more robust to domain
randomization, resulting in a transfer ratio of 84% on the Franka Research 3
arm.",2310.04517v1
2023-12-07,Hole Flying Qubits in Quantum Dot Arrays,"Quantum information transfer is fundamental for scalable quantum computing in
any potential platform and architecture. Hole spin qubits, owing to their
intrinsic spin-orbit interaction (SOI), promise fast quantum operations which
are fundamental for the implementation of quantum gates. Yet, the influence of
SOI in quantum transfer protocols remains an open question. Here, we
investigate hole flying qubits using shortcuts to adiabaticity protocols, i.e.,
the long-range transfer of hole spin states and the quantum distribution of
entangled pairs in semiconductor quantum dot arrays. We show that electric
field manipulation allows dynamical control of the SOI, enabling simultaneously
the implementation of quantum gates during the transfer, with the potential to
significantly accelerate quantum algorithms. By harnessing the ability to
perform quantum gates in parallel with the transfer, we employ dynamical
decoupling schemes to focus and preserve the spin state, leading to higher
transfer fidelity.",2312.04631v3
2021-10-28,On the Potential of Fourier-Encoded Saturation Transfers for Sensitizing Solid-State Magic-Angle Spinning NMR Experiments,"Chemical exchange saturation transfer (CEST) is widely used for enhancing the
solution NMR signatures of magnetically-dilute spin pools; in particular
species at low concentrations undergoing chemical exchanges with an abundant
spin pool. CEST's main feature involves encoding and then detecting the weak
NMR signals of the magnetically dilute spin pools on a magnetically abundant
spin pool of much easier detection - for instance the protons of H2O. Inspired
by this method, we propose and exemplify a methodology to enhance the
sensitivity of magic-angle spinning (MAS) solid-state NMR spectra. Our proposal
uses the abundant 1H reservoir arising in organic solids as the magnetically
abundant spin pool, and relies on proton spin diffusion in lieu of chemical
exchange to mediate polarization transfer between a magnetically dilute spin
pool and this magnetically abundant spin reporter. As an initial test of this
idea we target the spectroscopy of naturally-abundant 13C, and rely on a
Fourier-encoded version of the CEST experiment for achieving broadbandness in
coordination with both MAS and heteronuclear decoupling - features normally
absent in CEST. Arbitrary evolutions of multiple 13C sites can thus be
imprinted on the entire 1H reservoir, which is subsequently detected.
Theoretical predictions suggest that orders-of-magnitude signal enhancements
should be achievable in this manner - on the order of the ratio between the 13C
and the 1H reservoirs' abundances. Experiments carried out under magic-angle
spinning conditions evidenced ca. 5-10x enhancements. Further opportunities and
challenges arising in this Fourier-Encoded Saturation Transfer (FEST) MAS NMR
approach are briefly discussed.",2110.15451v1
2015-10-13,Fermi level dependent charge-to-spin current conversion by Dirac surface state of topological insulators,"The spin-momentum locking at the Dirac surface state of a topological
insulator (TI) offers a distinct possibility of a highly efficient
charge-to-spin current (C-S) conversion compared with spin Hall effects in
conventional paramagnetic metals. For the development of TI-based spin current
devices, it is essential to evaluate its conversion efficiency quantitatively
as a function of the Fermi level EF position. Here we exemplify a coefficient
of qICS to characterize the interface C-S conversion effect by using spin
torque ferromagnetic resonance (ST-FMR) for (Bi1-xSbx)2Te3 thin films whose EF
is tuned across the band gap. In bulk insulating conditions, interface C-S
conversion effect via Dirac surface state is evaluated as nearly constant large
values of qICS, reflecting that the qICS is inversely proportional to the Fermi
velocity vF that is almost constant. However, when EF traverses through the
Dirac point, the qICS is remarkably suppressed possibly due to the degeneracy
of surface spins or instability of helical spin structure. These results
demonstrate that the fine tuning of the EF in TI based heterostructures is
critical to maximizing the efficiency using the spin-momentum locking
mechanism.",1510.03572v1
2016-09-21,A Modern Approach to Superradiance,"In this paper, we provide a simple and modern discussion of rotational
superradiance based on quantum field theory. We work with an effective theory
valid at scales much larger than the size of the spinning object responsible
for superradiance. Within this framework, the probability of absorption by an
object at rest completely determines the superradiant amplification rate when
that same object is spinning. We first discuss in detail superradiant
scattering of spin 0 particles with orbital angular momentum $\ell=1$, and then
extend our analysis to higher values of orbital angular momentum and spin.
Along the way, we provide a simple derivation of vacuum friction---a ""quantum
torque"" acting on spinning objects in empty space. Our results apply not only
to black holes but to arbitrary spinning objects. We also discuss superradiant
instability due to formation of bound states and, as an illustration, we
calculate the instability rate $\Gamma$ for bound states with massive spin 1
particles. For a black hole with mass $M$ and angular velocity $\Omega$, we
find $\Gamma \sim (G M \mu)^7 \Omega$ when the particle's Compton wavelength
$1/\mu$ is much greater than the size $GM$ of the spinning object. This rate is
parametrically much larger than the instability rate for spin 0 particles,
which scales like $(GM \mu)^9 \Omega$. This enhanced instability rate can be
used to constrain the existence of ultralight particles beyond the Standard
Model.",1609.06723v2
2018-09-14,Femtosecond control of terahertz spin-charge conversion in ferromagnetic heterostructures,"Employing electron spin instead of charge to develop spintronic devices holds
the merits of low-power consumption in information technologies. Meanwhile, the
demand for increasing speed in spintronics beyond current CMOS technology has
further triggered intensive researches for ultrafast control of spins even up
to unprecedent terahertz regime. The femtosecond laser has been emerging as a
potential technique to generate an ultrafast spin-current burst for
magnetization manipulation. However, there is a great challenge to establish
all-optical control and monitor of the femtosecond transient spin current. Deep
insights into the physics and mechanism are extremely essential for the
technique. Here, we demonstrate coherently nonthermal excitation of femtosecond
spin-charge current conversion parallel to the magnetization in W/CoFeB/Pt
heterostructures driven by linearly polarized femtosecond laser pulses. Through
systematical investigation we observe the terahertz emission polarization
depends on both the magnetization direction and structural asymmetry. We
attribute this phenomenon of the terahertz generation parallel to the
magnetization induced by linearly polarized femtosecond laser pulses probably
to inverse spin-orbit torque effect. Our work not only is beneficial to the
deep understanding of spin-charge conversion and spin transportation, but also
helps develop novel on-chip terahertz opto-spintronic devices.",1809.05391v2
2020-08-17,Enhancement of spin Hall conductivity in W-Ta alloy,"Generating pure spin currents via the spin Hall effect in heavy metals has
been an active topic of research in the last decade. In order to reduce the
energy required to efficiently switch neighbouring ferromagnetic layers for
applications, one should not only increase the charge- to-spin conversion
efficiency but also decrease the longitudinal resistivity of the heavy metal.
In this work, we investigate the spin Hall conductivity in W_{1-x}Ta_{x} /
CoFeB / MgO (x = 0 - 0.2) using spin torque ferromagnetic resonance
measurements. Alloying W with Ta leads to a factor of two change in both the
damping-like effective spin Hall angle (from - 0.15 to - 0.3) and longitudinal
resistivity (60 - 120 {\mu}W cm). At 11% Ta concentration, a remarkably high
spin Hall angle value of - 0.3 is achieved with a low longitudinal resistivity
100 {\mu}W cm, which could lead to a very low power consumption for this
W-based alloy. This work demonstrates sputter-deposited W-Ta alloys could be a
promising material for power-efficient spin current generation.",2008.07572v1
2019-05-22,Stellar winds as a mechanism to tilt the spin axes of Sun-like stars,"The rotation axis of the Sun is misaligned from the mean angular momentum
plane of the Solar system by about 6 degrees. This obliquity significantly
exceeds the ~1-2 degree distribution of inclinations among the planetary orbits
and therefore requires a physical explanation. In concert, Sun-like stars are
known to spin down by an order of magnitude throughout their lifetimes. This
spin-down is driven by the stellar wind, which carries angular momentum from
the star. If the mean angular momentum axis of the stellar wind deviates from
that of the stellar spin axis, it will lead to a component of the spin-down
torque that acts to tilt the star. Here, we show that Solar-like tilts of 6
degrees naturally arise during the first 10-100 Myr after planet formation as a
result of stellar winds that deviate by about 10 degrees from the star's spin
axis. These results apply to the idealized case of a dipolar field, mildly
inclined to the spin axis. Time-variability in the misalignment between the
magnetic and spin poles is modeled as stochastic fluctuations, autocorrelated
over timescales comparable to the primordial spin-down time of several million
years. In addition to wind direction, time-variability in mass-loss rate and
magnetic topology over the stellar lifetime may alternatively generate
obliquity. We hypothesize that the gaseous environments of young, open clusters
may provide forcing over sufficient timescales to tilt the astrospheres of
young stars, exciting modest obliquities. The more extreme, retrograde stellar
obliquities of extrasolar planetary systems likely arise through separate
mechanisms.",1905.09094v1
2020-10-19,The spin-spin model and the capture into the double synchronous resonance,"The aim of this article is to propose a model, that is a planar version of
the Full Two-Body Problem, and discuss the existence and stability of a
relevant periodic solution. Consider two homogeneous ellipsoids orbiting around
each other in fixed coplanar Keplerian orbits. Moreover, their respective spin
axes are assumed to be perpendicular to the orbital plane, that is also a
common equatorial plane. The spin-spin model deals with the coupled rotational
dynamics of both ellipsoids. For a non-zero orbital eccentricity, it has the
structure of a non-autonomous system of coupled pendula. This model is a
natural extension of the classical spin-orbit problem for two extended bodies.
In addition, we consider dissipative tidal torques, that can trigger the
capture of the system into spin-orbit and spin-spin resonances. In this paper
we give some theoretical results for both the conservative model and the
dissipative one. The conservative model has a Hamiltonian structure. We use
properties of Hamiltonian systems to give some sufficient conditions in the
space of parameters of the model, that guarantee existence, uniqueness and
linear stability of an odd periodic solution. This solution represents a double
synchronous resonance in the conservative regime. Such solution can be
continued to the dissipative regime, where it becomes asymptotically stable. We
see asymptotic stability as a dynamical mechanism for the capture into the
double synchronous resonance. Finally we apply our results to several cases
including the Pluto-Charon binary system and the Trojan binary asteroid 617
Patroclus, target of the LUCY mission.",2010.09354v1
2021-01-27,Response to Comment on: Tunneling in DNA with Spin Orbit coupling,"The comment by O. Entin-Wohlman, A. Aharony, and Y. Utsumi, on our paper S.
Varela, I. Zambrano, B. Berche, V. Mujica, and E. Medina, Phys. Rev. B 101,
241410(R) (2020) makes a few points related to the validity of our model,
especially in the light of the interpretation of Bardarson's theorem: ""in the
presence of time reversal symmetry and for half-integral spin the transmission
eigenvalues of the two terminal scattering matrix come in (Kramers) degenerate
pairs"". The authors of the comment first propose an ansatz for the wave
function in the spin active region and go on to show that the resulting
transmission does not show spin dependence, reasoning that spin dependence
would violate Bardarson's assertion. Here we clearly show that the ansatz
presented assumes spin-momentum independence from the outset and thus just
addresses the spinless particle problem. We then find the appropriate
eigenfunction contemplating spin-momentum coupling and show that the resulting
spectrum obeys Bardarson's theorem. Finally we show that the allowed
wavevectors are the ones assumed in the original paper and thus the original
conclusions follow. We recognize that the Hamiltonian in our paper written in
local coordinates on a helix was deceptively simple and offer the expressions
of how it should be written to more overtly convey the physics involved. The
relation between spin polarization and torque becomes clear, as described in
our paper. This response is a very important clarification in relation to the
implications of Bardarson's theorem concerning the possibility of spin
polarization in one dimensional systems in the linear regime.",2101.11271v1
2021-06-08,Observation of the out-of-plane polarized spin current from CVD grown WTe2,"Weyl semimetal Td-phase WTe2 possesses the spin-resolved band structure with
strong spin-orbit coupling, holding promises as a useful spin source material.
The noncentrosymmetric crystalline structure of Td-WTe2 endows the generation
of the out-of-plane polarized spin, which is of great interest in magnetic
memory applications. Previously, WTe2 was explored in spin devices based on
mechanically exfoliated single crystal flakes with a size of micrometers. For
practical spintronics applications, it is highly desirable to implement
wafer-scale thin films. In this work, we utilize centimeter-scale chemical
vapor deposition (CVD)-grown Td-WTe2 thin films and study the spin current
generation by the spin torque ferromagnetic resonance technique. We find the
in-plane and out-of-plane spin conductivities of 7.36 x 10^3 (h/2e) (ohm-m)^-1
and 1.76 x 10^3 (h/2e) (ohm-m)^-1, respectively, in CVD-growth 5 nm-WTe2. We
further demonstrate the current-induced magnetization switching in WTe2/NiFe at
room temperature in the domain wall motion regime, which may invigorate
potential spintronic device innovations based on Weyl semimetals.",2106.04154v1
2021-06-21,Local non-linear excitation of sub-100 nm bulk-type spin waves by edge-localized spin waves in magnetic films,"The excitation of high-frequency short-wavelength spin waves is a challenge
limiting the application of these propagating magnetization disturbances in
information processing systems. We propose a method of local excitation of the
high-frequency spin waves using the non-linear nature of magnetization
dynamics. We demonstrate with numeric simulations that an edge-localized spin
wave can be used to excite plane waves propagating obliquely from the film's
edge at a doubled frequency and over twice shorter in wavelength. The
excitation mechanism is a direct result of the ellipticity of the magnetic
moments precession that is related to the edge-mode propagation. As a
consequence, the magnetization component tangential to the equilibrium
orientation oscillates with doubled temporal and spatial frequencies, which
leads to efficient excitation of the plane spin waves. Threshold-less
non-linear process of short-wavelength spin-wave excitation proposed in our
study is promising for integration with an inductive or point-like spin-torque
source of edge spin waves.",2106.11114v1
2022-12-24,Spin-to-charge conversion by spin pumping in sputtered polycrystalline Bi$_x$Se$_{1-x}$,"Topological materials are of high interest due to the promise to obtain low
power and fast memory devices based on efficient spin-orbit torque switching or
spin-orbit magnetic state read-out. In particular, sputtered polycrystalline
Bi$_x$Se$_{1-x}$ is one of the materials with more potential for this purpose
since it is relatively easy to fabricate and has been reported to have a very
high spin Hall angle. We study the spin-to-charge conversion in
Bi$_x$Se$_{1-x}$ using the spin pumping technique coming from the ferromagnetic
resonance in a contiguous permalloy thin film. We put a special emphasis on the
interfacial properties of the system. Our results show that the spin Hall angle
of Bi$_x$Se$_{1-x}$ has an opposite sign to the one of Pt. The charge current
arising from the spin-to-charge conversion is, in contrast, lower than Pt by
more than one order of magnitude. We ascribe this to the interdiffusion of
Bi$_x$Se$_{1-x}$ and permalloy and the changes in chemical composition produced
by this effect, which is an intrinsic characteristic of the system and is not
considered in many other studies.",2212.12697v2
2023-02-02,Rapid Black Hole Spin-down by Thick Magnetically Arrested Disks,"Black hole (BH) spin can play an important role in galaxy evolution by
controlling the amount of energy and momentum ejected from near the BH into the
surroundings. We focus on the magnetically-arrested disk (MAD) state in the
sub- and super-Eddington regimes, when the accretion disk is
radiatively-inefficient and geometrically-thick, and the system launches strong
BH-powered jets. Using a suite of 3D general relativistic magnetohydrodynamic
(GRMHD) simulations, we find that for any initial spin, a MAD rapidly spins
down the BH to the equilibrium spin of $0 < a_{\rm eq} \lesssim 0.1$, very low
compared to $a_{\rm eq} = 1$ for the standard thin luminous (Novikov-Thorne)
disks. This implies that rapidly accreting (super-Eddington) BHs fed by MADs
tend to lose most of their rotational energy to magnetized relativistic
outflows. In a MAD, a BH only needs to accrete $10\%$ of its own mass to spin
down from $a=1$ to $a=0.2$. We construct a semi-analytic model of BH spin
evolution in MADs by taking into account the torques on the BH due to both the
hydrodynamic disk and electromagnetic jet components, and find that the low
value of $a_{\rm eq}$ is due to both the jets slowing down the BH rotation and
the disk losing a large fraction of its angular momentum to outflows. Our
results have crucial implications on how BH spins evolve in active galaxies and
other systems such as collapsars, where BH spin-down timescale can be short
enough to significantly affect the evolution of BH-powered jets.",2302.01351v1
2023-04-21,The spin-down accretion regime of Galactic ultra-luminous X-ray pulsar Swift J0243.6+6124,"The relative high fluxes of the Galactic ultra-luminous X-ray pulsar Swift
J0243 allow a detailed study of its spin-down regime in quiescence state, for a
first time. After the 2017 giant outburst, its spin frequencies show a linear
decreasing trend with some variations due to minor outbursts. The linear
spin-down rate is $\sim-1.9\times10^{-12}$ Hz/s during the period of lowest
luminosity, from which one can infer a dipole field $\sim1.75\times10^{13}$ G.
The $\dot{\nu}-L$ relation during the spin-down regime is complex, and the
$\dot{\nu}$ is close to 0 when the luminosity reaches both the high end
($L_{38}\sim0.3$) and the lowest value ($L_{38}\sim0.03$). The luminosity of
zero-torque is different for the giant outburst and other minor outbursts. It
is likely due to different accretion flows for different types of outburst, as
evidenced by the differences of the spectra and pulse profiles at a similar
luminosity for different types of outburst (giant or not). The pulse profile
changes from double peaks in the spin-up state to a single broad peak in the
low spin-down regime, indicating the emission beam/region is larger in the low
spin-down regime. These results show that accretion is still ongoing in the low
spin-down regime for which the neutron star is supposed to be in a propeller
state.",2304.10815v1
2023-10-09,Mapping of Spin-Wave Transport in Thulium Iron Garnet Thin Films Using Diamond Quantum Microscopy,"Spin waves, collective dynamic magnetic excitations, offer crucial insights
into magnetic material properties. Rare-earth iron garnets offer an ideal
spin-wave (SW) platform with long propagation length, short wavelength,
gigahertz frequency, and applicability to magnon spintronic platforms. Of
particular interest, thulium iron garnet (TmIG) has attracted a huge interest
recently due to its successful growth down to a few nanometers, observed
topological Hall effect and spin orbit torque-induced switching effects.
However, there is no direct spatial measurement of its SW properties. This work
uses diamond nitrogen vacancy (NV) magnetometry in combination with SW
electrical transmission spectroscopy to study SW transport properties in TmIG
thin films. NV magnetometry allows probing spin waves at the sub-micrometer
scale, seen by the amplification of the local microwave magnetic field due to
the coupling of NV spin qubits with the stray magnetic field produced by the
microwave-excited spin waves. By monitoring the NV spin resonances, the SW
properties in TmIG thin films are measured as function of the applied magnetic
field, including their amplitude, decay length (~ 50 um), and wavelength (0.8 -
2 um). These results pave the way for studying spin qubit-magnon interactions
in rare-earth magnetic insulators, relevant to quantum magnonics applications.",2310.06188v4
2021-11-23,Polarization transfer from optically-pumped NV center ensembles to multinuclear spin baths,"NV-diamonds have attracted keen interest for nanoscale sensing and spin
manipulation. In particular, the non-equilibrium electron spin polarization
after optical excitation of single NV centers has successfully been transferred
to nuclear spin baths in the surrounding of the defects. However, these
experiments need to be extended to NV-ensembles which have promising practical
applications in the hyperpolarization of bulk sample volumes for NMR signal
enhancement. Here, we use a dense, shallow ensemble of NV-centers to
demonstrate polarization transfer to nuclear spins in a well-defined composite
diamond sample system. This allows us to address three different types of
nuclear spins in different positions with respect to the NV polarization
source: from the close proximity of $^{13}$C inside the diamond lattice to the
self-assembled molecular system consisting of $^{1}$H and $^{19}$F spins
outside the diamond and over multiple interfaces. We show that ensemble NV
experiments face problems different from single NV experiments. In particular,
using spinlock pulses, the inhomogeneously broadened ESR line of the NV
ensemble limits the minimal resonance linewidth with which the transfer
protocol can occur. Furthermore, we compare the NV spin-polarization losses and
polarization transfer rates to the different nuclear baths and discuss the role
of spin-diffusion as detrimentally affecting the direct observation of nuclear
polarization build-up within the detection volume of nanoscale NV-NMR
experiments.",2111.11804v1
1998-08-19,The alignment of disk and black hole spins in active galactic nuclei,"The inner parts of an accretion disk around a spinning black hole are forced
to align with the spin of the hole by the Bardeen-Petterson effect. Assuming
that any jet produced by such a system is aligned with the angular momentum of
either the hole or the inner disk, this can, in principle provide a mechanism
for producing steady jets in AGN whose direction is independent of the angular
momentum of the accreted material. However, the torque which aligns the inner
disk with the hole, also, by Newton's third law, tends to align the spin of the
hole with the outer accretion disk. In this letter, we calculate this alignment
timescale for a black hole powering an AGN, and show that it is relatively
short. This timescale is typically much less than the derived ages for jets in
radio loud AGN, and implies that the jet directions are not in general
controlled by the spin of the black hole. We speculate that the jet directions
are most likely controlled either by the angular momentum of the accreted
material or by the gravitational potential of the host galaxy.",9808187v1
1999-12-10,Magnetic Field Limits on SGRs,"We measure the period and spin-down rate for SGR 1900+14 during the
quiescient period two years before the recent interval of renewed burst
activity. We find that the spin-down rate doubled during the burst activity
which is inconsistent with both mangetic dipole driven spin down and a magnetic
field energy source for the bursts. We also show that SGRs 1900+14 and 1806-20
have braking indices of $\sim$1 which indicate that the spin-down is due to
wind torques and not magnetic dipole radiation. We further show that a
combination of dipole radiation, and wind luminosity, coupled with estimated
ages and present spin parameters, imply that the magnetic fields of SGRs
1900+14 and 1806-20 are less than the critical field of 4$\times10^{13}$ G and
that the efficiency for conversion of wind luminosity to x-ray luminosity is
<2%.",9912237v1
1999-12-27,Evidence for a 304-day Orbital Period for GX 1+4,"In this paper we report strong evidence for a ~304-day periodicity in the
spin history of the accretion-powered pulsar GX 1+4 that is very likely to be a
signature of the orbital period of the system. Using BATSE public-domain data,
we show a highly-significant periodic modulation of the pulsar frequency from
1991 to date which is in excellent agreement with the ephemeris proposed by
Cutler, Dennis & Dolan in 1986, which were based on a few events of enhanced
spin-up that occurred during the pulsar's spin-up era in the 1970s. Our results
indicate that the orbital period of GX 1+4 is 303.8+-1.1 days, making it by far
the widest low-mass X-ray binary system known. A likely scenario for this
system is an elliptical orbit in which the neutron star decreases its spin-down
rate (or even exhibits a momentary spin-up behavior) at periastron passages due
to the higher torque exerted by the accretion disk onto the magnetosphere of
the neutron star.",9912519v1
2001-02-02,Resolution of the Age Discrepancies in Pulsar/SNR Associations,"Pulsars associated with supernova remnants (SNRs) are valuable because they
provide constraints on the mechanism(s) of pulsar spin-down. Here we discuss
two SNR/pulsar associations in which the SNR age is much greater than the age
of the pulsar obtained by assuming pure magnetic dipole radiation (MDR)
spin-down. The PSR B1757-24/SNR G5.4-1.2 association has a minimum age of ~40
kyr from proper motion upper limits, yet the MDR timing age of the pulsar is
only 16 kyr, and the newly discovered pulsar PSR J1846-0258 in the >2 kyr old
SNR Kes 75 has an MDR timing age of just 0.7 kyr. These and other pulsar/SNR
age discrepancies imply that the pulsar spin-down torque is not due to pure
MDR, and we discuss a model for the spin-down of the pulsars similar to the
ones recently proposed to explain the spin-down of soft gamma-ray repeaters and
anomalous x-ray pulsars.",0102049v1
2001-09-28,Gravity Waves from Rotating Neutron Stars and Evaluation of Fast Chirp Transform Techniques,"X-ray observations suggest that neutron stars in low mass X-ray binaries
(LMXB) are rotating with frequencies from 300 - 600 Hz. These spin rates are
significantly less than the break-up rates for essentially all realistic
neutron star equations of state, suggesting that some process may limit the
spin frequencies of accreting neutron stars to this range. If the accretion
induced spin up torque is in equilibrium with gravitational radiation losses,
these objects could be interesting sources of gravity waves. I present a brief
summary of current measurements of neutron star spins in LMXBs based on the
observations of high-Q oscillations during thermonuclear bursts (so called
``burst oscillations''). Further measurements of neutron star spins will be
important in exploring the gravitational radiation hypothesis in more detail.
To this end I also present a study of fast chirp transform (FCT) techniques as
described by Jenet & Prince (2000) in the context of searching for the chirping
signals observed during X-ray bursts.",0109559v1
2004-12-22,Topology and spin dynamics in magnetic molecules,"We investigate the role of topology and distortions in the quantum dynamics
of magnetic molecules, using a cyclic spin system as reference. We consider
three variants of antiferromagnetic molecular ring, i.e. Cr$_8$, Cr$_7$Zn and
Cr$_7$Ni, characterized by low lying states with different total spin $S$. We
theoretically and experimentally study the low-temperature behavior of the
magnetic torque as a function of the applied magnetic field. Near level
crossings, this observable selectively probes quantum fluctuations of the total
spin (''$S$ mixing"") induced by lowering of the ideal ring symmetry. We show
that while a typical distortion of a model molecular structure is very
ineffective in opening new $S$-mixing channels, the spin topology is a major
ingredient to control the degree of $S$ mixing. This conclusion is further
substantiated by low-temperature heat capacity measurements.",0412628v1
2005-11-03,Classical and quantum depinning of a domain wall with a spin-polarized current,"We study in detail the classical and quantum depinning of a domain wall (DW)
induced by a fast-varying spin-polarized current. By confirming the adiabatic
condition for calculating the spin-torque in fast-varying current case, we show
that the time-dependent spin current has two critical values that determine the
classical depinning of DW. This discovery successfully explains the recent
experiments. Furthermore, a feasible way is proposed to lower the threshold of
spin currents and control the direction of DW's motion. Finally, the quantum
properties for the depinning of DW are also investigated in this paper.",0511069v3
2007-03-28,Field-induced level crossings in spin clusters: Thermodynamics and magneto-elastic instability,"Quantum spin clusters with dominant antiferromagnetic Heisenberg exchange
interactions typically exhibit a sequence of field-induced level crossings in
the ground state as function of magnetic field. For fields near a level
crossing, the cluster can be approximated by a two-level Hamiltonian at low
temperatures. Perturbations, such as magnetic anisotropy or spin-phonon
coupling, sensitively affect the behavior at the level-crossing points. The
general two-level Hamiltonian of the spin system is derived in first-order
perturbation theory, and the thermodynamic functions magnetization, magnetic
torque, and magnetic specific heat are calculated. Then a magneto-elastic
coupling is introduced and the effective two-level Hamilitonian for the
spin-lattice system derived in the adiabatic approximation of the phonons. At
the level crossings the system becomes unconditionally unstable against lattice
distortions due to the effects of magnetic anisotropy. The resultant
magneto-elastic instabilities at the level crossings are discussed, as well as
the magnetic behavior.",0703747v1
2009-12-07,Origin and evolution of galactic spin from looking at galaxy pairs,"To study if the angular momentum gain for each member of a galaxy pair was
the result of tidal torques imprinted by the same tidal field, we search for
correlations between the spin in pairs of spiral galaxies identified using the
Sloan Digital Sky Survey. We find a weak, but statistically significant
correlation between the spin magnitude of neighbouring galaxies. We show that
events such as close interactions with neighbours play an important role in the
value of the spin for the final configuration, as we find these interactions
tend to reduce the value of the $\lambda$ spin parameter of late-type galaxies
considerably. This implies that the original tidal field for each pair could
have been similar, but the redistribution of angular momentum at later stages
of evolution is important",0912.1151v1
2010-12-20,Conduction Electron Scattering and Spin-Flipping at Sputtered Co/Ni Interfaces,"Current-perpendicular-to-plane magnetoresistance (CPP-MR) measurements let us
quantify conduction electron scattering and spin-flipping at a sputtered
ferromagnetic/ferromagnetic (F1/F2 = Co/Ni) interface, with important
consequences for CPP-MR and spin-torque experiments with perpendicular
anisotropy. We use ferromagnetically coupled ([Ni/Co]xn)Ni multilayers, and
Py-based, symmetric double exchange-biased spin-valves (DEBSVs) containing
inserts of ferromagnetically coupled ([Co/Ni]xn)Co or ([Ni/Co]xn)Ni
multilayers, to derive Co/Ni interface specific resistances AR(Co/Ni)(Up) =
0.03 (+0.02)(-0.03) f-ohm-m^2 and AR(Co/Ni)(down) = 1.00 +/- 0.07 f-ohm-m^2,
and interface spin-flipping parameter delta(Co/Ni) = 0.35 +/- 0.05. The
specific resistances are consistent with our no-free-parameter calculations for
an interface thickness between 2 and 4 monolayers (ML) that is compatible with
expectations.",1012.4388v1
2011-08-02,Spin down of superfluid-filled vessels: theory versus experiment,"The spin up of helium II is studied by calculating the spin-down recovery of
a superfluid-filled container after an impulsive acceleration and comparing
with experiments. The calculation takes advantage of a recently published
analytic solution for the spin up of a Hall-Vinen-Bekharevich-Khalatnikov
superfluid that treats the back-reaction torque exerted by the viscous
component self-consistently in arbitrary geometry for the first time. Excellent
agreement at the 0.5% level is obtained for experiments at $T=1.57\,{\rm K}$,
after correcting for the non-uniform rotation in the initial state, confirming
that vortex tension and pinning (which are omitted from the theory) play a
minimal role under certain conditions (small Rossby number, smooth walls). The
dependence of the spin-down time on temperature and the mass fraction of the
viscous component are also investigated. Closer to the lambda point, the
predicted onset of turbulence invalidates the linear Ekman theory.",1108.0478v1
2011-11-11,Near-Earth Binaries and Triples: Origin and Evolution of Spin-Orbital Properties,"In the near-Earth asteroid population, binary and triple systems have been
discovered with mutual orbits that have significant eccentricities as well as
large semi-major axes. All known systems with eccentric orbits and all
widely-separated primary-satellite pairs have rapidly rotating satellites. Here
we study processes that can elucidate the origin of these spin-orbital
properties. Binary formation models based on rotational fissioning can
reproduce asynchronous satellites on orbits with high eccentricities and a wide
range of separations, but do not match observed properties. We explore whether
any evolutionary mechanisms can link the spin and orbital parameters expected
from post-fission dynamics to those observed today. We investigate four
processes: tidal torques, radiative perturbations (BYORP), close planetary
encounters, and Kozai oscillations. We find that a combination of post-fission
dynamics and tidal evolution can explain nearly all the spin-orbit properties
in a sample of nine well-characterized near-Earth binaries and triples. The
other mechanisms may act but are not required to explain the observed data.
Lastly, we describe evolutionary pathways between observed spin-orbital states
including synchronous and circular, asynchronous and circular, and asynchronous
and eccentric configurations.",1111.2794v1
2012-05-28,Spin-Based Neuron Model with Domain Wall Magnets as Synapse,"We present artificial neural network design using spin devices that achieves
ultra low voltage operation, low power consumption, high speed, and high
integration density. We employ spin torque switched nano-magnets for modelling
neuron and domain wall magnets for compact, programmable synapses. The spin
based neuron-synapse units operate locally at ultra low supply voltage of 30mV
resulting in low computation power. CMOS based inter-neuron communication is
employed to realize network-level functionality. We corroborate circuit
operation with physics based models developed for the spin devices. Simulation
results for character recognition as a benchmark application shows 95% lower
power consumption as compared to 45nm CMOS design.",1205.6022v2
2014-10-22,A three-dimensional spin-diffusion model for micromagnetics,"We implement a finite-element scheme that solves the Landau-Lifshitz-Gilbert
equation coupled to a diffusion equation accounting for spin-polarized
currents. The latter solves for the spin accumulation not only in magnetic
materials but also in nonmagnetic conductors. The presented method incorporates
the model by Slonczewski for the description of spin torque in magnetic
multilayers as well as the model of Zhang and Li for the description of current
driven domain-wall motion. Furthermore it is able to do both resolve the time
evolution of the spin accumulation or treat it in an adiabatic fashion by the
choice of sufficiently large time steps.",1410.6067v2
2014-11-03,"Obliquities of ""Top-Shaped"" Asteroids May Not Imply Reshaping by YORP Spin-up","The timescales over which the YORP effect alters the rotation period and the
obliquity of a small asteroid can be very different, because the corresponding
torques couple to different aspects of the object's shape. For nearly
axisymmetric, ""top-shaped"" near-Earth asteroids such as 101955 Bennu, spin
timescales are an order of magnitude or more longer than obliquity timescales,
which are of order 10^5 to 10^6 yr. The observed low obliquities (near 0 or 180
degrees) of top-shaped asteroids do not constitute evidence that they acquired
their present shapes and spins through YORP spin-up, because low obliquities
are expected regardless of the spin-up or reshaping mechanism.",1411.0638v2
2015-02-16,Effect of non-uniform exchange field in ferromagnetic graphene,"We have presented here the consequences of the non-uniform exchange field on
the spin transport issues in spin chiral configuration of ferromagnetic
graphene. Taking resort to the spin orbit coupling (SOC) term and non-uniform
exchange coupling term we are successful to express the expression of Hall
conductivity in terms of the exchange field and SOC parameters through the Kubo
formula approach. However, for a specific configuration of the exchange
parameter we have evaluated the Berry curvature of the system. We also have
paid attention to the study of SU(2) gauge theory of ferromagnetic graphene.
The generation of anti damping spin orbit torque in spin chiral magnetic
graphene is also briefly discussed.",1502.04453v1
2015-03-25,X-Ray Detection of Transient Magnetic Moments Induced by a Spin Current in Cu,"We have used a MHz lock-in x-ray spectro-microscopy technique to directly
detect changes of magnetic moments in Cu due to spin injection from an adjacent
Co layer. The elemental and chemical specificity of x-rays allows us to
distinguish two spin current induced effects. We detect the creation of
transient magnetic moments of $3\times 10^{-5}$ $\mu_\mathrm{B}$ on Cu atoms
within the bulk of the 28 nm thick Cu film due to spin-accumulation. The moment
value is compared to predictions by Mott's two current model. We also observe
that the hybridization induced existing magnetic moments on Cu interface atoms
are transiently increased by about 10% or $4\times 10^{-3}$ $\mu_\mathrm{B}$.
This reveals the dominance of spin-torque alignment over Joule heat induced
disorder of the interfacial Cu moments during current flow.",1503.07275v2
2015-04-02,Electron-Magnon Scattering in Magnetic Heterostructures Far Out-of-Equilibrium,"We present a theory of out-of-equilibrium ultrafast spin dynamics in magnetic
heterostructures based on the s-d model of ferromagnetism. Both in the bulk and
across interfaces, the exchange processes between the itinerant s and the
localized d electrons are described by kinetic rate equations for
electron-magnon spin-flop scattering. The principal channel for dissipation of
angular momentum is provided by spin relaxation of the itinerant electrons. Our
theory extends interfacial spin phenomena such as torques, pumping, and the
Peltier and Seebeck effects to address laser-induced rapid spin dynamics, in
which the effective electron temperature may approach or even exceed the Curie
temperature.",1504.00511v1
2016-04-20,Robust Picosecond writing of a Layered Antiferromagnet by Staggered Spin-Orbit-Fields,"Ultrafast electrical switching by current-induced staggered spin-orbit
fields, with minimal risk of overshoot, is shown in layered easy-plane
antiferromagnets with basal-plane biaxial anisotropy. The reliable switching is
due to the field-like torque, relaxing stringent requirements with respect to
precision in the time-duration of the excitation pulse. We investigate the
switching characteristics as a function of the spin-orbit field strength, pulse
duration, pulse rise and fall time and damping by atomistic spin dynamics
simulations and an effective equation of motion for the antiferromagnetic
order-parameter. The condition, determining the critical spin-orbit field
strength for switching is determined and we go on to show that robust
picosecond writing is possible at feasible current magnitudes.",1604.05918v1
2016-05-17,Direct observation of dynamic modes excited in a magnetic insulator by pure spin current,"Excitation of magnetization dynamics by pure spin currents has been recently
recognized as an enabling mechanism for spintronics and magnonics, which allows
implementation of spin-torque devices based on low-damping insulating magnetic
materials. Here we report the first spatially-resolved study of the dynamic
modes excited by pure spin current in nanometer-thick microscopic insulating
Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear
self-broadening preventing the formation of the self-localized magnetic bullet,
which plays a crucial role in the stabilization of the single-mode
magnetization oscillations in all-metallic systems. This peculiarity associated
with the efficient nonlinear mode coupling in low-damping materials can be
among the main factors governing the interaction of pure spin currents with the
dynamic magnetization in high-quality magnetic insulators.",1605.05211v1
2017-08-18,Do phonons carry spin?,"Recently the question of phonon angular momentum has been raised : phonon
angular momentum in a magnetic crystal could play an important role in the
angular momentum balance in the Einstein-de Haas effect. This proposition is
quite natural and understandable, however the idea of phonon spin seems
ambiguous in the literature. In 1988 McLellan presented phonon angular momentum
states for circular and elliptical polarizations of phonons that represent
orbital angular momentum and also pointed out analogy to isotropic quantum
harmonic oscillator. In view of its fundamental importance we investigate this
issue and conclude that phonon spin hypothesis is physically untenable, and the
phonon angular momentum has to be interpreted as orbital. The photon-phonon
analogy is also misleading. It is argued that Cosserat elastic medium having
internal torque may have lattice excitations different from phonons having spin
one or spin two that we term as Cosseratons. In addition a new source of
angular momentum balance originationg from anomalous electron magnetic moment
is suggested.",1708.07407v3
2019-10-31,Quantum spin liquids by geometric lattice design,"On a lattice composed of triangular plaquettes where antiferromagnetic
exchange interactions between localized spins cannot be simultaneously
satisfied, the system becomes geometrically frustrated with magnetically
disordered phases remarkably different from a simple paramagnet. Spin liquid
belongs to one of these exotic states, in which a macroscopic degeneracy of the
ground state gives rise to the rich spectrum of collective phenomena. Here, we
report on the discovery of a new magnetic state in the heterostructures derived
from a single unit cell (111)-oriented spinel CoCr2O4 sandwiched between
nonmagnetic Al2O3 spacers. The artificial quasi-two-dimensional material
composed of three triangle and one kagome atomic planes shows a degree of
magnetic frustration which is almost two orders of magnitude enlarged compared
to the bulk crystals. Combined resonant X-ray absorption and torque
magnetometry measurements confirm that the designer system exhibits no sign of
spin ordering down to 30 mK, implying a possible realization of a quantum spin
liquid state in the two dimensional limit.",1911.00100v1
2019-11-08,Giant anisotropy of Gilbert damping in a Rashba honeycomb antiferromagnet,"Giant Gilbert damping anisotropy is identified as a signature of strong
Rashba spin-orbit coupling in a two-dimensional antiferromagnet on a honeycomb
lattice. The phenomenon originates in spin-orbit induced splitting of
conduction electron subbands that strongly suppresses certain spin-flip
processes. As a result, the spin-orbit interaction is shown to support an
undamped non-equilibrium dynamical mode that corresponds to an ultrafast
in-plane N\'eel vector precession and a constant perpendicular-to-the-plane
magnetization. The phenomenon is illustrated on the basis of a two dimensional
$s$-$d$ like model. Spin-orbit torques and conductivity are also computed
microscopically for this model. Unlike Gilbert damping these quantities are
shown to reveal only a weak anisotropy that is limited to the semiconductor
regime corresponding to the Fermi energy staying in a close vicinity of
antiferromagnetic gap.",1911.03408v1
2018-08-20,Overcoming the speed limit in skyrmion racetrack devices by suppressing the skyrmion Hall effect,"Magnetic skyrmions are envisioned as carriers of information in racetrack
storage devices. Unfavorably, the skyrmion Hall effect hinders the fast
propagation of skyrmions along an applied electric current and limits the
device's maximum operation speed. In this Rapid Communication, we show that the
maximum skyrmion velocity increases by a factor of 10 when the skyrmion Hall
effect is suppressed, since the straight-line motion of the skyrmion allows for
the application of larger driving currents. We consider a ferromagnet on a
heavy metal layer, which converts the applied charge current into a spin
current by the spin Hall effect. The spin current drives the skyrmions in the
ferromagnet via spin-orbit torque. We show by analytical considerations and
simulations that the deflection angle decreases, when the spin current is
polarized partially along the applied current direction and derive the
condition for complete suppression of the skyrmion Hall effect.",1808.06391v2
2017-06-02,Coherent Terahertz Spin-Wave Emission Associated with Ferrimagnetic Domain Wall Dynamics,"We theoretically study the dynamics of ferrimagnetic domain walls in the
presence of Dzyaloshinskii-Moriya interaction. We find that an application of a
DC magnetic field can induce terahertz spin-wave emission by driving
ferrimagnetic domain walls, which is not possible for ferromagnetic or
antiferromagnetic domain walls. Dzyaloshinskii-Moriya interaction is shown to
facilitate the teraherz spin-wave emission in wide ranges of net angular
momentum by increasing the Walkerbreakdown field. Moreover, we show that
spin-orbit torque combined with Dzyaloshinskii-Moriya interaction also drives a
fast ferrimagnetic domain wall motion with emitting terahertz spin-waves in
wide ranges of net angular momentum.",1706.00549v1
2017-10-12,Magnetic droplet solitons generated by pure spin currents,"Magnetic droplets are dynamical solitons that can be generated by locally
suppressing the dynamical damping in magnetic films with perpendicular
anisotropy. To date, droplets have been observed only in nanocontact
spin-torque oscillators operated by spin-polarized electrical currents. Here,
we experimentally demonstrate that magnetic droplets can be nucleated and
sustained by pure spin currents in nanoconstriction-based spin Hall devices.
Micromagnetic simulations support our interpretation of the data, and indicate
that in addition to the stationary droplets, propagating solitons can be also
generated in the studied system, which can be utilized for the information
transmission in spintronic applications.",1710.04430v1
2017-10-19,Composition-dependent magnetic response properties of Mn$_{1-x}$Fe$_x$Ge alloys,"The composition-dependent behavior of the Dzyaloshinskii-Moriya interaction
(DMI), the spin-orbit torque (SOT), as well as anomalous and spin Hall
conductivities of Mn$_{1-x}$Fe$_x$Ge alloys have been investigated by
first-principles calculations using the relativistic multiple scattering
Korringa-Kohn-Rostoker (KKR) formalism. The $D_{\rm xx}$ component of the DMI
exhibits a strong dependence on the Fe concentration, changing sign at $x
\approx 0.85$ in line with previous theoretical calculations as well as with
experimental results demonstrating the change of spin helicity at $x \approx
0.8$. A corresponding behavior with a sign change at $x \approx 0.5$ is
predicted also for the Fermi sea contribution to the SOT, as this is closely
related to the DMI. In the case of anomalous and spin Hall effects it is shown
that the calculated Fermi sea contributions are rather small and the
composition-dependent behavior of these effects are determined mainly by the
electronic states at the Fermi level. The spin-orbit-induced scattering
mechanisms responsible for both these effects suggest a common origin of the
minimum of the AHE and the sign change of the SHE conductivities.",1710.07248v1
2021-10-29,Spin conservation of cosmic filaments,"Cosmic filaments are the largest collapsing structure in the Universe.
Recently both observations and simulations inferred that cosmic filaments have
coherent angular momenta (spins). Here we use filament finders to identify the
filamentary structures in cosmological simulations and study their physical
origins, which are well described by the primordial tidal torque of their
Lagrangian counterpart regions -- protofilaments. This initial angular momenta
statistically preserve their directions to low redshifts. We further show that
a spin reconstruction method can predict the spins of filaments and potentially
relate their spins to the initial conditions of the Universe. This correlation
provides a new way of constraining and obtaining additional information of the
initial perturbations of the Universe.",2110.15512v2
2019-01-17,Spin of Primordial Black Holes,"Primordial black holes, formed from rare peaks in the primordial fluctuations
$\zeta$, are non-rotating at zeroth order in $\zeta_{\rm rms}$. We show that
the spin also vanishes at first order in $\zeta_{\rm rms}$, suggesting the
dimensionless spin parameter $a_{\rm rms} \sim \zeta_{\rm rms}^2$. We identify
one quadratic contribution to the spin by calculating (and extrapolating to the
formation time) the torque on a black hole due to ambient acoustic waves. For a
reasonable density of primordial black holes this implies a percent level spin
parameter.",1901.05963v3
2019-08-04,Efficient spin excitation via ultrafast damping-like torques in antiferromagnets,"Damping effects form the core of many emerging concepts for high-speed
spintronic applications. Important characteristics such as device switching
times and magnetic domain-wall velocities depend critically on the damping
rate. While the implications of spin damping for relaxation processes are
intensively studied, damping effects during impulsive spin excitations are
assumed to be negligible because of the shortness of the excitation process.
Herein, we show that, unlike in ferromagnets, ultrafast damping plays a crucial
role in antiferromagnets because of their strongly elliptical spin precession.
In time-resolved measurements, we find that ultrafast damping results in an
immediate spin canting along the short precession axis. The interplay between
antiferromagnetic exchange and magnetic anisotropy amplifies this canting by
several orders of magnitude towards large-amplitude modulations of the
antiferromagnetic order parameter. This leverage effect discloses a highly
efficient route towards the ultrafast manipulation of magnetism in
antiferromagnetic spintronics.",1908.01359v3
2020-01-02,Origin of Strong Two-Magnon Scattering in Heavy Metal/Ferromagnet/Oxide Heterostructures,"We experimentally investigate the origin of the two-magnon scattering (TMS)
in heavy-metal (HM)/ferromagnet (FM)/oxide heterostructures (FM = Co, Ni81Fe19,
or Fe60Co20B20) by varying the materials located above and below the FM layers.
We show that strong TMS in HM/FM/oxide systems arises primarily at the HM/FM
interface and increases with the strength of interfacial spin-orbit coupling
and magnetic roughness at this interface. TMS at the FM/oxide interface is
relatively weak, even in systems where spin-orbit coupling at this interface
generates strong interfacial magnetic anisotropy. We also suggest that the
spin-current-induced excitation of non-uniform short-wavelength magnon at the
HM/FM interface may function as a mechanism of spin memory loss for the
spin-orbit torque exerted on the uniform mode.",2001.00300v1
2020-05-21,Non-Hermitian coherent coupling of nanomagnets by exchange spin waves,"Non-Hermitian physics has recently attracted much attention in optics and
photonics. Less explored is non-Hermitian magnonics that provides opportunities
to take advantage of the inevitable dissipation of magnons or spin waves in
magnetic systems. Here we demonstrate non-Hermitian coherent coupling of two
distant nanomagnets by fast spin waves with sub-50 nm wavelengths. Magnons in
two nanomagnets are unidirectionally phase-locked with phase shifts controlled
by magnon spin torque and spin-wave propagation. Our results are attractive for
analog neuromorphic computing that requires unidirectional information
transmission.",2005.10452v1
2021-03-23,Magnetic field-driven transition between valence bond solid and antiferromagnetic order in distorted triangular lattice,"A molecular Mott insulator $\kappa$-(ET)$_2$B(CN)$_4$ [ET =
bis(ethylenedithio)tetrathiafulvalene] with a distorted triangular lattice
exhibits a quantum disordered state with gapped spin excitation in the ground
state. $^{13}$C nuclear magnetic resonance, magnetization, and magnetic torque
measurements reveal that magnetic field suppresses valence bond order and
induces long-range magnetic order above a critical field $\sim 8$ T. The
nuclear spin-lattice relaxation rate $1/T_1$ shows persistent evolution of
antiferromagnetic correlation above the transition temperature, highlighting a
quantum spin liquid state with fractional excitations. The field-induced
transition as observed in the spin-Peierls phase suggests that the valence bond
order transition is driven through renormalized one-dimensionality and
spin-lattice coupling.",2103.12249v1
2021-06-03,Spin Vortex Crystal Order in Organic Triangular Lattice Compound,"Organic salts represent an ideal experimental playground for studying the
interplay between magnetic and charge degrees of freedom, which has culminated
in the discovery of several spin-liquid candidates, such as
$\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ ($\kappa$-Cu). Recent theoretical studies
indicate the possibility of chiral spin liquids stabilized by ring-exchange,
but the parent states with chiral magnetic order have not been observed in this
material family. In this work, we discuss the properties of the recently
synthesized $\kappa$-(BETS)$_2$Mn[N(CN)$_2$]$_3$ ($\kappa$-Mn). Based on
analysis of specific heat, magnetic torque, and NMR measurements combined with
ab initio calculations, we identify a spin-vortex crystal order. These
observations definitively confirm the importance of ring-exchange in these
materials, and support the proposed chiral spin-liquid scenario for triangular
lattice organics.",2106.02130v1
2021-12-28,Spin-orbit coupling for close-in planets,"We study the spin evolution of close-in planets in multi-body systems and
present a very general formulation of the spin-orbit problem. This includes a
simple way to probe the spin dynamics from the orbital perturbations, a new
method for computing forced librations and tidal deformation, and general
expressions for the tidal torque and capture probabilities in resonance. We
show that planet-planet perturbations can drive the spin of Earth-size planets
into asynchronous or chaotic states, even for nearly circular orbits. We apply
our results to Mercury and to the KOI-1599 system of two super-Earths in a 3/2
mean motion resonance.",2112.14335v1
2022-03-30,Atomistic modeling of spin and electron dynamics in two-dimensional magnets switched by two-dimensional topological insulators,"To design fast memory devices, we need material combinations which can
facilitate fast read and write operation. We present a heterostructure
comprising a two-dimensional (2D) magnet and a 2D topological insulator (TI) as
a viable option for designing fast memory devices. We theoretically model
spin-charge dynamics between the 2D magnets and 2D TIs. Using the adiabatic
approximation, we combine the non-equilibrium Green's function method for
spin-dependent electron transport, and time-quantified Monte-Carlo for
simulating magnetization dynamics. We show that it is possible to switch the
magnetic domain of a ferromagnet using spin-torque from spin-polarized edge
states of 2D TI. We further show that the switching between TIs and 2D magnets
is strongly dependent on the interface exchange ($J_{\mathrm{int}}$), and an
optimal interface exchange depending on the exchange interaction within the
magnet is required for efficient switching. Finally, we compare the
experimentally grown Cr-compounds and show that Cr-compounds with higher
anisotropy (such as $\rm CrI_3$) results in lower switching speed but more
stable magnetic order.",2203.16008v1
2022-08-06,Giant spin Hall effect in half-Heusler alloy topological semimetal YPtBi grown at low temperature,"Half-Heusler alloy topological semimetal YPtBi is a promising candidate for
an efficient spin source material having both large spin Hall angle
${\theta}$$_{SH}$ and high thermal stability. However, high-quality YPtBi thin
films with low bulk carrier density are usually grown at 600${\deg}$C, which
exceeds the limitation of 400${\deg}$C for back end of line (BEOL) process.
Here, we investigate the crystallinity and spin Hall effect of YPtBi thin films
grown at lower growth temperature down to 300${\deg}$C. Although
${\theta}$$_{SH}$ degraded with lowering the growth temperature to 300${\deg}$C
due to degradation of the crystallinity, it was recovered by reducing the
sputtering Ar gas pressure. We achieved a giant ${\theta}$$_{SH}$ up to 8.2 and
demonstrated efficient spin-orbit torque magnetization switching by ultralow
current density of ~10$^5$ A/cm$^2$ in YPtBi grown at 300${\deg}$C with the Ar
gas pressure of 1 Pa. Our results provide the recipe to achieve giant
${\theta}$$_{SH}$ in YPtBi grown at lower growth temperature suitable for BEOL
process.",2208.03413v1
2023-01-27,A semi-analytical model to simulate the spin-diode effect and accelerate its use in neuromorphic computing,"The spin-diode effect is studied both experimentally and with our original
semi-analytical method. The latter is based on an improved version of the
Thiele equation approach (TEA) that we combine to micromagnetic simulation data
to accurately model the non-linear dynamics of spin-torque vortex oscillator
(STVO). This original method, called data-driven Thiele equation approach
(DD-TEA), absorbs the difference between the analytical model and micromagnetic
simulations to provide a both ultra-fast and quantitative model. The DD-TEA
model predictions also agree very well with the experimental data. The reversal
of the spin-diode effect with the chirality of the vortex, the impact of the
input current and the origin of a variation at half of the STVO frequency are
presented as well as the ability of the model to reproduce the experimental
behavior. Finally, the spin-diode effect and its simulation using the DD-TEA
model are discussed as a promising perspective in the framework of neuromorphic
computing.",2301.11980v1
2023-05-15,Magnetoresistive RAM with n-doped AlGaAs/GaAs writing/reading channels,"We show that the tunable gate voltage in n-doped AlGaAs/GaAs QW (quantum
well) is a key in designing an efficient and ultrafast MRAM (magnetoresistive
random access memory). The Rashba spin-orbit coupling in such QWs can be tuned
appropriately by the gate voltage to create an intense spin-Hall field which in
turns interacts with the ferromagnetic layer of the MRAM through the mechanism
of spin orbit torque. The strong spin-Hall field leads to an infinitesimally
small switching time of the MRAM. Our proposed MRAM is thus a better
alternative to the conventional ferromagnetic/spin-Hall effect bi-layers MRAM
for the reason that the switching time can be varied with ease, which is
unfeasible in the later. Concisely, not only that this work signals a
possibility to design an ultra-fast MRAM, but it also suggests a model to
fabricate a tunable switching time MRAM.",2305.08565v1
2024-01-26,Rotational evolution of young-to-old stars with data-driven three-dimensional wind models,"Solar-type stars form with a wide range of rotation rates. A wide range
persists until a stellar age of 0.6 Gyr, after which solar-type stars exhibit
Skumanich spin-down. Rotational evolution models incorporating polytropic
stellar winds struggle to simultaneously reproduce these two regimes, namely
the initially wide range and the Skumanich spin-down without imposing an
a-priori cap on the wind mass-loss rate. We show that a three-dimensional wind
model driven by Alfv\'en waves and observational data yields wind torques that
agree with the observed age distribution of rotation rates. In our models of
the Sun and twenty-seven open cluster stars aged from 0.04 to 0.6 Gyr that have
observationally derived surface magnetic maps and rotation rates, we find
evidence of exponential spin-down in young stars that are rapid rotators and
Skumanich spin-down for slow rotators. The two spin-down regimes emerge
naturally from our data-driven models. Our modelling suggests that the observed
age distribution of stellar rotation rates arises as a consequence of magnetic
field strength saturation in rapid rotators.",2401.14747v1
2022-02-24,Magnon boundary states tailored by longitudinal spin-spin interactions and topology,"Since longitudinal spin-spin interaction is ubiquitous in magnetic materials,
it is very interesting to explore the interplay between topology and
longitudinal spin-spin interaction. Here, we examine the role of longitudinal
spin-spin interaction on topological magnon excitations. Remarkably, even for
single-magnon excitations, we discover topological edge states and defect edge
states of magnon excitations in a dimerized Heisenberg XXZ chain and their
topological properties can be distinguished via adiabatic quantum transport. We
uncover topological phase transitions induced by longitudinal spin-spin
interactions whose boundary is analytically obtained via the transfer matrix
method. For multi-magnon excitations, even-magnon bound states are found to be
always topologically trivial, but odd-magnon bound states may be topologically
nontrivial due to the interplay between the transverse dimerization and the
longitudinal spin-spin interaction. For two-dimensional spin systems, the
longitudinal spin-spin interaction contributes to the coexistence of defect
corner states, second-order topological corner states and first-order
topological edge states. Our work opens an avenue for exploring topological
magnon excitations and has potential applications in topological magnon
devices.",2202.13780v2
2007-12-11,Adiabatic Quantum Transport in a Spin Chain with a Moving Potential,"Many schemes to realize quantum state transfer in spin chains are not robust
to random fluctuations in the spin-spin coupling strength. In efforts to
achieve robust quantum state transfer, an adiabatic quantum population transfer
scheme is proposed in this study. The proposed scheme makes use of a slowly
moving external parabolic potential and is qualitatively explained in terms of
the adiabatic following of a quantum state with a moving separatrix structure
in the classical phase space of a pendulum analogy. Detailed aspects of our
adiabatic population transfer scheme, including its robustness, is studied
computationally. Applications of our adiabatic scheme in quantum information
transfer are also discussed, with emphasis placed on the usage of a dual spin
chain to encode quantum phases. The results should also be useful for the
control of electron tunneling in an array of quantum dots.",0712.1628v1
2009-02-21,Quantum Data Bus in Dipolar Coupled Nuclear Spin Qubits,"We implement an iterative quantum state transfer exploiting the natural
dipolar couplings in a spin chain of a liquid crystal NMR system. During each
iteration a finite part of the amplitude of the state is transferred and by
applying an external operation on only the last two spins the transferred state
is made to accumulate on the spin at the end point. The transfer fidelity
reaches one asymptotically through increasing the number of iterations. We also
implement the inverted version of the scheme which can transfer an arbitrary
state from the end point to any other position of the chain and entangle any
pair of spins in the chain, acting as a full quantum data bus.",0902.3719v3
2010-05-17,Quantum state transfer in spin chains with q-deformed interaction terms,"We study the time evolution of a single spin excitation state in certain
linear spin chains, as a model for quantum communication. Some years ago it was
discovered that when the spin chain data (the nearest neighbour interaction
strengths and the magnetic field strengths) are related to the Jacobi matrix
entries of Krawtchouk polynomials or dual Hahn polynomials, so-called perfect
state transfer takes place. The extension of these ideas to other types of
discrete orthogonal polynomials did not lead to new models with perfect state
transfer, but did allow more insight in the general computation of the
correlation function. In the present paper, we extend the study to discrete
orthogonal polynomials of q-hypergeometric type. A remarkable result is a new
analytic model where perfect state transfer is achieved: this is when the spin
chain data are related to the Jacobi matrix of q-Krawtchouk polynomials. The
other cases studied here (affine q-Krawtchouk polynomials, quantum q-Krawtchouk
polynomials, dual q-Krawtchouk polynomials, q-Hahn polynomials, dual q-Hahn
polynomials and q-Racah polynomials) do not give rise to models with perfect
state transfer. However, the computation of the correlation function itself is
quite interesting, leading to advanced q-series manipulations.",1005.2912v1
2010-07-27,Effect of perturbations on information transfer in spin chains,"Spin chains have been proposed as a reliable and convenient way of
transferring information and entanglement in a quantum computational context.
Nonetheless, it has to be expected that any physical implementation of these
systems will be subject to several perturbative factors which could potentially
diminish the transfer quality. In this paper, we investigate a number of
possible fabrication defects in the spin chains themselves as well as the
effect of non-synchronous or imperfect input operations, with a focus on the
case of multiple excitation/qubit transfer. We consider both entangled and
unentangled states, and in particular the transfer of an entangled pair of
adjacent spins at one end of a chain under the mirroring rule and also the
creation of entanglement resulting from injection at both end spins.",1007.4746v3
2014-03-28,Quantum-state transfer in spin chains via isolated resonance of terminal spins,"We propose a quantum-state transfer protocol in a spin chain that requires
only the control of the spins at the ends of the quantum wire. The protocol is
to a large extent insensitive to inhomogeneity caused by local magnetic fields
and perturbation of exchange couplings. Moreover, apart from the free evolution
regime, it allows one to induce an adiabatic spin transfer, which provides the
possibility of performing the transfer on demand. We also show that the amount
of information leaking into the central part of the chain is small throughout
the whole transfer process (which protects the information sent from being
eavesdropped) and can be controlled by the magnitude of the external magnetic
field.",1403.7359v2
2020-05-04,Almost exact state transfer in a spin chain via pulse control,"Quantum communication through spin chains has been extensively investigated.
In this scenario, state transfer through linearly arranged spins connected by
uniform nearest-neighbor couplings qualifies as a natural choice, with minimal
control requirements. However, quantum states usually cannot be perfectly
transferred through a uniformly coupled chain due to the dispersion of the
chain. Here, we propose an effective quantum control technique to realize
almost exact state transfer (AEST) in a quantum spin chain. The strategy is to
add a leakage elimination operator (LEO) Hamiltonian to the evolution, which
implements a sequence of pulse control acting on a perfect state transfer
subspace. By using the one-component Feshbach PQ partitioning technique, we
obtain the conditions over the required pulses. AEST through a spin chain can
then be obtained under a suitable pulse intensity and duration.",2005.01311v1
2007-12-07,Tidal friction in close-in satellites and exoplanets. The Darwin theory re-visited,"This report is a review of Darwin's classical theory of bodily tides in which
we present the analytical expressions for the orbital and rotational evolution
of the bodies and for the energy dissipation rates due to their tidal
interaction. General formulas are given which do not depend on any assumption
linking the tidal lags to the frequencies of the corresponding tidal waves
(except that equal frequency harmonics are assumed to span equal lags).
Emphasis is given to the cases of companions having reached one of the two
possible final states: (1) the super-synchronous stationary rotation resulting
from the vanishing of the average tidal torque; (2) the capture into a 1:1
spin-orbit resonance (true synchronization). In these cases, the energy
dissipation is controlled by the tidal harmonic with period equal to the
orbital period (instead of the semi-diurnal tide) and the singularity due to
the vanishing of the geometric phase lag does not exist. It is also shown that
the true synchronization with non-zero eccentricity is only possible if an
extra torque exists opposite to the tidal torque. The theory is developed
assuming that this additional torque is produced by an equatorial permanent
asymmetry in the companion. The results are model-dependent and the theory is
developed only to the second degree in eccentricity and inclination
(obliquity). It can easily be extended to higher orders, but formal accuracy
will not be a real improvement as long as the physics of the processes leading
to tidal lags is not better known.",0712.1156v3
2010-09-23,Time dependent configuration interaction simulations of spin swap in spin orbit coupled double quantum dots,"We perform time-dependent simulations of spin exchange for an electron pair
in laterally coupled quantum dots. The calculation is based on configuration
interaction scheme accounting for spin-orbit (SO) coupling and
electron-electron interaction in a numerically exact way. Noninteracting
electrons exchange orientations of their spins in a manner that can be
understood by interdot tunneling associated with spin precession in an
effective SO magnetic field that results in anisotropy of the spin swap. The
Coulomb interaction blocks the electron transfer between the dots but the spin
transfer and spin precession due to SO coupling is still observed. The
electron-electron interaction additionally induces an appearance of spin
components in the direction of the effective SO magnetic field which are
opposite in both dots. Simulations indicate that the isotropy of the spin swap
is restored for equal Dresselhaus and Rashba constants and properly oriented
dots.",1009.4562v1
2002-04-13,An Analytical Approach to the Spin-Distribution of Dark Halos,"We derive the distribution of the dimensionless specific angular momentum of
dark matter halos, $P(j)$, in the framework of the standard tidal torque
theory, and explain the characteristic shape of $P(j)$ commonly observed in
N-body simulations. A scalar quantity (shear scalar), $r$, is introduced for
measuring the effective strength of the tidal torque force acting upon the halo
from the surrounding matter. It is found that the ubiquitous and broad shape of
$P(j)$ can mostly be attributed to the unique property of the shear scalar $r$,
and also that $P(j)$ is insensitve to the underlying collapse dynamics. Our
result demonstrates that although the shape of $P(j)$ is ubiquitous and close
to log-normal, the distribution is not exactly log-normal but decays
exponentially at the high angular momentum end, and drops slowly as a power-law
with an index 2 at the low angular momentum end.",0204221v1
2002-04-22,The Effects of Burst Activity on Soft Gamma Repeater Pulse Properties and Persistent Emission,"Soft Gamma Repeaters (SGRs) undergo changes in their pulse properties and
persistent emission during episodes of intense burst activity. SGR 1900+14 has
undergone large flux increases following recent burst activity. Both SGR
1900+14 and SGR 1806-20 have shown significant changes in their pulse profile
and spin-down rates during the last several years. The pulse profile changes
are linked with the burst activity whereas the torque variations are not
directly correlated with the bursts. Here, we review the observed dynamics of
the pulsed and persistent emission of SGR 1900+14 and SGR 1806-20 during burst
active episodes and discuss what implications these results have for the burst
emission mechanism, the magnetic field dynamics of magnetars, the nature of the
torque variability, and SGRs in general.",0204369v1
2003-10-08,Accretion Onto Fast X-Ray Pulsars,"The recent emergence of a new class of accretion-powered, transient,
millisecond X-ray pulsars presents some difficulties for the conventional
picture of accretion onto rapidly rotating magnetized neutron stars and their
spin behavior during outbursts. In particular, it is unclear from the standard
paradigm how these systems manage to accrete over such a wide range in dM/dt
(i.e., >~ a factor of 50), and why the neutron stars exhibit a high rate of
spindown in at least a number of cases. Following up on prior suggestions, we
propose that `fast' X-ray pulsars can continue to accrete, and that their
accretion disks terminate at approximately the corotation radius. We
demonstrate the existence of such disk solutions by modifying the
Shakura-Sunyaev equations with a simple magnetic torque prescription. The
solutions are completely analytic, and have the same dependence on dM/dt and
alpha (the viscosity parameter) as the original Shakura-Sunyaev solutions; but,
the radial profiles can be considerably modified, depending on the degree of
fastness. We apply these results to compute the torques expected during the
outbursts of the transient millisecond pulsars, and find that we can explain
the large spindown rates that are observed for quite plausible surface magnetic
fields of ~10^9 G.",0310224v1
2004-03-03,On the nature of eclipses in binary pulsar J0737-3039,"We consider magnetohydrodynamical interaction between relativistic pulsar
wind and static magnetosphere in binary pulsar system PSR J0737-3039. We
construct semi-analytical model describing the form of the interface separating
the two pulsars.
  An assumption of vacuum dipole spin down for Pulsar B leads to eclipse
duration ten times longer than observed. We discuss possible Pulsar B torque
modification and magnetic field estimates due to the interaction with
  Pulsar A wind.
  Unless the orbital inclination is $\leq 86 ^\circ$, the duration of eclipses
is typically shorter than the one implied by the size of the eclipsing region.
We propose that eclipses occur due to synchrotron absorption by mildly
relativistic particles in the shocked Pulsar A wind. The corresponding optical
depth may be high enough if Pulsar A wind density is at the upper allowed
limits. We derive jump conditions at oblique, relativistic,
magnetohydrodynamical shocks and discuss the structure of the shocked Pulsar A
wind. Finally, we speculate on a possible mechanism of orbital modulation of
Pulsar B radio emission.",0403076v2
2004-03-26,Does Disk Locking Solve the Stellar Angular Momentum Problem?,"We critically examine the theory of disk locking, which assumes that the
angular momentum deposited on an accreting protostar is exactly removed by
torques carried along magnetic field lines connecting the star to the disk. In
this letter, we consider that the differential rotation between the star and
disk naturally leads to an opening (i.e., disconnecting) of the magnetic field
between the two. We find that this significantly reduces the spin-down torque
on the star by the disk. Thus, disk-locking cannot account for the slow
rotation ($\sim$10% of breakup speed) observed in several systems and for which
the model was originally developed.",0403635v2
2008-08-01,Review: galactic angular momenta and angular momentum correlations in the cosmological large-scale structure,"I review the theory of angular momentum acquisition of galaxies by tidal
torquing, the resulting angular momentum distribution, the angular momentum
correlation function and discuss the implications of angular momentum
alignments on weak lensing measurements: Starting from linear models for tidal
torquing I summarise perturbative approaches and the results from n-body
simulations of cosmic structure formation. Then I continue to discuss the
validity of decompositions of the tidal shear and inertia fields, the effects
of angular momentum biasing, the applicability of parameterised angular
momentum correlation models and the consequences of angular momentum
correlations for shape alignments. I compile the result of observations of
shape alignments in recent galaxy surveys as well as in n-body simulations.
Finally, I review the contamination of weak lensing surveys by spin-induced
shape alignments and methods for suppressing this contamination.",0808.0203v1
2009-01-12,Bose-Einstein Condensation of Triplons in Ba3Cr2O8,"By performing heat capacity, magnetocaloric effect, torque magnetometry and
force magnetometry measurements up to 33 T, we have mapped out the T-H phase
diagram of the S = 1/2 spin dimer compound Ba3Cr2O8. We found evidence for
field-induced magnetic order between Hc1 = 12.52(2) T and Hc2 = 23.65(5) T,
with the maximum transition temperature Tc = 2.7 K at H = 18 T. The lower
transition can likely be described by Bose-Einstein condensation of triplons
theory, and this is consistent with the absence of any magnetization plateaus
in our magnetic torque and force measurements. In contrast, the nature of the
upper phase transition appears to be quite different as our measurements
suggest that this transition is actually first order.",0901.1623v2
2009-05-26,Scattering Theory of Charge-Current Induced Magnetization Dynamics,"In ferromagnets, charge currents can excite magnons via the spin-orbit
coupling. We develop a novel and general scattering theory of charge current
induced macrospin magnetization torques in normal metal$|$ferromagnet$|$normal
metal layers. We apply the formalism to a dirty GaAs$|$(Ga,Mn)As$|$GaAs system.
By computing the charge current induced magnetization torques and solving the
Landau-Lifshitz-Gilbert equation, we find magnetization switching for current
densities as low as $ 5\times 10^{6}$~A/cm$^2$. Our results are in agreement
with a recent experimental observation of charge-current induced magnetization
switching in (Ga,Mn)As.",0905.4170v2
2010-11-05,Determination of the Upper Critical Field of a Single Crystal LiFeAs: The Magnetic Torque Study up to 35 Tesla,"We report on the upper critical field B_c2 of a superconducting LiFeAs single
crystal with T_c~16 K, determined from magnetic torque measurements in
dc-magnetic fields up to 35 T and at temperatures down to 0.3 K. B_c2 at 0.3 K
is obtained to be 26.4 T and 15.5 T for the applied field B_a||ab and B_a||c,
respectively. The anisotropy parameter $\Gamma$=$B_c2^ab / B_c2^c$ is ~ 3 at
T_c and decreases to 1.7 as $T \rightarrow 0$, showing rather isotropic
superconductivity. While B_c2 is orbitally-limited for B_a||c, the
spin-paramagnetic effect is evident in the temperature dependence of B_c2 for
B_a||ab",1011.1334v3
2011-10-29,Thin Disk Theory with a Non-Zero Torque Boundary Condition and Comparisons with Simulations,"We present an analytical solution for thin disk accretion onto a Kerr black
hole that extends the standard Novikov-Thorne alpha-disk in three ways: (i) it
incorporates nonzero stresses at the inner edge of the disk, (ii) it extends
into the plunging region, and (iii) it uses a corrected vertical gravity
formula. The free parameters of the model are unchanged. Nonzero boundary
stresses are included by replacing the Novikov-Thorne no torque boundary
condition with the less strict requirement that the fluid velocity at the
innermost stable circular orbit is the sound speed, which numerical models show
to be the correct behavior for luminosities below ~30% Eddington. We assume the
disk is thin so we can ignore advection. Boundary stresses scale as alpha*h and
advection terms scale as h^2 (where h is the disk opening angle (h=H/r)), so
the model is self-consistent when h < alpha. We compare our solution with slim
disk models and general relativistic magnetohydrodynamic disk simulations. The
model may improve the accuracy of black hole spin measurements.",1110.6556v1
2012-04-23,Rotating skyrmion lattices by spin torques and field or temperature gradients,"Chiral magnets like MnSi form lattices of skyrmions, i.e. magnetic whirls,
which react sensitively to small electric currents j above a critical current
density jc. The interplay of these currents with tiny gradients of either the
magnetic field or the temperature can induce a rotation of the magnetic pattern
for j>jc. Either a rotation by a finite angle of up to 15 degree or -- for
larger gradients -- a continuous rotation with a finite angular velocity is
induced. We use Landau-Lifshitz-Gilbert equations extended by extra damping
terms in combination with a phenomenological treatment of pinning forces to
develop a theory of the relevant rotational torques. Experimental neutron
scattering data on the angular distribution of skyrmion lattices suggests that
continuously rotating domains are easy to obtain in the presence of remarkably
small currents and temperature gradients.",1204.5051v1
2012-07-13,Binary Black-Hole Mergers in Magnetized Disks: Simulations in Full General Relativity,"We present results from the first fully general relativistic,
magnetohydrodynamic (GRMHD) simulations of an equal-mass black hole binary
(BHBH) in a magnetized, circumbinary accretion disk. We simulate both the pre
and post-decoupling phases of a BHBH-disk system and both ""cooling"" and
""no-cooling"" gas flows. Prior to decoupling, the competition between the binary
tidal torques and the effective viscous torques due to MHD turbulence depletes
the disk interior to the binary orbit. However, it also induces a two-stream
accretion flow and mildly relativistic polar outflows from the BHs. Following
decoupling, but before gas fills the low-density ""hollow"" surrounding the
remnant, the accretion rate is reduced, while there is a prompt electromagnetic
(EM) luminosity enhancement following merger due to shock heating and accretion
onto the spinning BH remnant. This investigation, though preliminary, previews
more detailed GRMHD simulations we plan to perform in anticipation of future,
simultaneous detections of gravitational and EM radiation from a merging
BHBH-disk system.",1207.3354v2
2012-10-01,Staggered Dynamics in Antiferromagnets by Collective Coordinates,"Antiferromagnets can be used to store and manipulate spin information, but
the coupled dynamics of the staggered field and the magnetization are very
complex. We present a theory which is conceptually much simpler and which uses
collective coordinates to describe staggered field dynamics in
antiferromagnetic textures. The theory includes effects from dissipation,
external magnetic fields, as well as reactive and dissipative current-induced
torques. We conclude that, at low frequencies and amplitudes, currents induce
collective motion by means of dissipative rather than reactive torques. The
dynamics of a one-dimensional domain wall, pinned at 90$^{\circ}$ at its ends,
are described as a driven harmonic oscillator with a natural frequency
inversely proportional to the length of the texture.",1210.0429v2
2013-06-10,"Magnetospheric ""anti-glitches"" in magnetars","We attribute the rapid spindown of magnetar 1E 2259+586 observed by Archibald
et al. (2013), termed the ""anti-glitch"", to partial opening of the
magnetosphere during the X-ray burst, followed by changes of the structure of
the closed field line region. To account for the observed spin decrease during
the X- ray flare all that is needed is the transient opening, for just one
period, of a relatively small fraction of the magnetosphere, of the order of
only few percent. More generally, we argue that in magnetars all timing
irregularities have magnetospheric origin and are induced either by (i) the
fluctuations in the current structure of the magnetosphere (similar to the long
term torque variations in the rotationally powered pulsars); or, specifically
to magnetars, by (ii) opening of a fraction of the magnetosphere during bursts
and flares - the latter events are always accompanied by rapid spindown, an
""anti-glitch"". Slow rotational motion of the neutron star crust, driven by
crustal magnetic fields, leads beyond some twist limit to explosive instability
of the external magnetic fields and transient opening of a large magnetic flux
in a CME-type event, the post-flares increase of magnetospheric currents
accompanied by enhanced X-luminosity and spindown rate, changing profiles, as
well as spectral hardening, all in agreement with the magnetospheric model of
torque fluctuations.",1306.2264v1
2013-08-06,Spin Hall torque magnetometry of Dzyaloshinskii domain walls,"Current-induced domain wall motion in the presence of the
Dzyaloshinskii-Moriya interaction (DMI) is experimentally and theoretically
investigated in heavy-metal/ferromagnet bilayers. The angular dependence of the
current-induced torque and the magnetization structure of Dzyaloshinskii domain
walls are described and quantified simultaneously in the presence of in-plane
fields. We show that the DMI strength depends strongly on the heavy metal,
varying by a factor of 20 between Ta and Pa, and that strong DMI leads to wall
distortions not seen in conventional materials. These findings provide
essential insights for understanding and exploiting chiral magnetism for
emerging spintronics applications.",1308.1432v2
2016-07-05,Magnetic moment of inertia within the breathing model,"An essential property of magnetic devices is the relaxation rate in magnetic
switching which strongly depends on the energy dissipation and magnetic inertia
of the magnetization dynamics. Both parameters are commonly taken as a
phenomenological entities. However very recently, a large effort has been
dedicated to obtain Gilbert damping from first principles. In contrast, there
is no ab initio study that so far has reproduced measured data of magnetic
inertia in magnetic materials. In this letter, we present and elaborate on a
theoretical model for calculating the magnetic moment of inertia based on the
torque-torque correlation model. Particularly, the method has been applied to
bulk bcc Fe, fcc Co and fcc Ni in the framework of the tight-binding
approximation and the numerical values are comparable with recent experimental
measurements. The theoretical results elucidate the physical origin of the
moment of inertia based on the electronic structure. Even though the moment of
inertia and damping are produced by the spin-orbit coupling, our analysis shows
that they are caused by undergo different electronic structure mechanisms.",1607.01307v1
2017-07-19,"Optical forces, torques and force densities calculated at a microscopic level using a self-consistent hydrodynamics method","The calculation of optical force density distribution within a material is
challenging at the nanoscale, where quantum and non-local effects emerge and
macroscopic parameters such as permittivity become ill-defined. We demonstrate
that the microscopic optical force density of nanoplasmonic systems can be
defined and calculated using a self-consistent hydrodynamics model that
includes quantum, non-local and retardation effects. We demonstrate this
technique by calculating the microscopic optical force density distributions
and the optical binding force induced by external light on nanoplasmonic
dimers. We discover that an uneven distribution of optical force density can
lead to a spinning torque acting on individual particles.",1707.06178v1
2017-12-20,Effects of Disk Warping on the Inclination Evolution of Star-Disk-Binary Systems,"Several recent studies have suggested that circumstellar disks in young
stellar binaries may be driven into misalignement with their host stars due to
secular gravitational interactions between the star, disk and the binary
companion. The disk in such systems is twisted/warped due to the gravitational
torques from the oblate central star and the external companion. We calculate
the disk warp profile, taking into account of bending wave propagation and
viscosity in the disk. We show that for typical protostellar disk parameters,
the disk warp is small, thereby justifying the ""flat-disk"" approximation
adopted in previous theoretical studies. However, the viscous dissipation
associated with the small disk warp/twist tends to drive the disk toward
alignment with the binary or the central star. We calculate the relevant
timescales for the alignment. We find the alignment is effective for
sufficiently cold disks with strong external torques, especially for systems
with rapidly rotating stars, but is ineffective for the majority of
star-disk-binary systems. Viscous warp driven alignment may be necessary to
account for the observed spin-orbit alignment in multi-planet systems if these
systems are accompanied by an inclined binary companion.",1712.07655v2
2018-01-14,The quantum centripetal force on a free particle confined to the surface of a sphere and a cylinder,"The momentum operator for a spin-less particle when confined to a 2D surface
embedded into 3D space acquires a geometrical component proportional to the
mean curvature that renders it Hermitian. As a consequence, the quantum force
operator for a particle confined to spherical and cylindrical surfaces, and
free otherwise, derived by applying the Heisenberg equation of motion is found
to have an apparently no-radial component in addition to the standard classical
radial centripetal force. This component which renders the force operator
Hermitian is shown to be essential for the vanishing of the torque the force
exerts on the particle and so for the conservation of orbital angular momentum
and energy. It is demonstrated that the total force is in fact radial as should
be the case for a torque-less one and so can be identified as the quantum
centripetal force.",1801.04610v1
2018-03-27,A new equilibrium state for singly synchronous binary asteroids,"The evolution of rotation states of small asteroids is governed by the YORP
effect, nonetheless some asteroids can stop their YORP evolution by attaining a
stable equilibrium. The same is true for binary asteroids subjected to the
BYORP effect. Here we discuss a new type of equilibrium that combines these
two, which is possible in a singly synchronous binary system. This equilibrium
occurs when the normal YORP, the tangential YORP and the binary YORP compensate
each other, and tidal torques distribute the angular momentum between the
components of the system and dissipate energy. Such a system if unperturbed
would remain singly synchronous in perpetuity with constant spin and orbit
rates, as the tidal torques dissipate the incoming energy from impinging
sunlight at the same rate. The probability of the existence of this kind of
equilibrium in a binary system is found to be on the order of a few percent.",1803.10020v1
2018-05-08,Electric-field-induced Three-terminal pMTJ Switching in the absence of an External Magnetic Field,"Since it is undesirable to require an external magnetic field for on-chip
memory applications, we investigate the use of a Rashba effective field
alternatively for assisting the electric-field-induced switching operation of a
three terminal perpendicular magnetic tunnel junction (pMTJ). By conducting
macro-spin simulation, we show that a pMTJ with thermal stability of 61 can be
switched in 0.5 ns consuming a switching energy of 6 fJ, and the voltage
operation margin can be improved to 0.8 ns. Furthermore, the results also
demonstrate that a heavy metal system that can provide large field-like torque
rather than damping-like torque is favored for the switching.",1805.02793v1
2019-11-25,Periodic Orbits of Active Particles induced by Hydrodynamic Monopoles,"Terrestrial experiments on active particles, such as Volvox, involve
gravitational forces, torques and accompanying monopolar fluid flows. Taking
these into account, we analyse the dynamics of a pair of self-propelling,
self-spinning active particles between widely separated parallel planes.
Neglecting flow reflected by the planes, the dynamics of orientation and
horizontal separation is symplectic, with a Hamiltonian exactly determining
limit cycle oscillations. Near the bottom plane, gravitational torque damps and
reflected flow excites this oscillator, sustaining a second limit cycle that
can be perturbatively related to the first. Our work provides a theory for
dancing Volvox and highlights the importance of monopolar flow in active
matter.",1911.10970v3
2017-05-26,Dust cluster spin in complex (dusty) plasmas,"The spontaneous rotation of small dust clusters confined inside a cubical
glass box in the sheath of a complex plasma was observed in experiment. Due to
strong coupling between the dust particles, these clusters behave like a
rigid-body where cluster rotation is contingent upon their configuration and
symmetry. By evaluating the effects of distinct contributing forces, it is
postulated that the rotation observed is driven by the net torque exerted on
the cluster by the ion wake force. The configuration and symmetry of a cluster
determines whether the net torque induced by the ion wake force is nonzero, in
turn leading to cluster rotation. A COPTIC (Cartesian mesh, oblique boundary,
particles and thermals in cell) simulation is employed to obtain the ion wake
potential providing a theoretical model of cluster rotation which includes both
the ion wake force and neutral drag and predicts rotation rates and direction
in agreement with experimental results. These results are then used to diagnose
the ion flow within the box.",1705.09683v1
2018-02-08,Exploiting Spin-Orbit Torque Devices as Reconfigurable Logic for Circuit Obfuscation,"Circuit obfuscation is a frequently used approach to conceal logic
functionalities in order to prevent reverse engineering attacks on fabricated
chips. Efficient obfuscation implementations are expected with lower design
complexity and overhead but higher attack difficulties. In this paper, an
emerging obfuscation approach is proposed by leveraging spinorbit torque (SOT)
devices based look-up-tables (LUTs) as reconfigurable logic to replace the
carefully selected gates. It is essentially impossible to identify the
obfuscated gate with SOTs inside according to the physical geometry
characteristics because the configured functionalities are represented by
magnetization states. Such an obfuscation approach makes the circuit security
further improved with high exponential attack complexities. Experiments on MCNC
and ISCAS 85/89 benchmark suits show that the proposed approach could reduce
the area overheads due to obfuscation by 10% averagely.",1802.02789v1
2020-09-24,Magnetic anisotropy and exchange paths for octa- and tetrahedrally coordinated Mn$^{2+}$ ions in the honeycomb multiferroic Mn$_2$Mo$_3$O$_8$,"We investigated the static and dynamic magnetic properties of the polar
ferrimagnet Mn$_2$Mo$_3$O$_8$ in three magnetically ordered phases via
magnetization, magnetic torque, and THz absorption spectroscopy measurements.
The observed magnetic field dependence of the spin-wave resonances, including
Brillouin zone-center and zone-boundary excitations, magnetization, and torque,
are well described by an extended two-sublattice antiferromagnetic classical
mean-field model. In this orbitally quenched system, the competing weak
easy-plane and easy-axis single-ion anisotropies of the two crystallographic
sites are determined from the model and assigned to the tetra- and octahedral
sites, respectively, by ab initio calculations.",2009.11683v1
2020-11-09,Precession of triaxially deformed neutron stars,"A deformed neutron star (NS) will precess if the instantaneous spin axis and
the angular momentum are not aligned. Such a precession can produce continuous
gravitational waves (GWs) and modulate electromagnetic pulse signals of
pulsars. In this contribution we extend our previous work in a more convenient
parameterization. We treat NSs as rigid triaxial bodies and give analytical
solutions for angular velocities and Euler angles. We summarize the general GW
waveforms from freely precessing triaxial NSs and use Taylor expansions to
obtain waveforms with a small wobble angle. For pulsar signals, we adopt a
simple cone model to study the timing residuals and pulse profile modulations.
In reality, the electromagnetic torque acts on pulsars and affects the
precession behavior. Thereof, as an additional extension to our previous work,
we consider a vacuum torque and display an illustrative example for the
residuals of body-frame angular velocities. Detailed investigations concerning
continuous GWs and modulated pulsar signals from forced precession of triaixal
NSs will be given in future studies.",2011.04472v1
2017-03-01,The maximum dipole moments of neutron stars implied by the Barrow-Gibbons conjecture,"The maximum magnetic moment to angular momentum conjecture, recently posed by
Barrow \& Gibbons, is in tension with the generally accepted parameters of
magnetars. According to the conjecture the dimensionless
Schuster-Wilson-Blacket number, $c\mu/J\sqrt{G}$ where $\mu$ is the magnetic
moment and $J$ is the angular momentum, should be of order unity. A resolution
is to assume that not only the low-magnetic field magnetars, but all magnetars
have their super-critical fields in the higher multipoles. This requires the
presence of external torques other than the magnetic dipole torque, such as
from fallback disks or winds, on these systems to yield the measured high
spin-down rates.",1703.00358v2
2020-12-10,Observation of Magnetic Droplets in Magnetic Tunnel Junctions,"Magnetic droplets, a class of highly non-linear magnetodynamical solitons,
can be nucleated and stabilized in nanocontact spin-torque nano-oscillators
where they greatly increase the microwave output power. Here, we experimentally
demonstrate magnetic droplets in magnetic tunnel junctions (MTJs). The droplet
nucleation is accompanied by a power increase of over 300 times compared to its
ferromagnetic resonance modes. The nucleation and stabilization of droplets are
ascribed to the double-CoFeB free layer structure in the all-perpendicular MTJ
which provides a low Zhang-Li torque and a high pinning field. Our results
enable better electrical sensitivity in the fundamental studies of droplets and
show that the droplets can be utilized in MTJ-based applications.",2012.05596v1
2022-11-23,Resonant friction on discs in galactic nuclei,"We argue that resonant friction has a dramatic effect on a disc whose
rotation direction is misaligned with that of its host nuclear star cluster.
The disc's gravity causes gravitational perturbation of the cluster that in
turn exerts a strong torque back onto the disc. We argue that this torque may
be responsible for the observed disruption of the clockwise disc of young stars
in the Galactic Center, and show in numerical experiments that it produces the
observed features in the distribution of the stars' angular momenta. More
generally, we speculate that the rotation of nuclear star clusters has a
stabilizing effect on the orientation of transient massive accretion discs
around the supermassive black holes residing in their centers, and thus on the
directions and magnitudes of the black-hole spins.",2211.12754v1
2023-02-22,Effects of Barnett magnetic dipole-dipole interaction on grain growth and destruction,"Rapidly spinning magnetic grains can acquire large magnetic dipole moments
due to the Barnett effect. Here we study the new effect of Barnett magnetic
dipole-dipole interaction on grain-grain collisions and grain growth, assuming
grains spun up by radiative torques. We find that the collision rate between
grains having embedded iron inclusions can be significantly enhanced due to
Barnett magnetic dipole-dipole interaction when grains rotate suprathermally by
radiative torques. We discuss the implications of enhanced collision rate for
grain growth and destruction in the circumstellar envelope of evolved stars,
photodissociation regions, and protostellar environments. Our results first
reveal the importance of the dust magnetic properties and the local radiation
field on grain growth and destruction.",2302.11690v1
2023-10-26,Trading particle shape with fluid symmetry: on the mobility matrix in 3D chiral fluids,"Chiral fluids - such as fluids under rotation or a magnetic field as well as
synthetic and biological active fluids - flow in a different way than ordinary
ones. Due to symmetries broken at the microscopic level, chiral fluids may have
asymmetric stress and viscosity tensors, for example giving rise to a
hydrostatic torque or non-dissipative (odd) and parity-violating viscosities.
In this article, we investigate the motion of rigid bodies in such an
anisotropic fluid in the incompressible Stokes regime through the mobility
matrix, which encodes the response of a solid body to forces and torques. We
demonstrate how the form of the mobility matrix, which is usually determined by
particle geometry, can be analogously controlled by the symmetries of the
fluid. By computing the mobility matrix for simple shapes in a
three-dimensional anisotropic chiral fluid, we predict counter-intuitive
phenomena such as motion perpendicular to applied forces and spinning under the
force of gravity.",2310.17528v1
2024-02-16,Nonlinear optics driven magnetism reorientation in semiconductors,"Based on nonlinear optics, we develop a band theory to elucidate how light
could manipulate magnetization, which is rooted by the quantum geometric
structure and topological nature of electronic wavefunctions. Their existence
are determined by the light polarization and specific material symmetry, based
on the magnetic group theory. In general, both circularly and linearly
polarized light could exert an effective magnetic field and torque effect, to
reorient the magnetization. They are contributed by spin and orbital angular
momenta simultaneously. Aided by group theory and first-principles
calculations, we illustrate this theory using a showcase example of monolayer
NiCl2, showing that light irradiation effectively generates an out-of-plane
effective magnetic torque, which lifts its in-plane easy magnetization.
According to magnetic dynamic simulations, the in-plane magnetization could be
switched to the out-of-plane direction in a few nanoseconds under a modest
light intensity, demonstrating its ultrafast nature desirable for quantum
manipulation.",2402.10518v1
2006-12-12,Evolution of the Obliquities of the Giant Planets in Encounters during Migration,"Tsiganis et al. (2005) have proposed that the current orbital architecture of
the outer solar system could have been established if it was initially compact
and Jupiter and Saturn crossed the 2:1 orbital resonance by divergent
migration. The crossing led to close encounters among the giant planets, but
the orbital eccentricities and inclinations were damped to their current values
by interactions with planetesimals. Brunini (2006) has presented widely
publicized numerical results showing that the close encounters led to the
current obliquities of the giant planets. We present a simple analytic argument
which shows that the change in the spin direction of a planet relative to an
inertial frame during an encounter between the planets is very small and that
the change in the obliquity (which is measured from the orbit normal) is due to
the change in the orbital inclination. Since the inclinations are damped by
planetesimal interactions on timescales much shorter than the timescales on
which the spins precess due to the torques from the Sun, especially for Uranus
and Neptune, the obliquities should return to small values if they are small
before the encounters. We have performed simulations using the symplectic
integrator SyMBA, modified to include spin evolution due to the torques from
the Sun and mutual planetary interactions. Our numerical results are consistent
with the analytic argument for no significant remnant obliquities.",0612330v2
2010-04-23,Time domain study of frequency-power correlation in spin-torque oscillators,"This paper describes a numerical experiment, based on full micromagnetic
simulations of current-driven magnetization dynamics in nanoscale spin valves,
to identify the origins of spectral linewidth broadening in spin torque
oscillators. Our numerical results show two qualitatively different regimes of
magnetization dynamics at zero temperature: regular (single-mode precessional
dynamics) and chaotic. In the regular regime, the dependence of the oscillator
integrated power on frequency is linear, and consequently the dynamics is well
described by the analytical theory of current-driven magnetization dynamics for
moderate amplitudes of oscillations. We observe that for higher oscillator
amplitudes, the functional dependence of the oscillator integrated power as a
function of frequency is not a single-valued function and can be described
numerically via introduction of nonlinear oscillator power. For a range of
currents in the regular regime, the oscillator spectral linewidth is a linear
function of temperature. In the chaotic regime found at large current values,
the linewidth is not described by the analytical theory. In this regime we
observe the oscillator linewidth broadening, which originates from sudden jumps
of frequency of the oscillator arising from random domain wall nucleation and
propagation through the sample. This intermittent behavior is revealed through
a wavelet analysis that gives superior description of the frequency jumps
compared to several other techniques.",1004.4184v1
2012-06-11,Synchronization of spin-torque driven nanooscillators for point contacts on a quasi-1D nanowire: Micromagnetic simulations,"In this paper we present detailed numerical simulation studies on the
synchronization of two spin-torque nanooscillators (STNO) in the quasi-1D
geometry: magnetization oscillations are induced in a thin NiFe nanostripe by a
spin polarized current injected via square-shaped CoFe nanomagnets on the top
of this stripe. In a sufficiently large out-of-plane field, a propagating
oscillation mode appears in such a system. Due to the absence of the
geometrically caused wave decay in 1D systems, this mode is expected to enable
a long-distance synchronization between STNOs. Indeed, our simulations predict
that synchronization of two STNOs on a nanowire is possible up to the
intercontact distance 3 mkm (for the nanowire width 50 nm). However, we have
also found several qualitatively new features of the synchronization behaviour
for this system, which make the achievement of a stable synchronization in this
geometry to a highly non-trivial task. In particular, there exist a minimal
distance between the nanocontacts, below which a synchronization of STNOs can
not be achieved. Further, when the current value in the first contact is kept
constant, the amplitude of synchronized oscillations depends non-monotonously
on the current value in the second contact. Finally, for one and the same
currents values through the contacts there might exist several synchronized
states (with different frequencies), depending on the initial conditions.",1206.2323v1
2014-01-04,Rotational Behaviors and Magnetic Field Evolution of Radio Pulsars,"The observed long-term spin-down evolution of isolated radio pulsars cannot
be explained by the standard magnetic dipole radiation with a constant braking
torque. However how and why the torque varies still remains controversial,
which is an outstanding problem in our understanding of neutron stars. We have
constructed a phenomenological model of the evolution of surface magnetic
fields of pulsars, which contains a long-term decay modulated by short-term
oscillations; a pulsar's spin is thus modified by its magnetic field evolution.
The predictions of this model agree with the precisely measured spin evolutions
of several individual pulsars; the derived parameters suggest that the Hall
drift and Hall waves in the NS crusts are probably responsible for the
long-term change and short-term quasi-periodical oscillations, respectively.
Many statistical properties of the timing noise of pulsars can be well
re-produced with this model, including correlations and the distributions of
the observed braking indices of the pulsars, which span over a range of more
than 100 millions. We have also presented a phenomenological model for the
recovery processes of classical and slow glitches, which can successfully model
the observed slow and classical glitch events without biases.",1401.0772v1
2014-11-14,Evolution of angular-momentum-losing exoplanetary systems : Revisiting Darwin stability,"We assess the importance of tidal evolution and its interplay with magnetic
braking in the population of hot-Jupiter planetary systems. By minimizing the
total mechanical energy of a given system under the constraint of stellar
angular momentum loss, we rigorously find the conditions for the existence of
dynamical equilibrium states. We estimate their duration, in particular when
the wind torque spinning down the star is almost compensated by the tidal
torque spinning it up. We introduce dimensionless variables to characterize the
tidal evolution of observed hot Jupiter systems and discuss their spin and
orbital states using generalized Darwin diagrams based on our new approach. We
show that their orbital properties are related to the effective temperature of
their host stars. The long-term evolution of planets orbiting F- and G-type
stars is significantly different owing to the combined effect of magnetic
braking and tidal dissipation. The existence of a quasi-stationary state, in
the case of short-period planets, can significantly delay their tidal evolution
that would otherwise bring the planet to fall into its host star. Most of the
planets known to orbit F-type stars are presently found to be near this
stationary state, probably in a configuration not too far from that they had
when their host star settled on the zero-age main sequence. Considering the
importance of angular momentum loss in the early stages of stellar evolution,
our results indicate that it has to be taken into account also to properly test
the migration scenarios of planetary system formation.",1411.3802v2
2014-12-18,The unusual glitch recoveries of the high magnetic field pulsar J1119$-$6127,"Providing a link between magnetars and radio pulsars, high magnetic field
neutron stars are ideal targets to investigate how bursting/magnetospheric
activity and braking torque variations are connected to rotational glitches.
The last spin-up glitch of the highly magnetised pulsar J1119$-$6127 back in
2007 was the first glitch in a rotationally powered radio pulsar to be
accompanied by radiative changes. Moreover, it was followed by an uncommon
glitch relaxation that resulted in a smaller spin-down rate relative to the
prediction of the pre-glitch timing model. Here, we present 4 years of new
radio timing observations and analyse the total of 16 years of timing data for
this source. The new data uncover an ongoing evolution of the spin-down rate,
thereby allowing us to exclude permanent changes in the external or internal
torque as a stand-alone cause of the peculiar features of the glitch recovery.
Furthermore, no additional variations of the radio pulse profile are detected,
strengthening the association of the previously observed transient emission
features with the glitching activity. A self-consistent measurement of the
braking index yields a value $n\simeq2.7$, indicating a trajectory in the
$P-\dot{P}$ plane inclined towards the magnetars. Such a potential evolutionary
link might be strengthened by a, possibly permanent, reduction of $\sim15\%$ in
$n$ at the epoch of the 2007 glitch.",1412.5853v1
2015-11-10,Low braking index of PSR J1734-3333: an interaction between fall-back disk and magnetic field?,"Recent timing observation reported that the radio pulsar PSR J1734 - 3333
with a rotating period $P=1.17~\rm s$ is slowing down with a period derivative
$\dot{P}=2.28\times 10^{-12}\rm s\,s^{-1}$. Its derived braking index $n=0.9
\pm 0.2$ is the lowest value among young radio pulsars with the measured
braking indices. In this Letter, we attempt to investigate the influence of the
braking torque caused by the interaction between the fall-back disk and the
strong magnetic field of the pulsar on the spin evolution of PSR J1734 - 3333.
Analytical result show that this braking torque is obviously far more than that
by magnetic dipole radiation for pulsars with spin period of $> 0.1$ s, and
play an important role during the spin-down of the pulsars. Our simulated
results indicate that, for some typical neutron star parameters, the braking
index and the period derivative approximately in agreement with the measured
value of PSR J1734 - 3333 if the material inflow rate in the fallback disk is
$2 \times 10^{17} \rm g\,s^{-1}$. In addition, our scenario can account for the
measured braking indices of four young pulsars. However, our predicted X-ray
luminosity are 1 -2 order of magnitude higher than the observation. We proposed
that this discrepancy may originate from the instability of fall-back disk.",1511.03111v1
2017-09-13,Field-free perpendicular magnetization switching through domain wall motion in Pt/Co/Cr racetracks by spin orbit torques with the assistance of accompanying Joule heating effect,"Heavy metal/ferromagnetic layers with perpendicular magnetic anisotropy (PMA)
have potential applications for high-density information storage in racetrack
memories and nonvolatile magnetic random access memories. Writing and erasing
of information in these devices are carried out by domain wall (DW) motion and
deterministic magnetization switching via electric current generated spin
orbital torques (SOTs) with an assistance of in-plane bias field to break the
symmetry. Improvements in energy efficiency could be obtained when the
switching of perpendicular magnetization is controlled by an electric current
generated SOTs without the in-plane bias fields. Here, we report on reversible
electric-current-driven magnetization switching through DW motion in Pt/Co/Cr
trilayers with PMA at room temperature due to the formation of homochiral
Neel-type domain, in which an in-plane effective Dzyaloshinskii-Moriya
interaction field exists. Fully deterministic magnetic magnetization switching
in this trilayers is based on the enhancement of SOTs from a dedicated design
of Pt/Co/Cr structures with two heavy metals Pt and Cr which show the opposite
sign of spin Hall angles. We also demonstrated that the simultaneously
accompanying Joule heating effect also plays a key role for field-free
magnetization switching through the decrease of the propagation field.",1709.04315v1
2018-11-23,Deviations from tidal torque theory: environment dependences on halo angular momentum growth,"The tidal torque theory (TTT) relates the origin and evolution of angular
momentum with the environment in which dark matter (DM) haloes form. The
deviations introduced by late non-linearities are commonly thought as noise in
the model. In this work, we analyze a cosmological simulation looking for
systematics on these deviations, finding that the classification of DM haloes
according to their angular momentum growth results in samples with different
internal alignment, spin parameter distribution and assembly history. Based on
this classification, we obtain that low mass haloes are embedded in denser
environments if they have acquired angular momentum below the TTT expectations
(L haloes), whereas at high masses enhanced clustering is typically associated
with higher angular momentum growths (W haloes). Additionally, we find that the
low mass signal has a weak dependence on the direction, whereas the high mass
signal is entirely due to the structure perpendicular to the angular momentum.
Finally, we study the anisotropy of the matter distribution around haloes as a
function of their mass. We find that the angular momentum direction of W (L)
haloes remains statistically perpendicular (parallel) to the surrounding
structure across the mass range
$11<\mathrm{log}(M/h^{-1}\mathrm{M}_{\odot})<14$, whereas haloes following TTT
show a ""spin flip"" mass consistent with previously reported values ($\sim 5
\times 10^{12}$ $h^{-1}\mathrm{M}_\odot$). Hence, whether the spin flip mass of
the deviated samples is highly shifted or straightly undefined, our results
indicate that is remarkably connected to the haloes angular momentum growth.",1811.09487v2
2019-11-02,Efficient Spin-Orbit Torque Switching with Non-Epitaxial Chalcogenide Heterostructures,"The spin-orbit torques (SOTs) generated from topological insulators (TIs)
have gained increasing attention in recent years. These TIs, which are
typically formed by epitaxially grown chalcogenides, possess extremely high SOT
efficiencies and have great potential to be employed in the next-generation
spintronics devices. However, epitaxy of these chalcogenides is required to
ensure the existence of topologically-protected surface state (TSS), which
limits the feasibility of using these materials in industry. In this work, we
show that non-epitaxial Bi$_{x}$Te$_{1-x}$/ferromagnet heterostructures
prepared by conventional magnetron sputtering possess giant SOT efficiencies
even without TSS. Through harmonic voltage measurement and hysteresis loop
shift measurement, we find that the damping-like SOT efficiencies originated
from the bulk spin-orbit interactions of such non-epitaxial heterostructures
can reach values greater than 100% at room temperature. We further demonstrate
current-induced SOT switching in these Bi$_{x}$Te$_{1-x}$-based
heterostructures with thermally stable ferromagnetic layers, which indicates
that such non-epitaxial chalcogenide materials can be potential efficient SOT
sources in future SOT magnetic memory devices.",1911.00740v2
2018-04-16,Strong orientation dependent spin-orbit torque in antiferromagnet Mn2Au,"Antiferromagnets with zero net magnetic moment, strong anti-interference and
ultrafast switching speed have potential competitiveness in high-density
information storage. Body centered tetragonal antiferromagnet Mn2Au with
opposite spin sub-lattices is a unique metallic material for N\'eel-order
spin-orbit torque (SOT) switching. Here we investigate the SOT switching in
quasi-epitaxial (103), (101) and (204) Mn2Au films prepared by a simple
magnetron sputtering method. We demonstrate current induced antiferromagnetic
moment switching in all the prepared Mn2Au films by a short current pulse at
room temperature, whereas different orientated films exhibit distinguished
switching characters. A direction-independent reversible switching is attained
in Mn2Au (103) films due to negligible magnetocrystalline anisotropy energy,
while for Mn2Au (101) and (204) films, the switching is invertible with the
current applied along the in-plane easy axis and its vertical axis, but becomes
attenuated seriously during initially switching circles when the current is
applied along hard axis, because of the existence of magnetocrystalline
anisotropy energy. Besides the fundamental significance, the strong orientation
dependent SOT switching, which was not realized irrespective of ferromagnet and
antiferromagnet, provides versatility for spintronics.",1804.05465v1
2019-03-01,Highly efficient spin-orbit torque and switching of layered ferromagnet Fe3GeTe2,"Among van der Waals (vdW) layered ferromagnets, Fe3GeTe2 (FGT) is an
excellent candidate material to form FGT/heavy metal heterostructures for
studying the effect of spin-orbit torques (SOT). Its metallicity, strong
perpendicular magnetic anisotropy built in the single atomic layers, relatively
high Curie temperature (Tc about 225 K) and electrostatic gate tunability offer
a tantalizing possibility of achieving the ultimate high SOT limit in monolayer
all-vdW nanodevices. The spin current generated in Pt exerts a damping-like SOT
on FGT magnetization. At about 2.5x1011 A/m2 current density,SOT causes the FGT
magnetization to switch, which is detected by the anomalous Hall effect of FGT.
To quantify the SOT effect, we measure the second harmonic Hall responses as
the applied magnetic field rotates the FGT magnetization in the plane. Our
analysis shows that the SOT efficiency is comparable with that of the best
heterostructures containing three-dimensional (3D) ferromagnetic metals and
much larger than that of heterostructures containing 3D ferrimagnetic
insulators. Such large efficiency is attributed to the atomically flat FGT/Pt
interface, which demonstrates the great potential of exploiting vdW
heterostructures for highly efficient spintronic nanodevices.",1903.00571v1
2019-03-12,Current closure through the neutron star crust,"Force-free pulsar magnetospheres develop a large scale poloidal electric
current circuit that flows along open magnetic field lines from the neutron
star to the termination shock. The electric current closes through the interior
of the neutron star where it provides the torque that spins-down the star. In
the present work, we study the internal electric current in an axisymmetric
rotator. We evaluate the path of the electric current by requiring the
minimization of internal Ohmic losses. We find that, in millisecond pulsars,
the current reaches the base of the crust, while in pulsars with periods of a
few seconds, the bulk of the electric current does not penetrate deeper than
about $100$ m. The region of maximum spin-down torque in millisecond pulsars is
the base of the crust, while in slowly spinning ones it is the outer crust. We
evaluate the corresponding Maxwell stresses and find that, in typical
rotation-powered radio pulsars, they are well below the critical stress that
can be sustained by the crust. For magnetar-level fields, the Maxwell stresses
near the surface are comparable to the critical stress and may lead to the
decoupling of the crust from the rest of the stellar rotation.",1903.05093v3
2019-10-01,A novel compound synapse using probabilistic spin-orbit-torque switching for MTJ based deep neural networks,"Analog electronic non-volatile memories mimicking synaptic operations are
being explored for the implementation of neuromorphic computing systems.
Compound synapses consisting of ensembles of stochastic binary elements are
alternatives to analog memory synapses to achieve multilevel memory operation.
Among existing binary memory technologies, magnetic tunneling junction (MTJ)
based Magnetic Random Access Memory (MRAM) technology has matured to the point
of commercialization. More importantly for this work, stochasticity is natural
to the MTJ switching physics e.g devices referred as p-bits which mimic binary
stochastic neurons. In this article, we experimentally demonstrate a novel
compound synapse that uses stochastic spin-orbit torque (SOT) switching of an
ensemble of nano-magnets that are located on one shared spin Hall effect (SHE)
material channel, i.e. tantalum. By using a properly chosen pulse scheme, we
are able to demonstrate linear potentiation and depression in the synapse, as
required for many neuromorphic architectures. In addition to this experimental
effort, we also performed circuit simulations on an SOT-MRAM based 784*200*10
deep belief network (DBN) consisting of p-bit based neurons and compound
synapses. MNIST pattern recognition was used to evaluate the system
performance, and our findings indicate that a significant reduction in
recognition error rates can be achieved when using our incremental pulse scheme
rather than a non-linear potentiation and depression as obtained when employing
identical pulses.",1910.00171v1
2019-10-09,Rotational evolution of solar-type protostars during the star-disk interaction phase,"The early pre-main sequence phase during which they are still likely
surrounded by an accretion disk represents a puzzling stage of the rotational
evolution of solar-mass stars. While they are still accreting and contracting
they do not seem to spin-up substantially. It is usually assumed that the
magnetospheric star-disk interaction tends to maintain the stellar rotation
period constant (disklocking), but this hypothesis has never been thoroughly
verified. Our aim is to investigate the impact of the star-disk interaction
mechanism on the stellar spin evolution during the accreting pre-main sequence
phases. We devise a model for the torques acting onto the stellar envelope
based on studies of stellar winds and develop a new prescription for the
star-disk coupling grounded on numerical simulations of star-disk interaction
and magnetospheric ejections. We then use this torque model to follow the
long-term evolution of the stellar rotation. Magnetospheric ejections and
accretion powered stellar winds play an important role in the spin evolution of
solar-type stars. However, kG dipolar magnetic fields are not uncommon but not
ubiquitous. Besides, it is unclear how massive stellar winds can be powered,
while numerical models of the propeller regime display a strong variability
that has no observational confirmation. Better observational statistics and
more realistic models could contribute to soften our calculations'
requirements.",1910.03995v2
2020-06-23,Antiferromagnetic Half-skyrmions and Bimerons at room temperature,"In the quest for post-CMOS technologies, ferromagnetic skyrmions and their
anti-particles have shown great promise as topologically protected solitonic
information carriers in memory-in-logic or neuromorphic devices. However, the
presence of dipolar fields in ferromagnets, restricting the formation of
ultra-small topological textures, and the deleterious skyrmion Hall effect when
driven by spin torques have thus far inhibited their practical implementations.
Antiferromagnetic analogues, which are predicted to demonstrate relativistic
dynamics, fast deflection-free motion and size scaling have recently come into
intense focus, but their experimental realizations in natural antiferromagnetic
systems are yet to emerge. Here, we demonstrate a family of topological
antiferromagnetic spin-textures in $\alpha$-Fe$_2$O$_3$ - an earth-abundant
oxide insulator - capped with a Pt over-layer. By exploiting a first-order
analogue of the Kibble-Zurek mechanism, we stabilize exotic merons-antimerons
(half-skyrmions), and bimerons, which can be erased by magnetic fields and
re-generated by temperature cycling. These structures have characteristic sizes
of the order ~100 nm that can be chemically controlled via precise tuning of
the exchange and anisotropy, with pathways to further scaling. Driven by
current-based spin torques from the heavy-metal over-layer, some of these AFM
textures could emerge as prime candidates for low-energy antiferromagnetic
spintronics at room temperature.",2006.12699v2
2021-02-28,Temporal and spectral study of the X-ray pulsar 2S 1553-542 during the 2021 outburst,"We study the timing and spectral properties of the X-ray pulsar 2S 1553--542
using the NuSTAR, and NICER during the outburst in January--February 2021.
During the outburst, the spin period of the neutron star was 9.2822 s based on
NuSTAR data. The pulse profiles are studied using different NICER observations,
which implies that the profile is more or less sinusoidal with a single peak
and the beaming patterns are mostly dominated by the pencil beam. The NICER
spectra of the source are studied for different days of the outburst and can be
well described by a model consisting of a blackbody emission and power law
along with a photoelectric absorption component. The variation of spectral
parameters with luminosity is studied over the outburst. The photon index shows
anti-correlation with luminosity below the critical luminosity, which implies
that the source was accreting in the sub-critical accretion regime during the
NICER observations. We also report the anti-correlation between pulsed fraction
(PF) and luminosity of the 2S 1553--542 using NICER observations. The evolution
of spin-up rate with luminosity is studied during the outburst, which implies
that both are strongly correlated. The torque-luminosity model is applied to
estimate the magnetic field at different spin-up rates. The magnetic field is
estimated to be 2.56 $\times 10^{12}$ G from the torque-luminosity model using
the source distance of 20 kpc. The magnetic field is also estimated using the
critical luminosity, which is also consistent with our findings.",2103.00603v3
2021-06-16,Spin-Torque-driven Terahertz Auto Oscillations in Non-Collinear Coplanar Antiferromagnets,"We theoretically and numerically study the terahertz auto oscillations in
thin-film metallic non-collinear coplanar antiferromagnets (AFMs), such as
$\mathrm{Mn_{3}Sn}$ and $\mathrm{Mn_{3}Ir}$, under the effect of anti-damping
spin-torque with spin polarization perpendicular to the plane of the film. To
obtain the order parameter dynamics in these AFMs, we solve three
Landau-Lifshitz-Gilbert equations coupled by exchange interactions assuming
both single- and multi-domain (micromagnetics) dynamical processes. In the
limit of strong exchange interaction, the oscillatory dynamics of the order
parameter in these AFMs, which have opposite chiralities, could be mapped to
that of a linear damped-driven pendulum in the case of $\mathrm{Mn_{3}Sn}$, and
a non-linear damped-driven pendulum in case of $\mathrm{Mn_{3}Ir}$. The
theoretical framework allows us to identify the input current requirements as a
function of the material and geometry parameters for exciting an oscillatory
response. We also obtain a closed-form approximate solution of the oscillation
frequency for large input currents in case of both $\mathrm{Mn_{3}Ir}$ and
$\mathrm{Mn_{3}Sn}$. Our analytical predictions of threshold current and
oscillation frequency agree well with the numerical results and thus can be
used as compact models to design and optimize the auto oscillator. Employing a
circuit model, based on the principle of tunnel anisotropy magnetoresistance,
we present detailed models of the output power and efficiency versus
oscillation frequency of the auto oscillator. Finally, we explore the spiking
dynamics of two unidirectional as well as bidirectional coupled AFM oscillators
using non-linear damped-driven pendulum equations.",2106.08528v2
2021-11-28,Room temperature energy-efficient spin-orbit torque switching in wafer-scale all-vdW heterostructure,"The emergent two-dimensional (2D) ferromagnetic materials with unique
magnetic properties have endowed great potential for next-generation spintronic
devices with extraordinary merits of high flexibility, easy controllability,
and high heretointegrability, which is expected to promote the development of
Moore's Law continuously. However, it is extremely challenging to realize
magnetic switching with ultra-low power consumption at room temperature. Here,
we demonstrate the room-temperature spin-orbit torque (SOT) driven
magnetization switching in a well-epitaxial all-van der Waals (vdW)
heterostructure. The topological insulator Bi2Te3 not only helps to elevate the
Curie temperature of Fe3GeTe2 (FGT) through interfacial exchange coupling but
also works as a spin current source allowing to switch FGT at a low current
density of 2.2 * 106 A cm2. A large SOT efficiency of 0.7 is measured at room
temperature, and the thickness of FGT is further adjusted to reduce the
influence of the thermal contribution on the second-harmonic signal.
Furthermore, the temperature and thickness-dependent SOT efficiency prove that
the large SOT in our system mainly originates from the nontrivial origin of
topological materials. Our experiment has enabled an all-vdW SOT structure and
lays a solid foundation for the implementation of room-temperature all-vdW
spintronic devices in the future.",2111.14128v1
2022-04-09,Bifurcation analysis of strongly nonlinear injection locked spin torque oscillators,"We investigate the dynamics of an injection locked in-plane uniform spin
torque oscillator for several forcing configurations at large driving
amplitudes. For the analysis, the spin wave amplitude equation is used to
reduce the dynamics to a general oscillator equation in which the forcing is a
complex valued function $F(p,{\psi})\propto{\epsilon}_1
(p)cos({\psi})+i{\epsilon}_2 (p)sin({\psi})$. Assuming that the oscillator is
strongly nonisochronous and/or forced by a power forcing
$(|{\nu}{\epsilon}_1/{\epsilon}_2 |\gg 1)$, we show that the parameters
${\epsilon}_{1,2} (p)$ govern the main bifurcation features of the Arnold
tongue diagram : (i) the locking range asymmetry is mainly controlled by
$d{\epsilon}_1 (p)/dp$, (ii) the Taken-Bogdanov bifurcation occurs for a power
threshold depending on ${\epsilon}_{1,2} (p)$ and (iii) the frequency
hysteretic range is related to the transient regime through the resonant
frequency at zero mismatch frequency. Then, the model is compared with the
macrospin simulation for driving amplitudes as large as $10^0-10^3 A/m$ for the
magnetic field and $10^{10}-10^{12} A/m^2$ for the current density. As
predicted by the model, the forcing configuration (nature of the driving
signal, applied direction, the harmonic orders) affects substantially the
oscillator dynamic. However, some discrepancies are observed. In particular,
the prediction of the frequency and power locking range boundaries may be
misestimated if the hysteretic boundaries are of same magnitude order.
Moreover, the misestimation can be of two different types according if the
bifurcation is Saddle node or Taken Bogdanov. These effects are a further
manifestation of the complexity of the dynamics in nonisochronous
auto-oscillators.",2204.04454v1
2022-07-08,On the Peculiar Rotational Evolution of PSR B0950+08,"The long-term rotational evolution of the old, isolated pulsar, PSR B0950+08
is intriguing in that its spin-down rate displays sinusoidal-like oscillations
due to alternating variations, both in magnitude and sign, of the second time
derivative of the pulse frequency. We show that the large internal temperature
to pinning energy ratio towards the base of the crust implied by the recent
high surface temperature measurement of PSR B0950+08 leads to linear creep
interaction between vortex lines and pinning sites to operate in this pulsar.
Vortex lines assume a parabolic shape due to pinning to nuclear clusters and
finite tension of vortices acts as a restoring force that tends to bring a
vortex back to its straight shape. The resulting low frequency oscillations of
vortex lines combined with the time variable coupling between the internal
superfluid components and the external pulsar braking torque give rise to an
oscillatory spin-down rate. We apply this model to PSR B0950+08 observations
for several external torque models. Our model has potential to constrain the
radial extension of the closed magnetic field region in the outer core of
neutron stars from the oscillation period of the spin-down rate.",2207.04111v2
2022-12-15,Emulation of Neuron and Synaptic Functions in Spin-Orbit Torque Domain Wall Devices,"Neuromorphic computing (NC) architecture has shown its suitability for
energy-efficient computation. Amongst several systems, spin-orbit torque (SOT)
based domain wall (DW) devices are one of the most energy-efficient contenders
for NC. To realize spin-based NC architecture, the computing elements such as
synthetic neurons and synapses need to be developed. However, there are very
few experimental investigations on DW neurons and synapses. The present study
demonstrates the energy-efficient operations of neurons and synapses by using
novel reading and writing strategies. We have used a W/CoFeB-based
energy-efficient SOT mechanism to drive the DWs at low current densities. We
have used the concept of meander devices for achieving synaptic functions. By
doing this, we have achieved 9 different resistive states in experiments. We
have experimentally demonstrated the functional spike and step neurons.
Additionally, we have engineered the anomalous Hall bars by incorporating
several pairs, in comparison to conventional Hall crosses, to increase the
sensitivity as well as signal-to-noise ratio (SNR). We performed micromagnetic
simulations and transport measurements to demonstrate the above-mentioned
functionalities.",2212.07833v1
2023-01-18,Magnon-magnon interactions induced by spin pumping-driven symmetry breaking in synthetic antiferromagnets,"The richness in both the dispersion and energy of antiferromagnetic magnons
has spurred the magnetism community to consider antiferromagnets for future
spintronic/magnonic applications. However, the excitation and control of
antiferromagnetic magnons remains challenging, especially when compared to
ferromagnetic counterparts. A middle ground is found with synthetic
antiferromagnet metamaterials, where acoustic and optical magnons exist at GHz
frequencies. In these materials, the magnon energy spectrum can be tuned by
static symmetry-breaking external fields or dipolar interactions hybridizing
optical and acoustic magnon branches. Here, we experimentally measure the
magnon energy spectrum of synthetic antiferromagnetic tetralayers, and discover
avoided energy level crossings in the energy spectrum that are unexplained by
the antiferromagnetic interlayer coupling. We explain our experimental results
using a phenomenological model incorporating both fieldlike and dampinglike
torques generated by spin pumping in noncollinear magnetic multilayers
separated by normal-metal spacers. We show that an asymmetry in the fieldlike
torques acting on different magnetic layers can lift the spectral degeneracies
of acoustic and optical magnon branches and yield symmetry-breaking induced
magnon-magnon interactions. Our work extends the phenomenology of spin pumping
to noncollinear magnetization configurations and significantly expands ways of
engineering magnon-magnon interactions within antiferromagnets and quantum
hybrid magnonic materials.",2301.07311v1
2023-05-05,Nonlinear terahertz Néel spin-orbit torques in antiferromagnetic Mn$_2$Au,"Antiferromagnets have large potential for ultrafast coherent switching of
magnetic order with minimum heat dissipation. In novel materials such as
Mn$_2$Au and CuMnAs, electric rather than magnetic fields may control
antiferromagnetic order by N\'eel spin-orbit torques (NSOTs), which have,
however, not been observed on ultrafast time scales yet. Here, we excite
Mn$_2$Au thin films with phase-locked single-cycle terahertz electromagnetic
pulses and monitor the spin response with femtosecond magneto-optic probes. We
observe signals whose symmetry, dynamics, terahertz-field scaling and
dependence on sample structure are fully consistent with a uniform in-plane
antiferromagnetic magnon driven by field-like terahertz NSOTs with a torkance
of (150$\pm$50) cm$^2$/A s. At incident terahertz electric fields above 500
kV/cm, we find pronounced nonlinear dynamics with massive N\'eel-vector
deflections by as much as 30{\deg}. Our data are in excellent agreement with a
micromagnetic model which indicates that fully coherent N\'eel-vector switching
by 90{\deg} within 1 ps is within close reach.",2305.03368v1
2023-05-15,Order parameter dynamics in Mn$_3$Sn driven by DC and pulsed spin-orbit torques,"We numerically investigate and develop analytic models for both the DC and
pulsed spin-orbit-torque (SOT)-driven response of order parameter in
single-domain Mn$_3$Sn, which is a metallic antiferromagnet with an anti-chiral
120$^\circ$ spin structure. We show that DC currents above a critical threshold
can excite oscillatory dynamics of the order parameter in the gigahertz to
terahertz frequency spectrum. Detailed models of the oscillation frequency
versus input current are developed and found to be in excellent agreement with
the numerical simulations of the dynamics. In the case of pulsed excitation,
the magnetization can be switched from one stable state to any of the other
five stable states in the Kagome plane by tuning the duration or the amplitude
of the current pulse. Precise functional forms of the final switched state
versus the input current are derived, offering crucial insights into the
switching dynamics of Mn$_3$Sn. The readout of the magnetic state can be
carried out via either the anomalous Hall effect, or the recently demonstrated
tunneling magnetoresistance in an all-Mn$_3$Sn junction. We also discuss
possible disturbance of the magnetic order due to heating that may occur if the
sample is subject to large currents. Operating the device in pulsed mode or
using low DC currents reduces the peak temperature rise in the sample due to
Joule heating. Our predictive modeling and simulation results can be used by
both theorists and experimentalists to explore the interplay of SOT and the
order dynamics in Mn$_3$Sn, and to further benchmark the device performance.",2305.08728v2
2023-05-30,Driving skyrmions in flow regime in synthetic ferrimagnets,"Despite significant advances in the last decade regarding the room
temperature stabilization of skyrmions or their current induced dynamics, the
impact of local material inhomogeneities still remains an important issue that
impedes to reach the regime of steady state motion of these spin textures.
Here, we study the spin-torque driven motion of skyrmions in synthetic
ferrimagnetic multilayers with the aim of achieving high mobility and reduced
skyrmion Hall effect. We consider Pt|Co|Tb multilayers of various thicknesses
with antiferromagnetic coupling between the Co and Tb magnetization. The
increase of Tb thickness in the multilayers allows to reduce the total magnetic
moment and increases the spin-orbit torques allowing to reach velocities up to
400 m.s-1 for skyrmions with diameters of about 160 nm. We demonstrate that due
to reduced skyrmion Hall effect, combined with the edge repulsion of the
magnetic track making the skyrmions moving along the track without any
transverse deflection. Further, by comparing the field-induced domain wall
motion and current-induced skyrmion motion, we demonstrate that the skyrmions
at the largest current densities present all the characteristics of a dynamical
flow regime.",2305.19208v2
2023-06-15,An abrupt change in the stellar spin-down law at the fully convective boundary,"The importance of the existence of a radiative core in generating a
solar-like magnetic dynamo is still unclear. Analytic models and
magnetohydrodynamic simulations of stars suggest the thin layer between a
star's radiative core and its convective zone can produce shearing that
reproduces key characteristics of a solar-like dynamo. However, recent studies
suggest fully and partially convective stars exhibit very similar
period-activity relations, hinting that dynamos generated by stars with and
without radiative cores hold similar properties. Here, using kinematic ages, we
discover an abrupt change in the stellar spin-down law across the fully
convective boundary. We found that fully convective stars exhibit a higher
angular momentum loss rate, corresponding to a torque that is $\sim$ 2.25 times
higher for a given angular velocity than partially convective stars around the
fully convective boundary. This requires a dipole field strength that is larger
by a factor of $\sim$2.5, a mass loss rate that is $\sim$4.2 times larger, or
some combination of both of those factors. Since stellar-wind torques depend
primarily on large-scale magnetic fields and mass loss rates, both of which
derive from magnetic activity, the observed abrupt change in spin-down law
suggests that the dynamos of partially and fully convective stars may be
fundamentally different",2306.09119v1
2023-07-03,Efficient current-induced spin torques and field-free magnetization switching in a room-temperature van der Waals magnet,"The discovery of magnetism in van der Waals (vdW) materials has established
unique building blocks for the research of emergent spintronic phenomena. In
particular, owing to their intrinsically clean surface without dangling bonds,
the vdW magnets hold the potential to construct a superior interface that
allows for efficient electrical manipulation of magnetism. Despite several
attempts in this direction, it usually requires a cryogenic condition and the
assistance of external magnetic fields, which is detrimental to the real
application. Here, we fabricate heterostructures based on Fe3GaTe2 flakes that
possess room-temperature ferromagnetism with excellent perpendicular magnetic
anisotropy. The current-driven non-reciprocal modulation of coercive fields
reveals a high spin-torque efficiency in the Fe3GaTe2/Pt heterostructures,
which further leads to a full magnetization switching by current. Moreover, we
demonstrate the field-free magnetization switching resulting from out-of-plane
polarized spin currents by asymmetric geometry design. Our work could expedite
the development of efficient vdW spintronic logic, memory and neuromorphic
computing devices.",2307.01329v1
2023-10-04,Van der Waals Spin-Orbit Torque Antiferromagnetic Memory,"The technique of conventional ferromagnet/heavy-metal spin-orbit torque (SOT)
offers significant potential for enhancing the efficiency of magnetic memories.
However, it faces fundamental physical limitations, including hunting effects
from the metallic layer, broken symmetry for enabling antidamping switching,
spin scattering caused by interfacial defects, and sensitivity to stray
magnetic fields. To address these issues, we here propose a van der Waals (vdW)
field-free SOT antiferromagnetic memory using a vdW bilayer LaBr$_2$ (an
antiferromagnet with perpendicular magnetic anisotropy) and a monolayer T$_d$
phase WTe$_2$ (a Weyl semimetal with broken inversion symmetry). By
systematically employing density functional theory in conjunction with
non-equilibrium Green's function methods and macrospin simulations, we
demonstrate that the proposed vdW SOT devices exhibit remarkably low critical
current density approximately 10 MA/cm$^2$ and rapid field-free magnetization
switching in 250 ps. This facilitates excellent write performance with
extremely low energy consumption. Furthermore, the device shows a significantly
low read error rate, as evidenced by a high tunnel magnetoresistance ratio of
up to 4250%. The superior write and read performance originates from the unique
strong on-site (insulating phase) and off-site (magnetic phase) Coulomb
interactions in electride LaBr$_2$, a large non-zero z-component polarization
in WTe$_2$, and the proximity effect between them.",2310.02805v1
2024-01-25,Electrical switching of the perpendicular Neel order in a collinear antiferromagnet,"Electrical manipulation of magnetic order by current-induced spin torques
lays the foundation for spintronics. One promising approach is encoding
information in the N\'eel vector of antiferromagnetic (AFM) materials,
particularly to collinear antiferromagnets with the perpendicular magnetic
anisotropy (PMA), as the negligible stray fields and terahertz spin dynamics
can enable memory devices with higher integration density and ultrafast speed.
Here we demonstrate that the N\'eel order information in a prototypical
collinear AFM insulator with PMA, Cr2O3, can be reliably readout via the
anomalous Hall effect and efficiently switched by the spin-orbit torque (SOT)
effect with a low current density of 5.8*106 A/cm2. Moreover, using Cr2O3 as a
mediator, we electrically switch the magnetization of a Y3Fe5O12 film
exchange-coupled to the Cr2O3 layer, unambiguously confirming the N\'eel order
switching of the Cr2O3 layer. This work provides a significant basis for
developing AFM memory devices based on collinear AFM materials with PMA.",2401.14044v1
2014-04-30,Many-qubit quantum state transfer via spin chains,"The transfer of an unknown quantum state, from a sender to a receiver, is one
of the main requirements to perform quantum information processing tasks. In
this respect, the state transfer of a single qubit by means of spin chains has
been widely discussed, and many protocols aiming at performing this task have
been proposed. Nevertheless, the state transfer of more than one qubit has not
been properly addressed so far. In this paper, we present a modified version of
a recently proposed quantum state transfer protocol [Phys. Rev. A 87, 062309
(2013)] to obtain a quantum channel for the transfer of two qubits. This goal
is achieved by exploiting Rabi-like oscillations due to excitations induced by
means of strong and localized magnetic fields. We derive exact analytical
formulae for the fidelity of the quantum state transfer, and obtain a
high-quality transfer for general quantum states as well as for specific
classes of states relevant for quantum information processing.",1404.7837v1
2006-02-17,The Prelude to and Aftermath of the Giant Flare of 2004 December 27: Persistent and Pulsed X-ray Properties of SGR 1806-20 from 1993 to 2005,"On 2004 December 27, a highly-energetic giant flare was recorded from the
magnetar candidate SGR 1806-20. In the months preceding this flare, the
persistent X-ray emission from this object began to undergo significant
changes. Here, we report on the evolution of key spectral and temporal
parameters prior to and following this giant flare. Using the Rossi X-ray
Timing Explorer, we track the pulse frequency of SGR 1806-20 and find that the
spin-down rate of this SGR varied erratically in the months before and after
the flare. Contrary to the giant flare in SGR 1900+14, we find no evidence for
a discrete jump in spin frequency at the time of the December 27th flare
(|dnu/nu| < 5 X 10^-6). In the months surrounding the flare, we find a strong
correlation between pulsed flux and torque consistent with the model for
magnetar magnetosphere electrodynamics proposed by Thompson, Lyutikov &
Kulkarni (2002). As with the flare in SGR 1900+14, the pulse morphology of SGR
1806-20 changes drastically following the flare. Using the Chandra X-ray
Observatory and other publicly available imaging X-ray detector observations,
we construct a spectral history of SGR 1806-20 from 1993 to 2005. The usual
magnetar persistent emission spectral model of a power-law plus a blackbody
provides an excellent fit to the data. We confirm the earlier finding by
Mereghetti et al. (2005) of increasing spectral hardness of SGR 1806-20 between
1993 and 2004. Contrary to the direct correlation between torque and spectral
hardness proposed by Mereghetti et al., we find evidence for a sudden torque
change that triggered a gradual hardening of the energy spectrum on a timescale
of years. Interestingly, the spectral hardness, spin-down rate, pulsed, and
phase-averaged of SGR 1806-20 all peak months before the flare epoch.",0602402v2
2013-10-09,Coherent Backaction of Quantum Dot Detectors: Qubit Isospin Precession,"A sensitive technique for the readout of the state of a qubit is based on the
measurement of the conductance through a proximal sensor quantum dot (SQD).
Here, we theoretically study the coherent backaction of such a measurement on a
coupled SQD-charge-qubit system. We derive Markovian kinetic equations for the
ensemble-averaged state of the SQD-qubit system, expressed in the coupled
dynamics of two charge-state occupations of the SQD and two qubit isospin
vectors, one for each SQD charge state. We find that aside from introducing
dissipation, the detection also renormalizes the coherent evolution of the
SQD-qubit system. Basically, if the electron on the detector has time to probe
the qubit, then it also has time to fluctuate and thereby renormalize the
system parameters. In particular, this induces torques on the qubit isospins,
similar to the spin torque generated by the spintronic exchange field in
noncollinear spin-valve structures. Secondly, we show that for a consistent
description of the detection, one must also include the renormalization effects
in the next-to-leading order in the electron tunneling rates, especially at the
point of maximal sensitivity of the detector. Although we focus on a
charge-qubit model, our findings are generic for qubit readout schemes that are
based on spin-to-charge conversion using a quantum-dot detector. Furthermore,
our study of the stationary current through the SQD, a test measurement
verifying that the qubit couples to the detector current, already reveals
various significant effects of the isospin torques on the qubit. Our kinetic
equations provide a starting point for further studies of the time evolution in
charge-based qubit readout. Finally, we provide a rigorous sum rule that
constrains such approximate descriptions of the qubit isospin dynamics and show
that it is obeyed by our kinetic equations.",1310.2519v2
2018-02-22,Resonant torsion magnetometry in anisotropic quantum materials,"Unusual behavior of quantum materials commonly arises from their effective
low-dimensional physics, which reflects the underlying anisotropy in the spin
and charge degrees of freedom. Torque magnetometry is a highly sensitive
technique to directly quantify the anisotropy in quantum materials, such as the
layered high-T$_c$ superconductors, anisotropic quantum spin-liquids, and the
surface states of topological insulators. Here we introduce the magnetotropic
coefficient $k=\partial^2 F/\partial \theta^2$, the second derivative of the
free energy F with respect to the angle $\theta$ between the sample and the
applied magnetic field, and report a simple and effective method to
experimentally detect it. A sub-$\mu$g crystallite is placed at the tip of a
commercially available atomic force microscopy cantilever, and we show that $k$
can be quantitatively inferred from a shift in the resonant frequency under
magnetic field. While related to the magnetic torque $\tau=\partial F/\partial
\theta$, $k$ takes the role of torque susceptibility, and thus provides
distinct insights into anisotropic materials akin to the difference between
magnetization and magnetic susceptibility. The thermodynamic coefficient $k$ is
discontinuous at second-order phase transitions and subject to Ehrenfest
relations with the specific heat and magnetic susceptibility. We apply this
simple yet quantitative method on the exemplary cases of the Weyl-semimetal NbP
and the spin-liquid candidate RuCl$_3$, yet it is broadly applicable in quantum
materials research.",1802.08211v1
2020-04-25,"Effects of Oxidation of Top and Bottom Interfaces on the Electric, Magnetic, and Spin-Orbit Torque Properties of Pt/Co/AlOx Trilayers","Oxidation strongly influences the properties of magnetic layers employed in
spintronic devices. We study the effect of oxidation on the structural,
magnetic, and electrical properties as well as current-induced spin-orbit
torques (SOTs) in Pt/Co/AlOx, Pt/CoOx/Co/AlOx, and PtOx/Co/AlOx layers. We show
how the saturation magnetization, perpendicular magnetic anisotropy, anomalous
Hall resistance, and SOT are systematically affected by the degree of oxidation
of both the Pt/Co and Co/Al interfaces. Oxidation of the Co/Al interface
results in a 21% and 42% variation of the dampinglike and fieldlike SOT
efficiencies, which peak at 0.14 and 0.07, respectively. The insertion of a
paramagnetic CoOx layer between Pt and Co maintains a very strong perpendicular
magnetic anisotropy and improves the dampinglike and fieldlike SOT
efficiencies, up to 0.26 and 0.20, respectively. In contrast with recent
reports, we do not find that the oxidation of Pt leads to a significant
enhancement of the torques. Rather, we find that oxygen migrates from Pt to the
Co and Al layers, leading to a time-dependent oxidation profile and an
effective spin Hall conductivity that decreases with increasing oxygen
concentration. Finally, we study current-induced switching in Pt/Co/AlOx with
different degrees of oxidation and find a linear relationship between the
critical switching current and the effective magnetic anisotropy controlled by
the oxidation of Al. These results highlight the importance of interfaces and
oxidation effects on the SOT and magnetotransport properties of heavy
metal/ferromagnet/oxide trilayers and provide information on how to improve the
SOT efficiency and magnetization-switching characteristics of these systems.",2004.12115v1
2021-02-17,Growth optimization of TaN for superconducting spintronics,"We have optimized the growth of superconducting TaN thin films on \ch{SiO2}
substrates via dc magnetron sputtering and extract a maximum superconducting
transition temperature of $T_{\mathrm{c}}=5$ K as well as a maximum critical
field $\mu_0H_{\mathrm{c2}}=(13.8\pm0.1)$ T. To investigate the impact of
spin-orbit interaction in superconductor/ferromagnet heterostructures, we then
analyze the magnetization dynamics of both normal state and superconducting
TaN/\ch{Ni80Fe20}(Permalloy, Py)-bilayers as a function of temperature using
broadband ferromagnetic resonance (bbFMR) spectroscopy. The phase sensitive
detection of the microwave transmission signal is used to quantitatively
extract the inverse current-induced torques of the bilayers. The results are
compared to our previous study on NbN/Py-bilayers. In the normal state of TaN,
we detect a positive damping-like current-induced torque $\sigma_{\mathrm{d}}$
from the inverse spin Hall effect (iSHE) and a small field-like torque
$\sigma_{\mathrm{f}}$ attributed to the inverse Rashba-Edelstein effect (iREE)
at the TaN/Py-interface. In the superconducting state of TaN, we detect a
negative $\sigma_{\mathrm{d}}$ attributed to the quasiparticle mediated inverse
spin Hall effect (QMiSHE) and the unexpected manifestation of a large positive
field-like $\sigma_{\mathrm{f}}$ of unknown origin matching our previous
results for NbN/Py-bilayers.",2102.09018v1
2021-04-19,Voltage-Gate Assisted Spin-Orbit Torque Magnetic Random Access Memory for High-Density and Low-Power Embedded Application,"Voltage-gate assisted spin-orbit torque (VGSOT) writing scheme combines the
advantages from voltage control of magnetic anisotropy (VCMA) and spin-orbit
torque (SOT) effects, enabling multiple benefits for magnetic random access
memory (MRAM) applications. In this work, we give a complete description of
VGSOT writing properties on perpendicular magnetic tunnel junction (pMTJ)
devices, and we propose a detailed methodology for its electrical
characterization. The impact of gate assistance on the SOT switching
characteristics are investigated using electrical pulses down to 400ps. The
VCMA coefficient ({\xi}) extracted from current switching scheme is found to be
the same as that from the magnetic field switch method, which is in the order
of 15fJ/Vm for the 80nm to 150nm devices. Moreover, as expected from the pure
electronic VCMA effect, {\xi} is revealed to be independent of the writing
speed and gate length. We observe that SOT switching current characteristics
are modified linearly with gate voltage (V_g), similar as for the magnetic
properties. We interpret this linear behavior as the direct modification of
perpendicular magnetic anisotropy (PMA) and nucleation energy induced by VCMA.
At V_g = 1V, the SOT write current is decreased by 25%, corresponding to a 45%
reduction in total energy down to 30fJ/bit at 400ps speed for the 80nm devices
used in this study. Further, the device-scaling criteria are proposed, and we
reveal that VGSOT scheme is of great interest as it can mitigate the complex
material requirements of achieving high SOT and VCMA parameters for scaled
MTJs. Finally, how that VGSOT-MRAM can enable high-density arrays close to two
terminal geometries, with high-speed performance and low-power operation,
showing great potential for embedded memories as well as in-memory computing
applications at advanced technology nodes.",2104.09599v1
2019-07-24,The dynamical evolution of close-in binary systems formed by a super-Earth and its host star. Case of the Kepler-21 system,"The aim of this work is to develop a formalism for the study of the secular
evolution of a binary system which includes interaction due to the tides that
each body imparts on the other. We also consider the influence of the
$J_2$-related secular terms on the orbital evolution and the torque, caused by
the triaxiality, on the rotational evolution, both of which are associated only
to one of the bodies. We apply these set of equations to the study of the
orbital and rotational evolution of a binary system composed of a rocky planet
and its host star in order to characterize the dynamical evolution at work,
particularly near spin-orbit resonances. We used the equations of motion that
give the time evolution of the orbital elements and the spin rates of each body
to study the time evolution of the Kepler-21 system as an example of how the
formalism that we have developed can be applied. We obtained a set of equations
of motion without singularities for vanishing eccentricities and inclinations.
This set gives, on one hand, the time evolution of the orbital elements due to
the tidal potentials generated by both members of the system as well as the
triaxiality of one of them. On the other hand, it gives the time evolution of
the stellar spin rate due to the corresponding tidal torque and of the planet's
rotation angle due to both the tidal and triaxiality-induced torques. We found
that for the parameters and the initial conditions explored here, the tidally
and triaxiality-induced modifications of the tidal modes can be more
significative than expected and that the time of tidal synchronization strongly
depends on the values of the rheological parameters.",1907.10575v4
2006-03-24,Spin entanglement loss by local correlation transfer to the momentum,"We show the decrease of spin-spin entanglement between two s=1/2 fermions or
two photons due to local transfer of correlations from the spin to the momentum
degree of freedom of one of the two particles. We explicitly show how this
phenomenon operates in the case where one of the two fermions (photons) passes
through a local homogeneous magnetic field (optically-active medium), losing
its spin correlations with the other particle.",0603225v2
2006-03-25,Decoherence effects on the quantum spin channels,"An open ended spin chain can serves as a quantum data bus for the coherent
transfer of quantum state information. In this paper, we investigate the
efficiency of such quantum spin channels which work in a decoherence
environment. Our results show that, the decoherence will significantly reduce
the fidelity of quantum communication through the spin channels. Generally
speaking, as the distance increases, the decoherence effects become more
serious, which will put some constraints on the spin chains for long distance
quantum state transfer.",0603228v3
2007-02-02,Robust state transfer and rotation through a spin chain via dark passage,"Quantum state transfer through a spin chain via adiabatic dark passage is
proposed. This technique is robust against control field fluctuations and
unwanted environmental coupling of intermediate spins. Our method can be
applied to spin chains with more than three spins. We also propose single qubit
rotation using this technique.",0702019v3
2016-05-21,Electrically tunable quantum interfaces between photons and spin qubits in carbon nanotube quantum dots,"We present a new scheme for quantum interfaces to accomplish the
interconversion of photonic qubits and spin qubits based on optomechanical
resonators and the spin-orbit-induced interactions in suspended carbon nanotube
quantum dots. This interface implements quantum spin transducers and further
enables electrical manipulation of local electron spin qubits, which lays the
foundation for all-electrical control of state transfer protocols between two
distant quantum nodes in a quantum network. We numerically evaluate the state
transfer processes and proceed to estimate the effect of each coupling strength
on the operation fidelities.",1605.06649v1
2022-08-29,The Effect of Duschinskii Rotations on Spin-Dependent Electron Transfer Dynamics,"We investigate spin-dependent electron transfer in the presence of a
Duschinskii rotation. In particular, we propagate dynamics for a two-level
model system for which spin-orbit coupling introduces an interstate coupling of
the form $e^{iWx}$, which is both position(x)-dependent and complex-valued. We
demonstrate that two-level systems coupled to Brownian oscillators with
Duschinskii rotations (and thus entangled normal modes) can produce marked
increases in transient spin polarization relative to two-level systems coupled
to simple shifted harmonic oscillators. These conclusions should have
significant relevance for modeling the effect of nuclear motion on chiral
induced spin selectivity.",2208.13378v1
2015-08-06,Fuzzy Logic Based Direct Torque Control Of Induction Motor With Space Vector Modulation,"The induction motors have wide range of applications for due to its
well-known advantages like brushless structures, low costs and robust
performances. Over the past years, many kind of control methods are proposed
for the induction motors and direct torque control has gained huge importance
inside of them due to fast dynamic torque responses and simple control
structures. However, the direct torque control method has still some handicaps
against the other control methods and most of the important of these handicaps
is high torque ripple. This paper suggests a new approach, Fuzzy logic based
space vector modulation, on the direct torque controlled induction motors and
aim of the approach is to overcome high torque ripple disadvantages of
conventional direct torque control. In order to test and compare the proposed
direct torque control method with conventional direct torque control method
simulations, in Matlab/Simulink,have been carried out in different working
conditions. The simulation results showed that a significant improvement in the
dynamic torque and speed responses when compared to the conventional direct
torque control method.",1508.01345v1
2019-08-04,Experimental observation of coupled valley and spin Hall effect in p-doped WSe2 devices,"Giant spin Hall effect (GSHE) has been observed in heavy metal materials such
as Ta, Pt, and W, where spins are polarized in the surface plane and
perpendicular to the charge current direction. Spins generated in these
materials have successfully switched magnets with in-plane magnetic anisotropy
(IMA) and perpendicular magnetic anisotropy (PMA) through spin orbit torque
(SOT) mechanism. It is generally accepted that PMA magnets are preferred over
IMA magnets in data storage applications owing to their large thermal stability
even at ultra scaled dimensions. However, SOT switching of PMA magnets by
conventional GSHE materials requires either a small external magnetic field, a
local dipolar field, or introducing tilted anisotropy to break the symmetry
with respect to the magnetization. To deterministically switch a PMA without
any additional assistance, nonconventional GSHE materials that can generate
spins with polarization perpendicular to the surfaces are needed. Several
monolayer transition metal dichalcogenides (TMDs) have been predicted to
generate such out of plane spins due to their 2D nature and unique band
structures. Interestingly, opposite spins are locked to their respective
sub-band in each K valley of the TMD valence band with substantially large
energy splitting, which enables polarized spins to be accessible through
electrical gating and spatially separated by electric field through the valley
Hall effect (VHE). Therefore, spatial separation and accumulation of spins in
these 2D TMDs are uniquely referred to as coupled valley and spin Hall effect.
Here, we report an experiment of electrical generation of spin current with out
of plane polarization in monolayer WSe2 and detection of spin signals through a
nonlocal spin valve structure built on a lateral graphene spin diffusion
channel that partially overlaps with WSe2.",1908.01396v1
2007-05-16,Viscous Torque and Dissipation in the Inner Region of a Thin Accretion Disk: Implications for Measuring Black Hole Spin,"We consider a simple Newtonian model of a steady accretion disk around a
black hole. The model is based on height-integrated hydrodynamic equations,
alpha-viscosity, and a pseudo-Newtonian potential that results in an innermost
stable circular orbit (ISCO) that closely approximates the one predicted by GR.
We find that the hydrodynamic models exhibit increasing deviations from the
standard disk model of Shakura & Sunyaev as disk thickness H/R or the value of
alpha increases. The latter is an analytical model in which the viscous torque
is assumed to vanish at the ISCO. We consider the implications of the results
for attempts to estimate black hole spin by using the standard disk model to
fit continuum spectra of black hole accretion disks. We find that the error in
the spin estimate is quite modest so long as H/R < 0.1 and alpha < 0.2. At
worst the error in the estimated value of the spin parameter is 0.1 for a
non-spinning black hole; the error is much less for a rapidly spinning hole. We
also consider the density and disk thickness contrast between the gas in the
disk and that inside the ISCO. The contrast needs to be large if black hole
spin is to be successfully estimated by fitting the relativistically-broadened
X-ray line profile of fluorescent iron emission from reflection off an
accretion disk. In our hydrodynamic models, the contrast in density and
thickness is low when H/R>0.1, sugesting that the iron line technique may be
most reliable in extemely thin disks. We caution that these results have been
obtained with a viscous hydrodynamic model and need to be confirmed with MHD
simulations of radiatively cooled thin disks.",0705.2244v3
2016-10-20,Magnetic excitations in quasi-one dimensional helimagnets: Magnon decays and in uence of the inter-chain interactions,"We present a comprehensive study of the magnetic properties of the long-range
ordered quasi-one dimensional $J_{1}$-$J_{2}$ systems with a newly developed
torque equilibrium spin-wave expansion approach, which can describe the spin
Casimir and magnon decay effects in a unified framework. While the framework
does not lose the generality, our discussion will be restricted to two
representative types of inter-chain coupling systems: $J_{3}$- or
$J_{4}$-system respectively. In spite of the long-range spiral order, the
dynamical properties of these systems turn out to be highly nontrivial due to
the incommensurate noncollinear spin configuration and the strong quantum
fluctuation effects enhanced by the frustration and low-dimensionality. Both
the systems show prominent spin Casimir effects induced by the vacuum
fluctuation of the spin waves and related modification of the ordering vector,
Lifshitz point's position and sublattice magnetization. Significant and
spontaneous magnon decay effects are manifested in the quantum corrections to
the excitation spectrum. By adjusting the strength of magnetic anisotropy and
varying the approximation scheme, it is revealed that these striking distinct
features are quite robust and have deep connection with both the spin Casimir
and the magnon decay effects. Thus these special consequences of the
inter-chain coupling on the spin wave dynamics may be served as a set of probes
for different types of inter-chain couplings in experiments. At last, to guide
experimental measurements such as inelastic neutron scattering in realistic
materials and complement our theoretical framework, we develop the analytical
theory of the dynamical structure factor within the torque equilibrium
formulism and provide the explicit results of the quasi-one dimensional
$J_{1}$-$J_{2}$ systems.",1610.06365v2
2020-06-08,Role of Dirac nodal lines and strain on the high spin Hall conductivity of epitaxial IrO2 thin films,"Since the discovery of a 'giant' spin Hall effect (SHE) in certain heavy
metal elements there has been an intense effort to identify and develop new and
technologically viable, heavy-metal-based thin film materials that could
generate spin currents with even greater efficiency to exert spin-orbit torques
(SOT) on adjacent ferromagnetic nanostructures. In parallel, there have been
wide ranging fundamental studies of the spin currents that can arise from
robust, intrinsic spin-orbit interaction (SOI) effects in more exotic systems
including topological insulators, transition metal dichalcogenides with broken
crystalline symmetry, Weyl and Dirac semimetals where gapless electronic
excitations are protected by topology and symmetry. Here we experimentally
study strong SOT from the topological semimetal IrO2 in (001) and (110) normal
films, which exhibit distinctly different SHE strengths. Angle resolved
photoemission spectroscopy studies have shown IrO2 exhibits Dirac nodal lines
(DNL) in the band structure, which could enable a very high spin Hall
conductivity (SHC). The (001) films exhibit exceptionally high damping like
torque efficiency ranging from 0.45 at 293 K to 0.65 at 30 K which sets the
lower bound of SHC that is ten times higher and of opposite sign than the
theoretical prediction. We observe a substantial reduction of SHC in
anisotropically strained (110) films, which suggests that the DNLs that are
present in the (001) films and contribute to SHC, are disrupted and gapped due
to the large anisotropic strain in (110) films, which in turn significantly
lowers SHC. Very large value of SHC at room temperature of this Dirac semimetal
could be very promising for the practical application.",2006.04365v1
2004-06-22,Quantum state transmission via a spin ladder as a robust data bus,"We explore the physical mechanism to coherently transfer the quantum
information of spin by connecting two spins to an isotropic antiferromagnetic
spin ladder system as data bus. Due to a large spin gap existing in such a
perfect medium, the effective Hamiltonian of the two connected spins can be
archived as that of Heisenberg type, which possesses a ground state with
maximal entanglement. We show that the effective coupling strength is inversely
proportional to the distance of the two spins and thus the quantum information
can be transferred between the two spins separated by a longer distance, i.e.
the characteristic time of quantum state transferring linearly depends on the
distance.",0406159v1
2012-06-12,Using hybrid topological-spin qubit systems for two-qubit-spin gates,"We investigate a hybrid quantum system involving spin qubits, based on the
spins of electrons confined in quantum dots, and topological qubits, based on
Majorana fermions. In such a system, gated control of the charge on the quantum
dots allows transfer of quantum information between the spin and topological
qubits, and the topological system can be used to facilitate transfer of spin
qubits between spatially separated quantum dots and to initialize entangled
spin-qubit pairs. Here, we show that the coupling to the topological system
also makes it possible to perform entangling two-qubit gates on spatially
separated spin qubits. The two-qubit gates are based on a combination of
topologically protected braiding operations, gate-controlled charge transfer
between the dots and edge Majorana modes, and measurements of the state of the
topological qubits.",1206.2455v2
2021-06-11,The origin of chirality induced spin selectivity in photo-induced electron transfer,"Here we propose a mechanism by which spin polarization can be generated
dynamically in chiral molecular systems undergoing photo-induced electron
transfer. The proposed mechanism explains how spin polarization emerges in
systems where charge transport is dominated by incoherent hopping, mediated by
spin orbit and electronic exchange couplings through an intermediate charge
transfer state. We derive a simple expression for the spin polarization that
predicts a non-monotonic temperature dependence consistent with recent
experiments. We validate this theory using approximate quantum master equations
and the numerically exact hierarchical equations of motion. The proposed
mechanism of chirality induced spin selectivity should apply to many chiral
systems, and the ideas presented here have implications for the study of spin
transport at temperatures relevant to biology, and provide simple principles
for the molecular control of spins in fluctuating environments.",2106.06554v1
2023-09-27,Direct Sensing of Remote Nuclei: Expanding the Reach of Cross-Effect Dynamic Nuclear Polarization,"Dynamic Nuclear Polarization (DNP) has revolutionized the field of
solid-state NMR spectroscopy by significantly enhancing the sensitivity of
nuclear magnetic resonance experiments. Conventionally, cross effect DNP relies
on biradicals to transfer polarization from coupled electron spins to nearby
nuclear spins and subsequent relay to target nuclei via spin diffusion
mechanism. However, the direct transfer of polarization to distant nuclei
remains a significant challenge, limiting its applicability in various
contexts. In this work, we propose a novel biradical design concept that
involves a very strong electron-electron coupling, with a magnitude of hundreds
of MHz, which enables efficient direct polarization transfer from electron
spins to nuclear spins over much longer distances, exceeding 2.0 nm. We discuss
the potential of this tailored biradicals in scenarios where conventional spin
diffusion mechanisms are inefficient or when direct nuclear spin sensing
through electron spin interactions is desired. Our study presents a promising
avenue for expanding the scope of cross effect DNP in solid-state NMR
spectroscopy and opens new opportunities for investigating a wide range of
biological and material systems. Our research also provides insight into the
DNP buildup time of commercially available biradicals.",2309.15653v1
2006-01-30,Multiple transfer of angular momentum quanta from a spin-polarized hole to magnetic ions in ZnMnSe/ZnBeSe quantum wells,"The magnetization kinetics in (Zn,Mn)Se/(Zn,Be)Se quantum wells has been
studied on a ps-time scale after pulsed laser excitation. The magnetization
induced by an external magnetic field is reduced by up to 30% during ~100 ps
due to spin and energy transfer from photocarriers to Mn spin system. The giant
Zeeman splitting leads to a complete spin polarization of the carriers,
resulting in a strong suppression of flip-flop processes between carriers and
magnetic ions. Therefore a multiple angular momentum transfer from each
spin-polarized hole to the Mn ions becomes the dominant mechanism in the
magnetization dynamics. A model based on spin-momentum coupling in the valence
band is suggested for explaining this transfer.",0601661v1
2007-05-10,Spin Star as Switch for Quantum Networks,"Quantum state transfer is an important task in quantum information
processing. It is known that one can engineer the couplings of a
one-dimensional spin chain to achieve the goal of perfect state transfer. To
leverage the value of these spin chains, a spin star is potentially useful for
connecting different parts of a quantum network. In this work, we extend the
spin-chain engineering problem to the problems with a topology of a star
network. We show that a permanently coupled spin star can function as a network
switch for transferring quantum states selectively from one node to another by
varying the local potentials only. Together with one-dimensional chains, this
result allows applications of quantum state transfer be applied to more general
quantum networks.",0705.1560v2
2011-10-07,State transfer in intrinsic decoherence spin channels,"By analytically solving the master equation, we investigate quantum state
transfer, creation and distribution of entanglement in the model of Milburn's
intrinsic decoherence. Our results reveal that the ideal spin channels will be
destroyed by the intrinsic decoherence environment, and the detrimental effects
become severe as the decoherence rate $\gamma$ and the spin chain length $N$
increase. For infinite evolution time, both the state transfer fidelity and the
concurrence of the created and distributed entanglement approach steady state
values, which are independent of the decoherence rate $\gamma$ and decrease as
the spin chain length $N$ increases. Finally, we present two modified spin
chains which may serve as near perfect spin channels for long distance state
transfer even in the presence of intrinsic decoherence environments $\mathcal
{F}{[\rho(t)]}$.",1110.1480v1
2013-07-22,Linking covariant and canonical LQG II: Spin foam projector,"In a seminal paper, Kaminski, Kisielowski an Lewandowski for the first time
extended the definition of spin foam models to arbitrary boundary graphs. This
is a prerequisite in order to make contact to the canonical formulation of Loop
Quantum Gravity (LQG) whose Hilbert space contains all these graphs. This makes
it finally possible to investigate the question whether any of the presently
considered spin foam models yields a rigging map for any of the presently
defined Hamiltonian constraint operators.
  In the analysis of this would-be spin foam rigging map we are able to
identify an elementary spin foam transfer matrix that allows to generate any
finite foam as a finite power of the transfer matrix. However, it transpires
that the resulting object, as written, does not define a projector on the
physical Hilbert space. This statement is independent of the concrete spin foam
model and Hamiltonian constraint. Nevertehless, the transfer matrix potentially
contains the necessary ingredient in order to construct a proper rigging map in
terms of a modified transfer matrix.",1307.5885v2
2011-10-24,Multiple-spin coherence transfer in linear Ising spin chains and beyond: numerically-optimized pulses and experiments,"We study multiple-spin coherence transfers in linear Ising spin chains with
nearest neighbor couplings. These constitute a model for efficient information
transfers in future quantum computing devices and for many multi-dimensional
experiments for the assignment of complex spectra in nuclear magnetic resonance
spectroscopy. We complement prior analytic techniques for multiple-spin
coherence transfers with a systematic numerical study where we obtain strong
evidence that a certain analytically-motivated family of restricted controls is
sufficient for time-optimality. In the case of a linear three-spin system,
additional evidence suggests that prior analytic pulse sequences using this
family of restricted controls are time-optimal even for arbitrary local
controls. In addition, we compare the pulse sequences for linear Ising spin
chains to pulse sequences for more realistic spin systems with additional
long-range couplings between non-adjacent spins. We experimentally implement
the derived pulse sequences in three and four spin systems and demonstrate that
they are applicable in realistic settings under relaxation and experimental
imperfections-in particular-by deriving broadband pulse sequences which are
robust with respect to frequency offsets.",1110.5262v1
1994-09-21,Spectrum of transfer matrix for $U_q(B_n)$-invariant $A^{(2)}_{2n}$ open spin chain,"We propose an expression for the eigenvalues of the transfer matrix for the
$U_q(B_n)$-invariant open quantum spin chain associated with the fundamental
representation of $A^{(2)}_{2n}$. By assumption, the Bethe Ansatz equations are
``doubled'' with respect to those of the corresponding closed chain with
periodic boundary conditions. We verify that the transfer matrix eigenvalues
have the correct analyticity properties and asymptotic behavior. We also
briefly discuss the structure of the eigenstates of the transfer matrix.",9409130v1
2004-07-07,Quantum state transfer in imperfect artificial spin networks,"High-fidelity quantum computation and quantum state transfer are possible in
short spin chains. We exploit a system based on a dispersive qubit-boson
interaction to mimic XY coupling. In this model, the usually assumed
nearest-neighbors coupling is no more valid: all the qubits are mutually
coupled. We analyze the performances of our model for quantum state transfer
showing how pre-engineered coupling rates allow for nearly optimal state
transfer. We address a setup of superconducting qubits coupled to a microstrip
cavity in which our analysis may be applied.",0407058v2
2007-10-15,Signal and Charge Transfer Efficiency of Few Electrons Clocked on Microscopic Superfluid Helium Channels,"Electrons floating on the surface of liquid helium are possible spin-qubits
for quantum information processing. Varying electric potentials are not
expected to modify spin states, which allows their transport on helium using a
charge-coupled device (CCD)-like array of underlying gates. This approach
depends upon efficient inter-gate transfer of individual electrons.
Measurements are presented here of the charge transfer efficiency (CTE) of few
electrons clocked back and forth above a short microscopic CCD-like structure.
A charge transfer efficiency of 0.99999992 is obtained for a clocking frequency
of 800 kHz.",0710.2909v1
2010-06-08,Strong-interaction approximation for transfer matrix method,"Using transfer-matrix method a correspondence between $2D$ classical spin
systems ($2D$ Ising model and six-vertex model) and $1D$ quantum spin systems
is considered. We find the transfer matrix in two limits - in a well-known
strong-anisotropy limit and a novel strong-interaction limit. In contrast to
the usual strong-anisotropy approximation, within the strong-interaction
approximation we take into account the non-commutativity of transfer-matrix
components. The latter approximation is valid for low temperatures or strong
interaction in one spatial dimension. We observe that the Hamiltonian of the
corresponding quantum chains contains multispin interactions.",1006.1608v1
2010-10-01,Prefect Transfer of Quantum States on Spin Chain with Dzyaloshinskii- Moriya interaction in inhomogeneous Magnetic field,"In this work, we use the Hamiltonian of a modified Dzyaloshinskii-Moriya
model and investigate the perfect transfer of the quantum state on the spin
networks. In this paper, we calculate fidelity in which fidelity depends on
magnetic field and another parameters. Then, by using the numerical analysis we
show that the fidelity of the transferred state is determined by magnetic field
$B$, exchange coupling $J$ and the Dzyaloshinskii- Moriya interaction $D$. We
also found that the perfect transfer of the quantum state is possible with
condition $B \gg \Gamma^2\omega^{N/2}$ where $\Gamma =((J+iD)/2)$ and
$\omega=\Gamma^*/ \Gamma$.",1010.0084v1
2011-03-29,Transfer operator analysis of the parallel dynamics of disordered Ising chains,"We study the synchronous stochastic dynamics of the random field and random
bond Ising chain. For this model the generating functional analysis methods of
De Dominicis leads to a formalism with transfer operators, similar to transfer
matrices in equilibrium studies, but with dynamical paths of spins and
(conjugate) fields as arguments, as opposed to replicated spins. In the
thermodynamic limit the macroscopic dynamics is captured by the dominant
eigenspace of the transfer operator, leading to a relative simple and
transparent set of equations that are easy to solve numerically. Our results
are supported excellently by numerical simulations.",1103.5595v1
2009-10-29,Dual black holes in merger remnants. II: spin evolution and gravitational recoil,"Using high resolution hydrodynamical simulations, we explore the spin
evolution of massive dual black holes orbiting inside a circumnuclear disc,
relic of a gas-rich galaxy merger. The black holes spiral inwards from
initially eccentric co or counter-rotating coplanar orbits relative to the
disc's rotation, and accrete gas that is carrying a net angular momentum. As
the black hole mass grows, its spin changes in strength and direction due to
its gravito-magnetic coupling with the small-scale accretion disc. We find that
the black hole spins loose memory of their initial orientation, as accretion
torques suffice to align the spins with the angular momentum of their orbit on
a short timescale (<1-2 Myr). A residual off-set in the spin direction relative
to the orbital angular momentum remains, at the level of <10 degrees for the
case of a cold disc, and <30 degrees for a warmer disc. Alignment in a cooler
disc is more effective due to the higher coherence of the accretion flow near
each black hole that reflects the large-scale coherence of the disc's rotation.
If the massive black holes coalesce preserving the spin directions set after
formation of a Keplerian binary, the relic black hole resulting from their
coalescence receives a relatively small gravitational recoil. The distribution
of recoil velocities inferred from a simulated sample of massive black hole
binaries has median <70 km/s much smaller than the median resulting from an
isotropic distribution of spins.",0910.5729v2
2012-11-22,Spin motive force induced by Rashba interaction in the strong sd coupling regime,"Spin motive force induced by the Rashba interaction in the presence of strong
sd interaction between conduction electron and localized spin is theoretically
studied. The motive force is calculated by evaluating the time-derivative of
the current density on the basis of microscopic formalism. It is shown that
there are two motive forces, one proportional to $\EvR\times\dot{\nv}$, the
other, perpendicular component, proportional to
$\EvR\times(\nv\times\dot{\nv})$, where $\EvR$ and $\nv$ are the Rashba
electric field and localized spin direction, respectively. The second type
arises in the strong sd coupling regime from the spin relaxation. The
appearance of perpendicular component from the spin relaxation is understood
from the analogy with the current-induced torques. In the case of domain wall
motion, the two contributions to the spin motive force are the same order of
magnitude, while the first term dominates in the case of precession of uniform
magnetization. Our result explains appearance of the perpendicular component in
the weak sd coupling limit, recently discussed in the context of spin damping
monopole. Detection of AC voltage induced by the precession of uniform
magnetization serves as a experimental evidence of the Rashba interaction in
films and wires.",1211.5205v1
2014-10-14,The origin of spin in galaxies: clues from simulations of atomic cooling halos,"In order to elucidate the origin of spin in both dark matter and baryons in
galaxies, we have performed hydrodynamical simulations from cosmological
initial conditions. We study atomic cooling haloes in the redshift range $100 >
z > 9$ with masses of order $10^9{\rm M_{\odot}}$ at redshift $z=10$. We assume
that the gas has primordial composition and that ${\rm H_2}$-cooling and prior
star-formation in the haloes have been suppressed. We present a comprehensive
analysis of the gas and dark matter properties of four halos with very low
($\lambda \approx 0.01$), low ($\lambda \approx 0.04$), high ($\lambda \approx
0.06$) and very high ($\lambda \approx 0.1$) spin parameter. Our main
conclusion is that the spin orientation and magnitude is initially well
described by tidal torque linear theory, but later on is determined by the
merging and accretion history of each halo. We provide evidence that the
topology of the merging region, i.e. the number of colliding filaments, gives
an accurate prediction for the spin of dark matter and gas: halos at the center
of knots will have low spin while those in the center of filaments will have
high spin. The spin of a halo is given by $\lambda \approx 0.05 \times
\left(\frac{7.6}{\rm number\,\,\, of \,\,\, filaments}\right)^{5.1}$.",1410.4061v1
2015-09-01,Magnon-driven longitudinal spin Seebeck effect in F|N and N|F|N structures: role of asymmetric in-plane magnetic anisotropy,"The influence of an asymmetric in-plane magnetic anisotropy on the thermally
activated spin current is studied theoretically for two different systems; (i)
the system consisting of a ferromagnetic insulator in a direct contact with a
nonmagnetic metal, and the sandwich structure consisting of a ferromagnetic
insulating part sandwiched between two nonmagnetic metals. It is shown that
when the difference between the temperatures of the two nonmagnetic metals in a
structure is not large, the spin pumping currents from the magnetic part to the
nonmagnetic ones are equal in amplitude and have opposite directions, so only
the spin torque current contributes to the total spin current. The spin current
flows then from the nonmagnetic metal with the higher temperature to the
nonmagnetic metal having a lower temperature. Its amplitude varies linearly
with the difference in temperatures. In addition, we have found that if the
magnetic anisotropy is in the layer plane, then the spin current increases with
the magnon temperature, while in the case of an out-of-plane magnetic
anisotropy the spin current decreases when the magnon temperature enhances.
Enlarging the difference between the temperatures of the nonmagnetic metals,
the linear response becomes important, as confirmed by analytical expressions
inferred from the Fokker-Planck approach and by the results obtained upon a
full numerical integration of the stochastic Landau-Lifshitz-Gilbert equation.",1509.00376v1
2016-06-14,Relation between halo spin and cosmic web filaments at z=3,"We investigate the spin evolution of dark matter haloes and their dependence
on the number of connected filaments from the cosmic web at high redshift
(spin-filament relation hereafter). To this purpose, we have simulated $5000$
haloes in the mass range $5\times10^{9}h^{-1}M_{\odot}$ to
$5\times10^{11}h^{-1}M_{\odot}$ at $z=3$ in cosmological N-body simulations. We
confirm the relation found by Prieto et al. 2015 where haloes with fewer
filaments have larger spin. We also found that this relation is more
significant for higher halo masses, and for haloes with a passive (no major
mergers) assembly history. Another finding is that haloes with larger spin or
with fewer filaments have their filaments more perpendicularly aligned with the
spin vector. Our results point to a picture in which the initial spin of haloes
is well described by tidal torque theory and then gets subsequently modified in
a predictable way because of the topology of the cosmic web, which in turn is
given by the currently favoured LCDM model. Our spin-filament relation is a
prediction from LCDM that could be tested with observations.",1606.04562v2
2017-11-30,Changes in the pulse phase dependence of X-ray emission lines in 4U 1626-67 with a torque reversal,"We report results from an observation with the XMM-Newton observatory of a
unique X-ray pulsar 4U 1626-67. EPIC-pn data during the current spin-up phase
of 4U 1626-67 have been used to study pulse phase dependence of low energy
emission lines. We found strong variability of low energy emission line at
0.915 keV with the pulse phase, varying by a factor of 2, much stronger than
the continuum variability. Another interesting observation is that behavior of
one of the low energy emission lines across the pulse phase is quite different
from that observed during the spin-down phase. This indicates that the
structures in the accretion disk that produce pulse phase dependence of
emission features have changed from spin-down to spin-up phase. This is well
supported by the differences in the timing characteristics (like pulse
profiles, QPOs etc) between spin-down and spin-up phases. We have also found
that during the current spin-up phase of 4U 1626-67, the X-ray pulse profile
below 2 keV is different compared to the spin-down phase. The X-ray light curve
also shows flares which produce a feature around 3 mHz in power density
spectrum of 4U 1626-67. Since flares are dominant at lower energies, the
feature around 3 mHz is prominent at low energies.",1711.11305v1
2018-10-25,"Exceptionally high, strongly temperature dependent, spin Hall conductivity of SrRuO3","Spin-orbit torques (SOT) in thin film heterostructures originate from strong
spin-orbit interactions (SOI) that, in the bulk, generate a spin current as the
result of extrinsic spin-dependent, skew or/and side-jump, scattering, or in
the intrinsic case due to Berry curvature in the conduction band. While most
SOT studies have focused on materials with heavy metal components, the oxide
perovskite SrRuO3 has been predicted to have a pronounced Berry curvature.
Through quantification of its spin current by the SOT exerted on an adjacent Co
ferromagnetic layer, we determine that SrRuO3 has a strongly temperature (T)
dependent spin Hall conductivity which becomes particularly high at low T, e.g.
\sigma_{SH} \geqslant (\hbar/2e)3x10^{5} \Omega^{-1}m^{-1} at 60 K. Below the
SrRuO3 ferromagnetic transition, non-standard SOT components develop associated
with the magnetic characteristics of the oxide, but these do not dominate as
with spin currents from a conventional ferromagnet. Our results establish a new
approach for the study of SOI in epitaxial conducting oxide heterostructures
and confirm SrRuO3 as a promising candidate material for achieving new and
enhanced spintronics functionalities.",1810.11136v1
2018-12-01,Rectification in Spin-Orbit Materials Using Low Energy Barrier Magnets,"The coupling of spin-orbit materials to high energy barrier ($\sim$40-60
$k_BT$) nano-magnets has attracted growing interest for exciting new physics
and various spintronic applications. We predict that a coupling between the
spin-momentum locking (SML) observed in spin-orbit materials and low-energy
barrier magnets (LBM) should exhibit a unique multi-terminal rectification for
arbitrarily small amplitude channel currents. The basic idea is to measure the
charge current induced spin accumulation in the SML channel in the form of a
magnetization dependent voltage using an LBM, either with an in-plane or
perpendicular anisotropy (IMA or PMA). The LBM feels an instantaneous
spin-orbit torque due to the accumulated spins in the channel which causes the
average magnetization to follow the current, leading to the non-linear
rectification. We discuss the frequency band of this multi-terminal
rectification which can be understood in terms of the angular momentum
conservation in the LBM. For a fixed spin-current from the SML channel, the
frequency band is same for LBMs with IMA and PMA, as long as they have the same
total magnetic moment in a given volume. The proposed all-metallic structure
could find application as highly sensitive passive rf detectors and as energy
harvesters from weak ambient sources where standard technologies may not
operate.",1812.00286v2
2017-02-17,Spin conductance of YIG thin films driven from thermal to subthermal magnons regime by large spin-orbit torque,"We report a study on spin conductance in ultra-thin films of Yttrium Iron
Garnet (YIG), where spin transport is provided by propagating spin waves, that
are generated and detected by direct and inverse spin Hall effects in two Pt
wires deposited on top. While at low current the spin conductance is dominated
by transport of thermal magnons, at high current, the spin conductance is
dominated by low-damping non-equilibrium magnons thermalized near the spectral
bottom by magnon-magnon interaction, with consequent a sensitivity to the
applied magnetic field and a longer decay length. This picture is supported by
microfocus Brillouin Light Scattering spectroscopy.",1702.05226v3
2017-02-21,All-optical Detection of Spin Hall Angle in W/CoFeB/SiO2 Heterostructures by Varying Tungsten Layer Thickness,"The development of advanced spintronics devices hinges on the efficient
generation and utilization of pure spin current. In materials with large
spin-orbit coupling, the spin Hall effect may convert charge current to pure
spin current and a large conversion efficiency, which is quantified by spin
Hall angle (SHA), is desirable for the realization of miniaturized and energy
efficient spintronic devices. Here, we report a giant SHA in beta-tungsten
(\b{eta}-W) thin films in Sub/W(t)/Co20Fe60B20(3 nm)/SiO2(2 nm)
heterostructures with variable W thickness. We employed an all-optical
time-resolved magneto-optical Kerr effect microscope for an unambiguous
determination of SHA using the principle of modulation of Gilbert damping of
the adjacent ferromagnetic layer by the spin-orbit torque from the W layer. A
non-monotonic variation of SHA with W layer thickness (t) is observed with a
maximum of about 0.4 at about t = 3 nm, followed by a sudden reduction to a
very low value at t = 6 nm. This variation of SHA with W-thickness correlates
well with the thickness dependent structural phase transition and resistivity
variation of W above the spin diffusion length of W, while below this length
the interfacial electronic effect at W/CoFeB influences the estimation of SHA.",1702.06258v1
2017-02-28,Tidal interactions in spin-orbit misaligned systems,"Spin-orbit misalignments have been detected in exoplanetary systems and
binary star systems. Tidal interactions may have played an important role in
the evolution of the spin-orbit angle. In this study, we investigate the tidal
interactions in spin-orbit misaligned systems. In particular, we focus on the
tidal response of a rotating fluid body to the obliquity tide, which may be
important for the evolution of the spin-orbit angle but hardly affects the
orbital evolution. The obliquity tide also provides a torque for the mutual
precession of the spin and orbital axes around the total angular momentum
vector, which has not yet been considered in previous studies on the tidal
interactions. In this paper, we first formulate a set of linearized equations
describing the tidal response in spin-orbit misaligned systems, taking into
account the precessional motion. Numerical solutions in a homogeneous fluid and
in a polytrope of index 1 show that dissipative inertial waves can be excited
on top of precession by the obliquity tide in the presence of a rigid core. The
tidal quality factor associated with the obliquity tide $Q'_{210}$ can be
several orders of magnitude smaller than those associated with other tidal
components if their frequencies fall outside the frequency range of inertial
waves. Therefore, it is possible that the spin-orbit misalignment undergoes
much more rapid decay than the orbital decay in hot Jupiter systems owing to
the enhanced dissipation of the obliquity tide.",1702.08805v1
2020-09-22,Magnon-mediated spin currents in Tm3Fe5O12/Pt with perpendicular magnetic anisotropy,"The control of pure spin currents carried by magnons in magnetic insulator
(MI) garnet films with a robust perpendicular magnetic anisotropy (PMA) is of
great interest to spintronic technology as they can be used to carry, transport
and process information. Garnet films with PMA present labyrinth domain
magnetic structures that enrich the magnetization dynamics, and could be
employed in more efficient wave-based logic and memory computing devices. In
MI/NM bilayers, where NM being a normal metal providing a strong spin-orbit
coupling, the PMA benefits the spin-orbit torque (SOT) driven magnetization's
switching by lowering the needed current and rendering the process faster,
crucial for developing magnetic random-access memories (SOT-MRAM). In this
work, we investigated the magnetic anisotropies in thulium iron garnet (TIG)
films with PMA via ferromagnetic resonance measurements, followed by the
excitation and detection of magnon-mediated pure spin currents in TIG/Pt driven
by microwaves and heat currents. TIG films presented a Gilbert damping constant
{\alpha}~0.01, with resonance fields above 3.5 kOe and half linewidths broader
than 60 Oe, at 300 K and 9.5 GHz. The spin-to-charge current conversion through
TIG/Pt was observed as a micro-voltage generated at the edges of the Pt film.
The obtained spin Seebeck coefficient was 0.54 {\mu}V/K, confirming also the
high interfacial spin transparency.",2009.10299v1
2019-07-31,Spin-spiral formalism based on the multiple scattering Green's function technique with applications to ultrathin magnetic films and multilayers,"Based on the Korringa-Kohn-Rostoker Green's function technique we present a
computational scheme for calculating the electronic structure of layered
systems with homogeneous spin-spiral magnetic state. From the self-consistent
non-relativistic calculations the total energy of the spin-spiral states is
determined as a function of the wave vector, while a relativistic extension of
the formalism in first order of the spin-orbit coupling gives an access to the
effect of the Dzyaloshinskii-Moriya interactions. We demonstrate that the newly
developed method properly describes the magnetic ground state of a Mn monolayer
on W(001) and that of a Co monolayer on Pt(111). The obtained spin-spiral
energies are mapped to a classical spin model, the parameters of which are
compared to those calculated directly from the relativistic torque method. In
case of the Co/Pt(111) system we find that the isotropic interaction between
the Co atoms is reduced and the Dzyaloshinskii-Moriya interaction is increased
when capped by a Ru layer. In addition, we perform spin-spiral calculations on
Ir/Fe/Co/Pt and Ir/Co/Fe/Pt multilayer systems and find a spin-spiral ground
state with very long wavelength due to the frustrated isotropic couplings
between the Fe atoms, whereas the Dzyaloshinskii-Moriya interaction strongly
depends on the sequence of the Fe and Co layers.",1907.13328v1
2020-01-23,Induced Spin-texture at 3$d$ Transition Metal/Topological Insulator Interfaces,"While some of the most elegant applications of topological insulators, such
as quantum anomalous Hall effect, require the preservation of Dirac surface
states in the presence of time-reversal symmetry breaking, other phenomena such
as spin-charge conversion rather rely on the ability for these surface states
to imprint their spin texture on adjacent magnetic layers. In this work, we
investigate the spin-momentum locking of the surface states of a wide range of
monolayer transition metals (3$d$-TM) deposited on top of Bi$_{2}$Se$_{3}$
topological insulators using first principles calculations. We find an
anticorrelation between the magnetic moment of the 3$d$-TM and the magnitude of
the spin-momentum locking {\em induced} by the Dirac surface states. While the
magnetic moment is large in the first half of the 3$d$ series, following Hund's
rule, the spin-momentum locking is maximum in the second half of the series. We
explain this trend as arising from a compromise between intra-atomic magnetic
exchange and covalent bonding between the 3$d$-TM overlayer and the Dirac
surface states. As a result, while Cr and Mn overlayers can be used
successfully for the observation of quantum anomalous Hall effect or the
realization of axion insulators, Co and Ni are substantially more efficient for
spin-charge conversion effects, e.g. spin-orbit torque and charge pumping.",2001.08538v2
2022-08-01,Observation of gigantic spin conversion anisotropy in bismuth,"Whilst the g-factor can be anisotropic due to the spin-orbit interaction
(SOI), its existence in solids cannot be simply asserted from a band structure,
which hinders progress on studies from such the viewpoints. The g-factor in
bismuth (Bi) is largely anisotropic; especially for holes at T-point, the
g-factor perpendicular to the trigonal axis is negligibly small (< 0.112),
whereas the g-factor along the trigonal axis is very large (62.7). We clarified
in this work that the large g- factor anisotropy gives rise to the gigantic
spin conversion anisotropy in Bi from experimental and theoretical approaches.
Spin-torque ferromagnetic resonance was applied to estimate the spin conversion
efficiency in rhombohedral (110) Bi to be 17%, which is unlike the negligibly
small efficiency in Bi(111). Harmonic Hall measurements supports the large spin
conversion efficiency in Bi(110). This is the first observation of gigantic
spin conversion anisotropy as the clear manifestation of the g-factor
anisotropy. Beyond the emblematic case of Bi, our study unveiled the
significance of the g-factor anisotropy in condensed-matter physics and can
pave a pathway toward establishing novel spin physics under g-factor control.",2208.00589v3
2022-11-07,Room temperature charge-to-spin conversion from q-2DEG at SrTiO3-based interfaces,"Interfacial two-dimensional electron gas (2DEG), especially the SrTiO3-based
ones at the unexpected interface of insulators, have emerged to be a promising
candidate for efficient charge-spin current interconversion. In this article,
to gain insight into the mechanism of the charge-spin current interconversion
at the oxide-based 2DEG, we focused on conducting interfaces between insulating
SrTiO3 and two types of aluminium-based amorphous insulators, namely SrTiO3/AlN
and SrTiO3/Al2O3, and estimated their charge-spin conversion efficiency,
{\theta}_cs. The two types of amorphous insulators were selected to explicitly
probe the overlooked contribution of oxygen vacancy to the {\theta}_cs. We
proposed a mechanism to explain results of spin-torque ferromagnetic resonance
(ST-FMR) measurements and developed an analysis protocol to reliably estimate
the {\theta}_cs of the oxide based 2DEG. The resultant {\theta}_cs/t, where t
is the thickness of the 2DEG, were estimated to be 0.244 nm-1 and 0.101 nm-1
for the SrTiO3/AlN and SrTiO3/Al2O3, respectively, and they are strikingly
comparable to their crystalline counterparts. Furthermore, we also observe a
large direct current modulation of resonance linewidth in SrTiO3/AlN samples,
confirming its high {\theta}_cs and attesting an oxygen-vacancy-enabled
charge-spin conversion. Our findings emphasize the defects' contribution to the
charge-spin interconversion, especially in the oxide-based low dimensional
systems, and provide a way to create and enhance charge-spin interconversion
via defect engineering.",2211.03383v1
2022-11-24,Analogs of Rashba-Edelstein effect from density functional theory,"Studies of structure-property relationships in spintronics are essential for
the design of materials that can fill specific roles in devices. For example,
materials with low symmetry allow unconventional configurations of
charge-to-spin conversion which can be used to generate efficient spin-orbit
torques. Here, we explore the relationship between crystal symmetry and
geometry of the Rashba-Edelstein effect (REE) that causes spin accumulation in
response to an applied electric current. Based on a symmetry analysis performed
for 230 crystallographic space groups, we identify classes of materials that
can host conventional or collinear REE. Although transverse spin accumulation
is commonly associated with the so-called 'Rashba materials', we show that the
presence of specific spin texture does not easily translate to the
configuration of REE. More specifically, bulk crystals may simultaneously host
different types of spin-orbit fields, depending on the crystallographic point
group and the symmetry of the specific $k$-vector, which, averaged over the
Brillouin zone, determine the direction and magnitude of the induced spin
accumulation. To explore the connection between crystal symmetry, spin texture,
and the magnitude of REE, we perform first-principles calculations for
representative materials with different symmetries. We believe that our results
will be helpful for further computational and experimental studies, as well as
the design of spintronics devices.",2211.13693v3
2023-11-20,Spin Hall conductivity in Bi$_{1-x}$Sb$_x$ as an experimental test of bulk-boundary correspondence,"Bulk-boundary correspondence is a foundational principle underlying the
electronic band structure and physical behavior of topological quantum
materials. Although it has been rigorously tested in topological systems where
the physical properties involve charge currents, it remains unclear whether
bulk-boundary correspondence should also hold for non-conserved spin currents.
We study charge-to-spin conversion in a canonical topological insulator,
Bi$_{1-x}$Sb$_x$, to address this fundamentally unresolved question. We use
spin-torque ferromagnetic resonance measurements to accurately probe the
charge-to-spin conversion efficiency in epitaxial Bi$_{1-x}$Sb$_x$~thin films
of high structural quality spanning the entire range of composition, including
both trivial and topological band structures, as verified using {\it in vacuo}
angle-resolved photoemission spectroscopy. From these measurements, we deduce
the effective spin Hall conductivity (SHC) and find excellent agreement with
the values predicted by tight-binding calculations for the intrinsic SHC of the
bulk bands. These results provide strong evidence that the strong spin-orbit
entanglement of bulk states well below the Fermi energy connects directly to
the SHC in epitaxial Bi$_{1-x}$Sb$_x$~films interfaced with a metallic
ferromagnet. The excellent agreement between theory and experiment points to
the generic value of analyses focused entirely on bulk properties, even for
topological systems involving non-conserved spin currents.",2311.11933v1
2023-11-26,Electric Field Switching of Magnon Spin Current in a Compensated Ferrimagnet,"Manipulation of directional magnon propagation, known as magnon spin current,
is essential for developing magnonic memory and logic devices featuring
nonvolatile functionalities and ultralow power consumption. Magnon spin current
can usually be modulated by magnetic field or current-induced spin torques.
However, these approaches may lead to energy dissipation caused by Joule
heating. Electric-field switching of magnon spin current without charge current
is highly desired but very challenging to realize. By integrating magnonic and
piezoelectric materials, we demonstrate manipulation of the magnon spin current
generated by the spin Seebeck effect in the ferrimagnetic insulator Gd3Fe5O12
(GdIG) film on a piezoelectric substrate. We observe reversible electric-field
switching of magnon polarization without applied charge current. Through
strain-mediated magnetoelectric coupling, the electric field induces the
magnetic compensation transition between two magnetic states of the GdIG,
resulting in its magnetization reversal and the simultaneous switching of
magnon spin current. Our work establishes a prototype material platform that
pave the way for developing magnon logic devices characterized by all electric
field reading and writing and reveals the underlying physics principles of
their functions.",2311.15183v1
2016-07-08,Observation of the spin Nernst effect,"The observation of the spin Hall effect triggered intense research on pure
spin current transport. With the spin Hall effect, the spin Seebeck effect, and
the spin Peltier effect already observed, our picture of pure spin current
transport is almost complete. The only missing piece is the spin Nernst
(-Ettingshausen) effect, that so far has only been discussed on theoretical
grounds. Here, we report the observation of the spin Nernst effect. By applying
a longitudinal temperature gradient, we generate a pure transverse spin current
in a Pt thin film. For readout, we exploit the
magnetization-orientation-dependent spin transfer to an adjacent Yttrium Iron
Garnet layer, converting the spin Nernst current in Pt into a controlled change
of the longitudinal thermopower voltage. Our experiments show that the spin
Nernst and the spin Hall effect in Pt are of comparable magnitude, but differ
in sign, as corroborated by first-principles calculations.",1607.02277v2
2018-03-21,Spin caloric effects in antiferromagnets assisted by an external spin current,"Searching for novel spin caloric effects in antiferromagnets we study the
properties of thermally activated magnons in the presence of an external spin
current and temperature gradient. We predict the spin Peltier effect --
generation of a heat flux by spin accumulation -- in an antiferromagnetic
insulator with cubic or uniaxial magnetic symmetry. This effect is related with
spin-current induced splitting of the relaxation times of the magnons with
opposite spin direction. We show that the Peltier effect can trigger
antiferromagnetic domain wall motion with a force whose value grows with the
temperature of a sample. At a temperature, larger than the energy of the
low-frequency magnons, this force is much larger than the force caused by
direct spin transfer between the spin current and the domain wall. We also
demonstrate that the external spin current can induce the magnon spin Seebeck
effect. The corresponding Seebeck coefficient is controlled by the current
density. These spin-current assisted caloric effects open new ways for the
manipulation of the magnetic states in antiferromagnets.",1803.07949v1
2020-12-08,Flipping spins in mass transferring binaries and origin of spin-orbit misalignment in binary black holes,"Close stellar binaries are prone to undergo a phase of stable mass transfer
in which a star loses mass to its companion. Assuming that the donor star loses
mass along the instantaneous interstellar axis, we derive the orbit-averaged
equations of motion describing the evolution of the donor rotational angular
momentum vector (spin) which accompanies the transfer of mass. We consider: (i)
a model in which the mass transfer rate is constant within each orbit and (ii)
a phase-dependent rate in which all mass per orbit is lost at periapsis. In
both cases, we find that the ejection of $\gtrsim 30$ per cent of the donor's
initial mass causes its spin to nearly flip onto the orbital plane of the
binary, independently of the initial spin-orbit alignment. Moreover, we show
that the spin flip due to mass transfer can easily dominate over tidal
synchronisation in any giant stars and main-sequence stars with masses
$\sim1.5$ to $5\,\rm M_\odot$. Finally, the general equations of motion,
including tides, are used to evolve a realistic population of massive binary
stars leading to the formation of binary black holes. Assuming that the stellar
core and envelope are fully coupled, the resulting tilt of the first-born black
hole reduces its spin projection onto the orbit normal by a factor
$\sim\mathcal{O}(0.1)$. This result supports previous studies in favour of an
insignificant contribution to the effective spin projection, $\chi_{\rm eff}$,
in binary black holes formed from the evolution of field binaries.",2012.06329v2
2010-04-07,Temperature dependence of the nonlocal voltage in an Fe/GaAs electrical spin injection device,"The nonlocal spin resistance is measured as a function of temperature in a
Fe/GaAs spin-injection device. For nonannealed samples that show minority-spin
injection, the spin resistance is observed up to room temperature and decays
exponentially with temperature at a rate of 0.018\,K$^{-1}$. Post-growth
annealing at 440\,K increases the spin signal at low temperatures, but the
decay rate also increases to 0.030\,K$^{-1}$. From measurements of the
diffusion constant and the spin lifetime in the GaAs channel, we conclude that
sample annealing modifies the temperature dependence of the spin transfer
efficiency at injection and detection contacts. Surprisingly, the spin transfer
efficiency increases in samples that exhibit minority-spin injection.",1004.1034v1
2011-04-08,A topological classification of interaction-driven spin pumps,"When adiabatically varied in time, certain one-dimensional band insulators
allow for the quantized noiseless pumping of spin even in the presence of
strong spin orbit scattering. These spin pumps are closely related to the
quantum spin Hall system, and their properties are protected by a time-reversal
restriction on the pumping cycle. In this paper we study pumps formed of
one-dimensional insulators with a time-reversal restriction on the pumping
cycle and a bulk energy gap which arises due to interactions. We find that the
correlated gapped phase can lead to novel pumping properties. In particular,
systems with $d$ different ground states can give rise to $d+1$ different
classes of spin pumps, including a trivial class which does not pump quantized
spin and $d$ non-trivial classes allowing for the pumping of quantized spin
$\hbar/n $ on average per cycle, where $1\leq n\leq d$. We discuss an example
of a spin pump that transfers on average spin $ \hbar/2$ without transferring
charge.",1104.1516v1
2015-10-07,Nanosecond spin-transfer over tens of microns in a bare GaAs/AlGaAs layer,"The spin-conserving length-scale is a key parameter determining
functionalities of a broad range of spintronic devices including magnetic
multilayer spin-valves in the commercialized magnetic memories or lateral spin
transistors in experimental spin-logic elements. Spatially resolved optical
pump-and-probe experiments in the lateral devices allow for the direct
measurement of the lengthscale and the time-scale at which spin-information is
transferred from the injector to the detector. Using this technique, we
demonstrate that in an undoped GaAs/AlGaAs layer spins are detected at
distances reaching more than ten microns from the injection point at times as
short as nanoseconds after the pump-pulse. The observed unique combination of
the long-range and highrate electronic spin-transport requires simultaneous
suppression of mechanisms limiting the spin life-time and mobility of carriers.
Unlike earlier attempts focusing on elaborate doping, gating, or
heterostructures we demonstrate that the bare GaAs/AlGaAs layer intrinsically
provides superior spin-transport characteristics whether deposited directly on
the substrate or embedded in complex heterostructures.",1510.01978v1
2001-10-12,Solving the open XXZ spin chain with nondiagonal boundary terms at roots of unity,"We consider the open XXZ quantum spin chain with nondiagonal boundary terms.
For bulk anisotropy value \eta = i \pi/(p+1), p= 1, 2, ..., we propose an exact
(p+1)-order functional relation for the transfer matrix, which implies
Bethe-Ansatz-like equations for the corresponding eigenvalues. The key
observation is that the fused spin-(p+1)/2 transfer matrix can be expressed in
terms of a lower-spin transfer matrix, resulting in the truncation of the
fusion hierarchy.",0110116v3
2008-01-11,Thermal Dynamics in Symmetric Magnetic Nanopillars Driven by Spin Transfer,"We study the effects of spin transfer on thermally activated dynamics of
magnetic nanopillars with identical thicknesses of the magnetic layers. The
symmetric nanopillars exhibit anomalous dependencies of switching statistics on
magnetic field and current. We interpret our data in terms of simultaneous
current-induced excitation of both layers. We also find evidence for coupling
between the fluctuations of the layers due to the spin transfer.",0801.1807v1
2008-05-28,Perfect state transfer on a spin-chain without state initialization,"We demonstrate that perfect state transfer can be achieved using an
engineered spin chain and clean local end-chain operations, without requiring
the initialization of the state of the medium nor fine tuning of
control-pulses. This considerably relaxes the prerequisites for obtaining
reliable transfer of quantum information across interacting-spin systems.
Moreover, it allows us to shed light on the interplay among purity,
entanglement and operations on a class of many-body systems potentially useful
for quantum information processing tasks.",0805.4365v3
2011-01-24,Long-range interactions and information transfer in spin chains,"One of the main proposed tools to transfer information in a quantum
computational context are spin chains. While spin chains have shown to be
convenient and reliable, it has to be expected that, as with any implementation
of a physical system, they will be subject to various errors and perturbative
factors. In this work we consider the transfer of entangled as well as
unentangled states to investigate the effects of various errors, paying
particular attention to unwanted long-range interactions.",1101.4509v1
2012-10-05,Transfer matrix for Kogut-Susskind fermions in the spin basis,"In the absence of interaction it is well known that the Kogut-Susskind
regularizations of fermions in the spin and flavor basis are equivalent to each
other. In this paper we clarify the difference between the two formulations in
the presence of interaction with gauge fields. We then derive an explicit
expression of the transfer matrix in the spin basis by a unitary transformation
on that one in the flavor basis which is known. The essential key ingredient is
the explicit construction of the fermion Fock space for variables which live on
blocks. Therefore the transfer matrix generates time translations of two
lattice units.",1210.1786v1
2018-06-13,Photon-assisted quantum state transfer and entanglement generation in spin chains,"We propose a protocol for state transfer and entanglement generation between
two distant spin qubits (sender and receiver) that have different energies. The
two qubits are permanently coupled to a far off-resonant spin-chain, and the
qubit of the sender is driven by an external field, which provides the energy
required to bridge the energy gap between the sender and the receiver. State
transfer and entanglement generation are achieved via virtual single-photon and
multi-photon transitions to the eigenmodes of the channel.",1806.05122v1
2016-12-26,Spin-selective electron transfer in quantum dot array,"We propose a spin-selective coherent electron transfer in a
silicon-quantum-dot array. Oscillating magnetic fields and temporally
controlled gate voltages are utilised to separate the electron wave function
into different quantum dots depending on the spin state. We introduce
non-adiabatic and adiabatic protocols which offer fast electron transfer and
the robustness against the error in the control-field pulse area, respectively.
We also study a shortcut-to-adiabaticity protocol which compromises these two
protocols. We show that this scheme can be extended to multi-electron systems
straightforwardly and used for non-local manipulations of the electrons.",1612.08389v2
2021-08-05,Longitudinal and Transverse Spin Transfer of $Λ$ and $\overlineΛ$ Hyperons in Polarized $p$+$p$ Collisions at $\sqrt{s} = 200$ GeV at RHIC-STAR,"Measurements of the longitudinal spin transfer, $D_{LL}$, and the transverse
spin transfer, $D_{TT}$, of the $\Lambda(\bar{\Lambda}$) hyperon in polarized
$p$+$p$ collisions are expected to be sensitive to the helicity distribution
and transversity distribution of the $s(\bar{s})$ quark in proton and the
corresponding polarized fragmentation functions. This contribution presents the
new preliminary results of the $\Lambda(\bar{\Lambda}$) $D_{LL}$ and $D_{TT}$
using data collected at RHIC-STAR experiment in 2015, with twice larger
statistics than previously published results.",2108.02349v1
2008-06-03,High-Probability Quantum State Transfer in the Alternating Open Chains of 1/2 Spins with XY Hamiltonian,"This paper concerns the problem of non-ideal state transfer along the
alternating open chain of spins $s=1/2$ with XY Hamiltonian. It is found that
the state transfer along the chain with even number of spins $N$ ($N=4,6,8$)
may be realized with high probability. Privilege of even $N$ in comparison with
odd $N$ is demonstrated.",0806.0506v2
2021-05-31,Einstein--de Haas fluctuation of a nanoparticle in spin polarized gases,"We theoretically study angular momentum (AM) transfer from a spin-polarized
dilute gas into an nanoparitcle (NP) tightly trapped in optical tweezers. We
formulate a microscopic model based on the spin tunneling Hamiltonian method
and derive a macroscopic stochastic differential equation (SDE) which governs
the AM-transfer-induced rotational motion of the NP. It is shown that the AM
transfer rate at the NP surface can be extracted via the inference of the SDE.
This work will open the door to the manipulation of nano-spintronic systems in
gaseous environments.",2105.14684v1
2022-11-25,Routing a quantum state in a bio-inspired network,"We consider a spin network resembling an $\alpha$-helix structure and study
quantum information transfer over this bio-inspired network. The model we use
is the Davydov model in its elementary version without a phononic environment.
We investigate analytically and numerically the perfect state transfer (PST) in
such a network which provides an upper bound on the probability of quantum
states transfer from one node to another. We study PST for different boundary
conditions on the network and show it is reachable between certain nodes and
with suitable spin-spin couplings.",2211.14176v2
2021-05-19,Optical manipulation of Rashba-split 2-Dimensional Electron Gas,"In spintronic devices, the two main approaches to actively control the
electrons' spin degree of freedom involve either static magnetic or electric
fields. An alternative avenue relies on the application of optical fields to
generate spin currents, which promises to bolster spin-device performance
allowing for significantly faster and more efficient spin logic. To date,
research has mainly focused on the optical injection of spin currents through
the photogalvanic effect, and little is known about the direct optical control
of the intrinsic spin splitting. Here, to explore the all-optical manipulation
of a material's spin properties, we consider the Rashba effect at a
semiconductor interface. The Rashba effect has long been a staple in the field
of spintronics owing to its superior tunability, which allows the observation
of fully spin-dependent phenomena, such as the spin-Hall effect, spin-charge
conversion, and spin-torque in semiconductor devices. In this work, by means of
time and angle-resolved photoemission spectroscopy (TR-ARPES), we demonstrate
that an ultrafast optical excitation can be used to manipulate the
Rashba-induced spin splitting of a two-dimensional electron gas (2DEG)
engineered at the surface of the topological insulator Bi$_{2}$Se$_{3}$. We
establish that light-induced photovoltage and charge carrier redistribution --
which in concert modulate the spin-orbit coupling strength on a sub-picosecond
timescale -- can offer an unprecedented platform for achieving all
optically-driven THz spin logic devices.",2105.09320v2
2002-08-01,The transfer matrix with Kogut-Susskind fermions,"A transfer matrix for gauge theories on a lattice with Kogut-Susskind
fermions in the flavour basis is constructed and some difficulties in the
spin-diagonal basis are pointed out.",0208005v1
2005-04-26,"Spin correlations in the reaction ""pi \vec D --> \vecΣΘ^+"" and the parity of Theta^+","We analyze two types of spin observables in the reaction $\pi \vec
D\to\vec\Sigma\Theta^+$ near the threshold. One concerns the spin-transfer
coefficients $K_x^x$ and $K_z^z$. The second one is the deuteron spin
anisotropy. These observables are sensitive to the $\Theta^+$ parity and can be
used as a tool for the $\Theta^+$ parity determination.",0504073v1
2013-03-21,Anisotropic quantum transport in monolayer graphene in the presence of Rashba spin-orbit coupling,"We have studied spin-depend electron tunnelling through the Rashba barrier in
a monolayer graphene lattice. The transfer matrix method, have been employed to
obtain the spin dependent transport properties of the chiral particles. It is
shown that graphene sheets in presence of Rashba spin-orbit barrier will act as
an electron spin- inverter.",1303.5209v1
2012-08-30,Spin Evolution of Supermassive Black Holes and Galactic Nuclei,"The spin angular momentum S of a supermassive black hole (SBH) precesses due
to torques from orbiting stars, and the stellar orbits precess due to dragging
of inertial frames by the spinning hole. We solve the coupled post-Newtonian
equations describing the joint evolution of S and the stellar angular momenta
Lj, j = 1...N in spherical, rotating nuclear star clusters. In the absence of
gravitational interactions between the stars, two evolutionary modes are found:
(1) nearly uniform precession of S about the total angular momentum vector of
the system; (2) damped precession, leading, in less than one precessional
period, to alignment of S with the angular momentum of the rotating cluster.
Beyond a certain distance from the SBH, the time scale for angular momentum
changes due to gravitational encounters between the stars is shorter than
spin-orbit precession times. We present a model, based on the
Ornstein-Uhlenbeck equation, for the stochastic evolution of star clusters due
to gravitational encounters and use it to evaluate the evolution of S in nuclei
where changes in the Lj are due to frame dragging close to the SBH and to
encounters farther out. Long-term evolution in this case is well described as
uniform precession of the SBH about the cluster's rotational axis, with an
increasingly important stochastic contribution when SBH masses are small. Spin
precessional periods are predicted to be strongly dependent on nuclear
properties, but typical values are 10-100 Myr for low-mass SBHs in dense
nuclei, 100 Myr - 10 Gyr for intermediate mass SBHs, and > 10 Gyr for the most
massive SBHs. We compare the evolution of SBH spins in stellar nuclei to the
case of torquing by an inclined, gaseous accretion disk.",1208.6274v1
2020-12-17,Identifying the origin of the non-monotonic thickness dependence of spin-orbit torques and interfacial Dzyaloshinskii-Moriya interaction in a ferrimagnetic insulator heterostructure,"Electrical manipulation of magnetism via spin-orbit torques (SOTs) promises
efficient spintronic devices. In systems comprising magnetic insulators and
heavy metals, SOTs have started to be investigated only recently, especially in
systems with interfacial Dzyaloshinskii-Moriya interaction (iDMI). Here, we
quantitatively study the SOT efficiency and iDMI in a series of gadolinium
gallium garnet (GGG) / thulium iron garnet (TmIG) / platinum (Pt)
heterostructures with varying TmIG and Pt thicknesses. We find that the
non-monotonic SOT efficiency as a function of the magnetic layer thickness is
not consistent with the 1/thickness dependence expected from a simple
interfacial SOT mechanism. Moreover, considering the insulating nature of TmIG,
our results cannot be explained by the SOT mechanism established for metallic
magnets where the transverse charge spin current can inject and dephase in the
magnetic layers. Rather we can explain this non-monotonic behavior by a model
based on the interfacial spin mixing conductance that is affected by the
thickness-dependent exchange splitting energy by determining the phase
difference of the reflected spin-up and spin-down electrons at the TmIG / Pt
interface. By studying the Pt thickness dependence, we find that the effective
DMI for GGG / TmIG / Pt does not depend on the Pt thickness, which indicates
that the GGG / TmIG interface is the source of the iDMI in this system. Our
work demonstrates that SOT and DMI can originate from two different interfaces,
which enables independent optimization of DMI and SOT for advanced chiral
spintronics with low damping magnetic insulators.",2012.09358v1
2007-06-03,Iterative quantum state transfer along a chain of nuclear spin qubits,"Transferring quantum information between two qubits is a basic requirement
for many applications in quantum communication and quantum information
processing. In the iterative quantum state transfer (IQST) proposed by D.
Burgarth et al. [Phys. Rev. A 75, 062327 (2007)], this is achieved by a static
spin chain and a sequence of gate operations applied only to the receiving end
of the chain. The only requirement on the spin chain is that it transfers a
finite part of the input amplitude to the end of the chain, where the gate
operations accumulate the information. For an appropriate sequence of
evolutions and gate operations, the fidelity of the transfer can asymptotically
approach unity. We demonstrate the principle of operation of this transfer
scheme by implementing it in a nuclear magnetic resonance quantum information
processor.",0706.0352v3
2022-05-05,Robust population transfer of spin states by geometric formalism,"Accurate population transfer of uncoupled or weakly coupled spin states is
crucial for many quantum information processing tasks. In this paper, we
propose a fast and robust scheme for population transfer which combines
invariant-based inverse engineering and geometric formalism for robust quantum
control. Our scheme is not constrained by the adiabatic condition and therefore
can be implemented fast. It can also effectively suppress the dominant noise in
spin systems, which together with the fast feature guarantees the accuracy of
the population transfer. Moreover, the control parameters of the driving
Hamiltonian in our scheme are easy to design because they correspond to the
curvature and torsion of a three-dimensional visual space curve derived by
using geometric formalism for robust quantum control. We test the efficiency of
our scheme by numerically simulating the ground-state population transfer in
$^{15}$N nitrogen vacancy centers and comparing our scheme with stimulated
Raman transition, stimulated Raman adiabatic passage and conventional shortcuts
to adiabaticity based schemes, three types of popularly used schemes for
population transfer. The numerical results clearly show that our scheme is
advantageous over these previous ones.",2205.02701v1
2004-06-21,Decoherence of Nuclear Spin Quantum Memory in Quantum Dot,"Recently an ensemble of nuclear spins in a quantum dot have been proposed as
a long-lived quantum memory. A quantum state of an electron spin in the dot can
be faithfully transfered into nuclear spins through controlled hyperfine
coupling. Here we study the decoherence of this memory due to nuclear spin
dipolar coupling and inhomogeneous hyperfine interaction during the {\it
storage} period. We calculated the maximum fidelity of writing, storing and
reading operations. Our results show that nuclear spin dynamics can severely
limits the performance of the proposed device for quantum information
processing and storage based on nuclear spins.",0406478v1
2005-12-14,Electronic spin precession and interferometry from spin-orbital entanglement in a double quantum dot,"A double quantum dot inserted in parallel between two metallic leads allows
to entangle the electron spin with the orbital (dot index) degree of freedom.
An Aharonov-Bohm orbital phase can then be transferred to the spinor
wavefunction, providing a geometrical control of the spin precession around a
fixed magnetic field. A fully coherent behaviour is obtained in a mixed
orbital/spin Kondo regime. Evidence for the spin precession can be obtained,
either using spin-polarized metallic leads or by placing the double dot in one
branch of a metallic loop.",0512324v3
2012-08-09,Interference-mediated intensity modulation of spin waves,"The modulation of propagating spin-wave amplitude in Ni81Fe19 (Py) films,
resulting from constructive and destructive interference of spin wave, has been
demonstrated. Spin waves were excited and detected inductively using pulse
inductive time domain measurements. Two electrical impulses were used for
launching two interfering Gaussian spin wave packets in Py films. The applied
bias magnetic field or the separation between two pulses was used for tuning
the amplitude of the resulting spin wave packets. This may thus be useful for
spin wave based low-power information transfer and processing.",1208.1848v1
2018-05-03,"Exact Intrinsic Localized Excitation of an Anisotropic Ferromagnetic Spin Chain in External Magnetic Field with Gilbert Damping, Spin Current and PT-Symmetry","We obtain the exact one-spin intrinsic localized excitation in an anisotropic
Heisenberg ferromagnetic spin chain in a constant/variable external magnetic
field with Gilbert damping included. We also point out how an appropriate
magnitude spin current term in a spin transfer nano-oscillator (STNO) can
stabilize the tendency towards damping. Further, we show how this excitation
can be sustained in a recently suggested PT-symmetric magnetic nanostructure.
We also briefly consider more general spin excitations.",1805.01230v1
2023-01-19,Higher-order Bloch spheres: A generalized representation of electron spin states with azimuthal phase factor,"Using the similarity between spin states on the Bloch sphere (BS) and
polarization states on the Poincare sphere (PS), we construct higher-order spin
states on the higher-order BS corresponding to higher-order polarization states
of photons on the higher-order PS. We investigate the time evolution of
higher-order spin states in a magnetic field and establish an extended form of
the conventional Larmor precession. The results provide insights on coherent
transfer from extended photons to extended spin qubit systems with spin and
orbital angular momenta and the operation of extended spin qubits.",2301.08024v1
1999-02-09,The recent pulse period evolution of SMC X-1,"We report observations of SMC X-1 in three new high-intensity states with
ROSAT HRI in December 1995, May 1997, and March 1998 in which pulsations with a
period of 0.70769+/-0.00006 sec, 0.70706+/-0.00001 sec, and 0.706707+/-0.00001
sec respectively were detected. Combining the pulse periods from observations
with ROSAT PSPC in high-intensity states in October 1991 and March 1998,
respectively, we obtain the spin-up rate of the pulsar in recent 6.5 years,
-dP/dt = 1.18+/-0.06 10^-11 s s^-1, consistent with the average spin-up rate
-dP/dt = 1.2 10^-11 s s^-1 determined from previous measurements indicating
that the stable spin-up has continued. Pulsations with a period of
0.709103+/-0.000003 sec were also detected ~2 weeks after an X-ray turn-off
during an X-ray low-intensity state in October 1991, and the period derivative
derived within ~10 days is -dP/dt ~ (1.1+/-0.7) 10^-11 s s^-1. This is
consistent with a constant accretion torque in sign and magnitude. The
magnitude of the magnetic moment of the pulsar is discussed based on different
description of the apparent spin-up behavior.",9902139v1
2001-11-09,Detection of Galaxy Spin Alignments in the PSCz Shear Field,"We report the first direct observational evidence for alignment of galaxy
spin axes with the local tidal shear field. We measure quantitatively the
strength of this directional correlation of disk galaxies from the Tully
catalog with the local shear field reconstructed from PSCz galaxies. We
demonstrate that the null hypothesis of random galaxy alignments relative to
the shear frame can be ruled out more than 99.98 % confidence. The observed
intrinsic correlation averaged over the censored samples that have detected
non-zero signals is measured in terms of the alignment parameter 'a=0.17 +/-
0.04', which includes only statistical errors of the censored data, but not the
cosmic variance error. The reconstruction procedure is likely to underestimates
'a' systematically. Our result is consistent with the linear tidal torque
model, and supports the idea that the present galaxy spins may be used as a
probe of primordial tidal shear and mass density fields. The intrinsic
alignments of galaxy spins dominate over weak gravitational lensing for shallow
surveys such like SDSS, while it should be negligible for deeper surveys at z ~
1.",0111186v2
2006-11-16,Phase transitions of barotropic flow coupled to a massive rotating sphere - derivation of a fixed point equation by the Bragg method,"The kinetic energy of barotropic flow coupled to an infnitely massive
rotating sphere by an unresolved complex torque mechanism is approximated by a
discrete spin-lattice model of fluid vorticity on a rotating sphere, analogous
to a one-step renormalized Ising model on a sphere with global interactions.
The constrained energy functional is a function of spin-spin coupling and spin
coupling with the rotation of the sphere. A mean field approximation similar to
the Curie-Weiss theory, modeled after that used by Bragg and Williams to treat
a two dimensional Ising model of ferromagnetism, is used to find the barotropic
vorticity states at thermal equilibrium for given temperature and rotational
frequency of the sphere. A fixed point equation for the most probable
barotropic flow state is one of the main results.",0611430v2
2007-08-17,Current-Induced Motion of Narrow Domain Walls and Dissipation in Ferromagnetic Metals,"Spin transport equations in a non-homogeneous ferromagnet are derived in the
limit where the sd exchange coupling between the electrons in the conduction
band and those in the d band is dominant. It is shown that spin diffusion in
ferromagnets assumes a tensor form. The diagonal terms are renormalized with
respect to that in normal metals and enhances the dissipation in the magnetic
system while the off-diagonal terms renormalize the precessional frequency of
the conduction electrons and enhances the non-adiabatic spin torque. To
demonstrate the new physics in our theory, we show that self-consistent
solutions of the spin diffusion equations and the Landau-Lifshitz equations in
the presence of a current lead to a an increase in the terminal velocity of a
domain wall which becomes strongly dependent on its width. We also provide a
simplified equation that predicts damping due to the conduction electrons.",0708.2412v1
2008-03-26,Ordered magnetic phases of the frustrated spin-dimer compound Ba3Mn2O8,"Ba3Mn2O8 is a spin-dimer compound based on pairs of S=1, 3d^2, Mn^{5+} ions
arranged on a triangular lattice. Antiferromagnetic intradimer exchange leads
to a singlet ground state in zero-field. Here we present the first results of
thermodynamic measurements for single crystals probing the high-field ordered
states of this material associated with closing the spin gap to the excited
triplet states. Specific heat, magnetocaloric effect, and torque magnetometry
measurements were performed in magnetic fields up to 32 T and temperatures down
to 20 mK. For fields above H_{c1} ~ 8.7 T, these measurements reveal a single
magnetic phase for H parallel to c, but two distinct phases (approximately
symmetric about the center of the phase diagram) for H perpendicular to c.
Analysis of the simplest possible spin Hamiltonian describing this system
yields candidates for these ordered states corresponding to a simple spiral
structure for H parallel to c, and to two distinct modulated phases for H
perpendicular to c. Both single-ion anisotropy and geometric frustration play
crucial roles in defining the phase diagram.",0803.3830v1
2008-11-19,Angular momentum and clustering properties of early dark matter halos,"In this paper we study the angular momentum properties of simulated dark
matter halos at high redshift that likely host the first stars in the Universe.
Calculating the spin distributions of these $10^6 - 10^7 \Msun$ halos in
redshift slices from $z = 15 - 6$, we find that they are well fit by a
log-normal distribution as is found for lower redshift and more massive halos
in earlier work. We find that both the mean value of the spin and dispersion
are largely unchanged with redshift for all halos. Our key result is that
subsamples of low and high spin $10^6 \Msun$ and $10^7 \Msun$ halos show
difference in clustering strength. In both mass bins, higher spin halos are
more strongly clustered in concordance with a tidal torquing picture for the
growth of angular momentum in dark matter halos in the CDM paradigm.",0811.3214v1
2009-02-12,A decade of timing an accretion-powered millisecond pulsar: The continuing spin down and orbital evolution of SAX J1808.4-3658,"The Rossi X-ray Timing Explorer has observed five outbursts from the
transient 2.5 ms accretion-powered pulsar SAX J1808.4-3658 during 1998-2008. We
present a pulse timing study of the most recent outburst and compare it with
the previous timing solutions. The spin frequency of the source continues to
decrease at a rate of (-5.5+/-1.2)x10^-18 Hz/s, which is consistent with the
previously determined spin derivative. The spin-down occurs mostly during
quiescence, and it is most likely due to the magnetic dipole torque from a B =
1.5x10^8 G dipolar field at the neutron star surface. We also find that the 2
hr binary orbital period is increasing at a rate of (3.80+/-0.06)x10^-12 s/s,
also consistent with previous measurements. It remains uncertain whether this
orbital change reflects secular evolution or short-term variability.",0902.2112v2
2009-06-15,Ultrafast switching of a nanomagnet by a combined out-of-plane and in-plane polarized spin-current pulse,"We report on spin valve devices that incorporate both an out-of-plane
polarizer (OPP) to quickly excite spin torque (ST) switching and an in-plane
polarizer/analyzer (IPP). For pulses < 200 ps we observe reliable precessional
switching due largely to ST from the OPP. Compared to a conventional spin
valve, for a given current in the short pulse regime the addition of the OPP
can decrease the pulse width necessary for switching by a factor of 10 or more.
The influence of the IPP is most obvious at longer, smaller pulses, but also
has beneficial ST consequences for short pulse switching.",0906.2585v1
2009-08-18,Clues on the origin of galactic angular momentum from looking at galaxy pairs,"We search for correlations between the spin in pairs of spiral galaxies, to
study if the angular momentum gain for each galaxy was the result of tidal
torques imprint by the same tidal field. To perform our study we made use of a
sample of galaxy pairs identified using the Sloan Digital Sky Survey. We find a
weak, but statistically significant correlation between the spin magnitude of
neighbouring galaxies, but no clear alignment between their orientation. We
show that events such as interactions with close neighbours play an important
role in the value of the spin for the final configuration, as we find these
interactions tend to reduce the value of the $\lambda$ spin parameter of
late-type galaxies considerably, with dependence on the morphology of the
neighbour. This implies that the original tidal field for each pair could have
been similar, but the redistribution of angular momentum at later stages of
evolution is important.",0908.2486v2
2009-12-30,Spin torque and critical currents for magnetic vortex nano-oscillator in nanopillars,"We calculated the main dynamic parameters of the spin polarized current
induced magnetic vortex oscillations in nanopillars, such as the range of
current density, where a vortex steady oscillations exist, the oscillation
frequency and orbit radius. We accounted for both the non-linear vortex
frequency and non-linear vortex damping. To describe the vortex excitations by
the spin polarized current we used a generalized Thiele approach to motion of
the vortex core as a collective coordinate. All the calculation results are
represented via the free layer sizes, saturation magnetization, Gilbert damping
and the degree of the spin polarization of the fixed layer. Predictions of the
developed model can be checked experimentally.",0912.5521v1
2011-12-21,Orbital Decay and Evidence of Disk Formation in the X-ray Binary Pulsar OAO 1657-415,"OAO 1657-415 is an eclipsing X-ray binary wind-fed pulsar that has exhibited
smooth spin-up/spin-down episodes and has undergone several torque reversals
throughout its long history of observation. We present a frequency history
spanning nearly 19 years of observations from the Burst and Transient Source
Experiment (CGRO/BATSE) and from the Gamma-Ray Burst Monitor (Fermi/GBM). The
analysis suggests two modes of accretion: one resulting in steady spin-up
during which we believe a stable accretion disk is present and one that results
in what appears to be a random walk in spin frequency where an unstable
accretion disk forms alternating in direction (""flip flop""). Orbital elements
of the pulsar system are determined at several intervals throughout this
history. With these ephemerides, statistically significant orbital decay
($\dot{P}/P =(-3.40 \pm0.15)\times10^{-6} \mathrm{yr^{-1}}$) is established
suggesting a transition between wind-fed and disk-mediated accretion.",1112.5190v4
2012-02-15,Current-induced motion of a transverse magnetic domain wall in the presence of spin Hall effect,"We theoretically study the current-induced dynamics of a transverse magnetic
domain wall in bi-layer nanowires consisting of a ferromagnet on top of a
nonmagnet having strong spin-orbit coupling. Domain wall dynamics is
characterized by two threshold current densities, $J_{th}^{WB}$ and
$J_{th}^{REV}$, where $J_{th}^{WB}$ is a threshold for the chirality switching
of the domain wall and $J_{th}^{REV}$ is another threshold for the reversed
domain wall motion caused by spin Hall effect. Domain walls with a certain
chirality may move opposite to the electron-flow direction with high speed in
the current range $J_{th}^{REV} < J < J_{th}^{WB}$ for the system designed to
satisfy the conditions $J_{th}^{WB} > J_{th}^{REV}$ and \alpha > \beta, where
\alpha is the Gilbert damping constant and \beta is the nonadiabaticity of spin
torque. Micromagnetic simulations confirm the validity of analytical results.",1202.3450v1
2012-06-30,Evidence for spin alignment of spiral and elliptical/S0 galaxies in filaments,"Galaxies are not distributed randomly in the cosmic web but are instead
arranged in filaments and sheets surrounding cosmic voids. Observationally
there is still no convincing evidence of a link between the properties of
galaxies and their host structures. However, by the tidal torque theory (our
understanding of the origin of galaxy angular momentum), such a link should
exist. Using the presently largest spectroscopic galaxy redshift survey (SDSS)
we study the connection between the spin axes of galaxies and the orientation
of their host filaments.
  We use a three dimensional field of orientations to describe cosmic
filaments. To restore the inclination angles of galaxies, we use a 3D
photometric model of galaxies that gives these angles more accurately than
traditional 2D models.
  We found evidence that the spin axes of bright spiral galaxies have a weak
tendency to be aligned parallel to filaments. For elliptical/S0 galaxies, we
have a statistically significant result that their spin axes are aligned
preferentially perpendicular to the host filaments; we show that this signal
practically does not depend on the accuracy of the estimated inclination angles
for elliptical/S0 galaxies.",1207.0068v2
2012-07-05,Retrograde wind accretion -- an alternative mechanism for long spin-period of SFXTs,"A new class of high-mass X-ray binaries (HMXBs) --- supergiant fast X-ray
transients (SFXTs) --- are discovered by INTEGRAL, which are associated with OB
supergiants and present long spin periods. Observational evidence indicates
that some accreting neutron stars in HMXBs display accretion reversals. It has
been suggested that the inverted torque can lead to a very slow rotator.
According to three characteristic radii in wind-fed accretion, we developed a
retrograde accretion scenario and divided the accretion phase into three
regimes, to interpret the formation of the long spin period of SFXTs. The
accretion regime in some SFXT systems can be determined by their spin and
orbital periods.",1207.1180v2
2013-02-25,Anisotropic Monopole Heat Transport in the Spin-Ice Compound Dy$_2$Ti$_2$O$_7$,"We report a study of the thermal conductivity $\kappa$ of the spin-ice
material Dy$_2$Ti$_2$O$_7$. From the anisotropic magnetic-field dependence of
\kappa$ and by additional measurements on the phononic reference compounds
Y$_2$Ti$_2$O$_7$ and DyYTi$_2$O$_7$, we are able to separate the phononic and
the magnetic contributions to the total heat transport, i.e. $\kappa_{ph}$ and
$\kappa_{mag}$, respectively, which both depend on the magnetic field. The
field dependent $\kappa_{ph}$ arises from lattice distortions due to
magnetic-field induced torques on the non-collinear magnetic moments of the Dy
ions. For $\kappa_{mag}$, we observe a highly anisotropic magnetic-field
dependence, which correlates with the corresponding magnetization data
reflecting the different magnetic-field induced spin-ice ground states. The
magnitude of $\kappa_{mag}$ increases with the degree of the ground-state
degeneracy. This anisotropic field dependence as well as various hysteresis
effects suggest that $\kappa_{mag}$ is essentially determined by the mobility
of the magnetic monopole excitations in spin ice.",1302.6114v1
2013-03-28,Spin wave mode coexistence on the nano-scale: A consequence of the Oersted field induced asymmetric energy landscape,"It has been argued that if multiple spin wave modes are competing for the
same centrally located energy source, as in a nanocontact spin torque
oscillator, that only one mode should survive in the steady state. Here, the
experimental conditions necessary for mode coexistence are explored. Mode
coexistence is facilitated by the local field asymmetries induced by the
spatially inhomogeneous Oersted field, which leads to a physical separation of
the modes, and is further promoted by spin wave localization at reduced applied
field angles. Finally, both simulation and experiment reveal a low frequency
signal consistent with the intermodulation of two coexistent modes.",1303.7148v1
2014-05-25,Spin Hall phenomenology of magnetic dynamics,"We study the role of spin-orbit interactions in the coupled magnetoelectric
dynamics of a ferromagnetic film coated with an electrical conductor. While the
main thrust of this work is phenomenological, several popular simple models are
considered microscopically in some detail, including Rashba and Dirac
two-dimensional electron gases coupled to a magnetic insulator, as well as a
diffusive spin Hall system. We focus on the long-wavelength magnetic dynamics
that experiences current-induced torques and produces fictitious electromotive
forces. Our phenomenology provides a suitable framework for analyzing
experiments on current-induced magnetic dynamics and reciprocal charge pumping,
including the effects of magnetoresistance and Gilbert-damping anisotropies,
without a need to resort to any microscopic considerations or modeling.
Finally, some remarks are made regarding the interplay of spin-orbit
interactions and magnetic textures.",1405.6354v2
2015-01-22,Anatomy of Dzyaloshinskii-Moriya Interaction at Co/Pt Interfaces,"The Dzyaloshinskii-Moriya Interaction (DMI) between spins is induced by
spin-orbit coupling in magnetic materials lacking inversion symmetry. DMI is
recognized to play a crucial role at the interface between ferromagnetic (FM)
and heavy nonmagnetic (NM) metals to create topological textures called
magnetic skyrmions which are very attractive for ultra-dense information
storage and spintronic devices. DMI also plays an essential role for fast
domain wall (DW) dynamics driven by spin-orbit torques. Here, we present first
principles calculations which clarify the main features and microscopic
mechanisms of DMI in Co/Pt bilayers. DMI is found to be predominantly located
at the interfacial Co layer, originating from spin-orbit energy provided by the
adjacent NM layer. Furthermore, no direct correlation is found between DMI and
proximity induced magnetism in Pt. These results clarify underlying mechanisms
of DMI at FM/NM bilayers and should help optimizing material combinations for
skyrmion- and DW-based storage and memory devices.",1501.05511v1
2015-12-27,Electromagnetic spin down of a transient accreting millisecond pulsar during quiescence,"The measured spin-down rates in quiescence of the transient accreting
millisecond pulsars IGR J00291+5934, XTE J1751-305, SAX J1808.4-3658, and Swift
J1756.9-2508 have been used to estimate the magnetic moments of these objects
assuming standard magnetic dipole braking. It is shown that this approach leads
to an overestimate, if the amount of residual accretion is enough to distort
the magnetosphere away from a force-free configuration, through magnetospheric
mass loading or crushing, so that the lever arm of the braking torque migrates
inside the light cylinder. We derive an alternative spin-down formula and
calculate the residual accretion rates where the formula is applicable. As a
demonstration, we apply the alternative spin-down formula to produce updated
magnetic moment estimates for the four objects above. We note that, based on
current uncertain observations of quiescent accretion rates, magnetospheric
mass loading and crushing are neither firmly indicated nor ruled out in these
four objects. Because quiescent accretion rates are not measured directly (only
upper limits are placed), it is impossible to be confident without more data
whether the thresholds for magnetospheric mass loading or crushing are reached
or not.",1512.08196v1
2017-07-11,Spin switching via quantum dot spin valves,"We develop a theory for spin transport and magnetization dynamics in a
quantum-dot spin valve, i.e., two magnetic reservoirs coupled to a quantum dot.
Our theory is able to take into account effects of strong correlations. We
demonstrate that, as a result of these strong correlations, the dot gate
voltage enables control over the current-induced torques on the magnets, and,
in particular, enables voltage-controlled magnetic switching. The electrical
resistance of the structure can be used to read out the magnetic state. Our
model may be realized by a number of experimental systems, including magnetic
scanning-tunneling microscope tips and artificial quantum dot systems.",1707.03373v4
2017-08-21,Micromagnetic simulations of magnetoelastic spin wave excitation in scaled magnetic waveguides,"We study the excitation of spin waves in scaled magnetic waveguides using the
magnetoelastic effect. In uniformly magnetized systems, normal strains parallel
or perpendicular to the magnetization direction do not lead to spin wave
excitation since the magnetoelastic torque is zero. Using micromagnetic
simulations, we show that the nonuniformity of the magnetization in submicron
waveguides due to the effect of the demagnetizing field leads to the excitation
of spin waves for oscillating normal strains both parallel and perpendicular to
the magnetization. The excitation by biaxial normal in-plane strain was found
to be much more efficient than by uniaxial normal out-of-plane strain. For
narrow waveguides with widths of 200\,nm, the excitation efficiency of biaxial
normal in-plane strain was comparable to that of shear strain.",1708.06428v1
2017-12-04,Accurate analysis for harmonic Hall voltage measurement for spin-orbit torques,"An accurate method is developed to extract the spin-orbit effective fields
through analysis of the results of harmonic Hall voltage measurements by
deriving detailed analytical equations, in which both the z-component of the
applied magnetic field and the second-order perpendicular magnetic anisotropy
are taken into account. The method is tested by analyzing the results of a
macrospin simulation. The spin-orbit effective fields extracted from the
analysis are found to be in excellent agreement with the input spin-orbit
effective fields used for the macrospin simulation over the entire range of the
polar magnetization angle and a wide range (0-2) of the ratio of the planar to
the anomalous Hall voltage considered in this study. The accuracy of the
proposed method is demonstrated more clearly via a systematic study involving a
comparison of its results with those of the conventional analytical method.",1712.00902v1
2018-03-28,Split Fermi Surfaces of the Spin-Orbit-Coupled Metal Cd2Re2O7 Probed by de Haas-van Alphen Effect,"The superconducting pyrochlore oxide Cd2Re2O7 shows a structural transition
with inversion symmetry breaking (ISB) at Ts1 = 200 K. A recent theory [L. Fu,
Phys. Rev. Lett. 115, 026401 (2015)] suggests that the origin is an electronic
instability that leads to a multipolar order in the spin-orbit-coupled metal.
To observe the Fermi surface of the low-temperature phase of Cd2Re2O7, we
perform de Haas-van Alphen effect measurements by means of magnetic torque. In
reference to a calculated band structure, the spin-split Fermi surfaces with
large cyclotron masses of 5-9m0 are revealed. The splitting is suggested to be
due to an antisymmetric spin-orbit coupling induced by ISB, the strength of
which is estimated to be approximately 67 K, which is rather smaller than those
of typical non-centrosymmetric metals.",1803.10472v1
2018-06-05,A classical approach to the electron g-factor,"According to a prevailing opinion, the electron g-factor ge = 2 is
exclusively a quantum feature. Here we demonstrate it could be explained
classically only in relativistic terms. The electron is treated as an extended,
continuous, but rigid Gaussian body (RGB) spinning at finite angular frequency.
In contrast to expectations, the mechanical energy and spin angular momentum of
the particle are not diverging but standard values are reproduced. The g-factor
value ge = 2 immediately follows from the ratio of non-relativistic and
relativistic angular momenta which can be both attributed to a spinning
electron of known rest mass. A detailed analysis of the inertia tensor and
limit, torque-free precession reveals a multiplication factor of -2 between the
external and internal precession angular frequency which might resemble the
spin-1/2 appearance of the particle. Furthermore, the theory of Li\'enard and
Wiechert is used to derive a static electromagnetic field. A continuous form of
Gaussian charge density ensures an absence of infinities in electromagnetic
energy and angular momentum. Introducing the associated electromagnetic angular
momentum as a small correction to the mechanical spin angular momentum, we
obtain a modified g-factor ge* = 2.0021 which is close to the measured value ge
= 2.0023.",1806.02274v1
2018-11-15,Boltzmann transport from density matrix theory: interband and intraband coherences,"To account for the anomalous/spin Hall conductivities and spin-orbit torque
in the zeroth order of electron scattering time in strongly spin-orbit coupled
systems, the Boltzmann transport theory in the case of weak disorder-potentials
has been augmented by adding some interband coherence effects by hand. In this
work these interband coherence terms are derived systematically from analyzing
the equation of motion of the single-particle density matrix in the Bloch
representation. Interband elements of the out-of-equilibrium density matrix are
related to only one part of interband-coherence responses. Disorder-induced
off-diagonal elements of the equilibrium density matrix are shown to be vital
in producing the coordinate-shift anomalous driving term in the modified
Boltzmann equation. Moreover, intraband coherence is inherent in the Boltzmann
equation, whose contribution to anomalous/spin Hall conductivities is
parametrically the same as the interband coherence.",1811.06204v1
2018-07-06,Side-Jump Induced Spin-Orbit Interaction of Chiral Fluids from Kinetic Theory,"We apply the Wigner-function approach and chiral kinetic theory to
investigate the angular momentum and polarization of chiral fluids composed of
Weyl fermions with background electric/magnetic fields and vorticity. It is
found that the quantum corrections in Wigner functions give rise to nonzero
anti-symmetric components in the canonical energy-momentum tensors, which are
responsible for the spin-orbit interaction. In global equilibrium, conservation
of the canonical angular momentum reveals the cancellation between the orbital
component stemming from side jumps with nonzero vorticity and the spin
component in the presence of an axial chemical potential. We further analyze
the conservation laws near local equilibrium. It turns out that the canonical
angular momentum is no longer conserved even in the absence of background
fields due to the presence of a local torque coming from the spin-orbit
interaction involving temperature/chemical-potential gradients, which is
implicitly led by collisions.",1807.02395v2
2018-08-23,First harmonic measurements of the spin Seebeck effect,"We present measurements of the spin Seebeck effect (SSE) by a technique that
combines alternating currents (AC) and direct currents (DC). The method is
applied to a ferrimagnetic insulator/heavy metal bilayer,
Y$_3$Fe$_5$O$_{12}$(YIG)/Pt. Typically, SSE measurements use an AC current to
produce an alternating temperature gradient and measure the voltage generated
by the inverse spin-Hall effect in the heavy metal at twice the AC frequency.
Here we show that when Joule heating is associated with AC and DC bias
currents, the SSE response occurs at the frequency of the AC current drive and
can be larger than the second harmonic SSE response. We compare the first and
second harmonic responses and show that they are consistent with the SSE. The
field dependence of the voltage response is used to characterize the
damping-like and field-like torques. This method can be used to explore
nonlinear thermoelectric effects and spin dynamics induced by temperature
gradients.",1808.07813v1
2016-12-09,Symmetry Reduction in the Quantum Kagome Antiferromagnet Herbertsmithite,"Employing complementary torque magnetometry and electron spin resonance on
single crystals of herbertsmithite, the closest realization to date of a
quantum kagome antiferromagnet featuring a spin-liquid ground state, we provide
novel insight into different contributions to its magnetism. At low
temperatures, two distinct types of defects with different magnetic couplings
to the kagome spins are found. Surprisingly, their magnetic response
contradicts the three-fold symmetry of the ideal kagome lattice, suggesting the
presence of a global structural distortion that may be related to the
establishment of the spin-liquid ground state.",1612.02923v2
2017-02-10,Gyrotropic elastic response of skyrmion crystals to current-induced tensions,"We theoretically study the dynamics of skyrmion crystals in
electrically-insulating chiral magnets subjected to current-induced spin
torques by adjacent metallic layers. We develop an elasticity theory that
accounts for the gyrotropic force engendered by the non-trivial topology of the
spin texture, tensions at the boundaries due to the exchange of linear and spin
angular momentum with the metallic reservoirs, and dissipation in the bulk of
the film. A steady translation of the skyrmion crystal is triggered by the
current-induced tensions and subsequently sustained by dissipative forces,
generating an electromotive force on itinerant spins in the metals. This
phenomenon should be revealed as a negative drag in an open two-terminal
geometry, or equivalently, as a positive magnetoresistance when the terminals
are connected in parallel. We propose non-local transport measurements with
these salient features as a tool to characterize the phase diagram of
insulating chiral magnets.",1702.03347v2
2017-06-21,Uniform magnetization dynamics of a submicron ferromagnetic coin driven by the spin-orbit coupled spin torque,"A simple model of magnetization dynamics in a ferromagnet/doped semiconductor
hybrid structure with Rashba spin-orbit interaction (SOI) driven by an applied
pulse of the electric field is proposed. The electric current excited by the
applied field is spin-polarized due to the SOI and therefore it induces the
magnetization rotation in the ferromagnetic layer via s-d exchange coupling.
Magnetization dynamics dependence on the electric pulse shape and magnitude is
analyzed for realistic values of parameters. We show that it is similar to the
dynamics of a damped nonlinear oscillator with the time-dependent frequency
proportional to the square root of the applied electric field. The
magnetization switching properties of an elliptic magnetic element are examined
as a function of the applied field magnitude and direction.",1706.06909v1
2017-10-28,High frequency dynamics modulated by collective magnetization reversal in artificial spin ice,"Spin-torque ferromagnetic resonance (ST-FMR) arises in heavy
metal/ferromagnet heterostructures when an alternating charge current is passed
through the bilayer stack. The methodology to detect the resonance is based on
the anisotropic magnetoresistance, which is the change in the electrical
resistance due to different orientations of the magnetization. In connected
networks of ferromagnetic nanowires, known as artificial spin ice, the
magnetoresistance is rather complex owing to the underlying collective behavior
of the geometrically frustrated magnetic domain structure. Here, we demonstrate
ST-FMR investigations in a square artificial spin-ice system and correlate our
observations to magnetotransport measurements. The experimental findings are
described using a simulation approach that highlights the importance of the
correlated dynamics response of the magnetic system. Our results open the
possibility of designing reconfigurable microwave oscillators and
magnetoresistive devices based on connected networks of nanomagnets.",1710.10534v1
2018-04-22,Magnetic Droplet Soliton Nucleation in Oblique Fields,"We study the auto-oscillating magnetodynamics in orthogonal spin torque
nano-oscillators (STNOs) as a function of the out-of-plane (OOP) magnetic field
angle. In perpendicular fields and at OOP field angles down to approximately 50
degrees we observe the nucleation of a droplet. However, for field angles below
50 degrees, experiments indicate that the droplet gives way to propagating spin
waves, in agreement with our micromagnetic simulations. Theoretical
calculations show that the physical mechanism behind these observations is the
sign changing of spin-wave nonlinearity (SWN) by angle. In addition, we show
that the presence of a strong perpendicular magnetic anisotropy (PMA) free
layer in the system reverses the angular dependence of the SWN and dynamics in
STNOs with respect to the known behavior determined for the in-plane magnetic
anisotropy free layer. Our results are of fundamental interest in understanding
the rich dynamics of nanoscale solitons and spin-wave dynamics in STNOs.",1804.08047v2
2020-03-31,Discovery of a retrogradely rotating neutron star in the X-ray pulsar GX 301$-$2,"We report on the analysis of the spin evolution of a slow X-ray pulsar GX
301$-$2 along the orbit using long-term monitoring by Fermi/GBM. Based on the
observationally confirmed accretion scenario and an analytical model for the
accretion of angular momentum we demonstrate that in this system, the neutron
star spins retrogradely, that is, in a direction opposite to the orbital
motion. This first-of-a-kind discovery of such a system proves the principal
possibility of retrograde rotation in accreting systems with suitable accretion
torque, and might have profound consequences for our understanding of the spin
evolution of X-ray pulsars, estimates of their initial spin periods, and the
ultimate result of their evolution.",2003.14347v1
2019-10-08,Orbital Nernst Effect of Magnons,"In the past, magnons have been shown to mediate thermal transport of spin in
various systems. Here, we reveal that the fundamental coupling of scalar spin
chirality, inherent to magnons, to the electronic degrees of freedom in the
system can result in the generation of sizeable orbital magnetization and
thermal transport of orbital angular momentum. We demonstrate the emergence of
the latter phenomenon of orbital Nernst effect by referring to the spin-wave
Hamiltonian of kagome ferromagnets, predicting that in a wide range of systems
the transverse current of orbital angular momentum carried by magnons in
response to an applied temperature gradient can overshadow the accompanying
spin current. We suggest that the discovered effect fundamentally correlates
with the topological Hall effect of fluctuating magnets, and it can be utilized
in magnonic devices for generating magnonic orbital torques.",1910.03317v2
2019-12-11,Chirality-induced linear response properties in non-coplanar Mn$_3$Ge,"Taking the non-collinear antiferromagnetic hexagonal Heusler compound
Mn$_3$Ge as a reference system, the contributions to linear response phenomena
arising solely from the chiral coplanar and non-coplanar spin configurations
are investigated. Orbital moments, X-ray absorption, anomalous and spin Hall
effects, as well as corresponding spin-orbit torques and Edelstein
polarizations are studied depending on a continuous variation of the polar
angle relative to the Kagome planes of corner-sharing triangles between the
non-collinear antiferromagnetic and the ferromagnetic limits. By scaling the
speed of light from the relativistic Dirac case to the non-relativistic limit
the chirality-induced or topological contributions can be identified by
suppressing the spin-orbit coupling.",1912.05211v1
2021-03-12,A New Measurement of the Spin and Orbital Parameters of the High Mass X-ray Binary Centaurus X-3 using AstroSat,"We present the timing results of out-of-eclipse observations of Centaurus X-3
spanning half a binary orbit, performed on 12-13 December, 2016 with the Large
Area X-ray Proportional Counter (LAXPC) on-board AstroSat. The pulse profile
was confirmed to exhibit a prominent pulse peak with a secondary inter-pulse.
The systemic spin period of the pulsar was found to be $4.80188 \pm 0.000085$ s
in agreement with its spin up trend. The spin up timescale seems to have
increased to $7709 \pm 58$ yr that points to negative torque effects in the
inner accretion disk. We also report the derived values of projected semi-major
axis and orbital velocity of the neutron star.",2103.07204v1
2021-09-02,Enhanced magnon spin current using the bosonic Klein paradox,"Efficient manipulation of magnons for information processing is a central
topic in spintronics and magnonics. An outstanding challenge for long-distance
spin transport with minimal dissipation is to overcome the relaxation of
magnons and to amplify the spin current they carry. Here, we propose to amplify
magnon currents based on the realization of the bosonic Klein paradox in
magnetic nanostructures. This paradox involves the magnon's antiparticle, the
antimagnon, of which the existence is usually precluded by magnetic
instabilities as it is an excitation at negative energy. We show that, by
appropriately tuning the effective dissipation through spin-orbit torques, both
magnons and antimagnons are dynamically stabilized. As a result, we find that
the reflection coefficient of incident magnons at an interface between two
coupled magnets can become larger than one, thereby amplifying the reflected
magnon current. Our findings can lead to magnon amplifier devices for
spintronic applications. Furthermore, our findings yield a solid-state platform
to study the relativistic behavior of bosonic particles, which is an
outstanding challenge with fundamental particles.",2109.00865v3
2022-01-27,Simultaneous measurement of the exchange parameter and saturation magnetization using propagating spin waves,"The exchange interaction in ferromagnetic ultra-thin films is a critical
parameter in magnetization-based storage and logic devices, yet the accurate
measurement of it remains a challenge. While a variety of approaches are
currently used to determine the exchange parameter, each has its limitations,
and good agreement among them has not been achieved. To date, neutron
scattering, magnetometry, Brillouin light scattering, spin-torque ferromagnetic
resonance spectroscopy, and Kerr microscopy have all been used to determine the
exchange parameter. Here we present a novel method that exploits the wavevector
selectivity of Brillouin light scattering to measure the spin wave dispersion
in both the backward volume and Damon-Eshbach orientations. The exchange,
saturation magnetization, and magnetic thickness are then determined by a
simultaneous fit of both dispersion branches with general spin wave theory
without any prior knowledge of the thickness of a magnetic ""dead layer"". In
this work, we demonstrate the strength of this technique for ultrathin metallic
films, typical of those commonly used in industrial applications for magnetic
random-access memory.",2201.11270v1
2022-07-21,Unidirectional Spin Hall Magnetoresistance in Antiferromagnetic Heterostructures,"Unidirectional spin Hall magnetoresistance (USMR) has been widely reported in
the heavy metal / ferromagnet (HM/FM) bilayer systems. We observe the USMR in
the Pt/{\alpha}-Fe2O3 bilayers where the {\alpha}-Fe2O3 is an antiferromagnetic
(AFM) insulator. Systematic field and temperature dependent measurements
confirm the magnonic origin of the USMR. The appearance of AFM-USMR is driven
by the imbalance of creation and annihilation of AFM magnons by spin orbit
torque due to thermal random field. However, unlike its ferromagnetic
counterpart, theoretical modeling reveals that the USMR in Pt/{\alpha}-Fe2O3 is
determined by the antiferromagtic magnon number, and with a non-monotonic field
dependence. Our findings extend the generality of the USMR which pave the ways
for the highly sensitive detection of AF spin state.",2207.10346v1
2023-06-26,Study of recently discovered Be/X-ray pulsar MAXI J0655-013 using NuSTAR,"We study the recently discovered Be/X-ray pulsar MAXI J0655--013 using the
2022 \emph{NuSTAR} observations. The paper is the first detailed study of the
timing and spectral properties of the source. The pulse profiles of the pulsar
vary with energy. The pulsed fraction is found to increase monotonically with
energy. In between the two \emph{NuSTAR} observations, a large spin-up rate of
$\sim$ -1.23 s d$^{-1}$ is observed, which can be due to large spin-up torque
acting on the pulsar during an outburst. Such a large spin-up rate is observed
for the first time in an X-ray pulsar during an outburst. The variation of the
spin period with time can be employed to obtain the orbital parameters of the
binary system, and we found the orbital period to be $\sim$ 27.9 d. The second
\emph{NuSTAR} observation is done in a low luminosity state ($L_{X}
\sim$3.9$\times$10$^{34}$ \unilum). We have detected the pulsation of the
pulsar in such a low luminosity state. In such a low luminosity state, the
pulsar MAXI J0655--013 might be accreting from the cold disk.",2306.14970v1
2023-07-20,Spin vectors in the Koronis family: V. Resolving the ambiguous rotation period of (3032) Evans,"A sidereal rotation counting approach is demonstrated by resolving an
ambiguity in the synodic rotation period of Koronis family member (3032) Evans,
whose rotation lightcurves' features did not easily distinguish between doubly-
and quadruply-periodic. It confirms that Evans's spin rate does not exceed the
rubble-pile spin barrier and thus presents no inconsistency with being a ~14-km
reaccumulated object. The full spin vector solution for Evans is comparable to
those for the known prograde low-obliquity comparably-fast rotators in the
Koronis family, consistent with having been spun up by YORP thermal radiation
torques.",2307.10526v1
2024-04-01,"Harnessing Interlayer Magnetic Coupling for Efficient, Field-Free Current-Induced Magnetization Switching in a Magnetic Insulator","Owing to the unique features of low Gilbert damping, long spin-diffusion
lengths and zero Ohmic losses, magnetic insulators are promising candidate
materials for next-generation spintronic applications. However, due to the
localized magnetic moments and the complex metal-oxide interface between
magnetic insulators and heavy metals, spin-functional Dzyaloshinskii-Moriya
interactions or spin Hall and Edelstein effects are weak, which diminishes the
performance of these typical building blocks for spintronic devices. Here, we
exploit the exchange coupling between metallic and insulating magnets for
efficient electrical manipulation of heavy metal/magnetic insulator
heterostructures. By inserting a thin Co layer, we enhance the spin-orbit
torque efficiency by more than 20 times, which significantly reduces the
switching current density. Moreover, we demonstrate field-free current-induced
magnetization switching caused by a symmetry-breaking non-collinear magnetic
texture. Our work launches magnetic insulators as an alternative platform for
low-power spintronic devices.",2404.00845v1
2005-01-03,Spin Chains as Perfect Quantum State Mirrors,"Quantum information transfer is an important part of quantum information
processing. Several proposals for quantum information transfer along linear
arrays of nearest-neighbor coupled qubits or spins were made recently. Perfect
transfer was shown to exist in two models with specifically designed strongly
inhomogeneous couplings. We show that perfect transfer occurs in an entire
class of chains, including systems whose nearest-neighbor couplings vary only
weakly along the chain. The key to these observations is the Jordan-Wigner
mapping of spins to noninteracting lattice fermions which display perfectly
periodic dynamics if the single-particle energy spectrum is appropriate. After
a half-period of that dynamics any state is transformed into its mirror image
with respect to the center of the chain. The absence of fermion interactions
preserves these features at arbitrary temperature and allows for the transfer
of nontrivially entangled states of several spins or qubits.",0501007v3
2015-01-09,Optimized dynamical control of state transfer through noisy spin chains,"We propose a method of optimally controlling the tradeoff of speed and
fidelity of state transfer through a noisy quantum channel (spin-chain). This
process is treated as qubit state-transfer through a fermionic bath. We show
that dynamical modulation of the boundary-qubits levels can ensure state
transfer with the best tradeoff of speed and fidelity. This is achievable by
dynamically optimizing the transmission spectrum of the channel. The resulting
optimal control is robust against both static and fluctuating noise in the
channel's spin-spin couplings. It may also facilitate transfer in the presence
of diagonal disorder (on site energy noise) in the channel.",1501.02133v1
2019-03-25,State transfer in an inhomogeneous spin chain,"We present an analytical study of state transfer in a spin chain in the
presence of an inhomogeneous set of exchange coefficients. We initially
consider the homogeneous case and describe a method to obtain the energy
spectrum of the system. Under certain conditions, the state transfer time can
be predicted by taking into account the energy gap between the two lowest
energy eigenstates. We then generalize our approach to the inhomogeneous case
and show that including a barrier in the chain can lead to a reduction of the
state transfer time. We additionally extend our analysis to the case of
multiple barriers. These advances may contribute to the understanding of spin
transfer dynamics in long chains where connections between neighboring spins
can be manipulated.",1903.10538v2
2003-04-08,Large frequency drifts during Type I X-ray bursts,"We study the spin-down of a neutron star atmosphere during the Type I X-ray
burst in low mass X-ray binaries. Using polar cap acceleration models, we show
that the resulting stellar ``wind'' torque on the burning shell due to the
flowing charged particles (electrons, protons and ions) from the star's polar
caps may change the shell's angular momentum during the burst. We conclude that
the net change in the angular momentum of the star's atmosphere can account for
rather large frequency drifts observed during Type I X-ray burst.",0304153v2
2006-05-01,Searching for sub-millisecond pulsars: A theoretical view,"Sub-millisecond pulsars should be triaxial (Jacobi ellipsoids), which may not
spin down to super-millisecond periods via gravitation wave radiation during
their lifetimes if they are extremely low mass bare strange quark stars. It is
addressed that the spindown of sub-millisecond pulsars would be torqued
dominantly by gravitational wave radiation (with braking index n ~ 5). The
radio luminosity of sub-millisecond pulsars could be high enough to be detected
in advanced radio telescopes. Sub-millisecond pulsars, if detected, should be
very likely quark stars with low masses and/or small equatorial ellipticities.",0605028v2
1999-09-29,The Symmetries and Origins of the Order Parameters for Pairing and Phase Coherence in Cuprates,"The symmetries and origins of the order parameters (OPs) for pairing and
long-range phase coherence in hole-doped cuprates are discussed. By analyzing
tunneling, inelastic neutron scattering and torque measurements we conclude
that the Cooper pairs in cuprates consist of spinons, and the pairing OP has an
anisotropic s-wave symmetry, whereas the OP for long-range phase coherence has
the magnetic origin due to spin fluctuations and, has the d-wave symmetry. All
conclusions are based exclusively on experimental facts.",9909430v1
2005-07-16,Interplay of Magnetic and Superconducting Proximity Effects in FSF Trilayers,"We present theoretical results on the interplay of magnetic and
superconducting orders in diffusive ferromagnet-superconductor-ferromagnet
trilayers. The induced triplet superconducting correlations throughout the
trilayer lead to an induced spin magnetization. We include self-consistency of
the order parameter in the superconducting layer at arbitrary temperatures,
arbitrary interface transparency, and any relative orientation of the exchange
fields in the two ferromagnets. We propose to use the torque on the trilayer in
an external magnetic field as a probe of the presence of triplet correlations
in the superconducting phase.",0507398v1
2005-08-30,Effects of current on vortex and transverse domain walls,"By using the spin torque model in ferromagnets, we compare the response of
vortex and transverse walls to the electrical current. For a defect-free sample
and a small applied current, the steady state wall mobility is independent of
the wall structure. In the presence of defects, the minimum current required to
overcome the wall pinning potential is much smaller for the vortex wall than
for the transverse wall. During the wall motion, the vortex wall tends to
transform to the transverse wall. We construct a phase diagram for the wall
mobility and the wall transformation driven by the current.",0508736v1
2005-10-28,Antiferromagnetic Metal Spintronics,"Spintronics in ferromagnetic metals is built on a complementary set of
phenomena in which magnetic configurations influence transport coefficients and
transport currents alter magnetic configurations. In this Letter we propose
that corresponding effects occur in circuits containing antiferromagnetic
metals. The critical current for switching can be smaller in the
antiferromagnetic case because of the absence of shape anisotropy and because
spin torques act through the entire volume of an antiferromagnet. Our findings
suggest that current-induced order parameter dynamics can be used to coarsen
the microstructure of antiferromagnetic thin films.",0510797v1
2006-05-04,Current-driven vortex domain wall dynamics by micromagnetic simulations,"Current-driven vortex wall dynamics is studied by means of a two-dimensional
analytical model and micromagnetic simulation. By constructing a trial function
for the vortex wall in the magnetic wire, we analytically solve for domain wall
velocity and deformation in the presence of the current-induced spin torque. A
critical current for the domain wall transformation from the vortex wall to the
transverse wall is calculated. A comparison between the field- and
current-driven wall dynamics is carried out. Micromagnetic simulations are
performed to verify our analytical results.",0605125v2
2006-07-25,Thermally-Assisted Current-Driven Domain Wall Motion,"Starting from the stochastic Landau-Lifschitz-Gilbert equation, we derive
Langevin equations that describe the nonzero-temperature dynamics of a rigid
domain wall. We derive an expression for the average drift velocity of the
domain wall as a function of the applied current, and find qualitative
agreement with recent magnetic semiconductor experiments. Our model implies
that at any nonzero temperature the average domain-wall velocity initially
varies linearly with current, even in the absence of non-adiabatic spin
torques.",0607663v1
2007-02-02,Current-induced magnetic vortex core switching in a Permalloy nanodisk,"We report on the switching of a magnetic vortex core in a sub-micron
Permalloy disk, induced by a short current pulse applied in the film plane.
Micromagnetic simulations including the adiabatic and non-adiabatic spin-torque
terms are used to investigate the current-driven magnetization dynamics. We
predict that a core reversal can be triggered by current bursts a tenth of a
nanosecond long. The vortex core reversal process is found to be the same as
when an external field pulse is applied. The control of a vortex core's
orientation using current pulses introduces the technologically relevant
possibility to address individual nanomagnets within dense arrays.",0702048v1
2007-09-24,Interaction and ablation of fall-back disks in isolated neutron stars,"An analysis of ablation processes is made for a fall-back disk with inner and
outer radii external to the neutron-star light cylinder. The calculated
ablation rate leads, with certain other assumptions, to a simple expression
relating the inner radius and mean mass per unit area of any long-lived
fall-back disk. Expressions for the torque components generated by interaction
with the pulsar wind are obtained. It is not impossible that these could be
responsible for small observable variations in pulse shape and spin-down rate
but they are unlikely to be the source of the periodic changes seen in several
pulsars.",0709.3730v1
2008-04-22,Effects of current on nanoscale ring-shaped magnetic tunnel junctions,"We report the observation and micromagnetic analysis of current-driven
magnetization switching in nanoscale ring-shaped magnetic tunnel junctions.
When the electric current density exceeds a critical value of the order of
$6\times 10^{6}$A/cm$^2$, the magnetization of the two magnetic rings can be
switched back and forth between parallel and antiparallel onion states.
Theoretical analysis and micromagnetic simulation show that the dominant
mechanism for the observed current-driven switching is the spin torque rather
than the current-induced circular Oersted field.",0804.3524v1
2008-10-19,Magnetic anisotropy of single 3d spins on CuN surface,"First-principles calculations of the magnetic anisotropy energy for Mn- and
Fe-atoms on CuN/Cu(001) surface are performed making use of the torque method.
The easy magnetization direction is found to be different for Mn and Fe atoms
in accord with the experiment. It is shown the magnetic anisotropy has a
single-ion character and mainly originates from the local magnetic moment of
Mn- and Fe-atoms. The uniaxial magnetic anisotropy constants are calculated in
reasonable agreement with the experiment.",0810.3389v1
2008-11-08,Quadratic Magnetoelectric Effect and Magnetic Field Induced Pyroelectric Effect in Multiferroic BaMnF4,"The experimental studies of magnetoelectric effects in pulse magnetic field
up to 250 kOe and their theoretical analysis on the basis of magnetic symmetry
consideration are carried out. It is shown that the nonvanishing components of
quadratic magnetoelectric effect tensor corresponding to the electric
polarization along b- and c-axes point out the triclinic distortion of the
crystal symmetry. Anomalous temperature dependence of magnetically induced
polarization Pa(Hb) testifies to the magnetically induced pyroelectric effect.
The torque curves measurements show the deflection of the spin orientation from
the b-axis at 9 degrees of arc.",0811.1505v1
2010-03-25,Magnetic phase diagram of the S=1/2 triangular layered compound NaNiO2: a single crystal study,"Using magnetic torque measurement on a NaNiO2 single crystal, we have
established the magnetic phase diagram of this triangular compound. It presents
5 different phases depending on the temperature (4 K - 300 K) and magnetic
field (0 - 22 T) revealing several spin reorientations coupled to different
magnetic anisotropies.",1003.4848v1
2010-06-18,Levitated Spinning Graphene,"A method is described for levitating micron-sized few layer graphene flakes
in a quadrupole ion trap. Starting from a liquid suspension containing
graphene, charged flakes are injected into the trap using the electrospray
ionization technique and are probed optically. At micro-torr pressures, torques
from circularly polarized light cause the levitated particles to rotate at
frequencies >1 MHz, which can be inferred from modulation of light scattering
off the rotating flake when an electric field resonant with the rotation rate
is applied. Possible applications of these techniques will be presented, both
to fundamental measurements of the mechanical and electronic properties of
graphene and to new approaches to graphene crystal growth, modification and
manipulation.",1006.3774v1
2010-10-27,Classical zitterbewegung in reduced plasma dynamics,"The process of dynamical reduction of the Vlasov-Maxwell equations leads to
the introduction of classical {\it zitterbewegung} effects in reduced plasma
dynamics. These effects manifest themselves in the form of an asymmetric
canonical energy-momentum tensor involving the decoupling of the reduced
kinetic momentum ${\bf p}$ from the reduced velocity ${\bf u}$ (i.e., ${\bf
u}\btimes{\bf p} \neq 0$) as well as reduced polarization and magnetization
effects. The reduced intrinsic torque generated by the antisymmetric part of
the canonical energy-momentum tensor, which is calculated from the reduced
ponderomotive potential, acts as the source for the intrinsic (spin) angular
momentum.",1010.5710v1
2010-11-11,Thin accretion discs around millisecond X-ray pulsars,"Millisecond x-ray pulsars have weak magnetic dipole moments of $\sim
10^{16}$\,T\,m$^3$ compared to ordinary X-ray pulsars with dipole moments of
$10^{20}$\,T\,m$^3$. For this reason a surrounding accretion disc can extend
closer to the neutron star, and thus reach a higher temperature, at which the
opacity is dominated by electron scattering and radiation pressure is strong.
We compute the self-similar structure of such a geometrically thin axisymmetric
accretion disc with an internal dynamo. Such models produce significantly
stronger torques on the neutron star than models without dynamos, and can
explain the strong spin variations in some millisecond X-ray pulsars.",1011.2621v1
2011-03-31,Electromagnetic propulsion and separation by chirality of nanoparticles in liquids,"We introduce a new mechanism for the propulsion and separation by chirality
of small ferromagnetic particles suspended in a liquid. Under the action of a
uniform d.c. magnetic field H and an a.c. electric field E isomers with
opposite chirality move in opposite directions. Such a mechanism could have a
significant impact on a wide range of emerging technologies. The component of
the chiral velocity that is odd in H is found to be proportional to the
intrinsic orbital and spin angular momentum of the magnetized electrons. This
effect arises because a ferromagnetic particle responds to the applied torque
as a small gyroscope.",1104.0026v1
2011-08-30,"Spin-orbit coupling effect in (Ga,Mn)As films: anisotropic exchange interactions and magnetocrystalline anisotropy","The magneto-crystalline anisotropy (MCA) of (Ga,Mn)As films has been studied
on the basis of ab-initio electronic structure theory by performing magnetic
torque calculations. An appreciable contribution to the in-plane uniaxial
anisotropy can be attributed to an extended region adjacent to the surface.
Calculations of the exchange tensor allow to ascribe a significant part to the
MCA to the exchange anisotropy, caused either by a tetragonal distortion of the
lattice or by the presence of the surface or interface.",1108.5870v1
2011-11-04,Interpreting superfluid spin up through the response of the container,"A recipe is presented for interpreting non-invasively the transport processes
at work during relaxation of a cylindrical, superfluid-filled vessel, after it
is accelerated impulsively and then allowed to respond to the viscous torque
exerted by the contained fluid. The recipe exploits a recently published
analytic solution for Ekman pumping in a two-component superfluid, which treats
the back-reaction self-consistently in arbitrary geometry for the first time.
The applicability of the recipe to He II, 3He, 3He-4He mixtures and
Bose-Einstein condensates is assessed, and the effects of turbulence discussed.",1111.1057v1
2011-11-10,Magnonic band structure of a two-dimensional magnetic superlattice,"The frequencies and linewidths of spin waves in a two-dimensional periodic
superlattice of magnetic materials are found, using the Landau-Lifshitz-Gilbert
equations. The form of the exchange field from a surface-torque-free boundary
between magnetic materials is derived, and magnetic-material combinations are
identified which produce gaps in the magnonic spectrum across the entire
superlattice Brillouin zone for hexagonal and square-symmetry superlattices.",1111.2506v1
2011-11-24,Domain wall attraction and repulsion during spin-torque-induced coherent motion,"We calculate the interaction between two magnetic domain walls during their
current-induced motion. This interaction produces a separation-dependent
resistance and also a differential velocity, causing domains in motion to
experience an effective attraction at large separations and an effective
repulsion at short separations. In an intermediate range of currents the two
domain walls will reach a natural equilibrium spacing that depends on the
magnitude of the current flowing through the material.",1111.5868v1
2012-05-30,Stirring Unmagnetized Plasma,"A new concept for spinning unmagnetized plasma is demonstrated
experimentally. Plasma is confined by an axisymmetric multi-cusp magnetic field
and biased cathodes are used to drive currents and impart a torque in the
magnetized edge. Measurements show that flow viscously couples momentum from
the magnetized edge (where the plasma viscosity is small) into the unmagnetized
core (where the viscosity is large) and that the core rotates as a solid body.
To be effective, collisional viscosity must overcome the ion-neutral drag due
to charge exchange collisions.",1205.6704v1
2013-11-16,Negative azimuthal force of a nanofiber-guided light on a particle,"We calculate the force of a quasicircularly polarized guided light field of a
nanofiber on a dielectric spherical particle. We show that the orbital parts of
the axial and azimuthal components of the Poynting vector are always positive
while the spin parts can be either positive or negative. We find that, for
appropriate values of the size parameter of the particle, the azimuthal
component of the force is directed oppositely to the circulation direction of
the energy flow around the nanofiber. The occurrence of such a negative
azimuthal force indicates that the particle undergoes a negative torque.",1311.4054v1
2016-04-19,Phenomenology of current-induced skyrmion motion in antiferromagnets,"We study current-driven skyrmion motion in uniaxial thin film
antiferromagnets in the presence of the Dzyaloshinskii-Moriya interactions and
in an external magnetic field. We phenomenologically include relaxation and
current-induced torques due to both spin-orbit coupling and spatially
inhomogeneous magnetic textures in the equation for the N\'eel vector of the
antiferromagnet. Using the collective coordinate approach we apply the theory
to a two-dimensional antiferromagnetic skyrmion and estimate the skyrmion
velocity under an applied DC electric current.",1604.05712v1
2016-05-19,Rotating Particle in the Near Field of the Surface at Arbitrary Direction of Angular Velocity Vector,"We study the fluctuation-electromagnetic interaction between a small rotating
particle with an arbitrary direction of angular velocity vector and evanescent
field of the heated surface, and obtain the general expressions for the force
of attraction, rate of heating and components of torque. The particle rotation
dynamics is analyzed. It is shown that during most time of motion the particle
slows down provided that a quasiequilibrium thermal state has been reached,
while at any initial direction of the angular velocity vector it tends to
orient perpendicular to the surface with spin direction depending on the
initial conditions. Moreover, the angular velocity vector executes precessional
motion around surface normal.",1605.06036v1
2017-12-13,Theoretical Proposal for Determining Angular Momentum Compensation in Ferrimagnets,"This work demonstrates that the magnetization and angular momentum
compensation temperature (TMC and TAMC) in ferrimagnets (FiM) can be
unambiguously determined by performing two sets of temperature dependent
current switching, with the symmetry reverses at TMC and TAMC, respectively. A
theoretical model based on the modified Landau-Lifshitz-Bloch equation is
developed to systematically study the spin torque effect under different
temperatures, and numerical simulations are performed to corroborate our
proposal. Furthermore, we demonstrate that the recently reported linear
relation between TAMC and TMC can be explained using the Curie-Weiss theory.",1712.04624v1
2018-10-25,Use of Magnetoresistive Random-Access Memory as Approximate Memory for Training Neural Networks,"Hardware neural networks that implement synaptic weights with embedded
non-volatile memory, such as spin torque memory (ST-MRAM), are a major lead for
low energy artificial intelligence. In this work, we propose an approximate
storage approach for their memory. We show that this strategy grants effective
control of the bit error rate by modulating the programming pulse amplitude or
duration. Accounting for the devices variability issue, we evaluate energy
savings, and show how they translate when training a hardware neural network.
On an image recognition example, 74% of programming energy can be saved by
losing only 1% on the recognition performance.",1810.10836v1
2017-06-07,Optical Angular Momentum in Classical Electrodynamics,"Invoking Maxwell's classical equations in conjunction with expressions for
the electromagnetic (EM) energy, momentum, force, and torque, we use a few
simple examples to demonstrate the nature of the EM angular momentum. The
energy and the angular momentum of an EM field will be shown to have an
intimate relationship; a source radiating EM angular momentum will, of
necessity, pick up an equal but opposite amount of mechanical angular momentum;
and the spin and orbital angular momenta of the EM field, when absorbed by a
small particle, will be seen to elicit different responses from the particle.",1706.02407v1
2017-01-23,Concepts of antiferromagnetic spintronics,"Antiferromagnetic spintronics is an emerging research field whose focus is on
the electrical and optical control of the antiferromagnetic order parameter and
its utility in information technology devices. An example of recently
discovered new concepts is the N\'{e}el spin-orbit torque which allows for the
antiferromagnetic order parameter to be controlled by an electrical current in
common microelectronic circuits. In this review we discuss the utility of
antiferromagnets as active and supporting materials for spintronics, the
interplay of antiferromagnetic spintronics with other modern research fields in
condensed matter physics, and its utility in future ""More than Moore""
information technologies.",1701.06556v1
2017-03-22,Generalized Papapetrou's equations of motion for an extended test body within static and isotropic metrics,"Applying Dixon's general equations of motion for extended bodies, we compute
the Papapetrou's equations for an extended test body on static and isotropic
metrics. We incorporate the force and the torque terms which involve multipole
moments, beyond dipole moment, from the energy-momentum tensor. We obtain the
vector form equations for both Corinaldesi-Papapetrou and Tulczyjew-Dixon spin
supplementary conditions. An expanded effective mass, including interactions
between the structure of the body and the gravitational field, is also found.",1703.07874v1
2020-10-07,Hydrodynamic theory of chiral angular momentum generation in metals,"We present a hydrodynamic theory to describe a chiral electron system with a
Weyl spin-orbit interaction on a field-theoretic basis. Evaluating the momentum
flux density as a linear response to a driving electric field, we derive an
equation of motion for the orbital angular momentum. It is shown that the
chiral nature leads to a dynamic bulk angular momentum generation by inducing a
global torque as a response to the applied field. The steady state angular
momentum is calculated taking account of rotational viscosity.",2010.03238v1
2022-03-17,"Force-free and twisted, relativistic neutron star magnetospheres","In this poster we present the structure of an axisymmetric, force-free
magnetosphere of a twisted, aligned rotating dipole within a corotating
plasma-filled magnetosphere. We explore various profiles for the twist. We find
that as the current increases more field lines cross the light cylinder leading
to more efficient spin-down. Moreover, we notice that the twist cannot be
increased indefinitely and after a finite twist of about ${\pi}/2$ the field
becomes approximately radial. This could have implications for torque
variations of magnetars related to outbursts.",2203.09187v2
2022-08-22,"Existence, uniqueness and regularity of solutions to the stochastic Landau-Lifschitz-Slonczewski equation","In this paper we are concerned with the stochastic
Landau-Lifshitz-Slonczewski equation (LLS) that describes magnetisation of an
inifnite nanowire evolving under current driven spin torque. The current brings
into the system a multiplicative gradient noise that appears as a transport
term in the equation. We prove the existence, uniqueness and regularity of
pathwise solutions to this equation.",2208.10065v1
2023-06-27,Radiation of Optical Angular Momentum from a Dipole Source in a Magneto-birefringent disordered Environment,"We investigate the radiation of optical angular momentum by a dipole gas
under uniform magnetic field with an unpolarized source at its center.
Conservation of angular momentum implies that the radiation of angular momentum
results in a torque on both the source and the surrounding environment.
Moreover, we study the spin and orbital contributions to the radiated angular
momentum.",2306.15639v2
2024-03-22,Cross-layer Modeling and Design of Content Addressable Memories in Advanced Technology Nodes for Similarity Search,"In this paper we present a comprehensive design and benchmarking study of
Content Addressable Memory (CAM) at the 7nm technology node in the context of
similarity search applications. We design CAM cells based on SRAM, spin-orbit
torque, and ferroelectric field effect transistor devices and from their
layouts extract cell parasitics using state of the art EDA tools. These
parasitics are used to develop SPICE netlists to model search operations. We
use a CAM-based dataset search and a sequential recommendation system to
highlight the application-level performance degradation due to interconnect
parasitics. We propose and evaluate two solutions to mitigate interconnect
effects.",2403.15328v1
2021-08-20,"Analytic ""Newton's cradles"" with perfect transfer and fractional revival","Analytic mass-spring chains with dispersionless pulse transfer and fractional
revival are presented. These are obtained using the properties of the
para-Racah polynomials. This provides classical analogs of the quantum spin
chains that realize important tasks in quantum information: perfect state
transfer and entanglement generation.",2108.09386v1
2000-04-19,A spin-coherent semiconductor photo-detector for quantum communication,"We describe how quantum information may be transferred from photon
polarization to electron spin in a semiconductor device. The transfer of
quantum information relies on selection rules for optical transitions, such
that two superposed photon polarizations excite two superposed spin states.
Entanglement of the electron spin state with the spin state of the remaining
hole is prevented by using a single, non-degenerate initial valence band. The
degeneracy of the valence band is lifted by the combination of strain and a
static magnetic field. We give a detailed description of a semiconductor
structure that transfers photon polarization to electron spin coherently, and
allows electron spins to be stored and to be made available for quantum
information processing.",0004078v2
2020-10-18,Quantifying power flow processes mediated by spin currents,"The power flow process mediated by spin current in the bilayer device
consisting of ferromagnetic metal (FM) and non-magnetic metal (NM) layers is
examined by realizing experimental evaluations for each process from the
microwave absorption to electromotive force (EMF) output. The absorption power
by ferromagnetic resonance (FMR) of the thin FM layer during the EMF output is
directly measured in operando using an antenna probe system. The transfer
efficiency of the absorption power into the NM layer by spin pumping is
estimated from strict linewidth evaluation of EMF spectra. The maximum transfer
efficiency of the spin pumping power to the external load via the inverse spin
Hall effect is determined to be 4.2X10^(-8) under 160mW microwave irradiation
using an analysis model assuming a parallel circuit. The main factors reducing
the efficiency are found to be low resistivity of the NM layer and the
interface loss. These quantifications are important as a first step to consider
the efficient transfer of spin energy mediated by spin currents.",2010.08997v3
2021-05-11,Symmetry-Induced Universal Momentum-Transfer Dependencies for Inelastic Neutron Scattering on Anisotropic Spin Clusters,"Inelastic neutron scattering (INS) is a key method for studying magnetic
excitations in spin systems, including molecular spin clusters. The method has
significantly advanced in recent years and now permits to probe the scattering
intensity as a function of the energy transfer and the momentum-transfer vector
Q. It was recently shown that high molecular symmetry facilitates the analysis
of spectra. Point-group symmetry imposes selection rules in isotropic as well
as anisotropic spin models. Furthermore, the Q-dependence of the INS intensity
may be completely determined by the point-group symmetry of the states involved
in a transition, thereby affording a clear separation of dynamics (energies,
transition strengths) and geometrical features (Q-dependencies). The present
work addresses this issue for anisotropic spin models. We identify a number of
cases where the Q-dependence is completely fixed by the point-group symmetry.
For six- and eight-membered planar spin rings and two polyhedra (the cube and
the icosahedron) we tabulate and plot the corresponding powder-averaged
universal intensity functions. The outlined formalism straightforwardly applies
to other highly-symmetric systems and should be useful for future analyses of
INS spectra by focusing on those features that contain information on either
spin dynamics or the point-group symmetry of states.",2105.04853v1
2022-10-25,Constant-adiabaticity ultralow magnetic field manipulations of parahydrogen-induced polarization: application to an AA'X spin system,"The field of magnetic resonance imaging with hyperpolarized contrast agents
is rapidly expanding, and parahydrogen-induced polarization (PHIP) is emerging
as an inexpensive and easy-to-implement method for generating the required
hyperpolarized biomolecules. Hydrogenative PHIP delivers hyperpolarized proton
spin order to a substrate via chemical addition of H2 in the spin-singlet
state, but prior to imaging it is typically necessary to transfer the proton
polarization to a heteronucleus (usually 13C) in the molecule. Adiabatic
ultralow magnetic field manipulations can be used to induce the polarization
transfer, but this is necessarily a slow process, which is undesirable since
the spins continually relax back to thermal equilibrium. Here we demonstrate
constant-adiabaticity field cycling and field sweeping for optimal polarization
transfer on a model AA$'$X spin system, [1-13C]fumarate. We introduce a method
for calculating constant-adiabaticity magnetic field ramps and demonstrate that
they enable much faster spin-order conversion as compared to linear ramps used
before. The present method can thus be utilized to manipulate nonthermal order
in heteronuclear spin systems.",2210.14342v1
2006-09-04,Information transfer rates in spin quantum channels,"We analyze the communication efficiency of quantum information transfer along
unmodulated spin chains by computing the communication rates of various
protocols. The effects of temporal correlations are discussed, showing that
they can be exploited to boost the transmission efficiency.",0609022v2
2011-01-18,Functoriality for General Spin Groups,"We establish the functorial transfer of generic, automorphic representations
from the quasi-split general spin groups to general linear groups over
arbitrary number fields, completing an earlier project. Our results are
definitive and, in particular, we determine the image of this transfer
completely and give a number of applications.",1101.3467v1
2011-09-07,Planar approximation for spin transfer systems with application to tilted polarizer devices,"Planar spin-transfer devices with dominating easy-plane anisotropy can be
described by an effective one-dimensional equation for the in-plane angle. Such
a description provides an intuitive qualitative understanding of the magnetic
dynamics. We give a detailed derivation of the effective planar equation and
use it to describe magnetic switching in devices with tilted polarizer.",1109.1331v1
2011-09-07,Planar approximation for the frequencies of spin transfer oscillators,"A large class of spin transfer oscillators use the free layer with a strong
easy plane anisotropy, which forces its magnetization to move close to the
plane. We show that in this situation the effective planar approximation
provides a fast and accurate way of calculating the oscillator frequency.",1109.1335v1
2014-11-10,Spin-dependent thermoelectric effects in transport through a nanoscopic junction involving spin impurity,"Conventional and spin-related thermoelectric effects in transport through a
magnetic tunnel junction with a large-spin impurity, such as a magnetic
molecule or atom, embedded into the corresponding barrier are studied
theoretically in the linear-response regime. The impurity is described by the
giant spin Hamiltonian, with both uniaxial and transverse magnetic anisotropy
taken into account. Owing to the presence of transverse component of magnetic
anisotropy, spin of a tunneling electron can be reversed during scattering on
the impurity, even in the low temperature regime. This reversal appears due to
exchange interaction of tunneling electrons with the magnetic impurity. We
calculate Seebeck and spin Seebeck coefficients, and analyze their dependence
on various parameters of the spin impurity and tunnel junction. In addition,
conventional and spin figures of merit, as well as the electronic contribution
to heat conductance are considered. We also show that pure spin current can be
driven by a spin bias applied to the junction with spin impurity, even if no
electron transfer between the electrodes can take place. The underlying
mechanism employs single-electrode tunneling processes (electrode-spin exchange
interaction) and the impurity as an intermediate reservoir of angular momentum.",1411.2375v1
2022-08-30,Spin-polarized hot electron transport versus spin pumping mediated by local heating,"A `toy model' - aimed at capturing the essential physics - is presented that
jointly describes spin-polarized hot electron transport and spin pumping driven
by local heating. These two processes both contribute to spin-current
generation in laser-excited magnetic heterostructures. The model is used to
compare the two contributions directly. The spin-polarized hot electron current
is modeled as one generation of hot electrons with a spin-dependent excitation
and relaxation scheme. Upon decay, the excess energy of the hot electrons is
transferred to a thermalized electron bath. The elevated electron temperature
leads to an increased rate of electron-magnon scattering processes and yields a
local accumulation of spin. This process is dubbed as spin pumping by local
heating. The built-up spin accumulation is effectively driven out of the
ferromagnetic system by (interfacial) electron transport. Within our model, the
injected spin current is dominated by the contribution resulting from spin
pumping, while the hot electron spin current remains relatively small. We
derive that this observation is related to the ratio between the Fermi
temperature and Curie temperature, and we show what other fundamental
parameters play a role.",2208.14342v1
2015-06-17,Spin Casimir Effect in Non-collinear Quantum Antiferromagnets,"The Casimir effect is a general phenomenon in physics, which arises when the
vacuum fluctuation of an arbitrary field is modified by static or slowly
varying boundary. However, its spin version is rarely addressed, mainly due to
the fact that a macroscopic boundary in quantum spin systems is hard to define.
In this article, we explore the spin Casimir effect induced by the zero-point
fluctuation of spin waves in a general non-collinear ordered quantum
antiferromagnet. This spin Casimir effect results in a spin torque between
local spins and further causes various singular and divergent results in the
framework of spin-wave theory, which invalidate the standard $1/S$ expansion
procedure. To avoid this dilemma, we develop a self-consistent spin-wave
expansion approach, which preserves the spin-wave expansion away from
singularities and divergence. A detailed spin-wave analysis of the
antiferromagnetic spin-1/2 Heisenberg model on a spatially anisotropic
triangular lattice is undertaken within our approach. Our results indicate that
the spiral order is only stable in the region $0.5<\alpha<1.2$, where $\alpha$
is the ratio of the coupling constants. In addition, the instability in the
region $1.2<\alpha<2$ is owing to the spin Casimir effect instead of the
vanishing sublattice magnetization. And this extended spiral instable region
may host some quantum disordered phases besides the quantum order by disorder
induced Neel phase. Furthermore, our method provides an efficient and
convenient tool that can estimate the correct exchange parameters and outline
the quantum phase diagrams, which can be useful for experimental fitting
processes in frustrated quantum magnets.",1506.05211v2
2005-02-03,Atomistic Theory of Coherent Spin Transfer between Molecularly Bridged Quantum Dots,"Time-resolved Faradary rotation experiments have demonstrated coherent
transfer of electron spin between CdSe colloidal quantum dots coupled by
conjugated molecules. We employ here a Green's function approach, using
semi-empirical tight-binding to treat the nanocrystal Hamiltonian and Extended
Huckel theory to treat the linking molecule Hamiltonian, to obtain the coherent
transfer probabilities from atomistic calculations, without the introduction of
any new parameters. Calculations on 1,4-dithiolbenzene and
1,4-dithiolcyclohexane linked nanocrystals agree qualitatively with experiment
and provide support for a previous transfer Hamiltonian model. We find a
striking dependence on the transfer probabilities as a function of nanocrystal
surface site attachment and linking molecule conformation. Additionally, we
predict quantum interference effects in the coherent transfer probabilities for
2,7-dithiolnaphthalene and 2,6-dithiolnaphthalene linking molecules. We suggest
possible experiments based on these results that would test the coherent,
through-molecule transfer mechanism.",0502080v1
2002-03-16,Ultra-broadband Heteronuclear Hartmann-Hahn polarization transfer,"It is showed on the basis of the multiple-quantum operator algebra space
formalism that ultra-broadband heteronuclear Hartmann-Hahn polarization
transfer could be achieved by the amplitude- and frequency-modulation
quasi-adiabatic excitation (90 degree) pulses, while it is usually difficult
for the adiabatic inversion pulses to achieve effectively broadband
Hartmann-Hahn transfer in a heteronuclear coupled two-spin system. The
adiabatic and quasi-adiabatic pulses have an important property that within
their activation bandwidth flip angle of the pulses is independent of the pulse
duration and the bandwidth increases as the pulse duration. This property is
importanr for construction of the heteronuclear Hartmann-Hahn transfer
sequences with the quasi-adiabatic 90 degree pulses. Theoretic analysis and
numerical simulation show that the heteronuclear Hartmann-Hahn transfer is
performed in the even-order multiple- quantum operator algebra subspace of the
two-spin system. The multiple-quantum operator algebra space formalism may give
a powerful guide to the construction of ultra- broadband heteronuclear
Hartmann-Hahn transfer sequences with the quasi-adiabatic 90 degree pulses.",0203079v2
2013-04-24,"Charge transfer, confinement, and ferromagnetism in LaMnO$_3$/LaNiO$_3$ (001)-superlattice","Using first-principles density functional theory calculations, we
investigated the electronic structure and magnetic properties of
(LaMnO$_3$)$_m$/(LaNiO$_3$)$_n$ superlattices stacked along (001)-direction.
The electrons are transferred from Mn to Ni, and the magnetic moments are
induced at Ni sites that are paramagnetic in bulk and other types of
superlattices. The size of induced moment is linearly proportional to the
amount of transferred electrons, but it is larger than the net charge transfer
because the spin and orbital directions play important roles and complicate the
transfer process. The charge transfer and magnetic properties of the ($m$,$n$)
superlattice can be controlled by changing the $m/n$ ratio. Considering the
ferromagnetic couplings between Mn and Ni spins and the charge transfer
characteristic, we propose the (2,1) superlattice as the largest moment
superlattice carrying $\sim8\mu_B$ per formula unit.",1304.6555v1
2021-05-24,Quantum State Transfer Between NV Center -- $13_C$ System Coupled To A CPW Cavity,"Quantum state transfer is a very important process in building a quantum
network when information from flying Qubit is transferred to the stationary
Qubit in a node via a quantum state transfer. NV centers due to their long
coherence time and the presence of nearby $13_C$ nuclear spin is an excellent
candidate for multi-Qubit quantum memory. Here we propose a theoretical
description for such a quantum state transfer from a cavity to a nearest
neighbour $13_C$ nuclear spin of a single Nitrogen vacancy center in diamond;
it shows great potential in realizing scalable quantum networks and quantum
simulation. The full Hamiltonian was considered with the zeroth-order and
interaction terms in the Hamiltonian and the theory of effective hamiltonian
theory was applied. We study the time evolution of the combined cavity-$13_C$
state through analytical calculation and simulation using QuTip. Graphs for
state transfer and fidelity measurement are presented here. We show that our
theoretical description verifies a high fidelity quantum state transfer from
the cavity to $13_C$ center by choosing suitable system parameters.",2105.11507v1
2014-09-01,Dynamical corotation torques on low-mass planets,"We study torques on migrating low-mass planets in locally isothermal discs.
Previous work on low-mass planets generally kept the planet on a fixed orbit,
after which the torque on the planet was measured. In addition to these static
torques, when the planet is allowed to migrate it experiences dynamical
torques, which are proportional to the migration rate and whose sign depends on
the background vortensity gradient. We show that in discs a few times more
massive than the Minimum Mass Solar Nebula, these dynamical torques can have a
profound impact on planet migration. Inward migration can be slowed down
significantly, and if static torques lead to outward migration, dynamical
torques can take over, taking the planet beyond zero-torque lines set by
saturation of the corotation torque in a runaway fashion. This means the region
in non-isothermal discs where outward migration is possible can be larger than
what would be concluded from static torques alone.",1409.0372v1
2004-11-19,Multi-Temperature Blackbody Spectrum of a Thin Accretion Disk around a Kerr Black Hole: Model Computations and Comparison with Observations,"We use a ray-tracing technique to compute the observed spectrum of a thin
accretion disk around a Kerr black hole. We include all relativistic effects
such as frame-dragging, Doppler boost, gravitational redshift, and bending of
light by the gravity of the black hole. We also include self-irradiation of the
disk as a result of light deflection. Assuming that the disk emission is
locally blackbody, we show how the observed spectrum depends on the spin of the
black hole, the inclination of the disk, and the torque at the inner edge of
the disk. We find that the effect of a nonzero torque on the spectrum can, to a
good approximation, be absorbed into a zero-torque model by adjusting the mass
accretion rate and the normalization. We describe a computer model, called
KERRBB, which we have developed for fitting the spectra of black hole X-ray
binaries. Using KERRBB within the X-ray data reduction package XSPEC, and
assuming a spectral hardening factor f_col = 1.7, we analyze the spectra of
three black hole X-ray binaries: 4U1543-47, XTE J1550-564, and GRO J1655-40. We
estimate the spin parameters of the black holes in 4U1543-47 and GRO J1655-40
to be a/M ~ 0.6 and ~ 0.6-0.7, respectively. If f_col ~ 1.5-1.6, as in a recent
study, then we find a/M ~ 0.7-0.8 and ~ 0.8-0.9, respectively. These estimates
are subject to additional uncertainties in the assumed black hole masses,
distances and disk inclinations.",0411583v2
2022-12-09,Evolution of Spin Period and Magnetic Field of the Crab Pulsar: Decay of the Braking Index by the Particle Wind Flow Torque,"The evolutions of a neutron star's rotation and magnetic field (B-field) have
remained unsolved puzzles for over half a century. We ascribe the rotational
braking torques of pulsar to both components, the standard magnetic dipole
radiation (MDR) and particle wind flow ( MDR + Wind, hereafter named MDRW),
which we apply to the Crab pulsar (B0531 + 21), the only source with a known
age and long-term continuous monitoring by radio telescope. Based on the above
presumed simple spin-down torques, we obtain the exact analytic solution on the
rotation evolution of the Crab pulsar, together with the related outcomes as
described below: (1) unlike the constant characteristic B-field suggested by
the MDR model, this value for the Crab pulsar increases by a hundred times in
50~kyr while its real B-field has no change; (2) the rotational braking index
evolves from $\sim$3 to 1 in the long-term, however, it drops from 2.51 to 2.50
in $\sim$45 years at the present stage, while the particle flow contributes
approximately 25% of the total rotational energy loss rate; (3) strikingly, the
characteristic age has the maximum limit of $\sim$10 kyr, meaning that it is
not always a good indicator of real age. Furthermore, we discussed the
evolutionary path of the Crab pulsar from the MDR to the wind domination by
comparing it with the possible wind braking candidate pulsar PSR J1734-3333.",2212.04674v1
1994-03-10,On the spin parameter of dark-matter haloes,"The study by White (1984) on the growth of angular momentum in dark haloes is
extended towards a more detailed investigation of the spin parameter
$\lambda\equiv L\sqrt{E}/{G M^{2.5}}$. Starting from the Zel'dovich
approximation to structure formation, a dark halo is approximated by a
homogeneous ellipsoid with the inertial tensor of the (highly irregular)
Lagrangian region $\Upsilon$ from which the dark halo forms. Within this
approximation, an expression for the spin parameter can be derived, which
depends on the geometry of $\Upsilon$, the cosmological density parameter
$\Omega_0$, the overdensity of the dark halo, and the tidal torque exerted on
it. For Gaussian random fields, this expression can be evaluated statistically.
As a result, we derive a probability distribution of the spin parameter which
gives $\lambda\simeq0.07^{+0.04}_{-0.05}$, consistent with numerical
investigations. This probability distribution steeply rises with increasing
spin parameter, reaching its maximum at $\lambda\simeq0.025$. The 10 (50,90)
percentile values are $\lambda=0.02$ (0.05,0.11, respectively). There is a weak
anticorrelation of the spin parameter with the peak height $\nu$ of the density
fluctuation field $\lambda\propto \nu^{-0.29}$. The dependence on $\Omega_0$
and the variance $\sigma$ of the density-contrast field is very weak; there is
only a marginal tendency for the spin parameter to be slightly larger for
late-forming objects in an open universe. Due to the weak dependence on
$\sigma$, our results should be quite generally applicable and independent on",9403017v1
2001-05-10,Modeling Angular-Momentum History in Dark-Matter Halos,"We model the acquisition of spin by dark-matter halos in semi-analytic merger
trees. We explore two different algorithms; one in which halo spin is acquired
from the orbital angular momentum of merging satellites, and another in which
halo spin is gained via tidal torquing on shells of material while still in the
linear regime. We find that both scenarios produce the characteristic spin
distribution of halos found in N-body simulations, namely, a log-normal
distribution with mean ~0.04 and standard deviation ~0.5 in the log. A perfect
match requires fine-tuning of two free parameters. Both algorithms also
reproduce the general insensitivity of the spin distribution to halo mass,
redshift and cosmology seen in N-body simulations. The spin distribution can be
made strictly constant by physically motivated scalings of the free parameters.
In addition, both schemes predict that halos which have had recent major
mergers have systematically larger spin values. These algorithms can be
implemented within semi-analytic models of galaxy formation based on merger
trees. They yield detailed predictions of galaxy properties that strongly
depend on angular momentum (such as size and surface brightness) as a function
of merger history and environment.",0105168v3
2001-10-26,The spin evolution of nascent neutron stars,"The loss of angular momentum due to unstable r-modes in hot young neutron
stars has been proposed as a mechanism for achieving the spin rates inferred
for young pulsars. One factor that could have a significant effect on the
action of the r-mode instability is fallback of supernova remnant material. The
associated accretion torque could potentially counteract any gravitational-wave
induced spin-down, and accretion heating could affect the viscous damping rates
and hence the instability. We discuss the effects of various external agents on
the r-mode instability scenario within a simple model of supernova fallback on
to a hot young magnetized neutron star. We find that the outcome depends
strongly on the strength of the star's magnetic field. Our model is capable of
generating spin rates for young neutron stars that accord well with initial
spin rates inferred from pulsar observations. The combined action of r-mode
instability and fallback appears to cause the spin rates of neutron stars born
with very different spin rates to converge, on a timescale of about a year. The
results suggest that stars with magnetic fields $\le10^{13}$ G could emit a
detectable gravitational wave signal for perhaps several years after the
supernova event. Stars with higher fields (magnetars) are unlikely to emit a
detectable gravitational wave signal via the r-mode instability. The model also
suggests that the r-mode instability could be extremely effective in preventing
young neutron stars from going dynamically unstable to the bar-mode.",0110573v2
2007-06-11,The Alignments of the Galaxy Spins with the Real-Space Tidal Field Reconstructed from the Two Mass Redshift Survey,"We report a direct observational evidence for the existence of the galaxy
spin alignments with the real space tidal field. We calculate the real space
tidal field from the real space density field reconstructed recently from the
Two Mass Redshift Survey (2MRS) by Erdogdu et al. in 2006. Using a total of
12122 nearby spiral galaxies from the Tully Galaxy Catalog, we calculate the
orientations of their spin axes relative to the 2MRS tidal field. We find a
clear signal of the intrinsic correlations between the galaxy spins and the
intermediate principal axes of the tidal shears. The null hypothesis of no
correlation is rejected at 99.99 % confidence level. We also investigate the
dependence of the intrinsic correlations on the galaxy morphological type and
the environment. It is found that (i) the intrinsic correlation depends weakly
on the morphological type of the spiral galaxies but tends to decrease slightly
as the type increases; (ii) it is stronger in the high-density regions than in
the low-density regions. The observational result is quantitatively consistent
with analytic prediction based on the tidal torque theory. It is concluded that
the galaxy spin orientations may provide in principle a new complimentary probe
of the dark matter distribution.",0706.1412v2
2010-02-01,Spin Torques in Point Contacts to Exchange-Biased Ferromagnetic Films,"Hysteretic magneto-resistance of point contacts formed between non-magnetic
tips and single ferromagnetic films exchange-pinned by antiferromagnetic films
is investigated. The analysis of the measured current driven and field driven
hysteresis agrees with the recently proposed model of the surface spin-valve,
where the spin orientation at the interface can be different from that in the
bulk of the film. The switching in magneto-resistance at low fields is observed
to depend significantly on the direction of the exchange pinning, which allows
identifying this transition as a reversal of interior spins of the pinned
ferromagnetic films. The switching at higher fields is thus due to a spin
reversal in the point contact core, at the top surface of the ferromagnet, and
does not exhibit any clear field offset when the exchange-pinning direction or
the magnetic field direction is varied. This magnitude of the switching field
of the surface spins varies substantially from contact to contact and sometimes
from sweep to sweep, which suggests that the surface coercivity can change
under very high current densities and/or due to the particular microstructure
of the point contact. In contrast, no changes in the effect of the exchange
biasing on the interior spins are observed at high currents, possibly due to
the rapid drop in the current density away from nanometer sized point contact
cores.",1002.0209v1
2011-11-29,Accelerated Orbital Expansion And Secular Spin Down of the Accreting Millisecond Pulsar SAX J1808.4-3658,"The accreting millisecond pulsar SAX J1808.4-3658 has shown a peculiar
orbital evolution in the past with an orbital expansion much faster than
expected from standard binary evolutionary scenarios. Previous limits on the
pulsar spin frequency derivative during transient accretion outbursts were
smaller than predicted by standard magnetic accretion torque theory, while the
spin evolution between outbursts was consistent with magnetic dipole spin-down.
In this paper we present the results of a coherent timing analysis of the 2011
outburst observed by the Rossi X-ray Timing Explorer and extend our previous
long-term measurements of the orbital and spin evolution over a baseline of
thirteen years. We find that the expansion of the 2 hr orbit is accelerating at
a rate 1.6E-20 s/s^2 and we interpret this as the effect of short-term angular
momentum exchange between the mass donor and the orbit. The gravitational
quadrupole coupling due to variations in the oblateness of the companion can be
a viable mechanism for explaining the observations. No significant spin
frequency derivatives are detected during the 2011 outburst (<4E-13 Hz/s) and
the long term spin down remains stable over thirteen years with a rate of
approximately -1E-15 Hz/s.",1111.6967v2
2012-01-30,The cosmic history of the spin of dark matter haloes within the large scale structure,"We use N-body simulations to investigate the evolution of the orientation and
magnitude of dark matter halo angular momentum within the large scale structure
since z=3. We look at the evolution of the alignment of halo spins with
filaments and with each other, as well as the spin parameter, which is a
measure of the magnitude of angular momentum. It was found that the angular
momentum vectors of dark matter haloes at high redshift have a weak tendency to
be orthogonal to filaments and high mass haloes have a stronger orthogonal
alignment than low mass haloes. Since z=1, the spins of low mass haloes have
become weakly aligned parallel to filaments, whereas high mass haloes kept
their orthogonal alignment. This recent parallel alignment of low mass haloes
casts doubt on tidal torque theory as the sole mechanism for the build up of
angular momentum. We see evidence for bulk flows and the broadening of
filaments over time in the alignments of halo spin and velocities. We find a
significant alignment of the spin of neighboring dark matter haloes only at
very small separations, $r<0.3$Mpc/h, which is driven by substructure. A
correlation of the spin parameter with halo mass is confirmed at high redshift.",1201.6108v3
2014-10-23,Spectroscopic confirmation of linear relation between Heisenberg- and interfacial Dzyaloshinskii-Moriya-exchange in polycrystalline metal films,"Proposals for novel spin-orbitronic logic1 and memory devices2 are often
predicated on assumptions as to how materials with large spin-orbit coupling
interact with ferromagnets when in contact. Such interactions give rise to a
host of novel phenomena, such as spin-orbit torques3,4 , chiral
spin-structures5,6 and chiral spin-torques. These chiral properties are related
to the anti-symmetric exchange, also referred to as the interfacial
Dzyaloshinskii-Moriya interaction (DMI)9,10. For numerous phenomena, the
relative strengths of the symmetric Heisenberg exchange and the DMI is of great
importance. Here, we use optical spin-wave spectroscopy (Brillouin light
scattering) to directly determine the DMI vector for a series of Ni80Fe20/Pt
samples, and then compare the nearest-neighbor DMI coupling energy with the
independently measured Heisenberg exchange integral. We find that the
Ni80Fe20-thickness-dependencies of both the microscopic symmetric- and
antisymmetric-exchange are identical, consistent with the notion that the basic
mechanisms of the DMI and Heisenberg exchange essentially share the same
underlying physics, as was originally proposed by Moriya11. While of
significant fundamental importance, this result also leads us to a deeper
understanding of DMI and how it could be optimized for spin-orbitronic
applications.",1410.6243v1
2018-06-28,"Neutron star bulk viscosity, ""spin-flip"" and GW emission of newly born magnetars","The viscosity-driven ""spin-flip"" instability in newborn magnetars with
interior toroidal magnetic fields is re-examined. We calculate the bulk
viscosity coefficient ($\zeta$) of cold, $npe \mu$ matter in neutron stars
(NS), for selected values of the nuclear symmetry energy and in the regime
where $\beta$-equilibration is slower than characteristic oscillation periods.
We show that: i) $\zeta$ is larger than previously assumed and the instability
timescale correspondingly shorter; ii) for a magnetically-induced ellipticity
$\epsilon_B \lesssim 4 \times 10^{-3}$, typically expected in newborn
magnetars, spin-flip occurs for initial spin periods $\lesssim 2-3$ ms, with
some dependence on the NS equation of state (EoS). We then calculate the
detectability of GW signals emitted by newborn magnetars subject to
""spin-flip"", by accounting also for the reduction in range resulting from
realistic signal searches. For an optimal range of $\epsilon_B \sim (1-5)
\times 10^{-3}$, and birth spin period $\lesssim 2$ ms, we estimate an horizon
of $\gtrsim 4$ Mpc, and $\gtrsim 30$ Mpc, for Advanced and third generation
interferometers at design sensitivity, respectively. A supernova (or a
kilonova) is expected as the electromagnetic counterpart of such GW events.
Outside of the optimal range for GW emission, EM torques are more efficient in
extracting the NS spin energy, which may power even brighter EM transients.",1806.11164v1
2018-08-19,Spin-dependent scattering and magnetic proximity effect in Ni-doped Co/Cu multilayers as a probe of atomic magnetism,"We investigate the spin transport and ferromagnetic resonance properties of
giant magnetoresistive (GMR) Co/Cu-Ni multilayers with variable levels of Ni
doping in the Cu spacer. We present an experimental evidence for a
magnetic-to-diamagnetic transition in the atomic magnetic moment of Ni in the
Cu matrix for concentrations below 15 at. % Ni. As its concentration is
increased, Ni atoms turn into spin scattering centers, which is manifested
experimentally as a step-like change in the GMR of the multilayers. This
behavior is observed in multilayers with gradient-doped Cu spacers, where only
the inner region was doped with Ni. In the uniformly doped spacers the GMR
decreases monotonously with increasing Ni content, indicating that Ni atoms are
magnetic and act as spin relaxation centers in the entire dopant-concentration
range studied. We explain the difference in the observed GMR behavior as due to
a strong magnetic proximity effect in the uniform spacers, which is efficiently
suppressed in the gradient spacers. The observed magnetic phase transition is
fully supported by our detailed ab-initio calculations, taking into
consideration structural relaxation in the system as well as potential Ni
clustering. Controlling the loss or gain of the atomic magnetism for a specific
dopant can be a tool in probing and controlling spin relaxation in materials
and devices for spin-valve and spin-torque based applications.",1808.06198v1
2020-10-04,Unified Framework for Charge-Spin Interconversion in Spin-Orbit Materials,"Materials with spin-orbit coupling are of great interest for various
spintronics applications due to the efficient electrical generation and
detection of spin-polarized electrons. Over the past decade, many materials
have been studied, including topological insulators, transition metals, Kondo
insulators, semimetals, semiconductors, and oxides; however, there is no
unifying physical framework for understanding the physics and therefore
designing a material system and devices with the desired properties. We present
a model that binds together the experimental data observed on the wide variety
of materials in a unified manner. We show that in a material with a given
spin-momentum locking, the density of states plays a crucial role in
determining the charge-spin interconversion efficiency, and a simple inverse
relationship can be obtained. Remarkably, experimental data obtained over the
last decade on many different materials closely follow such an inverse
relationship. We further deduce two figure-of-merits of great current interest:
the spin-orbit torque (SOT) efficiency (for the direct effect) and the inverse
Rashba-Edelstein effect length (for the inverse effect), which statistically
show good agreement with the existing experimental data on wide varieties of
materials. Especially, we identify a scaling law for the SOT efficiency with
respect to the carrier concentration in the sample, which agrees with existing
data. Such an agreement is intriguing since our transport model includes only
Fermi surface contributions and fundamentally different from the conventional
views of the SOT efficiency that includes contributions from all the occupied
states.",2010.01484v2
2020-12-20,Chiral tunneling in single layer graphene with Rashba spin-orbit coupling: spin currents,"We study forward scattering of 2D massless Dirac electrons at Fermi energy
{\varepsilon} > 0 in single layer graphene through a 1D rectangular barrier of
height {u_0} in the presence of uniform Rashba spin-orbit coupling (of strength
{\lambda}). The role of the Klein paradox in graphene spintronics is thereby
exposed. It is shown that (1) For {\varepsilon} - 2{\lambda} < {u_0}<
{\varepsilon} + 2{\lambda} there is partial Klein tunneling, wherein the
transmission is bounded by 1 and, quite remarkably, for small {\lambda} >
{\lambda_0} {\approx} 0.1 meV, the transmission nearly vanishes when the
scattering energy equals the barrier height, {\varepsilon}={u_0}. (2) Spin
density and spin-current density are shown to be remarkably different than
these observables predicted in bulk single layer graphene. In particular, they
are sensitive to {\lambda} and {u_0}. (3) Spin current densities are space
dependent, implying the occurrence of non-zero spin torque density. Such a
system may serve as a graphene based spintronic device without the use of an
external magnetic field or magnetic materials.",2012.10971v4
2021-07-09,Emergence of Dynamical Coherence in a Driven One-dimensional Interacting Rotor Model,"In order to understand the dynamics of active matter, we examine a
minimalistic model where interacting spins on a one-dimensional lattice are
driven by a self-propelled spin at the centre with a fixed rotational velocity
$({\omega}_{0})$. The other spins execute rotational Brownian motion by
following the Shore-Zwanzig model of rotational dynamics. The simplicity of the
model allows us to inquire about several relevant microscopic quantities. The
continuous 'active' torque on the central spin is propagated through nearest
neighbour interactions with a uniform coupling parameter, J. We have found a
bounded region in the J-${\omega}_{0}$ plane where the system exhibits 'active
matter like behaviour'. Interestingly, in the limits of large J and
${\omega}_{0}$, we observe a 'slipping behaviour'. The site specific average
rotational velocity of the spin, as one moves away from the central spin
exhibits a nearly exponential decay with distance, allowing the definition of a
correlation length $({\xi})$ which grows rapidly with an increase of the
coupling (J) between the spins. Site specific average velocity exhibits a
change from a single exponential to biexponential decay pattern as the system
enters the active region of the phase diagram, accompanied by a non-monotonic
behavior of the correlation length. We conclude that a macroscopic coherent
state can emerge in the presence of a small concentration of active molecules.
We discuss experimental relevance of our results.",2107.04215v1
2021-11-01,Cluster magnetic octupole induced out-of-plane spin polarization in antiperovskite antiferromagnet,"Out-of-plane spin polarization {\sigma}_z has attracted increasing interests
of researchers recently, due to its potential in high-density and low-power
spintronic devices. Noncollinear antiferromagnet (AFM), which has unique
120{\deg} triangular spin configuration, has been discovered to possess
{\sigma}_z. However, the physical origin of {\sigma}_z in noncollinear AFM is
still not clear, and the external magnetic field-free switching of
perpendicular magnetic layer using the corresponding {\sigma}_z has not been
reported yet. Here, we use the cluster magnetic octupole in antiperovskite AFM
Mn3SnN to demonstrate the generation of {\sigma}_z. {\sigma}_z is induced by
the precession of carrier spins when currents flow through the cluster magnetic
octupole, which also relies on the direction of the cluster magnetic octupole
in conjunction with the applied current. With the aid of {\sigma}_z, current
induced spin-orbit torque (SOT) switching of adjacent perpendicular ferromagnet
is realized without external magnetic field. Our findings present a new
perspective to the generation of out-of-plane spin polarizations via
noncollinear AFM spin structure, and provide a potential path to realize
ultrafast high-density applications.",2111.00646v1
2021-12-07,Estimating the spin of the black hole candidate MAXI J1659-152 with the X-ray continuum-fitting method,"As a transient X-ray binary, MAXI J1659-152 contains a black hole candidate
as its compact star. MAXI J1659-152 was discovered on 2010 September 25 during
its only known outburst. Previously-published studies of this outburst indicate
that MAXI J1659-152 may have an extreme retrograde spin, which, if confirmed,
would provide an important clue as to the origin of black hole spin. In this
paper, utilizing updated dynamical binary-system parameters (i.e. the black
hole mass, the orbital inclination and the source distance) provided by
\cite{Torres2021}, we analyze 65 spectra of MAXI J1659-152 from
\emph{RXTE}/PCA, in order to assess the spin parameter. With a final selection
of 9 spectra matching our $f_{\mathrm{sc}} \lesssim 25 \%$, soft-state
criteria, we apply a relativistic thin disk spectroscopic model
\texttt{kerrbb2} over 3.0-45.0 keV. We find that inclination angle correlates
inversely with spin, and, considering the possible values for inclination
angle, we constrain spin to be $-1 < a_{*} \lesssim 0.44$ at 90\% confidence
interval via X-ray continuum-fitting. We can only rule out an extreme prograde
(positive) spin. We confirm that an extreme retrograde solution is possible and
is not ruled out by considering accretion torques given the young age of the
system.",2112.03479v1
2022-03-07,Manipulating quantum impurity spins via dynamical modes of nanomagnets,"Quantum impurity (QI) spins offer promising information processing and
sensing applications by harnessing up to room-temperature quantum coherence.
Challenged by the requirement of designing local coherent drives and improving
sensitivity to various signals for such applications, the search of hybrid
systems coupling QI spins with matter excitations have garnered significant
recent interest. We propose and theoretically study a hybrid system that
couples spin-1 QI with the dynamical excitations of nanomagnets, which are
controlled by mechanisms uncovered in classical spintronics. We show that in
such systems the QI-spin decoherence, due to coupling to thermally excited
modes of the nanomagnet, can be designed across a wide range by exploiting the
control over nanomagnet's mode ellipticity and the chiral nature of the
coupling between the QI spin and nanomagnet. On the other hand, when activated
electrically via voltage-induced torques, we demonstrate that QI spins can be
driven coherently with large quality factors at room temperature by leveraging
inherent non-linear precessional modes of the nanomagnet. Our results provide
theoretical guidance for enabling unique quantum spintronic functionalities,
such as local coherent driving of QI spins up to ambient conditions, and the
design of nanomagnet-enhanced QI-based hybrid sensors.",2203.03652v1
2022-03-31,Theory of magnetic spin and orbital Hall and Nernst effects in bulk ferromagnets,"The magnetic spin Hall effect (MSHE) is an anomalous charge-to-spin
conversion phenomenon which occurs in ferromagnetic materials. In contrast to
the conventional spin Hall effect (SHE), being a time-reversal even effect, the
magnetic counterpart is time-reversal odd. In this work, we use ab initio
calculations to investigate the MSHE for the bulk ferromagnets Fe, Co, and Ni.
The magnitudes of the MSHE of Fe and Co are comparable to those of the SHE, but
the MSHE is strongly dependent on the electron lifetime and the MSHE and SHE
can moreover have opposite signs. For Ni the MSHE is smaller than the SHE, but
in general, the MSHE cannot be ignored for spin-orbit torques. Considering a
charge current we analyze how both the MSHE and SHE contribute to a total Hall
angle. We extend our analysis of the MSHE to its orbital counterpart, that is,
the magnetic orbital Hall effect (MOHE), for which we show that the MOHE is in
general smaller than the orbital Hall effect (OHE). We compute furthermore the
thermal analogs, i.e., the spin and orbital Nernst effects, and their magnetic
counterparts. Here our calculations show that the magnetic spin and orbital
Nernst effects of Ni are substantially larger than those of Fe and Co.",2203.17025v2
2023-02-26,Spin-Orbit Coupling of Europa's Ice Shell and Interior,"Europa is an icy ocean world, differentiated into a floating ice shell and
solid interior, separated by a global ocean. The classical spin-orbit coupling
problem considers a satellite as a single rigid body, but in the case of
Europa, the existence of the subsurface ocean enables independent motion of the
ice shell and solid interior. This paper explores the spin-orbit coupling
problem for Europa from a dynamical perspective, yielding illuminating
analytical and numerical results. We determine that the spin behavior of Europa
is influenced by processes not captured by the classical single rigid body
spin-orbit coupling analysis. The tidal locking process for Europa is governed
by the strength of gravity-gradient coupling between the ice shell and solid
interior, with qualitatively different behavior depending on the scale of this
effect. In this coupled rigid model, the shell can potentially undergo large
angular displacements from the solid interior, and the coupling plays an
outsize role in the dynamical evolution of the moon, even without incorporating
the dissipative effects of shell non-rigidity. We additionally discuss the
effects of a realistic viscoelastic shell, and catalogue other torques that we
expect to be sub-dominant in Europa's spin dynamics, or whose importance is
unknown. Finally, we explore how the choice of tidal model affects the
resulting equilibrium spin state.",2302.13226v3
2023-06-09,Secular dynamics of stellar spin driven by planets inside Kozai-Lidov resonance,"In many exoplanetary systems with `hot Jupiters', it is observed that the
spin axes of host stars are highly misaligned to planetary orbital axes. In
this study, a possible channel is investigated for producing such a
misalignment under a hierarchical three-body system where the evolution of
stellar spin is subjected to the gravitational torque induced from the planet
inside Kozai--Lidov (KL) resonance. In particular, two special configurations
are explored in detail. The first one corresponds to the configuration with
planets at KL fixed points, and the second one corresponds to the
configurations with planets moving on KL librating cycles. When the planet is
located at the KL fixed point, the corresponding Hamiltonian model is of one
degree of freedom and there are three branches of libration centres for stellar
spin. When the planet is moving on KL cycles, the technique of Poincar\'e
section is taken to reveal global structures of stellar spin in phase space. To
understand the complex structures, perturbative treatments are adopted to study
rotational dynamics. It shows that analytical structures in phase portraits
under the resonant model can agree well with numerical structures arising in
Poincar\'e sections, showing that the complicated dynamics of stellar spin are
governed by the primary resonance under the unperturbed Hamiltonian model in
combination with the 2:1 (high-order and/or secondary) spin-orbit resonances.",2306.05639v1
1996-04-15,Evolution of the angular momentum of protogalaxies from tidal torques: Zel'dovich approximation,"The growth of the angular momentum L of protogalaxies induced by tidal
torques is reconsidered within the Zel'dovich approximation. We obtain a
general expression for the ensemble expectation value of the square of L in
terms of the first and second invariant of the inertia tensor of the Lagrangian
volume enclosing the protoobject's collapsing mass. We then specialize the
formalism to the particular case in which this volume is centered on a peak of
the smoothed Gaussian density field and approximated by an isodensity
ellipsoid. The result is the appropriate analytical estimate for the rms
angular momentum of peaks to be compared against simulations that make use of
the Hoffman-Ribak algorithm to set up a constrained density field that contains
a peak with given shape. Extending the work of Heavens & Peacock, we calculate
the joint probability distribution function for several spin parameters and
peak mass M using the distribution of peak shapes, for different initial power
spectra. The values of observed specific angular momentum versus mass are well
fitted by our theoretical isoprobability contours. In contrast, the observed
lower values for the specific angular momentum for ellipticals of the same mass
cannot be accounted for within our linear regime investigation, highlighting
the importance of strongly non-linear phenomena to explain the spin of such
objects.",9604077v1
2002-05-14,On Fossil Disk Models of Anomalous X-Ray Pulsars,"Currently, two competing models are invoked in order to explain the
observable properties of Anomalous X-ray Pulsars (AXPs). One model assumes that
AXP emission is powered by a strongly magnetized neutron star - i.e., a
magnetar. Other groups have postulated that the unusually long spin periods
associated with AXPs could, instead, be due to accretion. As there are severe
observational constraints on any binary accretion model, fossil disk models
have been suggested as a plausible alternative. Here we analyze fossil disk
models of AXPs in some detail, and point out some of their inherent
inconsistencies. For example, we find that, unless it has an exceptionally high
magnetic field strength, a neutron star in a fossil disk cannot be observed as
an AXP if the disk opacity is dominated by Kramers' law. However, standard
alpha-disk models show that a Kramers opacity must dominate for the case log B
> 12, making it unlikely that a fossil disk scenario can successfully produce
AXPs. Additionally, we find that in order to sufficiently spin down a neutron
star in a fossil disk, an unusually efficient propeller torque must be used.
Such torques are inconsistent with observations of other accreting sytems -
particularly High Mass X-ray Binaries. Thus, our analysis lends credence to the
magnetar model of AXPs.",0205212v1
2002-08-28,Complex rotation with internal dissipation. Applications to cosmic-dust alignment and to wobbling comets and asteroids,"Neutron stars, asteroids, comets, cosmic-dust granules, spacecraft, as well
as whatever other freely spinning body dissipate energy when they rotate about
any axis different from principal. We discuss the internal-dissipation-caused
relaxation of a freely precessing rotator towards its minimal-energy mode (mode
that corresponds to the spin about the maximal-inertia axis). While the body
nutates at some rate, the internal stresses and strains within the body
oscillate at frequencies both higher and lower than this rate. The internal
dissipation takes place mostly the second and higher harmonics. We discuss the
application of our findings to asteroids. Regarding the comets, estimates show
that the currently available angular resolution of spacecraft-based instruments
makes it possible to observe wobble damping within year- or maybe even
month-long spans of time. We also discuss cosmic-dust astrophysics; in
particular, the role played by precession damping in the dust alignment. We
show that this damping provides coupling of the grain's rotational and
vibrational degrees of freedom; this entails occasional flipping of dust grains
due to thermal fluctuations. During such a flip, grain preserves its angular
momentum, but the direction of torques arising from H2 formation reverses. As a
result, flipping grain will not rotate fast in spite of the action of
uncompensated H2 formation torques. The grains get ``thermally trapped,'' and
their alignment is marginal.",0208489v1
2004-01-08,The Pulsed Spectra of Two Extraordinary Pulsars,"We report on X-ray monitoring of two isolated pulsars within the same RXTE
field of view. PSR J1811-1925 in the young supernova remnant G11.2-0.3 has a
nearly sinusoidal pulse profile with a hard pulsed spectrum (photon index
\~1.2). The pulsar is a highly efficient (~ 1% of spin-down energy) emitter of
2-50 keV pulsed X-rays despite having a fairly typical B ~ 2e12 G magnetic
field. PSR J1809-1943/XTE J1810-197 is a newly discovered slow (P=5.54 s),
apparently isolated X-ray pulsar which increased in flux by a factor of ~100 in
2003 January. Nine months of monitoring observations have shown a decrease in
pulsed flux of ~ 30% without a significant change in its apparently thermal
spectrum (kT ~0.7 keV) or pulse profile. During this time, the spin-down torque
has fluctuated by a factor of ~ 2. Both the torque and the flux have remained
steady for the last 3 months, at levels consistent with a magnetar
interpretation.",0401111v1
2007-06-18,VLT/NACO observations of the High-Magnetic field radio pulsar PSR J1119-6127,"Recent radio observations have unveiled the existence of a number of radio
pulsars with spin-down derived magnetic fields in the magnetar range. However,
their observational properties appears to be more similar to classical radio
pulsars than to magnetars. To shed light on this puzzle we first have to
determine whether the spin-down derived magnetic field values for these radio
pulsars are indeed representative of the actual neutron star magnetic field or
if they are polluted, e.g. by the effects of a torque from a fallback disk. To
investigate this possibility, we have performed deep IR observations of one of
these high magnetic field radio pulsars (PSR J1119-6127) with the ESO VLT to
search for IR emission which can be associated with a disk. No IR emission is
detected from the pulsar position down to J=24, H=23, Ks=22. By comparing our
flux upper limits with the predictions of fallback disk models, we have found
that we can only exclude the presence of a disk with accretion rate dot M
>3x10^16 g/s. This lower limit cannot rule out the presence of a substantial
disk torque on the pulsar, which would then lead to overestimate the value of
the magnetic field inferred from P and dot P.",0706.2573v1
2008-09-16,Association of the 3:2 HFQPO Pairs with the Broad Fe K Line in XTE J1550-564 and GRO J1655-40,"Association of the high-frequency quasi-periodic oscillation (HFQPO) pairs
with the broad Fe K line in XTE J1550-564 and GRO J1655-40 is discussed based
on the magnetic coupling (MC) of a rotating black hole (BH) with its
surrounding disc. The 3:2 HFQPO pairs are interpreted by virtue of the inner
and outer hotspots arising from non-axisymmetric magnetic field, where the
inner hotspot is produced by a torque exerted at the inner edge of the disc,
and the outer hotspot is created by the screw instability of the large-scale
magnetic field. The very steep emissivity index is created predominantly by the
torque exerted at the inner edge of the disc. It turns out that the 3:2 HFQPO
pairs observed in the two sources can be fitted by tuning several model
parameters, such as the BH spin, and the main features of this model lie in
three aspects. (1) The condition for only one HFQPO is discussed based on the
two mechanisms for producing the 3:2 HFQPO pairs, (2) an explanation is given
for a systematic shift away from disc dominated flux with the increasing
power-law flux as the HFQPO pairs shift from the higher to lower frequencies,
which is consistent with the analysis given by Remillard et al. (2002), and (3)
the BH spin in XTE J1550-564 and GRO J1655-40 can be estimated by combining the
3:2 HFQPO pairs with the very steep emissivity index required for fitting the
broad Fe K emission line.",0809.2695v1
2012-05-15,The influence of fallback discs on the spectral and timing properties of neutron stars,"Fallback discs around neutron stars (NSs) are believed to be an expected
outcome of supernova explosions. Here we investigate the consequences of such a
common outcome for the timing and spectral properties of the associated NS
population, using Monte Carlo population synthesis models. We find that the
long-term torque exerted by the fallback disc can substantially influence the
late-time period distribution, but with quantitative differences which depend
on whether the initial spin distribution is dominated by slow or fast pulsars.
For the latter, a single-peaked initial spin distribution becomes bimodal at
later times. Timing ages tend to underestimate the real age of older pulsars,
and overestimate the age of younger ones. Braking indices cluster in the range
1.5 <~ n <~ 3 for slow-born pulsars, and -0.5 <~ n <~ 5 for fast-born pulsars,
with the younger objects found predominantly below n <~ 3. Large values of n,
while not common, are possible, and associated with torque transitions in the
NS+disc system. The 0.1-10 keV thermal luminosity of the NS+disc system is
found to be generally dominated by the disc emission at early times, t <~ 10^3
yr, but this declines faster than the thermal surface emission of the NS.
Depending on the initial parameters, there can be occasional periods in which
some NSs switch from the propeller to the accretion phase, increasing their
luminosity up to the Eddington limit for ~ 10^3-10^4 years.",1205.3259v1
2012-07-18,Spin torque antiferromagnetic nanooscillator in the presence of magnetic noise,"Spin-torque effects in antiferromagnetic (AFM) materials are of great
interest due to the possible applications as high-speed spintronic devices. In
the present paper we analyze the statistical properties of the current-driven
AFM nanooscillator that result from the white Gaussian noise of magnetic
nature. According to the peculiarities of deterministic dynamics, we derive the
Langevin and Fokker-Planck equations in the energy representation of two normal
modes. We find the stationary distribution function in the subcritical and
overcritical regimes and calculate the current dependence of the average
energy, energy fluctuation and their ratio (quality factor). The noncritical
mode shows the Boltzmann statistics with the current-dependent effective
temperature in the whole range of the current values. The effective temperature
of the other, i.e., soft, mode critically depends on the current in the
subcritical region. Distribution function of the soft mode follows the Gaussian
law above the generation threshold. In the overcritical regime, the total
average energy and the quality factor grow with the current value. This raises
the AFM nanooscillators to the promising candidates for active spintronic
components.",1207.4344v2
2013-09-03,Measurements of Cyclotron Features and Pulse Periods in the High-Mass X-Ray Binaries 4U 1538-522 and 4U 1907+09 with INTEGRAL,"We present a spectral and timing analysis of INTEGRAL observations of two
high mass X-ray binaries, 4U 1538-522 and 4U 1907+09. Our timing measurements
for 4U 1538-522 find the pulse period to have exhibited a spin-up trend until
approximately 2009, after which there is evidence for a torque reversal, with
the source beginning to spin down to the most recently-measured period of
525.407 +/- 0.001 s. The most recent INTEGRAL observations of 4U 1907+09 are
not found to yield statistically significant pulse periods due to the
significantly lower flux from the source compared to 4U 1538-522. A spectral
model consisting of a power-law continuum with an exponential cutoff and
modified by two cyclotron resonance scattering features is found to fit both
sources well, with the cyclotron scattering features detected at ~22 and ~49
keV for 4U 1538-522 and at ~18 and ~36 keV in 4U 1907+09. The spectral
parameters of 4U 1538-522 are generally not found to vary significantly with
flux, and there is little to no variation across the torque reversal. Examining
our results in conjunction with previous work, we find no evidence for a
correlation between cyclotron line energy and luminosity for 4U 1538-522. 4U
1907+09 shows evidence for a positive correlation between cyclotron line energy
and luminosity, which would make it the fourth, and lowest-luminosity,
cyclotron line source to exhibit this relationship",1309.0875v1
2013-09-12,Energy-Efficient and Robust Associative Computing with Electrically Coupled Dual Pillar Spin-Torque Oscillators,"Dynamics of coupled spin-torque oscillators can be exploited for non-Boolean
information processing. However, the feasibility of coupling large number of
STOs with energy-efficiency and sufficient robustness towards
parameter-variation and thermal-noise, may be critical for such computing
applications. In this work, the impacts of parameter-variation and
thermal-noise on two different coupling mechanisms for STOs, namely,
magnetic-coupling and electrical-coupling are analyzed. Magnetic coupling is
simulated using dipolar-field interactions. For electricalcoupling we employed
global RF-injection. In this method, multiple STOs are phase-locked to a common
RF-signal that is injected into the STOs along with the DC bias. Results for
variation and noise analysis indicate that electrical-coupling can be
significantly more robust as compared to magnetic-coupling. For
room-temperature simulations, appreciable phase-lock was retained among tens of
electrically coupled STOs for up to 20% 3s random variations in critical device
parameters. The magnetic-coupling technique however failed to retain locking
beyond ~3% 3s parameter-variations, even for small-size STO clusters with
near-neighborhood connectivity. We propose and analyze Dual-Pillar STO (DP-STO)
for low-power computing using the proposed electrical coupling method. We
observed that DP-STO can better exploit the electrical-coupling technique due
to separation between the biasing RF signal and its own RF output.",1309.3306v1
2013-10-25,Magnetic field structure and torque in accretion discs around millisecond pulsars,"Millisecond pulsars are rather weakly-magnetized neutron stars which are
thought to have been spun up by disc accretion, with magnetic linkage between
the star and the disc playing a key role. Their spin history depends
sensitively on details of the magnetic field structure, but idealized models
from the 1980s and 1990s are still commonly used for calculating the magnetic
field components. This paper is the third in a series presenting results from a
step-by-step analysis which we are making of the problem, starting with very
simple models and then progressively including additional features one at a
time, with the aim of gaining new insights into the mechanisms involved. In our
first two papers, the magnetic field structure in the disc was calculated for a
standard Shakura and Sunyaev model, by solving the magnetic induction equation
numerically in the stationary limit within the kinematic approximation; here we
consider a more general velocity field in the disc, including backflow. We find
that the profiles of the poloidal and toroidal components of the magnetic field
are fairly similar in the two cases but that they can be very different from
those in the models mentioned above, giving important consequences for the
torque exerted on the central object. In particular we find that, contrary to
what is usually thought, some regions of the disc outward of the co-rotation
point (rotating more slowly than the neutron star) may nevertheless contribute
to spinning up the neutron star on account of the detailed structure of the
magnetic field in those parts of disc.",1310.7012v1
2013-11-04,Switching of perpendicular magnetization by spin-orbit torques in the absence of external magnetic fields,"Magnetization switching by current-induced spin-orbit torques (SOTs) is of
great interest due to its potential applications for ultralow-power memory and
logic devices. In order to be of technological interest, SOT effects need to
switch ferromagnets with a perpendicular (out-of-plane) magnetization.
Currently, however, this typically requires the presence of an in-plane
external magnetic field, which is a major obstacle for practical applications.
Here we report for the first time on SOT-induced switching of out-of-plane
magnetized Ta/Co20Fe60B20/TaOx structures without the need for any external
magnetic fields, driven by in-plane currents. This is achieved by introducing a
lateral structural asymmetry into our devices during fabrication. The results
show that a new field-like SOT is induced by in-plane currents in such
asymmetric structures. The direction of the current-induced effective field
corresponding to this new field-like SOT is out-of-plane, which facilitates
switching of perpendicular magnets. This work thus provides a pathway towards
bias-field-free SOT devices.",1311.0929v1
2014-04-03,Dynamics of rotationally fissioned asteroids: Source of observed small asteroid systems,"We present a model of near-Earth asteroid (NEA) rotational fission and
ensuing dynamics that describes the creation of synchronous binaries and all
other observed NEA systems including: doubly synchronous binaries, high- e
binaries, ternary systems, and contact binaries. Our model only presupposes the
Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, ""rubble pile"" asteroid
geophysics, and gravitational interactions. The YORP effect torques a ""rubble
pile"" asteroid until the asteroid reaches its fission spin limit and the
components enter orbit about each other (Scheeres, D.J. [2007]. Icarus 189,
370-385). Non-spherical gravitational potentials couple the spin states to the
orbit state and chaotically drive the system towards the observed asteroid
classes along two evolutionary tracks primarily distinguished by mass ratio.
Related to this is a new binary process termed secondary fission - the
secondary asteroid of the binary system is rotationally accelerated via
gravitational torques until it fissions, thus creating a chaotic ternary
system. The initially chaotic binary can be stabilized to create a synchronous
binary by components of the fissioned secondary asteroid impacting the primary
asteroid, solar gravitational perturbations, and mutual body tides. These
results emphasize the importance of the initial component size distribution and
configuration within the parent asteroid. NEAs may go through multiple binary
cycles and many YORP-induced rotational fissions during their approximately 10
Myr lifetime in the inner Solar System. Rotational fission and the ensuing
dynamics are responsible for all NEA systems including the most commonly
observed synchronous binaries.",1404.0801v1
2014-10-03,Sharp magnetization jump at the first-order superconducting transition in Sr2RuO4,"The magnetization and magnetic torque of a high-quality single crystal of
Sr$_2$RuO$_4$ have been measured down to 0.1 K under a precise control of the
magnetic-field orientation. When the magnetic field is applied exactly parallel
to the $ab$ plane, a sharp magnetization jump $4\pi\delta M$ of $(0.74 \pm
0.15)$ G at the upper critical field $H_{{\rm c2},{ab}} \sim 15$ kOe with a
field hysteresis of 100 Oe is observed at low temperatures, evidencing a
first-order superconducting-normal transition. A strong magnetic torque
appearing when $H$ is slightly tilted away from the $ab$ plane confirms an
intrinsic anisotropy $\varGamma=\xi_a/\xi_c$ of as large as 60 even at 100 mK,
in contrast with the observed $H_{{\rm c2}}$ anisotropy of $\sim 20$. The
present results raise fundamental issues in both the existing spin-triplet and
spin-singlet scenarios, providing, in turn, crucial hints toward the resolution
of the superconducting nature of Sr$_2$RuO$_4$.",1410.0798v2
2014-10-21,Comprehensive and Macrospin-Based Magnetic Tunnel Junction Spin Torque Oscillator Model - Part I: Analytical Model of the MTJ STO,"Magnetic tunnel junction (MTJ) spin torque oscillators (STO) have shown the
potential to be used in a wide range of microwave and sensing applications. To
evaluate potential uses of MTJ STO technology in various applications, an
analytical model that can capture MTJ STO's characteristics, while enabling
system- and circuit-level designs, is of great importance. An analytical model
based on macrospin approximation is necessary for these designs since it allows
implementation in hardware description languages. This paper presents a new
macrospin-based, comprehensive and compact MTJ STO model, which can be used for
various MTJ STOs to estimate the performance of MTJ STOs together with their
application-specific integrated circuits. To adequately present the complete
model, this paper is divided into two parts. In Part I, the analytical model is
introduced and verified by comparing it against measured data of three
different MTJ STOs, varying the angle and magnitude of the magnetic field, as
well as the DC biasing current. The proposed analytical model is suitable for
being implemented in Verilog-A and used for efficient simulations at device-,
circuit- and system-levels. In Part II, the full Verilog-A implementation of
the analytical model with accurate phase noise generation is presented and
verified by simulations.",1410.5711v3
2014-10-21,Comprehensive and Macrospin-Based Magnetic Tunnel Junction Spin Torque Oscillator Model - Part II: Verilog-A Model Implementation,"The rapid development of the magnetic tunnel junction (MTJ) spin torque
oscillator (STO) technology demands an analytical model to enable building MTJ
STO-based circuits and systems so as to evaluate and utilize MTJ STOs in
various applications. In Part I of this paper, an analytical model based on the
macrospin approximation, has been introduced and verified by comparing it with
the measurements of three different MTJ STOs. In Part II, the full Verilog-A
implementation of the proposed model is presented. To achieve a reliable model,
an approach to reproduce the phase noise generated by the MTJ STO has been
proposed and successfully employed. The implemented model yields a time domain
signal, which retains the characteristics of operating frequency, linewidth,
oscillation amplitude and DC operating point, with respect to the magnetic
field and applied DC current. The Verilog-A implementation is verified against
the analytical model, providing equivalent device characteristics for the full
range of biasing conditions. Furthermore, a system that includes an MTJ STO and
CMOS RF circuits is simulated to validate the proposed model for system- and
circuit-level designs. The simulation results demonstrate that the proposed
model opens the possibility to explore STO technology in a wide range of
applications.",1410.5731v3
2016-04-07,Describing synchronization and topological excitations in arrays of magnetic spin torque oscillators through the Kuramoto model,"The collective dynamics in populations of magnetic spin torque oscillators
(STO) is an intensely studied topic in modern magnetism. Here, we show that
arrays of STO coupled via dipolar fields can be modeled using a variant of the
Kuramoto model, a well-known mathematical model in non-linear dynamics. By
investigating the collective dynamics in arrays of STO we find that the
synchronization in such systems is a finite size effect and show that the
critical coupling-for a complete synchronized state-scales with the number of
oscillators. Using realistic values of the dipolar coupling strength between
STO we show that this imposes an upper limit for the maximum number of
oscillators that can be synchronized. Further, we show that the lack of long
range order is associated with the formation of topological defects in the
phase field similar to the two-dimensional XY model of ferromagnetism. Our
results shed new light on the synchronization of STO, where controlling the
mutual synchronization of several oscillators is considered crucial for
applications.",1604.01927v3
2016-04-15,Super-harmonic injection locking of nano-contact spin-torque vortex oscillators,"Super-harmonic injection locking of single nano-contact (NC) spin-torque
vortex oscillators (STVOs) subject to a small microwave current has been
explored. Frequency locking was observed up to the fourth harmonic of the STVO
fundamental frequency $f_{0}$ in microwave magneto-electronic measurements. The
large frequency tunability of the STVO with respect to $f_{0}$ allowed the
device to be locked to multiple sub-harmonics of the microwave frequency
$f_{RF}$, or to the same sub-harmonic over a wide range of $f_{RF}$ by tuning
the DC current. In general, analysis of the locking range, linewidth, and
amplitude showed that the locking efficiency decreased as the harmonic number
increased, as expected for harmonic synchronization of a non-linear oscillator.
Time-resolved scanning Kerr microscopy (TRSKM) revealed significant differences
in the spatial character of the magnetization dynamics of states locked to the
fundamental and harmonic frequencies, suggesting significant differences in the
core trajectories within the same device. Super-harmonic injection locking of a
NC-STVO may open up possibilities for devices such as nanoscale frequency
dividers, while differences in the core trajectory may allow mutual
synchronisation to be achieved in multi-oscillator networks by tuning the
spatial character of the dynamics within shared magnetic layers.",1604.04462v1
2016-08-21,Manipulating antiferromagnets with magnetic fields: ratchet motion of multiple domain walls induced by asymmetric field pulses,"Future applications of antiferromagnets (AFs) in many spintronics devices
rely on the precise manipulation of domain walls. The conventional approach
using static magnetic fields is inefficient due to the low susceptibility of
AFs. Recently proposed electrical manipulation with spin-orbit torques is
restricted to metals with a specific crystal structure.
  Here we propose an alternative, broadly applicable approach: using asymmetric
magnetic field pulses to induce controlled ratchet motion of AF domain walls.
  The efficiency of this approach is based on three peculiarities of AF
dynamics. First, a time-dependent magnetic field couples with an AF order
parameter stronger than a static magnetic field, which leads to higher mobility
of the domain walls. Second, the rate of change of the magnetic field couples
with the spatial variation of the AF order parameter inside the domain and this
enables synchronous motion of multiple domain walls with the same structure.
Third, tailored asymmetric field pulses in combination with static friction can
prevent backward motion of domain walls and thus lead to the desired controlled
ratchet effect.
  The proposed use of an external field, rather than internal spin-orbit
torques, avoids any restrictions on size, conductivity, and crystal structure
of the AF material.
  We believe that our approach paves a way for the development of new AF-based
devices based on controlled motion of AF domain walls.",1608.05967v1
2017-07-05,Direct observation of magnetic droplet solitons in all-perpendicular spin torque nano-oscillators,"Magnetic droplets are non-topological dynamical solitons that can be
nucleated and sustained in nano-contact based spin torque nano-oscillators
(NC-STNOs) with perpendicular anisotropy free layers. While originally
predicted in all-perpendicular NC-STNOs, all experimental demonstrations have
so far relied on orthogonal devices with an in-plane polarizing layer that
requires a strong magnetic field for droplet nucleation. Here, we instead show
the nucleation and sustained operation of magnetic droplets in
all-perpendicular NC-STNOs in modest perpendicular fields and over a wide range
of nano-contact size. The droplet is observed electrically as an intermediate
resistance state accompanied by broadband low-frequency microwave noise. Using
canted fields, which introduce a non-zero relative angle between the free and
fixed layer, the actual droplet precession frequency can also be determined.
Finally, the droplet size, its perimeter width, and its fully reversed core are
directly observed underneath a 80 nm diameter nano-contact using scanning
transmission x-ray microscopy on both the Ni and Co edges. The droplet diameter
is 150 nm, i.e. almost twice the nominal size of the nano-contact, and the
droplet has a perimeter width of about 70 nm.",1707.01595v1
2017-09-20,Efficient and controlled domain wall nucleation for magnetic shift registers,"Ultrathin ferromagnetic strips with high perpendicular anisotropy have been
proposed for the development of memory devices where the information is coded
in tiny domains separated by domain walls. The design of practical devices
requires creating, manipulating and detecting domain walls in ferromagnetic
strips. Recent observations have shown highly efficient current-driven domain
wall dynamics in multilayers lacking structural symmetry, where the walls adopt
a chiral structure and can be driven at high velocities. However, putting such
a device into practice requires the continuous and synchronous injection of
domain walls as the first step. Here, we propose and demonstrate an efficient
and simple scheme for nucleating domain walls using the symmetry of the spin
orbit torques. Trains of short sub-nanosecond current pulses are injected in a
double bit line to generate a localized longitudinal Oersted field in the
ferromagnetic strip. Simultaneously, other current pulses are injected through
the heavy metal under the ferromagnetic strip. Notably, the Slonczewski-like
spin orbit torque assisted by the Oersted field allows the controlled injection
of a series of domain walls, giving rise to a controlled manner for writing
binary information and, consequently, to the design of a simple and efficient
domain wall shift register.",1709.06753v1
2017-11-08,Vowel recognition with four coupled spin-torque nano-oscillators,"Substantial evidence indicates that the brain uses principles of non-linear
dynamics in neural processes, providing inspiration for computing with
nanoelectronic devices. However, training neural networks composed of dynamical
nanodevices requires finely controlling and tuning their coupled oscillations.
In this work, we show that the outstanding tunability of spintronic
nano-oscillators can solve this challenge. We successfully train a hardware
network of four spin-torque nano-oscillators to recognize spoken vowels by
tuning their frequencies according to an automatic real-time learning rule. We
show that the high experimental recognition rates stem from the high frequency
tunability of the oscillators and their mutual coupling. Our results
demonstrate that non-trivial pattern classification tasks can be achieved with
small hardware neural networks by endowing them with non-linear dynamical
features: here, oscillations and synchronization. This demonstration is a
milestone for spintronics-based neuromorphic computing.",1711.02704v4
2017-11-29,Thermal contribution to the spin-orbit torque in metallic/ferrimagnetic systems,"We report a systematic study of current-induced perpendicular magnetization
switching in W/Co$_{x}$Tb$_{1-x}$/Al thin films with strong perpendicular
magnetic anisotropy. Various Co$_{x}$Tb$_{1-x}$ ferrimagnetic alloys with
different magnetic compensation temperatures are presented. The systems are
characterized using MOKE, SQUID and anomalous Hall resistance at different
cryostat temperature ranging from 10 K to 350 K. The current-switching
experiments are performed in the spin-orbit torque geometry where the current
pulses are injected in plane and the magnetization reversal is detected by
measuring the Hall resistance. The full reversal magnetization has been
observed in all samples. Some experimental results could only be explained by
the strong sample heating effect during the current pulses injection. We have
found that, for a given composition $x$ and switching polarity, the devices
always reach the same temperature $\textit{T}_{switch}(x)$ before switching
independently of the cryostat temperature. $\textit{T}_{switch}$ seems to scale
with the Curie temperature of the Co$_{x}$Tb$_{1-x}$ ferrimagnetic alloys. This
explains the evolution of the critical current (and critical current density)
as a function of the alloy concentration. Future application could take
advantages of this heating effect which allows reducing the in-plane external
field. Unexpected double magnetization switching has been observed when the
heat generated by the current allows crosses the compensation temperature.",1711.10790v1
2018-06-13,Ultra-fast wide band spectrum analyzer based on a rapidly tuned spin-torque nano-oscillator,"A spintronic method of ultra-fast broadband microwave spectrum analysis is
proposed. It uses a rapidly tuned spin torque nano-oscillator (STNO), and does
not require injection locking. This method treats an STNO generating a
microwave signal as an element with an oscillating resistance. When an external
signal is applied to this ""resistor"" for analysis, it is mixed with the signal
generated by the STNO. The resulting mixed voltage contains the ""sum"" and
""difference"" frequencies, and the latter produces a DC component when the
external frequency matches the frequency generated by the STNO. The mixed
voltage is processed using a low pass filter to exclude the ""sum"" frequency
components, and a matched filter to exclude the dependence of the resultant DC
voltage on the phase difference between the two signals. It is found
analytically and by numerical simulation, that the proposed spectrum analyzer
has a frequency resolution at a theoretical limit in a real-time scanning
bandwidth of 10~GHz, and a frequency scanning rate above 1~GHz/ns, while
remaining sensitive to signal power as low as the Johnson-Nyquist thermal noise
floor.",1806.04806v1
2019-11-10,Stochastic Computing Implemented by Skyrmionic Logic Devices,"Magnetic skyrmion, topologically non-trivial spin texture, has been
considered as promising information carrier in future electronic devices
because of its nanoscale size, low depinning current density and high motion
velocity. Despite the broad interests in skyrmion racetrack memory, researchers
have been recently exploiting logic functions enabled by using the
particle-like behaviors of skyrmions. These functions can be applied to
unconventional computing, such as stochastic computing (SC), which treats data
as probabilities and is superior to binary computing due to its simplicity of
logic operation. In this work, we demonstrate SC implemented by skyrmionic
logic devices. We propose a skyrmionic AND-OR logic device as a multiplier in
the stochastic domain and two skyrmionic multiplexer (MUX) logic devices as
stochastic adders. With the assist of voltage controlled magnetic anisotropy
(VCMA), the precise control of skyrmions collision is not required in the
skyrmionic AND-OR logic device, thus improving the operation robustness. In the
two MUX logic devices, skyrmions can be driven by Zhang-Li torque or spin orbit
torque (SOT). Particularly, we can flexibly regulate the skyrmion motion by
VCMA or voltage controlled Dzyaloshinskii-Moriya Interaction (VCDMI) in the SOT
case. Furthermore, 3-bit stochastic multiplier and adder are demonstrated by
micromagnetic simulations. In addition, simulations in synthetic
antiferromagnets (SAF) show that the performance of our skyrmionic logic gates
can be optimized through advanced materials. Our work opens up perspective to
implement SC using skyrmionic logic devices.",1911.03917v2
2016-12-22,Co-sputtered PtMnSb thin films and PtMnSb/Pt bilayers for spin-orbit torque investigations,"The manipulation of the magnetization by spin-orbit torques (SOTs) has
recently been extensively studied due to its potential for efficiently writing
information in magnetic memories. Particular attention is paid to
non-centrosymmetric systems with space inversion asymmetry, where SOTs emerge
even in single-layer materials. The half-metallic half-Heusler PtMnSb is an
interesting candidate for studies of this intrinsic SOT. Here, we report on the
growth and epitaxial properties of PtMnSb thin films and PtMnSb/Pt bilayers
deposited on MgO(001) substrates by dc magnetron co-sputtering at high
temperature in ultra-high vacuum. The film properties were investigated by
x-ray diffraction, x-ray reflectivity, atomic force microscopy, and electron
microscopy. Thin PtMnSb films present a monocrystalline C1b phase with (001)
orientation, coexisting at increasing thickness with a polycrystalline phase
with (111) texture. Films thinner than about 5 nm grow in islands, whereas
thicker films grow layer-by-layer, forming a perfect MgO/PtMnSb interface. The
thin PtMnSb/Pt bilayers also show island growth and a defective transition
zone, while thicker films grow layer-by-layer and Pt grows epitaxially on the
half-Heusler compound without significant interdiffusion.",1612.07614v1
2019-05-03,Toggle Spin-Orbit Torque MRAM with Perpendicular Magnetic Anisotropy,"Spin-orbit torque (SOT) is a promising switching mechanism for magnetic
random-access memory (MRAM) as a result of the potential for improved switching
speed and energy-efficiency. It is of particular interest to develop an
SOT-MRAM device with perpendicular magnetic anisotropy (PMA) in order to
leverage the greater density and thermal stability achievable with PMA as
opposed to in-plane magnetic anisotropy. However, the orthogonality between SOT
and PMA prevents deterministic directional switching without an additional
device component that breaks the symmetry, such as an external magnetic field
or complex physical structure; not only do these components complicate
fabrication, they also are not robust to variations in fabrication and applied
switching current. This letter therefore proposes a simple SOT-MRAM structure
with PMA in which deterministic toggle switching is achieved without requiring
additional device components. Furthermore, this toggle PMA SOT-MRAM is shown to
be far more robust than previous approaches for directional PMA SOT-MRAM, with
greater than 50% tolerance to applied switching current magnitude. This letter
describes the physical structure and toggle switching mechanism, provides
micromagnetic simulations demonstrating its feasibility, and evaluates the
robustness and tolerance to material parameters to guide the fabrication of
optimized devices that will jumpstart the third generation of MRAM.",1905.01125v1
2019-04-14,"The First Day in the Life of a Magnetar: Evolution of the Inclination Angle, Magnetic Dipole Moment and Braking Index of Millisecond Magnetars During Gamma-Ray Burst Afterglows","The afterglow emission of some gamma-ray bursts (GRBs) show a shallow decay
(plateau) phase implying continuous injection of energy. The source of this
energy is very commonly attributed to the spin-down power of a nascent
millisecond magnetar. The magnetic dipole radiation torque is considered to be
the mechanism causing the spin-down of the neutron star. This torque has a
component working for the alignment of the angle between rotation and magnetic
axis, i.e., inclination angle, which has been neglected in modelling GRB
afterglow light curves. Here, we demonstrate the evolution of the inclination
angle and magnetic dipole moment of nascent magnetars associated with GRBs. We
constrain the initial inclination angle, magnetic dipole moment and rotation
period of seven magnetars by modelling the seven long-GRB afterglow light
curves. We find that, in its first day, the inclination angle of a magnetar
decreases rapidly. The rapid alignment of the magnetic and rotation axis may
address the lack of persistent radio emission from mature magnetars. We also
find that in three cases the magnetic dipole moments of magnetars decrease
exponentially to a value a few times smaller than the initial value. The
braking index of nascent magnetars, as a result of the alignment and magnetic
dipole moment decline, is variable during the afterglow phase and always
greater than three.",1904.06769v2
2019-07-08,Angular momentum transport in massive stars and natal neutron star rotation rates,"The internal rotational dynamics of massive stars are poorly understood. If
angular momentum (AM) transport between the core and the envelope is
inefficient, the large core AM upon core-collapse will produce rapidly rotating
neutron stars (NSs). However, observations of low-mass stars suggest an
efficient AM transport mechanism is at work, which could drastically reduce NS
spin rates. Here we study the effects of the baroclinic instability and the
magnetic Tayler instability in differentially rotating radiative zones.
Although the baroclinic instability may occur, the Tayler instability is likely
to be more effective for AM transport. We implement Tayler torques as
prescribed by Fuller et al. 2019 into models of massive stars, finding they
remove the vast majority of the core's AM as it contracts between the main
sequence and helium-burning phases of evolution. If core AM is conserved during
core-collapse, we predict natal NS rotation periods of $P_{\rm NS} \approx
50-200 \, {\rm ms}$, suggesting these torques help explain the relatively slow
rotation rates of most young NSs, and the rarity of rapidly rotating
engine-driven supernovae. Stochastic spin-up via waves just before
core-collapse, asymmetric explosions, and various binary evolution scenarios
may increase the initial rotation rates of many NSs.",1907.03713v2
2019-09-20,Field-free spin-orbit torque switching through domain wall motion,"Deterministic current-induced spin-orbit torque (SOT) switching of
magnetization in a heavy transition metal/ferromagnetic metal/oxide magnetic
heterostructure with the ferromagnetic layer being perpendicularly-magnetized
typically requires an externally-applied in-plane field to break the switching
symmetry. We show that by inserting an in-plane magnetized ferromagnetic layer
CoFeB underneath the conventional W/CoFeB/MgO SOT heterostructure,
deterministic SOT switching of the perpendicularly-magnetized top CoFeB layer
can be realized without the need of in-plane bias field. Kerr imaging study
further unveils that the observed switching is mainly dominated by domain
nucleation and domain wall motion, which might limit the potentiality of using
this type of multilayer stack design for nanoscale SOT-MRAM application.
Comparison of the experimental switching behavior with micromagnetic
simulations reveals that the deterministic switching in our devices cannot be
explained by the stray field contribution of the in-plane magnetized layer, and
the roughness-caused N\'eel coupling effect might play a more important role in
achieving the observed field-free deterministic switching.",1909.09604v1
2019-12-13,Nonmutual torques and the unimportance of motility for long-range order in two-dimensional flocks,"As the constituent particles of a flock are polar and in a driven state,
their interactions must, in general, be fore-aft asymmetric and non-reciprocal.
Within a model that explicitly retains the classical spin angular momentum
field of the particles we show that the resulting asymmetric contribution to
interparticle torques, if large enough, leads to a buckling instability of the
flock. Precisely this asymmetry also yields a natural mechanism for a
difference between the speed of advection of information along the flock and
the speed of the flock itself, concretely establishing that the absence of
detailed balance, and not merely the breaking of Galilean invariance, is
crucial for this distinction. To highlight this we construct a model of
asymmetrically interacting spins fixed to lattice points and demonstrate that
the speed of advection of polarisation remains non-zero. We delineate the
conditions on parameters and wavenumber for the existence of the buckling
instability. Our theory should be consequential for interpreting the behaviour
of real animal groups as well as experimental studies of artificial flocks
composed of polar motile rods on substrates.",1912.06581v4
2020-06-07,Magnetocrystalline anisotropy of the easy-plane metallic antiferromagnet Fe$_2$As,"Magnetocrystalline anisotropy is a fundamental property of magnetic materials
that determines the dynamics of magnetic precession, the frequency of spin
waves, the thermal stability of magnetic domains, and the efficiency of
spintronic devices. We combine torque magnetometry and density functional
theory calculations to determine the magnetocrystalline anisotropy of the
metallic antiferromagnet Fe$_2$As. Fe$_2$As has a tetragonal crystal structure
with the N\'eel vector lying in the (001) plane. We report that the four-fold
magnetocrystalline anisotropy in the (001)-plane of Fe$_2$As is extremely
small, ${K_{22}} = - 150~{\rm{ J/}}{{\rm{m}}^{\rm{3}}}$ at T = 4 K, much
smaller than perpendicular magnetic anisotropy of ferromagnetic structure
widely used in spintronics device. ${K_{22}}$ is strongly temperature dependent
and close to zero at T > 150 K. The anisotropy ${K_1}$ in the (010) plane is
too large to be measured by torque magnetometry and we determine ${K_1} =
-830~{\rm{ kJ/}}{{\rm{m}}^{\rm{3}}}$ using first-principles density functional
theory. Our simulations show that the contribution to the anisotropy from
classical magnetic dipole-dipole interactions is comparable to the contribution
from spin-orbit coupling. The calculated four-fold anisotropy in the (001)
plane ${K_{22}}$ ranges from $- 292~{\rm{ J/}}{{\rm{m}}^{\rm{3}}}$ to
$280~{\rm{ J/}}{{\rm{m}}^{\rm{3}}}$, the same order of magnitude as the
measured value. We use ${K_1}$ from theory to predict the frequency and
polarization of the lowest frequency antiferromagnetic resonance mode and find
that the mode is linearly polarized in the (001)-plane with $f = $ 670 GHz.",2006.04192v1
2020-07-24,The Sublimative Evolution of (486958) Arrokoth,"We consider the history of New Horizons target (486958) Arrokoth in the
context of its sublimative evolution. Shortly after the Sun's protoplanetary
disk (PPD) cleared, the newly intense sunlight sparked a sublimative period in
Arrokoth's early history that lasted for ~10-100 Myr. Although this sublimation
was too weak to significantly alter Arrokoth's spin state, it could drive mass
transport around the surface significant enough to erase topographic features
on length scales of ~10-100 m. This includes craters up to ~50-500 m in
diameter, which suggests that the majority of Arrokoth's craters may not be
primordial (dating from the merger of Arrokoth's lobes), but rather could date
from after the end of this sublimative period. Thereafter, Arrokoth entered a
Quiescent Period (which lasts to the present day), in which volatile production
rates are at least 13 orders of magnitude less than the ~10^24 molecules/s
detection limit of the New Horizons spacecraft (Lisse et al. 2020). This is
insufficient to drive either mass transport or sublimative torques. These
results suggest that the observed surface of Arrokoth is not primordial, but
rather dates from the Quiescent Period. By contrast, the inability of
sublimative torques to meaningfully alter Arrokoth's rotation state suggests
that its shape is indeed primordial, and its observed rotation is
representative of its spin state after formation.",2007.12657v1
2020-12-10,Pulse-width and Temperature Dependence of Memristive Spin-Orbit Torque Switching,"It is crucial that magnetic memory devices formed from magnetic
heterostructures possess sizable spin-orbit torque (SOT) efficiency and high
thermal stability to realize both efficient SOT control and robust storage of
such memory devices. However, most previous studies on various types of
magnetic heterostructures have focused on only their SOT efficiencies, whereas
the thermal stabilities therein have been largely ignored. In this work, we
study the temperature-dependent SOT and stability properties of two types of
W-based heterostructures, namely W/CoFeB/MgO (standard) and CoFeB/W/CoFeB/MgO
(field-free), from 25 ^{\circ}C (298 K) to 80 ^{\circ}C (353 K). Via
temperature-dependent SOT characterization, the SOT efficacies for both systems
are found to be invariant within the range of studied temperatures.
Temperature-dependent current-induced SOT switching measurements further show
that the critical switching current densities decrease with respect to the
ambient temperature; thermal stability factors ({\Delta}) are also found to
degrade as temperature increases for both standard and field-free systems. The
memristive SOT switching behaviors in both systems with various pulse-widths
and temperatures are also examined. Our results suggest that although the SOT
efficacy is robust against thermal effects, the reduction of {\Delta} at
elevated temperatures could be detrimental to standard memory as well as
neuromorphic (memristive) device applications.",2012.05531v1
2021-01-21,Field-free spin-orbit torque-induced switching of perpendicular magnetization in a ferrimagnetic layer with vertical composition gradient,"Current-induced spin-orbit torques (SOTs) are of interest for fast and
energy-efficient manipulation of magnetic order in spintronic devices. To be
deterministic, however, switching of perpendicularly magnetized materials by
SOT requires a mechanism for in-plane symmetry breaking. Existing methods to do
so involve the application of an in-plane bias magnetic field, or incorporation
of in-plane structural asymmetry in the device, both of which can be difficult
to implement in practical applications. Here, we reported bias-field-free SOT
switching in a single perpendicular CoTb layer with an engineered vertical
composition gradient. The vertical structural inversion asymmetry induces
strong intrinsic SOTs and a gradient-driven Dzyaloshinskii-Moriya interaction
(g-DMI), which breaks the in-plane symmetry during the switching process.
Micromagnetic simulations are in agreement with experimental results, and
elucidate the role of g-DMI in the deterministic switching. This
bias-field-free switching scheme for perpendicular ferrimagnets with g-DMI
provides a strategy for efficient and compact SOT device design.",2101.08518v1
2021-03-29,Spin-orbit torques in strained PtMnSb from first principles,"We compute spin-orbit torques (SOTs) in strained PtMnSb from first
principles. We consider both tetragonal strain and shear strain. We find a
strong linear dependence of the field-like SOTs on these strains, while the
antidamping SOT is only moderately sensitive to shear strain and even
insensitive to tetragonal strain. We also study the dependence of the SOT on
the magnetization direction. In order to obtain analytical expressions suitable
for fitting our numerical \textit{ab-initio} results we derive a general
expansion of the SOT in terms of all response tensors that are allowed by
crystal symmetry. Our expansion includes also higher-order terms beyond the
usually considered lowest order. We find that the dependence on the strain is
much smaller for the higher-order terms than for the lowest order terms. In
order to judge the sensitivity of the SOT on the exchange correlation potential
we compute the SOT in both GGA and LDA. We find that the higher-order terms
depend significantly on the exchange-correlation potential, while the lowest
order terms are insensitive to it. Since the higher-order terms are small in
comparison to the lowest order terms the total SOT is insensitive to the
exchange correlation potential in strained PtMnSb.",2103.15663v2
2021-06-28,Stabilization of a nonlinear bullet coexisting with a Bose-Einstein condensate in a rapidly cooled magnonic system driven by a spin-orbit torque,"We have recently shown that injection of magnons into a magnetic dielectric
via the spin-orbit torque (SOT) effect in the adjacent layer of a heavy metal
subjected to the action of short (0.1 $\mu$s) current pulses allows for control
of a magnon Bose-Einstein Condensate (BEC). Here, the BEC was formed in the
process of rapid cooling (RC), when the electric current heating the sample is
abruptly terminated. In the present study, we show that the application of a
longer (1.0 $\mu$s) electric current pulse triggers the formation of a
nonlinear localized magnonic bullet below the linear magnon spectrum. After
pulse termination, the magnon BEC, as before, is formed at the bottom of the
linear spectrum, but the nonlinear bullet continues to exist, stabilized for
additional 30 ns by the same process of RC-induced magnon condensation. Our
results suggest that a stimulated condensation of excess magnons to all highly
populated magnonic states occurs.",2106.14710v1
2021-07-07,Rapid parameter estimation of a two-component neutron star model with spin wandering using a Kalman filter,"The classic, two-component, crust-superfluid model of a neutron star can be
formulated as a noise-driven, linear dynamical system, in which the angular
velocities of the crust and superfluid are tracked using a Kalman filter
applied to electromagnetic pulse timing data and gravitational wave data, when
available. Here it is shown how to combine the marginal likelihood of the
Kalman filter and nested sampling to estimate full posterior distributions of
the six model parameters, extending previous analyses based on a
maximum-likelihood approach. The method is tested across an astrophysically
plausible parameter domain using Monte Carlo simulations. It recovers the
injected parameters to $\lesssim 10$ per cent for time series containing $\sim
10^3$ samples, typical of long-term pulsar timing campaigns. It runs
efficiently in $\mathcal O(1)$ CPU-hr for data sets of the above size. In a
present-day observational scenario, when electromagnetic data are available
only, the method accurately estimates three parameters: the relaxation time,
the ensemble-averaged spin-down of the system, and the amplitude of the
stochastic torques applied to the crust. In a future observational scenario,
where gravitational wave data are also available, the method also estimates the
ratio between the moments of inertia of the crust and the superfluid, the
amplitude of the stochastic torque applied to the superfluid, and the
crust-superfluid lag. These empirical results are consistent with a formal
identifiability analysis of the linear dynamical system.",2107.03047v1
2022-02-22,Time Division Multiplexing Ising Computer Using Single Tunable True Random Number Generator Based on Spin Torque Nano-Oscillator,"Ising computer is a powerful computation scheme to deal with NP-hard
optimization problems that cannot be efficiently addressed by conventional
computers. A robust probabilistic bit (P-Bit) which is realized by a hardware
entity fluctuating in time between -1 and 1 plays a key role in the success of
Ising computer. Spintronics technology, such as stochastic nanomagnet, is
recently proposed as a good platform for the hardware emulation of P-Bit. Here,
we report, for the first time, a Time Division Multiplexing (TDM) Ising
computer using single tunable true random number generator which is comprised
of a Spin Torque Nano-Oscillator (STNO). First, the intrinsic frequency
fluctuation of the STNO is utilized to design a simple digital true random
number generator (TRNG). The true random number generator is further evolved
into a tunable random number generator to act as a P-Bit. Second, in order to
accomplish combinational optimization with our proposed P-Bit under Ising
model, a novel incremental coupling rule is proposed. With such coupling rule
between P-Bit array, high fidelity NOT and XOR logic gate is demonstrated.
Third, it is proposed that our digital TRNG can be simply reused acting as a
P-Bit array by time division multiplexing. The whole Ising computer can be
implemented by one single STNO, and integer factorization of as high as 87%
accuracy rate is achieved.",2202.10634v1
2022-06-16,A vector magnetometer based on a single spin-orbit torque anomalous Hall device,"In many applications, the ability to measure the vector information of a
magnetic field with high spatial resolution and low cost is essential, but it
is still a challenge for existing magnetometers composed of multiple sensors.
Here, we report a single-device based vector magnetometer, which is enabled by
spin-orbit torque, capable of measuring a vector magnetic field using the
harmonic Hall resistances of a superparamagnetic ferromagnet (FM)/heavy metal
(HM) bilayer. Under an ac driving current, the first and second harmonic Hall
resistances of the FM/HM bilayer show a linear relationship with the vertical
and longitudinal component (along the current direction) of the magnetic field,
respectively. By employing a L-shaped Hall device with two orthogonal arms, we
can measure all the three field components simultaneously, so as to detect both
the amplitude and direction of magnetic field in a three-dimensional space. As
proof of concepts, we demonstrate both angular position sensing on the three
coordinate planes and vector mapping of magnetic field generated by a permanent
magnet, both of which are in good agreement with the simulation results.
Crosstalk between vertical and longitudinal field components at large field is
discussed using theoretical models.",2206.07888v1
2022-08-29,Room temperature spin-orbit torque efficiency and magnetization switching in SrRuO3-based heterostructures,"Spin-orbit torques (SOTs) from transition metal oxides (TMOs) in conjunction
with magnetic materials have recently attracted tremendous attention for
realizing high-efficient spintronic devices. SrRuO3 is a promising candidate
among TMOs due to its large and tunable SOT-efficiency as well as high
conductivity and chemical stability. However, a further study for benchmarking
the SOT-efficiency and realizing SOT-driven magnetization switching in SrRuO3
is still highly desired so far. Here, we systematically study the SOT
properties of high-quality SrRuO3 thin film heterostructuring with different
magnetic alloys of both IMA and PMA configuration by the harmonic Hall voltage
technique. Our results indicate that SrRuO3 possesses pronounced SOT-efficiency
of about 0.2 at room temperature regardless of the magnetic alloys, which is
comparable to typical heavy metals (HMs). Furthermore, we achieve SOT-driven
magnetization switching with a low threshold current density of 3.8x10^10
A/m^2, demonstrating the promising potential of SrRuO3 for practical devices.
By making a comprehensive comparison with HMs, our work unambiguously
benchmarks the SOT properties and concludes the advantages of SrRuO3, which may
bring more diverse choices for SOT applications by utilizing hybrid-oxide/metal
and all-oxide systems.",2208.13574v1
2022-09-13,Integrated Artificial Neural Network with Trainable Activation Function Enabled by Topological Insulator-based Spin-Orbit Torque Devices,"Non-volatile memristors offer a salient platform for artificial neural
network (ANN), but the integration of different function blocks into one
hardware system remains challenging. Here we demonstrate the implementation of
brain-like synaptic (SOT-S) and neuronal (SOT-N) functions in the Bi2Te3/CrTe2
heterostructure-based spin-orbit torque (SOT) device. The SOT-S unit exhibits
highly linear (linearity error < 4.19%) and symmetrical long-term
potentiation/depression process, resulting in better performance compared to
other memristor synapses. Meanwhile, the Sigmoid-shape transition curve
inherited in the SOT-N cell replaces the software-based activation function
block, hence reducing the system complexity. On this basis, we employ a
serial-connected, voltage-mode sensing ANN architecture to enhance the
vector-matrix multiplication signal strength with low reading error of 0.61%.
Furthermore, the trainable activation function of SOT-N enables the integrated
SOT-ANN to execute the Batch Normalization algorithm and activation operation
within one clock cycle, which bring about improved on/off-chip training
performance close to the ideal baseline.",2209.06001v2
2022-11-24,Electrical Tunable Spintronic Neuron with Trainable Activation Function,"Spintronic devices have been widely studied for the hardware realization of
artificial neurons. The stochastic switching of magnetic tunnel junction driven
by the spin torque is commonly used to produce the sigmoid activation function.
However, the shape of the activation function in previous studies is fixed
during the training of neural network. This restricts the updating of weights
and results in a limited performance. In this work, we exploit the physics
behind the spin torque induced magnetization switching to enable the dynamic
change of the activation function during the training process. Specifically,
the pulse width and magnetic anisotropy can be electrically controlled to
change the slope of activation function, which enables a faster or slower
change of output required by the backpropagation algorithm. This is also
similar to the idea of batch normalization that is widely used in the machine
learning. Thus, this work demonstrates that the algorithms are no longer
limited to the software implementation. They can in fact be realized by the
spintronic hardware using a single device. Finally, we show that the accuracy
of hand-written digit recognition can be improved from 88% to 91.3% by using
these trainable spintronic neurons without introducing additional energy
consumption. Our proposals can stimulate the hardware realization of spintronic
neural networks.",2211.13391v1
2023-02-02,Spin-orbit torque switching in 2D ferromagnet / topological insulator heterostructure grown by molecular beam epitaxy,"Topological insulators (TIs) are a promising class of materials for
manipulating the magnetization of an adjacent ferromagnet (FM) through the
spin-orbit torque (SOT) mechanism. However, current studies combining TIs with
conventional FMs present large device-to-device variations, resulting in a
broad distribution of SOT magnitudes. It has been identified that the
interfacial quality between the TI and the FM is of utmost importance in
determining the nature and efficiency of the SOT. To optimize the SOT magnitude
and enable ultra-low-power magnetization switching, an atomically smooth
interface is necessary. To this end, we have developed the growth of a full van
der Waals FM/TI heterostructure by molecular beam epitaxy. The compensated TI
(Bi0.4Sb0.6)2Te3 and ferromagnetic Fe3GeTe2 (FGT) were chosen because of their
exceptional crystalline quality, low carrier concentration in BST and
relatively large Curie temperature and perpendicular magnetic anisotropy in
FGT. We characterized the magnitude of the SOTs by using thorough harmonic
magnetotransport measurements and showed that the magnetization of an ultrathin
FGT film could be switched with a current density Jc < 10^10 A/m^2. In
comparison to previous studies utilizing traditional FMs, our findings are
highly reliable, displaying little to no variation between devices.",2302.01101v1
2023-05-09,Robust negative longitudinal magnetoresistance and spin-orbit torque in sputtered Pt3Sn topological semimetal,"Contrary to topological insulators, topological semimetals possess a
nontrivial chiral anomaly that leads to negative magnetoresistance and are
hosts to both conductive bulk states and topological surface states with
intriguing transport properties for spintronics. Here, we fabricate
highly-ordered metallic Pt3Sn and Pt3SnxFe1-x thin films via sputtering
technology. Systematic angular dependence (both in-plane and out-of-plane)
study of magnetoresistance presents surprisingly robust quadratic and linear
negative longitudinal magnetoresistance features for Pt3Sn and Pt3SnxFe1-x,
respectively. We attribute the anomalous negative longitudinal
magnetoresistance to the type-II Dirac semimetal phase (pristine Pt3Sn) and/or
the formation of tunable Weyl semimetal phases through symmetry breaking
processes, such as magnetic-atom doping, as confirmed by first-principles
calculations. Furthermore, Pt3Sn and Pt3SnxFe1-x show the promising performance
for facilitating the development of advanced spin-orbit torque devices. These
results extend our understanding of chiral anomaly of topological semimetals
and can pave the way for exploring novel topological materials for spintronic
devices.",2305.05801v1
2023-06-05,Stochastic p-Bits Based on Spin-Orbit Torque Magnetic Tunnel Junctions,"Stochastic p-Bit devices play a pivotal role in solving NP-hard problems,
neural network computing, and hardware accelerators for algorithms such as the
simulated annealing. In this work, we focus on Stochastic p-Bits based on
high-barrier magnetic tunnel junctions (HB-MTJs) with identical stack structure
and cell geometry, but employing different spin-orbit torque (SOT) switching
schemes. We conducted a comparative study of their switching probability as a
function of pulse amplitude and width of the applied voltage. Through
experimental and theoretical investigations, we have observed that the Y-type
SOT-MTJs exhibit the gentlest dependence of the switching probability on the
external voltage. This characteristic indicates superior tunability in
randomness and enhanced robustness against external disturbances when Y-type
SOT-MTJs are employed as stochastic p-Bits. Furthermore, the random numbers
generated by these Y-type SOT-MTJs, following XOR pretreatment, have
successfully passed the National Institute of Standards and Technology (NIST)
SP800-22 test. This comprehensive study demonstrates the high performance and
immense potential of Y-type SOT-MTJs for the implementation of stochastic
p-Bits.",2306.02780v1
2023-06-20,High frequency oscillations in spin-torque nano oscillator due to bilinear coupling,"Exchange coupling in an interfacial context is crucial for spin-torque nano
oscillator (STNO) that consists of a non-magnetic spacer which is alloyed with
a ferromagnetic material. Currently, investigations on the dynamics of the free
layer magnetization and frequency enhancement in the STNO with bilinear
coupling are still being actively pursued. In the present work, we investigate
the dynamics of the STNO in the presence of bilinear coupling but in the
absence of an external magnetic field by analyzing the associated
Landau-Lifshitz-Gilbert-Sloncewski(LLGS) equation, and consequently the impact
of the bilinear coupling on the dynamics of the magnetization of the free layer
is studied. It is observed that the frequency of the oscillations in the
magnetization component along the direction of the pinned layer polarization
can be enhanced above 300 GHz by positive bilinear coupling and up to around 30
GHz by negative bilinear coupling. We further reveal a transition from in-plane
to out-of-plane precession both for positive and negative bi-linear couplings.
We also analyze the switching of the magnetization for different values of
current and bilinear coupling. Our detailed investigations of STNO with
bilinear coupling aim at the possibilities of high-frequency devices by
considering the applied current and bilinear coupling in the absence of a
magnetic field.",2306.11415v1
2023-06-20,Towards mutual synchronization of serially connected Spin Torque Oscillators based on magnetic tunnel junctions,"Multiple neuromorphic applications require the tuning of two or more devices
to a common signal. Various types of neuromorphic computation can be realized
using spintronic oscillators, where the DC current induces magnetization
precession, which turns into an AC voltage generator. However, in spintronics,
synchronization of two oscillators using a DC signal is still a challenging
problem because it requires a certain degree of similarity between devices that
are to be synchronized, which may be difficult to achieve due to device
parameter distribution during the fabrication process. In this work, we present
experimental results on the mechanisms of synchronization of spin-torque
oscillators. Devices are based on magnetic tunnel junction with a
perpendicularly magnetized free layer and take advantage of a uniform
magnetization precision in the presence of the magnetic field and a DC bias. By
using an external microwave source, we show the optimal condition for the
synchronization of the magnetic tunnel junctions. Finally, we present results
on the in-series connection of two junctions and discuss the possible path
towards improving oscillation power and linewidth. In addition, using numerical
simulations of the coupled oscillators model, we aim to reproduce the
conditions of the experiments and determine the tolerance for achieving
synchronization.",2306.11608v2
2023-07-21,Gigantic Anisotropy of Self-Induced Spin-Orbit Torque in Weyl Ferromagnet Co2MnGa,"Spin-orbit torque (SOT) is receiving tremendous attention from both
fundamental and application-oriented aspects. Co2MnGa, a Weyl ferromagnet that
is in a class of topological quantum materials, possesses cubic-based high
structural symmetry, the L21 crystal ordering, which should be incapable of
hosting anisotropic SOT in conventional understanding. Here we show the
discovery of a gigantic anisotropy of self-induced SOT in Co2MnGa. The
magnitude of the SOT is comparable to that of heavy metal/ferromagnet bilayer
systems despite the high inversion symmetry of the Co2MnGa structure. More
surprisingly, a sign inversion of the self-induced SOT is observed for
different crystal axes. This finding stems from the interplay of the
topological nature of the electronic states and their strong modulation by
external strain. Our research enriches the understanding of the physics of
self-induced SOT and demonstrates a versatile method for tuning SOT
efficiencies in a wide range of materials for topological and spintronic
devices.",2307.11358v1
2023-08-25,Coexistence of non-trivial van der Waals magnetic orders enable field-free spin-orbit torque switching at room temperature,"The discovery of van der Waals (vdW) materials exhibiting non-trivial and
tunable magnetic interactions at room temperature can give rise to exotic
magnetic states, which are not readily attainable with conventional materials.
Such vdW magnets can provide a unique platform for studying new magnetic
phenomena and realising magnetization dynamics for energy-efficient and
non-volatile spintronic memory and logic technologies. Recent developments in
vdW magnets have revealed their potential to enable spin-orbit torque (SOT)
induced magnetization dynamics. However, the deterministic and field-free SOT
switching of vdW magnets at room temperature has been lacking, prohibiting
their potential applications. Here, we demonstrate magnetic field-free and
deterministic SOT switching of a vdW magnet (Co0.5Fe0.5)5GeTe2 (CFGT) at room
temperature, capitalizing on its non-trivial intrinsic magnetic ordering. We
discover a coexistence of ferromagnetic and antiferromagnetic orders in CFGT at
room temperature, inducing an intrinsic exchange bias and canted perpendicular
magnetism. The resulting canted perpendicular magnetization of CFGT introduces
symmetry breaking, facilitating successful magnetic field-free magnetization
switching in the CFGT/Pt heterostructure devices. Furthermore, the SOT-induced
magnetization dynamics and their efficiency are evaluated using 2nd harmonic
Hall measurements. This advancement opens new avenues for investigating tunable
magnetic phenomena in vdW material heterostructures and realizing field-free
SOT-based spintronic technologies.",2308.13408v1
2023-09-20,Did atmospheric thermal tides cause a daylength locking in the Precambrian? A review on recent results,"After the initial suggestion by Zahnle and Walker (1987) that the torque
accelerating the spin rate of the Earth and produced by the heating of the
atmosphere by the Sun could counteract the braking lunir-solar gravitational
torque in the Precambrian, several authors have recently revisited this
hypothesis. In these studies, it is argued that the geological evidences of the
past spin state of the Earth play in favor of this atmospheric tidal locking of
the length of the day (LOD). In the present review of the recent literature, we
show that the drawn conclusions depend crucially on the consideration of the
stromatolite geological LOD estimates obtained by Pannella at 1.88 and 2.0 Ga,
which are subject to large uncertainties. When only the most robust
cyclostatigraphic estimates of the LOD are retained, the LOD locking hypothesis
is not supported. Moreover, the consideration of the published General
Circulation Model numerical simulations and of new analytical models for the
thermal atmospheric tides suggest that the atmospheric tidal resonance, which
is the crucial ingredient for the LOD locking in the Precambrian, was never of
sufficiently large amplitude to allow for this tidal LOD lock.",2309.11479v2
2023-09-22,Associative memory by virtual oscillator network based on single spin-torque oscillator,"A coupled oscillator network may be able to perform an energy-efficient
associative memory operation. However, its realization has been difficult
because inhomogeneities unavoidably arise among the oscillators during
fabrication and lead to an unreliable operation. This issue could be resolved
if the oscillator network were able to be formed from a single oscillator.
Here, we performed numerical simulations and theoretical analyses on an
associative memory operation that uses a virtual oscillator network based on a
spin-torque oscillator. The virtual network combines the concept of coupled
oscillators with that of feedforward neural networks. Numerical experiments
demonstrate successful associations of $60$-pixel patterns with various
memorized patterns. Moreover, the origin of the associative memory is shown to
be forced synchronization driven by feedforward input, where phase differences
among oscillators are fixed and correspond to the colors of the pixels in the
pattern.",2309.13198v3
2023-11-07,Evidence for saturated and disrupted magnetic braking from samples of detached close binaries with M and K dwarfs,"Context. Recent observations of close detached eclipsing M and K dwarf
binaries have provided substantial support for magnetic saturation when stars
rotate sufficiently fast, leading to a magnetic braking (MB) torque
proportional to the spin of the star.
  Aims. We investigated here how strong MB torques need to be to reproduce the
observationally-inferred relative numbers of white dwarf plus M dwarf
post-common-envelope binaries under the assumption of magnetic saturation.
  Methods. We carried out binary population simulations with the BSE code
adopting empirically-derived inter-correlated main-sequence binary
distributions as initial binary populations and compared the simulation
outcomes with observations.
  Results. We found that the dearth of extreme mass ratio binaries in the
inter-correlated initial distributions is key to reproduce the large fraction
of post-common-envelope binaries hosting low-mass M dwarfs (${\sim0.1-0.2}$
M$_\odot$). In addition, orbital angular momentum loss rates due to MB should
be high for M dwarfs with radiative cores and orders of magnitude smaller for
fully convective stars to explain the observed dramatic change of the fraction
of short-period binaries at the fully convective boundary.
  Conclusions. We conclude that saturated but disrupted, that is, dropping
drastically at the fully convective boundary, MB can explain the observations
of both close main-sequence binaries containing M and K dwarfs and
post-common-envelope binaries. Whether a similar prescription can explain the
spin down rates of single stars and of binaries containing more massive stars
needs to be tested.",2311.04309v1
2024-01-10,"Static and fluctuating zigzag order, and possible signatures of Kitaev physics, in torque measurements of $α$-RuCl${_3}$","We have measured magnetic torque on a T${_N}$ = 7 K single crystal of
${\alpha}$-RuCl${_3}$ , as a function of the field angle in the ab-plane,
focusing on temperatures between 2 and 20 K and fields from 0 to 9 T. We find a
rich spectrum of signals, many of which can be classified by their angular
periodicity. The sample shows an oscillation with a period of 180$^{\circ}$
(i.e. two-fold periodicity) which we argue is due to residual strain within the
crystal, rather than being intrinsic. In addition, within the magnetically
ordered zigzag phase there is a 60$^{\circ}$ period (i.e. six-fold) sawtooth
pattern, which can be explained by reorientation of the zigzag domains as the
crystal rotates in the applied field. Suppressing the zigzag order with an
applied field above ${\sim}$ 8 T at low temperature, a six-fold sinusoidal
signal remains, suggesting that there is fluctuating zigzag order in the
putative field-induced quantum spin liquid state. Finally, our key finding is a
sharp, step-like feature that appears at low temperature for fields just above
the zigzag phase boundary, at the so-called B2-axes. This is similar to
theoretically predicted behaviour for a state with Ising topological order,
which is expected for a Kitaev spin liquid in an applied magnetic field.",2401.05546v1
2024-01-22,Time-Resolved Imaging Reveals Transiently Chaotic Spin-Orbit-Torque-Driven Dynamics Under Controlled Conditions,"Spin-orbit torques (SOTs) act as efficient drivers for nanoscale magnetic
systems, such as in magnetic tunnel junctions, nano-oscillators and racetrack
geometries. In particular, in combination with materials exhibiting high
Dzyaloshinskii--Moriya interaction, SOTs are considered to result in
well-controlled deterministic magnetisation dynamics and are, therefore, used
as robust drives to move and create magnetic skyrmions. In contrast to these
expectations, we here find unpredictable, transiently chaotic dynamics induced
by SOT at an artificial anisotropy-engineered defect in a magnetic racetrack.
Based on these controlled conditions, we directly observe the nanoscale
dynamics with holography-based, time-resolved x-ray imaging. In concert with
micromagnetic simulations, we disclose a regime of violent picosecond
fluctuations, including topological instabilities that, remarkably, result in
deterministic final configurations. In addition, our images expose previously
unseen skyrmion shedding and highlight the potential of transiently chaotic
pathways for topological switching. Our approach offers new perspectives for
the investigation and application of highly non-linear SOT dynamics in
spintronics materials.",2401.12130v1
2024-03-24,Strongly asymmetric magnetization switching and programmable complete Boolean logic enabled by long-range intralayer Dzyaloshinskii-Moriya interaction,"Electrical switching of magnetization is central to spintronics. Despite the
enormous efforts on the spin torques and the Dzyaloshinskii-Moriya interaction
(DMI) effects, some fundamental physics for electrical switching of
magnetization is still missing as indicated by a number of remarkable
long-standing puzzles. Here, we report the discovery of the long-range
intralayer DMI effect widely existing in magnetic heterostructure, which is
distinct from the yet-known DMI effects as it describes the chiral coupling of
two orthogonal magnetic domains within the same magnetic layer via the
mediation of an adjacent heavy metal layer. The long-range intralayer DMI
generates a strong perpendicular effective magnetic field (H_DMI^z) on the
perpendicular magnetization. Characteristically, H_DMI^z varies with the
sign/magnitude of the interfacial DMI constant, the applied in-plane magnetic
fields, and the distribution of the perpendicular magnetic anisotropy. The
long-range intralayer DMI results in striking consequences including the
strongly asymmetric current/field switching of perpendicular magnetization,
hysteresis loop shift of perpendicular magnetization in the absence of in-plane
direct current, and sharp, complete switching of perpendicular magnetization
purely by an in-plane magnetic field. Utilizing the long-range intralayer DMI
effect, we demonstrate programable, complete Boolean logic operations (i.e.,
AND, NAND, NOT, OR, and NOR) within a single spin-orbit torque device. These
results will stimulate the investigation of the long-range intralayer DMI
effect and its impacts on a variety of spintronic devices.",2403.16035v1
2024-03-25,Skyrmionic device for three dimensional magnetic field sensing enabled by spin-orbit torques,"Magnetic skyrmions are topologically protected local magnetic solitons that
are promising for storage, logic or general computing applications. In this
work, we demonstrate that we can use a skyrmion device based on [W/CoFeB/MgO] 1
0 multilayers for three-dimensional magnetic field sensing enabled by
spin-orbit torques (SOT). We stabilize isolated chiral skyrmions and stripe
domains in the multilayers, as shown by magnetic force microscopy images and
micromagnetic simulations. We perform magnetic transport measurements to show
that we can sense both in-plane and out-of-plane magnetic fields by means of a
differential measurement scheme in which the symmetry of the SOT leads to
cancelation of the DC offset. With the magnetic parameters obtained by
vibrating sample magnetometry and ferromagnetic resonance measurements, we
perform finite-temperature micromagnetic simulations, where we investigate the
fundamental origin of the sensing signal. We identify the topological
transformation between skyrmions, stripes and type-II bubbles that leads to a
change in the resistance that is read-out by the anomalous Hall effect. Our
study presents a novel application for skyrmions, where a differential
measurement sensing concept is applied to quantify external magnetic fields
paving the way towards more energy efficient applications in skyrmionics based
spintronics.",2403.16725v1
2004-12-23,Quantum information storage and state transfer based on spin systems,"The idea of quantum state storage is generalized to describe the coherent
transfer of quantum information through a coherent data bus. In this universal
framework, we comprehensively review our recent systematical investigations to
explore the possibility of implementing the physical processes of quantum
information storage and state transfer by using quantum spin systems, which may
be an isotropic antiferromagnetic spin ladder system or a ferromagnetic
Heisenberg spin chain. Our studies emphasize the physical mechanisms and the
fundamental problems behind the various protocols for the storage and transfer
of quantum information in solid state systems.",0412183v1
2007-05-25,Role of interference in quantum state transfer through spin chains,"We examine the role that interference plays in quantum state transfer through
several types of finite spin chains, including chains with isotropic Heisenberg
interaction between nearest neighbors, chains with reduced coupling constants
to the spins at the end of the chain, and chains with anisotropic coupling
constants. We evaluate quantitatively both the interference corresponding to
the propagation of the entire chain, and the interference in the effective
propagation of the first and last spins only, treating the rest of the chain as
black box. We show that perfect quantum state transfer is possible without
quantum interference, and provide evidence that the spin chains examined
realize interference-free quantum state transfer to a good approximation.",0705.3777v2
2009-04-22,Nonstationary theory of magnetic field induced current for molecular spin nanojunction,"For the study of molecular spin junctions, we take into account two types of
couplings between the molecule and the metal leads: (i) electron transfer that
gives rise to net current in the biased junction and (ii) energy transfer
between the molecule and the leads. Using a rotating wave approximation in the
Heisenberg representation, we derive a set of differential equations for the
expectation values of relevant variables: electron and phonon populations and
molecular polarization. A magnetic field control method to enhance the charge
transfer at spin nanojunctions, which characterizes the molecule feature, is
discussed. An approximate analytical solution of the resulting dynamical
equation is supported by numerical solution. The magnetic control by charge
transfer is described by transient pseudo-fermions of electrons interacting
with spins. The rapid adiabatic passage of the energy between the molecule and
the leads is taken into account. The current for molecular spin nanojunctions
is derived.",0904.3461v1
2009-12-17,Longitudinal Spin Transfer to $Λ$ and $\barΛ$ in Polarized Proton-Proton Collisions at $\sqrt{s} = 200 Gev at Star,"We report our measurement on longitudinal spin transfer, $D_{LL}$, from high
energy polarized protons to $\Lambda$ and $\bar{\Lambda}$ hyperons in
proton-proton collisions at $\sqrt{s} = 200GeV$ with the STAR detector at RHIC.
The measurements cover $\Lambda$, $\bar\Lambda$ pseudorapidity $|\eta| < 1.2$
and transverse momenta $p_T$ up to $4GeV/c$. The longitudinal spin transfer is
found to be $D_{LL}= -0.03\pm 0.13(stat) \pm 0.04(syst)$ for inclusive
$\Lambda$ and $D_{LL} = -0.12 \pm 0.08(stat) \pm 0.03(syst)$ for inclusive
$\bar{\Lambda}$ hyperons with $<\eta> = 0.5$ and $<p_T> = 3.7GeV/c$. The
prospect on transverse spin transfer measurement is also given.",0912.3353v1
2012-01-15,Transfer of spin squeezing and particle entanglement between atoms and photons in coupled cavities via two-photon exchange,"We examine transfer of particle entanglement and spin squeezing between
atomic and photonic subsystems in optical cavities coupled by two-photon
exchange. Each cavity contains a single atom, interacting with cavity photons
with a two-photon cascade transition. Particle entanglement is characterized by
evaluating optimal spin squeezing inequalities, for the cases of initially
separable and entangled two-photon states. It is found that particle
entanglement is first generated among the photons in separate cavities and then
transferred to the atoms. The underlying mechanism is recognized as an
inter-cavity two-axis twisting spin squeezing interaction, induced by
two-photon exchange, and its optimal combination with the intra-cavity
atom-photon coupling. Relative effect of non-local two-photon exchange and
local atom-photon interactions of cavity photons on the spin squeezing and
entanglement transfer is pointed out.",1201.3125v3
2013-08-31,Ballistic quantum state transfer in spin chains: general theory for quasi-free models and arbitrary initial states,"Ballistic quantum-information transfer through spin chains is based on the
idea of making the spin dynamics ruled by collective excitations with linear
dispersion relation. Unlike perfect state transfer schemes, a ballistic
transmission requires only a minimal engineering of the interactions; in fact,
for most practical purposes, the optimization of the couplings to the ends of
the chain is sufficient to obtain an almost perfect transmission. In this work
we review different ballistic quantum-state transfer protocols based on the
dynamics of quasi-free spin chains, and further generalize them both at zero
and finite temperature. In particular, besides presenting novel analytical
results for XX, XY, and Ising spin models, it is shown how, via a complete
control on the first and last two qubits of the chain, destructive thermal
effects can be cancelled, leading to a high-quality state transmission
irrespective of the temperature.",1309.0069v2
2015-06-11,Efficient Synchronization of Dipolarly Coupled Vortex-Based Spin Transfer Nano-Oscillators,"Due to their nonlinear properties, spin transfer nano-oscillators can easily
adapt their frequency to external stimuli. This makes them interesting model
systems to study the effects of synchronization and brings some opportunities
to improve their microwave characteristics in view of their applications in
information and communication technologies and to design innovative computing
architectures. So far, mutual synchronization of spin transfer nano-oscillators
through propagating spin-waves and exchange coupling in a common magnetic layer
has been demonstrated. Here we show that the dipolar interaction is also an
efficient mechanism to synchronize neighbouring oscillators. We experimentally
study a pair of vortex-based spin-transfer nano-oscillators, in which mutual
synchronization can be achieved despite a significant frequency mismatch
between oscillators. Importantly, the coupling efficiency is controlled by the
magnetic configuration of the vortices, as confirmed by an analytical model
highlighting the physics at play in the synchronization process as well as by
micromagnetic simulations.",1506.03603v2
2015-09-11,Comparison between a quantum kinetic theory of spin transfer dynamics in Mn doped bulk semiconductors and its Markov limit for non-zero Mn magnetization,"We investigate the transfer between carrier and Mn spins due to the
s-d-exchange interaction in a Mn doped bulk semiconductor within a microscopic
quantum kinetic theory. We demonstrate that the spin transfer dynamics is
qualitatively different for components of the carrier spin parallel and
perpendicular to the Mn magnetization. From our quantum kinetic equations we
have worked out the corresponding Markov limit which is equivalent to rate
equations based on Fermi's golden rule. The resulting equations resemble the
widely used Landau-Lifshitz-Gilbert-equations, but also describe genuine spin
transfer due to quantum corrections. Although it is known that the Markovian
rate description works well for bulk systems when the initial Mn magnetization
is zero, we find large qualitative deviations from the full quantum kinetic
theory for finite initial Mn magnetizations. These deviations mainly reflect
corrections of higher than leading order in the interaction which are not
accounted for in golden rule-type rates.",1509.03479v1
2018-07-26,Cross-entangling electronic and nuclear spins of distant nitrogen-vacancy centers in noisy environments by means of quantum microwave radiation,"Nitrogen-vacancy (NV) defect centers in diamond are strong candidates to
generate entangled states in solid-state environments even at room temperature.
Quantum correlations in spatially separated NV systems, for distances between
NVs ranging from a few nanometers to a few kilometers, have been recently
reported. In the present work we consider the entanglement transfer from two-
mode microwave squeezed (entangled) photons, which are in resonance with the
two lowest NV electron spin states, to initially unentangled NV centers. We
first demonstrate that the entanglement transfer process from quantum
microwaves to isolated NV electron spins is feasible. We then proceed to extend
the previous results to more realistic scenarios where 13 C nuclear spin baths
surrounding each NV are included, quantifying the entanglement transfer
efficiency and robustness under the effects of dephasing/dissipation noisy
nuclear baths. Finally, we address the issue of assessing the possibility of
entanglement transfer from the squeezed microwave light to two remote nuclear
spins closely linked to different NV centers.",1807.09910v1
2022-08-08,Excitation transfer in disordered spin chains with long-range exchange interactions,"We examine spin excitation or polarization transfer via long-range
interacting spin chains with diagonal and off-diagonal disorder. To this end,
we determine the mean localization length of the single-excitation eigenstates
of the chain for various strengths of the disorder. We then identify the energy
eigenstates of the system with large localization length and sufficient support
at the chain boundaries that are suitable to transfer an excitation between the
sender and receiver spins connected to the opposite ends of the chain. We
quantify the performance of two transfer schemes involving weak static
couplings of the sender and receiver spins to the chain, and time-dependent
couplings realizing stimulated adiabatic passage of the excitation via the
intermediate eigenstates of the chain which exhibits improved performance.",2208.04161v3
2023-12-17,Spin control with triplet and doublet excitons in organic semiconductors,"Spin triplet exciton formation sets limits on technologies using organic
semiconductors that are confined to singlet-triplet photophysics. In contrast,
excitations in the spin doublet manifold in organic radical semiconductors can
show efficient luminescence. Here we explore the dynamics of the spin allowed
process of intermolecular energy transfer from triplet to doublet excitons. We
employ a carbene-metal-amide (CMA-CF3) as a model triplet donor host, since
following photoexcitation it undergoes extremely fast intersystem crossing to
set up a population of triplet excitons within 4 ps. This enables a
foundational study for tracking energy transfer from triplets to a model
radical semiconductor, TTM-3PCz. Over 90% of all radical luminescence
originates from the triplet channel in this system under photoexcitation. We
find that intermolecular triplet-to-doublet energy transfer can occur directly
and rapidly, with 12% of triplet excitons transferring already on sub-ns
timescales. This enhanced triplet harvesting mechanism is utilised in efficient
near-infrared organic light-emitting diodes, which can be extended to other
opto-electronic and -spintronic technologies by radical-based spin control in
molecular semiconductors.",2312.10595v1
2024-01-02,Electron transfer channel in the sugar recognition system assembled on nano gold particle,"Existence of 1D spin diffusion in the electrochemical sugar recognition
system consisting of a nano-sized gold particle (GNP), a ruthenium complex and
a phenylboronic acid was investigated by NMR and muSR. When sugar molecules are
recognized by the phenylboronic site, the response of electrochemical
voltammetry of the Ru site changes, enabling the system to work as a sensitive
sugar-sensor. In this recognition process, the change in the electronic state
at the boron site caused by sugar must be transferred to the Ru site via alkyl
chains. We have utilized the muon-labelled electrons method and the proton NMR
to find out a channel of the electron transfer from the phenylboronic acid site
to the gold nano particle via the one dimensional alkyl chain. If this transfer
is driven by diffusive spin channel, characteristic field dependence is
expected in the longitudinal spin relaxation rate of muSR and 1H-NMR. We have
observed significant decrease in the spin relaxation rates with increasing
applied field. The result is discussed in terms of low dimensional spin
diffusion.",2401.01087v1
2006-09-22,Antiproton polarization induced by lepton interactions,"We present expressions for electromagnetic helicity amplitudes and spin
observables for any elastic spin 1/2 - spin 1/2 scattering to first order in
QED. In particular all electromagnetic helicity amplitudes and spin observables
for elastic antiproton-electron and antiproton-proton scattering via single
t-channel photon exchange are presented. Spin observables are required to
describe the rate of increase of polarization in spin filtering. The PAX
collaboration at GSI Darmstadt is interested in the buildup of polarization of
an antiproton beam by repeated interaction with a hydrogen gas target in a
storage ring. In order for the beam particles to remain in the ring after
scattering it is important to consider small angle scattering, hence small
momentum transfer t. In the low momentum transfer region electromagnetic
effects dominate the hadronic effects. Of immediate importance is whether the
polarization of an antiproton beam can be built up by spin filtering off
polarized electrons either in a target or in a beam. We present the theoretical
background for this discussion.",0609233v1
2011-10-03,Inelastic electron transport through Quantum Dot coupled with an nano mechancial oscillator in the presence of strong applied magnetic field,"In this study we explain the role of applied magnetic field in inelastic
conduction properties of a Quantum Dot coupled with an oscillator . In the
presence of strong applied magnetic field coulomb blockade effects become weak
due to induced Zeeman splitting in spin degenerate eigen states of Quantum
Dot.By contacting Quantum Dot by identical metallic leads tunneling rates of
spin down and spin up electrons between Quantum Dot and electrodes will be
symmetric. For symmetric tunneling rates of spin down and spin up electrons
onto Quantum Dot, first oscillator get excited by spin down electrons and then
spin up elctrons could excite it further. Where as average energy transferred
to oscillator coupled with Quantum Dot by spin down electrons will further
increase by average energy transferred by spin up electrons to oscillator. Here
we have also discussed that with increasing Quantum Dot and electrodes coupling
strength phononic side band peaks start hiding up, which happens because with
increasing tunneling rates electronic states of Quantum Dot start gettting
broadened.",1110.0369v1
2014-03-13,Coupling theory of emergent spin electromagnetic field and electromagnetic field,"In ferromagnetic metals, an effective electromagnetic field which couples to
conduction electron spin is induced by the sd exchange interaction. We
investigate how this effective field, spin electromagnetic field, interacts
with the ordinary electromagnetic field by deriving an effective Hamiltonian
based on the path-integral formalism. It turns out that the dominant coupling
term is the product of the electric field and the spin gauge field. This term
descrives the spin-transfer effect, as was pointed out before. The electric
field couples also to the spin electric field, but this contribution is smaller
than the spin-transfer contribution in the low frequency regime. The magnetic
field couples to the spin magnetic field, and this interaction suggests an
intriguing intrinsic mechanism of frustration in very weak metallic
ferromagnets under a uniform magnetic field. We also propose a voltage
generation mechanism due to a non-linear effect of non-monochromatic spin wave
excitation.",1403.3214v3
2020-04-12,Collisional spin transfer in an atomic heteronuclear spinor Bose gas,"We observe spin transfer within a non-degenerate heteronuclear spinor atomic
gas comprised of a small $^7$Li population admixed with a $^{87}$Rb bath, with
both elements in their $F=1$ hyperfine spin manifolds and at temperatures of
10's of $\mu$K. Prepared in a non-equilibrium initial state, the $^7$Li spin
distribution evolves through incoherent spin-changing collisions toward a
steady-state distribution. We identify and measure the cross-sections of all
three types of spin-dependent heteronuclear collisions, namely the
spin-exchange, spin-mixing, and quadrupole-exchange interactions, and find
agreement with predictions of heteronuclear $^7$Li-$^{87}$Rb interactions at
low energy. Moreover, we observe that the steady state of the $^7$Li spinor gas
can be controlled by varying the composition of the $^{87}$Rb spin bath with
which it interacts.",2004.05663v2
2020-06-29,Electronic charge transfer driven by spin cycloidal structure,"Muon spin rotation and resonant soft X-ray scattering experiments on
prototype multiferroics RMn2O5 (R = Y, Sm) are used to demonstrate that the
local electric displacements are driven by the spin-current (SC) mechanism.
Small local electric displacements were evaluated by observing spin
polarization at ligand O ions, for which implanted muons served as an extremely
sensitive probe. Our results for YMn2O5 provide evidence that the spin
polarization of O ions forming a spin cycloid chain with Mn spins increases in
proportion to the vector spin chirality (Si x Sj ) of the Mn ions. This
relationship strongly indicates that the charge transfer between O and Mn ions
is driven by the SC mechanism, which leads to the ferroelectricity accompanying
O spin polarization.",2006.15834v2
2004-08-18,Irreversible spin-transfer and magnetization reversal under spin-injection,"In the context of spin electronics, the two spin-channel model assumes that
the spin carriers are composed of two distinct populations: the conduction
electrons of spin up, and the conduction electrons of spin down. In order to
distinguish the paramagnetic and ferromagnetic contributions in spin injection,
we describe the current injection with four channels : the two spin populations
of the conduction bands ($s$ or paramagnetic) and the two spin populations of
the more correlated electrons ($d$ or ferromagnetic). The redistribution of the
conduction electrons at the interface is described by relaxation mechanisms
between the channels. Providing that the $d$ majority-spin band is frozen,
$s-d$ relaxation essentially concerns the minority-spin channels. Accordingly,
even in the abscence of spin-flip scattering (i.e. without standard
spin-accumulation or giant magnetoresistance), the $s-d$ relaxation leads to a
$d$ spin accumulation effect. The coupled diffusion equations for the two
relaxation processes ($s-d$ and spin-flip) are derived. The link with the
ferromagnetic order parameter $\vec{M}$ is performed by assuming that only the
$d$ channel contributes to the Landau-Lifshitz-Gilbert equation. The effect of
magnetization reversal induced by spin injection is explained by these
relaxations under the assumption that the spins of the conduction electrons act
as environmental degrees of freedom on the magnetization.",0408410v1
2005-10-04,Wave Excitation in Three-Dimensional Disks by External Potential,"We study the excitation of density and bending waves and the associated
angular momentum transfer in gaseous disks with finite thickness by a rotating
external potential. The disk is assumed to be isothermal in the vertical
direction and has no self-gravity. The disk perturbations are decomposed into
different modes, each characterized by the azimuthal index m and the vertical
index n, which specifies the nodal number of the density perturbation along the
disk normal direction. The n=0 modes correspond to the two-dimensional density
waves previously studied by Goldreich & Tremaine and others. In a
three-dimensional disk, waves can be excited at both Lindblad resonances (for
modes with n=0,1,2...) and vertical resonances (for the $n\ge 1$ modes only).
The torque on the disk is positive for waves excited at outer Linblad/vertical
resonances and negative at inner Lindblad/vertical resonances. While the n=0
modes are evanescent around corotation, the $n\ge 1$ modes can propagate into
the corotation region where they are damped and deposit their angular momenta.
We have derived analytical expressions for the amplitudes of different wave
modes excited at Lindblad and/or vertical resonances and the resulting torques
on the disk. It is found that for $n\ge 1$, angular momentum transfer through
vertical resonances is much more efficient than Lindblad resonances. This
implies that in some situations (e.g., a circumstellar disk perturbed by a
planet in an inclined orbit), vertical resonances may be an important channel
of angular momentum transfer between the disk and the external potential. We
have also derived new formulae for the angular momentum deposition at
corotation and studied wave excitations at disk boundaries.",0510069v2
2021-02-24,Accretion Torque Reversals in GRO J1008-57 Revealed by Insight-HXMT,"GRO J1008-57, as a Be/X-ray transient pulsar, is considered to have the
highest magnetic field in known neutron star X-ray binary systems.
Observational data of the X-ray outbursts in GRO J1008-57 from 2017 to 2020
were collected by the Insight-HXMT satellite. In this work, the spin period of
the neutron star in GRO J1008-57 was determined to be about 93.28 seconds in
August 2017, 93.22 seconds in February 2018, 93.25 seconds in June 2019 and
93.14 seconds in June 2020. GRO J1008-57 evolved in the spin-up process with a
mean rate of $-(2.10\pm 0.05)\times$10$^{-4}$ s/d from 2009 -- 2018, and turned
into a spin down process with a rate of $(6.7\pm 0.6)\times$10$^{-5}$ s/d from
Feb 2018 to June 2019. During the type II outburst of 2020, GRO J1008-57 had
the spin-up torque again. During the torque reversals, the pulse profiles and
continuum X-ray spectra did not change significantly, and the cyclotron
resonant scattering feature around 80 keV was only detected during the
outbursts in 2017 and 2020. Based on the observed mean spin-up rate, we
estimated the inner accretion disk radius in GRO J1008-57 (about 1 - 2 times of
the Alfv\'{e}n radius) by comparing different accretion torque models of
magnetic neutron stars. During the spin-down process, the magnetic torque
should dominate over the matter accreting inflow torque, and we constrained the
surface dipole magnetic field $B\geq 6\times 10^{12}$ G for the neutron star in
GRO J1008-57, which is consistent with the magnetic field strength obtained by
cyclotron line centroid energy.",2102.12085v1
2017-07-27,Improved torque formula for low and intermediate mass planetary migration,"The migration of planets on nearly circular, non-inclined orbits in
protoplanetary discs is entirely described by the disc's torque. This torque is
a complex function of the disc parameters, and essentially amounts to the sum
of two components: the Lindblad torque and the corotation torque. Known torque
formulae do not reproduce accurately the torque actually experienced in
numerical simulations by low- and intermediate- mass planets in radiative
discs. One of the main reasons for this inaccuracy is that these formulae have
been worked out in two-dimensional analyses. Here we revisit the torque formula
and update many of its dimensionless coefficients by means of tailored, three-
dimensional numerical simulations. In particular, we derive the dependence of
the Lindblad torque on the temperature gradient, the dependence of the
corotation torque on the radial entropy gradient (and work out a suitable
expression of this gradient in a three-dimensional disc). We also work out the
dependence of the corotation torque on the radial temperature gradient,
overlooked so far. Corotation torques are known to scale very steeply with the
width of the horseshoe region. We extend the expression of this width to the
domain of intermediate mass planets, so that our updated torque formula remains
valid for planets up to typically several tens of Earth masses, provided these
relatively massive planets do not significantly deplete their coorbital region.
Our torque expression can be applied to low- and intermediate-mass planets in
optically thick protoplanetary discs, as well as protomoons embedded in
circumplanetary discs.",1707.08988v1
2019-09-16,Rotational disruption of dust grains by mechanical torques for high-velocity gas-grain collisions,"Dust grains moving at hypersonic velocities of $v_{d}\gtrsim 100\rm
km~s^{-1}$ through an ambient gas are known to be destroyed by nonthermal
sputtering. Yet, previous studies of nonthermal sputtering disregarded the fact
that dust grains can be spun-up to suprathermal rotation by stochastic
mechanical torques from gas-grain collisions. In this paper, we show that such
grain suprathermal rotation can disrupt a small grain into small fragments
because induced centrifugal stress exceeds the maximum tensile strength of
grain material, $S_{\rm max}$. We term this mechanism {\it MEchanical Torque
Disruption} (METD). We find that METD is more efficient than nonthermal
sputtering in destroying smallest grains ($a<10$ nm) of nonideal structures
moving with velocities of $v_{d}<500 \rm km~s^{-1}$. The ratio of rotational
disruption to sputtering time is $\tau_{\rm disr}/\tau_{\rm sp}\sim 0.7(S_{\rm
max}/10^{9}\rm erg~cm^{-3})(\bar{A}_{\rm sp}/12)(Y_{\rm sp}/0.1)(a/0.01\mu
m)^{3}(300\rm km~s^{-1}/v_{d})^{2}$ where $a$ is the radius of spherical
grains, and $Y_{\rm sp}$ is sputtering yield. We also consider the high-energy
regime and find that the rate of METD is reduced and becomes less efficient
than sputtering for $v_{d}>500\rm km~s^{-1}$ because impinging particles only
transfer part of their momentum to the grain. We finally discuss implications
of the METD mechanism for the destruction of hypersonic grains accelerated by
radiation pressure as well as grains in fast shocks. Our results suggest that
the destruction of small grains by METD in fast shocks of supernova remnants
may be more efficient than previously predicted by nonthermal sputtering,
depending on grain internal structures.",1909.07001v3
1996-07-11,Exact results for resonating valence bonds states on 2D (narrow) systems,"It is shown that the problem of calculating spin-spin correlation functions,
in the dimers RVB states, on a possibly diluted 2D square lattice, can be
formulated in terms of a transfer matrix. The transfer matrix is used for exact
numerical calculations of spin-spin correlation functions on ladders up to four
units wide.",9607076v2
2002-03-23,Thermally-Activated Magnetic Reversal Induced by a Spin-Polarized Current,"We have measured the statistical properties of magnetic reversal in
nanomagnets driven by a spin-polarized current. Like reversal induced by a
magnetic field, spin-transfer-driven reversal near room temperature exhibits
the properties of thermally-activated escape over an effective barrier.
However, the spin-transfer effect produces qualitatively different behaviors
than an applied magnetic field. We discuss an effective current vs. field phase
diagram. If the current and field are tuned so that their effects oppose one
another, the magnet can be driven superparamagnetic.",0203487v1
2005-07-15,Spin transference and magnetoresistance amplification in a transistor,"A current problem in semiconductor spin-based electronics is the difficulty
of experimentally expressing the effect of spin-polarized current in electrical
circuit measurements. We present a theoretical solution with the principle of
transference of the spin diffusion effects in the semiconductor channel of a
system with three magnetic terminals. A notable result of technological
consequences is the room temperature amplification of the magneto-resistive
effect, integrable with electronics circuits, demonstrated by computation of
current dependence on magnetization configuration in such a system with
currently achievable parameters.",0507378v2
2004-10-25,Spin structure of nucleon and spin transfer in high energy fragmentation process,"Spin transfer in high energy fragmentation process is determined by the
hadronization mechanism and spin structure of hadrons.It can be studied by
measuring the polarizations of hyperons and/or vector mesons in e+e-
annihilation, in the current fragmentation region of polarized deeply inelastic
lN-scatterings, and high p_T-jets in polarized pp-collisions.Theoretical
calculations have been made using different models.In this talk, I will briefly
summarize the main features of the models, the results obtained and the
comparison with available data. They can be used for future tests by
experiments.",0410325v1
2010-02-19,Information transfer using a single particle path-spin hybrid entangled state,"The path-spin entangled state of a single spin-1/2 particle is considered
which is generated by using a beam-spitter and a spin-flipper. Using this
hybrid entanglement at the level of a single particle as a resource, we
formulate a protocol for transferring of the state of an unknown qubit to a
distant location. Our scheme is implemented by a sequence of unitary operations
along with suitable spin-measurements, as well as by using classical
communication between the two spatially separated parties. This protocol, thus,
demonstrates the possibility of using intraparticle entanglement as a physical
resource for performing information theoretic tasks.",1002.3694v1
2010-03-03,Remote quantum gates mediated by spin chains,"There has been much recent study on the application of spin chains to quantum
state transfer and communication. Here we demonstrate that spin chains set up
for perfect quantum state transfer can be utilised to generate remote quantum
gates, between spin qubits injected at the ends of the chain. The natural
evolution of the system across different excitation number sectors generates a
maximally-entangling and universal gate between the injected qubits,
independent of the length of the chain.",1003.0869v2
2012-06-20,Spatial control of electron spins by electric and magnetic fields in double quantum wells,"A system of two quantum wells (QW), one made of HgCdTe and the other of
HgCdMnTe, subjected to electric and magnetic fields $F$ and $B$ parallel to the
growth direction, is proposed and described theoretically. It is shown that in
such a system the spin $g$ factor of mobile electrons strongly depends on the
sign and magnitude of electric field. Adjusting $F$ at a constant $B$ one can
transfer almost all electrons into one or the other QW and polarize their spins
along the desired orientation. Changing $B$ at a constant $F$ can produce a
similar transfer and polarization effect. Possible applications of the spatial
reservoirs filled with spin-polarized electrons are discussed.",1206.4457v1
2013-01-31,Electric-field switching magnetization and spin transfer in ultrathin BiFeO3 film,"First-principles density-functional theory calculations show switching
magnetization by 90 degree can be achieved in ultrathin BFO film by applying
external electric-field. Up-spin carriers appear to the surface with positive
field while down-spin ones to the negative field surface, arising from the
redistribution of Fe-t2g orbital. The half-metallic behavior of Fe-3d states in
the surface of R phase film makes it a promising candidate for AFM/FM bilayer
heterostructure possessing electric-field tunable FM magnetization reversal and
opens a new way towards designing spintronic multiferroics. The interface
exchange-bias effect in this BFO/FM bilayer is mainly driven by the Fe-t2g
orbital reconstruction, as well as spin transferring and rearrangement.",1301.7559v1
2015-12-21,Tunable self-assembled spin chains of strongly interacting cold atoms,"We have developed an efficient computational method to treat long,
one-dimensional systems of strongly-interacting atoms forming self-assembled
spin chains. Such systems can be used to realize many spin chain model
Hamiltonians tunable by the external confining potential. As a concrete
demonstration, we consider quantum state transfer in a Heisenberg spin chain
and we show how to determine the confining potential in order to obtain
nearly-perfect state transfer.",1512.06722v3
2003-12-01,Full Counting Statistics of Spin Currents,"We discuss how to detect fluctuating spin currents and derive full counting
statistics of electron spin transfers. It is interesting to consider several
detectors in series that simultaneously monitor different components of the
spins transferred. We have found that in general the statistics of the
measurement outcomes cannot be explained with the projection postulate and
essentially depends on the quantum dynamics of the detectors.",0312045v1
1998-05-07,Angular Momentum Transport in the Central Region of the Galaxy,"We discuss mechanisms for angular momentum transport in the clumpy medium of
the circumnuclear disk at the Galactic center. The viscosity due to clump-clump
collisions is found to be less than some critical viscosity; this meets the
conditions at which a collective mode of nonaxisymmetric shear perturbations in
the disk is able to grow until going into the saturation regime where fully
developed turbulence is established. We find that the angular momentum transfer
due to this turbulent viscosity turns out to comparable to the transport due to
magnetic torques. Taken together, the turbulent and magnetic transfer of
angular momentum are able to provide the inflow of mass into the central parsec
with a rate of about 10^{-2} M_{sun}/yr, consistent with the available data.",9805098v1
2011-10-27,Angular Momentum Loss Mechanisms in Cataclysmic Variables below the Period Gap,"Mass transfer in cataclysmic variables (CVs) is usually considered to be
caused by angular momentum loss (AML) driven by magnetic braking and
gravitational radiation (GR) above the period gap, and solely by GR below the
period gap. The best-fit revised model of CV evolution recently by
\citet{kbp11}, however, indicates that AML rate below the period gap is
$2.47(\pm 0.22)$ times the GR rate, suggesting the existence of some other AML
mechanisms. We consider several kinds of consequential AML mechanisms often
invoked in the literature: isotropic wind from the accreting white dwarfs,
outflows from the Langrangian points, and the formation of a circumbinary disk.
We found that neither isotropic wind from the white dwarf nor outflow from the
$L_1$ point can explain the extra AML rate, while ouflow from the $L_2$ point
or a circumbinary disk can effectively extract the angular momentum provided
that $\sim (15-45)%$ of the transferred mass is lost from the binary. A more
promising mechanism is a circumbinary disk exerting gravitational torque on the
binary. In this case the mass loss fraction can be as low as $\lesssim
10^{-3}$.",1110.5952v1
2018-06-01,Transient temperature calculation method for complex fluid-solid heat transfer problems with scattering boundary conditions,"A calculation method for engine temperatures is presented. Special focus is
placed on the transient and scattering boundary conditions within the
combustion chamber, including fired and coasting conditions, as well as the
dynamic heat transfer of the water jacket. Model reduction is achieved with
dimensional analysis and the application of probability density functions,
which allows for a timescale separation. Stationary in-cylinder pressure
measurements are used as input values and, according to the transient behavior,
modified with an own part-load model. A turbocharged SI race engine is equipped
with 70 thermocouples at various positions in proximity to the combustion
chamber. Differentiating from already published works, the method deals with
the transient engine behavior during a race lap, which undergoes a frequency
range of 0.1-1 Hz. This includes engine speed build-ups under gear changes,
torque variations, or the transition from fired to coasting conditions.
Different thermal behaviors of various measuring positions can be simulated
successfully. Additionally, cylinder individual temperature effects resulting
from an unsymmetrical ignition sequence and different volumetric efficiencies
with unequal residual gas can be predicted. Up to a few percent, the energy
balance of the water jacket is fulfilled and variations of water inlet
temperatures can be simulated accurately enough.",1806.01790v1
2021-09-25,System Identification in Multi-Actuator Hard Disk Drives with Colored Noises using Observer/Kalman Filter Identification (OKID) Framework,"Multi Actuator Technology in Hard Disk drives (HDDs) equips drives with two
dual stage actuators (DSA) each comprising of a voice coil motor (VCM) actuator
and a piezoelectric micro actuator (MA) operating on the same pivot point. Each
DSA is responsible for controlling half of the drive's arms. As both the DSAs
operate independently on the same pivot timber, the control forces and torques
generated by one affect the operation of the other. The feedback controllers
might not completely reject these transferred disturbances and a need to design
feedforward controllers arises, which require a good model of the disturbance
process. The usual system identification techniques produce a biased estimate
because of the presence of the runout which is a colored noise. In this paper,
we use the OKID framework to estimate this disturbance cross transfer function
from the VCM control input of one DSA to the output of the other DSA from the
collected time series data corrupted by colored noise.",2109.12460v1
2022-02-19,Training Robots without Robots: Deep Imitation Learning for Master-to-Robot Policy Transfer,"Deep imitation learning is promising for robot manipulation because it only
requires demonstration samples. In this study, deep imitation learning is
applied to tasks that require force feedback. However, existing demonstration
methods have deficiencies; bilateral teleoperation requires a complex control
scheme and is expensive, and kinesthetic teaching suffers from visual
distractions from human intervention. This research proposes a new
master-to-robot (M2R) policy transfer system that does not require robots for
teaching force feedback-based manipulation tasks. The human directly
demonstrates a task using a controller. This controller resembles the kinematic
parameters of the robot arm and uses the same end-effector with force/torque
(F/T) sensors to measure the force feedback. Using this controller, the
operator can feel force feedback without a bilateral system. The proposed
method can overcome domain gaps between the master and robot using gaze-based
imitation learning and a simple calibration method. Furthermore, a Transformer
is applied to infer policy from F/T sensory input. The proposed system was
evaluated on a bottle-cap-opening task that requires force feedback.",2202.09574v2
2022-09-21,DenseTact 2.0: Optical Tactile Sensor for Shape and Force Reconstruction,"Collaborative robots stand to have an immense impact on both human welfare in
domestic service applications and industrial superiority in advanced
manufacturing with dexterous assembly. The outstanding challenge is providing
robotic fingertips with a physical design that makes them adept at performing
dexterous tasks that require high-resolution, calibrated shape reconstruction
and force sensing. In this work, we present DenseTact 2.0, an optical-tactile
sensor capable of visualizing the deformed surface of a soft fingertip and
using that image in a neural network to perform both calibrated shape
reconstruction and 6-axis wrench estimation. We demonstrate the sensor accuracy
of 0.3633mm per pixel for shape reconstruction, 0.410N for forces, 0.387Nmm for
torques, and the ability to calibrate new fingers through transfer learning,
which achieves comparable performance with only 12% of the non-transfer
learning dataset size.",2209.10122v2
2004-09-22,Galaxy Formation and the Cosmological Angular Momentum Problem,"The importance of angular momentum in regulating the sizes of galactic disks
and by this their star formation history is highlighted. Tidal torques and
accretion of satellites in principle provide enough angular momentum to form
disks with sizes that are in agreement with observations. However three major
problems have been identified that challenge cold dark matter theory and affect
models of galaxy evolution: (1) too much angular momentum is transferred from
the gas to the dark halos during infall, leading to disks with scale lengths
that are too small, (2) bulgeless disks require more specific angular momentum
than is generated cosmologically even if gas would not lose angular momentum
during infall, (3) gravitational torques and hierarchical merging produce a
specific angular momentum distribution that does not match the distribution
required to form exponential disks naturally; some gas has exceptionally high
angular momentum, leading to extended outer disks while another large gas
fraction will contain very little specific angular momentum and is expected to
fall into the galactic center, forming a massive and dominant bulge component.
Any self-consistent theory of galaxy formation will require to provide
solutions to these questions. Selective mass loss of low-angular-momentum gas
in an early phase of galaxy evolution currently seems to be the most promising
scenario. Such a process would have a strong affect on the early protogalactic
evolution phase, the origin and evolution of galactic morphologies and link
central properties of galaxies like the origin of central massive black holes
with their global structure.",0409540v1
2006-08-31,On the role of the current loss in radio pulsar evolution,"The aim of this article is to draw attention to the importance of the
electric current loss in the energy output of radio pulsars. We remind that
even the losses attributed to the magneto-dipole radiation of a pulsar in
vacuum can be written as a result of an Ampere force action of the electric
currens flowing over the neutron star surface (Michel, 1991, Beskin et al.,
1993). It is this force that is responsible for the transfer of angular
momentum of a neutron star to an outgoing magneto-dipole wave. If a pulsar is
surrounded by plasma, and there is no longitudinal current in its
magnetosphere, there is no energy loss (Beskin et al., 1993, Mestel et al.,
1999). It is the longitudinal current closing within the pulsar polar cap that
exerts the retardation torque acting on the neutron star. This torque can be
determined if the structure of longitudinal current is known. Here we remind of
the solution by Beskin, Gurevitch & Istomin (1993) and discuss the validity of
such an assumption. The behavior of the recently observed ""part-time job""
pulsar B1931+24 can be naturally explained within the model of current loss
while the magneto-dipole model faces difficulties.",0608689v2
2006-09-06,Simulations of polarized dust emission,"Our aim is to study the polarization of thermal dust emission to see if the
alignment of grain by radiative torques could explain the observed relation
between the degree of polarization and the intensity in dense cores.
Predictions are made for polarimetry observations with the Planck satellite.
Our results are based on model clouds derived from MHD simulations of
magnetized turbulent flows, while the continuum radiative transfer problem is
solved with Monte Carlo methods in order to estimate the three-dimensional
distribution of dust emission and the radiation field strength affecting the
grain alignment. The influence of grain alignment efficiency is examined in the
calculated polarization maps. We are able to reproduce the P/I-relation with
the grain alignment by radiative torques. The decrease in intrinsic
polarization and total emission means that sub-mm polarimetry carries only
little information about the magnetic fields in dense cores with high visual
extinction. The interpretation of the observations will be further complicated
by the unknown magnetic field geometry and the fact that what is observed as
individual cores may, in fact, be a superposition of several density
enhancements. According to our calculations, Planck will be able to map dust
polarization reliably when A_V > 2 mag at spatial resolution of 15'.",0609143v2
2007-01-09,On the role of the current loss mechanism in radio pulsar evolution,"The aim of this article is to draw attention to the importance of the
electric current loss in the energy output of radio pulsars. We remind that
even the losses attributed to the magneto-dipole radiation of a pulsar in
vacuum can be written as a result of Ampere force action of the electric
currents flowing over the neutron star surface (Michel 1991, Beskin, Gurevich &
Istomin 1993). It is this force that is responsible for the transfer of angular
momentum of a neutron star to an outgoing magneto-dipole wave. If a pulsar is
surrounded by plasma, and there is no longitudinal current in its
magnetosphere, there is no energy loss (Beskin, Gurevich & Istomin 1993,
Mestel, Panagi & Shibata 1999). It is the longitudinal current closing within
the pulsar polar cap that exerts the retardation torque acting on the neutron
star. This torque can be determined if the structure of longitudinal current is
known. Here we remind of the solution by Beskin, Gurevich & Istomin (1993) and
discuss the validity of such an assumption. Finally, it is shown that the
behaviour of the recently observed ""part-time job"" pulsar B1931+24 can be
naturally explained within the model of current loss while the magneto-dipole
model faces difficulties.",0701261v1
1999-04-01,Elastic Rod Model of a Supercoiled DNA Molecule,"We study the elastic behaviour of a supercoiled DNA molecule. The simplest
model is that of a rod like chain, involving two elastic constants, the bending
and the twist rigidities. We show that this model is singular and needs a small
distance cut-off, which is a natural length scale giving the limit of validity
of the model, of the order of the double helix pitch. The rod like chain in
presence of the cutoff is able to reproduce quantitatively the experimentally
observed effects of supercoiling on the elongation-force characteristics, in
the small supercoiling regime. An exact solution of the model, using both
transfer matrix techniques and its mapping to a quantum mechanics problem,
allows to extract, from the experimental data,the value of the twist rigidity.
We also analyse the variation of the torque and the writhe to twist ratio
versus supercoiling, showing analytically the existence of a rather sharp
crossover regime which can be related to the excitation of plectonemic-like
structures. Finally we study the extension fluctuations of a stretched and
supercoiled DNA molecule, both at fixed torque and at fixed supercoiling angle,
and we compare the theoretical predictions to some preliminary experimental
data.",9904018v2
2013-07-24,Migration of massive black hole binaries in self--gravitating accretion discs: Retrograde versus prograde,"We study the interplay between mass transfer, accretion and gravitational
torques onto a black hole binary migrating in a self-gravitating, retrograde
circumbinary disc. A direct comparison with an identical prograde disc shows
that: (i) because of the absence of resonances, the cavity size is a factor
a(1+e) smaller for retrograde discs; (ii) nonetheless the shrinkage of a
circular binary semi--major axis, a, is identical in both cases; (iii) a
circular binary in a retrograde disc remains circular while eccentric binaries
grow more eccentric. For non-circular binaries, we measure the orbital decay
rates and the eccentricity growth rates to be exponential as long as the binary
orbits in the plane of its disc. Additionally, for these co-planar systems, we
find that interaction (~ non--zero torque) stems only from the cavity edge plus
a(1+e) in the disc, i.e. for dynamical purposes, the disc can be treated as a
annulus of small radial extent. We find that simple 'dust' models in which the
binary- disc interaction is purely gravitational can account for all main
numerical results, both for prograde and retrograde discs. Furthermore, we
discuss the possibility of an instability occurring for highly eccentric
binaries causing it to leave the disc plane, secularly tilt and converge to a
prograde system. Our results suggest that there are two stable configurations
for binaries in self-gravitating discs: the special circular retrograde case
and an eccentric (e~ 0.6) prograde configuration as a stable attractor.",1307.6283v1
2020-11-10,Model Predictive Control for Human-Centred Lower Limb Robotic Assistance,"Loss of mobility or balance resulting from neural trauma is a critical
consideration in public health. Robotic exoskeletons hold great potential for
rehabilitation and assisted movement, yet optimal assist-as-needed (AAN)
control remains unresolved given pathological variance among patients. We
introduce a model predictive control (MPC) architecture for lower limb
exoskeletons centred around a fuzzy logic algorithm (FLA) identifying modes of
assistance based on human involvement. Assistance modes are: 1) passive for
human relaxed and robot dominant, 2) active-assist for human cooperation with
the task, and 3) safety in the case of human resistance to the robot. Human
torque is estimated from electromyography (EMG) signals prior to joint motions,
enabling advanced prediction of torque by the MPC and selection of assistance
mode by the FLA. The controller is demonstrated in hardware with three subjects
on a 1-DOF knee exoskeleton tracking a sinusoidal trajectory with human relaxed
assistive, and resistive. Experimental results show quick and appropriate
transfers among the assistance modes and satisfied assistive performance in
each mode. Results illustrate an objective approach to lower limb robotic
assistance through on-the-fly transition between modes of movement, providing a
new level of human-robot synergy for mobility assist and rehabilitation.",2011.05079v1
2021-04-12,Thermoelectric Precession in Turbulent Magnetoconvection,"We present laboratory measurements of the interaction between thermoelectric
currents and turbulent magnetoconvection. In a cylindrical volume of liquid
gallium heated from below and cooled from above and subject to a vertical
magnetic field, it is found that the large scale circulation (LSC) can undergo
a slow axial precession. Our experiments demonstrate that this LSC precession
occurs only when electrically conducting boundary conditions are employed, and
that the precession direction reverses when the axial magnetic field direction
is flipped. A thermoelectric magnetoconvection (TEMC) model is developed that
successfully predicts the zeroth-order magnetoprecession dynamics. Our TEMC
magnetoprecession model hinges on thermoelectric current loops at the top and
bottom boundaries, which create Lorentz forces that generate horizontal torques
on the overturning large-scale circulatory flow. The thermoelectric torques in
our model act to drive a precessional motion of the LSC. This model yields
precession frequency predictions that are in good agreement with the
experimental observations. We postulate that thermoelectric effects in
convective flows, long argued to be relevant in liquid metal heat transfer and
mixing processes, may also have applications in planetary interior
magnetohydrodynamics.",2104.05231v2
2021-08-17,"Microscopic theory of photon-induced energy, momentum, and angular momentum transport in the nonequilibrium regime","We set up a general microscopic theory for the transfer of energy, momentum,
and angular momentum mediated by photons. Using the nonequilibrium Green's
function method, we propose a unified Meir-Wingreen formalism for the energy
emitted, force experienced, and torque experienced by the objects due to the
fluctuating electromagnetic field. Our theory does not require the local
thermal equilibrium that is the central assumption of the conventional theory
of fluctuational electrodynamics (FE). The obtained formulas are valid for
arbitrary objects as well as the environment without the requirement of
reciprocity. To show the capability of our microscopic theory, we apply the
general formulas to transport problems of graphene edges in both equilibrium
and nonequilibrium situations. We show the local equilibrium energy radiation
of graphene obeys the well-known $T^4$ law with a converged theoretical
emissivity of 2.058$\%$. In the ballistic nonequilibrium situation driven by
chemical potential biases, we observe nonzero results for force and torque from
the graphene edges, which go beyond the predictive ability of the FE theory.
Our method is general and efficient for large systems, which paves the way for
studying more complex transport phenomena in the nonequilibrium regime.",2108.07649v3
2021-11-08,Minimum-lap-time Control Strategies for All-wheel Drive Electric Race Cars via Convex Optimization,"This paper presents a convex optimization framework to compute the
minimum-lap-time control strategies of all-wheel drive (AWD) battery electric
race cars, accounting for the grip limitations of the individual tyres.
Specifically, we first derive the equations of motion (EOM) of the race car and
simplify them to a convex form. Second, we leverage convex models of the
electric motors (EMs) and battery, and frame the time-optimal final-drives
design and EMs control problem in space domain. The resulting optimization
problem is fully convex and can be efficiently solved with global optimality
guarantees using second-order conic programming algorithms. Finally, we
validate our modeling assumptions via the original non-convex EOM, and simulate
our framework on the Formula Student Netherlands endurance race track. Thereby,
we compare a torque vectoring with a fixed power split configuration, showing
that via torque vectoring we can make a better use of the individual tyre grip,
and significantly improve the achievable lap time by more than 4%. Finally, we
present a design study investigating the respective impact of the front and
rear EM size on lap time, revealing that the rear motor sizing is predominant
due to the higher vertical rear tyre load caused by the center of pressure
position and rearwards load transfer under acceleration.",2111.04650v2
2023-07-27,On the origin of outward migration of Population III stars,"Outward migration of massive binary stars or black holes in their
circumbinary disc is often observed in simulations and it is key to the
formation of wide black hole binaries. Using numerical simulations of
Population III (Pop III) star formation, we study the angular momentum of Pop
III binaries and the torques between stars and gas discs to understand the
origin of outward migration and high ellipticity. The outward migration of
protostars is produced by gravitational torques exerted on them by their
circumstellar minidiscs. The minidiscs, on the other hand, migrate outward
mainly by gaining angular momentum by accreting gas from the circumbinary disc.
The angular momentum transfer is most efficient for rapidly accreting
equal-mass binaries, and weaker when the secondary mass is small or the massive
companion evaporates the gas disc via radiative feedback. We conclude that
outward migration and the formation of wide equal-mass massive binaries is
common in metal-free/metal-poor star formation, mainly driven by their large
accretion rates. We expect that the lower gas temperature and accretion rates
in metal-enriched circumstellar discs would lead more often to inward migration
and closer binary separations. We also observe inward migration for smaller
mass Pop III protostars/fragments, leading to the rapid merging of sink
particles and likely the formation of close binary black holes that, however,
reach separations below the resolution of our simulations. We discuss the
implications that Pop III separations and ellipticity may have on the
interpretation that gravitational wave signals from merging intermediate-mass
black holes come from Pop III remnants.",2307.14562v2
2023-12-13,Design and Control of an Energy Accumulative Hopping Robot,"Jumping and hopping locomotion are efficient means of traversing unstructured
rugged terrain with the former being the focus of roboticists. This focus has
led to significant performance and understanding in jumping robots but with
limited practical applications as they require significant time between jumps
to store energy, thus relegating jumping to a secondary role in locomotion.
Hopping locomotion, however, can preserve and transfer energy to subsequent
hops without long energy storage periods. Therefore, hopping has the potential
to be far more energy efficient and agile than jumping. However, to date, only
a single untethered hopping robot exists with limited payload and hopping
heights (< 1 meter). This is due to the added design and control complexity
inherent in the requirements to input energy during dynamic locomotion and
control the orientation of the system throughout the hopping cycle, resulting
in low energy input and control torques; a redevelopment from basic principles
is necessary to advance the capabilities of hopping robots. Here we report
hopping robot design principles for efficient and robust systems with high
energy input and control torques that are validated through analytical,
simulation, and experimental results. The resulting robot (MultiMo-MHR) can hop
nearly 4 meters (> 6 times the current state-of-the-art); and is only limited
by the impact mechanics and not energy input. The results also directly
contradict a recent work that concluded hopping with aerodynamic energy input
would be less efficient than flight for hops greater than 0.4 meters.",2312.08301v1
2023-12-13,Dynamical tides in binaries: Inconsistencies in the implementation of Zahn's prescription,"Binary evolution codes are essential tools to help in understanding the
evolution of binary systems. They contain a great deal of physics, for example
stellar evolution, stellar interactions, mass transfer, tides, orbital
evolution. Since many of these processes are difficult to account for in
detail, we often rely on prescriptions obtained in earlier studies. We
highlight that the impact of the dynamical tides with radiative damping has
been implemented inconsistently with respect to its original theoretical
formulation in many studies. We derive a new analytical solution for the
evolution toward synchronization in the case of circular orbits and propose
turnkey equations for the case of eccentric orbits that can be used in
population synthesis studies. We compare the strength of the tidal torque
obtained with this new formula with respect to that obtained with the formula
generally used in literature by studying how the evolution toward
synchronization of main sequence stellar models is affected. We conclude that
by using an incorrect formula for the tidal torque, as has been done in many
binary codes, the strength of the dynamical tides with radiative damping is
over- or underestimated depending on whether the star is close to or far from
synchronization.",2312.08437v1
2024-02-22,Deep Generative Model-based Synthesis of Four-bar Linkage Mechanisms with Target Conditions,"Mechanisms are essential components designed to perform specific tasks in
various mechanical systems. However, designing a mechanism that satisfies
certain kinematic or quasi-static requirements is a challenging task. The
kinematic requirements may include the workspace of a mechanism, while the
quasi-static requirements of a mechanism may include its torque transmission,
which refers to the ability of the mechanism to transfer power and torque
effectively. In this paper, we propose a deep learning-based generative model
for generating multiple crank-rocker four-bar linkage mechanisms that satisfy
both the kinematic and quasi-static requirements aforementioned. The proposed
model is based on a conditional generative adversarial network (cGAN) with
modifications for mechanism synthesis, which is trained to learn the
relationship between the requirements of a mechanism with respect to linkage
lengths. The results demonstrate that the proposed model successfully generates
multiple distinct mechanisms that satisfy specific kinematic and quasi-static
requirements. To evaluate the novelty of our approach, we provide a comparison
of the samples synthesized by the proposed cGAN, traditional cVAE and NSGA-II.
Our approach has several advantages over traditional design methods. It enables
designers to efficiently generate multiple diverse and feasible design
candidates while exploring a large design space. Also, the proposed model
considers both the kinematic and quasi-static requirements, which can lead to
more efficient and effective mechanisms for real-world use, making it a
promising tool for linkage mechanism design.",2402.14882v1
2021-09-01,Optical detection of the rapidly spinning white dwarf in V1460 Her,"Accreting magnetic white dwarfs offer an opportunity to understand the
interplay between spin-up and spin-down torques in binary systems. Monitoring
of the white dwarf spin may reveal whether the white dwarf spin is currently in
a state of near-equilibrium, or of uni-directional evolution towards longer or
shorter periods, reflecting the recent history of the system and providing
constraints for evolutionary models. This makes the monitoring of the spin
history of magnetic white dwarfs of high interest. In this paper we report the
results of a campaign of follow-up optical photometry to detect and track the
39 sec white dwarf spin pulses recently discovered in Hubble Space Telescope
data of the cataclysmic variable V1460 Her. We find the spin pulsations to be
present in g-band photometry at a typical amplitude of 0.4%. Under favourable
observing conditions, the spin signal is detectable using 2-meter class
telescopes. We measured pulse-arrival times for all our observations, which
allowed us to derive a precise ephemeris for the white dwarf spin. We have also
derived an orbital modulation correction that can be applied to the
measurements. With our limited baseline of just over four years, we detect no
evidence yet for spin-up or spin-down of the white dwarf, obtaining a lower
limit of |P/Pdot|> 4e7 years, which is already 4 to 8 times longer than the
timescales measured in two other cataclysmic variable systems containing
rapidly rotating white dwarfs, AE Aqr and AR Sco.",2109.00553v1
2004-03-30,CHANDRA Observations of V407 Vul: Confirmation of the Spin-up,"V407 Vul is a candidate double-degenerate binary with a putative 1.756 mHz
(9.5 min) orbital frequency. In a previous timing study using archival ROSAT
and ASCA data we reported evidence for an increase of this frequency at a rate
consistent with expectations for gravitational radiation from a detached
ultracompact binary system. Here we report the results of new CHANDRA timing
observations which confirm the previous indications of spin-up of the X-ray
frequency, and provide much tighter constraints on the frequency derivative. We
obtained with CHANDRA a total of 90 ksec of exposure in two epochs separated in
time by 11.5 months. The total time span of the archival ROSAT, ASCA and new
CHANDRA data is now 10.5 years. This more than doubles the interval spanned by
the ROSAT and ASCA data alone, providing much greater sensitivity to a
frequency derivative. With the addition of the CHANDRA data an increasing
frequency is unavoidable, with a value df/dt = 7.0 x 10-18 Hz/s. Although a
long-term spin-up trend is confirmed, there is excess variance in the phase
timing residuals, perhaps indicative of shorter timescale torque fluctuations
or phase instability associated with the source of the X-ray flux. Power
spectral searches for periods longward of the 9.5 minute period do not find any
significant modulations, however, the sensitivity of searches in this frequency
range are somewhat compromised by the dithering of the Chandra attitude. The
observed spin-up is of a magnitude consistent with that expected from
gravitational radiation decay, however, the factor of 3 variations in flux
combined with the timing noise could conceivably result from accretion-induced
spin-up of a white dwarf. Continued monitoring to explore correlations of
torque with X-ray flux could provide a further test of this hypothesis.",0403675v1
2015-08-18,Frequency Domain Storage Ring Method for Electric Dipole Moment Measurement,"Precise measurement of the electric dipole moments (EDM) of fundamental
charged particles would provide a significant probe of physics beyond the
standard model. Any measurably large EDM would imply violation of both time
reversal and parity conservation, with implications for the matter/anti-matter
imbalance of the universe, not currently understood within the standard model.
A frequency domain (i.e. difference of frequencies) method is proposed for
measuring the EDM of electrons or protons or, with modifications, deuterons.
Anticipated precision (i.e. reproducibility) is $10^{-30}\,$e-cm for the proton
EDM, with comparable accuracy (i.e. including systematic error). This would be
almost six orders of magnitude smaller than the present upper limit, and will
provide a stringent test of the standard model.
  Resonant polarimetry, made practical by the large polarized beam charge, is
the key (most novel, least proven) element of the method. Along with the
phase-locked, rolling polarization ""Koop spin wheel,"" resonant polarimetry
measures beam polarization as amplitude rather than as intensity.
  The polarization roll, at 100\,Hz for example, and adjustable by a constant
control current, causes spurious torques due to field errors to average to zero
to high accuracy. Since these torques have been considered to be the dominant
source of systematic error in truly frozen spin operation, this is a major
improvement resulting from the rolling polarization. Important sources of
systematic errors remain, the main one being due to Wien filter reversal
uncertainty.
  Both electron and proton spins can be ""frozen"" in all-electric storage rings,
and their EDM precisions should be comparable. Freezing the deuteron spin
requires a superimposed electric and magnetic guide field; otherwise the
rolling spin method and precision should be similar.",1508.04366v2
2021-04-23,Roadmap of spin-orbit torques,"Spin-orbit torque (SOT) is an emerging technology that enables the efficient
manipulation of spintronic devices. The initial processes of interest in SOTs
involved electric fields, spin-orbit coupling, conduction electron spins and
magnetization. More recently interest has grown to include a variety of other
processes that include phonons, magnons, or heat. Over the past decade, many
materials have been explored to achieve a larger SOT efficiency. Recently,
holistic design to maximize the performance of SOT devices has extended
material research from a nonmagnetic layer to a magnetic layer. The rapid
development of SOT has spurred a variety of SOT-based applications. In this
Roadmap paper, we first review the theories of SOTs by introducing the various
mechanisms thought to generate or control SOTs, such as the spin Hall effect,
the Rashba-Edelstein effect, the orbital Hall effect, thermal gradients,
magnons, and strain effects. Then, we discuss the materials that enable these
effects, including metals, metallic alloys, topological insulators,
two-dimensional materials, and complex oxides. We also discuss the important
roles in SOT devices of different types of magnetic layers. Afterward, we
discuss device applications utilizing SOTs. We discuss and compare
three-terminal and two-terminal SOT-magnetoresistive random-access memories
(MRAMs); we mention various schemes to eliminate the need for an external
field. We provide technological application considerations for SOT-MRAM and
give perspectives on SOT-based neuromorphic devices and circuits. In addition
to SOT-MRAM, we present SOT-based spintronic terahertz generators,
nano-oscillators, and domain wall and skyrmion racetrack memories. This paper
aims to achieve a comprehensive review of SOT theory, materials, and
applications, guiding future SOT development in both the academic and
industrial sectors.",2104.11459v2
2021-08-31,Toward 100% Spin-Orbit Torque Efficiency with High Spin-Orbital Hall Conductivity Pt-Cr Alloys,"5d transition metal Pt is the canonical spin Hall material for efficient
generation of spin-orbit torques (SOTs) in Pt/ferromagnetic layer (FM)
heterostructures. However, for a long while with tremendous engineering
endeavors, the damping-like SOT efficiencies (${\xi}_{DL}$) of Pt and Pt alloys
have still been limited to ${\xi}_{DL}$<0.5. Here we present that with proper
alloying elements, particularly 3d transition metals V and Cr, a high
spin-orbital Hall conductivity
(${\sigma}_{SH}{\sim}6.5{\times}10^{5}({\hbar}/2e){\Omega}^{-1}{\cdot} m^{-1}$)
can be developed. Especially for the Cr-doped case, an extremely high
${\xi}_{DL}{\sim}0.9$ in a Pt$_{0.69}$Cr$_{0.31}$/Co device can be achieved
with a moderate Pt$_{0.69}$Cr$_{0.31}$ resistivity of ${\rho}_{xx}{\sim}133
{\mu}{\Omega}{\cdot}cm$. A low critical SOT-driven switching current density of
$J_{c}{\sim}3.2{\times}10^{6} A{\cdot}cm^{-2}$ is also demonstrated. The
damping constant (${\alpha}$) of Pt$_{0.69}$Cr$_{0.31}$/FM structure is also
found to be reduced to 0.052 from the pure Pt/FM case of 0.078. The overall
high ${\sigma}_{SH}$, giant ${\xi}_{DL}$, moderate ${\rho}_{xx}$, and reduced
${\alpha}$ of such a Pt-Cr/FM heterostructure makes it promising for versatile
extremely low power consumption SOT memory applications.",2108.13857v3
2019-10-01,Monitoring the Superorbital Period Variation and the Spin Period Evolution of SMC X-1,"The X-ray pulsar SMC X-1 shows a superorbital modulation with an unstable
cycle length in the X-ray band. We present its timing behaviors, including the
spin, orbital, and superorbital modulations, beyond the end of the Rossi X-ray
Timing Explorer mission. The time-frequency maps derived by the wavelet
Z-transform and the Hilbert-Huang transform suggest that a new superorbital
period excursion event occurred in ~MJD 57100 (2015 March). This indicates the
excursion is recurrent and probably (quasi)periodic. The hardness ratio
obtained with the Monitor of All-sky X-ray Image (MAXI) suggests increased
absorption during the transition from the high to the low state in the
superorbital cycle. Compared to the regular epochs, the superorbital profile
during the excursion epochs has a shallower and narrower valley, likely caused
by a flatter warp. By tracking the spin period evolution with the MAXI Gas Slit
Camera in 2-20 keV, we derive an averaged spin-up rate of
$\dot{\nu}=2.515(3)\times10^{-11}$ s$^{-2}$ during the period between MJD 55141
(2009 November) and 58526 (2019 February). We obtain no positive correlation
between the spin frequency residual and the superorbital frequency, but a
torque change accompanying the superorbital period excursion is possible. We
suggest that the accretion torque on the neutron star could be changed by
various mechanisms, including the change of mass accretion rate and the warp
angle. We update the value of the orbital decay as
$\dot{P}_{\rm{orb}}/P_{\rm{orb}}=-3.380(6)\times10^{-6}$ yr$^{-1}$. Finally, we
reconfirm the detection of the superorbital modulation in the optical band and
its coherence in phase with the X-ray modulation.",1910.00200v2
2023-11-28,"Dynamics and spin alignment in massive, gravito-turbulent circumbinary discs around supermassive black hole binaries","Parsec-scale separation supermassive black hole binaries in the centre of
gas-rich galaxy merger remnants could be surrounded by massive circumbinary
discs (CBDs). Black hole mass and spin evolution during the gas-rich binary
inspiral are crucial in determining the direction and power of relativistic
jets that radio observations with LOFAR and SKAO will probe, and for predicting
gravitational wave (GW) emission that IPTA and LISA will measure. We present 3D
hydrodynamic simulations capturing gas-rich, self-gravitating CBDs around a
$2\times 10^6$M$_{\odot}$ supermassive black hole binary, that probe different
mass ratios, eccentricities and inclinations. We employ a sub-grid
Shakura-Sunyaev accretion disc to self-consistently model black hole mass and
spin evolution together with super-Lagrangian refinement techniques to resolve
gas flows, streams and mini-discs within the cavity, which play a fundamental
role in torquing and feeding the binary. We find that higher mass ratio and
eccentric binaries result in larger cavities, while retrograde binaries result
in smaller cavities. All of the simulated binaries are expected to shrink with
net gravitational torques being negative. Unlike previous simulations, we do
not find preferential accretion onto the secondary black hole. This implies
smaller chirp masses at coalescence and hence a weaker GW background.
Critically this means that spin-alignment is faster than the binary inspiral
timescale even for low mass ratios. However, we find that mini-disc and hence
spin alignment is not guaranteed in initially misaligned systems, potentially
leading to a significant fraction of recoiled remnants displaced from their
host galaxies if chaotic accretion is the dominant feeding channel.",2311.17144v1
2012-02-24,Dynamical Magnetic and Nuclear Polarization in Complex Spin Systems: Semi-magnetic II-VI Quantum Dots,"Dynamical magnetic and nuclear polarization in complex spin systems is
discussed on the example of transfer of spin from exciton to the central spin
of magnetic impurity in a quantum dot in the presence of a finite number of
nuclear spins. The exciton is described in terms of the electron and heavy hole
spins interacting via exchange interaction with magnetic impurity, via
hypeprfine interaction with a finite number of nuclear spins and via dipole
interaction with photons. The time-evolution of the exciton, magnetic impurity
and nuclear spins is calculated exactly between quantum jumps corresponding to
exciton radiative recombination. The collapse of the wavefunction and the
refilling of the quantum dot with new spin polarized exciton is shown to lead
to build up of magnetization of the magnetic impurity as well as nuclear spin
polarization. The competition between electron spin transfer to magnetic
impurity and to nuclear spins simultaneous with the creation of dark excitons
is elucidated. The technique presented here opens up the possibility of
studying optically induced Dynamical Magnetic and Nuclear Polarization in
Complex Spin Systems.",1202.5352v3
2018-12-05,Observations of Spin-Down in Post-Mast-Transfer Stars and the Possibility for Blue Straggler Gyrochronology,"Blue stragglers and other mass transfer/collision products are likely born
with rapid rotation rates due to angular momentum transfer during
mass-transfer, merger or collisional formation. However, less is known about
the angular momentum evolution of these stars as they age. Here we compare
rotation rates and post-formation ages of mass-transfer products to models of
angular momentum evolution for normal main-sequence stars and collisionally
formed blue stragglers. In our sample, we include both F- and G-type blue
stragglers in the cluster NGC 188 and post-mass-transfer GK main-sequence stars
in the field, all binaries with WD companions. We compare ages derived from WD
cooling models to photometric rotation periods and/or spectral vsini
measurements. We demonstrate that these systems have rapid rotation rates soon
after formation. They then spin down as they age much as standard solar-type
main-sequence stars do. We discuss the physical implications of this result,
which suggests that the spin-down of post-mass transfer stars can be described
by standard magnetic-braking prescriptions. This opens up the possibility of
using gyrochronology as a method to determine the time since formation of blue
straggler stars and other post-mass-transfer binaries.",1812.02181v1
2024-03-23,Quantum state transfer performance of Heisenberg spin chains with site-dependent interactions designed using a generic genetic algorithm,"Designing a good transfer channel for arbitrary quantum states in spin chains
implies optimizing a cost function, usually the averaged fidelity of
transmission. The fidelity of transmission measures how much the transferred
state resembles the state prepared at the beginning of the transfer protocol.
When averaged over all the possible initial states, the figure of merit
quantifies the quality of the protocol. There are proposals for optimizing a
given Hamiltonian to accomplish a particular task. The transfer of quantum
states is one of them. In particular, we consider the design of Heisenberg spin
chains using a genetic algorithm. This very efficient algorithm allows us to
study different properties of Hamiltonians with good to excellent transfer
ability. One apparent drawback of using a random search method is that it
results in exchange coefficient strengths that change abruptly from site to
site. Modifying the cost function, we obtain Hamiltonians with exchange
coefficients varying smoothly along the chain length. Our results show that the
smoothed Hamiltonians have the same, or less, transfer ability than the rough
ones, and both kinds show similar robustness against static disorder. By
studying the statistical properties of the eigenvalues of Hamiltonians with
varying transfer abilities, we determine the ensemble of random matrices to
which the spectra belong.",2403.15909v1
2004-10-16,On the entanglement entropy for a XY spin chain,"The entanglement entropy for the ground state of a XY spin chain is related
to the corner transfer matrices of the triangular Ising model and expressed in
closed form.",0410416v1
2008-03-02,Large Deviations in Quantum Spin Chain,"We show the full large deviation principle for KMS-states and $C^*$-finitely
correlated states on a quantum spin chain. We cover general local observables.
Our main tool is Ruelle's transfer operator method.",0803.0113v1
2015-08-18,Fast spin information transfer between distant quantum dots using individual electrons,"Transporting ensembles of electrons over long distances without losing their
spin polarization is an important benchmark for spintronic devices. It requires
usually to inject and to probe spin polarized electrons in conduction channels
using ferromagnetic contacts or optical excitation. Parallel to this
development, an important effort has been dedicated to the control of
nanocircuits at the single electron level. The detection and the coherent
manipulation of the spin of a single electron trapped in a quantum dot are now
well established. Combined with the recent control of the displacement of
individual electrons between two distant quantum dots, these achievements
permit to envision the realization of spintronic protocols at the single
electron level. Here, we demonstrate that spin information carried by one or
two electrons can be transferred between two quantum dots separated by a
distance of 4 micrometers with a classical fidelity of 65 %. We show that it is
presently limited by spin flips occurring during the transfer procedure prior
to and after the electron displacement. Being able to encode and control
information in the spin degree of freedom of a single electron while being
transferred over distances of a few microns on nanosecond timescales paves the
way towards ""quantum spintronics"" devices where large scale spin-based quantum
information processing could be implemented.",1508.04307v2
2017-12-04,Trend reversal in the magnetic-field dependence of exciton spin-transfer rates in diluted magnetic semiconductors due to non-Markovian dynamics,"We investigate theoretically the influence of an external magnetic field on
the spin dynamics of excitons in diluted magnetic semiconductor quantum wells.
To this end, we apply a quantum kinetic theory beyond the Markov approximation
which reveals that non-Markovian effects can significantly influence the
exciton spin dynamics. If the magnetic field is oriented parallel to the growth
direction of the well, the Markovian spin-transfer rate decreases monotonically
with increasing field as predicted by Fermi's golden rule. The quantum kinetic
theory follows this result qualitatively but predicts pronounced quantitative
differences in the spin-transfer rate as well as in the long-time spin
polarization. However, for an in-plane magnetic field, where the Markovian
spin-transfer rate first drops and then increases again, quantum kinetic
effects become so pronounced that the Markovian trend is completely reversed.
This is made evident by a distinct maximum of the rate followed by a monotonic
decrease. The deviations can be traced back to a redistribution of carriers in
energy space caused by correlations between excitons and magnetic dopants. The
same effect leads to a finite electron-spin polarization at long times in
longitudinal as well as transverse fields which is much larger than the
corresponding Markovian prediction.",1712.00978v2
2019-03-27,Materials Physics and Spin Glasses,"Comparisons and analogies are drawn between materials ferroic glasses and
conventional spin glasses, in terms of both experiment and theoretical
modelling, with inter-system conceptual transfers leading to suggestions of
further issues to investigate.",1903.11414v1
2023-05-25,Optically controlling the competition between spin flips and intersite spin transfer in a Heusler half-metal on sub-100 fs timescales,"The direct manipulation of spins via light may provide a path toward
ultrafast energy-efficient devices. However, distinguishing the microscopic
processes that can occur during ultrafast laser excitation in magnetic alloys
is challenging. Here, we study the Heusler compound Co2MnGa, a material that
exhibits very strong light-induced spin transfers across the entire M-edge. By
combining the element-specificity of extreme ultraviolet high harmonic probes
with time-dependent density functional theory, we disentangle the competition
between three ultrafast light-induced processes that occur in Co2MnGa:
same-site Co-Co spin transfer, intersite Co-Mn spin transfer, and ultrafast
spin-flips mediated by spin-orbit coupling. By measuring the dynamic magnetic
asymmetry across the entire M-edges of the two magnetic sublattices involved,
we uncover the relative dominance of these processes at different probe energy
regions and times during the laser pulse. Our combined approach enables a
comprehensive microscopic interpretation of laser-induced magnetization
dynamics on timescales shorter than 100 fs.",2305.16455v2
2004-06-03,Dynamics of Spin Relaxation near the Edge of Two-Dimensional Electron Gas,"We report calculations of spin relaxation dynamics of two-dimensional
electron gas with spin-orbit interaction at the edge region. It is found that
the relaxation of spin polarization near the edge is more slow than relaxation
in the bulk. That results finally in the spin accumulation at the edge. Time
dependence of spin polarization density is calculated analytically and
numerically. The mechanism of slower spin relaxation near the edge is related
to electrons reflections from the boundary and the lack of the translation
symmetry. These reflections partially compensate electron spin precession
generated by spin-orbit interaction, consequently making the spin polarization
near the edge long living. This effect is accompanied by spin polarization
oscillations and spin polarization transfer from the perpendicular to in-plane
component.",0406064v1
2010-03-09,Generation and Manipulation of Spin Current in Graphene Nanodisks: Robustness against Randomness and Lattice Defects,"Trigonal zigzag graphene nanodisk exhibits magnetism whose spin is
proportional to the edge length of the nanodisk. Its spin can be designed from
1/2 to a huge value. The spins form a quasiferromagnet, which has intermediate
properties between a single spin and a ferromagnet. In other words, the
ferromagnet order has a relatively long life time, and yet the nanodisk spin
can be rotated by external field or current. We consider a nanodisk connected
with two leads. This system acts as a spin filter just as in a
metal-ferromagnet-metal junction. In this way we can generate a spin current.
Furthermore we can manipulate spin current by spin valve, spin switch and other
spintronic devices made of graphene nanodisks. We also show that nanodisk spins
are robust against the effect of randomness in site energy, transfer energy and
lattice defects.",1003.1766v1
2014-12-01,Dissipation due to pure spin-current generated by spin pumping,"Based on spin-dependent transport theory and thermodynamics, we develop a
generalized theory of the Joule heating in the presence of a spin current.
Along with the conventional Joule heating consisting of an electric current and
electrochemical potential, it is found that the spin current and spin
accumulation give an additional dissipation because the spin-dependent
scatterings inside bulk and ferromagnetic/nonmagnetic interface lead to a
change of entropy. The theory is applied to investigate the dissipation due to
pure spin-current generated by spin pumping across a
ferromagnetic/nonmagnetic/ferromagnetic multilayer. The dissipation arises from
an interface because the spin pumping is a transfer of both the spin angular
momentum and the energy from the ferromagnet to conduction electrons near the
interface. It is found that the dissipation is proportional to the enhancement
of the Gilbert damping constant by spin pumping.",1412.0688v1
2016-07-31,Simulating Quantum Spin Models using Rydberg-Excited Atomic Ensembles in Magnetic Microtrap Arrays,"We propose a scheme to simulate lattice spin models based on strong and
long-range interacting Rydberg atoms stored in a large-spacing array of
magnetic microtraps. Each spin is encoded in a collective spin state involving
a single $nP$ Rydberg atom excited from an ensemble of ground-state alkali
atoms prepared via Rydberg blockade. After the excitation laser is switched off
the Rydberg spin states on neighbouring lattice sites interact via general
isotropic or anisotropic spin-spin interactions. To read out the collective
spin states we propose a single Rydberg atom triggered avalanche scheme in
which the presence of a single Rydberg atom conditionally transfers a large
number of ground-state atoms in the trap to an untrapped state which can be
readily detected by site-resolved absorption imaging. Such a quantum simulator
should allow the study of quantum spin systems in almost arbitrary
two-dimensional configurations. This paves the way towards engineering exotic
spin models, such as spin models based on triangular-symmetry lattices which
can give rise to frustrated-spin magnetism.",1608.00251v1
2018-07-25,Nuclear spin dynamics influenced and detected by electron spin polarization in CdTe/CdMgTe quantum wells,"Nuclear spin coherence and relaxation dynamics of all constituent isotopes of
an n-doped CdTe/(Cd,Mg)Te quantum well structure are studied employing
optically detected nuclear magnetic resonance. Using time-resolved pump-probe
Faraday ellipticity, we generate and detect the coherent spin dynamics of the
resident electrons. The photogenerated electron spin polarization is
transferred into the nuclear spin system, which becomes polarized and acts back
on the electron spins as the Overhauser field. Under the influence of resonant
radio frequency pulses, we trace the coherent spin dynamics of the nuclear
isotopes $^{111}$Cd, $^{113}$Cd, and $^{125}$Te. We measure nuclear Rabi
oscillations, the inhomogeneous dephasing time $T_2^*$, the spin coherence time
$T_2$, and the longitudinal relaxation time $T_1$. Furthermore, we investigate
the influence of the laser excitation and the corresponding electron spin
polarization on the nuclear spin relaxation time and find a weak extension of
this time induced by interaction with the electron spins.",1807.09672v2
2016-12-29,Theory of electron transport and magnetization dynamics in metallic ferromagnets,"Magnetic electric effects in ferromagnetic metals are discussed from the
viewpoint of effective spin electromagnetic field that couples to conduction
electron spin. The effective field in the adiabatic limit is the spin Berry's
phase in space and time, and it leads to spin motive force (voltage generated
by magnetization dynamics) and topological Hall effect due to spin chirality.
Its gauge coupling to spin current describes the spin transfer effect, where
magnetization structure is driven by an applied spin current. The idea of
effective gauge field can be extended to include spin relaxation and Rashba
spin-orbit interaction. Voltage generation by the inverse Edelstein effect in
junctions is interpreted as due to the electric component of Rashba-induced
spin gauge field. The spin gauge field arising from the Rashba interaction
turns out to coincides with troidal moment, and causes asymmetric light
propagation (directional dichroism) as a result of the Doppler shift. Rashba
conductor without magnetization is shown to be natural metamaterial exhibiting
negative refraction.",1612.09019v1
2021-08-05,Polarizing electron spins with a superconducting flux qubit,"Electron spin resonance (ESR) is a useful tool to investigate properties of
materials in magnetic fields where high spin polarization of target electron
spins is required in order to obtain high sensitivity. However, the smaller
magnetic fields becomes, the more difficult high polarization is passively
obtained by thermalization. Here, we propose to employ a superconducting flux
qubit (FQ) to polarize electron spins actively. We have to overcome a large
energy difference between the FQ and electron spins for efficient energy
transfer among them. For this purpose, we adopt a spin-lock technique on the FQ
where the Rabi frequency associated with the spin-locking can match the
resonance (Larmor) one of the electron spins. We find that adding dephasing on
the spins is beneficial to obtain high polarization of them, because otherwise
the electron spins are trapped in dark states that cannot be coupled with the
FQ. We show that our scheme can achieve high polarization of electron spins in
realistic experimental conditions.",2108.02463v1
2021-12-01,Strong Long-Range Spin-Spin Coupling via a Kerr Magnon Interface,"Strong long-range coupling between distant spins is crucial for spin-based
quantum information processing. However, achieving such a strong spin-spin
coupling remains challenging. Here we propose to realize a strong coupling
between two distant spins via the Kerr effect of magnons in a
yttrium-iron-garnet nanosphere. By applying a microwave field on this
nanosphere, the Kerr effect of magnons can induce the magnon squeezing, so that
the coupling between the spin and the squeezed magnons can be exponentially
enhanced. This in turn allows the spin-magnon distance to increase from nano-
to micrometer scale. By considering the virtual excitation of the squeezed
magnons in the dispersive regime, strong spin-spin coupling mediated by the
squeezed magnons can be achieved, and a remote quantum-state transfer, as well
as the nonlocal two-qubit ISWAP gate with high fidelity becomes implementable.
Our approach offers a feasible scheme to perform quantum information processing
among distant spins.",2112.00452v3
2023-01-06,Interfacial magnetic anisotropy controlled spin pumping in Co60Fe20B20/Pt stack,"Controlled spin transport in magnetic stacks is required to realize pure spin
current-driven logic and memory devices. The control over the generation and
detection of the pure spin current is achieved by tuning the spin to charge
conversion efficiency of the heavy metal interfacing with ferromagnets. Here,
we demonstrate the direct tunability of spin angular momentum transfer and
thereby spin pumping, in CoFeB/Pt stack, with interfacial magnetic anisotropy.
The ultra-low thickness of CoFeB thin film tilts the magnetic easy axis from
in-plane to out-of-plane due to surface anisotropy. The Ferromagnetic resonance
measurements are performed to investigate the magnetic anisotropy and spin
pumping in CoFeB/Pt stacks. We clearly observe tunable spin pumping effect in
the CoFeB/Pt stacks with varying CoFeB thicknesses. The spin current density,
with varying ferromagnetic layer thickness, is found to increase from 0.11 to
0.24 MA/m2, with increasing in-plane anisotropy field. Such interfacial
anisotropy-controlled generation of pure spin current can potentially lead to
next-generation anisotropic spin current-controlled spintronic devices.",2301.02370v1
2023-09-07,Hyperpolarisation of nuclear spins: polarisation blockade,"Efficient hyperpolarisation of nuclear spins via optically active defect
centers, such as the nitrogen vacancy (NV) center in diamond, has great
potential for enhancing NMR based quantum information processing and nanoscale
magnetic resonance imaging. Recently, pulse-based protocols have been shown to
efficiently transfer optically induced polarisation of the electron defect spin
to surrounding nuclear spins -- at particular resonant pulse intervals. In this
work, we investigate the performance of these protocols, both analytically and
experimentally, with the electronic spin of a single NV defect. We find that
whenever polarisation resonances of nuclear spins are near-degenerate with a
`blocking' spin, which is single spin with stronger off-diagonal coupling to
the electronic central spin, they are displaced out of the central resonant
region -- without, in general, significant weakening of the resonance. We
analyse the underlying physical mechanism and obtain a closed form expression
for the displacement. We propose that spin blocking represents a common but
overlooked effect in hyperpolarisation of nuclear spins and suggest solutions
for improved protocol performance in the presence of (naturally occurring)
blocking nuclear spins.",2309.03761v1
2024-03-13,Spin-resolved counting statistics as a sensitive probe of spin correlation in transport through a quantum dot spin valve,"We investigate the noise in spin transport through a single quantum dot (QD)
tunnel coupled to ferromagnetic electrodes with noncollinear magnetizations.
Based on a spin-resolved quantum master equation, auto- and cross-correlations
of spin-resolved currents are analyzed to reveal the underlying spin transport
dynamics and characteristics for various polarizations. We find the currents of
majority and minority spins could be strongly autocorrelated despite
uncorrelated charge transfer. The interplay between tunnel coupling and the
Coulomb interaction gives rise to an exchange magnetic field, leading to the
precession of the accumulated spin in the QD. It strongly suppresses the
bunching of spin tunneling events and results in a unique double-peak structure
in the noise of the net spin current. The spin autocorrelation is found to be
susceptible to magnetization alignments, which may serve as a sensitive tool to
measure the magnetization directions between the ferromagnetic electrodes.",2403.08621v1
2018-08-09,Spin-selective electron transfer reactions of radical pairs: beyond the Haberkorn master equation,"Radical pair recombination reactions are normally described using a quantum
mechanical master equation for the electronic and nuclear spin density
operator. The electron spin state selective (singlet and triplet) recombination
processes are described with a Haberkorn reaction term in this master equation.
Here we consider a general spin state selective electron transfer reaction of a
radical pair and use Nakajima-Zwanzig theory to derive the master equation for
the spin density operator, thereby elucidating the relationship between
non-adiabatic reaction rate theory and the Haberkorn reaction term. A second
order perturbation theory treatment of the diabatic coupling naturally results
in the Haberkorn master equation with an additional reactive scalar electron
spin coupling term. This term has been neglected in previous spin chemistry
calculations, but we show that it will often be quite significant. We also show
that beyond second order in perturbation theory, i.e., beyond the Fermi golden
rule limit, an additional reactive singlet-triplet dephasing term appears in
the master equation. A closed form expression for the reactive scalar electron
spin coupling in terms of the Marcus theory parameters that determine the
singlet and triplet recombination rates is presented. By performing simulations
of radical pair reactions with the exact Hierarchical Equations of Motion
(HEOM) method, we demonstrate that our master equations provide a very accurate
description of radical pairs undergoing spin-selective non-adiabatic electron
transfer reactions. The existence of a reactive electron spin coupling may well
have implications for biologically relevant radical pair reactions such as
those which have been suggested to play a role in avian magnetoreception.",1808.03211v1
2015-02-18,Quenching of dynamic nuclear polarization by spin-orbit coupling in GaAs quantum dots,"The central-spin problem, in which an electron spin interacts with a nuclear
spin bath, is a widely studied model of quantum decoherence. Dynamic nuclear
polarization (DNP) occurs in central spin systems when electronic angular
momentum is transferred to nuclear spins and is exploited in spin-based quantum
information processing for coherent electron and nuclear spin control. However,
the mechanisms limiting DNP remain only partially understood. Here, we show
that spin-orbit coupling quenches DNP in a GaAs double quantum dot, even though
spin-orbit coupling in GaAs is weak. Using Landau-Zener sweeps, we measure the
dependence of the electron spin-flip probability on the strength and direction
of in-plane magnetic field, allowing us to distinguish effects of the
spin-orbit and hyperfine interactions. To confirm our interpretation, we
measure high-bandwidth correlations in the electron spin-flip probability and
attain results consistent with a significant spin-orbit contribution. We
observe that DNP is quenched when the spin-orbit component exceeds the
hyperfine, in agreement with a theoretical model. Our results shed new light on
the surprising competition between the spin-orbit and hyperfine interactions in
central-spin systems.",1502.05400v1
2022-05-03,Quantum transfer of interacting qubits,"The transfer of quantum information between different locations is key to
many quantum information processing tasks. Whereas, the transfer of a single
qubit state has been extensively investigated, the transfer of a many-body
system configuration has insofar remained elusive. We address the problem of
transferring the state of n interacting qubits. Both the exponentially
increasing Hilbert space dimension, and the presence of interactions
significantly scale-up the complexity of achieving high-fidelity transfer. By
employing tools from random matrix theory and using the formalism of quantum
dynamical maps, we derive a general expression for the average and the variance
of the fidelity of an arbitrary quantum state transfer protocol for n
interacting qubits. Finally, by adopting a weak-coupling scheme in a spin
chain, we obtain the explicit conditions for high-fidelity transfer of 3 and 4
interacting qubits.",2205.01579v1
2010-09-27,Spin-transfer pulse switching: From the dynamic to the thermally activated regime,"The effect of thermal fluctuations on spin-transfer switching has been
studied for a broad range of time scales (sub-ns to seconds) in a model system,
a uniaxial thin film nanomagnet. The nanomagnet is incorporated into a
spin-valve nanopillar, which is subject to spin-polarized current pulses of
variable amplitude and duration. Two physical regimes are clearly
distinguished: a long pulse duration regime, in which reversal occurs by
spin-transfer assisted thermal activation over an energy barrier, and a short
time large pulse amplitude regime, in which the switching probability is
determined by the spin angular momentum in the current pulse.",1009.5240v1
2011-01-14,Three-Body Model Calculation of Spin Distribution in Two-Nucleon Transfer Reaction,"The differential cross sections of two-nucleon transfer reactions
238U(18O,16O)240U around 10 MeV per nucleon are calculated by one-step
Born-approximation with a 16O+2n+238U three-body model. The three-body wave
function in the initial channel is obtained with the continuum-discretized
coupled-channels method, and that in the final channel is evaluated with
adiabatic approximation. The resulting cross sections have a peak around the
grazing angle, and the spin distribution, i.e., the cross section at the peak
as a function of the transferred spin, is investigated. The shape of the spin
distribution is found not sensitive to the incident energies, optical
potentials, and treatment of the breakup channels both in the initial and final
states, while it depends on the excitation energy of the residual nucleus 240U.
The peak of the spin distribution moves to the large-spin direction as the
excitation energy increases. To fulfill the condition that the peak position
should not exceeds 10 hbar, which is necessary for the surrogate ratio method
to work, it is concluded that the excitation energy of 240U must be less than
10 MeV.",1101.2732v1
2016-04-17,Superadiabatic quantum state transfer in spin chains,"In this letter we propose a superadiabatic protocol where quantum state
transfer can be achieved with arbitrarily high accuracy and minimal control
across long spin chains with an odd number of spins. The quantum state transfer
protocol only requires the control of the couplings between the qubits on the
edge and the spin chain. We predict fidelities above 0.99 for an evolution of
nanoseconds using typical spin exchange coupling values of {\mu}eV.
Furthermore, by building a superadiabatic formalism on top of this protocol, we
propose a effective superadiabatic protocol that retains the minimal control
over the spin chain and improves the fidelity by up to 20%.",1604.04885v3
2016-06-01,Nanosecond-timescale spin transfer using individual electrons in a quadruple-quantum-dot device,"The ability to coherently transport electron-spin states between different
sites of gate-defined semiconductor quantum dots is an essential ingredient for
a quantum-dot-based quantum computer. Previous shuttles using electrostatic
gating were too slow to move an electron within the spin dephasing time across
an array. Here we report a nanosecond-timescale spin transfer of individual
electrons across a quadruple-quantum-dot device. Utilizing enhanced relaxation
rates at a so-called `hot spot', we can upper bound the shuttle time to at most
150 ns. While actual shuttle times are likely shorter, 150 ns is already fast
enough to preserve spin coherence in e.g. silicon based quantum dots. This work
therefore realizes an important prerequisite for coherent spin transfer in
quantum dot arrays.",1606.00292v1
2019-04-10,Coherent spin state transfer via Heisenberg exchange,"Quantum information science has the potential to revolutionize modern
technology by providing resource-efficient approaches to computing,
communication, and sensing. Although the physical qubits in a realistic quantum
device will inevitably suffer errors, quantum error correction creates a path
to fault-tolerant quantum information processing. Quantum error correction,
however, requires that individual qubits can interact with many other qubits in
the processor. Engineering this high connectivity can pose a challenge for
platforms like electron spin qubits that naturally favor linear arrays. Here,
we present an experimental demonstration of the transmission of electron spin
states via Heisenberg exchange in an array of spin qubits. We transfer both
single-spin and entangled states back and forth in a quadruple quantum-dot
array without moving any electrons. Because it is scalable to large numbers of
qubits, state transfer through Heisenberg exchange will be especially useful
for multi-qubit gates and error-correction in spin-based quantum computers.",1904.05372v3
2003-07-01,Nuclear-Powered Millisecond Pulsars and the Maximum Spin Frequency of Neutron Stars,"Millisecond pulsars are neutron stars (NSs) that are thought to have been
spun-up by mass accretion from a stellar companion. It is unknown whether there
is a natural brake for this process, or if it continues until the centrifugal
breakup limit is reached at submillisecond periods. Many NSs that are accreting
from a companion exhibit thermonuclear X-ray bursts that last tens of seconds,
caused by unstable nuclear burning on their surfaces. Millisecond brightness
oscillations during bursts from ten NSs (as distinct from other rapid X-ray
variability that is also observed) are thought to measure the stellar spin, but
direct proof of a rotational origin has been lacking. Here, we report the
detection of burst oscillations at the known spin frequency of an accreting
millisecond pulsar, and we show that these oscillations always have the same
rotational phase. This firmly establishes burst oscillations as nuclear-powered
pulsations tracing the spin of accreting NSs, corroborating earlier evidence.
The distribution of spin frequencies of the 11 nuclear-powered pulsars cuts off
well below the breakup frequency for most NS models, supporting theoretical
predictions that gravitational radiation losses can limit accretion torques in
spinning up millisecond pulsars.",0307029v1
2004-02-02,Orientations of Spin and Magnetic Dipole Axes of Pulsars in the J0737--3039 Binary Based on Polarimetry Observations at the Green Bank Telescope,"We report here the first polarimetric measurements of the pulsars in the
J0737-3039 binary neutron star system using the Green Bank Telescope. We
conclude both that the primary star (A) has a wide hollow cone of emission,
which is an expected characteristic of the relatively open magnetosphere given
its short spin period, and that A has a small angle between its spin and
magnetic dipole axes, $4\pm 3$ degrees. This near alignment of axes suggests
that A's wind pressure on B's magnetosphere will depend on orbital phase. This
variable pressure is one mechanism for the variation of flux and profile shape
of B with respect to the orbital phase that has been reported. The response of
B to the A wind pressure will also depend on the particular side of its
magnetosphere facing the wind at the spin phase when B is visible. This is a
second possible mechanism for variability. We suggest that B may have its spin
axis aligned with the orbital angular momentum owing to A's wind torque that
contributes to its spindown. Monitoring the pulsars while geodetic precession
changes spin orientations will provide essential evidence to test detailed
theoretical models. We determine the Rotation Measures of the two stars to be
$-112.3\pm 1.5$ and $-118\pm 12$ rad m$^{-2}$.",0402025v1
2003-10-17,Influence Of Current Leads On Critical Current For Spin Precession In Magnetic Multilayers,"In magnetic multilayers, a dc current induces a spin precession above a
certain critical current. Drive torques responsible for this can be calculated
from the spin accumulation $\bar{\Delta\mu}$. Existing calculations of
$\bar{\Delta\mu}$ assume a uniform cross section of conductors. But most
multilayer samples are pillars with current leads flaring out immediately to a
much wider cross-section area than that of the pillar itself. We write
spin-diffusion equations of a form valid for variable cross section, and solve
the case of flat electrodes with radial current distribution perpendicular to
the axis of the pillar. Because of the increased volume available for
conduction-electron spin relaxation in such leads, $\bar{\Delta\mu}$ is reduced
in the pillar by at least a factor of 2 below its value for uniform cross
section, for given current density in the pillar. Also, $\bar{\Delta\mu}$ and
the critical current density for spin precession become nearly independent of
the thickness of the pinned magnetic layer, and more dependent on the thickness
of the spacer, in better agreement with measurements by Albert et al. (2002).",0310408v3
2005-04-07,"Coriolis force, geometric phase, and spin-electric coupling in semiconductors","We consider the response of an effective spin of a charge carrier to an
adiabatic rotation of its crystal momentum induced by electric field. This
rotation gives rise to Coriolis pseudo-force that is responsible for torque
acting on the orbital momentum of a particle. Mediated by a spin-orbit coupling
in the valence band this perturbation leads to a spin-electric coupling that
may affect the coherent transport properties of a charge carrier and cause a
spin precession in zero magnetic fields. In the static uniform electric field
the derived effective spin-Hamiltonians of the carriers in the conduction and
light hole bands are homologous to the Rashba Hamiltonian. These effects may be
also interpreted as a manifestation of, in general, a non-Abelian gauge
potential and can be described in purely geometric terms as a consequence of
the corresponding holonomy. We demonstrate that in the conduction band the
strength of the associated covariant gauge field is proportional to the
effective electron g-tensor and is controllable by gate fields or a strain
applied to the crystal.",0504183v6
2009-04-21,Tensor damping in metallic magnetic multilayers,"The mechanism of spin-pumping, described by Tserkovnyak et al., is formally
analyzed in the general case of a magnetic multilayer consisting of two or more
metallic ferromagnetic (FM) films separated by normal metal (NM) layers. It is
shown that the spin-pumping-induced dynamic coupling between FM layers modifies
the linearized Gilbert equations in a way that replaces the scalar Gilbert
damping constant with a nonlocal matrix of Cartesian damping tensors. The
latter are shown to be methodically calculable from a matrix algebra solution
of the Valet-Fert transport equations. As an example, explicit analytical
results are obtained for a 5-layer (spin-valve) of form NM/FM/NM'/FM/NM.
Comparisons with earlier well known results of Tserkovnyak et al. for the
related 3-layer FM/NM/FM indicate that the latter inadvertently hid the tensor
character of the damping, and instead singled out the diagonal element of the
local damping tensor along the axis normal to the plane of the two
magnetization vectors. For spin-valve devices of technological interest, the
influence of the tensor components of the damping on thermal noise or
spin-torque critical currents are strongly weighted by the relative magnitude
of the elements of the nonlocal, anisotropic stiffness-field tensor-matrix, and
for in-plane magnetized spin-valves are generally more sensitive to the
in-plane element of the damping tensor.",0904.3150v2
2015-03-02,Alignments Of Black Holes With Their Warped Accretion Disks And Episodic Lifetimes Of Active Galactic Nuclei,"Warped accretion disks have attracted intensive attention because of their
critical role on shaping the spin of supermassive massive black holes (SMBHs)
through the Bardeen-Petterson effect, a general relativistic effect that leads
to final alignments or anti-alignments between black holes and warped accretion
disks. We study such alignment processes by explicitly taking into account the
finite sizes of accretion disks and the episodic lifetimes of AGNs that
delineate the duration of gas fueling onto accretion disks. We employ an
approximate global model to simulate the evolution of accretion disks, allowing
to determine the gravitomagnetic torque that drives the alignments in a quite
simple way. We then track down the evolutionary paths for mass and spin of
black holes both in a single activity episode and over a series of episodes.
Given with randomly and isotropically oriented gas fueling over episodes, we
calculate the spin evolution with different episodic lifetimes and find that it
is quite sensitive to the lifetimes. We therefore propose that spin
distribution of SMBHs can place constraints on the episodic lifetimes of AGNs
and vice versa. Applications of our results on the observed spin distributions
of SMBHs and the observed episodic lifetimes of AGNs are discussed, although
both the measurements at present are yet ambiguous to draw a firm conclusion.
Our prescription can be easily incorporated into semi-analytic models for black
hole growth and spin evolution.",1503.00432v1
2016-01-12,Exploration of Spin-down Rate of Neutron Star in High Mass X-ray Binaries,"We use the evolutionary population synthesis method to investigate the
statistical properties of the wind-fed neutron star (NS) compact ($P_{\rm
orb}<10$ days) high-mass X-ray binaries (HMXBs) in our Galaxy, based on
different spin-down models. We find that the spin-down rate in the supersonic
propeller phase given \textbf{by assuming that the surrounding material is
treated as forming a quasi-static atmosphere} or \textbf{by assuming that the
characteristic velocity of matter and the typical Alfv$\acute{e}$n velocity of
material in the magnetospheric boundary layer are comparable to the sound speed
in the external medium} is too low to produce the observed number of compact
HMXBs. We also find that the models suggested \textbf{by assuming that the
infalling material is ejected with the corotation velocity at the
magnetospheric radius when the magnetospheric radius is larger than the
corotation radius} and \textbf{by simple integration of the magnetic torque
over the magnetosphere} with a larger spin-down rate than that given by
\citet{dav81} or \citet{is75} can predict a reasonable number of observed
wind-fed NS compact HMXBs. Our calculated results indicate that subsonic
propeller phase may not exist at all by comparing with the observed particular
distributions of wind-fed NS compact HMXBs in the $P_s-P_{orb}$ diagram.
However, the spin-down rate suggested by \citet{wan85,dai06,jia05} and that
given by \citet{dav73} both seem reasonable to produce the observed
distribution of wind-fed NS compact HMXBs in the $P_s-P_{orb}$ diagram. We
cannot find which spin-down rate seems more reasonable from our calculations.",1601.02891v1
2016-01-19,Application of the Ghosh & Lamb Relation to the Spin-up/down Behavior in the X-ray Binary Pulsar 4U 1626-67,"We analyzed continuous MAXI/GSC data of the X-ray binary pulsar 4U 1626-67
from 2009 October to 2013 September, and determined the pulse period and the
pulse-period derivative for every 60-d interval by the epoch folding method.
The obtained periods are consistent with those provided by the Fermi/GBM pulsar
project. In all the 60-d intervals, the pulsar was observed to spin up, with
the spin-up rate positively correlated with the 2-20 keV flux. We applied the
accretion torque model proposed by Ghosh & Lamb (1979, ApJ, 234, 296) to the
MAXI/GSC data, as well as the past data including both spin-up and spin-down
phases. The Ghosh & Lamb relation was confirmed to successfully explain the
observed relation between the spin-up/down rate and the flux. By comparing the
model-predicted luminosity with the observed flux, the source distance was
constrained as 5-13 kpc, which is consistent with that by Chakrabarty (1998,
ApJ, 492, 342). Conversely, if the source distance is assumed, the data can
constrain the mass and radius of the neutron star, because the Ghosh & Lamb
model depends on these parameters. We attempted this idea, and found that an
assumed distance of, e.g., 10 kpc gives a mass in the range of 1.81-1.90 solar
mass, and a radius of 11.4-11.5 km, although these results are still subject to
considerable systematic uncertainties other than that in the distance.",1601.04894v1
2016-07-08,Spin accumulation in asymmetric topological insulator thin films in out of plane magnetic fields,"In this work we study the spin accumulation due to an in-plane electric field
in an asymmetric topological insulator (TI) thin film system with an out of
plane magnetic field and an in-plane magnetization. A TI thin film differs from
the more typically studied thick TI system in that the former has both a top
and a bottom surface where the states localized at both surfaces can couple to
each other due to the finite thickness. In typical spin torque experiments on
TI thin film systems, the top and bottom surfaces of the film are asymmetric as
the former is in contact with a ferromagnetic layer while the latter is
adjacent to a non magnetic substrate. This may lead to differing (i) potentials
and (ii) magnetization strengths experienced by the top and bottom surface
states. We show, via Kubo formula calculations, that each of these two effects
can lead to in-plane spin accumulation perpendicular to the magnetization
direction which are otherwise absent in a top-bottom symmetric TI thin film
system. This spin accumulation results from the breaking of the antisymmetry of
the spin accumulation around the zero magnetic field equal energy contours.",1607.02550v1
2018-01-27,The LArase Satellites Spin mOdel Solutions (LASSOS): a comprehensive model for the spin evolution of the LAGEOS and LARES satellites,"The two LAGEOS and LARES are laser-ranged satellites tracked with the best
accuracy ever achieved. Using their range measurements many geophysical
parameters were calculated and some General Relativity effects were directly
observed. To obtain precise and refined measurements of the effects due to the
predictions of General Relativity on the orbit of these satellites, it is
mandatory to model with high precision and accuracy all other forces, reducing
the free parameters introduced in the orbit determination. A main category of
non-gravitational forces to be considered are those of thermal origin, whose
fine modeling strongly depends on the knowledge of the evolution of the spin
vector. We present a complete model, named LASSOS, to describe the evolution of
the spin of the LAGEOS and LARES satellites. In particular, we solved Euler
equations of motion considering not-averaged torques. This is the most general
case, and the predictions of the model well fit the available observations of
the satellites spin. We also present the predictions of our model in the
fast-spin limit, based on the application of averaged equations. The results
are in good agreement with those already published, but with our approach we
have been able to highlight small errors within these previous works. LASSOS
was developed within the LARASE research program. LARASE aims to improve the
dynamical model of the two LAGEOS and LARES satellites to provide very precise
and accurate measurements of relativistic effects on their orbit, and also to
bring benefits to geophysics and space geodesy.",1801.09098v1
2014-06-16,Early Excitation of Spin-Orbit Misalignments in Close-in Planetary Systems,"Continued observational characterization of transiting planets that reside in
close proximity to their host stars has shown that a substantial fraction of
such objects posses orbits that are inclined with respect to the spin axes of
their stars. Mounting evidence for the wide-spread nature of this phenomenon
has challenged the conventional notion that large-scale orbital transport
occurs during the early epochs of planet formation and is accomplished via
planet-disk interactions. However, recent work has shown that the excitation of
spin-orbit misalignment between protoplanetary nebulae and their host stars can
naturally arise from gravitational perturbations in multi-stellar systems as
well as magnetic disk-star coupling. In this work, we examine these processes
in tandem. We begin with a thorough exploration of the
gravitationally-facilitated acquisition of spin-orbit misalignment and
analytically show that the entire possible range of misalignments can be
trivially reproduced. Moreover, we demonstrate that the observable spin-orbit
misalignment only depends on the primordial disk-binary orbit inclination.
Subsequently, we augment our treatment by accounting for magnetic torques and
show that more exotic dynamical evolution is possible, provided favorable
conditions for magnetic tilting. Cumulatively, our results suggest that
observed spin-orbit misalignments are fully consistent with disk-driven
migration as a dominant mechanism for the origin of close-in planets.",1406.4183v1
2019-03-24,QED effects are negligible for neutron-star spin-down,"The energy loss of a rotationally powered pulsar is primarily carried away as
electromagnetic radiation and a particle wind. Considering that the magnetic
field strength of pulsars ranges from about $10^8$ to $10^{15}$ G, one could
expect quantum electrodynamics (QED) to play a role in their spin-down,
especially for strongly magnetized ones (magnetars). In fact several authors
have argued that QED corrections will dominate the spin-down for slowly
rotating stars. They called this effect quantum vacuum friction (QVF). However,
QVF was originally derived using a problematic self-torque technique, which
leads to a dramatic overestimation of this spin-down effect. Here, instead of
using QVF, we explicitly calculate the energy loss from rotating neutron stars
using the Poynting vector and a model for a particle wind, and we include the
QED one-loop corrections. We express the excess emission as QED one-loop
corrections to the radiative magnetic moment of a neutron star. We do find a
small component of the spin-down luminosity that originates from the vacuum
polarization. However, it never exceeds one percent of the classical magnetic
dipole radiation in neutron stars for all physically interesting field
strengths. Therefore, we find that the radiative corrections of QED are
irrelevant in the energetics of neutron-star spin-down.",1903.10050v2
2019-05-20,Orbitally Dominated Rashba-Edelstein Effect in Noncentrosymmetric Antiferromagnets,"Efficient manipulation of magnetic order with electric current pulses is
desirable for achieving fast spintronic devices. The Rashba-Edelstein effect,
wherein a spin polarization is electrically induced in noncentrosymmetric
systems, provides a mean to achieve current-induced staggered spin-orbit
torques. Initially predicted for spin, the orbital counterpart of this effect
has been disregarded up to now. Here, we present a generalized Rashba-Edelstein
effect, which generates not only spin polarization but also orbital
polarization, which we find to be far from being negligible and could play a
crucial role in the magnetization dynamics. We show that the orbital
Rashba-Edelstein effect does not require spin-orbit coupling to exist. We
present first-principles calculations of the frequency-dependent spin and
orbital Rashba-Edelstein susceptibility tensors for the noncentrosymmetric
antiferromagnets CuMnAs and Mn2Au. We show that the electrically induced local
magnetization has both staggered in-plane components and non-staggered
out-of-plane components, and can exhibit Rashba-like or Dresselhaus-like
symmetries, depending on the magnetic configuration. Furthermore, there is an
induced local magnetization on the nonmagnetic atoms as well, that is smaller
in Mn2Au than in CuMnAs. We compute sizable induced magnetizations at optical
frequencies, which suggest that electric-field driven switching could be
achieved at much higher frequencies.",1905.08279v1
2019-05-22,Current-Induced Dynamics and Chaos of Antiferromagnetic Bimerons,"A magnetic bimeron is a topologically non-trivial spin texture carrying an
integer topological charge, which can be regarded as the counterpart of
skyrmion in easy-plane magnets. The controllable creation and manipulation of
bimerons are crucial for practical applications based on topological spin
textures. Here, we analytically and numerically study the dynamics of an
antiferromagnetic bimeron driven by a spin current. Numerical simulations
demonstrate that the spin current can create an isolated bimeron in the
antiferromagnetic thin film via the damping-like spin torque. The spin current
can also effectively drive the antiferromagnetic bimeron without a transverse
drift. The steady motion of an antiferromagnetic bimeron is analytically
derived and is in good agreement with the simulation results. Also, we find
that the alternating-current-induced motion of the antiferromagnetic bimeron
can be described by the Duffing equation due to the presence of the nonlinear
boundary-induced force. The associated chaotic behavior of the bimeron is
analyzed in terms of the Lyapunov exponents. Our results demonstrate the
inertial dynamics of an antiferromagnetic bimeron, and may provide useful
guidelines for building future bimeron-based spintronic devices.",1905.09007v2
2017-01-27,Application of Spin-Exchange Relaxation-Free Magnetometry to the Cosmic Axion Spin Precession Experiment,"The Cosmic Axion Spin Precession Experiment (CASPEr) seeks to measure
oscillating torques on nuclear spins caused by axion or axion-like-particle
(ALP) dark matter via nuclear magnetic resonance (NMR) techniques. A sample
spin-polarized along a leading magnetic field experiences a resonance when the
Larmor frequency matches the axion/ALP Compton frequency, generating precessing
transverse nuclear magnetization. Here we demonstrate a Spin-Exchange
Relaxation-Free (SERF) magnetometer with sensitivity $\approx 1~{\rm
fT/\sqrt{Hz}}$ and an effective sensing volume of 0.1 $\rm{cm^3}$ that may be
useful for NMR detection in CASPEr. A potential drawback of
SERF-magnetometer-based NMR detection is the SERF's limited dynamic range. Use
of a magnetic flux transformer to suppress the leading magnetic field is
considered as a potential method to expand the SERF's dynamic range in order to
probe higher axion/ALP Compton frequencies.",1701.08082v5
2020-05-07,Effect of interfacial oxidation layer in spin pumping experiments on Ni$_{80}$Fe$_{20}$/SrIrO$_3$ heterostructures,"SrIrO$_3$ with its large spin-orbit coupling and low charge conductivity has
emerged as a potential candidate for efficient spin-orbit torque magnetization
control in spintronic devices. We here report on the influence of an
interfacial oxide layer on spin pumping experiments in Ni$_{80}$Fe$_{20}$
(NiFe)/SrIrO$_3$ bilayer heterostructures. To investigate this scenario we have
carried out broadband ferromagnetic resonance (BBFMR) measurements, which
indicate the presence of an interfacial antiferromagnetic oxide layer. We
performed in-plane BBFMR experiments at cryogenic temperatures, which allowed
us to simultaneously study dynamic spin pumping properties (Gilbert damping)
and static magnetic properties (such as the effective magnetization and
magnetic anisotropy). The results for NiFe/SrIrO$_3$ bilayer thin films were
analyzed and compared to those from a NiFe/NbN/SrIrO$_3$ trilayer reference
sample, where a spin-transparent, ultra-thin NbN layer was inserted to prevent
oxidation of NiFe. At low temperatures, we observe substantial differences in
the magnetization dynamics parameters of these samples, which can be explained
by an antiferromagnetic interfacial layer in the NiFe/SrIrO$_3$ bilayers.",2005.03727v1
2021-11-04,Cosmic Filament Spin from Dark Matter Vortices,"The recent observational evidence for cosmic filament spin on megaparsec
scales (Wang et al, Nature Astronomy 5, 839-845 (2021)) demands an explanation
in the physics of dark matter. Conventional collisionless cold particle dark
matter is conjectured to generate cosmic filament spin through tidal torquing,
but this explanation requires extrapolating from the quasi-linear regime to the
non-linear regime. Meanwhile no alternative explanation exists in the context
of ultra-light (e.g., axion) dark matter, and indeed these models would naively
predict zero spin for cosmic filaments. In this Letter we study cosmic filament
spin in theories of ultra-light dark matter, such as ultra-light axions, and
bosonic and fermionic condensates, such as superfluids and superconductors.
These models are distinguished from conventional particle dark matter models by
the possibility of dark matter vortices. We take a model agnostic approach, and
demonstrate that a collection of dark vortices can explain the data reported in
Wang et al. Modeling a collection of vortices with a simple two-parameter
analytic model, corresponding to an averaging of the velocity field, we find an
excellent fit to the data. We perform a Markov Chain Monte Carlo analysis and
find constraints on the number of vortices, the dark matter mass, and the
radius of the inner core region where the vortices are distributed, in order
for ultra-light dark matter to explain spinning cosmic filaments.",2111.03061v1
2022-01-21,Spin Hall magnetoresistance in paramagnetic NdGaO3,"In recent years, spin Hall magnetoresistance (SMR) has emerged as an
efficient way to probe the spontaneous magnetization state in ordered magnetic
systems, by electrical current. Less known is its versatility as a probe of
materials that do not possess spontaneous magnetization such as in paramagnets.
In this work, SMR is used to probe paramagnetic NdGaO3 (NGO), a rare earth
oxide, possessing a sizable spin orbit interaction (L=6). NGO has not been
investigated earlier for its efficiency in propagating spins. We have performed
extensive temperature and angle dependent-magnetoresistance (ADMR) studies
along dissimilar crystallographic axes in NGO, using platinum (Pt) as spin
injector and detector and utilizing (inverse) spin Hall effect. We find a close
correlation between the temperature dependence of the ADMR response with
magnetization in NGO and a linear current bias dependence of the ADMR
amplitudes. These are chacteristics of SMR effect in Pt/NGO, arising from the
torque acting on localized moments in NGO and considering crystal field induced
intermultiplet transitions with temperature. Control experiments on Pt/SrTiO3
and Pt/SiO2 devices were also carried out in order to validate the observed SMR
response in Pt/NGO bilayer and to rule out magnetoresistive contributions from
Pt.",2201.08685v1
2023-04-03,Nonrelativistic and nonmagnetic control of terahertz charge currents via electrical anisotropy in RuO2 and IrO2,"Precise and ultrafast control over photo-induced charge currents across
nanoscale interfaces could lead to important applications in energy harvesting,
ultrafast electronics, and coherent terahertz sources. Recent studies have
shown that several relativistic mechanisms, including inverse spin-Hall effect,
inverse Rashba-Edelstein effect and inverse spin-orbit-torque effect, can
convert longitudinally injected spin-polarized currents from magnetic materials
to transverse charge currents, thereby harnessing these currents for terahertz
generation. However, these mechanisms typically require external magnetic
fields and suffer from low spin-polarization rates and low efficiencies of
relativistic spin-to-charge conversion. In this work, we present a novel
nonrelativistic and nonmagnetic mechanism that directly utilizes the
photo-excited high-density charge currents across the interface. We demonstrate
that the electrical anisotropy of conductive oxides RuO2 and IrO2 can
effectively deflect injected charge currents to the transverse direction,
resulting in efficient and broadband terahertz radiation. Importantly, this new
mechanism has the potential to offer much higher conversion efficiency compared
to previous methods, as conductive materials with large electrical anisotropy
are readily available, whereas further increasing the spin-Hall angle of
heavy-metal materials would be challenging. Our new findings offer exciting
possibilities for directly utilizing these photo-excited high-density currents
across metallic interfaces for ultrafast electronics and terahertz
spectroscopy.",2304.00692v1
2023-06-20,Convolutional neural networks for large-scale dynamical modeling of itinerant magnets,"Complex spin textures in itinerant electron magnets hold promises for
next-generation memory and information technology. The long-ranged and often
frustrated electron-mediated spin interactions in these materials give rise to
intriguing localized spin structures such as skyrmions. Yet, simulations of
magnetization dynamics for such itinerant magnets are computationally difficult
due to the need for repeated solutions to the electronic structure problems. We
present a convolutional neural network (CNN) model to accurately and
efficiently predict the electron-induced magnetic torques acting on local
spins. Importantly, as the convolutional operations with a fixed kernel
(receptive field) size naturally take advantage of the locality principle for
many-electron systems, CNN offers a scalable machine learning approach to spin
dynamics. We apply our approach to enable large-scale dynamical simulations of
skyrmion phases in itinerant spin systems. By incorporating the CNN model into
Landau-Lifshitz-Gilbert dynamics, our simulations successfully reproduce the
relaxation process of the skyrmion phase and stabilize a skyrmion lattice in
larger systems. The CNN model also allows us to compute the effective receptive
fields, thus providing a systematic and unbiased method for determining the
locality of the original electron models.",2306.11833v1
2023-07-21,Magnetic Proximity induced efficient charge-to-spin conversion in large area PtSe$_{2}$/Ni$_{80}$Fe$_{20}$ heterostructures,"As a topological Dirac semimetal with controllable spin-orbit coupling and
conductivity, PtSe$_2$, a transition-metal dichalcogenide, is a promising
material for several applications from optoelectric to sensors. However, its
potential for spintronics applications is yet to be explored. In this work, we
demonstrate that PtSe$_{2}$/Ni$_{80}$Fe$_{20}$ heterostructure can generate a
large damping-like current-induced spin-orbit torques (SOT), despite the
absence of spin-splitting in bulk PtSe$_{2}$. The efficiency of charge-to-spin
conversion is found to be $(-0.1 \pm 0.02)$~nm$^{-1}$ in
PtSe$_{2}$/Ni$_{80}$Fe$_{20}$, which is three times that of the control sample,
Ni$_{80}$Fe$_{20}$/Pt. Our band structure calculations show that the SOT due to
the PtSe$_2$ arises from an unexpectedly large spin splitting in the
interfacial region of PtSe$_2$ introduced by the proximity magnetic field of
the Ni$_{80}$Fe$_{20}$ layer. Our results open up the possibilities of using
large-area PtSe$_{2}$ for energy-efficient nanoscale devices by utilizing the
proximity-induced SOT.",2307.11524v1
2024-01-15,Meta-generalized-gradient exchange-correlation functionals for spin-orbit coupled electrons,"The prominence of density functional theory (DFT) in the field of electronic
structure computation stems from its ability to usefully balance accuracy and
computational effort. At the base of this ability is a functional of the
electron density: the exchange-correlation (xc) energy. This functional
satisfies known exact conditions that guide the derivation of approximations.
The strongly-constrained-appropriately-normed (SCAN) approximation stands out
as a successful, modern, example. In the presence of spin-orbit coupling,
however, the xc energy must depend not only on the electron density but also on
spin currents -- a fact which is not captured by SCAN or by any mainstream
functional approximation. In this work, we demonstrate how the SU(2)
gauge-invariance of the {\em exact} functional allows us to add the necessary
dependence on spin currents in the SCAN functional (here called JSCAN) -- and
similar meta-generalized-gradient functional approximations -- in a
non-empirical manner. The prescription further ensures that the conjugate
xc-fields of the spin currents have vanishing local torques as in the exact
case. In passing, a spin-current dependent generalization of the electron
localization function (here called JELF) is also derived. The extended forms
are implemented in a developer's version of the \textsc{Crystal23} program.
Applications on molecules and materials confirm the practical relevance of the
extensions.",2401.07581v1
2024-01-25,The ongoing spin-down episode of 4U 1626-67,"We report the X-ray characteristics of the persistent X-ray pulsar 4U 1626-67
using simultaneous NuSTAR and NICER observations. The X-ray pulsar 4U 1626-67
has just encountered a torque reversal in 2023 and is presently in the
spin-down state. We have examined the temporal and spectral characteristics of
the source during its ongoing spin-down episode. The pulse profiles of the
source are characterized by multiple substructures at lower energies and a wide
asymmetric single-peaked structure at higher energies. The pulse fraction
follows an overall increasing trend with energy. We confirm the existence of
mHz quasi-periodic oscillation (QPO) exclusively during the current spin-down
phase in all the observations. The source is spinning down at 0.00045(4)\; s\;
$yr^{-1}$. The broadband spectrum during this phase is described by empirical
NPEX model and a soft blackbody component with kT $\sim$ 0.25 keV. In addition
to the iron emission line, we also confirm the presence of cyclotron line at
$\sim$ 36 keV. The source flux continues to decrease during the current
spin-down phase, and the corresponding luminosity $\sim$ (3.3-4.9)\;$\times
10^{36}\; ergs\; s^{-1}$ lies in the intermediate range of accreting X-ray
pulsars that may be associated with a hybrid accretion geometry. The magnetic
field strengths estimated using the cyclotron line measurements and QPO
frequency are consistent. The evolution of the spectral parameters relative to
the pulsed phase is examined using phase-resolved spectroscopy.",2401.13978v1
2015-03-06,Optical and spin-optical superpositions modulated by Aharonov-Bohm effect,"Generation of Aharonov-Bohm (AB) phase has achieved a state-of-the-art in
mesoscopic systems with manipulation and control of the AB effect. The
possibility of transfer information enconded in such systems to non-classical
states of light increases the possible scenarios where the information can be
manipulated and transfered. In this paper we propose a quantum transfer of the
AB phase generated in a spintronic device, a topological spin transistor (TST),
to an quantum optical device, a coherent state superposition in high-Q cavity
and discuss optical and spin-optical superpositions in the presence of an AB
phase. We demonstrate that the AB phase generated in the TST can be transfered
to the coherent state superposition, considering the interaction with the spin
state and the quantum optical manipulation of the coherent state superposition.
We show that these cases provide examples of two-qubit states modulated by AB
effect and that the phase parameter can be used to control the degree of
rotation of the qubit state. We also show under a measurement on the spin
basis, an optical one-qubit state that can be modulated by the AB effect. In
these cases, we consider a dispesive interaction between a coherent state and a
spin state with an acquired AB phase and also discuss a dissipative case where
a given Lindblad equation is achieved and solved. Keywords: Quantum transfer;
Aharonov-Bohm phase; Spintronics; Quantum Optical Devices.",1503.02070v3
2002-01-21,Spin Fluctuation Induced Dephasing in a Mesoscopic Ring,"We investigate the persistent current in a hybrid Aharonov-Bohm ring -
quantum dot system coupled to a reservoir which provides spin fluctuations. It
is shown that the spin exchange interaction between the quantum dot and the
reservoir induces dephasing in the absence of direct charge transfer. We
demonstrate an anomalous nature of this spin-fluctuation induced dephasing
which tends to enhance the persistent current. We explain our result in terms
of the separation of the spin from the charge degree of freedom. The nature of
the spin fluctuation induced dephasing is analyzed in detail.",0201362v1
2002-09-30,Datta-Das transistor with enhanced spin control,"We consider a two-channel spin transistor with weak spin-orbit induced
interband coupling. We show that the coherent transfer of carriers between the
coupled channels gives rise to an \textit{additional} spin rotation. We
calculate the corresponding spin-resolved current in a Datta-Das geometry and
show that a weak interband mixing leads to enhanced spin control.",0209682v2
2004-10-29,How many electrons are needed to flip a local spin?,"Considering the spin of a local magnetic atom as a quantum mechanical
operator, we illustrate the dynamics of a local spin interacting with a
ballistic electron represented by a wave packet. This approach improves the
semi-classical approximation and provides a complete quantum mechanical
understanding for spin transfer phenomena. Sending spin-polarized electrons
towards a local magnetic atom one after another, we estimate the minimum number
of electrons needed to flip a local spin.",0410775v1
2006-03-01,Stochastic theory of spin-transfer oscillator linewidths,"We present a stochastic theory of linewidths for magnetization oscillations
in spin-valve structures driven by spin-polarized currents. Starting from a
nonlinear oscillator model derived from spin-wave theory, we derive Langevin
equations for amplitude and phase fluctuations due to the presence of thermal
noise. We find that the spectral linewidths are inversely proportional to the
spin-wave intensities with a lower bound that is determined purely by
modulations in the oscillation frequencies. Reasonable quantitative agreement
with recent experimental results from spin-valve nanopillars is demonstrated.",0603019v1
2006-11-03,Spin-polarized quantum transport through a T-shape quantum dot-array: a model of spin splitter,"We in this paper study theoretically the spin-polarized quantum transport
through a T-shape quantum dot-array by means of transfer-matrix method along
with the Green^{,}s function technique. Multi-magnetic fields are used to
produce the spin-polarized transmission probabilities and therefore the spin
currents, which are shown to be tunable in a wide range by adjusting the
energy, and the direction-angle of magnetic fields as well. Particularly the
opposite- spin- polarization currents separately flowing out to two electrodes
can be generated and thus the system acts as a spin splitter.",0611071v1
2004-12-10,Single spin detection by qubit SWAP to a molecular nanomagnet,"Spin state detection is a key but very challenging step for any spin-based
solid-state quantum computing technology. In fullerene based quantum computer
technologies, we here propose to detect the single spin inside a fullerene by
transferring the quantum information from the endohedral spin to the ground
states of a molecular nanomagnet Fe$_{8}$, with large spin S=10. We show how to
perform the required SWAP operation and how to read out the information through
state-of-the-art techniques such as micro-SQUID.",0412081v2
2009-01-20,Role of Bound Magnon in Magnetic Domain Wall Motion,"We report on a quantum description of the domain wall (DW) motion under a
spin current. A bound magnon, which is the zero mode of DW, is found to play a
dominant role in DW dynamics. The bound magnon acquires its inertia by the hard
axis anisotropy and is a free particle even under the spin current. The full
transfer of spin angular momentum from the spin current to DW via the bound
magnon leads to the DW motion with the adiabatic velocity, decoupling of spin
waves from DW, and no Doppler shift in spin waves.",0901.3066v1
2012-07-29,Squeezing of Collective Excitations in Spin Ensembles,"We analyse the possibility to create two-mode spin squeezed states of two
separate spin ensembles by inverting the spins in one ensemble and allowing
spin exchange between the ensembles via a near resonant cavity field. We
investigate the dynamics of the system using a combination of numerical and
analytic calculations, and we obtain squeezing for a wide range of parameters.
We also investigate the transfer of the squeezing properties to the cavity
field and to an output mode from the cavity. Finally, we investigate how the
squeezing is affected by effects of inhomogeneities which would be present in
solid state implementations of the spin ensembles.",1207.6772v1
2013-07-12,Fermi liquid theory of resonant spin pumping,"We study resonant all-electric adiabatic spin pumping through a quantum dot
with two nearby levels by using a Fermi liquid approach in the strongly
interacting regime, combined with a projective numerical renormalization group
(NRG) theory. Due to spin-orbit coupling, a strong spin pumping resonance
emerges at every charging transition, which allows for the transfer of a spin
$~ \hbar/2$ through the device in a single pumping cycle. Depending on the
precise geometry of the device, controlled pure spin pumping is also possible.",1307.3416v2
2013-08-08,Spin filtering in nanowire directional coupler,"The spin transport characteristics of a nanowire directional electronic
coupler have been evaluated theoretically via a transfer matrix approach. The
application of a gate field in the region of mixing allows for control of spin
current through the different leads of the coupler via the Rashba spin-orbit
interaction. The combination of spin-orbit interaction and applied gate
voltages on different legs of the coupler give rise to a controllable
modulation of the spin polarization. Both structural factors and field strength
tuning lead to a rich phenomenology that could be exploited in spintronic
devices.",1308.1882v1
2021-03-16,Effect of compression in molecular spin-crossover chains,"In this work, we investigate thermodynamic properties of the one-dimensional
(1D) spin-crossover molecular chain being a subject of a constant external
pressure. Effective compressible degenerate Ising model is used as a
theoretical framework. Using transfer matrix formalism analytic results for the
low spin -- high spin crossover were obtained. We derive the exact expressions
for the fraction of molecules in the high spin state, correlation function and
heat capacity. We provide analysis of parameters region where the spin
crossover takes place and demonstrate how pressure changes location of the
crossover.",2103.09278v1
2024-04-08,"Spin Radiation of Electrons, Excitons, and Phonons","In the celebrated Stern-Gerlach experiment an inhomogeneous static magnetic
field separates a beam of charge-neutral atoms with opposite spins, thereby
driving a ``spin current"" normal to the propagation direction. Here we
generalize it to the dynamic scenario by demonstrating a spin transfer between
an AC inhomogeneous magnetic field and intraband electrons or charge-neutral
excitons and phonons. We predict that parametric pumping can efficiently
radiate their DC spin currents from local AC magnetic sources with van der
Waals semiconductors as prototypes. This mechanism brings a unified and
efficient paradigm in the spin transport of distinct mobile carriers.",2404.05593v1
2023-06-14,Quantum state transfer using 1D Heisenberg Hamiltonian on quasi-1D lattices,"We consider transfer of single and multi-qubit states on a quasi-1D lattice,
where the time evolutions involved in the state transfer protocol are generated
by only 1D Hamiltonians. We use the quasi-1D isotropic Heisenberg model under a
magnetic field along the $z$ direction, where the spin-spin interaction
strengths along the vertical sublattices, referred to as rungs, are much
stronger than the interactions along other sublattices. Tuning the
field-strength to a special value, in the strong rung-coupling limit, the
quasi-1D isotropic Heisenberg model can be mapped to an effective 1D XXZ model,
where each rung mimics an effective two-level system. Consequently, the
transfer of low-energy rung states from one rung to another can be represented
by a transfer of an arbitrary single-qubit state from one lattice site to
another using the 1D XXZ model. Exploiting this, we propose protocols for
transferring arbitrary single-qubit states from one lattice site to another by
using specific encoding of the single-qubit state into a low-energy rung state,
and a subsequent decoding of the transferred state on the receiver rung. These
encoding and decoding protocols involve a time evolution generated by the 1D
rung Hamiltonian and single-qubit phase gates, ensuring that all
time-evolutions required for transferring the single-qubit state are generated
from 1D Hamiltonians. We show that the performance of the single-qubit state
transfer using the proposed protocol is always better than the same when a
time-evolution generated by the full quasi-1D Hamiltonian is used.",2306.08440v1
2006-04-03,Full counting statistics of spin transfer through the Kondo dot,"We calculate the spin current distribution function for a Kondo dot in two
different regimes. In the exactly solvable Toulouse limit the linear response,
zero temperature statistics of the spin transfer is trinomial, such that all
the odd moments vanish and the even moments follow a binomial distribution. On
the contrary, the corresponding spin-resolved distribution turns out to be
binomial. The combined spin and charge statistics is also determined. In
particular, we find that in the case of a finite magnetic field or an
asymmetric junction the spin and charge measurements become statistically
dependent. Furthermore, we analyzed the spin counting statistics of a generic
Kondo dot at and around the strong-coupling fixed point (the unitary limit).
Comparing these results with the Toulouse limit calculation we determine which
features of the latter are generic and which ones are artifacts of the spin
symmetry breaking.",0604051v2
2007-01-11,Transfer-matrix renormalization group study of the spin ladders with cyclic four-spin interactions,"The temperature dependence of the specific heat and spin susceptibility of
the spin ladders with cyclic four-spin interactions in the rung-singlet phase
is explored by making use of the transfer-matrix renormalization group method.
The values of spin gap are extracted from the specific heat and susceptibility,
respectively. It is found that for different relative strength between
interchain and intrachain interactions, the spin gap is approximately linear
with the cyclic four-spin interaction in the region far away from the critical
point. Furthermore, we show that the dispersion for the one-triplet magnon
branch can be obtained by numerically fitting on the partition function.",0701243v1
2013-07-02,Preparation of Nuclear Spin Singlet States using Spin-Lock Induced Crossing,"We introduce a broadly applicable technique to create nuclear spin singlet
states in organic molecules and other many-atom systems. We employ a novel
pulse sequence to produce a spin-lock induced crossing (SLIC) of the spin
singlet and triplet energy levels, which enables triplet/singlet polarization
transfer and singlet state preparation. We demonstrate the utility of the SLIC
method by producing a long-lived nuclear spin singlet state on two
strongly-coupled proton pairs in the tripeptide molecule
phenylalanine-glycine-glycine dissolved in D2O, and by using SLIC to measure
the J-couplings, chemical shift differences, and singlet lifetimes of the
proton pairs. We show that SLIC is more efficient at creating nearly-equivalent
nuclear spin singlet states than previous pulse sequence techniques, especially
when triplet/singlet polarization transfer occurs on the same timescale as
spin-lattice relaxation.",1307.0832v1
2015-03-25,Intercombination Effects in Resonant Energy Transfer,"We investigate the effect of intercombination transitions in excitation
hopping processes such as those found in F\""orster resonance energy transfer.
Taking strontium Rydberg states as our model system, the breakdown of
$LS$-coupling leads to weakly allowed transitions between Rydberg states of
different spin quantum number. We show that the long-range interactions between
two Rydberg atoms can be affected by these weakly allowed spin transitions, and
the effect is greatest when there is a near-degeneracy between the initial
state and a state with a different spin quantum number. We also consider a case
of four atoms in a spin chain, and show that a spin impurity can resonantly hop
along the chain. By engineering the many-body energy levels of the spin-chain,
the breakdown of $LS$ coupling due to inter-electronic effects in individual
atoms can be mapped onto a spatial separation of the total spin and the total
orbital angular momentum along the spin chain.",1503.07417v4
2015-09-11,Non-perturbative Correlation Effects in Diluted Magnetic Semiconductors,"The effects of carrier-impurity correlations due to a Kondo-like spin-spin
interaction in diluted magnetic semiconductors are investigated. These
correlations are not only responsible for a transfer of spins between the
carriers and the impurities, but also produce non-perturbative effects in the
spin dynamics such as renormalization of the precession frequency of the
carrier spins, which can reach values of several percent in CdMnTe quantum
wells. In two-dimensional systems, the precession frequency renormalization for
a single electron spin with defined wave vector shows logarithmic divergences
similar to those also known from the Kondo problem in metals. For smooth
electron distributions, however, the divergences disappear due to the
integrability of the logarithm. A possible dephasing mechanism caused by the
wave-vector dependence of the electron spin precession frequencies is found to
be of minor importance compared to the spin transfer from the carrier to the
impurity system. In the Markov limit of the theory, a quasi-equilibrium
expression for the carrier-impurity correlation energy can be deduced
indicating the formation of strongly correlated carrier-impurity states for
temperatures in the mK range.",1509.03442v1
2016-02-11,Probing ultrafast spin dynamics in the antiferromagnetic multiferroic HoMnO$_3$ through a magnon resonance,"We demonstrate a new approach for directly measuring the ultrafast energy
transfer between elec- trons and magnons, enabling us to track spin dynamics in
an antiferromagnet (AFM). In multiferroic HoMnO3, optical photoexcitation
creates hot electrons, after which changes in the spin order are probed with a
THz pulse tuned to a magnon resonance. This reveals a photoinduced
transparency, which builds up over several picoseconds as the spins heat up due
to energy transfer from hot elec- trons via phonons. This spin-lattice
thermalization time is ?10 times faster than that of typical ferromagnetic (FM)
manganites. We qualitatively explain the fundamental differences in
spin-lattice thermalization between FM and AFM systems and apply a Boltzmann
equation model for treating AFMs. Our work gives new insight into spin-lattice
thermalization in AFMs and demonstrates a new approach for directly monitoring
the ultrafast dynamics of spin order in these systems.",1602.03872v2
2016-10-10,Quantum spin transistor with a Heisenberg spin chain,"We propose and analyze a scheme for conditional state transfer in a
Heisenberg $XXZ$ spin chain which realizes a quantum spin transistor. In our
scheme, the absence or presence of a control spin excitation in the central
gate part of the spin chain results in either perfect transfer of an arbitrary
state of a target spin between the weakly coupled input and output ports, or
its complete blockade at the input port. We also present a possible realization
of the corresponding spin chain with a one-dimensional ensemble of cold atoms
with strong contact interactions.",1610.02938v1
2018-07-18,Spin-dependent heat signatures of single-molecule spin dynamics,"We investigate transient spin-dependent thermoelectric signatures in a
single-molecule magnet under the effect of a time-dependent voltage pulse. We
model the system using nonequilibrium Green's functions and a generalized spin
equation of motion incorporating the dynamic electronic structure of the
molecule. We show that the generated heat current in the system is due to both
charge and spin contributions, related to the Peltier and the spin-dependent
Peltier effect. There is also a clear signature in the heat current due to the
spin dynamics of the single-molecule and a possibility to control the
spin-dependent heat currents by bias, tunneling coupling and exchange
interaction. A reversal of the net heat transfer in the molecule is found for
increasing bias voltage due to the local Zeeman split and we can correlate the
net heat transfer with the local anisotropies and dynamic exchange fields in
the system.",1807.07019v2
2017-04-07,Probing Proton Spin Structure: A Measurement of g2p at Four-momentum Transfer of 2 to 6 GeV^2,"The Spin Asymmetries of the Nucleon Experiment investigated the spin
structure of the proton via inclusive electron scattering at the Continuous
Electron Beam Accelerator Facility at Jefferson Laboratory in Newport News, VA.
A double--polarization measurement of polarized asymmetries was performed using
the University of Virginia solid polarized ammonia target with target
polarization aligned longitudinal and near transverse to the electron beam,
allowing the extraction of the spin asymmetries $A_1$ and $A_2$, and spin
structure functions $g_1$ and $g_2$. Polarized electrons of energies of 4.7 and
5.9 GeV were scattered to be viewed by a novel, non-magnetic array of detectors
observing a four-momentum transfer range of 2 to 6 GeV$^2$. This document
addresses the extraction of the spin asymmetries and spin structure functions,
with a focus on spin structure function $g_2$, which we have measured as a
function of $x$ and $W$ in four $Q^2$ bins.",1704.02308v1
2020-10-01,Modeling coupled spin and lattice dynamics,"A unified model of molecular and atomistic spin dynamics is presented
enabling simulations both in microcanonical and canonical ensembles without the
necessity of additional phenomenological spin damping. Transfer of energy and
angular momentum between the lattice and the spin systems is achieved by a
coupling term based upon the spin-orbit interaction. The characteristic spectra
of the spin and phonon systems are analyzed for different coupling strength and
temperatures. The spin spectral density shows magnon modes together with the
uncorrelated noise induced by the coupling to the lattice. The effective
damping parameter is investigated showing an increase with both coupling
strength and temperature. The model paves the way to understanding magnetic
relaxation processes beyond the phenomenological approach of the Gilbert
damping and the dynamics of the energy transfer between lattice and spins.",2010.00642v1
2023-02-04,"Calculating spin-lattice interactions in ferro- and antiferromagnets: the role of symmetry, dimension and frustration","Recently, the interplay between spin and lattice degrees of freedom has
gained a lot of attention due to its importance for various fundamental
phenomena as well as for spintronic and magnonic applications. Examples are
ultrafast angular momentum transfer between the spin and lattice subsystems
during ultrafast demagnetization, frustration driven by structural distortions
in transition metal oxides, or in acoustically driven spin-wave resonances. In
this work, we provide a systematic analysis of spin-lattice interactions for
ferro- and antiferromagnetic materials and focus on the role of lattice
symmetries and dimensions, magnetic order, and the relevance of spin-lattice
interactions for angular momentum transfer as well as magnetic frustration. For
this purpose, we use a recently developed scheme which allows an efficient
calculation of spin-lattice interaction tensors from first principles. In
addition to that, we provide a more accurate and self consistent scheme to
calculate ab initio spin lattice interactions by using embedded clusters which
allows to benchmark the performance of the scheme introduced previously.",2302.02066v2
1998-05-04,Spin-down rate of 1E 2259+586 from RXTE observation,"We present new X-ray observations of the X-ray pulsar 1E 2259+586, obtained
during March 1997, with the Rossi X-Ray Timing Explorer (RXTE). We have
measured the pulse frequency derivative $\dot \nu = (-1.08 \pm 0.04) \times
10^{-14}$ Hz s$^{-1}$ from pulse arrival times obtained in a sequence of 5
observations spread over one month. This $\dot\nu$ is consistent with the long
term spin-down trend. We also found that the observed X-ray luminosity is
consistent with that measured at quiescent X-ray flux levels by previous
missions. Our observations imply that 1E 2259+586 was spinning down steadily
without exhibiting any stochastic torque noise fluctuations during the month
covered by our observations.",9805020v1
1998-10-07,Accretion disk reversal and the spin-up/spin-down of accreting pulsars,"We numerically investigate the hydrodynamics of accretion disk reversal and
relate our findings to the observed spin-rate changes in the accreting X-ray
pulsar GX~1+4. In this system, which accretes from a slow wind, the accretion
disk contains two dynamically distinct regions. In the inner part viscous
forces are dominant and disk evolution occurs on a viscous timescale. In the
outer part dynamical mixing of material with opposite angular momentum is more
important, and the externally imposed angular momentum reversal timescale
governs the flow. In this outer region the disk is split into concentric rings
of material with opposite senses of rotation that do not mix completely but
instead remain distinct, with a clear gap between them. We thus predict that
torque reversals resulting from accretion disk reversals will be accompanied by
minima in accretion luminosity.",9810118v1
1999-08-25,Magnetar Spin-Down,"We examine the effects of a relativistic wind on the spin down of a neutron
star and apply our results to the study of Soft Gamma Repeaters (SGRs), thought
to be neutron stars with magnetic fields > 10^{14} G. We derive a spin-down
formula that includes torques from both dipole radiation and episodic or
continuous particle winds. We find that if SGR1806-20 puts out a continuous
particle wind of 10^{37} {\rm erg} {\rm s}^{-1}, then the pulsar age is
consistent with that of the surrounding supernova remnant, but the derived
surface dipole magnetic field is only 3 \times 10^{13} G, in the range of
normal radio pulsars. If instead, the particle wind flows are episodic with
small duty cycle, then the observed period derivatives imply magnetar-strength
fields, while still allowing characteristic ages within a factor of two of the
estimated supernova remnant age. Close monitoring of the periods of SGRs will
be able to establish or place limits on the wind duty cycle and thus the
magnetic field and age of the neutron star.",9908279v2
2003-06-25,"Isolated magnetar spin-down, soft X-ray emission and RXJ1856.5-3754","When an isolated magnetar with magnetic dipole field B ~ 10^15 G moves at
high velocity (v > 10^7 cm/s) through the ISM, its transition into propeller
effect driven spin-down may occur in less than 10^6 years. We propose that the
nearby neutron star RXJ1856.5-3754 is such a magnetar, and has spun down by the
propeller effect to a period greater than 10^4 sec within ~5*10^5 years. This
magnetar scenario is consistent with observed thermal X-ray emission properties
and the absence of detectable spin-modulations of them. Detection of other
rapidly moving long period (> 100 sec) magnetars with known ages would strongly
constrain the very great variety of predicted propeller-effect torque
magnitudes.",0306516v1
2004-04-14,"The Spin History of Protostars: Disk Locking, Revisited","In this talk, we take a new look at the theory of disk locking, which assumes
that an accreting protostar rids itself of accreted angular momentum through a
magnetic coupling with the accretion disk. We consider that differential
rotation between the star and disk twists the field lines. For large enough
twist, the magnetic field lines connecting the star and disk open and
disconnect. This significantly reduces the spin-down torque on the star by the
disk, and so we find that disk-locking theory predicts spin periods that are
much too short to account for typical observed systems.",0404279v1
2006-05-04,A Neutron Star in F-sharp,"In this short introductory commentary on the paper (Hessels et al 2006,
Science, 311, 1901) reporting the discovery of the shortest spin period
millisecond pulsar (MSP) Ter5-ad in the globular cluster Terzan 5, I also point
out a new explanation for possible minimum spin periods, P, of MSPs without
requiring gravitational radiation (or other) slow-down torques. If the
accretion of matter required to spinup a MSP also reduces (buries) the neutron
star (NS) magnetic field, B, as commonly believed, an inverse correlation
between neutron star mass, M, and B is expected together with a positive
correlation between P and B. Both are suggested for the 4 MSPs with NS mass
measures reported (Latimer and Prakash 2004, Science, 304, 536) to have <~10%
uncertainties. The correlations imply the Ter5-ad NS has ~2.5 Msun, B ~5 x 10^7
G and thus Pdot ~3 x 10^-21 s/s -- which can be tested when a timing solution
is found. If confirmed, the highest spin frequency NSs do not pulse simply
because their B fields are too low.",0605117v1
2007-01-23,Understanding the Spins of Young Stars,"We review the theoretical efforts to understand why pre-main-sequence stars
spin much more slowly than expected. The first idea put forward was that
massive stellar winds may remove substantial angular momentum. Since then, it
has become clear that the magnetic interaction between the stars and their
accretion disks explains many of the observed emission properties. The disk
locking scenario, which assumes the magnetic star-disk interaction also solves
the stellar spin problem, has received the most attention in the literature to
date. However, recent considerations suggest that the torques in the star-disk
interaction are insufficient for disk locking to explain the slow rotators.
This prompts us to revisit stellar winds, and we conclude that stellar winds,
working in conjunction with magnetospheric accretion, are a promising candidate
for solving the angular momentum problem. We suggest future directions for both
observations and theory, to help shed light on this issue.",0701648v1
2006-01-05,Micromagnetic simulations of the magnetization precession induced by a spin polarized current in a point contact geometry,"This paper is devoted to numerical simulations of the magnetization dynamics
driven by a spin-polarized current in extended ferromagnetic multilayers when a
point-contact setup is used. We present (i) detailed analysis of methodological
problems arising by such simulations and (ii) physical results obtained on a
system similar to that studied in Rippard et al., Phys. Rev. Lett., v. 92,
027201 (2004). We demonstrate that the usage of a standard Slonczewski
formalism for the phenomenological treatment of a spin-induced torque leads to
a qualitative disagreement between simulation results and experimental
observations and discuss possible reasons for this discrepancy.",0601099v1
1993-12-10,Electromagnetic Deflection of Spinning Particles,"We show that it is possible to obtain self-consistent and physically
acceptable relativistic classical equations of motion for a point-like
spin-half particle possessing an electric charge and a magnetic dipole moment,
directly from a manifestly covariant Lagrangian, if the classical degrees of
freedom are appropriately chosen. It is shown that the equations obtained
encompass the well-tested Lorentz force and Thomas--Bargmann--Michel--Telegdi
spin equations, as well as providing a definite specification of the classical
_magnetic_dipole_ force_, whose exact form has been the subject of recent
debate. Radiation reaction---the force and torque on an accelerated particle
due to its self-interaction---is neglected at this stage.",9312256v1
1997-10-22,The Aharonov-Casher Effect for Particles of Arbitrary Spin,"The Aharonov-Casher (AC) effect for quantum motion of a neutral magnetized
particle in the electric field is believed to be a topological effect closely
related to the known Aharonov-Bohm (AB) effect. We study how it depends on the
spin of the particle involved. Duality of the AB and AC effects is demonstrated
to exist only for two extreme spin (and magnetic moment) projections.
  Classical consideration confirms the conclusion. Motion of a classical
magnetized particle with generally oriented magnetic moment in the AC field
appears to be subjected to both forces and torques. Only for two special
orientations of the magnetic moment (same as in the quantum case) the motion is
effectively free and similar to the AB motion of a charged particle. Thus, the
AC effect is not really topological.
  Presence of higher multipoles totally destroys the possible AB-AC duality.",9710433v1
2006-02-13,"An Instructional Scaffolding for Intuitive Explanation of ""Why does not a spinning top collapse?""","""Why does not a spinning top collapse?"" is a puzzling question. Standard
solution using angular momentum and torque is not intuitive enough. Thus
intuitive explanations for the question have been proposed. We provide
scaffolding for an intuitive explanation for the question. Accelerated
point-masses in the top exert forces on the frame, which balances the effect
due to gravity. The explanation is supplemented by the two following points. A
more rigorous conceptual framework of the explanation is provided. A full
calculation of trajectory is given. Nutation of spinning top is a difficult
issue to understand physically. However, the nutation can also be understood by
the intuitive explanation. We discuss another intuitive explanation.",0602078v4
2007-10-05,Measuring the spin up of the Accreting Millisecond Pulsar XTE J1751-305,"We perform a timing analysis on RXTE data of the accreting millisecond pulsar
XTE J1751-305 observed during the April 2002 outburst. After having corrected
for Doppler effects on the pulse phases due to the orbital motion of the
source, we performed a timing analysis on the phase delays, which gives, for
the first time for this source, an estimate of the average spin frequency
derivative <nu_dot> = (3.7 +/- 1.0)E-13 Hz/s. We discuss the torque resulting
from the spin-up of the neutron star deriving a dynamical estimate of the mass
accretion rate and comparing it with the one obtained from X-ray flux.
Constraints on the distance to the source are discussed, leading to a lower
limit of \sim 6.7 kpc.",0710.1215v1
2008-03-10,Current- and field-driven magnetic antivortices,"Antivortices in ferromagnetic thin-film elements are in-plane magnetization
configurations with a core pointing perpendicular to the plane. By using
micromagnetic simulations, we find that magnetic antivortices gyrate on
elliptical orbits similar to magnetic vortices when they are excited by
alternating magnetic fields or by spin-polarized currents. The phase between
high-frequency excitation and antivortex gyration is investigated. In case of
excitation by spin-polarized currents the phase is determined by the
polarization of the antivortex, while for excitation by magnetic fields the
phase depends on the polarization as well as on the in-plane magnetization.
Simultaneous excitation by a current and a magnetic field can lead to a maximum
enhancement or to an entire suppression of the amplitude of the core gyration,
depending on the angle between excitation and in-plane magnetization. This
variation of the amplitude can be used to experimentally distinguish between
spin-torque and Oersted-field driven motion of an antivortex core.",0803.1236v1
2008-03-10,1E161348-5055 in the Supernova Remnant RCW 103: A Magnetar in a Young Low Mass Binary System?,"We suggest that the unique X-ray source 1E161348-5055 at the centre of the
supernova remnant RCW 103 consists of a neutron star in close orbit with a low
mass main sequence star. The time signature of 6.67 hr is interpreted as the
neutron star's spin period. This requires the neutron star to be endowed with a
high surface magnetic field of~10^15 G. Magnetic or/and material (propeller)
torques are able to spin rapidly the young neutron star down to an asymptotic,
equilibrium spin period in close synchronism with the orbital period, similarly
to what happens in the Polar Cataclysmic Variables. 1E161348-5055 could be the
first case of a magnetar born in a young low mass binary system.",0803.1373v1
2008-12-11,Cascade of magnetic-field-induced quantum phase transitions in a spin $\bm{1/2}$ triangular-lattice antiferromagnet,"We report magnetocaloric and magnetic-torque evidence that in
Cs$_{2}$CuBr$_{4}$ -- a geometrically frustrated Heisenberg $S=1/2$
triangular-lattice antiferromagnet -- quantum fluctuations stabilize a series
of spin states at simple increasing fractions of the saturation magnetization
$M_{s}$. Only the first of these states -- at $M={1/3}M_{s}$ -- has been
theoretically predicted. We discuss how the higher fraction quantum states
might arise and propose model spin arrangements. We argue that the first-order
nature of the transitions into those states is due to strong lowering of the
energies by quantum fluctuations, with implications for the general character
of quantum phase transitions in geometrically frustrated systems.",0812.2077v2
2010-09-15,Dimensionality-driven spin-flop transition in quasi-one-dimensional PrBa2Cu4O8,"In the quasi-one-dimensional cuprate PrBa$_2$Cu$_4$O$_8$, the Pr cations
order antiferromagnetically at 17 K in zero field. Through a combination of
magnetic susceptibility, torque magnetometry, specific heat and interchain
transport measurements, the anisotropic temperature-magnetic field phase
diagram associated with this ordering has been mapped out. A low-temperature
spin-flop transition in the Pr sub-lattice is found to occur at the same
magnetic field strength and orientation as a dimensional crossover in the
ground state of the metallic CuO chains. This coincidence suggests that the
spin reorientation is driven by a change in the anisotropic
Rudermann-Kittel-Kasuya-Yosida (RKKY) interaction induced by a corresponding
change in effective dimensionality of the conduction electrons.",1009.2885v1
2011-01-05,The Fascinating World of Landau-Lifshitz-Gilbert Equation: An Overview,"The Landau-Lifshitz-Gilbert (LLG) equation is a fascinating nonlinear
evolution equation both from mathematical and physical points of view. It is
related to the dynamics of several important physical systems such as
ferromagnets, vortex filaments, moving space curves, etc. and has intimate
connections with many of the well known integrable soliton equations, including
nonlinear Schr\""odinger and sine-Gordon equations. It can admit very many
dynamical structures including spin waves, elliptic function waves, solitons,
dromions, vortices, spatio-temporal patterns, chaos, etc. depending on the
physical and spin dimensions and the nature of interactions. An exciting recent
development is that the spin torque effect in nanoferromagnets is described by
a generalization of the LLG equation which forms a basic dynamical equation in
the field of spintronics. This article will briefly review these developments
as a tribute to Robin Bullough who was a great admirer of the LLG equation.",1101.1005v1
2011-06-10,Type IA supernovae from very long delayed explosion of core - WD merger,"We study the spinning down time scale of rapidly rotating white dwarfs (WDs)
in the frame of the core-degenerate (CD) scenario for type Ia supernovae (SNe
Ia). In the CD scenario the Chandrasekhar or super-Chandrasekhar mass WD is
formed at the termination of the common envelope phase or during the planetary
nebula phase, from a merger of a WD companion with the hot core of a massive
asymptotic giant branch star. In the CD scenario the rapidly rotating WD is
formed shortly after the stellar formation episode, and the delay from stellar
formation to explosion is basically determined by the spin-down time of the
rapidly rotating merger remnant. We find that gravitational radiation is
inefficient in spinning down WDs, while the magneto-dipole radiation torque can
lead to delay times that are required to explain SNe Ia.",1106.2027v3
2011-12-11,A pre-Caloris synchronous rotation for Mercury,"The planet Mercury is locked in a spin-orbit resonance where it rotates three
times about its spin axis for every two orbits about the Sun. The current
explanation for this unique state assumes that the initial rotation of this
planet was prograde and rapid, and that tidal torques decelerated the planetary
spin to this resonance. When core-mantle boundary friction is accounted for,
capture into the 3/2 resonance occurs with a 26% probability, but the most
probable outcome is capture into one of the higher-order resonances. Here we
show that if the initial rotation of Mercury were retrograde, this planet would
be captured into synchronous rotation with a 68% probability. Strong spatial
variations of the impact cratering rate would have existed at this time, and
these are shown to be consistent with the distribution of pre-Calorian impact
basins observed by Mariner 10 and MESSENGER. Escape from this highly stable
resonance is made possible by the momentum imparted by large basin-forming
impact events, and capture into the 3/2 resonance occurs subsequently under
favourable conditions.",1112.2384v1
2012-02-10,A model of magnetic order in hexagonal HoMnO3,"Symmetry arguments are used to develop a spin Hamiltonian for the description
of the complex magnetic ordering in HoMnO$_3$. Using a novel application of the
Landau Lifshitz Gilbert dynamic torque equations to this model of the
frustrated Mn ions on an $AB$ stacked triangular antiferromagnetic, it is shown
that the four principal spin configurations observed in this compound are
stabilized. Ho-Mn coupling is found to be a consequence of an unusual trigonal
anisotropy term which is responsible for simultaneous Mn spin reorientation and
onset of Ho magnetic order. Based on these microscopic considerations, a
mean-field Landau-type free energy is derived which reproduces the succession
of observed temperature driven magnetic phase transitions at zero field,
including re-entrant behavior. In addition, our analysis suggests that the
basal-plane magnetic order should be slightly incommensurate with the lattice.",1202.2321v1
2012-03-05,Hidden and antiferromagnetic order as a rank-5 superspin in URu2Si2,"We propose a candidate for the hidden order in URu2Si2: a rank-5 E type spin
density wave between Uranium 5f crystal field doublets breaking time reversal
and lattice tetragonal symmetry in a manner consistent with recent torque
measurements [R. Okazaki et al, Science 331, 439 (2011)]. We argue that
coupling of this order parameter to magnetic probes can be hidden by crystal
field effects, while still having significant effects on transport,
thermodynamics and magnetic susceptibilities. In a simple tight-binding model
for the heavy quasiparticles, we show the connection between the hidden order
and antiferromagnetic phases arises since they form different components of
this single rank-5 pseudo-spin vector. Using a phenomenological theory, we show
the experimental pressure-temperature phase diagram can be qualitatively
reproduced by tuning terms which break pseudo-spin rotational symmetry. As a
test of our proposal, we predict the presence of small magnetic moments in the
basal plane oriented in the [110] direction ordered at the wave-vector (0,0,1).",1203.1047v2
2012-12-10,Heat-induced damping modification in YIG/Pt hetero-structures,"We experimentally demonstrate the manipulation of magnetization relaxation
utilizing a temperature difference across the thickness of an yttrium iron
garnet/platinum (YIG/Pt) hetero-structure: the damping is either increased or
decreased depending on the sign of the temperature gradient. This effect might
be explained by a thermally-induced spin torque on the magnetization
precession. The heat-induced variation of the damping is detected by microwave
techniques as well as by a DC voltage caused by spin pumping into the adjacent
Pt layer and the subsequent conversion into a charge current by the inverse
spin Hall effect.",1212.2073v1
2013-06-26,Periodic magnetic structures generated by spin-polarized currents in nanostripes,"The influence of a spin-polarized current on long ferromagnetic nanostripes
is studied numerically. The current flows perpendicularly to the stripe. The
study is based on the Landau-Lifshitz phenomenological equation with the
Slonczewski-Berger spin-torque term. The magnetization behavior is analyzed for
all range of the applied currents, up to the saturation. It is shown that the
saturation current is a nonmonotonic function of the stripe width. For a stripe
width increasing it approaches the saturation value for an infinite film. A
number of stable periodic magnetization structures are observed below the
saturation. Type of the periodical structure depends on the stripe width.
Besides the one-dimensional domain structure, typical for narrow wires, and the
two-dimensional vortex-antivortex lattice, typical for wide films, a number of
intermediate structures are observed, e.g. cross-tie and diamond state. For
narrow stripes an analytical analysis is provided.",1306.6296v1
2014-01-22,Current-induced magnetization dynamics at the edge of a two-dimensional electron system with strong spin-orbit coupling,"We experimentally investigate electron transport through the interface
between a permalloy ferromagnet and the edge of a two-dimensional electron
system with strong Rashba-type spin-orbit coupling. We observe strongly
non-linear transport around zero bias at millikelvin temperatures. The observed
nonlinearity is fully suppressed above some critical values of temperature,
magnetic field, and current through the interface. We interpret this behavior
as the result of spin accumulation at the interface and its current-induced
absorption as a magnetization torque.",1401.5719v2
2014-09-29,Anisotropic conductivity in magnetic topological insulators,"We study the surface conductivity of a three dimensional topological
insulator doped with magnetic impurities. The spin-momentum locking of surface
electrons makes their scattering from magnetic impurities anisotropic and the
standard relaxation time approximation is not applicable. Using the
semiclassical Boltzmann approach together with a generalized relaxation time
scheme, we obtain closed forms for the relaxation times and analytic
expressions for the surface conductivities of the system as functions of the
bulk magnetization and the orientation of the aligned surface magnetic
impurities. We show that the surface conductivity is anisotropic, and strongly
depends both on the direction of the spins of magnetic impurities and on the
magnitude of the bulk magnetization. In particular, we find that the surface
conductivity has its minimum value when the spin of surface impurities are
aligned perpendicular to the surface of TI, and therefore the backscattering
probability is enhanced due to the magnetic torque exerted by impurities on the
surface electrons.",1409.8066v2
2014-11-04,An ultraluminous nascent millisecond pulsar,"If the ultraluminous source (ULX) M82 X-2 sustains its measured spin-up value
of $\dot \nu= 10^{-10}\,{\rm s^{-2}}$, it will become a millisecond pulsar in
less than $10^5\,$ years. The observed (isotropic) luminosity of $10^{40}\,$
erg/s also supports the notion that the neutron star will spin up to a
millisecond period upon accreting about $0.1\,{\rm M_\odot}$---the reported
hard X-ray luminosity of this ULX, together with the spin-up value, implies
torques consistent with the accretion disk extending down to the vicinity of
the stellar surface, as expected for low values of the stellar dipole magnetic
field ($B\lesssim 10^9\,$G). This suggests a new channel of millisecond pulsar
formation---in high-mass X-ray binaries (HMXBs)---and may have implications for
studies of gravitational waves, and possibly for the formation of low-mass
black holes through accretion-induced collapse.",1411.1005v3
2015-02-12,Peculiar Glitch of PSR J1119-6127 and Extension of the Vortex Creep Model,"Glitches are sudden changes in rotation frequency and spin-down rate,
observed from pulsars of all ages. Standard glitches are characterized by a
positive step in angular velocity ($\Delta\Omega$ $ > $ $0$) and a negative
step in the spin-down rate ($\Delta \dot \Omega$ $ < $ $0$) of the pulsar.
There are no glitch-associated changes in the electromagnetic signature of
rotation-powered pulsars in all cases so far. For the first time, in the last
glitch of PSR J1119-6127, there is clear evidence for changing emission
properties coincident with the glitch. This glitch is also unusual in its
signature. Further, the absolute value of the spin-down rate actually decreases
in the long term. This is in contrast to usual glitch behaviour. In this paper
we extend the vortex creep model in order to take into account these
peculiarities. We propose that a starquake with crustal plate movement towards
the rotational poles of the star induces inward vortex motion which causes the
unusual glitch signature. The component of the magnetic field perpendicular to
the rotation axis will decrease, giving rise to a permanent change in the
pulsar external torque.",1502.03786v1
2015-02-20,Magnetization patterning induced by electrical spin-polarized current in nanostripes,"The combined action of a transverse spin-polarized current and the
current-induced {\O}rsted field on long ferromagnetic nanostripes is studied
numerically and analytically. The magnetization behavior is analyzed for
stripes with various widths and for all range of the applied current density.
It is established that {\O}rsted field does not destroy periodical
magnetization structures induced by the spin-torque, e.g. vortex-antivortex
crystal and cross-tie domain walls. However, the action of the {\O}rsted field
disables the saturation state for the strong currents: a stationary state with
a single longitudinal domain wall appears instead. Shape of this wall remains
constant with the current increasing. The latter phenomenon is studied both
numerically and analytically.",1502.05885v1
2015-04-03,The effect of the magnon dispersion on the longitudinal spin Seebeck effect in yttrium iron garnets (YIG),"We study the temperature dependence of the longitudinal spin-Seebeck effect
(LSSE) in a yttrium iron garnet Y3Fe5O12 (YIG) / Pt system for samples of
different thicknesses. In this system, the thermal spin torque is
magnon-driven. The LSSE signal peaks at a specific temperature that depends on
the YIG sample thickness. We also observe freeze-out of the LSSE signal at high
magnetic fields, which we attribute to the opening of an energy gap in the
magnon dispersion. We observe partial freeze-out of the LSSE signal even at
room temperature, where kBT is much larger than the gap. This suggests that a
subset of the magnon population with an energy below kB x TC (TC about 40 K)
contribute disproportionately to the LSSE; at temperatures below TC, we label
these magnons subthermal magnons. The T-dependence of the LSSE at temperatures
below the maximum is interpreted in terms of a new empirical model that
ascribes most of the temperature dependence to that of the thermally driven
magnon flux.",1504.00895v1
2015-04-11,Pauli-paramagnetic effects on mixed state properties in a strongly anisotropic superconductor ---Application to Sr_2_RuO_4_---,"We study theoretically the mixed state properties of a strong
uniaxially-anisotropic type II superconductor with the Pauli paramagnetic
effect, focusing on their behaviors when the magnetic field orientation is
tilted from the conduction layer ab plane. On the basis of Eilenberger theory,
we quantitatively estimate significant contributions of the Pauli paramagnetic
effects on a variety of physical observables, including transverse and
longitudinal components of the flux line lattice form factors, magnetization
curves, Sommerfeld coefficient, field distributions and magnetic torques. We
apply these studies to Sr_2_RuO_4_ and quantitatively explain several seemingly
curious behaviors, including the H_c2_ suppression for the ab plane direction,
the larger anisotropy ratio and intensity found by the spin-flip small angle
neutron scattering, and the first order transition observed recently in
magneto-caloric, specific heat and magnetization measurements in a coherent and
consistent manner. Those lead us to conclude that Sr_2_RuO_4_ is either a
spin-singlet or a spin-triplet pairing with the d-vector components in the ab
plane.",1504.02836v1
2015-06-01,Electrical detection of magnetization reversal without auxiliary magnets,"First-generation magnetic random access memories based on anisotropic
magnetoresistance required magnetic fields for both writing and reading. Modern
all-electrical read/write memories use instead non-relativistic spin-transport
connecting the storing magnetic layer with a reference ferromagnet. Recent
studies have focused on electrical manipulation of magnetic moments by
relativistic spin-torques requiring no reference ferromagnet. Here we report
the observation of a counterpart magnetoresistance effect in such a
relativistic system which allows us to electrically detect the sign of the
magnetization without an auxiliary magnetic field or ferromagnet. We observe
the effect in a geometry in which the magnetization of a uniaxial (Ga,Mn)As
epilayer is set either parallel or antiparallel to a current-induced
non-equilibrium spin polarization of carriers. In our structure, this
linear-in-current magnetoresistance reaches 0.2\% at current density of $10^6$
A cm$^{-2}$.",1506.00400v1
2015-11-06,Curvature and torsion effects in the spin-current driven domain wall motion,"The domain wall motion along a helix-shaped nanowire is studied for the case
of spin-current driving via Bazaliy-Zhang-Li mechanism. The analysis is based
on collective variable approach. Two new effects are ascertained: (i) the
curvature results in appearance of the Walker limit for a uniaxial wire, (ii)
the torsion results in effective shift of the nonadiabatic spin torque
parameter $\beta$. The latter effect changes considerably the domain wall
velocity and can result in negative domain wall mobility. This effect can be
also used for an experimental determination of the nonadiabatic parameter
$\beta$ and damping coefficient $\alpha$.",1511.02193v1
2015-11-23,Perpendicular magnetization reversal in Pt/[Co/Ni]$_3$/Al multilayers via the Spin Hall Effect of Pt,"We experimentally investigate the current-induced magnetization reversal in
Pt/[Co/Ni]$_3$/Al multilayers combining the anomalous Hall effect and
magneto-optical Kerr effect techniques in crossbar geometry. The magnetization
reversal occurs through nucleation and propagation of a domain of opposite
polarity for a current density of the order of 0.3 TA/m$^2$. In these
experiments we demonstrate a full control of each stage: i)the {\O}rsted field
controls the domain nucleation and ii) domain-wall propagation occurs by spin
torque from the Pt spin Hall effect. This scenario requires an in-plane
magnetic field to tune the domain wall center orientation along the current for
efficient domain wall propagation. Indeed, as nucleated, domain walls are
chiral and N\'eel like due to the interfacial Dzyaloshinskii-Moriya
interaction.",1511.07478v1
2015-12-16,Domain Wall in a Quantum Anomalous Hall Insulator as a Magnetoelectric Piston,"We theoretically study the magnetoelectric coupling in a quantum anomalous
Hall insulator state induced by interfacing a dynamic magnetization texture to
a topological insulator. In particular, we propose that the quantum anomalous
Hall insulator with a magnetic configuration of a domain wall, when contacted
by electrical reservoirs, acts as a magnetoelectric piston. A moving domain
wall pumps charge current between electrical leads in a closed circuit, while
applying an electrical bias induces reciprocal domain-wall motion. This
piston-like action is enabled by a finite reflection of charge carriers via
chiral modes imprinted by the domain wall. Moreover, we find that, when
compared with the recently discovered spin-orbit torque-induced domain-wall
motion in heavy metals, the reflection coefficient plays the role of an
effective spin-Hall angle governing the efficiency of the proposed electrical
control of domain walls. Quantitatively, this effective spin-Hall angle is
found to approach a universal value of $2$, providing an efficient scheme to
reconfigure the domain-wall chiral interconnects for possible memory and logic
applications.",1512.05310v2
2016-05-27,A reduced model for precessional switching of thin-film nanomagnets under the influence of spin-torque,"We study the magnetization dynamics of thin-film magnetic elements with
in-plane magnetization subject to a spin-current flowing perpendicular to the
film plane. We derive a reduced partial differential equation for the in-plane
magnetization angle in a weakly damped regime. We then apply this model to
study the experimentally relevant problem of switching of an elliptical element
when the spin-polarization has a component perpendicular to the film plane,
restricting the reduced model to a macrospin approximation. The macrospin
ordinary differential equation is treated analytically as a weakly damped
Hamiltonian system, and an orbit-averaging method is used to understand
transitions in solution behaviors in terms of a discrete dynamical system. The
predictions of our reduced model are compared to those of the full
Landau--Lifshitz--Gilbert--Slonczewski equation for a macrospin.",1605.08698v1
2016-08-11,Manifestations of the rotation and gravity of the Earth in high-energy physics experiments,"The inertial (due to rotation) and gravitational fields of the Earth affect
the motion of an elementary particle and its spin dynamics. This influence is
not negligible and should be taken into account in high-energy physics
experiments. Earth's influence is manifest in perturbations in the particle
motion, in an additional precession of the spin, and in a change of the
constitutive tensor of the Maxwell electrodynamics. Bigger corrections are
oscillatory, and their contributions average to zero. Other corrections due to
the inhomogeneity of the inertial field are not oscillatory but they are very
small and may be important only for the storage ring electric dipole moment
experiments. Earth's gravity causes the Newton-like force, the reaction force
provided by a focusing system, and additional torques acting on the spin.
However, there are no observable indications of the electromagnetic effects due
to Earth's gravity.",1608.03808v1
2016-10-06,Spin-torque switching and control using chirped oscillating currents,"We propose to use oscillating spin currents with slowly varying frequency
(chirp) to manipulate and control the magnetization dynamics in a nanomagnet.
By recasting the Landau-Lifshitz-Slonczewski equation in a quantum-like
two-level formalism, we show that a chirped spin current polarized in the
direction normal to the anisotropy axis can induce a stable precession of the
magnetic moment at any angle (up to $90^\circ$) with respect to the anisotropy
axis. The drive current can be modest ($10^6\,\rm A/cm^2$ or lower) provided
the chirp rate is sufficiently slow. The induced precession is stable against
thermal noise, even for small nano-objects at room temperature. Complete
reversal of the magnetization can be achieved by adding a small external
magnetic field antiparallel to the easy axis. Alternatively, a combination of
chirped ac and dc currents with different polarization directions can also be
used to trigger the reversal.",1610.01819v2
2017-08-17,Biaxial magnetic field setup for angular magnetic measurements of thin films and spintronic nanodevices,"The biaxial magnetic-field setup for angular magnetic measurements of thin
film and spintronic devices is designed and presented. The setup allows for
application of the in-plane magnetic field using a quadrupole electromagnet,
controlled by power supply units and integrated with an electromagnet biaxial
magnetic field sensor. In addition, the probe station is equipped with a
microwave circuitry, which enables angle-resolved spin torque oscillation
measurements. The angular dependencies of magnetoresistance and spin diode
effect in a giant magnetoresistance strip are shown as an operational
verification of the experimental setup. We adapted an analytical macrospin
model to reproduce both the resistance and spin-diode angular dependency
measurements.",1708.05434v1
2017-11-22,Laser induced THz emission from femtosecond photocurrents in Co/ZnO/Pt and Co/Cu/Pt multilayers,"The ultrashort laser excitation of Co/Pt magnetic heterostructures can
effectively generate spin and charge currents at the interfaces between
magnetic and nonmagnetic layers. The direction of these photocurrents can be
controlled by the helicity of the circularly polarized laser light and an
external magnetic field. Here, we employ THz time-domain spectroscopy to
investigate further the role of interfaces in these photo-galvanic phenomena.
In particular, the effects of either Cu or ZnO interlayers on the photocurrents
in Co/X/Pt (X = Cu, ZnO) have been studied by varying the thickness of the
interlayers up to 5 nm. The results are discussed in terms of spin-diffusion
phenomena and interfacial spin-orbit torque.",1711.08342v4
2018-01-24,Quantization of magnetoelectric fields,"The effect of quantum coherence involving macroscopic degree of freedom, and
occurring in systems far larger than individual atoms are one of the topical
fields in modern physics. Because of material dispersion, a phenomenological
approach to macroscopic quantum electrodynamics, where no canonical formulation
is attempted, is used. The problem becomes more complicated when geometrical
forms of a material structure have to be taken into consideration. Magnetic
dipolar mode (MDM) oscillations in a magnetically saturated quasi 2D ferrite
disk are macroscopically quantized states. In this ferrimagnetic structure,
long range dipole dipole correlation in positions of electron spins can be
treated in terms of collective excitations of a system as a whole. The near
fields in the proximity of a MDM ferrite disk have space and time symmetry
breakings. Such MDM-originated fields, called magnetoelectric (ME) fields,carry
both spin and orbital angular momentums. By virtue of unique topology, ME
fields are different from free space electromagnetic (EM) fields. The ME fields
are quantum fluctuations in vacuum. We call these quantized states ME photons.
There are not virtual EM photons. We show that energy, spin and orbital angular
momenta of MDM oscillations constitute the key physical quantities that
characterize the ME field configurations. We show that vacuum can induce a
Casimir torque between a MDM ferrite disk, metal walls, and dielectric samples.",1801.08042v1
2018-05-10,Broadband optomechanical transduction of nanomagnetic spin modes,"The stable vortex state that occurs in micron-scale magnetic disks is one of
the most interesting and potentially useful phenomenon in nanomagnetism. A
variety of tools have been applied to study the vortex state, and collective
spin excitations corresponding to harmonic motion of the vortex, but to-date
these tools have measured either strongly driven vortex resonances or have been
unable to simultaneously measure static properties such as the magnetization.
Here we show that by combining the sensitivity of cavity optomechanics with the
technique of torque mixing resonance spectroscopy, we are able to measure the
magnetization, in-plane susceptibility, and spin resonances of individual
vortices in the low-drive limit. These measurements elucidate the complex
behavior of the vortex as it moves through the pinning landscape of the disk.
Furthermore, we observe gyrotropic resonances as high as 1.1 GHz, suggesting
the use of engineering defects for applications such as microwave-to-optical
wavelength conversion.",1805.04186v1
2018-06-06,Modification of Dzyaloshinskii-Moriya interaction stabilized domain wall chirality by driving currents,"We measure and analyze the chirality of the Dzyaloshinskii-Moriya interaction
(DMI) stabilized spin textures in multilayers of
Ta/Co$_{20}$Fe$_{60}$B$_{20}$/MgO. The effective DMI is measured experimentally
using domain wall motion measurements, both in the presence (using spin orbit
torques) and absence of driving currents (using magnetic fields). We observe
that the current-induced domain wall motion yields a change in effective DMI
magnitude and opposite domain wall chirality when compared to field-induced
domain wall motion (without current). We explore this effect, which we refer to
as current-induced DMI, by providing possible explanations for its emergence,
and explore the possibilty of its manifestation in the framework of recent
theoretical predictions of DMI modifications due to spin currents.",1806.02439v1
2018-06-24,Large unidirectional spin Hall and Rashba-Edelstein magnetoresistance in topological insulator/magnetic insulator heterostructures,"Thanks to its unique symmetry, the unidirectional spin Hall and
Rashba-Edelstein magnetoresistance (USRMR) is of great fundamental and
practical interest, particularly in the context of reading magnetization states
in two-terminal spin-orbit torque switching memory and logic devices. Recent
studies show that topological insulators could improve USRMR amplitude.
However, the topological insulator device configurations studied so far in this
context, namely ferromagnetic metal/topological insulator bilayers and
magnetically doped topological insulators, suffer from current shunting by the
metallic layer and low Curie temperature, respectively. Here, we report large
USRMR in a new material category - magnetic insulator/topological insulator
bi-layered heterostructures. Such structures exhibit USRMR that is about an
order of magnitude larger than the highest values reported so far in all-metal
Ta/Co bilayers. We also demonstrate current-induced magnetization switching
aided by an Oersted field, and electrical read out by the USRMR, as a prototype
memory device.",1806.09066v1
2018-11-21,The high-frequency dynamics of domain walls with strong Dzyaloshinskii-Moriya interaction,"Domain walls (DWs) in perpendicularly magnetized nanotracks (PMNTs) with
interfacial Dzyaloshinskii-Moriya interaction (DMI) have become the primary
objects of theoretical and experimental interest due to their technological
suitability in spintronic nanodevices. Chiral DWs in PMNTs can be driven
efficiently by the spin-orbit torque. However, the high-frequency dynamic
behavior of the chiral DW has not been explored. In this work, using
micromagnetic calculation, we have discovered a novel dynamic mode, the sway
mode, of DWs under an out-of-plane high-frequency alternating current (AC)
magnetic field in a PMNT with strong DMI. This dynamic phenomenon is strictly
related with DMI-related boundary effect and can be understood in terms of the
propagation of an amplitude-tuned spin wave in the DW plane. The spin wave
exhibits some characteristic frequencies due to the space-confinement of DW.
This work offers the possibility of a visual route for characterizing DMI.",1811.08590v1
2018-10-10,Magnetization Dynamics,"Magnetism primarily describes the physics and materials science of systems
presenting a magnetization -- a macroscopic order parameter characterizing
electron angular momentum. The order parameter is associated with the
electronic exchange interactions, which is fundamentally quantum mechanical.
Its dynamic behavior bridges the macroscopic and the microscopic worlds. On
macroscopic length and time-scales, it interacts with electromagnetic fields
dictated by the Maxwells equations. On a microscopic scale, it involves the
quantum-mechanical electronic states both in spin-space and momentum space,
thus giving rise to a wide range of behavior that extend down to femtoseconds.
Thanks to the development of modern metrology, there have been many new and
noteworthy observations of magnetism-related phenomena across the entire range
-- from spin-torque induced antidamping dynamics, to ultrafast laser induced
femtosecond electron dynamics that involve spin current and angular momentum
conservation. In this review we introduce some observations on magnetodynamics,
and the scientific subjects these new results give rise to.",1810.04591v1
2018-10-21,Spectra and Structure of Accretion Disks with Nonzero Inner Torque,"We present numerical spectral and vertical structure calculations appropriate
for near-Eddington-luminosity, radiation-pressure-dominated accretion disks
around stellar-mass black holes. We cover a wide range of black hole spins and
incorporate dissipation profiles based on first-principles three-dimensional
MHD disk interior simulations. We also include nonzero stresses at the
innermost stable circular orbit, which results in the disk effective
temperature increasing rapidly toward the black hole and gives rise to rather
extreme conditions with high temperatures and low surface densities. We found
that local annulus spectra become increasingly characteristic of saturated
Comptonization with decreasing distance to the black hole. While the spectra
become harder with increasing black hole spin, they do not give rise to a broad
power-law tail even at maximum spin. We discuss the implications of our results
in the context of the steep power-law state and the associated high-frequency
quasi- periodic oscillations observed in some X-ray binary systems.",1810.08908v1
2018-10-26,Mechanism of Néel order switching in antiferromagnetic thin films revealed by magnetotransport and direct imaging,"We probe the current-induced magnetic switching of insulating
antiferromagnet/heavy metals systems, by electrical spin Hall magnetoresistance
measurements and direct imaging, identifying a reversal occurring by domain
wall (DW) motion. We observe switching of more than one third of the
antiferromagnetic domains by the application of current pulses. Our data reveal
two different magnetic switching mechanisms leading together to an efficient
switching, namely the spin-current induced effective magnetic anisotropy
variation and the action of the spin torque on the DWs.",1810.11326v2
2018-10-31,Theory of chiral effects in magnetic textures with spin-orbit coupling,"We present a theoretical study of two-dimensional spatially and temporally
varying magnetic textures in the presence of spin-orbit coupling (SOC) of both
the Rashba and Dresselhaus types. We show that the effective gauge field due to
these SOCs, contributes to the dissipative and reactive spin torques in exactly
the same way as in electromagnetism. Our calculations reveal that Rashba
(Dresselhaus) SOC induces a chiral dissipation in interfacial (bulk) inversion
asymmetric magnetic materials. Furthermore, we show that in addition to chiral
dissipation $\alpha_c$, these SOCs also produce a chiral renormalization of the
gyromagnetic ratio $\tilde{\gamma}_c$, and show that the latter is
intrinsically linked to the former via a simple relation $\alpha_c =
(\tau/\tau_{\rm ex}) \tilde{\gamma}_c$, where $\tau_{\rm ex}$ and $\tau$ are
the exchange time and the electron relaxation time, respectively. Finally, we
propose a theoretical scheme based on the Scattering theory to calculate and
investigate the properties of damping in chiral magnets. Our findings should in
principle provide a guide for material engineering of effects related to chiral
dynamics in magnetic textures with SOC.",1810.13065v1
2019-02-12,Thermally assisted Skyrmion drag in a nonuniform electric field,"Magnetic skyrmions are topologically protected excitations of the
magnetization vector field with promising applications in spintronics and
spin-caloritronics, particularly due to their high mobility. Skyrmions can be
steered by a spin-polarized charge current or by exposure to a magnonic spin
current. Here, we propose a further method for driving skyrmions by applying an
inhomogeneous electric field and a homogeneous thermal bias. We show that the
inhomogeneous electric torque leads to an efficient skyrmionic drag which can
be thermally assisted as to enhance the skyrmion velocity. The calculations and
analysis are limited to insulating samples; for conducting materials the
influence of the inhomogeneous electric field on the charge carriers need to be
taken also into account.",1902.04432v1
2019-02-19,Spin-wave mediated interactions for Majority Computation using Skyrmions and Spin-torque Nano-oscillators,"Recent progress in all-electrical nucleation, detection and manipulation of
magnetic skyrmions has unlocked the tremendous potential of skyrmion-based
spintronic devices. Here, we show via micromagnetic simulations that the stable
magnetic oscillations of STNO radiate spin waves (SWs) that can be scattered in
the presence of skyrmions in the near vicinity. Interference between SWs
emitted by the STNO and SWs scattered by the skyrmion gives rise to interesting
dynamics that leads to amplification or attenuation of STNO's magnetic
oscillations. In the presence of strong Dzyaloshinskii-Moriya interaction
(DMI), the amplified magnetic oscillations evolve into a new skyrmion. These
interactions between skyrmions and STNOs are found to be identical for both
Neel-type and Bloch-type skyrmions, and are not observed between domain walls
and STNOs. These findings offer a novel perspective in processing information
using single skyrmions and we propose a 3-bit majority gate for logic
applications.",1902.06925v2
2016-11-30,Temperature-dependent magnetic anisotropy from directional-dependent interactions,"Magnetic anisotropy of spin models with directional-dependent interactions in
the high-temperature paramagnetic phase is theoretically studied. Using a high
temperature expansion, we show that the Ising type directional-dependent
interaction gives rise to magnetic anisotropy which depends on the temperature
as $\propto T^{-5}$. This phenomenon arises from the anisotropic exchange
interaction, and is distinct from the orbital effect, such as van Vleck
susceptibility. It is shown that while the quadratic term in the magnetization
favors to point the spins along the bond, the fourth order term in
magnetization prefers to point spins to the perpendicular direction. The theory
is applied to the Heisenberg-Kitaev model on the honeycomb lattice and a cubic
lattice model that is potentially relevant to perovskite iridates. We show
that, in these models, the anisotropic terms in quadratic order cancels out,
and the leading order for the magnetic anisotropy arises from the fourth order
contribution. The result shows that the anisotropy from the
directional-dependent interaction gives rise to $\langle100\rangle$ magnetic
anisotropy. These results are potentially relevant to heavy transition metal
oxides such as iridates. Experimental observation of the magnitude of
anisotropic interactions using magnetic torque measurement is also discussed.",1612.00057v1
2018-04-03,Adjustable current-induced magnetization switching utilizing interlayer exchange coupling,"Electrical current-induced deterministic magnetization switching in a
magnetic multilayer structure without external magnetic field is realized by
utilizing interlayer exchange coupling. Two ferromagnetic Co layers, with
in-plane and out-of-plane anisotropy respectively, are separated by a spacer Ta
layer, which plays a dual role of inducing antiferromagnetic interlayer
coupling, and contributing to the current-induced effective magnetic field
through the spin Hall effect. The current-induced magnetization switching
behavior can be tuned by pre-magnetizing the in-plane Co layer. The
antiferromagnetic exchange coupling field increases with decreasing thickness
of the Ta layer, reaching 630+-5 Oe for a Ta thickness of 1.5nm. The magnitude
of the current-induced perpendicular effective magnetic field from spin-orbit
torque is 9.2 Oe/(107Acm-2). The large spin Hall angle of Ta, opposite in sign
to that of Pt, results in a low critical current density of 9*10^6A/cm^2. This
approach is promising for the electrical switching of magnetic memory elements
without external magnetic field.",1804.00798v1
2018-04-06,Magnetic phase diagram of the strongly frustrated quantum spin chain system PbCuSO$_4$(OH)$_2$ in tilted magnetic fields,"We report the $\mathbf{H}-T$ phase diagram of $S=1/2$ strongly frustrated
anisotropic spin chain material linarite PbCuSO$_4$(OH)$_2$ in tilted magnetic
fields up to 10 T and temperatures down to 0.2 K. By means of torque
magnetometry we investigate the phase diagram evolution as the magnetic field
undergoes rotation in $\mathbf{ba}^{\ast}$ and $\mathbf{bc}$ planes. The key
finding is the robustness of the high field spin density wave-like phase, which
may persist even as the external field goes orthogonal to the chain direction
$\mathbf{b}$. In contrast, the intermediate collinear antiferromagnetic phase
collapses at moderate deflection angles with respect to $\mathbf{b}$ axis.",1804.02215v2
2019-03-27,Magnetoelectric Response in Electric Octupole State: Possible Hidden Order in Cuprate Superconductors,"Motivated by recent studies of odd-parity multipole order in condensed matter
physics, we theoretically study magnetoelectric responses in an electric
octupole state. Investigating the Edelstein effect and spin Hall effect in a
locally noncentrosymmetric bilayer Rashba model, we clarify characteristic
properties due to parity violation in the electric octupole state. Furthermore,
a possible realization of electric octupole order in bilayer high-Tc cuprate
superconductors is proposed. Our calculation of magnetic torque is consistent
with recent experimental observation of a kink above the superconducting
transition temperature. We also show significant enhancement of the in-plane
anisotropy in spin susceptibility due to the superconductivity, and propose an
experimental test by means of the nuclear magnetic resonance in the
superconducting state. A spin-orbit coupled metal state in Cd2Re2O7 is also
discussed.",1903.11258v1
2020-11-09,Topological Insulators-Based Magnetic Heterostructure,"The combination of magnetism and topology in magnetic topological insulators
(MTIs) has led to unprecedented advancements of time reversal symmetry-breaking
topological quantum physics in the past decade. Compared with the uniform
films, the MTI heterostructures provide a better framework to manipulate the
spin-orbit coupling and spin properties. In this review, we summarize the
fundamental mechanisms related to the physical orders host in
(Bi,Sb)2(Te,Se)3-based hybrid systems. Besides, we provide an assessment on the
general strategies to enhance the magnetic coupling and spin-orbit torque
strength through different structural engineering approaches and effective
interfacial interactions. Finally, we offer an outlook of MTI
heterostructures-based spintronics applications, particularly in view of their
feasibility to achieve room-temperature operation.",2011.04148v1
2021-10-17,Non-collinear density functional theory,"An approach to generalize any kind of collinear functionals in density
functional theory to non-collinear functionals is proposed. This approach, for
the very first time, satisfies the correct collinear limit for any kind of
functionals, guaranteeing that the exact collinear functional after generalized
is still exact for collinear spins. Besides, it has well-defined and
numerically stable functional derivatives, a desired feature for non-collinear
and spin-flip time-dependent density functional theory. Furthermore, it
provides local torque, hinting at its applications in spin dynamics.",2110.09897v2
2017-01-16,The Timing Noise of Magnetars,"We represent noise strength analysis of Anomalous X-Ray Pulsars (AXPs) 4U
0142+61, 1RXS J170849.9-400910, 1E 1841-045, 1E 2259+586 and Soft Gamma
Repeaters (SGRs) SGR J1833-0832, SWIFT J1822.3-1606 and SWIFT J1834.9-0846
together with the X-Ray binaries GX 1+4 and 4U 1907+09 for comparison with
accreting sources. Using our timing solutions, we extracted residuals of pulse
arrival times after removal of spin down trends and we calculated assoicated
noise strength of each source. Our preliminary results indicate that the noise
strength is scaling up with spin-down rate. This indicates that, increase in
spin-down rate leads to more torque noise on the magnetars. In addition, we
present our analysis with Bayesian statistics on the previously reported
transient QPO feature of 4U 1907+09.",1701.04332v1
2017-03-28,Weak ferromagnetic order breaking the threefold rotational symmetry of the underlying kagomé lattice in CdCu$_3$(OH)$_6$(NO$_3$)$_2\cdot$H$_2$O,"Novel magnetic phases are expected to occur in highly frustrated spin
systems. Here we study the structurally perfect kagom\'e antiferromagnet
CdCu$_3$(OH)$_6$(NO$_3$)$_2\cdot$H$_2$O by magnetization, magnetic torque, and
heat capacity measurements using single crystals.An antiferromagnetic order
accompanied by a small spontaneous magnetization that surprisingly is confined
in the kagom\'e plane sets in at $T_\mathrm{N}\approx$4 K, well below the
nearest-neighbor exchange interaction $J / k_B$ = 45 K.This suggests that a
unique $\bf q = 0$ type 120$^\circ$ spin structure with ""negative"" (downward)
vector chirality, which breaks the underlying threefold rotational symmetry of
the kagom\'e lattice and thus allows a spin canting within the plane, is
exceptionally realized in this compound rather than a common one with
""positive"" (upward) vector chirality. The origin is discussed in terms of the
Dzyaloshinskii-Moriya interaction.",1703.09357v1
2017-03-29,From materials to systems: a multiscale analysis of nanomagnetic switching,"With the increasing demand for low-power electronics, nanomagnetic devices
have emerged as strong potential candidates to complement present day
transistor technology. A variety of novel switching effects such as spin torque
and giant spin Hall offer scalable ways to manipulate nano-sized magnets.
However, the low intrinsic energy cost of switching spins is often compromised
by the energy consumed in the overhead circuitry in creating the necessary
switching fields. Scaling brings in added concerns such as the ability to
distinguish states (readability) and to write information without spontaneous
backflips (reliability). A viable device must ultimately navigate a complex
multi-dimensional material and design space defined by volume, energy budget,
speed and a target read-write-retention error. In this paper, we review the
major challenges facing nanomagnetic devices and present a multi-scale
computational framework to explore possible innovations at different levels
(material, device, or circuit), along with a holistic understanding of their
overall energy-delay-reliability tradeoff.",1703.10214v2
2019-01-29,Low-impedance superconducting microwave resonators for strong coupling to small magnetic mode volumes,"Recent experiments on strongly coupled microwave and ferromagnetic resonance
modes have focused on large volume bulk crystals such as yttrium iron garnet,
typically of millimeter-scale dimensions. We extend these experiments to lower
volumes of magnetic material by exploiting low-impedance lumped-element
microwave resonators. The low impedance equates to a smaller magnetic mode
volume, which allows us to couple to a smaller number of spins in the
ferromagnet. Compared to previous experiments, we reduce the number of
participating spins by two orders of magnitude, while maintaining the strength
of the coupling rate. Strongly coupled devices with small volumes of magnetic
material may allow the use of spin orbit torques, which require high current
densities incompatible with existing structures.",1901.10395v1
2019-07-26,Frequency Modulation and Voltage Locking of the Voltage Controlled Spin Oscillators (VCSOs),"The oscillating frequency of typical Spin Torque Nano Oscillators (STNOs) can
be modulated by injected DC current or bias magnetic field. And phase locking
of STNOs to an external Radio Frequency (RF) signal can be imposed by AC
current or RF bias magnetic field. However, in this study, we have proposed a
Voltage Controlled Spin Oscillators (VCSOs) by introducing Voltage Controlled
Magnetic Anisotropy (VCMA) effect. The oscillating frequency of VCSOs can be
modulated by VCMA voltage as well as injected DC current. Furthermore, we have
shown a novel locking mechanism caused by AC VCMA voltage. Both the frequency
modulation and voltage locking mechanism are analyzed theoretically by
Nonlinear Auto-oscillator theory and verified by numerical simulation. At last,
we proposed that by utilizing negative capacitance material to enhance VCMA
effect, the locking range for voltage locking can be expanded thus may lead to
easy mutual synchronization of multiple VCSOs.",1907.11395v1
2020-01-04,Observation of spin-motive force in ferrimagnetic GdFeCo alloy films,"Non-uniform magnetic structures produce emergent electromagnetic phenomena
such as the topological Hall effect and the spin-motive force (SMF). The
experimental reports on the SMF, however, are very few and the relationship
between the SMF and material parameters is still unclear. In this study, we
investigated the SMF in ferrimagnetic GdFeCo alloy films using the
spin-torque-induced ferromagnetic resonance method and clarified the
relationship. The amplitude of the detected SMF becomes larger than that of the
transition metal alloy FeCo by the Gd doping and reaches the maximum near a Gd
composition of the boundary between in-plane and perpendicularly magnetized
films. According to the analytical calculation, the enhancement is related to
the trajectory of the magnetization precession. Moreover, we find that the SMF
induced by the magnetic resonance is inversely proportional to the square of
the damping constant.",2001.01042v2
2020-02-03,Giant magnetoresistance in antiferromagnetic Mn$_2$Au-based tunnel junction,"Recent studies on the electrical switching of tetragonal antiferromagnet
(AFM) via N{\'e}el spin-orbit torque have paved the way for the economic use of
antiferromagnetic materials. The most difficult obstacle that presently limits
the application of antiferromagnetic materials in spintronics, especially in
memory storage applications, could be the small and fragile magnetoresistance
(MR) in the AFM-based nanostructure. In this study, we investigated the spin
transports in Mn$_2$Au-based tunnel junctions based onthe first-principle
scattering theory. Giant MRs more than $1000\%$ are predicted in some
Fe/MgO/Ag/Mn$_2$Au/Ta junctions that are about the same order as that in an
MgO-based ferromagnetic tunnel junction with same barrier thickness. The
interplay of the spin filtering effect, the quantum well resonant states, and
the interfacial resonant states could be responsible for the unusual giant and
robust MRs observed in these Mn$_2$Au-based junctions.",2002.00621v1
2020-02-25,Bias-field-free spin Hall nano-oscillators with an out-of-plane precession mode,"Spin Hall nano-oscillators (SHNOs) are promising candidates for new microwave
oscillators with high durability due to a small driving current. However,
conventional SHNOs with an in-plane precession (IPP) mode require a bias field
for stable oscillations which is not favored in certain applications such as
neuromorphic computing. Here, we propose and theoretically analyze a
bias-field-free SHNO with an in-plane hard axis and an out-of-plane precession
(OPP) mode by solving the Landau-Lifshitz-Gilbert (LLG) equation analytically
and numerically. We derive formulas for driving currents and precession
frequency, and show that they are in good agreement with numerical simulation
results. We show that our proposed SHNOs can be driven by much smaller bias
current than conventional spin torque nano-oscillators.",2002.10753v1
2020-10-02,Synthetic chiral magnets promoted by the Dzyaloshinskii-Moriya interaction,"The ability to engineer the interactions in assemblies of nanoscale magnets
is central to the development of artificial spin systems and spintronic
technologies. Following the emergence of the Dzyaloshinskii-Moriya interaction
(DMI) in thin film magnetism, new routes have been opened to couple the
nanomagnets via strong chiral interactions, which is complementary to the
established dipolar and exchange coupling mechanisms. In this Perspective, we
review recent progress in the engineering of synthetic magnets coupled by the
interlayer and intralayer DMI. We show how multilayer chiral magnetic
structures and two-dimensional synthetic antiferromagnets, skyrmions, and
artificial spin systems can be realized by simultaneous control of the DMI and
magnetic anisotropy. In addition, we show that, with the combination of DMI and
current-induced spin-orbit torques, field-free switching of synthetic magnetic
elements is obtained as well as all-electric domain wall logic circuits.",2010.01077v1
2020-12-03,Persistent Emission Properties of SGR J1935+2154 During Its 2020 Active Episode,"We present detailed spectral and temporal characteristics of the persistent
X-ray emission of SGR J1935+2154 based on our XMM-Newton and Chandra
observations taken in the aftermath of its April 2020 burst storm, during which
hundreds of energetic X-ray bursts were emitted, including one associated with
an extraordinary fast radio burst. We clearly detect the pulsed X-ray emission
in the XMM-Newton data. An average spin-down rate of 1.6$\times$10$^{-11}$ s
s$^{-1}$ is obtained using our spin period measurement combined with three
earlier values reported from the same active episode. Our investigations of the
XMM-Newton and Chandra spectra with a variety of phenomenological and
physically-motivated models, concluded that the magnetic field topology of SGR
J1935+2154 is most likely highly non-dipolar. The spectral models indicate that
surface field strengths in somewhat localized regions substantially exceed the
polar value of 4.4$\times$10$^{14}$ G inferred from a spin-down torque
associated with a rotating magnetic dipole.",2012.01871v1
2021-09-23,The free energy of twisting spins in Mn$_3$Sn,"The magnetic free energy is usually quadratic in magnetic field and depends
on the mutual orientation of the magnetic field and the crystalline axes. Tiny
in magnitude, this magnetocrystalline anisotropy energy (MAE) is nevertheless
indispensable for the existence of permanent magnets. Here, we show that in
Mn$_3$Sn, a non-collinear antiferromagnet attracting much attention following
the discovery of its large anomalous Hall effect, the free energy of spins has
superquadratic components, which drive the MAE. We experimentally demonstrate
that the thermodynamic free energy includes terms odd in magnetic field
($\mathcal{O}(H^3)+\mathcal{O}(H^5)$) and generating sixfold and twelve-fold
angular oscillations in the torque response. We show that they are
quantitatively explained by theory, which can be used to quantify relevant
energy scales (Heisenberg, Dzyaloshinskii-Moriya, Zeeman and single-ion
anisotropy) of the system. Based on the theory, we conclude that, in contrast
with common magnets, what drives the MAE in Mn$_3$Sn is the field-induced
deformation of the spin texture.",2109.11122v1
2021-12-16,Spin Hall Conductivity and Anomalous Hall Conductivity in Full Heusler compounds,"The spin Hall conductivity (SHC) and anomalous Hall conductivity (AHC) in
more than 120 full Heusler compounds are calculated using density functional
theory in a high-throughtput way. The electronic structures are mapped to the
Wannier basis and the linear response theory is used to get the conductivity.
Our results show that the mechanism under the SHC or AHC cannot be simply
related to the valence electron numbers or atomic weights, is related to the
very details of the electronic structure, which can only be obtained by
calculations. A high throughput calculation is efficient to screen out the
desired materials. According to our present results, Cu2CoSn, as well as
Co2MnAl and Co2MnGa are candidates in spintronic materials regarding to their
high SHC and AHC values, which can benefit the spin-torque-driven nanodevices.",2112.08630v1
2022-01-31,Current induced switching in Mn2Au from first principles,"It is well established that it is possible to switch certain antiferromagnets
electrically, yet the interplay of N\'{e}el-spin-orbit torques and thermal
activation is only poorly understood. Combining ab initio calculations and
atomistic spin dynamics simulations we develop a multiscale model to study the
current induced switching in Mn2Au. We compute from first principles the
strength and direction of the electrically induced magnetic moments, caused by
the Rashba--Edelstein effect, and take these into account in atomistic spin
dynamics simulations. Our simulations reveal the switching paths as well as the
time scales for switching. The size of the induced moments, however, turns out
to be insufficient to lead to fully deterministic switching. Instead, we find
that a certain degree of thermal activation is required to help overcoming the
relevant energy barrier.",2201.13137v1
2022-03-08,Generating Stellar Obliquity in Systems with Broken Protoplanetary Disks,"Recent advances in sub-millimeter observations of young circumstellar nebulae
have opened an unprecedented window into the structure of protoplanetary disks,
which has revealed the surprising ubiquity of broken and misaligned disks. In
this work, we demonstrate that such disks are capable of torquing the spin axis
of their host star, representing a hitherto unexplored pathway by which stellar
obliquities may be generated. The basis of this mechanism is a crossing of the
stellar spin precession and inner disk regression frequencies, resulting in
adiabatic excitation of the stellar obliquity. We derive analytical expressions
for the characteristic frequencies of the inner disk and star as a function of
the disk gap boundaries, and place an approximate limit on the disk
architectures for which frequency crossing and resulting obliquity excitation
are expected, thereby illustrating the efficacy of this model. Cumulatively,
our results support the emerging concensus that significant spin-orbit
misalignments are an expected outcome of planet formation.",2203.04429v1
2022-03-21,Hydrodynamic spin-orbit coupling in asynchronous optically driven micro-rotors,"Vortical flows of rotating particles describe interactions ranging from
molecular machines to atmospheric dynamics. Yet to date, direct observation of
the hydrodynamic coupling between artificial micro-rotors has been restricted
by the details of the chosen drive, either through synchronization (using
external magnetic fields) or confinement (using optical tweezers). Here we
present a new active system that illuminates the interplay of rotation and
translation in free rotors. We developed a non-tweezing circularly polarized
beam that simultaneously rotates hundreds of silica-coated birefringent
colloids. The particles rotate asynchronously in the optical torque field while
freely diffusing in the plane. We observe that neighboring particles orbit each
other with an angular velocity that depends on their spins. We derive an
analytical model in the Stokes limit for pairs of spheres that quantitatively
explains the observed dynamics. We then find that the geometrical nature of the
low Reynolds fluid results in a universal hydrodynamic spin-orbit coupling. Our
findings are of significance for the understanding and development of
far-from-equilibrium materials.",2203.11051v2
2022-03-27,Low power In Memory Computation with Reciprocal Ferromagnet/Topological Insulator Heterostructures,"The surface state of a 3D topological insulator (3DTI) is a spin-momentum
locked conductive state, whose large spin hall angle can be used for the
energy-efficient spin orbit torque based switching of an overlying ferromagnet
(FM). Conversely, the gated switching of the magnetization of a separate FM in
or out of the TI surface plane, can turn on and off the TI surface current. The
gate tunability of the TI Dirac cone gap helps reduce its sub-threshold swing.
By exploiting this reciprocal behaviour, we can use two FM/3DTI
heterostructures to design a 1-Transistor 1-magnetic tunnel junction random
access memory unit (1T1MTJ RAM) for an ultra low power Processing-in-Memory
(PiM) architecture. Our calculation involves combining the Fokker-Planck
equation with the Non-equilibrium Green Function (NEGF) based flow of
conduction electrons and Landau-Lifshitz-Gilbert (LLG) based dynamics of
magnetization. Our combined approach allows us to connect device performance
metrics with underlying material parameters, which can guide proposed
experimental and fabrication efforts.",2203.14389v3
2022-04-29,Electrically Active Domain Wall Magnons in Layered van der Waals Antiferromagnets,"We study theoretically domain wall (DW) magnons-elementary collective
excitations of magnetic DWs -- in easy-axis layered van der Waals (vdW)
antiferromagnets, where they behave as normal modes of coupled spin
superfluids. We uncover that, due to spin-charge coupling in vdW magnets, such
DW magnons can be activated by voltage-induced torques, thereby providing a
path for their low-dissipation and nanoscale excitation. Moreover, the
electrical activation and the number of DW magnons at a frequency can be
controlled by applying symmetry-breaking static magnetic field, adding
tunability of signal transmission by them. Our results highlight that domain
walls in vdW magnets provide a promising platform to route coherent spin
information for a broad range of explorations in spintronics and magnetism.",2204.13909v1
2022-05-27,"Electronic structures and stability investigation of the new class of large band gap topological insulators MTl$_4$Te$_3$ (M = Cd, Hg)","By means of ternary chemical potential phase diagram and phonon spectrum
calculations, we propose that $M$Tl$_4$Te$_3$ ($M$ = Cd, Hg), the derivatives
of Tl$_5$Te$_3$, are thermodynamically and dynamically stable in the body
centered tetragonal crystal structure with $I$4/$mcm$ symmetry. Our electronic
structures calculations confirm that a robust $s$-$p$ band inversion occurs
near the Fermi level in $M$Tl$_4$Te$_3$, and a topological band gap about 0.13
eV in CdTl$_4$Te$_3$ is induced by the spin-orbit coupling. These results
suggest that $M$Tl$_4$Te$_3$ are a new class of large band gap 3D strong
topological insulators that are stable and synthesizable in experiments, which
could be used to design efficient spin torque equipment and spin device.",2205.13749v2
2022-07-26,All-electrical switching of a topological non-collinear antiferromagnet at room temperature,"Non-collinear antiferromagnetic Weyl semimetals, combining the advantages of
a zero stray field and ultrafast spin dynamics as well as a large anomalous
Hall effect and the chiral anomaly of Weyl fermions, have attracted extensive
interests. However, the all-electrical control of such systems at room
temperature, a crucial step toward practical applications, has not been
reported. Here using a small writing current of around 5*10^{6} A/cm^{2}, we
realize the all-electrical current-induced deterministic switching of the
non-collinear antiferromagnet Mn3Sn with a strong readout signal at room
temperature in the Si/SiO2/Mn3Sn/AlOx structure, without external magnetic
field and injected spin current. Our simulations reveal that the switching is
originated from the current-induced intrinsic non-collinear spin-orbit torques
in Mn3Sn itself. Our findings pave the way for the development of topological
antiferromagnetic spintronics.",2207.12885v1
2022-09-05,Generation and routing of nanoscale droplet solitons without compensation of magnetic damping,"Magnetic droplet soliton is a localized dynamic spin state which can serve as
a nanoscale information carrier and nonlinear oscillator. The present opinion
is that the formation of droplet solitons requires the compensation of magnetic
damping by a torque created by a spin-polarized electric current or pure spin
current. Here we demonstrate theoretically that nanoscale droplet solitons can
be generated and routed in ferromagnetic nanostructures with voltage-controlled
magnetic anisotropy in the presence of uncompensated magnetic damping.
Performing micromagnetic simulations for the MgO/Fe/MgO trilayer with almost
perpendicular-to-plane magnetization, we reveal the formation of the droplet
soliton under a nanoscale gate electrode subjected to a sub-nanosecond voltage
pulse. The soliton lives up to 50 ns at room temperature and can propagate over
micrometer distances in a ferromagnetic waveguide due to nonzero gradient of
the demagnetizing field. Furthermore, we show that an electrical routing of the
soliton to different outputs of a spintronic device can be realized with the
aid of an additional semiconducting nanostripe electrode creating controllable
gradient of the perpendicular magnetic anisotropy.",2209.01893v1
2022-12-12,Gradient-induced Dzyaloshinskii-Moriya interaction,"The Dzyaloshinskii-Moriya interaction (DMI) that arises in the magnetic
systems with broken inversion symmetry plays an essential role in topological
spintronics. Here, by means of atomistic spin calculations, we study an
intriguing type of DMI (g-DMI) that emerges in the films with composition
gradient. We show that both the strength and chirality of g-DMI can be
controlled by the composition gradient even in the disordered system. The
layer-resolved analysis of g-DMI unveils its additive nature inside the bulk
layers and clarifies the linear thickness dependence of g-DMI observed in
experiments. Furthermore, we demonstrate the g-DMI induced chiral magnetic
structures, such as spin spirals and skyrmions, and the g-DMI driven field-free
spin-orbit torque (SOT) switching, both of which are crucial towards practical
device application. These results elucidate the underlying mechanisms of g-DMI
and open up a new way to engineer the topological magnetic textures.",2212.05741v1
2022-12-19,Confined phase singularities reveal the spin-to-orbital angular momentum conversion of sound waves,"We identify an acoustic process in which the conversion of angular momentum
between its spin and orbital form takes place. The interaction between an
evanescent wave propagating at the interface of two immiscible fluids and an
isolated droplet is considered. The elliptical motion of the fluid supporting
the incident wave is associated with a simple state of spin angular momentum, a
quantity recently introduced for acoustic waves in the literature. We
experimentally observe that this field predominantly forces a directional wave
transport circling the droplet's interior, revealing the existence of confined
phase singularities. The circulation of the phase, around a singular point, is
characteristic of angular momentum in its orbital form, thereby demonstrating
the conversion mechanism. The numerical and experimental observations presented
in this work have implications for the fundamental understanding of the angular
momentum of acoustic waves, and for applications such as particle manipulation
with radiation forces or torques, acoustic sensing and imaging.",2212.09439v2
2023-03-23,Mechanism of electrical switching of ultra-thin CoO/Pt bilayers,"We study current-induced switching of the N\'eel vector in CoO/Pt bilayers to
understand the underlaying antiferromagnetic switching mechanism. Surprisingly,
we find that for ultra-thin CoO/Pt bilayers electrical pulses along the same
path can lead to an increase or decrease of the spin Hall magnetoresistance
signal, depending on the current density of the pulse. By comparing the results
of these electrical measurements to XMLD-PEEM imaging of the antiferromagnetic
domain structure before and after the application of current pulses, we reveal
the reorientation of the N\'eel vector in ultra-thin CoO(4 nm). This allows us
to determine that even opposite resistance changes can result from a
thermomagnetoelastic switching mechanism. Importantly, our spatially resolved
imaging shows that regions where the current pulses are applied and regions
further away exhibit different switched spin structures, which can be explained
by a spin-orbit torque based switching mechanism that can dominate in very thin
films.",2303.13308v1
2023-08-22,Skyrmion motion in magnetic anisotropy gradients: Acceleration caused by deformation,"Magnetic skyrmions are nano-sized topologically non-trivial spin textures
that can be moved by external stimuli such as spin currents and internal
stimuli such as spatial gradients of a material parameter. Since the total
energy of a skyrmion depends linearly on most of these parameters, like the
perpendicular magnetic anisotropy, the exchange constant, or the
Dzyaloshinskii-Moriya interaction strength, a skyrmion will move uniformly in a
weak parameter gradient. In this paper, we show that the linear behavior
changes once the gradients are strong enough so that the magnetic profile of a
skyrmion is significantly altered throughout the propagation. In that case, the
skyrmion experiences acceleration and moves along a curved trajectory.
Furthermore, we show that when spin-orbit torques and material parameter
gradients trigger a skyrmion motion, it can move on a straight path along the
current or gradient direction. We discuss the significance of suppressing the
skyrmion Hall effect for spintronic and neuromorphic applications of skyrmions.
Lastly, we extend our discussion and compare it to a gradient generated by the
Dzyaloshinskii-Moriya interaction.",2308.11361v1
2023-09-26,Orbital Pumping by Magnetization Dynamics in Ferromagnets,"We show that dynamics of the magnetization in ferromagnets can pump the
orbital angular momentum, which we denote by orbital pumping. This is the
reciprocal phenomenon to the orbital torque that induces magnetization dynamics
by the orbital angular momentum in non-equilibrium. The orbital pumping is
analogous to the spin pumping established in spintronics but requires the
spin-orbit coupling for the orbital angular momentum to interact with the
magnetization. We develop a formalism that describes the generation of the
orbital angular momentum by magnetization dynamics within the adiabatic
perturbation theory. Based on this, we perform first-principles calculation of
the orbital pumping in prototypical $3d$ ferromagnets, Fe, Co, and Ni. The
results show that the ratio between the orbital pumping and the spin pumping
ranges from 5 to 15 percents, being smallest in Fe and largest in Ni. This
implies that ferromagnetic Ni is a good candidate for measuring the orbital
pumping. Implications of our results on experiments are also discussed.",2309.14817v2
2023-11-15,Strongly pinned skyrmionic bubbles and higher-order nonlinear Hall resistances at the interface of Pt/FeSi bilayer,"Engineering of magnetic heterostructures for spintronic applications has
entered a new phase, driven by the recent discoveries of topological materials
and exfoliated van der Waals materials. Their low-dimensional properties can be
dramatically modulated in designer heterostructures via proximity effects from
adjacent materials, thus enabling the realization of diverse quantum states and
functionalities. Here we investigate spin-orbit coupling (SOC) proximity
effects of Pt on the recently discovered quasi-two-dimensional ferromagnetic
state at FeSi surface. Skyrmionic bubbles (SkBs) are formed as a result of the
enhanced interfacial Dzyloshinskii-Moriya interaction. The strong pinning
effects on the SkBs are evidenced from the significant dispersion in size and
shape of the SkBs and are further identified as a greatly enhanced threshold
current density required for depinning of the SkBs. The robust integrity of the
SkB assembly leads to the emergence of higher-order nonlinear Hall effects in
the high current density regime, which originate from nontrivial Hall effects
due to the noncollinearity of the spin texture, as well as from the
current-induced magnetization dynamics via the augmented spin-orbit torque.",2311.08730v1
2023-12-13,Ultrafast light-induced magnetization in non-magnetic films: from orbital and spin Hall phenomena to the inverse Faraday effect,"The field of orbitronics has emerged with great potential to impact
information technology by enabling environmentally friendly electronic devices.
The main electronic degree of freedom at play is the orbital angular momentum,
which can give rise to a myriad of phenomena such as the orbital Hall effect
(OHE), torques and orbital magnetoelectric effects. Here, we explore via
realistic time-dependent electronic structure simulations the magnetic response
of a non-magnetic material, an ultrathin Pt film, to ultrafast laser pulses of
different polarizatons and helicities. We demonstrate the generation of
significant orbital and spin magnetizations and identify the underlying
mechanisms consisting of the interplay of the OHE, inverse Faraday effect and
spin-orbit interaction. Our discoveries advocate for the prospect of encoding
magnetic information using light in materials that are not inherently magnetic.",2312.07888v1
2023-12-21,Antiferromagnetic Tunnel Junctions for Spintronics,"Antiferromagnetic (AFM) spintronics has emerged as a subfield of spintronics,
where an AFM N\'eel vector is used as a state variable. Efficient electric
control and detection of the N\'eel vector are critical for spintronic
applications. This review article features fundamental properties of AFM tunnel
junctions (AFMTJs) as spintronic devices where such electric control and
detection can be realized. We emphasize critical requirements for observing a
large tunneling magnetoresistance (TMR) effect in AFMTJs with collinear and
noncollinear AFM electrodes, such as a momentum-dependent spin polarization and
N\'eel spin currents. We further discuss spin torques in AFMTJs that are
capable of N\'eel vector switching. Overall, AFMTJs have potential to become a
new standard for spintronics providing larger magnetoresistive effects, few
orders of magnitude faster switching speed, and much higher packing density
than conventional magnetic tunnel junctions (MTJs).",2312.13507v1
2007-04-05,"Complete Set of Polarization Transfer Observables for the $^{12}{\rm C}(p,n)$ Reaction at 296 MeV and 0$^{\circ}$","A complete set of polarization transfer observables has been measured for the
$^{12}{\rm C}(p,n)$ reaction at $T_p=296 {\rm MeV}$ and $\theta_{\rm
lab}=0^{\circ}$. The total spin transfer $\Sigma(0^{\circ})$ and the observable
$f_1$ deduced from the measured polarization transfer observables indicate that
the spin--dipole resonance at $E_x \simeq 7 {\rm MeV}$ has greater $2^-$
strength than $1^-$ strength, which is consistent with recent experimental and
theoretical studies. The results also indicate a predominance of the spin-flip
and unnatural-parity transition strength in the continuum. The exchange tensor
interaction at a large momentum transfer of $Q \simeq 3.6 {\rm fm}^{-1}$ is
discussed.",0704.0670v1
2010-05-20,High probability state transfer in spin-1/2 chains: Analytical and numerical approaches,"This article is devoted to the development of analytical and numerical
approaches to the problem of the end-to-end quantum state transfer along the
spin-1/2 chain using two methods: (a) a homogeneous spin chain with week end
bonds and equal Larmor frequencies and (b) a homogeneous spin chain with end
Larmor frequencies different from inner ones. A tridiagonal matrix
representation of the XY Hamiltonian with nearest neighbor interactions
relevant to the quantum state transfer is exactly diagonalized for a
combination of the above two methods. In order to take into account
interactions of the remote spins we used numerical simulations of the quantum
state transfer in ten-node chains. We compare the state transfer times obtained
using the two above methods for chains governed by the both XY and XXZ
Hamiltonians and using both nearest neighbor and all node interactions.",1005.3614v2
2014-03-26,Mechanism of charge transfer/disproportionation in LnCu3Fe4O12 (Ln: Lanthanides),"The Fe-Cu intersite charge transfer and Fe charge disproportionation are
interesting phenomena observed in some LnCu3Fe4O12 (Ln: Lanthanides) compounds
containing light and heavy Ln atoms, respectively. We show that a change in the
spin state is responsible for the intersite charge transfer in the light Ln
compounds. At the high spin state, such systems prefer an unusual Cu-d^8
configuration, whereas at the low spin state they retreat to the normal Cu-d^9
configuration through a charge transfer from Fe to Cu-3d_{xy} orbital. We find
that the strength of the crystal field splitting and the relative energy
ordering between Cu-3d_{xy} and Fe-3d states are the key parameters,
determining the intersite charge transfer (charge disproportionation) in light
(heavy) Ln compounds. It is further proposed that the size of Ln affects the
onsite interaction strength of Cu-3d states, leading to a strong modification
of the Cu-L_3 edge spectrum, as observed by the X-ray absorption spectroscopy.",1403.6589v1
2021-08-09,Controlled transfer of transverse optical angular momentum to optically trapped birefringent particles,"We report on the observation and measurement of the transfer of transverse
angular momentum to birefringent particles several wavelengths in size. A
trapped birefringent particle is much larger than the nano-particles systems
for which transverse angular momentum was previously investigated. The larger
birefringent particle interacts more strongly with both the trapping beam and
fluid surrounding it. This technique could be used to transfer transverse
angular momentum for studies of diverse micro-systems. Thus, it can be used for
investigation of the dynamics of complex fluids in 3D as well as for shear on
cell mono-layers. The trapping of such a particle with highly focused light is
complex and can lead to the emergence of effects such as spin--orbit coupling.
We estimate the transfer of spin angular momentum using Stokes measurements. We
outline the physics behind the construction of the beam used to control the
particles, perform quantitative measurement of transverse spin angular momentum
transfer, as well as demonstrate the generation of fluid flow around multiple
rotation axes.",2108.04239v1
2017-01-03,Quantum state transfer on distance regular spin networks with intrinsic decoherence,"By considering distance-regular graphs as spin networks, we investigate the
state transfer fidelity in this class of networks. The effect of environment on
the dynamics of state transfer is modeled using Milburn's intrinsic decoherence
[G. J. Milburn, Phys. Rev. A 44, 5401 (1991)]. We consider a particular type of
spin Hamiltonians which are extended version of those of Christandl et al
[Phys. Rev. A 71, 032312 (2005)]. It is shown that decoherence destroys perfect
communication channels. Using optimal coupling strengths derived by Jafarizadeh
and Sufiani [Phys. Rev. A 77, 022315 (2008)], we show that destructive effect
of environment on the communication channel increases by increasing the
decoherence rate, however the state transfer fidelity reaches a steady value as
time approaches infinity which is independent of the decoherence rate.
Moreover, it is shown that for a given decoherence rate, the fidelity of
transfer decreases by increasing the distance between the sender and the
receiver.",1701.00647v1
2002-05-14,The co-orbital corotation torque in a viscous disk: numerical simulations,"The torque felt by a non-accreting protoplanet on a circular orbit embedded
in a uniform surface density protoplanetary disk is analyzed by means of
time-dependent numerical simulations. Varying the viscosity enables one to
disentangle the Lindblad torque (which is independent of viscosity) from the
corotation torque, which saturates at low viscosity and is unsaturated at high
viscosity. The dependence of the corotation torque upon the viscosity and upon
the width of the librating zone is compared with previous analytical
expressions, and shown to be in agreement with those. The effect of the
potential smoothing respectively on the Lindblad torque and on the corotation
torque is investigated, and the question of whether 3D effects and their impact
on the total torque sign and magnitude can be modeled by an adequate smoothing
prescription in a 2D simulation is addressed. As a side result, this study
shows that the total torque acting on a Neptune-sized protoplanet is positive
in a sufficiently thin, viscous disk (H/r < 4%, \alpha > 10^-2), but the inward
migration time of smaller bodies is still very short, making it unlikely that
they reach the torque reversal mass before having migrated all the way to the
central object.",0205211v1
2006-08-13,Spin-orbit interactions in black-hole binaries,"We perform numerical simulations of black-hole binaries to study the exchange
of spin and orbital angular momentum during the last, highly nonlinear, stages
of the coalescence process. To calculate the transfer of angular momentum from
orbital to spin, we start with two quasi-circular configurations, one with
initially non-spinning black holes, the other with corotating black holes. In
both cases the binaries complete almost two orbits before merging. We find
that, during these last orbits, the specific spin (a/m) of each horizon
increases by only 0.012 for the initially non-spinning configuration, and by
only 0.006 for the initially corotating configuration. By contrast, the
corotation value for the specific spin should increase from 0.1 at the initial
proper separation of 10M to 0.33 when the proper separation is 5M. Thus the
spin-orbit coupling is far too weak to tidally lock the binary to a corotating
state during the late-inspiral phase. We also study the converse transfer from
spin into orbital motion. In this case, we start the simulations with parallel,
highly-spinning non-boosted black holes. As the collision proceeds, the system
acquires a non-head-on orbital motion, due to spin-orbit coupling, that leads
to the radiation of angular momentum. We are able to accurately measure the
energy and angular momentum losses and model their dependence on the initial
spins.",0608275v4
2010-03-08,A theoretical study of spin filtering and its application to polarizing antiprotons,"There has been much recent research into possible methods of polarizing an
antiproton beam, the most promising being spin filtering, the theoretical
understanding of which is currently incomplete. The method of polarization
buildup by spin filtering requires many of the beam particles to remain within
the beam after repeated interaction with an internal target in a storage ring.
Hence small scattering angles, where we show that electromagnetic effects
dominate hadronic effects, are important. All spin-averaged and spin-dependent
electromagnetic cross-sections and spin observables for elastic spin 1/2 - spin
1/2 scattering, for both point-like particles and non-point-like particles with
internal structure defined by electromagnetic form factors, are derived to
first order in QED. Particular attention is paid to spin transfer and
depolarization cross-sections in antiproton-proton, antiproton-electron and
positron-electron scattering, in the low | t | region of momentum transfer. A
thorough mathematical treatment of spin filtering is then presented,
identifying the key physical processes involved and highlighting the dynamical
properties of the physical system. We present and solve sets of differential
equations which describe the buildup of polarization by spin filtering in many
different scenarios of interest. The advantages of using a lepton target are
outlined, and finally a proposal to polarize antiprotons by spin filtering off
an opposing polarized electron beam is investigated.",1003.1604v1
2017-11-20,Multi-spin-assisted optical pumping of bulk 13C nuclear spin polarization in diamond,"One of the most remarkable properties of the nitrogen-vacancy (NV) center in
diamond is that optical illumination initializes its electronic spin almost
completely, a feature that can be exploited to polarize other spin species in
their proximity. Here we use field-cycled nuclear magnetic resonance (NMR) to
investigate the mechanisms of spin polarization transfer from NVs to 13C spins
in diamond at room temperature. We focus on the dynamics near 51 mT, where a
fortuitous combination of energy matching conditions between electron and
nuclear spin levels gives rise to alternative polarization transfer channels.
By monitoring the 13C spin polarization as a function of the applied magnetic
field, we show 13C spin pumping takes place via a multi-spin cross relaxation
process involving the NV- spin and the electronic and nuclear spins of
neighboring P1 centers. Further, we find that this mechanism is insensitive to
the crystal orientation relative to the magnetic field, although the absolute
level of 13C polarization - reaching up to ~3% under optimal conditions - can
vary substantially depending on the interplay between optical pumping
efficiency, photo-generated carriers, and laser-induced heating.",1711.07576v1
2018-12-20,Continuous dynamical decoupling of spin chains: modulating the spin-environment and spin-spin interactions,"For spins chains to be useful for quantum information processing tasks, the
interaction between the spin chain and its environment generally needs to be
suppressed. In this paper, we propose the use of strong static and oscillating
control fields in order to effectively remove the spin chain-environment
interaction. We find that our control fields can also effectively transform the
spin chain Hamiltonian. In particular, interaction terms which are absent in
the original spin chain Hamiltonian appear in the time-averaged effective
Hamiltonian once the control fields are applied, implying that spin-spin
interactions can be engineered via the application of static and oscillating
control fields. This transformation of the spin chain can then potentially be
used to improve the performance of the spin chain for quantum information
processing tasks. For example, our control fields can be used to achieve almost
perfect quantum state transfer across a spin chain even in the presence of
noise. As another example, we show how the use of particular static and
oscillating control fields not only suppresses the effect of the environment,
but can also improve the generation of two-spin entanglement in the spin chain.",1812.08403v3
2013-02-02,Transfers of entanglement qudit states in quantum networks,"The issue of quantum states' transfer -- in particular, for so-called Perfect
State Transfer (PST) -- in the networks represented by the spin chains seems to
be one of the major concerns in quantum computing. Especially, in the context
of future communication methods that can be used in broadly defined computer
science. The chapter presents a definition of Hamiltonian describing the
dynamics of quantum data transfer in one-dimensional spin chain, which is able
to transfer the state of unknown qudits. The main part of the chapter is the
discussion about possibility of entangled states' perfect transfer, in
particular, for the generalized Bell states for qudits. One of the sections
also contains the results of numerical experiments for the transmission of
quantum entangled state in a noisy quantum channel.",1302.0366v1
2005-04-19,Observation of spin-transfer switching in deep submicron-sized and low-resistance magnetic tunnel junctions,"The spin-transfer effect has been studied in magnetic tunnel junctions
(PtMn/CoFe/Ru/CoFe/Al2O3/CoFe/NiFe) with dimensions down to 0.1x0.2 um2 and
resistance-area product RA in the range of 0.5-10 Ohm m2 (dR/R=1-20%).
Current-induced magnetization switching is observed with a critical current
density of about 8e6 A/cm2. The attribution of the switching to the
spin-transfer effect is supported by a current-induced dR/R value identical to
the one obtained from the R versus H measurements. Furthermore, the critical
switching current density has clear dependence on the applied magnetic field,
consistent with what has been observed previously in the case of spin-transfer
induced switching in metallic multilayer systems.",0504486v1
2005-09-13,Synchronization of spin-transfer oscillators driven by stimulated microwave currents,"We have simulated the non-linear dynamics of networks of spin-transfer
oscillators. The oscillators are magnetically uncoupled but electrically
connected in series. We use a modified Landau-Lifschitz- Gilbert equation to
describe the motion of each oscillator in the presence of the oscillations of
all the others. We show that the oscillators of the network can be synchronized
not only in frequency but also in phase. The coupling is due to the microwave
components of the current induced in each oscillator by the oscillations in all
the other oscillators. Our results show how the emitted microwave power of
spin-transfer oscillators can be considerably enhanced by current-induced
synchronization in an electrically connected network. We also discuss the
possible application of our synchronization mechanism to the interpretation of
the surprisingly narrow microwave spectrum in some isolated spin-transfer
oscillators.",0509326v2
2008-11-21,Numerical Study of Current-Induced Domain-Wall Dynamics: Crossover from Spin Transfer to Momentum Transfer,"We study current-induced dynamics of a magnetic domain wall by solving a
time-dependent Schr\""{o}dinger equation combined with Landau-Lifshitz-Gilbert
equation in a one-dimensional electron system coupled to localized spins. Two
types of domain-wall motions are observed depending on the hard-axis
anisotropy, $K_{\perp}$, of the localized spin system. For small values of
$K_{\perp}$, the magnetic domain wall shows a streaming motion driven by spin
transfer. In contrast, for large values of $K_{\perp}$, a stick-slip motion
driven by momentum transfer is obtained. We clarify the origin of these
characters of domain-wall motions in terms of the dynamics of one-particle
energy levels and distribution functions.",0811.3545v2
2009-01-22,Relationship between probabilities of the state transfers and entanglements in spin systems with simple geometrical configurations,"In this paper we derive analytical relations between probabilities of the
excited state transfers and entanglements calculated by both the Wootters and
positive partial transpose (PPT) criteria for the arbitrary spin system with
single excited spin in the external magnetic field and Hamiltonian commuting
with $I_z$. We apply these relations to study the arbitrary state transfers and
entanglements in the simple systems of nuclear spins having two- and
three-dimensional geometrical configurations with $XXZ$ Hamiltonian. It is
shown that High-Probability State Transfers (HPSTs) are possible among all four
nodes placed in the corners of the rectangle with the proper ratio of sides as
well as among all eight nodes placed in the corners of the parallelepiped with
the proper ratio of sides. Entanglements responsible for these HPSTs have been
identified.",0901.3424v3
2015-02-09,Transfer of arbitrary two qubit states via a spin chain,"We investigate the fidelity of the quantum state transfer (QST) of two qubits
by means of an arbitrary spin-1/2 network, on a lattice of any dimensionality.
Under the assumptions that the network Hamiltonian preserves the magnetization
and that a fully polarized initial state is taken for the lattice, we obtain a
general formula for the average fidelity of the two qubits QST, linking it to
the one- and two-particle transfer amplitudes of the spin-excitations among the
sites of the lattice. We then apply this formalism to a 1D spin chain with
XX-Heisenberg type nearest-neighbour interactions adopting a protocol that is a
generalization of the single qubit one proposed in Ref. [Phys. Rev. A 87,
062309 (2013)]. We find that a high-quality two qubit QST can be achieved
provided one can control the local fields at sites near the sender and
receiver. Under such conditions, we obtain an almost perfect transfer in a time
that scales either linearly or, depending on the spin number, quadratically
with the length of the chain.",1502.02458v1
2022-01-21,Transverse Spin Transfer of $Λ$ and $\overlineΛ$ Hyperons in Polarized $p$+$p$ Collisions at $\sqrt{s} = 200$ GeV at RHIC-STAR,"The transverse spin transfer, $D_{TT}$, of $\Lambda$ and $\overline{\Lambda}$
hyperons in $p$+$p$ collisions is expected to be sensitive to the $s$ and
$\bar{s}$ quark transversity distributions in the proton and to the
transversely polarized fragmentation functions. The STAR experiment has
published the first measurement of the transverse spin transfer of $\Lambda$
and $\overline{\Lambda}$ hyperons in transversely polarized $p$+$p$ collisions
at $\sqrt{s}$ = 200 GeV within pseudo-rapidity $|\eta| < 1.2$ and for the
transverse momenta up to 8 GeV/$c$ based on the data taken in 2012. In 2015, a
data sample of $p$+$p$ collisions at $\sqrt{s}$ = 200 GeV, about two times
larger than the 2012 data, was collected. This contribution presents the
preliminary results of the transverse spin transfer, $D_{TT}$, of $\Lambda$ and
$\overline{\Lambda}$ hyperon versus transverse momentum and fractional momentum
of the hyperon within a jet, based on 2015 data.",2201.08602v1
2023-06-29,$γ$-ray Angular Distributions in Single Nucleon Transfer Reactions with Exotic Strontium Isotopes,"$\gamma$-ray angular distributions help assign spin and parity to excited
energy levels in nuclei. The spectroscopy of $^{94,96}$Sr studied through the
single neutron transfer reactions with $^{95}$Sr beam in inverse kinematics
[$^{95}$Sr(d,p)$^{96}$Sr; $^{95}$Sr(d,t)$^{94}$Sr] revealed a rich nuclear
structure with many excited states. While the spin-parities were assigned to
low lying states through techniques like particle angular distributions and
angular momentum transfer, those for higher lying states were ambiguous. The
goal of this project is to develop the Gamma-ray angular distributions and
correlations techniques to assign spin-parity to these states. In this work,
the $\gamma$-ray angular distributions for 815 keV transition from the first
excited state to ground state $(2^{+} \rightarrow 0^{+})$ in $^{96}$Sr are
measured. The alignment of this state is calculated from these measurements and
compared to the theoretically calculated alignment for this state which is
determined by coupling the spins of reactants and the orbital angular momentum
transfered. The values agree within experimental limits justifying the
technique. It is then applied to some other transitions and important results
are discussed. Angular correlations cannot be performed with this data since
statistics turn out to be limiting factor at the crystal level.",2306.17048v1
1997-07-10,Observations of Accreting Pulsars,"We summarize five years of continuous monitoring of accretion-powered pulsars
with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray
Observatory. Our 20-70 keV observations have determined or refined the orbital
parameters of 13 binaries, discovered 5 new transient accreting pulsars,
measured the pulsed flux history during outbursts of 12 transients (GRO
J1744-28, 4U 0115+634, GRO J1750-27, GS 0834-430, 2S 1417-624, GRO J1948+32,
EXO 2030+375, GRO J1008-57, A 0535+26, GRO J2058+42, 4U 1145-619 and A
1118-616), and also measured the accretion torque history of during outbursts
of 6 of those transients whose orbital parameters were also known. We have also
continuously measured the pulsed flux and spin frequency for eight persistently
accreting pulsars (Her X-1, Cen X-3, Vela X-1, OAO 1657-415, GX 301-2, 4U
1626-67, 4U 1538-52, and GX 1+4). Because of their continuity and uniformity
over a long baseline, BATSE observations have provided new insights into the
long-term behavior of accreting magnetic stars. We have found that all
accreting pulsars show stochastic variations in their spin frequencies and
luminosities, including those displaying secular spin-up or spin-down on long
time scales, blurring the conventional distinction between disk-fed and
wind-fed binaries. Pulsed flux and accretion torque are strongly correlated in
outbursts of transient accreting pulsars, but uncorrelated, or even
anticorrelated, in persistent sources.",9707125v2
2018-10-29,Dust Rotational Dynamics in C-shocks: Rotational Disruption of Nanoparticles by Stochastic Mechanical Torques and Spinning Dust Emission,"Polycyclic aromatic hydrocarbons (PAHs) and nanoparticles are expected to
play an important role in many astrophysical processes due to its dominant
surface area, including gas heating, chemistry, star formation , and anomalous
microwave emission. In dense magnetized molecular clouds where C-shocks are
present, PAHs and nanoparticles are widely believed to originate from grain
shattering due to grain-grain collisions. The remaining question is whether
these nanoparticles can survive in the dense and hot shocked regions, and how
to constrain their size and abundance with observations. In this paper, we
present a new mechanism to destroy nanoparticles in C-shocks based on
centrifugal stress within rapidly spinning nanoparticles spun-up by stochastic
atomic bombardment, which is termed rotational disruption. We find that, due to
supersonic neutral gas-charged grain drift in C-shocks, nanoparticles can be
spun-up to suprathermal rotation by stochastic torques exerted by supersonic
neutral flow. The resulting centrifugal stress within suprathermally rotating
nanoparticles can exceed the maximum tensile strength of grain material
($S_{\max}$), resulting in rapid disruption of nanoparticles smaller than
$a\sim 1$ nm for $S_{\max}\sim 10^{9}\erg\cm^{-3}$. The proposed disruption
mechanism is shown to be more efficient than thermal sputtering in controlling
the lower cutoff of grain size distribution in C-shocks. We model microwave
emission from spinning nanoparticles in C-shocks subject to supersonic neutral
drift and rotational disruption. We find that suprathermally rotating
nanoparticles can emit strong microwave radiation, and both peak flux and peak
frequency increase with increasing the shock velocity. We suggest spinning dust
as a new method to constrain nanoparticles and trace shock velocities in dense,
shocked regions.",1810.12007v2
2012-09-25,Isotropic Heating of Galaxy Cluster Cores via Rapidly Reorienting AGN Jets,"AGN jets carry more than sufficient energy to stave off catastrophic cooling
of the intracluster medium (ICM) in the cores of cool-core clusters. However,
in order to prevent catastrophic cooling, the ICM must be heated in a
near-isotropic fashion and narrow bipolar jets with $P_{\rm jet}=10^{44-45}$
ergs/s, typical of radio AGNs at cluster centres, are inefficient at heating
the gas in the transverse direction to the jets. We argue that due to existent
conditions in cluster cores, the SMBHs will, in addition to accreting gas via
radiatively inefficient flows, experience short stochastic episodes of enhanced
accretion via thin discs. In general, the orientation of these accretion discs
will be misaligned with the spin axis of the black holes and the ensuing
torques will cause the black hole's spin axis (and therefore, the jet axis) to
slew and rapidly change direction. This model not only explains recent
observations showing successive generations of jet-lobes-bubbles in individual
cool-core clusters that are offset from each other in the angular direction
with respect to the cluster center, but also shows that AGN jets {\it can} heat
the cluster core nearly isotropically on the gas cooling timescale. Our model
{\it does} require that the SMBHs at the centers of cool-core clusters be
spinning relatively slowly. Torques from individual misaligned discs are
ineffective at tilting rapidly spinning black holes by more than a few degrees.
Additionally, since SMBHs that host thin accretion discs will manifest as
quasars, we predict that roughly 1--2 rich clusters within $z<0.5$ should have
quasars at their centers.",1209.5748v2
2020-04-10,Cosmic spin and mass evolution of black holes and its impact,"We build an evolution model of the central black hole that depends on the
processes of gas accretion, the capture of stars, mergers as well as
electromagnetic torque. In case of gas accretion in the presence of cooling
sources, the flow is momentum-driven, after which the black hole reaches a
saturated mass; subsequently, it grows only by stellar capture and mergers. We
model the evolution of the mass and spin with the initial seed mass and spin in
$\Lambda$CDM cosmology. For stellar capture, we have assumed a power-law
density profile for the stellar cusp in a framework of relativistic loss cone
theory that include the effects of black hole spin, Carter's constant, loss
cone angular momentum, and capture radius. Based on this, the predicted capture
rates of $10^{-5}$--$10^{-6}$ yr$^{-1}$ are closer to the observed range. We
have considered the merger activity to be effective for $z \lesssim 4$, and we
self-consistently include the Blandford-Znajek torque. We calculate these
effects on the black hole growth individually and in combination, for deriving
the evolution. Before saturation, accretion dominates the black hole growth
($\sim 95\%$ of the final mass), and subsequently, stellar capture and mergers
take over with roughly equal contribution. The simulations of the evolution of
the $M_{\bullet} - \sigma$ relation using these effects are consistent with
available observations. We run our model backward in time and retrodict the
parameters at formation. Our model will provide useful inputs for building
demographics of the black holes and in formation scenarios involving stellar
capture.",2004.05000v3
2019-07-26,Magnetoelectric control of topological phases in graphene,"Topological antiferromagnetic (AFM) spintronics is an emerging field of
research, which involves the topological electronic states coupled to the AFM
order parameter known as the N$\acute{\rm e}$el vector. The control of these
states is envisioned through manipulation of the N$\acute{\rm e}$el vector by
spin-orbit torques driven by electric currents. Here we propose a different
approach favorable for low-power AFM spintronics, where the control of the
topological states in a two-dimensional material, such as graphene, is
performed via the proximity effect by the voltage induced switching of the
N$\acute{\rm e}$el vector in an adjacent magnetoelectric AFM insulator, such as
chromia. Mediated by the symmetry protected boundary magnetization and the
induced Rashba-type spin-orbit coupling at the interface between graphene and
chromia, the emergent topological phases in graphene can be controlled by the
N$\acute{\rm e}$el vector. Using density functional theory and tight-binding
Hamiltonian approaches, we model a graphene/Cr2O3 (0001) interface and
demonstrate non-trivial band gap openings in the graphene Dirac bands
asymmetric between the K and K' valleys. This gives rise to an unconventional
quantum anomalous Hall effect (QAHE) with a quantized value of $2e^2/h$ and an
additional step-like feature at a value close to $e^2/2h$, and the emergence of
the spin-polarized valley Hall effect (VHE). Furthermore, depending on the
N$\acute{\rm e}$el vector orientation, we predict the appearance and
transformation of different topological phases in graphene across the
$180^{\circ}$ AFM domain wall, involving the QAHE, the valley-polarized QAHE
and the quantum VHE (QVHE), and the emergence of the chiral edge state along
the domain wall. These topological properties are controlled by voltage through
magnetoelectric switching of the AFM insulator with no need for spin-orbit
torques.",1907.11689v1
2023-03-23,Effects of accretion on the Structure and Rotation of Forming Stars,"Rotation period measurements of low-mass stars show that the spin
distributions in young clusters do not exhibit the spin-up expected due to
contraction, during the phase when a large fraction of stars are still
surrounded by accretion discs. During this stage, the stars accrete mass and
angular momentum and may experience accretion enhanced-magnetised winds. At the
same time, the accretion of mass and energy has a significant impact on the
evolution of stellar structure and moment of inertia. We compute evolution
models of accreting very young stars and determine, in a self-consistent way,
the effect of accretion on stellar structure and the angular momentum exchanges
between the stars and their disc. We then vary the deuterium content, the
accretion history, the entropy content of the accreted material, and the
magnetic field as well as the efficiency of the accretion-enhanced winds. It
comes that the models are driven alternatively both by the evolution of the
momentum of inertia, and by the star-disc interaction torques. Of all the
parameters we tested, the magnetic field strength, the accretion history and
the Deuterium content have the largest impact. The injection of heat only plays
a major role early in the evolution. This work demonstrates the importance of
the moment of inertia's evolution under the influence of accretion to explain
the constant rotation rates distributions that are observed over the star-disc
interactions. When accounting for rotation, the models computed with an
up-to-date torque along with a consistent structural evolution of the accreting
star are able to explain the almost constant spin evolution for the whole range
of parameter we investigated, albeit only reproducing a narrow range around the
median of the observed spin rate distributions.",2303.13184v1
2007-07-11,Switched Control of Electron Nuclear Spin Systems,"In this article, we study control of electron-nuclear spin dynamics at
magnetic field strengths where the Larmor frequency of the nucleus is
comparable to the hyperfine coupling strength. The quantization axis for the
nuclear spin differs from the static B_0 field direction and depends on the
state of the electron spin. The quantization axis can be switched by flipping
the state of electron spin, allowing for universal control on nuclear spin
states. We show that by performing a sequence of flips (each followed by a
suitable delay), we can perform any desired rotation on the nuclear spins,
which can also be conditioned on the state of the electron spin. These
operations, combined with electron spin rotations can be used to synthesize any
unitary transformation on the coupled electron-nuclear spin system. We discuss
how these methods can be used for design of experiments for transfer of
polarization from the electron to the nuclear spins.",0707.1572v1
2013-07-09,Spin-noise correlations and spin-noise exchange driven by low-field spin-exchange collisions,"The physics of spin exchange collisions have fueled several discoveries in
fundamental physics and numerous applications in medical imaging and nuclear
magnetic resonance. We here report on the experimental observation and
theoretical justification of spin-noise exchange, the transfer of spin-noise
from one atomic species to another. The signature of spin-noise exchange is an
increase of the total spin-noise power at low magnetic fields, on the order of
1 mG, where the two-species spin-noise resonances overlap. The underlying
physical mechanism is the two-species spin-noise correlation induced by
spin-exchange collisions.",1307.2596v3
2014-04-15,Superfluid spin transport through antiferromagnetic insulators,"A theoretical proposal for realizing and detecting spin supercurrent in an
isotropic antiferromagnetic insulator is reported. Superfluid spin transport is
achieved by inserting the antiferromagnet between two metallic reservoirs and
establishing a spin accumulation in one reservoir such that a spin bias is
applied across the magnet. We consider a class of bipartite antiferromagnets
with Neel ground states, and temperatures well below the ordering temperature,
where spin transport is mediated essentially by the condensate. Landau-Lifshitz
and magneto-circuit theories are used to directly relate spin current in
different parts of the heterostructure to the spin-mixing conductances
characterizing the antiferromagnet|metal interfaces and the antiferromagnet
bulk damping parameters, quantities all obtainable from experiments. We study
the efficiency of spin angular-momentum transfer at an antiferromagnet|metal
interface by developing a microscopic scattering theory for the interface and
extracting the spin-mixing conductance for a simple model. Within the model, a
quantitative comparison between the spin-mixing conductances obtained for the
antiferromagnet|metal and ferromagnet|metal interfaces is made.",1404.3987v1
2016-09-08,Pumping dynamics of nuclear spins in GaAs quantum wells,"Irradiating a semiconductor with circularly polarized light creates
spin-polarized charge carriers. If the material contains atoms with non-zero
nuclear spin, they interact with the electron spins via the hyperfine coupling.
Here, we consider GaAs/AlGaAs quantum wells, where the conduction-band electron
spins interact with three different types of nuclear spins. The hyperfine
interaction drives a transfer of spin polarization to the nuclear spins, which
therefore acquire a polarization that is comparable to that of the electron
spins. In this paper, we analyze the dynamics of the optical pumping process in
the presence of an external magnetic field while irradiating a single quantum
well with a circularly polarized laser. We measure the time dependence of the
photoluminescence polarization to monitor the buildup of the nuclear spin
polarization and thus the average hyperfine interaction acting on the electron
spins. We present a simple model that adequately describes the dynamics of this
process and is in good agreement with the experimental data.",1609.02319v1
2018-03-09,Spin transport across antiferromagnets induced by the spin Seebeck effect,"For prospective spintronics devices based on the propagation of pure spin
currents, antiferromagnets are an interesting class of materials that
potentially entail a number of advantages as compared to ferromagnets. Here, we
present a detailed theoretical study of magnonic spin current transport in
ferromagnetic-antiferromagnetic multilayers by using atomistic spin dynamics
simulations. The relevant length scales of magnonic spin transport in
antiferromagnets are determined. We demonstrate the transfer of angular
momentum from a ferromagnet into an antiferromagnet due to the excitation of
only one magnon branch in the antiferromagnet. As an experimental system, we
ascertain the transport across an antiferromagnet in
YIG$|$Ir$_{20}$Mn$_{80}|$Pt heterostructures. We determine the spin transport
signals for spin currents generated in the YIG by the spin Seebeck effect and
compare to measurements of the spin Hall magnetoresistance in the
heterostructure stack. By means of temperature-dependent and
thickness-dependent measurements, we deduce conclusions on the spin transport
mechanism across IrMn and furthermore correlate it to its
paramagnetic-antiferromagnetic phase transition.",1803.03416v1
2017-01-05,Coherent long-distance displacement of individual electron spins,"Controlling nanocircuits at the single electron spin level is a possible
route for large-scale quantum information processing. In this context,
individual electron spins have been identified as versatile quantum information
carriers to interconnect different nodes of a spin-based semiconductor quantum
circuit. Despite important experimental efforts to control the electron
displacement over long distances, keeping the electron spin coherence after
transfer remained up to now elusive. Here we demonstrate that individual
electron spins can be displaced coherently over a distance of 5 micrometers.
This displacement is realized on a closed path made of three tunnel-coupled
lateral quantum dots. Using fast quantum dot control, the electrons tunnel from
one dot to another at a speed approaching 100 m/s. We find that the spin
coherence length is 8 times longer than expected from the electron spin
coherence without displacement. Such an enhanced spin coherence points at a
process similar to motional narrowing observed in nuclear magnetic resonance
experiments6. The demonstrated coherent displacement will enable long-range
interaction between distant spin-qubits and will open the route towards
non-abelian and holonomic manipulation of a single electron spin.",1701.01279v1
2019-04-29,Unconventional spin currents in magnetic films,"A spin current - a flow of spin angular momentum - can be carried either by
spin polarised free electrons or by magnons, the quanta of a moving collective
oscillation of localised electron spins - a spin wave. Traditionally, it was
assumed, that a spin wave in a magnetic film with spin-sink-free surfaces can
transfer energy and angular momentum only along its propagation direction. In
this work, using Brillouin light scattering spectroscopy in combination with a
theory of dipole-exchange spin-wave spectra, we show that in obliquely
magnetized free magnetic films the in-plane propagation of spin waves is
accompanied by a transverse spin current along the film normal without any
corresponding transverse transport of energy.",1904.12610v1
2021-05-06,Visualization of optical polarization transfer to photoelectron spin vector emitted from the spin-orbit coupled surface state,"Similar to light polarization that is selected by a superposition of optical
basis, electron spin direction can be controlled through a superposition of
spin basis. We investigate such a spin interference occurring in photoemission
of the spin-orbit coupled surface state in Bi2Se3 by using spin- and
angle-resolved photoemission spectroscopy combined with laser light source
(laser-SARPES). Our laser-SARPES with three-dimensional spin detection and
tunable laser polarization including elliptical and circular polarization
enables us to directly visualize how the direction of the fully-polarized
photoelectron spin changes according to the optical phase and orientation of
the incident laser polarization. By this advantage of our laser-SARPES, we
demonstrate that such optical information can be projected to the
three-dimensional spin vector of the photoelectrons. Our results, therefore,
present a novel spin-polarized electron source permitting us to optically
control the pure spin state pointing to the arbitrary direction.",2105.02749v2
2021-12-02,Antiferromagnetic spin pumping via hyperfine interaction,"Spin pumping is an interfacial spin current generation from the ferromagnetic
layer to the non-magnetic metal at its interface. The polarization of the
pumped spin current $\textbf{J}_s \propto \textbf{m}\times \dot{\textbf{m}}$
depends on the dynamics of the magnetic moment $\textbf{m}$. When the materials
are based on light transition metals, mechanism behind the spin current
transfer is dominated by the exchange interaction between spin of localized
d-electrons and itinerant conduction electrons. In heavier transition metals,
however, the interaction is not limited to the exchange interaction. The spin
of the conduction electron can interact to its nuclear spin by means of
hyperfine interaction, as observed in the shift of NMR frequency. By studying
the spin polarization of conduction electron of the non-magnetic metallic layer
due to a nuclear magnetic moment $\textbf{I}$ of the ferromagnetic layer, we
show that the hyperfine interaction can mediate the spin pumping. The
polarization of the spin current generation is shown to have a similar form
$J_s\propto \textbf{I}\times\dot{\textbf{I}}$.",2112.01111v1
2022-09-26,Imprinting spatial helicity structure of vector vortex beam on spin texture in semiconductors,"We present the transfer of the spatially variant polarization of
topologically structured light to the spatial spin texture in a semiconductor
quantum well. The electron spin texture, which is a circular pattern with
repeating spin-up and spin-down states whose repetition rate is determined by
the topological charge, is directly excited by a vector vortex beam with a
spatial helicity structure. The generated spin texture efficiently evolves into
a helical spin wave pattern owing to the spin-orbit effective magnetic fields
in the persistent spin helix state by controlling the spatial wave number of
the excited spin mode. By tuning the repetition length and azimuthal angle, we
simultaneously generate helical spin waves with opposite phases by a single
beam.",2209.12496v1
2023-10-27,Ultrafast switchable spin-orbit coupling for silicon spin qubits via spin valves,"Recent experimental breakthroughs, particularly for single-qubit and
two-qubit gates exceeding the error correction threshold, highlight silicon
spin qubits as leading candidates for fault-tolerant quantum computation. In
the existing architecture, intrinsic or synthetic spin-orbit coupling (SOC) is
critical in various aspects, including electrical control, addressability,
scalability, etc. However, the high-fidelity SWAP operation and quantum state
transfer (QST) between spin qubits, crucial for qubit-qubit connectivity,
require the switchable nature of SOC which is rarely considered. Here, we
propose a flexible architecture based on spin valves by electrically changing
its magnetization orientation within sub-nanoseconds to generate ultrafast
switchable SOC. Based on the switchable SOC architecture, both SWAP operation
of neighbor spin qubits and resonant QST between distant spins can be realized
with fidelity exceeding 99% while considering the realistic experimental
parameters. Benefiting from the compatible processes with the modern
semiconductor industry and experimental advances in spin valves and spin
qubits, our results pave the way for future construction of silicon-based
quantum chips.",2310.17993v1
2024-03-13,Electrically Tunable Spin Exchange Splitting in Graphene Hybrid Heterostructure,"Graphene, with spin and valley degrees of freedom, fosters unexpected
physical and chemical properties for the realization of next-generation quantum
devices. However, the spin symmetry of graphene is rather robustly protected,
hampering manipulation of the spin degrees of freedom for the application of
spintronic devices such as electric gate tunable spin filters. We demonstrate
that a hybrid heterostructure composed of graphene and LaCoO3 epitaxial thin
film exhibits an electrically tunable spin exchange splitting. The large and
adjustable spin exchange splitting of 155.9 - 306.5 meV was obtained by the
characteristic shifts in both the spin symmetry broken quantum Hall states and
the Shubnikov-de-Haas oscillations. Strong hybridization induced charge
transfer across the hybrid heterointerface has been identified for the observed
spin exchange splitting. The substantial and facile controllability of the spin
exchange splitting provides an opportunity for spintronics applications with
the electrically-tunable spin polarization in hybrid heterostructures.",2403.08908v1
2003-08-23,Theory of Current-Driven Domain Wall Motion: A Poorman's Approach,"A self-contained theory of the domain wall dynamics in ferromagnets under
finite electric current is presented.
  The current is shown to have two effects; one is momentum transfer, which is
proportional to the charge current and wall resistivity ($\rhow$), and the
other is spin transfer, proportional to spin current.
  For thick walls, as in metallic wires, the latter dominates and the threshold
current for wall motion is determined by the hard-axis magnetic anisotropy,
except for the case of very strong pinning.
  For thin walls, as in nanocontacts and magnetic semiconductors, the
momentum-transfer effect dominates, and the threshold current is proportional
to $\Vz/\rhow$, $\Vz$ being the pinning potential.",0308464v1
2007-01-03,Meromorphic continuation of dynamical zeta functions via transfer operators,"We describe a general method to prove meromorphic continuation of dynamical
zeta functions to the entire complex plane under the condition that the
corresponding partition functions are given via a dynamical trace formula from
a family of transfer operators. Further we give general conditions for the
partition functions associated with general spin chains to be of this type and
provide various families of examples for which these conditions are satisfied.
  Keywords: Dynamical zeta function, transfer operator, trace formulae,
thermodynamic formalism, spin chain, Fock space, regularized determinants,
weighted composition operator.",0701097v1
2003-09-17,Perfect state transfer in quantum spin networks,"We propose a class of qubit networks that admit perfect transfer of any
quantum state in a fixed period of time. Unlike many other schemes for quantum
computation and communication, these networks do not require qubit couplings to
be switched on and off. When restricted to N-qubit spin networks of identical
qubit couplings, we show that 2 log_3 N is the maximal perfect communication
distance for hypercube geometries. Moreover, if one allows fixed but different
couplings between the qubits then perfect state transfer can be achieved over
arbitrarily long distances in a linear chain.",0309131v2
2008-12-04,Quantum state transfer in a q-deformed chain,"We investigate the quantum state transfer in a chain of particles satisfying
q-deformed oscillators algebra. This general algebraic setting includes the
spin chain and the bosonic chain as limiting cases. We study conditions for
perfect state transfer depending on the number of sites and excitations on the
chain. They are formulated by means of irreducible representations of a quantum
algebra realized through Jordan-Schwinger maps. Playing with deformation
parameters, we can study the effects of nonlinear perturbations or interpolate
between the spin and bosonic chain.",0812.0891v2
2011-01-06,All Possible Coupling Schemes in XY Spin Chains for Perfect State Transfer,"We investigate quantum state transfer in XY spin chains and propose a
recursive procedure to construct the nonuniform couplings of these chains with
arbitrary length to achieve perfect state transfer(PST). We show that this
method is capable of finding all possible coupling schemes for PST. These
schemes, without external control fields, only involve preengineered couplings
but not dynamical control of them, so they can be simply realized
experimentally. The analytical solutions provide all information for coupling
design.",1101.1156v1
2012-03-09,Quantum State Transfer in a Two-dimensional Regular Spin Lattice of Triangular Shape,"Quantum state transfer in a triangular domain of a two-dimensional,
equally-spaced, spin lat- tice with non-homogeneous nearest-neighbor couplings
is analyzed. An exact solution of the one- excitation dynamics is provided in
terms of 2-variable Krawtchouk orthogonal polynomials that have been recently
defined. The probability amplitude for an excitation to transit from one site
to another is given. For some values of the parameters, perfect transfer is
shown to take place from the apex of the lattice to the boundary hypotenuse.",1203.2128v2
2012-05-21,Almost perfect state transfer in quantum spin chains,"The natural notion of almost perfect state transfer (APST) is examined. It is
applied to the modelling of efficient quantum wires with the help of $XX$ spin
chains. It is shown that APST occurs in mirror-symmetric systems, when the
1-excitation energies of the chains are linearly independent over rational
numbers. This result is obtained as a corollary of the Kronecker theorem in
Diophantine approximation. APST happens under much less restrictive conditions
than perfect state transfer (PST) and moreover accommodates the unavoidable
imperfections. Some examples are discussed.",1205.4680v3
2012-01-13,Gravitational wave diagnosis of a circumbinary disk,"When binary black holes are embedded in a gaseous environment, a rotating
disk surrounding them, the so-called circumbinary disk, will be formed. The
binary exerts a gravitational torque on the circumbinary disk and thereby the
orbital angular momentum is transferred to it, while the angular momentum of
the circumbinary disk is transferred to the binary through the mass accretion.
The binary undergoes an orbital decay due to both the gravitational wave
emission and the binary-disk interaction. This causes the phase evolution of
the gravitational wave signal. The precise measurement of the gravitational
wave phase thus may provide information regarding the circumbinary disk. In
this paper, we assess the detectability of the signature of the binary-disk
interaction using the future space-borne gravitational wave detectors such as
DECIGO and BBO by the standard matched filtering analysis. We find that the
effect of the circumbinary disk around binary black holes in the mass range
$6M_sun\le{M}\lesssim3\times10^3M_sun$ is detectable at a statistically
significant level in five year observation, provided that gas accretes onto the
binary at a rate greater than $\dot{M}\sim1.4\times10^{17} [gs^{-1}]
j^{-1}(M/10M_sun)^{33/23}$ with 10% mass-to-energy conversion efficiency, where
j represents the efficiency of the angular momentum transfer from the binary to
the circumbinary disk. We show that $O(0.1)$ coalescence events are expected to
occur in sufficiently dense molecular clouds in five year observation. We also
point out that the circumbinary disk is detectable, even if its mass at around
the inner edge is by over 10 orders of magnitude less than the binary mass.",1201.2858v1
2017-11-01,Protostellar Jets and Outflows in low-mass star formation,"The driving mechanism of protostellar outflows and jets and their effects on
the star formation process obtained from recent theoretical and numerical
studies are described. Low-velocity outflows are driven by an outer region of
the circumstellar disk, while high-velocity jets are driven near an inner edge
of the disk. The disk angular momentum is effectively transferred by magnetic
effects in the outflow and jet driving regions where the magnetic field is well
coupled with neutral gas. On the other hand, in a high density gas region of
the disk (or intermediate region), the magnetic field dissipates and is
decoupled from neutral gas. Thus, in such a magnetically inactive region, no
outward flow appears and the disk angular momentum is not effectively
transferred by magnetic effects. Therefore, in the disk intermediate region,
the disk surface density continues to increase and gravitational instability
occurs and produce a non-axisymmetric (or spiral) structure. After spiral arms
sufficiently develop, the disk angular momentum is transferred by gravitational
torque and a large amount of the disk mass accretes onto the central protostar
from the circumstellar disk. The episodic accretion induces time-variable
high-velocity jets. The jets do not significantly contribute to a dynamical
evolution of the protostar and circumstellar disk, while the low-velocity
outflows can eject a large fraction of the infalling gas and determine the
final stellar mass.",1711.00384v1
2019-03-13,Rotation Period Evolution in Low-Mass Binary Stars: The Impact of Tidal Torques and Magnetic Braking,"We examine how tides, stellar evolution, and magnetic braking shape the
rotation period (P$_{rot}$) evolution of low-mass stellar binaries up to
orbital periods (P$_{orb}$) of 100 d across a wide range tidal dissipation
parameters using two common equilibrium tidal models. We find that many
binaries with P$_{orb} < 20$ d tidally lock, and most with $P_{orb} < 4$ d
tidally lock into synchronous rotation on circularized orbits. At short
P$_{orb}$, tidal torques produce a population of fast rotators that single-star
only models of magnetic braking fail to produce. In many cases, we show that
the competition between magnetic braking and tides produces a population of
subsynchronous rotators that persists for Gyrs, even in short P$_{orb}$
binaries, qualitatively reproducing the subsynchronous eclipsing binaries (EBs)
discovered in the Kepler field by Lurie et al. (2017). Both equilibrium tidal
models predict that binaries can tidally-interact out to P$_{orb} \approx 80$
d, while the Constant Phase Lag tidal model predicts that binaries can tidally
lock out to P$_{orb} \approx 100$ d. Tidal torques often force the P$_{rot}$
evolution of stellar binaries to depart from the long-term magnetic
braking-driven spin down experienced by single stars, revealing that P$_{rot}$
is not be a valid proxy for age in all cases, i.e. gyrochronology can
underpredict ages by up to $300\%$ unless one accounts for binarity. We suggest
that accurate determinations of orbital eccentricties and P$_{rot}$ can be used
to discriminate between which equilibrium tidal models best describes tidal
interactions in low-mass binary stars.",1903.05686v2
2021-04-16,SDSS-IV MaNGA: 3D spin alignment of spiral and S0 galaxies,"We investigate the 3D spin alignment of galaxies with respect to the
large-scale filaments using the MaNGA survey. The cosmic web is reconstructed
from the Sloan Digital Sky Survey using Disperse and the 3D spins of MaNGA
galaxies are estimated using the thin disk approximation with integral field
spectroscopy kinematics. Late-type spiral galaxies are found to have their
spins parallel to the closest filament's axis. The alignment signal is found to
be dominated by low-mass spirals. Spins of S0-type galaxies tend to be oriented
preferentially in perpendicular direction with respect to the filament's axis.
This orthogonal orientation is found to be dominated by S0s that show a notable
misalignment between their kinematic components of stellar and ionised gas
velocity fields and/or by low mass S0s with lower rotation support compared to
their high mass counterparts. Qualitatively similar results are obtained when
splitting galaxies based on the degree of ordered stellar rotation, such that
galaxies with high spin magnitude have their spin aligned, and those with low
spin magnitude in perpendicular direction to the filaments. In the context of
conditional tidal torque theory, these findings suggest that galaxies' spins
retain memory of their larger-scale environment. In agreement with measurements
from hydrodynamical cosmological simulations, the measured signal at low
redshift is weak, yet statistically significant. The dependence of the
spin-filament orientation of galaxies on their stellar mass, morphology and
kinematics highlights the importance of sample selection to detect the signal.",2104.08275v1
2022-02-09,Emergent Non-Abelian Gauge Theory in Coupled Spin-Electron Dynamics,"A clear separation of the time scales governing the dynamics of ""slow"" and
""fast"" degrees of freedom often serves as a prerequisite for the emergence of
an independent low-energy theory. Here, we consider (slow) classical spins
exchange coupled to a tight-binding system of (fast) conduction electrons. The
effective equations of motion are derived under the constraint that the quantum
state of the electron system at any instant of time $t$ lies in the
$n$-dimensional low-energy subspace for the corresponding spin configuration at
$t$. The effective low-energy theory unfolds itself straightforwardly and takes
the form of a non-abelian gauge theory with the gauge freedom given by the
arbitrariness of the basis spanning the instantaneous low-energy sector. The
holonomic constraint generates a gauge covariant spin-Berry curvature tensor in
the equations of motion for the classical spins. In the non-abelian theory for
$n>1$, opposed to the $n=1$ adiabatic spin dynamics theory, the spin-Berry
curvature is generically nonzero, even for time-reversal symmetric systems. Its
expectation value with the representation of the electron state is gauge
invariant and gives rise to an additional {\em geometrical} spin torque.
Besides anomalous precession, the $n\ge 2$ theory also captures the spin
nutational motion, which is usually considered as a retardation effect. This is
demonstrated by proof-of-principle numerical calculations for a minimal model
with a single classical spin. Already for $n=2$ and in parameter regimes where
the $n=1$ adiabatic theory breaks down, we find good agreement with results
obtained from the full (unconstrained) theory.",2202.04694v2
2021-09-02,"Heteronuclear transfers from labile protons in biomolecular NMR: Cross Polarization, revisited","INEPT- and HMQC-based pulse sequences are widely used to transfer
polarization between heteronuclei, particularly in biomolecular spectroscopy:
they are easy to setup and involve low power deposition. Still, these
short-pulse polarization transfers schemes are challenged by fast solvent
chemical exchange. An alternative to improve these heteronuclear transfers is
J-driven cross polarization (J-CP), which transfers polarization by
spin-locking the coupled spins under Hartmann-Hahn conditions. J-CP provides
certain immunity against chemical exchange and other T2-like relaxation
effects, a behavior that is here examined in depth by both Liouville-space
numerical and analytical derivations describing the transfer efficiency. While
superior to INEPT-based transfers, fast exchange may also slow down these J-CP
transfers, hurting their efficiency. This study therefore explores the
potential of repeated projective operations to improve 1H->15N and 1H->15N->13C
J-CP transfers in the presence of fast solvent chemical exchanges. It is found
that while repeating J-CP provides little 1H->15N transfer advantages over a
prolonged CP, multiple contacts that keep both the water and the labile protons
effectively spin-locked can improve 1H->15N->13C transfers in the presence of
chemical exchange. The ensuing Looped, Concatenated Cross Polarization (L-CCP)
compensates for single J-CP losses by relying on the 13C longer lifetimes,
leading to a kind of algorithmic cooling that can provide high polarization for
the 15N as well as carbonyl and alpha 13Cs. This can facilitate certain
experiments, as demonstrated with triple resonance experiments on intrinsically
disordered proteins involving labile, chemically exchanging protons.",2109.01079v1
2014-08-16,Information Transfer Fidelity in Spin Networks and Ring-based Quantum Routers,"Spin networks are endowed with an Information Transfer Fidelity (ITF), which
defines an absolute upper bound on the probability of transmission of an
excitation from one spin to another. The ITF is easily computable but the bound
can be reached asymptotically in time only under certain conditions. General
conditions for attainability of the bound are established and the process of
achiev-ing the maximum transfer probability is given a dynamical model, the
translation on the torus. The time to reach the maximum probability is
estimated using the simultaneous Diophantine approximation, implemented using a
variant of the Lenstra-Lenstra-Lovasz (LLL) algorithm. For a ring with uniform
couplings, the network can be made a metric space by defining a distance
(satisfying the triangle inequality) that quantifies the lack of transmission
fidelity between two nodes. It is shown that transfer fidelities and transfer
times can be improved significantly by means of simple controls taking the form
of non-dynamic, spatially localized bias fields, opening up the possibility for
intelligent design of spin networks and dynamic routing of information encoded
in them, while being more flexible than engineering fixed couplings to favor
some transfers, and less demanding than control schemes requiring fast dynamic
controls.",1408.3765v3
1993-01-21,Yang-Baxter equation in spin chains with long range interactions,"We consider the $ su(n) $ spin chains with long range interactions and the
spin generalization of the Calogero-Sutherland models. We show that their
properties derive from a transfer matrix obeying the Yang-Baxter equation. We
obtain the expression of the conserved quantities and we diagonalize them.",9301084v1
2008-01-31,Quantum communication beyond the localization length in disordered spin chains,"We study the effects of localization on quantum state transfer in spin
chains. We show how to use quantum error correction and multiple parallel spin
chains to send a qubit with high fidelity over arbitrary distances; in
particular distances much greater than the localization length of the chain.",0801.4867v1
2015-09-29,A novel analytic spin chain model with fractional revival,"New analytic spin chains with fractional revival are introduced. Their
nearest-neighbor couplings and local magnetic fields correspond to the
recurrence coefficients of para-Racah polynomials which are orthogonal on
quadratic bi-lattices. These models generalize the spin chain associated to the
dual-Hahn polynomials. Instances where perfect state transfer also occurs are
identified.",1509.08965v1
2005-09-09,Perfect State Transfer: Beyond Nearest-Neighbor Couplings,"In this paper we build on the ideas presented in previous works for perfectly
transferring a quantum state between opposite ends of a spin chain using a
fixed Hamiltonian. While all previous studies have concentrated on
nearest-neighbor couplings, we demonstrate how to incorporate additional terms
in the Hamiltonian by solving an Inverse Eigenvalue Problem. We also explore
issues relating to the choice of the eigenvalue spectrum of the Hamiltonian,
such as the tolerance to errors and the rate of information transfer.",0509065v2
2009-04-28,Quantum state transfer through a qubit network with energy shifts and fluctuations,"We study quantum state transfer through a qubit network modeled by spins with
XY interaction, when relying on a single excitation. We show that it is
possible to achieve perfect transfer by shifting (adding) energy to specific
vertices. This technique appears to be a potentially powerful tool to change,
and in some cases improve, transfer capabilities of quantum networks.
Analytical results are presented for all-to-all networks and all-to-all
networks with a missing link. Moreover, we evaluate the effect of random
fluctuations on the transmission fidelity.",0904.4510v1
2009-11-26,Quantum state transfer via temporal kicking of information,"We propose a strategy for perfect state transfer in spin chains based on the
use of an unmodulated coupling Hamiltonian whose coefficients are explicitly
time dependent. We show that, if specific and non-demanding conditions are
satisfied by the temporal behavior of the coupling strengths, our model allows
perfect state transfer. The paradigma put forward by our proposal holds the
promises to set an alternative standard to the use of clever encoding and
coupling-strength engineering for perfect state transfer.",0911.5160v2
2013-03-28,Statistics of a quantum-state-transfer Hamiltonian in the presence of disorder,"We present a statistical analysis on the performance of a protocol for the
faithful transfer of a quantum state in finite qubit or spin chains, in the
presence of diagonal and off-diagonal disorder. It is shown that the
average-state fidelity, typically employed in the literature for the
quantification of the transfer, may overestimate considerably the performance
of the protocol in a single realization, leading to faulty conclusions about
the success of the transfer.",1303.7063v1
2013-10-06,Dynamical control of state transfer through noisy quantum channels: optimal tradeoff of speed and fidelity,"We propose a method of optimally controlling state transfer through a noisy
quantum channel (spin-chain). This process is treated as qubit state-transfer
through a fermionic bath. We show that dynamical modulation of the
boundary-qubits levels suffices to ensure fast and high-fidelity state
transfer. This is achievable by dynamically optimizing the transmission
spectrum of the channel. The resulting optimal control is robust against both
static and fluctuating noise.",1310.1621v1
2016-07-05,Robust quantum state transfer via topologically protected edge channels in dipolar arrays,"We show how to realize quantum state transfer between distant qubits using
the chiral edge states of a two-dimensional topological spin system. Our
implementation based on Rydberg atoms allows to realize the quantum state
transfer protocol in state of the art experimental setups. In particular, we
show how to adapt the standard state transfer protocol to make it robust
against dispersive and disorder effects.",1607.01154v1
2023-01-23,M-neighbor approximation in one-qubit state transfer along zigzag and alternating spin-1/2 chains,"We consider the $M$-neighbor approximation in the problem of one-qubit pure
state transfer along the $N$-node zigzag and alternating spin chains governed
by the $XXZ$-Hamiltonian with the dipole-dipole interaction. We show that
always $M>1$, i.e., the nearest neighbor approximation is not applicable to
such interaction. Moreover, only all-node interaction ($M=N-1$) properly
describes the dynamics in the alternating chain. We reveal the region in the
parameter space characterizing the chain geometry and orientation which provide
the high-probability state-transfer. The optimal state-transfer probability and
appropriate time instant for the zigzag and alternating chains are compared.",2301.09464v1
2008-03-12,Analysis of spin precession in binary black hole systems including quadrupole-monopole interaction,"We analyze in detail the spin precession equations in binary black hole
systems, when the tidal torque on a Kerr black hole due to quadrupole-monopole
coupling is taken into account. We show that completing the precession
equations with this term reveals the existence of a conserved quantity at 2PN
order when averaging over orbital motion. This quantity allows one to solve the
(orbit-averaged) precession equations exactly in the case of equal masses and
arbitrary spins, neglecting radiation reaction. For unequal masses, an exact
solution does not exist in closed form, but we are still able to derive
accurate approximate analytic solutions. We also show how to incorporate
radiation reaction effects into our analytic solutions adiabatically, and
compare the results to solutions obtained numerically. For various
configurations of the binary, the relative difference in the accumulated
orbital phase computed using our analytic solutions versus a full numerical
solution vary from about 0.3% to 1.8% over the 80 - 140 orbital cycles
accumulated while sweeping over the orbital frequency range 20 - 300 Hz. This
typically corresponds to a discrepancy of order 5-6 radians. While this may not
be accurate enough for implementation in LIGO template banks, we still believe
that our new solutions are potentially quite useful for comparing numerical
relativity simulations of spinning binary black hole systems with
post-Newtonian theory. They can also be used to gain more understanding of
precession effects, with potential application to the gravitational recoil
problem, and to provide semi-analytical templates for spinning, precessing
binaries.",0803.1820v3
2008-09-04,Galaxy Zoo: Chiral correlation function of galaxy spins,"Galaxy Zoo is the first study of nearby galaxies that contains reliable
information about the spiral sense of rotation of galaxy arms for a sizeable
number of galaxies. We measure the correlation function of spin chirality (the
sense in which galaxies appear to be spinning) of face-on spiral galaxies in
angular, real and projected spaces. Our results indicate a hint of positive
correlation at separations less than ~0.5 Mpc at a statistical significance of
2-3 sigma. This is the first experimental evidence for chiral correlation of
spins. Within tidal torque theory it indicates that the inertia tensors of
nearby galaxies are correlated. This is complementary to the studies of nearby
spin axis correlations that probe the correlations of the tidal field.
Theoretical interpretation is made difficult by the small distances at which
the correlations are detected, implying that substructure might play a
significant role, and our necessary selection of face-on spiral galaxies,
rather than a general volume-limited sample.",0809.0717v2
2009-02-26,Effects of Magnetic Braking and Tidal Friction on Hot Jupiters,"Tidal friction is thought to be important in determining the long-term
spin-orbit evolution of short-period extrasolar planetary systems. Using a
simple model of the orbit-averaged effects of tidal friction Eggleton, Kiseleva
& Hut (1998), we analyse the effects of the inclusion of stellar magnetic
braking on the evolution of such systems. A phase-plane analysis of a
simplified system of equations, including only the stellar tide together with a
model of the braking torque proposed by Verbunt & Zwaan (1981), is presented.
The inclusion of stellar magnetic braking is found to be extremely important in
determining the secular evolution of such systems, and its neglect results in a
very different orbital history. We then show the results of numerical
integrations of the full tidal evolution equations, using the misaligned spin
and orbit of the XO-3 system as an example, to study the accuracy of simple
timescale estimates of tidal evolution. We find that it is essential to
consider coupled evolution of the orbit and the stellar spin in order to model
the behaviour accurately. In addition, we find that for typical Hot Jupiters
the stellar spin-orbit alignment timescale is of the same order as the inspiral
time, which tells us that if a planet is observed to be aligned, then it
probably formed coplanar. This reinforces the importance of Rossiter-McLaughlin
effect observations in determining the degree of spin-orbit alignment in
transiting systems.",0902.4554v1
2010-01-14,Isolated pulsar spin evolution on the P-Pdot Diagram,"We look at two contrasting spin-down models for isolated radio pulsars and,
accounting for selection effects, synthesize observable populations. While our
goal is to reproduce all of the observable characteristics, in this paper we
pay particular attention to the form of the spin period vs. period derivative
(P-Pdot) diagram and its dependence on various pulsar properties. We analyse
the initial spin period, the braking index, the magnetic field, various beaming
models, as well as the pulsar's luminosity. In addition to considering the
standard magnetic dipole model for pulsar spin-down, we also consider the
recent hybrid model proposed by Contopoulos & Spitkovsky. The magnetic dipole
model, however, does a better job of reproducing the observed pulsar
population. We conclude that random alignment angles and period dependent
luminosity distributions are essential to reproduce the observed P-Pdot
diagram. We also consider the time decay of alignment angles, and attempt to
reconcile various models currently being studied. We conclude that, in order to
account for recent evidence for the alignment found by Weltevrede & Johnston,
the braking torque on a neutron star should not depend strongly on the
inclination. Our simulation code is publically available and includes a
web-based interface to examine the results and make predictions for yields of
current and future surveys.",1001.2483v1
2010-02-06,Anisotropic phase diagram of the frustrated spin dimer compound Ba3Mn2O8,"Heat capacity and magnetic torque measurements are used to probe the
anisotropic temperature-field phase diagram of the frustrated spin dimer
compound Ba3Mn2O8 in the field range from 0T to 18T. For fields oriented along
the c axis a single magnetically ordered phase is found in this field range,
whereas for fields oriented along the a axis two distinct phases are observed.
The present measurements reveal a surprising non-monotonic evolution of the
phase diagram as the magnetic field is rotated in the [001]-[100] plane. The
angle dependence of the critical field (Hc1) that marks the closing of the spin
gap can be quantitatively accounted for using a minimal spin Hamiltonian
comprising superexchange between nearest and next nearest Mn ions, the Zeeman
energy and single ion anisotropy. This Hamiltonian also predicts a
non-monotonic evolution of the transition between the two ordered states as the
field is rotated in the a-c plane. However, the observed effect is found to be
significantly larger in magnitude, implying that either this minimal spin
Hamiltonian is incomplete or that the magnetically ordered states have a
slightly different structure than previously proposed.",1002.1334v2
2010-02-09,The Large-Scale Orientations of Disk Galaxies,"We use a 380 h-1 pc resolution hydrodynamic AMR simulation of a cosmic
filament to investigate the orientations of a sample of ~100 well-resolved
galactic disks spanning two orders of magnitude in both stellar and halo mass.
We find: (i) At z=0, there is an almost perfect alignment at a median angle of
18 deg, in the inner dark matter halo regions where the disks reside, between
the spin vector of the gaseous and stellar galactic disks and that of their
inner host haloes. The alignment between galaxy spin and spin of the entire
host halo is however significantly weaker, ranging from a median of ~46 deg at
z=1 to ~50 deg at z=0. (ii) The most massive galaxy disks have spins
preferentially aligned so as to point along their host filaments. (iii) The
spin of disks in lower-mass haloes shows, at redshifts above z~0.5 and in
regions of low environmental density, a clear signature of alignment with the
intermediate principal axis of the large-scale tidal field. This behavior is
consistent with predictions of linear tidal torque theory. This alignment
decreases with increasing environmental density, and vanishes in the highest
density regions. Non-linear effects in the high density environments are
plausibly responsible for establishing this density-alignment correlation. We
expect that our numerical results provide important insights for both
understanding intrinsic alignment in weak lensing from the astrophysical
perspective and formation and evolution processes of galactic disks in a
cosmological context.",1002.1964v1
2011-10-17,Theory of quasi-spherical accretion in X-ray pulsars,"A theoretical model for quasi-spherical subsonic accretion onto slowly
rotating magnetized neutron stars is constructed. In this model the accreting
matter subsonically settles down onto the rotating magnetosphere forming an
extended quasi-static shell. This shell mediates the angular momentum removal
from the rotating neutron star magnetosphere during spin-down episodes by
large-scale convective motions. The accretion rate through the shell is
determined by the ability of the plasma to enter the magnetosphere. The
settling regime of accretion can be realized for moderate accretion rates $\dot
M< \dot M_*\simeq 4\times 10^{16}$ g/s. At higher accretion rates a free-fall
gap above the neutron star magnetosphere appears due to rapid Compton cooling,
and accretion becomes highly non-stationary. From observations of the
spin-up/spin-down rates (the angular rotation frequency derivative $\dot
\omega^*$, and $\partial\dot\omega^*/\partial\dot M$ near the torque reversal)
of X-ray pulsars with known orbital periods, it is possible to determine the
main dimensionless parameters of the model, as well as to estimate the magnetic
field of the neutron star. We illustrate the model by determining these
parameters for three wind-fed X-ray pulsars GX 301-2, Vela X-1, and GX 1+4. The
model explains both the spin-up/spin-down of the pulsar frequency on large
time-scales and the irregular short-term frequency fluctuations, which can
correlate or anti-correlate with the X-ray flux fluctuations in different
systems. It is shown that in real pulsars an almost iso-angular-momentum
rotation law with $\omega \sim 1/R^2$, due to strongly anisotropic radial
turbulent motions sustained by large-scale convection, is preferred.",1110.3701v1
2012-01-27,The evolution of massive black holes and their spins in their galactic hosts,"[Abridged] [...] We study the mass and spin evolution of massive black holes
within a semianalytical galaxy-formation model that follows the evolution of
dark-matter halos along merger trees, as well as that of the baryonic
components (hot gas, stellar and gaseous bulges, and stellar and gaseous
galactic disks). This allows us to study the mass and spin evolution of massive
black holes in a self-consistent way, by taking into account the effect of the
gas present in galactic nuclei both during the accretion phases and during
mergers. Also, we present predictions, as a function of redshift, for the
fraction of gas-rich black-hole mergers -- in which the spins prior to the
merger are aligned due to the gravito-magnetic torques exerted by the
circumbinary disk -- as opposed to gas-poor mergers, in which the orientation
of the spins before the merger is roughly isotropic. These predictions may be
tested by LISA or similar spaced-based gravitational-wave detectors such as
eLISA/NGO or SGO.",1201.5888v3
2013-04-18,A Primordial Origin for Misalignments Between Stellar Spin Axes and Planetary Orbits,"The presence of gaseous giant planets whose orbits lie in extreme proximity
to their host stars (""hot Jupiters""), can largely be accounted for by planetary
migration, associated with viscous evolution of proto-planetary nebulae.
Recently, observations of the Rossiter-McLaughlin effect during planetary
transits have revealed that a considerable fraction of detected hot Jupiters
reside on orbits that are misaligned with respect to the spin-axes of their
host stars. This observational fact has cast significant doubts on the
importance of disk-driven migration as a mechanism for production of hot
Jupiters, thereby reestablishing the origins of close-in planetary orbits as an
open question. Here we show that misaligned orbits can be a natural consequence
of disk migration. Our argument rests on an enhanced abundance of binary
stellar companions in star formation environments, whose orbital plane is
uncorrelated with the spin axes of the individual stars. We analyze the
dynamical evolution of idealized proto-planetary disks under perturbations from
massive distant bodies and demonstrate that the resulting gravitational torques
act to misalign the orbital planes of the disks relative to the spin poles of
their host stars. As a result, we predict that in the absence of strong
disk-host star angular momentum coupling or sufficient dissipation that acts to
realign the stellar spin axis and the planetary orbits, the fraction of
planetary systems (including systems of hot Neptunes and Super-Earths), whose
angular momentum vectors are misaligned with respect to their host-stars should
be commensurate with the rate of primordial stellar multiplicity.",1304.5166v1
2016-07-28,Tidal spin down rates of homogeneous triaxial viscoelastic bodies,"We use numerical simulations to measure the sensitivity of the tidal spin
down rate of a homogeneous triaxial ellipsoid to its axis ratios by comparing
the drift rate in orbital semi-major axis to that of a spherical body with the
same mass, volume and simulated rheology. We use a mass-spring model
approximating a viscoelastic body spinning around its shortest body axis, with
spin aligned with orbital spin axis, and in circular orbit about a point mass.
The torque or drift rate can be estimated from that predicted for a sphere with
equivalent volume if multiplied by $0.5 (1 + b^4/a^4)(b/a)^{-4/3}
(c/a)^{-\alpha_c}$ where $b/a$ and $c/a$ are the body axis ratios and index
$\alpha_c \approx 1.05$ is consistent with the random lattice mass spring model
simulations but $\alpha_c = 4/3$ suggested by scaling estimates.
  A homogeneous body with axis ratios 0.5 and and 0.8, like Haumea, has orbital
semi-major axis drift rate about twice as fast as a spherical body with the
same mass, volume and material properties. A simulation approximating a mostly
rocky body but with 20\% of its mass as ice concentrated at its ends has a
drift rate 10 times faster than the equivalent homogeneous rocky sphere.
However, this increase in drift rate is not enough to allow Haumea's satellite,
Hi'iaka, to have tidally drifted away from Haumea to its current orbital
semi-major axis.",1607.08591v2
2018-05-14,"The dynamics of asteroid rotation, governed by YORP effect: the kinematic ansatz","The main motivation of this research is the analytical exploration of the
dynamics of asteroid rotation when it moves in elliptic orbit through Space.
According to the results of Efroimsky, Frouard (2016), various perturbations
(collisions, close encounters, YORP effect) destabilize the rotation of a small
body (asteroid), deviating it from the initial-current spin state. This yields
evolution of the spin towards rotation about maximal-inertia axis due to the
process of nutation relaxation or to the proper spin state corresponding to
minimal energy with a fixed angular momentum. We consider in our research the
aforementioned spin state of asteroid but additionally under non-vanishing
influence of the effects of non-gravitational nature (YORP effect), which is
destabilizing the asteroid rotation during its motion far from giant planets.
Meanwhile, new solutions for asteroid rotation dynamics in case of negligible
(time-dependent) applied torques have been obtained in our development. New
method for solving Euler equations for rigid body rotation is suggested; an
elegant example for evolution of spin towards the rotation about
maximal-inertia axis is calculated.",1805.06304v2
2019-11-27,Spin flop and crystalline anisotropic magnetoresistance in CuMnAs,"Recent research works have shown that the magnetic order in some
antiferromagnetic materials can be manipulated and detected electrically, due
to two physical mechanisms: Neel-order spin-orbit torques and anisotropic
magnetoresistance. While these observations open up opportunities to use
antiferromagnets for magnetic memory devices, different physical
characterization methods are required for a better understanding of those
mechanisms. Here we report a magnetic field induced rotation of the
antiferromagnetic Neel vector in epitaxial tetragonal CuMnAs thin films. Using
soft x-ray magnetic linear dichroism spectroscopy, x-ray photoemission electron
microscopy, integral magnetometry and magneto-transport methods, we demonstrate
spin-flop switching and continuous spin reorientation in antiferromagnetic
films with uniaxial and biaxial magnetic anisotropies, respectively. From
field-dependent measurements of the magnetization and magnetoresistance, we
obtain key material parameters including the anisotropic magnetoresistance
coefficients, magnetocrystalline anisotropy, spin-flop and exchange fields.",1911.12381v2
2019-03-04,The Initial Spin Probability Distribution of Primordial Black Holes,"We study the spin of primordial black holes produced by the collapse of large
inhomogeneities in the early universe. Since such primordial black holes
originate from peaks, that is, from maxima of the local overdensity, we resort
to peak theory to obtain the probability distribution of the spin at formation.
We show that the spin is a first-order effect in perturbation theory: it
results from the action of first-order tidal gravitational fields generating
first-order torques upon horizon-crossing, and from the asphericity of the
collapsing object. Assuming an ellipsoidal shape, the typical value of the
dimensionless parameter $a_{\rm s}=S/G_N M^2$, where $S$ is the spin and $M$ is
the mass of the primordial black hole, is about
$\sigma_\delta\sqrt{1-\gamma^2}/2\pi$. Here, $\sigma^2_\delta$ is the variance
of the overdensity at horizon crossing and the parameter $\gamma$ is a measure
of the width of the power spectrum giving rise to primordial black holes. One
has $\gamma=1$ for monochromatic spectra. For these narrow spectra, the
suppression arises because the velocity shear, which is strongly correlated
with the inertia tensor, tends to align with the principal axis frame of the
collapsing object. Typical values of $a_{\rm s}$ are at the percent level.",1903.01179v3
2019-03-08,A Néel-type antiferromagnetic order in the spin 1/2 rare-earth honeycomb YbCl$_3$,"Most of the searches for Kitaev materials deal with $4d/5d$ magnets with
spin-orbit-coupled ${J=1/2}$ local moments such as iridates and
$\alpha$-RuCl$_3$. Here we propose the monoclinic YbCl$_3$ with a Yb$^{3+}$
honeycomb lattice for the exploration of Kiteav physics. We perform
thermodynamic, $ac$ susceptibility, angle-dependent magnetic torque and neutron
diffraction measurements on YbCl$_3$ single crystal. We find that the Yb$^{3+}$
ion exhibits a Kramers doublet ground state that gives rise to an effective
spin ${J_{\text{eff}}=1/2}$ local moment. The compound exhibits short-range
magnetic order below 1.20 K, followed by a long-range N\'eel-type
antiferromagnetic order at 0.60 K, below which the ordered Yb$^{3+}$ spins lie
in the $ac$ plane with an angle of 16(11)$^{\circ}$ away from the $a$ axis.
These orders can be suppressed by in-plane and out-of-plane magnetic fields at
around 6 and 10 T, respectively. Moreover, the N\'eel temperature varies
non-monotonically under the out-of-plane magnetic fields. The in-plane magnetic
anisotropy and the reduced order moment 0.8(1) $\mu_B$ at 0.25 K indicate that
YbCl$_3$ could be a two-dimensional spin system to proximate the Kitaev
physics.",1903.03615v3
2019-05-09,Spin-Hall Topological Hall Effect in Highly Tunable Pt/Ferrimagnetic-Insulator Bilayers,"Electrical detection of topological magnetic textures such as skyrmions is
currently limited to conducting materials. While magnetic insulators offer key
advantages for skyrmion technologies with high speed and low loss, they have
not yet been explored electrically. Here, we report a prominent topological
Hall effect in Pt/Tm$_3$Fe$_5$O$_{12}$ bilayers, where the pristine
Tm$_3$Fe$_5$O$_{12}$ epitaxial films down to 1.25 unit cell thickness allow for
tuning of topological Hall stability over a broad range from 200 to 465 K
through atomic-scale thickness control. Although Tm$_3$Fe$_5$O$_{12}$ is
insulating, we demonstrate the detection of topological magnetic textures
through a novel phenomenon: 'spin-Hall topological Hall effect' (SH-THE), where
the interfacial spin-orbit torques allow spin-Hall-effect generated spins in Pt
to experience the unique topology of the underlying skyrmions in
Tm$_3$Fe$_5$O$_{12}$. This novel electrical detection phenomenon paves a new
path for utilizing a large family of magnetic insulators in future skyrmion
technologies.",1905.03650v1
2021-02-02,Living with Neighbors. III. The Origin of the Spin$-$Orbit Alignment of Galaxy Pairs: A Neighbor versus the Large-scale Structure,"Recent observations revealed a coherence between the spin vector of a galaxy
and the orbital motion of its neighbors. We refer to the phenomenon as ""the
spin$-$orbit alignment (SOA)"" and explore its physical origin via the
IllustrisTNG simulation. This is the first study to utilize a cosmological
hydrodynamic simulation to investigate the SOA of galaxy pairs. In particular,
we identify paired galaxies at $z = 0$ having the nearest neighbor with mass
ratios from 1/10 to 10 and calculate the spin$-$orbit angle for each pair. Our
results are as follows. (a) There exists a clear preference for prograde
orientations (i.e., SOA) for galaxy pairs, qualitatively consistent with
observations. (b) The SOA is significant for both baryonic and dark matter
spins, being the strongest for gas and the weakest for dark matter. (c) The SOA
is stronger for less massive targets and for targets having closer neighbors.
(d) The SOA strengthens for galaxies in low-density regions, and the signal is
dominated by central$-$satellite pairs in low-mass halos. (e) There is an
explicit dependence of the SOA on the duration of interaction with its current
neighbor. Taken together, we propose that the SOA witnessed at $z = 0$ has been
developed mainly by interactions with a neighbor for an extended period of
time, rather than tidal torque from the ambient large-scale structure.",2102.01701v1
2021-08-08,The Effect of the Angular Momentum in the Formation and Evolution of Low Surface Brightness Galaxies,"Using observed data from the literature, we compare in one single publication
the angular momentum (AM) of low surface brightness galaxies (LSBGs), with that
of high surface brightness galaxies (HSBGs), a comparison that either is
currently spread across many unconnected references, or simply does not exist.
Partly because of the subject, this has received little attention outside the
realm of simulations. We use previous results of the stellar specific AM
$j_{*}$ from the SPARC database containing Spitzer 3.6 $\mu$m photometry and
accurate H I rotation curves from Lelli et al. using a sample of 38 LSBGs and
82 HSBGs. We do this with the objective of comparing both galaxy populations,
finding that LSBGs are higher in the Fall relation by about 0.174 dex.
Additionally, we apply and test different masses and formation models to
estimate the spin parameter $\lambda$, which quantifies the rotation obtained
from the tidal torque theory, finding no clear evidence of a difference in the
spin of LSBGs and HSBGs under a classic disk formation model that assumes the
ratio ($f_{j}$) between $j_{*}$ and the specific AM of the halo is $\sim 1$. In
another respect, by using the biased collapse model, where $f_{j}$ depends on
the star formation efficiency, it was found that LSBGs clearly show higher spin
values, having an average spin of $\sim 2$ times the average spin of HSBGs.
This latter result is consistent with those obtained from simulations by
Dalcanton et al.",2108.03620v1
2019-12-16,Universal spin-resolved thermal radiation laws for nonreciprocal bianisotropic media,"A chiral absorber of light can emit spin-polarized (circularly polarized)
thermal radiation based on Kirchhoff's law which equates spin-resolved
emissivity with spin-resolved absorptivity for reciprocal media at thermal
equilibrium. No such law is known for nonreciprocal media. In this work, we
discover three spin-resolved Kirchhoff's laws of thermal radiation applicable
for both reciprocal and nonreciprocal planar media. In particular, these laws
are applicable to multi-layered or composite slabs of generic bianisotropic
material classes which include (uniaxial or biaxial) birefringent crystals,
(gyrotropic) Weyl semimetals, magnetized semiconductors, plasmas, ferromagnets
and ferrites, (magnetoelectric) topological insulators, metamaterials and
multiferroic media. We also propose an experiment to verify these laws using a
single system of doped Indium Antimonide (InSb) thin film in an external
magnetic field. Furthermore, we reveal a surprising result that the planar
slabs of all these material classes can emit partially circularly polarized
thermal light without requiring any surface patterning, and identify planar
configurations which can experience nontrivial thermal optomechanical forces
and torques upon thermal emission into the external environment at lower
temperature (nonequilibrium). Our work also provides a new fundamental insight
of detailed balance of angular momentum (in addition to energy) of equilibrium
thermal radiation, and paves the way for practical functionalities based on
thermal radiation using nonreciprocal bianisotropic materials.",1912.07177v2
2020-01-19,Impact of the magnetic proximity effect in Pt on the total magnetic moment of Pt/Co/Ta trilayers studied by x-ray resonant magnetic reflectivity,"In this work, we study the influence of the magnetic proximity effect (MPE)
in Pt on the total magnetic moment of thin film trilayer systems consisting of
the ferromagnet (FM) Co adjacent to the heavy metals (HMs) Pt and Ta. We
investigate the trilayer systems HM1/FM/HM2 with different stacking order as
well as a reference bilayer without any MPE. X-ray resonant magnetic
reflectivity (XRMR) is a powerful tool to probe induced magnetism, especially
when buried at interfaces in a multilayer. By using XRMR, we are able to obtain
magnetic depth profiles of the structural, optical and magnetic parameters. By
fitting the experimental data with a Gaussian-like magnetooptic profile taking
the structural roughness at the interface into account, we can extract the
magnetic moment of the spin-polarized layer. Comparing the obtained moments to
the measured total moment of the sample, we can determine the impact of the MPE
on the total magnetic moment of the system. Such information can be critical
for analyzing spin transport experiments, including spin-orbit torque and spin
Hall angle measurements, where the saturation magnetization $M_s$ has to be
taken into account. Therefore, by combining magnetization measurements and XRMR
methods we were able to get a complete picture of the magnetic moment
distribution in these trilayer systems containing spin-polarized Pt.",2001.06857v1
2020-10-28,Excitation of Spin-Orbit Misalignments in Stellar Binaries with Circumbinary Disks: Application to DI Herculis,"The large spin-orbit misalignments in the DI Herculis stellar binary system
have resolved the decades-long puzzle of the anomalously slow apsidal
precession rate, but raise new questions regarding the origin of the
obliquities. This paper investigates obliquity evolution in stellar binaries
hosting modestly-inclined circumbinary disks. As the disk and binary axes
undergo mutual precession, each oblate star experiences a torque from its
companion star, so that the spin and orbital axes undergo mutual precession. As
the disk loses mass through a combination of winds and accretion, the system
may be captured into a high-obliquity Cassini state (a spin-orbit resonance).
The final obliquity depends on the details of the disk dispersal. We construct
a simple disk model to emulate disk dispersal due to viscous accretion and
photoevaporation, and identify the necessary disk properties for producing the
observed obliquities in DI Herculis. The disk must be massive (at least $10 \%$
of the binary mass). If accretion onto the binary is suppressed, the observed
high stellar obliquities are reproduced with a binary-disk inclination of $\sim
5^\circ - 10^\circ$, but if substantial accretion occurs, the inclination must
be larger, $\sim 20^\circ - 30^\circ$. If moderate accretion occurs, initially
the disk must lose its mass slowly, but eventually lose its remaining mass
abruptly, analogous to the observed two-timescale behavior for disks around
T-Tauri stars. The spin feedback on the binary orbit causes the binary-disk
inclination to decay as the obliquity evolves, a feature that is absent from
the standard Cassini state treatment.",2010.15122v2
2021-05-10,Observation of the Orbital Rashba-Edelstein Magnetoresistance,"We report the observation of magnetoresistance (MR) originating from the
orbital angular momentum transport (OAM) in a Permalloy (Py) / oxidized Cu
(Cu*) heterostructure: the orbital Rashba-Edelstein magnetoresistance. The
angular dependence of the MR depends on the relative angle between the induced
OAM and the magnetization in a similar fashion as the spin Hall
magnetoresistance (SMR). Despite the absence of elements with large spin-orbit
coupling, we find a sizable MR ratio, which is in contrast to the conventional
SMR which requires heavy elements. By varying the thickness of the Cu* layer,
we confirm that the interface is responsible for the MR, suggesting that the
orbital Rashba-Edelstein effect is responsible for the generation of the OAM.
Through Py thickness-dependence studies, we find that the effective values for
the spin diffusion and spin dephasing lengths of Py are significantly larger
than the values measured in Py / Pt bilayers, approximately by the factor of 2
and 4, respectively. This implies that another mechanism beyond the
conventional spin-based scenario is responsible for the MR observed in Py / Cu*
structures originated in a sizeable transport of OAM. Our findings not only
unambiguously demonstrate the current-induced torque without using any heavy
element via the OAM channel but also provide an important clue towards the
microscopic understanding of the role that OAM transport can play for
magnetization dynamics.",2105.04495v2
2021-07-04,Survival of itinerant excitations and quantum spin state transitions in YbMgGaO$_4$ with chemical disorder,"A recent focus of quantum spin liquid (QSL) studies is how
disorder/randomness in a QSL candidate affects its true magnetic ground state.
The ultimate question is whether the QSL survives disorder or the disorder
leads to a ""spin-liquid-like"" state, such as the proposed random-singlet (RS)
state. Since disorder is a standard feature of most QSL candidates, this
question represents a major challenge for QSL candidates. YbMgGaO$_4$, a
triangular lattice antiferromagnet with effective spin-1/2 Yb$^{3+}$ ions, is
an ideal system to address this question, since it shows no long-range magnetic
ordering with Mg/Ga site disorder. Despite the intensive study, it remains
unresolved as to whether YbMgGaO$_4$ is a QSL or in the RS state. Here, through
ultralow-temperature thermal conductivity and magnetic torque measurements,
plus specific heat and DC magnetization data, we observed a residual
$\kappa_0/T$ term and series of quantum spin state transitions in the zero
temperature limit for YbMgGaO$_4$. These observations strongly suggest that a
QSL state with itinerant excitations and quantum spin fluctuations survives
disorder in YbMgGaO$_4$.",2107.01585v1
2022-11-07,Disentanglement of intrinsic and extrinsic side-jump scattering induced spin Hall effect in N-implanted Pt,"The rapidly evolving utilization of spin Hall effect (SHE) arising from
spin-orbit coupling in 5d transition metals and alloys have made giant strides
in the development of designing low-power, robust and non-volatile magnetic
memory. Recent studies, on incorporating non-metallic lighter elements such as
oxygen, nitrogen and sulfur into 5d transition metals, have shown an
enhancement in damping-like torque efficiency {\theta}_DL due to the modified
SHE, but the mechanism behind this enhancement is not clear. In this paper, we
study {\theta}_DL at different temperatures (100-293 K) to disentangle the
intrinsic and extrinsic side-jump scattering induced spin Hall effect in
N-implanted Pt. We observe a crossover of intrinsic to extrinsic side-jump
mechanism as the implantation dose increases from 2*10^16 ions/cm2 to 1*10^17
ions/cm2. A sudden decrease in the intrinsic spin Hall conductivity is
counterbalanced by the increase in the side-jump induced SHE efficiency. These
results conclude that studying {\theta}_DL as a function of implantation dose,
and also as a function of temperature, is important to understand the physical
mechanism contributing to SHE, which has so far been unexplored in
incorporating non-metallic element in 5d transition metals.",2211.03355v1
2023-04-29,Dynamics and reversible control of the vortex Bloch-point vortex domain wall in short cylindrical magnetic nanowires,"Fast and efficient switching of nanomagnets is one of the main challenges in
the development of future magnetic memories. We numerically investigate the
evolution of the static and dynamic spin wave (SW) magnetization in short
(50-400 nm length and 120 nm diameter) cylindrical ferromagnetic nanowires,
where competing single vortex (SV) and vortex domain wall with a Bloch point
(BP-DW) magnetization configurations could be formed. For a limited nanowire
length range (between 150 and 300 nm) we demonstrate a reversible microwave
field induced (forward) and opposite spin currents (backwards) transitions
between the topologically different SV and BP-DW states. By tuning the nanowire
length, excitation frequency, the microwave pulse duration and the spin current
values we show that the optimum (low power) manipulation of the BP-DW could be
reached by a microwave excitation tuned to the main SW mode and for nanowire
lengths around 230-250 nm, where single vortex domain wall magnetization
reversal via nucleation and propagation of SV-DW takes place. An analytical
model for dynamics of the Bloch point provides an estimation of the gyrotropic
mode frequency close the one obtained via micromagnetic simulations. A
practical implementation of the method on a device has been proposed involving
microwave excitation and the generation of the opposite spin currents via spin
orbit torque. Our findings open a new pathway for the creation of unforeseen
topological magnetic memories.",2305.00346v1
2024-01-31,Electrical 180o switching of Néel vector in spin-splitting antiferromagnet,"Antiferromagnetic spintronics have attracted wide attention due to its great
potential in constructing ultra-dense and ultra-fast antiferromagnetic memory
that suits modern high-performance information technology. The electrical 180o
switching of N\'eel vector is a long-term goal for developing
electrical-controllable antiferromagnetic memory with opposite N\'eel vectors
as binary ""0"" and ""1"". However, the state-of-art antiferromagnetic switching
mechanisms have long been limited for 90o or 120o switching of N\'eel vector,
which unavoidably require multiple writing channels that contradicts
ultra-dense integration. Here, we propose a deterministic switching mechanism
based on spin-orbit torque with asymmetric energy barrier, and experimentally
achieve electrical 180o switching of spin-splitting antiferromagnet Mn5Si3.
Such a 180o switching is read out by the N\'eel vector-induced anomalous Hall
effect. Based on our writing and readout methods, we fabricate an
antiferromagnet device with electrical-controllable high and low resistance
states that accomplishes robust write and read cycles. Besides fundamental
advance, our work promotes practical spin-splitting antiferromagnetic devices
based on spin-splitting antiferromagnet.",2401.17608v1
2024-02-03,Spintronic devices and applications using noncollinear anti-chiral antiferromagnets,"Antiferromagnetic materials have a vanishingly small net magnetization, which
generates weak dipolar fields and makes them robust against external magnetic
perturbation and rapid magnetization dynamics, as dictated by the geometric
mean of their exchange and anisotropy energies. However, experimental and
theoretical techniques to detect and manipulate the antiferromagnetic order in
a fully electrical manner must be developed to enable advanced spintronic
devices with antiferromagnets (AFMs) as their active spin-dependent elements.
Among the various AFMs, conducting AFMs offer high electrical and thermal
conductivities and strong electron-spin-phonon interactions. Noncollinear
metallic AFMs with negative chirality, including Mn3Sn, Mn3Ge, and Mn3GaN,
offer rich physics that arises from their topology. In this review article, we
introduce the crystal structure and the physical phenomena observed in negative
chirality AFMs. Experimental and theoretical advances related to
current-induced dynamics on the spin structure of Mn3Sn are discussed. We then
present a potential AFM spintronic device that can serve as a non-volatile
memory, high-frequency signal generator, neuron emulator, and even a
probabilistic bit, depending on the design parameters and the input stimuli,
i.e., amplitude and pulse width of the injected spin current and the external
magnetic field. In this device, spin-orbit torques can be used to manipulate
the order parameter, while the device state can be read via tunneling
magnetoresistance. We also present analytic models that relate the performance
characteristics of the device with its design parameters, thus enabling a rapid
technology-device assessment. Effects of Joule heating and thermal noise on the
device characteristics are briefly discussed. We close the paper by summarizing
the status of research and present our outlook in this rapidly evolving
research field.",2402.01977v1
2024-03-18,Skyrmion on Magnetic Tunnel Junction: Interweaving Quantum Transport with Micro-magnetism,"Over the last two decades, non-trivial magnetic textures, especially the
magnetic skyrmion family, have been extensively explored out of fundamental
interest, and diverse possible applications. Given the possible technological
and scientific ramifications of skyrmion-texture on magnetic tunnel junction
(ST-MTJ), in this work, we present non-equilibrium Green's function (NEGF)
based description of ST-MTJs both for N\'eel and Bloch textures, to capture the
spin/charge current across different voltages, temperatures, and sizes. We
predict the emergence of a textured spin current from the uniform layer of the
ST-MTJs, along with a radially varying, asymmetrical voltage dependence of spin
torque. We delineate the voltage-induced rotation of the spin current texture,
coupled with the appearance of helicity in spin current, particularly in the
case of N\'eel skyrmions on MTJs. We describe the TMR roll-off in ST-MTJ with
lower cross-sectional area and higher temperature based on transmission spectra
analysis. We also introduce a computationally efficient coupled spatio-eigen
framework of NEGF to address the 3D-NEGF requirement of the ST-MTJs. With
analytical underpinning, we establish the generic nature of the spatio-eigen
framework of NEGF, alleviating the sine-qua-non of the 3D-NEGF for systems that
lack transnational invariance and simultaneous eigen-basis in the transverse
directions.",2403.11666v3
2023-02-28,Quantum simulation of the central spin model with a Rydberg atom and polar molecules in optical tweezers,"Central spin models, where a single spinful particle interacts with a spin
environment, find wide application in quantum information technology and can be
used to describe, e.g., the decoherence of a qubit over time. We propose a
method of realizing an ultracold quantum simulator of a central spin model with
XX (spin-exchanging) interactions. The proposed system consists of a single
Rydberg atom (""central spin"") and surrounding polar molecules (""bath spins""),
coupled to each other via dipole-dipole interactions. By mapping internal
particle states to spin states, spin-exchanging interactions can be simulated.
As an example system geometry, we consider a ring-shaped arrangement of bath
spins, and show how it allows us to exact precise control over the interaction
strengths. We numerically analyze two example dynamical scenarios which can be
simulated in this setup: a decay of central spin polarization, which can
represent qubit decoherence in a disordered environment, and a transfer of an
input spin state to a specific output spin, which can represent the
transmission of a single bit across a quantum network. We demonstrate that this
setup allows us to realize a central spin model with highly tunable parameters
and geometry, for applications in quantum science and technology.",2302.14774v2
2023-06-29,Control of an environmental spin defect beyond the coherence limit of a central spin,"Electronic spin defects in the environment of an optically-active spin can be
used to increase the size and hence the performance of solid-state quantum
registers, especially for applications in quantum metrology and quantum
communication. Previous works on multi-qubit electronic-spin registers in the
environment of a Nitrogen-Vacancy (NV) center in diamond have only included
spins directly coupled to the NV. As this direct coupling is limited by the
central spin coherence time, it significantly restricts the register's maximum
attainable size. To address this problem, we present a scalable approach to
increase the size of electronic-spin registers. Our approach exploits a
weakly-coupled probe spin together with double-resonance control sequences to
mediate the transfer of spin polarization between the central NV spin and an
environmental spin that is not directly coupled to it. We experimentally
realize this approach to demonstrate the detection and coherent control of an
unknown electronic spin outside the coherence limit of a central NV. Our work
paves the way for engineering larger quantum spin registers with the potential
to advance nanoscale sensing, enable correlated noise spectroscopy for error
correction, and facilitate the realization of spin-chain quantum wires for
quantum communication.",2306.17155v3
2010-05-04,Interacting Binaries with Eccentric Orbits. III. Orbital Evolution due to Direct Impact and Self-Accretion,"The rapid circularization and synchronization of the stellar components in an
eccentric binary system at the onset of Roche lobe overflow (RLO) is a
fundamental assumption common to all binary stellar evolution and population
synthesis codes, even though the validity of this assumption is questionable
both theoretically and observationally. Here we calculate the evolution of the
orbital elements of an eccentric binary through the direct three-body
integration of a massive particle ejected through the inner Lagrangian point of
the donor star at periastron. The trajectory of this particle leads to three
possible outcomes: direct accretion (DA) onto the companion star within a
single orbit, self-accretion (SA) back onto the donor star within a single
orbit, or a quasi-periodic orbit around the companion star. We calculate the
secular evolution of the binary orbit in the first two cases and conclude that
DA can increase or decrease the orbital semi-major axis and eccentricity, while
SA always decreases the orbital both orbital elements. In cases where mass
overflow contributes to circularizing the orbit, circularization can set in on
timescales as short as a few per cent of the mass transfer timescale. In cases
where mass overflow increases the eccentricity, the orbital evolution is
governed by competition between mass overflow and tidal torques. In the absence
of tidal torques, mass overflow resulting in DI can lead to substantially
subsynchronously rotating donor stars. Contrary to common assumptions, DI
furthermore does not always provide a strong sink of orbital angular momentum
in close mass-transferring binaries; in fact we instead find that a significant
part can be returned to the orbit during the particle orbit. The formulation
presented here can be combined with stellar and binary evolution codes to
generate a better picture of the evolution of eccentric, RLO binary star
systems.",1005.0625v2
2012-11-03,"Dynamical Tides in Compact White Dwarf Binaries: Helium Core White Dwarfs, Tidal Heating, and Observational Signatures","Tidal dissipation in compact white dwarf (WD) binary systems significantly
influences the physical conditions (such as surface temperature and rotation
rate) of the WDs prior to mass transfer or merger. In these systems, the
dominant tidal effects involve the excitation of gravity waves and their
dissipation in the outer envelope of the star. We calculate the amplitude of
tidally excited gravity waves in low-mass (0.3M_\odot) helium-core (He) WDs as
a function of the tidal forcing frequency \omega. Like carbon-oxygen (CO) WDs
studied in our previous paper, we find that the dimensionless tidal torque
F(\omega) (inversely proportional to the effective tidal quality factor) has an
erratic dependence on \omega. On average, F(\omega) scales approximately as
\omega^6, and is several orders of magnitude smaller for He WDs than for CO
WDs. We find that tidal torques can begin to synchronize the WD rotation when
the orbital period is less than about a hour, although a nearly constant
asynchronization is maintained even at small periods. We examine where the
tidally excited gravity waves experience non-linear breaking or resonant
absorption at a critical layer, allowing us to estimate the location and
magnitude of tidal heating in the WD envelope. We then incorporate tidal
heating in the MESA stellar evolution code, calculating the physical conditions
of the WD as a function of orbital period for different WD models. We find that
tidal heating makes a significant contribution to the WD luminosity for
short-period (~10 min) systems such as SDSS J0651+2844. We also find that for
WDs containing a hydrogen envelope, tidal heating can trigger runaway hydrogen
shell burning, leading to a nova-like event before the onset of mass transfer.",1211.0624v2
2022-09-15,"On distributions law of planetary rotations and revolutions as a function of aphelia, following Lagrange's formulation","Earth rotation is determined by polar motion (PM) and length of day (lod).
The excitation sources of PM are torques linked to fluid circulations
(""geophysical excitations""), and those of lod to luni-solar tides
(""astronomical excitations""). We explore the links between the rotations and
revolutions of planets, following Lagrange's (1853) presentation of mechanics.
The energy of a planet in motion in a central field is the sum of kinetic,
centrifugal (planet dependent) and centripetal (identical for all planets)
energies. For each planet, one can calculate a ""constant of gravitation"" Gp .
For the giant planets, Gp decreases as a function of aphelia. There is no such
organized behavior for the terrestrial planets. The perturbing potential of
other planets generates a small angular contribution to the displacement : this
happens to be identical to Einstein's famous formula for precession. Delays in
the planet's perihelia follow a (-5/2) power law of a. This is readily
understood in the Lagrange formalism (the centrifugal term takes over for small
distances). The telluric planets have lost energy, probably transferred to the
planets rotations. The ratio of areal velocities to rotation obeys a -5/2 power
law of a. The ratio of areal velocity to integrated period R also fits a -5/2
power dependence, implying linearity of the energy exchange between revolution
and rotation. For Einstein deformation of space-time by the Sun is the origin
of the field perturbation. For Lagrange the perturbation could only be due to
the interactions of torques. The perihelion delays, the areal velocities and
the planetary rotations display power laws of aphelia, whose behavior contrasts
with that of the kinetic moment. The areal velocity being linearly linked to
the kinetic moment of planets, this must be the level at which the transfer is
achieved.",2209.07213v3
2023-07-29,Dimensionless Policies based on the Buckingham $π$ Theorem: Is This a Good Way to Generalize Numerical Results?,"The answer to the question posed in the title is yes if the context (the list
of variables defining the motion control problem) is dimensionally similar.
This article explores the use of the Buckingham $\pi$ theorem as a tool to
encode the control policies of physical systems into a more generic form of
knowledge that can be reused in various situations. This approach can be
interpreted as enforcing invariance to the scaling of the fundamental units in
an algorithm learning a control policy. First, we show, by restating the
solution to a motion control problem using dimensionless variables, that (1)
the policy mapping involves a reduced number of parameters and (2) control
policies generated numerically for a specific system can be transferred exactly
to a subset of dimensionally similar systems by scaling the input and output
variables appropriately. Those two generic theoretical results are then
demonstrated, with numerically generated optimal controllers, for the classic
motion control problem of swinging up a torque-limited inverted pendulum and
positioning a vehicle in slippery conditions. We also discuss the concept of
regime, a region in the space of context variables, that can help to relax the
similarity condition. Furthermore, we discuss how applying dimensional scaling
of the input and output of a context-specific black-box policy is equivalent to
substituting new system parameters in an analytical equation under some
conditions, using a linear quadratic regulator (LQR) and a computed torque
controller as examples. It remains to be seen how practical this approach can
be to generalize policies for more complex high-dimensional problems, but the
early results show that it is a promising transfer learning tool for numerical
approaches like dynamic programming and reinforcement learning.",2307.15852v2
2009-10-15,Spin Transfer from the point of view of the ferromagnetic degrees of freedom,"Spintronics is the generic term that describes magnetic systems coupled to an
electric generator, taking into account the spin attached to the charge
carriers. For this topical review of {\it Spin Caloritronics}, we focus our
attention on the study of {\it irreversible processes} occuring in spintronic
devices, that involve both the spins of the conduction electrons and the
ferromagnetic degrees of freedom. The aim of this report is to clarify the
nature of the different kinds of power dissipated in metallic ferromagnets
contacted to an electric generator, and to exploit it in the framework of the
theory of mesoscopic non-equilibrium thermodynamics. The expression of the
internal power (i.e. the internal entropy production multiplied by the
temperature) dissipated by a generic system connected to different reservoirs,
allows the corresponding kinetic equations to be derived with the introduction
of the relevant phenomenological kinetic coefficients. After derivation of the
kinetic equations for the ferromagnetic degrees of freedom (i.e. the
Landau-Lifshitz equation) and the derivation of the kinetic equations for the
spin-accumulation effects (within a two channel model), the kinetic equations
describing spin-transfer are obtained. Both spin-dependent relaxation (usual
spin-accumulation) and spin-precession in quasi-ballistic regime (transverse
spin-accumulation) are taken into account. The generalization of the
Landau-Lifshitz equation to spin-accumulation is then performed with the
introduction of two potential energy terms, that are experimentally accessible.",0910.2890v2
2019-07-09,Spinning up planetary bodies by pebble accretion,"Most major planetary bodies in the solar system rotate in the same direction
as their orbital motion: their spin is prograde. Theoretical studies to explain
the direction as well as the magnitude of the spin vector have had mixed
success. When the accreting building blocks are $\sim$ km-size planetesimals --
as predicted by the classical model -- the accretion process is so symmetric
that it cancels out prograde with retrograde spin contributions, rendering the
net spin minute. For this reason, the currently-favored model for the origin of
planetary rotation is the giant impact model, in which a single collision
suffices to deliver a spin, which magnitude is close to the breakup rotation
rate. However, the giant impact model does not naturally explain the preference
for prograde spin. Similarly, an increasing number of spin-vector measurement
of asteroids also shows that the spin vector of large (primordial) asteroids is
not isotropic. Here, we re-assess the viability of smaller particles to bestow
planetary bodies with a net spin, focusing on the pebble accretion model in
which gas drag and gravity join forces to accrete small particles at a large
cross section. Similar to the classical calculation for planetesimals, we
integrate the pebble equation of motion and measure the angular momentum
transfer at impact. We consider a variety of disk conditions and pebble
properties and conduct our calculations in the limits of 2D (planar) and 3D
(homogeneous) pebble distributions. We find that in certain regions of the
parameter space the angular momentum transfer is significant, much larger than
with planetesimals and on par with or exceeding the current spin of planetary
bodies.",1907.04368v2
2019-12-11,Coherent transfer of spin angular momentum by evanescent spin waves within antiferromagnetic NiO,"Insulating antiferromagnets are efficient and robust conductors of spin
current. To realise the full potential of these materials within spintronics,
the outstanding challenges are to demonstrate scalability down to nanometric
lengthscales and the transmission of coherent spin currents. Here, we report
the coherent transfer of spin angular momentum by excitation of evanescent spin
waves of GHz frequency within antiferromagnetic NiO at room temperature. Using
element-specific and phase-resolved x-ray ferromagnetic resonance, we probe the
injection and transmission of ac spin current, and demonstrate that insertion
of a few nanometre thick epitaxial NiO(001) layer between a ferromagnet and
non-magnet can even enhance the flow of spin current. Our results pave the way
towards coherent control of the phase and amplitude of spin currents at the
nanoscale, and enable the realization of spin-logic devices and spin current
amplifiers that operate at GHz and THz frequencies.",1912.05621v1
1996-12-19,Disorientation of Suprathermally Rotating Grains and Grain Alignment Problem,"We discuss the dynamics of dust grains subjected to uncompensated torques
arising from H_2 formation. In particular, we discuss grain dynamics when a
grain spins down and goes through a ``crossover''. As first pointed out by
Spitzer & McGlynn (1979), the grain angular momentum before and after a
crossover event are correlated, and the degree of this correlation affects the
alignment of dust grains by paramagnetic dissipation. We calculate the
correlation including the important effects of thermal fluctuations within the
grain material. These fluctuations limit the degree to which the grain angular
momentum J is coupled with the grain principal axis a_1 of maximal inertia. We
show that this imperfect coupling of a_1 with J plays a critical role during
crossovers and can substantially increase the efficiency of paramagnetic
alignment for grains larger than 10^{-5} cm. As a result, we show that for
reasonable choices of parameters, the observed alignment of $a\gtrsim 10^{-5}$
cm grains could be produced by paramagnetic dissipation in suprathermally
rotating grains, if radiative torques due to starlight were not present. We
also show that the efficiency of mechanical alignment in the limit of long
alignment times is not altered by the thermal fluctuations in the grain
material.",9612199v1
2003-11-17,Translational Velocities and Rotational Rates of Interstellar Dust Grains,"Interstellar dust grains exhibit complex dynamics which is essential for
understanding many key interstellar processes that involve dust, including
grain alignment, grain growth, grain shattering etc. Grain rotational and
translational motions are affected not only by gaseous collisions, but also by
interactions with ions, photons, magnetic fields etc. Some of those
interactions, e.g. interactions of ions with the dipole electric moment of dust
grains, require the quantum nature of the process to be accounted for.
Similarly, coupling of rotational and vibrational degrees of freedom in a grain
happens due to relaxation processes, among which the process related to nuclear
spins frequently is the dominant one. This coupling modifies substantially both
the dynamics of rotational and translational motions by inducing grain flips.
The flipping averages our certain systematic torques and forces that act on
grains. As the rate of flipping is larger for smaller grains, these grains can
be ``thermally trapped'', i.e. rotate at a thermal rate in spite of the
presence of systematic torques. Moreover, a subset of small grains with high
dipole moments may rotate at subthermal rates due to high damping arising from
grain emission in microwave range of frequencies. Translational dynamics of
grains is mostly dominated by grain interactions with magnetohydrodynamic
turbulence. Efficient turbulent mixing of dust grains limits the degree to
which grains of different sizes may be segregated in space.",0311370v1
2004-07-02,The Effect of Rotational Gravity Darkening on Magnetically Torqued Be Star Disks,"In the magnetically torqued disk (MTD) model for hot star disks, as proposed
and formulated by \citet{cassi02}, stellar wind mass loss was taken to be
uniform over the stellar surface. Here account is taken of the fact that as
stellar spin rate S_o (=\sqrt {\Omega_o^2 R^3/GM}) is increased, and the
stellar equator is gravity darkened, the equatorial mass flux and terminal
speed are reduced, compared to the poles, for a given total \mdot. As a result,
the distribution of equatorial disk density, determined by the impact of north
and southbound flows, is shifted further out from the star. This results, for
high S_o (\gtrsim 0.5), in a fall in the disk mass and emission measure, and
hence in the observed emission line EW, scattering polarization, and IR
emission. Consequently, contrary to expectations, critical rotation S_o \to 1
is not the optimum for creation of hot star disks which, in terms of EM for
example, is found to occur in a broad peak around S_o\approx 0.5-0.6 depending
slightly on the wind velocity law.
  The relationship of this analytic quasi-steady parametric MTD model to other
work on magnetically guided winds is discussed. In particular the failures of
the MTD model for Be-star disks alleged by \citet{owo03} are shown to revolve
largely around open observational tests, rather in the basic MTD physics, and
around their use of insufficiently strong fields.",0407039v1
2012-08-04,"Coupled evolutions of the stellar obliquity, orbital distance, and planet's radius due to the Ohmic dissipation induced in a diamagnetic hot Jupiter around a magnetic T Tauri star","We revisit the calculation of the Ohmic dissipation in a hot Jupiter
presented in Laine et al. (2008) by considering more realistic interior
structures, stellar obliquity, and the resulting orbital evolution. In this
simplified approach, the young hot Jupiter of one Jupiter mass is modelled as a
diamagnetic sphere with a finite resistivity, orbiting across tilted stellar
magnetic dipole fields in vacuum. Since the induced Ohmic dissipation occurs
mostly near the planet's surface, we find that the dissipation is unable to
significantly expand the young hot Jupiter. Nevertheless, the planet inside a
small co-rotation orbital radius can undergo orbital decay by the dissipation
torque and finally overfill its Roche lobe during the T Tauri star phase. The
stellar obliquity can evolve significantly if the magnetic dipole is
parallel/anti-parallel to the stellar spin. Our results are validated by the
general torque-dissipation relation in the presence of the stellar obliquity.
We also run the fiducial model in Laine et al. (2008) and find that the
planet's radius is sustained at a nearly constant value by the Ohmic heating,
rather than being thermally expanded to the Roche radius as suggested by the
authors.",1208.0933v2
2013-08-08,Dynamics of warped accretion discs,"Accretion discs are present around both stellar-mass black holes in X-ray
binaries and supermassive black holes in active galactic nuclei. A wide variety
of circumstantial evidence implies that many of these discs are warped. The
standard Bardeen--Petterson model attributes the shape of the warp to the
competition between Lense--Thirring torque from the central black hole and
viscous angular-momentum transport within the disc. We show that this
description is incomplete, and that torques from the companion star (for X-ray
binaries) or the self-gravity of the disc (for active galactic nuclei) can play
a major role in determining the properties of the warped disc. Including these
effects leads to a rich set of new phenomena. For example, (i) when a companion
star is present and the warp arises from a misalignment between the companion's
orbital axis and the black hole's spin axis, there is no steady-state solution
of the Pringle--Ogilvie equations for a thin warped disc when the viscosity
falls below a critical value; (ii) in AGN accretion discs, the warp can excite
short-wavelength bending waves that propagate inward with growing amplitude
until they are damped by the disc viscosity. We show that both phenomena can
occur for plausible values of the black hole and disc parameters, and briefly
discuss their observational implications.",1308.1964v1
2013-11-06,Time evolution of pulsar obliquity angle from 3D simulations of magnetospheres,"The rotational period of isolated pulsars increases over time due to the
extraction of angular momentum by electromagnetic torques. These torques also
change the obliquity angle $\alpha$ between the magnetic and rotational axes.
Although actual pulsar magnetospheres are plasma-filled, the time evolution of
$\alpha$ has mostly been studied for vacuum pulsar magnetospheres. In this
work, we self-consistently account for the plasma effects for the first time by
analysing the results of time-dependent 3D force-free and magnetohydrodynamic
simulations of pulsar magnetospheres. We show that if a neutron star is
spherically symmetric and is embedded with a dipolar magnetic moment, the
pulsar evolves so as to minimise its spin-down luminosity: both vacuum and
plasma-filled pulsars evolve toward the aligned configuration ($\alpha=0$).
However, they approach the alignment in qualitatively different ways. Vacuum
pulsars come into alignment exponentially fast, with $\alpha \propto
\exp(-t/\tau)$ and $\tau \sim$ spindown timescale. In contrast, we find that
plasma-filled pulsars align much more slowly, with $\alpha \propto
(t/\tau)^{-1/2}$. We argue that the slow time evolution of obliquity of
plasma-filled pulsars can potentially resolve several observational puzzles,
including the origin of normal pulsars with periods of $\sim1$ second, the
evidence that oblique pulsars come into alignment over a timescale of $\sim
10^7$ years, and the observed deficit, relative to an isotropic obliquity
distribution, of pulsars showing interpulse emission.",1311.1513v2
2015-04-07,"A uniformly moving and rotating polarizable particle in thermal radiation field: frictional force and torque, radiation and heating","We study the fluctuation-electromagnetic interaction and dynamics of a small
spinning polarizable particle moving with a relativistic velocity in a vacuum
background of arbitrary temperature. Using the standard formalism of the
fluctuation electromagnetic theory, a complete set of equations describing the
decelerating tangential force, the components of the torque and the intensity
of nonthermal and thermal radiation is obtained along with equations describing
the dynamics of translational and rotational motion, and the kinetics of
heating. An interplay between various parameters is discussed. Numerical
estimations for conducting particles were carried out using MATHCAD code. In
the case of zero temperature of a particle and background radiation, the
intensity of radiation is independent of the linear velocity, the angular
velocity orientation and the linear velocity value are independent of time. In
the case of a finite background radiation temperature, the angular velocity
vector tends to be oriented perpendicularly to the linear velocity vector. The
particle temperature relaxes to a quasistationary value depending on the
background radiation temperature, the linear and angular velocities, whereas
the intensity of radiation depends on the background radiation temperature, the
angular and linear velocities. The time of thermal relaxation is much less than
the time of angular deceleration, while the latter time is much less than the
time of linear deceleration.",1504.01588v3
2015-04-24,Evolution of non-spherical pulsars with plasma-filled magnetospheres,"Pulsars are famous for their rotational stability. Most of them steadily spin
down and display a highly repetitive pulse shape. But some pulsars experience
timing irregularities such as nulling, intermittency, mode changing and timing
noise. As changes in the pulse shape are often correlated with timing
irregularities, precession is a possible cause of these phenomena. Whereas
pulsar magnetospheres are filled with plasma, most pulsar precession studies
were carried out within the vacuum approximation and neglected the effects of
magnetospheric currents and charges. Recent numerical simulations of
plasma-filled pulsar magnetospheres provide us with a detailed quantitative
description of magnetospheric torques exerted on the pulsar surface. In this
paper, we present the study of neutron star evolution using these new torque
expressions. We show that they lead to (1) much slower long-term evolution of
pulsar parameters and (2) much less extreme solutions for these parameters than
the vacuum magnetosphere models. To facilitate the interpretation of observed
pulsar timing residuals, we derive an analytic model that (1) describes the
time evolution of non-spherical pulsars and (2) translates the observed pulsar
timing residuals into the geometrical parameters of the pulsar. We apply this
model to two pulsars with very different temporal behaviours. For the pulsar
B1828-11, we demonstrate that the timing residual curves allow two pulsar
geometries: one with stellar deformation pointing along the magnetic axis and
one along the rotational axis. For the Crab pulsar, we use the model show that
the recent observation of its magnetic and rotational axes moving away from
each other can be explained by precession.",1504.06626v1
2015-09-21,Magnetization of underdoped YBa$_2$Cu$_3$O$_{y}$ above the irreversibility field,"Torque magnetization measurements on YBa$_2$Cu$_3$O$_{y}$ (YBCO) at doping
$y=6.67$($p=0.12$), in DC fields ($B$) up to 33 T and temperatures down to 4.5
K, show that weak diamagnetism persists above the extrapolated irreversibility
field $H_{\rm irr} (T=0) \approx 24$ T. The differential susceptibility
$dM/dB$, however, is more rapidly suppressed for $B\gtrsim 16$ T than expected
from the properties of the low field superconducting state, and saturates at a
low value for fields $B \gtrsim 24$ T. In addition, torque measurements on a
$p=0.11$ YBCO crystal in pulsed field up to 65 T and temperatures down to 8 K
show similar behaviour, with no additional features at higher fields. We
discuss several candidate scenarios to explain these observations: (a)
superconductivity survives but is heavily suppressed at high field by
competition with CDW order; (b) static superconductivity disappears near 24 T
and is followed by a region of fluctuating superconductivity, which causes
$dM/dB$ to saturate at high field; (c) the stronger 3D ordered CDW that sets in
above 15 T may suppress the normal state spin susceptibility sufficiently to
give an apparent diamagnetism of the magnitude observed.",1509.06206v1
2015-09-28,A Far-Infrared Observational Test of the Directional Dependence in Radiative Grain Alignment,"The alignment of interstellar dust grains with magnetic fields provides a key
method for measuring the strength and morphology of the fields. In turn, this
provides a means to study the role of magnetic fields from diffuse gas to dense
star-forming regions. The physical mechanism for aligning the grains has been a
long-term subject of study and debate. The theory of radiative torques, in
which an anisotropic radiation field imparts sufficient torques to align the
grains while simultaneously spinning them to high rotational velocities, has
passed a number of observational tests. Here we use archival polarization data
in dense regions of the Orion molecular cloud (OMC-1) at 100, 350, and
$850\,\mu$m to test the prediction that the alignment efficiency is dependent
upon the relative orientations of the magnetic field and radiation anisotropy.
We find that the expected polarization signal, with a 180-degree period, exists
at all wavelengths out to radii of 1.5 arcminutes centered on the BNKL object
in OMC-1. The probabilities that these signals would occur due to random noise
are low ($\lesssim$1\%), and are lowest towards BNKL compared to the rest of
the cloud. Additionally, the relative magnetic field to radiation anisotropy
directions accord with theoretical predictions in that they agree to better
than 15 degrees at $100\,\mu$m and 4 degrees at $350\,\mu$m.",1509.08542v1
2015-10-15,Rashba Torque Driven Domain Wall Motion in Magnetic Helices,"Manipulation of the domain wall propagation in magnetic wires is a key
practical task for a number of devices including racetrack memory and magnetic
logic. Recently, curvilinear effects emerged as an efficient mean to impact
substantially the statics and dynamics of magnetic textures. Here, we
demonstrate that the curvilinear form of the exchange interaction of a magnetic
helix results in an effective anisotropy term and Dzyaloshinskii--Moriya
interaction with a complete set of Lifshitz invariants for a one-dimensional
system. In contrast to their planar counterparts, the geometrically induced
modifications of the static magnetic texture of the domain walls in magnetic
helices offer unconventional means to control the wall dynamics relying on
spin-orbit Rashba torque. The chiral symmetry breaking due to the
Dzyaloshinskii-Moriya interaction leads to the opposite directions of the
domain wall motion in left- or right-handed helices. Furthermore, for the
magnetic helices, the emergent effective anisotropy term and
Dzyaloshinskii-Moriya interaction can be attributed to the clear geometrical
parameters like curvature and torsion offering intuitive understanding of the
complex curvilinear effects in magnetism.",1510.04725v2
2016-07-14,Spin-orbit Misalignment as a Driver of the Kepler Dichotomy,"During its 5 year mission, the Kepler spacecraft has uncovered a diverse
population of planetary systems with orbital configurations ranging from
single-transiting planets to systems of multiple planets co-transiting the
parent star. By comparing the relative occurrences of multiple to
single-transiting systems, recent analyses have revealed a significant
over-abundance of singles. Dubbed the ""Kepler Dichotomy,"" this feature has been
interpreted as evidence for two separate populations of planetary systems: one
where all orbits are confined to a single plane, and a second where the
constituent planetary orbits possess significant mutual inclinations, allowing
only a single member to be observed in transit at a given epoch. In this work,
we demonstrate that stellar obliquity, excited within the disk-hosting stage,
can explain this dichotomy. Young stars rotate rapidly, generating a
significant quadrupole moment which torques the planetary orbits, with inner
planets influenced more strongly. Given nominal parameters, this torque is
sufficiently strong to excite significant mutual inclinations between planets,
enhancing the number of single-transiting planets, sometimes through a
dynamical instability. Furthermore, as hot stars appear to possess
systematically higher obliquities, we predict that single-transiting systems
should be relatively more prevalent around more massive stars. We analyze the
Kepler data and confirm this signal to be present.",1607.03999v1
2017-12-06,Angular momentum transport by heat-driven g-modes in slowly pulsating B stars,"Motivated by recent interest in the phenomenon of waves transport in massive
stars, we examine whether the heat-driven gravity (g) modes excited in
slowly-pulsating B (SPB) stars can significantly modify the stars' internal
rotation. We develop a formalism for the differential torque exerted by g
modes, and implement this formalism using the GYRE oscillation code and the
MESASTAR stellar evolution code. Focusing first on a $4.21$ $M_\odot$ model, we
simulate 1,000 years of stellar evolution under the combined effects of the
torque due to a single unstable prograde g mode (with an amplitude chosen on
the basis of observational constraints), and diffusive angular momentum
transport due to convection, overshooting, and rotational instabilities.
  We find that the g mode rapidly extracts angular momentum from the surface
layers, depositing it deeper in the stellar interior. The angular momentum
transport is so efficient that by the end of the simulation the initially
non-rotating surface layers are spun in the retrograde direction to
$\approx30\%$ of the critical rate. However, the additional inclusion of
magnetic stresses in our simulations, almost completely inhibits this spin-up.
  Expanding our simulations to cover the whole instability strip, we show that
the same general behavior is seen in all SPB stars. After providing some
caveats to contextualize our results, we hypothesize that the observed slower
surface rotation of SPB stars (as compared to other B-type stars) may be the
direct consequence of the angular momentum transport that our simulations
demonstrate.",1712.02420v1
2018-03-16,"Turbulence, Accretion Braking Torques and Efficient Jets Without Magnetocentrifugal Acceleration: Core Concepts","I discuss three mutually-supportive notions or assumptions regarding jets and
accretion. The first is magnetocentrifugal acceleration (MCA), the
overwhelmingly favored mechanism for the production of jets in most steady
accreting systems. The second is the zero-torque inner boundary condition. The
third is that effective viscous dissipation is like real dissipation, leading
directly to heating. All three assumptions fit nicely together in a manner that
is simple, persuasive, and mutually-consistent. All, I argue, are incorrect.
For concreteness I focus on protostars. Magnetohydrodynamic (MHD) turbulence in
accretion is not a sink of energy, but a reservoir, capable of doing mechanical
work directly and therefore efficiently, rather than solely through ohmic
(""viscous"") heating. Advection of turbulence energy reduces the effective
radiative efficiency, and may help solve the missing boundary-layer emission
problem. The angular momentum problem, whereby accretion spins up a protostar
to breakup, is resolved by allowing direct viscous coupling to the protostar,
permitting substantially greater energy to be deposited into the accretion flow
than otherwise possible. This goes not into heat, but into a turbulent,
tangled, buoyant toroidal magnetic field. I argue that there is neither an
angular momentum problem nor an efficiency problem that MCA is needed to solve.
Moreover, the turbulent magnetic field has ample ability not just to collimate
but to accelerate gas, first radially inwards through tension forces and then
vertically through pressure forces, without any MCA mechanism. I suggest then
that jets, particularly the most powerful and well-collimated protostellar
jets, are not magnetocentrifugally driven.",1803.06094v1
2017-05-13,Spin-down evolution and radio disappearance of the magnetar PSR J1622$-$4950,"We report on 2.4 yr of radio timing measurements of the magnetar PSR
J1622$-$4950 using the Parkes telescope, between 2011 November and 2014 March.
During this period the torque on the neutron star (inferred from the rotational
frequency derivative) varied greatly, though much less erratically than in the
2 yr following its discovery in 2009. During the last year of our measurements
the frequency derivative decreased in magnitude monotonically by 20\%, to a
value of $-1.3\times10^{-13}$ s$^{-2}$, a factor of 8 smaller than when
discovered. The flux density continued to vary greatly during our monitoring
through 2014 March, reaching a relatively steady low level after late 2012. The
pulse profile varied secularly on a similar timescale as the flux density and
torque. A relatively rapid transition in all three properties is evident in
early 2013. After PSR J1622$-$4950 was detected in all of our 87 observations
up to 2014 March, we did not detect the magnetar in our resumed monitoring
starting in 2015 January and have not detected it in any of the 30 observations
done through 2016 September.",1705.04899v1
2017-10-10,A binary main belt comet,"The asteroids are primitive solar system bodies which evolve both
collisionally and through disruptions due to rapid rotation [1]. These
processes can lead to the formation of binary asteroids [2-4] and to the
release of dust [5], both directly and, in some cases, through uncovering
frozen volatiles. In a sub-set of the asteroids called main-belt comets (MBCs),
the sublimation of excavated volatiles causes transient comet-like activity
[6-8]. Torques exerted by sublimation measurably influence the spin rates of
active comets [9] and might lead to the splitting of bilobate comet nuclei
[10]. The kilometer-sized main-belt asteroid 288P (300163) showed activity for
several months around its perihelion 2011 [11], suspected to be sustained by
the sublimation of water ice [12] and supported by rapid rotation [13], while
at least one component rotates slowly with a period of 16 hours [14]. 288P is
part of a young family of at least 11 asteroids that formed from a ~10km
diameter precursor during a shattering collision 7.5 million years ago [15].
Here we report that 288P is a binary main-belt comet. It is different from the
known asteroid binaries for its combination of wide separation, near-equal
component size, high eccentricity, and comet-like activity. The observations
also provide strong support for sublimation as the driver of activity in 288P
and show that sublimation torques may play a significant role in binary orbit
evolution.",1710.03454v1
2020-11-03,The Formation of Bilobate Comet Shapes through Sublimative Torques,"Recent spacecraft and radar observations have found that ~70 percent of
short-period comet nuclei, mostly Jupiter-family comets (JFCs), have bilobate
shapes (two masses connected by a narrow neck). This is in stark contrast to
the shapes of asteroids of similar sizes, of which ~14% are bilobate. This
suggests that a process or mechanism unique to comets is producing these
shapes. Here we show that the bilobate shapes of JFC nuclei are a natural
byproduct of sublimative activity during their dynamical migration from their
trans-Neptunian reservoir, through the Centaur population, and into the Jupiter
family. We model the torques resulting from volatile sublimation during this
dynamical migration and find that they tend to spin up these nuclei to
disruption. Once disrupted, the rubble pile-like material properties of comet
nuclei (tensile strengths of ~1-10 Pa and internal friction angles of
~35$^\circ$) cause them to reform as bilobate objects. We find that JFCs likely
experienced rotational disruption events prior to entering the Jupiter family,
which could explain the prevalence of bilobate shapes. These results suggest
that the bilobate shapes of observed comets developed recently in their history
(within the past ~1-10 Myr), rather than during solar system formation or
collisions during planet migration and residency in the trans-Neptunian
population.",2011.01394v1
2021-08-16,Drag and lift forces on a rigid sphere immersed in a wall-bounded linear shear flow,"We report on a series of fully resolved simulations of the flow around a
rigid sphere translating steadily near a wall, either in a fluid at rest or in
the presence of a uniform shear. Non-rotating and freely rotating spheres
subject to a torque-free condition are both considered to evaluate the
importance of spin-induced effects. The separation distance between the sphere
and wall is varied from values at which the wall influence is weak down to gaps
of half the sphere radius. The Reynolds number based on the sphere diameter and
relative velocity with respect to the ambient fluid spans the range $0.1-250$,
and the relative shear rate defined as the ratio of the shear-induced velocity
variation across the sphere to the relative velocity is varied from $-0.5$ to
$+0.5$, so that the sphere either leads the fluid or lags behind it. The
wall-induced interaction mechanisms at play in the various flow regimes are
analyzed qualitatively by examining the flow structure, especially the spanwise
and streamwise vorticity distributions. Variations of the drag and lift forces
at low-but-finite and moderate Reynolds number are compared with available
analytical and semiempirical expressions, respectively. In more inertial
regimes, empirical expressions for the two force components are derived based
on the numerical data, yielding accurate fits valid over a wide range of
Reynolds number and wall-sphere separations for both non-rotating and
torque-free spheres.",2108.07196v1
2019-09-04,Disintegrating In-Bound Long-Period Comet C/2019 J2,"We present observations of the disintegrating long-period comet C/2019 J2
(Palomar) taken to determine the nature of the object and the cause of its
demise. The data are consistent with break-up of a sub-kilometer nucleus into a
debris cloud of mass or order 1e9 kg, peaking on UT 2019 May 24+/-$12. This is
56 days before perihelion and at a heliocentric distance of 1.9 AU. We consider
potential mechanisms of disintegration. Tidal disruption is ruled-out, because
the comet has not passed within the Roche sphere of any planet. Impact
disruption is implausible, because the comet orbit is highly inclined
(inclination 105.1 deg) and disruption occurred far above the ecliptic, where
asteroids are rare. The back-pressure generated by sublimation (0.02 to 0.4
N/m2) is orders of magnitude smaller than the reported compressive strength (30
to 150 N/m2) of cometary material and, therefore, is of no importance. The
depletion of volatiles by sublimation occurs too slowly to render the nucleus
inactive on the timescale of infall. However, we find that the e-folding
timescale for spin-up of the nucleus by the action of sublimation torques is
shorter than the infall time, provided the nucleus radius is smaller than 0.4
km. Thus, the disintegration of C/2019 J2 is tentatively interpreted as the
rotational disruption of a sub-kilometer nucleus caused by outgassing torques.",1909.01964v1
2019-10-31,Magnetar birth: rotation rates and gravitational-wave emission,"Understanding the evolution of the angle $\chi$ between a magnetar's rotation
and magnetic axes sheds light on the star's birth properties. This evolution is
coupled with that of the stellar rotation $\Omega$, and depends on the
competing effects of internal viscous dissipation and external torques. We
study this coupled evolution for a model magnetar with a strong internal
toroidal field, extending previous work by modelling -- for the first time in
this context -- the strong proto-magnetar wind acting shortly after birth. We
also account for the effect of buoyancy forces on viscous dissipation at late
times. Typically we find that $\chi\to 90^\circ$ shortly after birth, then
decreases towards $0^\circ$ over hundreds of years. From observational
indications that magnetars typically have small $\chi$, we infer that these
stars are subject to a stronger average exterior torque than radio pulsars, and
that they were born spinning faster than $\sim 100-300$ Hz. Our results allow
us to make quantitative predictions for the gravitational and electromagnetic
signals from a newborn rotating magnetar. We also comment briefly on the
possible connection with periodic Fast Radio Burst sources.",1910.14336v2
2020-02-11,Precessing flaring magnetar as a source of repeating FRB 180916.J0158+65,"Recently, CHIME detected periodicity in the bursting rate of the repeating
FRB 180916.J0158+65. In a popular class of models, the fast radio bursts (FRBs)
are created by giant magnetic flares of a hyper-active magnetar driven by fast
ambipolar diffusion in the core. We point out that in this scenario the
magnetar is expected to precess freely with a period of hours to weeks. The
internal magnetic field $B\sim 10^{16}$G deforms the star, and magnetic flares
induce sudden changes in magnetic stresses. The resulting torques and
displacements of the principal axes of inertia are capable of pumping a
significant amplitude of precession. The anisotropy of the flaring FRB
activity, combined with precession, implies a strong periodic modulation of the
visible bursting rate. The ultra-strong field invoked in the magnetar model
provides: (1) energy for the frequent giant flares, (2) the high rate of
ambipolar diffusion, releasing the magnetic energy on the timescale $\sim
10^9$s, (3) the core temperature $T\approx 10^9$K, likely above the critical
temperature for neutron superfluidity, (4) strong magnetospheric torques, which
efficiently spin down the star, and (5) deformation with ellipticity $\epsilon>
10^{-6}$, much greater than the rotational deformation. These conditions result
in a precession with negligible viscous damping, and can explain the observed
16 day period in FRB 180916.J0158+65.",2002.04595v2
2020-07-09,Broadband X-ray characteristics of the transient pulsar GRO J2058+42,"The Be X-ray binary GRO J2058+42 recently went through a Type-II outburst
during March-April 2019 lasting for about 50 days. This outburst was detected
with the operating all sky X-ray monitors like the Fermi-GBM, Swift-BAT and
MAXI-GSC. Two NuSTAR observations were also made, one during the rise and other
during the decay of the outburst. It gave us the unique opportunity to analyze
the broadband characteristics of the pulsar for the first time and accretion
torque characteristics of the pulsar over a range of X-ray luminosity. The
pulse profiles are strongly energy dependent, with at least four different
pulse components at low energy (< 20 keV) which evolves to a single-peaked
profile at high energy (> 30 keV). In each of the narrow energy bands, the
pulse profiles are nearly identical in the two NuSTAR observations. The spectra
from both the observations are fitted well to a power-law with a Fermi-Dirac
type high energy cutoff. We ruled out presence of a cyclotron line in the pulse
phase averaged X-ray spectrum in the NuSTAR band with an optical depth greater
than 0.15. An iron emission line is detected in both the NuSTAR spectra with an
equivalent width of about 125 eV. We looked at the dependence of the spin-up
rate on the luminosity and estimated the magnetic field strength from that,
which came out to be much higher compared to other known BeXRB pulsars. Lastly,
we discussed the inadequacy of the torque-luminosity relation for determination
of magnetic field strength of neutron stars.",2007.04519v1
2022-02-15,Investigation of the magnetoelastic coupling anisotropy in the Kitaev material $α$-RuCl$_3$,"The Kitaev material $\alpha$-RuCl$_3$ is among the most prominent candidates
to host a quantum spin-liquid state endowed with fractionalized excitations.
Recent experimental and theoretical investigations have separately revealed the
importance of both the magnetoelastic coupling and the magnetic anisotropy, in
dependence of the applied magnetic field direction. In this combined
theoretical and experimental research, we investigate the anisotropic magnetic
and magnetoelastic properties for magnetic fields applied along the main
crystallographic axes as well as for fields canted out of the honeycomb plane.
We found that the magnetostriction anisotropy is unusually large compared to
the anisotropy of the magnetization, which is related to the strong
magnetoelastic $\widetilde{\Gamma'}$-type coupling in our \textit{ab-initio}
derived model. We observed large, non-symmetric magnetic anisotropy for
magnetic fields canted out of the honeycomb $ab$-plane in opposite directions,
namely towards the $+c^*$ or $-c^*$ axes, respectively. The observed
directional anisotropy is explained by considering the relative orientation of
the magnetic field with respect to the co-aligned RuCl$_6$ octahedra.
Magnetostriction measurements in canted fields support this non-symmetric
magnetic anisotropy, however these experiments are affected by magnetic torque
effects. Comparison of theoretical predictions with experimental findings allow
us to recognize the significant contribution of torque effects in experimental
setups where $\alpha$-RuCl$_3$ is placed in canted magnetic fields.",2202.07102v1
2022-10-10,Non-synchronous rotation on Europa driven by ocean currents,"It has been suggested that the ice shell of Jupiter's moon Europa may drift
non-synchronously due to tidal torques. Here we argue that torques applied by
the underlying ocean are also important and can result in non-synchronous
rotation (NSR). The resulting spin rate can be slightly slower than the
synchronous angular rate that would have kept the same point of the ice shell
facing Jupiter. We develop an ice shell rotation model, driven by ocean stress
calculated using a high-resolution state-of-the-art ocean general circulation
model, and take into account the viscoelastic deformation of the ice shell. We
use the ice shell model results together with observed limits on the ice shell
drift speed to constrain ice shell parameters such as effective viscosity,
which is currently uncertain by at least four orders of magnitude. Our results
suggest, at best, sluggish ice shell convection. Depending on the relaxation
time scale of the ice shell and on the ocean currents, the ice shell may
exhibit negligible drift, constant drift, or oscillatory drift superimposed on
random fluctuations. The expected rotation rate exceeds $\sim$30~m/yr; future
spacecraft observations can be used to test these predictions and yield insight
into the properties of the ice shell and underlying ocean.",2210.04961v3
2022-11-30,The Cosmic Neutrino Background on the Surface of the Earth,"We argue that the reflection of relic neutrinos from the surface of the Earth
results in a significant local $\nu-\bar{\nu}$ asymmetry, far exceeding the
expected primordial lepton asymmetry. The net fractional electron neutrino
number $\frac{n_{\nu_e}-n_{\bar{\nu}_e}}{n_{\nu_e}}$ is up to
$\mathcal{O}(10^5) \sqrt{\frac{m_\nu}{0.1~\text{eV}}}$ larger than that implied
by the baryon asymmetry. This enhancement is due to the weak 4-Fermi repulsion
of the $\nu_e$ from ordinary matter which slows down the $\nu_e$ near the
Earth's surface, and to the resulting evanescent neutrino wave that penetrates
below the surface. This repulsion thus creates a net $\nu_e$ overdensity in a
shell $\sim 7~\text{meters} \sqrt{\frac{0.1~\text{eV}}{m_\nu}}$ thick around
the Earth's surface. Similarly the repulsion between $\bar{\nu}_\mu$ or
$\bar{\nu}_\tau$ and ordinary matter creates an overdensity of $\bar{\nu}_{\mu,
\tau}$ of similar size. These local enhancements increase the size of
$\mathcal{O}(G_F)$ torques of the $C\nu B$ on spin-polarized matter by a factor
of order $10^5$. In addition, they create a gradient of the net neutrino
density which naturally provides a way out of the forty-year-old ``no-go''
theorems on the vanishing of $\mathcal{O}(G_F)$ forces. The torque resulting
from such a gradient force can be $10^8$ times larger than that of earlier
proposals. Although the size of these effects is still far from current reach,
they may point to new directions for $C\nu B$ detection.",2212.00036v2
2023-02-04,Flow past a sphere translating along the axis of a rotating fluid: Revisiting numerically Maxworthy's experiments,"We compute the flow induced by the steady translation of a rigid sphere along
the axis of a large cylindrical container filled with a low-viscosity fluid set
in rigid-body rotation, the sphere being constrained to spin at the same rate
as the undisturbed fluid. The parameter range covered by the simulations is
similar to that explored experimentally by Maxworthy [\textit{J. Fluid Mech.},
vol. 40, pp. 453-479 (1970)]. We describe the salient features of the flow,
especially the internal characteristics of the Taylor columns that form ahead
of and behind the body and the inertial wave pattern, and determine the drag
and torque acting on the sphere. Torque variations are found to obey two
markedly different laws under rapid- and slow-rotation conditions,
respectively. The corresponding scaling laws are predicted by examining the
dominant balances governing the axial vorticity distribution in the body
vicinity. Results for the drag agree well with the semi-empirical law proposed
for inertialess regimes by Tanzosh \& Stone [\textit{J. Fluid Mech.}, vol. 275,
pp. 225-256 (1994)]. This law is found to apply even in regimes where inertial
effects are large, provided rotation effects are also large enough. Influence
of axial confinement is shown to increase dramatically the drag in rapidly
rotating configurations, and the container length has to be approximately a
thousand times larger than the sphere for this influence to become negligibly
small. The reported simulations establish that this confinement effect is at
the origin of the long-standing discrepancy existing between Maxworthy's
results and theoretical predictions.",2302.02129v2
2023-04-18,Anomalous impact of thermal fluctuations on spintransfer torque induced ferrimagnetic switching,"The dynamics of a spin torque driven ferrimagnetic (FiM) system is
investigated using the two-sublattice macrospin model. We demonstrate an
ultrafast switching in the picosecond range. However, we find that the
excessive current leads to the magnetic oscillation. Therefore, faster
switching cannot be achieved by unlimitedly increasing the current. By
systematically studying the impact of thermal fluctuations, we find the
dynamics of FiMs can also be distinguished into the precessional region, the
thermally activated region, and the cross-over region. However, in the
precessional region, there is a significant deviation between FiM and
ferromagnet (FM), i.e., the FM is insensitive to thermal fluctuations since its
switching is only determined by the amount of net charge. In contrast, we find
that the thermal effect is pronounced even a very short current pulse is
applied to the FiM. We attribute this anomalous effect to the complex relation
between the anisotropy and overdrive current. By controlling the magnetic
anisotropy, we demonstrate that the FiM can also be configured to be
insensitive to thermal fluctuations. This controllable thermal property makes
the FiM promising in many emerging applications such as the implementation of
tunable activation functions in the neuromorphic computing.",2304.08765v1
2023-06-21,"Tidal heating and torquing of the primary black hole in eccentric-orbit, non-spinning extreme-mass-ratio inspirals to 22PN order","We calculate the high-order post-Newtonian (PN) expansion of the energy and
angular momentum fluxes onto the horizon of a nonspinning black hole primary in
eccentric-orbit extreme-mass-ratio inspirals. The first-order black hole
perturbation theory calculation uses \textsc{Mathematica} and makes an analytic
expansion of the Regge-Wheeler-Zerilli functions using the Mano-Suzuki-Takasugi
formalism. The horizon absorption, or tidal heating and torquing, is calculated
to 18PN relative to the leading horizon flux (i.e., 22PN order relative to the
leading quadrupole flux at infinity). Each PN term is a function of
eccentricity $e$ and is calculated as a series to $e^{10}$. A second expansion,
to 10PN horizon-relative order (or 14PN relative to the flux at infinity), is
computed deeper in eccentricity to $e^{20}$. A number of resummed closed-form
functions are found for the low PN terms in the series. Using a separate
Teukolsky perturbation code, numerical comparisons are made to test how
accurate the PN expansion is when extended to a close $p=10$ orbit. We find
that the horizon absorption expansion is not as convergent as a previously
computed infinity-side flux expansion. However, given that the horizon
absorption is suppressed by 4PN, useful results can be obtained even with an
orbit as tight as this for $e \le 1/2$. Combining the present results with our
earlier expansion of the fluxes to infinity makes the knowledge of the total
dissipation known to 19PN for eccentric-orbit nonspinning EMRIs.",2306.12481v1
2024-02-29,Probing AGN jet precession with LISA,"The precession of astrophysical jets produced by active-galactic nuclei is
likely related to the dynamics of the accretion disks surrounding the central
supermassive black holes (BHs) from which jets are launched. The two main
mechanisms that can drive jet precession arise from Lense-Thirring precession
and tidal torquing. These can explain direct and indirect observations of
precessing jets; however, such explanations often utilize crude approximations
of the disk evolution and observing jet precession can be challenging with
electromagnetic facilities. Simultaneously, the Laser Interferometer Space
Antenna (LISA) is expected to measure gravitational waves from the mergers of
massive binary BHs with high accuracy and probe their progenitor evolution. In
this paper, we connect the LISA detectability of binary BH mergers to the
possible jet precession during their progenitor evolution. We make use of a
semi-analytic model that self-consistently treats disk-driven BH alignment and
binary inspiral and includes the possibility of disk breaking. We find that
tidal torquing of the accretion disk provides a wide range of jet precession
timescales depending on the binary separation and the spin direction of the BH
from which the jet is launched. Efficient disk-driven BH alignment results in
shorter timescales of $\sim 1$ yr which are correlated with higher LISA
signal-to-noise ratios. Disk breaking results in the longest possible times of
$\sim 10^7$ yrs, suggesting a deep interplay between the disk critical
obliquity (i.e. where the disk breaks) and jet precession. Studies such as ours
will help to reveal the cosmic population of precessing jets that are
detectable with gravitational waves.",2403.00066v1
2019-11-15,Optical vortex torque measured with optically trapped microbarbells,"Optical vortex beams carry orbital angular momentum and thus exert torque on
illuminated objects. A dielectric microtool - a microbarbell - is used in a
two-laser optical tweezers to measure the torque of a focused optical vortex.
The tool was either freely rotating due to the applied torque or set into
oscillations by the counteracting force. Four different trapping configurations
provided different ways of sensing the torque and gave consistent results. The
value of torque was determined by confronting the experimental results with
numerical and analytical models.",1911.06749v1
2006-10-10,Spin-transfer in an open ferromagnetic layer: from negative damping to effective temperature,"Spin-transfer is a typical spintronics effect that allows a ferromagnetic
layer to be switched by spin-injection. Most of the experimental results about
spin transfer are described on the basis of the Landau-Lifshitz-Gilbert
equation of the magnetization, in which additional current-dependent damping
factors are added, and can be positive or negative. The origin of the damping
can be investigated further by performing stochastic experiments, like one shot
relaxation experiments under spin-injection in the activation regime of the
magnetization. In this regime, the N\'eel-Brown activation law is observed
which leads to the introduction of a current-dependent effective temperature.
In order to justify the introduction of these counterintuitive parameters
(effective temperature and negative damping), a detailed thermokinetic analysis
of the different sub-systems involved is performed. We propose a thermokinetic
description of the different forms of energy exchanged between the electric and
the ferromagnetic sub-systems at a Normal/Ferromagnetic junction. The
corresponding Fokker Planck equations, including relaxations, are derived. The
damping coefficients are studied in terms of Onsager-Casimir transport
coefficients, with the help of the reciprocity relations. The effective
temperature is deduced in the activation regime.",0610264v1
2007-09-18,Full counting statistics of spin transfer through ultrasmall quantum dots,"We analyze the spin-resolved full counting statistics of electron transfer
through an ultrasmall quantum dot coupled to metallic electrodes. Modelling the
setup by the Anderson Hamiltonian, we explicitly take into account the onsite
Coulomb repulsion $U$. We calculate the cumulant generating function for the
probability to transfer a certain number of electrons with a preselected spin
orientation during a fixed time interval. With the cumulant generating function
at hand we are then able to calculate the spin current correlations which are
of outmost importance in the emerging field of spintronics. We confirm the
existing results for the charge statistics and report the discovery of the new
type of correlation between the spin-up and -down polarized electrons flows,
which has a potential to become a powerful new instrument for the investigation
of the Kondo effect in nanostructures.",0709.2779v1
2009-06-12,Spacetime constraints on accreting black holes,"We study the spin dependence of accretion onto rotating Kerr black holes
using analytic techniques. In its linear regime, angular momentum transport in
MHD turbulent accretion flow involves the generation of radial magnetic field
connecting plasma in a differentially rotating flow. We take a first principles
approach, highlighting the constraint that limits the generation and
amplification of radial magnetic fields, stemming from the transfer of energy
from mechanical to magnetic form. Because the energy transferred in magnetic
form is ultimately constrained by gravitational potential energy or Killing
energy, the spin-dependence of the latter allows us to derive spin-dependent
constraints on the success of the accreting plasma to expel its angular
momentum and accrete. We find an inverse relationship between this ability and
black hole spin. If this radial magnetic field generation forms the basis for
angular momentum transfer in accretion flows, accretion rates involving Kerr
black holes are expected to be lower as the black hole spin increases in the
prograde sense.",0906.2398v1
2013-08-08,Dynamics of a two-level system under the simultaneous influence of a spin bath and a boson bath,"We study dynamics of a two-level system coupled simultaneously to a pair of
dissimilar reservoirs, namely, a spin bath and a boson bath, which are
connected via finite interbath coupling. It is found that the steady-state
energy transfer in the two-level system increases with its coupling to the spin
bath while optimal transfer occurs at intermediate coupling in the transient
process. If the two-level system is strongly coupled to the spin bath, the
population transfer is unidirectional barring minor population oscillations of
minute amplitudes. If the spin bath is viewed as an atomic ensemble, robust
generation of macroscopic superposition states exists against parameter
variations of the two-level system and the boson bath.",1308.1764v1
2013-12-02,Optimized quantum state transfer through an XY spin chain,"Quantum state transfer along a one-dimensional spin chain has become a
fundamental ingredient for quantum communication between distant nodes in a
quantum network. We study the average fidelity of quantum state transfer (QST)
along a XY spin chain by adjusting the basis identification between the first
spin and the last spin. In a proper choice of the basis identification, we find
that the QST fidelity depends only on the average parity of the initial state
linearly. We propose a simple scheme to adjusting the basis identification to
optimize the average fidelity such that it depends linearly on the absolute
value of the average parity. In the case that the absolute value of the average
parity is $1$ we prove that the fidelity takes the maximum at any time over
arbitrary initial state and basis identification.",1312.0360v2
2017-11-06,Low field nuclear polarization using Nitrogen Vacancy centers in diamonds,"It was recently demonstrated that bulk nuclear polarization can be obtained
using Nitrogen Vacancy (NV) color centers in diamonds, even at ambient
conditions. This is based on the optical polarization of the NV electron spin,
and using several polarization transfer methods. One such method is the NOVEL
sequence, where a spin-locked sequence is applied on the NV spin, with a
microwave power equal to the nuclear precession frequency. This was performed
at relatively high fields, to allow for both polarization transfer and noise
decoupling. As a result, this scheme requires accurate magnetic field alignment
in order preserve the NV properties. Such a requirement may be undesired or
impractical in many practical scenareios. Here we present a new sequence,
termed the refocused NOVEL, which can be used for polarization transfer (and
detection) even at low fields. Numerical simulations are performed, taking into
account both the spin Hamiltonian and spin-decoherence, and we show that, under
realistic parameters, it can outperform the NOVEL sequence.",1711.01802v1
2017-06-26,Quantum State Transfer from a Single Photon to a Distant Quantum-Dot Electron Spin,"Quantum state transfer from flying photons to stationary matter qubits is an
important element in the realization of quantum networks. Self-assembled
semiconductor quantum dots provide a promising solid-state platform hosting
both single photon and spin, with an inherent light-matter interface. Here, we
develop a method to coherently and actively control the single-photon frequency
bins in superposition using electro-optic modulators, and measure the
spin-photon entanglement with a fidelity of $0.796\pm0.020$. Further, by
Greenberger-Horne-Zeilinger-type state projection on the frequency, path and
polarization degrees of freedom of a single photon, we demonstrate quantum
state transfer from a single photon to a single electron spin confined in an
InGaAs quantum dot, separated by 5 meters. The quantum state mapping from the
photon's polarization to the electron's spin is demonstrated along three
different axis on the Bloch sphere, with an average fidelity of $78.5\%$.",1706.08242v1
2020-11-10,Shortcuts to Dynamic Polarization,"Dynamic polarization protocols aim to hyperpolarize a spin bath by
transferring spin polarization from a well-controlled qubit such as a quantum
dot or a color defect. Building on techniques from shortcuts to adiabaticity,
we design fast and efficient dynamic polarization protocols in central spin
models that apply to dipolarly interacting systems. The protocols maximize the
transfer of polarization via bright states at a nearby integrable point,
exploit the integrability-breaking terms to reduce the statistical weight on
dark states that do not transfer polarization, and realize experimentally
accessible local counterdiabatic driving through Floquet-engineering. A master
equation treatment suggests that the protocol duration scales linearly with the
number of bath spins with a prefactor that can be orders of magnitude smaller
than that of unassisted protocols. This work opens new pathways to cool spin
baths and extend qubit coherence times for applications in quantum information
processing and metrology.",2011.05349v2
2022-01-17,Longitudinal Spin Transfer to $Λ$ Hyperons in CLAS12,"Using the self-analyzing decay of the $\Lambda$, the longitudinal spin
transfer $D_{LL'}$ to the hyperon from a polarized electron beam scattering off
an unpolarized proton target can be determined. For $\Lambda$s produced in the
current fragmentation region, this quantity is proportional to the helicity
dependent fragmentation function $G_1^\Lambda$ and can provide insight into the
spin structure of the $\Lambda$. Currently, limited experimental data on
$D_{LL'}$ cannot discriminate between different models of $\Lambda$ spin
structure. This contribution reports on the status of the ongoing analysis of
the longitudinal spin transfer using data taken by the CLAS12 spectrometer at
Jefferson Lab with a 10.6 GeV polarized electron beam. We also report on the
novel use of Graph Neural Networks (GNNs) to identify signal events.",2201.06480v1
2004-02-20,Spin observables in the $NN\to YΘ^+$ reaction at the threshold and quantum numbers of the $Θ^+$ pentaquark,"General formulae for the spin-spin correlation parameters $C_{i,j}$ and
spin-transfer coefficients $K_i^j$ are derived for the reaction $N N\to Y
\Theta^+$ at the threshold for an arbitrary spin of the pentaquark $\Theta^+$.
It is shown that a measurement of the sign of $C_{y,y}$ or an observation of
the non-zero polarization transfer from the nucleon to the hyperon $Y$ allow
one to determine the P-parity of the $\Theta^+$ unambiguously and independently
on the spin of the $\Theta^+$.
  Measurement of these spin observables in the both $pp$- and $pn$- channels of
this reaction determines also the isospin of the $\Theta^+$.",0402216v1
2004-08-11,The Spin Interaction of a Dirac Particle in an Aharonov-Bohm Potential in First Order Scattering,"For a Dirac particle in an Aharonov-Bohm (AB) potential, it is shown that the
spin interaction (SI) operator which governs the transitions in the spin sector
of the first order S-matrix is related to one of the generators of rotation in
the spin space of the particle. This operator, which is given by the projection
of the spin operator $\mathbf{\Sigma}$ along the direction of the total
momentum of the system, and the two operators constructed from the projections
of the $\mathbf{\Sigma}$ operator along the momentum transfer and the
z-directions close the SU(2) algebra.It is suggested, then, that these two
directions of the total momentum and the momentum transfer form some sort of
natural intrinsic directions in terms of which the spin dynamics of the
scattering process at first order can be formulated conveniently. A formulation
and an interpretation of the conservation of helicity at first order using the
spin projection operators along these directions is presented .",0408093v2
2004-11-04,Analytical Bethe Ansatz for closed and open gl(n)-spin chains in any representation,"We present an ""algebraic treatment"" of the analytical Bethe Ansatz. For this
purpose, we introduce abstract monodromy and transfer matrices which provide an
algebraic framework for the analytical Bethe Ansatz. It allows us to deal with
a generic gl(n)-spin chain possessing on each site an arbitrary
gl(n)-representation. For open spin chains, we use the classification of the
reflection matrices to treat all the diagonal boundary cases. As a result, we
obtain the Bethe equations in their full generality for closed and open spin
chains. The classifications of finite dimensional irreducible representations
for the Yangian (closed spin chains) and for the reflection algebras (open spin
chains) are directly linked to the calculation of the transfer matrix
eigenvalues. As examples, we recover the usual closed and open spin chains, we
treat the alternating spin chains and the closed spin chain with impurity.",0411021v1
1994-07-01,"Relativistic treatment of spin-transfer observables in quasielastic $(\vec{\bf p},\vec{\bf n})$ scattering","We calculate all spin-transfer observables for the quasielastic
$(\vec{p},\vec{n})$ reaction in a relativistic plane-wave impulse
approximation. The nuclear-structure information is contained in a large set of
nuclear-response functions that are computed in nuclear matter using a
relativistic random-phase approximation to the Walecka model. A reduced value
of the nucleon mass in the medium induces important dynamical changes in the
residual isovector interaction relative to its nonrelativistic counterpart. As
a result, good agreement is found for all spin observables --- including the
spin-longitudinal to spin-transverse ratio --- when compared to the original
($q=1.72$~fm$^{-1}$) NTOF experiment. In contrast, the spin-longitudinal to
spin-transverse ratio is underpredicted at $q=1.2$~fm$^{-1}$ and overpredicted
at $q=2.5$~fm$^{-1}$. We comment on the role of distortions as a possible
solution to this discrepancy.",9407001v1
2003-05-13,Relations between bosonic quadrature squeezing and atomic spin squeezing,"We study relations between bosonic quadrature squeezing and atomic spin
squeezing, and find that the latter reduces to the former in the limit of a
large number of atoms for even and odd states. We demonstrate this reduction by
treating even and odd spin coherent states, for which analytical solutions are
readily obtained, and prove that even spin coherent states always exhibit spin
squeezing, whereas odd spin coherent states do not, analogous to the squeezing
characteristic of even and odd bosonic coherent states. Finally, we examine the
squeezing transfer between photons and atoms via the Dicke Hamiltonian, where a
perfect transfer of squeezing is demonstrated in the limit of a large number of
atoms.",0305066v2
2015-08-27,Localization and spin transport in honeycomb structures with spin-orbit coupling,"Transfer-matrix methods are used for a tight-binding description of electron
transport in graphene-like geometries, in the presence of spin-orbit couplings.
Application of finite-size scaling and phenomenological renormalization
techniques shows that, for strong enough spin-orbit interactions and increasing
on-site disorder, this system undergoes a metal-insulator transition
characterized by the exponents $\nu=2.71(8)$, $\eta=0.174(2)$. We show how one
can extract information regarding spin polarization decay with distance from an
injection edge, from the evolution of wave-function amplitudes in the
transfer-matrix approach. For (relatively weak) spin-orbit coupling intensity
$\mu$, we obtain that the characteristic length $\Lambda_s$ for
spin-polarization decay behaves as $\Lambda_s \propto \mu^{-2}$.",1508.06873v2
2016-04-05,Designing spin channel geometries for entanglement distribution,"We investigate different geometries of spin-1/2 nitrogen impurity channels
for distributing entanglement between pairs of remote nitrogen vacancy centers
(NVs) in diamond. To go beyond the system size limits imposed by directly
solving the master equation, we implement a matrix product operator method to
describe the open system dynamics. In so doing, we provide an early
demonstration of how this technique can be used for simulating real systems.
For a fixed NV separation there is an interplay between incoherent impurity
spin decay and coherent entanglement transfer: Long transfer time, few-spin
systems experience strong dephasing that can be overcome by increasing the
number of spins in the channel. We examine how missing spins and disorder in
the coupling strengths affect the dynamics, finding that in some regimes a spin
ladder is a more effective conduit for information than a single spin chain.",1604.01297v1
2016-05-13,Spin injection into multilayer graphene from highly spin-polarized Co2FeSi Heusler alloy,"We demonstrate electrical spin injection into multilayer graphene (MLG) in a
lateral spin valve device from a highly spin-polarized Co2FeSi (CFS) Huesler
electrode. Exfoliated MLG was transferred onto pre-patterned epitaxial CFS
wires grown on an Si(111) substrate by a polymer-based transfer method. This
method enabled us to fabricate multiple single-crystal CFS electrodes in
contact with MLG. Electrical spin injection from CFS to MLG was detected
through non-local magnetoresistance (MR) measurement. A non-local spin signal
of 430 ohm was observed; this is the largest value among all reported non-local
MR values in graphene-based devices.",1605.04213v1
2018-12-01,Quantitative quantum mechanical approach to SABRE hyperpolarization at high magnetic fields,"A theoretical approach is proposed for quantitative modeling of SABRE (Signal
Amplification By Reversible Exchange) experiments performed at a high magnetic
field of an NMR spectrometer. SABRE is a method, which exploits the spin order
of parahydrogen (the H$_2$ molecule in its nuclear singlet state) for
hyper-polarizing the spins of various substrates to enhance their NMR signals.
An important feature of SABRE is that the substrate is not modified chemically:
instead spin order transfer takes place in a transient complex with
parahydrogen. In high-field SABRE experiments, such a transfer is achieved by
using suitable NMR excitation schemes. The approach presented here can
explicitly treat the spin dynamics in the SABRE complex as well as the kinetics
of substrate exchange (between the free and bound form) and complex interplay
of spin evolution and chemical processes. One more important effect included in
the model is the alteration of the spin state of parahydrogen giving rise to
the formation of anti-phase spin order from the initial singlet order. Such a
treatment enables a detailed analysis of known high-field SABRE schemes,
quantitative comparison with experiments and elucidation of the key factors
that limit the resulting NMR signal enhancement.",1812.00206v1
2019-12-04,Role of charge transfer in hybridization-induced spin transition in metal-organic molecules,"The spin-crossover in organometallic molecules constitutes one of the most
promising routes towards the realization of molecular spintronic devices. In
this article, we explore the hybridization-induced spin-crossover in
metal-organic complexes. We propose a minimal many-body model that captures the
essence of the spin-state switching in a generic parameter space, thus
providing insight into the underlying physics. Combining the model with density
functional theory (DFT), we then study the spin-crossover in isomeric
structures of Ni-porphyrin (Ni-TPP). We show that metal-ligand charge transfer
plays a crucial role in the determination of the spin-state in Ni-TPP. Finally,
we propose a spin-crossover mechanism based on mechanical strain, which does
not require a switch between isomeric structures.",1912.01951v1
2021-11-15,Phase diagram and post-quench dynamics in a double spin-chain system in transverse fields,"We propose and explore the physics of a toy multiferroic model by coupling
two distinct dipolar XXZ models in transverse fields. We determine first the
rich ground-state phase diagram of the model using density matrix
renormalization group techniques. Then, we explore the dynamics of the system
after global and local quenches, using the time-evolving block decimation
algorithm. After a global quench, the system displays decaying coupled
oscillations of the electric and magnetic spins, in agreement with the
Eigenstate Thermalization Hypothesis (ETH) for many-body interacting quantum
systems. Notably, the spin-spin interactions lead to a sizeable quadratic shift
in the oscillation frequency as the inter-chain coupling is increased. Local
quenches lead to a light-cone-like propagation of excitations. In this case,
the inter-chain coupling drives a transfer of energy between the chains that
generates a novel fast spin-wave mode along the 'magnetic' chain at the speed
of the 'electric' spin-wave. This suggests a limited control mechanism for
faster information transfer in magnetic spin chains using electric fields that
harnesses the electric dipoles as intermediaries.",2111.07831v1
2022-03-28,Stable mass transfer can explain massive binary black hole mergers with a high spin component,"Recent gravitational wave observations showed that binary black hole (BBH)
mergers with massive components are more likely to have high effective spins.
In the model of isolated binary evolution, BH spins mainly originate from the
angular momenta of the collapsing cores before BH formation. Both observations
and theories indicate that BHs tend to possess relatively low spins, the origin
of fast-spinning BHs remains a puzzle. We investigate an alternative process
that stable Case A mass transfer may significantly increase BH spins during the
evolution of massive BH binaries. We present detailed binary evolution
calculations and find that this process can explain observed high spins of some
massive BBH mergers under the assumption of mildly super-Eddington accretion.",2203.14529v1
2022-12-22,Hybrid Magnonic-Oscillator System,"We propose a hybrid magnonic-oscillator system based on the combination of a
spin transfer auto-oscillator and a magnonic waveguide to open new perspectives
for spin-wave based circuits. The system is composed of a spin transfer
oscillator based on a vortex state which is dipolarly coupled to a nanoscale
spin-wave waveguide with longitudinal magnetization. In its auto-oscillating
regime, the oscillator emits coherent spin waves with tunable and controllable
frequencies, directions and amplitudes into the waveguide. We demonstrate the
principle of this method using micromagnetic simulations and show that
reconfiguration of the system is possible by changing the chirality and
polarity of the magnetic vortex. Spin waves are emitted into the waveguide with
high non-reciprocity and the preferred direction depends on the core polarity
of the vortex. In contrast, different vortex chiralities lead to different
amplitudes of the emitted waves. Our findings open up a novel way to design an
agile spintronic device for the coherent and tunable generation of propagating
spin waves.",2212.11532v1
2003-04-22,Optical spin transfer in ferromagnetic semiconductors,"Circularly polarized laser pulses that excite electron-hole pairs across the
band gap of (III,Mn)V ferromagnetic semiconductors can be used to manipulate
and to study collective magnetization dynamics. The initial spin orientation of
a photocarrier in a (III,V) semiconductors is determined by the polarization
state of the laser. We show that the photocarrier spin can be irreversibly
transferred to the collective magnetization, whose dynamics can consequently be
flexibly controlled by suitably chosen laser pulses. As illustrations we
demonstrate the feasibility of all optical ferromagnetic resonance and optical
magnetization reorientation.",0304492v2
2004-09-17,Snapshot Observation for 2D Classical Lattice Models by Corner Transfer Matrix Renormalization Group,"We report a way of obtaining a spin configuration snapshot, which is one of
the representative spin configurations in canonical ensemble, in a finite area
of infinite size two-dimensional (2D) classical lattice models. The corner
transfer matrix renormalization group (CTMRG), a variant of the density matrix
renormalization group (DMRG), is used for the numerical calculation. The matrix
product structure of the variational state in CTMRG makes it possible to
stochastically fix spins each by each according to the conditional probability
with respect to its environment.",0409445v1
1997-01-27,Lambda and Lambda-bar Polarization in Lepton Induced Processes,"The study of the longitudinal polarization of Lambda and Lambda-bar hyperons
produced in polarized deep inelastic scattering, neutrino scattering, and in Z0
decays allows to access the spin dynamics of the quark fragmentation process.
Different phenomenological spin transfer mechanisms are considered and
predictions for the Lambda and Lambda-bar longitudinal polarization in various
processes using unpolarized and polarized targets are made. Current and future
semi-inclusive deep inelastic scattering experiments will provide soon accurate
enough data to study these phenomena and distinguish between various models for
the spin transfer mechanisms.",9701384v2
1998-06-29,Bounds on Transverse Spin Asymmetries for Lambda Baryon Production in pp Collisions at BNL RHIC,"We study inclusive Lambda hyperon production in pp collisions at BNL RHIC,
with just one transversely polarized proton. We show that the measurement of
the spin transfer between the initial proton and the produced Lambda is
sensitive to the proton transversity distributions and to the corresponding
Lambda transversity fragmentation functions. In view of our present ignorance
of these distributions and fragmentation functions, we resort to positivity
bounds for making some predictions for the corresponding spin transfer
asymmetry.",9806513v1
2005-12-19,Factorization of the transfer matrices for the quantum sl(2) spin chains and Baxter equation,"It is shown that the transfer matrices of homogeneous sl(2) invariant spin
chains with generic spin, both closed and open, are factorized into the product
of two operators. The latter satisfy the Baxter equation that follows from the
structure of the reducible representations of the sl(2) algebra.",0512047v2
2005-03-25,Simulation of a Heisenberg XY- chain and realization of a perfect state transfer algorithm using liquid nuclear magnetic resonance,"The three- spin chain with Heisenberg XY- interaction is simulated in a
three- qubit nuclear magnetic resonance (NMR) quantum computer. The evolution
caused by the XY- interaction is decomposed into a series of single- spin
rotations and the $J$- coupling evolutions between the neighboring spins. The
perfect state transfer (PST) algorithm proposed by M. Christandl et al [Phys.
Rev. Lett, 92, 187902(2004)] is realized in the XY- chain.",0503199v2
2005-04-20,Long-lived quantum memory with nuclear atomic spins,"We propose to store non-classical states of light into the macroscopic
collective nuclear spin ($10^{18}$ atoms) of a $^3$He vapor, using
metastability exchange collisions. These collisions, commonly used to transfer
orientation from the metastable state $2^{3}S\_1$ to the ground state state of
$^3$He, can also transfer quantum correlations. This gives a possible
experimental scheme to map a squeezed vacuum field state onto a nuclear spin
state with very long storage times (hours).",0504152v2
2005-05-13,Unmodulated spin chains as universal quantum wires,"We study a quantum state transfer between two qubits interacting with the
ends of a quantum wire consisting of linearly arranged spins coupled by an
excitation conserving, time-independent Hamiltonian. We show that if we control
the coupling between the source and the destination qubits and the ends of the
wire, the evolution of the system can lead to an almost perfect transfer even
in the case in which all nearest-neighbour couplings between the internal spins
of the wire are equal.",0505097v1
2005-12-21,Squeezing and entangling nuclear spins in helium 3,"We present a realistic model for transferring the squeezing or the
entanglement of optical field modes to the collective ground state nuclear spin
of $^3$He using metastability exchange collisions. We discuss in detail the
requirements for obtaining good quantum state transfer efficiency and study the
possibility to readout the nuclear spin state optically.",0512186v2
2006-08-12,Multiuser quantum communication networks,"We study a quantum state transfer between spins interacting with an arbitrary
network of spins coupled by uniform XX interactions. It is shown that in such a
system under fairly general conditions, we can expect a nearly perfect transfer
of states. Then we analyze a generalization of this model to the case of many
network users, where the sender can choose which party he wants to communicate
with by appropriately tuning his local magnetic field. We also remark that a
similar idea can be used to create an entanglement between several spins
coupled to the network.",0608107v1
2006-09-20,Negative Polarization through Photon to Electron Spin Polarization Transfer in GaAs Quantum Wells,"We demonstrate negative polarization created by light-hole exciton excitation
in g-factor engineered GaAs quantum wells measured by time-resolved Kerr
rotation and polarization-resolved photoluminescence. This negative
polarization is a result of polarization transfer from a photon to an electron
spin mediated by a light hole. This demonstration is an important step towards
achieving quantum media conversion from a photonic qubit to an electron spin
qubit required for building a quantum repeater.",0609152v1
2007-02-28,Controlled Quantum State Transfer in a Spin Chain,"Control of the transfer of quantum information encoded in quantum wavepackets
moving along a spin chain is demonstrated. Specifically, based on a
relationship with control in a paradigm of quantum chaos, it is shown that
wavepackets with slow dispersion can automatically emerge from a class of
initial superposition states involving only a few spins, and that arbitrary
unspecified travelling wavepackets can be nondestructively stopped and later
relaunched with perfection. The results establish an interesting application of
quantum chaos studies in quantum information science.",0702265v1
2007-08-27,Theoretical analysis of the optimal conditions for photon-spin quantum state transfer,"We analyzed the yield and fidelity of the quantum state transfer (QST) from a
photon polarization qubit to an electron spin qubit in a spin-coherent photo
detector consisting of a semiconductor quantum dot. We used a model consisting
of the quantum dot, where the QST is carried out, coupled with a photonic
cavity. We determined the optimal conditions that allow the realization of both
high-yield and high-fidelity QST.",0708.3551v1
2008-07-25,High fidelity state transfer in binary tree spin networks,"Quantum state propagation over binary tree configurations is studied in the
context of quantum spin networks. For binary tree of order two a simple
protocol is presented which allows to achieve arbitrary high transfer fidelity.
It does not require fine tuning of local fields and two-nodes coupling of the
intermediate spins. Instead it assumes simple local operations on the intended
receiving node: their role is to brake the transverse symmetry of the network
that induces an effective refocusing of the propagating signals. Some ideas on
how to scale up these effect to binary tree of arbitrary order are discussed.",0807.4030v2
2008-07-31,Perfect state transfer in long-range interacting spin chains,"We investigate the most general conditions under which a finite ferromagnetic
long-range inter- acting spin chain achieves unitary fidelity and the shortest
transfer time in transmitting an unknown input qubit. A deeper insight into
system dynamics, allows us to identify an ideal system involving sender and
receiver only. However, this two-spin ideal chain is unpractical due to the
rapid decrease of the coupling strength with the distance. Therefore, we
propose an optimization scheme for ap- proaching the ideal behaviour, while
keeping the interaction strength still reasonably high. The procedure is
scalable with the size of the system and straightforward to implement.",0807.5018v1
2009-04-30,Density functional analysis of the simultaneous charge/spin order and the associated Cu-Fe intersite charge transfer in LaCu3Fe4O12,"LaCu3Fe4O12 undergoes a phase transition at 393 K involving the spin order
(SO) of the Fe sites and the charge order (CO) resulting in Cu-Fe intersite
charge transfer. On the basis of density functional calculations, we show that
this simultaneous CO/SO phenomenon is a consequence of two electronic effects,
namely, the competition between the Fe-Fe and Fe-Cu antiferromagnetic spin
exchange and the dependence of the width of the Fe d-block bands on the SO of
the Fe atoms.",0904.4809v1
2010-03-01,Non-uniformity of a planar polarizer as a reason of spin-transfer induced vortex oscillations at zero field,"We discuss a possible mechanism of the spin-transfer induced oscillations of
a vortex in the free layer of spin-valve nanostructures, in which the polarizer
layer has a planar magnetization. We demonstrate that if such planar polarizer
is essentially non-uniform, steady gyrotropic vortex motion with large
amplitude can be excited. The best excitation efficiency is obtained for a
circular magnetization distribution in the polarizer. In this configuration,
the conditions for the onset of the oscillations depend on the vortex chirality
but not on the direction of its core.",1003.0303v1
2010-04-16,Three-Dimensional Multiband d-p Model of Superconductivity in Spin-Chain Ladder Cuprate,"We study the superconductivity in the three-dimensional multiband d-p model,
in which a Cu$_2$O$_3$-ladder layer and a CuO$_2$-chain layer are alternately
stacked, as a model of the superconducting spin-chain ladder cuprate.
$p_z$-Wave-like triplet superconductivity is found to be the most stable, and
its dependence on interlayer coupling can explain the superconducting
transition temperature dependence on pressure in real superconducting
spin-chain ladder cuprates. The superconductivity may be enhanced if hole
transfer from the chain layer to the ladder layer can be promoted beyond the
typical transfer rate.",1004.2823v1
2011-02-08,Bypassing state initialisation in perfect state transfer protocols on spin-chains,"Although a complete picture of the full evolution of complex quantum systems
would certainly be the most desirable goal, for particular Quantum Information
Processing schemes such an analysis is not necessary. When quantum correlations
between only specific elements of a many-body system are required for the
performance of a protocol, a more distinguished and specialised investigation
is helpful. Here, we provide a striking example with the achievement of perfect
state transfer in a spin chain without state initialisation, whose realisation
has been shown to be possible in virtue of the correlations set between the
first and last spin of the transmission-chain.",1102.1685v1
2011-02-16,Geometry and Curvature of Spin Networks,"A measure for the maximum quantum information transfer capacity (ITC) between
nodes of a spin network is defined, and shown to induce a metric on a space of
equivalence classes of nodes for homogeneous chains with XX and Heisenberg
couplings. The geometry and curvature of spin chains with respect of this
metric are studied and compared to the physical network geometry. For general
networks hierarchical clustering is used to elucidate the proximity of nodes
with regard to the maximum ITC. Finally, it is shown how minimal control can be
used to overcome intrinsic limitations and speed up information transfer.",1102.3208v1
2012-03-21,Accurate computation of low-temperature thermodynamics for quantum spin chains,"We apply the biorthonormal transfer-matrix renormalization group (BTMRG)
[Phys. Rev. E 83, 036702 (2011)] to study low-temperature properties of quantum
spin chains. Simulation on isotropic Heisenberg spin-1/2 chain demonstrates
that the BTMRG outperforms the conventional transfer-matrix renormalization
group (TMRG) by successfully accessing far lower temperature unreachable by
conventional TMRG, while retaining the same level of accuracy. The power of the
method is further illustrated by the calculation of the low-temperature
specific heat for a frustrated spin chain.",1203.4848v2
2012-06-06,Manipulation of qubits in non-orthogonal collective storage modes,"We present an analysis of transfer of quantum information between the
collective spin degrees of freedom of a large ensemble of two-level systems and
a single central qubit. The coupling between the central qubit and the
individual ensemble members may be varied and thus provides access to more than
a single storage mode. Means to store and manipulate several independent qubits
are derived for the case where the variation in coupling strengths does not
allow addressing of orthogonal modes of the ensemble. While our procedures and
analysis may apply to a number of different physical systems, for concreteness,
we study the transfer of quantum states between a single electron spin and an
ensemble of nuclear spins in a quantum dot.",1206.1315v1
2014-03-02,Characterization and Control of Quantum Spin Chains and Rings,"Information flow in quantum spin networks is considered. Two types of control
-- temporal bang-bang switching control and control by varying spatial degrees
of freedom -- are explored and shown to be effective in speeding up information
transfer and increasing transfer fidelities. The control is model-based and
therefore relies on accurate knowledge of the system parameters. An efficient
protocol for simultaneous identification of the coupling strength and the exact
number of spins in a chain is presented.",1403.0226v1
2018-09-21,Adiabatic state distribution using anti-ferromagnetic spin systems,"Transporting quantum information is an important prerequisite for quantum
computers. We study how this can be done in Heisenberg-coupled spin networks
using adiabatic control over the coupling strengths. We find that qudits can be
transferred and entangled pairs can be created between distant sites of
bipartite graphs with a certain balance between the maximum spin of both parts,
extending previous results that were limited to linear chains. The transfer
fidelity in a small star-shaped network is numerically analysed, and possible
experimental implementations are discussed.",1809.08158v2
2019-03-07,Heat transfer in a nonequilibrium spin-boson model: A perturbative approach,"We investigate the heat transport in a nonequilibrium spin-boson model, where
a two level system bridging two harmonic reservoirs at different temperatures,
by employing a unitary transformation along with a resolvent operator expansion
technique. Analytical expressions of the heat current and the thermal
conductance of this model are obtained. Compared with the performances of other
methods, namely, the nonequilibrium Green's function method and the equation of
motion formulation, our approach provides a reasonable description of heat
transfer properties of the nonequilibrium spin-boson model for the
weak-coupling region at low temperature.",1903.02751v2
2011-04-11,Which weighted circulant networks have perfect state transfer?,"The question of perfect state transfer existence in quantum spin networks
based on weighted graphs has been recently presented by many authors. We give a
simple condition for characterizing weighted circulant graphs allowing perfect
state transfer in terms of their eigenvalues. This is done by extending the
results about quantum periodicity existence in the networks obtained by Saxena,
Severini and Shparlinski and characterizing integral graphs among weighted
circulant graphs. Finally, classes of weighted circulant graphs supporting
perfect state transfer are found. These classes completely cover the class of
circulant graphs having perfect state transfer in the unweighted case. In fact,
we show that there exists an weighted integral circulant graph with $n$
vertices having perfect state transfer if and only if $n$ is even. Moreover we
prove the non-existence of perfect state transfer for several other classes of
weighted integral circulant graphs of even order.",1104.1823v1
2011-11-09,Spin chains for robust state transfer: Modified boundary couplings vs. completely engineered chains,"Quantum state transfer in the presence of noise is one of the main challenges
in building quantum computers. We compare the quantum state transfer properties
for two classes of qubit chains under the influence of static randomness. In
fully engineered chains all nearest-neighbor couplings are tuned in such a way
that a single-qubit state can be transferred perfectly between the ends of the
chain, while in boundary-controlled chains only the two couplings between the
transmitting and receiving qubits and the remainder of the chain can be
optimized. We study how the noise in the couplings affects the state transfer
fidelity depending on the noise model and strength as well as the chain type
and length. We show that the desired level of fidelity and transfer time are
important factors in designing a chain. In particular we demonstrate that
transfer efficiency comparable or better than that of the most robust
engineered systems can also be reached in boundary-controlled chains without
the demanding engineering of a large number of couplings.",1111.2238v2
2018-07-11,Pretty good state transfer via adaptive quantum error correction,"We examine the role of quantum error correction (QEC) in achieving pretty
good quantum state transfer over a class of $1$-d spin Hamiltonians. Recasting
the problem of state transfer as one of information transmission over an
underlying quantum channel, we identify an adaptive QEC protocol that achieves
pretty good state transfer. Using an adaptive recovery and approximate QEC
code, we obtain explicit analytical and numerical results for the fidelity of
transfer over ideal and disordered $1$-d Heisenberg chains. In the case of a
disordered chain, we study the distribution of the transition amplitude, which
in turn quantifies the stochastic noise in the underlying quantum channel. Our
analysis helps us to suitably modify the QEC protocol so as to ensure pretty
good state transfer for small disorder strengths and indicates a threshold
beyond which QEC does not help in improving the fidelity of state transfer.",1807.04062v2
2009-01-15,"On corotation torques, horseshoe drag and the possibility of sustained stalled or outward protoplanetary migration","We study the torque on low mass protoplanets on fixed circular orbits,
embedded in a protoplanetary disc in the isothermal limit. For low mass
protoplanets and large viscosity the corotation torque behaves as expected from
linear theory. However, when the viscosity becomes small enough to enable
horseshoe turns to occur, the linear corotation torque exists only temporarily
after insertion of a planet into the disc, being replaced by the horseshoe drag
first discussed by Ward. This happens after a time that is equal to the
horseshoe libration period reduced by a factor amounting to about twice the
disc aspect ratio. This torque scales with the radial gradient of specific
vorticity, as does the linear torque, but we find it to be many times larger.
If the viscosity is large enough for viscous diffusion across the coorbital
region to occur within a libration period, we find that the horseshoe drag may
be sustained. If not, the corotation torque saturates leaving only the linear
Lindblad torques. As the magnitude of the non linear coorbital torque
(horseshoe drag) is always found to be larger than the linear torque, we find
that the sign of the total torque may change even for for mildly positive
surface density gradients. In combination with a kinematic viscosity large
enough to keep the torque from saturating, strong sustained deviations from
linear theory and outward or stalled migration may occur in such cases
(abridged).",0901.2265v1
2012-06-06,Direct Numerical Simulations of Local and Global Torque in Taylor-Couette Flow up to Re=30.000,"The torque in turbulent Taylor-Couette flows for shear Reynolds numbers Re_S
up to 3x10^4 at various mean rotations is studied by means of direct numerical
simulations for a radius ratio of \eta=0.71. Convergence of simulations is
tested using three criteria of which the agreement of dissipation values
estimated from the torque and from the volume dissipation rate turns out to be
most demanding. We evaluate the influence of Taylor vortex heights on the
torque for a stationary outer cylinder and select a value of the aspect ratio
of \Gamma=2, close to the torque maximum. The connection between the torque and
the transverse current J^\omega of azimuthal motion which can be computed from
the velocity field enables us to investigate the local transport resulting in
the torque. The typical spatial distribution of the individual convective and
viscous contributions to the local current is analysed for a turbulent flow
case. To characterise the turbulent statistics of the transport, PDF's of local
current fluctuations are compared to experimental wall shear stress
measurements. PDF's of instantaneous torques reveal a fluctuation enhancement
in the outer region for strong counter-rotation. Moreover, we find for
simulations realising the same shear Re_S>=2x10^4 the formation of a torque
maximum for moderate counter-rotation with angular velocities
\omega_o\approx-0.4\omega_i. In contrast, for Re_S<=4x10^3 the torque features
a maximum for a stationary outer cylinder. In addition, the effective torque
scaling exponent is shown to also depend on the mean rotation state. Finally,
we evaluate a close connection between boundary-layer thicknesses and the
torque.",1206.1286v1
1999-04-02,Exact correlation functions of Bethe lattice spin models in external fields,"We develop a transfer matrix method to compute exactly the spin-spin
correlation functions of Bethe lattice spin models in the external magnetic
field h and for any temperature T. We first compute the correlation function
for the most general spin - S Ising model, which contains all possible
single-ion and nearest-neighbor pair interactions. This general spin - S Ising
model includes the spin-1/2 simple Ising model and the Blume-Emery-Griffiths
(BEG) model as special cases. From the spin-spin correlation functions, we
obtain functions of correlation length for the simple Ising model and BEG
model, which show interesting scaling and divergent behavior as T approaches
the critical temperature. Our method to compute exact spin-spin correlation
functions may be applied to other Ising-type models on Bethe and Bethe-like
lattices.",9904036v1
2008-07-14,Electric-field induced spin excitations in two-dimensional spin-orbit coupled systems,"Rigorous coupled spin-charge drift-diffusion equations are derived from
quantum-kinetic equations for the spin-density matrix that incorporate effects
due to k-linear spin-orbit interaction, an in-plane electric field, and the
elastic scattering on nonmagnetic impurities. The explicit analytical solution
for the induced magnetization exhibits a pole structure, from which the
dispersion relations of spin excitations are identified. Applications of the
general approach refer to the excitation of long-lived field-induced spin waves
by optically generated spin and charge patterns. This approach transfers
methods known in the physics of space-charge waves to the treatment of spin
eigenmodes. In addition, the amplification of an oscillating electric field by
spin injection is demonstrated.",0807.2142v1
2009-01-26,Robust photon-spin entangling gate using a quantum-dot spin in a microcavity,"Semiconductor quantum dots (known as artificial atoms) hold great promise for
solid-state quantum networks and quantum computers. To realize a quantum
network, it is crucial to achieve light-matter entanglement and coherent
quantum-state transfer between light and matter. Here we present a robust
photon-spin entangling gate with high fidelity and high efficiency (up to 50
percent) using a charged quantum dot in a double-sided microcavity. This gate
is based on giant circular birefringence induced by a single electron spin, and
functions as an optical circular polariser which allows only one
circularly-polarized component of light to be transmitted depending on the
electron spin states. We show this gate can be used for single-shot quantum
non-demolition measurement of a single electron spin, and can work as an
entanglement filter to make a photon-spin entangler, spin entangler and photon
entangler as well as a photon-spin quantum interface. This work allows us to
make all building blocks for solid-state quantum networks with single photons
and quantum-dot spins.",0901.3964v1
2014-02-20,Rashba-Zeeman-effect-induced spin filtering energy windows in a quantum wire,"We perform a numerical study on the spin-resolved transport in a quantum wire
(QW) under the modulation of both Rashba spin-orbit coupling (SOC) and a
perpendicular magnetic field (MF) by adopting the developed Usuki
transfer-matrix method in combination with the Landauer-Buttiker formalism.
Wide spin filtering energy windows can be achieved in this system for a
spin-unpolarized injection. In addition, both the width of these energy windows
and the magnitude of the spin conductance within these energy widows can be
tuned by varying the Rashba SOC strength, which can be apprehended by analyzing
the energy dispersions and the spin-polarized density distributions inside the
QW, respectively. Further study also demonstrates that these
Rashba-SOC-controlled spin filtering energy windows show a strong robustness
against disorders. These findings may not only benefit to further understand
the spin-dependent transport properties of the QW in the presence of external
fields but also provide a theoretical instruction to design a spin filter
device.",1402.4909v1
2016-02-08,Spin lifetimes exceeding 12 nanoseconds in graphene non-local spin valve devices,"We show spin lifetimes of 12.6 ns and spin diffusion lengths as long as 30.5
\mu m in single layer graphene non-local spin transport devices at room
temperature. This is accomplished by the fabrication of Co/MgO-electrodes on a
Si/SiO$_2$ substrate and the subsequent dry transfer of a graphene-hBN-stack on
top of this electrode structure where a large hBN flake is needed in order to
diminish the ingress of solvents along the hBN-to-substrate interface.
Interestingly, long spin lifetimes are observed despite the fact that both
conductive scanning force microscopy and contact resistance measurements reveal
the existence of conducting pinholes throughout the MgO spin
injection/detection barriers. The observed enhancement of the spin lifetime in
single layer graphene by a factor of 6 compared to previous devices exceeds
current models of contact-induced spin relaxation which paves the way towards
probing intrinsic spin properties of graphene.",1602.02725v1
2016-09-27,Spin equilibrium in strongly-magnetized accreting stars,"Strongly magnetized accreting stars are often hypothesized to be in `spin
equilibrium' with their surrounding accretion flows, which requires that the
accretion rate changes more slowly than it takes the star to reach spin
equilibrium. This is not true for most magnetically accreting stars, which have
strongly variable accretion outbursts on time-scales much shorter than the time
it would take to reach spin equilibrium. This paper examines how accretion
outbursts affect the time a star takes to reach spin equilibrium and its final
equilibrium spin period. I consider several different models for angular
momentum loss -- either carried away in an outflow, lost to a stellar wind, or
transferred back to the accretion disc (the `trapped disc'). For transient
sources, the outflow scenario leads to significantly longer times to reach spin
equilibrium ($\sim$10x), and shorter equilibrium spin periods than would be
expected from spin equilibrium arguments, while the `trapped disc' does not.
The results suggest that disc trapping plays a significant role in the spin
evolution of strongly magnetic stars, with some caveats for young stellar
objects.",1609.08654v2
2017-09-03,Spin controlled atom-ion inelastic collisions,"The control of the ultracold collisions between neutral atoms is an extensive
and successful field of study. The tools developed allow for ultracold chemical
reactions to be managed using magnetic fields, light fields and spin-state
manipulation of the colliding particles among other methods. The control of
chemical reactions in ultracold atom-ion collisions is a young and growing
field of research. Recently, the collision energy and the ion electronic state
were used to control atom-ion interactions. Here, we demonstrate
spin-controlled atom-ion inelastic processes. In our experiment, both
spin-exchange and charge-exchange reactions are controlled in an ultracold
Rb-Sr$^+$ mixture by the atomic spin state. We prepare a cloud of atoms in a
single hyperfine spin-state. Spin-exchange collisions between atoms and ion
subsequently polarize the ion spin. Electron transfer is only allowed for
(RbSr)$^+$ colliding in the singlet manifold. Initializing the atoms in various
spin states affects the overlap of the collision wavefunction with the singlet
molecular manifold and therefore also the reaction rate. We experimentally show
that by preparing the atoms in different spin states one can vary the
charge-exchange rate in agreement with theoretical predictions.",1709.00775v1
2019-06-20,Effects of spin-orbit coupling on the neutron spin resonance in iron-based superconductors,"The so-called neutron spin resonance consists of a prominent enhancement of
the magnetic response at a particular energy and momentum transfer upon
entering the superconducting state of unconventional superconductors. In the
case of iron-based superconductors, the neutron resonance has been extensively
studied experimentally, and a peculiar spin-space anisotropy has been
identified by polarized inelastic neutron scattering experiments. Here we
perform a theoretical study of the energy- and spin-resolved magnetic
susceptibility in the superconducting state with $ s_{+-} $-wave order
parameter, relevant to iron-pnictide and iron-chalcogenide superconductors. Our
model is based on a realistic bandstructure including spin-orbit coupling with
electronic Hubbard-Hund interactions included at the RPA level. Spin-orbit
coupling is taken into account both in the generation of spin-fluctuation
mediated pairing, as well as the numerical computation of the spin
susceptibility in the superconducting state. We find that spin-orbit coupling
and superconductivity in conjunction can reproduce the salient experimentally
observed features of the magnetic anisotropy of the neutron resonance. This
includes the possibility of a double resonance, the tendency for a $c$-axis
polarized resonance, and the existence of enhanced magnetic anisotropy upon
entering the superconducting phase.",1906.08566v1
2020-07-22,"Comment on: ""Spin-orbit interaction and spin selectivity for tunneling electron transfer in DNA""","The observation of chiral-induced spin selectivity (CISS) in biological
molecules still awaits a full theoretical explanation. In a recent Rapid
Communication, Varela et al. [Phys. Rev. B 101, 241410(R) (2020)] presented a
model for electron transport in biological molecules by tunneling in the
presence of spin-orbit interactions. They then claimed that their model
produces a strong spin asymmetry due to the intrinsic atomic spin-orbit
strength. As their Hamiltonian is time-reversal symmetric, this result
contradicts a theorem by Bardarson [J. Phys. A: Math. Theor. 41, 405203
(2008)], which states that such a Hamiltonian cannot generate a spin asymmetry
for tunneling between two terminals (in which there are only a spin-up and a
spin-down channels). Here we solve the model proposed by Varela et al. and show
that it does not yield any spin asymmetry, and therefore cannot explain the
observed CISS effect.",2007.11238v4
2024-01-03,"Minimal Model for Chirally Induced Spin Selectivity: Spin-orbit coupling, tunneling and decoherence","Chirally Induced Spin Selectivity (CISS) is a transport phenomenon observed
in both linear and non-linear regimes, where the spin-orbit coupling (SOC) acts
as the key driver and electron tunneling serves as the dominant mechanism for
charge transfer. Despite SOC's inherent time-reversal symmetry (TRS)
preservation, conventional reciprocity relations limit spin polarization and
the differential treatment of spin species. In experimental systems, an
additional factor, spin-independent decoherence, disrupts TRS and reciprocity.
We introduce decoherence using the Buttiker voltage probe within the scattering
matrix framework. Our results reveal the importance of under-the-barrier
decoherence as an order-of-magnitude polarization enhancement mechanism.
Polarization arises by the disruption of spin precession around the spin-orbit
magnetic field with a new spin component along the field direction. The
alignment of polarization depends on interference effects produced by the
voltage probe. We discuss the connection of our model to a more realistic
decoherence mechanism in molecular systems.",2401.01994v1
2024-01-09,Topological transverse spin transport in a canted antiferromagnet/heavy metal heterostructure,"We theoretically study the conditions under which a spin Nernst effect - a
transverse spin current induced by an applied temperature gradient - can occur
in a canted antiferromagnetic insulator, such as ${\rm LaFeO_3}$ and other
materials of the same family. The spin Nernst effect may provide a microscopic
mechanism for an experimentally observed anomalous thermovoltage in ${\rm
LaFeO_3}$/Pt heterostructures, where spin is transferred across the
insulator/metal interface when a temperature gradient is applied to ${\rm
LaFeO_3}$ parallel to the interface [W. Lin ${\it et \; al}$, Nat. Phys. ${\bf
18}$, 800 (2022)]. We find that ${\rm LaFeO_3}$ exhibits a topological spin
Nernst effect when inversion symmetry is broken on the axes parallel to both
the applied temperature gradient and the direction of spin transport, which can
result in a spin injection across the insulator/metal interface. Our work
provides a general derivation of a symmetry-breaking-induced spin Nernst
effect, which may open a path to engineering a finite spin Nernst effect in
systems where it would otherwise not arise.",2401.04582v1
2006-01-17,Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights,"The temperature dependence and anisotropy of optical spectral weights
associated with different multiplet transitions is determined by the spin and
orbital correlations. To provide a systematic basis to exploit this close
relationship between magnetism and optical spectra, we present and analyze the
spin-orbital superexchange models for a series of representative
orbital-degenerate transition metal oxides with different multiplet structure.
For each case we derive the magnetic exchange constants, which determine the
spin wave dispersions, as well as the partial optical sum rules. The magnetic
and optical properties of early transition metal oxides with degenerate
$t_{2g}$ orbitals (titanates and vanadates with perovskite structure) are shown
to depend only on two parameters, viz. the superexchange energy $J$ and the
ratio $\eta$ of Hund's exchange to the intraorbital Coulomb interaction, and on
the actual orbital state. In $e_g$ systems important corrections follow from
charge transfer excitations, and we show that KCuF$_3$ can be classified as a
charge transfer insulator, while LaMnO$_3$ is a Mott insulator with moderate
charge transfer contributions. In some cases orbital fluctuations are quenched
and decoupling of spin and orbital degrees of freedom with static orbital order
gives satisfactory results for the optical weights. On the example of cubic
vanadates we describe a case where the full quantum spin-orbital physics must
be considered. Thus information on optical excitations, their energies,
temperature dependence and anisotropy, combined with the results of magnetic
neutron scattering experiments, provides an important consistency test of the
spin-orbital models, and indicates whether orbital and/or spin fluctuations are
important in a given compound.",0601381v1
2017-06-01,Magnetization-control and transfer of spin-polarized Cooper pairs into a half-metal manganite,"The pairing state and critical temperature (T$_c$) of a thin s-wave
superconductor (S) on two or more ferromagnets (F) are controllable through the
magnetization-alignment of the F layers. Magnetization misalignment can lead to
spin-polarized triplet pair creation, and since such triplets are compatible
with spin-polarized materials they are able to pass deeply into the F layers
and so, cause a decrease in T$_c$. Various experiments on S/F$_1$/F$_2$
""triplet spin-valves"" have been performed with the most pronounced suppression
of T$_c$ reported in devices containing the half-metal ferromagnet (HMF)
CrO$_2$ (F$_2$) albeit using out-of-plane magnetic fields to tune magnetic
non-collinearity [Singh et al., Phys. Rev. X 5, 021019 (2015)]. Routine
transfer of spin-polarized triplets to HMFs is a major goal for superconducting
spintronics so as to maximize triplet-state spin-polarization. However, CrO$_2$
is chemically unstable and out-of-plane fields are undesirable for
superconductivity. Here, we demonstrate magnetization-tuneable pair conversion
and transfer of spin-polarized triplet pairs to the chemically stable mixed
valence manganite La$_{2/3}$Ca$_{1/3}$MnO$_3$ in a pseudo spin-valve device
using in-plane magnetic fields. The results match microscopic theory and offer
full control over the pairing state.",1706.00332v2
2023-07-26,Establishing Magnetic Coupling in Spin-crossover-2D Hybrid Nanostructures via Interfacial Charge-transfer Interaction,"Despite a clear demonstration of bistability in spin-crossover (SCO)
materials, the absence of long-range magnetic order and poor electrical
conductivity limit their prospect in spintronic and nanoelectronic
applications. Intending to create hybrid devices made of spin-crossover
(SCO)-2D architecture, here, we report an easily processable Fe-based SCO
nanostructures grown on 2D reduced graphene oxide (rGO). The heterostructure
shows enhanced cooperativity due to formation of interfacial charge transfer
induced inter-molecular interaction. The spin transition temperature is
controlled by tuning the coverage area of SCO nanostructured networks over the
2D surfaces, thus manipulating hysteresis (aka memory) of the heterostructure.
The enhanced magnetic coupling of the heterostructure leads to the spontaneous
magnetization states with a large coercive field of $\sim$ 3000 Oe.
Additionally, the low conductivity of the pristine SCO nanostructures is
addressed by encapsulating them on suitable 2D rGO template, enabling detection
of magnetic bistable spin states during high-spin/low-spin conductance change.
This adds spin functionality in conductance switching for realizing hybrid 2D
spintronic devices. Ab-inito calculations, on the experimentally proposed
nanostructures, corroborate the enhanced magnetic interaction in the proposed
architecture facilitated by interfacial charge transfer and provide insights on
the microscopic mechanism.",2307.14135v1
2023-08-16,Accelerating micromagnetic and atomistic simulations using multiple GPUs,"It is shown micromagnetic and atomistic spin dynamics simulations can use
multiple GPUs in order to reduce computation time, but also to allow for a
larger simulation size than is possible on a single GPU. Whilst interactions
which depend on neighbouring spins, such as exchange interactions, may be
implemented efficiently by transferring data between GPUs using halo regions,
or alternatively using direct memory accesses, implementing the long-range
demagnetizing interaction is the main difficulty in achieving good performance
scaling, where the data transfer rate between GPUs is a significant bottleneck.
A multi-GPU convolution algorithm is developed here, which relies on single-GPU
FFTs executed in parallel. It is shown that even for micromagnetic simulations
where the demagnetizing interaction computation time dominates, good
performance scaling may be achieved, with speedup factors up to 1.8, 2.5, and
3.1, for 2, 3, and 4 GPUs respectively. The code developed here can be used for
any number of GPUs in parallel, with performance scaling strongly dependent on
inter-GPU data transfer rate and connection topology. This is further improved
in micromagnetic simulations which include a spin transport solver, obtaining
speedup factors up to 1.96, 2.8, and 3.7, for 2, 3, and 4 GPUs respectively.
The best case scenario is obtained for atomistic spin dynamics simulations,
where the demagnetizing interaction is implemented with spin-averaged cells.
Using a single workstation with 4 GPUs, it is shown atomistic spin dynamics
simulations with up to 1 billion spins, and atomistic Monte Carlo simulations
with up to 2 billion spins are possible, with a near-ideal performance scaling.",2308.08447v2
2020-07-19,Magnetization transfer from protons to quadrupolar nuclei in solid-state NMR using PRESTO or dipolar-mediated refocused INEPT methods,"We compare here the performances of two approaches to achieve such transfer:
PRESTO (Phase-shifted Recoupling Effects a Smooth Transfer of Order), which is
currently the method of choice to achieve the magnetization transfer from
protons to quadrupolar nuclei and which has been shown to supersede
Cross-Polarization under Magic-Angle Spinning (MAS) for quadrupolar nuclei and
D-RINEPT (Dipolar-mediated Refocused Insensitive Nuclei Enhanced by
Polarization Transfer) using symmetry-based SR4${}_1{}^2$ recoupling, which has
already been employed to transfer the magnetization in the reverse way from
half-integer quadrupolar spin to protons. We also test the PRESTO sequence with
R16${}_7{}^6$ recoupling using 270${}_0$90${}_180$ composite $\pi$-pulses as
inversion elements. This recoupling scheme has not so far been employed to
reintroduce dipolar couplings with protons. These various techniques to
transfer the magnetization from protons to quadrupolar nuclei are analyzed
using (i) an average Hamiltonian theory, (ii) numerical simulations of spin
dynamics, and (iii) experimental ${}^1$H $\rightarrow {}^{27}$Al and ${}^{1}$H
$\rightarrow {}^{17}$O transfers in as-synthesized AlPO4-14 and
${}^{17}$O-labelled fumed silica, respectively. The experiments and simulations
are done at two magnetic fields (9.4 and 18.8 T) and several spinning speeds
(15, 18-24 and 60 kHz). This analysis indicates that owing to its
$\gamma$-encoded character, PRESTO yields the highest transfer efficiency at
low magnetic fields and MAS frequencies, whereas owing to its higher robustness
to rf-field inhomogeneity and chemical shifts, D-RINEPT is more sensitive at
high fields and MAS frequencies, notably for protons exhibiting large offset or
CSA, such as those involved in hydrogen bonds.",2007.09731v1
2014-01-08,Dynamic exchange via spin currents in acoustic and optical modes of ferromagnetic resonance in spin-valve structures,"Two ferromagnetic layers magnetically decoupled by a thick normal metal
spacer layer can be, nevertheless, dynamically coupled via spin currents
emitted by the spin-pump and absorbed through the spin-torque effects at the
neighboring interfaces. A decrease of damping in both layers due to a partial
compensation of the angular momentum leakage in each layer was previously
observed at the coincidence of the two ferromagnetic resonances. In case of
non-zero magnetic coupling, such a dynamic exchange will depend on the mutual
precession of the magnetic moments in the layers. A difference in the linewidth
of the resonance peaks is expected for the acoustic and optical regimes of
precession. However, the interlayer coupling hybridizes the resonance responses
of the layers and therefore can also change their linewidths. The interplay
between the two mechanisms has never been considered before. In the present
work, the joint influence of the hybridization and non-local damping on the
linewidth has been studied in weakly coupled NiFe/CoFe/Cu/CoFe/MnIr spin-valve
multilayers. It has been found that the dynamic exchange by spin currents is
different in the optical and acoustic modes, and this difference is dependent
on the interlayer coupling strength. In contrast to the acoustic precession
mode, the dynamic exchange in the optical mode works as an additional damping
source. A simulation in the framework of the Landau-Lifshitz-Gilbert formalism
for two ferromagnetic layers coupled magnetically and by spin currents has been
done to separate the effects of the non-local damping from the resonance modes
hybridization. In our samples both mechanisms bring about linewidth changes of
the same order of magnitude, but lead to a distinctly different angular
behavior. The obtained results are relevant for a broad class of coupled
magnetic multilayers with ballistic regime of the spin transport.",1401.1672v1
2014-07-03,Dynamics of the radiative envelope of rapidly rotating stars: Effects of spin-down driven by mass loss,"(abridged) This paper aims at deciphering the dynamics of the envelope of a
rotating star when some angular momentum loss due to mass loss is present. We
especially wish to know when the spin-down flow forced by the mass loss
supersedes the baroclinic flows that pervade the radiative envelope of rotating
stars. We consider a Boussinesq fluid enclosed in a rigid sphere whose flows
are forced both by the baroclinic torque, the spin-down of an outer layer, and
an outward mass flux. The spin-down forcing is idealized in two ways: either by
a rigid layer that imposes its spinning down velocity at some interface or by a
turbulent layer that imposes a stress at this same interface to the interior of
the star. In the case where the layer is rigid and imposes its velocity, we
find that, as the mass-loss rate increases, the flow inside the star shows two
transitions: the meridional circulation associated with baroclinic flows is
first replaced by its spin-down counterpart, while at much stronger mass-loss
rates the baroclinic differential rotation is superseded by the spin-down
differential rotation. In fact, we find three wind regimes: weak (or no wind),
moderate, and strong. In the first case, the flow in the radiative envelope is
of baroclinic origin. In the moderate case, the circulation results from the
spin-down while the differential rotation may either be of baroclinic or of
spin-down origin, depending on the coupling between mass and angular momentum
losses. For fast rotating stars, our model says that the moderate wind regime
starts when mass loss is higher than ~1e-11 Msun/yr. In the strong wind case,
the flow in the radiative envelope is mainly driven by angular momentum
advection. This latter transition depends on the mass and the rotation rate of
the star, being around 1e-8 Msun/yr for a 3 Msun ZAMS star rotating at 200 km/s
according to our model.",1407.0946v1
2018-12-26,"Hydrodynamic description of long-distance spin transport through noncollinear magnetization states: the role of dispersion, nonlinearity, and damping","Nonlocal compensation of magnetic damping by spin injection has been
theoretically shown to establish dynamic, noncollinear magnetization states
that carry spin currents over micrometer distances. Such states can be
generically referred to as dissipative exchange flows (DEFs) because spatially
diffusing spin currents are established by the mutual exchange torque exerted
by neighboring spins. Analytical studies to date have been limited to the weak
spin injection assumption whereby the equation of motion for the magnetization
is mapped to hydrodynamic equations describing spin flow and then linearized.
Here, we analytically and numerically study easy-plane ferromagnetic channels
subject to spin injection of arbitrary strength at one extremum under a unified
hydrodynamic framework. We find that DEFs generally exhibit a nonlinear profile
along the channel accompanied by a nonlinear frequency tuneability. At large
injection strengths, we fully characterize a novel magnetization state we call
a contact-soliton DEF (CS-DEF) composed of a stationary soliton at the
injection site, which smoothly transitions into a DEF and exhibits a negative
frequency tuneability. The transition between a DEF and a CS-DEF occurs at the
maximum precessional frequency and coincides with the Landau criterion: a
subsonic to supersonic flow transition. Leveraging the hydraulic-electrical
analogy, the current-voltage characteristics of a nonlinear DEF circuit are
presented. Micromagnetic simulations of nanowires that include
magnetocrystalline anisotropy and non-local dipole fields are in qualitative
agreement with the analytical results. The magnetization states found here
along with their characteristic profile and spectral features provide
quantitative guidelines to pursue an experimental demonstration of DEFs in
ferromagnetic materials and establishes a unified description for long-distance
spin transport.",1812.10438v3
2020-07-27,Theoretical Description of Hyperpolarization Formation in the SABRE-relay Method,"SABRE (Signal Amplification By Reversible Exchange) has become a widely used
method for hyper-polarizing nuclear spins, thereby enhancing their Nuclear
Magnetic Resonance (NMR) signals by orders of magnitude. In SABRE experiments,
non-equilibrium spin order is transferred from parahydrogen to a substrate in a
transient organometallic complex. Applicability of SABRE is expanded by the
methodology of SABRE-relay, in which polarization can be relayed to a second
substrate either by direct chemical exchange of hyperpolarized nuclei or by
polarization transfer between two substrates in a second organometallic
complex. To understand the mechanism of the polarization transfer and study the
transfer efficiency, we propose a theoretical approach to SABRE-relay, which
can treat both spin dynamics and chemical kinetics as well as the interplay
between them. The approach is based on a set of equations for the spin density
matrices of the spin systems involved (i.e., SABRE substrates and complexes),
which can be solved numerically. Using this method, we perform a detailed study
of polarization formation and analyse in detail the dependence of attainable
polarization level on various chemical kinetic and spin dynamic parameters. We
foresee applications of the present approach for optimizing SABRE-relay
experiments with the ultimate goal of achieving maximal NMR signal enhancements
for substrates of interest.",2007.13301v1
2022-07-28,Do high-spin high-mass X-ray binaries contribute to the population of merging binary black holes?,"Gravitational-wave observations of binary black hole (BBH) systems point to
black hole spin magnitudes being relatively low. These measurements appear in
tension with high spin measurements for high-mass X-ray binaries (HMXBs). We
use grids of MESA simulations combined with the rapid population-synthesis code
COSMIC to examine the origin of these two binary populations. It has been
suggested that Case-A mass transfer while both stars are on the main sequence
can form high-spin BHs in HMXBs. Assuming this formation channel, we show that
depending on critical mass ratios for the stability of mass transfer, 48-100%
of these Case-A HMXBs merge during the common-envelope phase and up to 42%
result in binaries too wide to merge within a Hubble time. Both MESA and COSMIC
show that high-spin HMXBs formed through Case-A mass transfer can only form
merging BBHs within a small parameter space where mass transfer can lead to
enough orbital shrinkage to merge within a Hubble time. We find that only up to
11% of these Case-A HMXBs result in BBH mergers, and at most 20% of BBH mergers
came from Case-A HMXBs. Therefore, it is not surprising that these two spin
distributions are observed to be different.",2207.14290v2
1998-01-05,Shadow Bands and Tunneling Magnetoresistance in Itinerant Electron Ferromagnets,"In itinerant electron ferromagnets spectral weight is transferred at finite
temperatures from quasiparticle peaks located at majority and minority-spin
band energies to shadow-band peaks. For a given Bloch wavevector and band
index, the majority-spin shadow-band peak is located near the minority-spin
quasiparticle energy and the minority-spin shadow-band peak is located near the
majority-spin quasiparticle energy. This property can explain much of the
temperature dependence seen in the magnetoresistance of magnetic tunnel
junctions.",9801023v1
1998-05-15,Frustrated Spin System in theta-(BEDT-TTF)_2RbZn(SCN)_4,"The origin of the spin gap behavior in the low-temperature dimerized phase of
theta-(BEDT-TTF)_2RbZn(SCN)_4 has been theoretically studied based on the
Hartree-Fock approximation for the on-site Coulomb interaction at absolute
zero. Calculations show that, in the parameter region considered to be relevant
to this compound, antiferromagnetic ordering is stabilized between dimers
consisting of pairs of molecules coupled with the largest transfer integral.
Based on this result an effective localized spin 1/2 model is constructed which
indicates the existence of the frustration among spins. This frustration may
result in the formation of spin gap.",9805184v1
1998-08-17,Thermodynamics of quantum Heisenberg spin chains,"Thermodynamic properties of the quantum Heisenberg spin chains with S = 1/2,
1, and 3/2 are investigated using the transfer-matrix renormalization-group
method. The temperature dependence of the magnetization, susceptibility,
specific heat, spin-spin correlation length, and several other physical
quantities in a zero or finite applied field are calculated and compared. Our
data agree well with the Bethe ansatz, exact diagonalization, and quantum Monte
Carlo results and provide further insight into the quantum effects in the
antiferromagnetic Heisenberg spin chains.",9808179v1
2000-12-10,Theory of spin wave excitations of metallic A-type antiferromagnetic manganites,"The spin dynamic of the metallic A-type antiferromagnetic manganites is
studied. An effective nearest-neighbour Heisenberg spin wave dispersion is
derived from the double exchange model taking into account the superexchange
interaction between the core spins. The result of inelastic neutron scattering
experiment on ${Nd}_{0.45}{Sr}_{0.55}{Mn} {O}_{3}$ is qualitatively reproduced.
Comparing theory with experimental data two main parameters of the model:
nearest-neighbour electron transfer amplitude and superexchange coupling
between the core spins are estimated.",0012166v2
2002-12-05,Dynamic stiffness of spin valves,"The dynamics of the magnetic order parameters of
ferromagnet/normal-metal/ferromagnet spin valves and isolated ferromagnets may
be very different. We investigate the role of the nonequilibrium spin-current
exchange between the ferromagnets in the magnetization precession and
switching. We find a (low-temperature) critical current bias for a coherent
current-induced magnetization excitation in spin valves, which unifies and
generalizes previous ideas of Slonczewski and Berger. In the absence of an
applied bias, the effect of the spin transfer can be expressed as
magnetic--configuration-dependent Gilbert damping.",0212130v2
2003-04-04,Dynamic exchange coupling and Gilbert damping in magnetic multilayers,"We theoretically study dynamic properties of thin ferromagnetic films in
contact with normal metals. Moving magnetizations cause a flow of spins into
adjacent conductors, which relax by spin flip, scatter back into the
ferromagnet, or are absorbed by another ferromagnet. Relaxation of spins
outside the moving magnetization enhances the overall damping of the
magnetization dynamics in accordance with the Gilbert phenomenology. Transfer
of spins between different ferromagnets by these nonequilibrium spin currents
leads to a long-ranged dynamic exchange interaction and novel collective
excitation modes. Our predictions agree well with recent
ferromagnetic-resonance experiments on ultrathin magnetic films.",0304116v1
2004-08-17,Full Counting Statistics with Spin-sensitive Detectors reveals Spin-singlets,"We study the full counting statistics of electric current to several drain
terminals with spin-dependent entrance conductances. We show that the
statistics of charge transfers can be interpreted in terms of single electrons
and spin-singlet pairs coming from the source. If the source contains transport
channels of high transparency, a significant fraction of electrons comes in
spin-singlet pairs.",0408377v2
2004-11-22,Spin current through a tunnel junction,"We derive an expression for the spin-current through a tunnel barrier in
terms of many-body Green's functions. The spin current has two contributions.
One can be associated with angular-momentum transfer by spin-polarized charge
currents crossing the junction. If there are magnetic moments on both sides of
the tunnel junction, due to spin accumulation or ferromagnetic ordering, then
there is a second contribution related to the exchange coupling between the
moments.",0411562v1
2005-09-02,Spin-dependent resonant tunneling in ZnSe/ZnMnSe heterostructures,"Using the transfer matrix method and the effective-mass approximation, the
effect of resonant states on spin transport is studied in
ZnSe/ZnMnSe/ZnSe/ZnMnSe/ZnSe structures under the influence of both electric
and magnetic fields. The numerical results show that the ZnMnSe layers, which
act as spin filters, polarize the electric currents. Variation of thickness of
the central ZnSe layer shifts the resonant levels and exhibits an oscillatory
behavior in spin current densities. It is also shown that the spin polarization
of the tunneling current in geometrical asymmetry of the heterostructure where
two ZnMnSe layers have different Mn concentrations, depends strongly on the
thickness and the applied bias.",0509067v1
2002-10-30,Properties of the Spin-flip Amplitude of Hadron Elastic Scattering and Possible Polarization Effects at RHIC,"With relation to the RHIC spin program we research the polarization effects
in elastic proton-proton scattering at small momentum transfer and in the
diffraction dip region. The calculations take into account the Coulomb-hadron
interference effects including the additional Coulomb-hadron phase. In
particular we show the impact of the form of the hadron potential at large
distances on the behavior of the hadron spin-flip amplitude at small angles.
The $t$-dependence of the spin-flip amplitude of high energy hadron elastic
scattering is analyzed under different assumptions on the hadron interaction.",0210418v1
2005-07-28,Quantum entanglement dynamics and decoherence wave in spin chains at finite temperatures,"We analyze the quantum entanglement at the equilibrium in a class of exactly
solvable one-dimensional spin models at finite temperatures and identify a
region where the quantum fluctuations determine the behavior of the system. We
probe the response of the system in this region by studying the spin dynamics
after projective measurement of one local spin which leads to the appearance of
the ``decoherence wave''. We investigate time-dependent spin correlation
functions, the entanglement dynamics, and the fidelity of the quantum
information transfer after the measurement.",0507266v1
2009-12-03,Method for deducing anisotropic spin-exchange rates,"Using measured spin-transfer rates from alkali atoms to He-3, combined with
spin-relaxation rates of the alkali atoms due to He-3 and He-4, it should be
possible to differentiate between isotropic and anisotropic spin-exchange. This
would give a fundamental limit on the He-3 polarization attainable in
spin-exchange optical pumping. For K-He, we find the limit to be 0.90+-0.11.",0912.0747v2
2013-06-25,Thermodynamics of quantum spin chains with competing interactions,"We consider integrable quantum spin chains with competing interactions. We
apply the quantum transfer matrix approach to these spin chains. This allowed
us to derive a set of non-linear integral equations for the thermodynamics of
these spin chains. We provide numerical solution of these integral equations
for the entropy as function of magnetic field, temperature and the coupling
constant. This allow us to assess, at low but finite temperature, the picture
describing the ground state diagram for high spin chain and longer range
interchain interactions.",1306.6040v1
2015-05-06,Spintronics and Magnon Bose-Einstein Condensation,"Spintronics is the science and technology of electric control over spin
currents in solid-state-based devices. Recent advances have demonstrated a
coupling between electronic spin currents in non-magnetic metals and magnons in
magnetic insulators. The coupling is due to spin transfer and spin pumping at
interfaces between the normal metals and magnetic insulators. In this Chapter,
we review these developments and the prospects they raise for electric control
of quasi-equilibrium magnon Bose-Einstein condensates and spin superfluidity.",1505.01329v1
2017-04-05,Spectroscopy and spin dynamics for strongly interacting few spinor bosons in one-dimensional traps,"We consider a one-dimensional trapped gas of strongly interacting few spin-1
atoms which can be described by an effective spin chain Hamiltonian. Away from
the SU(3) integrable point, where the energy spectrum is highly degenerate, the
rules of ordering and crossing of the energy levels and the symmetry of the
eigenstates in the regime of large but finite repulsion have been elucidated.
We study the spin-mixing dynamics which is shown to be very sensitive to the
ratio between the two channel interactions g0/g2 and the effective spin chain
transfers the quantum states more perfectly than the Heisenberg
bilinear-biquadratic spin chain.",1704.01245v1
2017-07-03,The Reversible Spin Switch by External Control of Interval Distance of CuPc and C59N with the investigation of DFT,"In this paper, we introduce a new kind of spin switch based on a joint system
of copper phthalocyanine (CuPc) and C59N. Using density functional theory, we
investigate the total magnetic moment of this system when gradually changing
the interval distance between two molecules. The spin hopping happens during
the critical distance with very low energy. This phenomenon shows a possible
reality of reversible spin switch by external control of the interval distance.
With orbital analysis and electron transfer consideration, the form of C59N+-
CuPc- ion pair support this spin hopping phenomenon.",1707.00413v2
2019-03-18,Theory of spin transport through antiferromagnetic insulator,"A theoretical formulation for spin transport through an antiferromagnetic
(AF) insulator is presented in the case driven/detected by direct/inverse spin
Hall effect in two heavy metal contacts. The spin signal is shown to be
transferred by the ferromagnetic correlation function of the antiferromagnet,
which is calculated based on a magnon representation. To cover high temperature
regimes, we include an auxiliary field representing short AF correlations and a
temperature-dependent damping due to magnon scattering. The diffusion length
for spin is long close to the degeneracy of the two AF magnons, and has a
maximum as function of temperature near the N\'eel transition.",1903.07223v1
2019-06-14,Application of the Landauer formalism to the calculation of spin current,"In this communication we apply the Landauer method and transfer matrix
formalism to the calculation of spin current in magnetic multilayered
structures within a ballistic quantum-mechanical regime. The method provides an
elegant and intuitive formalism with which to study spin current properties and
within which closed-form expressions with a transparent physical interpretation
can be obtained. We apply the method to illuminate origin and the symmetry
properties of the various spin current components within the parabolic band
approximation. We also apply the stationary phase approximation to develop
asymptotic approximations to the total spin current within this formalism, and
show that these give excellent agreement with full numerical calculations for
both barrier and well systems.",1906.06097v1
2020-07-22,Nanomagnonic cavities for strong spin-magnon coupling,"We present a theoretical approach to use ferro- or ferrimagnetic
nanoparticles as microwave nanomagnonic cavities to concentrate microwave
magnetic fields into deeply subwavelength volumes $\sim 10^{-13}$ mm$^3$. We
show that the field in such nanocavities can efficiently couple to isolated
spin emitters (spin qubits) positioned close to the nanoparticle surface
reaching the single magnon-spin strong-coupling regime and mediate efficient
long-range quantum state transfer between isolated spin emitters. Nanomagnonic
cavities thus pave the way towards magnon-based quantum networks and
magnon-mediated quantum gates.",2007.11595v1
2021-11-29,Transforming spin chains with a continuous driving field,"A continuous, sinusoidal control field is used to suitably transform quantum
spin chains. In particular, we are able to transform the quantum Ising chain to
the quantum XY model, and the XY model to the XYZ spin chain. Our applied
control field can also mitigate the effect of noise on the spin chain. We show
how these spin chain transformations can be useful for quantum state transfer
as well as entanglement generation.",2111.14644v1
2002-05-14,On the coorbital corotation torque in a viscous disk and its impact on planetary migration,"We evaluate the coorbital corotation torque on a planet on a fixed circular
orbit embedded in a viscous protoplanetary disk, for the case of a steady flow
in the planet frame. This torque can be evaluated just from the flow properties
at the separatrix between the librating (horseshoe) and circulating
streamlines. A stationary solution is searched for the flow in the librating
region. When used to evaluate the torque exerted by the circulating material of
the outer and inner disk on the trapped material of the librating region, this
solution leads to an expression of the coorbital corotation torque in agreement
with previous estimates. An analytical expression is given for the corotation
torque as a function of viscosity. Lastly, we show that additional terms in the
torque expression can play a crucial role. In particular, they introduce a
coupling with the disk density profile perturbation (the `dip' which surrounds
the planet) and add to the corotation torque a small, positive fraction of the
one-sided Lindblad torque. As a consequence, the migration could well be
directed outwards in very thin disks (aspect ratio smaller than a few percent).
This 2D analysis is especially relevant for mildly embedded protoplanets
(sub-Saturn sized objects).",0205209v1
2007-09-24,Pairing Symmetry of CeCoIn$_5$ Detected by In-plane Torque Measurements,"In-plane torque measurements were performed on heavy fermion CeCoIn$_5$
single crystals in the temperature $T$ range 1.8 K $\leq T \leq 10$ K and
applied magnetic field $H$ up to 14 T. The normal-state torque is given by
$\tau_n \propto H^4(1+T/T_K)^{-1}\sin 4\phi$. The reversible part of the
mixed-state torque, obtained after subtracting the corresponding normal state
torque, shows also a four-fold symmetry. In addition, sharp peaks are present
in the irreversible torque at angles of $\pi/$4, 3$\pi$/4, 5$\pi$/4, 7$\pi$/4,
etc. Both the four-fold symmetry in the reversible torque and the sharp peaks
in the irreversible torque of the mixed state imply $d_{xy}$ symmetry of the
superconducting order parameter. The field and temperature dependences of the
reversible mixed-state torque provide further evidence for $d_{xy}$ wave
symmetry. The four-fold symmetry in the normal state has a different origin
since it has different field and temperature dependences than the one in the
mixed state. The possible reasons of the normal state four-fold symmetry are
discussed.",0709.3771v1
2007-09-26,Torques on Spheroidal Silicate Grains Exposed to Anisotropic Interstellar Radiation Fields,"Radiative torques, due to the absorption and scattering of starlight, are
thought to play a major role in the alignment of grains with the interstellar
magnetic field. The absorption of radiation also gives rise to recoil torques,
associated with the photoelectric effect and photodesorption. The recoil
torques are much more difficult to model and compute than the direct radiative
torque. Here, we consider the relatively simple case of a spheroidal grain.
Given our best estimates for the photoelectric yield and other relevant grain
physical properties, we find that the recoil torques contribute at the 10%
level or less compared with the direct radiative torque. We recommend that the
recoil torques not be included in models of radiation-driven grain alignment at
this time. However, additional experimental characterization of the surface
properties and photoelectric yield for sub-micron grains is needed to better
quantify the magnitude of these torques.",0709.4159v1
2010-10-21,Van der Waals torque induced by external magnetic fields,"We present a method for inducing and controlling van der Waals torques
between two parallel slabs using a constant magnetic field. The torque is
calculated using the Barash theory of dispersive torques. In III-IV
semiconductors such as $InSb$, the effect of an external magnetic field is to
induce an optical anisotropy, in an otherwise isotropic material, that will in
turn induce a torque.
  The calculations of the torque are done in the Voigt configuration, with the
magnetic field parallel to the surface of the slabs. As a case study we
consider a slab made of calcite and a second slab made of $InSb$. In the
absence of magnetic field there is no torque. As the magnetic field increases,
the optical anisotropy of $InSb$ increases and the torque becomes different
from zero, increasing with the magnetic field. The resulting torque is of the
same order of magnitude as that calculated using permanent anisotropic
materials when the magnetic fields is close to 1 T.",1010.4553v1
2015-05-20,The optical torque on small bi-isotropic particles,"Most previous theoretical studies on the optical torque exerted by light on
dipolar particles are incomplete. Here we establish the equations for the
time-averaged optical torque on dipolar bi-isotropic particles. Due to the
interference of scattered fields, it has a term additional to that commonly
employed in theory and experiments. Its consequences for conservation of
energy, angular momentum, and effects like negative torques, are discussed.",1505.05357v2
2017-06-10,Neoclassical toroidal viscosity torque in tokamak edge pedestal induced by external resonant magnetic perturbation,"The characteristic profile and magnitude are predicted in theory for the
neoclassical toroidal viscosity (NTV) torque induced by plasma response to the
resonant magnetic perturbation (RMP) in a tokamak with an edge pedestal. For a
low-$\beta$ equilibrium, the NTV torque is dominated by the toroidal component
with the same dominant toroidal mode number of RMP. The NTV torque profile is
found to be localized, whose peak location is determined by profiles of both
the equilibrium temperature (pressure) and the plasma response. In general, the
peak of NTV torque profile is found to track the pedestal position. The
magnitude of NTV torque strongly depends on the $\beta$ value of pedestal,
which suggests a more significant role of NTV torque in higher plasma $\beta$
regimes. For a fixed plasma $\beta$, decreasing density hence increasing
temperature can also enhance the amplitude of NTV torque due to the reduced
collisionality in the $1/\nu$ regime. Based on those findings, we identify the
tokamak operation regimes where the significance of NTV torque in edge pedestal
induced by RMP can approach those from other momentum sources such as the
neutral beam injections.",1706.03213v1
2023-11-09,Forceps with direct torque control,"This study presents a conceptual design of laparoscopic forceps whose
grasping torque can be directly controlled by the user. By integrating an
adjustable constant torque mechanism, the handle opening angle is converted to
the grasping torque irrespective of the jaw opening angle. This feature
overcomes the limitation regarding of the lack of direct haptic feedback in
laparoscopic minimally invasive surgery, preventing damage of delicate tissue
during forceps grasping.",2311.05178v1
2001-05-10,Testing Tidal-Torque Theory: II. Alignment of Inertia and Shear and the Characteristics of Proto-haloes,"We investigate the cross-talk between the two key components of tidal-torque
theory, the inertia (I) and shear (T) tensors, using a cosmological N-body
simulation with thousands of well-resolved haloes. We find that the principal
axes of I and T are strongly aligned, even though I characterizes the
proto-halo locally while T is determined by the large-scale structure. Thus,
the resultant galactic spin, which plays a key role in galaxy formation, is
only a residual due to ~10 per cent deviations from perfect alignment of T and
I. The T-I correlation induces a weak tendency for the proto-halo spin to be
perpendicular to the major axes of T and I, but this correlation is erased by
non-linear effects at late times, making the observed spins poor indicators of
the initial shear field. However, the T-I correlation implies that the shear
tensor can be used for identifying the positions and boundaries of proto-haloes
in cosmological initial conditions -- a missing piece in galaxy formation
theory. The typical configuration is of a prolate proto-halo lying
perpendicular to a large-scale high-density ridge, with the surrounding voids
inducing compression along the major and intermediate inertia axes of the
proto-halo. This leads to a transient sub-halo filament along the large-scale
ridge, whose sub-clumps then flow along the filament and merge into the final
halo. The centres of proto-haloes tend to lie in ~1 sigma over-density regions,
but their association with linear density maxima smoothed on galactic scales is
vague: only ~40 per cent of the proto-haloes contain peaks within them. Several
other characteristics distinguish proto-haloes from density peaks, e.g., they
tend to compress along two principal axes while many peaks compress along three
axes.",0105165v2
2006-06-04,The Spin of the Near-Extreme Kerr Black Hole GRS 1915+105,"Based on a spectral analysis of the X-ray continuum that employs a fully
relativistic accretion-disk model, we conclude that the compact primary of the
binary X-ray source GRS 1915+105 is a rapidly-rotating Kerr black hole. We find
a lower limit on the dimensionless spin parameter of a* greater than 0.98. Our
result is robust in the sense that it is independent of the details of the data
analysis and insensitive to the uncertainties in the mass and distance of the
black hole. Furthermore, our accretion-disk model includes an advanced
treatment of spectral hardening. Our data selection relies on a rigorous and
quantitative definition of the thermal state of black hole binaries, which we
used to screen all of the available RXTE and ASCA data for the thermal state of
GRS 1915+105. In addition, we focus on those data for which the accretion disk
luminosity is less than 30% of the Eddington luminosity. We argue that these
low-luminosity data are most appropriate for the thin alpha-disk model that we
employ. We assume that there is zero torque at the inner edge of the disk, as
is likely when the disk is thin, although we show that the presence of a
significant torque does not affect our results. Our model and the model of the
relativistic jets observed for this source constrain the distance and black
hole mass and could thus be tested by determining a VLBA parallax distance and
improving the measurement of the mass function. Finally, we comment on the
significance of our results for relativistic-jet and core-collapse models, and
for the detection of gravitational waves.",0606076v2
2001-07-27,Conventional Forces can Explain the Anomalous Acceleration of Pioneer 10,"Anderson, et al. find the measured trajectories of Pioneer 10 and 11
spacecraft deviate from the trajectories computed from known forces acting on
them. This unmodelled acceleration (and the less well known, but similar,
unmodelled torque) can be accounted for by non-isotropic radiation of
spacecraft heat. Various forms of non-isotropic radiation were proposed by
Katz, Murphy, and Scheffer, but Anderson, et al. felt that none of these could
explain the observed effect. This paper calculates the known effects in more
detail and considers new sources of radiation, all based on spacecraft
construction. These effects are then modelled over the duration of the
experiment. The model reproduces the acceleration from its appearance at a
heliocentric distance of 5 AU to the last measurement at 71 AU to within 10
percent. However, it predicts a larger decrease in acceleration between
intervals I and III of the Pioneer 10 observations than is observed. This is a
2 sigma discrepancy from the average of the three analyses (SIGMA, CHASMP, and
Markwardt). A more complex (but more speculative) model provides a somewhat
better fit. Radiation forces can also plausibly explain the previously
unmodelled torques, including the spindown of Pioneer 10 that is directly
proportional to spacecraft bus heat, and the slow but constant spin-up of
Pioneer 11. In any case, by accounting for the bulk of the acceleration, the
proposed mechanism makes it much more likely that the entire effect can be
explained without the need for new physics.",0107092v5
2012-08-03,Dynamical evolution and spin-orbit resonances of potentially habitable exoplanets. The case of GJ 581d,"GJ 581d is a potentially habitable super-Earth in the multiple system of
exoplanets orbiting a nearby M dwarf. We investigate this planet's long-term
dynamics, with an emphasis on its probable final rotation states acquired via
tidal interaction with the host.
  The published radial velocities for the star are re-analysed with a benchmark
planet detection algorithm, to confirm that there is no evidence for the
recently proposed two additional planets (f and g). Limiting the scope to the
four originally detected planets, we assess the dynamical stability of the
system and find bounded chaos in the orbital motion. For the planet d, the
characteristic Lyapunov time is 38 yr. Long-term numerical integration reveals
that the system of four planets is stable, with the eccentricity of the planet
d changing quasi-periodically in a tight range around 0.27, and with its
semimajor axis varying only a little.
  The spin-orbit interaction of GJ 581d with its host star is dominated by the
tides exerted by the star on the planet. We model this interaction, assuming a
terrestrial composition of the mantle. Besides the customarily included secular
parts of the triaxiality-caused and tidal torques, we also include these
torques' oscillating components. It turns out that, dependent on the mantle
temperature, the planet gets trapped into the 2:1 or an even higher spin-orbit
resonance. It is very improbable that the planet could have reached the 1:1
resonance. This enhances the possibility of the planet being suitable for
sustained life.",1208.0814v5
2017-06-27,Dissipation in a tidally perturbed body librating in longitude,"Internal dissipation in a tidally perturbed librating body differs from the
tidal dissipation in a steadily spinning rotator. First, libration changes the
spectral distribution of tidal damping across the tidal modes, as compared to
the case of steady spin. This changes both the tidal heating rate and the tidal
torque. Second, while a non-librating rotator experiences alternating
deformation only due to the potential force exerted on it by the perturber, a
librating body is also subject to a toroidal force proportional to the angular
acceleration. Third, while the centrifugal force in a steadily spinning body
renders only a permanent deformation, in a librating body this force contains
two alternating components $-$ one radial, another a degree-2 potential force.
Both contribute to heating, as well as to the tidal torque and potential.
  We build a formalism to describe dissipation in a homogeneous terrestrial
body performing small-amplitude libration in longitude. This formalism
incorporates a linear rheological law defining the response of the material to
forcing. While the formalism can work with an arbitrary linear rheology, we
consider a simple example of a Maxwell material.
  We show that, independent of rheology, the forced libration in longitude can
provide a considerable and even leading input in the tidal heating. Based on
the observed parameters, this input amounts to 52% in Phobos, 33% in Mimas, 23%
in Enceladus, and 96% in Epimetheus. This supports the hypothesis by Makarov &
Efroimsky (2014) that the additional damping due to forced libration may have
participated in the early heating up of some moons. As one possibility, a moon
could have been chipped by collisions $-$ whereby it acquired a higher
triaxiality and a higher forced-libration magnitude and, consequently, a higher
heating rate. After the moon warms up, its triaxiality reduces, and so does the
tidal heating.",1706.08999v4
2019-03-31,Spin-Orbit Torque Devices for Hardware Security: From Deterministic to Probabilistic Regime,"Protecting intellectual property (IP) has become a serious challenge for chip
designers. Most countermeasures are tailored for CMOS integration and tend to
incur excessive overheads, resulting from additional circuitry or device-level
modifications. On the other hand, power density is a critical concern for
sub-50 nm nodes, necessitating alternate design concepts. Although initially
tailored for error-tolerant applications, imprecise computing has gained
traction as a general-purpose design technique. Emerging devices are currently
being explored to implement ultra-low-power circuits for inexact computing
applications. In this paper, we quantify the security threats of imprecise
computing using emerging devices. More specifically, we leverage the innate
polymorphism and tunable stochastic behavior of spin-orbit torque (SOT)
devices, particularly, the giant spin-Hall effect (GSHE) switch. We enable IP
protection (by means of logic locking and camouflaging) simultaneously for
deterministic and probabilistic computing, directly at the GSHE device level.
We conduct a comprehensive security analysis using state-of-the-art Boolean
satisfiability (SAT) attacks; this study demonstrates the superior resilience
of our GSHE primitive when tailored for deterministic computing. We also
demonstrate how probabilistic computing can thwart most, if not all, existing
SAT attacks. Based on this finding, we propose an attack scheme called
probabilistic SAT (PSAT) which can bypass the defense offered by logic locking
and camouflaging for imprecise computing schemes. Further, we illustrate how
careful application of our GSHE primitive can remain secure even on the
application of the PSAT attack. Finally, we also discuss side-channel attacks
and invasive monitoring, which are arguably even more concerning threats than
SAT attacks.",1904.00421v1
2019-09-30,First-principles theory of proximity spin-orbit torque on a two-dimensional magnet: Current-driven antiferromagnet-to-ferromagnet reversible transition in bilayer CrI$_3$,"The recently discovered two-dimensional (2D) magnetic insulator CrI$_3$ is an
intriguing case for basic research and spintronic applications since it is a
ferromagnet in the bulk, but an antiferromagnet in bilayer form, with its
magnetic ordering amenable to external manipulations. Using first-principles
quantum transport approach, we predict that injecting unpolarized charge
current parallel to the interface of bilayer-CrI$_3$/monolayer-TaSe$_2$ van der
Waals heterostructure will induce spin-orbit torque (SOT) and thereby driven
dynamics of magnetization on the first monolayer of CrI$_3$ in direct contact
with TaSe$_2$. By combining calculated complex angular dependence of SOT with
the Landau-Lifshitz-Gilbert equation for classical dynamics of magnetization,
we demonstrate that current pulses can switch the direction of magnetization on
the first monolayer to become parallel to that of the second monolayer, thereby
converting CrI$_3$ from antiferromagnet to ferromagnet while not requiring any
external magnetic field. We explain the mechanism of this reversible
current-driven nonequilibrium phase transition by showing that first monolayer
of CrI$_3$ carries current due to evanescent wavefunctions injected by metallic
transition metal dichalcogenide TaSe$_2$, while concurrently acquiring strong
spin-orbit coupling (SOC) via such proximity effect, whereas the second
monolayer of CrI$_3$ remains insulating. The transition can be detected by
passing vertical read current through the vdW heterostructure, encapsulated by
bilayer of hexagonal boron nitride and sandwiched between graphite electrodes,
where we find tunneling magnetoresistance of $\simeq 240$%.",1909.13876v2
2020-05-15,Helium Ion Microscopy for Reduced Spin Orbit Torque Switching Currents,"Spin orbit torque driven switching is a favourable way to manipulate
nanoscale magnetic objects for both memory and wireless communication devices.
The critical current required to switch from one magnetic state to another
depends on the geometry and the intrinsic properties of the materials used,
which are difficult to control locally. Here we demonstrate how focused helium
ion beam irradiation can modulate the local magnetic anisotropy of a Co thin
film at the microscopic scale. Real-time in-situ characterisation using the
anomalous Hall effect showed up to an order of magnitude reduction of the
magnetic anisotropy under irradiation, and using this, multi-level switching is
demonstrated. The result is that spin-switching current densities, down to 800
kA cm$^{-2}$, can be achieved on predetermined areas of the film, without the
need for lithography. The ability to vary critical currents spatially has
implications not only for storage elements, but also neuromorphic and
probabilistic computing.",2005.07626v2
2024-03-29,Dynamical tides during the inspiral of rapidly spinning neutron stars: Solutions beyond mode resonance,"We investigate the dynamical tide in coalescing binaries involving neutron
stars (NSs). The deformed NS is assumed to spin rapidly, with its spin axis
anti-aligned with the orbit. Such an NS may exist if the binary forms
dynamically, and it can lead to a strong tide because the NS f-mode can be
resonantly excited during the inspiral. We present a new analytical solution
for the f-mode resonance by decomposing the tide into a resummed equilibrium
component varying at the forcing frequency and a dynamical component varying at
the mode eigenfrequency. This solution simplifies numerical implementations by
avoiding the subtraction of two diverging terms. It also extends the solution's
validity to frequencies beyond mode resonance. When the dynamical tide back
reacts on the orbit, the effective Love number alone is insufficient because it
does not capture the tidal torque on the orbit that dominates the back reaction
during resonance. An additional dressing factor is therefore introduced to
model the torque. The dissipative interaction between the NS and the orbital
mass multipoles is computed including the dynamical tide and shown to be
subdominant compared to the conservative interaction. We show that orbital
phase shifts caused by the $l=3$ and $l=2$ f-modes can reach 0.5 and 10 radians
at their respective resonances. Because of the large impact of the dynamical
tide, a linearized description becomes insufficient, calling for future
developments to incorporate higher-order corrections. After mode excitation,
the orbit cannot remain quasi-circular, and the eccentricity excited by the
$l=2$ dynamical tide can approach nearly $e\simeq 0.1$, leading to
non-monotonic frequency evolution. Lastly, we demonstrate that the GW radiation
from the resonantly excited f-mode alone can be detected with a signal-to-noise
ratio exceeding unity at a distance of 50 Mpc with the next-generation GW
detectors.",2404.00147v1
2004-02-03,Semiclassical kinetic theory of electron spin relaxation in semiconductors,"We develop a semiclassical kinetic theory for electron spin relaxation in
semiconductors. Our approach accounts for elastic as well as inelastic
scattering and treats Elliott-Yafet and motional-narrowing processes, such as
D'yakonov-Perel' and variable g-factor processes, on an equal footing. Focusing
on small spin polarizations and small momentum transfer scattering, we derive,
starting from the full quantum kinetic equations, a Fokker-Planck equation for
the electron spin polarization. We then construct, using a rigorous multiple
time scale approach, a Bloch equation for the macroscopic ($\vec{k}$-averaged)
spin polarization on the long time scale, where the spin polarization decays.
Spin-conserving energy relaxation and diffusion, which occur on a fast time
scale, after the initial spin polarization has been injected, are incorporated
and shown to give rise to a weight function which defines the energy averages
required for the calculation of the spin relaxation tensor in the Bloch
equation. Our approach provides an intuitive way to conceptualize the dynamics
of the spin polarization in terms of a ``test'' spin polarization which
scatters off ``field'' particles (electrons, impurities, phonons). To
illustrate our approach, we calculate for a quantum well the spin lifetime at
temperatures and densities where electron-electron and electron-impurity
scattering dominate. The spin lifetimes are non-monotonic functions of
temperature and density. Our results show that at electron densities and
temperatures, where the cross-over from the non-degenerate to the degenerate
regime occurs, spin lifetimes are particularly long.",0402085v4
2010-08-12,"Semiconductor Spin Noise Spectroscopy: Fundamentals, Accomplishments, and Challenges","Semiconductor spin noise spectroscopy (SNS) has emerged as a unique
experimental tool that utilizes spin fluctuations to provide profound insight
into undisturbed spin dynamics in doped semiconductors and semiconductor
nanostructures. The technique maps ever present stochastic spin polarization of
free and localized carriers at thermal equilibrium via the Faraday effect onto
the light polarization of an off-resonant probe laser and was transferred from
atom optics to semiconductor physics in 2005. The inimitable advantage of spin
noise spectroscopy to all other probes of semiconductor spin dynamics lies in
the fact that in principle no energy has to be dissipated in the sample, i.e.,
SNS exclusively yields the intrinsic, undisturbed spin dynamics and promises
optical non-demolition spin measurements for prospective solid state based
optical spin quantum information devices. SNS is especially suitable for small
electron ensembles as the relative noise increases with decreasing number of
electrons. In this review, we first introduce the basic principles of SNS and
the difference in spin noise of donor bound and of delocalized conduction band
electrons. We continue the introduction by discussing the spectral shape of
spin noise and prospects of spin noise as a quantum interface between light and
matter. In the main part, we give a short overview about spin relaxation in
semiconductors and summarize corresponding experiments employing SNS. Finally,
we give in-depth insight into the experimental aspects and discuss possible
applications of SNS.",1008.2191v2
2017-07-22,Transverse spinning of light with globally unique handedness,"Access to the transverse spin of light has unlocked new regimes in
topological photonics and optomechanics. To achieve the transverse spin of
nonzero longitudinal fields, various platforms that derive transversely
confined waves based on focusing, interference, or evanescent waves have been
suggested. Nonetheless, because of the transverse confinement inherently
accompanying sign reversal of the field derivative, the resulting transverse
spin handedness experiences spatial inversion, which leads to a mismatch
between the densities of the wavefunction and its spin component and hinders
the global observation of the transverse spin. Here, we reveal a globally pure
transverse spin in which the wavefunction density signifies the spin
distribution, by employing inverse molding of the eigenmode in the spin basis.
Starting from the target spin profile, we analytically obtain the potential
landscape and then show that the elliptic-hyperbolic transition around the
epsilon-near-zero permittivity allows for the global conservation of transverse
spin handedness across the topological interface between anisotropic
metamaterials. Extending to the non-Hermitian regime, we also develop
annihilated transverse spin modes to cover the entire Poincare sphere of the
meridional plane. Our results enable the complete transfer of optical energy to
transverse spinning motions and realize the classical analogy of 3-dimensional
quantum spin states.",1707.07099v1
2017-10-20,Spin relaxation of a donor electron coupled to interface states,"An electron spin qubit in a silicon donor atom is a promising candidate for
quantum information processing because of its long coherence time. To be sensed
with a single-electron transistor, the donor atom is usually located near an
interface, where the donor states can be coupled with interface states. Here we
study the phonon-assisted spin-relaxation mechanisms when a donor is coupled to
confined (quantum-dot-like) interface states. We find that both Zeeman
interaction and spin-orbit interaction can hybridize spin and orbital states,
each contributing to phonon-assisted spin relaxation in addition to the spin
relaxation for a bulk donor or a quantum dot. When the applied magnetic field
$B$ is weak (compared to orbital spacing), the phonon assisted spin relaxation
shows the $B^5$ dependence. We find that there are peaks (hot-spots) in the
$B$-dependent and detuning dependent spin relaxation due to strong
hybridization of orbital states with opposite spin. We also find spin
relaxation dips (cool-spots) due to the interference of different relaxation
channels. Qubit operations near spin relaxation hot-spots can be useful for the
fast spin initialization and near cool-spots for the preservation of quantum
information during the transfer of spin qubits.",1710.07674v2
2017-06-05,Robust techniques for polarization and detection of nuclear spin ensembles,"Highly sensitive nuclear spin detection is crucial in many scientific areas
including nuclear magnetic resonance spectroscopy (NMR), imaging (MRI) and
quantum computing. The tiny thermal nuclear spin polarization represents a
major obstacle towards this goal which may be overcome by Dynamic Nuclear Spin
Polarization (DNP) methods. The latter often rely on the transfer of the
thermally polarized electron spins to nearby nuclear spins, which is limited by
the Boltzmann distribution of the former. Here we demonstrate the polarization
and read out of a nuclear spin bath consisting of $^{13}$C nuclear spins in
diamond by using a single nitrogen-vacancy (NV) center. Our method utilizes
microwave dressed states to transfer the NV's high ($>$~92~\%) non-equilibrium
electron spin polarization induced by short laser pulses to the surrounding
carbon nuclear spins, where the NV is repeatedly repolarized optically, thus
providing an effectively infinite polarization reservoir. A saturation of the
polarization in the nuclear ""frozen core"" is achieved, which is confirmed by
the decay of the polarization transfer signal and shows an excellent agreement
with theoretical simulations. Hereby we introduce the Polarization Read Out by
Polarization Inversion (PROPI) method as a quantitative magnetization measure
of the nuclear spin bath. Moreover, we show that using the integrated solid
effect both for single and double quantum transitions a nuclear spin
polarization can be achieved even when the static magnetic field is not aligned
along the NV's crystal axis. This opens a path for the application of our DNP
technique to spins in and outside of nanodiamonds, enabling their application
as MRI tracers.",1706.01315v2
2014-04-28,Experimental Heat-Bath Cooling of Spins,"Algorithmic cooling (AC) is a method to purify quantum systems, such as
ensembles of nuclear spins, or cold atoms in an optical lattice. When applied
to spins, AC produces ensembles of highly polarized spins, which enhance the
signal strength in nuclear magnetic resonance (NMR). According to this cooling
approach, spin-half nuclei in a constant magnetic field are considered as bits,
or more precisely, quantum bits, in a known probability distribution.
Algorithmic steps on these bits are then translated into specially designed NMR
pulse sequences using common NMR quantum computation tools. The $algorithmic$
cooling of spins is achieved by alternately combining reversible,
entropy-preserving manipulations (borrowed from data compression algorithms)
with $selective$ $reset$, the transfer of entropy from selected spins to the
environment. In theory, applying algorithmic cooling to sufficiently large spin
systems may produce polarizations far beyond the limits due to conservation of
Shannon entropy.
  Here, only selective reset steps are performed, hence we prefer to call this
process ""heat-bath"" cooling, rather than algorithmic cooling. We experimentally
implement here two consecutive steps of selective reset that transfer entropy
from two selected spins to the environment. We performed such cooling
experiments with commercially-available labeled molecules, on standard
liquid-state NMR spectrometers. Our experiments yielded polarizations that
$bypass$ $Shannon's$ $entropy$-$conservation$ $bound$, so that the entire
spin-system was cooled. This paper was initially submitted in 2005, first to
Science and then to PNAS, and includes additional results from subsequent years
(e.g. for resubmission in 2007). The Postscriptum includes more details.",1404.6885v1
2018-02-13,Efficient conversion of anti-phase spin order of protons into 15N magnetization using SLIC-SABRE,"SABRE (Signal Amplification By Reversible Exchange) is a technique for
enhancement of NMR (Nuclear Magnetic Resonance) signals, which utilizes
parahydrogen (pH2, the H2 molecule in its nuclear spin state) as a source of
non-thermal spin order. In SABRE experiments, pH2 binds to an organometallic
complex with a to-be-polarized substrate; subsequently, spin order transfer
takes place and the substrate acquires non-thermal spin polarization resulting
in strong NMR signal enhancement. In this work we argue that the spin order of
H2 in SABRE experiments performed at high magnetic fields is not necessarily
the singlet order but rather anti-phase polarization, $S_{1z}S_{2z}$. Although
SABRE exploits pH2, i.e., the starting spin order of H2 is supposed to be the
singlet order, in solution S-T0 conversion becomes efficient once pH2 binds to
a complex. Such a variation of the spin order, which becomes $S_{1z}S_{2z}$,
has an important consequence: NMR methods used for transferring SABRE
polarization need to be modified. Here we demonstrate that methods proposed for
the initial singlet order may not work for the S_1z S_2z order; however, a
simple modification makes them efficient again. A theoretical treatment of the
problem under consideration is proposed; these considerations are supported by
high-field SABRE experiments. Hence, for efficient use of SABRE one should note
that polarization formation is a complex multi-stage process: careful
optimization of this process may not only deal with chemical aspects but also
with the spin dynamics, including the spin dynamics of H2.",1802.04471v1
2021-12-14,Rapidly enhanced spin polarization injection in an optically pumped spin ratchet,"Rapid injection of spin polarization into an ensemble of nuclear spins is a
problem of broad interest, spanning dynamic nuclear polarization (DNP) to
quantum information science. We report on a strategy to boost the spin
injection rate by exploiting electrons that can be rapidly polarized via
high-power optical pumping. We demonstrate this in a model system of Nitrogen
Vacancy center electrons injecting polarization into a bath of 13C nuclei in
diamond. We deliver >20W of continuous, nearly isotropic, optical power to the
sample, constituting a substantially higher power than in previous experiments.
Through a spin-ratchet polarization transfer mechanism, we show boosts in spin
injection rates by over two orders of magnitude. Our experiments elucidate
bottlenecks in the DNP process caused by rates of electron polarization,
polarization transfer to proximal nuclei, and spin diffusion. This work
demonstrates opportunities for rapid spin injection employing non-thermally
generated electron polarization, and has relevance to a broad class of
experimental systems including in DNP, quantum sensing, and spin-based MASERs.",2112.07223v3
2009-07-13,A multideterminant assessment of mean field methods for the description of electron transfer in the weak coupling regime,"Multideterminant calculations have been performed on model systems to
emphasize the role of many-body effects in the general description of charge
quantization experiments. We show numerically and derive analytically that a
closed-shell ansatz, the usual ingredient of mean-field methods, does not
properly describe the step-like electron transfer characteristic in weakly
coupled systems. With the multideterminant results as a benchmark, we have
evaluated the performance of common ab initio mean field techniques, such as
Hartree Fock (HF) and Density Functional Theory (DFT) with local and hybrid
exchange correlation functionals, with a special focus on spin-polarization
effects. For HF and hybrid DFT, a qualitatively correct open-shell solution
with distinct steps in the electron transfer behaviour can be obtained with a
spin-unrestricted (i.e., spin-polarized) ansatz though this solution differs
quantitatively from the multideterminant reference. We also discuss the
relationship between the electronic eigenvalue gap and the onset of charge
transfer for both HF and DFT and relate our findings to recently proposed
practical schemes for calculating the addition energies in the Coulomb blockade
regime for single molecule junctions from closed-shell DFT within the local
density approximation.",0907.2166v1
2011-07-21,Theory of quantum energy transfer in spin chains: From superexchange to ballistic motion,"Quantum energy transfer in a chain of two-level (spin) units, connected at
its ends to two thermal reservoirs, is analyzed in two limits: (i) In the
off-resonance regime, when the characteristic subsystem excitation energy gaps
are larger than the reservoirs frequencies, or the baths temperatures are low.
(ii) In the resonance regime, when the chain excitation gaps match populated
bath modes. In the latter case the model is studied using a master equation
approach, showing that the dynamics is ballistic for the particular chain model
explored. In the former case we analytically study the system dynamics
utilizing the recently developed Energy-Transfer Born-Oppenheimer formalism
[Phys. Rev. E {\bf 83}, 051114 (2011)], demonstrating that energy transfers
across the chain in a superexchange (bridge assisted tunneling) mechanism, with
the energy current decreasing exponentially with distance. This behavior is
insensitive to the chain details. Since at low temperatures the excitation
spectrum of molecular systems can be truncated to resemble a spin chain model,
we argue that the superexchange behavior obtained here should be observed in
widespread systems satisfying the off-resonance condition.",1107.4334v1
2011-10-07,State transfer in dissipative and dephasing environments,"By diagonalization of a generalized superoperator for solving the master
equation, we investigated effects of dissipative and dephasing environments on
quantum state transfer, as well as entanglement distribution and creation in
spin networks. Our results revealed that under the condition of the same
decoherence rate $\gamma$, the detrimental effects of the dissipative
environment are more severe than that of the dephasing environment. Beside
this, the critical time $t_c$ at which the transfer fidelity and the
concurrence attain their maxima arrives at the asymptotic value
$t_0=\pi/2\lambda$ quickly as the spin chain length $N$ increases. The transfer
fidelity of an excitation at time $t_0$ is independent of $N$ when the system
subjects to dissipative environment, while it decreases as $N$ increases when
the system subjects to dephasing environment. The average fidelity displays
three different patterns corresponding to $N=4r+1$, $N=4r-1$ and $N=2r$. For
each pattern, the average fidelity at time $t_0$ is independent of $r$ when the
system subjects to dissipative environment, and decreases as $r$ increases when
the system subjects to dephasing environment. The maximum concurrence also
decreases as $N$ increases, and when $N\rightarrow\infty$, it arrives at an
asymptotic value determined by the decoherence rate $\gamma$ and the structure
of the spin network.",1110.1461v1
2012-01-17,Quantum state transfer through a spin chain in a multi-excitation subspace,"We investigate the quality of quantum state transfer through a uniformly
coupled antiferromagnetic spin chain in a multi-excitation subspace. The
fidelity of state transfer using multi-excitation channels is found to compare
well with communication protocols based on the ground state of a spin chain
with ferromagnetic interactions. Our numerical results support the conjecture
that the fidelity of state transfer through a multi-excitation subspace only
depends on the number of initial excitations present in the chain and is
independent of the excitation ordering. Based on these results, we describe a
communication scheme which requires little effort for preparation.",1201.3576v4
2012-01-23,Number-Theoretic Nature of Communication in Quantum Spin Systems,"The last decade has witnessed substantial interest in protocols for
transferring information on networks of quantum mechanical objects. A variety
of control methods and network topologies have been proposed, on the basis that
transfer with perfect fidelity --- i.e. deterministic and without information
loss --- is impossible through unmodulated spin chains with more than a few
particles. Solving the original problem formulated by Bose [Phys. Rev. Lett.
91, 207901 (2003)], we determine the exact number of qubits in unmodulated
chains (with XY Hamiltonian) that permit the transfer with fidelity arbitrarily
close to 1, a phenomenon called pretty good state transfer. We prove that this
happens if and only if the number of nodes is n=p-1, 2p-1, where p is a prime,
or n=2^{m}-1. The result highlights the potential of quantum spin system
dynamics for reinterpreting questions about the arithmetic structure of
integers, and, in this case, primality.",1201.4822v2
2013-04-26,High-dimensional quantum state transfer through a quantum spin chain,"In this paper, we investigate a high-dimensional quantum state transfer
protocol. An arbitrary unknown high-dimensional state can be transferred with
high fidelity between two remote registers through a XX coupling spin chain of
arbitrary length. The evolution of the state transfer is determined by the
natural dynamics of the chain without external modulation and coupling strength
engineering. As a consequence, entanglement distribution with high efficiency
can be achieved. Also the strong field and high spin quantum number can
counteract partly the effect of finite temperature to ensure high fidelity of
the protocol when the quantum data bus is in the thermal equilibrium state
under an external magnetic field.",1304.7060v1
2014-10-16,Nonequilibrium Energy Transfer at Nanoscale: A Unified Theory from Weak to Strong Coupling,"We investigate the microscopic mechanism of quantum energy transfer in the
nonequilibrium spin-boson model. By developing a nonequilibrium
polaron-transformed Redfield equation based on fluctuation decoupling, we
dissect the energy transfer into multi-boson associated processes with even or
odd parity. Based on this, we analytically evaluate the energy flux, which
smoothly bridges the transfer dynamics from the weak spin-boson coupling regime
to the strong-coupling one. Our analysis explains previous limiting predictions
and provides a unified interpretation of several observations, including
coherence-enhanced heat flux and absence of negative differential thermal
conductance in the nonequilibrium spin-boson model. The results may find wide
applications for the energy and information control in nanodevices.",1410.4366v1
2015-08-04,Time optimal information transfer in spintronics networks,"Propagation of information encoded in spin degrees of freedom through
networks of coupled spins enables important applications in spintronics and
quantum information processing. We study control of information propagation in
networks of spin-$\tfrac{1}{2}$ particles with uniform nearest neighbour
couplings forming a ring with a single excitation in the network as simple
prototype of a router for spin-based information. Specifically optimising
spatially distributed potentials, which remain constant during information
transfer, simplifies the implementation of the routing scheme. However, the
limited degrees of freedom makes finding a control that maximises the transfer
probability in a short time difficult. We show that the structure of the
eigenvalues and eigenvectors must fulfill a specific condition to be able to
maximise the transfer fidelity, and demonstrate that a specific choice among
the many potential structures that fulfill this condition significantly
improves the solutions found by optimal control.",1508.00928v1
2016-03-17,Ultrafast Local Magnetization and Demagnetization in Heusler Alloys,"With the goal of pushing Spintronic devices towards faster and faster
timescales, we demonstrate, using ab-intio time-dependent density functional
theory simulations of bulk Heusler compounds subject to ultrashort intense
laser pulses, that the local magnetic moment can increase or decrease in a few
femtoseconds. This speed is due to the all optical nature of the process, which
transfers spin moment from one sublattice to another. This transfer depends on
easily tunable laser parameters. By comparing the spin dynamics of a variety of
Heusler (or half-Heusler) compounds, we demonstrate that the density of states
explains the observed moment transfer; most the physics of inter sublattice
moment transfer is due to the flow of spin current which is governed by
availability of states above the Fermi level.",1603.05603v1
2017-04-28,Transfer of Phase Information between Optical and Microwave Fields via an Electron Spin,"We demonstrate the coherent coupling and the resulting transfer of phase
information between microwave and optical fields in a single nitrogen vacancy
center in diamond. The relative phase of two microwave fields is encoded in a
coherent superposition spin state. This phase information is then retrieved
with a pair of optical fields. A related process is also used for the transfer
of phase information from optical to microwave fields. These studies show the
essential role of dark states, including optical pumping into the dark states,
in the coherent microwave-optical coupling and open the door to the full
quantum state transfer between microwave and optical fields in a solid-state
spin ensemble.",1705.00093v2
2017-10-02,Well-protected quantum state transfer in a dissipative spin chain,"In this work, a mechanism for improving the quantum state transfer efficiency
in a spin chain, which is in contact with a dissipative structured reservoir,
is investigated. The efficiency of the method is based on the addition of
similar non-interacting auxiliary chains into the reservoir. In this regard, we
obtain the exact solution for the master equation of the spin chain in the
presence of dissipation. It is found out that entering more auxiliary chains
into the reservoir causes, in general, the better improvement of the fidelity
of state transfer along the mentioned chain. Furthermore, it is reveal that the
protocol has better efficiency for a chain with longer length. Therefore, by
this method, quantum state transfer along a linear chain with an arbitrary
number of qubits, can be well-protected against the dissipative noises.",1710.00514v2
2019-01-29,Initialisation of single spin dressed states using shortcuts to adiabaticity,"We demonstrate the use of shortcuts to adiabaticity protocols for
initialisation, readout, and coherent control of dressed states generated by
closed-contour, coherent driving of a single spin. Such dressed states have
recently been shown to exhibit efficient coherence protection, beyond what
their two-level counterparts can offer. Our state transfer protocols yield a
transfer fidelity of ~ 99.4(2) % while accelerating the transfer speed by a
factor of 2.6 compared to the adiabatic approach. We show bi-directionality of
the accelerated state transfer, which we employ for direct dressed state
population readout after coherent manipulation in the dressed state manifold.
Our results enable direct and efficient access to coherence-protected dressed
states of individual spins and thereby offer attractive avenues for
applications in quantum information processing or quantum sensing.",1901.10488v1
2019-04-07,Polarity and spin-orbit coupling induced large interfacial exchange coupling an asymmetric charge transfer in iridate-manganite heterostructure,"Charge transfer is of particular importance in manipulating the interface
physics in transition-metal oxide heterostructures. In this work, we have
fabricated epitaxial bilayers composed of polar 3d LaMnO3 and nonpolar 5d
SrIrO3. Systematic magnetic measurements reveal an unexpectedly large exchange
bias effect in the bilayer, together with a dramatic enhancement of the
coercivity of LaMnO3. Based on first-principles calculations and x-ray
absorption spectroscopy measurements, such a strong interfacial magnetic
coupling is found closely associated with the polar nature of LaMnO3 and the
strong spin-orbit interaction in SrIrO3, which collectively drives an
asymmetric interfacial charge transfer and leads to the emergence of an
interfacial spin glass state. Our study provides new insight into the charge
transfer in transition-metal oxide heterostructures and offers a novel means to
tune the interfacial exchange coupling for a variety of device applications.",1904.03613v2
2021-08-08,Exchange scaling of ultrafast angular momentum transfer in 4$\it{f}$ antiferromagnets,"Ultrafast manipulation of the magnetic state of matter bears great potential
for future information technologies. While demagnetisation in ferromagnets is
governed by dissipation of angular momentum, materials with multiple spin
sublattices, e.g. antiferromagnets, can allow direct angular momentum transfer
between opposing spins, promising faster functionality. In lanthanides,
4$\it{f}$ magnetic exchange is mediated indirectly through the conduction
electrons (the Ruderman-Kittel-Kasuya-Yosida interaction, RKKY), and the effect
of such conditions on direct spin transfer processes is largely unexplored.
Here, we investigate ultrafast magnetization dynamics in 4f antiferromagnets,
and systematically vary the 4$\it{f}$ occupation, thereby altering the
magnitude of RKKY. By combining time-resolved soft x-ray diffraction with
ab-initio calculations, we find that the rate of direct transfer between
opposing moments is directly determined by the magnitude of RKKY. Given the
high sensitivity of RKKY to the conduction electrons, our results offer a novel
approach for fine-tuning the speed of magnetic devices.",2108.03714v1
1993-02-10,The Least Action Principle And The Spin Of Galaxies In The Local Group,"Using Peebles' least action principle, we determine trajectories for the
galaxies in the Local Group and the more massive galaxies in the Local
Neighbourhood. We deduce the resulting angular momentum for the whole of the
Local Group and study the tidal force acting on the Local Group and its
galaxies. Although Andromeda and the Milky Way dominate the tidal force acting
on each other during the present epoch, we show that there is a transition time
at $z\approx 1$ before which the tidal force is dominated by galaxies outside
the Local Group in each case. This shows that the Local Group can not be
considered as an isolated system as far as the tidal forces are concerned. We
integrate the tidal torques acting on the Milky Way and Andromeda and derive
their spin angular momenta, obtaining results which are comparable with
observation.",9302007v3
2000-08-01,Phase Diagram for Spinning and Accreting Neutron Stars,"Neutron star configurations are considered as thermodynamical systems for
which a phase diagram in the angular velocity (Omega) - baryon number (N) plane
is obtained with a dividing line N_{crit}(Omega) for quark core configurations.
Trajectories of neutron star evolution in this diagram are studied for
different scenarios defined by the external torque acting on the star due to
radiation and/or mass accretion. They show a characteristic change in the
rotational kinematics when the star enters the quark core regime. For isolated
pulsars the braking index signal for deconfinement has been studied in its
dependence on the mass of the star. Model calculations of the spin evolution of
accreting low-mass X-ray binaries in the phase diagram have been performed for
different values of the initial magnetic field, its decay time as well as
initial mass and mass accretion rate. Population clustering of these objects at
the line N_{crit}(Omega) in the phase diagram is suggested as an observable
signal for the deconfinement phase transition if it exists for spinnning and
accreting neutron stars.",0008005v3
2001-11-30,Viscoelastic Analogy for the Acceleration and Collimation of Astrophysical Jets,"Jets are ubiquitous in astronomy. It has been conjectured that the existence
of jets is intimately connected with the spin of the central object and the
viscous angular momentum transport of the inner disk. Bipolar jet-like
structures propelled by the viscous torque on a spinning central object are
also known in a completely different context, namely the flow in the laboratory
of a viscoelastic fluid. On the basis of an analogy of the tangled magnetic
field lines of magnetohydrodynamic (MHD) turbulence to the tangled polymers of
viscoelastic polymer solutions, we propose a viscoelastic description of the
dynamics of highly turbulent conductive fluid. We argue that the same mechanism
that forms jets in viscoelastic fluids in the laboratory may be responsible for
collimating and powering astrophysical jets by the angular momentum of the
central object.",0111603v1
2002-01-29,On the accretion mode of the intermediate polar V1025 Centauri,"The long white-dwarf spin periods in the magnetic cataclysmic variables EX
Hya and V1025 Cen imply that if the systems possess accretion discs then they
cannot be in equilibrium. It has been suggested that instead they are discless
accretors in which the spin-up torques resulting from accretion are balanced by
the ejection of part of the accretion flow back towards the secondary. We
present phase-resolved spectroscopy of V1025 Cen aimed at deducing the nature
of the accretion flow, and compare this with simulations of a discless
accretor. We find that both the conventional disc-fed model and the
discless-accretor model have strengths and weaknesses, and that further work is
needed before we can decide which applies to V1025 Cen.",0201474v1
2002-11-30,Arresting Accretion Torques with Gravitational Radiation,"Recent theoretical work has made it plausible for neutron stars (NSs) to lose
angular momentum via gravitational radiation on long timescales (around Myrs)
while actively accreting. The gravitational waves (GWs) can either be emitted
via the excitation of r-modes or from a deformed crust. GW emission can thus
intervene to slow-down or halt the otherwise relentless spin-up from accretion.
Prior to this theoretical work (and the measurements of NS rotation rates in
LMXBs) the community was rather confident that an accreting NS would be spun-up
to rotation rates near breakup, motivating searches for sub-millisecond
objects. After only briefly describing the physics of the GW processes, I argue
that the limiting spin frequency might be appreciably lower than the breakup
frequency. Millisecond radio pulsar observers would likely discover the impact
of GW emission as a dropoff in the number of pulsars beyond 600 Hz, and I show
here that the millisecond pulsar inventory in 47 Tuc might already exhibit such
a cutoff. These theoretical ideas will be tested by GW searches with
ground-based interferometers, such as the advanced LIGO instrument proposed for
operation by 2008.",0212004v1
2003-01-17,Presupernova Evolution of Rotating Massive Stars and the Rotation Rate of Pulsars,"Rotation in massive stars has been studied on the main sequence and during
helium burning for decades, but only recently have realistic numerical
simulations followed the transport of angular momentum that occurs during more
advanced stages of evolution. The results affect such interesting issues as
whether rotation is important to the explosion mechanism, whether supernovae
are strong sources of gravitational radiation, the star's nucleosynthesis, and
the initial rotation rate of neutron stars and black holes. We find that when
only hydrodynamic instabilities (shear, Eddington-Sweet, etc.) are included in
the calculation, one obtains neutron stars spinning at close to critical
rotation at their surface -- or even formally in excess of critical. When
recent estimates of magnetic torques (Spruit 2002) are added, however, the
evolved cores spin about an order of magnitude slower. This is still more
angular momentum than observed in young pulsars, but too slow for the collapsar
model for gamma-ray bursts.",0301374v2
2003-12-19,Turbulent Magnetohydrodynamic Jet Collimation and Thermal Driving,"We have argued that magnetohydrodynamic (MHD) turbulence in an accretion disk
naturally produces hoop-stresses, and that in a geometrically-thick flow these
stresses could both drive and collimate an outflow. We based this argument on
an analogy of turbulent MHD fluids to viscoelastic fluids, in which azimuthal
shear flow creates hoop-stresses that cause a variety of flow phenomena,
including the Weissenberg effect in which a fluid climbs a spinning rod. One of
the more important differences between the Weissenberg effect and astrophysical
jets is the source of power. In our previous analysis, we only considered the
power due to the spin-down torque on the central object, and thus found that we
could only drive an outflow if the central object were maximally rotating. Here
we take into account the energy that is liberated by the accreting matter, and
describe a scenario in which this energy couples to the outflow to create a
thermodynamic engine.",0312513v2
2005-02-14,The Propeller Regime of Disk Accretion to a Rapidly Rotating Magnetized Star,"The propeller regime of disk accretion to a rapidly rotating magnetized star
is investigated here for the first time by axisymmetric 2.5D
magnetohydrodynamic simulations. An expanded, closed magnetosphere forms in
which the magnetic field is predominantly toroidal. A smaller fraction of the
star's poloidal magnetic flux inflates vertically, forming a magnetically
dominated tower. Matter accumulates in the equatorial region outside
magnetosphere and accretes to the star quasi-periodically through elongated
funnel streams which cause the magnetic field to reconnect. The star spins-down
owing to the interaction of the closed magnetosphere with the disk. For the
considered conditions, the spin-down torque varies with the angular velocity of
the star omega* as omega*^1.3 for fixed mass accretion rate. The propeller
stage may be important in the evolution of X-ray pulsars, cataclysmic variables
and young stars. In particular, it may explain the present slow rotation of the
classical T Tauri stars.",0502266v1
2005-04-25,"Superfluid Spin-down, with Random Unpinning of the Vortices","The so-called ``creeping'' motion of the pinned vortices in a rotating
superfluid involves ``random unpinning'' and ``vortex motion'' as two
physically separate processes. We argue that such a creeping motion of the
vortices need not be (biased) in the direction of an existing radial Magnus
force, nor should a constant microscopic radial velocity be assigned to the
vortex motion, in contradiction with the basic assumptions of the ``vortex
creep'' model. We point out internal inconsistencies in the predictions of this
model which arise due to this unjustified foundation that ignores the role of
the actual torque on the superfluid. The proper spin-down rate of a pinned
superfluid is then calculated and turns out to be much less than that suggested
in the vortex creep model, hence being of even less observational significance
for its possible application in explaining the post-glitch relaxations of the
radio pulsars.",0504531v1
2005-11-08,Evolution of Gamma-Ray Burst Progenitors at Low Metallicity,"Despite the growing evidence that long Gamma-Ray Bursts (GRBs) are associated
with deaths of Wolf-Rayet stars, the evolutionary path of massive stars to GRBs
and the exact nature of GRB progenitors remained poorly known. However, recent
massive star evolutionary models indicate that -- for sufficiently low
metallicity -- initially very rapidly rotating stars can satisfy the conditions
for collapsar formation. Even though magnetic torques are included in these
models, a strong core spin-down is avoided through quasi-chemically homogeneous
evolution induced by rotational mixing. Here, we explore for which initial mass
and spin-range single stars of Z=Zsun/20 are expected to produce GRBs. We
further find a dichotomy in the chemical structure of GRB progenitors, where
lower initial masses end their lives with a massive helium envelope which still
contains some amounts of hydrogen, while higher initial masses explode with
C/O-dominated hydrogen-free atmospheres.",0511222v1
2006-02-27,The Alignments of Disk Galaxies with the Local Pancakes,"We analyze the Tully catalog of nearby galaxies to investigate the local
pancaking effect on the orientation of disk galaxies. We first select only
those edge-on disk galaxies in the catalog whose axis-ratios are less than 0.1
to measure their spin axes unambiguously. A local pancake at the location of
each selected galaxy is found as a plane encompassing the two nearest neighbor
disks. Then, we examine statistically the inclinations of the galaxy spin axes
relative to the local pancake planes. It is detected that the Tully disk
galaxies tend to be inclined onto the local pancake planes, and the average
inclination angles decrease with the pancake scale. We also construct a
theoretical model for the inclination of disk galaxies relative to the local
pancakes in the frame of the linear tidal torque theory. The comparison of the
theoretical prediction with the observational result demonstrates a good
agreement. Finally, we conclude that it is a first detection of the local
pancaking effect on the orientation of disk galaxies, which is consistent with
the scenario that the gravitational tidal field promotes the formation of
pancakes on small mass scale.",0602575v1
2006-03-01,Evolution of the periodicities in 2S 0114+650,"We have analysed nine years of data from the All Sky Monitor on the Rossi
X-ray Timing Explorer for 2S 0114+650 to study the evolution of its spin,
binary and super-orbital periods. The spin history of the neutron star in this
system exhibits torque reversals lasting ~1 yr. The newly discovered
super-orbital period has remained stable over the 9-yr span, making 2S 0114+650
the fourth known system to exhibit stable super-orbital modulation. We compare
its super-orbital period evolution with those of the other three such systems.",0603008v1
2006-08-24,A torque reversal of 4U 1907+09,"We present an analysis of the accreting X-ray pulsar system 4U 1907+09 based
on INTEGRAL data. The main focus of this analysis is a study of the timing
behavior of this source. In addition we also show an analysis of the 5-90 keV
spectrum. The data were extracted using the official INTEGRAL software OSA 5.1.
Timing analysis was performed using epoch folding and pulsar pulse phasing. We
have measured 12 individual pulse periods for the years 2003 to 2005. We
confirm earlier RXTE results that during 2003 the spin down became slower and
show furthermore that after this phase 4U 1907+09 started to spin up with dP/dt
= -0.158 s/yr in 2004. The similarity of the pulse period histories of 4U
1907+09 and 4U 1626-26 suggests that accretion onto an oblique rotator, as
recently proposed by Perna et al., is a possible explanation for this change.",0608518v1
2007-03-05,Alignment of the spins of supermassive black holes prior to coalescence,"Recent numerical relativistic simulations of black hole coalescence suggest
that in certain alignments the emission of gravitational radiation can produce
a kick of several thousand kilometers per second. This exceeds galactic escape
speeds, hence unless there a mechanism to prevent this, one would expect many
galaxies that had merged to be without a central black hole. Here we show that
in most galactic mergers, torques from accreting gas suffice to align the orbit
and spins of both black holes with the large-scale gas flow. Such a
configuration has a maximum kick speed <200 km/s, safely below galactic escape
speeds. We predict, however, that in mergers of galaxies without much gas, the
remnant will be kicked out several percent of the time. We also discuss other
predictions of our scenario, including implications for jet alignment angles
and X-type radio sources.",0703054v2
2002-07-19,Gilbert Damping in Magnetic Multilayers,"We study the enhancement of the ferromagnetic relaxation rate in thin films
due to the adjacent normal metal layers. Using linear response theory, we
derive the dissipative torque produced by the s-d exchange interaction at the
ferromagnet-normal metal interface. For a slow precession, the enhancement of
Gilbert damping constant is proportional to the square of the s-d exchange
constant times the zero-frequency limit of the frequency derivative of the
local dynamic spin susceptibility of the normal metal at the interface.
Electron-electron interactions increase the relaxation rate by the Stoner
factor squared. We attribute the large anisotropic enhancements of the
relaxation rate observed recently in multilayers containing palladium to this
mechanism. For free electrons, the present theory compares favorably with
recent spin-pumping result of Tserkovnyak et al. [Phys. Rev. Lett.
\textbf{88},117601 (2002)].",0207471v1
2003-01-21,Ferromagnetic coupling and magnetic anisotropy in molecular Ni(II) squares,"We investigated the magnetic properties of two isostructural Ni(II) metal
complexes [Ni4Lb8] and [Ni4Lc8]. In each molecule the four Ni(II) centers form
almost perfect regular squares. Magnetic coupling and anisotropy of single
crystals were examined by magnetization measurements and in particular by
high-field torque magnetometry at low temperatures. The data were analyzed in
terms of an effective spin Hamiltonian appropriate for Ni(II) centers. For both
compounds, we found a weak intramolecular ferromagnetic coupling of the four
Ni(II) spins and sizable single-ion anisotropies of the easy-axis type. The
coupling strengths are roughly identical for both compounds, whereas the
zero-field-splitting parameters are significantly different. Possible reasons
for this observation are discussed.",0301373v1
2003-11-22,Influence of a Uniform Current on Collective Magnetization Dynamics in a Ferromagnetic Metal,"We discuss the influence of a uniform current, $\vec{j} $, on the
magnetization dynamics of a ferromagnetic metal. We find that the magnon energy
$\epsilon(\vec{q})$ has a current-induced contribution proportional to
$\vec{q}\cdot \vec{\cal J}$, where $\vec{\cal J}$ is the spin-current, and
predict that collective dynamics will be more strongly damped at finite ${\vec
j}$. We obtain similar results for models with and without local moment
participation in the magnetic order. For transition metal ferromagnets, we
estimate that the uniform magnetic state will be destabilized for $j \gtrsim
10^{9} {\rm A} {\rm cm}^{-2}$. We discuss the relationship of this effect to
the spin-torque effects that alter magnetization dynamics in inhomogeneous
magnetic systems.",0311522v1
2004-10-30,Dynamics of Domain Wall in a Biaxial Ferromagnet With Spin-torque,"The dynamics of the domain wall (DW) in a biaxial ferromagnet interacting
with a spin-polarized current are described by sine-gordon (SG) equation
coupled with Gilbert damping term in this paper. Within our frame-work of this
model, we obtain a threshold of the current in the motion of a single DW with
the perturbation theory on kink soliton solution to the corresponding
ferromagnetic system, and the threshold is shown to be dependent on the Gilbert
damping term. Also, the motion properties of the DW are discussed for the zero-
and nonzero-damping cases, which shows that our theory to describe the dynamics
of the DW are self-consistent.",0411005v3
2006-07-05,Theory of the spin-torque-driven ferromagnetic resonance in a ferromagnet/normal-metal/ferromagnet structure,"We present a theoretical analysis of current driven ferromagnetic resonance
in a ferromagnet/normal-metal/ferromagnet tri-layer. This method of driving
ferromagnetic resonance was recently realized experimentally by Tulapurkar et
al. [Nature 438, 339 (2005)] and Sankey et al. [Phys. Rev. Lett. 96, 227601
(2006)]. The precessing magnetization rectifies the alternating current applied
to drive the ferromagnetic resonance and leads to the generation of a dc
voltage. Our analysis shows that a second mechanism to generate a dc voltage,
rectification of spin currents emitted by the precessing magnetization, has a
contribution to the dc voltage that is of approximately equal size for the thin
ferromagnetic films used in the experiment.",0607145v2
2000-08-09,Gravitational Wave Damping of Neutron Star Wobble,"We calculate the effect of gravitational wave (gw) back-reaction on realistic
neutron stars (NS's) undergoing torque-free precession. By `realistic' we mean
that the NS is treated as a mostly-fluid body with an elastic crust, as opposed
to a rigid body. We find that gw's damp NS wobble on a timescale tau_{theta}
approx 2 x 10^5 yr [10^{-7}/(DId/I_0)]^2 (kHz/ nu_s)^4, where nu_s is the spin
frequency and DId is the piece of the NS's inertia tensor that ""follows"" the
crust's principal axis (as opposed to its spin axis). We give two different
derivations of this result: one based solely on energy and angular momentum
balance, and another obtained by adding the Burke-Thorne radiation reaction
force to the Newtonian equations of motion. This problem was treated long ago
by Bertotti and Anile (1973), but their claimed result is wrong. When we
convert from their notation to ours, we find that their tau_{theta} is too
short by a factor of order 10^5 for typical cases of interest, and even has the
wrong sign for DId negative. We show where their calculation went astray.",0008021v1
2007-08-06,An unexpected outburst from A0535+262,"A0535+262 is a transient Be/X-ray binary system which was in a quiescent
phase from 1994-2005. In this paper we report on the timing and spectral
properties of the INTEGRAL detection of the source in October 2003. The source
is detected for ~6000 seconds in the 18-100 keV energy band at a luminosity of
~3.8 x 10^{35} erg s^{-1}; this is compatible with the high end of the range of
luminosities expected for quiescent emission. The system is observed to be
outside of the centrifugal inhibition regime and pulsations are detected with
periodicity, P=103.7 +/- 0.1 seconds. An examination of the pulse history of
the source shows that it had been in a constant state of spin-down since it
entered the quiescent phase in 1994. The rate of spin-down implies the
consistent presence of an accretion disk supplying torques to the pulsar. The
observations show that the system is still active and highly variable even in
the absence of recent Type I or Type II X-ray outbursts.",0708.0791v1
2007-09-13,Angular Momemtum of Binary Asteroids: Implication for their possible origin,"We describe in this work a thorough study of the physical and orbital
characteristics of extensively observed main-belt and Trojan binaries, mainly
taken from the LAOSA (Large Adaptive Optics Survey of Asteroids, Marchis et
al., 2006c) database, along with a selection of bifurcated objects.
Dimensionless quantities, such as the specific angular momentum and the primary
spin rate, are computed and discussed for each system. They suggest that these
asteroidal systems might be the outcome of rotational fission or mass shedding
of a parent body presumably subjected to an external torque.
  One of the most striking features of separated binaries composed of a large
primary (Rp > 100 km) with a much smaller secondary (Rs < 20 km) is that they
all have total angular momentum of 0.27. This value is quite close to the
Maclaurin-Jacobi bifurcation (0.308) of a spinning fluid body. Alternatively,
contact binaries and tidally locked double asteroids, made of components of
similar size, have an angular momentum larger than 0.48. They compare
successfully with the fission equilibrium sequence of a rotating fluid mass. In
conclusion, we find that total angular momentum is a useful proxy to assess
internal structure of such systems.",0709.2028v1
2007-09-24,Anomalous Paramagnetic Magnetization in Mixed State of CeCoIn$_5$ single crystals,"Magnetization and torque measurements were performed on CeCoIn$_5$ single
crystals to study the mixed-state thermodynamics. These measurements allow the
determination of both paramagnetic and vortex responses in the mixed-state
magnetization. The paramagnetic magnetization is suppressed in the mixed state
with the spin susceptibility increasing with increasing magnetic field. The
dependence of spin susceptibility on magnetic field is due to the fact that
heavy electrons contribute both to superconductivity and paramagnetism and a
large Zeeman effect exists in this system. No anomaly in the vortex response
was found within the investigated temperature and field range.",0709.3819v3
2007-10-05,"On the X-Ray Light Curve, Pulsed-Radio Emission, and Spin Frequency Evolution of the Transient Anomalous X-Ray Pulsar Xte J1810--197 During its X-Ray Outburst","We show that: (i) the long-term X-ray outburst light curve of the transient
AXP XTE J1810-197 can be accounted for by a fallback disk that is evolving
towards quiescence through a disk instability after having been heated by a
soft gamma-ray burst, (ii) the spin-frequency evolution of this source in the
same period can also be explained by the disk torque acting on the
magnetosphere of the neutron star, (iii) most significantly, recently observed
pulsed-radio emission from this source coincides with the epoch of minimum
X-ray luminosity. This is natural in terms of a fallback disk model, as the
accretion power becomes so low that it is not sufficient to suppress the beamed
radio emission from XTE J1810-197.",0710.1201v1
2008-05-08,A Double Myers-Perry Black Hole in Five Dimensions,"Using the inverse scattering method we construct a six-parameter family of
exact, stationary, asymptotically flat solutions of the 4+1 dimensional vacuum
Einstein equations, with U(1)^2 rotational symmetry. It describes the
superposition of two Myers-Perry black holes, each with a single angular
momentum parameter, both in the same plane. The black holes live in a
background geometry which is the Euclidean C-metric with an extra flat time
direction. This background possesses conical singularities in two adjacent
compact regions, each corresponding to a set of fixed points of one of the U(1)
actions in the Cartan sub-algebra of SO(4). We discuss several aspects of the
black holes geometry, including the conical singularities arising from force
imbalance, and the torsion singularity arising from torque imbalance. The
double Myers-Perry solution presented herein is considerably simpler than the
four dimensional double Kerr solution and might be of interest in studying
spin-spin interactions in five dimensional general relativity.",0805.1206v2
2008-10-30,INTEGRAL observes the 2007 outburst of the Be transient SAX J2103.5+4545,"We performed a detailed study of the 2007 outburst of the 352s pulsar
SAXJ2103.5+4545, a Be/X-ray transient observed by INTEGRAL, to study its
spectral and temporal properties during the evolution of the outburst.
SAXJ2103.5+4545 was observed with IBIS/ISGRI from 25 to 27 April 2007 and from
6 to 8 May 2007. The 20-100keV spectrum is well described by a bremsstrahlung
model with a temperature kT = 24keV. The pulse profiles are variable with time
and energy. A pulse period derivative of pdot = -3.4E-7 s/s has been observed
during the outburst. Instead, a spin-down of pdot = 5.5E-9 s/s is observed
between the 2007 outburst reported here and the previous one occurred in
December 2004. This is the largest spin-down measured for SAXJ2103.5+4545 since
its discovery. We estimate a neutron star magnetic field in the range
(1.6-3)E13 G using the Ghosh & Lamb torque model.",0810.5453v1
2008-11-13,Template nanowires for spintronics applications: nanomagnet microwave resonators functioning in zero applied magnetic field,"Low-cost spintronic devices functioning in zero applied magnetic field are
required for bringing the idea of spin-based electronics into the real-world
industrial applications. Here we present first microwave measurements performed
on nanomagnet devices fabricated by electrodeposition inside porous membranes.
In the paper, we discuss in details a microwave resonator consisting of three
nanomagnets, which functions in zero external magnetic field. By applying a
microwave signal at a particular frequency, the magnetization of the middle
nanomagnet experiences the ferromagnetic resonance (FMR), and the device
outputs a measurable direct current (spin-torque diode effect). Alternatively,
the nanodevice can be used as a microwave oscillator functioning in zero field.
In order to test the resonators at microwave frequencies, we developed a simple
measurement set-up.",0811.2241v1
2008-12-12,Hydrodynamic orienting of asymmetric microobjects under gravity,"It is shown that nonsymmetric microobjects orient while settling under
gravity in a viscous fluid. To analyze this process, a simple shape is chosen:
a non-deformable `chain'. The chain consists of two straight arms, made of
touching solid spheres. In the absence of external torques, the spheres are
free to spin along the arms. The motion of the chain is evaluated by solving
the Stokes equations with the use of the multipole method. It is demonstrated
that the spinning beads speed up sedimentation by a small amount, and increase
the orientation rate significantly in comparison to the corresponding rigid
chain. It is shown that chains orient towards the V-shaped stable stationary
configuration. In contrast, rods and star-shaped microobjects do not rotate.
The hydrodynamic orienting is relevant for efficient swimming of non-symmetric
microobjects, and for sedimenting suspensions.",0812.2487v1
2008-12-15,A refined model for spinning dust radiation,"We present a comprehensive treatment of the spectrum of electric dipole
emission from spinning dust grains, updating the commonly used model of Draine
and Lazarian. Grain angular velocity distributions are computed using the
Fokker-Planck equation; we revisit the drift and diffusion coefficients for the
major torques on the grain, including collisions, grain-plasma interactions,
and infrared emission. We use updated grain optical properties and size
distributions. The theoretical formalism is implemented in the companion code,
SPDUST, which is publicly available. The effect of some environmental and grain
parameters on the emissivity is shown and analysed.",0812.2904v2
2008-12-17,Origin of intrinsic Gilbert damping,"The damping of magnetization, represented by the rate at which it relaxes to
equilibrium, is successfully modeled as a phenomenological extension in the
Landau-Lifschitz-Gilbert equation. This is the damping torque term known as
Gilbert damping and its direction is given by the vector product of the
magnetization and its time derivative. Here we derive the Gilbert term from
first principles by a non-relativistic expansion of the Dirac equation. We find
that the Gilbert term arises when one calculates the time evolution of the spin
observable in the presence of the full spin-orbital coupling terms, while
recognizing the relationship between the curl of the electric field and the
time varying magnetic induction.",0812.3184v2
2009-01-12,Detecting gravitational waves from accreting neutron stars,"The gravitational waves emitted by neutron stars carry unique information
about their structure and composition. Direct detection of these gravitational
waves, however, is a formidable technical challenge. In a recent study we
quantified the hurdles facing searches for gravitational waves from the known
accreting neutron stars, given the level of uncertainty that exists regarding
spin and orbital parameters. In this paper we reflect on our conclusions, and
issue an open challenge to the theoretical community to consider how searches
should be designed to yield the most astrophysically interesting upper limits.
With this in mind we examine some more optimistic emission scenarios involving
spin-down, and show that there are technically feasible searches, particularly
for the accreting millisecond pulsars, that might place meaningful constraints
on torque mechanisms. We finish with a brief discussion of prospects for
indirect detection.",0901.1680v1
2009-10-10,Agility of vortex-based nanocontact spin torque oscillators,"We study the agility of current-tunable oscillators based on a magnetic
vortex orbiting around a point contact in spin-valves. Theory predicts
frequency-tuning by currents occurs at constant orbital radius, so an
exceptional agility is anticipated. To test this, we have inserted an
oscillator in a microwave interferometer to apply abrupt current variations
while time resolving its emission. Using frequency shift keying, we show that
the oscillator can switch between two stabilized frequencies differing by 25%
in less than ten periods. With a wide frequency tunability and a good agility,
such oscillators possess desirable figures of merit for modulation-based rf
applications.",0910.1941v1
2010-08-27,Electron-Doped Sr2IrO4-delta (0 <= delta <= 0.04): Evolution of a Disordered Jeff = 1/2 Mott Insulator into an Exotic Metallic State,"Stoichiometric Sr2IrO4 is a ferromagnetic Jeff = 1/2 Mott insulator driven by
strong spin-orbit coupling. Introduction of very dilute oxygen vacancies into
single-crystal Sr2IrO4-delta with delta < 0.04 leads to significant changes in
lattice parameters and an insulator-to-metal transition at TMI = 105 K. The
highly anisotropic electrical resistivity of the low-temperature metallic state
for delta ~ 0.04 exhibits anomalous properties characterized by non-Ohmic
behavior and an abrupt current-induced transition in the resistivity at T* = 52
K, which separates two regimes of resisitive switching in the nonlinear I-V
characteristics. The novel behavior illustrates an exotic ground state and
constitutes a new paradigm for devices structures in which electrical
resistivity is manipulated via low-level current densities ~ 10 mA/cm2
(compared to higher spin-torque currents ~ 107-108 A/cm2) or magnetic
inductions ~ 0.1-1.0 T.",1008.4725v1
2011-03-31,Gross-Pitaevskii model of pulsar glitches,"The first large-scale quantum mechanical simulations of pulsar glitches are
presented, using a Gross-Pitaevskii model of the crust-superfluid system in the
presence of pinning. Power-law distributions of simulated glitch sizes are
obtained, in accord with astronomical observations, with exponents ranging from
-0.55 to -1.26. Examples of large-scale simulations, containing $\sim 200$
vortices, reveal that these statistics persist in the many-vortex limit.
Waiting-time distributions are also constructed. These and other statistics
support the hypothesis that catastrophic unpinning mediated by collective
vortex motion produces glitches; indeed, such collective events are seen in
time-lapse movies of superfluid density. Three principal trends are observed.
(1) The glitch rate scales proportional to the electromagnetic spin-down
torque. (2) A strong positive correlation is found between the strength of
vortex pinning and mean glitch size. (3) The spin-down dynamics depend less on
the pinning site abundance once the latter exceeds one site per vortex,
suggesting that unpinned vortices travel a distance comparable to the
inter-vortex spacing before repinning.",1103.6090v1
2011-06-27,Constitutive equations for granular flow with uniform mean shear and spin fields,"Numerical simulations of two-dimensional granular flows under uniform shear
and external body torque were performed in order to extract the constitutive
equations for the system. The outcome of the numerical simulations is analyzed
on the basis of the micropolar fluid model. Uniform mean shear field and mean
spin field, which is not subordinate to the vorticity field, are realized in
the simulations. The estimates of stresses based on kinetic theory by Lun [Lun,
J. Fluid Mech., 1991, 233, 539] are in good agreement with the simulation
results for a low area fraction $\nu=0.1$ but the agreement becomes weaker as
the area fraction gets higher. However, the estimates in the kinetic theory can
be fitted to the simulation results up to $\nu=0.7$ by renormalizing the
coefficient of roughness. For a relatively dense granular flow ($\nu=0.8$), the
simulation results are also compared with Kanatani's theory [Kanatani, Int. J.
Eng. Sci., 1979, 17, 419]. It is found that the dissipation function and its
decomposition into the constitutive equations in Kanatani's theory are not
consistent with the simulation results.",1106.5306v1
2011-09-14,Antiferromagnetic coupling across silicon regulated by tunneling currents,"We report on the enhancement of antiferromagnetic coupling in epitaxial
Fe/Si/Fe structures by voltage-driven spin-polarized tunneling currents. Using
the ballistic electron magnetic microscopy we established that the hot-electron
collector current reflects magnetization alignment and the magnetocurrent
exceeds 200% at room temperature. The saturation magnetic field for collector
current corresponding to parallel alignment of magnetizations rises up with the
tunneling current, thus demonstrating stabilization of the antiparallel
alignment and increasing antiferromagnetic coupling. We connect the enhancement
of antiferromagnetic coupling with local dynamic spin torques mediated by
tunneling electrons",1109.3106v1
2011-09-21,The core-degenerate scenario for type Ia supernovae,"In the core-degenerate (CD) scenario for the formation of Type Ia supernovae
(SNe) the Chandrasekhar or super-Chandrasekhar mass white dwarf (WD) is formed
at the termination of the common envelope phase or during the planetary nebula
phase, from a merger of a WD companion with the hot core of a massive
asymptotic giant branch (AGB) star. The WD is destructed and accreted onto the
more massive core. In the CD scenario the rapidly rotating WD is formed shortly
after the stellar formation episode, and the delay from stellar formation to
explosion is basically determined by the spin-down time of the rapidly rotating
merger remnant. The spin-down is due to the magneto-dipole radiation torque.
Several properties of the CD scenario make it attractive compared with the
double-degenerate (DD) scenario. (1) Off-center ignition of carbon during the
merger process is not likely to occur. (2) No large envelope is formed. Hence
avoiding too much mass loss that might bring the merger remnant below the
critical mass. (3) This model explains the finding that more luminous SNe Ia
occur preferentially in star forming galaxies.",1109.4652v1
2011-10-04,Zero and finite temperature mean field study of magnetic field induced electric polarization in Ba2CoGe2O7,"We investigate the spin-induced polarization in the multiferroic compound
Ba2CuGe2O7 using variarional and finite temperature mean field approaches. The
compound is described by a spin-3/2 Heisenberg model extended with easy plane
anisotropy and Dzyaloshinskii-Moriya (DM) interaction. Applying magnetic field
parallel to the [110] axis, three phases can be distinguished: (i) At high
magnetic field we find a partially magnetized phase with spins parallel to the
fields and uniform polarization; (ii) Below a critical field the ground state
is a twofold degenerate canted antiferromagnet, where the degeneracy can be
lifted by a finite DM interaction; (iii) At zero field a U(1) symmetry breaking
phase takes place, exhibiting a Goldstone-mode. To reproduce the magnetization
and polarization measurements reported in Murakawa et al. [Phys. Rev. Lett.
105, 137202 (2010)], we introduce an additional term in the Hamiltonian that
couples the polarizations on neighboring tetrahedra. This results in the
appearance of a canted ferrimagnetic phase for h < 1 T, characterized by a
finite staggered polarization, as well as by a finite magnetization along the
[-1,1,0] axis that leads to torque anomalies.",1110.0788v1
2011-10-19,Current-induced switching in transport through anisotropic magnetic molecules,"Anisotropic single-molecule magnets may be thought of as molecular switches,
with possible applications to molecular spintronics. In this paper, we consider
current-induced switching in single-molecule junctions containing an
anisotropic magnetic molecule. We assume that the carriers interact with the
magnetic molecule through the exchange interaction and focus on the regime of
high currents in which the molecular spin dynamics is slow compared to the time
which the electrons spend on the molecule. In this limit, the molecular spin
obeys a non-equilibrium Langevin equation which takes the form of a generalized
Landau-Lifshitz-Gilbert equation and which we derive microscopically by means
of a non-equilibrium Born-Oppenheimer approximation. We exploit this Langevin
equation to identify the relevant switching mechanisms and to derive the
current-induced switching rates. As a byproduct, we also derive S-matrix
expressions for the various torques entering into the Landau-Lifshitz-Gilbert
equation which generalize previous expressions in the literature to
non-equilibrium situations.",1110.4270v2
2012-02-15,"Propagation and control of nano-scale, magnetic droplet solitons","The propagation and controlled manipulation of strongly nonlinear,
two-dimensional solitonic states in a thin, anisotropic ferromagnet are
theoretically demonstrated. It has been recently proposed that spin-polarized
currents in a nanocontact device could be used to nucleate a stationary
dissipative droplet soliton. Here, an external magnetic field is introduced to
accelerate and control the propagation of the soliton in a lossy medium.
Soliton perturbation theory corroborated by two-dimensional micromagnetic
simulations predicts several intriguing physical effects, including the
acceleration of a stationary soliton by a magnetic field gradient, the
stabilization of a stationary droplet by a uniform control field in the absence
of spin torque, and the ability to control the soliton's speed by use of a
time-varying, spatially uniform external field. Soliton propagation distances
approach 10 $\mu$m in low loss media, suggesting that droplet solitons could be
viable information carriers in future spintronic applications, analogous to
optical solitons in fiber optic communications.",1202.3421v2
2012-10-09,Micromagnetic theory of spin relaxation and ferromagnetic resonance in multilayered metallic films,"Spin relaxation in the ultrathin metallic films of stacked microelectronic
devices is investigated on the basis of a modified Landau-Lifshitz equation of
micromagnetic dynamics in which the damping torque is treated as originating
from the coupling between precessing magnetization-vector and the introduced
stress-tensors of intrinsic and extrinsic magnetic anisotropy. Particular
attention is given to the time of exponential relaxation and ferromagnetic
resonance linewidth which are derived in analytic form from the equation of
magnetization energy loss and Gabor uncertainty relation between the
full-width-at-half-maximum in resonance-shaped line and lifetime of resonance
excitation. The potential of developed theory is briefly discussed in the
context of recent measurements.",1210.2609v3
2012-10-23,Averaged equation for energy diffusion on a graph reveals bifurcation diagram and thermally assisted reversal times in spin-torque driven nanomagnets,"Driving nanomagnets by spin-polarized currents offers exciting prospects in
magnetoelectronics, but the response of the magnets to such currents remains
poorly understood. We show that an averaged equation describing the diffusion
of energy on a graph captures the low-damping dynamics of these systems. From
this equation we obtain the bifurcation diagram of the magnets, including the
critical currents to induce stable precessional states and magnetization
switching, as well as the mean times of thermally assisted magnetization
reversal in situations where the standard reaction rate theory of Kramers is no
longer valid. These results match experimental observations and give a
theoretical basis for a N\'eel-Brown-type formula with an effective energy
barrier for the reversal times.",1210.6253v3
2013-03-13,"Ferromagnetic exchange, spin-orbit coupling and spiral magnetism at the LaAlO_3/SrTiO_3 interface","The electronic properties of the polar interface between insulating oxides is
a subject of great current interest. An exciting new development is the
observation of robust magnetism at the interface of two non-magnetic materials
LaAlO_3 (LAO) and SrTiO_3 (STO). Here we present a microscopic theory for the
formation and interaction of local moments, which depends on essential features
of the LAO/STO interface. We show that correlation-induced moments arise due to
interfacial splitting of orbital degeneracy. We find that gate-tunable Rashba
spin-orbit coupling at the interface influences the exchange interaction
mediated by conduction electrons. We predict that the zero-field ground state
is a long-wavelength spiral and show that its evolution in an external field
accounts semi-quantitatively for torque magnetometry data. Our theory describes
qualitative aspects of the scanning SQUID measurements and makes several
testable predictions for future experiments.",1303.3275v2
2014-01-08,Evidence for Magneto-Levitation Accretion in Long-Period X-ray Pulsars,"Study of observed spin evolution of long-period X-ray pulsars challenges
quasi-spherical and Keplerian disk accretion scenarios. It suggests that the
magnetospheric radius of the neutron stars is substantially smaller than Alfven
radius and the spin-down torque applied to the star from accreting material
significantly exceeds the value predicted by the theory. We show that these
problems can be avoided if the fossil magnetic field of the accretion flow
itself is incorporated into the accretion model. The initially spherical flow
in this case decelerates by its own magnetic field and converts into a
non-Keplerian disk (magnetic slab) in which the material is confined by its
intrinsic magnetic field (""levitates"") and slowly moves towards the star on a
diffusion timescale. Parameters of pulsars expected within this
magneto-levitation accretion scenario are evaluated.",1401.1654v1
2014-01-17,"Transient times, resonances and drifts of attractors in dissipative rotational dynamics","In a dissipative system the time to reach an attractor is often influenced by
the peculiarities of the model and in particular by the strength of the
dissipation. In particular, as a dissipative model we consider the spin-orbit
problem providing the dynamics of a triaxial satellite orbiting around a
central planet and affected by tidal torques. The model is ruled by the
oblateness parameter of the satellite, the orbital eccentricity, the
dissipative parameter and the drift term. We devise a method which provides a
reliable indication on the transient time which is needed to reach an attractor
in the spin-orbit model; the method is based on an analytical result, precisely
a suitable normal form construction. This method provides also information
about the frequency of motion. A variant of such normal form used to
parametrize invariant attractors provides a specific formula for the drift
parameter, which in turn yields a constraint - which might be of interest in
astronomical problems - between the oblateness of the satellite and its orbital
eccentricity.",1401.4378v1
2014-03-13,Hidden and Hastatic Orders in URu2Si2,"The hidden order developing below 17.5K in the heavy fermion material URu2Si2
has eluded identification for over twenty five years. This paper will review
the recent theory of ``hastatic order,'' a novel two-component order parameter
capturing the hybridization between half-integer spin (Kramers) conduction
electrons and the non-Kramers 5f^2 Ising local moments, as strongly indicated
by the observation of Ising quasiparticles in de Haas-van Alphen measurements.
Hastatic order differs from conventional magnetism as it is a spinor order that
breaks both single and double time-reversal symmetry by mixing states of
different Kramers parity. The broken time-reversal symmetry simply explains
both the pseudo-Goldstone mode between the hidden order and antiferromagnetic
phases and the nematic order seen in torque magnetometry. The spinorial nature
of the hybridization also explains how the Kondo effect gives a phase
transition, with the hybridization gap turning on at the hidden order
transition as seen in scanning tunneling microscopy. Hastatic order also has a
number of new predictions: a basal-plane magnetic moment of order .01\mu_B, a
gap to longitudinal spin fluctuations that vanishes continuously at the first
order antiferromagnetic transition and a narrow resonant nematic feature in the
scanning tunneling spectra.",1403.3422v1
2014-04-10,Tunable chiral spin texture in magnetic domain-walls,"Magnetic domain-walls (DWs) with a preferred chirality exhibit very efficient
current-driven motion. Since structural inversion asymmetry (SIA) is required
for their stability, the observation of chiral domain walls in highly symmetric
Pt/Co/Pt is intriguing. Here, we tune the layer asymmetry in this system and
observe, by current-assisted DW depinning experiments, a small chiral field
which sensitively changes. Moreover, we convincingly link the observed
efficiency of DW motion to the DW texture, using DW resistance as a direct
probe for the internal orientation of the DW under the influence of in-plane
fields. The very delicate effect of capping layer thickness on the chiral field
allows for its accurate control, which is important in designing novel
materials for optimal spin-orbit-torque-driven DW motion.",1404.2945v1
2014-07-09,"Temperature dependence of spin-orbit torque effective fields in the diluted magnetic semiconductor (Ga,Mn)As","We report on a study of the temperature-dependence of current-induced
effective magnetic fields due to spin-orbit interactions in the diluted
ferromagnetic semiconductor (Ga,Mn)As. Contributions from the effective fields
as well as from the anomalous Nernst effect are evident in the difference
between transverse resistance measurements as a function of an external
magnetic field for opposite orientations of the applied current. We separately
extract these contributions by fitting to a model of coherently rotating
magnetization. The component of the effective field with Dresselhaus symmetry
is substantially enhanced with increasing temperature, while no significant
temperature-dependence is observed for the component with Rashba symmetry.",1407.2409v1
2014-10-10,Collective dynamics in a binary mixture of hydrodynamically coupled micro-rotors,"We study, numerically, the collective dynamics of self-rotating nonaligning
particles by considering a monolayer of spheres driven by constant clockwise or
counterclockwise torques. We show that hydrodynamic interactions alter the
emergence of large-scale dynamical patterns compared to those observed in dry
systems. In dilute suspensions, the flow stirred by the rotors induces
clustering of opposite-spin rotors, while at higher densities same-spin rotors
phase separate. Above a critical rotor density, dynamic hexagonal crystals
form. Our findings underscore the importance of inclusion of the many-body,
long-range hydrodynamic interactions in predicting the phase behavior of active
particles.",1410.2878v2
2014-11-12,An accreting low magnetic field magnetar for the ultraluminous X-ray source in M82,"One ultraluminous X-ray source in M82 is identified as an accreting neutron
star recently (named as NuSTAR J095551+6940.8). It has a super-Eddington
luminosity and is spinning up. For an aged magnetar, it is more likely to be a
low magnetic field magnetar. An accreting low magnetic field magnetar may
explain both the super-Eddington luminosity and the rotational behavior of this
source. Considering the effect of beaming, the spin-up rate is understandable
using the traditional form of accretion torque. The transient nature, spectral
properties of M82 X-2 are discussed. The theoretical period range of accreting
magnetar is provided. Three observational appearances of accreting magnetars
are summarized.",1411.3168v2
2015-03-11,Dynamical influence of vortex-antivortex pairs in magnetic vortex oscillators,"We study the magnetization dynamics in a nanocontact magnetic vortex
oscillators as function of temperature. Low temperature experiments reveal that
the dynamics at low and high currents differ qualitatively. At low currents, we
excite a temperature independent standard oscillation mode, consisting in the
gyrotropic motion of a free layer vortex about the nanocontact. Above a
critical current, a sudden jump of the frequency is observed, concomitant with
a substantial increase of the frequency versus current slope factor. Using
micromagnetic simulation and analytical modeling, we associate this new regime
to the creation of a vortex-antivortex pair in the pinned layer of the spin
valve. The vortex-antivortex distance depends on the Oersted field which favors
a separation, and on the exchange bias field, which favors pair merging. The
pair in the pinned layer provides an additional spin torque altering the
dynamics of the free layer vortex, which can be quantitatively accounted for by
an analytical model.",1503.03365v2
2015-09-15,Orbital parameters of V 0332+53 from 2015 giant outburst data,"We present the updated orbital solution for the transient Be X-ray binary V
0332+53 comple- menting historical measurements with the data from the
gamma-ray burst monitor onboard Fermi obtained during the outburst in
June-October 2015. We model the observed changes in the spin- frequency of the
pulsar and deduce the orbital parameters of the system. We significantly
improve existing constrains and show that contrary to the previous findings no
change in orbital parameters is required to explain the spin evolution of the
source during the outbursts in 1983, 2005 and 2015. The reconstructed intrinsic
spin-up of the neutron star during the latest outburst is found to be
comparable with previosly observed values and predictions of the accretion
torque theory.",1509.04490v2
2015-11-14,Generation of magnetic skyrmion bubbles by inhomogeneous spin Hall currents,"Recent experiments have shown that magnetic skyrmion bubbles can be generated
and injected at room temperature in thin films [W. Jiang et al, Science vol.
349, 283 (2015)]. Here, we demonstrate, using micromagnetic modeling, that such
skyrmions can be generated by an inhomogeneous spin Hall torque in the presence
of Dzyaloshinskii-Moriya interactions (DMIs). In the experimental
Ta/Co$_{20}$Fe$_{60}$B$_{20}$ thin films, the DMI is rather small;
nevertheless, the skyrmion bubbles are stable, or at least metastable on
observational time scales.",1511.04630v2
2016-03-01,Mobile Néel skyrmions at room temperature: status and future,"Magnetic skyrmions are topologically protected spin textures that exhibit
many fascinating features. As compared to the well-studied cryogenic Bloch
skyrmions in bulk materials, we focus on the room-temperature N\'eel skyrmions
in thin-film systems with an interfacial broken inversion symmetry in this
article. Specifically, we show the stabilization, the creation, and the
implementation of N\'eel skyrmions that are enabled by the electrical
current-induced spin-orbit torques. Towards the nanoscale N\'eel skyrmions, we
further discuss the challenges from both material optimization and imaging
characterization perspectives.",1603.00443v1
2016-03-29,Static transport properties of random alloys: vertex corrections in conserving approximations,"The theoretical formulation and numerical evaluation of the vertex
corrections in multiorbital techniques of theories of electronic properties of
random alloys are analyzed. It is shown that current approaches to static
transport properties within the so-called conserving approximations lead to the
inversion of a singular matrix as a direct consequence of the Ward identity
relating the vertex corrections to one-particle self-energies. We propose a
simple removal of the singularity for quantities (operators) with vanishing
average values for electron states at the Fermi energy, such as the velocity or
the spin torque; the proposed scheme is worked out in details in the
self-consistent Born approximation and the coherent potential approximation.
Applications involve calculations of the residual resistivity for various
random alloys, including spin-polarized and relativistic systems, treated on an
ab initio level, with particular attention paid to the role of different
symmetries (inversion of space and time).",1603.08677v2
2016-04-29,Current induced magnetization dynamics and magnetization switching in superconducting ferromagnetic hybrid (F$|$S$|$F) structures,"We investigate the current induced magnetization dynamics and magnetization
switching in an unconventional p-wave superconductor sandwiched between two
misaligned ferromagnetic layers by numerically solving Landau-Lifshitz-Gilbert
equation modified with current induced Slonczewski's spin torque term. A
modified form of Ginzburg-Landau free energy functional has been used for this
purpose. We demonstrated the possibility of current induced magnetization
switching in the spin-triplet ferromagnetic superconducting hybrid structures
with strong easy axis anisotropy and the condition for magnetization reversal.
The switching time for such arrangement is calculated and is found to be highly
dependent on the magnetic configuration along with the biasing current. This
study would be useful in designing practical superconducting-spintronic
devices.",1604.08704v3
2016-07-14,Solar Obliquity Induced by Planet Nine,"The six-degree obliquity of the sun suggests that either an asymmetry was
present in the solar system's formation environment, or an external torque has
misaligned the angular momentum vectors of the sun and the planets. However,
the exact origin of this obliquity remains an open question. Batygin & Brown
(2016) have recently shown that the physical alignment of distant Kuiper Belt
orbits can be explained by a 5-20 Earth-mass planet on a distant, eccentric,
and inclined orbit, with an approximate perihelion distance of ~250 AU. Using
an analytic model for secular interactions between Planet Nine and the
remaining giant planets, here we show that a planet with similar parameters can
naturally generate the observed obliquity as well as the specific pole position
of the sun's spin axis, from a nearly aligned initial state. Thus, Planet Nine
offers a testable explanation for the otherwise mysterious spin-orbit
misalignment of the solar system.",1607.03963v2
2016-10-04,Performance of synthetic antiferromagnetic racetrack memory: domain wall vs skyrmion,"A storage scheme based on racetrack memory, where the information can be
coded in a domain or a skyrmion, seems to be an alternative to conventional
hard disk drive for high density storage. Here, we perform a full micromagnetic
study of the performance of synthetic antiferromagnetic (SAF) racetrack memory
in terms of velocity and sensitivity to defects by using experimental
parameters. We find that to stabilize a SAF skyrmion, the Dzyaloshinskii-Moriya
Interaction in the top and the bottom ferromagnet should have an opposite sign.
The velocity of SAF skyrmion and SAF Neel domain wall are of the same order and
can reach values larger than 1200 m/s if a spin-orbit torque from the spin-Hall
effect with opposite sign is applied to both ferromagnets.",1610.00894v2
2017-01-29,Current-driven skyrmion dynamics in disordered films,"A theoretical study of the current-driven dynamics of magnetic skyrmions in
disordered perpendicularly-magnetized ultrathin films is presented. The
disorder is simulated as a granular structure in which the local anisotropy
varies randomly from grain to grain. The skyrmion velocity is computed for
different disorder parameters and ensembles. Similar behavior is seen for
spin-torques due to in-plane currents and the spin Hall effect, where a pinning
regime can be identified at low currents with a transition towards the
disorder-free case at higher currents, similar to domain wall motion in
disordered films. Moreover, a current-dependent skyrmion Hall effect and
fluctuations in the core radius are found, which result from the interaction
with the pinning potential.",1701.08357v2
2017-02-21,Spin texture motion in antiferromagnetic and ferromagnetic nanowires,"We propose a Hamiltonian dynamics formalism for the current and magnetic
field driven dynamics of ferromagnetic and antiferromagnetic domain walls in
one dimensional systems. To demonstrate the power of this formalism, we derive
Hamilton equations of motion via Poisson brackets based on the
Landau-Lifshitz-Gilbert phenomenology, and add dissipative dynamics via the
evolution of the energy. We use this approach to study current induced domain
wall motion and compute the drift velocity. For the antiferromagnetic case, we
show that a nonzero magnetic moment is induced in the domain wall, which
indicates that an additional application of a magnetic field would influence
the antiferromagnetic domain-wall dynamics. We consider both cases of the
magnetic field being parallel and transverse to the N{\'e}el field. Based on
this formalism, we predict an orientation switch mechanism for
antiferromagnetic domain walls which can be tested with the recently discovered
N{\'e}el spin orbit torques.",1702.06274v1
2017-02-22,Control of spectral characteristics of spin-current auto-oscillator by electric field,"We study the effects of electrostatic gating on the magnetization
auto-oscillations induced by the local injection of electric current into a
ferromagnet/heavy metal bilayer. We find that the characteristic currents
required for the excitation, the intensity and the spectral characteristics of
the generated dynamical states can be tuned by the voltage applied to the
metallic gate separated from the bilayer by a thin insulating layer. We show
that the effect of electrostatic gating becomes enhanced in the strongly
nonlinear oscillation regime at sufficiently large driving currents. Analysis
shows that the observed effects are caused by a combination of electric
field-dependent surface anisotropy and electric field-dependent contribution to
the current-induced spin-orbit torques. The demonstrated ability to control the
microwave emission and spectral characteristics provides an efficient approach
to the development of electrically tunable microwave nano-oscillators.",1702.06638v1
2017-02-24,Description of statistical switching in perpendicular STT-MRAM within an analytical and numerical micromagnetic framework,"The realistic modeling of STT-MRAM for the simulations of hybrid
CMOS/Spintronics devices in comprehensive simulation environments require a
full description of stochastic switching processes in state of the art
STT-MRAM. Here, we derive an analytical formulation that takes into account the
spin-torque asymmetry of the spin polarization function of magnetic tunnel
junctions studying. We studied its validity range by comparing the analytical
formulas with results achieved numerically within a full micromagnetic
framework. We also find that a reasonable fit of the probability density
function (PDF) of the switching time is given by a Pearson Type IV PDF. The
main results of this work underlines the need of data-driven design of STT-MRAM
that uses a full micromagnetic simulation framework for the statistical
proprieties PDF of switching processes.",1702.07739v1
2017-02-24,Route Towards Dirac and Weyl Antiferromagnetic Spintronics,"Topological quantum matter and spintronics research have been developed to a
large extent independently. In this Review we discuss a new role that the
antiferromagnetic order has taken in combining topological matter and
spintronics. This occurs due to the complex microscopic symmetries present in
antiferromagnets that allow, e.g., for topological relativistic quasiparticles
and the newly discovered N\'{e}el spin-orbit torques to coexist. We first
introduce the concepts of topological semimetals and spin-orbitronics.
Secondly, we explain the antiferromagnetic symmetries on a minimal Dirac
semimetal model and the guiding role of $\textit{ab initio}$ calculations in
predictions of examples of Dirac, and Weyl antiferromagnets:
SrMnBi$_{\text{2}}$, CuMnAs, and Mn$_{\text{3}}$Ge. Lastly, we illustrate the
interplay of Dirac quasiparticles, topology and antiferromagnetism on: (i) the
experimentally observed quantum Hall effect in EuMnBi$_{\text{2}}$, (ii) the
large anomalous Hall effect in Mn$_{\text{3}}$Ge, and (iii) the theoretically
predicted topological metal-insulator transition in CuMnAs.",1702.07788v1
2017-03-10,Quantum Oscillations in the Anomalous Spin Density Wave State of FeAs,"Quantum oscillations in the binary antiferromagnetic metal FeAs are presented
and compared to theoretical predictions for the electronic band structure in
the anomalous spin density wave state of this material. Demonstrating a new
method for growing single crystals out of Bi flux, we utilize the highest
quality FeAs to perform torque magnetometry experiments up to 35 T, using
rotations of field angle in two planes to provide evidence for one electron and
one hole band in the magnetically ordered state. The resulting picture agrees
with previous experimental evidence for multiple carriers at low temperatures,
but the exact Fermi surface shape differs from predictions, suggesting that
correlations play a role in deviation from ab initio theory and cause up to a
four-fold enhancement in the effective carrier mass.",1703.03833v2
2017-03-16,Hamiltonian formulation of the spin-orbit model with time-varying non-conservative forces,"In a realistic scenario, the evolution of the rotational dynamics of a
celestial or artificial body is subject to dissipative effects. Time-varying
non-conservative forces can be due to, for example, a variation of the moments
of inertia or to tidal interactions. In this work, we consider a simplified
model describing the rotational dynamics, known as the spin-orbit problem,
where we assume that the orbital motion is provided by a fixed Keplerian
ellipse. We consider different examples in which a non-conservative force acts
on the model and we propose an analytical method, which reduces the system to a
Hamiltonian framework. In particular, we compute a time parametrisation in a
series form, which allows us to transform the original system into a
Hamiltonian one. We also provide applications of our method to study the
rotational motion of a body with time-varying moments of inertia, e.g. an
artificial satellite with flexible components, as well as subject to a tidal
torque depending linearly on the velocity.",1703.05825v1
2017-05-10,Evolution of newborn rapidly rotating magnetars: effects of r-mode and fall-back accretion,"In this paper we investigate effects of the $r$-mode instability on a newborn
rapidly-rotating magnetar with fall-back accretion. Such a magnetar could
usually occur in core-collapse supernovae and gamma-ray bursts. We find that
the magnetar's spin and $r$-mode evolution are influenced by accretion. If the
magnetar is sufficiently spun up to a few milliseconds, gravitational radiation
leads to the growth of the $r$-mode amplitude significantly. The maximum
$r$-mode amplitude reaches an order $\sim 0.001$ when the damping due to the
growth of a toroidal magnetic field balances the growth of the $r$-mode
amplitude. If such a sufficiently spun-up magnetar was located at a distance
less than 1\,Mpc, then gravitational waves would be detectable by the Einstein
Telescope but would have an extremely low event rate. However, if the spin-up
is insufficient, the growth of the $r$-mode amplitude is mainly due to the
accretion torque. In this case, the maximum $r$-mode amplitude is of the order
of $\sim 10^{-6}-10^{-5}$.",1705.03579v1
2017-11-14,Radiation-Reaction Force on a Small Charged Body to Second Order,"In classical electrodynamics, an accelerating charged body emits radiation
and experiences a corresponding radiation-reaction force, or self force. We
extend to higher order in the total charge a previous rigorous derivation of
the electromagnetic self force in flat spacetime by Gralla, Harte, and Wald.
The method introduced by Gralla, Harte, and Wald computes the self force from
the Maxwell field equations and conservation of stress-energy in a limit where
the charge, size, and mass of the body go to zero, and does not require
regularization of a singular self field. For our higher order computation, an
adjustment of the definition of the mass of the body is necessary to avoid
including self energy from the electromagnetic field sourced by the body in the
distant past. We derive the evolution equations for the mass, spin, and
center-of-mass position of the body through second order. We derive, for the
first time, the second-order acceleration dependence of the evolution of the
spin (self torque), as well as a mixing between the extended body effects and
the acceleration dependent effects on the overall body motion.",1711.05212v2
2017-10-24,THz electrical writing speed in an antiferromagnetic memory,"The speed of writing of state-of-the-art ferromagnetic memories is physically
limited by an intrinsic GHz threshold. Recently, an alternative research
direction has been initiated by realizing memory devices based on
antiferromagnets in which spin directions periodically alternate from one
atomic lattice site to the next. In our work we experimentally demonstrate at
room temperature that the speed of reversible electrical writing in a memory
device can be scaled up to THz using an antiferromagnet. Efficient
current-induced spin-torque mechanism is responsible for the switching in our
memory devices throughout the twelve orders of magnitude range of writing
speeds from Hz to THz. Our work opens the path towards the development of
memory-logic technology reaching the elusive THz band.",1711.08444v1
2017-11-10,Overview of the Cosmic Axion Spin Precession Experiment (CASPEr),"An overview of our experimental program to search for axion and
axion-like-particle (ALP) dark matter using nuclear magnetic resonance (NMR)
techniques is presented. An oscillating axion field can exert a time-varying
torque on nuclear spins either directly or via generation of an oscillating
nuclear electric dipole moment (EDM). Magnetic resonance techniques can be used
to detect such an effect. The first-stage experiments explore many decades of
ALP parameter space beyond the current astrophysical and laboratory bounds. It
is anticipated that future versions of the experiments will be sensitive to the
axions associated with quantum chromodynamics (QCD) having masses $\lesssim
10^{-9}~{\rm eV}/c^2$.",1711.08999v3
2018-04-16,Symmetry and topology in antiferromagnetic spintronics,"Antiferromagnetic spintronics focuses on investigating and using
antiferromagnets as active elements in spintronics structures. Last decade
advances in relativistic spintronics led to the discovery of the staggered,
current-induced field in antiferromagnets. The corresponding N\'{e}el
spin-orbit torque allowed for efficient electrical switching of
antiferromagnetic moments and, in combination with electrical readout, for the
demonstration of experimental antiferromagnetic memory devices. In parallel,
the anomalous Hall effect was predicted and subsequently observed in
antiferromagnets. A new field of spintronics based on antiferromagnets has
emerged. We will focus here on the introduction into the most significant
discoveries which shaped the field together with a more recent spin-off
focusing on combining antiferromagnetic spintronics with topological effects,
such as antiferromagnetic topological semimetals and insulators, and the
interplay of antiferromagnetism, topology, and superconductivity in
heterostructures.",1804.05628v1
2018-11-05,Nonlinear localization of light using the Pancharatnam-Berry phase,"Since its introduction by Sir Michael Berry in 1984, geometric phase became
of fundamental importance in physics, with applications ranging from solid
state physics to optics. In optics, Pancharatnam-Berry phase allows the
tailoring of optical beams by a local control of their polarization. Here we
discuss light propagation in the presence of an intensity-dependent local
modulation of the Pancharatnam-Berry phase. The corresponding self-modulation
of the wavefront counteracts the natural spreading due to diffraction, i.e.,
self-focusing takes place. No refractive index variation is associated with the
self-focusing: the confinement is uniquely due to a nonlinear spin-orbit
interaction. The phenomenon is investigated, both theoretically and
experimentally, considering the reorientational nonlinearity in liquid
crystals, where light is able to rotate the local optical axis through an
intensity-dependent optical torque. Our discoveries pave the way to the
investigation of a new family of nonlinear waves featuring a strong interaction
between the spin and the orbital degrees of freedom.",1811.01819v1
2018-12-26,Magnonic Band Structure Established by Chiral Spin-Density Waves in Thin Film Ferromagnets,"Recent theoretical studies have demonstrated the possibility to excite and
sustain noncollinear magnetization states in ferromagnetic nanowires. The
resulting state is referred to as a spin-density wave (SDW). SDWs can be
interpreted as hydrodynamic states with a constant fluid density and fluid
velocity in systems with easy-plane anisotropy. Here, we consider the effect of
the nonlocal dipole field arising from the finite thickness of magnetic thin
films on the spatial profile of the SDW and on the associated magnon
dispersion. Utilizing a hydrodynamic formulation of the Larmor torque equation,
it is found that the nonlocal dipole field modulates the fluid velocity. Such a
modulation induces a magnonic band structure unlike the typical dispersion
relation for magnons on uniform magnetization. The analytical results are
validated by micromagnetic simulations. Band gaps on the order of GHz are
numerically observed to depend on the SDW fluid velocity and film thickness for
realistic material parameters. The presented results suggest that SDWs can find
applications as reconfigurable magnonic crystals.",1812.10571v1
2018-12-31,Electric field switching of the uniaxial magnetic anisotropy of an antiferromagnet,"Electric field control of magnetic anisotropy in ferromagnets has been
intensively pursued in spintronics to achieve efficient memory and computing
devices with low energy consumption. Compared with ferromagnets,
antiferromagnets hold huge potential in high-density information storage for
their ultrafast spin dynamics and vanishingly small stray field. However, the
switching of magnetic anisotropy of antiferromagnets via electric field remains
elusive. Here we use ferroelastic strain from piezoelectric materials to switch
the uniaxial magnetic anisotropy and the N\'eel order reversibly in
antiferromagnetic Mn2Au films with an electric field of only a few kV/cm at
room temperature. Owing to the uniaxial magnetic anisotropy, a ratchet-like
switching behavior driven by the N\'eel spin-orbit torque is observed in the
Mn2Au, which can be reversed by electric fields.",1812.11868v1
2019-01-07,Giant anisotropy of Gilbert damping in epitaxial CoFe films,"Tailoring Gilbert damping of metallic ferromagnetic thin films is one of the
central interests in spintronics applications. Here we report a giant Gilbert
damping anisotropy in epitaxial Co$_{50}$Fe$_{50}$ thin film with a
maximum-minimum damping ratio of 400 \%, determined by broadband spin-torque as
well as inductive ferromagnetic resonance. We conclude that the origin of this
damping anisotropy is the variation of the spin orbit coupling for different
magnetization orientations in the cubic lattice, which is further corroborate
from the magnitude of the anisotropic magnetoresistance in Co$_{50}$Fe$_{50}$.",1901.01941v1
2019-01-10,Braking index jumps in young pulsars,"The departure of all measured pulsar braking indexes from the ""canonical""
dipole value 3 has been attributed to several causes in the past. Careful
monitoring of the Crab pulsar has revealed permanent changes in the spin-down
rate which are most likely the accumulation of small jumps in the angle
$\alpha$ between the magnetic and spin axis. Recently, a large permanent change
in the braking index of the in the ""Crab twin"" pulsar B0540-69 has been
reported, and an analogous phenomenon seen in the high-field pulsar PSR
1846-0258 has been seen following a glitch, while another similar event (in PSR
J119-6127) needs to be confirmed. We argue in this work that a common physical
origin of all these observations can be attributed to the counter-alignment of
the axis without serious violations of the observed features and with very
modest inferred values of the hypothesized jump in the $\alpha$ angle. In
addition, detected increases of the X-ray luminosities after the events are an
additional ingredient for this interpretation. We argue that a component of a
time-dependent torque has been identified, being an important ingredient
towards a full solution of observed pulsar timing behavior which is in search
of a consistent modeling.",1901.03405v1
2019-03-01,Individual skyrmion manipulation by local magnetic field gradients,"Magnetic skyrmions are topologically protected spin textures, stabilised in
systems with strong Dzyaloshinskii-Moriya interaction (DMI). Several studies
have shown that electrical currents can move skyrmions efficiently through
spin-orbit torques. While promising for technological applications,
current-driven skyrmion motion is intrinsically collective and accompanied by
undesired heating effects. Here we demonstrate a new approach to control
individual skyrmion positions precisely, which relies on the magnetic
interaction between sample and a magnetic force microscopy (MFM) probe. We
investigate perpendicularly magnetised X/CoFeB/MgO multilayers, where for X = W
or Pt the DMI is sufficiently strong to allow for skyrmion nucleation in an
applied field. We show that these skyrmions can be manipulated individually
through the local field gradient generated by the scanning MFM probe with an
unprecedented level of accuracy. Furthermore, we show that the probe stray
field can assist skyrmion nucleation. Our proof-of-concepts results offer
current-free paradigms to efficient individual skyrmion control.",1903.00367v1
2019-03-29,Electrical Néel-order switching in magnetron-sputtered CuMnAs thin films,"Antiferromagnetic materials as active components in spintronic devices
promise insensitivity against external magnetic fields, the absence of own
magnetic stray fields, and ultrafast dynamics at the picosecond time scale.
Materials with certain crystal-symmetry show an intrinsic N\'eel-order
spin-orbit torque that can efficiently switch the magnetic order of an
antiferromagnet. The tetragonal variant of CuMnAs was shown to be electrically
switchable by this intrinsic spin-orbit effect and its use in memory cells with
memristive properties has been recently demonstrated for high-quality films
grown with molecular beam epitaxy. Here, we demonstrate that the magnetic order
of magnetron-sputtered CuMnAs films can also be manipulated by electrical
current pulses. The switching efficiency and relaxation as a function of
temperature, current density, and pulse width can be described by a
thermal-activation model. Our findings demonstrate that CuMnAs can be
fabricated with an industry-compatible deposition technique, which will
accelerate the development cycle of devices based on this remarkable material.",1903.12387v2
2019-04-16,Large tunneling magnetoresistance in VSe2/MoS2 magnetic tunnel junction,"Two-dimensional (2D) van der Waals (vdW) materials provide the possibility of
realizing heterostructures with coveted properties. Here, we report a
theoretical investigation of the vdW magnetic tunnel junction (MTJ) based on
VSe2/MoS2 heterojunction, where the VSe2 monolayer acts as the ferromagnet with
the room-temperature ferromagnetism. We propose the concept of spin-orbit
torque (SOT) vdW MTJ with reliable reading and efficient writing operations.
The non-equilibrium study reveals a large tunneling magnetoresistance (TMR) of
846 % at 300 Kelvin, identifying significantly its parallel and anti-parallel
states. Thanks to the strong spin Hall conductivity of MoS2, SOT is promising
for the magnetization switching of VSe2 free layer. Quantum-well states come
into being and resonances appear in MTJ, suggesting that the voltage control
can adjust transport properties effectively. The SOT vdW MTJ based on VSe2/MoS2
provides desirable performance and experimental feasibility, offering new
opportunities for 2D spintronics.",1904.07499v1
2019-04-23,Current-induced switching of YIG/Pt bilayers with in-plane magnetization due to Oersted fields,"We report on the switching of the in-plane magnetization of thin yttrium iron
garnet (YIG)/Pt bilayers induced by an electrical current. The switching is
either field-induced and assisted by a dc current, or current-induced and
assisted by a static magnetic field. The reversal of the magnetization occurs
at a current density as low as $10^5$~A/cm$^{2}$ and magnetic fields of $\sim
40$~$\mu$T, two orders of magnitude smaller than in ferromagnetic metals,
consistently with the weak uniaxial anisotropy of the YIG layers. We use the
transverse component of the spin Hall magnetoresistance to sense the magnetic
orientation of YIG while sweeping the current. Our measurements and simulations
reveal that the current-induced effective field responsible for switching is
due to the Oersted field generated by the current flowing in the Pt layer
rather than by spin-orbit torques, and that the switching efficiency is
influenced by pinning of the magnetic domains.",1904.10517v1
2019-07-22,Generalized Abraham Forces on Molecules: from classical to quantum,"Abraham forces are defined as electromagnetic forces on neutral objects
caused by the presence of slow, time-dependent, homogeneous electromagnetic
fields.
  Only a few experimental observations have been reported, and different
formulations exist in literature. The ``standard"" Abraham force is usually
associated with the full derivative $\partial_t(\mathbf{E} \times \mathbf{B})$
of homogeneous electric and magnetic fields. We show that this full derivative
is wrong in general, since the classical Maxwell theory contains subtle
induced-dipole forces that contribute to the Abraham force, which thus breaks
the dual symmetry between electric and magnetic components. We investigate
other manifestations of Abraham forces and torques and estimate orders of
magnitude, e.g related to chiral, moving or rotating matter. Some of them are
also severely violating dual symmetry. We provide a quantum description of the
Abraham force. Apart from being more elegant and less technical, this quantum
treatment paves the way for future studies of Abraham forces on complex
molecules involving spin and spin-orbit coupling, and also facilitates the
inclusion of the quantum vacuum.",1907.09345v1
2019-08-09,Gating effects in antiferromagnetic CuMnAs,"Antiferromagnets (AFs) attract much attention due to potential applications
in spintronics. Both the electric current and the electric field are considered
as tools suitable to control properties and the N\'eel vector direction of AFs.
Among AFs, CuMnAs has been shown to exhibit specific properties that result in
the existence of the current-induced spin-orbit torques commensurate with spin
directions and topological Dirac quasiparticles. Here, we report on the
observation of a reversible effect of an electric field on the resistivity of
CuMnAs thin films, employing ionic liquid as a gate insulator. The data allow
to determine the carrier type, concentration, and mobility independently of the
Hall effect that may be affected by an anomalous component.",1908.03521v1
2019-08-23,Precession-free domain wall dynamics in compensated ferrimagnets,"One fundamental obstacle to efficient ferromagnetic spintronics is magnetic
precession, which intrinsically limits the dynamics of magnetic textures, We
demonstrate that the domain wall precession fully vanishes with a record
mobility when the net angular momentum is compensated (TAC) in DWs driven by
spin-orbit torque in a ferrimagnetic GdFeCo/Pt track. We use transverse
in-plane fields to reveal the internal structure of DWs and provide a robust
and parameter-free measurement of TAC. Our results highlight the mechanism of
faster and more efficient dynamics in materials with multiple spin lattices and
reduced net angular momentum, promising for high-speed, low-power spintronics
applications.",1908.08867v2
2019-10-18,Resistive contribution in electrical switching experiments with antiferromagnets,"Recent research demonstrated the electrical switching of antiferromagnets via
intrinsic spin-orbit torque or the spin Hall effect of an adjacent heavy metal
layer. The electrical readout is typically realized by measuring the transverse
anisotropic magnetoresistance at planar cross- or star-shaped devices with four
or eight arms, respectively. Depending on the material, the current density
necessary to switch the magnetic state can be large, often close to the
destruction threshold of the device. We demonstrate that the resulting
electrical stress changes the film resistivity locally and thereby breaks the
fourfold rotational symmetry of the conductor. This symmetry breaking due to
film inhomogeneity produces signals, that resemble the anisotropic
magnetoresistance and is experimentally seen as a ""saw-tooth""-shaped transverse
resistivity. This artifact can persist over many repeats of the switching
experiment and is not easily separable from the magnetic contribution. We
discuss the origin of the artifact, elucidate the role of the film
crystallinity, and propose approaches how to separate the resistive
contribution from the magnetic contribution.",1910.08576v1
2019-10-21,Dynamics of an elliptical ferromagnetic skyrmion driven by the spin-orbit torque,"Magnetic skyrmion is a promising building block for developing information
storage and computing devices. It can be stabilized in a ferromagnetic thin
film with the Dzyaloshinskii-Moriya interaction (DMI). The moving ferromagnetic
skyrmion may show the skyrmion Hall effect, that is, the skyrmion shows a
transverse shift when it is driven by a spin current. Here, we numerically and
theoretically study the current-driven dynamics of a ferromagnetic nanoscale
skyrmion in the presence of the anisotropic DMI, where the skyrmion has an
elliptical shape. The skyrmion Hall effect of the elliptical skyrmion is
investigated. It is found that the skyrmion Hall angle can be controlled by
tuning the profile of elliptical skyrmion. Our results reveal the relation
between the skyrmion shape and the skyrmion Hall effect, which could be useful
for building skyrmion-based spintronic devices with preferred skyrmion Hall
angle. Also, our results provide a method for the minimization of skyrmion Hall
angle for applications based on in-line motion of skyrmions.",1910.09341v2
2019-12-06,Rotation of a submerged finite cylinder moving down a soft incline,"A submerged finite cylinder moving under its own weight along a soft incline
lifts off and slides at a steady velocity while also spinning. Here, we
experimentally quantify the steady spinning of the cylinder and show
theoretically that it is due to a combination of an elastohydrodynamic torque
generated by flow in the variable gap, and the viscous friction on the edges of
the finite-length cylinder. The relative influence of the latter depends on the
aspect ratio of the cylinder as well as the deformability of the substrate,
which we express in term of a single scaled compliance parameter. By varying
this compliance parameter, we show that our experimental results are consistent
with a transition from an edge-effect dominated regime for short cylinders to a
gap-dominated elastohydrodynamic regime when the cylinder is very long.",1912.03038v1
2020-01-03,Self focusing Hybrid Skyrmions in spatially varying canted ferromagnetic systems,"Magnetic skyrmions are quasiparticle configurations in a magnetic film that
can act as information carrying bits for ultrasmall, all-electronic nonvolatile
memory. The skyrmions can be nucleated and driven by spin-orbit torque from a
current driven in a heavy metal underlayer. Along its gyrotropic path, a Magnus
force can cause a skyrmion to be annihilated at the boundaries. By combining
interfacial and bulk Dzyaloshinskii-Moriya interactions (DMIs), for instance by
using a B20 material on top of a heavy metal layer with high spin-orbit
coupling, it is possible to engineer a hybrid skyrmion that will travel
parallel to the racetrack with zero Magnus force. We show that by using a
spatially varying interfacial DMI, a hybrid skyrmion will automatically
self-focus onto such a track as its domain angle evolves along the path.
Furthermore, using a gate driven voltage controlled magnetic anisotropy, we can
control the trajectory of the hybrid skyrmion and its eventual convergence path
and lane selection in a racetrack geometry.",2001.00729v3
2020-01-06,Giant anomalous Hall and Nernst effect in magnetic cubic Heusler compounds,"The interplay of magnetism and topology opens up the possibility for exotic
linear response effects, such as the anomalous Hall effect and the anomalous
Nernst effect, which can be strongly enhanced by designing a strong Berry
curvature in the electronic structure. It is even possible to utilize this to
create a quantum anomalous Hall state at high temperatures by reducing the
dimensionality. Magnetic Heusler compounds are a promising class of materials
for this purpose because they grow in thin films, have a high Curie
temperature, and their electronic structure hosts strong topological features.
Here, we provide a comprehensive study of the intrinsic anomalous transport for
magnetic cubic full Heusler compounds and we illustrate that several Heusler
compounds outperform the best so far reported materials. The results reveal the
importance of symmetries, especially mirror planes, in combination with
magnetism for giant anomalous Hall and Nernst effects, which should be valid in
general for linear responses (spin Hall effect, spin orbital torque, etc.)
dominated by intrinsic contributions.",2001.01698v3
2020-05-10,A new decomposition of the Kubo-Bastin formula,"The Smrcka-Streda version of Kubo's linear response formula is widely used in
the literature to compute non-equilibrium transport properties of
heterostructures. It is particularly useful for the evaluation of intrinsic
transport properties associated with the Berry curvature of the Bloch states,
such as anomalous and spin Hall currents as well as the damping-like component
of the spin-orbit torque. Here, we demonstrate in a very general way that the
widely used decomposition of the Kubo-Bastin formula introduced by Smrcka and
Streda contains an overlap, which has lead to widespread confusion in the
literature regarding the Fermi surface and Fermi sea contributions. To remedy
this pathology, we propose a new decomposition of the Kubo-Bastin formula based
on the permutation properties of the correlation function and derive a new set
of formulas, without an overlap, that provides direct access to the transport
effects of interest. We apply these new formulas to selected cases and
demonstrate that the Fermi sea and Fermi surface contributions can be uniquely
addressed with our symmetrized approach.",2005.04678v1
2020-06-19,Coupled skyrmion breathing modes in synthetic ferri- and antiferromagnets,"We present micromagnetic simulations of the dynamic GHz-range resonance modes
of skyrmions excited by either out-of-plane ac magnetic fields or spin torques
in prototypical synthetic ferri- and antiferromagnetic trilayer structures. The
observed features in the calculated power spectra exhibit a systematic
dependence on the coupling strength between the individual magnetic layers and
are related to pure in-phase and anti-phase breathing modes as well as to
hybridizations of breathing and spin-wave modes that are characteristic for the
considered circular-shaped geometry. The experimental detection of these
resonant oscillation modes may provide a means for skyrmion sensing
applications and for the general characterization of skyrmion states in
multilayer stacks with antiferromagnetic interlayer exchange coupling.",2006.11318v2
2020-07-12,Transient gravitational waves from pulsar post-glitch recoveries,"This work explores whether gravitational waves (GWs) from neutron star (NS)
mountains can be detected with current 2nd-generation and future 3rd-generation
GW detectors. In particular, we focus on a scenario where transient mountains
are formed immediately after a NS glitch. In a glitch, a NS's spin frequency
abruptly increases and then often exponentially recovers back to, but never
quite reaches, the spin frequency prior to the glitch. If the recovery is
ascribed to an additional torque due to a transient mountain, we find that GWs
from that mountain are marginally-detectable with Advanced LIGO at design
sensitivity and is very likely to be detectable for 3rd-generation detectors
such as the Einstein Telescope. Using this model, we are able to find
analytical expressions for the GW amplitude and its duration in terms of
observables.",2007.05893v2
2020-07-21,"Granular packings with sliding, rolling and twisting friction","Intuition tells us that a rolling or spinning sphere will eventually stop due
to the presence of friction and other dissipative interactions. The resistance
to rolling and spinning/twisting torque that stops a sphere also changes the
microstructure of a granular packing of frictional spheres by increasing the
number of constraints on the degrees of freedom of motion. We perform discrete
element modeling simulations to construct sphere packings implementing a range
of frictional constraints under a pressure-controlled protocol. Mechanically
stable packings are achievable at volume fractions and average coordination
numbers as low as 0.53 and 2.5, respectively, when the particles experience
high resistance to sliding, rolling and twisting. Only when the particle model
includes rolling and twisting friction, were experimental volume fractions
reproduced.",2007.10860v1
2020-07-31,Two-phase crystallisation in a carpet of inertial spinners,"We study the dynamics of torque driven spherical spinners settled on a
surface, and demonstrate that hydrodynamic interactions at finite Reynolds
numbers can lead to a concentration dependent and non-uniform crystallisation.
At semi-dilute concentrations, we observe a rapid formation of a uniform
hexagonal structure in the spinner monolayer. We attribute this to repulsive
hydrodynamic interactions created by the secondary flow of the spinning
particles. Increasing the surface coverage leads to a state with two
co-existing spinner densities. The uniform hexagonal structure deviates into a
high density crystalline structure surrounded by a continuous lower density
hexatically ordered state. We show that this phase separation occurs due to a
non-monotonic hydrodynamic repulsion, arising from a concentration dependent
spinning frequency.",2007.16142v1
2020-12-10,Angular momentum anisotropy of Dirac carriers: A new twist in graphene,"Dirac carriers in graphene are commonly characterized by a pseudospin degree
of freedom, arising from the degeneracy of the two inequivalent sublattices.
The inherent chirality of the quasiparticles leads to a topologically
non-trivial band structure, where the in-plane component of sublattice spin and
momentum are intertwined. Equivalently, sublattice imbalance is intimately
connected with angular momentum, inducing a torque of opposite sign at each
Dirac point. In this work we develop an intuitive picture that associates
sublattice spin and winding number with angular momentum. We develop a
microscopic perturbative model to obtain the finite angular momentum
contributions along the main crystallographic directions. Our results can be
employed to determine the angular dependence of the g-factor and of light
absorption in honeycomb bipartite structures.",2012.05733v2
2020-12-22,Perovskite oxide heterojunction for Rashba-Dresselhaus assisted antiferromagnetic spintronics,"A major impediment towards realizing technologies based on the emerging
principles of antiferromagnetic spintronics is the shortage of suitable
materials. In this paper, we propose a design of polar|nonpolar
heterostructures of perovskite oxides, where a single unit cell of SrIrO3 is
sandwiched between a thin film of LaAlO3 and a substrate of SrTiO3. Our
calculations within the framework of density-functional theory + Hubbard U +
spin-orbit coupling reveal a two-dimensional conducting layer with electron and
hole pockets at the interface, exhibiting a strong anisotropic
Rashba-Dresselhaus effect along with noncollinear antiferromagnetism,
indicating the possibility of realizing a spin-orbit torque. An insightful
physical model for the anisotropic Rashba-Dresselhaus effect nicely interprets
our results, providing an estimate for the Rashba-Dresselhaus coefficients and
illustrating pseudospin orientation.We also observe a proximity-induced
prominent Rashba-like effect for Ti 3d empty bands. Our results suggest that
the heterostructure may possess the essential ingredients for antiferromagnetic
spintronics, deserving experimental verification.",2012.11868v1
2021-01-25,Anomalous symmetry breaking in Weyl semimetal CeAlGe,"CeAlGe, a proposed type-II Weyl semimetal, orders antiferromagnetically below
5 K. At 2 K, spin-flop and a spin-flip transitions to less than 1 $\mu_B$/Ce
are observed in the $M(H)$ data below 30 kOe, ($\bf{H}\|\bf{a}$ and $\bf{b}$,
and 4.3 kOe, $\bf{H}\|\langle110\rangle$, respectively, indicating a four-fold
symmetry of the $M(H)$ data along the principal directions in the tetragonal
$\it{ab}$ plane with $\langle110\rangle$ set of easy directions. However,
anomalously robust and complex twofold symmetry is observed in the angular
dependence of resistivity and magnetic torque data in the magnetically ordered
state once the field is swept in the $\it{ab}$ plane. This twofold symmetry is
independent of temperature and field hystereses and suggests a magnetic phase
transition that separates two different magnetic structures in the $\it{ab}$
plane. The boundary of this magnetic phase transition and possibly the type of
low-field magnetic structure can be tuned by an Al deficiency.",2101.10411v3
2021-06-03,Quaternary-digital data storage based on magnetic bubbles in anisotropic materials,"The topologically non-trivial nano-whirls, called magnetic skyrmions, are
often considered attractive for spintronic applications like the racetrack data
storage device. However, skyrmions do not move parallel to applied currents and
typically do not coexist with other nano-objects, making the realization of
such storage concepts difficult. Herein we consider materials with an
anisotropic DMI, like tetragonal Heusler materials, and show that four distinct
types of topologically trivial bubbles can coexist. We show that each of them
can be written by spin torques and that they can be distinguished using a
single magnetic tunneling junction. Due to their trivial topology, the four
types of bubbles move parallel to applied electrical currents and remain
equidistant under motion. Still, the bubbles have a small size and high
stability comparable to topologically non-trivial spin textures. This allows to
construct a quaternary-digit-based racetrack storage device that overcomes the
two mentioned drawbacks of skyrmion-based racetracks.",2106.01747v2
2021-06-07,Voltage-control of damping constant in magnetic-insulator/topological-insulator bilayers,"The magnetic damping constant is a critical parameter for magnetization
dynamics and the efficiency of memory devices and magnon transport. Therefore,
its manipulation by electric fields is crucial in spintronics. Here, we
theoretically demonstrate the voltage-control of magnetic damping in ferro- and
ferrimagnetic-insulator (FI)/topological-insulator (TI) bilayers. Assuming a
capacitor-like setup, we formulate an effective dissipation torque induced by
spin-charge pumping at the FI/TI interface as a function of an applied voltage.
By using realistic material parameters, we find that the effective damping for
a FI with 10nm thickness can be tuned by one order of magnitude under the
voltage with 0.25V. Also, we provide perspectives on the voltage-induced
modulation of the magnon spin transport on proximity-coupled FIs.",2106.03332v1
2021-08-10,Electric-Field-Controlled Antiferromagnetic Spintronic Devices,"In recent years, the field of antiferromagnetic spintronics has been
substantially advanced. Electric-field control is a promising approach to
achieving ultra-low power spintronic devices via suppressing Joule heating. In
this article, cutting-edge research, including electric-field modulation of
antiferromagnetic spintronic devices using strain, ionic liquids, dielectric
materials, and electrochemical ionic migration, are comprehensively reviewed.
Various emergent topics such as the Neel spin-orbit torque, chiral spintronics,
topological antiferromagnetic spintronics, anisotropic magnetoresistance,
memory devices, two-dimensional magnetism, and magneto-ionic modulation with
respect to antiferromagnets are examined. In conclusion, we envision the
possibility of realizing high-quality room-temperature antiferromagnetic tunnel
junctions, antiferromagnetic spin logic devices, and artificial
antiferromagnetic neurons. It is expected that this work provides an
appropriate and forward-looking perspective that will promote the rapid
development of this field.",2108.04446v1
2021-08-24,Higher-order ferromagnetic resonances in periodic arrays of synthetic-antiferromagnet nanodiscs,"We investigate spin dynamics in nanodisc arrays of synthetic-antiferromagnets
(SAF) made of Py/NiCu/Py trilayers, where the NiCu spacer undergoes a Curie
transition at about 200 K. The observed ferromagnetic resonance spectra have
three distinct resonance modes at room temperature, which are fully recreated
in our micromagnetic simulations showing also how the intra-SAF asymmetry can
be used to create and control the higher-order resonances in the structure.
Below the Curie temperature of the spacer, the system effectively transitions
into a single-layer nanodisc array with only two resonance modes. Our results
show how multi-layering of nano-arrays can add tunable GHz functionality
relevant for such rapidly developing fields as magnetic meta-materials,
magnonic crystals, arrays of spin-torque oscillators and neuromorphic
junctions.",2108.10581v1
2021-09-07,Inertial spin dynamics in epitaxial cobalt films,"We investigate the spin dynamics driven by terahertz magnetic fields in
epitaxial thin films of cobalt in its three crystalline phases. The terahertz
magnetic field generates a torque on the magnetization which causes it to
precess for about 1 ps, with a sub-picosecond temporal lag from the driving
force. Then, the magnetization undergoes natural damped THz oscillations at a
frequency characteristic of the crystalline phase. We describe the experimental
observations solving the inertial Landau-Lifshitz-Gilbert equation. Using the
results from the relativistic theory of magnetic inertia, we find that the
angular momentum relaxation time $\eta$ is the only material parameter needed
to describe all the experimental evidence. Our experiments suggest a
proportionality between $\eta$ and the strength of the magneto-crystalline
anisotropy.",2109.03076v2
2021-09-26,Transition state dynamics of a driven magnetic free layer,"Magnetization switching in ferromagnetic structures is an important process
for technical applications such as data storage in spintronics, and therefore
the determination of the corresponding switching rates becomes essential. We
investigate a free-layer system in an oscillating external magnetic field
resulting in an additional torque on the spin. The magnetization dynamics
including inertial damping can be described by the phenomenological Gilbert
equation. The magnetization switching between the two stable orientations on
the sphere then requires the crossing of a potential region characterized by a
moving rank-1 saddle. We adopt and apply recent extensions of transition state
theory for driven systems to compute both the time-dependent and average
switching rates of the activated spin system in the saddle region.",2109.12605v1
2021-12-22,Machine learning nonequilibrium electron forces for adiabatic spin dynamics,"We present a generalized potential theory of nonequilibrium torques for the
Landau-Lifshitz equation. The general formulation of exchange forces in terms
of two potential energies allows for the implementation of accurate machine
learning models for adiabatic spin dynamics of out-of-equilibrium itinerant
magnetic systems. To demonstrate our approach, we develop a deep-learning
neural network that successfully learns the forces in a driven s-d model
computed from the nonequilibrium Green's function method. We show that the
Landau-Lifshitz dynamics simulations with forces predicted from the neural-net
model accurately reproduce the voltage-driven domain-wall propagation. Our work
opens a new avenue for multi-scale modeling of nonequilibrium dynamical
phenomena in itinerant magnets and spintronics based on machine-learning
models.",2112.12124v1
2022-03-03,NuSTAR discovery of a cyclotron line in GRO J1750-27,"GRO J1750-27, discovered during an outburst in 1995 with CGRO-BATSE, is one
of the farthest known galactic Be-X-ray binary systems. This relatively poorly
studied system recently went into an outburst in September 2021. The source was
observed during the latest outburst using the NuSTAR telescope during the
rising phase of the outburst. We estimate the spin period of the source to be
4.45 s using which we produced energy-resolved pulse profiles between 3 and 65
keV. We find that the profile is double-peaked at low energies (<18 keV) while
evolving into a single peak at higher energies (>18 keV). The broadband
spectrum of this source was fitted well with a high energy cutoff power-law
model and we report the discovery of a cyclotron resonant scattering feature
(CRSF) in this source at 43 keV, indicating a magnetic field strength of $3.7
\times 10^{12}$ G. Our estimate of the magnetic field strength using the
cyclotron line is consistent with the estimates made earlier using the
accretion torque model from measurements of spin-up rates and fluxes during the
previous outbursts.",2203.01863v2
2022-05-19,Bifurcation of a Topological Skyrmion String,"Manipulation of three-dimensional (3D) topological objects is of both
fundamental interest and practical importance in many branches of physics.
Here, we show by spin dynamics simulations that the bifurcation of a 3D
skyrmion string in a layered frustrated system could be induced by the
dampinglike spin-orbit torque. The bifurcation of a skyrmion string happens
when the skyrmion string carries a minimal topological charge of $Q=2$. We
demonstrate that three types of bifurcations could be realized by applying
different current injection geometries, which lead to the transformation from
I-shaped skyrmion strings to Y-, X-, and O-shaped ones. Besides, different
branches of a bifurcated skyrmion string may merge into an isolated skyrmion
string spontaneously. The mechanism of bifurcation should be universal to any
skyrmion strings with $Q\geq 2$ in the layered frustrated system and could
offer a general approach to manipulate 3D stringlike topological objects for
spintronic functions.",2205.09258v1
2022-07-01,Antiferromagnetic half-skyrmions electrically generated and controlled at room temperature,"Topologically protected magnetic textures, such as skyrmions, half-skyrmions
(merons) and their antiparticles, constitute tiny whirls in the magnetic order.
They are promising candidates for information carriers in next-generation
memory devices, as they can be efficiently propelled at very high velocities
using current-induced spin torques. Antiferromagnets have been shown to host
versions of these textures, which have gained significant attention because of
their potential for terahertz dynamics, deflection free motion, and improved
size scaling due to the absence of stray field. Here we show that topological
spin textures, merons and antimerons, can be generated at room temperature and
reversibly moved using electrical pulses in thin film CuMnAs, a semimetallic
antiferromagnet that is a testbed system for spintronic applications. The
electrical generation and manipulation of antiferromagnetic merons is a crucial
step towards realizing the full potential of antiferromagnetic thin films as
active components in high density, high speed magnetic memory devices.",2207.00286v1
2022-07-19,Temperature-dependent critical spin-orbit field for orthogonal switching in antiferromagnets,"The discovery of current-induced spin-orbit torque (SOT) orthogonal
reorientation, also known as orthogonal switching, of metallic Mn$_2$Au and
CuMnAs has opened the door for ultrafast writing of an antiferromagnet (AFM).
Phenomenological theory predicts that the minimum field necessary for SOT
switching -- critical field -- for ultrashort pulses increases inversely
proportional to the pulse duration, thereby limiting the use of ultrafast
stimulus as driving force for switching. We explore the possibility that by
varying the working temperature the critical field reduces enabling orthogonal
switching in response to ultrashort pulses. To do so, we extend previous theory
to finite temperature and show that the critical field for an orthogonal
switching strongly depends on temperature. We determine how the temperature
dependence of the critical field varies as a function of the pulse duration.
While for long pulses, the temperature dependence of the critical field is
determined by the anisotropy field, for ultrashort pulses, it is determined by
the characteristic frequency of the AFM. We show that the short and long pulse
duration limits for the critical field can be connected by an analytical
expression.",2207.09563v1
2022-12-06,Tailoring Elastic Scattering of Relativistic Antiferromagnetic Domain Walls for Collision-based Computing,"Soliton-based computing is relied on their unique properties for transporting
energy and emerging intact from head-on collisions. Magnetic domain walls are
often referred to as solitons disregarding the strict mathematical definition
requiring the above scattering property. Here we demonstrate the conditions of
elastic and inelastic scattering for spin-orbit torque-induced dynamics of
antiferromagnetic domain walls on the example of a technologically relevant
Mn$_2$Au material. We show that even domain walls with opposite winding numbers
can experience elastic scattering and we present a corresponding phase diagram
as a function of the spin-orbit field strength and duration. The elastic
collision requires minimum domain walls speed which we explain assuming an
attractive potential created by domain wall pair. On the contrary, when the
domain walls move at lower speeds, their collision is inelastic and results in
a dispersing breather. Our findings will be important for the development
soliton-based computing using antiferromagnetic spintronics and we discuss
these perspective on our suggestions of how to create NOT and XOR gates.",2212.03126v1
2023-02-13,Zero-frequency chiral magnonic edge states protected by non-equilibrium topology,"Topological bosonic excitations must, in contrast to their fermionic
counterparts, appear at finite energies. This is a key challenge for magnons,
as it prevents straightforward excitation and detection of
topologically-protected magnonic edge states and their use in magnonic devices.
In this work, we show that in a non-equilibrium state, in which the
magnetization is pointing against the external magnetic field, the
topologically-protected chiral edge states in a magnon Chern insulator can be
lowered to zero frequency, making them directly accessible by existing
experimental techniques. We discuss the spin-orbit torque required to stabilize
this non-equilibrium state, and show explicitly using numerical
Landau-Lifshitz-Gilbert simulations that the edge states can be excited with a
microwave field. Finally, we consider a propagating spin wave spectroscopy
experiment, and demonstrate that the edge states can be directly detected.",2302.06597v3
2023-03-29,Coarse-graining collective skyrmion dynamics in confined geometries,"Magnetic skyrmions are magnetic quasi-particles with enhanced stability and
different manipulation mechanisms using external fields and currents making
them promising candidates for future applications for instance in neuromorphic
computing. Recently, several measurements and simulations have shown that
thermally activated skyrmions in confined geometries, as they are necessary for
device applications, arrange themselves predominantly based on commensurability
effects. In this simulational study, based on the Thiele model, we investigate
the enhanced dynamics and degenerate non-equilibrium steady state of a system
in which the intrinsic skyrmion-skyrmion and skyrmion-boundary interaction
compete with thermal fluctuations as well as current-induced spin-orbit
torques. The investigated system is a triangular-shaped confinement geometry
hosting four skyrmions, where we inject spin-polarized currents between two
corners of the structure. We coarse-grain the skyrmion states in the system to
analyze the intricacies of skyrmion arrangements of the skyrmion ensemble. In
the context of neuromorphic computing, such methods address the key challenge
of optimizing read-out positions in confined geometries and form the basis to
understand collective skyrmion dynamics in systems with competing interactions
on different scales.",2303.16472v1
2023-05-05,Hardware in Loop Learning with Spin Stochastic Neurons,"Despite the promise of superior efficiency and scalability, real-world
deployment of emerging nanoelectronic platforms for brain-inspired computing
have been limited thus far, primarily because of inter-device variations and
intrinsic non-idealities. In this work, we demonstrate mitigating these issues
by performing learning directly on practical devices through a hardware-in-loop
approach, utilizing stochastic neurons based on heavy metal/ferromagnetic
spin-orbit torque heterostructures. We characterize the probabilistic switching
and device-to-device variability of our fabricated devices of various sizes to
showcase the effect of device dimension on the neuronal dynamics and its
consequent impact on network-level performance. The efficacy of the
hardware-in-loop scheme is illustrated in a deep learning scenario achieving
equivalent software performance. This work paves the way for future large-scale
implementations of neuromorphic hardware and realization of truly autonomous
edge-intelligent devices.",2305.03235v3
2023-06-25,Current-induced deterministic switching of van der Waals ferromagnet at room temperature,"Recent discovery of emergent magnetism in van der Waals magnetic materials
(vdWMM) has broadened the material space for developing spintronic devices for
energy-efficient computation. While there has been appreciable progress in
vdWMM discovery, with strong perpendicular magnetic anisotropy (PMA) and Curie
temperatures exceeding room temperature, a solution for non-volatile,
deterministic switching of vdWMMs at room temperature has been missing,
limiting the prospects of their adoption into commercial spintronic devices.
Here, we report the first demonstration of current-controlled non-volatile,
deterministic magnetization switching in a vdW magnetic material at room
temperature. We have achieved spin-orbit torque (SOT) switching of the PMA vdW
magnet Fe3GaTe2 using a Pt spin-Hall layer up to 320 K, with a threshold
switching current density as low as $J_{sw} = 1.69\times10^6 A/cm^2$ at room
temperature. We have also quantitatively estimated the anti-damping-like SOT
efficiency of our Fe3GaTe2/Pt bilayer system to be $\xi_{DL}$ = 0.093, using
second harmonic Hall voltage measurement technique. These results mark a
crucial step in making vdW magnetic materials a viable choice for the
development of scalable, future spintronic devices.",2306.14355v1
2023-07-24,Multistability and Gibbs entropy in the planar dissipative spin-orbit problem,"In this work, we numerically investigate and visually illustrate the
dynamical properties of the dissipative spin-orbit problem such as the
co-existence of multiple periodic and quasi-periodic attractors, and the
complexity of the corresponding basins of attraction. Our model is composed by
a triaxial satellite (planet) orbiting a planet (star) in a fixed Keplerian
orbit with zero obliquity. A dissipative tidal torque that is proportional to
its rotational angular velocity is assumed to be acting on the satellite. We
use Hyperion as a toy model to characterize the methodology used, since this
system has a very rich conservative dynamical scenario, and we later apply our
methodology to the Moon and Mercury. Our results show that the basins of
attraction may possess an intricate structure in all cases which changes with
the orbital eccentricity, and that the Gibbs entropy is a good measure on how
dominant one basin is over the others in the phase space.",2307.12969v1
2023-07-28,Field-Free Switching in Symmetry Breaking Multilayers: The Critical Role of Interlayer Chiral Exchange,"It is crucial to realize field-free, deterministic, current-induced switching
in spin-orbit torque magnetic random-access memory (SOT-MRAM) with
perpendicular magnetic anisotropy (PMA). A tentative solution has emerged
recently, which employs the interlayer chiral exchange coupling or the
interlayer Dzyaloshinskii-Moriya interaction (i-DMI) to achieve symmetry
breaking. We hereby investigate the interlayer DMI in a Pt/Co multilayer system
with orthogonally magnetized layers, using repeatedly stacked [Pt/Co]n
structure with PMA, and a thick Co layer with in-plane magnetic anisotropy
(IMA). We clarify the origin and the direction of such symmetry breaking with
relation to the i-DMI effective field, and show a decreasing trend of the said
effective field magnitude to the stacking number (n). By comparing the
current-induced field-free switching behavior for both PMA and IMA layers, we
confirm the dominating role of i-DMI in such field-free switching, excluding
other possible mechanisms such as tilted-anisotropy and unconventional spin
currents that may have arisen from the symmetry breaking.",2307.15258v2
2023-08-15,Current-induced magnetization switching in a magnetic topological insulator heterostructure,"We present the current-induced switching of the internal magnetization
direction in a magnetic topological insulator/topological insulator
heterostructure in the quantum anomalous Hall regime. The switching process is
based on the bias current dependence of the coercive field, which is attributed
to the effect of the spin-orbit torque provided by the unpolarized bias
current. Increasing the bias current leads to a decrease in the magnetic order
in the sample. When the applied current is subsequently reduced, the magnetic
moments align with an externally applied magnetic field, resulting in
repolarization in the opposite direction. This includes a reversal of the spin
polarisation and hence a reversal of the chiral edge mode. Possible
applications in spintronic devices are discussed.",2308.07657v1
2023-09-29,Self-interaction correction schemes for non-collinear spin-density-functional theory,"We extend some of the well established self-interaction correction (SIC)
schemes of density-functional theory to the case of systems with noncollinear
magnetism. Our proposed SIC schemes are tested on a set of molecules and
metallic clusters in combination with the widely used local spin-density
approximation. As expected from the collinear SIC, we show that the
averaged-density SIC works well for improving ionization energies but fails to
improve more subtle quantities like the dipole moments of polar molecules. We
investigate the exchange-correlation magnetic field produced by our extension
of the Perdew-Zunger SIC, showing that it is not aligned with the local total
magnetization, thus producing an exchange-correlation torque.",2310.18321v1
2023-11-13,Magnetoresistive detection of perpendicular switching in a magnetic insulator,"Spintronics offers promising routes for efficient memory, logic, and
computing technologies. The central challenge in spintronics is electrically
manipulating and detecting magnetic states in devices. The electrical control
of magnetization via spin-orbit torques is effective in both conducting and
insulating magnetic layers. However, the electrical readout of magnetization in
the latter is inherently difficult, limiting its use in practical applications.
Here, we demonstrate magnetoresistive detection of perpendicular magnetization
reversal in an electrically insulating ferrimagnet, terbium iron garnet (TbIG).
To do so, we use TbIG|Cu|TbCo, where TbCo is a conducting ferrimagnet and
serves as the reference layer, and Cu is a nonmagnetic spacer. Current
injection through Cu|TbCo allows us to detect the magnetization reversal of
TbIG with a simple resistance readout during an external magnetic field sweep.
By examining the effect of measurement temperature, TbCo composition, and Cu
thickness on the sign and amplitude of the magnetoresistance, we conclude that
the spin-dependent electron scattering at the TbIG|Cu interface is the
underlying cause. Technologically-feasible magnetoresistive detection of
perpendicular switching in a ferrimagnetic garnet is a breakthrough, as it
opens broad avenues for novel insulating spintronic devices and concepts.",2311.07350v1
2023-11-28,Constraining Stellar Rotation at the Zero-Age Main Sequence with TESS,"The zero-age main sequence (ZAMS) is a critical phase for stellar angular
momentum evolution, as stars transition from contraction-dominated spin-up to
magnetic wind-dominated spin-down. We present the first robust observational
constraints on rotation for FGK stars at $\approx40$ Myr. We have analyzed TESS
light curves for 1410 members of five young open clusters with ages between
25-55 Myr: IC 2391, IC 2602, NGC 2451A, NGC 2547, and Collinder 135. In total,
we measure 868 rotation periods, including 96 new, high-quality periods for
stars around 1 ${M_{\odot}}$. This is an increase of ten times the existing
literature sample at the ZAMS. We then use the $\tau^2$ method to compare our
data to models for stellar angular momentum evolution. Although the ages
derived from these rotation models do not match isochronal ages, we show these
observations can clearly discriminate between different models for stellar wind
torques. Finally, $\tau^2$ fits indicate that magnetic braking and/or internal
angular momentum transport significantly impact rotational evolution even on
the pre-main sequence.",2311.17184v1
2023-12-18,Physical Signatures of Fermion-Coupled Axion Dark Matter,"In the presence of axion dark matter, fermion spins experience an ""axion
wind"" torque and an ""axioelectric"" force. We investigate new experimental
probes of these effects and find that magnetized analogs of multilayer
dielectric haloscopes can explore orders of magnitude of new parameter space
for the axion-electron coupling. We also revisit the calculation of axion
absorption into in-medium excitations, showing that axioelectric absorption is
screened in spin-polarized targets, and axion wind absorption can be
characterized in terms of a magnetic energy loss function. Finally, our
detailed theoretical treatment allows us to critically examine recent claims in
the literature. We find that axioelectric corrections to electronic energy
levels are smaller than previously estimated and that the purported electron
electric dipole moment due to a constant axion field is entirely spurious.",2312.11601v1
2023-12-22,Tailoring Interlayer Chiral Exchange by Azimuthal Symmetry Engineering,"Recent theoretical and experimental studies of the interlayer
Dzyaloshinskii-Moriya interaction (DMI) has sparked great interest in its
implementation into practical magnetic random-access memory (MRAM) devices, due
to its capability to mediate long-range chiral spin textures. So far,
experimental reports focused on the observation of interlayer DMI, leaving the
development of strategies to control interlayer DMI's magnitude unaddressed.
Here, we introduce an azimuthal symmetry engineering protocol capable of
additive/subtractive tuning of interlayer DMI through the control of wedge
deposition of separate layers, and demonstrate its capability to mediate
field-free spin-orbit torque (SOT) magnetization switching in both orthogonally
magnetized and synthetic antiferromagnetically coupled systems. Furthermore, we
showcase the spatial inhomogeneity brought about by wedge depositon can be
suppressed by specific azimuthal engineering design, ideal for practical
implementation. Our findings provide guidelines for effective manipulations of
interlayer DMI strength, beneficial for future design of SOT-MRAM or other
spintronic devices utilizing interlayer DMI.",2312.14462v2
2023-12-24,Internal dissipation in the tennis racket effect,"The phenomenon known as the tennis racket effect is observed when a rigid
body experiences unstable rotation around its intermediate axis. In free space,
this leads to the Dzhanibekov effect, where triaxial objects like a spinning
wing bolt may continuously flip their rotational axis. Over time, however,
dissipation ensures that a torque free spinning body will eventually rotate
around its major axis, in a process called precession relaxation, which
counteracts the tennis racket effect. Euler's equations for a rigid body
effectively describe the tennis racket effect, but cannot account for the
precession relaxation effect. A recent theory has put forward a generalization
of Euler's equations that includes dissipation in a thermodynamically
consistent way. The theory displays two dissipative mechanisms: orientational
diffusion and viscoelasticity. Here we show that orientational diffusion,
rather than viscoelasticity, primarily drives precession relaxation and
effectively suppresses the tennis racket effect.",2312.15448v1
2024-01-19,Hybridized magnonic materials for THz frequency applications,"The capability of magnons to hybridize and strongly couple with diverse
excitations offers a promising avenue for realizing and controlling emergent
properties that hold significant potential for applications in devices,
circuits, and information processing. In this letter, we present recent
theoretical and experimental developments in magnon-based hybrid systems,
focusing on the combination of magnon excitation in an antiferromagnet with
other excitations, namely plasmons in a topological insulator, phonons in a 2D
AFM, and photons. The existence of THz frequency magnons, plasmons, and phonons
makes magnon-based hybrid systems particularly appealing for
high-operating-speed devices. In this context, we explore several directions to
advance magnon hybrid systems, including strong coupling between a surface
plasmon and magnon polariton in a TI/AFM bilayer, a giant spin Nernst effect
induced by magnon phonon coupling in 2D AFMs, and control of magnon-photon
coupling using spin torque.",2401.11010v2
2024-03-20,Magneto-Ionic Vortices: Voltage-Reconfigurable Swirling-Spin Analog-Memory Nanomagnets,"Rapid progress in information technologies has spurred the need for
innovative memory concepts, for which advanced data-processing methods and
tailor-made materials are required. Here we introduce a previously unexplored
nanoscale magnetic object: an analog magnetic vortex controlled by
electric-field-induced ion motion, termed magneto-ionic vortex or ""vortion"".
This state arises from paramagnetic FeCoN through voltage gating and gradual
N3-ion extraction within patterned nanodots. Unlike traditional vortex states,
vortions offer comprehensive analog adjustment of key properties such as
magnetization amplitude, nucleation/annihilation fields, or coercivity using
voltage as an energy-efficient tuning knob. This manipulation occurs
post-synthesis, obviating the need for energy-demanding methods like laser
pulses or spin-torque currents. By leveraging an overlooked aspect of
N3-magneto-ionics -- planar ion migration within nanodots -- precise control of
the magnetic layer's thickness is achieved, which enables reversible
transitions among paramagnetic, single-domain, and vortion states, offering
future prospects for analog computing, multi-state data storage, or
brain-inspired devices.",2403.13722v1
1993-04-13,Computing Masses from Effective Transfer Matrices,"We study the use of effective transfer matrices for the numerical computation
of masses (or correlation lengths) in lattice spin models. The effective
transfer matrix has a strongly reduced number of components. Its definition is
motivated by a renormalization group transformation of the full model onto a
1-dimensional spin model. The matrix elements of the effective transfer matrix
can be determined by Monte Carlo simulation. We show that the mass gap can be
recovered exactly from the spectrum of the effective transfer matrix. As a
first step towards application we performed a Monte Carlo study for the
2-dimensional Ising model. For the simulations in the broken phase we employed
a multimagnetical demon algorithm. The results for the tunnelling correlation
length are particularly encouraging.",9304006v2
2010-08-27,"Noncompact sl(N) spin chains: BGG-resolution, Q-operators and alternating sum representation for finite dimensional transfer matrices","We study properties of transfer matrices in the sl(N) spin chain models. The
transfer matrices with an infinite dimensional auxiliary space are factorized
into the product of N commuting Baxter Q-operators. We consider the transfer
matrices with auxiliary spaces of a special type (including the finite
dimensional ones). It is shown that they can be represented as the alternating
sum over the transfer matrices with infinite dimensional auxiliary spaces. We
show that certain combinations of the Baxter Q-operators can be identified with
the Q-functions which appear in the Nested Bethe Ansatz.",1008.4734v2
2012-08-14,Optimal Control for Electron Shuttling,"In this paper we apply an optimal control technique to derive control fields
that transfer an electron between ends of a chain of donors or quantum dots. We
formulate the transfer as an optimal steering problem, and then derive the
dynamics of the optimal control. A numerical algorithm is developed to
effectively generate control pulses. We apply this technique to transfer an
electron between sites of a triple quantum dot and an ionized chain of
phosphorus dopants in silicon. Using the optimal pulses for the spatial
shuttling of phosphorus dopants, we then add hyperfine interactions to the
Hamiltonian and show that a 500 G magnetic field will transfer the electron
spatially as well as transferring the spin components of two of the four
hyperfine states of the electron-nuclear spin pair.",1208.2781v2
2015-09-20,Enhancement factor for two-neutron transfer reactions with a schematic coupled-channels model,"Probabilities for two-neutron transfer reactions, $P_{\rm 2n}$, are often
discussed in comparison with the square of the corresponding probabilities for
one-neutron transfer process, $(P_{\rm 1n})^2$, implicitly assuming that
$(P_{\rm 1n})^2$ provides the probability of two-neutron transfer reactions in
the absence of the pairing correlation. We use a schematic coupled-channels
model, in which the transfers are treated as effective inelastic channels, and
demonstrate that this model leads to $P_{\rm 2n}=(P_{\rm 1n})^2/4$, rather than
$P_{\rm 2n}=(P_{\rm 1n})^2$, in the pure sequential limit. We argue that a
simple model with spin-up and spin-down neutrons in a single-particle orbital
also leads to the same conclusion.",1509.06012v1
2017-11-13,On the transfer matrix of the supersymmetric eight-vertex model. I. Periodic boundary conditions,"The square-lattice eight-vertex model with vertex weights $a,b,c,d$ obeying
the relation $(a^2+ab)(b^2+ab) = (c^2+ab)(d^2+ab)$ and periodic boundary
conditions is considered. It is shown that the transfer matrix of the model for
$L=2n+1$ vertical lines and periodic boundary conditions along the horizontal
direction possesses the doubly degenerate eigenvalue $\Theta_n = (a+b)^{2n+1}$.
This proves a conjecture by Stroganov from 2001. The proof uses the
supersymmetry of a related XYZ spin-chain Hamiltonian. The eigenstates of the
transfer matrix corresponding to $\Theta_n$ are shown to be the ground states
of the spin-chain Hamiltonian. Moreover, for positive vertex weights $\Theta_n$
is the largest eigenvalue of the transfer matrix.",1711.04397v2
2018-12-13,Integrable quenches in nested spin chains II: fusion of boundary transfer matrices,"We consider quantum quenches in the integrable $SU(3)$-invariant spin chain
(Lai-Sutherland model), and focus on the family of integrable initial states.
By means of a Quantum Transfer Matrix approach, these can be related to
""soliton-non-preserving"" boundary transfer matrices in an appropriate
transverse direction. In this work, we provide a technical analysis of such
integrable transfer matrices. In particular, we address the computation of
their spectrum: this is achieved by deriving a set of functional relations
between the eigenvalues of certain ""fused operators"" that are constructed
starting from the soliton-non-preserving boundary transfer matrices (namely the
$T$- and $Y$-systems). As a direct physical application of our analysis, we
compute the Loschmidt echo for imaginary and real times after a quench from the
integrable states. Our results are also relevant for the study of the spectrum
of $SU(3)$-invariant Hamiltonians with open boundary conditions.",1812.05330v3
2022-03-07,Quantum state transfer between a frequency-encoded photonic qubit and a quantum dot spin in a nanophotonic waveguide,"We propose a deterministic yet fully passive scheme to transfer the quantum
state from a frequency-encoded photon to the spin of a quantum-dot mediated by
a nanophotonic waveguide. We assess the quality of the state transfer by
studying the effects of all relevant experimental imperfections on the
state-transfer fidelity. We show that a transfer fidelity exceeding 95% is
achievable for experimentally realistic parameters. Our work sets the stage for
deterministic solid-state quantum networks tailored to frequency-encoded
photonic qubits.",2203.03347v1
2021-01-08,Pretty good quantum state transfer on isotropic and anisotropic Heisenberg spin chains with tailored site dependent exchange couplings,"Using a global optimization algorithm we obtain spin chains with
site-dependent exchange coefficients which allow almost perfect quantum state
transfer between the extremes of the chains without any further time-dependent
external control. We consider chains with isotropic and anisotropic Heisenberg
Hamiltonian with up to 100 spins. The method allow us to choose the arrival of
the transferred state by changing the range available to the exchange coupling
strengths. We consider short transferred times, in particular shorter than
those achievable with known time-dependent control schemes. The chains obtained
with the optimization method show some remarkable and interesting traits as,
for instance, the scaling of the magnitude of the exchange couplings needed to
achieve near perfect state transfer with the length of the chain and the
arrival time. This scaling makes it possible to decide if the chain with
site-dependent coefficients can be implemented in an actual system according to
the range of interactions allowed in it. We compare the robustness of the
transmission protocol against static disorder on the exchange coefficients
using different figures of merit, which allow us to conclude that the isotropic
Heisenberg chain is the best option when compared with anisotropic chains. This
comparison is relevant since the method allow us to start with chains that all
achieve near perfect quantum state transfer, regime that was not available
previously in these chains without time-dependent external control.",2101.03194v3
2023-01-04,State Transfer in Complex Quantum Walks,"Given a graph with Hermitian adjacency matrix $H$, perfect state transfer
occurs from vertex $a$ to vertex $b$ if the $(b,a)$-entry of the unitary matrix
$\exp(-iHt)$ has unit magnitude for some time $t$. This phenomenon is relevant
for information transmission in quantum spin networks and is known to be
monogamous under real symmetric matrices. We prove the following results:
  1. For oriented graphs (whose nonzero weights are $\pm i$), the oriented
$3$-cycle and the oriented edge are the only graphs where perfect state
transfer occurs between every pair of vertices. This settles a conjecture of
Cameron et al. On the other hand, we construct an infinite family of oriented
graphs with perfect state transfer between any pair of vertices on a subset of
size four.
  2. There are infinite families of Hermitian graphs with one-way perfect state
transfer, where perfect state transfer occurs without periodicity. In contrast,
perfect state transfer implies periodicity whenever the adjacency matrix has
algebraic entries (as shown by Godsil).
  3. There are infinite families with non-monogamous pretty good state transfer
in rooted graph products. In particular, we generalize known results on double
stars (due to Fan and Godsil) and on paths with loops (due to Kempton, Lippner
and Yau). The latter extends the experimental observation of quantum transport
(made by Zimbor\'{a}s et al.) and shows non-monogamous pretty good state
transfer can occur amongst distant vertices.",2301.01473v1
2004-09-09,Magnetically Driven Accretion Flows in the Kerr Metric IV: Dynamical Properties of the Inner Disk,"This paper continues the analysis of a set of general relativistic 3D MHD
simulations of accreting tori in the Kerr metric with different black hole
spins. We focus on bound matter inside the initial pressure maximum, where the
time-averaged motion of gas is inward and an accretion disk forms. We use the
flows of mass, angular momentum, and energy in order to understand dynamics in
this region. The sharp reduction in accretion rate with increasing black hole
spin reported in Paper I of this series is explained by a strongly
spin-dependent outward flux of angular momentum conveyed electromagnetically;
when a/M > 0.9, this flux can be comparable to the inward angular momentum flux
carried by the matter. In all cases, there is outward electromagnetic angular
momentum flux throughout the flow; in other words, contrary to the assertions
of traditional accretion disk theory, there is in general no ""stress edge"", no
surface within which the stress is zero. The retardation of accretion in the
inner disk by electromagnetic torques also alters the radial distribution of
surface density, an effect that may have consequences for observable properties
such as Compton reflection. The net accreted angular momentum is sufficiently
depressed by electromagnetic effects that in the most rapidly-spinning black
holes mass growth can lead to spindown. Spinning black holes also lose energy
by Poynting flux; this rate is also a strongly increasing function of black
hole spin, rising to 10% or more of the rest-mass accretion rate at very high
spin. As the black hole spins faster, the path of the Poynting flux changes
from being predominantly within the accretion disk to predominantly within the
funnel outflow.",0409231v1
2011-05-11,"Spinning Dust Emission: Effects of irregular grain shape, transient heating and comparison with WMAP results","Planck is expected to answer crucial questions on the early Universe, but it
also provides further understanding on anomalous microwave emission. Electric
dipole emission from spinning dust grains continues to be the favored
interpretation of anomalous microwave emission. In this paper, we present a
method to calculate the rotational emission from small grains of irregular
shape with moments of inertia $I_{1}> I_{2}> I_{3}$. We show that a torque-free
rotating irregular grain with a given angular momentum radiates at multiple
frequency modes. The resulting spinning dust spectrum has peak frequency and
emissivity increasing with the degree of grain shape irregularity, which is
defined by $I_{1}:I_{2}:I_{3}$. We discuss how the orientation of dipole moment
$\bmu$ in body coordinates affects the spinning dust spectrum for different
regimes of internal thermal fluctuations. We show that the spinning dust
emissivity for the case of strong thermal fluctuations is less sensitive to the
orientation of $\bmu$ than in the case of weak thermal fluctuations. We
calculate spinning dust spectra for a range of gas density and dipole moment.
The effect of compressible turbulence on spinning dust emission intensity is
investigated. We show that the emission intensity in a turbulent medium
increases by a factor from 1.2-1.4 relative to that in a uniform medium, as
sonic Mach number $M_{s}$ increases from 2-7. Finally, spinning dust parameters
are constrained by fitting our improved model to five-year {\it Wilkinson
Microwave Anisotropy Probe} cross-correlation foreground spectra, for both the
H$\alpha$-correlated and 100 $\mu$m-correlated emission spectra.",1105.2302v3
2015-09-30,Roadmap for Emerging Materials for Spintronic Device Applications,"The Technical Committee of the IEEE Magnetics Society has selected 7 research
topics to develop their roadmaps, where major developments should be listed
alongside expected timelines; (i) hard disk drives, (ii) magnetic random access
memories, (iii) domain-wall devices, (iv) permanent magnets, (v) sensors and
actuators, (vi) magnetic materials and (vii) organic devices. Among them,
magnetic materials for spintronic devices have been surveyed as the first
exercise. In this roadmap exercise, we have targeted magnetic tunnel and
spin-valve junctions as spintronic devices. These can be used for example as a
cell for a magnetic random access memory and spin-torque oscillator in their
vertical form as well as a spin transistor and a spin Hall device in their
lateral form. In these devices, the critical role of magnetic materials is to
inject spin-polarised electrons efficiently into a non-magnet. We have
accordingly identified 2 key properties to be achieved by developing new
magnetic materials for future spintronic devices: (1) Half-metallicity at room
temperature (RT); (2) Perpendicular anisotropy in nano-scale devices at RT. For
the first property, 5 major magnetic materials are selected for their
evaluation for future magnetic/spintronic device applications: Heusler alloys,
ferrites, rutiles, perovskites and dilute magnetic semiconductors. These alloys
have been reported or predicted to be half-metallic ferromagnets at RT. They
possess a bandgap at the Fermi level EF only for its minority spins, achieving
100% spin polarisation at EF. We have also evaluated L10-alloys and
D022-Mn-alloys for the development of a perpendicularly anisotropic ferromagnet
with large spin polarisation. We have listed several key milestones for each
material on their functionality improvements, property achievements, device
implementations and interdisciplinary applications within 35 years time scale.",1509.08997v1
2019-12-29,Giant momentum-dependent spin splitting in centrosymmetric low Z antiferromagnets,"The energy vs. crystal momentum E(k) diagram for a solid (band structure)
constitutes the road map for navigating its optical, magnetic, and transport
properties. By selecting crystals with specific atom types, composition and
symmetries, one could design a target band structure and thus desired
properties. A particularly attractive outcome would be to design energy bands
that are split into spin components with a momentum-dependent splitting, as
envisioned by Pekar and Rashba [Zh. Eksperim. i Teor. Fiz. 47 (1964)], enabling
spintronic application. The current paper provides ""design principles"" for
wavevector dependent spin splitting (SS) of energy bands that parallels the
traditional Dresselhaus and Rashba spin-orbit coupling (SOC) - induce
splitting, but originates from a fundamentally different source --
antiferromagnetism. We identify a few generic AFM prototypes with distinct SS
patterns using magnetic symmetry design principles. These tools allow also the
identification of specific AFM compounds with SS belonging to different
prototypes. A specific compound -- centrosymmetric tetragonal MnF2 -- is used
via density functional band structure calculations to quantitatively illustrate
one type of AFM SS. Unlike the traditional SOC-induced effects restricted to
non-centrosymmetric crystals, we show that antiferromagnetic-induced spin
splitting broadens the playing field to include even centrosymmetric compounds,
and gives SS comparable in magnitude to the best known ('giant') SOC effects,
even without SOC, and consequently does not rely on the often-unstable high
atomic number elements required for high SOC. We envision that use of the
current design principles to identify an optimal antiferromagnet with
spin-split energy bands would be beneficial for efficient spin-charge
conversion and spin orbit torque applications without the burden of requiring
compounds containing heavy elements.",1912.12689v3
2022-11-07,Quantum-classical approach to spin and charge pumping and the ensuing radiation in THz spintronics: Example of ultrafast-light-driven Weyl antiferromagnet Mn$_3$Sn,"The interaction of fs light pulses with magnetic materials has been intensely
studied for more than two decades in order to understand ultrafast
demagnetization in single magnetic layers or THz emission from their bilayers
with nonmagnetic spin-orbit (SO) materials. Here we develop a multiscale
quantum-classical formalism -- where conduction electrons are described by
quantum master equation of the Lindblad type; classical dynamics of local
magnetization is described by the Landau-Lifshitz-Gilbert (LLG) equation; and
incoming light is described by classical vector potential while outgoing
electromagnetic radiation is computed using Jefimenko equations for retarded
electric and magnetic fields -- and apply it a bilayer of antiferromagnetic
Weyl semimetal Mn$_3$Sn with noncollinear local magnetization in contact with
SO-coupled nonmagnetic material. Our QME+LLG+Jefimenko scheme makes it possible
to understand how fs light pulse generates directly spin and charge pumping and
electromagnetic radiation by the latter, including both odd and even high
harmonics (of the pulse center frequency) up to order $n \le 7$. The directly
pumped spin current then exert spin torque on local magnetization whose
dynamics, in turn, pumps additional spin and charge currents radiating in the
THz range. By switching on and off LLG dynamics and SO couplings, we unravel
which microscopic mechanism contribute the most to emitted THz radiation --
charge pumping by local magnetization of Mn$_3$Sn in the presence of its
intrinsic SO coupling is far more important than standardly assumed (for other
types of magnetic layers) spin pumping and subsequent spin-to-charge conversion
within the neighboring nonmagnetic SO-coupled material.",2211.03645v3
2022-12-23,Collective topological spin dynamics in a correlated spin glass,"The interplay between spin-orbit interaction (SOI) and magnetic order is
currently one of the most active research fields in condensed matter physics
and leading the search for materials with novel and tunable magnetic and spin
properties. Here we report on a variety of unexpected and unique observations
in thin multiferroic \Ge$_{1-x}$Mn$_x$Te films. The ferrimagnetic order in this
ferroelectric semiconductor is found to reverse with current pulses six orders
of magnitude lower as for typical spin-orbit torque systems. Upon a switching
event, the magnetic order spreads coherently and collectively over macroscopic
distances through a correlated spin-glass state. Lastly, we present a novel
methodology to controllably harness this stochastic magnetization dynamics,
allowing us to detect spatiotemporal nucleation of topological spin textures we
term ``skyrmiverres''.",2212.12262v1
1999-11-06,Quaking Neutron Stars,"Gravitational, magnetic and superfluid forces can stress the crust of an
evolving neutron star. Fracture of the crust under these stresses could affect
the star's spin evolution and generate high-energy emission. We study the
growth of strain in the crust of a spinning down, magnetized neutron star and
examine the initiation of crust cracking (a {\em starquake}). In preliminary
work (Link, Franco & Epstein 1998), we studied a homogeneous model of a neutron
star. Here we extend this work by considering a more realistic model of a
solid, homogeneous crust afloat on a liquid core. In the limits of
astrophysical interest, our new results qualitatively agree with those from the
simpler model: the stellar crust fractures under shear stress at the rotational
equator, matter moves to higher latitudes and the star's oblateness is reduced.
Magnetic stresses favor faults directed toward the magnetic poles. Thus our
previous conclusions concerning the star's spin response still hold; namely,
asymmetric redistribution of matter excites damped precession which could
ultimately lead to an increase in the spin-down torque. Starquakes associated
with glitches could explain the permanent {\em offsets} in period derivative
observed to follow glitches in at least three pulsars.",9911105v1
2001-02-25,On the age of PSR B1509-58,"It is generally accepted that the PSR B1509-58 is associated with the
supernova remnant (SNR) MSH 15-52 (G 320.4-01.2). The spin-down age of the
pulsar is \simeq 1700 years, while the size and the general appearance of the
SNR suggest that this system is much older. A few possible explanations of this
discrepancy have been put forward. We offer an alternative one and suggest that
the high spin-down rate of the pulsar characterizes only a relatively short
period of its (present) spin history, and that the enhanced braking torque is
connected with the interaction between the pulsar's magnetosphere and the dense
matter of a circumstellar clump (created during the late evolutionary stages of
the supernova (SN) progenitor star). Our suggestion implies that the ""true"" age
of PSR B1509-58 could be much larger than the spin-down age, and therefore the
SNR MSH 15-52 is a middle-aged remnant similar to the Vela SNR (G 263.9-3.3).
We also suggest that the dense (neutral) gas of the circumstellar clump could
be responsible for the enhanced neutral hydrogen absorption towards PSR
B1509-58, and that the optical emission of an optical counterpart for PSR
B1509-58 should rather be attributed to a bow shock around this pulsar than to
the pulsar itself.",0102431v3
2004-09-22,On the Rotational Dynamics of Magnetically Threaded Disks around Neutron Stars,"We investigate the rotational dynamics of disk accretion around a strongly
magnetized neutron star with an aligned dipole field. The magnetospheric field
is assumed to thread the disk plasma both inside and outside the corotation
radius. As a result of disk-star interaction, the magnetic torque on the disk
affects the structure of accretion flow to yield the observed spin-up or
spin-down rates for a source of given fastness, magnetic field strength, and
mass accretion rate. Within the model we obtain a prescription for the
dynamical viscosity of such magnetically modified solutions for a Keplerian
disk. We then use this prescription to find a model solution for the rotation
rate profile throughout the entire disk including the non-Keplerian inner disk.
We find that the non-Keplerian angular velocity transition region is not
necessarily narrow for a source of given spin state. The boundary layer
approximation, as in the standard magnetically threaded disk model, holds only
in the case of dynamical viscosity decreasing all the way to the innermost edge
of the disk. These results are applied to several observed disk-fed X-ray
pulsars that have exhibited quasi-periodic oscillations (QPOs). The QPO
frequencies provide a constraint on the fastness parameter and enable one to
determine uniquely the width of the angular velocity transition zone for each
source within model assumptions. We discuss the implications of these results
on the value of the critical fastness parameter for a magnetized star in spin
equilibrium. Applications of our model are also made with relevant parameters
from recent numerical simulations of quasi-stationary disk-magnetized star
interactions.",0409545v1
2006-12-04,Order in the Chaos: Spin-up and Spin-down during the 2002 Outburst of SAX J1808.4-3658,"We present a timing analysis of the 2002 outburst of the accreting
millisecond pulsar SAX J1808.4-3658. A study of the phase delays of the entire
pulse profile shows a behavior that is surprising and difficult to interpret:
superposed to a general trend, a big jump by about 0.2 in phase is visible,
starting at day 14 after the beginning of the outburst. An analysis of the
pulse profile indicates the presence of a significant first harmonic. Studying
the fundamental and the first harmonic separately, we find that the phase
delays of the first harmonic are more regular, with no sign of the jump
observed in the fundamental. The fitting of the phase delays of the first
harmonic with a model which takes into account the observed exponential decay
of the X-ray flux (and therefore of the mass accretion rate onto the neutron
star) gives important information on the torque acting on the neutron star
during the outburst. We find that the source shows spin-up in the first part of
the outburst, while a spin-down dominates at the end. From these results we
derive an estimate of the neutron star magnetic field strength.",0612093v1
2002-01-18,Model Exact Low-Lying States and Spin Dynamics in Ferric Wheels; Fe$_6$ to Fe$_{12}$,"Using an efficient numerical scheme that exploits spatial symmetries and
spin-parity, we have obtained the exact low-lying eigenstates of exchange
Hamiltonians for ferric wheels up to Fe$_{12}$. The largest calculation
involves the Fe$_{12}$ ring which spans a Hilbert space dimension of about 145
million for M$_s$=0 subspace. Our calculated gaps from the singlet ground state
to the excited triplet state agrees well with the experimentally measured
values. Study of the static structure factor shows that the ground state is
spontaneously dimerized for ferric wheels. Spin states of ferric wheels can be
viewed as quantized states of a rigid rotor with the gap between the ground and
the first excited state defining the inverse of moment of inertia. We have
studied the quantum dynamics of Fe$_{10}$ as a representative of ferric wheels.
We use the low-lying states of Fe$_{10}$ to solve exactly the time-dependent
Schr\""odinger equation and find the magnetization of the molecule in the
presence of an alternating magnetic field at zero temperature. We observe a
nontrivial oscillation of magnetization which is dependent on the amplitude of
the {\it ac} field. We have also studied the torque response of Fe$_{12}$ as a
function of magnetic field, which clearly shows spin-state crossover.",0201330v1
2007-07-11,The Nonlinear Evolution of Galaxy Intrinsic Alignments,"The non-Gaussian contribution to the intrinsic halo spin alignments is
analytically modeled and numerically detected. Assuming that the growth of
non-Gaussianity in the density fluctuations caused the tidal field to have
nonlinear-order effect on the orientations of the halo angular momentum, we
model the intrinsic halo spin alignments as a linear scaling of the density
correlations on large scales, which is different from the previous
quadratic-scaling model based on the linear tidal torque theory. Then, we
analyze the halo catalogs from the recent high-resolution Millennium Run
simulation at four different redshifts (z=0,0.5,1 and 2) and measure
quantitatively the degree of the nonlinear effect on the halo spin alignments
and its changes with redshifts. A clear signal of spin correlations is found on
scales as large as 10 Mpc/h at z=0, which marks a detection of the nonlinear
tidal effect on the intrinsic halo alignments. We also investigate how the
nonlinear effect depends on the intrinsic properties of the halos. It is found
that the degree of the nonlinear tidal effect increases as the halo mass scale
decreases, the halo specific angular momentum increases, and the halo peculiar
velocity decreases. We discuss implication of our result on the weak
gravitational lensing.",0707.1690v2
2011-10-06,Wind accretion in symbiotic X-ray binaries,"The properties of wind accretion in symbiotic X-ray binaries (SyXBs)
consisting of red-giant and magnetized neutron star (NS) are discussed. The
spin-up/spin-down torques applied to NS are derived based on a hydrodynamic
theory of quasi-spherical accretion onto magnetized NSs. In this model, a
settling subsonic accretion proceeds through a hot shell formed around the NS
magnetosphere. The accretion rate onto the NS is determined by the ability of
the plasma to enter the magnetosphere.Due to large Reynolds numbers in the
shell, the interaction of the rotating magnetosphere with plasma initiates a
subsonic turbulence. The convective motions are capable of carrying the angular
momentum through the shell. We carry out a population synthesis of SyXBs in the
Galaxy with account for the spin evolution of magnetized NS. The Galactic
number of SyXBs with bright (M_v<1) low-mass red-giant companion is found to be
from \sim 40 to 120, and their birthrate is \sim 5\times 10^{-5}-10^{-4} per
year. According to our model, among known SyXBs, Sct X-1 and IRXS
J180431.1-273932 are wind-fed accretors. GX 1+4 lies in the transition from the
wind-fed SyXBs to SyXBs in which the giants overflow their Roche lobe. The
model successfully reproduces very long NS spins (such as in IGR J16358-4724
and 4U 1954+31) without the need to invoke very strong magnetic fields.",1110.1156v1
2012-02-20,"Frame-dragging, disk warping, jet precessing, and dipped X-ray lightcurve of Sw J1644+57","The X-ray transient source Sw J1644+57 recently discovered by Swift is
believed to be triggered by tidal disruption of a star by a rapidly spinning
supermassive black hole (SMBH). For such events, the outer disk is very likely
misaligned with respect to the equatorial plane of the spinning SMBH, since the
incoming star before disruption most likely has an inclined orbital plane. The
tilted disk is subject to the Lense-Thirring torque, which tends to twist and
warp due to the Bardeen-Petterson effect. The inner disk tends to align with
the SMBH spin, while the outer region tends to remain in the stellar orbital
plane, with a transition zone around the Bardeen-Petterson radius. The
relativistic jet launched from the spinning SMBH would undergo precession. The
5-30 day X-ray lightcurve of Sw J1644+57 shows a quasi-periodic (2.7-day)
variation with noticeable narrow dips. We numerically solve a warped disk and
propose a jet-precessing model by invoking a Blandford-Znajek jet collimated by
a wind launched near the Bardeen-Petterson radius. Through simulations, we show
that the narrow dips in the X-ray lightcurve can be reproduced for a range of
geometric configurations. From data we infer that the inclination angle of the
initial stellar orbit is in the range of $10^{\circ}-20^{\circ}$ from the SMBH
equatorial plane, that the jet should have a moderately high Lorentz factor,
and that the inclination angle, jet opening angle, and observer's viewing angle
are such that the duty cycle of the line-of-sight sweeping the jet cone is
somewhat less than 0.5.",1202.4231v2
2013-08-10,"Ultra-High Density, High-Performance and Energy-Efficient All Spin Logic","All Spin Logic gates employ multiple nano-magnets interacting through
spin-torque using non-magnetic channels. Compactness, non-volatility and
ultra-low voltage operation are some of the attractive features of ASL, while,
low switching-speed (of nano-magnets as compared to CMOS gates) and
static-power dissipation can be identified as the major bottlenecks. In this
work we explore design techniques that leverage the specific device
characteristics of ASL to overcome the inefficiencies and to enhance the merits
of this technology, for a given set of device parameters. We exploit the
non-volatility of nano-magnets to model fully-pipelined ASL that can achieve
higher performance. Clocking of power supply in pipelined ASL would require
CMOS transistors that may consume significantly large voltage headroom and
area, as compared to the nano-magnets. We show that the use of leaky
transistors can significantly mitigate such bottlenecks, without sacrificing
energy-efficiency and robustness. Exploiting the inherent isolation between the
biasing charge current and spin-current paths in ASL, we propose to stack
multiple ASL metal layers, leading to ultra-high-density and energy-efficient
3-D computation blocks. Results for the design of an FIR filter show that ASL
can achieve performance and power consumption comparable to CMOS while the
ultra-high-density of ASL can be projected as its main advantage over CMOS.",1308.2280v1
2014-11-05,Spin Wave Neuroanalog of von Neumann's Microwave Computer,"Frequency and phase of neural activity play important roles in the behaving
brain. The emerging understanding of these roles has been informed by the
design of analog devices that have been important to neuroscience, among them
the neuroanalog computer developed by O. Schmitt in the 1930's. In the 1950's,
J. von Neumann, in a search for high performance computing using microwaves,
invented a logic machine based on similar devices, that can perform logic
functions including binary arithmetic. Described here is a novel embodiment of
his machine using nano-magnetics. The embodiment is based on properties of
ferromagnetic thin films that are governed by a nonlinear Schrodinger equation
for magnetization in a film. Electrical currents through point contacts on a
film create spin torque nano oscillators (STNO) that define the oscillator
elements of the system. These oscillators may communicate through directed
graphs of electrical connections or by radiation in the form of spin waves. It
is shown here how to construct a logic machine using STNO, that this machine
can perform several computations simultaneously using multiplexing of inputs,
that this system can evaluate iterated logic functions, and that spin waves can
communicate frequency, phase and binary information. Neural tissue and the
Schmitt, von Neumann and STNO devices share a common bifurcation structure,
although these systems operate on vastly different space and time scales. This
suggests that neural circuits may be capable of computational functionality
described here.",1411.1401v1
2016-06-07,"Fermi level position, Coulomb gap, and Dresselhaus splitting in (Ga,Mn)As","Carrier-induced nature of ferromagnetism in a ferromagnetic semiconductor,
(Ga,Mn)As, offers a great opportunity to observe novel spin-related phenomena
as well as to demonstrate new functionalities of spintronic devices. Here, we
report on low-temperature angle-resolved photoemission studies of the valence
band in this model compound. By a direct determination of the distance of the
split-off band to the Fermi energy EF, we conclude that EF is located within
the heavy/light hole band. However, the bands are strongly perturbed by
disorder and disorder-induced carrier correlations that lead to the Coulomb gap
at EF, which we resolve experimentally in a series of samples, and show that
its depth and width enlarge when the Curie temperature decreases. Furthermore,
we have detected surprising linear magnetic dichroism in photoemission spectra
of the split-off band. By a quantitative theoretical analysis we demonstrate
that it arises from the Dresselhaus-type spin-orbit term in zinc-blende
crystals. The spectroscopic access to the magnitude of such asymmetric part of
spin-orbit coupling is worthwhile, as they account for spin-orbit torque in
spintronic devices of ferromagnets without inversion symmetry.",1606.02047v1
2016-08-10,Ejector and propeller spin-down: How might a superluminous supernova millisecond magnetar become the 6.67 hr pulsar in RCW103,"The X-ray source 1E 161348-5055 in the supernova remnant RCW 103 recently
exhibited X-ray activity typical of magnetars, i.e. neutron stars with magnetic
fields > 10^14-10^15 G. However, 1E 161348-5055 has an observed period of 6.67
hr, in contrast to magnetars which have a spin period of seconds. Here we
describe a simple model which can explain the spin evolution of 1E 161348-5055,
as well as other magnetars, from an initial period of milliseconds that would
be required for dynamo generation of magnetar-strength magnetic fields. We
propose that the key difference between 1E 161348-5055 and other magnetars is
the persistence of a remnant disk of small total mass. This disk caused 1E
161348-5055 to undergo ejector and propeller phases in its life, during which
strong torques caused a rapid increase of its spin period. By matching its
observed spin period and ~1-3 kyr age, we find that 1E 161348-5055 has the
(slightly) highest magnetic field of all known magnetars, with B~5x10^15 G, and
that its disk had a mass of ~10^24 g, comparable to that of the asteroid Ceres.",1608.03149v2
2016-12-06,The gravitational interaction between planets on inclined orbits and protoplanetary disks as the origin of primordial spin--orbit misalignments,"Many of the observed spin--orbit alignment properties of exoplanets can be
explained in the context of the primordial disk misalignment model, in which an
initially aligned protoplanetary disk is torqued by a distant stellar companion
on a misaligned orbit, resulting in a precessional motion that can lead to
large-amplitude oscillations of the spin--orbit angle. We consider a variant of
this model in which the companion is a giant planet with an orbital radius of a
few au. Guided by the results of published numerical simulations, we model the
dynamical evolution of this system by dividing the disk into inner and outer
parts---separated at the location of the planet---that behave as distinct,
rigid disks. We show that the planet misaligns the inner disk even as the
orientation of the outer disk remains unchanged. In addition to the
oscillations induced by the precessional motion, whose amplitude is larger the
smaller the initial inner-disk-to-planet mass ratio, the spin--orbit angle also
exhibits a secular growth in this case---driven by ongoing mass depletion from
the disk---that becomes significant when the inner disk's angular momentum
drops below that of the planet. Altogether, these two effects can produce
significant misalignment angles for the inner disk, including retrograde
configurations. We discuss these results within the framework of the Stranded
Hot Jupiter scenario and consider their implications, including to the
interpretation of the alignment properties of debris disks.",1612.01985v1
2017-07-27,Synchrotron radiation induced magnetization in magnetically-doped and pristine topological insulators,"Quantum mechanics postulates that any measurement influences the state of the
investigated system. Here, by means of angle-, spin-, and time-resolved
photoemission experiments and ab initio calculations we demonstrate how
non-equal depopulation of the Dirac cone (DC) states with opposite momenta in
V-doped and pristine topological insulators (TIs) created by a photoexcitation
by linearly polarized synchrotron radiation (SR) is followed by the
hole-generated uncompensated spin accumulation and the SR-induced magnetization
via the spin-torque effect. We show that the photoexcitation of the DC is
asymmetric, that it varies with the photon energy, and that it practically does
not change during the relaxation. We find a relation between the
photoexcitation asymmetry, the generated spin accumulation and the induced spin
polarization of the DC and V 3d states. Experimentally the SR-generated
in-plane and out-of-plane magnetization is confirmed by the
$k_{\parallel}$-shift of the DC position and by the splitting of the states at
the Dirac point even above the Curie temperature. Theoretical predictions and
estimations of the measurable physical quantities substantiate the experimental
results.",1707.08798v1
2017-08-09,Glitches: the exact quantum signatures of pulsars metamorphosis,"The observed recurrence of glitches in pulsars and neutron stars carry rich
information about the evolution of their internal structures. In this article I
show that the glitch-events observed in pulsars are exact quantum signatures
for their metamorphosis into dark super-baryons (SBs), whose interiors are made
of purely incompressible superconducting gluon-quark superfluids. Here the
quantum nuclear shell model is adopted to describe the permitted energy levels
of the SB, which are assumed to be identical to the discrete spinning rates
$\Omega_{SB},$ that SBs are allowed to rotate with. Accordingly, a glitch-event
corresponds to a prompt spin-down of the superconducting SB from one energy
level to the next, thereby expelling a certain number of vortices, which in
turn spins-up the ambient medium. The process is provoked mainly by the
negative torque of the ambient dissipative nuclear fluid and by a universal
scalar field $\phi$ at the background of a supranuclear dense matter. As
dictated by the Onsager-Feynman equation, the prompt spin-down must be
associated with increase of the dimensions of the embryonic SB to finally
convert the entire pulsar into SB-Objects on the scale of Gyrs. Based on our
calculations, a Vela-like pulsar should display billions of glitches during its
lifetime, before it metamorphoses entirely into a maximally compact SB-object
and disappears from our observational windows. The present model predicts the
mass of SBs and $\Delta \Omega/\Omega$ in young pulsars to be relatively lower
than their older counterparts.",1708.02887v2
2017-08-16,Magneto Acoustic Spin Hall Oscillators,"This paper introduces a novel oscillator that combines the tunability of spin
Hall-driven nano oscillators with the high quality factor (Q) of high overtone
bulk acoustic wave resonators (HBAR), integrating both reference and tunable
oscillators on the same chip with CMOS. In such magneto acoustic spin Hall
(MASH) oscillators, voltage oscillations across the magnetic tunnel junction
(MTJ) that arise from a spin-orbit torque (SOT) are shaped by the transmission
response of the HBAR that acts as a multiple peak-bandpass filter and a delay
element due to its large time constant, providing delayed feedback. The
filtered voltage oscillations can be fed back to the MTJ via a) strain, b)
current, or c) magnetic field. We develop a SPICE-based circuit model by
combining experimentally benchmarked models including the stochastic
Landau-Lifshitz-Gilbert (sLLG) equation for magnetization dynamics and the
Butterworth Van Dyke (BVD) circuit for the HBAR. Using the self-consistent
model, we project up to $\sim$ 50X enhancement in the oscillator linewidth with
Q reaching up to 52825 at 3 GHz, while preserving the tunability by locking the
STNO to the nearest high Q peak of the HBAR. We expect that our results will
inspire MEMS-based solutions to spintronic devices by combining attractive
features of both fields for a variety of applications.",1708.04735v2
2017-10-03,Temperature- dependence of anomalous Hall conductivity in Rashba-type ferromagnets,"The applicability and usefulness of Rashba model have been extended by recent
observations in the field of spintronics, such as the spin-orbit torque at the
junction interfaces between ferromagnetic (FM) metals and non-magnetic (NM)
metals and the perpendicular anomalous magnetoresistance (AMR) in
heterostructures such as FI/NM or FM/NI (I denotes an insulator). In
particular, the observations of the perpendicular AMR effect stimulate further
interest in the Rashba-type spin-orbit interaction (SOI) at interfaces. Thus,
the Rashba model with exchange splitting (EXS) is considered not only to play
as an effective model for the physical understanding but also to reflect actual
bi-layer systems in current spintronics devices. In the present work, we have
first investigated the temperature dependence of anomalous Hall conductivity
(AHC) of Rashba-type ferromagnets considered effects of spin fluctuations
within the disordered local moment (DLM) scheme. The most distinctive feature
that we observed is that intrinsic AHC increases with increasing temperature.
This can be understood from the aspect of spin chirality, which indicates that
the AHC increases with decreasing EXS when the SOI is much smaller than the
EXS. The extrinsic part of the Fermi surface term also increases with
increasing temperature and has a large contribution, comparable to that of the
intrinsic part. Although, such a behaviour has not yet been observed
experimentally, we suggest that the physical picture found in this work might
lurk in an anomalous Hall effects in Rashbe-type ferromagnets.",1710.00982v1
2018-05-15,Ultrathin All-in-one Spin Hall Magnetic Sensor with Built-in AC Excitation Enabled by Spin Current,"Magnetoresistance (MR) sensors provide cost-effective solutions for diverse
industrial and consumer applications, including emerging fields such as
internet-of-things (IoT), artificial intelligence and smart living.
Commercially available MR sensors such as anisotropic magnetoresistance (AMR)
sensor, giant magnetoresistance (GMR) sensor and tunnel magnetoresistance (TMR)
sensors typically require an appropriate magnetic bias for both output
linearization and noise suppression, resulting in increased structural
complexity and manufacturing cost. Here, we demonstrate an all-in-one spin Hall
magnetoresistance (SMR) sensor with built-in AC excitation and rectification
detection, which effectively eliminates the requirements of any linearization
and domain stabilization mechanisms separate from the active sensing layer.
This was made possible by the coexistence of SMR and spin-orbit torque (SOT) in
ultrathin NiFe/Pt bilayers. Despite the simplest possible structure, the
fabricated Wheatstone bridge sensor exhibits essentially zero DC offset,
negligible hysteresis, and a detectivity of around 1nT/sqrt(Hz) at 1Hz. In
addition, it also shows an angle dependence to external field similar to those
of GMR and TMR, though it does have any reference layer (unlike GMR and TMR).
The superior performances of SMR sensors are evidently demonstrated in the
proof-of-concept experiments on rotation angle measurement, and vibration and
finger motion detection.",1805.05616v1
2019-01-11,Quantitative imaging of hybrid chiral spin textures in magnetic multilayer systems by Lorentz microscopy,"Chiral magnetic textures in ultrathin perpendicularly magnetised multilayer
film stacks with an interfacial Dzyaloshinskii-Moriya interaction have been the
focus of much research recently. The chirality associated with the broken
inversion symmetry at the interface between an ultrathin ferromagnetic layer
and a heavy metal with large spin-orbit coupling supports homochiral N\'eel
domain walls and hedgehog (N\'eel) skyrmions. Under spin-orbit torques these
N\'eel type magnetic structures are predicted, and have been measured, to move
at high velocities. However recent studies have indicated that some
multilayered systems may possess a more complex hybrid domain wall
configuration, due to the competition between interfacial DMI and interlayer
dipolar fields. These twisted textures are expected to have thickness dependent
N\'eel and Bloch contributions to the domain or skyrmion walls. In this work,
we use the methods of Lorentz microscopy to measure quantitatively for the
first time experimentally both; i) the contributions of the N\'eel and Bloch
contributions and ii) their spatial spin variation at high resolution. These
are compared with modelled and simulated structures which are in excellent
agreement with our experimental results. Our quantitative analysis provides
powerful direct evidence of the Bloch wall component which exists in these
hybrid walls and will be significant when exploiting such phenomena in
spintronic applications.",1901.03652v1
2019-08-24,Probing the Bardeen-Petterson effect in tidal disruption events with spectral line reverberation mapping,"For an inclined accretion flow around a rotating black hole, the combined
effect of the Lense-Thirring precession and viscous torque tends to align the
inner part of the flow with the black hole spin, leading to the formation of a
warped disc, known as the Bardeen-Petterson effect (Bardeen & Petterson 1975).
In tidal disruption events (TDEs) in which a super-massive black hole starts to
accrete the bound debris, if the black hole is spinning, in general the stellar
orbit is inclined with the black hole spin. So is the accretion disc formed
following circularization and radiative cooling of the debris. Xiang-Gruess et
al. (2016) studied in detail the stellar debris evolution and disc formation in
TDEs when the stellar orbit is inclined, and found that a warped disc would
form under certain conditions. In this work we investigate properties of
time-resolved fluorescent iron line originating from a warped disc that is
irradiated by the initial X-ray flare. We find that the time-resolved spectrum
shows distinct features before and after a critical time. This critical time
depends on the Bardeen-Petterson radius $r_{\rm BP}$, i.e., the outer boundary
of the inner aligned disc; while the line width during the later stage of the
X-ray flare is sensitive to the inclination of the outer disc flow. This
demonstrates that time-resolved X-ray spectroscopy can be a powerful tool to
probe the Bardeen-Petterson effect in TDE flares and can be used to measure the
Bardeen-Petterson radius as well as put constraint on the black hole mass and
spin.",1908.09093v1
2020-03-11,Timing of the accreting millisecond pulsar IGR J17591-2342: evidence of spin-down during accretion,"We report on the phase-coherent timing analysis of the accreting millisecond
X-ray pulsar IGR J17591-2342, using Neutron Star Interior Composition Explorer
(NICER) data taken during the outburst of the source between 2018 August 15 and
2018 October 17. We obtain an updated orbital solution of the binary system. We
investigate the evolution of the neutron star spin frequency during the
outburst, reporting a refined estimate of the spin frequency and the first
estimate of the spin frequency derivative ($\dot{\nu} \sim -7\times 10^{-14}$
Hz s$^{-1}$), confirmed independently from the modelling of the fundamental
frequency and its first harmonic. We further investigate the evolution of the
X-ray pulse phases adopting a physical model that accounts for the accretion
material torque as well as the magnetic threading of the accretion disc in
regions where the Keplerian velocity is slower than the magnetosphere velocity.
From this analysis we estimate the neutron star magnetic field $B_{eq} =
2.8(3)\times10^{8}$ G. Finally, we investigate the pulse profile dependence on
energy finding that the observed behaviour of the pulse fractional amplitude
and lags as a function of energy are compatible with a thermal Comptonisation
of the soft photons emitted from the neutron star caps.",2003.05069v1
2020-06-09,Ferromagnetism out of charge fluctuation of strongly correlated electrons in $κ$-(BEDT-TTF)$_2$Hg(SCN)$_2$Br,"We perform magnetic susceptibility and magnetic torque measurements on the
organic $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Br, which is recently suggested to
host an exotic quantum dipole-liquid in its low-temperature insulating phase.
Below the metal-insulator transition temperature, the magnetic susceptibility
follows a Curie-Weiss law with a positive Curie-Weiss temperature, and a
particular $M\propto \sqrt{H}$ curve is observed. The emergent
ferromagnetically interacting spins amount to about 1/6 of the full spin moment
of localized charges. Taking account of the possible inhomogeneous
quasi-charge-order that forms a dipole-liquid, we construct a model of
antiferromagnetically interacting spin chains in two adjacent charge-ordered
domains, which are coupled via fluctuating charges on a Mott-dimer at the
boundary. We find that the charge fluctuations can draw a weak ferromagnetic
moment out of the spin singlet domains.",2006.05221v2
2020-08-04,The permanent ellipticity of the neutron star in PSR J1023+0038,"A millisecond pulsar having an ellipticity, that is an asymmetric mass
distribution around its spin-axis, could emit continuous gravitational waves,
which have not been detected so far. An indirect way to infer such waves is to
estimate the contribution of the waves to the spin-down rate of the pulsar. The
transitional pulsar PSR J1023+0038 is ideal and unique for this purpose,
because this is the only millisecond pulsar for which the spin-down rate has
been measured in both accreting and non-accreting states. Here we infer, from
our formalism based on the complete torque budget equations and the pulsar
magnetospheric origin of observed $\gamma$-rays in the two states, that PSR
J1023+0038 should emit gravitational waves due to a permanent ellipticity of
the pulsar. The formalism also explains some other main observational aspects
of this source in a self-consistent way. As an example, our formalism naturally
infers the accretion disc penetration into the pulsar magnetosphere, and
explains the observed X-ray pulsations in the accreting state using the
standard and well-accepted scenario. This, in turn, infers the larger pulsar
spin-down power in the accreting state, which, in our formalism, explains the
observed larger $\gamma$-ray emission in this state. Exploring wide ranges of
parameter values of PSR J1023+0038, and not assuming an additional source of
stellar ellipticity in the accreting state, we find the misaligned mass
quadrupole moment of the pulsar in the range of $(0.92-1.88)\times10^{36}$ g
cm$^2$, implying an ellipticity range of $(0.48-0.93)\times10^{-9}$.",2008.01716v1
2020-10-14,Dynamic detection of current-induced spin-orbit magnetic fields: a phase independent approach,"Current induced spin-orbit torques (SOTs) in ferromagnet/non-magnetic metal
heterostructures open vast possibilities to design spintronic devices to store,
process and transmit information in a simple architecture. It is a central task
to search for efficient SOT-devices, and to quantify the magnitude as well as
the symmetry of current-induced spin-orbit magnetic fields (SOFs). Here, we
report a novel approach to determine the SOFs based on magnetization dynamics
by means of time-resolved magneto-optic Kerr microscopy. A microwave current in
a narrow Fe/GaAs (001) stripe generates an Oersted field as well as SOFs due to
the reduced symmetry at the Fe/GaAs interface, and excites standing spin wave
(SSW) modes because of the lateral confinement. Due to their different
symmetries, the SOFs and the Oersted field generate distinctly different mode
patterns. Thus it is possible to determine the magnitude of the SOFs from an
analysis of the shape of the SSW patterns. Specifically, this method, which is
conceptually different from previous approaches based on lineshape analysis, is
phase independent and self-calibrated. It can be used to measure the current
induced SOFs in other material systems, e.g., ferromagnetic metal/non-magnetic
metal heterostructures.",2010.06960v1
2020-10-29,Tidal Love Numbers of Kerr Black Holes,"The open question of whether a Kerr black hole can become tidally deformed or
not has profound implications for fundamental physics and gravitational-wave
astronomy. We consider a Kerr black hole embedded in a weak and slowly varying,
but otherwise arbitrary, multipolar tidal environment. By solving the static
Teukolsky equation for the gauge-invariant Weyl scalar $\psi_0$, and by
reconstructing the corresponding metric perturbation in an ingoing radiation
gauge, for a general harmonic index $\ell$, we compute the linear response of a
Kerr black hole to the tidal field. This linear response vanishes identically
for a Schwarzschild black hole and for an axisymmetric perturbation of a
spinning black hole. For a nonaxisymmetric perturbation of a spinning black
hole, however, the linear response does not vanish, and it contributes to the
Geroch-Hansen multipole moments of the perturbed Kerr geometry. As an
application, we compute explicitly the rotational black hole tidal Love numbers
that couple the induced quadrupole moments to the quadrupolar tidal fields, to
linear order in the black hole spin, and we introduce the corresponding notion
of tidal Love tensor. Finally, we show that those induced quadrupole moments
are closely related to the well-known physical phenomenon of tidal torquing of
a spinning body interacting with a tidal gravitational environment.",2010.15795v2
2020-12-17,Magnetic reversal and pinning in a perpendicular zero moment half-metal,"Compensated ferrimagnets are promising materials for fast spintronic
applications based on domain wall motion as they combine the favourable
properties of ferromagnets and antiferromagnets. They inherit from
antiferromagnets immunity to external fields, fast spin dynamics and rapid
domain wall motion. From ferromagnets they inherit straightforward ways to read
out the magnetic state, especially in compensated half metals, where electrons
flow in only one spin channel. Here, we investigate domain structure in
compensated half-metallic Mn2Ru0.5Ga films and assess their potential in domain
wall motion-based spin-electronic devices. Our focus is on understanding and
reducing domain wall pinning in unpatterned epitaxial thin films. Two modes of
magnetic reversal, driven by nucleation or domain wall motion, are identified
for different thin film deposition temperatures $(T_{dep})$. The magnetic
aftereffect is analysed to extract activation volumes $(V^*)$, activation
energies $(E_A)$, and their variation $({\Delta}E_A)$. The latter is decisive
for the magnetic reversal regime, where domain wall motion dominated reversal
(weak pinning) is found for ${\Delta}E_A<0.2$ eV and nucleation dominated
reversal (strong pinning) for ${\Delta}E_A>0.5$ eV. A minimum ${\Delta}E_A=28$
meV is found for $T_{dep}=290{\deg}$C. Prominent pinning sites are visualized
by analysing virgin domain patterns after thermal demagnetization. In the
sample investigated they have spacings of order 300 nm, which gives an upper
limit of the track-width of spin-torque domain-wall motion-based devices.",2012.09515v1
2021-03-24,Magnetic ordering of the distorted kagome antiferromagnet Y$_3$Cu$_9$(OH)$_{18}$[Cl$_8$(OH)] prepared via optimal synthesis,"Experimental studies of high-purity kagome-lattice antiferromagnets (KAFM)
are of great importance in attempting to better understand the predicted
enigmatic quantum spin-liquid ground state of the KAFM model. However,
realizations of this model can rarely evade magnetic ordering at low
temperatures due to various perturbations to its dominant isotropic exchange
interactions. Such a situation is for example encountered due to sizable
Dzyaloshinskii-Moriya magnetic anisotropy in YCu$_3$(OH)$_6$Cl$_3$, which
stands out from other KAFM materials by its perfect crystal structure. We find
evidence of magnetic ordering also in the distorted sibling compound
Y$_3$Cu$_9$(OH)$_{18}$[Cl$_8$(OH)], which has recently been proposed to feature
a spin-liquid ground state arising from a spatially anisotropic kagome lattice.
Our findings are based on a combination of bulk susceptibility, specific heat,
and magnetic torque measurements that disclose a N\'eel transition temperature
of $T_N=11$~K in this material, which might feature a coexistence of magnetic
order and persistent spin dynamics as previously found in
YCu$_3$(OH)$_6$Cl$_3$. Contrary to previous studies of single crystals and
powders containing impurity inclusions, we use high-purity single crystals of
Y$_3$Cu$_9$(OH)$_{18}$[Cl$_8$(OH)] grown via an optimized hydrothermal
synthesis route that minimizes such inclusions. This study thus demonstrates
that the lack of magnetic ordering in less pure samples of the investigated
compound does not originate from the reduced symmetry of spin lattice but is
instead of extrinsic origin.",2103.13254v2
2021-05-01,Anisotropy and Current Control of Magnetization in SrRuO$_3$ SrTiO$_3$ Heterostructures for Spin-Memristors,"Spintronics-based nonvolatile components in neuromorphic circuits offer the
possibility of realizing novel functionalities at low power. Current-controlled
electrical switching of magnetization is actively researched in this context.
Complex oxide heterostructures with perpendicular magnetic anisotropy (PMA),
consisting of SrRuO$_3$ (SRO) grown on SrTiO$_3$ (STO) are strong material
contenders. Utilizing the crystal orientation, magnetic anisotropy in such
simple heterostructures can be tuned to either exhibit a perfect or slightly
tilted PMA. Here, we investigate current-induced magnetization modulation in
such tailored ferromagnetic layers with a material with strong spin-orbit
coupling (Pt), exploiting the spin Hall effect. We find significant differences
in the magnetic anisotropy between the SRO/STO heterostructures, as manifested
in the first and second harmonic magnetoresistance measurements.
Current-induced magnetization switching can be realized with spin-orbit
torques, but for systems with perfect PMA this switching is probabilistic as a
result of the high symmetry. Slight tilting of the PMA can break this symmetry
and allow the realization of deterministic switching. Control over the magnetic
anisotropy of our heterostructures therefore provides control over the manner
of switching. Based on our findings, we propose a three-terminal spintronic
memristor, with a magnetic tunnel junction design, that shows several resistive
states controlled by electric charge. Non-volatile states can be written
through SOT by applying an in-plane current, and read out as a tunnel current
by applying a small out-of-plane current. Depending on the anisotropy of the
SRO layer, the writing mechanism is either deterministic or probabilistic
allowing for different functionalities to emerge. We envisage that the
probabilistic MTJs could be used as synapses while the deterministic devices
can emulate neurons",2105.00269v1
2021-11-30,Bilinear magnetoresistance in HgTe topological insulator: opposite signs at opposite interfaces demonstrated by gate control,"Spin-orbit effects appearing in topological insulators (TI) and at Rashba
interfaces are currently revolutionizing how we can manipulate spins and have
led to several newly discovered effects, from spin-charge interconversion and
spin-orbit torques to novel magnetoresistance phenomena. In particular, a
puzzling magnetoresistance has been evidenced, bilinear in electric and
magnetic fields. Here, we report the observation of bilinear magnetoresistance
(BMR) in strained HgTe, a prototypical TI. We show that both the amplitude and
sign of this BMR can be tuned by controlling, with an electric gate, the
relative proportions of the opposite contributions of opposite surfaces. At
magnetic fields of 1 T, the magnetoresistance is of the order of 1 \% and has a
larger figure of merit than previously measured TIs. We propose a theoretical
model giving a quantitative account of our experimental data. This phenomenon,
unique to TI, offers novel opportunities to tune their electrical response for
spintronics.",2111.15594v2
2021-12-27,Ellipsoidal equilibrium figure and Cassini states of rotating planets and satellites deformed by a tidal potential in the spatial case,"The equilibrium figure of an inviscid tidally deformed body is the starting
point for the construction of many tidal theories such as Darwinian tidal
theories or the hydrodynamical Creep tide theory. This paper presents the
ellipsoidal equilibrium figure when the spin rate vector of the deformed body
is not perpendicular to the plane of motion of the companion. We obtain the
equatorial and the polar flattenings as functions of the Jeans and the
Maclaurin flattenings, and of the angle $\theta$ between the spin rate vector
and the radius vector. The equatorial vertex of the equilibrium ellipsoid does
not point toward the companion, which produces a torque perpendicular to the
rotation vector, which introduces terms of precession and nutation. We find
that the direction of spin may differ significantly from the direction of the
principal axis of inertia $C$, so the classical approximation
$\mathsf{I}\vec{\omega}\approx C\vec{\omega}$ only makes sense in the
neighborhood of the planar problem. We also study the so-called Cassini states.
Neglecting the short-period terms in the differential equation for the spin
direction and assuming a uniform precession of the line of the orbital
ascending node, we obtain the same differential equation as that found by
Colombo (1966). That is, a tidally deformed inviscid body has exactly the same
Cassini states as a rotating axisymmetric rigid body, the tidal bulge having no
secular effect at first order.",2112.13767v1
2022-12-20,Coherent backscattering in the topological Hall effect,"The mutual interplay between electron transport and magnetism has attracted
considerable attention in recent years, primarily motivated by strategies to
manipulate magnetic degrees of freedom electrically, such as spin-orbit torques
and domain wall motion. Within this field the topological Hall effect, which
originates from scalar spin chirality, is an example of inter-band quantum
coherence induced by real-space inhomogeneous magnetic textures, and its
magnitude depends on the winding number and chiral spin features that establish
the total topological charge of the system. Remarkably, in the two decades
since its discovery, there has been no research on the quantum correction to
the topological Hall effect. Here we will show that, unlike the ordinary Hall
effect, the inhomogeneous magnetization arising from the spin texture will give
additional scattering terms in the kinetic equation, which result in a quantum
correction to the topological Hall resistivity. We focus on 2D systems, where
weak localization is strongest, and determine the complicated gradient
corrections to the Cooperon and kinetic equation. Whereas the weak localization
correction to the topological Hall effect is not large in currently known
materials, we show that it is experimentally observable in dilute magnetic
semiconductors. Our theoretical results will stimulate experiments on the
topological Hall effect and fill the theoretical knowledge gap on weak
localization corrections to transverse transport.",2212.10588v1
2023-01-19,Current-driven dynamics and ratchet effect of skyrmion bubbles in a ferrimagnetic insulator,"Magnetic skyrmions are compact chiral spin textures that exhibit a rich
variety of topological phenomena and hold potential for developing high-density
memory devices and novel computing schemes driven by spin currents. Here, we
demonstrate room temperature interfacial stabilization and current-driven
control of skyrmion bubbles in the ferrimagnetic insulator Tm3Fe5O12 (TmIG)
coupled to Pt. We track the current-induced motion of individual skyrmion
bubbles. The ferrimagnetic order of the crystal together with the interplay of
spin-orbit torques and pinning determine the skyrmion dynamics in TmIG and
result in a strong skyrmion Hall effect characterized by a negative deflection
angle and hopping motion. Further, we show that the velocity and depinning
threshold of the skyrmion bubbles can be modified by exchange coupling TmIG to
an in-plane magnetized Y3Fe5O12 layer, which distorts the spin texture of the
skyrmions and leads to a directional-dependent rectification of their dynamics.
This effect, which is equivalent to a magnetic ratchet, is exploited to control
the skyrmion flow in a racetrack-like device.",2301.08183v1
2023-11-20,Interplay between moment-dependent and field-driven unidirectional magnetoresistance in CoFeB/InSb/CdTe heterostructures,"Magnetoresistance effects are crucial for understanding the charge/spin
transport as well as propelling the advancement of spintronic applications.
Here we report the coexistence of magnetic moment-dependent (MD) and magnetic
field-driven (FD) unidirectional magnetoresistance (UMR) effects in
CoFeB/InSb/CdTe heterostructures. The strong spin-orbital coupling of InSb and
the matched impedance at the CoFeB/InSb interface warrant a distinct MD-UMR
effect at room temperature, while the interaction between the in-plane magnetic
field and the Rashba effect at the InSb/CdTe interface induces the marked
FD-UMR signal that dominates the high-field region. Moreover, owning to the
different spin transport mechanisms, these two types of nonreciprocal charge
transport show opposite polarities with respect to the magnetic field
direction, which further enable an effective phase modulation of the
angular-dependent magnetoresistance. Besides, the demonstrations of both the
tunable UMR response and two-terminal spin-orbit torque-driven magnetization
switching validate our CoFeB/InSb/CdTe system as a suitable integrated building
block for multifunctional spintronic device design.",2311.11843v1
2024-03-17,Primordial black hole formation from a nonspherical density profile with a misaligned deformation tensor,"We perform the numerical simulation of primordial black hole formation from a
nonspherical profile of the initial curvature perturbation $\zeta$. We consider
the background expanding universe filled with the perfect fluid with the linear
equation of state $p=w\rho$ ($w=1/3$ or $1/5$), where $p$ and $\rho$ are the
pressure and the energy density, respectively. The initial condition is set in
a way such that the principal directions of the second derivatives of $\zeta$
and $\triangle \zeta$ at the central peak are misaligned, where $\triangle$ is
the Laplacian. In this setting, since the linearized density is proportional to
$\triangle \zeta$, the inertia tensor and deformation tensor
$\partial_i\partial_j \zeta$ are misaligned. Thus tidal torque may act and the
spin of a resultant primordial black hole would be non-zero in general,
although it is estimated to be very small from previous perturbative
analyses.As a result, we do not find a finite value of the spin within our
numerical precision, giving support for the negligibly small value of the black
hole spin for $1/5\lesssim w \lesssim 1/3$. More specifically, our results
suggest that the dimensionless PBH spin $s$ is typically so small that
$s\ll0.1$ for $w\gtrsim0.2$.",2403.11147v1
2023-06-05,Verification of ultrafast spin transfer effects in FeNi alloys,"The optical intersite spin transfer (OISTR) effect was recently verified in
Fe$_{50}$Ni$_{50}$ using magneto-optical Kerr measurements in the extreme
ultraviolet range. However, one of the main experimental signatures analyzed in
this work, namely a magnetic moment increase at a specific energy in Ni, was
subsequently found also in pure Ni, where no transfer from one element to
another is possible. Hence, it is a much-discussed issue whether OISTR in FeNi
alloys is real and whether it can be verified experimentally or not. Here, we
present a comparative study of spin transfer in Fe$_{50}$Ni$_{50}$,
Fe$_{19}$Ni$_{81}$ and pure Ni. We conclusively show that an increase in the
magneto-optical signal is indeed insufficient to verify OISTR. However, we also
show how an extended data analysis overcomes this problem and allows to
unambiguously identify spin transfer effects. Concomitantly, our work solves
the long-standing riddle about the origin of delayed demagnetization behavior
of Ni in FeNi alloys.",2306.02793v2
2004-02-05,Aharonov-Bohm Physics with Spin II: Spin-Flip Effects in Two-dimensional Ballistic Systems,"We study spin effects in the magneto-conductance of ballistic mesoscopic
systems subject to inhomogeneous magnetic fields. We present a numerical
approach to the spin-dependent Landauer conductance which generalizes recursive
Green function techniques to the case with spin. Based on this method we
address spin-flip effects in quantum transport of spin-polarized and
-unpolarized electrons through quantum wires and various two-dimensional
Aharonov-Bohm geometries. In particular, we investigate the range of validity
of a spin switch mechanism recently found which allows for controlling spins
indirectly via Aharonov-Bohm fluxes. Our numerical results are compared to a
transfer-matrix model for one-dimensional ring structures presented in the
first paper (Hentschel et al., submitted to Phys. Rev. B) of this series.",0402168v1
2005-08-15,Collective effects in spin-crossover chains with exchange interaction,"The collective properties of spin-crossover chains are studied.
Spin-crossover compounds contain ions with a low-spin ground state and low
lying high-spin excited states and are of interest for molecular memory
applications. Some of them naturally form one-dimensional chains. Elastic
interaction and Ising exchange interaction are taken into account. The
transfer-matrix approach is used to calculate the partition function, the
fraction of ions in the high-spin state, the magnetization, susceptibility,
etc., exactly. The high-spin-low-spin degree of freedom leads to collective
effects not present in simple spin chains. The ground-state phase diagram is
mapped out and compared to the case with Heisenberg exchange interaction. The
various phases give rise to characteristic behavior at nonzero temperatures,
including sharp crossovers between low- and high-temperature regimes. A
Curie-Weiss law for the susceptibility is derived and the paramagnetic Curie
temperature is calculated. Possible experiments to determine the exchange
coupling are discussed.",0508345v2
2008-07-08,"Spin rotation, spin filtering, and spin transfer in directional tunneling through non-centrosymmetric semiconductor barriers","We consider spin-dependent tunneling through a gallium arsenide barrier, a
material which has no inversion symmetry. We are dealing with free electrons,
with one effective mass and a spin-splitting in the barrier material. When we
take into account both the spin-orbit interaction and the absence of the
inversion symmetry, the evanescent states in the barrier are spin split and the
tunneling process can become rather involved. Along some crystallographic
directions, the incident wave experiences spin filtering during the tunneling.
These results open stimulating perspectives for spin manipulation in tunnel
devices.",0807.1243v3
2010-12-09,Spin-Currents and Spin-Pumping Forces for Spintronics,"A general definition of the Spintronics concept of spin-pumping is proposed
as generalized forces conjugated to the spin degrees of freedom in the
framework of the theory of mesoscopic non-equilibrium thermodynamics. It is
shown that at least three different kinds of spin-pumping forces and associated
spin-currents can be defined in the most simple spintronics system (the
Ferromagnetic/Non-Ferromagnetic metal interface). Furthermore, the generalized
force associated to the ferromagnetic collective variable is also introduced in
an equal footing, in order to describe the coexistence of the spin of the
conduction electrons (paramagnetic spins attached to $s$-band electrons) and
the ferromagnetic-order parameter. The dynamical coupling between these two
kinds of magnetic degrees of freedom is presented, and interpreted in terms of
spin-transfer effects.",1012.2083v1
2011-11-22,Optical spin injection and spin lifetime in Ge heterostructures,"We demonstrate optical orientation in Ge/SiGe quantum wells and study their
spin properties. The ultrafast electron transfer from the center of the
Brillouin zone to its edge allows us to achieve high spin-polarization
efficiencies and to resolve the spin dynamics of holes and electrons. The
circular polarization degree of the direct-gap photoluminescence exceeds the
theoretical bulk limit, yielding ~37% and ~85% for transitions with heavy and
light holes states, respectively. The spin lifetime of holes at the top of the
valence band is found to be ~0.5 ps and it is governed by transitions between
heavy and light hole states. Electrons at the bottom of the conduction band, on
the other hand, have a spin lifetime that exceeds 5 ns below 150 K. Theoretical
analysis of the electrons spin relaxation indicates that phonon-induced
intervalley scattering dictates the spin lifetime.",1111.5209v1
2011-12-21,Direct detection of magnon spin transport by the inverse spin Hall effect,"Conversion of traveling magnons into an electron carried spin current is
demonstrated in a time resolved experiment using a spatially separated
inductive spin-wave source and an inverse spin Hall effect (ISHE) detector. A
short spin-wave packet is excited in a yttrium-iron garnet (YIG) waveguide by a
microwave signal and is detected at a distance of 3 mm by an attached Pt layer
as a delayed ISHE voltage pulse. The delay in the detection appears due to the
finite spin-wave group velocity and proves the magnon spin transport. The
experiment suggests utilization of spin waves for the information transfer over
macroscopic distances in spintronic devices and circuits.",1112.4969v1
2013-04-02,Nonlocal spin correlations mediated by a superconductor,"Nonlocal charge correlations induced in two normal metals contacted
separately to a supercon- ductor have been studied intensively in the past few
years. Here we investigate nonlocal correlations induced by the transfer of
pure spin currents through a superconductor on a scale comparable to the
superconducting coherence length. As with charge currents, two processes
contribute to the nonlocal spin signal: crossed Andreev reflection (CAR), where
an electron with spin up injected from one normal metal into the superconductor
results in a hole with spin down being injected into the second normal metal,
and elastic cotunneling (EC), where the electron with spin up injected from the
first normal metal results in an electron with spin up being injected into the
second normal metal. Unlike charge currents, however, the spin currents
associated with CAR and EC add due to the fact that the bulk superconductor
cannot sustain a net spin current.",1304.0669v1
2013-10-22,Conduction of spin currents through insulating oxides,"Spintronics is a field of electronics based on using the electron spin
instead of its charge. The recent advance in the manipulation of pure spin
currents, i.e. angular momentum transfer not associated to conventional charge
currents, has opened new opportunities to build spin based devices with low
energy consumption. It has also allowed to integrate ferromagnetic insulators
in spintronic devices, either as spin sources or spin conductors using their
magnetic excitations to propagate a spin signal. Antiferromagnetic insulators
belong to another class of materials that can also sustain magnetic
excitations, even with a higher group velocity. Hence, they have potential as
angular momentum conductors, possibly making faster spin devices. At the
opposite end, angular momentum insulators are also required in spintronic
circuits. The present letter underlines some essential features relevant for
spin current conduction, based on measurements of angular momentum transmission
in antiferromagnetic NiO and in the non-magnetic light element insulator
SiO$_2$.",1310.6000v1
2015-09-04,Spin frustration and fermionic entanglement in an exactly solved hybrid diamond chain with the localized Ising spins and mobile electrons,"The strongly correlated spin-electron system on a diamond chain containing
localized Ising spins on its nodal lattice sites and mobile electrons on its
interstitial sites is exactly solved in a magnetic field using the
transfer-matrix method. We have investigated in detail all available ground
states, the magnetization processes, the spin-spin correlation functions around
an elementary plaquette, fermionic quantum concurrence and spin frustration. It
is shown that the fermionic entanglement between mobile electrons hopping on
interstitial sites and the kinetically-induced spin frustration are closely
related yet independent phenomena. In the ground state, quantum entanglement
only appears within a frustrated unsaturated paramagnetic phase, while thermal
fluctuations can promote some degree of quantum entanglement above the
non-frustrated ground states with saturated paramagnetic or classical
ferrimagnetic spin arrangements.",1509.01639v1
2017-01-28,Magnetic Domain Walls as Hosts of Spin Superfluids and Generators of Skyrmions,"A domain wall in a magnet with easy-axis anisotropy is shown to harbor spin
superfluid associated with its spontaneous breaking of the U(1) spin-rotational
symmetry. The spin superfluid is shown to have several topological properties,
which are absent in conventional superfluids. First, the associated phase slips
create and destroy skyrmions to obey the conservation of the total skyrmion
charge, which allows us to use a domain wall as a generator and detector of
skyrmions. Secondly, the domain wall engenders the emergent magnetic flux for
magnons along its length, which are proportional to the spin supercurrent
flowing through it, and thereby provides a way to manipulate magnons. Thirdly,
the spin supercurrent can be driven by the magnon current traveling across it
owing to the spin transfer between the domain wall and magnons, leading to the
magnonic manipulation of the spin superfluid. The theory for superfluid spin
transport within the domain wall is confirmed by numerical simulations.",1701.08273v2
2018-07-24,Symmetry Restoration in Mixed-Spin Paired Heavy Nuclei,"The nature of the nuclear pairing condensates in heavy nuclei, specifically
neutron-proton (spin-triplet), versus identical-particle (spin-singlet) pairing
has been an active area of research for quite some time. In this work, we probe
three candidates that should display spin-triplet, spin-singlet, and mixed-spin
pairing. Using theoretical approaches such as the gradient method and symmetry
restoration techniques, we find the ground state of these nuclei in
Hartree-Fock-Bogoliubov theory and compute ground-state to ground-state
pair-transfer amplitudes to neighbouring isotopes while simultaneously
projecting to specific particle number and nuclear spin values. We identify
specific reactions for future experimental research that could shed light on
spin-triplet and mixed-spin pairing.",1807.09294v2
2019-02-08,Initialization and Readout of Nuclear Spins via negatively charged Silicon-Vacancy Center in Diamond,"In this work, we demonstrate initialization and readout of nuclear spins via
a negatively charged silicon-vacancy (SiV) electron spin qubit. Under
Hartmann-Hahn conditions the electron spin polarization is coherently
transferred to the nuclear spin. The readout of the nuclear polarization is
observed via the fluorescence of the SiV. We also show that the coherence time
of the nuclear spin (6 ms) is limited by the electron spin-lattice relaxation
due to the hyperfine coupling to the electron spin. This work paves the way
towards realization of building blocks of quantum hardware with an efficient
spin-photon interface based on the SiV color center coupled to a long lasting
nuclear memory.",1902.02965v3
2019-08-22,Conditional Teleportation of Quantum-Dot Spin States,"Among the different platforms for quantum information processing, individual
electron spins in semiconductor quantum dots stand out for their long coherence
times and potential for scalable fabrication. The past years have witnessed
substantial progress in the capabilities of spin qubits. However, coupling
between distant electron spins, which is required for quantum error correction,
presents a challenge, and this goal remains the focus of intense research.
Quantum teleportation is a canonical method to transmit qubit states, but it
has not been implemented in quantum-dot spin qubits. Here, we present evidence
for quantum teleportation of electron spin qubits in semiconductor quantum
dots. Although we have not performed quantum state tomography to definitively
assess the teleportation fidelity, our data are consistent with conditional
teleportation of spin eigenstates, entanglement swapping, and gate
teleportation. Such evidence for all-matter spin-state teleportation
underscores the capabilities of exchange-coupled spin qubits for
quantum-information transfer.",1908.08306v2
2019-10-18,Focusing on the dynamics of the entanglement in spin junction,"We study the dynamics of entanglement in the one-dimensional spin-1/2 XY
model in the presence of a transverse magnetic field. A pair of spins are
considered as an open quantum system, while the rest of the chain plays the
role of the environment. Our study focuses on the pair of spins in the system,
the edge spins, and the environment. It is observed that the entanglement
between the pair of spins in the system decreases and it can transfer to the
rest of the spins. For a value of anisotropy leading to the Ising model, the
entanglement is completely back to the system by passing time. On the other
hand, the entanglement can only be seen under certain conditions between edge
spins of the system and the environment. The pair of spins on the edge will be
entangled very quickly and it will disappear after a very short time. A pair of
spins far from the system was chosen to examine the behavior of entanglement in
the environment. As expected, the transmission of entanglement from the system
to the environment takes notable time.",1910.08633v1
2020-04-03,Spin-Excitations Anisotropy in the Bilayer Iron-Based Superconductor CaKFe$_4$As$_4$,"We use polarized inelastic neutron scattering to study the spin-excitations
anisotropy in the bilayer iron-based superconductor CaKFe$_4$As$_4$ ($T_c$ = 35
K). In the superconducting state, both odd and even $L-$modulations of spin
resonance have been observed in our previous unpolarized neutron scattering
experiments (T. Xie {\it et al.} Phys. Rev. Lett. {\bf 120}, 267003 (2018)).
Here we find that the high-energy even mode ($\sim 18$ meV) is isotropic in
spin space, but the low-energy odd modes consist of a $c-$axis polarized mode
around 9 meV along with another partially overlapped in-plane mode around 12
meV. We argue that such spin anisotropy is induced by the spin-orbit coupling
in the spin-vortex-type fluctuations of this unique compound. The spin
anisotropy is strongly affected by the superconductivity, where it is weak
below 6 meV in the normal state and then transferred to higher energy and
further enhanced in the odd mode of spin resonance below $T_c$.",2004.01405v1
2020-10-26,Quantum repeaters based on individual electron spins and nuclear-spin-ensemble memories in quantum dots,"Inspired by recent developments in the control and manipulation of quantum
dot nuclear spins, which allow for the transfer of an electron spin state to
the surrounding nuclear-spin ensemble for storage, we propose a quantum
repeater scheme that combines individual quantum dot electron spins and
nuclear-spin ensembles, which serve as spin-photon interfaces and quantum
memories respectively. We consider the use of low-strain quantum dots embedded
in high-cooperativity optical microcavities. Quantum dot nuclear-spin ensembles
allow for the long-term storage of entangled states, and heralded entanglement
swapping is performed using cavity-assisted gates. We highlight the advances in
quantum dot technologies required to realize our quantum repeater scheme which
promises the establishment of high-fidelity entanglement over long distances
with a distribution rate exceeding that of the direct transmission of photons.",2010.13863v4
2020-11-03,Intensity equations for birefringent spin lasers,"Semiconductor spin lasers are distinguished from their conventional
counterparts by the presence of spin-polarized carriers. The transfer of
angular momentum of the spin-polarized carriers to photons provides important
opportunities for the operation of lasers. With the injection of spin-polarized
carriers, which lead to the circularly polarized light, the polarization of the
emitted light can be changed an order of magnitude faster than its intensity.
This ultrafast operation of spin lasers relies on a large birefringence,
usually viewed as detrimental in spin and conventional lasers. We introduce a
transparent description of spin lasers using intensity equations, which
elucidate the influence of birefringence on the intensity and polarization
modulation of lasers. While intensity modulation is independent of
birefringence, for polarization modulation an increase in birefringence
directly increases the resonant frequency. Our results for dynamical operation
of lasers provide a guide for their spin-dependent response and spintronic
applications beyond magnetoresistance.",2011.01486v1
2021-06-04,Insights on the coupling between vibronically active molecular vibrations and lattice phonons in molecular nanomagnets,"Spin-lattice relaxation is a key open problem to understand the spin dynamics
of single-molecule magnets and molecular spin qubits. While modelling the
coupling between spin states and local vibrations allows to determine the more
relevant molecular vibrations for spin relaxation, this is not sufficient to
explain how energy is dissipated towards the thermal bath. Herein, we employ a
simple and efficient model to examine the coupling of local vibrational modes
with long-wavelength longitudinal and transverse phonons in the clock-like spin
qubit [Ho(W$_5$O$_{18}$)$_2$]$^{9-}$. We find that in crystals of this
polyoxometalate the vibrational mode previously found to be vibronically active
at low temperature does not couple significantly to lattice phonons. This means
that further intramolecular energy transfer via anharmonic vibrations is
necessary for spin relaxation in this system. Finally, we discuss implications
for the spin-phonon coupling of [Ho(W$_5$O$_{18}$)$_2$]$^{9-}$ deposited on a
MgO (001) substrate, offering a simple methodology that can be extrapolated to
estimate the effects on spin relaxation of different surfaces, including 2D
materials.",2106.02611v1
2021-06-09,Chiral control of quantum states in non-Hermitian spin-orbit-coupled fermions,"Spin-orbit coupling is an essential mechanism underlying quantum phenomena
such as the spin Hall effect and topological insulators. It has been widely
studied in well-isolated Hermitian systems, but much less is known about the
role dissipation plays in spin-orbit-coupled systems. Here, we implement
dissipative spin-orbit-coupled bands filled with ultracold fermions, and
observe parity-time symmetry breaking as a result of the competition between
the spin-orbit coupling and dissipation. Tunable dissipation, introduced by
state-selective atom loss, enables us to tune the energy gap and close it at
the critical dissipation value, the so-called exceptional point. In the
vicinity of the critical point, the state evolution exhibits a chiral response,
which enables us to tune the spin-orbit coupling and dissipation dynamically,
revealing topologically robust chiral spin transfer when the quantum state
encircles the exceptional point. This demonstrates that we can explore
non-Hermitian topological states with spin-orbit coupling.",2106.04874v2
2022-03-27,Creating quantum spin chains through edge reconstruction in pure graphene armchair nanoribbons towards ballistic spin transport,"It is well-known that ferromagnetism can be realized along the zigzag
graphene nanoribbon edges, but the armchair graphene nanoribbon edges (AGNEs)
are nonmagnetic. Here, we achieve Heisenberg antiferromagnetic spin chains
through edge reconstruction along the AGNEs. The reconstructed edge consists of
pentagonal carbon rings or a hybrid of pentagonal and hexagonal carbon rings.
The resultant nanoribbons are narrow-gap semiconductors and the band edge
states are either spin-degenerate edge states or nonmagnetic bulk states. The
spin is located on the outermost carbon of the pentagonal ring, and the
inter-spin exchange is the nearest-neighbor antiferromagnetic interaction. For
finite chain lengthes or nonzero magnetization, there are nonzero spin Drude
weights and thus ballistic quantum spin transport can be achieved along the
reconstructed edges, These could be used for quantum spin information transfer
and spintronic applications.",2203.14288v1
2023-08-01,Ultrafast magnetization enhancement and spin current injection in magnetic multilayers by exciting the nonmagnetic metal,"A systematic investigation of spin injection behavior in Au/FM (FM = Fe and
Ni) multilayers is performed using the superdiffusive spin transport theory. By
exciting the nonmagnetic layer, the laser-induced hot electrons may transfer
spin angular momentum into the adjacent ferromagnetic (FM) metals resulting in
ultrafast demagnetization or enhancement. We find that these experimental
phenomena sensitively depend on the particular interface reflectivity of hot
electrons and may reconcile the different observations in experiment.
Stimulated by the ultrafast spin currents carried by the hot electrons, we
propose the multilayer structures to generate highly spin polarized currents
for development of future ultrafast spintronics devices. The spin polarization
of the electric currents carried by the hot electrons can be significantly
enhanced by the joint effects of bulk and interfacial spin filtering. Meanwhile
the intensity of the generated spin current can be optimized by varying the
number of repeated stacking units and the thickness of each metallic layer.",2308.00427v1
2023-08-14,Converting a triplet Cooper pair supercurrent into a spin-signal,"Superconductivity with spin-polarized Cooper pairs is known to emerge by
combining conventional spinless superconductors with materials that have
spin-dependent interactions, such as magnetism and spin-orbit coupling. This
enables a dissipationless and conserved flow of spin. However, actually
utilizing the spin-polarization of such supercurrents have proven challenging.
Here, we predict an experimental signature of current-carrying triplet Cooper
pairs in the form of an induced spin-signal. We show that a supercurrent
carried only by triplet Cooper pairs induces a non-local magnetization that is
controlled by the polarization direction of the triplet Cooper pairs. This
provides a measurement protocol to directly use the spin-polarization of the
triplet Cooper pairs in supercurrents to transfer spin information in a
dissipationless manner.",2308.07226v1
2023-09-29,Effect of irradiation on the spin of millisecond pulsars,"A millisecond pulsar (MSP) is an old neutron star (NS) that has accreted
material from its companion star, causing it to spin up, which is known as the
recycling scenario. During the mass transfer phase, the system manifests itself
as an X-ray binary. PSR J1402+13 is an MSP with a spin period of $5.89~{\rm
ms}$ and a spin period derivative of $\log\dot{P}_{\rm spin}=-16.32$. These
properties make it a notable object within the pulsar population, as MSPs
typically exhibit low spin period derivatives. In this paper, we aim to explain
how an MSP can posses high spin period derivative by binary evolution. By
utilizing the stellar evolution code \textsc{MESA}, we examine the effects of
irradiation on the companion star and the propeller effect on the NS during
binary evolution. We demonstrate that irradiation can modify the spin period
and mass of an MSP, resulting in a higher spin period derivative. These results
suggest that the irradiation effect may serve as a key factor in explaining
MSPs with high spin period derivatives.",2309.16963v1
2024-04-09,Hydrostatic pressure control of the spin-orbit proximity effect and spin relaxation in a phosphorene-WSe$_2$ heterostructure,"Effective control of interlayer interactions is a key element in modifying
the properties of van der Waals heterostructures and the next step toward their
practical applications. Focusing on the phosphorene-WSe$_2$ heterostructure, we
demonstrate, using first-principles calculations, how the spin-orbit coupling
can be transferred from WSe$_2$, a strong spin-orbit coupling material, to
phosphorene and further amplified by applying vertical pressure. We simulate
external pressure by changing the interlayer distance between bilayer
constituents and show that it is possible to tune the spin-orbit field of
phosphorene holes in a controllable way. By fitting effective electronic states
of the proposed Hamiltonian to the first principles data, we reveal that the
spin-orbit coupling in phosphorene hole bands is enhanced more than two times
for experimentally accessible pressures up to 17 kbar. Finally, we find that
the pressure-enhanced spin-orbit coupling boosts the Dyakonov-Perel spin
relaxation mechanism, reducing the spin lifetime of phosphorene holes by factor
4.",2404.06097v1
2006-09-11,Effect of light Sr doping on the spin-state transition in LaCoO_3,"We present an inelastic neutron scattering study of the low energy
crystal-field excitations in the lightly doped cobalt perovskite
La_0.998Sr_0.002CoO_3. In contrast to the parent compound LaCoO_3 an inelastic
peak at energy transfer ~0.75 meV was found at temperatures below 30 K. This
excitation apparently corresponds to a transition between a ground state
orbital singlet and a higher excited orbital doublet, originating from a
high-spin triplet split by a small trigonal crystal field. Another inelastic
peak at an energy transfer ~0.6 meV was found at intermediate temperatures
starting from T > 30 K. This confirms the presence of a thermally induced
spin-state transition from the low-spin Co^3+ to a magnetic high-spin state in
the non-disturbed LaCoO_3 matrix. We suggest that hole doping of LaCoO_3 leads
to the creation of a magnetic polaron and hence to the low-to-high spin state
transition on the relevant Co sites.",0609247v1
2002-12-06,Quantum Communication Through an Unmodulated Spin Chain,"We propose a scheme for using an unmodulated and unmeasured spin-chain as a
channel for short distance quantum communications. The state to be transmitted
is placed on one spin of the chain and received later on a distant spin with
some fidelity. We first obtain simple expressions for the fidelity of quantum
state transfer and the amount of entanglement sharable between any two sites of
an arbitrary Heisenberg ferromagnet using our scheme. We then apply this to the
realizable case of an open ended chain with nearest neighbor interactions. The
fidelity of quantum state transfer is obtained as an inverse discrete cosine
transform and as a Bessel function series. We find that in a reasonable time, a
qubit can be directly transmitted with better than classical fidelity across
the full length of chains of up to 80 spins. Moreover, the spin-chain channel
allows distillable entanglement to be shared over arbitrarily large distances.",0212041v2
2008-02-08,Quantum Communication through Spin Chain Dynamics: an Introductory Overview,"We present an introductory overview of the use of spin chains as quantum
wires, which has recently developed into a topic of lively interest. The
principal motivation is in connecting quantum registers without resorting to
optics. A spin chain is a permanently coupled 1D system of spins. When one
places a quantum state on one end of it, the state will be dynamically
transmitted to the other end with some efficiency if the spins are coupled by
an exchange interaction. No external modulations or measurements on the body of
the chain, except perhaps at the very ends, is required for this purpose. For
the simplest (uniformly coupled) chain and the simplest encoding (single qubit
encoding), however, dispersion reduces the quality of transfer. We present a
variety of alternatives proposed by various groups to achieve perfect quantum
state transfer through spin chains. We conclude with a brief discussion of the
various directions in which the topic is developing.",0802.1224v1
2012-05-31,"Response functions of cold neutron matter: density, spin and current fluctuations","We study the response of a single-component pair-correlated baryonic
Fermi-liquid to density, spin, and their current perturbations. A complete set
of response functions is derived in the low-temperature regime both within an
effective theory based on a small momentum transfer expansion and within a
numerical scheme valid for arbitrary momentum transfers. A comparison of these
two approaches validates the perturbative approximation within the domain of
its convergence. We derive the spectral functions of collective excitations
associated with the density, density-current, spin, and spin-current
perturbations. The dispersion relations of density and spin fluctuations are
derived and it is shown that the density fluctuations lead to exciton-like
undamped bound states, whereas the spin excitations correspond to diffusive
modes above the pair-breaking threshold. The contribution of the collective
pair-breaking modes to the specific heat of neutron matter at subnuclear
densities is computed and is shown to be comparable to that of the degenerate
electron gas at not too low temperatures.",1205.6902v2
2013-12-06,Spin-transfer assisted thermally activated switching distributions in perpendicularly magnetized spin valve nanopillars,"We present switching field distributions of spin-transfer assisted
magnetization reversal in perpendicularly magnetized Co/Ni multilayer
spin-valve nanopillars at room temperature. Switching field measurements of the
Co/Ni free layer of spin-valve nanopillars with a 50 nm x 300 nm ellipse cross
section were conducted as a function of current. The validity of a model that
assumes a spin-current dependent effective barrier for thermally activated
reversal is tested by measuring switching field distributions under applied
direct currents. We show that the switching field distributions deviate
significantly from the double exponential shape predicted by the effective
barrier model, beginning at applied currents as low as half of the zero field
critical current. Barrier heights extracted from switching field distributions
for currents below this threshold are a monotonic function of the current.
However, the thermally-induced switching model breaks down for currents
exceeding the critical threshold.",1312.1994v1
2016-02-29,Clocked single-spin source based on a spin-split superconductor,"We propose an accurate clocked single-spin source for ac-spintronic
applications. Our device consists of a superconducting island covered by a
ferromagnetic insulator layer through which it is coupled to superconducting
leads. Single-particle transfer relies on the energy gaps and the island's
charging energy, and is enabled by a bias and a time-periodic gate voltage.
Accurate spin transfer is achieved by the ferromagnetic insulator layer which
polarizes the island, provides spin-selective tunneling barriers and improves
the precision by suppressing Andreev reflection. We analyze realistic material
combinations and experimental requirements which allow for a clocked spin
current in the MHz regime.",1602.09068v3
2017-10-23,Frequency and wavenumber selective excitation of spin waves through coherent energy transfer from elastic waves,"Using spin-wave tomography (SWaT), we have investigated the excitation and
the propagation dynamics of optically-excited magnetoelastic waves, i.e.
hybridized modes of spin waves and elastic waves, in a garnet film. By using
time-resolved SWaT, we reveal the excitation dynamics of magnetoelastic waves
through coherent-energy transfer between optically-excited pure-elastic waves
and spin waves via magnetoelastic coupling. This process realizes frequency and
wavenumber selective excitation of spin waves at the crossing of the dispersion
relations of spin waves and elastic waves. Finally, we demonstrate that the
excitation mechanism of the optically-excited pure-elastic waves, which are the
source of the observed magnetoelastic waves, is dissipative in nature.",1710.08087v2
2019-10-22,Electron spin relaxation in radical pairs: Beyond the Redfield approximation,"Relaxation processes can have a large effect on the spin selective electron
transfer reactions of radical pairs. These processes are often treated using
phenomenological relaxation superoperators or with some model for the
microscopic relaxation mechanism treated within Bloch-Redfield-Wangsness
theory. Here, we demonstrate that an alternative perturbative relaxation
theory, based on the Nakajima-Zwanzig equation, has certain advantages over
Redfield theory. In particular, the Nakajima-Zwanzig equation does not suffer
from the severe positivity problem of Redfield theory in the static disorder
limit. Combining the Nakajima-Zwanzig approach consistently with the
Schulten-Wolynes semiclassical method, we obtain an efficient method for
modeling the spin dynamics of radical pairs containing many hyperfine-coupled
nuclear spins. This is then used to investigate the spin-dependent electron
transfer reactions and intersystem crossing of
dimethyljulolidine-naphthalenediimide (DMJ-NDI) radical ion pairs. By comparing
our simulations with experimental data, we find evidence for a
field-independent contribution to the triplet quantum yields of these reactions
which cannot be explained by electron spin relaxation alone.",1910.09870v1
2022-01-04,Enhanced coupling of electron and nuclear spins by quantum tunneling resonances,"Noble-gas spins feature hours long coherence times owing to their great
isolation from the environment, and find practical usage in various
applications. However, this isolation leads to extremely slow preparation
times, relying on weak spin transfer from an electron-spin ensemble. Here we
propose a controllable mechanism to enhance this transfer rate. We analyze the
spin dynamics of helium-3 atoms with hot, optically-excited potassium atoms and
reveal the formation of quasi-bound states in resonant binary collisions. We
find a resonant enhancement of the spin-exchange cross section by up to six
orders of magnitude and two orders of magnitude enhancement for the thermally
averaged, polarization rate-coefficient. We further examine the effect for
various other noble gases and find that the enhancement is universal. We
outline feasible conditions under which the enhancement may be experimentally
observed and practically utilized.",2201.01255v1
2022-01-23,Measurement of longitudinal spin transfer of the $Λ(\barΛ)$ hyperon in polarized p+p collisions at $\sqrt{s}=200$ GeV at RHIC-STAR,"Since the first surprising results on the spin structure of the proton by the
EMC experiment in the late 1980s, much progress has been made in understanding
the origin of the proton spin. However, the sea quark contribution to the
proton spin, for example, the helicity distributions of the strange quark
(anti-quark), $s(\bar{s})$, is still not well constrained by experimental data.
Since the $s(\bar{s})$ is expected to carry a substantial fraction of the spin
of the $\Lambda(\bar{\Lambda})$ hyperon, measurements of the longitudinal spin
transfer, $D_{LL}$, of the $\Lambda(\bar{\Lambda}$) hyperon can thus shed light
on the helicity distribution of the $s(\bar{s})$ and the longitudinally
polarized fragmentation functions. In these proceedings, we will present the
status of the $\Lambda(\bar{\Lambda}$) $D_{LL}$ analysis using data collected
at RHIC-STAR in 2015, for the pseudo-rapidity $|\eta| < 1.2$ and transverse
momenta up to $8.0$ GeV$/c$. The $D_{LL}$ as a function of the longitudinal
momentum fraction of the $\Lambda(\bar{\Lambda})$ hyperon in the jet is also
investigated. This data set is about twice as large as the 2009 data used for
the previously published $D_{LL}$ results.",2201.09218v1
2023-01-08,"Chiral anomalies in 3D spin-orbit coupled metals: electrical, thermal, and gravitational anomaly","The discovery of a chiral anomaly in Weyl semimetals, the non-conservation of
chiral charge and energy across two opposite chirality Weyl nodes, has sparked
immense interest in understanding its impact on various physical phenomena.
Here, we demonstrate the existence of electrical, thermal, and gravitational
quantum chiral anomalies in 3D spin-orbit coupled systems. Notably, these
anomalies involve chiral charge transfer across two Fermi surfaces linked to a
single Weyl-like point, rather than across opposite chirality Weyl nodes as in
Weyl semimetals. Our findings reveal that the Berry curvature flux piercing the
Fermi surface plays a critical role in distinguishing the `chirality' of the
carriers and the corresponding chiral charge and energy transfer. Importantly,
we demonstrate that these quantum chiral anomalies lead to interesting thermal
spin transport such as the spin Nernst effect. Our results suggest that 3D
spin-orbit coupled metals offer a promising platform for investigating the
interplay between quantum chiral anomalies and charge and spin transport in
non-relativistic systems.",2301.02965v1
2023-08-18,Suppression of Pulsed Dynamic Nuclear Polarization by Many-Body Spin Dynamics,"We study a mechanism by which nuclear hyperpolarization due to the
polarization transfer from a microwave-pulse-controlled electron spin is
suppressed. From analytical and numerical calculations of the unitary dynamics
of multiple nuclear spins, we uncover that, combined with the formation of the
dark state within a cluster of nuclei, coherent higher-order nuclear spin
dynamics impose limits on the efficiency of the polarization transfer even in
the absence of mundane depolarization processes such as nuclear spin diffusion
and relaxation. Furthermore, we show that the influence of the dark state can
be partly mitigated by introducing a disentangling operation. Our analysis is
applied to the nuclear polarizations observed in $^{13}$C nuclei coupled with a
single nitrogen-vacancy center in diamond [Science 374, 1474 (2021) by J.
Randall et al.]. Our work sheds light on collective engineering of nuclear
spins as well as future designs of pulsed dynamic nuclear polarization
protocols.",2308.09272v1
2023-11-06,Direct Observation of Chirality-Induced Spin Selectivity in Electron Donor-Acceptor Molecules,"The role of chirality in determining the spin dynamics of photoinduced
electron transfer in donor-acceptor molecules remains an open question.
Although chirality-induced spin selectivity (CISS) has been demonstrated in
molecules bound to substrates, experimental information about whether this
process influences spin dynamics in the molecules themselves is lacking. Here
we use time-resolved electron paramagnetic resonance spectroscopy to show that
CISS strongly influences the spin dynamics of isolated covalent donor-chiral
bridge-acceptor (D-B$\chi$-A) molecules in which selective photoexcitation of D
is followed by two rapid, sequential electron transfer events to yield
D$^+$-B$\chi$-A$^-$. Exploiting this phenomenon affords the possibility of
using chiral molecular building blocks to control electron spin states in
quantum information applications.",2311.03599v1
2024-02-02,Theory of acoustic-phonon involved exciton spin flip in perovskite semiconductors,"We present a theory of the acoustic phonon assisted spin-flip Raman
scattering (SFRS), or resonant photoluminescence with the spin flip of a
photoexcited exciton localized in a bulk cubic-phase perovskite semiconductor.
We consider the spin-flip transitions between the ground-state exciton spin
sublevels in external magnetic field B and discuss the variation of their
probability rate and polarization selection rules with the increase of B. The
transitions are treated as two-quantum processes with the virtual to and fro
transfer of the electron in the electron-hole pair between the bottom and first
excited conduction bands. The transfer occurs due to both the electron-hole
exchange interaction and the electron-phonon interaction. The theoretical
results allow one to distinguish the phonon assisted Raman scattering from (a)
the resonant Raman scattering with the combined spin flip of the localized
resident electron and hole and (b) the biexciton-mediated SFRS analyzed
previously.",2402.01556v1
2020-12-23,Maximising Dynamic Nuclear Polarisation via Selective Hyperfine Tuning,"Dynamic nuclear polarisation (DNP) refers to a class of techniques used to
increase the signal in nuclear magnetic resonance measurements by transferring
spin polarisation from ensembles of highly polarised electrons to target
nuclear analytes. These techniques, however, require the application of strong
magnetic fields to maximise electron spin polarisation, limiting pathways for
electron-nuclear (hyperfine) spin coupling and transfer. In this work we show
that, for systems of electronic spin $S\geq1$ possessing an intrinsic
zero-field splitting, a separate class of stronger hyperfine interactions based
on lab-frame cross relaxation may be utilised to improve DNP efficiency and
yield, whilst operating at moderate fields. We analytically review existing
methods, and determine that this approach increases the rate of polarisation
transfer to the nuclear ensemble by up to an order of magnitude over existing
techniques. This result is demonstrated experimentally at room temperature
using the optically polarisable $S=1$ electron spin system of the nitrogen
vacancy (NV) defect in diamond as the source of electron spin polarisation.
Finally we assess the utility of these NV-based approaches for the polarisation
of macroscopic quantities of molecular spins external to the diamond for NMR
and MRI applications.",2012.12508v1
2023-08-31,Resonance contributions to nucleon spin structure in Holographic QCD,"We study polarized inelastic electron-nucleon scattering at low momentum
transfer in the Witten-Sakai-Sugimoto model of holographic QCD, focusing on
resonance production contributions to the nucleon spin structure functions. Our
analysis includes both spin $3/2$ and spin $1/2$ low-lying nucleon resonances
with positive and negative parity. We determine, in turn, the helicity
amplitudes for nucleon-resonance transitions and the resonance contributions to
the neutron and proton generalized spin polarizabilities. Extrapolating the
model parameters to realistic QCD data, our analysis, triggered by recent
experimental results from Jefferson Lab, agrees with the observation that the
$\Delta(1232)$ resonance gives the dominant contribution to the forward spin
polarizabilities at low momentum transfer. The contribution is negative and
tends to zero as the momentum transfer increases. As expected, the contribution
of the $\Delta(1232)$ to the longitudinal-transverse polarizabilities is
instead negligible. The latter, for both nucleons, turn out the be negative
functions with zero asymptote. The holographic results, at least for the proton
where enough data are available, are in qualitative agreement with the
resonance contributions to the spin polarizabilities extracted from
experimental data on the helicity amplitudes.",2308.16833v2
2024-03-25,Stellar Spin Down in Post-Mass Transfer Binary Systems,"Motivated by measurements of the rotation speed of accretor stars in
post-mass-transfer (post-MT) systems, we investigate how magnetic braking
affects the spin-down of individual stars during binary evolution with the
\texttt{MESAbinary} module. Unlike the conventional assumption of tidal
synchronization coupled with magnetic braking in binaries, we first calculate
whether tides are strong enough to synchronize the orbit. Subsequently, this
influences the spin-down of stars and the orbital separation. In this study, we
apply four magnetic braking prescriptions to reduce the spin angular momentum
of the two stars throughout the entire binary evolution simulation. Our
findings reveal that despite magnetic braking causing continuous spin-down of
the accretor, when the donor begins to transfer material onto the accretor, the
accretor can rapidly spin up to its critical rotation rate. After MT, magnetic
braking becomes more important in affecting the angular momentum evolution of
the stars. Post-MT accretor stars thus serve as a valuable testbed for
observing how the magnetic braking prescriptions operate in spinning down stars
from their critical rotation, including the saturation regimes of the magnetic
braking. The rotation rate of the accretor star, combined with its mass, could
provide age information since the cessation of MT. By comparing the models
against observation, the magnetic braking prescription by Garraffo et al.
(2018b) is found to better align with the rotation data of post-MT accretors.",2403.17279v1
2008-03-13,Solid state quantum memory using the 31P nuclear spin,"The transfer of information between different physical forms is a central
theme in communication and computation, for example between processing entities
and memory. Nowhere is this more crucial than in quantum computation, where
great effort must be taken to protect the integrity of a fragile quantum bit.
Nuclear spins are known to benefit from long coherence times compared to
electron spins, but are slow to manipulate and suffer from weak thermal
polarisation. A powerful model for quantum computation is thus one in which
electron spins are used for processing and readout while nuclear spins are used
for storage. Here we demonstrate the coherent transfer of a superposition state
in an electron spin 'processing' qubit to a nuclear spin 'memory' qubit, using
a combination of microwave and radiofrequency pulses applied to 31P donors in
an isotopically pure 28Si crystal. The electron spin state can be stored in the
nuclear spin on a timescale that is long compared with the electron decoherence
time and then coherently transferred back to the electron spin, thus
demonstrating the 31P nuclear spin as a solid-state quantum memory. The overall
store/readout fidelity is about 90%, attributed to systematic imperfections in
radiofrequency pulses which can be improved through the use of composite
pulses. We apply dynamic decoupling to protect the nuclear spin quantum memory
element from sources of decoherence. The coherence lifetime of the quantum
memory element is found to exceed one second at 5.5K.",0803.2021v2
2003-04-11,"Spin Photocurrents in Quantum Wells review part I, (part II: cond-mat/one of the next numbers)","Spin photocurrents generated by homogeneous optical excitation with
circularly polarized radiation in quantum wells (QWs) are reviewed. The
absorption of circularly polarized light results in optical spin orientation
due to the transfer of the angular momentum of photons to electrons of a
two-dimensional electron gas (2DEG). It is shown that in quantum wells
belonging to one of the gyrotropic crystal classes a non-equilibrium spin
polarization of uniformly distributed electrons causes a directed motion of
electron in the plane of the QW. A characteristic feature of this electric
current, which occurs in unbiased samples, is that it reverses its direction
upon changing the radiation helicity from left-handed to right-handed and vice
versa.
  Two microscopic mechanisms are responsible for the occurrence of an electric
current linked to a uniform spin polarization in a QW: the spin polarization
induced circular photogalvanic effect and the spin-galvanic effect. In both
effects the current flow is driven by an asymmetric distribution of spin
polarized carriers in k-space of systems with lifted spin degeneracy due to
k-linear terms in the Hamiltonian. Spin photocurrents provide methods to
investigate spin relaxation and to conclude on the in-plane symmetry of QWs.
The effect can also be utilized to develop fast detectors to determine the
degree of circular polarization of a radiation beam. Furthermore spin
photocurrents at infrared excitation were used to demonstrate and investigate
monopolar spin orientation of free carriers.",0304266v1
2003-04-11,"Spin Photocurrents in Quantum Wells review part II, (part I: cond-mat/0304266)","Spin photocurrents generated by homogeneous optical excitation with
circularly polarized radiation in quantum wells (QWs) are reviewed. The
absorption of circularly polarized light results in optical spin orientation
due to the transfer of the angular momentum of photons to electrons of a
two-dimensional electron gas (2DEG). It is shown that in quantum wells
belonging to one of the gyrotropic crystal classes a non-equilibrium spin
polarization of uniformly distributed electrons causes a directed motion of
electron in the plane of the QW. A characteristic feature of this electric
current, which occurs in unbiased samples, is that it reverses its direction
upon changing the radiation helicity from left-handed to right-handed and vice
versa.
  Two microscopic mechanisms are responsible for the occurrence of an electric
current linked to a uniform spin polarization in a QW: the spin polarization
induced circular photogalvanic effect and the spin-galvanic effect. In both
effects the current flow is driven by an asymmetric distribution of spin
polarized carriers in k-space of systems with lifted spin degeneracy due to
k-linear terms in the Hamiltonian. Spin photocurrents provide methods to
investigate spin relaxation and to conclude on the in-plane symmetry of QWs.
The effect can also be utilized to develop fast detectors to determine the
degree of circular polarization of a radiation beam. Furthermore spin
photocurrents at infrared excitation were used to demonstrate and investigate
monopolar spin orientation of free carriers.",0304268v1
2004-07-09,Thermal transport in antiferromagnetic spin-chain materials,"We study the problem of heat transport in one-dimensional (1D) spin-chain
systems weakly coupled to three-dimensional phonons and impurities. We consider
the limit of fast spin excitations and slow phonons, applicable to a number of
compounds of the cuprates family, such as Sr2CuO3, where the superexchange J is
much larger than the Debye energy. In this case the Umklapp scattering among
the spin excitations is strongly suppressed for all relevant temperatures. We
argue that the leading scattering mechanism for the spin excitations at not too
low temperatures is the ""normal"" (as opposed to the Umklapp) spin-phonon
scattering in which the non-equilibrium momentum is transferred from the spin
subsystem to phonons where it quickly relaxes through the ""phonon bath"".
Because of the lower dimensionality of the spin excitations it is only the
momentum along the chains which is conserved in such a scattering. We find that
this effect leads to a particular momentum- and temperature-dependence of the
spin-phonon relaxation rate valid for the broad class of low-dimensional spin
systems. Subsequently we demonstrate that the spin-phonon relaxation mechanism
is insufficient for the low-energy, long-wavelength 1D spin-chain excitations,
which make the thermal conductivity diverge. We complete our consideration by
taking into account the impurity scattering, which in 1D cuts off the
quasi-ballistic spin excitations and renders the thermal conductivity finite.
Our results compare very well with the existing experimental data for Sr2CuO3.
Using our microscopic insight into the problem we propose further experiments
and predict an unusual impurity concentration dependence for a number of
quantities.",0407257v3
2004-11-28,Parity and spin of the $Θ^+$ pentaquark in the $NN\to YΘ^+$ reaction at the threshold,"Spin observables of a binary reaction $1+2\to 3+4$ are discussed at the
threshold in general form using P-parity and angular momentum conservation.
General formulae for polarization transfer, spin-spin correlation parameters in
the initial and final states and induced tensor polarization are derived for
arbitrary spins of participating particles. This formalism is worked out in
detail for the $NN\to Y\Theta^+$ reaction. Assuming that the spin of the
pentaquark $\Theta^+$ takes the values 1/2, 3/2 and 5/2, whereas the spin of
the hyperon $Y$ equals 1/2, explicite formulae are obtained for the observables
in terms of few non-vanishing at the threshold spin amplitudes separately for
the spin-singlet and spin-triplet initial NN states. In case of all particles
in the $NN\to Y\Theta^+$ reaction have the spin-1/2 a full spin-structure for
totally polarized cross sections is derived. Some of the obtained spin
observables strongly depend on the intrinsic P-parity of the $\Theta^+$ and the
total isospin of the reaction. Therefore, a measurement of these observables
allows one to determine the P-parity of the pentaquark $\Theta^+$ in a model
independent way for any spin of the $\Theta^+$.",0411113v2
2015-03-05,Spin and charge transport in graphene-based spin transport devices with Co/MgO spin injection and spin detection electrodes,"In this review we discuss spin and charge transport properties in
graphene-based single-layer and few-layer spin-valve devices. We give an
overview of challenges and recent advances in the field of device fabrication
and discuss two of our fabrication methods in more detail which result in
distinctly different device performances. In the first class of devices, Co/MgO
electrodes are directly deposited onto graphene which results in rough
MgO-to-Co interfaces and favor the formation of conducting pinholes throughout
the MgO layer. We show that the contact resistance area product (R$_c$A) is a
benchmark for spin transport properties as it scales with the measured spin
lifetime in these devices indicating that contact-induced spin dephasing is the
bottleneck for spin transport even in devices with large R$_c$A values. In a
second class of devices, Co/MgO electrodes are first patterned onto a silicon
substrate. Subsequently, a graphene-hBN heterostructure is directly transferred
onto these prepatterned electrodes which provides improved interface
properties. This is seen by a strong enhancement of both charge and spin
transport properties yielding charge carrier mobilities exceeding 20000
cm$^2$/(Vs) and spin lifetimes up to 3.7 ns at room temperature. We discuss
several shortcomings in the determination of both quantities which complicates
the analysis of both extrinsic and intrinsic spin scattering mechanisms.
Furthermore, we show that contacts can be the origin of a second charge
neutrality point in gate dependent resistance measurements which is influenced
by the quantum capacitance of the underlying graphene layer.",1503.01735v2
2019-07-11,Spin-orbit coupling in elemental two-dimensional materials,"The fundamental spin-orbit coupling and spin mixing in graphene and rippled
honeycomb lattice materials silicene, germanene, stanene, blue phosphorene,
arsenene, antimonene, and bismuthene is investigated from first principles. The
intrinsic spin-orbit coupling in graphene is revisited using multi-band $k\cdot
p$ theory, showing the presence of non-zero spin mixing in graphene despite the
mirror symmetry. However, the spin mixing itself does not lead to the the
Elliott-Yafet spin relaxation mechanism, unless the mirror symmetry is broken
by external factors. For other aforementioned elemental materials we present
the spin-orbit splittings at relevant symmetry points, as well as the spin
admixture $b^2$ as a function of energy close to the band extrema or Fermi
levels. We find that spin-orbit coupling scales as the square of the atomic
number Z, as expected for valence electrons in atoms. For isolated bands, it is
found that $b^2\sim Z^4$. The spin-mixing parameter also exhibits giant
anisotropy which, to a large extent, can be controlled by tuning the Fermi
level. Our results for $b^2$ can be directly transferred to spin relaxation
time due to the Elliott-Yafet mechanism, and therefore provide an estimate of
the upper limit for spin lifetimes in materials with space inversion center.",1907.05152v1
2020-05-08,$s$-$d$ model for local and nonlocal spin dynamics in laser-excited magnetic heterostructures,"We discuss a joint microscopic theory for the laser-induced magnetization
dynamics and spin transport in magnetic heterostructures based on the $s$-$d$
interaction. Angular momentum transfer is mediated by scattering of itinerant
$s$ electrons with the localized ($d$ electron) spins. We use the corresponding
rate equations and focus on a spin one-half $d$ electron system, leading to a
simplified analytical expression for the dynamics of the local magnetization
that is coupled to an equation for the non-equilibrium spin accumulation of the
$s$ electrons. We show that this description converges to the microscopic
three-temperature model in the limit of a strong $s$-$d$ coupling. The equation
for the spin accumulation is used to introduce diffusive spin transport. The
presented numerical solutions show that during the laser-induced
demagnetization in a ferromagnetic metal a short-lived spin accumulation is
created that counteracts the demagnetization process. Moreover, the spin
accumulation leads to the generation of a spin current at the interface of a
ferromagnetic and non-magnetic metal. Depending on the specific magnetic
system, both local spin dissipation and interfacial spin transport are able to
enhance the demagnetization rate by providing relaxation channels for the spin
accumulation that is build up during demagnetization in the ferromagnetic
material.",2005.03905v2
1995-11-29,Spin effects in hard exclusive reactions,"The present status of applications of perturbative QCD to large momentum
transfer exclusive reactions is discussed. It is argued that in the region of
momentum transfer accessible to present day experiments soft contributions
dominate the exclusive processes.",9511452v1
2001-11-13,Polarization transfer in SIDIS for Lambda production,"Polarization transfer from the longitudinally polarized positron to the
final-state quark is considered for the underlying QCD subprocesses giving rise
to the reaction e+(pol) + p --> e+ + Lambda(pol) + X at the HERMES energy.",0111106v1
2008-02-27,A deeper insight into quantum state transfer from an information flux viewpoint,"We use the recently introduced concept of information flux in a many-body
register in order to give an alternative viewpoint on quantum state transfer in
linear chains of many spins.",0802.3980v2
2005-09-04,Sum Rules and Moments of the Nucleon Spin Structure Functions,"The nucleon has been used as a laboratory to investigate its own spin
structure and Quantum Chromodynamics. New experimental data on nucleon spin
structure at low to intermediate momentum transfers combined with existing high
momentum transfer data offer a comprehensive picture of the transition region
from the {\it confinement} regime of the theory to its {\it asymptotic freedom}
regime. Insight for some aspects of the theory is gained by exploring lower
moments of spin structure functions and their corresponding sum rules (i.e. the
Gerasimov-Drell-Hearn, Bjorken and Burkhardt-Cottingham). These moments are
expressed in terms of an operator product expansion using quark and gluon
degrees of freedom at moderately large momentum transfers. The sum rules are
verified to a good accuracy assuming that no singular behavior of the structure
functions is present at very high excitation energies. The higher twist
contributions have been examined through the moments evolution as the moments
evolution as the momentum transfer varies from higher to lower values.
Furthermore, QCD-inspired low-energy effective theories, which explicitly
include chiral symmetry breaking, are tested at low momentum transfers. The
validity of these theories is further examined as the momentum transfer
increases to moderate values. It is found that chiral perturbation calculations
agree reasonably well with the first moment of the spin structure function
$g_1$ at momentum transfer of 0.1 GeV$^2$ but fail to reproduce the neutron
data in the case of the generalized polarizability $\delta_{LT}$.",0509007v3
2010-01-21,Moments of Spin Structure Functions: Sum Rules and Polarizabilities,"Nucleon structure study is one of the most important research areas in modern
physics and has challenged us for decades. Spin has played an essential role
and often brought surprises and puzzles to the investigation of the nucleon
structure and the strong interaction. New experimental data on nucleon spin
structure at low to intermediate momentum transfers combined with existing high
momentum transfer data offer a comprehensive picture in the strong region of
the interaction and of the transition region from the strong to the
asymptotic-free region. Insight for some aspects of the theory for the strong
interaction, Quantum Chromodynamics (QCD), is gained by exploring lower moments
of spin structure functions and their corresponding sum rules. These moments
are expressed in terms of an operator-product expansion using quark and gluon
degrees of freedom at moderately large momentum transfers. The higher-twist
contributions have been examined through the evolution of these moments as the
momentum transfer varies from higher to lower values. Furthermore, QCD-inspired
low-energy effective theories, which explicitly include chiral symmetry
breaking, are tested at low momentum transfers. The validity of these theories
is further examined as the momentum transfer increases to moderate values. It
is found that chiral perturbation theory calculations agree reasonably well
with the first moment of the spin structure function g_1 at low momentum
transfer of 0.05 - 0.1 GeV^2 but fail to reproduce some of the higher moments,
noticeably, the neutron data in the case of the generalized polarizability
Delta_LT. The Burkhardt-Cottingham sum rule has been verified with good
accuracy in a wide range of Q^2 assuming that no singular behavior of the
structure functions is present at very high excitation energies.",1001.3898v1
2005-01-21,Sporadically Torqued Accretion Disks Around Black Holes,"The assumption that black hole accretion disks possess an untorqued inner
boundary, the so-called zero torque boundary condition, has been employed by
models of black hole disks for many years. However, recent theoretical and
observational work suggests that magnetic forces may appreciably torque the
inner disk. This raises the question of the effect that a time-changing
magnetic torque may have on the evolution of such a disk. In particular, we
explore the suggestion that the ``Deep Minimum State'' of the Seyfert galaxy
MCG--6-30-15 can be identified as a sporadic inner disk torquing event. This
suggestion is motivated by detailed analyses of changes in the profile of the
broad fluorescence iron line in XMM-Newton spectra. We find that the response
of such a disk to a torquing event has two phases; an initial damming of the
accretion flow together with a partial draining of the disk interior to the
torque location, followed by a replenishment of the inner disk as the system
achieves a new (torqued) steady-state. If the Deep Minimum State of
MCG--6-30-15 is indeed due to a sporadic torquing event, we show that the
fraction of the dissipated energy going into X-rays must be smaller in the
torqued state. We propose one such scenario in which Compton cooling of the
disk corona by ``returning radiation'' accompanying a central-torquing event
suppresses the 0.5-10 keV X-ray flux coming from all but the innermost regions
of the disk.",0501455v2
2023-08-03,Gravitational torque in circumbinary discs: global radial oscillations,"Circumbinary discs (CBDs) arise in many astrophysical settings, including
young stellar binaries and supermassive black hole binaries. Their structure is
mediated by gravitational torques exerted on the disc by the central binary.
The spatial distribution of the binary torque density (so-called excitation
torque density) in CBDs is known to feature global large-amplitude,
quasi-periodic oscillations, which are often interpreted in terms of the local
resonant Lindblad torques. Here we investigate the nature of these torque
oscillations using 2D, inviscid hydrodynamic simulations and theoretical
calculations. We show that torque oscillations arise due to the gravitational
coupling of the binary potential to the density waves launched near the inner
cavity and freely propagating out in the disc. We provide analytical
predictions for the radial periodicity of the torque density oscillations and
verify them with simulations, showing that disc sound speed and the
multiplicity of the density wave spiral arms are the key factors setting the
radial structure of the oscillations. Resonant Lindblad torques play no direct
role in determining the radial structure and periodicity of the torque
oscillations and manifest themselves only by driving the density waves in the
disc. We also find that vortices forming at the inner edge of the disc can
provide a non-trivial contribution to the angular momentum transport in the
CBD. Our results can be applied to understanding torque behaviour in other
settings, e.g. discs in cataclysmic variables and X-ray binaries.",2308.01967v1
1999-05-18,First-Principles Calculations of Hyperfine Interactions in La_2CuO_4,"We present the results of first-principles cluster calculations of the
electronic structure of La_2CuO_4. Several clusters containing up to nine
copper atoms embedded in a background potential were investigated.
Spin-polarized calculations were performed both at the Hartree-Fock level and
with density functional methods with generalized gradient corrections to the
local density approximation. The distinct results for the electronic structure
obtained with these two methods are discussed. The dependence of the
electric-field gradients at the Cu and the O sites on the cluster size is
studied and the results are compared to experiments. The magnetic hyperfine
coupling parameters are carefully examined. Special attention is given to a
quantitative determination of on-site and transferred hyperfine fields. We
provide a detailed analysis that compares the hyperfine fields obtained for
various cluster sizes with results from additional calculations of spin states
with different multiplicities. From this we conclude that hyperfine couplings
are mainly transferred from nearest neighbor Cu^{2+} ions and that
contributions from further distant neighbors are marginal. The mechanisms
giving rise to transfer of spin density are worked out. Assuming conventional
values for the spin-orbit coupling, the total calculated hyperfine interaction
parameters are compared to informations from experiments.",9905246v1
2001-09-05,Construction of some missing eigenvectors of the XYZ spin chain at the discrete coupling constants and the exponentially large spectral degeneracy of the transfer matrix,"We discuss an algebraic method for constructing eigenvectors of the transfer
matrix of the eight vertex model at the discrete coupling parameters. We
consider the algebraic Bethe ansatz of the elliptic quantum group $E_{\tau,
\eta}(sl_2)$ for the case where the parameter $\eta$ satisfies $2 N \eta = m_1
+ m_2 \tau $ for arbitrary integers $N$, $m_1$ and $m_2$. When $m_1$ or $m_2$
is odd, the eigenvectors thus obtained have not been discussed previously.
Furthermore, we construct a family of degenerate eigenvectors of the XYZ spin
chain, some of which are shown to be related to the $sl_2$ loop algebra
symmetry of the XXZ spin chain. We show that the dimension of some degenerate
eigenspace of the XYZ spin chain on $L$ sites is given by $N 2^{L/N}$, if $L/N$
is an even integer. The construction of eigenvectors of the transfer matrices
of some related IRF models is also discussed.",0109078v4
2004-11-04,Frequency Modulation of Spin-Transfer Oscillators,"Spin-polarized dc electric current flowing into a magnetic layer can induce
precession of the magnetization at a frequency that depends on current. We show
that addition of an ac current to this dc bias current results in a frequency
modulated (FM) spectral output, generating sidebands spaced at the modulation
frequency. The sideband amplitudes and shift of the center frequency with drive
amplitude are in good agreement with a nonlinear FM model that takes into
account the nonlinear frequency-current relation generally induced by spin
transfer. Single-domain simulations show that ac current modulates the cone
angle of the magnetization precession, in turn modulating the frequency via the
demagnetizing field. These results are promising for communications and signal
processing applications of spin-transfer oscillators.",0411114v1
2006-09-01,Spin momentum transfer and Oersted field induce a vortex nano-oscillator in thin ferromagnetic film devices,"A nonlinear model of spin-wave excitation involving a point contact in a thin
ferromagnetic film that includes the Oersted magnetic field contribution is
presented. We consider the case of an external dc field applied perpendicular
to the film plane. The two-dimensional vectorial model reduces to an exact
one-dimensional equation of motion. Large-amplitude vortex modes are computed,
which represent a fundamental shift in the geometrical understanding of spin
transfer nano-oscillators. Odd symmetry forces the magnetization to be pinned
in the center of the point contact. Using the spin transfer efficiency as a
single fitting parameter, the calculated dependence of frequency on current and
contact size is in good agreement with recent experimental data. These vortex
states are geometrically very different from previously computed cylindrical
modes that exhibit even symmetry when the Oersted field is ignored.",0609030v2
2004-06-15,Conclusive and arbitrarily perfect quantum state transfer using parallel spin chain channels,"We suggest a protocol for perfect quantum communication through spin chain
channels. By combining a dual-rail encoding with measurements only at the
receiving end, we can get conclusively perfect state transfer, whose
probability of success can be made arbitrarily close to unity. As an example of
such an amplitude delaying channel, we show how two parallel Heisenberg spin
chains can be used as quantum wires. Perfect state transfer with a probability
of failure lower than P in a Heisenberg chain of N spin-1/2 particles can be
achieved in a timescale of the order of N^1.7|ln(P)|. We demonstrate that our
scheme is more robust to decoherence and non-optimal timing than any scheme
using single spin chains.",0406112v4
2005-02-23,From perfect to fractal transmission in spin chains,"Perfect state transfer is possible in modulated spin chains, imperfections
however are likely to corrupt the state transfer. We study the robustness of
this quantum communication protocol in the presence of disorder both in the
exchange couplings between the spins and in the local magnetic field. The
degradation of the fidelity can be suitably expressed, as a function of the
level of imperfection and the length of the chain, in a scaling form. In
addition the time signal of fidelity becomes fractal. We further characterize
the state transfer by analyzing the spectral properties of the Hamiltonian of
the spin chain.",0502148v2
2008-08-04,Measuring entropy generated by spin-transfer,"An experimental protocol is presented that allows the entropy generated by
spin-transfer to be measured. The effect of a strong spin-polarized current
injected on a ferromagnetic nanostructure is investigated with focusing on the
quasi-static equilibrium states of a ferromagnetic single domain. The samples
are single contacted Ni nanowires obtained by electrodeposition in a nanoporous
template. The thermal susceptibility of the magnetoresistance is measured as a
function of the magnetic field for different values of the current injected
through the wire. This quantity is related to the thermal magnetic
susceptibility of the ferromagnetic wire through the anisotropic
magnetoresistance. The ferromagnetic entropy generated by the current injection
is deduced thanks to a thermodynamic Maxwell relation. This study shows that
the effect of the spin-transfer in our samples results in the generation of
incoherent excitations instead of rotation of the magnetization.",0808.0463v1
2010-11-09,Periodic Ising Correlations,"In this paper, we first rework B. Kaufman's 1949 paper, ""Crystal Statistics.
II. Partition Function Evaluated by Spinor Analysis"", by using representation
theory. Our approach leads to a simpler and more direct way of deriving the
spectrum of the transfer matrix for the finite periodic Ising model. We then
determine formulas for the spin correlation functions that depend on the matrix
elements of the induced rotation associated with the spin operator in a basis
of eigenvectors for the transfer matrix. The representation of the spin matrix
elements is obtained by considering the spin operator as an intertwining map.
We exhibit the ""new"" elements V+ and V- in the Bugrij-Lisovyy formula as part
of a holomorphic factorization of the periodic and anti-periodic summability
kernels on the spectral curve associated with the induced rotation for the
transfer matrix.",1011.2223v1
2010-11-11,Robust Quantum State Transfer in Random Unpolarized Spin Chains,"We propose and analyze a new approach for quantum state transfer between
remote spin qubits. Specifically, we demonstrate that coherent quantum coupling
between remote qubits can be achieved via certain classes of random,
unpolarized (infinite temperature) spin chains. Our method is robust to
coupling strength disorder and does not require manipulation or control over
individual spins. In principle, it can be used to attain perfect state transfer
over arbitrarily long range via purely Hamiltonian evolution and may be
particularly applicable in a solid-state quantum information processor. As an
example, we demonstrate that it can be used to attain strong coherent coupling
between Nitrogen-Vacancy centers separated by micrometer distances at room
temperature. Realistic imperfections and decoherence effects are analyzed.",1011.2762v2
2011-02-03,Heisenberg Spin Bus as a Robust Transmission Line for Perfect State Transfer,"We study the protocol known as quantum state transfer for a strongly coupled
antiferromagnetic spin chain or ring (acting as a spin bus), with weakly
coupled external qubits. By treating the weak coupling as a perturbation, we
find that perfect state transfer (PST) is possible when second order terms are
included in the expansion. We also show that PST is robust against variations
in the couplings along the spin bus and between the bus and the qubits. As
evidence of the quantum interference which mediates PST, we show that the
optimal time for PST can be smaller with larger qubit separations, for an
even-size chain or ring.",1102.0762v1
2011-03-09,Interstitial iron tuning of the spin fluctuations in Fe1+xTe,"Using neutron inelastic scattering, we investigate the low-energy spin
fluctuations in Fe1+xTe as a function of both temperature and interstitial iron
concentration. For Fe1.057(7)Te the magnetic structure is defined by a
commensurate wavevector of (1/2,0,1/2). The spin fluctuations are gapped with a
sharp onset at 7 meV and are three dimensional in momentum transfer, becoming
two dimensional at higher energy transfers. On doping with interstitial iron,
we find in Fe1.141(5)Te the ordering wavevector is located at the (0.38, 0,
1/2) position and the fluctuations are gapless with the intensity peaked at an
energy transfer of 4 meV. These results show that the spin fluctuations in the
Fe1+xTe system a can be tuned not only through selenium doping, but also with
interstitial iron. We also compare these results with superconducting
concentrations and in particular the resonance mode in the Fe_1+xTe_1-ySe_y
system.",1103.1811v2
2011-10-17,Topologically Protected Quantum State Transfer in a Chiral Spin Liquid,"Topology plays a central role in ensuring the robustness of a wide variety of
physical phenomena. Notable examples range from the robust current carrying
edge states associated with the quantum Hall and the quantum spin Hall effects
to proposals involving topologically protected quantum memory and quantum logic
operations. Here, we propose and analyze a topologically protected channel for
the transfer of quantum states between remote quantum nodes. In our approach,
state transfer is mediated by the edge mode of a chiral spin liquid. We
demonstrate that the proposed method is intrinsically robust to realistic
imperfections associated with disorder and decoherence. Possible experimental
implementations and applications to the detection and characterization of spin
liquid phases are discussed.",1110.3788v1
2011-12-14,Classical tau-function for quantum spin chains,"For an arbitrary generalized quantum integrable spin chain we introduce a
""master T -operator"" which represents a generating function for commuting
quantum transfer matrices constructed by means of the fusion procedure in the
auxiliary space.
  We show that the functional relations for the transfer matrices are
equivalent to an infinite set of model-independent bilinear equations of the
Hirota form for the master T -operator, which allows one to identify it with
{\tau}-function of an integrable hierarchy of classical soliton equations.
  In this paper we consider spin chains with rational GL(N)-invariant
R-matrices but the result is independent of a particular functional form of the
transfer matrices and directly applies to quantum integrable models with more
general (trigonometric and elliptic) R-matrices and to supersymmetric spin
chains.",1112.3310v2
2013-02-03,"Spectral non-uniform temperature, non-local heat transfer, and the spin Seebeck effect","We present a theory of the spin Seebeck effect driven by subthermal non-local
phonon heat transfer and spectral non-uniform temperature distribution. The
theory explains the non-local behavior of the effect arising from the fact that
phonons that store the energy (thermal) and the phonons that transfer it
(subthermal) are located in different parts of the spectrum and have very
different kinetics. This gives rise to a spectral phonon distribution function
that deviates from local equilibrium along the substrate and is sensitive to
boundary conditions. The theory also predicts a non-magnon origin of the effect
in ferromagnetic metals in agreement with observations in recent experiments.
Equilibration of the heat flow out of the substrate to the Pt probe and
backwards leads to a measurable vertical spin-current produced by the spin
polarized electrons dragged by the local thermal phonons. We predict specific
sample length limits and other dependencies that can be probed experimentally,
and obtain the correct magnitude of the effect.",1302.0499v1
2013-03-18,Non-Markovian spin transfer dynamics in magnetic semiconductors despite short memory times,"A quantum kinetic theory of the spin transfer between carriers and Mn atoms
in a Mn doped diluted magnetic semiconductor is presented. It turns out that
the typical memory time associated with these processes is orders of magnitude
shorter than the time scale of the spin transfer. Nevertheless, Markovian rate
equations, which are obtained by neglecting the memory, work well only for bulk
systems. For quantum wells and wires the quantum kinetic results qualitatively
deviate from the Markovian limit under certain conditions. Instead of a
monotonic decay of an initially prepared excess electron spin, an overshoot or
even coherent oscillations are found. It is demonstrated that these features
are caused by energetic redistributions of the carriers due to the energy-time
uncertainty.",1303.4322v1
2013-03-22,Ultralow-current-density and bias-field-free spin-transfer nano-oscillator,"The spin-transfer nano-oscillator (STNO) offers the possibility of using the
transfer of spin angular momentum via spin-polarized currents to generate
microwave signals. However, at present STNO microwave emission mainly relies on
both large drive currents and external magnetic fields. These issues hinder the
implementation of STNOs for practical applications in terms of power
dissipation and size. Here, we report microwave measurements on STNOs built
with MgO-based magnetic tunnel junctions having a planar polarizer and a
perpendicular free layer, where microwave emission with large output power,
excited at ultralow current densities, and in the absence of any bias magnetic
fields is observed. The measured critical current density is over one order of
magnitude smaller than previously reported. These results suggest the
possibility of improved integration of STNOs with complementary
metal-oxide-semiconductor technology, and could represent a new route for the
development of the next-generation of on-chip oscillators.",1303.5562v1
2013-07-12,Noise to lubricate qubit transfer in a spin network,"We consider quantum state transfer in a fully connected spin network, in
which the results indicate that it is impossible to achieve high fidelity by
free dynamics. However, the addition of certain kinds of noise can be helpful
for this purpose. In fact, we introduce a model of Gaussian white noise
affecting the spin-spin couplings (edges), except those linked to the input and
output node, and prove that it enhances the fidelity of state transfer. The
observed noise benefit is scale free as it applies to a quantum network of any
size. The amount of the fidelity enhancement, depending on the noise strength
as well as on the number of edges to which it is applied, can be so high as to
take the fidelity close to one.",1307.3465v2
2015-07-02,"Unnatural-parity (p,p') reactions in a factorized impulse-approximation model for polarization transfer and spin responses","Linear combinations $D_K$ of the complete polarization-transfer observables,
Dij, in the (p,p') reaction at intermediate energies are demonstrated. A
comparison between systematized measured and calculated values of the
combinations $D_K$ for the $1^+$ (T = 0 and T = 1) levels in $^{12}$C, for the
$4^-$ (T = 0 and T = 1) states in $^{16}$O, and for the $6^-$ (T = 0 and T = 1)
levels in $^{28}$Si are reported. Particularities in angular distributions of
transverse- and longitudinal-spin-transfer probabilities, $D_K$, for the T = 0
and T = 1 unnatural-parity states in the indicated nuclei are discussed. The
spin-observable combinations Dls allowed to differentiate reliably the strength
of the isoscalar and isovector spin-orbit interactions. The comparison of
experimental $D_K$ and calculated $D_K$ with the use of zero-range treatment
(LEA code) and exact finite-range calculations (DWBA-91 program) made it
possible to identify the role of exchange contributions.",1507.00468v1
2015-09-15,Spin-polarized Voltages on a 2D Self-assembled Plasmonic Crystal,"The Photon Drag Effect (PDE) is a nonlinear process akin to optical
rectification in which the momentum of light is transferred to charged carriers
and converted to a DC voltage. Here, we experimentally demonstrate the
spin-polarized voltage, associated with the transference of light's spin
angular momenta to the linear momenta of charges, with visible-light
illumination on a nanovoid self-assembled plasmonic crystal surface. Numerical
calculations show that the gradient force, generally considered independent of
polarization, is responsible for the majority of the momentum transfer. The PDE
in this achiral system represents a distinct spin-orbit interaction that
produces asymmetric hotspots whose locations change with circular polarization
handedness. Our results significantly advance our understanding of the PDE and
demonstrate realistic potential for scalable plasmonic materials that utilize
PDE.",1509.04739v1
2017-03-11,Approach to Dark Spin Cooling in a Diamond Nanocrystal,"Using a Hartman-Hahn protocol, we demonstrate spin polarization transfer from
a single, optically-polarized nitrogen-vacancy (NV) center to the ensemble of
paramagnetic defects hosted by an individual diamond nanocrystal. Owing to the
strong NV-bath coupling, the transfer takes place on a short, microsecond time
scale. Upon fast repetition of the pulse sequence we observe strong
polarization transfer blockade, which we interpret as an indication of spin
bath cooling. Numerical simulations indicate that the spin bath polarization is
non-uniform throughout the nanoparticle averaging approximately 5% over the
crystal volume, but reaching up to 25% in the immediate vicinity of the NV.
These observations may prove relevant to the planning of future bath-assisted
magnetometry tests.",1703.03988v1
2017-09-19,Considering non-uniform current distributions in magnetoresistive sensor designs and their implications for the resistance transfer function,"Non-uniform current distributions of spin valves with disk shaped free layers
are investigated. In the context of spin valves, the vortex state, which is the
ground-state in many disk shaped magnetic bodies, allows for distinct parallel
channels of high and low resistivity. The readout current is thus able to evade
high resistivity regions in favor of low resistivity regions, giving rise to
'conductive inhomogeneities'. Therefore, the total resistance of the spin valve
does not always correspond exactly to the total average magnetization of the
free layer. In addition, the resistance transfer function can be significantly
influenced by the spatial placement of the electrodes, giving rise to
'geometric inhomogeneities'. The resulting deviations from resistance to
magnetization transfer function are investigated for different spin valve
geometries and compared to measurements of comparable devices.",1709.06394v1
2018-01-10,Quantum state transfer in spin chains via shortcuts to adiabaticity,"Based on shortcuts to adiabaticity and quantum Zeno dynamics, we present a
protocol to implement quantum state transfer (QST) in a quantum spin-1/2 chain.
In the protocol, the complex Hamiltonian of an $N$-site system is simplified,
and a simple effective Hamiltonian is present. It is shown that only the
control of the coupling strengths between the boundary spins and the bulk spins
are required for QST. Numerical simulations demonstrate that the protocol
possesses high efficiency and is robust against the decay and the fluctuations
of the control fields. The protocol might provide an alternative choice for
transferring quantum states via spin chain systems.",1801.03330v1
2019-04-02,Direct evidence for efficient ultrafast charge separation in epitaxial WS$_2$/graphene heterostructure,"We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to
investigate ultrafast charge transfer in an epitaxial heterostructure made of
monolayer WS$_2$ and graphene. This heterostructure combines the benefits of a
direct gap semiconductor with strong spin-orbit coupling and strong
light-matter interaction with those of a semimetal hosting massless carriers
with extremely high mobility and long spin lifetimes. We find that, after
photoexcitation at resonance to the A-exciton in WS$_2$, the photoexcited holes
rapidly transfer into the graphene layer while the photoexcited electrons
remain in the WS$_2$ layer. The resulting charge transfer state is found to
have a lifetime of $\sim1$\,ps. We attribute our findings to differences in
scattering phase space caused by the relative alignment of WS$_2$ and graphene
bands as revealed by high resolution ARPES. In combination with spin-selective
excitation using circularly polarized light the investigated WS$_2$/graphene
heterostructure might provide a new platform for efficient optical spin
injection into graphene.",1904.01379v1
2021-06-15,Experimental confirmation of the delayed Ni demagnetization in FeNi alloy,"Element-selective techniques are central for the understanding of ultrafast
spin dynamics in multi-element materials like magnetic alloys. Recently,
though, it turned out that the commonly used technique of transverse
magneto-optical Kerr effect (T-MOKE) in the EUV range may have linearity issues
including unwanted cross talk between different elemental signals. This problem
can be sizeable, which puts recent observations of ultrafast spin transfer from
Fe to Ni sites in FeNi alloys into question. In this study, we investigate the
Fe-to-Ni spin transfer in a cross-talk-free time-resolved X-ray magnetic
circular dichroism (XMCD) experiment with a reliable time reference. We find a
very similar Fe and Ni dynamics with XMCD as with T-MOKE from identical
samples. Considering the non-linearities of the T-MOKE response, the agreement
with our findings appears fortuitous. We discuss possible reasons why T-MOKE
seems to give accurate results in this case. Our data provide the ongoing
discussion about ultrafast spin-transfer mechanisms in FeNi systems with a
sound experimental basis.",2106.07956v1
2022-02-15,Electron Transfer and Spin-Orbit Coupling: How Strong are Berry Force Effects In and Out of Equilibrium in the Presence of Nuclear Friction?,"We investigate a spin-boson inspired model of electron transfer, where the
diabatic coupling is given by a position-dependent phase, exp(iWx). We consider
both equilibrium and nonequilibrium initial conditions. We show that, for this
model, all equilibrium results are completely invariant to the sign of W(to
infinite order). However, the nonequilibrium results do depend on the sign of
W, suggesting that photo-induced electron transfer dynamics are meaningfully
affected by Berry forces even in the presence of nuclear friction; furthermore,
whenever there is spin-orbit coupling, electronic spin polarization can emerge
(at least for some time).",2202.07204v1
2022-03-21,A Unified Description for Polarization-Transfer Mechanisms in Magnetic Resonance in Static Solids: Cross Polarization and DNP,"Polarization transfers are crucial building blocks in magnetic resonance
experiments, i.e., they can be used to polarize insensitive nuclei and
correlate nuclear spins in multidimensional NMR spectroscopy. The polarization
can be transferred either across different nuclear spin species or from
electron spins to the relatively low-polarized nuclear spins. The former route
occurring in solid-state NMR (ssNMR) can be performed via cross polarization
(CP), while the latter route is known as dynamic nuclear polarization (DNP).
Despite having different operating conditions, we opinionate that both
mechanisms are theoretically similar processes in ideal conditions, i.e., the
electron is merely another spin-1/2 particle with a much higher gyromagnetic
ratio. Here, we show that the CP and DNP processes can be described using a
unified theory based on average Hamiltonian theory (AHT) combined with
fictitious operators. The intuitive and unified approach has allowed new
insights on the cross effect (CE) DNP mechanism, leading to better design of
DNP polarizing agents and extending the applications beyond just
hyperpolarization. We explore the possibility of exploiting theoretically
predicted DNP transients for electron-nucleus distance measurements--like
routine dipolar-recoupling experiments in solid-state NMR.",2203.11339v1
2022-10-12,Quantum amplification of spin currents in cavity magnonics by a parametric drive induced long-lived mode,"Cavity-mediated magnon-magnon coupling can lead to a transfer of spin-wave
excitations between two spatially separated magnetic samples. We enunciate how
the application of a two-photon parametric drive to the cavity can lead to
stark amplification in this transfer efficiency. The recurrent multiphoton
absorption by the cavity opens up an infinite ladder of accessible energy
levels, which can induce higher-order transitions within the magnon Fock space.
This is reflected in a heightened spin-current response from one of the
magnetic samples when the neighboring sample is coherently pumped. The
enhancement induced by the parametric drive can be considerably high within the
stable dynamical region. Specifically, near the periphery of the stability
boundary, the spin current is amplified by several orders of magnitude. Such
striking enhancement factors are attributed to the emergence of parametrically
induced strong coherences precipitated by a long-lived mode. While
contextualized in magnonics, the generality of the principle would allow
applications to energy transfer between systems contained in parametric
cavities.",2210.05898v1
2023-03-29,Dynamical criticality of magnetization transfer in integrable spin chains,"Recent studies have found that fluctuations of magnetization transfer in
integrable spin chains violate the central limit property. Here we revisit the
problem of anomalous counting statistics in the Landau-Lifshitz field theory by
specializing to two distinct anomalous regimes featuring a dynamical critical
point. By performing optimized numerical simulations using an integrable
space-time discretization we extract the algebraic growth exponents of
time-dependent cumulants which attain their threshold values. The distinctly
non-Gaussian statistics of magnetization transfer in the easy-axis regime is
found to converge towards the universal distribution of charged single-file
systems. At the isotropic point we infer a weakly non-Gaussian distribution,
corroborating the view that superdiffusive spin transport in integrable spin
chains does not belong to any known dynamical universality class.",2303.16691v5
2023-04-27,Enhancing polarization transfer from nitrogen-vacancy centers in diamond to external nuclear spins via dangling bond mediators,"The use of nitrogen-vacancy centers in diamond as a non-invasive platform for
hyperpolarizing nuclear spins in molecular samples is a promising area of
research with the potential to enhance the sensitivity of nuclear magnetic
resonance experiments. Transferring NV polarization out of the diamond
structure has been achieved on nanoscale targets using dynamical nuclear
polarization methods, but extending this to relevant NMR volumes poses
significant challenges. One major technical hurdle is the presence of
paramagnetic defects in the diamond surface which can interfere with
polarization outflow. However, these defects can also be harnessed as
intermediaries for the interaction between NVs and nuclear spins. We present a
method that benefits from existing microwave sequences, namely the PulsePol, to
transfer polarization efficiently and robustly using dangling bonds or other
localized electronic spins, with the potential to increase polarization rates
under realistic conditions.",2304.14282v3
1996-02-20,On the Nature of the Bursting X-Ray Pulsar GRO J1744-28,"The unusual properties of the bursting X-ray pulsar GRO J1744-28 are
explained in terms of a low-mass X-ray binary system consisting of an evolved
stellar companion transferring mass through Roche-lobe overflow onto a neutron
star, implying that the inclination of the system is < 18 degrees.
Interpretation of the QPO at frequency nu(QPO) = 40 Hz using the beat-frequency
model of Alpar \& Shaham and the measured period derivative with the Ghosh \&
Lamb accretion-torque model implies that the persistent X-ray luminosity of the
source is approximately equal to the Eddington luminosity and that the neutron
star has a surface equatorial magnetic field = 2e10 [40 Hz/nu(QPO)] G for
standard neutron star parameters. This implies a distance to GRO J1744-28 of ~
5 [nu(QPO)/40 Hz]^{1/6} b^{1/2} kpc, where b < 1 is a correction factor that
depends on the orientation of the neutron star.",9602102v2
2002-03-27,Formation of Galactic Disks,"We review progress in understanding the formation of galactic disks in the
standard cosmogonic scenario involving gravitational clustering of baryons and
dark matter and dissipative collapse of the baryons. This scenario accounts
remarkably well for the observed properties of galactic disks if they have
retained most of the specific angular momentum they acquired by tidal torques.
Early simulations, which included cooling of the gas but not star formation and
the associated feedback, indicated instead that most of the angular momentum of
the baryons would be transferred to the dark matter. Recent simulations
indicate that this angular-momentum problem can be solved partially, and in
some cases entirely, by feedback and other effects.",0203492v1
2002-08-28,Magnetic Fields via Polarimetry: Progress of Grain Alignment Theory,"Most astrophysical systems, e.g. stellar winds, the diffuse interstellar
medium, molecular clouds, are magnetized with magnetic fields that influence
almost all of their properties. One of the most informative techniques of
magnetic field studies is based on the use of starlight polarization and
polarized emission arising from aligned dust. How reliable the interpretation
of the polarization maps in terms of magnetic fields is the issue that the
grain alignment theory addresses. Although grain alignment is a problem of half
a century standing, recent progress achieved in the field makes us believe that
we are approaching the solution of this mystery. I review basic physical
processes involved in grain alignment and discuss the niches for different
alignment mechanisms. I show why mechanisms that were favored for decades do
not look so promising right now, while the radiative torque mechanism ignored
for more than 20 years looks so attractive. I define the observational tests
and outline the circumstances when grain alignment theory predicts that new yet
untapped information of magnetic field structure is available through
polarimetry. In particular, I touch upon mapping magnetic fields in
circumstellar regions, interplanetary space and in comet comae.",0208487v1
2005-08-08,The Progenitor Stars of Gamma-Ray Bursts,"Those massive stars that, during their deaths, give rise to gamma-ray bursts
(GRBs) must be endowed with an unusually large amount of angular momentum in
their inner regions, one to two orders of magnitude greater than the ones that
make common pulsars. Yet the inclusion of mass loss and angular momentum
transport by magnetic torques during the precollapse evolution is known to sap
the core of the necessary rotation. Here we explore the evolution of very
rapidly rotating, massive stars, including stripped down helium cores that
might result from mergers or mass transfer in a binary, and single stars that
rotate unusually rapidly on the main sequence. For the highest possible
rotation rates (about 400 km/s), a novel sort of evolution is encountered in
which single stars mix completely on the main sequence, never becoming red
giants. Such stars, essentially massive ""blue stragglers"", produce
helium-oxygen cores that rotate unusually rapidly. Such stars might comprise
roughly 1% of all stars above 10 solar masses and can, under certain
circumstances retain enough angular momentum to make GRBs. Because this
possibility is very sensitive to mass loss, GRBs will be much more probable in
regions of low metallicity.",0508175v1
2007-02-08,Evolving to type Ia supernovae with long delay time,"Recent investigations on the delay time of type Ia supernovae have set useful
constraints on the progenitors of type Ia supernovae. Here we have calculated
the evolution of close binaries consisting of a white dwarf and a main-sequence
or subgiant companion. We assume that, once Roche lobe overflow occurs a small
fraction of the lost mass from the system forms a circumbinary disk, which
extracts the orbital angular momentum from the system through tidal torques.
Our calculations indicate that the existence of circumbinary disk can enhance
the mass transfer rate and cause secular orbital shrinkage. The white dwarf can
grow in mass efficiently to trigger type Ia supernovae even with relatively
low-mass ($\la 2 M_{\odot}$) donor stars. Thus this scenario suggest a new
possible evolutionary channel to those type Ia supernovae with long delay time
$\sim 1-3$ Gyr.",0702218v1
2002-09-05,Ferrofluids as thermal ratchets,"Colloidal suspensions of ferromagnetic nano-particles, so-called ferrofluids,
are shown to be suitable systems to demonstrate and investigate thermal ratchet
behavior: By rectifying thermal fluctuations, angular momentum is transferred
to a resting ferrofluid from an oscillating magnetic field without net rotating
component. Via viscous coupling the noise driven rotation of the microscopic
ferromagnetic grains is transmitted to the carrier liquid to yield a
macroscopic torque. For a simple setup we analyze the rotation of the
ferrofluid theoretically and show that the results are compatible with the
outcome of a simple demonstration experiment.",0209137v2
2008-01-02,Secular evolution of disk galaxies,"Galaxy disks evolve through angular momentum transfers between
sub-components, like gas, stars, or dark matter halos, through non
axi-symmetric instabilities. The speed of this evolution is boosted in presence
of a large fraction of cold and dissipative gas component. When the visible
matter dominates over the whole disk, angular momentum is exchanged between gas
and stars only. The gas is driven towards the center by bars, stalled
transiently in resonance rings, and driven further by embedded bars, which it
contributes to destroy. From a small-scale molecular torus, the gas can then
inflow from viscous torques, dynamical friction, or m=1 perturbations.
  In the weakened bar phases, multiple-speed spiral patterns can develop and
help the galaxy to accrete external gas flowing from cosmic filaments. The
various phases of secular evolution are illustrated by numerical simulations.",0801.0343v1
2008-12-01,Stimulated Raman adiabatic passage analogs in classical physics,"Stimulated Raman adiabatic passage (STIRAP) is a well established technique
for producing coherent population transfer in a three-state quantum system. We
here exploit the resemblance between the Schrodinger equation for such a
quantum system and the Newton equation of motion for a classical system
undergoing torque to discuss several classical analogs of STIRAP, notably the
motion of a moving charged particle subject to the Lorentz force of a
quasistatic magnetic field, the orientation of a magnetic moment in a slowly
varying magnetic field, the Coriolis effect and the inertial frame dragging
effect. Like STIRAP, those phenomena occur for counterintuitively ordered field
pulses and are robustly insensitive to small changes in the interaction
properties.",0812.0361v1
2009-07-05,Tidal interaction of black holes and Newtonian viscous bodies,"The tidal interaction of a (rotating or nonrotating) black hole with nearby
bodies produces changes in its mass, angular momentum, and surface area.
Similarly, tidal forces acting on a Newtonian, viscous body do work on the
body, change its angular momentum, and part of the transferred gravitational
energy is dissipated into heat. The equations that describe the rate of change
of the black-hole mass, angular momentum, and surface area as a result of the
tidal interaction are compared with the equations that describe how the tidal
forces do work, torque, and produce heat in the Newtonian body. The equations
are strikingly similar, and unexpectedly, the correspondence between the
Newtonian-body and black-hole results is revealed to hold in near-quantitative
detail. The correspondence involves the combination k_2 \tau of ``Love
quantities'' that incorporate the details of the body's internal structure; k_2
is the tidal Love number, and \tau is the viscosity-produced delay between the
action of the tidal forces and the body's reaction. The combination k_2 \tau is
of order GM/c^3 for a black hole of mass M; it does not vanish, in spite of the
fact that k_2 is known to vanish individually for a nonrotating black hole.",0907.0874v1
2012-01-08,Van der Waals interaction in uniaxial anisotropic media,"Van der Waals interactions between flat surfaces in uniaxial anisotropic
media are investigated in the nonretarded limit. The main focus is the effect
of nonzero tilt between the optical axis and the surface normal on the strength
of van der Waals attraction. General expressions for the van der Waals free
energy are derived using the surface mode method and the transfer-matrix
formalism. To facilitate numerical calculations a temperature-dependent
three-band parameterization of the dielectric tensor of the liquid crystal 5CB
is developed. A solid slab immersed in a liquid crystal experiences a van der
Waals torque that aligns the surface normal relative to the optical axis of the
medium. The preferred orientation is different for different materials. Two
solid slabs in close proximity experience a van der Waals attraction that is
strongest for homeotropic alignment of the intervening liquid crystal for all
the materials studied. The results have implications for the stability of
colloids in liquid crystal hosts.",1201.1615v2
2012-08-10,Binary Evolution Leads to Two Populations of White Dwarf Companions,"Planets and other low-mass binary companions to stars face a variety of
potential fates as their host stars move off the main sequence and grow to
subgiants and giants. Stellar mass loss tends to make orbits expand, and tidal
torques tend to make orbits shrink, sometimes to the point that a companion is
directly engulfed by its primary. Furthermore, once engulfed, the ensuing
common envelope (CE) phase can result in the companion becoming fully
incorporated in the primary's envelope; or, if the companion is massive enough,
it can transfer enough energy to eject the envelope and remain parked in a
tight orbit around the white dwarf core. Therefore, ordinary binary evolution
ought to lead to two predominant populations of planets around white dwarfs:
those that have been through a CE phase and are in short-period orbits, and
those that have entirely avoided the CE and are in long-period orbits.",1208.2276v3
2013-12-16,Magnetoelectric Effects in Local Light-Matter Interactions,"We study the generic interaction of a monochromatic electromagnetic field
with bi-isotropic nanoparticles. Such an interaction is described by
dipole-coupling terms associated with the breaking of dual, P- and
T-symmetries, including the chirality and the nonreciprocal magnetoelectric
effect. We calculate absorption rates, radiation forces, and radiation torques
for the nanoparticles and introduce novel characteristics of the field
quantifying the transfer of energy, momentum, and angular-momentum in these
interactions. In particular, we put forward the concept of 'magnetoelectric
energy density', quantifying the local PT-symmetry of the field. Akin to the
'super-chiral' light suggested recently for sensitive local probing of
molecular chirality [Phys. Rev. Lett. 104, 163901 (2010); Science 332, 333
(2011)], here we describe a complex field for sensitive probing of the
nonreciprocal magnetoelectric effect in nanoparticles or molecules.",1312.4325v2
2014-02-28,Lyman edges in supermassive black hole binaries,"We propose a new spectral signature for supermassive black hole binaries
(SMBHBs) with circumbinary gas disks: a sharp drop in flux blueward of the
Lyman limit. A prominent edge is produced if the gas dominating the emission in
the Lyman continuum region of the spectrum is sufficiently cold (T < 20,000 K)
to contain significant neutral hydrogen. Circumbinary disks may be in this
regime if the binary torques open a central cavity in the disk and clear most
of the hot gas from the inner region, and if any residual UV emission from the
individual BHs is either dim or intermittent. We model the vertical structure
and spectra of circumbinary disks using the radiative transfer code TLUSTY, and
identify the range of BH masses and binary separations producing a Lyman edge.
We find that compact supermassive binaries with orbital periods of ~0.1 - 10
yr, whose gravitational waves (GWs) are expected to be detectable by pulsar
timing arrays (PTAs), could have prominent Lyman edges. Such strong spectral
edge features are not typically present in AGN spectra and could serve as
corroborating evidence for the presence of a SMBHB.",1403.0002v2
2014-06-19,Numerical simulation of moving rigid body in rarefied gases,"In this paper we present a numerical scheme to simulate a moving rigid body
with arbitrary shape suspended in a rarefied gas. The rarefied gas is simulated
by solving the Boltzmann equation using a DSMC particle method. The motion of
the rigid body is governed by the Newton-Euler equations, where the force and
the torque on the rigid body is computed from the momentum transfer of the gas
molecules colliding with the body. On the other hand, the motion of the rigid
body influences the gas flow in its surroundings. We validate the numerical
results by testing the Einstein relation for Brownian motion of the suspended
particle. The translational as well as the rotational degrees of freedom are
taken into account. It is shown that the numerically computed translational and
rotational diffusion coefficients converge to the theoretical values.",1406.5176v1
2015-06-01,Subthermal switching with nanomechanical relays,"We present a physical model for electronic switching in cantilever based
nano-electro-mechanical field effect transistors, focusing on the steepness of
its switching curve. We find that the subthreshold swing of the voltage
transfer characteristic is governed by two separate considerations - the
ability of the charges to correlate together through dipolar interactions and
amplify the active torque, versus the active pull-in forces that drive an
abrupt phase transition and close the air gap between the tip of the cantilever
and the drain. For small sized relays, dipolar and short-range Van Der Waals
'sticking' forces dominate, while for longer cantilevers the capacitive energy
acquires a major role. The individual pull-in and pull-out phases demonstrate a
remarkably low subthreshold swing driven by the capacitive forces, sharpened
further by dipolar correlation. The sharp switching, however, comes at the
expense of strong hysteresis as the metastable and stable states interchange
along the forward and reverse phases of the voltage scan.",1506.00315v1
2017-01-09,Radiative grain alignment in protoplanetary disks: Implications for polarimetric observations,"We apply the theory of radiative torque (RAT) alignment for studying
protoplanetary disks around a T-Tauri star and perform 3D radiative transfer
calculations to provide the expected maps of polarized radiation to be compared
with observations, such as with ALMA. We revisit the issue of grain alignment
for large grains expected in the protoplanetary disks and find that mm-sized
grains at midplane do not align with the magnetic field as the Larmor
precession timescale for such large grains becomes longer than the gaseous
damping timescale. Hence, for these grains the RAT theory predicts that the
alignment axis is determined by the grain precession with respect to the
radiative flux. As a result, we expect that the polarization will be in the
azimuthal direction for a face-on disk. It is also shown that if dust grains
have superparamagnetic inclusions, magnetic field alignment is possible for
(sub-)micron grains at the surface layer of disks, and this can be tested by
mid-infrared polarimetric observations.",1701.02063v3
2017-06-19,Force and torque of a string on a pulley,"Every university introductory physics course considers the problem of
Atwood's machine taking into account the mass of the pulley. In the usual
treatment the tensions at the two ends of the string are offhandedly taken to
act on the pulley and be responsible for its rotation. However such a free-body
diagram of the forces on the pulley is not {\it a priori} justified, inducing
students to construct wrong hypotheses such as that the string transfers its
tension to the pulley or that some symmetry is in operation. We reexamine this
problem by integrating the contact forces between each element of the string
and the pulley and show that although the pulley does behave as if the tensions
were acting on it, this comes only as the end result of a detailed analysis. We
also address the question of how much friction is needed to prevent the string
from slipping over the pulley. Finally, we deal with the case in which the
string is on the verge of sliding and show that this will never happen unless
certain conditions are met by the coefficient of friction and the masses
involved.",1706.10139v1
2017-07-27,Secular evolution of Milky Way-type galaxies,"The internal evolution of disk galaxies like the Milky Way are driven by
non-axisymmetries (bars) and the implied angular momentum transfer of the
matter; baryons are essentially driven inwards to build a more concentrated
disk. This mass concentration may lead to the decoupling of a secondary bar,
since the orbit precessing frequency is then much enhanced. Vertical resonances
with the bar will form a box/peanut bulge in a Gyr time-scale. Gas flows due to
gravity torques can lead to a young nuclear disk forming stars, revealed by a
sigma-drop in velocity dispersion. These gas flows moderated by feedback
produce intermittent accretion of the super-massive black hole, and cycles of
AGN activity. The fountain effect due to nuclear star formation may lead to
inclined, and even polar nuclear disks.",1707.08733v1
2017-10-30,Structure-preserving discrete-time optimal maneuvers of a wheeled inverted pendulum,"The Wheeled Inverted Pendulum (WIP) is a nonholonomic, underactuated
mechanical system, and has been popularized commercially as the {\it Segway}.
Designing optimal control laws for point-to-point state-transfer for this
autonomous mechanical system, while respecting momentum and torque constraints
as well as the underlying manifold, continues to pose challenging problems. In
this article we present a successful effort in this direction: We employ
geometric mechanics to obtain a discrete-time model of the system, followed by
the synthesis of an energy-optimal control based on a discrete-time maximum
principle applicable to mechanical systems whose configuration manifold is a
Lie group. Moreover, we incorporate state and momentum constraints into the
discrete-time control directly at the synthesis stage. The control is
implemented on a WIP with parameters obtained from an existing prototype; the
results are highly encouraging, as demonstrated by numerical experiments.",1710.10932v2
2019-01-03,Self-supervised Learning of Image Embedding for Continuous Control,"Operating directly from raw high dimensional sensory inputs like images is
still a challenge for robotic control. Recently, Reinforcement Learning methods
have been proposed to solve specific tasks end-to-end, from pixels to torques.
However, these approaches assume the access to a specified reward which may
require specialized instrumentation of the environment. Furthermore, the
obtained policy and representations tend to be task specific and may not
transfer well. In this work we investigate completely self-supervised learning
of a general image embedding and control primitives, based on finding the
shortest time to reach any state. We also introduce a new structure for the
state-action value function that builds a connection between model-free and
model-based methods, and improves the performance of the learning algorithm. We
experimentally demonstrate these findings in three simulated robotic tasks.",1901.00943v1
2020-05-25,Role of vortical structures for enstrophy and scalar transport in flows with and without stable stratification,"In this paper, we investigate the enstrophy dynamics in relation to objective
Eulerian coherent structures (OECSs) and their impact on the enstrophy and
scalar transport near the turbulent/non-turbulent interface (TNTI) in flows
with and without stable stratification. We confirm that vortex-stretching
produces enstrophy inside the boundaries of the OECSs, while viscous diffusion
transfers the enstrophy across the boundaries of the structures. Although often
overlooked in the literature, viscous dissipation of enstrophy within the
boundaries of vortical structures is significant. Conversely, for the weakly
stratified flows also investigated here, the effect of the baroclinic torque is
negligible. We provide evidence that the OECSs advect the passive/active scalar
and redistribute it via molecular diffusion. Finally, we use conditional
analysis to show that the typical profiles of the enstrophy and scalar
transport equation terms across the TNTI are compatible with the presence of
OECSs positioned at the edge between the turbulent sublayer and the turbulent
core region. We show that when these profiles are further conditioned to the
presence of OECSs, their magnitude is considerably higher.",2005.12329v1
2020-07-17,Weakly-supervised Learning of Human Dynamics,"This paper proposes a weakly-supervised learning framework for dynamics
estimation from human motion. Although there are many solutions to capture pure
human motion readily available, their data is not sufficient to analyze quality
and efficiency of movements. Instead, the forces and moments driving human
motion (the dynamics) need to be considered. Since recording dynamics is a
laborious task that requires expensive sensors and complex, time-consuming
optimization, dynamics data sets are small compared to human motion data sets
and are rarely made public. The proposed approach takes advantage of easily
obtainable motion data which enables weakly-supervised learning on small
dynamics sets and weakly-supervised domain transfer. Our method includes novel
neural network (NN) layers for forward and inverse dynamics during end-to-end
training. On this basis, a cyclic loss between pure motion data can be
minimized, i.e. no ground truth forces and moments are required during
training. The proposed method achieves state-of-the-art results in terms of
ground reaction force, ground reaction moment and joint torque regression and
is able to maintain good performance on substantially reduced sets.",2007.08969v2
2020-08-27,Lense-Thirring Precession of Misaligned Discs I,"We study Lense-Thirring precession of inviscid and viscous misaligned
$\alpha-$discs around a black hole using a gravitomagnetic term in the momentum
equation. For weak misalignments, $i \lesssim 10^{\circ}$, the discs behave
like rigid bodies, undergoing the full suite of classical harmonic oscillator
dynamics including, weak and critically damped motion (due to viscosity),
precession (due to Lense-Thirring torque) and nutation (due to apsidal
precession). For strong misalignments, $i \gtrsim 30^{\circ}$, we find
sufficiently thin, $h/r \lesssim 0.05$ discs break, form a gap and the inner
and outer sub-discs evolve quasi independently apart from slow mass transfer.
Assuming the sound speed sets the communication speed of warps in the disc, we
can estimate the breaking radius by requiring that the inner sub-disc precesses
like a rigid body. We explicitly show for the first time using a grid code that
an Einstein potential is needed to reproduce the analytic properties of the
inner disc edge and find disc breaking. At large inclination angles we find
multiple disc breaks, consistent with recent GRMHD simulations of highly
inclined discs. Our results suggest that the inclusion of a gravitomagnetic
term and appropriate pseudo-Newtonian potential captures the important
quantitative features of misaligned discs.",2008.12381v1
2020-09-25,Fundamental limitations to no-jerk gearshifts of multi-speed transmission architectures in electric vehicles,"Multi-speed transmissions can enhance the performance and reduce the overall
cost of an electric vehicle, but they also introduce a challenge: avoiding
gearshift jerk, which may sometimes prove to be impossible in the presence of
motor and clutch saturation. In this article, we introduce three theorems that
explicitly define the fundamental limitations to no-jerk gearshifts resulting
from motor or actuator saturation. We compare gearshifts that consist of
transferring transmission torque from one friction clutch to another, to the
case in which one of the clutches is a one-way clutch. We show that systems
with a one-way clutch are more prone to motor saturation, causing gearshift
jerk to be more often inevitable. We also study the influence of planetary
gearsets on the gearshift dynamical trajectories, and expose the impact on the
no-jerk limitations. This work offers tools to compare transmission
architectures during the conceptual design phase of a new electric vehicle.",2009.12410v2
2020-11-23,COCOI: Contact-aware Online Context Inference for Generalizable Non-planar Pushing,"General contact-rich manipulation problems are long-standing challenges in
robotics due to the difficulty of understanding complicated contact physics.
Deep reinforcement learning (RL) has shown great potential in solving robot
manipulation tasks. However, existing RL policies have limited adaptability to
environments with diverse dynamics properties, which is pivotal in solving many
contact-rich manipulation tasks. In this work, we propose Contact-aware Online
COntext Inference (COCOI), a deep RL method that encodes a context embedding of
dynamics properties online using contact-rich interactions. We study this
method based on a novel and challenging non-planar pushing task, where the
robot uses a monocular camera image and wrist force torque sensor reading to
push an object to a goal location while keeping it upright. We run extensive
experiments to demonstrate the capability of COCOI in a wide range of settings
and dynamics properties in simulation, and also in a sim-to-real transfer
scenario on a real robot (Video: https://youtu.be/nrmJYksh1Kc)",2011.11270v1
2021-03-13,Error-Aware Policy Learning: Zero-Shot Generalization in Partially Observable Dynamic Environments,"Simulation provides a safe and efficient way to generate useful data for
learning complex robotic tasks. However, matching simulation and real-world
dynamics can be quite challenging, especially for systems that have a large
number of unobserved or unmeasurable parameters, which may lie in the robot
dynamics itself or in the environment with which the robot interacts. We
introduce a novel approach to tackle such a sim-to-real problem by developing
policies capable of adapting to new environments, in a zero-shot manner. Key to
our approach is an error-aware policy (EAP) that is explicitly made aware of
the effect of unobservable factors during training. An EAP takes as input the
predicted future state error in the target environment, which is provided by an
error-prediction function, simultaneously trained with the EAP. We validate our
approach on an assistive walking device trained to help the human user recover
from external pushes. We show that a trained EAP for a hip-torque assistive
device can be transferred to different human agents with unseen biomechanical
characteristics. In addition, we show that our method can be applied to other
standard RL control tasks.",2103.07732v1
2021-05-10,The Coupling of Galactic Dark Matter Halos with Stellar Bars,"Resonant torques couple stellar bars to dark matter halos. Here we use
high-resolution numerical simulations to demonstrate long-term angular momentum
transfer between stellar bars and dark matter orbits of varying orientation. We
show that bar-driven reversals of dark matter orbit orientations can play a
surprisingly large role in the evolution of the bar pattern speed.
  In predominantly prograde (co-rotating) halos, dark matter orbits become
trapped in the stellar bar forming a parallel dark matter bar. This dark matter
bar reaches more than double the vertical height of the stellar bar. In halos
dominated by retrograde orbits, a dark matter wake forms oriented perpendicular
to the stellar bar. These dark matter over-densities provide a novel space to
look for dark matter annihilation or decay signals. % We predict that the Milky
Way hosts a dark matter bar aligned with the stellar bar as well as a dark
matter wake the near-side of which should extend from Galactic center to a
galactic longitude of $l \approx 323^\circ$.",2105.04698v1
2021-10-12,Adaptive Feedforward Reference Design for Active Vibration Rejection in Multi-Actuator Hard Disk Drives,"In December 2017, Seagate unveiled the Multi Actuator Technology to double
the data performance of the future generation hard disk drives (HDD). This
technology will equip drives with two dual stage actuators (DSA) each
comprising of a voice coil motor (VCM) actuator and a piezoelectric micro
actuator (MA) operating on the same pivot point. Each DSA is responsible for
controlling half of the drive's arms. As both the DSAs operate independently on
the same pivot timber, the control forces and torques generated by one can
affect the operation of the other and thereby worsening the performance
drastically. In this paper, a robust adaptive feedforward controller is
designed as an add-on controller to an existing stabilizing feedback controller
to reject the disturbances transferred through the common pivot timber by
shaping the references to the VCM actuator and the total output of the dual
stage system.",2110.05669v1
2022-12-09,Current-induced mechanical torque in chiral molecular rotors,"A great endeavor has been undertaken to engineer molecular rotors operated by
an electrical current. A frequently met operation principle is the transfer of
angular momentum taken from the incident flux. In this paper we present an
alternative driving agent that works also in situations where angular momentum
of the incoming flux is conserved. This situation arises typically with
molecular rotors that exhibit an easy axis of rotation. For quantitative
analysis we investigate here a classical model, where molecule and wires are
represented by a rigid curved path. We demonstrate that in the presence of
chirality the rotor generically undergoes a directed motion, provided that the
incident current exceeds a threshold value. Above threshold, the corresponding
rotation frequency (per incoming particle current) for helical geometries turns
out to be $2\pi m/M_1$, where $m/M_1$ is the ratio of the mass of an incident
charge carrier and the mass of the helix per winding number.",2212.04910v1
2022-12-17,Cascaded Compositional Residual Learning for Complex Interactive Behaviors,"Real-world autonomous missions often require rich interaction with nearby
objects, such as doors or switches, along with effective navigation. However,
such complex behaviors are difficult to learn because they involve both
high-level planning and low-level motor control. We present a novel framework,
Cascaded Compositional Residual Learning (CCRL), which learns composite skills
by recursively leveraging a library of previously learned control policies. Our
framework learns multiplicative policy composition, task-specific residual
actions, and synthetic goal information simultaneously while freezing the
prerequisite policies. We further explicitly control the style of the motion by
regularizing residual actions. We show that our framework learns joint-level
control policies for a diverse set of motor skills ranging from basic
locomotion to complex interactive navigation, including navigating around
obstacles, pushing objects, crawling under a table, pushing a door open with
its leg, and holding it open while walking through it. The proposed CCRL
framework leads to policies with consistent styles and lower joint torques,
which we successfully transfer to a real Unitree A1 robot without any
additional fine-tuning.",2212.08954v1
2022-12-24,Harnessing Elastic Energy to Transfer Reciprocating Actuation into Rotary Motion,"The ability to convert reciprocating, i.e., alternating, actuation into
rotary motion using linkages is hindered fundamentally by their poor torque
transmission capability around kinematic singularity configurations. Here, we
harness the elastic potential energy of a linear spring attached to the coupler
link of four-bar mechanisms to manipulate force transmission around the
kinematic singularities. We developed a theoretical model to explore the
parameter space for proper force transmission in slider-crank and rocker-crank
four-bar kinematics. Finally, we verified the proposed model and methodology by
building and testing a macro-scale prototype of a slider-crank mechanism. We
expect this approach to enable the development of small-scale rotary engines
and robotic devices with closed kinematic chains dealing with serial kinematic
singularities, such as linkages and parallel manipulators.",2212.12740v1
2023-06-13,SayTap: Language to Quadrupedal Locomotion,"Large language models (LLMs) have demonstrated the potential to perform
high-level planning. Yet, it remains a challenge for LLMs to comprehend
low-level commands, such as joint angle targets or motor torques. This paper
proposes an approach to use foot contact patterns as an interface that bridges
human commands in natural language and a locomotion controller that outputs
these low-level commands. This results in an interactive system for quadrupedal
robots that allows the users to craft diverse locomotion behaviors flexibly. We
contribute an LLM prompt design, a reward function, and a method to expose the
controller to the feasible distribution of contact patterns. The results are a
controller capable of achieving diverse locomotion patterns that can be
transferred to real robot hardware. Compared with other design choices, the
proposed approach enjoys more than 50% success rate in predicting the correct
contact patterns and can solve 10 more tasks out of a total of 30 tasks. Our
project site is: https://saytap.github.io.",2306.07580v3
2023-06-27,Statistics of a 2D immersed granular gas magnetically forced in volume,"We present an experimental study of the dynamics of a set of magnets within a
fluid in which a remote torque applied by a vertical oscillating magnetic field
transfers angular momentum to individual magnets. This system differs from
previous experimental studies of granular gas where the energy is injected by
vibrating the boundaries. Here, we do not observe any cluster formation,
orientational correlation and equipartition of the energy. The magnets' linear
velocity distributions are stretched exponentials, similar to 3D
boundary-forced dry granular gas systems, but the exponent does not depend on
the number of magnets. The value of the exponent of the stretched exponential
distributions is close to the value of 3/2 previously derived theoretically.
Our results also show that the conversion rate of angular momentum into linear
momentum during the collisions controls the dynamics of this
homogenously-forced granular gas. We report the differences between this
homogeneously-forced granular gas, ideal gas, and nonequilibrium
boundary-forced dissipative granular gas.",2306.15456v1
2023-07-20,Aspherical PIC code (APIC) for modeling non-spherical dust in plasmas using shape-conforming coordinates,"The 2D3V Aspherical Particle-in-Cell (APIC) code is developed for modeling of
interactions of non-spherical dust grains with plasmas. It simulates the motion
of plasma electrons and ions in a self-consistent electric field of
plasma-screened charged dust particle. Due to absorption/recombination of
plasma particles impinging on the grain surface, they transfer charge,
momentum, angular momentum, as well as kinetic and binding energy, creating
currents, forces, torques, and heat fluxes to the grain. The values of such
physical parameters determine dust behavior in plasma, including its dynamics
and ablation, and can be used in various plasma studies and applications, such
as dusty plasmas, fusion devices, laboratory experiments, and astrophysical
research. Obtaining these physical values for select non-spherical shapes of
conducting dust grains is the main goal of the APIC code simulations.",2307.11107v1
2023-07-21,"Photon mediated energy, linear and angular momentum transport in fullerene and graphene systems beyond local equilibrium","Based on a tight-binding model for the electron system, we investigate the
transfer of energy, momentum, and angular momentum mediated by electromagnetic
fields among buckminsterfullerene (C$_{60}$) and graphene nano-strips. Our
nonequilibrium Green's function approach enables calculations away from local
thermal equilibrium where the fluctuation-dissipation theorem breaks down. For
example, the forces between C$_{60}$ and current-carrying nano-strips are
predicted. It is found that the presence of current usually enhances the van
der Waals attractive forces. For two current-carrying graphene strips rotated
at some angle, the fluctuational force and torque are much stronger at the
nanoscale compared to that of the static Biot-Savart law.",2307.11361v2
2023-10-12,Multicriteria Optimization of Lower Limb Exoskeleton Mechanism,"Typical leg exoskeletons employ open-loop kinematic chains with motors placed
directly on movable joints; while this design offers flexibility, it leads to
increased costs and heightened control complexity due to the high number of
degrees of freedom. The use of heavy servo-motors to handle torque in active
joints results in complex and bulky designs, as highlighted in existing
literature. In this study, we introduced a novel synthesis method with
analytical solutions provided for synthesizing lower-limb exoskeleton.
Additionally, we have incorporated multicriteria optimization by six designing
criteria. As a result, we offer several mechanisms, comprising only six links,
well-suited to the human anatomical structure, exhibit superior trajectory
accuracy, efficient force transmission, satisfactory step height, and having
internal transfer segment of the foot.",2310.08308v1
2013-06-07,Quantum state transfer in disordered spin chains: How much engineering is reasonable?,"The transmission of quantum states through spin chains is an important
element in the implementation of quantum information technologies. Speed and
fidelity of transfer are the main objectives which have to be achieved by the
devices even in the presence of imperfections which are unavoidable in any
manufacturing process. To reach these goals, several kinds of spin chains have
been suggested, which differ in the degree of fine-tuning, or engineering, of
the system parameters. In this work we present a systematic study of two
important classes of such chains. In one class only the spin couplings at the
ends of the chain have to be adjusted to a value different from the bulk
coupling constant, while in the other class every coupling has to have a
specific value. We demonstrate that configurations from the two different
classes may perform similarly when subjected to the same kind of disorder in
spite of the large difference in the engineering effort necessary to prepare
the system. We identify the system features responsible for these similarities
and we perform a detailed study of the transfer fidelity as a function of chain
length and disorder strength, yielding empirical scaling laws for the fidelity
which are similar for all kinds of chain and all disorder models. These results
are helpful in identifying the optimal spin chain for a given quantum
information transfer task. In particular, they help in judging whether it is
worthwhile to engineer all couplings in the chain as compared to adjusting only
the boundary couplings.",1306.1695v2
2016-09-19,Nonequilibrium spin-boson model: from weak to strong coupling,"We present a general theory to explore energy transfer in nonequilibrium
spin-boson models within the framework of nonequilibrium Green's function
(NEGF). In contrast to conventionally used NEGF methods based on a perturbation
expansion in the system-bath coupling, we adopt the polaron transformation to
the Hamiltonian and identify the tunneling term as a perturbation with the
system-bath coupling being treated nonperturbatively, herein termed the
polaron-transformed NEGF method. To evaluate terms in the Dyson series, we
further utilize the Majorana-fermion representation. The proposed method not
only allows us to deal with weak as well as strong coupling regime, but also
enables an investigation on the role of bias. As an application of the method,
we study the energy transfer between two Ohmic bosonic baths mediated by a
spin. For a unbiased spin system, our energy current result smoothly bridges
predictions of two benchmarks, namely, the quantum master equation and the
nonequilibrium non-interacting blip approximation, thus our method is beyond
existing theories. In case of a biased spin system, we reveal a bias-induced
nonmomotonic behavior of the energy conductance in the intermediate coupling
regime, due to the resonant character of the energy transfer. This finding may
offer a nontrivial quantum control knob over energy transfer at the nanoscale.",1609.05598v3
2018-12-27,Longitudinal and transverse spin transfer to $Λ$ and $\barΛ$ hyperons in p+p collisions at STAR,"The longitudinal or transverse spin transfer to Lambda and anti-Lambda
hyperons in polarized proton-proton collisions is expected to be sensitive to
the helicity or transversity distributions of strange and anti-strange quarks
of the proton, and to the corresponding polarized fragmentation function. We
report the first measurement of the transverse spin transfer to $\Lambda$ and
$\bar \Lambda$ along the polarization direction of the fragmenting quark,
$D_{TT}$, in transversely polarized proton-proton collisions at 200 GeV with
the STAR experiment at RHIC. The data correspond to an integrated luminosity of
18 pb$^{-1}$, and cover a kinematic range of |$\eta$|< 1.2 and transverse
momentum $p_T$ up to 8 GeV/c. We also report an improved measurement of the
longitudinal spin transfer $D_{LL}$ to $\Lambda$ and $\bar \Lambda$ with $p_T$
up to 6 GeV/c, using data with about twelve times larger figure-of-merit than
the previously published STAR results. The prospects of hyperon polarization
measurements in the forward pseudo-rapidity region (2.5<$\eta$<4) in p+p
collision in the year of 2021 and beyond will also be discussed, which is based
on the STAR forward detector upgrade plan including a forward tracking system
and a forward calorimeter system.",1812.10621v1
2021-07-23,Generalized Bloch model: a theory for pulsed magnetization transfer,"Purpose: The paper introduces a classical model to describe the dynamics of
large spin-1/2 ensembles associated with nuclei bound in large molecule
structures, commonly referred to as the semi-solid spin pool, and their
magnetization transfer (MT) to spins of nuclei in
  Theory and Methods: Like quantum-mechanical descriptions of spin dynamics and
like the original Bloch equations, but unlike existing MT models, the proposed
model is based on the algebra of angular momentum in the sense that it
explicitly models the rotations induced by radio-frequency (RF) pulses. It
generalizes the original Bloch model to non-exponential decays, which are,
e.g., observed for semi-solid spin pools. The combination of rotations with
non-exponential decays is facilitated by describing the latter as Green's
functions, comprised in an integro-differential equation.
  Results: Our model describes the data of an inversion-recovery
magnetization-transfer experiment with varying durations of the inversion pulse
substantially better than established models. We made this observation for all
measured data, but in particular for pulse durations small than 300$\mu$s.
Furthermore, we provide a linear approximation of the generalized Bloch model
that reduces the simulation time by approximately a factor 15,000, enabling
simulation of the spin dynamics caused by a rectangular RF-pulse in roughly
2$\mu$s.
  Conclusion: The proposed theory unifies the original Bloch model, Henkelman's
steady-state theory for magnetization transfer, and the commonly assumed
rotation induced by hard pulses (i.e., strong and infinitesimally short
applications of RF fields) and describes experimental data better than previous
models.",2107.11000v3
2005-05-12,The Evolution of the Dark Halo Spin Parameters lambda and lambda' in a LCDM Universe: The Role of Minor and Major Mergers,"The evolution of the spin parameter of dark halos and the dependence on the
halo merging history in a set of dissipationless cosmological LCDM simulations
is investigated. Special focus is placed on the differences of the two commonly
used versions of the spin parameter, namely lambda=J*E^1/2/(G*M^5/2) (Peebles
80) and lambda'=J/(sqrt(2)*M_vir*R_vir*V_vir) (Bullock et al. 01). Though the
distribution of the spin transfer rate defined as the ratio of the spin
parameters after and prior to a merger is similar to a high degree for both,
lambda and lambda', we find considerable differences in the time evolution:
while lambda' is roughly independent of redshift, lambda turns out to increase
significantly with decreasing redshift. This distinct behaviour arises from
small differences in the spin transfer during accretion events. The evolution
of the spin parameter is strongly coupled with the virial ratio
eta:=2*E_kin/|E_pot| of dark halos. Major mergers disturb halos and increase
both their virial ratio and spin parameter for 1-2 Gyrs. At high redshifts
(z=2-3) many halos are disturbed with an average virial ratio of eta = 1.3
which approaches unity until z=0. We find that the redshift evolution of the
spin parameters is dominated by the huge number of minor mergers rather than
the rare major merger events.",0505249v1
2005-07-15,Structure of Metastable States in Phase Transitions with High-Spin Low-Spin Degree of Freedom,"Difference of degeneracy of the low-spin (LS) and high-spin (HS) states
causes interesting entropy effects on spin-crossover phase transitions and
charge transfer phase transitions in materials composed of the spin-crossover
atoms. Mechanisms of the spin-crossover (SC) phase transitions have been
studied by using Wajnflasz model, where the degeneracy of the spin states (HS
or LS) is taken into account and cooperative natures of the spin-crossover
phase transitions have been well described. Recently, a charge transfer (CT)
phase transition due to electron hopping between LS and HS sites has been
studied by using a generalized Wajnflasz model. In the both systems of SC and
CT, the systems have a high temperature structure (HT) and a low temperature
structure (LT), and the change between them can be a smooth crossover or a
discontinuous first order phase transition depending on the parameters of the
systems. Although apparently the standard SC system and the CT system are very
different, it is shown that both models are equivalent under a certain
transformation of variables. In both systems, the structure of metastable state
at low temperatures is a matter of interest. We study temperature dependence of
fraction of HT systematically in a unified model, and find several structures
of equilibrium and metastable states of the model as functions of system
parameters. In particular, we find a reentrant type metastable branch of HT in
a low temperature region, which would play an important role to study the
photo-irradiated processes of related materials.",0507362v1
2018-05-14,Quantum state transfer of angular momentum via single electron photo-excitation from a Zeeman-resolved light hole,"Electron spins in GaAs quantum dots have been used to make qubits with
high-fidelity gating and long coherence time, necessary ingredients in
solid-state quantum computing. The quantum dots can also host photon qubits
with energy applicable for optical communication, and can show a promising
photon-to-spin conversion. The coherent interface is established through
photo-excitation of a single pair of an electron and a Zeeman-resolved
light-hole, not heavy-hole. However, no experiments on the single photon to
spin conversion have been performed yet. Here we report on single shot readout
of a single electron spin generated in a GaAs quantum dot by spin-selective
excitation with linearly polarized light. A photo-electron spin generated from
a Zeeman-resolved light-hole exciton is detected using an optical spin blockade
method in a single quantum dot and a Pauli spin blockade method in a double
quantum dot. We found that the blockade probability strongly depends on the
photon polarization and the hole state, heavy- or light-hole, indicating a
transfer of the angular momentum from single photons to single electron spins.
Our demonstration will open a pathway to further investigation on fundamental
quantum physics such as quantum entanglement between a wide variety of quantum
systems and applications of quantum networking technology.",1805.05147v1
2020-04-02,Tunable and Enhanced Rashba Spin-Orbit Coupling in Iridate-Manganite Heterostructures,"Tailoring spin-orbit interactions and Coulomb repulsion are the key features
to observe exotic physical phenomena such as magnetic anisotropy and
topological spin texture at oxide interfaces. Our study proposes a novel
platform for engineering the magnetism and spin-orbit coupling at LaMnO3/SrIrO3
(3d-5d oxide) interfaces by tuning the LaMnO3 growth conditions which controls
the lattice displacement and spin-correlated interfacial coupling through
charge transfer. We report on a tunable and enhanced interface-induced Rashba
spin-orbit coupling and Elliot-Yafet spin relaxation mechanism in LaMnO3/SrIrO3
bilayer with change in the underlying magnetic order of LaMnO3. We also
observed enhanced spin-orbit coupling strength in LaMnO3/SrIrO3 compared to
previously reported SrIrO3 layers. The X-Ray spectroscopy measurement reveals
the quantitative valence of Mn and their impact on charge transfer. Further, we
performed angle-dependent magnetoresistance measurements, which show signatures
of magnetic proximity effect in SrIrO3 while reflecting the magnetic order of
LaMnO3. Our work thus demonstrates a new route to engineer the interface
induced Rashba spin-orbit coupling and magnetic proximity effect in 3d-5d oxide
interfaces which makes SrIrO3 an ideal candidate for spintronics applications.",2004.00800v1
2020-05-28,Spin-Pumping-Induced Non-Linear Electric Current on the Surface of a Ferromagnetic Topological Insulator,"We investigate the spin-pumping-induced electric current on the surface of a
three-dimensional topological insulator hybridized with a ferromagnet, namely,
ferromagnetic topological insulator. In order to do this, we establish the
microscopic formalism and construct the perturbation theory using a Keldysh
Green's function approach. We analyze how this electric current is generated by
an exchange interaction and an external ac magnetic field, which is the driving
force of ferromagnetic resonance as well as the spin pumping. The mechanism is
as follows. First, the ferromagnetic resonance is driven and a zero-momentum
magnon emerges. It is the fluctuation from the saturation magnetization
pointing parallel to the precession axis of the ferromagnetic resonance. After
then, the spin pumping is generated with the zero-momentum magnon being the
carrier of spin. The zero-momentum magnon and the topological insulator surface
state couples through the exchange interaction and the spin carried by the
magnon is transferred to it. Owing to the spin-momentum locking, the
transferred spin is converted into the momentum of topological insulator
surface state leading to the generation of electric current flowing
perpendicular to the precession axis of the ferromagnetic resonance. It is
quadratic in the amplitude of external ac magnetic field whereas it is linear
to the strength of the exchange interaction. The associated electric voltage is
described by the spectrum of zero-momentum magnon. The non-linearity of
spin-pumping-induced electric current in the ac magnetic field as well as the
linearity in the exchange-interaction strength reflects that the surface of
ferromagnetic topological insulator has a high-performing functionality of
generating the electric charge current by magnetic controlling.",2005.13850v1
2021-03-14,Lower and upper bounds of quantum battery power in multiple central spin systems,"We study the energy transfer process in quantum battery systems consisting of
multiple central spins and bath spins. Here with ""quantum battery"" we refer to
the central spins, whereas the bath serves as the ""charger"". For the single
central-spin battery, we analytically derive the time evolutions of the energy
transfer and the charging power with arbitrary number of bath spins. For the
case of multiple central spins in the battery, we find the scaling-law relation
between the maximum power $P_{max}$ and the number of central spins $N_B$. It
approximately satisfies a scaling law relation $P_{max}\propto N_{B}^{\alpha}$,
where scaling exponent $\alpha$ varies with the bath spin number $N$ from the
lower bound $\alpha =1/2$ to the upper bound $\alpha =3/2$. The lower and upper
bounds correspond to the limits $N\to 1$ and $N\gg N_B$, respectively. In
thermodynamic limit, by applying the Holstein-Primakoff (H-P) transformation,
we rigorously prove that the upper bound is $P_{max}=0.72 B A \sqrt{N}
N_{B}^{3/2}$, which shows the same advantage in scaling of a recent charging
protocol based on the Tavis-Cummins model. Here $B$ and $A $ are the external
magnetic field and coupling constant between the battery and the charger.",2103.07828v1
2022-07-29,How To Spin Black Holes Up In High-Mass X-ray Binaries And Not Merge In The Attempt,"Astrophysical black holes (BHs) can be fully described by their mass and
spin. However, producing rapidly spinning ones is extremely difficult as the
stars that produce them lose most of their angular momentum before the BH is
formed. Binaries where the progenitor is paired with a low-mass star in a tight
orbit can produce rapidly spinning BHs (through tides), whereas those with
massive companions cannot (as they do not fit in such an orbit). A few
rapidly-spinning black holes (BHs) have been observed paired with very massive
companion stars, defying stellar-formation paradigm. Models which reduce the
stellar-core--envelope interaction (and winds) do not match observations nor
theory well; I show they also miss explaining the energetics. BH spins cannot
be produced during stellar collapse; using orbital spin through
explosion-fallback material does not match the observations; spinning BHs up
through accepted mass-transfer channels takes longer than their lifetimes, it
is usually discarded. I show that fast mass-transfer mechanisms, predicted to
merge the BH and star, successfully spin the BHs up and show a mechanism to
avoid said mergers and main dangers of the alternatives while naturally
explaining the observations. The implications are potentially paradigm-shifting
and far-reaching in the high-energy, BH astrophysics context.",2207.14765v1
2023-05-25,Nonlinear spin dynamics of ferromagnetic ring in the vortex state and its application for spin-transfer nano-oscillator,"We study a nonlinear spin dynamics of a ferromagnetic ring in a vortex state
induced by the spin-polarized current. We also suggest to use the ferromagnetic
ring as a free layer of a coreless vortex spin-transfer nano-oscillator. The
calculated working frequency is about several GHz, that is much higher than the
gyromode frequency of the disk-based vortex oscillator. The response of the
vortex-state ring to the spin-polarized current has hysteretic behavior with
the reasonable values of the thresholds current densities: ignition threshold
is about $10^{8} \text{A}\text{cm}^{-2}$, and elimination current to maintain
the oscillations has much lower values about $10^{6} \text{A} \text{cm}^{-2}$.
The output signal can be extracted by the help of the inverse spin Hall effect
or by the giant magnetoresistance. The output electromotive force averaged over
all sample vanishes, and we suggest to use a ferromagnetic ring or disk in a
vortex state as a GMR analyzer. For an inverse spin Hall analyser we advise to
use two heavy metals with different signs of Spin-Hall angle. The ring-based
STNO is supposed to increase the areas of practical application of the STNOs.",2305.16019v2
2010-02-02,Dimerization-assisted energy transport in light-harvesting complexes,"We study the role of the dimer structure of light-harvesting complex II (LH2)
in excitation transfer from the LH2 (without a reaction center (RC)) to the LH1
(surrounding the RC), or from the LH2 to another LH2. The excited and
un-excited states of a bacteriochlorophyll (BChl) are modeled by a quasi-spin.
In the framework of quantum open system theory, we represent the excitation
transfer as the total leakage of the LH2 system and then calculate the transfer
efficiency and average transfer time. For different initial states with various
quantum superposition properties, we study how the dimerization of the B850
BChl ring can enhance the transfer efficiency and shorten the average transfer
time.",1002.0496v2
2010-03-31,Perfect Function Transfer in two- and three- dimensions without initialization,"We find analytic models that can perfectly transfer, without state
initializati$ or remote collaboration, arbitrary functions in two- and
three-dimensional interacting bosonic and fermionic networks. We elaborate on a
possible implementation of state transfer through bosonic or fermionic atoms
trapped in optical lattices. A significant finding is that the state of a spin
qubit can be perfectly transferred through a fermionic system. Families of
Hamiltonians, both linear and nonlinear, are described which are related to the
linear Boson model and that enable the perfect transfer of arbitrary functions.
This includes entangled states such as decoherence-free subsystems enabling
noise protection of the transferred state.",1004.0010v1
2014-01-12,Ultrafast Manipulation of a Double Quantum Dot via Lyapunov Control Method,"For a double quantum dot (DQD) system, here we propose alternative ultrafast
manipulate approach: Lyapunov control method, to transfer the state from R to L
on the picosecond scale, orders of magnitude faster and transfer probability
higher than the previously measured electrically controlled charge- or
spin-based quits. The control laws are composed of two-direction components,
one is used to eliminate the dissipation in the system, another is used to
transfer the state. The control theory's stability ensures the system can be
transferred to the target state in high probability, and the coefficients in
control laws leads very fast convergence. The role of eliminating the
dissipation plays the suppression of decoherence effect. Numerical simulation
results show that under the realistic implementation conditions, the transfer
probability and fidelity can be increased up to 98.79% and 98.97%,
respectively. This is the first result directly applicable to a DQD system's
state transferring using the Lyapunov control method. We also give specific
experimental realization scheme.",1401.2614v1
2015-10-30,Asymptotically perfect efficient quantum state transfer across uniform chains with two impurities,"The ability to transfer quantum information from one location to another with
high fidelity is of central importance to quantum information science.
Unfortunately for the simplest system of a uniform chain (a spin chain or a
particle in a one-dimensional lattice), the state transfer time grows
exponentially in the chain length $N$ at fixed fidelity. In this work we show
that the addition of an impurity near each endpoint, coupled to the uniform
chain with strength $w$, is sufficient to ensure efficient and high-fidelity
state transfer. An eigenstate localized in the vicinity of the impurity can be
tuned into resonance with chain extended states by tuning $w(N)\propto
N^{1/2}$; the resulting avoided crossing yields resonant eigenstates with large
amplitudes on the chain endpoints and approximately equidistant eigenvalues.
The state transfer time scales as $t\propto N^{3/2}$ and its fidelity $F$
approaches unity in the thermodynamic limit $N\to\infty$; the error scales as
$1-F\propto N^{-1}$. Thus, with the addition of two impurities, asymptotically
perfect state transfer with a uniform chain is possible even in the absence of
external control.",1511.00038v1
2016-02-09,"A public code for general relativistic, polarised radiative transfer around spinning black holes","Ray tracing radiative transfer is a powerful method for comparing theoretical
models of black hole accretion flows and jets with observations. We present a
public code, grtrans, for carrying out such calculations in the Kerr metric,
including the full treatment of polarised radiative transfer and parallel
transport along geodesics. The code is written in Fortran 90 and efficiently
parallelises with OpenMP, and the full code and several components have Python
interfaces. We describe several tests which are used for verifiying the code,
and we compare the results for polarised thin accretion disc and semi-analytic
jet problems with those from the literature as examples of its use. Along the
way, we provide accurate fitting functions for polarised synchrotron emission
and transfer coefficients from thermal and power law distribution functions,
and compare results from numerical integration and quadrature solutions of the
polarised radiative transfer equations. We also show that all transfer
coefficients can play an important role in predicted images and polarisation
maps of the Galactic center black hole, Sgr A*, at submillimetre wavelengths.",1602.03184v1
2016-02-29,"Charge transfer, band-like transport, and magnetic ions at F16CoPc/rubrene interfaces","Organic semiconductors offer an unprecedented flexibility to control the
electronic state of interfacial electronic systems. Here we present a first
step in realizing organic charge transfer interfaces that combine both a large
electrical conductivity and the presence of magnetic ions. We have performed a
detailed investigation of F16CoPc/rubrene interface by means of temperature
dependent charge transport measurements, Hall effect, scanning Kelvin probe
microscopy and photoelectron spectroscopy. Our finding is that the charge
transfer leads to significantly enhanced electrical conductivity and the
band-like transport. We have determined the density, mobility and nature of
charge carriers in the system (holes in rubrene). We have also found that the
amount of charge transfer in F16CoPc/rubrene is high enough to cause the
band-like transport in rubrene crystals at the interface. Finally, our XPS and
UPS measurements have shown that the charge transfer in F16CoPc/rubrene
involves electronic orbitals centered on the magnetic Co ions of the
phthalocyanine molecules causing a change in their spin. Thus, F16CoPc/rubrene
is the first organic interface where the charge transfer responsible for the
interfacial conductivity fully involves the metal Co core of the phthalocyanine
molecules, providing a link between charge transport and magnetic properties.",1602.08885v1
2018-06-30,Scalable Dissolution-Dynamic Nuclear Polarization with Rapid Transfer of a Polarized Solid,"In dissolution-dynamic nuclear polarization, nuclear spins are hyperpolarized
at cryogenic temperatures using radicals and microwave irradiation. The
hyperpolarized solid is dissolved with hot solvent and the solution is
transferred to a secondary magnet where strongly enhanced magnetic resonance
signals are observed. Here we present a method for transferring the
hyperpolarized solid. A bullet containing the frozen, hyperpolarized sample is
ejected using pressurized helium gas, and shot into a receiving structure in
the secondary magnet, where the bullet is retained and the polarized solid is
dissolved rapidly. The transfer takes approximately 70 ms. A solenoid, wound
along the entire transfer path ensures adiabatic transfer and limits
radical-induced low-field relaxation. The method is fast and scalable towards
small volumes suitable for high-resolution nuclear magnetic resonance
spectroscopy while maintaining high concentrations of the target molecule.
Polarization levels of approximately 30% have been observed for 1-$^{\sf
13}$C-labelled pyruvic acid in solution.",1807.00223v2
2019-04-03,Exact Entanglement dynamics in Three Interacting Qubits,"Motivated by recent experimental study on coherent dynamics transfer in three
interacting atoms or electron spins \cite{Barredo:2015,Rosenfeld:2018}, here we
study entanglement entropy transfer in three interacting qubits. We
analytically calculate time evolutions of wave function, density matrix and
entanglement of the system. We find that initially entangled two qubits may
alternatively transfer their entanglement entropy to other two qubit pairs. So
that dynamical evolution of three interacting qubits may produce a genuine
three-partite entangled state through entanglement entropy transfers. In
particular, different pairwise interactions of the three qubits endow symmetric
and asymmetric evolutions of the entanglement transfer, characterized by the
quantum mutual information and concurence. Finally, we discuss an experimental
proposal of three Rydberg atoms for testing the entanglement dynamics transfer
of this kind.",1904.01977v1
2002-02-12,"Atmospheric Circulation and Tides of ""51Peg b-like"" Planets","We examine the properties of the atmospheres of extrasolar giant planets at
orbital distances smaller than 0.1 AU from their stars. We show that these
``51Peg b-like'' planets are rapidly synchronized by tidal interactions, but
that small departures from synchronous rotation can occur because of
fluid-dynamical torques within these planets. Previous radiative-transfer and
evolution models of such planets assume a homogeneous atmosphere. Nevertheless,
we show using simple arguments that, at the photosphere, the day-night
temperature difference and characteristic wind speeds may reach ~500 K and ~2
km/s, respectively. Substantial departures from chemical equilibrium are
expected. The cloud coverage depends sensitively on the dynamics; clouds could
exist predominantly either on the dayside or nightside, depending on the
circulation regime. Radiative-transfer models that assume homogeneous
conditions are therefore inadequate in describing the atmospheric properties of
51Peg b-like planets. We present preliminary three-dimensional, nonlinear
simulations of the atmospheric circulation of HD209458b that indicate plausible
patterns for the circulation and generally agree with our simpler estimates.
Furthermore, we show that kinetic energy production in the atmosphere can lead
to the deposition of substantial energy in the interior, with crucial
consequences for the evolution of these planets. Future measurements of
reflected and thermally-emitted radiation from these planets will help test our
ideas.",0202236v1
2004-06-29,Virgo High-Resolution CO Survey IV. Spiral-Driven Gas Dynamics in the Non-Barred Seyfert Galaxy NGC 4501,"We report on high-resolution interferometer observations of the 12CO(J=1-0)
emission in the central 5 kpc region of the Seyfert 2 galaxy NGC 4501. The
observations were made using the Nobeyama Millimeter Array during a long-term
CO line survey of Virgo spirals. The major features are: (1) a nuclear
concentration with a radius of r~5'' (390 pc), which is resolved into double
peaks, and (2) spiral arms which extend out from the nuclear region. The
nuclear component has a mass of 1.3x10^8 Mo, which corresponds to ~3.5% of the
dynamical mass, and shows a slight non-circular motion. The double peaks are
separated by ~4''.7. (370 pc), and located on the root of optical spiral arms
in a HST image. The gas arms are associated with the spiral dust lanes, and are
linked to the central double peaks. The non-circular motions along the
molecular arms indicate the fact that the gas is driven by the density wave,
rather than the stochastic processes. We calculated the gas cloud orbits in a
stellar spiral potential, and explained the observed CO spiral arms and
non-circular motions. We suggest that the central gas condensation arises from
spiral-driven gas transfer. We estimated and compared the effect of two
possible mechanisms of angular-momentum transfer: galactic shock, and
gravitational torques. We discuss that the galactic shock is dominant.",0406647v1
2005-08-30,Halo evolution in the presence of a disc bar,"Angular momentum transfer from a rotating stellar bar has been proposed by
Weinberg & Katz (2002) as a mechanism to destroy dark-matter cusps in a few
rotation periods. The N-body simulations performed by these authors in support
of their claim employed spherical harmonics for the force computation and were,
as shown by Sellwood (2003), very sensitive to inclusion of asymmetric terms
(odd l,m). In order to disentangle possible numerical artifacts due to the
usage of spherical harmonics from genuine stellar dynamical effects, we
performed similar experiments using a tree code and find that significant cusp
destruction requires substantially more angular momentum than is realistically
available. However, we find that the simplified model (a N-body halo torqued by
a rotating bar pinned to the origin) undergoes an instability in which the cusp
moves away from the origin. In presence of this off-centring, spherical density
profiles centred on the origin display an apparent cusp-removal. We strongly
suspect that it is this effect which Weinberg & Katz observed. When suppressing
the artificial instability, cusp removal is very slow and requires much more
angular momentum to be transferred to the halo than a realistic stellar bar
possibly possesses.",0508647v1
2006-03-08,Gravitational Instabilities in Gaseous Protoplanetary Disks and Implications for Giant Planet Formation,"Protoplanetary gas disks are likely to experience gravitational instabilites
(GI's) during some phase of their evolution. Density perturbations in an
unstable disk grow on a dynamic time scale into spiral arms that produce
efficient outward transfer of angular momentum and inward transfer of mass
through gravitational torques. In a cool disk with rapid enough cooling, the
spiral arms in an unstable disk form self-gravitating clumps. Whether gas giant
protoplanets can form by such a disk instability process is the primary
question addressed by this review. We discuss the wide range of calculations
undertaken by ourselves and others using various numerical techniques, and we
report preliminary results from a large multi-code collaboration. Additional
topics include -- triggering mechanisms for GI's, disk heating and cooling,
orbital survival of dense clumps, interactions of solids with GI-driven waves
and shocks, and hybrid scenarios where GI's facilitate core accretion. The
review ends with a discussion of how well disk instability and core accretion
fare in meeting observational constraints.",0603179v1
2013-05-15,A Semi-Analytical Description for the Formation and Gravitational Evolution of Protoplanetary Disks,"We investigate the formation process of self-gravitating protoplanetary disks
in unmagnetized molecular clouds. The angular momentum is redistributed by the
action of gravitational torques in the massive disk during its early formation.
We develop a simplified one-dimensional accretion disk model that takes into
account the infall of gas from the envelope onto the disk and the transfer of
angular momentum in the disk with an effective viscosity. First we evaluate the
gas accretion rate from the cloud core onto the disk by approximately
estimating the effects of gas pressure and gravity acting on the cloud core. We
formulate the effective viscosity as a function of the Toomre Q parameter that
measures the local gravitational stability of the rotating thin disk. We use a
function for viscosity that changes sensitively with Q when the disk is
gravitationally unstable. We find a strong self-regulation mechanism in the
disk evolution. During the formation stage of protoplanetary disks, the
evolution of the surface density does not depend on the other details of the
modeling of effective viscosity, such as the prefactor of the viscosity
coefficient. Next, to verify our model, we compare the time evolution of the
disk calculated with our formulation with that of three-dimensional
hydrodynamical simulations. The structures of the resultant disks from the
one-dimensional accretion disk model agree well with those of the
three-dimensional simulations. Our model is a useful tool for the further
modeling of chemistry, radiative transfer, and planet formation in
protoplanetary disks.",1305.3413v1
2019-04-09,The First Two Thousand Years of Star Formation,"Starting from a prestellar core with a size of $1.2\times10^4$ AU, we
calculate the evolution of a gravitationally collapsing core until $\sim2000$
yr after protostar formation using a three-dimensional resistive
magnetohydrodynamic simulation, in which the protostar is resolved with a
spatial resolution of $5.6\times10^{-3}$ AU. Following protostar formation, a
rotationally supported disk is formed. Although the disk size is as small as
$\sim2-4$ AU, it remains present until the end of the simulation. Since the
magnetic field dissipates and the angular momentum is then not effectively
transferred by magnetic effects, the disk surface density gradually increases
and spiral arms develop due to gravitational instability. The disk angular
momentum is then transferred mainly by gravitational torques, which induce an
episodic mass accretion onto the central protostar. The episodic accretion
causes a highly time-variable mass ejection (the high-velocity jet) near the
disk inner edge, where the magnetic field is well coupled with the neutral gas.
As the mass of the central protostar increases, the jet velocity gradually
increases and exceeds $\sim100$ km s$^{-1}$. The jet opening angle widens with
time at its base, while the jet keeps a very good collimation on the large
scale. In addition, a low-velocity outflow is driven from the disk outer edge.
A cavity-like structure, a bow shock and several knots, all of which are
usually observed in star-forming regions, are produced in the outflowing
region.",1904.04424v1
2019-10-04,"A review of the disc instability model for dwarf novae, soft X-ray transients and related objects","I review the basics of the disc instability model (DIM) for dwarf novae and
soft-X-ray transients and its most recent developments, as well as the current
limitations of the model, focusing on the dwarf nova case. Although the DIM
uses the Shakura-Sunyaev prescription for angular momentum transport, which we
know now to be at best inaccurate, it is surprisingly efficient in reproducing
the outbursts of dwarf novae and soft X-ray transients, provided that some
ingredients, such as irradiation of the accretion disc and of the donor star,
mass transfer variations, truncation of the inner disc, etc., are added to the
basic model. As recently realized, taking into account the existence of winds
and outflows and of the torque they exert on the accretion disc may
significantly impact the model. I also discuss the origin of the superoutbursts
that are probably due to a combination of variations of the mass transfer rate
and of a tidal instability. I finally mention a number of unsolved problems and
caveats, among which the most embarrassing one is the modelling of the low
state. Despite significant progresses in the past few years both on our
understanding of angular momentum transport, the DIM is still needed for
understanding transient systems.",1910.01852v1
2020-08-18,ReLMoGen: Leveraging Motion Generation in Reinforcement Learning for Mobile Manipulation,"Many Reinforcement Learning (RL) approaches use joint control signals
(positions, velocities, torques) as action space for continuous control tasks.
We propose to lift the action space to a higher level in the form of subgoals
for a motion generator (a combination of motion planner and trajectory
executor). We argue that, by lifting the action space and by leveraging
sampling-based motion planners, we can efficiently use RL to solve complex,
long-horizon tasks that could not be solved with existing RL methods in the
original action space. We propose ReLMoGen -- a framework that combines a
learned policy to predict subgoals and a motion generator to plan and execute
the motion needed to reach these subgoals. To validate our method, we apply
ReLMoGen to two types of tasks: 1) Interactive Navigation tasks, navigation
problems where interactions with the environment are required to reach the
destination, and 2) Mobile Manipulation tasks, manipulation tasks that require
moving the robot base. These problems are challenging because they are usually
long-horizon, hard to explore during training, and comprise alternating phases
of navigation and interaction. Our method is benchmarked on a diverse set of
seven robotics tasks in photo-realistic simulation environments. In all
settings, ReLMoGen outperforms state-of-the-art Reinforcement Learning and
Hierarchical Reinforcement Learning baselines. ReLMoGen also shows outstanding
transferability between different motion generators at test time, indicating a
great potential to transfer to real robots.",2008.07792v2
2023-12-28,Evolution of the Angular Momentum of Molecular Cloud Cores in Magnetized Molecular Filaments,"The angular momentum of molecular cloud cores plays a key role in the star
formation process. However, the evolution of the angular momentum of molecular
cloud cores formed in magnetized molecular filaments is still unclear. In this
paper, we perform three-dimensional magnetohydrodynamics simulations to reveal
the effect of the magnetic field on the evolution of the angular momentum of
molecular cloud cores formed through filament fragmentation. As a result, we
find that the angular momentum decreases by 30% and 50% at the mass scale of
1Msun in the case of weak and strong magnetic field, respectively. By analyzing
the torques exerted on fluid elements, we identify the magnetic tension as the
dominant process for angular momentum transfer for mass scales < 3Msun for the
strong magnetic field case. This critical mass scale can be understood
semi-analytically as the timescale of magnetic braking. We show that the
anisotropy of the angular momentum transfer due to the presence of strong
magnetic field changes the resultant angular momentum of the core only by a
factor of two. We also find that the distribution of the angle between the
rotation axis and the magnetic field does not show strong alignment even just
before the first core formation. Our results also indicate that the variety of
the angular momentum of the cores are inherited from the difference of the
phase of the initial turbulent velocity field. The variety could contribute to
the diversity in size and other properties of protoplanetary disks recently
reported by observations.",2312.16920v1
2023-03-22,Physical conditions for dust grain alignment in Class 0 protostellar cores II. The role of the radiation field in models aligning/disrupting dust grains,"The polarized dust emission observed in Class 0 protostellar cores at high
angular resolution with ALMA has raised several concerns about the grain
alignment conditions in these regions. We aim to study the role of the
radiation field on the grain alignment mechanisms occurring in the interior
(<1000 au) of Class 0 protostars. We produce synthetic observations of the
polarized dust emission from a MHD model of protostellar formation, using the
POLARIS dust radiative transfer tool, which includes dust alignment with
Radiative Torques Alignment (RATs). We test how the polarized dust emission
from the model core depends on the irradiation conditions in the protostellar
envelope, by varying the radiation due to accretion luminosity propagating from
the central protostellar embryo throughout the envelope. The level of grain
alignment efficiency obtained in the radiative transfer models is then compared
to (sub-) millimeter ALMA dust polarization observations of Class 0 protostars.
Our radiative transfer calculations have a central irradiation that reproduces
the protostellar luminosities typically observed towards low- to
intermediate-mass protostars, as well as super-paramagnetic grains, and grains
>10 micron, which are required to bring the dust grain alignment efficiencies
of the synthetic observations up to observed levels. Our radiative transfer
calculations show that irradiation plays an important role in the mechanisms
that dictate the size range of aligned grains in Class 0 protostars. Regions of
the envelope that are preferentially irradiated harbor strong polarized dust
emission but can be affected by the rotational disruption of dust grains.
Episodes of high luminosity could affect grain alignment and trigger grain
disruption mechanisms. [abridged]",2303.12275v1
1997-07-09,Correlation Between Luminosity and Accretion Torque in 4U 1626-67 and GX 301-2,"We present X-ray light curves and energy spectra for the persistent accreting
pulsars 4U 1626-67 and GX 301-2 measured by the All-Sky Monitor (ASM) on Ginga
from 1987 March - 1991 October. We compare these with simultaneous and near
simultaneous measurements of spin frequency and flux by other instruments,
principally the Burst and Transient Source Experiment (BATSE) on the Compton
Gamma Ray Observatory (CGRO). A dramatic change in the shape of the X-ray
spectrum and a 20% decrease in the 1-20 keV X-ray flux accompany the 1990
transition from steady spin up to steady spin down in 4U 1626-67. The Ginga ASM
is the only instrument to observe 4U 1626-67 during both spin up and spin down.
We show that the distance to 4U 1626-67 is greater than 5 kpc. If 4U 1626-67 is
a near-equilibrium rotator and if the 0.04 Hz Quasi-Period Oscillations seen
during spin up are magnetospheric beat-frequency oscillations, then the
distance to the source is 5 kpc, assuming a neutron-star mass of 1.4 solar
masses, radius 10 km, and moment of inertia 10^45 g cm^2. The X-ray flux of GX
301-2 measured with the ASM varies with orbital phase. The flux peaks shortly
before periastron, with a secondary maximum near apastron. Such variations were
seen previously in the 20-50 keV pulsed flux with BATSE. The ASM observations
confirm that the 20-50 keV pulsed flux in GX 301-2 is a good tracer of the
bolometric flux. The X-ray flux in GX 301-2 was a factor of 2 larger than
average during the periastron passage prior to an episode of persistent spin up
in 1991 July observed with BATSE that lasted half an orbit and resembled
outbursts seen in transient X-ray pulsars.",9707105v1
2015-02-26,The spin rate of pre-collapse stellar cores: wave-driven angular momentum transport in massive stars,"The core rotation rates of massive stars have a substantial impact on the
nature of core-collapse supernovae and their compact remnants. We demonstrate
that internal gravity waves (IGW), excited via envelope convection during a red
supergiant phase or during vigorous late time burning phases, can have a
significant impact on the rotation rate of the pre-SN core. In typical ($10 \,
M_\odot \lesssim M \lesssim 20 \, M_\odot$) supernova progenitors, IGW may
substantially spin down the core, leading to iron core rotation periods $P_{\rm
min,Fe} \gtrsim 30 \, {\rm s}$. Angular momentum (AM) conservation during the
supernova would entail minimum NS rotation periods of $P_{\rm min,NS} \gtrsim 3
\, {\rm ms}$. In most cases, the combined effects of magnetic torques and IGW
AM transport likely lead to substantially longer rotation periods. However, the
stochastic influx of AM delivered by IGW during shell burning phases inevitably
spin up a slowly rotating stellar core, leading to a maximum possible core
rotation period. We estimate maximum iron core rotation periods of $P_{\rm
max,Fe} \lesssim 5 \times 10^3 \, {\rm s}$ in typical core-collapse supernova
progenitors, and a corresponding spin period of $P_{\rm max, NS} \lesssim 500
\, {\rm ms}$ for newborn neutron stars. This is comparable to the typical birth
spin periods of most radio pulsars. Stochastic spin-up via IGW during shell
O/Si burning may thus determine the initial rotation rate of most neutron
stars. For a given progenitor, this theory predicts a Maxwellian distribution
in pre-collapse core rotation frequency that is uncorrelated with the spin of
the overlying envelope.",1502.07779v3
2016-10-09,Eccentricity and Spin-Orbit Misalignment in Short-Period Stellar Binaries as a Signpost of Hidden Tertiary Companions,"Eclipsing binaries are observed to have a range of eccentricities and
spin-orbit misalignments (stellar obliquities). Whether such properties are
primordial, or arise from post-formation dynamical interactions remains
uncertain. This paper considers the scenario in which the binary is the inner
component of a hierarchical triple stellar system, and derives the requirements
that the tertiary companion must satisfy in order to raise the eccentricity and
obliquity of the inner binary. Through numerical integrations of the secular
octupole-order equations of motion of stellar triples, coupled with the spin
precession of the oblate primary star due to the torque from the secondary, we
obtain a simple, robust condition for producing spin-orbit misalignment in the
inner binary: In order to excite appreciable obliquity, the precession rate of
the stellar spin axis must be smaller than the orbital precession rate due to
the tertiary companion. This yields quantitative requirements on the mass and
orbit of the tertiary. We also present new analytic expressions for the maximum
eccentricity and range of inclinations allowing eccentricity excitation
(Lidov-Kozai window), for stellar triples with arbitrary masses and including
the non-Keplerian potentials introduced by general relativity, stellar tides
and rotational bulges. The results of this paper can be used to place
constraints on unobserved tertiary companions in binaries that exhibit high
eccentricity and/or spin-orbit misalignment, and will be helpful in guiding
efforts to detect external companions around stellar binaries. As an
application, we consider the eclipsing binary DI Herculis, and identify the
requirements that a tertiary companion must satisfy to produce the observed
spin-orbit misalignment.",1610.02626v2
2018-02-15,Spin and charge pumping by steady or pulse current-driven magnetic domain wall: A self-consistent multiscale time-dependent-quantum/time-dependent-classical approach,"We introduce a multiscale framework which combines time-dependent
nonequilibrium Green function (TD-NEGF) algorithms, scaling linearly in the
number of time steps and describing quantum-mechanically conduction electrons
in the presence of time-dependent fields of arbitrary strength or frequency,
with classical time evolution of localized magnetic moments described by the
Landau-Lifshitz-Gilbert (LLG) equation. The TD-NEGF+LLG framework can be
applied to a variety of problems where current-driven spin torque induces
dynamics of magnetic moments as the key resource for next generation
spintronics. Using magnetic domain wall (DW) as an example, we predict that its
motion will pump time-dependent spin and charge currents (on the top of
unpolarized DC charge current injected through normal metal leads to drive the
DW motion). The conversion of AC components of spin current, whose amplitude
increases (decreases) as the DW approaches (distances from) the normal metal
lead, into AC voltage via the inverse spin Hall effect offers a tool to
precisely track the DW position along magnetic nanowire. We also quantify the
DW transient inertial displacement due to its acceleration and deceleration by
pulse current and the entailed spin and charge pumping. Finally, TD-NEGF+LLG as
a nonperturbative (i.e., numerically exact) framework allows us to establish
the limits of validity of the so-called spin-motive force (SMF) theory for
pumped charge current by time-dependent magnetic textures---the perturbative
analytical formula of SMF theory becomes inapplicable for large frequencies
(but unrealistic in magnetic system) and, more importantly, for increasing
noncollinearity when the angles between neighboring magnetic moments exceed
$\simeq 10^\circ$.",1802.05682v3
2019-07-24,Modeling rotational disruption of grains and microwave emission from spinning dust in AGB envelopes,"Radio observations of some Asymptotic Giant Branch (AGB) star envelopes show
the excess emission at frequencies below 100 GHz which cannot be explained by
thermal dust emission (hereafter anomalous microwave emission-AME). Moreover,
AGB envelopes are a common place where gas molecules condense to form
nanoparticles (e.g., polycyclic aromatic hydrocarbons) and large grains. In
this paper, we will study whether electric dipole emission from rapidly
spinning nanoparticles can reproduce the AME observed toward AGB stars. To
properly model the size distribution of nanoparticles in the AGB envelope, we
take into account both the increase of nanoparticles due to rotational
disruption of large grains spun-up by radiative torques and the decrease of
smallest nanoparticles due to rotational disruption driven by stochastic gas
collisions. We then perform detailed modeling of microwave emission from
rapidly spinning nanoparticles from both C-rich and O-rich AGB envelopes using
the grain size distribution constrained by rotational disruption. We find that
spinning dust emission is dominant over thermal dust emission at frequencies
below 100 GHz. We attempt to fit the observational data of AME using our
spinning dust model and demonstrate that spinning dust can reproduce the
observed AME in six AGB stars. Finally, we discuss that microwave emission from
spinning dust in AGB envelopes could be observed with high-resolution upcoming
radio telescopes such as ngVLA and ALMA Band 1. This would be a major leap for
understanding AGB envelopes, formation, evolution, and internal structures of
dust. Observations would help to distinguish the carrier of AME from comparing
C-rich to O-rich stars, because PAHs are formed in C-rich AGB stars while
silicates are formed in O-rich stars.",1907.10654v3
2023-01-24,Spin Dynamics in van der Waals Magnetic Systems,"The discovery of atomic monolayer magnetic materials has stimulated intense
research activities in the two-dimensional (2D) van der Waals (vdW) materials
community. The field is growing rapidly and there has been a large class of 2D
vdW magnetic compounds with unique properties, which provides an ideal platform
to study magnetism in the atomically thin limit. In parallel, based on
tunneling magnetoresistance and magneto-optical effect in 2D vdW magnets and
their heterostructures, emerging concepts of spintronic and optoelectronic
applications such as spin tunnel field-effect transistors and spin-filtering
devices are explored. While the magnetic ground state has been extensively
investigated, reliable characterization and control of spin dynamics play a
crucial role in designing ultrafast spintronic devices. Ferromagnetic resonance
(FMR) allows direct measurements of magnetic excitations, which provides
insight into the key parameters of magnetic properties such as exchange
interaction, magnetic anisotropy, gyromagnetic ratio, spin-orbit coupling,
damping rate, and domain structure. In this review article, we present an
overview of the essential progress in probing spin dynamics of 2D vdW magnets
using FMR techniques. Given the dynamic nature of this field, we focus mainly
on broadband FMR, optical FMR, and spin-torque FMR, and their applications in
studying prototypical 2D vdW magnets. We conclude with the recent advances in
laboratory- and synchrotron-based FMR techniques and their opportunities to
broaden the horizon of research pathways into atomically thin magnets.",2301.09822v2
2023-02-07,Probing the nature of the low state in the extreme ultraluminous X-ray pulsar NGC 5907 ULX1,"NGC 5907 ULX1 is the most luminous ultra-luminous X-ray pulsar (ULXP) known
to date, reaching luminosities in excess of 1e41 erg/s. The pulsar is known for
its fast spin-up during the on-state. Here, we present a long-term monitoring
of the X-ray flux and the pulse period between 2003-2022. We find that the
source was in an off- or low-state between mid-2017 to mid-2020. During this
state, our pulse period monitoring shows that the source had spun down
considerably. We interpret this spin-down as likely being due to the propeller
effect, whereby accretion onto the neutron star surface is inhibited. Using
state-of-the-art accretion and torque models, we use the spin-up and spin-down
episodes to constrain the magnetic field. For the spin-up episode, we find
solutions for magnetic field strengths of either around 1e12G or 1e13G,
however, the strong spin-down during the off-state seems only to be consistent
with a very high magnetic field, namely, >1e13G. This is the first time a
strong spin-down is seen during a low flux state in a ULXP. Based on the
assumption that the source entered the propeller regime, this gives us the best
estimate so far for the magnetic field of NGC 5907 ULX1.",2302.03425v1
2017-01-13,Polarization-transfer observables with polarized beams,"A review is given of our present knowledge of different parametrization of
experimental results in inelastic scattering process with polarized proton
beams. Spin observables in inelastic proton scattering for a set of lightweight
nuclei are studied at intermediate energies in the region of 100-500 MeV. Two
important types of DWIA calculations are used in the analysis of experiments.
Important spin observables representing the difference functions (P-Ay) and
(P-Ay)sigma are examined along with the polarization-transfer (spin-transfer)
coefficients D(ij), i.e. D with indices NN, SS, LL, LS and SL, in inelastic
scattering of polarized protons. The above indicated value of sigma is the
differential cross section. These spin observables are treated in the context
of the exchange features of the effective interaction. The linear combinations
D(K), D(i) of the complete polarization-transfer observables D(ij) in inelastic
proton scattering at intermediate energies are extensively demonstrated. A
comparison between systematized, measured and calculated quantities of the
combinations D(K) and, partially, sigma D(K) for the 1+ (T=0 and T=1) levels in
12-C, for the 4- (T=0 and T=1) states in 16-O, and for the 6- (T=0 and T=1)
levels in 28-Si are reported. Particularities in angular distributions of
transverse- and longitudinal-spin-transfer probabilities D(K) for T=0 and T=1
unnatural-parity states in some nuclei are discussed. The spin-observable
combinations D(Ls) allowed to differentiate reliably the strength of isoscalar
and isovector spin-orbit. interactions. The comparison of the experimental and
calculated D(K) for the 1+, T = 0 state in 12- C with the use of zero-range
treatment (LEA code) and exact finite-range calculations (DWBA-91 program) made
it possible to identify the role of exchange contributions. Other observables
are also considered for the same purposes.",1701.03582v1
2017-03-27,Thrust vectoring of an electric solar wind sail with a realistic sail shape,"The shape of a rotating electric solar wind sail under the centrifugal force
and solar wind dynamic pressure is modeled to address the sail attitude
maintenance and thrust vectoring. The sail rig assumes centrifugally stretched
main tethers that extend radially outward from the spacecraft in the sail spin
plane. Furthermore, the tips of the main tethers host remote units that are
connected by auxiliary tethers at the sail rim. Here, we derive the equation of
main tether shape and present both a numerical solution and an analytical
approximation for the shape as parametrized both by the ratio of the electric
sail force to the centrifugal force and the sail orientation with respect to
the solar wind direction. The resulting shape is such that near the spacecraft,
the roots of the main tethers form a cone, whereas towards the rim, this coning
is flattened by the centrifugal force, and the sail is coplanar with the sail
spin plane. Our approximation for the sail shape is parametrized only by the
tether root coning angle and the main tether length. Using the approximate
shape, we obtain the torque and thrust of the electric sail force applied to
the sail. As a result, the amplitude of the tether voltage modulation required
for the maintenance of the sail attitude is given as a torque-free solution.
The amplitude is smaller than that previously obtained for a rigid single
tether resembling a spherical pendulum. This implies that less thrusting margin
is required for the maintenance of the sail attitude. For a given voltage
modulation, the thrust vectoring is then considered in terms of the radial and
transverse thrust components.",1703.08975v1
2017-11-10,The open flux evolution of a solar-mass star on the main sequence,"Magnetic activity is known to be correlated to the rotation period for
moderately active main sequence solar-like stars. In turn, the stellar rotation
period evolves as a result of magnetised stellar winds that carry away angular
momentum. Understanding the interplay between magnetic activity and stellar
rotation is therefore a central task for stellar astrophysics. Angular momentum
evolution models typically employ spin-down torques that are formulated in
terms of the surface magnetic field strength. However, these formulations fail
to account for the magnetic field geometry, unlike those that are expressed in
terms of the open flux, i.e. the magnetic flux along which stellar winds flow.
  In this work, we model the angular momentum evolution of main sequence
solar-mass stars using a torque law formulated in terms of the open flux. This
is done using a potential field source surface model in conjunction with the
Zeeman-Doppler magnetograms of a sample of roughly solar-mass stars. We explore
how the open flux of these stars varies with stellar rotation and choice of
source surface radii. We also explore the effect of field geometry by using two
methods of determining the open flux. The first method only accounts for the
dipole component while the second accounts for the full set of spherical
harmonics available in the Zeeman-Doppler magnetogram. We find only a small
difference between the two methods, demonstrating that the open flux, and
indeed the spin-down, of main sequence solar-mass stars is likely dominated by
the dipolar component of the magnetic field.",1711.03904v1
2018-08-07,Rotationally induced failure of irregularly shaped asteroids,"Many asteroids are rubble piles with irregular shapes. While the irregular
shapes of large asteroids may be attributed to collisional events, those of
small asteroids may result from not only impact events but also rotationally
induced failure, a long-term consequence of small torques caused by, for
example, solar radiation pressure. A better understanding of shape deformation
induced by such small torques will allow us to give constraints on the
evolution process of an asteroid and its structure. However, no quantitative
study has been reported to provide the relationship between an asteroid's shape
and its failure mode due to its fast rotation. Here, we use a finite element
model (FEM) technique to analyze the failure modes and conditions of 24
asteroids with diameters less than 30 - 40 km, which were observed at high
resolution by ground radar or asteroid exploration missions. Assuming that the
material distribution is uniform, we investigate how these asteroids fail
structurally at different spin rates. Our FEM simulations describe the detailed
deformation mode of each irregularly shaped asteroid at fast spin. The failed
regions depend on the original shape. Spheroidal objects structurally fail from
the interior, while elongated objects experience structural failure on planes
perpendicular to the minimum moment of inertia axes in the middle of their
structure. Contact binary objects have structural failure across their most
sensitive cross sections. We further investigate if our FEM analysis is
consistent with earlier works that theoretically explored a uniformly rotating
triaxial ellipsoid. The results show that global shape variations may
significantly change the failure condition of an asteroid. Our work suggests
that it is critical to take into account the actual shapes of asteroids to
explore their failure modes in detail.",1808.02168v1
2019-01-14,Gas Jet Morphology and the Very Rapidly Increasing Rotation Period of Comet 41P/Tuttle-Giacobini-Kresak,"We present results from our 47-night imaging campaign of Comet
41P/Tuttle-Giacobini-Kresak conducted from Lowell Observatory between 2017
February 16 and July 2. Coma morphology revealed gas jets, whose appearance and
motion as a function of time yielded the rotation period and other properties.
All narrowband CN images exhibited either one or two jets; one jet appeared as
a partial face-on spiral with clockwise rotation while the second jet evolved
from a side-on corkscrew, through face-on, and finally corkscrew again, with
only a slow evolution throughout the apparition due to progressive viewing
geometry changes. A total of 78 period determinations were made over a 7-week
interval, yielding a smooth and accelerating rotation period starting at 24 hr
(March 21&22) and passing 48 hr on April 28. While this is by far the fastest
rate of change ever measured for a comet nucleus, the torque required is
readily within what can exist given likely properties of the nucleus. If the
torque remained constant, we estimate that the nucleus could have stopped
rotating and/or began to tumble as soon as only two months following
perihelion, and will certainly reach this stage by early in the next
apparition. Working backwards in time, Tuttle-Giacobini-Kresak would have been
rotating near its rotational break-up velocity 3-4 orbits earlier, suggesting
that its extreme 7-magnitude outburst observed in 2001 might have been caused
by a partial fragmentation at that time, as might the pair of 1973 8-magnitude
outbursts if there had been an earlier spin-down and spin-up cycle.",1901.04565v1
2021-04-22,Spin-torque induced wall motion in perpendicularly magnetized discs: ballistic versus oscillatory behavior,"We use time-resolved measurement and modeling to study the spin-torque
induced motion of a domain wall in perpendicular anisotropy magnets. In disc of
diameters between 70 and 100 nm, the wall drifts across the disc with
pronounced back-and-forth oscillations that arise because the wall moves in the
Walker regime. Several switching paths occur stochastically and lead to
distinct switching durations. The wall can cross the disc center either in a
ballistic manner or with variably marked oscillations before and after the
crossing. The crossing of the center can even occur multiple times if a
vertical Bloch line nucleates within the wall. The wall motion is analyzed
using a collective coordinate model parametrized by the wall position $q$ and
the tilt $\phi$ of its in-plane magnetization projection. The dynamics results
from the stretch field, which describes the affinity of the wall to reduce its
length and the wall stiffness field describing the wall tendency to reduce
dipolar energy by rotating its tilt. The wall oscillations result from the
continuous exchange of energy between to the two degrees of freedom $q$ and
$\phi$. The stochasticity of the wall dynamics can be understood from the
concept of the retention pond: a region in the $q-\phi$ space in which walls
are transiently bound to the disc center. Walls having trajectories close to
the pond must circumvent it and therefore have longer propagation times. The
retention pond disappears for a disc diameter of typically 40 nm: the wall then
moves in a ballistic manner irrespective of the dynamics of its tilt. The
propagation time is then robust against fluctuations hence reproducible.",2104.10929v1
2021-12-13,Mechanism of Spin-Orbit Torques in Platinum Oxide Systems,"Spin-Orbit Torque (SOT) Magnetic Random-Access Memories (MRAM) have shown
promising results towards the realization of fast, non-volatile memory systems.
Oxidation of the heavy-metal (HM) layer of the SOT-MRAM has been proposed as a
method to increase its energy efficiency. But the results are widely divergent
due to the difficulty in controlling the HM oxidation because of its low
enthalpy of formation. Here, we reconcile these differences by performing a
gradual oxidation procedure, which allows correlating the chemical structure to
the physical properties of the stack. As an HM layer, we chose Pt because of
the strong SOT and the low enthalpy of formation of its oxides. We find
evidence of an oxide inversion layer at the FM/HM interface: the oxygen is
drawn into the FM, while the HM remains metallic near the interface. We further
demonstrate that the oxygen migrates in the volume of the FM layer rather than
being concentrated at the interface. Consequently, we find that the intrinsic
magnitude of the SOT is unchanged compared to the fully metallic structure. The
previously reported apparent increase of SOTs is not intrinsic to platinum
oxide and instead arises from systemic changes produced by oxidation.",2112.07034v1
2022-10-23,Tidally excited gravity waves in the cores of solar-type stars: resonances and critical-layer formation,"We simulate the propagation and dissipation of tidally induced nonlinear
gravity waves in the cores of solar-type stars. We perform hydrodynamical
simulations of a previously developed Boussinesq model using a spectral-element
code to study the stellar core as a wave cavity that is periodically forced at
the outer boundary with a given azimuthal wavenumber and an adjustable
frequency. For low-amplitude forcing, the system exhibits resonances with
standing g-modes at particular frequencies, corresponding to a situation in
which the tidal torque is highly frequency-dependent. For high-amplitude
forcing, the excited waves break promptly near the centre and spin up the core
so that subsequent waves are absorbed in an expanding critical layer, as found
in previous work, leading to a tidal torque with a smooth frequency-dependence.
For intermediate-amplitude forcing, we find that linear damping of the waves
gradually spins up the core such that the resonance condition can be altered
drastically. The system can evolve towards or away from g-mode resonances,
depending on the difference between the forcing frequency and the closest
eigenfrequency. Eventually, a critical layer forms and absorbs the incoming
waves, leading to a situation similar to the high-amplitude case in which the
waves break promptly. We study the dependence of this process on the forcing
amplitude and frequency, as well as on the diffusion coefficients. We emphasize
that the small Prandtl number in the centre of solar-like stars facilitates the
development of a differentially rotating core owing to the nonlinear feedback
of waves. Our simulations and analysis reveal that this important mechanism may
drastically change the phase of gravity waves and thus the classical picture of
resonance locking in solar-type stars needs to be revised.",2210.12880v2
2023-03-08,Measurement of the angular momenta of pre-main-sequence stars: early evolution of slow and fast rotators and empirical constraints on spin-down torque mechanisms,"We use TESS full-frame imaging data to investigate the angular momentum
evolution of young stars in Orion Complex. We confirm recent findings that
stars with rotation periods faster than 2 d are overwhelmingly binaries, with
typical separations of tens of AU; such binaries quickly clear their disks,
leading to a tendency for rapid rotators to be diskless. Among (nominally
single) stars with rotation periods slower than 2 d, we observe the familiar,
gyrochronological horseshoe-shaped relationship of rotation period versus
$T_{\rm eff}$, indicating that the processes which govern the universal
evolution of stellar rotation on Gyr timescales are already in place within the
first few Myr. Using spectroscopic $v\sin i$ we determine the distribution of
$\sin i$, revealing that the youngest stars are biased toward more pole-on
orientations, which may be responsible for the systematics between stellar mass
and age observed in star-forming regions. We are also able for the first time
to make empirical, quantitative measurements of angular momenta and their time
derivative as functions of stellar mass and age, finding these relationships to
be much simpler and monotonic as compared to the complex relationships
involving rotation period alone; evidently, the relationship between rotation
period and $T_{\rm eff}$ is largely a reflection of mass-dependent stellar
structure and not of angular momentum per se. Our measurements show that the
stars experience spin-down torques in the range ~$10^{37}$ erg at ~1 Myr to
~$10^{35}$ erg at ~10 Myr, which provide a crucial empirical touchstone for
theoretical mechanisms of angular momentum loss in young stars.",2303.04834v1
2023-08-28,Magnetically threaded accretion disks in resistive magnetohydrodynamic simulations and asymptotic expansion,"Aims. A realistic model of magnetic linkage between a central object and its
accretion disk is a prerequisite for understanding the spin history of stars
and stellar remnants. To this end, we aim to provide an analytic model in
agreement with magnetohydrodynamic (MHD) simulations.
  Methods. For the first time, we wrote a full set of stationary asymptotic
expansion equations of a thin magnetic accretion disk, including the induction
and energy equations. We also performed a resistive MHD simulation of an
accretion disk around a star endowed with a magnetic dipole, using the publicly
available code PLUTO. We compared the analytical results with the numerical
solutions, and discussed the results in the context of previous solutions of
the induction equation describing the star-disk magnetospheric interaction.
  Results. We found that the magnetic field threading the disk is suppressed by
orders of magnitude inside thin disks, so the presence of the stellar magnetic
field does not strongly affect the velocity field, nor the density profile
inside the disk. Density and velocity fields found in the MHD simulations match
the radial and vertical profiles of the analytic solution. Qualitatively, the
MHD simulations result in an internal magnetic field similar to the solutions
previously obtained by solving the induction equation in the disk alone.
However, the magnetic field configuration is quantitatively affected by
magnetic field inflation outside the disk; this is reflected in the net torque.
The torque on the star is an order of magnitude larger in the magnetic than in
the non-magnetic case. Spin-up of the star occurs on a timescale comparable to
the accretion timescale in the MHD case, and is an order of magnitude slower in
the absence of a stellar magnetic field.",2308.14910v1
2024-02-21,High-resolution spectroscopy of the intermediate polar EX Hydrae: II. The inner disk radius,"EX Hya is one of the best studied, but still enigmatic intermediate polars.
We present phase-resolved blue VLT/UVES high-resolution ($\lambda/\Delta
\lambda\simeq16.000$) spectra of EX Hya taken in January 2004. Our analysis
involves a unique decomposition of the Balmer line profiles into the
spin-modulated line wings that represent streaming motions in the magnetosphere
and the orbital-phase modulated line core that represents the accretion disk.
Spectral analysis and tomography show that the division line between the two is
solidly located at $\mid\upsilon_{rad}\mid\simeq1200$ km s$^{-1}$, defining the
inner edge of the accretion disk at $r_{in}\simeq{7}\times 10^{9}$ cm or
$\sim10 R_1$ (WD radii). This large central hole allows an unimpeded view of
the tall accretion curtain at the lower pole with a shock height up to
$h_{sh}\sim1 R_1$ that is required by X-ray and optical observations. Our
results contradict models that advocate a small magnetosphere and a small inner
disk hole. Equating $r_{in}$ with the magnetospheric radius in the orbital
plane allows us to derive a magnetic moment of the WD of $\mu_1\simeq1.3\times
10^{32}$ G cm$^{3}$ and a surface field strength $B_1\sim0.35$ MG. Given a
polar field strength $B_{p} \lesssim 1.0$ MG, optical circular polarization is
not expected. With an accretion rate $\dot M = 3.9\times10^{-11}$
$M_{\odot}$yr$^{-1}$, the accretion torque is $G_{acc}\simeq 2.2 \times
10^{33}$ g cm$^{2}$s$^{-2}$. The magnetostatic torque is of similar magnitude,
suggesting that EX Hya is not far from being synchronized. We measured the
orbital radial-velocity amplitude of the WD, $K_1=58.7\pm3.9$ km s$^{-1}$, and
found a spin-dependent velocity modulation as well. The former is in perfect
agreement with the mean velocity amplitude obtained by other researchers,
confirming the published component masses $M_1\simeq0.79 M_\odot$ and
$M_2\simeq0.11 M_\odot$.",2402.13834v1
2018-02-09,Electron Spin Coherences in Rare-Earth Optically Excited States for Microwave to Optical Quantum Transducers,"Efficient and reversible optical to microwave coherent transducers are
required to enable entanglement transfer between superconducting qubits and
light for quantum networks. Rare-earth-doped crystals that possess narrow
optical and spin transitions are a promising way to implement these devices.
Current approaches use ground-state electron spin transitions that have
coherence lifetimes ($T_2$) often limited by spin flip-flop processes and/or
spectral diffusion, even at very low temperatures. Here, we investigate spin
coherence in an optically excited state of an Er$^{3+}$:Y$_2$SiO$_5$ crystal at
temperatures from 1.6 to 3.5 K and under a weak 8.7 mT magnetic field. Spin
coherence and population lifetimes of up to 1.6 $\mu$s and 1.2 ms,
respectively, are measured by 2- and 3-pulse optically-detected spin echo
experiments. Analysis of the dephasing processes suggest that ms $T_2$ can be
reached at lower temperatures for the excited-state spins, whereas ground-state
spin states could be limited to a few $\mu$s due to resonant interactions with
the other Er$^{3+}$ spins in the lattice (spin diffusion). We propose a quantum
transducer scheme with the potential for close to unit efficiency that exploits
the specific advantages offered by the spin states of optically excited
electronic energy levels.",1802.03354v2
2020-04-11,Understanding the mechanism of oxygen evolution reaction (OER) with the consideration of spin,"Oxygen evolution reaction (OER) with intractable high overpotential is the
rate-limiting step for rechargeable metal-air battery, water electrolysis
systems, and solar fuels devices. There exists a spin state transition from
spin singlet OH-/H2O reactant to spin triplet O2 product, which has not
received enough attention yet. In this perspective, we attempt to retrospect
electron behaviours during the whole OER process, with the consideration of
spin attribute. Regardless of the adopted mechanisms by different
electrocatalysts, for example, adsorbate evolution mechanism (AEM) or lattice
oxygen mechanism (LOM), the underlying rationale is that active sites have to
extract three in four electrons with the same spin direction before the
formation of O=O. This spin-sensitive nature of OER superimposes additional
high requirements on the electrocatalysts, especially on the spin structure, to
compliment the fast electron transfer in the interface with spin selection and
smoothly delivery afterwards. When optimizing the geometric and electronic
structures catering for the spin-sensitive OER, awareness of the couplings
between spin, charge, orbital and lattice is necessary. Some spin-correlated
physical properties, such as (1) crystal field, (2) coordination, (3)
oxidation, (4) bonding, (5) eg electron number, (6) conductivity and (7)
magnetism, are also discussed briefly. It is hoped that our perspective could
shed lights on the underlying physics of the slow kinetics of OER, providing a
rational guidance for more effective energy conversion electrocatalysts
designs.",2004.05326v1
2020-07-30,Electrical and Thermal Generation of Spin Currents by Magnetic Graphene,"The demand for compact, high-speed and energy-saving circuitry urges higher
efficiency of spintronic devices that can offer a viable alternative for the
current electronics. The route towards this goal suggests implementing
two-dimensional (2D) materials that provide large spin polarization of charge
current together with the long-distance transfer of the spin information. Here,
for the first time, we experimentally demonstrate a large spin polarization of
the graphene conductivity ($\approx 14\%$) arising from a strong induced
exchange interaction in proximity to a 2D layered antiferromagnetic. The strong
coupling of charge and spin currents in graphene with high efficiency of spin
current generation, comparable to that of metallic ferromagnets, together with
the observation of spin-dependent Seebeck and anomalous Hall effects, all
consistently confirm the magnetic nature of graphene. The high sensitivity of
spin transport in graphene to the magnetization of the outermost layer of the
adjacent interlayer antiferromagnet, also provides a tool to read out a single
magnetic sub-lattice. The first time observations of the electrical and thermal
generation of spin currents by magnetic graphene suggest it as the ultimate
building block for ultra-thin magnetic memory and sensory devices, combining
gate tunable spin-dependent conductivity, long-distance spin transport and
spin-orbit coupling all in a single 2D material.",2007.15597v1
2020-11-05,Nanophotonic structures with optical surface modes for tunable spin current generation,"Heat generated by spin currents in spintronics-based devices is typically
much less than that generated by charge current flows in conventional
electronic devices. However, the conventional approaches for excitation of spin
currents based on spin-pumping and spin Hall effect are limited in efficiency
which restricts their application for viable spintronic devices. We propose a
novel type of photonic-crystal (PC) based structures for efficient and tunable
optically-induced spin current generation via the Spin Seebeck and inverse spin
Hall effects. It is experimentally demonstrated that optical surface modes
localized at the PC surface covered by ferromagnetic layer and materials with
giant spin-orbit coupling (SOC) notably increase the efficiency of the
optically-induced spin current generation and provides its tunability by
modifying light wavelength or angle of incidence. Up to 100% of the incident
light power can be transferred to heat within the SOC layer and, therefore, to
spin current. Importantly, high efficiency becomes accessible even for
ultra-thin SOC layers. Moreover, surface patterning of the PC-based spintronic
nanostructure allows local generation of spin currents at the pattern scales
rather than diameter of the laser beam.",2011.02770v2
2022-07-06,Robust millisecond coherence times of erbium electron spins,"Erbium-doped solids are prime candidates for optical quantum communication
networks due to erbium's telecom C-band emission. A long-lived electron spin of
erbium with millisecond coherence time is highly desirable for establishing
entanglement between adjacent quantum repeater nodes while long-term storage of
the entanglement could rely on transferring to erbium's second-long coherence
nuclear spins. Here we report GHz-range electron spin transitions of
$^{167}\mathrm{Er}^{3+}$ in yttrium oxide ($\mathrm{Y_2O_3}$) matrix with
coherence times that are consistently longer than a millisecond. Instead of
addressing field-specific Zero First-Order Zeeman transitions, we probe weakly
mixed electron spins with the field orientation along the lower g-factors.
Using pulsed electron spin resonance spectroscopy, we find paramagnetic
impurities are the dominant source of decoherence, and by polarizing them we
achieve a Hahn echo spin $\mathrm{T_2}$ up to 1.46 ms, and a coherence time up
to 7.1 ms after dynamical decoupling. These coherence lifetimes are among the
longest found in crystalline hosts especially those with nuclear spins. We
further enhance the coherence time beyond conventional dynamical decoupling,
using customized sequences to simultaneously mitigate spectral diffusion and
Er-Er dipolar interactions. Despite nuclear and impurity spins in the host,
this work shows that long-lived erbium spins comparable to non-nuclear spin
hosts can be achieved. Our study not only establishes $^{167}\mathrm{Er}^{3+}$:
$\mathrm{Y_2 O_3}$ as a significantly promising quantum memory platform but
also provides a general guideline for engineering long-lived erbium spins in a
variety of host materials for quantum technologies.",2207.02708v1
2001-06-04,Tidal Torques and Galactic Warps,"We investigate the tilting and warping of galactic disks in response to tidal
torquing. The strength of the torque is determined from cosmological N-body
simulations. We find the tidal torques to be dominated by substructure in the
galactic halo, such as dwarf satellites, and by a misalignment between the disk
angular momentum and the figure axes of the dark matter halo. The radial
dependence of the torque can approximated by a power law of index -2.5. A
massless disk subjected to such a torque develops a trailing warp similar to
those seen in a large number of disk galaxies, i.e. the inner regions of the
disk tilt faster than the outer disk. In the case of massive disks, self
gravity causes the inner disk to stay locally flat and only the outer regions
show the signatures of warps. The radius outside of which a massive disk is
warped depends on the local surface density of the disk and on the product of
the strength of the torque and the exposure time to this torque.",0106049v1
2008-05-16,Free Energy of Twisted Semiflexible Polymers,"We investigate the role of fluctuations in single molecule measurements of
torque-link ($t-lk$) curves. For semiflexible polymers of finite persistence
length (i.e. polymers with contour length $L$ comparable to the persistence
length $L_P$), the torque versus link curve in the constant torque (isotorque)
ensemble is distinct from the one in the constant link (isolink) ensemble.
Thus, one encounters the conceptually interesting issue of a ``free energy of
transition'' in switching ensembles while making torque-link measurements. We
predict the dependence on the semiflexibility parameter $\beta = L/L_P$ of this
extra contribution to the free energy which shows up as an area in the
torque-link plane. This can be tested against future torque-link experiments
with single biopolymers. We bring out the inequivalence of torque-link curves
for a stiff polymer and present explicit analytical expressions for the {\it
distinct} torque-link relations in the two ensembles and the free energy
difference in switching ensembles in this context. The predictions of our work
can be tested against single molecule experiments on torsionally constrained
biopolymers.",0805.2458v1
2013-10-31,Linear Corotation Torques in Non-Barotropic Disks,"I derive a fully analytic expression for the linear corotation torque to
first order in eccentricity for planets in non-barotropic protoplanetary disks,
taking into account the effect of disk entropy gradients. This torque formula
is applicable to both the co-orbital corotation torque and the non co-orbital
corotation torques -- for planets in orbits with non-zero eccentricity -- in
disks where the thermal diffusivity and viscosity are sufficient to maintain
linearity of these interactions. While the co-orbital corotation torque is
important for migration of planets in Type I migration, the non co-orbital
corotation torque plays an important role in the eccentricity evolution of
giant planets that have opened gaps in the disk. The presence of an entropy
gradient in the disk can significantly modify the corotation torque in both
these cases.",1310.8626v2
2016-04-14,Population synthesis of planet formation using a torque formula with dynamic effects,"Population synthesis studies into planet formation have suggested that
distributions consistent with observations can only be reproduced if the actual
Type I migration timescale is at least an order of magnitude longer than that
deduced from linear theories. Although past studies considered the effect of
the Type I migration of protoplanetary embryos, in most cases they used a
conventional formula based on static torques in isothermal disks, and employed
a reduction factor to account for uncertainty in the mechanism details.
However, in addition to static torques, a migrating planet experiences dynamic
torques that are proportional to the migration rate. These dynamic torques can
impact on planet migration and predicted planetary populations. In this study,
we derived a new torque formula for Type I migration by taking into account
dynamic corrections. This formula was used to perform population synthesis
simulations with and without the effect of dynamic torques. In many cases,
inward migration was slowed significantly by the dynamic effects. For the
static torque case, gas giant formation was effectively suppressed by Type I
migration; however, when dynamic effects were considered, a substantial
fraction of cores survived and grew into gas giants.",1604.04116v1
2017-04-27,Detecting Casimir torque with an optically levitated nanorod,"The linear momentum and angular momentum of virtual photons of quantum vacuum
fluctuations can induce the Casimir force and the Casimir torque, respectively.
While the Casimir force has been measured extensively, the Casimir torque has
not been observed experimentally though it was predicted over forty years ago.
Here we propose to detect the Casimir torque with an optically levitated
nanorod near a birefringent plate in vacuum. The axis of the nanorod tends to
align with the polarization direction of the linearly polarized optical
tweezer. When its axis is not parallel or perpendicular to the optical axis of
the birefringent crystal, it will experience a Casimir torque that shifts its
orientation slightly. We calculate the Casimir torque and Casimir force acting
on a levitated nanorod near a birefringent crystal. We also investigate the
effects of thermal noise and photon recoils on the torque and force detection.
We prove that a levitated nanorod in vacuum will be capable of detecting the
Casimir torque under realistic conditions.",1704.08770v2
2019-08-09,Ultrasensitive torque detection with an optically levitated nanorotor,"Torque sensors such as the torsion balance enabled the first determination of
the gravitational constant by Cavendish and the discovery of Coulomb's law.
Torque sensors are also widely used in studying small-scale magnetism, the
Casimir effect, and other applications. Great effort has been made to improve
the torque detection sensitivity by nanofabrication and cryogenic cooling. The
most sensitive nanofabricated torque sensor has achieved a remarkable
sensitivity of $10^{-24} \rm{Nm}/\sqrt{\rm{Hz}}$ at millikelvin temperatures in
a dilution refrigerator. Here we dramatically improve the torque detection
sensitivity by developing an ultrasensitive torque sensor with an optically
levitated nanorotor in vacuum. We measure a torque as small as $(1.2 \pm 0.5)
\times 10^{-27} \rm{Nm}$ in 100 seconds at room temperature. Our system does
not require complex nanofabrication or cryogenic cooling. Moreover, we drive a
nanoparticle to rotate at a record high speed beyond 5 GHz (300 billion rpm).
Our calculations show that this system will be able to detect the long-sought
vacuum friction near a surface under realistic conditions. The optically
levitated nanorotor will also have applications in studying nanoscale magnetism
and quantum geometric phase.",1908.03453v1
2011-07-14,Corotation torques experienced by planets embedded in weakly magnetized turbulent discs,"The migration of low-mass planets is driven by the differential Lindblad
torque and the corotation torque in non-magnetic viscous models of
protoplanetary discs. The corotation torque has recently received detailed
attention as it may slow down, stall, or reverse migration. In laminar viscous
disc models, the long-term evolution of the corotation torque is intimately
related to viscous and thermal diffusion processes in the planet's horseshoe
region. This paper examines the properties of the corotation torque in discs
where MHD turbulence develops as a result of the magnetorotational instability,
considering a weak initial toroidal magnetic field. We present results of 3D
MHD simulations carried out with two different codes. Non-ideal MHD effects and
the disc's vertical stratification are neglected, and locally isothermal disc
models are considered. The running time-averaged torque exerted by the disc on
a fixed planet is evaluated in three disc models. We first present results with
an inner disc cavity (planet trap). As in viscous disc models, the planet is
found to experience a positive running time-averaged torque over several
hundred orbits, which highlights the existence of an unsaturated corotation
torque maintained in the long term in MHD turbulent discs. Two disc models with
initial power-law density and temperature profiles are also adopted, in which
the time-averaged torque is found to be in decent agreement with its
counterpart in laminar viscous disc models with similar viscosity at the planet
location. Detailed analysis of the averaged torque density distributions
indicates that the differential Lindblad torque takes very similar values in
MHD turbulent and laminar viscous discs, and there exists an unsaturated
corotation torque in MHD turbulent discs. This analysis also reveals the
existence of an additional corotation torque in weakly magnetized discs.",1107.2774v1
1998-07-13,Staggered-spin contribution to nuclear spin-lattice relaxation in two-leg antiferromagnetic spin-1/2 ladders,"We study the nuclear spin-lattice relaxation rate $1/T_1$ in the two-leg
antiferromagnetic spin-1/2 Heisenberg ladder. More specifically, we consider
the contribution to $1/T_1$ from the processes with momentum transfer
$(\pi,\pi)$. In the limit of weak coupling between the two chains, this
contribution is of activation type with gap $2\Delta$ at low temperatures
($\Delta$ is the spin gap), but crosses over to a slowly-decaying temperature
dependence at the crossover temperature $T\approx\Delta$. This crossover
possibly explains the recent high-temperature NMR results on ladder-containing
cuprates by T. Imai et al.",9807187v1
1998-11-29,Statistical Mechanics and error-correction Codes,"I will show that there is a deep relation between error-correction codes and
certain mathematical models of spin glasses. In particular minimum error
probability decoding is equivalent to finding the ground state of the
corresponding spin system. The most probable value of a symbol is related to
the magnetization at a different temperature. Convolutional codes correspond to
one-dimensional spin systems and Viterbi's decoding algorithm to the transfer
matrix algorithm of Statistical Mechanics. A particular spin-glass model, which
is exactly soluble, corresponds to an ideal code, i.e. a code which allows
error-free communication if the rate is below channel capacity.",9811406v1
1999-05-13,Dynamics of the Measurement of Nuclear Spins in a Solid-State Quantum Computer,"We study numerically the process of nuclear spin measurement in a solid-state
quantum computer of the type proposed by Kane by modeling the quantum dynamics
of two coupled nuclear spins on $^{31}$P donors implanted in silicon. We
estimate the minimum measurement time necessary for the reliable transfer of
quantum information from the nuclear spin subsystem to the electronic
subsystem. We also calculate the probability of error for typical values of the
external noise.",9905200v1
2000-07-03,Charge Ordering and Spin Dynamics in NaV2O5,"We report high-resolution neutron inelastic scattering experiments on the
spin excitations of NaV2O5. Below Tc, two branches associated with distinct
energy gaps are identified. From the dispersion and intensity of the spin
excitation modes, we deduce the precise zig-zag charge distribution on the
ladder rungs and the corresponding charge order (about 0.6). We argue that the
spin gaps observed in the low-T phase of this compound are primarily due to the
charge transfer.",0007025v2
2002-05-19,Adiabatic spin pumping through a quantum dot with a single orbital level,"We investigate an adiabatic spin pumping through a quantum dot with a single
orbital energy level under the Zeeman effect. Electron pumping is produced by
two periodic time dependent parameters, a magnetic field and a difference of
the dot-lead coupling between the left and right barriers of the dot. The
maximum charge transfer per cycle is found to be $e$, the unit charge in the
absence of a localized moment in the dot. Pumped charge and spin are different,
and spin pumping is possible without charge pumping in a certain situation.
They are tunable by changing the minimum and maximum value of the magnetic
field.",0205395v2
2003-09-12,Conductance fluctuations in the presence of spin scattering,"Electron transport through disordered systems that include spin scatterers is
studied numerically. We consider three kinds of magnetic impurities: the Ising,
the XY and the Heisenberg. By extending the transfer matrix method to include
the spin degree of freedom, the two terminal conductance is calculated. The
variance of conductance is halved as the number of spin components of the
magnetic impurities increases. Application of the Zeeman field in the lead
causes a further halving of the variance under certain conditions.",0309308v1
2003-10-15,Spin-filter magnetoresistance in magnetic barrier junctions,"The tunnel current and magnetoresistance (TMR) are investigated in magnetic
tunnel junctions consisting of a spin-filter tunnel barrier, sandwiched between
a ferromagnetic (FM) electrode and a nonmagnetic (NM) electrode. The
investigations are based on the transfer matrix method and the free-electron
approximation. The numerical results show that the spin transport depends on
the relative magnetization orientation of the FM electrode and the spin-filter
barrier, such that the tunnel current reaches its maximum when the magnetic
moments of the FM electrode and the magnetic barrier are parallel. It is also
found that the TMR increases with increasing the applied voltage.",0310345v1
2004-06-22,Co-operative density wave and giant spin gap in the quarter-filled zigzag ladder,"Strong co-operative interactions occur between four different broken
symmetries involving charge-ordering and bond distortions in the quarter-filled
correlated zigzag electron ladder. The ground state is singlet, with spin gap
several times larger than in the spin-Peierls state of the one-dimensional
quarter-filled chain with the same parameters. We propose the quarter-filled
zigzag electron ladder model for several different organic charge-transfer
solids with coupled pairs of quasi-one-dimensional stacks, the spin-gap
transition temperatures in which are unusually high.",0406525v2
2004-11-01,Double-Exchange Model on Triangle Chain,"We study ground state properties of the double-exchange model on triangle
chain in the classical limit on $t_{2g}$ spins. The ground state is determined
by a competition among the kinetic energy of the $e_g$ electron, the
antiferromagnetic exchange energy between the $t_{2g}$ spins, and frustration
due to a geometric structure of the lattice. The phase diagrams are obtained
numerically for two kinds of the models which differ only in the transfer
integral being real or complex. The properties of the states are understood
from the viewpoint of the spin-induced Peierls instability. The results suggest
the existence of a chiral glass phase which is characterized by a local spin
chirality and a continuous degeneracy.",0411023v1
2005-04-18,An exact algorithm for spin correlation functions of the two dimensional +/-J Ising spin glass in the ground state,"We introduce an exact algorithm for the computation of spin correlation
functions for the two dimensional +/-J Ising spin glass in the ground state.
Unlike with the transfer matrix method, there is no particular restriction on
the shape of the lattice sample, and unlike Monte Carlo based methods it avoids
extrapolation from finite temperatures. The computational requirements depend
only on the number and distribution of frustrated plaquettes.",0504423v1
2005-09-25,"Tight-binding model of spin-polarized tunnelling in (Ga,Mn)As-based structures","The Landauer-Buettiker formalism combined with the tight-binding transfer
matrix method is used to describe the results of recent experiments: the high
tunneling magnetoresistance (TMR) in (Ga,Mn)As-based trilayers and highly
polarized spin injection in p-(Ga,Mn)As/n-GaAs Zener diode. For both TMR and
Zener spin current polarization, the calculated values agree well with those
observed experimentally. The role played in the spin dependent tunneling by
carrier concentration and magnetic ion content is also studied.",0509629v1
2005-12-19,Spin injection into a short DNA chain,"Quantun spin transport through a short DNA chain connected to ferromagnetic
electrodes has been investigated by the transfer matrix method. We describe the
system by a tight-binding model where the parameters are extracted from the
experimental data and realistic metal energy bands. For ferromagnetic iron
electrodes, the magnetoresistance of a 30-basepair Poly(G)-Poly(C) DNA is found
to be lower than 10% at a bias of < 4 V, but can rach up to 20% at a bias of 5
V. In the presence of the spin-flip mechanism, the magnetoresistance is
significantly enhanced when the spin-flip coupling is weak but as the coupling
becomes stronger the decreasing magnetoresistance develops an oscillatory
behavior.",0512473v1
2006-07-14,Vortex polarity switching by a spin--polarized current,"The spin-transfer effect is investigated for the vortex state of a magnetic
nanodot. A spin current is shown to act similarly to an effective magnetic
field perpendicular to the nanodot. Then a vortex with magnetization (polarity)
parallel to the current polarization is energetically favorable. Following a
simple energy analysis and using direct spin--lattice simulations, we predict
the polarity switching of a vortex. For magnetic storage devices, an electric
current is more effective to switch the polarity of a vortex in a nanodot than
the magnetic field.",0607362v2
2006-12-26,Magnetization plateaus in the Ising limit of the multiple-spin exchange model on plaquette chain,"We consider the Ising spin system, which stems out from the corresponding
Multiple-spin exchange (MSE) Hamiltonian, on the special one--dimensional
lattice, diamond-plaquette chain. Using the technique e of transfer-matrix we
obtain the exact expression for system free energy with the aid of which we
obtain the magnetization function. Analyzing magnetization curves for varies
values of temperature and couplin constants we found the magnetization plateaux
at 1/3 and 2/3 of the full moment.
  The corresponding microscopic spin configurations are unknown by virtue of
high frustration.",0612630v1
2007-02-09,Spin-dependent transport properties in GaMnAs-based spin hot-carrier transistors,"We have investigated the spin-dependent transport properties of GaMnAs-based
three-terminal semiconductor spin hot-carrier transistor (SSHCT) structures.
The emitter-base bias voltage VEB dependence of the collector current IC,
emitter current IE, and base current IB shows that the current transfer ratio
alpha (= IC / IE) and the current gain beta (= IC / IB) are 0.8-0.95 and 1-10,
respectively, which means that GaMnAs-based SSHCTs have current amplifiability.
In addition, we observed an oscillatory behavior of the tunneling
magnetoresistance (TMR) ratio with the increasing bias, which can be explained
by the resonant tunneling effect in the GaMnAs quantum well.",0702239v1
2000-01-31,Lambda polarization and single-spin left-right asymmetry in diffractive hadron-hadron collisions,"We discuss Lambda polarization and single-spin left-right asymmetry in
diffractive hadron-hadron scattering at high energies. We show that the
physical picture proposed in a recent Letter is consistent with the
experimental observation that $\Lambda$ polarization in the diffractive
process, $pp\to \Lambda K^+p$, is much higher than that in the inclusive
reaction, $pp\to \Lambda X$. We make predictions for the left-right asymmetry,
A_N, and for the spin transfer, $D_{NN}^\Lambda$, in the single-spin process
$p(\uparrow)p\to \Lambda K^+p$ and suggest further experimental tests of the
proposed picture.",0001329v1
2001-07-02,An absolute polarimeter for high energy protons,"A study of the spin asymmetries for polarized elastic proton proton
collisions in the electromagnetic hadronic interference (CNI) region of
momentum transfer provides a method of self calibration of proton polarization.
The method can be extended to non-identical spin half scattering so that, in
principle, the polarization of a proton may be obtained through an analysis of
its elastic collision with a different polarized particle, helium 3 for
instance. Sufficiently large CNI spin asymmetries provide enough information to
facilitate the evaluation of nearly all the helicity amplitudes at small t as
well as the polarization of both initial spin half fermions. Thus it can serve
equally well as a polarimeter for helium 3.",0107013v1
2004-06-21,Nuclear spin structure in dark matter search: The zero momentum transfer limit,"We review the calculation of spin-dependent matrix elements relevant to
scattering of weakly interacting massive particles on nuclei. A comprehensive
list, to our knowledge, of the proton and neutron total spin expectation values
($<{\bf S}_{p}>$ and $<{\bf S}_{n}>$) calculated within different nuclear
models is presented. These values allow a conclusion about the event rate
expected in direct dark matter search experiments due to spin-dependent
neutralino-nucleon interaction, provided neutralino is a dark matter particle.",0406218v1
2004-10-11,A Method to Polarize Stored Antiprotons to a High Degree,"Polarized antiprotons can be produced in a storage ring by spin--dependent
interaction in a purely electron--polarized hydrogen gas target. The polarizing
process is based on spin transfer from the polarized electrons of the target
atoms to the orbiting antiprotons. After spin filtering for about two beam
lifetimes at energies $T\approx 40-170$ MeV using a dedicated large acceptance
ring, the antiproton beam polarization would reach $P=0.2-0.4$. Polarized
antiprotons would open new and unique research opportunities for spin--physics
experiments in $\bar{p}p$ interactions.",0410067v1
2005-04-08,Geometric Effects and Computation in Spin Networks,"When initially introduced, a Hamiltonian that realises perfect transfer of a
quantum state was found to be analogous to an x-rotation of a large spin. In
this paper we extend the analogy further to demonstrate geometric effects by
performing rotations on the spin. Such effects can be used to determine
properties of the chain, such as its length, in a robust manner. Alternatively,
they can form the basis of a spin network quantum computer. We demonstrate a
universal set of gates in such a system by both dynamical and geometrical
means.",0504063v1
2005-12-15,Spintronic devices as quantum networks,"We explore spintronics from a quantum information (QI) perspective. We show
that QI specific methods can be an effective tool in designing new devices.
Using the formalism of quantum gates acting on spin and mode degrees of
freedom, we provide a solution to a reverse engineering problem, namely how to
design a device performing a given transformation between input and output.
Among these, we describe an orientable Stern-Gerlach device and a new scheme to
entangle two spins by transferring the entanglement from orbital to spin
degrees of freedom. Finally, we propose a simple scheme to produce
hyper-entangle electrons, i.e., particles entangled in both spin and mode
degrees of freedom.",0512116v1
2006-10-12,Enhancement of entanglement transfer in a spin chain by phase shift-control,"We study the effect of a phase shift on the amount of transferrable two-spin
entanglement in a spin chain. We consider a ferromagnetic Heisenberg/XY spin
chain, both numerically and analytically, and two mechanisms to generate a
phase shift, the Aharonov-Casher effect and the Dzyaloshinskii-Moriya
interaction. In both cases, the maximum attainable entanglement is shown to be
significantly enhanced, suggesting its potential usefulness in quantum
information processing.",0610103v2
2007-05-09,Controllable Adiabatic Manipulation of the Qubit State,"We propose a scheme which implements a controllable change of the state of
the target spin qubit in such a way that both the control and the target spin
qubits remain in their ground states. The interaction between the two spins is
mediated by an auxiliary spin, which can transfer to its excited state. Our
scheme suggests a possible relationship between the gate and adiabatic quantum
computation.",0705.1255v1
2007-07-27,Spin-triplet pairing instability of the spinon Fermi surface in a U(1) spin liquid,"Recent experiments on the organic compound \kappa-(ET)_2Cu_2(CN)_3 have
provided a promising example of a two dimensional spin liquid state. This phase
is described by a two-dimensional spinon Fermi sea coupled to a U(1) gauge
field. We study Kohn-Luttinger-like pairing instabilities of the spinon Fermi
surface due to singular interaction processes with twice-the-Fermi-momentum
transfer. We find that under certain circumstances the pairing instability
occurs in odd-orbital-angular-momentum/spin-triplet channels. Implications to
experiments are discussed.",0707.4031v1
2007-11-12,Chiral Odd Generalized Parton Distributions in Impact Parameter Space,"We investigate the chiral odd generalized parton distributions (GPDs) for the
quantum fluctuations of an electron in QED. The light-front wave function
(LFWF) of this system gives a template for the quark spin-one diquark structure
of the valence LFWF of the proton. We express the GPDs in terms of overlaps of
LFWFs and obtain their representation in impact parameter space when the
momentum transfer is purely transverse. We show the spin-orbit correlation
effect of the two-particle LFWF as well as the correlation between the
constituent spin and the transverse spin of the target.",0711.1566v2
2008-02-04,Detection of spin reversal and nutations through current measurements,"The dynamics of a single spin embedded in a the tunnel junction between
ferromagnetic contacts is strongly affected by the exchange coupling to the
tunneling electrons. Moment reversal of the local spin induced by the bias
voltage across the junction is shown to have a measurable effect on the
tunneling current. Furthermore, the frequency of a harmonic bias voltage is
picked up by the local spin dynamics and transferred back to the current
generating a double frequency component.",0802.0473v2
2008-07-27,Exactly solvable Ising--Heisenberg chain with triangular XXZ-Heisenberg plaquettes,"A mixed Ising-Heisenberg spin system consisting of triangular XXZ-Heisenberg
spin clusters assembled into a chain by alternating with Ising spins
interacting to all three spins in the triangle is considered. The exact
solution of the model is given in terms of the generalized
decoration--iteration map and within the transfer-matrix technique. Exact
expressions for thermodynamic functions are derived. Ground state phase
diagrams, thermodynamic and magnetic properties of the system are examined.",0807.4300v3
2009-03-16,Controlled multiqubit entangled states and quantum transmission in quantum molecule-spin systems,"he multiqubit entangled states are coherently controlled in the quantum spin
systems composed of $N+1$ interacting antiferromagnetic molecular rings. The
tunable intermolecular couplings arise from the local exchange interactions
between electron spins of $N$ circumjacent magnets and those of one central
molecular ring. The quantum dynamics of such system is analytically deduced by
the effective spin hamiltonian with anisotropic Heisenberg couplings. It is
found that entangled $W$ states can be generated with a high precision under
the circumstance of quantum fluctuations. The multiqubit entangled state is
also transferred from some molecular rings to others by the selection of
intermolecular couplings.",0903.2705v1
2009-06-04,Quark-Hadron Duality in Neutron Spin-Structure and g_2 moments at intermediate Q**2,"Jefferson Lab experiment E01-012 measured the He-3 spin-structure functions
and virtual photon asymmetries in the resonance region in the momentum transfer
range 1.0<Q**2<4.0(GeV/c)**2. Our data, when compared with existing deep
inelastic scattering data, were used to test quark-hadron duality in g_1 and
A_1 for He-3 and the neutron. In addition, preliminary results on the He-3
spin-structure function g_2, on the Burkhardt-Cottingham sum rule and on higher
twist effects through the x**2-weighted moment d_2 of the neutron were
presented.",0906.0928v1
2009-06-09,Spin-wave theory for dimerized ferromagnetic chains,"We describe a Peierls dimerization which occurs in ferromagnetic spin chains
at finite temperature, within the modified spin-wave theory. Usual spin-wave
theory is modified by introducing a Lagrange multiplier which enforces a
nonmagnetic state at finite temperature. It is shown that this method gives
results in excellent agreement with the density--matrix renormalization group
applied to transfer matrices for dimerized ferromagnetic chains. We study bond
correlation functions and explore the characteristic features of dimerization
in the specific heat.",0906.1758v1
2009-10-09,High Fidelity State Transfer Over an Unmodulated Linear XY Spin Chain,"We provide a class of initial encodings that can be sent with a high fidelity
over an unmodulated, linear, XY spin chain. As an example, an average fidelity
of ninety-six percent can be obtained using an eleven-spin encoding to transmit
a state over a chain containing ten-thousand spins. An analysis of the magnetic
field dependence is given, and conditions for field optimization are provided.",0910.1829v2
2009-11-26,Two-photon Exchange Corrections to Single Spin Asymmetry of Neutron and $^3$He,"In a simple hadronic model, the two-photon exchange contributions to the
single spin asymmetries for the nucleon and the $^3$He are estimated. The
results show that the elastic contributions of two-photon exchange to the the
single spin asymmetries for the nucleon are rather small while those for the
$^3$He are relatively large. Besides the strong angular dependence, the
two-photon contributions to the single spin asymmetry for the $^3$He are very
sensitive to the momentum transfer.",0911.5001v1
2010-02-04,Itinerant Flat-Band Magnetism in Hydrogenated Carbon Nanotubes,"We investigate the electronic and magnetic properties of hydrogenated carbon
nanotubes using ab initio spin-polarized calculations within both the local
density approximation (LDA) and the generalized gradient approximation (GGA).
We find that the combination of charge transfer and carbon network distortion
makes the spin-polarized flat-band appear in the tube's energy gap. Various
spin-dependent ground state properties are predicted with the changes of the
radii, the chiralities of the tubes and the concentration of hydrogen (H). It
is found that strain or external electric field can effectively modulate the
flat-band spin-splitting, and even induce an insulator-metal transition.",1002.1030v2
2011-07-02,Silicon spin communication,"Recent experimental breakthroughs have demonstrated that the electron spin in
silicon can be reliably injected and detected as well as transferred over
distances exceeding 1 mm. We propose an on-chip communication paradigm which is
based on modulating spin polarization of a constant current in silicon wires.
We provide figures of merit for this scheme by studying spin relaxation and
drift-diffusion models in silicon.",1107.0359v1
2011-10-24,Spin and charge orderings in the atomic limit of the U-V-J model,"In this paper we study a generalization of the 1D Hubbard model by
considering density-density and Ising-type spin-spin nearest neighbor (NN)
interactions, parameterized by $V$ and $J$, respectively. We present the T=0
phase diagram for both ferro ($J>0$) and anti-ferro ($J<0$) coupling obtained
in the narrow-band limit by means of an extension to zero-temperature of the
transfer-matrix method. Based on the values of the Hamiltonian parameters, we
identify a number of phases that involve orderings of the double occupancy, NN
density and spin correlations, being these latter very fragile.",1110.5237v1
2012-05-21,Emergence of spatial spin-wave correlations in a cold atomic gas,"Rydberg spin waves are optically excited in a quasi-one-dimensional atomic
sample of Rb atoms. Pair-wise spin-wave correlations are observed by a
spatially selective transfer of the quantum state onto a light field and
photoelectric correlation measurements of the light. The correlations are
interpreted in terms of the dephasing of multiply-excited spin waves by
long-range Rydberg interactions.",1205.4708v2
2012-08-08,Quantum communication in the spin chain with multiplespin exchange interaction,"The transmission of quantum states in the anisotropic Heisenberg XXZ chain
model with three-spin exchange interaction is studied. The average fidelity is
used to evaluate the state transfer. It is found out that quantum communication
can be enhanced by the anisotropic coupling and multiple spin interaction. Such
spin model can reduce the time required for the perfect state transmission
where the fidelity is unity. The maximally entangled Bell states can be
generated and separated from the whole quantum systems.",1208.1557v1
2012-11-13,About the two spin-channel model for ferromagnetic excitations and spin-dependent heat transfer equations,"The two spin-channel model is generalized to the case of transport of
ferromagnetic excitations in electric conductors and insulators. The two
channels are defined by reducing the ferromagnetic degrees of freedom to a
bivaluated variable, i.e. to an effective spin one-half. The reduction is
performed after defining the local magnetic configuration space by a sphere
$\Sigma_x$, and integrating the relevant physical quantities over the two
hemispheres $\Sigma_x^{\uparrow}$ and $\Sigma_x^{\downarrow}$. The
configuration space is then extended to the $x$ direction for non-uniform
magnetization excitations. The transport equations for both magnetic moments
and magnetic energy are deduced, including the relaxation from one channel to
the other. The heat transport equations for ferromagnets is deduced.",1211.3033v1
2013-05-11,Quantum teleportation of spin coherent states: beyond continuous variables teleportation,"We introduce a quantum teleportation scheme that can transfer a macroscopic
spin coherent state between two locations. In the scheme a large number of
copies of a qubit, such as realized in a coherent two-component Bose-Einstein
condensate, is teleported onto a distant macroscopic spin coherent state using
only elementary operations and measurements. We analyze the error of the
protocol with the number of particles N in the spin coherent state under
decoherence and find that it scales favorably with N.",1305.2479v2
2015-06-28,Exact Fractional Revival in Spin Chains,"The occurrence of fractional revival in quantum spin chains is examined.
Analytic models where this phenomenon can be exhibited in exact solutions are
provided. It is explained that spin chains with fractional revival can be
obtained by isospectral deformations of spin chains with perfect state
transfer.",1506.08434v3
2015-09-14,Spin measurement using cycling transitions of a two-electron quantum dot molecule,"Two-electron charged self-assembled quantum dot molecules exhibit a
decoherence-avoiding singlet-triplet qubit subspace and an efficient
spin-photon interface. Here, we demonstrate that the cycling transitions
originating from auxiliary ground states in the same system allow for an
efficient optical read-out of a singlet-triplet qubit. By implementing a
spin-selective state transfer to the auxiliary state using a resonant laser
field, we observe an improvement approaching two orders of magnitude in
fidelity as compared to spin measurement by light scattering directly from the
qubit states. Embedding the quantum dot molecule inside a low quality-factor
micro-cavity structure should enable single-shot qubit read-out.",1509.04171v1
2015-12-16,High Energy Hadron Spin Flip Amplitude,"The high energy part of the hadron spin flip amplitude is examined in the
framework of the new high energy general structure (HEGS) model of the elastic
hadron scattering at high energies. The different forms of the hadron spin flip
amplitude are compared in the impact parameters representation. It is shown
that the existing experimental data of the proton-proton and proton-antiproton
elastic scattering at high energy in the region of the diffraction minimum and
at large momentum transfer give support in the presence of the
energy-independent part of the hadron spin flip amplitude with the momentum
dependence proposed in the works by Galynskii-Kuraev.",1512.05130v1
2016-12-15,Doping-dependent magnetization plateaus of a coupled spin-electron chain: exact results,"A coupled spin-electron chain composed of localized Ising spins and mobile
electrons is exactly solved in an external magnetic field within the
transfer-matrix method. The ground-state phase diagram involves in total seven
different ground states, which differ in the number of mobile electrons per
unit cell and the respective spin arrangements. A rigorous analysis of the
low-temperature magnetization process reveals doping-dependent magnetization
plateaus, which may be tuned through the density of mobile electrons. It is
demonstrated that the fractional value of the electron density is responsible
for an enhanced magnetocaloric effect due to an annealed bond disorder of the
mobile electrons.",1612.04968v1
2018-06-21,Pulse sequences for controlled 2- and 3-qubit gates in a hybrid quantum register,"We propose and demonstrate a quantum control scheme for hybrid quantum
registers that can reduce the operation time, and therefore the effects of
relaxation, compared to existing implementations. It combines resonant
excitation pulses with periods of free precession under the internal
Hamiltonian of the qubit system. We use this scheme to implement quantum gates
like controlled-NOT operations on electronic and nuclear spins of the
nitrogen-vacancy center in diamond. As a specific application, we transfer
population between electronic and nuclear spin qubits and use it to measure the
Rabi oscillations of a nuclear spin in a system with multiple coupled spins.",1806.08408v1
2020-02-20,Thermal rectification and spin-spin coupling of non-reciprocal localized and surface modes,"We study the rectification of near-field radiative heat transfer between two
InSb nano-particles due to the presence of non-reciprocal surface modes in a
nearby InSb sample when an external magnetic field is applied and its
dependence on the magnetic field strength. We reveal the spin-spin coupling
mechanism of the localized particle resonances and the surface mode resonances
which is substantiated by the directional heat flux in the given setup. We
discuss further the interplay of the frequency shift, the propagation length,
and local density of states on the strength and directionality of the
rectification as well as the non-reciprocal heating effect of the
nanoparticles.",2002.08752v1
2022-01-22,Spin and polarization analysis of $Z_{cs}$ state,"A polarization analysis is performed for the recent observation of $Z_{cs}$
exotic state in the $e^+e^-$ annihilation experiment with motivation for
measuring its spin quantum number in the future. Starting with the unpolarized
electron and positron beam, the polarization transfer to the $Z_{cs}$ state and
its decay angular distribution patterns are investigated. Some observables are
suggested for determination of the spin parity quantum numbers. An ensemble of
Monte-Carlo events are used to show some moment distributions special for
manifestation of the different $Z_{cs}$ spin scenarios.",2201.09066v1
2024-01-30,One-excitation spin dynamics in homogeneous closed chain governed by XX-Hamiltonian,"We analytically investigate the one-excitation spin dynamics in a homogeneous
closed spin-1/2 chain via diagonalization of the one-excitation block of the
XX-Hamiltonian, which allows to derive the analytical expressions for
probability amplitudes describing state transfers between any two spins of a
chain. We analytically investigate the $M$-neighbor approximation ($M\ge 1$) of
spin dynamics with arbitrary initial state and analyze its accuracy using
special integral characteristics defined in terms of the above probability
amplitudes. We find $M$ providing the required accuracy of evolution
approximation for chains of different lengths.",2401.16902v1
1996-11-07,Substitution effects on spin fluctuations in the spin-Peierls compound CuGeO_3,"Using Raman scattering we studied the effect of substitutions on 1D spin
fluctuations in CuGeO_3 observed as a spinon continuum in frustration induced
exchange scattering. For temperatures below the spin-Peierls transition
(T_{SP}=14K) the intensity of this continuum at 120-500 cm^{-1} is
exponentially suppressed and transferred into a 3D two-magnon density of
states. Besides a spin-Peierls gap-induced mode at 30 cm^{-1} and additional
modes at 105 and 370 cm^{-1} are observed. Substitution of Zn on the Cu-site
and Si on the Ge-site of CuGeO_3 quenches easily the spin-Peierls state.
Consequently a suppression of the spin-Peierls gap observable below T_{SP}=14K
as well as a change of the temperature dependence of the spinon continuum are
observed. These effects are discussed in the context of a dimensional crossover
of this compound below T_{SP} and strong spin-lattice interaction.",9611053v1
2001-02-13,Isotopically engineered silicon/silicon-germanium nanostructures as basic elements for a nuclear spin quantum computer,"The idea of quantum computation is the most promising recent developments in
the high-tech domain, while experimental realization of a quantum computer
poses a formidable challenge. Among the proposed models especially attractive
are semiconductor based nuclear spin quantum computer's (S-NSQC), where nuclear
spins are used as quantum bistable elements, ''qubits'', coupled to the
electron spin and orbital dynamics. We propose here a scheme for implementation
of basic elements for S-NSQC's which are realizable within achievements of the
modern nanotechnology. These elements are expected to be based on a
nuclear-spin-controlled isotopically engineered Si/SiGe heterojunction, because
in these semiconductors one can vary the abundance of nuclear spins by
engineering the isotopic composition. A specific device is suggested, which
allows one to model the processes of recording, reading and information
transfer on a quantum level using the technique of electrical detection of the
magnetic state of nuclear spins. Improvement of this technique for a
semiconductor system with a relatively small number of nuclei might be applied
to the manipulation of nuclear spin ''qubits'' in the future S-NSQC.",0102228v1
2003-08-25,Initialization of a nuclear spin system over the quantum Hall regime for quantum information processing,"The application of the quantum mechanical properties of physical systems to
realize novel computational schemes and innovative device functions have been
topics of recent interest. Proposals for associated devices are to be found in
diverse branches of physics. Here, we are concerned with the experimental
realization of some elements needed for quantum information processing using
nuclear spin immersed in a confined electronic system in the quantum Hall
regime. Thus, we follow a spin-handling approach that (a) uses the Overhauser
effect in the quantum Hall regime to realize a large nuclear polarization at
relatively high temperatures, (b) detects the nuclear spin state by measuring
the influence of the associated magnetic field on Electron Spin Resonance, and
(c) seeks to apply the electronic spin exciton as the spin transfer mechanism.
Some measurements examining the viability of this approach are shown, and the
utility of the approach for initializing a nuclear spin system at a relatively
high temperature is pointed out",0308501v1
2006-10-26,Manipulation of collective spin correlations in semiconductors with polarization squeezed vacuum,"We calculate the transfer rate of correlations from polarization entangled
photons to the collective spin of a many-electron state in a two-band system.
It is shown that when a semiconductor absorbs pairs of photons from a two-mode
squeezed vacuum, certain fourth order electron-photon processes correlate the
spins of the excited electron pairs of different quasi-momenta. Different
distributions of the quantum Stokes vector of the light lead to either
enhancement or reduction of the collective spin correlations, depending on the
symmetry of the distribution. We find that as the squeezing of the light
becomes non-classical, the spin correlations exhibit a crossover from being
positive with a $\sim N^2$ ($N$ is average photon number) scaling, to being
negative with $\sim N$ scaling, even when $N$ is not small. Negative spin
correlations mean a preponderance of spin singlets in the optically generated
state. We discuss the possibility to measure the collective spin correlations
in a combined measurement of the Faraday rotation fluctuation spectrum and
excitation density in a steady-state configuration.",0610719v1
1994-08-30,Spin Effects in High Energy Photon-Hadron Scattering in QCD,"The spin effects at high energies and momenta transferred $|t|>1 GeV^2$ are
analysed for quark-photon scattering. The energy independence of the ratio of
spin-flip and spin-non-flip amplitudes in the same $\alpha_s$ order of QCD is
obtained. It is shown that the contribution of the spin-dependent quark-pomeron
vertex to the spin-flip amplitude is intensified by off-mass-shell effects in
the quark loop. As a result, the magnitude of this amplitude can reach 20-30\%
from a spin-non-flip one. The dependence of the cross-section on the
form-factor and $\alpha_s^3$ spin-non-flip contributions are observed.",9408388v1
2001-11-28,Behavior of the Hadron Potential at Large Distances and Properties of the Hadron Spin-flip Amplitude,"The impact of the form of the hadron potential at large distances on the
behaviour of the hadron spin-flip amplitude at small angles is examined. The
$t$-dependence of the spin-flip amplitude of high energy hadron elastic
scattering is analyzed under different assumptions on the hadron interaction.
It is shown that the long tail of the non-Gaussian form of the hadron potential
of the hadron interaction in the impact parameter representation leads to a
large value of the slope of the spin-flip amplitude (without the kinematical
factor $\sqrt{|t|}$) as compared with the slope of the spin-non-flip amplitude.
This effect can explain the form of the differential cross section and the
analyzing power at small transfer momenta. The methods for the definition of
the spin-dependent part of the hadron scattering amplitude are presented. A
possibility to investigate the structure of the hadron spin-flip amplitude from
the accurate measure of the differential cross section and the spin correlation
parameters is shown.",0111367v1
2002-05-22,A switchable controlled-NOT gate in a spin-chain NMR quantum computer,"A method of switching a controlled-NOT gate in a solid-stae NMR quantum
computer is presented. Qubits of I=1/2 nuclear spins are placed periodically
along a quantum spin chain (1-D antiferromagnet) having a singlet ground state
with a finite spin gap to the lowest excited state caused by some quantum
effect. Irradiation of a microwave tuned to the spin gap energy excites a
packet of triplet magnons at a specific part of the chain where control and
target qubits are involved. The packet switches on the Suhl-Nakamura
interaction between the qubits, which serves as a controlled NOT gate. The
qubit initialization is achieved by a qubit initializer consisting of
semiconducting sheets attached to the spin chain, where spin polarizations
created by the optical pumping method in the semiconductors are transferred to
the spin chain. The scheme allows us to separate the initialization process
from the computation, so that one can optimize the computation part without
being restricted by the initialization scheme, which provides us with a wide
selection of materials for a quantum computer.",0205135v1
2008-03-20,Exchange Control of Nuclear Spin Diffusion in a Double Quantum Dot,"Coherent two-level systems, or qubits, based on electron spins in GaAs
quantum dots are strongly coupled to the nuclear spins of the host lattice via
the hyperfine interaction. Realizing nuclear spin control would likely improve
electron spin coherence and potentially enable the nuclear environment to be
harnessed for the long-term storage of quantum information. Toward this goal,
we report experimental control of the relaxation of nuclear spin polarization
in a gate-defined two-electron GaAs double quantum dot. A cyclic gate-pulse
sequence transfers the spin of an electron pair to the host nuclear system,
establishing a local nuclear polarization that relaxes on a time scale of
seconds. We find nuclear relaxation depends on magnetic field and
gate-controlled two-electron exchange, consistent with a model of electron
mediated nuclear spin diffusion.",0803.3082v1
2010-01-25,Spin relaxation due to deflection coupling in nanotube quantum dots,"We consider relaxation of an electron spin in a nanotube quantum dot due to
its coupling to flexural phonon modes, and identify a new spin-orbit mediated
coupling between the nanotube deflection and the electron spin. This mechanism
dominates other spin relaxation mechanisms in the limit of small energy
transfers. Due to the quadratic dispersion law of long wavelength flexons,
$\omega \propto q^2$, the density of states $dq/d\omega \propto \omega^{-1/2}$
diverges as $\omega \to 0$. Furthermore, because here the spin couples directly
to the nanotube deflection, there is an additional enhancement by a factor of
$1/q$ compared to the deformation potential coupling mechanism. We show that
the deflection coupling robustly gives rise to a minimum in the magnetic field
dependence of the spin lifetime $T_1$ near an avoided crossing between
spin-orbit split levels in both the high and low-temperature limits. This
provides a mechanism that supports the identification of the observed $T_1$
minimum with an avoided crossing in the single particle spectrum by Churchill
et al.[Phys. Rev. Lett. {\bf 102}, 166802 (2009)].",1001.4306v2
2010-02-05,"Electron spin coherence in metallofullerenes: Y, Sc and La@C82","Endohedral fullerenes encapsulating a spin-active atom or ion within a carbon
cage offer a route to self-assembled arrays such as spin chains. In the case of
metallofullerenes the charge transfer between the atom and the fullerene cage
has been thought to limit the electron spin phase coherence time (T2) to the
order of a few microseconds. We study electron spin relaxation in several
species of metallofullerene as a function of temperature and solvent
environment, yielding a maximum T2 in deuterated o-terphenyl greater than 200
microseconds for Y, Sc and La@C82. The mechanisms governing relaxation (T1, T2)
arise from metal-cage vibrational modes, spin-orbit coupling and the nuclear
spin environment. The T2 times are over 2 orders of magnitude longer than
previously reported and consequently make metallofullerenes of interest in
areas such as spin-labelling, spintronics and quantum computing.",1002.1282v1
2010-03-25,Creation and manipulation of entanglement in spin chains far from equilibrium,"We investigate creation, manipulation, and steering of entanglement in spin
chains from the viewpoint of quantum communication between distant parties. We
demonstrate how global parametric driving of the spin-spin coupling and/or
local time-dependent Zeeman fields produce a large amount of entanglement
between the first and the last spin of the chain. This occurs whenever the
driving frequency meets a resonance condition, identified as ""entanglement
resonance"". Our approach marks a promising step towards an efficient quantum
state transfer or teleportation in solid state system. Following the reasoning
of Zueco et al. [1], we propose generation and routing of multipartite
entangled states by use of symmetric tree-like structures of spin chains.
Furthermore, we study the effect of decoherence on the resulting spin
entanglement between the corresponding terminal spins.",1003.4846v1
2013-10-19,Bipolar spin blockade and coherent state superpositions in a triple quantum dot,"Spin qubits based on interacting spins in double quantum dots have been
successfully demonstrated. Readout of the qubit state involves a conversion of
spin to charge information, universally achieved by taking advantage of a spin
blockade phenomenon resulting from Pauli's exclusion principle. The archetypal
spin blockade transport signature in double quantum dots takes the form of a
rectified current. Currently more complex spin qubit circuits including triple
quantum dots are being developed. Here we show both experimentally and
theoretically (a) that in a linear triple quantum dot circuit, the spin
blockade becomes bipolar with current strongly suppressed in both bias
directions and (b) that a new quantum coherent mechanism becomes relevant.
Within this mechanism charge is transferred non-intuitively via coherent states
from one end of the linear triple dot circuit to the other without involving
the centre site. Our results have implications in future complex
nano-spintronic circuits.",1310.5269v1
2013-11-06,Observation of zero-point quantum fluctuations of a single-molecule magnet through the relaxation of its nuclear spin bath,"A single-molecule magnet placed in a magnetic field perpendicular to its
anisotropy axis can be truncated to an effective two-level system, with easily
tunable energy splitting. The quantum coherence of the molecular spin is
largely determined by the dynamics of the surrounding nuclear spin bath. Here
we report the measurement of the nuclear spin--lattice relaxation in a single
crystal of the single-molecule magnet Mn$_{12}$-ac, at $T \approx 30$ mK in
perpendicular fields $B_{\perp}$ up to 9 T. Although the molecular spin is in
its ground state, we observe an increase of the nuclear relaxation rates by
several orders of magnitude up to the highest $B_{\perp}$. This unique finding
is a consequence of the zero-point quantum fluctuations of the Mn$_{12}$-ac
spin, which allow it to efficiently transfer energy from the excited nuclear
spin bath to the lattice. Our experiment highlights the importance of quantum
fluctuations in the interaction between an `effective two-level system' and its
surrounding spin bath.",1311.1373v1
2014-05-06,Influence of Nuclear Quadrupole Moments on Electron Spin Coherence in Semiconductor Quantum Dots,"We theoretically investigate the influence of the fluctuating Overhauser
field on the spin of an electron confined to a quantum dot (QD). The
fluctuations arise from nuclear angular momentum being exchanged between
different nuclei via the nuclear magnetic dipole coupling. We focus on the role
of the nuclear electric quadrupole moments (QPMs), which generally cause a
reduction in internuclear spin transfer efficiency in the presence of electric
field gradients. The effects on the electron spin coherence time are studied by
modeling an electron spin echo experiment. We find that the QPMs cause an
increase in the electron spin coherence time and that an inhomogeneous
distribution of the quadrupolar shift, where different nuclei have different
shifts in energy, causes an even larger increase in the electron coherence time
than a homogeneous distribution. Furthermore, a partial polarization of the
nuclear spin ensemble amplifies the effect of the inhomogeneous quadrupolar
shifts, causing an additional increase in electron coherence time, and provides
an alternative to the experimentally challenging suggestion of full dynamic
nuclear spin polarization.",1405.1329v1
2014-08-13,Efficient injection of spin-polarized excitons and optical spin orientation of a single Mn2+ ion in a CdSe/ZnSe quantum dot,"Circularly polarized optical excitation is used to demonstrate the efficient
injection of spin-polarized excitons to individual self-assembled CdSe quantum
dots in ZnSe barrier. The exciton spin-transfer is studied by means of
polarization-resolved single dot spectroscopy performed in magnetic field
applied in Faraday configuration. Detailed analysis of the neutral exciton
photoluminescence spectra reveals the presence of exciton spin relaxation
during its lifetime in a quantum dot. This process is seen for both nonmagnetic
dots and those containing single Mn$^{2+}$ ions. Taking this into account we
determine the spin-polarization degree of excitons injected to a dot under
circularly polarized below-the-barrier optical excitation at 488 nm. It is
found to be close to 40% in the entire range of the applied magnetic field.
Exploiting the established spin-conserving excitation channel we demonstrate
the optical spin orientation of a single Mn$^{2+}$ ion embedded in a CdSe/ZnSe
quantum dot.",1408.2928v1
2014-12-16,Attempt to explain black hole spin in X-ray binaries with new physics,"It is widely believed that the spin of black holes in X-ray binaries is
mainly natal. A significant spin-up from accretion is not possible. If the
secondary has a low mass, the black hole spin cannot change too much even if
the black hole swallows the whole stellar companion. If the secondary has a
high mass, its lifetime is too short to transfer the necessary amount of matter
and spin the black hole up. However, while black holes formed from the collapse
of a massive star with Solar metallicity are expected to have low birth spin,
current spin measurements show that some black holes in X-ray binaries are
rotating very rapidly. Here I show that, if these objects are not the Kerr
black holes of general relativity, the accretion of a small amount of matter
($\sim 2$~$M_\odot$) can make them look like very fast-rotating Kerr black
holes. Such a possibility is not in contradiction with any observation and it
can explain current spin measurements in a very simple way.",1412.4987v1
2015-09-14,Antiferromagnonic Spin Transport from Y$_3$Fe$_5$O$_{12}$ into NiO,"We observe highly efficient dynamic spin injection from Y$_3$Fe$_5$O$_{12}$
(YIG) into NiO, an antiferromagnetic (AF) insulator, via strong coupling, and
robust spin propagation in NiO up to 100-nm thickness mediated by its AF spin
correlations. Strikingly, the insertion of a thin NiO layer between YIG and Pt
significantly enhances the spin currents driven into Pt, suggesting
exceptionally high spin transfer efficiency at both YIG/NiO and NiO/Pt
interfaces. This offers a powerful platform for studying AF spin pumping and AF
dynamics as well as for exploration of spin manipulation in tailored structures
comprising metallic and insulating ferromagnets, antiferromagnets and
nonmagnetic materials.",1509.04337v1
2015-12-05,Alternating-spin-chain compound AgVOAsO$_4$ probed by $^{75}$As NMR,"$^{75}$As NMR measurements were performed on a polycrystalline sample of
spin-1/2 alternating-spin-chain Heisenberg antiferromagnet AgVOAsO$_4$.
Temperature-dependent NMR shift $K(T)$, which is a direct measure of the
intrinsic spin susceptibility, agrees very well with the spin-1/2
alternating-chain model, justifying the assignment of the spin lattice. From
the analysis of $K(T)$, magnetic exchange parameters were estimated as follows:
the leading exchange $J/k_{\rm B} \simeq 38.4$ K, alternation ratio $\alpha =
J'/J \simeq 0.68$, and spin gap $\Delta/k_{\rm B} \simeq 15$ K. The transferred
hyperfine coupling between the $^{75}$As nucleus and V$^{4+}$ spins obtained by
comparing the NMR shift with bulk susceptibility amounts to $A_{\rm hf} \simeq
3.3$ T/$\mu_{\rm B}$. Our temperature-dependent spin-lattice relaxation rate
$1/T_1(T)$ also shows an activated behaviour at low temperatures, thus
confirming the presence of a spin gap in AgVOAsO$_4$.",1512.01650v1
2016-06-17,Spin dynamics of an individual Cr atom in a semiconductor quantum dot under optical excitation,"We studied the spin dynamics of a Cr atom incorporated in a II-VI
semiconductor quantum dot using photon correlation techniques. We used recently
developed singly Cr-doped CdTe/ZnTe quantum dots (A. Lafuente-Sampietro {\it et
al.}, [1]) to access the spin of an individual magnetic atom. Auto-correlation
of the photons emitted by the quantum dot under continuous wave optical
excitation reveals fluctuations of the localized spin with a timescale in the
10 ns range. Cross-correlation gives quantitative transfer time between Cr spin
states. A calculation of the time dependence of the spin levels population in
Cr-doped quantum dots shows that the observed spin dynamics is controlled by
the exciton-Cr interaction. These measurements also provide a lower bound in
the 20 ns range for the intrinsic Cr spin relaxation time.",1606.05476v1
2016-08-02,Magnetic Domain Wall Floating on a Spin Superfluid,"We theoretically investigate the transfer of angular momentum between a spin
superfluid and a domain wall in an exchange coupled easy-axis and easy-plane
magnetic insulator system. A domain wall in the easy-axis magnet absorbs spin
angular momentum via disrupting the flow of a superfluid spin current in the
easy-plane magnet. Focusing on an open geometry, where the spin current is
injected electrically via a nonequilibrium spin accumulation, we derive
analytical expressions for the resultant superfluid-mediated motion of the
domain wall. The analytical results are supported by micromagnetic simulations.
The proposed phenomenon extends the regime of magnon-driven domain-wall motion
to the case when the magnons are condensed and exhibit superfluidity.
Furthermore, by controlling the pinning of the domain wall, we propose a
realization of a reconfigurable spin transistor. The long-distance
dissipationless character of spin superfluids can thus be exploited for
manipulating soliton-based memory and logic devices.",1608.00683v1
2018-02-01,Manipulating spins of magnetic molecules: Hysteretic behavior with respect to bias voltage,"Formation of a magnetic hysteresis loop with respect to a bias voltage is
investigated theoretically in a spin-valve device based on a single magnetic
molecule. We consider a device consisting of two ferromagnetic electrodes
bridged by a carbon nanotube, acting as a quantum dot, to which a
spin-anisotropic molecule is exchange coupled. Such a coupling allows for
transfer of angular momentum between the molecule and a spin current flowing
through the dot, and thus, for switching orientation of the molecular spin. We
demonstrate that this current-induced switching process exhibits a hysteretic
behavior with respect to a bias voltage applied to the device. The analysis is
carried out with the use of the real-time diagrammatic technique in the
lowest-order expansion of the tunnel coupling of the dot to electrodes. The
influence of both the intrinsic properties of the spin-valve device (the spin
polarization of electrodes and the coupling strength of the molecule to the
dot) and those of the molecule itself (magnetic anisotropy and spin relaxation)
on the size of the magnetic hysteresis loop is discussed.",1802.00205v1
2019-06-27,Spin-dependent conductance statistics in systems with spin-orbit coupling,"Spin-dependent partial conductances are evaluated in a tight-binding
description of electron transport in the presence of spin-orbit (SO) couplings,
using transfer-matrix methods. As the magnitude of SO interactions increases,
the separation of spin-switching channels from non-spin-switching ones is
gradually erased. Spin-polarised incident beams are produced by including a
Zeeman-like term in the Hamiltonian. The exiting polarisation is shown to
exhibit a maximum as a function of the intensity of SO couplings. For moderate
site disorder, and both weak and strong SO interactions, no evidence is found
for a decay of exiting polarisation against increasing system length. With very
low site disorder and weak SO couplings a spin-filter effect takes place, as
polarisation {\em increases} with increasing system length.",1906.11804v3
2020-02-04,One-way reflection-free exciton-polariton spin filtering channel,"We consider theoretically exciton-polaritons in a strip of honeycomb lattice
with zigzag edges and it is shown that the interplay among the spin-orbit
coupling, Zeeman splitting, and an onsite detuning between sublattices can give
rise to a band structure where all the edge states of the system split in
energy. Within an energy interval, one of the spin polarized edge states
resides with the gap-less bulk having opposite spin. Being surrounded by
opposite spin and the absence of the backward propagating edge state ensures
both reflection free and feedback suppressed one-way flow of polaritons with
one particular spin in the system. The edge states in this system are more
localized than those in the standard topological polariton systems and are
fully spin polarized. This paves the way for feedback free spin-selective
polariton channels for transferring information in polariton networks.",2002.01168v1
2020-03-11,Excitation and relaxation dynamics of spin-waves triggered by ultrafast photo-induced demagnetization in a ferrimagnetic insulator,"Excitation and propagation dynamics of spin waves in an iron-based garnet
film under out-of-plane magnetic field were investigated by time-resolved
magneto-optical imaging. The experimental results and the following data
analysis by phase-resolved spin-wave tomography reveal the excitation of spin
waves triggered by photo-induced demagnetization (PID) along the sample depth
direction. Moreover, the fast relaxation of PID accompanied by the spin
transfer due to spin-wave emission was observed. Possible scenarios of PID in
the garnet film are discussed. Finally, we develop a model for the spin-wave
excitation triggered by PID and explain the magnetic-field dependence in the
amplitude of the observed spin waves.",2003.05159v1
2020-09-09,Superconductivity-enhanced spin pumping: Role of Andreev resonances,"We describe a simple hybrid superconductor$|$ferromagnetic-insulator
structure manifesting spin-resolved Andreev bound states in which dynamic
magnetization is employed to probe spin related physics. We show that, at low
bias and below $T_c$, the transfer of spin angular momentum pumped by an
externally driven ferromagnetic insulator is greatly affected by the formation
of spin-resolved Andreev bound states. Our results indicate that these bound
states capture the essential physics of condensate-facilitated spin flow. For
finite thicknesses of the superconducting layer, comparable to the coherence
length, resonant Andreev bound states render highly transmitting subgap spin
transport channels. We point out that the resonant enhancement of the subgap
transport channels establishes a prototype Fabry-P\'erot resonator for spin
pumping.",2009.04423v4
2020-11-25,Perovskite as a spin current generator,"We theoretically show that materials with perovskite-type crystal structures
provide a platform for spin current generation, taking advantage of a mechanism
requiring neither the spin-orbit coupling nor a ferromagnetic moment, but is
based on spin-split band structures in certain kinds of collinear
antiferromagnetic states. By investigating a multiband Hubbard model for
transition metal compounds by means of the Hartree-Fock approximation and the
Boltzmann transport theory, we find that a pure spin current is induced by an
electric field applied to a C-type antiferromagnetic metallic phase. The spin
current generation originates from a cooperative effect of spatially
anisotropic electron transfer integrals owing to the GdFeO$_3$-type lattice
distortion, which is ubiquitous in many perovskites, and the collinear spin
configuration. We discuss our finding from the symmetry point of view, in
comparison with other spin current generator candidates with collinear
antiferomagnetism. We also propose several ways to detect the phenomenon in
candidate perovskite materials.",2011.12459v1
2021-05-12,Probing Strong Coupling between a Microwave Cavity and a Spin Ensemble with Raman Heterodyne Spectroscopy,"Raman heterodyne spectroscopy is a powerful tool for characterizing the
energy and dynamics of spins. The technique uses an optical pump to transfer
coherence from a spin transition to an optical transition where the coherent
emission is more easily detected.
  Here Raman heterodyne spectroscopy is used to probe an isotopically purified
ensemble of erbium dopants, in a yttrium orthosilicate (Y$_2$SiO$_5$) crystal
coupled to a microwave cavity. Because the erbium electron spin transition is
strongly coupled to the microwave cavity, we observed Raman heterodyne signals
at the resonant frequencies of the hybrid spin-cavity modes (polaritons) rather
than the bare erbium spin transition frequency. Using the coupled system, we
made saturation recovery measurements of the ground state spin relaxation time
T$_1$ = 10$\pm$3 seconds, and also observed Raman heterodyne signals using an
excited state spin transition. We discuss the implications of these results for
efforts towards converting microwave quantum states to optical quantum states.",2105.05387v1
2021-08-30,Entanglement Limits in Hybrid Spin-Mechanical Systems,"We investigate how to generate continuous-variable entanglement between
distant optomechanical and spin systems, by transferring input two-mode
squeezed vacuum state to the system. Such a setup has been proposed for
backaction evading gravitational-wave measurement, squeezing the output noise
below the standard quantum limit. We find that the spin cavity entanglement
saturates to a particular value when no mechanics are involved even though the
entanglement of the input beam increases steadily, and drops down when the
mechanical oscillator interacts with the cavity. Our study also reveals that
the spin optical readout rate enables the robustness of the spin-cavity
entanglement with input squeezing whereas the optomechanical coupling strength
disables it. The entanglement reaches its maximum when the effective resonance
frequency and bandwidth of the cavity match the spin system. Determining
collective quadrature fluctuations, our analysis also shows that even though
the entanglement between spin and cavity, and cavity and mechanics is
significantly present; it is still impossible to obtain entanglement between
spin and mechanical oscillator.",2108.13216v1
2022-03-27,Making a case for femto- phono- magnetism with FePt,"In the field of femtomagnetism magnetic matter is controlled by ultrafast
laser pulses; here we show that coupling phonon excitations of the nuclei to
spin and charge leads to femto-phono-magnetism, a powerful route to control
magnetic order at ultrafast times. With state-of-the-art theoretical
simulations of coupled spin-, charge-, and lattice-dynamics we identify strong
non-adiabatic spin-phonon coupled modes that dominate early time spin dynamics.
Activating these phonon modes we show leads to an additional (up to 40\% extra)
loss of moment in FePt occurring within 40 femtoseconds of the pump laser
pulse. Underpinning this enhanced ultrafast loss of spin moment we identify a
physical mechanism in which minority spin-current drives an enhanced inter-site
minority charge transfer, in turn promoting increased on-site spin flips. Our
finding demonstrates that the nuclear system, often assumed to play only the
role of an energy sink aiding long time re-magnetisation of the spin system,
can play a profound role in controlling femtosecond spin-dynamics in materials.",2203.14234v1
2022-09-28,Tunneling magnetoresistance and spin-valley polarization of aperiodic magnetic silicene superlattices,"Magnetic silicene superlattices (MSSLs) are versatile structures with
spin-valley polarization and tunneling magnetoresistance (TMR) capabilities.
However, the oscillating transport properties related to the superlattice
periodicity impede stable spin-valley polarization states reachable by
reversing the magnetization direction. Here, we show that aperiodicity can be
used to improve the spin-valley polarization and TMR by reducing the
characteristic conductance oscillations of periodic MSSLs (P-MSSLs). Using the
Landauer-B\""uttiker formalism and the transfer matrix method, we investigate
the spin-valley polarization and the TMR of Fibonacci (F-) and Thue-Morse (TM-)
MSSLs as typical aperiodic superlattices. Our findings indicate that aperiodic
superlattices with higher disorder provide better spin-valley polarization and
TMR values. In particular, TM-MSSLs reduce considerably the conductance
oscillations giving rise to two well-defined spin-valley polarization states
and a better TMR than F- and P-MSSLs. F-MSSLs also improve the spin-valley
polarization and TMR, however they depend strongly on the parity of the
superlattice generation.",2209.13783v1
2023-06-02,Interplay of magnetic field and magnetic impurities in Ising superconductors,"Phonon-driven $s$-wave superconductivity is fundamentally antagonistic to
uniform magnetism, and field-induced suppression of the critical temperature is
one of its canonical signatures. Examples of the opposite are unique and
require fortuitous cancellations and very fine parameter tuning. The recently
discovered Ising superconductors violate this rule: an external magnetic field
applied in a certain direction does not suppress superconductivity in an ideal,
impurity-free material. We propose a simple and experimentally accessible
system where the effects of spin-conserving and spin-flip scattering can be
studied in a controlled way, namely NbSe$_2$ monolayers dozed with magnetic
$3d$ atoms. We predict that the critical temperature is slightly increased by
an in-plane magnetic field in NbSe$_2$ dozed with Cr. Due to the band spin
splitting, magnetic spin-flip scattering requires a finite momentum transfer,
while spin-conserving scattering does not. If the magnetic anisotropy is
easy-axis, an in-plane field reorients the impurity spins and transforms
spin-conserving scattering into spin-flip. The critical temperature is enhanced
if the induced magnetization of NbSe$_2$ has a substantial long-range
component, as is the case for Cr ions.",2306.01700v1
2023-09-25,Fast coherent control of nitrogen-14 spins associated with nitrogen-vacancy centers in diamonds using dynamical decoupling,"A nitrogen-vacancy (NV) center in a diamond enables the access to an electron
spin, which is expected to present highly sensitive quantum sensors. Although
exploiting a nitrogen nuclear spin improves the sensitivity, manipulating it
using a resonant pulse requires a long gate time owing to its small
gyromagnetic ratio. Another technique to control nuclear spins is a conditional
rotation gate based on dynamical decoupling, which is faster but unavailable
for nitrogen spins owing to the lack of transverse hyperfine coupling with the
electron spin. In this study, we generated effective transverse coupling by
applying a weak off-axis magnetic field. An effective coupling depends on the
off-axis field; the conditional rotation gate on the nitrogen-14 spins of an NV
center was demonstrated within 4.2 {\mu}s under an 1.8% off-axis field and a
longitudinal field of approximately 280 mT. We estimated that a population
transfer from the electron to nitrogen spins can be implemented with 8.7
{\mu}s. Our method is applicable to an ensemble of NV centers, in addition to a
single NV center.",2309.14278v1
2023-12-22,Opportunities for the direct manipulation of a phase-driven Andreev spin qubit,"In a Josephson junction, the transfer of Cooper pairs from one superconductor
to the other one can be associated with the formation of Andreev bound states.
In a Josephson junction made with a semiconducting nanowire, the spin
degeneracy of these Andreev states can be broken thanks to the presence of
spin-orbit coupling and a finite phase difference between the two
superconducting electrodes. The lifting of the spin degeneracy opened the way
to the realization of Andreev spin qubits that do not require the application
of a large magnetic field. So far the operation of these qubits relied on a
Raman process involving two microwave tones and a third Andreev state [M. Hays
et al., Science 373, 430 (2021)]. Still, time-reversal preserving impurities in
the nanowire allow for spin-flip scattering processes. Here, using the
formalism of scattering matrices, we show that these processes generically
couple Andreev states with opposite spins. In particular, the non-vanishing
current matrix element between them allows for the direct manipulation of
phase-driven Andreev spin qubits, thereby circumventing the use of the
above-mentioned Raman process.",2312.14865v1
2006-11-13,Spin Sum Rules and Polarizabilities: Results from Jefferson Lab,"The nucleon spin structure has been an active, exciting and intriguing
subject of interest for the last three decades. Recent experimental data on
nucleon spin structure at low to intermediate momentum transfers provide new
information in the confinement regime and the transition region from the
confinement regime to the asymptotic freedom regime. New insight is gained by
exploring moments of spin structure functions and their corresponding sum rules
(i.e. the generalized Gerasimov-Drell-Hearn, Burkhardt-Cottingham and Bjorken).
The Burkhardt-Cottingham sum rule is verified to good accuracy. The spin
structure moments data are compared with Chiral Perturbation Theory
calculations at low momentum transfers. It is found that chiral perturbation
calculations agree reasonably well with the first moment of the spin structure
function $g_1$ at momentum transfer of 0.05 to 0.1 GeV$^2$ but fail to
reproduce the neutron data in the case of the generalized polarizability
$\delta_{LT}$ (the $\delta_{LT}$ puzzle). New data have been taken on the
neutron ($^3$He), the proton and the deuteron at very low $Q^2$ down to 0.02
GeV$^2$. They will provide benchmark tests of Chiral dynamics in the kinematic
region where the Chiral Perturbation theory is expected to work.",0611024v2
2015-11-16,High fidelity transfer and storage of photon states in a single nuclear spin,"Building a quantum repeater network for long distance quantum communication
requires photons and quantum registers that comprise qubits for interaction
with light, good memory capabilities and processing qubits for storage and
manipulation of photons. Here we demonstrate a key step, the coherent transfer
of a photon in a single solid-state nuclear spin qubit with an average fidelity
of 98% and storage over 10 seconds. The storage process is achieved by
coherently transferring a photon to an entangled electron-nuclear spin state of
a nitrogen vacancy centre in diamond, confirmed by heralding through high
fidelity single-shot readout of the electronic spin states. Stored photon
states are robust against repetitive optical writing operations, required for
repeater nodes. The photon-electron spin interface and the nuclear spin memory
demonstrated here constitutes a major step towards practical quantum networks,
and surprisingly also paves the way towards a novel entangled photon source for
photonic quantum computing.",1511.04939v2
2017-11-14,Magnon Splitting Induced by Charge Transfer in the Three-Orbital Hubbard Model,"Understanding spin excitations and their connection to unconventional
superconductivity have remained a central issue since the discovery of the
cuprates. Direct measurement of the dynamical spin structure factor in the
parent compounds can provide key information on important interactions relevant
in the doped regime, and variations in the magnon dispersion have been linked
closely to differences in crystal structure between families of cuprate
compounds. Here, we elucidate the relationship between spin excitations and
various controlling factors thought to be significant in high-$T_c$ materials
by systematically evaluating the dynamical spin structure factor for the
three-orbital Hubbard model, revealing differences in the spin dispersion along
the Brillouin zone axis and the diagonal. Generally, we find that the absolute
energy scale and momentum dependence of the excitations primarily are sensitive
to the effective charge-transfer energy, while changes in the on-site Coulomb
interactions have little effect on the details of the dispersion. In
particular, our result highlights the splitting between spin excitations along
the axial and diagonal directions in the Brillouin zone. This splitting
decreases with increasing charge-transfer energy and correlates with changes in
the apical oxygen position, and general structural variations, for different
cuprate families.",1711.04931v2
2018-01-13,An exact alternative solution method of 1D Ising model with Block-spin transformation at $H=0$,"An alternative exact explicit solution of 1D Ising chain is presented without
using any boundary conditions (or free boundary condition) by the help of
applying successively block-spin transformation. Exact relation are obtained
between spin-spin correlation functions in the absence of external field. To
evaluate average magnetization (or the order parameter), it is assumed that the
average magnetization can be related to infinitely apart two spin correlation
function as $<\sigma>^{2}=<\sigma_{0}\sigma_{N}>$. A discussion to justify this
consideration is given in the introduction with a relevant manner. It is
obtained that $<\sigma_{0}\sigma_{1}>=\tanh{K}$, which is exactly the same
relation as the previously derived relation by considering the configurational
space equivalence of $\{\sigma_{i}\sigma_{i+1}\}=\{s_{i}\}$ and the result of
transfer matrix method in the absence of external field. By applying further
block-spin transformation, it is obtained that
$\{\sigma_{0}\sigma_{j}\}=(\tanh{K})^{j}$, here $j$ assumes the values of
$j=2^n$, here $n$ is an integer numbers. We believe that this result is really
important in that it is the only exact unique treatment of the 1D Ising chain
beside with the transfer matrix method. It is also pointed out the irrelevances
of some of the alternative derivation appearing in graduate level text books.
The obtained unique correlation relation in this this study leads in the limit
of $N\rightarrow\infty$ to $<\sigma_{i}>=(\tanh{K})^{N/2}$, indicating that the
second order phase transition is only possible in the limit of
$K\rightarrow\infty$. The obtained results in this work are exactly the same as
those of obtained by the transfer matrix method which considers periodic
boundary condition.",1801.04452v1
2021-12-13,Symmetry constraints on spin order transfer in parahydro-gen-induced polarization (PHIP),"It is well known that the association of parahydrogen (pH2) with an
unsaturated molecule or a transient metalorganic complex can enhance the
intensity of NMR signals; the effect is known as parahydrogen-induced
polarization (PHIP). During the last decades, numerous methods were proposed
for converting pH2-derived nuclear spin order to the observable magnetization
of pro-tons or other nuclei of interest, usually 13C or 15N. Here, we analyze
the constraints imposed by the topological symmetry of the spin systems on the
amplitude of transferred polarization. In asymmetric systems, heteronuclei can
be polarized to 100%. However, the amplitude drops to 75% in A2BX systems and
further to 50% in A3B2X systems. The latter case is of primary importance for
biological applications of PHIP using sidearm hydrogenation (PHIP-SAH). If the
polarization is transferred to the same type of nuclei, i.e. 1H, symmetry
constraints impose significant boundaries on the spin-order distribution. For
AB, A2B, A3B, A2B2, AA'(AA') systems, the maxi-mum average polarization for
each spin is 100%, 50%, 33.3%, 25%, and 0, respectively, when A and B (or A')
came from pH2 We also discuss the effect of dipole-dipole induced pH2
spin-order distribution in heterogeneous catalysis or nematic liquid crystals.
Practical examples from the literature illustrate our theoretical analysis.",2112.06852v1
2024-03-01,Unveiling the physics of the spin-orbit coupling at the surface of a model topological insulator: from theory to experiments,"Spin-orbit interaction affects the band structure of topological insulators
beyond the opening of an inverted gap in the bulk bands, and the understanding
of its effects on the surface states is of primary importance to access the
underlying physics of these exotic states. Here, we propose an $\textit{ab
initio}$ approach benchmarked by pump-probe angle-resolved photoelectron
spectroscopy data to model the effect of spin-orbit coupling on the surface
states of a topological insulator. The critical novelty of our approach lies in
the possibility of accounting for a partial transfer of the spin-orbit coupling
to the surface states, mediated by the hybridization with the surface resonance
states. In topological insulators, the fraction of transferred spin-orbit
coupling influences the strength of the hexagonal warping of the surface
states, which we use as a telltale of the capability of our model to reproduce
the experimental dispersion. The comparison between calculations and
measurements, of both the unoccupied and part of the occupied Dirac cone,
indicates that the fraction of spin-orbit coupling transferred to the surface
states by hybridization with the resonance states is between 70% and 85% of its
full atomic value. This offers a valuable insight to improve the modeling of
surface state properties in topological insulators for both scientific purposes
and technological applications.",2403.01029v1
2011-09-26,Magnetic torque oscillations from warped helical surface states in topological insulators,"A magnetic torque method is proposed that probes the warping and mass gap of
Dirac cone surface states in topological insulators like Bi2X3 (X=Se,Te). A
rotating field parallel to the surface induces a paramagnetic moment in the
helical surface states for nonzero warping. It is non-collinear with the
applied field and therefore produces torque oscillations as function of the
field angle which are a direct signature of the surface states. The torque
dependence on field strength and angle, the chemical potential and the Dirac
cone parameters like warping strength and mass gap is calculated. It is shown
that the latter leads to a symmetry reduction in the fourfold torque
oscillations.",1109.5538v1
2018-11-26,Phase-dependent light-induced torque,"Optical torque on individual atoms in a Bose-Einstein condensate can rotate
the ensemble and generate a current flow [Phys. Rev. A 82, 051402 (2010)]. We
exploit the fact to suggest a new mechanism for enhanced and well-controlled
rotational motions and show how atoms, interacting with Laguerre-Gaussian
beams, experience a torque whose features depend on relative phase of applied
fields so that zero and large positive, or even negative, values for the torque
can be obtained. Such controllable torque, along with simplicity of tuning the
relative phase, can simplify a possible implementation of current flows in
Bose-Einstein condensates.",1811.10193v1
2020-11-12,Accessible Torque Bandwidth of a Series Elastic Actuator Considering the Thermodynamic Limitations,"Within the scope of the paper, electromechanical and thermodynamic models are
derived for a series elastic actuator and open loop and closed loop torque
bandwidth parameters are analysed considering the thermodynamic behaviour of
the actuator. It was observed that the closed loop torque bandwidth of the
electromechanical subsystem of the actuator was not accessible in the entire
torque reference amplitude range due to thermodynamic limitations. Therefore, a
stator winding temperature estimation based adaptive controller is utilised and
analysed to improve the accessibility of the controller based torque bandwidth.
This paper implements the methodology on a HEBI Robotics X5-9 actuator as a
case study.",2011.06217v1
2022-09-07,Inertial torque on a squirmer,"A small spheroid settling in a quiescent fluid experiences an inertial torque
that aligns it so that it settles with its broad side first. Here we show that
an active particle experiences such a torque too, as it settles in a fluid at
rest. For a spherical squirmer, the torque is $\boldsymbol{T}^\prime =
-{\tfrac{9}{8}} m_f (\boldsymbol{v}_s^{(0)} \wedge \boldsymbol{v}_g^{(0)})$
where $\boldsymbol{v}_s^{(0)}$ is the swimming velocity,
$\boldsymbol{v}_g^{(0)}$ is the settling velocity in the Stokes approximation,
and $m_f$ is the equivalent fluid mass. This torque aligns the swimming
direction against gravity: swimming up is stable, swimming down is unstable.",2209.03129v1
2023-10-30,Trace expressions and associated limits for equilibrium Casimir torque,"We exploit fluctuational electrodynamics to present trace expressions for the
torque experienced by arbitrary objects in a passive, nonabsorbing,
rotationally invariant background environment. We present trace expressions for
equilibrium Casimir torque which complement recently derived nonequilibrium
torque expressions and explicate their relation to the Casimir free energy. We
then use the derived trace expressions to calculate, via Lagrange duality,
semianalytic structure-agnostic bounds on the Casimir torque between an
anisotropic (reciprocal or nonreciprocal) dipolar particle and a macroscopic
body composed of a local isotropic electric susceptibility, separated by
vacuum.",2310.19728v1
2020-02-26,A systematic study of radiative torque grain alignment in the diffuse interstellar medium,"Context. Planck observations demonstrated that the grain alignment efficiency
is almost constant in the diffuse ISM. Aims. We test if the Radiative Torque
(RAT) theory is compatible with observational constraints on grain alignment.
Methods. We combine a numerical simulation with the radiative transfer code
POLARIS that incorporates a physical dust model and the detailed grain
alignment physics of RATs. A dust model is designed to reproduce the spectral
dependence of extinction of the ISM. From a RAMSES simulation of interstellar
turbulence, we extract a cube representative of the diffuse ISM. We
post-process the cube with POLARIS to get the grain temperature and RATs to
simulate synthetic dust polarization maps. Results. In our simulation the grain
alignment efficiency is correlated with gas pressure, but not with the RAT
intensity. Because of the low dust extinction, the magnitude of RATs varies
little, decreasing only for high column densities $N_H$. Comparing our maps
with a uniform alignment efficiency, we find no systematic difference. The
dependence of polarization fraction $p$ with $N_H$ or polarization dispersion
$S$ is similar. The drop of RATs in dense regions barely affects the
polarization pattern, the signal being dominated by the LOS and magnetic field
geometry. If a star is inserted, the polarization increases, with no specific
pattern around the star. The angle-dependence of RATs is not observed in the
maps, and is weak using a uniform magnetic field. Conclusions. RATs are
compatible with Planck data for the diffuse ISM such that both uniform
alignment and RAT alignment lead to similar observations. To further test the
predictions of RATs where an important drop of grain alignment is expected,
polarization observations of dense regions must be confronted to numerical
simulations sampling high column densities through dense clouds, with enough
statistics.",2002.11792v1
2020-05-13,"The inertial sea wave energy converter (ISWEC) technology: device-physics, multiphase modeling and simulations","In this paper we investigate the dynamics of the inertial wave energy
converter (ISWEC) device using fully-resolved computational fluid dynamics
(CFD) simulations. Originally prototyped by Polytechnic University of Turin,
the device consists of a floating, boat-shaped hull that is slack-moored to the
sea bed. Internally, a gyroscopic power take off (PTO) unit converts the
wave-induced pitch motion of the hull into electrical energy. The CFD model is
based on the incompressible Navier-Stokes equations and utilizes the fictitious
domain Brinkman penalization technique to couple the device physics and water
wave dynamics. A numerical wave tank is used to emulate realistic sea operating
conditions. A Froude scaling analysis is performed to enable two- and
three-dimensional simulations for a scaled-down (1:20) ISWEC model. It is
demonstrated that the scaled-down 2D model is sufficient to accurately simulate
the hull's pitching motion and to predict the power generation capability of
the converter. A systematic parameter study of the ISWEC is conducted, and its
optimal performance in terms of power generation is determined based on the
hull and gyroscope control parameters. It is demonstrated that the device
achieves peak performance when the gyroscope specifications are chosen based on
reactive control theory. It is shown that a proportional control of the PTO
control torque is required to generate continuous gyroscope precession effects,
without which the device generates no power. In an inertial reference frame, it
is demonstrated that the yaw and pitch torques acting on the hull are of the
same order of magnitude, informing future design investigations of the ISWEC
technology. Further, an energy transfer pathway from the water waves to the
hull, the hull to the gyroscope, and the gyroscope to the PTO unit is
analytically described and numerically verified.",2005.06108v1
2023-12-11,Vertical shear instability in two-moment radiation-hydrodynamical simulations of irradiated protoplanetary disks II. Secondary instabilities and stability regions,"The vertical shear instability (VSI) is a hydrodynamical instability likely
to produce turbulence in the dead zones of protoplanetary disks. Various
aspects of this instability remain to be understood, including the disk regions
where it can operate and the physical phenomena leading to its saturation. In
this work, we studied the growth and evolution of secondary instabilities
parasitic to the VSI, examining their relation with its saturation in
axisymmetric radiation-hydrodynamical simulations of protoplanetary disks. We
also constructed stability maps for our disk models, considering temperature
stratifications enforced by stellar irradiation and radiative cooling and
incorporating the effects of dust-gas collisions and molecular line emission.
We found that the flow pattern produced by the interplay of the axisymmetric
VSI modes and the baroclinic torque forms bands of nearly uniform specific
angular momentum. In the high-shear regions in between these bands, the
Kelvin-Helmholtz instability (KHI) is triggered. The significant transfer of
kinetic energy to small-scale eddies produced by the KHI and possibly even the
baroclinic acceleration of eddies limit the maximum energy of the VSI modes,
likely leading to the saturation of the VSI. A third instability mechanism,
consisting of an amplification of eddies by baroclinic torques, forms
meridional vortices with Mach numbers up to $\sim 0.4$. Our stability analysis
suggests that protoplanetary disks can be VSI-unstable in surface layers up to
tens of au for reasonably high gas emissivities, even in regions where the
midplane is stable. This picture is consistent with current observations of
disks showing thin midplane millimeter-sized dust layers while appearing
vertically extended in optical and near-infrared wavelengths.",2312.06890v1
2024-01-16,Investigating a single-domain approach for modeling coupled porous solid-fluid systems: applications in buoyant reacting plume formation and ignition,"Many natural and industrial processes involve mixed porous-solid fluid
domains where multiple physics of reactions, heat transfer, and fluid flow
interact over disparate length scales, such as the combustion of multi-species
solid fuels. This range of problems covers small-scale fuel burning to
large-scale forest fires when plant canopies can be modeled as porous media.
Although many modeling studies so far have concentrated on detailed physics
within the single fluid or porous phase, few consider both phases, in part due
to the challenge in determining suitable boundary conditions between the
regions, particularly in turbulent flows where eddies might penetrate the
porous region. In this work, we develop a single-domain approach that
eliminates the need for boundary conditions at the interface, and numerically
study scenarios involving porous-solids and a surrounding fluid. Similar to the
methods used in large eddy simulation, the flow is averaged over a small
spatial volume--but over the entire domain. We focus on the ignition and
related interfacial phenomena, a problem that has rarely been studied in detail
from a modeling standpoint. After verifying and validating the model, we
examine the emission of buoyant reacting plumes from the surface of a heated
solid and the near-field flow dynamics. We observed indications of flow
instabilities similar to those seen in Rayleigh-Taylor and Kelvin-Helmholtz
phenomena. Our analysis highlighted that the inflectional velocity profile
close to the interface triggers the generation of vorticity due to viscous
torque, linked with Kelvin-Helmholtz instabilities. Gravitational and
baroclinic torques play key roles in vortex growth in the surrounding fluid
region. These flow characteristics could significantly influence the mixing of
oxidizer and fuel, ignition processes, and fire propagation.",2401.08874v1
1997-05-29,Transfer Matrix DMRG for Thermodynamics of One-Dimensional Quantum Systems,"The transfer matrix DMRG method for one dimensional quantum lattice systems
has been developed by considering the symmetry property of the transfer matrix
and introducing the asymmetric reduced density matrix. We have evaluated a
number of thermodynamic quantities of the anisotropic spin-1/2 Heisenberg model
using this method and found that the results agree very accurately with the
exact ones. The relative errors for the spin susceptibility are less than
$10^{-3}$ down to $T=0.01J$ with 80 states kept.",9705301v1
2003-04-22,Orbital ordering in charge transfer insulators,"We discuss a new mechanism of orbital ordering, which in charge transfer
insulators is more important than the usual exchange interactions and which can
make the very type of the ground state of a charge transfer insulator, i.e. its
orbital and magnetic ordering, different from that of a Mott-Hubbard insulator.
This purely electronic mechanism allows us to explain why orbitals in
Jahn-Teller materials typically order at higher temperatures than spins, and to
understand the type of orbital ordering in a number of materials, e.g.
K_2CuF_4, without invoking the electron-lattice interaction.",0304494v1
2004-10-01,Polarization Transfer in Proton Compton Scattering at High Momentum Transfer,"Compton scattering from the proton was investigated at s=6.9 (GeV/c)**2 and
\t=-4.0 (GeV/c)**2 via polarization transfer from circularly polarized incident
photons. The longitudinal and transverse components of the recoil proton
polarization were measured. The results are in excellent agreement with a
prediction based on a reaction mechanism in which the photon interacts with a
single quark carrying the spin of the proton and in disagreement with a
prediction of pQCD based on a two-gluon exchange mechanism.",0410001v1
1994-11-29,The Drell-Hearn-Gerasimov Sum Rule,"The Drell-Hearn-Gerasimov (DHG) sum rule relates the helicity structure of
the photoabsorption cross section to the anomalous magnetic moment of the
nucleon. It is based on Lorentz and gauge invariance, crossing symmetry,
causality and unitarity. A generalized DHG sum rule my be derived for virtual
photons. At low momentum transfer this generalized sum rule is saturated by the
resonance region, at high momentum transfer it may be expressed by the parton
spin distributions measured in deep inelastic scattering. The
longitudinal-transverse interference determines the Cottingham sum rule, which
is related to the electric and magnetic form factors over the whole range of
momentum transfer.",9411034v1
2003-12-23,Quantum state transfer between field and atoms in Electromagnetically Induced Transparency,"We show that a quasi-perfect quantum state transfer between an atomic
ensemble and fields in an optical cavity can be achieved in Electromagnetically
Induced Transparency (EIT). A squeezed vacuum field state can be mapped onto
the long-lived atomic spin associated to the ground state sublevels of the
Lambda-type atoms considered. The EIT on-resonance situation show interesting
similarities with the Raman off-resonant configuration. We then show how to
transfer the atomic squeezing back to the field exiting the cavity, thus
realizing a quantum memory-type operation.",0312189v1
2004-12-22,Criteria for quantum coherent transfer of excitons between chromophores in a polar solvent,"We show that the quantum decoherence of Forster resonant energy transfer
between two optically active molecules can be described by a spin-boson model.
This allows us to give quantitative criteria, in terms of experimentally
measurable system parameters, that are necessary for coherent Bloch
oscillations of excitons between the chromophores. Experimental tests of our
results should be possible with Flourescent Resonant Energy Transfer (FRET)
spectroscopy. Although we focus on the case of protein-pigment complexes our
results are also relevant to quantum dots and organic molecules in a dielectric
medium.",0412170v1
2007-06-25,Coulomb effects in polarization transfer in elastic antiproton and proton electron scattering at low energies,"The influence of Coulomb distortion on the polarization transfer in elastic
proton and antiproton electron scattering at low energies is calculated in a
distorted wave Born approximation. For antiproton electron scattering Coulomb
effects reduce substantially the spin transfer cross section compared to the
plane wave Born approximation whereas for proton electron scattering they lead
to a dramatic increase for kinetic proton lab energies below about 20 keV.",0706.3576v3
2007-12-12,Generalized Parton Distrbutions and Nucleon Form Factors,"The Dirac and Pauli form factors of the proton and neutron are obtained in
the framework of the generalized parton distributions (GPDs) with some simple
momentum transfer dependence. It is shown that both sets of the existing
experimental data of the form factors, obtained by the Rosenbluth and
polarization transfer, can be described by changing only the slope of the GPDs
$E$. The description of neutron form factors is substantially better when the
proton data obtained by the studies of polarization transfer are used.",0712.1947v2
2008-05-13,Perfect transfer of m-qubit GHZ states,"By using some techniques such as spectral distribution and stratification
associated with the graphs, employed in [1,2] for the purpose of Perfect state
transfer (PST) of a single qubit over antipodes of distance-regular spin
networks and PST of a $d$-level quantum state over antipodes of pseudo-distance
regular networks, PST of an m-qubit GHZ state is investigated. To do so, we
employ the particular distance-regular networks (called Johnson networks)
J(2m,m) to transfer an m-qubit GHZ state initially prepared in an arbitrary
node of the network (called the reference node) to the corresponding antipode,
perfectly.
  Keywords: Perfect state transferenc, GHZ states, Johnson network,
Stratification, Spectral distribution
  PACs Index: 01.55.+b, 02.10.Yn",0805.1866v1
2009-02-06,Perfect State Transfer without State Initialization and Remote Collaboration,"We present a perfect state transfer protocol via a qubit chain with the
evolution governed by the $xx$ Hamiltonian. In contrast to the recent protocol
announced in [Phys. Rev. Lett. {\bf 101}, 230502 (2008)], our method does not
demand any remote-cooperated initialization and sending classical information
about measurement outcomes. We achieve the perfect state transfer only with the
assumption of access to two spins at each end of the chain, while the initial
state of the whole chain is irrelevant.",0902.1095v4
2010-03-17,Functional equations for transfer-matrix operators in open Hecke chain models,"We consider integrable open chain models formulated in terms of generators of
affine Hecke algebras. The hierarchy of commutative elements (which are analogs
of the commutative transfer-matrices) are constructed by using the fusion
procedure. These elements satisfy a set of functional relations which
generalize functional relations among a family of transfer-matrices in solvable
spin chain models of U_q(gl(n|m)) type.",1003.3385v1
2011-09-30,Deterministic qubit transfer between orbital and spin angular momentum of single photons,"In this work we experimentally implement a deterministic transfer of a
generic qubit initially encoded in the orbital angular momentum of a single
photon to its polarization. Such transfer of quantum information, completely
reversible, has been implemented adopting a electrically tunable q-plate device
and a Sagnac interferomenter with a Dove's prism. The adopted scheme exhibits a
high fidelity and low losses.",1109.6747v1
2012-07-26,Reactant-Product Quantum Coherence in Electron Transfer Reactions,"We investigate the physical meaning of quantum superposition states between
reactants and products in electron transfer reactions. We show that such
superpositions are strongly suppressed and to leading orders of perturbation
theory do not pertain in electron transfer reactions. This is because of the
intermediate manifold of states separating the reactants from the products. We
provide an intuitive description of these considerations with Feynman diagrams.
We also discuss the relation of such quantum coherences to understanding the
fundamental quantum dynamics of spin-selective radical-ion-pair reactions.",1207.6316v1
2012-09-03,Time-Optimal Transfer of Coherence,"We provide exact analytical solutions for the problem of time-optimal
transfer of coherence from one spin polarization to a three-fold coherence in a
trilinear Ising chain with a fixed energy available and subject to local
controls with a non negligible time cost. The time of transfer is optimal and
consistent with a previous numerical result obtained assuming instantaneous
local controls.",1209.0405v3
2013-01-09,Quantum-state transfer via resonant tunnelling through local field induced barriers,"Efficient quantum-state transfer is achieved in a uniformly coupled spin-1/2
chain, with open boundaries, by application of local magnetic fields on the
second and last-but-one spins, respectively. These effective \textit{barriers}
induce appearance of two eigenstates, bi-localized at the edges of the chain,
which allow a high quality transfer also at relatively long distances. The same
mechanism may be used to send an entire e-bit (e.g., an entangled qubit pair)
from one to the other end of the chain.",1301.1774v2
2013-12-23,Translating Concepts of State Transfer to Spin-1 Chains,"State transfer is a well-known routine for various systems of
spins-$\frac{1}2$. Still, it is not well studied for chains of spins of larger
magnitudes. In this contribution we argue that while perfect state transfer may
seem unnatural in spin-1 systems, it is still feasible for arrays of V-type
three-level atoms. Tomography of such 1D array is also shown to be possible by
acting on one atom from such an array.",1312.6543v2
2014-01-26,Decoherence-assisted transport in quantum networks,"It is shown that energy transfer in a homogeneous fully connected quantum
network is assisted by a decohering interaction with environmental spins.
Analytic expressions for the transfer probabilities are obtained for the zero
temperature case, and the effect is shown to persist at physiological
temperatures. This model of decoherence-assisted energy transfer is applied to
the Fenna-Matthews-Olson complex.",1401.6660v1
2014-05-12,Transfer arbitrary photon state along a cavity array without initialization,"We propose a quantum state transfer (QST) scheme that transfers any
single-mode photon state along a one-dimensional coupled-cavity array (CCA). By
building a map from QST in a CCA to that in a spin-$\frac{1}{2}$ chain, we show
that all the previous results of QST schemes for the spin chain system find
paralleled applications in that in the CCA system. Further more, high fidelity
QST along a long CCA can be achieved for arbitrary initial states. Using
numerical simulations we provide a visual presentation of the result: at some
time $\tau$ the CCA system get high fidelity QST under different initial
conditions. Finally we discuss possible experimental realizations of our QST
scheme.",1405.2634v1
2015-03-30,Protected quantum-state transfer in decoherence-free subspaces,"We propose and analyse a robust quantum state transfer protocol by the use of
a combination of coherent quantum coupling and decoherence-free subspaces in a
coupled quantum spin chain. Under decoherence, an arbitrary unknown quantum
state embedded in a decoherence-free subspace can be perfectly transferred
through a noisy channel being weakly coupled to two end registers. The method
protects quantum information from both the channel noise and the environmental
decoherence. A special case of utilizing two physical qubits to encode one
logical qubit is considered as an example and the robustness is confirmed by
numerical performances.",1503.08617v2
2015-10-19,Bounds on probability of state transfer with respect to readout time and edge weight,"We analyse the sensitivity of a spin chain modelled by an undirected weighted
connected graph exhibiting perfect state transfer to small perturbations in
readout time and edge weight in order to obtain physically relevant bounds on
the probability of state transfer. At the heart of our analysis is the concept
of the numerical range of a matrix; our analysis of edge weight errors
additionally makes use of the spectral and Frobenius norms.",1510.05550v2
2016-07-09,Analytic next-to-nearest neighbour XX models with perfect state transfer and fractional revival,"Certain non-uniformly coupled spin chains can exhibit perfect transfer of
quantum states from end to end. Motivated by recent experimental
implementations, we extend the simplest such chain to next-to-nearest neighbour
(NNN) couplings. It is shown analytically that perfect state transfer can be
maintained under the extension and that end-to-end entanglement generation
(fractional revival) can occur.",1607.02639v1
2017-06-01,Scale invariant transfer matrices and Hamiltionians,"Given a direct system of Hilbert spaces $s\mapsto \mathcal H_s$ (with
isometric inclusion maps $\iota_s^t:\mathcal H_s\rightarrow \mathcal H_t$ for
$s\leq t$) corresponding to quantum systems on scales $s$, we define notions of
scale invariant and weakly scale invariant operators. Is some cases of quantum
spin chains we find conditions for transfer matrices and nearest neighbour
Hamiltonians to be scale invariant or weakly so. Scale invariance forces
spatial inhomogeneity of the spectral parameter. But weakly scale invariant
transfer matrices may be spatially homogeneous in which case the change of
spectral parameter from one scale to another is governed by a classical
dynamical system exhibiting fractal behaviour.",1706.00515v1
1999-03-19,"Two-Step Contribution to Intermediate Energy (p,p') and (p,n) Reactions","We calculate the two-step contribution to (p,p') and (p,n) reactions at
intermediate energy. We describe the motion of the incident nucleon with plane
wave and compare the contribution from the two-step processes with that from
the one-step processes. To describe the two-step processes, we extende the
response functions into the nondiagonal ones with respect to the momentum
transfer q.
  We performed a numerical calculation for the cross sections of the $^{12}$C,
$^{40}$Ca(p,p') scatterings and the spin longitudinal and the spin transverse
cross sections of the $^{12}$C,$^{40}$Ca(p,n) reactions at 346 MeV and 494 MeV.
We found that the two-step contribution is appreciable in comparison with the
one-step processes in higher energy transfer region for the spin longitudinal
and the spin transverse (p,n) reactions. We also found that the two-step
processes give larger contribution to the spin transverse (p,n) reaction than
to the spin longitudinal reaction. This finding is very encouraging to
interpret the discrepancy between the DWIA calculation and the experimental
results of the spin longitudinal and the spin transverse cross sections.",9903049v2
2008-08-18,Entangled quantum heat engines based on two two-spin systems with Dzyaloshinski-Moriya anisotropic antisymmetric interaction,"We construct an entangled quantum heat engine (EQHE) based on two two-spin
systems with Dzyaloshinski-Moriya (DM) anisotropic antisymmetric interaction.
By applying the explanations of heat transferred and work performed at the
quantum level in Kieu's work [PRL, 93, 140403 (2004)], the basic thermodynamic
quantities, i.e., heat transferred, net work done in a cycle and efficiency of
EQHE are investigated in terms of DM interaction and concurrence. The validity
of the second law of thermodynamics is confirmed in the entangled system. It is
found that there is a same efficiency for both antiferromagnetic and
ferromagnetic cases, and the efficiency can be controlled in two manners: 1.
only by spin-spin interaction J and DM interaction D; 2. only by the
temperature T and concurrence C. In order to obtain a positive net work, we
need not entangle all qubits in two two-spin systems and we only require the
entanglement between qubits in a two-spin system not be zero. As the ratio of
entanglement between qubits in two two-spin systems increases, the efficiency
will approach infinitely the classical Carnot one. An interesting phenomenon is
an abrupt transition of the efficiency when the entanglements between qubits in
two two-spin systems are equal.",0808.2409v1
2009-10-04,Proposals of nuclear spin quantum memory in group IV elemental and II-VI semiconductors,"New schemes for the nuclear spin quantum memory are proposed based on a
system composed of two electrons or one electron coupled to a single nuclear
spin in isotopically purified group IV elemental and II-VI compound
semiconductors. The qubit consists of the singlet state and one of the triplet
states of two electrons or simply of an electron spin. These systems are free
from the decoherence due to the nuclear dipole-dipole interaction and are
advantageous for the long memory time. In the case of two electrons, the
protocol for the quantum state transfer between the electron spin qubit and the
nuclear spin qubit is based on the magnetic or electric field tuning of the
singlet-triplet state crossing and on the hyperfine coupling supplemented with
a well-defined scheme to initialize the nuclear spin. In the case of a single
electron qubit, the quantum state transfer is driven by the hyperfine
interaction itself without the need of the nuclear spin initialization. Many
practical systems are considered, e.g., two electrons loaded on a Si or ZnSe
quantum dot, a single electron charged state in a Si quantum dot doped with a P
atom, a single electron charged $ ^{28}$Si quantum dot doped with an isotope
atom of $ ^{29}$Si, and a localized electron system of Si:P and ZnSe:F in the
bulk crystal. General aspects of these systems are investigated and a
comparison of merits and demerits is made between the two-electron qubit and
the single-electron qubit.",0910.0584v2
2013-05-14,Long-range FMR driven spin pumping through a nonmagnetic insulator,"Ferromagnetic resonance (FMR) driven spin pumping is an emerging technique
for injection of a pure spin current from a ferromagnet (FM) into a
non-magnetic (NM) material without an accompanying charge current. It is widely
believed that this pumping proceeds exclusively via a short-range exchange
interaction at the FM/NM interface. Here we report robust, long-range spin
pumping from the ferrimagnetic double perovskite Sr2FeMoO6 (SFMO) into Pt
across an insulating barrier up to 200 nm thick, and systematically rule out
all known spurious effects. This result demonstrates dynamic spin injection
over a distance far beyond the coupling range of the exchange interaction,
exposing the need to consider other coupling mechanisms. The characteristic
length scale for magnetic textures in Sr2FeMoO6 is approximately 150 nm,
resulting from structural antiphase boundaries, thus raising the possibility
that magnetic dipole coupling underlies the observed long range spin transfer.
This discovery reveals a route to dynamic angular momentum transfer between a
FM and a NM in the absence of mediation by itinerant electrons and promises new
spin-functional devices employing long-range spin pumping.",1305.3016v2
2015-05-06,Bipolar polaron pair recombination in P3HT/PCBM solar cells,"The unique properties of organic semiconductors make them versatile base
materials for many applications ranging from light emitting diodes to
transistors. The low spin-orbit coupling typical for carbon-based materials and
the resulting long spin lifetimes give rise to a large influence of the
electron spin on charge transport which can be exploited in spintronic devices
or to improve solar cell efficiencies. Magnetic resonance techniques are
particularly helpful to elucidate the microscopic structure of paramagnetic
states in semiconductors as well as the transport processes they are involved
in. However, in organic devices the nature of the dominant spin-dependent
processes is still subject to considerable debate. Using multi-frequency pulsed
electrically detected magnetic resonance (pEDMR), we show that the
spin-dependent response of P3HT/PCBM solar cells at low temperatures is
governed by bipolar polaron pair recombination involving the positive and
negative polarons in P3HT and PCBM, respectively, thus excluding a unipolar
bipolaron formation as the main contribution to the spin-dependent charge
transfer in this temperature regime. Moreover the polaron-polaron coupling
strength and the recombination times of polaron pairs with parallel and
antiparallel spins are determined. Our results demonstrate that the pEDMR pulse
sequences recently developed for inorganic semiconductor devices can very
successfully be transferred to the study of spin and charge transport in
organic semiconductors, in particular when the different polarons can be
distinguished spectrally.",1505.01411v1
2017-09-03,Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy,"Understanding the transfer of spin angular momentum is essential in modern
magnetism research. A model case is the generation of magnons in magnetic
insulators by heating an adjacent metal film. Here, we reveal the initial steps
of this spin Seebeck effect with <27fs time resolution using terahertz
spectroscopy on bilayers of ferrimagnetic yttrium-iron garnet and platinum.
Upon exciting the metal with an infrared laser pulse, a spin Seebeck current
$j_\textrm{s}$ arises on the same ~100fs time scale on which the metal
electrons thermalize. This observation highlights that efficient spin transfer
critically relies on carrier multiplication and is driven by conduction
electrons scattering off the metal-insulator interface. Analytical modeling
shows that the electrons' dynamics are almost instantaneously imprinted onto
$j_\textrm{s}$ because their spins have a correlation time of only ~4fs and
deflect the ferrimagnetic moments without inertia. Applications in material
characterization, interface probing, spin-noise spectroscopy and terahertz spin
pumping emerge.",1709.00768v5
2022-09-21,Spin current driven by ultrafast magnetization of FeRh,"Laser-induced ultrafast demagnetization is an important phenomenon that
probes arguably ultimate limits of the angular momentum dynamics in solid.
Unfortunately, many aspects of the dynamics remain unclear except that the
demagnetization transfers the angular momentum eventually to the lattice. In
particular, roles of electron-carried spin current are debated. Here we
experimentally probe the spin current in the opposite phenomenon, i.e.,
laser-induced ultrafast magnetization of FeRh, where the laser pump pulse
initiates the angular momentum build-up rather than its dissipation. Using the
time-resolved magneto-optical Kerr effect, we directly measure the
ultrafast-magnetization-driven spin current in a FeRh/Cu heterostructure.
Strong correlation between the spin current and the net magnetization change
rate of FeRh is found even though the spin filter effect is negligible in this
opposite process. This result implies that the angular momentum build-up is
achieved by an angular momentum transfer from the electron bath (supplier) to
the magnon bath (receiver) and followed by the spatial transport of angular
momentum (spin current) and dissipation of angular momentum to the phonon bath
(spin relaxation).",2209.10290v1
2023-07-21,The influence of a static planetary atmosphere on spin transfer during pebble accretion,"We study the effect an atmosphere has on pebble orbits and spin build-up on a
planet's surface during pebble accretion in the extreme case of a static
atmosphere. We numerically integrate the equations of motion of pebbles in a
planar, global frame with a planet, a central star and gas from a
protoplanetary disc. An adiabatic atmosphere is then placed around the planet,
and the spin deposited onto the planet's surface is measured. These simulations
are evaluated for different distances to the star, Stokes numbers, and planet
masses. Pebble feedback to the gas is not taken into account. We find that a
static atmosphere dampens the spin the planet's surface receives by absorbing
part of the angular momentum of the pebbles and circularising their orbits.
This could prevent the excessive spin values predicted in some 3D pebble
accretion simulations without an atmosphere. For planets larger than 0.5 Earth
masses, a stationary atmosphere absorbs all angular momentum, leaving no spin
for the surface. Significant quantities of angular momentum are stored in the
inner and intermediate atmosphere ($<0.3$ Bondi radii). Depending on the
atmospheric and disc model, this spin could be transported either to the disc
through atmospheric recycling or to the planet through drag between the surface
and the atmosphere. Further research is required to quantify the spin transfer
within the atmosphere.",2307.11847v1
1995-06-12,Fermi Liquid - Non-Fermi Liquid Transition in the Double Exchange Model,"Motivated by recent discovery of colossal magnetoresistance in
La$_(1-x)$Ca$x$MnO$_3$ and other manganites, we have studied the double
exchange model. We argue that the forced alignment of conduction-electron spin
with the core spins that causes ferromagnetism also projects out a large part
of the Hilbert space needed for coherent propagation of electrons carrying spin
and charge. As a result, the electron becomes a composite object and its
Green's function exhibits a two-fluid character: a coherent Fermi-liquid
component associated with the ferromagnetically ordered core spins, and a
non-Fermi liquid component associated with the disordered spins. With
increasing temperature, there is continuous transfer of spectral weight from
the Fermi liquid to the non-Fermi liquid component, until the former disappears
above $T_c$. In an applied field spectral weight is transferred from the
non-Fermi liquid to the component. Implications for the manganites are
discussed.",9506051v1
2000-06-29,"Coexistence of charge density waves, bond order waves and spin density waves in quasi-one dimensional charge transfer salts","Charge, spin, as well as lattice instabilities are investigated in isolated
or weakly coupled chains of correlated electrons at quarter-filling. Our
analysis is based on extended Hubbard models including nearest neighbor
repulsion and Peierls coupling to lattice degrees of freedom. While treating
the electronic quantum fluctuations exactly, the lattice structure is optimized
self-consistently. We show that, generically, isolated chains undergo
instabilities towards coexisting charge density waves (CDW) and bond order
waves (BOW) insulating spin-gapped phases. The spin and charge gaps of the
BOW-CDW phase are computed. In the presence of an interchain magnetic coupling
spin density waves phases including a CDW or a BOW component are also found.
Our results are discussed in the context of insulating charge transfer salts.",0006460v2
2001-07-11,First-Principles Calculation of Electric Field Gradients and Hyperfine Couplings in YBa2Cu3O7,"The local electronic structure of YBa2Cu3O7 has been calculated using
first-principles cluster methods. Several clusters embedded in an appropriate
background potential have been investigated. The electric field gradients at
the copper and oxygen sites are determined and compared to previous theoretical
calculations and experiments. Spin polarized calculations with different spin
multiplicities have enabled a detailed study of the spin density distribution
to be made and a simultaneous determination of magnetic hyperfine coupling
parameters. The contributions from on-site and transferred hyperfine fields
have been disentangled with the conclusion that the transferred spin densities
essentially are due to nearest neighbour copper ions only with marginal
influence of ions further away. This implies that the variant temperature
dependencies of the planar copper and oxygen NMR spin-lattice relaxation rates
are only compatible with commensurate antiferromagnetic correlations. The
theoretical hyperfine parameters are compared with those derived from
experimental data.",0107224v1
2004-03-31,Spin-Transfer Effects in Nanoscale Magnetic Tunnel Junctions,"We report measurements of magnetic switching and steady-state magnetic
precession driven by spin-polarized currents in nanoscale magnetic tunnel
junctions with low-resistance, < 5 Ohm-micron-squared, barriers. The current
densities required for magnetic switching are similar to values for
all-metallic spin-valve devices. In the tunnel junctions, spin-transfer-driven
switching can occur at voltages that are high enough to quench the tunnel
magnetoresistance, demonstrating that the current remains spin-polarized at
these voltages.",0404002v2
2005-04-09,Spin Hall Effect and Spin Transfer in Disordered Rashba Model,"Based on numerical study of the Rashba model, we show that the spin Hall
conductance remains finite in the presence of disorder up to a characteristic
length scale, beyond which it vanishes exponentially with the system size. We
further perform a Laughlin's gauge experiment numerically and find that all
energy levels cannot cross each other during an adiabatic insertion of the flux
in accordance with the general level-repulsion rule. It results in zero spin
transfer between two edges of the sample as each state always evolves back
after the insertion of one flux quantum, in contrast to the quantum Hall
effect. It implies that the topological spin Hall effect vanishes with the
turn-on of disorder.",0504218v2
2005-10-08,Spin Transfer Switching and Spin Polarization in Magnetic Tunnel Junctions with Mgo and Alox Barriers,"We present spin transfer switching results for MgO based magnetic tunneling
junctions (MTJs)with large tunneling magnetoresistance (TMR) ratio of up to
150% and low intrinsic switching current density of 2-3 x 10 MA/cm2. The
switching data are compared to those obtained on similar MTJ nanostructures
with AlOx barrier. It is observed that the switching current density for MgO
based MTJs is 3-4 times smaller than that for AlOx based MTJs, and that can be
attributed to higher tunneling spin polarization (TSP) in MgO based MTJs. In
addition, we report a qualitative study of TSP for a set of samples, ranging
from 0.22 for AlOx to 0.46 for MgO based MTJs, and that shows the TSP (at
finite bias) responsible for the current-driven magnetization switching is
suppressed as compared to zero-bias tunneling spin polarization determined from
TMR.",0510204v1
2001-03-25,Spin transfer in high energy fragmentation processes,"We point out that measuring longitudinal polarizations of different hyperons
produced in lepton induced reactions are ideal to study the spin transfer of
the fragtmenting quark to produced hadron in high energy hadronization
processes. We briefly summarize the method used in calculating the hyperon
polarizations in these processes, then present some of the results for e+e- and
e-p or \nu p reactions obtained using two different pictures for the spin
structure of hyperon: that drawn from polarized deep inelastic lepton-nucleon
scattering data or that using SU(6) symmetric wave functions. The results show
in particular that measurements of such polarizations should provide useful
information to the question of which picture is more suitable in describing the
spin effects in the fragmentation processes.",0103266v1
2008-08-26,State Preparation by Optical Pumping in Erbium Doped Solids using Stimulated Emission and Spin Mixing,"Erbium doped solids are potential candidates for the realization of a quantum
memory for photons at telecommunication wavelengths. The implementation of
quantum memory proposals in rare earth ion doped solids require spectral
tailoring of the inhomogeneous absorption profile by efficient population
transfer between ground state levels (spin polarization) using optical pumping.
In this article we investigate the limiting factors of efficient optical
pumping between ground state Zeeman levels in an erbium doped Y2SiO5 crystal.
We introduce two methods to overcome these limiting factors: stimulated
emission using a second laser and spin mixing using radio frequency excitation.
Both methods significantly improve the degree of spin polarization. Population
transfer between two Zeeman levels with less than 10 % of the total population
in the initial ground state is achieved, corresponding to a spin polarization
greater than 90 %. In addition, we demonstrate spectral tailoring by isolating
a narrow absorption peak within a large transparency window.",0808.3537v1
2012-06-12,Form factors and complete spectrum of XXX antiperiodic higher spin chains by quantum separation of variables,"The antiperiodic transfer matrix associated to higher spin representations of
the rational 6-vertex Yang-Baxter algebra is analyzed by generalizing the
approach introduced recently in [1], for the cyclic representations, in [2],
for the spin-1/2 highest weight representations, and in [3], for the spin 1/2
representations of the reflection algebra. Here, we derive the complete
characterization of the transfer matrix spectrum and we prove its simplicity in
the framework of Sklyanin's quantum separation of variables (SOV). Then, the
characterization of local operators by Sklyanin's quantum separate variables
and the expression of the scalar products of separates states by determinant
formulae allow to compute the form factors of the local spin operators by one
determinant formulae similar to the scalar product ones. Finally, let us
comment that these results represent the SOV analogous in the antiperiodic
higher spin XXX quantum chains of the results obtained for the periodic chains
in [4] in the framework of the algebraic Bethe ansatz.",1206.2418v2
2015-06-07,Chirality of nanophotonic waveguide with embedded quantum emitter for unidirectional spin transfer,"Scalable quantum technologies require faithful conversion between matter
qubits storing the quantum information and photonic qubits carrying the
information in integrated circuits and waveguides. We demonstrate that the
electromagnetic field chirality which arises in nanophotonic waveguides leads
to unidirectional emission from an embedded quantum dot quantum emitter, with
resultant in-plane transfer of matter-qubit (spin) information. The chiral
behavior occurs despite the non-chiral geometry and material of the waveguides.
Using dot registration techniques we achieve a quantum emitter
deterministically positioned at a chiral point and realize spin-path conversion
by design. We measure and compare the phenomena in single mode nanobeam and
photonic crystal waveguides. The former is much more tolerant to dot position,
exhibits experimental spin-path readout as high as 95 +/- 5% and has potential
to serve as the basis of future spin-logic and network implementations.",1506.02266v1
2017-02-02,Exploring nucleon spin structure through neutrino neutral-current interactions in MicroBooNE,"The net contribution of the strange quark spins to the proton spin, $\Delta
s$, can be determined from neutral current elastic neutrino-proton interactions
at low momentum transfer combined with data from electron-proton scattering.
The probability of neutrino-proton interactions depends in part on the axial
form factor, which represents the spin structure of the proton and can be
separated into its quark flavor contributions. Low momentum transfer neutrino
neutral current interactions can be measured in MicroBooNE, a high-resolution
liquid argon time projection chamber (LArTPC) in its first year of running in
the Booster Neutrino Beamline at Fermilab. The signal for these interactions in
MicroBooNE is a single short proton track. We present our work on the automated
reconstruction and classification of proton tracks in LArTPCs, an important
step in the determination of neutrino- nucleon cross sections and the
measurement of $\Delta s$.",1702.00854v1
2019-06-01,Polarized inelastic neutron scattering of non-reciprocal spin waves in MnSi,"We report spin-polarized inelastic neutron scattering of the dynamical
structure factor of the conical magnetic helix in the cubic chiral magnet MnSi.
We find that the spectral weight of spin-flip scattering processes is
concentrated on single branches for wavevector transfer parallel to the helix
axis as inferred from well-defined peaks in the neutron spectra. In contrast,
for wavevector transfers perpendicular to the helix the spectral weight is
distributed among different branches of the magnon band structure as reflected
in broader features of the spectra. Taking into account the effects of
instrumental resolution, our experimental results are in excellent quantitative
agreement with parameter-free theoretical predictions. Whereas the dispersion
of the spin waves in MnSi appears to be approximately reciprocal at low
energies and small applied fields, the associated spin-resolved spectral weight
displays a pronounced non-reciprocity that implies a distinct non-reciprocal
response in the limit of vanishing uniform magnetization at zero magnetic
field.",1906.00221v3
2019-09-12,Longitudinal Spin Seebeck effect in Pyrochlore Iridates with Bulk and Interfacial Dzyaloshinskii-Moriya interaction,"The longitudinal spin-Seebeck effect (SSE) in magnetic
insulator$|$non-magnetic metal heterostructures has been theoretically studied
primarily with the assumption of an isotropic interfacial exchange coupling.
Here, we present a general theory of the SSE in the case of an antisymmetric
Dzyaloshinskii-Moriya interaction (DMI) at the interface, in addition to the
usual Heisenberg form. We numerically evaluate the dependence of the spin
current on the temperature and bulk DMI using a pyrochlore iridate as a model
insulator with all-in all-out (AIAO) ground state configuration. We also
compare the results of different crystalline surfaces arising from different
crystalline orientations and conclude that the relative angles between the
interfacial moments and Dzyaloshinskii-Moriya vectors play a significant role
in the spin transfer. Our work extends the theory of the SSE by including the
anisotropic nature of the interfacial Dzyaloshinskii-Moriya exchange
interaction in magnetic insulator$|$non-magnetic metal heterostructures and can
suggest possible materials to optimize the interfacial spin transfer in
spintronic devices.",1909.05450v2
2020-07-20,Tunable transverse spin-motion coupling for quantum information processing,"Laser-controlled entanglement between atomic qubits (`spins') and collective
motion in trapped ion Coulomb crystals requires conditional momentum transfer
from the laser. Since the spin-dependent force is derived from a spatial
gradient in the spin-light interaction, this force is typically longitudinal --
parallel and proportional to the average laser $k$-vector (or two beams'
$k$-vector difference), which constrains both the direction and relative
magnitude of the accessible spin-motion coupling. Here, we show how momentum
can also be transferred perpendicular to a single laser beam due to the
gradient in its transverse profile. By controlling the transverse gradient at
the position of the ion through beam shaping, the relative strength of the
sidebands and carrier can be tuned to optimize the desired interaction and
suppress undesired, off-resonant effects that can degrade gate fidelity. We
also discuss how this effect may already be playing an unappreciated role in
recent experiments.",2007.10437v1
2022-03-10,Ultrafast optically induced magnetic state transition in 2D antiferromagnets,"Manipulating spin in antiferromagnetic (AFM) materials has great potential in
AFM opto-spintronics. Laser pulses can induce a transient ferromagnetic (FM)
state in AFM metallic systems, but have never been proven in two-dimensional
(2D) AFM semiconductors and related van der Waals (vdW) heterostructures. Here,
using 2D vdW heterostructures of FM MnS2 and AFM MXenes as prototypes, we
investigated optically induced interlayer spin transfer dynamics based on the
real-time time-dependent density functional theory (rt-TDDFT). We observed that
laser pulses induce significant spin injection and the interfacial
atom-mediated spin transfer from MnS2 to Cr2CCl2. In particular, we first
demonstrated the transient FM state in semiconducting AFM/FM heterostructures
during photoexcited processes. Because the proximity magnetism breaks the
magnetic symmetry of Cr2CCl2 in heterostructures. Our results provide the
microscopic understanding for optically controlled interlayer spin dynamics in
2D magnetic heterostructures and open a new way to manipulate magnetic orders
in ultrafast opto-spintronics.",2203.05124v1
2022-04-29,Optimal quantum optical control of spin in diamond,"The nitrogen-vacancy (NV) center spin represents an appealing candidate for
quantum information processing. Besides the widely used microwave control, its
coherent manipulation may also be achieved using laser as mediated by the
excited energy levels. Nevertheless, the multiple levels of the excited state
of NV center spin make the coherent transition process become complex and may
affect the fidelity of coherent manipulation. Here, we adopt the strategy of
optimal quantum control to accelerate coherent state transfer in the ground
state manifold of NV center spin using laser. The results demonstrate improved
performance in both the speed and the fidelity of coherent state transfer which
will be useful for optical control of NV center spin in diamond.",2204.13984v1
2023-01-02,Noise-resistant quantum memory enabled by Hamiltonian engineering,"Nuclear spins in quantum dots are promising candidates for fast and scalable
quantum memory. By utilizing the hyperfine interaction between the central
electron and its surrounding nuclei, quantum information can be transferred to
the collective state of the nuclei and be stored for a long time. However,
nuclear spin fluctuations in a partially polarized nuclear bath deteriorate the
quantum memory fidelity. Here we introduce a noise-resistant protocol to
realize fast and high-fidelity quantum memory through Hamiltonian engineering.
With analytics and numerics, we show that high-fidelity quantum state transfer
between the electron and the nuclear spins is achievable at relatively low
nuclear polarizations, due to the strong suppression of nuclear spin noises.
For a realistic quantum dot with $10^4$ nuclear spins, a fidelity surpassing
80% is possible at a polarization as low as 30%. Our approach reduces the
demand for high nuclear polarization, making experimentally realizing quantum
memory in quantum dots more feasible.",2301.00575v1
2023-08-07,Exciton-spin interactions in antiferromagnetic charge-transfer insulators,"We derive exciton-spin interactions from a microscopic correlated model that
captures important aspects of the physics of charge-transfer (CT) insulators to
address magnetism associated with exciton creation. We present a minimal model
consisting of coupled clusters of transition metal d and ligand p orbitals that
captures the essential features of the local atomic and electronic structure.
First, we identify the lowest-energy state and optically allowed excited states
within a cluster by applying the molecular orbital picture to the ligand p
orbitals. Then, we derive the effective interactions between two clusters
mediated by intercluster hoppings, which include exciton-spin couplings. The
interplay of the correlations and the spatial structure of the CT exciton leads
to strong magnetic exchange couplings with spatial anisotropy. Finally, we
calculate an optical excitation spectrum in our effective model to obtain
insights into magnetic sidebands optically observed in magnetic materials. We
demonstrate that the spin-flip excitation due to the strongly enhanced local
spin interactions around the exciton gives rise to the magnetic sidebands.",2308.03309v2
1996-12-19,Random Matrix Theory and Classical Statistical Mechanics: Spin Models,"We present a statistical analysis of spectra of transfer matrices of
classical lattice spin models; this continues the work on the eight-vertex
model of the preceding paper. We show that the statistical properties of these
spectra can serve as a criterion of integrability. It provides also an
operational numerical method to locate integrable varieties. In particular, we
distinguish the notions of integrability and criticality considering the two
examples of the three-dimensional Ising critical point and the two-dimensional
three-state Potts critical point. For complex spectra which appear frequently
in the context of transfer matrices, we show that the notion of independence of
eigenvalues for integrable models still holds.",9612178v1
1997-05-08,Corner Transfer Matrix Algorithm for Classical Renormalization Group,"We report a real-space renormalization group (RSRG) algorithm, which is
formulated through Baxter's corner transfer matrix (CTM), for two-dimensional
(d = 2) classical lattice models. The new method performs the renormalization
group transformation according to White's density matrix algorithm, so that
variational free energies are minimized within a restricted degree of freedom
m. As a consequence of the renormalization, spin variables on each corner of
CTM are replaced by a m-state block spin variable. It is shown that the
thermodynamic functions and critical exponents of the q = 2, 3 Potts models can
be precisely evaluated by use of the renormalization group method.",9705072v1
1997-08-05,Charge separation in photosynthesis via a spin exchange coupling mechanism,"A new mechanism for the primary photoinduced charge separation in
photosynthesis is proposed. It involves as real intermediate between the
excited special pair state P* and the primary charge separated state P+HL- a
trip-trip-singlet PTBLT, which consists of a triplet on the dimer P and a
further triplet on the monomer BL. Both combine to a singlet. The electron
transfer is caused by spin exchange couplings. The transient spectrum of the
short lived intermediate, formerly taken as evidence for the charge transfer
state P+BL-, is reinterpreted as a transient excitation of this trip-trip
singlet.",9708033v1
1998-02-11,Charge-transfer metal-insulator transitions in the spin-one-half Falicov-Kimball model,"The spin-one-half Falicov-Kimball model is solved exactly on an
infinite-coordination-number Bethe lattice in the thermodynamic limit. This
model is a paradigm for a charge-transfer metal-insulator transition where the
occupancy of localized and delocalized electronic orbitals rapidly changes at
the metal-insulator transition (rather than the character of the electronic
states changing from insulating to metallic as in a Mott-Hubbard transition).
The exact solution displays both continuous and discontinuous (first-order)
transitions.",9802120v1
1998-08-28,Quasielastic magnetic scattering of neutrons at the systems with heavy fermions,"The theory of the quasielastic magnetic scattering of neutrons at the spin
liquid with RVB (resonance valence bonds) correlations is presented.
Calculations demonstrate that the dependence of the scattering cross section on
the energy transfer reproduces experimental shape of quasielastic peak in heavy
fermion systems. It is shown that Fermi statistics of the spin liquid
elementary excitations leads to the oscillations of the quasielastic scattering
total cross section as a function of the momentum transfer.",9808314v1
1998-12-01,Impurity corrections to the thermodynamics in spin chains using a transfer-matrix DMRG method,"We use the density matrix renormalization group (DMRG) for transfer matrices
to numerically calculate impurity corrections to thermodynamic properties. The
method is applied to two impurity models in the spin-1/2 chain, namely a weak
link in the chain and an external impurity spin. The numerical analysis
confirms the field theory calculations and gives new results for the crossover
behavior.",9812001v1
2005-08-15,The Structure of the Pairing Interaction in the 2D Hubbard Model,"Dynamic cluster Monte Carlo calculations for the doped two-dimensional
Hubbard model are used to study the irreducible particle-particle vertex
responsible for $d_{x^2-y^2}$ pairing in this model. This vertex increases with
increasing momentum transfer and decreases when the energy transfer exceeds a
scale associated with the $Q=(\pi, \pi)$ spin susceptibility. Using an exact
decomposition of this vertex into a fully irreducible two-fermion vertex and
charge and magnetic exchange channels, the dominant part of the effective
pairing interaction is found to come from the magnetic, spin S=1 exchange
channel.",0508361v2
2006-03-20,Zigzag spin chains with antiferromagnetic-ferromagnetic interactions: Transfer-matrix renormalization group study,"Properties of the zigzag spin chains with various nearest-neighbor and
next-nearest-neighbor interactions are studied by making use of the
transfer-matrix renormalization group method. Thermodynamic quantities of the
systems (temperature dependence of the susceptibility and the specific heat),
as well as the field dependence of the magnetization are analyzed numerically
with a high accuracy in the thermodynamic limit. The results have been compared
with the recent experimental data on Rb$_2$Cu$_{2}$Mo$_{3}$O$_{12}$.",0603519v2
2002-08-01,The chemical potential in the transfer matrix and in the path integral formulation of QCD on a lattice,"We define the chemical potential as the Lagrange multiplier of the baryon
charge operator in the transfer matrix formalism of QCD on a lattice.
Transforming the partition function into an euclidean path integral we get the
Hasenfratz-Karsh action both for Wilson and Kogut-Susskind fermions. In the
latter case the chemical potential in the spin-diagonal basis is half that in
the flavour basis. Some open problems in the spin-diagonal basis are pointed
out.",0208002v1
1998-09-29,Spin Asymmetries In Proton-Proton Scattering At High Energies And Moderately Large Momentum Transfer,"We study $pp$ scattering at high energies and moderately large momentum
transfer using a QCD--based model in which the proton is viewed as being
composed of a quark and a diquark. This model leads to spin asymmetries which
are neither small nor vanish at high energies. The predicted ratio of helicity
flip and non-flip amplitudes is about 0.2-0.3 and $A_n$ asymmetry is about
20-30% for $|t| > 4 {GeV}^2$.",9809578v1
2002-08-28,Nucleon Compton Scattering with Two Space--Like Photons,"We calculated two--photon exchange effects for elastic electron--proton
scattering at high momentum transfers. The corresponding nucleon Compton
amplitude is defined by two space--like virtual photons that appear to have
significant virtualities. We make predictions for a) a single--spin beam
asymmetry, and b) a single--spin target asymmetry or recoil proton polarization
caused by an unpolarized electron beam.",0208260v1
2003-06-26,Features of high energy pp elastic scattering at small t,"A method of determination of the real part of the elastic scattering
amplitude is examined for high energy proton-proton and proton-nuclei elastic
scattering at small momentum transfer. The method allows to decrease the number
of model assumptions, to obtain the real parts of the spin non-flip and
spin-flip amplitudes in the narrow region of momentum transfer.",0306256v3
2005-06-22,Spin transfer and polarization of antihyperons in lepton induced reactions,"We study the polarization of antihyperon in lepton induced reactions such as
$e^+e^-\to\bar H+X$ and $l+p\to l'+\bar H+X$ with polarized beams using
different models for spin transfer in high energy fragmentation processes. We
compare the results with the available data and those for hyperons. We make
predictions for future experiments.",0506207v2
2002-03-19,Transfer operators and dynamical zeta functions for a class of lattice spin models,"We investigate the location of zeros and poles of a dynamical zeta function
arizing in a class of lattice spin models introduced in the 60-ties by M. Kac.
The transfer operator method allows us to prove the xistence of infinitely
nontrivial zeros of this function on the real line. For certain parameter
values there exist also infinitely many trivial equally spaced zeros on a line
parallel to the imaginary axis. Hence also for this kind of dynamical zeta
function some kind of Riemann hypothesis seems to hold.",0203191v1
2004-11-01,Generic Transfer for General Spin Groups,"We prove Langlands functoriality for the generic spectrum of general spin
groups (both odd and even). Contrary to other recent instances of
functoriality, our resulting automorphic representations on the general linear
group will not be self-dual. Together with cases of classical groups, this
completes the list of cases of split reductive groups whose L-groups have
classical derived groups. The important transfer from GSp(4) to GL(4) follows
from our result as a special case.",0411035v1
2006-08-17,Decoherence problem in quantum state transfer via an engineered spin chain,"A perfect quantum state transfer(QST) has been shown in an engineered spin
chain with ""always-on interaction"". Here, we consider a more realistic problem
for such a protocol, the quantum decoherence induced by a spatially distributed
environment, which is universally modeled as a bath of harmonic oscillators. By
making use of the irreducible tensor method in angular momentum theory, we
investigate the effect of decoherence on the efficiency of QST for both cases
at zero and finite temperatures. We not only show the generic exponential decay
of QST efficiency as the number of sites increase, but also find some
counterintuitive effect, the QST can be enhanced as temperature increase.",0608135v1
2007-11-15,From Characters to Quantum (Super)Spin Chains via Fusion,"We give an elementary proof of the Bazhanov-Reshetikhin determinant formula
for rational transfer matrices of the twisted quantum super-spin chains
associated with the gl(K|M) algebra. This formula describes the most general
fusion of transfer matrices in symmetric representations into arbitrary finite
dimensional representations of the algebra and is at the heart of analytical
Bethe ansatz approach. Our technique represents a systematic generalization of
the usual Jacobi-Trudi formula for characters to its quantum analogue using
certain group derivatives.",0711.2470v2
2008-02-28,Coupling efficiency for phase locking of a spin transfer oscillator to a microwave current,"The phase locking behavior of spin transfer nano-oscillators (STNOs) to an
external microwave signal is experimentally studied as a function of the STNO
intrinsic parameters. We extract the coupling strength from our data using the
derived phase dynamics of a forced STNO. The predicted trends on the coupling
strength for phase locking as a function of intrinsic features of the
oscillators i.e. power, linewidth, agility in current, are central to optimize
the emitted power in arrays of mutually coupled STNOs.",0802.4162v3
2008-04-04,Spin-transfer switching and thermal stability in an FePt/Au/FePt nanopillar prepared by alternate monatomic layer deposition,"We fabricated a current-perpendicular-to-plane giant magnetoresistance
(CPP-GMR) nanopillar with a 1-nm-thick FePt free layer having perpendicular
anisotropy using the alternate monatomic layer deposition method. Nanopillars
consisting of [Fe (1 monolayer (ML))/Pt (1 ML)]n (n: the number of the
alternation period) ferromagnetic layers and an Au spacer layer showed
spin-transfer induced switching at room temperature.",0804.0688v1
2008-04-30,Impact of the electrical connection of N Spin Transfer Oscillators on their synchronization : an analytical study,"Spin Transfer Nano-Oscillators (STNOs) are good candidates for applications
to telecommunications, but their output power is very low, under the nW. A
possible solution to overcome this problem is to synchronize an assembly of
STNOs. For manufacturing purposes, large number of STNOs will have to be
electrically connected. In this letter, we study analytically the impact of
electrical connection on the synchronization of STNOs. Our analysis shows that
the phase dynamics of the coupled STNOs can be described in the framework of
the Kuramoto model. The conditions for successful synchronization of an
assembly of STNOs are derived.",0804.4855v1
2008-06-29,Dynamical Regimes Induced by Spin Transfer in Magnetic Nanopillars,"We demonstrate the predicted out-of-plane precession induced by spin transfer
in magnetic nanostructures with in-plane magnetic field. We show that other
magnetic excitations have a significant effect on the stability of the out-of
plane precession, making it extremely sensitive to the orientation of the
applied magnetic field. The data are supported with micromagnetic simulations.
Our results elucidate the relation between the excitation spectrum and the
specific dynamical behaviors of nanoscale magnets.",0806.4731v2
2008-09-11,High-probability quantum state transfer among nodes of an open XXZ spin chain,"This paper concerns the problem of the high probability state transfer among
$2^s$ symmetrically placed nodes of the $N$-nodes spins 1/2 chain with the
  ${XXZ}$ Hamiltonian. We consider examples with $(N,s)=(4,4)$, $(N,s)=(6,4)$
and $(N,s)=(8,8)$.",0809.1967v3
2009-07-10,"Fast, high fidelity information transmission through spin chain quantum wires","Spin chains have been proposed as quantum wires for information transfer in
solid state quantum architectures. We show that huge gains in both transfer
speed and fidelity are possible using a minimalist control approach that relies
only a single, local, on-off switch actuator. Effective switching time
sequences can be determined using optimization techniques for both ideal and
disordered chains. Simulations suggest that effective optimization is possible
even in the absence of accurate models.",0907.1887v1
2010-05-07,"Polarization observables and spin-aligned fusion rates in 2H(d,p)3H and 2H(d,n)3He reactions","Nucleon transfer reactions in low-energy deuteron-deuteron scattering are
described by solving exact four-particle equations in momentum space. The
Coulomb interaction between the protons is included using the screening and
renormalization method. Various realistic potentials are used between nucleon
pairs. The energy dependence of the differential cross section, analyzing
powers, polarizations, spin-transfer coefficient, and the quintet suppression
factor is studied.",1005.1308v1
2011-01-07,Charge-transfer in time-dependent density-functional theory via spin-symmetry-breaking,"Long-range charge-transfer excitations pose a major challenge for
time-dependent density functional approximations. We show that
spin-symmetry-breaking offers a simple solution for molecules composed of
open-shell fragments, yielding accurate excitations at large separations when
the acceptor effectively contains one active electron. Unrestricted
exact-exchange and self-interaction-corrected functionals are performed on
one-dimensional models and the real LiH molecule within the pseudopotential
approximation to demonstrate our results.",1101.1378v1
2011-09-20,Revisiting the Y=0 open spin chain at one loop,"In 2005, Berenstein and Vazquez determined an open spin chain Hamiltonian
describing the one-loop anomalous dimensions of determinant-like operators
corresponding to open strings attached to Y=0 maximal giant gravitons. We
construct the transfer matrix (generating functional of conserved quantities)
containing this Hamiltonian, thereby directly proving its integrability. We
find the eigenvalues of this transfer matrix and the corresponding Bethe
equations, which we compare with proposed all-loop Bethe equations. We note
that the Bethe ansatz solution has a certain ""gauge"" freedom, and is not
completely unique.",1109.4366v1
2011-10-28,Para-Krawtchouk polynomials on a bi-lattice and a quantum spin chain with perfect state transfer,"Analogs of Krawtchouk polynomials defined on a bi-lattice are introduced.
They are shown to provide a (novel) spin chain with perfect transfer. Their
characterization is given as well as their connection to the quadratic Hahn
algebra",1110.6475v3
2013-12-17,Nested off-diagonal Bethe ansatz and exact solutions of the su(n) spin chain with generic integrable boundaries,"The nested off-diagonal Bethe ansatz method is proposed to diagonalize
multi-component integrable models with generic integrable boundaries. As an
example, the exact solutions of the su(n)-invariant spin chain model with both
periodic and non-diagonal boundaries are derived by constructing the nested T-Q
relations based on the operator product identities among the fused transfer
matrices and the asymptotic behavior of the transfer matrices.",1312.4770v2
2014-05-25,Heat transfer in the spin-boson model: A comparative study in the incoherent tunneling regime,"We study the transfer of heat in the non-equilibrium spin-boson model with an
Ohmic dissipation. In the non-adiabatic limit we derive a formula for the
thermal conductance based on a rate equation formalism at the level of the
non-interacting blip approximation, valid for temperatures $T>T_K$, with $T_K$
as the Kondo temperature. We evaluate this expression analytically assuming
either weak or strong couplings, and demonstrate that our results agree with
exact relations. Far-from-equilibrium situations are further examined, showing
a close correspondence to the linear response limit.",1405.6358v1
2014-10-17,"Spin lattices, state transfer and bivariate Krawtchouk polynomials","The quantum state transfer properties of a class of two-dimensional spin
lattices on a triangular domain are investigated. Systems for which the
1-excitation dynamics is exactly solvable are identified. The exact solutions
are expressed in terms of the bivariate Krawtchouk polynomials that arise as
matrix elements of the unitary representations of the rotation group on the
states of the three-dimensional harmonic oscillator.",1410.4703v1
2015-01-15,Baxter Q- operator and functional relations,"We obtain the Baxter Q-operators in the $U_q(\hat{sl}_2)$ invariant
integrable models as a special limits of the quantum transfer matrices
corresponding to different spins in the auxiliary space both from the
functional relations and from the explicit calculations. We derive the Baxter
equation from the well known fusion relations for the transfer matrices. Our
method is valid for an arbitrary integrable model corresponding to the quantum
group $U_q(\hat{sl}_2)$ for example for the XXZ- spin chain.",1501.03663v2
2016-11-14,Low-temperature evolution of the spectral weight of a spin-up carrier moving in a ferromagnetic background,"We derive the lowest-temperature correction to the self-energy of a spin-up
particle injected in a ferromagnetic background. The background is modeled with
both Heisenberg and Ising Hamiltonians so that differences due to gapless vs.
gapped magnons can be understood. Beside the expected thermal broadening of the
quasiparticle peak as it becomes a resonance inside a continuum, we also find
that spectral weight is transferred to regions lying outside this continuum. We
explain the origin of this spectral weight transfer and its low-temperature
evolution.",1611.04575v1
2020-08-10,QQ-system and Weyl-type transfer matrices in integrable SO(2r) spin chains,"We propose the full system of Baxter Q-functions (QQ-system) for the
integrable spin chains with the symmetry of the $D_r$ Lie algebra. We use this
QQ-system to derive new Weyl-type formulas expressing transfer matrices in all
symmetric and antisymmetric (fundamental) representations through $r+1$ basic
Q-functions. Our functional relations are consistent with the Q-operators
proposed recently by one of the authors and verified explicitly on the level of
operators at small finite length.",2008.04336v3
2020-12-15,Factorization identities and algebraic Bethe ansatz for $D^{(2)}_{2}$ models,"We express $D^{(2)}_{2}$ transfer matrices as products of $A^{(1)}_{1}$
transfer matrices, for both closed and open spin chains. We use these
relations, which we call factorization identities, to solve the models by
algebraic Bethe ansatz. We also formulate and solve a new integrable XXZ-like
open spin chain with an even number of sites that depends on a continuous
parameter, which we interpret as the rapidity of the boundary.",2012.08367v3
2022-07-25,Encoded State Transfer: Beyond the Uniform Chain,"In a recent work (arXiv:2207.01954), we showed that a uniformly coupled chain
could be symmetrically extended by engineered spin chains in such a way that we
could choose part of the spectrum of the overall system. When combined with an
encoding that avoids the uncontrolled eigenvalues, this resulted in the
possibility of achieving a range of tasks such as perfect quantum state
transfer. In this paper, we apply the same strategy to a much broader range of
initial systems - arbitrary chains, and even coupled networks of spins - while
providing guarantees on the existence of solutions.",2207.12189v1
2022-09-28,On Bethe eigenvectors and higher transfer matrices for supersymmetric spin chains,"We study the $\mathfrak{gl}_{m|n}$ XXX spin chains defined on tensor products
of highest $\mathfrak{gl}_{m|n}$-modules. We show that the on-shell Bethe
vectors are eigenvectors of higher transfer matrices and compute the
corresponding eigenvalues, confirming Conjecture 5.15 of arXiv:2007.15573 and
extending the main results of arXiv:0605015 to supersymmetric case. We then
take the classical limits and obtain the corresponding results for the
$\mathfrak{gl}_{m|n}$ Gaudin models.",2209.14416v2
2023-04-20,Accelerated quantum control in a three-level system by jumping along the geodesics,"In a solid-state spin system, we experimentally demonstrate a protocol for
quantum-state population transfer with an improved efficiency compared to
traditional stimulated Raman adiabatic passage (STIRAP). Using the ground-state
triplet of the nitrogen-vacancy center in diamond, we show that the required
evolution time for high-fidelity state transfer can be reduced by almost one
order of magnitude. Furthermore, we establish an improved robustness against
frequency detuning caused by magnetic noise as compared to STIRAP. These
results provide a powerful tool for coherent spin manipulation in the context
of quantum sensing and quantum computation.",2304.10672v1
2024-02-27,Adiabatically-manipulated systems interacting with spin baths beyond the Rotating Wave Approximation,"The Stimulated Raman Adiabatic Passage on a three-state system interacting
with a spin bath is considered focusing on the efficiency of the population
transfer. Our analysis is based on the perturbation treatment of the
interaction term evaluated beyond the Rotating Wave Approximation, thus
focusing on the limit of weak system-bath coupling. The analytical expression
of the correction to the efficiency and consequent numerical analysis show that
in most of the cases the effects of the environment are negligible, confirming
the robustness of the population transfer.",2402.17661v1
2007-02-14,The Stability of Double White Dwarf Binaries Undergoing Direct Impact Accretion,"We present numerical simulations of dynamically unstable mass transfer in a
double white dwarf binary with initial mass ratio, q = 0.4. The binary
components are approximated as polytropes of index n = 3/2 and the initially
synchronously rotating, semi-detached equilibrium binary is evolved
hydrodynamically with the gravitational potential being computed through the
solution of Poisson's equation. Upon initiating deep contact in our baseline
simulation, the mass transfer rate grows by more than an order of magnitude
over approximately ten orbits, as would be expected for dynamically unstable
mass transfer. However, the mass transfer rate then reaches a peak value, the
binary expands and the mass transfer event subsides. The binary must therefore
have crossed the critical mass ratio for stability against dynamical mass
transfer. Despite the initial loss of orbital angular momentum into the spin of
the accreting star, we find that the accretor's spin saturates and angular
momentum is returned to the orbit more efficiently than has been previously
suspected for binaries in the direct impact accretion mode. To explore this
surprising result, we directly measure the critical mass ratio for stability by
imposing artificial angular momentum loss at various rates to drive the binary
to an equilibrium mass transfer rate. For one of these driven evolutions, we
attain equilibrium mass transfer and deduce that effectively q_crit has evolved
to approximately 2/3. Despite the absence of a fully developed disk, tidal
interactions appear effective in returning excess spin angular momentum to the
orbit.",0702388v2
1999-04-29,Bumpy Spin-Down of Anomalous X-Ray Pulsars: The Link with Magnetars,"The two anomalous X-ray pulsars (AXPs) with well-sampled timing histories, 1E
1048.1-5937 and 1E 2259+586, are known to spin down irregularly, with `bumps'
superimposed on an overall linear trend. Here we show that if AXPs are
non-accreting magnetars, i.e. isolated neutron stars with surface magnetic
fields B_0 > 10^{10} T, then they spin down electromagnetically in exactly the
manner observed, due to an effect called `radiative precession'. Internal
hydromagnetic stresses deform the star, creating a fractional difference
epsilon=(I_3-I_1)/I_1 ~ 10^{-8} between the principal moments of inertia I_1
and I_3; the resulting Eulerian precession couples to an oscillating component
of the electromagnetic torque associated with the near-zone radiation fields,
and the star executes an anharmonic wobble with period tau_pr ~ 2 pi / epsilon
Omega(t) ~ 10 yr, where Omega(t) is the rotation frequency as a function of
time t. We solve Euler's equations for a biaxial magnet rotating in vacuo; show
that the computed Omega(t) matches the measured timing histories of 1E
1048.1-5937 and 1E 2259+586; predict Omega(t) for the next 20 years for both
objects; predict a statistical relation between <d(Omega)/dt> and tau_pr, to be
tested as the population of known AXPs grows; and hypothesize that radiative
precession will be observed in future X-ray timing of soft gamma-ray repeaters
(SGRs).",9904403v1
1999-08-05,"Magnetic Stress at the Marginally Stable Orbit: Altered Disk Structure, Radiation, and Black Hole Spin Evolution","Magnetic connections to the plunging region can exert stresses on the inner
edge of an accretion disk around a black hole. We recompute the relativistic
corrections to the thin-disk dynamics equations when these stresses take the
form of a time-steady torque on the inner edge of the disk. The additional
dissipation associated with these stresses is concentrated relatively close
outside the marginally stable orbit, scaling as r to the -7/2 at large radius.
As a result of these additional stresses: spin-up of the central black hole is
retarded; the maximum spin-equilibrium accretion efficiency is 36%, and occurs
at a/M=0.94; the disk spectrum is extended toward higher frequencies; line
profiles (such as Fe K-alpha) are broadened if the line emissivity scales with
local flux; limb-brightening, especially at the higher frequencies, is
enhanced; and the returning radiation fraction is substantially increased, up
to 58%. This last effect creates possible explanations for both synchronized
continuum fluctuations in AGN, and polarization rises shortward of the Lyman
edge in quasars. We show that no matter what additional stresses occur, when
a/M < 0.36, the second law of black hole dynamics sets an absolute upper bound
on the accretion efficiency.",9908049v1
1999-10-04,The Orbital Period of the Accreting Pulsar GX1+4,"We report strong evidence for a ~304-day periodicity in the spin history of
the accretion-powered pulsar GX1+4 that is most probably associated with the
orbital period of the system. We have used data from the Burst and Transient
Source Experiment on the Compton Gamma Ray Observatory to show a clear periodic
modulation of the pulsar frequency from 1991 to date, in excellent agreement
with the ephemeris proposed by Cutler, Dennis & Dolan (1986). Our results
indicate that the orbital period of GX1+4 is 303.8 +- 1.1 days, making it the
widest known low-mass X-ray binary system by more than one order of magnitude
and putting this long-standing question to rest. A likely scenario for this
system is an elliptical orbit in which the neutron star decreases its spin-down
rate (or even exhibits a momentary spin-up behavior) at periastron passages due
to the higher torque exerted by the accretion disk onto the magnetosphere of
the neutron star. These results are not inconsistent with both the X-ray pulsed
flux light curve measured by BATSE during the same epoch and the X-ray flux
history from the All-Sky Monitor (ASM) onboard the Rossi X-Ray Timing Explorer.",9910053v1
2000-12-18,Spin and magnetism in old neutron stars,"The thermal, spin and magnetic evolution of neutron stars in the old low mass
binaries is first explored. Recycled to very short periods via accretion
torques, the neutron stars lose their magnetism progressively. If accretion
proceeds undisturbed for 100 Myrs these stars can rotate close to break up with
periods far below the minimum observed of 1.558 ms. We investigate their
histories using population synthesis models to show that a tail should exist in
the period distribution below 1.558 ms. The search of these ultrafastly
spinning neutron stars as pulsars can help discriminating among the various
equations of state for nuclear matter, and can shed light into the physics of
binary evolution.
  The evolution of isolated neutron stars in the Galaxy is explored beyond the
pulsar phase. Moving through the tenuous interstellar medium, these old
solitary neutron stars lose their rotational energy. Whether also their
magnetism fades is still a mystery. A population synthesis model has revealed
that only a tiny fraction of them is able to accrete from the interstellar
medium, shining in the X-rays. There is the hope that these solitary stars will
eventually appear as faint sources in the Chandra sky survey. This might give
insight on the long term evolution of the magnetic field in isolated objects.",0012394v1
2002-04-15,Hot Settling Accretion Flow onto a Spinning Black Hole,"We study the structure and properties of hot MHD accretion onto a Kerr black
hole. In such a system, the hole is magnetically coupled to the inflowing gas
and exerts a torque onto the accretion flow. A hot settling flow can form
around the hole and transport the angular momentum outward, to the outer edge
of the flow. Unlike other hot flows, such as advection- and
convection-dominated flows and inflow-outflow solutions (ADAFs, CDAFs, and
ADIOS), the properties of the hot settling flow are determined by the spin of
the central black hole, but are insensitive to the mass accretion rate.
Therefore, it may be possible to identify rapidly spinning BHs simply from
their broad-band spectra.
  Observationally, the hot settling flow around a Kerr hole is somewhat similar
to other hot flows in that they all have hard, power-law spectra and relatively
low luminosities. Thus, most black hole candidates in the low/hard and,
perhaps, intermediate X-ray state may potentially accrete via the hot settling
flow. However, a settling flow will be somewhat more luminous than
ADAFs/CDAFs/ADIOS, will exhibit high variability in X-rays, and may have
relativistic jets. This suggests that galactic microquasars and active galactic
nuclei may be powered by hot settling flows. We identify several galactic X-ray
sources as the best candidates.",0204254v1
2005-07-06,The free precession and libration of Mercury,"An analysis based on the direct torque equations including tidal dissipation
and a viscous core-mantle coupling is used to determine the damping time scales
of O(10^5) years for free precession of the spin about the Cassini state and
free libration in longitude for Mercury. The core-mantle coupling dominates the
damping over the tides by one to two orders of magnitude for the plausible
parameters chosen. The short damping times compared with the age of the solar
system means we must find recent or on-going excitation mechanisms if such free
motions are found by the current radar experiments or the future measurement by
the MESSENGER and BepiColombo spacecraft that will orbit Mercury. We also show
that the average precession rate is increased by about 30% over that obtained
from the traditional precession constant because of a spin-orbit resonance
induced contribution by the C_{22} term in the expansion of the gravitational
field. The C_{22} contribution also causes the path of the spin during the
precession to be slightly elliptical with a variation in the precession rate
that is a maximum when the obliquity is a minimum. An observable free
precession will compromise the determination of obliquity of the Cassini state
and hence of C/MR^2 for Mercury, but a detected free libration will not
compromise the determination of the forced libration amplitude and thus the
verification of a liquid core",0507117v1
2006-11-27,Exactly-solvable Ising-Heisenberg model for the coupled barotropic fluid - rotating solid sphere system - condensation of super and sub-rotating barotropic flow states,"Exact solutions of a family of Heisenberg-Ising spin-lattice models for a
coupled barotropic flow - massive rotating sphere system under microcanonical
constraint on relative enstrophy is obtained by the method of spherical
constraint. Phase transitions representative of Bose-Einstein condensation in
which highly ordered super and sub-rotating states self-organize from random
initial vorticity states are calculated exactly and related to three key
parameters - spin of sphere, kinetic energy of the barotropic flow which is
specified by the inverse temperature and amount of relative enstrophy which is
held fixed. Angular momentum of the barotropic fluid relative to the rotating
frame of the infinitely massive sphere is the main order parameter in this
statistical mechanics problem $-$ it is not constrained either canonically nor
microcanonically as coupling between the fluid and the rotating sphere by a
complex torque is responsible for its change. This coupling and exchange of
angular momentum is a necessary condition for condensation in this spin-lattice
system. There is no low temperature defects in this model - the partition
function is calculated in closed form for all positive and negative
temperatures. Also note-worthy is the fact that this statistical equilibrium
model is not a mean field model and can be extended to treat fluctuations if
required in more complex coupled flows.",0611050v1
2008-11-06,The accretion powered spin-up of GRO J1750-27,"The timing properties of the 4.45 s pulsar in the Be X-ray binary system GRO
J1750-27 are examined using hard X-ray data from INTEGRAL and Swift during a
Type II outburst observed during 2008. The orbital parameters of the system are
measured and agree well with those found during the last known outburst of the
system in 1995. Correcting the effects of the doppler shifting of the period,
due to the orbital motion of the pulsar, leads to the detection of an intrinsic
spin-up that is well described by a simple model including Pdot and Pdotdot
terms of -7.5E-10 ss^-1 and 1E-16 ss^-2 respectively. The model is then used to
compare the time-resolved variation of the X-ray flux and intrinsic spin-up
against the accretion torque model of Ghosh & Lamb (1979); this finds that GRO
J1750-27 is likely located 12-22 kpc distant and that the surface magnetic
field of the neutron star is ~2E12 G. The shape of the pulse and the pulsed
fraction shows different behaviour above and below 20 keV indicating that the
observed pulsations are the convolution of many complex components.",0811.0975v1
2009-01-07,Thermal Tides in Short Period Exoplanets,"Time-dependent insolation in a planetary atmosphere induces a mass quadrupole
upon which the stellar tidal acceleration can exert a force. This ""thermal
tide"" force can give rise to secular torques on the planet and orbit as well as
radial forces causing eccentricity evolution. We apply this idea to the
close-in gas giant exoplanets (""hot Jupiters""). The response of radiative
atmospheres is computed in a hydrostatic model which treats the insolation as a
time-dependent heat source, and solves for thermal radiation using flux-limited
diffusion. Fully nonlinear numerical simulations are compared to solutions of
the linearized equations, as well as analytic approximations, all of which are
in good agreement. We find generically that thermal tide density perturbations
{\it lead} the semi-diurnal forcing. As a result thermal tides can generate
asynchronous spin and eccentricity. Our results are as follows: (1) Departure
from synchronous spin is significant for hot Jupiters, and increases with
orbital period. (2) Ongoing gravitational tidal dissipation in spin equilibrium
leads to steady-state internal heating rates up to $\sim 10^{28} {\rm erg\
s^{-1}}$. If deposited sufficiently deep, these heating rates may explain the
anomalously large radii of many hot Jupiters in terms of a ""tidal main
sequence"" where cooling balances tidal heating. At fixed stellar type, planet
mass and tidal $Q$, planetary radius increases strongly toward the star inside
orbital periods $\la 2$ weeks. (3) There exists a narrow window in orbital
period where small eccentricities, $e$, grow exponentially with a large rate.
This window may explain the $\sim 1/4$ of hot Jupiters which should have been
circularized by the gravitational tide long ago, but are observed to have
significant nonzero $e$.(Abridged)",0901.0735v1
2009-06-05,Galaxy Zoo: A correlation between coherence of galaxy spin chirality and star formation efficiency,"We report on the finding of a correlation between galaxies' past star
formation activity and the degree to which neighbouring galaxies rotation axes
are aligned. This is obtained by cross-correlating star formation histories,
derived with MOPED, and spin direction (chirality), as determined by the Galaxy
Zoo project, for a sample of SDSS galaxies. Our findings suggest that spiral
galaxies which formed the majority of their stars early (z > 2) tend to display
coherent rotation over scales of ~10 Mpc/h. The correlation is weaker for
galaxies with significant recent star formation. We find evidence for this
alignment at more than the 5-sigma level, but no correlation with other galaxy
stellar properties. This finding can be explained within the context of
hierarchical tidal-torque theory if the SDSS galaxies harboring the majority of
the old stellar population where formed in the past, in the same filament and
at about the same time. Galaxies with significant recent star formation instead
are in the field, thus influenced by the general tidal field that will align
them in random directions or had a recent merger which would promote star
formation, but deviate the spin direction.",0906.0994v2
2010-02-17,Measurement of Gilbert damping parameters in nanoscale CPP-GMR spin-valves,"In-situ, device level measurement of thermal mag-noise spectral linewidths in
60nm diameter CPP-GMR spin-valve stacks of IrMn/ref/Cu/free, with reference and
free layer of similar CoFe/CoFeGe alloy, are used to simultaneously determine
the intrinsic Gilbert damping for both magnetic layers. It is shown that
careful alignment at a ""magic-angle"" between free and reference layer static
equilibrium magnetization can allow direct measurement of the broadband
intrinsic thermal spectra in the virtual absence of spin-torque effects which
otherwise grossly distort the spectral line shapes and require linewidth
extrapolations to zero current (which are nonetheless also shown to agree well
with the direct method). The experimental magic-angle spectra are shown to be
in good qualitative and quantitative agreement with both macrospin calculations
and micromagnetic eigenmode analysis. Despite similar composition and
thickness, it is repeatedly found that the IrMn exchange pinned reference layer
has ten times larger intrinsic Gilbert damping (alpha ~ 0.1) than that of the
free-layer (alpha ~ 0.01). It is argued that the large reference layer damping
results from strong, off -resonant coupling to to lossy modes of an IrMn/ref
couple, rather than commonly invoked two-magnon processes.",1002.3295v1
2010-03-08,The Spiral Modes of the Standing Accretion Shock Instability,"A stalled spherical accretion shock, such as that arising in core-collapse
supernovae, is unstable to non-spherical perturbations. In three dimensions,
this Standing Accretion Shock Instability (SASI) can develop spiral modes that
spin-up the protoneutron star. Here we study these non-axisymmetric modes by
combining linear stability analysis and three-dimensional, time-dependent
hydrodynamic simulations with Zeus-MP, focusing on characterizing their spatial
structure and angular momentum content. We do not impose any rotation on the
background accretion flow, and use simplified microphysics with no neutrino
heating or nuclear dissociation. Spiral modes are examined in isolation by
choosing flow parameters such that only the fundamental mode is unstable for a
given polar index, leading to good agreement with linear theory. We find that
any superposition of sloshing modes with non-zero relative phases survives in
the nonlinear regime and leads to angular momentum redistribution. It follows
that the range of perturbations required to obtain spin-up is broader than that
needed to obtain the limiting case of a phase shift of pi/2. The bulk of the
angular momentum redistribution occurs during a phase of exponential growth,
and arises from internal torques that are second order in the perturbation
amplitude. This redistribution gives rise to at least two counter rotating
regions, with the maximum angular momentum of a given sign approaching a
significant fraction of the mass accretion rate times the shock radius squared
(Mdot * r_shock^2 ~ 1E+47 g/cm^2/s, spin period ~60 ms). Nonlinear mode
coupling at saturation causes the angular momentum to fluctuate in all
directions with much smaller amplitudes.",1003.1730v2
2010-09-13,High-Frequency Electron-Spin-Resonance Study of the Octanuclear Ferric Wheel CsFe$_8$,"High-frequency ($f$ = 190 GHz) electron paramagnetic resonance (EPR) at
magnetic fields up to 12 T as well as Q-band ($f$ = 34.1 GHz) EPR were
performed on single crystals of the molecular wheel CsFe$_8$. In this molecule,
eight Fe(III) ions, which are coupled by nearest-neighbor antiferromagnetic
(AF) Heisenberg exchange interactions, form a nearly perfect ring. The
angle-dependent EPR data allow for the accurate determination of the spin
Hamiltonian parameters of the lowest spin multiplets with $S \leq$ 4.
Furthermore, the data can well be reproduced by a dimer model with a uniaxial
anisotropy term, with only two free parameters $J$ and $D$. A fit to the dimer
model yields $J$ = -15(2) cm$^{-1}$ and $D$ = -0.3940(8) cm$^{-1}$. A rhombic
anisotropy term is found to be negligibly small, $E$ = 0.000(2) cm$^{-1}$. The
results are in excellent agreement with previous inelastic neutron scattering
(INS) and high-field torque measurements. They confirm that the CsFe$_8$
molecule is an excellent experimental model of an AF Heisenberg ring. These
findings are also important within the scope of further investigations on this
molecule such as the exploration of recently observed magnetoelastic
instabilities.",1009.2327v1
2011-05-23,Studies of Thermally Unstable Accretion Disks around Black Holes with Adaptive Pseudospectral Domain Decomposition Method. II. Limit-Cycle Behavior in accretion disks around Kerr black holes,"For the first time ever, we derive equations governing the time-evolution of
fully relativistic slim accretion disks in the Kerr metric, and numerically
construct their detailed non-stationary models. We discuss applications of
these general results to a possible limit-cycle behavior of thermally unstable
disks. Our equations and numerical method are applicable in a wide class of
possible viscosity prescriptions, but in this paper we use a diffusive form of
the ""standard alpha prescription"" that assumes the viscous torque is
proportional to the total pressure. In this particular case, we find that the
parameters which dominate the limit-cycle properties are the mass-supply rate
and the value of the alpha-viscosity parameter. Although the duration of the
cycle (or the outburst) does not exhibit any clear dependence on the black hole
spin, the maximal outburst luminosity (in the Eddington units) is positively
correlated with the spin value. We suggest a simple method for a rough estimate
of the black hole spin based on the maximal luminosity and the ratio of
outburst to cycle durations. We also discuss a temperature-luminosity relation
for the Kerr black hole accretion discs limit-cycle. Based on these results we
discuss the limit-cycle behavior observed in microquasar GRS 1915+105. We also
extend this study to several non-standard viscosity prescriptions, including a
""delayed heating"" prescription recently stimulated by the recent MHD
simulations of accretion disks.",1105.4534v1
2011-06-13,Implications of the measured parameters of PSR J1903+0327 for its progenitor neutron star,"Using the intrinsic PSR J1903+0327 parameters evaluated from radio
observations (mass, rotation period and dipole magnetic field deduced from the
timing properties) we calculate the mass of its neutron star progenitor, M_i,
at the onset of accretion. Simultaneously, we derive constraints on average
accretion rate Mdot and the pre-accretion magnetic field B_i. Spin-up is
modelled by accretion from a thin disk, using the magnetic-torque disk-pulsar
coupling model proposed by Kluzniak and Rappaport (2007), improved for the
existence of relativistic marginally-stable circular orbit. Orbital parameters
in the disk are obtained using the space-time generated by a rotating neutron
star in the framework of General Relativity. We employ an observationally
motivated model of the surface magnetic field decay. We also seek for the
imprint of the poorly known equation of state of dense matter on the spin-up
tracks - three equations of state of dense matter, consistent with the
existence of 2 Msun neutron star, are considered. We find that the minimum
average accretion rate should be larger than 2-8 10^(-10) Msun/yr, the highest
lower bound corresponding to the stiffest equation of state. We conclude that
the influence of magnetic field in the ""recycling"" process is crucial - it
leads to a significant decrease of spin-up rate and larger accreted masses, in
comparison to the B=0 model. Allowed B_i-dependent values of M_i are within
1.0-1.4 Msun, i.e., much lower than an oversimplified but widely used B=0
result, where one gets M_i>1.55 Msun. Estimated initial neutron-star mass
depends on the assumed dense-matter equation of state.",1106.2432v2
2012-03-15,Power and linewidth of propagating and localized modes in nanocontact spin-torque oscillators,"Integrated power and linewidth of a propagating and a self-localized spin
wave modes excited by spin-polarized current in an obliquely magnetized
magnetic nanocontact are studied experimentally as functions of the angle
$\theta_e$ between the external bias magnetic field and the nanocontact plane.
It is found that the power of the propagating mode monotonically increases with
$\theta_e$, while the power of the self-localized mode has a broad maximum near
$\theta_e = 40$ deg, and exponentially vanishes near the critical angle
$\theta_e = 58$ deg, at which the localized mode disappears. The linewidth of
the propagating mode in the interval of angles $58<\theta_e<90$ deg, where only
this mode is excited, is adequtely described by the existing theory, while in
the angular interval where both modes can exist the observed linewidth of both
modes is substantially broadened due to the telegraph switching between the
modes. Numetical simulations and an approximate analytical model give good
semi-quantitative description of the observed results.",1203.3244v1
2012-07-11,Layer thickness dependence of the current induced effective field vector in Ta|CoFeB|MgO,"The role of current induced effective magnetic field in ultrathin magnetic
heterostructures is increasingly gaining interest since it can provide
efficient ways of manipulating magnetization electrically. Two effects, known
as the Rashba spin orbit field and the spin Hall spin torque, have been
reported to be responsible for the generation of the effective field. However,
quantitative understanding of the effective field, including its direction with
respect to the current flow, is lacking. Here we show vector measurements of
the current induced effective field in Ta|CoFeB|MgO heterostructrures. The
effective field shows significant dependence on the Ta and CoFeB layers'
thickness. In particular, 1 nm thickness variation of the Ta layer can result
in nearly two orders of magnitude difference in the effective field. Moreover,
its sign changes when the Ta layer thickness is reduced, indicating that there
are two competing effects that contribute to the effective field. The relative
size of the effective field vector components, directed transverse and parallel
to the current flow, varies as the Ta thickness is changed. Our results
illustrate the profound characteristics of just a few atomic layer thick metals
and their influence on magnetization dynamics.",1207.2521v1
2012-07-18,Possible changes of state and relevant timescales for a neutron star in LS I +61°303,"The properties of the short, energetic bursts recently observed from the
gamma-ray binary LS I +61{\deg}303, are typical of those showed by high
magnetic field neutron stars, and thus provide a strong indication in favor of
a neutron star being the compact object in the system. Here, we discuss the
transitions among the states accessible to a neutron star in a system like LS I
+61{\deg}303, such as the ejector, propeller and accretor phases, depending on
the NS spin period, magnetic field and rate of mass captured. We show how the
observed bolometric luminosity (>= few x 1E35 erg/s), and its broad-band
spectral distribution, indicate that the compact object is most probably close
to the transition between working as an ejector all along its orbit, and being
powered by the propeller effect when it is close to the orbit periastron, in a
so-called flip-flop state. By assessing the torques acting onto the compact
object in the various states, we follow the spin evolution of the system,
evaluating the time spent by the system in each of them. Even taking into
account the constraint set by the observed gamma-ray luminosity, we found that
the total age of the system is compatible with being ~5-10 kyr, comparable to
the typical spin-down ages of high-field neutron stars. The results obtained
are discussed in the context of the various evolutionary stages expected for a
neutron star with a high mass companion.",1207.4341v1
2012-10-01,Novel Pauli-paramagnetic quantum phase in a Mott insulator,"In Mott insulators, the strong electron-electron Coulomb repulsion prevents
metallicity and charge excitations are gapped. In dimensions greater than one,
their spins are usually ordered antiferromagnetically at low temperatures.
Geometrical frustrations can destroy this long-range order, leading to exotic
quantum spin liquid (QSL) states. However, their magnetic ground states have
been a long-standing mystery. Here we show that a QSL state in the organic Mott
insulator EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ with two-dimensional triangular lattice
has Pauli-paramagnetic-like low-energy excitations, which are a hallmark of
itinerant fermions. Our torque magnetometry down to low temperatures (30 mK) up
to high fields (32 T) reveal distinct residual paramagnetic susceptibility
comparable to that in a half-filled two-dimensional metal. This demonstrates
that the system is in a magnetically gapless ground state, a critical state
with infinite magnetic correlation length. Moreover, our results are robust
against deuteration, pointing toward the emergence of an extended `quantum
critical phase', in which low-energy spin excitations behave as in paramagnetic
metals with Fermi surface, despite the frozen charge degree of freedom.",1210.0407v1
2013-11-05,Counterrotating Stars in Simulated Galaxy Disks,"Counterrotating stars in disk galaxies are a puzzling dynamical feature whose
origin has been ascribed to either satellite accretion events or to disk
instabilities triggered by deviations from axisymmetry. We use a cosmological
simulation of the formation of a disk galaxy to show that counterrotating
stellar disk components may arise naturally in hierarchically-clustering
scenarios even in the absence of merging. The simulated disk galaxy consists of
two coplanar, overlapping stellar components with opposite spins: an inner
counterrotating bar-like structure made up mostly of old stars surrounded by an
extended, rotationally-supported disk of younger stars. The opposite-spin
components originate from material accreted from two distinct filamentary
structures which at turn around, when their net spin is acquired, intersect
delineating a ""V""-like structure. Each filament torques the other in opposite
directions; the filament that first drains into the galaxy forms the inner
counterrotating bar, while material accreted from the other filament forms the
outer disk. Mergers do not play a substantial role and most stars in the galaxy
are formed in situ; only 9% of all stars are contributed by accretion events.
The formation scenario we describe here implies a significant age difference
between the co- and counterrotating components, which may be used to
discriminate between competing scenarios for the origin of counterrotating
stars in disk galaxies.",1311.1215v1
2014-11-05,Coupled Spin and Shape Evolution of Small Rubble-Pile Asteroids: Self-Limitation of the YORP Effect,"We present the first self-consistent simulations of the coupled spin-shape
evolution of small gravitational aggregates under the influence of the YORP
effect. Because of YORP's sensitivity to surface topography, even small
centrifugally driven reconfigurations of aggregates can alter the YORP torque
dramatically, resulting in spin evolution that can differ qualitatively from
the rigid-body prediction. One third of our simulations follow a simple
evolution described as a modified YORP cycle. Two-thirds exhibit one or more of
three distinct behaviors---stochastic YORP, self-governed YORP, and stagnating
YORP---which together result in YORP self-limitation. Self-limitation confines
rotation rates of evolving aggregates to far narrower ranges than those
expected in the classical YORP cycle, greatly prolonging the times over which
objects can preserve their sense of rotation. Simulated objects are initially
randomly packed, disordered aggregates of identical spheres in rotating
equilibrium, with low internal angles of friction. Their shape evolution is
characterized by rearrangement of the entire body, including the deep interior.
They do not evolve to axisymmetric top shapes with equatorial ridges. Mass loss
occurs in one-third of the simulations, typically in small amounts from the
ends of a prolate-triaxial body. We conjecture that YORP self-limitation may
inhibit formation of top-shapes, binaries, or both, by restricting the amount
of angular momentum that can be imparted to a deformable body. Stochastic YORP,
in particular, will affect the evolution of collisional families whose orbits
drift apart under the influence of Yarkovsky forces, in observable ways.",1411.1114v2
2015-03-05,Higher dimensional Wannier functions of multi-parameter Hamiltonians,"When using Wannier functions to study the electronic structure of
multi-parameter Hamiltonians $H^{(\boldsymbol k,\bf \lambda)}$ carrying a
dependence on crystal momentum $\boldsymbol k$ and an additional periodic
parameter $\bf\lambda$, one usually constructs several sets of Wannier
functions for a set of values of $\bf\lambda$. We present the concept of higher
dimensional Wannier functions (HDWFs), which provide a minimal and accurate
description of the electronic structure of multi-parameter Hamiltonians based
on a single set of HDWFs. The obstacle of non-orthogonality of Bloch functions
at different $\bf\lambda$ is overcome by introducing an auxiliary real space,
which is reciprocal to the parameter $\bf\lambda$. We derive a generalized
interpolation scheme and emphasize the essential conceptual and computational
simplifications in using the formalism, for instance, in the evaluation of
linear response coefficients. We further implement the necessary machinery to
construct HDWFs from ab initio within the full-potential linearized augmented
plane-wave method (FLAPW). We apply our implementation to accurately
interpolate the Hamiltonian of a one-dimensional magnetic chain of Mn atoms in
two important cases of $\bf\lambda$: (i) the spin-spiral vector $\boldsymbol
q$, and (ii) the direction of the ferromagnetic magnetization $\hat{\boldsymbol
m}$. Using the generalized interpolation of the energy, we extract the
corresponding values of magneto-crystalline anisotropy energy, Heisenberg
exchange constants, and spin stiffness, which compare very well with the values
obtained from direct first principles calculations. For toy models we
demonstrate that the method of HDWFs can also be used in applications such as
the virtual crystal approximation, ferroelectric polarization and spin torques.",1503.01717v1
2015-04-28,Microwave soft x-ray microscopy for nanoscale magnetization dynamics in the 5-10 GHz frequency range,"We present a scanning transmission x-ray microscopy setup combined with a
novel microwave synchronization scheme in order to study high frequency
magnetization dynamics at synchrotron light sources. The sensitivity necessary
to detect small changes of the magnetization on short time scales and nanometer
spatial dimensions is achieved by combination of the developed excitation
mechanism with a single photon counting electronics that is locked to the
synchrotron operation frequency. The required mechanical stability is achieved
by a compact design of the microscope. Our instrument is capable of creating
direct images of dynamical phenomena in the 5-10 GHz range, with 35 nm
resolution. When used together with circularly polarized x-rays, the above
capabilities can be combined to study magnetic phenomena at microwave
frequencies, such as ferromagnetic resonance (FMR) and spin waves. We
demonstrate the capabilities of our technique by presenting phase resolved
images of a 6 GHz nanoscale spin wave generated by a spin torque oscillator, as
well as the uniform ferromagnetic precession with ~0.1 deg amplitude at 9 GHz
in a micrometer-sized cobalt strip.",1504.07561v1
2015-05-04,The aperiodic X-ray variability of the accreting millisecond pulsar SAX J1808.4-3658,"We have studied the aperiodic variability of the 401 Hz accreting millisecond
X-ray pulsar SAX J1808.4-3658 using the complete data set collected with the
Rossi X-ray Timing Explorer over 14 years of observation. The source shows a
number of exceptional aperiodic timing phenomena that are observed against a
backdrop of timing properties that show consistent trends in all five observed
outbursts and closely resemble those of other atoll sources. We performed a
detailed study of the enigmatic ~410 Hz QPO, which has only been observed in
SAX J1808.4-3658. We find that it appears only when the upper kHz QPO frequency
is less than the 401 Hz spin frequency. The difference between the ~410 Hz QPO
frequency and the spin frequency follows a similar frequency correlation as the
low frequency power spectral components, suggesting that the ~410 Hz QPO is a
retrograde beat against the spin frequency of a rotational phenomenon in the 9
Hz range. Comparing this 9 Hz beat feature with the Low-Frequency QPO in SAX
J1808.4-3658 and other neutron star sources, we conclude that these two might
be part of the same basic phenomenon. We suggest that they might be caused by
retrograde precession due to a combination of relativistic, classical and
magnetic torques. Additionally we present two new measurements of the lower kHz
QPO, allowing us, for the first time, to measure the frequency evolution of the
twin kHz QPOs in this source. The twin kHz QPOs are seen to move together over
150 Hz, maintaining a centroid frequency separation of $(0.446 \pm 0.009)
\nu_{spin}$.",1505.00596v1
2015-10-29,The Magnetic Field Evolution of ULX NuSTAR J095551+6940.8 in M82--A Legacy of Accreting Magnetar,"Ultra-luminous X-ray sources are usually believed to be black holes with mass
about $10^{2-3}M_{\odot}$. However, the recent discovery of NuSTAR
J095551+6940.8 in M82 by Bachetti et al. shows that it holds the spin period
$P=1.37\rm\,s$ and period {\bf derivative}
$\dot{P}\approx-2\times10^{-10}\rm\,s\,s^{-1}$, which provides a strong
evidence that some ultra-luminous X-ray sources could be neutron stars. We
obtain that the source may be an evolved magetar, according to our simulation
by employing the model of accretion induced the polar magnetic field decay and
standard spin-up torque of an accreting neutron star. The results show that
NuSTAR J095551+6940.8 is still in the spin-up process, and the polar magnetic
field decays to about $4.5\times10^{12}\rm\,G$ after accreting $\sim
10^{-2.5}$\ms, while the strong magnetic field exists in the out-polar region,
which could be responsible for the observed low field magnetar. The ultra
luminosity of the source can be explained by the beaming effort and two kinds
of accretion--radial random accretion and disk accretion. Since the birth rate
of magnetars is about ten percent of the normal neutron stars, we guess that
several ultra-luminous X-ray sources should share the similar properties to
that of NuSTAR J095551+6940.8.",1510.08597v3
2016-03-23,Direct Observation of the Skyrmion Hall Effect,"The well-known Hall effect describes the transverse deflection of charged
particles (electrons or holes) in an electric-current carrying conductor under
the influence of perpendicular magnetic fields, as a result of the Lorentz
force. Similarly, it is intriguing to examine if quasi-particles without an
electric charge, but with a topological charge, show related transverse motion.
Chiral magnetic skyrmions with a well-defined spin topology resulting in a unit
topological charge serve as good candidates to test this hypothesis. In spite
of the recent progress made on investigating magnetic skyrmions, direct
observation of the skyrmion Hall effect in real space has, remained elusive.
Here, by using a current-induced spin Hall spin torque, we experimentally
observe the skyrmion Hall effect by driving skyrmions from creep motion into
the steady flow motion regime. We observe a Hall angle for the magnetic
skyrmion motion as large as 15 degree for current densities smaller than 10
MA/cm^(2) at room temperature. The experimental observation of transverse
transport of skyrmions due to topological charge may potentially create many
exciting opportunities for the emerging field of skyrmionics, including novel
applications such as topological selection.",1603.07393v1
2016-04-06,Rotating Stars and the Formation of Bipolar Planetary Nebulae II: Tidal Spin-up,"We present new binary stellar evolution models that include the effects of
tidal forces, rotation, and magnetic torques with the goal of testing Planetary
Nebulae (PNe) shaping via binary interaction. We explore whether tidal
interaction with a companion can spin up the AGB envelope. To do so we have
selected binary systems with main sequence masses of 2.5 \Mo and of 0.8 \Mo and
evolve them allowing initial separations of 5, 6, 7, and 8 AU. The binary
stellar evolution models have been computed all the way to the PNe formation
phase or until Roche lobe overflow (RLOF) is reached, whatever happens first.
We show that with initial separations of 7 and 8 AU, the binary avoids entering
into RLOF, and the AGB star reaches moderate rotational velocities at the
surface ($\sim 3.5 $ and $\sim 2 $ \kms respectively) during the inter-pulse
phases, but after the thermal pulses it drops to a final rotational velocity of
only $\sim 0.03 $ \kms. For the closest binary separations explored, 5 and 6
AU, the AGB star reaches rotational velocities of $\sim 6 $ and $\sim 4 $ \kms
respectively when the RLOF is initiated. We conclude that the detached binary
models that avoid entering the RLOF phase during the AGB will not shape bipolar
PNe, since the acquired angular momentum is lost via the wind during the last
two thermal pulses. This study rules out tidal spin-up in non-contact binaries
as a sufficient condition to form bipolar PNe.",1604.01671v1
2017-09-08,Observation of Magnetic Radial Vortex Nucleation in a Multilayer Stack with Tunable Anisotropy,"Recently discovered exotic magnetic configurations, namely magnetic solitons
appearing in the presence of bulk or interfacial Dzyaloshinskii-Moriya
Interaction (i-DMI), have excited scientists to explore their potential
applications in emerging spintronic technologies such as race-track magnetic
memory, spin logic, radio frequency nano-oscillators and sensors. Such studies
are motivated by their foreseeable advantages over conventional micro-magnetic
structures due to their small size, topological stability and easy spin-torque
driven manipulation with much lower threshold current densities giving way to
improved storage capacity, and faster operation with efficient use of energy.
In this work, we show that in the presence of i-DMI in Pt/CoFeB/Ti multilayers
by tuning the magnetic anisotropy (both in-plane and perpendicular-to-plane)
via interface engineering and postproduction treatments, we can stabilize a
variety of magnetic configurations such as N\'eel skyrmions, horseshoes and
most importantly for the first time, the recently predicted isolated radial
vortices at room temperature and under zero bias field. Especially, the radial
vortex state with its absolute convergence to or divergence from a single point
can potentially offer exciting new applications such as particle
trapping/detrapping in addition to magnetoresistive memories with efficient
switching, where the radial vortex state can act as a source of spin-polarized
current with radial polarization.",1709.02876v1
2017-09-22,Spin Precession Experiments for Light Axionic Dark Matter,"Axion-like particles are promising candidates to make up the dark matter of
the universe, but it is challenging to design experiments that can detect them
over their entire allowed mass range. Dark matter in general, and in particular
axion-like particles and hidden photons, can be as light as roughly $10^{-22}
\;\rm{eV}$ ($\sim 10^{-8} \;\rm{Hz}$), with astrophysical anomalies providing
motivation for the lightest masses (""fuzzy dark matter""). We propose
experimental techniques for direct detection of axion-like dark matter in the
mass range from roughly $10^{-13} \;\rm{eV}$ ($\sim 10^2 \;\rm{Hz}$) down to
the lowest possible masses. In this range, these axion-like particles act as a
time-oscillating magnetic field coupling only to spin, inducing effects such as
a time-oscillating torque and periodic variations in the spin-precession
frequency with the frequency and direction set by fundamental physics. We show
how these signals can be measured using existing experimental technology,
including torsion pendulums, atomic magnetometers, and atom interferometry.
These experiments demonstrate a strong discovery capability, with future
iterations of these experiments capable of pushing several orders of magnitude
past current astrophysical bounds.",1709.07852v2
2017-11-13,Galaxy spin as a formation probe: the stellar-to-halo specific angular momentum relation,"We derive the stellar-to-halo specific angular momentum relation (SHSAMR) of
galaxies at $z=0$ by combining i) the standard $\Lambda$CDM tidal torque theory
ii) the observed relation between stellar mass and specific angular momentum
(Fall relation) and iii) various determinations of the stellar-to-halo mass
relation (SHMR). We find that the ratio $f_j = j_\ast/j_{\rm h}$ of the
specific angular momentum of stars to that of the dark matter i) varies with
mass as a double power-law, ii) it always has a peak in the mass range explored
and iii) it is $3-5$ times larger for spirals than for ellipticals. The results
have some dependence on the adopted SHMR and we provide fitting formulae in
each case. For any choice of the SHMR, the peak of $f_j$ occurs at the same
mass where the stellar-to-halo mass ratio $f_\ast = M_\ast/M_{\rm h}$ has a
maximum. This is mostly driven by the straightness and tightness of the Fall
relation, which requires $f_j$ and $f_\ast$ to be correlated with each other
roughly as $f_j\propto f_\ast^{2/3}$, as expected if the outer and more angular
momentum rich parts of a halo failed to accrete onto the central galaxy and
form stars (biased collapse). We also confirm that the difference in the
angular momentum of spirals and ellipticals at a given mass is too large to be
ascribed only to different spins of the parent dark-matter haloes (spin bias).",1711.04763v2
2018-06-04,Hydrodynamic Stability Analysis of the Neutron Star Core,"Hydrodynamic instabilities and turbulence in neutron stars have been
suggested to be related to observable spin variations in pulsars, such as spin
glitches, timing noise, and precession (nutation). Accounting for the
stabilizing effects of the stellar magnetic field, we revisit the issue of
whether the inertial modes of a neutron star can become unstable when the
neutron and proton condensates flow with respect to one another. The neutron
and proton condensates are coupled through the motion of imperfectly pinned
vorticity (vortex slippage) and vortex-mediated scattering (mutual friction).
Two-stream instabilities that occur when the two condensates rotate with
respect to one another in the outer core are stabilized by the toroidal
component of the magnetic field. This stabilization occurs when the Alfv\'en
speed of the toroidal component of the magnetic field becomes larger than the
relative rotational velocity of the condensates, corresponding to toroidal
field strengths in excess of $\simeq 10^{10}\,{\rm G}$. In contrast with
previous studies, we find that spin down of a neutron star under a steady
torque is stable. The Donnelly--Glaberson instability is not stabilized by the
magnetic field, and could play an important role if neutron stars undergo
precession.",1806.00967v2
2018-06-04,The 2016 outburst of PSR J1119-6127: cooling & a spin-down dominated glitch,"We report on the aftermath of a magnetar outburst from the young,
high-magnetic-field radio pulsar PSR J1119-6127 that occurred on 2016 July 27.
We present the results of a monitoring campaign using the Neil Gehrels Swift
X-ray Telescope, NuSTAR, and XMM-Newton. After reaching a peak luminosity of
~300 times the quiescent luminosity, the pulsar's X-ray flux declined by factor
of ~50 on a time scale of several months. The X-ray spectra are well described
by a blackbody and a hard power-law tail. After an initial rapid decline during
the first day of the outburst, we observe the blackbody temperature rising from
kT = 0.9 keV to 1.05 keV during the first two weeks of the outburst, before
cooling to 0.9 keV. During this time, the blackbody radius decreases
monotonically by a factor of ~4 over a span of nearly 200 days. We also report
a heretofore unseen highly pulsed hard X-ray emission component, which fades on
a similar timescale to the soft X-ray flux, as predicted by models of
relaxation of magnetospheric current twists. The previously reported spin-up
glitch which accompanied this outburst was followed by a period of enhanced and
erratic torque, leading to a net spin-down of $\sim3.5\times10^{-4}$ Hz, a
factor of ~24 over-recovery. We suggest that this and other radiatively loud
magnetar-type glitch recoveries are dominated by magnetospheric processes, in
contrast to conventional radio pulsar glitch recoveries which are dominated by
internal physics.",1806.01414v1
2018-07-17,An application of the Ghosh & Lamb model to the accretion powered X-ray pulsar X Persei,"The accretion-induced pulse-period changes of the Be/X-ray binary pulsar X
Persei were investigated over a period of 1996 January to 2017 September. This
study utilized the monitoring data acquired with the RXTE/ASM in 1.5$-$12 keV
and MAXI/GSC in 2$-$20 keV. The source intensity changed by a factor of 5$-$6
over this period. The pulsar was spinning down for 1996$-$2003, and has been
spinning up since 2003, as already reported. The spin up/down rate and the
3$-$12 keV flux, determined every 250 d, showed a clear negative correlation,
which can be successfully explained by the accretion torque model proposed by
Ghosh & Lamb (1979). When the mass, radius and distance of the neutron star are
allowed to vary over a range of 1.0$-$2.4 solar masses, 9.5$-$15 km, and
0.77$-$0.85 kpc, respectively, the magnetic field strength of $B=(4-25)
\times10^{13}\ \rm G$ gave the best fits to the observation. In contrast, the
observed results cannot be explained by the values of $B\sim10^{12}\ \rm G$
previously suggested for X Persei, as long as the mass, radius, and distance
are required to take reasonable values. Assuming a distance of $0.81\pm0.04$
kpc as indicated by optical astrometry, the mass of the neutron star is
estimated as $M=2.03\pm0.17$ solar masses.",1807.06252v2
2018-10-10,Quantitative agreement of Dzyaloshinskii-Moriya interactions for domain-wall motion and spin-wave propagation,"The magnetic exchange interaction is the one of the key factors governing the
basic characteristics of magnetic systems. Unlike the symmetric nature of the
Heisenberg exchange interaction, the interfacial Dzyaloshinskii-Moriya
interaction (DMI) generates an antisymmetric exchange interaction which offers
challenging opportunities in spintronics with intriguing antisymmetric
phenomena. The role of the DMI, however, is still being debated, largely
because distinct strengths of DMI have been measured for different magnetic
objects, particularly chiral magnetic domain walls (DWs) and non-reciprocal
spin waves (SWs). In this paper, we show that, after careful data analysis,
both the DWs and SWs experience the same strength of DMI. This was confirmed by
spin-torque efficiency measurement for the DWs, and Brillouin light scattering
measurement for the SWs. This observation, therefore, indicates the unique role
of the DMI on the magnetic DW and SW dynamics and also guarantees the
compatibility of several DMI-measurement schemes recently proposed.",1810.04375v1
2019-02-05,Dust rotational dynamics in non-stationary shock: rotational disruption of nanoparticles by stochastic mechanical torques and spinning dust emission,"In a previous work, Hoang and Tram discovered a new mechanism for destruction
of nanoparticles due to suprathermal rotation of grains in stationary C-shocks,
which is termed rotational disruption. In this paper, we extend our previous
study for non-stationary shocks driven by outflows and young supernovae
remnants that have dynamical ages shorter than the time required to establish a
stationary C-shock, which is composed of a C-shock and a J-shock tail (referred
as CJ-shock). For the C-shock component, we find that smallest nanoparticles
(size $\lesssim 1$ nm) of weak materials (i.e., tensile strength $S_{\rm max}
\lesssim 10^{9}\ \rm erg\ cm^{-3}$) can be rotationally disrupted due to
suprathermal rotation induced by supersonic neutral drift. For the J-shock
component, although nanoparticles are rotating thermally, the smallest ones can
still be disrupted because the gas is heated to higher temperatures by
J-shocks. We then model microwave emission from rapidly spinning nanoparticles
where the grain size distribution has the lower cutoff determined by rotational
disruption for the different shock models. We also calculate the spectral flux
of microwave emission from a shocked region at distance of 100 pc from the
observer for the different gas density, shock age, and shock velocities. We
suggest that microwave emission from spinning dust can be used to trace
nanoparticles and shock velocities in dense molecular outflows. Finally, we
discuss a new way that can release molecules from the nanoparticle surface into
the gas in the shocked regions, which we name rotational desorption.",1902.01921v3
2019-02-25,Tidal Disruption Event Disks around Supermassive Black Holes: Disk Warp and Inclination Evolution,"After the Tidal Disruption Event (TDE) of a star around a SuperMassive Black
Hole (SMBH), the bound stellar debris rapidly forms an accretion disk. If the
accretion disk is not aligned with the spinning SMBH's equatorial plane, the
disk will be driven into Lense-Thirring precession around the SMBH's spin axis,
possibly affecting the TDE's light curve. We carry out an eigenmode analysis of
such a disk to understand how the disk's warp structure, precession, and
inclination evolution are influenced by the disk's and SMBH's properties. We
find an oscillatory warp may develop as a result of strong non-Keplarian motion
near the SMBH. The global disk precession frequency matches the Lense-Thirring
precession frequency of a rigid disk around a spinning black hole within a
factor of a few when the disk's accretion rate is high, but deviates
significantly at low accretion rates. Viscosity aligns the disk with the SMBH's
equatorial plane over timescales of days to years, depending on the disk's
accretion rate, viscosity, and SMBH's mass. We also examine the effect of
fall-back material on the warp evolution of TDE disks, and find that the
fall-back torque aligns the TDE disk with the SMBH's equatorial plane in a few
to tens of days for the parameter space investigated. Our results place
constraints on models of TDE emission which rely on the changing disk
orientation with respect to the line of sight to explain observations.",1902.09546v2
2019-03-11,"THz emission from Co/Pt bilayers with varied roughness, crystal structure, and interface intermixing","Femtosecond laser excitation of a Co/Pt bilayer results in the efficient
emission of picosecond THz pulses. Two known mechanisms for generating THz
emission are spin-polarized currents through a Co/Pt interface, resulting in
helicity-independent electric currents in the Pt layer due to the inverse
spin-Hall effect and helicity-dependent electric currents at the Co/Pt
interface due to the inverse spin-orbit torque effect. Here we explore how
roughness, crystal structure and intermixing at the Co/Pt interface affect the
efficiency of the THz emission. In particular, we varied the roughness of the
interface, in the range of 0.1-0.4 nm, by tuning the deposition pressure
conditions during the fabrication of the Co/Pt bilayers. To control the
intermixing at the Co/Pt interface a 1-2 nm thick CoxPt1-x alloy spacer layer
was introduced with various compositions of Co and Pt. Finally, the crystal
structure of Co was varied from face centered cubic to hexagonal close packed.
Our study shows that the roughness of the interface is of crucial importance
for the efficiency of helicity-dependent THz emission induced by femtosecond
laser pulses. However, it is puzzling that intermixing while strongly enhancing
the helicity-independent THz emission had no effect on the helicity-dependent
THz emission which is suppressed and similar to the smooth interfaces.",1903.04423v2
2019-05-08,X-ray timing studies of the low-field magnetar CXOU J164710.2-455216,"We report results of X-ray timing analyses for the low-field magnetar
CXOU~J164710.2$-$455216 which exhibited multiple outbursts. We use data taken
with NICER, NuSTAR, Chandra, and Neil-Gehrels-Swift telescopes between 2017 and
2018 when the source was in an active state. We perform semi-phase-coherent
timing analyses to measure the spin parameters and a spin-inferred
magnetic-field strength ($B_s$) of the magnetar. Using a semi-phase-coherent
method, we infer the magnetic field strengths to be $3-4\times 10^{13}\rm \ G$
at the observation period ($\sim$MJD 58000), and by comparing with previous
frequency measurements (MJD 54000) a long-term average value of $B_s$ is
estimated to be $\approx4\times 10^{13}\rm \ G$. So this analysis may add
CXOU~J164710.2$-$455216 to the ranks of low-field magnetars. The inferred
characteristic age ($\tau_c$) is 1--2 Myr which is smaller than the age of
Westerlund~1, so the magnetar's association with the star cluster is still
secure. For the low dipole field and the large age, recent multiple outbursts
observed from the source are hard to explain unless it has strong magnetic
multipole components. We also find timing anomalies around outburst epochs,
which suggests that there may be spin-down torque applied to the magnetar near
the epochs as was proposed in magnetar models.",1905.02862v1
2019-05-30,Alignment and precession of a black hole misaligned with its accretion disc: Application to Low Mass X-ray Binaries,"A thin viscous accretion disc around a Kerr black hole, which is warped due
to the Lense-Thirring (LT) effect, was shown to cause the spin axis of the
black hole to precess and align with the outer disc. We calculate the total LT
torque acting on the black hole, and compute the alignment and precession
time-scales for both persistent and transient accretors. In our analysis, we
consider the contribution of the inner disc, as it can stay misaligned with the
black hole spin for a reasonable range of parameter values. We find that the
alignment time-scale increases with a decrease in the Kerr parameter below a
critical Kerr parameter value, contrary to earlier predictions. Besides, the
time-scales are generally longer for transience than the time-scales calculated
for persistent accretion. From our analysis of the transient case, we find that
the black hole in the low mass X-ray binary (LMXB) 4U 1543-47 could be
misaligned, whereas that in the LMXB XTE J1550-564 has aligned itself with the
outer disc. The age of the LMXB H 1743-322 is estimated assuming a misaligned
disc. We also find that the black hole in a typical Galactic LMXB can take a
significantly longer time to align than what was estimated in the past. This
may have an important implication on the measurement of black hole spin using
the continuum X-ray spectral fitting method.",1905.12858v1
2019-08-14,Asymmetric accretion and thermal `mountains' in magnetized neutron star crusts,"Accreting neutron stars are one of the main targets for continuous
gravitational wave searches, as asymmetric accretion may lead to quadrupolar
deformations, or `mountains', on the crust of the star, which source
gravitational wave emission at twice the rotation frequency. The gravitational
wave torque may also impact on the spin evolution of the star, possibly
dictating the currently observed spin periods of neutron stars in Low Mass
X-ray Binaries and leading to the increased spindown rate observed during
accretion in PSR J1023+0038. Previous studies have shown that deformed reaction
layers in the crust of the neutron star lead to thermal and compositional
gradients that can lead to gravitational wave emission. However, there are no
realistic constraints on the level of asymmetry that is expected. In this paper
we consider a natural source of asymmetry, namely the magnetic field, and
calculate the density and pressure perturbations that are expected in the crust
of accreting neutron stars. In general we find that only the outermost reaction
layers of the neutron star are strongly perturbed. The mass quadrupole that we
estimate is generally small and cannot explain the increase of spin-down rate
of PSR J1023+0038. However, if strong shallow heating sources are present at
low densities in the crust, as cooling observations suggest, these layers will
be strongly perturbed and the resulting quadrupole could explain the observed
spindown of PSR J1023+0038, and lead to observable gravitational wave signals
from systems with higher accretion rates.",1908.05038v2
2019-09-24,Diffusiophoretic design of self-spinning microgears from colloidal microswimmers,"Design strategies to assemble dissipative building blocks are essential to
create novel and smart materials and machines. We recently demonstrated the
hierarchical self-assembly of phoretic microswimmers into self-spinning
microgears and their synchronization by diffusiophoretic interactions [Aubret
\textit{et al., Nature Physics}, 2018]. In this paper, we adopt a pedagogical
approach and expose our strategy to control self-assembly and build machines
using phoretic phenomena. We notably introduce Highly Inclined Laminated
Optical sheets microscopy (HILO) to image and quantify anisotropic and dynamic
diffusiophoretic interactions, which could not be observed by standard
fluorescence microscopy. The dynamics of a (haematite) photocalytic material
immersed in (hydrogen peroxide) fuel under various illumination patterns is
first described and quantitatively rationalized by a model of diffusiophoresis,
the migration of a colloidal particle in a concentration gradient. It is
further exploited to design phototactic microswimmers, that direct towards the
high intensity of light, as a result of the the torque exerted by the haematite
in a light gradient on a microswimmer. We finally demonstrate the assembly of
self-spinning microgears from colloidal microswimmers by controlling
dissipative diffusiophoretic interactions, that we characterize using HILO and
quantitatively compare to analytical and numerical predictions. Because the
approach described hereby is generic, this works paves the way for the rational
design of machines by controlling phoretic phenomena.",1909.11121v1
2019-12-04,Compensated magnetic insulators for extremely fast spin-orbitronics,"The fast spin dynamics provide many opportunities for the future
communication and memory technologies. One of the most promising examples is
the domain wall (DW) racetrack memory. To achieve fast device performances, the
high-speed motion of DWs is naturally demanded that leaves antiferromagnets
(AFMs) and compensated ferrimagnets (FIMs) as the promising materials. While
controlling and probing the dynamics of DWs in AFMs remains challenging, the
fast motion of DWs with velocities around 1500 m/s has been demonstrated in
metallic FIMs. The velocity of DWs in metallic FIMs is, however, suppressed by
the magnetic damping of conduction electrons, which motivates us to explore how
fast DWs can move in insulating FIMs where the conduction electron is absent.
In this work, through synthesizing compensated FIM insulator Gd3Fe5O12 thin
films with a perpendicular magnetic anisotropy, we demonstrate that the
spin-orbit torque (SOT) induced motion of DWs along the Gd3Fe5O12/Pt racetrack
can approach 6000 m/s. Our results show that the exceptionally fast motion of
DWs can be achieved in compensated FIM insulators owing to small damping
inherent to magnetic insulators, which could potentially facilitate the
emerging ultrahigh-speed spintronic logics and racetrack memories by
introducing insulating compensated FIMs as a new material platform.",1912.01775v1
2019-12-05,Steering magnonic dynamics and permeability at exceptional points in a parity-time symmetric waveguide,"Tuning the low-energy magnetic dynamics is a key element in designing novel
magnetic metamaterials, spintronic devices and magnonic logic circuits. This
study uncovers a new, highly effective way of controlling the magnetic
permeability via shaping the magnonic properties in coupled magnetic waveguides
separated by current carrying spacer with strong spin-orbit coupling. The
spin-orbit torques exerted on the waveguides leads to an externally tunable
enhancement of magnetic damping in one waveguide and a decreased damping in the
other, constituting so a magnetic parity-time (PT) symmetric system with
emergent magnetic properties at the verge of the exceptional point where
magnetic gains/losses are balanced. In addition to controlling the magnetic
permeability, phenomena inherent to PT-symmetric systems are identified,
including the control on magnon power oscillations, nonreciprocal magnon
propagation, magnon trapping and enhancement as well as the increased
sensitivity to magnetic perturbation and abrupt spin reversal. These
predictions are demonstrated analytically and confirmed by full numerical
simulations under experimentally feasible conditions. The position of the
exceptional points and the strength of the spontaneous PT symmetry breaking can
be tuned by external electric and/or magnetic fields. The roles of the
intrinsic magnetic damping, and the possibility of an electric control via
Dzyaloshinskii-Moriya interaction are exposed and utilized for mode dispersion
shaping and magnon amplification and trapping. The results point to a new route
to designing optomagnonic waveguides, traps, sensors, and circuits.",1912.02500v1
2019-12-22,"Acoustic versus electromagnetic field theory: scalar, vector, spinor representations and the emergence of acoustic spin","We construct a novel Lagrangian representation of acoustic field theory that
describes the local vector properties of longitudinal (curl-free) acoustic
fields. In particular, this approach accounts for the recently-discovered
nonzero spin angular momentum density in inhomogeneous sound fields in fluids
or gases. The traditional acoustic Lagrangian representation with a ${\it
scalar}$ potential is unable to describe such vector properties of acoustic
fields adequately, which are however observable via local radiation forces and
torques on small probe particles. By introducing a displacement ${\it vector}$
potential analogous to the electromagnetic vector potential, we derive the
appropriate canonical momentum and spin densities as conserved Noether
currents. The results are consistent with recent theoretical analyses and
experiments. Furthermore, by an analogy with dual-symmetric electromagnetic
field theory that combines electric- and magnetic-potential representations, we
put forward an acoustic ${\it spinor}$ representation combining the scalar and
vector representations. This approach also includes naturally coupling to
sources. The strong analogies between electromagnetism and acoustics suggest
further productive inquiry, particularly regarding the nature of the apparent
spacetime symmetries inherent to acoustic fields.",1912.10522v2
2020-06-18,Current-induced magnetization switching in CoTb amorphous single layer,"We demonstrate spin-orbit torque (SOT) switching of amorphous CoTb single
layer films with perpendicular magnetic anisotropy (PMA). The switching
sustains even the film thickness is above 10 nm, where the critical switching
current density keeps almost constant. Without the need of overcoming the
strong interfacial Dzyaloshinskii-Moriya interaction caused by the heavy metal,
a quite low assistant field of ~20 Oe is sufficient to realize the fully
switching. The SOT effective field decreases and undergoes a sign change with
the decrease of the Tb-concentration, implying that a combination of the spin
Hall effect from both Co and Tb as well as an asymmetric spin current
absorption accounts for the SOT switching mechanism. Our findings would advance
the use of magnetic materials with bulk PMA for energy-efficient and
thermal-stable non-volatile memories, and add a different dimension for
understanding the ordering and asymmetry in amorphous thin films.",2006.10319v1
2020-07-22,Gyr-timescale destruction of high-eccentricity asteroids by spin and why 2006 HY51 has been spared,"Asteroids and other small celestial bodies have markedly prolate shapes, and
the perturbative triaxial torques which are applied during pericenter passages
in highly eccentric orbits trigger and sustain a state of chaotic rotation.
Because the prograde spin rate around the principal axis of inertia is not
bounded from above, it can accidentally reach the threshold value corresponding
to rotational break-up. Previous investigations of this process were limited to
integrations of $\sim 10^3$ orbits because of the stiff equation of motion. We
present here a fast 1D simulation method to compute the evolution of this spin
rate over $\sim 10^9$ orbits. We apply the method to the most eccentric solar
system asteroid known, 2006 HY51 (with $e = 0.9684$), and find that for any
reasonably expected shape parameters, it can never be accelerated to break-up
speed. However, primordial solar system asteroids on more eccentric orbits may
have already broken up from this type of rotational fission. The method also
represents a promising opportunity to investigate the long-term evolution of
extremely eccentric triaxial exo-asteroids ($e > 0.99$), which are thought to
be common in white dwarf planetary systems",2007.11487v1
2020-11-25,Domain wall motion in axially symmetric spintronic nanowires,"This article is concerned with the dynamics of magnetic domain walls (DWs) in
nanowires as solutions to the classical Landau-Lifschitz-Gilbert equation
augmented by a typically non-variational Slonczewski term for spin-torque
effects. Taking applied field and spin-polarization as the primary parameters,
we study dynamic stability as well as selection mechanisms analytically and
numerically in an axially symmetric setting. Concerning the stability of the
DWs' asymptotic states, we distinguish the bistable (both stable) and the
monostable (one unstable, one stable) parameter regime. In the bistable regime,
we extend known stability results of an explicit family of precessing solutions
and identify a relation of applied field and spin-polarization for standing
DWs. We verify that this family is convectively unstable into the monostable
regime, thus forming so-called pushed fronts, before turning absolutely
unstable. In the monostable regime, we present explicit formulas for the
so-called absolute spectrum of more general matrix operators. This allows us to
relate translation and rotation symmetries to the position of the singularities
of the pointwise Green's function. Thereby, we determine the linear selection
mechanism for the asymptotic velocity and frequency of DWs and corroborate
these by long-time numerical simulations. All these results include the axially
symmetric Landau-Lifschitz-Gilbert equation.",2012.01343v1
2021-07-27,Empirical Assessment of Aperiodic and Periodic Radio Bursts from Young Precessing Magnetars,"We analyze the slow periodicities identified in burst sequences from FRB
121102 and FRB 180916 with periods of about 16 and 160 d, respectively, while
also addressing the absence of any fast periodicity that might be associated
with the spin of an underlying compact object. Both phenomena can be accounted
for by a young, highly magnetized, precessing neutron star that emits beamed
radiation with significant imposed phase jitter. Sporadic narrow-beam emission
into an overall wide solid angle can account for the necessary phase jitter,
but the slow periodicities with 25 to 55 % duty cycles constrain beam
traversals to be significantly smaller. Instead, phase jitter may result from
variable emission altitudes that yield large retardation and aberration delays.
A detailed arrival-time analysis for triaxial precession includes wobble of the
radio beam and the likely larger, cyclical torque resulting from the changes in
the spin-magnetic moment angle. These effects will confound identification of
the fast periodicity in sparse data sets longer than about a quarter of a
precession cycle unless fitted for and removed as with orbital fitting.
Stochastic spin noise, likely to be much larger than in radio pulsars, may
hinder detection of any fast-periodicity in data spans longer than a few days.
These decoherence effects will dissipate as FRB sources age, so they may evolve
into objects with properties similar to Galactic magnetars.",2107.12874v2
2021-08-30,Highly efficient nonvolatile magnetization switching and multi-level states by current in single van der Waals topological ferromagnet Fe3GeTe2,"Robust multi-level spin memory with the ability to write information
electrically is a long-sought capability in spintronics, with great promise for
applications. Here we achieve nonvolatile and highly energy-efficient
magnetization switching in a single-material device formed of van-der-Waals
topological ferromagnet Fe3GeTe2, whose magnetic information can be readily
controlled by a tiny current. Furthermore, the switching current density and
power dissipation are about 400 and 4000 times smaller than those of the
existing spin-orbit-torque magnetic random access memory based on conventional
magnet/heavy-metal systems. Most importantly, we also demonstrate multi-level
states, switched by electrical current, which can dramatically enhance the
information capacity density and reduce computing costs. Thus, our observations
combine both high energy efficiency and large information capacity density in
one device, showcasing the potential applications of the emerging field of
van-der-Waals magnets in the field of spin memory and spintronics.",2108.13022v1
2021-12-31,The influence of a fluid core and a solid inner core on the Cassini sate of Mercury,"We present a model of the Cassini state of Mercury that comprises an inner
core, a fluid core and a mantle. Our model includes inertial and gravitational
torques between interior regions, and viscous and electromagnetic (EM) coupling
at the boundaries of the fluid core. We show that the coupling between
Mercury's interior regions is sufficiently strong that the obliquity of the
mantle spin axis deviates from that of a rigid planet by no more than 0.01
arcmin. The mantle obliquity decreases with increasing inner core size, but the
change between a large and no inner core is limited to 0.015 arcmin. EM
coupling is stronger than viscous coupling at the inner core boundary and, if
the core magnetic field strength is above 0.3 mT, locks the fluid and solid
cores into a common precession motion. Because of the strong gravitational
coupling between the mantle and inner core, the larger the inner core is, the
more this co-precessing core is brought into an alignment with the mantle, and
the more the obliquity of the polar moment of inertia approaches that expected
for a rigid planet. The misalignment between the polar moment of inertia and
mantle spin axis increases with inner core size, but is limited to 0.007
arcmin. Our results imply that the measured obliquities of the mantle spin axis
and polar moment of inertia should coincide at the present-day level of
measurement errors, and cannot be distinguished from the obliquity of a rigid
planet.",2201.00037v1
2022-04-04,Chaos over Order: Mapping 3D Rotation of Triaxial Asteroids and Minor Planets,"Celestial bodies approximated with rigid triaxial ellipsoids in a two-body
system can rotate chaotically due to the time-varying gravitational torque from
the central mass. At small orbital eccentricity values, rotation is short-term
orderly and predictable within the commensurate spin-orbit resonances, while at
eccentricity approaching unity, chaos completely takes over. Here, we present
the full 3D rotational equations of motion around all three principle axes for
triaxial minor planets and two independent methods of numerical solution based
on Euler rotations and quaternion algebra. The domains of chaotic rotation are
numerically investigated over the entire range of eccentricity with a
combination of trial integrations of Euler's equations of motion and the
GALI($k$) method. We quantify the dependence of the order--chaos boundaries on
shape by changing a prolateness parameter, and find that the main 1:1
spin-orbit resonance disappears for specific moderately prolate shapes already
at eccentricities as low as 0.3. The island of short-term stability around the
main 1:1 resonance shrinks with increasing eccentricity at a fixed low degree
of prolateness and completely vanishes at approximately 0.8. This island is
also encroached by chaos on longer time scales indicating longer Lyapunov
exponents. Trajectories in the close vicinity of the 3:2 spin-orbit resonance
become chaotic at smaller eccentricities, but separated enclaves of orderly
rotation emerge at eccentricities as high as 0.8. Initial perturbations of
rotational velocity in latitude away from the exact equilibrium result in a
spectrum of free libration, nutation, and polar wander, which is not well
matched by the linearized analysis omitting the inertial terms.",2204.01854v1
2022-07-29,Orthogonal Spin Current Injected Magnetic Tunnel Junction for Convolutional Neural Networks,"We propose that a spin Hall effect driven magnetic tunnel junction device can
be engineered to provide a continuous change in the resistance across it when
injected with orthogonal spin currents. Using this concept, we develop a hybrid
device-circuit simulation platform to design a network that realizes multiple
functionalities of a convolutional neural network. At the atomistic level, we
use the Keldysh non-equilibrium Green's function technique that is coupled
self-consistently with the stochastic Landau-Lifshitz-Gilbert-Slonczewski
equations, which in turn is coupled with the HSPICE circuit simulator. We
demonstrate the simultaneous functionality of the proposed network to evaluate
the rectified linear unit and max-pooling functionalities. We present a
detailed power and error analysis of the designed network against the thermal
stability factor of the free ferromagnets. Our results show that there exists a
non-trivial power-error trade-off in the proposed network, which enables an
energy-efficient network design based on unstable free ferromagnets with
reliable outputs. The static power for the proposed ReLU circuit is $0.56\mu W$
and whereas the energy cost of a nine-input rectified linear unit-max-pooling
network with an unstable free ferromagnet($\Delta=15$) is $3.4pJ$ in the
worst-case scenario. We also rationalize the magnetization stability of the
proposed device by analyzing the vanishing torque gradient points.",2207.14603v3
2022-08-31,Perpendicular magnetic anisotropy in as-deposited CoFeB/MgO thin films,"Fabrication of perpendicularly magnetized ferromagnetic films on various
buffer layers, especially on numerous newly discovered spin-orbit torque (SOT)
materials to construct energy-efficient spin-orbitronic devices, is a
long-standing challenge. Even for the widely used CoFeB/MgO structures,
perpendicular magnetic anisotropy (PMA) can only be established on limited
buffer layers through post-annealing above 300 {\deg}C. Here, we report that
the PMA of CoFeB/MgO films can be established reliably on various buffer layers
in the absence of post-annealing. Further results show that precise control of
MgO thickness, which determines oxygen diffusion in the underneath CoFeB layer,
is the key to obtaining the as-deposited PMA. Interestingly, contrary to
previous understanding, post-annealing does not influence the well-established
as-deposited PMA significantly but indeed enhances unsaturated PMA with a thick
MgO layer by modulating oxygen distributions, rather than crystallinity or Co-
and Fe-O bonding. Moreover, our results indicate that oxygen diffusion also
plays a critical role in the PMA degradation at high temperature. These results
provide a practical approach to build spin-orbitronic devices based on various
high-efficient SOT materials.",2208.14913v1
2022-09-01,Magnon dynamics in parity-time-symmetric dipolarly coupled waveguides and magnonic crystals,"We consider the magnonic properties of two dipolarly coupled magnetic
stripes, both deposited on a normal conductive substrate with strong spin-orbit
coupling. A charge current in the substrate acts on the adjacent magnets with
spin-orbit torques, which result in magnonic damping or antidamping of the spin
waves, and hence a gain-loss coupling of the two magnetic stripes. The whole
setup is demonstrated to exhibit features typical for parity-time (PT)
symmetric systems. Phenomena are demonstrated that can be functionalized in
magnonic devices, including reconfigurable magnonic diodes and logic devices.
Alternative stripes designs and PT-symmetric, periodic, coupled magnonic
textures are studied. Analytical and full numerical analysis identify the
conditions for the appearance of exceptional points (EPs), where magnonic gain
and loss are balanced and evidence nonreciprocal magnon propagation and
enhanced magnon excitation around EPs. Furthermore, the dipolar coupling is
shown to bring in a wave vector-dependent PT-symmetric behavior. Proposing and
simulating a PT-symmetric magnonic crystal, we show how EPs and hence
associated phenomena can be steered to a particular wave vector in a gaped
spectrum via material design. The phenomena offer additional tools for
magnonic-based communication and computational devices.",2209.00180v1
2022-09-16,Valley-Spin Hall Effect-based Nonvolatile Memory with Exchange-Coupling-Enabled Electrical Isolation of Read and Write Paths,"Valley-spin hall (VSH) effect in monolayer WSe2 has been shown to exhibit
highly beneficial features for nonvolatile memory (NVM) design. Key advantages
of VSH-based magnetic random-access memory (VSH-MRAM) over spin orbit torque
(SOT)-MRAM include access transistor-less compact bit-cell and low power
switching of perpendicular magnetic anisotropy (PMA) magnets. Nevertheless,
large device resistance in the read path (RS) due to low mobility of WSe2 and
Schottky contacts deteriorates sense margin, offsetting the benefits of
VSH-MRAM. To address this limitation, we propose another flavor of VSH-based
MRAM that (while inheriting most of the benefits of VSH-MRAM) achieves lower RS
in the read path by electrically isolating the read and write terminals. This
is enabled by coupling VSH with electrically-isolated but magnetically-coupled
PMA magnets via interlayer exchange-coupling. Designing the proposed devices
using object oriented micro magnetic framework (OOMMF) simulation, we ensure
the robustness of the exchange-coupled PMA system under process variations. To
maintain a compact memory footprint, we share the read access transistor across
multiple bit-cells. Compared to the existing VSH-MRAMs, our design achieves
39%-42% and 36%-46% reduction in read time and energy, respectively, along with
1.1X-1.3X larger sense margin at a comparable area. This comes at the cost of
1.7X and 2.0X increase in write time and energy, respectively. Thus, the
proposed design is suitable for applications in which reads are more dominant
than writes.",2209.08188v1
2022-11-16,Spin-Reorientation-Driven Linear Magnetoelectric Effect in Topological Antiferromagnet Cu$_3$TeO$_6$,"The search for new materials for energy-efficient electronic devices has
gained unprecedented importance. Among the various classes of magnetic
materials driving this search are antiferromagnets, magnetoelectrics, and
systems with topological spin excitations. Cu$_3$TeO$_6$ is a material that
belongs to all three of these classes. Combining static electric polarization
and magnetic torque measurements with phenomenological simulations we
demonstrate that magnetic-field-induced spin reorientation needs to be taken
into account to understand the linear magnetoelectric (ME) effect in
Cu$_3$TeO$_6$. Our calculations reveal that the magnetic field pushes the
system from the nonpolar ground state to the polar magnetic structures.
However, nonpolar structures only weakly differing from the obtained polar ones
exist due to the weak effect that the field-induced breaking of some symmetries
has on the calculated structures. Among those symmetries is the $PT$
($\overline{1}'$) symmetry, preserved for Dirac points found in Cu$_3$TeO$_6$.
Our findings establish Cu$_3$TeO$_6$ as a promising playground to study the
interplay of spintronics-related phenomena.",2211.08902v2
2022-11-16,Continuous Electrical Manipulation of Magnetic Anisotropy and Spin Flopping in van der Waals Ferromagnetic Devices,"Controlling the magnetic anisotropy of ferromagnetic materials plays a key
role in magnetic switching devices and spintronic applications. Examples of
spin-orbit torque devices with different magnetic anisotropy geometries
(in-plane or out-of-plane directions) have been demonstrated with novel
magnetization switching mechanisms for extended device functionalities.
Normally, the intrinsic magnetic anisotropy in ferromagnetic materials is
unchanged within a fixed direction, and thus, it is difficult to realize
multifunctionality devices. Therefore, continuous modulation of magnetic
anisotropy in ferromagnetic materials is highly desired but remains
challenging. Here, we demonstrate a gate-tunable magnetic anisotropy transition
from out-of-plane to canted and finally to in-plane in layered Fe$_5$GeTe$_2$
by combining the measurements of the angle-dependent anomalous Hall effect and
magneto-optical Kerr effect with quantitative Stoner-Wohlfarth analysis. The
magnetic easy axis continuously rotates in a spin-flop pathway by gating or
temperature modulation. Such observations offer a new avenue for exploring
magnetization switching mechanisms and realizing new spintronic
functionalities.",2211.08909v1
2022-11-24,Transition of latitudinal differential rotation as a possible cause of weakened magnetic braking of solar-type stars,"We investigate the role of latitudinal differential rotation (DR) in the spin
evolution of solar-type stars. Recent asteroseismic observation detected the
strong equator-fast DR in some solar-type stars. Numerical simulations show
that the strong equator-fast DR is a typical feature of young fast-rotating
stars and that this tendency is gradually reduced with stellar age.
Incorporating these properties, we develop a model for the long-term evolution
of stellar rotation. The magnetic braking is assumed to be regulated dominantly
by the rotation rate in the low-latitude region. Therefore, in our model, stars
with the equator-fast DR spin down more efficiently than those with the
rigid-body rotation. We calculate the evolution of stellar rotation in ranges
of stellar mass, $0.9 \, \mathrm{M}_{\odot} \le M \le 1.2\,
\mathrm{M}_{\odot}$, and metallicity, $0.5\, \mathrm{Z}_{\odot} \le Z \le 2\,
\mathrm{Z}_{\odot}$, where $\mathrm{M}_{\odot}$ and $\mathrm{Z}_{\odot}$ are
the solar mass and metallicity, respectively. Our model, using the observed
torque in the present solar wind, nicely explains both the current solar
rotation and the average trend of the rotation of solar-type stars, including
the dependence on metallicity. In addition, our model naturally reproduces the
observed trend of the weakened magnetic braking in old slowly rotating
solar-type stars because strong equator-fast DR becomes reduced. Our results
indicate that LDR and its transition are essential factors that control the
stellar spin down.",2211.13522v3
2023-04-13,The dark Stodolsky effect: constraining effective dark matter operators with spin-dependent interactions,"We present a comprehensive discussion of the Stodolsky effect for dark matter
(DM), and discuss two techniques to measure the effect and constrain the DM
parameter space. The Stodolsky effect is the spin-dependent shift in the energy
of a Standard Model (SM) fermion sitting in a bath of neutrinos. This effect,
which scales linearly in the effective coupling, manifests as a small torque on
the SM fermion spin and has historically been proposed as a method of detecting
the cosmic neutrino background. We generalise this effect to DM, and give
expressions for the induced energy shifts for DM candidates from spin-$0$ to
spin-$\frac 32$, considering all effective operators up to mass dimension-6. In
all cases, the effect scales inversely with the DM mass, but requires an
asymmetric background. We show that a torsion balance experiment is sensitive
to energy shifts of $\Delta E \gtrsim 10^{-28}\,\mathrm{eV}$, whilst a more
intricate setup using a SQUID magnetometer is sensitive to shifts of $\Delta E
\gtrsim 10^{-32}\,\mathrm{eV}$. Finally, we compute the energy shifts for a
model of scalar DM, and demonstrate that the Stodolsky effect can be used to
constrain regions of parameter space that are not presently excluded.",2304.06750v2
2023-09-05,Relativistic magnetic interactions from non-orthogonal basis sets,"We propose a method to determine the magnetic exchange interaction and
on-site anisotropy tensors of extended Heisenberg spin models from density
functional theory including relativistic effects. The method is based on the
Liechtenstein-Katsnelson-Antropov-Gubanov torque formalism, whereby energy
variations upon infinitesimal rotations are performed. We assume that the
Kohn-Sham Hamiltonian is expanded in a non-orthogonal basis set of
pseudo-atomic orbitals. We define local operators that are both hermitian and
satisfy relevant sum rules. We demonstrate that in the presence of spin-orbit
coupling a correct mapping from the density functional total energy to a spin
model that relies on the rotation of the exchange field part of the Hamiltonian
can not be accounted for by transforming the full Hamiltonian. We derive a set
of sum rules that pose stringent validity tests on any specific calculation. We
showcase the flexibility and accuracy of the method by computing the exchange
and anisotropy tensors of both well-studied magnetic nanostructures and of
recently synthesized two-dimensional magnets. Specifically, we benchmark our
approach against the established Korringa-Kohn-Rostoker Green's function method
and show that they agree well. Finally, we demonstrate how the application of
biaxial strain on the two-dimensional magnet T-CrTe2 can trigger a magnetic
phase transition.",2309.02558v3
2023-10-20,X-Type Antiferromagnets,"Magnetically ordered materials reveal various types of magnetic moment
alignment that affects their functional properties. This makes the exploration
of unconventional magnetic orderings promising for the discovery of new
physical phenomena and spintronic applications. Here, we introduce cross-chain
antiferromagnets, dubbed X-type antiferromagnets, as an uncharted class of
magnetically ordered crystals, where the stacking of two magnetic sublattices
form an orthogonal pattern of intersecting atomic chains. These largely
unexplored X-type antiferromagnets reveal unique spin-dependent transport
properties that are not present in conventional magnets. Using $\beta$-Fe2PO5
as a representative example of such X-type antiferromagnets, we predict the
emergence of sublattice-selective spin-polarized transport, where one magnetic
sublattice is conducting, while the other is not. As a result, spin torque can
be exerted solely on a single sublattice, leading to unconventional ultrafast
dynamics of the N\`eel vector capable of deterministic switching of the
antiferromagnetic domains. Our work uncovers a previously overlooked type of
magnetic moment alignment in antiferromagnets and reveals sublattice-selective
physical properties promising for high-performance spintronic applications.",2310.13271v1
2023-11-14,Berry curvature induced giant intrinsic spin-orbit torque in single layer magnetic Weyl semimetal thin films,"Topological quantum materials can exhibit unconventional surface states and
anomalous transport properties, but their applications to spintronic devices
are restricted as they require the growth of high-quality thin films with
bulk-like properties. Here, we study 10--30 nm thick epitaxial ferromagnetic
Co$_{\rm 2}$MnGa films with high structural order. Very high values of the
anomalous Hall conductivity, $\sigma_{\rm xy}=1.35\times10^{5}$ $\Omega^{-1}
m^{-1}$, and the anomalous Hall angle, $\theta_{\rm H}=15.8\%$, both comparable
to bulk values. We observe a dramatic crystalline orientation dependence of the
Gilbert damping constant of a factor of two and a giant intrinsic spin Hall
conductivity, $\mathit{\sigma_{\rm SHC}}=(6.08\pm 0.02)\times 10^{5}$
($\hbar/2e$) $\Omega^{-1} m^{-1}$, which is an order of magnitude higher than
literature values of single-layer Ni$_{\rm 80}$Fe$_{\rm 20}$, Ni, Co, Fe, and
multilayer Co$_{\rm 2}$MnGa stacks. Theoretical calculations of the intrinsic
spin Hall conductivity, originating from a strong Berry curvature, corroborate
the results and yield values comparable to the experiment. Our results open up
for the design of spintronic devices based on single layers of topological
quantum materials.",2311.08145v2
2024-02-14,Rapid spin changes around a magnetar fast radio burst,"Magnetars are neutron stars with extremely high magnetic fields that exhibit
various X-ray phenomena such as sporadic sub-second bursts, long-term
persistent flux enhancements, and variable rates of rotation period change. In
2020, a fast radio burst (FRB), akin to cosmological millisecond-duration radio
bursts, was detected from the Galactic magnetar SGR 1935+2154, confirming the
long-suspected association between some FRBs and magnetars. However, the
mechanism for FRB generation in magnetars remains unclear. Here we report the
X-ray discovery of an unprecedented double glitch in SGR 1935+2154 within a
time interval of approximately nine hours, bracketing an FRB that occurred on
October 14, 2022. Each glitch involved a significant increase in the magnetar's
spin frequency, being among the largest abrupt changes in neutron star rotation
ever observed. Between the glitches, the magnetar exhibited a rapid spin-down
phase, accompanied by a profound increase and subsequent decline in its
persistent X-ray emission and burst rate. We postulate that a strong,
ephemeral, magnetospheric wind provides the torque that rapidly slows the
star's rotation. The trigger for the first glitch couples the star's crust to
its magnetosphere, enhances the various X-ray signals, and spawns the wind that
alters magnetospheric conditions that might produce the FRB.",2402.09291v1
2024-02-20,Gimbal Actuator Modeling for a Spin-Stabilized Spacecraft Equipped with a 1DoF Gimbaled-Thruster and two Reaction Wheels,"Attitude control of spacecraft during an impulsive orbital maneuver is a
vital task. Many spacecraft and launchers use the gimbaled thrust vector
control (TVC) in their attitude control system during an orbital maneuver.
Mathematical modeling of the gimbal actuator is an important task because we
should show the applicability of the gimbaled-TVC in a spacecraft. In this
paper, a spin-stabilized spacecraft equipped with one degree of freedom (DoF)
gimbaled-thruster and two reaction wheels (RWs) is considered. The control
goals are disturbance rejection and thrust vector (spin-axis) stabilization
based on one DoF gimbal actuator and two RWs. The gimbal is assumed to be
equipped with a gearbox and a DC electric motor. This actuator must supply the
gimbal torque to rotate the spacecraft nozzle. The mathematical model of the
mentioned spacecraft is extended with respect to the DC motor equations. In
order to investigate the applicability of the proposed method, an industrial DC
electric motor is considered for the gimbal actuator. The simulation results
prove that an industrial DC electric motor is able to be used for attitude
control of the mentioned spacecraft. The simulation results indicate the
applicability of the proposed control method in an impulsive orbital maneuver.",2402.12922v1
2024-03-19,Interlayer Dzyaloshinskii-Moriya interaction in synthetic ferrimagnets,"The antisymmetric interlayer exchange interaction, i.e., interlayer
Dzyaloshinskii-Moriya interaction (IL-DMI) has attracted significant interest
since this long-range chiral spin interaction provides a new dimension for
controlling spin textures and dynamics. However, the role of IL-DMI in the
field induced and spin-orbit torque (SOT) induced switching of synthetic
ferrimagnets (SFi) has not been uncovered. Here, we exploit interlayer chiral
exchange bias fields in SFi to address both the sign and magnitude of the
IL-DMI. Depending on the degree of imbalance between the two magnetic moments
of the SFi, the amount of asymmetry, addressed via loop shifts of the
hysteresis loops under an in-plane field reveals a unidirectional and chiral
nature of the IL-DMI. The devices are then tested with SOT switching
experiments and the process is examined via both transient state and steady
state detection. In addition to field-free SOT switching, we find that the
combination of IL-DMI and SOT give rise to multi-resistance states, which
provides a possible direction for the future design of neuromorphic computing
devices based on SOT. This work is a step towards characterizing and
understanding the IL-DMI for spintronic applications.",2403.12642v1
1992-04-16,Microcanonical cluster algorithms,"I propose a numerical simulation algorithm for statistical systems which
combines a microcanonical transfer of energy with global changes in clusters of
spins. The advantages of the cluster approach near a critical point augment the
speed increases associated with multi-spin coding in the microcanonical
approach. The method also provides a limited ability to tune the average
cluster size.",9204005v1
2002-12-20,High-energy spin effects and structure of elastic scattering amplitude,"A behavior of imaginary and real parts of the high-energy elastic hadron
scattering amplitude is examined in the diffraction region. It is shown that
the interference between Coulomb and hadronic scattering at small momentum
transfers and especially in the region of diffractive minimum can bring some
information about the structure of the hadron spin-non-flip amplitude.",0212313v1
2007-12-15,Local control of entanglement in a spin chain,"In a ferromagnetic spin chain, the control of the local effective magnetic
field allows to manipulate the static and dynamical properties of entanglement.
In particular, the propagation of quantum correlations can be driven to a great
extent so as to achieve an entanglement transfer on demand toward a selected
site.",0712.2509v1
2010-03-23,Spin Angular Momentum Evolution of the Long Period Algols,"We consider the spin angular momentum evolution of the accreting components
of Algol-type binary stars. In wider Algols the accretion is through a disc so
that the accreted material can transfer enough angular momentum to the gainer
that material at its equator should be spinning at break-up. We demonstrate
that even a small amount of mass transfer, much less than required to produce
today's mass ratios, transfers enough angular momentum to spin the gainer up to
this critical rotation velocity. However the accretors in these systems have
spins typically between 10 and $40\,$per cent of the critical rate. So some
mechanism for angular momentum loss from the gainers is required. We consider
generation of magnetic fields in the radiative atmospheres in a differentially
rotating star and the possibility of angular momentum loss driven by strong
stellar winds in the intermediate mass stars, such as the primaries of the
Algols. Differential rotation, induced by the accretion itself, may produce
such winds which carry away enough angular momentum to reduce their rotational
velocities to the today's observed values. We apply this model to two systems
with initial periods of 5\,d, one with initial masses 5 and $3\,\rm{M}_{\odot}$
and the other with 3.2 and $2\,\rm{M}_{\odot}$. Our calculations show that, if
the mass outflow rate in the stellar wind is about $10\,$per cent of the
accretion rate and the dipole magnetic field is stronger than about $1\,$kG,
the spin rate of the gainer is reduced to below break-up velocity even in the
fast phase of mass transfer. Larger mass loss is needed for smaller magnetic
fields. The slow rotation of the gainers in the classical Algol systems is
explained by a balance between the spin-up by mass accretion and spin-down by a
stellar wind linked to a magnetic field.",1003.4392v1
2010-07-26,Thermodynamics of classical frustrated spin chain at the ferromagnet-helimagnet transition point,"Low-temperature thermodynamics of the classical frustrated ferromagnetic spin
chain is studied. Using transfer-matrix method we found the behavior of the
correlation function and zero-field susceptibility at the ferromagnetic-helical
transition point. It is shown that the critical exponent for the susceptibility
is changed from 2 to 4/3 at the transition point.",1007.4536v1
2010-08-02,Spin Matrix for the Scaled Periodic Ising Model,"The matrix elements of the spin operator for the periodic Ising model in a
basis of eigenvectors for the transfer matrix are calculated in the massive
scaling limit.",1008.0352v2
2011-03-21,Eigenspaces of the Spin Dirac operator over S^3,"We calculate the spectrum and a basis of eigenvectors for the Spin Dirac
operator over the standard 3-sphere. For the spectrum, we use the method of
Hitchin which we transfer to quaternions and explain in more detail. The
eigenbasis (in terms of polynomials) will be computed by means of
representations of sl(2,C).",1103.4097v2
2011-03-28,On the origin of high- spin states in nuclear fission fragments,"In the ""nucleon-phase"" model of binary fission, the transfer of nucleons
between an A =126 {\guillemotleft} nucleon core {\guillemotright} and the
primordial ""cluster"" can explain both the formation of high- spin states and
the saw-tooth behavior of the variation, as a function of fragment mass, of the
average angular momentum.",1103.5341v1
2016-05-30,On the Coupling of Photon Spin to Electron Orbital Angular Momentum,"Partially gold coated 90 degree glass wedges and a semi - infinite slit in a
thin film of gold ending in a conducting nano-junction serve as samples to
investigate the transfer of photon spin to electron orbital angular momentum.
These structures were specifically designed as samples where an incident beam
of light is retroreflected. Since in the process of retroreflection the turning
sense of a circularly polarized beam of light does not change and the direction
of propagation is inverted, the photon spin is inverted. Due to conservation of
angular momentum a transfer of photon spin to electron orbital angular momentum
of conduction electrons occurs. In the structures a circular movement of
electrons is blocked and therefore the transfered spin can be detected as a
photovoltage due to an electromotive force which is induced by the transfer of
angular momentum. Depending on the polarization of the incident beam, a maximum
photovoltage of about 0,2 micro V was measured for both structures. The results
are interpreted in terms of a classical electrodynamic model of the
monochromatic linearly polarized photon as a propagating solitary
electromagnetic wave of finite energy hf which carries an angular momentum
h/2pi which is elaborated elsewhere where h is Plancks constant and f the
frequency of light. The relative values of the measured photovoltages for
different polarizations can well be explained by the electrodynamic model of a
photon and an associated spin angular momentum. The absolute values of the
measured photovoltages are also consistent with the interpretation. The
observed effects are closely related to the lateral Fedorov Imbert shift of
focused beams in optics and the optical spin Hall effect and to other non
linear optical effects such as the inverse faraday effect for which a new
interpretation is given here in terms of the electrodynamic model of the photon
and its spin.",1609.05218v1
2016-10-15,Exact State Revival in a Spin Chain with Next-To-Nearest Neighbour Interactions,"An extension with next-to-nearest neighbour interactions of the simplest XX
spin chain with perfect state transfer (PST) is presented. The conditions for
PST and entanglement generation (balanced fractional revival) can be obtained
exactly and are discussed.",1610.04796v1
2022-06-18,Diffuse scattering on Ising chain with competing interactions,"We considered the Ising 1D chain in an external magnetic field taking into
account the nearest and next-nearest neighbor interactions. By the method of
Kramers--Wannier transfer-matrix, the rigorous analytical expression for
Fourier-transform of pair spin-spin correlation function was obtained, and the
temperature evolution of the scattering was analyzed for various relations of
exchange parameters.",2206.09181v1
2005-09-13,Light scattering in Cooper-paired Fermi atoms,"We present a detailed theoretical study of light scattering off superfluid
trapped Fermi gas of atoms at zero temperature. We apply Nambu-Gorkov formalism
of superconductivity to calculate the response function of superfluid gas due
to stimulated light scattering taking into account the final state
interactions. The polarization of light has been shown to play a significant
role in response of Cooper-pairs in the presence of a magnetic field.
Particularly important is a scheme of polarization-selective light scattering
by either spin-component of the Cooper-pairs leading to the single-particle
excitations of one spin-component only. These excitations have a threshold of
$2\Delta$ where $\Delta$ is the superfluid gap energy. Furthermore,
polarization-selective light scattering allows for unequal energy and momentum
transfer to the two partner atoms of a Cooper-pair. In the regime of low energy
($<< 2\Delta$) and low momentum ($<2\Delta/(\hbar v_F)$, $v_F$ being the Fermi
velocity) transfer, a small difference in momentum transfers to the two
spin-components may be useful in exciting Bogoliubov-Anderson phonon mode. We
present detailed results on the dynamic structure factor (DSF) deduced from the
response function making use of generalized fluctuation-dissipation theorem.
Model calculations using local density approximation for trapped superfluid
Fermi gas shows that when the energy transfer is less than $2\Delta_0$, where
$\Delta_0$ refers to the gap at the trap center, DSF as a function of energy
transfer has reduced gradient compared to that of normal Fermi gas.",0509328v2
2014-08-08,Ultrafast electronic read-out of diamond NV centers coupled to graphene,"Nonradiative transfer processes are often regarded as loss channels for an
optical emitter1, since they are inherently difficult to be experimentally
accessed. Recently, it has been shown that emitters, such as fluorophores and
nitrogen vacancy centers in diamond, can exhibit a strong nonradiative energy
transfer to graphene. So far, the energy of the transferred electronic
excitations has been considered to be lost within the electron bath of the
graphene. Here, we demonstrate that the trans-ferred excitations can be
read-out by detecting corresponding currents with picosecond time resolution.
We electrically detect the spin of nitrogen vacancy centers in diamond
electronically and con-trol the nonradiative transfer to graphene by electron
spin resonance. Our results open the avenue for incorporating nitrogen vacancy
centers as spin qubits into ultrafast electronic circuits and for harvesting
non-radiative transfer processes electronically.",1408.1864v1
1996-05-09,Radiative Torques on Interstellar Grains: I. Superthermal Spinup,"Irregular dust grains are subject to radiative torques when irradiated by
interstellar starlight. It is shown how these radiative torques may be
calculated using the discrete dipole approximation. Calculations are carried
out for one irregular grain geometry, and three different grain sizes. It is
shown that radiative torques can play an important dynamical role in spinup of
interstellar dust grains, resulting in rotation rates which may exceed even
those expected from H_2 formation on the grain surface. Because the radiative
torque on an interstellar grain is determined by the overall grain geometry
rather than merely the state of the grain surface, the resulting superthermal
rotation is expected to be long-lived. By itself, long-lived superthermal
rotation would permit grain alignment by normal paramagnetic dissipation on the
""Davis-Greenstein"" timescale. However, radiative torques arising from
anisotropy of the starlight background can act directly to alter the grain
alignment on much shorter timescales, and are therefore central to the process
of interstellar grain alignment.
  Radiative torques depend strongly on the grain size, measured by a_eff, the
radius of a sphere of equal volume. In diffuse clouds, radiative torques
dominate the torques due to H2 formation for a_eff=0.2micron grains, but are
relatively unimportant for a_eff<0.05micron grains. This may provide a natural
explanation for the observation that $a_eff>0.1 micron grains in diffuse clouds
are aligned, while there is little alignment of a_eff < 0.05 micron grains. We
show that radiative torques are ineffective at producing superthermal rotation
within quiescent dark clouds, but can be very effective in star-forming regions
such as the M17 molecular cloud.",9605046v1
2010-09-09,Saturated torque formula for planetary migration in viscous disks with thermal diffusion: recipe for protoplanet population synthesis,"We provide torque formulae for low mass planets undergoing type I migration
in gaseous disks. These torque formulae put special emphasis on the horseshoe
drag, which is prone to saturation: the asymptotic value reached by the
horseshoe drag depends on a balance between coorbital dynamics (which tends to
cancel out or saturate the torque) and diffusive processes (which tend to
restore the unperturbed disk profiles, thereby desaturating the torque). We
entertain here the question of this asymptotic value, and we derive torque
formulae which give the total torque as a function of the disk's viscosity and
thermal diffusivity. The horseshoe drag features two components: one which
scales with the vortensity gradient, and one which scales with the entropy
gradient, and which constitutes the most promising candidate for halting inward
type I migration. Our analysis, which is complemented by numerical simulations,
recovers characteristics already noted by numericists, namely that the viscous
timescale across the horseshoe region must be shorter than the libration time
in order to avoid saturation, and that, provided this condition is satisfied,
the entropy related part of the horseshoe drag remains large if the thermal
timescale is shorter than the libration time. Side results include a study of
the Lindblad torque as a function of thermal diffusivity, and a contribution to
the corotation torque arising from vortensity viscously created at the contact
discontinuities that appear at the horseshoe separatrices. For the convenience
of the reader mostly interested in the torque formulae, section 8 is
self-contained.",1009.1913v2
2010-09-16,Electrostatic Patch Effect in Cylindrical Geometry. III. Torques,"We continue to study the effect of uneven voltage distribution on two close
cylindrical conductors with parallel axes started in our papers [1] and [2],
now to find the electrostatic torques. We calculate the electrostatic potential
and energy to lowest order in the gap to cylinder radius ratio for an arbitrary
relative rotation of the cylinders about their symmetry axis. By energy
conservation, the axial torque, independent of the uniform voltage difference,
is found as a derivative of the energy in the rotation angle. We also derive
both the axial and slanting torques by the surface integration method: the
torque vector is the integral over the cylinder surface of the cross product of
the electrostatic force on a surface element and its position vector. The
slanting torque consists of two parts: one coming from the interaction between
the patch and the uniform voltages, and the other due to the patch interaction.
General properties of the torques are described. A convenient model of a
localized patch suggested in [2] is used to calculate the torques explicitly in
terms of elementary functions. Based on this, we analyze in detail patch
interaction for one pair of patches, namely, the torque dependence on the patch
parameters (width and strength) and their mutual positions. The effect of the
axial torque is then studied for the experimental conditions of the STEP
mission.",1009.3294v1
2012-06-13,On type-I migration near opacity transitions. A generalized Lindblad torque formula for planetary population synthesis,"We give an expression for the Lindblad torque acting on a low-mass planet
embedded in a protoplanetary disk that is valid even at locations where the
surface density or temperature profile cannot be approximated by a power law,
such as an opacity transition. At such locations, the Lindblad torque is known
to suffer strong deviation from its standard value, with potentially important
implications for type I migration, but the full treatment of the tidal
interaction is cumbersome and not well suited to models of planetary population
synthesis. The expression that we propose retains the simplicity of the
standard Lindblad torque formula and gives results that accurately reproduce
those of numerical simulations, even at locations where the disk temperature
undergoes abrupt changes. Our study is conducted by means of customized
numerical simulations in the low-mass regime, in locally isothermal disks, and
compared to linear torque estimates obtained by summing fully analytic torque
estimates at each Lindblad resonance. The functional dependence of our modified
Lindblad torque expression is suggested by an estimate of the shift of the
Lindblad resonances that mostly contribute to the torque, in a disk with sharp
gradients of temperature or surface density, while the numerical coefficients
of the new terms are adjusted to seek agreement with numerics. As side results,
we find that the vortensity related corotation torque undergoes a boost at an
opacity transition that can counteract migration, and we find evidence from
numerical simulations that the linear corotation torque has a non-negligible
dependency upon the temperature gradient, in a locally isothermal disk.",1206.2867v1
2020-11-25,Numerical study of coorbital thermal torques on cold or hot satellites,"We evaluate the thermal torques exerted on low-mass planets embedded in
gaseous protoplanetary discs with thermal diffusion, by means of
high-resolution three-dimensional hydrodynamics simulations. We confirm that
thermal torques essentially depend on the offset between the planet and its
corotation, and find a good agreement with analytic estimates when this offset
is small compared to the size of the thermal disturbance. For larger offsets
that may be attained in discs with a large pressure gradient or a small thermal
diffusivity, thermal torques tend toward an asymptotic value broadly compatible
with results from a dynamical friction calculation in an unsheared medium. We
perform a convergence study and find that the thermal disturbance must be
resolved over typically 10 zones for a decent agreement with analytic
predictions. We find that the luminosity at which the net thermal torque
changes sign matches that predicted by linear theory within a few percents. Our
study confirms that thermal torques usually supersede Lindblad and corotation
torques by almost an order of magnitude for low mass planets. As we increase
the planetary mass, we find that the ratio of thermal torques to Lindblad and
corotation torques is progressively reduced, and that the thermal disturbance
is increasingly distorted by the horseshoe flow. Overall, we find that thermal
torques are dominant for masses up to an order of magnitude larger than
implemented in recent models of planetary population synthesis. We finally
briefly discuss the case of stellar or intermediate-mass objects embedded in
discs around AGNs.",2011.12484v1
2021-08-10,The importance of thermal torques on the migration of planets growing by pebble accretion,"A key process in planet formation is the exchange of angular momentum between
a growing planet and the protoplanetary disc, which makes the planet migrate
through the disc. Several works show that in general low-mass and
intermediate-mass planets migrate towards the central star, unless corotation
torques become dominant. Recently, a new kind of torque, called the thermal
torque, was proposed as a new source that can generate outward migration of
low-mass planets. While the Lindblad and corotation torques depend mostly on
the properties of the protoplanetary disc and on the planet mass, the thermal
torque depends also on the luminosity of the planet, arising mainly from the
accretion of solids. Thus, the accretion of solids plays an important role not
only in the formation of the planet but also in its migration process. In a
previous work, we evaluated the thermal torque effects on planetary growth and
migration mainly in the planetesimal accretion paradigm. In this new work, we
study the role of the thermal torque within the pebble accretion paradigm.
Computations are carried out consistently in the framework of a global model of
planet formation that includes disc evolution, dust growth and evolution, and
pebble formation. We also incorporate updated prescriptions of the thermal
torque derived from high resolution hydrodynamical simulations. Our simulations
show that the thermal torque generates extended regions of outward migration in
low viscosity discs. This has a significant impact in the formation of the
planets.",2108.04880v1
2023-06-12,Torque wiggles -- a robust feature of the global disc-planet interaction,"Gravitational coupling between planets and protoplanetary discs is
responsible for many important phenomena such as planet migration and gap
formation. The key quantitative characteristics of this coupling is the
excitation torque density -- the torque (per unit radius) imparted on the disc
by planetary gravity. Recent global simulations and linear calculations found
an intricate pattern of low-amplitude, quasi-periodic oscillations in the
global radial distribution of torque density in the outer disc, which we call
torque wiggles. Here we show that torque wiggles are a robust outcome of global
disc-planet interaction and exist despite the variation of disc parameters and
thermodynamic assumptions (including $\beta$-cooling). They result from
coupling of the planetary potential to the planet-driven density wave freely
propagating in the disc. We developed analytical theory of this phenomenon
based on approximate self-similarity of the planet-driven density waves in the
outer disc. We used it, together with linear calculations and simulations, to
show that (a) the radial periodicity of the wiggles is determined by the global
shape of the planet-driven density wave (its wrapping in the disc) and (b) the
sharp features in the torque density distribution result from constructive
interference of different azimuthal (Fourier) torque contributions at radii
where the planetary wake crosses the star-planet line. In the linear regime the
torque wiggles represent a weak effect, affecting the total (integrated) torque
by only a few per cent. However, their significance should increase in the
non-linear regime, when a gap (or a cavity) forms around the perturber's orbit.",2306.07341v1
2024-02-17,MOB-Net: Limb-modularized Uncertainty Torque Learning of Humanoids for Sensorless External Torque Estimation,"Momentum observer (MOB) can estimate external joint torque without requiring
additional sensors, such as force/torque or joint torque sensors. However, the
estimation performance of MOB deteriorates due to the model uncertainty which
encompasses the modeling errors and the joint friction. Moreover, the
estimation error is significant when MOB is applied to high-dimensional
floating-base humanoids, which prevents the estimated external joint torque
from being used for force control or collision detection in the real humanoid
robot. In this paper, the pure external joint torque estimation method named
MOB-Net, is proposed for humanoids. MOB-Net learns the model uncertainty torque
and calibrates the estimated signal of MOB. The external joint torque can be
estimated in the generalized coordinate including whole-body and virtual joints
of the floating-base robot with only internal sensors (an IMU on the pelvis and
encoders in the joints). Our method substantially reduces the estimation errors
of MOB, and the robust performance of MOB-Net for the unseen data is validated
through extensive simulations, real robot experiments, and ablation studies.
Finally, various collision handling scenarios are presented using the estimated
external joint torque from MOB-Net: contact wrench feedback control for
locomotion, collision detection, and collision reaction for safety.",2402.11221v1
2024-03-02,Automated Continuous Force-Torque Sensor Bias Estimation,"Six axis force-torque sensors are commonly attached to the wrist of serial
robots to measure the external forces and torques acting on the robot's
end-effector. These measurements are used for load identification, contact
detection, and human-robot interaction amongst other applications. Typically,
the measurements obtained from the force-torque sensor are more accurate than
estimates computed from joint torque readings, as the former is independent of
the robot's dynamic and kinematic models. However, the force-torque sensor
measurements are affected by a bias that drifts over time, caused by the
compounding effects of temperature changes, mechanical stresses, and other
factors. In this work, we present a pipeline that continuously estimates the
bias and the drift of the bias of a force-torque sensor attached to the wrist
of a robot. The first component of the pipeline is a Kalman filter that
estimates the kinematic state (position, velocity, and acceleration) of the
robot's joints. The second component is a kinematic model that maps the
joint-space kinematics to the task-space kinematics of the force-torque sensor.
Finally, the third component is a Kalman filter that estimates the bias and the
drift of the bias of the force-torque sensor assuming that the inertial
parameters of the gripper attached to the distal end of the force-torque sensor
are known with certainty.",2403.01068v1
2018-02-26,Automatic spin-chain learning to explore the quantum speed limit,"One of the ambitious goals of artificial intelligence is to build a machine
that outperforms human intelligence, even if limited knowledge and data are
provided. Reinforcement Learning (RL) provides one such possibility to reach
this goal. In this work, we consider a specific task from quantum physics, i.e.
quantum state transfer in a one-dimensional spin chain. The mission for the
machine is to find transfer schemes with fastest speeds while maintaining high
transfer fidelities. The first scenario we consider is when the Hamiltonian is
time-independent. We update the coupling strength by minimizing a loss function
dependent on both the fidelity and the speed. Compared with a scheme proven to
be at the quantum speed limit for the perfect state transfer, the scheme
provided by RL is faster while maintaining the infidelity below $5\times
10^{-4}$. In the second scenario where a time-dependent external field is
introduced, we convert the state transfer process into a Markov decision
process that can be understood by the machine. We solve it with the deep
Q-learning algorithm. After training, the machine successfully finds transfer
schemes with high fidelities and speeds, which are faster than previously known
ones. These results show that Reinforcement Learning can be a powerful tool for
quantum control problems.",1802.09248v2
2000-01-25,"$Λ$, $\barΛ$ Polarization and Spin Transfer in Lepton Deep-Inelastic Scattering","The flavor and helicity distributions of the $\Lambda$ and $\bar{\Lambda}$
hyperons for both valence and sea quarks are calculated in a perturbative QCD
(pQCD) based model. We relate these quark distributions to the fragmentation
functions of the $\Lambda$ and $\bar{\Lambda}$, and calculate the
$z$-dependence of the longitudinal spin transfer to the $\Lambda$ and
$\bar{\Lambda}$ in lepton deep-inelastic scattering (DIS). It is shown that the
spin transfer to the $\Lambda$ is compatible with the first HERMES results at
DESY and further tests are suggested. We also make predictions for the
$z$-dependence of the $\Lambda$ and $\bar{\Lambda}$ longitudinal polarizations
in neutrino (antineutrino) DIS processes. We investigate the sea contribution
to the fragmentation functions, and we test a possible scenario where sea
quarks in $\Lambda$ (or sea antiquarks in $\bar{\Lambda}$) are negatively
polarized, whereas sea antiquarks in the $\Lambda$ (or sea quarks in
$\bar{\Lambda}$) are positively polarized. The asymmetry of the polarized
fragmentation functions of sea quarks and antiquarks to $\Lambda$ and
$\bar{\Lambda}$ provides a way to understand the different behaviour between
the $\Lambda$ and $\bar{\Lambda}$ spin transfers observed in the recent E665
experiment at FNAL.",0001259v4
2023-09-15,Emergence of π-Magnetism in Fused Aza-Triangulenes: Symmetry and Charge Transfer Effects,"On-surface synthesis has paved the way towards the fabrication and
characterization of conjugated carbon-based molecular materials that exhibit
{\pi}-magnetism such as triangulenes. Aza-triangulene, a nitrogen-substituted
derivative, was recently shown to display rich on-surface chemistry, offering
an ideal platform to investigate structure-property relations regarding
spin-selective charge transfer and magnetic fingerprints. Herein, we study
electronic changes upon fusing single molecules into larger dimeric
derivatives. We show that the closed-shell structure of aza-triangulene on
Ag(111) leads to closed-shell dimers covalently coupled through sterically
accessible carbon atoms. Meanwhile, its open-shell structure on Au(111) leads
to coupling via atoms displaying high spin density, resulting in symmetric or
asymmetric dimer products. Interestingly, whereas all fused products on Au(111)
exhibit similar charge transfer properties, only asymmetric dimers show
magnetic fingerprints. We rationalize this in terms of molecular bonding
structure and {\pi}-conjugation: in contrast to the symmetric and highly
conjugated dimer, asymmetric dimers display more localized orbitals, which
result in a larger Coulomb repulsion and thus promote single electron
occupancies with associated spin density and {\pi}-magnetism. These results
expose a clear relationship between molecular symmetry, charge transfer, and
spin states in {\pi}-conjugated carbon-based nanostructures.",2309.08492v1
2024-04-10,Uncovering quantum characteristics of incipient evolutions at the photosynthetic oxygen evolving complex,"Water oxidation of photosynthesis at the oxygen evolving complex (OEC) is
driven by the polarization field induced by the photoelectric hole. By
highlighting the role of the polarization field in reshaping the spin-orbit
coupling deduced from the Dirac quantum mechanics, we reveal in this work the
characteristics and underlying mechanism in the relatively simpler OEC
evolutions within the states S0 - S2 prior to the water oxidation. The
characteristic shifts of the density of states (DOS) of the electron donor Mn
atom are observed in the vicinity of the Fermi surface to occur with the spin
flips of Mn atoms and the change of the Mn oxidation states during the electron
transfer. Notably, the spin flips of Mn atoms point to the resulting spin
configuration of the next states. It is found that the electron transfer tend
to stabilize the catalyst OEC itself, whereas the proton transfer pushes the
evolution forward by preparing a new electron donor. Meanwhile, it shows that
the Mn-O bonds around the candidate Mn atom of the electron donor undergo
characteristic changes in the bond lengths during the electron transfer. These
concomitant phenomena uncovered in first-principle calculations characterize
the essential equilibrium of the OEC between the state evolution and stability
that forms a ground of the dynamic OEC cycles.",2404.07048v1
2003-06-11,Electron transfer rates for asymmetric reactions,"We use a numerically exact real-time path integral Monte Carlo scheme to
compute electron transfer dynamics between two redox sites within a spin-boson
approach. The case of asymmetric reactions is studied in detail in the least
understood crossover region between nonadiabatic and adiabatic electron
transfer. At intermediate-to-high temperature, we find good agreement with
standard Marcus theory, provided dynamical recrossing effects are captured. The
agreement with our data is practically perfect when temperature renormalization
is allowed. At low temperature we find peculiar electron transfer kinetics in
strongly asymmetric systems, characterized by rapid transient dynamics and
backflow to the donor.",0306269v1
2006-10-12,A Q-operator for the quantum transfer matrix,"Baxter's Q-operator for the quantum transfer matrix of the XXZ spin-chain is
constructed employing the representation theory of quantum groups. The spectrum
of this Q-operator is discussed and novel functional relations which describe
the finite temperature regime of the XXZ spin-chain are derived. For
non-vanishing magnetic field the previously known Bethe ansatz equations can be
replaced by a system of quadratic equations which is an important advantage for
numerical studies. For vanishing magnetic field and rational coupling values it
is argued that the quantum transfer matrix exhibits a loop algebra symmetry
closely related to the one of the classical six-vertex transfer matrix at roots
of unity.",0610028v2
2007-06-27,Analytic Bethe Ansatz and Baxter equations for long-range psl(2|2) spin chain,"We study the largest particle-number-preserving sector of the dilatation
operator in maximally supersymmetric gauge theory. After exploring one-loop
Bethe Ansatze for the underlying spin chain with psl(2|2) symmetry for simple
root systems related to several Kac-Dynkin diagrams, we use the analytic Bethe
Anzats to construct eigenvalues of transfer matrices with finite-dimensional
atypical representations in the auxiliary space. We derive closed Baxter
equations for eigenvalues of nested Baxter operators. We extend these
considerations for a non-distinguished root system with FBBF grading to all
orders of perturbation theory in 't Hooft coupling. We construct generating
functions for all transfer matrices with auxiliary space determined by Young
supertableaux (1^a) and (s) and find determinant formulas for transfer matrices
with auxiliary spaces corresponding to skew Young supertableaux. The latter
yields fusion relations for transfer matrices with auxiliary space
corresponding to representations labelled by square Young supertableaux. We
derive asymptotic Baxter equations which determine spectra of anomalous
dimensions of composite Wilson operators in noncompact psl(2|2) subsector of
N=4 super-Yang-Mills theory.",0706.4121v1
2015-02-14,The Entanglement Level and the Detection of Quantum Data Transfer Correctness in Short Qutrit Spin Chains,"The quantum entanglement is an important feature of many protocols in the
field of quantum computing. In this paper we evaluate a level of entanglement
in short qutrit chains. This evaluation is carried out with use of the CCNR
criterion and the concurrence measure. We also present some explicit formulae
describing the values of CCNR criterion and concurrence for exemplary short
spin chains. Utilizing the obtained results, we indicate that analyzing the
level of entanglement allows to detect the noise or deviation in the transfer
process, in comparison to the perfect transfer where only operation realizing
transfer is present.",1502.04257v4
2019-07-29,Near-field energy transfer between a luminescent 2D material and color centers in diamond,"Energy transfer between fluorescent probes lies at the heart of many
applications ranging from bio-sensing and -imaging to enhanced photo-detection
and light harvesting. In this work, we study F\""orster resonance energy
transfer (FRET) between shallow defects in diamond --- nitrogen-vacancy (NV)
centers --- and atomically-thin, two-dimensional materials --- tungsten
diselenide (WSe$_2$). By means of fluorescence lifetime imaging, we demonstrate
the occurrence of FRET in the WSe$_2$/NV system. Further, we show that in the
coupled system, NV centers provide an additional excitation pathway for WSe$_2$
photoluminescence. Our results constitute the first step towards the
realization of hybrid quantum systems involving single-crystal diamond and
two-dimensional materials that may lead to new strategies for studying and
controlling spin transfer phenomena and spin valley physics.",1907.12248v2
2019-09-18,Population transfer via a dissipative structural continuum,"We propose a model to study quantum population transfer via a structural
continuum. The model is composed of two spins which are coupled to two bosonic
modes separately by two control pulses, and the two bosonic modes are coupled
to a common structural continuum. We show that efficient population transfer
can be achieved between the two spins by using a multi-level stimulated Raman
adiabatic passage (STIRAP) across the continuum, which we refer to as straddle
STIRAP via continuum. We also consider the stability of this model against
different control parameters and show that efficient population transfer can be
achieved even in presence a moderate dissipation.",1909.08481v2
2020-01-10,Multipartite entanglement transfer in spin chains,"We investigate the transfer of genuine multipartite entanglement across a
spin-1/2 chain with nearest-neighbor XX-type interaction. We focus on the
perturbative regime, where a block of spins is weakly coupled at each edge of a
quantum wire, embodying the role of a multiqubit sender and receiver,
respectively. We find that high-quality multipartite entanglement transfer is
achieved at the same time that three excitations are transferred to the
opposite edge of the chain. Moreover, we find that both a finite concurrence
and tripartite negativity is attained at much shorter time, making
GHZ-distillation protocols feasible. Finally, we investigate the robustness of
our protocol with respect to non-perturbative couplings and increasing lengths
of the quantum wire.",2001.03529v1
2021-11-16,Helicity transfer in strong laser fields via the electron anomalous magnetic moment,"Electron beam longitudinal polarization during the interaction with
counterpropagating circularly-polarized ultraintense laser pulses is
investigated, while accounting for the anomalous magnetic moment of the
electron. Although it is known that the helicity transfer from the laser
photons to the electron beam is suppressed in linear and nonlinear Compton
scattering processes, we show that the helicity transfer nevertheless can
happen via an intermediate step of the electron radiative transverse
polarization, phase-matched with the driving field, followed up by spin
rotation into the longitudinal direction as induced by the anomalous magnetic
moment of the electron. With spin-resolved QED Monte Carlo simulations, we
demonstrate the consequent helicity transfer from laser photons to the electron
beam with a degree up to 10%, along with an electron radial polarization up to
65% after multiple photon emissions in a femtosecond timescale. This effect is
detectable with currently achievable laser facilities, evidencing the role of
the leading QED vertex correction to the electron anomalous magnetic moment in
the polarization dynamics in ultrastrong laser fields.",2111.08167v2
2021-12-10,Effect of Emitters on Quantum State Transfer in Coupled Cavity Arrays,"Over the last decade, conditions for perfect state transfer in quantum spin
chains have been discovered, and their experimental realizations addressed. In
this paper, we consider an extension of such studies to quantum state transfer
in a coupled cavity array including the effects of atoms in the cavities which
can absorb and emit photons as they propagate down the array. Our model is
equivalent to previously examined spin chains in the one-excitation sector and
in the absence of emitters. We introduce a Monte Carlo approach to the inverse
eigenvalue problem which allows the determination of the inter-cavity and
cavity-emitter couplings resulting in near-perfect quantum state transfer
fidelity, and examine the time dependent polariton wave function through exact
diagonalization of the resulting Tavis-Cummings-Hubbard Hamiltonian. The effect
of inhomogeneous emitter locations is also evaluated.",2112.05740v2
2022-09-01,The spin-up of a star gaining mass in a close binary system on the thermal time scale,"We investigate the exchange of mass in a binary system as a channel through
which a Be star can receive a rapid rotation. The mass-transfer phase in a
massive close binary system in the Hertzsprung-gap is accompanied by the
spinning up of the accreting component. We consider a case when the mass of the
accreting component increases by 1.5 times. The component acquires mass and
angular momentum while in a state of critical rotation. The angular momentum of
the component increases by 50 times. Meridional circulation effectively
transports angular momentum inside the component during the mass-transfer phase
and during the thermal time scale after the end of the mass-transfer phase. As
a result of mass transfer, the component acquires the rotation typical of
classical Be stars.",2209.00270v1
2022-12-13,"Time transfer functions without enhanced terms in stationary spacetime -- Application to an isolated, axisymmetric spinning body","We develop a new perturbation method for determining a class of time transfer
functions in a stationary spacetime when its metric is a small deformation of a
background metric for which the time transfer functions are known in a closed
form. The perturbation terms are expressed as line integrals along the null
geodesic paths of the background metric. Unlike what happens with the other
procedures proposed until now, the time transfer functions obtained in this way
are completely free of unbounded terms and do not generate any enhancement in
the light travel time. Our procedure proves to be very efficient when the
background metric is a linearized Schwarzschild-like metric. Its application to
an isolated body slowly rotating about an axis of symmetry leads to integrals
which can be calculated with any symbolic computer program. Explicit
expressions are obtained for the mass dipole and quadrupole moments and for the
leading gravitomagnetic term induced by the spin of the body. A brief numerical
discussion is given for the 2002 Cassini experiment.",2212.06671v1
2023-03-24,Data-driven estimation of transfer integrals in undoped cuprates,"Undoped cuprates are an abundant class of magnetic insulators, in which the
synergy of rich chemistry and sizable quantum fluctuations leads to a variety
of magnetic behaviors. Understanding the magnetism of these materials is
impossible without the knowledge of the underlying spin model. The typically
dominant antiferromagnetic superexchanges can be accurately estimated from the
respective electronic transfer integrals. Density functional theory
calculations mapped onto an effective one-orbital model in the Wannier basis
are an accurate, albeit computationally cumbersome method to estimate such
transfer integrals in cuprates. We demonstrate that instead an Artificial
Neural Network (ANN), trained on the results of high-throughput calculations,
can predict the transfer integrals using the crystal structure as the only
input. Descriptors of the ANN model encode the spatial configuration and the
chemical composition of the local crystalline environment. A virtual toolbox
employing our model can be readily employed to determine leading superexchange
paths as well as for rapidly assessing the relevant spin model in yet unknown
cuprates.",2303.14033v2
2000-02-16,Theoretical Perspectives on Spintronics and Spin-Polarized Transport,"Selected problems of fundamental importance for spintronics and
spin-polarized transport are reviewed, some of them with a special emphasis on
their applications in quantum computing and coherent control of quantum
dynamics. The role of the solid-state environment in the decoherence of
electron spins is discussed. In particular, the limiting effect of the
spin-orbit interaction on spin relaxation of conduction electrons is carefully
examined in the light of recent theoretical and experimental progress. Most of
the proposed spintronic devices involve spin-polarized transport across
interfaces in various hybrid structures. The specific example discussed here,
of a magnetic semiconductor/superconductor interface, displays many intricacies
which a complex spin-dependent interface introduces in the spin-polarized
transport. It is proposed that pairs of entangled electrons in a superconductor
(Cooper pairs) can be transfered to a non-superconducting region, and
consequently separated for a transport study of the spin entanglement. Several
important theoretical proposals for quantum computing are based on electronic
and nuclear spin entanglement in a solid. Physical requirements for these
proposals to be useful are discussed and some alternative views are presented.
Finally, a recent discovery of optical control of nuclear spins in
semiconductors is reviewed and placed in the context of a long-standing search
for electronic control of nuclear dynamics.",0002256v1
2005-08-09,Many-spin effects in inelastic neutron scattering and electron paramagnetic resonance of molecular nanomagnets,"Many molecular magnetic clusters, such as single-molecule magnets, are
characterized by spin ground states with defined total spin S exhibiting
zero-field-splittings. In this work, the spectroscopic intensities of the
transitions within the ground-state multiplet are analyzed. In particular, the
effects of a mixing with higher-lying spin multiplets, which is produced by
anisotropic interactions and is neglected in the standard single-spin
description, are investigated systematically for the two experimental
techniques of inelastic neutron scattering (INS) and electron paramagnetic
resonance (EPR), with emphasis on the former technique. The spectroscopic
transition intensities are calculated analytically by constructing
corresponding effective spin operators perturbationally up to second order and
consequently using irreducible tensor operator techniques. Three main effects
of spin mixing are observed. Firstly, a pronounced dependence of the INS
intensities on the momentum transfer Q, with a typical oscillatory behavior,
emerges in first order, signaling the many-spin nature of the wave functions in
exchange-coupled clusters. Secondly, as compared to the results of a
first-order calculation, the intensities of the transitions within the spin
multiplet are affected differently by spin mixing. This allows one, thirdly, to
differentiate the higher-order contributions to the cluster magnetic anisotropy
which come from the single-ion ligand-field terms and spin mixing,
respectively. The analytical results are illustrated by means of the three
examples of an antiferromagnetic heteronuclear dimer, the Mn-[3 x 3] grid
molecule, and the single-molecule magnet Mn12.",0508225v1
2013-05-28,Protection of center-spin coherence by dynamically polarizing nuclear spin core in diamond,"We experimentally investigate the protection of electron spin coherence of
nitrogen vacancy (NV) center in diamond by dynamical nuclear polarization. The
electron spin decoherence of an NV center is caused by the magnetic ield
fluctuation of the $^{13}$C nuclear spin bath, which contributes large thermal
fluctuation to the center electron spin when it is in equilibrium state at room
temperature. To address this issue, we continuously transfer the angular
momentum from electron spin to nuclear spins, and pump the nuclear spin bath to
a polarized state under Hartman-Hahn condition. The bath polarization effect is
verified by the observation of prolongation of the electron spin coherence time
($T_2^*$). Optimal conditions for the dynamical nuclear polarization (DNP)
process, including the pumping pulse duration and depolarization effect of
laser pulses, are studied. Our experimental results provide strong support for
quantum information processing and quantum simulation using polarized nuclear
spin bath in solid state systems.",1305.6424v1
2015-07-09,Nanosecond spin lifetimes in bottom-up fabricated bilayer graphene spin-valves with atomic layer deposited Al$_2$O$_3$ spin injection and detection barriers,"We present spin transport studies on bi- and trilayer graphene non-local
spin-valves which have been fabricated by a bottom-up fabrication method. By
this technique, spin injection electrodes are first deposited onto
Si$^{++}$/SiO$_2$ substrates with subsequent mechanical transfer of a
graphene/hBN heterostructure. We showed previously that this technique allows
for nanosecond spin lifetimes at room temperature combined with carrier
mobilities which exceed 20,000 cm$^2$/(Vs). Despite strongly enhanced spin and
charge transport properties, the MgO injection barriers in these devices
exhibit conducting pinholes which still limit the measured spin lifetimes. We
demonstrate that these pinholes can be partially diminished by an oxygen
treatment of a trilayer graphene device which is seen by a strong increase of
the contact resistance area products of the Co/MgO electrodes. At the same
time, the spin lifetime increases from 1 ns to 2 ns. We believe that the
pinholes partially result from the directional growth in molecular beam
epitaxy. For a second set of devices, we therefore used atomic layer deposition
of Al$_2$O$_3$ which offers the possibility to isotropically deposit more
homogeneous barriers. While the contacts of the as-fabricated bilayer graphene
devices are non-conductive, we can partially break the oxide barriers by
voltage pulses. Thereafter, the devices also exhibit nanosecond spin lifetimes.",1507.02677v1
2020-08-21,Correlation of interface transmission in THz spintronic emitters with spin mixing conductance in spin pumping experiments,"The field of THz spintronics is a novel direction in the research field of
spintronics that combines magnetism with optical physics and ultrafast
photonics. The experimental scheme of the field involves the use of femtosecond
laser pulses to trigger ultrafast spin and charge dynamics in bilayers composed
of ferromagnetic (FM) and non-magnetic (NM) thin films where the NM layer
features a strong spin-orbit coupling. The key technological and scientific
challenges of THz spintronic emitters is to increase their intensity and
frequency bandwidth. To achieve this the control of the source of the
radiation, namely the transport of the ultrafast spin current is required.
However, the transfer of a spin current from a FM to a NM layer is a highly
interface-sensitive effect. In this work we study the properties of the spin
current transport through the interface measuring the strength of the THz
emission and compare it to the effective spin mixing conductance, one of the
key concepts in the spin current transport through interfaces. The results show
an enhancement of the spin mixing conductance for interfaces with higher degree
of epitaxy similarly to the improvement of the THz emission. The
proportionality between spin mixing conductance and THz emission can define new
directions in engineering the emission of spintronic THz emitters.",2008.09537v1
2021-05-24,Role of two-dimensional Ising superconductivity in the non-equilibrium quasiparticle spin-to-charge conversion efficiency,"Non-equilibrium studies of two-dimensional (2D) superconductors (SCs) with
Ising spin-orbit coupling are prerequisite for their successful application to
equilibrium spin-triplet Cooper pairs and, potentially, Majorana fermions. By
taking advantage of the recent discoveries of 2D SCs and their compatibility
with any other materials, we fabricate here non-local magnon devices to examine
how such 2D Ising superconductivity affects the conversion efficiency of magnon
spin to quasiparticle charge in superconducting flakes of 2H-NbSe2 transferred
onto ferrimagnetic insulating Y3Fe5O12. Comparison with a reference device
based on a conventionally paired superconductor shows that the Y3Fe5O12-induced
in-plane (IP) exchange spin-splitting in the NbSe2 flake is hindered by its
inherent out-of-plane (OOP) spin-orbit-field, which, in turn, limits the
transition-state enhancement of the spin-to-charge conversion efficiency. Our
out-of-equilibrium study highlights the significance of symmetry matching
between underlying Cooper pairs and exchange-induced spin-splitting for the
giant transition-state spin-to-charge conversion and may have implications
towards proximity-engineered spin-polarized triplet pairing via tuning the
relative strength of IP exchange and OOP spin-orbit fields in ferromagnetic
insulator/2D Ising SC bilayers.",2105.11159v4
2023-01-19,RIXS observation of bond-directional nearest-neighbor excitations in the Kitaev material Na$_2$IrO$_3$,"Spin-orbit coupling locks spin direction and spatial orientation and
generates, in semi-classical magnets, a local spin easy-axis and associated
ordering. Quantum spin-1/2's defy this fate: rather than spins becoming locally
anisotropic, the spin-spin interactions do. Consequently interactions become
dependent on the spatial orientation of bonds between spins, prime theoretical
examples of which are Kitaev magnets. Bond-directional interactions imply the
existence of bond-directional magnetic modes, predicted spin excitations that
render crystallographically equivalent bonds magnetically inequivalent, which
yet have remained elusive experimentally. Here we show that resonant inelastic
x-ray scattering allows us to explicitly probe the bond-directional character
of magnetic excitations. To do so, we use a scattering plane spanned by one
bond and the corresponding spin component and scan a range of momentum transfer
that encompasses multiple Brillouin zones. Applying this approach to
Na$_2$IrO$_3$ we establish the different bond-directional characters of
magnetic excitations at 10 meV and 45 meV. Combined with the observation of
spin-spin correlations that are confined to a single bond, this experimentally
validates the Kitaev character of exchange interactions long proposed for this
material.",2301.08340v1
2023-04-20,Revealing Hidden Spin Polarization in Centrosymmetric van der Waals Materials on Ultrafast Timescales,"One of the key challenges for spintronic and novel quantum technologies is to
achieve active control of the spin angular momentum of electrons in nanoscale
materials on ultrafast, femtosecond timescales. While conventional
ferromagnetic materials and materials supporting spin texture suffer both from
conceptional limitations in miniaturization and in efficiency of optical and
electronic manipulation, non-magnetic centrosymmetric layered materials with
hidden spin polarization may offer an alternative pathway to manipulate the
spin degree of freedom by external stimuli. Here we demonstrate a novel
approach to generate transient spin polarization on a femtosecond timescale in
the otherwise spin-unpolarized band structure of the centrosymmetric 2H-stacked
group VI transition metal dichalcogenide WSe$_{2}$. Using ultrafast optical
excitation of a fullerene layer grown on top of WSe$_{2}$, we trigger an
ultrafast interlayer electron transfer from the fullerene layer into the
WSe$_{2}$ crystal. The resulting transient charging of the C$_{60}$/WSe$_{2}$
interface leads to a substantial interfacial electric field that by means of
spin-layer-valley locking ultimately creates ultrafast spin polarization
without the need of an external magnetic field. Our findings hence open a novel
pathway for optically engineering spin functionalities such as the
sub-picosecond generation and manipulation of ultrafast spin currents in 2D
heterostructures.",2304.10237v1
2002-11-22,Single and binary Black Holes and their active environment,"In this short review we describe some of the latest endeavours to understand
the activity around Black Holes. First, it has been possible to demonstrate
that a large part of the electromagnetic emission observed can be interpreted
as arising from the jet; this explains at once all spectral features and their
variability. Second we dwell on the concept that merging galaxies naturally
lead to merging Black Holes. Here we emphasize two aspects: a) the torque
exerted by the binary Black Holes carves a torus like distribution out of the
stellar population near to the Black Hole binary; b) We consider the last
stages of the Black Hole binary merger, taking into account the angle between
the spin of the primary Black Hole, and the orbital spin of the second Black
Hole. We show that the loss of orbital angular momentum is very strongly
spin-dependent; for large angles between the two spins the angular momentum
loss is strongly inhibited, allowing spin flip of the primary Black Hole which
preserves a high angular momentum relative to the maximum allowed. This ensures
that both before and after the merger the accretion disk may reach to very
small distances from the central Black Hole, with very high local temperatures
right near the base of the jet: This is especially interesting in the case that
forming the jet requires the formation of an ADAF like ring near the inner edge
of the disk, as suggested by some earlier work. It also may have consequences
for the initial hadronic interactions right near the base of the jet. Finally,
this may also have important implications for the discovery of gravitational
radiation bursts from the merger of black holes; the spin dependence needs to
be taken into account.",0211503v2
2006-02-14,The evolution of misaligned accretion discs and spinning black holes,"In this paper we consider the process of alignment of a spinning black hole
and a surrounding misaligned accretion disc. We use a simplified set of
equations, that describe the evolution of the system in the case where the
propagation of warping disturbances in the accretion disc occurs diffusively, a
situation likely to be common in the thin discs in Active Galactic Nuclei
(AGN). We also allow the direction of the hole spin to move under the action of
the disc torques. In such a way, the evolution of the hole-disc system is
computed self-consistently. We consider a number of different situations and we
explore the relevant parameter range, by varying the location of the warp
radius $R_{\rm w}$ and the propagation speed of the warp. We find that the
dissipation associated with the twisting of the disc results in a large
increase in the accretion rate through the disc, so that AGN accreting from a
misaligned disc are likely to be significantly more luminous than those
accreting from a flat disc. We compute explicitly the time-scales for the
warping of the disc and for the alignment process and compare our results with
earlier estimates based on simplified steady-state solutions. We also confirm
earlier predictions that, under appropriate circumstances, accretion can
proceed in a counter-aligned fashion, so that the accreted material will
spin-down the hole, rather than spinning it up. Our results have implication in
a number of different observational features of AGN such as the orientation and
shape of jets, the shape of X-ray iron lines, and the possibility of
obscuration and absorption of X-ray by the outer disc as well as the general
issue of the spin history of black holes during their growth.",0602306v1
2006-12-01,Tidal dissipation within hot Jupiters: a new appraisal,"Eccentricity or obliquity tides have been proposed as the missing energy
source that may explain the anomalously large radius of some transiting ``hot
Jupiters''. To maintain a non-zero and large obliquity, it was argued that the
planets can be locked in a Cassini state, i.e. a resonance between spin and
orbital precessions. We compute the tidal heating within ``inflated'' close-in
giant planets with a non-zero eccentricity or obliquity. We further inspect
whether the spin of a ``hot Jupiter'' could have been trapped and maintained in
a Cassini state during its early despinning and migration. We estimate the
capture probability in a spin-orbit resonance between $\sim$ 0.5 AU (a distance
where tidal effects become significant) and 0.05 AU for a wide range of secular
orbital frequencies and amplitudes of gravitational perturbations. Numerical
simulations of the spin evolution are performed to explore the influence of
tidal despinning and migration processes on the resonance stability. We find
that tidal heating within a non-synchronous giant planet is about twice larger
than previous estimates based on the hypothesis of synchronization. Chances of
capture in a spin-orbit resonance are very good around 0.5 AU but they decrease
dramatically with the semi-major axis. Furthermore, even if captured, both
tidal despinning and migration processes cause the tidal torque to become large
enough that the obliquity ultimately leaves the resonance and switches to near
$0^{\circ}$. Locking a ``hot Jupiter'' in an isolated spin-orbit resonance is
unlikely at 0.05 AU but could be possible at larger distances. Another
mechanism is then required to maintain a large obliquity and create internal
heating through obliquity tides",0612044v1
2007-08-01,"The long-term evolution of the spin, pulse shape, and orbit of the accretion-powered millisecond pulsar SAX J1808.4-3658","We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4-3658,
an X-ray transient with a recurrence time of ~2 yr, using data from the Rossi
X-ray Timing Explorer covering 4 transient outbursts (1998-2005). We verify
that the 401 Hz pulsation traces the spin frequency fundamental and not a
harmonic. Substantial pulse shape variability, both stochastic and systematic,
was observed during each outburst. Analysis of the systematic pulse shape
changes suggests that, as an outburst dims, the X-ray ""hot spot"" on the pulsar
surface drifts longitudinally and a second hot spot may appear. The overall
pulse shape variability limits the ability to measure spin frequency evolution
within a given X-ray outburst (and calls previous nudot measurements of this
source into question), with typical upper limits of |nudot| < 2.5x10^{-14} Hz/s
(2 sigma). However, combining data from all the outbursts shows with high (6
sigma) significance that the pulsar is undergoing long-term spin down at a rate
nudot = (-5.6+/-2.0)x10^{-16} Hz/s, with most of the spin evolution occurring
during X-ray quiescence. We discuss the possible contributions of magnetic
propeller torques, magnetic dipole radiation, and gravitational radiation to
the measured spin down, setting an upper limit of B < 1.5x10^8 G for the
pulsar's surface dipole magnetic field and and Q/I < 5x10^{-9} for the
fractional mass quadrupole moment. We also measured an orbital period
derivative of Pdot = (3.5+/-0.2)x10^{-12} s/s. This surprising large Pdot is
reminiscent of the large and quasi-cyclic orbital period variation observed in
the so-called ""black widow"" millisecond radio pulsars, supporting speculation
that SAX J1808.4-3658 may turn on as a radio pulsar during quiescence. In an
appendix we derive an improved (0.15 arcsec) source position from optical data.",0708.0211v2
2011-09-22,Tidal Dissipation in Planet-Hosting Stars: Damping of Spin-Orbit Misalignment and Survival of Hot Jupiters,"Observations of hot Jupiters around solar-type stars with very short orbital
periods (~day) suggest that tidal dissipation in such stars is not too
efficient so that these planets can survive against rapid orbital decay. This
is consistent with recent theoretical works, which indicate that the tidal Q of
planet-hosting stars can indeed be much larger than the values inferred from
stellar binaries. On the other hand, recent measurements of Rossiter-McLaughlin
effects in transiting hot Jupiter systems not only reveal that many such
systems have misaligned stellar spin with respect to the orbital axis, but also
show that systems with cooler host stars tend to have aligned spin and orbital
axes. Winn et al. suggested that this obliquity - temperature correlation may
be explained by efficient damping of stellar obliquity due to tidal dissipation
in the star. This explanation, however, is in apparent contradiction with the
survival of these short-period hot Jupiters. We show that in the solar-type
parent stars of close-in exoplanetary systems, the effective tidal Q governing
the damping of stellar obliquity can be much smaller than that governing
orbital decay. This is because for misaligned systems, the tidal potential
contains a Fourier component with frequency equal to the stellar spin frequency
(in the rotating frame of the star). This component can excite inertial waves
in the convective envelope of the star, and the dissipation of inertial waves
then leads to a spin-orbit alignment torque, but not orbital decay. By
contrast, for aligned systems, such inertial wave excitation is forbidden since
the tidal forcing frequency is much larger than the stellar spin frequency. We
derive a general effective tidal evolution theory for misaligned binaries,
taking account of different tidal responses and dissipation rates for different
tidal forcing components.",1109.4703v2
2013-06-29,Spin-orbit evolution of Mercury revisited,"While it is accepted that the eccentricity of Mercury (0.206) favours
entrapment into the 3:2 spin-orbit resonance, open is the question how and when
the capture took place. A recent work by Makarov (2012) has demonstrated that
trapping into this resonance is certain if the eccentricity is larger than 0.2,
provided that we use a realistic tidal model, the one which is based on the
Darwin-Kaula expansion of the tidal torque. The physics-based tidal model
changes dramatically the statistics of the possible final spin states. First,
we discover that after only one encounter with the spin-orbit 3:2 resonance
this resonance becomes the most probable end-state. Second, if a capture into
this (or any other) resonance takes place, the capture becomes final, several
crossings of the same state being forbidden by our model. Third, within our
model the trapping of Mercury happens much faster than previously believed: for
most histories, 10 - 20 Myr are sufficient. Fourth, even a weak laminar
friction between the solid mantle and a molten core would most likely result in
a capture in the 2:1 or even higher resonance. So the principal novelty of our
paper is that the 3:2 end-state is more ancient than the same end-state
obtained when the constant time lag model is employed. The swift capture
justifies our treatment of Mercury as a homogeneous, unstratified body whose
liquid core had not yet formed by the time of trapping. We also provide a
critical analysis of the hypothesis by Wieczorek et al. (2012) that the early
Mercury might had been retrograde, whereafter it synchronised its spin and then
accelerated it to the 3:2 resonance. Accurate processing of the available data
on cratering does not support that hypothesis, while the employment of a
realistic rheology invalidates a key element of the hypothesis, an intermediate
pseudosynchronous state needed to spin-up to the 3:2 resonance.",1307.0136v7
2014-09-15,Magnetic anisotropy of FePt nanoparticles,"We carry out a systematic theoretical investigation of Magneto Crystalline
Anisotropy (MCA) of L10 FePt clusters with alternating Fe and Pt planes along
the (001) direction. We calculate the structural relaxation and magnetic moment
of each cluster by using ab initio spin-polarized density functional theory
(DFT), and the MCA with both spin-polarized DFT (including spin-orbit coupling
self-consistently) and the torque method. We find that the MCA of any composite
structure of a given size is enhanced with respect to that of the same-sized
pure Pt or pure Fe cluster as well as to that of any pair of Fe and Pt atoms in
bulk L10 FePt. This enhancement results from the hybridization we observe
between the 3d orbital of the Fe atoms and the 5d orbital of their Pt
neighbors. This hybridization, however, affects the electronic properties of
the component atoms in significantly different ways. While it somewhat
increases the spin moment of the Fe atoms, it has little effect on their
orbital moment; at the same time, it greatly increases both the spin and
orbital moment of the Pt atoms. Given the fact that the spin-orbit coupling
(SOC) constant of Pt is about 7 times greater than that of Fe, this Fe-induced
jump in the orbital moment of the Pt atoms produces the increase in MCA of the
composite structures over that of their pure counterparts. That any composite
structure exhibits higher MCA than bulk L10 FePt results from the lower
coordination of Pt atoms in the cluster, whether Fe or Pt predominates within
it. We also find that bipyramidal clusters whose central layer is Pt have
higher MCA than their same-sized counterparts whose central layer is Fe. This
results from the fact that Pt atoms in such configurations are coordinated with
more Fe atoms than in the latter. By thus participating in more instances of
hybridization, they contribute higher orbital moments to the overall MCA of the
unit.",1409.4318v3
2016-06-08,Hidden Markov model tracking of continuous gravitational waves from a neutron star with wandering spin,"Gravitational wave searches for continuous-wave signals from neutron stars
are especially challenging when the star's spin frequency is unknown a priori
from electromagnetic observations and wanders stochastically under the action
of internal (e.g. superfluid or magnetospheric) or external (e.g. accretion)
torques. It is shown that frequency tracking by hidden Markov model (HMM)
methods can be combined with existing maximum likelihood coherent matched
filters like the F-statistic to surmount some of the challenges raised by spin
wandering. Specifically it is found that, for an isolated, biaxial rotor whose
spin frequency walks randomly, HMM tracking of the F-statistic output from
coherent segments with duration T_drift = 10d over a total observation time of
T_obs = 1yr can detect signals with wave strains h0 > 2e-26 at a noise level
characteristic of the Advanced Laser Interferometer Gravitational Wave
Observatory (Advanced LIGO). For a biaxial rotor with randomly walking spin in
a binary orbit, whose orbital period and semi-major axis are known
approximately from electromagnetic observations, HMM tracking of the
Bessel-weighted F-statistic output can detect signals with h0 > 8e-26. An
efficient, recursive, HMM solver based on the Viterbi algorithm is
demonstrated, which requires ~10^3 CPU-hours for a typical, broadband (0.5-kHz)
search for the low-mass X-ray binary Scorpius X-1, including generation of the
relevant F-statistic input. In a ""realistic"" observational scenario, Viterbi
tracking successfully detects 41 out of 50 synthetic signals without spin
wandering in Stage I of the Scorpius X-1 Mock Data Challenge convened by the
LIGO Scientific Collaboration down to a wave strain of h0 = 1.1e-25, recovering
the frequency with a root-mean-square accuracy of <= 4.3e-3 Hz.",1606.02412v1
2016-08-02,Atomic-scale observation and manipulation of plaquette antiferromagnetic order in iron-based superconductor,"The symmetry requirement and the origin of magnetic orders coexisting with
superconductivity have been strongly debated issues of iron-based
superconductors (FeSCs). Observation of C$_4$-symmetric antiferromagnetism in
violation of the inter-band nesting condition of spin-density waves in
superconducting ground state will require significant change in our
understanding of the mechanism of FeSC. The superconducting material
Sr$_2$VO$_3$FeAs, a bulk version of monolayer FeSC in contact with a perovskite
layer with its magnetism (T$_N$ ~ 50 K) and superconductivity (T$_c$ ~ 37 K)
coexisting at parent state, has no reported structural orthorhombic distortion
and thus makes a perfect system to look for theoretically expected C$_4$
magnetisms. Based on variable temperature spin-polarized scanning tunneling
microscopy (SPSTM) with newly discovered imaging mechanism that removes the
static surface reconstruction (SR) pattern by fluctuating it rapidly with
spin-polarized tunneling current, we could visualize underlying C$_4$ symmetric
(2$\times$2) magnetic domains and its phase domain walls. We find that this
magnetic order is perfectly consistent with the plaquette antiferromagnetic
order in tetragonal Fe spin lattice expected from theories based on the
Heisenberg exchange interaction of local Fe moments and the quantum order by
disorder. The inconsistency of its modulation Q vectors from the nesting
condition also implies that the nesting-based C$_2$ symmetric magnetism is not
a unique prerequisite of high-T$_c$ FeSC. Furthermore, the plaquette
antiferromagnetic domain wall dynamics under the influence of small spin torque
effect of spin-polarized tunneling current are shown to be consistent with
theoretical simulation based on the extended Landau-Lifshitz-Gilbert equation.",1608.00884v3
2016-11-02,Topological insulator in a helicoidal magnetization field,"A key feature of topological insulators is the robustness of the electron
energy spectrum. At a surface of a topological insulator, Dirac point is
protected by the characteristic symmetry of the system. The breaking of the
symmetry opens a gap in the energy spectrum. Therefore, topological insulators
are very sensitive to magnetic fields, which can open a gap in the electronic
spectrum. Concerning ""internal"" magnetic effects, for example the situation
with doped magnetic impurities, is not trivial. A single magnetic impurity is
not enough to open the band gap, while in the case of a ferromagnetic chain of
deposited magnetic impurities the Dirac point is lifted. However, a much more
interesting case is when localized magnetic impurities form a chiral spin
order. Our first principle density functional theory calculations have shown
that this is the case for Fe deposited on the surface of Bi2Se3 topological
insulator. But not only magnetic impurities can form a chiral helicoidal spin
texture. An alternative way is to use chiral multiferroics (prototype material
is LiCu2O2) that induce a proximity effect. The theoretical approach we present
here is valid for both cases. We observed that opposite to a ferromagnetically
ordered case, a chiral spin order does not destroy the Dirac point. We also
observed that the energy gap appears at the edges of the new Brillouin zone.
Another interesting result concerns the spin dynamics. We derived an equation
for the spin density dynamics with a spin current and relaxation terms. We have
shown that the motion of the conductance electron generates a magnetic torque
and exerts a certain force on the helicoidal texture.",1611.00642v1
2017-10-04,Abraham-based momentum and spin of optical fields under conditions of total reflection,"This memo contains a collection of formulas describing the electromagnetic
energy, momentum and spin distribution of an optical field formed in dielectric
media separated by a plane interface when an incident monochromatic plane wave
is totally reflected. The formulas are based on the Abraham momentum definition
and include the momentum decomposition into the orbital (canonical) and spin
parts as well as explicit dual-symmetric separation of the electric and
magnetic contributions. This material was prepared in February 2013 but it had
not been finalized and published because of the difficulties in physical
interpretation of singular terms in the spin and orbital momentum expressions
associated with the sharp interface. Meanwhile, it has become clear that the
""naive"" Abraham approach is not correct for this problem and the
electromagnetic spin and momentum in inhomogeneous media are better
characterized by the more elaborated relations based on the Minkowski paradigm
[see, e.g., Phys. Rev. A 83, 013823 (2011); 86, 055802 (2012);
arXiv:1706.05493]. In application to the total-reflection situation this
Minkowski-based description was recently illustrated in arXiv:1706.06263, so
the present material is mainly of historical interest. However, it seems useful
to make it known for a wide audience, at least for comparison with the recent
improved approaches and for suitable references. The last section, treating the
ponderomotive action experienced by a Mie particle in the evanescent wave, is
independent of the Abraham - Minkowski controversy. The numerical calculations
preserve their validity, and association of the various force and torque
components with corresponding components of the optical momentum and spin
remains legal in the Minkowski pattern. The results of the last section were
partly used in other published works [e.g., Nature Commun. 5, 3300 (2014)].",1710.01561v2
2018-09-17,Galaxy orientation with the cosmic web across cosmic time,"This work investigates the alignment of galactic spins with the cosmic web
across cosmic time using the cosmological hydrodynamical simulation
Horizon-AGN. The cosmic web structure is extracted via the persistent skeleton
as implemented in the DISPERSE algorithm. It is found that the spin of low-mass
galaxies is more likely to be aligned with the filaments of the cosmic web and
to lie within the plane of the walls while more massive galaxies tend to have a
spin perpendicular to the axis of the filaments and to the walls. The mass
transition is detected with a significance of 9 sigmas. This galactic alignment
is consistent with the alignment of the spin of dark haloes found in pure dark
matter simulations and with predictions from (anisotropic) tidal torque theory.
However, unlike haloes, the alignment of low-mass galaxies is weak and
disappears at low redshifts while the orthogonal spin orientation of massive
galaxies is strong and increases with time, probably as a result of mergers. At
fixed mass, alignments are correlated with galaxy morphology: the high-redshift
alignment is dominated by spiral galaxies while elliptical centrals are mainly
responsible for the perpendicular signal. These predictions for spin alignments
with respect to cosmic filaments and unprecendently walls are successfully
compared with existing observations. The alignment of the shape of galaxies
with the different components of the cosmic web is also investigated. A
coherent and stronger signal is found in terms of shape at high mass. The two
regimes probed in this work induce competing galactic alignment signals for
weak lensing, with opposite redshift and luminosity evolution. Understanding
the details of these intrinsic alignments will be key to exploit future major
cosmic shear surveys like Euclid or LSST.",1809.06212v1
2019-01-31,Spirit: Multifunctional Framework for Atomistic Spin Simulations,"The \textit{Spirit} framework is designed for atomic scale spin simulations
of magnetic systems of arbitrary geometry and magnetic structure, providing a
graphical user interface with powerful visualizations and an easy to use
scripting interface. An extended Heisenberg type spin-lattice Hamiltonian
including competing exchange interactions between neighbors at arbitrary
distance, higher-order exchange, Dzyaloshinskii-Moriya and dipole-dipole
interactions is used to describe the energetics of a system of classical spins
localised at atom positions. A variety of common simulations methods are
implemented including Monte Carlo and various time evolution algorithms based
on the Landau-Lifshitz-Gilbert equation of motion, which can be used to
determine static ground state and metastable spin configurations, sample
equilibrium and finite temperature thermodynamical properties of magnetic
materials and nanostructures or calculate dynamical trajectories including spin
torques induced by stochastic temperature or electric current. Methods for
finding the mechanism and rate of thermally assisted transitions include the
geodesic nudged elastic band method, which can be applied when both initial and
final states are specified, and the minimum mode following method when only the
initial state is given. The lifetime of magnetic states and rate of transitions
can be evaluated within the harmonic approximation of transition-state theory.
The framework offers performant CPU and GPU parallelizations. All methods are
verified and applications to several systems, such as vortices, domain walls,
skyrmions and bobbers are described.",1901.11350v1
2020-07-16,Ultrafast time-evolution of chiral Néel magnetic domain walls probed by circular dichroism in x-ray resonant magnetic scattering,"Non-collinear spin textures in ferromagnetic ultrathin films are attracting a
renewed interest fueled by possible fine engineering of several magnetic
interactions, notably the interfacial Dzyaloshinskii-Moriya interaction. This
allows the stabilization of complex chiral spin textures such as chiral
magnetic domain walls (DWs), spin spirals, and magnetic skyrmions. We report
here on the ultrafast behavior of chiral DWs after optical pumping in
perpendicularly magnetized asymmetric multilayers, probed using time-resolved
circular dichroism in x-ray resonant magnetic scattering (CD-XRMS). We observe
a picosecond transient reduction of the CD-XRMS, which is attributed to the
spin current-induced coherent and incoherent torques within the continuously
dependent spin texture of the DWs. We argue that a specific demagnetization of
the inner structure of the DW induces a flow of hot spins from the interior of
the neighboring magnetic domains. We identify this time-varying change of the
DW textures shortly after the laser pulse as a distortion of the homochiral
N'eel shape toward a transient mixed Bloch-N\'eel-Bloch textures along a
direction transverse to the DW. Our study highlights how time-resolved CD-XRMS
can be a unique tool for studying the time evolution in other systems showing a
non-collinear electric/magnetic ordering such as skyrmion lattices,
conical/helical phases, as well as the recently observed antiskyrmion lattices,
in metallic or insulating materials.",2007.08583v2
2023-02-02,The Density Parity Model for the Evolution of the Subhalo Inner Spin Alignments with the Cosmic Web,"We develop a new model within which the radius-dependent transition of the
subhalo inner spins with respect to the cosmic web and the variation of the
transition threshold radius ($r_{\rm th}$) with subhalo mass ($M_{\rm vir}$),
smoothing scale ($r_{f}$), and redshift ($z$) can be coherently explained. The
key tenet of this model is that the competition between the pressure effect of
the inner mass and the compression effect of the local tidal field determines
which principal direction of the tidal field the inner spins are aligned with.
If the former predominates, then only the tidal torques turn on, resulting in
the alignments of the inner spins with the intermediate principal axes of the
tidal field. Otherwise, the subhalo spins acquire a tendency to be aligned with
the shortest axes of the subhalo shapes, which is in the major principal
directions of the tidal field. Quantifying the two effects in terms of the
densities, we make a purely analytical prediction for $r_{\rm th}(M_{\rm vir},
z, r_{f})$. Testing this model against the numerical results from a
high-resolution dark matter only N-body simulation in the redshift range of
$0\le z\le 3$ on the galactic mass scale of $11.8\le \log[M_{\rm
vir}/(h^{-1}M_{\odot})]\le 12.6$ for two different cases of $r_{f}/(h^{-1}{\rm
Mpc})=0.5$ and $1$, we find excellent agreements of the model predictions with
the numerical results. It is also shown that this model naturally predicts the
alignments between the inner spins of the present subhalos with the principal
axes of the high-$z$ tidal field at the progenitors' locations.",2302.00679v2
2013-05-27,Mass transfer in eccentric binary systems using the binary evolution code BINSTAR,"We present the first calculations of mass transfer via RLOF for a binary
system with a significant eccentricity using our new binary stellar evolution
code. The study focuses on a 1.50+1.40 Msun main sequence binary with an
eccentricity of 0.25, and an orbital period of about 0.7 d. The reaction of the
stellar components due to mass transfer is analyzed, and the evolution of mass
transfer during the periastron passage is compared to recent smooth particle
hydrodynamics (SPH) simulations. The impact of asynchronism and non-zero
eccentricity on the Roche lobe radius, and the effects of tidal and rotational
deformation on the stars' structures, are also investigated. Calculations were
performed using the state-of-the-art binary evolution code BINSTAR, which
calculates simultaneously the structure of the two stars and the evolution of
the orbital parameters. The evolution of the mass transfer rate during an orbit
has a Gaussian-like shape, with a maximum at periastron, in qualitative
agreement with SPH simulations. The Roche lobe radius is modified by the donor
star's spin and the orbital eccentricity. This has a significant impact on both
the duration and the rate of mass transfer. We find that below some critical
rotation rate, mass transfer never occurs, while above some threshold, mass is
transferred over the entire orbit. Tidal and rotational deformation of the
donor star causes it to become over-sized, enhancing the mass transfer rate
further by about a factor of ten, leading to non-conservative mass transfer.
The modulation of mass transfer rate with orbital phase produces short-term
variability in the surface luminosity and radius of each star. The longer-term
behaviour shows, in accordance with studies of circular systems with radiative
stars, that the donor becomes ever small and under-luminous, while the converse
is the case for the accretor.",1305.6092v1
2019-09-25,Adiabatic electron charge transfer between two quantum dots in presence of 1/f noise,"Controlled adiabatic transfer of a single electron through a chain of quantum
dots has been recently achieved in GaAs and Si/SiGe based quantum dots, opening
prospects for turning stationary spin qubits into mobile ones, and solving in
this way the problem of long-distance communication between quantum registers
in a scalable quantum computing architecture based on quantum dots. We consider
theoretically the process of such an electron transfer between two
tunnel-coupled quantum dots, focusing on control by slowly varying the detuning
of energy levels in the dots. We take into account the fluctuations in detuning
caused by $1/f$-type noise that is ubiquitous in semiconductor nanostructures,
and analyze their influence on probability of successful transfer of an
electron in a spin eigenstate. With numerical and analytical calculations we
show that probability of electron not being transferred due to $1/f^\beta$
noise in detuning is $\propto \sigma^2 t^{\beta-1}/v$, where $\sigma$
characterizes the noise amplitude, $t$ is the interdot tunnel coupling, and $v$
is the detuning sweep rate. Interestingly, this means that the noise-induced
errors in charge transfer are independent of $t$ for $1/f$ noise. For realistic
parameters taken from experiments on silicon-based quantum dots, we obtain the
minimal probability of charge transfer failure between a pair of dots is
limited by $1/f$ noise in detuning to be the on order of $0.01$. This means
that in order to reliably transfer charges across many quantum dots, charge
noise in the devices should be further suppressed, or tunnel couplings should
be increased, in order to allow for faster transfer (and less exposure to
noise), while not triggering the deterministic Landau-Zener excitation.",1909.11780v2
2000-01-03,Spin-Orbit Couplings in X-ray Binaries,"We discuss the influence of tidal spin-orbit interactions on the orbital
dynamics of close intermediate-mass X-ray binaries. In particular we consider
here a process in which spin angular momentum of a contracting RLO donor star,
in a synchronous orbit, is converted into orbital angular momentum and thus
helps to stabilize the mass transfer by widening the orbit. Binaries which
would otherwise suffer from dynamically unstable mass transfer (leading to the
formation of a common envelope and spiral-in evolution) are thus shown to
survive a phase of extreme mass transfer on a sub-thermal timescale.
Furthermore, we discuss the orbital evolution prior to RLO in X-ray binaries
with low-mass donors, caused by the competing effects of wind mass loss and
tidal effects due to expansion of the (sub)giant.",0001014v1
2002-09-05,Ground state properties of ferromagnetic metal/conjugated polymer interfaces,"We theoretically investigate the ground state properties of ferromagnetic
metal/conjugated polymer interfaces. The work is partially motivated by recent
experiments in which injection of spin polarized electrons from ferromagnetic
contacts into thin films of conjugated polymers was reported. We use a
one-dimensional nondegenerate Su-Schrieffer-Heeger (SSH) Hamiltonian to
describe the conjugated polymer and one-dimensional tight-binding models to
describe the ferromagnetic metal. We consider both a model for a conventional
ferromagnetic metal, in which there are no explicit structural degrees of
freedom, and a model for a half-metallic ferromagnetic colossal
magnetoresistance (CMR) oxide which has explicit structural degrees of freedom.
The Fermi energy of the magnetic metallic contact is adjusted to control the
degree of electron transfer into the polymer. We investigate electron charge
and spin transfer from the ferromagnetic metal to the organic polymer, and
structural relaxation near the interface. Bipolarons are the lowest energy
charge state in the bulk polymer for the nondegenerate SSH model Hamiltonian.
As a result electrons (or holes) transferred into the bulk of the polymer form
spinless bipolarons. However, there can be spin density in the polymer
localized near the interface.",0209145v1
2005-04-15,Critical Current Distribution in Spin Transfer Switched Magnetic Tunnel Junctions,"The spin transfer switching current distribution within a cell was studied in
magnetic tunnel junction based structures having alumina barriers with
resistance-area product (RA) of 10 to 30 Ohm-um2 and tunneling
magneto-resistance (TMR) of ~20%. These were patterned into current
perpendicular to plane configured nano-pillars having elliptical cross-sections
of area ~0.02 um2. The width of the critical current distribution
(sigma/average of distribution), measured using 30 ms current pulse width, was
found to be 7.5% and 3.5% for cells with thermal factor (KuV/kBT) of 40 and 65
respectively. The distribution width did not change significantly for pulse
widths between 1 s and 4 ms. An analytical expression for probability density
function, p(I/Ico) was derived considering the thermally activated spin
transfer model, which supports the experimental observation that the thermal
factor is the most significant parameter in determining the within cell
critical current distribution width.",0504390v1
2007-03-23,Integrable spin-boson models descending from rational six-vertex models,"We construct commuting transfer matrices for models describing the
interaction between a single quantum spin and a single bosonic mode using the
quantum inverse scattering framework. The transfer matrices are obtained from
certain inhomogeneous rational vertex models combining bosonic and spin
representations of SU(2), subject to non-diagonal toroidal and open boundary
conditions. Only open boundary conditions are found to lead to integrable
Hamiltonians combining both rotating and counter-rotating terms in the
interaction. If the boundary matrices can be brought to triangular form
simultaneously, the spectrum of the model can be obtained by means of the
algebraic Bethe ansatz after a suitable gauge transformation; the corresponding
Hamiltonians are found to be non-hermitian. Alternatively, a certain
quasi-classical limit of the transfer matrix is considered where hermitian
Hamiltonians are obtained as members of a family of commuting operators; their
diagonalization, however, remains an unsolved problem.",0703630v2
2002-04-27,Longitudinal polarization of hyperons in high $p_\perp$ jets in singly polarized pp collisions at high energies,"We calculate the longitudinal polarizations of hyperons in high $p_\perp$
jets in $pp$ collisions in which one of the protons is longitudinally polarized
at RHIC energies using different models for the spin transfer in fragmentation
process. The results show that the measurements of these polarizations can be
used to study the spin transfer in high energy fragmentation processes in
general and to test the different models in particular. Our results show
especially that the magnitude of the polarization of $\Lambda$ is rather small
whereas that of $\Sigma^+$ is considerably larger in the large rapidity region.
The differences between the results from different pictures for $\Sigma^+$
polarizations is also much larger. Hence, the measurement of $\Sigma^+$
polarization should be more effective to distinguish between different models
especially the SU(6) or the DIS picture for spin transfer in fragmentation
processes.",0204318v1
2006-06-27,Periodic structure of spin-transfer current in ferromagnetic multilayers,"We show that the drift-diffusion mechanism in a normal-metal layer in
combination with the resonance electron-magnon interactions at
ferromagnet-normal interface of F-N-F heterostucture creates spatial
instability modes and, out of these modes, a quasi-stable periodic structure of
spin-transfer d.c. current can arise with certain channel step and
step-to-radius ratio. The ferromagnetic resonance conditions determine
spin-transfer current density. Independent nano-oscillators creating
intersecting arrays of channels can phase-lock on sub-micrometer distance,
which depends on multilayer geometry and applied fields. By decreasing the
layer thickness, the number of channels affected by each independent
d.c.-current source and their radius may be diminished. Phase-locking of
multiple independent nano-oscillators can be used for enhancement of output
power.",0606064v1
2006-04-19,State Transfer and Spin Measurement,"We present a Hamiltonian that can be used for amplifying the signal from a
quantum state, enabling the measurement of a macroscopic observable to
determine the state of a single spin. We prove a general mapping between this
Hamiltonian and an exchange Hamiltonian for arbitrary coupling strengths and
local magnetic fields. This facilitates the use of existing schemes for perfect
state transfer to give perfect amplification. We further prove a link between
the evolution of this fixed Hamiltonian and classical Cellular Automata,
thereby unifying previous approaches to this amplification task.
  Finally, we show how to use the new Hamiltonian for perfect state transfer in
the, to date, unique scenario where total spin is not conserved during the
evolution, and demonstrate that this yields a significantly different response
in the presence of decoherence.",0604137v2
2006-12-17,Transfer of d-Level quantum states through spin chains by random swapping,"We generalize an already proposed protocol for quantum state transfer to spin
chains of arbitrary spin. An arbitrary unknown $d-$ level state is transferred
through a chain with rather good fidelity by the natural dynamics of the chain.
We compare the performance of this protocol for various values of $d$. A
by-product of our study is a much simpler method for picking up the state at
the destination as compared with the one proposed previously. We also discuss
entanglement distribution through such chains and show that the quality of
entanglement transition increases with the number of levels $d$.",0612144v3
2008-01-12,"Theoretical aspects of quantum state transfer, correlation measurement and electron-nuclei coupled dynamics in quantum dots","Photons and electrons are the key quantum media for the quantum information
processing based on solid state devices. The essential ingredients to
accomplish the quantum repeater were investigated and their underlying physics
were revealed. The relevant elementary processes of the quantum state transfer
between a single photon and a single electron were analyzed, to clarify the
conditions to be satisfied to achieve the high fidelity of the quantum state
transfer. An optical method based on the Faraday rotation was proposed to carry
out the Bell measurement of two electrons which is a key operation in the
entanglement swapping for the quantum repeater and its feasibility was
confirmed. Also investigated was the quantum dynamics in the electron-nuclei
coupled spin system in quantum dots and a couple of new phenomena were
predicted related to the correlations induced by the hyperfine interaction,
namely, bunching and revival in the electron spin measurements. These findings
will pave the way to accomplish the efficient and robust quantum repeater and
nuclear spin quantum memory.",0801.1871v1
2008-03-13,Excitation transfer in two two-level systems coupled to an oscillator,"We consider a generalization of the spin-boson model in which two different
two-level systems are coupled to an oscillator, under conditions where the
oscillator energy is much less than the two-level system energies, and where
the oscillator is highly excited. We find that the two-level system transition
energy is shifted, producing a Bloch-Siegert shift in each two-level system
similar to what would be obtained if the other were absent. At resonances
associated with energy exchange between a two-level system and the oscillator,
the level splitting is about the same as would be obtained in the spin-boson
model at a Bloch-Siegert resonance. However, there occur resonances associated
with the transfer of excitation between one two-level system and the other, an
effect not present in the spin-boson model. We use a unitary transformation
leading to a rotated system in which terms responsible for the shift and
splittings can be identified. The level splittings at the anticrossings
associated with both energy exchange and excitation transfer resonances are
accounted for with simple two-state models and degenerate perturbation theory
using operators that appear in the rotated Hamiltonian.",0803.1906v1
2008-08-12,Optically induced energy and spin transfer in non-resonantly coupled pairs of self-assembled CdTe/ZnTe quantum dots,"Asymmetrical horizontal interdot coupling was demonstrated to exist in a
system of a single plane of self-assembled CdTe/ZnTe quantum dots.
Photoluminescence excitation (PLE), second order photon correlation and optical
orientation were used as main experimental tools. Each individual absorbing dot
was identified by a sharp PLE resonance, assigned to neutral exciton
transition, while the corresponding emission contained several excitonic
transitions of different charge states in another single quantum dot different
from the absorbing one. Energy and spin transfer dynamics were studied. A high
efficiency of spin transfer was found from optical orientation in a vertical
magnetic field (70%) as well as without the magnetic field (40%), in spite of a
significant anisotropic exchange splitting of the absorbing dot. Coherent
mechanism of linear-to-circular polarization conversion was identified, with an
efficiency (43%) close to the theoretical limit of 50%.",0808.1621v1
2009-08-20,NMR and NQR study of pressure-induced superconductivity and the origin of critical-temperature enhancement in the spin-ladder cuprate Sr$_2$Ca$_{12}$Cu$_{24}$O$_{41}$,"Pressure-induced superconductivity was studied for a spin-ladder cuprate
Sr$_2$Ca$_{12}$Cu$_{24}$O$_{41}$ using nuclear magnetic resonance (NMR) under
pressures up to the optimal pressure 3.8 GPa. Pressure application leads to a
transitional change from a spin-gapped state to a Fermi-liquid state at
temperatures higher than $T_c$. The relaxation rate $1/T_1$ shows
activated-type behavior at an onset pressure, whereas Korringa-like behavior
becomes predominant at the optimal pressure, suggesting that an increase in the
density of states (DOS) at the Fermi energy leads to enhancement of $T_c$.
Nuclear quadrupole resonance (NQR) spectra suggest that pressure application
causes transfer of holes from the chain to the ladder sites. The transfer of
holes increases DOS below the optimal pressure. A dome-shaped $T_c$ versus
pressure curve arises from naive balance between the transfer of holes and
broadening of the band width.",0908.2845v1
2009-09-03,Entanglement and Quantum Information Transfer in Arrays of Interacting Quantum Systems,"This thesis examines some of the more fundamental requirements of a
successful quantum computation, namely the ability to transmit quantum
information with maximum efficiency, and the creation of entanglement. I focus
specifically on neutron entanglement, showing that the spins of two or more
distinct neutrons can be measurably entangled by forward-scattering from an
isotropic medium. The interpretation of `time' in scattering experiments is
also discussed. I present a simple treatment based on the Heisenberg S-matrix,
from which it emerges that in certain situations the quantum-mechanical time
parameter appearing in the effective time-evolution operator for the spin
system has an intuitive physical interpretation. The final part of the thesis
deals with quantum information transfer in arrays of permanently coupled
dipolar systems. It is shown that spin chains with dipolar couplings offer high
fidelity long-distance state transmission, but transfer times in unmodulated
chains are unfeasibly long. Possible optimization methods are discussed,
concluding with a review of recent achievements in this field.",0909.0655v1
2009-10-08,Longitudinal Spin Transfer to $Λ$ and $\barΛ$ Hyperons in Polarized Proton-Proton Collisions at $\sqrt{s}$ = 200 GeV,"The longitudinal spin transfer, $D_{LL}$, from high energy polarized protons
to $\Lambda$ and $\bar{\Lambda}$ hyperons has been measured for the first time
in proton-proton collisions at $\sqrt{s} = 200 \mathrm{GeV}$ with the STAR
detector at RHIC. The measurements cover pseudorapidity, $\eta$, in the range
$|\eta| < 1.2$ and transverse momenta, $p_\mathrm{T}$, up to $4
\mathrm{GeV}/c$. The longitudinal spin transfer is found to be $D_{LL}=
-0.03\pm 0.13(\mathrm{stat}) \pm 0.04(\mathrm{syst})$ for inclusive $\Lambda$
and $D_{LL} = -0.12 \pm 0.08(\mathrm{stat}) \pm 0.03(\mathrm{syst})$ for
inclusive $\bar{\Lambda}$ hyperons with $<\eta> = 0.5$ and $<p_\mathrm{T}> =
3.7 \mathrm{GeV}/c$. The dependence on $\eta$ and $p_\mathrm{T}$ is presented.",0910.1428v1
2009-11-25,Perfect Entanglement Transport in Quantum Spin Chain Systems,"We propose a mechanism for perfect entanglement transport in
anti-ferromagnetic (AFM) quantum spin chain systems with modulated exchange
coupling along the xy plane and in the z direction. We use the principle of
adiabatic quantum pumping process for entanglement transfer in the spin chain
systems. In our proposed mechanism, perfect entanglement transfer can be
achieved over an arbitraly long distance. We explain analytically and
physically why the entanglement hops in alternate sites. We solve this problem
by using the Berry phase analysis and Abelian bosonization methods. We find the
condition for blocking of entanglement transport even in the perfect pumping
condition. We also explain physically why entanglement transfer in AFM chain
out performs the ferromagnetic chain. Our analytical solution interconnects
quantum many body physics and quantum information science.",0911.4762v1
2010-03-22,Quantum Control Theory for State Transformations: Dark States and their Enlightenment,"For many quantum information protocols such as state transfer, entanglement
transfer and entanglement generation, standard notions of controllability for
quantum systems are too strong. We introduce the weaker notion of accessible
pairs, and prove an upper bound on the achievable fidelity of a transformation
between a pair of states based on the symmetries of the system. A large class
of spin networks is presented for which this bound can be saturated. In this
context, we show how the inaccessible dark states for a given
excitation-preserving evolution can be calculated, and illustrate how some of
these can be accessed using extra catalytic excitations. This emphasises that
it is not sufficient for analyses of state transfer in spin networks to
restrict to the single excitation subspace. One class of symmetries in these
spin networks is exactly characterised in terms of the underlying graph
properties.",1003.4290v3
2010-11-02,Coherent state transfer via highly mixed quantum spin chains,"Spin chains have been proposed as quantum wires in many quantum information
processing architectures. Coherent transmission of quantum information over
short distances is enabled by their internal dynamics, which drives the
transport of single-spin excitations in perfectly polarized chains. Given the
practical challenge of preparing the chain in a pure state, we propose to use a
chain that is initially in the maximally mixed state. We compare the transport
properties of pure and mixed-state chains, finding similarities that enable the
experimental study of pure-state transfer by its simulation via mixed-state
chains, and demonstrate protocols for the perfect transfer of quantum
information in these chains. Remarkably, mixed-state chains allow the use of
Hamiltonians which do not preserve the total number of excitations, and which
are more readily obtainable from the naturally occurring magnetic dipolar
interaction. We propose experimental implementations using solid-state nuclear
magnetic resonance and defect centers in diamond.",1011.0736v1
2010-12-09,Longitudinal spin transfer of Lambda and anti-Lambda in polarized pp collisions at \sqrt s=200 GeV at STAR,"We report our measurement on longitudinal spin transfer, D_LL, from high
energy polarized protons to $\Lambda$ and $\bar{\Lambda}$ hyperons in
proton-proton collisions at $\sqrt{s} = 200 GeV$ with the STAR detector at
RHIC. The current measurements cover $\Lambda$, $\bar\Lambda$ pseudorapidity
$|\eta| < 1.2$ and transverse momenta $p_T$ up to $4GeV/c$ using the data taken
in 2005. The longitudinal spin transfer is found to be D_LL= -0.03\pm 0.13
(stat) \pm 0.04(syst)$ for inclusive $\Lambda$ and $D_{LL} = -0.12 \pm
0.08(stat) \pm 0.03(syst)$ for inclusive $\bar{\Lambda}$ hyperons with $<eta> =
0.5$ and $<p_T> = 3.7 GeV/c$. The prospects with 2009 data and the future
measurements are also given.",1012.1970v1
2012-04-26,"Investigations of the EPR parameters for the tetrahedral [FeX_4]^- clusters in AgX (X=Cl, Br)","The EPR parameters g factors and the superhyperfine parameters for the
tetrahedral [FeX_4]^- clusters in AgX (X=Cl, Br) are theoretically investigated
from the perturbation formulas of these parameters for a 3d^5 ion under
tetrahedra by considering both the crystal-field and charge transfer
contributions. The related model parameters are quantitatively determined from
the cluster approach in a uniform way. The g-shift \Delta g (=g-g_s, where
g_s\approx 2.0023 is the spin only value) from the charge transfer contribution
is opposite (positive) in sign and much larger in magnitude as compared with
that from the crystal-field one. The importance of the charge transfer
contribution increases rapidly with increasing the covalency and the spin-orbit
coupling coefficient of the ligand and thus exhibits the order of AgCl<AgBr.
The unpaired spin densities of the halogen ns, np\sigma\ and np\pi\ orbitals
are quantitatively determined from the related molecular orbital coefficients
based on the cluster approach.",1204.5996v1
2012-05-21,Antiperiodic spin-1/2 XXZ quantum chains by separation of variables: Complete spectrum and form factors,"In this paper we consider the spin 1/2 highest weight representations for the
6-vertex Yang-Baxter algebra on a finite lattice and analyze the integrable
quantum models associated to the antiperiodic transfer matrix. For these
models, which in the homogeneous limit reproduces the XXZ spin 1/2 quantum
chains with antiperiodic boundary conditions, we obtain in the framework of
Sklyanin's quantum separation of variables (SOV) the following results: I) The
complete characterization of the transfer matrix spectrum
(eigenvalues/eigenstates) and the proof of its simplicity. II) The
reconstruction of all local operators in terms of Sklyanin's quantum separate
variables. III) One determinant formula for the scalar products of separates
states, the elements of the matrix in the scalar product are sums over the SOV
spectrum of the product of the coefficients of the states. IV) The form factors
of the local spin operators on the transfer matrix eigenstates by a one
determinant formula given by simple modifications of the scalar product
formula.",1205.4537v1
2013-11-25,Response to noise of a spin transfer vortex based nano-oscillator,"We investigate experimentally and analytically the impact of thermal noise on
the sustained gyrotropic mode of vortex magnetization in spin transfer
nano-oscillators and its consequence on the linewidth broadening due to the
different nonlinear contributions. Performing some time domain measurements, we
are able to extract separately the phase noise and the amplitude noise at room
temperature for several values of dc current and perpendicular field. For a
theoretical description of the experiments, we extend the general model of
nonlinear auto-oscillators to the case of vortex core dynamics and provide some
analytical expressions of the response-to-noise of the system as the coupling
coefficient between the phase and the amplitude of the vortex core dynamics due
to the nonlinearities. From the analysis of our experimental results, we
demonstrate the major role of the amplitude-to-phase noise conversion on the
linewidth broadening, and propose some solutions to improve the spectral
coherence of vortex based spin transfer nano-oscillators.",1311.6299v1
2014-05-16,Damping of Confined Modes in a Ferromagnetic Thin Insulating Film: Angular Momentum Transfer Across a Nanoscale Field-defined Interface,"We observe a dependence of the damping of a confined mode of precessing
ferromagnetic magnetization on the size of the mode. The micron-scale mode is
created within an extended, unpatterned YIG film by means of the intense local
dipolar field of a micromagnetic tip. We find that damping of the confined mode
scales like the surface-to-volume ratio of the mode, indicating an interfacial
damping effect (similar to spin pumping) due to the transfer of angular
momentum from the confined mode to the spin sink of ferromagnetic material in
the surrounding film. Though unexpected for insulating systems, the measured
intralayer spin-mixing conductance $g_{\uparrow \downarrow} = 5.3 \times
10^{19} {\rm m}^{-2}$ demonstrates efficient intralayer angular momentum
transfer.",1405.4203v2
2014-12-17,Nucleon strange $s\bar s$ asymmetry to the $Λ/\barΛ$ fragmentation,"The difference between the $\Lambda$ and $\bar \Lambda$ longitudinal spin
transfers in the semi-inclusive deep inelastic scattering process is
intensively studied. The study is performed in the current fragmentation
region, by considering the intermediate hyperon decay processes and sea quark
fragmentation processes, while the strange sea $s\bar s$ asymmetry in the
nucleon is taken into account. The calculation in the light-cone quark-diquark
model shows that the strange sea asymmetry gives a proper trend to the
difference between the $\Lambda$ and $\bar \Lambda$ longitudinal spin
transfers. When considering the nonzero final hadron transverse momentum, our
results can explain the COMPASS data reasonably. The nonzero final hadron
transverse momentum is interpreted as a natural constraint to the final hadron
$z$ range where the longitudinal spin transfer is more sensitive to the strange
sea $s\bar s$ asymmetry.",1412.5266v1
2015-03-16,High-dimensional quantum state transfer in a noisy network environment,"We propose and analyze an efficient high-dimensional quantum state transfer
protocol in an XX coupling spin network with a hypercube structure or chain
structure. Under free spin wave approximation, unitary evolution results in a
perfect high-dimensional quantum swap operation requiring neither external
manipulation nor weak coupling. Evolution time is independent of either
distance between registers or dimensions of sent states, which can enable
improvements in computational efficiency. In the low temperature regime and
thermodynamic limit, the decoherence by noisy environment is studied with a
model of an antiferromagnetic spin bath coupled to quantum channels via an
Ising type interaction is studied. it is found that while the decoherence
reduces the fidelity of state transfer, increasing intra-channel coupling can
strongly suppress such effects. These observations demonstrate that robustness
of the proposed scheme.",1503.04550v2
2015-05-19,Robust state transfer with high fidelity in spin-1/2 chains by Lyapunov control,"Based on the Lyapunov control, we present a scheme to realize state transfer
with high fidelity by only modulating the boundary spins in a quantum spin-1/2
chain. Recall that the conventional transmission protocols aim at nonstationary
state (or information) transfer from the first spin to the end spin at a fixed
time. The present scheme possesses the following advantages. First, the scheme
does not require precise manipulations of the control time. Second, it is
robust against uncertainties in the initial states and fluctuations in the
control fields. Third, the controls are exerted only on the boundary sites of
the chain. It works for variable spin-1/2 chains with different periodic
structures and has good scalability. The feasibility to replace the control
fields by square pules is explored, which simplifies the realization in
experiments.",1505.04862v1
2019-09-18,Perfect quantum state transfer on diamond fractal graphs,"In the quest for designing novel protocols for quantum information and
quantum computation, an important goal is to achieve perfect quantum state
transfer for systems beyond the well-known one dimensional cases, such as 1d
spin chains. We use methods from fractal analysis and probability to find a new
class of quantum spin chains on fractal-like graphs (known as diamond fractals)
which support perfect quantum state transfer, and which have a wide range of
different Hausdorff and spectral dimensions. The resulting systems are spin
networks combining Dyson hierarchical model structure with transverse
permutation symmetries of varying order.",1909.08668v2
2019-12-12,Dimensionality-enhanced quantum state transfer in long-range interacting spin systems,"In this work we study the single-qubit quantum state transfer in uniform
long-range spin XXZ systems in high-dimensional geometries. We consider
prototypical long-range spin exchanges that are relevant for experiments in
cold atomic platforms: Coulomb, dipolar and van der Waals-like interactions. We
find that in all these cases the fidelity increases with the dimensionality of
the lattice. This can be related to the emergence of a pair of bilocalized
states on the sender and receiver site due to the onset of an effective
weak-coupling Hamiltonian. The enhancement of the quantum state transfer
fidelity is more pronounced both with the increase of the couplings interaction
range and in going from a 1D to a 2D lattice. Finally, we test our predictions
in the presence of temperature-induced disorder introducing a model for the
thermal displacement of the lattice sites, considered as a set of local
adiabatic oscillators.",1912.06239v1
2021-08-30,Spin to orbital angular momentum transfer in nonlinear wave mixing,"We demonstrate the spin to orbital angular momentum transfer in the nonlinear
mixing of structured light beams. A vector vortex is coupled to a circularly
polarized Gaussian beam in noncollinear second harmonic generation under
type-II phase match. The second harmonic beam inherits the Hermite-Gaussian
components of the vector vortex, however, the relative phase between them is
determined by the polarization state of the Gaussian beam. This effect creates
an interesting crosstalk between spin and orbital degrees of freedom, allowing
the angular momentum transfer between them. Our experimental results match the
theoretical predictions for the nonlinear optical response.",2108.13190v1
2023-01-10,Probing the longitudinal spin transfer via dihadron polarization correlations in unpolarized $e^+e^-$ and $pp$ collisions,"The longitudinal spin transfer represents the probability density of
producing longitudinally polarized hadrons from longitudinally polarized quarks
or circularly polarized gluons. It thus was usually measured in polarized
reactions or high-energy collisions where weak interaction dominates. In this
work, we propose the dihadron polarization correlation as a novel probe of this
quantity. Such an observable does not require the fragmenting partons to be
polarized and therefore can be measured in the currently available experimental
facilities, such as Belle, RHIC, Tevatron, and the LHC. We make quantitative
predictions for these experiments. In light of the data already harvested, the
experimental investigation of this observable provides more opportunity for the
quantitative study of the longitudinal spin transfer. In particular, the
measurements in pp collisions can significantly constrain the fragmentation
function of a circularly polarized gluon.",2301.04096v2
2023-03-28,Fast Bit-Flipping based on a Stability Transition of Coupled Spins,"A bipartite spin system is proposed for which a fast transfer from one
defined state into another exists. For sufficient coupling between the spins,
this implements a bit-flipping mechanism which is much faster than that induced
by tunneling. The states correspond in the semiclassical limit to equilibrium
points with a stability transition from elliptic-elliptic stability to complex
instability for increased coupling. The fast transfer is due to the spiraling
characteristics of the complex unstable dynamics. Based on the classical system
we find a universal scaling for the transfer time, which even applies in the
deep quantum regime. By investigating a simple model system, we show that the
classical stability transition is reflected in a fundamental change of the
structure of the eigenfunctions.",2303.16171v2
2023-11-07,Dissipative transfer of quantum correlations from light to atomic arrays,"We show how the directional collective response of atomic arrays to light can
be exploited for the dissipative generation of entangled atomic states,
relevant for e.g. quantum metrology. We consider an atomic array illuminated by
a paraxial beam of a squeezed-vacuum field and demonstrate that
quantum-squeezing correlations are dissipatively transferred to the array
atoms, resulting in an atomic spin-squeezed steady state. We find that the
entanglement transfer efficiency and hence the degree of spin squeezing are
determined by the resonant optical reflectivity of the array. Considering
realistic cases of finite-size array and illuminating beam, we find how the
spin-squeezing strength scales with system parameters, such as the number of
layers in the array and its spatial overlap with the beam. We discuss
applications in atomic clocks both in optical and microwave domains.",2311.03898v1
2023-11-13,Control of the nonlinear frequency shift for the spin-transfer nanooscillator using a bias magnetic field,"We investigated the possibilities of controlling the nonlinear frequency
shift of the magnetization oscillations in a spin-transfer nanoscillator by
varying the magnitude and direction of the bias magnetic field. We considered
both isotropic ferromagnetic materials and crystals with uniaxial and cubic
crystallographic anisotropies. We have shown that achieving a zero nonlinear
frequency shift is possible with a certain orientation of the bias magnetic
field vector. The results of the theoretical analysis based on the method of
Hamiltonian formalism are in good agreement with the micromagnetic simulations.
Our research reveals the way to control the frequency tuning of a spin transfer
nanoscillator, which is crucial for spintronic signal generation devices.",2311.07757v1
2024-01-14,Robust Parahydrogen-Induced Polarization at High Concentrations,"Parahydrogen-Induced Polarization (PHIP) is a potent technique for generating
target molecules with high nuclear spin polarization. The PHIP process involves
a chemical reaction between parahydrogen and a target molecule, followed by the
transformation of nuclear singlet spin order into magnetization of a designated
nucleus through magnetic field manipulations. Although the
singlet-to-magnetization polarization transfer process works effectively at
moderate concentrations, it is observed to become much less efficient at high
molar polarization, defined as the product of polarization and concentration.
This strong dependence on the molar polarization is attributed to interference
from the field produced by the sample's magnetization during polarization
transfer, which leads to complex dynamics and can severely impact the
scalability of the technique. We address this challenge with a pulse sequence
that negates the influence of the distant dipolar field, while simultaneously
achieving singlet-to-magnetization polarization transfer to the desired target
spins, free from restrictions on the molar polarization.",2401.07243v1
2024-04-01,Non-Hermitian unidirectional routing of photonic qubits,"Efficient and tunable qubit unidirectional routers and spin-wave diodes play
an important role in both classical and quantum information processing domains.
Here, we reveal that multi-level neutral cold atoms can mediate both
dissipative and coherent couplings. Interestingly, we investigate and
practically implement this paradigm in experiments, successfully synthesizing a
system with dual functionality as both a photonic qubit unidirectional router
and a spin-wave diode. By manipulating the helicity of the field, we can
effectively balance the coherence coupling and dissipative channel, thereby
ensuring the unidirectional transfer of photonic qubits. The qubit fidelity
exceeds 97.49%, and the isolation ratio achieves $16.8\pm0.11$ dB while the
insertion loss is lower than 0.36 dB. Furthermore, we show that the spin-wave
diode can effectively achieve unidirectional information transfer by
appropriately setting the coherent coupling parameters. Our work not only
provides new ideas for the design of extensive components in quantum networks,
but also opens up new possibilities for non-Hermitian quantum physics, complex
quantum networks, and unidirectional quantum information transfer.",2404.01211v1
2017-11-16,The spin rates and spin evolution of the O components in WR+O binaries,"Despite 50 years of extensive binary research we have to conclude that the
Roche lobe overflow/mass transfer process that governs close binary evolution
is still poorly understood. It is the scope of the present paper to lift a tip
of the veil by studying the spin-up and spin-down processes of the O-type
components of WR+O binaries. We critically analyze the available observational
data of rotation speeds of the O-type components in WR+O binaries. By combining
a binary evolutionary code and a formalism that describes the effects of tides
in massive stars with an envelope in radiative equilibrium, we compute the
corresponding rotational velocities during the Roche lobe overflow of the
progenitor binaries. In all the studied WR+O binaries, we find that the O-type
stars were affected by accretion of matter during the RLOF of the progenitor.
This means that common envelope evolution which excludes any accretion onto the
secondary O-star, has not played an important role to explain the WR+O
binaries. Moreover, although it is very likely that the O-type star progenitors
were spun-up by the mass transfer, many ended the RLOF/mass transfer phase with
a rotational velocity that is significantly smaller than the critical rotation
speed. This may indicate that during the mass transfer phase there is a
spin-down process which is of the same order as, although significantly less
than that of the spin-up process. We propose a Spruit-Tayler type dynamo
spin-down suggested in the past to explain the rotation speeds of the mass
gainers in long-period Algols.",1711.05989v2
2000-05-18,"Enhanced Spin Polarization of Conduction Electrons in Ni, explained by comparison with Cu","The spin-split Fermi level crossings of the conduction band in Ni are mapped
out by high-resolution photoemission and compared to the equivalent crossing in
Cu. The area of the quasiparticle peak decreases rapidly below Ef in Ni, but
not in Cu. Majority spins have larger spectral weight at Ef than minority
spins, thereby enhancing the spin-polarization beyond that expected from the
density of states. A large part of the effect can be traced to a rapid
variation of the matrix element with {\bf k} at the point where the s,p-band
begins to hybridize with the $dz^2$ state. However, it is quite possible that
the intensity drop in Ni is reinforced by a transfer of spectral weight from
single-particle to many-electron excitations. The results suggest that the
matrix element should be considered for explaining the enhanced spin
polarization observed for Ni in spin-polarized tunneling.",0005296v1
2003-05-27,Phase coherent quantum mechanical spin tranport in a weakly disordered quasi one-dimensional channel,"A transfer matrix technique is used to model phase coherent spin transport in
the weakly disordered quasi one-dimensional channel of a gate-controlled
electron spin interferometer [Datta and Das, Appl. Phys. Lett., 56, 665
(1990)]. It includes the effects of an axial magnetic field in the channel of
the interferometer (caused by the ferromagnetic contacts), a Rashba spin-orbit
interaction, and elastic (non-magnetic) impurity scattering. We show that in
the presence of the axial magnetic field, non-magnetic impurities can cause
spin relaxation in a manner similar to the Elliott-Yafet mechanism. The
amplitudes and phases of the conductance oscillations of the interferometer,
and the degree of spin-conductance polarization, are found to be quite
sensitive to the height of the interface barrier at the contact, as well as the
strength, locations and nature (attractive or repulsive) of just a few elastic
non-magnetic impurities in the channel. This can seriously hinder practical
applications of spin interferometers.",0305622v1
2004-12-10,Spin-orbit induced mixed-spin ground state in $R$NiO$_3$ perovskites probed by XAS: new insight into the metal to insulator transition,"We report on a Ni L$_{2,3}$ edges x-ray absorption spectroscopy (XAS) study
in $R$NiO$_3$ perovskites. These compounds exhibit a metal to insulator ($MI$)
transition as temperature decreases. The L$_{3}$ edge presents a clear
splitting in the insulating state, associated to a less hybridized ground
state. Using charge transfer multiplet calculations, we establish the
importance of the crystal field and 3d spin-orbit coupling to create a
mixed-spin ground state. We explain the $MI$ transition in $R$NiO$_3$
perovskites in terms of modifications in the Ni$^{3+}$ crystal field splitting
that induces a spin transition from an essentially low-spin (LS) to a
mixed-spin state.",0412276v1
2006-03-02,Quantum Spin Hall Effect and Topologically Invariant Chern Numbers,"We present a topological description of quantum spin Hall effect (QSHE) in a
two-dimensional electron system on honeycomb lattice with both intrinsic and
Rashba spin-orbit couplings. We show that the topology of the band insulator
can be characterized by a $2\times 2$ traceless matrix of first Chern integers.
The nontrivial QSHE phase is identified by the nonzero diagonal matrix elements
of the Chern number matrix (CNM). A spin Chern number is derived from the CNM,
which is conserved in the presence of finite disorder scattering and spin
nonconserving Rashba coupling. By using the Laughlin's gedanken experiment, we
numerically calculate the spin polarization and spin transfer rate of the
conducting edge states, and determine a phase diagram for the QSHE.",0603054v1
2003-12-15,Interactions at large distances and spin effects in nucleon-nucleon and nucleon-nuclei scattering,"The momentum-transfer dependence of the slopes of the spin-non-flip and
spin-flip amplitudes is analysed. It is shown that the long tail of the
hadronic potential in impact parameter space leads for hadron-hadron
interactions to a larger value of the slope for the reduced spin-flip amplitude
than for the spin-non-flip amplitude. It is shown that the preliminary
measurement of AN obtained by the E950 Collaboration confirms such a behaviour
of the hadron spin-flip amplitude.",0312195v2
1996-02-06,Correlation Functions in the Multiple Ising Model Coupled to Gravity,"The model of p Ising spins coupled to 2d gravity, in the form of a sum over
planar phi-cubed graphs, is studied and in particular the two-point and
spin-spin correlation functions are considered. We first solve a toy model in
which only a partial summation over spin configurations is performed and, using
a modified geodesic distance, various correlation functions are determined. The
two-point function has a diverging length scale associated with it. The
critical exponents are calculated and it is shown that all the standard scaling
relations apply. Next the full model is studied, in which all spin
configurations are included. Many of the considerations for the toy model apply
for the full model, which also has a diverging geometric correlation length
associated with the transition to a branched polymer phase. Using a transfer
function we show that the two-point and spin-spin correlation functions decay
exponentially with distance. Finally, by assuming various scaling relations, we
make a prediction for the critical exponents at the transition between the
magnetized and branched polymer phases in the full model.",9602028v1
2003-05-01,Spin effects and baryon resonance dynamics in phi-meson photoproduction at few GeV,"The diffractive $\phi$-meson photoproduction amplitude is dominated by the
Pomeron exchange process and contains the terms that govern the spin-spin and
spin-orbital interactions.
  We show that these terms are responsible for the spin-flip transitions at
forward photoproduction angles and appear in the angular distributions of
$\phi\to K^+K^-$ -decay in reactions with unpolarized and polarized photon
beams.
  At large momentum transfers, the main contribution to the $\phi$-meson
photoproduction is found to be due to the excitation of nucleon resonances.
  Combined analysis of $\omega$ and $\phi$ photoproduction indicates strong
OZI-rule violation in $\phi NN^*$ - couplings.
  We also show that the spin observables are sensitive to the dynamics of
$\phi$-meson photoproduction at large angles and could help distinguish
different theoretical models of nucleon resonances.
  Predictions for spin effects in $\phi$-meson photoproduction are presented
for future experimental tests.",0305002v2
2007-05-31,Rapid Diffusion of dipolar order enhances dynamic nuclear polarization,"In a dynamic nuclear polarization experiment on a 40 mM solution of
4-amino-TEMPO in a 40:60 water/glycerol mixture, we have observed that the bulk
dipolar reservoir is cooled to a spin temperature of 15.5 micro-K, following
microwave irradiation for 800 s. This is significantly cooler than the 35 mK
spin temperature of the Zeeman reservoir. Equilibration of the two reservoirs
results in a 50 % increase in the NMR signal intensity, corresponding to a
Zeeman spin temperature of 23 mK. In order to achieve this polarization
directly, it was necessary to irradiate the sample with microwaves for 1500 s.
Cooling of the dipolar reservoir occurs during polarization transport through
the magnetic field gradient around the paramagnetic impurity, and is rapidly
communicated to the bulk by dipolar spin diffusion. As dipolar spin diffusion
is significantly faster than Zeeman spin diffusion, the bulk dipolar reservoir
cools faster than the Zeeman reservoir. This process can be exploited to
rapidly polarize the nuclear spins, by repeatedly cooling the dipolar system
and transferring the polarization to the Zeeman reservoir.",0705.4671v1
2008-12-22,Spin-wave contributions to current-induced domain wall dynamics,"We examine theoretically the role of spin-waves on current-induced domain
wall dynamics in a ferromagnetic wire. At room temperature, we find that an
interaction between the domain wall and the spin waves appears when there is a
finite difference between the domain wall velocity $\dot{x}_0$ and the spin
current $u$. Three important consequences of this interaction are found.
Firstly, spin-wave emission leads to a Landau-type damping of the
current-induced domain wall motion towards restoring the solution $\dot{x}_0 =
u$, where spin angular momentum is perfectly transfered from the conduction
electrons to the domain wall. Secondly, the interaction leads to a modification
of the domain wall width and mass, proportional to the kinetic energy of the
domain wall. Thirdly, the coupling by the electrical current between the domain
wall and the spin waves leads to temperature-dependent effective wall mass.",0812.4084v1
2009-01-26,Cumulative identical spin rotation effects in collisionless trapped atomic gases,"We discuss the strong spin segregation in a dilute trapped Fermi gas recently
observed by Du et al. with ""anomalous"" large time scale and amplitude. In a
collisionless regime, the atoms oscillate rapidly in the trap and average the
inhomogeneous external field in an energy dependent way, which controls their
transverse spin precession frequency. During interactions between atoms with
different spin directions, the identical spin rotation effect (ISRE) transfers
atoms to the up or down spin state, depending on their motional energy. Since
low energy atoms are closer to the center of the trap than high energy atoms,
the final outcome is a strong correlation between spins and positions.",0901.4008v2
2009-03-26,Spin Excitations in BaFe1.84Co0.16As2 Superconductor Observed by Inelastic Neutron Scattering,"Superconductivity appears to compete against the spin-density-wave in Fe
pnictides. However, optimally cobalt doped samples show a quasi-two-dimensional
spin excitation centered at the (0.5, 0.5, L) wavevector, ""the spin resonance
peak"", that is strongly tied to the onset of superconductivity. By inelastic
neutron scattering on single crystals we show the similarities and differences
of the spin excitations in BaFe1.84Co0.16As2, with respect to the spin
excitations in the high-temperature superconducting cuprates. As in the
cuprates the resonance occurs as an enhancement to a part of the spin
excitation spectrum which extends to higher energy transfer and higher
temperature. However, unlike in the cuprates, the resonance peak in this
compound is asymmetric in energy.",0903.4621v3
2009-04-08,Architecture for high-sensitivity single-shot readout and control of the electron spin of individual donors in silicon,"We describe a method to control and detect in single-shot the electron spin
state of an individual donor in silicon with greatly enhanced sensitivity. A
silicon-based Single-Electron Transistor (SET) allows for spin-dependent
tunneling of the donor electron directly into the SET island during the
read-out phase. Simulations show that the charge transfer signals are typically
\Delta q > 0.2 e - over an order of magnitude larger than achievable with
metallic SETs on the SiO2 surface. A complete spin-based qubit structure is
obtained by adding a local Electron Spin Resonance line for coherent spin
control. This architecture is ideally suited to demonstrate and study the
coherent properties of donor electron spins, but can be expanded and integrated
with classical control electronics in the context of scale-up.",0904.1271v4
2009-05-07,Electrical Spin Injection into Silicon using MgO Tunnel Barrier,"We observed spin injection into silicon through Fe/MgO tunnel barrier by
using non-local magnetoresistance measurement technique. Fe/MgO tunnel barrier
contacts with a lateral spin valve structure were fabricated on phosphorous
doped silicon-on-insulator substrate. Spin injection signals in the non-local
scheme were observed up to 120K, which is the highest value where band
transferred spins in Si have ever been reported, and spin diffusion length was
estimated to be about 2.25um at 8K. Temperature dependence and injection
current dependence of the non-local voltage were also investigated. It is
clarified that MgO tunnel barrier is effective for the spin injection into
silicon.",0905.0942v1
2009-05-25,A silicon-based cluster state quantum computer,"It has been over ten years since Kane's influential proposal for a
silicon-based nuclear spin quantum computer using phosphorous donors. Since
then, silicon-based architectures have been refined as the experimental
challenges associated with the original proposal have become better understood,
while simultaneously a number of powerful and generic models for quantum
computation have emerged. Here, I discuss how the cluster state or ""one-way""
model for quantum computing might be advantageously applied to donors in
silicon, with the potential to substantially reduce the practical requirements
of a successful implementation. The essence of the scheme is to use the
electron spin associated with a donor to weave an entangled network between 31P
donor nuclear spins. This resource has been shown to have exceptional coherence
times and supports universal quantum computation through local measurements on
the nuclear spins. Some of the key ingredients, such as global spin
manipulation, have been robustly established, while others, such as single spin
measurement, have seen much progress in recent years. A key challenge will be
the demonstration of electron transfer between donors that preserves spin
coherence.",0905.4008v1
2009-06-11,The influence of the discretized Rashba spin-orbit interaction on the Harper model,"The movement of the electrons under the simultaneous influence of a scalar
periodic potential and of a uniform transversal magnetic field is described by
the well-known second order discrete Harper equation. This equation originates
from a two-dimensional energy dispersion law under the minimal substitution.
Here one deals with the Harper model under the additional influence of the
discretized spin orbit interaction. Converting the spin-orbit interaction in
terms of discrete derivatives opens the way for analytical and numerical
studies. One finds coupled equations for the spin dependent wave functions,
which leads to an appreciable alteration of the nested energy subbands
characterizing the self-similar structure of the usual Harper spectrum. To this
aim the transfer matrix method has been applied to selected spin-up and
spin-down wavefunctions. Accordingly, very manifestations of spinfiltering and
of spin correlations are accounted for. Our energy-bands calculations show that
the splitting effect implemented by such wavefunctions is appreciable.",0906.2054v1
2009-07-09,Spin-lattice coupling in frustrated antiferromagnets,"We review the mechanism of spin-lattice coupling in relieving the geometrical
frustration of pyrochlore antiferromagnets, in particular spinel oxides. The
tetrahedral unit, which is the building block of the pyrochlore lattice,
undergoes a spin-driven Jahn-Teller instability when lattice degrees of freedom
are coupled to the antiferromagnetism. By restricting our considerations to
distortions which preserve the translational symmetries of the lattice, we
present a general theory of the collective spin-Jahn-Teller effect in the
pyrochlore lattice. One of the predicted lattice distortions breaks the
inversion symmetry and gives rise to a chiral pyrochlore lattice, in which
frustrated bonds form helices with a definite handedness. The chirality is
transferred to the spin system through spin-orbit coupling, resulting in a
long-period spiral state, as observed in spinel CdCr2O4. We discuss explicit
models of spin-lattice coupling using local phonon modes, and their
applications in other frustrated magnets.",0907.1693v1
2009-09-25,Thermodynamics of multiferroic spin chains,"The minimal model to describe many spin chain materials with ferroelectric
properties is the Heisenberg model with ferromagnetic nearest neighbor coupling
J1 and antiferromagnetic next-nearest neighbor coupling J2. Here we study the
thermodynamics of this model using a density-matrix algorithm applied to
transfer matrices. We find that the incommensurate spin-spin correlations -
crucial for the ferroelectric properties and the analogue of the classical
spiral pitch angle - depend not only on the ratio J2/|J1| but also strongly on
temperature. We study small easy-plane anisotropies which can stabilize a
vector chiral order as well as the finite-temperature signatures of multipolar
phases, stable at finite magnetic field. Furthermore, we fit the
susceptibilities of LiCuVO4, LiCu2O2, and Li2ZrCuO4. Contrary to the
literature, we find that for LiCuVO4 the best fit is obtained with J2 ~ 90 K
and J2/|J1| ~ 0.5 and show that these values are consistent with the observed
spin incommensurability. Finally, we discuss our findings concerning the
incommensurate spin-spin correlations and multipolar orders in relation to
future experiments on these compounds.",0909.4579v3
2011-04-18,Enhanced photon-assisted spin transport in a quantum dot attached to ferromagnetic leads,"We investigate real-time dynamics of spin-polarized current in a quantum dot
coupled to ferromagnetic leads in both parallel and antiparallel alignments.
While an external bias voltage is taken constant in time, a gate terminal,
capacitively coupled to the quantum dot, introduces a periodic modulation of
the dot level. Using non equilibrium Green's function technique we find that
spin polarized electrons can tunnel through the system via additional
photon-assisted transmission channels. Owing to a Zeeman splitting of the dot
level, it is possible to select a particular spin component to be
photon-transfered from the left to the right terminal, with spin dependent
current peaks arising at different gate frequencies. The ferromagnetic
electrodes enhance or suppress the spin transport depending upon the leads
magnetization alignment. The tunnel magnetoresistance also attains negative
values due to a photon-assisted inversion of the spin-valve effect.",1104.3483v2
2011-10-19,Fano resonances and electron spin transport through a two-dimensional spin-orbit-coupled quantum ring,"Electron transport through a spin-orbit-coupled quantum ring is investigated
within linear response theory. We show that the finite width of the ring
results in the appearance of Fano resonances in the conductance. This turns out
to be a consequence of the spin-orbit interaction that leads to a breaking of
the parity of the states localized in the ring. The resonances appear when the
system is close to maxima of Aharonov-Casher conductance oscillations where
spin transfer is heavily modified. When the spin-orbit coupling strength is
detuned from the Aharonov-Casher maxima the resonances are broadened resulting
in a dependence of the spin transport on the electron Fermi energy in contrast
to predictions from one-dimensional models",1110.4233v1
2012-03-28,Bias asymmetry in the conductance profile of magnetic ions on surfaces probed by scanning tunneling microscopy,"The conductance profiles of magnetic transition metal atoms, such as Fe, Co
and Mn, deposited on surfaces and probed by a scanning tunneling microscope
(STM), provide detailed information on the magnetic excitations of such
nano-magnets. In general the profiles are symmetric with respect to the applied
bias. However a set of recent experiments has shown evidence for inherent
asymmetries when either a normal or a spin-polarized STM tip is used. In order
to explain such asymmetries here we expand our previously developed
perturbative approach to electron-spin scattering to the spin- polarized case
and to the inclusion of out of equilibrium spin populations. In the case of a
magnetic STM tip we demonstrate that the asymmetries are driven by the
non-equilibrium occupation of the various atomic spin-levels, an effect that
reminds closely that electron spin-transfer. In contrast when the tip is not
spin-polarized such non-equilibrium population cannot be build up. In this
circumstance we propose that the asymmetry simply originates from the
transition metal ion density of state, which is included here as a
non-vanishing real component to the spin-scattering self-energy.",1203.6238v1
2012-04-12,Information transfer by vector spin chirality in finite magnetic chains,"Vector spin chirality is one of the fundamental characteristics of complex
magnets. For a one-dimensional spin-spiral state it can be interpreted as the
handedness, or rotational sense of the spiral. Here, using spin-polarized
scanning tunneling microscopy, we demonstrate the occurrence of an atomic-scale
spin-spiral in finite individual bi-atomic Fe chains on the (5x1)-Ir(001)
surface. We show that the broken inversion symmetry at the surface promotes one
direction of the vector spin chirality, leading to a unique rotational sense of
the spiral in all chains. Correspondingly, changes in the spin direction of one
chain end can be probed tens of nanometers away, suggesting a new way of
transmitting information about the state of magnetic objects on the nanoscale.",1204.2650v1
2012-12-21,Domain-wall-controlled transverse spin injection,"We propose an effect whereby an electric current along the interface between
a ferromagnetic and normal metal leads to injection of pure spin current into
the normal metal, if the magnetization-direction in the ferromagnet varies
along the direction of current. For the specific example of a ferromagnetic
domain wall, we compute the inverse spin-Hall effect voltage this spin current
gives rise to when injected into a Pt layer. Furthermore, we show that this
pure spin current leads to modification of the parameters that govern spin
transfer and current-driven domain-wall motion, which can be use to optimize
the latter in layered magnetic systems. This effect in principle enables
control over the location of spin-current injection in devices.",1212.5435v1
2013-01-14,Spin coherent states in NMR quadrupolar system: experimental and theoretical applications,"Working with nuclear magnetic resonance (NMR) in quadrupolar spin systems, in
this paper we transfer the concept of atomic coherent state to the nuclear spin
context, where it is referred to as pseudo-nuclear spin coherent state
(pseudo-NSCS). Experimentally, we discuss the initialization of the
pseudo-NSCSs and also their quantum control, implemented by polar and azimuthal
rotations. Theoretically, we compute the geometric phases acquired by an
initial pseudo-NSCS on undergoing three distinct cyclic evolutions: $ i) $ the
free evolution of the NMR quadrupolar system and, by analogy with the evolution
of the NMR quadrupolar system, that of $ii)$ single-mode and $ iii)$ two-mode
Bose-Einstein Condensate like system. By means of these analogies, we derive,
through spin angular momentum operators, results equivalent to those presented
in the literature for orbital angular momentum operators. The pseudo-NSCS
description is a starting point to introduce the spin squeezed state and
quantum metrology into nuclear spin systems of liquid crystal or solid matter.",1301.2862v1
2013-08-15,Detection of the microwave spin pumping using the inverse spin Hall effect,"We report electrical detection of the dynamical part of the spin pumping
current emitted during ferromagnetic resonance (FMR) using the inverse Spin
Hall Effect (ISHE). The experiment is performed on a YIG$|$Pt bilayer. The
choice of YIG, a magnetic insulator, ensures that no charge current flows
between the two layers and only pure spin current produced by the magnetization
dynamics are transferred into the adjacent strong spin-orbit Pt layer via spin
pumping. To avoid measuring the parasitic eddy currents induced at the
frequency of the microwave source, a resonance at half the frequency is induced
using parametric excitation in the parallel geometry. Triggering this nonlinear
effect allows to directly detect on a spectrum analyzer the microwave component
of the ISHE voltage. Signals as large as 30 $\mu$V are measured for precession
angles of a couple of degrees. This direct detection provides a novel efficient
means to study magnetization dynamics on a very wide frequency range with great
sensitivity.",1308.3433v2
2014-02-25,Unusual Two-stage Dynamics of the Spin-Lattice Polaron Formation,"We follow the formation of a spin-lattice polaron after a quantum quench that
simulates absorption of the pump{pulse in the time-resolved experiments. We
discover a two-stage relaxation where spin and lattice degrees of freedom
represent an integral part of the relaxation mechanism. In the first stage the
kinetic energy of the spin-lattice polaron relaxes towards its ground state
value while relaxation processes via spin and phonon degrees of freedom remain
roughly independent. In the second, typically much longer stage, a subsequent
energy transfer between lattice and spin degrees of freedom via the charge
carrier emerges. The excess local spin energy radiates away via magnon
excitations.",1402.6104v1
2014-03-20,Mechanically-controlled spin-selective transport,"A device enabling mechanically-controlled spin and electric transport in
mesoscopic structures is proposed. It is based on the transfer of electrons
through weak links formed by suspended nanowires, on which the charge carriers
experience a strong Rashba spin-orbit interaction that twists their spins. It
is demonstrated that when the weak link bridges two magnetically-polarised
electrodes, a significant spintro-voltaic effect takes place. Then, by
monitoring the generated voltage one is able to measure electronic spins
accumulated in the electrodes, induced e.g., by circularly-polarised light, or
alternatively, the amount of spin twisting. Mechanically-tuning the device by
bending the nanowire allows one to achieve full control over the spin
orientations of the charge carriers.",1403.5200v3
2014-06-10,Nanosecond spin lifetimes in single- and few-layer graphene-hBN heterostructures at room temperature,"We present a new fabrication method of graphene spin-valve devices which
yields enhanced spin and charge transport properties by improving both the
electrode-to-graphene and graphene-to-substrate interface. First, we prepare
Co/MgO spin injection electrodes onto Si$^{++}$/SiO$_2$. Thereafter, we
mechanically transfer a graphene-hBN heterostructure onto the prepatterned
electrodes. We show that room temperature spin transport in single-, bi- and
trilayer graphene devices exhibit nanosecond spin lifetimes with spin diffusion
lengths reaching 10$\mu$m combined with carrier mobilities exceeding 20,000
cm$^2$/Vs.",1406.2439v1
2015-02-13,Antiferromagnet-Mediated Spin Transfer Between Metal and Ferromagnet,"We develop a theory for spin transported by coherent Neel dynamics through an
antiferromagnetic insulator coupled to a ferromagnetic insulator on one side
and a current-carrying normal metal with strong spin-orbit coupling on the
other. The ferromagnet is considered within the mono-domain limit and we assume
its coupling to the local antiferromagnet Neel order at the
ferromagnet|antiferromagnet interface through exchange coupling. Coupling
between the charge current and the local Neel order at the other interface is
described using spin Hall phenomenology. Spin transport through the
antiferromagnet, assumed to possess an easy-axis magnetic anisotropy, is solved
within the adiabatic approximation and the effect of spin current flowing into
the ferromagnet on its resonance linewidth is evaluated. Onsager reciprocity is
used to evaluate the inverse spin Hall voltage generated across the metal by a
dynamic ferromagnet as a function the antiferromagnet thickness.",1502.04128v1
2015-03-17,Exploring the transport properties of polytypic and twin-plane nanowires: from tunneling phase-time to spin-orbit interaction effects,"The variety of nanowire crystal structures gave rise to unique and novel
transport phenomena. In particular, we have explored the superlattice profile
generated by strain field modulation in twinplane nanowires for the tuning of
transport channels and the built-in spin-orbit potential profile of polytypic
nanowires, in order to realize a spin filter. The Multicomponent Scattering
Approach has been used in terms of the Transfer Matrix Method to describe the
phase-time of charge carriers. This system showed advantages for attaining
conditions for the propagation of wave packets with negative group velocity.
Moreover, the spin transport effect of a potential profile with volumetric
spin-orbit bulk inversion asymmetry, as present on polytypic nanowires, was
described through the Reverse Runge-Kutta Method. Using the peculiar symmetry
of the excited states we have characterized a dominant spin dependence on
structural parameters that results in effective spin filtering.",1503.05223v1
2015-10-22,Towards a spin-ensemble quantum memory for superconducting qubits,"This article reviews efforts to build a new type of quantum device, which
combines an ensemble of electronic spins with long coherence times, and a
small-scale superconducting quantum processor. The goal is to store over long
times arbitrary qubit states in orthogonal collective modes of the
spin-ensemble, and to retrieve them on-demand. We first present the protocol
devised for such a multi-mode quantum memory. We then describe a series of
experimental results using NV center spins in diamond, which demonstrate its
main building blocks: the transfer of arbitrary quantum states from a qubit
into the spin ensemble, and the multi-mode retrieval of classical microwave
pulses down to the single-photon level with a Hahn-echo like sequence. A reset
of the spin memory is implemented in-between two successive sequences using
optical repumping of the spins.",1510.06565v1
2015-11-18,Transformation of spin current by antiferromagnetic insulators,"It is demonstrated theoretically that a thin layer of an anisotropic
antiferromagnetic (AFM) insulator can effectively conduct spin current by
excitation of a pair of evanescent AFM spin wave modes. The spin current
flowing through the AFM is not conserved due to the interaction between the
excited AFM modes and the AFM lattice, and, depending on the excitation
conditions, can be either attenuated or enhanced. When the phase difference
between the excited evanescent modes is close to $\pi/2$, there is an optimum
AFM thickness for which the output spin current reaches a maximum, that can
significantly exceed the magnitude of the input spin current. The spin current
transfer through the AFM depends on the ambient temperature and increases
substantially when temperature approaches the Neel temperature of the AFM
layer.",1511.05785v4
2015-12-10,Spin frustration of a spin-1/2 Ising-Heisenberg three-leg tube as an indispensable ground for thermal entanglement,"The spin-1/2 Ising-Heisenberg three-leg tube composed of the Heisenberg spin
triangles mutually coupled through the Ising inter-triangle interaction is
exactly solved in a zero magnetic field. By making use of the local
conservation for the total spin on each Heisenberg spin triangle the model can
be rigorously mapped onto a classical composite spin-chain model, which is
subsequently exactly treated through the transfer-matrix method. The
ground-state phase diagram, correlation functions, concurrence, Bell function,
entropy and specific heat are examined in detail. It is shown that the spin
frustration represents an indispensable ground for a thermal entanglement,
which is quantified with the help of concurrence. The specific heat displays
diverse temperature dependences, which may include a sharp low-temperature peak
mimicking a temperature-driven first-order phase transition. It is convincingly
evidenced that this anomalous peak originates from massive thermal excitations
from the doubly degenerate ground state towards an excited state with a high
macroscopic degeneracy due to chiral degrees of freedom of the Heisenberg spin
triangles.",1512.03231v1
2015-12-21,Correlated impurities and intrinsic spin liquid physics in the kagome material Herbertsmithite,"Low energy inelastic neutron scattering on single crystals of the kagome spin
liquid compound ZnCu3(OD)6Cl2 (Herbertsmithite) reveals antiferromagnetic
correlations between impurity spins for energy transfers E < 0.8 meV (~J/20).
The momentum dependence differs significantly from higher energy scattering
which arises from the intrinsic kagome spins. The low energy fluctuations are
characterized by diffuse scattering near wavevectors (1 0 0) and (0 0 3/2),
which is consistent with antiferromagnetic correlations between pairs of
nearest neighbor Cu impurities on adjacent triangular (Zn) interlayers. The
corresponding impurity lattice resembles a simple cubic lattice in the dilute
limit below the percolation threshold. Such an impurity model can describe
prior neutron, NMR, and specific heat data. The low energy neutron data are
consistent with the presence of a small spin-gap (Delta ~ 0.7 meV) in the
kagome layers, similar to that recently observed by NMR. The ability to
distinguish the scattering due to Cu impurities from that of the planar kagome
Cu spins provides a new avenue for probing intrinsic spin liquid physics.",1512.06807v1
2016-05-22,Spin control of light with hyperbolic metasurfaces,"Transverse spin angular momentum is an inherent feature of evanescent waves
which may have applications in nanoscale optomechanics, spintronics, and
quantum information technology due to the robust spin-directional coupling.
Here we analyze a local spin angular momentum density of hybrid surface waves
propagating along anisotropic hyperbolic metasurfaces. We reveal that, in
contrast to bulk plane waves and conventional surface plasmons at isotropic
interfaces, the spin of the hybrid surface waves can be engineered to have an
arbitrary angle with the propagation direction. This property allows to tailor
directivity of surface waves via the magnetic control of the spin projection of
quantum emitters, and it can be useful for optically controlled spin transfer.",1605.06781v2
2016-09-02,Potential Energy Driven Spin Manipulation via a Controllable Hydrogen Ligand,"Spin-bearing molecules can be stabilized on surfaces and in junctions with
desirable properties such as a net spin that can be adjusted by external
stimuli. Using scanning probes, initial and final spin states can be deduced
from topographic or spectroscopic data, but how the system transitioned between
these states is largely unknown. Here we address this question by manipulating
the total spin of magnetic cobalt hydride complexes on a corrugated boron
nitride surface with a hydrogen- functionalized scanning probe tip by
simultaneously tracking force and conductance. When the additional hydrogen
ligand is brought close to the cobalt monohydride, switching between a corre-
lated S = 1 /2 Kondo state, where host electrons screen the magnetic moment,
and a S = 1 state with magnetocrystalline anisotropy is observed. We show that
the total spin changes when the system is transferred onto a new potential
energy surface defined by the position of the hydrogen in the junction. These
results show how and why chemically functionalized tips are an effective tool
to manipulate adatoms and molecules, and a promising new method to selectively
tune spin systems.",1609.00612v2
2016-11-21,Controlling a nuclear spin in a nanodiamond,"The sensing capability of a single optically bright electronic spin in
diamond can be enhanced by making use of proximal dark nuclei as ancillary
spins. Such systems, so far only realized in bulk diamond, provide orders of
magnitude higher sensitivity and spectral resolution in the case of magnetic
sensing, as well as improved readout fidelity and state storage time in quantum
information schemes. In nanodiamonds, which offer additional opportunities as
mobile nanoscale sensors, electronic-nuclear spin complexes have remained
inaccessible. We demonstrate coherent control of a 13C nuclear spin located
4{\AA} from a nitrogen-vacancy center in a nanodiamond and show quantum-state
transfer between the two components of this hybrid spin system. We extract a
nuclear-spin free precession time of T2* = 26 us, which exceeds the bare
electron free precession time in nanodiamond by two orders of magnitude.",1611.06898v1
2017-07-31,High-efficiency optical pumping of nuclear polarization in a GaAs quantum well,"The dynamic polarization of nuclear spins by photoexcited electrons is
studied in a high quality GaAs/AlGaAs quantum well. We find a surprisingly high
efficiency of the spin transfer from the electrons to the nuclei as reflected
by a maximum nuclear field of 0.9 T in a tilted external magnetic field of 1 T
strength only. This high efficiency is due to a low leakage of spin out of the
polarized nuclear system, because mechanisms of spin relaxation other than the
hyperfine interaction are strongly suppressed, leading to a long nuclear
relaxation time of up to 1000 s. A key ingredient to that end is the low
impurity concentration inside the heterostructure, while the electrostatic
potential from charged impurities in the surrounding barriers becomes screened
through illumination by which the spin relaxation time is increased compared to
keeping the system in the dark. This finding indicates a strategy for obtaining
high nuclear spin polarization as required for long-lasting carrier spin
coherence.",1708.00053v2
2017-09-07,Tunable spin pumping in exchange coupled magnetic trilayers,"Magnetic thin films at ferromagnetic resonance (FMR) leak angular momentum,
which may be absorbed by adjacent layers. This phenomenon, known as spin
pumping, is manifested by an increase in the resonance linewidth ($\Delta H$),
and the closely related Gilbert damping. Another effect of this transfer of
spin currents is a dynamical and long-range coupling that can drive two
magnetic layers into a collective precession when their FMR frequencies
coincide. A collective behavior is also found in magnetic trilayers with
interlayer exchange coupling (IEC). In this study we investigate the interplay
between IEC and spin pumping, using Co/Cu/Py pseudo-spin values. We employ
broadband FMR spectroscopy to explore both the frequency and coupling-strength
dependence of $\Delta H$. Our observations show that there exists a cut-off
frequency, set by the IEC strength, below which the precession is truly
collective and the spin pumping is suppressed. These results demonstrate that
it is possible to control the spin pumping efficiency by varying the frequency
or the interlayer exchange coupling.",1709.02295v1
2017-12-30,Sensing coherent dynamics of electronic spin clusters in solids,"We present experimental observations and a study of quantum dynamics of
strongly interacting electronic spins, at room temperature in the solid state.
In a diamond substrate, a single nitrogen vacancy (NV) center coherently
interacts with two adjacent S = 1/2 dark electron spins. We quantify
NV-electron and electron-electron couplings via detailed spectroscopy, with
good agreement to a model of strongly interacting spins. The electron-electron
coupling enables an observation of coherent flip-flop dynamics between
electronic spins in the solid state, which occur conditionally on the state of
the NV. Finally, as a demonstration of coherent control, we selectively couple
and transfer polarization between the NV and the pair of electron spins. These
results demonstrate a key step towards full quantum control of electronic spin
registers in room temperature solids.",1801.00198v2
2019-07-01,Rate Distortion Theorem and the Multicritical Point of Spin Glass,"A spin system can be thought of as an information coding system that
transfers information of the interaction configuration into information of the
equilibrium state of the spin variables. Hence it can be expected that the
relations between the interaction configuration and equilibrium states are
consistent with the known laws of information theory. We show that Shannon's
rate-distortion theorem can be used to obtain an universal constraint on
neighboring spin correlations for a broad range of Ising spin systems with
two-body spin interactions. Remarkably, this constraint gives a bound for the
multicritical point in the phase diagram, when a mean-field behavior for the
neighboring spin pairs can be expected in the paramagnetic phase.",1907.01048v4
2019-09-30,Magnetic circular dichroism in hard x-ray Raman scattering as a probe of local spin polarization,"We argue that the magnetic circular dichroism (MCD) of the hard x-ray Raman
scattering (XRS) could be used as an element selective probe of local spin
polarization. The magnitude of the XRS-MCD signal is directly proportional to
the local spin polarization when the angle between the incident wavevector and
the magnetization vector is $135^{\circ}$ or $-45^{\circ}$. By comparing the
experimental observation and the configuration interaction calculation at the
$L_{2,3}$ and $M_{2,3}$ edges of ferromagnetic iron, we suggest that the
integrated MCD signal in terms of the transferred energy could be used to
estimate the local spin moment even in the case where the application of the
spin sum-rule in X-ray absorption is questionable. We also point out that
XRS-MCD signal could be observed at the $M_{1}$ edge with a magnitude
comparable to that at the $M_{2,3}$ edge, although the spin-orbit coupling is
absent in the core orbital. By combining the XRS-MCD at various edges, spin
polarization distribution depending on the orbital magnetic quantum number
would be determined.",1909.13490v1
2020-03-30,Adiabatic spin-dependent momentum transfer in an SU(N) degenerate Fermi gas,"We introduce a spin-orbit coupling scheme, where a retro-reflected laser beam
selectively diffracts two spin components in opposite directions. Spin
sensitivity is provided by sweeping through a magnetic-field sensitive
transition while dark states ensure that spontaneous emission remains low. The
scheme is adiabatic and thus inherently robust. This tailored spin-orbit
coupling allows simultaneous measurements of the spin and momentum
distributions of a strontium degenerate Fermi gas, and thus opens the path to
momentum-resolved spin correlation measurements on SU(N) quantum magnets.",2003.13444v3
2020-12-16,Nucleon structure and spin effects in elastic hadron scattering,"Soft diffraction phenomena in elastic nucleon scattering are considered from
the viewpoint of the spin dependence of the interaction potential.
Spin-dependent pomeron effects are analyzed for elastic $pp$ scattering,
spin-dependent differential cross sections and spin correlation parameters are
calculated. The spin correlation parameter $A_N$ is examined on the basis of
experimental data from $\sqrt{s} = 4.9 \ GeV$ up to $23.4 \ $GeV in the
framework of the extended High Energy Generalized Structure (HEGS) model. It is
shown that the existing experimental data of proton-proton and
proton-antiproton elastic scattering at high energy in the region of the
diffraction minimum and at large momentum transfer give the support of the
existence of the energy-independent part of the hadron spin flip amplitude.",2012.08891v3
2021-05-13,CVD bilayer graphene spin valves with 26 $μ$m spin diffusion length at room temperature,"We present inverted spin-valves fabricated from CVD-grown bilayer graphene
(BLG) that show more than a doubling in device performance at room temperature
compared to state-of-the art bilayer graphene spin-valves. This is made
possible by a PDMS droplet-assisted full-dry transfer technique that
compensates for previous process drawbacks in device fabrication.
Gate-dependent Hanle measurements show spin lifetimes of up to 5.8 ns and a
spin diffusion length of up to 26 $\mu$m at room temperature combined with a
charge carrier mobility of $\approx$ 24 000 cm$^{2}$(Vs)$^{-1}$ for the best
device. Our results demonstrate that CVD-grown BLG shows equally good room
temperature spin transport properties as both CVD-graphene and even exfoliated
single-layer graphene.",2105.06277v2
2022-06-08,Emergence of Spinmerism for Molecular Spin-Qubits Generation,"Molecular platforms are regarded as promising candidates in the generation of
units of information for quantum computing. Herein, a strategy combining
spin-crossover metal ions and radical ligands is proposed from a model
Hamiltonian first restricted to exchange interactions. Unusual spin states
structures emerge from the linkage of a singlet/triplet commutable metal centre
with two doublet-radical ligands. The ground state nature is modulated by
charge transfers and can exhibit a mixture of triplet and singlet local metal
spin states. Besides, the superposition reaches a maximum for $2K_M = K_1 +
K_2$, suggesting a necessary competition between the intramolecular $K_M$ and
inter-metal-ligand $K_1$ and $K_2$ direct exchange interactions. The results
promote \textit{spinmerism}, an original manifestation of quantum entanglement
between the spin states of a metal centre and radical ligands. The study
provides insights into spin-coupled compounds and inspiration for the
development of molecular spin-qubits.",2206.03978v2
2022-09-16,Rashba-like spin-orbit interaction and spin texture at the KTaO$_\text{3}$ (001) surface from DFT calculations,"Rashba-like spin-orbit interaction at oxide heterostructures emerges as a
much sought-after feature in the context of oxide spintronics and
spin-orbitronics. KTaO$_3$ (KTO) is one of the best substrates available for
the purpose, owing to its strong spin-orbit interaction and alternating $+1|-1$
charged layers along the (001) direction. Employing first-principles
calculations within density functional theory (DFT) and proposing a possible
electrostatic model for charge transfer to the surfaces of KTO slabs, we
comprehensively analyze Rashba-like spin-orbit interaction with the help of
three-dimensional band dispersion, isoenergetic contours, and projected spin
textures $-$ all directly obtained from our DFT results $-$ in a thin
insulating slab and a conducting thick slab of KTO. Our results reveal
reasonably strong linear Rashba interaction with no signature of Dresselhaus or
higher order Rashba interactions in the systems considered here. The rigorous
analysis presented here may be crucial for future developments in oxide
spintronics.",2209.07723v1
2022-09-22,Electric Control of Spin Transitions at the Atomic Scale,"Electric control of spins has been a longstanding goal in the field of solid
state physics due to the potential for increased efficiency in information
processing. This efficiency can be optimized by transferring spintronics to the
atomic scale. We present electric control of spin resonance transitions in
single molecules by employing electron spin resonance scanning tunneling
microscopy (ESR-STM). We find strong bias voltage dependent shifts in the ESR
signal of about ten times its linewidth, which is due to the electric field
induced displacement of the spin system in the tunnel junction. This opens up
new avenues for ultrafast control of coupled spin systems, even towards atomic
scale quantum computing, and expands on understanding and optimizing spin
electric coupling in bulk materials.",2209.10969v1
2022-11-07,Simulation of the Einstein-de Haas effect combining molecular and spin dynamics,"The spin and lattice dynamics of a ferromagnetic nanoparticle are studied via
molecular dynamics and with semi-classical spin dynamics simulations where spin
and lattice degrees of freedom are coupled via a dynamic uniaxial anisotropy
term. We show that this model conserves total angular momentum, whereas spin
and lattice angular momentum are not conserved. We carry out simulations of the
the Einstein-de Haas effect for a Fe nanocluster with more than 500 atoms that
is free to rotate, using a modified version of the open-source spinlattice
dynamics code (SPILADY). We show that the rate of angular momentum transfer
between spin and lattice is proportional to the strength of the magnetic
anisotropy interaction. The addition of the anisotropy allows full spin-lattice
relaxation to be achieved on previously reported timescales of \sim 100 ps and
for tight-binding magnetic anisotropy energies comparable to those of small Fe
nanoclusters.",2211.03706v1
2022-11-28,Secondary spin current driven efficient THz spintronic emitters,"Femtosecond laser-induced photoexcitation of ferromagnet (FM)/heavy metal
(HM) heterostructures have attracted attention by emitting broadband terahertz
frequencies. The phenomenon relies on the formation of ultrafast spin current,
which is largely attributed to the direct photoexcitation of the FM layer.
However, we reveal that during the process, the FM layer also experiences a
secondary excitation led by the hot electrons from the HM layer that travel
across the FM/HM interface and transfer additional energy in the FM. Thus, the
generated secondary spins enhance the total spin current formation and lead to
amplified spintronic terahertz emission. The results also emphasize the
significance of the secondary spin current, which even exceeds the primary spin
currents when FM/HM heterostructures with thicker HM are used. An analytical
model is developed to provide deeper insights into the microscopic processes
within the individual layers, underlining the generalized ultrafast
superdiffusive spin-transport mechanism.",2211.15135v2
2023-05-25,Polarization response of spin-lasers under amplitude modulation,"Lasers with injected spin-polarized carriers show an outstanding performance
in both static and dynamic operation. In addition to the intensity response of
conventional lasers, without spin-polarized carriers, both intensity and
polarization of light can be exploited for optical communication in
spin-lasers. However, the polarization dynamics of spin-lasers under amplitude
modulation has been largely overlooked. Here we reveal, analytically and
numerically, a nontrivial polarization response that accompanies the well-known
intensity dynamics of a spin-laser under amplitude modulation. We evaluate the
polarization and intensity response under the same amplitude modulation, and
further assess the capability of such a polarization response in digital data
transfer with eye diagram simulations. Our results provide a more complete
understanding of the modulation response in spin-lasers and open up unexplored
opportunities in optical communication and spintronics.",2305.15819v1
2023-06-08,Unidirectionality of spin waves in Synthetic Antiferromagnets,"We study the frequency non-reciprocity of the spin waves in symmetric
CoFeB/Ru/CoFeB synthetic antiferromagnets stacks set in the scissors state by
in-plane applied fields. Using a combination of Brillouin Light Scattering and
propagating spin wave spectroscopy experiments, we show that the acoustical
spin waves in synthetic antiferromagnets possess a unique feature if their
wavevector is parallel to the applied field: the frequency non-reciprocity due
to layer-to-layer dipolar interactions can be so large that the acoustical spin
waves transfer energy in a unidirectional manner for a wide and bipolar
interval of wavevectors. Analytical modeling and full micromagnetic
calculations are conducted to account for the dispersion relations of the
optical and acoustical spin waves for arbitrary field orientations. Our
formalism provides a simple and direct method to understand and design devices
harnessing unidirectional propagation of spin waves in synthetic
antiferromagnets.",2306.05259v2
2023-07-24,Scalable Quantum Spin Networks from Unitary Construction,"Spin network systems can be used to achieve quantum state transfer with high
fidelity and to generate entanglement. A new approach to design
spin-chain-based spin network systems, for shortrange quantum information
processing and phase-sensing, has been proposed recently in [1]. In this paper,
we investigate the scalability of such systems, by designing larger spin
network systems that can be used for longer-range quantum information tasks,
such as connecting together quantum processors. Furthermore, we present more
complex spin network designs, which can produce different types of entangled
states. Simulations of disorder effects show that even such larger spin network
systems are robust against realistic levels of disorder.",2307.12978v2
2024-02-19,Photoelectron Polarization Vortexes in Strong-Field Ionization,"The spin polarization of photoelectrons induced by an intense linearly
polarized laser field is investigated using numerical solutions of the
time-dependent Schr\""odinger equation in companion with our analytic treatment
via the spin-resolved strong-field approximation and classical trajectory Monte
Carlo simulations. We demonstrate that, even though the total polarization
vanishes upon averaging over the photoelectron momentum, momentum-resolved spin
polarization is significant, typically exhibiting a vortex structure relative
to the laser polarization axis. The polarization arises from the transfer of
spin-orbital coupling in the bound state to the spin-correlated quantum orbits
in the continuum. The rescattering of photoelectrons at the atomic core plays
an important role in forming the polarization vortex structure, while there is
no significant effect of the spin-orbit coupling during the continuum dynamics.
Furthermore, spin-polarized electron holography is demonstrated, feasible for
extracting fine structural information about the atom.",2402.11825v1
2024-03-22,Coherent Phonon Control of Ultrafast Magnetization Dynamics in Fe$_\text{3}$GeTe$_\text{2}$ from Time-Dependent Ab Initio Theory,"Exploring ultrafast magnetization control in two-dimensional (2D) magnets
through optically driven coherent phonons has been well-established. Yet, the
microscopic interplay between spin dynamics and lattice degrees of freedom
remains less explored. Employing real-time time-dependent density functional
theory (rt-TDDFT) coupled with Ehrenfest dynamics, we systematically
investigate laser-induced spin-nuclei dynamics with coherent phonon excitation
in the 2D ferromagnet Fe3GeTe2. We found that selectively pre-exciting three
typical coherent phonon modes results in up to a 53% additional spin moment
loss in an out-of-plane A2 1g mode within ~50 fs. Coherent phonon control of
spin dynamics is closely linked to laser pulse parameters. The underlying
microscopic mechanism of this phenomenon is primarily governed by coherent
phonon-induced asymmetric spin-resolved charge transfer following the
disappearance of the laser pulse, thereby enabling effective control of the
spin moment loss. Our findings offer a novel insight into the coupling of
coherent phonons with spin systems in 2D limits on femtosecond timescales.",2403.15204v1
2001-09-06,Where May Ultra-Fast Rotating Neutron Stars Be Hidden?,"The existence of ultra-fast rotating neutron stars (spin period P < 1 ms) is
expected on the basis of current models for the secular evolution of
interacting binaries, though they have not been detected yet. Their formation
depends on the quantity of matter accreted by the neutron star which, in turn,
is limited by the mechanism of mass ejection from the binary. An efficient mass
ejection can avoid the formation of ultra-fast pulsars or their accretion
induced collapse to a black hole. We propose that significant reductions of the
mass-transfer rate may cause the switch-on of a radio pulsar phase, whose
radiation pressure may be capable of ejecting out of the system most of the
matter transferred by the companion. This can prevent, for long orbital periods
and if a sufficiently fast spin has been reached, any further accretion, even
if the original transfer rate is restored, thus limiting the minimum spin
period attainable by the neutron star. We show that close systems (orbital
periods P_orb \sim 1 hr are the only possible hosts for ultra-fast spinning
neutron stars. This could explain why ultra-fast radio pulsars have not been
detected so far, as the detection of pulsars with very short spin periods in
close systems is hampered, in current radio surveys, by strong Doppler
modulation and computational limitations.",0109088v1
2014-06-09,"Quasilocal conservation laws in XXZ spin-1/2 chains: open, periodic and twisted boundary conditions","A continuous family of quasilocal exact conservation laws is constructed in
the anisotropic Heisenberg (XXZ) spin-1/2 chain for periodic (or twisted)
boundary conditions and for a set of commensurate anisotropies densely covering
the entire easy plane interaction regime. All local conserved operators follow
from the standard (Hermitian) transfer operator in fundamental representation
(with auxiliary spin s=1/2), and are all even with respect to a spin flip
operation. However, the quasilocal family is generated by differentiation of a
non-Hermitian highest weight transfer operator with respect to a complex
auxiliary spin representation parameter s and includes also operators of odd
parity. For a finite chain with open boundaries the time derivatives of
quasilocal operators are not strictly vanishing but result in operators
localized near the boundaries of the chain. We show that a simple modification
of the non-Hermitian transfer operator results in exactly conserved, but still
quasilocal operators for periodic or generally twisted boundary conditions. As
an application, we demonstrate that implementing the new exactly conserved
operator family for estimating the high-temperature spin Drude weight results,
in the thermodynamic limit, in exactly the same lower bound as for almost
conserved family and open boundaries. Under the assumption that the bound is
saturating (suggested by agreement with previous thermodynamic Bethe ansatz
calculations) we propose a simple explicit construction of infinite time
averages of local operators such as the spin current.",1406.2258v2
2014-11-17,Oscillatory Non-collinear Magnetism Induced by Interfacial Charge Transfer in Metallic Oxide Superlattices,"Interfaces between correlated complex oxides are promising avenues to realize
new forms of magnetism that arise as a result of charge transfer, proximity
effects and locally broken symmetries. We report upon the discovery of a
non-collinear magnetic structure in superlattices of the ferromagnetic metallic
oxide La2/3Sr1/3MnO3 (LSMO) and the correlated metal LaNiO3 (LNO). The exchange
interaction between LSMO layers is mediated by the intervening LNO, such that
the angle between the magnetization of neighboring LSMO layers varies in an
oscillatory manner with the thickness of the LNO layer. The magnetic field,
temperature, and spacer thickness dependence of the non-collinear structure are
inconsistent with the bilinear and biquadratic interactions that are used to
model the magnetic structure in conventional metallic multilayers. A model that
couples the LSMO layers to a helical spin state within the LNO fits the
observed behavior. We propose that the spin-helix results from the interaction
between a spatially varying spin susceptibility within the LNO and interfacial
charge transfer that creates localized Ni2+ states. This provides a new
approach to engineering non-collinear spin textures in metallic oxide
heterostructures that can be exploited in devices based on both spin and charge
transport.",1411.4344v1
2018-05-15,Magnetocaloric effect in the distorted Ising-Heisenberg double sawtooth spin ladders,"The entropy and cooling rate of the both antiferromagnetic spin-1/2 double
sawtooth IsingHeisenberg model and mixed-spin (1,1/2) double sawtooth
Ising-Heisenberg model on the distorted ladders are rigorously investigated
under an adiabatic demagnetization process using the quantum transfer-matrix
technique. The models include the XXZ interaction between the interstitial
Heisenberg dimers, the Ising coupling between nearest-neighbor spins of the
legs and rungs, and additional cyclic four-spin exchange (ring exchange) in the
square plaquette of each block. Close to field-induced quantum phase
transitions, we compare both models together in the ability of cooling/heating
near the quantum critical points. However, we observe a large magnetocaloric
effect for both models, the mixed-spin double sawtooth ladder shows much more
magneticaloric efficiency than the spin-1/2 double sawtooth ladder. During an
adiabatic demagnetization process it can be seen a temperature dropping in the
vicinity of the zero-temperature quantum phase transitions. Various fixed
values of the Isotropic and anisotropic parameters explicitly alter the quality
of the magnetocaloric effect. This properties suggest double sawtooth
Ising-Heisenberg ladders as promising alternative refrigerant materials for
low-temperature magnetic refrigeration.",1805.05607v2
2018-09-28,Hydrogen adsorption-induced nanomagnetism at the Si(111)-(7$\times$7) surface,"The creation of magnetism on non-magnetic semiconductor surfaces is of
importance for the realization of spintronics devices. Especially, the coupling
of electron spins within quantum nanostructures can be utilized for
nanomagnetism applications. Here, we demonstrate, based on first-principles
density-functional theory calculations, that the adsorption of H atoms on the
Si(111)-(7$\times$7) surface induces the spin polarization of surrounding Si
dangling bonds (DBs) and their spin orderings. It is revealed that the H
adsorption on a rest-atom site exhibits a Jahn-Teller-like distortion that
accompanies a charge transfer from the rest atom to the nearest neighboring
adatoms. This charge transfer increases the local density of states of such
three adatoms at the Fermi level, thereby inducing a Stoner-type instability to
produce a ferrimagnetic order of adatom DBs around the adsorbed H atom.
Meanwhile, the H adsorption on an adatom site cannot induce spin polarization,
but, as adsorbed H atoms increase, the ferrimagnetic order of rest-atom DBs
emerges through the charge transfer from rest atoms to adatoms. Our findings
provide a microscopic mechanism of the H-induced spin orderings of Si DBs at
the atomic scale, which paves a novel way to the design of nanoscale magnetism
in the representative semiconductor surface.",1809.10880v1
2021-03-23,57Fe and 151Eu Mössbauer studies of 3d-4f spin interplay in EuFe(2-x)Ni(x)As2,"The EuFe(2-x)Ni(x)As2 compounds exhibiting 3d and/or 4f magnetic order were
investigated by means of 57Fe and 151Eu M\""ossbauer spectroscopy. Additionally,
results for the end members of this system, i.e. EuFe2As2 and EuNi2As2, are
reported for comparison. It was found that spin-density-wave order of the Fe
itinerant moments is monotonically suppressed by Ni-substitution. However, the
3d magnetic order survives at the lowest temperature up to at least x = 0.12
and it is certainly completely suppressed for x = 0.20. The Eu localized
moments order regardless of the Ni concentration, but undergo a spin
reorientation with increasing x from the alignment parallel to the a-axis in
the parent compound, toward c-axis alignment for x > 0.07. The change of the 4f
spins ordering from antiferromagnetic to ferromagnetic takes place
simultaneously with a disappearance of the 3d spins order what is the evidence
of a strong coupling between magnetism of Eu2+ ions and the conduction
electrons of [Fe(2-x)Ni(x)As2]2- layers. The Fe nuclei experience the
transferred hyperfine magnetic field due to the Eu2+ ordering for
Ni-substituted samples with x > 0.04, while the transferred field is
undetectable in EuFe2As2 and for compound with a low Ni-substitution level. It
seems that the 4f ferromagnetic component arising from a tilt of the Eu2+
moments to the crystallographic c-axis leads to the transferred magnetic field
at the Fe atoms.",2103.12698v2
1996-10-29,Hydrodynamical Studies of Wind Accretion Onto Compact Objects: Two-Dimensional Calculations,"We present the results of hydrodynamical simulations of nonaxisymmetric gas
flow past a gravitating compact object in two dimensions. Calculations were
performed with uniform flow as well as with transverse velocity and density
gradients. We find that the flow is highly nonsteady, exhibiting the
``flip-flop'' behavior seen in previous studies in which accretion disks form
with alternating directions of rotation. We investigate the periodicity of the
flip-flop behavior, and study the effects of spatial resolution on the results.
We find that the flip-flop motion creates accretion torques which, in some
cases, may be large enough to explain the erratic spin behavior observed in
some massive X-ray pulsars.",9610245v1
2000-09-04,Spin induced galaxy alignments and their implications for weak lensing measurements,"Large scale correlations in the orientations of galaxies can result from
alignments in their angular momentum vectors. These alignments arise from the
tidal torques exerted on neighboring proto-galaxies by the smoothly varying
shear field. We compute the predicted amplitude of such ellipticity
correlations using the Zel'dovich approximation for a realistic distribution of
galaxy shapes. Weak gravitational lensing can also induce ellipticity
correlations since the images of neighboring galaxies will be distorted
coherently. On comparing these two effects that induce shape correlations, we
find that for current weak lensing surveys with a median redshift of z_m = 1,
the intrinsic signal is of order 1 - 10 percent of the measured signal.
However, for shallower surveys with z_m < 0.3, the intrinsic correlations
dominate over the lensing signal. The distortions induced by lensing are
curl-free, whereas those resulting from intrinsic alignments are not. This
difference can be used to disentangle these two sources of ellipticity
correlations.",0009052v1
2001-12-05,Propeller vs. Magnetar Concepts for SGR/AXPs,"Two lines of thought exist as to the nature of Soft Gamma-ray Repeaters
(SGRs) and Anomalous X-ray Pulsars (AXPs). On the one hand,we have neutron
stars with super-critical magnetic fields, which spin-down the stars and power
the gamma-ray bursts. On the other hand, are neutron stars with typical pulsar
magnetic fields, which are spun-down by magnetospheric ``propeller'' torques
from fallback or fossil disks in addition to magnetic dipole radiation. Many
observational facts are available for comparing and contrasting these two
concepts. The facts are described and whether or not each is compatible with
these concepts is presented.",0112121v1
2002-07-04,Gravitational radiation from highly magnetized nascent neutron stars in supernova remnants,"We consider the spin evolution of highly magnetized neutron stars in a
hypercritical inflow just after their birth in supernovae. Presence of a strong
magnetic field could deform the star and if the symmetry axis of the field is
misaligned with that of stellar rotation, the star will be an emitter of
gravitational wave. Here we investigate the possibility of gravitational
radiation from such a star when there is a hypercritical inflow onto it. The
stellar configuration is slightly deformed away from spherical by the intense
magnetic field; the rotational angular frequency of the star is determined by
the balance between the accretion torque and the magnetic dipole radiation. An
estimation of the characteristic amplitude of the gravitational radiation from
such systems is given. (abridged abstract)",0207118v1
2003-04-21,The Dynamic Behavior of Soft Gamma Repeaters,"Soft Gamma Repeaters (SGRs) undergo changes in their pulse properties and
persistent emission during episodes of intense burst activity. Both SGR 1900+14
and SGR 1806-20 have shown significant changes in their spin-down rates during
the last several years, yet the bulk of this variability is not correlated with
burst activity. SGR 1900+14 has undergone large changes in flux and a dramatic
pulse profile change following burst activity in 1998. The flux level of SGR
1627$-$41 has been decreasing since its only recorded burst activity. Here, we
review the global properties of SGRs as well as the observed dynamics of the
pulsed and persistent emission properties of SGR 1900+14, SGR 1806-20 and SGR
1627-41 during and following burst active episodes and discuss what
implications these results have for the burst emission mechanism, the magnetic
field dynamics of magnetars, the nature of the torque variability, and SGRs in
general.",0304372v1
2003-09-04,67P/Churyumov-Gerasimenko - potential target for the Rosetta mission,"An influence of the non-gravitational effects on the motion of short-period
comet 67P/Churyumov-Gerasimenko is investigated. It was found that the normal
component of the non-gravitational force exceeds the transverse one and a model
of the motion including A_1, A_2, A_3 better fits the observations than model
neglecting A_3. Assuming asymmetry in g(r) with respect to the perihelion the
large value of displacement \tau was derived (about 34 days), and very small
negative value of transverse component A_2 was obtained. The models of rotating
non-spherical nucleus also suggest the large shift of light curve with respect
to perihelion (\tau greater than 30 days). The forced precession model of 67P
with \tau = 34 days gives a prolate spheroidal shape of the rotating nucleus
with axial ratio R_b/R_a = 1.16, rotational period to equatorial radius
P_{rot}/R_a = 4.6\pm 1.4 hrs/km, and torque factor f_{tor}=3\cdot 10^5 day/AU.
The much larger \tau = 54 days gives distinctly prolate shape of nucleus with
axial ratio R_b/R_a = 1.71. The orientation of spin axis of the nucleus and its
evolution are presented. The past and the future dynamical evolution of comet
67P is also widely discussed.",0309130v1
2003-12-15,Twisted accretion curtains in the intermediate polar FO Aquarii,"We report on a ~37-ks XMM-Newton observation of the intermediate polar FO
Aquarii, presenting X-ray and UV data from the EPIC and OM cameras. We find
that the system has changed from its previously reported state of disc-overflow
accretion to one of purely disc-fed accretion. We detect the previously
reported `notch' feature in the X-ray spin pulse, and explain it as a partial
occultation of the upper accretion pole. Maximum flux of the quasi-sinusoidal
UV pulse coincides with the notch, in keeping with this idea. However, an
absorption dip owing to the outer accretion curtains occurs 0.27 later than the
expected phase, which implies that the accretion curtains are twisted, trailing
the magnetic poles. This result is the opposite of that reported in PQ Gem,
where accreting field lines were found to lead the pole. We discuss how such
twists relate to the accretion torques and thus the observed period changes of
the white dwarfs, but find no simple connection.",0312379v1
2004-01-19,Three-dimensional Simulations of Disk Accretion to an Inclined Dipole: I. Magnetospheric Flow at Different Theta,"We present results of fully three-dimensional MHD simulations of disk
accretion to a rotating magnetized star with its dipole moment inclined at an
angle Theta to the rotation axis of the disk. We observed that matter accretes
from the disk to a star in two or several streams depending on Theta. Streams
may precess around the star at small Theta. The inner regions of the disk are
warped. The warping is due to the tendency of matter to co-rotate with inclined
magnetosphere. The accreting matter brings positive angular momentum to the
(slowly rotating) star tending to spin it up. The corresponding torque N_z
depends only weakly on Theta. The angular momentum flux to the star is
transported predominantly by the magnetic field; the matter component
contributes < 1 % of the total flux. Results of simulations are important for
understanding the nature of classical T Tauri stars, cataclysmic variables, and
X-ray pulsars.",0401375v1
2005-02-28,"Magnetic Fields, Accretion, and the Central Engine of Gamma-Ray Bursts","I briefly review magnetic effects in accretion physics, and then go on to
discuss a possible central engine for gamma-ray bursts. A rotating black hole
immersed in a non-axisymmetric magnetic field experiences a torque trying to
align spin and field. I suggest that gamma-ray burst hosts may provide
conditions where this effect allows rapid extraction of a significant fraction
of the hole's rotational energy. I argue that much of the electromagnetic
emission is in two narrow beams parallel and antiparallel to the asymptotic
field direction. This picture suggests that only a mass 10^-5 Msun is expelled
in a relativistic outflow, as required by the fireball picture.",0502570v1
2005-05-11,"Hydrodynamical stellar models including rotation, internal gravity waves and atomic diffusion. I. Formalism and tests on Pop I dwarfs","In this paper, we develop a formalism in order to incorporate the
contribution of internal gravity waves to the transport of angular momentum and
chemicals over long time-scales in stars. We show that the development of a
double peaked shear layer acts as a filter for waves, and how the asymmetry of
this filter produces momentum extraction from the core when it is rotating
faster than the surface. Using only this filtered flux, it is possible to
follow the contribution of internal waves over long (evolutionary) time-scales.
  We then present the evolution of the internal rotation profile using this
formalism for stars which are spun down via magnetic torquing. We show that
waves tend to slow down the core, creating a ""slow"" front that may then
propagate from the core to the surface. Further spin down of the surface leads
to the formation of a new front. Finally we show how this momentum transport
reduces rotational mixing in a 1.2Msun, Z=0.02 model, leading to a surface
lithium abundance in agreement with observations in the Hyades.",0505229v1
2006-04-03,On the Environmental Dependence of Galaxy Properties Established by the Initial Cosmological Conditions,"We study theoretically how the initial cosmological conditions establish the
dependence of galaxy properties on the environment. First, we adopt the linear
tidal torque theory according to which the angular momentum of a proto-galaxy
is generated at first order by the misalignment between the proto-galaxy
inertia tensor and the local tidal tensor. Then, we quantify analytically the
degree of the misalignment between the two tensors, and show quantitatively
that it increases as the density of the environment decreases. It implies that
the proto-galaxies forming in the lower density regions should end up with
having higher angular momentum than those in the higher density regions, which
is consistent with recent numerical finding that the void and field galaxies
have higher spin parameters than the cluster galaxies. Since the galaxy angular
momentum plays a role of developing a disk-like structure and hindering the
star-formation, our theoretical insight provides an answer to such fundamental
observational question as why the large void galaxies have young stellar
populations and high specific star formation rate, which was not explained by
the previous morphology-density relation.",0604017v2
2006-10-09,Mimicking neutron star precession by polar cap current-pattern drifting,"We propose a model for rotating current patterns within radiopulsar polar cap
accelerators which has observational consequences that mimic those which have
been attributed to neutron star free precession. The model is a simple
extension of a canonical one for the origin of the ""drifting subpulses"" often
observed within the pulse envelope of radiopulsars.
  The new model's current pattern rotation period (with respect to the neutron
star) is estimated to be of order a year. Associated with that rotation are
small oscillations in spin-down torque, pulse arrival time, and radiobeam
direction with this same period. These have estimated magnitudes which support
a reinterpretation of free precession ""observations"" which could resolve the
severe problem of obtaining anywhere near the otherwise required precession
parameters with canonical neutron star models.",0610238v1
2006-12-22,Evolution of the inclination angle of radio pulsars is observable effect,"It is shown that the slow glitches in the spin rate of the pulsar B1822-09
can be explained by the reconstruction of the neutron star shape, which is not
matched with the star rotation axis. Owing to the evolution of the inclination
angle, i.e. the angle between the rotation axis and the axis of the magnetic
dipole, under the action of the braking torque, there appears the disagreement
between the rotation axis and the symmetry axis. After the angle between the
axis of symmetry and the axis of the rotation achieves the maximum value of
alpha ~ 2x10^-4 the shape of the neutron star becomes matching with the
rotation axis. Such reconstruction is observed as the slow glitch.",0612681v1
2002-03-24,Molecular elasticity and the geometric phase,"We present a method for solving the Worm Like Chain (WLC) model for twisting
semiflexible polymers to any desired accuracy. We show that the WLC free energy
is a periodic function of the applied twist with period 4 pi. We develop an
analogy between WLC elasticity and the geometric phase of a spin half system.
These analogies are used to predict elastic properties of twist-storing
polymers. We graphically display the elastic response of a single molecule to
an applied torque. This study is relevant to mechanical properties of
biopolymers like DNA.",0203491v4
2004-05-20,Anisotropy and internal field distribution of MgB2 in the mixed state at low temperatures,"Magnetization and muon spin relaxation on MgB2 were measured as a function of
field at 2 K. Both indicate an inverse-squared penetration depth strongly
decreasing with increasing field H below about 1 T. Magnetization also suggests
the anisotropy of the penetration depth to increase with increasing H,
interpolating between a low Hc1 and a high Hc2 anisotropy. Torque vs angle
measurements are in agreement with this finding, while also ruling out drastic
differences between the mixed state anisotropies of the two basic length scales
penetration depth and coherence length.",0405495v1
2004-05-21,Molecular engineering of antiferromagnetic rings for quantum computation,"The substitution of one metal ion in a Cr-based molecular ring with dominant
antiferromagnetic couplings allows to engineer its level structure and
ground-state degeneracy. Here we characterize a Cr7Ni molecular ring by means
of low-temperature specific-heat and torque-magnetometry measurements, thus
determining the microscopic parameters of the corresponding spin Hamiltonian.
The energy spectrum and the suppression of the leakage-inducing S-mixing render
the Cr7Ni molecule a suitable candidate for the qubit implementation, as
further substantiated by our quantum-gate simulations.",0405507v3
1998-11-02,Optical Trapping by Radiometric Flow,"Micron sized, neutral, non-dielectric particles immersed in a viscous fluid
can be trapped in the focal plane of a Gaussian beam. A particle can absorb
energy from such a beam with a large radial intensity gradient, resulting in
substantial temperature gradients and a radiometric torque which causes it to
spin rapidly about an axis perpendicular to the flux of radiant energy. The
particles are also observed to orbit around the optical axis. Here we
investigate the fundamental physics of this system, the Radiometric Particle
Trap, and discuss its force laws using gas-kinetic theory.",9811002v4
1995-01-13,"Topology, Locality, and Aharonov-Bohm Effect with Neutrons","Recent neutron interferometry experiments have been interpreted as
demonstrating a new topological phenomenon similar in principle to the usual
Aharonov-Bohm (AB) effect, but with the neutron's magnetic moment replacing the
electron's charge. We show that the new phenomenon, called Scalar AB (SAB)
effect, follows from an ordinary local interaction, contrary to the usual AB
effect, and we argue that the SAB effect is not a topological effect by any
useful definition. We find that SAB actually measures an apparently novel spin
autocorrelation whose operator equations of motion contain the local torque in
the magnetic field. We note that the same remarks apply to the Aharonov-Casher
effect.",9501012v1
2007-08-15,Alignment and Precession of a Black Hole with a Warped Accretion Disc,"We consider the shape of an accretion disc whose outer regions are misaligned
with the spin axis of a central black hole and calculate the steady state form
of the warped disc in the case where the viscosity and surface densities are
power laws in the distance from the central black hole. We discuss the shape of
the resulting disc in both the frame of the black hole and that of the outer
disc. We note that some parts of the disc and also any companion star maybe
shadowed from the central regions by the warp. We compute the torque on the
black hole caused by the Lense-Thirring precession and hence compute the
alignment and precession timescales. We generalise the case with viscosity and
hence surface density independent of radius to more realistic density
distributions for which the surface density is a decreasing function of radius.
We find that the alignment timescale does not change greatly but the precession
timescale is more sensitive. We also determine the effect on this timescale if
we truncate the disc. For a given truncation radius, the the timescales are
less affected for more sharply falling density distributions.",0708.2034v1
2007-11-27,Nonequilibrium interacting electrons in a ferromagnet,"Dynamics of the magnetization in ferromagnets is examined in the presence of
transport electrons allowing the latter to interact. It is found that the
existence of inhomogeneities such as domain wall (DW) structures, leads to
changes that affect the dynamical structure of the equations of motion for the
magnetization. Only in the limit of uniform magnetizations or sufficiently wide
DW's, the equations of motion maintain the form they have in the noninteracting
case. In this limit, results like the spin torques, the Gilbert parameter, and
the DW velocities become renormalized. However the length scale that defines
such a limit depends on the strength of the interaction. It is shown that if
large ferromagnetic fluctuations exist in the metallic band then the range for
which conformity with the noninteracting case holds extends to the limit of
arbitrarily narrow DW's.",0711.4170v2
2007-12-15,Disc-Magnetosphere interactions in Cataclysmic Variable Stars,"I review, from an observational perspective, the interactions of accretion
discs with magnetic fields in cataclysmic variable stars. I start with systems
where the accretion flows via a stream, and discuss the circumstances in which
the stream forms into an accretion disc, pointing to stars which are close to
this transition. I then turn to disc-fed systems and discuss what we know about
how material threads on to field lines, as deduced from the pattern of
accretion footprints on the white dwarf. I discuss whether distortions of the
field lines are related to accretion torques and the changing spin periods of
the white dwarfs. I also review the effect on the disc-magnetosphere
interaction of disc-instability outbursts. Lastly, I discuss the temporary,
dynamo-driven magnetospheres thought to occur in dwarf-nova outbursts, and
whether slow-moving waves are excited at the inner edges of the disc.",0712.2520v1
2008-07-25,Source Tracking for Sco X-1,"Sco X-1, the brightest low mass X-ray binary, is likely to be a source for
gravitational wave emission. In one mechanism, emission of a gravitational wave
arrests the increase in spin frequency due to the accretion torque in a low
mass X-ray binary. Since the gravitational waveform is unknown, a detection
method assuming no apriori knowledge of the signal is preferable. In this
paper, we propose to search for a gravitational wave from Sco X-1 using a {{\it
source tracking}} method based on a coherent network analysis. In the method,
we combine data from several interferometric gravitational wave detectors
taking into account of the direction to Sco X-1, and reconstruct two
polarization waveforms at the location of Sco X-1 in the sky as Sco X-1 is
moving. The source tracking method opens up the possibility of searching for a
wide variety of signals. We perform Monte Carlo simulations and show results
for bursts, modeled, short duration periodic sources using a simple excess
power and a matched filter method on the reconstructed signals.",0807.4171v1
2008-07-30,Fermi surface of superconducting LaFePO determined by quantum oscillations,"We report extensive measurements of quantum oscillations in the normal state
of the Fe-based superconductor LaFePO, (Tc ~ 6 K) using low temperature torque
magnetometry and transport in high static magnetic fields (45 T). We find that
the Fermi surface is in broad agreement with the band-structure calculations
with the quasiparticle mass enhanced by a factor ~2. The quasi-two dimensional
Fermi surface consist of nearly-nested electron and hole pockets, suggesting
proximity to a spin/charge density wave instability.",0807.4890v2
2008-08-21,Three-Dimensional Simulations of Magnetized Thin Accretion Disks around Black Holes: Stress in the Plunging Region,"We describe three-dimensional general relativistic magnetohydrodynamic
simulations of a geometrically thin accretion disk around a non-spinning black
hole. The disk has a thickness $h/r\sim0.05-0.1$ over the radial range
$(2-20)GM/c^2$. In steady state, the specific angular momentum profile of the
inflowing magnetized gas deviates by less than 2% from that of the standard
thin disk model of
  Novikov & Thorne (1973). Also, the magnetic torque at the radius of the
innermost stable circular orbit (ISCO) is only $\sim2%$ of the inward flux of
angular momentum at this radius. Both results indicate that magnetic coupling
across the ISCO is relatively unimportant for geometrically thin disks.",0808.2860v2
2008-10-07,Auto-oscillation threshold and line narrowing in MgO-based spin-torque oscillators,"We present an experimental study of the power spectrum of current-driven
magnetization oscillations in MgO tunnel junctions under low bias. We find the
existence of narrow spectral lines, down to 8 MHz in width at a frequency of
10.7 GHz, for small applied fields with clear evidence of an auto-oscillation
threshold. Micromagnetics simulations indicate that the excited mode
corresponds to an edge mode of the synthetic antiferromagnet.",0810.1110v3
2009-04-09,Evaluating the locality of intrinsic precession damping in transition metals,"The Landau-Lifshitz-Gilbert damping parameter is typically assumed to be a
local quantity, independent of magnetic configuration. To test the validity of
this assumption we calculate the precession damping rate of small amplitude
non-uniform mode magnons in iron, cobalt, and nickel. At scattering rates
expected near and above room temperature, little change in the damping rate is
found as the magnon wavelength is decreased from infinity to a length shorter
than features probed in recent experiments. This result indicates that
non-local effects due to the presence of weakly non-uniform modes, expected in
real devices, should not appreciably affect the dynamic response of the element
at typical operating temperatures. Conversely, at scattering rates expected in
very pure samples around cryogenic temperatures, non-local effects result in an
order of magnitude decrease in damping rates for magnons with wavelengths
commensurate with domain wall widths. While this low temperature result is
likely of little practical importance, it provides an experimentally testable
prediction of the non-local contribution of the spin-orbit torque-correlation
model of precession damping. None of these results exhibit strong dependence on
the magnon propagation direction.",0904.1455v1
2009-08-15,Thermal-magnetic noise measurement of spin-torque effects on ferromagnetic resonance in MgO-based magnetic tunnel junctions,"Thermal-magnetic noise at ferromagnetic resonance (T-FMR) can be used to
measure magnetic perpendicular anisotropy of nanoscale magnetic tunnel
junctions (MTJs). For this purpose, T-FMR measurements were conducted with an
external magnetic field up to 14 kOe applied perpendicular to the film surface
of MgO-based MTJs under a dc bias. The observed frequency-field relationship
suggests that a 20 A CoFeB free layer has an effective demagnetization field
much smaller than the intrinsic bulk value of CoFeB, with 4PiMeff = (6.1 +/-
0.3) kOe. This value is consistent with the saturation field obtained from
magnetometry measurements on extended films of the same CoFeB thickness.
In-plane T-FMR on the other hand shows less consistent results for the
effective demagnetization field, presumably due to excitations of more complex
modes. These experiments suggest that the perpendicular T-FMR is preferred for
quantitative magnetic characterization of nanoscale MTJs.",0908.2164v1
2009-10-15,The long-term evolution of the accreting millisecond X-ray pulsar Swift J1756.9-2508,"We present a timing analysis of the 2009 outburst of the accreting
millisecond X-ray pulsar Swift J1756.9-2508, and a re-analysis of the 2007
outburst. The source shows a short recurrence time of only ~2 years between
outbursts. Thanks to the approximately 2 year long baseline of data, we can
constrain the magnetic field of the neutron star to be 0.4x10^8 G < B < 9x10^8
G, which is within the range of typical accreting millisecond pulsars. The 2009
timing analysis allows us to put constraints on the accretion torque: the spin
frequency derivative within the outburst has an upper limit of $|\dot{\nu}| <
3x10^-13 Hz/s at the 95% confidence level. A study of pulse profiles and their
evolution during the outburst is analyzed, suggesting a systematic change of
shape that depends on the outburst phase.",0910.2920v1
2009-10-25,Nanoscale Magnetic Heat Pumps and Engines,"We present the linear response matrix for a sliding domain wall in a
rotatable magnetic nanowire, which is driven out of equilibrium by temperature
and voltage bias, mechanical torque, and magnetic field. An expression for
heat-current induced domain wall motion is derived. Application of Onsager's
reciprocity relation leads to a unified description of the Barnett and
Einstein-de Haas effects as well as spin-dependent thermoelectric properties.
We envisage various heat pumps and engines, such as coolers driven by magnetic
fields or mechanical rotation as well as nanoscale motors that convert
temperature gradients into useful work. All parameters (with the exception of
mechanical friction) can be computed microscopically by the scattering theory
of transport.",0910.4712v2
2009-11-28,Field Dependent Superfluid Density in the Optimally Doped SmFeAsO_(1-x)F_y Superconductor,"The magnetic field dependence of the in-plane magnetic penetration depth for
optimally doped SmFeAsO_(1-x)F_y was investigated by combining torque
magnetometry, SQUID magnetometry, and muon-spin rotation. The results obtained
from these techniques show all a pronounced decrease of the superfluid density
as the field is increased up to 1.4 T. This behavior is analysed within a
two-band model with self-consistently derived coupled gaps, where the
superfluid density related to the larger gap is field independent and the
superfluid density related to the smaller gap is strongly suppressed with
increasing field.",0911.5420v2
2009-12-08,Magnetic field induced quantum phase transition of the $S = 1/2$ antiferromagnet $K_2NaCrO_8$,"The magnetic properties of alkali-metal peroxychromate K$_2$NaCrO$_8$ are
governed by the $S = 1/2$ pentavalent chromium cation, Cr$^{5+}$. Specific
heat, magnetocalorimetry, ac magnetic susceptibility, torque magnetometry, and
inelastic neutron scattering data have been acquired over a wide range of
temperature, down to 60 mK, and magnetic field, up to 18 T. The magnetic
interactions are quasi-two-dimensional prior to long-range ordering, where $T_N
= 1.66$ K in $H = 0$. In the $T \to 0$ limit, the magnetic field tuned
antiferromagnetic-ferromagnetic phase transition suggests a critical field $H_c
= 7.270$ T and a critical exponent $\alpha = 0.481 \pm 0.004$. The neutron data
indicate the magnetic interactions may extend over intra-planar
nearest-neighbors and inter-planar next-nearest-neighbor spins.",0912.1507v1
2010-02-18,Pressure-driven flow of a micro-polar fluid: measurement of the velocity profile,"The pressure-driven flow of a suspension of spinning particles in a
rectangular channel is studied using an acoustic method. The suspension is made
of insulating particles (PMMA) dispersed in a slightly conducting oil (Ugilec +
Dielec) and is subjected to a DC electric field. In such a case, the particles
are polarized in the direction opposite to that of the electric field and begin
to rotate in order to flip their dipoles in the field direction. Such a
rotation of the particles is known as Quincke rotation and is responsible for
an important decrease of the effective viscosity of the suspension. Indeed, due
to the electric torque exerted on the particles, the stress tensor in the
suspension is not symmetric anymore and a driving effect arises from the
anti-symmetric part. When such a suspension flows through a rectangular
channel, the velocity profile is expected to deviate from the usual Poiseuille
flow. In this paper, the velocity profiles are measured using Pulsed Ultrasound
Doppler Velocimetry technique. They compare well with those that are computed
from the otherwise measured rheological law.",1002.3548v2
2011-01-28,Optical anisotropy induced by torsion stresses in LiNbO3 crystals: appearance of an optical vortex,"We report the results of studies of torsion effect on the optical
birefringence in LiNbO3 crystals. We have found that twisting of those crystals
causes a birefringence distribution revealing non-trivial peculiarities. In
particular, it has a special point at the center of cross section perpendicular
to the torsion axis where zero birefringence value occurs. It has also been
ascertained that the surface of the spatial birefringence distribution has a
conical shape, with the cone axis coinciding with the torsion axis. We have
revealed that an optical vortex, with the topological charge equal to unity,
appears under the torsion of LiNbO3 crystals. It has been shown that, contrary
to the q-plate, both the efficiency of spin-orbital coupling and the orbital
momentum of the emergent light can be operated by the torque moment.",1101.5478v1
2011-12-26,Thin-Film Magnetization Dynamics on the Surface of a Topological Insulator,"We theoretically study the magnetization dynamics of a thin ferromagnetic
film exchange-coupled with a surface of a strong three-dimensional topological
insulator. We focus on the role of electronic zero modes imprinted by domain
walls (DW's) or other topological textures in the magnetic film.
Thermodynamically reciprocal hydrodynamic equations of motion are derived for
the DW responding to electronic spin torques, on the one hand, and fictitious
electromotive forces in the electronic chiral mode fomented by the DW, on the
other. An experimental realization illustrating this physics is proposed based
on a ferromagnetic strip, which cuts the topological insulator surface into two
gapless regions. In the presence of a ferromagnetic DW, a chiral mode
transverse to the magnetic strip acts as a dissipative interconnect, which is
itself a dynamic object that controls (and, inversely, responds to) the
magnetization dynamics.",1112.5884v2
2012-01-30,Magnetoresistance and negative differential resistance in Ni/Graphene/Ni vertical heterostructures driven by finite bias voltage: A first-principles study,"Using the nonequilibrium Green function formalism combined with density
functional theory, we study finite-bias quantum transport in Ni/Gr_n/Ni
vertical heterostructures where $n$ graphene layers are sandwiched between two
semi-infinite Ni(111) electrodes. We find that recently predicted ""pessimistic""
magnetoresistance of 100% for $n \ge 5$ junctions at zero bias voltage $V_b
\rightarrow 0$, persists up to $V_b \simeq 0.4$ V, which makes such devices
promising for spin-torque-based device applications. In addition, for parallel
orientations of the Ni magnetizations, the $n=5$ junction exhibits a pronounced
negative differential resistance as the bias voltage is increased from $V_b=0$
V to $V_b \simeq 0.5$ V. We confirm that both of these nonequilibrium effects
hold for different types of bonding of Gr on the Ni(111) surface while
maintaining Bernal stacking between individual Gr layers.",1201.6279v2
2012-04-01,Intrinsic Structural Disorder and the Magnetic Ground State in Bulk EuTiO3,"The magnetic properties of single-crystal EuTiO3 are suggestive of nanoscale
disorder below its cubic-tetragonal phase transition. We demonstrate that
electric field cooling acts to restore monocrystallinity, thus confirming that
emergent structural disorder is an intrinsic low-temperature property of this
material. Using torque magnetometry, we deduce that tetragonal EuTiO3 enters an
easy-axis antiferromagnetic phase at 5.6 K, with a first-order transition to an
easy-plane ground state below 3 K. Our data is reproduced by a 3D anisotropic
Heisenberg spin model.",1204.0150v1
2012-04-17,Low frequency noise due to magnetic inhomogeneities in submicron FeCoB/MgO/FeCoB magnetic tunnel junctions,"We report on room temperature low frequency noise due to magnetic
inhomogeneities/domain walls (MI/DWs) in elliptic submicron FeCoB/MgO/FeCoB
magnetic tunnel junctions with an area between 0.0245 and 0.0675{\mu}m2. In the
smaller area junctions we found an unexpected random telegraph noise (RTN1),
deeply in the parallel state, possibly due to stray field induced MI/DWs in the
hard layer. The second noise source (RTN2) is observed in the antiparallel
state for the largest junctions. Strong asymmetry of RTN2 and of related
resistance steps with current indicate spin torque acting on the MI/DWs in the
soft layer at current densities below 5x10^5 A/cm2.",1204.3744v1
2012-05-06,A new look at spherical accretion in High Mass X-ray Binaries,"Currently used model of spherical accretion onto a magnetized rotating
neutron star encounters major difficulties in explaining the entry rate of
accreting material into the stellar field and spin evolution of long-period
X-ray pulsars. These difficulties can be, however, avoided if the magnetic
field of the material captured by the neutron star is incorporated into the
model. The magnetic field of the flow itself under certain conditions controls
the accretion process and significantly affects the parameters of the accreting
material. The mode by which the accretion flow enters the stellar magnetosphere
in that case can be associated with Bohm (or turbulent) diffusion and the
torque applied to the neutron star appears to be substantially higher than that
evaluated in the non-magnetized accretion scenario.",1205.1220v1
2012-05-25,Dynamics of Rotation of Super-Earths,"We numerically investigate the dynamics of rotation of several close-in
terrestrial exoplanet candidates. In our model, the rotation of the planet is
disturbed by the torque of the central star due to the asymmetric equilibrium
figure of the planet. We model the shape of the planet by a Jeans spheroid. We
use surfaces of section and spectral analysis to explore numerically the
rotation phase space of the systems adopting different sets of parameters and
initial conditions close to the main spin-orbit resonant states. One of the
parameters, the orbital eccentricity, is critically discussed here within the
domain of validity of orbital circularization timescales given by tidal models.
We show that, depending on some parameters of the system like the radius and
mass of the planet, eccentricity etc, the rotation can be strongly perturbed
and a chaotic layer around the synchronous state may occupy a significant
region of the phase space. 55 Cnc e is an example.",1205.5704v5
2012-06-11,Magnetic Braking Formulation for Sun-Like Stars: Dependence on Dipole Field Strength and Rotation Rate,"We use two-dimensional axisymmetric magnetohydrodynamic simulations to
compute steady-state solutions for solar-like stellar winds from rotating stars
with dipolar magnetic fields. Our parameter study includes 50 simulations
covering a wide range of relative magnetic field strengths and rotation rates,
extending from the slow- and approaching the fast-magnetic-rotator regimes.
Using the simulations to compute the angular momentum loss, we derive a
semi-analytic formulation for the external torque on the star that fits all of
the simulations to a precision of a few percents. This formula provides a
simple method for computing the magnetic braking of sun-like stars due to
magnetized stellar winds, which properly includes the dependence on the
strength of the magnetic field, mass loss rate, stellar radius, suface gravity,
and spin rate and which is valid for both slow and fast rotators.",1206.2354v1
2012-06-25,Understanding nanoscale temperature gradients in magnetic nanocontacts,"We determine the temperature profile in magnetic nanocontacts submitted to
the very large current densities that are commonly used for spin-torque
oscillator behavior. Experimentally, the quadratic current-induced increase of
the resistance through Joule heating is independent of the applied temperature
from 6 K to 300 K. The modeling of the experimental rate of the current-induced
nucleation of a vortex under the nanocontact, assuming a thermally-activated
process, is consistent with a local temperature increase between 150 K and 220
K. Simulations of heat generation and diffusion for the actual tridimensional
geometry were conducted. They indicate a temperature-independent efficiency of
the heat sinking from the electrodes, combined with a localized heating source
arising from a nanocontact resistance that is also essentially
temperature-independent. For practical currents, we conclude that the local
increase of temperature is typically 160 K and it extends 450 nm about the
nanocontact. Our findings imply that taking into account the current-induced
heating at the nanoscale is essential for the understanding of magnetization
dynamics in nanocontact systems.",1206.5680v1
2012-07-19,Hastatic Order in URu2Si2,"The development of collective long-range order via phase transitions occurs
by the spontaneous breaking of fundamental symmetries. Magnetism is a
consequence of broken time-reversal symmetry while superfluidity results from
broken gauge invariance. The broken symmetry that develops below 17.5K in the
heavy fermion compound URu2Si2 has long eluded such identification. Here we
show that the recent observation of Ising quasiparticles in URu2Si2 results
from a spinor order parameter that breaks double time-reversal symmetry, mixing
states of integer and half-integer spin. Such ""hastatic order"" hybridizes
conduction electrons with Ising 5f^{2} states of the uranium atoms to produce
Ising quasiparticles; it accounts for the large entropy of condensation and the
magnetic anomaly observed in torque magnetometry. Hastatic order predicts a
tiny transverse moment in the conduction sea, a collosal Ising anisotropy in
the nonlinear susceptibility anomaly and a resonant energy-dependent nematicity
in the tunneling density of states.",1207.4828v1
2012-08-16,Site-selective quantum correlations revealed by magnetic anisotropy in the tetramer system SeCuO3,"We present the investigation of a monoclinic compound SeCuO3 using x-ray
powder diffraction, magnetization, torque and electron-spin-resonance (ESR).
Structurally based analysis suggests that SeCuO3 can be considered as a 3D
network of tetramers. The values of intra-tetramer exchange interactions are
extracted from the temperature dependence of the susceptibility and amount to
~200 K. The inter-tetramer coupling leads to the development of long-range
antiferromagnetic order at TN = 8 K. An unusual temperature dependence of the
effective g-tensors is observed, accompanied with a rotation of macroscopic
magnetic axes. We explain this unique observation as due to site-selective
quantum correlations.",1208.3326v1
2012-09-01,Incomplete devil's staircase in the magnetization curve of SrCu2(BO3)2,"We report on NMR and torque measurements on the frustrated
quasi-two-dimensional spin-dimer system SrCu2(BO3)2 in magnetic fields up to 34
T that reveal a sequence of magnetization plateaus at 1/8, 2/15, 1/6, and 1/4
of the saturation and two incommensurate phases below and above the 1/6
plateau. The magnetic structures determined by NMR involve a stripe order of
triplets in all plateaus, suggesting that the incommensurate phases originate
from proliferation of domain walls. We propose that the magnetization process
of SrCu2(BO3)2 is best described as an incomplete devil's staircase.",1209.0069v2
2012-12-03,Impact of Rotation on the Retarded Interaction between a Permanent Dipole Particle and a Polarizable Surface,"We have calculated components of torque and the interaction energy of small
rotating particle with a permanent dipole moment in the case where the rotation
axis is perpendicular to the surface and the dipole axis is inclined to it. The
retardation effects were taken into account. An important property of this
system is its quasistationarity. When the dipole axis coincides with the
rotation axis, the particle does not experience damping and may revolve for
infinitely long time. When the axis of dipole particle is inclined to the
surface, the situation is possible where the particle is repelled off the
surface and its spin increases.",1212.0428v1
2013-01-16,The Case for a Solar Influence on Certain Nuclear Decay Rates,"Power-spectrum analyses of the decay rates of certain nuclides reveal (at
very high confidence levels) an annual oscillation and periodicities that may
be attributed to solar rotation and to solar r-mode oscillations. A comparison
of spectrograms (time-frequency displays) formed from decay data and from solar
neutrino data reveals a common periodicity with frequency 12.5 year-1, which is
indicative of the solar radiative zone. We propose that the neutrino flux is
modulated by the solar magnetic field (via Resonant Spin Flavor Precession) in
that region, and we estimate the force and the torque that could be exerted on
a nuclide by the solar neutrino flux.",1301.3754v1
2013-03-01,Parallel pumping of magnetic vortex gyrations in spin-torque nano-oscillators,"We experimentally demonstrate that large magnetic vortex oscillations can be
parametrically excited in a magnetic tunnel junction by the injection of
radio-frequency (rf) currents at twice the natural frequency of the gyrotropic
vortex core motion. The mechanism of excitation is based on the parallel
pumping of vortex motion by the rf orthoradial field generated by the injected
current. Theoretical analysis shows that experimental results can be
interpreted as the manifestation of parametric amplification when rf current is
small, and of parametric instability when rf current is above a certain
threshold. By taking into account the energy nonlinearities, we succeed to
describe the amplitude saturation of vortex oscillations as well as the
coexistence of stable regimes.",1303.0225v1
2013-04-22,Coupled-Oscillator Associative Memory Array Operation,"Operation of the array of coupled oscillators underlying the associative
memory function is demonstrated for various interconnection schemes
(cross-connect, star phase keying and star frequency keying) and various
physical implementation of oscillators (van der Pol, phase-locked loop, spin
torque). The speed of synchronization of oscillators and the evolution of the
degree of matching is studied as a function of device parameters. The
dependence of errors in association on the number of the memorized patterns and
the distance between the test and the memorized pattern is determined for Palm,
Furber and Hopfield association algorithms.",1304.6125v1
2013-05-27,Magnetization reversal in sub-100nm magnetic tunnel junctions with ultrathin MgO barrier biased along hard axis,"We report on room temperature magnetoresistance and low frequency noise in
sub-100nm elliptic CoFeB/MgO/CoFeB magnetic tunnel junctions with ultrathin
(0.9nm) barriers. For magnetic fields applied along the hard axis, we observe
current induced magnetization switching between the antiparallel and parallel
alignments at DC current densities as low as 4*106A/cm2. We attribute the low
value of the critical current to the influence of localized reductions in the
tunnel barrier, which affects the current distribution. The analysis of random
telegraph noise, which appears in the field interval near a magnetization
switch, provides an estimate to the dimension of the pseudo pinholes that
trigger the magnetization switching via local spin torque. Micromagnetic
simulations qualitatively and quantitatively reproduce the main experimental
observations.",1305.6209v1
2013-08-01,Vortex precession frequency and its amplitude-dependent shift in cylindrical nanomagnets,"Frequency of free magnetic vortex precession in circular soft ferromagnetic
nano-cylinders (magnetic dots) of various sizes is an important parameter, used
in design of spintronic devices (such as spin-torque microwave
nano-oscillators) and characterization of magnetic nanostructures. Here, using
a recently developed collective-variable approach to non-linear dynamics of
magnetic textures in planar nano-magnets, this frequency and its
amplitude-dependent shift are computed analytically and plotted for the full
range of cylinder geometries. The frequency shift is positive in large planar
dots, but becomes negative in smaller and more elongated ones. At certain dot
dimensions a zero frequency shift is realized, which can be important for
enhancing frequency stability of magnetic nano-oscillators.",1308.0240v2
2013-10-11,Pulsar timing noise from superfluid turbulence,"Shear-driven turbulence in the superfluid interior of a neutron star exerts a
fluctuating torque on the rigid crust, causing the rotational phase to walk
randomly. The phase fluctuation spectrum is calculated analytically for
incompressible Kolmogorov turbulence and is found to be red; the half-power
point is set by the observed spin-down rate, the crust-superfluid lag, and the
dynamical response time of the superfluid. Preliminary limits are placed on the
latter quantities using selected time- and frequency-domain data. It is found
that measurements of the normalization and slope of the power spectrum are
reproduced for reasonable choices of the turbulence parameters. The results
point preferentially to the neutron star interior containing a turbulent
superfluid rather than a turbulent Navier-Stokes fluid. The implications for
gravitational wave detection by pulsar timing arrays are discussed briefly.",1310.3108v1
2014-01-15,Chiral magnetization textures stabilized by the Dzyaloshinskii-Moriya interaction during spin-orbit torque switching,"We study the effect of the Dzyaloshinskii-Moriya interaction (DMI) on
current-induced magnetic switching of a perpendicularly magnetized
heavy-metal/ferromagnet/oxide trilayer both experimentally and through
micromagnetic simulations. We report the generation of stable helical
magnetization stripes for a sufficiently large DMI strength in the switching
region, giving rise to intermediate states in the magnetization confirming the
essential role of the DMI on switching processes. We compare the simulation and
experimental results to a macrospin model, showing the need for a micromagnetic
approach. The influence of the temperature on the switching is also discussed.",1401.3526v2
2014-02-28,Rashba induced chirality switching of domain walls and suppression of the Walker breakdown,"In conventional domain wall systems the aim of a high domain wall velocity
may be hindered by the occurrence of a Walker breakdown at comparably low
current density. We show how a Rashba interaction can stabilize the domain wall
dynamics and thereby shift the Walker breakdown to higher current densities.
The Rashba interaction creates a field like spin torque, which breaks the
symmetry of the system and modifies the internal structure of the domain wall.
Besides a shift of the Walker breakdown it can additionally induce a chirality
switch of the domain wall at sufficient Rashba fields. The preferred chirality
may then be chosen by the direction of the current flow. Both, the suppression
of the Walker breakdown and the chirality switching, affect the domain wall
velocity. This is even more pronounced for short current pulses, where an
additional domain wall movement after the pulse in either positive or negative
direction can determine the final position of the domain wall.",1402.7175v2
2014-05-17,Noise-enhanced synchronization of stochastic magnetic oscillators,"We present an experimental study of phase-locking in a stochastic magnetic
oscillator. The system comprises a magnetic tunnel junction with a
superparamagnetic free layer, whose magnetization dynamics is driven with spin
torques through an external periodic driving current. We show that
synchronization of this stochastic oscillator to the input current is possible
for current densities below $3 \times 10^6$ A/cm$^2$, and occurs for input
frequencies lower than the natural mean frequency of the stochastic oscillator.
We show that such injection-locking is robust and leads to a drastic reduction
in the phase diffusion of the stochastic oscillator, despite the presence of a
frequency mismatch between the oscillator and the excitation.",1405.4360v1
2014-06-29,Mechanism for intensity induced chimera states in globally coupled oscillators,"We identify the mechanism behind the existence of intensity induced chimera
states in globally coupled oscillators. We find that the effect of intensity in
the system is to cause multistability by increasing the number of fixed points.
This in turn increases the number of multistable attractors and we find that
their stability is determined by the strength of coupling . This causes the
coexistence of different collective states in the system depending upon the
initial state. We demonstrate that intensity induced chimera is generic to both
periodic and chaotic systems. We have discussed possible applications of our
results to real world systems like the brain and spin torque nano oscillators.",1406.7504v2
2014-08-30,Geometric Quantum Noise of Spin,"The presence of geometric phases is known to affect the dynamics of the
systems involved. Here we consider a quantum degree of freedom, moving in a
dissipative environment, whose dynamics is described by a Langevin equation
with quantum noise. We show that geometric phases enter the stochastic noise
terms. Specifically, we consider small ferromagnetic particles (nano-magnets)
or quantum dots close to Stoner instability, and investigate the dynamics of
the total magnetization in the presence of tunneling coupling to the metallic
leads. We generalize the Ambegaokar-Eckern-Sch\""on (AES) effective action and
the corresponding semiclassical equations of motion from the U(1) case of the
charge degree of freedom to the SU(2) case of the magnetization. The Langevin
forces (torques) in these equations are strongly influenced by the geometric
phase. As a first but nontrivial application we predict low temperature quantum
diffusion of the magnetization on the Bloch sphere, which is governed by the
geometric phase. We propose a protocol for experimental observation of this
phenomenon.",1409.0150v2
2014-09-09,Magnetization pumping and dynamics in a Dzyaloshinskii-Moriya magnet,"We formulate a phenomenological description of thin ferromagnetic layers with
inversion asymmetry where the single-domain magnetic dynamics experiences
magnon current-induced torques and leads to magnon-motive forces. We first
construct a phenomenological theory based on irreversible thermodynamics,
taking into account the symmetries of the system. Furthermore, we confirm that
these effects originate from Dzyaloshinskii-Moriya interactions from the
analysis based on the stochastic Landau-Lifshitz-Gilbert equation. Our
phenomenological results generalize to a general form of Dzyaloshinskii-Moriya
interactions and to other systems, such as pyrochlore crystals and chiral
magnets. Possible applications include spin current generation, magnetization
reversal and magnonic cooling.",1409.2846v3
2014-12-21,Macrospin in external magnetic field: Entropy production and fluctuation theorems,"We consider stochastic rotational dynamics of a macrospin at a constant
temperature, in presence of an external magnetic field. Starting from the
appropriate Langevin equation which contains multiplicative noise, we calculate
entropy production (EP) along stochastic trajectories, and obtain fluctuation
theorems. The system remains inherently out of equilibrium due to a spin torque
supporting azimuthal current, leading to an excess EP apart from the EP due to
heat dissipation. The anomaly may be removed using a redefinition of dissipated
heat and stochastic work done. Using numerical simulations, we obtain
distribution functions for entropy production along stochastic trajectories to
find good agreement with the detailed fluctuation theorem.",1412.6812v3
2015-01-06,Hastatic Order in URu2Si2 : Hybridization with a Twist,"The broken symmetry that develops below 17.5K in the heavy fermion compound
URu2Si2 has long eluded identification. Here we argue that the recent
observation of Ising quasiparticles in URu2Si2 results from a spinor
hybridization order parameter that breaks double time-reversal symmetry by
mixing states of integer and half-integer spin. Such ""hastatic order""
(hasta:[Latin]spear) hybridizes Kramers conduction electrons with Ising,
non-Kramers 5f2 states of the uranium atoms to produce Ising quasiparticles.
The development of a spinorial hybridization at 17.5K accounts for both the
large entropy of condensation and the magnetic anomaly observed in torque
magnetometry. This paper develops the theory of hastatic order in detail,
providing the mathematical development of its key concepts. Hastatic order
predicts a tiny transverse moment in the conduction sea, a collosal Ising
anisotropy in the nonlinear susceptibility anomaly and a resonant
energy-dependent nematicity in the tunneling density of states.",1501.01281v1
2015-01-22,Magnetization reversal assisted by half antivortex states in nanostructured circular cobalt disks,"The half antivortex, a fundamental topological structure which determines
magnetization reversal of submicron magnetic devices with domain walls, has
been suggested also to play a crucial role in spin torque induced vortex core
reversal in circular disks. Here we report on magnetization reversal in
circular disks with nanoholes through consecutive metastable states with half
antivortices. In-plane anisotropic magnetoresistance and broadband
susceptibility measurements accompanied by micromagnetic simulations reveal
that cobalt disks with two and three linearly arranged nanoholes directed at 45
and 135 degrees with respect to the external magnetic field show reproducible
step-like changes in the anisotropic magnetoresistance and magnetic
permeability due to transitions between different intermediate states mediated
by vortices and half antivortices confined to the dot nanoholes and edges,
respectively. Our findings are relevant for the development of multi-hole based
spintronic and magnetic memory devices.",1501.05436v1
2015-02-28,Large amplitude vortex gyration in Permalloy/Bi$_2$Se$_3$-like heterostructures,"We consider the excitation of large amplitude gyrotropic vortex core
precession in a Permalloy nanodisk by the torques originating from the in-plane
microwave current flowing along the interface of the Permalloy/Bi$_2$Se$_3$
heterostructures, in which the huge charge-to-spin conversion ratio is observed
\cite{Mellnik-2014}. We consider analytically and by micromagnetic modelling
the dependence of this excitation on the frequency and magnitude of the
microwave current. The analogies of the vortex dynamics and the Landau phase
transitions theory is demonstrated. These findings open the possibility to
excite gyrotropic vortex motion with the current densities far lower than by
any other means.",1503.00089v3
2015-04-25,Magnetic phase transitions in Ta/CoFeB/MgO multilayers,"We study thin films and magnetic tunnel junction nanopillars based on
Ta/Co$_{20}$Fe$_{60}$B$_{20}$/MgO multilayers by electrical transport and
magnetometry measurements. These measurements suggest that an ultrathin
magnetic oxide layer forms at the Co$_{20}$Fe$_{60}$B$_{20}$/MgO interface. At
approximately 160 K, the oxide undergoes a phase transition from an insulating
antiferromagnet at low temperatures to a conductive weak ferromagnet at high
temperatures. This interfacial magnetic oxide is expected to have significant
impact on the magnetic properties of CoFeB-based multilayers used in spin
torque memories.",1504.06716v1
2015-06-16,Cavity-assisted manipulation of freely rotating silicon nanorods in high vacuum,"Optical control of nanoscale objects has recently developed into a thriving
field of research with far-reaching promises for precision measurements,
fundamental quantum physics and studies on single-particle thermodynamics.
Here, we demonstrate the optical manipulation of silicon nanorods in high
vacuum. Initially, we sculpture these particles into a silicon substrate with a
tailored geometry to facilitate their launch into high vacuum by laser-induced
mechanical cleavage. We manipulate and trace their center-of-mass and
rotational motion through the interaction with an intense intra-cavity field.
Our experiments show optical forces on nanorotors three times stronger than on
silicon nanospheres of the same mass. The optical torque experienced by the
spinning rods will enable cooling of the rotational motion and torsional
opto-mechanics in a dissipation-free environment.",1506.04881v1
2015-08-04,Scanning Kerr microscopy of current induced switching in Ta/CoFeB/MgO films with perpendicular magnetic anisotropy,"Ta/CoFeB/MgO trilayers with perpendicular magnetic anisotropy are expected to
play a key role in the next generation of current and electric field switched
memory and logic devices. In this study we use Kerr microscopy alongside
electrical transport measurement to gain insight into the underlying switching
mechanisms of such devices. We find switching to be a stochastic, domain wall
driven process, the speed of which is strongly dependent on the switching
current. Kerr imaging shows domain nucleation at the edge of the device which
modelling reveals is likely assisted by the perpendicular component of the
Oersted field. Further domain growth, leading to magnetisation reversal may be
assisted by spin torques.",1508.00833v2
2015-09-08,Ultra-fast perpendicular Spin Orbit Torque MRAM,"We demonstrate ultra-fast (down to 400 ps) bipolar magnetization switching of
a three-terminal perpendicular Ta/FeCoB/MgO/FeCoB magnetic tunnel junction. The
critical current density rises significantly as the current pulse shortens
below 10 ns, which translates into a minimum in the write energy in the ns
range. Our results show that SOT-MRAM allows fast and low power write
operations, which renders it promising for non-volatile cache memory
applications.",1509.02375v2
2015-10-11,Transverse Force on Quarks in DIS,"Generalized Parton Distributions (GPDs) provide information on the
distribution of quarks in impact paarmeter space. For transversely polarized
nucleons, these impact parameter distributions are transversely distorted and
this deviation from axial symmetry leads on average to a net transverse force
from the spectators on the active quark in a DIS experiment. %The strength of
that force can be related to twist-3 PDFs. This force when acting along the
whole trajectory of the active quark leads to a transverse single-spin
asymmetries. For a longitudinally polarized nucleon target, the transverse
force implies a torque acting on the quark Orbital Angular Momentum (OAM). The
resulting change in OAM as the quark leaves the target equals the difference
between the Jaffe-Manohar and Ji OAMs.",1510.03112v1
2015-10-19,Minimum Anisotropy of a Magnetic Nanoparticle out of Equilibrium,"In this article we study magnetotransport in single nanoparticles of Ni,
Py=Ni$_{0.8}$Fe$_{0.2}$, Co, and Fe, with volumes $15\pm 6$nm$^3$, using
sequential electron tunneling at 4.2K temperature. We measure current versus
magnetic field in the ensembles of nominally the same samples, and obtain the
abundances of magnetic hysteresis. The hysteresis abundance varies among the
metals as Ni:Py:Co:Fe=4\,:50\,:100\,:100(\%), in good correlation with the
magnetostatic and magnetocrystalline anisotropy. The abrupt change in the
hysteresis abundance among these metals suggests a concept of minimum magnetic
anisotropy required for magnetic hysteresis, which is found to be $\approx
13$meV. The minimum anisotropy is explained in terms of the residual
magnetization noise arising from the spin-orbit torques generated by sequential
electron tunneling. The magnetic hysteresis abundances are weakly dependent on
the tunneling current through the nanoparticle, which we attribute to current
dependent damping.",1510.05325v1
2016-03-25,Orthogonal Magnetization and Symmetry Breaking in Pyrochlore Iridate Eu2Ir2O7,"Electrons in the pyrochore iridates experience a large interaction energy in
addition to a strong spin-orbit interaction. Both features make the iridates
promising for realizing novel states such as the Topological Mott Insulator.
The pyrochlore iridate Eu$_2$Ir$_2$O$_7$ shows a metal-insulator transition at
$T_N \sim$ 120 K below which a magnetically ordered state develops. Using
torque magnetometry, we uncover a highly unusual magnetic response. A magnetic
field $\bf H$ applied in its $a$-$b$ plane produces a nonlinear magnetization
$M_\perp$ orthogonal to the plane. $M_\perp$ displays a $d$-wave field-angle
pattern consistent with octupolar order, with a handedness dictated by field
cooling, leading to symmetry breaking of the chirality $\omega$. A surprise is
that the lobe orientation of the $d$-wave pattern is sensitive to the direction
of the field when the sample is field-cooled below $T_N$, suggestive of an
additional order parameter $\eta$ already present at 300 K.",1603.08022v2
2016-04-21,Ferromagnetic resonance of exchange-coupled perpendicularly magnetized bilayers,"Strong ferromagnetic interlayer exchange couplings $J$ in perpendicularly
magnetized systems are becoming increasingly desirable for applications. We
study whether ferromagnetic interlayer exchange couplings can be measured by a
combination of broadband ferromagnetic resonance methods and magnetometry
hysteresis loops. For this we model the switching and the eigenexcitations in
bilayer systems comprising a soft layer coupled to a thicker harder layer that
possesses higher perpendicular magnetic anisotropy. For large $J >0$ the
switching fields are essentially independent of $J$ but the frequency of the
optical eigenmode of the bilayer and the linewidth of the acoustical and
optical eigenmode are directly sensitive to the coupling. We derive a corpus of
compact analytical expressions to analyze these frequencies, their linewidth
and discuss the meaning thereof. We illustrate this corpus on a system
mimicking the fixed layers of a magnetic tunnel junction meant for spin torque
applications.",1604.06332v1
2016-04-27,Influence of nonlocal damping on the field-driven domain wall motion,"We derive the complete expression of nonlocal damping in noncollinear
magnetization due to the nonuniform spin current pumped by precessional
magnetization and incorporate it into a generalized Thiele equation to study
its effects on the dynamics of the transverse and vortex domain walls (DWs) in
ferromagnetic nanowires. We demonstrate that the transverse component of
nonlocal damping slows down the field-driven DW propagation and increases the
Walker breakdown field whereas it is neglected in many previous works in
literature. The experimentally measured DW mobility variation with the damping
tuned by doping with heavy rare-earth elements that had discrepancy from
micromagnetic simulation are now well understood with the nonlocal damping. Our
results suggest that the nonlocal damping should be properly included as a
prerequisite for quantitative studies of current-induced torques in
noncollinear magnetization.",1604.07971v2
2016-05-12,Torsional optomechanics of a levitated nonspherical nanoparticle,"An optically levitated nanoparticle in vacuum is a paradigm optomechanical
system for sensing and studying macroscopic quantum mechanics. While its
center-of-mass motion has been investigated intensively, its torsional
vibration has only been studied theoretically in limited cases. Here we report
the first experimental observation of the torsional vibration of an optically
levitated nonspherical nanoparticle in vacuum. We achieve this by utilizing the
coupling between the spin angular momentum of photons and the torsional
vibration of a nonspherical nanoparticle whose polarizability is a tensor. The
torsional vibration frequency can be one order of magnitude higher than its
center-of-mass motion frequency, which is promising for ground state cooling.
We propose a simple yet novel scheme to achieve ground state cooling of its
torsional vibration with a linearly-polarized Gaussian cavity mode. A levitated
nonspherical nanoparticle in vacuum will also be an ultrasensitive nanoscale
torsion balance with a torque detection sensitivity on the order of $10^{-29}
~\mathrm{N}\cdot \mathrm{m}/\sqrt{\mathrm{ Hz}}$ under realistic conditions.",1605.03990v2
2016-05-31,Electric field control of magnon-induced magnetization dynamics in multiferroics,"We consider theoretically the effect of an inhomogeneous magnetoelectric
coupling on the magnon-induced dynamics of a ferromagnet. The magnon-mediated
magnetoelectric torque affects both the homogeneous magnetization and
magnon-driven domain wall motion. In the domains, we predict a reorientation of
the magnetization, controllable by the applied electric field, which is almost
an order of magnitude larger than that observed in other physical systems via
the same mechanism. The applied electric field can also be used to tune the
domain wall speed and direction of motion in a linear fashion, producing domain
wall velocities several times the zero field velocity. These results show that
multiferroic systems offer a promising arena to achieve low-dissipation
magnetization rotation and domain wall motion by exciting spin-waves.",1606.00007v2
2016-06-28,Tides and angular momentum redistribution inside low-mass stars hosting planets: a first dynamical model,"We introduce a general mathematical framework to model the internal transport
of angular momentum in a star hosting a close-in planetary/stellar companion.
By assuming that the tidal and rotational distortions are small and that the
deposit/extraction of angular momentum induced by stellar winds and tidal
torques are redistributed solely by an effective eddy-viscosity that depends on
the radial coordinate, we can formulate the model in a completely analytic way.
It allows us to compute simultaneously the evolution of the orbit of the
companion and of the spin and the radial differential rotation of the star. An
illustrative application to the case of an F-type main-sequence star hosting a
hot Jupiter is presented. The general relevance of our model to test more
sophisticated numerical dynamical models and to study the internal rotation
profile of exoplanet hosts, submitted to the combined effects of tides and
stellar winds, by means of asteroseismology are discussed.",1606.08623v1
2016-07-21,Effect of annealing on the interfacial Dzyaloshinskii-Moriya interaction in Ta/CoFeB/MgO trilayers,"The interfacial Dzyaloshinskii-Moriya interaction (DMI) has been shown to
stabilize homochiral N\'eel-type domain walls in thin films with perpendicular
magnetic anisotropy and as a result permit them to be propagated by a spin Hall
torque. In this study, we demonstrate that in Ta/Co$_{20}$Fe$_{60}$B$_{20}$/MgO
the DMI may be influenced by annealing. We find that the DMI peaks at
$D=0.057\pm0.003$ mJ/m$^{2}$ at an annealing temperature of 230 $^{\circ}$C.
DMI fields were measured using a purely field-driven creep regime domain
expansion technique. The DMI field and the anisotropy field follow a similar
trend as a function of annealing temperature. We infer that the behavior of the
DMI and the anisotropy are related to interfacial crystal ordering and B
expulsion out of the CoFeB layer as the annealing temperature is increased.",1607.06405v1
2016-08-02,Radiation from an off-centred rotating dipole in vacuum,"When a neutron star forms, after the collapse of its progenitor, a strong
magnetic field survives in its interior. This magnetic topology is usually
assumed to be well approximated by a dipole located right at the centre of the
star. However, there is no particular reason why this dipole should be attached
to this very special point. A slight shift from the stellar centre could have
strong implications for the surrounding electromagnetic field configuration
leading to clear observational signatures. We study the effect of the most
general off-centred dipole anchored in the neutron star interior. Exact
analytical solutions are given in vacuum outside the star to any order of
accuracy in the small parameter $\epsilon = d/R$, where $d$ is the displacement
of the dipole from the stellar centre and $R$ the neutron star radius. As a
simple diagnostic of this decentred dipole, the spin-down luminosity and the
torque exerted on its crust are computed to the lowest leading order
in~$\epsilon$. Results are compared to earlier works and a discussion on
repercussions on pulsar braking index and multi-wavelength light curves is
proposed.",1608.01015v1
2016-08-12,Wide-Range Probing of Dzyaloshinskii-Moriya Interaction,"Dzyaloshinskii-Moriya interaction (DMI) in magnetic objects is of enormous
interest, because it generates a built-in chirality of magnetic domain walls
(DWs) and topologically-protected skyrmions for efficient motion driven by
spin-orbit torques. Because of its importance for perspective applications and
academic curiosities, many experimental efforts have been devoted to DMI
investigation. However, current experimental probing techniques cover only
limited ranges of the DMI with specific sample requirements, and there are no
versatile techniques covering a wide range of DMI. Here, we present a unique
experimental scheme to quantify DMI over a wide range based on the angular
dependence of asymmetric DW motion. It can determine DMI even larger than the
maximum magnetic field strength, demonstrating that various strengths of DMI
can be quantified using a single measurement setup. This scheme provides a
standard technique over a wide range of DMI, which is essential to DMI-related
emerging fields in nanotechnology.",1608.03678v1
2016-08-12,Evaluating Spintronic Devices Using The Modular Approach,"Over the past decade a large family of spintronic devices have been proposed
as candidates for replacing CMOS for future digital logic circuits. Using the
recently developed Modular Approach framework, we investigate and identify the
physical bottlenecks and engineering challenges facing current spintronic
devices. We then evaluate how systematic advancements in material properties
and device design innovations impact the performance of spintronic devices, as
a possible continuation of Moore's Law, even though some of these projections
are speculative and may require technological breakthroughs. Lastly, we
illustrate the use of the Modular Approach as an exploratory tool for
probabilistic networks, using superparamagnetic magnets as building blocks for
such networks. These building blocks leverage the inherent physics of
stochastic spin-torque switching and could provide ultra-compact and efficient
hardware for beyond-Boolean computational paradigms.",1608.03681v2
2016-09-26,Ferromagnetic resonance study of composite Co/Ni - FeCoB free layers with perpendicular anisotropy,"We study the properties of composite free layers with perpendicular
anisotropy. The free layers are made of a soft FeCoB layer ferromagnetically
coupled by a variable spacer (Ta, W, Mo) to a very anisotropic [Co/Ni]
multilayer embodied in a magnetic tunnel junction meant for spin torque memory
applications. For this we use broadband ferromagnetic resonance to follow the
field dependence of the acoustical and optical excitation of the composite free
layer in both in-plane and out-of-plane applied fields. The modeling provides
the interlayer exchange coupling, the anisotropies and the damping factors. The
popular Ta spacer are outperformed by W and even more by Mo, which combines the
strongest interlayer exchange coupling without sacrificing anisotropies,
damping factors and transport properties.",1609.07863v1
2016-09-27,Anomalous Feedback and Negative Domain Wall Resistance,"Magnetic induction can be regarded as a negative feedback effect, where the
motive-force opposes the change of magnetic flux that generates the
motive-force. In artificial electromagnetics emerging from spintronics,
however, this is not necessarily the case. By studying the current-induced
domain wall dynamics in a cylindrical nanowire, we show that the spin
motive-force exerting on electrons can either oppose or support the applied
current that drives the domain wall. The switching into the anomalous feedback
regime occurs when the strength of the dissipative torque {\beta} is about
twice the value of the Gilbert damping constant {\alpha}. The anomalous
feedback manifests as a negative domain wall resistance, which has an analogy
with the water turbine.",1609.08250v1
2016-11-02,Current-induced skyrmion generation and dynamics in symmetric bilayers,"Magnetic skyrmions are textures behaving as quasiparticles which are
topologically different from other states. Their discovery in systems with
broken inversion symmetry sparked the search for materials containing such
magnetic phase at room temperature. Their topological properties combined with
the chirality-related spin-orbit torques make them interesting objects to
control the magnetization at nanoscale. Here we show that a pair of coupled
skyrmions with the same topological charge and opposite chiralities can be
stabilized in a symmetric magnetic bilayer system by combining
Dzyaloshinskii-Moriya interaction (DMI) and dipolar coupling effects. This
effect opens a new path for skyrmion stabilization with much lower DMI. We then
demonstrate in a single device with two different electrodes that such
skyrmions can be efficiently and independently written and shifted by electric
current at large velocities. The skyrmionic nature of the observed
quasiparticles is further confirmed by using the gyrotropic force as a
topological filter. These results set the ground for emerging spintronic
technologies where issues concerning skyrmion stability, nucleation, and
propagation are paramount.",1611.00647v2
2017-01-10,Current-driven skyrmion expulsion from magnetic nanostrips,"We study the current-driven skyrmion expulsion from magnetic nanostrips using
micromagnetic simulations and analytic calculations. We explore the threshold
current density for the skyrmion expulsion, and show that this threshold is
determined by the critical boundary force as well as the spin-torque
parameters. We also find the dependence of the critical boundary force on the
magnetic parameters; the critical boundary force decreases with increasing the
exchange stiffness and perpendicular anisotropy constants, while it increases
with increasing Dzyaloshinskii-Moriya interaction and saturation magnetization
constants. Using a simple model describing the skyrmion and locally-tilted edge
magnetization, we reveal the underlying physics of the dependence of the
critical boundary force on the magnetic parameters based on the relation
between the scaled Dzyaloshinskii-Moriya-interaction parameter and the critical
boundary force. This work provides a fundamental understanding of the skyrmion
expulsion and the interaction between the skymion and boundaries of devices and
shows that the stability of the skyrmion in devices can be related to the
scaled Dzyaloshinskii-Moriya-interaction parameter of magnetic materials.",1702.05672v2
2017-02-22,An analysis of the V-band light curve of the Be star omega CMa with the viscous decretion disk model,"We analyze the V-band photometry data of the Be star omega CMa, observed
during the last four decades. The data is fitted by hydrodynamic models based
on the viscous decretion disk (VDD) theory, in which a disk around a
fast-spinning Be star is formed by material ejected by the central star and
driven to progressively wider orbits by means of viscous torques. For the first
time, we apply the model for both the disk build up and the dissipation phases.
Our simulations offer a good description of the photometric variability in both
phases, which suggests that the VDD model adequately describes the disk
structural evolution. Furthermore, our analysis allowed us to determine the
viscosity parameter (alpha) of the gas, as well as the net mass loss rate. We
find that alpha is variable, ranging from 0.1 to 1.0, and that build up phases
have larger values of alpha than the dissipation phases. Additionally, we find
that, contrary to what is generally assumed, even during quiescence the outward
mass flux is never zero, suggesting that the star alternates between a high
mass-loss phase (outburst) and a low mass-loss phase (quiescence).",1702.06982v1
2017-03-14,Gaps and length asymmetry in the stellar stream Palomar 5 as effects of Galactic bar rotation,"Recent Pan-STARRS data show that the leading arm from the globular cluster
Palomar 5 (Pal 5) appears shorter than the trailing arm, while simulations of
Pal 5 predict similar angular extents. We demonstrate that including the
spinning Galactic bar with appropriate pattern speeds in the dynamical modeling
of Pal 5 can reproduce the Pan-STARRS data. As the bar sweeps by, some stream
stars experience a difference in net torques near pericenter. This leads to the
formation of apparent gaps along Pal 5's tidal streams and these gaps grow due
to an energy offset from the rest of the stream members. We conclude that only
streams orbiting far from the Galactic center or streams on retrograde orbits
(with respect to the bar) can be used to unambiguously constrain dark matter
subhalo interactions. Additionally, we expect that the Pal 5 leading arm debris
should re-appear south of the Pan-STARRS density truncation.",1703.04627v2
2017-05-02,Analysis of the current-driven domain wall motion in a ratchet ferromagnetic strip,"The current-driven domain wall motion in a ratchet memory due to spin-orbit
torques is studied from both full micromagnetic simulations and the one
dimensional model. Within the framework of this model, the integration of the
anisotropy energy contribution leads to a new term in the well known q-$\Phi$
equations, being this contribution responsible for driving the domain wall to
an equilibrium position. The comparison between the results drawn by the one
dimensional model and full micromagnetic simulations proves the utility of such
a model in order to predict the current-driven domain wall motion in the
ratchet memory. Additionally, since current pulses are applied, the paper shows
how the proper working of such a device requires the adequate balance of
excitation and relaxation times, being the latter longer than the former.
Finally, the current-driven regime of a ratchet memory is compared to the
field-driven regime described elsewhere, then highlighting the advantages of
this current-driven regime.",1705.00905v1
2017-05-29,Origin of threshold current density for asymmetric magnetoresistance in Pt/Py bilayers,"An asymmetric magnetoresistance (MR) is investigated in Py/Pt bilayers. The
asymmetric MR linearly increases with current density up to a threshold, and
increases more rapidly above the threshold. To reveal the origin of threshold
behavior, we investigate the magnetic field dependence of the asymmetric MR. It
is found that the magnetic field strongly suppresses the asymmetric MR only
above the threshold current density. Micromagnetic simulation reveals that the
reduction of magnetization due to the spin-torque oscillation can be the origin
of the threshold behavior of asymmetric MR.",1705.10059v1
2017-06-13,EXO 2030+375 Restarts in Reverse,"The Be X-ray binary pulsar EXO 2030+375, first detected in 1985, has shown a
significant detected X-ray outburst at nearly every periastron passage of its
46-day orbit for the past ~25 years, with one low state accompanied by a torque
reversal in the 1990s. In early 2015 the outbursts progressively became fainter
and less regular while the monotonic spin-up flattened. At the same time a
decrease in the H$\alpha$ line equivalent width was reported, indicating a
change in the disk surrounding the mass donor.
  In order to explore the source behaviour in the poorly explored low-flux
state with a possible transition to a state of centrifugal inhibition of
accretion we have undertaken an observing campaign with Swift/XRT, NuSTAR and
the Nordic Optical Telescope (NOT). This conference contribution reports the
preliminary results obtained from our campaign.",1706.03969v1
2017-09-27,Geometric Dynamics of Magnetization: Electronic Contribution,"To give a general description of the influences of electric fields or
currents on magnetization dynamics, we developed a semiclassical theory for the
magnetization implicitly coupled to electronic degrees of freedom. In the
absence of electric fields the Bloch electron Hamiltonian changes the Berry
curvature, the effective magnetic field, and the damping in the dynamical
equation of the magnetization, which we classify into intrinsic and extrinsic
effects. Static electric fields modify these as first-order perturbations,
using which we were able to give a physically clear interpretation of the
current-induced spin-orbit torques. We used a toy model mimicking a
ferromagnet-topological-insulator interface to illustrate the various effects,
and predicted an anisotropic gyromagnetic ratio and the dynamical stability for
an in-plane magnetization. Our formalism can also be applied to the slow
dynamics of other order parameters in crystalline solids.",1709.09513v3
2017-12-04,Band structure of CuMnAs probed by optical and photoemission spectroscopy,"Tetragonal phase of CuMnAs progressively appears as one of the key materials
for antiferromagnetic spintronics due to efficient current-induced spin-orbit
torques whose existence can be directly inferred from crystal symmetry.
Theoretical understanding of spintronic phenomena in this material, however,
relies on the detailed knowledge of electronic structure (band structure and
corresponding wave functions) which has so far been tested only to a limited
extent. We show that AC permittivity (obtained from ellipsometry) and UV
photoelectron spectra agree with density functional calculations. Together with
the x-ray diffraction and precession electron diffraction tomography, our
analysis confirms recent theoretical claim [Phys.Rev.B 96, 094406 (2017)] that
copper atoms occupy lattice positions in the basal plane of the tetragonal unit
cell.",1712.01007v2
2017-12-18,Pancharatnam-Berry phase and kinetic magnetoelectric effect in a three-dimensional helical crystal (Te),"We study the kinetic magnetoelectric effect (current-induced magnetization
including both the orbital and spin contributions) in three-dimensional
conductors, specializing to the case of p-doped trigonal tellurium. We include
both intrinsic and extrinsic contributions to the effect, which stem from the
band structure of the crystal, and from disorder scattering, respectively.
Specifically, we determine the dependence of the kinetic magnetoelectric
response on the hole doping in tellurium, and show that the intrinsic and
extrinsic effects dominate for low and high levels of doping, respectively. The
results of this work imply that three-dimensional helical metals are promising
for spintronics applications, in particular, they can provide robust control
over current-induced magnetic torques.",1712.06586v1
2017-12-20,A new development in quantum field equations of dyons,"In this study, we describe a novel approach to quantum phenomena of the
generalized electromagnetic fields of dyons with quaternionic analysis.
Starting with quaternionic quantum wave equations, we have established a
quantized condition for time coordinate that transforms microscopic to
macroscopic fields. In view of classical electromagnetic field equation, we
propose a new set of quantized Proca-Maxwell's equations for dyons.
Furthermore, a quantized form of four-currents densities and the quantized
Lorentz gauge conditions, respectively for electric and magnetic potentials of
dyons are obtained. We have established the new quantized continuity equations
for electric and magnetic densities of dyons which associated with a torque
density result from the two spin states. The quantized Klein-Gordon like field
equations and the unified quaternionic electromagnetic potential wave equations
for massive dyons are demonstrated. Moreover, we investigate the quaternionic
quantized relativistic Dirac field equations for massive dyons, which indicated
that there will be the existence of antiparticle of dyons called antidyons.",1712.08512v2
2018-02-01,An analytical computation of magnetic field generated from a cylinder ferromagnet,"An analytical formulation to compute a magnetic field generated from an
uniformly magnetized cylinder ferromagnet is developed. Exact solutions of the
magnetic field generated from the magnetization pointing in an arbitrary
direction are derived, which are applicable both inside and outside the
ferromagnet. The validities of the present formulas are confirmed by comparing
them with demagnetization coefficients estimated in earlier works. The results
will be useful for designing practical applications, such as high-density
magnetic recording and microwave generators, where nanostructured ferromagnets
are coupled to each other through the dipole interactions and show cooperative
phenomena such as synchronization. As an example, the magnetic field generated
from a spin torque oscillator for magnetic recording based on microwave
assisted magnetization reversal is studied.",1802.00384v1
2018-02-26,Relationship between Magnetic Anisotropy Below Pseudogap Temperature and Short-Range Antiferromagnetic Order in High-Temperature Cuprate Superconductor,"The central issue in high-temperature cuprate superconductors is the
pseudogap state appearing below the pseudogap temperature $T^*$, which is well
above the superconducting transition temperature. In this study, we
theoretically investigate the rapid increase of the magnetic anisotropy below
the pseudogap temperature detected by the recent torque-magnetometry
measurements on YBa$_2$Cu$_3$O$_y$ [Y. Sato et al., Nat. Phys., 13, 1074
(2017)]. Applying the spin Green's function formalism including the
Dzyaloshinskii--Moriya interaction arising from the buckling of the CuO$_2$
plane, we obtain results that are in good agreement with the experiment and
find a scaling relationship. Our analysis suggests that the characteristic
temperature associated with the magnetic anisotropy, which coincides with
$T^*$, is not a phase transition temperature but a crossover temperature
associated with the short-range antiferromagnetic order.",1802.09163v2
2018-06-01,Pulse Frequency Fluctuations of Magnetars,"Using \emph{RXTE}, \emph{Chandra}, \emph{XMM-Newton} and \emph{Swift}
observations, we for the first time construct the power spectra and torque
noise strengths of magnetars. For some of the sources, we measure strong red
noise on timescales months to years which might be a consequence of their
outbursts. We compare noise strengths of magnetars with those of radio pulsars
by investigating possible correlations of noise strengths with spin-down rate,
magnetic field and age. Using these correlations, we find that magnetar noise
strengths are obeying similar trends with radio pulsars. On the contrary, we do
not find any correlation between noise strength and X-ray luminosity which was
seen in accretion powered pulsars. Our findings suggest that the noise
behaviour of magnetars resembles that of radio pulsars but they possess higher
noise levels likely due to their stronger magnetic fields.",1806.00401v2
2018-06-04,A bistable pulsar magnetosphere: nulls and mode-changes,"It is shown that the ion-proton magnetosphere is unstable in a limited area
of the P - Pdot plane against transitions to a self-sustaining inverse Compton
scattering mode in which the particles accelerated are mainly protons with a
small component of positrons. It is argued that this mode cannot be absolutely
stable. The number density of any outward-moving pair plasma is small and
electron and positron Lorentz factors too high to support growth of any
collective mode capable of exciting normal pulsar coherent radio emission.
Particle fluxes and the position at which they pass through the light cylinder
are mode-dependent and in principle, transitions can be accompanied by changes
in spin-down torque. The properties of the system are discussed in relation to
observations of nulls, mode-changes, and the group of long-term intermittent
pulsars.",1806.01053v1
2018-06-24,Circuit-Level Evaluation of the Generation of Truly Random Bits with Superparamagnetic Tunnel Junctions,"Many emerging alternative models of computation require massive numbers of
random bits, but their generation at low energy is currently a challenge. The
superparamagnetic tunnel junction, a spintronic device based on the same
technology as spin torque magnetoresistive random access memory has recently
been proposed as a solution, as this device naturally switches between two easy
to measure resistance states, due only to thermal noise. Reading the state of
the junction naturally provides random bits, without the need of write
operations. In this work, we evaluate a circuit solution for reading the state
of superparamagnetic tunnel junction. We see that the circuit may induce a
small read disturb effect for scaled superparamagnetic tunnel junctions, but
this effect is naturally corrected in the whitening process needed to ensure
the quality of the generated random bits. These results suggest that
superparamagnetic tunnel junctions could generate truly random bits at 20
fJ/bit, including overheads, orders of magnitudes below CMOS-based solutions.",1806.09124v1
2018-07-17,Impact of further-range exchange and cubic anisotropy on magnetic excitations in the fcc kagome antiferromagnet IrMn3,"Exchange interactions up to fourth nearest neighbor are shown within a
classical local-moment Heisenberg approach to be important to model inelastic
neutron scattering data on the fcc kagome antiferromagnet IrMn$_3$. Spin wave
frequencies are calculated using the torque equation and the magnetic
scattering function, $S({\bf Q},\omega)$, is determined by a Green's function
method, as an extension of our previous work, LeBlanc et al, Phys. Rev. B 90,
144403 (2014). Results are compared with intensity contour data on powder
samples of ordered IrMn$_3$, where magnetic Mn ions occupy lattice sites of ABC
stacked kagome planes. Values of exchange parameters taken from DFT
calculations used in our model provide good agreement with the experimental
results only if further-neighbor exchange is included. Estimates of the
observed energy gap support the existence of strong cubic anisotropy predicted
by DFT calculations.",1807.06659v1
2018-07-24,Excitation and control of large amplitude standing magnetization waves,"A robust approach to excitation and control of large amplitude standing
magnetization waves in an easy axis ferromagnetic by starting from a ground
state and passage through resonances with chirped frequency microwave or spin
torque drives is proposed. The formation of these waves involves two stages,
where in the first stage, a spatially uniform, precessing magnetization is
created via passage through a resonance followed by a self-phase-locking
(autoresonance) with a constant amplitude drive. In the second stage, the
passage trough an additional resonance with a spatial modulation of the driving
amplitude yields transformation of the uniform solution into a doubly
phase-locked standing wave, whose amplitude is controlled by the variation of
the driving frequency. The stability of this excitation process is analyzed
both numerically and via Whitham's averaged variational principle.",1807.09033v1
2018-08-10,Fermi surface reconstruction and dimensional topology change in Nd-doped CeCoIn$_5$,"We performed low-temperature de Haas-van Alphen (dHvA) effect measurements on
a Ce$_{1-x}$Nd$_x$CoIn$_5$ series, for x = 0.02, 0.05, 0.1, and 1, down to T =
40 mK using torque magnetometry in magnetic felds up to 35 T. Our results
indicate that a Fermi-surface (FS) reconstruction occurs from a
quasi-two-dimensional (2D) topology for Nd-2% to a rather three-dimensional
(3D) for Nd-5%, thus reducing the possibility of perfect FS nesting. The FS
evolves further with increasing Nd content with no observed divergence of the
effective mass between Nd-2% and 10%, consistent with the crossing of a spin
density wave (SDW) type of quantum critical point (QCP). Our results elucidate
the origin of the Q-phase observed at the 5% Nd-doping level [Raymond et al.,
J. Phys. Soc. Jpn. 83, 013707 (2014)].",1808.03470v1
2018-09-05,Lorenz-Mie scattering of focused light via complex focus fields: an analytic treatment,"The Lorenz-Mie scattering of a wide class of focused electromagnetic fields
off spherical particles is studied. The focused fields in question are
constructed through complex focal displacements, leading to closed-form
expressions that can exhibit several interesting physical properties, such as
orbital and/or spin angular momentum, spatially-varying polarization, and a
controllable degree of focusing. These fields constitute complete bases that
can be considered as nonparaxial extensions of the standard Laguerre-Gauss
beams and the recently proposed polynomials-of-Gaussians beams. Their analytic
form turns out to lead also to closed-form expressions for their multipolar
expansion. Such expansion can be used to compute the field scattered by a
spherical particle and the resulting forces and torques exerted on it, for any
relative position between the field's focus and the particle.",1809.01755v1
2018-10-22,SOT-MRAM 300mm integration for low power and ultrafast embedded memories,"We demonstrate for the first time full-scale integration of top-pinned
perpendicular MTJ on 300 mm wafer using CMOS-compatible processes for
spin-orbit torque (SOT)-MRAM architectures. We show that 62 nm devices with a
W-based SOT underlayer have very large endurance (> 5x10^10), sub-ns switching
time of 210 ps, and operate with power as low as 300 pJ.",1810.10356v1
2018-11-06,Phase programming in coupled spintronic oscillators,"Neurons in the brain behave as a network of coupled nonlinear oscillators
processing information by rhythmic activity and interaction. Several
technological approaches have been proposed that might enable mimicking the
complex information processing of neuromorphic computing, some of them relying
on nanoscale oscillators. For example, spin torque oscillators are promising
building blocks for the realization of artificial high-density, low-power
oscillatory networks (ON) for neuromorphic computing. The local external
control and synchronization of the phase relation of oscillatory networks are
among the key challenges for implementation with nanotechnologies. Here we
propose a new method of phase programming in ONs by manipulation of the
saturation magnetization, and consequently the resonance frequency of a single
oscillator via Joule heating by a simple DC voltage input. We experimentally
demonstrate this method in a pair of stray field coupled magnetic vortex
oscillators. Since this method only relies on the oscillatory behavior of
coupled oscillators, and the temperature dependence of the saturation
magnetization, it allows for variable phase programming in a wide range of
geometries and applications that can help advance the efforts of high frequency
neuromorphic spintronics up to the GHz regime.",1811.02154v1
2018-12-04,Nematic superconductivity in doped Bi2Se3 topological superconductors,"Nematic superconductivity is a novel class of superconductivity characterized
by spontaneous rotational-symmetry breaking in the superconducting gap
amplitude and/or Cooper-pair spins with respect to the underlying lattice
symmetry. Doped Bi2Se3 superconductors, such as CuxBi2Se3, SrxBi2Se3, and
NbxBi2Se3, are considered as candidates for nematic superconductors, in
addition to the anticipated topological superconductivity. Recently, various
bulk probes, such as nuclear magnetic resonance, specific heat,
magnetotransport, magnetic torque, and magnetization, have consistently
revealed two-fold symmetric behavior in their in-plane magnetic-field-direction
dependence, although the underlying crystal lattice possesses three-fold
rotational symmetry. More recently, nematic superconductivity is directly
visualized using scanning tunneling microscopy and spectroscopy. In this short
review, we summarize the current researches on the nematic behavior in
superconducting doped Bi2Se3 systems, and discuss issues and perspectives.",1812.01378v2
2018-12-11,Advanced method for reliable estimation of the spin-orbit torque efficiency in low coercive ferromagnetic multilayers,"An experimental study of current-induced magnetization reversal of the
Ru/Co/Ru and Ru/Co/Ru/W structures was carried out. In the considered
structures, due to the small value of the coercive force comparable in
magnitude to the Oersted field and the SOT effect field, magnetization reversal
is carried out by moving a domain wall parallel to the direction of current
injection. For such a case, a new method for estimating the effective field of
SOT based on the analysis of the domain wall position taking into account the
distribution of the Oersted field was proposed. This method allowed determining
the effective longitudinal field and the efficiency of SOT equal 0.03 in the
quasi-symmetric Ru/Co/Ru structure. It was found that adding the W capping
layer enhances the SOT effect by 5 times.",1812.04375v1
2018-12-13,Current-induced nucleation and dynamics of skyrmions in a Co-based Heusler alloy,"We demonstrate room-temperature stabilization of dipolar magnetic skyrmions
with diameters in the range of $100$ nm in a single ultrathin layer of the
Heusler alloy Co$_2$FeAl (CFA) under moderate magnetic fields. Current-induced
skyrmion dynamics in microwires is studied with a scanning Nitrogen-Vacancy
magnetometer operating in the photoluminescence quenching mode. We first
demonstrate skyrmion nucleation by spin-orbit torque and show that its
efficiency can be significantly improved using tilted magnetic fields, an
effect which is not specific to Heusler alloys and could be advantageous for
future skyrmion-based devices. We then show that current-induced skyrmion
motion remains limited by strong pinning effects, even though CFA is a magnetic
material with a low magnetic damping parameter.",1812.05345v1
2018-12-17,The reason for the tilting of domain wall with Dzyaloshinskii-Moriya interaction from a microscopic dynamical perspective,"The interfacial Dzyaloshinskii-Moriya interaction (DMI) of a heavy metal
(HM)/ferromagnetic (FM) metal heterostructure is vital to the current-induced
domain wall motion (CIDWM) at an ultrahigh velocity. However, strong DMI also
tilts the moving domain wall (DW) plane, and the mechanism for this tilting is
not quite clear. In this work, we have found that this tilting may be
understood based on a micromagnetic calculation from a microscopic dynamical
perspective. The DMI-induced antisymmetric moment structure at the two
boundaries of the track needs to be paid attention. In the early stage of CIDWM
induced by spin-orbit torque, this antisymmetry is destroyed. Afterwards, the
moments at the two boundaries experience distinct rotation processes with
different energy paths towards their final stable antisymmetric moment
structure. This results in different initial velocities of the local DW regions
at the two boundaries. In mathematics, this distinct DW dynamical progresses at
the two boundaries can be approximately revealed by modifying the initial
conditions for solving the Thiele equations.",1812.06865v1
2019-01-21,Non-collinear coupling across RuCo and RuFe alloys,"Spintronic applications, which rely on spin torques for operation, would
greatly benefit from a non-collinear alignment between magnetizations of
adjacent ferromagnetic layers for maximum performance and reliability. We
demonstrate that such an alignment can be created and controlled by coupling
two ferromagnetic layers across magnetic coupling layers. These coupling layers
consist of a non-magnetic material, Ru, alloyed with ferromagnetic elements of
Co or Fe. Changing the composition and thickness of the coupling layer enables
control of the relative angle between the magnetizations of ferromagnetic
layers between 0 and 180 degrees. The onset of the non-collinear alignment
between ferromagnetic layers coincide with the advent of magnetic order in the
coupling layer. This study will map the range of concentrations and thicknesses
of RuCo and RuFe coupling layers that give rise to non-collinearity between Co
layers.",1901.07055v1
2019-01-23,Physical reservoir computing built by spintronic devices for temporal information processing,"Spintronic nanodevices have ultrafast nonlinear dynamic and recurrence
behaviors on a nanosecond scale that promises to enable spintronic reservoir
computing (RC) system. Here two physical RC systems based on a single magnetic
skyrmion memristor (MSM) and 24 spin-torque nano-oscillators (STNOs) were
proposed and modeled to process image classification task and nonlinear dynamic
system prediction, respectively. Based on our micromagnetic simulation results
on the nonlinear responses of MSM and STNO with current pulses stimulation, the
handwritten digits recognition task domesticates that an RC system using one
single MSM has the outstanding performance on image classification. In
addition, the complex unknown nonlinear dynamic problems can also be well
solved by a physical RC system consisted of 24 STNOs confirmed in a
second-order nonlinear dynamic system and NARMA10 tasks. The capability of both
high accuracy and fast information processing promises to enable one type of
brain-like chip based on spintronics for various artificial intelligence tasks.",1901.07879v2
2019-02-06,Imaging of current induced Néel vector switching in antiferromagnetic Mn$_2$Au,"The effects of current induced N\'eel spin-orbit torques on the
antiferromagnetic domain structure of epitaxial Mn$_2$Au thin films were
investigated by X-ray magnetic linear dichroism - photoemission electron
microscopy (XMLD-PEEM). We observed current induced switching of AFM domains
essentially corresponding to morphological features of the samples. Reversible
as well as irreversible N\'eel vector reorientation was obtained in different
parts of the samples and the switching of up to 30 % of all domains in the
field of view of 10 $\mu$m is demonstrated. Our direct microscopical
observations are compared to and fully consistent with anisotropic
magnetoresistance effects previously attributed to current induced N\'eel
vector switching in Mn$_2$Au.",1902.02063v1
2019-02-22,Strongly Enhanced Gilbert Damping in 3d Transition Metal Ferromagnet Monolayers in Contact with Topological Insulator Bi2Se3,"Engineering Gilbert damping of ferromagnetic metal films is of great
importance to exploit and design spintronic devices that are operated with an
ultrahigh speed. Based on scattering theory of Gilbert damping, we extend the
torque method originally used in studies of magnetocrystalline anisotropy to
theoretically determine Gilbert dampings of ferromagnetic metals. This method
is utilized to investigate Gilbert dampings of 3d transition metal ferromagnet
iron, cobalt and nickel monolayers that are contacted by the prototypical
topological insulator Bi2Se3. Amazingly, we find that their Gilbert dampings
are strongly enhanced by about one order in magnitude, compared with dampings
of their bulks and free-standing monolayers, owing to the strong spin-orbit
coupling of Bi2Se3. Our work provides an attractive route to tailoring Gilbert
damping of ferromagnetic metallic films by putting them in contact with
topological insulators.",1902.08700v1
2019-03-03,Chaos in Magnetic Nanocontact Vortex Oscillators,"We present an experimental study of spin-torque driven vortex
self-oscillations in magnetic nanocontacts. We find that above a certain
threshold in applied currents, the vortex gyration around the nanocontact is
modulated by relaxation oscillations, which involve periodic reversals of the
vortex core. This modulation leads to the appearance of commensurate but also
more interestingly here, incommensurate states, which are characterized by
devil's staircases in the modulation frequency. We use frequency- and
time-domain measurements together with advanced time-series analyses to provide
experimental evidence of chaos in incommensurate states of vortex oscillations,
in agreement with theoretical predictions.",1903.00921v2
2019-04-16,"Processing-In-Memory Acceleration of Convolutional Neural Networks for Energy-Efficiency, and Power-Intermittency Resilience","Herein, a bit-wise Convolutional Neural Network (CNN) in-memory accelerator
is implemented using Spin-Orbit Torque Magnetic Random Access Memory (SOT-MRAM)
computational sub-arrays. It utilizes a novel AND-Accumulation method capable
of significantly-reduced energy consumption within convolutional layers and
performs various low bit-width CNN inference operations entirely within MRAM.
Power-intermittence resiliency is also enhanced by retaining the partial state
information needed to maintain computational forward-progress, which is
advantageous for battery-less IoT nodes. Simulation results indicate
$\sim$5.4$\times$ higher energy-efficiency and 9$\times$ speedup over
ReRAM-based acceleration, or roughly $\sim$9.7$\times$ higher energy-efficiency
and 13.5$\times$ speedup over recent CMOS-only approaches, while maintaining
inference accuracy comparable to baseline designs.",1904.07864v1
2019-05-03,Chiral excitations of magnetic droplet solitons driven by their own inertia,"The inertial effects of magnetic solitons play a crucial role in their
dynamics and stability. Yet governing their inertial effects is a challenge for
their use in real devices. Here, we show how to control the inertial effects of
magnetic droplet solitons. Magnetic droplets are strongly nonlinear and
localized autosolitons than can form in current-driven nanocontacts. Droplets
can be considered as dynamical particles with an effective mass. We show that
the dynamical droplet bears a second excitation under its own inertia. These
excitations comprise a chiral profile, and appear when the droplet resists the
force induced by the Oersted field of the current injected into the
nanocontact. We reveal the role of the spin torque on the excitation of these
chiral modes and we show how to control these modes using the current and the
field.",1905.01085v2
2019-07-01,Chemical potential of an antiferromagnetic magnon gas,"Understanding the statistics of quasi-particle excitations in magnetic
systems is essential for exploring new magnetic phases and collective quantum
phenomena. While the chemical potential of a ferromagnetic gas has been
extensively investigated both theoretically and experimentally, its
antiferromagnetic counterpart remains uncharted. Here, we derive the statistics
of a two-component U(1)-symmetric Bose gas and apply our results to an
axially-symmetric antiferromagnetic insulator. We find that the two magnon
eigenmodes of the system are described by an equal and opposite chemical
potential, in analogy with a particle-antiparticle pair. Furthermore, we derive
the thermomagnonic torques describing the interaction between the coherent and
incoherent antiferromagnetic spin dynamics. Our results show that the magnitude
and sign of the chemical potential can be tuned via an AC magnetic field
driving resonantly one of the magnon modes. Finally, we propose NV-center
relaxometry as a method to experimentally test our predictions.",1907.00931v1
2019-07-10,Temperature dependence of magnetic resonance in ferrimagnetic GdFeCo alloys,"We provide a macroscopic theory and experimental results for magnetic
resonances of antiferromagnetically-coupled ferrimagnets. Our theory, which
interpolates the dynamics of antiferromagnets and ferromagnets smoothly, can
describe ferrimagnetic resonances across the angular momentum compensation
point. We also present experimental results for spin-torque induced
ferrimagnetic resonance at several temperatures. The spectral analysis based on
our theory reveals that the Gilbert damping parameter, which has been
considered to be strongly temperature dependent, is insensitive to temperature.
We envision that our work will facilitate further investigation of
ferrimagnetic dynamics by providing a theoretical framework suitable for a
broad range of temperatures.",1907.04540v1
2019-07-11,The angular momentum decomposition in the scalar diquark model,"One of the challenges of hadronic physics is to fully understand the
structure of the proton. In particular, there is nowadays a great interest in
the decomposition of its total angular momentum into orbital angular momentum
and intrinsic spin, as well as identifying contributions from valence quarks,
sea quarks and gluons. The most common decompositions of angular momentum are
the Jaffe-Manohar (canonical) and Ji (kinetic) decompositions, which differ in
the way contributions are attributed to quarks and gluons. Using perturbation
theory, explicit one-loop calculations found that the difference between such
decompositions vanishes. We justify within the diquark model in QED that the
difference appears at two-loop level, supporting the interpretation of such a
difference as originating from the torque exerted by the spectator system on
the struck quark.",1907.05268v2
2019-07-12,Electrical current switching of the noncollinear antiferromagnet Mn$_3$GaN,"We report electrical current switching of noncollinear antiferromagnetic
(AFM) Mn$_3$GaN/Pt bilayers at room temperature. The Hall resistance of these
bilayers can be manipulated by applying a pulse current of
$1.5\times10^6$~A/cm$^2$, whereas no significant change is observed up to
$\sim10^8$~A/cm$^2$ in Mn$_3$GaN single films, indicating that the Pt layer
plays an important role. In comparison with ferrimagnetic Mn$_3$GaN/Pt
bilayers, a lower electrical current switching of noncollinear AFM Mn$_3$GaN is
demonstrated, with a critical current density two orders of magnitude smaller.
Our results highlight that a combination of a noncollinear AFM antiperovskite
nitride and a spin-torque technique is a good platform of AFM spintronics.",1907.05544v1
2019-07-17,Impact of an off-centred dipole on neutron star binaries,"Neutron stars are strongly magnetized rotating compact objects. Therefore
they also produce huge electric fields accelerating particles to
ultra-relativistic energies. The simplest magnetic topology is a dipole
traditionally located at the stellar centre. In this paper, we reinvestigate
the consequences of an off-centred rotating magnetic dipole, showing accurate
magnetic field line geometries, the associated spin-down luminosity as well as
the corresponding electromagnetic kick and torque imprinted to the neutron
star. Results are obtained by time dependent numerical simulations of Maxwell
equations in vacuum using pseudo-spectral methods. We compare our results to
known analytical expressions available to lowest order in the parameter
$\epsilon = d/R$, where $d$ is the displacement of the dipole from the stellar
centre and $R$ the neutron star radius. We found good agreement between our
numerical computations and our analytical approximations even for well
off-centred dipoles having large displacements with a sizeable fraction of the
radius, i.e. $\epsilon \lesssim 1$. An explanation for binary neutron star
eccentricity distribution functions is given with an emphasize on highly
eccentric systems as an alternative scenario to traditional binary formation.",1907.07551v2
2019-08-14,Magnetic Skyrmion Field-Effect Transistors,"Magnetic skyrmions are of considerable interest for low-power memory and
logic devices because of high speed at low current and high stability due to
topological protection. We propose a skyrmion field-effect transistor based on
a gate-controlled Dzyaloshinskii-Moriya interaction. A key working principle of
the proposed skyrmion field-effect transistor is a large transverse motion of
skyrmion, caused by an effective equilibrium damping-like spin-orbit torque due
to spatially inhomogeneous Dzyaloshinskii-Moriya interaction. This large
transverse motion can be categorized as the skyrmion Hall effect, but has been
unrecognized previously. The propose device is capable of multi-bit operation
and Boolean functions, and thus is expected to serve as a low-power logic
device based on the magnetic solitons.",1908.04931v1
2019-09-06,Effect of Tantalum spacer thickness and deposition conditions on the properties of MgO/CoFeB/Ta/CoFeB/MgO free layers,"To get stable perpendicularly magnetized tunnel junctions at small device
dimensions, composite free layers that comprise two MgO/FeCoB interfaces as
sources of interface anisotropy are generally used. Proper cristallisation and
annealing robustness is typically ensured by the insertion of a spacer layer of
the early transition metal series within the FeCoB layer. We study the
influence of the spacer thickness and growth condition on the switching metrics
of tunnel junctions thermally annealed at 400$^\circ$C for the case of 1-4
\r{A} Ta spacers. Thick Ta spacer results in a large anisotropies indicative of
a better defined top FeCoB/MgO interface, but this is achieved at the
systematic expense of a stronger damping. For the best anisotropy-damping
compromise, junctions of diameter 22 nm can still be stable and spin-torque
switched. Coercivity and inhomogeneous linewidth broadening, likely arising
from roughness at the FeCoB/Ta interface, can be reduced if a sacrificial Mg
layer is inserted before the Ta spacer deposition.",1909.02741v1
2019-10-15,Spontaneous Rotational Symmetry Breaking in a Kramers Two-Level System,"Here, I develop a model for a two-level system that respects the
time-reversal symmetry of the atom Hamiltonian and the Kramers theorem. The
two-level system is formed by two Kramers pairs of excited and ground states.
It is shown that due to the spin-orbit interaction it is in general impossible
to find a basis of atomic states for which the crossed transition dipole moment
vanishes. The parametric electric polarizability of the Kramers two-level
system for a definite ground-state is generically nonreciprocal. I apply the
developed formalism to study Casimir-Polder forces and torques when the
two-level system is placed nearby either a reciprocal or a nonreciprocal
substrate. In particular, I investigate the stable equilibrium orientation of
the two-level system when both the atom and the reciprocal substrate have
symmetry of revolution about some axis. Surprisingly, it is found that when
chiral-type dipole transitions are dominant the stable ground state is not the
one in which the symmetry axes of the atom and substrate are aligned. The
reason is that the rotational symmetry may be spontaneously broken by the
quantum vacuum fluctuations, so that the ground state has less symmetry than
the system itself.",1910.07005v1
2019-10-30,Enhanced skyrmion motion via strip domain wall,"When magnetic skyrmions move under spin orbit torque in magnetic nanowires,
they experience a skyrmion Hall effect, which pushes them towards the nanowire
edge where they risk being annihilated; this puts an upper limit on how fast
they can be driven. However, the same magnetic multilayer harboring skyrmions
can sustain a N\'eel-type strip domain wall along the nanowire length,
potentially keeping the skyrmions separated from the edge. Here we study the
interplay between current driven skyrmions and domain walls and find that they
increase the annihilation current and allow the skyrmions to move faster. Based
on the Thiele formalism, we confirm that the emergent longitudinal repulsive
force and the modified energy landscape linked to the domain wall are
responsible for the enhanced skyrmion motion. Furthermore, we identify that the
longitudinal repulsive force emerges because of the broken axisymmetry in the
local magnetization in front of the skyrmion. Our study uncovers key aspects in
the interplay between two topological magnetic textures from different homotopy
groups and may inspire new device concepts.",1910.13677v3
2019-10-29,Gyro-Control of a Solar Sailing Satellite,"Recent successes in the deployment of sails in space have reduced the risk
associated with solar sailing missions. The attitude control requirements for a
solar sailing mission is low with only slow attitude maneuvers needed to
maintain a stable attitude and produce a required solar thrust. Future science
missions will require large attitude maneuvers with a fully deployed sail. This
article investigates the current options for attitude control on solar sails
and proposes a gyro-controlled solar sailing. This concept uses a spinning
solar sail to construct a control moment gyroscope capable to produce large
torques. Steering laws for performing attitude maneuvers and simulation results
are presented which demonstrates the capabilities of such a solution.",1910.13841v1
2019-11-02,Tuning Non-Gilbert-type damping in FeGa films on MgO(001) via oblique deposition,"The ability to tailor the damping factor is essential for spintronic and
spin-torque applications. Here, we report an approach to manipulate the damping
factor of FeGa/MgO(001) films by oblique deposition. Owing to the defects at
the surface or interface in thin films, two-magnon scattering (TMS) acts as a
non-Gilbert damping mechanism in magnetization relaxation. In this work, the
contribution of TMS was characterized by in-plane angular dependent
ferromagnetic resonance (FMR). It is demonstrated that the intrinsic Gilbert
damping is isotropic and invariant, while the extrinsic mechanism related to
TMS is anisotropic and can be tuned by oblique deposition. Furthermore, the two
and fourfold TMS related to the uniaxial magnetic anisotropy (UMA) and
magnetocrystalline anisotropy were discussed. Our results open an avenue to
manipulate magnetization relaxation in spintronic devices.",1911.00728v1
2019-11-20,Adaptive Non-Uniform Compressive Sensing using SOT-MRAM Multibit Crossbar Arrays,"A Compressive Sensing (CS) approach is applied to utilize intrinsic
computation capabilities of Spin-Orbit Torque Magnetic Random Access Memory
(SOT-MRAM) devices for IoT applications wherein lifetime energy, device area,
and manufacturing costs are highly-constrained while the sensing environment
varies rapidly. In this manuscript, we propose the Adaptive Compressed-sampling
via Multibit Crossbar Array (ACMCA) approach to intelligently generate the CS
measurement matrix using a multibit SOT-MRAM crossbar array. SPICE circuit and
MATLAB algorithm simulation results indicate that ACMCA reduces reconstruction
Time-Averaged Normalized Mean Squared Error (TNMSE) by 5dB on average while
providing up to 160$\mu$m$^2$ area reduction compared to a similar previous
design presented in the literature while incurring a negligible increase in the
energy consumption of generating the CS measurement matrix.",1911.08633v3
2020-01-22,Macroscopic Manifestation of Domain-wall Magnetism and Magnetoelectric Effect in a Néel-type Skyrmion Host,"We report a magnetic state in GaV$_4$Se$_8$ which emerges exclusively in
samples with mesoscale polar domains and not in polar mono-domain crystals. Its
onset is accompanied with a sharp anomaly in the magnetic susceptibility and
the magnetic torque, distinct from other anomalies observed also in polar
mono-domain samples upon transitions between the cycloidal, the N\'eel-type
skyrmion lattice and the ferromagnetic states. We ascribe this additional
transition to the formation of magnetic textures localized at structural domain
walls, where the magnetic interactions change stepwise and spin textures with
different spiral planes, hosted by neighbouring domains, need to be matched. A
clear anomaly in the magneto-current indicates that the domain-wall-confined
magnetic states also have strong contributions to the magnetoelectric response.
We expect polar domain walls to commonly host such confined magnetic edge
states, especially in materials with long wavelength magnetic order.",2001.08076v1
2020-01-28,Effects of magnetic field on the radiation pressure dominated discs around neutron stars,"We supplement the analytic solution obtained by Matthews O. M., et. al.,
2005, MNRAS, \textbf{356}, 66 to investigate the steady-state structure of
radiation pressure dominated disc under the influence of a stellar magnetic
field which deploys a torque. The solutions converge to the non-magnetic
Shakura N. I., Sunyaev R. A., 1973, A\& A, \textbf{24}, 337 form when magnetic
field of the star tends to zero and also at large radii. Effects of varying the
mass accretion rates and the spin period of a typical neutron star on the disc
parameters are presented. We further report that the presence of a magnetic
correction term $k$ reduces the radial extent upto which radiation pressure and
electron scattering continue to be the major source of pressure and opacity
respectively. We also report that magnetic effects amplify the viscous
timescale several times in the inner disc.",2001.10307v1
2020-02-14,Synchronization properties and reservoir computing capability of hexagonal spintronic oscillator arrays,"The influence of array geometry on synchronization properties of a 2-D
oscillator array is investigated based on a comparison between a rectangular
and a hexagonal grid. The Kuramoto model is solved for a nearest-neighbor case
with periodic boundary conditions and for a small-scale, realistic coupling
case with 1/r^3 decay characteristic of spintronic oscillators. In both cases,
it is found that the hexagonal grid choice leads to lower synchronization
threshold and higher emission power than its rectangular counterpart, which
results from increased connectivity, as well as, in the realistic-coupling
case, from decreased contributions of the array edges. Additionally, a more
general spin-torque oscillator model including both amplitude and phase as
degrees of freedom is employed for reservoir computing simulations, showing
that by using hexagonal grid one can increase the short-term memory capacity
but not the parity-check capacity of the system.",2002.07060v1
2020-04-22,Magnetic phase diagram of the linear quantum ferro-antiferromagnet Cs$_{2}$Cu$_{2}$Mo$_{3}$O$_{12}$,"A single-crystal sample of the frustrated quasi one-dimensional quantum
magnet Cs$_{2}$Cu$_{2}$Mo$_{3}$O$_{12}$ is investigated by magnetic and
thermodynamic measurements.A combination of specific heat and magnetic torque
measurements maps out the entire $H$-$T$ phase diagram for three
orientations.Remarkably, a new phase emerges below the saturation field,
irrespective of the crystal orientation. It is suggested that the presaturation
phase represents spin-nematic order or other multi-magnon condensate. The phase
diagrams within the long-range ordered dome are qualitatively different for
each geometry. In particular, multiple transitions are identified in the field
along the chain direction.",2004.10636v3
2020-06-01,SOT-MRAM based Sigmoidal Neuron for Neuromorphic Architectures,"In this paper, the intrinsic physical characteristics of spin-orbit torque
(SOT) magnetoresistive random-access memory (MRAM) devices are leveraged to
realize sigmoidal neurons in neuromorphic architectures. Performance
comparisons with the previous power- and area-efficient sigmoidal neuron
circuits exhibit 74x and 12x reduction in power-area-product values for the
proposed SOT-MRAM based neuron. To verify the functionally of the proposed
neuron within larger scale designs, we have implemented a circuit realization
of a 784x16x10 SOT-MRAM based multiplayer perceptron (MLP) for MNIST pattern
recognition application using SPICE circuit simulation tool. The results
obtained exhibit that the proposed SOT-MRAM based MLP can achieve accuracies
comparable to an ideal binarized MLP architecture implemented on GPU, while
realizing orders of magnitude increase in processing speed.",2006.01238v1
2020-06-17,Muon g-2 and EDM experiments as muonic dark matter detectors,"The detection of ultralight dark matter through interactions with nucleons,
electrons, and photons has been explored in depth. In this work we propose to
use precision muon experiments, specifically muon g-2 and electric dipole
moment measurements, to detect ultralight dark matter that couples
predominantly to muons. We set direct, terrestrial limits on DM-muon
interactions using existing g-2 data, and show that a time-resolved reanalysis
of ongoing and upcoming precession experiments will be sensitive to dark matter
signals. Intriguingly, we also find that the current muon g-2 anomaly can be
explained by a spin torque applied to muons from a pseudoscalar dark matter
background that induces an oscillating electric dipole moment for the muon.
This explanation may be verified by a time-resolved reanalysis.",2006.10069v1
2020-08-12,Direct imaging of current-induced antiferromagnetic switching revealing a pure thermomagnetoelastic switching mechanism,"We unravel the origin of current-induced magnetic switching of insulating
antiferromagnet/heavy metal systems. We utilize concurrent transport and
magneto-optical measurements to image the switching of antiferromagnetic
domains in specially engineered devices of NiO/Pt bilayers. Different
electrical pulsing and device geometries reveal different final states of the
switching with respect to the current direction. We can explain these through
simulations of the temperature induced strain and we identify the
thermomagnetoelastic switching mechanism combined with thermal excitations as
the origin, in which the final state is defined by the strain distributions and
heat is required to switch the antiferromagnetic domains. We show that such a
potentially very versatile non-contact mechanism can explain the previously
reported contradicting observations of the switching final state, which were
attributed to spin-orbit torque mechanisms.",2008.05219v1
2020-08-03,Rotary dynamics of the rigid body electric dipole under the radiation reaction,"Rotation of a permanently polarized rigid body under the radiation reaction
torque is considered. Dynamics of the spinning top is derived from a balance
condition of the angular momentum. It leads to the non-integrable nonlinear
2nd-order equations for angular velocities, and then to the reduced 1st-order
Euler equations. The example of an axially symmetric top with the longitudinal
dipole is solved exactly, with the transverse dipole is analyzed qualitatively
and numerically. Physical solutions describe the asymptotic power-law slowdown
to stop or the exponential drift to a residual rotation; this depends on
initial conditions and a shape of the top.",2008.06115v1
2020-08-18,"Survey of 360$^{\circ}$ domain walls in magnetic heterostructures: topology, chirality and current-driven dynamics","Chirality and current-driven dynamics of topologically nontrivial
360$^{\circ}$ domain walls (360DWs) in magnetic heterostructures (MHs) are
systematically investigated. For MHs with normal substrates, the static 360DWs
are N\'{e}el-type with no chirality. While for those with heavy-metal
substrates, the interfacial Dzyaloshinskii-Moriya interaction (iDMI) therein
makes 360DWs prefer specific chirality. Under in-plane driving charge currents,
as the direct result of ""full-circle"" topology a certain 360DW does not undergo
the ""Walker breakdown""-type process like a well-studied 180$^{\circ}$ domain
wall as the current density increases. Alternatively, it keeps a fixed
propagating mode (either steady-flow or precessional-flow, depending on the
effective damping constant of the MH) until it collapses or changes to other
types of solition when the current density becomes too high. Similarly, the
field-like spin-orbit torque (SOT) has no effects on the dynamics of 360DWs,
while the anti-damping SOT has. For both modes, modifications to the mobility
of 360DWs by iDMI and anti-damping SOT are provided.",2008.08196v1
2020-11-10,Superconductivity beyond Pauli's limit in bulk NbS2: Evidence for the Fulde-Ferrell-Larkin-Ovchinnikov state,"We present magnetic torque, specific heat and thermal expansion measurements
combined with a piezo rotary positioner of the bulk transition metal
dichalcogenide (TMD) superconductor NbS2 in high magnetic fields applied
strictly parallel to its layer structure. The upper critical field of
superconducting TMDs in the 2D form is known to be dramatically enhanced by a
special form of Ising spin orbit coupling. This Ising superconductivity is very
robust against the Pauli limit for superconductivity. We find that
superconductivity beyond the Pauli limit still exists in bulk single crystals
of NbS2. However, the comparison of our upper critical field transition line
with numerical simulations rather points to the development of a
Fulde-Ferrell-Larkin-Ovchinnikov state above the Pauli limit as a cause. This
is also consistent with the observation of a magnetic field driven phase
transition in the thermodynamic quantities within the superconducting state
near the Pauli limit.",2011.04880v1
2020-11-23,Topological defects in solids with odd elasticity,"Crystallography typically studies collections of point particles whose
interaction forces are the gradient of a potential. Lifting this assumption
generically gives rise in the continuum limit to a form of elasticity with
additional moduli known as odd elasticity. We show that such odd elastic moduli
modify the strain induced by topological defects and their interactions, even
reversing the stability of, otherwise, bound dislocation pairs. Beyond
continuum theory, isolated dislocations can self propel via microscopic work
cycles active at their cores that compete with conventional Peach-Koehler
forces caused, for example, by an ambient torque density. We perform molecular
dynamics simulations isolating active plastic processes and discuss their
experimental relevance to solids composed of spinning particles, vortex-like
objects, and robotic metamaterials.",2011.11543v4
2020-12-04,A Single-Cycle MLP Classifier Using Analog MRAM-based Neurons and Synapses,"In this paper, spin-orbit torque (SOT) magnetoresistive random-access memory
(MRAM) devices are leveraged to realize sigmoidal neurons and binarized
synapses for a single-cycle analog in-memory computing (IMC) architecture.
First, an analog SOT-MRAM-based neuron bitcell is proposed which achieves a 12x
reduction in power-area-product compared to the previous most power- and
area-efficient analog sigmoidal neuron design. Next, proposed neuron and
synapse bit cells are used within memory subarrays to form an analog IMC-based
multilayer perceptron (MLP) architecture for the MNIST pattern recognition
application. The architecture-level results exhibit that our analog IMC
architecture achieves at least two and four orders of magnitude performance
improvement compared to a mixed-signal analog/digital IMC architecture and a
digital GPU implementation, respectively while realizing a comparable
classification accuracy.",2012.02695v1
2020-12-07,Magnetic anisotropy from linear defect structures in correlated electron systems,"Correlated electron systems, particularly iron-based superconductors, are
extremely sensitive to strain, which inevitably occurs in the crystal growth
process. Built-in strain of this type has been proposed as a possible
explanation for experiments where nematic order has been observed at high
temperatures corresponding to the nominally tetragonal phase of iron-based
superconductors. Strain is assumed to produce linear defect structures, e.g.
dislocations, which are quite similar to O vacancy chainlets in the underdoped
cuprate superconductor YBCO. Here we investigate a simple microscopic model of
dislocations in the presence of electronic correlations, which create defect
states that can drive magnetic anisotropy of this kind, if spin orbit
interaction is present. We estimate the contribution of these dislocations to
magnetic anisotropy as detected by current torque magnetometry experiments in
both cuprates and Fe-based systems.",2012.03824v2
2020-12-08,Direct Imaging of Electrical Switching of Antiferromagnetic Néel Order in $α$-Fe$_2$O$_3$ Epitaxial Films,"We report the direct observation of switching of the N\'eel vector of
antiferromagnetic (AFM) domains in response to electrical pulses in
micron-scale Pt/$\alpha$-Fe$_2$O$_3$ Hall bars using photoemission electron
microscopy. Current pulses lead to reversible and repeatable switching, with
the current direction determining the final state, consistent with Hall effect
experiments that probe only the spatially averaged response. Current pulses
also produce irreversible changes in domain structure, in and even outside the
current path. In both cases only a fraction of the domains switch in response
to pulses. Further, analysis of images taken with different x-ray polarizations
shows that the AFM N\'eel order has an out-of-plane component in equilibrium
that is important to consider in analyzing the switching data. These results
show that -in addition to effects associated with spin-orbit torques from the
Pt layer, which can produce reversible switching-changes in AFM order can be
induced by purely thermal effects.",2012.04127v1
2020-12-30,RF signal detector and energy harvester based on a spin-torque diode with perpendicular magnetic anisotropy,"We demonstrate theoretically that in a spintronic diode (SD), having a free
magnetic layer with perpendicular magnetic anisotropy of the first and second
order and no external bias magnetic field, the out-of-plane regime of
magnetization precession can be excited by sufficiently large (exceeding a
certain threshold) RF signals with the frequencies <~250 MHz. We also show that
such a device can operate as a broadband energy harvester capable of converting
incident RF power into a DC power with the conversion efficiency of ~5%. The
developed analytical theory of the bias-free SD operation can be used for the
optimization of high-efficiency RF detectors and energy harvesters based on
SDs.",2012.15107v1
2021-01-26,Tuning the dynamics of magnetic droplet solitons using dipolar interactions,"Magnetic droplets are dissipative magnetodynamical solitons that can form
under current driven nanocontacts in magnetic layers with large perpendicular
magnetic anisotropy. Here, we extend the original droplet theory by studying
the impact of the dipolar interactions on the dynamics of droplet solitons. By
varying the thickness of the free layer of a spin torque nano-oscillator, we
systematically tune the internal field of the free layer to investigate the
dynamics of droplet solitons. Our numerical results show that increasing the
free layer thickness increases the droplet threshold current, decreases the
droplet frequency and diameter, enlarges the current hysteresis and also
modifies the structure of the droplet. The Oersted field of the current breaks
the phase coherency and deteriorates the stability of the droplet in free
layers with larger thicknesses. Moreover, our findings show a simple relation
to determine the impact of the free layer thickness on the droplet nucleation
boundaries. Our study presents the missing brick on the physics behind magnetic
droplet solitons, and further illustrates that magnetic droplets in thinner
layers possess more promising characteristics for spintronic applications and
enable devices with higher speed of operation.",2101.10716v1
2021-02-01,Real-time Hall-effect detection of current-induced magnetization dynamics in ferrimagnets,"Measurements of the transverse Hall resistance are widely used to investigate
electron transport, magnetization phenomena, and topological quantum states.
Owing to the difficulty of probing transient changes of the transverse
resistance, the vast majority of Hall effect experiments are carried out in
stationary conditions using either dc or ac currents. Here we present an
approach to perform time-resolved measurements of the transient Hall resistance
during current-pulse injection with sub-nanosecond temporal resolution. We
apply this technique to investigate in real-time the magnetization reversal
caused by spin-orbit torques in ferrimagnetic GdFeCo dots. Single-shot Hall
effect measurements show that the current-induced switching of GdFeCo is widely
distributed in time and characterized by significant activation delays, which
limit the total switching speed despite the high domain-wall velocity typical
of ferrimagnets. Our method applies to a broad range of current-induced
phenomena and can be combined with non-electrical excitations to perform
pump-probe Hall effect measurements.",2102.00716v1
2021-02-15,Fermi-surface reconstruction at the metamagnetic high-field transition in uranium mononitride,"We report on the electronic and thermodynamic properties of the
antiferromagnetic metal uranium mononitride with a N\'eel temperature
$T_N\approx 53\,$K. The fabrication of microstructures from single crystals
enables us to study the low-temperature metamagnetic transition at
approximately $58\,$T by high-precision magnetotransport, Hall-effect, and
magnetic-torque measurements. We confirm the evolution of the high-field
transition from a broad and complex behavior to a sharp first-order-like step,
associated with a spin flop at low temperature. In the high-field state, the
magnetic contribution to the temperature dependence of the resistivity is
suppressed completely. It evolves into an almost quadratic dependence at low
temperatures indicative of a metallic character. Our detailed investigation of
the Hall effect provides evidence for a prominent Fermi-surface reconstruction
as the system is pushed into the high-field state.",2102.07512v2
2021-04-03,Biasing topological charge injection in topological matter,"We explore the interplay between topologies in the momentum and real spaces
to formulate a thermodynamic description of nonequilibrium injection of
topological charges under external bias. We show that the edge modes engendered
by the momentum-space topology can play a functional role of connecting the
external reservoirs to the bulk transport of topological charges in the real
space. We illustrate our general results with two examples: the spin-torque
injection of skyrmions in an electrically-biased integer quantum Hall system,
and the vortex injection in a topological $p\,+\,i\,p$ superconductor coupled
to heat reservoirs. Based on the universal fractional entropy of the Majorana
zero modes bound to the vortices, their controllable injection proposed in this
work could provide a route for creating and manipulating Majorana fermions.",2104.01479v2
2021-05-27,Noether's Theorem in Statistical Mechanics,"Noether's calculus of invariant variations yields exact identities from
functional symmetries. The standard application to an action integral allows to
identify conservation laws. Here we rather consider generating functionals,
such as the free energy and the power functional, for equilibrium and driven
many-body systems. Translational and rotational symmetry operations yield
mechanical laws. These global identities express vanishing of total internal
and total external forces and torques. We show that functional differentiation
then leads to hierarchies of local sum rules that interrelate density
correlators as well as static and time direct correlation functions, including
memory. For anisotropic particles, orbital and spin motion become
systematically coupled. The theory allows us to shed new light on the
spatio-temporal coupling of correlations in complex systems. As applications we
consider active Brownian particles, where the theory clarifies the role of
interfacial forces in motility-induced phase separation. For active
sedimentation, the center-of-mass motion is constrained by an internal Noether
sum rule.",2105.13238v2
2021-05-28,Deep searches for X-ray pulsations from Scorpius X-1 and Cygnus X-2 in support of continuous gravitational wave searches,"Neutron stars in low mass X-ray binaries are hypothesised to emit continuous
gravitational waves that may be detectable by ground-based observatories. The
torque balance model predicts that a higher accretion rate produces
larger-amplitude gravitational waves, hence low mass X-ray binaries with high
X-ray flux are promising targets for gravitational wave searches. The detection
of X-ray pulsations would identify the spin frequency of these neutron stars,
and thereby improve the sensitivity of continuous gravitational-wave searches
by reducing the volume of the search parameter space. We perform a
semi-coherent search for pulsations in the two low mass X-ray binaries Scorpius
X-1 and Cygnus X-2 using X-ray data from the \textit{ Rossi X-ray Timing
Explorer} Proportional Counter Array. We find no clear evidence for pulsations,
and obtain upper limits (at $90\%$ confidence) on the fractional pulse
amplitude, with the most stringent being $0.034\%$ for Scorpius X-1 and
$0.23\%$ for Cygnus X-2. These upper limits improve upon those of Vaughan et
al. (1994) by factors of $\sim 8.2$ and $\sim 1.6$ respectively.",2105.13803v1
2021-05-24,An In-Memory Analog Computing Co-Processor for Energy-Efficient CNN Inference on Mobile Devices,"In this paper, we develop an in-memory analog computing (IMAC) architecture
realizing both synaptic behavior and activation functions within non-volatile
memory arrays. Spin-orbit torque magnetoresistive random-access memory
(SOT-MRAM) devices are leveraged to realize sigmoidal neurons as well as
binarized synapses. First, it is shown the proposed IMAC architecture can be
utilized to realize a multilayer perceptron (MLP) classifier achieving orders
of magnitude performance improvement compared to previous mixed-signal and
digital implementations. Next, a heterogeneous mixed-signal and mixed-precision
CPU-IMAC architecture is proposed for convolutional neural networks (CNNs)
inference on mobile processors, in which IMAC is designed as a co-processor to
realize fully-connected (FC) layers whereas convolution layers are executed in
CPU. Architecture-level analytical models are developed to evaluate the
performance and energy consumption of the CPU-IMAC architecture. Simulation
results exhibit 6.5% and 10% energy savings for CPU-IMAC based realizations of
LeNet and VGG CNN models, for MNIST and CIFAR-10 pattern recognition tasks,
respectively.",2105.13904v1
2021-06-06,Base flow decomposition for complex moving objects in linear hydrodynamics: application to helix-shaped flagellated microswimmers,"The motion of microswimmers in complex flows is ruled by the interplay
between swimmer propulsion and the dynamics induced by the fluid velocity
field. Here we study the motion of a chiral microswimmer whose propulsion is
provided by the spinning of a helical tail with respect to its body in a simple
shear flow. Thanks to an efficient computational strategy that allowed us to
simulate thousands of different trajectories, we show that the tail shape
dramatically affects the swimmer's motion. In the shear dominated regime, the
swimmers carrying an elliptical helical tail show several different
Jeffery-like (tumbling) trajectories depending on their initial configuration.
As the propulsion torque increases, a progressive regularization of the motion
is observed until, in the propulsion dominated regime, the swimmers converge to
the same final trajectory independently on the initial configuration. Overall,
our results show that elliptical helix swimmer presents a much richer variety
of trajectories with respect to the usually studied circular helix tails.",2106.03133v1
2021-07-07,Extended two-body problem for rotating rigid bodies,"A new technique that utilizes surface integrals to find the force, torque and
potential energy between two non-spherical, rigid bodies is presented. The
method is relatively fast, and allows us to solve the full rigid two-body
problem for pairs of spheroids and ellipsoids with 12 degrees of freedom. We
demonstrate the method with two dimensionless test scenarios, one where
tumbling motion develops, and one where the motion of the bodies resemble
spinning tops. We also test the method on the asteroid binary (66391) 1999 KW4,
where both components are modelled either as spheroids or ellipsoids. The two
different shape models have negligible effects on the eccentricity and
semi-major axis, but have a larger impact on the angular velocity along the
$z$-direction. In all cases, energy and total angular momentum is conserved,
and the simulation accuracy is kept at the machine accuracy level.",2107.03274v1
2021-08-11,Enhancement of in-plane anisotropy in MoS2/CoFeB bilayers,"Transition metal dichalcogenides (TMD) possess novel properties which makes
them potential candidates for various spintronic applications. Heterostructures
of TMD with magnetic thin film have been extensively considered for
spin-orbital torque, enhancement of perpendicular magnetic anisotropy etc.
However, the effect of TMD on magnetic anisotropy in heterostructures of
in-plane magnetization has not been studied so far. Further the effect of the
TMD on the domain structure and magnetization reversal of the ferromagnetic
system is another important aspect to be understood. In this context we study
the effect of MoS2, a well-studied TMD material, on magnetic properties of
CoFeB in MoS2/CoFeB heterostructures. The reference CoFeB film possess a weak
in-plane anisotropy. However, when the CoFeB is deposited on MoS2 the in-plane
anisotropy is enhanced as observed from magneto optic Kerr effect (MOKE)
microscopy as well as ferromagnetic resonance (FMR). Magnetic domain structure
and magnetization reversal have also been significantly modified for the
MoS2/CoFeB bilayer as compared to the reference CoFeB layer. Frequency and
angle dependent FMR measurement show that the magnetic anisotropy of CoFeB
increases with increase in thickness of MoS2 in the MoS2/CoFeB
heterostructures.",2108.05130v1
2021-09-01,Collective hydrodynamic transport of magnetic microrollers,"We investigate the collective transport properties of microscopic magnetic
rollers that propel close to a surface due to a circularly polarized, rotating
magnetic field. The applied field exerts a torque to the particles, which
induces a net rolling motion close to a surface. The collective dynamics of the
particles result from the balance between magnetic dipolar interactions and
hydrodynamic ones. We show that, when hydrodynamics dominate, i.e. for high
particle spinning, the collective mean velocity linearly increases with the
particle density. In this regime we analyse the clustering kinetics, and find
that hydrodynamic interactions between the anisotropic, elongated particles,
induce preferential cluster growth along a direction perpendicular to the
driving one, leading to dynamic clusters that easily break and reform during
propulsion.",2109.00289v2
2021-11-14,Current controlled non-hysteresis magnetic switching in the ansence of magnetic field,"By means of local ion implantation, we investigated the influence of lateral
interface on current-induced magnetic switching by spin-orbit torque in a
perpendicularly magnetized Pt/Co/Ta multilayer. The experimental results show
that, in this system, the domain wall motion under electrical current can be
affected by two mechanisms: symmetry breaking and current-driven N\'eel wall
motion at the lateral interface. The dominant mechanism is symmetry breaking
(current-driven N\'eel wall motion) at the large (small) current. Due to the
competitive relationship of these two mechanisms, the non-hysteresis effect
magnetic switching without an external magnetic field is obtained. Based on the
non-hysteresis effect magnetic switching, we can realize AND and OR logic gates
without resetting.",2111.07296v1
2021-11-16,Ultrathin ferrimagnetic GdFeCo films with very low damping,"Ferromagnetic materials dominate as the magnetically active element in
spintronic devices, but come with drawbacks such as large stray fields, and low
operational frequencies. Compensated ferrimagnets provide an alternative as
they combine the ultrafast magnetization dynamics of antiferromagnets with a
ferromagnet-like spin-orbit-torque (SOT) behavior. However to use ferrimagnets
in spintronic devices their advantageous properties must be retained also in
ultrathin films (t < 10 nm). In this study, ferrimagnetic Gdx(Fe87.5Co12.5)1-x
thin films in the thickness range t = 2-20 nm were grown on high resistance
Si(100) substrates and studied using broadband ferromagnetic resonance
measurements at room temperature. By tuning their stoichiometry, a nearly
compensated behavior is observed in 2 nm Gdx(Fe87.5Co12.5)1-x ultrathin films
for the first time, with an effective magnetization of Meff = 0.02 T and a low
effective Gilbert damping constant of {\alpha} = 0.0078, comparable to the
lowest values reported so far in 30 nm films. These results show great promise
for the development of ultrafast and energy efficient ferrimagnetic spintronic
devices.",2111.08768v1
2021-12-22,Spontaneously rotating clusters of active droplets,"We report on the emergence of spontaneously rotating clusters in active
emulsions. Ensembles of self-propelling droplets sediment and then
self-organise into planar, hexagonally ordered clusters which hover over the
container bottom while spinning around the plane normal. This effect exists for
symmetric and asymmetric arrangements of isotropic droplets and is therefore
not caused by torques due to geometric asymmetries. We found, however, that
individual droplets exhibit a helical swimming mode in a small window of
intermediate activity in a force-free bulk medium. We show that by forming an
ordered cluster, the droplets cooperatively suppress their chaotic dynamics and
turn the transient instability into a steady rotational state. We analyse the
collective rotational dynamics as a function of droplet activity and cluster
size and further propose that the stable collective rotation in the cluster is
caused by a cooperative coupling between the rotational modes of individual
droplets in the cluster.",2112.11801v1
2022-01-21,How a skyrmion can appear both massive and massless,"When a magnetic skyrmion is modeled as a point particle, its dynamics depends
on the precise definition of the skyrmion center. The guiding-center position,
defined as the first moment of the skyrmion density, exhibits Thiele's massless
dynamics; position based on the first moment of magnetization component $m_z$
shows Larmor oscillations characteristic of a massive particle. We show that,
even with the latter definition, the Larmor oscillations may be absent for
certain types of external forces such as adiabatic spin torque. We offer an
alternative mechanical model of a skyrmion featuring two coupled massless
particles.",2201.08519v6
2022-02-02,Antiferromagnetic parametric resonance driven by voltage-controlled magnetic anisotropy,"Voltage controlled magnetic anisotropy (VCMA) is a low-energy alternative to
manipulate the ferromagnetic state, which has been recently considered also in
antiferromagnets (AFMs). Here, we theoretically demonstrate that VCMA can be
used to excite linear and parametric resonant modes in easy-axis AFMs with
perpendicular anisotropy, thus opening the way for an efficient electrical
control of the Neel vector, and for detection of high-frequency dynamics. Our
work leads to two key results: (i) VCMA parametric pumping experiences the
so-called exchange enhancement of the coupling efficiency and, thus, is 1-2
orders of magnitude more efficient than microwave magnetic fields or
spin-orbit-torques, and (ii) it also allows for zero-field parametric
resonance, which cannot be achieved by other parametric pumping mechanisms in
AFMs with out-of-plane easy axis. Therefore, we demonstrate that the VCMA
parametric pumping is the most promising method for coherent excitation and
manipulation of AFM order in perpendicular easy-axis AFMs.",2202.01156v1
2022-02-24,Deterministic Generation and Guided Motion of Magnetic Skyrmions by Focused He$^+$-Ion Irradiation,"Magnetic skyrmions are quasiparticles with non-trivial topology, envisioned
to play a key role in next-generation data technology while simultaneously
attracting fundamental research interest due to their emerging topological
charge. In chiral magnetic multilayers, current-generated spin-orbit torques or
ultrafast laser excitation can be used to nucleate isolated skyrmions on a
picosecond timescale. Both methods, however, produce randomly arranged
skyrmions, which inherently limits the precision on the location at which the
skyrmions are nucleated. Here, we show that nanopatterning of the anisotropy
landscape with a He$^+$-ion beam creates well-defined skyrmion nucleation
sites, thereby transforming the skyrmion localization into a deterministic
process. This approach allows to realize control of individual skyrmion
nucleation as well as guided skyrmion motion with nanometer-scale precision,
which is pivotal for both future fundamental studies of skyrmion dynamics and
applications.",2202.12057v2
2022-03-21,Minimum-Time Reorientation of Axisymmetric Rigid Spacecraft Using Three Controls,"A minimum-time reorientation of an axisymmetric rigid spacecraft controlled
by three torques is studied. The orientation of the body is modeled such that
the attitude kinematics are representative of a spin-stabilized spacecraft. The
optimal control problem considered is shown to have a switching control
structure. Moreover, under certain assumptions, the solutions contain segments
that lie on a singular arc. A numerical optimization study is performed using a
recently developed method that is designed to accurately solve bang-bang and
singular optimal control problems. The optimality conditions for the resulting
optimal control problem are derived and analyzed for a variety of cases. Also,
the results obtained in this study are compared to a previous method existing
in the literature. The key features of the optimized trajectories and controls
are identified, and the aforementioned method for solving bang-bang and
singular optimal control problems is shown to efficiently and accurately solve
the problem under consideration.",2203.11394v1
2022-04-21,MRAM-based Analog Sigmoid Function for In-memory Computing,"We propose an analog implementation of the transcendental activation function
leveraging two spin-orbit torque magnetoresistive random-access memory
(SOT-MRAM) devices and a CMOS inverter. The proposed analog neuron circuit
consumes 1.8-27x less power, and occupies 2.5-4931x smaller area, compared to
the state-of-the-art analog and digital implementations. Moreover, the
developed neuron can be readily integrated with memristive crossbars without
requiring any intermediate signal conversion units. The architecture-level
analyses show that a fully-analog in-memory computing (IMC) circuit that use
our SOT-MRAM neuron along with an SOT-MRAM based crossbar can achieve more than
1.1x, 12x, and 13.3x reduction in power, latency, and energy, respectively,
compared to a mixed-signal implementation with analog memristive crossbars and
digital neurons. Finally, through cross-layer analyses, we provide a guide on
how varying the device-level parameters in our neuron can affect the accuracy
of multilayer perceptron (MLP) for MNIST classification.",2204.09918v1
2022-04-21,Transport theory for topological Josephson junctions with a Majorana qubit,"We construct a semiclassical theory for the transport of topological
junctions starting from a microscopic Hamiltonian that comprehensively includes
the interplay among the Majorana qubit, the Josephson phase, and the
dissipation process. With the path integral approach, we derive a set of
semiclassical equations of motion that can be used to calculate the time
evolution of the Josephson phase and the Majorana qubit. In the equations we
reveal rich dynamical phenomena such as the qubit induced charge pumping, the
effective spin-orbit torque, and the Gilbert damping. We demonstrate the
influence of these dynamical phenomena on the transport signatures of the
junction. We apply the theory to study the Shapiro steps of the junction, and
find the suppression of the first Shapiro step due to the dynamical feedback of
the Majorana qubit.",2204.09923v1
2022-04-28,Local Rotational Jamming and Multi-Scale Hyperuniformities in an Active Spinner System,"An active system consisting of many self-spinning dimers is simulated, and a
distinct local rotational jamming transition is observed as the density
increases. In the low density regime, the system stays in an absorbing state,
in which each dimer rotates independently subject to the applied torque. While
in the high density regime, a fraction of the dimers become rotationally jammed
into local clusters, and the system exhibits spinodal-decomposition like
two-phase morphologies. For high enough densities, the system becomes
completely jammed in both rotational and translational degrees of freedom. Such
a simple system is found to exhibit rich and multiscale disordered
hyperuniformities among the above phases: the absorbing state shows a critical
hyperuniformity of the strongest class and subcritically preserves the
vanishing density-fluctuation scaling up to some length scale; the
locally-jammed state shows a two-phase hyperuniformity conversely beyond some
length scale with respect to the phase cluster sizes; the totally jammed state
appears to be a monomer crystal, but intrinsically loses large-scale
hyperuniformity. These results are inspiring for designing novel
phase-separation and disordered hyperuniform systems through dynamical
organization.",2204.13391v1
2022-05-11,Domain wall damped harmonic oscillations induced by curvature gradients in elliptical magnetic nanowires,"Understanding the domain wall (DW) dynamics in magnetic nanowires (NW) is
crucial for spintronic-based applications demanding the use of DWs as
information carriers. This work focuses on the dynamics of a DW displacing
along a bent NW with an elliptical shape under the action of spin-polarized
electric currents and external magnetic fields. Our results evidence that a
curvature gradient induces an exchange-driven effective tangential field
responsible for pinning a DW near the maximum curvature point in a NW. The DW
equilibrium position depends on the competition between the torques produced by
the external stimuli and the curvature-induced effective fields. When the
external stimuli are below a certain threshold, the DW follows a damped
harmonic oscillation around the equilibrium position. Above this threshold, DW
displaces along the NW under an oscillatory translational motion.",2205.05716v1
2022-05-13,"Weyl locally integrable conformal gravity, rotation curves and cosmic filaments","Weyl's conformal theory of gravity is an extension of Einstein's theory of
general relativity which associates metrics with 1-forms . In the case of
locally integrable (closed non-exact) 1-forms the spacetime manifolds are no
more simply connected. The Weil connections yield curvature tensors which
satisfy the basic properties of Riemann curvature tensors. The Ricci tensors
are symmetric, conformally invariant, and the Einstein tensors computed with
the Weyl connections implicate a cosmological term replacing the cosmological
constant by a function of spacetime, and a shear stress tensor. A toy model
based on the Schwarzschild metric is presented where the associated 1-form is
proportional to $d\varphi$ in Schwarzschild coordinates. This implies a
singularity on the whole z-axis and it generates a torque effect on geodesics.
According to initial conditions planar geodesics show almost constant
velocities independently of r. In the free case spin effects occur in the
neighbourhood of the singularity which are comparable to recent observations
concerning cosmic filaments.",2205.06534v2
2022-05-17,Cubic magneto-optic Kerr effect in Ni(111) thin films with and without twinning,"In most studies utilizing the magneto-optic Kerr effect (MOKE), the detected
change of polarized light upon reflection from a magnetized sample is supposed
to be proportional to the magnetization $\boldsymbol{M}$. However, MOKE
signatures quadratic in $\boldsymbol{M}$ have also been identified and
utilized, e.g., to sense the structural order in Heusler compounds, to detect
spin-orbit torques or to image antiferromagnetic domains. In our study, we
observe a strong anisotropic MOKE contribution of third order in
$\boldsymbol{M}$ in Ni(111) thin films, attributed to a cubic magneto-optic
tensor $\propto $ $\boldsymbol{M}^3$. We further show that the angular
dependence of cubic MOKE (CMOKE) is affected by the amount of structural domain
twinning in the sample. Our detailed study on CMOKE for two selected photon
energies will open up new opportunities for CMOKE applications with sensitivity
to twinning properties of thin films, e.g. CMOKE spectroscopy and microscopy or
time-resolved CMOKE.",2205.08298v2
2022-07-18,Magnetoelectric effects in Josephson junctions,"The review is devoted to the fundamental aspects and characteristic features
of the magnetoelectric effects, reported in the literature on Josephson
junctions (JJs). The main focus of the review is on the manifestations of the
direct and inverse magnetoelectric effects in various types of Josephson
systems. They provide a coupling of the magnetization in
superconductor/ferromagnet/superconductor JJs to the Josephson current. The
direct magnetoelectric effect is a driving force of spin torques acting on the
ferromagnet inside the JJ. Therefore it is of key importance for the electrical
control of the magnetization. The inverse magnetoelectric effect accounts for
the back action of the magnetization dynamics on the Josephson subsystem, in
particular, making the JJ to be in the resistive state in the presence of the
magnetization dynamics of any origin. The perspectives of the coupling of the
magnetization in JJs with ferromagnetic interlayers to the Josephson current
via the magnetoelectric effects are discussed.",2207.08876v1
2022-08-08,Current-driven writing process in antiferromagnetic Mn2Au for memory applications,"Current pulse driven Neel vector rotation in metallic antiferromagnets is one
of the most promising concepts in antiferromagnetic spintronics. We show
microscopically that the Neel vector of epitaxial thin films of the
prototypical compound Mn2Au can be reoriented reversibly in the complete area
of cross shaped device structures using single current pulses. The resulting
domain pattern with aligned staggered magnetization is long term stable
enabling memory applications. We achieve this switching with low heating of 20
K, which is promising regarding fast and efficient devices without the need for
thermal activation. Current polarity dependent reversible domain wall motion
demonstrates a Neel spin-orbit torque acting on the domain walls.",2208.04048v2
2022-08-08,Destruction of Long-Period Comets,"We identify a sample of 27 long-period comets for which both
non-gravitational accelerations and Lyman-alpha based gas production rates are
available. Seven of the 27 comets (i.e. 25 percent) did not survive perihelion
because of nucleus fragmentation or complete disintegration. Empirically, the
latter nuclei have the smallest gas production rates and the largest
non-gravitational accelerations, which are both indicators of small size.
Specifically, the disintegrating nuclei have a median radius of only 0.41 km,
one quarter of the 1.60 km median radius of those surviving perihelion. The
disintegrating comets also have a smaller median perihelion distance (0.48 au)
than do the survivors (0.99 au). We compare the order of magnitude timescale
for outgassing torques to change the nucleus spin, tau, with the time spent by
each comet in strong sublimation, Dt, finding that the disrupted comets are
those with tau < Dt. The destruction of near-Sun long-period comets is thus
naturally explained as a consequence of rotational break-up. We discuss this
process as a contributor to Oort's long mysterious ``fading parameter''.",2208.04469v1
2022-08-17,Nanoscale three-dimensional magnetic sensing with a probabilistic nanomagnet driven by spin-orbit torque,"Detection of vector magnetic fields at nanoscale dimensions is critical in
applications ranging from basic material science, to medical diagnostic.
Meanwhile, an all-electric operation is of great significance for achieving a
simple and compact sensing system. Here, we propose and experimentally
demonstrate a simple approach to sensing a vector magnetic field at nanoscale
dimensions, by monitoring a probabilistic nanomagnet's transition probability
from a metastable state, excited by a driving current due to SOT, to a settled
state. We achieve sensitivities for Hx, Hy, and Hz of 1.02%/Oe, 1.09%/Oe and
3.43%/Oe, respectively, with a 200 x 200 nm^2 nanomagnet. The minimum
detectable field is dependent on the driving pulse events N, and is expected to
be as low as 1 uT if N = 3 x 10^6.",2208.08074v1
2022-09-23,Magnetostatics of Room Temperature Compensated Co/Gd/Co/Gd-based Synthetic Ferrimagnets,"Flexibility for interface engineering, and access to all-optical switching of
the magnetization, make synthetic ferrimagnets an interesting candidate for
advanced opto-spintronic devices. Moreover, due to their layered structure and
disordered interfaces they also bear promise for the emerging field of graded
magnetic materials. The fastest and most efficient spin-orbit torque driven
manipulation of the magnetic order in this material system generally takes
place at compensation. Here, we present a systematic experimental and modeling
study of the conditions for magnetization compensation and perpendicular
magnetic anisotropy in the synthetic ferrimagnetic Co/Gd/Co/Gd system. A model
based on partial intermixing at the Co/Gd interfaces of this system has been
developed which explains the experiments well, and provides a new tool to
understand its magnetic characteristics. More specifically, this work provides
new insight in the decay of the Co proximity-induced magnetization in the Gd,
and the role the capping layer plays in the Gd magnetization.",2209.11562v1
2022-10-04,Voltage-Controlled High-Bandwidth Terahertz Oscillators Based On Antiferromagnets,"Producing compact voltage-controlled frequency generators and sensors
operating in the terahertz (THz) regime represents a major technological
challenge. Here, we show that noncollinear antiferromagnets (NCAFM) with kagome
structure host gapless self-oscillations whose frequencies are tunable from 0
Hz to the THz regime via electrically induced spin-orbit torques (SOTs). The
auto-oscillations' initiation, bandwidth, and amplitude are investigated by
deriving an effective theory, which captures the reactive and dissipative SOTs.
We find that the dynamics strongly depends on the ground state's chirality,
with one chirality having gapped excitations, whereas the opposite chirality
provides gapless self-oscillations. Our results reveal that NCAFMs offer unique
THz functional components, which could play a significant role in filling the
THz technology gap.",2210.01529v2
2022-10-18,Simultaneous multitone microwave emission by DC-driven spintronic nano-element,"Current-induced self-sustained magnetization oscillations in spin-torque
nano-oscillators (STNOs) are promising candidates for ultra-agile microwave
sources or detectors. While usually STNOs behave as a monochrome source, we
report here clear bimodal simultaneous emission of incommensurate microwave
oscillations, where the two tones correspond to two parametrically coupled
eigenmodes with tunable splitting. The emission range is crucially sensitive to
the change in hybridization of the eigenmodes of free and fixed layers, for
instance, through a slight tilt of the applied magnetic field from the normal
of the nano-pillar. Our experimental findings are supported both analytically
and by micromagnetic simulations, which ascribe the process to four-magnon
scattering between a pair of radially symmetric magnon modes and a pair of
magnon modes with opposite azimuthal index. Our findings open up new
possibilities for cognitive telecommunications and neuromorphic systems that
use frequency multiplexing to improve communication performance.",2210.09752v1
2022-10-25,Ultrafast Switching in Synthetic Antiferromagnet with Bilayer Rare-Earth Transition-Metal Ferrimagnets,"In spintronics, it is important to be able to manipulate magnetization
rapidly and reliably. Several methods can control magnetization, such as by
applying current pulses or magnetic fields. An applied current can reverse
magnetization with nanosecond speed through the spin torque effect. For faster
switching, subpicosecond switching with femtoseconds laser pulse has been
achieved in amorphous rare-earth transition-metal ferrimagnets. In this study,
we employed atomistic simulations to investigate ultrafast switching in a
synthetic antiferromagnet with bilayer amorphous FeGd ferrimagnets. Using a
two-temperature model, we demonstrated ultrafast switching in this synthetic
antiferromagnet without external magnetic fields. Furthermore, we showed that
if we initially stabilize a skyrmion in this heterostructure, the ultrafast
laser can switch the skyrmion state using the same mechanism. Furthermore, this
bilayer design allows the control of each ferrimagnetic layer individually and
opens the possibility for a magnetic tunnel junction.",2210.14119v1
2022-12-05,Current-induced nucleation and motion of zero field skyrmion,"We study the stabilization and electrical manipulation of skyrmions in
magnetic ultrathin films in the absence of an applied magnetic field. We show
that this requires an increased magnetic anisotropy, controlled by the sample
thickness, as compared to usual skyrmionic samples, so that the uniform state
corresponds to the zero field ground state and the skyrmions to metastable
excitations. Although skyrmion stabilization at zero field is demonstrated over
a broad range of thicknesses, electrical control appeared to be more demanding
to avoid skyrmion deformation. In the thinnest samples, the large magnetic
anisotropy prevents skyrmion deformations and we show that they can be
nucleated progressively by current pulses, which underlines that the only
possible transition occurs between uniform and skyrmion states. The solitonic
skyrmions in zero applied magnetic field have the same properties as compared
to field stabilized ones, with a long-term stability and high mobility when
excited by a spin-orbit torque.",2212.02351v1
2022-12-08,Acoustic-Driven Magnetic Skyrmion Motion,"Magnetic skyrmions have great potential for developing novel spintronic
devices. The electrical manipulation of skyrmions has mainly relied on
current-induced spin-orbit torques. A recent theoretical model suggested that
the skyrmions could be more efficiently manipulated by surface acoustic waves
(SAW), an elastic wave that can couple with magnetic moment through
magnetoelastic effect. However, the directional motion of skyrmions that is
driven by SAW is still missing. Here, we experimentally demonstrate the motion
of N\'eel-type skyrmions in Ta/CoFeB/MgO/Ta multilayers driven by propagating
SAW pulses from on-chip piezoelectric transducers. Our results reveal that the
elastic wave with longitudinal and shear vertical displacements (Rayleigh wave)
traps skyrmions, while the shear horizontal wave effectively drives the motion
of skyrmions. In particular, a longitudinal motion along the SAW propagation
direction and a transverse motion due to topological charge, are observed and
further confirmed by our micromagnetic simulations. This work demonstrates a
promising approach based on acoustic waves for manipulating skyrmions, which
could offer new opportunities for ultra-low power spintronics.",2212.04049v1
2022-12-19,Voltage Gated Domain Wall Magnetic Tunnel Junction-based Spiking Convolutional Neural Network,"We propose a novel spin-orbit torque (SOT) driven and voltage-gated domain
wall motion (DWM)-based MTJ device and its application in neuromorphic
computing. We show that by utilizing the voltage-controlled gating effect on
the DWM, the access transistor can be eliminated. The device provides more
control over individual synapse writing and shows highly linear synaptic
behavior. The linearity dependence on material parameters such as DMI and
temperature is evaluated for real-environment performance analysis.
Furthermore, using skyrmion-based leaky integrate and fire neuron model, we
implement the spiking convolutional neural network for pattern recognition
applications on the CIFAR-10 data set. The accuracy of the device is above 85%,
proving its applicability in SNN.",2212.09444v1
2022-12-23,Quantum oscillations in a centrosymmetric skyrmion-hosting magnet GdRu2Si2,"We have performed magnetic torque and resistivity measurements on a
centrosymmetric skyrmion-host GdRu2Si2, in which the dominant magnetic
interaction leading to skyrmion formation is under debate. We observe both the
de Haas-van Alphen and Shubnikov-de Haas oscillations in the forced
ferromagnetic phase. The angular dependence of the quantum oscillation
frequencies can be reproduced by the ab-initio calculation. The de Haas-van
Alphen oscillation is also observed in the double-Q phase with a different
frequency to that in the forced ferromagnetic phase, indicating a Fermi surface
reconstruction due to the coupling between localized spins and conduction
electrons. Based on these experimental findings, the magnetic interactions in
this system are discussed.",2212.12280v2
2023-01-04,Deterministic multi-level spin orbit torque switching using He+ microscopy patterning,"He$^+$ ion irradiation is used to pattern multiple areas of Pt/Co/W films
with different irradiation doses in Hall bars. The resulting perpendicular
magnetic anisotropy landscape enables selective multilevel current-induced
switching, with full deterministic control of the position and order of the
individual switching elements. Key pattern design parameters are specified,
opening a way to scalable multilevel switching devices.",2301.02188v1
2023-03-28,Analysis of ultrafast magnetization switching dynamics in exchange-coupled ferromagnet-ferrimagnet heterostructures,"Magnetization switching in ferromagnets has so far been limited to the
current-induced spin-orbit-torque effects. Recent observation of
helicity-independent all-optical magnetization switching in exchange-coupled
ferromagnet ferrimagnet heterostructures expanded the range and applicability
of such ultrafast heat-driven magnetization switching. Here we report the
element-resolved switching dynamics of such an exchange-coupled system, using a
modified microscopic three-temperature model. We have studied the effect of i)
the Curie temperature of the ferromagnet, ii) ferrimagnet composition, iii) the
long-range RKKY exchange-coupling strength, and iv) the absorbed optical energy
on the element-specific time-resolved magnetization dynamics. The phase-space
of magnetization illustrates how the RKKY coupling strength and the absorbed
optical energy influence the switching time. Our analysis demonstrates that the
threshold switching energy depends on the composition of the ferrimagnet and
the switching time depends on the Curie temperature of the ferromagnet as well
as RKKY coupling strength. This simulation anticipates new insights into
developing faster and more energy-efficient spintronics devices.",2303.16294v1
2023-04-24,Quantum-limit phenomena and bandstructure in the magnetic topological semimetal EuZn2As2,"We have experimentally investigated the low-temperature (0.6 K) electronic
and magnetic properties of the layered antiferromagnet EuZn2As2 in pulsed
magnetic fields of up to 60 T at a temperature of 0.6 K, giant positive
magnetoresistance (MR) is observed above \mu_{0}H ~ 20 T, a regime in which the
spins are already fully polarized. Both magnetic torque and proximity detector
oscillator (PDO) data show no corresponding anomaly at or close to this field.
By analyzing the quantum oscillations observed in the MR and PDO frequency, we
find that (1) the oscillation frequency F = 46 \pm 6 T for H // c and 42 \pm 2
T for H // ab; (2) the corresponding Berry phase is close to \pi for H // c,
implying a nontrivial topology; and (3) the large linear MR at high fields
corresponds to the quantum limit (i.e., only the last Landau level being
occupied). From these observations we conclude that the linear MR can be
understood by considering diffusing cyclotron centers in the quantum limit. Our
findings help understand the intimate relationship between magnetism and
electronic topology in EuZn2As2 under extremely high fields and suggest reasons
for the emergent behavior in the quantum limit.",2304.12426v1
2023-05-04,Let's Sweep: The Effect of Evolving $J_2$ on the Resonant Structure of a Three-Planet System,"Short and ultra-short planets are a peculiar type of exoplanets with periods
as short as a few days or less. Although it is challenging to detect them,
already several are observed with many additional candidates. If these planets
have formation pathways to their longer period counterparts, they are predicted
to reside in multi-planet systems. Thus, gravitational perturbation from
potential planetary neighbors may affect their orbital configuration. However,
due to their close proximity to their host star, they are also subjects to
general relativity precession and torques from the stellar spin quadrupole
moment ($J_2$). Here we show that an evolving $J_2$ due to magnetic braking,
affects the magnitude and location of secular resonances of the short period
planet in a multi-planet system. Thus, driving the short period planet into and
out of a secular resonance, exciting the planet's eccentricity and inclination.
The high inclination can hinder transit observation, and, in some cases, the
high eccentricity may result in an unstable configuration. We propose that
evolving $J_2$ in a multi-planet system can be critical in understanding the
detectability and stability of short-period planets.",2305.03104v1
2023-06-07,Helicity-dependent optical control of the magnetization state emerging from the Landau-Lifshitz-Gilbert equation,"It is well known that the Gilbert relaxation time of a magnetic moment scales
inversely with the magnitude of the externally applied field, H, and the
Gilbert damping, {\alpha}. Therefore, in ultrashort optical pulses, where H can
temporarily be extremely large, the Gilbert relaxation time can momentarily be
extremely short, reaching even picosecond timescales. Here we show that for
typical ultrashort pulses, the optical control of the magnetization emerges by
merely considering the optical magnetic field in the Landau-Lifshitz-Gilbert
(LLG) equation. Surprisingly, when circularly polarized optical pulses are
introduced to the LLG equation, an optically induced helicity-dependent torque
results. We find that the strength of the interaction is determined by
{\eta}={\alpha}{\gamma}H/f_opt, where f_opt and {\gamma} are the optical
frequency and gyromagnetic ratio. Our results illustrate the generality of the
LLG equation to the optical limit and the pivotal role of the Gilbert damping
in the general interaction between optical magnetic fields and spins in solids.",2306.04617v2
2023-07-18,Neuromorphic spintronics simulated using an unconventional data-driven Thiele equation approach,"In this study, we developed a quantitative description of the dynamics of
spin-torque vortex nano-oscillators (STVOs) through an unconventional model
based on the combination of the Thiele equation approach (TEA) and data from
micromagnetic simulations (MMS). Solving the STVO dynamics with our analytical
model allows to accelerate the simulations by 9 orders of magnitude compared to
MMS while reaching the same level of accuracy. Here, we showcase our model by
simulating a STVO-based neural network for solving a classification task. We
assess its performance with respect to the input signal current intensity and
the level of noise that might affect such a system. Our approach is promising
for accelerating the design of STVO-based neuromorphic computing devices while
decreasing drastically its computational cost.",2307.09262v1
2023-09-06,Numerical analysis of voltage-controlled magnetization switching operation in magnetic-topological-insulator-based devices,"We theoretically investigate influences of electronic circuit delay, noise
and temperature on write-error-rate (WER) in voltage-controlled magnetization
switching operation of a magnetic-topological-insulator-based (MTI) device by
means of the micromagnetic simulation. This device realizes magnetization
switching via spin-orbit torque(SOT) and voltage-controlled magnetic anisotropy
(VCMA) which originate from 2D-Dirac electronic structure. We reveal that the
device operation is extremely robust against circuit delay and signal-to-noise
ratio. We demonstrate that the WER on the order of approximately $10^{-4}$ or
below is achieved around room temperature due to steep change in VCMA. Also, we
show that the larger SOT improves thermal stability factor. This study provides
a next perspective for developing voltage-driven spintronic devices with
ultra-low power consumption.",2309.03043v1
2023-09-14,SOT-MRAM-Enabled Probabilistic Binary Neural Networks for Noise-Tolerant and Fast Training,"We report the use of spin-orbit torque (SOT) magnetoresistive random-access
memory (MRAM) to implement a probabilistic binary neural network (PBNN) for
resource-saving applications. The in-plane magnetized SOT (i-SOT) MRAM not only
enables field-free magnetization switching with high endurance (> 10^11), but
also hosts multiple stable probabilistic states with a low device-to-device
variation (< 6.35%). Accordingly, the proposed PBNN outperforms other neural
networks by achieving an 18* increase in training speed, while maintaining an
accuracy above 97% under the write and read noise perturbations. Furthermore,
by applying the binarization process with an additional SOT-MRAM dummy module,
we demonstrate an on-chip MNIST inference performance close to the ideal
baseline using our SOT-PBNN hardware.",2309.07789v2
2023-09-22,Emergence Of Directional Rotation In Optothermally Activated Colloidal System,"We experimentally demonstrate the emergence of directional rotation in
thermally active-passive colloidal structures under optical confinement. The
observed handedness of rotation of the structure can be controlled by changing
the relative position of the constituent colloids. We show that the angular
velocity of rotation is sensitive to the intensity of the incident optical
fields and the size of the constituent colloidal entities. The emergence of
rotational dynamics can be understood in the context of asymmetric temperature
distribution in the system and the relative location of the active colloid,
which creates a local imbalance of optothermal torques to the confined system.
Our work demonstrates how localized optothermal fields lead to directional
rotational dynamics without explicitly utilizing spin or orbital angular
momentum of light. We envisage that our results will have implications in
realizing Brownian engines, and can directly relate to rotational dynamics in
biological and ecological systems.",2309.12740v1
2023-10-09,Spatial asymmetry of optically excited spin waves in anisotropic ferromagnetic film,"We analytically discuss and micromagnetically prove the ways to tune the
spatial asymmetry of the initial phase, amplitude, and wavevectors of
magnetostatic waves driven by ultrafast laser excitation. We consider that the
optical pulse heats a thin ferromagnetic metallic film and abruptly decreases
the saturation magnetization and the parameter of uniaxial anisotropy. The two
corresponding terms of laser-induced torque have different azimuthal
symmetries, with the 4-fold symmetry of the demagnetization-related term, and
the isotropic distribution of the anisotropy-related term. As a result, the
initial phase and amplitude of excited magnetostatic waves have a non-trivial
azimuthal distribution tunable with the angle between the external magnetic
field and anisotropy axis, and the laser spot diameter. Moreover, the variation
of these parameters tunes the distribution of wavevectors, resulting in
additional asymmetry between the spectral components of the waves propagating
in different directions.",2310.05895v1
2023-10-27,Strain-Tunable Magnetic Compensation Temperature of Epitaxial Tb$_3$Fe$_5$O$_{12}$ Thin Films,"High-quality rare-earth iron garnet (ReIG) Tb$_3$Fe$_5$O$_{12}$ (TbIG) thin
films are epitaxially grown on a series of (111)-oriented garnet substrates
with various lattice constants. The coherent growth induces a
substrate-dependent in-plane tensile or compressive strain in the TbIG film.
Measurements of the anomalous Hall-like effect (AHLE) in TbIG/Pt
heterostructures show that the compensation temperature of TbIG films
monotonically changes with the film strain. The strain results in a variation
of the distances between magnetic atoms in the TbIG crystal and therefore the
corresponding exchange interactions. The latter is explicitly calculated as a
function of the lattice strain based on density functional theory, reproducing
the observed experimental results. This work provides a versatile way to
optimize ReIG-based spin-orbit torque devices.",2310.17841v1
2023-11-19,Fermi surface topology and electronic transport properties of a chiral crystal NbGe$_2$ with strong electron-phonon interaction,"We report the electronic structures and transport properties of a chiral
crystal NbGe$_2$, which is a candidate for a coupled electron-phonon liquid.
The electrical resistivity and thermoelectric power of NbGe$_2$ exhibit clear
differences compared to those of NbSi2 even though both niobium ditetrelides
are isostructural and isoelectronic. We discuss the intriguing transport
properties of NbGe$_2$ based on a van Hove-type singularity in the density of
states. The analysis of de Haas-van Alphen oscillations measured by the field
modulation and magnetic torque methods reveals the detailed shape of the Fermi
surface of NbGe$_2$ by comparison with the results of energy band structure
calculations using a local density approximation. The electron and hole Fermi
surfaces of NbGe$_2$ split into two because of the anti-symmetric spin-orbit
interaction. The temperature dependence of quantum oscillations indicates that
the effective mass is isotropically enhanced in NbGe$_2$ due to strong
electron-phonon interaction.",2311.11341v1
2023-11-20,Unbiased Random Number Generation using Injection-Locked Spin-Torque Nano-Oscillators,"Unbiased sources of true randomness are critical for the successful
deployment of stochastic unconventional computing schemes and encryption
applications in hardware. Leveraging nanoscale thermal magnetization
fluctuations provides an efficient and almost cost-free means of generating
truly random bitstreams, distinguishing them from predictable pseudo-random
sequences. However, existing approaches that aim to achieve randomness often
suffer from bias, leading to significant deviations from equal fractions of 0
and 1 in the bitstreams and compromising their inherent unpredictability. This
study presents a hardware approach that capitalizes on the intrinsic balance of
phase noise in an oscillator injection locked at twice its natural frequency,
leveraging the stability of this naturally balanced physical system. We
demonstrate the successful generation of unbiased and truly random bitstreams
through extensive experimentation. Our numerical simulations exhibit excellent
agreement with the experimental results, confirming the robustness and
viability of our approach.",2311.11982v1
2024-01-11,Deterministic and stochastic aspects of current-induced magnetization reversal in perpendicular nanomagnets,"We study the incubation and transition times that characterize the
magnetization switching induced by spin-orbit torques in nanomagnets with
perpendicular anisotropy. We present a phenomenological model to interpret the
dependence of the incubation time on the amplitude of the voltage pulse and
assisting magnetic field and estimate the volume of the seed domain that
triggers the switching. Our measurements evidence a correlation between the
incubation and transition times that is mediated by the temperature variation
during the electric pulse. In addition, we discuss the stochastic distributions
of the two times in terms of the energy barriers opposing the nucleation and
expansion of the seed domain. We propose two models based on the log-normal and
gamma functions to account for the different origin of the variability of the
incubation and transition times, which are associated with a single nucleation
barrier and multiple pinning sites, respectively.",2401.05704v1
2024-01-22,Evidence for Unfolded Fermi Surfaces in the Charge-Density-Wave State of Kagome Metal FeGe Revealed by de Haas-van Alphen Effect,"The antiferromagnetic kagome lattice compound FeGe has been revealed to host
an emergent charge-density-wave (CDW) state which manifests complex interplay
between the spin, charge and lattice degrees of freedom. Here, we present a
comprehensive study of the de Haas-van Alphen effect by measuring torque
magnetometry under magnetic fields up to 45.2 T to map Fermi surfaces in this
unusual CDW state. For field along the $c$ direction, we resolve four cyclotron
orbits; the largest one roughly corresponding to the area of the 2$\times$2
folded Brillouin zone. Three smaller orbits are characterized by light
effective cyclotron masses range from (0.18-0.30) $m_e$. Angle-resolved
measurements identify one Fermi surface segment with weak anisotropy. Combined
with band structure calculations, our results suggest that features of unfolded
Fermi surfaces are robust against CDW reconstruction, corroborating the novel
effect of a short-ranged CDW on the electronic structure.",2401.11770v1
2024-03-22,All van der Waals three-terminal SOT-MRAM realized by topological ferromagnet Fe3GeTe2,"Magnetic van der Waals (vdW) materials have attracted massive attention
because of their academic interest and application potential for the past few
years. Its main advantage is the intrinsic two-dimensionality, enabling much
smaller devices of novel concepts. One particular exciting direction lies in
the current-driven spin-orbit torque (SOT). Here, we, for the first time,
realize an all vdW three-terminal SOT memory, employing the unique physics
principle of gigantic intrinsic SOT of Fe3GeTe2 (FGT) and the well-known
industry-adopted tunnelling magnetoresistance (TMR) effect. We designed the
device operation procedure and fabricated the FGT/h-BN/FGT vdW heterostructure
as a proof of concept. This device exhibits a classical TMR effect and
unambiguously demonstrates the conception by precise performance as expected:
the magnetic information of the top-FGT is written by current-driven SOT and
read out by TMR separately. The writing and reading current paths are
physically decoupled, enhancing the design and optimization flexibility
substantially and further strengthening the device's endurance naturally. Our
work would prompt more expansive use of vdW magnets for spintronic
applications.",2403.15020v1
2024-03-28,"A noise-tolerant, resource-saving probabilistic binary neural network implemented by the SOT-MRAM compute-in-memory system","We report a spin-orbit torque(SOT) magnetoresistive random-access
memory(MRAM)-based probabilistic binary neural network(PBNN) for
resource-saving and hardware noise-tolerant computing applications. With the
presence of thermal fluctuation, the non-destructive SOT-driven magnetization
switching characteristics lead to a random weight matrix with controllable
probability distribution. In the meanwhile, the proposed CIM architecture
allows for the concurrent execution of the probabilistic vector-matrix
multiplication (PVMM) and binarization. Furthermore, leveraging the
effectiveness of random binary cells to propagate multi-bit probabilistic
information, our SOT-MRAM-based PBNN system achieves a 97.78\% classification
accuracy under a 7.01\% weight variation on the MNIST database through 10
sampling cycles, and the number of bit-level computation operations is reduced
by a factor of 6.9 compared to that of the full-precision LeNet-5 network. Our
work provides a compelling framework for the design of reliable neural networks
tailored to the applications with low power consumption and limited
computational resources.",2403.19374v1
2024-04-08,NAND-like SOT-MRAM-based Approximate Storage for Error-Tolerant Applications,"We demonstrate approximate storage based on NAND-like spin-orbit torque (SOT)
MRAM, through ""device-modeling-architecture"" explorations. We experimentally
achieve down to 1E-5 level selectivity. Selectivity and low-power solutions are
established by numerical calculation workflow. System-level power consumption
is evaluated in the 512 KB last-level cache according to 5 quality levels.
Error-tolerant applications, such as image processing, alleviate the demand for
selectivity down to the 5E-2 level, leading to 54% ~ 61% energy-saving. Our
proposal paves the novel and suitable path for high-density and low-power
NAND-like SOT-MRAM.",2404.05528v1
2024-04-14,Achieving High Yield of Perpendicular SOT-MTJ Manufactured on 300 mm Wafers,"The large-scale fabrication of three-terminal magnetic tunnel junctions
(MTJs) with high yield is becoming increasingly crucial, especially with the
growing interest in spin-orbit torque (SOT) magnetic random access memory
(MRAM) as the next generation of MRAM technology. To achieve high yield and
consistent device performance in MTJs with perpendicular magnetic anisotropy,
an integration flow has been developed that incorporates special MTJ etching
technique and other CMOS-compatible processes on a 300 mm wafer manufacturing
platform. Systematic studies have been conducted on device performance and
statistical uniformity, encompassing magnetic properties, electrical switching
behavior, and reliability. Achievements include a switching current of 680 uA
at 2 ns, a TMR as high as 119%, ultra-high endurance (over 1012 cycles), and
excellent uniformity in the fabricated SOT-MTJ devices, with a yield of up to
99.6%. The proposed integration process, featuring high yield, is anticipated
to streamline the mass production of SOT-MRAM.",2404.09125v1
2002-05-19,Crossover from nonadiabatic to adiabatic electron transfer reactions: Multilevel blocking Monte Carlo simulations,"The crossover from nonadiabatic to adiabatic electron transfer has been
theoretically studied under a spin-boson model (dissipative two-state system)
description. We present numerically exact data for the thermal transfer rate
and the time-dependent occupation probabilities in largely unexplored regions
of parameter space, using real-time path-integral Monte Carlo simulations. The
dynamical sign problem is relieved by employing a variant of the recently
proposed multilevel blocking algorithm. We identify the crossover regime
between nonadiabatic and adiabatic electron transfer, both in the classical
(high-temperature) and the quantum (low-temperature) limit. The electron
transfer dynamics displays rich behaviors, including multi-exponential decay
and the breakdown of a rate description due to vibrational coherence.",0205400v1
2002-07-06,Charge transfer in molecular conductors -- oxidation or reduction?,"We discuss the nature of charge transfer in molecular conductors upon
connecting to two metallic contacts and imposing a voltage bias across them.
The sign of the charge transfer (oxidation vs. reduction) depends on the
position of the metal Fermi energy with respect to the molecular levels. In
addition, the charge transfer depends on the strength of the coupling
(chemisorption vs. physisorption) with the contacts. A convenient way to
establish the nature and onset of the charge transfer and the corresponding
features in the I-V is to draw an energy level diagram for each spin species.
Starting from such a level diagram, we argue that transport in the Tour-Reed
switching molecules, which consist of a central phenyl ring with a nitroamine
redox center, involves the oxidation of a highest occupied molecular orbital
(HOMO)-based level.",0207174v1
2005-03-29,Transfer of entanglement from electrons to photons by optical selection rules,"The entanglement transfer from electrons localized in a pair of quantum dots
to circularly polarized photons is governed by optical selection rules,
enforced by conservation of angular momentum. We point out that the transfer
can not be achieved by means of unitary evolution unless the angular momentum
of the two initial qubit states differs by 2 units. In particular, for
spin-entangled electrons the difference in angular momentum is 1 unit -- so the
transfer fails. Nevertheless, the transfer can be successfully completed if the
unitary evolution is followed by a measurement of the angular momentum of each
quantum dot and post-processing of the photons using the measured values as
input.",0503676v4
2006-10-24,Quantum State Transfer in Spin-1 Chains,"We study the transfer of quantum information through a Heisenberg spin-1
chain prepared in its ground state. We measure the efficiency of such a quantum
channel {\em via} the fidelity of retrieving an arbitrarily prepared state and
{\em via} the transfer of quantum entanglement. The Heisenberg spin-1 chain has
a very rich quantum phase diagram. We show that the phase boundaries are
reflected in sharp variations of the transfer efficiency. In the vicinity of
the border between the dimer and the ferromagnetic phase (in the conjectured
spin-nematic region), we find strong indications for a qualitative change of
the excitation spectrum. Moreover, we identify two regions of the phase diagram
which give rise to particularly high transfer efficiency; the channel might be
non-classical even for chains of arbitrary length, in contrast to spin-1/2
chains.",0610210v3
2008-08-17,Quantum state transfer with untuneable couplings,"We present a general scheme for implementing bi-directional quantum state
transfer in a quantum swapping channel. Unlike many other schemes for quantum
computation and communication, our method does not require qubit couplings to
be switched on and off. The only control variable is the bias acting on
individual qubits. We show how to derive the parameters of the system (fixed
and variable) such that perfect state transfer can be achieved. Since these
parameters vary linearly with the pulse width, our scheme allows flexibility in
the time scales under which qubits evolve. Unlike quantum spin networks, our
scheme allows the transmission of several quantum states at a time, requiring
only a two qubit separation between quantum states. By pulsing the biases of
several qubits at the same time, we show that only eight bias control lines are
required to achieve state transfer along a channel of arbitrary length.
Furthermore, when the information to be transferred is purely classical in
nature, only three bias control lines are required, greatly simplifying the
circuit complexity.",0808.2306v1
2010-04-24,Optimal control of population transfer in Markovian open quantum systems,"There has long been interest to control the transfer of population between
specified quantum states. Recent work has optimized the control law for closed
system population transfer by using a gradient ascent pulse engineer- ing
algorithm [1]. Here, a spin-boson model consisting of two-level atoms which
interact with the dissipative environment, is investigated. With opti- mal
control, the quantum system can invert the populations of the quantum logic
states. The temperature plays an important role in controlling popula- tion
transfer. At low temperatures the control has active performance, while at high
temperatures it has less erect. We also analyze the decoherence be- havior of
open quantum systems with optimal population transfer control, and we find that
these controls can prolong the coherence time. We hope that active optimal
control can help quantum solid-state-based engineering.",1004.4301v2
2011-05-30,Long quantum channels for high-quality entanglement transfer,"High-quality quantum-state and entanglement transfer can be achieved in an
unmodulated spin bus operating in the ballistic regime, which occurs when the
endpoint qubits A and B are coupled to the chain by an exchange interaction
$j_0$ comparable with the intrachain exchange. Indeed, the transition amplitude
characterizing the transfer quality exhibits a maximum for a finite optimal
value $j_0^{opt}(N)$, where $N$ is the channel length. We show that
$j_0^{opt}(N)$ scales as $N^{-1/6}$ for large $N$ and that it ensures a
high-quality entanglement transfer even in the limit of arbitrarily long
channels, almost independently of the channel initialization. For instance, the
average quantum-state transmission fidelity exceeds 90% for any chain length.
We emphasize that, taking the reverse point of view, should $j_0$ be
experimentally constrained, high-quality transfer can still be obtained by
adjusting the channel length to its optimal value.",1105.6058v1
2014-07-29,Comparing different modes of quantum state transfer in a XXZ spin chain,"We study the information transferring ability of a spin-1/2 XXZ Hamiltonian
for two different modes of state transfer, namely, the well studied attaching
scenario and the recently proposed measurement induced transport. The latter
one has been inspired by recent achievements in optical lattice experiments for
local addressability of individual atoms and their time evolution when only
local rotations and measurements are available and local control of the
Hamiltonian is very limited. We show that while measurement induced transport
gives higher fidelity for quantum state transfer around the isotropic
Heisenberg point, its superiority is less pronounced in non-interacting free
fermionic XX phase. Moreover, we study the quality of state transfer in the
presence of thermal fluctuations and environmental interactions and show that
measurement scheme gives higher fidelity for low temperatures and weak
interaction with environment.",1407.7681v2
2016-09-05,Engineering and probing topological properties of Dirac semimetal films by asymmetric charge transfer,"Dirac semimetals (DSMs) have topologically robust three-dimensional Dirac
(doubled Weyl) nodes with Fermi-arc states. In heterostructures involving DSMs,
charge transfer occurs at the interfaces, which can be used to probe and
control their bulk and surface topological properties through surface-bulk
connectivity. Here we demonstrate that despite a band gap in DSM films,
asymmetric charge transfer at the surface enables one to accurately identify
locations of the Dirac-node projections from gapless band crossings and to
examine and engineer properties of the topological Fermi-arc surface states
connecting the projections, by simulating adatom-adsorbed DSM films using a
first-principles method with an effective model. The positions of the
Dirac-node projections are insensitive to charge transfer amount or slab
thickness except for extremely thin films. By varying the amount of charge
transfer, unique spin textures near the projections and a separation between
the Fermi-arc states change, which can be observed by gating without adatoms.",1609.01268v1
2019-08-22,Network-Accelerated Non-Contiguous Memory Transfers,"Applications often communicate data that is non-contiguous in the send- or
the receive-buffer, e.g., when exchanging a column of a matrix stored in
row-major order. While non-contiguous transfers are well supported in HPC
(e.g., MPI derived datatypes), they can still be up to 5x slower than
contiguous transfers of the same size. As we enter the era of network
acceleration, we need to investigate which tasks to offload to the NIC: In this
work we argue that non-contiguous memory transfers can be transparently
networkaccelerated, truly achieving zero-copy communications. We implement and
extend sPIN, a packet streaming processor, within a Portals 4 NIC SST model,
and evaluate strategies for NIC-offloaded processing of MPI datatypes, ranging
from datatype-specific handlers to general solutions for any MPI datatype. We
demonstrate up to 10x speedup in the unpack throughput of real applications,
demonstrating that non-contiguous memory transfers are a first-class candidate
for network acceleration.",1908.08590v1
2019-11-27,Perturbatively-perfect many-body transfer,"The coherent transfer of excitations between different locations of a quantum
many-body system is of primary importance in many research areas, from
transport properties in spintronics and atomtronics to quantum state transfer
in quantum information processing. We address the transfer of $n>1$ bosonic and
fermionic excitations between the edges of a one-dimensional chain modeled by a
quadratic hopping Hamiltonian, where the block edges, embodying the sender and
the receiver sites, are weakly coupled to the quantum wire. We find that
perturbatively perfect coherent transfer is attainable in the weak-coupling
limit, for both bosons and fermions, only for certain modular arithmetic
equivalence classes of the wire's length. Finally we apply our findings to the
transport of spins and the charging of a many-body quantum battery.",1911.12211v1
2021-09-28,Quantum anomalous Hall effect from inverted charge transfer gap,"A general mechanism is presented by which topological physics arises in
strongly correlated systems without flat bands. Starting from a charge transfer
insulator, topology emerges when the charge transfer energy between the cation
and anion is reduced to invert the lower Hubbard band and the spin-degenerate
charge transfer band. A universal low-energy theory is developed for the
inversion of charge transfer gap in a quantum antiferromagnet. The inverted
state is found to be a quantum anomalous Hall (QAH) insulator with non-coplanar
magnetism. Interactions play two essential roles in this mechanism: producing
the insulating gap and quasiparticle bands prior to the band inversion, and
causing the change of magnetic order necessary for the QAH effect after
inversion. Our theory explains the electric field induced transition from
correlated insulator to QAH state in AB-stacked TMD bilayer MoTe$_2$/WSe$_2$.",2109.13909v2
2021-12-22,Transfer matrices of rational spin chains via novel BGG-type resolutions,"We obtain BGG-type formulas for transfer matrices of irreducible
finite-dimensional representations of the classical Lie algebras
$\mathfrak{g}$, whose highest weight is a multiple of a fundamental one and
which can be lifted to the representations over the Yangian $Y(\mathfrak{g})$.
These transfer matrices are expressed in terms of transfer matrices of certain
infinite-dimensional highest weight representations (such as parabolic Verma
modules and their generalizations) in the auxiliary space. We further factorise
the corresponding infinite-dimensional transfer matrices into the products of
two Baxter $Q$-operators, arising from our previous study (arXiv:2001.04929,
arXiv:2104.14518) of the degenerate Lax matrices. Our approach is crucially
based on the new BGG-type resolutions of the finite-dimensional
$\mathfrak{g}$-modules, which naturally arise geometrically as the restricted
duals of the Cousin complexes of relative local cohomology groups of ample line
bundles on the partial flag variety $G/P$ stratified by $B_{-}$-orbits.",2112.12065v2
2011-11-11,Multiferroicity in an organic charge-transfer salt: Electric-dipole-driven magnetism,"Multiferroics, showing simultaneous ordering of electrical and magnetic
degrees of freedom, are remarkable materials as seen from both the academic and
technological points of view. A prominent mechanism of multiferroicity is the
spin-driven ferroelectricity, often found in frustrated antiferromagnets with
helical spin order. There, similar to conventional ferroelectrics, the
electrical dipoles arise from an off-centre displacement of ions. However,
recently a different mechanism, namely purely electronic ferroelectricity,
where charge order breaks inversion symmetry, has attracted considerable
interest. Here we provide evidence for this exotic type of ferroelectricity,
accompanied by antiferromagnetic spin order, in a two-dimensional organic
charge-transfer salt, thus representing a new class of multiferroics. Quite
unexpectedly for electronic ferroelectrics, dipolar and spin order arise nearly
simultaneously. This can be ascribed to the loss of spin frustration induced by
the ferroelectric ordering. Hence, here the spin order is driven by the
ferroelectricity, in marked contrast to the spin-driven ferroelectricity in
helical magnets.",1111.2752v2
2011-11-17,Critical properties of joint spin and Fortuin-Kasteleyn observables in the two-dimensional Potts model,"The two-dimensional Potts model can be studied either in terms of the
original Q-component spins, or in the geometrical reformulation via
Fortuin-Kasteleyn (FK) clusters. While the FK representation makes sense for
arbitrary real values of Q by construction, it was only shown very recently
that the spin representation can be promoted to the same level of generality.
In this paper we show how to define the Potts model in terms of observables
that simultaneously keep track of the spin and FK degrees of freedom. This is
first done algebraically in terms of a transfer matrix that couples three
different representations of a partition algebra. Using this, one can study
correlation functions involving any given number of propagating spin clusters
with prescribed colours, each of which contains any given number of distinct FK
clusters. For 0 <= Q <= 4 the corresponding critical exponents are all of the
Kac form h_{r,s}, with integer indices r,s that we determine exactly both in
the bulk and in the boundary versions of the problem. In particular, we find
that the set of points where an FK cluster touches the hull of its surrounding
spin cluster has fractal dimension d_{2,1} = 2 - 2 h_{2,1}. If one constrains
this set to points where the neighbouring spin cluster extends to infinity, we
show that the dimension becomes d_{1,3} = 2 - 2 h_{1,3}. Our results are
supported by extensive transfer matrix and Monte Carlo computations.",1111.4033v1
2013-06-28,Close binary evolution I. The tidally induced shear mixing in rotating binaries,"We study how tides in a binary system induce some specific internal shear
mixing, able to substantially modify the evolution of close binaries prior to
mass transfer. We construct numerical models accounting for tidal interactions,
meridional circulation, transport of angular momentum, shears and horizontal
turbulence and consider a variety of orbital periods and initial rotation
velocities. Depending on orbital periods and rotation velocities, tidal effects
may spin down (spin down Case) or spin up (spin up Case) the axial rotation. In
both cases, tides may induce a large internal differential rotation. The
resulting tidally induced shear mixing (TISM) is so efficient that the internal
distributions of angular velocity and chemical elements are greatly influenced.
The evolutionary tracks are modified, and in both cases of spin down and spin
up, large amounts of nitrogen can be transported to the stellar surfaces before
any binary mass transfer. Meridional circulation, when properly treated as an
advection, always tends to counteract the tidal interaction, tending to spin up
the surface when it is braked down and vice versa. As a consequence, the times
needed for the axial angular velocity to become equal to the orbital angular
velocity may be larger than given by typical synchronization timescales. Also,
due to meridional circulation some differential rotation remains in tidally
locked binary systems.",1306.6731v1
2014-11-12,Magnonic Holographic Memory: from Proposal to Device,"In this work, we present recent developments in magnonic holographic memory
devices exploiting spin waves for information transfer. The devices comprise a
magnetic matrix and spin wave generating/detecting elements placed on the edges
of the waveguides. The matrix consists of a grid of magnetic waveguides
connected via cross junctions. Magnetic memory elements are incorporated within
the junction while the read-in and read-out is accomplished by the spin waves
propagating through the waveguides. We present experimental data on spin wave
propagation through NiFe and YIG magnetic crosses. The obtained experimental
data show prominent spin wave signal modulation (up to 20 dB for NiFe and 35 dB
for YIG) by the external magnetic field, where both the strength and the
direction of the magnetic field define the transport between the cross arms. We
also present experimental data on the 2-bit magnonic holographic memory built
on the double cross YIG structure with micro-magnets placed on the top of each
cross. It appears possible to recognize the state of each magnet via the
interference pattern produced by the spin waves with all experiments done at
room temperature. Magnonic holographic devices aim to combine the advantages of
magnetic data storage with wave-based information transfer. We present
estimates on the spin wave holographic devices performance, including power
consumption and functional throughput. According to the estimates, magnonic
holographic devices may provide data processing rates higher than 10^18
bits/cm2/s while consuming 0.15uW. Technological challenges and fundamental
physical limits of this approach are also discussed.",1411.3388v1
2020-05-04,Thermodynamic behavior of modified integer-spin Kitaev models on the honeycomb lattice,"We study the thermodynamic properties of modified spin-$S$ Kitaev models
introduced by Baskaran, Sen and Shankar (Phys. Rev. B 78, 115116 (2008)). These
models have the property that for half-odd-integer spins their eigenstates map
on to those of spin-1/2 Kitaev models, with well-known highly entangled quantum
spin-liquid states and Majorana fermions. For integer spins, the Hamiltonian is
made out of commuting local operators. Thus, the eigenstates can be chosen to
be completely unentangled between different sites, though with a significant
degeneracy for each eigenstate. For half-odd-integer spins, the thermodynamic
properties can be related to the spin-1/2 Kitaev models apart from an
additional degeneracy. Hence we focus here on the case of integer spins. We use
transfer matrix methods, high temperature expansions and Monte Carlo
simulations to study the thermodynamic properties of ferromagnetic and
antiferromagnetic models with spin $S=1$ and $S=2$. Apart from large residual
entropies, which all the models have, we find that they can have a variety of
different behaviors. Transfer matrix calculations show that for the different
models, the correlation lengths can be finite as $T\to 0$, become critical as
$T\to 0$ or diverge exponentially as $T\to 0$. There is a conserved $Z_2$ flux
variable associated with each hexagonal plaquette which saturates at the value
$+1$ as $T\rightarrow0$ in all models except the $S=1$ antiferromagnet where
the mean flux remains zero as $T\to 0$. We provide qualitative explanations for
these results.",2005.01255v2
2022-07-19,Extending MIEZE spectroscopy towards thermal wavelengths,"We propose a Modulation of intensity with zero effort (MIEZE) set-up for
high-resolution neutron spectroscopy at momentum transfers up to
3\r{A}$^{-1}$,energy transfers up to ~ 20 meV, and an energy resolution in the
$\mu$eV-range using both thermal and cold neutrons. MIEZE has two prominent
advantages compared to classical neutron spin-echo. The first one is the
possibility to investigate spin-depolarizing samples or samples in strong
magnetic fields without loss of signal amplitude and intensity. This allows for
the study of spin fluctuations in ferromagnets, and facilitates the study of
samples with strong spin-incoherent scattering. The second advantage is that
multi-analyzer setups can be implemented with comparatively small effort. The
use of thermal neutrons increases the range of validity of the spin-echo
approximation towards shorter spin-echo times. In turn, the thermal MIEZE
option for greater ranges (TIGER) closes the gap between classical neutron
spin-echo spectroscopy and conventional high-resolution neutron spectroscopy
techniques such as triple-axis, time-of-flight, and back-scattering. To
illustrate the feasibility of TIGER we present the details of an implementation
at the beamline RESEDA at FRM II by means of an additional velocity selector,
polarizer and analyzer.",2207.09276v2
2022-12-21,Charge transfer and disorder-induced spin relaxation in La2NiMnO6 crystallites,"Investigation of the electronic and spin structure in double perovskites is
recently attracting significant attention, mainly driven by their unique
multifunctional properties and other underlying charge and spin dynamics.
Herein, using X-ray photoelectron spectroscopy (XPS), we explore the influence
of variable fractions of Mn3+/Mn4+ cation in different crystallite sizes of
La2NiMnO6 that control the various completing exchange interactions of Ni/Mn
cations responsible for multiple magnetic transitions. The enhanced itinerant
electron due to Mn4+ + Ni2+ to Mn3+ + Ni3+ charge transfer emerged as a
shoulder like characteristics at the low binding energy in the Mn-2P core-level
spectrum. The various approaches such as difference in saturation
magnetization, presence of multiple charge valance, and magnetic entropy
calculations confirm the presence of antisites disorder and it varies as a
function of milling. As milling provides excess energy that helps with
nucleation or cation ordering. Competing magnetic interactions driven by mixed
valences and disorder were established across a cluster glassy phase in the
crystallites. Electron spin resonance spectroscopy (ESR) was utilized to probe
the temperature-driven ferromagnetic-cluster spin-glass transition with
modified g-factor ranging from 2.050 to 2.037. The line width of the ESR
signals increases across the ferromagnetic to cluster-glass phase transition
due to spin freezing. This phase transition is further characterized by
temperature-dependent ac-magnetic susceptibility measurements. Argand diagram
for the ac-susceptibility of the interacting crystallites suggests a collective
magnetization relaxation dynamic in the proximity of spin-glass freezing
temperature of La2NiMnO6.",2212.10845v2
2023-06-20,Spin-orbit interaction enabled electronic Raman scattering from charge collective modes,"Electronic Raman scattering in the fully symmetric channel couples to the
charge excitations in the system, including the plasmons. However, the plasmon
response has a spectral weight of $\sim q^2$, where $q$, the momentum
transferred by light, is small. In this work, we show that in inversion
symmetry broken systems where Rashba type spin-orbit coupling affects the
states at the Fermi energy (which is a known low energy effect) as well as the
transition elements to other states (a high energy effect), there is an
additional coupling of the plasmons to the Raman vertex, even at zero momentum
transfer, that results in a spectral weight that is proportional to the
spin-orbit coupling. The high energy effect is due to the breaking of SU(2)
spin invariance in the spin-flip transitions to the intermediate state. We
present a theory for this coupling near the resonant regime of Raman scattering
and show that in giant Rashba systems it can dominate over the conventional
$q^2$ weighted coupling. We also provide experimental support along with a
symmetry based justification for this spin-mediated coupling by identifying a
prominent c-axis plasmon peak in the fully symmetric channel of the resonant
Raman spectrum of the giant Rashba material BiTeI. This new coupling could lead
to novel ways of manipulating coherent charge excitations in inversion-broken
systems. This process is also relevant for spectroscopic studies in ultrafast
spectroscopies, certain driven Floquet systems and topologically non-trivial
phases of matter where strong inversion-breaking spin-orbit coupling plays a
role.",2306.11240v2
2023-07-19,A spin-rotation mechanism of Einstein-de Haas effect based on a ferromagnetic disk,"Spin-rotation coupling (SRC) is a fundamental phenomenon that connects
electronic spins with the rotational motion of a medium. We elucidate the
Einstein-de Haas (EdH) effect and its inverse with SRC as the microscopic
mechanism using the dynamic spin-lattice equations derived by elasticity theory
and Lagrangian formalism. By applying the coupling equations to an iron disk in
a magnetic field, we exhibit the transfer of angular momentum and energy
between spins and lattice, with or without damping. The timescale of the
angular momentum transfer from spins to the entire lattice is estimated by our
theory to be on the order of 0.01 ns, for the disk with a radius of 100 nm.
Moreover, we discover a linear relationship between the magnetic field strength
and the rotation frequency, which is also enhanced by a higher ratio of Young's
modulus to Poisson's coefficient. In the presence of damping, we notice that
the spin-lattice relaxation time is nearly inversely proportional to the
magnetic field. Our explorations will contribute to a better understanding of
the EdH effect and provide valuable insights for magneto-mechanical
manufacturing.",2307.10390v2
2006-01-06,Angular momentum transport and disk morphology in SPH simulations of galaxy formation,"We perform controlled N-Body/SPH simulations of disk galaxy formation by
cooling a rotating gaseous mass distribution inside equilibrium cuspy spherical
and triaxial dark matter halos. We systematically study the angular momentum
transport and the disk morphology as we increase the number of dark matter and
gas particles from 10^4 to 10^6, and decrease the gravitational softening from
2 kpc to 50 parsecs. The angular momentum transport, disk morphology and radial
profiles depend sensitively on force and mass resolution. At low resolution,
similar to that used in most current cosmological simulations, the cold gas
component has lost half of its initial angular momentum via different
mechanisms. The angular momentum is transferred primarily to the hot halo
component, by resolution-dependent hydrodynamical and gravitational torques,
the latter arising from asymmetries in the mass distribution. In addition,
disk-particles can lose angular momentum while they are still in the hot phase
by artificial viscosity. In the central disk, particles can transfer away over
99% of their initial angular momentum due to spiral structure and/or the
presence of a central bar. The strength of this transport also depends on force
and mass resolution - large softening will suppress the bar instability, low
mass resolution enhances the spiral structure. This complex interplay between
resolution and angular momentum transfer highlights the complexity of
simulations of galaxy formation even in isolated haloes. With 10^6 gas and dark
matter particles, disk particles lose only 10-20% of their original angular
momentum, yet we are unable to produce pure exponential profiles.",0601115v2
2018-10-10,Hydrodynamics of circumbinary accretion: Angular momentum transfer and binary orbital evolution,"We carry out 2D viscous hydrodynamical simulations of circumbinary accretion
using the AREPO code. We self-consistently compute the accretion flow over a
wide range of spatial scales, from the circumbinary disk (CBD) far from the
central binary, through accretion streamers, to the disks around individual
binary components, resolving the flow down to 2% of the binary separation. We
focus on equal-mass binaries with arbitrary eccentricities. We evolve the flow
over long (viscous) timescales until a quasi-steady is reached, in which the
mass supply rate at large distances $\dot{M}_0$ (assumed constant) equals the
time-averaged mass transfer rate across the disk and the total mass accretion
rate onto the binary components. This quasi-steady state allows us to compute
the secular angular momentum transfer rate onto the binary,
$\langle\dot{J}_b\rangle$, and the resulting orbital evolution. Through direct
computation of the gravitational and accretion torques on the binary, we find
that $\langle\dot{J}_b\rangle$ is consistently positive (i.e., the binary gains
angular momentum), with $l_0\equiv\langle\dot{J}_b\rangle/\dot M_0$ in the
range of $(0.4-0.8)a_b^2\Omega_b$, depending on the binary eccentricity (where
$a_b,~\Omega_b$ are the binary semi-major axis and angular frequency); we also
find that this $\langle\dot{J}_b\rangle$ is equal to the net angular momentum
current across the CBD, indicating that global angular momentum balance is
achieved in our simulations. We compute the time-averaged rate of change of the
binary orbital energy for eccentric binaries, and thus obtain the secular rates
$\langle\dot a_b\rangle$ and $\langle \dot{e}_b\rangle$. In all cases,
$\langle\dot{a}_b\rangle$ is positive, i.e., the binary expands while
accreting. We discuss the implications of our results for the merger of
supermassive binary black holes and for the formation of close stellar
binaries.",1810.04676v2
2020-06-04,Fast CRDNN: Towards on Site Training of Mobile Construction Machines,"The CRDNN is a combined neural network that can increase the holistic
efficiency of torque based mobile working machines by about 9% by means of
accurately detecting the truck loading cycles. On the one hand, it is a robust
but offline learning algorithm so that it is more accurate and much quicker
than the previous methods. However, on the other hand, its accuracy can not
always be guaranteed because of the diversity of the mobile machines industry
and the nature of the offline method. To address the problem, we utilize the
transfer learning algorithm and the Internet of Things (IoT) technology.
Concretely, the CRDNN is first trained by computer and then saved in the
on-board ECU. In case that the pre-trained CRDNN is not suitable for the new
machine, the operator can label some new data by our App connected to the
on-board ECU of that machine through Bluetooth. With the newly labeled data, we
can directly further train the pretrained CRDNN on the ECU without overloading
since transfer learning requires less computation effort than training the
networks from scratch. In our paper, we prove this idea and show that CRDNN is
always competent, with the help of transfer learning and IoT technology by
field experiment, even the new machine may have a different distribution. Also,
we compared the performance of other SOTA multivariate time series algorithms
on predicting the working state of the mobile machines, which denotes that the
CRDNNs are still the most suitable solution. As a by-product, we build up a
human-machine communication system to label the dataset, which can be operated
by engineers without knowledge about Artificial Intelligence (AI).",2006.03169v1
2020-07-01,Multifractal Dynamics of the QREM,"We study numerically the population transfer protocol on the Quantum Random
Energy Model and its relation to quantum computing, for system sizes of $n\leq
20$ quantum spins. We focus on the energy matching problem, i.e. finding
multiple approximate solutions to a combinatorial optimization problem when a
known approximate solution is provided as part of the input. We study the
delocalization process induced by the population transfer protocol by observing
the saturation of the Shannon entropy of the time-evolved wavefunction as a
measure of its spread over the system. The scaling of the value of this entropy
at saturation with the volume of the system identifies the three known
dynamical phases of the model. In the non-ergodic extended phase, we observe
that the time necessary for the population transfer to complete follows a
long-tailed distribution. We devise two statistics to quantify how effectively
and uniformly the protocol populates the target energy shell. We find that
population transfer is most effective if the transverse-field parameter
$\Gamma$ is chosen close to the critical point of the Anderson transition of
the model. In order to assess the use of population transfer as a quantum
algorithm we perform a comparison with random search. We detect a ""black box""
advantage in favour of PT, but when the running times of population transfer
and random search are taken into consideration we do not see strong indications
of a speedup at the system sizes that are accessible to our numerical methods.
We discuss these results and the impact of population transfer on NISQ devices.",2007.00315v1
2008-02-29,Estimation of Domain Size in Nano Ferroelectrics from NMR T1 Measurements,"The spin lattice relaxation of I=3/2 quadrupolar spin system due to domain
walls in order-disorder ferroelectrics has been studied and a general method is
proposed for the measurement of domain width in nano ferroelectrics. Based on
the fact that electric polarization undergoes spiral orientation as one moves
from one domain to the other, it is assumed that at low temperatures the spins
at and near domain walls undergo relaxation due to possible easy reorientation
of electric polarization in domain walls even though such a relaxation in the
main body of the domain has almost ceased. The spins present inside the domain
undergo relaxation through transfer of magnetization to the domain walls
through a spin diffusion process by nearest neighbour interaction. Rate
equations for spin populations are formed by representing the ferroelectric
domain by a one-dimensional chain of equidistant spins having dipolar coupling.
Spin populations are calculated as a function of time for different ratios of
quadrupolar to dipolar transition probabilities for a sample subjected to
selective rf pulse. Expression for spin- lattice relaxation time T1 is derived
in terms of domain width and ratio of quadrupolar to dipolar transition
probabilities. It is found that the domain width can be estimated provided the
value of spin lattice relaxation time T1 is known for the corresponding crystal
with normal sized grains. The results are quite general and can be applied to
any order disorder ferroelectric with nano sized domains and having spin I=3/2
nuclei.",0802.4316v1
2011-02-21,Spin-Up/Spin-Down models for Type Ia Supernovae,"In the single degenerate scenario for Type Ia supernova (SNeIa), a white
dwarf (WD) must gain a significant amount of matter from a companion star.
Because the accreted mass carries angular momentum, the WD is likely to achieve
fast spin periods, which can increase the critical mass, $M_{crit}$, needed for
explosion. When $M_{crit}$ is higher than the maximum mass achieved by the WD,
the WD must spin down before it can explode. This introduces a delay between
the time at which the WD has completed its epoch of mass gain and the time of
the explosion. Matter ejected from the binary during mass transfer therefore
has a chance to become diffuse, and the explosion occurs in a medium with a
density similar to that of typical regions of the interstellar medium. Also,
either by the end of the WD's mass increase or else by the time of explosion,
the donor may exhaust its stellar envelope and become a WD. This alters,
generally diminishing, explosion signatures related to the donor star.
Nevertheless, the spin-up/spin-down model is highly predictive. Prior to
explosion, progenitors can be super-$M_{Ch}$ WDs in either wide binaries with
WD companions, or else in cataclysmic variables. These systems can be
discovered and studied through wide-field surveys. Post explosion, the
spin-up/spin-down model predicts a population of fast-moving WDs, low-mass
stars, and even brown dwarfs. In addition, the spin-up/spin-down model provides
a paradigm which may be able to explain both the similarities and the diversity
observed among SNeIa.",1102.4342v1
2012-09-02,Nanoscale magnetic imaging of a single electron spin under ambient conditions,"The detection of ensembles of spins under ambient conditions has
revolutionized the biological, chemical, and physical sciences through magnetic
resonance imaging and nuclear magnetic resonance. Pushing sensing capabilities
to the individual-spin level would enable unprecedented applications such as
single molecule structural imaging; however, the weak magnetic fields from
single spins are undetectable by conventional far-field resonance techniques.
In recent years, there has been a considerable effort to develop nanoscale
scanning magnetometers, which are able to measure fewer spins by bringing the
sensor in close proximity to its target. The most sensitive of these
magnetometers generally require low temperatures for operation, but measuring
under ambient conditions (standard temperature and pressure) is critical for
many imaging applications, particularly in biological systems. Here we
demonstrate detection and nanoscale imaging of the magnetic field from a single
electron spin under ambient conditions using a scanning nitrogen-vacancy (NV)
magnetometer. Real-space, quantitative magnetic-field images are obtained by
deterministically scanning our NV magnetometer 50 nanometers above a target
electron spin, while measuring the local magnetic field using dynamically
decoupled magnetometry protocols. This single-spin detection capability could
enable single-spin magnetic resonance imaging of electron spins on the nano-
and atomic scales and opens the door for unique applications such as mechanical
quantum state transfer.",1209.0203v1
2014-11-20,First Measurements of Spin Correlation Using Semi-leptonic $t\bar{t}$ Events at ATLAS,"The top quark decays before it hadronizes. Before its spin state can be
changed in a process of strong interaction, it is directly transferred to the
top quark decay products. The top quark spin can be deduced by studying angular
distributions of the decay products. The Standard Model predicts the
top/anti-top quark ($t\bar{t}$) pairs to have correlated spins. The degree is
sensitive to the spin and the production mechanisms of the top quark. Measuring
the spin correlation allows to test the predictions. New physics effects can be
reflected in deviations from the prediction. The measurement of the spin
correlation of $t\bar{t}$ pairs, produced at the LHC with a center-of-mass
energy of $\sqrt{s} = 7$ TeV and reconstructed with the ATLAS detector, is
presented. The dataset corresponds to an integrated luminosity of 4.6
$\textrm{fb}^{-1}$. $t\bar{t}$ pairs are reconstructed in the $\ell$+jets
channel using a kinematic likelihood fit offering the identification of light
up- and down-type quarks from the $t \rightarrow bW \rightarrow bq\bar{q}'$
decay. The spin correlation is measured via the distribution of the azimuthal
angle $\Delta \phi$ between two top quark spin analyzers in the laboratory
frame. It is expressed as the degree of $t\bar{t}$ spin correlation predicted
by the Standard Model, $f_{\textrm{SM}}$. The result of $f_{\textrm{SM}}= 1.12
\pm 0.11\,\text{(stat.)} \pm 0.22\,\text{(syst.)}$ is consistent with the
Standard Model prediction of $f_{\textrm{SM}}= 1.0$.",1411.5529v1
2015-02-27,"Phonon mediated spin relaxation in a moving quantum dot: Doppler shift, Cherenkov radiation, and spin relaxation boom","We study relaxation of a moving spin qubit caused by phonon noise. As we vary
the speed of the qubit, we observe several interesting features in spin
relaxation and the associated phonon emission, induced by Doppler effect. In
particular, in the supersonic regime, the phonons emitted by the relaxing qubit
is concentrated along certain directions, similar to the shock waves produced
in classical Cherenkov effect. As the speed of the moving qubit increases from
the subsonic regime to the supersonic regime, the qubit experiences a peak in
the spin relaxation rate near the speed of sound, which we term a spin
relaxation boom in analogy to the classical sonic boom. We also find that the
moving spin qubit may have a lower relaxation rate than a static qubit, which
hints at the possibility of coherence-preserving transportation for a spin
qubit. While the physics we have studied here has strong classical analogies,
we do find that quantum confinement for the spin qubit plays an important role
in all the phenomena we observe. Specifically, it produces a correction on the
Cherenkov angle, and removes the divergence in relaxation rate at the sonic
barrier. It is our hope that our results would encourage further research into
approaches for transferring and preserving quantum information in spin qubit
architectures.",1503.00014v1
2018-03-02,Coherent electron transport in silicon quantum dots,"With silicon being the go-to material for spin qubits, and motivated by the
demand of a scalable quantum computer architecture for fast and reliable
quantum information transfer on-chip, we study coherent electron transport in a
silicon double quantum dot. We first examine the valley-orbital dynamics in a
silicon double dot, and discuss how to properly measure the tunnel couplings as
well as the valley phase difference between two quantum dots. We then focus on
possible phase and spin flip errors during spin transport across a silicon
double dot. In particular, we clarify correction on the effective $g$-factor
for the electron spin from the double dot confinement potential, and quantify
the resulting phase error. We then study spin fidelity loss due to spin-valley
mixing, which is a unique feature of silicon quantum dots. We show that a small
phase correction between valleys can cause a significant coherence loss. We
also investigate spin flip errors caused by either an external inhomogeneous
magnetic field or the intrinsic spin-orbit coupling. We show that the presence
of valleys makes it possible to have much broader (in terms of interdot
detuning) level anti-crossings compared to typical anti-crossings in, for
example, a GaAs double dot, and such broad anti-crossings lead to amplification
of spin flip errors. Lastly, we design a pulse sequence to suppress various
possible spin flip errors by taking advantage of the multiple level
anti-crossings in a silicon double dot and employing Landau-Zener transitions.",1803.00749v3
2018-03-14,Classical correlation and quantum entanglement in the mixed-spin Ising-XY model with Dzyaloshinskii-Moriya interaction,"In the present work, initially a mixed-three-spin (1/2,1,1/2) cell of a
mixed-N-spin chain with Ising-XY model is introduced, for which pair spins
(1,1/2) have Ising-type interaction and pair spins (1/2,1/2) have both XY-type
and Dzyaloshinskii-Moriya(DM) interactions together. An external homogeneous
magnetic field B is considered for the system in thermal equilibrium.
Integer-spins have a single-ion anisotropy property with coefficient {\zeta}.
Then, we investigate the quantum entanglement between half-spins (1/2,1/2), by
means of the concurrence. Classical correlation(CC) for this pair of spins is
investigated as well as the concurrence and some interesting the temperature,
the magnetic field and the DM interaction properties are expressed. Moreover,
single-ion anisotropy effects on the correlation between half-spins is
verified. According to the verifications based on the communication channels
category by D. Rossini, V. Giovannetti and R. Fazio 63, we theoretically
consider such tripartite spin model as an ideal quantum channel, then calculate
its information transmission rate and express some differences in behaviour
between this suggested model and introduced simple models in the previous
works(chains without spin integer and DM interaction) from information
transferring protocol point of view.",1803.05129v1
2022-04-25,Scattering phenomena for spin transport in Kitaev spin liquid,"The Kitaev model exhibits a canonical quantum spin liquid as a ground state
and hosts two fractional quasiparticles, itinerant Majorana fermion and
localized flux excitation. The former can carry heat and spin modulations in
the quantum spin liquid, but the role of the latter remains unknown for the
transport phenomena. Here, we focus on spin transport in the presence of
excited fluxes and report that they yield strong interference in the
propagation of the Majorana fermions, which feel gauge-like potential emergent
around the fluxes. We examine the transient spin dynamics triggered by a pulsed
magnetic field at an edge. In the absence of excited fluxes, the magnetic-field
pulse creates the plane wave of the Majorana fermions, which flows in the
quantum spin liquid. Although this wave does not accompany the change of local
spin moments in bulk, it induces local moments at the side opposite to the edge
under the magnetic-field pulse. We observe the spatial modulation of induced
spin moments when fluxes are excited in the bulk region. This behavior is more
striking than the case of lattice defects. Moreover, we find that, although the
amplitude of the spatial change is almost independent of the distance between
lattice defects, it is strongly enhanced by increasing the distance for the
case of excited fluxes. The difference is understood from the influence on the
itinerant Majorana fermions; the lattice defects change the system locally, but
flux excitations alter all the transfer integrals on the string connecting
them. The present results will provide another route to observing intrinsic
flux excitations distinguished from extrinsic effects such as lattice defects.",2204.11578v1
2022-06-11,Chirality as Generalized Spin-Orbit Interaction in Spintronics,"This review focuses on the chirality observed in the excited states of the
magnetic order, dielectrics, and conductors that hold transverse spins when
they are evanescent. Even without any relativistic effect, the transverse spin
of the evanescent waves are locked to the momentum and the surface normal of
their propagation plane. This chirality thereby acts as a generalized
spin-orbit interaction, which leads to the discovery of various chiral
interactions between magnetic, phononic, electronic, photonic, and plasmonic
excitations in spintronics that mediate the excitation of quasiparticles into a
single direction, leading to phenomena such as chiral spin and phonon pumping,
chiral spin Seebeck, spin skin, magnonic trap, magnon Doppler, and spin diode
effects. Intriguing analogies with electric counterparts in the nano-optics and
plasmonics exist. After a brief review of the concepts of chirality that
characterize the ground state chiral magnetic textures and chirally coupled
magnets in spintronics, we turn to the chiral phenomena of excited states. We
present a unified electrodynamic picture for dynamical chirality in spintronics
in terms of generalized spin-orbit interaction and compare it with that in
nano-optics and plasmonics. Based on the general theory, we subsequently review
the theoretical progress and experimental evidence of chiral interaction, as
well as the near-field transfer of the transverse spins, between various
excitations in magnetic, photonic, electronic and phononic nanostructures at
GHz time scales. We provide a perspective for future research before concluding
this article.",2206.05535v2
2022-10-26,Effects of Inner Halo Angular Momentum on the Peanut/X-shapes of Bars,"Cosmological simulations show that dark matter halos surrounding baryonic
disks have a wide range of angular momenta, measured by the spin parameter
($\lambda$). In this study, we bring out the importance of inner angular
momentum($<$30 kpc), measured in terms of the halo spin parameter, on the
secular evolution of the bar using N-body simulations. We have varied the halo
spin parameter $\lambda$ from 0 to 0.1 for co-rotating (prograde) spinning
halos and one counter-rotating (retrograde) halo spin ($\lambda$=-0.1) with
respect to the disk. We report that as the halo spin increases, the buckling is
also triggered earlier and is followed by a second buckling phase in high-spin
halo models. The timescale for the second buckling is significantly longer than
the first buckling. We find that bar strength does not reduce significantly
after the buckling in all of our models, which provides new insights about the
role of inner halo angular momentum, unlike previous studies. Also, the buckled
bar can still transfer significant angular momentum to the halo in the secular
evolution phase, but it reduces with increasing halo spin. In the secular
evolution phase, the bar strength increases and saturates to nearly equal
values for all the models irrespective of halo spin and the sense of rotation
with respect to the disk. The final boxy/peanut shape is more pronounced
($\sim$20 $\%$) in high spin halos having higher angular momentum in the inner
region compared to non-rotating halos. We explain our results with angular
momentum exchanges between the disk and halo.",2210.14526v1
2023-08-05,Optical vortex harmonic generation facilitated by photonic spin-orbit entanglement,"Photons can undergo spin-orbit coupling, by which the polarization (spin) and
spatial profile (orbit) of the electromagnetic field interact and mix. Strong
photonic spin-orbit coupling may reportedly arise from light propagation
confined in a small cross-section, where the optical modes feature spin-orbit
entanglement. However, while photonic Hamiltonians generally exhibit
nonlinearity, the role and implication of spin-orbit entanglement in nonlinear
optics have received little attention and are still elusive. Here, we report
the first experimental demonstration of nonlinear optical frequency conversion,
where spin-orbit entanglement facilitates spin-to-orbit transfer among
different optical frequencies. By pumping a multimode optical nanofiber with a
spin-polarized Gaussian pump beam, we produce an optical vortex at the third
harmonic, which has long been regarded as a forbidden process in isotropic
media. Our findings offer a unique and powerful means for efficient optical
vortex generation that only incorporates a single Gaussian pump beam, in sharp
contrast to any other approaches employing structured pump fields or
sophisticatedly designed media. Our work opens up new possibilities of
spin-orbit-coupling subwavelength waveguides, inspiring fundamental studies of
nonlinear optics involving various types of structured light, as well as paving
the way for the realization of hybrid quantum systems comprised of telecom
photonic networks and long-lived quantum memories.",2308.02911v1
2024-02-14,Giant asymmetric proximity-induced spin-orbit coupling in twisted graphene/SnTe heterostructure,"We analyze the spin-orbit coupling effects in a three-degree twisted bilayer
heterostructure made of graphene and an in-plane ferroelectric SnTe, with the
goal of transferring the spin-orbit coupling from SnTe to graphene, via the
proximity effect. Our results indicate that the point-symmetry breaking due to
the incompatible mutual symmetry of the twisted monolayers and a strong
hybridization has a massive impact on the spin splitting in graphene close to
the Dirac point, with the spin splitting values greater than 20 meV. The band
structure and spin expectation values of graphene close to the Dirac point can
be described using a symmetry-free model, triggering different types of
interaction with respect to the threefold symmetric graphene/transition-metal
dichalcogenide heterostructure. We show that the strong hybridization of the
Dirac cone's right movers with the SnTe band gives rise to a large asymmetric
spin splitting in the momentum space. Furthermore, we discover that the
ferroelectricity-induced Rashba spin-orbit coupling in graphene is the dominant
contribution to the overall Rashba field, with the effective in-plane electric
field that is almost aligned with the (in-plane) ferroelectricity direction of
the SnTe monolayer. We also predict an anisotropy of the in-plane spin
relaxation rates. Our results demonstrate that the group-IV monochalcogenides
MX (M=Sn, Ge; X=S, Se, Te) are a viable alternative to transition-metal
dichalcogenides for inducing strong spin-orbit coupling in graphene.",2402.09045v1
2010-07-28,A torque formula for non-isothermal Type I planetary migration - II. Effects of diffusion,"We study the effects of diffusion on the non-linear corotation torque, or
horseshoe drag, in the two-dimensional limit, focusing on low-mass planets for
which the width of the horseshoe region is much smaller than the scale height
of the disc. In the absence of diffusion, the non-linear corotation torque
saturates, leaving only the Lindblad torque. Diffusion of heat and momentum can
act to sustain the corotation torque. In the limit of very strong diffusion,
the linear corotation torque is recovered. For the case of thermal diffusion,
this limit corresponds to having a locally isothermal equation of state. We
present some simple models that are able to capture the dependence of the
torque on diffusive processes to within 20% of the numerical simulations.",1007.4964v1
2012-03-15,Recent developments in planet migration theory,"Planetary migration is the process by which a forming planet undergoes a
drift of its semi-major axis caused by the tidal interaction with its parent
protoplanetary disc. One of the key quantities to assess the migration of
embedded planets is the tidal torque between the disc and planet, which has two
components: the Lindblad torque and the corotation torque. We review the latest
results on both torque components for planets on circular orbits, with a
special emphasis on the various processes that give rise to additional, large
components of the corotation torque, and those contributing to the saturation
of this torque. These additional components of the corotation torque could help
address the shortcomings that have recently been exposed by models of planet
population syntheses. We also review recent results concerning the migration of
giant planets that carve gaps in the disc (type II migration) and the migration
of sub-giant planets that open partial gaps in massive discs (type III
migration).",1203.3294v1
2014-04-14,Effect of the number of vortices on the torque scaling in Taylor-Couette flow,"Torque measurements in Taylor-Couette flow, with large radius ratio and large
aspect ratio, over a range of velocities up to a Reynolds number of 24 000 are
presented. Following a specific procedure, nine states with distinct number of
vortices along the axis were found and the aspect ratio of the vortices were
measured. The relationship between the speed and the torque for a given number
of vortices is reported. In the turbulent Taylor vortex flow regime, at
relatively high Reynolds number, a change in behaviour is observed
corresponding to intersections of the torque-speed curves for different states.
Before each intersection, the torque for a state with larger number of vortices
is higher. After each intersection, the torque for a state with larger number
of vortices is lower. The exponent, from the scaling laws of the torque, always
depends on the aspect ratio of the vortices. When the Reynolds number is
rescaled using the mean aspect ratio of the vortices, only a partial collapse
of the exponent data is found.",1404.3505v1
2014-12-27,Halting Migration: Numerical Calculations of Corotation Torques in the Weakly Nonlinear Regime,"Planets in their formative years can migrate due to the influence of
gravitational torques in the protoplanetary disk they inhabit. For low-mass
planets in an isothermal disk, it is known that there is a strong negative
torque on the planet due to its linear perturbation to the disk, causing fast
inward migration. The current investigation demonstrates that in these same
isothermal disks, for intermediate-mass planets, there is a strong positive
nonlinear corotation torque due to the effects of gas being pulled through a
gap on horseshoe orbits. For intermediate-mass planets, this positive torque
can partially or completely cancel the linear (Type I) torque, leading to
slower or outward migration, even in an isothermal disk. The effect is most
significant for Super-Earth and Sub-Jovian planets, during the transition from
a low-mass linear perturber to a non-linear gap-opening planet, when the planet
has opened a so-called 'partial gap'. In this study, numerical calculations of
planet-disk interactions calculate these torques explicitly, and scalings are
empirically constructed for migration rates in this weakly nonlinear regime.
These results find outward migration is possible for planets with masses in the
20 - 100 Earth Mass range.",1412.8092v2
2015-01-20,Numerical Estimation of Frictional Torques with Rate and State Friction,"In this paper, numerical estimation of frictional torques is carried out of a
rotary elastic disc on a hard and rough surface under different rotating
conditions. A one dimensional spring- mass rotary system is numerically solved
under the quasistatic condition with the rate and state dependent friction
model. It is established that torque of frictional strength as well as torque
of steady dynamic stress increases with radius and found to be maximum at the
periphery of the disc. Torque corresponding to frictional strength estimated
using the analytical solution matches closely with the simulation only in the
case of high stiffness of the connecting spring. In steady relaxation
simulation, a steadily rotating disc is suddenly stopped and relaxational
angular velocity and corresponding frictional torque decreases with both steady
angular velocity and stiffness of the connecting spring in the velocity
strengthening regime. In velocity weakening regime, in contrast, torque of
relaxation stress deceases but relaxation velocity increases. The reason for
the contradiction is explained.",1502.01302v1
2016-02-01,Torque-Induced Rotational Dynamics in Polymers: Torsional Blobs and Thinning,"By using the blob theory and computer simulations, we investigate the
properties of a linear polymer performing a stationary rotational motion around
a long impenetrable rod. In particular, in the simulations the rotation is
induced by a torque applied to the end of the polymer that is tethered to the
rod. Three different regimes are found, in close analogy with the case of
polymers pulled by a constant force at one end. For low torques the polymer
rotates maintaining its equilibrium conformation. At intermediate torques the
polymer assumes a trumpet shape, being composed by blobs of increasing size. At
even larger torques the polymer is partially wrapped around the rod. We derive
several scaling relations between various quantities as angular velocity,
elongation and torque. The analytical predictions match the simulation data
well. Interestingly, we find a ""thinning"" regime where the torque has a very
weak (logarithmic) dependence on the angular velocity. We discuss the origin of
this behavior, which has no counterpart in polymers pulled by an applied force.",1602.00551v1
2016-02-03,Non-ideal torque control of wind turbine systems: Impacts on annual energy production,"We discuss non-ideal torque control in wind turbine systems (WTS). Most
high-level controllers generate a reference torque which is then send to the
underlying electrical drive system (generator+inverter) of the WTS to steer the
turbine/generator to its optimal operation point (depending on the wind speed).
The energy production heavily depends on the mechanical power (i.e. the product
of rotational speed and generator torque). However, since torque sensors in the
MW range are not available or extremely expensive, the torque controllers are
implemented as feedforward controllers and, therefore, are inherently sensitive
to parameter variations/uncertainties. Based on real wind data and a dynamical
WTS model, we discuss causes and impacts of non-ideal (feedforward) torque
control on the energy production and the gross earnings.",1602.01225v1
2019-03-13,On the opposing roles of the Boussinesq and non-Boussinesq baroclinic torques in surface gravity wave propagation,"Here we suggest an alternative understanding of the surface gravity wave
propagation mechanism based on the baroclinic torque, which operates to
translate the interfacial vorticity anomalies at the air-water interface. We
demonstrate how the non-Boussinesq term of the baroclinic torque acts against
the Boussinesq one to hinder wave propagation. By standard vorticity inversion
and mirror imaging, we then show how the existence of the bottom boundary
affects the two types of torque. Since the opposing non-Boussinesq torque
results solely from the mirror image, it vanishes in the deep water limit and
its magnitude is half of the Boussinesq torque in the shallow water limit. This
reveals that Boussinesq approximation is valid in the deep water limit, even
though the density contrast between air and water is large. The mechanistic
roles, played by the Boussinesq and non-Boussinesq parts of the baroclinic
torque, remain obscured in the standard derivation where the time-dependent
Bernoulli equation is implemented instead of the interfacial vorticity
equation. Finally, we note on passing that the Virial theorem for surface
gravity waves can be obtained solely from considerations of the dynamics at the
air-water interface.",1903.05518v2
2019-12-30,Acoustic radiation torque exerted on a subwavelength spheroidal particle by a traveling and standing plane wave,"The nonlinear interaction of ultrasonic waves with a nonspherical particle
may give rise to the acoustic radiation torque on the particle. This phenomenon
is investigated here considering a rigid prolate spheroidal particle of
subwavelength dimensions that is much smaller than the wavelength. Using the
partial wave expansion in spheroidal coordinates, the radiation torque of a
traveling and standing plane wave with arbitrary orientation is exactly derived
in the dipole approximation. We obtain asymptotic expressions of the torque as
the particle geometry approaches a sphere and a straight line. As the particle
is trapped in a pressure node of a standing plane wave, its radiation torque
equals that of a traveling plane wave. We also find how the torque changes with
the particle aspect ratio. Our findings are in excellent agreement with
previous numerical computations. Also, by analyzing the torque potential
energy, we determine the stable and unstable spatial configuration available
for a particle.",1912.12933v1
2022-02-25,On the Use of Torque Measurement in Centroidal State Estimation,"State of the art legged robots are either capable of measuring torque at the
output of their drive systems, or have transparent drive systems which enable
the computation of joint torques from motor currents. In either case, this
sensor modality is seldom used in state estimation. In this paper, we propose
to use joint torque measurements to estimate the centroidal states of legged
robots. To do so, we project the whole-body dynamics of a legged robot into the
nullspace of the contact constraints, allowing expression of the dynamics
independent of the contact forces. Using the constrained dynamics and the
centroidal momentum matrix, we are able to directly relate joint torques and
centroidal states dynamics. Using the resulting model as the process model of
an Extended Kalman Filter (EKF), we fuse the torque measurement in the
centroidal state estimation problem. Through real-world experiments on a
quadruped robot with different gaits, we demonstrate that the estimated
centroidal states from our torque-based EKF drastically improve the recovery of
these quantities compared to direct computation.",2202.12574v3
2022-09-12,Effects of Radiative Diffusion on the Dynamical Corotation Torque in Three-Dimensional Protoplanetary Disks,"The dynamical corotation torque arising from the deformation of the horseshoe
orbits, along with the vortensity gradient in the background disk, is important
for determining orbital migration rate and direction of low-mass planets.
Previous two-dimensional studies predicted that the dynamical corotation torque
is positive, decelerating the inward planet migration. In contrast, recent
three-dimensional studies have shown that buoyancy resonance makes the
dynamical corotation torque negative, accelerating the inward migration. In
this paper, we study the dependence of the dynamical corotation torque on the
thermal transport using three-dimensional simulations. We first show that our
results are consistent with previous three-dimensional studies when the disk is
fully adiabatic. In more realistic radiative disks, however, radiative
diffusion suppresses the buoyancy resonance significantly, especially at
high-altitude regions, and yields a positive dynamical corotation torque. This
alleviates the issue of a rapid migration caused by the negative dynamical
corotation torque in the adiabatic disks. Our results suggest that radiative
diffusion together with stellar irradiation and accretion heating is needed to
accurately describe the migration of low-mass planets.",2209.05417v1
2024-02-28,UKF-Based Sensor Fusion for Joint-Torque Sensorless Humanoid Robots,"This paper proposes a novel sensor fusion based on Unscented Kalman Filtering
for the online estimation of joint-torques of humanoid robots without
joint-torque sensors. At the feature level, the proposed approach considers
multimodal measurements (e.g. currents, accelerations, etc.) and non-directly
measurable effects, such as external contacts, thus leading to joint torques
readily usable in control architectures for human-robot interaction. The
proposed sensor fusion can also integrate distributed, non-collocated
force/torque sensors, thus being a flexible framework with respect to the
underlying robot sensor suit. To validate the approach, we show how the
proposed sensor fusion can be integrated into a twolevel torque control
architecture aiming at task-space torquecontrol. The performances of the
proposed approach are shown through extensive tests on the new humanoid robot
ergoCub, currently being developed at Istituto Italiano di Tecnologia. We also
compare our strategy with the existing state-of-theart approach based on the
recursive Newton-Euler algorithm. Results demonstrate that our method achieves
low root mean square errors in torque tracking, ranging from 0.05 Nm to 2.5 Nm,
even in the presence of external contacts.",2402.18380v1
2007-04-05,Spin Evolution of Accreting Neutron Stars: Nonlinear Development of the R-mode Instability,"The nonlinear saturation of the r-mode instability and its effects on the
spin evolution of Low Mass X-ray Binaries (LMXBs) are modeled using the triplet
of modes at the lowest parametric instability threshold. We solve numerically
the coupled equations for the three mode amplitudes in conjunction with the
spin and temperature evolution equations. We observe that very quickly the mode
amplitudes settle into quasi-stationary states. Once these states are reached,
the mode amplitudes can be found algebraically and the system of equations is
reduced from eight to two equations: spin and temperature evolution.
Eventually, the system may reach thermal equilibrium and either (1) undergo a
cyclic evolution with a frequency change of at most 10%, (2) evolve toward a
full equilibrium state in which the accretion torque balances the gravitational
radiation emission, or (3) enter a thermogravitational runaway on a very long
timescale of about $10^6$ years. Alternatively, a faster thermal runaway
(timescale of about 100 years) may occur. The sources of damping considered are
shear viscosity, hyperon bulk viscosity and boundary layer viscosity. We vary
proprieties of the star such as the hyperon superfluid transition temperature
T_c, the fraction of the star that is above the threshold for direct URCA
reactions, and slippage factor, and map the different scenarios we obtain to
ranges of these parameters. For all our bound evolutions the r-mode amplitude
remains small $\sim 10^{-5}$. The spin frequency is limited by boundary layer
viscosity to $\nu_{max} \sim 800 Hz [S_{ns}/(M_{1.4} R_6)]^{4/11} T_8^{-2/11}$.
We find that for $\nu > 700$ Hz the r-mode instability would be active for
about 1 in 1000 LMXBs and that only the gravitational waves from LMXBs in the
local group of galaxies could be detected by advanced LIGO interferometers.",0704.0799v3
2007-05-07,X-ray Timing of PSR J1852+0040 in Kesteven 79: Evidence of Neutron Stars Weakly Magnetized at Birth,"The 105-ms X-ray pulsar J1852+0040 is the central compact object (CCO) in SNR
Kes 79. We report a sensitive upper limit on its radio flux density of 12 uJy
at 2 GHz using the NRAO GBT. Timing using XMM and Chandra over a 2.4 yr span
reveals no significant change in its spin period. The 2 sigma upper limit on
the period derivative leads, in the dipole spin-down formalism, to an energy
loss rate E-dot < 7e33 ergs/s, surface magnetic field strength B_p < 1.5e11 G,
and characteristic age tau_c = P/2P-dot > 8 Myr. This tau_c exceeds the age of
the SNR by 3 orders of magnitude, implying that the pulsar was born spinning at
its current period. However, the X-ray luminosity of PSR J1852+0040, L(bol) ~
3e33(d/7.1 kpc)^2 ergs/s is a large fraction of E-dot, which challenges the
rotation-powered assumption. Instead, its high blackbody temperature,
0.46+/-0.04 keV, small blackbody radius ~ 0.8 km, and large pulsed fraction, ~
80%, may be evidence of accretion onto a polar cap, possibly from a fallback
disk made of supernova debris. If B_p < 1e10 G, an accretion disk can penetrate
the light cylinder and interact with the magnetosphere while resulting torques
on the neutron star remain within the observed limits. A weak B-field is also
inferred in another CCO, the 424-ms pulsar 1E 1207.4-5209, from its steady spin
and soft X-ray absorption lines. We propose this origin of radio-quiet CCOs:
the B-field, derived from a turbulent dynamo, is weaker if the NS is formed
spinning slowly, which enables it to accrete SN debris. Accretion excludes
neutron stars born with both B_p < 1e11 G and P > 0.1 s from radio pulsar
surveys, where B_p < 1e11 G is not encountered except among very old (tau_c >
40 Myr) or recycled pulsars. Finally, such a CCO, if born in SN 1987A, could
explain the non-detection of a pulsar there.",0705.0978v1
2010-11-26,On the Intrinsic Alignments of the Late-Type Spiral Galaxies from the Sloan Digital Sky Survey Data Release 7,"A robust detection of the tidally induced intrinsic alignments of the
late-type spiral galaxies with high statistical significance is reported. From
the spectroscopic galaxy sample of SDSS DR7 compiled by Huertas-Company et al.
which lists each galaxy's probabilities of being in five Hubble types,
P(E),P(Ell), P(S0),P(Sab), P(Scd), we select the nearby large late-type spiral
galaxies which have redshifts of 0<=z<=0.02, probabilities of P(Scd)>=0.5 and
angular sizes of D>=7.92 arcsec. The spin axes of the selected nearby large
late-type spiral galaxies are determined up to the two-fold ambiguity with the
help of the circular thin-disk approximation and their spatial correlations are
measured as a function of the separation distance r. A clear signal of the
intrinsic correlation as high as 3.4 sigma and 2.4 sigma is found at the
separation distance of r~1Mpc/h and r~2Mpc/h, respectively. The comparison of
this observational results with the analytic model based on the tidal torque
theory reveals that the spin correlation function for the late-type spiral
galaxies follow the quadratic scaling of the linear density correlation and
that the intrinsic correlations of the galaxy spin axes are stronger than that
of the underlying dark halos. We investigate a local density dependence of the
galaxy spin correlations and found that the correlations are stronger for the
galaxies located in dense regions having more than 10 neighbors within 2Mpc/h.
We also attempt to measure a luminosity dependence of the galaxy spin
correlations, but find that it is impossible with our magnitude-split samples
to disentangle a luminosity from a redshift dependence. We provide the physical
explanations for these observational results and also discuss the effects of
possible residual systematics on the results.",1011.5755v2
2015-01-21,Circularization of Tidally Disrupted Stars around Spinning Supermassive Black Holes,"We study the circularization of tidally disrupted stars on bound orbits
around spinning supermassive black holes by performing three-dimensional
smoothed particle hydrodynamic simulations with Post-Newtonian corrections. Our
simulations reveal that debris circularization depends sensitively on the
efficiency of radiative cooling. There are two stages in debris circularization
if radiative cooling is inefficient: first, the stellar debris streams
self-intersect due to relativistic apsidal precession; shocks at the
intersection points thermalize orbital energy and the debris forms a
geometrically thick, ring-like structure around the black hole. The ring
rapidly spreads via viscous diffusion, leading to the formation of a
geometrically thick accretion disk. In contrast, if radiative cooling is
efficient, the stellar debris circularizes due to self-intersection shocks and
forms a geometrically thin ring-like structure. In this case, the dissipated
energy can be emitted during debris circularization as a precursor to the
subsequent tidal disruption flare. The possible radiated energy is up to
~2*10^{52} erg for a 1 Msun star orbiting a 10^6 Msun black hole. We also find
that a retrograde (prograde) black hole spin causes the shock-induced
circularization timescale to be shorter (longer) than that of a non-spinning
black hole in both cooling cases. The circularization timescale is remarkably
long in the radiatively efficient cooling case, and is also sensitive to black
hole spin. Specifically, Lense-Thirring torques cause dynamically important
nodal precession, which significantly delays debris circularization. On the
other hand, nodal precession is too slow to produce observable signatures in
the radiatively inefficient case. We also discuss the relationship between our
simulations and the parabolic TDEs that are characteristic of most stellar
tidal disruptions.",1501.05207v2
2015-09-29,The dependence of stellar mass and angular momentum losses on latitude and on active region and dipolar magnetic fields,"Rotation evolution of late-type stars is dominated by magnetic braking and
the underlying factors that control this angular momentum loss are important
for the study of stellar spin-down. In this work, we study angular momentum
loss as a function of two different aspects of magnetic activity using a
calibrated Alfv\'en wave-driven magnetohydrodynamic wind model: the strengths
of magnetic spots and their distribution in latitude. By driving the model
using solar and modified solar surface magnetograms, we show that the topology
of the field arising from the net interaction of both small-scale and
large-scale field is important for spin-down rates and that angular momentum
loss is not a simple function of large scale magnetic field strength. We find
that changing the latitude of magnetic spots can modify mass and angular
momentum loss rates by a factor of two. The general effect that causes these
differences is the closing down of large-scale open field at mid- and
high-latitudes by the addition of the small-scale field. These effects might
give rise to modulation of mass and angular momentum loss through stellar
cycles, and present a problem for ab initio attempts to predict stellar
spin-down based on wind models. For all the magnetogram cases considered here,
from dipoles to various spotted distributions, we find that angular momentum
loss is dominated by the mass loss at mid-latitudes. The spin-down torque
applied by magnetized winds therefore acts at specific latitudes and is not
evenly distributed over the stellar surface, though this aspect is unlikely to
be important for understanding spin-down and surface flows on stars.",1509.08936v1
2016-10-04,Gravitomagnetic dynamical friction,"A supermassive black hole moving through a field of stars will
gravitationally scatter the stars, inducing a backreaction force on the black
hole known as dynamical friction. In Newtonian gravity, the axisymmetry of the
system about the black hole's velocity $\mathbf{v}$ implies that the dynamical
friction must be anti-parallel to $\mathbf{v}$. However, in general relativity
the black hole's spin $\mathbf{S}$ need not be parallel to $\mathbf{v}$,
breaking the axisymmetry of the system and generating a new component of
dynamical friction similar to the Lorentz force $\mathbf{F} = q\mathbf{v}
\times \mathbf{B}$ experienced by a particle with charge $q$ moving in a
magnetic field $\mathbf{B}$. We call this new force gravitomagnetic dynamical
friction and calculate its magnitude for a spinning black hole moving through a
field of stars with Maxwellian velocity dispersion $\sigma$, assuming that both
$v$ and $\sigma$ are much less than the speed of light $c$. We use
post-Newtonian equations of motion accurate to $\mathcal{O}(v^3/c^3)$ needed to
capture the effect of spin-orbit coupling and also include direct stellar
capture by the black hole's event horizon. Gravitomagnetic dynamical friction
will cause a black hole with uniform speed to spiral about the direction of its
spin, similar to a charged particle spiraling about a magnetic field line, and
will exert a torque on a supermassive black hole orbiting a galactic center,
causing the angular momentum of this orbit to slowly precess about the
black-hole spin. As this effect is suppressed by a factor $(\sigma/c)^2$ in
nonrelativistic systems, we expect it to be negligible in most astrophysical
contexts but provide this calculation for its theoretical interest and
potential application to relativistic systems.",1610.01590v2
2017-10-17,Accretion-induced spin-wandering effects on the neutron star in Scorpius X-1: Implications for continuous gravitational wave searches,"The LIGO's discovery of binary black hole mergers has opened up a new era of
transient gravitational wave astronomy. The potential detection of
gravitational radiation from another class of astronomical objects, rapidly
spinning non-axisymmetric neutron stars, would constitute a new area of
gravitational wave astronomy. Scorpius X-1 (Sco X-1) is one of the most
promising sources of continuous gravitational radiation to be detected with
present-generation ground-based gravitational wave detectors, such as Advanced
LIGO and Advanced Virgo. As the sensitivity of these detectors improve in the
coming years, so will power of the search algorithms being used to find
gravitational wave signals. Those searches will still require integation over
nearly year long observational spans to detect the incredibly weak signals from
rotating neutron stars. For low mass X-ray binaries such as Sco X-1 this
difficult task is compounded by neutron star ""spin wandering"" caused by
stochastic accretion fluctuations. In this paper, we analyze X-ray data from
the RXTE satellite to infer the fluctuating torque on the neutron star in Sco
X-1. We then perform a large-scale simulation to quantify the statistical
properties of spin-wandering effects on the gravitational wave signal frequency
and phase evolution. We find that there are a broad range of expected maximum
levels of frequency wandering corresponding to maximum drifts of between 0.3-50
{\mu}Hz/sec over a year at 99% confidence. These results can be cast in terms
of the maximum allowed length of a coherent signal model neglecting
spin-wandering effects as ranging between 5-80 days. This study is designed to
guide the development and evaluation of Sco X-1 search algorithms.",1710.06185v1
2019-06-12,A self-consistent weak friction model for the tidal evolution of circumbinary planets,"We present a self-consistent model for the tidal evolution of circumbinary
planets. Based on the weak-friction model, we derive expressions of the
resulting forces and torques considering complete tidal interactions between
all the bodies of the system. Although the tidal deformation suffered by each
extended mass must take into account the combined gravitational effects of the
other two bodies, the only tidal forces that have a net effect on the dynamic
are those that are applied on the same body that exerts the deformation, as
long as no mean-motion resonance exists between the masses. We apply the model
to the Kepler-38 binary system. The evolution of the spin equations shows that
the planet reaches a stationary solution much faster than the stars, and the
equilibrium spin frequency is sub-synchronous. The binary components evolve on
a longer timescale, reaching a super-synchronous solution very close to that
derived for the 2-body problem. After reaching spin stationarity, the
eccentricity is damped in all bodies and for all the parameters analyzed here.
A similar effect is noted for the binary separation. The semimajor axis of the
planet, on the other hand, may migrate inwards or outwards, depending on the
masses and orbital parameters. In some cases the secular evolution of the
system may also exhibit an alignment of the pericenters, requiring to include
additional terms in the tidal model. Finally, we derived analytical expressions
for the variational equations of the orbital evolution and spin rates based on
low-order elliptical expansions in the semimajor axis ratio and the
eccentricities. These are found to reduce to the 2-body case when one of the
masses is taken equal to zero. This model allow us to find a close and simple
analytical expression for the stationary spin rates of all the bodies, as well
as predicting the direction and magnitude of the orbital migration.",1906.05195v1
2019-08-29,Pushing down the lateral dimension of single and coupled magnetic dots to the nanometric scale: characteristics and evolution of the spin-wave eigenmodes,"Planar magnetic nanoelements, either single- or multi-layered, are exploited
in a variety of current or forthcoming spintronic and/or ICT devices, such as
read heads, magnetic memory cells, spin-torque nano-oscillators, nanomagnetic
logic circuits, magnonic crystals and artificial spin-ices. The lateral
dimensions of the elemental magnetic components have been squeezed down during
the last decade to a few tens of nanometers, but they are still an order of
magnitude larger that the exchange correlation length of the constituent
materials. This means that the spectrum of spin-wave eigenmodes, occurring in
the GHz range, is relatively complex and cannot be described within a simple
macrospin approximation. On the other hand, a detailed knowledge of the
dynamical spectrum is needed to understand or to predict crucial
characteristics of the devices. With this focused review we aim at the analysis
and the rationalization of the characteristics of the eigenmodes spectrum of
magnetic nanodots, paying special attention to the following key points: (i)
Consider and compare the case of in-plane and out of-plane orientation of the
magnetization, as well as of single- and multi-layered dots, putting in
evidence similarities and diversities, and proposing a unifying nomenclature
and labelling scheme; (ii) Underline the evolution of the spectrum when the
lateral size of magnetic dots is squeezed down from hundreds to tens of
nanometers, as in current devices, with emphasis given to the occurrence of
soft modes and to the change of spatial localization of the fundamental mode
for in-plane magnetized dots; (iii) Extend the analysis from isolated elements
to twins of dots, as well as to dense arrays of dipolarly interacting dots,
showing how the discretized eigenmodes distinctive of the single element
transform in finite-width frequency bands of spin waves propagating through the
array.",1908.11098v1
2020-10-29,Magnetoresistance oscillation study of the half-quantum vortex in doubly connected mesoscopic superconducting cylinders of Sr2RuO4,"The observation of the highly unusual half-quantum vortex (HQV) in a single
crystalline superconductor excludes unequivocally the spin-singlet symmetry of
the superconducting order parameter. HQVs were observed previously in
mesoscopic samples of Sr2RuO4 in cantilever torque magnetometry measurements,
thus providing direct evidence for spin-triplet pairing in the material. In
addition, it raised important questions on HQV, including its stability and
dynamics. These issues have remained largely unexplored, in particular,
experimentally. We report in this paper the detection of HQVs in mesoscopic,
doubly connected cylinders of single-crystalline Sr2RuO4 of a mesoscopic size
and the examination of the effect of the in-plane magnetic field needed for the
observation of the HQV by magnetoresistance (MR) oscillations measurements.
Several distinct features found in our data, especially a dip and secondary
peaks in the MR oscillations seen only in the presence of a sufficiently large
in-plane magnetic field as well as a large measurement current, are linked to
the formation of the HQV fluxoid state in and crossing of an Abrikosov HQV
through the sample. The conclusion is drawn from the analysis of our data using
a model of thermally activated vortex crossing overcoming a free-energy barrier
which is modulated by the applied magnetic flux enclosed in the cylinder as
well as the measurement current. Evidence for the trapping of an HQV fluxoid
state in the sample was also found. Our observation of the HQV in mesoscopic
Sr2RuO4 provided not only additional evidence for spin-triplet
superconductivity in Sr2RuO4 but also insights into the physics of HQV,
including its spontaneous spin polarization, stability, and dynamics. Our study
also revealed a possible effect of the measurement current on the magnitude of
the spontaneous spin polarization associated with the HQV.",2010.15800v1
2022-10-11,Accurate computations up to break-down of quasi-periodic attractors in the dissipative spin-orbit problem,"We consider a Celestial Mechanics model: the spin-orbit problem with a
dissipative tidal torque, which is a singular perturbation of a conservative
system. The goal of this paper is to show that it is possible to compute
quasi-periodic attractors accurately and reliably for parameter values
extremely close to the breakdown. Therefore, it is possible to obtain
information on mathematical phenomena at breakdown. The method we use
incorporates the same time numerical and rigorous improvements. Among them (i)
the formalism is based on studying the time-one map of the spin-orbit problem
(which reduces the dimensionality of the problem) and has mathematical
advantages; (ii) very accurate integration of the ODE (high order Taylor
methods implemented with extended precision) for the map at its jets; (iii) a
very efficient KAM method for maps which computes the attractor and its tangent
spaces ( quadratically convergent step with low storage requirements, and low
operation count); (iv) the algorithms are backed by a rigorous a-posteriori KAM
Theorem, which establishes that if the algorithm, produces a very approximate
solution of functional equation with reasonable condition numbers. then there
is a true solution nearby; and (v) the continuation algorithm is guaranteed to
reach arbitrarily close to the border of existence if it is given enough
computer resources. As a byproduct of the accuracy that we maintain till
breakdown, we study several scale invariant observables of the tori used in the
renormalization group of infinite dimensional spaces. In contrast with
previously studied simple models, the behavior at breakdown of the spin-orbit
problem does not satisfy standard scaling relations which implies that the
spin-orbit problem is not described by a hyperbolic fixed point of a
renormalization operator.",2210.05796v2
2022-11-08,Stellar Bars in Spinning Halos: Delayed Buckling and Absence of Slowdown,"We use high resolution numerical simulations in order to analyze the stellar
bar evolution in spinning dark matter (DM) halos. Previous works have shown
that the halo spin has a substantial effect on the bar evolution and can lead
to bar dissolution following the vertical buckling instability. Here, we invoke
the DM spin sequence, $\lambda=0-0.09$, and study the effect of DM density
along this $\lambda$-sequence by varying the compactness of DM halo. We find
that (1) varying the DM density has a profound effect on the stellar bar
evolution along the $\lambda$-sequence, namely, on its amplitude, pattern
speed, buckling time, etc.; (2) For $\lambda\gtrsim 0.04$, the buckling
instability has been delayed progressively, and does not occur when the bar has
reached its maximal strength; (3) Instead, stellar bars remain near maximal
strength, and their amplitude plateau stage extends over $\sim 1-7$ Gyr,
terminating with the buckling instability; (4) Although stellar bars remain
strong during the plateau, their pattern speed stays nearly constant. The
reason for this unusual behavior of stellar bars follows from the highly
reduced gravitational torques which they experience due to the DM bar being
aligned with the stellar bar. The performed orbital analysis shows that the
delayed buckling results from a slow evolution of stellar oscillations along
the bar major and vertical axes -- thus postponing the action of the vertical
2:1 resonance which pumps the rotational energy into vertical motions; (5)
Peanut/boxy shaped bulges form at the beginning of the plateau and grow with
time; (6) Strong stellar bars in spinning halos can avoid fast braking,
resolving the long standing discrepancy between observations and $N$-body
simulations. This behavior of stellar bars along the $\lambda$- and DM
density-sequences, reveals a wealth of stellar bar properties which require
additional study.",2211.04484v2
2013-07-11,Experimental observation of a large ac-spin Hall effect,"In spinelectronics the spin degree of freedom is used to transmit and store
information. Ideally this occurs without net charge currents in order to avoid
energy dissipation due to Joule heating. To this end the ability to create pure
spin currents i.e.without net charge transfer is essential. Spin pumping is the
most popular approach to generate pure spin currents in metals, semiconductors,
graphene, and even organic materials. When the magnetization vector in a
ferromagnet (FM) - normal metal (NM) junction is excited the spin pumping
effect leads to the injection of pure spin currents in the normal metal. The
polarization of this spin current is time dependent and contains a very small
dc component. The dc-component of the injected spin current has been intensely
studied in recent years and has given rise to controversial discussions
concerning the magnitude the spin Hall angle which is a material dependent
measure of the efficiency of spin to charge conversion . However in contrast to
the rather well understood dc component the two orders of magnitude larger ac
component has escaped experimental detection so far. Here we show that the
large ac component of the spin currents can be detected very efficiently using
the inverse spin Hall effect (ISHE). The observed ac-ISHE voltages are one
order of magnitude larger than the conventional dc-ISHE measured on the same
device. The spectral shape, angular dependence, power scaling behavior and
absolute magnitude of the signals are in line with spin pumping and ISHE
effects. Our results demonstrate that FM-NM junctions are very efficient
sources of pure spin currents in the GHz frequency range and we believe that
our result will stimulate the emerging field of ac spintronics.",1307.2961v3
1999-08-08,Physical Mechanisms for the Variable Spin-down of SGR 1900+14,"We consider the physical implications of the rapid spindown of Soft Gamma
Repeater 1900+14, and of the apparent ""braking glitch"", \Delta P/P = l x 10^-4,
that was concurrent with the Aug. 27th giant flare. A radiation-hydrodynamical
outflow associated with the flare could impart the required torque, but only if
the dipole magnetic field is stronger than ~ 10^14 G and the outflow lasts
longer and/or is more energetic than the observed X-ray flare. A positive
period increment is also a natural consequence of a gradual, plastic
deformation of the neutron star crust by an intense magnetic field, which
forces the neutron superfluid to rotate more slowly than the crust. Sudden
unpinning of the neutron vortex lines during the August 27th event would then
induce a glitch opposite in sign to those observed in young pulsars, but of a
much larger magnitude as a result of the slower rotation.
  The change in the persistent X-ray lightcurve following the August 27 event
is ascribed to continued particle heating in the active region of that
outburst. The enhanced X-ray output can be powered by a steady current flowing
through the magnetosphere, induced by the twisting motion of the crust. The
long term rate of spindown appears to be accelerated with respect to a simple
magnetic dipole torque. Accelerated spindown of a seismically-active magnetar
will occur when its persistent output of Alfven waves and particles exceeds its
spindown luminosity. We suggest that SGRs experience some episodes of relative
inactivity, with diminished spindown rates, and that such inactive magnetars
are observed as Anomalous X-ray Pulsars (AXPs). The rapid reappearence of
persistent X-ray emission following August 27 flare gives evidence against
accretion-powered models.",9908086v1
2013-06-18,Wave-like warp propagation in circumbinary discs I. Analytic theory and numerical simulations,"In this paper we analyse the propagation of warps in protostellar
circumbinary discs. We use these systems as a test environment in which to
study warp propagation in the bending-wave regime, with the addition of an
external torque due to the binary gravitational potential. In particular, we
want to test the linear regime, for which an analytic theory has been
developed. In order to do so, we first compute analytically the steady state
shape of an inviscid disc subject to the binary torques. The steady state tilt
is a monotonically increasing function of radius. In the absence of viscosity,
the disc does not present any twist. Then, we compare the time-dependent
evolution of the warped disc calculated via the known linearised equations both
with the analytic solutions and with full 3D numerical simulations, which have
been performed with the PHANTOM SPH code using 2 million particles. We find a
good agreement both in the tilt and in the phase evolution for small
inclinations, even at very low viscosities. Moreover, we have verified that the
linearised equations are able to reproduce the diffusive behaviour when
{\alpha} > H/R, where {\alpha} is the disc viscosity parameter. Finally, we
have used the 3D simulations to explore the non-linear regime. We observe a
strongly non-linear behaviour, which leads to the breaking of the disc. Then,
the inner disc starts precessing with its own precessional frequency. This
behaviour has already been observed with numerical simulations in accretion
discs around spinning black holes. The evolution of circumstellar accretion
discs strongly depends on the warp evolution. Therefore the issue explored in
this paper could be of fundamental importance in order to understand the
evolution of accretion discs in crowded environments, when the gravitational
interaction with other stars is highly likely, and in multiple systems.",1306.4331v1
2013-08-27,Modeling quasar accretion disc temperature profiles,"Microlensing observations indicate that quasar accretion discs have
half-light radii larger than expected from standard theoretical predictions
based on quasar fluxes or black hole masses. Blackburne and colleagues have
also found a very weak wavelength dependence of these half-light radii. We
consider disc temperature profile models that might match these observations.
Nixon and colleagues have suggested that misaligned accretion discs around
spinning black holes will be disrupted at radii small enough for the
Lense-Thirring torque to overcome the disc's viscous torque. Gas in precessing
annuli torn off a disc will spread radially and intersect with the remaining
disc, heating the disc at potentially large radii. However, if the intersection
occurs at an angle of more than a degree or so, highly supersonic collisions
will shock-heat the gas to a Compton temperature of T~10^7 K, and the spectral
energy distributions (SEDs) of discs with such shock-heated regions are poor
fits to observations of quasar SEDs. Torn discs where heating occurs in
intermittent weak shocks that occur whenever the intersection angle reaches a
tenth of a degree pose less of a conflict with observations, but do not have
significantly larger half-light radii than standard discs. We also study two
phenomenological disc temperature profile models. We find that discs with a
temperature spike at relatively large radii and lowered temperatures at radii
inside the spike yield improved and acceptable fits to microlensing sizes in
most cases. Such temperature profiles could in principle occur in sub-Keplerian
discs partially supported by magnetic pressure. However, such discs overpredict
the fluxes from quasars studied with microlensing except in the limit of
negligible continuum emission from radii inside the temperature spike.",1308.6010v1
2015-04-22,Gravitational waves from Sco X-1: A comparison of search methods and prospects for detection with advanced detectors,"The low-mass X-ray binary Scorpius X-1 (Sco X-1) is potentially the most
luminous source of continuous gravitational-wave radiation for interferometers
such as LIGO and Virgo. For low-mass X-ray binaries this radiation would be
sustained by active accretion of matter from its binary companion. With the
Advanced Detector Era fast approaching, work is underway to develop an array of
robust tools for maximizing the science and detection potential of Sco X-1. We
describe the plans and progress of a project designed to compare the numerous
independent search algorithms currently available. We employ a mock-data
challenge in which the search pipelines are tested for their relative
proficiencies in parameter estimation, computational efficiency, robust- ness,
and most importantly, search sensitivity. The mock-data challenge data contains
an ensemble of 50 Scorpius X-1 (Sco X-1) type signals, simulated within a
frequency band of 50-1500 Hz. Simulated detector noise was generated assuming
the expected best strain sensitivity of Advanced LIGO and Advanced VIRGO ($4
\times 10^{-24}$ Hz$^{-1/2}$). A distribution of signal amplitudes was then
chosen so as to allow a useful comparison of search methodologies. A factor of
2 in strain separates the quietest detected signal, at $6.8 \times 10^{-26}$
strain, from the torque-balance limit at a spin frequency of 300 Hz, although
this limit could range from $1.2 \times 10^{-25}$ (25 Hz) to $2.2 \times
10^{-26}$ (750 Hz) depending on the unknown frequency of Sco X-1. With future
improvements to the search algorithms and using advanced detector data, our
expectations for probing below the theoretical torque-balance strain limit are
optimistic.",1504.05889v1
2015-08-10,A nonextensive view of the stellar braking indices,"The present work is based on a description for the angular mometum loss rate
due to magnetic braking for main-sequence stars on the relationship between
stellar rotation and age. In general, this loss rate denoted by $\mathrm
dJ/\mathrm dt$ depends on angular velocity $\Omega$ in the form $\mathrm
dJ/\mathrm dt\propto\Omega^{q}$, where $q$ is a parameter extracted from
nonextensive statistical mechanics. Already, in context of stellar rotation,
this parameter is greater than unity and it is directly related to the braking
index. For $q$ equal to unity, the scenario of saturation of the magnetic field
is recovered, otherwise $q$ indicates an unsaturated field. This new approach
have been proposed and investigated by de Freitas \& De Medeiros for
unsaturated field stars. In present work, we propose a nonextensive approach
for the stellar rotational evolution based on the Reiners \& Mohanthy model. In
this sense, we developed a nonextensive version of Reiners \& Mohanthy torque
and also compare this generalized version with the model proposed in de Freitas
\& De Medeiros based on the spin-down Kawaler torque for the main-sequence
stars with F and G spectral types. We use the same sample of $\sim16 000$ field
stars with rotational velocity $v \sin i$ limited in age and mass. As a result,
we show that the Kawaler and Reiners \& Mohanthy models exhibit strong
discrepancies, mainly in relation to the domain of validity of the entropic
index $q$. These discrepancies are mainly due to sensitivity on the stellar
radius. Finally, our results showed that modified Kawaler prescription is
compatible with a wider mass range, while the Reiners \& Mohanty model is
restricted to masses less than G6 stars.",1508.02237v1
2016-11-15,Atmospheric tides in Earth-like planets,"Atmospheric tides can strongly affect the rotational dynamics of planets. In
the family of Earth-like planets, such as Venus, this physical mechanism
coupled with solid tides makes the angular velocity evolve over long timescales
and determines the equilibrium configurations of their spin. Contrary to the
solid core, the atmosphere is submitted to both tidal gravitational potential
and insolation flux coming from the star. The complex response of the gas is
intrinsically linked to its physical properties. This dependence has to be
characterized and quantified to study the large variety of extrasolar planetary
systems. We develop a theoretical global model where radiative losses, which
are predominant in slowly rotating atmospheres, are taken into account. We
analytically compute the tidal perturbation of pressure, density, temperature
and velocity field from which we deduce the expressions of atmospheric Love
numbers and tidal torque exerted by the star. The dynamics of atmospheric tides
depends on the frequency regime of the tidal perturbation: the thermal regime
near synchronization and the dynamical regime characterizing fast-rotating
planets. The dependence of the torque on the tidal frequency is quantified for
Earth-like and Venus-like exoplanets and is in good agreement with the results
given by Global Climate Models (GCM) simulations. Introducing dissipative
processes such as radiation regularizes the tidal response of the atmosphere,
otherwise it is singular at synchronization. We demonstrate the important role
played by the physical and dynamical properties of a super-Earth atmosphere
(e.g. Coriolis, stratification, background pressure, density, temperature,
radiative emission) and point out the key parameters defining tidal regimes
(e.g. inertia, Brunt-V\""ais\""al\""a, radiative frequencies, tidal frequency) and
characterize the behaviour of the fluid shell with dissipation.",1611.04806v1
2017-03-28,Anatomy of an Asteroid Break-Up: The Case of P/2013 R3,"We present an analysis of new and published data on P/2013 R3, the first
asteroid detected while disintegrating. Thirteen discrete components are
measured in the interval between UT 2013 October 01 and 2014 February 13. We
determine a mean, pair-wise velocity dispersion amongst these components of
$\Delta v = 0.33\pm0.03$ m s$^{-1}$ and find that their separation times are
staggered over an interval of $\sim$5 months. Dust enveloping the system has,
in the first observations, a cross-section $\sim$30 km$^2$ but fades
monotonically at a rate consistent with the action of radiation pressure
sweeping. The individual components exhibit comet-like morphologies and also
fade except where secondary fragmentation is accompanied by the release of
additional dust. We find only upper limits to the radii of any embedded solid
nuclei, typically $\sim$100 to 200 m (geometric albedo 0.05 assumed). Combined,
the components of P/2013 R3 would form a single spherical body with radius
$\lesssim$400 m, which is our best estimate of the size of the precursor
object. The observations are consistent with rotational disruption of a weak
(cohesive strength $\sim$50 to 100 N m$^{-2}$) parent body, $\sim$400 m in
radius. Estimated radiation (YORP) spin-up times of this parent are $\lesssim$1
Myr, shorter than the collisional lifetime. If present, water ice sublimating
at as little as 10$^{-3}$ kg s$^{-1}$ could generate a torque on the parent
body rivaling the YORP torque. Under conservative assumptions about the
frequency of similar disruptions, the inferred asteroid debris production rate
is $\gtrsim$10$^3$ kg s$^{-1}$, which is at least 4% of the rate needed to
maintain the Zodiacal Cloud.",1703.09668v1
2017-07-21,Exomoon Habitability and Tidal Evolution in Low-Mass Star Systems,"Discoveries of extrasolar planets in the habitable zone (HZ) of their parent
star lead to questions about the habitability of massive moons orbiting planets
in the HZ. Around low-mass stars, the HZ is much closer to the star than for
Sun-like stars. For a planet-moon binary in such a HZ, the proximity of the
star forces a close orbit for the moon to remain gravitationally bound to the
planet. Under these conditions the effects of tidal heating, distortion
torques, and stellar perturbations become important considerations for exomoon
habitability.
  Utilizing a model that considers both dynamical and tidal interactions
simultaneously, we performed a computational investigation into exomoon
evolution for systems in the HZ of low-mass stars ($\lesssim 0.6\ M_{\odot}$).
We show that dwarf stars with masses $\lesssim 0.2\ M_{\odot}$ cannot host
habitable exomoons within the stellar HZ due to extreme tidal heating in the
moon. Perturbations from a central star may continue to have deleterious
effects in the HZ up to $\approx 0.5\ M_{\odot}$, depending on the host
planet's mass and its location in the HZ, amongst others. In addition to
heating concerns, torques due to tidal and spin distortion can lead to the
relatively rapid inward spiraling of a moon. Therefore, moons of giant planets
in HZs around the most abundant type of star are unlikely to have habitable
surfaces. In cases with lower intensity tidal heating the stellar perturbations
may have a positive influence on exomoon habitability by promoting long-term
heating and possibly extending the HZ for exomoons.",1707.07040v1
2018-06-18,Formation of hot Jupiters through disk migration and evolving stellar tides,"Here we address the hot Jupiter (hJ) pile-up at 0.05 AU around young
solar-type stars observed in stellar radial velocity surveys, the hJ longterm
orbital stability in the presence of stellar tides, and the hJ occurrence rate
of 1.2 (+-0.38)% in one framework. We calculate the combined torques on the
planet from the stellar dynamical tide and from the protoplanetary disk in the
type II migration regime. We model a 2D nonisothermal viscous disk
parameterized to reproduce the minimum-mass solar nebula and simulate an inner
disk cavity at various radial positions near the star. We choose stellar
rotation periods according to observations of young star clusters. The planet
is on a circular orbit in the disk midplane and in the star's equatorial plane.
We show that the torques can add up to zero beyond the corotation radius around
young stars and stop inward migration. Monte Carlo simulations predict hot
Jupiter survival rates between ~3% (alpha disk viscosity of 1e-1) and 15%
(alpha = 1e-3). Once the protoplanetary disk has been fully accreted, the
surviving hJs are pushed outward from their tidal migration barrier and pile up
near 0.05 AU, as we demonstrate using a numerical implementation of a stellar
dynamical tide model. Orbital decay is negligible on a one-billion-year
timescale due to the contraction of the highly dissipative convective envelopes
in young Sun-like stars. We find that the higher pile-up efficiency around
metal-rich stars can at least partly explain the observed positive correlation
between stellar metallicity and hJ occurrence. Combined with the observed hJ
occurrence rate, our results for the survival rate imply that <8 % (alpha =
1e-3) to <43 % (alpha = 1e-1) of sun-like stars initially encounter an inward
migrating hJ. This reconciles models and observations of young spinning stars
with the observed hJ pile up and hJ occurrence rates.",1806.06601v3
2020-03-19,Origin of Star-Forming Rings around Massive Centres in Massive Galaxies at $z\!<\!4$,"Using analytic modeling and simulations, we address the origin of an
abundance of star-forming, clumpy, extended gas rings about massive central
bodies in massive galaxies at $z \!<\! 4$. Rings form by high-angular-momentum
streams and survive in galaxies of $M_{\rm star} \!>\! 10^{9.5-10} M_\odot$
where merger-driven spin flips and supernova feedback are ineffective. The
rings survive after events of compaction to central nuggets. Ring longevity was
unexpected based on inward mass transport driven by torques from violent disc
instability. However, evaluating the torques from a tightly wound spiral
structure, we find that the timescale for transport per orbital time is long
and $\propto\! \delta_{\rm d}^{-3}$, with $\delta_{\rm d}$ the cold-to-total
mass ratio interior to the ring. A long-lived ring forms when the ring
transport is slower than its replenishment by accretion and the interior
depletion by SFR, both valid for $\delta_{\rm d} \!<\! 0.3$. The central mass
that lowers $\delta_{\rm d}$ is a compaction-driven bulge and/or dark matter,
aided by the lower gas fraction at $z \!<\! 4$, provided that it is not too
low. The ring is Toomre unstable for clump and star formation. The high-$z$
dynamic rings are not likely to arise form secular resonances or collisions.
AGN feedback is not expected to affect the rings. Mock images of simulated
rings through dust indicate qualitative consistency with observed rings about
bulges in massive $z\!\sim\!0.5\!-\!3$ galaxies, in $H_{\alpha}$ and deep HST
imaging. ALMA mock images indicate that $z\!\sim\!0.5\!-\!1$ rings should be
detectable. We quote expected observable properties of rings and their central
nuggets.",2003.08984v2
2021-02-15,A backward-spinning star with two coplanar planets,"It is widely assumed that a star and its protoplanetary disk are initially
aligned, with the stellar equator parallel to the disk plane. When observations
reveal a misalignment between stellar rotation and the orbital motion of a
planet, the usual interpretation is that the initial alignment was upset by
gravitational perturbations that took place after planet formation. Most of the
previously known misalignments involve isolated hot Jupiters, for which
planet-planet scattering or secular effects from a wider-orbiting planet are
the leading explanations. In theory, star/disk misalignments can result from
turbulence during star formation or the gravitational torque of a wide-orbiting
companion star, but no definite examples of this scenario are known. An ideal
example would combine a coplanar system of multiple planets -- ruling out
planet-planet scattering or other disruptive post-formation events -- with a
backward-rotating star, a condition that is easier to obtain from a primordial
misalignment than from post-formation perturbations. There are two previously
known examples of a misaligned star in a coplanar multi-planet system, but in
neither case has a suitable companion star been identified, nor is the stellar
rotation known to be retrograde. Here, we show that the star K2-290 A is tilted
by $124\pm 6$ degrees compared to the orbits of both of its known planets, and
has a wide-orbiting stellar companion that is capable of having tilted the
protoplanetary disk. The system provides the clearest demonstration that stars
and protoplanetary disks can become grossly misaligned due to the gravitational
torque from a neighbouring star.",2102.07677v1
2021-05-05,Creep Tide Model for the 3-Body Problem. The rotational evolution of a circumbinary planet,"We present a tidal model for treating the rotational evolution in the general
three-body problem with arbitrary viscosities, in which all the masses are
considered to be extended and all the tidal interactions between pairs are
taken into account. Based on the creep tide theory, we present the set of
differential equations that describes the rotational evolution of each body, in
a formalism that is easily extensible to the N tidally-interacting body
problem. We apply our model to the case of a circumbinary planet and use a
Kepler-38 like binary system as a working example. We find that, in this low
planetary eccentricity case, the most likely final stationary rotation state is
the 1:1 spin-orbit resonance, considering an arbitrary planetary viscosity
inside the estimated range for the solar system planets. We derive analytical
expressions for the mean rotational stationary state, based on high-order power
series of the semimajor axes ratio a1 /a2 and low-order expansions of the
eccentricities. These are found to reproduce very accurately the mean behaviour
of the low-eccentric numerical integrations for arbitrary planetary relaxation
factors, and up to a1/a2 \sim 0.4. Our analytical model is used to predict the
stationary rotation of the Kepler circumbinary planets and find that most of
them are probably rotating in a sub-synchronous state, although the synchrony
shift is much less important than the one estimated in Zoppetti et al. (2019,
2020). We present a comparison of our results with those obtained with the
Constant Time Lag and find that, unlike what we assumed in our previous works,
the cross torques have a non-negligible net secular contribution, and must be
taken into account when computing the tides over each body in an
N-extended-body system from an arbitrary reference frame. These torques are
naturally taken into account in the creep theory.",2105.02336v1
2023-02-04,Timing analysis of EXO 2030+375 during its 2021 giant outburst observed with Insight-HXMT,"We report the evolution of the X-ray pulsations of EXO 2030+375 during its
2021 outburst using the observations from \textit{Insight}-HXMT. Based on the
accretion torque model, we study the correlation between the spin frequency
derivatives and the luminosity. Pulsations can be detected in the energy band
of 1--160 keV. The pulse profile evolves significantly with luminosity during
the outburst, leading to that the whole outburst can be divided into several
parts with different characteristics. The evolution of the pulse profile
reveals the transition between the super-critical (fan-beam dominated) and the
sub-critical accretion (pencil-beam dominated) mode. From the accretion torque
model and the critical luminosity model, based on a distance of 7.1 kpc, the
inferred magnetic fields are $(0.41-0.74) \times 10^{12}$ G and $(3.48-3.96)
\times 10^{12}$ G, respectively, or based on a distance of 3.6 kpc, the
estimated magnetic fields are $(2.4-4.3) \times 10^{13}$ G and
$(0.98-1.11)\times 10^{12}$ G, respectively. Two different sets of magnetic
fields both support the presence of multipole magnetic fields of the NS.",2302.02167v2
2023-12-06,Evidence for the novel type of orbital Fulde-Ferrell-Larkin-Ovchinnikov state in the bulk limit of 2H-NbSe2,"The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, an unusual superconducting
state, defies high magnetic fields beyond the Pauli paramagnetic limit. It
exhibits a spatial modulation of the superconducting order parameter in real
space and is exceptionally rare. Recently, an even more exotic variant - the
orbital FFLO state - was predicted and identified in the transition metal
dichalcogenide superconductor 2H-NbSe2. This state emerges in thin samples with
thicknesses below ~40 nm, at the boundary between two and three dimensions. The
complex interplay between Ising spin orbit coupling and the Pauli paramagnetic
effect can lead to a stabilization of the FFLO state in a relatively large
range of the magnetic phase diagram, even well below the Pauli limit. In this
study, we present experimental evidence of the formation of this orbital FFLO
state in bulk 2H-NbSe2 samples. This evidence was obtained using
high-resolution DC magnetization and magnetic torque experiments in magnetic
fields applied strictly parallel to the NbSe2 basal plane. Both quantities
display a crossover to a discontinuous first-order superconducting transition
at the normal state boundary in magnetic fields of 4 T and above. This is
usually seen as a sign that Pauli paramagnetic pair breaking effects affect the
superconducting state. The magnetic torque reveals a small step-like reversible
anomaly, indicating a magnetic field-induced thermodynamic phase transition
within the superconducting state. This anomaly bears many similarities to the
FFLO transitions in other FFLO superconductors, suggesting the potential
existence of an orbital FFLO state in bulk 2H-NbSe2 samples. Additionally, we
observe a pronounced in-plane 6-fold symmetry of the upper critical field in
the field range above this phase transition, which has previously been
interpreted as a hallmark of the orbital FFLO state in thin 2H-NbSe2.",2312.03215v3
2006-01-10,Surface density jumps as planet traps,"[Abridged] The tidal torque exerted by a protoplanetary disk with power law
surface density and temperature profiles onto an embedded protoplanetary embryo
is generally a negative quantity that leads to the embryo inwards migration.
Here we investigate how the tidal torque balance is affected at a disk surface
density radial jump. The jump has two consequences :
  - it affects the differential Lindblad torque. In particular if the disk is
merely empty on the inner side, the differential Lindblad torque almost amounts
to the large negative outer Lindblad torque.
  - It affects the corotation torque, which is a quantity very sensitive to the
local gradient of the disk surface density. In particular if the disk is
depleted on the inside and if the jump occurs radially over a few pressure
scale-heights, the corotation torque is a positive quantity that is much larger
than in a power-law disk.
  We show by means of customized numerical simulations of low mass planets
embedded in protoplanetary nebulae with a surface density jump that the second
effect is dominant, that is that the corotation torque largely dominates the
differential Lindblad torque on the edge of a central depletion. As a
consequence the type I migration of low mass objects reaching the jump should
be halted, and all these objects should be trapped there.",0601222v1
2012-01-03,Motor-Driven Bacterial Flagella and Buckling Instabilities,"Many types of bacteria swim by rotating a bundle of helical filaments also
called flagella. Each filament is driven by a rotary motor and a very flexible
hook transmits the motor torque to the filament. We model it by discretizing
Kirchhoff's elastic-rod theory and develop a coarse-grained approach for
driving the helical filament by a motor torque. A rotating flagellum generates
a thrust force, which pushes the cell body forward and which increases with the
motor torque. We fix the rotating flagellum in space and show that it buckles
under the thrust force at a critical motor torque. Buckling becomes visible as
a supercritical Hopf bifurcation in the thrust force. A second buckling
transition occurs at an even higher motor torque. We attach the flagellum to a
spherical cell body and also observe the first buckling transition during
locomotion. By changing the size of the cell body, we vary the necessary thrust
force and thereby obtain a characteristic relation between the critical thrust
force and motor torque. We present a sophisticated analytical model for the
buckling transition based on a helical rod which quantitatively reproduces the
critical force-torque relation. Real values for motor torque, cell body size,
and the geometry of the helical filament suggest that buckling should occur in
single bacterial flagella. We also find that the orientation of pulling
flagella along the driving torque is not stable and comment on the biological
relevance for marine bacteria.",1201.0628v1
2016-06-30,Approaching the Standard Quantum Limit of Mechanical Torque Sensing,"Mechanical transduction of torque has been key to probing a number of
physical phenomena, such as gravity, the angular momentum of light, the Casimir
effect, magnetism, and quantum oscillations. Following similar trends as mass
and force sensing, mechanical torque sensitivity can be dramatically improved
by scaling down the physical dimensions, and therefore moment of inertia, of a
torsional spring. Yet now, through precision nanofabrication and sub-wavelength
cavity optomechanics, we have reached a point where geometric optimization can
only provide marginal improvements to torque sensitivity. Instead, nanoscale
optomechanical measurements of torque are overwhelmingly hindered by thermal
noise. Here we present cryogenic measurements of a cavity-optomechanical
torsional resonator cooled in a dilution refrigerator to a temperature of 25
mK, corresponding to an average phonon occupation of <n> = 35, that demonstrate
a record-breaking torque sensitivity of 2.9 yNm/Hz^{1/2}. This a 270-fold
improvement over previous optomechanical torque sensors and just over an order
of magnitude from its standard quantum limit. Furthermore, we demonstrate that
mesoscopic test samples, such as micron-scale superconducting disks, can be
integrated with our cryogenic optomechanical torque sensing platform, in
contrast to other cryogenic optomechanical devices, opening the door for
mechanical torque spectroscopy of intrinsically quantum systems.",1607.00069v1
2017-08-31,Coorbital thermal torques on low-mass protoplanets,"Using linear perturbation theory, we investigate the torque exerted on a
low-mass planet embedded in a gaseous protoplanetary disc with finite thermal
diffusivity. When the planet does not release energy into the ambient disc, the
main effect of thermal diffusion is the softening of the enthalpy peak near the
planet, which results in the appearance of two cold and dense lobes on either
side of the orbit, of size smaller than the thickness of the disc. The lobes
exert torques of opposite sign on the planet, each comparable in magnitude to
the one-sided Lindblad torque. When the planet is offset from corotation, the
lobes are asymmetric and the planet experiences a net torque, the `cold'
thermal torque, which has a magnitude that depends on the relative value of the
distance to corotation to the size of the lobes $\sim\sqrt{\chi/\Omega_p}$,
$\chi$ being the thermal diffusivity and $\Omega_p$ the orbital frequency. We
believe that this effect corresponds to the phenomenon named `cold finger'
recently reported in numerical simulations, and we argue that it constitutes
the dominant mode of migration of sub-Earth-mass objects. When the planet is
luminous, the heat released into the ambient disc results in an additional
disturbance that takes the form of hot, low-density lobes. They give a torque,
named heating torque in previous work, that has an expression similar, but of
opposite sign, to the cold thermal torque.",1708.09807v2
2019-02-19,Design and Control of a Quasi-Direct Drive Soft Exoskeleton for Knee Injury Prevention during Squatting,"This paper presents design and control innovations of wearable robots that
tackle two barriers to widespread adoption of powered exoskeletons, namely
restriction of human movement and versatile control of wearable co-robot
systems. First, the proposed quasi-direct drive actuation comprising of our
customized high torque density motors and low ratio transmission mechanism
significantly reduces the mass of the robot and produces high backdrivability.
Second, we derive a biomechanics model-based control that generates biological
torque profile for versatile control of both squat and stoop lifting
assistance. The control algorithm detects lifting postures using compact
inertial measurement unit (IMU) sensors to generate an assistive profile that
is proportional to the biological torque produced from our model. Experimental
results demonstrate that the robot exhibits low mechanical impedance (1.5 Nm
resistive torque) when it is unpowered and 0.5 Nm resistive torque with
zero-torque tracking control. Root mean square (RMS) error of torque tracking
is less than 0.29 Nm (1.21% error of 24 Nm peak torque). Compared with
squatting without the exoskeleton, the controller reduces 87.5%, 80% and 75% of
the of three knee extensor muscles (average peak EMG of 3 healthy subjects)
during squat with 50% of biological torque assistance.",1902.07106v2
2020-02-25,Low-mass planet migration in three dimensional wind-driven inviscid discs: a negative corotation torque,"We present simulations of low-mass planet--disc interactions in inviscid
three-dimensional discs. We show that a wind-driven laminar accretion flow
through the surface layers of the disc does not significantly modify the
migration torque experienced by embedded planets. More importantly, we find
that 3D effects lead to a dramatic change in the behaviour of the dynamical
corotation torque compared to earlier 2D theory and simulations. Although it
was previously shown that the dynamical corotation torque could act to slow and
essentially stall the inward migration of a low-mass planet, our results in 3D
show that the dynamical corotation torque has the complete opposite effect and
speeds up inward migration. Our numerical experiments implicate buoyancy
resonances as the cause. These have two effects: (i) they exert a direct torque
on the planet, whose magnitude relative to the Lindblad torque is measured in
our simulations to be small; (ii) they torque the gas librating on horseshoe
orbits in the corotation region and drive evolution of its vortensity, leading
to the negative dynamical corotation torque. This indicates that at low
turbulent viscosity, the detailed vertical thermal structure of the
protoplanetary disc plays an important role in determining the migration
behaviour of embedded planets. If this result holds up under a more refined
treatment of disc thermal evolution, then it has important implications for
understanding the formation and early evolution of planetary systems.",2002.11161v3
2000-09-28,"Pairing, Charge, and Spin Correlations in the Three-Band Hubbard Model","Using the Constrained Path Monte Carlo (CPMC) method, we simulated the
two-dimensional, three-band Hubbard model to study pairing, charge, and spin
correlations as a function of electron and hole doping and the Coulomb
repulsion $V_{pd}$ between charges on neighboring Cu and O lattice sites. As a
function of distance, both the $d_{x^2 - y^2}$-wave and extended s-wave pairing
correlations decayed quickly. In the charge-transfer regime, increasing
$V_{pd}$ decreased the long-range part of the correlation functions in both
channels, while in the mixed-valent regime, it increased the long-range part of
the s-wave behavior but decreased that of the d-wave behavior. Still the d-wave
behavior dominated. At a given doping, increasing $V_{pd}$ increased the
spin-spin correlations in the charge-transfer regime but decreased them in the
mixed-valent regime. Also increasing $V_{pd}$ suppressed the charge-charge
correlations between neighboring Cu and O sites. Electron and hole doping away
from half-filling was accompanied by a rapid suppression of anti-ferromagnetic
correlations.",0009433v1
2003-06-11,Microwave Oscillations of a Nanomagnet Driven by a Spin-Polarized Current,"We describe direct electrical measurements of microwave-frequency dynamics in
individual nanomagnets that are driven by spin transfer from a DC
spin-polarized current. We map out the dynamical stability diagram as a
function of current and magnetic field, and we show that spin transfer can
produce several different types of magnetic excitations, including small-angle
precession, a more complicated large-angle motion, and a high-current state
that generates little microwave signal. The large-angle mode can produce a
significant emission of microwave energy, as large as 40 times the
Johnson-noise background.",0306259v1
2003-12-18,Current induced magnetization dynamics in current perpendicular to the plane spin valves,"We observe magnetization dynamics induced by spin momentum transfer in the
noise spectra of current perpendicular to the plane giant magnetoresistance
spin valves. The dynamics are observable only for those combinations of current
direction and magnetic configuration in which spin transfer acts to reorient
the free layer magnetization away from the direction set by the net magnetic
field. Detailed measurements as a function of magnetic configuration reveal an
evolution of the noise spectra, going from a spectrum with a well-defined noise
peak when the free layer is roughly collinear with the pinned layer to a
spectrum dominated by 1/f noise when the free layer is in an orthogonal
configuration. Finally, the amplitude of the corresponding resistance noise
increases rapidly with increasing current until it saturates at a value that is
a substantial fraction of the magnetoresistance between parallel and
antiparallel states.",0312504v2
2004-04-05,"Large-angle, gigahertz-rate random telegraph switching induced by spin-momentum transfer","We show that spin-polarized dc current passing through a small magnetic
element induces two-state, random telegraph switching of the magnetization via
the spin-momentum transfer effect. The resistances of the states differ by up
to 50% of the change due to complete magnetization reversal. Fluctuations are
seen for a wide range of currents and magnetic fields, with rates that can
exceed 2 GHz, and involve collective motion of a large volume (10^4 nm^3) of
spins. Switching rate trends with field and current indicate that increasing
temperature alone cannot explain the dynamics. The rates approach a stochastic
regime wherein dynamics are governed by both precessional motion and thermal
perturbations.",0404109v1
2004-11-09,Entanglement transfer from electron spins to photons in spin light-emitting diodes containing quantum dots,"We show that electron recombination using positively charged excitons in
single quantum dots provides an efficient method to transfer entanglement from
electron spins onto photon polarizations. We propose a scheme for the
production of entangled four-photon states of GHZ type. From the GHZ state, two
fully entangled photons can be obtained by a measurement of two photons in the
linear polarization basis, even for quantum dots with observable fine structure
splitting for neutral excitons and significant exciton spin decoherence.
Because of the interplay of quantum mechanical selection rules and
interference, maximally entangled electron pairs are converted into maximally
entangled photon pairs with unity fidelity for a continuous set of observation
directions. We describe the dynamics of the conversion process using a
master-equation approach and show that the implementation of our scheme is
feasible with current experimental techniques.",0411235v3
2004-11-13,Spin transfer switching of spin valve nanopillars using nanosecond pulsed currents,"Spin valve nanopillars are reversed via the mechanism of spin momentum
transfer using current pulses applied perpendicular to the film plane of the
device. The applied pulses were varied in amplitude from 1.8 mA to 7.8 mA, and
varied in duration within the range of 100 ps to 200 ns. The probability of
device reversal is measured as a function of the pulse duration for each pulse
amplitude. The reciprocal pulse duration required for 95% reversal probability
is linearly related to the pulse current amplitude for currents exceeding 1.9
mA. For this device, 1.9 mA marks the crossover between dynamic reversal at
larger currents and reversal by thermal activation for smaller currents.",0411363v1
2005-10-30,Multicritical point of Ising spin glasses on triangular and honeycomb lattices,"The behavior of two-dimensional Ising spin glasses at the multicritical point
on triangular and honeycomb lattices is investigated, with the help of
finite-size scaling and conformal-invariance concepts. We use transfer-matrix
methods on long strips to calculate domain-wall energies, uniform
susceptibilities, and spin-spin correlation functions. Accurate estimates are
provided for the location of the multicritical point on both lattices, which
lend strong support to a conjecture recently advanced by Takeda, Sasamoto, and
Nishimori. Correlation functions are shown to obey rather strict
conformal-invariance requirements, once suitable adaptations are made to
account for geometric aspects of the transfer-matrix description of triangular
and honeycomb lattices. The universality class of critical behavior upon
crossing the ferro-paramagnetic phase boundary is probed, with the following
estimates for the associated critical indices: $\nu=1.49(2)$, $\gamma=2.71(4)$,
$\eta_1= 0.183(3)$, distinctly different from the percolation values.",0510816v2
2006-06-13,A Mechanism for Photoinduced Effects In Tetracyanoethylene-Based Organic Magnets,"The photoinduced magnetism in manganese-tetracyanoethylene (Mn-TCNE)
molecule-based magnets is ascribed to charge-transfer excitations from
manganese to TCNE. Charge-transfer energies are calculated using Density
Functional Theory; photoinduced magnetization is described using a model
Hamiltonian based on a double-exchange mechanism. Photoexciting electrons from
the manganese core spin into the lowest unoccupied orbital of TCNE with photon
energies around 3 eV increases the magnetization through a reduction of the
canting angle of the manganese core spins for an average electron density on
TCNE less than one. When photoexciting with a smaller energy, divalent TCNE
molecules are formed. The delocalization of the excited electron causes a local
spin flip of a manganese core spin.",0606343v1
1998-04-08,Mixing of Ground States in Vertex Models,"We consider the analogue of the 6-vertex model constructed from alternating
spin n/2 and spin m/2 lines, where $1\leq n<m$. We identify the transfer matrix
and the space on which it acts in terms of the representation theory of
$U_q(sl_2)$. We diagonalise the transfer matrix and compute the S-matrix. We
give a trace formula for local correlation functions. When n=1, the 1-point
function of a spin m/2 local variable for the alternating lattice with a
particular ground state is given as a linear combination of the 1-point
functions of the pure spin m/2 model with different ground states. The mixing
ratios are calculated exactly and are expressed in terms of irreducible
characters of $U_q(sl_2)$ and the deformed Virasoro algebra.",9804063v3
1999-09-27,"Model-independent determination of the 12C(p,p')12C*(15.11 MeV, 1+, T=1) transition amplitude at 200 MeV","Using data obtained through simultaneous measurements of (p,p') spin-transfer
observables and (p,p'gamma) coincident spin observables, we have made a
model-independent determination of the complete scattering amplitude for the
15.11 MeV, 1+, T=1 state in 12C at an incident proton energy of 200 MeV, for
four center of mass proton scattering angles ranging from 5.5 to 16.5 degrees.
At each angle, 16 different observables were determined, whereas only 11
independent quantities are required to specify the transition amplitude for
this state. It had been shown previously that the set of observables measured
span the allowed space; hence the system is overdetermined, which allowed us to
extract, in a model-independent fashion, each of the individual spin-operator
amplitudes that characterize the reaction. Additional insight into the physical
mechanisms that drive this transition is obtained by mapping out the
momentum-transfer dependence of these amplitudes. We also compare the
magnitudes and phases determined for each of the spin-operator amplitudes to
the predictions of calculations performed in both relativistic and
nonrelativistic frameworks, and discuss the physics content of these
comparisons.",9909016v1
2008-04-03,Current-induced domain wall motion in Rashba spin-orbit system,"Current-induced magnetic domain wall motion, induced by transfer of spin
transfer effect due to exchange interaction, is expected to be useful for next
generation high-density storages. We here show that efficient domain wall
manipulation can be achieved by introduction of Rashba spin-orbit interaction,
which induces spin precession of conduction electron and acts as an effective
magnetic field. Its effect on domain wall motion depends on the wall
configuration. We found that the effect is significant for Bloch wall with the
hard axis along the current, since the effective field works as $\beta$ or
field-like term and removes the threshold current if in extrinsic pinning is
absent. For N\'eel wall and Bloch wall with easy axis perpendicular to Rashba
plane, the effective field induces a step motion of wall corresponding to a
rotation of wall plane by the angle of approximately $\pi$ at current lower
than intrinsic threshold. Rashba interaction would therefore be useful to
assist efficient motion of domain walls at low current.",0804.0458v1
2008-10-14,Quantum information transfer from spin to orbital angular momentum of photons,"The optical ""spin-orbit"" coupling occurring in a suitably patterned
nonuniform birefringent plate known as `q-plate' allows entangling the
polarization of a single photon with its orbital angular momentum (OAM). This
process, in turn, can be exploited for building a bidirectional ""spin-OAM
interface"", capable of transposing the quantum information from the spin to the
OAM degree of freedom of photons and \textit{vice versa}. Here, we
experimentally demonstrate this process by single-photon quantum tomographic
analysis. Moreover, we show that two-photon quantum correlations such as those
resulting from coalescence interference can be successfully transferred into
the OAM degree of freedom.",0810.2417v2
2009-08-20,Selective spin transport through a quantum heterostructure: Transfer matrix method,"In the present work we propose that a one-dimensional quantum heterostructure
composed of magnetic and non-magnetic atomic sites can be utilized as a spin
filter for a wide range of applied bias voltage. A simple tight-binding
framework is given to describe the conducting junction where the
heterostructure is coupled to two semi-infinite one-dimensional non-magnetic
electrodes. Based on transfer matrix method all the calculations are performed
numerically which describe two-terminal spin dependent transmission probability
along with junction current through the wire. Our detailed analysis may provide
fundamental aspects of selective spin transport phenomena in one-dimensional
heterostructures at nano-scale level.",0908.2857v3
2009-10-05,Spin Sum Rules and Polarizabilities,"The Gerasimov-Drell-Hearn sum rule and related dispersive integrals connect
real and virtual Compton scattering to inclusive photo- and electroproduction.
Being based on universal principles as causality, unitarity, and gauge
invariance, these relations provide a unique testing ground to study the
internal degrees of freedom that hold a system together. The present
contribution reviews the spin-dependent sum rules and cross sections of the
nucleon. At small momentum transfer, the data sample information on the long
range phenomena (Goldstone bosons and collective resonances), whereas the
primary degrees of freedom (quarks and gluons) become visible at large momentum
transfer (short distance). The rich body of new data covers a wide range of
phenomena from coherent to incoherent processes, and from the generalized spin
polarizabilities on the low-energy side to higher twist effects in deep
inelastic scattering.",0910.0719v1
2011-04-22,Knitting distributed cluster state ladders with spin chains,"There has been much recent study on the application of spin chains to quantum
state transfer and communication. Here we discuss the utilisation of spin
chains (set up for perfect quantum state transfer) for the knitting of
distributed cluster state structures, between spin qubits repeatedly injected
and extracted at the ends of the chain. The cluster states emerge from the
natural evolution of the system across different excitation number sectors. We
discuss the decohering effects of errors in the injection and extraction
process as well as the effects of fabrication and random errors.",1104.4434v2
2011-06-17,Duplex quantum communication through a spin chain,"Data multiplexing within a quantum computer can allow for the simultaneous
transfer of multiple streams of information over a shared medium thereby
minimizing the number of channels needed for requisite data transmission. Here,
we investigate a two-way quantum communication protocol using a spin chain
placed in an external magnetic field. In our scheme, Alice and Bob each play
the role of a sender and a receiver as two states cos({\theta}1/2)|0> +
sin({\theta}1/2)exp(i{\phi}1)|1>, cos({\theta}2/2)|0> +
sin({\theta}2/2)exp(i{\phi}2)|1> are transferred through one channel
simultaneously. We find that the transmission fidelity at each end of a spin
chain can usually be enhanced by the presence of a second party. This is an
important result for establishing the viability of duplex quantum communication
through spin chain networks.",1106.3502v1
2011-10-10,Generalized Holstein model for spin-dependent electron transfer reaction,"Some chemical reactions are described by electron transfer (ET) processes.
The underlying mechanism could be modeled as a polaron motion in the molecular
crystal-the Holstein model. By taking spin degrees of freedom into
consideration, we generalize the Holstein model (molecular crystal model) to
microscopically describe an ET chemical reaction. In our model, the electron
spins in the radical pair simultaneously interact with a magnetic field and
their nuclear-spin environments. By virtue of the perturbation approach, we
obtain the chemical reaction rates for different initial states. It is
discovered that the chemical reaction rate of the triplet state demonstrates
its dependence on the direction of the magnetic field while the counterpart of
the singlet state does not. This difference is attributed to the explicit
dependence of the triplet state on the direction when the axis is rotated. Our
model may provide a possible candidate for the microscopic origin of avian
compass.",1110.1918v1
2012-02-23,Transference Principles for Log-Sobolev and Spectral-Gap with Applications to Conservative Spin Systems,"We obtain new principles for transferring log-Sobolev and Spectral-Gap
inequalities from a source metric-measure space to a target one, when the
curvature of the target space is bounded from below. As our main application,
we obtain explicit estimates for the log-Sobolev and Spectral-Gap constants of
various conservative spin system models, consisting of non-interacting and
weakly-interacting particles, constrained to conserve the mean-spin. When the
self-interaction is a perturbation of a strongly convex potential, this
partially recovers and partially extends previous results of Caputo,
Chafa\""{\i}, Grunewald, Landim, Lu, Menz, Otto, Panizo, Villani, Westdickenberg
and Yau. When the self-interaction is only assumed to be (non-strongly) convex,
as in the case of the two-sided exponential measure, we obtain sharp estimates
on the system's spectral-gap as a function of the mean-spin, independently of
the size of the system.",1202.5318v1
2012-05-26,Spin and Orbital Angular Momenta of Light Reflected from a Cone,"We examine several retro-reflecting optical elements, each involving two
reflections. In the case of a hollow metallic cone having an apex angle of
90\degree, a circularly-polarized incident beam acquires, upon reflection, the
opposite spin angular momentum. However, no angular momentum is transferred to
the cone, because the reflected beam picks up an orbital angular momentum that
is twice as large but opposite in direction to that of its spin. A 90\degree
cone made of a transparent material in which the incident light suffers two
total internal reflections before returning, may be designed to endow the
retro-reflected beam with different mixtures of orbital and spin angular
momenta. Under no circumstances, however, is it possible to transfer angular
momentum from the light beam to the cone without either allowing absorption or
breaking the axial symmetry of the cone. A simple example of broken symmetry is
provided by a wedge-shaped metallic reflector having an apex angle of
90\degree, which picks up angular momentum upon reflecting a
circularly-polarized incident beam.",1205.5897v1
2012-07-24,Perfect quantum transport in arbitrary spin networks,"Spin chains have been proposed as wires to transport information between
distributed registers in a quantum information processor. Unfortunately, the
challenges in manufacturing linear chains with engineered couplings has
hindered experimental implementations. Here we present strategies to achieve
perfect quantum information transport in arbitrary spin networks. Our proposal
is based on the weak coupling limit for pure state transport, where information
is transferred between two end-spins that are only weakly coupled to the rest
of the network. This regime allows disregarding the complex, internal dynamics
of the bulk network and relying on virtual transitions or on the coupling to a
single bulk eigenmode. We further introduce control methods capable of tuning
the transport process and achieve perfect fidelity with limited resources,
involving only manipulation of the end-qubits. These strategies could be thus
applied not only to engineered systems with relaxed fabrication precision, but
also to naturally occurring networks; specifically, we discuss the practical
implementation of quantum state transfer between two separated nitrogen vacancy
(NV) centers through a network of nitrogen substitutional impurities.",1207.5580v1
2012-09-20,Holonomy Spin Foam Models: Boundary Hilbert spaces and Time Evolution Operators,"In this and the companion paper a novel holonomy formulation of so called
Spin Foam models of lattice gauge gravity are explored. After giving a natural
basis for the space of simplicity constraints we define a universal boundary
Hilbert space, on which the imposition of different forms of the simplicity
constraints can be studied. We detail under which conditions this Hilbert space
can be mapped to a Hilbert space of projected spin networks or an ordinary spin
network space.
  These considerations allow to derive the general form of the transfer
operators which generates discrete time evolution. We will describe the
transfer operators for some current models on the different boundary Hilbert
spaces and highlight the role of the simplicity constraints determining the
concrete form of the time evolution operators.",1209.4539v1
2012-10-24,Quantum states experimentally achieving high-fidelity transmission over a spin chain,"A uniformly coupled double quantum Hamiltonian for a spin chain has recently
been implemented experimentally. We propose a method for the determination of
initial quantum states that will provide perfect or near-perfect state
transmission for an arbitrary Hamiltonian including this one. By calculating
the eigenvalues and eigenvectors of a unitary operator obtained from the free
evolution plus an exchange operator, we find that the double quantum
Hamiltonian spin chain will support a three-spin initial encoding that will
transfer along the chain with remarkably high fidelity. The fidelity is also
found to decrease very slowly with increasing chain length. In addition, we are
able to explain previous results showing exceptional transfer using this
method.",1210.6550v1
2013-11-28,Conservative effects in spin-transfer-driven magnetization dynamics,"It is shown that under appropriate conditions spin-transfer-driven
magnetization dynamics in a single-domain nanomagnet is conservative in nature
and admits a specific integral of motion, which is reduced to the usual
magnetic energy when the spin current goes to zero. The existence of this
conservation law is connected to the symmetry properties of the dynamics under
simultaneous inversion of magnetisation and time. When one applies an external
magnetic field parallel to the spin polarization, the dynamics is transformed
from conservative into dissipative. More precisely, it is demonstrated that
there exists a state function such that the field induces a monotone relaxation
of this function toward its minima or maxima, depending on the field
orientation. These results hold in the absence of intrinsic damping effects.
When intrinsic damping is included in the description, a competition arises
between field-induced and damping-induced relaxations, which leads to the
appearance of limit cycles, that is, of magnetization self-oscillations.",1311.7344v1
2014-02-26,Determination of magnetic form factors for organic charge transfer salts: a first principles investigation,"Organic charge transfer salts show a variety of complex phases ranging from
antiferromagnetic long-range order, spin liquid, bad metal or even
superconductivity. A powerful method to investigate magnetism is spin-polarized
inelastic neutron scattering. However, such measurements have often been
hindered in the past by the small size of available crystals as well as by the
fact that the spin in these materials is distributed over molecular rather than
atomic orbitals and good estimates for the magnetic form factors are missing.
By considering Wannier functions obtained from density functional theory
calculations, we derive magnetic form factors for a number of representative
organic molecules. Compared to Cu2+, the form factors |F(q)|2 fall off more
rapidly as function of q reflecting the fact that the spin density is very
extended in real space. Form factors |F(q)|2 for TMTTF, BEDT-TTF and
(BEDT-TTF)2 have anisotropic and nonmonotonic structure.",1402.6599v1
2015-03-21,Transfer of high-dimensional quantum state through an XXZ-Heisenberg quantum spin chain,"We propose and analyze an efficient high-dimensional quantum state transfer
scheme through an $XXZ$-Heisenberg spin chain in an inhomogeneous magnetic
field. By the use of a combination of coherent quantum coupling and free
spin-wave approximation, pure unitary evolution results in a perfect
high-dimensional swap operation between two remote quantum registers mediated
by a uniform quantum data bus, and the feasibility is confirmed by numerical
simulations. Also, we observe that either the strong $z$-directional coupling
or high quantum spin number can partly suppress the thermal excitations and
protect quantum information from the thermal noises when the quantum data bus
is in the thermal equilibrium state.",1503.06274v2
2015-04-13,Insensitivity of spin dynamics to the orbital angular momentum transferred from twisted light to extended semiconductors,"We study the spin dynamics of carriers due to the Rashba interaction in
semiconductor quantum disks and wells after excitation with light with orbital
angular momentum. We find that although twisted light transfers orbital angular
momentum to the excited carriers and the Rashba interaction conserves their
total angular momentum, the resulting electronic spin dynamics is essentially
the same for excitation with light with orbital angular momentum $l=+|l|$ and
$l=-|l|$. The differences between cases with different values of $|l|$ are due
to the excitation of states with slightly different energies and not to the
different angular momenta per se, and vanish for samples with large radii where
a $k$-space quasi-continuum limit can be established. These findings apply not
only to the Rashba interaction but also to all other envelope-function
approximation spin-orbit Hamiltonians like the Dresselhaus coupling.",1504.03098v1
2015-07-21,Quantum spin chains with fractional revival,"A systematic study of fractional revival at two sites in $XX$ quantum spin
chains is presented and analytic models with this phenomenon are exhibited. The
generic models have two essential parameters and a revival time that does not
depend on the length of the chain. They are obtained by combining two basic
ways of realizing fractional revival in a spin chain each bringing one
parameter. The first proceeds through isospectral deformations of spin chains
with perfect state transfer. The second arises from the recurrence coefficients
of the para-Krawtchouk polynomials with a bi-lattice orthogonality grid. It
corresponds to an analytic model previously identified that can possess perfect
state transfer in addition to fractional revival.",1507.05919v1
2016-02-25,Study of the ultrafast dynamics of ferromagnetic materials with a Quantum Monte Carlo atomistic model,"We study of the ultrafast dynamics of the atomic angular momentum in
ferrimagnets irradiated by laser pulses. My apply a quantum atomistic spin
approach based on the Monte Carlo technique. Our model describes the coherent
transfer of angular momentum between the spin and the orbital momentum as well
as the quenching of the orbital momentum induced by the lattice field. The
Elliott-Yafet collision mechanism is also included. We focus on elementary
mechanisms that lead to the dissipation of the total angular momentum in a rare
earth-transition metal (RE-TM) alloy in which the two sublattices have opposite
spin orientation. Our model shows that the observed ultrafast quenching of the
magnetization can be explained microscopically by the transfer of spin between
the sublattices and by the quenching of the localized orbital angular momentum.",1602.07950v1
2017-03-10,Ultrafast and Energy-Efficient Quenching of Spin Order: Antiferromagnetism Beats Ferromagnetism,"By comparing femtosecond laser pulse induced ferro- and antiferromagnetic
dynamics in one and the same material - metallic dysprosium - we show both to
behave fundamentally different. Antiferromagnetic order is considerably faster
and much more efficiently manipulated by optical excitation than its
ferromagnetic counterpart. We assign the fast and extremely efficient process
in the antiferromagnet to an interatomic transfer of angular momentum within
the spin system. Our findings do not only reveal this angular momentum transfer
channel effective in antiferromagnets and other magnetic structures with
non-parallel spin alignment, they also point out a possible route towards
energy-efficient spin manipulation for magnetic devices.",1703.03689v3
2018-03-15,Microwave-assisted cross-polarization of nuclear spin ensembles from optically-pumped nitrogen-vacancy centers in diamond,"The ability to optically initialize the electronic spin of the
nitrogen-vacancy (NV) center in diamond has long been considered a valuable
resource to enhance the polarization of neighboring nuclei, but efficient
polarization transfer to spin species outside the diamond crystal has proven
challenging. Here we demonstrate variable-magnetic-field, microwave-enabled
cross-polarization from the NV electronic spin to protons in a model viscous
fluid in contact with the diamond surface. Slight changes in the
cross-relaxation rate as a function of the wait time between successive
repetitions of the transfer protocol suggest slower molecular diffusion near
the diamond surface compared to that in bulk, an observation consistent with
present models of the microscopic structure of a fluid close to a solid
interface.",1803.05608v1
2019-10-13,Theoretical Study of Spin Observables in $pd$ Elastic Scattering at Energies $T_p = 800-1000$ MeV,"Various spin observables (analyzing powers and spin-correlation parameters)
in $pd$ elastic scattering at $T_p = 800-1000$ MeV are analyzed within the
framework of the refined Glauber model. The theoretical model uses as input
spin-dependent $NN$ amplitudes obtained from the most recent partial-wave
analysis and also takes into account the deuteron $D$ wave and charge-exchange
effects. Predictions of the refined Glauber model are compared with the
existing experimental data. Reasonable agreement between the theoretical
calculations and experimental data at low momentum transfers $|t| \lesssim 0.2$
(GeV/$c)^2$ is found for all observables considered. Moderate discrepancies
found in this region are shown to be likely due to uncertainties in the input
$NN$ amplitudes. Qualitative agreement at higher momentum transfers is also
found for most observables except the tensor ones with mixed $x$ and $z$
polarization components. Possible reasons for observed deviations of the model
calculations from the data at $|t| > 0.2$ (GeV/$c)^2$ are discussed.",1910.05722v1
2020-05-02,Optically driven ultrafast magnetic order transitions in two-dimensional ferrimagnets,"Laser-induced switching and manipulation of the spins in magnetic materials
are of great interest to revolutionize future magnetic storage technology and
spintronics with fastest speed and least power dissipative. Inspired by the
recent discovery of intrinsic two-dimensional (2D) magnets, which provide
unique platform to explore the new phenomenon for light-control magnetism in
the 2D limit, we propose to realize light can efficiently tune magnetic
properties of 2D ferrimagnets in early time. Here, using the 2D ferrimagnetic
MXenes as prototype systems, our real-time density functional theory (TDDFT)
simulation show that laser pulses can directly induce ultrafast spin-selective
charge transfer between two magnetic sublattices on a few femtoseconds, and
further generate dramatic changes in the magnetic structure of these MXenes,
including a magnetic order transition from ferrimagnetic (FiM) to transient
ferromagnetic (FM). The microscopic mechanism underpinning this ultrafast
switching of magnetic order in MXenes is governed by optically induced
inter-site spin transfer (OISTR) effect, which theoretically enables the
ultrafast direct optical manipulation of the magnetic state in MXenes-based
materials. Our results open new opportunities to optically manipulate the spin
in 2D magnets.",2005.00871v1
2020-12-07,Where does the spin angular momentum go in laser induced demagnetisation?,"The dynamics of ultrafast demagnetisation in 3$d$ magnets is complicated by
the presence of both spin ${\v S}$ and orbital ${\v L}$ angular momentum, with
the microscopic mechanism by which the magnetic moment is redistributed to the
lattice, and at what time scales, yet to be resolved. Employing
state-of-the-art time dependent density function theory we disentangle the
dynamics of these two momenta. Utilising ultra short (5~fs) pulses that
separate spin-orbit (SO) and direct optical excitation time scales, we
demonstrate a two-step microscopic mechanism: (i) an initial loss of ${\v L}$
due to laser excitation, followed post pulse by (ii) an increase of ${\v L}$ as
${\v S}$ transfers to ${\v L}$ during subsequent ($> 15$~fs) SO induced
spin-flip demagnetisation. We also show that to see an unambiguous transfer of
${\v S}$ to ${\v L}$ a short pulse is required.",2012.03657v1
2021-01-30,Real-space charge distribution of the cobalt ion and its relation with charge and spin states,"The charge state of an ion provides a simplified electronic picture of the
bonding in compounds, and heuristically explains the basic electronic structure
of a system. Despite its usefulness, the physical and chemical definition of a
charge state is not a trivial one, and the essential idea of electron transfer
is found to be not a realistic explanation. Here, we study the real-space
charge distribution of a cobalt ion in its various charge and spin states, and
examine the relation between the formal charge/spin states and the static
charge distribution. Taking the prototypical cobalt oxides, La/SrCoO$_3$, and
bulk Co metal, we confirm that no prominent static charge transfer exists for
different charge states. However, we show that small variations exist in the
integrated charges for different charge states, and these are compared to the
various spin state cases.",2102.00130v1
2021-11-29,Element selective ultrafast magnetization dynamics of hybrid Stoner-Heisenberg magnets,"Stoner and Heisenberg excitations in magnetic materials are inherently
different. The former involves an effective reduction of the exchange
splitting, whereas the latter comprises excitation of spin-waves. In this work,
we test the impact of these two excitations in the hybrid Stoner-Heisenberg
system FePd. We present a microscopic picture of ultrafast demagnetization
dynamics in this alloy, which represents both components of strong local
exchange splitting in Fe, and induced polarization in Pd. We identify
spin-orbit coupling and optical inter-site spin transfer as the two dominant
factors for demagnetization at ultrashort timescales. By tuning the external
laser pulse, the extrinsic inter-site spin transfer can be manipulated for site
selective demagnetization on femtosecond time scales providing the fastest way
for optical and selective control of the magnetization dynamics in alloys.
Remarkably, the drastic difference in origin of the magnetic moment of the Fe
and Pd species is not deciding the initial magnetization dynamics in this
alloy.",2111.14607v1
2022-05-22,Rashba spin-orbit interaction induced modulation of magnetic anisotropy,"In past few decades, Rashba spin-orbit coupling (SOC) has been successfully
employed for the emergence of exotic phenomena at the quantum oxide interfaces.
In these systems, the combined effect of charge transfer, broken symmetries and
SOC yields intriguing interfacial magnetism and transport properties. Here, we
provide an insight to control and tune interfacial phenomena in CaMnO3/CaIrO3
based 3d-5d oxide heterostructures by the charge transfer driven Rashba SOC.
Anomalous Hall effect in these canted antiferromagnetic heterostructures
originates from the intrinsic contribution associated with the topology of the
electronic band structure and it is mostly confined to the interface. Rashba
SOC reconstructs the Berry curvature and enhances the anomalous Hall
conductivity by two orders of magnitude. From the anisotropy magnetoresistance
measurements we demonstrate that Rashba SOC is instrumental in tailoring
magnetic anisotropy where magnetization easy-axis rotates from the out-of-plane
direction to the in-plane direction. The ability to tune Rashba SOC and
resulting competing magnetic anisotropy provides a route to manipulate
electronic band structure for the origin of non-trivial spin texture useful for
spin-orbitronics applications.",2205.10859v1
2024-02-06,The QISG suite: high-performance codes for studying Quantum Ising Spin Glasses,"We release a set of GPU programs for the study of the Quantum ($S=1/2$) Spin
Glass on a square lattice, with binary couplings. The library contains two main
codes: MCQSG (that carries out Monte Carlo simulations using both the
Metropolis and the Parallel Tempering algorithms, for the problem formulated in
the Trotter-Suzuki approximation), and EDQSG (that obtains the extremal
eigenvalues of the Transfer Matrix using the Lanczos algorithm). EDQSG has
allowed us to diagonalize transfer matrices with size up to
$2^{36}\times2^{36}$. From its side, MCQSG running on four NVIDIA A100 cards
delivers a sub-picosecond time per spin-update, a performance that is
competitive with dedicated hardware. We include as well in our library GPU
programs for the analysis of the spin configurations generated by MCQSG.
Finally, we provide two auxiliary codes: the first generates the lookup tables
employed by the random number generator of MCQSG; the second one simplifies the
execution of multiple runs using different input data.",2402.03920v1
2024-02-28,A scalable cavity-based spin-photon interface in a photonic integrated circuit,"A central challenge in quantum networking is transferring quantum states
between different physical modalities, such as between flying photonic qubits
and stationary quantum memories. One implementation entails using spin-photon
interfaces that combine solid-state spin qubits, such as color centers in
diamond, with photonic nanostructures. However, while high-fidelity spin-photon
interactions have been demonstrated on isolated devices, building practical
quantum repeaters requires scaling to large numbers of interfaces yet to be
realized. Here, we demonstrate integration of nanophotonic cavities containing
tin-vacancy (SnV) centers in a photonic integrated circuit (PIC). Out of a
six-channel quantum micro-chiplet (QMC), we find four coupled SnV-cavity
devices with an average Purcell factor of ~7. Based on system analyses and
numerical simulations, we find with near-term improvements this multiplexed
architecture can enable high-fidelity quantum state transfer, paving the way
towards building large-scale quantum repeaters.",2402.18057v1
2002-08-20,Tidal Torques and Galactic Warps,"(Abridged) We investigate how galactic disks react to external tidal torques.
We calculate the strength and radial dependence of torques on disks that arise
from a misalignment between the disk and the main axis system of a flattened
dark matter halo. We find that except for in the very inner regions, the
torques are well-described by a power law of the form $\tau \propto r^{-2.5}$.
The magnitude of the torque is large enough for the entire disk to react to the
torque in less than the Hubble time. We demonstrate analytically that disks
which are originally located in the $xy$-plane and which are subjected to a
torque around the x-axis tilt around the y-axis, as also found in fully
non-linear N-body simulations. We further demonstrate that that the torque
causes the radius of a chosen particle to increase with time. Investigations of
tilting disks which treat the disk as a set of solid rings thus may
systematically overestimate the effects of the torque by a factor of two. For
torques of the form we investigate, the inner regions of the disk react to the
torque faster than the outer regions, resulting in a trailing warp. We then
study the effect of the self-gravity of the disk in such a scenario using
numerical N-body models. Self-gravity flattens out the inner regions of the
disk, but these regions are tilted with respect to their initial plane followed
by a non-flat outer region whose tilt decreases with radius. The ``warp
radius,'' which marks the end of the inner flat disk, grows throughout the disk
at a rate that depends only on the strength of the torque and the local surface
density of the disk.",0208380v1
2001-02-06,Casimir Torques between Anisotropic Boundaries in Nematic Liquid Crystals,"Fluctuation-induced interactions between anisotropic objects immersed in a
nematic liquid crystal are shown to depend on the relative orientation of these
objects. The resulting long-range ``Casimir'' torques are explicitely
calculated for a simple geometry where elastic effects are absent. Our study
generalizes previous discussions restricted to the case of isotropic walls, and
leads to new proposals for experimental tests of Casimir forces and torques in
nematics.",0102099v1
2006-07-19,Vibrations of a Pendulum with Oscillating Support and Extra Torque,"The motion of a driven planar pendulum with vertically periodically
oscillating point of suspension and under the action of an additional constant
torque is investigated. We study the influence of the torque strength on the
transition to chaotic motions of the pendulum using Melnikov's analysis.",0607043v1
2011-09-20,Analysis of a Three Phase Induction Motor Directly from Maxwell's Equations,"The torque developed in a three phase AC squirrel cage motor is usually
expressed in terms of resistances and reactances of the stator, the rotor, and
the motor as a whole. We use Maxwell's equations to find the torque in terms of
geometrical parameters. This allows us to estimate the torque developed by a
motor without knowing the details of its circuitry.",1109.4203v1
2013-04-28,The Casimir Torque on a Cylindrical Gear,"We utilize Effective Field Theory(EFT) techniques to calculate the casimir
torque on a cylindrical gear in the presence of a polarizable but neutral
object. We present results for the energy and torque as a function of angle for
a gear with multiple cogs, as well as for the case of a concentric cylindrical
gear.",1304.7475v2
2013-07-31,Casimir Torque for a Perfectly Conducting Wedge: A Canonical Quantum Field Theoretical Approach,"The torque density per unit height exerted on a perfectly conducting wedge
due to the quantum vacuum fluctuations (the Casimir torque) is obtained. A
canonical quantum field theoretical approach with the method of calculating
vacuum-to-vacuum propagator (Green function) [1] is used.",1308.0006v1
2014-05-31,The Superrotation of Venus: Where's the Torque?,"The superrotation of the atmosphere of Venus requires a large torque on the
up- per atmosphere. Mechanisms for providing a net balancing of this through
waves or ionospheric motions to other parts of the atmosphere have been
proposed but all have difficulties. Here we demonstrate that the albedo
gradient from the day to night side of the cloud layer allows a gradient of
light pressure that is sufficient to provide an external torque to drive this
flow.",1406.0116v1
2015-07-30,Casimir torque between nanostructured plates,"We investigate in detail the Casimir torque induced by quantum vacuum
fluctuations between two nanostructured plates. Our calculations are based on
the scattering approach and take into account the coupling between different
modes induced by the shape of the surface which are neglected in any sort of
proximity approximation or effective medium approach. We then present an
experimental setup aiming at measuring this torque.",1507.08604v1
2011-08-23,Modelling the spinning dust emission from dense interstellar clouds,"Electric dipole emission arising from PAHs is often invoked to explain the
anomalous microwave emission (AME). This assignation is based on an observed
tight correlation between the mid-IR emission of PAHs and the AME; and a good
agreement between models of spinning dust and the broadband AME spectrum. So
far often detected at large scale in the diffuse interstellar medium, the AME
has recently been studied in detail in well-known dense molecular clouds with
the help of Planck data. While much attention has been given to the physics of
spinning dust emission, the impact of varying local physical conditions has not
yet been considered in detail. Our aim is to study the emerging spinning dust
emission from interstellar clouds with realistic physical conditions and
radiative transfer. We use the DustEM code from Compiegne et al. to describe
the extinction and IR emission of all dust populations. The spinning dust
emission is obtained with SpDust, as described by Silsbee et al., that we have
coupled to DustEM. We carry out full radiative transfer simulations and
carefully estimate the local gas state as a function of position within
interstellar clouds. We show that the spinning dust emission is sensitive to
the abundances of the major ions and we propose a simple scheme to estimate
these abundances. We also investigate the effect of changing the cosmic-ray
rate. In dense media, where radiative transfer is mandatory, we show that the
relationship between the spinning and mid-IR emissivities of PAHs is no longer
linear and that the spinning dust emission may actually be strong at the centre
of clouds where the mid-IR PAH emission is weak. These results provide new ways
to trace grain growth from diffuse to dense medium and will be useful for the
analysis of AME at the scale of interstellar clouds.",1108.4563v2
2015-10-30,"The spin rates of O stars in WR + O binaries. I. Motivation, methodology and first results from SALT","The black holes (BH) in merging BH-BH binaries are likely progeny of binary O
stars. Their properties, including their spins, will be strongly influenced by
the evolution of their progenitor O stars. The remarkable observation that many
single O stars spin very rapidly can be explained if they accreted angular
momentum from a mass-transferring, O-type or Wolf-Rayet companion before that
star blew up as a supernova. To test this prediction, we have measured the spin
rates of eight O stars in Wolf-Rayet (WR) + O binaries, increasing the total
sample size of such O stars' measured spins from two to ten. Polarimetric and
other determinations of these systems' sin i allow us to determine an average
equatorial rotation velocity from HeI (HeII) lines of $v_e$ = 348 (173) km/s
for these O stars, with individual star's $v_e$ from HeI (HeII) lines ranging
from 482 (237) to 290 (91) km/s. We argue that the $\sim$ 100\% difference
between HeI and HeII speeds is due to gravity darkening. Super-synchronous
spins, now observed in all 10 O stars in WR + O binaries where it has been
measured, are strong observational evidence that Roche lobe overflow mass
transfer from a WR progenitor companion has played a critical role in the
evolution of WR+OB binaries. While theory predicts that this mass transfer
rapidly spins-up the O-type mass gainer to a nearly break-up rotational
velocity $v_e \sim 530 $ km/s, the observed average $v_e$ of the O-type stars
in our sample is 65\% that speed. This demonstrates that, even over the
relatively short WR-phase timescale, tidal and/or other effects causing
rotational spin-down must be efficient. A challenge to tidal synchronization
theory is that the two longest-period binaries in our sample (with periods of
29.7 and 78.5 days) unexpectedly display super-synchronous rotation.",1511.00046v3
2022-05-11,Direct detection of spin polarization in photoinduced charge transfer through a chiral bridge,"It is well assessed that the charge transport through a chiral potential
barrier can result in spin-polarized charges. The possibility of driving this
process through visible photons holds tremendous potential for several aspects
of quantum information science, e.g., the optical control and readout of
qubits. In this context, the direct observation of this phenomenon via
spin-sensitive spectroscopies is of utmost importance to establish future
guidelines to control photo-driven spin selectivity in chiral structures. Here,
we provide direct proof that time-resolved electron paramagnetic resonance
(EPR) can be used to detect long-lived spin polarization generated by
photoinduced charge transfer through a chiral bridge. We propose a system
comprising CdSe QDs, as a donor, and C60, as an acceptor, covalently linked
through a saturated oligopeptide helical bridge (\c{hi}) with a rigid structure
of ~ 10{\AA}. Time-resolved EPR spectroscopy shows that the charge transfer in
our system results in a C60 radical anion, whose spin polarization maximum is
observed at longer times with respect to that of the photogenerated C60 triplet
state. Notably, the theoretical modeling of the EPR spectra reveals that the
observed features may be compatible with chirality-induced spin selectivity and
identifies which parameters need optimization for unambiguous detection of the
phenomenon. This work lays the basis for the optical generation and direct
manipulation of spin polarization induced by chirality.",2205.05353v1
2000-06-25,Time Optimal Control in Spin Systems,"In this paper, we study the design of pulse sequences for NMR spectroscopy as
a problem of time optimal control of the unitary propagator. Radio frequency
pulses are used in coherent spectroscopy to implement a unitary transfer of
state. Pulse sequences that accomplish a desired transfer should be as short as
possible in order to minimize the effects of relaxation and to optimize the
sensitivity of the experiments. Here, we give an analytical characterization of
such time optimal pulse sequences applicable to coherence transfer experiments
in multiple-spin systems. We have adopted a general mathematical formulation,
and present many of our results in this setting, mindful of the fact that new
structures in optimal pulse design are constantly arising. Moreover, the
general proofs are no more difficult than the specific problems of current
interest. From a general control theory perspective, the problems we want to
study have the following character. Suppose we are given a controllable right
invariant system on a compact Lie group, what is the minimum time required to
steer the system from some initial point to a specified final point? In NMR
spectroscopy and quantum computing, this translates to, what is the minimum
time required to produce a unitary propagator? We also give an analytical
characterization of maximum achievable transfer in a given time for the two
spin system.",0006114v2
2009-03-24,"Polarization transfer measurements for $^{12}{\rm C}(\vec{p},\vec{n})^{12}{\rm N (g.s.},1^+)$ at 296 MeV and nuclear correlation effects","Differential cross sections and complete sets of polarization observables are
presented for the Gamow-Teller $^{12}{\rm C}(\vec{p},\vec{n})^{12}{\rm N}({\rm
g.s.},1^+)$ reaction at a bombarding energy of 296 MeV with momentum transfers
$q$ of 0.1 to $2.2{\rm fm}^{-1}$. The polarization transfer observables are
used to deduce the spin-longitudinal cross section, $ID_q$, and spin-transverse
cross sections, $ID_p$ and $ID_n$. The data are compared with calculations
based on the distorted wave impulse approximation (DWIA) using shell-model wave
functions. Significant differences between the experimental and theoretical
results are observed for all three spin-dependent $ID_i$ at momentum transfers
of $q \gtrsim 0.5{\rm fm}^{-1}$, suggesting the existence of nuclear
correlations beyond the shell model. We also performed DWIA calculations
employing random phase approximation (RPA) response functions and found that
the observed discrepancy is partly resolved by the pionic and rho-mesonic
correlation effects.",0903.4105v2
2017-08-18,Frequency-dependent current noise in quantum heat transfer with full counting statistics,"To investigate frequency-dependent current noise (FDCN) in open quantum
systems at steady states, we present a theory which combines Markovian quantum
master equations with a finite time full counting statistics. Our formulation
of the FDCN generalizes previous zero-frequency expressions and can be viewed
as an application of MacDonald's formula for electron transport to heat
transfer. As a demonstration, we consider the paradigmatic example of quantum
heat transfer in the context of a non-equilibrium spin-boson model. We adopt a
recently developed polaron-transformed Redfield equation which allows us to
accurately investigate heat transfer with arbitrary system-reservoir coupling
strength, arbitrary values of spin bias as well as temperature differences. We
observe maximal values of FDCN in moderate coupling regimes, similar to the
zero-frequency cases. We find the FDCN with varying coupling strengths or bias
displays a universal Lorentzian-shape scaling form in the weak coupling regime,
and a white noise spectrum emerges with zero bias in the strong coupling regime
due to a distinctive spin dynamics. We also find the bias can suppress the FDCN
in the strong coupling regime, in contrast to its zero-frequency counterpart
which is insensitive to bias changes. Furthermore, we utilize the Saito-Utsumi
relation as a benchmark to validate our theory and study the impact of
temperature differences at finite frequencies. Together, our results provide
detailed dissections of the finite time fluctuation of heat current in open
quantum systems.",1708.05537v2
1997-04-14,Non-linear evolution of the tidal angular momentum of protostructures II: non-Gaussian initial conditions,"The formalism that describes the non-linear growth of the angular momentum L
of protostructures from tidal torques in a Friedmann Universe, as developed in
a previous paper, is extended to include non-Gaussian initial conditions. We
restrict our analysis here to a particular class of non-Gaussian primordial
distributions, namely multiplicative models. In such models, strongly
correlated phases are produced by obtaining the gravitational potential via a
nonlinear local transformation of an underlying Gaussian random field. The
dynamical evolution of the system is followed by describing the trajectories of
fluid particles using second-order Lagrangian perturbation theory. In the
Einstein-de Sitter universe, the lowest-order perturbative correction to the
variance of the linear angular momentum of collapsing structures grows as t^8/3
for generic non-Gaussian statistics, which contrasts with the t^10/3 growth
rate characteristic of Gaussian statistics. This is a consequence of the fact
that the lowest-order perturbative spin contribution in the non-Gaussian case
arises from the third moment of the gravitational potential, which is
identically zero for a Gaussian field. Evaluating these corrections at the
maximum expansion time of the collapsing structure, we find that these
non-Gaussian and non-linear terms can be as high as the linear estimate,
without the degree of non-Gaussianity as quantified by skewness and kurtosis of
the density field being unacceptably large. The results suggest that
higher-order terms in the perturbative expansion may contribute significantly
to galactic spin which contrasts with the straightforward Gaussian case.",9704119v1
1997-04-28,A Laboratory for Magnetized Accretion Disk Model: Ultraviolet and X-ray Emission from Cataclysmic Variable GK Persei,"We analyze the ultraviolet spectrum of the cataclysmic variable GK Per at
maximum light. The flat ultraviolet spectrum in this system requires a
truncated inner accretion disk and an unusually flat radial temperature
profile. This requirement is not satisfied by any non-magnetic steady or
non-steady disk model. We consider a magnetized accretion disk model to explain
the ultraviolet spectrum. The available data on the white dwarf spin and
possible quasi-periodic oscillations constrain the magnetic field, $B_{*}$, and
the disk accretion rate, ${\dot M}$, to lie along a well-defined
spin-equilibrium condition $({\dot M}/10^{17} ~ g ~ s^{-1}) \sim
100(B_{*}/10^7G)^2$. Our self-consistent treatment of the magnetic torque on
the disk flattens the disk temperature distribution outside the disk truncation
radius. This modified temperature distribution is too steep to explain the UV
spectrum for reasonable field strengths. X-ray heating is a plausible
alternative to magnetic heating in GK Per. We estimate that the disk intercepts
$\sim$ 5% of the accretion energy in outburst, which results in an extra disk
luminosity of $\sim$ 5--10 $L_{\odot}$. Model spectra of optically thick disks
are too blue to match observations. The UV spectrum of an optically thick disk
with an optically thin, X-ray heated corona resembles the observed spectrum.
The X-ray luminosity observed during the outburst indicates ${\dot M}<10^{18} ~
g ~ s^{-1}$, which is a factor of 10 lower than that required to explain the
ultraviolet luminosity. Radiation drag on material flowing inward along the
accretion column lowers the shock temperature and reduces the X-ray luminosity.
Most of the accretion energy is then radiated at extreme ultraviolet
wavelengths.",9704270v1
1999-09-02,X-ray observations during a Her X-1 anomalous low-state,"Results of a 1999 July 8-10 BeppoSAX observation during an anomalous
low-state of Her X-1 are presented. The standard on-state power-law and
blackbody continuum model is excluded at high confidence unless partial
covering is included. This gives a power-law photon index of 0.63 +/- 0.02 and
implies that 0.28 +/- 0.03 of the flux undergoes additional absorption of (27
+/- 7) 10^22 atom/cm2. 11% of the observed 0.1-10 keV flux is from the 0.068
+/- 0.015 keV blackbody. 1.237747(2) s pulses with a semi-amplitude of 2.1 +/-
0.8% are detected at >99.5% confidence and confirmed by RXTE measurements. This
implies that Her X-1 underwent substantial spin-down close to the start of the
anomalous low-state. The spectral and temporal changes are similar to those
recently reported from 4U1626-67. These may result from a strongly warped disk
that produces a spin-down torque. The X-ray source is then mostly viewed
through the inner regions of the accretion disk. A similar mechanism could be
responsible for the Her X-1 anomalous low-states. Shadowing by such an
unusually warped disk could produce observable effects in the optical and UV
emission from the companion star.",9909039v1
2000-01-08,Deformations of Accreting Neutron Star Crusts and Gravitational Wave Emission,"Motivated by the narrow range of spin frequencies of nearly 20 accreting
neutron stars, Bildsten (1998) conjectured that their spin-up had been halted
by the emission of gravitational waves. He also pointed out that small
nonaxisymmetric temperature variations in the accreted crust will lead to
""wavy"" electron capture layers, whose horizontal density variations naturally
create a mass quadrupole moment.
  We present a full calculation of the crust's elastic adjustment to these
density perturbations and find that the elastic response of the crust reduces
Bildsten's original estimate of the quadrupole moment in the thin outer crust
by a factor of 20-50. However, this basic picture, when applied to capture
layers in the deep inner crust, can generate quadrupoles in the necessary range
as long as there are ~5% lateral temperature variations in the inner crust. By
calculating the thermal flow throughout the core and the crust, we find that
temperature gradients this large are easily maintained by asymmetric heat
sources or lateral composition gradients in the crust.
  We also derive a general relation between the stresses and strains in the
crust and the maximum quadrupole moment they can generate. We show under quite
general conditions that maintaining a quadrupole of the magnitude necessary to
balance the accretion torque requires dimensionless strains close to 0.01 at
near-Eddington accretion rates, of order the breaking strain of conventional
materials.",0001136v2
2000-04-04,Radiative Precession of an Isolated Neutron Star,"Euler's equations of motion are derived exactly for a rigid, triaxial,
internally frictionless neutron star spinning down electromagnetically in
vacuo. It is shown that the star precesses, but not freely: its regular
precession relative to the principal axes of inertia couples to the component
of the radiation torque associated with the near-zone radiation fields and is
modified into an anharmonic wobble. The wobble period \tau_1 typically
satisfies \tau_1 < 10^{-2}\tau_0, where \tau_0 is the braking time-scale; the
wobble amplitude evolves towards a constant non-zero value, oscillates, or
decreases to zero, depending on the degree of oblateness or prolateness of the
star and its initial spin state; and the (negative) angular frequency
derivative d{\omega}/dt oscillates as well, exhibiting quasi-periodic spikes
for triaxial stars of a particular figure. In light of these properties, a
young, Crab-like pulsar ought to display fractional changes of order unity in
the space of a few years in its pulse profile, magnetic inclination angle, and
d{\omega}/dt. Such changes are not observed, implying that the wobble is damped
rapidly by internal friction, if its amplitude is initially large upon
crystallization of the stellar crust. If the friction is localized in the inner
and outer crusts, the thermal luminosity of the neutron star increases by a
minimum amount \Delta L = 3*10^{31} (\epsilon / 10^{-12}) (\omega / 10^3 rad
s^{-1})^2 (\tau_d / 1 yr)^{-1} erg s^{-1}, where epsilon is the ellipticity and
\tau_d is the damping time-scale, with the actual value of \Delta L determined
in part by the thermal conduction time \tau_cond. The increased luminosity is
potentially detectable as thermal X-rays lasting for a time max(tau_d,tau_cond)
following crystallization of the crust.",0004035v1
2000-08-06,A 700 year-old Pulsar in the Supernova Remnant Kes 75,"Since their discovery 30 years ago, pulsars have been understood to be
neutron stars (NSs) born rotating rapidly (~ 10-100 ms). These neutron stars
are thought to be created in supernova explosions involving massive stars,
which give rise to expanding supernova remnants (SNRs). With over 220 Galactic
SNRs known (Green 1998) and over 1200 radio pulsars detected (Camilo et al.
2000), it is quite surprising that few associations between the two populations
have been identified with any certainty. Here we report the discovery of a
remarkable 0.3 sec X-ray pulsar, PSR J1846-0258, associated with the supernova
remnant Kes 75. With a characteristic age of only 723 yr, consistent with the
age of Kes 75, PSR J1846-0258 is the youngest pulsar yet discovered and is
being rapidly spun down by torques from a large magnetic dipole of strength ~
5E13 G, just above the so-called quantum critical field. PSR J1846-0258 resides
in this transitional regime where the magnetic field is hypothesized to
separate the regular pulsars from the so-called magnetars. PSR J1846-0258 is
evidently a Crab-like pulsar, however, its period, spin-down rate, spin-down
conversion efficiency, are each an order-of-magnitude greater, likely the
result of its extreme magnetic field.",0008097v1
2000-09-28,Bound near-equatorial orbits around neutron stars,"Recent discovery of kilohertz quasi-periodic brightness oscillations of low
mass X-ray binaries (LMXBs) has attracted attention to highly relativistic
periodic motion near accreting neutron stars. Most models proposed so far
involve (almost) inertial motion in the vicinity of the stars' innermost stable
circular orbits. In the present paper we study general-relativistic circular
and eccentric orbits around spinning neutron stars assuming the orbits are
slightly tilted with respect to the stars' equatorial planes. We develop
analytical and numerical techniques for integrating bound timelike geodesics in
fully relativistic neutron star spacetimes obtained by modern numerical codes.
We use equations of state of neutron star matter that span a broad range of
stiffness, while the explored range of masses M > 1.7 M(solar) and spin
frequencies nu_s < 600 Hz is motivated by the observations of LMXBs. We
investigate the general-relativistic effects of periastron advance and nodal
precession in the strong gravitational fields of rotating neutron stars and
compare quantitatively the associated orbital frequencies with the more readily
obtainable frequencies of orbits around Kerr black holes on the one hand, and
low-order post-Newtonian (PN) expansions, on the other. While Kerr results
approximate the periastron advance frequency much better than the PN
expressions, the retrograde torque caused by the high quadrupole moments of the
rotating stars clearly favours the PN approximation in the case of nodal
precession. The methods developed in the present paper are used in the
companion paper to test recent hypotheses regarding the origin of
quasi-periodic oscillations in accreting neutron star sources.",0009450v1
2001-03-14,The Evolution of Relativistic Binary Progenitor Systems,"Relativistic binary pulsars, such as B1534+12 and B1913+16 are characterized
by having close orbits with a binary separation of ~ 3 R_\sun. The progenitor
of such a system is a neutron star, helium star binary. The helium star, with a
strong stellar wind, is able to spin up its compact companion via accretion.
The neutron star's magnetic field is then lowered to observed values of about
10^{10} Gauss. As the pulsar lifetime is inversely proportional to its magnetic
field, the possibility of observing such a system is, thus, enhanced by this
type of evolution. We will show that a nascent (Crab-like) pulsar in such a
system can, through accretion-braking torques (i.e. the ""propeller effect"") and
wind-induced spin-up rates, reach equilibrium periods that are close to
observed values. Such processes occur within the relatively short helium star
lifetimes. Additionally, we find that the final outcome of such evolutionary
scenarios depends strongly on initial parameters, particularly the initial
binary separation and helium star mass. It is, indeed, determined that the
majority of such systems end up in the pulsar ""graveyard"", and only a small
fraction are strongly recycled. This fact might help to reconcile theoretically
expected birth rates with limited observations of relativistic binary pulsars.",0103216v1
2002-08-19,Kerr black holes and time profiles of gamma-ray bursts,"The cumulative light curves of gamma-ray bursts (GRBs) smooth the spiky
nature of the running light curve. The cumulative count increases in an
approximately linear way with time t for most bursts. In 19 out of 398 GRBs
with T90 > 2s, the cumulative light curve was found to increase with time as
\~t^2 implying a linear increase in the running light curve. The non-linear
sections last for a substantial fraction of the GRB duration, have a large
proportion of the cumulative count and many resolved pulses that usually end
with the highest pulse in the burst. The reverse behaviour was found in 11 GRBs
where the running light curve decreased with time and some bursts are good
mirror images of the increases. These GRBs are among the spectrally hardest
bursts observed by BATSE. The most likely interpretation is that these effects
are signatures of black holes that are either being spun up or down in the
accretion process. In the spin up case, the increasing Kerr parameter of the
black hole allows additional rotational and accretion energy to become
available for extraction. The process is reversed if the black hole is spun
down by magnetic field torques. The luminosity changes in GRBs are consistent
with the predictions of the BZ process and neutrino annihilation and thus
provide the link to spinning black holes. GRBs provide a new window for
studying the general relativistic effects of Kerr black holes.",0208349v1
2003-06-03,The near-synchronous polar V1432 Aql (RX J1940.1-1025): Accretion geometry and synchronization time scale,"The magnetic Cataclysmic Variable (mCV) V1432 Aql (RX 1940.1-1025) belongs to
the four-member subclass of near-synchronous polars with a slight
non-synchronism (<2 %) between the spin period of the white dwarf and the
binary period. In these systems the accretion geometry changes periodically
with phase of the beat cycle. We present the application of a dipole accretion
model for near-synchronous systems developed by Geckeler & Staubert (1997a) to
extended optical and X-ray data. We detect a significant secular change of the
white dwarf spin period in V1432 Aql of dP_spin/dt = -5.4 (+3.7/-3.2) 10-9 s/s
from the optical data set alone. This corresponds to a synchronization time
scale tau_sync = 199 (+441/-75) yr, comparable to the time scale of 170 yr for
V1500 Cyg. The synchronization time scale in V1432 Aql is in excellent
agreement with the theoretical prediction from the dominating magnetic torque
in near-synchronous systems. We also present period analyses of optical CCD
photometry and RXTE X-ray data, which argue against the existence of a 4000 s
period and an interpretation of V1432 Aql as an intermediate polar. The dipole
accretion model also allows to constrain the relevant parameters of the
accretion geometry in this system: the optical data allow an estimate of the
dimensionless parameter (R_t0'/R_wd)1/2 sin(beta) = 3.6 (+2.7/-1.1), with a
lower limit for the threading radius of R_t0' > 10 R_wd (68% confidence).",0306072v1
2004-04-05,Anomalous X-ray Pulsar 1E 1048.1-5937: Pulsed Flux Flares and Large Torque Variations,"We report on continued monitoring of the Anomalous X-ray pulsar (AXP) 1E
1048.1-5937 using the Rossi X-ray Timing Explorer. We confirm that this pulsar
has exhibited significant pulsed flux variability. The principal features of
this variability are two pulsed X-ray flares. Both flares lasted several months
and had well-resolved few-week-long rises. The long rise times of the flares
are a phenomenon not previously reported for this class of object. The epochs
of the flare peaks were MJD 52,218.8+/-4.5 and 52,444.4+/-7.0. Both flares had
shorter rise than fall times. The flares had peak fluxes of 2.21+/-0.16 and
3.00+/-0.13 times the quiescent value. We estimate a total 2-10 keV energy
release of ~2.7x10^40 ergs and ~2.8x10^41 ergs for the flares, assuming a
distance of 5 kpc. We also report large (factor of ~12) changes to the pulsar's
spin-down rate on time scales of weeks to months, shorter than has been
reported previously. We find marginal evidence for correlation between the flux
and spin-down rate variability, with probability of nonrandom correlation 6%.
We discuss the implications of our findings for AXP models.",0404113v2
2005-06-08,Three-Dimensional Numerical Simulations of Thermal-Gravitational Instability in Protogalactic Halo Environment,"We study thermal-gravitational instability in simplified models for
protogalactic halos using three-dimensional hydrodynamic simulations. The
simulations followed the evolution of gas with radiative cooling down to T =
10^4 K, background heating, and self-gravity. Then cooled and condensed clouds
were identified and their physical properties were examined in detail. During
early stage clouds start to form around initial density peaks by thermal
instability. Small clouds appear first and they are pressure-bound.
Subsequently, the clouds grow through compression by the background pressure as
well as gravitational infall. During late stage cloud-cloud collisions become
important, and clouds grow mostly through gravitational merging.
Gravitationally bound clouds with mass M_c > ~6 X 10^6 Msun are found in the
late stage. They are approximately in virial equilibrium and have radius R_c =
\~150 - 200 pc. Those clouds have gained angular momentum through tidal torque
as well as merging, so they have large angular momentum with the spin parameter
<lambda_s> ~ 0.3. The clouds formed in a denser background tend to have smaller
spin parameters. We discuss briefly the implications of our results on the
formation of protoglobular cluster clouds in protogalactic halos. (abridged)",0506160v1
2007-03-16,Cassini States with Dissipation: Why Obliquity Tides Cannot Inflate Hot Jupiters,"Some short-period exoplanets (hot Jupiters) are observed by their transits to
have anomalously large radii. It has been suggested that these planets are in a
resonance involving persistent misalignment and synchronous precession of their
spin and orbital angular momenta, a Cassini state, and that the attendant tidal
heating inflates the planet. We argue against this. Using explicit tidal
integrations, we show that although an oblique Cassini state can dissipate many
times the rotational energy of the planet, the rate of dissipation must be much
less than hypothesized. Dissipation causes the planetary spin to lie at an
angle to the plane containing the orbital and total angular momenta. If
dissipation is too rapid, this angle becomes so large that Cassini equilibrium
is lost. A separate consideration limits the total energy that can be extracted
from the orbit. The source of the torque on the orbit, either an oblique parent
star or an inclined third body, aligns with the orbit as it absorbs the angular
momentum shed by the planet. Alignment removes the orbital precession required
by the Cassini state. In combination with observational bounds on the mass and
semimajor axis of a possible second planet and with bounds on the stellar
rotation and obliquity, these constraints make it very unlikely that obliquity
tides can be the explanation for inflated hot Jupiters, especially HD 209458b.",0703418v1
2006-10-31,Uniform and staggered magnetizations induced by Dzyaloshinskii-Moriya interactions in isolated and coupled spin 1/2 dimers in a magnetic field,"We investigate the interplay of Dzyaloshinskii-Moriya interactions and an
external field in spin 1/2 dimers. For isolated dimers and at low field, we
derive simple expressions for the staggered and uniform magnetizations which
show that the orientation of the uniform magnetization can deviate
significantly from that of the external field. In fact, in the limit where the
${\bf D}$ vector of the Dzyaloshinskii-Moriya interaction is parallel to the
external field, the uniform magnetization actually becomes {\it perpendicular}
to the field. For larger fields, we show that the staggered magnetization of an
isolated dimer has a maximum close to one-half the polarization, with a large
maximal value of $0.35 g\mu_B$ in the limit of very small Dzyaloshinskii-Moriya
interaction. We investigate the effect of inter-dimer coupling in the context
of ladders with Density Matrix Renormalization Group (DMRG) calculations and
show that, as long as the values of the Dzyaloshinskii-Moriya and of the
exchange interaction are compatible with respect to the development of a
staggered magnetization, the simple picture that emerges for isolated dimers is
also valid for weakly coupled dimers with minor modifications. The results are
compared with torque measurements on
Cu$_{2}$(C$_{5}$H$_{12}$N$_{2}$)$_{2}$Cl$_{4}$.",0610861v1
2004-01-28,The Maxwell equations including magnetic monopoles,"The derivation of the Maxwell equations is reproduced whereby magnetic
charges are included. This ansatz yields the results: 1) Longitudinal Ampere
forces in a differential magnetostatic force law are improbable. Otherwise an
electric current would generate magnetic charges. 2) Simple magnetic and
electric induced polarization phenomena are completely analogous and are
described by a Laplace equation. 3) Magnetic charges are the topological
defects of a magnetic spin field similar like electric charges are the
topological defects of an electric field. The magnetic charges should be
interconnected with an elastic or inertial field which compensates the torque
field generated by the magnetic moments of the anisotropic distributed spins.
4) Permanent magnetic fields can be understood to be caused by magnetic
charges. Consequently, a moving permanent magnet represents a magnetic current
which generates an electric field. 5) The electromagnetic tensors of energy and
momentum have some additional terms which are written down generally. 6)
Nonlinear electro-thermodynamic systems may violate the second law of
thermodynamics. This is illustrated by an electric cycle with a data storing
FET invented by Yusa & Sakaki.",0401151v3
2008-01-11,A study of the long term evolution of quasi periodic oscillations in the accretion powered X-ray pulsar 4U 1626-67,"We report here a study of the long term properties of Quasi Periodic
Oscillations (QPO) in an unusual accreting X-ray pulsar, 4U 1626--67. This is a
unique accretion powered X-ray pulsar in which we have found the QPOs to be
present during all sufficiently long X-ray observations with a wide range of
X-ray observatories. In the present spin-down era of this source, the QPO
central frequency is found to be decreasing. In the earlier spin-up era of this
source, there are only two reports of QPO detections, in 1983 with EXOSAT and
1988 with GINGA with an increasing trend. The QPO frequency evolution in 4U
1626--67 during the last 22 years changed from a positive to a negative trend,
somewhat coincident with the torque reversal in this source. In the accretion
powered X-ray pulsars, the QPO frequency is directly related to the inner
radius of the accretion disk, as per Keplerian Frequency Model (KFM) and Beat
Frequency Model (BFM). A gradual depletion of accretion disk is reported
earlier from the X-ray spectral, flux and pulse profile measurements. The
present QPO frequency evolution study shows that X-ray flux and mass accretion
rate may not change by the same factor, hence the simple KFM and BFM are not
able to explain the QPO evolution in this source. This is the only X-ray pulsar
to show persistent QPOs and is also the first accreting X-ray pulsar in which
the QPO history is reported for a long time scale relating it with the long
term evolution of the accretion disk.",0801.1761v1
2009-03-13,Spin-torque driven magnetization dynamics in a nanocontact setup for low external fields: numerical simulation study,"We present numerical simulation studies of the steady-state magnetization
dynamics driven by a spin-polarized current in a point contact geometry for the
case of a relatively large contact diameter (D = 80 nm) and small external
field (H = 30 Oe). We show, that under these conditions the magnetization
dynamics is qualitatively different from the dynamics observed for small
contacts in large external fields. In particular, the 'bullet' mode with a
homogeneous mode core, which was the dominating localized mode for small
contacts, is not found here. Instead, all localized oscillation modes observed
in simulations correspond to different motion kinds of vortex-antivortex (V-AV)
pairs. These kinds include rotational and translational motion of pairs with
the V-AV distance d ~ D and creation/annihilation of much smaller (satellite)
V-AV pairs. We also show that for the geometry studied here the Oersted field
has a qualitative effect on the magnetization dynamics of a 'free' layer. This
effect offers a possibility to control magnetization dynamics by a suitable
electric contact setup, optimized to produce a desired Oersted field. Finally,
we demonstrate that when the magnetization dynamics of the 'fixed' layer
(induced only by the stray field interaction with the 'free' layer) is taken
into account, the threshold current for the oscillation onset is drastically
reduced and new types of localized modes appear. In conclusion, we show that
our simulations reproduce semiquantitatively several important features of the
magnetization dynamics in a point contact system for low external fields
reported experimentally.",0903.2416v1
2009-12-11,Thermal Tides in Fluid Extrasolar Planets,"Asynchronous rotation and orbital eccentricity lead to time-dependent
irradiation of the close-in gas giant exoplanets -- the hot Jupiters. This
time-dependent surface heating gives rise to fluid motions which propagate
throughout the planet. We investigate the ability of this ""thermal tide"" to
produce a quadrupole moment which can couple to the stellar gravitational tidal
force. While previous investigations discussed planets with solid surfaces,
here we focus on entirely fluid planets in order to understand gas giants with
small cores. The Coriolis force, thermal diffusion and self-gravity of the
perturbations are ignored for simplicity. First, we examine the response to
thermal forcing through analytic solutions of the fluid equations which treat
the forcing frequency as a small parameter. In the ""equilibrium tide"" limit of
zero frequency, fluid motion is present but does not induce a quadrupole
moment. In the next approximation, finite frequency corrections to the
equilibrium tide do lead to a nonzero quadrupole moment, the sign of which
torques the planet {\it away} from synchronous spin. We then numerically solve
the boundary value problem for the thermally forced, linear response of a
planet with neutrally stratified interior and stably stratified envelope. The
numerical results find quadrupole moments in agreement with the analytic
non-resonant result at sufficiently long forcing period. Surprisingly, in the
range of forcing periods of 1-30 days, the induced quadrupole moments can be
far larger than the analytic result due to response of internal gravity waves
which propagate in the radiative envelope. We discuss the relevance of our
results for the spin, eccentricity and thermal evolution of hot Jupiters.",0912.2313v1
2009-12-28,Universality between current- and field-driven domain wall dynamics in ferromagnetic nanowires,"Spin-polarized electric current exerts torque on local magnetic spins,
resulting in magnetic domain-wall (DW) motion in ferromagnetic nanowires. Such
current-driven DW motion opens great opportunities toward next-generation
magnetic devices controlled by current instead of magnetic field. However, the
nature of the current-driven DW motion--considered qualitatively different from
magnetic-field-driven DW motion--remains yet unclear mainly due to the
painfully high operation current densities J_OP, which introduce uncontrollable
experimental artefacts with serious Joule heating. It is also crucial to reduce
J_OP for practical device operation. By use of metallic Pt/Co/Pt nanowires with
perpendicular magnetic anisotropy, here we demonstrate DW motion at current
densities down to the range of 10^9 A/m^2--two orders smaller than existing
reports. Surprisingly the current-driven motion exhibits a scaling behaviour
identical to the field-driven motion and thus, belongs to the same universality
class despite their qualitative differences. Moreover all DW motions driven by
either current or field (or by both) collapse onto a single curve, signalling
the unification of the two driving mechanisms. The unified law manifests
non-vanishing current efficiency at low current densities down to the practical
level, applicable to emerging magnetic nanodevices.",0912.5127v2
2010-06-08,"Misaligned Angular Momentum in Hydrodynamic Cosmological Simulations: Warps, Outer Discs, and Thick Discs","We present a detailed analysis of a disc galaxy forming in a high-resolution
fully cosmological simulation to investigate the nature of the outer regions of
discs and their relevance for the disc formation process. Specifically, we
focus on the phenomenon of misaligned disc components and find that the outer
disc warp is a consequence of the misalignment between the inner disc and the
surrounding hot gaseous halo. As the infalling cold gas sinks toward the centre
of the galaxy, it is strongly torqued by the hot gas halo. By the time the
fresh gas reaches the central disc-forming region its angular momentum is
completely aligned with the spin of the hot gas halo. If the spin of the hot
gas halo, in turn, is not aligned with that of the inner disc, a misaligned
outer disc forms comprised of newly accreted material. The inner and outer
components are misaligned with each other because they respond differently to
infalling substructure and accretion. The warped disc feeds the main gas disc
due to viscous angular momentum losses, but small amounts of star formation in
the warp itself form a low-metallicity thick disc. We show that observations of
resolved stellar populations in warped galaxies in the local universe could
provide evidence for the presence of these processes and therefore indirectly
reveal ongoing gas accretion and the existence of hot gas halos.",1006.1659v1
2013-01-14,Measurement of Permanent Electric Dipole Moments of Charged Hadrons in Storage Rings,"Permanent Electric Dipole Moments (EDMs) of elementary particles violate two
fundamental symmetries: time reversal invariance (T) and parity (P). Assuming
the CPT theorem this implies CP-violation. The CP-violation of the Standard
Model is orders of magnitude too small to be observed experimentally in EDMs in
the foreseeable future. It is also way too small to explain the asymmetry in
abundance of matter and anti-matter in our universe. Hence, other mechanisms of
CP violation outside the realm of the Standard Model are searched for and could
result in measurable EDMs.
  Up to now most of the EDM measurements were done with neutral particles. With
new techniques it is now possible to perform dedicated EDM experiments with
charged hadrons at storage rings where polarized particles are exposed to an
electric field. If an EDM exists the spin vector will experience a torque
resulting in change of the original spin direction which can be determined with
the help of a polarimeter. Although the principle of the measurement is simple,
the smallness of the expected effect makes this a challenging experiment
requiring new developments in various experimental areas.
  Complementary efforts to measure EDMs of proton, deuteron and light nuclei
are pursued at Brookhaven National Laboratory and at Forschungszentrum Juelich
with an ultimate goal to reach a sensitivity of 10^{-29} e cm.",1301.2937v3
2013-03-10,RXTE and SWIFT Observations of SWIFT J1729.9-3437,"We analyze \emph{RXTE} and \emph{Swift} observations of SWIFT J1729.9$-$3437
after its outburst from 2010 July 20 to 2010 August 12. We calculate a spin
frequency and spin frequency derivative of $1.8734(8) \times 10^{-3}$ Hz and
$6.42(6) \times 10^{-12}$ Hz/s respectively from the quadratic fit of pulse
arrival times. The quadratic fit residuals fit well to a circular orbital model
with a period of $15.3(2)$ days and a mass function of about $1.3M_{\odot}$,
but they can also be explained by a torque noise strength of $6.8 \times
10^{-18}$ Hz sec$^{-2}$. Pulse profiles switches from double-peaked to
single-peaked as the source flux continues to decrease. We find that the pulse
shape generally shows no strong energy dependence. The hardness ratios reveal
that the source becomes softer with decreasing flux. We construct a single
spectrum from all the available RXTE and Swift observations. We find that
adding an \emph{Fe} line complex feature around 6.51 keV slightly improves the
spectral fit and that this feature is more likely to originate from the source
rather than the Galactic ridge. From the pulse phase spectral analysis, it is
shown that that photon index and folding energy of the high energy cut-off vary
with varying pulse phase.",1303.2340v2
2013-04-23,1 Hz Flaring in the Accreting Millisecond Pulsar NGC 6440 X-2: Disk Trapping and Accretion Cycles,"The dynamics of the plasma in the inner regions of an accretion disk around
accreting millisecond X-ray pulsars is controlled by the magnetic field of the
neutron star. The interaction between an accretion disk and a strong magnetic
field is not well-understood, particularly at low accretion rates (the
so-called ``propeller regime'). This is due in part to the lack of clear
observational diagnostics to constrain the physics of the disk-field
interaction. Here we associate the strong ~1 Hz modulation seen in the
accreting millisecond X-ray pulsar NGC 6440 X-2 with an instability that arises
when the inner edge of the accretion disk is close to the corotation radius
(where the stellar rotation rate matches the Keplerian speed in the disk). A
similar modulation has previously been observed in another accreting
millisecond X-ray pulsar (SAX J1808.4-3658) and we suggest that the two
phenomena are related and that this may be a common phenomenon among other
magnetized systems. Detailed comparisons with theoretical models suggest that
when the instability is observed, the interaction region between the disk and
the field is very narrow -- of the order of 1 km. Modelling further suggests
that there is a transition region (~1-10 km) around the corotation radius where
the disk-field torque changes sign from spin up to spin down. This is the first
time that a direct observational constraint has been placed on the width of the
disk-magnetosphere interaction region, in the frame of the trapped-disk
instability model.",1304.6430v2
2013-07-17,General Relativistic Magnetohydrodynamic Simulations of Blandford-Znajek Jets and the Membrane Paradigm,"Recently it has been observed that the scaling of jet power with black hole
spin in galactic X-ray binaries is consistent with the predictions of the
Blandford-Znajek (BZ) jet model. These observations motivate us to revisit the
BZ model using general relativistic magnetohydrodynamic simulations of
magnetized jets from accreting (h/r ~ 0.3), spinning (0 < a_* < 0.98) black
holes. We have three main results. First, we quantify the discrepancies between
the BZ jet power and our simulations: assuming maximum efficiency and uniform
fields on the horizon leads to a ~10% overestimate of jet power, while ignoring
the accretion disk leads to a further ~50% overestimate. Simply reducing the
standard BZ jet power prediction by 60% gives a good fit to our simulation
data. Our second result is to show that the membrane formulation of the BZ
model correctly describes the physics underlying simulated jets: torques,
dissipation, and electromagnetic fields on the horizon. This provides intuitive
yet rigorous pictures for the black hole energy extraction process. Third, we
compute the effective resistance of the load region and show that the load and
the black hole achieve near perfect impedance matching. Taken together, these
results increase our confidence in the BZ model as the correct description of
jets observed from astrophysical black holes.",1307.4752v1
2013-09-02,MHD Simulation of a Disk Subjected to Lense-Thirring Precession,"When matter orbits around a central mass obliquely with respect to the mass's
spin axis, the Lense-Thirring effect causes it to precess at a rate declining
sharply with radius. Ever since the work of Bardeen & Petterson (1975), it has
been expected that when a fluid fills an orbiting disk, the orbital angular
momentum at small radii should then align with the mass's spin. Nearly all
previous work has studied this alignment under the assumption that a
phenomenological ""viscosity"" isotropically degrades fluid shears in accretion
disks, even though it is now understood that internal stress in flat disks is
due to anisotropic MHD turbulence. In this paper we report a pair of matched
simulations, one in MHD and one in pure (non-viscous) HD in order to clarify
the specific mechanisms of alignment. As in the previous work, we find that
disk warps induce radial flows that mix angular momentum of different
orientation; however, we also show that the speeds of these flows are
generically transonic and are only very weakly influenced by internal stresses
other than pressure. In particular, MHD turbulence does not act in a manner
consistent with an isotropic viscosity. When MHD effects are present, the disk
aligns, first at small radii and then at large; alignment is only partial in
the HD case. We identify the specific angular momentum transport mechanisms
causing alignment and show how MHD effects permit them to operate more
efficiently. Lastly, we relate the speed at which an alignment front propagates
outward (in the MHD case) to the rate at which Lense-Thirring torques deliver
angular momentum at smaller radii.",1309.0290v1
2013-09-09,Will Comet ISON (C/2012 S1) Survive Perihelion?,"On 2013 November 28 Comet ISON (C/2012 S1) will pass by the Sun with a
perihelion distance of 2.7 solar radii. Understanding the possible outcomes for
the comet's response to such a close passage by the Sun is important for
planning observational campaigns and for inferring ISON's physical properties.
We present new numerical simulations and interpret them in context with the
historical track record of comet disruptions and of sungrazing comet behavior.
Historical data suggest that sizes below ~200 m are susceptible to destruction
by sublimation driven mass loss, while we find that for ISON's perihelion
distance, densities lower than 0.1 g cm^-3 are required to tidally disrupt a
retrograde or non-spinning body. Such low densities are substantially below the
range of the best-determined comet nucleus densities, though dynamically new
comets such as ISON have few measurements of physical properties. Disruption
may occur for prograde rotation at densities up to 0.7 g cm^-3, with the
chances of disruption increasing for lower density, faster prograde rotation,
and increasing elongation of the nucleus. Given current constraints on ISON's
nucleus properties and the typically determined values for these properties
among all comets, we find tidal disruption to be unlikely unless other factors
(e.g., spin-up via torquing) affect ISON substantially. Whether or not
disruption occurs, the largest remnant must be big enough to survive subsequent
mass loss due to sublimation in order for ISON to remain a viable comet well
after perihelion.",1309.2288v1
2014-03-21,Timing and Flux Evolution of the Galactic Center Magnetar SGR J1745-2900,"We present the X-ray timing and spectral evolution of the Galactic Center
magnetar SGR J1745-2900 for the first ~4 months post-discovery using data
obtained with the Nuclear Spectroscopic Telescope Array (NuSTAR)} and Swift
observatories. Our timing analysis reveals a large increase in the magnetar
spin-down rate by a factor of 2.60 +/- 0.07 over our data span. We further show
that the change in spin evolution was likely coincident with a bright X-ray
burst observed in 2013 June by Swift, and if so, there was no accompanying
discontinuity in the frequency. We find that the source 3-10 keV flux has
declined monotonically by a factor of ~2 over an 80-day period post-outburst
accompanied by a ~20% decrease in the source's blackbody temperature, although
there is evidence for both flux and kT having levelled off. We argue that the
torque variations are likely to be magnetospheric in nature and will dominate
over any dynamical signatures of orbital motion around Sgr A*.",1403.5344v1
2014-04-14,Effects of Extreme Obliquity Variations on the Habitability of Exoplanets,"We explore the impact of obliquity variations on planetary habitability in
hypothetical systems with high mutual inclination. We show that large
amplitude, high frequency obliquity oscillations on Earth-like exoplanets can
suppress the ice-albedo feedback, increasing the outer edge of the habitable
zone. We restrict our exploration to hypothetical systems consisting of a
solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 larger planets. We
verify that these systems are stable for $10^8$ years with N-body simulations,
and calculate the obliquity variations induced by the orbital evolution of the
Earth-mass planet and a torque from the host star. We run a simplified energy
balance model on the terrestrial planet to assess surface temperature and ice
coverage on the planet's surface, and we calculate differences in the outer
edge of the habitable zone for planets with rapid obliquity variations. For
each hypothetical system, we calculate the outer edge of habitability for two
conditions: 1) the full evolution of the planetary spin and orbit, and 2) the
eccentricity and obliquity fixed at their average values. We recover previous
results that higher values of fixed obliquity and eccentricity expand the
habitable zone, but also find that obliquity oscillations further expand
habitable orbits in all cases. Terrestrial planets near the outer edge of the
habitable zone may be more likely to support life in systems that induce rapid
obliquity oscillations as opposed to fixed-spin planets. Such planets may be
the easiest to directly characterize with space-borne telescopes.",1404.3686v1
2015-06-02,On the Physical Nature of the Source of Ultraluminous X-ray Pulsations,"To reconcile the observed unusual high luminosity of NuSTAR X-ray pulsations
from M82X-2 with the most extreme violation of the Eddington limit, and in view
that the persistent X-ray radiation from M82X-2 almost precludes the
possibility of common pulsars, we tackle the problem by the implications of
{\em microscopic theory of black hole} (MTBH). The preceding developments of
MTBH are proved to be quite fruitful for the physics of ultra-high energy (UHE)
cosmic-rays. Namely, replacing a central singularity by the infrastructures
inside event horizon, subject to certain rules, MTBH explains the origin of
ZeV-neutrinos which are of vital interest for the source of UHE-particles. The
M82X-2 is assumed to be a spinning intermediate mass black hole resided in
final stage of growth. As a corollary, the thermal blackbody X-ray emission
arisen due to the rotational kinetic energy of black hole escapes from event
horizon through the vista to outside world that detected as ultraluminous X-ray
pulsations. The M82X-2 indeed releases $\sim 99.6\%$ of its pulsed radiative
energy predominantly in the X-ray bandpass $0.3-30$ keV. We derive a pulse
profile and give a quantitative account of energetics and orbital parameters of
the semi-detached X-ray binary containing a primary accretor M82X-2 of inferred
mass $M\simeq 138.5-226\,M_{\odot}$ and secondary massive, $M_{2}> 48.3-
64.9\,M_{\odot}$, O/B-type donor star with radius of $R> 22.1-
25.7\,R_{\odot}$, respectively. We compute the torque added to M82X-2 per unit
mass of accreted matter which yields the measured spin-up rate.",1506.01222v2
2015-07-27,Interplay between effective mass anisotropy and Pauli paramagnetic effects in a multiband superconductor--Application to Sr2RuO4--,"We investigate the mixed state properties in a type II multiband
superconductor with uniaxial anisotropy under the Pauli paramagnetic effects.
Eilenberger theory extended to a multiband superconductor is utilized to
describe the detailed vortex lattice properties, such as the flux line form
factors, the vortex lattice anisotropy and magnetic torques. We apply this
theory to Sr$_2$RuO$_4$ to analyze those physical quantities obtained
experimentally, focusing on the interplay between the strong two-dimensional
anisotropy and the Pauli paramagnetic effects. This study allows us to
understand the origin of the disparity between the vortex lattice anisotropy
($\sim$60) and the $H_{\rm c2}$ anisotropy ($\sim$20). Among the three bands;
$\gamma$ with the effective mass anisotropy $\sim$180, $\alpha$ with $\sim$120,
and $\beta$ with $\sim$60, the last one is found to be the major band,
responsible for various magnetic responses while the minor $\gamma$ band plays
an important role in the vortex formation. Namely, in a field orientation
slightly tilted away from the two dimensional basal plane those two bands
cooperatively form the optimal vortex anisotropy which exceeds that given by
the effective mass formula with infinite anisotropy. This is observed by small
angle neutron scattering experiments on Sr$_2$RuO$_4$. The pairing symmetry of
Sr$_2$RuO$_4$ realized is either spin singlet or spin triplet with the d-vector
strongly locked in the basal plane. The gap structure is that the major $\beta$
band has a full gap and the minor $\gamma$ band has a $d_{x^2-y^2}$ like gap.",1507.07364v1
2015-07-30,Asymmetric driven dynamics of Dzyaloshinskii domain walls in ultrathin ferromagnetic strips with perpendicular magnetic anisotropy,"The dynamics of domain walls in ultrathin ferromagnetic strips with
perpendicular magnetic anisotropy is studied from both numerical and analytical
micromagnetics. The influence of the interfacial Dzyaloshinskii-Moriya
interaction associated to a bi-layer strip arrangement has been considered,
giving rise to the formation of Dzyaloshinskii domain walls. Such walls possess
under equilibrium conditions an inner magnetization structure defined by a
certain orientation angle that make them to be considered as intermediate
configurations between Bloch and N\'eel walls. Two different dynamics are
considered, a field-driven and a current-driven dynamics, in particular, the
one promoted by the spin torque due to the Spin-Hall effect. Results show an
inherent asymmetry associated with the rotation of the domain wall
magnetization orientation before reaching the stationary regime, characterized
by a constant terminal speed. For a certain initial DW magnetization
orientation at rest, the rotation determines whether the reorientation of the
DW magnetization prior to reach stationary motion is smooth or abrupt. This
asymmetry affects the DW motion that can even reverse for a short period of
time. Additionally, it is found that the terminal speed in the case of the
current-driven dynamics may depend on either the initial DW magnetization
orientation at rest or the sign of the longitudinally injected current.",1507.08406v2
2015-12-02,NuSTAR discovery of a cyclotron absorption line in the transient X-ray pulsar 2S 1553-542,"We report results of a spectral and timing analysis of the poorly studied
transient X-ray pulsar 2S 1553-542 using data collected with the NuSTAR and
Chandra observatories and the Fermi/GBM instrument during an outburst in 2015.
Properties of the source at high energies (>30 keV) are studied for the first
time and the sky position had been essentially improved. The source broadband
spectrum has a quite complicated shape and can be reasonably described by a
composite model with two continuum components - a black body emission with the
temperature about 1 keV at low energies and a power law with an exponential
cutoff at high energies. Additionally an absorption feature at $\sim23.5$ keV
is discovered both in phase-averaged and phase-resolved spectra and interpreted
as the cyclotron resonance scattering feature corresponding to the magnetic
field strength of the neutron star $B\sim3\times10^{12}$ G. Based on the
Fermi/GBM data the orbital parameters of the system were substantially
improved, that allowed us to determine the spin period of the neutron star P =
9.27880(3) s and a local spin-up $\dot P \simeq -7.5\times10^{-10}$ s s$^{-1}$
due to the mass accretion during the NuSTAR observations. Assuming accretion
from the disk and using standard torque models we have estimated the distance
to the system $d=20\pm4$ kpc.",1512.00851v1
2016-04-25,Frequency-based nanoparticle sensing over large field ranges using the ferromagnetic resonances of a magnetic nanodisc,"Using finite element micromagnetic simulations, we study how resonant
magnetisation dynamics in thin magnetic discs with perpendicular anisotropy are
influenced by magnetostatic coupling to a magnetic nanoparticle. We identify
resonant modes within the disc using direct magnetic eigenmode calculations and
study how their frequencies and profiles are changed by the nanoparticle's
stray magnetic field. We demonstrate that particles can generate shifts in the
resonant frequency of the disc's fundamental mode which exceed resonance
linewidths in recently studied spin torque oscillator devices. Importantly, it
is shown that the simulated shifts can be maintained over large field ranges
(here up to 1T). This is because the resonant dynamics (the basis of
nanoparticle detection here) respond directly to the nanoparticle stray field,
i.e. detection does not rely on nanoparticle-induced changes to the magnetic
ground state of the disk. A consequence of this is that in the case of small
disc-particle separations, sensitivities to the particle are highly mode- and
particle-position-dependent, with frequency shifts being maximised when the
intense stray field localised directly beneath the particle can act on a large
proportion of the disc's spins that are undergoing high amplitude precession.",1604.07277v2
2016-09-14,Fragmentation Kinematics in Comet 332P/Ikeya-Murakami,"We present initial time-resolved observations of the split comet
332P/Ikeya-Murakami taken using the Hubble Space Telescope. Our images reveal a
dust-bathed cluster of fragments receding from their parent nucleus at
projected speeds in the range 0.06 to 3.5 m s$^{-1}$ from which we estimate
ejection times from October to December 2015. The number of fragments with
effective radii $\gtrsim$20 m follows a differential power law with index
$\gamma$ = -3.6$\pm$0.6, while smaller fragments are less abundant than
expected from an extrapolation of this power-law. We argue that, in addition to
losses due to observational selection, torques from anisotropic outgassing are
capable of destroying the small fragments by driving them quickly to rotational
instability. Specifically, the spin-up times of fragments $\lesssim$20 m in
radius are shorter than the time elapsed since ejection from the parent
nucleus. The effective radius of the parent nucleus is $r_e \le$ 275 m
(geometric albedo 0.04 assumed). This is about seven times smaller than
previous estimates and results in a nucleus mass at least 300 times smaller
than previously thought. The mass in solid pieces, $2\times10^9$ kg, is about
4% of the mass of the parent nucleus. As a result of its small size, the parent
nucleus also has a short spin-up time. Brightness variations in time-resolved
nucleus photometry are consistent with rotational instability playing a role in
the release of fragments.",1609.04452v1
2017-03-06,The energy-momentum tensor of electromagnetic fields in matter,"We present a complete resolution of the Abraham-Minkowski controversy . This
is done by considering several new aspects which invalidate previous
discussions. We show that: 1)For polarized matter the center of mass theorem is
no longer valid in its usual form. A contribution related to microscopic spin
should be considered. 2)The electromagnetic dipolar energy density contributes
to the inertia of matter and should be incorporated covariantly to the the
energy-momentum tensor of matter. Then there is an electromagnetic component in
matter's momentum density whose variation explains the results of the only
experiment which supports Abraham's force. 3)Averaging the microscopic
Lorentz's force results in the unambiguos expression for the force density
exerted by the field. This force density is consistent with all the
experimental evidence. 4)Momentum conservation determines the electromagnetic
energy-momentum tensor. This tensor is different from Abraham's and Minkowski's
tensors, but one recovers Minkowski's expression for the momentum density. The
energy density is different from Poynting's expression but Poynting's vector
remains the same. Our tensor is non-symmetric which allows the field to exert a
distributed torque on matter. We use our results to discuss momentum and
angular momentum exchange in various situations of physical interest. We find
complete consistency of our equations in the description of the systems
considered. We also show that several alternative expressions of the field
energy-momentum tensor and force-density cannot be successfully used in all our
examples. In particular we verify in two of these examples that the center of
mass and spin introduced by us moves with constant velocity, but that the
standard center of mass does not.",1703.02109v1
2017-07-23,General relativistic radiation magnetohydrodynamics simulations of supercritical accretion onto magnetized neutron star; -modeling of ultra luminous x-ray pulsars,"By performing 2.5-dimensional general relativistic radiation
magnetohydrodynamic simulations, we demonstrate supercritical accretion onto a
non-rotating, magnetized neutron star, where the magnetic field strength of
dipole fields is $10^{10}$ G on the star surface. We found the supercritical
accretion flow consists of two parts; the accretion columns and the truncated
accretion disk. The supercritical accretion disk, which appears far from the
neutron star, is truncated at around $\sim 3R_*$ ($R_*=10^6$ cm is the neutron
star radius), where the magnetic pressure via the dipole magnetic fields
balances with the radiation pressure of the disks. The angular momentum of the
disk around the truncation radius is effectively transported inward through
magnetic torque by dipole fields, inducing the spin up of a neutron star. The
evaluated spin up rate, $\sim -10^{-11}$ s s$^{-1}$, is consistent with the
recent observations of the ultra luminous X-ray pulsars. Within the truncation
radius, the gas falls onto neutron star along dipole fields, which results in a
formation of accretion columns onto north and south hemispheres. The net
accretion rate and the luminosity of the column are $\sim 66L_{\rm Edd}/c^2$
and $\lesssim 10L_{\rm Edd}$, where $L_{\rm Edd}$ is the Eddington luminosity
and c is the light speed. Our simulations support a hypothesis whereby the
ultra luminous X-ray pulsars are powered by the supercritical accretion onto
the magnetized neutron stars.",1707.07356v2
2017-10-19,Obliquity Variations of Habitable Zone Planets Kepler-62f and Kepler-186f,"Obliquity variability could play an important role in the climate and
habitability of a planet. Orbital modulations caused by planetary companions
and the planet's spin axis precession due to the torque from the host star may
lead to resonant interactions and cause large-amplitude obliquity variability.
Here we consider the spin axis dynamics of Kepler-62f and Kepler-186f, both of
which reside in the habitable zone around their host stars. Using
{\emph{N}}-body simulations and secular numerical integrations, we describe
their obliquity evolution for particular realizations of the planetary systems.
We then use a generalized analytic framework to characterize regions in
parameter space where the obliquity is variable with large amplitude. We find
that the locations of variability are fine-tuned over the planetary properties
and system architecture in the lower-obliquity regimes ($\lesssim 40^\circ$).
As an example, assuming a rotation period of 24 hr, the obliquities of both
Kepler-62f and Kepler-186f are stable below $\sim 40^\circ$, whereas the
high-obliquity regions ($60^\circ - 90^\circ$) allow moderate variabilities.
However, for some other rotation periods of Kepler-62f or Kepler-186f, the
lower-obliquity regions could become more variable owing to resonant
interactions. Even small deviations from coplanarity (e.g. mutual inclinations
$\sim 3^\circ$) could stir peak-to-peak obliquity variations up to $\sim
20^\circ$. Undetected planetary companions and/or the existence of a satellite
could also destabilize the low-obliquity regions. In all cases, the
high-obliquity region allows for moderate variations, and all obliquities
corresponding to retrograde motion (i.e. $> 90^\circ$) are stable.",1710.07303v2
2018-09-19,A semi-coherent analysis method to search for continuous gravitational waves emitted by ultra-light boson clouds around spinning black holes,"As a consequence of superradiant instability induced in Kerr black holes,
ultra-light boson clouds can be a source of persistent gravitational waves,
potentially detectable by current and future gravitational-wave detectors.
These signals have been predicted to be nearly monochromatic, with a small
steady frequency increase (spin-up), but given the several assumptions and
simplifications done at theoretical level, it is wise to consider, from the
data analysis point of view, a broader class of gravitational signals in which
the phase (or the frequency) slightly wander in time. Also other types of
sources, e.g. neutron stars in which a torque balance equilibrium exists
between matter accretion and emission of persistent gravitational waves, would
fit in this category. In this paper we present a robust and computationally
cheap analysis pipeline devoted to the search of such kind of signals. We
provide a full characterization of the method, through both a theoretical
sensitivity estimation and through the analysis of syntethic data in which
simulated signals have been injected. The search setup for both all-sky
searches and higher sensitivity directed searches is discussed.",1809.07202v1
2019-01-11,"A Piezoelectric, Strain-Controlled Antiferromagnetic Memory Insensitive to Magnetic Fields","Spintronic devices based on antiferromagnetic (AFM) materials hold the
promise of fast switching speeds and robustness against magnetic fields.
Different device concepts have been predicted and experimentally demonstrated,
such as low-temperature AFM tunnel junctions that operate as spin-valves, or
room-temperature AFM memory, for which either thermal heating in combination
with magnetic fields, or N\'eel spin-orbit torque is used for the information
writing process. On the other hand, piezoelectric materials were employed to
control magnetism by electric fields in multiferroic heterostructures, which
suppresses Joule heating caused by switching currents and may enable low
energy-consuming electronic devices. Here, we combine the two material classes
to explore changes of the resistance of the high-N\'eel-temperature
antiferromagnet MnPt induced by piezoelectric strain. We find two non-volatile
resistance states at room temperature and zero electric field, which are stable
in magnetic fields up to 60 T. Furthermore, the strain-induced resistance
switching process is insensitive to magnetic fields. Integration in a tunnel
junction can further amplify the electroresistance. The tunneling anisotropic
magnetoresistance reaches ~11.2% at room temperature. Overall, we demonstrate a
piezoelectric, strain-controlled AFM memory which is fully operational in
strong magnetic fields and has potential for low-energy and high-density memory
applications.",1901.03551v1
2019-02-14,High-speed domain wall racetracks in a magnetic insulator,"Recent reports of current-induced switching of ferrimagnetic oxides coupled
to a heavy metal layer have opened realistic prospects for implementing
magnetic insulators into electrically addressable spintronic devices. However,
key aspects such as the configuration and dynamics of magnetic domain walls
driven by electrical currents in insulating oxides remain unexplored. Here, we
investigate the internal structure of the domain walls in Tm3Fe5O12 (TmIG) and
TmIG/Pt bilayers and demonstrate their efficient manipulation by spin-orbit
torques with velocities of up to 400 m s$^{-1}$ and minimal current threshold
for domain wall flow of 5 x 10$^{6}$ A cm$^{-2}$. Domain wall racetracks
embedded in TmIG are defined by the deposition of Pt current lines, which allow
us to control the domain propagation and magnetization switching in selected
regions of an extended magnetic layer. Scanning nitrogen-vacancy magnetometry
reveals that the domain walls of thin TmIG films are N\'eel walls with
left-handed chirality, with the domain wall magnetization rotating towards an
intermediate N\'eel-Bloch configuration upon deposition of Pt. These results
indicate the presence of a sizable interfacial Dzyaloshinskii-Moriya
interaction in TmIG, which leads to novel possibilities to control the
formation of chiral spin textures in magnetic insulators. Ultimately, domain
wall racetracks provide an efficient scheme to pattern the magnetic landscape
of TmIG in a fast and reversible way",1902.05639v1
2019-02-19,Generation and Hall effect of skyrmions enabled via using nonmagnetic point contacts,"To enable functional skyrmion based spintronic devices, the controllable
generation and manipulation of skyrmions is essential. While the generation of
skyrmions by using a magnetic geometrical constriction has already been
demonstrated, this approach is difficult to combine with a subsequent
controlled manipulation of skyrmions. The high efficiency of skyrmion
generation from magnetic constrictions limits the useful current density,
resulting in stochastic skyrmion motion, which may obscure topological
phenomena such as the skyrmion Hall effect. In order to address this issue, we
designed a nonmagnetic conducting Ti/Au point contact in devices made of
Ta/CoFeB/TaOx trilayer films. By applying high voltage pulses, we
experimentally demonstrated that skyrmions can be dynamically generated.
Moreover, the accompanied spin topology dependent skyrmion dynamics, the
skyrmion Hall effect is also experimentally observed in the same devices. The
creation process has been numerically reproduced through micromagnetic
simulations in which the important role of skyrmion-antiskyrmion pair
generation is identified. The motion and Hall effect of the skyrmions,
immediately after their creation is described using a modified Thiele equation
after taking into account the contribution from spatially inhomogeneous
spin-orbit torques and the Magnus force. The simultaneous generation and
manipulation of skyrmions using a nonmagnetic point contact could provide a
useful pathway for designing novel skyrmion based devices.",1902.06954v1
2019-03-03,Separated Edge-Soliton Meditated Dynamic Switching of Vortex Chirality and Polarity,"Magnetic vortices are characterized by the senses of in-plane magnetization
chirality and by the polarity of the vortex core. The electrical control of
vortex polarity and chirality is highly demanded not only for fundamental
understanding on spin dynamics in nano-disks under different circumstances, but
also for technological applications, such as magnetic non-volatile memories and
spin torque oscillators for neuromorphic computing. Here we report a novel
approach that enables one to electrically control both the vortex chirality and
polarity with low energy consumption. Thorough micromagnetic simulations, we
show that in thin nano-disks of diameter larger than 160 nm, with the presence
of current-induced Oersted field, the dynamic transformation of the edge
solitons is able to efficiently switch both vortex chirality and polarity with
low current under certain circumstances. We then developed an approach to
directly write any of the four vortex states by electrical current pulses from
a random state. We further investigated the switching phase diagram as a
function of disk diameters. The results show that the switching process is
highly size-dependent. As disk diameter is smaller than 160 nm, the switch of
VC chirality and polarity always takes place at the same time, resulting in an
unchanged handedness before and after switch. Furthermore, the critical switch
current can be as low as 3 x 10^6 A/cm^2 , indicating a possible way for low
current switch of vortex chirality in small disks.",1903.01018v1
2019-07-24,Nonlinear anomalous Hall effect for Néel vector detection,"Antiferromagnetic (AFM) spintronics exploits the N\'eel vector as a state
variable for novel spintronic devices. Recent studies have shown that the
field-like and antidamping spin-orbit torques (SOT) can be used to switch the
N\'eel vector in antiferromagnets with proper symmetries. However, the precise
detection of the N\'eel vector remains a challenging problem. In this letter,
we predict that the nonlinear anomalous Hall effect (AHE) can be used to detect
the N\'eel vector in most compensated antiferromagnets supporting the
antidamping SOT. We show that the magnetic crystal group symmetry of these
antiferromagnets combined with spin-orbit coupling produce a sizable Berry
curvature dipole and hence the nonlinear AHE. As a specific example, we
consider half-Heusler alloy CuMnSb, which N\'eel vector can be switched by the
antidamping SOT. Based on density functional theory calculations, we show that
the nonlinear AHE in CuMnSb results in a measurable Hall voltage under
conventional experimental conditions. The strong dependence of the Berry
curvature dipole on the N\'eel vector orientation provides a new detection
scheme of the N\'eel vector based on the nonlinear AHE. Our predictions enrich
the material platform for studying non-trivial phenomena associated with the
Berry curvature and broaden the range of materials useful for AFM spintronics.",1907.10696v3
2019-09-10,Geometric driving of two-level quantum systems,"We investigate a class of cyclic evolutions for %the cyclic evolution of
driven two-level quantum systems (effective spin-1/2) with a particular focus
on the geometric characteristics of the driving and their specific imprints on
the quantum dynamics. By introducing the concept of geometric field curvature
for any field trajectory in the parameter space we are able to unveil
underlying patterns in the overall quantum behavior: the knowledge of the field
curvature provides a non-standard and fresh access to the interrelation between
field and spin trajectories, and the corresponding quantum phases acquired in
non-adiabatic cyclic evolutions. In this context, we single out setups in which
the driving field curvature can be employed to demonstrate a pure geometric
control of the quantum phases. Furthermore, the driving field curvature can be
naturally exploited to introduce the geometrical torque and derive a general
expression for the total quantum phase acquired in a cycle. Remarkably, such
relation allows to access the mechanisms controlling the changeover of the
quantum phase across a topological transition and to disentangle the role of
the spin and field topological windings. As for implementations, we discuss a
series of physical systems and platforms to demonstrate how the geometric
control of the quantum phases can be realized for pendular field drivings. This
includes setups based on superconducting islands coupled to a Josephson
junction and inversion asymmetric nanochannels with suitably tailored geometric
shapes.",1909.04291v1
2019-10-13,Statistical Mechanics of Gravitational Systems with Regular Orbits: Rigid Body Model of Vector Resonant Relaxation,"I consider a self-gravitating, N-body system assuming that the N constituents
follow regular orbits about the center of mass of the cluster, where a central
massive object may be present. I calculate the average over a characteristic
timescale of the full, N-body Hamiltonian including all kinetic and potential
energy terms. The resulting effective system allows for the identification of
the orbital planes with N rigid, disk-shaped tops, that can rotate about their
fixed common centre and are subject to mutual gravitational torques. The
time-averaging imposes boundaries on the canonical generalized momenta of the
resulting canonical phase space. I investigate the statistical mechanics
induced by the effective Hamiltonian on this bounded phase space and calculate
the thermal equilibrium states. These are a result of the relaxation of spins'
directions, identified with orbital planes' orientations, which is called
vector resonant relaxation. I calculate the dependence of spins' angular
velocity dispersion on temperature and calculate the velocity distribution
functions. I argue that the range of validity of the gravitational phase
transitions, identified in the special case of zero kinetic term by Roupas,
Kocsis & Tremaine, is expanded to non-zero values of the ratio of masses
between the cluster of N-bodies and the central massive object. The relevance
with astrophysics is discussed focusing on stellar clusters. The same analysis
performed on an unbounded phase space accounts for continuous rigid tops.",1910.05735v2
2019-11-26,Gravitational Waves from Newborn Accreting Millisecond Magnetars,"Two accretion columns have been argued to form over the surface of a newborn
millisecond magnetar for an extremely high accretion rate
$\gtrsim1.8\times10^{-2}M_\odot\ {\rm s^{-1}}$ that may occur in the
core-collapse of a massive star. In this paper, we investigate the
characteristics of these accretion columns and their gravitational wave (GW)
radiation. For a typical millisecond magnetar (surface magnetic field strength
$B\sim10^{15}$ G and initial spin period $P\sim1$ ms), we find (1) its
accretion columns are cooled via neutrinos and can reach a height $\sim1$ km
over the stellar surface; (2) its column-induced characteristic GW strain is
comparable to the sensitivities of the next generation ground-based GW
detectors within a horizon $\sim1$ Mpc; (3) the magnetar can survive only a few
tens of seconds; (4) during the survival timescale, the height of the accretion
columns increases rapidly to the peak and subsequently decreases slowly; (5)
the column mass, characteristic GW strain, and maximum GW luminosity have
simultaneous peaks in a similar rise-fall evolution. In addition, we find that
the magnetar's spin evolution is dominated by the column accretion torque. A
possible association with failed supernova is also discussed.",1911.11296v1
2019-12-11,The Nucleus of Interstellar Comet 2I/Borisov,"We present high resolution imaging observations of interstellar comet
2I/Borisov (formerly C/2019 Q4) obtained using the Hubble Space Telescope.
Scattering from the comet is dominated by a coma of large particles
(characteristic size 0.1 mm) ejected anisotropically. Convolution modeling of
the coma surface brightness profile sets a robust limit to the
spherical-equivalent nucleus radius r_n < 0.5 km (geometric albedo 0.04
assumed). We obtain an independent constraint based on the non-gravitational
acceleration of the nucleus, finding r_n > 0.2 km (nucleus density 500 kg/m3
assumed). The profile and the non-gravitational constraints cannot be
simultaneously satisfied if density < 25 kg/m3; the nucleus of comet Borisov
cannot be a low density fractal assemblage of the type proposed elsewhere for
the nucleus of 1I/'Oumuamua. We show that the spin-up timescale to outgassing
torques, even at the measured low production rates, is comparable to or shorter
than the residence time in the Sun's water sublimation zone. The spin angular
momentum of the nucleus should be changed significantly during the current
solar fly-by. Lastly, we find that the differential interstellar size
distribution in the 0.5 mm to 100 m size range can be represented by power laws
with indices < 4 and that interstellar bodies of 100 m size scale strike Earth
every one to two hundred million years.",1912.05422v2
2019-12-20,Picosecond spin-orbit torque switching of ferrimagnets,"Spintronics provides an efficient platform for realizing non-volatile memory
and logic devices. In these systems, data is stored in the magnetization of
magnetic materials, and magnetization is switched in the writing process. In
conventional spintronic devices, ferromagnetic materials are used which have a
magnetization dynamics timescale of around the nanoseconds, setting a limit for
the switching speed. Increasing the magnetization switching speed has been one
of the challenges in spintronic research. In this work we take advantage of the
ultrafast magnetization dynamics in ferrimagnetic materials instead of
ferromagnets, and we use femtosecond laser pulses and a photoconductive Auston
switch to create picosecond current pulses for switching the ferrimagnet. By
anomalous Hall and magneto-optic Kerr (MOKE) measurement, we demonstrate the
robust picosecond SOT driven magnetization switching of ferrimagnetic GdFeCo.
The time-resolved MOKE shows more than 50 GHz magnetic resonance frequency of
GdFeCo, indicating faster than 20 ps spin dynamics and tens of picosecond SOT
switching speed. Our work provides a promising route to realize picosecond
operation speed for non-volatile magnetic memory and logic applications.",1912.10129v1
2020-01-28,The Impact of Metallicity on the Evolution of Rotation and Magnetic Activity of Sun-Like Stars,"The rotation rates and magnetic activity of Sun-like and low-mass (< 1.4
Msun) main-sequence stars are known to decline with time, and there now exist
several models for the evolution of rotation and activity. However, the role
that chemical composition plays during stellar spin-down has not yet been
explored. In this work, we use a structural evolution code to compute the
rotational evolution of stars with three different masses (0.7, 1.0, and
1.3Msun and six different metallicities, ranging from [Fe/H]=-1.0 to
[Fe/H]=+0.5. We also implement three different wind-braking formulations from
the literature (two modern and one classical) and compare their predictions for
rotational evolution. The effect that metallicity has on stellar structural
properties, and in particular the convective turnover timescale, leads the two
modern wind-braking formulations to predict a strong dependence of the torque
on metallicity. Consequently, they predict that metal rich stars spin-down more
effectively at late ages (> 1 Gyr) than metal poor stars, and the effect is
large enough to be detectable with current observing facilities. For example,
the formulations predict that a Sun-like (solar-mass and solar-aged) star with
[Fe/H]=-0.3 will have a rotation period of less than 20 days. Even though old,
metal poor stars are predicted to rotate more rapidly at a given age, they have
larger Rossby numbers and are thus expected to have lower magnetic activity
levels. Finally, the different wind-braking formulations predict quantitative
differences in the metallicity-dependence of stellar rotation, which may be
used to test them.",2001.10404v1
2020-02-07,Multiple Dirac Nodes and Symmetry Protected Dirac Nodal Line in Orthorhombic $α$-RhSi,"Owing to their chiral cubic structure, exotic multifold topological
excitations have been predicted and recently observed in transition metal
silicides like $\beta$-RhSi. Herein, we report that the topological character
of RhSi is also observed in its orthorhombic $\alpha$-phase which displays
multiple types of Dirac nodes very close to the Fermi level ($\varepsilon_F$)
with the near absence of topologically trivial carriers. We discuss the
symmetry analysis, band connectivity along high-symmetry lines using group
representations, the band structure, and the nature of the Dirac points and
nodal lines occurring near $\varepsilon_F$. The de Haas-van Alphen effect
(dHvA) indicates a Fermi surface in agreement with the calculations. We find an
elliptically-shaped nodal line very close to $\varepsilon_F$ around and near
the $S$-point on the $k_y-k_z$ plane that results from the intersection of two
upside-down Dirac cones. The two Dirac points of the participating Kramers
degenerate bands are only 5 meV apart, hence an accessible magnetic field might
induce a crossing between the spin-up partner of the upper-Dirac cone and the
spin-down partner of the lower Dirac cone, possibly explaining the anomalies
observed in the magnetic torque.",2002.03020v1
2020-02-26,How much do underestimated field strengths from Zeeman-Doppler imaging affect spin-down torque estimates?,"Numerous attempts to estimate the rate at which low-mass stars lose angular
momentum over their lifetimes exist in the literature. One approach is to use
magnetic maps derived from Zeeman-Doppler imaging (ZDI) in conjunction with
so-called ""braking laws"". The use of ZDI maps has advantages over other methods
because it allows information about the magnetic field geometry to be
incorporated into the estimate. However, ZDI is known to underestimate
photospheric field strengths due to flux cancellation effects. Recently,
Lehmann et al. (2018) conducted synthetic ZDI reconstructions on a set of flux
transport simulations to help quantify the amount by which ZDI underestimates
the field strengths of relatively slowly rotating and weak activity solar-like
stars. In this paper, we evaluate how underestimated angular momentum-loss rate
estimates based on ZDI maps may be. We find that they are relatively accurate
for stars with strong magnetic fields but may be underestimated by a factor of
up to $\sim$10 for stars with weak magnetic fields. Additionally, we
re-evaluate our previous work that used ZDI maps to study the relative
contributions of different magnetic field modes to angular momentum-loss. We
previously found that the dipole component dominates spin-down for most
low-mass stars. This conclusion still holds true even in light of the work of
Lehmann et al. (2018).",2002.11774v1
2020-03-27,Observation of the in-plane magnetic field-induced phase transitions in FeSe,"We investigate the thermodynamic properties of FeSe under the in-plane
magnetic fields using torque magnetometry, specific heat, magnetocaloric
measurements. Below the upper critical field Hc2, we observed the field-induced
anomalies at H1 ~ 15 T and H2 ~ 22 T near H//ab and below a characteristic
temperature T* ~ 2 K. The transition magnetic fields H1 and H2 exhibit
negligible dependence on both temperature and field orientation. This contrasts
with the strong temperature and angle dependence of Hc2, suggesting that these
anomalies are attributed to the field-induced phase transitions, originating
from the inherent spin-density-wave instability of quasiparticles near the
superconducting gap minima or possible Flude-Ferrell-Larkin-Ovchinnikov state
in the highly spin-polarized Fermi surfaces. Our observations imply that FeSe,
an atypical multiband superconductor with extremely small Fermi energies,
represents a unique model system for stabilizing unusual superconducting orders
beyond the Pauli limit.",2003.12351v1
2020-04-30,Unifying femtosecond and picosecond single-pulse magnetic switching in GdFeCo,"Many questions are still open regarding the physical mechanisms behind the
magnetic switching in GdFeCo alloys by single optical pulses. Phenomenological
models suggest a femtosecond scale exchange relaxation between sublattice
magnetization as the driving mechanism for switching. The recent observation of
thermally induced switching in GdFeCo by using both several picosecond optical
laser pulse as well as electric current pulses has questioned this previous
understanding. This has raised the question of whether or not the same
switching mechanics are acting at the femo- and picosecond scales. In this
work, we aim at filling this gap in the understanding of the switching
mechanisms behind thermal single-pulse switching. To that end, we have studied
experimentally thermal single-pulse switching in GdFeCo alloys, for a wide
range of system parameters, such as composition, laser power and pulse
duration. We provide a quantitative description of the switching dynamics using
atomistic spin dynamics methods with excellent agreement between the model and
our experiments across a wide range of parameters and timescales, ranging from
femtoseconds to picoseconds. Furthermore, we find distinct element-specific
damping parameters as a key ingredient for switching with long picosecond
pulses and argue, that switching with pulse durations as long as 15 picoseconds
is possible due to a low damping constant of Gd. Our findings can be easily
extended to speed up dynamics in other contexts where ferrimagnetic GdFeCo
alloys have been already demonstrated to show fast and energy-efficient
processes, e.g. domain-wall motion in a track and spin-orbit torque switching
in spintronics devices.",2004.14844v1
2020-05-04,Current-driven skyrmionium in a frustrated magnetic system,"Magnetic skyrmionium can be used as a nanometer-scale non-volatile
information carrier, which shows no skyrmion Hall effect due to its special
structure carrying zero topological charge. Here, we report the static and
dynamic properties of an isolated nanoscale skyrmionium in a frustrated
magnetic monolayer, where the skyrmionium is stabilized by competing
interactions. The frustrated skyrmionium has a size of about $10$ nm, which can
be further reduced by tuning perpendicular magnetic anisotropy or magnetic
field. It is found that the nanoscale skyrmionium driven by the damping-like
spin-orbit torque shows directional motion with a favored Bloch-type helicity.
A small driving current or magnetic field can lead to the transformation of an
unstable N\'eel-type skyrmionium to a metastable Bloch-type skyrmionium. A
large driving current may result in the distortion and collapse of the
Bloch-type skyrmionium. Our results are useful for the understanding of
frustrated skyrmionium physics, which also provide guidelines for the design of
spintronic devices based on topological spin textures.",2005.01403v2
2020-05-18,Hardware implementation of Bayesian network building blocks with stochastic spintronic devices,"Bayesian networks are powerful statistical models to understand causal
relationships in real-world probabilistic problems such as diagnosis,
forecasting, computer vision, etc. For systems that involve complex causal
dependencies among many variables, the complexity of the associated Bayesian
networks become computationally intractable. As a result, direct hardware
implementation of these networks is one promising approach to reducing power
consumption and execution time. However, the few hardware implementations of
Bayesian networks presented in literature rely on deterministic CMOS devices
that are not efficient in representing the inherently stochastic variables in a
Bayesian network. This work presents an experimental demonstration of a
Bayesian network building block implemented with naturally stochastic
spintronic devices. These devices are based on nanomagnets with perpendicular
magnetic anisotropy, initialized to their hard axes by the spin orbit torque
from a heavy metal under-layer utilizing the giant spin Hall effect, enabling
stochastic behavior. We construct an electrically interconnected network of two
stochastic devices and manipulate the correlations between their states by
changing connection weights and biases. By mapping given conditional
probability tables to the circuit hardware, we demonstrate that any two node
Bayesian networks can be implemented by our stochastic network. We then present
the stochastic simulation of an example case of a four node Bayesian network
using our proposed device, with parameters taken from the experiment. We view
this work as a first step towards the large scale hardware implementation of
Bayesian networks.",2005.08418v1
2020-09-24,Evidence for Metallicity-Dependant Spin Evolution in the Kepler field,"A curious rotation period distribution in the Color-Magnitude-Period Diagram
(CMPD) of the Kepler field was recently revealed, thanks to data from Gaia and
Kepler spacecraft. It was found that redder and brighter stars are spinning
slower than the rest of the main sequence. On the theoretical side, it was
demonstrated that metallicity should affect the rotational evolution of stars
as well as their evolution in the Hertzprung-R\""ussel or Color-Magnitude
diagram. In this work we combine this dataset with medium and high resolution
spectroscopic metallicities and carefully select main sequence single stars in
a given mass range. We show that the structure seen in the CMPD also
corresponds to a broad correlation between metallicity and rotation, such that
stars with higher metallicity rotate on average more slowly than those with low
metallicity. We compare this sample to theoretical rotational evolution models
that include a range of different metallicities. They predict a correlation
between rotation rate and metallicity that is in the same direction and of
about the same magnitude as that observed. Therefore metallicity appears to be
a key parameter to explain the observed rotation period distributions. We also
discuss a few different ways in which metallicity can affect the observed
distribution of rotation period, due to observational biases and age
distributions, as well as the effect on stellar wind torques.",2009.11785v1
2020-09-24,Measuring interfacial Dzyaloshinskii-Moriya interaction in ultra-thin magnetic films,"The Dzyaloshinskii-Moriya interaction (DMI), being one of the origins of
chiral magnetism, is currently attracting considerable attention in the
research community focusing on applied magnetism and spintronics. For future
applications, an accurate measurement of its strength is indispensable. Here we
present a review of the state-of-the-art of measuring the coefficient of the
Dzyaloshinskii-Moriya interaction, the DMI constant $D$, focusing on systems
where the interaction arises from the interface between two materials (i.e.
interfacial DMI). We give an overview of the experimental techniques as well as
their theoretical background and models for the quantification of the DMI
constant. The measurement techniques are divided into three categories: a)
domain wall-based measurements, b) spin wave-based measurements and c)
spin-orbit torque-based measurements. We analyze the advantages and
disadvantages of each method and compare $D$ values at different interfaces.
The review aims to obtain a better understanding of the applicability of the
different techniques to various stacks and of the origin of apparent
disagreements among literature values.",2009.11830v3
2020-10-17,Ferromagnetic Gyroscopes for Tests of Fundamental Physics,"A ferromagnetic gyroscope (FG) is a ferromagnet whose angular momentum is
dominated by electron spin polarization and that will precess under the action
of an external torque, such as that due to a magnetic field. Here we model and
analyze FG dynamics and sensitivity, focusing on practical schemes for
experimental realization. In the case of a freely floating FG, we model the
transition from dynamics dominated by libration in relatively high externally
applied magnetic fields, to those dominated by precession at relatively low
applied fields. Measurement of the libration frequency enables in situ
measurement of the magnetic field and a technique to reduce the field below the
threshold for which precession dominates the FG dynamics. We note that evidence
of gyroscopic behavior is present even at magnetic fields much larger than the
threshold field below which precession dominates. We also model the dynamics of
an FG levitated above a type-I superconductor via the Meissner effect, and find
that for FGs with dimensions larger than about 100 nm the observed precession
frequency is reduced compared to that of a freely floating FG. This is akin to
negative feedback that arises from the distortion of the field from the FG by
the superconductor. Finally we assess the sensitivity of an FG levitated above
a type-I superconductor to exotic spin-dependent interactions under practical
experimental conditions, demonstrating the potential of FGs for tests of
fundamental physics.",2010.08731v1
2021-02-02,Current-induced dynamics of skyrmion tubes in synthetic antiferromagnetic multilayers,"Topological spin textures can be found in both two-dimensional and
three-dimensional nanostructures, which are of great importance to advanced
spintronic applications. Here we report the current-induced skyrmion tube
dynamics in three-dimensional synthetic antiferromagnetic (SyAF) bilayer and
multilayer nanostructures. It is found that the SyAF skyrmion tube made of
thinner sublayer skyrmions is more stable during its motion, which ensures that
a higher speed of the skyrmion tube can be reached effectively at larger
driving current. In the SyAF multilayer with a given total thickness, the
current-induced deformation of the SyAF skyrmion tube decreases with an
increasing number of interfaces; namely, the rigidity of the SyAF skyrmion tube
with a given thickness increases with the number of ferromagnetic (FM) layers.
For the SyAF multilayer with an even number of FM layers, the skyrmion Hall
effect can be eliminated when the thicknesses of all FM layers are identical.
Larger damping parameter leads to smaller deformation and slower speed of the
SyAF skyrmion tube. Larger fieldlike torque leads to larger deformation and a
higher speed of the SyAF skyrmion tube. Our results are useful for
understanding the dynamic behaviors of three-dimensional topological spin
textures and may provide guidelines for building SyAF spintronic devices.",2102.01252v3
2021-02-16,Dynamic symmetry breaking in chiral magnetic systems,"The Dzyaloshinskii-Moriya interaction (DMI) in magnetic systems stabilizes
spin textures with preferred chirality, applicable to next-generation memory
and computing architectures. In perpendicularly magnetized
heavy-metal/ferromagnet films, the interfacial DMI originating from structural
inversion asymmetry and strong spin-orbit coupling favors chiral N\'eel-type
domain walls (DWs) whose energetics and mobility remain at issue. Here, we
characterize a new effect in which domains expand unidirectionally in response
to a combination of out-of-plane and in-plane magnetic fields, with the growth
direction controlled by the in-plane field strength. These growth
directionalities and symmetries with applied fields cannot be understood from
static treatments alone. We theoretically demonstrate that perpendicular field
torques stabilize steady-state magnetization profiles highly asymmetric in
elastic energy, resulting in a dynamic symmetry breaking consistent with the
experimental findings. This phenomenon sheds light on the mechanisms governing
the dynamics of N\'eel-type DWs and expands the utility of field-driven DW
motion to probe and control chiral DWs.",2102.07909v4
2021-04-15,Multipole analysis on gyroscopic precession in $f(R)$ gravity with irreducible Cartesian tensors,"In $f(R)$ gravity, the metric, presented in the form of the multipole
expansion, for the external gravitational field of a spatially compact
supported source up to $1/c^3$ order is provided, where $c$ is the velocity of
light in vacuum. The metric consists of General Relativity-like part and $f(R)$
part, where the latter is the correction to the former in $f(R)$ gravity. At
the leading pole order, the metric can reduce to that for a point-like or
ball-like source. For the gyroscope moving around the source without
experiencing any torque, the multipole expansions of its spin's angular
velocities of gravitoelectric-type precession, gravitomagnetic-type precession,
$f(R)$ precession, and Thomas precession are all derived. The first two types
of precession are collectively called General Relativity-like precession, and
the $f(R)$ precession is the correction in $f(R)$ gravity. At the leading pole
order, these expansions can recover the results for the gyroscope moving around
a point-like or ball-like source. If the gyroscope has a nonzero
four-acceleration, its spin's total angular velocity of precession up to
$1/c^3$ order in $f(R)$ gravity is the same as that in General Relativity.",2104.07529v3
2021-05-10,Spin reorientation in tetragonally distorted spinel oxide NiCo$_2$O$_4$ epitaxial films,"We experimentally investigated the magnetic properties of NiCo$_2$O$_4$
epitaxial films known to be conductive oxides with perpendicular magnetic
anisotropy (PMA) at room temperature. Both magneto-torque and magnetization
measurements at various temperatures provide clear experimental evidence of the
spin reorientation transition at which the MA changes from PMA to easy-cone
magnetic anisotropy (ECMA) at a certain temperature ($T_{\rm{SR}}$). ECMA was
commonly observed in films grown by pulsed laser deposition and reactive radio
frequency magnetron sputtering, although $T_{\mathrm{SR}}$ is dependent on the
growth method as well as the conditions. The cone angles measured from the
$c$-axis increased successively at $T_{\mathrm{SR}}$ and approached a maximum
of 45-50 degrees at the lowest measurement temperature of 5 K. Calculation with
the cluster model suggests that the Ni$^{3+}$ ions occupying the $T_d$ site
could be the origin of the ECMA. Both the magnetic properties and the results
of the calculation based on the cluster model indicate that the ECMA is
attributable to the cation anti-site distribution of Ni$^{3+}$, which is
possibly formed during the growth process of the thin films.",2105.04115v1
2022-01-09,Disk Tearing Leads to Low and High Frequency Quasi Periodic Oscillations in a GRMHD Simulation of a Thin Accretion Disk,"Black hole X-ray binaries (BHXRBs) display a wide range of variability
phenomena, from long duration spectral state changes to short-term broadband
variability and quasi-periodic oscillations (QPOs). A particularly puzzling
aspect is the production of QPOs, which -- if properly understood -- could be
used as a powerful diagnostic tool of black hole accretion and evolution. In
this work we analyse a high resolution three-dimensional general relativistic
magnetohydrodynamic simulation of a geometrically thin accretion disk which is
tilted by $65^{\circ}$ with respect to the black hole spin axis. We find that
the Lense-Thirring torque from the rapidly spinning 10 $M_\odot$ black hole
causes several sub-disks to tear off within $\sim 10-20$ gravitational radii.
Tearing occurs in cycles on timescales of seconds. During each tearing cycle
the inner sub-disk precesses for 1-5 periods before it falls into the black
hole. We find a precession frequency of $\sim 3\rm Hz$, consistent with
observed low-frequency QPOs. In addition, we find a high frequency QPO (HFQPO)
with centroid frequency of $\sim55$Hz in the power spectra of the mass-weighted
radius of the inner disk. This signal is caused by radial epicyclic
oscillations of a dense ring of gas at the tearing radius, which strongly
suggests a corresponding modulation of the X-ray lightcurve and may thus
explain some of the observed HFQPOs.",2201.03085v1
2022-02-06,Enhancing Perpendicular Magnetic Anisotropy in Garnet Ferrimagnet by Interfacing with Few-Layer WTe2,"Engineering magnetic anisotropy in a ferro- or ferrimagnetic (FM) thin film
is crucial in spintronic device. One way to modify the magnetic anisotropy is
through the surface of the FM thin film. Here, we report the emergence of a
perpendicular magnetic anisotropy (PMA) induced by interfacial interactions in
a heterostructure comprised of a garnet ferrimagnet, Y3Fe5O12 (YIG), and the
low-symmetry, high spin orbit coupling (SOC) transition metal dichalcogenide,
WTe2. At the same time, we also observed an enhancement in Gilbert damping in
the WTe2 covered YIG area. Both the magnitude of interface-induced PMA and the
Gilbert damping enhancement have no observable WTe2 thickness dependence down
to single quadruple-layer, indicating that the interfacial interaction plays a
critical role. The ability of WTe2 to enhance the PMA in FM thin film, combined
with its previously reported capability to generate out-of-plane damping like
spin torque, makes it desirable for magnetic memory applications.",2202.02834v1
2022-02-14,Evolution of the long-period pulsar GLEAM-X J162759.5-523504.3,"The long-period ($P = 1091$ s) of the recently discovered pulsar GLEAM-X
J162759.5-523504.3 can be attained by neutron stars evolving with fallback
discs and magnetic dipole moments of a few $10^{30}$ G cm$^3$ at ages greater
than $\sim 2 \times 10^5$ yr consistently with the observational upper limits
to the period derivative, $\dot{P}$, and the X-ray luminosity, $L_X$, of the
source. The current upper limits for $\dot{P}$ allow two alternative present
states: (1) The disc is still active with ongoing accretion at a low rate such
that the accretion luminosity is much less than the neutron star's cooling
luminosity, which in turn is below the upper limit for $L_X$. In this scenario
the spin-down will continue at $\dot{P} \sim 10^{-10}$ s s$^{-1}$ until the
disc becomes inactive; the final period will be $P \sim$ a few $10^3$ s. (2)
The disc is already inactive, there is no accretion. In this case the period
evolution has leveled off to the observed value in the final period range. The
remaining, very weak, dipole torque sustaining asymptotic spin-down at $\dot{P}
\sim 4 \times 10^{-18}$ s s$^{-1}$. Long periods $P \sim$ a few $10^3$ s were
predicted for the final states of soft gamma repeaters and anomalous X-ray
pulsars with relatively strong dipole fields in earlier work with the fallback
disc model.",2202.06852v2
2022-04-01,GRMHD Simulations of Accreting Neutron Stars with Non-Dipole Fields,"NASA's NICER telescope has recently provided evidence for non-dipolar
magnetic field structures in rotation-powered millisecond pulsars. These stars
are assumed to have gone through a prolonged accretion spin-up phase, begging
the question of what accretion flows onto stars with complex magnetic fields
would look like. We present results from a suite of GRMHD simulations of
accreting neutron stars for dipole, quadrupole, and quadrudipolar stellar field
geometries. This is a first step towards simulating realistic hotspot shapes in
a general relativistic framework to understand hotspot variability in accreting
millisecond pulsars. We find that the location and size of the accretion
columns resulting in hotspots changes significantly depending on initial
stellar field strength and geometry. We also find that the strongest
contributions to the stellar torque are from disk-connected fieldlines and the
pulsar wind, leading to spin-down in almost all of the parameter regime
explored here. We further analyze angular momentum transport in the accretion
disk due to large scale magnetic stresses, turbulent stresses, wind- and
compressible effects which we identify with convective motions. The disk
collimates the initial open stellar flux forming jets. For dipoles, the
disk-magnetosphere interaction can either enhance or reduce jet power compared
to the isolated case. However for quadrupoles, the disk always leads to an
enhanced net open flux making the jet power comparable to the dipolar case. We
discuss our results in the context of observed neutron star jets and provide a
viable mechanism to explain radio power both in the low- and high-magnetic
field case.",2204.00249v1
2022-05-17,New pulse profile variability associated with a glitch of PSR J0738-4042,"The close correlation observed between emission state and spin-down rate
change of pulsars has many implications both for the magnetospheric physics and
the neutron star interior. The middle-aged pulsar PSR J0738$-$4042, which had
been observed to display variations in the pulse profile associated with its
spin-down rate change due to external effects, is a remarkable example. In this
study, based on the 12.5-yr combined public timing data from UTMOST and Parkes,
we have detected a new emission-rotation correlation in PSR J0738$-$4042
concurrent with a glitch. A glitch that occurred at MJD 57359(5) (December 3,
2015) with $\Delta\nu/\nu \sim 0.36(4)\times 10^{-9}$ is the first glitch event
observed in this pulsar and is probably the underlying cause of the
emission-rotation correlation. Unlike the usual post-glitch behaviours, the
braking torque on the pulsar has continued to increase over 1380 d,
corresponding to a significant decrease in $\ddot{\nu}$. As for changes in the
pulse profile after the glitch, the relative amplitude of the leading component
weakens drastically, while the middle component becomes stronger. A combined
model of crustquake induced platelet movement and vortex creep response is
invoked to account for this rare correlation. In this scenario, magnetospheric
state-change is naturally linked to the pulsar-intrinsic processes that give
rise to a glitch.",2205.08296v2
2022-05-20,On the X-ray pulsar HD 49798: a contracting white dwarf with debris disk?,"HD49798/RX J0648.0-4418 is a peculiar binary including a hot subdwarf of O
spectral type and a compact companion in a 1.55 day orbit. According to the
steady spin period derivative $\dot{P}=(-2.17\pm0.01)\times10^{-15} ~\rm
s\,s^{-1}$ , the compact object was thought to be a contracting young white
dwarf (WD). However, the X-ray luminosity producing by the wind accretion of
massive WD is one order of magnitude smaller than the observed value. In this
work, we propose an alternative model to account for the observed X-ray
luminosity. If the WD was surrounded by a debris disk, the accretion from the
debris disk can produce the observed X-ray luminosity and X-ray pulses. Based
on the time-varying accretion rate model, the current mass of the debris disk
is constrained to be $3.9\times10^{-6}~\rm M_{\odot}$. Comparing with the
contraction of the WD, the accretion torque exerting by such a debris disk can
only influence the spin evolution of the WD in the early stage. According to
the accretion theory, the magnetic field of the WD is constrained to be $\sim
(0.7-7)\times10^{4}$ G. The calculated conventional polar cap radius of the WD
is larger than the observed emitting-zone radius, which probably originate from
the existence of strong and small-scale local magnetic field in the polar cap
surface. We expect that further multiband observations on this source can help
us to confirm or rule out the existence of a debris disk.",2205.09982v1
2022-09-08,"A direct N-body integrator for modelling the chaotic, tidal dynamics of multi-body extrasolar systems: TIDYMESS","Tidal dissipation plays an important role in the dynamical evolution of
moons, planets, stars and compact remnants. The interesting complexity
originates from the interplay between the internal structure and external tidal
forcing. Recent and upcoming observing missions of exoplanets and stars in the
Galaxy help to provide constraints on the physics of tidal dissipation. It is
timely to develop new N-body codes, which allow for experimentation with
various tidal models and numerical implementations. We present the open-source
N-body code TIDYMESS, which stands for ``TIdal DYnamics of Multi-body
ExtraSolar Systems''. This code implements a creep deformation law for the
bodies, parametrized by their fluid Love numbers and fluid relaxation times.
Due to tidal and centrifugal deformations, we approximate the general shape of
a body to be an ellipsoid. We calculate the associated gravitational field to
quadruple order, from which we derive the gravitational accelerations and
torques. The equations of motion for the orbits, spins and deformations are
integrated directly using a fourth-order integration method based on a
symplectic composition. We implement a novel integration method for the
deformations, which allows for a time step solely dependent on the orbits, and
not on the spin periods or fluid relaxation times. This feature greatly speeds
up the calculations, while also improving the consistency when comparing
different tidal regimes. We demonstrate the capabilities and performance of
TIDYMESS, particularly in the niche regime of parameter space where orbits are
chaotic and tides become non-linear.",2209.03955v1
2022-09-27,Shape model and rotation acceleration of (1685) Toro and (85989) 1999 JD6 from optical observations,"The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect is a net torque
caused by solar radiation directly reflected and thermally re-emitted from the
surface of small asteroids and is considered to be crucial in their dynamical
evolution. By long-term photometric observations of selected near-Earth
asteroids, it's hoped to enlarge asteroid samples with a detected YORP effect
to facilitate the development of a theoretical framework. Archived light-curve
data are collected and photometric observations are made for (1685) Toro and
(85989) 1999 JD6, which enables measurement of their YORP effect by inverting
the light curve to fit observations from a convex shape model. For (1685) Toro,
a YORP acceleration $\upsilon=(3.2\pm0.3)\times10^{-9}\ \rm{rad\cdot
d^{-2}}(1\sigma\ error)$ is updated, which is consistent with previous YORP
detection based on different light-curve data; for (85989) 1999 JD6, it is
determined that the sidereal period is $7.667749\pm 0.000009$ h, the rotation
pole direction locates is at $\lambda=232\pm 2^{\circ},\ \beta = -59\pm
1^{\circ}$, the acceleration is detected to be $\upsilon =
(2.4\pm0.3)\times10^{-8}\ \rm{rad\cdot d^{-2}}(1\sigma\ error)$ and in addition
to obtaining an excellent agreement between the observations and model. YORP
should produce both spin-up and spin-down cases. However, including (85989)
1999 JD6, the $\rm{d}\omega/\rm{d}t$ values of eleven near-Earth asteroids are
positive totally, which suggests that there is either a bias in the sample of
YORP detections or a real feature needs to be explained.",2209.13333v1
2022-10-09,Baryonic Effects on Lagrangian Clustering and Angular Momentum Reconstruction,"Recent studies illustrate the correlation between the angular momenta of
cosmic structures and their Lagrangian properties. However, only baryons are
observable and it is unclear whether they reliably trace the cosmic angular
momenta. We study the Lagrangian mass distribution, spin correlation, and
predictability of dark matter, gas, and stellar components of galaxy-halo
systems using IllustrisTNG, and show that the primordial segregations between
components are typically small. Their protoshapes are also similar in terms of
the statistics of moment of inertia tensors. Under the common gravitational
potential they are expected to exert the same tidal torque and the strong spin
correlations are not destroyed by the nonlinear evolution and complicated
baryonic effects, as confirmed by the high-resolution hydrodynamic simulations.
We further show that their late-time angular momenta traced by total gas,
stars, or the central galaxies, can be reliably reconstructed by the initial
perturbations. These results suggest that baryonic angular momenta can
potentially be used in reconstructing the parameters and models related to the
initial perturbations.",2210.04203v2
2022-10-12,Current-induced switching of thin film $α$-Fe$_2$O$_3$ devices imaged using a scanning single-spin microscope,"Electrical switching of N\'eel order in an antiferromagnetic insulator is
desirable as a basis for memory applications. Unlike electrically-driven
switching of ferromagnetic order via spin-orbit torques, electrical switching
of antiferromagnetic order remains poorly understood. Here we investigate the
low-field magnetic properties of 30 nm thick, c-axis oriented
$\alpha$-Fe$_2$O$_3$ Hall devices using a diamond nitrogen-vacancy (NV) center
scanning microscope. Using the canted moment of $\alpha$-Fe$_2$O$_3$ as a
magnetic handle on its N\'eel vector, we apply a saturating in-plane magnetic
field to create a known initial state before letting the state relax in low
field for magnetic imaging. We repeat this procedure for different in-plane
orientations of the initialization field. We find that the magnetic field
images are characterized by stronger magnetic textures for fields along
$[\bar{1}\bar{1}20]$ and $[11\bar{2}0]$, suggesting that despite the expected
3-fold magneto-crystalline anisotropy, our $\alpha$-Fe$_2$O$_3$ thin films have
an overall in-plane uniaxial anisotropy. We also study current-induced
switching of the magnetic order in $\alpha$-Fe$_2$O$_3$. We find that the
fraction of the device that switches depends on the current pulse duration,
amplitude and direction relative to the initialization field. Specifically, we
find that switching is most efficient when current is applied along the
direction of the initialization field.",2210.06233v1
2022-11-02,High-field quantum spin liquid transitions and angle-field phase diagram of Kitaev magnet $α$-RuCl$_3$,"The pursuit of quantum spin liquid (QSL) in the Kitaev honeycomb magnets has
drawn intensive attention recently. In particular, $\alpha$-RuCl$_3$ has been
widely recognized as a promising candidate for the Kitaev QSL. Although the
compound exhibits an antiferromagnetic order under zero field, it is believed
to be endowed with fractionalized excitations, and can be driven to the QSL
phase by magnetic fields. Here, based on a realistic $K$-$J$-$\Gamma$-$\Gamma'$
model for $\alpha$-RuCl$_3$ [1], we exploit the exponential tensor
renormalization group approach to explore the phase diagram of the compound
under magnetic fields. We calculate the thermodynamic quantities, including the
specific heat, Gr\""uneisen parameter, magnetic torque, and the magnetotropic
susceptibility, etc, under a magnetic field with a tilting angle $\theta$ to
the $c^*$-axis perpendicular to the honeycomb plane. We find an extended QSL in
the angle-field phase diagram determined with thermodynamic responses. The
gapless nature of such field-induced QSL is identified from the specific heat
and entropy data computed down to very low temperatures. The present study
provides guidance for future high-field experiments for the QSL in
$\alpha$-RuCl$_3$ and other candidate Kitaev magnets.",2211.01360v2
2022-11-30,The evolution of circumstellar discs in the Galactic Centre: an application to the G-clouds,"The Galactic Centre is known to have undergone a recent star formation
episode a few Myrs ago, which likely produced many T Tauri stars hosting
circumstellar discs. It has been suggested that these discs may be the compact
and dusty ionized sources identified as ``G-clouds''. Given the Galactic
Centre's hostile environment, we study the possible evolutionary pathways these
discs experience. We compute new external photoevaporation models applicable to
discs in the Galactic Centre that account for the sub-sonic launching of the
wind and absorption of UV photons by dust. Using evolutionary disc
calculations, we find that photoevaporation's rapid truncation of the disc
causes them to accrete onto the central star rapidly. Ultimately, an accreting
circumstellar disc has a lifetime $\lesssim1~$Myr, which would fail to live
long enough to explain the G-clouds. However, we identify a new evolutionary
pathway for circumstellar discs in the Galactic Centre. Removal of disc
material by photoevaporation prevents the young star from spinning down due to
magnetic braking, ultimately causing the rapidly spinning young star to torque
the disc into a ``decretion disc'' state which prevents accretion. At the same
time, any planetary companion in the disc will trap dust outside its orbit,
shutting down photoevaporation. The disc can survive for up to $\sim$10 Myr in
this state. Encounters with other stars are likely to remove the planet on Myr
timescales, causing photoevaporation to restart, giving rise to a G-cloud
signature. A giant planet fraction of $\sim10\%$ can explain the number of
observed G-clouds.",2212.00029v1
2023-04-16,Anomalous and Topological Hall Resistivity in Ta/CoFeB/MgO Magnetic Systems for Neuromorphic Computing Applications,"Topologically protected spin textures, such as magnetic skyrmions, have the
potential for dense data storage as well as energy-efficient computing due to
their small size and a low driving current. The evaluation of the writing and
reading of the skyrmion's magnetic and electrical characteristics is a key step
toward the implementation of these devices. In this paper, we present the
magnetic heterostructure Hall bar device and study the anomalous Hall and
topological Hall signals in the device. Using the combination of different
measurements like magnetometry at different temperatures, Hall effect
measurement from 2K to 300K, and magnetic force microscopy imaging, we
investigate the magnetic and electrical characteristics of the magnetic
structure. We measure the skyrmion topological resistivity at different
temperatures as a function of the magnetic field. The topological resistivity
is maximum around the zero magnetic field and it decreases to zero at the
saturating field. This is further supported by MFM imaging. Interestingly the
resistivity decreases linearly with the field, matching the behavior observed
in the corresponding micromagnetic simulations. We combine the experimental
results with micromagnetic simulations, thus propose a skyrmion-based synaptic
device and show spin-orbit torque-controlled potentiation/depression in the
device. The device performance as the synapse for neuromorphic computing is
further evaluated in a convolutional neural network CNN. The neural network is
trained and tested on the MNIST data set we show devices acting as synapses
achieving a recognition accuracy close to 90%, on par with the ideal
software-based weights which offer an accuracy of 92%.",2304.07742v1
2023-04-24,Timing analysis of Swift J0243.6+6124 with NICER and Fermi/GBM during the decay phase of the 2017-2018 outburst,"We present a timing and noise analysis of the Be/X-ray binary system Swift
J0243.6+6124 during its 2017-2018 super-Eddington outburst using NICER/XTI
observations. We apply a synthetic pulse timing analysis to enrich the
Fermi/GBM spin frequency history of the source with the new measurements from
NICER/XTI. We show that the pulse profiles switch from double-peaked to
single-peaked when the X-ray luminosity drops below $\sim$$7\times 10^{36}$ erg
s$^{-1}$. We suggest that this transitional luminosity is associated with the
transition from a pencil beam pattern to a hybrid beam pattern when the Coulomb
interactions become ineffective to decelerate the accretion flow, which implies
a dipolar magnetic field strength of $\sim$$5\times 10^{12}$ G. We also
obtained the power density spectra (PDS) of the spin frequency derivative
fluctuations. The red noise component of the PDS is found to be steeper
($\omega^{-3.36}$) than the other transient accreting sources. We find
significantly high noise strength estimates above the super-Eddington
luminosity levels, which may arise from the torque fluctuations due to
interactions with the quadrupole fields at such levels.",2304.11937v2
2023-05-08,Ultralow power and shifting-discretized magnetic racetrack memory device driven by chirality switching and spin current,"Magnetic racetrack memory has significantly evolved and developed since its
first experimental verification and is considered as one of the most promising
candidates for future high-density on-chip solid state memory. However, the
lack of a fast and precise magnetic domain wall (DW) shifting mechanism and the
required extremely high DW motion (DWM) driving current both make the racetrack
difficult to commercialize. Here, we propose a method for coherent DWM that is
free from above issues, which is driven by chirality switching (CS) and an
ultralow spin-orbit-torque (SOT) current. The CS, as the driving force of DWM,
is achieved by the sign change of DM interaction which is further induced by a
ferroelectric switching voltage. The SOT is used to break the symmetry when the
magnetic moment is rotated to the Bloch direction. We numerically investigate
the underlying principle and the effect of key parameters on the DWM through
micromagnetic simulations. Under the CS mechanism, a fast (102 m/s), ultralow
energy (5 attojoule), and precisely discretized DWM can be achieved.
Considering that skyrmions with topological protection and smaller size are
also promising for future racetrack, we similarly evaluate the feasibility of
applying such a CS mechanism to a skyrmion. However, we find that the CS only
causes it to ""breathe"" instead of moving. Our results demonstrate that the CS
strategy is suitable for future DW racetrack memory with ultralow power
consumption and discretized DWM.",2305.04671v1
2023-05-10,3D evolution of neutron star magnetic-fields from a realistic core-collapse turbulent topology,"We present the first 3D fully coupled magneto-thermal simulations of neutron
stars (including the most realistic background structure and microphysical
ingredients so far) applied to a very complex initial magnetic field topology
in the crust, similar to what recently obtained by proto-neutron star dynamo
simulations. In such configurations, most of the energy is stored in the
toroidal field, while the dipolar component is a few percent of the mean
magnetic field. This initial feature is maintained during the long-term
evolution (1e6 yr), since the Hall term favours a direct cascade (compensating
for Ohmic dissipation) rather than a strong inverse cascade, for such an
initial field topology. The surface dipolar component, responsible for the
dominant electromagnetic spin-down torque, does not show any increase in time,
when starting from this complex initial topology. This is at contrast with the
timing properties of young pulsars and magnetars which point to higher values
of the surface dipolar fields. A possibility is that the deep-seated magnetic
field (currents in the core) is able to self-organize in large scales (during
the collapse or in the early life of a neutron star). Alternatively, the
dipolar field might be lower than is usually thought, with magnetosphere
substantially contributing to the observed high spin-down, via e.g., strong
winds or strong coronal magnetic loops, which can also provide a natural
explanation to the tiny surface hotspots inferred from X-ray data.",2305.06342v1
2023-06-05,Full-scale field-free spin-orbit switching of the CoPt layer grown on vicinal substrates,"A simple, reliable and field-free spin orbit torque (SOT)-induced
magnetization switching is a key ingredient for the development of the
electrical controllable spintronic devices. Recently, the SOT induced
deterministic switching of the CoPt single layer has attracts a lot of
interests, as it could simplifies the structure and add new flexibility in the
design of SOT devices, compared with the Ferromagnet/Heavy metal bilayer
counterparts. Unfortunately, under the field-free switching strategies used
nowadays, the switching of the CoPt layer is often partial, which sets a major
obstacle for the practical applications. In this study, by growing the CoPt on
vicinal substrates, we could achieve the full-scale (100% switching ratio)
field-free switching of the CoPt layer. We demonstrate that when grown on
vicinal substrates, the magnetic easy axis of the CoPt could be tilted from the
normal direction of the film plane; the strength of Dzyaloshinskii Moriya
interaction (DMI) would be also be tuned as well. Micromagnetic simulation
further reveal that the field-free switching stems from tilted magnetic
anisotropy induced by the vicinal substrate, while the enhancement of DMI help
reducing the critical switching current. In addition, we also found that the
vicinal substrates could also enhance the SOT efficiency. With such simple
structure, full-scale switching, tunable DMI and SOT efficiency, our results
provide a new knob for the design SOT-MRAM and future spintronic devices.",2306.02616v1
2023-08-25,Tuning the Curie temperature of a 2D magnet/topological insulator heterostructure to above room temperature by epitaxial growth,"Heterostructures of two-dimensional (2D) van der Waals (vdW) magnets and
topological insulators (TI) are of substantial interest as candidate materials
for efficient spin-torque switching, quantum anomalous Hall effect, and chiral
spin textures. However, since many of the vdW magnets have Curie temperatures
below room temperature, we want to understand how materials can be modified to
stabilize their magnetic ordering to higher temperatures. In this work, we
utilize molecular beam epitaxy to systematically tune the Curie temperature
($T_C$) in thin film Fe$_3$GeTe$_2$/Bi$_2$Te$_3$ from bulk-like values
($\sim$220 K) to above room temperature by increasing the growth temperature
from 300 $^\circ$C to 375 $^\circ$C. For samples grown at 375 $^\circ$C,
cross-sectional scanning transmission electron microscopy (STEM) reveals the
spontaneous formation of different Fe$_m$Ge$_n$Te$_2$ compositions (e.g.
Fe$_5$Ge$_2$Te$_2$ and Fe$_7$Ge$_6$Te$_2$) as well as intercalation in the vdW
gaps, which are possible origins of the enhanced Curie temperature. This
observation paves the way for developing various Fe$_m$Ge$_n$Te$_2$/TI
heterostructures with novel properties.",2308.13620v1
2023-09-12,On the non-dissipative tidal evolution of the misalignment between spin and orbital angular momenta,"We extend our previous work on the evolution of close binary systems with
misaligned orbital and spin angular momenta resulting from non-dissipative
tidal interaction to include all physical effects contributing to apsidal
motion. In addition to tidal distortion of the primary by the compact secondary
these include relativistic Einstein precession and the rotational distortion of
the primary. The influence of the precession of the line of nodes is included.
The dependence of the tidal torque on the apsidal angle $\hat\varpi$ couples
the apsidal motion to the rate of evolution of the misalignment angle $\beta$
which is found to oscillate. We provide analytical estimates for the
oscillation amplitude $\Delta\beta$ over a wide range of parameter space
confirmed by numerical integrations. This is found to be more significant near
critical curves on which $d{\hat \varpi } /dt=0$ for a specified $\beta$.
  We find that to obtain $0.1 < \Delta\beta < \sim 1,$ the mass ratio, $q >
\sim1$ the initial eccentricity should be modest, $\cos \beta < 1/\sqrt{5},$
with $\cos\beta <0 $ corresponding to retrograde rotation, initially, and the
primary rotation rate should be sufficiently large. The extended discussion of
apsidal motion and its coupled evolution to the misalignment angle given here
has potential applications to close binaries with anomalous apsidal motion as
well as transiting exoplanets such as warm Jupiters.",2309.06334v1
2023-09-25,Domain wall dynamics driven by a transient laser-induced magnetisation,"One of the fundamental effects of the laser-matter interaction is the
appearance of an induced transient magnetisation. While the underlying
phenomena differ in their microscopic origin and cover a diverse array of
materials, here we address a fundamental question about the possibility to
drive domain-wall dynamics on the femtosecond timescale of the exchange
interactions solely by longitudinal changes of the magnetic moments. We verify
the viability of this hypothesis in the case of a generic ferromagnetic system
described in the framework of the high-temperature micromagnetic model based on
the Landau-Lifshitz-Bloch equation. The effect is investigated in a 1D model at
constant temperature as well as in a full micromagnetic framework considering
realistic laser-induced heating. Our results demonstrate that domain-wall
deformation in a femtosecond timeframe leads to the displacement of the wall on
a larger timescale up to nanoseconds accompanied by a release of excess energy
in the form of spin waves. The domain wall deformation leads to the appearance
of a magnetisation gradient across the wall which promotes the motion towards
the region consisting of spins with decreased magnetisation length. The total
displacement is enhanced at larger temperatures and smaller damping due to an
increase of the longitudinal relaxation time which ensures the longer presence
of the induced magnetisation gradient. We also demonstrate an enhanced domain
wall motion in the presence of the Dzyaloshinskii-Moriya interaction attributed
to augmented magnonic torques. Our results are important towards the
understanding of ultrafast magnetism phenomena on the sub-picosecond timescale.",2309.14287v1
2023-09-29,Long-term evolution of Cyclotron Line energy in an eclipsing pulsar 4U 1538-522,"We present the timing and spectral analysis of the HMXB source 4U 1538-522
using NuSTAR observations. One of the observations partially covers the X-ray
eclipse of the source along with eclipse ingress. The source is found to spin
down at the rate of 0.163 $\pm$ 0.002 s $\text{yr}^{-1}$ between $\sim$
(54973-58603) MJD. It is evident that at time $\sim$ 58620 MJD, a torque
reversal occurred, thereafter the source exhibited a spin-up trend at the rate
- (0.305 $\pm$ 0.018) s $\text{yr}^{-1}$ until 59275 MJD. A recent NuSTAR
observation finds the pulse period of the source: (526.2341 $\pm$ 0.0041) s.
The pulse profile exhibits a transition from double-peaked to single-peaked
nature above $\sim$ 30 keV. We analyzed the overall trend of the temporal
evolution of fundamental Cyclotron Resonance Scattering Feature (CRSF),
$\text{E}_\text{cyc}$, incorporating recent NuSTAR measurements. Initially,
during the time span $\sim$ (50452.16-55270.8) MJD, the cyclotron line energy
is found to increase at a rate of 0.11 $\pm$ 0.03 keV $\text{yr}^{-1}$ which is
further followed by a decrease at a rate - 0.14 $\pm$ 0.01 keV $\text{yr}^{-1}$
between (55270.8-59267) MJD. The combined measurements in the time span
(50452.16-59267) MJD reveal that the cyclotron line energy is increasing
linearly at a rate of 0.08 $\pm$ 0.02 keV $\text{yr}^{-1}$.",2309.17013v1
2023-10-02,Learning manipulation of steep granular slopes for fast Mini Rover turning,"Future planetary exploration missions will require reaching challenging
regions such as craters and steep slopes. Such regions are ubiquitous and
present science-rich targets potentially containing information regarding the
planet's internal structure. Steep slopes consisting of low-cohesion regolith
are prone to flow downward under small disturbances, making it very challenging
for autonomous rovers to traverse. Moreover, the navigation trajectories of
rovers are heavily limited by the terrain topology and future systems will need
to maneuver on flowable surfaces without getting trapped, allowing them to
further expand their reach and increase mission efficiency.
  In this work, we used a laboratory-scale rover robot and performed
maneuvering experiments on a steep granular slope of poppy seeds to explore the
rover's turning capabilities. The rover is capable of lifting, sweeping, and
spinning its wheels, allowing it to execute leg-like gait patterns. The
high-dimensional actuation capabilities of the rover facilitate effective
manipulation of the underlying granular surface. We used Bayesian Optimization
(BO) to gain insight into successful turning gaits in high dimensional search
space and found strategies such as differential wheel spinning and pivoting
around a single sweeping wheel. We then used these insights to further
fine-tune the turning gait, enabling the rover to turn 90 degrees at just above
4 seconds with minimal slip. Combining gait optimization and human-tuning
approaches, we found that fast turning is empowered by creating anisotropic
torques with the sweeping wheel.",2310.01273v1
2023-11-22,Controlling selection rules for magnon scattering in nanomagnets by spatial symmetry breaking,"Nanomagnets are the building blocks of many existing and emergent spintronic
technologies. Magnetization dynamics of nanomagnets is often dominated by
nonlinear processes, which have been recently shown to have many surprising
features and far-reaching implications for applications. Here we develop a
theoretical framework uncovering the selection rules for multimagnon processes
and discuss their underlying mechanisms. For its technological relevance, we
focus on the degenerate three-magnon process in thin elliptical nanodisks to
illustrate our findings. We parameterize the selection rules through a set of
magnon interaction coefficients which we calculate using micromagnetic
simulations. We postulate the selection rules and investigate how they are
altered by perturbations, that break the symmetry of static magnetization
configuration and spatial spin-wave profiles and that can be realized by
applying off-symmetry-axis or nonuniform magnetic fields. Our work provides the
phenomenological understanding into the mechanics of magnon interaction as well
as the formalism for determining the interaction coefficients from simulations
and experimental data. Our results serve as a guide to analyze magnon processes
inherently present in spin-torque devices for boosting their performance or to
engineer a specific nonlinear response of a nanomagnet used in neuromorphic or
quantum magnonic application.",2311.13726v1
2023-12-14,Revisiting RXTE observations of MXB 0656-072 during the type I outbursts in 2007-2008,"We report on the timing characteristics of MXB 0656-072 throughout its
2007-2008 type I outbursts utilising RXTE/PCA and Fermi/GBM data. Using pulse
timing technique, we explore the spin frequency evolution of the source during
this interval. Subsequently, by examining the torque-luminosity relation, we
show that the overall frequency evolution is substantially in line with the
Ghosh-Lamb model. Furthermore, the residuals of the spin frequencies do not
exhibit clear orbital modulations, which possibly indicate that the system is
observed on a relatively top view. In the RXTE/PCA observations, the pulsed
emission is found to be disappearing below $\sim$$5 \times 10^{36}$ erg
s$^{-1}$, whereas the profiles maintain stability above this value within our
analysis timeframe. In addition, we incorporate two novel methods along with
the conventional Deeter method in order to generate higher-resolution power
density spectra (PDS). A red noise pattern in the PDSs is also verified in
these new methods, common in disk-fed sources, with a steepness of $\Gamma \sim
-2$, reaching saturation at a time-scale of $\sim$150 d. Considering the models
for spectral transitions, we discuss the possible scenarios for the dipolar
magnetic field strength of MXB 0656-072 and its coherence with deductions from
the cyclotron resonance scattering feature (CRSF).",2312.08943v1
2024-01-21,Nonlinear Model Predictive Detumbling of Small Satellites with a Single-axis Magnetorquer,"Various actuators are used in spacecraft to achieve attitude stabilization,
including thrusters, momentum wheels, and control moment gyros. Small
satellites, however, have stringent size, weight, and cost constraints, which
makes many actuator choices prohibitive. Consequently, magnetic torquers have
commonly been applied to spacecraft to attenuate angular rates. Approaches for
dealing with under-actuation due to magnetic control torque's dependency on the
magnetic field and required high magnetic flux densities have been previously
considered. Generally speaking, control of a satellite that becomes
under-actuated as a result of on-board failures has been a recurrent theme in
the literature. Methods for controlling spacecraft with fewer actuators than
degrees of freedom are increasingly in demand due to the increased number of
small satellite launches. Magnetic torquers have been extensively investigated
for momentum management of spacecraft with momentum wheels and for nutation
damping of spin satellites, momentum-biased, and dual-spin satellites.
Nonetheless, severely under-actuated small spacecraft that carry only a
single-axis magnetic torquer have not been previously treated. This note
considers the detumbling of a small spacecraft using only a single-axis
magnetic torquer. Even with a three-axis magnetic torquer, the spacecraft is
under-actuated, while, in the case of only a single axis magnetic torquer, the
problem is considerably more demanding. Our note examines the feasibility of
spacecraft attitude control with a single-axis magnetic torquer and possible
control methods that can be used.",2401.11536v1
2004-11-25,On the mass transfer in AE Aquarii,"The observed properties of the close binary AE Aqr indicate that the mass
transfer in this system operates via the Roche lobe overflow mechanism, but the
material transferred from the normal companion is neither accreted onto the
surface of the white dwarf nor stored in a disk around its magnetosphere. As
previously shown, such a situation can be realized if the white dwarf operates
as a propeller. At the same time, the efficiency of the propeller action by the
white dwarf is insufficient to explain the rapid braking of the white dwarf,
which implies that the spin-down power is in excess of the bolometric
luminosity of the system. To avoid this problem we have simulated the
mass-transfer process in AE Aqr assuming that the observed braking of the white
dwarf is governed by a pulsar-like spin-down mechanism. We show that the
expected H_alpha Doppler tomogram in this case resembles the tomogram observed
from the system. We find that the agreement between the simulated and the
observed tomograms is rather good provided the mean value of the mass-transfer
rate <\dot{M}> ~5x10^16 g/s. Three spatially separated sources of H_alpha
emission can be distinguished within this approach. The structure of the
tomogram depends on the relative contributions of these sources to the H_alpha
emission and is expected to vary from night to night.",0411697v1
2002-09-20,Radiative charge transfer lifetime of the excited state of (NaCa)$^+$,"New experiments were proposed recently to investigate the regime of cold
atomic and molecular ion-atom collision processes in a special hybrid
neutral-atom--ion trap under high vacuum conditions. The collisional cooling of
laser pre-cooled Ca$^+$ ions by ultracold Na atoms is being studied. Modeling
this process requires knowledge of the radiative lifetime of the excited
singlet A$^1\Sigma^+$ state of the (NaCa)$^+$ molecular system. We calculate
the rate coefficient for radiative charge transfer using a semiclassical
approach. The dipole radial matrix elements between the ground and the excited
states, and the potential curves were calculated using Complete Active Space
Self-Consistent field and M\""oller-Plesset second order perturbation theory
(CASSCF/MP2) with an extended Gaussian basis, 6-311+G(3df). The semiclassical
charge transfer rate coefficient was averaged over a thermal Maxwellian
distribution. In addition we also present elastic collision cross sections and
the spin-exchange cross section. The rate coefficient for charge transfer was
found to be $2.3\times 10^{-16}$ cm$^3$/sec, while those for the elastic and
spin-exchange cross sections were found to be several orders of magnitude
higher ($1.1\times 10^{-8}$ cm$^3$/sec and $2.3\times 10^{-9}$ cm$^3$/sec,
respectively). This confirms our assumption that the milli-Kelvin regime of
collisional cooling of calcium ions by sodium atoms is favorable with the
respect to low loss of calcium ions due to the charge transfer.",0209077v2
2016-05-31,Spatio-temporal correlations in models of collective motion ruled by different dynamical laws,"Information transfer is an essential factor in determining the robustness of
collective behaviour in biological systems with distributed control. The most
direct way to study the information transfer mechanisms is to experimentally
detect the propagation across the system of a signal triggered by some
perturbation. However, for field experiments this method is inefficient, as the
possibilities of the observer to perturb the group are limited and empirical
observations must rely on rare natural perturbations. An alternative way is to
use spatio-temporal correlations to assess the information transfer mechanism
directly from the spontaneous fluctuations of the system, without the need to
have an actual propagating signal on record. We test the approach on ground
truth data provided by numerical simulations in three dimensions of two models
of collective behaviour characterized by very different dynamical equations and
information transfer mechanisms: the classic Vicsek model, describing an
overdamped noninertial dynamics and the inertial spin model, characterized by
an un- derdamped inertial dynamics. By using dynamical finite size scaling, we
show that spatio-temporal correlations are able to distinguish unambiguously
the diffusive information transfer mechanism of the Vicsek model from the
linear mechanism of the inertial spin model.",1605.09628v3
2019-03-08,Optimal Bounds on State Transfer Under Quantum Channels with Application to Spin System Engineering,"Modern applications of quantum control in quantum information science and
technology require the precise characterization of quantum states and quantum
channels. In particular, high-performance quantum state engineering often
demands that quantum states are transferred with optimal efficiency via
realizable controlled evolution, the latter often modeled by quantum channels.
When an appropriate quantum control model for an interested system is
constructed, the exploration of optimal bounds on state transfer for the
underlying quantum channel is then an important task. In this work, we analyze
the state transfer efficiency problem for different class of quantum channels,
including unitary, mixed unitary and Markovian. We then apply the theory to
nuclear magnetic resonance (NMR) experiments. We show that two most commonly
used control techniques in NMR, namely gradient field control and phase
cycling, can be described by mixed unitary channels. Then we show that
employing mixed unitary channels does not extend the unitarily accessible
region of states. Also, we present a strategy of optimal experiment design,
which incorporates coherent radio-frequency field control, gradient field
control and phase cycling, aiming at maximizing state transfer efficiency and
meanwhile minimizing the number of experiments required. Finally, we perform
pseudopure state preparation experiments on two- and three-spin systems, in
order to test the bound theory and to demonstrate the usefulness of non-unitary
control means.",1903.03569v2
2021-08-08,On the Electron Pairing Mechanism of Copper-Oxide High Temperature Superconductivity,"The elementary CuO2 plane sustaining cuprate high-temperature
superconductivity occurs typically at the base of a periodic array of
edge-sharing CuO5 pyramids. Virtual transitions of electrons between adjacent
planar Cu and O atoms, occurring at a rate $t/{\hbar}$ and across the
charge-transfer energy gap E, generate 'superexchange' spin-spin interactions
of energy $J\approx4t^4/E^3$ in an antiferromagnetic correlated-insulator
state. However, Hole doping the CuO2 plane converts this into a very high
temperature superconducting state whose electron-pairing is exceptional. A
leading proposal for the mechanism of this intense electron-pairing is that,
while hole doping destroys magnetic order it preserves pair-forming
superexchange interactions governed by the charge-transfer energy scale E. To
explore this hypothesis directly at atomic-scale, we combine single-electron
and electron-pair (Josephson) scanning tunneling microscopy to visualize the
interplay of E and the electron-pair density nP in ${Bi_2Sr_2CaCu_2O_{8+x}}$.
The responses of both E and nP to alterations in the distance {\delta} between
planar Cu and apical O atoms are then determined. These data reveal the
empirical crux of strongly correlated superconductivity in CuO2, the response
of the electron-pair condensate to varying the charge transfer energy.
Concurrence of predictions from strong-correlation theory for hole-doped
charge-transfer insulators with these observations, indicates that
charge-transfer superexchange is the electron-pairing mechanism of
superconductive ${Bi_2Sr_2CaCu_2O_{8+x}}$.",2108.03655v3
1995-03-01,Geometrization of spin systems using cycle expansions,"It is shown that a spin system with long range interactions can be converted
into a chaotic dynamical system that is differentiable and low-dimensional. The
thermodynamic limit of the spin system is then equivalent to studying the long
term behavior of the dynamical system. Cycle expansions of chaotic systems
(expansion of the Fredholm determinant) are then used to study the
thermodynamic limit. By considering the smooth dynamical system, it is possible
to converge to the thermodynamic limit faster than with transfer matrices.",9502023v1
1994-02-03,Exact Results for Spin and Charge Dynamics of Electrons with Supersymmetry,"Excitation spectra in the SU($\nu +1$,1) supersymmetric t-J model with
long-range exchange and transfer has quadratic dependence on spin and charge
currents for all energies. After brief review on the supersymmetry, this paper
gives a simple explanation for the spin-charge separation on the basis of a
first-quantized representation. A useful identity is derived on permutation
properties of SU($\nu$) Jastrow-type wave functions, which constitute the
ground states for a class of 1/$r^2$ interaction models.",9402009v1
1994-04-18,Intensity correlations in electronic wave propagation in a disordered medium: the influence of spin-orbit scattering,"We obtain explicit expressions for the correlation functions of transmission
and reflection coefficients of coherent electronic waves propagating through a
disordered quasi-one-dimensional medium with purely elastic diffusive
scattering in the presence of spin-orbit interactions. We find in the metallic
regime both large local intensity fluctuations and long-range correlations
which ultimately lead to universal conductance fluctuations. We show that the
main effect of spin-orbit scattering is to suppress both local and long-range
intensity fluctuations by a universal symmetry factor 4. We use a scattering
approach based on random transfer matrices.",9404054v1
1994-05-13,Re-Structuring Method for the Negative Sign Problem in Quantum Spin Systems,"We present detailed discussions on a new approach we proposed in a previous
paper to numerically study quantum spin systems. This method, which we will
call re-structuring method hereafter, is based on rearrangement of intermediate
states in the path integral formulation. We observed our approach brings
remarkable improvement in the negative sign problem when applied to
one-dimensional quantum spin $1/2$ system with next-to-nearest neighbor
interactions. In this paper we add some descriptions on our method and show
results from analyses by the exact diagonalization and by the transfer matrix
method of the system on a small chain. These results also indicate that our
method works quite effectively.",9405037v1
1994-12-09,Constrained annealing for spin glasses,"The quenched free energy of spin glasses is estimated by means of annealed
averages where the frustration is constrained to its average value. We discuss
the case of d-dimensional Ising models with random nearest neighbour coupling,
and we introduce a new method to obtain constrained annealed averages without
recurring to Lagrange multipliers. It requires to perform quenched averages
either on small volumes in an analytic way, or on finite size strips via
products of random transfer matrices. We thus give a sequence of converging
lower bounds for the quenched free energy of 2d spin glasses.",9412046v1
1997-11-16,Bethe ansatz for the one-dimensional small-polaron model with open boundary conditions,"The one-dimensional small-polaron model with open boundary conditions is
considered in the framework of the quantum inverse scattering method. The spin
model which is equivalent to the small-polaron model is the Heisenberg $XXZ$
spin chain in an external magnetic field. For spin model, the solutions of the
reflection equation (RE) and the dual RE are obtained. The eigenvalues and
eigenvectors problems are solved by using the algebraic Bethe ansatz method.
The case of the fermion model is also studied, the commuting of the transfer
matrix can be proved, and the eigenvalues and the Bethe ansatz equations for
fermion model are obtained.",9711150v1
1998-03-20,Transitions between Phases with Equal Wave Numbers in a Double Ising Spin Model. Application to Betaine Calcium Chloride Dihydrate,"A Double Ising Spin model for uniaxially structurally modulated materials
exhibits as a special feature phase transitions between phases with equal wave
numbers but different pseudo spin configurations. The character of these
`internal' transitions is investigated in mean field approximation, with the
mean field transfer matrix method, and in Monte Carlo simulations. The
structural changes at the transitions are characterized by different strengths
of harmonics in a Fourier analysis of the spatial modulation. A dielectric
anomaly in the phase diagram of betaine calcium chloride dihydrate (BCCD) and
seemingly contradictory structure analyses are explained.",9803252v1
1999-07-08,Nuclear spin relaxation rates in two-leg spin ladders,"Using the transfer-matrix DMRG method, we study the nuclear spin relaxation
rate 1/T_1 in the two-leg s=1/2 ladder as function of the inter-chain
(J_{\perp}) and intra-chain (J_{|}) couplings. In particular, we separate the
q_y=0 and \pi contributions and show that the later contribute significantly to
the copper relaxation rate ^{63}(1/T_1) in the experimentally relevant coupling
and temperature range. We compare our results to both theoretical predictions
and experimental measures on ladder materials.",9907117v2
2000-01-21,Thermodynamics of the spin-flop transition in a quantum XYZ chain,"A special limit of an antiferromagnetic XYZ chain was recently shown to
exhibit interesting bulk as well as surface spin-flop transitions at T=0. Here
we provide a complete calculation of the thermodynamics of the bulk transition
using a transfer-matrix-renormalization-group (TMRG) method that addresses
directly the thermodynamic limit of quantum spin chains. We also shed some
light on certain spinwave anomalies at low temperature predicted earlier by
Johnson and Bonner.",0001313v1
2000-10-31,Analytic approach to the one-dimensional spin-Peierls system in the entire frequency range,"We use the two cut-off renormalization group (RG) method to study the
spin-Peierls model in one-dimension for the entire phonon frequency range. We
integrate out the phonon and solve the effective Fermion system via mean field
and RG methods. We make use of the symmetry that the Neel, dimerization, and
spin current order parameters form an SU(2) triplet based on resolving the
Fermion into left and right movers. We present the phase diagram and discuss
its implications for the organic charge-transfer salt (TMTTF)$_2$PF$_6$.",0010499v1
2001-10-02,"Spin-polarized Zener tunneling in (Ga,Mn)As","We investigate spin-polarized inter-band tunneling through measurement of
(Ga,Mn)As based Zener tunnel diode. By placing the diode under reverse bias,
electron spin polarization is transferred from the valence band of p-type
(Ga,Mn)As to the conduction band of an adjacent n-GaAs layer. The resulting
current is monitored by injection into a quantum well light emitting diode
whose electroluminescence polarization is found to track the magnetization of
the (Ga,Mn)As layer as a function of both temperature and magnetic field.",0110062v1
2002-07-11,Why temperature chaos in spin glasses is hard to observe,"The overlap length of a three-dimensional Ising spin glass on a cubic lattice
with Gaussian interactions has been estimated numerically by transfer matrix
methods and within a Migdal-Kadanoff renormalization group scheme. We find that
the overlap length is large, explaining why it has been difficult to observe
spin glass chaos in numerical simulations and experiment.",0207300v1
2002-10-18,Quantum and thermal fluctuations in the SU(N) Heisenberg spin-glass model near the quantum critical point,"We solve for the SU(N) Heisenberg spin-glass in the limit of large N focusing
on small S and T. We study the effect of quantum and thermal fluctuations in
the frequency dependent response function and observed interesting transfers of
spectral weight. We compute the T-dependence of the order parameter and the
specific heat and find an unusual T^2 behavior for the latter at low
temperatures in the spin-glass phase. We find a remarkable qualitative
agreement with various experiments on the quantum frustrated magnet
SrCr_{9p}Ga_{12-9p}O_{19}.",0210407v1
2003-05-21,A turnstile electron-spin entangler in semiconductors,"We propose a single-electron doped quantum dot in a field-effect structure as
an optically triggered turnstile for spin-entangled electrons. A short laser
pulse excites a charged exciton, whose quantum properties are transferred
through tunneling and relaxation to the spin entanglement between electrons in
the dot and contact. We identify the pertinent disentanglement mechanisms, and
discuss experimental detection and possible application schemes.",0305494v1
2003-11-28,Contact-induced spin polarization in carbon nanotubes,"Motivated by the possibility of combining spintronics with molecular
structures, we investigate the conditions for the appearance of
spin-polarization in low-dimensional tubular systems by contacting them to a
magnetic substrate. We derive a set of general expressions describing the
charge transfer between the tube and the substrate and the relative energy
costs. The mean-field solution of the general expressions provides an
insightful formula for the induced spin-polarization. Using a tight-binding
model for the electronic structure we are able to estimate the magnitude and
the stability of the induced moment. This indicates that a significant magnetic
moment in carbon nanotubes can be observed.",0311637v1
2003-12-15,Thermodynamics of a one-dimensional S=1/2 spin-orbital model,"The thermodynamic properties of a one-dimensional model describing spin
dynamics in the presence of a twofold orbital degeneracy are studied
numerically using the transfer-matrix renormalization group (TMRG). The model
contains an integrable SU(4)-symmetric point and a gapless phase which is SU(4)
invariant up to a rescaling of the velocities for spin and orbital degrees of
freedom which allows detailed comparison of the numerical results with
conformal field theory. We pay special attention to the correlation lengths
which show an intriguing evolution with temperature. We find that the model
shows an intrinsic tendency towards dimerization at finite temperature even if
the ground state is not dimerized.",0312365v1
2005-05-18,Non-Degenerate Ground State in the Antiferromagnetic Double-Exchange Model on a Triangular Lattice,"In order to study effects of frustration in an itinerant electron system, we
investigate ground states of the antiferromagnetic double-exchange model on a
triangular lattice. In this model, pseudo-spins are coupled to electron
transfer integrals in such a way that antiparallel configurations of
pseudo-spins gain kinetic energies. Although the antiferromagnetic Ising model
on a triangular lattice shows macroscopic dengenerate ground states, the
present model shows that the degeneracy is lifted due to long-range natures of
the double exchange interactions. Spin ordering at the ground state is also
discussed.",0505442v1
2006-06-07,Generation of spin current by Coulomb drag,"Coulomb drag between two quantum wires is exponentially sensitive to the
mismatch of their electronic densities. The application of a magnetic field can
compensate this mismatch for electrons of opposite spin directions in different
wires. The resulting enhanced momentum transfer leads to the conversion of the
charge current in the active wire to the spin current in the passive wire.",0606185v2
2006-09-08,Dynamics of photoexcited states in one-dimensional dimerized Mott insulators,"Dynamical properties of photoexcited states are theoretically studied in a
one-dimensional Mott insulator dimerized by the spin-Peierls instability.
Numerical calculations combined with a perturbative analysis have revealed that
the lowest photoexcited state without nearest-neighbor interaction corresponds
to an interdimer charge transfer excitation that belongs to dispersive
excitations. This excited state destabilizes the dimerized phase, leading to a
photoinduced inverse spin-Peierls transition. We discuss the purely electronic
origin of midgap states that are observed in a latest photoexcitation
experiment of an organic spin-Peierls compound, K-TCNQ
(potassium-tetracyanoquinodimethane).",0609186v1
2006-10-04,Correlated electrons systems on the Apollonian network,"Strongly correlated electrons on an Apollonian network are studied using the
Hubbard model. Ground-state and thermodynamic properties, including specific
heat, magnetic susceptibility, spin-spin correlation function, double occupancy
and one-electron transfer, are evaluated applying direct diagonalization and
quantum Monte Carlo. The results support several types of magnetic behavior. In
the strong-coupling limit, the quantum anisotropic spin 1/2 Heisenberg model is
used and the phase diagram is discussed using the renormalization group method.
For ferromagnetic coupling, we always observe the existence of long-range
order. For antiferromagnetic coupling, we find a paramagnetic phase for all
finite temperatures.",0610111v1
2007-01-17,Doped Spin Ladder: Zhang-Rice Singlets or Rung-centred Holes?,"We formulate charge transfer model for a single doped spin ladder, relevant
for the intrinsically doped plane of coupled spin ladders in
Sr$_{3}$Ca$_{11}$Cu$_{24}$O$_{41}$. Assuming the presence of the experimentally
observed charge order in the system we solve the model using Hartree-Fock
approximation. Our results show the profound stability of the Zhang-Rice
singlets with respect to other configurations of doped holes, in agreement with
recent x-ray absorption measurements.",0701418v1
1998-09-16,Study of Instanton Contributions to Moments of Nucleon Spin-Dependent Structure Functions,"Instantons are the natural mechanism in non-perturbative QCD to remove
helicity from valence quarks and transfer it to gluons and quark-antiquark
pairs. To understand the extent to which instantons explain the so-called ""spin
crisis"" in the nucleon, we calculate moments of spin-dependent structure
functions in quenched QCD and compare them with the results obtained with
cooled configurations from which essentially all gluon contributions except
instantons have been removed. Preliminary results are presented.",9809132v1
2000-08-29,The GDH Sum Rule and Related Integrals,"The spin structure of the nucleon resonance region is analyzed on the basis
of our phenomenological model MAID. Predictions are given for the
Gerasimov-Drell-Hearn sum rule as well as generalized integrals over spin
structure functions. The dependence of these integrals on momentum transfer is
studied and rigorous relationships between various definitions of generalized
Gerasimov-Drell-Hearn integrals and spin polarizabilities are derived. These
results are compared to the predictions of chiral perturbation theory and
phenomenological models.",0008306v1
2001-01-22,Coulomb-hadron phase factor and spin phenomena in a wide region of transfer momenta,"The Coulomb-hadron interference effects are examined at small and large $t$.
The methods for the definition of spin-dependent parts of hadron scattering
amplitude are presented. The additional contributions to analyzing power $A_N$
and the double spin correlation parameter $A_{NN}$ owing to the
electromagnetic-hadron interference are determined in the diffraction dip
domain of high-energy elastic hadron scattering.",0101238v1
2002-06-24,Mapping the Transverse Nucleon Spin,"The transverse nucleon spin can be transferred to the quarks and gluons in
several ways. In the factorizing, hard scattering processes to be considered,
these are parameterized at leading twist by the transversity distribution
function and at next-to-leading twist by quark-gluon correlation functions. The
latter enter the description of the structure function $g_2$ and possibly of
single spin asymmetries. It is discussed what is known about these functions
and what are the remaining open issues.",0206235v2
2004-04-23,Beam normal spin asymmetry in elastic lepton-nucleon scattering,"We discuss the two-photon exchange contribution to observables which involve
lepton helicity flip in elastic lepton-nucleon scattering. This contribution is
accessed through the spin asymmetry for a lepton beam polarized normal to the
scattering plane. We estimate this beam normal spin asymmetry at large momentum
transfer using a parton model and we express the corresponding amplitude in
terms of generalized parton distributions.",0404206v1
2004-12-22,Impact of saturation on spin effects in proton-proton scattering,"For pomerons described by a sum of two simple-pole terms, a soft and a hard
pomeron, the unitarity bounds from saturation in impact-parameter space are
examined. We consider the effect of these bounds on observables linked with
polarisation, such as the analyzing power in elastic proton-proton scattering,
for LHC energies. We obtain the s and t dependence of the Coulomb-nuclear
interference at small momentum transfer, and show that the effect of the hard
pomeron may be observed at the LHC.",0412341v1
1994-03-10,Symmetry Under $α\rightarrow α+ 1$ is Forbidden by Helicity Conservation,"The question as to whether helicity conservation in spin one-half Aharonov
Bohm scattering is sufficient in itself to determine uniquely the form of the
spinor wave function near the origin is examined. Although it is found that a
one parameter family of solutions is compatible with this conservation law,
there must nonetheless be singular solutions which break the symmetry $\alpha
\rightarrow \alpha +1$ required for an anyon interpretation. Thus the free
parameter which occurs does not allow one to eliminate the singular solutions
even though it does in principle mean that they can be transferred at will
between the spin up and spin down configurations.",9403065v1
1994-03-24,Quantum Integrals of Motion for the Heisenberg Spin Chain,"An explicit expression for all the quantum integrals of motion for the
isotropic Heisenberg $s=1/2$ spin chain is presented.
  The conserved quantities are expressed in terms of a sum over simple
polynomials in spin variables. This construction is direct and independent of
the transfer matrix formalism. Continuum limits of these integrals in both
ferrromagnetic and antiferromagnetic sectors are briefly discussed.",9403149v1
1997-06-12,The Monodromy Matrices of the XXZ Model in the Infinite Volume Limit,"We consider the XXZ model in the infinite volume limit with spin half quantum
space and higher spin auxiliary space. Using perturbation theory arguments, we
relate the half infinite transfer matrices of this class of models to certain
$U_q(\hat{sl_2})$ intertwiners introduced by Nakayashiki. We construct the
monodromy matrices, and show that the one with spin one auxiliary space gives
rise to the L operator.",9706086v1
1998-07-28,Spontaneous Magnetization in the Finite XXZ Spin Chain with Boundaries,"The finite XXZ spin chain with boundaries is studied. We derive the transfer
matrix from the q-difference equation discovered by Cherednik and construct its
eigenstates by the vertex operator approach. We point out that the eigenstates
with no magnetic fields have a symmetry called the turning symmetry. Making use
of this symmetry we calculate the spontaneous magnetization in the
thermodynamic limit, which is roughly twice as large as that in the
half-infinite XXZ spin chain.",9807201v3
2000-06-12,Fusion and Analytical Bethe Ansatz for the $A_{\n-1}^{(1)}$ Open Spin Chain,"We generalise the fusion procedure for the $A_{\n-1}^{(1)}$ open spin chain
($\n>2$) and we show that the transfer matrix satisfies a crossing property. We
use these results to solve the $A_{\n-1}^{(1)}$ open spin chain with $U_{q}
(SU(\n))$ symmetry by means of the analytical Bethe ansatz method. Our results
coincide with the known ones obtained by means of the nested Bethe ansatz.",0006081v1
2000-06-26,"Quantum spin chain with ""soliton non-preserving"" boundary conditions","We consider the case of an integrable quantum spin chain with ""soliton
non-peserving"" boundary conditions. This is the first time that such boundary
conditions have been considered in the spin chain framework. We construct the
transfer matrix of the model, we study its symmetry and we find explicit
expressions for its eigenvalues. Moreover, we derive a new set of Bethe ansatz
equations by means of the analytical Bethe ansatz method.",0006197v2
2005-09-06,A Bethe Ansatz Study of Free Energy and Excitation Spectrum for Even Spin Fateev Zamolodchikov Model,"A Bethe Ansatz study of a self dual Z_N spin model is undertaken for even
spin system. One has to solve a coupled system of Bethe Ansatz Equations (BAE)
involving zeroes of two families of transfer matrices. A numerical study on
finite size lattices is done for identification of elementary excitations over
the Ferromagnetic and Antiferromagnetic ground states. The free energies for
both Ferromagnetic and Antiferromagnetic ground states and dispersion relation
for elementary excitations are found.",0509045v1
1996-10-03,Low-energy interaction of composite spin-half systems with scalar and vector fields,"We consider a composite spin-half particle moving in spatially-varying scalar
and vector fields. The vector field is assumed to couple to a conserved charge,
but no assumption is made about either the structure of the composite or its
coupling to the scalar field. A general form for the piece of the spin-orbit
interaction of the composite with the scalar and vector fields which is
first-order in momentum transfer ${\bf Q}$ and second-order in the fields is
derived.",9610007v1
2004-11-04,Spin and Isospin Effects in the NN -> NK Lambda Reaction Near Threshold,"The spin and isospin structure of the amplitudes and observables for K+Lambda
production in nucleon-nucleon collisions in the near-threshold region is
analysed. It is shown that, with reasonable values for the relative strengths
of the pi and rho terms in a meson-exchange model, one expects production on
the neutron to be significantly stronger than that on the proton. Negative
values of the spin-transfer coefficient D_NN are also predicted due to pi-rho
interference.",0411019v1
2005-12-30,On the Experimental Identification of Spin-Parities and Single-Particle Configurations in $^{257}$No and Its $α$-Decay Daughter $^{253}$Fm,"Recently measured lifetimes of the favored $\alpha$ decays from $^{257}$No
have been calculated using the quantum mechanical tunneling within WKB
approximation using microscopic nuclear potentials. Results obtained assuming
previously assigned (ambiguous) parent spin of $\frac{7^+}{2}$ and newly
assigned configuration $\frac{3^+}{2}$ [622] have been compared. Hindrance
factors for the favored decays have also been compared with the calculated
hindrances using higher angular momenta transfers. Although the calculations
substantiate the findings, yet it makes the spin-parity assignment of
$\frac{3^+}{2}$ for the ground state of $^{257}$No less definite.",0512106v1
2006-04-10,Effects of spin-orbit interaction on nuclear response and neutrino mean free path,"The effects of the spin-orbit component of the particle-hole interaction on
nuclear response functions and neutrino mean free path are examined. A complete
treatment of the full Skyrme interaction in the case of symmetric nuclear
matter and pure neutron matter is given. Numerical results for neutron matter
are discussed. It is shown that the effects of the spin-orbit interaction
remain small, even at momentum transfer larger than the Fermi momentum. The
neutrino mean free paths are marginally affected.",0604019v1
1999-12-22,Automatic Quantum Error Correction,"Criteria are given by which dissipative evolution can transfer populations
and coherences between quantum subspaces, without a loss of coherence. This
results in a form of quantum error correction that is implemented by the joint
evolution of a system and a cold bath. It requires no external intervention
and, in principal, no ancilla. An example of a system that protects a qubit
against spin-flip errors is proposed. It consists of three spin 1/2 magnetic
particles and three modes of a resonator. The qubit is the triple quantum
coherence of the spins, and the photons act as ancilla.",9912104v1
2008-09-12,The Case for Hypercritical Accretion in M33 X-7,"The spin parameter of the black hole in M33 X-7 has recently been measured to
be a*=0.77+-0.05 (Liu et al. 2008). It has been proposed that the spin of the
15.65 M_sun black hole is natal. We show that this is not a viable evolutionary
path given the observed binary orbital period of 3.45 days since the explosion
that would produce a black hole with the cited spin parameter and orbital
period would disrupt the binary. Furthermore, we show that the system has to be
evolved through the hypercritical mass transfer of about 5 M_sun from the
secondary star to the black hole.",0809.2146v1
2010-08-07,Gravitation form-factors and spin asymmetries in hadron elastic scattering,"In the framework of the model, where the scattering amplitude is determined
by the first and second moments of the GPDs, the qualitative description of all
existing experimental data at $\sqrt{s} \geq 52.8 $ GeV, including the Coulomb
range and large momentum transfers, is obtained with only 4 free parameters.
The spin-flip amplitude of the nucleon-nucleon elastic scattering is determined
taking into account the spin-dependence part of the second moment of the
generalized parton distributions (GPDs) with a new set of $t $-dependence.
  The corresponding value of the % analyzing power $A_N$ for the $pp$ at high
energy (RHIC) elastic scattering is obtained.",1008.1323v1
2010-09-26,Hybrid optical pumping of optically dense alkali-metal vapor without quenching gas,"Optical pumping of an optically thick atomic vapor typically requires a
quenching buffer gas, such as N$_{2}$, to prevent radiation trapping of
unpolarized photons which would depolarize the atoms. We show that optical
pumping of a trace contamination of Rb present in K metal results in a 4.5
times higher polarization of K than direct optical pumping of K in the absence
of N$_{2}$. Such spin-exchange polarization transfer from optically-thin
species is useful in a variety of areas, including spin-polarized nuclear
scattering targets and electron beams, quantum-non-demolition spin
measurements, and ultra-sensitive magnetometry.",1009.5047v1
2010-10-19,Spontaneous Quantum Hall States in Chirally-stacked Few-Layer Graphene Systems,"Chirally stacked N-layer graphene systems with N >= 2 exhibit a variety of
distinct broken symmetry states in which charge density contributions from
different spins and valleys are spontaneously transferred between layers. We
explain how these states are distinguished by their charge, spin, and valley
Hall conductivities, by their orbital magnetizations, and by their edge state
properties. We argue that valley Hall states have [N/2] edge channels per
spin-valley.",1010.4003v1
2012-07-04,Y-junction splitting spin states of moving quantum dot,"The development of a working quantum computer utilizing electron spin states
as qubits is a major goal for many theorists and experimentalists. The future
applications of quantum information technology would also require a reliable
method for the transportation of quantum information. A promising such method
is the propagation of electrons by a surface acoustic wave (SAW). In this
paper, we simulate the SAW transfer of two interacting electrons through a
Y-shaped junction. Our results show that the singlet and triplet states can be
differentiated in the Y-junction by an electrostatic detuning potential, an
effect that could be used in for example measuring the state of a two-spin
qubit.",1207.1099v1
2012-07-13,Magnetic relaxation in bilayers of yttrium iron garnet/platinum due to the dynamic coupling at the interface,"We show that in ferromagnetic (FM)/normal metal (NM) bilayers the dynamic
coupling at the interface transfers an additional magnetic relaxation from the
heavily damped motion of the conduction electron spins in the NM layer to the
FM spins. While the FM relaxation rates due to two-magnon scattering and spin
pumping decrease rapidly with increasing FM film thickness, the damping due to
the dynamic coupling does not depend on the FM film thickness. The proposed
mechanism explains the very large broadening of ferromagnetic resonance lines
in thick films of yttrium iron garnet after deposition of a Pt layer.",1207.3330v1
2013-05-30,Electrical spin injection into graphene through monolayer hexagonal boron nitride,"We demonstrate electrical spin injection from a ferromagnet to a bilayer
graphene (BLG) through a monolayer (ML) of single-crystal hexagonal boron
nitride (h-BN). A Ni81Fe19/ML h-BN/BLG/h-BN structure is fabricated using a
micromechanical cleavage and dry transfer technique. The transport properties
across the ML h-BN layer exhibit tunnel barrier characteristics. Spin injection
into BLG has been detected through non local magnetoresistance measurements.",1305.7095v1
2013-11-14,Recent Results in Polarized Proton-Proton Elastic Scattering at STAR,"RHIC is the only spin-polarized proton collider ever built. With a special
optics run of $\beta^\star \approx 22$ m STAR detector system is suitable for
an investigation of the spin dependence of elastic proton-proton scattering.
This is a brief summary of measurements of spin asymmetries at the center of
mass energy $\sqrt{s}=200$ GeV and in the four-momentum transfer squared $-t$
range $0.003 < -t < 0.035$ GeV$^2$ by the STAR experiment at RHIC.",1311.3401v2
2014-02-18,Linear response theory in asymmetric nuclear matter for Skyrme functionals including spin-orbit and tensor terms,"The formalism of linear response theory for a Skyrme functional including
spin-orbit and tensor terms is generalized to the case of infinite nuclear
matter with arbitrary isospin asymmetry. Response functions are obtained by
solving an algebraic system of equations, which is explicitly given.
Spin-isospin strength functions are analyzed varying the conditions of density,
momentum transfer, asymmetry and temperature. The presence of instabilities,
including the spinodal one, is studied by means of the static susceptibility.",1402.4284v1
2014-04-02,"On the Equivalence of Trapped Colloids, Pinned Vortices, and Spin Ice","We investigate the recently reported analogies between pinned vortices in
nano-structured superconductors or colloids in optical traps, and spin ice
materials. The frustration of the two models, one describing colloids and
vortices, the other describing spin ice, differs essentially. However, their
effective energetics is made identical by the contribution of an emergent field
associated to a topological charge. This equivalence extends to the local
low-energy dynamics of the ice manifold, yet breaks down in lattices of mixed
coordination, because of topological charge transfer between sub-latices.",1404.0451v1
2015-06-11,The accretion rate and minimum spin period of accreting pulsars,"We consider combined rotational, magnetic, and thermal evolution of the
neutron star during the accretion phase in a binary system. A rapid
accretion-driven decay of the magnetic field decreases substantially the
efficiency of angular momentum transfer. As a result, the neutron star cannot
spin up to periods shorter than some limiting value even if accretion is very
long and accretion rate is high. The proposed mechanism can explain a
discrepancy between the shortest detected period and minimal possible spin
period of neutron stars.",1506.03660v2
2015-06-16,Quasilocal conserved operators in isotropic Heisenberg spin 1/2 chain,"Composing higher auxiliary-spin transfer matrices and their derivatives, we
construct a family of quasilocal conserved operators of isotropic Heisenberg
spin 1/2 chain and rigorously establish their linear independence from the
well-known set of local conserved charges.",1506.05049v2
2015-12-10,Origin of spin dependent tunneling through chiral molecules,"The functionality of many biological systems depends on reliable electron
transfer with minimal heating. Unlike man-made electric circuits, nature
realizes electron transport via insulating chiral molecules. Here we include
spin into the analysis of tunneling through these molecules, and demonstrate
its importance for efficient transport. We show that the helical geometry
induces robust spin filtering accompanied by, and intimately related to,
strongly enhanced transmission. Thus, we resolve two key questions posed by
transport measurements through organic molecules, demonstrating their common
origin.",1512.03435v2
2015-12-29,Phonon induced two-mode squeezing of nitrogen-vacancy center ensembles,"We propose a potentially practical scheme for realization of two-mode
squeezed state with respect to two distant nitrogen-vacancy center ensembles
coupled to two interconnected mechanical modes of diamond nanoresonators. By
making use of the tunable phonon-spin interaction and the engineered
phonon-phonon tunneling, both the desired excitation transfer process and the
optimal two-mode squeezing between spin ensembles can be realized. We
investigate the dynamics of the total system under infulences from the
mechanical decay using both analytical and numerical methods, where the
realistic conditions that leads to optimized squeezing between spin ensembles
are analyzed.",1512.08605v1
2016-09-06,Generating Quantum States through Spin Chain Dynamics,"Spin chains can realise perfect quantum state transfer between the two ends
via judicious choice of coupling strengths. In this paper, we study what other
states can be created by engineering a spin chain. We conclude that, up to
local phases, all single excitation quantum states with support on every site
of the chain can be created. We pay particular attention to the generation of
W-states that are superposed over every site of the chain.",1609.01398v2
2016-11-04,"An ultracold, optically trapped mixture of {87}Rb and metastable {4}He atoms","We report on the realization of an ultracold (<25~muK) mixture of rubidium
({87}Rb) and metastable triplet helium ({4}He) in an optical dipole trap. Our
scheme involves laser cooling in a dual-species magneto-optical trap,
simultaneous MW- and RF-induced forced evaporative cooling in a quadrupole
magnetic trap, and transfer to a single-beam optical dipole trap. We observe
long trapping lifetimes for the doubly spin-stretched spin-state mixture and
measure much shorter lifetimes for other spin-state combinations. We discuss
prospects for realizing quantum degenerate mixtures of alkali-metal and
metastable helium atoms.",1611.01430v1
2017-04-25,On stably trivial spin torsors over low-dimensional schemes,"The paper discusses stably trivial torsors for spin and orthogonal groups
over smooth affine schemes over infinite perfect fields of characteristic
unequal to 2. We give a complete description of all the invariants relevant for
the classification of such objects over schemes of dimension at most $3$, along
with many examples. The results are based on the
$\mathbb{A}^1$-representability theorem for torsors and transfer of known
computations of $\mathbb{A}^1$-homotopy sheaves along the sporadic isomorphisms
to spin groups.",1704.07768v1
2017-11-18,On a Microscopic Representation of Space-Time VII -- On Spin,"We recall some basic aspects of line and line Complex representations, of
symplectic symmetry emerging in bilinear point transformations as well as of
Lie transfer of lines to spheres. Here, we identify SU(2) spin in terms of
(classical) projective geometry and obtain spinorial representations from
lines, i.e.~we find a natural non-local geometrical description associated to
spin. We discuss the construction of a Lagrangean in terms of line/Complex
invariants. We discuss the edges of the fundamental tetrahedron which allows to
associate the most real form SU(4) with its various related real forms covering
SO($n$,$m$), $n+m=6$.",1711.09005v1
2017-12-29,Relay entanglement and clusters of correlated spins,"Considering a spin-1/2 chain, we {suppose} that the entanglement passes from
a given pair of particles to another one, thus establishing the relay transfer
of entanglement along the chain. Therefore, we introduce the relay entanglement
as a sum of all pairwise entanglements in a spin chain. For more detailed
studying the effects of {remote} pairwise entanglements, we use the partial
sums collecting entanglements between the spins separated by up to a certain
number of nodes. The problem of entangled cluster formation is considered, and
the geometric mean entanglement is introduced as a {characteristics} of quantum
correlations in a cluster. Generally, the life-time of a cluster decreases with
an increase in its size.",1712.10188v2
2018-02-22,Unexpected Phenomenology in Particle-Based Ice Absent in Magnetic Spin Ice,"While particle-based ices are often considered essentially equivalent to
magnet-based spin ices, the two differ essentially in frustration and
energetics. We show that at equilibrium particle-based ices correspond exactly
to spin ices coupled to a background field. In trivial geometries, such a field
has no effect, and the two systems are indeed thermodynamically equivalent. In
other cases, however, the field controls a richer phenomenology, absent in
magnetic ices, and still largely unexplored: ice rule fragility, topological
charge transfer, radial polarization, decimation induced disorder, and
glassiness.",1802.07900v2
2018-12-30,Multi-Faced Entanglement,"Detailed analysis of behavior of spin-entangled particle pairs under
arbitrary rotations in their Hilbert space has been performed. It shows a rich
range of varieties (faces) of entanglement in different bases. Analytic
criteria are obtained for the respective faces of an entangled state. The
corresponding conditions generally depend on both the state itself and the
chosen basis. The most important result is revealing a deep analogy between a
spin-entangled electronic qubit pair and momentum-entangled photon pair. Both
cases exhibit coherence transfer from individual particles to nonlocal state of
the system. This analogy allows us to predict certain features of the
interference patterns in spin-entangled qubit pairs.",1901.00374v1
2019-03-01,"Spin Chains, Graphs and State Revival","Connections between the 1-excitation dynamics of spin lattices and quantum
walks on graphs will be surveyed. Attention will be paid to perfect state
transfer (PST) and fractional revival (FR) as well as to the role played by
orthogonal polynomials in the study of these phenomena. Included is a
discussion of the ordered Hamming scheme, its relation to multivariate
Krawtchouk polynomials of the Tratnik type, the exploration of quantum walks on
graphs of this association scheme and their projection to spin lattices with
PST and FR.",1903.00145v1
2019-05-28,Linear response theory in asymmetric nuclear matter for Skyrme functionals including spin-orbit and tensor terms II: Charge Exchange,"We present the formalism of linear response theory both at zero and finite
temperature in the case of asymmetric nuclear matter excited by an isospin flip
probe. The particle-hole interaction is derived from a general Skyrme
functional that includes spin-orbit and tensor terms. Response functions are
obtained by solving a closed algebraic system of equations. Spin strength
functions are analyzed for typical values of density, momentum transfer,
asymmetry and temperature.",1905.12049v2
2019-12-03,Mass and spin constraint on black holes in long GRBs,"We compute the evolution of a quasi-spherical, slowly rotating accretion flow
around a black hole, whose mass and spin evolve adequately to the mass-energy
transfer through the horizon. Our model is relevant for the central engine
driving a long gamma ray burst, that originates from the collapse of a massive
star. Our results show how much mass and spin a newly formed black hole should
possess during collapsar to launch long GRB.",1912.03116v1
2020-04-26,Spin Current Generation by a Surface Plasmon Polariton,"Surface plasmon polariton (SPP) is an electromagnetic wave which is tightly
localised beyond the diffraction limit at metallic surfaces. Recently, it is
theoretically proposed that the angular momentum conversion between the SPP and
electrons. In this work, we have successfully measured SPP induced spin
currents, which proves the fact that the angular momenta are interconverted.
Such conversion from light to a spin current can be used as a coupler in a next
generation spintronic computing with optical data transfer or storage.",2004.12348v1
2021-06-09,Einstein-de Haas Nanorotor,"We propose a nanoscale rotor embedded between two ferromagnetic electrodes
that is driven by spin injection. The spin-rotation coupling allows this
nanorotor to continuously receive angular momentum from an injected spin under
steady current flow between ferromagnetic electrodes in an antiparallel
magnetization configuration. We develop a quantum theory of this angular
momentum transfer and show that a relaxation process from a precession state
into a sleeping top state is crucial for the efficient driving of the nanorotor
by solving the master equation. Our work clarifies a general strategy for
efficient driving of a nanorotor.",2106.04861v3
2022-07-28,Protecting information in a parametrically driven hybrid quantum system,"The transfer and storage of quantum information in a hybrid quantum system,
consisting of an ensemble of atoms or spins interacting with a cavity, is
adversely affected by the inhomogeneity of the spins, which negates the
coherent exchange of excitations between the physical components. Using a full
quantum treatment based on variational renormalization group, we show how
quantum information encoded in the states of a parametrically driven hybrid
system is strongly protected against any decoherence that may arise due to the
inhomogeneity in the spin-ensemble.",2207.14354v2
2022-11-29,Kekule spin-orbit dimer phase and triplon dynamics,"We derive and study a spin-orbital model for ions with $d^1$ electronic
configuration on a honeycomb lattice. In this system, the directional character
of $t_{2g}$ orbital leads to extensively degenerate dimerized ground states. We
find that additional interactions from charge transfer processes completely
lift the degeneracy and stabilize the Kekule spin-orbit dimerized phase where
dimers form a kagome superlattice. For such phase, the triplon band spectrum
resembles the electronic band structure of the kagome lattice and becomes
topologically non-trivial in the presence of inter-dimer Dzyaloshinskii-Moriya
interactions. As an experimental verification of the Kekule dimerized phase, we
propose the thermal Hall experiment, which can directly uncover the topological
profile of the corresponding triplon band spectrum.",2211.16094v1
2015-03-12,Theory of box-model hyperfine couplings and transport signatures of long-range nuclear-spin coherence in a quantum-dot spin valve,"We have theoretically analyzed coherent nuclear-spin dynamics induced by
electron transport through a quantum-dot spin valve. The hyperfine interaction
between electron and nuclear spins in a quantum dot allows for the transfer of
angular momentum from spin-polarized electrons injected from ferromagnetic or
half-metal leads to the nuclear spin system under a finite voltage bias.
Accounting for a local nuclear-spin dephasing process prevents the system from
becoming stuck in collective dark states, allowing a large nuclear polarization
to be built up in the long-time limit. After reaching a steady state, reversing
the voltage bias induces a transient current response as the nuclear
polarization is reversed. Long-range nuclear-spin coherence leads to a strong
enhancement of spin-flip transition rates (by an amount proportional to the
number of nuclear spins) and is revealed by an intense current burst, analogous
to superradiant light emission. The crossover to a regime with incoherent spin
flips occurs on a relatively long time scale, on the order of the
single-nuclear-spin dephasing time, which can be much longer than the time
scale for the superradiant current burst. This conclusion is confirmed through
a general master equation. For the two limiting regimes (coherent/incoherent
spin flips) the general master equation recovers our simpler treatment based on
rate equations, but is also applicable at intermediate dephasing. Throughout
this work we assume uniform hyperfine couplings, which yield the strongest
coherent enhancement. We propose realistic strategies, based on isotopic
modulation and wavefunction engineering in core-shell nanowires, to realize
this analytically solvable ""box-model"" of hyperfine couplings.",1503.03645v2
2006-01-24,Black hole spin in GRS 1915+105,"Microquasars are galactic black hole binary systems with radio jets which can
sometimes be spatially resolved to show superluminal motion. The first and best
known of this class of objects is GRS 1915+105, the brightest accreting source
in our Galaxy. There is persistent speculation that strong jet emission could
be linked to black hole spin. If so, the high spin should also be evident in
accretion disc spectra. We search the RXTE archive to find disc-dominated X-ray
spectra from this object, as these are the only ones which can give reliable
spin determinations by this method. Finding these is complicated by the rapid,
unique limit cycle variability, but we are able to identify such spectra by
going to the shortest possible time resolution (16 s). We fit them with a
simple multicolour disc blackbody diskbb, and with the best current model which
include full radiative transfer as well as relativistic effects bhspec. Both
these models show that the spin is intermediate, neither zero nor maximal.
bhspec, the most physical model, gives a value for the dimensionless spin of a*
\~ 0.7 for a distance of 12.5 kpc and inclination of 66 deg. This, together
with the range of spins 0.1 < a* < 0.8 derived using this method for other
black holes, suggests that jet emission is probably fundamentally powered by
gravity rather than spin, and implies that high-to-maximal spin is not a
pre-requisite for powerful relativistic jets.",0601540v2
2007-03-23,Semiclassical dynamics and long time asymptotics of the central-spin problem in a quantum dot,"The spin of an electron trapped in a quantum dot is a promising candidate
implementation of a qubit for quantum information processing. We study the
central spin problem of the effect of the hyperfine interaction between such an
electron and a large number of nuclear moments. Using a spin coherent path
integral, we show that in this limit the electron spin evolution is well
described by classical dynamics of both the nuclear and electron spins. We then
introduce approximate yet systematic methods to analyze aspects of the
classical dynamics, and discuss the importance of the exact integrability of
the central spin Hamiltonian. This is compared with numerical simulation.
Finally, we obtain the asymptotic long time decay of the electron spin
polarization. We show that this is insensitive to integrability, and determined
instead by the transfer of angular momentum to very weakly coupled spins far
from the center of the quantum dot. The specific form of the decay is shown to
depend sensitively on the form of the electronic wavefunction.",0703631v5
2004-08-25,Selective coherence transfers in homonuclear dipolar coupled spin systems,"Mapping the physical dipolar Hamiltonian of a solid-state network of nuclear
spins onto a system of nearest-neighbor couplings would be extremely useful for
a variety of quantum information processing applications, as well as NMR
structural studies. We demonstrate such a mapping for a system consisting of an
ensemble of spin pairs, where the coupling between spins in the same pair is
significantly stronger than the coupling between spins on different pairs. An
amplitude modulated RF field is applied on resonance with the Larmor frequency
of the spins, with the frequency of the modulation matched to the frequency of
the dipolar coupling of interest. The spin pairs appear isolated from each
other in the regime where the RF power (omega_1) is such that omega_weak <<
omega_1 << omega_strong. Coherence lifetimes within the two-spin system are
increased from 19 us to 11.1 ms, a factor of 572.",0408158v2
2009-03-17,Spin Fluctuations and the Pseudogap in Organic Superconductors,"We show that there are strong similarities in the spin lattice relaxation of
non-magnetic organic charge transfer salts, and that these similarities can be
understood in terms of spin fluctuations. Further, we show that, in all of the
kappa-phase organic superconductors for which there is nuclear magnetic
resonance data, the energy scale for the spin fluctuations coincides with the
energy scale for the pseudogap. This suggests that the pseudogap is caused by
short-range spin correlations. In the weakly frustrated metals
k-(BEDT-TTF)_2Cu[N(CN)_2]Br, k-(BEDT-TTF)_2Cu(NCS)_2, and
k-(BEDT-TTF)_2Cu[N(CN)_2]Cl (under pressure) the pseudogap opens at the same
temperature as coherence emerges in the (intralayer) transport. We argue that
this is because the spin correlations are cut off by the loss of intralayer
coherence at high temperatures. We discuss what might happen to these two
energy scales at high pressures, where the electronic correlations are weaker.
In these weakly frustrated materials the data is well described by the chemical
pressure hypothesis (that anion substitution is equivalent to hydrostatic
pressure). However, we find important differences in the metallic state of
k-(BEDT-TTF)_2Cu_2(CN)_3, which is highly frustrated and displays a spin liquid
insulating phase. We also show that the characteristic temperature scale of the
spin fluctuations in (TMTSF)_2ClO_4 is the same as superconducting critical
temperature, which may be evidence that spin fluctuations mediate the
superconductivity in the Bechgaard salts.",0903.2881v2
2010-07-01,Electric-Field-control of spin rotation in bilayer graphene,"The manipulation of the electron spin degree of freedom is at the core of the
spintronics paradigm, which offers the perspective of reduced power
consumption, enabled by the decoupling of information processing from net
charge transfer. Spintronics also offers the possibility of devising hybrid
devices able to perform logic, communication, and storage operations. Graphene,
with its potentially long spin-coherence length, is a promising material for
spin-encoded information transport. However, the small spin-orbit interaction
is also a limitation for the design of conventional devices based on the
canonical Datta-Das spin-FET. An alternative solution can be found in magnetic
doping of graphene, or, as discussed in the present work, in exploiting the
proximity effect between graphene and Ferromagnetic Oxides (FOs). Graphene in
proximity to FO experiences an exchange proximity interaction (EPI), that acts
as an effective Zeeman field for electrons in graphene, inducing a spin
precession around the magnetization axis of the FO. Here we show that in an
appropriately designed double-gate field-effect transistor, with a bilayer
graphene channel and FO used as a gate dielectric, spin-precession of carriers
can be turned ON and OFF with the application of a differential voltage to the
gates. This feature is directly probed in the spin-resolved conductance of the
bilayer.",1007.0091v1
2013-05-13,Jumps in entropy and magnetic susceptibility at the valence and spin-state transition in a cobalt oxide,"A wide family of cobalt oxides of formulation (Pr,Ln,Ca)CoO3 (Ln being a
lanthanide) exhibits a coupled valence and spin-state transition (VSST) at a
temperature T*, which involves two concomitant modifications: (i) a change in
the spin state of Co3+ from low-spin (T < T*) to a higher spin-state (T > T*),
and (ii) a change in the valence state of Pr, from a mixed Pr4+/Pr3+ state (T <
T*) to a purely trivalent state (T > T*), accompanied by an equivalent charge
transfer within the Co3+/Co4+ subsystem. In the present paper, the VSST taking
place in (Pr0.7Sm0.3)0.7Ca0.3CoO3 at T* = about 90 K is investigated by
magnetization and heat capacity measurements. First, we quantitatively
characterized the jumps in magnetic susceptibility (khi) and entropy (S) around
T*. Then, these values were compared to those calculated as a function of the
variations in the population of the different cationic species involved in the
VSST. X-ray absorption spectroscopy experiments recently showed that the higher
spin state above T* should be regarded as an inhomogeneous mixture between
low-spin (LS) and high-spin (HS) states. In the frame of this description, we
demonstrate that the jumps in both khi and S can be associated to the same
change in the Co3+ HS content around T*. This result lends further support to
the relevance of the LS/HS picture for the VSST, challenging the currently
dominant interpretation based on the occurrence of an intermediate-spin (IS)
state of Co3+ above T*.",1305.2829v1
2014-07-02,Spin Waves in Ferromagnetic Insulators Coupled via a Normal Metal,"Herein, we study the spin-wave dispersion and dissipation in a ferromagnetic
insulator--normal metal--ferromagnetic insulator system. Long-range dynamic
coupling because of spin pumping and spin transfer lead to collective magnetic
excitations in the two thin-film ferromagnets. In addition, the dynamic dipolar
field contributes to the interlayer coupling. By solving the
Landau-Lifshitz-Gilbert-Slonczewski equation for macrospin excitations and the
exchange-dipole volume as well as surface spin waves, we compute the effect of
the dynamic coupling on the resonance frequencies and linewidths of the various
modes. The long-wavelength modes may couple acoustically or optically. In the
absence of spin-memory loss in the normal metal, the spin-pumping-induced
Gilbert damping enhancement of the acoustic mode vanishes, whereas the optical
mode acquires a significant Gilbert damping enhancement, comparable to that of
a system attached to a perfect spin sink. The dynamic coupling is reduced for
short-wavelength spin waves, and there is no synchronization. For intermediate
wavelengths, the coupling can be increased by the dipolar field such that the
modes in the two ferromagnetic insulators can couple despite possible small
frequency asymmetries. The surface waves induced by an easy-axis surface
anisotropy exhibit much greater Gilbert damping enhancement. These modes also
may acoustically or optically couple, but they are unaffected by thickness
asymmetries.",1407.0635v1
2014-08-12,The Origin of Black Hole Spin in Galactic Low-Mass X-ray Binaries,"Galactic field black hole (BH) low-mass X-ray binaries (LMXBs) are believed
to form in situ via the evolution of isolated binaries. In the standard
formation channel, these systems survived a common envelope phase, after which
the remaining helium core of the primary star and the subsequently formed BH
are not expected to be highly spinning. However, the measured spins of BHs in
LMXBs cover the whole range of spin parameters. We propose here that the BH
spin in LMXBs is acquired through accretion onto the BH after its formation. In
order to test this hypothesis, we calculated extensive grids of detailed binary
mass-transfer sequences. For each sequence, we examined whether, at any point
in time, the calculated binary properties are in agreement with their
observationally inferred counterparts of 16 Galactic LMXBs. The ""successful""
sequences give estimates of the mass that the BH has accreted since the onset
of Roche-Lobe overflow. We find that in all Galactic LMXBs with measured BH
spin, the origin of the spin can be accounted for by the accreted matter, and
we make predictions about the maximum BH spin in LMXBs where no measurement is
yet available. Furthermore, we derive limits on the maximum spin that any BH
can have depending on current properties of the binary it resides in. Finally
we discuss the implication that our findings have on the BH birth-mass
distribution, which is shifted by ~1.5 Msolar towards lower masses, compared to
the currently observed one.",1408.2661v2
2016-01-22,Optically induced dynamic nuclear spin polarisation in diamond,"The sensitivity of Magnetic Resonance Imaging (MRI) depends strongly on
nuclear spin polarisation and, motivated by this observation, dynamical nuclear
spin polarisation has recently been applied to enhance MRI protocols
(Kurhanewicz, J., et al., Neoplasia 13, 81 (2011)). Nuclear spins associated
with the 13 C carbon isotope (nuclear spin I = 1/2) in diamond possess uniquely
long spin lattice relaxation times (Reynhardt, E.C. and G.L. High, Prog. in
Nuc. Mag. Res. Sp. 38, 37 (2011)) If they are present in diamond nanocrystals,
especially when strongly polarised, they form a promising contrast agent for
MRI. Current schemes for achieving nuclear polarisation, however, require
cryogenic temperatures. Here we demonstrate an efficient scheme that realises
optically induced 13 C nuclear spin hyperpolarisation in diamond at room
temperature and low ambient magnetic field. Optical pumping of a
Nitrogen-Vacancy (NV) centre creates a continuously renewable electron spin
polarisation which can be transferred to surrounding 13 C nuclear spins.
Importantly for future applications we also realise polarisation protocols that
are robust against an unknown misalignment between magnetic field and crystal
axis.",1601.05967v1
2016-08-03,Angular momentum properties of haloes and their baryon content in the Illustris simulation,"The angular momentum properties of virialised dark matter haloes have been
measured with good statistics in collisionless N-body simulations, but an
equally accurate analysis of the baryonic spin is still missing. We employ the
Illustris simulation suite, one of the first simulations of galaxy formation
with full hydrodynamics that produces a realistic galaxy population in a
sizeable volume, to quantify the baryonic spin properties for more than $\sim$
320,000 haloes. We first compare the systematic differences between different
spin parameter and halo definitions, and the impact of sample selection
criteria on the derived properties. We confirm that dark matter only haloes
exhibit a close to self-similar spin distribution in mass and redshift of
lognormal form. However, the physics of galaxy formation radically changes the
baryonic spin distribution. While the dark matter component remains largely
unaffected, strong trends with mass and redshift appear for the spin of diffuse
gas and the formed stellar component. With time the baryons staying bound to
the halo develop a misalignment of their spin vector with respect to dark
matter, and increase their specific angular momentum by a factor of $\sim$ 1.3
in the non-radiative case and $\sim$ 1.8 in the full physics setup at z = 0. We
show that this enhancement in baryonic spin can be explained by the combined
effect of specific angular momentum transfer from dark matter onto gas during
mergers and from feedback expelling low specific angular momentum gas from the
halo. Our results challenge certain models for spin evolution and underline the
significant changes induced by baryonic physics in the structure of haloes.",1608.01323v2
2016-08-29,Multi-fractal Geometry of Finite Networks of Spins,"Quantum spin networks overcome the challenges of traditional charge-based
electronics by encoding the information into spin degrees of freedom. Although
beneficial for transmitting information with minimal losses when compared to
their charge-based counterparts, the mathematical formalization of the
information propagation in a spin(tronic) network is challenging due to its
complicated scaling properties. In this paper, we propose a geometric
approach---specific to finite networks---for unraveling the
information-theoretic phenomena of spin chains and rings by abstracting them as
weighted graphs, where the vertices correspond to the spin excitation states
and the edges represent the information theoretic distance between pair of
nodes. The weighted graph representation of the quantum spin network dynamics
exhibits a complex self-similar structure (where subgraphs repeat to some
extent over various space scales). To quantify this complex behavior, we
develop a new box counting inspired algorithm which assesses the mono-fractal
versus multi-fractal properties of quantum spin networks. Besides specific to
finite networks, multi-fractality is further compounded by ""engineering"" or
""biasing"" the network for selective transfer, as selectivity makes the network
more heterogeneous. To demonstrate criticality in finite size systems, we
define a thermodynamics inspired framework for describing information
propagation and show evidence that some spin chains and rings exhibit an
informational phase transition phenomenon, akin to the metal-to-insulator phase
transition in Anderson localization in finite media.}",1608.08192v1
2016-12-15,The Effect of Transient Accretion on the Spin-Up of Millisecond Pulsars,"A millisecond pulsar is a neutron star that has been substantially spun up by
accretion from a binary companion. A previously unrecognized factor governing
the spin evolution of such pulsars is the crucial effect of non-steady or
transient accretion. We numerically compute the evolution of accreting neutron
stars through a series of outburst and quiescent phases considering the drastic
variation of the accretion rate and the standard disk-magnetosphere
interaction. We find that, for the same long-term average accretion rate, X-ray
transients can spin up pulsars to rates several times higher than can
persistent accretors, even when the spin down due to electromagnetic radiation
during quiescence is included. We also compute an analytical expression for the
equilibrium spin frequency in transients, by taking spin equilibrium to mean
that no net angular momentum is transferred to the neutron star in each
outburst cycle. We find that the equilibrium spin rate for transients, which
depends on the peak accretion rate during outbursts, can be much higher than
that for persistent sources. This explains our numerical finding. This finding
implies that any meaningful study of neutron star spin and magnetic field
distributions requires the inclusion of the transient accretion effect, since
most accreting neutron star sources are transients. Our finding also implies
the existence of a submillisecond pulsar population, which is not observed.
This may point to the need for a competing spin-down mechanism for the
fastest-rotating accreting pulsars, such as gravitational radiation.",1612.04962v1
2017-04-08,Effect of Frustrated Exchange Interactions and Spin-half Impurity on the Electronic Structure of Strongly Correlated NiFe$_{2}$O$_{4}$,"Spin-polarized density functional calculations, magnetization, and neutron
diffraction measurements are carried out to investigate the magnetic exchange
interactions and strong correlation effects in Yb substituted inverse spinel
nickel ferrite. In the pristine form, the compound is found to be a mixed
insulator under the Zaanen-Sawtazsky-Allen classification scheme as it features
both charge transfer and Mott insulator mechanism. Estimation of magnetic
exchange couplings reveals that both octahedral-octahedral and
octahedral-tetrahedral spin-spin interactions are antiferromagnetic which is
typical of a spin-frustrated triangular lattice. However, the latter is
dominant compared to the former leading to a forced parallel alignment of the
spins at the octahedral site which is in agreement with the results of neutron
diffraction measurements. The substituent Yb is found to be settled in +3
charge state, as confirmed from the XPS measurements, to behave like a
spin-half impurity carried by the localized $f_{z(x^2-y^2)}$ orbital. The
impurity $f$ spin significantly weakens the antiferromagnetic coupling with the
spins at the tetrahedral site, which explains the experimental observation of
fall in Curie temperature with Yb substitution.",1704.02454v2
2017-05-21,Non-Magnetic Half-Metals,"Half-metals are a class of materials that are metallic only for one spin
direction, and are essential for spintronics applications where one needs to
read, write, store and transfer spin-data. This spin sensitivity appears to
restrict them to be magnetic, and the known examples indeed are. The
fabrication of real spintronic devices from such materials is often hampered,
however, by stray magnetic fields, domain walls, short spin coherence times,
scattering on magnetic atoms or magnetically active interfaces, and other
characteristics that come along with the magnetism. The surfaces of topological
insulators, or Dirac or Weyl semimetals, could be an alternative, but
production of high-quality thin films without the presence of the bulk states
at the Fermi level remains very challenging. Here we introduce non-magnetic
half-metals and demonstrate that this state is realized in IrBiSe. Using
angle-resolved photoemission spectroscopy and band structure calculations we
find a record-high Dresselhaus spin-orbit splitting, fully spin-polarized
remnant Fermi surfaces and a chiral 3D spin-texture, all with no magnetism
present. Promising applications include using IrBiSe as a source of
spin-polarized electrons, and lightly doped IrBiSe is expected to generate
electric-field-controlled spin-polarized currents, free from back scattering,
and could host triplet superconductivity.",1705.07431v1
2018-03-29,Spinning dust emission from circumstellar disks and its role in excess microwave emission,"Electric dipole emission from rapidly spinning polycyclic aromatic
hydrocarbons (PAHs) is widely believed as an origin of anomalous microwave
emission (AME), but recently it encounters a setback due to the non-correlation
of AME with PAH abundance seen in a full-sky analysis. Microwave observations
for specific regions with well-constrained PAH features would be crucial to
test the spinning dust hypothesis. In this paper, we present physical modeling
of microwave emission from spinning PAHs from protoplanetary disks (PPDs)
around Herbig Ae/Be stars and T-Tauri stars where PAH features are well
observed. Guided by the presence of 10 $\mu$m silicate features in some PPDs,
we also model microwave emission from spinning nanosilicates. Thermal emission
from big dust grains is computed using the Monte Carlo radiative transfer code.
Our numerical results demonstrate that microwave emission from either spinning
PAHs or spinning nanosilicates dominates over thermal dust at frequencies $\nu<
60$ GHz, even in the presence of significant grain growth. Finally, we attempt
to fit mm-cm observational data with both thermal dust and spinning dust for
several disks around Herbig Ae/Be stars that exhibit PAH features and find that
spinning dust can successfully reproduce the observed excess microwave emission
(EME). Future radio observations with ngVLA, SKA and ALMA Band 1 would be
valuable for elucidating the origin of EME and potentially open a new window
for probing nanoparticles in circumstellar disks.",1803.11028v3
2018-08-01,Spin fluctuations in the light-induced high spin state of Cobalt valence tautomers,"We present a study of the static magnetic properties and spin dynamics in
Cobalt valence tautomers (VT), molecules where a low-spin (LS) to high-spin
(HS) crossover driven by an intramolecular electron transfer can be controlled
by the temperature, by the external pressure or by light irradiation. In the
investigated complex, a LS-Co(III) ion bound to a dinegative organic ligand can
be reversibly converted into the HS-Co(II) bound to a mononegative one. By
combining magnetization measurements with Nuclear Magnetic Resonance (NMR) and
Muon Spin Relaxation ({\mu}SR), we have investigated the static magnetic
properties and the spin dynamics as a function of the temperature. Moreover,
the effect of the external pressure as well as of the infrared light
irradiation have been explored through magnetometry and NMR measurements to
determine the spin dynamics of the HS state. The photoinduced HS state, which
can have a lifetime of several hours below 30 K, is characterized by spin
dynamics in the MHz range, which persist at least down to 10 K. The application
of an external pressure causes a progressive increase of the LS-HS crossover,
which reaches room temperature for pressures around 10 kbar.",1808.04229v1
2019-01-07,Spin dynamics of edge-sharing spin chains in SrCa13Cu24O41,"The low-energy magnetic excitation from the highly Ca-doped
quasi-one-dimensional magnet SrCa13Cu24O41 was studied in the magnetic ordered
state by using inelastic neutron scattering. We observed the gapless spin-wave
excitation, dispersive along the a and c axes but nondispersive along the b
axis. Such excitations are attributed to the spin wave from the spin-chain
sublattice. Model fitting to the experimental data gives the nearest-neighbour
interaction Jc as 5.4 meV and the interchain interaction Ja = 4.4 meV. Jc is
antiferromagnetic and its value is close to the nearest-neighbour interactions
of the similar edge-sharing spin-chain systems such as CuGeO3. Comparing with
the hole-doped spin chains in Sr14Cu24O41, which shows a spin gap due to spin
dimers formed around Zhang-Rice singlets, the chains in SrCa13Cu24O41 show a
gapless excitation in this study. We ascribe such a change from gapped to
gapless excitations to holes transferring away from the chain sublattice into
the ladder sublattice upon Ca doping.",1901.02102v1
2019-04-18,Two-electron-spin ratchets as a platform for microwave-free dynamic nuclear polarization of arbitrary material targets,"Optically-pumped color centers in semiconductor powders can potentially
induce high levels of nuclear spin polarization in surrounding solids or fluids
at or near ambient conditions, but complications stemming from the random
orientation of the particles and the presence of unpolarized paramagnetic
defects hinder the flow of polarization beyond the defect's host material.
Here, we theoretically study the spin dynamics of interacting nitrogen-vacancy
(NV) and substitutional nitrogen (P1) centers in diamond to show that outside
protons spin-polarize efficiently upon a magnetic field sweep across the NV-P1
level anti-crossing. The process can be interpreted in terms of an NV-P1 spin
ratchet, whose handedness - and hence the sign of the resulting nuclear
polarization - depends on the relative timing of the optical excitation pulse.
Further, we find that the polarization transfer mechanism is robust to NV
misalignment relative to the external magnetic field, and efficient over a
broad range of electron-electron and electron-nuclear spin couplings, even if
proxy spins feature short coherence or spin-lattice relaxation times.
Therefore, these results pave the route towards the dynamic nuclear
polarization of arbitrary spin targets brought in proximity with a diamond
powder under ambient conditions.",1904.08563v1
2019-06-02,Optical spin locking of a solid-state qubit,"Quantum control of solid-state spin qubits typically involves pulses in the
microwave domain, drawing from the well-developed toolbox of magnetic resonance
spectroscopy. Driving a solid-state spin by optical means offers a high-speed
alternative, which in the presence of limited spin coherence makes it the
preferred approach for high-fidelity quantum control. Bringing the full
versatility of magnetic spin resonance to the optical domain requires full
phase and amplitude control of the optical fields. Here, we imprint a
programmable microwave sequence onto a laser field and perform electron spin
resonance in a semiconductor quantum dot via a two-photon Raman process. We
show that this approach yields full SU(2) spin control with over 98%
pi-rotation fidelity. We then demonstrate its versatility by implementing a
particular multi-axis control sequence, known as spin locking. Combined with
electron-nuclear Hartmann-Hahn resonances which we also report in this work,
this sequence will enable efficient coherent transfer of a quantum state from
the electron spin to the mesoscopic nuclear ensemble.",1906.00427v2
2020-11-24,Ground state properties and exact thermodynamics of a 2-leg anisotropic spin ladder system,"We study a frustrated two-leg spin ladder with alternate isotropic Heisenberg
and Ising rung exchange interactions, whereas, interactions along legs and
diagonals are Ising-type. All the interactions in the ladder are
anti-ferromagnetic in nature and induce frustration in the system. This model
shows four interesting quantum phases: (i) stripe rung ferromagnetic (SRFM),
(ii) stripe rung ferromagnetic with edge singlet (SRFM-E), (iii) anisotropic
antiferromagnetic (AAFM), and (iv) stripe leg ferromagnetic (SLFM) phase. We
construct a quantum phase diagram for this model and show that in stripe rung
ferromagnet (SRFM), the same type of sublattice spins (either $S$ or
$\sigma$-type spins) are aligned in the same direction. Whereas, in anisotropic
antiferromagnetic phase, both $S$ and $\sigma$-type of spins are
anti-ferromagnetically aligned with each other, two nearest $S$ spins along the
rung form an anisotropic singlet bond whereas two nearest $\sigma$ spins form
an Ising bond. In large Heisenberg rung exchange interaction limit, spins on
each leg are ferromagnetically aligned, but spins on different legs are
anti-ferromagnetically aligned. The thermodynamic quantities like $Cv(T)$,
$\chi(T)$ and $S(T)$ are also calculated using the transfer matrix method for
different phase. The magnetic gap in the SRFM and the SLFM can be notice from
$\chi(T)$ and $Cv(T)$ curves.",2011.11901v1
2021-01-15,Bethe strings in the spin dynamical structure factor of the Mott-Hubbard phase in one-dimensional fermionic Hubbard model,"The spectra and role in the spin dynamical properties of bound states of
elementary magnetic excitations named Bethe strings that occur in some
integrable spin and electronic one-dimensional models have recently been
identified and realized in several materials by experiments. Corresponding
theoretical studies have usually relied on the one-dimensional spin-1/2
Heisenberg antiferromagnet in a magnetic field. At the isotropic point, it
describes the large onsite repulsion U limit of the spin degrees of freedom of
the one-dimensional fermionic Hubbard model with one electron per site in a
magnetic field h. In this paper we consider the thermodynamic limit and study
the effects of lowering the latter quantum problem ratio u=U/4t, where t is the
first-neighbor transfer integral, on the line-shape singularities in regions at
and just above the lower thresholds of the transverse and longitudinal spin
dynamical structure factors. The most significant spectral weight contribution
from Bethe strings leads to a gapped continuum in the spectrum of the spin
dynamical structure factor +-. Our study focuses on the line shape
singularities at and just above the gapped lower threshold of that continuum,
which have been identified in experiments. Our results are consistent with the
contribution of Bethe strings to the spin dynamical structure factor zz being
small at low spin densities and becoming negligible upon increasing that
density. Our results provide physically important information about how
electron itinerancy affects the spin dynamics.",2101.06198v1
2022-04-20,Magnetic Field Tuning of Parallel Spin Stripe Order and Fluctuations near the Pseudogap Quantum Critical Point in La$_{1.36}$Nd$_{0.4}$Sr$_{0.24}$CuO$_4$,"A quantum critical point in the single layer, hole-doped cuprate system
La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ (Nd-LSCO), near $x$ = 0.23 has been
proposed as an organizing principle for understanding high temperature
superconductivity. Our earlier neutron diffraction work on Nd-LSCO at optimal
and high doping revealed static parallel spin stripes to exist out to the QCP
and slightly beyond, at $x$ = 0.24 and 0.26. We examine more closely the
parallel spin stripe order parameter in Nd-LSCO in both zero magnetic field and
fields up to 8 T for H // c in these single crystals. In contrast to earlier
studies at lower doping, we observe that H //c in excess of $\sim$ 2.5 T
eliminates the incommensurate quasi-Bragg peaks associated with parallel spin
stripes. But this elastic scattering is not destroyed by the field; rather it
is transferred to commensurate {\textbf{Q} = 0} Bragg positions, implying that
the spins participating in the spin stripes have been polarized. Inelastic
neutron scattering measurements at high fields show an increase in the low
energy, parallel spin stripe fluctuations and evidence for a spin gap,
$\Delta_{spin}$= 3 $\pm$ 0.5 meV for Nd-LSCO with $x$ = 0.24. This is shown to
be consistent with spin gap measurements as a function of superconducting T$_C$
over five different families of cuprate superconductors, which follow the
approximate linear relation, $\Delta_{spin}$ = 3.5 k$_B$T$_C$.",2204.09503v2
2022-05-24,Which black hole formed first? Mass-ratio reversal in massive binary stars from gravitational-wave data,"Population inference of gravitational-wave catalogues is a useful tool to
translate observations of black-hole mergers into constraints on compact-binary
formation. Different formation channels predict identifiable signatures in the
astrophysical distributions of source parameters, such as masses and spins. One
example within the scenario of isolated binary evolution is mass-ratio
reversal: even assuming efficient core-envelope coupling in massive stars and
tidal spin-up of the stellar companion by the first-born black hole, a compact
binary with a lighter, non-spinning first-born black hole and a heavier,
spinning second-born black hole can still form through mass transfer from the
initially more to less massive progenitor. Using current LIGO/Virgo
observations, we measure the fraction of sources in the underlying population
with this mass-spin combination and interpret it as a constraint on the
occurrence of mass-ratio reversal in massive binary stars. We modify commonly
used population models by including negligible-spin subpopulations and, most
crucially, non-identical component spin distributions. We do not find evidence
for subpopulations of black holes with negligible spins and measure the
fraction of massive binary stars undergoing mass-ratio reversal to be
consistent with zero and $<32\%$ ($99\%$ confidence). The dimensionless spin
peaks around $0.2\unicode{x2013}0.3$ appear robust, however, and are yet to be
explained by progenitor formation scenarios.",2205.12329v2
2022-06-15,Addressing electron spins embedded in metallic graphene nanoribbons,"Spin-hosting graphene nanostructures are promising metal-free systems for
elementary quantum spintronic devices. Conventionally, spins are protected from
quenching by electronic bandgaps, which also hinder electronic access to their
quantum state. Here, we present a narrow graphene nanoribbon substitutionally
doped with boron heteroatoms that combines a metallic character with the
presence of localized spin 1/2 states in its interior. The ribbon was
fabricated by on-surface synthesis on a Au(111) substrate. Transport
measurements through ribbons suspended between the tip and the sample of a
scanning tunnelling microscope revealed their ballistic behavior,
characteristic of metallic nanowires. Conductance spectra show fingerprints of
localized spin states in form of Kondo resonances and inelastic tunnelling
excitations. Density functional theory rationalizes the metallic character of
the graphene nanoribbon due to the partial depopulation of the valence band
induced by the boron atoms. The transferred charge builds localized magnetic
moments around the boron atoms. The orthogonal symmetry of the spin-hosting
state's and the valence band's wavefunctions protects them from mixing,
maintaining the spin states localized. The combination of ballistic transport
and spin localization into a single graphene nanoribbon offers the perspective
of electronically addressing and controlling carbon spins in real device
architectures.",2206.07583v1
2022-12-08,"Spin Relaxation, Diffusion and Edelstein Effect in Chiral Metal Surface","We study electron spin transport at spin-splitting surface of
chiral-crystalline-structured metals and Edelstein effect at the interface, by
using the Boltzmann transport equation beyond the relaxation time
approximation. We first define spin relaxation time and spin diffusion length
for two-dimensional systems with anisotropic spin--orbit coupling through the
spectrum of the integral kernel in the collision integral. We then explicitly
take account of the interface between the chiral metal and a nonmagnetic metal
with finite thickness. For this composite system, we derive analytical
expressions for efficiency of the charge current--spin current interconversion
as well as other coefficients found in the Edelstein effect. We also develop
the Onsager's reciprocity in the Edelstein effect along with experiments so
that it relates local input and output, which are respectively defined in the
regions separated by the interface. We finally provide a transfer matrix
corresponding to the Edelstein effect through the interface, with which we can
easily represent the Onsager's reciprocity as well as the charge--spin
conversion efficiencies we have obtained. We confirm the validity of the
Boltzmann transport equation in the present system starting from the Keldysh
formalism in the supplemental material. Our formulation also applies to the
Rashba model and other spin-splitting systems.",2212.04202v2
2023-07-14,Dark matter detection using nuclear magnetization in magnet with hyperfine interaction,"We consider the possibility to detect cosmic light dark matter (DM), i.e.,
axions and dark photons, of mass $\sim 10^{-6}$ eV and $\sim 10^{-4}$ eV, by
magnetic excitation in a magnet with strong hyperfine interaction. In
particular, we consider a canted anti-ferromagnet, MnCO$_3$, as a concrete
candidate material. With spin transfer between nuclear and electron spins
allowed by the hyperfine interaction, nuclear spins become naturally highly
polarized due to an effective (electron-spin-induced) magnetic field, and have
long-range interactions with each other. The collective precession of nuclear
spins, i.e., a nuclear magnon, can be generated by the DM field through the
nucleon-DM interaction, while they are also sensitive to the electron-DM
interaction through the electron-nuclear spin mixing. Compared with
conventional nuclear-spin precession experiments, this system as a DM sensor is
sensitive to higher frequency needing only a small static magnetic field
applied. The system also has collective precession of electron spins, mixed
with nuclear spins, as the additional channels that can be used for DM probes.
We estimate the sensitivity under appropriate readout setups such as an
inductive pick-up loop associated with an LC resonant circuit, or a photon
cavity with a photon counting device. We show that this method covers an
unexplored parameter region of light bosonic DM.",2307.08577v2
1996-01-05,NMR and Neutron Scattering Experiments on the Cuprate Superconductors: A Critical Re-Examination,"We show that it is possible to reconcile NMR and neutron scattering
experiments on both LSCO and YBCO, by making use of the Millis-Monien-Pines
mean field phenomenological expression for the dynamic spin-spin response
function, and reexamining the standard Shastry-Mila-Rice hyperfine Hamiltonian
for NMR experiments. The recent neutron scattering results of Aeppli et al on
LSCO (x=14%) are shown to agree quantitatively with the NMR measurements of
$^{63}T_1$ and the magnetic scaling behavior proposed by Barzykin and Pines.
The reconciliation of the $^{17}T_1$ relaxation rates with the degree of
incommensuration in the spin fluctuation spectrum seen in neutron experiments
is achieved by introducing a new transferred hyperfine coupling $C'$ between
oxygen nuclei and their next nearest neighbor $Cu^{2+}$ spins; this leads to a
near-perfect cancellation of the influence of the incommensurate spin
fluctuation peaks on the oxygen relaxation rates of LSCO. The inclusion of the
new $C'$ term also leads to a natural explanation, within the one-component
model, the different temperature dependence of the anisotropic oxygen
relaxation rates for different field orientations, recently observed by
Martindale $et~al$. The measured significant decrease with doping of the
anisotropy ratio, $R= ^{63}T_{1ab}/^{63}T_{1c}$ in LSCO system, from $R =3.9$
for ${\rm La_2CuO_4}$ to $R ~ 3.0$ for LSCO (x=15%) is made compatible with the
doping dependence of the shift in the incommensurate spin fluctuation peaks
measured in neutron experiments, by suitable choices of the direct and
transferred hyperfine coupling constants $A_{\beta}$ and B.",9601016v1
2004-12-14,Current-induced magnetization changes in a spin valve due to incoherent emission of non-equilibrium magnons,"We describe spin transfer in a ferromagnet/normal metal/ferromagnet
spin-valve point contact. Spin is transferred from the spin-polarized device
current to the magnetization of the free layer by the mechanism of incoherent
magnon emission by electrons. Our approach is based on the rate equation for
the magnon occupation, using Fermi's golden rule for magnon emission and
absorption and the non-equilibrium electron distribution for a biased spin
valve. The magnon emission reduces the magnetization of the free layer. For
anti-parallel alignment of the magnetizations of the layers and at a critical
bias a magnon avalanche occurs, characterized by a diverging effective magnon
temperature. This critical behavior can result in magnetization reversal and
consequently to suppression of magnon emission. However, magnon-magnon
scattering can lead to saturation of the magnon concentration at a large but
finite value. The further behavior depends on the parameters of the system. In
particular, gradual evolution of the magnon concentration followed by a
magnetization reversal is possible. Another scenario corresponds to a step-like
increase of the magnon concentration followed by a slow decrease. In the latter
case a spike in the differential resistance is expected due to a contribution
of electron-magnon scattering. A comparison of the obtained results to existing
experimental data and theoretical approches is given.",0412348v1
2006-10-18,Magnetic Properties and Metastable States in Spin-Crossover Transition of Co-Fe Prussian Blue Analogues,"The combination of spin transitions and magnetic ordering provides an
interesting structure of phase transitions in Prussian blue analogues (PBAs).
To understand the structure of stable and metastable states of Co-Fe PBA, it is
necessary to clarify free energy as a function of magnetization and the
fraction of the high-temperature component. Including the magnetic interaction
between high-temperature states, we study the magnetic phase transition of
Co-Fe PBA in addition to spin transitions. Here, we take into account the
degeneracy changes due to charge transfer between Co and Fe atoms accompanying
the spin transition. In this study, the charge transfer between Co and Fe atoms
is explicitly taken into account and also the ferrimagnetic structure of Co-Fe
PBAs is expressed in the proper way. First, we found systematic changes in the
structures of stable and metastable states as functions of system parameters
using mean field theory. In particular, the existence of a metastable
magnetic-ordered high-temperature state is confirmed at temperatures lower than
that of the hysteresis region of spin transitions. Second, we found that the
magnetic interaction causes complex ordering processes of a spin transition and
a magnetic phase transition. The effect of a magnetic field on the phase
structure is also investigated and we found metamagnetic magnetization
processes. Finally, the dynamical properties of this metastable state are
studied by Monte Carlo method.",0610500v2
2011-02-08,The Paired Electron Crystal: order from frustration in the quarter-filled band,"We present a study of the effects of simultaneous charge- and
spin-frustration on the two-dimensional strongly correlated quarter-filled band
on an anisotropic triangular lattice. The broken-symmetry states that dominate
in the weakly frustrated region near the rectangular lattice limit are the well
known antiferromagnetic state with in-phase lattice dimerization along one
direction, and the Wigner crystal state with the checkerboard charge order. For
moderate to strong frustration, however, the dominant phase is a novel
spin-singlet paired-electron crystal (PEC), consisting of pairs of charge-rich
sites separated by pairs of charge-poor sites. The PEC, with coexisting
charge-order and spin-gap in two dimension, is the quarter-filled band
equivalent of the valence bond solid (VBS) that can appear in the frustrated
half-filled band within antiferromagnetic spin Hamiltonians. We discuss the
phase diagram as a function of on-site and intersite Coulomb interactions as
well as electron-phonon coupling strength. We speculate that the spin-bonded
pairs of the PEC can become mobile for even stronger frustration, giving rise
to a paired-electron liquid. We discuss the implications of the PEC concept for
understanding several classes of quarter-filled band materials that display
unconventional superconductivity, focusing in particular on organic charge
transfer solids. Our work points out the need to go beyond quantum spin liquid
(QSL) concepts for highly frustrated organic charge-transfer solids such as
kappa-(BEDT-TTF)_2Cu_2(CN)_3 and EtMe_3Sb[Pd(dmit)_2]_2, which we believe show
frustration-induced charge disproportionation at low temperatures. We discuss
possible application to layered cobaltates and 1/4-filled band spinels.",1102.1731v1
2013-07-03,Quantum Teleportation from a Propagating Photon to a Solid-State Spin Qubit,"The realization of a quantum interface between a propagating photon used for
transmission of quantum information, and a stationary qubit used for storage
and manipulation, has long been an outstanding goal in quantum information
science. A method for implementing such an interface between dissimilar qubits
is quantum teleportation, which has attracted considerable interest not only as
a versatile quantum-state-transfer method but also as a quantum computational
primitive. Here, we experimentally demonstrate transfer of quantum information
carried by a photonic qubit to a quantum dot spin qubit using quantum
teleportation. In our experiment, a single photon in a superposition state of
two colors -- a photonic qubit is generated using selective resonant excitation
of a neutral quantum dot. We achieve an unprecedented degree of
indistinguishability of single photons from different quantum dots by using
local electric and magnetic field control. To teleport a photonic qubit, we
generate an entangled spin-photon state in a second quantum dot located 5
meters away from the first and interfere the photons from the two dots in a
Hong-Ou-Mandel set-up. A coincidence detection at the output of the
interferometer heralds successful teleportation, which we verify by measuring
the resulting spin state after its coherence time is prolonged by an optical
spin-echo pulse sequence. The demonstration of successful inter-conversion of
photonic and semiconductor spin qubits constitute a major step towards the
realization of on-chip quantum networks based on semiconductor nano-structures.",1307.1142v2
2016-04-08,Coherent transfer of electron spin correlations assisted by dephasing noise,"Quantum coherence of superposed states, especially of entangled states, is
indispensable for many quantum technologies. However, it is vulnerable to
environmental noises, posing a fundamental challenge in solid-state systems
including spin qubits. Here we show a scheme of entanglement engineering where
pure dephasing assists the generation of quantum entanglement at distant sites
in a chain of electron spins confined in semiconductor quantum dots. One party
of an entangled spin pair, prepared at a single site, is transferred to the
next site and then adiabatically swapped with a third spin using a transition
across a multi-level avoided crossing. This process is accelerated by the
noise-induced dephasing through a variant of the quantum Zeno effect, without
sacrificing the coherence of the entangled state. Our finding brings insight
into the spin dynamics in open quantum systems coupled to noisy environments,
opening an avenue to quantum state manipulation utilizing decoherence effects.",1604.02232v2
2022-01-26,Directly Revealing Entanglement Dynamics through Quantum Correlation Transfer Functions with Resultant Demonstration of the Mechanism of Many-Body Localization,"The fundamental link between entanglement dynamics and non-equilibrium
statistics in isolated quantum systems has been established in theory and
confirmed via experiment. However, the understanding of several consequential
phenomena, such as the Many-Body Localization (MBL), has been obstructed by the
lack of a systematic approach to obtain many-body entanglement dynamics. This
paper introduces the Quantum Correlation Transfer Function (QCTF) approach to
entanglement dynamics in many-body quantum systems and employs this new
framework to demonstrate the mechanism of MBL in disordered spin chains. We
show that in the QCTF framework, the entanglement dynamics of two-level
constituent particles of a many-body quantum system can be fully characterized
directly from the system's Hamiltonian, which circumvents the bottleneck of
calculating the many-body system's time-evolution. By employing the QCTF-based
approach to entanglement dynamics, we demonstrate MBL dynamics in disordered
Heisenberg spin chains through the suppressed quasi-periodic spin's
entanglement evolution after a quench from an anti-ferromagnetic state.
Furthermore, we prove the validity of a previous fundamental conjecture
regarding the MBL phase by showing that in strongly-disordered spin chains with
short-range interactions, the quantum correlation between particles is
exponentially attenuated with respect to the site-to-site distance. Moreover,
we obtain the lowest possible amplitude of the quasi-periodic spin's
entanglement as a function of disorder in the chain. The QCTF analysis is
verified by exact numerical simulation of the system's evolution. We also show
that QCTF provides a new foundation to study the Eigenstate Thermalization
Hypothesis (ETH). The QCTF methodology can be extended in various ways to
address general issues regarding non-equilibrium quantum thermodynamics in spin
lattices with different geometries.",2201.11223v1
2022-11-30,Stark control of solid-state quantum memory with spin-wave storage,"Quantum memories for quantum communication need to be able to store photons
for an extended time and then to release them on demand. This can be achieved
in atomic frequency comb ensemble based quantum memories by control pulses that
transfer the excitation to and from long-lived spin states. However, such
pulses can give rise to coherent and incoherent noise due to their interaction
with the memory ensemble. In this article, we experimentally demonstrate the
ability to switch off the coherent noise from such control pulses during the
echo emission in a spin-wave quantum memory, using the linear Stark effect in
rare-earth-ion doped crystals. By applying an electric field pulse, the echo
emission was coherently switched off prior to the first spin transfer pulse,
and the stored data pulse was restored only when both an optical recall pulse
and a re-phasing electrical pulse were applied, giving a high degree of control
of both desired and undesired emissions. We estimate the effectiveness of this
technique by turning off the free induction decay of a narrow ensemble of ions.
This technique can thus improve the noise performance of spin-wave storage at
the single photon level by quenching coherent optical radiation created by the
strong control pulses. The method demonstrated here represents a
proof-of-principle that the spin-wave storage scheme can be combined with Stark
control. The combined scheme serves as an addition to the toolbox of techniques
that can be used to realize a full version of a quantum repeater.",2211.17206v1
2023-08-21,Dynamic evolution of S$_0$-S$_3$ at the oxygen evolving complex with spin markers under photoelectric polarization,"Water oxidation at the oxygen evolving complex (OEC) of the photosystem II is
catalyzed by the core cluster CaMn$_4$O$_5$ which was projected to experience
five intermediate states S$\rm_i$ in the Kok's cycle since 1970's. However, the
detailed dynamics of state evolutions still remains unclear, albeit with the
general fact that the process is initiated by the transfer of photoelectrons
with the steady electron donors of the water molecules. Based on density
functional simulations, we find that the spin flips of Manganese atoms between
the consecutive states in the electric polarization field can be used as a
marker to uncover the intricate dynamic evolutions and the underlying dynamics.
The dynamic electron and proton transfers and water insertion and dissociation
are traced to reveal the evolution pathways of S$_0$-S$_3$ with commensurate
spin flips towards the exact spin configuration of the next state. In
particular, the various water insertions and dissociations at coordination
sites of the S$_2$ open and closed cubane isomers are predicted with
constraints on the necessary spin flips. Our study paves a way to uncover the
animated OEC evolutions with the spin flips that await for more experimental
verifications and lays a solid ground for revealing the mechanism of dioxygen
generation via the pending S$_4$ state.",2308.10769v2
2023-11-09,Electrically induced angular momentum flow between separated ferromagnets,"Converting angular momentum between different degrees of freedom within a
magnetic material results from a dynamic interplay between electrons, magnons
and phonons. This interplay is pivotal to implementing spintronic device
concepts that rely on spin angular momentum transport. We establish a new
concept for long-range angular momentum transport that further allows to
address and isolate the magnonic contribution to angular momentum transport in
a nanostructured metallic ferromagnet. To this end, we electrically excite and
detect spin transport between two parallel and electrically insulated
ferromagnetic metal strips on top of a diamagnetic substrate. Charge-to-spin
current conversion within the ferromagnetic strip generates electronic spin
angular momentum that is transferred to magnons via electron-magnon coupling.
We observe a finite angular momentum flow to the second ferromagnetic strip
across a diamagnetic substrate over micron distances, which is electrically
detected in the second strip by the inverse charge-to-spin current conversion
process. We discuss phononic and dipolar interactions as the likely cause to
transfer angular momentum between the two strips. Moreover, our work provides
the experimental basis to separate the electronic and magnonic spin transport
and thereby paves the way towards magnonic device concepts that do not rely on
magnetic insulators.",2311.05290v1
2016-02-02,Carrier-impurity spin transfer dynamics in paramagnetic II-VI diluted magnetic semiconductors in the presence of a wave-vector-dependent magnetic field,"Quantum kinetic equations of motion for carrier and impurity spins in
paramagnetic II-VI diluted magnetic semiconductors in a $\mathbf{k}$-dependent
effective magnetic field are derived, where the carrier-impurity correlations
are taken into account. In the Markov limit, rates for the electron-impurity
spin transfer can be derived for electron spins parallel and perpendicular to
the impurity spins corresponding to measurable decay rates in Kerr experiments
in Faraday and Voigt geometry. Our rigorous microscopic quantum kinetic
treatment automatically accounts for the fact that, in an individual spin
flip-flop scattering process, a spin flip of an electron is necessarily
accompanied by a flop of an impurity spin in the opposite direction and the
corresponding change of the impurity Zeeman energy influences the final energy
of the electron after the scattering event. This shift in the electron energies
after a spin flip-flop scattering processes, which usually has been overlooked
in the literature, turns out to be especially important in the case of
extremely diluted magnetic semiconductors in an external magnetic field. As a
specific example for a $\mathbf{k}$-dependent effective magnetic field the
effects of a Rashba field on the dynamics of the carrier-impurity correlations
in a Hg$_{1-x-y}$Cd$_y$Mn$_x$Te quantum well are described. It is found that,
although accounting for the Rashba interaction in the dynamics of the
correlations leads to a modified $\mathbf{k}$-space dynamics, the time
evolution of the total carrier spin is not significantly influenced.
Furthermore, a connection between the present theory and the description of
collective carrier-impurity precession modes is presented.",1602.00911v2
2017-11-13,Mechanisms of optical orientation of an individual Mn$^{2+}$ ion spin in a II-VI quantum dot,"We provide a theoretical description of the optical orientation of a single
Mn$^{2+}$ ion spin under quasi-resonant excitation demonstrated experimentally
by Goryca et al. [Phys. Rev. Lett. 103, 087401 (2009)]. We build and analyze a
hierarchy of models by starting with the simplest assumptions (transfer of
perfectly spin-polarized excitons from Mn-free dot to the other dot containing
a single Mn$^{2+}$ spin, followed by radiative recombination) and subsequently
adding more features, such as spin relaxation of electrons and holes.
Particular attention is paid to the role of the influx of the dark excitons and
the process of biexciton formation, which are shown to contribute significantly
to the orientation process in the quasi-resonant excitation case. Analyzed
scenarios show how multiple features of the excitonic complexes in
magnetically-doped quantum dots, such as the values of exchange integrals, spin
relaxation times, etc., lead to a plethora of optical orientation processes,
characterized by distinct dependencies on light polarization and laser
intensity, and occurring on distinct timescales. Comparison with experimental
data shows that the correct description of the optical orientation mechanism
requires taking into account Mn$^{2+}$ spin-flip processes occurring not only
when the exciton is already in the orbital ground state of the light-emitting
dot, but also those that happen during the exciton transfer from high-energy
states to the ground state. Inspired by the experimental results on energy
relaxation of electrons and holes in nonmagnetic dots, we focus on the process
of biexciton creation allowed by mutual spin-flip of an electron and the
Mn$^{2+}$ spin, and we show that by including it in the model, we obtain good
qualitative and quantitative agreement with the experimental data on
quasi-resonantly driven Mn$^{2+}$ spin orientation.",1711.04405v1
2018-03-28,"Electronic structure of the Co(0001)/MoS2 interface, and its possible use for electrical spin injection in a single MoS2 layer","The ability to perform efficient electrical spin injection from ferromagnetic
metals into two-dimensional semiconductor crystals based on transition metal
dichalcogenide monolayers is a prerequisite for spintronic and valleytronic
devices using these materials. Here, the hcp Co(0001)/MoS2 interface electronic
structure is investigated by first-principles calculations based on the density
functional theory. In the lowest energy configuration of the hybrid system
after optimization of the atomic coordinates, we show that interface sulfur
atoms are covalently bound to one, two or three cobalt atoms. A decrease of the
Co atom spin magnetic moment is observed at the interface, together with a
small magnetization of S atoms. Mo atoms also hold small magnetic moments which
can take positive as well as negative values. The charge transfers due to
covalent bonding between S and Co atoms at the interface have been calculated
for majority and minority spin electrons and the connections between these
interface charge transfers and the induced magnetic properties of the MoS2
layer are discussed. Band structure and density of states of the hybrid system
are calculated for minority and majority spin electrons, taking into account
spin-orbit coupling. We demonstrate that MoS2 bound to the Co contact becomes
metallic due to hybridization between Co d and S p orbitals. For this metallic
phase of MoS2, a spin polarization at the Fermi level of 16 % in absolute value
is calculated, that could allow spin injection into the semiconducting MoS2
monolayer channel. Finally, the symmetry of the majority and minority spin
electron wave functions at the Fermi level in the Co-bound metallic phase of
MoS2 and the orientation of the border between the metallic and semiconducting
phases of MoS2 are investigated, and their impact on spin injection into the
MoS2 channel is discussed.",1803.10612v1
2021-12-09,Spinning Language Models: Risks of Propaganda-As-A-Service and Countermeasures,"We investigate a new threat to neural sequence-to-sequence (seq2seq) models:
training-time attacks that cause models to ""spin"" their outputs so as to
support an adversary-chosen sentiment or point of view -- but only when the
input contains adversary-chosen trigger words. For example, a spinned
summarization model outputs positive summaries of any text that mentions the
name of some individual or organization.
  Model spinning introduces a ""meta-backdoor"" into a model. Whereas
conventional backdoors cause models to produce incorrect outputs on inputs with
the trigger, outputs of spinned models preserve context and maintain standard
accuracy metrics, yet also satisfy a meta-task chosen by the adversary.
  Model spinning enables propaganda-as-a-service, where propaganda is defined
as biased speech. An adversary can create customized language models that
produce desired spins for chosen triggers, then deploy these models to generate
disinformation (a platform attack), or else inject them into ML training
pipelines (a supply-chain attack), transferring malicious functionality to
downstream models trained by victims.
  To demonstrate the feasibility of model spinning, we develop a new
backdooring technique. It stacks an adversarial meta-task onto a seq2seq model,
backpropagates the desired meta-task output to points in the word-embedding
space we call ""pseudo-words,"" and uses pseudo-words to shift the entire output
distribution of the seq2seq model. We evaluate this attack on language
generation, summarization, and translation models with different triggers and
meta-tasks such as sentiment, toxicity, and entailment. Spinned models largely
maintain their accuracy metrics (ROUGE and BLEU) while shifting their outputs
to satisfy the adversary's meta-task. We also show that, in the case of a
supply-chain attack, the spin functionality transfers to downstream models.",2112.05224v2
1999-01-21,WZ Sagittae as a DQ Herculis star,"We argue that quiescent WZ Sge is a rapidly spinning magnetic rotator in
which most of the matter transfered from the secondary is ejected from the
system. Assuming that the observed 27.87 s oscillation period is due to the
spinning white dwarf we propose that the other observed principal period of
28.96 s is a beat due to reprocessing of the rotating white dwarf beam on
plasma blobs in Keplerian rotation at the outer disc rim. The weaker,
transient, 29.69 s period is identified as a beat with the Keplerian period of
the magnetosphere. WZ Sge evolves through a cycle of spin-up and spin-down
phases. During the spin-down phase it is a DQ Her star, during the spin-up
phase it should be a ER UMa star.",9901295v1
1999-12-06,Coherent spin dynamics in diluted-magnetic quantum wells,"Spins of charge carriers, paramagnetic centers, and nuclei in semiconductor
structures are known to be oriented if circular-polarized light is shined upon
the structure. This is due to transfer of angular momentum from photons to
various excitations in the semiconductor. What would happen if the structure is
anisotropic, so that the angular momentum is not conserved? Experiments
performed on diluted-magnetic II-VI quantum wells (such as CdMnTe/CdMgTe) show
that at some conditions the effect of light upon the spin state of the
semiconductor structure can be greatly amplified. Exchange field of
photoexcited heavy holes initiates a coherent evolution of a great number of
localized spins of Mn-ions. In the simplest case, it is just a precession in an
effective field, but generally the spin dynamics is more intricate. It shows
up, for instance, in long sequences of spin-flip peaks in Raman spectra, in
enhanced magnetic-polaron effect, and in modulation of optical response within
the picosecond time scale.",9912084v1
2002-04-17,Theory of the spin singlet filling factor $ν=2$ quantum Hall droplet,"A theory of electronic properties of a spin-singlet quantum Hall droplet at
filling factor $\nu=2$ in a parabolic quantum dot is developed. The excitation
spectrum and the stability of the droplet due to the transfer of electrons into
the second Landau level at low magnetic fields and due to spin flip at the edge
at higher magnetic fields is determined using Hartree-Fock, exact
diagonalisation, and spin-density functional methods. We show that above a
critical number of electrons $N_c$ the unpolarised $\nu=2$ quantum Hall droplet
ceases to be a ground state in favor of spin-polarised phases. We determine the
characteristic pattern in the addition and current-amplitude Coulomb blockade
spectra associated with the stable $\nu=2$ droplet. We show that the spin
transition of the droplet at a critical number of electrons is accompanied by
the reversal of the current amplitude modulation at the $\nu=2$ line, as
observed in recent experiments.",0204385v1
2002-10-29,Ferromagnetism in diluted magnetic semiconductor quantum dot arrays embedded in semiconductors,"We present an Anderson-type model Hamiltonian with exchange coupling between
the localized spins and the confined holes in the quantum dots to study the
ferromagnetism in diluted magnetic semiconductor (DMS) quantum dot arrays
embedded in semiconductors. The hybridization between the quantum-confined
holes in the DMS quantum dots and the itinerant holes in the semiconductor
valence band makes hole transfer between quantum dots, which can induce the
long range ferromagnetic order of the localized spins. In addition, it makes
the carrier spins both in the DMS quantum dots and in the semiconductors
polarized. The spontaneous magnetization of the localized spins and the spin
polarization of the holes are calculated using both the Weiss mean field
approximation and the self-consistent spin wave approximation, which are
developed for the present model.",0210643v1
2004-03-08,Mean-field magnetization relaxation in conducting ferromagnets,"Collective ferromagnetic motion in a conducting medium is damped by the
transfer of the magnetic moment and energy to the itinerant carriers. We
present a calculation of the corresponding magnetization relaxation as a
linear-response problem for the carrier dynamics in the effective exchange
field of the ferromagnet. In electron systems with little intrinsic spin-orbit
interaction, a uniform magnetization motion can be formally eliminated by going
into the rotating frame of reference for the spin dynamics. The ferromagnetic
damping in this case grows linearly with the spin-flip rate when the latter is
smaller than the exchange field and is inversely proportional to the spin-flip
rate in the opposite limit. These two regimes are analogous to the
""spin-pumping"" and the ""breathing Fermi-surface"" damping mechanisms,
respectively. In diluted ferromagnetic semiconductors, the hole-mediated
magnetization can be efficiently relaxed to the itinerant-carrier degrees of
freedom due to the strong spin-orbit interaction in the valence bands.",0403224v2
2004-07-06,Gapped spin liquid states in a one-dimensional Hubbard model with antiferromagnetic exchange interaction,"We study the phase diagram of a one-dimensional extended Hubbard model with
antiferromagnetic exchange interaction analytically and numerically. The
bosonization and transfer-matrix renormalization group methods are used in the
corresponding coupling regimes. At half-filling, the system is a Mott insulator
with a finite spin excitation gap if the on-site Coulomb repulsion is fairly
smaller than the antiferromagnetic exchange J. This Mott-insulator is
characterized by the bond-charge-density-wave order or spontaneously
dimerization. In the weak-coupling regime where the spin-charge separation
holds approximately, the critical point separating the gapless and gapped spin
liquid phases is U_c\sim J/2. However, as J increases, the spin-charge
couplings become important and the critical point U_c is significantly
suppressed and eventually tends to zero as J\to \infty. Away from half-filling,
the charge gap completely collapses but the spin gap persists.",0407114v1
2004-08-26,Role of vertex corrections in the spin-fluctuation mediated pairing mechanism,"We study numerically and partly diagrammatically the renormalization of the
electron-spin interaction or vertex in a two-dimensional one-band Hubbard model
with spin-fluctuation momentum transfer ${\vv q}=(\pi,\pi)$. We find that the
renormalized electron-spin vertex decreases quite generally with decreasing
temperature at all doping densities. As a combination of two concurring
effects, i.e. the decrease of the vertex and the increase of the spin
susceptibility, the effective pairing interaction increases with lowering
temperature in the intermediate-correlation regime, but {\it flattens off} in
the strong-correlation regime. Our findings indicate that in the high-T$_c$
cuprates the pairing mediated by antiferromagnetic spin fluctuations is
substantially reduced due to vertex corrections.",0408564v2
2006-01-20,Dimerization-induced enhancement of the spin gap in the quarter-filled two-leg rectangular ladder,"We report density-matrix renormalization group calculations of spin gaps in
the quarter-filled correlated two-leg rectangular ladder with bond-dimerization
along the legs of the ladder. In the small rung-coupling region, dimerization
along the leg bonds can lead to large enhancement of the spin gap.
Electron-electron interactions further enhance the spin gap, which is nonzero
for all values of the rung electron hopping and for arbitrarily small
bond-dimerization. Very large spin gaps, as are found experimentally in
quarter-filled band organic charge-transfer solids with coupled pairs of
quasi-one-dimensional stacks, however, occur within the model only for large
dimerization and rung electron hopping that are nearly equal to the hopping
along the legs. Coexistence of charge order and spin gap is also possible
within the model for not too large intersite Coulomb interaction.",0601481v2
2006-03-01,Renormalization of the electron-spin-fluctuation interaction in the t-t'-U Hubbard model,"We study the renormalization of the electron-spin-fluctuation (el-sp) vertex
in a two-dimensional Hubbard model with nearest-neighbor (t) and
next-nearest-neighbor (t') hopping by a Quantum-Monte-Carlo calculation. Our
results show that for t'=0, the renormalized el-sp vertex decreases quite
generally with decreasing temperature at all spin-fluctuation momentum
transfers. The suppression of the el-sp vertex results in a substantial
reduction of the effective pairing interaction mediated by antiferromagnetic
spin fluctuations in both the intermediate- and strong-correlation regimes. The
inclusion of a finite t'/t<0, increases the Landau damping rate of spin
fluctuations, especially in the overdoped region. The increased damping rate
leads to smaller vertex corrections, in agreement with earlier diagrammatic
calculations. Still, the vertex correction reduces the spin-fermion vertex, as
at t'=0.",0603014v3
2006-03-03,Dark solitons in F=1 spinor Bose--Einstein condensate,"We study dark soliton solutions of a multi-component Gross--Pitaevskii
equation for hyperfine spin F=1 spinor Bose--Einstein condensate. The
interactions are supposed to be inter-atomic repulsive and anti-ferromagnetic
ones of equal magnitude. The solutions are obtained from those of an integrable
$2\times 2$ matrix nonlinear Schr\""{o}dinger equation with nonvanishing
boundary conditions. We investigate the one-soliton and two-soliton solutions
in detail. One-soliton is classified into two kinds. The ferromagnetic state
has wavefunctions of domain-wall shape and its total spin is nonzero. The polar
state provides a hole soliton and its total spin is zero. These two states are
selected by choosing the type of the boundary conditions. In two-soliton
collisions, we observe the spin-mixing or spin-transfer. It is found that, as
""magnetic"" carriers, solitons in the ferromagnetic state are operative for the
spin-mixing while those in the polar are passive.",0603070v1
1999-03-18,Regge description of spin-spin asymmetry in photon diffractive dissociation,"We explore the possibility whether the gluon helicity distribution $\Delta
G(x)$ can be extracted from a comparison of experimental data on the
longitudinal spin-spin asymmetry $A_{LL}$ in $\gamma p$ diffractive deep
inelastic scattering with calculations performed within the framework of
perturbative QCD (pQCD). The data could be obtained at the future HERA collider
in scattering of polarized electrons/positrons off polarized protons. In this
paper we look for such kinematical regions where contributions to $A_{LL}$ from
soft processes (reggeon exchanges) are suppressed to guarantee an applicability
of pQCD. It is shown that for the square of the center-of-mass energy
$s_{\gamma p} \geq 10^3 GeV^2$, the hadronic diffractive mass $M_X \leq 10
GeV/c^2$, the momentum transferred to the proton $\Delta_T\leq 0.5 GeV/c$, and
$Q^2\geq4 (GeV/c)^2$ the longitudinal spin-spin asymmetry due to reggeon
exchanges is less than 10^{-4}. This value is presumably lower than the
asymmetry which can be measured with modern experimental technique. This means
that the pQCD prediction can be reliably compared with data in this kinematical
region.",9903405v2
1999-10-29,Quark Spin and Orbital Angular Momentum in the Baryon,"The spin and orbital angular momentum carried by different quark flavors in
the nucleon are calculated in the SU(3) chiral quark model with
symmetry-breaking. The model is extended to all octet and decuplet baryons. In
this model, the reduction of the quark spin, due to the spin dilution in the
chiral splitting processes, is transferred into the orbital motion of quarks
and antiquarks. The orbital angular momentum for each quark flavor in the
proton as function of the partition factor $\kappa$ and the chiral splitting
probability $a$ is shown. Although the total amount of the quark spin reduction
is canceled by the the equal amount increase of the quark orbital angular
momentum, the cancellation does not apply to each quark flavor. Especially, the
cancellation between the spin and orbital contributions in the baryon magnetic
moment is discussed. Comparisons of our results with other models are also
shown.",9910539v2
2000-12-21,Quark Orbital Angular Momentum in the Baryon,"Analytical and numerical results, for the orbital and spin content carried by
different quark flavors in the baryons, are given in the chiral quark model
with symmetry breaking. The reduction of the quark spin, due to the spin
dilution in the chiral splitting processes, is transferred into the orbital
motion of quarks and antiquarks. The orbital angular momentum for each quark
flavor in the proton as a function of the partition factor $\kappa$ and the
chiral splitting probability $a$ is shown. The cancellation between the spin
and orbital contributions in the spin sum rule and in the baryon magnetic
moments is discussed.",0012295v3
2002-11-05,Small Angle Scattering of Polarized Protons,"Experiment E950 at AGS, BNL has provided data with high statistics for the
left-right asymmetry of proton-carbon elastic scattering in the Coulomb-nuclear
interference region of momentum transfer. It allows to access information about
spin properties of the Pomeron and has practical implications for polarimetry
at high energies. Relying on Regge factorization the results for the parameter
r_5, ratio of spin-flip to non-flip amplitudes, is compared with the same
parameter measured earlier in pion-proton elastic and charge exchange
scattering. While data for Im r_5 agree (within large systematic errors), there
might be a problem for Re r_5. The \pi N data indicate at a rather small
contribution of the f-Reggeon to the spin-flip part of the iso-scalar amplitude
which is dominated by the Pomeron. This conclusion is supported by direct
analysis of data for elastic and charge exchange pp and pn scattering which
also indicate at a vanishing real part of the hadronic spin-flip amplitude at
energies 20 GeV and higher. This is a good news for polarimetry, since the E950
results enhanced by forthcoming new measurements at AGS can be safely used for
polarimetry at RHIC at higher energies.",0211061v1
2004-01-08,The high-energy hadron spin-flip amplitude at small momentum transfer and new AN data from RHIC,"In the case of elastic high-energy hadron-hadron scattering, the impact of
the large-distance contributions on the behaviour of the slopes of the
spin-non-flip and of the spin-flip amplitudes is analysed. It is shown that the
long tail of the hadronic potential in impact parameter space leads to a value
of the slope of the reduced spin-flip amplitude larger than that of the
spin-non-flip amplitude. This effect is taken into account in the calculation
of the analysing power in proton-nucleus reactions at high energies. It is
shown that the preliminary measurement of AN obtained by the E950 Collaboration
indeed favour a spin-flip-amplitude with a large slope. Predictions for AN at
pL = 250 GeV/c are given.",0401040v2
2004-01-20,A possibility to determine the P-parity of the $Θ^+$ pentaquark in the ${p}{n}\to Λ^0Θ^+$ reaction,"Spin structure of the reaction ${\vec p}{\vec n}\to {\vec \Lambda^0} {\vec
\Theta}$ is analysed at the threshold in a model independent way under
assumption that the $\Theta^+$ is an isosinglet. We found that the sign of the
spin-spin correlation parameter $C_{x,x}$ being measured in a double-spin
experiment, determines the P-parity of the $\Theta^+$ unambiguously.
Furthermore we show that the polarization coefficients $K_x^x,K_y^y$ and
$K_z^z$ which describe the polarization transfer from polarized beam or target
to the final $\Lambda^0$ and $\Theta^+$ are nonzero for a positive parity of
the $\Theta^+$ and equal zero for a negative parity. It allows one to determine
the P-parity of the $\Theta^+$ in a single-spin measurement, since the
polarization of the $\Lambda^0$ can be measured via its decay $\Lambda^0\to
\pi^-+ p$.",0401150v2
2003-12-12,Polarization phenomena in hyperon-nucleon scattering,"We investigate polarization observables in hyperon-nucleon scattering by
decomposing scattering amplitudes into spin-space tensors, where each component
describes scattering by corresponding spin-dependent interactions, so that
contributions of the interactions in the observables are individually
identified. In this way, for elastic scattering we find some linear
combinations of the observables sensitive to particular spin-dependent
interactions such as symmetric spin-orbit (LS) interactions and antisymmetric
LS ones. These will be useful to criticize theoretical predictions of the
interactions when the relevant observables are measured. We treat vector
analyzing powers, depolarizations, and coefficients of polarization transfers
and spin correlations, a part of which is numerically examined in $\Sigma^{+}
p$ scattering as an example. Total cross sections are studied for polarized
beams and targets as well as for unpolarized ones to investigate spin
dependence of imaginary parts of forward scattering amplitudes.",0312036v1
2002-06-21,Hydrogenic Spin Quantum Computing in Silicon: A Digital Approach,"We suggest an architecture for quantum computing with spin-pair encoded
qubits in silicon. Electron-nuclear spin-pairs are controlled by a dc magnetic
field and electrode-switched on and off hyperfine interaction. This digital
processing is insensitive to tuning errors and easy to model. Electron
shuttling between donors enables multi-qubit logic. These hydrogenic spin
qubits are transferable to nuclear spin-pairs, which have long coherence times,
and electron spin-pairs, which are ideally suited for measurement and
initialization. The architecture is scalable to highly parallel operation.",0206159v4
2005-08-05,Resurrection of Schrodinger Cat,"Quantum decoherence is the major obstacle in using the potential of
engineered quantum dynamics to revolutionize high-precision measurements,
sensitive detection, or information processing. Here we experimentally
demonstrate that quantum state of a system can be recovered after the state is
destroyed by uncontrollable natural decoherence. Physical system is a cluster
of seven dipolar-coupled nuclear spins of single-labeled 13C-benzene in liquid
crystal. 13C spin plays a role of a device for measuring protons' ""cat"" state,
a superposition of states with six spins up (alive) and six spins down (dead).
Information about the state, stored in the 13C spin, is used to bring the
protons' subsystem into the alive state, while the excess entropy produced by
decoherence is transferred to the ""measuring device"", the 13C spin.",0508052v1
2006-05-18,Quantum Teleportation in One-Dimensional Quantum Dots System,"We present a model of quantum teleportation protocol based on one-dimensional
quantum dots system. Three quantum dots with three electrons are used to
perform teleportation, the unknown qubit is encoded using one electron spin on
quantum dot A, the other two dots B and C are coupled to form a mixed
space-spin entangled state. By choosing the Hamiltonian for the mixed
space-spin entangled system, we can filter the space (spin) entanglement to
obtain pure spin (space) entanglement and after a Bell measurement, the unknown
qubit is transfered to quantum dot B. Selecting an appropriate Hamiltonian for
the quantum gate allows the spin-based information to be transformed into a
charge-based information. The possibility of generalizing this model to
N-electrons is discussed.",0605165v1
2007-12-30,Spin observables of the reaction pd-3He eta and quasi-bound 3He-eta pole,"A formalism for spin observables of the reaction
  $pd\to ~^3He\eta$ is derived in a model independent way.
  The general case with a full set of six independent spin amplitudes is
studied. Furthermore, approximations by five and four spin amplitudes are
investigated in the near threshold region. This region is of great interest to
search for a quasi-bound $^3He-\eta$ state, in particular, by measurement of
energy dependence of relative phases of s- and p-wave amplitudes. Complete
polarization experiments, allowing determination of spin amplitudes, are
analyzed. It is shown that measurement of only analyzing powers and spin
correlation coefficients hardly allows one to separate the s- and p-wave
amplitudes, but additional measurement of polarization transfer coefficients
simplifies this problem. Specific observables, given by products of one s- and
one p-wave amplitudes, are found. Measurement of these observables will provide
new independent information on the $^3He-\eta$ pole position.",0801.0118v1
2008-11-18,Optical manipulation of a single Mn spin in a CdTe-based quantum dot,"A system of two coupled CdTe quantum dots, one of them containing a single Mn
ion, was studied in continuous wave and modulated photoluminescence,
photoluminescence excitation, and photon correlation experiments. Optical
writing of information in the spin state of the Mn ion has been demonstrated,
using orientation of the Mn spin by spin-polarized carriers transferred from
the neighbor quantum dot. Mn spin orientation time values from 20 ns to 100 ns
were measured, depending on the excitation power. Storage time of the
information in the Mn spin was found to be enhanced by application of a static
magnetic field of 1 T, reaching hundreds of microseconds in the dark. Simple
rate equation models were found to describe correctly static and dynamical
properties of the system.",0811.2898v1
2009-09-02,Swapping path-spin intraparticle entanglement onto spin-spin interparticle entanglement,"Based on a scheme that produces an entanglement between the spin and the path
variables of a single spin-1/2 particle (qubit) using a beam-splitter and a
spin-flipper, we formulate a procedure for transferring this intraparticle
hybrid entanglement to an interparticle entanglement between the spin variables
of two other spatially separated spin-1/2 particles which never interact with
each other during the entire process. This procedure of entanglement swapping
is accomplished by a Mach-Zehnder setup in conjunction with the Stern-Gerlach
measuring device, using suitable unitary operations. The proposed protocol,
thus, enables the use of intraparticle entanglement as a resource - a feature
that has remained unexplored.",0909.0425v3
2010-11-11,Interaction between hopping and static spins in a discrete network,"We consider a process where a spin hops across a discrete network and at
certain sites couples to static spins. While this setting is implementable in
various scenarios (e.g quantum dots or coupled cavities) the physics of such
processes is still basically unknown. Here, we take a first step along this
line by scrutinizing a two-site and a three-site lattices, each with two static
spins. Despite a generally complex dynamics occurs, we show a regime such that
the spin dynamics is described by an effective three-spin chain. Tasks such as
entanglement generation and quantum state transfer can be achieved accordingly.",1011.2734v2
2011-01-11,Analog of Electromagnetically Induced Transparency Effect for Two Nano/Micro-mechanical Resonators Coupled With Spin Ensemble,"We study a hybrid nano-mechanical system coupled to a spin ensemble as a
quantum simulator to favor a quantum interference effect, the
electromagnetically induced transparency (EIT). This system consists of two
nano-mechanical resonators (NAMRs), each of which coupled to a nuclear spin
ensemble. It could be regarded as a crucial element in the quantum network of
NAMR arrays coupled to spin ensembles. Here, the nuclear spin ensembles behave
as a long-lived transducer to store and transfer the NAMRs' quantum
information. This system shows the analog of EIT effect under the driving of a
probe microwave field. The double-EIT phenomenon emerges in the large $N$ (the
number of the nuclei) limit with low excitation approximation, because the
interactions between the spin ensemble and the two NAMRs are reduced to the
coupling of three harmonic oscillators. Furthermore, the group velocity is
reduced in the two absorption windows.",1101.2115v1
2011-10-17,"Spin frustration, charge ordering, and enhanced antiferromagnetism in TMTTF$_2$SbF$_6$","We theoretically investigate the effects of charge order and spin frustration
on the spin ordering in TMTTF salts. Using first-principles band calculations,
we find that a diagonal inter-chain transfer integral $t_{q1}$, which causes
spin frustration between the inter-chain dimers in the dimer-Mott insulating
state, strongly depends on the choice of anion. Within the numerical Lanczos
exact diagonalization method, we show that the ferroelectric charge order
changes the role of $t_{q1}$ from the spin frustration to the enhancement of
the two-dimensionality in spin sector. The results indicate that $t_{q1}$
assists the cooperative behavior between charge order and antiferromagnetic
state observed in TMTTF$_2$SbF$_6$.",1110.3575v2
2011-11-05,Coherent storage of photoexcited triplet states using 29Si nuclear spins in silicon,"Pulsed electron paramagnetic resonance spectroscopy of the photoexcited,
metastable triplet state of the oxygen-vacancy center in silicon reveals that
the lifetime of the ms = \pm1 sub-levels differ significantly from that of the
ms =0 state. We exploit this significant difference in decay rates to the
ground singlet state to achieve nearly ~100% electron spin polarization within
the triplet. We further demonstrate the transfer of a coherent state of the
triplet electron spin to, and from, a hyperfine-coupled, nearest-neighbor 29Si
nuclear spin. We measure the coherence time of the 29 Si nuclear spin employed
in this operation and find it to be unaffected by the presence of the triplet
electron spin and equal to the bulk value measured by nuclear magnetic
resonance.",1111.1344v1
2012-07-12,Quantum mechanical limitations to spin diffusion in the unitary Fermi gas,"We compute spin transport in the unitary Fermi gas using the strong-coupling
Luttinger-Ward theory. In the quantum degenerate regime the spin diffusivity
attains a minimum value of $D_s \simeq 1.3 \hbar/m$ approaching the quantum
limit of diffusion for a particle of mass $m$. Conversely, the spin drag rate
reaches a maximum value of $\Gamma_\sd \simeq 1.2 k_B T_F/\hbar$ in terms of
the Fermi temperature $T_F$. The frequency-dependent spin conductivity
$\sigma_s(\omega)$ exhibits a broad Drude peak, with spectral weight
transferred to a universal high-frequency tail $\sigma_s(\omega \to\infty) =
\hbar^{1/2}C/3\pi(m\omega)^{3/2}$ proportional to the Tan contact density $C$.
For the spin susceptibility $\chi_s(T)$ we find no downturn in the normal
phase.",1207.3103v2
2012-08-16,Holonomy Spin Foam Models: Definition and Coarse Graining,"We propose a new holonomy formulation for spin foams, which naturally extends
the theory space of lattice gauge theories. This allows current spin foam
models to be defined on arbitrary two-complexes as well as to generalize
current spin foam models to arbitrary, in particular finite groups. The
similarity with standard lattice gauge theories allows to apply standard coarse
graining methods, which for finite groups can now be easily considered
numerically. We will summarize other holonomy and spin network formulations of
spin foams and group field theories and explain how the different
representations arise through variable transformations in the partition
function. A companion paper will provide a description of boundary Hilbert
spaces as well as a canonical dynamic encoded in transfer operators.",1208.3388v1
2012-10-10,Field-Driven Evolution of Chiral Spin Textures in Thin Nanodisk of the Helimagnets,"The magnetic field-driven evolution of chiral spin textures in thin
helimagnet nanodisk with varied size are investigated by means of Monte Carlo
simulation. It is demonstrated that the complex spin texture may simply be
regarded as the superposition of the edged state with in plane spin orientation
perpendicular or parallel to the edge and the bulk state with the features
similar to two-dimensional chiral magnetic films. With the increase of the
external field, the proportion of the parallel spins of the edge state
increases, and the spin textures finally transfers into edged magnetic vortex.
The arrangement of skyrmions strongly depends on the disk size. In addition,
the uniaxial anisotropy and dipolar coupling in certain ranges are able to
stabilize a special magnetic vortex with Skyrmionic core while the disk size is
comparable with the wavelength of helix state.",1210.2859v1
2012-10-21,Spin-dependent exciton quenching and intrinsic spin coherence in CdSe/CdS nanocrystals,"Large surface to volume ratios of semiconductor nanocrystals cause
susceptibility to charge trapping, which can modify luminescence yields and
induce single-particle blinking. Optical spectroscopies cannot differentiate
between bulk and surface traps in contrast to spin-resonance techniques, which
in principle avail chemical information on such trap sites. Magnetic resonance
detection via spin-controlled photoluminescence enables the direct observation
of interactions between emissive excitons and trapped charges. This approach
allows the discrimination of two functionally different trap states in CdSe/CdS
nanocrystals underlying the fluorescence quenching and thus blinking
mechanisms: a spin-dependent Auger process in charged particles; and a
charge-separated state pair process, which leaves the particle neutral. The
paramagnetic trap centers offer control of energy transfer from the wide-gap
CdS to the narrow-gap CdSe, i.e. light harvesting within the heterostructure.
Coherent spin motion within the trap states of the CdS arms of nanocrystal
tetrapods is reflected by spatially remote luminescence from CdSe cores with
surprisingly long coherence times of >300 ns at 3.5 K.",1210.5684v1
2012-11-08,A hybrid quantum circuit consisting of a superconducting flux qubit coupled to both a spin ensemble and a transmission-line resonator,"We propose an experimentally realizable hybrid quantum circuit for achieving
a strong coupling between a spin ensemble and a transmission-line resonator via
a superconducting flux qubit used as a data bus. The resulting coupling can be
used to transfer quantum information between the spin ensemble and the
resonator. In particular, in contrast to the direct coupling without a data
bus, our approach requires far less spins to achieve a strong coupling between
the spin ensemble and the resonator (e.g., three to four orders of magnitude
less). This proposed hybrid quantum circuit could enable a long-time quantum
memory when storing information in the spin ensemble, and allows the
possibility to explore nonlinear effects in the ultrastrong-coupling regime.",1211.1827v2
2013-06-21,Suspended nanowires as mechanically-controlled Rashba spin-splitters,"Suspended nanowires are shown to provide mechanically-controlled coherent
mixing/splitting of the spin states of transmitted electrons, caused by the
Rashba spin-orbit interaction. The sensitivity of the latter to mechanical
bending makes the wire a tunable nano-electro-mechanical (NEM) weak link
between reservoirs. When the reservoirs are populated with misbalanced ""spin
up/down"" electrons, the wire becomes a source of split spin currents, which are
not associated with electric charge transfer and which do not depend on
temperature or driving voltages. The mechanical vibrations of the bended wires
allow for additional tunability of these splitters by applying a magnetic field
and varying the temperature. Clean metallic carbon nanotubes of a few microns
length are good candidates for generating spin conductance of the same order as
the charge conductance (divided by $e^2$) which would have been induced by
electric driving voltages.",1306.5125v2
2013-08-26,Spin lock composite and shaped pulses for efficient and robust pumping of dark states in magnetic resonance,"Long-lived (symmetry protected) hyperpolarized spin states offer important
new opportunities (for example, in clinical MR imaging), but existing methods
for producing these states are limited by either excess energy dissipation or
high sensitivity to inhomogeneities. We extend recent work on continuous-wave
irradiation of nearly-equivalent spins (spin-lock induced crossing) by
designing composite pulse and adiabatic shaped-pulse excitations which overcome
the limitations. These composite and adiabatic pulses differ drastically from
the traditional solutions in two-level systems. We also show this works in
chemically equivalent spin pairs, which has the advantage of allowing for
polarization transfer from and to remote spins. The approach is broadly
applicable to systems where varying excitation strength induces an avoided
crossing to a dark state, and thus to many other spectroscopic regimes.",1308.5666v1
2014-02-19,Dark State Adiabatic Passage with spin-one particles,"Adiabatic transport of information is a widely invoked resource in connection
with quantum information processing and distribution. The study of adiabatic
transport via spin-half chains or clusters is standard in the literature, while
in practice the true realisation of a completely isolated two-level quantum
system is not achievable. We explore here, theoretically, the extension of
spin-half chain models to higher spins. Considering arrangements of three
spin-one particles, we show that adiabatic transport, specifically a
generalisation of the Dark State Adiabatic Passage procedure, is applicable to
spin-one systems. We thus demonstrate a qutrit state transfer protocol. We
discuss possible ways to physically implement this protocol, considering
quantum dot and nitrogen-vacancy implementations.",1402.4552v2
2014-03-02,Quantum networks: Anti-core of spin chains,"The purpose of this paper is to exhibit a quantum network phenomenon - the
anti-core---that goes against the classical network concept of congestion core.
Classical networks idealized as infinite, Gromov hyperbolic spaces with
least-cost path routing (and subject to a technical condition on the Gromov
boundary) have a congestion core, defined as a subnetwork that routing paths
have a high probability of visiting. Here, we consider quantum networks, more
specifically spin chains, define the so-called maximum excitation transfer
probability $p_{\max}(i,j)$ between spin $i$ and spin $j$, and show that the
central spin has among all other spins the lowest probability of being excited
or transmitting its excitation. The anti-core is singled out by analytical
formulas for $p_{\mathrm{max}}(i,j)$, revealing the number theoretic properties
of quantum chains. By engineering the chain, we further show that this
probability can be made vanishingly small.",1403.0159v1
2014-03-04,Off-Resonant Manipulation of Spins in Diamond via Precessing Magnetization of a Proximal Ferromagnet,"We report the manipulation of nitrogen vacancy (NV) spins in diamond when
nearby ferrimagnetic insulator, yttrium iron garnet, is driven into precession.
The change in NV spin polarization, as measured by changes in
photoluminescence, is comparable in magnitude to that from conventional
optically detected magnetic resonance, but relies on a distinct mechanism as it
occurs at a microwave frequency far removed from the magnetic resonance
frequency of the NV spin. This observation presents a new approach to
transferring ferromagnetic spin information into a paramagnet and then
transducing the response into a robust optical signal. It also opens new
avenues for studying ferromagnetism and spin transport at the nanoscale.",1403.0656v1
2014-05-22,Longitudinal double spin asymmetry $A_1^p$ and spin-dependent structure function $g_1^p$ of the proton at low $x$ and low $Q^2$ from COMPASS,"The COMPASS experiment at CERN has collected a large sample of events of
inelastic scattering of longitudinally polarised muons off longitudinally
polarised protons in the non-perturbative region (four-momentum transfer
squared $Q^2<1$ GeV$^2$/$c^2$), with a Bjorken scaling variable in the range
$4\times 10^{-5}<x<4\times 10^{-2}$. The data set is two orders of magnitude
larger than the similar sample collected by the SMC experiment. These data
complement our data for polarised deuterons. They allow the accurate
determination of the longitudinal double spin asymmetry $A_1^p$ and of the
spin-dependent structure function $g_1^p$ of the proton in the region of low
$x$ and low $Q^2$. The preliminary results of the analysis of these data yield
non zero and positive asymmetries and of the structure function $g_1^p$. This
is the first time that spin effects are observed at such low $x$.",1405.5811v2
2014-07-02,Donor-driven spin relaxation in multi-valley semiconductors,"We present a theory for spin relaxation of electrons due to scattering off
the central-cell potential of impurities in silicon. Taking into account the
multivalley nature of the conduction band and the violation of translation
symmetry, the spin-flip amplitude is dominated by this short-range impurity
scattering after which the electron is transferred to a valley on a different
axis in $k$-space (the so called $f$-process). These $f$-processes dominate the
spin relaxation at all temperatures, where scattering off the impurity
central-cell dominate at low temperatures, and scattering with $\Sigma$-axis
phonons at elevated temperatures. To the best of our knowledge, the theory is
the first to explain and accurately quantify the empirically-found dependence
of spin relaxation on the impurity identity. Accordingly, the new formalism
fills a longstanding gap in the spin relaxation theory of $n$-type silicon, and
it is valuable for characterization of silicon-based spintronic devices.",1407.0725v1
2014-11-26,Full Bloch sphere teleportation of spinor Bose-Einstein condensates and spin ensembles,"Quantum teleportation is the transfer of quantum information between two
locations by the use of shared entanglement. Current teleportation schemes
broadly fall under one of two categories, of either qubit or continuous
variables teleportation. Spin coherent states on spin ensembles can be
teleported under the continuous variables approximation for states with small
deviations from a given polarization. However, for spin coherent states with
large deviations, no convenient teleportation protocol exists. Recently, we
introduced a teleportation scheme where a spin coherent state lying on the
equator of the Bloch sphere is teleported between distant parties (A.N. Pyrkov
and T. Byrnes, New. J. Phys. 16, 073038 (2014)). Here we generalize the
protocol to a spin coherent state with an arbitrary position on Bloch sphere.
Our proposed scheme breaks classical bounds based on communication in the
unconditional case and quantum state estimation with postselection.",1411.7173v1
2014-12-05,Nuclear structure aspects of spin-independent WIMP scattering off xenon,"We study the structure factors for spin-independent WIMP scattering off xenon
based on state-of-the-art large-scale shell-model calculations, which are shown
to yield a good spectroscopic description of all experimentally relevant
isotopes. Our results are based on the leading scalar one-body currents only.
At this level and for the momentum transfers relevant to direct dark matter
detection, the structure factors are in very good agreement with the
phenomenological Helm form factors used to give experimental limits for
WIMP-nucleon cross sections. In contrast to spin-dependent WIMP scattering, the
spin-independent channel, at the one-body level, is less sensitive to nuclear
structure details. In addition, we explicitly show that the structure factors
for inelastic scattering are suppressed by ~ 10^{-4} compared to the coherent
elastic scattering response. This implies that the detection of inelastic
scattering will be able to discriminate clearly between spin-independent and
spin-dependent scattering. Finally, we provide fits for all calculated
structure factors.",1412.6091v2
2015-02-25,Observation of a phononic Mollow triplet in a hybrid spin-nanomechanical system,"Reminiscent of the bound character of a qubit's dynamics confined on the
Bloch sphere, the observation of a Mollow triplet in the resonantly driven
qubit fluorescence spectrum represents one of the founding signatures of
Quantum Electrodynamics. Here we report on its observation in a hybrid
spin-nanomechanical system, where a Nitro-gen Vacancy spin qubit is
magnetically coupled to the vibrations of a Silicon Carbide nanowire. A
resonant microwave field turns the originally parametric hybrid interac-tion
into a resonant process, where acoustic phonons are now able to induce
transitions between the dressed qubit states, leading to synchronized
spin-oscillator dynamics. We further explore the vectorial character of the
hybrid coupling to the bidimensional de-formations of the nanowire. The
demonstrated microwave assisted synchronization of the spin-oscillator dynamics
opens novel perspectives for the exploration of spin-dependent forces, the
key-ingredient for quantum state transfer.",1502.07071v1
2015-03-09,Hybrid quantum device based on NV centers in diamond nanomechanical resonators plus superconducting waveguide cavities,"We propose and analyze a hybrid device by integrating a microscale diamond
beam with a single built-in nitrogen-vacancy (NV) center spin to a
superconducting coplanar waveguide (CPW) cavity. We find that under an ac
electric field the quantized motion of the diamond beam can strongly couple to
the single cavity photons via dielectric interaction. Together with the strong
spin-motion interaction via a large magnetic field gradient, it provides a
hybrid quantum device where the dia- mond resonator can strongly couple both to
the single microwave cavity photons and to the single NV center spin. This
enables coherent information transfer and effective coupling between the NV
spin and the CPW cavity via mechanically dark polaritons. This hybrid
spin-electromechanical de- vice, with tunable couplings by external fields,
offers a realistic platform for implementing quantum information with single NV
spins, diamond mechanical resonators, and single microwave photons.",1503.02437v2
2015-04-16,Thermoelectric and thermospin transport in a ballistic junction of graphene,"We consider theoretically a wide graphene ribbon, that on both ends is
attached to electronic reservoirs which generally have different temperatures.
The graphene ribbon is assumed to be deposited on a substrate, that leads to a
spin-orbit coupling of Rashba type. We calculate the thermally induced charge
current in the ballistic transport regime as well as the thermoelectric voltage
(Seebeck effect). Apart from this, we also consider thermally induced spin
current and spin polarization of the graphene ribbon. The spin currents are
shown to have generally two components; one parallel to the temperature
gradient and the other one perpendicular to this gradient. The latter
corresponds to the spin current due to the spin Nernst effect. Additionally, we
also consider the heat current between the reservoirs due to transfer of
electrons.",1504.04265v1
2015-06-03,Externally controlled selective spin transfer through a two-terminal bridge setup,"A new way of getting controlled spin dependent transport through a
two-terminal bridge setup is explored. The system comprises a magnetic quantum
ring which is directly coupled to a magnetic quantum wire and subjected to an
in-plane electric field perpendicular to the wire. Without directly changing
system parameters, one can regulate spin currents simply by tuning the external
electric field under a finite bias drop across the wire. For some particular
field strengths a high degree of spin polarization can be achieved and thus the
system can essentially be utilized as an externally controlled spin polarized
device. A detailed comparison of spin current magnitudes obtained from other
bridge setups is also examined to make the present investigation a self
contained study.",1506.01259v1
2015-06-30,Graphene on transition-metal dichalcogenides: a platform for proximity spin-orbit physics and optospintronics,"Hybrids of graphene and two dimensional transition metal dichalcogenides
(TMDC) have the potential to bring graphene spintronics to the next level. As
we show here by performing first-principles calculations of graphene on
monolayer MoS$_2$, there are several advantages of such hybrids over pristine
graphene. First, Dirac electrons in graphene exhibit a giant global proximity
spin-orbit coupling, without compromising the semimetallic character of the
whole system at zero field. Remarkably, these spin-orbit effects can be very
accurately described by a simple effective Hamiltonian. Second, the Fermi level
can be tuned by a transverse electric field to cross the MoS$_2$ conduction
band, creating a system of coupled massive and massles electron gases. Both
charge and spin transport in such systems should be unique. Finally, we propose
to use graphene/TMDC structures as a platform for optospintronics, in
particular for optical spin injection into graphene and for studying spin
transfer between TMDC and graphene.",1506.08954v1
2015-09-29,Self-similarity of proton spin and z-scaling,"The concept of z-scaling previously developed for analysis of inclusive
reactions in proton-proton collisions is applied for description of processes
with polarized particles. Hypothesis of self-similarity of the proton spin
structure is discussed. The possibility of extracting information on
spin-dependent fractal dimensions of hadrons and fragmentation process from the
cross sections and asymmetries is justified. The double longitudinal spin
asymmetry A_{LL} of jet and pi0-meson production and the coefficient of
polarization transfer D_{LL} measured in proton-proton collisions at sqrt s =
200 GeV at RHIC are analyzed in the framework of z-scaling. The spin-dependent
fractal dimension of proton is estimated.",1509.08854v1
2015-10-18,Electrical Control of Strong Spin-Phonon Coupling in a Carbon Nanotube,"We describe an approach to electrically control the strong interaction
between a single electron spin and the vibrational motion of a suspended carbon
nanotube resonator. The strength of the deflection-induced spin-phonon coupling
is dependent on the wavefunction of the electron confined in a lateral carbon
nanotube quantum dot. An electrical field along the nanotube shifts the
effective center of the quantum dot, leading to the corresponding modification
of the spin-phonon strength. Numerical simulations with experimentally
reachable parameters show that high fidelity quantum state transfer between
mechanical and spin qubits driven by electrical pulses is feasible. Our results
form the basis for the fully electrical control of the coherent interconvertion
between light and spin qubits and for manufacturing electrically driven quantum
information processing systems.",1510.05221v1
2016-01-27,Spin polarization and attosecond time delay in photoemission from spin degenerate states of solids,"After photon absorption, electrons from a dispersive band of a solid require
a finite time in the photoemission process before being photoemitted as free
particles, in line with recent attosecondresolved photoemission experiments.
According to the Eisenbud-Wigner-Smith model, the time delay is due to a phase
shift of different transitions that occur in the process. Such a phase shift is
also at the origin of the angular dependent spin polarization of the
photoelectron beam, observable in spin degenerate systems without angular
momentum transfer by the incident photon. We propose a semi-quantitative model
which permits to relate spin and time scales in photoemission from condensed
matter targets and to better understand spin- and angle-resolved photoemission
spectroscopy (SARPES) experiments on spin degenerate systems. We also present
the first experimental determination by SARPES of this time delay in a
dispersive band, which is found to be greater than 26 as for electrons emitted
from the sp-bulk band of the model system Cu(111).",1601.07309v2
2016-01-21,Nuclear spin correlations and collective excitations in supercritical H$_2$,"Nuclear spins are known to experience spontaneous long-range correlations
only below 2.5 mili-Kelvin in superfluid $^3$He. Here we present the first
evidence of nuclear spin coupling in molecular hydrogen (H$_2$) at 74-92 Kelvin
using neutron scattering, showing a fundamental change in nature from the
incoherent scattering universally expected from hydrogen, which reflects single
particle properties of uncorrelated nuclear spins, to coherent, with a peak
materializing on the elastic line, indicating H$_2$-H$_2$ nuclear spin
correlations. In this novel phase, the dynamic response of the system also
changes nature, and collective excitations with an effective mass of nine H$_2$
are observed with inelastic scattering at momentum transfers up to 37
\AA$^{-1}$, corresponding to length scales smaller than the H-H bond, where
previous experiments have always found single atom excitations. This novel
behavior has only been observed from H$_2$ within the subnanometer sized
graphitic pores of a carbon material, marking the first demonstration that a
confined materials environment can be used to control nuclear spin
correlations.",1602.01811v1
2016-02-12,High-precision force sensing using a single trapped ion,"We introduce quantum sensing schemes for measuring very weak forces with a
single trapped ion. They use the spin-motional coupling induced by the
laser-ion interaction to transfer the relevant force information to the
spin-degree of freedom. Therefore, the force estimation is carried out simply
by observing the Ramsey-type oscillations of the ion spin states. Three quantum
probes are considered, which are represented by systems obeying the
Jaynes-Cummings, quantum Rabi (in 1D) and Jahn-Teller (in 2D) models. By using
dynamical decoupling schemes in the Jaynes-Cummings and Jahn-Teller models, our
force sensing protocols can be made robust to the spin dephasing caused by the
thermal and magnetic field fluctuations. In the quantum-Rabi probe, the
residual spin-phonon coupling vanishes, which makes this sensing protocol
naturally robust to thermally-induced spin dephasing. We show that the proposed
techniques can be used to sense the axial and transverse components of the
force with a sensitivity beyond the yN $/\sqrt{\text{Hz}}$ range, i.e. in the
xN$ /\sqrt{\text{Hz}}$ (xennonewton, $10^{-27}$). The Jahn-Teller protocol, in
particular, can be used to implement a two-channel vector spectrum analyzer for
measuring ultra-low voltages.",1602.04072v1
2016-02-24,Super-Poissonian shot noise of squeezed-magnon mediated spin transport,"The magnetization of a ferromagnet (F) driven out of equilibrium injects pure
spin current into an adjacent conductor (N). Such F$|$N bilayers have become
basic building blocks in a wide variety of spin based devices. We evaluate the
shot noise of the spin current traversing the F$|$N interface when F is
subjected to a coherent microwave drive. We find that the noise spectrum is
frequency independent up to the drive frequency, and increases linearly with
frequency thereafter. The low frequency noise indicates super-Poissonian spin
transfer, which results from quasi-particles with effective spin $\hbar^* =
\hbar (1 + \delta)$. For typical ferromagnetic thin films, $\delta \sim 1$ is
related to the dipolar interaction-mediated squeezing of F eigenmodes.",1602.07513v2
2016-02-25,All electrical propagating spin wave spectroscopy with broadband wavevector capability,"We develop an all electrical experiment to perform the broadband
phase-resolved spectroscopy of propagating spin waves in micrometer sized thin
magnetic stripes. The magnetostatic surface spin waves are excited and detected
by scaled down to 125 nm wide inductive antennas, which award ultra broadband
wavevector capability. The wavevector selection can be done by applying an
excitation frequency above the ferromagnetic resonance. Wavevector
demultiplexing is done at the spin wave detector thanks to the rotation of the
spin wave phase upon propagation. A simple model accounts for the main features
of the apparatus transfer functions. Our approach opens an avenue for the all
electrical study of wavevector-dependent spin wave properties including
dispersion spectra or non-reciprocal propagation.",1602.08091v2
2017-06-06,Long-lived spin polarization in n-doped MoSe$_2$ monolayers,"Transition metal dichalcogenide monolayers are highly interesting for
potential valleytronic applications due to the coupling of spin and valley
degrees of freedom and valley-selective excitonic transitions. However,
ultrafast recombination of excitons in these materials poses a natural limit
for applications, so that a transfer of polarization to resident carriers is
highly advantageous. Here, we study the low-temperature spin-valley dynamics in
nominally undoped and n-doped MoSe$_2$ monolayers using time-resolved Kerr
rotation. In the n-doped MoSe$_2$, we find a long-lived component of the Kerr
signal which we attribute to the spin polarization of resident carriers. This
component is absent in the nominally undoped MoSe$_2$. The long-lived spin
polarization is stable under applied in-plane magnetic fields. Spatially
resolved measurements allow us to determine an upper boundary for the electron
spin diffusion constant in MoSe$_2$.",1706.01802v2
2017-09-14,Electric power transfer in spin pumping experiments,"Spin pumping is becoming an established method to generate voltages from
magnetic dynamics. The standard detection method of spin pumping is based on
open circuit voltage measurement across ferromagnetic (FM) and non-magnetic
(NM) bi-layers, where the inverse spin-Hall effect (ISHE) can convert spin
currents into electrical charge accumulation. In this paper, we present that it
is also possible to measure the associated electric charge current generated in
FM/NM bi-layers, by using a macroscopic closed circuitry detection method.
Using variable load resistors connected in series to the sample, we quantified
charge currents and associated electric power dissipation as a function of the
load resistance. By using basic circuit analysis, we are able to describe spin
pumping cells as a non-ideal voltage source or equivalent current source with
an internal resistor.",1709.04690v2
2017-12-20,Understanding the mechanism stabilizing intermediate spin states in Fe(II)-Porphyrin,"Spin fluctuations in Fe(II)-porphyrins are at the heart of heme-proteins
functionality. Despite significant progress in porphyrin chemistry, the
mechanisms that rule spin state stabilisation remain elusive. Here, it is
demonstrated by using multiconfigurational quantum chemical approaches,
including the novel Stochastic-CASSCF method, that electron delocalization
between the metal centre and the pi system of the macrocycle differentially
stabilises the triplet spin states over the quintet. This delocalisation takes
place via charge-transfer excitations, involving the out-of-plane iron d
orbitals, key linking orbitals between metal and macrocycle. Through a
correlated breathing mechanism, the 3d electrons can make transitions towards
the pi orbitals of the macrocycle. This guarantees a strong coupling between
the on-site radial correlation on the metal and electron delocalization.
Opposite-spin 3d electrons of the triplet can effectively reduce electron
repulsion in this manner. Constraining the out-of-plane orbitals from breathing
hinders delocalization and reverses the spin ordering. Our results find a
qualitative analogue in Kekul\'e resonance structures involving also the metal
centre.",1712.07710v1
2018-06-06,Excitation of magnon spin photocurrents in antiferromagnetic insulators,"In the circular photogalvanic effect, circularly polarized light can produce
a direct electron photocurrent in metals and the direction of the current
depends on the polarization. We suggest that an analogous nonlinear effect
exists for antiferromagnetic insulators wherein the total spin of light and
spin waves is conserved. In consequence, a spin angular momentum is expected to
be transfered from photons to magnons so that a circularly polarized
electromagnetic field will generate a direct magnon spin current. The direction
of the current is determined by the helicity of the light. We show that this
resonant effect appears as a second order light-matter interaction. We find
also a geometric contribution to the spin photocurrent, which appears for
materials with complex lattice structures and Dzyaloshinskii-Moriya
interactions.",1806.02442v2
2018-07-23,Ultrahigh-density spin-polarized H and D observed via magnetization quantum beats,"We measure nuclear and electron spin-polarized H and D densities of at least
10$^{19}\, cm^{-3}$ with $\sim$10 ns lifetimes, from the photodissociation of
HBr and DI with circularly-polarized UV light pulses. This density is $\sim$6
orders of magnitude higher than that produced by conventional
continuous-production methods, and, surprisingly, at least 100 times higher
than expected densities for this photodissociation method. We observe the
hyperfine quantum beating of the H and D magnetization with a pick-up coil,
i.e., the respective 0.7 and 3 ns periodic transfer of polarization from the
electrons to the nuclei and back. The $\rm{10^{19}\,cm^{-3}}$ spin-polarized H
and D density is sufficient for laser-driven ion acceleration of spin polarized
electrons, protons, or deuterons, the preparation of nuclear-spin-polarized
molecules, and for the demonstration of spin-polarized D-T or D-$\rm{{^3He}}$
laser fusion, for which a reactivity enhancement of $\rm{\sim50\%}$ is
expected.",1807.08796v1
2018-08-06,Formation of Spatial Patterns by Spin-selective Excitations of Interacting Fermions,"We describe the formation of charge- and spin-density patterns induced by
spin-selective photoexcitations of interacting fermionic systems in the
presence of a microstructure. As an example, we consider a one-dimensional
Hubbard-like system with a periodic magnetic microstructure, which has a
uniform charge distribution in its ground state, and in which a long-lived
charge-density pattern is induced by the spin-selective photoexcitation. Using
tensor-network methods, we study the full quantum dynamics in the presence of
electron-electron interactions and identify doublons as the main decay channel
for the induced charge pattern. Our setup is compared to the OISTR mechanism,
in which ultrafast optically induced spin transfer in Heusler and magnetic
compounds is associated to the difference of the local density of states of the
different elements in the alloys. We find that applying a spin-selective
excitation there induces spatially periodic patterns in local observables.
Implications for pump-probe experiments on correlated materials and experiments
with ultracold gases on optical lattices are discussed.",1808.02138v3
2019-01-17,Spin filtering in CrI$_3$ tunnel junctions,"The recently discovered magnetism of two-dimensional (2D) van der Waals
crystals have attracted a lot of attention. Among these materials is CrI$_3$ -
a magnetic semiconductor exhibiting transitions between antiferromagnetic and
ferromagnetic orderings under the influence of an applied magnetic field. Here,
using first-principles methods based on density functional theory, we explore
spin-dependent transport in tunnel junctions formed of fcc Cu (111) electrodes
and a CrI$_3$ tunnel barrier. We find about 100% spin polarization of the
tunneling current for a ferromagnetically-ordered four-monolayer CrI$_3$ and
tunneling magnetoresistance of about 3,000% associated with a change of
magnetic ordering in CrI$_3$. This behavior is understood in terms of the spin
and wave-vector dependent evanescent states in CrI$_3$ which control the
tunneling conductance. We find a sizable charge transfer from Cu to CrI$_3$
which adds new features to the mechanism of spin-filtering in CrI$_3$-based
tunnel junctions. Our results elucidate the mechanisms of spin filtering in
CrI3 tunnel junctions and provide important insights for the design of
magnetoresistive devices based on 2D magnetic crystals.",1901.05993v1
2019-02-25,Spin-orbit-induced hole spin relaxation in a quantum dot molecule: the effect of $s$-$p$ coupling,"We study the effect of the coupling between the hole $s$ shell of one quantum
dot and the $p$ shell in the other dot forming a quantum dot molecule on the
spin relaxation between the sublevels of the hole $s$ state. Using an effective
model that captures the spin-orbit effects in the $p$ shell irrespective of
their origin, we show that the strong spin mixing in the $p$ shell can be
transferred to the $s$ shell of the other dot, leading to enhanced spin
relaxation in a certain energy range around the $s$-$p$ resonance if the dots
are misaligned and the magnetic field is tilted from the sample plane.",1902.09161v1
2019-07-23,Influence of applied electric and magnetic fields on a thermally-induced reentrance of a coupled spin-electron model on a decorated square lattice,"The combination of an exact and Corner Transfer Matrix Renormalization Group
(CTMRG) methods is used to study an influence of external electric and magnetic
fields on existence of intriguing reentrant magnetic transitions in a coupled
spin-electron model on a decorated square lattice. The two-dimensional (2D)
decorated square lattice with localized nodal spins and delocalized electrons
is taken into account. It was found that the competition among all involved
interactions (the electron hopping, spin-spin and spin-electron interaction,
external electric and magnetic fields) in combination with thermal fluctuations
can produce new type of reentrant magnetic transitions. Depending on the model
parameters the non-zero fields can stabilize or destabilize magnetic
reentrance. In addition, an alternative and more effective way, for modulating
the magnetic reentrance is found. An origin of intriguing low-temperature round
maximum in the specific heat was explained as a consequence of rapid changes in
the sublattice magnetizations, which is induced through a competition of all
presented interactions.",1907.09733v1
2019-09-10,Bias induced spin state transition mediated by electron excitations,"Recent experiments reported that spin-state transitions were realized by
applying bias voltages. But these bias-induced spin state transitions (BISSTs)
are not fully understood, especially the mechanism. It is well known that the
metal-to-ligand charge transfer excitation (MLCT) and the metal-centered
excitation (MC) activated by light radiation can induce the transition from low
spin (LS) to high spin (HS) and that from HS to LS. Moreover, electronic
excitations are accessible by inelastic cotunneling in molecular junctions with
bias voltages applied. Based on these two experimental facts, we propose the
MLCT basically leads to the BISST from LS to HS, and the MC results in the
BISST from HS to LS. The rationality of the mechanism is demonstrated by
comparing first-principles results and experimental observations. The
calculated voltage threshold for activating the MLCT (MC) is close to the
experimental voltage for observing the BISST from LS to HS (from HS to LS). The
activation of MLCT (MC) depends on the bias polarity, which can explain the
bias-polarity dependence of BISST in the experiment. Our study is important for
further design of molecular spintronic devices working on spin state
transition.",1909.04254v1
2020-01-23,Non-Contact Spin Pumping by Microwave Evanescent Fields,"The angular momentum of evanescent light fields has been studied in
nano-optics and plasmonics, but not in the microwave regime. Here we predict
non-contact pumping of electron spin currents in conductors by the evanescent
stray fields of excited magnetic nanostructures. The coherent transfer of the
photon to the electron spin is proportional to the $g$-factor, which is large
in narrow-gap semiconductors and surface states of topological insulators. The
spin pumping current is chiral when the spin susceptibility displays
singularities that indicate collective states. However, 1D systems with linear
dispersion at the Fermi energy such as metallic carbon nanotubes are an
exception since spin pumping is chiral even without interactions.",2001.08513v2
2020-02-14,Spin-wave diode and circulator based on unidirectional coupling,"In magnonics, an emerging branch of wave physics characterized by low-energy
consumption, it is highly desirable to realize circuit elements within the
scope of spin-wave computing. Here, based on numerical simulations, we
demonstrate the functionality of the spin-wave diode and the circulator to
steer and manipulate spin waves over a wide range of frequency in the GHz
regime. They take advantage of the unidirectional coupling induced by the
interfacial Dzyaloshinskii-Moriya interaction to transfer the spin wave between
thin ferromagnetic layers in only one direction of propagation. Using the
multilayered structure consisting of Py and Co in direct contact with Pt, we
obtain sub-micrometer-size devices of high efficiency. In the diode, the power
loss ratio between forward and reverse direction reaches 22 dB, while in the
four-port circulator, the efficiency exceeds 13 dB. Thus, our work contributes
to the emerging branch of energy-efficient magnonic logic devices, where,
thanks to short wavelength of spin waves, it is possible to realize nanoscale
devices.",2002.06096v1
2020-04-17,Simulation of higher-order topological phases in 2D spin-phononic crystal networks,"We propose and analyse an efficient scheme for simulating higher-order
topological phases of matter in two dimensional (2D) spin-phononic crystal
networks. We show that, through a specially designed periodic driving, one can
selectively control and enhance the bipartite silicon-vacancy (SiV) center
arrays, so as to obtain the chiral symmetry-protected spin-spin couplings. More
importantly, the Floquet engineering spin-spin interactions support rich
quantum phases associated with topological invariants. In momentum space, we
analyze and simulate the topological nontrivial properties of the one- and
two-dimensional system, and show that higher-order topological phases can be
achieved under the appropriate periodic driving parameters. As an application
in quantum information processing, we study the robust quantum state transfer
via topologically protected edge states. This work opens up new prospects for
studying quantum acoustic, and offers an experimentally feasible platform for
the study of higher-order topological phases of matter.",2004.08049v1
2020-06-16,Gate tunability of highly efficient spin-to-charge conversion by spin Hall effect in graphene proximitized with WSe$_2$,"The proximity effect opens ways to transfer properties from one material into
another and is especially important in two-dimensional materials. In van der
Waals heterostructures, transition metal dichalcogenides (TMD) can be used to
enhance the spin-orbit coupling of graphene leading to the prediction of gate
controllable spin-to-charge conversion (SCC). Here, we report for the first
time and quantify the SHE in graphene proximitized with WSe$_2$ up to room
temperature. Unlike in other graphene/TMD devices, the sole SCC mechanism is
the spin Hall effect and no Rashba-Edelstein effect is observed. Importantly,
we are able to control the SCC by applying a gate voltage. The SCC shows a high
efficiency, measured with an unprecedented SCC length larger than 20 nm. These
results show the capability of two-dimensional materials to advance towards the
implementation of novel spin-based devices and future applications.",2006.09227v1
2021-06-28,Fully Resonant Magneto-elastic Spin-wave Excitation by Surface Acoustic Waves under Conservation of Energy and Linear Momentum,"We report on the resonant excitation of spin waves in micro-structured
magnetic thin films by surface acoustic waves (SAWs). The spin waves as well as
the acoustic waves are studied by micro-focused Brillouin light scattering
spectroscopy. Besides the excitation of the ferromagnetic resonance, a process
which does not fulfill momentum conservation, also the excitation of
finite-wavelength spin waves can be observed at low magnetic fields. Using
micromagnetic simulations, we verify that during this excitation both energy
and linear momentum are conserved and fully transferred from the SAW to the
spin wave.",2106.14705v3
2021-10-02,The role of surface spin polarization on ceria-supported Pt nanoparticles,"In this work, we employ first-principles simulations to investigate the spin
polarization of CeO$_2$-(111) surface and its impact on interactions between a
ceria support and Pt nanoparticles. For the first time, we report that the
CeO$_2$-(111) surface exhibits a robust surface spin polarization due to the
internal charge transfer between atomic Ce and O layers. In turn, it can lower
the surface oxygen vacancy formation energy and enhance the oxide reducibility.
We show that the inclusion of spin polarization can therefore significantly
reduce the major activation barrier in the proposed reaction pathway of CO
oxidation on ceria-supported Pt nanoparticles. For metal-support interactions,
surface spin polarization enhances the bonding between Pt nanoparticle and
ceria surface oxygen, while CO adsorption on Pt nanoparticles weakens the
interfacial interaction regardless of spin polarization.",2110.00710v1
2021-10-26,Ultrafast signatures of spin and orbital order in antiferromagnetic $α$-Sr$_2$CrO$_4$,"We used femtosecond optical spectroscopy to study ultrafast spin and orbital
ordering dynamics in the antiferromagnetic Mott insulator
$\alpha$-Sr$_2$CrO$_4$. This chromate system possesses multiple spin and
orbital ordered phases, and therefore could enable us to study the unique
interplay between these collective phases through their non-equilibrium
response to photoexcitation. Here, by varying the pump photon energy, we
selectively drove inter-site spin hopping between neighboring Cr $t_{2g}$
orbitals and charge transfer-type transitions between oxygen 2$p$ and Cr
$e_{g}$ orbitals. The resulting transient reflectivity dynamics revealed
temperature-dependent anomalies across the N${\textrm{\'e}}$el temperature for
spin ordering as well as the transition temperatures linked to different types
of orbital order. Our results reveal distinct relaxation timescales for spin
and orbital orders in $\alpha$-Sr$_2$CrO$_4$ and provide experimental evidence
for the phase transition at $T_\textrm{O}$, possibly related to antiferro-type
orbital ordering.",2110.14004v1
2021-11-19,Terahertz-Light Driven Coupling of Antiferromagnetic Spins to Lattice,"Understanding spin-lattice coupling represents a key challenge in modern
condensed matter physics, with crucial importance and implications for
ultrafast and 2D-magnetism. The efficiency of angular momentum and energy
transfer between spins and the lattice imposes fundamental speed limits on the
ability to control spins in spintronics, magnonics and magnetic data storage.
We report on an efficient nonlinear mechanism of spin-lattice coupling driven
by THz light pulses. A nearly single-cycle THz pulse resonantly interacts with
a coherent magnonic state in the antiferromagnet CoF2 and excites the
Raman-active THz phonon. The results reveal the unique functionality of
antiferromagnets allowing ultrafast spin-lattice coupling using light.",2111.10186v3
2022-10-23,Chiral Phonon Induced Spin-Polarization,"The current understanding of chirality suggests the existence of a connection
between structure and angular momentum, including spin. This is particularly
emphasised in the chiral induced spin selectivity effect, where chiral
structures act as spin filters. However, the recent discovery of chiral phonons
have demonstrated that phonons too may carry angular momentum which also can be
regarded as magnetic moments which add to the total moment. Here, it is shown
that chiral phonons may induce a non-trivial spin-texture in an otherwise
non-magnetic electronic structure. By considering a set-up in which electrons
and phonons are interfaced with each other, it is shown that chiral phonons may
transfer its angular momentum into the electron reservoir which, thereby,
becomes spin-polarized. It is, moreover, shown that an equivalent mechanism
does not exist whenever the electrons are interfaced with achiral phonons.",2210.12722v1
2022-10-25,Exact solutions for a spin-orbit coupled bosonic double-well system,"Exact solutions for spin-orbit (SO) coupled cold atomic systems are very
important and rare in physics. In this paper, we propose a simple method of
combined modulations to generate the analytic exact solutions for an SO-coupled
boson held in a driven double well. For the cases of synchronous combined
modulations and the spin-conserving tunneling, we obtain the general analytical
accurate solutions of the system respectively. For the case of spin-flipping
tunneling under asynchronous combined modulations, we get the special exact
solutions in simple form when the driving parameters satisfy certain
conditions. Based on these obtained exact solutions, we reveal some intriguing
quantum spin dynamical phenomena, for instance, the arbitrary population
transfer (APT) with and/or without spin-flipping, the controlled coherent
population conservation (CCPC), and the controlled coherent population
inversion (CCPI). The results may have potential applications in the
preparation of accurate quantum entangled states and quantum information
processing.",2210.13724v1
2023-05-18,Proximity spin-orbit coupling in an armchair carbon nanotube on monolayer bismuthene,"We study spin-orbit proximity effects in a hybrid heterostructure build of a
one-dimensional (1D) armchair carbon nanotube and two-dimensional (2D) buckled
monolayer bismuthene. We show, by performing first-principles calculations,
that Dirac electrons in the nanotube exhibit large spin-orbit coupling due to a
close vicinity of bismuthene. The calculated low-energy band structures of the
proximized nanotube display a strong dependence on the position of the nanotube
on the substrate, similar to twist-angle dependence found in 2D
heterostructures. Based on the first-principles results, we formulate an
effective low-energy Hamiltonian of the nanotube and identify key interactions
governing the proximity spin-orbit coupling. The proximity-induced spin
splitting of Dirac cone bands is in meV range, confirming an efficient transfer
of spin-orbit coupling from bismuthene to the nanotube.",2305.10902v1
2023-07-19,Zero-field spin waves in YIG nano-waveguides,"Spin-wave based transmission and processing of information is a promising
emerging nano-technology that can help overcome limitations of traditional
electronics based on the transfer of electrical charge. Among the most
important challenges for this technology is the implementation of spin-wave
devices that can operate without the need for an external bias magnetic field.
Here we experimentally demonstrate that this can be achieved using
sub-micrometer wide spin-wave waveguides fabricated from ultrathin films of
low-loss magnetic insulator - Yttrium Iron Garnet (YIG). We show that these
waveguides exhibit a highly stable single-domain static magnetic configuration
at zero field and support long-range propagation of spin waves with gigahertz
frequencies. The experimental results are supported by micromagnetic
simulations, which additionally provide information for optimization of
zero-field guiding structures. Our findings create the basis for the
development of energy-efficient zero-field spin-wave devices and circuits.",2307.09805v1
2023-08-31,Bethe ansatz inside Calogero-Sutherland models,"We study the trigonometric quantum spin-Calogero-Sutherland model, and the
Haldane-Shastry spin chain as a special case, using a Bethe-ansatz analysis. We
harness the model's Yangian symmetry to import the standard tools of
integrability for Heisenberg spin chains into the world of integrable
long-range models with spins. From the transfer matrix with a diagonal twist we
construct Heisenberg-style symmetries (Bethe algebra) that refine the usual
hierarchy of commuting Hamiltonians (quantum determinant) of the
spin-Calogero-Sutherland model. We compute the first few of these new conserved
charges explicitly, and diagonalise them by Bethe ansatz inside each
irreducible Yangian representation. This yields a new eigenbasis for the
spin-Calogero-Sutherland model that generalises the Yangian Gelfand-Tsetlin
basis of Takemura and Uglov. The Bethe-ansatz analysis involves non-generic
values of the inhomogeneities. Our review of the inhomogeneous Heisenberg XXX
chain, with special attention to how the Bethe ansatz works in the presence of
fusion, may be of independent interest.",2308.16865v1
2023-09-28,Spin Drude weight for the integrable XXZ chain with arbitrary spin,"Using generalized hydrodynamics (GHD), we exactly evaluate the
finite-temperature spin Drude weight at zero magnetic field for the integrable
XXZ chain with arbitrary spin and easy-plane anisotropy. First, we construct
the fusion hierarchy of the quantum transfer matrices ($T$-functions) and
derive functional relations ($T$- and $Y$-systems) satisfied by the
$T$-functions and certain combinations of them ($Y$-functions). Through
analytical arguments, the $Y$-system is reduced to a set of non-linear integral
equations, equivalent to the thermodynamic Bethe ansatz (TBA) equations. Then,
employing GHD, we calculate the spin Drude weight at arbitrary finite
temperatures. As a result, a characteristic fractal-like structure of the Drude
weight is observed at arbitrary spin, similar to the spin-1/2 case. In our
approach, the solutions to the TBA equations (i.e., the $Y$-functions) can be
explicitly written in terms of the $T$-functions, thus allowing for a
systematic calculation of the high-temperature limit of the Drude weight.",2309.16462v3
2023-10-24,Complex Poynting vector in gyromagnetic media and its impact on power flow in guided modes,"In this paper, we show the relation between the time-varying spinning nature
of the instantaneous Poynting vector and the phasor form of the complex
Poynting vector in the bulk of the gyromagnetic medium. We show the presence of
a transverse reactive power component in the bulk of the gyrotropic medium,
even for plane wave propagation. We use a simple quantification technique of
Poynting vector spin to analyze the rotation of the instantaneous Poynting
vector using the complex phasor form of the time-averaged Poynting vector. For
a transverse electric mode, we show the similarity between the Poynting vector
spin and the photonic spin of the magnetic field. The Poynting vector spin is
then used to represent the transverse power transfer across a ferrite-air
interface supporting TE surface wave modes. Considering a gyromagnetic
ferrite-filled rectangular waveguide following the TE mode profile, we show the
correspondence between the Poynting vector spin and the overall positive and
backward power flow. We analytically propose a mechanism to engineer the region
of the waveguide supporting backward and forward power propagation.",2310.15867v1
2010-10-22,Formation of the black-hole binary M33 X-7 via mass-exchange in a tight massive system,"M33 X-7 is among the most massive X-Ray binary stellar systems known, hosting
a rapidly spinning 15.65 Msun black hole orbiting an underluminous 70 Msun Main
Sequence companion in a slightly eccentric 3.45 day orbit. Although
post-main-sequence mass transfer explains the masses and tight orbit, it leaves
unexplained the observed X-Ray luminosity, star's underluminosity, black hole's
spin, and eccentricity. A common envelope phase, or rotational mixing, could
explain the orbit, but the former would lead to a merger and the latter to an
overluminous companion. A merger would also ensue if mass transfer to the black
hole were invoked for its spin-up. Here we report that, if M33 X-7 started as a
primary of 85-99 Msun and a secondary of 28-32 Msun, in a 2.8-3.1 day orbit,
its observed properties can be consistently explained. In this model, the Main
Sequence primary transferred part of its envelope to the secondary and lost the
rest in a wind; it ended its life as a ~16 Msun He star with a Fe-Ni core which
collapsed to a black hole (with or without an accompanying supernova). The
release of binding energy and, possibly, collapse asymmetries ""kicked"" the
nascent black hole into an eccentric orbit. Wind accretion explains the X-Ray
luminosity, while the black hole spin can be natal.",1010.4809v1
2016-01-18,Universal Bethe ansatz solution for the Temperley-Lieb spin chain,"We consider the Temperley-Lieb (TL) open quantum spin chain with ""free""
boundary conditions associated with the spin-$s$ representation of
quantum-deformed $sl(2)$. We construct the transfer matrix, and determine its
eigenvalues and the corresponding Bethe equations using analytical Bethe
ansatz. We show that the transfer matrix has quantum group symmetry, and we
propose explicit formulas for the number of solutions of the Bethe equations
and the degeneracies of the transfer-matrix eigenvalues. We propose an
algebraic Bethe ansatz construction of the off-shell Bethe states, and we
conjecture that the on-shell Bethe states are highest-weight states of the
quantum group. We also propose a determinant formula for the scalar product
between an off-shell Bethe state and its on-shell dual, as well as for the
square of the norm. We find that all of these results, except for the
degeneracies and a constant factor in the scalar product, are universal in the
sense that they do not depend on the value of the spin. In an appendix, we
briefly consider the closed TL spin chain with periodic boundary conditions,
and show how a previously-proposed solution can be improved so as to obtain the
complete (albeit non-universal) spectrum.",1601.04378v2
2017-10-04,Pulsed polarisation for robust DNP,"Dynamical nuclear polarisation (DNP) is an important technique that uses
polarisation transfer from electron to nuclear spins to achieve nuclear
hyperpolarisation. As the electron spin of the nitrogen vacancy (NV) centres in
diamond can be optically initialised nearly perfectly even at room temperature
and ambient conditions, new opportunities become possible by the combination of
efficient DNP with optically polarised NV centres. Among such applications are
nanoscale nuclear magnetic resonance spectroscopy of liquids, hyperpolarised
nanodiamonds as MRI contrast agents as well as the initialisation of nuclear
spin based diamond quantum simulators. Current realisations of DNP perform the
polarisation transfer by achieving energetic resonance between electrons and
nuclei via carefully tuned microwave fields or by using quasi-adiabatic
sweep-based schemes across resonance points. The former limits robustness
against control errors while the latter limits polarisation rates, making the
realisation of the applications extremely challenging. Here we introduce the
concept of Hamiltonian engineering by pulse sequences and use it for the
systematic design of polarisation sequences that are simultaneously robust and
fast. We derive sequences theoretically and demonstrate experimentally that
they are capable of efficient polarisation transfer from an optically polarised
nitrogen-vacancy centre in diamond to the surrounding $^{13}$C nuclear spin
bath even in the presence of control errors, making it an ideal tool for the
realisation of the above NV centre based applications.",1710.01508v2
2018-06-29,Proximity-induced topological transition and strain-induced charge transfer in graphene/MoS2 bilayer heterostructures,"Graphene/MoS2 heterostructures are formed by combining the nanosheets of
graphene and monolayer MoS2. The electronic features of both constituent
monolayers are rather well-preserved in the resultant heterostructure due to
the weak van der Waals interaction between the layers. However, the proximity
of MoS2 induces strong spin orbit coupling effect of strength ~1 meV in
graphene, which is nearly three orders of magnitude larger than the intrinsic
spin orbit coupling of pristine graphene. This opens a bandgap in graphene and
further causes anticrossings of the spin-nondegenerate bands near the Dirac
point. Lattice incommensurate graphene/MoS2 heterostructure exhibits
interesting moire' patterns which have been observed in experiments. The
electronic bandstructure of heterostructure is very sensitive to biaxial strain
and interlayer twist. Although the Dirac cone of graphene remains intact and no
charge-transfer between graphene and MoS2 layers occurs at ambient conditions,
a strain-induced charge-transfer can be realized in graphene/MoS2
heterostructure. Application of a gate voltage reveals the occurrence of a
topological phase transition in graphene/MoS2 heterostructure. In this chapter,
we discuss the crystal structure, interlayer effects, electronic structure,
spin states, and effects due to strain and substrate proximity on the
electronic properties of graphene/MoS2 heterostructure. We further present an
overview of the distinct topological quantum phases of graphene/MoS2
heterostructure and review the recent advancements in this field.",1806.11469v1
2021-01-29,Hyperpolarisation of external nuclear spins using nitrogen-vacancy centre ensembles,"The nitrogen-vacancy (NV) centre in diamond has emerged as a candidate to
non-invasively hyperpolarise nuclear spins in molecular systems to improve the
sensitivity of nuclear magnetic resonance (NMR) experiments. Several promising
proof of principle experiments have demonstrated small-scale polarisation
transfer from single NVs to hydrogen spins outside the diamond. However, the
scaling up of these results to the use of a dense NV ensemble, which is a
necessary prerequisite for achieving realistic NMR sensitivity enhancement, has
not yet been demonstrated. In this work, we present evidence for a polarising
interaction between a shallow NV ensemble and external nuclear targets over a
micrometre scale, and characterise the challenges in achieving useful
polarisation enhancement. In the most favourable example of the interaction
with hydrogen in a solid state target, a maximum polarisation transfer rate of
$\approx 7500$ spins per second per NV is measured, averaged over an area
containing order $10^6$ NVs. Reduced levels of polarisation efficiency are
found for liquid state targets, where molecular diffusion limits the transfer.
Through analysis via a theoretical model, we find that our results suggest
implementation of this technique for NMR sensitivity enhancement is feasible
following realistic diamond material improvements.",2101.12325v1
2021-07-26,Reservoir-engineering shortcuts to adiabaticity,"We propose a protocol that achieves fast adiabatic transfer between two
orthogonal states of a qubit by coupling with an ancilla. The qubit undergoes
Landau-Zener dynamics, whereas the coupling realizes a time-dependent
Hamiltonian, which is diagonal in the spin's instantaneous Landau-Zener
eigenstates. The ancilla (or meter), in turn, couples to a thermal bath, such
that the overall dynamics is incoherent. We analyse the protocol's fidelity as
a function of the strength of the coupling and of the relaxation rate of the
meter. When the meter's decay rate is the largest frequency scale of the
dynamics, the spin dynamics is encompassed by a master equation describing
dephasing of the spin in the instantaneous eigenbasis. In this regime the
fidelity of adiabatic transfer improves as the bath temperature is increased.
Surprisingly, the adiabatic transfer is significantly more efficient in the
opposite regime, where the time scale of the ancilla dynamics is comparable to
the characteristic spin time scale. Here, for low temperatures the coupling
with the ancilla tends to suppress diabatic transitions via effective cooling.
The protocol can be efficiently implemented by means of a pulsed, stroboscopic
coupling with the ancilla and is robust against moderate fluctuations of the
experimental parameters.",2107.12253v2
2021-08-11,Transverse Lambda production at the future Electron-Ion Collider,"We provide a comprehensive overview of transversely polarized $\Lambda$
production at the future Electron-Ion Collider (EIC). In particular, we study
both spontaneous transverse $\Lambda$ polarization as well as the transverse
spin transfer within the Transverse Momentum Dependent (TMD) factorization
region. To describe spontaneous $\Lambda$ polarization, we consider the
contribution from the TMD Polarizing Fragmentation Function (TMD PFF).
Similarly, we study the contribution of the transverse spin transfer
originating from the transversity TMD Fragmentation Function (TMD FF). We
provide projections for the statistical uncertainties in the corresponding spin
observables at the future EIC. Using these statistical uncertainties, we
characterize the role that the future EIC will play in constraining these
distributions. We perform an impact study in the semi-inclusive deep inelastic
scattering process for spontaneous $\Lambda$ polarization with a proton beam.
We find that the projected experimental data leads to a significant decrease in
the uncertainties for the $u$ and sea TMD PFFs. Furthermore, to access the
impact of the EIC on the transversity TMD FF, we perform the first extraction
of the transversity TMD FF from the recent COMPASS data. We compare the
statistical uncertainties of the future EIC with the theoretical uncertainties
from our extraction and find that the EIC could have a significant role in
constraining this distribution. Finally, we also provide projections for both
spontaneous $\Lambda$ polarization as well as the transverse spin transfer
inside the jets in back-to-back electron-jet production at the EIC.",2108.05383v2
2022-07-17,Rapid quantitative magnetization transfer imaging: utilizing the hybrid state and the generalized Bloch model,"Purpose: To explore efficient encoding schemes for quantitative magnetization
transfer (qMT) imaging with few constraints on model
  Theory and Methods: We combine two recently proposed models in a
Bloch-McConnell equation: the dynamics of the free spin pool are confined to
the hybrid state, and the dynamics of the semi-solid spin pool are described by
the generalized Bloch model. We numerically optimize the flip angles and
durations of a train of radio frequency pulses to enhance the encoding of three
qMT parameters while accounting for all 8 parameters of the 2-pool model. We
sparsely sample each time frame along this spin dynamics with a 3D radial
koosh-ball trajectory, reconstruct the data with subspace modeling, and fit the
qMT model with a neural network for computational efficiency.
  Results: We extracted qMT parameter maps of the whole brain with an effective
resolution of 1.24mm from a 12.6-minute scan. In lesions of multiple sclerosis
subjects, we observe a decreased size of the semi-solid spin pool and longer
relaxation times, consistent with previous
  Conclusion: The encoding power of the hybrid state, combined with regularized
image reconstruction, and the accuracy of the generalized Bloch model provide
an excellent basis for efficient quantitative magnetization transfer imaging
with few constraints on model parameters.",2207.08259v6
1997-06-05,The Symbiotic Neutron Star Binary GX 1+4/V2116 Ophiuchi,"We present multiwavelength observations of this S-type symbiotic LMXB which
consists of a 2-min X-ray pulsar accreting from an M6 III giant. This is the
only symbiotic system definitely known to contain a neutron star. The steady
interstellar extinction toward the binary (Av=5) contrasts the variable N_H
inferred from X-ray measurements, most likely evidence for a stellar wind. The
mass donor is probably near the tip of the first-ascent red giant branch, in
which case the system is 3-6 kpc distant and has an X-ray luminosity of 10^37
erg/s. It is also possible, though less likely, that the donor star is just
beginning its ascent of the asymptotic giant branch, in which case the system
is 12-15 kpc distant and has an X-ray luminosity of 10^38 erg/s. However, our
measured Av argues against such a large distance. We show that the dense (10^9
cm^-3) emission-line nebula enshrouding the binary is powered by UV radiation
from an accretion disk. The emission-line spectrum constrains the temperature
and inner radius of the disk (and thus the pulsar's magnetic field strength),
and we discuss this in the context of the accretion torque reversals observed
in the pulsar. We also show that the binary period must be >100 d and is most
likely >260 d, making GX 1+4 the only known LMXB with Porb>10 d. If the mass
donor fills its Roche lobe, the mass transfer must be highly super-Eddington,
requiring much mass loss from the binary. We discuss the alternative that the
disk forms from the slow, dense stellar wind expected from the red giant.",9706048v1
1998-08-13,Constraints on the Formation and Evolution of Circumstellar Disks in Rotating Magnetized Cloud Cores,"We use magnetic collapse models to place some constraints on the formation
and angular momentum evolution of circumstellar disks which are embedded in
magnetized cloud cores. Previous models have shown that the early evolution of
a magnetized cloud core is governed by ambipolar diffusion and magnetic
braking, and that the core takes the form of a nonequilibrium flattened
envelope which ultimately collapses dynamically to form a protostar. In this
paper, we focus on the inner centrifugally-supported disk, which is formed only
after a central protostar exists, and grows by dynamical accretion from the
flattened envelope. We estimate a centrifugal radius for the collapse of mass
shells within a rotating, magnetized cloud core. The centrifugal radius of the
inner disk is related to its mass through the two important parameters
characterizing the background medium: the background rotation rate $\Omb$ and
the background magnetic field strength $\Bref$. We also revisit the issue of
how rapidly mass is deposited onto the disk (the mass accretion rate) and use
several recent models to comment upon the likely outcome in magnetized cores.
Our model predicts that a significant centrifugal disk (much larger than a
stellar radius) will be present in the very early (Class 0) stage of
protostellar evolution. Additionally, we derive an upper limit for the disk
radius as it evolves due to internal torques, under the assumption that the
star-disk system conserves its mass and angular momentum even while most of the
mass is transferred to a central star.",9808140v1
1998-10-04,The Effect of Self-gravity of Gas on Gas Fueling in Barred Galaxies with a Supermassive Black Hole,"In our previous paper, we have shown that a gas disk in the nuclear region of
a barred galaxy which contains a central supermassive black hole (SMBH) rapidly
evolves into a nuclear gas ring by the effect of an additional inner Lindblad
resonance caused by the SMBH. In this paper, we investigate the fate of the gas
ring, involving self-gravity of gas, using two-dimensional hydrodynamical
simulations. We find that the gas ring becomes gravitationally unstable for a
gas surface density of gas above a critical value, and fragments into several
gas clumps. Some denser clumps increase their mass via the accretion of the
surrounding gas and collisions with other clumps, and finally a very massive
gas clump (10^7 M_sun) is formed. Due to the torque from the most massive
clump, a part of the gas in the ring loses its angular momentum and falls into
the galactic center. As a result, a nuclear gas disk (50 pc) is formed around
the SMBH. The accretion rate for $R<50$ pc attains about 1 M_sun/yr for
3.5*10^7 yr. At the final phase of the bar-driven fueling, self-gravity is
crucial for the angular momentum transfer of the gas. This is a new mechanism
for gas fueling to the vicinity of the SMBH.",9810052v1
2001-09-16,Numerical Simulation of Interaction between an L1 Stream and an Accretion Disk in a Close Binary System,"The hydrodynamic behavior of an accretion disk in a close binary system is
numerically simulated. Calculation is made for a region including the compact
star and the gas-supplying companion. The equation of state is that of an ideal
gas characterized by the specific heat ratio $\gamma$. Two cases with $\gamma$
of 1.01 and 1.2 are studied. Our calculations show that the gas, flowing from
the companion via a Lagrangian L1 point towards the accretion disk, forms a
fine gas beam (L1 stream), which penetrates into the disk. No hot spot
therefore forms in these calculations. Another fact discovered is that the gas
rotating with the disk forms, on collision with the L1 stream, a bow shock
wave, which may be called an L1 shock. The disk becomes hot because the L1
shock heats the disk gas in the outer parts of the disk, so that the spiral
shocks wind loosely even with $\gamma=1.01$. The L1 shock enhances the
non-axisymmetry of the density distribution in the disk, and therefore the
angular momentum transfer by the tidal torque works more effectively. The
maximum of the effective $\alpha$ becomes $\sim 0.3$. The 'hot spot' is not
formed in our simulations, but our results suggest the formation of the 'hot
line', which is the L1 shock elongated along the penetrating L1 stream.",0109238v1
2002-06-17,Gas accretion on spiral galaxies: bar formation and renewal,"The effects of gas accretion on spiral disk dynamics and stability are
studied through N-body simulations, including star formation and gas/stars mass
exchange. The detailed processes of bar formation, bar destruction and bar
re-formation are followed, while in the same time the disk to bulge ratio is
varying. The accreted gas might be first prevented to flow inwards to the
center by the bar gravity torques, which maintains it to the outer Lindblad
resonance. While the first bar is weakening, the accreted gas replenishes the
disk, increasing the disk-to-bulge ratio, and the disk self-gravity. A second
bar is then unstable, with a higher pattern speed, due both to the increased
mass, and shorter bar length. Three or four bar episodes have been followed
over a Hubble time. Their strength is decreasing with time, while their pattern
speed is increasing. Detailed balance of the angular momentum transfer and
evolution can account for these processes. The gas recycled through star
formation, and rejected through stellar mass loss plays also a role in the disk
dynamics. Implications on the spiral galaxy dynamics and evolution along the
Hubble sequence, and as a function of redshift are discussed.",0206273v1
2002-08-08,Orbital migration and the frequency of giant planet formation,"We present a statistical study of the post-formation migration of giant
planets in a range of initial disk conditions. For given initial conditions we
model the evolution of giant planet orbits under the influence of disk,
stellar, and mass loss torques. We determine the mass and semi-major axis
distribution of surviving planets after disk dissipation, for various disk
masses, lifetimes, viscosities, and initial planet masses. The majority of
planets migrate too fast and are destroyed via mass transfer onto the central
star. Most surviving planets have relatively large orbital semi-major axes of
several AU or larger. We conclude that the extrasolar planets observed to date,
particularly those with small semi-major axes, represent only a small fraction
(~25% to 33%) of a larger cohort of giant planets around solar-type stars, and
many undetected giant planets must exist at large (>1-2 AU) distances from
their parent stars. As sensitivity and completion of the observed sample
increases with time, this distant majority population of giant planets should
be revealed. We find that the current distribution of extrasolar giant planet
masses implies that high mass (more than 1-2 Jupiter masses) giant planet
formation must be relatively rare. Finally, our simulations imply that the
efficiency of giant planet formation must be high: at least 10% and perhaps as
many as 80% of solar-type stars possess giant planets during their pre-main
sequence phase. These predictions, including those for pre-main sequence stars,
are testable with the next generation of ground- and space-based planet
detection techniques",0208184v1
2003-07-16,V803 Centauri: Helium Dwarf Nova Mimicking a WZ Sge-Type Superoutburst,"We observed long-term behavior of the helium dwarf nova V803 Cen, and
clarified the existence of at least two distinct states (state with 77-d
supercycles and standstill-like state) which interchangeably appeared with a
time-scale of 1--2 yr. We also conducted a time-resolved CCD photometry
campaign during the bright outburst in 2003 June. The overall appearance of the
outburst closely resemble that of the late stage of the 2001 outburst of WZ
Sge, consisting of the initial peak stage (superoutburst plateau), the dip, and
the oscillating (rebrightening) states. During the initial peak stage, we
detected large-amplitude superhump-type variation with a period of 0.018686(4)
d = 1614.5(4) s, and during the oscillation stage, we detected variations with
a period of 0.018728(2) d = 1618.1(2) s. We consider that the former period
better represents the superhump period of this system, and the latter
periodicity may be better interpreted as arising from late superhumps. The
overall picture of the V803 Cen outburst resembles that of a WZ Sge-type
outburst, but apparently with a higher mass-transfer rate than in hydrogen-rich
WZ Sge-type stars. We suggest that this behavior may be either the result of
difficulty in maintaining the hot state in a helium disk, or the effect of an
extremely low tidal torque resulting from the extreme mass ratio.",0307308v2
2004-07-20,Dwarf elliptical galaxies with kinematically decoupled cores,"{We present, for the first time, photometric and kinematical evidence,
obtained with FORS2 on the VLT, for the existence of kinematically decoupled
cores (KDCs) in two dwarf elliptical galaxies; FS76 in the NGC5044 group and
FS373 in the NGC3258 group. Both kinematically peculiar subcomponents rotate in
the same sense as the main body of their host galaxy but betray their presence
by a pronounced bump in the rotation velocity profiles at a radius of about 1"".
The KDC in FS76 rotates at 10+/-3km/s, with the host galaxy rotating at
15+/-6km/s; the KDC in FS373 has a rotation velocity of 6+/-2km/s while the
galaxy itself rotates at 20+/-5km/s. FS373 has a very complex rotation velocity
profile with the velocity changing sign at 1.5 R_e. The velocity and velocity
dispersion profiles of FS76 are asymmetric at larger radii. This could be
caused by a past gravitational interaction with the giant elliptical NGC5044,
which is at a projected distance of 50kpc. We argue that these decoupled cores
are most likely not produced by mergers in a group or cluster environment
because of the prohibitively large relative velocities. A plausible alternative
is offered by flyby interactions between a dwarf elliptical or its disky
progenitor and a massive galaxy. The tidal forces during an interaction at the
relative velocities and impact parameters typical for a group environment exert
a torque on the dwarf galaxy that, according to analytical estimates, transfers
enough angular momentum to its stellar envelope to explain the observed
peculiar kinematics.",0407425v1
2005-06-26,Bars and Cold Dark Matter Halos,"The central part of a dark matter halo reacts to the presence and evolution
of a bar. Not only does the halo absorb angular momentum from the disk, it can
also be compressed and have its shape modified. We study these issues in a
series of cosmologically motivated, highly resolved N-body simulations of
barred galaxies run under different initial conditions. In all models we find
that the inner halo's central density increases. We model this density increase
using the standard adiabatic approximation and the modified formula by Gnedin
et al. and find that halo mass profiles are better reproduced by this latter.
In models with a strong bar, the dark matter in the central region forms a
bar-like structure (``dark matter bar''), which rotates together with the
normal bar formed by the stellar component (``stellar bar''). The
minor-to-major axial ratio of a halo bar changes with radius with a typical
value 0.7 in the central disk region. DM bar amplitude is mostly a function of
the stellar bar strength. Models in which the bar amplitude increases or stays
roughly constant with time, initially large (40%-60%) misalignment between the
halo and disk bars quickly decreases with time as the bar grows. The halo bar
is nearly aligned with the stellar bar (~10 degrees lag for the halo) after ~2
Gyr. The torque, which the halo bar exerts on the stellar bar, can serve as a
mechanism to regulate the angular momentum transfer from the disk to the halo.",0506627v3
2005-10-21,On the origin of warps and the role of the intergalactic medium,"In this paper we consider the viability of these non-gravitational torques to
take the gas off the plane. We show that magnetically generated warps are
clearly flawed because they would wrap up into a spiral in less than two or
three galactic rotations. The inclusion of any magnetic diffusivity to dilute
the wrapping effect, causes the amplitude of the warp to damp. We also consider
observational consequences of the accretion of an intergalactic plane-parallel
flow at infinity. We have computed the amplitude and warp asymmetry in the
accretion model, for a disc embedded in a flattened dark matter halo, including
self-consistently the contribution of the modes with azimuthal wavenumbers m=0
and m=1. This model predicts quite asymmetric warps, maximum gas displacements
on the two sides in the ratio 3:2 for the preferred Galactic parameters,and the
presence of a fraction ~3.5% of U-shaped warps, at least. The azimuthal
dependence of the moment transfer by the ram pressure would produce a strong
asymmetry in the thickness of the HI layer and asymmetric density distributions
in z, in conflict with observational data for the warp in our Galaxy and in
external galaxies. The amount of accretion that is required to explain the
Galactic warp would give gas scaleheights in the far outer disc that are too
small. We conclude that accretion of a flow with no net angular momentum,
cannot be the main and only cause of warps.",0510648v1
2006-06-29,Radio and X-ray Properties of Relativistic Beaming Models for Ultra-Luminous X-ray Sources,"We calculate the broadband radio--X-ray spectra predicted by microblazar and
microquasar models for Ultra-Luminous X-ray sources (ULXs), exploring the
possibility that their dominant power-law component is produced by a
relativistic jet, even at near-Eddington mass accretion rates. We do this by
first constructing a generalized disk--jet theoretical framework in which some
fraction of the total accretion power Pa is efficiently removed from the
accretion disk by a magnetic torque responsible for jet formation. Thus, for
different black hole masses, mass accretion rates and magnetic coupling
strength, we self-consistently calculate the relative importance of the
modified disk spectrum, as well as the overall jet emission due to synchrotron
and Compton processes. In general, transferring accretion power to a jet makes
the disk fainter and cooler than a standard disk at the same mass accretion
rate; this may explain why the soft spectral component appears less prominent
than the dominant power-law component in most bright ULXs. We show that the
apparent X-ray luminosity and spectrum predicted by the microquasar model are
consistent with the observed properties of most ULXs. We predict that the radio
synchrotron jet emission is too faint to be detected at the typical threshold
of radio surveys to date. This is consistent with the high rate of
non-detections over detections in radio counterpart searches. Conversely, we
conclude that the observed radio emission found associated with a few ULXs
cannot be due to beamed synchrotron emission from a relativistic jet.",0606707v1
2006-09-05,Evolution of black-hole intermediate-mass X-ray binaries: the influence of a circumbinary disc,"Justham, Rappaport & Podsiadlowski (2006) recently suggested that black-hole
low-mass X-ray binaries (BHLMXBs) with short orbital periods may have evolved
from black-hole intermediate-mass X-ray binaries (BHIMXBs). In their model the
secondaries in BHIMXBs are assumed to possess anomalously high magnetic fields,
so that magnetic braking can lead to substantial loss of angular momentum. In
this paper we propose an alternative mechanism for orbital angular momentum
loss in BHIMXBs. We assume that a small fraction $\delta$ of the transferred
mass from the donor star form a circumbinary disc surrounding the binary
system. The tidal torques exerted by the disc can effectively drain orbital
angular momentum from the binary. We have numerically calculated the
evolutionary sequences of BHIMXBs, to examine the influence of the circumbinary
disc on the binary evolution. Our results indicate when $\delta\la 0.01-0.1$
(depending on the initial orbital periods), the circumbinary disc can cause
secular orbital shrinking, leading to the formation of compact
  BHLMXBs, otherwise the orbits always expand during the evolution. This
scenario also suggests the possible existence of luminous, persistent BHLMXBs,
but it suffers the same problem as in Justham, Rappaport & Podsiadlowski (2006)
that, the predicted effective temperatures of the donor stars are significantly
higher than those of the observed donor stars in BHLMXBs.",0609093v1
2007-10-15,Bulges versus disks: the evolution of angular momentum in cosmological simulations of galaxy formation,"We investigate the evolution of angular momentum in simulations of galaxy
formation in a cold dark matter universe. We analyse two model galaxies
generated in the N-body/hydrodynamic simulations of Okamoto et al. Starting
from identical initial conditions, but using different assumptions for the
baryonic physics, one of the simulations produced a bulge-dominated galaxy and
the other one a disc-dominated galaxy. The main difference is the treatment of
star formation and feedback, both of which were designed to be more efficient
in the disc-dominated object. We find that the specific angular momentum of the
disc-dominated galaxy tracks the evolution of the angular momentum of the dark
matter halo very closely: the angular momentum grows as predicted by linear
theory until the epoch of maximum expansion and remains constant thereafter. By
contrast, the evolution of the angular momentum of the bulge-dominated galaxy
resembles that of the central, most bound halo material: it also grows at first
according to linear theory, but 90% of it is rapidly lost as pre-galactic
fragments, into which gas had cooled efficiently, merge, transferring their
orbital angular momentum to the outer halo by tidal effects. The disc-dominated
galaxy avoids this fate because the strong feedback reheats the gas which
accumulates in an extended hot reservoir and only begins to cool once the
merging activity has subsided. Our analysis lends strong support to the
classical theory of disc formation whereby tidally torqued gas is accreted into
the centre of the halo conserving its angular momentum.",0710.2901v2
2008-01-10,Mixing in the Solar Nebula: Implications for Isotopic Heterogeneity and Large-Scale Transport of Refractory Grains,"The discovery of refractory grains amongst the particles collected from Comet
81P/Wild 2 by the Stardust spacecraft (Brownlee et al. 2006) provides the
ground truth for large-scale transport of materials formed in high temperature
regions close to the protosun outward to the comet-forming regions of the solar
nebula. While accretion disk models driven by a generic turbulent viscosity
have been invoked as a means to explain such large-scale transport, the
detailed physics behind such an ``alpha'' viscosity remains unclear. We present
here an alternative physical mechanism for large-scale transport in the solar
nebula: gravitational torques associated with the transient spiral arms in a
marginally gravitationally unstable disk, of the type that appears to be
necessary to form gas giant planets. Three dimensional models are presented of
the time evolution of self-gravitating disks, including radiative transfer and
detailed equations of state, showing that small dust grains will be transported
upstream and downstream (with respect to the mean inward flow of gas and dust
being accreted by the central protostar) inside the disk on time scales of less
than 1000 yr inside 10 AU. These models furthermore show that any initial
spatial heterogeneities present (e.g., in short-lived isotopes such as 26Al)
will be homogenized by disk mixing down to a level of ~10%, preserving the use
of short-lived isotopes as accurate nebular chronometers, while simultaneously
allowing for the spread of stable oxygen isotope ratios. This finite level of
nebular spatial heterogeneity appears to be related to the coarse mixing
achieved by spiral arms, with radial widths of order 1 AU, over time scales of
~1000 yrs.",0801.1622v1
2009-04-15,Can angular momentum loss cause the period change of NN Ser?,"NN Ser is a non mass-transferring pre-cataclysmic variable containing a white
dwarf with a mass of $\sim 0.5 M_{\odot}$ and an M dwarf secondary star with a
mass of $\sim 0.2 M_{\odot}$. Based on the data detected by the high-speed CCD
camera ULTRACAM, it was observed that the orbital period of NN Ser is
decreasing, which may be caused by a genuine angular momentum loss or the
presence of a third body. However, neither gravitational radiation and magnetic
braking can ideally account for the period change of NN Ser. In this Letter, we
attempt to examine a feasible mechanism which can drain the angular momentum
from NN Ser. We propose that a fossil circumbinary disk (CB disk) around the
binary may have been established at the end of the common envelope phase, and
the tidal torques caused by the gravitational interaction between the disk and
the binary can efficiently extract the orbital angular momentum from the
system. We find that only if M dwarf has an ultra-high wind loss rates of $\sim
10^{-10} M_{\odot} \rm yr^{-1}$, and a large fraction ($\delta\sim 10 %$) of
wind loss is fed into the CB disk, the loss rates of angular momentum via the
CB disk can interpret the period change observed in NN Ser. Such a wind loss
rate and $\delta$-value seem to be incredible. Hence it seems that the presence
of a third body in a long orbit around the binary might account for the
changing period of NN Ser.",0904.2319v1
2009-09-09,"Radiatively heated, protoplanetary discs with dead zones. I. Dust settling and thermal structure of discs around M stars","The irradiation of protoplanetary discs by central stars is the main heating
mechanism for discs, resulting in their flared geometric structure. In a series
of papers, we investigate the deep links between 2D self-consistent disc
structure and planetary migration in irradiated discs, focusing particularly on
those around M stars. In this first paper, we analyse the thermal structure of
discs that are irradiated by an M star by solving the radiative transfer
equation by means of a Monte Carlo code. Our simulations of irradiated
hydrostatic discs are realistic and self-consistent in that they include dust
settling with multiple grain sizes (N=15), the gravitational force of an
embedded planet on the disc, and the presence of a dead zone (a region with
very low levels of turbulence) within it. We show that dust settling drives the
temperature of the mid-plane from an $r^{-3/5}$ distribution (well mixed dust
models) toward an $r^{-3/4}$. The dead zone, meanwhile, leaves a dusty wall at
its outer edge because dust settling in this region is enhanced compared to the
active turbulent disc at larger disc radii. The disc heating produced by this
irradiated wall provides a positive gradient region of the temperature in the
dead zone in front of the wall. This is crucially important for slowing
planetary migration because Lindblad torques are inversely proportional to the
disc temperature. Furthermore, we show that low turbulence of the dead zone is
self-consistently induced by dust settling, resulting in the Kelvin-Helmholtz
instability (KHI). We show that the strength of turbulence arising from the KHI
in the dead zone is $\alpha=10^{-5}$.",0909.1734v1
2010-07-09,Driving quantized vortices with quantum vacuum fluctuations,"We propose to use a rotating corrugated material plate in order to stir,
through the Casimir-Polder interaction, quantized vortices in an harmonically
trapped Bose-Einstein condensate. The emergence of such vortices within the
condensate cannot be explained with a computation of the Casimir-Polder
potential based on the pairwise summation approach or on the proximity force
approximation. It thus appears as a genuine signature of non-trivial geometry
effects on the electromagnetic vacuum fluctuations, which fully exploits the
superfluid nature of the sample. In order to discuss quantitatively the
generation of Casimir-driven vortices, we derive an exact non-perturbative
theory of the Casimir-Polder potential felt by the atoms in front of the
grating. Our numerical results for a Rb condensate close to a Si grating show
that the resulting quantum vacuum torque is strong enough to provide a
contactless transfer of angular momentum to the condensate and generate
quantized vortices under realistic experimental conditions at separation
distances around $3$ microns.",1007.1657v3
2011-03-17,Migration of protoplanets with surfaces through discs with steep temperature gradients,"We perform three-dimensional self-gravitating radiative transfer simulations
of protoplanet migration in circumstellar discs to explore the impact upon
migration of the radial temperature profiles in these discs. We model
protoplanets with masses ranging between 10-100 M\bigoplus, in discs with
surface density profiles of {\Sigma} \varpropto r^-1/2, and temperature
profiles of the form T \varpropto r^-{\beta}, where {\beta} ranges 0-2. We find
that steep ({\beta} > 1) temperature profiles lead to outward migration of low
mass protoplanets in interstellar grain opacity discs, but in more optically
thin discs the migration is always inwards. The trend in migration rates with
changing {\beta} obtained from our models shows good agreement with those
obtained using recent analytic descriptions which include consideration of the
co-orbital torques and their saturation. We find that switching between two
models of the protoplanet, one in which accretion acts by evacuating gas and
one in which gas piles up on a surface to form an atmosphere, leads to a small
shift in the migration rates. If comparing these models in discs with
conditions which lead to a marginally inward migration, the small shift can
lead to outward migration. However, the direction and speed of migration is
dominated by disc conditions rather than by the specific prescription used to
model the flow near the protoplanet.",1103.3502v1
2012-09-05,White Dwarf/M Dwarf Binaries as Single Degenerate Progenitors of Type Ia Supernovae,"Limits on the companions of white dwarfs in the single degenerate scenario
for the origin of Type Ia supernovae (SNIa) have gotten increasingly tight. The
only type of non-degenerate stars that survive the limits on the companions of
SNIa in SNR 0509-67.5 and SN1572 are M dwarfs. M dwarfs have special properties
that have not been considered in most work on the progenitors of SNIa: they
have small but finite magnetic fields, and they flare frequently. These
properties are explored in the context of SNIa progenitors. White dwarf/M dwarf
pairs may be sufficiently plentiful to provide an adequate rate of explosions.
Even modest magnetic fields on the white dwarf and M dwarf will yield adequate
torques to lock the two stars together, resulting in a slowly rotating white
dwarf, with the magnetic poles pointing at one another in the orbital plane.
The mass loss will be channeled by a ""magnetic bottle"" connecting the two
stars, landing on a concentrated polar area on the white dwarf. This enhances
the effective rate of accretion compared to spherical accretion. Luminosity
from accretion and hydrogen burning on the surface of the white dwarf may
induce self-excited mass transfer. The combined effects of self-excited mass
loss, polar accretion, and magnetic inhibition of mixing of accretion layers
give possible means to beat the ""nova limit"" and grow the white dwarf to the
Chandrasekhar mass even at rather moderate mass accretion rates.",1209.1021v2
2014-12-26,GCM simulations of Titan's middle and lower atmosphere and comparison to observations,"Simulation results are presented from a new general circulation model (GCM)
of Titan, the Titan Atmospheric Model (TAM), which couples the Flexible
Modeling System (FMS) spectral dynamical core to a suite of
external/sub-grid-scale physics. These include a new non-gray radiative
transfer module that takes advantage of recent data from Cassini-Huygens,
large-scale condensation and quasi-equilibrium moist convection schemes, a
surface model with ""bucket"" hydrology, and boundary layer turbulent diffusion.
The model produces a realistic temperature structure from the surface to the
lower mesosphere, including a stratopause, as well as satisfactory
superrotation. The latter is shown to depend on the dynamical core's ability to
build up angular momentum from surface torques. Simulated latitudinal
temperature contrasts are adequate, compared to observations, and polar
temperature anomalies agree with observations. In the lower atmosphere, the
insolation distribution is shown to strongly impact turbulent fluxes, and
surface heating is maximum at mid-latitudes. Surface liquids are unstable at
mid- and low-latitudes, and quickly migrate poleward. The simulated humidity
profile and distribution of surface temperatures, compared to observations,
corroborate the prevalence of dry conditions at low latitudes. Polar cloud
activity is well represented, though the observed mid-latitude clouds remain
somewhat puzzling, and some formation alternatives are suggested.",1412.7995v1
2015-11-02,Orbital period decay of compact black hole x-ray binaries: the influence of circumbinary disks?,"Recently, compact black hole X-ray binaries XTE J 1118+480 and A0620-00 have
been reported to be experiencing a fast orbital period decay, which is two
orders of magnitude higher than expected with gravitational wave radiation.
Magnetic braking of an Ap/Bp star has been suggested to account for the period
change when the surface magnetic field of the companion star $B_{\rm s}\ga
10^{4}$ G. However, our calculation indicates that anomalous magnetic braking
cannot significantly contribute to the large orbital period decay rates
observed in these two sources even if $B_{\rm s}\ga 10^{4}$ G. Observations
have provided evidence that circumbinary disks around two compact black hole
X-ray binaries may exist. Our analysis shows that, for some reasonable
parameters, tidal torque between the circumbinary disk and the binary can
efficiently extract the orbital angular momentum from the binary, and result in
a large orbital period change rate. Based on the circumbinary disk model, we
simulate the evolution of XTE J 1118+480 via a stellar evolution code. Our
computations are approximatively in agreement with the observed data (the
masses of two components, donor star radius, orbital period, and orbital period
derivative). The mass transfer rate and circumbinary disk mass are obviously
far greater than the inferred values from observations. Therefore, it seems
that the circumbinary disk is unlikely to be the main cause of the rapid
orbital decay observed in some compact black hole X-ray binaries.",1511.00534v1
2016-03-01,On the origins of polarization holes in Bok globules,"Context. Polarimetric observations of Bok globules frequently show a decrease
in the degree of polarization towards their central dense regions (polarization
holes). This behaviour is usually explained with increased disalignment owing
to high density and temperature, or insufficient angular resolution of a
possibly complex magnetic field structure.
  Aims. We investigate whether a significant decrease in polarized emission of
dense regions in Bok globules is possible under certain physical conditions.
For instance, we evaluate the impact of optical depth effects and various
properties of the dust phase.
  Methods. We use radiative transfer modelling to calculate the temperature
structure of an analytical Bok globule model and simulate the polarized thermal
emission of elongated dust grains. For the alignment of the dust grains, we
consider a magnetic field and include radiative torque and internal alignment.
  Results. Besides the usual explanations, selected conditions of the
temperature and density distribution, the dust phase and the magnetic field are
also able to significantly decrease the polarized emission of dense regions in
Bok globules. Taking submm/mm grains and typical column densities of existing
Bok globules into consideration, the optical depth is high enough to decrease
the degree of polarization by up to {\Delta}P~10%. If limited to the densest
regions, dust grain growth to submm/mm size and accumulated graphite grains
decrease the degree of polarization by up to {\Delta}P~10% and {\Delta}P~5%,
respectively. However, the effect of the graphite grains occurs only if they do
not align with the magnetic field.",1603.00270v2
2016-09-27,On the energy dissipation rate at the inner edge of circumbinary discs,"We study, by means of numerical simulations and analysis, the details of the
accretion process from a disc onto a binary system. We show that energy is
dissipated at the edge of a circumbinary disc and this is associated with the
tidal torque that maintains the cavity: angular momentum is transferred from
the binary to the disc through the action of compressional shocks and viscous
friction. These shocks can be viewed as being produced by fluid elements which
drift into the cavity and, before being accreted, are accelerated onto
trajectories that send them back to impact the disc. The rate of energy
dissipation is approximately equal to the product of potential energy per unit
mass at the disc's inner edge and the accretion rate, estimated from the disc
parameters just beyond the cavity edge, that would occur without the binary.
For very thin discs, the actual accretion rate onto the binary may be
significantly less. We calculate the energy emitted by a circumbinary disc
taking into account energy dissipation at the inner edge and also irradiation
arising there from reprocessing of light from the stars. We find that, for
tight PMS binaries, the SED is dominated by emission from the inner edge at
wavelengths between 1-4 and 10 $\mu$m. This may apply to systems like CoRoT
223992193 and V1481 Ori.",1609.08465v1
2017-01-05,The angular momentum of cosmological coronae and the inside-out growth of spiral galaxies,"Massive and diffuse haloes of hot gas (coronae) are important intermediaries
between cosmology and galaxy evolution, storing mass and angular momentum
acquired from the cosmic web until eventual accretion on to star-forming discs.
We introduce a method to reconstruct the rotation of a galactic corona, based
on its angular momentum distribution (AMD). This allows us to investigate in
what conditions the angular momentum acquired from tidal torques can be
transferred to star forming discs and explain observed galaxy-scale processes,
such as inside-out growth and the build-up of abundance gradients. We find that
a simple model of an isothermal corona with a temperature slightly smaller than
virial and a cosmologically motivated AMD is in good agreement with galaxy
evolution requirements, supporting hot-mode accretion as a viable driver for
the evolution of spiral galaxies in a cosmological context. We predict
moderately sub-centrifugal rotation close to the disc and slow rotation close
to the virial radius. Motivated by the observation that the Milky Way has a
relatively hot corona (T ~ 2 x 10^6 K), we also explore models with a
temperature larger than virial. To be able to drive inside-out growth, these
models must be significantly affected by feedback, either mechanical (ejection
of low angular momentum material) or thermal (heating of the central regions).
However, the agreement with galaxy evolution constraints becomes, in these
cases, only marginal, suggesting that our first and simpler model may apply to
a larger fraction of galaxy evolution history.",1701.01442v2
2017-05-12,Multiple Disk Gaps and Rings Generated by a Single Super-Earth,"We investigate the observational signatures of super-Earths (i.e.,
Earth-to-Neptune mass planets) in their natal disks of gas and dust. Combining
two-fluid global hydrodynamics simulations with a radiative transfer code, we
calculate the distributions of gas and of sub-mm-sized dust in a disk perturbed
by a super-Earth, synthesizing images in near-infrared scattered light and the
mm-wave thermal continuum for direct comparison with observations. In low
viscosity gas ($\alpha\lesssim10^{-4}$), a super-Earth opens two annular gaps
to either side of its orbit by the action of Lindblad torques. This double gap
and its associated gas pressure gradients cause dust particles to be dragged by
gas into three rings: one ring sandwiched between the two gaps, and two rings
located at the gap edges farthest from the planet. Depending on system
parameters, additional rings may manifest for a single planet. A double gap
located at tens of AUs from a host star in Taurus can be detected in the dust
continuum by the Atacama Large Millimeter Array (ALMA) at an angular resolution
of ~0"".03 after two hours of integration. Ring and gap features persist in a
variety of background disk profiles, last for thousands of orbits, and change
their relative positions and dimensions depending on the speed and direction of
planet migration. Candidate double gaps have been observed by ALMA in systems
like HL Tau (D5 and D6) and TW Hya (at 37 and 43 AU); we submit that each
double gap is carved by one super-Earth in nearly inviscid gas.",1705.04687v2
2017-08-05,The chemistry of protoplanetary fragments formed via gravitational instabilities,"In this paper, we model the chemical evolution of a 0.25 M$_{\odot}$
protoplanetary disc surrounding a 1 M$_{\odot}$ star that undergoes
fragmentation due to self-gravity. We use Smoothed Particle Hydrodynamics
including a radiative transfer scheme, along with time-dependent chemical
evolution code to follow the composition of the disc and resulting fragments
over approximately 4000 yrs. Initially, four quasi-stable fragments are formed,
of which two are eventually disrupted by tidal torques in the disc. From the
results of our chemical modelling, we identify species that are abundant in the
fragments (e.g. H$_{\rm 2}$O, H$_{\rm 2}$S, HNO, N$_{\rm 2}$, NH$_{\rm 3}$,
OCS, SO), species that are abundant in the spiral shocks within the disc (e.g.
CO, CH$_{\rm 4}$, CN, CS, H$_{\rm 2}$CO), and species which are abundant in the
circumfragmentary material (e.g. HCO$^{\rm +}$). Our models suggest that in
some fragments it is plausible for grains to sediment to the core before
releasing their volatiles into the planetary envelope, leading to changes in,
e.g., the C/O ratio of the gas and ice components. We would therefore predict
that the atmospheric composition of planets generated by gravitational
instability should not necessarily follow the bulk chemical composition of the
local disc material.",1708.01815v1
2017-10-30,Turbulence strength in ultimate Taylor-Couette turbulence,"We provide experimental measurements for the effective scaling of the
Taylor-Reynolds number within the bulk $\text{Re}_{\lambda,\text{bulk}}$, based
on local flow quantities as a function of the driving strength (expressed as
the Taylor number Ta), in the ultimate regime of Taylor-Couette flow. The data
are obtained through flow velocity field measurements using Particle Image
Velocimetry (PIV). We estimate the value of the local dissipation rate
$\epsilon(r)$ using the scaling of the second order velocity structure
functions in the longitudinal and transverse direction within the inertial
range---without invoking Taylor's hypothesis. We find an effective scaling of
$\epsilon_{\text{bulk}} /(\nu^{3}d^{-4})\sim \text{Ta}^{1.40}$, (corresponding
to $\text{Nu}_{\omega,\text{bulk}} \sim \text{Ta}^{0.40}$ for the dimensionless
local angular velocity transfer), which is nearly the same as for the global
energy dissipation rate obtained from both torque measurements
($\text{Nu}_{\omega} \sim \text{Ta}^{0.40}$) and Direct Numerical Simulations
($\text{Nu}_{\omega} \sim \text{Ta}^{0.38}$). The resulting Kolmogorov length
scale is then found to scale as $\eta_{\text{bulk}}/d \sim \text{Ta}^{-0.35}$
and the turbulence intensity as $I_{\theta,\text{bulk}} \sim
\text{Ta}^{-0.061}$. With both the local dissipation rate and the local
fluctuations available we finally find that the Taylor-Reynolds number
effectively scales as Re$_{\lambda,\text{bulk}}\sim \text{Ta}^{0.18}$ in the
present parameter regime of $4.0 \times 10^8 < \text{Ta} < 9.0 \times 10^{10}$.",1710.11050v1
2018-05-09,Real-World Evolution Adapts Robot Morphology and Control to Hardware Limitations,"For robots to handle the numerous factors that can affect them in the real
world, they must adapt to changes and unexpected events. Evolutionary robotics
tries to solve some of these issues by automatically optimizing a robot for a
specific environment. Most of the research in this field, however, uses
simplified representations of the robotic system in software simulations. The
large gap between performance in simulation and the real world makes it
challenging to transfer the resulting robots to the real world. In this paper,
we apply real world multi-objective evolutionary optimization to optimize both
control and morphology of a four-legged mammal-inspired robot. We change the
supply voltage of the system, reducing the available torque and speed of all
joints, and study how this affects both the fitness, as well as the morphology
and control of the solutions. In addition to demonstrating that this real-world
evolutionary scheme for morphology and control is indeed feasible with
relatively few evaluations, we show that evolution under the different hardware
limitations results in comparable performance for low and moderate speeds, and
that the search achieves this by adapting both the control and the morphology
of the robot.",1805.03388v1
2018-09-12,Frequency-Aware Model Predictive Control,"Transferring solutions found by trajectory optimization to robotic hardware
remains a challenging task. When the optimization fully exploits the provided
model to perform dynamic tasks, the presence of unmodeled dynamics renders the
motion infeasible on the real system. Model errors can be a result of model
simplifications, but also naturally arise when deploying the robot in
unstructured and nondeterministic environments. Predominantly, compliant
contacts and actuator dynamics lead to bandwidth limitations. While classical
control methods provide tools to synthesize controllers that are robust to a
class of model errors, such a notion is missing in modern trajectory
optimization, which is solved in the time domain. We propose frequency-shaped
cost functions to achieve robust solutions in the context of optimal control
for legged robots. Through simulation and hardware experiments we show that
motion plans can be made compatible with bandwidth limits set by actuators and
contact dynamics. The smoothness of the model predictive solutions can be
continuously tuned without compromising the feasibility of the problem.
Experiments with the quadrupedal robot ANYmal, which is driven by
highly-compliant series elastic actuators, showed significantly improved
tracking performance of the planned motion, torque, and force trajectories and
enabled the machine to walk robustly on terrain with unmodeled compliance.",1809.04539v2
2018-10-15,Robust Learning of Tactile Force Estimation through Robot Interaction,"Current methods for estimating force from tactile sensor signals are either
inaccurate analytic models or task-specific learned models. In this paper, we
explore learning a robust model that maps tactile sensor signals to force. We
specifically explore learning a mapping for the SynTouch BioTac sensor via
neural networks. We propose a voxelized input feature layer for spatial signals
and leverage information about the sensor surface to regularize the loss
function. To learn a robust tactile force model that transfers across tasks, we
generate ground truth data from three different sources: (1) the BioTac rigidly
mounted to a force torque~(FT) sensor, (2) a robot interacting with a ball
rigidly attached to the same FT sensor, and (3) through force inference on a
planar pushing task by formalizing the mechanics as a system of particles and
optimizing over the object motion. A total of 140k samples were collected from
the three sources. We achieve a median angular accuracy of 3.5 degrees in
predicting force direction (66% improvement over the current state of the art)
and a median magnitude accuracy of 0.06 N (93% improvement) on a test dataset.
Additionally, we evaluate the learned force model in a force feedback grasp
controller performing object lifting and gentle placement. Our results can be
found on https://sites.google.com/view/tactile-force.",1810.06187v4
2019-07-25,Indirect evidence of significant grain growth in young protostellar envelopes from polarized dust emission,"How and when in the star formation sequence do dust grains start to grow into
pebbles is a cornerstone question to both star and planet formation. We compute
the polarized radiative transfer from a model solar-type protostellar core,
using the POLARIS code, aligning the dust grains with the local magnetic field,
following the radiative torques (RATs) theory. We test the dependency of the
resulting dust polarized emission with the maximum grain size of the dust size
distribution at the envelope scale, from amax = 1 micron to 50 micron. Our work
shows that, in the framework of RAT alignment, large dust grains are required
to produce polarized dust emission at levels similar to those currently
observed in solar-type protostellar envelopes at millimeter wavelengths.
Considering the current theoretical dificulties to align a large fraction of
small ISM-like grains in the conditions typical of protostellar envelopes, our
results suggest that grain growth (typically > 10 micron) might have already
significantly progressed at scales 100-1000 au in the youngest objects,
observed less than 10^5 years after the onset of collapse. Observations of dust
polarized emission might open a new avenue to explore dust pristine properties
and describe, for example, the initial conditions for the formation of
planetesimals.",1907.10945v1
2019-09-09,Trunk Pitch Oscillations for Joint Load Redistribution in Humans and Humanoid Robots,"Creating natural-looking running gaits for humanoid robots is a complex task
due to the underactuated degree of freedom in the trunk, which makes the motion
planning and control difficult. The research on trunk movements in human
locomotion is insufficient, and no formalism is known to transfer human motion
patterns onto robots. Related work mostly focuses on the lower extremities, and
simplifies the problem by stabilizing the trunk at a fixed angle. In contrast,
humans display significant trunk motions that follow the natural dynamics of
the gait. In this work, we use a spring-loaded inverted pendulum model with a
trunk (TSLIP) together with a virtual point (VP) target to create trunk
oscillations and investigate the impact of these movements. We analyze how the
VP location and forward speed determine the direction and magnitude of the
trunk oscillations. We show that positioning the VP below the center of mass
(CoM) can explain the forward trunk pitching observed in human running. The VP
below the CoM leads to a synergistic work between the hip and leg, reducing the
leg loading. However, it comes at the cost of increased peak hip torque. Our
results provide insights for leveraging the trunk motion to redistribute joint
loads and potentially improve the energy efficiency in humanoid robots.",1909.03687v1
2019-10-02,Modeling the Dense Spray Regime Using an Euler-Lagrange Approach With Volumetric Displacement Effects,"Modeling of a dense spray regime using an Euler-Lagrange approach is
challenging because of local high volume loading. A cluster of droplets, that
are assumed subgrid, can lead to locally low void fractions for the fluid
phase. Under these conditions, spatio-temporal changes in the fluid volume
fractions should be considered in an Euler-Lagrange, two-way coupling model.
This leads to zero-Mach number, variable density governing equations. Using
pressure-based solvers, this gives rise to a source term in the pressure
Poisson equation and a non-divergence free velocity field. To test the validity
and predictive capability of such an approach, a round jet laden with particles
is investigated using Direct Numerical Simulation coupled with point-Particle
based model and compared with available experimental data for a particulate
turbulent round jet with $Re_j=5712$. Standard force closures including drag,
lift, Magnus effect, pressure, added mass as well as viscous torque acting on
each individual particle are employed in the Point-Particle based model. In
addition, volume displacement effects due to the presence of solid particles or
liquid droplets, which is commonly neglected in the standard two-way coupling,
are taken into account in both continuity and inter-phase momentum transfer to
accurately capture the underlying structure of particle-turbulence
interactions. Prediction results are in well agreement with the corresponding
experiment.",1910.00746v1
2019-11-28,Modeling the Thermal Bulge of A Hot Jupiter with the Two-Stream Approximation,"We revisit the problem of thermal bulge of asynchronous hot Jupiters, using
HD 209458 b as a fiducial study. We improve upon previous works by using a
double-gray atmosphere model and interior structure from MESA as the background
state, and then solve for the thermal bulge in response to the semidiurnal
component of stellar insolation. The atmosphere model is based on the radiative
transfer with Eddington's two-stream approximation. Two opacity cases are
considered: the first introduces a greenhouse effect and the second exhibits a
strong temperature inversion. We find that for the predominant thermal bulges
excited by g-modes of lower orders, our results are qualitatively similar to
the adiabatic results from Arras and Socrates (2010). It arises because the
perturbed heating due to self-absorption of thermal emissions can be
significant (i.e., greenhouse effect) against Newtonian damping, thereby
leading to almost undamped thermal bulges. We also find that the contribution
to the thermal bulge from the evanescent waves in the convective zone is not
negligible, implying that the thermal bulge is not merely confined in the
atmosphere and radiative envelope. Assuming the torque balance between the
thermal and gravitational bulges, we estimate the tidal quality factor of the
planet for gravitational tides to match the observed radius. The limitations of
our model are also briefly discussed.",1911.12687v1
2020-04-21,Mechanical transmission of rotation for molecule gears and solid-state gears,"The miniaturization of gears towards the nanoscale is a formidable task
posing a variety of challenges to current fabrication technologies. In context,
the understanding, via computer simulations, of the mechanisms mediating the
transfer of rotational motion between nanoscale gears can be of great help to
guide the experimental designs. Based on atomistic molecular dynamics
simulations in combination with a nearly rigid-body approximation, we study the
transmission of rotational motion between molecule gears and solid-state gears,
respectively. For the molecule gears under continuous driving, we identify
different regimes of rotational motion depending on the magnitude of the
external torque. In contrast, the solid-state gears behave like ideal gears
with nearly perfect transmission. Furthermore, we simulate the manipulation of
the gears by a scanning-probe tip and we find that the mechanical transmission
strongly depends on the center of mass distance between gears. A new regime of
transmission is found for the solid-state gears.",2004.09857v1
2020-09-17,Efficiency-optimized design of PCB-integrated magnetorquers for CubeSats,"CubeSats are miniature satellites used to carry experimental payloads into
orbit, where it is often critical to precisely control their attitude. One way
to do this is through the use of magnetorquers, which can be integrated into
PCBs. This technique saves considerable space and capital when compared with
more common torque-rod magnetorquer systems. Here we derive a method of
analyzing different PCB-integrated magnetorquer geometries, parametrizing them
such that the magnetic moment and efficiency are optimized. Furthermore, by
modulating the trace width, the trace number, and other electrical
characteristics of the magnetorquer coil, this paper optimizes the generated
magnetic moment. Both constant voltage and constant current sources are
analyzed as inputs. These optimizations are then simulated in COMSOL for
multiple geometries, and it is found that there exists an optimal geometry,
given a specified power dissipation. Simulations verify the general trend and
maxima of these derivations, barring small, consistent re-scaling in the
magnitude of the coil resistance. It is also found that these PCB-integrated
magnetorquers provide a sufficient alternative to commercial coil magnetorquers
- particularly in volume-restricted configurations. This study extends such
analysis to larger CubeSat configurations, and finds that these larger
implementations increase magnetorquer efficiency. Optimizations for common
PCB-implementable geometries on small satellites are tabulated in the Appendix.",2009.07981v2
2020-12-03,Towards Human Haptic Gesture Interpretation for Robotic Systems,"Physical human-robot interactions (pHRI) are less efficient and communicative
than human-human interactions, and a key reason is a lack of informative sense
of touch in robotic systems. Interpreting human touch gestures is a nuanced,
challenging task with extreme gaps between human and robot capability. Among
prior works that demonstrate human touch recognition capability, differences in
sensors, gesture classes, feature sets, and classification algorithms yield a
conglomerate of non-transferable results and a glaring lack of a standard. To
address this gap, this work presents 1) four proposed touch gesture classes
that cover an important subset of the gesture characteristics identified in the
literature, 2) the collection of an extensive force dataset on a common pHRI
robotic arm with only its internal wrist force-torque sensor, and 3) an
exhaustive performance comparison of combinations of feature sets and
classification algorithms on this dataset. We demonstrate high classification
accuracies among our proposed gesture definitions on a test set, emphasizing
that neural net-work classifiers on the raw data outperform other combinations
of feature sets and algorithms. The accompanying video is here:
https://youtu.be/gJPVImNKU68",2012.01959v5
2020-12-06,Stabilizing Transient Disturbances With Utility-Scale Inverter-Based Resources,"This paper presents a trajectory tracking control strategy that modulates the
active power injected by geographically distributed inverter-based resources to
support transient stability. Each resource is independently controlled, and its
response drives the local bus voltage angle toward a trajectory that tracks the
angle of the center of inertia. The center-of-inertia angle is estimated in
real time from wide-area measurements. The main objectives are to stabilize
transient disturbances and increase the amount of power that can be safely
transferred over key transmission paths without loss of synchronism. Here we
envision the actuators as utility-scale energy storage systems; however,
equivalent examples could be developed for partially-curtailed photovoltaic
generation and/or Type 4 wind turbine generators. The strategy stems from a
time-varying linearization of the equations of motion for a synchronous
machine. The control action produces synchronizing torque in a special
reference frame that accounts for the motion of the center of inertia. This
drives the system states toward the desired trajectory and promotes rotor angle
stability. For testing we employ a reduced-order dynamic model of the North
American Western Interconnection. The results show that this approach improves
system reliability and can increase capacity utilization on stability-limited
transmission corridors.",2012.03161v1
2021-09-10,Anisotropic MagnetoMemristance,"In the last decade, nanoscale resistive devices with memory have been the
subject of intense study because of their possible use in brain-inspired
computing. However, operational endurance is one of the limiting factors in the
adoption of such technology. For this reason, we discuss the emergence of
current-induced memristance in magnetic materials, known for their durability.
We show analytically and numerically that a single ferromagnetic layer can
possess GHz memristance, due to a combination of two factors: a current-induced
transfer of angular momentum (Zhang-Li torque) and the anisotropic
magnetoresistance (AMR). We term the resulting effect the anisotropic
magneto-memristance (AMM). We connect the AMM to the topology of the
magnetization state, within a simple model of a 1-dimensional annulus-shaped
magnetic layer, confirming the analytical results with micromagnetic
simulations for permalloy. Our results open a new path towards the realization
of single-layer magnetic memristive devices operating at GHz frequencies.",2109.05101v3
2022-01-15,Parameter Identification and Motion Control for Articulated Rigid Body Robots Using Differentiable Position-based Dynamics,"Simulation modeling of robots, objects, and environments is the backbone for
all model-based control and learning. It is leveraged broadly across dynamic
programming and model-predictive control, as well as data generation for
imitation, transfer, and reinforcement learning. In addition to fidelity, key
features of models in these control and learning contexts are speed, stability,
and native differentiability. However, many popular simulation platforms for
robotics today lack at least one of the features above. More recently,
position-based dynamics (PBD) has become a very popular simulation tool for
modeling complex scenes of rigid and non-rigid object interactions, due to its
speed and stability, and is starting to gain significant interest in robotics
for its potential use in model-based control and learning. Thus, in this paper,
we present a mathematical formulation for coupling position-based dynamics
(PBD) simulation and optimal robot design, model-based motion control and
system identification. Our framework breaks down PBD definitions and
derivations for various types of joint-based articulated rigid bodies. We
present a back-propagation method with automatic differentiation, which can
integrate both positional and angular geometric constraints. Our framework can
critically provide the native gradient information and perform gradient-based
optimization tasks. We also propose articulated joint model representations and
simulation workflow for our differentiable framework. We demonstrate the
capability of the framework in efficient optimal robot design, accurate
trajectory torque estimation and supporting spring stiffness estimation, where
we achieve minor errors. We also implement impedance control in real robots to
demonstrate the potential of our differentiable framework in human-in-the-loop
applications.",2201.05753v1
2022-02-15,Hydrodynamical Evolution of Black-Hole Binaries Embedded in AGN Discs,"Stellar-mass binary black holes (BBHs) embedded in active galactic nucleus
(AGN) discs are possible progenitors of black-hole mergers detected in
gravitational waves by LIGO/VIRGO. To better understand the hydrodynamical
evolution of BBHs interacting with the disc gas, we perform a suite of
high-resolution 2D simulations of binaries in local disc (shearing-box) models,
considering various binary mass ratios, eccentricities and background disc
properties. We use the $\gamma$-law equation of state and adopt a robust
post-processing treatment to evaluate the mass accretion rate, torque and
energy transfer rate on the binary to determine its long-term orbital
evolution. We find that circular comparable-mass binaries contract, with an
orbital decay rate of a few times the mass doubling rate. Eccentric binaries
always experience eccentricity damping. Prograde binaries with higher
eccentricities or smaller mass ratios generally have slower orbital decay
rates, with some extreme cases exhibiting orbital expansion. The averaged
binary mass accretion rate depends on the physical size of the accretor. The
accretion flows are highly variable, and the dominant variability frequency is
the apparent binary orbital frequency (in the rotating frame around the central
massive BH) for circular binaries but gradually shifts to the radial epicyclic
frequency as the binary eccentricity increases. Our findings demonstrate that
the dynamics of BBHs embedded in AGN discs is quite different from that of
isolated binaries in their own circumbinary discs. Furthermore, our results
suggest that the hardening timescales of the binaries are much shorter than
their migration timescales in the disc, for all reasonable binary and disc
parameters.",2202.07633v2
2022-05-27,Direction and Trajectory Tracking Control for Nonholonomic Spherical Robot by Combining Sliding Mode Controller and Model Prediction Controller,"Spherical robot is a nonlinear, nonholonomic and unstable system which
increases the difficulty of the direction and trajectory tracking problem. In
this study, we propose a new direction controller HTSMC, an instruction
planning controller MPC, and a trajectory tracking framework MHH. The HTSMC is
designed by integrating a fast terminal algorithm, a hierarchical method, the
motion features of a spherical robot, and its dynamics. In addition, the new
direction controller has an excellent control effect with a quick response
speed and strong stability. MPC can obtain optimal commands that are then
transmitted to the velocity and direction controller. Since the two torque
controllers in MHH are all Lyapunov-based sliding mode controllers, the MHH
framework may achieve optimal control performance while assuring stability.
Finally, the two controllers eliminate the requirement for MPC's stability and
dynamic constraints. Finally, hardware experiments demonstrate the efficacy of
the HTSMC, MPC, and MHH.",2205.14181v1
2022-06-17,Mpemba-like effect protocol for granular gases of inelastic and rough hard disks,"We study the conditions under which a Mpemba-like effect emerges in granular
gases of inelastic and rough hard disks driven by a class of thermostats
characterized by the splitting of the noise intensity into translational and
rotational counterparts. Thus, granular particles are affected by a stochastic
force and a stochastic torque, which inject translational and rotational
energy, respectively. We realize that a certain choice of a thermostat of this
class can be characterized just by the total intensity and the fraction of
noise transferred to the rotational degree of freedom with respect to the
translational ones. Firstly, Mpemba effect is characterized by the appearance
of a crossing between the temperature curves of the considered samples. Later,
an overshoot of the temperature evolution with respect to the steady-state
value is observed and the mechanism of Mpemba effect generation is changed. The
election of parameters allows to design plausible protocols based on these
thermostats for generating the initial states to observe the Mpemba-like effect
in experiments. In order to obtain explicit results, we use a well-founded
Maxwellian approximation for the evolution dynamics and the steady-state
quantities. Finally, theoretical results are compared with direct simulation
Monte Carlo and molecular dynamics results, and a very good agreement is found.",2206.08846v2
2022-07-12,Constraints on Moon's orbit 3.2 billion years ago from tidal bundle data,"The angular momentum of the Earth-Moon system was initially dominated by
Earth's rotation with a short solar day of around 5 hours duration. Since then,
Earth gradually transferred angular momentum through tidal friction to the
orbit of the Moon, resulting in an increasing orbital radius and a deceleration
of Earth's rotation. Geologic observations of tidal deposits can be used to
verify and constrain models of lunar orbital evolution. In this work we
reexamine the oldest tidal record suitable for analysis from the Moodies Group,
South Africa, with an age of 3.22 billion years. Time frequency analysis of the
series of thicknesses of the sandstone-shale layers yields a periodicity of
15.0 layers, taking into account the possibility of missing laminae. Assuming a
mixed tidal system, the duration of two neap-spring-neap cycles was 30.0 lunar
days for dominant semidiurnal or 30.0 sidereal days for dominant diurnal tides.
We derive the relationship between this observation and the past Earth-Moon
distance and re-visit related published work. We find that the Earth-Moon
distance 3.2 billion years ago was about 70% of today's value. The Archean
solar day was around 13 hours long. The ratio of solar to lunar tide-raising
torque controls the leakage of angular momentum from the Earth-Moon system, but
deviation from the assumed ratio of 0.211 results in only moderate changes. A
duration of a postulated 21-hour atmospheric resonance shorter than 200 million
years would be consistent with our observation; it would significantly alter
Earth-Moon distance.",2207.05464v3
2023-02-19,Robust and Versatile Bipedal Jumping Control through Reinforcement Learning,"This work aims to push the limits of agility for bipedal robots by enabling a
torque-controlled bipedal robot to perform robust and versatile dynamic jumps
in the real world. We present a reinforcement learning framework for training a
robot to accomplish a large variety of jumping tasks, such as jumping to
different locations and directions. To improve performance on these challenging
tasks, we develop a new policy structure that encodes the robot's long-term
input/output (I/O) history while also providing direct access to a short-term
I/O history. In order to train a versatile jumping policy, we utilize a
multi-stage training scheme that includes different training stages for
different objectives. After multi-stage training, the policy can be directly
transferred to a real bipedal Cassie robot. Training on different tasks and
exploring more diverse scenarios lead to highly robust policies that can
exploit the diverse set of learned maneuvers to recover from perturbations or
poor landings during real-world deployment. Such robustness in the proposed
policy enables Cassie to succeed in completing a variety of challenging jump
tasks in the real world, such as standing long jumps, jumping onto elevated
platforms, and multi-axes jumps.",2302.09450v2
2023-04-24,Inductive sensing of magnetic microrobots under actuation by rotating magnetic fields,"The engineering space for magnetically manipulated biomedical microrobots is
rapidly expanding. This includes synthetic, bioinspired, and biohybrid designs,
some of which may eventually assume clinical roles aiding drug delivery or
performing other therapeutic functions. Actuating these microrobots with
rotating magnetic fields (RMFs) and the magnetic torques they exert offers the
advantages of efficient mechanical energy transfer and scalable
instrumentation. Nevertheless, closed-loop control still requires a
complementary noninvasive imaging modality to reveal position and trajectory,
such as ultrasound or x-rays, increasing complexity and posing a barrier to
use. Here, we investigate the possibility of combining actuation and sensing
via inductive detection of model microrobots under field magnitudes ranging
from 0.5 mT to 10s of mT rotating at 1 Hz to 100 Hz. A prototype apparatus
accomplishes this using adjustment mechanisms for both phase and amplitude to
finely balance sense and compensation coils, suppressing the background signal
of the driving RMF by 90 dB. Rather than relying on frequency decomposition to
analyze signals, we show that, for rotational actuation, phase decomposition is
more appropriate. We demonstrate inductive detection of a micromagnet placed in
distinct viscous environments using RMFs with fixed and time-varying
frequencies. Finally, we show how magnetostatic gating fields can spatially
isolate inductive signals from a micromagnet actuated by an RMF, with the
resolution set by the relative magnitude of the gating field and the RMF. The
concepts developed here lay a foundation for future closed-loop control schemes
for magnetic microrobots based on simultaneous inductive sensing and actuation.",2304.12144v1
2023-08-16,Autoencoding a Soft Touch to Learn Grasping from On-land to Underwater,"Robots play a critical role as the physical agent of human operators in
exploring the ocean. However, it remains challenging to grasp objects reliably
while fully submerging under a highly pressurized aquatic environment with
little visible light, mainly due to the fluidic interference on the tactile
mechanics between the finger and object surfaces. This study investigates the
transferability of grasping knowledge from on-land to underwater via a
vision-based soft robotic finger that learns 6D forces and torques (FT) using a
Supervised Variational Autoencoder (SVAE). A high-framerate camera captures the
whole-body deformations while a soft robotic finger interacts with physical
objects on-land and underwater. Results show that the trained SVAE model
learned a series of latent representations of the soft mechanics transferrable
from land to water, presenting a superior adaptation to the changing
environments against commercial FT sensors. Soft, delicate, and reactive
grasping enabled by tactile intelligence enhances the gripper's underwater
interaction with improved reliability and robustness at a much-reduced cost,
paving the path for learning-based intelligent grasping to support fundamental
scientific discoveries in environmental and ocean research.",2308.08510v1
2023-09-04,On the Analysis and Synthesis of Wind Turbine Side-Side Tower Load Control via Demodulation,"As wind turbine power capacities continue to rise, taller and more flexible
tower designs are needed for support. These designs often have the tower's
natural frequency in the turbine's operating regime, increasing the risk of
resonance excitation and fatigue damage. Advanced load-reducing control methods
are needed to enable flexible tower designs that consider the complex dynamics
of flexible turbine towers during partial-load operation. This paper proposes a
novel modulation-demodulation control (MDC) strategy for side-side tower load
reduction driven by the varying speed of the turbine. The MDC method
demodulates the periodic content at the once-per-revolution (1P) frequency in
the tower motion measurements into two orthogonal channels. The proposed scheme
extends the conventional tower controller by augmentation of the MDC
contribution to the generator torque signal. A linear analysis framework into
the multivariable system in the demodulated domain reveals varying degrees of
coupling at different rotational speeds and a gain sign flip. As a solution, a
decoupling strategy has been developed, which simplifies the controller design
process and allows for a straightforward (but highly effective) diagonal linear
time-invariant controller design. The high-fidelity OpenFAST wind turbine
software evaluates the proposed controller scheme, demonstrating effective
reduction of the 1P periodic loading and the tower's natural frequency
excitation in the side-side tower motion.",2309.01633v1
2023-11-06,Rotating convective turbulence in moderate to high Prandtl number fluids,"Rotating convective turbulence is ubiquitously found across geophysical
settings, such as surface and subsurface oceans, planetary atmospheres, molten
metal planetary cores, magma chambers, and magma oceans. Depending on the
thermal and material properties of the system, buoyant convection can be driven
thermally or compositionally, where a Prandtl number ($Pr = \nu / \kappa_i$)
defines the characteristic diffusion properties of the system, with $\kappa_i =
\kappa_T$ representing thermal diffusion and $\kappa_i = \kappa_C$ representing
chemical diffusion. These numbers vary widely for geophysical systems; for
example, the liquid iron undergoing thermal-compositional convection in Earth's
core is defined by $Pr_T \approx 0.1$ and $Pr_C \approx 100$, while a
thermally-driven liquid silicate magma ocean is defined by $Pr_T \approx 100$.
Currently, most numerical and laboratory data for rotating convective flows
exists at $Pr = O(1)$; high $Pr$ rotating convection relevant to
compositionally-driven core flow and other systems is less commonly studied.
Here, we address this deficit by carrying out a broad suite of rotating
convection experiments made over a range of $Pr$ values, employing water and
three different silicone oils as our working fluids ($Pr = $ 6, 41, 206, and
993). Using measurements of flow velocities (Reynolds, $Re$) and heat transfer
efficiency (Nusselt, $Nu$), a baroclinic torque balance is found to describe
the turbulence regardless of Prandtl number so long as $Re$ is sufficiently
large ($Re \gtrsim 10$). Estimated turbulent scales are found to remain close
to onset scales in all experiments, a result that may extrapolate to planetary
settings. Lastly, we use our data to build $Pr$-dependent predictive
nondimensional and dimensional scaling relations for rotating convective
velocities that can be applied across a broad range of geophysical fluid
dynamical settings.",2311.03495v1
2024-03-23,The Impact of Evolutionary Computation on Robotic Design: A Case Study with an Underactuated Hand Exoskeleton,"Robotic exoskeletons can enhance human strength and aid people with physical
disabilities. However, designing them to ensure safety and optimal performance
presents significant challenges. Developing exoskeletons should incorporate
specific optimization algorithms to find the best design. This study
investigates the potential of Evolutionary Computation (EC) methods in robotic
design optimization, with an underactuated hand exoskeleton (U-HEx) used as a
case study. We propose improving the performance and usability of the U-HEx
design, which was initially optimized using a naive brute-force approach, by
integrating EC techniques such as Genetic Algorithm and Big Bang-Big Crunch
Algorithm. Comparative analysis revealed that EC methods consistently yield
more precise and optimal solutions than brute force in a significantly shorter
time. This allowed us to improve the optimization by increasing the number of
variables in the design, which was impossible with naive methods. The results
show significant improvements in terms of the torque magnitude the device
transfers to the user, enhancing its efficiency. These findings underline the
importance of performing proper optimization while designing exoskeletons, as
well as providing a significant improvement to this specific robotic design.",2403.15812v1
2022-12-23,Spin vectors in the Koronis family: IV. Completing the sample of its largest members after 35 years of study,"An observational study of Koronis family members' spin properties was
undertaken with two primary objectives: to reduce selection biases for object
rotation period and lightcurve amplitude in the sample of members' known spin
vectors, and to better constrain future modeling of spin properties evolution.
Here we report rotation lightcurves of nineteen Koronis family members, and
derived results that increase the sample of determined spin vectors in the
Koronis family to include 34 of the largest 36 family members, completing it to
$H \approx 11.3$ ($D \sim 16$ km) for the largest 32 members. The program
observations were made during a total of 72 apparitions between 2005-2021, and
are reported here along with several earlier unpublished lightcurves. All of
the reported data were analyzed together with previously published lightcurves
to determine the objects' sidereal rotation periods, spin vector orientations,
and convex model shape solutions. The derived distributions of retrograde
rotation rates and pole obliquities appear to be qualitatively consistent with
outcomes of modification by thermal YORP torques. The distribution of spin
rates for the prograde rotators remains narrower than that for the retrograde
rotators; in particular, the absence of prograde rotators having periods longer
than about 20 h is real, while among the retrograde rotators are several
objects having longer periods up to about 65 h. None of the prograde objects
newly added to the sample appear to be trapped in an $s_6$ spin-orbit resonance
that is characteristic of most of the largest prograde objects; these smaller
objects either could have been trapped previously and have already evolved out,
or have experienced spin evolution tracks that did not include the resonance.",2212.12355v1
2002-03-21,Binary black holes and tori in AGN II. Can stellar winds constitute a dusty torus?,"We determine the properties of the stellar torus that we showed in a previous
paper to result as a product of two merging black holes. If the surrounding
stellar cluster is as massive as the binary black hole, the torque acting on
the stars ejects a fraction which extracts all the binary's angular momentum on
scales of ~10^7 yr, and a geometrically thick torus remains. In the present
article we show that a certain fraction of the stars has winds, shaped into
elongated tails by the central radiation pressure, which are optically thick
for line of sights aligned with them. These stars are sufficiently numerous to
achieve a covering factor of 1, so that the complete torus is optically thick.
We find the parameters of such a patchy torus to be in the right range to
explain the observed large column densities in AGN and their temporal
variations on time scales of about a decade. Within this model the BAL quasars
can be interpreted as quasars seen at intermediate inclination angles, with the
line of sight grazing the edge of the torus. The opening angle of the torus is
wider for major mergers and thus correlates with the central luminosity. In
this picture the spin of the merged black hole is possibly dominated by the
orbital angular momentum of the binary. Thus the spin of the merged black hole
points into a new direction, and consequently the jet experiences a spin-flip
according to the spin-paradigm. This re-orientation could be an explanation for
the X-shaped radio galaxies, and the advancing of a new jet through the ambient
medium for Compact Symmetric Objects.",0203359v2
2007-05-01,Accreting Neutron Stars in Low-Mass X-Ray Binary Systems,"Using the Rossi X-ray Timing Explorer (RossiXTE), astronomers have discovered
that disk-accreting neutron stars with weak magnetic fields produce three
distinct types of high-frequency X-ray oscillations. These oscillations are
powered by release of the binding energy of matter falling into the strong
gravitational field of the star or by the sudden nuclear burning of matter that
has accumulated in the outermost layers of the star. The frequencies of the
oscillations reflect the orbital frequencies of gas deep in the gravitational
field of the star and/or the spin frequency of the star. These oscillations can
therefore be used to explore fundamental physics, such as strong-field gravity
and the properties of matter under extreme conditions, and important
astrophysical questions, such as the formation and evolution of millisecond
pulsars. Observations using RossiXTE have shown that some two dozen neutron
stars in low-mass X-ray binary systems have the spin rates and magnetic fields
required to become millisecond radio-emitting pulsars when accretion ceases,
but that few have spin rates above about 600 Hz. The properties of these stars
show that the paucity of spin rates greater than 600 Hz is due in part to the
magnetic braking component of the accretion torque and to the limited amount of
angular momentum that can be accreted in such systems. Further study will show
whether braking by gravitational radiation is also a factor. Analysis of the
kilohertz oscillations has provided the first evidence for the existence of the
innermost stable circular orbit around dense relativistic stars that is
predicted by strong-field general relativity. It has also greatly narrowed the
possible descriptions of ultradense matter.",0705.0155v2
2007-11-10,CCO Pulsars as Anti-Magnetars: Evidence of Neutron Stars Weakly Magnetized at Birth,"Our new study of the two central compact object pulsars, PSR J1210-5226 (P =
424 ms) and PSR J1852+0040 (P = 105 ms), leads us to conclude that a weak natal
magnetic field shaped their unique observational properties. In the dipole
spin-down formalism, the 2-sigma upper limits on their period derivatives, <
2E-16 for both pulsars, implies surface magnetic field strengths of B_s < 3E11
G and spin periods at birth equal to their present periods to three significant
digits. Their X-ray luminosities exceed their respective spin-down
luminosities, implying that their thermal spectra are derived from residual
cooling and perhaps partly from accretion of supernova debris. For sufficiently
weak magnetic fields an accretion disk can penetrate the light cylinder and
interact with the magnetosphere while resulting torques on the neutron star
remain within the observed limits. We propose the following as the origin of
radio-quiet CCOs: the magnetic field, derived from a turbulent dynamo, is
weaker if the NS is formed spinning slowly, which enables it to accrete SN
debris. Accretion excludes neutron stars born with both B_s < 1E11 G and P >
0.1 s from radio pulsar surveys, where such weak fields are not encountered
except among very old (> 40 Myr) or recycled pulsars. We predict that these
birth properties are common, and may be attributes of the youngest detected
neutron star, the CCO in Cassiopeia A, as well as an undetected infant neutron
star in the SN 1987A remnant. In view of the far-infrared light echo discovered
around Cas A and attributed to an SGR-like outburst, it is especially important
to determine via timing whether Cas A hosts a magnetar or not. If not a
magnetar, the Cas A NS may instead have undergone a one-time phase transition
(corequake) that powered the light echo.",0711.1554v1
2010-07-05,Internal properties and environments of dark matter halos,"We use seven high-resolution $N$-body simulations to study the correlations
among different halo properties (assembly time, spin, shape and substructure),
and how these halo properties are correlated with the large-scale environment
in which halos reside. The large-scale tidal field estimated from halos above a
mass threshold is used as our primary quantity to characterize the large-scale
environment, while other parameters, such as the local overdensity and the
morphology of large-scale structure, are used for comparison. For halos at a
fixed mass, all the halo properties depend significantly on environment,
particularly the tidal field. The environmental dependence of halo assembly
time is primarily driven by local tidal field. The mass of the unbound fraction
in substructure is boosted in strong tidal force region, while the bound
fraction is suppressed. Halos have a tendency to spin faster in stronger tidal
field and the trend is stronger for more massive halos. The spin vectors show
significant alignment with the intermediate axis of the tidal field, as
expected from the tidal torque theory. Both the major and minor axes of halos
are strongly aligned with the corresponding principal axes of the tidal field.
In general, a halo that can accrete more material after the formation of its
main halo on average is younger, is more elongated, spins faster, and contains
a larger amount of substructure. Higher density environments not only provide
more material for halo to accrete, but also are places of stronger tidal field
that tends to suppress halo accretion. The environmental dependencies are the
results of these two competing effects. The tidal field based on halos can be
estimated from observation, and we discuss the implications of our results for
the environmental dependence of galaxy properties.",1007.0612v4
2011-01-07,Tidal Evolution of Close Binary Asteroid Systems,"We provide a generalized discussion of tidal evolution to arbitrary order in
the expansion of the gravitational potential between two spherical bodies of
any mass ratio. To accurately reproduce the tidal evolution of a system at
separations less than five times the radius of the larger primary component,
the tidal potential due to the presence of a smaller secondary component is
expanded in terms of Legendre polynomials to arbitrary order rather than
truncated at leading order as is typically done in studies of well-separated
system like the Earth and Moon. The equations of tidal evolution including
tidal torques, the changes in spin rates of the components, and the change in
semimajor axis (orbital separation) are then derived for binary asteroid
systems with circular and equatorial mutual orbits. Accounting for higher-order
terms in the tidal potential serves to speed up the tidal evolution of the
system leading to underestimates in the time rates of change of the spin rates,
semimajor axis, and mean motion in the mutual orbit if such corrections are
ignored. Special attention is given to the effect of close orbits on the
calculation of material properties of the components, in terms of the rigidity
and tidal dissipation function, based on the tidal evolution of the system. It
is found that accurate determinations of the physical parameters of the system,
e.g., densities, sizes, and current separation, are typically more important
than accounting for higher-order terms in the potential when calculating
material properties. In the scope of the long-term tidal evolution of the
semimajor axis and the component spin rates, correcting for close orbits is a
small effect, but for an instantaneous rate of change in spin rate, semimajor
axis, or mean motion, the close-orbit correction can be on the order of tens of
percent.",1101.1500v1
2012-12-12,Quasi-spherical accretion in low-luminosity X-ray pulsars: Theory vs. observations,"Quasi-spherical subsonic accretion can be realized in slowly rotating
wind-fed X-ray pulsars (XPSRs) at X-ray luminosities <4 10^{36} erg/s. In this
regime the accreting matter settles down subsonically onto the rotating
magnetosphere, forming an extended quasi-static shell. The shell mediates the
angular momentum removal from the rotating NS magnetosphere by shear turbulent
viscosity in the boundary layer or via large-scale convective motions. In the
last case the differential rotation law in the shell is close to
iso-angular-momentum rotation. The accretion rate through the shell is
determined by the ability of the plasma to enter the magnetosphere due to
Rayleigh-Taylor instabilities while taking cooling into account. Measurements
of spin-up/spin-down rates of quasi-spherically wind accreting XPSRs in
equilibrium with known orbital periods (like e.g. GX 301-2 and Vela X-1) enable
determination of the main dimensionless parameters of the model and the NS
magnetic field. For equilibrium pulsars with independent measurements of the
magnetic field, the stellar wind velocity from the companion can be estimated
without the use of complicated spectroscopic measurements. For non-equilibrium
pulsars, a maximum possible spin-down torque exerted on the accreting NS
exists. From observations of the spin-down rate and X-ray luminosity in such
pulsars (GX 1+4, SXP 1062, 4U 2206+54, etc.) a lower limit on the NS magnetic
field is derived, which in all cases turns out to be close to the standard one
and in agreement with cyclotron line measurements. The model explains the
existence of super slowly rotating XPSRs without the need to hypothesize on
additional accretion properties and magnetar-like magnetic fields in accreting
neutron stars.",1212.2841v1
2013-09-11,The Nucleus of Comet 10P/Tempel 2 in 2013 and Consequences Regarding Its Rotational State: Early Science from the Discovery Channel Telescope,"We present new lightcurve measurements of Comet 10P/Tempel 2 carried out with
Lowell Observatory's Discovery Channel Telescope in early 2013 when the comet
was at aphelion. These data represent some of the first science obtained with
this new 4.3-m facility. With Tempel 2 having been observed to exhibit a small
but ongoing spin-down in its rotation period for over two decades, our primary
goals at this time were two-fold. First, to determine its current rotation
period and compare it to that measured shortly after its most recent perihelion
passage in 2010, and second, to disentangle the spin-down from synodic effects
due to the solar day and the Earth's orbital motion and to determine the sense
of rotation, i.e. prograde or retrograde. At our midpoint of 2013 Feb 24, the
observed synodic period is 8.948+/-0.001 hr, exactly matching the predicted
prograde rotation solution based on 2010 results, and yields a sidereal period
of the identical value due to the solar and Earth synodic components just
canceling out during the interval of the 2013 observations. The retrograde
solution is ruled out because the associated sidereal periods in 2010 and 2013
are quite different even though we know that extremely little outgassing,
needed to produce torques, occurred in this interval. With a definitive sense
of rotation, the specific amounts of spin-down to the sidereal period could be
assessed. The nominal values imply that the rate of spin-down has decreased
over time, consistent with the secular drop in water production since 1988. Our
data also exhibited an unexpectedly small lightcurve amplitude which appears to
be associated with viewing from a large, negative sub-Earth latitude, and a
lightcurve shape deviating from a simple sinusoid implying a highly irregularly
shaped nucleus.",1309.2944v1
2015-01-30,Flow Patterns around Dark Matter Halos: the Link between Halo Dynamical Properties and Large Scale Tidal Field,"We study how halo intrinsic dynamical properties are linked to their
formation processes for halos in two mass ranges, $10^{12}-10^{12.5}h^{-1}{\rm
M_\odot}$ and $\ge 10^{13}h^{-1}{\rm M_\odot}$, and how both are correlated
with the large scale tidal field within which the halos reside at present. Halo
merger trees obtained from cosmological $N$-body simulations are used to
identify infall halos that are about to merge with their hosts. We find that
the tangential component of the infall velocity increases significantly with
the strength of the local tidal field, but no strong correlation is found for
the radial component. These results can be used to explain how the internal
velocity anisotropy and spin of halos depend on environment. The position
vectors and velocities of infall halos are aligned with the principal axes of
the local tidal field, and the alignment depends on the strength of the tidal
field. Opposite accretion patterns are found in weak and strong tidal fields,
in the sense that in a weak field the accretion flow is dominated by radial
motion within the local structure, while a large tangential component is
present in a strong field. These findings can be used to understand the strong
alignments we find between the principal axes of the internal velocity
ellipsoids of halos and the local tidal field, and their dependence on the
strength of tidal field. They also explain why halo spin increases with the
strength of local tidal field, but only in weak tidal fields does the
spin-tidal field alignment follow the prediction of the tidal torque theory. We
discuss how our results may be used to understand the spins of disk galaxies
and velocity structures of elliptical galaxies and their correlations with
large-scale structure.",1501.07764v2
2015-02-20,Improved angular momentum evolution model for solar-like stars II. Exploring the mass dependence,"We developed angular momentum evolution models for 0.5 and 0.8 $M_{\odot}$
stars. The parametric models include a new wind braking law based on recent
numerical simulations of magnetised stellar winds, specific dynamo and
mass-loss rate prescriptions, as well as core/envelope decoupling. We compare
model predictions to the distributions of rotational periods measured for low
mass stars belonging to star forming regions and young open clusters.
Furthermore, we explore the mass dependence of model parameters by comparing
these new models to the solar-mass models we developed earlier. Rotational
evolution models are computed for slow, median, and fast rotators at each
stellar mass. The models reproduce reasonably well the rotational behaviour of
low-mass stars between 1 Myr and 8-10 Gyr, including pre-main sequence to
zero-age main sequence spin up, prompt zero-age main sequence spin down, and
early-main sequence convergence of the surface rotation rates. Fast rotators
are found to have systematically shorter disk lifetimes than moderate and slow
rotators, thus enabling dramatic pre-main sequence spin up. They also have
shorter core-envelope coupling timescales, i.e., more uniform internal
rotation. As to the mass dependence, lower mass stars require significantly
longer core-envelope coupling timescale than solar-type ones, which results in
strong differential rotation developing in the stellar interior on the early
main sequence. Lower mass stars also require a weaker braking torque to account
for their longer spin down timescale on the early main sequence, while they
ultimately converge towards lower rotational velocities than solar-type stars
on the longer term due to their reduced moment of inertia. We also find
evidence that the mass-dependence of the wind braking efficiency may be related
to a change of the magnetic topology in lower mass stars.",1502.05801v2
2016-07-28,Outer-planet scattering can gently tilt an inner planetary system,"Chaotic dynamics are expected during and after planet formation, and a
leading mechanism to explain large eccentricities of gas giant exoplanets is
planet-planet gravitational scattering. The same scattering has been invoked to
explain misalignments of planetary orbital planes with respect to their host
star's spin. However, an observational puzzle is presented by Kepler-56, which
has two inner planets (b and c) that are nearly coplanar with each other, yet
are more than 45 degrees inclined to their star's equator. Thus the spin-orbit
misalignment might be primordial. Instead, we further develop the hypothesis in
the discovery paper, that planets on wider orbits generated misalignment
through scattering, and as a result gently torqued the inner planets away from
the equator plane of the star. We integrated the equations of motion for
Kepler-56 b and c along with an unstable outer system initialized with either
two or three Jupiter-mass planets. We address here whether the violent
scattering that generates large mutual inclinations can leave the inner system
intact, tilting it gently. In almost all of the cases initially with two outer
planets, either the inner planets remain nearly coplanar with each other in the
star's equator plane, or they are scattered violently to high mutual
inclination and high spin-orbit misalignment. On the contrary, of the systems
with three unstable outer planets, a spin-orbit misalignment large enough to
explain the observations is generated 28% of the time for coplanar inner
planets, which is consistent with the observed frequency of this phenomenon
reported so far. We conclude that multiple-planet scattering in the outer parts
of the system may account for this new population of coplanar planets hosted by
oblique stars.",1607.08630v1
2016-10-05,Timing Observations of PSR J1023+0038 During a Low-Mass X-ray Binary State,"Transitional millisecond pulsars (tMSPs) switch, on roughly multi-year
timescales, between rotation-powered radio millisecond pulsar (RMSP) and
accretion-powered low-mass X-ray binary (LMXB) states. The tMSPs have raised
several questions related to the nature of accretion flow in their LMXB state
and the mechanism that causes the state switch. The discovery of coherent X-ray
pulsations from PSR J1023+0038 (while in the LMXB state) provides us with the
first opportunity to perform timing observations and to compare the neutron
star's spin variation during this state to the measured spin-down in the RMSP
state. Whereas the X-ray pulsations in the LMXB state likely indicate that some
material is accreting onto the neutron star's magnetic polar caps, radio
continuum observations indicate the presence of an outflow. The fraction of the
inflowing material being ejected is not clear, but it may be much larger than
that reaching the neutron star's surface. Timing observations can measure the
total torque on the neutron star. We have phase-connected nine XMM-Newton
observations of PSR J1023+0038 over the last 2.5 years of the LMXB state to
establish a precise measurement of spin evolution. We find that the average
spin-down rate as an LMXB is 26.8+/-0.4% faster than the rate (-2.39x10^-15 Hz
s-1) determined during the RMSP state. This shows that negative angular
momentum contributions (dipolar magnetic braking and outflow) exceed positive
ones (accreted material), and suggests that the pulsar wind continues to
operate at a largely unmodified level. We discuss implications of this tight
observational constraint in the context of possible accretion models.",1610.01625v1
2020-02-03,From Stellar Coronæ to Gyrochronology: a theoretical and observational exploration,"Context. Stellar spin-down is the result of a complex process involving
rotation, dynamo, wind and magnetism. Multi-wavelength surveys of solar-like
stars have revealed the likely existence of relationships between their
rotation, X-ray luminosity, mass-losses and magnetism. Those impose strong
constraints on the corona and wind of cool stars.
  Aims. We aim to provide power-law prescriptions of the mass-loss of stars, of
their magnetic field, and of their base coronal density and temperature that
are compatible with their observationally-constrained spin-down.
  Methods. We link the magnetic field and the mass-loss rate from a wind torque
formulation in agreement with the distribution of stellar rotation periods in
open clusters and the Skumanich law. Given a wind model and an expression of
the X-ray luminosity from radiative losses, we constrain the coronal properties
by assuming different physical scenarii linking closed loops to coronal holes.
  Results. We find that the magnetic field and the mass loss are involved in a
one-to-one correspondence constrained from spin-down considerations. We show
that a magnetic field depending on both the Rossby number and the stellar mass
is required to keep a consistent spin-down model. The estimates of the magnetic
field and the mass-loss rate obtained from our formalism are consistent with
statistical studies as well as individual observations and give new leads to
constrain the magnetic field-rotation relation. The set of scaling-laws we
derived can be broadly applied to cool stars from the PMS to the end of the MS,
and allow for a stellar wind modelling consistent with all the observational
constraints available to date.",2002.00696v1
2020-04-24,Orbital Migration of Interacting Stellar Mass Black Holes in Disks around Supermassive Black Holes II. Spins and Incoming Objects,"The masses, rates, and spins of merging stellar-mass binary black holes
(BBHs) detected by aLIGO and Virgo provide challenges to traditional BBH
formation and merger scenarios. An active galactic nucleus (AGN) disk provides
a promising additional merger channel, because of the powerful influence of the
gas that drives orbital evolution, makes encounters dissipative, and leads to
migration. Previous work showed that stellar mass black holes (sBHs) in an AGN
disk migrate to regions of the disk, known as migration traps, where positive
and negative gas torques cancel out, leading to frequent BBH formation. Here we
build on that work by simulating the evolution of additional sBHs that enter
the inner disk by either migration or inclination reduction. We also examine
whether the BBHs formed in our models have retrograde or prograde orbits around
their centers of mass with respect to the disk, determining the orientation,
relative to the disk, of the spin of the merged BBHs. Orbiters entering the
inner disk form BBHs with sBHs on resonant orbits near the migration trap. When
these sBHs reach ~80 Msun, they form BBHs with sBHs in the migration trap,
which over 10 Myr reach ~1000 Msun. We find 68% of the BBHs in our simulation
orbit in the retrograde direction, which implies BBHs in our merger channel
will have small dimensionless aligned spins, \chi_eff. Overall, our models
produce BBHs that resemble both the majority of BBH mergers detected thus far
(0.66 to 120 Gpc^-3 yr^-1 ) and two recent unusual detections, GW190412 (~0.3
Gpc^-3 yr^-1 ) and GW190521 (~0.1 Gpc^-3 yr^-1 ).",2004.11936v2
2020-05-15,"Thermal generation, manipulation and detection of skyrmions","Recent years have witnessed significant progresses in realizing skyrmions in
chiral magnets1-4 and asymmetric magnetic multilayers5-13, as well as their
electrical manipulation2,7,8,10. Equally important, thermal generation,
manipulation and detection of skyrmions can be exploited for prototypical new
architecture with integrated computation14 and energy harvesting15. It has yet
to verify if skyrmions can be purely generated by heating16,17, and if their
resultant direction of motion driven by temperature gradients follows the
diffusion or, oppositely, the magnonic spin torque17-21. Here, we address these
important issues in microstructured devices made of multilayers:
(Ta_CoFeB_MgO)15, (Pt_CoFeB_MgO_Ta)15 and (Pt_Co_Ta)15 integrated with on-chip
heaters, by using a full-field soft X-ray microscopy. The thermal generation of
densely packed skyrmions is attributed to the low energy barrier at the device
edge, together with the thermally induced morphological transition from stripe
domains to skyrmions. The unidirectional diffusion of skyrmions from the hot
region towards the cold region is experimentally observed. It can be
theoretically explained by the combined contribution from repulsive forces
between skyrmions, and thermal spin-orbit torques in competing with magnonic
spin torques17,18,20,21 and entropic forces22. These thermally generated
skyrmions can be further electrically detected by measuring the accompanied
anomalous Nernst voltages23. The on-chip thermoelectric generation,
manipulation and detection of skyrmions could open another exciting avenue for
enabling skyrmionics, and promote interdisciplinary studies among spin
caloritronics15, magnonics24 and skyrmionics3,4,12.",2005.07441v1
2020-12-24,Evolution of magnetic-field-induced ordering in the layered structure quantum Heisenberg triangular-lattice antiferromagnet Ba$_3$CoSb$_2$O$_9$,"Quantum fluctuations in the effective spin one-half layered structure
triangular-lattice quantum Heisenberg antiferromagnet Ba$_3$CoSb$_2$O$_9$ lift
the classical degeneracy of the antiferromagnetic ground state in magnetic
field, producing a series of novel spin structures for magnetic fields applied
within the crystallographic ab plane. Theoretically unresolved, however, are
the effects of interlayer antferromagnetic coupling and transverse magnetic
fields on the ground states of this system. To address these issues, we have
used specific heat, neutron diffraction, thermal conductivity, and magnetic
torque measurements to map out the phase diagram as a function of magnetic
field intensity and orientation relative to the crystallographic ab plane. For
H parallel to the ab plane, we have discovered an additional, previously
unreported magnetic-field-induced phase transition at low temperature and an
unexpected tetracritical point in the high field phase diagram, which - coupled
with the apparent second-order nature of the phase transitions - eliminates
several theoretically proposed spin structures for the high field phases. Our
calorimetric measurements as a function of magnetic field orientation are in
general agreement with theory for field-orientation angles close to plane
parallel but diverge at angles near plane perpendicular; a predicted
convergence of two phase boundaries at finite angle and a corresponding change
in the order of the field induced phase transition is not observed
experimentally. Our results emphasize the role of interlayer coupling in
selecting and stabilizing field-induced phases, provide new guidance into the
nature of the magnetic order in each phase, and reveal the need for new physics
to account for the nature of magnetic ordering in this archetypal 2D spin
one-half triangular lattice quantum Heisenberg antiferromagnet.",2012.13030v2
2022-05-29,Construction of the spectral function from non-commuting spectral moment matrices,"The LDA+U method is widely used to study the properties of realistic solids
with strong electron correlations. One of its main shortcomings is that it does
not provide direct access to the temperature dependence of material properties
such as the Dzyaloshinskii-Moriya interaction, the anomalous Hall conductivity,
and the spin-orbit torque. While the method of spectral moments allows us in
principle to compute these quantities directly at finite temperatures, the
standard two-pole approximation can be applied only to Hamiltonians that are
effectively of single-band type. We do a first step to explore if the method of
spectral moments may replace the LDA+U method in first-principles calculations
of correlated solids with many bands in cases where the direct assessment of
the temperature dependence of equilibrium and response functions is desired:
The spectral moments of many-band Hamiltonians of correlated electrons do not
commute and therefore they do not possess a system of common eigenvectors. We
show that nevertheless the spectral function may be constructed from the
spectral moments by solving a system of coupled non-linear equations.
Additionally, we show how to compute the anomalous Hall conductivity of
correlated electrons from this spectral function. We demonstrate the method for
the Hubbard-Rashba model, where the standard two-pole approximation cannot be
applied, because spin-orbit interaction (SOI)couples the spin-up and the
spin-down bands. In the quest for new quantum states that arise from the
combination of SOI and correlation effects, the Hartree-Fock approximation is
frequently used to obtain a first approximation for the phase diagram. We
propose that using the many-band generalization of the selfconsistent moment
method instead of Hartree-Fock in such exploratory model calculations may
improve the accuracy significantly, while keeping the computational burden low.",2205.14581v2
2023-10-11,Modern topics in relativistic spin dynamics and magnetism,"Magnetism is a rich subject touching all aspects of physics. My goal with
this dissertation is to explore spin and magnetic moments in
\emph{relativistic} mechanics from both a quantum and classical perspective. We
emphasize the special case of gyromagnetic ratio $g\!=\!2$ and its relationship
to the algebraic spin structure of wave equations. In relativistic quantum
mechanics, we investigate generalizations of the Dirac equation for arbitrary
magnetic moments for fermions. We analyze the homogeneous magnetic field case
and the Coulomb problem for hydrogen-like atoms with emphasis on the role of
the anomalous magnetic moment (AMM). We explore alternative approaches which
combine mass and the magnetic moment. Classically, we propose a relativistic
covariant model of the Stern-Gerlach force via the introduction of a magnetic
four-potential. This model modifies the covariant torque equations and unites
the Amp\`erian and Gilbertian models for magnetic moments.
  We further study (transition) magnetic dipoles in Majorana neutrinos
specifically analyzing the relationship between flavor mixing and
electromagnetic (EM) fields. We demonstrate EM flavor mixing explicitly in the
2-flavor model and develop a dynamical mass basis with an EM rotation matrix.
EM induced neutrino mass splitting is compared to neutrino mass hierarchy.
  An interesting application of these theoretical developments is to study
primordial magnetization in the early universe during the hot dense
electron-positron plasma epoch. We propose a model of magnetic thermal
matter-antimatter plasmas. We analyze the paramagnetic characteristics of
electron-positron plasma when exposed to an external primordial field.
  Future research outlooks include: Second order equations for anomalous
quantum chromodynamic (QCD) moments, neutrino CP violation in strong EM fields,
and fifth-dimension spin dynamics in Kaluza-Klein theory.",2310.07193v1
2024-03-04,Probing the emission mechanism and nature of the pulsating compact object in the X-ray binary SAX J1324.4-6200,"Recently, there has been renewed interest in the Be X-ray binary (Be/XRB) SAX
J1324.4-6200 because of its spatial coincidence with a gamma-ray source
detected by Fermi/LAT. To explore more thoroughly its properties, new
observations were carried out in 2023 by NuSTAR, XMM-Newton, and Swift, jointly
covering the energy range 0.2-79 keV. The X-ray spectrum of SAX J1324.4-6200
fits well with an absorbed power law with a high energy cut-off. We measured a
NuSTAR spin period of 175.8127 +/- 0.0036 s and an XMM-Newton spin period of
175.862 +/- 0.025 s. All the available spin period measurements of SAX
J1324.4-6200, spanning 29 years, are correlated with time, resulting in a
remarkably stable spin-down of dP/dt=(6.09 +/- 0.06)*1E-9 s/s. If SAX
J1324.4-6200 hosts an accretion powered pulsar, accretion torque models
indicate a surface magnetic field of ~1E12-1E13 G. The X-ray properties
emerging from our analysis strenghten the hypothesis that SAX J1324.4-6200
belongs to the small group of persistent Be/XRBs. We also performed radio
observations with the Parkes Murriyang telescope, to search for radio
pulsations. However, no radio pulsations compatible with the rotational
ephemeris of SAX J1324.4-6200 were detected. We rule out the hypothesis that
SAX J1324.4-6200 is a gamma-ray binary where the emission is produced by
interactions between the pulsar and the companion winds. Other models commonly
used to account for the production of gamma-rays in accreting pulsars cannot
reproduce the bright emission from SAX J1324.4-6200. We examined other
mechanisms for the gamma-ray emission and noted that there is a ~0.5% chance
probability that an unknown extragalactic AGN observed through the Galactic
plane may coincidentally fall within the Fermi/LAT error circle of the source
and be the responsible of the gamma-ray emission. [Abridged]",2403.01941v1
2023-05-11,Low-temperature spectrum of the quantum transfer matrix of the XXZ chain in the massless regime,"The free energy per lattice site of a quantum spin chain in the thermodynamic
limit is determined by a single `dominant' Eigenvalue of an associated quantum
transfer matrix in the infinite Trotter number limit. For integrable quantum
spin chains, related with solutions of the Yang-Baxter equation, an appropriate
choice of the quantum transfer matrix enables to study its spectrum, e.g.\ by
means of the algebraic Bethe Ansatz. In its turn, the knowledge of the full
spectrum allows one to study its universality properties such as the appearance
of a conformal spectrum in the low-temperature regime. More generally,
accessing the full spectrum is a necessary step for deriving thermal form
factor series representations of the correlation functions of local operators
for the spin chain under consideration. These are statements that have been
established by physicists on a heuristic level and that are calling for a
rigorous mathematical justification. In this work we implement certain aspects
of this programme with the example of the XXZ quantum spin chain in the
antiferromagnetic massless regime and in the low-temperature limit. We
rigorously establish the existence, uniqueness and characterise the form of the
solutions to the non-linear integral equations that are equivalent to the Bethe
Ansatz equations for the quantum transfer matrix of this model. This allows us
to describe that part of the quantum transfer matrix spectrum that is related
to the Bethe Ansatz and that does not collapse to zero in the infinite Trotter
number limit. Within the considered part of the spectrum we rigorously identify
the dominant Eigenvalue and show that those correlations lengths that diverge
in the low-temperature limit are given, to the leading order, by the spectrum
of the free Boson $c=1$ conformal field theory. This rigorously establishes a
long-standing conjecture present in the physics literature.",2305.06679v2
2015-08-25,Collective excitations in Na$_2$IrO$_3$,"We study the collective excitations of Na$_2$IrO$_3$ in an itinerant electron
approach. We consider a multi-orbital tight-binding model with the electron
transfer between the Ir $5d$ states mediated via oxygen $2p$ states and the
direct $d$-$d$ transfer on a honeycomb lattice. The one-electron energy as well
as the ground state energy are investigated within the Hartree-Fock
approximation. When the direct $d$-$d$ transfer is weak, we obtain nearly flat
energy bands due to the formation of quasimolecular orbitals, and the ground
state exhibits the zigzag spin order. The evaluation of the density-density
correlation function within the random phase approximation shows that the
collective excitations emerge as bound states. For an appropriate value of the
direct $d$-$d$ transfer, some of them are concentrated in the energy region
$\omega <$ 50 meV (magnetic excitations) while the others lie in the energy
region $\omega >$ 350 meV (excitonic excitations). This behaviour is consistent
with the resonant inelastic x-ray scattering spectra. We also show that the
larger values of the direct $d$-$d$ transfer are unfavourable in order to
explain the observed aspects of Na$_2$IrO$_3$ such as the ordering pattern of
the ground state and the excitation spectrum. These findings may indicate that
the direct $d$-$d$ transfer is suppressed by the structural distortions in the
view of excitation spectroscopy, as having been pointed out in the \it{ab
initio} calculation.",1508.06050v2
2019-06-04,Transfer maps in generalized group homology via submanifolds,"Let $N \subset M$ be a submanifold embedding of spin manifolds of some
codimension $k \geq 1$. A classical result of Gromov and Lawson, refined by
Hanke, Pape and Schick, states that $M$ does not admit a metric of positive
scalar curvature if $k = 2$ and the Dirac operator of $N$ has non-trivial
index, provided that suitable conditions are satisfied. In the cases $k=1$ and
$k=2$, Zeidler and Kubota, respectively, established more systematic results:
There exists a transfer $\mathrm{KO}_\ast(\mathrm{C}^{\ast} \pi_1 M)\to
\mathrm{KO}_{\ast - k}(\mathrm{C}^\ast \pi_1 N)$ which maps the index class of
$M$ to the index class of $N$. The main goal of this article is to construct
analogous transfer maps $E_\ast(\mathrm{B}\pi_1M) \to
E_{\ast-k}(\mathrm{B}\pi_1N)$ for different generalized homology theories $E$
and suitable submanifold embeddings. The design criterion is that it is
compatible with the transfer $E_\ast(M) \to E_{\ast-k}(N)$ induced by the
inclusion $N \subset M$ for a chosen orientation on the normal bundle. Under
varying restrictions on homotopy groups and the normal bundle, we construct
transfers in the following cases in particular: In ordinary homology, it works
for all codimensions. This slightly generalizes a result of Engel and
simplifies his proof. In complex K-homology, we achieve it for $k \leq 3$. For
$k \leq 2$, we have a transfer on the equivariant KO-homology of the
classifying space for proper actions.",1906.01190v1
2019-08-26,Transfer learning for scalability of neural-network quantum states,"Neural-network quantum states have shown great potential for the study of
many-body quantum systems. In statistical machine learning, transfer learning
designates protocols reusing features of a machine learning model trained for a
problem to solve a possibly related but different problem. We propose to
evaluate the potential of transfer learning to improve the scalability of
neural-network quantum states. We devise and present physics-inspired transfer
learning protocols, reusing the features of neural-network quantum states
learned for the computation of the ground state of a small system for systems
of larger sizes. We implement different protocols for restricted Boltzmann
machines on general-purpose graphics processing units. This implementation
alone yields a speedup over existing implementations on multi-core and
distributed central processing units in comparable settings. We empirically and
comparatively evaluate the efficiency (time) and effectiveness (accuracy) of
different transfer learning protocols as we scale the system size in different
models and different quantum phases. Namely, we consider both the transverse
field Ising and Heisenberg XXZ models in one dimension, and also in two
dimensions for the latter, with system sizes up to 128 and 8 x 8 spins. We
empirically demonstrate that some of the transfer learning protocols that we
have devised can be far more effective and efficient than starting from
neural-network quantum states with randomly initialized parameters.",1908.09883v1
2021-01-08,Transfer of Large-Scale Two-Dimensional Semiconductors: Challenges and Developments,"Two-dimensional (2D) materials offer opportunities to explore both
fundamental science and applications in the limit of atomic thickness. Beyond
the prototypical case of graphene, other 2D materials have recently come to the
fore. Of particular technological interest are 2D semiconductors, of which the
family of materials known as the group-VI transition metal dichalcogenides
(TMDs) has attracted much attention. The presence of a bandgap allows for the
fabrication of high on-off ratio transistors and optoelectronic devices, as
well as valley/spin polarized transport. The technique of chemical vapour
deposition (CVD) has produced high-quality and contiguous wafer-scale 2D films,
however, they often need to be transferred to arbitrary substrates for further
investigation. In this Review, the various transfer techniques developed for
transferring 2D films will be outlined and compared, with particular emphasis
given to CVD-grown TMDs. Each technique suffers undesirable process-related
drawbacks such as bubbles, residue or wrinkles, which can degrade device
performance by for instance reducing electron mobility. This Review aims to
address these problems and provide a systematic overview of key methods to
characterize and improve the quality of the transferred films and
heterostructures. With the maturing technological status of CVD-grown 2D
materials, a robust transfer toolbox is vital.",2101.03004v1
2021-01-27,Transfer-tensor description of memory effects in open-system dynamics and multi-time statistics,"The non-Markovianity of an arbitrary open quantum system is analyzed in
reference to the multi-time statistics given by its monitoring at discrete
times. On the one hand, we exploit the hierarchy of inhomogeneous transfer
tensors, which provides us with relevant information about the role of
correlations between the system and the environment in the dynamics. The
connection between the transfer-tensor hierarchy and the CP-divisibility
property is then investigated, by showing to what extent quantum Markovianity
can be linked to a description of the open-system dynamics by means of the
composition of 1-step transfer tensors only. On the other hand, we introduce
the set of stochastic transfer tensor transformations associated with local
measurements on the open system at different times and conditioned on the
measurement outcomes. The use of the transfer-tensor formalism accounts for
different kinds of memory effects in the multi-time statistics and allows us to
compare them on a similar footing with the memory effects present in
non-monitored non-Markovian dynamics, as we illustrate on a spin-boson case
study.",2101.11662v3
2022-03-29,Theory of the Dark State of Polyenes and Carotenoids,"A theory is developed to describe the singlet dark state (usually labeled S1
or 2Ag) of polyenes and carotenoids. The theory assumes that in principle this
state is a linear combination of a singlet triplet-pair and an odd-parity
charge-transfer exciton. Crucially, these components only couple when the
triplet-pair occupies neighboring dimers, such that an electron transfer
between the triplets creates a nearest-neighbor charge-transfer excitation.
This local coupling stabilises the 2Ag state and induces a nearest neighbor
attraction between the triplets. In addition, because of the electron-hole
attraction in the exciton, the increased probability that the electron-hole
pair occupies neighboring dimers enhances the triplet-triplet attraction: the
triplet pair is `slaved' to the charge-transfer exciton. The theory also
predicts that as the Coulomb interaction is increased, the 2Ag state evolves
from a predominately odd-parity charge-transfer exciton state with a small
component of triplet-pair character to a state predominately composed of a
triplet-pair with some exciton character. Above a critical Coulomb interaction
there is a decoupling of the triplet-pair and charge-transfer exciton
subspaces, such that the 2Ag state becomes entirely composed of an unbound
spin-correlated triplet pair. The predictions of this theory are qualitatively
consistent with high-level density matrix renormalization group calculations of
the Pariser-Parr-Pople (or extended Hubbard) model.",2203.15520v1
2005-05-05,Prompt Mergers of Neutron Stars with Black Holes,"Mergers of neutron stars with black holes have been suggested as candidates
for short gamma-ray bursts. They have also been studied for their potential as
gravitational wave sources observable with ground-based detectors. For these
purposes, it is important to know under what circumstances such a merger could
leave an accretion disk or result in a period of stable mass transfer. We show
that, consistent with recent numerical simulations, it is expected that mergers
between neutron stars and black holes will be prompt, with no accretion disk
and no stable mass transfer, if the black hole has a mass greater than that of
the neutron star and is spinning slowly. The reason is that for comparable
masses, angular momentum loss to gravitational radiation starts a plunge orbit
well outside the innermost stable circular orbit, causing direct merging rather
than extended mass transfer. Even when the black hole is spinning rapidly and
exactly prograde with respect to the orbit, we show that it is possible within
current understanding that no accretion disk will form under any circumstances,
but resolution of this will require full general relativistic numerical
simulations with no approximations.",0505094v1
1999-08-02,Spin and charge ordering in self-doped Mott insulators,"We have investigated possible spin and charge ordered states in 3d
transition-metal oxides with small or negative charge-transfer energy, which
can be regarded as self-doped Mott insulators, using Hartree-Fock calculations
on d-p-type lattice models. It was found that an antiferromagnetic state with
charge ordering in oxygen 2p orbitals is favored for relatively large
charge-transfer energy and may be relevant for PrNiO$_3$ and NdNiO$_3$. On the
other hand, an antiferromagnetic state with charge ordering in transition-metal
3$d$ orbitals tends to be stable for highly negative charge-transfer energy and
can be stabilized by the breathing-type lattice distortion; this is probably
realized in YNiO$_3$.",9908016v1
2004-09-19,Transfer matrix functional relations for the generalized tau_2(t_q) model,"The $N$-state chiral Potts model in lattice statistical mechanics can be
obtained as a ``descendant'' of the six-vertex model, via an intermediate
``$Q$'' or ``$\tau_2 (t_q)$'' model. Here we generalize this to obtain a
column-inhomogeneous $\tau_2 (t_q)$ model, and derive the functional relations
satisfied by its row-to-row transfer matrix. We do {\em not} need the usual
chiral Potts relations between the $N$th powers of the rapidity parameters
$a_p, b_p, c_p, d_p$ of each column. This enables us to readily consider the
case of fixed-spin boundary conditions on the left and right-most columns. We
thereby re-derive the simple direct product structure of the transfer matrix
eigenvalues of this model, which is closely related to the superintegrable
chiral Potts model with fixed-spin boundary conditions.",0409493v1
2005-09-19,Quantum state transfer in arrays of flux qubits,"In this work, we describe a possible experimental realization of Bose's idea
to use spin chains for short distance quantum communication [S. Bose, {\it
Phys. Rev. Lett.} {\bf 91} 207901]. Josephson arrays have been proposed and
analyzed as transmission channels for systems of superconducting charge qubits.
Here, we consider a chain of persistent current qubits, that is appropriate for
state transfer with high fidelity in systems containing flux qubits. We
calculate the fidelity of state transfer for this system. In general, the
Hamiltonian of this system is not of XXZ-type, and we analyze the magnitude and
the effect of the terms that don't conserve the z-component of the total spin.",0509478v1
2006-06-01,Peierls distorted chain as a quantum data bus for quantum state transfer,"We systematically study the transfer of quantum state of electron spin as the
flying qubit along a half-filled Peierls distorted tight-binding chain
described by the Su-Schrieffer-Heeger (SSH) model, which behaves as a quantum
data bus. This enables a novel physical mechanism for quantum communication
with always-on interaction: the effective hopping of the spin carrier between
sites $A$ and $B$ connected to two sites in this SSH chain can be induced by
the quasi-excitations of the SSH model. As we prove, it is the Peierls energy
gap of the SSH quasi-excitations that plays a crucial role to protect the
robustness of the quantum state transfer process. Moreover, our observation
also indicates that such a scheme can also be employed to explore the intrinsic
property of the quantum system.",0606021v1
2006-07-03,Longitudinal Spin Transfer to the $Λ$ Hyperon in Semi-Inclusive Deep-Inelastic Scattering,"The transfer of polarization from a high-energy positron to a \lam hyperon
produced in semi-inclusive deep-inelastic scattering has been measured. The
data have been obtained by the HERMES experiment at DESY using the 27.6 GeV
longitudinally polarized positron beam of the HERA collider and unpolarized gas
targets internal to the positron (electron) storage ring. The longitudinal spin
transfer coefficient is found to be $\dll = 0.11 \pm 0.10 \mathrm{(stat)} \pm
0.03 \mathrm{(syst)}$ at an average fractional energy carried by the \lam
hyperon $<z >= 0.45$. The dependence of \dll on both the fractional energy $z$
and the fractional longitudinal momentum $x_F$ is presented.",0607004v2
1999-11-29,Nonstandard coproducts and the Izergin-Korepin open spin chain,"Corresponding to the Izergin-Korepin (A_2^(2)) R matrix, there are three
diagonal solutions (``K matrices'') of the boundary Yang-Baxter equation. Using
these R and K matrices, one can construct transfer matrices for open integrable
quantum spin chains. The transfer matrix corresponding to the identity matrix
K=1 is known to have U_q(o(3)) symmetry. We argue here that the transfer
matrices corresponding to the other two K matrices also have U_q(o(3))
symmetry, but with a nonstandard coproduct. We briefly explore some of the
consequences of this symmetry.",9911232v2
2006-10-31,Baxter Q-operator for graded SL(2|1) spin chain,"We study an integrable noncompact superspin chain model that emerged in
recent studies of the dilatation operator in the N=1 super-Yang-Mills theory.
It was found that the latter can be mapped into a homogeneous Heisenberg magnet
with the quantum space in all sites corresponding to infinite-dimensional
representations of the SL(2|1) group. We extend the method of the Baxter
Q-operator to spin chains with supergroup symmetry and apply it to determine
the eigenspectrum of the model. Our analysis relies on a factorization property
of the R-operators acting on the tensor product of two generic
infinite-dimensional SL(2|1) representations. It allows us to factorize an
arbitrary transfer matrix into a product of three `elementary' transfer
matrices which we identify as Baxter Q-operators. We establish functional
relations between transfer matrices and use them to derive the TQ-relations for
the Q-operators. The proposed construction can be generalized to integrable
models based on supergroups of higher rank and, in distinction to the Bethe
Ansatz, it is not sensitive to the existence of the pseudovacuum state in the
quantum space of the model.",0610332v1
2004-07-22,Broadband Relaxation-Optimized Polarization Transfer in Magnetic Resonance,"Many applications of magnetic resonance are limited by rapid loss of spin
coherence caused by large transverse relaxation rates. In nuclear magnetic
resonance (NMR) of large proteins, increased relaxation losses lead to poor
sensitivity of experiments and increased measurement time. In this paper we
develop broadband relaxation optimized pulse sequences (BB-CROP) which approach
fundamental limits of coherence transfer efficiency in the presence of very
general relaxation mechanisms that include cross-correlated relaxation. These
broadband transfer schemes use new techniques of chemical shift refocusing
(STAR echoes) that are tailored to specific trajectories of coupled spin
evolution. We present simulations and experimental data indicating significant
enhancement in the sensitivity of multi-dimensional NMR experiments of large
molecules by use of these methods.",0407178v1
2004-11-02,Perfect Transfer of Arbitrary States in Quantum Spin Networks,"We propose a class of qubit networks that admit perfect state transfer of any
two-dimensional quantum state in a fixed period of time. We further show that
such networks can distribute arbitrary entangled states between two distant
parties, and can, by using such systems in parallel, transmit the higher
dimensional systems states across the network. Unlike many other schemes for
quantum computation and communication, these networks do not require qubit
couplings to be switched on and off. When restricted to $N$-qubit spin networks
of identical qubit couplings, we show that $2\log_3 N$ is the maximal perfect
communication distance for hypercube geometries. Moreover, if one allows fixed
but different couplings between the qubits then perfect state transfer can be
achieved over arbitrarily long distances in a linear chain. This paper expands
and extends the work done in PRL 92, 187902.",0411020v2
2008-03-06,Tight-Binding Theory of Manganese and Iron Oxides,"The electronic structure is found to be understandable in terms of free-atom
term values and universal interorbital coupling parameters, since
self-consistent tight-binding calculations indicate that Coulomb shifts of the
d-state energies are small. Special-point averages over the bands are seen to
be equivalent to treatment of local octahedral clusters. The cohesive energy
per manganese for MnO, Mn2O3, and MnO2, in which manganese exists in valence
states Mn2+, Mn3+, and Mn4+, is very nearly the same and dominated by the
transfer of manganese s electrons to oxygen p states. There are small
corrections, one eV per Mn in all cases, from couplings of minority-spin
states. Transferring one majority-spin electron from an upper cluster state to
a nonbonding oxygen state adds 1.67 eV to the cohesion for Mn2O3, and two
transfers adds twice that for MnO2 . The electronic and magnetic properties are
consistent with this description and appear to be understandable in terms of
the same parameters.",0803.0994v1
2009-01-22,Full counting statistics of crossed Andreev reflection,"We calculate the full transport counting statistics in a three-terminal
tunnel device with one superconducting source and two normal-metal or
ferromagnet drains. We obtain the transport probability distribution from
direct Andreev reflection, crossed Andreev reflection, and electron transfer
which reveals how these processes' statistics are determined by the device
conductances. The cross-correlation noise is a result of competing
contributions from crossed Andreev reflection and electron transfer, as well as
antibunching due to the Pauli exclusion principle. For spin-active tunnel
barriers that spin polarize the electron flow, crossed Andreev reflection and
electron transfer statistics exhibit different dependencies on the
magnetization configuration, and can be controlled by relative magnetization
directions and voltage bias.",0901.3551v1
2009-07-02,Measurement of the Longitudinal Spin Transfer to Lambda and Anti-Lambda Hyperons in Polarised Muon DIS,"The longitudinal polarisation transfer from muons to lambda and anti-lambda
hyperons, D_LL, has been studied in deep inelastic scattering off an
unpolarised isoscalar target at the COMPASS experiment at CERN. The spin
transfers to lambda and anti-lambda produced in the current fragmentation
region exhibit different behaviours as a function of x and xF . The measured x
and xF dependences of D^lambda_LL are compatible with zero, while
D^anti-lambda_LL tends to increase with xF, reaching values of 0.4 - 0.5. The
resulting average values are D^lambda_LL = -0.012 +- 0.047 +- 0.024 and
D^anti-lambda_LL = 0.249 +- 0.056 +- 0.049. These results are discussed in the
frame of recent model calculations.",0907.0388v1
2010-07-18,Perfect state transfer via quantum probability theory,"The transfer of quantum states has played an important role in quantum
information processing. In fact, transfer of quantum states from point $A$ to
$B$ with unit fidelity is very important for us and we focus on this case. In
recent years, in represented works, they designed Hamiltonian in a way that a
mirror symmetry creates with with respect to network center. In this paper, we
stratify the spin network with respect to an arbitrary vertex of the spin
network o then we design coupling coefficient in a way to create a mirror
symmetry in Hamiltonian with respect to center. By using this Hamiltonian and
represented approach, initial state that have been encoded on the first vertex
in suitable time and with unit fidelity from it's antipodes vertex can be
received. In his work, there is no need to external control.",1007.3002v1
2013-02-06,Driving Dipolar Fermions into the Quantum Hall Regime by Spin-Flip Induced Insertion of Angular Momentum,"A new method to drive a system of neutral dipolar fermions into the lowest
Landau level regime is proposed. By employing adiabatic spin-flip processes in
combination with a diabatic transfer, the fermions are pumped to higher orbital
angular momentum states in a repeated scheme that allows for the precise
control over the final angular momentum. A simple analytical model is derived
to quantify the transfer and compare the approach to rapidly rotating systems.
Numerical simulations of the transfer process have been performed for small,
interacting systems.",1302.1308v3
2014-02-21,Interfacing Superconducting Qubits and Telecom Photons via a Rare-Earth Doped Crystal,"We propose a scheme to couple short single photon pulses to superconducting
qubits. An optical photon is first absorbed into an inhomogeneously broadened
rare-earth doped crystal using controlled reversible inhomogeneous broadening.
The optical excitation is then mapped into a spin state using a series of
$\pi$-pulses and subsequently transferred to a superconducting qubit via a
microwave cavity. To overcome the intrinsic and engineered inhomogeneous
broadening of the optical and spin transitions in rare earth doped crystals, we
make use of a special transfer protocol using staggered $\pi$-pulses. We
predict total transfer efficiencies on the order of 90%.",1402.5405v3
2014-04-17,Rényi Information flow in the Ising model with single-spin dynamics,"The $n$-index R\'enyi mutual information and transfer entropy for the
two-dimensional kinetic Ising model with arbitrary single-spin dynamics in the
thermodynamic limit are derived as functions of thermodynamic quantities. By
means of Monte Carlo simulations with the Wolff algorithm, we calculate the
information flows in the Ising model with the Metropolis dynamics and the
Glauber dynamics. We find that, not only the global R\'enyi transfer entropy,
but also the pairwise R\'enyi transfer entropy peaks in the disorder phase.
Therefore, the R\'enyi information flows may be used as better tools than the
Shannon counterparts in the study of phase transitions in complex dynamical
systems.",1404.4567v2
2016-12-02,Unifying quantum heat transfer in a nonequilibrium spin-boson model with full counting statistics,"To study the full counting statistics of quantum heat transfer in a driven
nonequilibrium spin-boson model, we develop a generalized nonequilibrium
polaron-transformed Redfield equation with an auxiliary counting field. This
enables us to study the impact of qubit-bath coupling ranging from weak to
strong regimes. Without external modulations, we observe maximal values of both
steady state heat flux and noise power at moderate coupling regimes, below
which we find those two transport quantities are enhanced by the finite qubit
energy bias. With external modulations, the geometric-phase-induced heat flux
shows monotonic decrease as increasing the qubit-bath coupling at zero qubit
energy bias (without bias). While under finite qubit energy bias (with bias),
the geometric-phase-induced heat flux exhibits an interesting reversal behavior
in strong coupling regime. Our results unify the seemingly contradictory
results in weak and strong qubit-bath coupling regimes, and provide detailed
dissections for the quantum fluctuation of nonequilibrium heat transfer.",1612.00533v2
2017-01-24,Realization of a cascaded quantum system: heralded absorption of a single photon qubit by a single-electron charged quantum dot,"Photonic losses pose a major limitation for implementation of quantum state
transfer between nodes of a quantum network. A measurement that heralds
successful transfer without revealing any information about the qubit may
alleviate this limitation. Here, we demonstrate heralded absorption of a single
photonic qubit generated by a single neutral quantum dot, by a single-electron
charged quantum dot that is located 5 meters away. The transfer of quantum
information to the spin degree of freedom takes place upon emission of a
photon: for a properly chosen or prepared quantum dot, detection of this photon
yields no information about the qubit. We show that this process can be
combined with local operations optically performed on the destination node, by
measuring classical correlations between the absorbed photon color and the
final state of the electron spin. Our work suggests alternative avenues for
realization of quantum information protocols based on cascaded quantum systems.",1701.06957v1
2017-04-07,Reconfigurable nano-scale spin-wave directional coupler,"A spin-wave (SW) directional coupler comprised of two laterally parallel
nano-scale dipolarly-coupled SW waveguides is proposed and studied using
micromagnetic simulations and analytical theory. The energy of a SW excited in
one of the waveguides in the course of propagation is periodically transferred
to the other waveguide and back, and the spatial half-period of this transfer
is defined as the coupling length. The coupling length is determined by the
dipolar coupling between the waveguides, and the fraction of the SW energy
transferred to the other waveguide at the device output can be varied with the
SW frequency, bias magnetic field, and relative orientation of the waveguide's
static magnetizations. The proposed design of a directional coupler can be used
in digital computing-oriented magnonics as a connector (multiplexer) of
magnonic conduits without a direct contact, or in the analog microwave signal
processing as a reconfigurable nano-scale power divider and/or frequency
separator.",1704.02255v1
2017-08-31,Sensitivity and Robustness of Quantum Spin-1/2 Rings to Parameter Uncertainty,"Selective transfer of information between spin-1/2 particles arranged in a
ring is achieved by optimizing the transfer fidelity over a readout time window
via shaping, externally applied, static bias fields. Such static control fields
have properties that clash with the expectations of classical control theory.
Previous work has shown that there are cases in which the logarithmic
differential sensitivity of the transfer fidelity to uncertainty in coupling
strength or spillage of the bias field to adjacent spins is minimized by
controllers that produce the best fidelity. Here we expand upon these examples
and examine cases of both classical and non-classical behavior of logarithmic
sensitivity to parameter uncertainty and robustness as measured by the $\mu$
function for quantum systems. In particular we examine these properties in an
11-spin ring with a single uncertainty in coupling strength or a single bias
spillage.",1708.09649v1
2018-02-13,Surveying the quantum group symmetries of integrable open spin chains,"Using anisotropic R-matrices associated with affine Lie algebras $\hat g$
(specifically, $A_{2n}^{(2)}, A_{2n-1}^{(2)}, B_n^{(1)}, C_n^{(1)}, D_n^{(1)}$)
and suitable corresponding K-matrices, we construct families of integrable open
quantum spin chains of finite length, whose transfer matrices are invariant
under the quantum group corresponding to removing one node from the Dynkin
diagram of $\hat g$. We show that these transfer matrices also have a duality
symmetry (for the cases $C_n^{(1)}$ and $D_n^{(1)}$) and additional $Z_2$
symmetries that map complex representations to their conjugates (for the cases
$A_{2n-1}^{(2)}, B_n^{(1)}, D_n^{(1)}$). A key simplification is achieved by
working in a certain ""unitary"" gauge, in which only the unbroken symmetry
generators appear. The proofs of these symmetries rely on some new properties
of the R-matrices. We use these symmetries to explain the degeneracies of the
transfer matrices.",1802.04864v1
2018-03-13,Gamow-Teller transitions and neutron-proton-pair transfer reactions,"We propose a schematic model of nucleons moving in spin--orbit partner
levels, $j=l\pm{\sfrac12}$, to explain Gamow--Teller and two-nucleon transfer
data in $N=Z$ nuclei above $^{40}$Ca. Use of the $LS$ coupling scheme provides
a more transparent approach to interpret the structure and reaction data.We
apply the model to the analysis of charge-exchange,
$^{42}$Ca($^3$He,t)$^{42}$Sc, and np-transfer, $^{40}$Ca($^3$He,p)$^{42}$Sc,
reactions data to define the elementary modes of excitation in terms of both
isovector and isoscalar pairs, whose properties can be determined by adjusting
the parameters of the model (spin--orbit splitting, isovector pairing strength
and quadrupole matrix element) to the available data. The overall agreement
with experiment suggests that the approach captures the main physics
ingredients and provides the basis for a boson approximation that can be
extended to heavier nuclei. Our analysis also reveals that the SU(4)-symmetry
limit is not realized in $^{42}$Sc.",1803.04704v1
2018-03-27,Interplay between speed and fidelity in off-resonant quantum-state transfer protocols,"An arbitrary qubit can be transmitted through a spin chain by perturbatively
coupling both communicating parties to it. Those so-called weak-coupling models
rely on effective Rabi oscillations between them, yielding nearly maximum
fidelity while offering great resilience against disorder with the cost of
having long transfer times. Considering this framework, here we address a 1D
non-symmetric channel connecting two spins, one placed at each end of it. Given
any pattern of nearest-neighbor coupling strengths, we obtain an analytical
expression that accounts for the effective long-range interaction between them
and study the interplay between transfer time and fidelity. Furthermore, we
show that homogeneous channels provide the best speed-fidelity tradeoff.",1803.10007v2
2018-04-30,Single-Nitrogen-vacancy-center quantum memory for a superconducting flux qubit mediated by a ferromagnet,"We propose a quantum memory scheme to transfer and store the quantum state of
a superconducting flux qubit (FQ) into the electron spin of a single
nitrogen-vacancy (NV) center in diamond via yttrium iron garnet (YIG), a
ferromagnet. Unlike an ensemble of NV centers, the YIG moderator can enhance
the effective FQ-NV-center coupling strength without introducing additional
appreciable decoherence. We derive the effective interaction between the FQ and
the NV center by tracing out the degrees of freedom of the collective mode of
the YIG spins. We demonstrate the transfer, storage, and retrieval procedures,
taking into account the effects of spontaneous decay and pure dephasing. Using
realistic experimental parameters for the FQ, NV center and YIG, we find that a
combined transfer, storage, and retrieval fidelity higher than 0.9, with a long
storage time of 10 ms, can be achieved. This hybrid system not only acts as a
promising quantum memory, but also provides an example of enhanced coupling
between various systems through collective degrees of freedom.",1804.11231v1
2019-01-13,Two-Loop Integrability of ABJM Open Spin Chain from Giant Graviton,"We prove the integrability of the two-loop open spin chain Hamiltonian from
ABJM determinant like operators given in arXiv:1809.09941. By explicitly
constructing R-matrices and K-matrices, we successfully obtain the two-loop
Hamiltonian from the double row transfer matrices. This proves the
integrability of our two-loop Hamiltonian. Based on the vacuum eigenvalues of
the transfer matrices, we make a conjecture on the eigenvalues of the transfer
matrices for general excited states. Bethe ansatz equations are simply obtained
from the analytic conditions at the superficial poles of the eigenvalues.",1901.03949v3
2019-07-09,Quantum state transfer via acoustic edge states in a 2D optomechanical array,"We propose a novel hybrid platform where solid-state spin qubits are coupled
to the acoustic modes of a two-dimensional array of optomechanical nano
cavities. Previous studies of coupled optomechanical cavities have shown that
in the presence of strong optical driving fields, the interplay between the
photon-phonon interaction and their respective inter-cavity hopping allows the
generation of topological phases of sound and light. In particular, the
mechanical modes can enter a Chern insulator phase where the time-reversal
symmetry is broken. In this context, we exploit the robust acoustic edge states
as a chiral phononic waveguide and describe a state transfer protocol between
spin qubits located in distant cavities. We analyze the performance of this
protocol as a function of the relevant system parameters and show that a
high-fidelity and purely unidirectional quantum state transfer can be
implemented under experimentally realistic conditions. As a specific example,
we discuss the implementation of such topological quantum networks in diamond
based optomechanical crystals where point defects such as silicon-vacancy
centers couple to the chiral acoustic channel via strain.",1907.04073v1
2019-12-09,Optical vortex-induced forward mass transfer: Manifestation of helical trajectory of optical vortex,"The orbital angular momentum of an optical vortex field is found to twist
high viscosity donor material to form a micron-scale 'spin jet'. This unique
phenomenon manifests the helical trajectory of the optical vortex. Going beyond
both the conventional ink jet and laser induced forward mass transfer (LIFT)
patterning technologies, it also offers the formation and ejection of a
micron-scale 'spin jet' of the donor material even with an ultrahigh viscosity
of 4 Pas. This optical vortex laser induced forward mass transfer (OV-LIFT)
patterning technique will enable the development of next generation printed
photonic/electric/spintronic circuits formed of ultrahigh viscosity donor dots
containing functional nanoparticles, such as quantum dots, metallic particles
and magnetic ferrite particles, with ultrahigh spatial resolution. It can also
potentially explore a completely new needleless drug injection.",1912.03907v1
2020-03-02,Production of Highly Polarized Positron Beams via Helicity Transfer from Polarized Electrons in a Strong Laser Field,"The production of a highly-polarized positron beam via nonlinear
Breit-Wheeler processes during the interaction of an ultraintense circularly
polarized laser pulse with a longitudinally spin-polarized ultrarelativistic
electron beam is investigated theoretically. A new Monte Carlo method employing
fully spin-resolved quantum probabilities is developed under the local constant
field approximation to include three-dimensional polarizations effects in
strong laser fields. The produced positrons are longitudinally polarized
through polarization transferred from the polarized electrons by the medium of
high-energy photons. The polarization transfer efficiency can approach 100\%
for the energetic positrons moving at smaller deflection angles. This method
simplifies the post-selection procedure to generate high-quality positrons in
further applications. In a feasible scenario, a highly polarized ($40\%-65\%$),
intense ($10^5$/bunch$-10^6 $/bunch), collimated ($5$mrad$-70$ mrad) positron
beam can be obtained in a femtosecond timescale. The longitudinally polarized
positron sources are desirable for applications in high-energy physics and
material science .",2003.01547v1
2020-04-08,Information transfer in coupled Langevin equations,"We provide a general formula, based on stochastic thermodynamics, that
describes the flow of information between an arbitrary number of coupled
complex-valued Langevin equations. This permits to describe the transfer of
information in complex networks of oscillators out of thermal equilibrium, that
can model a multitude of physical, biological and man made systems. The
information flow contains an incoherent component proportional to the amplitude
difference and a coherent one proportional to the phase difference between the
oscillators, which depends on their synchronisation. We illustrate the theory
by simulating the dynamics of a spin-Seebeck diode, described by two coupled
oscillators, that can rectify the flow of information, energy and spin.
Remarkably, the system can operate in a regime where the synchronisation is
broken and there is a flow of incoherent information without net transfer of
energy.",2004.03950v1
2020-05-15,Controlled quantum state transfer in $XX$ spin chains at the Quantum Speed Limit,"The Quantum Speed Limit can be found in many different situations, in
particular in the propagation of information through quantum spin chains. In
homogeneous chains it implies that taking information from one extreme of the
chain to the other will take a time $O(N/2)$, where $N$ is the chain length.
Using Optimal Control Theory we design control pulses that achieve near perfect
population transfer between the extremes of the chain at times on the order of
$N/2$, or larger, depending on which features of the transfer process are to be
studied. Our results show that the control pulses that govern the dynamical
behaviour of chains with different lengths are closely related, that larger
control times imply more complicated control pulses than those found at times
on the order of $N/2$ and also larger driving energies. The pulses were
constructed for control schemes involving one or two actuators in chains with
exchange couplings without static disorder. Our results also show that the two
actuator scheme is considerably more robust against the presence of static
disorder than the scheme that uses just a single one.",2005.07819v1
2022-09-23,Asymmetry effects on the phases of RKKY-coupled two-impurity Kondo systems,"In a related work [arXiv:2106.07519] we have shown that in the two-impurity
Anderson (2iA) model with two hosts coupled by spin exchange in the most
symmetric case there are either two phase transitions or none. The phases
comprise the conventional Kondo and RKKY regimes and a novel one, interpreted
as a Kondo-stabilized, metallic quantum spin liquid (QSL). Here we analyze how
various types of asymmetry affect this picture. We demonstrate that the
transitions are robust against the coupling and particle-hole asymmetries,
provided charge transfer is forbidden. This holds true despite the scattering
phase shift at each impurity taking non-universal values. Finally, for an
extended model including charge transfer between the hosts and a small Coulomb
interaction at the host sites directly coupled to impurities, we show that the
presence of charge transfer changes the phase transitions into crossovers.
Provided the inter-host hopping is sufficiently small, this leads to
qualitatively the same physics at non-zero temperature. The relevance of this
model for rare-earth atoms in a metallic host is discussed and potential
experimental setups for observing our findings are proposed.",2209.11556v1
2023-01-05,WIYN Open Cluster Study. LXXXVII. HST Ultraviolet Detection of Hot White Dwarf Companions to Blue Lurkers in M67,"We present the results of our Hubble Space Telescope far-ultraviolet survey
of the blue lurkers (BLs) in M67. We find evidence for two white dwarf
companions among the BLs that are indicative of mass transfer from an evolved
companion, one in WOCS 14020 and the other in WOCS 3001. The cooling ages of
the white dwarfs suggest that mass transfer in these systems occurred
$\sim$300--540 Myr and $\sim$600--900 Myr ago, respectively. The rotation
periods and cooling ages of the BLs are consistent with spin-up and subsequent
single-star spin-down models, and binary evolution models yield plausible
evolutionary pathways to both BLs via highly non-conservative mass transfer. We
conclude that the BLs are lower-luminosity analogues to the classical blue
stragglers.",2301.02303v1
2021-09-10,Selectively pulsed spin order transfer increases parahydrogen-induced NMR amplification of insensitive nuclei and makes polarization transfer more robust,"We describe a new method for pulsed spin order transfer (SOT) of parahydrogen
induced polarization (PHIP) that enables close to 100 % polarization in
incompletely 2H-labeled molecules by exciting only the desired protons in a
frequency-selective manner. While a selective pulse (SP) on 1H at the beginning
of pulsed SOT had been considered before, using SPs during the SOT suppresses
undesired indirect spin-spin interactions. As a result, we achieved a more
robust SOT for the SP variants of the phINEPT+ sequence that we refer to as
phSPINEPT+. Thereby, for the first time, we report a sequence that is effective
for all weakly coupled spin systems. Our simulations show that the method
converts close to 100 % of the parahydrogen-derived spin order into 13C
hyperpolarization in weakly coupled three-spin systems and partially or fully
2H-labeled molecules if relaxation is neglected. Experimentally we demonstrate
high hyperpolarization of 13C with 15.8 % for 1-13C-hydroxyethyl propionate-d3
and 12.6 % for 1-13C-ethyl acetate-d6, which corresponds to ~47 % and ~38 % if
the enrichment of parahydrogen had been 100 %. Even in non-2H-labeled
molecules, a remarkable 13C polarization is achieved, e.g. up to 20 % were
simulated for 100 % pH2, and 1.25 % were obtained experimentally for
1-13C-ethyl pyruvate and 50 % pH2, which can be further improved by faster
hydrogenation. As a result, full deuterium labeling may no longer be required
e.g., when new PHIP agents are investigated, the synthesis of fully deuterated
molecules is too complex, or when a kinetic isotope effect regarding the
metabolic conversion rate of an agent is to be avoided. Using SPs during SOT
seems very promising and may be extended to other sequences in the context of
PHIP and be-yond to make them less prone to experimental imperfections or real
molecular environments.",2109.04799v1
2005-03-04,Visco-magnetic torque at the core mantle boundary,"A magneto-hydrodynamic model of boundary layers at the Core-Mantle Boundary
(CMB) is derived and used to compute the viscous and electromagnetic torques
generated by the Earth's nutation forcing. The predicted electromagnetic torque
alone cannot account for the dissipation estimated from the observations of the
free core nutation. The presence of a viscous boundary layer in the
electromagnetic skin layer at the CMB, with its additional dissipative torques,
may explain the geodetic data. An apparent Ekman number at the top of the core
between 3 and $5 10^{-11}$ is inferred depending on the electrical conductivity
of the mantle.",0503038v2
2007-08-23,Current-induced torques due to compensated antiferromagnets,"We analyse the influence of current induced torques on the magnetization
configuration of a ferromagnet in a circuit containing a compensated
antiferromagnet. We argue that these torques are generically non-zero and
support this conclusion with a microscopic NEGF calculation for a circuit
containing antiferromagnetic NiMn and ferromagnetic Co layers. Because of
symmetry dictated differences in the form of the current-induced torque, the
phase diagram which expresses the dependence of ferromagnet configuration on
current and external magnetic field differs qualitatively from its
ferromagnet-only counterpart.",0708.3231v1
2008-03-24,Polarity-dependent dielectric torque in nematic liquid crystals,"The dielectric dispersion in the uniaxial nematic liquid crystals affects the
switching dynamics of the director, as the dielectric torque is determined by
not only the present values of the electric field and director but also by
their past values. We demonstrate that this dielectric memory leads to an
unusual contribution to the dielectric torque that is linear in the present
field and thus polarity-sensitive. This torque can be used to accelerate the
switch-off phase of director dynamics.",0803.3429v1
2008-09-03,Torque determination on DNA with magnetic tweezers,"We deduced the torque applied on a single stretched and twisted DNA by
integrating with respect to force the change in the molecule's extension as it
is coiled. While consistent with previous direct measurements of the torque at
high forces (F>1 pN) this method, which is simple and does not require a
sophisticated set-up, allows for lower force estimates. We used this approach
to deduce the effective torsional modulus of DNA, which decreases with force
and to estimate the buckling torque of DNA as a function of force in various
salt conditions.",0809.0621v1
2009-02-20,Interaction of the Torque-Induced Elastic Charge and Elastic Dipole with a Wall in a Nematic Liquid Crystal,"We show that the elastic charge of colloids in a nematic liquid crystal can
be generated by the vector of external torque. The torque components play the
role of two component charge (dyad) and give rise to the Coulomb-like
potential, while their conservation law plays the role similar to that of
Gauss' theorem in the electrostatics. The theory is applied to the
colloid-surface interaction. A wall with homeotropic or planar director is
shown to induce a repulsive 1/r^4 force on the elastic dipole. The external
torque, however, induces the elastic charge in this colloid and triggers
switching to the 1/r^2 repulsion.",0902.3543v2
2009-09-24,A torque formula for non-isothermal Type I planetary migration - I. Unsaturated horseshoe drag,"We study the torque on low-mass planets embedded in protoplanetary discs in
the two-dimensional approximation, incorporating non-isothermal effects. We
couple linear estimates of the Lindblad (or wave) torque to a simple, but
non-linear, model of adiabatic corotation torques (or horseshoe drag),
resulting in a simple formula that governs Type I migration in non-isothermal
discs. This formula should apply in optically thick regions of the disc, where
viscous and thermal diffusion act to keep the horseshoe drag unsaturated. We
check this formula against numerical hydrodynamical simulations, using three
independent numerical methods, and find good agreement.",0909.4552v1
2010-10-05,Lindblad resonance torques in relativistic discs: I. Basic equations,"Lindblad resonances have been suggested as an important mechanism for angular
momentum transport and heating in discs in binary black hole systems. We
present the basic equations for the torque and heating rate for relativistic
thin discs subjected to a perturbation. The Lindblad resonance torque is
written explicitly in terms of metric perturbations for an equatorial disc in a
general axisymmetric, time-stationary spacetime with a plane of symmetry. We
show that the resulting torque formula is gauge-invariant. Computations for the
Schwarzschild and Kerr spacetimes are presented in the companion paper.",1010.0758v2
2013-01-30,The Casimir Effect for Arbitrary Optically Anisotropic Materials,"We extend a fictitious-cavity approach to calculate the Casimir effect for
cavities bounded by flat anisotropic materials. We calculate the energy, force
and torque in terms only of the optical coefficients of the walls of the
cavity. We calculate the Casimir effect at zero and finite temperature for some
simple systems. As a non trivial application, we calculate the torque between a
semi-infinite anisotropic plate and an anisotropic film. We study the effect of
the film thickness in the torque and find an optimal width that maximizes the
torque.",1301.7306v1
2014-03-05,Non Linear Susceptibility from High DC Field Torque Magnetometry,"Torque magnetometry is a convenient technique to measure the magnetic
properties of anisotropic materials. Advances in micromachining and the
availability of robust materials with which such magnetometers can be
fabricated has made them reliable even in adverse conditions such as very high
magnetic fields and both high and very low temperatures. In most applications
with such magnetometers the measured torque signals are used to arrive at the
linear magnetic susceptibilities only. In this short note we extend torque
magnetometry to measure nonlinear susceptibilities and illustrate our methods
with representative data on the heavy fermion compound UPt3",1403.1287v1
2014-09-20,Electromagnetic force and torque in Lorentz and Einstein-Laub formulations,"The Lorentz force law of classical electrodynamics requires the introduction
of hidden energy and hidden momentum in situations where an electric field acts
on a magnetic material. In contrast, the Einstein-Laub formulation does not
invoke hidden entities. The total force and torque exerted by electromagnetic
fields on a given object are independent of whether the force and torque
densities are evaluated using the law of Lorentz or that of Einstein and Laub.
Hidden entities aside, the two formulations differ only in their predicted
force and torque distributions throughout material media.",1409.5860v1
2015-03-07,A chiral route to pulling optical forces and left-handed optical torques,"We analyze how chirality can generate pulling optical forces and left-handed
torques by cross-coupling linear-to-angular momenta between the light field and
the chiral object. In the dipolar regime, we reveal that such effects can
emerge from a competition between non-chiral and chiral contributions to
dissipative optical forces and torques, a competition balanced by the strength
of chirality of the object. We extend the analysis to large chiral spheres
where the interplay between chirality and multipolar resonances can give rise
to a break of symmetry that flips the signs of both optical forces and torques.",1503.02175v1
2016-05-06,Single-Interface Casimir Torque,"It is shown that the quantum fluctuations of the electromagnetic field
generally induce a torque at the interface of an anisotropic material with
another anisotropic or isotropic material. It is proven that this torque
depends on an interface zero-point energy determined by the dispersion of the
interface (localized and extended) modes. Our theory demonstrates that the
single-interface torque is essential to understand the Casimir physics of
material systems with anisotropic elements and determines the equilibrium
positions of the system.",1605.02116v1
2017-07-03,Transition and formation of the torque pattern of undulatory locomotion in resistive force dominated media,"In undulatory locomotion, torques along the body are required to overcome
external forces from the environment and bend the body. Using a resistive force
theory model, we find that the torque from external resistive forces has a
traveling wave pattern with decreasing speed as the wave number (the number of
wavelengths on the locomotor's body) increases from 0.5 to 1.8, and the torque
transitions into a two-wave-like pattern and complex patterns as the wave
number increases to values of 2 and greater values. Using phasor diagrams
analysis, we reveal the formation and transitions of the pattern as the
consequences of the integration and cancellation of force phasors.",1707.00492v2
2017-09-20,Contact Force and Joint Torque Estimation Using Skin,"In this paper, we present algorithms to estimate external contact forces and
joint torques using only skin, i.e. distributed tactile sensors. To deal with
gaps between the tactile sensors (taxels), we use interpolation techniques. The
application of these interpolation techniques allows us to estimate contact
forces and joint torques without the need for expensive force-torque sensors.
Validation was performed using the iCub humanoid robot.",1709.06902v1
2019-09-06,Collective cell migration of epithelial cells driven by chiral torque generation,"Various multicellular tissues show chiral morphology. Experimental studies
have shown this can originate from cell chirality. However, no theory has been
proposed to connect the cellular chiral torque and multicellular chiral
morphogenesis. We propose a model of confluent tissue dynamics with cellular
chiral torque. We found that cells migrate unidirectionally under a gradient of
cellular chiral torque. While the migration speed varies depending on the
tissue's mechanical parameters, it is scaled solely by a structural order
parameter for liquid-to-solid transition in confluent tissues.",1909.02771v1
2022-11-29,Robust design optimization taking into account manufacturing uncertainties of a permanent magnet assisted synchronous reluctance motor,"In this paper, deterministic and robust design optimizations of a permanent
magnet assisted synchronous reluctance machine were performed to increase its
mean torque while reducing torque ripple. These optimizations were carried out
using a surrogate model based on 2-D finite element simulations. The results of
the robust optimizations, which considered manufacturing uncertainties, were
compared to the deterministic optimization. The robust designs have shown not
only good mean torque and torque ripple performances, but they have also shown
improved robustness against design parameters uncertainties.",2211.16136v1
2023-05-22,Interplay between finite thickness and chirality effects on the Casimir-Lifshitz torque with nematic cholesteric liquid crystals,"We theoretically investigate the combined effects of the chirality and the
finite total thickness of nematic cholesteric liquid crystals on the
Casimir-Lifshitz torque. We find that, the larger the thickness, the more
sinusoidal the angular dependence of the torque becomes. We use a Fourier
decomposition to quantify this result. The general direction of the torque
depends on whether the configuration of two cholesterics is heterochiral or
homochiral.",2305.13011v1
2023-12-26,Magnetic vortex control with current-induced axial magnetization in centrosymmetric Weyl materials,"We consider magnetic Weyl metals as a platform to achieve current control of
magnetization textures with transport currents, utilizing their underlying band
geometry. We show that the transport current in a Weyl semimetal produces an
axial magnetization due to orbital magnetic moments of the Weyl electrons. The
associated axial magnetization can generate a torque acting on the localized
magnetic moments. For the case of a magnetic vortex in a nanodisk of Weyl
materials, this current-induced torque can be used to reverse its circulation
and polarity. We discuss the axial magnetization torques in Weyl metals on
general symmetry grounds, and compare their strength to current-induced torques
in more conventional materials.",2312.16122v1
2020-05-12,Propagation of spin waves through a Néel domain wall,"Spin waves have the potential to be used as a new platform for data transfer
and processing as they can reach wavelengths in the nanometer range and
frequencies in the terahertz range. To realize a spin-wave device, it is
essential to be able to manipulate the amplitude as well as the phase of spin
waves. Several theoretical and recently also experimental works have shown that
the spin-wave phase can be manipulated by the transmission through a domain
wall (DW). Here, we study propagation of spin waves through a DW by means of
micro-focused Brillouin light scattering microscopy ($\mu$BLS). The acquired 2D
spin-wave intensity maps reveal that spin-wave transmission through a N\'eel DW
is influenced by a topologically enforced circular Bloch line in the DW center
and that the propagation regime depends on the spin-wave frequency. In the
first regime, two spin-wave beams propagating around the circular Bloch line
are formed, whereas in the second regime, spin waves propagate in a single
central beam through the circular Bloch line. Phase-resolved $\mu$BLS
measurements reveal a phase shift upon transmission through the domain wall for
both regimes. Micromagnetic modelling of the transmitted spin waves unveils a
distortion of their phase fronts which needs to be taken into account when
interpreting the measurements and designing potential devices. Moreover, we
show, by means of micromagnetic simulations, that an external magnetic field
can be used to move the circular Bloch line within the DW and to manipulate
spin-wave propagation.",2005.05690v2
2022-03-15,Dressed-state control of effective dipolar interaction between strongly-coupled solid-state spins,"Strong interactions between spins in many-body solid-state quantum system is
a crucial resource for exploring and applying non-classical states. In
particular, electronic spins associated with defects in diamond system are a
leading platform for the study of collective quantum phenomena and for quantum
technology applications. While such solid-state quantum defect systems have the
advantage of scalability and operation under ambient conditions, they face the
key challenge of controlling interactions between the defects spins, since the
defects are spatially fixed inside the host lattice with relative positions
that cannot be well controlled during fabrication. In this work, we present a
dressed-state approach to control the effective dipolar coupling between
solid-state spins; and then demonstrate this scheme experimentally using two
strongly-coupled nitrogen vacancy (NV) centers in diamond. Including Rabi
driving terms between the m$_s$ = 0 and $\pm$1 states in the NV spin
Hamiltonian allows us to turn on and off or tune the effective dipolar coupling
between two NV spins. Through Ramsey spectroscopy, we detect the change of the
effective dipolar field generated by the control NV spin prepared in different
dressed states. To observe the change of interaction dynamics, we then deploy
spin-lock-based polarization transfer measurements via a Hartmann-Hahn matching
condition between two NV spins in different dressed states. We perform
simulations that indicate the promise for this robust scheme to control the
distribution of interaction strengths in strongly-interacting spin systems,
including interaction strength homogenization in a spin ensemble, which can be
a valuable tool for studying non-equilibrium quantum phases and generating high
fidelity multi-spin correlated states for quantum-enhanced sensing.",2203.07610v2
2020-10-30,The impact of mass-transfer physics on the observable properties of field binary black hole populations,"We study the impact of mass-transfer physics on the observable properties of
binary black hole populations formed through isolated binary evolution. We
investigate the impact of mass-accretion efficiency onto compact objects and
common-envelope efficiency on the observed distributions of $\chi_{eff}$,
$M_{chirp}$ and $q$. We find that low common envelope efficiency translates to
tighter orbits post common envelope and therefore more tidally spun up
second-born black holes. However, these systems have short merger timescales
and are only marginally detectable by current gravitational-waves detectors as
they form and merge at high redshifts ($z\sim 2$), outside current detector
horizons. Assuming Eddington-limited accretion efficiency and that the
first-born black hole is formed with a negligible spin, we find that all
non-zero $\chi_{eff}$ systems in the detectable population can come only from
the common envelope channel as the stable mass-transfer channel cannot shrink
the orbits enough for efficient tidal spin-up to take place. We find the local
rate density ($z\simeq 0.01$) for the common envelope channel is in the range
$\sim 17-113~Gpc^{-3}yr^{-1}$ considering a range of $\alpha_{CE} \in
[0.2,5.0]$ while for the stable mass transfer channel the rate density is $\sim
25~Gpc^{-3}yr^{-1}$. The latter drops by two orders of magnitude if the mass
accretion onto the black hole is not Eddington limited because conservative
mass transfer does not shrink the orbit as efficiently as non-conservative mass
transfer does. Finally, using GWTC-2 events, we constrain the lower bound of
branching fraction from other formation channels in the detected population to
be $\sim 0.2$. Assuming all remaining events to be formed through either stable
mass transfer or common envelope channels, we find moderate to strong evidence
in favour of models with inefficient common envelopes.",2010.16333v2
2011-12-13,Global models of planetary system formation in radiatively-inefficient protoplanetary discs,"(Abridged) We present the results of N-body simulations of planetary systems
formation in radiatively-inefficient disc models, where positive corotation
torques may counter the rapid inward migration of low mass planets driven by
Lindblad torques. The aim of this work is to examine the nature of planetary
systems that arise from oligarchic growth in such discs. We adapt the
commonly-used Mercury-6 symplectic integrator by including simple prescriptions
for planetary migration (types I and II), planetary atmospheres that enhance
the probability of planetesimal accretion by protoplanets, gas accretion onto
forming planetary cores, and gas disc dispersal. We perform a suite of
simulations for a variety of disc models with power-law surface density and
tempera- ture profiles, with a focus on models in which unsaturated corotation
torques can drive outward migration of protoplanets. In some models we account
for the quenching of corotation torques that arises when planetary orbits
become eccentric. Approximately half of our simulations lead to the successful
formation of gas giant planets with a broad range of masses and semimajor axes.
  We conclude that convergent migration induced by corotation torques operating
during planet formation can enhance the growth rate of planetary cores, but
these often migrate into the central star because corotation torques saturate.
Outward migration of planetary cores of modest mass can lead to the formation
of gas giant planets at large distances from the central star, similar to those
observed recently through direct imaging surveys. The excitation of planetary
eccentricities through planet-planet scat- tering during oligarchic growth may
quench the effects of corotation torques, however, such that inward migration
is driven by Lindblad torques.",1112.2997v1
2013-06-04,Spatial and temporal scales of force and torque acting on wall-mounted spherical particles in open channel flow,"Data from direct numerical simulation of open channel flow over a
geometrically rough wall at a bulk Reynolds number of 2900, generated by
Chan-Braun et al. [""Force and torque acting on particles in a transitionally
rough open-channel flow"", J. Fluid Mech. 684, 441--474 (2011),
10.1017/jfm.2011.311] are further analysed with respect to the time and length
scales of force and torque acting on the wall-mounted spheres. For the two
sizes of spheres in a square arrangement (11 and 49 wall units in diameter,
yielding hydraulically smooth and transitionally rough flow, respectively), the
spatial structure of drag, lift and spanwise torque is investigated. The
auto-correlation and spectra in time as well as the space-time correlation and
convection velocities are presented and discussed. It is found that the
statistics of spanwise particle torque are similar to those of shear stress at
a smooth wall. Particle drag and lift are shown to differ from spanwise
particle torque, exhibiting considerably smaller time and length scales; the
convection velocities of drag and lift are somewhat larger than those of
spanwise torque. Furthermore, correlations between the flow field and
particle-related quantities are presented. The spatial structure of the
correlation between streamwise velocity and drag/spanwise torque features
elongated shapes reminiscent of buffer-layer streaks. The correlation between
the pressure field and the particle drag exhibits two opposite-signed bulges on
the upstream and downstream sides of a particle.",1306.0680v1
2014-03-21,"Comment on ""Casimir torque on two rotating plates""","We discuss the recent result by Xiang Chen (Int. J. Mod. Phys. 27(14) 1350066
(2013)) and show that the formula obtained for the Casimir torque in the
systems of two isotropic rotating particles (plates) is incorrect.",1403.5412v1
2016-11-05,"On the optimal feedforward torque control problem of anisotropic synchronous machines: Quadrics, quartics and analytical solutions","The optimal feedforward torque control problem is tackled and solved
analytically for synchronous machines while stator resistance and
cross-coupling inductance are explicitly considered. Analytical solutions for
the direct and quadrature optimal reference currents are found for all major
operation strategies such as Maximum Torque per Current (MTPC) (or often called
as Maximum Torque per Ampere (MTPA)), Maximum Current (MC), Field Weakening
(FW), Maximum Torque per Voltage (MTPV) and Maximum Torque per Flux (MTPF).
Numerical methods (approximating the optimal solutions only) or simplifying
assumptions (neglecting stator resistance and/or cross-coupling inductance) are
no longer necessary. The presented results are based on one simple idea: all
optimization problems (e.g. MTPC, MTPV or MTPF) with their respective
constraints (e.g. current or voltage limit) and the computation of the
intersection point(s) of voltage ellipse, current circle, or torque, MTPC, MTPV
and MTPF hyperbolas are reformulated implicitly as quadrics (quadratic
surfaces) which allow to solve the feedforward torque control problem by
invoking the Lagrangian formalism and by finding the roots of a fourth-order
polynomial analytically. The proposed solutions are applicable to any
anisotropic (or isotropic) synchronous machine independent of the underlying
current control strategy.",1611.01629v5
2017-12-23,"Comment on ""Optical torque on small chiral particles in generic optical fields ""","We comment on mistakes and inaccuracies of a paper by Chen et al. concerning
the optical torque from generic optical fields on dipolar chiral particles,
i.e. on those whose scattering is fully described by the first electric,
magnetic and magnetoelectric Mie coefficients.",1712.08808v1
2018-05-22,Torques on low-mass bodies in retrograde orbit in gaseous disks,"We evaluate the torque acting on a gravitational perturber on a retrograde
circular orbit in the midplane of a gaseous disk. We assume that the mass of
this satellite is so low it weakly disturbs the disk (type I migration). The
perturber may represent the companion of a binary system with a small mass
ratio. We compare the results of hydrodynamical simulations with analytic
predictions. Our two-dimensional (2D) simulations indicate that the torque
acting on a perturber with softening radius $R_{\rm soft}$ can be accounted for
by a scattering approach if $R_{\rm soft}<0.3H$, where $H$ is defined as the
ratio between the sound speed and the angular velocity at the orbital radius of
the perturber. For $R_{\rm soft}>0.3H$, the torque may present large and
persistent oscillations, but the resultant time-averaged torque decreases
rapidly with increasing $R_{\rm soft}/H$, in agreement with previous analytical
studies. We then focus on the torque acting on small-size perturbers embedded
in full three-dimensional (3D) disks and argue that the density waves
propagating at distances $\lesssim H$ from the perturber contribute
significantly to the torque because they transport angular momentum. We find a
good agreement between the torque found in 3D simulations and analytical
estimates based on ballistic orbits. We compare the radial migration timescales
of prograde versus retrograde perturbers. For a certain range of the
perturber's mass and aspect ratio of the disk, the radial migration timescale
in the retrograde case may be appreciably shorter than in the prograde case. We
also provide the smoothing length required in 2D simulations in order to
account for 3D effects.",1805.08852v1
2019-02-01,A generic frequency dependence for the atmospheric tidal torque of terrestrial planets,"Thermal atmospheric tides have a strong impact on the rotation of terrestrial
planets. They can lock these planets into an asynchronous rotation state of
equilibrium. We aim at characterizing the dependence of the tidal torque
resulting from the semidiurnal thermal tide on the tidal frequency, the planet
orbital radius, and the atmospheric surface pressure. The tidal torque is
computed from full 3D simulations of the atmospheric climate and mean flows
using a generic version of the LMDZ general circulation model (GCM) in the case
of a nitrogen-dominated atmosphere. Numerical results are discussed with the
help of an updated linear analytical framework. Power scaling laws governing
the evolution of the torque with the planet orbital radius and surface pressure
are derived. The tidal torque exhibits i) a thermal peak in the vicinity of
synchronization, ii) a resonant peak associated with the excitation of the Lamb
mode in the high frequency range, and iii) well defined frequency slopes
outside these resonances. These features are well explained by our linear
theory. Whatever the star-planet distance and surface pressure, the torque
frequency spectrum -- when rescaled with the relevant power laws -- always
presents the same behaviour. This allows us to provide a single and easily
usable empirical formula describing the atmospheric tidal torque over the whole
parameter space. With such a formula, the effect of the atmospheric tidal
torque can be implemented in evolutionary models of the rotational dynamics of
a planet in a computationally efficient, and yet relatively accurate way.",1902.00280v1
2019-02-14,Performance Analysis of Series Elastic Actuator based on Maximum Torque Transmissibility,"The use of the Series Elastic Actuator (SEA) system as an actuator system
equipped with a compliant element has contributed not only to advances in human
interacting robots but also to a wide range of improvements in the robotics
area. Nevertheless, there are still limitations in its performance; the elastic
spring that is adopted to provide compliance is considered to limit the
actuator performance thus lowering the frequency bandwidth of force/torque
generation, and the bandwidth decreases even more when it is supposed to
provide large torque.
  This weakness is in turn owing to the limitations of motor and motor drives
such as torque and velocity limits. In this paper, mathematical tools to
analyze the impact of these limitations on the performance of SEA as a
transmission system are provided. A novel criterion called Maximum Torque
Transmissibility (MTT)is defined to assess the ability of SEA to fully utilize
maximum continuous motor torque. Moreover, an original frequency bandwidth
concept, maximum torque frequency bandwidth, which can indicate the maximum
frequency up to which the SEA can generate the maximum torque, is proposed
based on the proposed MTT. The proposed MTT can be utilized as a unique
criterion of the performance, and thus various design parameters including the
load condition, mechanical design parameters, and controller parameters of a
SEA can be evaluated with its use. Experimental results under various
conditions verify that MTT can precisely indicate the limitation of the
performance of SEA, and that it can be utilized to accurately analyze the
limitation of the controller of SEA.",1902.05346v1
2019-07-30,Solar Angular Momentum Loss Over the Past Several Millennia,"The Sun and Sun-like stars lose angular momentum to their magnetised stellar
winds. This braking torque is coupled to the stellar magnetic field, such that
changes in the strength and/or geometry of the field modifies the efficiency of
this process. Since the space-age, we have been able to directly measure solar
wind properties using in-situ spacecraft. Furthermore, indirect proxies such as
sunspot number, geomagnetic indices, and cosmogenic radionuclides, constrain
the variation of solar wind properties on centennial, and millennial
timescales. We use near-Earth measurements of the solar wind plasma and
magnetic field to calculate the torque on the Sun throughout the space-age.
Then, reconstructions of the solar open magnetic flux are used to estimate the
time-varying braking torque during the last nine millennia. We assume a
relationship for the solar mass loss rate based on observations during the
space-age which, due to the weak dependence of the torque on mass loss rate,
does not strongly affect our predicted torque. The average torque during the
last nine millennia is found to be $2.2\times10^{30}$erg, which is comparable
to the average value from the last two decades. Our dataset includes grand
minima (such as the Maunder Minimum), and maxima in solar activity, where the
torque varies from $\sim1-5\times10^{30}$erg (averaged on decadal timescales),
respectively. We find no evidence for any secular variation of the torque on
timescales of less than $9000$ years.",1907.13143v1
2019-11-13,Circumbinary Disks: Accretion and Torque as a Function of Mass Ratio and Disk Viscosity,"Using numerical hydrodynamics calculations and a novel method for densely
sampling parameter space, we measure the accretion and torque on a binary
system from a circumbinary disk. In agreement with previous studies, we find
that the net torque on the binary is positive for mass ratios close to unity,
and that accretion always drives the binary towards equal mass. Accretion
variability depends sensitively on the numerical sink prescription, but the
torque and relative accretion onto each component do not depend on the sink
timescale. Positive torque and highly variable accretion occurs only for mass
ratios greater than around $0.05$. This means that for mass ratios below
$0.05$, the binary would migrate inward until the secondary accreted sufficient
mass, after which it would execute a U-turn and migrate outward. We explore a
range of viscosities, from $\alpha = 0.03$ to $\alpha = 0.15$, and find that
this outward torque is proportional to the viscous torque, simply proportional
to viscosity in this range. Dependence of accretion and torque on mass ratio is
explored in detail, densely sampling mass ratios between $0.01$ and unity. For
mass ratio $q > 0.6$, accretion variability is found to exhibit a distinct
sawtooth pattern, typically with a five-orbit cycle that provides a ""smoking
gun"" prediction for variable quasars observed over long periods, as a potential
means to confirm the presence of a binary.",1911.05506v2
2020-03-31,A novel Algorithm for Hydrostatic-mechanical Mobile Machines with a Dual-Clutch Transmission,"Mobile machines using a hydrostatic transmission is highly efficient under
lower working-speed condition but less capable at higher transport velocities.
To enhance overall efficiency, we have improved the powertrain design by
combining a hydrostatic transmission with a dual-clutch transmission (DCT).
Compared with other mechanical gearboxes, the DCT avoids the interruption of
torque transmission in the process of shifting without sacrificing more
transmission efficiency. However, there are some problems of unstable torque
transmission during the shifting process, and an excessive torque drop
occurring at the end of the gear shift, which result in a poor drive comfort.
To enhance the performance of the novel structural possibility of powertrain
design, we designed a novel control strategy for the motor torque and the
clutch torques during the shifting process. The controller's task is tracking
the target drive torque and completing the gear shift as quickly as possible
with acceptable smoothness requirements. In the process of the controller
design, a specific control algorithm is firstly designed for a 10 ton wheel
loader. The model-based simulation has validated the control effect. As a
result, the control strategy employing clutch and motor torque control to
achieve a smooth shifting process is feasible since drive torque is well
tracked, and highly dynamical actuators are not required. Furthermore, only two
calibration parameters are designed to adjust the control performance
systematically. The novel control strategy is generalized for other mobile
machines with different sizes.",2003.14172v2
2020-07-21,Torques felt by solid accreting planets,"The solid material of protoplanetary discs forms an asymmetric pattern around
a low-mass planet (M_p<=10M_Earth) due to the combined effect of dust-gas
interaction and the gravitational attraction of the planet. Recently, it has
been shown that although the total solid mass is negligible compared to that of
gas in protoplanetary discs, a positive torque can be emerged by a certain size
solid species. The torque magnitude can overcome that of gas which may result
in outward planetary migration. In this study, we show that the accretion of
solid species by the planet strengthens the magnitude of solid torque being
either positive or negative. We run two-dimensional, high-resolution (1.5Kx3K)
global hydrodynamic simulations of an embedded low-mass planet in a
protoplanetary disc. The solid material is handled as a pressureless fluid.
Strong accretion of well-coupled solid species by a M_p<0.3M_Earth protoplanet
results in the formation of such a strongly asymmetric solid pattern close to
the planet that the positive solid torque can overcome that of gas by two
times. However, the accretion of solids in the pebble regime results in
increased magnitude negative torque felt by protoplanets and strengthened
positive torque for Earth-mass planets. For M_p>=3M_Earth planets the magnitude
of the solid torque is positive, however, independent of the accretion strength
investigated. We conclude that the migration of solid accreting planets can be
substantially departed from the canonical type-I prediction.",2007.11072v1
2021-08-02,Neuromechanical model-based adaptive control of bi-lateral ankle exoskeletons: biological joint torque and electromyogram reduction across walking conditions,"To enable the broad adoption of wearable robotic exoskeletons in medical and
industrial settings, it is crucial they can adaptively support large
repertoires of movements. We propose a new human-machine interface to
simultaneously drive bilateral ankle exoskeletons during a range of 'unseen'
walking conditions and transitions that were not used for establishing the
control interface. The proposed approach used person-specific neuromechanical
models to estimate biological ankle joint torques in real-time from measured
electromyograms (EMGS) and joint angles. A low-level controller based on a
disturbance observer translated biological torque estimates into exoskeleton
commands. We call this 'neuromechanical model-based control' (NMBC). NMBC
enabled six individuals to voluntarily control a bilateral ankle exoskeleton
across six walking conditions, including all intermediate transitions, i.e.,
two walking speeds, each performed at three ground elevations, with no need for
predefined torque profiles, nor a priori chosen neuromuscular reflex rules, or
state machines as common in literature. A single subject case-study was carried
out on a dexterous locomotion tasks involving moonwalking. NMBC always enabled
reducing biological ankle torques, as well as eight ankle muscle EMGs both
within (22% torque; 12% EMG) and between walking conditions (24% torque; 14%
EMG) when compared to non-assisted conditions. Torque and EMG reductions in
novel walking conditions indicated that the exoskeleton operated symbiotically,
as exomuscles controlled by the operator's neuromuscular system. This opens new
avenues for the systematic adoption of wearable robots as part of
out-of-the-lab medical and occupational settings.",2108.00980v2
2022-03-10,Learning Torque Control for Quadrupedal Locomotion,"Reinforcement learning (RL) has become a promising approach to developing
controllers for quadrupedal robots. Conventionally, an RL design for locomotion
follows a position-based paradigm, wherein an RL policy outputs target joint
positions at a low frequency that are then tracked by a high-frequency
proportional-derivative (PD) controller to produce joint torques. In contrast,
for the model-based control of quadrupedal locomotion, there has been a
paradigm shift from position-based control to torque-based control. In light of
the recent advances in model-based control, we explore an alternative to the
position-based RL paradigm, by introducing a torque-based RL framework, where
an RL policy directly predicts joint torques at a high frequency, thus
circumventing the use of a PD controller. The proposed learning torque control
framework is validated with extensive experiments, in which a quadruped is
capable of traversing various terrain and resisting external disturbances while
following user-specified commands. Furthermore, compared to learning position
control, learning torque control demonstrates the potential to achieve a higher
reward and is more robust to significant external disturbances. To our
knowledge, this is the first sim-to-real attempt for end-to-end learning torque
control of quadrupedal locomotion.",2203.05194v2
2022-10-03,On the evolution of pebble-accreting planets in evolving protoplanetary discs,"We examine the migration of luminous low-mass cores in laminar protoplanetary
discs where accretion occurs mainly because of disc winds and where the planet
luminosity is generated by pebble accretion. Using 2D hydrodynamical
simulations, we determine the eccentricities induced by thermal forces as a
function of gas and pebble accretion rates, and also evaluate the importance of
the torque exerted by the solid component relative to the gas torque. For a gas
accretion rate $\dot M= 2\times 10^{-8}$ $M_\odot/$yr and pebble flux $\dot
M_{peb}=170$ $M_\oplus$/Myr, we find that embryo eccentricities attain values
comparable to the disc aspect ratio. The planet radial excursion in the disc,
however, causes the torque exerted by inflowing pebbles to cancel on average
and migration to transition from outward to inward. This is found to arise
because the magnitude of thermal torques decreases exponentially with
increasing eccentricity, and we provide a fitting formula for the thermal
torque attenuation as a function of eccentricity. As the disc evolves, the
accretion luminosity becomes at some point too small to make the core
eccentricity grow such that the solid component can exert a non-zero torque on
the planet. This torque is positive and for gas accretion rates $\dot M
\lesssim 5\times 10^{-9}$ $M_\odot/$yr and pebble fluxes $\dot M_{peb} \lesssim
120$ $M_\oplus/$Myr, it is found to overcome the gas torque exerted on cores
with mass $m_p\lesssim$ $1M_\oplus$, resulting in outward migration.",2210.00932v1
2022-11-08,Torques and angular momenta of fluid elements in the octonion spaces,"The paper focuses on applying the octonions to explore the influence of the
external torque on the angular momentum of fluid elements, revealing the
interconnection of the external torque and the vortices of vortex streets. J.
C. Maxwell was the first to introduce the quaternions to study the physical
properties of electromagnetic fields. The contemporary scholars utilize the
quaternions and octonions to investigate the electromagnetic theory,
gravitational theory, quantum mechanics, special relativity, general relativity
and curved spaces and so forth. The paper adopts the octonions to describe the
electromagnetic and gravitational theories, including the octonionic field
potential, field strength, linear momentum, angular momentum, torque and force
and so on. In case the octonion force is equal to zero, it is able to deduce
eight independent equations, including the fluid continuity equation, current
continuity equation, and force equilibrium equation and so forth. Especially,
one of the eight independent equations will uncover the interrelation of the
external torque and angular momentums of fluid elements. One of its inferences
is that the direction, magnitude and frequency of the external torque must
impact the direction and curl of the angular momentum of fluid elements,
altering the frequencies of Karman vortex streets within the fluids. It means
that the external torque is interrelated with the velocity circulation, by
means of the liquid viscosity. The external torque is able to exert an
influence on the direction of downwash flows, improving the lift and drag
characteristics generated by the fluids.",2211.04225v1
2023-07-14,The Effect of Thermal Torques on AGN Disc Migration Traps and Gravitational Wave Populations,"Accretion discs in active galactic nuclei (AGN) foster black hole (BH)
formation, growth, and mergers. Stellar mass BHs migrate inwards under the
influence of hydrodynamical torques unless they encounter a region where the
torque flips sign. At these migration traps, BHs accumulate and merge via
dynamical or gas-assisted interactions, producing high-frequency
LIGO/Virgo/KAGRA (LVK) gravitational wave (GW) sources and potentially cutting
off the supply of extreme mass ratio inspirals that would otherwise make
low-frequency, {\it LISA}-band GWs. In this paper, we study the interplay
between different types of migration torques, focusing especially on the
``thermal torques'' generated by the thermal response of the AGN to embedded
stellar-mass BHs that accrete through their own mini-discs.In contrast to
previous work, we find that Type I torques cannot produce migration traps on
their own, but thermal torques often do, particularly in low-mass AGN. The
migration traps produced by thermal torques exist at much larger radii ($\sim
10^{3-5}$ gravitational radii) than do previously identified Type I traps,
carrying implications for GW populations at multiple frequencies. Finally, we
identify a bifurcation of AGN discs into two regimes: migration traps exist
below a critical AGN luminosity, and do not at higher luminosities. This
critical luminosity is fit as $\log_{10} L_{\rm AGN}^c = 45 - 0.32
\log_{10}{(\alpha/0.01)}$ where $\alpha$ is the AGN alpha viscosity parameter,
a range compatible with recent claims that LVK GWs are not preferentially
associated with high-luminosity AGN.",2307.07546v2
2022-02-23,Blueprint of a scalable spin qubit shuttle device for coherent mid-range qubit transfer in disordered Si/SiGe/SiO$_2$,"Silicon spin qubits stand out due to their very long coherence times,
compatibility with industrial fabrication, and prospect to integrate classical
control electronics. To achieve a truly scalable architecture, a coherent
mid-range link that moves the electrons between qubit registers has been
suggested to solve the signal fan-out problem. Here, we present a blueprint of
such a $\approx 10\,\mu$m long link, called a spin qubit shuttle, which is
based on connecting an array of gates into a small number of sets. To control
these sets, only a few voltage control lines are needed and the number of these
sets and thus the number of required control signals is independent of the
length of this link. We discuss two different operation modes for the spin
qubit shuttle: A qubit conveyor, i.e. a potential minimum that smoothly moves
laterally, and a bucket brigade, in which the electron is transported through a
series of tunnel-coupled quantum dots by adiabatic passage. We find the former
approach more promising considering a realistic Si/SiGe device including
potential disorder from the charged defects at the Si/SiO$_2$ layer, as well as
typical charge noise. Focusing on the qubit transfer fidelity in the conveyor
shuttling mode, we discuss in detail motional narrowing, the interplay between
orbital and valley excitation and relaxation in presence of $g$-factors that
depend on orbital and valley state of the electron, and effects from
spin-hotspots. We find that a transfer fidelity of 99.9 \% is feasible in
Si/SiGe at a speed of $\sim$10 m/s, if the average valley splitting and its
inhomogeneity stay within realistic bounds. Operation at low global magnetic
field $\approx 20$ mT and material engineering towards high valley splitting is
favourable for reaching high fidelities of transfer.",2202.11793v3
2022-08-05,The spins of stripped B stars support magnetic internal angular momentum transport,"In order to predict the spins of stellar remnants we need to understand the
evolution of the internal rotation of stars, and to identify at which stage the
rotation of the contracting cores of evolved stars decouples from their
expanding envelopes. The donor stars of mass transferring binaries lose almost
their entire envelope and may thus offer a direct view on their core rotation.
After the mass transfer event they contract and fade rapidly, although they are
well observable when caught in the short-lived B-star phase. The B-type primary
of the galactic binary system LB-1, which was originally suggested to contain a
massive black hole, is nicely explained as a stripped star accompanied by a
fainter Be star. The narrow absorption lines in the primary's spectrum signify
extremely slow rotation, atypical of B-type main-sequence stars. Here we
investigate the evolution of mass donors in generic grids of detailed binary
evolution models, where both stars include differential rotation, internal
angular momentum transport, and spin-orbit coupling. Whereas the mass gainers
are typically spun-up during the mass transfer, we find that the spins of the
stripped donor models depend sensitively on the employed mechanism for internal
angular momentum transport. Purely hydrodynamic transport cannot explain the
observed slow rotation, while models including magnetic angular momentum
transport are able to reproduce the observed rotation of LB-1 and similar
stars, independent of the initial rotation rate. In such models the spin of the
white dwarfs that emerge at the end of the evolution is independent of the mass
stripping. We find evidence that the mass transfer in LB-1 was moderately
non-conservative.",2208.03129v2
2021-02-27,"Hyperpolarization of cis-15N,15N'-azobenzene by parahydrogen at ultralow magnetic fields","Development of the methods to exploit nuclear hyperpolarization and search
for molecules whose nuclear spins can be efficiently hyperpolarized is an
active area in nuclear magnetic resonance. Of particular interest are those
molecules that have long nuclear relaxation times, making them to be suitable
candidates as contrast agents in magnetic resonance imaging. In this work, we
present a detailed study of SABRE SHEATH (Signal Amplification By Reversible
Exchange in Shield Enabled Alignment Transfer to Heteronuclei) experiments of
15N,15N' azobenzene. In SABRE SHEATH experiments nuclear spins of the target
are hyperpolarized by transfer of spin polarization from parahydrogen at
ultralow fields during a reversible chemical process. The studied system is
complicated, and we are concerned only about a subset of the data, presenting
details for the molecules that experience fast chemical exchange at the
catalytic complex and thus are involved in polarizing the free azobenzene.
Azobenzene exists in two isomers trans- and cis-. We show that all nuclear
spins in cis-azobenzene can be efficiently hyperpolarized by SABRE at suitable
magnetic fields. Enhancement factors (relative to 9.4 T) reach several
thousands of times for 15N spins and a few tens of times for the 1H spins.
There are two approaches to observe either hyperpolarized magnetization of
15N/1H spins or hyperpolarized singlet order of the 15N spin pair. We compare
these approaches and present the field dependencies of SABRE experiments for
them. No hyperpolarization of trans 15N,15N' azobenzene was observed. The
results presented here will be useful for further experiments where
hyperpolarized cis-15N,15N' azobenzene is switched by light to trans 15N,15N'
azobenzene for storing the produced hyperpolarization in the long-lived spin
state of the 15N pair of trans-15N,15N' azobenzene.",2103.00289v1
2022-01-29,"The mean flow, velocity dispersion, energy transfer and evolution of rotating and growing dark matter halos","By decomposing velocity dispersion into non-spin and spin-induced, mean flow
and dispersion are analytically solved for axisymmetric rotating and growing
halos. The polar flow can be neglected and azimuthal flow is directly related
to dispersion. The fictitious (""Reynolds"") stress acts on mean flow to enable
energy transfer from mean flow to random motion and maximize system entropy.
For large halos (high peak height $\nu$ at early stage of halo life) with
constant concentration, there exists a self-similar radial flow (outward in
core and inward in outer region). Halo mass, size and specific angular momentum
increase linearly with time via fast mass accretion. Halo core spins faster
than outer region. Large halos rotate with an angular velocity proportional to
Hubble parameter and spin-induced dispersion is dominant. All specific energies
(radial/rotational/kinetic/potential) are time-invariant. Both halo spin
($\sim$0.031) and anisotropic parameters can be analytically derived. For
""small"" halos with stable core and slow mass accretion (low peak height $\nu$
at late stage of halo life), radial flow vanishes. Small halos rotate with
constant angular velocity and non-spin axial dispersion is dominant. Small
halos are spherical in shape, incompressible, and isotropic. Radial and
azimuthal dispersion are comparable and greater than polar dispersion. Due to
finite spin, kinetic energy is not equipartitioned with the greatest energy
along azimuthal direction. Different from normal matter, small halos are hotter
with faster spin. Halo relaxation from early to late stage involves variation
of shape, density, mean flow, momentum, and energy. During relaxation, halo
isotopically ""stretches"" with conserved specific rotational kinetic energy,
increasing concentration and momentum of inertial. Halo ""stretching"" leads to
decreasing angular velocity, increasing angular momentum and spin parameter.",2201.12665v2
2006-03-31,Energy transfer by the scattering of resonant photons,"A formal derivation is presented of the energy transfer rate between
radiation and matter due to the scattering of an isotropic distribution of
resonant photons. The derivation is developed in the context of the two-level
atom in the absence of collisions and radiative transitions to and from the
continuum, but includes the full angle-averaged redistribution function for
photon scattering. The result is compared with previous derivations, all of
which have been based on the Fokker-Planck approximation to the radiative
transfer equation. A new Fokker-Planck approximation, including an extension to
higher (post-diffusive) orders, is derived to solve the radiative transfer
equation, and time-dependent numerical solutions are found. The relaxation of
the colour temperature to the matter temperature is computed as the radiation
field approaches statistical equilibrium through scattering. The results are
discussed in the context of the Wouthuysen-Field mechanism for coupling the
21cm spin temperature of neutral hydrogen to the kinetic temperature of the gas
through LyA scattering. The evolution of the heating rate is also computed, and
shown to diminish as the gas approaches statistical equilibrium.",0603855v2
2004-01-23,Mesoscopic one-way channels for quantum state transfer via the Quantum Hall Effect,"We show that the one-way channel formalism of quantum optics has a physical
realisation in electronic systems. In particular, we show that magnetic edge
states form unidirectional quantum channels capable of coherently transporting
electronic quantum information. Using the equivalence between one-way photonic
channels and magnetic edge states, we adapt a proposal for quantum state
transfer to mesoscopic systems using edge states as a quantum channel, and show
that it is feasible with reasonable experimental parameters. We discuss how
this protocol may be used to transfer information encoded in number, charge or
spin states of quantum dots, so it may prove useful for transferring quantum
information between parts of a solid-state quantum computer.",0401442v1
2004-04-01,Nonequilibrium transfer and decoherence in quantum impurity problems,"Using detailed balance and scaling properties of integrals that appear in the
Coulomb gas reformulation of quantum impurity problems, we establish exact
relations between the nonequilibrium transfer rates of the boundary sine-Gordon
and the anisotropic Kondo model at zero temperature. Combining these results
with findings from the thermodynamic Bethe ansatz, we derive exact closed form
expressions for the transfer rate in the biased spin-boson model in the scaling
limit. They illustrate how the crossover from weak to strong tunneling takes
place. Using a conjectured correspondence between the transfer and the
decoherence rate, we also determine the exact lower bound for damping of the
coherent oscillation as a function of bias and dissipation strength in this
paradigmic model for NMR and superposition of macroscopically distinct states
(qubits).",0404021v1
2005-04-12,Mott transition in the asymmetric Hubbard model at half-filling within dynamical mean-field theory,"We apply the approximate analytic methods to the investigation of the band
structure of the asymmetric Hubbard model where the chemical potentials and
electron transfer parameters depend on the electron spin (type of
quasiparticles). The Hubbard-I and alloy-analogy approximations are the
simplest approximations which are used. Within the alloy-analogy approximation,
the energy band of particles does not depend on the transfer parameter of
particles of another sort. It means that the gap in the spectrum opens at the
critical value $U_{c}$ that is the same in two different limiting cases: the
Falicov-Kimball model and the standard Hubbard model. The approximate analytic
scheme of the dynamical mean-field theory is developed to include into the
theory the scattering of particles responsible for the additional mechanism
(due to the transfer of particles of another sort) of the band formation. We
use the so-called GH3 approach that is a generalization of the Hubbard-III
approximation. The approach describes the continuous Mott transition with the
$U_{c}$ value dependent on a ratio of transfer parameters of different
particles.",0504289v1
2002-01-23,Boson-conserving one-nucleon transfer operator in the interacting boson model,"The boson-conserving one-nucleon transfer operator in the interacting boson
model (IBA) is reanalyzed. Extra terms are added to the usual form used for
that operator. These new terms change generalized seniority by one unit, as the
ones considered up to now. The results obtained using the new form for the
transfer operator are compared with those obtained with the traditional form in
a simple case involving the pseudo-spin Bose-Fermi symmetry $U^{B}(6) \otimes
U^F(12)$ in its $U^{BF}(5) \otimes U^F(2)$ limit. Sizeable differences are
found. These results are of relevance in the study of transfer reactions to
check nuclear supersymmetry and in the description of (\beta)-decay within IBA.",0201061v1
2005-11-18,Excitation and Entanglement Transfer Versus Spectral Gap,"We consider quantum many body systems as quantum channels and study the
relation between the transfer quality and the size of the spectral gap between
the system's ground and excited states. In our setup two ancillas are weakly
coupled to the quantum many body system at different sites, and we study the
propagation of an excitation and quantum information from one ancilla to the
other. We observe two different scenarios: a slow, but perfect transfer if the
gap large and a fast, but un-complete transfer otherwise. We provide a
numerical and analytical approach as well as a simplified physical model
explaining our findings. Our results relate the potential of spin chains acting
as quantum channels to the concept of quantum phase transitions and offer a
different approach to the characterisation of these.",0511185v2
2007-05-09,A method of state-selective transfer of atoms between microtraps based on the Franck-Condon Principle,"We present a method of transferring a cold atom between spatially separated
microtraps by means of a Raman transition between the ground motional states of
the two traps. The intermediate states for the Raman transition are the
vibrational levels of a third microtrap, and we determine the experimental
conditions for which the overlap of the wave functions leads to an efficient
transfer. There is a close analogy with the Franck-Condon principle in the
spectroscopy of molecules. Spin-dependent manipulation of neutral atoms in
microtraps has important applications in quantum information processing. We
also show that starting with several atoms, precisely one atom can be
transferred to the final potential well hence giving deterministic preparation
of single atoms.",0705.1258v2
2008-03-20,Eigenvectors in the Superintegrable Model II: Ground State Sector,"In 1993, Baxter gave $2^{m_Q}$ eigenvalues of the transfer matrix of the
$N$-state superintegrable chiral Potts model with spin-translation quantum
number $Q$, where $m_Q=\lfloor(NL-L-Q)/N\rfloor$. In our previous paper we
studied the Q=0 ground state sector, when the size $L$ of the transfer matrix
is chosen to be a multiple of $N$. It was shown that the corresponding $\tau_2$
matrix has a degenerate eigenspace generated by the generators of $r=m_0$
simple $sl_2$ algebras. These results enable us to express the transfer matrix
in the subspace in terms of these generators $E_m^{\pm}$ and $H_m$ for
$m=1,...,r$. Moreover, the corresponding $2^r$ eigenvectors of the transfer
matrix are expressed in terms of rotated eigenvectors of $H_m$.",0803.3029v4
2009-03-25,A Review of Perfect State Transfer and its Application as a Constructive Tool,"We review the subject of perfect state transfer; how one designs the (fixed)
interactions of a chain of spins so that a quantum state, initially inserted on
one end of the chain, is perfectly transferred to the opposite end in a fixed
time. The perfect state transfer systems are then used as a constructive tool
to design Hamiltonian implementations of other primitive protocols such as
entanglement generation and signal amplification in measurements, before
showing that, in fact, universal quantum computation can be implemented in this
way.",0903.4274v3
2010-01-05,"The 3-dimensional cube is the only periodic, connected cubic graph with perfect state transfer","There is perfect state transfer between two vertices of a graph, if a single
excitation can travel with fidelity one between the corresponding sites of a
spin system modeled by the graph. When the excitation is back at the initial
site, for all sites at the same time, the graph is said to be periodic. A graph
is cubic if each of its vertices has a neighbourhood of size exactly three. We
prove that the 3-dimensional cube is the only periodic, connected cubic graph
with perfect state transfer. We conjecture that this is also the only connected
cubic graph with perfect state transfer.",1001.0674v2
2011-03-08,Spectral Weight Transfer in Multi-Orbital Mott Systems,"We develop here a general formalism for multi-orbital Mott systems which can
be used to understand dynamical and static spectral weight transfer. We find
that the spectral weight transferred from the high energy scales is greatly
increased as a result of the multi-orbital structure. As a consequence
certainly dynamically generated symmetries obtain at lower values of doping
than in the single-band Hubbard model. For example, in the atomic limit, the
particle-hole symmetric condition in the lower band shifts from the one-band
result of $x=1/3$ to $x=1/(2n_o+1)$, where $n_o$ is the number of orbitals with
an unpaired spin. Transport properties computed from effective low-energy
theories which forbid double occupancy of bare electrons, such as the
multi-orbital t-J generalization, should all be be sensitive to this
particle-hole symmetric condition. Away from the atomic limit, the dynamical
contributions increase the transferred spectral weight. Consequently, any
phenomena which are sensitive to an emergent particle-hole symmetry should
obtain at $x<(1/(2n_o+1)$.",1103.1637v2
2012-02-08,"Coexisting pseudogap, charge transfer gap, and Mott gap energy scales in the resonant inelastic x-ray scattering spectra of electron-doped cuprates","We present a computation of Cu K-edge resonant inelastic x-ray scattering
(RIXS) spectra for electron-doped cuprates which includes coupling to bosonic
fluctuations. Comparison with experiment over a wide range of energy and
momentum transfers allows us to identify the signatures of three key
normal-state energy scales: the pseudogap, charge transfer gap, and Mott gap.
The calculations involve a three band Hubbard Hamiltonian based on Cu
$d_{x^2-y^2}$ and O $p_x$, $p_y$ orbitals, with a self-energy correction which
arises due to spin and charge fluctuations. Our theory reproduces
characteristic features e.g., gap collapse, large spectral weight broadening,
and spectral weight transfer as a function of doping, as seen in experiments.",1202.1599v1
2012-05-08,On non-commutative transfer operators and Radon-Nikodym derivatives,"We study relations between non-commutative Ruelle transfer operators over the
C$^*$-algebra $B(\mathcal{H})$ of linear bounded operators over separable
Hilbert spaces $\mathcal{H}$ (infinite-dimensional) and other completely
positive maps. Transfer operators possess a simple description in terms of the
so called non-commutative Radon-Nikodym derivatives. We describe the problem of
existence of a largest positive eigenvalue associated to a positive
eigenfunction and uniform convergence of sequences of iterates of transfer
operators over $B(\mathcal{H})$. Part of the proof related to the
Ruelle-Perron-Frobenius theorem is obtained by adapting results from quantum
spin chain analysis.",1205.1736v2
2013-03-13,Charge transfer in the cold Yb$^+$ + Rb collisions,"Charge-transfer cold Yb$^+$ + Rb collision dynamics is investigated
theoretically using high-level {\it ab initio} potential energy curves, dipole
moment functions and nonadiabatic coupling matrix elements. Within the
scalar-relativistic approximation, the radiative transitions from the entrance
$A^1\Sigma^+$ to the ground $X^1\Sigma^+$ state are found to be the only
efficient charge-transfer pathway. The spin-orbit coupling does not open other
efficient pathways, but alters the potential energy curves and the transition
dipole moment for the $A-X$ pair of states. The radiative, as well as the
nonradiative, charge-transfer cross sections calculated within the $10^{-3}-10$
cm$^{-1}$ collision energy range exhibit all features of the Langevin ion-atom
collision regime, including a rich structure associated with centrifugal
barrier tunneling (orbiting) resonances. Theoretical rate coefficients for two
Yb isotopes agree well with those measured by immersing Yb$^+$ ion in an
ultracold Rb ensemble in a hybrid trap. Possible origins of discrepancy in the
product distributions and relations to previously studied similar processes are
discussed.",1303.3093v2
2013-09-13,Quantum state transfer in the presence of non homogeneous external potentials,"Heisenberg-type spin models in the limit of a low number of excitations are
useful tools to study basic mechanisms in strongly correlated and magnetic
systems. Many of these mechanisms can be experimentally tested using ultracold
atoms. Here, we discuss the implementation of a quantum state transfer protocol
in a tight-binding chain in the presence of an inhomogeneous external
potential. We show that it can be used to extend the parameter range in which
high fidelity state transfer can be achieved beyond the well established
weak-coupling regime. Among the class of mirror-reflecting potentials that
allow for high-fidelity quantum state transfer, the harmonic case is especially
relevant because it allows us to formulate a proposal for the experimental
implementation of the protocol in the context of optical lattices.",1309.3379v2
2014-03-30,Arbitrary perfect state transfer in $d$-level spin chains,"We exploit a ferromagnetic chain of interacting $d$-level ($d>2$) particles
for arbitrary perfect transfer of quantum states with $(d-1)$ levels. The
presence of one extra degree of freedom in the Hilbert space of particles,
which is not used in encoding, allows to achieve perfect transfer even in a
uniform chain through a repeated measurement procedure with consecutive single
site measurements. Apart from the first iteration, for which the time of
evolution grows linearly with the size of the chain, in all other iterations,
the evolution times are short and does not scale with the length. The success
probability of the mechanism grows with the number of repetitions and
practically after a few iterations the transfer is accomplished with a high
probability.",1403.7833v2
2014-06-13,Mass Transfer by Stellar Wind,"I review the process of mass transfer in a binary system through a stellar
wind, with an emphasis on systems containing a red giant. I show how wind
accretion in a binary system is different from the usually assumed Bondi-Hoyle
approximation, first as far as the flow's structure is concerned, but most
importantly, also for the mass accretion and specific angular momentum loss.
This has important implications on the evolution of the orbital parameters. I
also discuss the impact of wind accretion, on the chemical pollution and change
in spin of the accreting star. The last section deals with observations and
covers systems that most likely went through wind mass transfer: barium and
related stars, symbiotic stars and central stars of planetary nebulae (CSPN).
The most recent observations of cool CSPN progenitors of barium stars, as well
as of carbon-rich post-common envelope systems, are providing unique
constraints on the mass transfer processes.",1406.3473v1
2014-07-11,Emulating quantum state transfer through a spin-1 chain on a 1D lattice of superconducting qutrits,"Spin-1 systems, in comparison to spin-1/2 systems, offer a better security
for encoding and transfer of quantum information, primarily due to their larger
Hilbert spaces. Superconducting artificial atoms possess multiple
energy-levels, thereby capable of emulating higher-spin systems. Here we
consider a 1D lattice of nearest-neighbor-coupled superconducting transmon
systems, and devise a scheme to transfer an arbitrary qutrit-state (a state
encoded in a three-level quantum system) across the chain. We assume adjustable
couplings between adjacent transmons, derive an analytic constraint for the
control-pulse, and show how to satisfy the constraint to achieve a
high-fidelity state-transfer under current experimental conditions. Our
protocol thus enables enhanced quantum communication and information processing
with promising superconducting qutrits.",1407.3229v2
2018-01-21,Charge transfer in H + He$^+$ and H$^+$ + He collisions in excited states,"We present a theoretical study of charge transfer in collisions of excited
($n=2,3$) hydrogen atoms with He$^+$ and in collisions of excited ($n=2,3$)
helium atoms with H$^+$, extending the results of Phys. Rev. A 82 012708
(2010). A combination of quantum-mechanical and semi-classical approaches is
employed to calculate the charge-exchange cross sections at collision energies
from 0.1 eV/u up to 1 keV/u. These methods are based on accurate ab initio
potential energy curves and non-adiabatic couplings for the molecular ion
HeH$^+$. Charge transfer can occur either in singlet or in triplet states, and
the differences between the singlet and triplet spin manifolds are discussed.
The dependence of the cross section on the quantum numbers $n$ and $l$ of the
initial state is demonstrated. The isotope effect on the charge transfer cross
sections, arising at low collision energy when H is substituted by D or T, is
investigated. Finally, the impact of the present calculations on models of
laboratory plasmas is discussed.",1801.06821v1
2018-05-30,Interference of the signal from a local dynamical process with the quantum state propagation in spin chains,"The effect of a local instantaneous quantum dynamical process (QDP), either
unitary or non-unitary, on the quantum state transfer through a unitary
Hamiltonian evolution is investigated for both integrable and non-integrable
dynamics. There are interference effects of the quantum state propagation and
the QDP signal propagation. The state transfer fidelity is small for further
sites, from the site where the information is coded, indicating a finite speed
for the propagation of the quantum correlation. There is a small change in the
state transfer fidelity for the case of non- unitary QDP intervening the
background unitary dynamics. In the case of unitary QDP, the change is more
pronounced, with a substantial increase in the fidelity for appropriate sites
and times. For the non-integrable case, viz. a kicked Harper model, the state
transfer fidelity is quite large for further sites for short times, indicating
a finite speed for the propagation of the quantum correlation cannot be
defined.",1805.11795v2
2018-10-22,The spectrum of quantum-group-invariant transfer matrices,"Integrable open quantum spin-chain transfer matrices constructed from
trigonometric R-matrices associated to affine Lie algebras $\hat g$, and from
certain K-matrices (reflection matrices) depending on a discrete parameter p,
were recently considered in arXiv:1802.04864 and arXiv:1805.10144. It was shown
there that these transfer matrices have quantum group symmetry corresponding to
removing the p-th node from the $\hat g$ Dynkin diagram. Here we determine the
spectrum of these transfer matrices by using analytical Bethe ansatz, and we
determine the dependence of the corresponding Bethe equations on p. We propose
formulas for the Dynkin labels of the Bethe states in terms of the numbers of
Bethe roots of each type.We also briefly study how duality transformations are
implemented on the Bethe ansatz solutions.",1810.09048v1
2018-11-07,Quantum network transfer and storage with compact localized states induced by local symmetries,"We propose modulation protocols designed to generate, store and transfer
compact localized states in a quantum network. Induced by parameter tuning or
local reflection symmetries, such states vanish outside selected domains of the
complete system and are therefore ideal for information storage. Their creation
and transfer is here achieved either via amplitude phase flips or via optimal
temporal control of inter-site couplings. We apply the concept to a decorated,
locally symmetric Lieb lattice where one sublattice is dimerized, and also
demonstrate it for more complex setups. The approach allows for a flexible
storage and transfer of states along independent paths in lattices supporting
flat energetic bands. The generic network and protocols proposed can be
utilized in various physical setups such as atomic or molecular spin lattices,
photonic waveguide arrays, and acoustic setups.",1811.02950v1
2019-02-24,Electron transfer in confined electromagnetic fields,"The interaction between molecular (atomic) electron(s) and the vacuum field
of a reflective cavity generates a significant interest thanks to the rapid
developments in nanophotonics. Such interaction which lies within the realm of
cavity quantum electrodynamic can substantially affect transport properties of
molecular systems. In this work we consider non-adiabatic electron transfer
process in the presence of a cavity mode. We present a generalized framework
for the interaction between a charged molecular system and a quantized
electromagnetic field of a cavity and apply it to the problem of electron
transfer between a donor and an acceptor placed in a confined vacuum
electromagnetic field. The effective system Hamiltonian corresponds to a
unified Rabi and spin-boson model which includes a self-dipole energy term. Two
limiting cases are considered: one where the electron is assumed much faster
than the cavity mode and another in which the electron tunneling time is
significantly larger than the mode period. In both cases a significant rate
enhancement can be produced by coupling to the cavity mode in the Marcus
inverted region. The results of this work offer new possibilities for
controlling electron transfer processes using visible and infrared plasmonics",1902.08896v1
2019-04-11,Spin entangled state transfer in quantum dot arrays: Coherent adiabatic and speed-up protocols,"Long-distance transfer of quantum states is an indispensable part of
large-scale quantum information processing. We propose a novel scheme for the
transfer of two-electron entangled states, from one edge of a quantum dot array
to the other by coherent adiabatic passage. This protocol is mediated by pulsed
tunneling barriers. In a second step, we seek for a speed up by shortcut to
adiabaticity techniques. This significantly reduces the operation time and,
thus, minimizes the impact of decoherence. For typical parameters of
state-of-the-art solid state devices, the accelerated protocol has an operation
time in the nanosecond range and terminates before a major coherence loss sets
in. The scheme represents a promising candidate for entanglement transfer in
solid state quantum information processing.",1904.05694v1
2019-11-08,On the transfer matrix of the supersymmetric eight-vertex model. II. Open boundary conditions,"The transfer matrix of the square-lattice eight-vertex model on a strip with
$L\geqslant 1$ vertical lines and open boundary conditions is investigated. It
is shown that for vertex weights $a,b,c,d$ that obey the relation
$(a^2+ab)(b^2+ab)=(c^2+ab)(d^2+ab)$ and appropriately chosen $K$-matrices
$K^\pm$ this transfer matrix possesses the remarkably simple, non-degenerate
eigenvalue $\Lambda_L = (a+b)^{2L}\,\text{tr}(K^+K^-)$. For positive vertex
weights, $\Lambda_L$ is shown to be the largest transfer-matrix eigenvalue. The
corresponding eigenspace is equal to the space of the ground states of the
Hamiltonian of a related XYZ spin chain. An essential ingredient in the proofs
is the supersymmetry of this Hamiltonian.",1911.03348v2
2020-08-06,Spectral functions of CVD grown MoS$_2$ monolayers after chemical transfer onto Au surface,"The recent rise of van der Waals (vdW) crystals has opened new prospects for
studying versatile and exotic fundamental physics with future device
applications such as twistronics. Even though the recent development on
Angle-resolved photoemission spectroscopy (ARPES) with Nano-focusing optics,
making clean surfaces and interfaces of chemically transferred crystals have
been challenging to obtain high-resolution ARPES spectra. Here, we show that by
employing nano-ARPES with submicron sized beam and polystyrene-assisted
transfer followed by annealing process in ultra-high vacuum environment,
remarkably clear ARPES spectral features such as spin-orbit splitting and band
renormalization of CVD-grown, monolayered MoS2 can be measured. Our finding
paves a way to exploit chemically transferred crystals for measuring
high-resolution ARPES spectra to observe exotic quasi-particles in vdW
heterostructures.",2008.02548v1
2020-08-14,Transferability of self-energy correction in tight-binding basis constructed from first principles,"We demonstrate in this work the transferability of self-energy(SE)
correction(SEC) of Kohn-Sham(KS) single particle states from smaller to larger
systems, when mapped through localized orbitals constructed from the KS states.
The approach results in a SE corrected TB framework, within which, the mapping
of SEC of TB parameters is found to be transferable from smaller to larger
systems of similar morphology, leading to a computationally inexpensive
approach for estimation of SEC in large systems with reasonably high accuracy.
The scheme has been demonstrated in insulating, semiconducting and magnetic
nanoribbons of graphene and hexagonal boron nitride, where SEC tends to
strengthen the individual pi bonds, leading to transfer of charge from edge to
bulk. Additionally in magnetic bipartite systems SEC tends to enhance
inter-sublattice spin separation. The proposed scheme thus promises to enable
estimation of SEC of band-gaps of large systems without needing to explicitly
calculate SEC of KS single particle levels which can be computationally
prohibitively expensive.",2008.06292v2
2020-08-14,Quantum heat statistics with time-evolving matrix product operators,"We present a numerically exact method to compute the full counting statistics
of heat transfer in non-Markovian open quantum systems, which is based on the
time-evolving matrix product operator (TEMPO) algorithm. This approach is
applied to the paradigmatic spin-boson model in order to calculate the mean and
fluctuations of the heat transferred to the environment during thermal
equilibration. We show that system-reservoir correlations make a significant
contribution to the heat statistics at low temperature and present a
variational theory that quantitatively explains our numerical results. We also
demonstrate a fluctuation-dissipation relation connecting the mean and variance
of the heat distribution at high temperature. Our results reveal that
system-bath interactions make a significant contribution to heat transfer even
when the dynamics of the open system is effectively Markovian. The method
presented here provides a flexible and general tool to predict the fluctuations
of heat transfer in open quantum systems in non-perturbative regimes.",2008.06491v3
2020-09-25,Information theoretical view of QCD effective model with heavy quarks,"To understand the phase transition phenomena, information theoretical
approaches can pick up some important properties of the phenomena based on the
probability distribution. In this paper, we show information theoretical
aspects of the 3-dimensional 3-state Potts model with the external field which
is corresponding to the QCD effective model with heavy quarks. The transfer
mutual information which represents the information flow of two spin variables
is numerically estimated based on the Markov-chain Monte-Carlo method. The
transfer mutual information has the peak near the confinement-deconfinement
transition, and it may be used to detect the precursors of the transition.
Since the transfer mutual information still have the peak even if the
Polyakov-loop changes continuously and smoothly, we may pick up some aspects of
the confinement-deconfinement nature from the information flow properties.
Particularly, the transfer mutual information shows the significantly different
behavior below and above the Roberge-Weiss endpoint existed in the pure
imaginary chemical potential region, which may indicate the system change by
the confinement-deconfinement transition.",2009.12067v1
2021-07-20,Coherent evolution of signal amplification by reversible exchange in two alternating fields (alt-SABRE),"Parahydrogen (pH2) is a convenient and cost efficient source for magnetic
resonance signal enhancement. Transient interaction of pH2 with a metal organic
complex in a signal amplification by reversible exchange (SABRE) experiment
enabled more than 10% polarization for some 15N molecules. Here, we analyzed a
variant of SABRE, consisting of an outer magnetic field alternating between a
low field of ~1 \muT, where a polarization transfer takes place, and a higher
field >50 \muT (alt-SABRE). We found effects of both of these fields on
amplitude and the frequency of polarization transfer. Deviation of a lower
magnetic field from a ""perfect"" condition of level anti-crossing increases the
frequency of polarization transfer that can be exploited for polarization of
short-lived transient SABRE complexes i.e. some substrates. Moreover, the
coherences responsible for polarization transfer at a lower field persisted
during magnetic field variation and continued their spin evolution at higher
field with a frequency of 2.5 kHz at 54 \muT. The latter should be taken into
consideration for an efficient alt-SABRE.",2107.09294v1
2022-07-21,A Transferable Recommender Approach for Selecting the Best Density Functional Approximations in Chemical Discovery,"Approximate density functional theory (DFT) has become indispensable owing to
its cost-accuracy trade-off in comparison to more computationally demanding but
accurate correlated wavefunction theory. To date, however, no single density
functional approximation (DFA) with universal accuracy has been identified,
leading to uncertainty in the quality of data generated from DFT. With electron
density fitting and transfer learning, we build a DFA recommender that selects
the DFA with the lowest expected error with respect to gold standard but
cost-prohibitive coupled cluster theory in a system-specific manner. We
demonstrate this recommender approach on vertical spin-splitting energy
evaluation for challenging transition metal complexes. Our recommender predicts
top-performing DFAs and yields excellent accuracy (ca. 2 kcal/mol) for chemical
discovery, outperforming both individual transfer learning models and the
single best functional in a set of 48 DFAs. We demonstrate the transferability
of the DFA recommender to experimentally synthesized compounds with distinct
chemistry.",2207.10747v1
2023-05-23,Topological edge state transfer via topological adiabatic passage,"The study of quantum state transfer has led to a variety of research efforts
utilizing quantum simulators. By exploiting the tunability of the qubit
frequency and qubit-qubit coupling, a superconducting qubit chain can simulate
various topological band models. In our study, we demonstrate that a spin-up
state can be transported along a topological qubit chain by modulating the
coupling strengths and the qubit frequencies. We show that the Hilbert space of
the qubit chain can be restricted to the subspace of two edge states in this
process, while the Hamiltonian degenerates into a two-state Landau-Zener (LZ)
model. Furthermore, we prove that the state transfer process in this
topological qubit chain is equivalent to the topological adiabatic passage of
the LZ model. With this analysis, we generalize the state transfer approach
from single-qubit Fock states to two-qubit Bell states.",2305.14529v3
2023-10-16,First-Principle Investigation Of Near-Field Energy Transfer Between Localized Quantum Emitters in Solids,"We present a predictive and general approach to investigate near-field energy
transfer processes between localized defects in semiconductors, which couples
first principle electronic structure calculations and a nonrelativistic quantum
electrodynamics description of photons in the weak-coupling regime. We apply
our approach to investigate an exemplar point defect in an oxide, the F center
in MgO, and we show that the energy transfer from a magnetic source, e.g., a
rare earth impurity, to the vacancy can lead to spin non conserving long-lived
excitation that are dominant processes in the near field, at distances relevant
to the design of photonic devices and ultra-high dense memories. We also define
a descriptor for coherent energy transfer to predict geometrical configurations
of emitters to enable long-lived excitations, that are useful to design optical
memories in semiconductor and insulators.",2310.10028v1
2023-12-14,A universal shortcut method for state transfer in quantum spin systems,"The need for fast and robust quantum state transfer is an essential element
in scalable quantum information processing, leading to widespread interest in
shortcuts to adiabaticity for speeding up adiabatic quantum protocols. However,
shortcuts to adiabaticity for systems with more than a few levels is
occasionally challenging to compute in theory and frequently difficult to
implement in experiments. In this work, we develop a protocol for constructing
shortcuts to adiabaticity through the multi-state Landau-Zener approach and a
stricter adiabatic condition. Importantly, our protocol only requires a few
pieces of information about the energy spectrum and adjusts the evolutionary
rate of the system, making it both generic for theoretical models and friendly
for experimental implementation. As examples, we apply our protocol to state
transfer in the non-Hermitian Su-Schrieffer-Heeger (SSH) model and the
topological Thouless pump models and find that it can speed up the manipulation
speed while remaining robust to Hamiltonian errors. Furthermore, our findings
can be realized using current technology and could potentially be extended to
many-body systems, dissipation cases, or Floquet processes. Overall, the
proposed shortcut protocol offers a promising avenue for enhancing the
efficiency and reliability of quantum state transfer protocols.",2312.08920v1
2005-08-04,Numerical Study of Spin Hall Transport in a Two Dimensional Hole Gas System,"We present a numerical study of the spin Hall effect in a two-dimensional
hole gas (2DHG) system in the presence of disorder. We find that the spin Hall
conductance (SHC), extrapolated to the thermodynamic limit, remains finite in a
wide range of disorder strengths for a closed system on torus. But there is no
intrinsic spin Hall accumulation as induced by an external electric field once
the disorder is turned on. The latter is examined by performing a Laughlin's
Gedanken gauge experiment numerically with the adiabatical insertion of a flux
quantum in a belt-shaped sample, in which the absence of level crossing is
found under the disorder effect. Without disorder, on the other hand, energy
levels do cross each other, which results in an oscillating
spin-density-modulation at the sample boundary after the insertion of one flux
quantum in the belt-shaped system. But the corresponding net spin transfer is
only about one order of magnitude smaller than what is expected from the bulk
SHC. These apparently contradictory results can be attributed to the violation
of the spin conservation law in such a system. We also briefly address the
dissipative Fermi surface contribution to spin polarization, which may be
relevant to experimental measurements.",0508116v2
2005-12-05,"Twin spin/charge roton mode and superfluid density: primary determining factors of $T_{c}$ in high-$T_{c}$ superconductors observed by neutron, ARPES, and $μ$SR","In the quest for primary factors which determine the transition temperature
$T_{c}$ of high-$T_{c}$ cuprate superconductors (HTSC), we develop a
phenomenological picture combining experimental results from muon spin
relaxation ($\mu$SR), neutron and Raman scattering, and angle-resolved
photoemission (ARPES) measurements, guided by an analogy with superfluid
$^{4}$He. The 41 meV neutron resonance mode and the ARPES superconducting
coherence peak (SCP) can be viewed as direct observations of spin and charge
soft modes, respectively, appearing near ($\pi,\pi$) and the center of the
Brillouin zone, having identical energy transfers and dispersion relations. We
present a conjecture that the mode energy of this twin spin/charge collective
excitation, as a roton analogue in HTSC, plays a primary role in determining
$T_{c}$, together with the superfluid density $n_{s}/m^{*}$ at $T \to 0$. We
further propose a microscopic model for pairing based on a resonant spin-charge
motion, which explains the extremely strong spin-charge coupling, relevant
energy scales, disappearence of pairing in the overdoped region, and the
contrasting spin-sensitivities of nodal and antinodal charges in HTSC systems.
Comparing collective versus single-particle excitations, pair formation versus
condensation, and local versus long-range phase coherence, we argue that many
fundamental features of HTSC systems, including the region of the Nernst
effect, can be understood in terms of condensation and fluctuation phenomena of
bosonic correlations formed above $T_{c}$.",0512075v1
2006-09-29,Bosonization approach to charge and spin dynamics of 1D fermions with band-curvature,"We consider one-dimensional (1D) spin-1/2 fermions in a clean quantum wire,
with forward scattering interactions and a non-linear single-particle spectrum,
$\xi_k = v|k| + k^2/2m$ where $v$ is the Fermi velocity and $1/m$ is the
band-curvature. We calculate the dynamical structure factor (DSF) of the model
at small wave-vector $q$ with the help of the bosonization technique. For
spinless fermions, we show that, starting from the single-parametric spectrum:
$\om = u |q|$, bosonization emulates the 2-parametric excitation spectrum: $\om
= u |q| \pm q^2/2m^*$, where $m^*$ decreases with increasing repulsive
interactions. Moreover, away from the excitation-cone, {\it i.e.} $\om \gg u
|q|$, bosonization yields the 2-pair excitation continuum of the DSF. For
spinful fermions, we show that the spin-charge coupling (SCC) due to
band-curvature affects charge and spin DSF in an asymmetric way. For the charge
DSF, SCC manifests as a two-peak structure: a charge peak at $\om = u_\rho |q|$
but also a spin peak at $\om = u_\sigma |q|$, as charge fluctuations may decay
via chargeless spin-singlet excitations. For the magnetic DSF, SCC manifests as
a continuous transfer of magnetic spectral weight to frequencies $\om >
u_\sigma |q|$, as spin fluctuations decay via pairs of chargeless spin and
spinless charge-neutral excitations.",0609754v2
2007-04-12,Temperature-driven transition from the Wigner Crystal to the Bond-Charge-Density Wave in the Quasi-One-Dimensional Quarter-Filled band,"It is known that within the interacting electron model Hamiltonian for the
one-dimensional 1/4-filled band, the singlet ground state is a Wigner crystal
only if the nearest neighbor electron-electron repulsion is larger than a
critical value. We show that this critical nearest neighbor Coulomb interaction
is different for each spin subspace, with the critical value decreasing with
increasing spin. As a consequence, with the lowering of temperature, there can
occur a transition from a Wigner crystal charge-ordered state to a spin-Peierls
state that is a Bond-Charge-Density Wave with charge occupancies different from
the Wigner crystal. This transition is possible because spin excitations from
the spin-Peierls state in the 1/4-filled band are necessarily accompanied by
changes in site charge densities. We apply our theory to the 1/4-filled band
quasi-one-dimensional organic charge-transfer solids in general and to 2:1
tetramethyltetrathiafulvalene (TMTTF) and tetramethyltetraselenafulvalene
(TMTSF) cationic salts in particular. We believe that many recent experiments
strongly indicate the Wigner crystal to Bond-Charge-Density Wave transition in
several members of the TMTTF family. We explain the occurrence of two different
antiferromagnetic phases but a single spin-Peierls state in the generic phase
diagram for the 2:1 cationic solids. The antiferromagnetic phases can have
either the Wigner crystal or the Bond-Charge-Spin-Density Wave charge
occupancies. The spin-Peierls state is always a Bond-Charge-Density Wave.",0704.1656v2
2011-02-08,Quantum control in spintronics,"Superposition and entanglement are uniquely quantum phenomena. Superposition
incorporates a phase which contains information surpassing any classical
mixture. Entanglement offers correlations between measurements in quantum
systems that are stronger than any which would be possible classically. These
give quantum computing its spectacular potential, but the implications extend
far beyond quantum information processing. Early applications may be found in
entanglement enhanced sensing and metrology. Quantum spins in condensed matter
offer promising candidates for investigating and exploiting superposition and
entanglement, and enormous progress is being made in quantum control of such
systems. In GaAs, individual electron spins can be manipulated and measured,
and singlet-triplet states can be controlled in double-dot structures. In
silicon, individual electron spins can be detected by ionisation of phosphorous
donors, and information can be transferred from electron spins to nuclear spins
to provide long memory times. Electron and nuclear spins can be manipulated in
nitrogen atoms incarcerated in fullerene molecules, which in turn can be
assembled in ordered arrays. Spin states of charged nitrogen vacancy centres in
diamond can be manipulated and read optically. Collective spin states in a
range of materials systems offer scope for holographic storage of information.
Conditions are now excellent for implementing superposition and entanglement in
spintronic devices, thereby opening up a new era of quantum technologies.",1102.1546v1
2012-06-17,P-wave Cooper pair splitting,"Splitting of Cooper pairs has recently been realized experimentally for
s-wave Cooper pairs. A split Cooper pair represents an entangled two-electron
pair state which has possible application in on-chip quantum computation.
Likewise the spin-activity of interfaces in nanoscale tunnel junctions has been
investigated theoretically and experimentally in recent years. However, the
possible implications of spin-active interfaces in Cooper pair splitters so far
have not been investigated. We analyse the current and the cross correlation of
currents in a superconductor ferromagnet beamsplitter including spin-active
scattering. Using the Hamiltonian formalism we calculate the cumulant
generating function of charge transfer. As a first step, we discuss
characteristics of the conductance for crossed Andreev reflection in
superconductor ferromagnet beamsplitters with s-wave and p-wave superconductors
and no spin-active scattering. In a second step, we consider spin-active
scattering and show how to realize p-wave splitting only using a s-wave
superconductor via the process of spin-flipped crossed Andreev reflection. We
present results for the conductance and cross correlations. Spin-activity of
interfaces in Cooper pair splitters allows for new features in ordinary s-wave
Cooper pair splitters, that can otherwise only be realised by using p-wave
superconductors. In particular it provides access to Bell states different from
the typical spin singlet state.",1206.3802v2
2015-04-09,Optical hyperpolarization of 13C nuclear spins in nanodiamond ensembles,"Here we propose and analyse in detail protocols that can achieve rapid
hyperpolarization of 13C nuclear spins in randomly oriented ensembles of
nanodiamonds at room temperature. Our protocols exploit a combination of
optical polarization of electron spins in nitrogen-vacancy centers and the
transfer of this polarization to 13C nuclei by means of microwave control to
overcome the severe challenges that are posed by the random orientation of the
nanodiamonds and their nitrogen-vacancy centers. Specifically, these random
orientations result in exceedingly large energy variations of the electron spin
levels that render the polarization and coherent control of the
nitrogen-vacancy center electron spins as well as the control of their coherent
interaction with the surrounding 13C nuclear spins highly inefficient. We
address these challenges by a combination of an off-resonant microwave double
resonance scheme in conjunction with a realization of the integrated solid
effect which, together with adiabatic rotations of external magnetic fields or
rotations of nanodiamonds, leads to a protocol that achieves high levels of
hyperpolarization of the entire nuclear-spin bath in a randomly oriented
ensemble of nanodiamonds even at room temperature. This hyperpolarization
together with the long nuclear spin polarization lifetimes in nanodiamonds and
the relatively high density of 13C nuclei has the potential to result in a
major signal enhancement in 13C nuclear magnetic resonance imaging and suggests
functionalized and hyperpolarized nanodiamonds as a unique probe for molecular
imaging both in vitro and in vivo.",1504.02368v1
2015-06-03,Development of hard x-ray photoelectron SPLEED-based spectrometer applicable for probing of buried magnetic layer valence states,"A novel design of high-voltage compatible polarimeter for spin-resolved hard
x-ray photoelectron spectroscopy (Spin-HAXPES) went into operation at beamline
BL09XU of SPring-8 in Hyogo, Japan. The detector is based on the
well-established principle of electron diffraction from a W(001) single-crystal
at a scattering energy of 103.5 eV. Its special feature is that it can be
operated at a high negative bias potential up to 10 kV, necessary to access the
HAXPES range. The polarimeter is operated behind a large hemispherical analyzer
(Scienta R-4000). It was optimized for high transmission of the transfer
optics. The exit plane of the analyzer contains a delay-line detector (20 mm
dia.) for conventional multichannel intensity spectroscopy simultaneously with
single-channel spin analysis. The performance of the combined setup is
demonstrated by the first spin-resolved data for the valence-region of a FeCo
functional layer of a tunneling device, buried beneath 3 nm of oxidic material.
The well-structured spin polarization spectrum validates Spin-HAXPES in the
valence energy range as powerful method for bulk electronic structure analysis.
The spin polarization spectrum exhibits a rich structure, originating from
clearly discernible transitions in the majority and minority partial spin
spectra.",1506.01356v1
2016-05-18,Spin filtering and switching action in a diamond network with magnetic-nonmagnetic atomic distribution,"We propose a simple model quantum network consisting of diamond-shaped
plaquettes with deterministic distribution of magnetic and non-magnetic atoms
in presence of a uniform external magnetic flux in each plaquette and predict
that such a simple model can be a prospective candidate for spin filter as well
as flux driven spintronic switch. The orientations and the amplitudes of the
substrate magnetic moments play a crucial role in the energy band engineering
of the two spin channels which essentially gives us a control over the spin
transmission leading to a spin filtering effect. The externally tunable
magnetic flux plays an important role in inducing a switch on-switch off effect
for both the spin states indicating the behavior like a spintronic switch. Even
a correlated disorder configuration in the on-site potentials and in the
magnetic moments may lead to disorder-induced spin filtering phenomenon where
one of the spin channel gets entirely blocked leaving the other one
transmitting over the entire allowed energy regime. All these features are
established by evaluating the density of states and the two terminal
transmission probabilities using the transfer-matrix formalism within a
tight-binding framework. Experimental realization of our theoretical study may
be helpful in designing new spintronic devices.",1605.05515v2
2017-09-06,Complex THz and DC inverse spin Hall effect in YIG/Cu$_{1-x}$Ir$_{x}$ bilayers across a wide concentration range,"We measure the inverse spin Hall effect of Cu$_{1-x}$Ir$_{x}$ thin films on
yttrium iron garnet over a wide range of Ir concentrations ($0.05 \leqslant x
\leqslant 0.7$). Spin currents are triggered through the spin Seebeck effect,
either by a DC temperature gradient or by ultrafast optical heating of the
metal layer. The spin Hall current is detected by, respectively, electrical
contacts or measurement of the emitted THz radiation. With both approaches, we
reveal the same Ir concentration dependence that follows a novel complex,
non-monotonous behavior as compared to previous studies. For small Ir
concentrations a signal minimum is observed, while a pronounced maximum appears
near the equiatomic composition. We identify this behavior as originating from
the interplay of different spin Hall mechanisms as well as a
concentration-dependent variation of the integrated spin current density in
Cu$_{1-x}$Ir$_{x}$. The coinciding results obtained for DC and ultrafast
stimuli show that the studied material allows for efficient spin-to-charge
conversion even on ultrafast timescales, thus enabling a transfer of
established spintronic measurement schemes into the terahertz regime.",1709.01890v1
2017-12-26,Quantum paramagnet near spin-state transition,"Spin-state transition, also known as spin crossover, plays a key role in
diverse systems, including minerals and biological materials. In theory, the
boundary range between the low- and high-spin states is expected to enrich the
transition and give rise to unusual physical states. However, no compound that
realizes a nearly degenerate critical range as the ground state without
requiring special external conditions has yet been experimentally identified.
This study reports that, by comprehensive measurements of macroscopic physical
properties, X-ray diffractometry, and neutron spectroscopy, the Sc substitution
in LaCoO$_3$ destabilizes its nonmagnetic low-spin state and generates an
anomalous paramagnetic state accompanied by the enhancement of transport gap
and magneto-lattice-expansion as well as the contraction of Co--O distance with
the increase of electron site-transfer. These phenomena are not well described
by the mixture of conventional low- and high-spin states, but by their quantum
superposition occurring on the verge of a spin-state transition. The present
study enables us to significantly accelerate the design of new advanced
materials without requiring special equipment based on the concept of quantum
spin-state criticality.",1712.09169v2
2018-03-06,Flux driven and geometry controlled spin filtering for arbitrary spins in aperiodic quantum networks,"We demonstrate that an aperiodic array of certain quantum networks comprising
magnetic and non-magnetic atoms can act as perfect spin filters for particles
with arbitrary spin state. This can be achieved by introducing minimal
quasi-one dimensionality in the basic structural units building up the array,
along with an appropriate tuning of the potential of the non-magnetic atoms,
the tunnel hopping integral between the non-magnetic atoms and the backbone,
and, in some cases, by tuning an external magnetic field. This latter result
opens up the interesting possibility of designing a flux controlled spin
demultiplexer using quantum networks. The proposed networks have close
resemblance with a family of recently developed photonic lattices, and the
scheme for spin filtering can thus be linked, in principle, to a possibility of
suppressing any one of the two states of polarization of a single photon,
almost at will. We use transfer matrices and a real space renormalization group
scheme to unravel the conditions under which any aperiodic arrangement of such
topologically different structures will filter out any given spin projection.
Our results are analytically exact, and corroborated by extensive numerical
calculations of the spin polarized transmission and the density of states of
such systems.",1803.02170v1
2020-02-01,Spin-dependent Schottky barriers and vacancy-induced spin-selective Ohmic contacts in magnetic vdW heterostructures,"The 2D ferromagnets, such as CrX3 (X=Cl, Br and I), have been attracting
extensive attentions since they provide novel platforms to fundamental physics
and device applications. Integrating CrX3 with other electrodes and substrates
is an essential step to their device realization. Therefore, it is important to
understand the interfacial properties between CrX3 and other 2D materials. As
an illustrative example, we have investigated the heterostructures between CrX3
and graphene (CrX3/Gr) from firstprinciples. We find unique Schottky contacts
type with strongly spin-dependent barriers in CrX3/Gr. This can be understood
by synergistic effects between the exchange splitting of semiconductor band of
CrX3 and interlayer charge transfer. The spinasymmetry of Schottky barriers may
result in different tunneling rates of spin-up and down electrons, and then
lead to spin-polarized current, namely spin-filter (SF) effect. Moreover, by
introducing X vacancy into CrX3/Gr, an Ohmic contact forms in spin-up
direction. It may enhance the transport of spin-up electrons, and improve SF
effect. Our systematic study reveals the unique interfacial properties of
CrX3/Gr, and provides a theoretical view to the understanding and designing of
spintronics device based on magnetic vdW heterostructures.",2002.00193v1
2020-09-30,Pathways for producing binary black holes with large misaligned spins in the isolated formation channel,"Binary black holes (BBHs) can form from the collapsed cores of isolated
high-mass binary stars. The masses and spins of these BBHs are determined by
the complicated interplay of phenomena such as tides, winds, accretion,
common-envelope evolution (CEE), supernova natal kicks, and stellar
core-envelope coupling. The gravitational waves emitted during the mergers of
BBHs depend on their masses and spins and can thus constrain these phenomena.
We present a simplified model of binary stellar evolution and identify regions
of the parameter space that produce BBHs with large spins misaligned with their
orbital angular momentum. In Scenario A (B) of our model, stable mass transfer
(SMT) occurs after Roche-lobe overflow (RLOF) of the more (less) massive star,
while CEE follows RLOF of the less (more) massive star. Each scenario is
further divided into Pathways 1 and 2 depending on whether the core of the more
massive star collapses before or after RLOF of the less massive star,
respectively. If the stellar cores are coupled weakly to their envelopes,
highly spinning BBHs can be produced if natal spins greater than $10\%$ of the
breakup value are inherited from the stellar progenitors. BBHs can
alternatively acquire large spins by tidal synchronization during the
Wolf-Rayet stage in Scenario A or by accretion onto the initially more massive
star during SMT in Scenario B. BBH spins can be highly misaligned if the kicks
are comparable to the orbital velocity, which is more easily achieved in
Pathway A1 where the kick of the more massive star precedes CEE.",2010.00078v2
2021-04-20,Spin-mechanics with nitrogen-vacancy centers and trapped particles,"Controlling the motion of macroscopic oscillators in the quantum regime has
been the subject of intense research in recent decades. In this direction,
opto-mechanical systems, where the motion of micro-objects is strongly coupled
with laser light radiation pressure, have had tremendous success. In
particular, the motion of levitating objects can be manipulated at the quantum
level thanks to their very high isolation from the environment under ultra-low
vacuum conditions. To enter the quantum regime, schemes using single long-lived
atomic spins, such as the electronic spin of nitrogen-vacancy (NV) centers in
diamond, coupled with levitating mechanical oscillators have been proposed. At
the single spin level, they offer the formidable prospect of transferring the
spins' inherent quantum nature to the oscillators, with foreseeable
far-reaching implications in quantum sensing and tests of quantum mechanics.
Adding the spin degrees of freedom to the experimentalists' toolbox would
enable access to a very rich playground at the crossroads between condensed
matter and atomic physics. We review recent experimental work in the field of
spin-mechanics that employ the interaction between trapped particles and
electronic spins in the solid state and discuss the challenges ahead. Our focus
is on the theoretical background close to the current experiments, as well as
on the experimental limits, that, once overcome, will enable these systems to
unleash their full potential.",2104.10244v2
2021-09-13,Single-photon-triggered spin squeezing with decoherence reduction in optomechanics via phase matching,"Quantum spin squeezing is an important resource for quantum information
processing, but its squeezing degree is not easy to preserve in an open system
with decoherence. Here, we propose a scheme to implement
single-photon-triggered spin squeezing with decoherence reduction in an open
system. In our system, a Dicke model (DM) is introduced into the quadratic
optomechanics, which can be equivalent to an effective DM manipulated by the
photon number. Besides, the phonon mode of the optomechanical system is coupled
to a squeezed vacuum reservoir with a phase matching, resulting in that the
thermal noise caused by the environment can be suppressed completely. We show
that squeezing of the phonon mode triggered by a single photon can be
transferred to the spin ensemble totally, and pairwise entanglement of the spin
ensemble can be realized if and only if there is spin squeezing. Importantly,
when considering the impact of the environment, our system can obtain a better
squeezing degree than the optimal squeezing that can be achieved in the
traditional DM. Meanwhile, the spin squeezing generated in our system is immune
to the thermal noise. This work offers an effective way to generate spin
squeezing with a single photon and to reduce decoherence in an open system,
which will have promising applications in quantum information processing.",2109.05692v2
2021-12-20,Spin current transport in hybrid Pt / multifunctional magnetoelectric Ga0.6Fe1.4O3 bilayers,"The low power manipulation of magnetization is currently a highly
sought-after objective in spintronics. Non ferromagnetic large spin-orbit
coupling heavy metal (NM) / ferromagnet (FM) heterostructures offer interesting
elements of response to this issue, by granting the manipulation of the FM
magnetization by the NM spin Hall effect (SHE) generated spin current.
Additional functionalities, such as the electric field control of the spin
current generation, can be offered using multifunctional ferromagnets. We have
studied the spin current transfer processes between Pt and the multifunctional
magnetoelectric Ga0.6Fe1.4O3 (GFO). In particular, via angular dependent
magnetotransport measurements, we were able to differentiate between magnetic
proximity effect (MPE)-induced anisotropic magnetoresistance (AMR) and spin
Hall magnetoresistance (SMR). Our analysis shows that SMR is the dominant
phenomenon at all temperatures and is the only one to be considered near room
temperature, with a magnitude comparable to those observed in Pd/YIG or Pt/YIG
heterostructures. These results indicate that magnetoelectric GFO thin films
show promises for achieving an electric-field control of the spin current
generation in NM/FM oxide-based heterostructures.",2112.10406v1
2022-02-04,Scrambling and quantum feedback in a nanomechanical system,"The question of how swiftly entanglement spreads over a system has attracted
vital interest. In this regard, the out-of-time ordered correlator (OTOC) is a
quantitative measure of the entanglement spreading process. Particular interest
concerns the propagation of quantum correlations in the lattice systems, {\it
e.g.}, spin chains. In a seminal paper D. A. Roberts, D. Stanford and L.
Susskind, J. High Energy Phys. 03, 051, (2015) the concept of the OTOC's radius
was introduced. The radius of the OTOC defines the front line reached by the
spread of entanglement. Beyond this radius operators commute. In the present
work, we propose a model of two nanomechanical systems coupled with two
Nitrogen-vacancy (NV) center spins. Oscillators are coupled to each other
directly while NV spins are not. Therefore, the correlation between the NV
spins may arise only through the quantum feedback exerted from the first NV
spin to the first oscillator and transferred from the first oscillator to the
second oscillator via the direct coupling. Thus nonzero OTOC between NV spins
quantifies the strength of the quantum feedback. We show that NV spins cannot
exert quantum feedback on classical nonlinear oscillators. We also discuss the
inherently quantum case with a linear quantum harmonic oscillator indirectly
coupling the two spins and verify that in the classical limit of the
oscillator, the OTOC vanishes.",2202.02345v1
2022-06-30,Experimental Demonstration of a Spin-Wave Lens Designed with Machine Learning,"We present the design and experimental realization of a device that acts like
a spin-wave lens i.e., it focuses spin waves to a specified location. The
structure of the lens does not resemble any conventional lens design, it is a
nonintuitive pattern produced by a machine learning algorithm. As a spin-wave
design tool, we used our custom micromagnetic solver ""SpinTorch"" that has
built-in automatic gradient calculation and can perform backpropagation through
time for spin-wave propagation. The training itself is performed with the
saturation magnetization of a YIG film as a variable parameter, with the goal
to guide spin waves to a predefined location. We verified the operation of the
device in the widely used mumax3 micromagnetic solver, and by experimental
realization. For the experimental implementation, we developed a technique to
create effective saturation-magnetization landscapes in YIG by direct
focused-ion-beam irradiation. This allows us to rapidly transfer the nanoscale
design patterns to the YIG medium, without patterning the material by etching.
We measured the effective saturation magnetization corresponding to the FIB
dose levels in advance and used this mapping to translate the designed
scatterer to the required dose levels. Our demonstration serves as a proof of
concept for a workflow that can be used to realize more sophisticated spin-wave
devices with complex functionality, e.g., spin-wave signal processors, or
neuromorphic devices.",2207.00055v1
2023-10-04,Nanotube spin defects for omnidirectional magnetic field sensing,"Optically addressable spin defects in three-dimensional (3D) crystals and
two-dimensional (2D) van der Waals (vdW) materials are revolutionizing
nanoscale quantum sensing. Spin defects in one-dimensional (1D) vdW nanotubes
will provide unique opportunities due to their small sizes in two dimensions
and absence of dangling bonds on side walls. However, optically detected
magnetic resonance of localized spin defects in a nanotube has not been
observed. Here, we report the observation of single spin color centers in boron
nitride nanotubes (BNNTs) at room temperature. Our findings suggest that these
BNNT spin defects possess a spin $S=1/2$ ground state without an intrinsic
quantization axis, leading to orientation-independent magnetic field sensing.
We harness this unique feature to observe anisotropic magnetization of a 2D
magnet in magnetic fields along orthogonal directions, a challenge for
conventional spin $S=1$ defects such as diamond nitrogen-vacancy centers.
Additionally, we develop a method to deterministically transfer a BNNT onto a
cantilever and use it to demonstrate scanning probe magnetometry. Further
refinement of our approach will enable atomic scale quantum sensing of magnetic
fields in any direction.",2310.02709v2
2023-11-09,Signature of surface anisotropy in the spin-flip neutron scattering cross section of spherical nanoparticles: atomistic simulations and analytical theory,"We investigate the signature of magnetic surface anisotropy in nanoparticles
in their spin-flip neutron scattering cross section. Taking into account the
isotropic exchange interaction, an external magnetic field, a uniaxial or cubic
magnetic anisotropy for the particle's core, and several models for the surface
anisotropy (N\'eel, conventional, random), we compute the spin-flip small-angle
neutron scattering (SANS) cross section from the equilibrium spin structures
obtained using the Landau-Lifshitz equation. The sign of the surface anisotropy
constant, which is related to the appearance of tangential- or radial-like spin
textures, can be distinguished from the momentum-transfer dependence of the
spin-flip signal. The data cannot be described by the well-known and often-used
analytical expressions for uniformly magnetized spherical or core-shell
particles, in particular at remanence or at the coercive field. Based on a
second-order polynomial expansion for the magnetization vector field, we
develop a novel minimal model for the azimuthally-averaged magnetic SANS cross
section. The theoretical expression considers a general magnetization
inhomogeneity and is not restricted to the presence of surface anisotropy. It
is shown that the model describes very well our simulation data as well as more
complex spin patterns such as vortex-like structures. Only seven expansion
coefficients and some basis functions are sufficient to describe the scattering
behavior of a very large number of atomic spins.",2311.05706v1
2023-11-20,The stellar bar - dark matter halo connection in the TNG50 simulations,"Stellar bars in disk galaxies grow by losing angular momentum to their
environments, including the Dark Matter (DM) halo, stellar and gas disks, and
interacting satellite galaxies. This exchange of angular momentum during galaxy
evolution hints at a connection between bar properties and the DM halo spin
$\lambda$ -- the dimensionless form of DM angular momentum. We investigate the
connection of halo spin $\lambda$ and galaxy properties in the presence/absence
of stellar bars, using the cosmological magneto-hydrodynamic TNG50 simulations
at three redshifts $z_r=0, 0.1$ and 1. We estimate the halo spin for barred and
unbarred galaxies (bar strength: $0<A_2/A_0<0.7$) at the central regions of the
DM halo close to the galaxy disk and far from the disk, close to halo virial
radius. At $z_r=0$, strongly barred galaxies ($A_2/A_0>0.4$) reside in DM halos
having low spin and low specific angular momentum, while unbarred and weakly
barred galaxies ($A_2/A_0<0.2$) are hosted in high spin and high specific
angular momentum halos. The inverse correlation between bar strength and halo
spin is surprising since previous studies show that bars transfer angular
momentum to DM halos. However, the bar strength-halo spin connection is more
complex at higher redshift ($z_r=1$) with higher halo spin for all galaxies
than that at $z_r=0$. Using galaxy samples across various DM halo mass ranges,
we highlight the importance of sample selection in obtaining meaningful
results. Investigating the bar--halo connection in further detail is crucial
for understanding the impact of bars on galaxy evolution models.",2311.11998v1
2004-08-11,Multi-Temperature Blackbody Spectra of Thin Accretion Disks With and Without a Zero-Torque Inner Boundary Condition,"The standard spectral model for analyzing the soft component of thermal
emission from a thin accretion disk around a black hole is the
multi-temperature blackbody (MTB) model. The widely used implementation of this
model, which is known as ``diskbb,'' assumes nonzero torque at the inner edge
of the accretion disk. This assumption is contrary to the classic and current
literature on thin-disk accretion, which advocates the use of a zero-torque
boundary condition. Consequently, we have written code for a zero-torque model,
``ezdiskbb,'' which we compare to the nonzero-torque model diskbb by fitting
RXTE spectra of three well-known black hole binaries: 4U 1543-47, XTE
J1550-564, and GRO J1655-40. The chief difference we find is that the
zero-torque model gives a value for the inner disk radius that is about 2.2
times smaller than the value given by diskbb. This result has important
implications, especially for the determination of black-hole angular momentum
and mass accretion rate.",0408209v1
2004-10-18,On the torque on birefringent plates induced by quantum fluctuations,"We present detailed numerical calculations of the mechanical torque induced
by quantum fluctuations on two parallel birefringent plates with in plane
optical anisotropy, separated by either vacuum or a liquid (ethanol). The
torque is found to vary as $\sin(2\theta)$, where $\theta$ represents the angle
between the two optical axes, and its magnitude rapidly increases with
decreasing plate separation $d$. For a 40 $\mu$m diameter disk, made out of
either quartz or calcite, kept parallel to a Barium Titanate plate at $d\simeq
100$ nm, the maximum torque (at $\theta={\pi\over 4}$) is of the order of
$\simeq 10^{-19}$ N$\cdot$m. We propose an experiment to observe this torque
when the Barium Titanate plate is immersed in ethanol and the other
birefringent disk is placed on top of it. In this case the retarded van der
Waals (or Casimir-Lifshitz) force between the two birefringent slabs is
repulsive. The disk would float parallel to the plate at a distance where its
net weight is counterbalanced by the retarded van der Waals repulsion, free to
rotate in response to very small driving torques.",0410136v1
2010-04-10,An Improved Fixed Switching Frequency Direct Torque Control of Induction Motor Drives Fed by Direct Matrix Converter,"A few papers have been interested by the fixed switching frequency direct
torque control fed by direct matrix converters, where we can find just the use
of direct torque controlled space vector modulated method. In this present
paper, we present an improved method used for a fixed switching frequency
direct torque control (DTC) using a direct matrix converter (DMC). This method
is characterized by a simple structure, a fixed switching frequency which
causes minimal torque ripple and a unity input power factor. Using this
strategy, we combine the direct matrix converters advantages with those of
direct torque control (DTC) schemes. The used technique for constant frequency
is combined with the input current space vector to create the switching table
of direct matrix converter (DMC). Simulation results clearly demonstrate a
better dynamic and steady state performances of the proposed method.",1004.1745v1
2011-05-17,Active motion assisted by correlated stochastic torques,"The stochastic dynamics of an active particle undergoing a constant speed and
additionally driven by an overall fluctuating torque is investigated. The
random torque forces are expressed by a stochastic differential equation for
the angular dynamics of the particle determining the orientation of motion. In
addition to a constant torque, the particle is supplemented by random torques
which are modeled as an Ornstein-Uhlenbeck process with given correlation time
$\tau_c$. These nonvanishing correlations cause a persistence of the particles'
trajectories and a change of the effective spatial diffusion coefficient. We
discuss the mean square displacement as a function of the correlation time and
the noise intensity and detect a nonmonotonic dependence of the effective
diffusion coefficient with respect to both correlation time and noise strength.
A maximal diffusion behavior is obtained if the correlated angular noise
straightens the curved trajectories, interrupted by small pirouettes, whereby
the correlated noise amplifies a straightening of the curved trajectories
caused by the constant torque.",1105.3363v2
2014-10-24,Can the self-propulsion of anisotropic microswimmers be described by using forces and torques?,"The self-propulsion of artificial and biological microswimmers (i.e., active
colloidal particles) has often been modelled by using a force and a torque
entering into the overdamped equations for the Brownian motion of passive
particles. This seemingly contradicts the fact that a swimmer is force-free and
torque-free, i.e., that the net force and torque on the particle vanish. Using
different models for mechanical and diffusiophoretic self-propulsion, we
demonstrate here that the equations of motion of microswimmers can be mapped
onto those of passive particles with the shape-dependent grand resistance
matrix and formally external effective forces and torques. This is consistent
with experimental findings on the circular motion of artificial asymmetric
microswimmers driven by self-diffusiophoresis. The concept of effective
self-propulsion forces and torques significantly facilitates the understanding
of the swimming paths, e.g., for a microswimmer under gravity. However, this
concept has its limitations when the self-propulsion mechanism of a swimmer is
disturbed either by another particle in its close vicinity or by interactions
with obstacles, such as a wall.",1410.6707v1
2015-03-04,"Electromagnetic Torques, Precession and Evolution of Magnetic Inclination of Pulsars","We present analytic calculations of the electromagnetic torques acting on a
magnetic neutron star rotating in vacuum, including near-zone torques
associated with the inertia of dipole and quadrupole magnetic fields. We
incorporate these torques into the rotational dynamics of a rigid-body neutron
star, and show that the effects of the inertial torque can be understood as a
modification of the moment of inertia tensor of the star. We apply our
rotational dynamics equation to the Crab pulsar, including intrinsic
distortions of the star and various electromagnetic torques, to investigate the
possibility that the counter-alignment of the magnetic inclination angle, as
suggested by recent observations, could be explained by pulsar precession. We
find that if the effective principal axis of the pulsar is nearly aligned with
either the magnetic dipole axis or the rotation axis, then precession may
account for the observed counter-alignment over decade timescales. Over the
spindown timescale of the pulsar, the magnetic inclination angle always
decreases.",1503.01486v2
2016-02-15,Alignment of interstellar grains by mechanical torques: suprathermally rotating Gaussian random spheres,"Collisions of gas particles with a drifting grain give rise to a mechanical
torque on the grain. Recent work by Lazarian & Hoang showed that mechanical
torques might play a significant role in aligning helical grains along the
interstellar magnetic field direction, even in the case of subsonic drift. We
compute the mechanical torques on 13 different irregular grains and examine
their resulting rotational dynamics, assuming steady rotation about the
principal axis of greatest moment of inertia. We find that the alignment
efficiency in the subsonic drift regime depends sensitively on the grain shape,
with more efficient alignment for shapes with a substantial mechanical torque
even in the case of no drift. The alignment is typically more efficient for
supersonic drift. A more rigorous analysis of the dynamics is required to
definitively appraise the role of mechanical torques in grain alignment.",1602.04775v1
2016-09-02,Marginally stable and turbulent boundary layers in low-curvature Taylor-Couette flow,"Marginal stability arguments are used to describe the rotation-number
dependence of torque in Taylor-Couette (TC) flow for radius ratios $\eta \geq
0.9$ and shear Reynolds number $Re_S=2\times 10^4$. With an approximate
representation of the mean profile by piecewise linear functions, characterized
by the boundary-layer thicknesses at the inner and outer cylinder and the
angular momentum in the center, profiles and torques are extracted from the
requirement that the boundary layers represent marginally stable TC subsystems
and that the torque at the inner and outer cylinder coincide. This model then
explains the broad shoulder in the torque as a function of rotation number near
$R_\Omega\approx 0.2$. For rotation numbers $R_\Omega < 0.07$ the TC stability
conditions predict boundary layers in which shear Reynolds numbers are very
large. Assuming that the TC instability is bypassed by some shear instability,
a second maximum in torque appears, in very good agreement with numerical
simulations. The results show that, despite the shortcomings of marginal
stability theory in other cases, it can explain quantitatively the
non-monotonic torque variation with rotation number for both the broad maximum
as well as the narrow maximum.",1609.00556v1
2018-06-12,"Dynamical and current-induced Dzyaloshinskii-Moriya interaction: Role for damping, gyromagnetism, and current-induced torques in noncollinear magnets","Both applied electric currents and magnetization dynamics modify the
Dzyaloshinskii-Moriya interaction (DMI), which we call current-induced DMI
(CIDMI) and dynamical DMI (DDMI), respectively. We report a theory of CIDMI and
DDMI. The inverse of CIDMI consists in charge pumping by a time-dependent
gradient of magnetization $\partial^2 M(r,t)/\partial r\partial t$, while the
inverse of DDMI describes the torque generated by $\partial^2 M(r,t)/\partial
r\partial t$. In noncollinear magnets CIDMI and DDMI depend on the local
magnetization direction. The resulting spatial gradients correspond to torques
that need to be included into the theories of Gilbert damping, gyromagnetism,
and current-induced torques (CITs) in order to satisfy the Onsager reciprocity
relations. CIDMI is related to the modification of orbital magnetism induced by
magnetization dynamics, which we call dynamical orbital magnetism (DOM), and
spatial gradients of DOM contribute to charge pumping. We present applications
of this formalism to the CITs and to the torque-torque correlation in textured
Rashba ferromagnets.",1806.04782v3
2018-10-18,Torque on slowly moving electric or magnetic dipoles in vacuo,"The torque on a moving electric or magnetic dipole in slow motion is deduced
using the Lorentz transformation of the fields to first order in v/c. It is
shown that the obtained equations are independent of the model adopted for the
dipole, whether it is of Amperian or Gilbertian type, thus showing the complete
validity of the Amp\`ere equivalence principle even in dynamical conditions.
The torque is made of three terms: beside that due to the direct torque on the
dipole there are two more terms: one due to the torque on the associated
perpendicular dual-dipole caused by motion, while the other is the inertial
torque due to the displacement of the dipole which carries with it the field
linear momentum, or the hidden momentum.",1810.08558v1
2021-11-12,Dynamic force and torque characteristic of annular gaps -- Simulation results and evaluation of the relevance of the tilt and torque coefficients,"We discuss the dynamic force and torque characteristic of annular gaps
resulting from an axial flow component. First, the rotordynamic influence of
annular gaps with an axial flow component is recapitulated. So far there is a
severe lack of understanding the dynamic force and torque characteristic of
annular gaps. Second, a new simulation method is presented, using a perturbed
integro-differential approach in combination with power-law ansatz functions
for the velocity profiles and a Hirs' model to calculate the dynamic force and
torque characteristics. Third, an extensive parameter study is carried out. To
evaluate whether or not the hydraulic tilt and torque coefficients need to be
taken into account, an effective stiffness is defined and the influence of the
annulus length, an eccentrically operated shaft, the centre of rotation, a
modified Reynolds number, the flow number and the pre-swirl is investigated.",2111.06646v2
2022-01-10,Gyrotactic cluster formation of bottom-heavy squirmers,"Squirmers that are bottom-heavy experience a torque that aligns them along
the vertical so that they swim upwards. In a suspension of many squirmers, they
also interact hydrodynamically via flow fields that are initiated by their
swimming motion and by gravity. Swimming under the combined action of flow
field vorticity and gravitational torque is called gyrotaxis. Using the method
of multi-particle collision dynamics, we perform hydrodynamic simulations of a
many-squirmer system floating above the bottom surface. Due to gyrotaxis they
exhibit pronounced cluster formation with increasing gravitational torque. The
clusters are more volatile at low values but compactify to smaller clusters at
larger torques. The mean distance between clusters is mainly controlled by the
gravitational torque and not the global density. Furthermore, we observe that
neutral squirmers form clusters more easily, whereas pullers require larger
gravitational torques due to their additional force-dipole flow fields. We do
not observe clustering for pusher squirmers. Adding a rotlet dipole to the
squirmer flow field induces swirling clusters. At high gravitational strengths,
the hydrodynamic interactions with the no-slip boundary create an additional
vertical alignment for neutral squirmers, which also supports cluster
formation.",2201.03357v1
2022-07-27,Trace Expressions and Associated Limits for Non-Equilibrium Casimir Torque,"We exploit fluctuational electrodynamics to present trace expressions for the
torque experienced by arbitrary objects in a passive, non-absorbing,
rotationally invariant background environment. Specializing to a single object,
this formalism, together with recently developed techniques for calculating
bounds via Lagrange duality, is then used to derive limits on the maximum
Casimir torque that a single object with an isotropic electric susceptibility
can experience when out of equilibrium with its surrounding environment. The
maximum torque achievable at any wavelength is shown to scale in proportion to
body volumes in both subwavelength (quasistatics) and macroscopic (ray optics)
settings, and come within an order of magnitude of achievable torques on
topology optimized bodies. Finally, we discuss how to extend the formalism to
multiple bodies, deriving expressions for the torque experienced by two
subwavelength particles in proximity to one another.",2207.13646v1
2022-12-22,Reduced-variance orientational distribution functions from torque sampling,"We introduce a method to sample the orientational distribution function in
computer simulations. The method is based on the exact torque balance equation
for classical many-body systems of interacting anisotropic particles in
equilibrium. Instead of the traditional counting of events, we reconstruct the
orientational distribution function via an orientational integral of the torque
acting on the particles. We test the torque sampling method in two- and
three-dimensions, using both Langevin dynamics and overdamped Brownian
dynamics, and with two interparticle interaction potentials. In all cases the
torque sampling method produces profiles of the orientational distribution
function with better accuracy than those obtained with the traditional counting
method. The accuracy of the torque sampling method is independent of the bin
size, and hence it is possible to resolve the orientational distribution
function with arbitrarily small angular resolutions.",2212.11576v2
2024-02-08,Investigating and Controlling the Libration and Rotation Dynamics of Nanoparticles in an Optomechanical System,"In optomechanical systems, the libration and rotation of nanoparticles offer
profound insights for ultrasensitive torque measurement and macroscopic quantum
superpositions. Achievements include transitioning libration to rotation up to
6 GHz and cooling libration to millikelvin temperatures. It is undoubted that
the libration and rotation are respectively driven by restoring and constant
optical torques. The transition mechanisms between these two states, however,
demand further exploration. In this perspective, it is demonstrated in this
manuscript that monitoring lateral-scattered light allows real-time observation
of libration/rotation transitions and associated hysteresis as ellipticities of
trapping laser fields vary. By calculating optical torques and solving the
Langevin equation, transitions are linked to the balance between
anisotropic-polarization-induced sinusoidal optical torques and constant ones,
with absorption identified as the main contributor to constant torques. These
findings enable direct weak torque sensing and precise nanoparticle control in
rotational degrees, paving the way for studying quantum effects like
nonadiabatic phase shifts and macroscopic quantum superpositions, thereby
enriching quantum optomechanics research.",2402.05490v1
2005-08-04,"Mergers of neutron star black hole binaries with small mass ratios: nucleosynthesis, gamma-ray bursts and electromagnetic transients","I discuss simulations of the coalescence of black hole neutron star binary
systems with black hole masses between 14 and 20 \msun. The calculations use a
three-dimensional smoothed particle hydrodynamics code, a
temperature-dependent, nuclear equation of state and a multi-flavor neutrino
scheme. General relativistic effects are mimicked using the \Pacz-Wiita
pseudo-potential and gravitational radiation reaction forces. Opposite to
previous, purely Newtonian calculations, in none of the explored cases episodic
mass transfer occurs. The neutron star is always completely disrupted after
most of its mass has been transferred directly into the hole. For black hole
masses between 14 and 16 \Msun an accretion disk forms, large parts of it,
however, are inside the last stable orbit and therefore falling with large
radial velocities into the hole. These disks are (opposite to the neutron star
merger case) thin and -apart from a spiral shock- essentially cold. For higher
mass black holes ($M_{\rm BH} \ge 18$ \msun) almost the complete neutron star
disappears in the hole without forming an accretion disk. In these cases the
surviving material is spun up by tidal torques and ejected as a half-ring of
neutron-rich matter. None of the investigated systems is a promising GRB
central engine. We find between 0.01 and 0.2 \Msun of the neutron star to be
dynamically ejected. Like in a type Ia supernova, the radioactive decay of this
material will power a light curve with a peak luminosity of a few times
$10^{44}$ erg/s. The maximum will be reached about three days after the
coalescence and will be mainly visible in the optical/near infrared band. The
coalescence itself may produce a precursor pulse with a thermal spectrum of
$\sim 10$ ms duration.",0508138v1
2016-10-24,"Viscous Hydrodynamics Simulations of Circumbinary Accretion Discs: Variability, Quasi-Steady State, and Angular Momentum Transfer","We carry out numerical simulations of circumbinary discs, solving the viscous
hydrodynamics equations on a polar grid covering an extended disc outside the
binary co-orbital region. We use carefully controlled outer boundary conditions
and long-term integrations to ensure that the disc reaches a quasi-steady
state, in which the time-averaged mass accretion rate onto the binary,
$\langle\dot{M}\rangle$, matches the mass supply rate at the outer disc. We
focus on binaries with comparable masses and a wide range of eccentricities
($e_\mathrm{B}$). For $e_\mathrm{B} \lesssim 0.05$, the mass accretion rate of
the binary is modulated at about $5$ times the binary period; otherwise it is
modulated at the binary period. The inner part of the circumbinary disc ($r
\lesssim 6 a_\mathrm{B}$) generally becomes coherently eccentric. For low and
high $e_\mathrm{B}$, the disc line of apsides precesses around the binary, but
for intermediate $e_\mathrm{B}$ ($0.2 - 0.4$), it instead becomes locked with
that of the binary. By considering the balance of angular momentum transport
through the disc by advection, viscous stress, and gravitational torque, we
determine the time-averaged net angular momentum transfer rate to the binary,
$\langle\dot{J}\rangle$. The specific angular momentum, $l_0 =
\langle\dot{J}\rangle/\langle\dot{M}\rangle$, depends non-monotonically on
$e_\mathrm{B}$. Contrary to previous claims, we find that $l_0$ is positive for
most $e_\mathrm{B}$, implying that the binary receives net angular momentum,
which may cause its separation to grow with time. The minimum $l_0$ occurs at
intermediate $e_\mathrm{B}$ ($0.2 - 0.4$), corresponding to the regime where
the inner eccentric disc is apsidally aligned with the binary.",1610.07263v2
2018-11-20,Dusty spirals triggered by shadows in transition discs,"Context. Despite the recent discovery of spiral-shaped features in
protoplanetary discs in the near-infrared and millimetric wavelengths, there is
still an active discussion to understand how they formed. In fact, the spiral
waves observed in discs around young stars can be due to different physical
mechanisms: planet/companion torques, gravitational perturbations or
illumination effects. Aims. We study the spirals formed in the gaseous phase
due to two diametrically opposed shadows cast at fixed disc locations. The
shadows are created by an inclined non-precessing disc inside the cavity, which
is assumed to be optically thick. In particular, we analyse the effect of these
spirals on the dynamics of the dust particles and discuss their detectability
in transition discs. Methods. We perform gaseous hydrodynamical simulations
with shadows, then we compute the dust evolution on top of the gaseous
distribution, and finally we produce synthetic ALMA observations of the dust
emission based on radiative transfer calculations. Results. Our main finding is
that mm- to cm-sized dust particles are efficiently trapped inside the
shadow-triggered spirals. We also observe that particles of various sizes
starting at different stellocentric distances are well mixed inside these
pressure maxima. This dynamical effect would favour grain growth and affect the
resulting composition of planetesimals in the disc. In addition, our radiative
transfer calculations show spiral patterns in the disc at 1.6 {\mu}m and 1.3
mm. Due to their faint thermal emission (compared to the bright inner regions
of the disc) the spirals cannot be detected with ALMA. Our synthetic
observations prove however that shadows are observable as dips in the thermal
emission.",1811.08441v1
2003-01-31,Thermal-timescale mass transfer and magnetic CVs,"We investigate the spin evolution of the unusual magnetic CV AE Aqr. As a
prototype for a potentially large population of CVs subject to a thermally
unstable phase of mass transfer, understanding its future is crucial. We
present a new definition of the magnetospheric radius in terms of the white
dwarf's spin period, and use this along with numerical simulations to follow
the spin evolution of AE Aqr. We also present preliminary SPH results
suggesting the existence of a stable propeller state. These results highlight
the complexity of mCVs and may provide am improved understanding of the
evolution of all types of CVs.",0301654v1
1994-05-27,Thermodynamics and spin gap of the Heisenberg ladder calculated by the look-ahead Lanczos algorithm,"We have developed an improved version of the quantum transfer matrix
algorithm. The extreme eigenvalues and eigenvectors of the transfer matrix are
calculated by the recently developed look-ahead Lanczos algorithm for
non-Hermitian matrices with higher efficiency and accuracy than by the power
method. We have applied this method to the Heisenberg ladder. The temperature
dependence of the susceptibility, specific heat, correlation length and nuclear
spin relaxation rate $1/T_1$ are calculated. Our results support the existence
of a spin gap of about $0.5 J$. The preprint is submitted as a uuencoded
compressed PostScript file. In case of printing problems the original TeX file
(without figures) can be retrieved by anonymous ftp to 'maggia.ethz.ch'
filename 'CSSP/preprints/hblad.tex'. Alternatively from June 1, 1994 by WWW:
URL ""http://www.ips.id.ethz.ch/CSSP/preprints.html""",9405085v1
1999-07-21,Wave-vector dependence of spin and density multipole excitations in quantum dots,"We have employed time-dependent local-spin density functional theory to
analyze the multipole spin and charge density excitations in GaAs-AlGaAs
quantum dots. The on-plane transferred momentum degree of freedom has been
taken into account, and the wave-vector dependence of the excitations is
discussed. In agreement with previous experiments, we have found that the
energies of these modes do not depend on the transferred wave-vector, although
their intensities do. Comparison with a recent resonant Raman scattering
experiment [C. Sch\""uller et al, Phys. Rev. Lett {\bf 80}, 2673 (1998)] is
made. This allows to identify the angular momentum of several of the observed
modes as well as to reproduce their energies.",9907321v1
2003-09-29,Integrable spin-boson interaction in the Tavis-Cummings model from a generic boundary twist,"We construct models describing interaction between a spin $s$ and a single
bosonic mode using a quantum inverse scattering procedure. The boundary
conditions are generically twisted by generic matrices with both diagonal and
off-diagonal entries. The exact solution is obtained by mapping the transfer
matrix of the spin-boson system to an auxiliary problem of a spin-$j$ coupled
to the spin-$s$ with general twist of the boundary condition. The corresponding
auxiliary transfer matrix is diagonalized by a variation of the method of
$Q$-matrices of Baxter. The exact solution of our problem is obtained applying
certain large-$j$ limit to $su(2)_j$, transforming it into the bosonic algebra.",0309680v2
2004-02-19,Replicated Transfer Matrix Analysis of Ising Spin Models on `Small World' Lattices,"We calculate equilibrium solutions for Ising spin models on `small world'
lattices, which are constructed by super-imposing random and sparse Poissonian
graphs with finite average connectivity c onto a one-dimensional ring. The
nearest neighbour bonds along the ring are ferromagnetic, whereas those
corresponding to the Poisonnian graph are allowed to be random. Our models thus
generally contain quenched connectivity and bond disorder. Within the replica
formalism, calculating the disorder-averaged free energy requires the
diagonalization of replicated transfer matrices. In addition to developing the
general replica symmetric theory, we derive phase diagrams and calculate
effective field distributions for two specific cases: that of uniform sparse
long-range bonds (i.e. `small world' magnets), and that of (+J/-J) random
sparse long-range bonds (i.e. `small world' spin-glasses).",0402504v1
2004-05-12,Diagonalization of replicated transfer matrices for disordered Ising spin systems,"We present an alternative procedure for solving the eigenvalue problem of
replicated transfer matrices describing disordered spin systems with (random)
1D nearest neighbor bonds and/or random fields, possibly in combination with
(random) long range bonds. Our method is based on transforming the original
eigenvalue problem for a $2^n\times 2^n$ matrix (where $n\to 0$) into an
eigenvalue problem for integral operators. We first develop our formalism for
the Ising chain with random bonds and fields, where we recover known results.
We then apply our methods to models of spins which interact simultaneously via
a one-dimensional ring and via more complex long-range connectivity structures,
e.g. $1+\infty$ dimensional neural networks and `small world' magnets.
Numerical simulations confirm our predictions satisfactorily.",0405269v2
2004-12-10,Anisotropic spin and charge excitations in superconductors: signature of electronic nematic order,"We study spin and charge susceptibilities in the d-wave superconducting state
whose underlying electronic dispersion is anisotropic due to the formation of
the electronic nematic order. We show that the amplitude of the incommensurate
peaks in the spin susceptibility near (\pi,\pi) reveals a pronounced anisotropy
in the momentum space. The relevance of our findings to the magnetic scattering
pattern observed in a recent neutron scattering measurement on untwinned
YBa_2Cu_3O_{6+x} is discussed. In the charge channel, we identify a
well-defined collective mode at small momentum transfer with strong anisotropic
amplitude depending on the direction of momentum transfer, which is associated
with the broken symmetry due to nematic ordering.",0412285v2
2005-10-02,Critical exponents for the long-range Ising chain using a transfer matrix approach,"The critical behavior of the Ising chain with long-range ferromagnetic
interactions decaying with distance $r^\alpha$, $1<\alpha<2$, is investigated
using a numerically efficient transfer matrix (TM) method. Finite size
approximations to the infinite chain are considered, in which both the number
of spins and the number of interaction constants can be independently
increased. Systems with interactions between spins up to 18 sites apart and up
to 2500 spins in the chain are considered. We obtain data for the critical
exponents $\nu$ associated with the correlation length based on the Finite
Range Scaling (FRS) hypothesis. FRS expressions require the evaluation of
derivatives of the thermodynamical properties, which are obtained with the help
of analytical recurrence expressions obtained within the TM framework. The Van
den Broeck extrapolation procedure is applied in order to estimate the
convergence of the exponents. The TM procedure reduces the dimension of the
matrices and circumvents several numerical matrix operations.",0510026v1
2005-11-01,Spin-transfer mechanism of ferromagnetism in polymerized fullerenes: $Ab initio$ calculations,"A mechanism of the high temperature ferromagnetism in polymerized fullerenes
is suggested. It is assumed that some of the C$_{60}$ molecules in the crystal
become magnetically active due to spin and charge transfer from the
paramagnetic impurities (atoms or groups), such as hydrogen, fluorine, hydroxyl
group OH, amino group NH$_2$, or methyl group CH$_3$, dispersed in the
fullerene matrix. The exchange interaction between the spins localized on the
magnetically active fullerenes is evaluated using \textit{ab initio}
calculations. The nearest neighbour and next nearest neighbour exchange
interaction is found to be in the range $0.1\div 0.3 $ eV, that is, high enough
to account for the room temperature ferromagnetism.",0511025v2
2006-01-16,Fermi arc in doped high-Tc cuprates,"We propose a $d$-density wave induced by the spin-orbit coupling in the CuO
plane. The spectral function of high-temperature superconductors in the under
doped and lightly doped regions is calculated in order to explain the Fermi arc
spectra observed recently by angle-resolved photoemission spectroscopy. We take
into account the tilting of CuO octahedra as well as the on-site
Coulombrepulsive interaction; the tilted octahedra induce the staggered
transfer integral between $p_{x,y}$ orbitals and Cu $t_{2g}$ orbitals, and
bring about nontrivial effects of spin-orbit coupling for the $d$ electrons in
the CuO plane. The spectral weight shows a peak at around ($\pi/2$,$\pi/2$) for
light doping and extends around this point forming an arc as the carrier
density increases, where the spectra for light doping grow continuously to be
the spectra in the optimally doped region. This behavior significantly agrees
with that of the angle-resolved photoemissionspectroscopy spectra. Furthermore,
the spin-orbit term and staggered transfer effectively induce a flux state, a
pseudo-gap with time-reversal symmetry breaking. We have a nodal metallic state
in the light-doping case since the pseudogap has a $d_{x^2-y^2}$ symmetry.",0601329v1
2007-01-17,Magnetic-field-induced spin excitations and renormalized spin gap of the underdoped superconductor La$_{1.895}$Sr$_{0.105}$CuO$_{4}$,"High-resolution neutron inelastic scattering experiments in applied magnetic
fields have been performed on La$_{1.895}$Sr$_{0.105}$CuO$_{4}$ (LSCO). In zero
field, the temperature dependence of the low-energy peak intensity at the
incommensurate momentum-transfer $\mathbf{Q}^{\
}_{\mathrm{IC}}=(0.5,0.5\pm\delta,0),(0.5\pm\delta,0.5,0)$ exhibits an anomaly
at the superconducting $T^{\}_{c}$ which broadens and shifts to lower
temperature upon the application of a magnetic field along the c-axis. A
field-induced enhancement of the spectral weight is observed, but only at
finite energy transfers and in an intermediate temperature range. These
observations establish the opening of a strongly downward renormalized spin gap
in the underdoped regime of LSCO. This behavior contrasts with the observed
doping dependence of most electronic energy features.",0701404v1
2006-12-14,Longitudinal Spin Transfer in Inclusive $Λ$ and $\bar Λ$ Production in Polarized Proton-proton Collisions at $\sqrt s$ =200 GeV,"This contribution reports on a proof-of-principle measurement of the
longitudinal spin transfer $D_{LL}$ in inclusive $\Lambda$ and $\bar \Lambda$
production in polarized proton-proton collisions at a center of mass energy
$\sqrt{s}$ = 200 GeV. The data sample consists of about 3 $\times$ $10^6$
minimum bias events collected in the year 2005 by the STAR experiment at RHIC
with proton beam polarizations of up to 50%. The $\Lambda$($\bar \Lambda$)
candidates are reconstructed at mid-rapidity ($|\eta|<1$) using the STAR Time
Projection Chamber via the dominant decay channel $\Lambda\to p \pi^-$ ($\bar
\Lambda \to \bar p \pi^+$). Their mean transverse momentum $p_T$ is about 1.3
GeV/c and longitudinal momentum fraction $x_F = 7.5 \times 10^{-3}$ . The
longitudinal $\Lambda$($\bar \Lambda$) polarization is determined using a
method in which the detector acceptance mostly cancels.",0612035v1
2005-03-08,Analytical Bethe Ansatz for open spin chains with soliton non preserving boundary conditions,"We present an ``algebraic treatment'' of the analytical Bethe ansatz for open
spin chains with soliton non preserving (SNP) boundary conditions. For this
purpose, we introduce abstract monodromy and transfer matrices which provide an
algebraic framework for the analytical Bethe ansatz. It allows us to deal with
a generic gl(N) open SNP spin chain possessing on each site an arbitrary
representation. As a result, we obtain the Bethe equations in their full
generality. The classification of finite dimensional irreducible
representations for the twisted Yangians are directly linked to the calculation
of the transfer matrix eigenvalues.",0503014v1
1995-12-26,A simple quantum oblivious transfer protocol,"A simple and efficient protocol for quantum oblivious transfer is proposed.
The protocol can easily be implemented with present technology and is secure
against cheaters with unlimited computing power provided the receiver does not
have the technology to store the particles for an arbitrarily long period of
time. The proposed protocol is a significant improvement over the previous
protocols. Unlike the protocol of Cr\'epeau and Kilian which is secure if only
if the spin of the particle is measured along the $x$ or the $y$ axis, the
present protocol is perfectly secure no matter along which axes the spin of the
particles are measured, and unlike the protocol of Bennett et al. which
requires tens of thousand of particles, the present protocol requires only two
particles.",9512026v2
2006-08-24,Effect of exchange interaction on fidelity of quantum state transfer from a photon qubit to an electron-spin qubit,"We analyzed the fidelity of the quantum state transfer (QST) from a
photon-polarization qubit to an electron-spin-polarization qubit in a
semiconductor quantum dot, with special attention to the exchange interaction
between the electron and the simultaneously created hole. In order to realize a
high-fidelity QST we had to separate the electron and hole as soon as possible,
since the electron-hole exchange interaction modifies the orientation of the
electron spin. Thus, we propose a double-dot structure to separate the electron
and hole quickly, and show that the fidelity of the QST can reach as high as
0.996 if the resonant tunneling condition is satisfied.",0608188v1
2007-06-14,Single electron-spin memory with a semiconductor quantum dot,"We show storage of the circular polarisation of an optical field,
transferring it to the spin-state of an individual electron confined in a
single semiconductor quantum dot. The state is subsequently readout through the
electronically-triggered emission of a single photon. The emitted photon shares
the same polarisation as the initial pulse but has a different energy, making
the transfer of quantum information between different physical systems
possible. With an applied magnetic field of 2 Tesla, spin memory is preserved
for at least 1000 times more than the exciton's radiative lifetime.",0706.2143v1
2007-09-05,Perfect state transfer over distance-regular spin networks,"By considering distance-regular graphs as spin networks, first we introduce
some particular spin Hamiltonians which are extended version of those of
Refs.\cite{8,9''}. Then, by using spectral analysis techniques and algebraic
combinatoric structure of distance-regular graphs such as stratification
introduced in \cite{obata, js} and Bose-Mesner algebra, we give a method for
finding a set of coupling constants in the Hamiltonians so that a particular
state initially encoded on one site of a network will evolve freely to the
opposite site without any dynamical controls, i.e., we show that how to derive
the parameters of the system so that perfect state transfer (PST) can be
achieved. As examples, the cycle networks with even number of vertices and
$d$-dimensional hypercube networks are considered in details and the method is
applied for some important distance-regular networks in appendix.",0709.0755v2
2007-11-27,A variant transfer matrix method suitable for transport through multi-probe systems,"We have developed a variant transfer matrix method that is suitable for
transport through multi-probe systems. Using this method, we have numerically
studied the quantum spin Hall effect (QSHE) on 2D graphene with both intrinsic
(Vso) and Rashba (Vr) spin-orbit (SO) couplings. The integer QSHE arises in the
presence of intrinsic SO interaction and is gradually destroyed by the Rashba
SO interaction and disorder fluctuation. We have numerically determined the
phase boundaries separating integer QSHE and spin Hall liquid. We have found
that when Vso> 0.2t with t the hopping constant the energy gap needed for the
integer QSHE is the largest satisfying |E|<t. For smaller Vso the energy gap
decreases linearly. In the presence of Rashba SO interaction or disorders, the
energy gap diminishes. With Rashba SO interaction the integer QSHE is robust at
the largest energy within the energy gap while at the smallest energy within
the energy gap the integer QSHE is insensitive to the disorder.",0711.4189v1
2008-07-07,How the surrounding water changes the electronic and magnetic properties of DNA,"Strong influence of water molecules on the transport and magnetic properties
of DNA, observed in this study, opens up real opportunities for application of
DNA in molecular electronics. Interaction of the nucleobases with water
molecules leads to breaking of some of the $\pi$ bonds and appearance of
unbound pi electrons. These unbound electrons contribute significantly to the
charge transfer at room temperature by up to 1000 times, but at low temperature
the efficiency of charge transfer is determined by the spin interaction of the
two unbound electrons located on the intrastrand nucleobases. The charge
exchange between the nucleobases is allowed only when the spins of unbound
electrons are antiparallel. Therefore, the conductance of the DNA molecule can
be controlled by a magnetic field. That effect has potential applications for
developing a nanoscale spintronic device based on the DNA molecule, where
efficiency of spin interaction will be determined by the DNA sequence.",0807.1048v1
2009-06-11,Solutions of the T-system and Baxter equations for supersymmetric spin chains,"We propose Wronskian-like determinant formulae for the Baxter Q-functions and
the eigenvalues of transfer matrices for spin chains related to the quantum
affine superalgebra U_{q}(hat{gl}(M|N)). In contrast to the supersymmetric
Bazhanov-Reshetikhin formula (the quantum supersymmetric Jacobi-Trudi formula)
proposed in [Z. Tsuboi, J. Phys. A: Math. Gen. 30 (1997) 7975], the size of the
matrices of these Wronskian-like formulae is less than or equal to M+N. Base on
these formulae, we give new expressions of the solutions of the T-system
(fusion relations for transfer matrices) for supersymmetric spin chains
proposed in the abovementioned paper. Baxter equations also follow from the
Wronskian-like formulae. They are finite order linear difference equations with
respect to the Baxter Q-functions. Moreover, the Wronskian-like formulae also
explicitly solve the functional relations for Backlund flows proposed in [V.
Kazakov, A. Sorin, A. Zabrodin, Nucl. Phys. B790 (2008) 345
[arXiv:hep-th/0703147]].",0906.2039v3
2009-09-29,Quantum state transfer in a XX chain with impurities,"One spin excitation states are involved in the transmission of quantum states
and entanglement through a quantum spin chain, the localization properties of
these states are crucial to achieve the transfer of information from one
extreme of the chain to the other. We investigate the bipartite entanglement
and localization of the one excitation states in a quantum $XX$ chain with one
impurity. The bipartite entanglement is obtained using the Concurrence and the
localization is analyzed using the inverse participation ratio. Changing the
strength of the exchange coupling of the impurity allows us to control the
number of localized or extended states. The analysis of the inverse
participation ratio allows us to identify scenarios where the transmission of
quantum states or entanglement can be achieved with a high degree of fidelity.
In particular we identify a regime where the transmission of quantum states
between the extremes of the chain is executed in a short transmission time
$\sim N/2$, where $N$ is the number of spins in the chain, and with a large
fidelity.",0909.5231v4
2009-10-28,Entanglement transfer from electrons to photons in quantum dots: An open quantum system approach,"We investigate entanglement transfer from a system of two spin-entangled
electron-hole pairs, each placed in a separate single mode cavity, to the
photons emitted during their recombination process. Dipole selection rules and
a splitting between the light-hole and the heavy-hole subbands are the crucial
ingredients establishing a one-to-one correspondence between electron spins and
circular photon polarizations. To account for the measurement of the photons as
well as dephasing effects, we choose a stochastic Schroedinger equation and a
conditional master equation approach, respectively. The influence of
interactions with the environment as well as asymmetries in the coherent
couplings on the photon-entanglement is analyzed for two concrete measurement
schemes. The first one is designed to violate the Clauser-Horne-Shimony-Holt
(CHSH) inequality, while the second one employs the visibility of interference
fringes to prove the entanglement of the photons. Because of the spatial
separation of the entangled electronic system over two quantum dots, a
successful verification of entangled photons emitted by this system would imply
the detection of nonlocal spin-entanglement of massive particles in a solid
state structure.",0910.5382v1
2009-11-11,Real-time dynamics of particle-hole excitations in Mott insulator-metal junctions,"Charge excitations in Mott insulators (MIs) are distinct from their
band-insulator counterparts and they can provide a mechanism for energy
harvesting in solar cells based on strongly correlated electronic materials. In
this paper, we study the real-time dynamics of holon-doublon pairs in a MI
connected to metallic leads using the time-dependent density matrix
renormalization group method. The transfer of charge across the MI-metal
interface is controlled by both the electron-electron interaction strength
within the MI and the voltage difference between the leads. We find an overall
enhancement of the charge transfer as compared to the case of a
(noninteracting) band insulator-metal interface with a similar band gap.
Moreover, the propagation of holon-doublon excitations within the MI
dynamically changes the spin-spin correlations, introducing time-dependent
phase shifts in the spin structure factor.",0911.2141v2
2009-11-18,Finding Traps in Non-linear Spin Arrays,"Precise knowledge of the Hamiltonian of a system is a key to many of its
applications. Tasks such state transfer or quantum computation have been well
studied with a linear chain, but hardly with systems, which do not possess a
linear structure. While this difference does not disturb the end-to-end
dynamics of a single excitation, the evolution is significantly changed in
other subspaces. Here we quantify the difference between a linear chain and a
pseudo-chain, which have more than one spin at some site (block). We show how
to estimate a number of all spins in the system and the intra-block coupling
constants. We also suggest how it is possible to eliminate excitations trapped
in such blocks, which may disturb the state transfer. Importantly, one uses
only at-ends data and needs to be able to put the system to either the
maximally magnetized or the maximally mixed state. This can obtained by
controlling a global decoherence parameter, such as temperature.",0911.3579v1
2011-05-12,"Complete set of polarization transfer observables for the ${}^{16}{\rm O}(\vec{p},\vec{n}){}^{16}{\rm F}$ reaction at 296 MeV and 0 degrees","We report measurements of the cross section and a complete set of
polarization transfer observables for the ${}^{16}{\rm
O}(\vec{p},\vec{n}){}^{16}{\rm F}$ reaction at a bombarding energy of $T_p$ =
296 MeV and a reaction angle of $\theta_{\rm lab}$ = $0^{\circ}$.
  The data are compared with distorted-wave impulse approximation calculations
employing the large configuration-space shell-model (SM) wave functions.
  The well-known Gamow-Teller and spin-dipole (SD) states at excitation
energies of $E_x$ $\lesssim$ 8 MeV have been reasonably reproduced by the
calculations except for the spin--parity $J^{\pi}$ = $2^-$ state at $E_x$ =
5.86 MeV.
  The SD resonance at $E_x$ $\simeq$ 9.5 MeV appears to have more $J^{\pi}$ =
$2^-$ strength than $J^{\pi}$ = $1^-$ strength, consistent with the
calculations.
  The data show significant strength in the spin-longitudinal polarized cross
section $ID_L(0^{\circ})$ at $E_x$ $\simeq$ 15 MeV, which indicates existence
of the $J^{\pi}$ = $0^-$ SD resonance as predicted in the SM calculations.",1105.2449v2
2011-10-31,Spin Transfer from a Ferromagnet into a Semiconductor through an Oxide barrier,"We present results on the magnetoresistance of the system Ni/Al203/n-doped
Si/Al2O3/Ni in fabricated nanostructures. The results at temperature of 14K
reveal a 75% magnetoresistance that decreases in value up to approximately 30K
where the effect disappears. We observe minimum resistance in the antiparallel
configurations of the source and drain of Ni. As a possibility, it seems to
indicate the existence of a magnetic state at the Si/oxide interface. The
average spin diffusion length obtained is of 650 nm approximately. Results are
compared to the window of resistances that seems to exist between the tunnel
barrier resistance and two threshold resistances but the spin transfer seems to
work in the range and outside the two thresholds.",1110.6810v1
2012-09-10,Spin-liquid versus spiral-order phases in the anisotropic triangular lattice,"We study the competition between magnetic and spin-liquid phases in the
Hubbard model on the anisotropic triangular lattice, which is described by two
hopping parameters t and t' in different spatial directions and is relevant for
layered organic charge-transfer salts. By using a variational approach that
includes spiral magnetic order, we provide solid evidence that a spin-liquid
phase is stabilized in the strongly-correlated regime and close to the
isotropic limit t'/t=1. Otherwise, a magnetically ordered spiral state is
found, connecting the (collinear) N\'eel and the (coplanar) 120{\deg} phases.
The pitch vector of the spiral phase obtained from the unrestricted
Hartree-Fock approximation is substantially renormalized in presence of
electronic correlations, and the N\'eel phase is stabilized in a wide regime of
the phase diagram, i.e., for t'/t < 0.75. We discuss these results in the
context of organic charge-transfer salts.",1209.1928v2
2012-09-21,Complete deterministic multi-electron Greenberger-Horne-Zeilinger state analyzer for quantum communication,"We present a scheme for the multi-electron Greenberger-Horne-Zeilinger (GHZ)
state analyzer, resorting to an interface between the polarization of a probe
photon and the spin of an electron in a quantum dot embedded in a microcavity.
All the multi-spin GHZ states can be completely discriminated by using
single-photon detectors and linear optical elements. Our scheme has some
features. First, it is a complete GHZ-state analyzer for multi-electron spin
systems. Second, the initial entangled states remain after being identified and
they can be used for a successive task. Third, the electron qubits are static
and the photons play a role of a medium for information transfer, which has a
good application in quantum repeater in which the electron qubits are used to
store the information and the photon qubits are used to transfer the
information between others.",1209.4732v1
2013-01-14,Coherent Storage of Temporally Multimode Light Using a Spin-Wave Atomic Frequency Comb Memory,"We report on coherent and multi-temporal mode storage of light using the full
atomic frequency comb memory scheme. The scheme involves the transfer of
optical atomic excitations in Pr3+:Y2SiO5 to spin-waves in the hyperfine levels
using strong single-frequency transfer pulses. Using this scheme, a total of 5
temporal modes are stored and recalled on-demand from the memory. The coherence
of the storage and retrieval is characterized using a time-bin interference
measurement resulting in visibilities higher than 80%, independent of the
storage time. This coherent and multimode spin-wave memory is promising as a
quantum memory for light.",1301.3048v1
2013-03-04,Temperature-dependent optical conductivity of layered LaSrFeO_4,"Compounds with intermediate-size transition metals such as Fe or Mn are close
to the transition between charge-transfer systems and Mott-Hubbard systems. We
study the optical conductivity \sigma(\omega) of insulating layered LaSrFeO_4
in the energy range 0.5 - 5.5 eV from 15 K to 250 K by the use of spectroscopic
ellipsometry in combination with transmittance measurements. A multipeak
structure is observed in both \sigma^a(\omega) and \sigma^c(\omega). The
layered structure gives rise to a pronounced anisotropy, thereby offering a
means to disentangle Mott-Hubbard and charge-transfer absorption bands. We find
strong evidence that the lowest dipole-allowed excitation in LaSrFeO_4 is of
Mott-Hubbard type. This rather unexpected result can be attributed to Fe 3d - O
2p hybridization and in particular to the layered structure with the associated
splitting of the e_g level. In general, Mott-Hubbard absorption bands may show
a strong dependence on temperature. This is not the case in LaSrFeO_4, in
agreement with the fact that spin-spin and orbital-orbital correlations between
nearest neighbors do not vary strongly below room temperature in this compound
with a high-spin 3d^5 configuration and a Neel temperature of T_N = 366 K.",1303.0709v1
2013-04-15,Universal Renyi mutual information in classical systems: the case of kagome ice,"We study the Renyi mutual information of classical systems characterized by a
transfer matrix. We first establish a general relationship between the Renyi
mutual information of such classical mixtures of configuration states, and the
Renyi entropy of a corresponding Rokhsar-Kivelson--type quantum superposition.
We then focus on chiral and nonchiral kagome-ice systems, classical spin
liquids on the kagome lattice, which respectively have critical and short-range
correlations. Through a mapping of the chiral kagome ice to the quantum
Liftshitz critical field theory, we predict a universal subleading term in the
Renyi mutual information of this classical spin liquid, which can be realized
in the pyrochlore spin ice in a magnetic field. We verify our prediction with
direct numerical transfer-matrix computations, and further demonstrate that the
nonchiral kagome ice (and the corresponding quantum Rokhsar-Kivelson
superposition) is a topologically trivial phase. Finally, we argue that the
universal term in the mutual information of the chiral kagome ice is fragile
against the presence of defects.",1304.4160v4
2013-09-24,Self Assembly of and Plasmon Enhanced Ultrafast Magnetization in Ag Co Hybrid Nanoparticles,"Ultrafast demagnetization in magnetic nanoparticles using pulsed laser has
attracted considerable attention because of its potential applications in
spintronics, such as data storage. In such applications, it is necessary to
control magnetization using low energy laser pulses, however, this poses the
problem of increasing the amount of energy from the excitation laser pulses to
the spin subsystem. We take advantage of the phenomenon known as localized
surface plasmon resonance (LSPR) to enhance the energy transfer from laser
pulses to the spin subsystem. To induce LSPR, hybrid nanoparticles consisting
of noble metal nanoparticles with LSPR absorption and magnetic metal
nanoparticles are prepared using a novel method. Specifically, AgCo hybrid
nanoparticles are prepared by a self assembly method using pulsed laser
deposition. We performed measurements of the static Faraday and time-resolved
Faraday effects using a pump probe technique on the AgCo hybrid nanoparticles
with various AgCo ratios. The data suggest that the LSPR absorption and
demagnetization amplitude increase with the increasing AgCo ratio. The results
indicate that the amount of energy transferred from the laser pulses to the
spin system of magnetic nanoparticles can increase via LSPR absorption.",1309.6171v2
2013-11-27,Perfect and robust phase-locking of a spin transfer vortex nano-oscillator to an external microwave source,"We study the synchronization of the auto-oscillation signal generated by the
spin transfer driven dynamics of two coupled vortices in a spin-valve
nanopillar to an external source. Phase-locking to the microwave field hrf
occurs in a range larger than 10% of the oscillator frequency for drive
amplitudes of only a few Oersteds. Using synchronization at the double
frequency, the generation linewidth is found to decrease by more than five
orders of magnitude in the phase-locked regime (down to 1 Hz, limited by the
resolution bandwidth of the spectrum analyzer) in comparison to the free
running regime (140 kHz). This perfect phase-locking holds for frequency
detuning as large as 2 MHz, which proves its robustness. We also analyze how
the free running spectral linewidth impacts the main characteristics of the
synchronization regime.",1311.7096v1
2014-06-10,Nematic and spin-charge orders driven by hole-doping a charge-transfer insulator,"Recent experimental discoveries have brought a diverse set of broken symmetry
states to the center stage of research on cuprate superconductors. Here, we
focus on a thematic understanding of the diverse phenomenology by exploring a
strong-coupling mechanism of symmetry breaking driven by frustration of
antiferromagnetic order. We achieve this through a variational study of a
three-band model of the CuO$_2$ plane with Kondo-type exchange couplings
between doped oxygen holes and classical copper spins. Two main findings from
this strong-coupling multi-band perspective are 1) that the symmetry hierarchy
of spin stripe, charge stripe, intra-unit-cell nematic order and isotropic
phases are all accessible microscopically within the model, 2) many
symmetry-breaking patterns compete with energy differences within a few meV per
Cu atom to produce a rich phase diagram. These results indicate that the
diverse phenomenology of broken-symmetry states in hole-doped antiferromagnetic
charge-transfer insulators may indeed arise from hole-doped frustration of
antiferromagnetism.",1406.2711v2
2014-07-21,"Fermi-Level Pinning, Charge Transfer, and Relaxation of Spin-Momentum Locking at Metal Contacts to Topological Insulators","Topological insulators are of interest for many applications in electronics
and optoelectronics, but harnessing their unique properties requires detailed
understanding and control of charge injection at electrical contacts. Here we
present large-scale ab initio calculations of the electronic properties of Au,
Ni, Pt, Pd, and graphene contacts to Bi2Se3. We show that regardless of the
metal, the Fermi level is located in the conduction band, leading to n-type
Ohmic contact to the first quintuplet. Furthermore, we find strong charge
transfer and band-bending in the first few quintuplets, with no Schottky
barrier for charge injection even when the topoplogical insulator is undoped.
Our calculations indicate that Au and graphene leave the spin-momentum locking
mostly unaltered, but on the other hand, Ni, Pd, and Pt strongly hybridize with
Bi2Se3 and relax spin-momentum locking. Our results indicate that judicious
choice of the contact metal is essential to reveal the unique surface features
of topological insulators.",1407.5594v1
2016-01-18,Exact solution of an su(n) spin torus,"The trigonometric su(n) spin chain with anti-periodic boundary condition
(su(n) spin torus) is demonstrated to be Yang-Baxter integrable. Based on some
intrinsic properties of the R-matrix, certain operator product identities of
the transfer matrix are derived. These identities and the asymptotic behavior
of the transfer matrix together allow us to obtain the exact eigenvalues in
terms of an inhomogeneous T-Q relation via the off-diagonal Bethe Ansatz.",1601.04389v3
2016-03-06,Anderson localisation in spin chains for perfect state transfer,"Anderson localisation is an important phenomenon arising in many areas of
physics, and here we explore it in the context of quantum information devices.
Finite dimensional spin chains have been demonstrated to be important devices
for quantum information transport, and in particular can be engineered to allow
for ""perfect state transfer"" (PST). Here we present extensive investigations of
disordered PST spin chains, demonstrating spatial localisation and transport
retardation effects, and relate these effects to conventional Anderson
localisation. We provide thresholds for Anderson localisation in these finite
quantum information systems for both the spatial and the transport domains.
Finally, we consider the effect of disorder on the eigenstate and energy
spectrum of our Hamiltonian, where results support our conclusions on the
presence of Anderson localisation.",1603.01881v3
2016-03-24,STIRAP preparation of a coherent superposition of ThO $H^3Δ_1$ states for an improved electron EDM measurement,"Experimental searches for the electron electric dipole moment (EDM) probe new
physics beyond the Standard Model. The current best EDM limit was set by the
ACME Collaboration [Science \textbf{343}, 269 (2014)], constraining time
reversal symmetry ($T$) violating physics at the TeV energy scale. ACME used
optical pumping to prepare a coherent superposition of ThO $H^3\Delta_1$ states
that have aligned electron spins. Spin precession due to the molecule's
internal electric field was measured to extract the EDM. We report here on an
improved method for preparing this spin-aligned state of the electron by using
STIRAP. We demonstrate a transfer efficiency of $75\pm5\%$, representing a
significant gain in signal for a next generation EDM experiment. We discuss the
particularities of implementing STIRAP in systems such as ours, where molecular
ensembles with large phase-space distributions are transfered via weak
molecular transitions with limited laser power and limited optical access.",1603.07707v1
2016-03-27,"A Model of Charge Transfer Excitons: Diffusion, Spin Dynamics, and Magnetic Field Effects","In this letter we explore how the microscopic dynamics of charge transfer
(CT) excitons are influenced by the presence of an external magnetic field in
disordered molecular semiconductors. This influence is driven by the dynamic
interplay between the spin and spatial degrees of freedom of the electron-hole
pair. To account for this interplay we have developed a numerical framework
that combines a traditional model of quantum spin dynamics with a
coarse-grained model of stochastic charge transport. This combination provides
a general and efficient methodology for simulating the effects of magnetic
field on CT state dynamics, therefore providing a basis for revealing the
microscopic origin of experimentally observed magnetic field effects. We
demonstrate that simulations carried out on our model are capable of
reproducing experimental results as well as generating theoretical predictions
related to the efficiency of organic electronic materials.",1603.08160v2
2016-10-12,Evidence for topological proximity effect in graphene coupled to topological insulator,"The emergence of topological order in graphene is in great demand for the
realization of quantum spin Hall states. Recently, it is theoretically proposed
that the spin textures of surface states in topological insulator can be
directly transferred to graphene by means of proximity effect. Here we report
the observations of the topological proximity effect in the
graphene-topological insulator Bi2Se3 heterojunctions via magnetotransport
measurements. The coupling between the p_z orbitals of graphene and the p
orbitals of surface states on the Bi2Se3 bottom surface can be enhanced by
applying perpendicular negative magnetic field, resulting in a giant negative
magnetoresistance at the Dirac point up to about -91%. An obvious resistivity
dip in the transfer curve at the Dirac point is also observed in the hybrid
devices, which is consistent with the theoretical predictions of the distorted
Dirac bands with unique spin textures inherited from Bi2Se3 surface states.",1610.03644v1
2016-11-09,Enhancing quantum state transfer efficiency in binary-tree spin networks by partially collapsing measurements,"In this work, quantum state transfer (QST) over binary-tree spin networks is
studied by using advantages of partially collapsing measurements. To this aim,
we perform initially a weak measurement (WM) on central qubit of the
binary-tree network, which encoding the state of concern and after time
evolution of the whole system, a quantum measurement reversal (QMR) on the
destined qubit is performed. By taking the optimal value of the QMR, it is
shown that the QST can be improved considerably by controlling the WM strength
and by choosing it close enough to 1, near-perfect QST can be achieved. We also
show that how entanglement distribution quality over the binary-tree spin
network can be obviously improved by using this approach.",1611.03035v2
2017-02-26,Finite size and finite temperature studies of the $osp(1|2)$ spin chain,"We study a quantum spin chain invariant by the superalgebra $osp(1|2)$. We
derived non-linear integral equations for the row-to-row transfer matrix
eigenvalue in order to analyze its finite size scaling behaviour and we
determined its central charge. We have also studied the thermodynamical
properties of the obtained spin chain via the non-linear integral equations for
the quantum transfer matrix eigenvalue. We numerically solved these NLIE and
evaluated the specific heat and magnetic susceptibility. The analytical low
temperature analysis was performed providing a different value for the
effective central charge. The computed values are in agreement with the
numerical predictions in the literature.",1702.08086v1
2017-06-08,Bang-Bang Optimal Control of Large Spin Systems: Enhancement of $^{13}$C-$^{13}$C Singlet-Order at Natural Abundance,"Using a Bang-Bang optimal control (BB) technique, we transfer polarization
from abundant high-$\gamma$ nuclei directly to singlet order. This approach is
analogous to algorithmic cooling (AC) procedure used in quantum state
purification. Specifically, we apply this method for enhancing the singlet
order in a natural abundant $^{13}$C-$^{13}$C spin pair using a set of nine
equivalent protons of an 11-spin system. Compared to the standard method not
involving polarization transfer, we find an enhancement of singlet order by
about three times. In addition, since the singlet magnetization is contributed
by the faster relaxing protons, the recycle delay is halved. Thus effectively
we observe a sensitivity enhancement by 4.2 times or a reduction in the overall
experimental time by a factor of 18. We also discuss a possible extension of
AC, known as heat-bath algorithmic cooling (HBAC).",1706.02594v2
2018-06-20,Exact generator and its high order expansions in the time-convolutionless generalized master equation: Applications to the spin-boson model and exictation energy transfer,"The time-convolutionless (TCL) quantum master equation provides a powerful
tool to simulate reduced dynamics of a quantum system coupled to a bath. The
key quantity in the TCL master equation is the so-called kernel or generator,
which describes effects of the bath degrees of freedom. Since the exact TCL
generators are usually hard to calculate analytically, most applications of the
TCL generalized master equation have relied on approximate generators using
second and fourth order perturbative expansions. By using the hierarchical
equation of motion (HEOM) and extended HEOM methods, we present a new approach
to calculate the exact TCL generator and its high order perturbative
expansions. The new approach is applied to the spin-boson model with different
sets of parameters, to investigate the convergence of the high order expansions
of the TCL generator. We also discuss circumstances where the exact TCL
generator becomes singular for the spin-boson model, and a model of excitation
energy transfer in the Fenna-Matthews-Olson complex.",1806.07540v2
2018-09-11,Shuttling a single charge across a one-dimensional array of silicon quantum dots,"Significant advances have been made towards fault-tolerant operation of
silicon spin qubits, with single qubit fidelities exceeding 99.9%, several
demonstrations of two-qubit gates based on exchange coupling, and the
achievement of coherent single spin-photon coupling. Coupling arbitrary pairs
of spatially separated qubits in a quantum register poses a significant
challenge as most qubit systems are constrained to two dimensions (2D) with
nearest neighbor connectivity. For spins in silicon, new methods for quantum
state transfer should be developed to achieve connectivity beyond
nearest-neighbor exchange. Here we demonstrate shuttling of a single electron
across a linear array of 9 series-coupled Si quantum dots in ~50 ns via a
series of pairwise interdot charge transfers. By progressively constructing
more complex pulse sequences we perform parallel shuttling of 2 and 3 electrons
at a time through the 9-dot array. These experiments establish that physical
transport of single electrons is feasible in large silicon quantum dot arrays.",1809.03976v1
2018-12-17,Transfer of a quantum state from a photonic qubit to a gate-defined quantum dot,"Interconnecting well-functioning, scalable stationary qubits and photonic
qubits could substantially advance quantum communication applications and serve
to link future quantum processors. Here, we present two protocols for
transferring the state of a photonic qubit to a single-spin and to a two-spin
qubit hosted in gate-defined quantum dots (GDQD). Both protocols are based on
using a localized exciton as intermediary between the photonic and the spin
qubit. We use effective Hamiltonian models to describe the hybrid systems
formed by the the exciton and the GDQDs and apply simple but realistic noise
models to analyze the viability of the proposed protocols. Using realistic
parameters, we find that the protocols can be completed with a success
probability ranging between 85-97%.",1812.06561v1
2019-10-14,Ultrafast enhancement of ferromagnetic spin exchange induced by ligand-to-metal charge transfer,"Directly modifying spin exchange energies in a magnetic material with light
can enable ultrafast control of its magnetic states. Current approaches rely on
tuning charge hopping amplitudes that mediate exchange by optically exciting
either virtual or real charge-transfer transitions (CT) between magnetic sites.
Here we show that when exchange is mediated by a non-magnetic ligand, it can be
substantially enhanced by optically exciting a real CT transition from the
ligand to magnetic site, introducing lower order virtual hopping contributions.
We demonstrate sub-picosecond enhancement in a superexchange dominated
ferromagnet CrSiTe3 through this mechanism using phase-resolved coherent phonon
spectroscopy. This technique can also be applied in the paramagnetic phase to
disentangle light induced exchange modification from other ultrafast effects
that alter the magnetization. This protocol can potentially be broadly applied
to engineer thermally inaccessible spin Hamiltonians in superexchange dominated
magnets.",1910.06376v1
2020-08-10,Coherent spin qubit transport in silicon,"A fault-tolerant quantum processor may be configured using stationary qubits
interacting only with their nearest neighbours, but at the cost of significant
overheads in physical qubits per logical qubit. Such overheads could be reduced
by coherently transporting qubits across the chip, allowing connectivity beyond
immediate neighbours. Here we demonstrate high-fidelity coherent transport of
an electron spin qubit between quantum dots in isotopically-enriched silicon.
We observe qubit precession in the inter-site tunnelling regime and assess the
impact of qubit transport using Ramsey interferometry and quantum state
tomography techniques. We report a polarization transfer fidelity of 99.97% and
an average coherent transfer fidelity of 99.4%. Our results provide key
elements for high-fidelity, on-chip quantum information distribution, as long
envisaged, reinforcing the scaling prospects of silicon-based spin qubits.",2008.04020v2
2020-10-22,Valley Depolarization in Monolayer Transition-Metal Dichalcogenides with Zone-Corner Acoustic Phonons,"Although single-layer transition-metal dichalcogenides with novel valley
functionalities are promising candidate to realize valleytronic devices, the
essential understanding of valley depolarization mechanisms is still
incomplete. Based on pump-probe experiments performed for MoSe2 and WSe2
monolayers and corroborating analysis from density functional calculations, we
demonstrate that coherent phonons at the K-point of the Brillouin zone can
effectively mediate the valley transfer of electron carriers. In the MoSe2
monolayer case, we identify this mode as the flexural acoustic ZA(K) mode,
which has broken inversion symmetry and thus can enable electron spin-flip
during valley transfer. On the other hand, in the monolayer WSe2 case where
spin-preserving inter-valley relaxations are preferred coherent LA(K) phonons
with even inversion symmetry are efficiently generated. These findings
establish that, while the specifics of inter-valley relaxations depend on the
spin alignments of energy bands, the K-point phonons should be taken into
account as an effective valley depolarization pathway in transition metal
dichalcogenide monolayers.",2010.11758v1
2020-12-29,Strongly modulated ultrafast demagnetization and magnetization precession dynamics in ferrimagnetic Gdx(CoFe)1-x alloys via 3d-4f intersublattice exchange coupling,"Manipulation of the intersublattice interaction strengh (JRE-TM) in rare
earth (RE)-transition metal (TM) alloys is a key issue to understand how
efficiently the laser-induced angular momentum transfers from 3d to 4f spins
and to have a better control of the ultrafast spin dynamics. In this work, the
relationships between laser-induced demagnetization process and the
intersublattice 3d-4f interaction for the GdCoFe alloys were systematically
studied. The ultrafast two-stage demagnetization process could change into a
one-stage mode as the angular momentum transferring channel between 3d and 4f
spins is switched off, which could be modulated by JRE-TM. Furthermore, both
the effective g-factor and damping constant deduced by the subsequently
laser-induced magnetization precession process diverge at the angular momentum
compensation point based on the ferromagnetic resonance method with the LLG
equations. The results provide an alternative way to efficiently manipulate the
ultrafast demagnetization time for practical applications.",2012.14620v1
2021-03-11,"Molecular DFT+U: A Transferable, Low-Cost Approach to Eliminate Delocalization Error","While density functional theory (DFT) is widely applied for its combination
of cost and accuracy, corrections (e.g., DFT+U) that improve it are often
needed to tackle correlated transition-metal chemistry. In principle, the
functional form of DFT+U, consisting of a set of localized atomic orbitals (AO)
and a quadratic energy penalty for deviation from integer occupations of those
AOs, enables the recovery of the exact conditions of piecewise linearity and
the derivative discontinuity. Nevertheless, for practical transition-metal
complexes, where both atomic states and ligand orbitals participate in bonding,
standard DFT+U can fail to eliminate delocalization error (DE). Here, we show
that by introducing an alternative valence-state (i.e., molecular orbital or
MO) basis to the DFT+U approach, we recover exact conditions in cases where
standard DFT+U corrections have no error-reducing effect. This MO-based DFT+U
also eliminates DE where standard AO-based DFT+U is already successful. We
demonstrate the transferability of our approach on a range of ligand field
strengths (i.e., from H_2O to CO), electron configurations (i.e., from Sc to Fe
to Zn), and spin states (i.e., low-spin and high-spin) in representative
transition-metal complexes.",2103.06781v1
2021-04-28,From Slater to Mott physics: epitaxial engineering of electronic correlations in oxide interfaces,"Using spin-assisted ab-initio random structure searches, we explore an
exhaustive quantum phase diagram of archetypal interfaced Mott insulators, i.e.
lanthanum-iron and lanthanum-titanium oxides. In particular, we report that the
charge transfer induced by the interfacial electronic reconstruction stabilises
a high spin ferrous Fe2+ state. We provide a pathway to control the strength of
correlation in this electronic state by tuning the epitaxial strain, yielding a
manifold of quantum electronic phases, i.e. Mott-Hubbard, charge transfer and
Slater insulating states. Furthermore we report that the electronic
correlations are closely related to the structural oxygen octahedral rotations,
whose control is able to stabilise the low spin state of Fe2+ at low pressure
previously observed only under the extreme high pressure conditions in the
Earth's lower mantle. Thus we provide avenues for magnetic switching via THz
radiations which have crucial implications for next generation of spintronics
technologies.",2104.13723v1
2021-08-16,Coherently Coupled Mixtures of Bose-Einstein Condensed Gases,"This paper summarizes some of the relevant features exhibited by bi-nary
mixtures of Bose-Einstein condensates in the presence of coherent coupling at
zero temperature. The coupling, which is experimentally produced by proper
photon transitions, can either involve negligible momentum transfer from the
electromagnetic radiation (Rabi coupling) or large momentum transfer (Raman
coupling) associated with spin-orbit effects.The nature of the quantum phases
exhibited by coherently coupled mixtures is discussed in detail, including
their paramagnetic, ferromagnetic, and, in the case of spin-orbit coupling,
supersolid phases.The behavior of the corresponding elementary excitations is
discussed, with explicit emphasis on the novel features caused by the spin-like
degree of freedom. Focus is further given to the topological excitations
(solitons, vortices) as well as to the superfluid properties. The paper also
points out relevant open questions which deserve more systematic theoretical
and experimental investigations.",2108.10159v1
2021-12-04,Quantum map approach to entanglement transfer and generation in spin chains,"Quantum information processing protocols are efficiently implemented on
spin-$\frac{1}{2}$ networks. A quantum communication protocol generally
involves a certain number of parties having local access to a subset of a
larger system, whose intrinsic dynamics are exploited in order to perform a
specific task. In this chapter, we address such a scenario with the quantum
dynamical map formalism, where the dynamics of the larger system is expressed
as a quantum map acting on the parties' access to their respective subsets of
spins. We reformulate widely investigated protocols, such as one-qubit quantum
state transfer and two-qubit entanglement distribution, with the quantum map
formalism and demonstrate its usefulness in exploring less investigated
protocols such as multi-qubit entanglement generation.",2112.02348v3
2022-09-14,Spin squeezing enhanced dual species atom interferometric accelerometer employing large momentum transfer for precision test of the equivalence principle,"We theoretically investigate the feasibility of applying spin squeezing to a
light pulse atom interferometer in the presence of large momentum transfer
using off-resonant Raman transitions, in order to enhance the sensitivity of
accelerometry close to the Heisenberg limit. We also show how to implement this
scheme in a dual-species atom interferometer for precision test of the
equivalence principle by measuring the Eotvos parameter, and identify the spin
squeezing protocol that is best suited for such an experiment. For a space
borne platform in low earth orbit, such a scheme may eventually enable the
measurement of the Eotvos parameter with a sensitivity of the order of
10^(-20).",2209.06549v4
2022-10-19,Dynamic structure factor of one-dimensional Fermi superfluid with spin-orbit coupling,"We theoretically calculate the density dynamic structure factor of
one-dimensional Fermi superfluid with Raman-type spin-orbit coupling, and
analyze its main dynamical character during phase transition between
Bardeen-Cooper-Schrieffer superfluid and topological superfluid. Our
theoretical results display four kinds of single-particle excitations induced
by the two-branch structure of single-particle spectrum, and the cross
single-particle excitation is much easier to be seen in the spin dynamic
structure factor at a small transferred momentum. Also we find a new roton-like
collective mode emerges at a fixed transferred momentum $q \simeq 2k_F$, and it
only appears once the system enters the topological superfluid state. The
occurrence of this roton-like excitation is related to switch of global minimum
in single-particle spectrum from $k=0$ to $k \simeq 2k_F$.",2210.10407v1
2023-02-20,Quantum routing in planar graph using perfect state transfer,"In this article, we consider a spin-spin interaction network governed by $XX
+ YY$ Hamiltonian. The vertices and edges of the network represent the spin
objects and their interactions, respectively. We take a privilege to switch on
or off any interaction, that assists us to perform multiple perfect state
transfers in a graph simultaneously. We also build up a salable network
allowing quantum communication between two arbitrary vertices. Later we utilize
the combinatorial characteristics of hypercube graphs to propose a static
routing schema to communicate simultaneously between a set of senders and a set
of receivers in a planar network. Our construction is new and significantly
powerful. We elaborate multiple examples of planar graphs supporting quantum
routing where classical routing is not possible.",2302.10074v1
2023-03-20,Transfer of spin to orbital angular momentum in the Bethe-Heitler process,"According to the conservation of angular momentum, when a plane-wave
polarized photon splits into a pair of electron-positron under the influence of
the Coulomb field, the spin angular momentum (SAM) of the photon is converted
into the angular momentum of the leptons. We investigate this process (the
Bethe-Heitler process) by describing the final electron and positron with
twisted states and find that the SAM of the incident photon is not only
converted into SAM of the produced pair, but also into their orbital angular
momentum (OAM), which has not been considered previously. The average OAM
gained by the leptons surpasses the average SAM, while their orientations
coincide. Both properties depend on the energy and open angle of the emitted
leptons. The demonstrated spin-orbit transfer shown in the Bethe-Heitler
process may exist in a large group of QED scattering processes.",2303.10851v1
2023-06-18,Real-time observation of phonon-electron energy and angular momentum flow in laser-heated nickel,"Identifying the microscopic nature of non-equilibrium energy transfer
mechanisms among electronic, spin and lattice degrees of freedom is central for
understanding ultrafast phenomena such as manipulating magnetism on the
femtosecond timescale. Here we use time and angle-resolved photoemission
spectroscopy to go beyond the often-employed ensemble-averaged view of
non-equilibrium dynamics in terms of quasiparticle temperature evolutions. We
show for ferromagnetic Ni that the non-equilibrium electron and spin dynamics
display pronounced variations with electron momentum whereas the magnetic
exchange interaction remains isotropic. This highlights the influence of
lattice-mediated scattering processes and opens a pathway towards unraveling
the still elusive microscopic mechanism of spin-lattice angular momentum
transfer.",2306.10637v2
2024-01-17,Optimal remote restoring of quantum states in communication lines via local magnetic field,"Optimal state transport across spin chains, which are proposed as quantum
wires for information transfer in solid state quantum architectures, is an
important topic for quantum technologies. In this work, we study {the remote
restoring of a quantum state transferred along a spin chain.} The structural
state-restoring technique provides proportionality between the appropriate
elements of the density matrices of the initial sender state and receiver state
at some time instant. We develop a {remote} state-restoring protocol which uses
an inhomogeneous magnetic field with step-wise time-dependent Larmor
frequencies as the state-control tool. For simulating the multiparametric
Hamiltonian we use two approximating models. First model is based on the
Trotter-Suzuki method, while the second model is based on using short pulses of
high intensity. In both cases we estimate the accuracy of the approximation and
find the optimal restoring parameters (Larmor frequencies) of the protocol
which maximize the coefficients in the proportionality for spin chains of
various lengths.",2401.09569v1
1996-03-12,Supernova Neutrino Scattering Rates Reduced by Nucleon Spin Fluctuations: Perturbative Limit,"In a nuclear medium, spin-dependent forces cause the nucleon spins to
fluctuate with a rate $\Gamma_\sigma$. We have previously shown that as a
consequence the effective axial-current neutrino-nucleon scattering cross
section is reduced. Here, we calculate this reduction explicitly in the
perturbative limit $\Gamma_\sigma\ll T$. By virtue of an exact sum rule of the
spin-density structure function, we express the modified cross section in terms
of the matrix element for neutrino-nucleon scattering in the presence of a
spin-dependent nuclear potential. This representation allows for a direct
comparison with and confirmation of Sawyer's related perturbative result. In a
supernova core with a typical temperature $T=10\,\rm MeV$, the perturbative
limit is relevant for densities $\rho\alt10^{13}\,\rm g\,cm^{-3}$ and thus
applies around the neutrino sphere. There, the cross-section reduction is of
order a few percent and thus not large; however, a new mode of energy transfer
between neutrinos and nucleons is enabled which may be important for neutrino
spectra formation. We derive an analytic perturbative expression for the rate
of energy transfer.",9603044v1
2010-11-04,The effect of the pseudogap on suppressing high energy inelastic neutron scattering in superconducting YBa2Cu3O6.5,"We have measured the spin fluctuations in the YBa2Cu3O6.5 (YBCO6.5, Tc=59 K)
superconductor at high-energy transfers above ~ 100 meV. Within experimental
error, the momentum dependence is isotropic at high-energies, similar to that
measured in the insulator for two dimensional spin waves, and the dispersion
extrapolates back to the incommensurate wave vector at the elastic position.
This result contrasts with previous expectations based on measurements around
50 meV which were suggestive of a softening of the spin-wave velocity with
increased hole doping. Unlike the insulator, we observe a significant reduction
in the intensity of the spin excitations for energy transfers above ~ 100 meV
similar to that observed above ~ 200 meV in the YBCO6.35 (Tc=18 K)
superconductor as the spin waves approach the zone boundary. We attribute this
high energy scale with a second gap and find agreement with measurements of the
pseudogap in the cuprates associated with electronic anomalies along the
antinodal positions. In addition, we observe a sharp peak at around 400 meV
whose energy softens with increased hole doping. We discuss possible origins of
this excitation including a hydrogen related molecular excitation and a
transition of electronic states between d levels.",1011.1277v1
2016-02-22,Valley and spin pump by scattering at non-magnetic disorders,"In solid, the crystalline structure can endow electron an internal degree of
freedom known as valley, which characterizes the degenerate energy minima in
momentum space. The recent success in optical pumping of valley polarization in
2D transition metal dichalcogenides (TMDs) has greatly promoted the concept of
valley-based informatics and electronics. However, between the demonstrated
valley polarization of transient electron-hole pair excitations and practical
valleytronic operations, there exist obvious gaps to fill, among which is the
valley pump of long-lived charge carriers. Here we discover that the quested
valley pump of electrons or holes can be realized simply by scattering at the
ubiquitous nonmagnetic disorders, not relying on any specific material
property. The mechanism is rooted in the nature of valley as a momentum space
index: the intervalley backscattering in general has valley contrasted rate due
to the distinct momentum transfers, causing a net transfer of population from
one valley to another. As examples, we numerically demonstrate the sizable
valley pump effects driven by charge current in nanoribbons of monolayer TMDs,
where the spin-orbit scattering by non-magnetic disorders also realizes spin
pump for the spin-valley locked holes. Our finding points to an unexpected new
opportunity towards valley-spintronics, turning disorders from a deleterious
factor to a resource of valley and spin polarization.",1602.06633v1
2019-04-05,"Restricted spin-range correction in the Oslo Method: The example of nuclear level density and $γ$-ray strength function from $^{239}\mathrm{Pu}(\mathrm{d,p}γ)^{240}\mathrm{Pu}$","The Oslo Method has been applied to particle-$\gamma$ coincidences following
the $^{239}\mathrm{Pu}$(d,p) reaction to obtain the nuclear level density (NLD)
and $\gamma$-ray strength function ($\gamma$SF) of $^{240}\mathrm{Pu}$. The
experiment was conducted with a 12 MeV deuteron beam at the Oslo Cyclotron
Laboratory. The low spin transfer of this reaction leads to a spin-parity
mismatch between populated and intrinsic levels. This is a challenge for the
Oslo Method as it can have a significant impact on the extracted NLD and
$\gamma$SF. We have developed an iterative approach to ensure consistent
results even for cases with a large spin-parity mismatch, in which we couple
Green's Function Transfer calculations of the spin-parity dependent population
cross-section to the nuclear decay code RAINIER. The resulting $\gamma$SF shows
a pronounced enhancement between 2-4 MeV that is consistent with the location
of the low-energy orbital $M1$ scissors mode.",1904.02932v2
2019-07-05,Non-relativistic Effective Interactions of Spin 1 Dark Matter,"We investigate the non-relativistic reduction of simplified models for spin 1
dark matter (DM) with the aim of identifying features in the phenomenology of
DM-quark interactions which are specific to vector DM. In the case of DM-quark
interactions mediated by a spin 1 particle, we find two DM-nucleon interaction
operators arising from the non-relativistic reduction of simplified models for
spin 1 DM that are specific to spin 1 DM, and which were not considered in
previous studies. They are quadratic in the momentum transfer, linear in a
symmetric combination of polarisation vectors for the DM particle, and arise
from simplified models which do not generate momentum transfer independent
operators as leading interactions in the non-relativistic expansion of
DM-nucleon scattering amplitudes. Within these simplified models, the new
operators cannot be neglected when computing DM signals at direct detection
experiments. For example, we find that nuclear recoil energy spectra computed
by including or neglecting the new operators can differ by up to one order of
magnitude for nuclear recoil energies larger than about 20 keV and DM masses
below $50$ GeV. Furthermore, the shape of the expected nuclear recoil spectra
depends significantly on whether the new operators are taken into account or
not. Finally, neglecting the contribution to DM direct detection signals from
the new operators leads to inaccurate conclusions when assessing the
compatibility of a future direct detection signal with CMB constraints on the
DM relic density, especially when the number of signal events is small, e.g.
$\mathcal{O}(1)$.",1907.02910v1
2019-09-24,Precision Small Scattering Angle Measurements of Elastic Proton-Proton Single and Double Spin Analyzing Powers at the RHIC Hydrogen Jet Polarimeter,"The Polarized Atomic Hydrogen Gas Jet Target polarimeter is employed by the
Relativistic Heavy Ion Collider (RHIC) to measure the absolute polarization of
each colliding proton beam. Polarimeter detectors and data acquisition were
upgraded in 2015 to increase solid angle, energy range and energy resolution.
These upgrades and advanced systematic error analysis along with improved beam
intensity and polarization in RHIC runs 2015
($E_\textrm{beam}=100\,\text{GeV}$) and 2017 ($255\,\text{GeV}$) allowed us to
greatly reduce the statistical and systematic uncertainties for elastic spin
asymmetries, $A_N(t)$ and $A_NN(t)$, in the Coulomb-nuclear interference
momentum transfer range $0.0013<-t<0.018\,\text{GeV}^2$. For the first time
hadronic single spin-flip $r_5$ and double spin-flip $r_2$ amplitude parameters
were reliably isolated at these energies and momentum transfers. Measurements
at two beam energies enable a separation of Pomeron and Regge pole
contributions to $r_5(s)$ and $r_2(s)$, indicating that the spin component may
persist at high energies.",1909.11135v1
2020-06-19,Floquet-Enhanced Spin Swaps,"The transfer of information between quantum systems is essential for quantum
communication and computation. In quantum computers, high connectivity between
qubits can improve the efficiency of algorithms, assist in error correction,
and enable high-fidelity readout. However, as with all quantum gates,
operations to transfer information between qubits can suffer from errors
associated with spurious interactions and disorder between qubits, among other
things. Here, we harness interactions and disorder between qubits to improve a
swap operation for spin eigenstates in semiconductor gate-defined quantum-dot
spins. We use a system of four electron spins, which we configure as two
exchange-coupled singlet-triplet qubits. Our approach, which relies on the
physics underlying discrete time crystals, enhances the quality factor of
spin-eigenstate swaps by up to an order of magnitude. Our results show how
interactions and disorder in multi-qubit systems can stabilize non-trivial
quantum operations and suggest potential uses for non-equilibrium quantum
phenomena, like time crystals, in quantum information processing applications.
Our results also confirm the long-predicted emergence of effective Ising
interactions between exchange-coupled singlet-triplet qubits.",2006.10913v2
2021-03-30,Photoinduced Transient States of Antiferromagnetic Orderings in La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$ and SrFeO${}_{3}$ Thin Films Observed through Time-resolved Resonant Soft X-ray Scattering,"The relationship between the magnetic interaction and photoinduced dynamics
in antiferromagnetic perovskites is investigated in this study. In
La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$ thin films, commensurate spin ordering is
accompanied by charge disproportionation, whereas SrFeO${}_{3}$ thin films show
incommensurate helical antiferromagnetic spin ordering due to increased
ferromagnetic coupling compared to La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$. To
understand the photoinduced spin dynamics in these materials, we investigate
the spin ordering through time-resolved resonant soft X-ray scattering. In
La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$, ultrafast quenching of the magnetic
ordering within 130 fs through a nonthermal process is observed, triggered by
charge transfer between the Fe atoms. We compare this to the photoinduced
dynamics of the helical magnetic ordering of SrFeO${}_{3}$. We find that the
change in the magnetic coupling through optically induced charge transfer can
offer an even more efficient channel for spin-order manipulation.",2103.16038v1
2021-10-12,"""Galton board"" nuclear hyperpolarization","We consider the problem of determining the spectrum of an electronic spin via
polarization transfer to coupled nuclear spins and their subsequent readout.
This suggests applications for employing dynamic nuclear polarization (DNP) for
""ESR-via-NMR"". In this paper, we describe the theoretical basis for this
process by developing a model for the evolution dynamics of the coupled
electron-nuclear system through a cascade of Landau-Zener anti-crossings
(LZ-LACs). We develop a method to map these traversals to the operation of an
equivalent ""Galton board"". Here, LZ-LAC points serve as analogues to Galton
board ""pegs"", upon interacting with which the nuclear populations redistribute.
The developed hyperpolarization then tracks the local electronic density of
states. We show that this approach yields an intuitive and analytically
tractable solution of the polarization transfer dynamics, including when DNP is
carried out at the wing of a homogeneously broadened electronic spectral line.
We apply this approach to a model system comprised of a Nitrogen Vacancy (NV)
center electron in diamond, hyperfine coupled to N neighboring 13C nuclear
spins, and discuss applications for nuclear-spin interrogated NV center
magnetometry. More broadly, the methodology of ""one-to-many""
electron-to-nuclear spectral mapping developed here suggests interesting
applications in quantum memories and sensing, as well as wider applications in
modeling DNP processes in the multiple nuclear spin limit.",2110.05742v2
2022-05-03,Signatures of mass ratio reversal in gravitational waves from merging binary black holes,"The spins of merging binary black holes offer insights into their formation
history. Recently it has been argued that in isolated binary evolution of two
massive stars the firstborn black hole is slowly rotating, whilst the
progenitor of the second-born black hole can be tidally spun up if the binary
is tight enough. Naively, one might therefore expect that only the less massive
black hole in merging binaries exhibits non-negligible spin. However, if the
mass ratio of the binary is ""reversed"" (typically during the first mass
transfer episode), it is possible for the tidally spun up second-born to become
the more massive black hole. We study the properties of such mass-ratio
reversed (MRR) binary black hole mergers using a large set of 560 population
synthesis models. We find that the more massive black hole is formed second in
$\gtrsim 70\%$ of binary black holes observable by LIGO, Virgo, and KAGRA for
most model variations we consider, with typical total masses $\gtrsim 20$
M$_{\odot}$ and mass ratios $q = m_2 / m_1 \sim 0.7$ (where $m_1 > m_2$). The
formation history of these systems typically involves only stable mass transfer
episodes. The second-born black hole has non-negligible spin ($\chi > 0.05$) in
up to $25\%$ of binary black holes, with among those the more (less) massive
black hole spinning in $0\%$--$80\%$ ($20\%$--$100\%$) of cases, varying
greatly in our models. We discuss our models in the context of several observed
gravitational-wave events and the observed mass ratio - effective spin
correlation.",2205.01693v1
2022-08-17,The importance of the interface for picosecond spin pumping in antiferromagnet-heavy metal heterostructures,"Interfaces between heavy metals (HMs) and antiferromagnetic insulators (AFIs)
have recently become highly investigated and debated systems in the effort to
create spintronic devices able to function at terahertz frequencies. Such
heterostructures have great technological potential because AFIs can generate
sub-picosecond spin currents which the HMs can convert into charge signals. In
this work we demonstrate an optically induced picosecond spin transfer at the
interface between AFIs and Pt using time-resolved THz emission spectroscopy. We
select two antiferromagnets in the same family of fluoride cubic perovskites,
KCoF3 and KNiF3, whose magnon frequencies at the centre of the Brillouin zone
differ by an order of magnitude. By studying their behaviour with temperature
we correlate changes in the spin transfer efficiency across the interface to
the opening of a gap in the magnon density of states below the N\'eel
temperature. Our observations are reproduced in a model based on the spin
exchange between the localized electrons in the antiferromagnet and the free
electrons in Pt. These results constitute an important step in the rigorous
investigation and understanding of the physics of AFIs/HMs interfaces on the
ultrafast timescale.",2208.08332v1
2006-05-03,Room temperature coherent control of coupled single spins in solid,"Coherent coupling between single quantum objects is at the heart of modern
quantum physics. When coupling is strong enough to prevail over decoherence, it
can be used for the engineering of correlated quantum states. Especially for
solid-state systems, control of quantum correlations has attracted widespread
attention because of applications in quantum computing. Such coherent coupling
has been demonstrated in a variety of systems at low temperature1, 2. Of all
quantum systems, spins are potentially the most important, because they offer
very long phase memories, sometimes even at room temperature. Although precise
control of spins is well established in conventional magnetic resonance3, 4,
existing techniques usually do not allow the readout of single spins because of
limited sensitivity. In this paper, we explore dipolar magnetic coupling
between two single defects in diamond (nitrogen-vacancy and nitrogen) using
optical readout of the single nitrogen-vacancy spin states. Long phase memory
combined with a defect separation of a few lattice spacings allow us to explore
the strong magnetic coupling regime. As the two-defect system was well-isolated
from other defects, the long phase memory times of the single spins was not
diminished, despite the fact that dipolar interactions are usually seen as
undesirable sources of decoherence. A coherent superposition of spin pair
quantum states was achieved. The dipolar coupling was used to transfer spin
polarisation from a nitrogen-vacancy centre spin to a nitrogen spin, with
optical pumping of a nitrogen-vacancy centre leading to efficient
initialisation. At the level anticrossing efficient nuclear spin polarisation
was achieved. Our results demonstrate an important step towards controlled spin
coupling and multi-particle entanglement in the solid state.",0605038v1
2016-06-24,Spin-liquid Mott quantum criticality in two dimensions: Destabilization of a spinon Fermi surface and emergence of one-dimensional spin dynamics,"Resorting to a recently developed theoretical device called dimensional
regularization for quantum criticality with a Fermi surface, we examine a
metal-insulator quantum phase transition from a Landau's Fermi-liquid state to
a U(1) spin-liquid phase with a spinon Fermi surface in two dimensions.
Unfortunately, we fail to approach the spin-liquid Mott quantum critical point
from the U(1) spin-liquid state within the dimensional regularization
technique. Self-interactions between charge fluctuations called holons are not
screened, which shows a run-away renormalization group flow, interpreted as
holons remain gapped. This leads us to consider another fixed point, where the
spinon Fermi surface can be destabilized across the Mott transition. Based on
this conjecture, we reveal the nature of the spin-liquid Mott quantum critical
point: Dimensional reduction to one dimension occurs for spin dynamics
described by spinons. As a result, Landau damping for both spin and charge
dynamics disappear in the vicinity of the Mott quantum critical point. When the
flavor number of holons is over its critical value, an interacting fixed point
appears to be identified with an inverted XY universality class, controlled
within the dimensional regularization technique. On the other hand, a
fluctuation-driven first order metal-insulator transition results when it is
below the critical number. We propose that the destabilization of a spinon
Fermi surface and the emergence of one-dimensional spin dynamics near the
spin-liquid Mott quantum critical point can be checked out by spin
susceptibility with a $2 k_{F}$ transfer momentum, where $k_{F}$ is a Fermi
momentum in the U(1) spin-liquid state: The absence of Landau damping in U(1)
gauge fluctuations gives rise to a divergent behavior at zero temperature while
it vanishes in the presence of a spinon Fermi surface.",1606.07544v3
2022-01-07,Voltage Dependent Symmetry Breaking Effects in the Spin Excitation Spectrum of Spin-$\frac{1}{2}$ Paramagnetic Molecular Junctions Driven Out of Equilibrium,"In the present work, we consider a spin 1/2 paramagnetic dimer embedded in a
magnetic tunnel junction driven out of equilibrium by means of an applied
voltage and an applied temperature gradient, in the presence of an external
magnetic bias, which can be turn on/off. Here, we derive the spin excitation
spectrum for a two spin 1/2 system analytically and show that an external
magnetic field is required to lift the degeneracy in the triplet state, whether
both spin units experience the magnetic field in the same direction or in
opposite staggered directions. We show that an applied bias voltage in the
absence of a magnetic field, transfers the magnetization from the magnetic
leads into the spin units embedded in the molecule, hence breaking a symmetry
and lifting the triplet degeneracy in the absence of external magnetization.
From this theoretical demonstration, we then propose two schemes of magnetic
driving to lift spin degeneracy in the spin excitation spectrum, which we named
PMD (Parallel Magnetic Driving) and AMD (Anti-Parallel Magnetic Driving). We
argue that a symmetry breaking is then required to project the spin
configuration of a dimer into quantum transport measurements, and hence propose
different schemes to detect the spin triplet state and the spin singlet state
using differential conductivity measurements in the non-degenerate
non-symmetric configuration of the spin dimer, and compare our results with the
ones reported in the literature.",2201.02642v3
1993-08-06,Corner transfer matrix of generalised free Fermion vertex systems,"The Hamiltonian limit of the corner transfer matrix (CTM) of a generalised
free Fermion vertex system of finite size leads to a quantum spin Hamiltonian
of the particular form: \[ {\cal H}_N=-\sum_{n=1}^{N-1}\left\{ n\left(
  \sigma_n^x\sigma_{n+1}^x
  +\lambda\sigma_n^y\sigma_{n+1}^y
  +h(\sigma_n^z+\sigma_{n+1}^z)
  \right)\right\} \] Diagonalisation may be achieved for all pairs of
parameters $(\lambda,h)$ with the use of some new elliptic polynomials which
extend the class of special polynomials known so far in the context of CTM.",9308009v2
2003-11-19,Dynamic Kerr Effect and Spectral Weight Transfer in the Manganites,"We perform pump-probe Kerr spectroscopy in the colossally magnetoresistive
manganite Pr0.67Ca0.33MnO3. Kerr effects uncover surface magnetic dynamics
undetected by established methods based on reflectivity and optical spectral
weight transfer. Our findings indicate the connection between spin and charge
dynamics in the manganites may be weaker than previously thought. Additionally,
important differences between this system and conventional ferromagnetic metals
manifest as long-lived, magneto-optical coupling transients, which may be
generic to all manganites.",0311452v2
2004-03-30,Valence-electron transfer and a metal-insulator transition in a strongly correlated perovskite oxide,"We present transport and thermal data for the quadruple-perovskites
MCu3(Ti1-xRux)4O12 where 0 < x < 1. A metal-insulator transition (MIT) occurs
for Ru concentrations x~0.75. At the same time, the Cu2+ antiferromagnetic
state is destroyed and it's magnetic entropy suppressed by Ru on a 1:1 basis.
This implies that each Ru transfers an electron to a Cu ion and thus the MIT
correlates with filling the Cu 3d shell. The Cu spin entropy in this strongly
correlated electron material provides a unique probe among MIT systems.",0403742v1
2006-07-04,Electron localization in linear chains of identical loop scatterers,"We show that electron localization is generic in a linear chain of identical
simple quantum wire loops with equal arm lengths in the presence of either a
perpendicular magnetic field or the spin-orbit interaction, and has less to do
with the shapes of the loops. We calculate the transfer matrices for a general
simple loop scatterer in the presence of these effects. Based on the knowledge
of the transfer matrices, we thus provide a criterion for the occurrence of the
localization and present a simple formalism to integrate the transmission
probability over the injection wave vector of electron.",0607088v1
1995-11-01,The Role of Strange and Charm Quarks in the Nucleon Spin Structure Function,"We perform an analysis of the relation between the factorization scale and
the masses of the quarks in the calculation of the hard gluon coefficient in
polarized deep inelastic scattering. Particular attention is paid to the role
of strange and charm quarks at finite momentum transfer. It is found that for
the momentum transfer of the present experiments, the contribution from the
charm quark is significant.",9510460v1
1997-05-13,Unusual behavior in pbar-p and l-p collisions involving high energy and momenum transfer: Z0(W+-) and scalar jets,"We show that the axial-vector coupling of Z0(W+-) to quarks, when acting
together with the emission of a hypothetical spin-zero jet-generating quantum
coupled to quarks results in an unusual behavior in certain processes, at high
energy and momentum transfer. This involves an excess jet production at the
subpicobarn level.",9705303v2
1998-07-16,Real Compton Scattering at High Transverse Momentum Transfer,"We discuss the physics motivation for a program of Real Compton Scattering on
the proton in the regime where both the incident energy and the transverse
momentum transfer are large. It is shown that such a program can test which of
the various hard scattering mechanisms is dominant and can allow a measurement
of a new generalized form factor that is sensitive to both the flavor and spin
structure of the proton. It is further shown that the measurements are
experimentally feasible using existing or already planned equipment up to
incident energies of 12 GeV.",9807397v1
2001-10-19,Gluonic effects in vector meson photoproduction at large momentum transfers,"Non-perturbative QCD mechanisms are of fundamental importance in strong
interaction physics. In particular, the flavor singlet axial anomaly leads to a
gluonic pole mechanism which has been shown to explain the $\eta^{\prime}$
mass, violations of the OZI rule and more recently the proton spin. We show
here that the interaction derived from the gluonic pole exchange explains the
high momentum transfer behavior of the photoproduction cross sections of vector
mesons at JLab energies.",0110268v3
2002-07-02,Diffractive vector mesons at large momentum transfer from the BFKL equation,"Diffractive vector meson photoproduction accompanied by proton dissociation
is studied for large momentum transfer. The process is described by the
non-forward BFKL equation, for which an analytical solution is found for all
conformal spins, giving the scattering amplitude. Results are compared to HERA
data on rho production.",0207034v1
2004-10-18,Nucleon Form Factors from Generalized Parton Distributions,"We discuss the links between Generalized Parton Distributions (GPDs) and
elastic nucleon form factors. These links, in the form of sum rules, represent
powerful constraints on parametrizations of GPDs. A Regge parametrization for
GPDs at small momentum transfer, is extended to the large momentum transfer
region and it is found to describe the basic features of proton and neutron
electromagnetic form factor data. This parametrization is used to estimate the
quark contribution to the nucleon spin.",0410251v2
1995-02-07,Exact solution and interfacial tension of the six-vertex model with anti-periodic boundary conditions,"We consider the six-vertex model with anti-periodic boundary conditions
across a finite strip. The row-to-row transfer matrix is diagonalised by the
`commuting transfer matrices' method. {}From the exact solution we obtain an
independent derivation of the interfacial tension of the six-vertex model in
the anti-ferroelectric phase. The nature of the corresponding integrable
boundary condition on the $XXZ$ spin chain is also discussed.",9502040v1
2003-07-03,Symmetric Brace Algebras,"We develop a symmetric analog of brace algebras and discuss the relation of
such algebras to $L_{\infty}$-algebras. We give an alternate proof that the
category of symmetric brace algebras is isomorphic to the category of pre-Lie
algebras. As an application, symmetric braces are used to describe transfers of
strongly homotopy structures. We then explain how these symmetric brace
algebras may be used to examine the $L_{\infty}$-algebras that result from a
particular gauge theory for massless particles of high spin.",0307054v3
1994-10-05,Relativistic Effect on Low-Energy Nucleon-Deuteron Scattering,"The relativistic effect on differential cross sections, nucleon-to-nucleon
and nucleon-to-deuteron polarization transfer coefficients, and the spin
correlation function, of nucleon-deuteron elastic scattering is investigated
employing several three-dimensional relativistic three-body equations and
several nucleon-nucleon potentials. The polarization transfer coefficients are
found to be sensitive to the details of the nucleon-nucleon potentials and the
relativistic dynamics employed, and prefer trinucleon models with the correct
triton binding energy. (To appear in Phys. Rev. C)",9410006v2
2006-10-26,Final State Interaction in Neutron Deuteron Charge Exchange Reaction at Small Transfer Momentum,"Analysis of the $nd\to p(nn)$ reaction in a Gev-energy region is performed in
the framework based on the multiple-scattering theory for the few nucleon
system. The special kinematic condition, when momentum transfer from neutron
beam to final proton closes to zero, is considered. The possibility to extract
the spin-flip term of the elementary $np\to pn $ amplitude from nd-breakup
process is investigated. The energy dependence of the ratio
  $R=\frac{d\sigma_{nd}} {d\Omega} / \frac{d\sigma_{np}}{d\Omega}$ is obtained
taking account of the final state interaction two outgoing neutrons in $^1
S_0$-state.",0610100v1
2001-05-23,Spin-Space Entanglement Transfer and Quantum Statistics,"Both the topics of entanglement and particle statistics have aroused enormous
research interest since the advent of quantum mechanics. Using two pairs of
entangled particles we show that indistinguishability enforces a transfer of
entanglement from the internal to the spatial degrees of freedom without any
interaction between these degrees of freedom. Moreover, sub-ensembles selected
by local measurements of the path will in general have different amounts of
entanglement in the internal degrees of freedom depending on the statistics
(either fermionic or bosonic) of the particles involved.",0105120v2
2001-10-09,"""Stopping"" of light and quantum memories for photons","A coherent technique for the control of photon propagation in optically thick
media and its application for quantum memories is discussed. Raman adiabatic
passage with an externally controlled Stokes field can be used to transfer the
quantum state of a light pulse (``flying'' qubit) to a collective
spin-excitation (stationary qubit) and thereby slow down its propagation
velocity to zero. The process is reversible and has a potential fidelity of
unity without the necessity for strongly coupling resonators. A simple
quasi-particle picture (dark-state polariton) of the transfer is presented. The
analytic theory is supplemented with exact numerical solutions. Finally the
influence of decoherence mechanisms on collective storage states, which are
N-particle entangled states, is analyzed.",0110056v1
2004-07-28,Manipulation and storage of optical field and atomic ensemble quantum states,"We study how to efficiently manipulate and store quantum information between
optical fields and atomic ensembles. We show how various non-dissipative
transfer schemes can be used to transfer and store quantum states such as
squeezed vacuum states or entangled states into the long-lived ground state
spins of atomic ensembles.",0407238v1
2005-11-03,Exact solution of qubit decoherence models by a transfer matrix method,"We present a new method for the solution of the behavior of an ensemble of
qubits in a random time-dependent external field. The forward evolution in time
is governed by a transfer matrix. The elements of this matrix determine the
various decoherence times. The method provides an exact solution in cases where
the noise is piecewise constant in time. We show that it applies, for example,
to a realistic model of decoherence of electron spins in semiconductors.
Results are obtained for the non-perturbative regimes of the models, and we see
a transition from weak relaxation to overdamped behavior as a function of noise
anisotropy.",0511021v2
2005-11-28,Controlling quantum state transfer in spin chain with the confined field,"As a demonstration of the spectrum-parity matching condition (SPMC) for
quantum state transfer, we investigate the propagation of single-magnon state
in the Heisenberg chain in the confined external tangent magnetic field
analytically and numerically. It shows that the initial Gaussian wave packet
can be retrieved at the counterpart location near-perfectly over a longer
distance if the dispersion relation of the system meets the SPMC approximately.",0511246v1
2005-12-25,Speedup of quantum state transfer by three- qubit interactions: Implementation by nuclear magnetic resonance,"Universal quantum information processing requires single-qubit rotations and
two-qubit interactions as minimal resources. A possible step beyond this
minimal scheme is the use of three-qubit interactions. We consider such
three-qubit interactions and show how they can reduce the time required for a
quantum state transfer in an XY spin chain. For the experimental
implementation, we use liquid-state nuclear magnetic resonance (NMR), where
three-qubit interactions can be implemented by sequences of radio-frequency
pulses.",0512229v3
2006-06-08,Perfect quantum state transfer with spinor bosons on weighted graphs,"A duality between the properties of many spinor bosons on a regular lattice
and those of a single particle on a weighted graph reveals that a quantum
particle can traverse an infinite hierarchy of networks with perfect
probability in polynomial time, even as the number of nodes increases
exponentially. The one-dimensional `quantum wire' and the hypercube are special
cases in this construction, where the number of spin degrees of freedom is
equal to one and the number of particles, respectively. An implementation of
near-perfect quantum state transfer across a weighted parallelepiped with
ultracold atoms in optical lattices is discussed.",0606065v1
2007-04-16,Corner Transfer Matrix Renormalization Group Method Applied to the Ising Model on the Hyperbolic Plane,"Critical behavior of the Ising model is investigated at the center of large
scale finite size systems, where the lattice is represented as the tiling of
pentagons. The system is on the hyperbolic plane, and the recursive structure
of the lattice makes it possible to apply the corner transfer matrix
renormalization group method. From the calculated nearest neighbor spin
correlation function and the spontaneous magnetization, it is concluded that
the phase transition of this model is mean-field like. One parameter
deformation of the corner Hamiltonian on the hyperbolic plane is discussed.",0704.1949v1
2007-04-20,Investigation of Neutron--Deuteron Charge-Exchange Reaction at Small Transfer Momentum,"Analysis of the $nd\to p(nn)$ reaction in a GeV-energy region is performed in
the framework based on the multiple-scattering theory for the few-nucleon
system. The special kinematic condition, when momentum transfer from neutron
beam to final proton closes to zero, is considered. The possibility to extract
the spin-dependent term of the elementary $np\to pn $ amplitude from
$nd$-breakup process is investigated. The energy dependence of the ratio
$R=\frac{d\sigma_{nd}} {d\Omega} / \frac{d\sigma_{np}}{d\Omega}$ is obtained
taking account of the final-state interaction of the two outgoing neutrons in
$^1 S_0$-state.",0704.2653v1
2007-06-29,Environment-Mediated Quantum State Transfer,"We propose a scheme for quantum state transfer(QST) between two qubits which
is based on their individual interaction with a common boson environment. The
corresponding single mode spin-boson Hamiltonian is solved by mapping it onto a
wave propagation problem in a semi-infinite ladder and the fidelity is
obtained. High fidelity occurs when the qubits are equally coupled to the boson
while the fidelity becomes smaller for nonsymmetric couplings. The complete
phase diagram for such an arbitrary QST mediated by bosons is discussed.",0706.4410v1
2007-07-24,Baryon resonances and polarization transfer in hyperon photoproduction,"A partial wave analysis is presented of data on photoproduction of hyperons
including single and double polarization observables. The large spin transfer
probability reported by the CLAS collaboration can be successfully described
with an isobar partial wave analysis.",0707.3596v2
2007-11-15,Quantum Wire as Open System,"The faithful exchange of quantum information will soon become one of the
challenges of the emerging quantum information technology. One of the possible
solutions is to transfer a superposition through a chain of properly coupled
spins. Such a system is called a quantum wire. We discuss the transfer in a
quantum wire \cite{christ,niko1,niko2}, when the process of thermalization of
the state takes place together with the free evolution. We investigate which
encoding scheme is more faithful in certain thermal conditions.",0711.2357v2
2008-03-13,Fusion hierarchies for N = 4 superYang-Mills theory,"We employ the analytic Bethe Anzats to construct eigenvalues of transfer
matrices with finite-dimensional atypical representations in the auxiliary
space for the putative long-range spin chain encoding anomalous dimensions of
all composite single-trace gauge invariant operators of the maximally
supersymmetric Yang-Mills theory. They obey an infinite fusion hierarchy which
can be reduced to a finite set of integral relations for a minimal set of
transfer matrices. This set is used to derive a finite systems of functional
equations for eigenvalues of nested Baxter polynomials.",0803.2035v2
2008-10-25,Bounds on new light particles from high-energy and very small momentum transfer np elastic scattering data,"We found that spin-one new light particle exchanges are strongly bounded by
high-energy and small momentum transfer np elastic scattering data; the
analogous bound for a scalar particle is considerably weaker, while for a
pseudoscalar particle no bounds can be set. These bounds are compared with the
bounds extracted from low-energy n-Pb scattering experiments and from the
bounds of pi0 and K+ meson decays.",0810.4653v3
2009-06-25,Bound State Transfer Matrix for AdS5 x S5 Superstring,"We apply the algebraic Bethe ansatz technique to compute the eigenvalues of
the transfer matrix constructed from the general bound state S-matrix of the
light-cone AdS5 x S5 superstring. This allows us to verify certain conjectures
on the quantum characteristic function, and to extend them to the general case.",0906.4783v3
2009-08-11,The high probability state transfers and entanglements between different nodes of the homogeneous spin 1/2 chain in inhomogeneous external magnetic field,"We consider the high probability state transfers and entanglements between
different nodes of the spin-1/2 chains governed by the XXZ-Hamiltonian using
the inhomogeneous stationary external magnetic field. Examples of three-,
four-, ten- and twenty-node chains are represented. A variant of realization of
the proper inhomogeneous magnetic field is discussed.",0908.1456v2
2009-12-18,Tests of Conformal Field Theory at the Yang-Lee Singularity,"This paper studies the Yang-Lee edge singularity of 2-dimensional (2D) Ising
model based on a quantum spin chain and transfer matrix measurements on the
cylinder. Based on finite-size scaling, the low-lying excitation spectrum is
found at the Yang-Lee edge singularity. Based on transfer matrix techniques,
the single structure constant is evaluated at the Yang-Lee edge singularity.
The results of both types of measurements are found to be fully consistent with
the predictions for the (A4;A1)minimal conformal field theory, which was
previously identified with this critical point.",0912.3654v1
2010-07-16,Perfect Quantum Routing in Regular Spin Networks,"Regular families of coupled quantum networks are described such the unknown
state of a qubit can be perfectly routed from any node to any other node in a
time linear in the distance. Unlike previous constructions, the transfer can be
achieved perfectly on a network that is local on any specified number of
spatial dimensions. The ability to route the state, and the regularity of the
networks, vastly improve the utility of this scheme in comparison to perfect
state transfer schemes. The structures can also be used for entanglement
generation.",1007.2786v2
2010-10-04,First-principles study of ultrathin (2 \times 2) Gd nanowires encapsulated in carbon nanotubes,"Using density functional calculations, we investigate the structural and
magnetic properties of ultrathin Gd and Gd-carbide nanowires (NWs) encapsulated
in narrow carbon nanotubes (CNTs). The equilibrium geometry of an encapsulated
(2 \times 2) Gd-NW is markedly different from that of bulk Gd crystals. The
charge-density analysis shows pronounced spin-dependent electron transfer in
the encapsulated Gd-NW in comparison with that of Gd-carbide NWs. We conclude
that Gd-CNT hybridization is primarily responsible for both the structural
difference and electron transfer in the encapsulated Gd-NW.",1010.0529v1
2011-03-13,Model independent analysis of polarization effects in elastic proton-electron scattering,"The experimental observables for the elastic reaction induced by protons on
electrons are calculated in the Born approximation. Model independent
expressions are derived for the differential cross section and polarization
observables. Numerical estimations are given for spin correlation coefficients,
polarization transfer coefficients and depolarization coefficients, in a wide
kinematical range. Specific attention is given to the kinematical conditions,
i.e., to the specific range of incident energy and transferred momentum.",1103.2540v2
2011-03-22,Discrete Time Quantum Walk Approach to State Transfer,"We show that a quantum state transfer, previously studied as a continuous
time process in networks of interacting spins, can be achieved within the model
of discrete time quantum walks with position dependent coin. We argue that due
to additional degrees of freedom, discrete time quantum walks allow to observe
effects which cannot be observed in the corresponding continuous time case.
First, we study a discrete time version of the engineered coupling protocol due
to Christandl et. al. [Phys. Rev. Lett. 92, 187902 (2004)] and then discuss the
general idea of conversion between continuous time quantum walks and discrete
time quantum walks.",1103.4185v1
2011-06-15,Electronic correlations and unconventional spectral weight transfer in BaFe$_{2-x}$Co$_{x}$As$_{2}$,"We report an infrared optical study of the pnictide high-temperature
superconductor BaFe$_{1.84}$Co$_{0.16}$As$_{2}$ and its parent compound
BaFe$_{2}$As$_{2}$. We demonstrate that electronic correlations are moderately
strong and do not change across the spin-density wave transition or with
doping. By examining the energy scale and direction of spectral weight
transfer, we argue that Hund's coupling \emph{J} is the primary mechanism that
gives rise to correlations.",1106.3114v1
2011-07-20,Extremely efficient clocked electron transfer on superfluid helium,"Unprecedented transport efficiency is demonstrated for electrons on the
surface of micron-scale superfluid helium filled channels by co-opting silicon
processing technology to construct the equivalent of a charge-coupled device
(CCD). Strong fringing fields lead to undetectably rare transfer failures after
over a billion cycles in two dimensions. This extremely efficient transport is
measured in 120 channels simultaneously with packets of up to 20 electrons, and
down to singly occupied pixels. These results point the way towards the large
scale transport of either computational qubits or electron spin qubits used for
communications in a hybrid qubit system.",1107.4040v1
2011-10-28,Dual -1 Hahn polynomials and perfect state transfer,"We find all the $XX$ spin chains with perfect state transfer (PST) that are
connected with the dual -1 Hahn polynomials $R_n(x; \alpha,\beta,N)$. For $N$
odd we recover a model that had already been identified while for $N$ even, we
obtain a new system exhibiting PST.",1110.6477v3
2012-02-14,How to Counteract Systematic Errors in Quantum State Transfer,"In the absence of errors, the dynamics of a spin chain, with a suitably
engineered local Hamiltonian, allow the perfect, coherent transfer of a quantum
state over large distances. Here, we propose encoding and decoding procedures
to recover perfectly from low rates of systematic errors. The encoding and
decoding regions, located at opposite ends of the chain, are small compared to
the length of the chain, growing linearly with the size of the error. We also
describe how these errors can be identified, again by only acting on the
encoding and decoding regions.",1202.2978v1
2012-03-25,99%-fidelity ballistic quantum-state transfer through long uniform channels,"Quantum-state transfer with fidelity higher than 0.99 can be achieved in the
ballistic regime of an arbitrarily long one-dimensional chain with uniform
nearest-neighbor interaction, except for the two pairs of mirror symmetric
extremal bonds, say x (first and last) and y (second and last-but-one). These
have to be roughly tuned to suitable values x ~ 2 N^{-1/3} and y ~ 2^{3/4}
N^{-1/6}, N being the chain length. The general framework can describe the
end-to-end response in different models, such as fermion or boson hopping
models and XX spin chains.",1203.5516v1
2014-01-14,Decoherence assisted transport in a dimer system,"The dynamics of a dimer coupled to two different environments each in a spin
star configuration under the influence of decoherence is studied. The exact
analytical expression for the transition probability in the dimer system is
obtained for different situations, i.e., independent and correlated
environments. In all cases considered, it is shown that there exist
well-defined ranges of parameters for which decoherent interaction with the
environment assists energy transfer in the dimer system. In particular, we find
that correlated environments can assist energy transfer more efficiently than
separate baths.",1401.3298v1
2014-04-25,Counterfactual quantum-information transfer,"We demonstrate quantum information can be transferred between two distant
participants without any physical particles travelling between them. The key
procedure of the counterfactual scheme is to entangle two nonlocal qubits with
each other without interaction, so the scheme can also be used to generate
nonlocal entanglement counterfactually. We here illustrate the scheme by using
flying photon qubits and stationary electron-spin qubits assisted by quantum
dots inside double-sided optical microcavities. Unlike the typical
teleportation, the present scheme does not require prior entanglement sharing
or classical communication between the two distant participants.",1404.6401v1
2014-07-21,Bijective combinatorial proof of the commutation of transfer matrices in the dense O(1) loop model,"The dense O(1) loop model is a statistical physics model with connections to
the quantum XXZ spin chain, alternating sign matrices, the six-vertex model and
critical bond percolation on the square lattice. When cylindrical boundary
conditions are imposed, the model possesses a commuting family of transfer
matrices. The original proof of the commutation property is algebraic and is
based on the Yang-Baxter equation. In this paper we give a new proof of this
fact using a direct combinatorial bijection.",1407.5357v1
2017-03-25,An Upper Bound on the Rate of Information Transfer in Optical Vortex Beams,"Light endowed with orbital angular momentum, commonly termed optical vortex
light, has an azimuthal phase indexed by the orbital quantum number $l$. In
contrast to the two basis states of the optical spin angular momentum, the
interest in the information content of optical vortex beams is centred on the
assumption that $\lvert{l}\rangle{}$ forms a countably infinite set of basis
states. The recent experimental observation that group velocity is inversely
proportional to $l$ provides a theoretical basis for a practical measure of
information transfer. This Letter sets an upper bound on that measure.",1703.08718v1
2018-01-15,Numerically exact full counting statistics of the nonequilibrium Anderson impurity model,"The time dependent full counting statistics of charge transport through an
interacting quantum junction is evaluated from its generating function,
controllably computed with the inchworm Monte Carlo method. Exact
noninteracting results are reproduced; then, we continue to explore the effect
of electron--electron interactions on the time-dependent charge cumulants,
first-passage time distributions and $n$-electron transfer distributions. We
observe a crossover in the noise from Coulomb blockade- to Kondo-dominated
physics as the temperature is decreased. In addition, we uncover long-tailed
spin distributions in the Kondo regime and analyze queuing behavior caused by
correlations between single electron transfer events.",1801.05010v1
2019-12-04,Electromagnetic and gravitomagnetic structure of pions and pion-nucleon scattering,"Taking into account PDFs obtained by various Collaborations, the momentum
transfer dependence of GPDs of the pion are obtained. The calculated
electromagnetic and gravitomagnetic form factors of the pions and nucleons are
used for the description of the pion-nucleon elastic scattering in a wide
energy and momentum transfer region with minimum fitting parameters.",1912.02632v1
2020-06-22,Macroscale non-local transfer of superconducting signatures to a ferromagnet in a cavity,"Cavity spintronics recently heralded non-local magnonic signal transfer
between magnetic samples. Here we show that by including superconductors in the
cavity, we can make use of these principles to bring composite
superconductor--ferromagnet systems to the macroscale. We analyze how a
superconductor's a.c. conductivity influences the spin dynamics of a spatially
separated magnet, and we discuss the potential impact on spintronic
applications.",2006.12516v2
2020-09-14,Perfect state transfer in two dimensions and the bivariate dual-Hahn polynomials,"A new solvable two-dimensional spin lattice model defined on a regular grid
of triangular shape is proposed. The hopping amplitudes between sites are
related to recurrence coefficients of certain bivariate dual-Hahn polynomials.
For a specific choice of the parameters, perfect state transfer and fractional
revival are shown to take place.",2009.06195v2
2021-03-23,Scalar product for the XXZ spin chain with general integrable boundaries,"We calculate the scalar product of Bethe states of the XXZ spin-$\frac{1}{2}$
chain with general integrable boundary conditions. The off-shell equations
satisfied by the transfer matrix and the off-shell Bethe vectors allow one to
derive a linear system for the scalar product of off-shell and on-shell Bethe
states. We show that this linear system can be solved in terms of a compact
determinant formula that involves the Jacobian of the transfer matrix
eigenvalue and certain q-Pochhammer polynomials of the boundary couplings.",2103.12501v1
2021-10-03,A classical model for perfect transfer and fractional revival based on $q$-Racah polynomials,"It is shown how choices based on the $q$-Racah polynomials for the masses and
spring constants along a chain give new systems that exactly allow
dispersionless end-to-end transmission of a pulse as well as periodic splitting
of the initial momentum between the first and last mass. This ``Newton's
cradle'' provides a classical analog of quantum spin devices that exhibit
perfect state transfer and fractional revival.",2110.01042v1
2022-12-13,Extended transfer matrix method for electron transmission in anisotropic 2D materials: Interplay of strain and (a)periodicity of potentials,"We extend the conventional transfer matrix method to include anisotropic
features for electron transmission in two-dimensional materials, such as
breaking reflection law in pseudo-spin phases and wave vectors. This method
allows to study transmission properties of anisotropic and stratified
electrostatic potential media from a wide range of tunable parameters, which
include strain tensor and gating. We apply the extended matrix method to obtain
the electron transmission, conductance, and Fano factor for the interplay of an
uniaxially strained graphene sheet with external one-dimensional aperiodic
potentials. Our results suggest the possibility of visualizing this interplay
from conductance measurements.",2212.06936v1
1997-11-06,"The Spin Dynamics of the Spin Ladder, Dimer Chain Material Sr14Cu24O41","We have performed inelastic neutron scattering on a single crystal sample of
Sr14Cu24O41 to study the spin dynamics of the Cu2O3 spin ladder layers, and
CuO2 chains. Data collected with incident energies of 50 meV, 200 meV, 350 meV
and 500 meV are best fitted with a dispersion with a spin gap of 32.5+/-0.1 meV
and a maximum of 193.52.4 meV, consistent with a coupling along the ladders,
J|| = 130 meV and a rung coupling J^=72 meV. We find that excitations with an
energy transfer of approximately 11.5 meV can be described solely in terms of a
dimer chain with an antiferromagnetic intra-dimer coupling, J1 = 11.2 meV,
between next-nearest-neighbour Cu ions and a ferromagnetic inter-dimer
coupling, J2 = -1.1 meV. The dimers are separated by two Cu ions providing a
periodicity for the dimer chain of five units.",9711053v1
1998-11-25,Metallic ferromagnetism without exchange splitting,"In the band theory of ferromagnetism there is a relative shift in the
position of majority and minority spin bands due to the self-consistent field
due to opposite spin electrons. In the simplest realization, the Stoner model,
the majority and minority spin bands are rigidly shifted with respect to each
other. Here we consider models at the opposite extreme, where there is no
overall shift of the energy bands. Instead, upon spin polarization one of the
bands broadens relative to the other. Ferromagnetism is driven by the resulting
gain in kinetic energy. A signature of this class of mechanisms is that a
transfer of spectral weight in optical absorption from high to low frequencies
occurs upon spin polarization. We show that such models arise from generalized
tight binding models that include off-diagonal matrix elements of the Coulomb
interaction. For certain parameter ranges it is also found that reentrant
ferromagnetism occurs. We examine properties of these models at zero and finite
temperatures, and discuss their possible relevance to real materials.",9811346v1
1998-12-15,Fermi Surface and gap parameter in high-Tc superconductors: the Stripe Quantum Critical Point scenario,"We study the single-particle spectral properties of electrons coupled to
quasicritical charge and spin fluctuations close to a stripe-phase, which is
governed by a Quantum Critical Point near optimum doping. We find that spectral
weight is transferred from the quasiparticle peak to incoherent dispersive
features. As a consequence the distribution of low-laying spectral weight is
modified with respect to the quasiparticle Fermi surface. The interplay of
charge and spin fluctuations reproduces features of the observed Fermi surface,
such as the asymmetric suppression of spectral weight near the M points of the
Brillouin zone.
  Within the model, we also analyze the interplay between repulsive spin and
attractive charge fluctuations in determining the symmetry and the peculiar
momentum dependence of the superconducting gap parameter. When both spin and
charge fluctuations are coupled to the electrons, we find $d_{x^2-y^2}$-wave
gap symmetry in a wide range of parameter. A crossover $d$- vs $s$-wave
symmetry of the gap may occur when the strength of charge fluctuations
increases with respect to spin fluctuations.",9812256v1
2001-08-30,"ESR study of (Sr,La,Ca)_{14}Cu_{24}O_{41}","We report an electron spin resonance (ESR) study of single crystals of the
spin-chain spin-ladder compound (Sr,La,Ca)_{14}Cu_{24}O_{41}. The data suggest
that in intrinsically hole doped Sr_{14-x}Ca_xCu_{24}O_{41} only a small amount
of holes is transferred from the chains to the ladders with increasing x,
resulting in a crossover from spin dimerized to uniform spin chains. In the
samples of La_{14-x}Ca_xCu_{24}O_{41} with reduced hole content a very broad
signal is observed in the paramagnetic state, indicative of a surprisingly
strong anisotropy of the nearest neighbor exchange in the chains.",0108512v1
2003-03-07,Correlation--function distributions at the Nishimori point of two-dimensional Ising spin glasses,"The multicritical behavior at the Nishimori point of two-dimensional Ising
spin glasses is investigated by using numerical transfer-matrix methods to
calculate probability distributions $P(C)$ and associated moments of spin-spin
correlation functions $C$ on strips. The angular dependence of the shape of
correlation function distributions $P(C)$ provides a stringent test of how well
they obey predictions of conformal invariance; and an even symmetry of $(1-C)
P(C)$ reflects the consequences of the Ising spin-glass gauge (Nishimori)
symmetry. We show that conformal invariance is obeyed in its strictest form,
and the associated scaling of the moments of the distribution is examined, in
order to assess the validity of a recent conjecture on the exact localization
of the Nishimori point. Power law divergences of $P(C)$ are observed near C=1
and C=0, in partial accord with a simple scaling scheme which preserves the
gauge symmetry.",0303128v3
2003-04-24,Shot noise of spin polarized electrons,"The shot noise of spin polarized electrons is shown to be generically
dependent upon spin-flip processes. Such a situation represents perhaps the
simplest instance where the two-particle character of current fluctuations out
of equilibrium is explicit, leading to trinomial statistics of charge transfer
in a single channel model. We calculate the effect of spin-orbit coupling,
magnetic impurities, and precession in an external magnetic field on the noise
in the experimentally relevant cases of diffusive wires and lateral
semiconductor dots, finding dramatic enhancements of the Fano factor. The
possibility of using the shot noise to measure the spin-relaxation time in an
open mesoscopic system is raised.",0304544v2
2003-05-30,Tunnel magnetoresistance in double spin filter junctions,"We consider a new type of magnetic tunnel junction, which consists of two
ferromagnetic tunnel barriers acting as spin filters (SFs), separated by a
nonmagnetic metal (NM) layer. Using the transfer matrix method and the
free-electron approximation, the dependence of the tunnel magnetoresistance
(TMR) on the thickness of the central NM layer, bias voltage and temperature in
the double SF junction are studied theoretically. It is shown that the TMR and
electron-spin polarization in this structure can reach very large values under
suitable conditions. The highest value of the TMR can reach 99%. By an
appropriate choice of the thickness of the central NM layer, the degree of spin
polarization in this structure will be higher than that of the single SF
junctions. These results may be useful in designing future spin-polarized
tunnelling devices.",0305713v1
2003-09-26,Explicit and Hidden Symmetries in Quantum Dots and Quantum Ladders,"The concept of dynamical hidden symmetries in the physics of electron
tunneling through composite quantum dots (CQD) and quantum ladders (QL) is
developed and elucidated. Quite generally, dynamical symmetries are realizable
in the space of low energy excited states in a given charge sector of
nanoobjects, which involve spin variables and/or electron-hole pairs. While
spin multiplets in an individual rung of a QL or in an isolated CQD form a
representation space of the usual rotation group, this SU(2) symmetry is broken
due to spin transfer (in QL) electron cotunneling through CQD. Dynamical
symmetries in the space of spin multiplets are then unravelled in these
processes. The corresponding symmetry groups are described by SO(n) or SU(n)
depending on the origin of rotation group symmetry breaking. The effective spin
Hamiltonians of QL and CQD are derived and expressed in terms of the pertinent
group generators. We employ fermionization procedure for analyzing the physical
content of these dynamical symmetries, including Kondo tunneling through CQD
and Haldane gap formation in QL.",0309606v1
2004-02-05,Spin-dependent transmission in waveguides with periodically modulated strength of the spin-orbit interaction,"The electron transmission $T$ is evaluated through waveguides, in which the
strength of the spin-orbit interaction(SOI) $\alpha$ is varied periodically,
using the transfer-matrix technique. It is shown that $T$ exhibits a {\it
spin-transistor} action, as a function of $\alpha$ or of the length of one of
the two subunits of the unit cell, provided only one mode is allowed to
propagate in the waveguide. A similar but not periodic behavior occurs as a
function of the incident electron energy. A transparent formula for $T$ through
one unit is obtained and helps explain its periodic behavior. The structure
considered is a good candidate for the establishment of a realistic spin
transistor.",0402151v1
2004-06-11,The effects of a magnetic barrier and a nonmagnetic spacer in tunnel structures,"The spin-polarized transport is investigated in a new type of magnetic tunnel
junction which consists of two ferromagnetic electrodes separated by a magnetic
barrier and a nonmagnetic metallic spacer. Based on the transfer matrix method
and the nearly-free-electron-approximation the dependence of the tunnel
magnetoresistance (TMR) and electron-spin polarization on the nonmagnetic layer
thickness and the applied bias voltage are studied theoretically. The TMR and
spin polarization show an oscillatory behavior as a function of the spacer
thickness and the bias voltage. The oscillations originate from the quantum
well states in the spacer, while the existence of the magnetic barrier gives
rise to a strong spin polarization and high values of the TMR. Our results may
be useful for the development of spin electronic devices based on coherent
transport.",0406290v1
2004-10-16,Phase transitions in spin-orbital coupled model for pyroxene titanium oxides,"We study the competing phases and the phase transition phenomena in an
effective spin-orbital coupled model derived for pyroxene titanium oxides
ATiSi2O6 (A=Na, Li). Using the mean-field-type analysis and the numerical
quantum transfer matrix method, we show that the model exhibits two different
ordered states, the spin-dimer and orbital-ferro state and the spin-ferro and
orbital-antiferro state. The transition between two phases is driven by the
relative strength of the Hund's-rule coupling to the onsite Coulomb repulsion
and/or by the external magnetic field. The ground-state phase diagram is
determined. There is a keen competition between orbital and spin degrees of
freedom in the multicritical regime, which causes large fluctuations and
significantly affects finite-temperature properties in the paramagnetic phase.",0410411v1
2005-04-19,Mechanism for lifting the degeneracy in the double-exchange spin ice model on a kagomé lattice: Dodecamer formation,"We investigated the double-exchange spin ice model on a kagom\'e lattice by
Monte Carlo simulation in order to study a mechanism for lifting the degeneracy
in frustrated electron systems. We show specific heat and vector spin chirality
data on a finite lattice. Specific heat has a double-peak structure: A broad
peak and a sharp peak are at $k_{\rm B}T/t \sim 0.15$ and 0.015, respectively,
where $t$ is the transfer integral of electrons. The broad peak corresponds to
a crossover to the spin ice-like state, on the other hand, the sharp one a
transition to a dodecagonal spin cluster (dodecamer) state. We discuss the
interplay between the formation of the dodecamer state and the lifting of the
macroscopic degeneracy.",0504472v1
2005-07-19,Energy-resolved inelastic electron scattering off a magnetic impurity,"We study inelastic scattering of energetic electrons off a Kondo impurity. If
the energy E of the incoming electron (measured from the Fermi level) exceeds
significantly the Kondo temperature T_K, then the differential inelastic
cross-section \sigma (E,w), i.e., the cross-section characterizing scattering
of an electron with a given energy transfer w, is well-defined. We show that
\sigma (E,w) factorizes into two parts. The E-dependence of \sigma (E,w) is
logarithmically weak and is due to the Kondo renormalization of the effective
coupling. We are able to relate the w-dependence to the spin-spin correlation
function of the magnetic impurity. Using this relation, we demonstrate that in
the absence of magnetic field the dynamics of the impurity spin causes the
electron scattering to be inelastic at any temperature. Quenching of the spin
dynamics by an applied magnetic field results in a finite elastic component of
the electron scattering cross-section. The differential scattering
cross-section may be extracted from the measurements of relaxation of hot
electrons injected in conductors containing localized spins.",0507431v2
2006-03-21,Influence of interface structure on electronic properties and Schottky barriers in Fe/GaAs magnetic junctions,"The electronic and magnetic properties of Fe/GaAs(001) magnetic junctions are
investigated using first-principles density-functional calculations. Abrupt and
intermixed interfaces are considered, and the dependence of charge transfer,
magnetization profiles, Schottky barrier heights, and spin polarization of
densities of states on interface structure is studied. With As-termination, an
abrupt interface with Fe is favored, while Ga-terminated GaAs favors the
formation of an intermixed layer with Fe. The Schottky barrier heights are
particularly sensitive to the abruptness of the interface. A significant
density of states in the semiconducting gap arises from metal interface states.
These spin-dependent interface states lead to a significant minority spin
polarization of the density of states at the Fermi level that persists well
into the semiconductor, providing a channel for the tunneling of minority spins
through the Schottky barrier. These interface-induced gap states and their
dependence on atomic structure at the interface are discussed in connection
with potential spin-injection applications.",0603564v1
2005-12-31,Measurement of the Analyzing Power $A_N$ in $pp$ Elastic Scattering in the CNI Region with a Polarized Atomic Hydrogen Gas Jet Target,"A precise measurement of the analyzing power $A_N$ in proton-proton elastic
scattering in the region of 4-momentum transfer squared $0.001 < |t| < 0.032
({\rm GeV}/c)^2$ has been performed using a polarized atomic hydrogen gas jet
target and the 100 GeV/$c$ RHIC proton beam. The interference of the
electromagnetic spin-flip amplitude with a hadronic spin-nonflip amplitude is
predicted to generate a significant $A_N$ of 4--5%, peaking at $-t \simeq 0.003
({\rm GeV}/c)^2$. This kinematic region is known as the Coulomb Nuclear
Interference region. A possible hadronic spin-flip amplitude modifies this
otherwise calculable prediction. Our data are well described by the CNI
prediction with the electromagnetic spin-flip alone and do not support the
presence of a large hadronic spin-flip amplitude.",0601001v1
2000-12-04,Spin Dependent Fragmentation Functions for Heavy Flavor Baryons and Single Heavy Hyperon Polarization,"Spin dependent fragmentation functions for heavy flavor quarks to fragment
into heavy baryons are calculated in a quark-diquark model. The production of
intermediate spin 1/2 and 3/2 excited states is explicity included. $\Lambda_b$
, $\Lambda_c$ and $\Xi_c$ production rate and polarization at LEP energies are
calculated and, where possible, compared with experiment. A different approach,
also relying on a heavy quark-diquark model, is proposed for the small momentum
transfer inclusive production of polarized heavy flavor hyperons. The predicted
$\Lambda_c$ polarization is roughly in agreement with experiment.",0012034v1
2001-07-20,Up and Down Quark Contributions to Spin Content of Lambda from Fragmentation,"We check the $u$ and $d$ quark contributions to the spin content of the
$\Lambda$ by means of the $q\to\Lambda$ fragmentation and find that the $u$ and
$d$ quarks of the $\Lambda$ are likely positively polarized. The parton
distributions in the $\Lambda$ are given by a successful statistical model
which can reproduce and correlate a vast body of polarized and unpolarized
structure function and parton distribution data of the nucleon. With the
Gribov-Lipatov relation between the quark distributions and fragmentation
functions, the longitudinal spin transfer for the $\Lambda$ production in the
polarized charged lepton deep inelastic scattering (DIS) process and the
$\Lambda$-polarization in the neutrino (antineutrino) DIS process are
predicted. The available experimental data suggests that the $u$ and $d$ quark
contributions to the spin of the $\Lambda$ are positive. In addition, our
results provide a collateral evidence for the SU(3) symmetry breaking in
hyperon semileptonic decays of the octet baryons, which is very important for a
deeper understanding of the proton 'spin crisis'.",0107222v1
2003-12-08,Higher moments of nucleon spin structure functions in heavy baryon chiral perturbation theory and in a resonance model,"The third moment $d_2$ of the twist-3 part of the nucleon spin structure
function $g_2$ is generalized to arbitrary momentum transfer $Q^2$ and is
evaluated in heavy baryon chiral perturbation theory (HBChPT) up to order
${\mathcal{O}}(p^4)$ and in a unitary isobar model (MAID). We show how to link
$d_2$ as well as higher moments of the nucleon spin structure functions $g_1$
and $g_2$ to nucleon spin polarizabilities. We compare our results with the
most recent experimental data, and find a good description of these available
data within the unitary isobar model. We proceed to extract the twist-4 matrix
element $f_2$ which appears in the $1/Q^2$ suppressed term in the twist
expansion of the spin structure function $g_1$ for proton and neutron.",0312102v1
2004-02-26,"Polarization observables in the processes $p+p\to Θ^+ +Σ^+$ and $n+p\to Θ^+ +Λ^0$, for any spin and parity of the $Θ^+$-hyperon in the threshold region","Using the symmetry properties of the strong interaction, such as the Pauli
principle, the P-invariance, the conservation of the total angular momentum and
isotopic invariance, we establish the spin structure of the threshold matrix
elements for the processes $p+p\to \Theta^+ +\Sigma^+$ and $n+p\to \Theta^+
+\Lambda^0$, in a model independent way, which applies to any spin and parity
of the $\Theta^+$-hyperon in the near threshold region. We predict the double
spin observables for these processes, such as the dependence of the
differential cross section on the polarizations of the colliding nucleons, and
the coefficients of polarization transfer from a nucleon beam or target to the
produced $\Sigma^+$ or $\Lambda^0$ hyperon. We prove that these observables are
sensitive to the P-parity of the $\Theta^+$ baryon, for any value of its spin.
As an example of dynamical considerations, we analyzed these reactions in the
framework of K-meson exchange.",0402277v1
2004-12-02,The Gluon Sivers Distribution in D production at RHIC,"The single transverse spin asymmetry in D meson production at RHIC can
provide a clean measure of the gluon Sivers distribution function. At
intermediate rapidity, D production is largely dominated by the elementary gg
-> c c-bar channel, where there cannot be any transverse spin transfer.
Therefore, any transverse single spin asymmetry observed for D's produced in
polarized proton-proton interactions can only originate from the Sivers effect
in the gluon distribution functions. A sizeable transverse single spin
asymmetry measured by PHENIX or STAR experiments would then give direct
information on the size of the gluon Sivers distribution function.",0412022v1
2007-02-08,Spin Observables for Polarizing Antiprotons,"The PAX project at GSI Darmstadt plans to polarize an antiproton beam by
repeated interaction with a hydrogen target in a storage ring. Many of the beam
particles are required to remain within the ring after interaction with the
target, so small scattering angles are important. Hence we concentrate on low
momentum transfer (small t), a region where electromagnetic effects dominate
the hadronic effects. A colliding beam of polarized electrons with energy
sufficient to provide scattering of antiprotons beyond ring acceptance may
polarize an antiproton beam by spin filtering. Expressions for spin observables
are provided and are used to estimate the rate of buildup of polarization of an
antiproton beam.",0702088v1
2004-02-24,Boundary non-local charges from the open spin chain,"The $N$ site open XXZ quantum spin chain with a right non-diagonal boundary
and special diagonal left boundary is considered. The boundary non-local
charges originally obtained from a field theoretical viewpoint, for the sine
Gordon model on the half line, are recovered from the spin chain point of view.
Furthermore, the symmetry of the open spin chain is exhibited. More
specifically, we show that certain non--local charges commute with the transfer
matrix of the open spin chain, depending on the choice of boundary conditions.
In addition, we show explicitly that for a special choice of the left boundary,
one of the non--local charges, in a particular representation, commutes with
each one of the generators of the blob algebra, and hence with the
corresponding local Hamiltonian.",0402067v3
2002-05-29,Quantum Entanglement of Moving Bodies,"We study the properties of quantum information and quantum entanglement in
moving frames. We show that the entanglement between the spins and the momenta
of two particles can be interchanged under a Lorentz transformation, so that a
pair of particles that is entangled in spin but not momentum in one reference
frame, may, in another frame, be entangled in momentum at the expense of
spin-entanglement. Similarly, entanglement between momenta may be transferred
to spin under a Lorentz transformation. While spin and momentum entanglement
each is not Lorentz invariant, the joint entanglement of the wave function is.",0205179v4
2004-09-27,Effective boson-spin model for nuclei ensemble based universal quantum memory,"We study the collective excitation of a macroscopic ensemble of polarized
nuclei fixed in a quantum dot. Under the approximately homogeneous condition
that we explicitly present in this paper, this many-particle system behaves as
a single mode boson interacting with the spin of a single conduction band
electron confined in this quantum dot. Within this effective spin-boson system,
the quantum information carried by the electronic spin can be coherently
transferred into the collective bosonic mode of excitation in the ensemble of
nuclei. In this sense, the collective bosonic excitation can serve as a stable
quantum memory to store the quantum information of spin state of electron.",0409185v2
2007-06-02,Magnetic impurities in a superconductor: Effect of domain walls and interference,"We consider the effect of magnetic impurities, modeled by classical spins, in
a conventional superconductor. We study their effect on the quasiparticles,
specifically on the spin density and local density of states (LDOS). As
previously emphasized, the impurities induce multiple scatterings of the
quasiparticle wave functions leading to complex interference phenomena. Also,
the impurities induce quantum phase transitions in the many-body system.
Previous authors studied the effect of either a small number of impurities
(from one to three) or a finite concentration of impurities, typically in a
disordered distribution. In this work we assume a regular set of spins
distributed inside the superconductor in such a way that the spins are
oriented, forming different types of domain walls, assumed stable. This
situation may be particularly interesting in the context of spin transfer due
to polarized currents traversing the material.",0706.0269v1
2007-06-21,Quantum and thermal fluctuations in a two-dimensional correlated band ferromagnet -- Goldstone-mode preserving investigation with self-energy and vertex corrections,"Ferromagnetism in the t-t' Hubbard model is investigated on a square lattice.
Correlation effects in the form of self-energy and vertex corrections are
systematically incorporated within a spin-rotationally-symmetric scheme which
explicitly preserves the Goldstone mode and is therefore in accord with the
Mermin-Wagner theorem. Interplay of band dispersion and correlation effects on
ferromagnetic-state stability are highlighted with respect to both long- and
short-wavelength fluctuations, which are shown to have substantially different
behaviour. Our approach provides a novel understanding of the enhancement of
ferromagnetism near van Hove filling for t'~0.5 in terms of strongly suppressed
saddle-point contribution to the destabilizing exchange part of spin stiffness.
Finite-temperature electron spin dynamics is investigated directly in terms of
spectral-weight transfer across the Fermi energy due to electron-magnon
coupling. Relevant in the context of recent magnetization measurements on
ultrathin films, the role of strong thermal spin fluctuations in low dimensions
is highlighted, in the anisotropy-stabilized ordered state, by determining the
thermal decay of magnetization and T_c within a renormalized spin-fluctuation
theory.",0706.3088v1
2007-12-02,Spin resonance in the d-wave superconductor CeCoIn5,"Neutron scattering is used to probe antiferromagnetic spin fluctuations in
the d-wave heavy fermion superconductor CeCoIn$_{5}$ (T$_{c}$=2.3 K).
Superconductivity develops from a state with slow ($\hbar\Gamma$=0.3 $\pm$ 0.15
meV) commensurate (${\bf{Q_0}}$=(1/2,1/2,1/2)) antiferromagnetic spin
fluctuations and nearly isotropic spin correlations. The characteristic
wavevector in CeCoIn$_{5}$ is the same as CeIn$_{3}$ but differs from the
incommensurate wavevector measured in antiferromagnetically ordered
CeRhIn$_{5}$. A sharp spin resonance ($\hbar\Gamma<0.07$ meV) at $\hbar \omega$
= 0.60 $\pm$ 0.03 meV develops in the superconducting state removing spectral
weight from low-energy transfers. The presence of a resonance peak is
indicative of strong coupling between f-electron magnetism and
superconductivity and consistent with a d-wave gap order parameter satisfying
$\Delta({\bf q+Q_0})=-\Delta({\bf q})$.",0712.0172v1
2007-12-28,An exact calculation of the transverse susceptibility for an antiferromagnetic Ising $Δ$ chain,"We study the transverse susceptibility of the fully frustrated
antiferromagnetic Ising $\Delta$-chain, extending Minami's transfer-matrix
method for the transverse susceptibility of general-type Ising linear-chains
[JPSJ 67,1998,2255]. For transverse fields $\Gamma_1$ on tip spin sites and
$\Gamma_2$ on bottom spin sites, we calculate zero-field
transverse-susceptibilities $\chi_{tip}^x=\lim_{\Gamma_1,\Gamma_2 ->
0}M_{tip}^x/\Gamma_1$ and $\chi_{bottom}^x=\lim_{\Gamma_1,\Gamma_2 ->
0}M^x_{bottom}/\Gamma_2$, where $M_{tip (bottom)}^x$ denotes the magnetization
for tip (bottom) spin sites. Both the transverse susceptibilities follow
Curie's law at low temperatures. We also calculate
$\chi_{bottom}^x(\Gamma_1>0)$, transverse susceptibility of the bottom spin
chain under finite tip-spin transverse-fields, to understand the Curie type
behavior in the zero-field susceptibility. Using the second-order perturbation
theory, we discuss the $\Gamma_1$ dependence of $\chi_{bottom}^x(\Gamma_1)$ at
zero temperature.",0712.4306v1
2008-02-21,Optical spectra and exchange-correlation effects in molecular crystals,"We report first-principles GW-Bethe Salpeter Equation and Quantum Monte Carlo
calculations of the optical and electronic properties of molecular and
crystalline rubrene (C$_{42}$H$_{28}$). Many-body effects dominate the optical
spectrum and quasi-particle gap of molecular crystals. We interpret the
observed yellow-green photoluminescence in rubrene microcrystals as a result of
the formation of intermolecular, charge-transfer spin-singlet excitons. In
contrast, spin-triplet excitons are localized and intramolecular with a
predicted phosphorescence at the red end of the optical spectrum. We find that
the exchange energy plays a fundamental role in raising the energy of
intramolecular spin-singlet excitons above the intermolecular ones. Exciton
binding energies are predicted to be around 0.5 eV (spin singlet) to 1 eV (spin
triplet). The calculated electronic gap is 2.8 eV. The theoretical absorption
spectrum agrees very well with recent ellipsometry data.",0802.3168v1
2009-01-09,Collective spin excitations in a quantum spin ladder probed by high-resolution Resonant Inelastic X-ray Scattering,"We investigate magnetic excitations in the spin-ladder compound
Sr$_{14}$Cu$_{24}$O$_{41}$ using high-resolution Cu $L_3$-edge Resonant
Inelastic X-ray Scattering (RIXS). Our findings demonstrate that RIXS couples
to collective spin excitations from a quantum spin-liquid ground state. In
contrast to Inelastic Neutron Scattering (INS), the RIXS cross section changes
only moderately over the entire Brillouin Zone (BZ), revealing a high
sensitivity also at small momentum transfers. The two-triplon energy gap is
found to be $100\pm 30$ meV. Our results are supported by calculations within
an effective Hubbard model for a finite-size cluster.",0901.1331v2
2009-04-09,Resonant tunneling-based spin ratchets,"We outline a generic ratchet mechanism for creating directed spin-polarized
currents in ac-driven double well or double dot structures by employing
resonant spin transfer through the system engineered by local external magnetic
fields. We show its applicability to semiconductor nanostructures by
considering coherent transport through two coupled lateral quantum dots, where
the energy levels of the two dots exhibit opposite Zeeman spin splitting. We
perform numerical quantum mechanical calculations for the I-V characteristics
of this system in the nonlinear regime, which requires a self-consistent
treatment of the charge redistribution due to the applied finite bias. We show
that this setting enables nonzero averaged net spin currents in the absence of
net charge transport.",0904.1518v1
2009-05-22,Spin and Orbital Rotation of Electrons and Photons via Spin-Orbit Interaction,"We show that when an electron or photon propagates in a cylindrically
symmetric waveguide, its spin angular momentum (SAM) and its orbital angular
momentum (OAM) interact. Remarkably, we find that the dynamics resulting from
this spin-orbit interaction are quantitatively described by a single expression
applying to both electrons and photons. This leads to the prediction of several
novel rotational effects: the spatial or time evolution of either particle's
spin/polarization vector is controlled by the sign of its OAM quantum number,
or conversely, its spatial wavefunction is controlled by its SAM. We show that
the common origin of these effects in electrons and photons is a universal
geometric phase. We demonstrate how these phenomena can be used to reversibly
transfer entanglement between the SAM and OAM degrees of freedom of
two-particle states.",0905.3778v2
2009-08-27,The Paired-Electron Crystal in the Two-Dimensional Frustrated Quarter-Filled Band,"The competition between antiferromagnetic and spin-singlet ground states
within quantum spin models and the 1/2-filled band Hubbard model has received
intense scrutiny. Here we demonstrate a frustration-induced transition from
N\'{e}el antiferromagnetism to spin-singlet in the interacting 1/4-filled band
on an anisotropic triangular lattice. While the antiferromagnetic state has
equal charge densities 0.5 on all sites, the spin-singlet state is a
paired-electron crystal, with pairs of charge-rich sites separated by pairs of
charge-poor sites. The paired-electron crystal provides a natural description
of the spin-gapped state proximate to superconductivity in many organic
charge-transfer solids. Pressure-induced superconductivity in these
correlated-electron systems is likely a transition from the 1/4-filled band
valence bond solid to a valence bond liquid.",0908.4109v2
2010-03-23,Low frequency spin dynamics in the quantum magnet copper pyrazine dinitrate,"The S=1/2 antiferromagnetic Heisenberg chain exhibits a magnetic field driven
quantum critical point. We study the low frequency spin dynamics in copper
pyrazine dinitrate (CuPzN), a realization of this model system of quantum
magnetism, by means of $^{13}$C-NMR spectroscopy. Measurements of the nuclear
spin-lattice relaxation rate $T_1^{-1}$ in the vicinity of the saturation field
are compared with quantum Monte Carlo calculations of the dynamic structure
factor. Both show a strong divergence of low energy excitations at temperatures
in the quantum regime. The analysis of the anisotropic $T_1^{-1}$-rates and
frequency shifts allows one to disentangle the contributions from transverse
and longitudinal spin fluctuations for a selective study and to determine the
transfer of delocalized spin moments from copper to the neighboring nitrogen
atoms.",1003.4535v1
2010-04-02,Electron spin coherence and electron nuclear double resonance of Bi donors in natural Si,"Donors in silicon hold considerable promise for emerging quantum
technologies, due to the their uniquely long electron spin coherence times. Bi
donors in silicon differ from P and other Group V donors in several significant
respects: they have the strongest binding energy (70.98 meV), a large nuclear
spin (I = 9/2) and strong hyperfine coupling constant (A = 1475.4 MHz). These
larger energy scales allow a detailed test of theoretical models describing the
spectral diffusion mechanism that is known to govern the electron spin
coherence time (T2e) of P-donors in natural silicon. We report the electron
nuclear double resonance spectra of the Bi donor, across the range 200 MHz to
1.4 GHz, and confirm that coherence transfer is possible between electron and
nuclear spin degrees of freedom at these higher frequencies.",1004.0340v3
2010-04-21,Numerical Study of Photo-Induced Dynamics in Double-Exchange Model,"Photo-induced spin and charge dynamics in double-exchange model are
numerically studied. The Lanczos method and the density-matrix
renormalization-group method are applied to one-dimensional finite-size
clusters. By photon irradiation in a charge ordered (CO) insulator associated
with antiferromagnetic (AFM) correlation, both the CO and AFM correlations
collapse rapidly, and appearances of new peaks inside of an insulating gap are
observed in the optical spectra and the one-particle excitation spectra. Time
evolutions of the spin correlation and the in-gap state are correlated with
each other, and are governed by the transfer integral of conduction electrons.
Results are interpreted by the charge kink/anti-kink picture and their
effective motions which depend on the localized spin correlation. Pump-photon
density dependence of spin and charge dynamics are also studied. Roles of spin
degree of freedom are remarkable in a case of weak photon density. Implications
of the numerical results for the pump-probe experiments in perovskite
manganites are discussed.",1004.3680v1
2010-11-21,Optical detection of spin transport in non-magnetic metals,"We determine the dynamic magnetization induced in non-magnetic metal wedges
composed of silver, copper and platinum by means of Brillouin light scattering
(BLS) microscopy. The magnetization is transferred from a ferromagnetic
Ni80Fe20 layer to the metal wedge via the spin pumping effect. The spin pumping
efficiency can be controlled by adding an insulating but transparent interlayer
between the magnetic and non-magnetic layer. By comparing the experimental
results to a dynamical macroscopic spin-transport model we determine the
transverse relaxation time of the pumped spin current which is much smaller
than the longitudinal relaxation time.",1011.4656v2
2011-07-14,The dimerized ferromagnetic Heisenberg chain,"Ferromagnetic, in contrast to antiferromagnetic, Heisenberg chains can
undergo a Spin-Peierls dimerization only at finite temperatures. They show
reentrant behavior as a function of temperature, which might play a role for
systems with small effective elastic constants as, for example, monatomic
chains on surfaces. We investigate the physical properties of the dimerized
ferromagnetic Heisenberg chain using a modified spin-wave theory. We calculate
the exponentially decaying spin and dimer correlation functions, analyze the
temperature dependence of the corresponding coherence lengths, the
susceptibility, as well as the static and dynamic spin structure factor. By
comparing with numerical data obtained by the density-matrix renormalization
group applied to transfer matrices, we find that the modified spin wave theory
yields excellent results for all these quantities for a wide range of
dimerizations and temperatures.",1107.2772v1
2011-10-30,Chaotic spin-dependent electron dynamics in a field-driven double dot potential,"We study the nonlinear classical dynamics of an electron confined in a double
dot potential and subjected to a spin-orbit coupling and a constant external
magnetic field. It is shown that due to the spin orbit coupling, the energy can
be transferred from the spin to the orbital motion. This naturally heats up the
orbital motion which, due to the presence of the separatrix line in the phase
space of the system, results in a motion of the electron between the dots. It
is shown that depending on the strength of the spin orbit coupling and the
energy of the system, the electronic orbital motion undergoes a transition from
the regular to the chaotic regime.",1110.6597v1
2011-11-22,Magnetic excitations in L-edge resonant inelastic x-ray scattering from one-dimensional cuprates,"We study the magnetic excitation spectra of L-edge resonant inelastic x-ray
scattering (RIXS) from the spin singlet ground state in one-dimensional undoped
cuprates. Analyzing the transition amplitudes of the magnetic excitations in
the second-order dipole allowed process, we find that the magnetic excitations
are brought about not only on the core-hole site but also on the neighboring
sites. The RIXS spectra are expressed by the one-spin correlation function in
the scattering channel with changing polarization, and the two-spin correlation
function in the scattering channel without changing polarization. The latter
could not be brought about within the so-called UCL approximation. We calculate
these correlation functions on a finite-size ring. An application to the
possible RIXS spectra in Sr_2CuO_3 demonstrates that the contribution of the
two-spin correlation function could be larger than that of the one-spin
correlation function in the \sigma polarization for the momentum transfer
around the zone center.",1111.5078v1
2012-01-31,Ultrafast Spin-Motion Entanglement and Interferometry with a Single Atom,"We report entanglement of a single atom's hyperfine spin state with its
motional state in a timescale of less than 3 ns. We engineer a short train of
intense laser pulses to impart a spin-dependent momentum transfer of +/- 2 hbar
k. Using pairs of momentum kicks, we create an atomic interferometer and
demonstrate collapse and revival of spin coherence as the motional wavepacket
is split and recombined. The revival after a pair of kicks occurs only when the
second kick is delayed by an integer multiple of the harmonic trap period, a
signature of entanglement and disentanglement of the spin with the motion. Such
quantum control opens a new regime of ultrafast entanglement in atomic qubits.",1201.6597v2
2012-02-06,Optical polarization of nuclear ensembles in diamond,"We report polarization of a dense nuclear-spin ensemble in diamond and its
dependence on magnetic field and temperature. The polarization method is based
on the transfer of electron spin polarization of negatively charged nitrogen
vacancy color centers to the nuclear spins via the excited-state level
anti-crossing of the center. We polarize 90% of the 14N nuclear spins within
the NV centers, and 70% of the proximal 13C nuclear spins with hyperfine
interaction strength of 13-14 MHz. Magnetic-field dependence of the
polarization reveals sharp decrease in polarization at specific field values
corresponding to cross-relaxation with substitutional nitrogen centers, while
temperature dependence of the polarization reveals that high polarization
persists down to 50 K. This work enables polarization of the 13C in bulk
diamond, which is of interest in applications of nuclear magnetic resonance, in
quantum memories of hybrid quantum devices, and in sensing.",1202.1072v4
2012-07-01,Engineering a spin-fet: spin-orbit phenomena and spin transport induced by a gate electric field,"In this work, we show that a gate electric field, applied in the base of the
field-effect devices, leads to inducing spin-orbit interactions (Rashba and
linear Dresselhauss) and confines the transport electrons in a two-dimensional
electron gas. On the basis of these phenomena we solve analytically the Pauli
equation when the Rashba strength and the linear Dresselhaus one are equal, for
a tuning value of the gate electric field $\mathcal{E}_g^*$. Using the transfer
matrix approach, we provide a joint description of the transport by varying the
bias electric field, $\mathcal{E}_b$. We can flip the spin of the incident
electrons, or block the spin-down completely. The robustness of this behavior
is proved when $\mathcal{E}_g^*$ changes by $\mathcal{E}_g^* \pm \delta
\mathcal{E}_g$.",1207.0251v1
2012-09-27,Temperature dependence of the paramagnetic spin excitations in BaFe$_2$As$_2$,"We use inelastic neutron scattering to study temperature dependence of the
paramagnetic spin excitations in iron pnictide BaFe$_2$As$_2$ throughout the
Brillouin zone. In contrast to a conventional local moment Heisenberg system,
where paramagnetic spin excitations are expected to have a Lorentzian function
centered at zero energy transfer, the high-energy ($\hbar\omega>100$ meV)
paramagnetic spin excitations in BaFe$_2$As$_2$ exhibit spin-wave-like features
up to at least 290 K ($T= 2.1T_N$). Furthermore, we find that the sizes of the
fluctuating magnetic moments $<m^2>\approx 3.6\ \mu^2_B$ per Fe are essentially
temperature independent from the AF ordered state at $0.05T_N$ to $2.1T_N$,
which differs considerably from the temperature dependent fluctuating moment
observed in the iron chalcogenide Fe$_{1.1}$Te [I. A. Zaliznyak {\it et al.},
Phys. Rev. Lett. {\bf 107}, 216403 (2011).]. These results suggest
unconventional magnetism and strong electron correlation effects in
BaFe$_2$As$_2$.",1209.6271v1
2012-10-25,Practicality of spin chain 'wiring' in diamond quantum technologies,"Coupled spin chains are promising candidates for 'wiring up' qubits in
solid-state quantum computing (QC). In particular, two nitrogen-vacancy centers
in diamond can be connected by a chain of implanted nitrogen impurities; when
driven by a suitable global fields the chain can potentially enable quantum
state transfer at room temperature. However, our detailed analysis of error
effects suggests that foreseeable systems may fall far short of the fidelities
required for QC. Fortunately the chain can function in the more modest role as
a mediator of noisy entanglement, enabling QC provided that we use subsequent
purification. For instance, a chain of 5 spins with inter-spin distances of 10
nm has finite entangling power as long as the T2 time of the spins exceeds 0.55
ms. Moreover we show that re-purposing the chain this way can remove the
restriction to nearest-neighbor interactions, so eliminating the need for
complicated dynamical decoupling sequences.",1210.6886v3
2012-11-30,Sensitive Magnetic Control of Ensemble Nuclear Spin Hyperpolarisation in Diamond,"Dynamic nuclear polarisation, which transfers the spin polarisation of
electrons to nuclei, is routinely applied to enhance the sensitivity of nuclear
magnetic resonance; it is also critical in spintronics, particularly when spin
hyperpolarisation can be produced and controlled optically or electrically.
Here we show the complete polarisation of nuclei located near the
optically-polarised nitrogen-vacancy (NV) centre in diamond. When approaching
the ground-state level anti-crossing condition of the NV electron spins, 13C
nuclei in the first-shell are polarised in a pattern that depends sensitively
and sharply upon the magnetic field. Based on the anisotropy of the hyperfine
coupling and of the optical polarisation mechanism, we predict and observe a
complete reversal of the nuclear spin polarisation with a few-mT change in the
magnetic field. The demonstrated sensitive magnetic control of nuclear
polarisation at room temperature will be useful for sensitivity-enhanced NMR,
nuclear-based spintronics, and quantum computation in diamond.",1212.0035v1
2013-02-14,Faithful Solid State Optical Memory with Dynamically Decoupled Spin Wave Storage,"We report an optical memory in a rare earth doped crystal with long storage
times, up to 20 ms, together with an optical bandwidth of 1.5 MHz. This is
obtained by transferring optical coherences to nuclear spin coherences, which
were then protected against environmental noise by dynamical decoupling. With
this approach, we achieved a 33 fold increase in spin wave storage time over
the intrinsic spin coherence lifetime. Comparison between different decoupling
sequences indicates that sequences insensitive to initial spin coherence
increase retrieval efficiency. Finally, an interference experiment shows that
relative phases of input pulses are preserved through the whole storage process
with a visibility close to 1, demonstrating the usefulness of dynamical
decoupling for extending the storage time of quantum memories.",1302.3358v1
2013-04-26,Landau-Lifshitz theory of the longitudinal spin Seebeck effect,"Thermal-bias-induced spin angular momentum transfer between a paramagnetic
metal and ferromagnetic insulator is studied theoretically based on the
stochastic Landau-Lifshitz-Gilbert (LLG) phenomenology. Magnons in the
ferromagnet establish a nonequilibrium steady state by equilibrating with
phonons via bulk Gilbert damping and electrons in the paramagnet via spin
pumping, according to the fluctuation-dissipation theorem. Subthermal magnons
and the associated spin currents are treated classically, while the appropriate
quantum crossover is imposed on high-frequency magnetic fluctuations. We
identify several length scales in the ferromagnet, which govern qualitative
changes in the dependence of the thermally-induced spin current on the magnetic
film thickness.",1304.7295v2
2014-01-06,Engineering spin-orbital magnetic insulator by tailoring superlattices,"Novel interplay of spin-orbit coupling and electron correlations in complex
Ir oxides recently emerged as a new paradigm for correlated electron physics.
Because of a large spin-orbit coupling of ~0.5 eV, which is comparable to the
transfer energy t and the crystal field splitting $\Delta$ and Coulomb U, a
variety of ground states including magnetic insulator, band insulator,
semimetal and metal, shows up in a narrow materials phase space. Utilizing such
subtle competition of the ground states, we successfully tailor a spin-orbital
magnetic insulator out of a semimetal SrIrO$_3$ by controlling dimensionality
using superlattice of [(SrIrO$_3$)$_m$, SrTiO$_3$] and show that a magnetic
ordering triggers the transition to magnetic insulator. Those results can be
described well by a first-principles calculation. This study is an important
step towards the design and the realization of topological phases in complex Ir
oxides with very strong spin-orbit coupling.",1401.1066v1
2014-01-25,On the Yang-Baxter equation for the six-vertex model,"In this paper we review the theory of the Yang-Baxter equation related to the
6-vertex model and its higher spin generalizations. We employ a 3D approach to
the problem. Starting with the 3D R-matrix, we consider a two-layer projection
of the corresponding 3D lattice model. As a result, we obtain a new expression
for the higher spin $R$-matrix associated with the affine quantum algebra
$U_q(\widehat{sl(2)})$. In the simplest case of the spin $s=1/2$ this
$R$-matrix naturally reduces to the $R$-matrix of the 6-vertex model. Taking a
special limit in our construction we also obtain new formulas for the
$Q$-operators acting in the representation space of arbitrary (half-)integer
spin. Remarkably, this construction can be naturally extended to any complex
values of spin $s$. We also give all functional equations satisfied by the
transfer-matrices and $Q$-operators.",1401.6494v2
2014-04-16,Protecting a Spin Ensemble against Decoherence in the Strong-Coupling Regime of Cavity QED,"Hybrid quantum systems based on spin ensembles coupled to superconducting
microwave cavities are promising candidates for robust experiments in cavity
quantum electrodynamics (QED) and for future technologies employing quantum
mechanical effects. Currently the main source of decoherence in these systems
is inho- mogeneous spin broadening, which limits their performance for the
coherent transfer and storage of quantum information. Here we study the
dynamics of a superconducting cavity strongly coupled to an ensemble of
nitrogen-vacancy centers in diamond. We experimentally observe for the first
time, how decoherence induced by a non-Lorentzian spin distribution can be
suppressed in the strong-coupling regime - a phenomenon known as ""cavity
protection"". To demonstrate the potential of this effect for coherent control
schemes, we show how appropriately chosen microwave pulses can increase the
amplitude of coherent oscillations between cavity and spin ensemble by two
orders of magnitude.",1404.4169v1
2014-06-29,Spin-Fluctuation-Driven Nematic Charge-Density-Wave in Cuprate Superconductors: Impact of Aslamazov-Larkin-Type Vertex Correction,"We present a microscopic derivation of the nematic charge-density-wave (CDW)
formation in cuprate superconductors based on the three-orbital d-p Hubbard
model, by introducing the vertex correction (VC) into the charge
susceptibility. The CDW instability at $q=(\Delta_{FS},0)$, $(0,\Delta_{FS})$
appears when the spin fluctuations are strong, due to the strong charge-spin
interference represented by the VC. Here, $\Delta_{FS}$ is the wavenumber
between the neighboring hot spots. The obtained spin-fluctuation-driven CDW is
expressed as the ""intra-unit-cell orbital order"" accompanied by the charge
transfer between the neighboring atomic orbitals, which is actually observed by
the STM measurements. We predict that the cuprate CDW and the nematic orbital
order in Fe-based superconductors are closely related spin-fluctuation-driven
phenomena.",1406.7520v3
2014-10-17,Coexistence of ferromagnetism and superconductivity in iron based pnictides: a time resolved magnetooptical study,"Ferromagnetism and superconductivity are antagonistic phenomena. Their
coexistence implies either a modulated ferromagnetic order parameter on a
lengthscale shorter than the superconducting coherence length or a weak
exchange coupling between the itinerant superconducting electrons and the
localized ordered spins. In some iron based pnictide superconductors the
coexistence of ferromagnetism and superconductivity has been clearly
demonstrated. The nature of the coexistence, however, remains elusive since no
clear understanding of the spin structure in the superconducting state has been
reached and the reports on the coupling strength are controversial. We show, by
a direct optical pump-probe experiment, that the coupling is weak, since the
transfer of the excess energy from the itinerant electrons to ordered localized
spins is much slower than the electron-phonon relaxation, implying the
coexistence without the short-lengthscale ferromagnetic order parameter
modulation. Remarkably, the polarization analysis of the coherently excited
spin wave response points towards a simple ferromagnetic ordering of spins with
two distinct types of ferromagnetic domains.",1410.4651v1
2014-12-17,Recursive polarization of nuclear spins in diamond at arbitrary magnetic fields,"We introduce an alternate route to dynamically polarize the nuclear spin host
of nitrogen-vacancy (NV) centers in diamond. Our approach articulates optical,
microwave and radio-frequency pulses to recursively transfer spin polarization
from the NV electronic spin. Using two complementary variants of the same
underlying principle, we demonstrate nitrogen nuclear spin initialization
approaching 80% at room temperature both in ensemble and single NV centers.
Unlike existing schemes, our approach does not rely on level anti-crossings and
is thus applicable at arbitrary magnetic fields. This versatility should prove
useful in applications ranging from nanoscale metrology to sensitivity-enhanced
NMR.",1412.5441v1
2014-12-18,Effective Equations for the Precession Dynamics of Electron Spins and Electron-Impurity Correlations in Diluted Magnetic Semiconductors,"Starting from a quantum kinetic theory for the spin dynamics in diluted
magnetic semiconductors, we derive simplified equations that effectively
describe the spin transfer between carriers and magnetic impurities for an
arbitrary initial impurity magnetization. Taking the Markov limit of these
effective equations, we obtain good quantitative agreement with the full
quantum kinetic theory for the spin dynamics in bulk systems at high magnetic
doping. In contrast, the standard rate description where the carrier-dopant
interaction is treated according to Fermi's golden rule, which involves the
assumption of a short memory as well as a perturbative argument, has been shown
previously to fail if the impurity magnetization is non-zero. The Markov limit
of the effective equations is derived, assuming only a short memory, while
higher order terms are still accounted for. These higher order terms represent
the precession of the carrier-dopant correlations in the effective magnetic
field due to the impurity spins. Numerical calculations show that the Markov
limit of our effective equations reproduces the results of the full quantum
kinetic theory very well. Furthermore, this limit allows for analytical
solutions and for a physically transparent interpretation.",1412.5898v1
2015-01-07,The Gonihedric Paradigm Extensions of the Ising Model,"We suggest a generalization of the Feynman path integral to an integral over
random surfaces. The proposed action is proportional to the linear size of the
random surfaces and is called gonihedric. The convergence and the properties of
the partition function are analysed. The model can also be formulated as a spin
system with identical partition function. The spin system represents a
generalisation of the Ising model with ferromagnetic, antiferromagnetic and
quartic interactions. Higher symmetry of the model allows to construct dual
spin systems in three and four dimensions. In three dimensions the transfer
matrix describes the propagation of closed loops and we found its exact
spectrum. It is a unique exact solution of the tree-dimensional statistical
spin system. In three and four dimensions the system exhibits the second order
phase transitions. The gonihedric spin systems have exponentially degenerated
vacuum states separated by the potential barriers and can be used as a storage
of binary information.",1501.01394v3
2015-06-09,Strain induced coherent dynamics of coupled carriers and Mn spins in a quantum dot,"We report on the coherent dynamics of the spin of an individual magnetic atom
coupled to carriers in a semiconductor quantum dot which has been investigated
by resonant photoluminescence of the positively charged exciton (X+). We
demonstrate that a positively charged CdTe/ZnTe quantum dot doped with a single
Mn atom forms an ensemble of optical Lambda systems which can be addressed
independently. We show that the spin dynamics of the X+Mn complex is dominated
by the electron-Mn exchange interaction and report on the coherent dynamics of
the electron-Mn spin system that is directly observed in the time domain.
Quantum beats reflecting the coherent transfer of population between
electron-Mn spin states, which are mixed by an anisotropic strain in the plane
of the quantum dot, are clearly observed. We finally highlight that this strain
induced coherent coupling is tunable with an external magnetic field.",1506.02821v1
2015-09-11,"Analogy between Jahn-Teller distortion and Rashba spin splitting, and Jahn-Teller counterpart of spin texture","In developing physical theories analogical reasoning has been found to be
very powerful, as attested by a number of important historical examples. An
analogy between two apparently different phenomena, once established, allows
one to transfer information and bring new concepts from one phenomenon to the
other. Here we discuss an important analogy between two widely different
physical problems, namely, the Jahn-Teller distortion in molecular physics and
the Rashba spin splitting in condensed matter physics. By exploring their
conceptual and mathematical features and by searching for the counterparts
between them, we examine the orbital texture in Jahn-Teller systems, as the
counterpart of the spin texture of the Rashba physics, and put forward a
possible way of experimentally detecting the orbital texture. Finally, we
discuss the analogy by comparing the coexistence of linear Rashba+Dresselhaus
effects and Jahn-Teller problems for specific symmetries, which allow for
non-trivial spin and orbital textures, respectively.",1509.03423v2
2016-01-12,Spin-dependent Bragg spectroscopy of a spinor Bose gas,"We develop a general theory of spin-dependent Bragg spectroscopy for spinor
Bose-Einstein condensates. This spectroscopy involves using a density and
spin-coupled optical probe to excite the system. We show that within the linear
response regime the momentum or energy transferred by the probe is determined
by a set of density and spin-density dynamic structure factors. We derive a set
of $f$-sum rules that provide rigorous constraints for the first energy moments
of these structure factors. As an application we compute the dynamic structure
factors for cases within all four distinct phases of a spin-1 condensate using
Bogoliubov theory. Our results demonstrate that spin-dependent Bragg
spectroscopy can be used to selectively investigate the various phonon and
magnon excitation branches and will be a useful tool for advancing our
understanding of spinor condensates.",1601.02716v2
2016-04-07,Magnon-mediated spin current noise in ferromagnet$|$non-magnetic conductor hybrids,"The quantum excitations of the collective magnetization dynamics in a
ferromagnet (F) - magnons - enable spin transport without an associated charge
current. This pure spin current can be transferred to electrons in an adjacent
non-magnetic conductor (N). We evaluate the finite temperature noise of the
magnon-mediated spin current injected into N by an adjacent F driven by a
coherent microwave field. We find that the dipolar interaction leads to
squeezing of the magnon modes giving them wavevector dependent non-integral
spin, which directly manifests itself in the shot noise. For temperatures
higher than the magnon gap, the thermal noise is dominated by large wavevector
magnons which exhibit negligible squeezing. The noise spectrum is white up to
the frequency corresponding to the maximum of the temperature or the magnon
gap. At larger frequencies, the noise is dominated by vacuum fluctuations. The
shot noise is found to be much larger than its thermal counterpart over a broad
temperature range, making the former easier to be measured experimentally.",1604.02079v2
2016-06-14,Antiferromagnetic spintronics,"Antiferromagnetic materials could represent the future of spintronic
applications thanks to the numerous interesting features they combine: they are
robust against perturbation due to magnetic fields, produce no stray fields,
display ultrafast dynamics and are capable of generating large
magneto-transport effects. Intense research efforts over the past decade have
been invested in unraveling spin transport properties in antiferromagnetic
materials. Whether spin transport can be used to drive the antiferromagnetic
order and how subsequent variations can be detected are some of the thrilling
challenges currently being addressed. Antiferromagnetic spintronics started out
with studies on spin transfer, and has undergone a definite revival in the last
few years with the publication of pioneering articles on the use of spin-orbit
interactions in antiferromagnets. This paradigm shift offers possibilities for
radically new concepts for spin manipulation in electronics. Central to these
endeavors are the need for predictive models, relevant disruptive materials and
new experimental designs. This paper reviews the most prominent spintronic
effects described based on theoretical and experimental analysis of
antiferromagnetic materials. It also details some of the remaining bottlenecks
and suggests possible avenues for future research.",1606.04284v2
2016-06-27,Spin-flavor structure of chiral-odd GPDs in the large-N_c limit,"We study the spin-flavor structure of the nucleon's chiral-odd generalized
parton distributions (transversity GPDs) in the large-N_c limit of QCD. In
contrast to the chiral-even case, only three combinations of the four
chiral-odd GPDs are non-zero in the leading order of the 1/N_c expansion:
E_T-bar = E_T + 2 H_T-tilde, H_T and E_T-tilde. The degeneracy is explained by
the absence of spin-orbit interactions correlating the transverse momentum
transfer with the transverse quark spin. It can also be deduced from the
natural N_c-scaling of the quark-nucleon helicity amplitudes associated with
the GPDs. In the GPD E_T-bar the flavor-singlet component u + d is leading in
the 1/N_c expansion, while in H_T and E_T-tilde it is the flavor-nonsinglet
components u - d. The large-N_c relations are consistent with the spin-flavor
structure extracted from hard exclusive pi0 and eta electroproduction data, if
it is assumed that the processes are mediated by twist-3 amplitudes involving
the chiral-odd GPDs and the chiral-odd pseudoscalar meson distribution
amplitudes.",1606.08388v1
2016-08-02,Picosecond spin Seebeck effect,"We report time-resolved magneto-optic Kerr effect measurements of the
longitudinal spin Seebeck effect driven by an interfacial temperature
difference between itinerant electrons and magnons. The measured time-evolution
of spin accumulation induced by laser-excitation indicates transfer of angular
momentum across Au/Y$_3$Fe$_5$O$_{12}$ and Cu/Y$_3$Fe$_5$O$_{12}$ interfaces on
a picosecond time-scale. The product of spin-mixing conductance and interfacial
spin Seebeck coefficient determined is of the order of $10^8$ A m$^{-2}$
K$^{-1}$.",1608.00702v1
2016-08-10,Creating arbitrary quantum vibrational states in a carbon nanotube,"We theoretically study the creation of single- and multi-phonon Fock states
and arbitrary superpositions of quantum phonon states in a nanomechanical
carbon nanotube (CNT) resonator. In our model, a doubly clamped CNT resonator
is initialized in the ground state and a single electron is trapped in a
quantum dot which is formed by a electric gate potential and brought into the
magnetic field of a micro-magnet. The preparation of arbitrary quantum phonon
states is based on the coupling between the mechanical motion of the CNT and
the electron spin which acts as a non-linearity. We assume that electrical
driving pulses with different frequencies are applied on the system. The
quantum information is transferred from the spin qubit to the mechanical motion
by the spin-phonon coupling and the electron spin qubit can be reset by the
single-electron spin resonance. We describe Wigner tomography which can be
applied at the end to obtain the phase information of the prepared phonon
states.",1608.03068v1
2016-08-23,Coherent manipulation of single electron spins with Landau-Zener sweeps,"We propose a novel method to manipulate the state of a single electron spin
in a semiconductor quantum dot (QD). The manipulation is achieved by tunnel
coupling a QD, labeled $L$, and occupied with an electron to an adjacent QD,
labeled $R$, which is not occupied by an electron but having an energy linearly
varying in time. We identify a parameter regime in which a complete population
transfer between the spin eigenstates $|L\uparrow\rangle$ and
$|L\downarrow\rangle$ is achieved without occupying the adjacent QD. This
method is convenient due to the fact that manipulation can be done
electrically, without the precise knowledge of the spin resonance condition,
and is robust against Zeeman level broadening caused by nuclear spins.",1608.06482v2
2016-09-08,Converting heat into directed transport on a tilted lattice,"We present a self-contained engine, which is made of one or more two-level
systems, each of which is coupled to a single bath, as well as to a common load
composed of a particle on a tilted lattice. We show that the energy and the
entropy absorbed by the spins are transferred to the particle thus setting it
into upward motion at an average constant speed, even when driven by a single
spin connected to a single bath. When considering an ensemble of different
spins, the velocity of the particle is larger when the tilt is on resonance
with any of the spins' energy splitting. Interestingly, we find regimes where
the spins' polarization enters periodic cycles with the oscillation period
being determined by the tilt of the lattice.",1609.02294v1
2017-02-01,Ab initio dynamical exchange interactions in frustrated anti-ferromagnets,"The ultrafast response to an optical pulse excitation of the spin-spin
exchange interaction in transition metal anti-ferromagnets is studied within
the framework of the time-dependent spin-density functional theory. We propose
a formulation for the purely dynamical exchange interaction, which is non-local
in space, and it is derived starting from {\it ab initio} arguments. Then, we
investigate the effect of the laser pulse on the onset of the dynamical
process. It is found that we can distinguish two types of excitations, both
activated immediately after the action of the laser pulse. While the first one
can be associated to a Stoner-like excitation and involves the transfer of spin
from one site to another, the second one is related to the ultrafast
modification of a Heisenberg-like exchange interaction and can trigger the
formation of spin waves in the first few hundred femtoseconds of the time
evolution.",1702.00375v1
2017-02-26,Magnon-photon coupling in antiferromagnets,"Magnon-photon coupling in antiferromagnets has many attractive features that
do not exist in ferro- or ferrimagnets. We show quantum-mechanically that, in
the absence of an external field, one of the two degenerated spin wave bands
couples with photons while the other does not. The photon mode anticrosses with
the coupled spin waves when their frequencies are close to each other. Similar
to its ferromagnetic counterpart, the magnon-photon coupling strength is
proportional to the square root of number of spins $\sqrt{N}$ in
antiferromagnets. An external field removes the spin wave degeneracy and both
spin wave bands couple to the photons, resulting in two anticrossings between
the magnons and photons. Two transmission peaks were observed near the
anticrossing frequency. The maximum damping that allows clear discrimination of
the two transmission peaks is proportional to $\sqrt{N}$ and it's well below
the damping of antiferromagnetic insulators. Therefore the strong magnon-photon
coupling can be realized in antiferromagnets and the coherent information
transfer between the photons and magnons is possible.",1702.07977v1
2017-04-19,Thermal entanglement in a spin-1/2 Ising-XYZ distorted diamond chain with the second-neighbor interaction between nodal Ising spins,"We consider a spin-1/2 Ising-XYZ distorted diamond chain with the XYZ
interaction between the interstitial Heisenberg dimers, the nearest-neighbor
Ising coupling between the nodal and interstitial spins, respectively, and the
second-neighbor Ising coupling between the nodal spins. The ground-state phase
diagram of the spin-1/2 Ising-XYZ distorted diamond chain exhibits several
intriguing phases due to the XY anisotropy and the second-neighbor interaction,
whereas the model can be exactly solved using the transfer-matrix technique.
The quantum entanglement within the Heisenberg spin dimers is studied through a
bipartite measure concurrence, which is calculated from a relevant reduced
density operator. The concurrence may either show a standard thermal dependence
with a monotonous decline with increasing temperature or a more peculiar
thermal dependence accompanied with reentrant behavior of the concurrence. It
is conjectured that the bipartite entanglement between the interstitial
Heisenberg spin pairs in the natural mineral azurite is quite insensitive to
the applied magnetic field and it persists up to approximately 30 Kelvins.",1704.05640v1
2017-06-29,Quantum spin liquid signatures in Kitaev-like frustrated magnets,"Motivated by recent experiments on $\alpha$-RuCl$_3$, we investigate a
possible quantum spin liquid ground state of the honeycomb-lattice spin model
with bond-dependent interactions. We consider the $K-\Gamma$ model, where $K$
and $\Gamma$ represent the Kitaev and symmetric-anisotropic interactions
between spin-1/2 moments on the honeycomb lattice. Using the infinite density
matrix renormalization group (iDMRG), we provide compelling evidence for the
existence of quantum spin liquid phases in an extended region of the phase
diagram. In particular, we use transfer matrix spectra to show the evolution of
two-particle excitations with well-defined two-dimensional dispersion, which is
a strong signature of quantum spin liquid. These results are compared with
predictions from Majorana mean-field theory and used to infer the quasiparticle
excitation spectra. Further, we compute the dynamical structure factor using
finite size cluster computations and show that the results resemble the
scattering continuum seen in neutron scattering experiments on
$\alpha$-RuCl$_3$. We discuss these results in light of recent and future
experiments.",1706.09908v2
2017-08-15,Coulomb correlations intertwined with spin and orbital excitations in LaCoO$_3$,"We carried out temperature-dependent (20 - 550 K) measurements of resonant
inelastic X-ray scattering on LaCoO$_3$ to investigate the evolution of its
electronic structure across the spin-state crossover. In combination with
charge-transfer multiplet calculations, we accurately quantized the
renormalized crystal-field excitation energies and spin-state populations. We
show that the screening of the on-site Coulomb interaction of 3d electrons is
orbital selective and coupled to the spin-state crossover in LaCoO$_3$. The
results establish that the gradual spin-state crossover is associated with a
relative change of Coulomb energy versus bandwidth, leading to a Mott-type
insulator-to-metal transition.",1708.04417v1
2017-08-30,Quantum Computing with Endohedral Fullerenes,"We review the present state of the art in using the endohedral fullerenes
N@C60 and P@C60 as qubits in a spin quantum computer. After a brief
introduction to spin quantum computing, we first discuss the rich spin
structure of these endohedral fullerenes and specific theoretical proposals for
architectures and operation models leading to a scalable quantum computer. We
then briefly discuss those aspects of materials science that are needed to
realize the proposed architectures. The central part of this chapter is a
review of quantum operations and entanglement realized with endohedral
fullerenes. Finally, we review efforts to realize single spin detection of
endohedral fullerenes and conclude with a brief outlook on outstanding problems
to be solved for obtaining a scalable quantum register.",1708.09298v1
2017-09-12,"Simulating spin chains using a superconducting circuit: gauge invariance, superadiabatic transport, and broken time-reversal symmetry","Simulation of materials by using quantum processors is envisioned to be a
major direction of development in quantum information science. Here we exploit
the mathematical analogies between a triangular spin lattice with
Dzyaloshinskii-Moriya coupling on one edge and a three-level system driven by
three fields in a loop configuation to emulate spin-transport effects. We show
that the spin transport efficiency, seen in the three-level system as
population transfer, is enhanced when the conditions for superadiabaticity are
satisfied. We demonstrate experimentally that phenomena characteristic to spin
lattices due to gauge invariance, non-reciprocity, and broken time-reversal
symmetry can be reproduced in the three-level system.",1709.03731v4
2018-02-19,"Thermodynamics of energy, charge and spin currents in thermoelectric quantum-dot spin valve","We provide a thermodynamically consistent description of energy, charge and
spin transfers in a thermoelectric quantum-dot spin valve in the collinear
configuration based on nonequilibrium Green's function and full counting
statistics. We use the fluctuation theorem symmetry and the concept of entropy
production to characterize the efficiency with which thermal gradients can
transduce charges or spins against their chemical potentials, arbitrary far
from equilibrium. Close to equilibrium, we recover the Onsager reciprocal
relations and the connection to linear response notions of performance such as
the figure of merit. We also identify regimes where work extraction is more
efficient far then close from equilibrium.",1802.06549v2
2018-08-01,Chiral spin liquid phase of the triangular lattice Hubbard model: a density matrix renormalization group study,"Motivated by experimental studies that have found signatures of a quantum
spin liquid phase in organic crystals whose structure is well described by the
two-dimensional triangular lattice, we study the Hubbard model on this lattice
at half filling using the infinite-system density matrix renormalization group
(iDMRG) method. On infinite cylinders with finite circumference, we identify an
intermediate phase between observed metallic behavior at low interaction
strength and Mott insulating spin-ordered behavior at strong interactions.
Chiral ordering from spontaneous breaking of time-reversal symmetry, a
fractionally quantized spin Hall response, and characteristic level statistics
in the entanglement spectrum in the intermediate phase provide strong evidence
for the existence of a chiral spin liquid in the full two-dimensional limit of
the model.",1808.00463v2
2018-09-04,Proximity-Induced Spin-Orbit Coupling in Graphene-Bi$_{1.5}$Sb$_{0.5}$Te$_{1.7}$Se$_{1.3}$ Heterostructures,"The weak intrinsic spin-orbit coupling in graphene can be greatly enhanced by
proximity coupling. Here we report on the proximity-induced spin-orbit coupling
in graphene transferred by hexagonal boron nitride (hBN) onto the topological
insulator Bi$_{1.5}$Sb$_{0.5}$Te$_{1.7}$Se$_{1.3}$ (BSTS) which was grown on a
hBN substrate by vapor solid synthesis. Phase coherent transport measurements,
revealing weak localization, allow us to extract the carrier density-dependent
phase coherence length $l_\phi$. While $l_\phi$ increases with increasing
carrier density in the hBN/graphene/hBN reference sample, it decreases in
BSTS/graphene due to the proximity-coupling of BSTS to graphene. The latter
behavior results from D'yakonov-Perel-type spin scattering in graphene with a
large proximity-induced spin-orbit coupling strength of at least 2.5 meV.",1809.01113v2
2018-10-24,Efficient Generation of the Triplet Bell State Between Coupled Spins Using Transitionless Quantum Driving and Optimal Control,"We consider a pair of coupled spins with Ising interaction in z-direction and
study the problem of generating efficiently the triplet Bell state. We
initially analyze the transitionless quantum driving shortcut to adiabaticity
method and point out its limitations when the available duration approaches
zero. In this short time limit we explicitly calculate the fidelity of the
method and find it to be much lower than unity, no matter how large become the
available control fields. We find that there is a lower bound on the necessary
time to complete this transfer, set by the finite value of the interaction
between the spins. We then use numerical optimal control to find bang-bang
pulse sequences, as well as, smooth controls, which can generate high levels of
the target Bell state in the minimum possible time. The results of the present
work are not restricted only to spin systems, but is expected to find also
applications in other physical systems which can be modeled as interacting
spins, such as, for example, coupled quantum dots.",1810.10233v2
2019-01-29,Near-Unitary Spin Squeezing in $^{171}$Yb,"Spin squeezing can improve atomic precision measurements beyond the standard
quantum limit (SQL), and unitary spin squeezing is essential for improving
atomic clocks. We report substantial and nearly unitary spin squeezing in
$^{171}$Yb, an optical lattice clock atom. The collective nuclear spin of $\sim
10^3$ atoms is squeezed by cavity feedback, using light detuned from the
system's resonances to attain unitarity. The observed precision gain over the
SQL is limited by state readout to 6.5(4) dB, while the generated states offer
a gain of 12.9(6) dB, limited by the curvature of the Bloch sphere. Using a
squeezed state within 30% of unitarity, we demonstrate an interferometer that
improves the averaging time over the SQL by a factor of 3.7(2). In the future,
the squeezing can be simply transferred onto the optical clock transition of
$^{171}$Yb.",1901.10499v3
2019-03-13,Linear and non-linear coherent coupling in a Bell-Bloom magnetometer,"Spin-exchange collisions in hot vapours are generally regarded as a
decoherence mechanism. In contrast, we show that linear and non-linear
spin-exchange coupling can lead to the generation of atomic coherence in a
Bell-Bloom magnetometer. In particular, we theoretically and experimentally
demonstrate that non-linear spin exchange coupling, acting in an analogous way
to a wave-mixing mechanism, can create new modes of coherent excitation which
inherit the magnetic properties of the natural Larmor coherence. The generated
coherences further couple via linear spin-exchange interaction, leading to an
increase of the natural coherence lifetime of the system. Notably, the
measurements are performed in a low-density caesium vapour and for non-zero
magnetic field, outside the standard conditions for collisional coherence
transfer. The strategies discussed are important for the development of
spin-exchange coupling into a resource for an improved measurement platform
based on room-temperature alkali-metal vapours.",1903.05605v1
2019-03-19,Giant localised spin-Peltier effect due to ultrafast domainwalls motion in antiferromagnetic metals,"Spin thermo-electric phenomena have attracted wide attention recently, e.g.
the Spin Peltier effect (SPE) heat generation by magnonic spin currents. Here
we find that the Spin Peltier ef-fect also manifests as a heat wave
accompanying fast moving magnetic textures. High speed andextreme magnetic
excitation localisation are paramount for efficient transfer of energy from
thespin-degrees of freedom to electrons and lattice. While satisfying both
conditions is subject to se-vere restrictions in ferromagnets, we find that
domain walls in antiferomagnets can overcome theselimitations due to their
potential ultrahigh mobility and ultra-small widths originating from the
rel-ativistic contraction. To illustrate our findings, we show that electric
current driven domain wallmotion in the antiferromagnetic metal Mn2Au can carry
a localised heat wave with the maximumamplitude up to 1 K . Since domain walls
are well localised nanoscale magnetic objects, this effecthas the potential for
nanoscale heating sensing and functionalities.",1903.08034v1
2019-04-17,Controlling Dipolar Exchange Interactions in a Dense 3D Array of Large Spin Fermions,"Dipolar interactions are ubiquitous in nature and rule the behavior of a
broad range of systems spanning from energy transfer in biological systems to
quantum magnetism. Here, we study magnetization-conserving dipolar induced
spin-exchange dynamics in dense arrays of fermionic erbium atoms confined in a
deep three-dimensional lattice. Harnessing the special atomic properties of
erbium, we demonstrate control over the spin dynamics by tuning the dipole
orientation and changing the initial spin state within the large 20 spin
hyperfine manifold. Furthermore, we demonstrate the capability to quickly turn
on and off the dipolar exchange dynamics via optical control. The experimental
observations are in excellent quantitative agreement with numerical
calculations based on discrete phase-space methods, which capture entanglement
and beyond-mean field effects. Our experiment sets the stage for future
explorations of rich magnetic behaviors in long-range interacting dipoles,
including exotic phases of matter and applications for quantum information
processing.",1904.08262v1
2019-05-27,Quantum information processing with nuclear spins mediated by a weak-mechanically controlled electron spin,"We propose a scheme to achieve nuclear-nuclear indirect interactions mediated
by a mechanically driven nitrogen-vacancy (NV) center in diamond. Here we
demonstrate two-qubit entangling gates and quantum-state transfer between two
carbon nuclei. When dipole-dipole interaction strength is much larger than the
driving field strength, the scheme is robust against decoherence caused by
coupling between the NV center (nuclear spins) and the environment.
Conveniently, precise control of dipole coupling is not required so this scheme
is insensitive to fluctuating positions of the nuclear spins and the NV center.
Our scheme provides a general blueprint for multi-nuclear-spin gates and for
multi-party communication.",1905.10919v4
2019-10-14,Generation of atomic spin orientation with a linearly polarised beam in room-temperature alkali-metal vapour,"Traditionally, atomic spin orientation is achieved by the transfer of angular
momentum from polarised light to an atomic system. We demonstrate the mechanism
of orientation generation in room-temperature caesium vapours that combines
three elements: optical pumping, non-linear spin dynamics and spin-exchange
collisions. Through the variation of the spin-exchange relaxation rate, the
transition between an aligned and an oriented atomic sample is presented. The
observation is performed by monitoring the atomic radio-frequency spectra. The
measurement configuration discussed, paves the way to simple and robust
radio-frequency atomic magnetometers that are based on a single low power laser
diode that approach the performance of multi-laser pump-probe systems.",1910.06131v2
2019-12-07,Mechanical rotation via optical pumping of paramagnetic impurities,"Hybrid quantum systems exhibiting coupled optical, spin, and mechanical
degrees of freedom can serve as a platform for sensing, or as a bus to mediate
interactions between qubits with disparate energy scales. These systems are
also creating opportunities to test foundational ideas in quantum mechanics,
including direct observations of the quantum regime in macroscopic objects.
Here, we make use of angular momentum conservation to study the dynamics of a
pair of paramagnetic centers featuring different spin numbers in the presence
of a properly tuned external magnetic field. We examine the interplay between
optical excitation, spin evolution, and mechanical motion, and theoretically
show that in the presence of continuous optical illumination, inter-spin
cross-relaxation must induce rigid rotation of the host crystal. The system
dynamics is robust to scattering of spin-polarized phonons, a result we build
on to show this form of angular momentum transfer should be observable using
state-of-the-art torsional oscillators or trapped nanoparticles.",1912.03524v1
2020-02-26,Demonstration of NV-detected ESR spectroscopy at 115 GHz and 4.2 Tesla,"High frequency electron spin resonance (ESR) spectroscopy is an invaluable
tool for identification and characterization of spin systems. Nanoscale ESR
using the nitrogen-vacancy (NV) center has been demonstrated down to the level
of a single spin. However, NV-detected ESR has exclusively been studied at low
magnetic fields, where spectral overlap prevents clear identification of
spectral features. Within this work, we demonstrate NV-detected ESR
measurements of single-substitutional nitrogen impurities in diamond at a NV
Larmor frequency of 115 GHz and the corresponding magnetic field of 4.2 Tesla.
The NV-ESR measurements utilize a double electron-electron resonance sequence
and are performed using both ensemble and single NV spin systems. In the single
NV experiment, chirp pulses are used to improve the population transfer and for
NV-ESR measurements. This work provides the basis for NV-based ESR measurements
of external spins at high magnetic fields.",2002.11845v2
2020-04-06,Distant spin entanglement via fast and coherent electron shuttling,"In the quest for large-scale quantum computing, networked quantum computers
offer a natural path towards scalability. Now that nearest neighbor
entanglement has been demonstrated for electron spin qubits in semiconductors,
on-chip long distance entanglement brings versatility to connect quantum core
units. Here we realize the controlled and coherent transfer of a pair of
entangled electron spins, and demonstrate their remote entanglement when
separated by a distance of 6 microns. Driven by coherent spin rotations induced
by the electron displacement, high-contrast spin quantum interferences are
observed and are a signature of the preservation of the entanglement all along
the displacement procedure. This work opens the route towards fast on-chip
deterministic interconnection of remote quantum bits in semiconductor quantum
circuits.",2004.02727v1
2020-06-10,Hard core run and tumble particles on a one dimensional lattice,"We study the large scale behavior of a collection of hard core run and tumble
particles on a one dimensional lattice with periodic boundary conditions. Each
particle has persistent motion in one direction decided by an associated spin
variable until the direction of spin is reversed. We map the run and tumble
model to a mass transfer model with fluctuating directed bonds. We calculate
the steady state single site mass distribution in the mass model within a mean
field approximation for larger spin-flip rates and by analyzing an appropriate
coalescence fragmentation model for small spin-flip rates. We also calculate
the hydrodynamic coefficients of diffusivity and conductivity for both large
and small spin-flip rates and show that the Einstein relation is violated in
both regimes. We also show how the non-gradient nature of the process can be
taken into account in a systematic manner to calculate the hydrodynamic
coefficients.",2006.05980v2
2020-08-28,Measurements of spin-orbit interaction in epitaxially grown InAs nanosheets,"We report on a low-temperature transport study of a single-gate, planar
field-effect device made from a free-standing, wurtzite-crystalline InAs
nanosheet. The nanosheet is grown via molecular beam epitaxy and the
field-effect device is characterized by gate transfer characteristic
measurements and by magnetic field orientation dependent transport
measurements. The measurements show that the device exhibits excellent
electrical properties and the electron transport in the nanosheet is of the
two-dimensional nature. Low-field magnetoconductance measurements are performed
for the device at different gate voltages and temperatures, and the
characteristic transport lengths, such as phase coherent length, spin-orbit
length and mean free path, in the nanosheet are extracted. It is found that the
spin-orbit length in the nanosheet is short, on the order of 150 nm,
demonstrating the presence of strong spin-orbit interaction in the InAs
nanosheet. Our results show that epitaxially grown, free-standing, InAs
nanosheets can serve as an emerging semiconductor nanostructure platform for
applications in spintronics, spin qubits and planar topological quantum
devices.",2008.12840v2
2020-12-23,Spintronics with a Weyl point in superconducting nanostructures,"We investigate transport in a superconducting nanostructure housing a Weyl
point in the spectrum of Andreev bound states. A minimum magnet state is
realized in the vicinity of the point. One or more normal-metal leads are
tunnel-coupled to the nanostructure. We have shown that this minimum magnetic
setup is suitable for realization of all common goals of spintronics: detection
of a magnetic state, conversion of electric currents into spin currents,
potentially reaching the absolute limit of one spin per charge transferred,
detection of spin accumulation in the leads. The peculiarity and possible
advantage of the setup is the ability to switch between magnetic and
non-magnetic states by tiny changes of the control parameters: superconducting
phase differences. We employ this property to demonstrate the feasibility of
less common spintronic effects: spin on demand and alternative spin current.",2012.13007v1
2021-03-05,Local heat emission due to unidirectional spin-wave heat conveyer effect observed by lock-in thermography,"Lock-in thermography measurements were performed to reveal heat source
distribution induced by the unidirectional spin-wave heat conveyer effect
(USHCE) of magnetostatic surface spin waves. When the magnetostatic surface
spin waves are excited in an yttrium iron garnet slab, the lock-in thermography
images show spatially biased sharp and complicated heating patterns, indicating
the importance of edge spin-wave dynamics for USHCE. The accessibility to the
local heat emission properties allows us to clarify a capability of remote
heating realized by USHCE; it can transfer energy for heating even through a
macro-scale air gap between two magnetic materials owing to the long-range
dipole-dipole coupling.",2103.03694v1
2021-04-16,Large spin-to-charge conversion at room temperature in extended epitaxial Sb2Te3 topological insulator chemically grown on Silicon,"Spin-charge interconversion phenomena at the interface between magnetic
materials and topological insulators (TIs) are attracting enormous interest in
the research effort towards the development of fast and ultra-low power devices
for the future information and communication technology. We report a large
spin-to-charge conversion efficiency in Au/Co/Au/Sb2Te3/Si(111)
heterostructures based on Sb2Te3 TIs grown by metal organic chemical vapor
deposition on 4 inches Si(111) substrates. By conducting room temperature spin
pumping ferromagnetic resonance, we measure an inverse Edelstein Effect length
{\lambda}IEE up to 0.75 nm, a record value for 3-dimensional chalcogenide-based
TIs heterostructures. Our results open the path toward the use of chemical
methods to produce TIs on large area Si substrates and characterized by highly
performing spin-charge conversion, thus marking a milestone toward future
technology-transfer.",2104.08124v1
2021-04-28,Magnetically induced polarization in centrosymmetric bonds,"We reveal the microscopic origin of electric polarization $\vec{P}$ induced
by noncollinear magnetic order. We show that in Mott insulators, such $\vec{P}$
is given by all possible combinations of position operators $\hat{\vec{r}}_{ij}
= (\vec{r}_{ij}^{\, 0},\vec{\boldsymbol{r}}_{ij}^{\phantom{0}})$ and transfer
integrals $\hat{t}_{ij} = (t_{ij}^{0},\boldsymbol{t}_{ij}^{\phantom{0}})$ in
the bonds, where $\vec{r}_{ij}^{\, 0}$ and $t_{ij}^{0}$ are spin-independent
contributions in the basis of Kramers doublet states, while
$\vec{\boldsymbol{r}}_{ij}^{\phantom{0}}$ and
$\boldsymbol{t}_{ij}^{\phantom{0}}$ stem solely from the spin-orbit
interaction. Among them, the combination $t_{ij}^{0}
\vec{\boldsymbol{r}}_{ij}^{\phantom{0}}$, which couples to the spin current,
remains finite in the centrosymmetric bonds, thus yielding finite $\vec{P}$ in
the case of noncollinear arrangement of spins. The form of the magnetoelectric
coupling, which is controlled by $\vec{\boldsymbol{r}}_{ij}^{\phantom{0}}$,
appears to be rich and is not limited to the phenomenological law $\vec{P} \sim
\boldsymbol{\epsilon}_{ij} \times [\boldsymbol{e}_{i} \times
\boldsymbol{e}_{j}]$ with $\boldsymbol{\epsilon}_{ij}$ being the bond vector
connecting the spins $\boldsymbol{e}_{i}$ and $\boldsymbol{e}_{j}$. Using
density-functional theory, we illustrate how the proposed mechanism work in the
spiral magnets CuCl$_2$, CuBr$_2$, CuO, and $\alpha$-Li$_2$IrO$_3$, providing
consistent explanation to available experimental data.",2104.13711v2
2021-05-18,Designing a mechanically driven spin-crossover molecular switch via organic embedding,"Among spin-crossover complexes, Fe-porphyrin (FeP) stands out for molecular
spintronic applications: An intricate, yet favourable balance between ligand
fields, charge transfer, and the Coulomb interaction makes FeP highly
manipulable, while its planar structure facilitates device integration. Here,
we theoretically design a mechanical spin-switch device in which external
strain triggers the intrinsic magneto-structural coupling of FeP through a
purely organic embedding. Exploiting the chemical compatibility and
stretchability of graphene nanoribbon electrodes, we overcome common
reliability and reproducibility issues of conventional inorganic setups. The
competition between the Coulomb interaction and distortion-induced changes in
ligand fields requires methodologies beyond the state-of-the-art: Combining
density functional theory with many-body techniques, we demonstrate
experimentally feasible tensile strain to trigger a low-spin ($S=1$) to
high-spin ($S=2$) crossover. Concomitantly, the current through the device
toggles by over an order of magnitude, adding a fully planar mechanical
current-switch unit to the panoply of molecular spintronics.",2105.08699v1
2021-08-17,Geometric model for the electron spin correlation,"The quantum formula for the spin correlation of the bipartite singlet spin
state, $C_{Q}(\boldsymbol{a},\boldsymbol{b})$, is derived on the basis of a
probability distribution $\rho(\phi)$ that is generic, i. e., independent of
$(\boldsymbol{a},\boldsymbol{b})$. In line with a previous result obtained
within the framework of the quantum formalism, the probability space is
partitioned according to the sign of the product $A=\alpha\beta$ of the
individual spin projections $\alpha$ and $\beta$ onto $\boldsymbol{a}$ and
$\boldsymbol{b}$. A specific partitioning and a corresponding set of
realizations {$ \phi$} are associated with every measurement setting
$(\boldsymbol{a},\boldsymbol{b})$; this precludes the transfer of $\alpha$ or
$\beta$ from $C_{Q}(\boldsymbol{a},\boldsymbol{b})$ to
$C_{Q}(\boldsymbol{a},\boldsymbol{b'})$, for
$\boldsymbol{b'}\neq\boldsymbol{b}.$ A geometric model that reproduces the spin
correlation serves to validate our approach, giving a concrete meaning to the
quantum result in terms of a (local random variable) probability distribution.",2108.07869v3
2021-10-12,Motion-induced spin transfer,"We propose a spin transport induced by inertial motion. Our system is
composed of two host media and a narrow vacuum gap in between. One of the hosts
is sliding at a constant speed relative to the other. This mechanical motion
causes the Doppler effect that shifts the density of states and the
nonequilibrium distribution function in the moving medium. Those shifts induce
the difference in the distribution function between the two media and result in
tunnelling spin current. The spin current is calculated from the
Schwinger-Keldysh formalism with a spin tunnelling Hamiltonian. This scheme
does not require either temperature difference, voltage or chemical potential.",2110.05871v2
2021-11-07,The Spin-dependent Scattering of Boosted Dark Matter,"Boosted dark matter provides a promising approach to probe the light dark
matter, whose computational framework in the spin-independent scattering
process is well developed. However, the spin-dependent one lacks a unified
treatment. The novelty of this paper is to give the first comprehensive
derivation of the cross-section for boosted dark matter in spin-dependent
scattering. When the transfer momentum is sufficiently large, there is a
sizable enhancement to the proton structure factor from the time component.
Besides, we find a residue momentum dependence in the quark-nucleon matching
procedure, even without a light mediator. Such behavior can enhance the
sensitivity compared with conventional contact interaction. We promote this
endeavor by deriving direct limits on sub-GeV spin-dependent boosted dark
matter through terrestrial data. The numerical results of the boosted structure
factor and the non-relativistic structure factor are given explicitly in the
paper and it shows that the excluded region of the boosted structure factor is
about six orders larger than the non-relativistic structure factor.",2111.04000v4
2021-12-16,Photocontrol of spin scalar chirality in centrosymmetric itinerant magnets,"Noncoplanar magnetic structures, such as magnetic skyrmions, are
characterized by spin chirality and usually favored by antisymmetric exchange
interactions in noncentrosymmetric magnets. Here, we show that a linearly
polarized electric-field pulse stabilizes a nonequilibrium spin scalar chiral
state in a centrosymmetric itinerant ferromagnet. The scalar chirality has a
nonmonotonic dependence on the electric-field strength, and its sign can be
controlled by circular polarization. Furthermore, magnetic skyrmions are
excited after the pulse decays. A photoinduced nonthermal electron distribution
plays an important role for instability towards the spin scalar chiral state as
well as the $120^{\circ}$ N\'eel state, depending on the next-nearest-neighbor
transfer integral. These results provide an alternative route to controlling
spin chirality by photoirradiation.",2112.08815v2
2022-02-23,Spin-Phonon-Photon Strong Coupling in a Piezomechanical Nanocavity,"We introduce a hybrid tripartite quantum system for strong coupling between a
semiconductor spin, a mechanical phonon, and a microwave photon. Consisting of
a piezoelectric resonator with an integrated diamond strain concentrator, this
system achieves microwave-acoustic and spin-acoustic coupling rates $\sim$MHz
or greater, allowing for simultaneous ultra-high cooperativities ($\sim 10^3$
and $\sim 10^2$, respectively). From finite-element modeling and master
equation simulations, we estimate photon-to-spin quantum state transfer
fidelities exceeding 0.97 based on separately demonstrated device parameters.
We anticipate that this device will enable hybrid quantum architectures that
leverage the advantages of both superconducting circuits and solid-state spins
for information processing, memory, and networking.",2202.11291v2
2022-02-23,Probing spin dynamics of 2D excitons with twisted light,"We propose a mechanism of intravalley spin-flip scattering in spin-valley
coupled two dimensional systems by transferring momentum of light into exciton
center of mass using optical vortex (OV) beams. By varying the dispersion of
light using the topological charge of OV beam, we demonstrate a unique approach
to control the intra-valley spin-flip scattering rate of excitons. From our
photoluminescence measurements, we demonstrate that the intra-valley scattering
rate in W-based TMDs can be tuned externally by OV beams. Variation of
photoluminescence intensity with topological charges shows a crossover
temperature (> 150 K), indicating competitions among time scales involving
radiative recombination, spin-flip scattering, and thermal relaxations. Our
proposed technique utilizing a structured light beam can open up a new approach
to explore the physics of excitons in 2D systems.",2202.11603v2
2022-05-12,Role of local structural distortions on the origin of j=1/2 pseudo-spin state in sodium iridate,"Na2IrO3 (NIO) is known to be a spin-orbit (SO) driven j=1/2 pseudo-spin
Mott-Hubbard (M-H) insulator. However, the microscopic origin of the
pseudo-spin state and the role of local structural distortions have not been
clearly understood. Using a combination of theoretical calculations and x-ray
spectroscopy, we show that the energetics in the vicinity of Fermi level (EF)
is governed by SO interactions, electron correlation and local octahedral
distortions. Contrary to the earlier understanding, here we show that the j=3/2
and 1/2 pseudo-spin states have admixture of both t2g and eg characters due to
local structural distortion. Reduction of local octahedral symmetry also
enables Ir 5d- O2p hybridization around the EF resulting in a M-H insulator
with enhanced charge transfer character. The possibility of Slater insulator
phase is also ruled out by a combination of absence of room temperature DoS in
valence band spectra, calculated moments and temperature dependent
magnetization measurements.",2205.05902v1
2022-09-14,Half-mirror for electrons on quantum Hall copropagating edge channels,"A half-mirror that divides a spin-polarized electron into two parallel
copropagating spin-resolved quantum Hall edge channels one half each is
presented in this study. The partition process was coherent, as confirmed by
observing the Aharonov-Bohm oscillation at a high visibility of up to 60% in a
Mach-Zehnder interferometer, which comprised two such half-mirrors. The device
characteristics were highly stable, making the device promising in the
application of quantum information processing. The beam-splitting process is
theoretically modelled, and the numerical simulation successfully reproduces
the experimental observation. The partition of the electron accompanied by the
spin rotation is explained by the angular momentum transfer from the orbital to
the spin via spin-orbit interactions.",2209.06725v1
2023-01-18,Coupling spin defects in hexagonal boron nitride to a microwave cavity,"Optically addressable spin defects in hexagonal boron nitride (hBN) have
become a promising platform for quantum sensing. While sensitivity of these
defects are limited by their interactions with the spin environment in hBN,
inefficient microwave delivery can further reduce their sensitivity. Hare, we
design and fabricate a microwave double arc resonator for efficient
transferring of the microwave field at 3.8 GHz. The spin transitions in the
ground state of VB- are coupled to the frequency of the microwave cavity which
results in enhanced optically detected magnetic resonance (ODMR) contrast. In
addition, the linewidth of the ODMR signal further reduces, achieving a
magnetic field sensitivity as low as 42.4 microtesla per square root of hertz.
Our robust and scalable device engineering is promising for future employment
of spin defects in hBN for quantum sensing.",2301.07304v1
2023-04-07,Quantum circuits for the Ising spin networks,"Spin network states are a powerful tool for constructing the $SU(2)$ gauge
theories on a graph. In loop quantum gravity (LQG), they have yielded many
promising predictions, although progress has been limited by the computational
challenge of dealing with high-dimensional Hilbert spaces. To explore more
general configurations, quantum computing methods can be applied by
representing spin network states as quantum circuits. In this article, we
introduce an improved method for constructing quantum circuits for 4-valent
Ising spin networks, which utilizes a smaller number of qubits than previous
approaches. This has practical implications for the implementation of quantum
circuits. We also demonstrate the procedure with various examples, including
the construction of a 10-node Ising spin network state. The key ingredient of
the method is the variational transfer of partial states, which we illustrate
through numerous examples. Our improved construction provides a promising
avenue for further exploring the potential of quantum computing methods in
quantum gravity research.",2304.03559v1
2023-04-13,Finite Temperature Dynamics of Spin Solitons with Applications in Thermocouples and Refrigerators,"The exploitation of spin Berry phases to generate emergent fields for
producing miniaturized and high-quality inductors has enjoyed considerable
popularity among proponents of quantum technologies [Nature 586, 202 (2020)}].
Inspired by this breakthrough, we extend its mechanism to spin thermoelectrics
by probing responses of ferrimagnetic domain walls (DWs) to thermal gradients.
Similarly, voltages here stem from DW-spin collective motion, in contrast to
normal electron transport phenomena. We further develop finite-temperature
dynamics to investigate thermoelectric figures of merit and attribute
corresponding quantum superiority to ultrafast spin evolution of ferrimagnetism
with tunable non-Abelian phases. We propose a more likely cause of DW motion
towards hot or cold regions (contrary to conclusions of previous reports) and
verify existence of efficient magnon-momentum transfers. These findings deepen
our understanding of heat-driven DW kinetics and suggest profitable new
directions in an emerging realm of spincaloritronics.",2304.06608v1
2023-04-27,Coherent magnetization dynamics in strongly quenched Ni thin films,"The remagnetization process after ultrafast demagnetization can be described
by relaxation mechanisms between the spin, electron, and lattice reservoirs.
Thereby, collective spin excitations in form of spin waves and their angular
momentum transfer play an important role on the longer timescales. In this
work, we address the question whether the strength of demagnetization affects
the coherency and the phase of the excited spin waves. We present a study of
coherent magnetization dynamics in thin nickel films after ultrafast
demagnetization using the all-optical, time-resolved magneto-optical
Kerr-effect (tr-MOKE) technique. The largest coherent oscillation amplitude was
observed for strongly quenched systems, showing the conservation of coherency
for demagnetizations of up to 90%. Moreover, the phase of the excited
spin-waves increases with pump power, indicating a delayed start of the
precession during the remagnetization.",2304.14325v1
2023-06-15,Stable $2R$ van der Waals heterostructures of NbS$_2$ and $M$Se$_2$ for $M$=Mo and W,"In this letter, we investigate the stable and commensurate van der Waals
heterostructures of metallic and semiconducting $1H$ transition-metal
dichalcogenides, NbS$_2$ and MoSe$_2$ (WSe$_2$), which possess almost the same
lattice constant of the pristine honeycomb structure. In the most stable
structure, the metallic and semiconducting layers are stacked in a similar
manner to $3R$ stacking but the period is a pair of a metallic layer and a
semiconducting layer. The heterostructure aligns the spin-polarization in each
valley among all layers and induces spin-selective charge transfer between the
metallic and semiconducting layers. Especially in hetero-trilayers, the
electronic spin is conserved due to mirror symmetry along the out-of-plane axis
in contrast to the $3R$ stacking structure. A drastic enhancement of spin Hall
effect is numerically shown as an example of electronic spin transport
phenomena in the hetero-trilayers.",2306.08790v1
2024-02-13,Self-Induced Superradiant Masing,"We study superradiant masing in a hybrid system composed of nitrogen-vacancy
center spins in diamond coupled to a superconducting microwave cavity. After
the first fast superradiant decay we observe transient pulsed and then
quasi-continuous masing. This emission dynamics can be described by a
phenomenological model incorporating the transfer of inverted spin excitations
into the superradiant window of spins resonant with the cavity. After
experimentally excluding cQED effects associated with the pumping of the masing
transition we conjecture that direct higher-order spin-spin interactions are
responsible for creating the dynamics and the transition to the sustained
masing. Our experiment thus opens up a novel way to explore many-body physics
in disordered systems through cQED and superradiance.",2402.08537v1
2011-11-25,The evolution of ultracompact X-ray binaries,"Context. Ultracompact X-ray binaries (UCXBs) typically consist of a white
dwarf donor and a neutron star or black hole accretor. The evolution of UCXBs
and very low mass ratio binaries in general is poorly understood. Aims. We
investigate the evolution of UCXBs in order to learn for which mass ratios and
accretor types these systems can exist, and if they do, what are their orbital
and neutron star spin periods, mass transfer rates and evolutionary timescales.
Methods. For different assumptions concerning accretion disk behavior we
calculate for which system parameters dynamical instability, thermal-viscous
disk instability or the propeller effect emerge. Results. At the onset of mass
transfer, the survival of the UCXB is determined by how efficiently the
accretor can eject matter in the case of a super-Eddington mass transfer rate.
At later times, the evolution of systems strongly depends on the binary's
capacity to return angular momentum from the disk to the orbit. We find that
this feedback mechanism most likely remains effective. In the case of steady
mass transfer, the propeller effect can stop accretion onto recycled neutron
stars completely at a sufficiently low mass transfer rate, based on energy
considerations. However, mass transfer will likely be non-steady because disk
instability allows for accretion of some of the transferred matter. Together,
the propeller effect and disk instability cause the low mass ratio UCXBs to be
visible a small fraction of the time at most, thereby explaining the lack of
observations of such systems. Conclusions. Most likely UCXBs avoid late-time
dynamically unstable mass transfer and continue to evolve as the age of the
Universe allows. This implies the existence of a large population of low mass
ratio binaries with orbital periods ~ 70 - 80 min, unless some other mechanism
has destroyed these binaries.",1111.5978v1
2010-09-06,Angular Momentum Changes Due to Direct Impact Accretion in a Simplified Binary System,"We model a circular mass-transferring binary system to calculate the exchange
of angular momentum between stellar spins and the orbit due to direct impact of
the mass transfer stream onto the surface of the accretor. We simulate mass
transfer by calculating the ballistic motion of a point mass ejected from the
$L_1$ point of the donor star, conserving the total linear and angular momentum
of the system, and treating the stars as uniform density spheres with main
sequence radii determined by their masses. We show that, contrary to previous
assumptions in the literature, direct impact does not always act as a sink of
orbital angular momentum and may in fact increase it by facilitating the
transfer of angular momentum from the spin of the donor to the orbit. Here, we
show an example of the exchange of angular momentum, as well as a measure of
the orbital angular momentum changes for a variety of binary star systems with
main sequence components.",1009.1167v3
2015-12-30,Electron-lattice interactions strongly renormalize the charge transfer energy in the spin-chain cuprate Li$_2$CuO$_2$,"Strongly correlated insulators are broadly divided into two classes:
Mott-Hubbard insulators, where the insulating gap is driven by the Coulomb
repulsion $U$ on the transition-metal cation, and charge-transfer insulators,
where the gap is driven by the charge transfer energy $\Delta$ between the
cation and the ligand anions. The relative magnitudes of $U$ and $\Delta$
determine which class a material belongs to, and subsequently the nature of its
low-energy excitations. These energy scales are typically understood through
the local chemistry of the active ions. Here we show that the situation is more
complex in the low-dimensional charge transfer insulator
Li$_\mathrm{2}$CuO$_\mathrm{2}$, where $\Delta$ has a large non-electronic
component. Combining resonant inelastic x-ray scattering with detailed
modeling, we determine how the elementary lattice, charge, spin, and orbital
excitations are entangled in this material. This results in a large
lattice-driven renormalization of $\Delta$, which significantly reshapes the
fundamental electronic properties of Li$_\mathrm{2}$CuO$_\mathrm{2}$.",1512.09043v1
2016-06-09,Charge transfer and weak bonding between molecular oxygen and graphene zigzag edges at low temperatures,"Electron paramagnetic resonance (EPR) study of air-physisorbed defective
carbon nano-onions evidences in favor of microwave assisted formation of
weakly-bound paramagnetic complexes comprising negatively-charged O2- ions and
edge carbon atoms carrying pi-electronic spins. These complexes being located
on the graphene edges are stable at low temperatures but irreversibly
dissociate at temperatures above 50-60 K. These EPR findings are justified by
density functional theory (DFT) calculations demonstrating transfer of an
electron from the zigzag edge of graphene-like material to oxygen molecule
physisorbed on the graphene sheet edge. This charge transfer causes changing
the spin state of the adsorbed oxygen molecule from S = 1 to S = 1/2 one. DFT
calculations show significant changes of adsorption energy of oxygen molecule
and robustness of the charge transfer to variations of the graphene-like
substrate morphology (flat and corrugated mono- and bi-layered graphene) as
well as edges passivation. The presence of H- and COOH- terminated edge carbon
sites with such corrugated substrate morphology allows formation of ZE-O2-
paramagnetic complexes characterized by small (<50 meV) binding energies and
also explains their irreversible dissociation as revealed by EPR.",1606.02870v1
2020-03-03,Holding and transferring matter-wave solitons against gravity by spin-orbit-coupling tweezers,"We consider possibilities to grasp and drag one-dimensional solitons in
two-component Bose- Einstein condensates (BECs), under the action of gravity,
by tweezers induced by spatially confined spin-orbit (SO) coupling applied to
the BEC, with the help of focused laser illumination. Solitons of two types are
considered, semi-dipoles and mixed modes. We find critical values of the
gravity force, up to which the solitons may be held or transferred by the
tweezers. The dependence of the critical force on the magnitude and spatial
extension of the localized SO interaction, as well as on the solitons norm and
speed (in the transfer regime), are systematically studied by means of
numerical methods, and analytically with the help of a quasi-particle
approximation for the soliton. In particular, a noteworthy finding is that the
critical gravity force increases with the increase of the transfer speed (i.e.,
moving solitons are more robust than quiescent ones). Nonstationary regimes are
addressed too, by considering abrupt application of gravity to solitons created
in the weightless setting. In that case, solitons feature damped shuttle
motion, provided that the gravity force does not exceed a dynamical critical
value, which is smaller than its static counterpart. The results may help to
design gravimeters based on ultracold atoms.",2003.01363v2
2020-10-22,Confirming the role of nuclear tunnelling in aqueous ferrous-ferric electron transfer,"We revisit the well-known aqueous ferrous-ferric electron transfer reaction
in order to address recent suggestions that nuclear tunnelling can lead to
significant deviation from the linear response assumption inherent in the
Marcus picture of electron transfer. A recent study of this reaction by
Richardson and coworkers has found a large difference between their new
path-integral method, GR-QTST, and the saddle point approximation of Wolynes
(Wolynes theory). They suggested that this difference could be attributed to
the existence of multiple tunnelling pathways, leading Wolynes theory to
significantly overestimate the rate. This was used to argue that the linear
response assumptions of Marcus theory may break down for liquid systems when
tunnelling is important. If true, this would imply that the commonly used
method for studying such systems, where the problem is mapped onto a spin-boson
model, is invalid. However, we have recently shown that size inconsistency in
GR-QTST can lead to poor predictions of the rate in systems with many degrees
of freedom. We have also suggested an improved method, the path-integral linear
golden-rule (LGR) approximation, which fixes this problem. Here we demonstrate
that the GR-QTST results for ferrous-ferric electron transfer are indeed
dominated by its size consistency error. Furthermore, by comparing the LGR and
Wolynes theory results, we confirm the established picture of nuclear
tunnelling in this system. Finally, by comparing our path-integral results to
those obtained by mapping onto the spin-boson model, we reassess the importance
of anharmonic effects and the accuracy of this commonly used mapping approach.",2010.11496v1
2015-07-09,Interference of quantum critical excitations and soft diffusive modes in a disordered antiferromagnetic metal,"We study the temperature-dependent quantum correction to conductivity due to
the interplay of spin density fluctuations and weak disorder for a
two-dimensional metal near an antiferromagnetic (AFM) quantum critical point.
AFM spin density fluctuations carry large momenta around the ordering vector
$\mathbf{Q}$ and, at lowest order of the spin-fermion coupling, only scatter
electrons between ""hot spots"" of the Fermi surface which are connected by
$\mathbf{Q}$. Earlier, it was seen that the quantum interference between AFM
spin density fluctuations and soft diffusive modes of the disordered metal is
suppressed, a consequence of the large-momentum scattering. The suppression of
this interference results in a non-singular temperature dependence of the
corresponding interaction correction to conductivity. However, at higher order
of the spin-fermion coupling, electrons on the entire Fermi surface can be
scattered successively by two spin density fluctuations and, in total, suffer a
small momentum transfer. This higher-order process can be described by
composite modes which carry small momenta. We show that the interference
between formally subleading composite modes and diffusive modes generates
singular interaction corrections which ultimately dominate over the
non-singular first-order correction at low temperatures. We derive an effective
low-energy theory from the spin-fermion model which includes the
above-mentioned higher-order process implicitly and show that for weak
spin-fermion coupling the small-momentum transfer is mediated by a composite
propagator. Employing the conventional diagrammatic approach to impurity
scattering, we find the correction $\delta \sigma \sim +\ln^2 T$ for
temperatures above an exponentially small crossover scale.",1507.02603v2
2015-08-13,Efficient Density Matrix Renormalization Group algorithm to study Y-Junctions with integer and half-integer spin,"An efficient density matrix renormalization group (DMRG) algorithm is
presented and applied to Y-junctions, systems with three arms of $n$ sites that
meet at a central site. The accuracy is comparable to DMRG of chains. As in
chains, new sites are always bonded to the most recently added sites and the
superblock Hamiltonian contains only new or once renormalized operators.
Junctions of up to $N = 3n + 1 \approx 500$ sites are studied with
antiferromagnetic (AF) Heisenberg exchange $J$ between nearest-neighbor spins
$S$ or electron transfer $t$ between nearest neighbors in half-filled Hubbard
models. Exchange or electron transfer is exclusively between sites in two
sublattices with $N_A \ne N_B$. The ground state (GS) and spin densities $
\rho_r = <S^z_r >$ at site $r$ are quite different for junctions with $S$ =
1/2, 1, 3/2 and 2. The GS has finite total spin $S_G = 2S (S)$ for even (odd)
$N$ and for $M_G =S_G$ in the $S_G$ spin manifold, $\rho_r > 0 (< 0)$ at sites
of the larger (smaller) sublattice. $S$ = 1/2 junctions have delocalized states
and decreasing spin densities with increasing $N$. $S$ = 1 junctions have four
localized $S_z = 1/2$ states at the end of each arm and centered on the
junction, consistent with localized states in $S$ = 1 chains with finite
Haldane gap. The GS of $S$ = 3/2 or 2 junctions of up to 500 spins is a spin
density wave (SDW) with increased amplitude at the ends of arms or near the
junction. Quantum fluctuations completely suppress AF order in $S$ = 1/2 or 1
junctions, as well as in half-filled Hubbard junctions, but reduce rather than
suppress AF order in $S$ = 3/2 or 2 junctions.",1508.03118v1
2016-07-04,Magnetoresistance of vertical Co-graphene-NiFe junctions controlled by charge transfer and proximity-induced spin splitting in graphene,"Graphene is hailed as an ideal material for spintronics due to weak intrinsic
spin-orbit interaction that facilitates lateral spin transport and tunability
of its electronic properties, including a possibility to induce magnetism in
graphene. Another promising application of graphene is related to its use as a
spacer separating ferromagnetic metals (FMs) in vertical magnetoresistive
devices, the most prominent class of spintronic devices widely used as magnetic
sensors. In particular, few-layer graphene was predicted to act as a perfect
spin filter. Here we show that the role of graphene in such devices (at least
in the absence of epitaxial alignment between graphene and the FMs) is
different and determined by proximity-induced spin splitting and charge
transfer with adjacent ferromagnetic metals, making graphene a weak FM
electrode rather than a spin filter. To this end, we report observations of
magnetoresistance (MR) in vertical Co-graphene-NiFe junctions with 1 to 4
graphene layers separating the ferromagnets, and demonstrate that the
dependence of the MR sign on the number of layers and its inversion at
relatively small bias voltages is consistent with spin transport between weakly
doped and differently spin-polarized layers of graphene. The proposed
interpretation is supported by the observation of an MR sign reversal in biased
Co-graphene-hBN-NiFe devices and by comprehensive structural characterization.
Our results suggest a new architecture for vertical devices with electrically
controlled MR.",1607.00983v3
2018-02-05,From charge- and spin-ordering to superconductivity in the organic charge-transfer solids,"We review recent progress in understanding the different spatial broken
symmetries that occur in the normal states of the family of charge-transfer
solids (CTS) that exhibit superconductivity (SC), and discuss how this
knowledge gives insight to the mechanism of the unconventional SC in these
systems. We show that a unified theory of the diverse broken symmetry states
necessarily requires explicit incorporation of strong electron-electron
interactions and lattice discreteness, and most importantly, the correct
bandfilling of one-quarter. Uniquely in the quarter-filled band, there is a
very strong tendency to form nearest neighbor spin-singlets, in both one and
two dimensions. The tendency to spin-singlets, a quantum effect, drives a
commensurate charge-order in the correlated quarter-filled band. This
charge-ordered spin-singlet, which we label as a paired-electron crystal (PEC),
is different from and competes with both the antiferromagnetic state and the
Wigner crystal of single electrons. Further, unlike these classical broken
symmetries, the PEC is characterized by a spin gap. The tendency to the PEC in
two dimensions is enhanced by lattice frustration. Following this
characterization of the spatial broken symmetries, we critically reexamine
spin-fluctuation and resonating valence bond theories of frustration-driven SC
within half-filled band Hubbard and Hubbard-Heisenberg Hamiltonians for the
superconducting CTS. We develop a valence-bond theory of SC within which the
superconducting state is reached by the destabilization of the PEC by
additional pressure-induced lattice frustration that makes the spin-singlets
mobile. Our proposed mechanism for SC is the same for CTS in which the
proximate semiconducting state is antiferromagnetic instead of charge-ordered,
with the only difference that SC in the former is generated via a fluctuating
spin-singlet state as opposed to static PEC.",1802.01551v2
2018-10-30,On the Origin of Black Hole Spin in High-mass X-Ray Binaries,"Black hole (BH) spins in low-mass X-ray binaries (LMXBs) cover a range of
values that can be explained by accretion after BH birth. In contrast, the
three BH spin measurements in high-mass X-ray binaries (HMXBs) show only values
near the maximum and likely have a different origin connected to the BH stellar
progenitor. We explore here two possible scenarios to explain the high spins of
BHs in HMXBs: formation in binaries that undergo mass transfer (MT) during the
main sequence (MS; Case-A MT), and very close binaries undergoing chemically
homogeneous evolution (CHE). We find that both scenarios are able to produce
high-spin BHs if internal angular momentum (AM) transport in the progenitor
star after its MS evolution is not too strong (i.e., weak coupling between the
stellar core and its envelope). If instead efficient AM transport is assumed,
we find that the resulting BH spins are always too low with respect to
observations. The Case-A MT model provides a good fit for the BH spins, the
masses of the two components, and the final orbital periods for two of the
three BHs in HMXBs with measured spins. For one of them, the mass predicted for
the BH companion is significantly lower than observed, but this depends
strongly on the assumed efficiency of mass transfer. The CHE models predict
orbital periods that are too large for all three cases considered here. We
expect the Case-A MT to be much more frequent at the metallicities involved, so
we conclude that the Case-A MT scenario is preferred. Finally, we predict that
the stellar companions of HMXBs formed through the Case-A MT have enhanced
nitrogen surface abundances, which can be tested by future observations.",1810.13016v3
2019-05-27,Nonequilibrium Majorana Dynamics by Quenching a Magnetic Field in Kitaev Spin Liquids,"The honeycomb Kitaev spin model provides a quantum spin liquid in the ground
state, where the spin excitations are fractionalized into itinerant and
localized Majorana fermions; the former spectrum has a broad continuum ranging
up to a high energy, while the latter has a sharp peak at a low energy. Despite
tremendous efforts, it remains elusive to clearly identify these distinct
Majorana excitations in experiments. Here we show their manifestation in the
time evolution after quenching the magnetic field, by using the time-dependent
Majorana mean-field theory for both the ferromagnetic and antiferromagnetic
Kitaev models. We find that the transient spin dynamics from the quantum spin
liquid states is qualitatively different from the conventional spin precessions
by the quench from the high-field forced-ferromagnetic state. We obtain
peculiar time evolutions with distinct time scales, i.e., short-time decay of
high-energy components associated with the itinerant Majorana excitations, and
long-lived excitations at a low energy by the localized ones. These peculiar
behaviors are caused by the energy transfer between the two Majorana
quasiparticles after the field quench. Moreover, we find that the Majorana
semimetal with the point nodes in equilibrium turns into a Majorana metal with
the transient ""Fermi surfaces"" by the energy transfer. In particular, for the
quench from the intermediate-field quantum spin liquid in the antiferromagnetic
Kitaev model, the Fermi surfaces change their topology in the time evolution,
which is regarded as a dynamical version of the Majorana ""Lifshitz transition"".
Our results unveil that the real-time dynamics provides another route to not
only the identification of the fractional Majorana excitations in candidate
materials of Kitaev magnets but also unprecedented quantum phases that cannot
be stabilized as the equilibrium states.",1905.10984v1
1997-03-10,Nucleon Spin Fluctuations and Neutrino-Nucleon Energy Transfer in Supernovae,"The formation of neutrino spectra in a supernova depends crucially on
strength and inelasticity of weak interactions in hot nuclear matter. Neutrino
interactions with nonrelativistic nucleons are mainly governed by the dynamical
structure function for the nucleon spin density which describes its
fluctuations. It has recently been shown that these fluctuations give rise to a
new mode of energy transfer between neutrinos and nucleons which inside the
neutrinosphere is of comparable or greater importance than ordinary recoil. We
calculate numerically the spin density structure function in the limit of a
dilute, non-degenerate medium from exact two-nucleon wave functions for some
representative nuclear interaction potentials. We show that spectrum and
magnitude of the energy transfer can deviate significantly from those based on
the Born approximation. They are, however, rather insensitive to the particular
nuclear potential as long as it reproduces experimental nucleon scattering
phase shifts at energies up to a few tens of MeV. We also compare with
calculations based on a one-pion exchange potential in Born approximation and
briefly comment on their applicability near the center of a supernova core. Our
study is relevant for numerical simulations of the neutrino spectra emerging
from type-II supernovae.",9703056v1
2006-03-30,Spin-Polarizing Cold Sodium Atoms in a Strong Magnetic Field,"The efficiency of evaporative cooling, which is used for the creation of a
Bose Einstein condensate, depends strongly on the number of particles at the
start of the evaporation. A high efficiency can be reached by filling the
magneto-optical trap with a large number of atoms and subsequently transferring
these atoms to the magnetic trap as efficiently as possible. In our case (for
sodium) this efficiency is limited to 1/3, because the magnetic substates of
the F = 1 state, which is used in the trapping process, are equally populated.
This limit can be overcome by spin-polarizing the sample before the transfer.
For sodium atoms, however, the improvement is very small when it is done in a
small magnetic field due to the large number of optical transitions in
combination with the high optical density. In this article we describe
spin-polarizing sodium atoms in a high magnetic field. The transfer efficiency
is increased by a factor of 2. The high magnetic field makes the process also
more robust against variations in the magnetic field, the laser frequency and
the polarization of the laser beam.",0603255v1
2007-09-14,Critically rotating stars in binaries - an unsolved problem -,"In close binaries mass and angular momentum can be transferred from one star
to the other during Roche-lobe overflow. The efficiency of this process is not
well understood and constitutes one of the largest uncertainties in binary
evolution.
  One of the problems lies in the transfer of angular momentum, which will spin
up the accreting star. In very tight systems tidal friction can prevent
reaching critical rotation, by locking the spin period to the orbital period.
Accreting stars in systems with orbital periods larger than a few days reach
critical rotation after accreting only a fraction of their mass, unless there
is an effective mechanism to get rid of angular momentum. In low mass stars
magnetic field might help. In more massive stars angular momentum loss will be
accompanied by strong mass loss. This would imply that most interacting
binaries with initial orbital periods larger than a few days evolve very
non-conservatively.
  In this contribution we wish to draw attention to the unsolved problems
related to mass and angular momentum transfer in binary systems. We do this by
presenting the first results of an implementation of spin up by accretion into
the TWIN version of the Eggleton stellar evolution code.",0709.2285v1
2008-11-28,Information Transferring Ability of the Different Phases of a finite XXZ Spin Chain,"We study the transmission of both classical or quantum information through
all the phases of a finite XXZ spin chain. This characterizes the merit of the
different phases in terms of their ability to act as a quantum wire. As far as
quantum information is concerned, we need only consider the transmission of
entanglement as the direct transmission of a quantum state is equivalent. The
isotropic anti-ferromagnetic spin chain is found to be the optimal point of the
phase diagram for the transmission of quantum entanglement when one considers
both the amount of transmitted entanglement, as well as the velocity with which
it is transmitted. But this optimal point in the phase diagram moves to the
Neel phase when decoherence or thermal fluctuations are taken to account. This
chain may also be able to transfer classical information even when, due to a
large magnitude of the noise, quantum information is not transmitted at all.
For a certain range of anisotropies of the model, a curious feature is found in
the flow of quantum information inside the chain, namely, a hopping mode of
entanglement transfer which skips the odd numbered sites. Our predictions will
potentially be testable in several physical systems.",0811.4695v2
2016-07-21,Measurement of polarization observables of the associated strangeness production in proton proton interactions,"The Lambda polarization, the analyzing power, and the Lambda spin transfer
coefficient of the reaction pp -> p K+ Lambda were measured at beam momenta of
2.70 GeV/c and 2.95 GeV/c, corresponding to excess energies of 122 MeV and 204
MeV. While the analyzing power and the spin transfer coefficient do not change
significantly with the excess energy, the Lambda polarization varies strongly
and changes its sign. As this is the first measurement of polarization
observables below an excess energy of 200 MeV, the change of the sign of the
Lambda polarization was not observed before. The high statistics of the data
(~200 k events for each momentum) enables detailed studies of the dependence of
the Lambda polarization and the analyzing power on the center of mass momentum
of the particles. The results of the spin transfer coefficient are in
qualitative agreement with the DISTO experiment. The Lambda polarization data
of 2.95 GeV/c are only conform with the DISTO experiment, while both the 2.70
GeV/c and 2.95 GeV/c data differ strongly from all previous measurements,
whether exclusive or inclusive.",1607.06305v2
2020-04-06,Disorder solutions for generalized 2D Ising Model with multi-spin interaction,"For generalized 2D Ising model in an external magnetic field with the
interaction of nearest neighbors, next nearest neighbors, all kinds of triple
interactions and the quadruple interaction the formulas for finding free energy
per lattice site in the thermodynamic limit were derived on a certain set of
exact disordered solutions depending on seven parameters. Lattice models are
considered with boundary conditions with a shift (similar to helical ones), and
with cyclic closure of the set of all points in natural ordering. The
elementary transfer matrix with nonnegative matrix elements are constructed. On
the set of disorder solutions the largest eigenvalue of the transfer matrix is
constant for every size of considering planar lattice, and, in particular, in
the thermodynamic limit. Free energy per lattice site in the thermodynamic
limit is expressed through the natural logarithm of the largest eigenvalue of
transfer matrix. This largest eigenvalue can be found for a special form of
eigenvector with positive components. The numerical example show the existence
of nontrivial solutions of the resulting systems of equations. The system of
equations and the value of free energy in the thermodynamic limit will remain
the same for 2D generalized Ising models with Hamiltonians, in which the values
of two (out of four) neighboring maximal spins in the natural ordering are
replaced by the values of the spins at any other two lattice points adjacent in
the natural ordering, this significantly expands the set of models having
disordered exact solutions. The high degree of symmetry and inductive
construction of the components of the eigenvectors, which disappear when going
beyond the framework of the obtained set of exact solutions, is an occasion to
search for phase transitions in the vicinity of this set of disordered
solutions.",2004.02427v1
2020-08-28,Uncovering the role of the density of states in controlling ultrafast spin dynamics,"At the ultrafast limit of optical spin manipulation is the theoretically
predicted phenomena of optical intersite spin transfer (OISTR), in which laser
induced charge transfer between the sites of a multi-component material leads
to control over magnetic order. A key prediction of this theory is that the
demagnetization efficiency is determined by the availability of unoccupied
states for intersite charge transfer. Employing state-of-the-art
magneto-optical Kerr effect measurements with femtosecond time resolution, we
probe this prediction via a systematic comparison of the ultrafast magnetic
response between the 3d ferromagnets, Fe, Co, and Ni, and their respective
Pt-based alloys and multilayers. We find that (i) the demagnetization
efficiency in the elemental magnets increases monotonically from Fe, via Co to
Ni and, (ii), that the gain in demagnetization efficiency of the
multi-component system over the pure element counterpart scales with the number
of empty 3d minority states, exactly as predicted by the OISTR effect. We
support these experimental findings with ab initio time-dependent density
functional theory calculations that we show to capture the experimental trends
very well.",2008.12612v2
2021-07-18,On the Transfer of Polarization from the Initial to the Final Proton in the Elastic Process $ e \vec {p} \to e \vec {p}$,"The $Q^2$ dependence of the ratio of the cross sections with and without
proton spin flip, as well as the polarization asymmetry in the process $e
\vec{p} \to e \vec{p}$ has been numerically analyzed using the results of JLab
polarization experiments on the measurements of the ratio of the Sachs form
factors in the $\vec{e} p \to e \vec{p}$ process. The calculations have been
made for the case where the initial (at rest) and final protons are fully
polarized and have a common spin quantization axis, which coincides with the
direction of motion of the final proton. The longitudinal polarization transfer
to the proton has been calculated in the case of the partially polarized
initial proton for a kinematics used in the experiment reported in [A. Liyanage
et al. (SANE Collaboration), Phys. Rev. C 101, 035206 (2020)], where the double
spin asymmetry was measured in the $\vec{e} \vec{p} \to e p$ process. A
noticeable sensitivity of the polarization transfer to the proton to the form
of the $Q^2$ dependence of the ratio $\mu_p G_E/G_M$ has been found. This
sensitivity may be used to conduct a new independent experiment to measure this
dependence in the $ e \vec{p} \to e \vec{p}$ process. A criterion to assess the
reliability of measurements of the ratio of Sachs form factors using the
Rosenbluth technique has been proposed and used to analyze the results of two
experiments.",2107.08503v2
2023-07-03,New Method for Measuring the Ratio $μ_p G_E/G_M$ Based on the Polarization Transfer from the Initial Proton to the Final Electron in the $e \vec p \to \vec e p$ Process,"In this letter, we propose a new method for measuring the Sachs form factors
ratio ($R =\mu_p G_E/G_M$) based on the transfer of polarization from the
initial proton to the final electron in the elastic $e \vec p \to \vec e p$
process, in the case when the axes of quantization of spins of the target
proton at rest and of the scattered electron are parallel, i.e., when an
electron is scattered in the direction of the spin quantization axis of the
proton target. To do this, in the kinematics of the SANE collaboration
experiment (2020) on measuring double spin asymmetry in the $\vec e\vec p \to e
p$ process, using Kelly (2004) and Qattan (2015) parametrizations, a numerical
analysis was carried out of the dependence of the longitudinal polarization
degree of the scattered electron on the square of the momentum transferred to
the proton, as well as on the scattering angles of the electron and proton. It
is established that the difference in the longitudinal polarization degree of
the final electron in the case of conservation and violation of scaling of the
Sachs form factors can reach 70%. This fact can be used to set up polarization
experiments of a new type to measure the ratio $R$.",2307.00992v2
1998-05-06,The Neutron Stars of Soft X-Ray Transients,"Soft X-ray Transients (SXRTs) have long been suspected to contain old, weakly
magnetic neutron stars that have been spun up by accretion torques. After
reviewing their observational properties, we analyse the different regimes that
likely characterise the neutron stars in these systems across the very large
range of mass inflow rates, from the peak of the outbursts to the quiescent
emission. While it is clear that close to the outburst maxima accretion onto
the neutron star surface takes place, as the mass inflow rate decreases,
accretion might stop at the magnetospheric boundary because of the centrifugal
barrier provided by the neutron star. For low enough mass inflow rates (and
sufficiently short rotation periods), the radio pulsar mechanism might turn on
and sweep the inflowing matter away. The origin of the quiescent emission,
observed in a number of SXRTs at a level of ~10^(32)-10^(33) erg/s, plays a
crucial role in constraining the neutron star magnetic field and spin period.
Accretion onto the neutron star surface is an unlikely mechanism for the
quiescent emission of SXRTs, as it requires very low magnetic fields and/or
long spin periods. Thermal radiation from a cooling neutron star surface in
between the outbursts can be ruled out as the only cause of the quiescent
emission. We find that accretion onto the neutron star magnetosphere and shock
emission powered by an enshrouded radio pulsar provide far more plausible
models. In the latter case the range of allowed neutron star spin periods and
magnetic fields is consistent with the values recently inferred from the
properties of kHz QPO in LMXRBs. If quiescent SXRTs contain enshrouded radio
pulsars, they provide a missing link between X-ray binaries and millisecond
pulsars.",9805079v1
2001-05-20,The origin of angular momentum in dark matter halos,"We propose a new explanation for the origin of angular momentum in galaxies
and their dark halos, in which the halos obtain their spin through the
cumulative acquisition of angular momentum from satellite accretion. In our
model, the build-up of angular momentum is a random walk process associated
with the mass assembly history of the halo's major progenitor. We assume no
correlation between the angular momenta of accreted objects. Using the extended
Press-Schechter approximation, we calculate the growth of mass, angular
momentum, and spin parameter $\lambda$ for many halos. Our random walk model
reproduces the key features of the angular momentum of halos found in N-body
simulations: a lognormal distribution in $\lambda$ with an average of
$<\lambda> \approx 0.04$, independent of mass and redshift. The evolution of
the spin parameter in individual halos in this model is quite different from
the steady increase with time of angular momentum in the tidal torque picture.
We find both in N-body simulations and in our random walk model that the value
of $\lambda$ changes significantly with time for a halo's major progenitor. It
typically has a sharp increase due to major mergers, and a steady decline
during periods of gradual accretion of small satellites. The model predicts
that on average the $\lambda$ of halos which had major mergers after redshift
$z=2$ should be substantially larger than the $\lambda$ of those which did not.
Perhaps surprisingly, this suggests that halos that host late-forming
elliptical galaxies should rotate faster than halos of spiral galaxies.",0105349v3
2005-12-23,Birth and Evolution of Isolated Radio Pulsars,"We investigate the birth and evolution of Galactic isolated radio pulsars. We
begin by estimating their birth space velocity distribution from proper motion
measurements of Brisken et al. (2002, 2003). We find no evidence for
multimodality of the distribution and favor one in which the absolute
one-dimensional velocity components are exponentially distributed and with a
three-dimensional mean velocity of 380^{+40}_{-60} km s^-1. We then proceed
with a Monte Carlo-based population synthesis, modelling the birth properties
of the pulsars, their time evolution, and their detection in the Parkes and
Swinburne Multibeam surveys. We present a population model that appears
generally consistent with the observations. Our results suggest that pulsars
are born in the spiral arms, with a Galactocentric radial distribution that is
well described by the functional form proposed by Yusifov & Kucuk (2004), in
which the pulsar surface density peaks at radius ~3 kpc. The birth spin period
distribution extends to several hundred milliseconds, with no evidence of
multimodality. Models which assume the radio luminosities of pulsars to be
independent of the spin periods and period derivatives are inadequate, as they
lead to the detection of too many old simulated pulsars in our simulations.
Dithered radio luminosities proportional to the square root of the spin-down
luminosity accommodate the observations well and provide a natural mechanism
for the pulsars to dim uniformly as they approach the death line, avoiding an
observed pile-up on the latter. There is no evidence for significant torque
decay (due to magnetic field decay or otherwise) over the lifetime of the
pulsars as radio sources (~100 Myr). Finally, we estimate the pulsar birthrate
and total number of pulsars in the Galaxy.",0512585v2
2009-02-26,On the tidal evolution of Hot Jupiters on inclined orbits,"Tidal friction is thought to be important in determining the long-term
spin-orbit evolution of short-period extrasolar planetary systems. Using a
simple model of the orbit-averaged effects of tidal friction, we study the
evolution of close-in planets on inclined orbits, due to tides. We analyse the
effects of the inclusion of stellar magnetic braking by performing a
phase-plane analysis of a simplified system of equations, including the braking
torque. The inclusion of magnetic braking is found to be important, and its
neglect can result in a very different system history. We then present the
results of numerical integrations of the tidal evolution equations, where we
find that it is essential to consider coupled evolution of the orbital and
rotational elements, including dissipation in both the star and planet, to
accurately model the evolution. The main result of our integrations is that for
typical Hot Jupiters, tidal friction aligns the stellar spin with the orbit on
a similar time as it causes the orbit to decay. This means that if a planet is
observed to be aligned, then it probably formed coplanar. This reinforces the
importance of Rossiter-McLaughlin effect observations in determining the degree
of spin-orbit alignment in transiting systems. We apply these results to the
XO-3 system, and constrain the tidal quality factors Q' in both the star and
planet in this system. Using a model in which inertial waves are excited by
tidal forcing in the outer convective envelope and dissipated by turbulent
viscosity, we calculate Q' for a range of F-star models, and find it to vary
considerably within this class of stars. This means that assuming a single Q'
applies to all stars is probably incorrect. We propose an explanation for the
survival of WASP-12 b & OGLE-TR-56 b, in terms of weak dissipation in the star.",0902.4563v1
2010-01-25,Fossil evidence for spin alignment of SDSS galaxies in filaments,"We search for and find fossil evidence that the distribution of the spin axes
of galaxies in cosmic web filaments relative to their host filaments are not
randomly distributed. This would indicate that the action of large scale tidal
torques effected the alignments of galaxies located in cosmic filaments. To
this end, we constructed a catalogue of clean filaments containing edge-on
galaxies. We started by applying the Multiscale Morphology Filter (MMF)
technique to the galaxies in a redshift-distortion corrected version of the
Sloan Digital Sky Survey DR5. From that sample we extracted those 426 filaments
that contained edge-on galaxies (b/a < 0.2). These filaments were then visually
classified relative to a variety of quality criteria. Statistical analysis
using ""feature measures"" indicates that the distribution of orientations of
these edge-on galaxies relative to their parent filament deviate significantly
from what would be expected on the basis of a random distribution of
orientations. The interpretation of this result may not be immediately
apparent, but it is easy to identify a population of 14 objects whose spin axes
are aligned perpendicular to the spine of the parent filament (\cos \theta <
0.2). The candidate objects are found in relatively less dense filaments. This
might be expected since galaxies in such locations suffer less interaction with
surrounding galaxies, and consequently better preserve their tidally induced
orientations relative to the parent filament. The technique of searching for
fossil evidence of alignment yields relatively few candidate objects, but it
does not suffer from the dilution effects inherent in correlation analysis of
large samples.",1001.4479v2
2011-05-25,Monotonic and cyclic components of radio pulsars spin-down,"In this article we revise the problem of anomalous values of pulsars' braking
indices n_{obs} and frequency second derivatives F2 arising in observations.
The intrinsic evolutionary braking is buried deep under superimposed irregular
processes, that prevent direct estimations of its parameters for the majority
of pulsars. We re-analyze the distribution of ""ordinary"" radio pulsars on a
F2-F1, F2-F0, F1-F0 and n_{obs}-tau_{ch} diagrams assuming their spin-down to
be the superposition of a ""true"" monotonous term and a symmetric oscillatory
term. We demonstrate that their effects may be clearly separated using simple
ad hoc arguments. Using maximum likelihood estimator we derive the parameters
of both components. We find characteristic timescales of such oscillations to
be of the order of 1e3-1e4 years, while its amplitudes are large enough to
modulate the observed spin-down rate up to 0.5-5 times and completely dominate
the second frequency derivatives. On the other hand, pulsars' secular evolution
is consistent with classical magnetodipolar model with braking index n ~ 3. So,
observed pulsars' characteristic ages (and similar estimators that depend on
the observed F1) are also affected by long term cyclic process and differ up to
0.5-5 times from their monotonous values. This fact naturally resolves the
discrepancy of characteristic and independently estimated physical ages of
several objects, as well as explains very large, up to 1e8 years,
characteristic ages of some pulsars. We discuss the possible physical
connection of long term oscillation with a complex neutron star rotation
relative its magnetic axis due to influence of the near-field part of
magnetodipolar torque.",1105.5019v2
2012-04-13,Cyclotron Resonance Energies and Orbital Elements of Accretion Pulsar 4U 0115+63 During the Giant Outburst in 2008,"We present both timing and spectral analysis of the outburst of 4U 0115+63 in
April -- May 2008 with INTEGRAL and RXTE observations. We have determined the
spin period of the neutron star at $\sim 3.61430 \pm 0.00003$ s, and a spin up
rate during the outburst of $\dot{P}=(-7.24 \pm 0.03)\times10^{-6} {\rm s
d^{-1}}$, the angle of periapsis $\omega=48.67^\circ \pm 0.04^\circ$ in 2008
and its variation (apsidal motion) $\dot{\omega} = 0.048^\circ \pm 0.003^\circ
{\rm yr}^{-1}$. We also confirm the relation of spin-up torque versus
luminosity in this source during the giant outburst. The hard X-ray spectral
properties of 4U 0115+63 during the outburst are studied with INTEGRAL and
RXTE. Four cyclotron absorption lines are detected using the spectra from
combined data of IBIS and JEM-X aboard INTEGRAL in the energy range of 3 -- 100
keV. The 5 -- 50 keV luminosities at an assumed distance of 7 kpc are
determined to be in the range of $(1.5-12)\times 10^{37} {\rm ergs s^{-1}}$
during the outburst. The fundamental absorption line energy varies during the
outburst: around 15 keV during the rising phase, and transiting to $\sim 10$
keV during the peak of the outburst, and further coming back to $\sim 15$ keV
during the decreasing phase. The variations of photon index show the
correlation with the fundamental line energy changes: the source becomes harder
around the peak of the outburst and softer in both rising and decreasing
phases. This correlation and transition processes during the outburst need
further studies in both observations and theoretical work. The known relation
of the fundamental line energy and X-ray luminosity is confirmed by our
results, however, our discoveries suggest that some other factors besides
luminosity play the important role in fundamental line energy variations and
spectral transitions.",1204.2908v1
2012-05-21,The role of the supermassive black hole spin in the estimation of the EMRI event rate,"A common result to all EMRI investigations on rates is that the possibility
that a compact object merges with the MBH after only one intense burst of GWs
is much more likely than a slow adiabatic inspiral, an EMRI. The later is
referred to as a ""plunge"" because the compact object dives into the MBH. The
event rates for plunges are orders of magnitude larger than slow inspirals. On
the other hand, nature MBH's are most likely Kerr and the magnitude of the spin
has been sized up to be high. We calculate the number of periapsis passages
that a compact object set on to an extremely radial orbit goes through before
being actually swallowed by the Kerr MBH and we then translate it into an event
rate for a LISA-like observatory, such as the proposed ESA mission eLISA/NGO.
We prove that a ""plunging"" compact object is conceptually indistinguishable
from an adiabatic, slow inspiral; plunges spend on average up to hundred of
thousands of cycles in the bandwidth of the detector for a two years mission.
This has an important impact on the event rate, enhancing in some cases
significantly, depending on the spin of the MBH and the inclination. Moreover,
it has been recently proved that the production of low-eccentricity EMRIs is
severely blocked by the presence of a blockade in the rate at which orbital
angular momenta change takes place. This is the result of relativistic
precession on to the stellar potential torques and hence affects EMRIs
originating via resonant relaxation at distances of about $\sim 10^{-2}$ pc
from the MBH. Since high-eccentricity EMRIs are a result of two-body
relaxation, they are not affected by this phenomenon. Therefore we predict that
eLISA EMRI event rates will be dominated by high-eccentricity binaries, as we
present here.",1205.4713v2
2012-10-25,Fake plunges are very eccentric real EMRIs in disguise ... they dominate the rates and are blissfully ignorant of angular momentum barriers,"The capture of a compact object in a galactic nucleus by a massive black hole
(MBH) is the best way to map space and time around it. Compact objects such as
stellar black holes on a capture orbit with a very high eccentricity have been
wrongly assumed to be lost for the system after an intense burst of radiation,
which has been described as a ""direct plunge"". We prove that these very
eccentric capture orbits spend actually a similar number of cycles in a
LISA-like detector as those with lower eccentricities if the central MBH is
spinning. Although the rates are higher for high-eccentricity EMRIs, the spin
also enhances the rates of lower-eccentricity EMRIs. This last kind have
received more attention because of the fact that high-eccentricity EMRIs were
thought to be direct plunges and thus negligible. On the other hand, recent
work on stellar dynamics has demonstrated that there seems to be a complot in
phase space acting on these lower-eccentricity captures, since their rates
decrease significantly by the presence of a blockade in the rate at which
orbital angular momenta change takes place. This so-called ""Schwarzschild
barrier"" is a result of the impact of relativistic precession on to the stellar
potential torques, and thus it affects the enhancement on lower-eccentricity
EMRIs that one would expect from resonant relaxation. We confirm and quantify
the existence of this barrier using a statitical sample of 2,500
direct-summation N-body simulations using both a post-Newtonian but also, and
for the first time, a geodesic approximation for the relativistic orbits. The
existence of the barrier prevents ""traditional EMRIs"" from approaching the
central MBH, but if the central MBH is spinning the rate will be anyway
dominated by highly-eccentric extreme-mass ratio inspirals, which insolently
ignore the presence of the barrier, because they are driven by two-body
relaxation.",1210.6983v2
2013-08-22,Viscoelastic Tidal Dissipation in Giant Planets and Formation of Hot Jupiters Through High-Eccentricity Migration,"We study the possibility of tidal dissipation in the solid cores of giant
planets and its implication for the formation of hot Jupiters through
high-eccentricity migration. We present a general framework by which the tidal
evolution of planetary systems can be computed for any form of tidal
dissipation, characterized by the imaginary part of the complex tidal Love
number, ${\rm Im}[{\tilde k}_2(\omega)]$, as a function of the forcing
frequency $\omega$. Using the simplest viscoelastic dissipation model (the
Maxwell model) for the rocky core and including the effect of a nondissipative
fluid envelope, we show that with reasonable (but uncertain) physical
parameters for the core (size, viscosity and shear modulus), tidal dissipation
in the core can accommodate the tidal-Q constraint of the Solar system gas
giants and at the same time allows exoplanetary hot Jupiters to form via tidal
circularization in the high-e migration scenario. By contrast, the often-used
weak friction theory of equilibrium tide would lead to a discrepancy between
the Solar system constraint and the amount of dissipation necessary for high-e
migration. We also show that tidal heating in the rocky core can lead to modest
radius inflation of the planets, particularly when the planets are in the
high-eccentricity phase ($e\sim 0.6$) during their high-e migration. Finally,
as an interesting by-product of our study, we note that for a generic tidal
response function ${\rm Im}[{\tilde k}_2(\omega)]$, it is possible that spin
equilibrium (zero torque) can be achieved for multiple spin frequencies (at a
given $e$), and the actual pseudo-synchronized spin rate depends on the
evolutionary history of the system.",1308.4968v2
2013-10-14,Swirling around filaments: are large-scale structure vortices spinning up dark halos?,"The kinematic analysis of dark matter and hydrodynamical simulations suggests
that the vorticity in large-scale structure is mostly confined to, and
predominantly aligned with their filaments, with an excess of probability of 20
per cent to have the angle between vorticity and filaments direction lower than
60 degrees relative to random orientations. The cross sections of these
filaments are typically partitioned into four quadrants with opposite vorticity
sign, arising from multiple flows, originating from neighbouring walls. The
spins of halos embedded within these filaments are consistently aligned with
this vorticity for any halo mass, with a stronger alignment for the most
massive structures up to an excess of probability of 165 per cent. On large
scales, adiabatic/cooling hydrodynamical simulations display the same vorticity
in the gas as in the dark matter. The global geometry of the flow within the
cosmic web is therefore qualitatively consistent with a spin acquisition for
smaller halos induced by this large-scale coherence, as argued in Codis et al.
(2012). In effect, secondary anisotropic infall (originating from the
vortex-rich filament within which these lower-mass halos form) dominates the
angular momentum budget of these halos. The transition mass from alignment to
orthogonality is related to the size of a given multi-flow region with a given
polarity. This transition may be reconciled with the standard tidal torque
theory if the latter is augmented so as to account for the larger scale
anisotropic environment of walls and filaments.",1310.3801v3
2015-01-24,Detecting gravitational waves from mountains on neutron stars in the Advanced Detector Era,"Rapidly rotating Neutron Stars (NSs) in Low Mass X-ray Binaries (LMXBs) are
thought to be interesting sources of Gravitational Waves (GWs) for current and
next generation ground based detectors, such as Advanced LIGO and the Einstein
Telescope. The main reason is that many of the NS in these systems appear to be
spinning well below their Keplerian breakup frequency, and it has been
suggested that torques associated with GW emission may be setting the observed
spin period. This assumption has been used extensively in the literature to
assess the strength of the likely gravitational wave signal. There is now,
however, a significant amount of theoretical and observation work that suggests
that this may not be the case, and that GW emission is unlikely to be setting
the spin equilibrium period in many systems. In this paper we take a different
starting point and predict the GW signal strength for two physical mechanisms
that are likely to be at work in LMXBs: crustal mountains due to thermal
asymmetries and magnetically confined mountains. We find that thermal crustal
mountains in transient LMXBs are unlikely to lead to detectable GW emission,
while persistent systems are good candidates for detection by Advanced LIGO and
by the Einstein Telescope. Detection prospects are pessimistic for the magnetic
mountain case, unless the NS has a buried magnetic field of $B\approx 10^{12}$
G, well above the typically inferred exterior dipole fields of these objects.
Nevertheless, if a system were to be detected by a GW observatory, cyclotron
resonant scattering features in the X-ray emission could be used to distinguish
between the two different scenarios.",1501.06039v1
2015-12-07,The alignment of galaxy spin with the shear field in observations,"Tidal torque theory suggests that galaxies gain angular momentum in the
linear stage of structure formation. Such a theory predicts alignments between
the spin of haloes and tidal shear field. However, non-linear evolution and
angular momentum acquisition may alter this prediction significantly. In this
paper, we use a reconstruction of the cosmic shear field from observed peculiar
velocities combined with spin axes extracted from galaxies within $115\,
\mathrm{Mpc} $ ($\sim8000 \, {\mathrm {km}}{\mathrm s}^{-1}$) from 2MRS
catalog, to test whether or not galaxies appear aligned with principal axes of
shear field. Although linear reconstructions of the tidal field have looked at
similar issues, this is the first such study to examine galaxy alignments with
velocity-shear field. Ellipticals in the 2MRS sample, show a statistically
significant alignment with two of the principal axes of the shear field. In
general, elliptical galaxies have their short axis aligned with the axis of
greatest compression and perpendicular to the axis of slowest compression.
Spiral galaxies show no signal. Such an alignment is significantly strengthened
when considering only those galaxies that are used in velocity field
reconstruction. When examining such a subsample, a weak alignment with the axis
of greatest compression emerges for spiral galaxies as well. This result
indicates that although velocity field reconstructions still rely on fairly
noisy and sparse data, the underlying alignment with shear field is strong
enough to be visible even when small numbers of galaxies are considered -
especially if those galaxies are used as constraints in the reconstruction.",1512.02236v2
2016-11-17,Testing the relativistic precession model using low frequency and kHz quasi-periodic oscillations in neutron star low mass X-ray binaries with known spin,"We analyze all available RXTE data on a sample of 13 low mass X-ray binaries
with known neutron star spin that are not persistent pulsars. We carefully
measure the correlations between the centroid frequencies of the quasi-periodic
oscillations (QPOs). We compare these correlations to the prediction of the
relativistic precession model (RPM) that, due to frame dragging, a QPO will
occur at the Lense-Thirring precession frequency $\nu_{LT}$ of a test particle
orbit whose orbital frequency is the upper kHz QPO frequency $\nu_u$. Contrary
to the most prominent previous studies, we find two different oscillations in
the range predicted for $\nu_{LT}$ that are simultaneously present over a wide
range of $\nu_u$. Additionally, one of the low frequency noise components
evolves into a (third) QPO in the $\nu_{LT}$ range when $\nu_u$ exceeds 600 Hz.
The frequencies of these QPOs all correlate to $\nu_u$ following power laws
with indices between 0.4$-$3.3, significantly exceeding the predicted value of
2.0 in 80$\%$ of the cases (at 3 to >20$\sigma$). Also, there is no evidence
that the neutron star spin frequency affects any of these three QPO frequencies
as would be expected for frame dragging. Finally, the observed QPO frequencies
tend to be higher than the $\nu_{LT}$ predicted for reasonable neutron star
specific moment of inertia. In the light of recent successes of precession
models in black holes, we briefly discuss ways in which such precession can
occur in neutron stars at frequencies different from test particle values and
consistent with those observed. A precessing torus geometry and other torques
than frame dragging may allow precession to produce the observed frequency
correlations, but can only explain one of the three QPOs in the $\nu_{LT}$
range.",1611.05860v1
2016-12-20,Inter-band Coherence Response to Electric Fields in Crystals,"In solid state conductors, linear response to a steady electric field is
normally dominated by Bloch state occupation number changes that are correlated
with group velocity and lead to a steady state current. However, for a number
of important physical observables, the most important response even in
conductors can be electric-field induced coherence between Bloch states in
different bands, such as that responsible for screening in dielectrics.
Examples include the anomalous and spin-Hall effects, spin torques, minimum
conductivities and the chiral anomaly. In this paper we present a general
quantum kinetic theory of linear response to an electric field which can be
applied to solids with arbitrarily complicated band structures and includes the
inter-band coherence response and the Bloch-state repopulation responses on an
equal footing. We aim to enable extensive transport theory applications using
computational packages based on maximally localized Wannier functions. The
formalism is based on density-matrix equations of motion, on a Born
approximation treatment of disorder, and on an expansion in scattering rate to
leading non-trivial order. The quasiparticle bands are treated in a completely
general manner that allows for arbitrary forms of the spin-orbit interaction
and for the broken time reversal symmetry of magnetic conductors. We
demonstrate that the inter-band response in conductors consists primarily of
two terms: an intrinsic contribution due to the entire Fermi sea that captures
the Berry curvature contribution to wave-packet dynamics, and an anomalous
contribution caused by scattering that is sensitive to the presence of the
Fermi surface. We solve for some electric-field response properties of simple
model systems that are known to be dominated by interband coherence
contributions and discuss an extensive list of complicated problems that cannot
be solved analytically.",1612.06865v2
2018-03-21,Linear Tidal Vestige found in the WM Sheet,"We present a vestige of the linear tidal influence on the spin orientations
of the constituent galaxies of the WM sheet discovered in the vicinity of the
Virgo cluster and the Local Void. The WM sheet is chosen as an optimal target
since it has a rectangular parallelepiped-like shape whose three sides are in
parallel with the supergalactic Cartesian axes. Determining three probability
density functions of the absolute values of the supergalactic Cartesian
components of the spin vectors of the WM sheet galaxies, we investigate their
alignments with the principal directions of the surrounding large-scale tidal
field. When the WM sheet galaxies located in the central region within the
distance of $2\,h^{-1}$Mpc are excluded, the spin vectors of the remaining WM
sheet galaxies are found to be weakly aligned, strongly aligned, and strongly
anti-aligned with the minor, intermediate and major principal directions of the
surrounding large-scale tidal field, respectively. To examine whether or not
the origin of the observed alignment tendency from the WM sheet is the linear
tidal effect, we infer the eigenvalues of the linear tidal tensor from the
axial ratios of the WM sheet with the help of the Zel'dovich approximation and
conduct a full analytic evaluation of the prediction of the linear tidal torque
model for the three probability density functions. A detailed comparison
between the analytical and the observational results reveals a good
quantitative agreement not only in the behaviors but also in the amplitudes of
the three probability density functions.",1803.07790v2
2018-11-15,Evolution of star-planet systems under magnetic braking and tidal interaction,"With the discovery over the last two decades of a large diversity of
exoplanetary systems, it is now of prime importance to characterize star-planet
interactions and how such systems evolve. We address this question by studying
systems formed by a solar-like star and a close-in planet. We focus on the
stellar wind spinning down the star along its main sequence phase and tidal
interaction causing orbital evolution of the systems. Despite recent
significant advances in these fields, all current models use parametric
descriptions to study at least one of these effects. Our objective is to
introduce simultaneously ab-initio prescriptions of the tidal and braking
torques, so as to improve our understanding of the underlying physics. We
develop a 1D numerical model of coplanar circular star-planet systems taking
into account stellar structural changes, wind braking and tidal interaction and
implement it in a code called ESPEM. We follow the secular evolution of the
stellar rotation assuming a bi-layer internal structure, and of the semi-major
axis of the orbit. After comparing our predictions to recent observations and
models, we perform tests to emphasize the contribution of ab-initio
prescriptions. Our secular model of stellar wind braking reproduces well the
recent observations of stellar rotation in open clusters. Our results show that
a planet can affect the rotation of its host star and that the resulting
spin-up or spin-down depends on the orbital semi-major axis and on the joint
influence of magnetic and tidal effects. The ab-initio prescription for tidal
dissipation that we used predicts fast outward migration of massive planet
orbiting fast-rotating young stars. Finally, we provide the reader with a
criterion based on the system's characteristics that allows us to assess
whether or not the planet will undergo orbital decay due to tidal interaction.",1811.06354v1
2020-03-24,The unusual behaviour of the young X-ray pulsar SXP 1062 during the 2019 outburst,"We present results of the first dedicated observation of the young X-ray
pulsar SXP 1062 in the broad X-ray energy band obtained during its 2019
outburst with the NuSTAR and XMM-Newton observatories. The analysis of the
pulse-phase averaged and phase-resolved spectra in the energy band from 0.5 to
70 keV did not reveal any evidence for the presence of a cyclotron line. The
spin period of the pulsar was found to have decreased to 979.48+/-0.06 s
implying a ~10% reduction compared to the last measured period during the
monitoring campaign conducted about five years ago, and is puzzling considering
that the system apparently did not show major outbursts ever since. The switch
of the pulsar to the spin-up regime supports the common assumption that torques
acting on the accreting neutron star are nearly balanced and thus SXP 1062
likely also spins with a period close to the equilibrium value for this system.
The current monitoring of the source revealed also a sharp drop of its soft
X-ray flux right after the outburst, which is in drastic contrast to the
behaviour during the previous outburst when the pulsar remained observable for
years with only a minor flux decrease after the end of the outburst. This
unexpected off state of the source lasted for at most 20 days after which SXP
1062 returned to the level observed during previous campaigns. We discuss this
and other findings in context of the modern models of accretion onto strongly
magnetized neutron stars.",2003.11030v1
2020-08-14,Bond Directional Anapole Order in a Spin-Orbit Coupled Mott Insulator Sr$_2$(Ir$_{1-x}$Rh$_x$)O$_{4}$,"An anapole state that breaks inversion and time reversal symmetries with
preserving translation symmetry of underlying lattice has aroused great
interest as a new quantum state, but only a few candidate materials have been
reported. Recently, in a spin-orbit coupled Mott insulator \SIR, the emergence
of a possible hidden order phase with broken inversion symmetry has been
suggested at $T_{\Omega}$ above the N\'{e}el temperature by optical second
harmonic generation measurements. Moreover, polarized neutron diffraction
measurements revealed the broken time reversal symmetry below $T_{\Omega}$,
which was supported by subsequent muon spin relaxation experiments. However,
the nature of this mysterious phase remains largely elusive. Here, we
investigate the hidden order phase through the combined measurements of the
in-plane magnetic anisotropy with exceptionally high-precision magnetic torque
and the nematic susceptibility with elastoresistance. A distinct two-fold
in-plane magnetic anisotropy along the [110] Ir-O-Ir bond direction sets in
below $\sim T_{\Omega}$, providing thermodynamic evidence for a nematic phase
transition with broken $C_4$ rotational symmetry. However, in contrast to the
even-parity nematic transition reported in other correlated electron systems,
the nematic susceptibility exhibits no divergent behavior towards $T_{\Omega}$.
These results provide bulk evidence for an odd-parity order parameter with
broken rotational symmetry in the hidden order state. We discuss the hidden
order in terms of an anapole state, in which polar toroidal moment is induced
by two current loops in each IrO$_6$ octahedron of opposite chirality. Contrary
to the simplest loop-current pattern previously suggested, the present results
are consistent with a pattern in which the intra-unit cell loop-current flows
along only one of the diagonal directions in the IrO$_4$ square.",2008.06380v1
2020-08-16,Binary Black Hole Mergers from LIGO/Virgo O1 and O2: Population Inference Combining Confident and Marginal Events,"We perform a statistical inference of the astrophysical population of binary
black hole (BBH) mergers observed during the first two observing runs of
Advanced LIGO and Advanced Virgo, including events reported in the GWTC-1 and
IAS catalogs. We derive a novel formalism to fully and consistently account for
events of arbitrary significance. We carry out a software injection campaign to
obtain a set of mock astrophysical events subject to our selection effects, and
use the search background to compute the astrophysical probabilities $p_{\rm
astro}$ of candidate events for several phenomenological models of the BBH
population. We emphasize that the values of $p_{\rm astro}$ depend on both the
astrophysical and background models. Finally, we combine the information from
individual events to infer the rate, spin, mass, mass-ratio and redshift
distributions of the mergers. The existing population does not discriminate
between random spins with a spread in the effective spin parameter, and a small
but nonzero fraction of events from tidally-torqued stellar progenitors. The
mass distribution is consistent with one having a cutoff at $m_{\rm max} =
41^{+10}_{-5}\,\rm M_\odot$, while the mass ratio favors equal masses; the mean
mass ratio $\bar q> 0.67$. The rate shows no significant evolution with
redshift. We show that the merger rate restricted to BBHs with a primary mass
between 20 and $30\, \rm M_\odot$, and a mass ratio $q > 0.5$, and at $z \sim
0.2$, is 1.5 to $5.3\,{\rm Gpc^{-3} yr^{-1}}$ (90\% c.l.); these bounds are
model independent and a factor of $\sim 3$ tighter than that on the local rate
of all BBH mergers, and hence are a robust constraint on all progenitor models.
Including the events in our catalog increases the Fisher information about the
BBH population by $\sim 47\%$, and tightens the constraints on population
parameters.",2008.07014v2
2020-10-23,"Superorbital Modulation in the High-Mass X-ray Binary 4U 1538-52, and Possible Modulation in IGR J16393-4643","Hard X-ray observations with the Neil Gehrels Swift Observatory Burst Alert
Telescope (BAT) reveal superorbital modulation in the wind-accreting supergiant
high-mass X-ray binary (HMXB) 4U 1538-52 at a period of 14.9130 +/- 0.0026 days
that is consistent with four times the 3.73 day orbital period. These periods
agree with a previously suggested correlation between superorbital and orbital
periods in similar HMXBs. During the ~14 years of observations the superorbital
modulation changes amplitude, and since ~MJD 57,650 it was no longer detected
in the power spectrum, although a peak near the second harmonic of this was
present for some time. Measurements of the spin period of the neutron star in
the system with the Fermi Gamma-ray Burst Monitor show a long-term spin-down
trend which halted towards the end of the light curve, suggesting a connection
between dP(spin)/dt and superorbital modulation, as proposed for 2S 0114+650.
However, an earlier torque reversal from INTEGRAL observations was not
associated with superorbital modulation changes. B and V band photometry from
the Las Cumbres Observatory reveals orbital ellipsoidal photometric
variability, but no superorbital optical modulation. However the photometry was
obtained when the 14.9130 day period was no longer detected in the BAT power
spectrum. We revisit possible superorbital modulation in BAT observations of
IGR J16393-4643 but cannot conclusively determine whether this is present,
although is not persistent. We consider superorbital modulation mechanisms, and
suggest that the Corotating Interaction Region model, with small deviations
from orbital synchronization, appears promising.",2010.12556v1
2021-01-04,Search for axion-like dark matter using solid-state nuclear magnetic resonance,"We report the results of an experimental search for ultralight axion-like
dark matter in the mass range 162 neV to 166 neV. The detection scheme of our
Cosmic Axion Spin Precession Experiment (CASPEr) is based on a precision
measurement of $^{207}$Pb solid-state nuclear magnetic resonance in a polarized
ferroelectric crystal. Axion-like dark matter can exert an oscillating torque
on $^{207}$Pb nuclear spins via the electric-dipole moment coupling $g_d$, or
via the gradient coupling $g_{\text{aNN}}$. We calibrated the detector and
characterized the excitation spectrum and relaxation parameters of the nuclear
spin ensemble with pulsed magnetic resonance measurements in a 4.4 T magnetic
field. We swept the magnetic field near this value and searched for axion-like
dark matter with Compton frequency within a 1 MHz band centered at 39.65 MHz.
Our measurements place the upper bounds
$|g_d|<9.5\times10^{-4}\,\text{GeV}^{-2}$ and
$|g_{\text{aNN}}|<2.8\times10^{-1}\,\text{GeV}^{-1}$ (95% confidence level) in
this frequency range. The constraint on $g_d$ corresponds to an upper bound of
$1.0\times 10^{-21}\,\text{e}\cdot\text{cm}$ on the amplitude of oscillations
of the neutron electric dipole moment, and $4.3\times 10^{-6}$ on the amplitude
of oscillations of CP-violating $\theta$ parameter of quantum chromodynamics.
Our results demonstrate the feasibility of using solid-state nuclear magnetic
resonance to search for axion-like dark matter in the nano-electronvolt mass
range.",2101.01241v3
2021-03-24,Timing and Spectral Studies of the X-ray Pulsar 2S 1417$-$624 During the Outburst in 2021,"We study the timing and spectral properties of the X-ray pulsar 2S 1417--624
during the recent outburst in January 2021 based on the Neutron Star Interior
Composition Explorer (NICER) observation. We also used some early data from the
2018 outburst to compare different temporal and spectral properties. The
evolution of the spin period and pulsed flux is studied with Fermi/GBM during
the outburst and the spin-up rate is found to be varied between
$\simeq(0.8-1.8)\times 10^{-11}$ Hz s$^{-1}$. The pulse profile shows energy
dependence and variability. The pulse profile shows multiple peaks and dips
which evolve with energy. The evolution of the spectral state of this source is
also studied using the hardness intensity diagram (HID). The HID shows a
transition from the horizontal to the diagonal branch, which implies the source
went through a state transition from the subcritical to supercritical accretion
regime. The NICER energy spectrum is well described by a composite model of a
power-law with a higher cut-off energy and blackbody components along with a
photo-electric absorption component. An iron emission line is detected near 6.4
keV in the NICER spectrum with an equivalent width of $\sim$0.05 keV. The
photon index shows an anti-correlation with flux below the critical flux. The
mass accretion rate is estimated to be $\simeq1.3\times10^{17}$ g s$^{-1}$ near
the peak of the outburst. We have found a positive correlation between the
pulse frequency derivatives and luminosity. The Ghosh and Lamb model is applied
to estimate the magnetic field at different spin-up rates, which is compared to
the earlier estimated magnetic field at a relatively high mass accretion rate.
The magnetic field is estimated to be $\simeq10^{14}$ G from the
torque-luminosity model using the distance estimated by Gaia, which is
comparatively higher than most of the other Be/XBPs.",2103.13444v4
2021-05-18,Computational Micromagnetics based on Normal Modes: bridging the gap between macrospin and full spatial discretization,"The Landau-Lifshitz equation governing magnetization dynamics is written in
terms of the amplitudes of normal modes associated with the micromagnetic
system's appropriate ground state. This results in a system of nonlinear
ordinary differential equations (ODEs), the right-hand side of which can be
expressed as the sum of a linear term and nonlinear terms with increasing order
of nonlinearity (quadratic, cubic, etc.). The application of the method to
nanostructured magnetic systems demonstrates that the accurate description of
magnetization dynamics requires a limited number of normal modes, which results
in a considerable improvement in computational speed. The proposed method can
be used to obtain a reduced-order dynamical description of magnetic
nanostructures which allows to adjust the accuracy between low-dimensional
models, such as macrospin, and micromagnetic models with full spatial
discretization. This new paradigm for micromagnetic simulations is tested for
three problems relevant to the areas of spintronics and magnonics: directional
spin-wave coupling in magnonic waveguides, high power ferromagnetic resonance
in a magnetic nanodot, and injection-locking in spin-torque nano-oscillators.
The case studies considered demonstrate the validity of the proposed approach
to systematically obtain an intermediate order dynamical model based on normal
modes for the analysis of magnetic nanosystems. The time-consuming calculation
of the normal modes has to be done only one time for the system. These modes
can be used to optimize and predict the system response for all possible
time-varying external excitations (magnetic fields, spin currents). This is of
utmost importance for applications where fast and accurate system simulations
are required, such as in electronic circuits including magnetic devices.",2105.08829v2
2021-07-06,KAM quasi-periodic tori for the dissipative spin-orbit problem,"We provide evidence of the existence of KAM quasi-periodic attractors for a
dissipative model in Celestial Mechanics. We compute the attractors extremely
close to the breakdown threshold.
  We consider the spin-orbit problem describing the motion of a triaxial
satellite around a central planet under the simplifying assumption that the
center of mass of the satellite moves on a Keplerian orbit, the spin-axis is
perpendicular to the orbit plane and coincides with the shortest physical axis.
We also assume that the satellite is non-rigid; as a consequence, the problem
is affected by a dissipative tidal torque that can be modeled as a
time-dependent friction, which depends linearly upon the velocity.
  Our goal is to fix a frequency and compute the embedding of a smooth
attractor with this frequency. This task requires to adjust a drift parameter.
  The goal of this paper is to provide numerical calculations of the condition
numbers and verify that, when they are applied to the numerical solutions, they
will lead to the existence of the torus for values of the parameters extremely
close to the parameters of breakdown. Computing reliably close to the breakdown
allows to discover several interesting phenomena, which we will report in
[CCGdlL20a].
  The numerical calculations of the condition numbers presented here are not
completely rigorous, since we do not use interval arithmetic to estimate the
round off error and we do not estimate rigorously the truncation error, but we
implement the usual standards in numerical analysis (using extended precision,
checking that the results are not affected by the level of precision,
truncation, etc.). Hence, we do not claim a computer-assisted proof, but the
verification is more convincing that standard numerics. We hope that our work
could stimulate a computer-assisted proof.",2107.02853v1
2022-11-11,A Non-Volatile All-Spin Non-Binary Matrix Multiplier: An Efficient Hardware Accelerator for Machine Learning,"We propose and analyze a compact and non-volatile nanomagnetic (all-spin)
non-binary matrix multiplier performing the multiply-and-accumulate (MAC)
operation using two magnetic tunnel junctions - one activated by strain to act
as the multiplier, and the other activated by spin-orbit torque pulses to act
as a domain wall synapse that performs the operation of the accumulator. It has
two advantages over the usual crossbar-based electronic non-binary matrix
multiplier. First, while the crossbar architecture requires N3 devices to
multiply two matrices, we require only 2N2 devices. Second, our matrix
multiplier is non-volatile and retains the information about the product matrix
after being powered off. Here, we present an example where each MAC operation
can be performed in ~5 ns and the maximum energy dissipated per operation is
~60Nmax aJ, where Nmax is the largest matrix size. This provides a very useful
hardware accelerator for machine learning and artificial intelligence tasks
which involve the multiplication of large matrices. The non-volatility allows
the matrix multiplier to be embedded in powerful non-von-Neumann architectures,
including processor-in-memory. It also allows much of the computing to be done
at the edge (of internet-of-things) while reducing the need to access the
cloud, thereby making artificial intelligence more resilient against
cyberattacks.",2211.06490v3
2022-12-02,Rimmed and Rippled Accretion Disc Models to Explain AGN Continuum Lags,"We propose a solution to the problem of accretion disc sizes in active
galactic nuclei being larger when measured by reverberation mapping than
predicted by theory. Considering blackbody reprocessing on a disc with
thickness profile $H(r)$, our solution invokes a steep rim or rippled
structures irradiated by the central lamp-post. We model the continuum lags and
the faint and bright disc spectral energy distribution (SED) in the
best-studied case NGC 5548 (black hole mass $M = 7\times10^{7} M_\odot$, disc
inclination $i=45^\circ$). With the lamp-post off, the observed disc SED
requires a low accretion rate ($\dot{M} \sim 0.0014 M_\odot$/yr) and high
prograde black hole spin ($a \sim 0.93$). Reprocessing on the thin disc gives
time lags increasing with wavelength but 3 times smaller than observed.
Introducing a steep $H(r)$ rim, or multiple crests, near $r = 5$ light days,
reprocessing on their steep centre-facing slopes increases temperatures from
$\sim1500$ K to $\sim6000$ K and this increases optical lags to match the lag
data. Most of the disc surface maintains the cooler $T\propto r^{-3/4}$
temperature profile that matches the SED. The bright lamp-post may be powered
by magnetic links tapping the black hole spin. The steep rim occurs near the
sublimation radius for dust in the disc, as in the ""failed disc wind model"" for
broad-line clouds. Lens-Thirring torques aligning the disc and black hole spin
may also raise a warp and associated waves. In both scenarios, the small
density scale height implied by the inferred value of $H(r)$ suggests possible
marginal gravitational instability in the disc.",2212.01379v1
2022-12-19,Timing analysis of the 2022 outburst of the accreting millisecond X-ray pulsar SAX J1808.4$-$3658: hints of an orbital shrinking,"We present a pulse timing analysis of NICER observations of the accreting
millisecond X-ray pulsar SAX J1808.4$-$3658 during the outburst that started on
2022 August 19. Similar to previous outbursts, after decaying from a peak
luminosity of $\simeq 1\times10^{36} \, \mathrm{erg \, s^{-1}}$ in about a
week, the pulsar entered in a $\sim 1$ month-long reflaring stage. Comparison
of the average pulsar spin frequency during the outburst with those previously
measured confirmed the long-term spin derivative of
$\dot{\nu}_{\textrm{SD}}=-(1.15\pm0.06)\times 10^{-15} \, \mathrm{Hz\,s^{-1}}$,
compatible with the spin-down torque of a $\approx 10^{26} \, \mathrm{G \,
cm^3}$ rotating magnetic dipole. For the first time in the last twenty years,
the orbital phase evolution shows evidence for a decrease of the orbital
period. The long-term behaviour of the orbit is dominated by a $\sim 11 \,
\mathrm{s}$ modulation of the orbital phase epoch consistent with a $\sim 21 \,
\mathrm{yr}$ period. We discuss the observed evolution in terms of a coupling
between the orbit and variations in the mass quadrupole of the companion star.",2212.09778v2
2023-09-19,Impact of strain on the SOT-driven dynamics of thin film Mn$_3$Sn,"Mn$_3$Sn, a metallic antiferromagnet with an anti-chiral 120$^\circ$ spin
structure, generates intriguing magneto-transport signatures such as a large
anomalous Hall effect, spin-polarized current with novel symmetries, anomalous
Nernst effect, and magneto-optic Kerr effect. When grown epitaxially as
MgO(110)[001]$\parallel$ Mn$_3$Sn($0\bar{1}\bar{1}0$)[0001], Mn$_3$Sn
experiences a uniaxial tensile strain, which changes the bulk six-fold
anisotropy landscape to a perpendicular magnetic anisotropy with two stable
states. In this work, we investigate the field-assisted spin orbit-torque
(SOT)-driven response of the order parameter in single-domain Mn$_3$Sn with
uniaxial tensile strain. We find that for a non-zero external magnetic field,
the order parameter can be switched between the two stable states if the
magnitude of the input current is between two field-dependent critical
currents. Below the lower critical current, the order parameter exhibits a
stationary state in the vicinity of the initial stable state. On the other
hand, above the higher critical current, the order parameter shows oscillatory
dynamics which could be tuned from the 100's of megahertz to the gigahertz
range. We obtain approximate expressions of the two critical currents and find
them to agree very well with the numerical simulations for experimentally
relevant magnetic fields. We also obtain unified functional form of the
switching time versus the input current for different magnetic fields. Finally,
we show that for lower values of Gilbert damping ($\alpha \leq 2\times
10^{-3}$), the critical currents and the final steady states depend
significantly on the damping constant. The numerical and analytic results
presented in our work can be used by both theorists and experimentalists to
understand the SOT-driven order dynamics in PMA Mn$_3$Sn and design future
experiments and devices.",2309.10246v2
2023-10-08,Floquet-engineering the exceptional points in parity-time-symmetric magnonics,"Magnons serve as a testing ground for fundamental aspects of Hermitian and
non-Hermitian wave mechanics and are of high relevance for information
technology. This study presents setups for realizing spatio-temporally driven
parity-time (PT) symmetric magnonics based on coupled magnetic waveguides and
magnonic crystals. A charge current in a metal layer with strong spin-orbit
coupling sandwiched between two insulating magnetic waveguides leads to gain or
loss in the magnon amplitude depending on the directions of the magnetization
and the charge currents. When gain in one waveguide is balanced by loss in the
other waveguide a PT-symmetric system hosting non-Hermitian degeneracies (or
exceptional points (EPs)) is realized. For AC current multiple EPs appear for a
certain gain/loss strength and mark the boundaries between the preserved
PT-symmetry and the broken PT-symmetry phases. The number of islands of broken
PT-symmetry phases and their extensions is tunable by the frequency and the
strength of the spacer current. At EP and beyond, the induced and amplified
magnetization oscillations are strong and self-sustained. In particular, these
magnetization auto-oscillations in broken PT-symmetry phase occur at low
current densities and do not require further adjustments such as tilt angle
between electric polarization and equilibrium magnetization direction in
spin-torque oscillators, pointing to a new design of these oscillators and
their utilization in computing and sensoric. It is also shown how the periodic
gain/loss mechanism allows for the generation of high-frequency spin waves with
low-frequency currents. For spatially-periodic gain/loss acting on a magnonic
crystal, magnon modes approaching each other at the Brillouin-zone boundaries
are highly susceptible to PT-symmetry, allowing for a wave-vector-resolved
experimental realization at very low currents.",2310.09300v1
2014-02-13,Angular Momentum Exchange in White Dwarf Binaries Accreting Through Direct Impact,"We examine the exchange of angular momentum between the component spins and
the orbit in semi-detached double white dwarf binaries undergoing mass transfer
through direct impact of the transfer stream. We approximate the stream as a
series of discrete massive particles ejected in the ballistic limit at the
inner Lagrangian point of the donor toward the accretor. This work improves
upon similar earlier studies in a number of ways. First, we self-consistently
calculate the total angular momentum of the orbit at all times. This includes
changes in the orbital angular momentum during the ballistic trajectory of the
ejected mass, as well as changes during the ejection/accretion due to the
radial component of the particle's velocity. Second, we calculate the
particle's ballistic trajectory for each system, which allows us to determine
the precise position and velocity of the particle upon accretion. We can then
include specific information about the radius of the accretor as well as the
angle of impact. Finally, we ensure that the total angular momentum is
conserved, which requires the donor star spin to vary self-consistently. We
calculate the angular momentum change of the orbit and each binary component
across the entire parameter space of direct impact double white dwarf binaries.
We find a significant decrease in the amount of angular momentum removed from
the orbit during mass transfer, as well as cases where this process increases
the angular momentum of the orbit at the expense of the spin angular momentum
of the donor. We conclude that, unlike earlier claims in the literature, mass
transfer through direct impact need not destabilize the binary and that the
quantity and sign of the orbital angular momentum transfer depends on the
binary properties. This stabilization may significantly impact the population
synthesis calculations of double white dwarf progenitors.",1402.3161v1
2013-01-10,Type I planet migration in weakly magnetised laminar discs,"[Abridged] The migration of low mass planets has been studied in
hydrodynamical disc models for more than three decades, but the impact of a
magnetic field in the protoplanetary disc is less known. When the disc's
magnetic field is strong enough to prevent horseshoe motion, the corotation
torque is replaced by a torque arising from magnetic resonances. For weak
enough magnetic fields, horseshoe motion and a corotation torque exist, and
recent turbulent MHD simulations have reported the existence of a new component
of the corotation torque in the presence of a mean toroidal field. The aim of
this paper is to investigate the physical origin and the properties of this new
corotation torque. We performed MHD simulations of a low mass planet embedded
in a 2D laminar disc threaded by a weak toroidal magnetic field, with the
effects of turbulence modelled by a viscosity and a resistivity. We confirm
that the interaction between the magnetic field and the horseshoe motion
results in an additional corotation torque on the planet, which we dub the MHD
torque excess. It is caused by the accumulation of the magnetic field along the
downstream separatrices of the planet's horseshoe region, which gives rise to
an azimuthally asymmetric underdense region at that location. The properties of
the MHD torque excess are characterised by varying the slope of the density,
temperature and magnetic field profiles, as well as the diffusion coefficients
and the strength of the magnetic field. The sign of the MHD torque excess
depends on the density and temperature gradients only, and is positive for
profiles expected in protoplanetary discs. Its magnitude is in turn mainly
determined by the strength of the magnetic field and the turbulent resistivity.
The MHD torque excess can be strong enough to reverse migration, even when the
magnetic pressure is less than one percent of the thermal pressure.",1301.2337v1
2013-07-09,"Investigations of the torque anomaly in an annular sector. II. Global calculations, electromagnetic case","Recently, it was suggested that there was some sort of breakdown of quantum
field theory in the presence of boundaries, manifesting itself as a torque
anomaly. In particular, Fulling et al. used the finite energy-momentum-stress
tensor in the presence of a perfectly conducting wedge, calculated many years
ago by Deutsch and Candelas, to compute the torque on one of the wedge
boundaries, where the latter was cutoff by integrating the torque density down
to minimum lower radius greater than zero. They observed that that torque is
not equal to the negative derivative of the energy obtained by integrating the
energy density down to the same minimum radius. This motivated a calculation of
the torque and energy in an annular sector obtained by the intersection of the
wedge with two coaxial cylinders. In a previous paper we showed that for the
analogous scalar case, which also exhibited a torque anomaly in the absence of
the cylindrical boundaries, the point-split regulated torque and energy indeed
exhibit an anomaly, unless the point-splitting is along the axis direction. In
any case, because of curvature divergences, no unambiguous finite part can be
extracted. However, that ambiguity is linear in the wedge angle; if the
condition is imposed that the linear term be removed, the resulting torque and
energy is finite, and exhibits no anomaly. In this paper, we demonstrate the
same phenomenon takes place for the electromagnetic field, so there is no
torque anomaly present here either. This is a nontrivial generalization, since
the anomaly found by Fulling et al. is linear for the Dirichlet scalar case,
but nonlinear for the conducting electromagnetic case.",1307.2535v1
2017-08-18,Low mass planet migration in magnetically torqued dead zones - I. Static migration torque,"Motivated by models suggesting that the inner planet forming regions of
protoplanetary discs are predominantly lacking in viscosity-inducing
turbulence, and are possibly threaded by Hall-effect generated large-scale
horizontal magnetic fields, we examine the dynamics of the corotation region of
a low-mass planet in such an environment. The corotation torque in an inviscid,
isothermal, dead zone ought to saturate, with the libration region becoming
both symmetrical and of a uniform vortensity, leading to fast inward migration
driven by the Lindblad torques alone. However, in such a low viscosity
situation, the material on librating streamlines essentially preserves its
vortensity. If there is relative radial motion between the disc gas and the
planet, the librating streamlines will no longer be symmetrical. Hence, if the
gas is torqued by a large scale magnetic field so that it undergoes a net
inflow or outflow past the planet, driving evolution of the vortensity and
inducing asymmetry of the corotation region, the corotation torque can grow,
leading to a positive torque. In this paper we treat this effect by applying a
symmetry argument to the previously studied case of a migrating planet in an
inviscid disc. Our results show that the corotation torque due to a laminar
Hall-induced magnetic field in a dead zone behaves quite differently from that
studied previously for a viscous disc. Furthermore, the magnetic field induced
corotation torque and the dynamical corotation torque in a low viscosity disc
can be regarded as one unified effect.",1708.05721v2
2020-04-02,Influence of migration models and thermal torque on planetary growth in the pebble accretion scenario,"Low-mass planets that are in the process of growing larger within
protoplanetary disks exchange torques with the disk and change their semi-major
axis accordingly. This process is called type I migration and is strongly
dependent on the underlying disk structure. As a result, there are many
uncertainties about planetary migration in general. In a number of simulations,
the current type I migration rates lead to planets reaching the inner edge of
the disk within the disk lifetime. A new kind of torque exchange between planet
and disk, the thermal torque, aims to slow down inward migration via the
heating torque. The heating torque may even cause planets to migrate outwards,
if the planetary luminosity is large enough. Here, we study the influence on
planetary migration of the thermal torque on top of previous type I models. We
find that the formula of Paardekooper et al. (2011) allows for more outward
migration than that of Jim\'enez & Masset (2017) in most configurations, but we
also find that planets evolve to very similar mass and final orbital radius
using both formulae in a single planet-formation scenario, including pebble and
gas accretion. Adding the thermal torque can introduce new, but small, regions
of outwards migration if the accretion rates onto the planet correspond to
typical solid accretion rates following the pebble accretion scenario. If the
accretion rates onto the planets become very large, as could be the case in
environments with large pebble fluxes (e.g., high-metallicity environments),
the thermal torque can allow more efficient outward migration. However, even
then, the changes for the final mass and orbital positions in our planet
formation scenario are quite small. This implies that for single planet
evolution scenarios, the influence of the heating torque is probably
negligible.",2004.00874v1
2020-11-03,Simultaneous three-axis torque measurements of micromagnetism,"Measurements of magnetic torque are most commonly preformed about a single
axis or component of torque. Such measurements are very useful for hysteresis
measurements of thin film structures in particular, where high shape anisotropy
yields a near-proportionality of in-plane magnetic moment and the magnetic
torque along the perpendicular in-plane axis. A technique to measure the full
magnetic torque vector (three orthogonal torque components) on micro- and
nano-scale magnetic materials is introduced. The method is demonstrated using a
modified, single-paddle silicon-on-insulator resonant torque sensor. The
mechanical compliances to all three orthogonal torque components are maximized
by clamping the sensor at a single point. Mechanically-resonant AC torques are
driven by an RF field containing a frequency component for each fundamental
torsional mode of the device, and the resulting displacements read out through
optical position-sensitive detection. The measurements are compared with
micromagnetic simulations of the mechanical torque to augment the
interpretation of the signals. As an application example, simultaneous
observations of hysteresis in the net magnetization along with the
field-dependent in-plane anisotropy is highly beneficial for studies of
exchange bias.",2011.01463v1
2017-11-29,Quantitative wave function analysis for excited states of transition metal complexes,"The character of an electronically excited state is one of the most important
descriptors employed to discuss the photophysics and photochemistry of
transition metal complexes. In transition metal complexes, the interaction
between the metal and the different ligands gives rise to a rich variety of
excited states, including metal-centered, intra-ligand, metal-to-ligand charge
transfer, ligand-to-metal charge transfer, and ligand-to-ligand charge transfer
states. Most often, these excited states are identified by considering the most
important wave function excitation coefficients and inspecting visually the
involved orbitals. This procedure is tedious, subjective, and imprecise.
Instead, automatic and quantitative techniques for excited-state
characterization are desirable. In this contribution we review the concept of
charge transfer numbers---as implemented in the TheoDORE package---and show its
wide applicability to characterize the excited states of transition metal
complexes. Charge transfer numbers are a formal way to analyze an excited state
in terms of electron transitions between groups of atoms based only on the
well-defined transition density matrix. Its advantages are many: it can be
fully automatized for many excited states, is objective and reproducible, and
provides quantitative data useful for the discussion of trends or patterns. We
also introduce a formalism for spin-orbit-mixed states and a method for
statistical analysis of charge transfer numbers. The potential of this
technique is demonstrated for a number of prototypical transition metal
complexes containing Ir, Ru, and Re. Topics discussed include orbital
delocalization between metal and carbonyl ligands, nonradiative decay through
metal-centered states, effect of spin-orbit couplings on state character, and
comparison among results obtained from different electronic structure methods.",1711.10707v2
2021-04-15,Interplay of charge noise and coupling to phonons in adiabatic electron transfer between quantum dots,"Long-distance transfer of quantum information in architectures based on
quantum dot spin qubits will be necessary for their scalability. One way of
achieving it is to simply move the electron between two quantum registers.
Precise control over the electron shuttling through a chain of tunnel-coupled
quantum dots is possible when interdot energy detunings are changed
adiabatically. Deterministic character of shuttling is however endangered by
coupling of the transferred electron to thermal reservoirs: sources of
fluctuations of electric fields, and lattice vibrations. We theoretically
analyse how the electron transfer between two quantum dots is affected by
electron-phonon scattering, and interaction with sources of $1/f$ and Johnson
charge noise in both detuning and tunnel coupling. The electron-phonon
scattering turns out to be irrelevant in Si quantum dots, while a competition
between the effects of charge noise and Landau-Zener effect leads to an
existence of optimal detuning sweep rate, at which probability of leaving the
electron behind is minimal. In GaAs quantum dots, on the other hand, coupling
to phonons is strong enough to make the phonon-assisted processes of interdot
transfer dominate over influence of charge noise. The probability of leaving
the electron behind depends then monotonically on detuning sweep rate, and
values much smaller than in silicon can be obtained for slow sweeps. However,
after taking into account limitations on transfer time imposed by need for
preservation of electron's spin coherence, minimal probabilities of leaving the
electron behind in both GaAs- and Si-based double quantum dots turn out to be
of the same order of magnitude. Bringing them down below $10^{-3}$ requires
temperatures $\leq \! 100$ mK and tunnel couplings above $20$ $\mu$eV.",2104.07581v1
2003-10-16,The Different Fates of a Low-Mass X-ray Binary. I: Conservative Mass Transfer,"We study the evolution of a low mass x-ray binary coupling a binary stellar
evolution code with a general relativistic code that describes the behavior of
the neutron star. We assume the neutron star to be low--magnetized (B~10^8 G).
In the systems investigated in this paper, our computations show that during
the binary evolution the companion transfers as much as 1 solar mass to the
neutron star, with an accretion rate of 10^-9 solar masses/yr. This is
sufficient to keep the inner rim of the accretion disc in contact with the
neutron star surface, thus preventing the onset of a propeller phase capable of
ejecting a significant fraction of the matter transferred by the companion. We
find that, for neutron stars governed by equations of state from soft up to
moderately stiff, an accretion induced collapse to a black hole is almost
unavoidable. The collapse to a black hole can occur either during the accretion
phase or after the end of the mass transfer when the neutron star is left in a
supramassive sequence. In this last case the collapse is driven by energy
losses of the fast spinning radio pulsar. For extremely supramassive neutron
stars these energy losses cause a spin up. As a consequence the pulsar will
have a much shorter lifetime than that of a canonical radio pulsar. This
behavior depends on the equation of state for ultra-dense matter and therefore
could be used to constrain the internal structure of the neutron star. If the
r-modes of the neutron star are excited during the accretion process, the
gravitational waves emisson limits the maximum spin attainable by a NS to
roughly 2 ms. In this case the collapse during the accretion phase is even more
common since the maximum mass achievable before the collapse to a black hole
during accretion is smaller due to the limited spin frequency.",0310463v1
1994-10-10,A Hybrid Method for Global Updates in Monte Carlo Study,"We propose a new algorithm which works effectively in global updates in Monte
Carlo study. We apply it to the quantum spin chain with next-nearest-neighbor
interactions. We observe that Monte Carlo results are in excellent agreement
with numerically exact ones obtained by the transfer matrix method.",9410027v1
2004-09-03,Helicoidal ordering in iron perovskites,"We consider magnetic ordering in materials with negative charge transfer
energy, such as iron perovskite oxides. We show that for a large weight of
oxygen holes in conduction bands, the double exchange mechanism favors a
helicoidal rather than ferromagnetic spin ordering both in metals, e.g. SrFeO_3
and insulators with a small gap, e.g. CaFeO_3. We discuss the magnetic
excitation spectrum and effects of pressure on magnetic ordering in these
materials.",0409068v1
2005-07-28,Electron Transport in Double Quantum Dot governed by Nuclear Magnetic Field,"We investigate theoretically electron transfer in a doble dot in a situation
where it is governed by nuclear magnetic field: This has been recently achieved
in experiment. We show how to partially compensate the nuclear magnetic field
to restore Spin Blockade.",0507680v1
2002-07-08,Gravitational deflection of light and helicity asymmetry,"The helicity modification of light polarization which is induced by the
gravitational deflection from a classical heavy rotating body, like a star or a
planet, is considered. The expression of the helicity asymmetry is derived;
this asymmetry signals the gravitationally induced spin transfer from the
rotating body to the scattered photons.",0207036v1
1995-06-01,Inclusive and Exclusive Semi-Leptonic Decays of $B$ Mesons,"In this paper, the semileptonic decays of heavy mesons are treated fully
relativistically. By means of an effective vertex, the effect of Fermi momentum
are included both at the inclusive and at the exclusive levels, and the spin of
both parent and daughter particles are taken into account. The differential
decay rates with respect to the lepton energy and momentum transfer are
compared with data from ARGUS and CLEO.",9506213v1
1999-09-06,The (BFKL) Pomeron-virtual photon-photon vertex for any conformal spin,"To study diffractive photon production at HERA, we compute the projection of
the virtual photon-photon impact-factor on the BFKL leading-order
eigenfunctions E(n,nu) for non-zero transfer. This calculation supplements
former ones performed for n=0. We provide an expression for n=+/-2 and check
that all the other components are zero.",9909263v1
1999-09-28,Exclusive meson production at COMPASS,"We explore the feasibility to study exclusive meson production (EMP) in hard
muon-proton scattering at the COMPASS experiment. These measurements constrain
the off-forward parton distributions (OFPD's) of the proton, which are related
to the quark orbital contribution to the proton spin.",9909534v1
2001-11-02,Form of analyzing power and the determination of the basic parameters of hadron scattering amplitude,"The determination of magnitudes of basic parameters of the high energy
elastic scattering amplitude are examined at small momentum transfers with
taking account of the Coulomb-hadron interference effects.",0111023v1
2006-11-21,Exceptional and non-exceptional contributions to the radiative πdecay,"We have studied the spin-one resonance dominated form factors governing the
radiative decay of the \pi, within the framework of resonance chiral theory. We
obtain predictions for their value at zero momentum transfer and also a
description of their q^2 dependence.",0611282v1
1993-05-14,Teleportation of Quantum States,"Bennett et al. (PRL 70, 1859 (1993)) have shown how to transfer (""teleport"")
an unknown spin quantum state by using prearranged correlated quantum systems
and transmission of classical information. I will show how their results can be
obtained in the framework of nonlocal measurements proposed by Aharonov and
Albert I will generalize the latter to the teleportation of a quantum state of
a system with continuous variables.",9305062v1
2003-04-09,Bethe Ansatz solution of the open XXZ chain with nondiagonal boundary terms,"We propose a set of conventional Bethe Ansatz equations and a corresponding
expression for the eigenvalues of the transfer matrix for the open spin-1/2 XXZ
quantum spin chain with nondiagonal boundary terms, provided that the boundary
parameters obey a certain linear relation.",0304092v2
1994-01-20,Electroproductions of Light $Λ$- and $Σ$-Hypernuclei,"Theoretical estimations of production cross sections of light $\Lambda$ and
$\Sigma$ hypernuclei in $(e,e'K^{+})$ reactions at around CEBAF energies are
given. Because of dominant spin-flip amplitudes and large momentum transfers,
unnatural parity states and stretched states of hypernuclei are favorably
excited. They are compared with quasifree hyperon productions.",9401017v2
2007-08-22,ILC Positron Production Target Simulation,"A photon-positron conversion target of the undulator or laser based polarized
positron source is optimized using a modified GEANT-3 program adapted to count
the spin transfer. High intensity positron beam with around 0.75 polarisation
could be achieved choosing tungsten conversion target of 0.3 and 0.7 radiation
lengths for the undulator and laser case respectively.",0708.2982v1
2008-02-11,Omega meson production in pp collisions with a polarized beam,"Model independent formulae are derived for the beam analyzing power $A_y$ and
beam to meson spin transfers in $pp \to pp \omega$ taking into consideration
all the six threshold partial wave amplitudes covering the $Ss, Sp$ and $Ps$
channels. Attention is also focussed on the empirical determination of the
lowest three partial wave amplitudes $f_1, f_2, f_3$ without any discrete
ambiguities.",0802.1474v1
2008-12-06,Directional Coupling for Quantum Computing and Communication,"We introduce the concept of directional coupling, i.e., the selective
transfer of a state between adjacent quantum wires, in the context of quantum
computing and short-distance communication. Our analysis rests upon a
mathematical analogy between a dual-channel directional coupler and a composite
spin system.",0812.1281v1
2009-02-09,Chiral Odd Generalized Parton Distributions in Position Space,"We report on a calculation of the chiral odd generalized parton distributions
(GPDs) for non-zero skewness $\zeta$ in transverse and longitudinal position
spaces by taking Fourier transform with respect to the transverse and
longitudinal momentum transfer respectively using overlaps of light-front wave
functions (LFWFs).",0902.1461v1
2010-03-21,Analysis of Optical Deshelving in Photon Echo-based Quantum Memories,"Storage time extension in photon echoes using optical deshelving via a robust
spin state has been investigated for absorption-dependent optical leakage,
where an incomplete population transfer, even by a \pi optical pulse obviates
the phase recovery condition of the deshelving. We analyze an optical
depth-dependent echo leakage mechanism in the storage time extended photon
echoes for the usage of optical deshelving to photon echo-based quantum
memories.",1003.3960v1
2011-02-04,On the exact solution of the mixed-spin Ising chain with axial and rhombic zero-field splitting parameters,"Ground-state phase diagram of the mixed spin-$1/2$ and spin-$1$ Ising chain
with axial and rhombic zero-field splitting parameters is exactly calculated
within the framework of the transfer-matrix method. It is shown that the
rhombic zero-field splitting parameter prefers the magnetically ordered phase
instead of the disordered phase.",1102.0846v1
2012-07-18,Vibrational and electronic ultrafast relaxation of the nitrogen-vacancy centers in diamond,"Two dimensional electronic spectroscopy and transient grating measurements
were performed, for the first time, on nitrogen-vacancy centers in diamond.
These measurements reveal energy transfer and vibrational pathways with
consequences for spin coherence.",1207.4251v1
2012-12-31,Perturbative QCD analysis of the Bjorken sum rule,"We study the polarized Bjorken sum rule at low momentum transfer squared
Q2<3GeV2 in the twist-two approximation and to the next-to-next-to-leading
order accuracy.",1212.6834v1
2013-03-22,Generalized hadron structure and elastic scattering,"The new parameterization of the Generalized Parton Distributions (GPDs)
t-dependence is investigated. It is shown that the new form of the GPDS allows
one to reproduce sufficiently well the electromagnetic form factors of the
proton and neutron at small and large momentum transfer and obtain a good
description of the elastic nucleon-nucleon scattering at high energies.",1303.5553v1
2019-09-16,On vanishing of all fourfold products of the Ray classes in symplectic cobordism,"This note provides certain computations with transfer associated with
projective bundles of Spin vector bundles. One aspect is to revise the proof of
the main result of \cite{B} which says that all fourfold products of the Ray
classes are zero in symplectic cobordism.",1909.07211v1
2019-11-21,Axial-vector weak coupling at medium momentum for astro neutrinos and double beta decays,"Neutrino nuclear responses associated with medium momentum transfer of
q=20-80 MeV for astro neutrinos and double beta decays were studied by using
charge exchange reactions on Te128 and Te130. Gamow-Teller and spin dipole
nuclear matrix elements are found to be reduced with respect to the pnQRPA
matrix elements by the coefficient of around 0.35. The reduction is discussed
in terms of the quenching of axial vector coupling (g_A).",1911.09269v1
2020-02-15,Creation of superconducting vortices by angular momentum of light,"We investigate a superconducting state irradiated by a laser beam with spin
and orbital angular momentum. It is shown that superconducting vortices are
created by the laser beam due to heating effect and transfer of angular
momentum of light. Possible experiments to verify our prediction are also
discussed.",2002.06361v2
2020-12-16,Dirac cohomology and character lifting,"The endoscopic transfer factor is expressed as difference of characters for
the even and odd parts of the spin modules, or Dirac index of the trivial
representation. The lifting of tempered characters in terms of index of Dirac
cohomology is calculated explicitly.",2012.08783v1
2021-03-10,Advances in bremsstrahlung: a review,"Recent developments in bremsstrahlung from electrons colliding with atoms and
nuclei at energies between 0.1 MeV and 500 MeV are reviewed. Considered are
cross sections differential in the photon degrees of freedom, including
coincidence geometries of photon and scattered electron. Also spin asymmetries
and polarization transfer for polarized electron beams are investigated. An
interpretation of the measurements in terms of the current bremsstrahlung
theories is furnished.",2103.06034v1
2021-08-17,Algebraic Bethe Ansatz for spinor R-matrices,"We present a supermatrix realisation of q-deformed spinor-spinor and
spinor-vector R-matrices. These R-matrices are then used to construct transfer
matrices for $U_{q^2}(\mathfrak{so}_{2n+1})$- and
$U_{q}(\mathfrak{so}_{2n+2})$-symmetric closed spin chains. Their eigenvectors
and eigenvalues are computed.",2108.07580v2
2023-06-22,Scalar products of Bethe vectors in the generalized algebraic Bethe ansatz,"We consider an $XYZ$ spin chain within the framework of the generalized
algebraic Bethe ansatz. We study scalar products of the transfer matrix
eigenvectors and arbitrary Bethe vectors. In the particular case of free
fermions we obtain explicit expressions for the scalar products with different
number of parameters in two Bethe vectors.",2306.12932v1
2005-08-11,"Inelastic cotunneling induced decoherence and relaxation, charge and spin currents in an interacting quantum dot under a magnetic field","We present a theoretical analysis of several aspects of nonequilibirum
cotunneling through a strong Coulomb-blockaded quantum dot (QD) subject to a
finite magnetic field in the weak coupling limit. We carry this out by
developing a generic quantum Heisenberg-Langevin equation approach leading to a
set of Bloch dynamical equations which describe the nonequilibrium cotunneling
in a convenient and compact way. These equations describe the time evolution of
the spin variables of the QD explicitly in terms of the response and
correlation functions of the free reservoir variables. This scheme not only
provides analytical expressions for the relaxation and decoherence of the
localized spin induced by cotunneling, but it also facilitates evaluations of
the nonequilibrium magnetization, the charge current, and the spin current at
arbitrary bias-voltage, magnetic field, and temperature. We find that all
cotunneling events produce decoherence, but relaxation stems only from {\em
inelastic} spin-flip cotunneling processes. Moreover, our specific calculations
show that cotunneling processes involving electron transfer (both spin-flip and
non-spin-flip) contribute to charge current, while spin-flip cotunneling
processes are required to produce a net spin current in the asymmetric coupling
case. We also point out that under the influence of a nonzero magnetic field,
spin-flip cotunneling is an energy-consuming process requiring a sufficiently
strong external bias-voltage for activation, explaining the behavior of
differential conductance at low temperature: in particular, the splitting of
the zero-bias anomaly in the charge current and a broad zero-magnitude ""window""
of differential conductance for the spin current near zero-bias-voltage.",0508278v3
2016-04-06,Spin filter for arbitrary spins by substrate engineering,"We design spin filters for particles with potentially arbitrary spin S (=
1/2, 1, 3/2,....) using a one-dimensional periodic chain of magnetic atoms as a
quantum device. Describing the system within a tight-binding formalism we
present an analytical method to unravel the analogy between a one-dimensional
magnetic chain and a multi-strand ladder network. This analogy is crucial, and
is subsequently exploited to engineer gaps in the energy spectrum by an
appropriate choice of the magnetic substrate. We obtain an exact correlation
between the magnitude of the spin of the incoming beam of particles and the
magnetic moment of the substrate atoms in the chain desired for opening up of a
spectral gap. Results of spin polarized transport, calculated within a transfer
matrix formalism, are presented for particles having half-integer as well as
higher spin states. We find that the chain can be made to act as a quantum
device which opens a transmission window only for selected spin components over
certain ranges of the Fermi energy, blocking them in the remaining part of the
spectrum. The results appear to be robust even when the choice of the substrate
atoms deviates substantially from the ideal situation, as verified by extending
the ideas to the case of a spin spiral. Interestingly, the spin spiral
geometry, apart from exhibiting the filtering effect, is also seen to act as a
device flipping spins - an effect that can be monitored by an interplay of the
system size and the period of the spiral. Our scheme is applicable to ultracold
quantum gases, and might inspire future experiments in this direction.",1604.01520v2
1999-08-26,A New Method to Calculate the Spin-Glass Order Parameter of the Two-Dimensional +/-J Ising Model,"A new method to numerically calculate the $n$th moment of the spin overlap of
the two-dimensional $\pm J$ Ising model is developed using the identity derived
by one of the authors (HK) several years ago. By using the method, the $n$th
moment of the spin overlap can be calculated as a simple average of the $n$th
moment of the total spins with a modified bond probability distribution. The
values of the Binder parameter etc have been extensively calculated with the
linear size, $L$, up to L=23. The accuracy of the calculations in the present
method is similar to that in the conventional transfer matrix method with about
$10^{5}$ bond samples. The simple scaling plots of the Binder parameter and the
spin-glass susceptibility indicate the existence of a finite-temperature
spin-glass phase transition. We find, however, that the estimation of $T_{\rm
c}$ is strongly affected by the corrections to scaling within the present data
($L\leq 23$). Thus, there still remains the possibility that $T_{\rm c}=0$,
contrary to the recent results which suggest the existence of a
finite-temperature spin-glass phase transition.",9908370v3
2010-10-13,Electric-field control of spin waves at room temperature in multiferroic BiFeO3,"To face the challenges lying beyond current CMOS-based technology, new
paradigms for information processing are required. Magnonics proposes to use
spin waves to carry and process information, in analogy with photonics that
relies on light waves, with several advantageous features such as potential
operation in the THz range and excellent coupling to spintronics. Several
magnonic analog and digital logic devices have been proposed, and some
demonstrated. Just as for spintronics, a key issue for magnonics is the large
power required to control/write information (conventionally achieved through
magnetic fields applied by strip lines, or by spin transfer from large
spin-polarized currents). Here we show that in BiFeO3, a room-temperature
magnetoelectric material, the spin wave frequency (>600 GHz) can be tuned
electrically by over 30%, in a non-volatile way and with virtually no power
dissipation. Theoretical calculations indicate that this effect originates from
a linear magnetoelectric effect related to spin-orbit coupling induced by the
applied electric field. We argue that these properties make BiFeO3 a promising
medium for spin wave generation, conversion and control in future magnonics
architectures.",1010.2678v1
2012-07-09,Electronic Transport Through EuO Spin Filter Tunnel Junctions,"Epitaxial spin filter tunnel junctions based on the ferromagnetic
semiconductor europium monoxide, EuO, are investigated by means of density
functional theory. In particular, we focus on the spin transport properties of
Cu(100)/EuO(100)/Cu(100) junctions. The dependence of the transmission
coefficient and the current-voltage curves on the interface spacing and on the
EuO thickness is explained in terms of the EuO density of states and the
complex band structure. Furthermore we also discuss the relation between the
spin transport properties and the Cu-EuO interface geometry. The level
alignment of the junction is sensitively affected by the interface spacing,
since this determines the charge transfer between EuO and the Cu electrodes.
Our calculations indicate that EuO epitaxially grown on Cu can act as a perfect
spin filter, with a spin polarization of the current close to 100%, and with
both the Eu-5d conduction band and the Eu-4f valence band states contributing
to the coherent transport. For epitaxial EuO on Cu a symmetry filtering is
observed, with the \Delta_1 states dominating the transmission. This leads to a
transport gap larger than the fundamental EuO band gap. Importantly the high
spin polarization of the current is preserved up to large bias voltages.",1207.2061v1
2012-07-31,Spin excitations in a single La$_2$CuO$_4$ layer,"The dynamics of S=1/2 quantum spins on a 2D square lattice lie at the heart
of the mystery of the cuprates
\cite{Hayden2004,Vignolle2007,Li2010,LeTacon2011,Coldea2001,Headings2010,Braicovich2010}.
In bulk cuprates such as \LCO{}, the presence of a weak interlayer coupling
stabilizes 3D N\'{e}el order up to high temperatures. In a truly 2D system
however, thermal spin fluctuations melt long range order at any finite
temperature \cite{Mermin1966}. Further, quantum spin fluctuations transfer
magnetic spectral weight out of a well-defined magnon excitation into a
magnetic continuum, the nature of which remains controversial
\cite{Sandvik2001,Ho2001,Christensen2007,Headings2010}. Here, we measure the
spin response of \emph{isolated one-unit-cell thick layers} of \LCO{}. We show
that coherent magnons persist even in a single layer of \LCO{} despite the loss
of magnetic order, with no evidence for resonating valence bond (RVB)-like spin
correlations \cite{Anderson1987,Hsu1990,Christensen2007}. Thus these
excitations are well described by linear spin wave theory (LSWT). We also
observe a high-energy magnetic continuum in the isotropic magnetic response.
This high-energy continuum is not well described by 2 magnon LSWT, or indeed
any existing theories.",1208.0018v1
2013-01-07,Hot-carrier transport and spin relaxation on the surface of topological insulator,"We study the charge and spin transport under high electric field (up to
several kV/cm) on the surface of topological insulator Bi$_2$Se$_3$, where the
electron-surface optical phonon scattering dominates except at very low
temperature. Due to the spin mixing of conduction and valence bands, the
electric field not only accelerates electrons in each band, but also leads to
inter-band precession. In the presence of the electric field, electrons can
transfer from the valence band to the conduction one via the inter-band
precession and inter-band electron-phonon scattering. The electron density in
each band varies with the electric field linearly when the electric field is
strong. Due to the spin-momentum locking, a transverse spin polarization, with
the magnitude proportional to the momentum scattering time, is induced by the
electric field. The induced spin polarization depends on the electric field
linearly when the latter is small. Moreover, its magnitude is inversely
proportional to the temperature and is insensitive to the electron density at
high temperature. Our investigation also reveals that due to the large relative
static dielectric constant, the Coulomb scattering is too weak to establish a
drifted Fermi distribution with a unified hot-electron temperature in the
steady state under the electric field. After turning off the electric field in
the steady state, the hot carriers cool down in a time scale of energy
relaxation which is very long (of the order of 100-1000 ps) while the spin
polarization relaxes in a time scale of momentum scattering which is quite
short (of the order of 0.01-0.1 ps).",1301.1092v1
2014-04-15,Muon spin rotation and relaxation in Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$: Magnetic and superconducting ground states,"Muon spin rotation and relaxation ($\mu$SR) experiments have been carried out
to characterize magnetic and superconducting ground states in the
Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ alloy series. In the ferromagnetic end compound
NdOs$_4$Sb$_{12}$ the spontaneous local field at positive-muon ($\mu^+$) sites
below the ordering temperature $T_C$ is greater than expected from dipolar
coupling to ferromagnetically aligned Nd$^{3+}$ moments, indicating an
additional indirect RKKY-like transferred hyperfine mechanism. For 0.45 $\le x
\le$ 0.75, $\mu^+$ spin relaxation rates in zero and weak longitudinal applied
fields indicate that static fields at $\mu^+$ sites below $T_C$ are reduced and
strongly disordered. We argue this is unlikely to be due to reduction of
Nd$^{3+}$ moments, and speculate that the Nd$^{3+}$-$\mu^+$ interaction is
suppressed and disordered by Pr doping. In an $x$ = 0.25 sample, which is
superconducting below $T_c$ = 1.3 K, there is no sign of ""spin freezing""
(static Nd$^{3+}$ magnetism), ordered or disordered, down to 25 mK. Dynamic
$\mu^+$ spin relaxation is strong, indicating significant Nd-moment
fluctuations. The $\mu^+$ diamagnetic frequency shift and spin relaxation in
the superconducting vortex-lattice phase decrease slowly below $T_c$,
suggesting pair breaking and/or possible modification of Fermi-liquid
renormalization by Nd spin fluctuations. For 0.25 $\le x \le$ 0.75, the $\mu$SR
data provide evidence against phase separation; superconductivity and Nd$^{3+}$
magnetism coexist on the atomic scale.",1404.4090v1
2014-10-14,Spin-up/spin-down of neutron star in Be-X-ray binary system GX 304-1,"We analyze spin-up/spin-down of the neutron star in Be X-ray binary system
GX\,304-1 observed by \textit{Swift}/XRT and \textit{Fermi}/GBM instruments in
the period of the source activity from April 2010 to January 2013 and discuss
possible mechanisms of angular momentum transfer to/from the neutron star. We
argue that the neutron star spin-down at quiescent states of the source with an
X-ray luminosity of $L_x\sim 10^{34}$~erg s$^{-1}$ between a series of Type I
outbursts and spin-up during the outbursts can be explained by quasi-spherical
settling accretion onto the neutron star. The outbursts occur near the neutron
star periastron passages where the density is enhanced due to the presence of
an equatorial Be-disc tilted to the orbital plane. We also propose an
explanation to the counterintuitive smaller spin-up rate observed at higher
luminosity in a double-peak Type I outburst due to lower value of the specific
angular momentum of matter captured from the quasi-spherical wind from the
Be-star by the neutron star moving in an elliptical orbit with eccentricity
$e\gtrsim 0.5$.",1410.3708v1
2015-07-02,Generation of heralded entanglement between distant hole spins,"Quantum entanglement emerges naturally in interacting quantum systems and
plays a central role in quantum information processing. Remarkably, it is
possible to generate entanglement even in the absence of direct interactions:
provided that which path information is erased, weak spin-state dependent light
scattering can be used to project two distant spins onto a maximally entangled
state upon detection of a single photon. Even though this approach is
necessarily probabilistic, successful generation of entanglement is heralded by
the photon detection event. Here, we demonstrate heralded quantum entanglement
of two quantum dot heavy-hole spins separated by 5 meters using single-photon
interference. Thanks to the long coherence time of hole spins and the efficient
spin-photon interface provided by self-assembled quantum dots embedded in leaky
microcavity structures, we generate 2300 entangled spin pairs per second, which
represents an improvement approaching three orders of magnitude as compared to
prior experiments. Delayed two-photon interference scheme we developed allows
for efficient verification of quantum correlations. Our results lay the
groundwork for the realization of quantum networks in semiconductor
nanostructures. Combined with schemes for transferring quantum information to a
long-lived memory qubit, fast entanglement generation we demonstrate could also
impact quantum repeater architectures.",1507.00465v2
2016-02-10,Imaging Spin Dynamics in Monolayer WS2 by Time-Resolved Kerr Rotation Microscopy,"Monolayer transition metal dichalcogenides (TMD) have immense potential for
future spintronic and valleytronic applications due to their two-dimensional
nature and long spin/valley lifetimes. We investigate the origin of these
long-lived states in n-type WS2 using time-resolved Kerr rotation microscopy
and photoluminescence microscopy with ~1 micron spatial resolution. Comparing
the spatial dependence of the Kerr rotation signal and the photoluminescence
reveals a correlation with neutral exciton emission, which is likely due to the
transfer of angular momentum to resident conduction electrons with long
spin/valley lifetimes. In addition, we observe an unexpected anticorrelation
between the Kerr rotation and trion emission, which provides evidence for the
presence of long-lived spin/valley-polarized dark trions. We also find that the
spin/valley polarization in WS2 is robust to magnetic fields up to 700 mT,
indicative of spins and valleys that are stabilized with strong spin-orbit
fields.",1602.03568v2
2017-03-22,Spin-mixing-tunneling network model for Anderson transitions in two-dimensional disordered spinful electrons,"We consider Anderson transitions in two-dimensional spinful electron gases
subject to random scalar potentials with time-reversal-symmetric spin-mixing
tunneling (SMT) and spin-preserving tunneling (SPT) at potential saddle points
(PSPs). A symplectic quantum network model, named as SMT-QNM, is constructed in
which SMT and SPT have the same status and contribute independent tunneling
channels rather than sharing a total-probability-fixed one. Two-dimensional
continuous Dirac Hamiltonian is then extracted out from this discrete network
model as the generator of certain unitary transformation. With the help of
high-accuracy numerics based on transfer matrix technique, finite-size analysis
on two-terminal conductance and normalized localization length provides a phase
diagram drawn in the SMT-SPT plane. As a manifestation of symplectic ensembles,
a normal-metal (NM) phase emerges between the quantum spin Hall (QSH) and
normal-insulator (NI) phases when SMT appears. We systematically analyze the
quantum phases on the boundary and in the interior of the phase space.
Particularly, the phase diagram is closely related to that of disordered
three-dimensional weak topological insulators by appropriate parameter mapping.
At last, if time-reversal symmetry in electron trajectories between PSPs is
destroyed, the system falls into unitary class with no more NM phase. A direct
SMT-driven transition from QSH to NI phases exists and can be explained by
spin-flip backscattering between the degenerate doublets at the same sample
edge.",1703.07723v2
2017-07-18,Spin and valley polarized one-way Klein tunneling in photonic topological insulators,"Advances of condensed matter physics in exploiting the spin degree of freedom
of electrons led to the emergence of the field of spintronics, which envisions
new and more efficient approaches to data transfer, computing, and storage
[1-3]. These ideas have been inspiring analogous approaches in photonics, where
the manipulation of an artificially engineered pseudo-spin degrees of freedom
is enabled by synthetic gauge fields acting on light [4,5,6]. The ability to
control these additional degrees of freedom can significantly expand the
landscape of available optical responses, which may revolutionize optical
computing and the basic means of controlling light in photonic devices across
the entire electromagnetic spectrum. Here we demonstrate a new class of
photonic systems, described by effective Hamiltonians in which competing
synthetic gauge fields engineered in pseudo-spin, chirality/sublattice and
valley subspaces result in band gap opening at one of the valleys, while the
other valley exhibits Dirac-like conical dispersion. It is shown that such
effective response has dramatic implications on photon transport, among which:
(i) spin-polarized and valley-polarized one-way Klein tunneling and (ii)
topological edge states that coexist within the Dirac continuum for opposite
valley and spin polarizations. These phenomena offer new ways to control light
in photonics, in particular for on-chip optical isolation, filtering and
wave-division multiplexing by selective action on their pseudo-spin and valley
degrees of freedom.",1707.05802v1
2019-03-16,Induced exchange and spin-orbit effects by proximity in graphene on Ni and Co,"The induced-proximity effects of nearly commensurate lattice structure of a
graphene layer on Ni(111) and Co(0001) substrates in the AC stacking
configuration are addressed through an analytical tight-binding approach within
the Slater-Koster method. A minimal Hamiltonian is constructed by considering
the hybridizations of the magnetic $3d$-orbitals of Ni(Co) atoms with the
$p_z$-orbitals of graphene, in addition to the atomic spin-orbit coupling and
the magnetization of the Ni(Co) atoms. A low-energy effective Hamiltonian for
graphene/Ni(Co) describing the perturbed $\pi$-bands in the vicinity of the
Dirac points is derived which enable us to get further insight on the physical
nature of the induced-effective couplings to the graphene layer. It is shown
that a magneto-spin-orbit type effect may emerge through two competing
mechanisms simultaneously present, namely the proximity induced exchange and
Rashba spin-orbit interaction. Such effects results in giant exchange
splittings and robust Rashba spin-orbit coupling transferred to the graphene
layer in agreement with recent density functional theory calculations and
experimental observations. We further analyze the physical conditions for the
appearance of intact Dirac cones in the minority spin bands as observed by
recent photoemission measurements with spin resolution.",1903.06959v1
2019-06-25,Spin-split band hybridization in graphene proximitized with $α$-RuCl$_3$ nanosheets,"Proximity effects induced in the 2D Dirac material graphene potentially open
access to novel and intriguing physical phenomena. Thus far, the coupling
between graphene and ferromagnetic insulators has been experimentally
established. However, only very little is known about graphene's interaction
with antiferromagnetic insulators. Here, we report a low temperature study of
the electronic properties of high quality van der Waals heterostructures
composed of a single graphene layer proximitized with $\alpha$-RuCl$_3$. The
latter is known to become antiferromagnetically ordered below 10 K. Shubnikov
de Haas oscillations in the longitudinal resistance together with Hall
resistance measurements provide clear evidence for a band realignment that is
accompanied by a transfer of electrons originally occupying the graphene's spin
degenerate Dirac cones into $\alpha$-RuCl$_3$ band states with in-plane spin
polarization. Left behind are holes in two separate Fermi pockets, only the
dispersion of one of which is distorted near the Fermi energy due to spin
selective hybridization with these spin polarized $\alpha$-RuCl$_3$ band
states. This interpretation is supported by our DFT calculations. An unexpected
damping of the quantum oscillations as well as a zero field resistance upturn
close to the N$\'e$el temperature of $\alpha$-RuCl$_3$ suggests the onset of
additional spin scattering due to spin fluctuations in the $\alpha$-RuCl$_3$.",1906.10405v1
2019-10-16,Ultra-high frequency magnetic resonance through strain-spin coupling in perpendicular magnetic multi-layers,"The interaction between strain and spin has received intensive attention in
the scientific community due to its abundant physical phenomena and huge
technological impact. Until now, there is no experimental report on ultra-high
frequency magnetic resonance through the strain-spin coupling for any
technologically relevant perpendicular magnetic material. Here we report the
experimental detection of the acoustic strain waves that have a response time
on the order of 10 picoseconds in perpendicular magnetic [Co/Pd]n multilayers
via a femtosecond laser pulse excitation. Through direct measurements of
acoustic strain waves, we observe an ultra-high frequency magnetic resonance up
to 60 GHz in [Co/Pd]n multilayers. We further report a theoretical model of the
strain-spin interaction. Our model reveals that the energy could be transferred
efficiently from the strain to the spins and well explains the existence of a
steady resonance state through exciting the spin system. The physical origins
of the resonance between strain waves and magnetic precession and the requested
conditions for obtaining magnetic resonance within thin magnetic films have
also been discussed after thorough analysis. These combined results point out a
potential pathway to enable an extremely high frequency (EHF) magnetic
resonance through the strain-spin coupling.",1910.07147v2
2020-05-01,Spin-Lasers: Spintronics Beyond Magnetoresistance,"Introducing spin-polarized carriers in semiconductor lasers reveals an
alternative path to realize room-temperature spintronic applications, beyond
the usual magnetoresistive effects. Through carrier recombination, the angular
momentum of the spin-polarized carriers is transferred to photons, thus leading
to the circularly polarized emitted light. The intuition for the operation of
such spin-lasers can be obtained from simple bucket and harmonic oscillator
models, elucidating their steady-state and dynamic response, respectively.
These lasers extend the functionalities of spintronic devices and exceed the
performance of conventional (spin-unpolarized) lasers, including an order of
magnitude faster modulation frequency. Surprisingly, this ultrafast operation
relies on a short carrier spin relaxation time and a large anisotropy of the
refractive index, both viewed as detrimental in spintronics and conventional
lasers. Spin-lasers provide a platform to test novel concepts in spin devices
and offer progress connected to the advances in more traditional areas of
spintronics.",2005.00591v1
2020-05-26,Nonlinear Spin Currents,"The cavity mediated spin current between two ferrite samples has been
reported by Bai et. al. [Phys. Rev. Lett. 118, 217201 (2017)]. This experiment
was done in the linear regime of the interaction in the presence of external
drive. In the current paper we develop a theory for the spin current in the
nonlinear domain where the external drive is strong so that one needs to
include the Kerr nonlinearity of the ferrite materials. In this manner the
nonlinear polaritons are created and one can reach both bistable and
multistable behavior of the spin current. The system is driven into a far from
equilibrium steady state which is determined by the details of driving field
and various interactions. We present a variety of steady state results for the
spin current. A spectroscopic detection of the nonlinear spin current is
developed, revealing the key properties of the nonlinear polaritons. The
transmission of a weak probe is used to obtain quantitative information on the
multistable behavior of the spin current. The results and methods that we
present are quite generic and can be used in many other contexts where cavities
are used to transfer information from one system to another, e.g., two
different molecular systems.",2005.12999v1
2020-10-15,Spin injection characteristics of Py/graphene/Pt by gigahertz and terahertz magnetization dynamics driven by femtosecond laser pulse,"Spin transport characteristics of graphene has been extensively studied so
far. The spin transport along c-axis is however reported by rather limited
number of papers. We have studied spin transport characteristics through
graphene along c-axis with permalloy(Py)/graphene(Gr)/Pt by gigahertz (GHz) and
terahertz (THz) magnetization dynamics driven by femtosecond laser pulses. The
relatively simple sample structure does not require electrodes on the sample.
The graphene layer was prepared by chemical vapor deposition and transferred on
Pt film. The quality of graphene layer was characterized by Raman microscopy.
Time resolved magneto-optical Kerr effect is used to characterize gigahertz
magnetization dynamics. Magnetization precession is clearly observed both for
Pt/Py and Pt/Gr/Py. The Gilbert damping constant of Pt/Py was 0.015, indicates
spin pumping effect from Py to Pt. The Gilbert damping constant of Pt/Gr/Py is
found to be 0.011, indicates spin injection is blocked by graphene layer. We
have also performed the measurement of THz emission for Pt/Py and Pt/Gr/Py.
While the THz emission is clearly observed for Pt/Py, a strong reduction of THz
emission is observed for Pt/Gr/Py. With these two different experiments, and
highly anisotropic resistivity of graphite, we conclude that the vertical spin
transport is strongly suppressed by the graphene layer.",2010.07694v1
2020-11-20,Exchange interactions and magnetic force theorem,"We critically reexamine the problem of interatomic exchange interactions,
which describe the total energy change caused by infinitesimal rotations of
spins near some equilibrium state. For the small variations, such interactions
can be always related to the response function. However, the form of this
relation can depend on additional approximations. Particularly, the commonly
used magnetic force theorem (MFT) prescribes the linear relation between the
exchange interactions and the response function, while the exact theory
requires this dependence to be inverse. We explore the origin and consequences
of these differences in the definition for the wide class of materials:
ferromagnetic Ni, antiferromagnetic NiO, half-metallic CrO2, multiferroic
HoMnO3, and layered magnets CrCl3 and CrI3. While in most of these cases, MFT
produces quite reasonable results and can be rigorously justifies in the long
wavelength and strong-coupling limits, the exact formulation appears to be more
consistent, especially in dealing with two important issues, which typically
arise in the theory of exchange interactions: (i) the treatment of the ligand
states, and (ii) the choice of the suitable variable for the description of
infinitesimal rotations of spins. Both issues can be efficiently resolved by
employing the ideas of adiabatic spin dynamics supplemented with the exact
expression for the exchange interactions. Particularly, we propose a simple
""downfolding"" procedure for the elimination of the ligand spins by transferring
their effect to the interaction parameters between the localized spins.
Furthermore, we argue that the rotations of spin moments are more suitable for
the description of low-energy excitations, while the rotations of the whole
magnetization matrix cause much stronger perturbation in the system of spins.",2011.10204v1
2021-04-01,Evolution of the spin of late-type galaxies caused by galaxy-galaxy interactions,"We use N-body/hydrodynamic simulations to study the evolution of the spin of
a Milky Way-like galaxy through interactions. We perform a controlled
experiment of co-planner galaxy-galaxy encounters and study the evolution of
disk spins of interacting galaxies. Specifically, we consider the cases where
the late-type target galaxy encounters an equally massive companion galaxy,
which has either a late or an early-type morphology, with the closest approach
distance of about 50 kpc, in prograde or retrograde sense. By examining the
time change of the circular velocity of the disk material of the target galaxy
from each case, we find that the target galaxy tends to lose the spin through
prograde collisions but hardly through retrograde collisions, regardless of the
companion galaxy type. The decrease of the spin results mainly from the
deflection of the orbit of the disk material by tidal disruption. Although
there is some disk material which gains the circular velocity through
hydrodynamic as well as gravitational interactions or by transferring material
from the companion galaxy, it turns out that the amount of the material is
generally insufficient to increase the overall galactic spin under the
conditions we set. It is found that the spin angular momentum of the target
galaxy disk decreases by 15 - 20% after a prograde collision. We conclude that
the accumulated effects of galaxy-galaxy interactions will play an important
role in determining the total angular momentum of late-type galaxies at current
stage.",2104.00493v1
2021-05-12,Coherent spin-wave transport in an antiferromagnet,"Magnonics is a research field complementary to spintronics, in which the
quanta of spin waves (magnons) replace electrons as information carriers,
promising less energy dissipation. The development of ultrafast nanoscale
magnonic logic circuits calls for new tools and materials to generate coherent
spin waves with frequencies as high, and wavelengths as short, as possible.
Antiferromagnets can host spin waves at THz frequencies and are therefore seen
as a future platform for the fastest and the least dissipative transfer of
information. However, the generation of short-wavelength coherent propagating
magnons in antiferromagnets has so far remained elusive. Here we report the
efficient emission and detection of a nanometer-scale wavepacket of coherent
propagating magnons in antiferromagnetic DyFeO3 using ultrashort pulses of
light. The subwavelength nanoscale confinement of the laser field due to large
absorption creates a strongly non-uniform spin excitation profile, thereby
enabling the propagation of a broadband continuum of coherent THz spin waves.
The wavepacket features magnons with detected wavelengths down to 125 nm and
supersonic velocities up to 13 km/s that propagate over macroscopic distances.
The long-sought source of coherent short-wavelength spin carriers demonstrated
here opens up new prospects for THz antiferromagnetic magnonics and coherence
mediated logic devices at THz frequencies.",2105.05886v1
2022-05-19,Energy-efficient quantum non-demolition measurement with a spin-photon interface,"Spin-photon interfaces (SPIs) are key devices of quantum technologies, aimed
at coherently transferring quantum information between spin qubits and
propagating pulses of polarized light. We study the potential of a SPI for
quantum non demolition (QND) measurements of a spin state. After being
initialized and scattered by the SPI, the state of a light pulse depends on the
spin state. It thus plays the role of a pointer state, information being
encoded in the light's temporal and polarization degrees of freedom. Building
on the fully Hamiltonian resolution of the spin-light dynamics, we show that
quantum superpositions of zero and single photon states outperform coherent
pulses of light, producing pointer states which are more distinguishable with
the same photon budget. The energetic advantage provided by quantum pulses over
coherent ones is maintained when information on the spin state is extracted at
the classical level by performing projective measurements on the light pulses.
The proposed schemes are robust against imperfections in state of the art
semi-conducting devices.",2205.09623v4
2022-09-27,Optimal microwave control pulse for nuclear spin polarization and readout in dense nitrogen-vacancy ensembles in diamond,"Nitrogen-vacancy centers possessing nuclear spins are promising candidates
for a novel nuclear spin gyroscope. Preparation of a nuclear spin state is a
crucial step to implement a sensor that utilizes a nuclear spin. In a low
magnetic field, such a preparation utilizes population transfer, from polarized
electronic spin to nuclear spin, using microwave pulses. The use of the
narrowband microwave pulse proposed earlier is inefficient when magnetic
transitions are not well resolved, particularly when applied to diamond with a
natural abundance of carbon atoms or dense ensembles of nitrogen-vacancy
centers. In this study, the authors performed optimization of the pulse shape
for 3 relatively easily accessible pulse shapes. The optimization was done for
a range of magnetic transition linewidths, corresponding to the practically
important range of nitrogen concentrations (5-50 ppm). It was found that, while
at low nitrogen concentrations, optimized pulse added very little to simple
square shape pulse, and in the case of dense nitrogen-vacancy ensembles, with a
rather wide magnetic transition width of 1.5 MHz optimal pulses, a factor of
15% improvement in the population of the target state was observed.",2209.13173v1
2023-02-18,"LIGHT-SABRE hyperpolarizes 1-^{13}C-pyruvate continuously, without magnetic field cycling","Nuclear spin hyperpolarization enables real-time observation of metabolism
and intermolecular interactions in vivo. 1-13C-Pyruvate is the leading
hyperpolarized tracer currently under evaluation in several clinical trials as
a promising molecular imaging agent. Still, the quest for a simple, fast, and
efficient hyperpolarization technique is ongoing. Here, we describe that
continuous, weak irradiation in the audio-frequency range of the 13C spin at
121 {\mu}T magnetic field (\sim twiceEarth\apos s field) enables spin order
transfer from parahydrogen to 13C magnetization of 1-13C-pyruvate. These
so-called LIGHT-SABRE pulses couple nuclear spin states of parahydrogen and
pyruvate via the J-coupling network of reversibly exchanging Ir-complexes.
Using \sim 100% parahydrogen at ambient pressure, we polarized 51 mM of
1-13C-pyruvate in the presence of 5.1 mM Ir-complex continuously and repeatedly
to a polarization of 1.1% averaged over free and catalyst-bound pyruvate. The
experiments were conducted at -8{\deg}C), where almost exclusively bound
pyruvate was observed, corresponding to an estimated 11% polarization on bound
pyruvate. The obtained hyperpolarization levels closely match those obtained
via SABRE-SHEATH under otherwise identical conditions. The creation of three
different types of spin orders was observed: transverse 13C magnetization along
the applied magnetic field, 13C z-magnetization along the main field B_0, and
13C-1H zz-spin-order. With a superconducting quantum interference device
(SQUID) for detection, we found that the generated spin orders result from tiny
1H-13C J-coupling interactions, which are not visible even with our narrow
linewidth below 0.3 Hz.",2302.09299v1
2023-03-12,Robust phase metrology with hybrid quantum interferometers against particle losses,"Entanglement is an important quantum resource to achieve high sensitive
quantum metrology. However, the rapid decoherence of quantum entangled states,
due to the unavoidable environment noise, result in practically the unwanted
sharp drop of the measurement sensitivity. To overcome such a difficulty, here
we propose a spin-oscillator hybrid quantum interferometer to achieve the
desirable precise estimation of the parameter encoded in the vibrations of the
oscillator. Differing from the conventional two-mode quantum interferometers
input by the two-mode NOON state or entangled coherent states (ECS), whose
achievable sensitivities are strongly limited by the decoherence of the
entangled vibrational states, we demonstrate that the present interferometer,
input by a spin-dependent two-mode entangled state, possesses a manifest
advantage, i.e., the measurement sensitivity of the estimated parameter is not
influenced by the decoherence from the spin-oscillator entanglement. This is
because that, by applying a spin-oscillator disentangled operation, the
information of the estimated parameter encoded originally in the vibrational
degrees can be effectively transferred into the spin degree and then can be
sensitively estimated by the precise spin-state population measurements. As
consequence, the proposed hybrid quantum interferometer possesses a manifest
robustness against the particle losses of the vibrational modes. Interestingly,
the achieved phase measurement sensitivity can still surpass the SQL obviously,
even if relatively large number of particle loss occurs in one of the two
modes. The potential application of the proposed spin-oscillator hybrid quantum
interferometer is also discussed.",2303.06604v1
2023-09-04,Impact of electrostatic crosstalk on spin qubits in dense CMOS quantum dot arrays,"Quantum processors based on integrated nanoscale silicon spin qubits are a
promising platform for highly scalable quantum computation. Current CMOS spin
qubit processors consist of dense gate arrays to define the quantum dots,
making them susceptible to crosstalk from capacitive coupling between a dot and
its neighbouring gates. Small but sizeable spin-orbit interactions can transfer
this electrostatic crosstalk to the spin g-factors, creating a dependence of
the Larmor frequency on the electric field created by gate electrodes
positioned even tens of nanometers apart. By studying the Stark shift from tens
of spin qubits measured in nine different CMOS devices, we developed a
theoretical frawework that explains how electric fields couple to the spin of
the electrons in increasingly complex arrays, including those electric
fluctuations that limit qubit dephasing times $T_2^*$. The results will aid in
the design of robust strategies to scale CMOS quantum technology.",2309.01849v1
2023-11-14,Prospects for measuring quark polarization and spin correlations in $b\bar b$ and $c\bar c$ samples at the LHC,"Polarization and spin correlations have been studied in detail for top quarks
at the LHC, but have been explored very little for the other flavors of quarks.
In this paper we consider the processes $pp\to q\bar{q}$ with $q = b$, $c$ or
$s$. Utilizing the partial preservation of the quark's spin information in
baryons in the jet produced by the quark, we examine possible analysis
strategies for ATLAS and CMS to measure the quark polarization and spin
correlations. We find polarization measurements for the $b$ and $c$ quarks to
be feasible, even with the currently available datasets. Spin correlation
measurements for $b\bar b$ are possible using the CMS Run 2 parked data, while
such measurements for $c\bar c$ will become possible with higher integrated
luminosity. For the $s$ quark, we find the measurements to be challenging with
the standard triggers. We also provide leading-order QCD predictions for the
polarization and spin correlations expected in the $b\bar b$ and $c\bar c$
samples with the cuts envisioned for the above analyses. Apart from
establishing experimentally the existence of spin correlations in $b\bar b$ and
$c\bar c$ systems produced in $pp$ collisions, the proposed measurements can
provide new information on the polarization transfer from quarks to baryons and
might even be sensitive to physics beyond the Standard Model.",2311.08226v2
2023-12-19,Cavity-resonated detection of spin polarization in a microfabricated atomic vapor cell,"We demonstrate continuous Pound-Drever-Hall (PDH) nondestructive monitoring
of the electron spin polarization of an atomic vapor in a microfabricated vapor
cell within an optical resonator. The two-chamber silicon and glass cell
contains $^{87}$Rb and 1.3 amagat of N$_{2}$ buffer gas, and is placed within a
planar optical resonator formed by two mirrors with dichroic dielectric
coatings to resonantly enhance the coupling to phase-modulated probe light near
the D$_2$ line at 780 nm. We describe the theory of signal generation in this
system, including the spin-dependent complex refractive index, cavity optical
transfer functions, and PDH signal response to spin polarization. We observe
cavity transmission and PDH signals across $\approx 200$ GHz of detuning around
the atomic resonance line. By resonant optical pumping on the 795 nm D$_1$
line, we observe spin-dependent cavity line shifts, in good agreement with
theory. We use the saturation of the line shift vs. optical pumping power to
calibrate the number density and efficiency of the optical pumping. In the
unresolved sideband regime, we observe quantum-noise-limited PDH readout of the
spin polarization density, with a flat noise floor of $9 \times 10^9$ spins
cm$^{-3}$ Hz$^{-1/2}$ for frequencies above 700 Hz. We note possible extensions
of the technique.",2312.12256v1
2024-04-06,Non-volatile spin transport in a single domain multiferroic,"Antiferromagnets have attracted significant attention in the field of
magnonics, as promising candidates for ultralow-energy carriers for information
transfer for future computing. The role of crystalline orientation distribution
on magnon transport has received very little attention. In multiferroics such
as BiFeO$_3$ the coupling between antiferromagnetic and polar order imposes yet
another boundary condition on spin transport. Thus, understanding the
fundamentals of spin transport in such systems requires a single domain, a
single crystal. We show that through Lanthanum(La) substitution, a single
ferroelectric domain can be engineered with a stable, single-variant spin
cycloid, controllable by an electric field. The spin transport in such a single
domain displays a strong anisotropy, arising from the underlying spin cycloid
lattice. Our work shows a pathway to understand the fundamental origins of spin
transport in such a single domain multiferroic.",2404.04746v1
1999-09-24,"Pulse Profiles, Accretion Column Dips and a Flare in GX 1+4 During a Faint State","The Rossi X-ray Timing Explorer (RXTE) spacecraft observed the X-ray pulsar
GX 1+4 for a period of 34 hours on July 19/20 1996. The source faded from an
intensity of ~20 mCrab to a minimum of <~0.7 mCrab and then partially recovered
towards the end of the observation. This extended minimum lasted ~40,000
seconds. Phase folded light curves at a barycentric rotation period of
124.36568 +/- 0.00020 seconds show that near the center of the extended minimum
the source stopped pulsing in the traditional sense but retained a weak dip
feature at the rotation period. Away from the extended minimum the dips are
progressively narrower at higher energies and may be interpreted as
obscurations or eclipses of the hot spot by the accretion column. The pulse
profile changed from leading-edge bright before the extended minimum to
trailing-edge bright after it. Data from the Burst and Transient Source
Experiment (BATSE) show that a torque reversal occurred <10 days after our
observation. Our data indicate that the observed rotation departs from a
constant period with a Pdot/P value of ~-1.5% per year at a 4.5 sigma
significance. We infer that we may have serendipitously obtained data, with
high sensitivity and temporal resolution about the time of an accretion disk
spin reversal. We also observed a rapid flare which had some precursor
activity, close to the center of the extended minimum.",9909412v1
1999-11-30,Influence of the r-mode instability on hypercritically accreting neutron stars,"We have investigated an influence of the r-mode instability on
hypercritically accreting ($\dot{M}\sim 1M_\odot {y}^{-1}$) neutron stars in
close binary systems during their common envelope phases based on the scenario
proposed by Bethe et al. \shortcite{bethe-brown-lee}. On the one hand neutron
stars are heated by the accreted matter at the stellar surface, but on the
other hand they are also cooled down by the neutrino radiation. At the same
time, the accreted matter transports its angular momentum and mass to the star.
We have studied the evolution of the stellar mass, temperature and rotational
frequency.
  The gravitational-wave-driven instability of the r-mode oscillation strongly
suppresses spinning-up of the star, whose final rotational frequency is well
below the mass-shedding limit, typically as small as 10% of that of the
mass-shedding state. On a very short time scale the rotational frequency tends
to approach a certain constant value and saturates there as far as the amount
of the accreted mass does not exceed a certain limit to collapse to a black
hole. This implies that the similar mechanism of gravitational radiation as the
so-called Wagoner star may work in this process. The star is spun up by
accretion until the angular momentum loss by gravitational radiation balances
the accretion torque. The time-integrated dimensionless strain of the radiated
gravitational wave may be large enough to be detectable by the gravitational
wave detectors such as LIGO II.",9911513v3
2002-03-07,Timing study of the isolated neutron star RX J0720.4-3125,"We present a combined analysis of XMM-Newton, Chandra and Rosat observations
of the isolated neutron star RX J0720.4-3125, spanning a total period of \sim 7
years. We develop a maximum likelihood periodogramme based on \Delta C
statistic and maximum likelihood method, which are appropriate for sparse event
lists. As an ""a posteriori"" check, we have folded a further BeppoSAX dataset
with the period predicted at the time of that observation, finding that the
phase is consistent. The value of the spin down rate, here measured for the
first time, is \approx 10^{-14} s/s and can not be explained in terms of
propeller or torque from a fossil disk. When interpreted in terms of dipolar
losses, it gives a magnetic field of B \approx 10^{13} G, making also
implausible that the source is accreting from the underdense surroundings. We
discuss the implications of this measure for the different mechanisms that have
been suggested to explain the X-ray emission. We conclude that the observed
properties are more compatible with a scenario in which the source is \approx
10^6 yrs old, and its magnetic field has not changed substantially over the
lifetime.",0203111v1
2004-02-20,Bulgeless Galaxies and their Angular Momentum Problem,"The specific angular momentum of Cold Dark Matter (CDM) halos in a
$\Lambda$CDM universe is investigated. Their dimensionless specific angular
momentum $\lambda'=\frac{j}{\sqrt{2}V_{vir} R{vir}}$ with $V_{vir}$ and
$R_{vir}$ the virial velocity and virial radius, respectively depends strongly
on their merging histories. We investigate a set of $\Lambda$CDM simulations
and explore the specific angular momentum content of halos formed through
various merging histories. Halos with a quiet merging history, dominated by
minor mergers and accretion until the present epoch, acquire by tidal torques
on average only 2% to 3% of the angular momentum required for their rotational
support ($\lambda'=0.02$). This is in conflict with observational data for a
sample of late-type bulgeless galaxies which indicates that those galaxies
reside in dark halos with exceptionally high values of $\lambda' \approx
0.06-0.07$. Minor mergers and accretion preserve or slowly increase the
specific angular momentum of dark halos with time. This mechanism is however
not efficient enough in order to explain the observed spin values for late-type
dwarf galaxies. Energetic feedback processes have been invoked to solve the
problem that gas loses a large fraction of its specific angular momentum during
infall. Under the assumption that dark halos hosting bulgeless galaxies acquire
their mass via quiescent accretion, our results indicate yet another serious
problem: the specific angular momentum gained during the formation of these
objects is not large enough to explain their observed rotational
properties,even if no angular momentum would be lost during gas infall.",0402504v2
2004-05-05,A Toy Model for Magnetic Extraction of Energy from Black Hole Accretion Disc,"A toy model for magnetic extraction of energy from black hole (BH) accretion
disk is discussed by considering the restriction of the screw instability to
the magnetic field configuration. Three mechanisms of extracting energy
magnetically are involved. (1) The Blandford-Znajek (BZ) process is related to
the open magnetic field lines connecting the BH with the astrophysical load;
(2) the magnetic coupling (MC) process is related to the closed magnetic field
lines connecting the BH with its surrounding disk; and (3) a new scenario
(henceforth the DL process) for extracting rotational energy from the disk is
related to the open field lines connecting the disk with the astrophysical
load. The expressions for the electromagnetic powers and torques are derived by
using the equivalent circuits corresponding to the above energy mechanisms. It
turns out that the DL power is comparable with the BZ and MC powers as the BH
spin approaches unity. The radiation from a quasi-steady thin disk is discussed
in detail by applying the conservation laws of mass, energy and angular
momentum to the regions corresponding to the MC and DL processes. In addition,
the poloidal currents and the current densities in BH magnetosphere are
calculated by using the equivalent circuits.",0405073v2
2004-08-31,Relativistic Accretion Disk Models of High State Black Hole X-ray Binary Spectra,"We present calculations of non-LTE, relativistic accretion disk models
applicable to the high/soft state of black hole X-ray binaries. We include the
effects of thermal Comptonization and bound-free and free-free opacities of all
abundant ion species. We present spectra calculated for a variety of accretion
rates, black hole spin parameters, disk inclinations, and stress prescriptions.
We also consider nonzero inner torques on the disk, and explore different
vertical dissipation profiles, including some which are motivated by recent
radiation MHD simulations of magnetorotational turbulence. Bound-free metal
opacity generally produces significantly less spectral hardening than previous
models which only considered Compton scattering and free-free opacity. It also
tends to keep the effective photosphere near the surface, resulting in spectra
which are remarkably independent of the stress prescription and vertical
dissipation profile, provided little dissipation occurs above the effective
photosphere. We provide detailed comparisons between our models and the widely
used multicolor disk model. Frequency dependent discrepancies exist that may
affect the parameters of other spectral components when this simpler disk model
is used to fit modern X-ray data. For a given source, our models predict that
the luminosity in the high/soft state should approximately scale with the
fourth power of the empirically inferred maximum temperature, but with a slight
hardening at high luminosities. This is in good agreement with observations.
(abridged)",0408590v2
2005-04-17,From Neutron Star Binaries to Gamma-ray bursts,"I summarize recent results about how a neutron star binary coalescence can
produce short gamma-ray bursts (GRBs). Two possibilities are discussed: the
annihilation of neutrino anti-neutrino pairs above the merged remnant and the
exponential amplification of magnetic fields in the central object up to values
close to equipartition. We find that the neutrino annihilation drives bipolar,
relativistic outflows with Lorentz-factors large enough to circumvent the GRB
'compactness problem'. The total energy within these outflows is moderate by
GRB-standards ($\sim 10^{48}-10^{49}$ ergs), but the interaction with the
baryonic material blown-off by the neutrinos collimates the outflows into
opening angles of typically 0.1 sterad, yielding isotropic energies close to
$10^{51}$ ergs. We further want to stress the plausibility of the central
object resisting the immediate collapse to a black hole. In this case the
central object will --similar to a proto-neutron star-- be subject to neutrino
driven convection that --together with the rapid, differential rotation-- will
lead to a drastic amplification of pre-existing magnetic fields. Within
fractions of a second, field strengths comparable to equipartition field
strength ($> 10^{17}$ G) will be reached. These will produce large torques that
will spin-down the object within about 0.2 s, and would thus naturally explain
the duration of short GRBs.",0504368v1
2005-08-10,Evolution of rapidly rotating metal-poor massive stars towards gamma-ray bursts,"Recent models of rotating massive stars including magnetic fields prove it
difficult for the cores of single stars to retain enough angular momentum to
produce a collapsar and gamma-ray burst. At low metallicity, even very massive
stars may retain a massive hydrogen envelope due to the weakness of the stellar
winds, posing an additional obstacle to the collapsar model. Here, we consider
the evolution of massive, magnetic stars where rapid rotation induces almost
chemically homogeneous evolution. We find that in this case, the requirements
of the collapsar model are rather easily fulfilled if the metallicity
sufficiently small: 1) Rapidly rotating helium stars are formed without the
need to remove the hydrogen envelope, avoiding mass-loss induced spin-down. 2)
Angular momentum transport from the helium core to hydrogen envelope by
magnetic torques is insignificant. We demonstrate this by calculating
evolutionary models of massive stars with various metallicities, and derive an
upper metallicity limit for this scenario based on currently proposed mass loss
rates. Our models also suggest the existence of a lower CO-core mass limit of
about 10 Msun -- which relates to an initial mass of only about 20 Msun within
our scenario -- for GRB production. We argue that the relative importance of
the considered GRB progenitor channel, compared to any channel related to
binary stars, may increase with decreasing metallicity, and that this channel
might be the major path to GRBs from first stars.",0508242v1
2006-05-05,Rocking the Lighthouse: Circumpulsar Asteroids and Radio Intermittency,"We propose that neutral, circumpulsar debris entering the light cylinder can
account for many time-dependent pulsar phenomena that are otherwise difficult
to explain. Neutral material avoids propeller ejection and injects sufficient
charges -- after heating, evaporation, and ionization -- to alter current flows
and pair-production and thus trigger, detune, or extinguish coherent emission.
Relevant phenomena, with time scales from seconds to months, include nulls,
rotating radio transients (RRATs), rapid changes in pulse profile (``mode
changes''), variable subpulse drift rates, quasi-periodic bursts from B1931+24,
and torque variations. Over the 10 Myr lifetime of a canonical pulsar with
trillion-gauss surface magnetic field, less than a millionth of an Earth mass
of material is needed to modulate the Goldreich-Julian current by 100%.
Circumpulsar material originates from metal-rich, supernova fallback gas that
aggregates into asteroids. Debris disks can inject sufficient material on time
scales of interest, yet be too tenuous to form large planets detectable in
pulse timing data. Asteroid migration results from collisions and the
radiation-driven Yarkovsky and Poynting-Robertson effects. For B1931+24, an
asteroid in a $\sim 40$~day elliptical orbit pollutes the magnetosphere
stochastically through collisions with other debris. Injection is less likely
for hot, young and highly magnetized pulsars or millisecond pulsars that
pre-ionize any debris material well outside their small magnetospheres.
Injection effects will therefore be most prominent in long-period, cooler
pulsars, consistent with the distribution of relevant objects in perid and
period derivative. A pulsar's spin history and its radiation-beam orientation
may influence whether it displays nulling, RRATs and other effects.",0605145v1
2005-05-05,Current-driven magnetic rearrangements in spin-polarized point contacts,"A new method for investigating the dynamics of atomic magnetic moments in
current-carrying magnetic point contacts under bias is presented. This combines
the non-equilibrium Green's function (NEGF) method for evaluating the current
and the charge density with a description of the dynamics of the magnetization
in terms of quasistatic thermally-activated transitions between stationary
configurations. This method is then implemented in a tight-binding (TB) model
with parameters chosen to simulate the main features of the electronic
structures of magnetic transition metals. We investigate the domain wall (DW)
migration in magnetic monoatomic chains sandwiched between magnetic leads, and
for realistic parameters find that collinear arrangement of the magnetic
moments of the chain is always favorable. Several stationary magnetic
configurations are identified, corresponding to a different number of Bloch
walls in the chain and to a different current. The relative stability of these
configurations depends on the geometrical details of the junction and on the
bias, however we predict transitions between different configurations with
activation barriers of the order of a few tens of meV. Since different magnetic
configurations are associated to different resistances, this suggests an
intrinsic random telegraph noise at microwave frequencies in the I-V
characteristics of magnetic atomic point contacts at room temperature. Finally,
we investigate whether or not current induced torques are conservative.",0505134v1
2005-07-05,Stiff dynamics of electromagnetic two-body motion,"We study the stability of circular orbits of the electromagnetic two-body
problem in an electromagnetic setting that includes retarded and advanced
interactions. We give a method to derive the equations of tangent dynamics
about circular orbits up to nonlinear terms and we derive the linearized
equations explicitly. In particular we study the normal modes of the linearized
dynamics that have an arbitrarily large imaginary eigenvalue. These large
imaginary eigenvalues define fast frequencies that introduce a fast (stiff)
timescale into the dynamics. As an application of Dirac's electrodynamics of
point charges with retarded-only interactions, we study the conditions for the
two charges to perform a fast gyrating motion of small radius about a circular
orbit. The fast gyration defines an angular momentum of the order of the
orbital angular momentum, a vector that rotates in the orbital plane at a
frequency of the order of the orbital frequency and causes a gyroscopic torque.
We explore a consequence of this multiscale solution, i.e; the resonance
condition that the angular momentum of the stiff spinning should rotate exactly
at the orbital frequency. The resonant orbits turn out to have angular momenta
that are integer multiples of Planck's constant to a good approximation. Among
the many qualitative agreements with quantum electrodynamics (QED), the orbital
frequency of the resonant orbits are given by a difference of two eigenvalues
of a linear operator and the emission lines of QED agree with our predictions
within a few percent.",0507030v3
2002-10-10,Precession and interference in the Aharonov-Casher and scalar Aharonov-Bohm effect,"The ideal scalar Aharonov-Bohm (SAB) and Aharonov-Casher (AC) effect involve
a magnetic dipole pointing in a certain fixed direction: along a purely time
dependent magnetic field in the SAB case and perpendicular to a planar static
electric field in the AC case. We extend these effects to arbitrary direction
of the magnetic dipole. The precise conditions for having nondispersive
precession and interference effects in these generalized set ups are delineated
both classically and quantally. Under these conditions the dipole is affected
by a nonvanishing torque that causes pure precession around the directions
defined by the ideal set ups. It is shown that the precession angles are in the
quantal case linearly related to the ideal phase differences, and that the
nonideal phase differences are nonlinearly related to the ideal phase
differences. It is argued that the latter nonlinearity is due the appearance of
a geometric phase associated with the nontrivial spin path. It is further
demonstrated that the spatial force vanishes in all cases except in the
classical treatment of the nonideal AC set up, where the occurring force has to
be compensated by the experimental arrangement. Finally, for a closed
space-time loop the local precession effects can be inferred from the
interference pattern characterized by the nonideal phase differences and the
visibilities. It is argued that this makes it natural to regard SAB and AC as
essentially local and nontopological effects.",0210070v1
2007-06-06,Jet-Driven Disk Accretion in Low Luminosity AGN?,"We explore an accretion model for low luminosity AGN (LLAGN) that attributes
the low radiative output to a low mass accretion rate rather than a low
radiative efficiency. In this model, electrons are assumed to drain energy from
the ions as a result of collisionless plasma microinstabilities. Consequently,
the accreting gas collapses to form a geometrically thin disk at small radii
and is able to cool before reaching the black hole. The accretion disk is not a
standard disk, however, because the radial disk structure is modified by a
magnetic torque which drives a jet and which is primarily responsible for
angular momentum transport. We also include relativistic effects. We apply this
model to the well known LLAGN M87 and calculate the combined disk-jet
steady-state broadband spectrum. A comparison between predicted and observed
spectra indicates that M87 may be a maximally spinning black hole accreting at
a rate of 10^{-3} solar masses per year. This is about 6 orders of magnitude
below the Eddington rate for the same radiative efficiency. Furthermore, the
total jet power inferred by our model is in remarkably good agreement with the
value independently deduced from observations of the M87 jet on kiloparsec
scales.",0706.0763v1
2007-06-28,Global General Relativistic MHD Simulation of a Tilted Black-Hole Accretion Disk,"This paper presents a continuation of our efforts to numerically study
accretion disks that are misaligned (tilted) with respect to the rotation axis
of a Kerr black hole. Here we present results of a global numerical simulation
which fully incorporates the effects of the black hole spacetime as well as
magnetorotational turbulence that is the primary source of angular momentum
transport in the flow. This simulation shows dramatic differences from
comparable simulations of untilted disks. Accretion onto the hole occurs
predominantly through two opposing plunging streams that start from high
latitudes with respect to both the black-hole and disk midplanes. This is due
to the aspherical nature of the gravitational spacetime around the rotating
black hole. These plunging streams start from a larger radius than would be
expected for an untilted disk. In this regard the tilted black hole effectively
acts like an untilted black hole of lesser spin. Throughout the duration of the
simulation, the main body of the disk remains tilted with respect to the
symmetry plane of the black hole; thus there is no indication of a
Bardeen-Petterson effect in the disk at large. The torque of the black hole
instead principally causes a global precession of the main disk body. In this
simulation the precession has a frequency of $3 (M_\odot/M)$ Hz, a value
consistent with many observed low-frequency quasi-periodic oscillations.
However, this value is strongly dependent on the size of the disk, so this
frequency may be expected to vary over a large range.",0706.4303v1
2007-08-08,"Pulsars: Progress, Problems and Prospects","I survey recent successes in the application of relativistic MHD and
force-free electrodynamics to the modeling of the pulsars' rotational energy
loss mechanism as well as to the structure and emission characteristics of
Pulsar Wind Nebulae. I suggest that unsteady reconnection in the current sheet
separating the closed from the open zones of the magnetosphere is responsible
for the torque fluctuations observed in some pulsars, as well as for departures
of the braking index from the canonical value of 3. I emphasize the
significance of the boundary layer between the closed and open zones as the
active site in the outer magnetopshere. I elaborate on the conflict between the
models currently in use to interpret the gamma ray and X-ray pulses from these
systems with the electric current flows found in the spin down models. Because
the polar cap ``gap'' is the essential component in the supply of plasma to
pulsar magnetospheres and to pulsar wind nebulae, I emphasize the importance of
high sensitivity gamma ray observations of pulsars with core components of
radio emission and high magnetospheric voltage, since these observations will
look directly into the polar plasma production region. I also discuss the shock
conversion of flow energy into the spectra of the synchrotron emitting
particles in the Nebulae. I comment on the prospects for future developments
and improvements in all these areas.",0708.1050v1
2007-08-18,Gyroscope precession in special and general relativity from basic principles,"In special relativity a gyroscope that is suspended in a torque-free manner
will precess as it is moved along a curved path relative to an inertial frame
S. We explain this effect, which is known as Thomas precession, by considering
a real grid that moves along with the gyroscope, and that by definition is not
rotating as observed from its own momentary inertial rest frame. From the basic
properties of the Lorentz transformation we deduce how the form and rotation of
the grid (and hence the gyroscope) will evolve relative to S. As an
intermediate step we consider how the grid would appear if it were not length
contracted along the direction of motion. We show that the uncontracted grid
obeys a simple law of rotation. This law simplifies the analysis of spin
precession compared to more traditional approaches based on Fermi transport. We
also consider gyroscope precession relative to an accelerated reference frame
and show that there are extra precession effects that can be explained in a way
analogous to the Thomas precession. Although fully relativistically correct,
the entire analysis is carried out using three-vectors. By using the
equivalence principle the formalism can also be applied to static spacetimes in
general relativity. As an example, we calculate the precession of a gyroscope
orbiting a static black hole. In an addendum the general reasoning is extended
to include also rotating reference frames.",0708.2490v1
2008-01-07,Precise Orbital Parameters and Anomalous Phase Variations of the Accretion-powered Millisecond Pulsar XTE J1807-294,"This study reports pulse variation analysis results for the forth discovered
accretion-powered millisecond pulsar XTE J1807-294 during its 2003 outburst
observed by {\it Rossi X-ray Timing Explorer}. The pulsation is significantly
detected only in the first $\sim$90d out of $\sim$150d observations. The pulse
phase variation is too complex to be described as an orbital motion plus a
simple polynomial model. The precise orbital parameters with
$P_{orb}=40.073601(8)$ min and ${\it a_x}\sin {\it i}=4.823(5)$ lt-ms were
obtained after applying the trend removal to the daily observed 150s segments
pulse phases folded with a constant spin frequency without Keplerian orbit
included. The binary barycenter corrected pulse phases show smooth evolution
and clear negative phase shifts coincident with the flares seen on the light
curve and the enhancements of fractional pulse amplitude. The non-flare pulse
phases for the first $\sim$60d data are well described as a fourth order
polynomial implying that the neutron star was spun-up during the first
$\sim$60d with a rate $\dot \nu=(1.7\pm0.3) \times 10^{-13}$ Hz/s at the
beginning of the outburst. Significant soft phase lags up to $\sim$500 $\mu s$
($\sim$10% cycle) between 2 to 20 keV were detected for the nonflare pulse
phases. We conclude that the anomalous phase shifts are unlikely due to the
accretion torque but could result from the ``hot spot'' moving on the surface
of neutron star.",0801.0909v1
2008-03-28,Detecting gravitational wave emission from the known accreting neutron stars,"Detection of gravitational waves from accreting neutron stars (NSs) in our
galaxy, due to ellipticity or internal oscillation, would be a breakthrough in
our understanding of compact objects and explain the absence of NSs rotating
near the break-up limit. Direct detection, however, poses a formidable
challenge. Using the current data available on the properties of the accreting
NSs in Low Mass X-Ray Binaries (LMXBs), we quantify the detectability for the
known accreting NSs, considering various emission scenarios and taking into
account the negative impact of parameter uncertainty on the data analysis
process. Only a few of the persistently bright NSs accreting at rates near the
Eddington limit are detectable by Advanced LIGO if they are emitting
gravitational waves at a rate matching the torque from accretion. A larger
fraction of the known population is detectable if the spin and orbital
parameters are known in advance, especially with the narrow-band Advanced LIGO.
We identify the most promising targets, and list specific actions that would
lead to significant improvements in detection probability. These include
astronomical observations (especially for unknown orbital periods),
improvements in data analysis algorithms and capabilities, and further detector
development.",0803.4097v2
2008-08-26,A New Class of Radio Pulsars - Back in 1982,"Basic ideas about the torques on the neutron star and the existence of an
equilibrium rotation period followed from the recognition that most X-ray
binaries contain accretion powered neutron stars. The evolution of binaries
through a phase of accretion onto the neutron star, eventually leading to a
post-accretion radio pulsar phase, was initially discussed as a way to
understand the scarcity of binaries among the radio pulsars and the relatively
short rotation periods of the first discovered binary radio pulsars in terms of
magnetic fields that would be smaller than the familiar $10^{12} G$ range. The
discovery of the millisecond pulsars made us realize that the fields can be
much lower in a new class of radio pulsars that have been spun up by accretion
in LMXBs. The predicted spin-down rates of the millisecond pulsar was soon
confirmed. The observers' search for millisecond X-ray periods was on, leading
first to the discovery of QPOs, and eventually to the discovery of the X-ray
millisecond pulsars. The theorists' quest for explanations of why X-ray
millisecond pulsations are not observed from LMXBs also started right away.",0808.3485v1
2010-04-06,Anisotropic superconducting properties of single-crystalline FeSe0.5Te0.5,"Iron-chalcogenide single crystals with the nominal composition
FeSe$_{0.5}$Te$_{0.5}$ and a transition temperature of $T_{c}\simeq14.6$ K were
synthesized by the Bridgman method. The structural and anisotropic
superconducting properties of those crystals were investigated by means of
single crystal X-ray and neutron powder diffraction, SQUID and torque
magnetometry, and muon-spin rotation. Room temperature neutron powder
diffraction reveals that 95% of the crystal volume is of the same tetragonal
structure as PbO. The structure refinement yields a stoichiometry of
Fe_1.045Se_0.406Te_0.594. Additionally, a minor hexagonal Fe_7Se_8 impurity
phase was identified. The magnetic penetration depth \lambda at zero
temperature was found to be 491(8) nm in the ab-plane and 1320(14) nm along the
c-axis. The zero-temperature value of the superfluid density \rho_s(0)
\lambda^-2(0) obeys the empirical Uemura relation observed for various
unconventional superconductors, including cuprates and iron-pnictides. The
temperature dependences of both \lambda_ab and \lambda_c are well described by
a two-gap s+s-wave model with the zero-temperature gap values of
\Delta_S(0)=0.51(3) meV and \Delta_L(0)=2.61(9) meV for the small and the large
gap, respectively. The magnetic penetration depth anisotropy parameter
\gamma_\lambda(T)=\lambda_c(T)/\lambda_{ab}(T) increases with decreasing
temperature, in agreement with \gamma_\lambda(T) observed in the iron-pnictide
superconductors.",1004.0812v1
2010-05-07,Discovery of a 0.02 Hz QPO feature in the Transient X-ray Pulsar KS 1947+300,"We report the discovery of Quasi Periodic Oscillations (QPO) at 0.02 Hz in a
transient high mass X-ray binary pulsar KS 1947+300 using {\em RXTE}-PCA. The
QPOs were detected during May-June 2001, at the end of a long outburst. This is
the 9th transient accretion powered high magnetic field X-ray pulsar in which
QPOs have been detected and the QPO frequency of this source is lowest in this
class of sources. The unusual feature of this source is that though the
outburst lasted for more than 100 days, the QPOs were detected only during the
last few days of the outburst when the X-ray intensity had decayed to 1.6% of
the peak intensity. The rms value of the QPO is large, $\sim15.4\pm1.0%$ with a
slight positive correlation with energy. The detection of QPOs and strong
pulsations at a low luminosity level suggests that the magnetic field strength
of the neutron star is not as high as was predicted earlier on the basis of a
correlation between the spin-up torque and the X-ray luminosity.",1005.1161v1
2010-06-30,Towards relativistic orbit fitting of Galactic center stars and pulsars,"The S stars orbiting the Galactic center black hole reach speeds of up to a
few percent the speed of light during pericenter passage. This makes, for
example, S2 at pericenter much more relativistic than known binary pulsars, and
opens up new possibilities for testing general relativity. This paper develops
a technique for fitting nearly-Keplerian orbits with perturbations from
Schwarzschild curvature, frame dragging, and spin-induced torque, to redshift
measurements distributed along the orbit but concentrated around pericenter.
Both orbital and light-path effects are taken into account. It turns out that
absolute calibration of rest-frame frequency is not required. Hence, if pulsars
on orbits similar to the S stars are discovered, the technique described here
can be applied without change, allowing the much greater accuracies of pulsar
timing to be taken advantage of. For example, pulse timing of 3 microsec over
one hour amounts to an effective redshift precision of 30 cm/s, enough to
measure frame dragging and the quadrupole moment from an S2-like orbit,
provided problems like the Newtonian ""foreground"" due to other masses can be
overcome. On the other hand, if stars with orbital periods of order a month are
discovered, the same could be accomplished with stellar spectroscopy from the
E-ELT at the level of 1 km/s.",1007.0007v2
2010-09-15,The Increasing Rotation Period of Comet 10P/Tempel 2,"We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March.
R-band lightcurves were obtained on 11 of these nights from 1999 April through
1999 June, prior to both the onset of significant coma activity and perihelion.
Phasing of the data yields a double-peaked lightcurve and indicates a nucleus
rotational period of 8.941 +/- 0.002 hr with a peak-to-peak amplitude of ~0.75
mag. Our data are sufficient to rule out all other possible double-peaked
solutions as well as the single- and triple- peaked solutions. This rotation
period agrees with one of five possible solutions found in post-perihelion data
from 1994 by Mueller and Ferrin (1996, Icarus, 123, 463-477), and unambiguously
eliminates their remaining four solutions. We applied our same techniques to
published lightcurves from 1988 which were obtained at an equivalent orbital
position and viewing geometry as in 1999. We found a rotation period of 8.932
+/- 0.001 hr in 1988, consistent with the findings of previous authors and
incompatible with our 1999 solution. This reveals that Tempel 2 spun-down by
~32 s between 1988 and 1999 (two intervening perihelion passages). If the
spin-down is due to a systematic torque, then the rotation period prior to
perihelion during the 2010 apparition is expected to be an additional 32 s
longer than in 1999.",1009.3019v1
2011-01-11,Direct Numerical Simulation of decaying two-dimensional turbulence in a no-slip square box using Smoothed Particle Hydrodynamics,"This paper explores the application of SPH to a Direct Numerical Simulation
(DNS) of decaying turbulence in a two-dimensional no-slip wall-bounded domain.
In this bounded domain, the inverse energy cascade, and a net torque exerted by
the boundary, result in a spontaneous spin up of the fluid, leading to a
typical end state of a large monopole vortex that fills the domain. The SPH
simulations were compared against published results using a high accuracy
pseudo-spectral code. Ensemble averages of the kinetic energy, enstrophy and
average vortex wavenumber compared well against the pseudo-spectral results, as
did the evolution of the total angular momentum of the fluid. However, while
the pseudo-spectral results emphasised the importance of the no-slip boundaries
as generators of long lived coherent vortices in the flow, no such generation
was seen in the SPH results. Vorticity filaments produced at the boundary were
always dissipated by the flow shortly after separating from the boundary layer.
The kinetic energy spectrum of the SPH results was calculated using a SPH
Fourier transform that operates directly on the disordered particles. The
ensemble kinetic energy spectrum showed the expected k-3 scaling over most of
the inertial range. However, the spectrum flattened at smaller length scales
(initially less than 7.5 particle spacings and growing in size over time),
indicating an excess of small-scale kinetic energy.",1101.2240v1
2011-01-15,Disk Formation in Magnetized Clouds Enabled by the Hall Effect,"Stars form in dense cores of molecular clouds that are observed to be
significantly magnetized. A dynamically important magnetic field presents a
significant obstacle to the formation of protostellar disks. Recent studies
have shown that magnetic braking is strong enough to suppress the formation of
rotationally supported disks in the ideal MHD limit. Whether non-ideal MHD
effects can enable disk formation remains unsettled. We carry out a first study
on how disk formation in magnetic clouds is modified by the Hall effect, the
least explored of the three non-ideal MHD effects in star formation (the other
two being ambipolar diffusion and Ohmic dissipation). For illustrative
purposes, we consider a simplified problem of a non-self-gravitating,
magnetized envelope collapsing onto a central protostar of fixed mass. We find
that the Hall effect can spin up the inner part of the collapsing flow to
Keplerian speed, producing a rotationally supported disk. The disk is generated
through a Hall-induced magnetic torque. Disk formation occurs even when the
envelope is initially non-rotating, provided that the Hall coefficient is large
enough. When the magnetic field orientation is flipped, the direction of disk
rotation is reversed as well. The implication is that the Hall effect can in
principle produce both regularly rotating and counter-rotating disks around
protostars. We conclude that the Hall effect is an important factor to consider
in studying the angular momentum evolution of magnetized star formation in
general and disk formation in particular.",1101.3018v1
2012-03-28,"Multifunctional L10-Mn1.5Ga films with ultrahigh coercivity, giant perpendicular magnetocrystalline anisotropy and large magnetic energy product","We present the fascinating magnetic properties in homogenous noble-metal-free
and rare-earth-free L10-Mn1.5Ga epitaxial films on GaAs (001), including
ultrahigh perpendicular coercivity remarkably tunable from 8.1 to 42.8 kOe,
giant perpendicular magnetocrystalline anisotropy with a maximum of 22.9
Merg/cc, easily controllable magnetization from 27.3 to 270.5 emu/cc, excellent
squareness exceeding 0.94 and large magnetic energy product up to 2.6 MGOe.
These magnificent room-temperature magnetic characteristics make our
L10-Mn1.5Ga films multifunctional as outstanding and cost-effective alternative
for not only perpendicular magnetic recording bits with areal density over 30
Tb inch-2 and thermal stability over 60 years, but variety of novel devices
with high magnetic-noise immunity and thermal stability like spin-torque MRAMs
and oscillators pillars below 5 nm in dimension, and giant magnetoresistance
sensors able to measure high fileds up to 42 kOe . Moreover, this kind of
materials can also be expected as permanent magnets for replacing the expensive
rare-earth magnets widely used today.",1203.6176v5
2012-05-29,Magnetic Interactions in Coalescing Neutron Star Binaries,"It is expected on both evolutionary and empirical grounds that many merging
neutron star (NS) binaries are composed of a highly magnetized NS in orbit with
a relatively low magnetic field NS. I study the magnetic interactions of these
binaries using the framework of a unipolar inductor model. The e.m.f. generated
across the non-magnetic NS as it moves through the magnetosphere sets up a
circuit connecting the two stars. The exact features of this circuit depend on
the uncertain resistance in the space between the stars R_space. Nevertheless,
I show that there are interesting observational and/or dynamical effects
irrespective of its exact value. When R_space is large, electric dissipation as
great as ~10^{46} erg/s (for magnetar-strength fields) occurs in the
magnetosphere, which would exhibit itself as a hard X-ray precursor in the
seconds leading up to merger. With less certainty, there may also be an
associated radio transient, but this would be observed well past merger (~hrs)
because of interstellar dispersion. When R_space is small, electric dissipation
largely occurs in the surface layers of the magnetic NS. This can reach
~10^{49} erg/s during the final ~1 sec before merger, similar to the energetics
and timescales of short gamma-ray bursts. In addition, for dipole fields
greater than ~10^{12} G and a small R_space, magnetic torques spin up the
magnetized NS. This drains angular momentum from the binary and accelerates the
inspiral. A faster coalescence results in less orbits occurring before merger,
which would impact matched-filtering gravitational-wave searches by
ground-based laser interferometers and could create difficulties for studying
alternative theories of gravity with compact inspirals.",1205.6482v1
2012-10-08,Knock-on processes in superfluid vortex avalanches and pulsar glitch statistics,"A framework is presented for a statistical theory of neutron star glitches,
motivated by the results emerging from recent Gross-Pitaevskii simulations of
pinned, decelerating quantum condensates. It is shown that the observed glitch
size distributions cannot be reproduced if superfluid vortices unpin
independently via a Poisson process; the central limit theorem yields a narrow
Gaussian for the size distribution, instead of the broad, power-law tail
observed. This conclusion is not altered fundamentally when a range of pinning
potentials is included, which leads to excavation of the potential distribution
of occupied sites, vortex accumulation at strong pinning sites, and hence the
occasional, abnormally large glitch. Knock-on processes are therefore needed to
make the unpinning rate of a vortex conditional on the pinning state of its
near and/or remote neighbours, so that the Gaussian size distributions
resulting generically from the central limit theorem are avoided. At least two
knock-on processes, nearest- neighbour proximity knock-on and remote acoustic
knock-on, are clearly evident in the Gross-Pitaevskii simulation output. It is
shown that scale-invariant (i.e. power-law) vortex avalanches occur when
knock-on is included, provided that two specific relations hold between the
temperature and spin-down torque. This fine tuning is unlikely in an
astronomical setting, leaving the overall problem partly unsolved. A
state-dependent Poisson formalism is presented which will form the basis of
future studies in this area.",1210.2203v1
2012-11-19,Relativity and the evolution of the Galactic center S-star orbits,"We consider the orbital evolution of the S-stars, the young main-sequence
stars near the supermassive black hole (SBH) at the Galactic center (GC), and
put constraints on competing models for their origin. Our analysis includes for
the first time the joint effects of Newtonian and relativistic perturbations to
the motion, including the dragging of inertial frames by a spinning SBH as well
as torques due to finite-N asymmetries in the field-star distribution (resonant
relaxation, RR). The evolution of the S-star orbits is strongly influenced by
the Schwarzschild barrier (SB), the locus in the (E,L) plane where RR is
ineffective at driving orbits to higher eccentricities. Formation models that
invoke tidal disruption of binary stars by the SBH tend to place stars below
(i.e., at higher eccentricities than) the SB; some stars remain below the
barrier, but most stars are able to penetrate it, after which they are subject
to RR and achieve a nearly thermal distribution of eccentricities. This process
requires roughly 50 Myr in nuclear models with relaxed stellar cusps, or >~10
Myr, regardless of the initial distribution of eccentricities, in nuclear
models that include a dense cluster of 10 M_Sun black holes. We find a
probability of <~1% for any S-star to be tidally disrupted by the SBH over its
lifetime.",1211.4594v2
2013-06-18,Dynamics of Strongly Twisted Relativistic Magnetospheres,"Magnetar magnetospheres are believed to be strongly twisted, due to shearing
of the stellar crust by internal magnetic stresses. We present time-dependent
axisymmetric simulations showing in detail the evolution of relativistic
force-free magnetospheres subjected to slow twisting through large angles. When
the twist amplitude is small, the magnetosphere moves quasi-statically through
a sequence of equilibria of increasing free energy. At some twist amplitude the
magnetosphere becomes tearing-mode unstable to forming a resistive current
sheet, initiating large-scale magnetic reconnection in which a significant
fraction of the magnetic free energy can be dissipated. This ""critical"" twist
angle is insensitive to the resistive length scale. Rapid shearing temporarily
stabilizes the magnetosphere beyond the critical angle, allowing the
magnetosphere of a rapidly differentially rotating star to store, and
dissipate, more free energy. In addition to these effects, shearing the surface
of a rotating star increases the spindown torque applied to the star. If
shearing is much slower than rotation, the resulting spikes in spindown rate
can occur on timescales anywhere from the long twisting timescale to the
stellar spin period or shorter, depending both on the stellar shear
distribution and the existing distribution of magnetospheric twists. A model in
which energy is stored in the magnetosphere, and released by a magnetospheric
instability, therefore predicts large changes in the measured spindown rate
before SGR giant flares.",1306.4335v2
2014-01-03,"Nonequilibrium quantum fluctuations of a dispersive medium: Spontaneous emission, photon statistics, entropy generation, and stochastic motion","We study the implications of quantum fluctuations of a dispersive medium,
under steady rotation, either in or out of thermal equilibrium with its
environment. A rotating object exhibits a quantum instability by dissipating
its mechanical motion via spontaneous emission of photons, as well as internal
heat generation. Universal relations are derived for the radiated energy and
angular momentum as trace formulas involving the object's scattering matrix. We
also compute the quantum noise by deriving the full statistics of the radiated
photons out of thermal and/or dynamic equilibrium. The (entanglement) entropy
generation is quantified, and the total entropy is shown to be always
increasing. Furthermore, we derive a Fokker-Planck equation governing the
stochastic angular motion resulting from the fluctuating back-reaction
frictional torque. As a result, we find a quantum limit on the uncertainty of
the object's angular velocity in steady rotation. Finally, we show in some
detail that a rotating object drags nearby objects, making them spin parallel
to its axis of rotation. A scalar toy model is introduced in the first part to
simplify the technicalities and ease the conceptual complexities; a detailed
discussion of quantum electrodynamics is presented in the second part.",1401.0701v1
2014-02-05,Magnetization dynamics: path-integral formalism for the stochastic Landau-Lifshitz-Gilbert equation,"We construct a path-integral representation of the generating functional for
the dissipative dynamics of a classical magnetic moment as described by the
stochastic generalization of the Landau-Lifshitz-Gilbert equation proposed by
Brown, with the possible addition of spin-torque terms. In the process of
constructing this functional in the Cartesian coordinate system, we critically
revisit this stochastic equation. We present it in a form that accommodates for
any discretization scheme thanks to the inclusion of a drift term. The
generalized equation ensures the conservation of the magnetization modulus and
the approach to the Gibbs-Boltzmann equilibrium in the absence of non-potential
and time-dependent forces. The drift term vanishes only if the mid-point
Stratonovich prescription is used. We next reset the problem in the more
natural spherical coordinate system. We show that the noise transforms
non-trivially to spherical coordinates acquiring a non-vanishing mean value in
this coordinate system, a fact that has been often overlooked in the
literature. We next construct the generating functional formalism in this
system of coordinates for any discretization prescription. The functional
formalism in Cartesian or spherical coordinates should serve as a starting
point to study different aspects of the out-of-equilibrium dynamics of magnets.
Extensions to colored noise, micro-magnetism and disordered problems are
straightforward.",1402.1200v2
2014-02-11,Librational response of a deformed 3-layer Titan perturbed by non-keplerian orbit and atmospheric couplings,"The analyses of Titan's gravity field obtained by Cassini space mission
suggest the presence of an internal ocean beneath its icy surface. The
characterization of the geophysical parameters of the icy shell and the ocean
is important to constrain the evolution models of Titan. The knowledge of the
librations, that are periodic oscillations around a uniform rotational motion,
can bring piece of information on the interior parameters. The objective of
this paper is to study the librational response in longitude from an analytical
approach for Titan composed of a deep atmosphere, an elastic icy shell, an
internal ocean, and an elastic rocky core perturbed by the gravitational
interactions with Saturn. We start from the librational equations developed for
a rigid satellite in synchronous spin-orbit resonance. We introduce explicitly
the atmospheric torque acting on the surface computed from the Titan IPSL GCM
(Institut Pierre Simon Laplace General Circulation Model) and the periodic
deformations of elastic solid layers due to the tides. We investigate the
librational response for various interior models in order to compare and to
identify the influence of the geophysical parameters and the impact of the
elasticity. The main librations arise at two well-separated forcing frequency
ranges: low forcing frequencies dominated by the Saturnian annual and
semi-annual frequencies, and a high forcing frequency regime dominated by
Titan's orbital frequency around Saturn. We find that internal structure models
including an internal ocean with elastic solid layers lead to the same order of
libration amplitude than the oceanless models, which makes more challenging to
differentiate them by the interpretation of librational motion.",1402.2493v1
2014-06-26,Population synthesis of isolated Neutron Stars with magneto--rotational evolution,"We revisit the population synthesis of isolated radio-pulsars incorporating
recent advances on the evolution of the magnetic field and the angle between
the magnetic and rotational axes from new simulations of the magneto-thermal
evolution and magnetosphere models, respectively. An interesting novelty in our
approach is that we do not assume the existence of a death line. We discuss
regions in parameter space that are more consistent with the observational
data. In particular, we find that any broad distribution of birth spin periods
with $P_0\lesssim 0.5$ s can fit the data, and that if the alignment angle is
allowed to vary consistently with the torque model, realistic magnetospheric
models are favoured compared to models with classical magneto-dipolar radiation
losses. Assuming that the initial magnetic field is given by a lognormal
distribution, our optimal model has mean strength $\langle\log B_0{\rm
[G]}\rangle \approx 13.0-13.2$ with width $\sigma (\log B_0) = 0.6-0.7$.
However, there are strong correlations between parameters. This degeneracy in
the parameter space can be broken by an independent estimate of the pulsar
birth rate or by future studies correlating this information with the
population in other observational bands (X-rays and $\gamma$-rays).",1406.6794v1
2014-07-31,Gravitational waves from rapidly rotating neutron stars,"Rapidly rotating neutron stars in Low Mass X-ray Binaries have been proposed
as an interesting source of gravitational waves. In this chapter we present
estimates of the gravitational wave emission for various scenarios, given the
(electromagnetically) observed characteristics of these systems. First of all
we focus on the r-mode instability and show that a 'minimal' neutron star model
(which does not incorporate exotica in the core, dynamically important magnetic
fields or superfluid degrees of freedom), is not consistent with observations.
We then present estimates of both thermally induced and magnetically sustained
mountains in the crust. In general magnetic mountains are likely to be
detectable only if the buried magnetic field of the star is of the order of
$B\approx 10^{12}$ G. In the thermal mountain case we find that gravitational
wave emission from persistent systems may be detected by ground based
interferometers. Finally we re-asses the idea that gravitational wave emission
may be balancing the accretion torque in these systems, and show that in most
cases the disc/magnetosphere interaction can account for the observed spin
periods.",1407.8254v1
2014-10-03,45 Years of Rotation of the Crab Pulsar,"The 30-Hz rotation rate of the Crab pulsar has been monitored at Jodrell Bank
Observatory since 1984 and by other observatories before then. Since 1968, the
rotation rate has decreased by about $0.5$\,Hz, interrupted only by sporadic
and small spin up events (glitches). 24 of these events have been observed,
including a significant concentration of 15 occurring over an interval of 11
years following MJD 50000. The monotonic decrease of the slowdown rate is
partially reversed at glitches. This reversal comprises a step and an
asymptotic exponential with a 320-day time constant, as determined in the three
best-isolated glitches. The cumulative effect of all glitches is to reduce the
decrease in slowdown rate by about 6\%. Overall, a low mean braking index of
$2.342(1)$ is measured for the whole period, compared with values close to
$2.5$ in intervals between glitches. Removing the effects of individual
glitches reveals an underlying power law slowdown with the same braking index
of 2.5. We interpret this value in terms of a braking torque due to a dipolar
magnetic field in which the inclination angle between the dipole and rotation
axes is increasing. There may also be further effects due to a monopolar
particle wind or infalling supernova debris.",1410.0886v1
2014-11-03,Non-equilibrium steady state and subgeometric ergodicity for a chain of three coupled rotors,"We consider a chain of three rotors (rotators) whose ends are coupled to
stochastic heat baths. The temperatures of the two baths can be different, and
we allow some constant torque to be applied at each end of the chain. Under
some non-degeneracy condition on the interaction potentials, we show that the
process admits a unique invariant probability measure, and that it is ergodic
with a stretched exponential rate. The interesting issue is to estimate the
rate at which the energy of the middle rotor decreases. As it is not directly
connected to the heat baths, its energy can only be dissipated through the two
outer rotors. But when the middle rotor spins very rapidly, it fails to
interact effectively with its neighbors due to the rapid oscillations of the
forces. By averaging techniques, we obtain an effective dynamics for the middle
rotor, which then enables us to find a Lyapunov function. This and an
irreducibility argument give the desired result. We finally illustrate
numerically some properties of the non-equilibrium steady state.",1411.0400v3
2014-11-19,The power of relativistic jets is larger than the luminosity of their accretion disks,"Theoretical models for the production of relativistic jets from active
galactic nuclei predict that jet power arises from the spin and mass of the
central black hole, as well as the magnetic field near the event horizon. The
physical mechanism mechanism underlying the contribution from the magnetic
field is the torque exerted on the rotating black hole by the field amplified
by the accreting material. If the squared magnetic field is proportional to the
accretion rate, then there will be a correlation between jet power and
accretion luminosity. There is evidence for such a correlation, but inadequate
knowledge of the accretion luminosity of the limited and inhomogeneous used
samples prevented a firm conclusion. Here we report an analysis of archival
observations of a sample of blazars (quasars whose jets point towards Earth)
that overcomes previous limitations. We find a clear correlation between jet
power as measured through the gamma-ray luminosity, and accretion luminosity as
measured by the broad emission lines, with the jet power dominating over the
disk luminosity, in agreement with numerical simulations. This implies that the
magnetic field threading the black hole horizon reaches the maximum value
sustainable by the accreting matter.",1411.5368v1
2015-02-18,Dynamical mass ejection from black hole-neutron star binaries,"We investigate properties of material ejected dynamically in the merger of
black hole-neutron star binaries by numerical-relativity simulations. We
systematically study the dependence of ejecta properties on the mass ratio of
the binary, spin of the black hole, and equation of state of the neutron-star
matter. Dynamical mass ejection is driven primarily by tidal torque, and the
ejecta is much more anisotropic than that from binary neutron star mergers. In
particular, the dynamical ejecta is concentrated around the orbital plane with
a half opening angle of 10--20deg and often sweeps out only a half of the
plane. The ejecta mass can be as large as ~0.1M_sun, and the velocity is
subrelativistic with ~0.2--0.3c for typical cases. The ratio of the ejecta mass
to the bound mass (disk and fallback components) is larger, and the ejecta
velocity is larger, for larger values of the binary mass ratio, i.e., for
larger values of the black-hole mass. The remnant black hole-disk system
receives a kick velocity of O(100)km/s due to the ejecta linear momentum, and
this easily dominates the kick velocity due to gravitational radiation.
Structures of postmerger material, velocity distribution of the dynamical
ejecta, fallback rates, and gravitational waves are also investigated. We also
discuss the effect of ejecta anisotropy on electromagnetic counterparts,
specifically a macronova/kilonova and synchrotron radio emission, developing
analytic models.",1502.05402v2
2015-04-09,Magnetic bilayer-skyrmions without skyrmion Hall effect,"Arising from emergent electromagnetic field of magnetic skyrmions due to
their nontrivial topology, the skyrmion Hall effect might be a roadblock for
practical applications since any longitudinal motions of skyrmions in nanotrack
is accompanied by a transverse motion. A direct consequence of such an effect
is easy destruction of skyrmions at the nanotrack edges during their fast
motions along the nanotrack, despite their topological protection. Here we
propose an entirely novel solution of completely inhibiting such skyrmion Hall
effect without affecting its topological properties based on a
antiferromagnetic-coupling bilayer system. We show that a pair of magnetic
skyrmions can be nucleated in such a bilayer system through vertical current
injection or converted from a current-driven domain-wall pair. Once nucleated,
the skyrmion pair can be displaced through current-induced spin torque either
from a vertical injected current or in-plane current. The skyrmion Hall effect
is completely suppressed due to the cancellation of back-action forces acting
on each individual skyrmion, resulting in a straight and fast motion of
skyrmions along the current direction. This proposal will be of fundamental
interests by introducing the bilayer degree of freedom into the system.
Moreover, it provides an easy way to engineer the transport properties of the
skyrmionic devices to achieve desired performance, making it highly promising
for practical applications such as ultradense memory and information-processing
devices based on skyrmions.",1504.02252v1
2015-04-17,Chiral damping of magnetic domain walls,"Structural symmetry breaking in magnetic materials is responsible for a
variety of outstanding physical phenomena. Examples range from the existence of
multiferroics, to current induced spin orbit torques (SOT) and the formation of
topological magnetic structures. In this letter we bring into light a novel
effect of the structural inversion asymmetry (SIA): a chiral damping mechanism.
This phenomenon is evidenced by measuring the field driven domain wall (DW)
motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers. The
difficulty in evidencing the chiral damping is that the ensuing DW dynamics
exhibit identical spatial symmetry to those expected from the
Dzyaloshinskii-Moriya interaction (DMI). Despite this fundamental resemblance,
the two scenarios are differentiated by their time reversal properties: while
DMI is a conservative effect that can be modeled by an effective field, the
chiral damping is purely dissipative and has no influence on the equilibrium
magnetic texture. When the DW motion is modulated by an in-plane magnetic
field, it reveals the structure of the internal fields experienced by the DWs,
allowing to distinguish the physical mechanism. The observation of the chiral
damping, not only enriches the spectrum of physical phenomena engendered by the
SIA, but since it can coexists with DMI it is essential for conceiving DW and
skyrmion devices.",1504.04411v1
2015-05-13,Angular momentum generation in cold gravitational collapse,"During the violent relaxation of a self-gravitating system a significant
fraction of its mass may be ejected. If the time varying gravitational field
also breaks spherical symmetry this mass can potentially carry angular
momentum. Thus starting initial configurations with zero angular momentum can
in principle lead to a bound virialized system with non-zero angular momentum.
We explore here, using numerical simulations, how much angular momentum can be
generated in a virialized structure in this way, starting from configurations
of cold particles which are very close to spherically symmetric. For initial
configurations in which spherical symmetry is broken only by the Poissonian
fluctuations associated with the finite particle number $N$, with $N$ in range
$10^3$ to $10^5$, we find that the relaxed structures have standard ""spin""
parameters $\lambda \sim 10^{-3}$, and decreasing slowly with $N$. For slightly
ellipsoidal initial conditions, in which the finite-$N$ fluctuations break the
residual reflection symmetries, we observe values $\lambda \sim 10^{-2}$, of
the same order of magnitude as those reported for elliptical galaxies. The net
angular momentum vector is typically aligned close to normal to the major
semi-axis of the triaxial relaxed structure, and also with that of the ejected
mass. This simple mechanism may provide an alternative, or complement, to
""tidal torque theory"" for understanding the origin of angular momentum in
astrophysical structures.",1505.03371v2
2015-09-21,The Feasibility of Using Black Widow Pulsars in Pulsar Timing Arrays for Gravitational Wave Detection,"In the past five years, approximately one third of the 65 pulsars discovered
by radio observations of Fermi unassociated sources are black widow pulsars
(BWPs). BWPs are binary millisecond pulsars with companion masses ranging from
0.01-0.1 solar masses which often exhibit radio eclipses. The bloated
companions in BWP systems exert small torques on the system causing the orbit
to change on small but measurable time scales. Because adding parameters to a
timing model reduces sensitivity to a gravitational wave (GW) signal, the need
to fit many orbital frequency derivatives to the timing data is potentially
problematic for using BWPs to detect GWs with pulsar timing arrays. Using
simulated data with up to four orbital frequency derivatives, we show that
fitting for orbital frequency derivatives absorbs less than 5% of the low
frequency spectrum expected from a stochastic gravitational wave background
signal. Furthermore, this result does not change with orbital period.
Therefore, we suggest that if timing systematics can be accounted for by
modeling orbital frequency derivatives and is not caused by spin frequency
noise, pulsar timing array experiments should include BWPs in their arrays.",1509.06662v1
2015-09-23,"From solar to stellar corona: the role of wind, rotation and magnetism","Observations of surface magnetic fields are now within reach for many stellar
types thanks to the development of Zeeman-Doppler Imaging. These observations
are extremely useful for constraining rotational evolution models of stars, as
well as for characterizing the generation of magnetic field. We recently
demonstrated that the impact of coronal magnetic field topology on the
rotational braking of a star can be parametrized with a scalar parameter: the
open magnetic flux. However, without running costly numerical simulations of
the stellar wind, reconstructing the coronal structure of the large scale
magnetic field is not trivial. An alternative -broadly used in solar physics-
is to extrapolate the surface magnetic field assuming a potential field in the
corona, to describe the opening of the field lines by the magnetized wind. This
technique relies on the definition of a so-called source surface radius, which
is often fixed to the canonical value of 2.5Rsun. However this value likely
varies from star to star. To resolve this issue, we use our extended set of
2.5D wind simulations published in 2015, to provide a criteria for the opening
of field lines as well as a simple tool to assess the source surface radius and
the open magnetic flux. This allows us to derive the magnetic torque applied to
the star by the wind from any spectropolarimetric observation. We conclude by
discussing some estimations of spin-down time scales made using our technique,
and compare them to observational requirements.",1509.06982v1
2015-10-01,"Hybrid Spintronic-CMOS Spiking Neural Network With On-Chip Learning: Devices, Circuits and Systems","Over the past decade Spiking Neural Networks (SNN) have emerged as one of the
popular architectures to emulate the brain. In SNN, information is temporally
encoded and communication between neurons is accomplished by means of spikes.
In such networks, spike-timing dependent plasticity mechanisms require the
online programming of synapses based on the temporal information of spikes
transmitted by spiking neurons. In this work, we propose a spintronic synapse
with decoupled spike transmission and programming current paths. The spintronic
synapse consists of a ferromagnet-heavy metal heterostructure where programming
current through the heavy metal generates spin-orbit torque to modulate the
device conductance. Low programming energy and fast programming times
demonstrate the efficacy of the proposed device as a nanoelectronic synapse. We
perform a simulation study based on an experimentally benchmarked
device-simulation framework to demonstrate the interfacing of such spintronic
synapses with CMOS neurons and learning circuits operating in transistor
sub-threshold region to form a network of spiking neurons that can be utilized
for pattern recognition problems.",1510.00432v4
2015-10-06,On the Segregation of Dark Matter Substructure,"We present the first comprehensive analysis of the segregation of dark matter
subhaloes in their host haloes. Using numerical simulations, we examine the
segregation of twelve different subhalo properties with respect to both orbital
energy and halo-centric radius (in real space as well as in projection).
Subhaloes are strongly segregated by accretion redshift, which is an outcome of
the inside-out assembly of their host haloes. Since subhaloes that were
accreted earlier have experienced more tidal stripping, subhaloes that have
lost a larger fraction of their mass at infall are on more bound orbits.
Subhaloes are also strongly segregated in their masses and maximum circular
velocities at accretion. We demonstrate that part of this segregation is
already imprinted in the infall conditions. For massive subhaloes it is
subsequently boosted by dynamical friction, but only during their first radial
orbit. The impact of these two effects is counterbalanced, though, by the fact
that subhaloes with larger accretion masses are accreted later. Because of
tidal stripping, subhaloes reveal little to no segregation by present-day mass
or maximum circular velocity, while the corresponding torques cause subhaloes
on more bound orbits to have smaller spin. There is a weak tendency for
subhaloes that formed earlier to be segregated towards the center of their host
halo, which is an indirect consequence of the fact that (sub)halo formation
time is correlated with other, strongly segregated properties. We discuss the
implications of our results for the segregation of satellite galaxies in galaxy
groups and clusters.",1510.01586v1
2015-12-07,Current Driven Domain Wall Depinning in Notched Permalloy Nanowires,"In this work, we have investigated the domain wall (DW) depinning behavior in
the notched nanowire by a micromagnetic simulation. A transverse domain wall
(TW) was initially positioned at the center of notch and 1 ns length current
pulse was applied to depin the DW with respect to the notch size s and the wire
width variation. We have observed the depinning current density Jd which was a
minimum current to escape DW from the notch. It was found that the depinning
current density decreased as the wire width and the notch size increased. In
the depinning process, we observed the inner structure of DW generally
transformed from TW to anti-vortex wall (AVW). Interestingly, for the case of s
less than 70 nm, AVW formed and depinned closely to the period when current
pulse was active, while for s larger than 70 nm, AVW formed until the current
pulse went to zero and then depinned after flipped TW was formed. It can be
explained that the transformation of DW inner structures were affected by the
spin torque energy and contributed to DW depinning behavior from the notched
nanowires.",1512.01954v1
2016-03-04,Inclination angle and braking index evolution of pulsars with plasma-filled magnetosphere: application to high braking index of PSR J1640-4631,"The recently discovered rotationally powered pulsar PSR J1640-4631 is the
first to have a braking index measured, with high enough precision, that is
greater than three. An inclined magnetic rotator in vacuum or plasma would be
subject not only to spin-down but also to an alignment torque. The vacuum model
can address the braking index only for an almost orthogonal rotator that is
incompatible with the single peaked pulse profile. The magnetic dipole model
with the corotating plasma predicts braking indices between $3-3.25$. We find
that the braking index of $3.15$ is consistent with two different inclination
angles, $18.5\pm 3$ degrees and $56 \pm 4$ degrees. The smaller angle is
preferred given the pulse profile has a single peak and the radio output of the
source is weak. We infer the change in the inclination angle to be at the rate
$-0.23$ degrees per century, three times smaller in absolute value than the
rate recently observed for the Crab pulsar.",1603.01487v3
2016-08-10,Antiferromagnetic multi-level memory cell,"Antiferromagnets (AFs) are remarkable magnetically ordered materials that due
to the absence of a net magnetic moment do not generate dipolar fields and are
insensitive to external magnetic field perturbations. However, it has been
notoriously difficult to control antiferromagnetic moments by any practical
means suitable for device applications. This has left AFs over their hundred
years history virtually unexploited and only poorly explored, in striking
contrast to the thousands of years of fascination and utility of
ferromagnetism. Very recently it has been predicted and experimentally
confirmed that relativistic spin-orbit torques can provide the means for
efficient electrical control of an AF. Here we place the emerging field of
antiferromagnetic spintronics on the map of non-volatile solid state memory
technologies. We demonstrate the complete write/store/read functionality in an
antiferromagnetic CuMnAs bit cell embedded in a standard printed circuit board
communicating with a computer via a USB interface. We show that the
elementary-shape bit cells fabricated from a single-layer AF are electrically
written on timescales ranging from milliseconds to nanoseconds and we
demonstrate their deterministic multi-level switching. The multi-level cell
characteristics, reflecting series of reproducible, electrically controlled
domain reconfigurations, allow us to integrate memory and signal counter
functionalities within the bit cell.",1608.03238v1
2016-08-25,Skyrmion Hall Effect Revealed by Direct Time-Resolved X-Ray Microscopy,"Magnetic skyrmions are highly promising candidates for future spintronic
applications such as skyrmion racetrack memories and logic devices. They
exhibit exotic and complex dynamics governed by topology and are less
influenced by defects, such as edge roughness, than conventionally used domain
walls. In particular, their finite topological charge leads to a predicted
""skyrmion Hall effect"", in which current-driven skyrmions acquire a transverse
velocity component analogous to charged particles in the conventional Hall
effect. Here, we present nanoscale pump-probe imaging that for the first time
reveals the real-time dynamics of skyrmions driven by current-induced spin
orbit torque (SOT). We find that skyrmions move at a well-defined angle
{\Theta}_{SH} that can exceed 30{\deg} with respect to the current flow, but in
contrast to theoretical expectations, {\Theta}_{SH} increases linearly with
velocity up to at least 100 m/s. We explain our observation based on internal
mode excitations in combination with a field-like SOT, showing that one must go
beyond the usual rigid skyrmion description to unravel the dynamics.",1608.07216v2
2016-09-21,Age dependence of wind properties for solar type stars: a 3d study,"Young and rapidly rotating stars are known for intense, dynamo generated
magnetic fields. Spectropolarimetric observations of those stars in precisely
aged clusters are key input for gyrochronology and magnetochronology. We use
ZDI maps of several young K-type stars of similar mass and radius but with
various ages and rotational periods, to perform 3D numerical MHD simulations of
their coronae and follow the evolution of their magnetic properties with age.
Those simulations yield the coronal structure as well as the instant torque
exerted by the magnetized, rotating wind on the star. As stars get older, we
find that the angular momentum loss decreases with $\Omega^3$, which is the
reason for the convergence on the Skumanich law. For the youngest stars of our
sample, the angular momentum loss show signs of saturation around
$8\Omega_{\odot}$, which is a common value used in spin evolution models for
K-type stars. We compare these results to semi-analytical models and existing
braking laws. We observe a complex wind speed distribution for the youngest
stars with slow, intermediate and fast wind components, which are the result of
the interaction with intense and non axisymmetric magnetic fields.
Consequently, in our simulations, the stellar wind structure in the equatorial
plane of young stars varies significantly from a solar configuration,
delivering insight about the past of the solar system interplanetary medium.",1609.06602v2
2016-09-23,Influence of heavy metal materials on magnetic properties of Pt/Co/heavy metal tri-layered structures,"Pt/Co/heavy metal (HM) tri-layered structures with interfacial perpendicular
magnetic anisotropy (PMA) are currently under intensive research for several
emerging spintronic effects, such as spinorbit torque, domain wall motion, and
room temperature skyrmions. HM materials are used as capping layers to generate
the structural asymmetry and enhance the interfacial effects. For instance, the
Pt/Co/Ta structure attracts a lot of attention as it may exhibit large
Dzyaloshinskii-Moriya interaction. However, the dependence of magnetic
properties on different capping materials has not been systematically
investigated. In this paper, we experimentally show the interfacial PMA and
damping constant for Pt/Co/HM tri-layered structures through time-resolved
magneto-optical Kerr effect measurements as well as magnetometry measurements,
where the capping HM materials are W, Ta, and Pd. We found that the Co/HM
interface plays an important role on the magnetic properties. In particular,
the magnetic multilayers with a W capping layer features the lowest effective
damping value, which may be attributed to the different spin-orbit coupling and
interfacial hybridization between Co and HM materials. Our findings allow a
deep understanding of the Pt/Co/HM tri-layered structures. Such structures
could lead to a better era of data storage and processing devices.",1609.07320v2
2016-09-30,Gravity field and solar component of the precession rate and nutation coefficients of Comet 67P Churyumov-Gerasimenko,"The aim of this study is first to determine the gravity field of the comet
67P Churyumov-Gerasimenko and second to derive the solar component of the
precession rate and nutation coefficients of the spin axis of the comet
nucleus, i.e. without the direct, usually larger, effect of outgassing. The
gravity field, and related moments of inertia, are obtained from two polyhedra,
that are provided by the OSIRIS and NAV-CAM experiments on Rosetta, and are
based on the assumption of uniform density for the comet nucleus. We also
calculate the forced precession rate as well as the nutation coefficients on
the basis of Kinoshita's theory of rotation of the rigid Earth and adapted it
to be able to indirectly include the effect of outgassing on the rotational
parameters. The 2nd degree denormalized Stokes coefficients of comet 67P C-G
turn out to be (bracketed numbers refer to second shape model) C20 = -6.74
[-7.93] * 10^-2, C22 = 2.60 [2.71] * 10^-2 consistent with normalized principal
moments of inertia A/MR^2 = 0.13 [0.11], B/MR^2 = 0.23 [0.22], with polar
moment c = C/MR^2 = 0.25, depending on the choice of the polyhedron model. The
obliquity between the rotation axis and the mean orbit normal is 52 degree, and
the precession rate only due to solar torques becomes 20-30 ""/y. Oscillations
in longitude caused by the gravitational pull of the Sun turn out to be of the
order of 1', oscillations in obliquity can be estimated to be of the order of
0.5'.",1609.09774v1
2016-12-01,Gas Accretion and Angular Momentum,"In this chapter, we review the role of gas accretion to the acquisition of
angular momentum, both in galaxies and in their gaseous halos. We begin by
discussing angular momentum in dark matter halos, with a brief review of tidal
torque theory and the importance of mergers, followed by a discussion of the
canonical picture of galaxy formation within this framework, where halo gas is
presumed to shock-heat to the virial temperature of the halo, following the
same spin distribution as the dark matter halo before cooling to the center of
the halo to form a galaxy there. In the context of recent observational
evidence demonstrating the presence of high angular momentum gas in galaxy
halos, we review recent cosmological hydrodynamic simulations that have begun
to emphasize the role of ""cold flow"" accretion---anisotropic gas accretion
along cosmic filaments that does not shock-heat before sinking to the central
galaxy. We discuss the implications of these simulations, reviewing a number of
recent developments in the literature, and suggest a revision to the canonical
model as it relates to the expected angular momentum content of gaseous halos
around galaxies.",1612.00513v1
2017-01-26,Precise Pointing of Cubesat Telescopes: Comparison Between Heat and Light Induced Attitude Control Methods,"CubeSats are emerging as low-cost tools to perform astronomy, exoplanet
searches and earth observation. These satellites can target an object for
science observation for weeks on end. This is typically not possible on larger
missions where usage time is shared. The problem of designing an attitude
control system for CubeSat telescopes is very challenging because current
choice of actuators such as reaction-wheels and magnetorquers can induce jitter
on the spacecraft due to moving mechanical parts and due to external
disturbances. These telescopes may contain cryo-pumps and servos that introduce
additional vibrations. A better solution is required. In our paper, we analyze
the feasibility of utilizing solar radiation pressure (SRP) and radiometric
force to achieve precise attitude control. Our studies show radiometric
actuators to be a viable method to achieve precise pointing. The device uses 8
thin vanes of different temperatures placed in a near-vacuum chamber. These
chambers contain trace quantities of lightweight, inert gasses like argon. The
temperature gradient across the vanes causes the gas molecules to strike the
vanes differently and thus inducing a force. By controlling these forces, it's
possible to produce a torque to precisely point or spin a spacecraft. We
present a conceptual design of a CubeSat that is equipped with these actuators.
We then analyze the potential slew maneuver and slew rates possible with these
actuators by simulating their performance. Our analytical and simulation
results point towards a promising pathway for laboratory testing of this
technology and demonstration of this technology in space.",1701.07562v1
2017-02-09,Split Active Asteroid P/2016 J1 (PANSTARRS),"We present a photometric and astrometric study of the split active asteroid
P/2016 J1 (PANSTARRS). The two components (hereafter J1-A and J1-B) separated
either $\sim$1500 days (2012 May to June) or 2300 days (2010 April) prior to
the current epoch, with a separation speed $V_{\mathrm{sep}} = 0.70 \pm 0.02$ m
s$^{-1}$ for the former scenario, or $0.83 \pm 0.06$ m s$^{-1}$ for the latter.
Keck photometry reveals that the two fragments have similar, Sun-like colors
which are comparable to the colors of primitive C- and G-type asteroids. With a
nominal comet-like albedo, $p_{R} = 0.04$, the effective, dust-contaminated
cross sections are estimated to be 2.4 km$^{2}$ for J1-A, and 0.5 km$^{2}$ for
J1-B. We estimate that the nucleus radii lie in the range $140 \lesssim
R_{\mathrm{N}} \lesssim 900$ m for J1-A and $40 \lesssim R_{\mathrm{N}}
\lesssim 400$ m, for J1-B. A syndyne-synchrone simulation shows that both
components have been active for 3 to 6 months, by ejecting dust grains at
speeds $\sim$0.5 m s$^{-1}$ with rates $\sim$1 kg s$^{-1}$ for J1-A and 0.1 kg
s$^{-1}$ for J1-B. In its present orbit, the rotational spin-up and
devolatilization times of 2016 J1 are very small compared to the age of the
solar system, raising the question of why this object still exists. We suggest
that ice that was formerly buried within this asteroid became exposed at the
surface, perhaps via a small impact, and that sublimation torques then rapidly
drove it to break-up. Further disintegration events are anticipated due to the
rotational instability.",1702.02766v1
2017-03-21,Annealing stability of magnetic tunnel junctions based on dual MgO free layers and [Co/Ni] based thin synthetic antiferromagnet fixed system,"We study the annealing stability of bottom-pinned perpendicularly magnetized
magnetic tunnel junctions based on dual MgO free layers and thin fixed systems
comprising a hard [Co/Ni] multilayer antiferromagnetically coupled to thin a Co
reference layer and a FeCoB polarizing layer. Using conventional magnetometry
and advanced broadband ferromagnetic resonance, we identify the properties of
each sub-unit of the magnetic tunnel junction and demonstrate that this
material option can ensure a satisfactory resilience to the 400$^\circ$C
thermal annealing needed in solid-state magnetic memory applications. The dual
MgO free layer possesses an anneal-robust 0.4 T effective anisotropy and
suffers only a minor increase of its Gilbert damping from 0.007 to 0.010 for
the toughest annealing conditions. Within the fixed system, the ferro-coupler
and texture-breaking TaFeCoB layer keeps an interlayer exchange above 0.8
mJ/m$^2$, while the Ru antiferrocoupler layer within the synthetic
antiferromagnet maintains a coupling above -0.5 mJ/m$^2$. These two strong
couplings maintain the overall functionality of the tunnel junction upon the
toughest annealing despite the gradual degradation of the thin Co layer
anisotropy that may reduce the operation margin in spin torque memory
applications. Based on these findings, we propose further optimization routes
for the next generation magnetic tunnel junctions.",1703.07154v1
2017-05-08,Experimental Verification of the Universality of Magnetic-Field-Induced Bose-Einstein Condensation of Magnons,"CsFeBr$_3$ is an $S\,{=}\,1$ hexagonal antiferromagnet that has a singlet
ground state owing to its large easy-plane single-ion anisotropy. The critical
behavior of the magnetic-field-induced phase transition for a magnetic field
parallel to the $c$ axis, which can be described by the Bose-Einstein
condensation (BEC) of magnons under the $U(1)$ symmetry, was investigated via
magnetization and specific heat measurements down to 0.1$\,$K. For the specific
heat measurement, we have developed a method of effectively suppressing the
torque acting on a sample with strong anisotropy that uses the spin dimer
compound Ba$_2$CoSi$_2$O$_6$Cl$_2$ with large and anisotropic Van Vleck
paramagnetism. The temperature dependence of the transition field $H_{\rm
c}(T)$ was found to follow the power-law $H_{\rm c}(T)\,{-}\,H_{\rm
c}\,{\propto}\,T^{\phi}$ with a critical exponent of
${\phi}\,{=}\,1.50\,{\pm}\,0.02$ and critical field of $H_{\rm c}\,{=}\,2.60$
T. This result verifies the universality of the three-dimensional BEC of
magnons described by ${\phi}_{\rm BEC}\,{=}\,3/2$.",1705.02739v2
2017-06-21,Deterministic creation and deletion of a single magnetic skyrmion observed by direct time-resolved X-ray microscopy,"Spintronic devices based on magnetic skyrmions are a promising candidate for
next-generation memory applications due to their nanometre-size,
topologically-protected stability and efficient current-driven dynamics. Since
the recent discovery of room-temperature magnetic skyrmions, there have been
reports of current-driven skyrmion displacement on magnetic tracks and
demonstrations of current pulse-driven skyrmion generation. However, the
controlled annihilation of a single skyrmion at room temperature has remained
elusive. Here we demonstrate the deterministic writing and deleting of single
isolated skyrmions at room temperature in ferrimagnetic GdFeCo films with a
device-compatible stripline geometry. The process is driven by the application
of current pulses, which induce spin-orbit torques, and is directly observed
using a time resolved nanoscale X-ray imaging technique. We provide a
current-pulse profile for the efficient and deterministic writing and deleting
process. Using micromagnetic simulations, we also reveal the microscopic
mechanism of the topological fluctuations that occur during this process.",1706.06726v2
2017-09-21,Neutron Stars in X-ray Binaries and their Environments,"Neutron stars in X-ray binary systems are fascinating objects that display a
wide range of timing and spectral phenomena in the X-rays. Not only parameters
of the neutron stars, like magnetic field strength and spin period evolve in
their active binary phase, the neutron stars also affect the binary systems and
their immediate surroundings in many ways. Here we discuss some aspects of the
interactions of the neutron stars with their environments that are revelaed
from their X-ray emission. We discuss some recent developments involving the
process of accretion onto high magnetic field neutron stars: accretion stream
structure and formation, shape of pulse profile and its changes with accretion
torque. Various recent studies of reprocessing of X-rays in the accretion disk
surface, vertical structures of the accretion disk and wind of companion star
are also discussed here. The X-ray pulsars among the binary neutron stars
provide excellent handle to make accurate measurement of the orbital parameters
and thus also evolution of the binray orbits that take place over time scale of
a fraction of a million years to tens of millions of years. The orbital period
evolution of X-ray binaries have shown them to be rather complex systems.
Orbital evolution of X-ray binaries can also be carried out from timing of the
X-ray eclipses and there have been some surprising results in that direction,
including orbital period glitches in two X-ray binaries and possible detection
of the most massive circum-binary planet around a Low Mass X-ray Binary.",1709.07428v1
2017-11-16,Enhancement of the effective mass at high magnetic fields in CeRhIn$_5$,"The Kondo-lattice compound CeRhIn$_5$ displays a field-induced Fermi surface
reconstruction at $B^*\approx30$ T, which occurs within the antiferromagnetic
state, prior to the quantum critical point at $B_{c0}\approx50$ T. Here, in
order to investigate the nature of the Fermi surface change, we measured the
magnetostriction, specific heat, and magnetic torque of CeRhIn$_5$ across a
wide range of magnetic fields. Our observations uncover the field-induced
itineracy of the $4f$ electrons, where above $B_{\rm onset}\approx17$ T there
is a significant enhancement of the Sommerfeld coefficient, and spin-dependent
effective cyclotron masses determined from quantum oscillations. Upon crossing
$B_{\rm onset}$, the temperature dependence of the specific heat also shows
distinctly different behavior from that at low fields. Our results indicate
that the Kondo coupling is remarkably robust upon increasing the magnetic
field. This is ascribed to the delocalization of the $4f$ electrons at the
Fermi surface reconstruction at $B^*$.",1711.06191v2
2017-12-18,Resampling to accelerate cross-correlation searches for continuous gravitational waves from binary systems,"Continuous-wave (CW) gravitational waves (GWs) call for
computationally-intensive methods. Low signal-to-noise ratio signals need
templated searches with long coherent integration times and thus fine
parameter-space resolution. Longer integration increases sensitivity. Low-mass
x-ray binaries (LMXBs) such as Scorpius X-1 (Sco X-1) may emit accretion-driven
CWs at strains reachable by current ground-based observatories. Binary orbital
parameters induce phase modulation. This paper describes how resampling
corrects binary and detector motion, yielding source-frame time series used for
cross-correlation. Compared to the previous, detector-frame, templated
cross-correlation method, used for Sco X-1 on data from the first Advanced LIGO
observing run (O1), resampling is about 20x faster in the costliest,
most-sensitive frequency bands. Speed-up factors depend on integration time and
search setup. The speed could be reinvested into longer integration with a
forecast sensitivity gain, 20 to 125 Hz median, of approximately 51%, or from
20 to 250 Hz, 11%, given the same per-band cost and setup. This paper's timing
model enables future setup optimization. Resampling scales well with longer
integration, and at 10x unoptimized cost could reach respectively 2.83x and
2.75x median sensitivities, limited by spin-wandering. Then an O1 search could
yield a marginalized-polarization upper limit reaching torque-balance at 100
Hz. Frequencies from 40 to 140 Hz might be probed in equal observing time with
2x improved detectors.",1712.06515v2
2018-01-12,A magnetar origin for the kilonova ejecta in GW170817,"The neutron star (NS) merger GW170817 was followed over several days by
optical-wavelength (""blue"") kilonova (KN) emission likely powered by the
radioactive decay of light r-process nuclei synthesized by ejecta with a low
neutron abundance (electron fraction Ye ~ 0.25-0.35). While the composition and
high velocities of the blue KN ejecta are consistent with shock-heated
dynamical material, the large quantity is in tension with the results of
numerical simulations. We propose an alternative ejecta source: the
neutrino-heated, magnetically-accelerated wind from the strongly-magnetized
hypermassive NS (HMNS) remnant. A rapidly-spinning HMNS with an ordered surface
magnetic field of strength B ~ 1-3e14 G and lifetime t_rem ~ 0.1-1 s can
simultaneously explain the velocity, total mass, and electron fraction of the
blue KN ejecta. The inferred HMNS lifetime is close to its Alfven crossing
time, suggesting global magnetic torques could be responsible for bringing the
HMNS into solid body rotation and instigating its gravitational collapse.
Different origins for the KN ejecta may be distinguished by their predictions
for the emission in the first hours after the merger, when the luminosity is
enhanced by heating from internal shocks; the latter are likely generic to any
temporally-extended ejecta source (e.g. magnetar or accretion disk wind) and
are not unique to the emergence of a relativistic jet. The same shocks could
mix and homogenizes the composition to a low but non-zero lanthanide mass
fraction, X_La ~ 1e-3, as advocated by some authors, but only if the mixing
occurs after neutrons are consumed in the r-process on a timescale >~ 1 s.",1801.04286v2
2018-04-04,"The Spin Evolution of Fast-Rotating, Magnetized Super-Chandrasekhar White Dwarfs in the Aftermath of White Dwarf Mergers","The evolution of the remnant of the merger of two white dwarfs is still an
open problem. Furthermore, few studies have addressed the case in which the
remnant is a magnetic white dwarf with a mass larger than the Chandrasekhar
limiting mass. Angular momentum losses might bring the remnant of the merger to
the physical conditions suitable for developing a thermonuclear explosion.
Alternatively, the remnant may be prone to gravitational or rotational
instabilities, depending on the initial conditions reached after the
coalescence. Dipole magnetic braking is one of the mechanisms that can drive
such losses of angular momentum. However, the timescale on which these losses
occur depend on several parameters, like the strength of the magnetic field. In
addition, the coalescence leaves a surrounding Keplerian disk that can be
accreted by the newly formed white dwarf. Here we compute the post-merger
evolution of a super-Chandrasekhar magnetized white dwarf taking into account
all the relevant physical processes. These include magnetic torques acting on
the star, accretion from the Keplerian disk, the threading of the magnetic
field lines through the disk, as well as the thermal evolution of the white
dwarf core. We find that the central remnant can reach the conditions suitable
to develop a thermonuclear explosion before other instabilities (such as the
inverse beta-decay instability or the secular axisymmetric instability) are
reached, which would instead lead to gravitational collapse of the magnetized
remnant.",1804.01275v1
2018-06-12,The life cycles of Be viscous decretion discs: The case of ω CMa,"We analyzed V-band photometry of the Be star {\omega} CMa, obtained during
the last four decades, during which the star went through four complete cycles
of disc formation and dissipation. The data were simulated by hydrodynamic
models based on a time-dependent implementation of the viscous decretion disc
(VDD) paradigm, in which a disc around a fast-spinning Be star is formed by
material ejected by the star and driven to progressively larger orbits by means
of viscous torques. Our simulations offer a good description of the photometric
variability during phases of disc formation and dissipation, which suggests
that the VDD model adequately describes the structural evolution of the disc.
Furthermore, our analysis allowed us to determine the viscosity parameter
{\alpha}, as well as the net mass and angular momentum (AM) loss rates. We find
that {\alpha} is variable, ranging from 0.1 to 1.0, not only from cycle to
cycle but also within a given cycle. Additionally, build-up phases usually have
larger values of {\alpha} than the dissipation phases. Furthermore, during
dissipation the outward AM flux is not necessarily zero, meaning that {\omega}
CMa does not experience a true quiescence but, instead, switches between a high
to a low AM loss rate during which the disc quickly assumes an overall lower
density but never zero. We confront the average AM loss rate with predictions
from stellar evolution models for fast-rotating stars, and find that our
measurements are smaller by more than one order of magnitude.",1806.04301v1
2018-09-10,Simulations of solar wind variations during an 11-year cycle and the influence of north-south asymmetry,"We want to study the connections between the magnetic field generated inside
the Sun and the solar wind impacting Earth, especially the influence of
north-south asymmetry on the magnetic and velocity fields. We study a
solar-like 11-year cycle in a quasi-static way: an asymmetric dynamo field is
generated through a 2.5-dimensional (2.5-D) flux-transport model with the
Babcock-Leighton mechanism, and then is used as bottom boundary condition for
compressible 2.5-D simulations of the solar wind. We recover solar values for
the mass loss rate, the spin-down time scale and the Alfv\'en radius, and are
able to reproduce the observed delay in latitudinal variations of the wind and
the general wind structure observed for the Sun. We show that the phase lag
between the energy of the dipole component and the total surface magnetic
energy has a strong influence on the amplitude of the variations of global
quantities. We show in particular that the magnetic torque variations can be
linked to topological variations during a magnetic cycle, while variations in
the mass loss rate appear to be driven by variations of the magnetic energy.",1809.03205v1
2018-11-25,On-chip learning for domain wall synapse based Fully Connected Neural Network,"Spintronic devices are considered as promising candidates in implementing
neuromorphic systems or hardware neural networks, which are expected to perform
better than other existing computing systems for certain data classification
and regression tasks. In this paper, we have designed a feedforward Fully
Connected Neural Network (FCNN) with no hidden layer using spin orbit torque
driven domain wall devices as synapses and transistor based analog circuits as
neurons. A feedback circuit is also designed using transistors, which at every
iteration computes the change in weights of the synapses needed to train the
network using Stochastic Gradient Descent (SGD) method. Subsequently it sends
write current pulses to the domain wall based synaptic devices which move the
domain walls and updates the weights of the synapses. Through a combination of
micromagnetic simulations, analog circuit simulations and numerically solving
FCNN training equations, we demonstrate ""on-chip"" training of the designed FCNN
on the MNIST database of handwritten digits in this paper. We report the
training and test accuracies, energy consumed in the synaptic devices for the
training and possible issues with hardware implementation of FCNN that can
limit its test accuracy.",1811.09966v1
2018-11-30,Active Asteroid P/2017 S5 (ATLAS),"Observations of active asteroid P/2017 S5 when near perihelion reveal the
ejection of large (0.1 to 10 mm) particles at 0.2 to 2 m/s speeds, with
estimated mass-loss rates of a few kg/s. The protracted nature of the mass loss
(continuous over 150 days) is compatible with a sublimation origin, meaning
that this object is likely an ice-bearing main-belt comet. Equilibrium
sublimation of exposed water ice covering as little as 0.1 sq. km can match the
data. Observations a year after perihelion show the object in an inactive state
from which we deduce a nucleus effective radius 450(+100/-60) m (albedo
0.06+/-0.02 assumed). The gravitational escape speed from a body of this size
is just 0.3 m/s, comparable to the inferred ejection speed of the dust.
Time-series photometry provides tentative evidence for rapid rotation
(lightcurve period 1.4 hour) that may also play a role in the loss of mass and
which, if real, is a likely consequence of spin-up by sublimation torques.
P/2017 S5 shares both physical and orbital similarities with the split active
asteroid pair P/2016 J1-A and J1-B, and all three objects are likely members of
the 7 Myr old, collisionally produced, Theobalda family.",1812.00060v1
2018-12-06,"The simultaneous formation of cored, tangentially biased, and kinematically decoupled centers in massive early-type galaxies","We study the impact of merging supermassive black holes (SMBHs) on the
central regions of massive early-type galaxies (ETGs) using a series of merger
simulations with varying mass ratios. The ETG models include realistic stellar
and dark matter components and are evolved with the GADGET based regularized
tree code KETJU. We show that observed key properties of the nuclear stellar
populations of massive ETGs, namely flat stellar density distributions (cores),
tangentially biased velocity distributions and kinematically decoupled
(counter-)rotation can naturally result from a single process $-$ the scouring
by SMBHs. Major mergers with mass ratios of $q>1/3$ produce flat, tangentially
biased cores with kinematically distinct components. These features originate
from spin reversals during the decay of the SMBH orbits caused by gravitational
torques from tidally expelled nuclear material. Minor mergers ($q\lesssim1/3$)
on the other hand, form non-rotating cores and the tidal reversal becomes less
important. Low-density stellar cores scoured in (multiple) minor mergers are
less tangentially biased. This implies that the nuclear stellar properties of
massive ETGs can be solely explained by stellar dynamical processes during
their final assembly without any need for `feedback' from accreting black
holes. We predict a strong correlation between decoupled cores, central
anisotropy and merger history: decoupled cores form in binary mergers and we
predict them to occur in elliptical galaxies with the strongest central
anisotropy. Measurements of the central orbital structure are the key to
understanding the number of mergers a given galaxy has experienced.",1812.02732v2
2019-02-13,GROJ1750-27: a neutron star far behind the Galactic Center switching into the propeller regime,"We report on analysis of properties of the X-ray binary pulsar GROJ1750-27
based on X-ray (Chandra, Swift, and Fermi/GBM), and near-infrared (VVV and
UKIDSS surveys) observations. An accurate position of the source is determined
for the first time and used to identify its infrared counterpart. Based on the
VVV data we investigate the spectral energy distribution (SED) of the
companion, taking into account a non-standard absorption law in the source
direction. A comparison of this SED with those of known Be/X-ray binaries and
early type stars has allowed us to estimate a lower distance limit to the
source at $>12$ kpc. An analysis of the observed spin-up torque during a giant
outburst in 2015 provides an independent distance estimate of $14-22$ kpc, and
also allows to estimate the magnetic field on the surface of the neutron star
at $B\simeq(3.5-4.5)\times10^{12}$ G. The latter value is in agreement with the
possible transition to the propeller regime, a strong hint for which was
revealed by Swift/XRT and Chandra. We conclude that GROJ1750-27 is located far
behind the Galactic Center, which makes it one of the furthest Galactic X-ray
binaries known.",1902.05153v1
2019-02-15,Current-driven magnetization switching in a van der Waals ferromagnet Fe3GeTe2,"The recent discovery of ferromagnetism in two-dimensional (2D) van der Waals
(vdW) materials holds promises for novel spintronic devices with exceptional
performances. However, in order to utilize 2D vdW magnets for building
spintronic nanodevices such as magnetic memories, key challenges remain in
terms of effectively switching the magnetization from one state to the other
electrically. Here, we devise a bilayer structure of Fe3GeTe2/Pt, in which the
magnetization of few-layered Fe3GeTe2 can be effectively switched by the
spin-orbit torques (SOTs) originated from the current flowing in the Pt layer.
The effective magnetic fields corresponding to the SOTs are further
quantitatively characterized using harmonic measurements. Our demonstration of
the SOT-driven magnetization switching in a 2D vdW magnet could pave the way
for implementing low-dimensional materials in the next-generation spintronic
applications.",1902.05794v1
2019-04-01,Rotating magnetic field driven antiferromagnetic domain wall motion: Role of Dzyaloshinskii-Moriya interaction,"In this work, we study the rotating magnetic field driven domain wall (DW)
motion in antiferromagnetic nanowires, using the micromagnetic simulations of
the classical Heisenberg spin model. We show that in low frequency region, the
rotating field alone could efficiently drive the DW motion even in the absence
of Dzyaloshinskii-Moriya interaction (DMI). In this case, the DW rotates
synchronously with the magnetic field, and a stable precession torque is
available and drives the DW motion with a steady velocity. In large frequency
region, the DW only oscillates around its equilibrium position and cannot
propagate. The dependences of the velocity and critical frequency
differentiating the two motion modes on several parameters are investigated in
details, and the direction of the DW motion can be controlled by modulating the
initial phase of the field. Interestingly, a unidirectional DW motion is
predicted attributing to the bulk DMI, and the nonzero velocity for high
frequency is well explained. Thus, this work does provide useful information
for further antiferromagnetic spintronics applications.",1904.00870v2
2019-05-20,Injection locking at fractional frequencies of magnetic tunnel junction (MTJ)-based read sensors' ferromagnetic resonance modes,"Being nonlinear dynamic systems, magnetic read sensors should respond to an
excitation signal of a frequency considerably different from their natural
ferromagnetic resonance (FMR) frequencies. Because of the magnetization
dynamics' inherent nonlinear nature, the sensors' response should be measured
at the DC, excitation frequency, and its multiples (harmonics). In this paper,
we present results of such measurements, accomplished using a one-port
nonlinear vector network analyzer (NVNA), which show distinct resonances at
fractional frequencies of the free layer (FL) FMR mode. Identification of these
resonances, resulting from the nonlinear nature of the spin-torque (ST)-induced
magnetization dynamics, was performed using micromagnetic modeling. In
particular, we show that the measured DC response at the above-mentioned
fractional frequencies can be explained by a low-order nonlinearity and strong
magnetodipolar feedback between magnetic layers adjacent to an MgO barrier.
Additionally, we determined that the simulated harmonic response is strongly
enhanced by the mutual ST effect between these layers. Finally, we demonstrate
that the read sensors' nonlinear magnetization dynamics and, by extension,
their harmonic response are highly sensitive to various magnetic and ST
parameters. Thus, this study shows that using NVNA measurements in conjunction
with micromagnetic modeling can clarify the uncertainty in the definition of
these parameters.",1905.08183v2
2019-06-03,Stochastic Computing for Hardware Implementation of Binarized Neural Networks,"Binarized Neural Networks, a recently discovered class of neural networks
with minimal memory requirements and no reliance on multiplication, are a
fantastic opportunity for the realization of compact and energy efficient
inference hardware. However, such neural networks are generally not entirely
binarized: their first layer remains with fixed point input. In this work, we
propose a stochastic computing version of Binarized Neural Networks, where the
input is also binarized. Simulations on the example of the Fashion-MNIST and
CIFAR-10 datasets show that such networks can approach the performance of
conventional Binarized Neural Networks. We evidence that the training procedure
should be adapted for use with stochastic computing. Finally, the ASIC
implementation of our scheme is investigated, in a system that closely
associates logic and memory, implemented by Spin Torque Magnetoresistive Random
Access Memory. This analysis shows that the stochastic computing approach can
allow considerable savings with regards to conventional Binarized Neural
networks in terms of area (62% area reduction on the Fashion-MNIST task). It
can also allow important savings in terms of energy consumption, if we accept
reasonable reduction of accuracy: for example a factor 2.1 can be saved, with
the cost of 1.4% in Fashion-MNIST test accuracy. These results highlight the
high potential of Binarized Neural Networks for hardware implementation, and
that adapting them to hardware constrains can provide important benefits.",1906.00915v1
2019-07-15,Current-driven domain wall dynamics in ferrimagnets: micromagnetic approach and collective coordinates model,"Theoretical studies dealing with current-driven domain wall dynamics in
ferrimagnetic alloys and, by extension, other antiferromagnetically coupled
systems as some multilayers, are here presented. The analysis has been made by
means of micromagnetic simulations that consider these systems as constituted
by two subsystems coupled in terms of an additional exchange interlacing them.
Both subsystems differ in their respective gyromagnetic ratios and temperature
dependence. Other interactions, as for example anisotropic exchange or
spin-orbit torques, can be accounted for differently within each subsystem
according to the physical structure. Micromagnetic simulations are also
endorsed by means of a collective coordinates model which, in contrast with
some previous approaches to these antiferromagnetically coupled systems, based
on effective parameters, also considers them as formed by two coupled
subsystems with experimentally definite parameters. Both simulations and the
collective model reinforce the angular moment compensation argument as
accountable for the linear increase with current of domain wall velocities in
these alloys at a certain temperature or composition. Importantly, the proposed
approach by means of two coupled subsystems permits to infer relevant results
in the development of future experimental setups that are unattainable by means
of effective models.",1907.06431v1
2019-08-12,Implementing Binarized Neural Networks with Magnetoresistive RAM without Error Correction,"One of the most exciting applications of Spin Torque Magnetoresistive Random
Access Memory (ST-MRAM) is the in-memory implementation of deep neural
networks, which could allow improving the energy efficiency of Artificial
Intelligence by orders of magnitude with regards to its implementation on
computers and graphics cards. In particular, ST-MRAM could be ideal for
implementing Binarized Neural Networks (BNNs), a type of deep neural networks
discovered in 2016, which can achieve state-of-the-art performance with a
highly reduced memory footprint with regards to conventional artificial
intelligence approaches. The challenge of ST-MRAM, however, is that it is prone
to write errors and usually requires the use of error correction. In this work,
we show that these bit errors can be tolerated by BNNs to an outstanding level,
based on examples of image recognition tasks (MNIST, CIFAR-10 and ImageNet):
bit error rates of ST-MRAM up to 0.1% have little impact on recognition
accuracy. The requirements for ST-MRAM are therefore considerably relaxed for
BNNs with regards to traditional applications. By consequence, we show that for
BNNs, ST-MRAMs can be programmed with weak (low-energy) programming conditions,
without error correcting codes. We show that this result can allow the use of
low energy and low area ST-MRAM cells, and show that the energy savings at the
system level can reach a factor two.",1908.04085v1
2019-10-24,On the frequency correlations of low-frequency QPOs with kilohertz QPOs in accreting millisecond X-ray pulsars,"We investigate frequency correlations of low frequency (LF, <80 Hz) and kHz
quasi-periodic oscillations (QPOs) using the complete RXTE data sets on 6
accreting millisecond X-ray pulsars (AMXPs) and compare them to those of
non-pulsating neutron star low mass X-ray binaries with known spin. For the
AMXPs SAX J1808.4-3658 and XTE J1807-294, we find frequency-correlation power
law indices that, surprisingly, are significantly lower than in the
non-pulsars, and consistent with the relativistic precession model (RPM)
prediction of 2.0 appropriate to test-particle orbital and Lense-Thirring
precession frequencies. As previously reported, power law normalizations are
significantly higher in these AMXPs than in the non-pulsating sources, leading
to requirements on the neutron star specific moment of inertia in this model
that cannot be satisfied with realistic equations of state. At least two other
AMXPs show frequency correlations inconsistent with those of SAX J1808.4-3658
and XTE J1807-294, and possibly similar to those of the non-pulsating sources;
for two AMXPs no conclusions could be drawn. We discuss these results in the
context of a model that has had success in black hole (BH) systems involving a
torus-like hot inner flow precessing due to (prograde) frame dragging, and a
scenario in which additional (retrograde) magnetic and classical precession
torques not present in BH systems are also considered. We show that a
combination of these interpretations may accommodate our results.",1910.11202v1
2019-10-28,Comparing domain wall synapse with other Non Volatile Memory devices for on-chip learning in Analog Hardware Neural Network,"Resistive Random Access Memory (RRAM) and Phase Change Memory (PCM) devices
have been popularly used as synapses in crossbar array based analog Neural
Network (NN) circuit to achieve more energy and time efficient data
classification compared to conventional computers. Here we demonstrate the
advantages of recently proposed spin orbit torque driven Domain Wall (DW)
device as synapse compared to the RRAM and PCM devices with respect to on-chip
learning (training in hardware) in such NN. Synaptic characteristic of DW
synapse, obtained by us from micromagnetic modeling, turns out to be much more
linear and symmetric (between positive and negative update) than that of RRAM
and PCM synapse. This makes design of peripheral analog circuits for on-chip
learning much easier in DW synapse based NN compared to that for RRAM and PCM
synapses. We next incorporate the DW synapse as a Verilog-A model in the
crossbar array based NN circuit we design on SPICE circuit simulator.
Successful on-chip learning is demonstrated through SPICE simulations on the
popular Fisher's Iris dataset. Time and energy required for learning turn out
to be orders of magnitude lower for DW synapse based NN circuit compared to
that for RRAM and PCM synapse based NN circuits.",1910.12919v1
2019-11-20,Absolute pressure and gas species identification with an optically levitated rotor,"The authors describe a novel variety of spinning-rotor vacuum gauge in which
the rotor is a ${\sim}4.7{\text -}\mu$m-diameter silica microsphere, optically
levitated. A rotating electrostatic field is used to apply torque to the
permanent electric dipole moment of the silica microsphere and control its
rotational degrees of freedom. When released from a driving field, the
microsphere's angular velocity decays exponentially with a damping time
inversely proportional to the residual gas pressure, and dependent on gas
composition. The gauge is calibrated by measuring the rotor mass with
electrostatic co-levitation, and assuming a spherical shape, confirmed
separately, and uniform density. The gauge is cross-checked against a
capacitance manometer by observing the torsional drag due to a number of
different gas species. The techniques presented can be used to perform absolute
vacuum measurements localized in space, owing to the small dimensions of the
microsphere and the ability to translate the optical trap in three dimensions,
as well as measurements in magnetic field environments. In addition, the
dynamics of the microsphere, paired with a calibrated vacuum gauge, can be used
to measure the effective molecular mass of a gas mixture without the need for
ionization and at pressures up to approximately 1 mbar.",1911.09090v2
2019-11-24,A SOT-MRAM-based Processing-In-Memory Engine for Highly Compressed DNN Implementation,"The computing wall and data movement challenges of deep neural networks
(DNNs) have exposed the limitations of conventional CMOS-based DNN
accelerators. Furthermore, the deep structure and large model size will make
DNNs prohibitive to embedded systems and IoT devices, where low power
consumption are required. To address these challenges, spin orbit torque
magnetic random-access memory (SOT-MRAM) and SOT-MRAM based
Processing-In-Memory (PIM) engines have been used to reduce the power
consumption of DNNs since SOT-MRAM has the characteristic of near-zero standby
power, high density, none-volatile. However, the drawbacks of SOT-MRAM based
PIM engines such as high writing latency and requiring low bit-width data
decrease its popularity as a favorable energy efficient DNN accelerator. To
mitigate these drawbacks, we propose an ultra energy efficient framework by
using model compression techniques including weight pruning and quantization
from the software level considering the architecture of SOT-MRAM PIM. And we
incorporate the alternating direction method of multipliers (ADMM) into the
training phase to further guarantee the solution feasibility and satisfy
SOT-MRAM hardware constraints. Thus, the footprint and power consumption of
SOT-MRAM PIM can be reduced, while increasing the overall system throughput at
the meantime, making our proposed ADMM-based SOT-MRAM PIM more energy
efficiency and suitable for embedded systems or IoT devices. Our experimental
results show the accuracy and compression rate of our proposed framework is
consistently outperforming the reference works, while the efficiency (area \&
power) and throughput of SOT-MRAM PIM engine is significantly improved.",1912.05416v1
2020-03-02,A New MRAM-based Process In-Memory Accelerator for Efficient Neural Network Training with Floating Point Precision,"The excellent performance of modern deep neural networks (DNNs) comes at an
often prohibitive training cost, limiting the rapid development of DNN
innovations and raising various environmental concerns. To reduce the dominant
data movement cost of training, process in-memory (PIM) has emerged as a
promising solution as it alleviates the need to access DNN weights. However,
state-of-the-art PIM DNN training accelerators employ either analog/mixed
signal computing which has limited precision or digital computing based on a
memory technology that supports limited logic functions and thus requires
complicated procedure to realize floating point computation. In this paper, we
propose a spin orbit torque magnetic random access memory (SOT-MRAM) based
digital PIM accelerator that supports floating point precision. Specifically,
this new accelerator features an innovative (1) SOT-MRAM cell, (2) full
addition design, and (3) floating point computation. Experiment results show
that the proposed SOT-MRAM PIM based DNN training accelerator can achieve
3.3$\times$, 1.8$\times$, and 2.5$\times$ improvement in terms of energy,
latency, and area, respectively, compared with a state-of-the-art PIM based DNN
training accelerator.",2003.01551v2
2020-03-24,Hysteretic Mutual Synchronization of PERP-STNO Pairs Analyzed by a Generalized Pendulum-like Model,"At present, the Kuramoto model is the standard and widely accepted
theoretical approach for analyzing the synchronization of spin-torque
nano-oscillators (STNOs) coupled by an interaction. Nevertheless, the
oscillatory decaying regime as well as the initial condition (IC)-dependence
(hysteretic) that exist in the synchronization of many types of STNOs cannot be
explained by this model. In order to more precisely elucidate the physical
mechanisms behind the two phenomena, in this paper we develop a generalized
pendulum-like model based on the two common features of non-linear
auto-oscillators: one is the stability of the amplitude/energy of dynamic
states; the other is the non-linear dynamic state energy of oscillators. In
this new model, we find that the Newtonian-like particle with sufficient
kinetic energy can overcome the barrier of phase-locking potential to evolve
into a stable asynchronization (AS) state, leading to the (IC)-dependent
synchronization. Furthermore, due to the presence of the kinetic energy, this
particle can also oscillate around the minima of the phase-locking potential,
leading to the oscillatory decaying regime. Thereby, in this work, we adopt
this new model to analyze the IC-dependent mutual synchronization of
perpendicularto-plane (PERP)-STNO pairs, and then we suggest that the initial
conditions can be controlled to avoid such a phenomenon by using magnetic
dipolar coupling.",2003.10729v2
2020-04-05,Emergent Elasticity in Amorphous Solids,"The mechanical response of naturally abundant amorphous solids such as gels,
jammed grains, and biological tissues are not described by the conventional
paradigm of broken symmetry that defines crystalline elasticity. In contrast,
the response of such athermal solids are governed by local conditions of
mechanical equilibrium, i.e., force and torque balance of its constituents.
Here we show that these constraints have the mathematical structure of a
generalized electromagnetism, where the electrostatic limit successfully
captures the anisotropic elasticity of amorphous solids. The emergence of
elasticity from local mechanical constraints offers a new paradigm for systems
with no broken symmetry, analogous to emergent gauge theories of quantum spin
liquids. Specifically, our $U(1)$ rank-2 symmetric tensor gauge theory of
elasticity translates to the electromagnetism of fractonic phases of matter
with the stress mapped to electric displacement and forces to vector charges.
We corroborate our theoretical results with numerical simulations of soft
frictionless disks in both two and three dimensions, and experiments on
frictional disks in two dimensions. We also present experimental evidence
indicating that force chains in granular media are sub-dimensional excitations
of amorphous elasticity similar to fractons.",2004.02230v2
2020-04-06,The 2019 super-Eddington outburst of RX J0209.6-7427: Detection of pulsations and constraints on the magnetic field strength,"In November 2019, MAXI detected an X-ray outburst from the known Be X-ray
binary system RX J0209.6-7427 located in the outer wing of the Small Magellanic
Cloud. We followed the outburst of the system with NICER which led to the
discovery of X-ray pulsations with a period of 9.3 s. We analyzed simultaneous
X-ray data obtained with NuSTAR and NICER allowing us to characterize the
spectrum and provide an accurate estimate of its bolometric luminosity. During
the outburst the maximum broadband X-ray luminosity of the system reached
$1-2\times10^{39}$ erg/s, thus exceeding by about one order of magnitude the
Eddington limit for a typical 1.4 $M_{\odot}$ mass neutron star (NS).
Monitoring observations with Fermi/GBM and NICER allowed us to study the spin
evolution of the NS and compare it with standard accretion torque models. We
found that the NS magnetic field should be of the order of $3\times10^{12}$ G.
We conclude that RX J0209.6-7427 exhibited one of the brightest outbursts
observed from a Be X-ray binary pulsar in the Magellanic Clouds, reaching
similar luminosity level to the 2016 outburst of SMC X-3. Despite the
super-Eddington luminosity of RX J0209.6-7427, the NS appears to have only a
moderate magnetic field strength.",2004.03022v1
2020-10-01,On the rate of crustal failures in young magnetars,"The activity of magnetars is powered by their intense and dynamic magnetic
fields and has been proposed as the trigger to extragalactic Fast Radio Bursts.
Here we estimate the frequency of crustal failures in young magnetars, by
computing the magnetic stresses in detailed magneto-thermal simulations
including Hall drift and Ohmic dissipation. The initial internal topology at
birth is poorly known but is likely to be much more complex than a dipole.
Thus, we explore a wide range of initial configurations, finding that the
expected rate of crustal failures varies by orders of magnitude depending on
the initial magnetic configuration. Our results show that this rate scales with
the crustal magnetic energy, rather than with the often used surface value of
the dipolar component related to the spin-down torque. The estimated frequency
of crustal failures for a given dipolar component can vary by orders of
magnitude for different initial conditions, depending on how much magnetic
energy is distributed in the crustal non-dipolar components, likely dominant in
newborn magnetars. The quantitative reliability of the expected event rate
could be improved by a better treatment of the magnetic evolution in the core
and the elastic/plastic crustal response, here not included. Regardless of
that, our results are useful inputs in modelling the outburst rate of young
Galactic magnetars, and their relation with the Fast Radio Bursts in our and
other galaxies.",2010.00617v1
2020-11-18,Can Lense-Thirring precession produce QPOs in supersonic accretion flows?,"The timing properties of X-ray binaries are still not understood,
particularly the presence of quasi-periodic oscillations (QPOs) in their X-ray
power spectra. The solid-body regime of Lense-Thirring precession is one
prominent model invoked to explain the most common type of QPOs, Type C.
However, solid-body precession requires a specific structure that has not been
examined in light of constrained properties of accretion flows. We assume in
this paper, as solid-body precession requires, a disk separated into two flows
at a transition radius $r_t$: a cold outer flow and a hot inner flow (playing
the role of the corona). We explore the physical structure of both flows using
model-independent estimates of accretion parameters. We show that, in order to
reproduce the observed X-ray spectra during luminous hard states, the hot flow
must accrete at sonic to supersonic speeds, unreachable with typical viscous
torques. As a result of this extreme accretion speed (or high $\alpha$
parameter), no region of the disk during these states lies in the `wave-like'
regime required for solid-body precession. Furthermore, we expect the flow to
align with the black hole spin axis via the Bardeen-Petterson effect inside a
radius $r_{\rm break}>r_t$. As a consequence, the hot inner flow cannot exhibit
solid body precession -- as currently pictured in the literature -- during
luminous hard states. Since Type C QPOs are prevalent in these states, we
conclude that this mechanism is unlikely to be responsible for producing Type C
QPOs around stellar mass black holes.",2011.09032v1
2020-12-03,Angular momentum evolution can be predicted from cosmological initial conditions,"The angular momentum of dark matter haloes controls their spin magnitude and
orientation, which in turn influences the galaxies therein. However, the
process by which dark matter haloes acquire angular momentum is not fully
understood; in particular, it is unclear whether angular momentum growth is
stochastic. To address this question, we extend the genetic modification
technique to allow control over the angular momentum of any region in the
initial conditions. Using this technique to produce a sequence of modified
simulations, we can then investigate whether changes to the angular momentum of
a specified region in the evolved universe can be accurately predicted from
changes in the initial conditions alone. We find that the angular momentum in
regions with modified initial conditions can be predicted between 2 and 4 times
more accurately than expected from applying tidal torque theory. This result is
masked when analysing the angular momentum of haloes, because particles in the
outskirts of haloes dominate the angular momentum budget. We conclude that the
angular momentum of Lagrangian patches is highly predictable from the initial
conditions, with apparent chaotic behaviour being driven by stochastic changes
to the arbitrary boundary defining the halo.",2012.02201v2
2020-12-18,Rare-earth-free ferrimagnetic Mn4N sub-20 nm thin films as high-temperature spintronic material,"Ferrimagnetic alloy thin films that exhibit perpendicular (out-of-plane)
magnetic anisotropy (PMA) with low saturation magnetization, such as GdCo and
Mn4N, were predicted to be favorable for hosting small Neel skyrmions for room
temperature applications. Due to the exponential decay of interfacial
Dzyaloshinskii-Moriya interaction (DMI) and the limited range of
spin-orbit-torques, which can be used to drive skyrmion motion, the thickness
of the ferrimagnetic layer has to be small, preferably under 20 nm. While there
are examples of sub-20 nm, rare earth-transition metal (RE-TM), ferrimagnetic
thin films fabricated by sputter deposition, to date rare-earth-free sub-20 nm
Mn4N films with PMA have only been reported to be achieved by molecular beam
epitaxy, which is not suitable for massive production. Here we report the
successful thermal growth of sub-20 nm Mn4N films with PMA at 400-450 {\deg}C
substrate temperatures on MgO substrates by reactive sputtering. The Mn4N films
were achieved by reducing the surface roughness of MgO substrate through a
high-temperature vacuum annealing process. The optimal films showed low
saturation magnetization (Ms = 43 emu/cc), low magnetic anisotropy energy (0.7
Merg/cc), and a remanent magnetization to saturation magnetization ratio
(Mr/Ms) near 1 at room temperature. Preliminary ab-initio density functional
theory (DFT) calculations have confirmed the ferrimagnetic ground state of Mn4N
grown on MgO. The magnetic properties, along with the high thermal stability of
Mn4N thin films in comparison with RE-TM thin films, provide the platform for
future studies of practical skyrmion-based spintronic materials.",2012.10493v1
2021-01-27,Modeling Solar Wind Variations over an 11-yr Cycle with Alfvén Wave Dissipation: a Parameter Study,"We study the behaviour and properties of the solar wind using a 2.5D Alfv\'en
wave driven wind model. We first systematically compare the results of an
Alfv\'en wave (AW) driven wind model with a polytropic approach. Polytropic
magnetohydrodynamic wind models are thermally driven, while Alfv\'en waves act
as additional acceleration and heating mechanisms in the Alfv\'en wave driven
model. We confirm that an AW-driven model is required to reproduce the observed
bimodality of slow and fast solar winds. We are also able to reproduce the
observed anti-correlation between the terminal wind velocity and the coronal
source temperature with the AW-driven wind model. We also show that the wind
properties along an eleven-year cycle differ significantly from one model to
the other. The AW-driven model again shows the best agreement with
observational data. Indeed, solar surface magnetic field topology plays an
important role in the Alfv\'en wave driven wind model, as it enters directly
into the input energy sources via the Poynting flux. On the other hand, the
polytropic wind model is driven by an assumed pressure gradient; thus it is
relatively less sensitive to the surface magnetic field topology. Finally, we
note that the net torque spinning down the Sun exhibits the same trends in the
two models, showing that the polytropic approach still captures correctly the
essence of stellar winds.",2101.11511v1
2021-03-11,Revealing three-dimensional quantum criticality by Sr-substitution in Han Purple,"Classical and quantum phase transitions (QPTs), with their accompanying
concepts of criticality and universality, are a cornerstone of statistical
thermodynamics. An exemplary controlled QPT is the field-induced magnetic
ordering of a gapped quantum magnet. Although numerous ""quasi-one-dimensional""
coupled spin-chain and -ladder materials are known whose ordering transition is
three-dimensional (3D), quasi-2D systems are special for several physical
reasons. Motivated by the ancient pigment Han Purple (BaCuSi$_{2}$O$_{6}$), a
quasi-2D material displaying anomalous critical properties, we present a
complete analysis of Ba$_{0.9}$Sr$_{0.1}$CuSi$_{2}$O$_{6}$. We measure the
zero-field magnetic excitations by neutron spectroscopy and deduce the magnetic
Hamiltonian. We probe the field-induced transition by combining magnetization,
specific-heat, torque and magnetocalorimetric measurements with low-temperature
nuclear magnetic resonance studies near the QPT. By a Bayesian statistical
analysis and large-scale Quantum Monte Carlo simulations, we demonstrate
unambiguously that observable 3D quantum critical scaling is restored by the
structural simplification arising from light Sr-substitution in Han Purple.",2103.06860v2
2021-04-29,The origin and evolution of magnetic white dwarfs in close binary stars,"The origin of magnetic fields in white dwarfs remains a fundamental
unresolved problem in stellar astrophysics. In particular, the very different
fractions of strongly (exceeding 1 MG) magnetic white dwarfs in evolutionarily
linked populations of close white dwarf binary stars cannot be reproduced by
any scenario suggested so far. Strongly magnetic white dwarfs are absent among
detached white dwarf binary stars that are younger than approximately 1 Gyr. In
contrast, in semi-detached cataclysmic variables in which the white dwarf
accretes from a low-mass star companion, more than one third host a strongly
magnetic white dwarf. Here we present binary star evolutionary models that
include the spin evolution of accreting white dwarfs and crystallization of
their cores, as well as magnetic field interactions between both stars. We show
that a crystallization- and rotation-driven dynamo similar to those working in
planets and low-mass stars can generate strong magnetic fields in the white
dwarfs in cataclysmic variables which explains their large fraction among the
observed population. When the magnetic field generated in the white dwarfs
connects with that of the secondary stars, synchronization torques and reduced
angular momentum loss cause the binary to detach for a relatively short period
of time. The few known strongly magnetic white dwarfs in detached binaries,
including AR Sco, are in this detached phase.",2104.14607v1
2021-05-05,Observation of current-induced switching in non-collinear antiferromagnetic IrMn$_3$ by differential voltage measurements,"There is accelerating interest in developing memory devices using
antiferromagnetic (AFM) materials, motivated by the possibility for
electrically controlling AFM order via spin-orbit torques, and its read-out via
magnetoresistive effects. Recent studies have shown, however, that high current
densities create non-magnetic contributions to resistive switching signals in
AFM/heavy metal (AFM/HM) bilayers, complicating their interpretation. Here we
introduce an experimental protocol to unambiguously distinguish current-induced
magnetic and nonmagnetic switching signals in AFM/HM structures, and
demonstrate it in IrMn$_3$/Pt devices. A six-terminal double-cross device is
constructed, with an IrMn$_3$ pillar placed on one cross. The differential
voltage is measured between the two crosses with and without IrMn$_3$ after
each switching attempt. For a wide range of current densities, reversible
switching is observed only when write currents pass through the cross with the
IrMn$_3$ pillar, eliminating any possibility of non-magnetic switching
artifacts. Micromagnetic simulations support our findings, indicating a complex
domain-mediated switching process.",2105.02277v1
2021-05-25,Weyl nodes close to the Fermi energy in NbAs,"The noncentrosymmetric transition metal monopnictides NbP, TaP, NbAs and TaAs
are a family of Weyl semimetals in which pairs of protected linear crossings of
spin-resolved bands occur. These so-called Weyl nodes are characterized by
integer topological charges of opposite sign associated with singular points of
Berry curvature in momentum space. In such a system anomalous magnetoelectric
responses are predicted, which should only occur if the crossing points are
close to the Fermi level and enclosed by Fermi surface pockets penetrated by an
integer flux of Berry curvature, dubbed Weyl pockets. TaAs was shown to possess
Weyl pockets whereas TaP and NbP have trivial pockets enclosing zero net flux
of Berry curvature. Here, via measurements of the magnetic torque, resistivity
and magnetisation, we present a comprehensive quantum oscillation study of
NbAs, the last member of this family where the precise shape and nature of the
Fermi surface pockets is still unknown. We detect six distinct frequency
branches, two of which have not been observed before. A comparison to density
functional theory calculations suggests that the two largest pockets are
topologically trivial, whereas the low frequencies might stem from tiny Weyl
pockets. The enclosed Weyl nodes are within a few meV of the Fermi energy.",2105.12090v1
2021-06-04,Readout of a antiferromagnetic spintronics systems by strong exchange coupling of Mn2Au and Permalloy,"In antiferromagnetic spintronics, the read-out of the staggered magnetization
or Neel vector is the key obstacle to harnessing the ultra-fast dynamics and
stability of antiferromagnets for novel devices. Here, we demonstrate strong
exchange coupling of Mn2Au, a unique metallic antiferromagnet that exhibits
Neel spin-orbit torques, with thin ferromagnetic Permalloy layers. This allows
us to benefit from the well-estabished read-out methods of ferromagnets, while
the essential advantages of antiferromagnetic spintronics are retained. We show
one-to-one imprinting of the antiferromagnetic on the ferromagnetic domain
pattern. Conversely, alignment of the Permalloy magnetization reorients the
Mn2Au Neel vector, an effect, which can be restricted to large magnetic fields
by tuning the ferromagnetic layer thickness. To understand the origin of the
strong coupling, we carry out high resolution electron microscopy imaging and
we find that our growth yields an interface with a well-defined morphology that
leads to the strong exchange coupling.",2106.02333v1
2021-06-14,Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Gravitational Wave Bursts and Electromagnetic Counterparts from Merging Stellar Black Hole Binaries,"The recent advanced LIGO/Virgo detections of gravitational waves (GWs) from
stellar binary black hole (BBH) mergers, in particular GW190521, which is
potentially associated with a quasar, have stimulated renewed interest in
active galactic nuclei (AGNs) as factories of merging BBHs. Compact objects
evolving from massive stars are unavoidably enshrouded by a massive envelope to
form accretion-modified stars (AMSs) in the dense gaseous environment of a
supermassive black hole (SMBH) accretion disk. We show that most AMSs form
binaries due to gravitational interaction with each other during radial
migration in the SMBH disk, forming BBHs inside the AMS. When a BBH is born,
its orbit is initially governed by the tidal torque of the SMBH. Bondi
accretion onto BBH at a hyper-Eddington rate naturally develops and then
controls the evolution of its orbits. We find that Bondi accretion leads to
efficient removal of orbital angular momentum of the binary, whose final merger
produces a GW burst. Meanwhile, the Blandford-Znajek mechanism pumps the spin
energy of the merged BH to produce an electromagnetic counterpart (EMC).
Moreover, hyper-Eddington accretion onto the BBH develops powerful outflows and
triggers a Bondi explosion, which manifests itself as a EMC of the GW burst,
depending on the viscosity of the accretion flow. Thermal emission from Bondi
sphere appears as one of EMCs. BBHs radiate GWs with frequencies $\sim
10^{2}\,$Hz, which are accessible to LIGO.",2106.07334v2
2021-07-05,Circuits and excitations to enable Brownian token-based computing with skyrmions,"Brownian computing exploits thermal motion of discrete signal carriers
(tokens) for computations. In this paper we address two major challenges that
hinder competitive realizations of circuits and application of Brownian
token-based computing in actual devices for instance based on magnetic
skyrmions. To overcome the problem that crossings generate for the fabrication
of circuits, we design a crossing-free layout for a composite half-adder
module. This layout greatly simplifies experimental implementations as wire
crossings are effectively avoided. Additionally, our design is shorter to speed
up computations compared to conventional designs. To address the key issue of
slow computation based on thermal excitations, we propose to overlay artificial
diffusion induced by an external excitation mechanism. For instance, if
magnetic skyrmions are used as tokens, artificially induced diffusion by
spin-orbit torques or other mechanisms increases the speed of computations by
several orders of magnitude. Combined with conventional Brownian computing the
latter could greatly enhance the application scenarios of token-based computing
for instance for low power devices such as autonomous sensors with limited
power that is harvested from the environment.",2107.02097v2
2021-07-06,Ciliary flocking and emergent instabilities enable collective agility in a non-neuromuscular animal,"Effective organismal behavior responds appropriately to changes in the
surrounding environment. Attaining this delicate balance of sensitivity and
stability is a hallmark of the animal kingdom. By studying the locomotory
behavior of a simple animal (\textit{Trichoplax adhaerens}) without muscles or
neurons, here, we demonstrate how monociliated epithelial cells work
collectively to give rise to an agile non-neuromuscular organism. Via direct
visualization of large ciliary arrays, we report the discovery of sub-second
ciliary reorientations under a rotational torque that is mediated by collective
tissue mechanics and the adhesion of cilia to the underlying substrate. In a
toy model, we show a mapping of this system onto an ""active-elastic resonator"".
This framework explains how perturbations propagate information in this array
as linear speed traveling waves in response to mechanical stimulus. Next, we
explore the implications of parametric driving in this active-elastic resonator
and show that such driving can excite mechanical 'spikes'. These spikes in
collective mode amplitudes are consistent with a system driven by parametric
amplification and a saturating nonlinearity. We conduct extensive numerical
experiments to corroborate these findings within a polarized active-elastic
sheet. These results indicate that periodic and stochastic forcing are valuable
for increasing the sensitivity of collective ciliary flocking. We support these
theoretical predictions via direct experimental observation of linear speed
traveling waves which arise from the hybridization of spin and overdamped
density waves. We map how these ciliary flocking dynamics result in agile
motility via coupling between an amplified resonator and a tuning
(Goldstone-like) mode of the system. This sets the stage for how activity and
elasticity can self-organize into behavior which benefits the organism as a
whole.",2107.02934v1
2021-07-29,Thermal Contribution in the Electrical Switching Experiments with Heavy Metal / Antiferromagnet Structures,"We examine the thermal origin of the detected ""saw-tooth"" shaped Hall
resistance (Rxy) signals in the spin-orbit torque switching experiment for
antiferromagnetic MnN. Compared with the results of the heavy metal /
antiferromagnet bilayers (MnN/Ta), the qualitatively same ""saw-tooth"" shaped
signals also appear in the samples with the heavy metal layer alone (either Ta
or Pt) without MnN layer. In addition, The Rxy signal changes oppositely in the
devices with Ta and Pt, due to the opposite temperature coefficient of
resistivity (TCR) of the two materials. All those results are consistent with
the ""localized Joule heating"" mechanism in devices with Hall crosses geometry.
Moreover, by utilizing a structure with separated writing current paths and
Hall cross area, the quadratic relationship between delta-Rxy and the writing
current's amplitude is observed, which provides quantitative evidence of the
thermal contribution. These results reveal the dominant thermal artifact in the
widely used Hall crosses geometry for Neel vector probing, and also provide a
strategy to semi-quantitatively evaluate the thermal effect, which can shed
light on a more conclusive experiment design.",2107.13859v1
2021-08-27,Gigantic current control of coercive field and magnetic memory based on nm-thin ferromagnetic van der Waals Fe3GeTe2,"Controlling magnetic states by a small current is essential for the
next-generation of energy-efficient spintronic devices. However, it invariably
requires considerable energy to change a magnetic ground state of intrinsically
quantum nature governed by fundamental Hamiltonian, once stabilized below a
phase transition temperature. We report that surprisingly an in-plane current
can tune the magnetic state of nm-thin van der Waals ferromagnet Fe3GeTe2 from
a hard magnetic state to a soft magnetic state. It is the direct demonstration
of the current-induced substantial reduction of the coercive field. This
surprising finding is possible because the in-plane current produces a highly
unusual type of gigantic spin-orbit torque for Fe3GeTe2. And we further
demonstrate a working model of a new nonvolatile magnetic memory based on the
principle of our discovery in Fe3GeTe2, controlled by a tiny current. Our
findings open up a new window of exciting opportunities for magnetic van der
Waals materials with potentially huge impacts on the future development of
spintronic and magnetic memory.",2108.12111v2
2021-11-01,Interface-enhanced ferromagnetism with long-distance effect in van der Waals semiconductor,"Ferromagnetic semiconductors discovered in two-dimensional (2D) materials
open an avenue for highly integrated and multifunctional spintronics. The Curie
temperature (TC) of existed 2D ferromagnetic semiconductors is extremely low
and the modulation effect of their magnetism is limited compared with their 2D
metallic counterparts. The interfacial effect was found to effectively
manipulate the three-dimensional magnetism, providing a unique opportunity for
tailoring the 2D magnetism. Here we demonstrate that the TC of 2D ferromagnetic
semiconductor Cr2Ge2Te6 can be enhanced by 130% (from ~65 K to above 150 K)
when adjacent to a tungsten layer. The interfacial W-Te bonding contributes to
the TC enhancement with a strong perpendicular magnetic anisotropy (PMA),
guaranteeing an efficient magnetization switching by the spin-orbit torque with
a low current density at 150 K. Distinct from the rapid attenuation in
conventional magnets, the interfacial effect exhibits a weak dependence on
Cr2Ge2Te6 thickness and a long-distance effect (more than 10 nanometers) due to
the weak interlayer coupling inherent to 2D magnets. Our work not only reveals
a unique interfacial behavior in 2D materials, but also advances the process
towards practical 2D spintronics.",2111.00645v1
2021-11-18,Fragmenting Active Asteroid 331P/Gibbs,"We describe active asteroid 331P/Gibbs (2012 F5) using archival Hubble Space
Telescope data taken between 2015 and 2018. 331P is an outer main-belt active
asteroid with a long-lived debris trail that formed in 2011. Embedded in the
debris trail we identify 19 fragments with radii between 0.04 and 0.11 km
(albedo 0.05 assumed) containing about 1 percent of the mass of the primary
nucleus. The largest shows a photometric range (1.5 magnitudes), a V-shaped
minimum and a two-peaked lightcurve period near 9 hours, consistent with a
symmetric contact binary (Drahus and Waniak 2016). Less convincing explanations
are that 331P-A is a monolithic, elongated splinter or that its surface shows
hemispheric 4:1 albedo variations. The debris trail is composed of centimeter
sized and larger particles ejected with characteristic 10 cm s$^{-1}$ speeds
following a size distribution with index q = 3.7+/-0.1 to 4.1+/-0.2. The HST
data show that earlier, ground-based measurements of the nucleus were
contaminated by near-nucleus debris, which cleared by 2015. We find that the
primary nucleus has effective radius 0.8+/-0.1 km and is in rapid rotation
(3.26+/-0.01 hour, range 0.25 magnitudes, minimum density 1600 kg/m3 if
strengthless. The properties of 331P are consistent with a) formation about 1.5
Myr ago by impact shattering of a precursor body (Novakovic et al. 2014) b)
spin-up by radiation torques to critical rotation c) ejection of about 1
percent of the nucleus mass in mid-2011 by rotational instability and d)
subsequent evolution of the fragments and dispersal of the debris by radiation
pressure.",2111.09900v1
2022-01-03,Viscous dissipation in the fluid core of the Moon,"The spin axes of the mantle, fluid core and solid inner core of the Moon
precess at frequency $\Omega_p=2\pi/18.6$ yr$^{-1}$ though with different
orientations, leading to viscous friction at the core-mantle boundary (CMB) and
inner core boundary (ICB). Here, we use a rotational model of the Moon with a
range of inner core and outer core radii to investigate the relative importance
of viscous dissipation at the CMB and ICB, and to show how this dissipation is
connected to the phase lead angle ($\phi_p$) of the mantle ahead of its Cassini
state. We show that when the inner core radius is $>80$ km and the free inner
core nutation frequency $\Omega_{ficn}$ approaches $\Omega_p$, viscous
dissipation at the ICB can be comparable to that at the CMB, and in the most
extreme cases exceed it by as much as a factor 10. If so, the viscous
dissipation in the lunar core projected back in time depends on how
$\Omega_{ficn}$ has evolved relative to $\Omega_p$. We further show that
constraints on the CMB and ICB radii of the lunar core can in principle be
extracted by matching the observed phase lead of $\phi_p=0.27$ arcsec; this
requires an improved estimate of tidal dissipation and an accurate model of the
turbulent viscous torque. Lastly, when our rotational model is constrained to
match $\phi_p=0.27$ arcsec, our results suggest that the viscous dissipation at
the ICB is likely insufficient to have ever been above the threshold to power a
thermally driven dynamo.",2201.00781v1
2022-01-26,Effect of Chiral Damping on the dynamics of chiral domain walls and skyrmions,"Friction plays an essential role in most physical processes that we
experience in our everyday life. Examples range from our ability to walk or
swim, to setting boundaries of speed and fuel efficiency of moving vehicles. In
magnetic systems, the displacement of chiral domain walls (DW) and skyrmions
(SK) by Spin Orbit Torques (SOT), is also prone to friction. Chiral damping,
the dissipative counterpart of the Dzyaloshinskii Moriya Interaction (DMI),
plays a central role in these dynamics. Despite experimental observation, and
numerous theoretical studies confirming its existence, the influence of chiral
damping on DW and SK dynamics has remained elusive due to the difficulty of
discriminating from DMI. Here we unveil the effect that chiral damping has on
the flow motion of DWs and SKs driven by current and magnetic field. We use a
static in-plane field to lift the chiral degeneracy. As the in-plane field is
increased, the chiral asymmetry changes sign. When considered separately,
neither DMI nor chiral damping can explain the sign reversal of the asymmetry,
which we prove to be the result of their competing effects. Finally, numerical
modelling unveils the non-linear nature of chiral dissipation and its critical
role for the stabilization of moving SKs.",2201.10742v1
2022-02-08,Dynamics of finite-size spheroids in turbulent flow: the roles of flow structures and particle boundary layers,"We study the translational and rotational dynamics of neutrally-buoyant
finite-size spheroids in hydrodynamic turbulence by means of fully resolved
numerical simulations. We examine axisymmetric shapes, from oblate to prolate,
and the particle volume dependences. We show that the accelerations and
rotations experienced by non-spherical inertial-scale particles result from
volume filtered fluid forces and torques, similar to spherical particles.
However, the particle orientations carry signatures of preferential alignments
with the surrounding flow structures, which is reflected in distinct axial and
lateral fluctuations for accelerations and rotation rates. The randomization of
orientations does not occur even for particles with volume equivalent diameter
size in the inertial range, here up to 60 $\eta$ at $Re_{\lambda}=120$.
Additionally, we demonstrate that the role of fluid boundary layers around the
particles cannot be neglected to reach a quantitative understanding of particle
statistical dynamics, as they affect the intensities of angular velocities, and
the relative importance of tumbling with respect to spinning rotations. This
study brings to the fore the importance of inertial-scale flow structures in
homogeneous and isotropic turbulence and their impacts on the transport of
neutrally-buoyant bodies with size in the inertial range.",2202.03937v1
2022-04-25,"Ergomagnetosphere, Ejection Disc, Magnetopause in M87. I Global Flow of Mass, Angular Momentum, Energy and Current","We interpret the 1.3mm VLBI observations made by the Event Horizon Telescope
of the black hole in M87. It is proposed that, instead of being a torus of
accreting gas, the observed annular ring is a rotating, magnetically-dominated
ergomagnetosphere that can transmit electromagnetic angular momentum and energy
outward to the disc through a combination of large scale magnetic torque and
small scale instabilities. It is further proposed that energy can be extracted
by magnetic flux threading the ergosphere through the efficient emission of
long wavelength electromagnetic disturbances onto negative energy orbits, when
the invariant $B^2-E^2$ becomes negative. In this way, the spinning black hole
and its ergosphere not only power the jets but also the ejection disc so as to
drive away most of the gas supplied near the Bondi radius. This outflow takes
the form of a MHD wind, extending over many decades of radius, with a
unidirectional magnetic field, that is collimated by the infalling gas across a
magnetopause. This wind, in turn, collimates the relativistic jets and the
emission observed from the jet sheath may be associated with a return current.
A model for the global flow of mass, angular momentum, energy and current, on
scales from the horizon to the Bondi radius, is presented and discussed.",2204.11995v2
2022-05-03,Electrical Switching of the Edge Current Chirality in Quantum Anomalous Hall Insulators,"A quantum anomalous Hall (QAH) insulator is a topological state of matter, in
which the interior is insulating but electrical current flows along the edges
of the sample, in either clockwise (right-handed) or counter-clockwise
(left-handed) direction dictated by the spontaneous magnetization orientation.
Such chiral edge current (CEC) eliminates any backscattering, giving rise to
quantized Hall resistance and zero longitudinal resistance. In this work, we
fabricate mesoscopic QAH sandwich (i.e. magnetic topological insulator
(TI)/TI/magnetic TI) Hall bar devices and succeed in switching the CEC
chirality in QAH insulators through spin-orbit torque (SOT) by applying a
current pulse and suitably controlled gate voltage. The well-quantized QAH
states with opposite CEC chiralities are demonstrated through four- and
three-terminal measurements before and after SOT switching. Our theoretical
calculations show that the SOT that enables the magnetization switching can be
generated by both bulk and surface carriers in QAH insulators, in good
agreement with experimental observations. Current pulse-induced switching of
the CEC chirality in QAH insulators will not only advance our knowledge in the
interplay between magnetism and topological states but also expedite easy and
instantaneous manipulation of the QAH state in proof-of-concept
energy-efficient electronic and spintronic devices as well as quantum
information applications.",2205.01581v1
2022-05-20,Effects of Crystalline Disorder on Interfacial and Magnetic Properties of Sputtered Topological Insulator/Ferromagnet Heterostructures,"Thin films of Topological insulators (TIs) coupled with ferromagnets (FMs)
are excellent candidates for energy-efficient spintronics devices. Here, the
effect of crystalline structural disorder of TI on interfacial and magnetic
properties of sputter-deposited TI/FM, Bi2Te3/Ni80Fe20, heterostructures is
reported. Ni and a smaller amount of Fe from Py was found to diffuse across the
interface and react with Bi2Te3. For highly crystalline c-axis oriented Bi2Te3
films, a giant enhancement in Gilbert damping is observed, accompanied by an
effective out-of-plane magnetic anisotropy and enhanced damping-like spin-orbit
torque (DL-SOT), possibly due to the topological surface states (TSS) of
Bi2Te3. Furthermore, a spontaneous exchange bias is observed in hysteresis loop
measurements at low temperatures. This is because of an antiferromagnetic
topological interfacial layer formed by reaction of the diffused Ni with Bi2Te3
which couples with the FM, Ni80Fe20. For increasing disorder of Bi2Te3, a
significant weakening of exchange interaction in the AFM interfacial layer is
found. These experimental results Abstract length is one paragraph.",2205.09913v1
2022-05-30,Skyrmion-Magnetic Tunnel Junction Synapse with Mixed Synaptic Plasticity for Neuromorphic Computing,"Magnetic skyrmion-based data storage and unconventional computing devices
have gained increasing attention due to their topological protection, small
size, and low driving current. However, skyrmion creation, deletion, and motion
are still being studied. In this study, we propose a skyrmion-based
neuromorphic magnetic tunnel junction (MTJ) device with both long- and
short-term plasticity (LTP and STP) (mixed synaptic plasticity). We showed that
plasticity could be controlled by magnetic field, spin-orbit torque (SOT), and
the voltage-controlled magnetic anisotropy (VCMA) switching mechanism. LTP
depends on the skyrmion density and is manipulated by the SOT and magnetic
field while STP is controlled by the VCMA. The LTP property of the device was
utilized for static image recognition. By incorporating the STP feature, the
device gained additional temporal filtering ability and could adapt to a
dynamic environment. The skyrmions were conserved and confined to a nanotrack
to minimize the skyrmion nucleation energy. The synapse device was trained and
tested for emulating a deep neural network. We observed that when the skyrmion
density was increased, the inference accuracy improved: 90% accuracy was
achieved by the system at the highest density. We further demonstrated the
dynamic environment learning and inference capabilities of the proposed device.",2205.14915v1
2022-07-07,Control of field- and current-driven magnetic domain wall motion by exchange-bias in Cr2O3/Co/Pt trilayers,"We investigate the motion of magnetic domain walls driven by magnetic fields
and current-driven spin-orbit torques in an exchange-biased system with
perpendicular magnetization. We consider Cr2O3/Co/Pt trilayers as model system,
in which the magnetization of the Co layer can be exchanged-biased out-of-plane
or in-plane depending on the field cooling direction. In field-driven
experiments, the in-plane exchange bias favors the propagation of the domain
walls with internal magnetization parallel to the exchange bias field. In
current-driven experiments, the domain walls propagate along the current
direction, but the domain wall velocity increases and decreases symmetrically
(anti-symmetrically) for both current polarities when the exchange bias is
parallel (perpendicular) to the current line. At zero external field, the
exchange bias modifies the velocity of current-driven domain wall motion by a
factor of ten. We also find that the exchange bias remains stable under
external fields up to 15 kOe and ns-long current pulses with current density up
to 3.5x10^12 A/m^2. Our results demonstrate versatile control of the domain
wall motion by exchange bias, which is relevant to achieve field-free switching
of the magnetization in perpendicular systems and current-driven manipulation
of domain walls velocity in spintronic devices.",2207.03311v2
2022-07-13,Wafer-scale epitaxial growth of the thickness-controllable van der Waals ferromagnet CrTe2 for reliable magnetic memory applications,"To harness the intriguing properties of two-dimensional van der Waals (vdW)
ferromagnets (FMs) for versatile applications, the key challenge lies in the
reliable material synthesis for scalable device production. Here, we
demonstrate the epitaxial growth of single-crystalline 1T-CrTe2 thin films on
2-inch sapphire substrates. Benefiting from the uniform surface energy of the
dangling bond-free Al2O3(0001) surface, the layer-by-layer vdW growth mode is
observed right from the initial growth stage, which warrants precise control of
the sample thickness and atomically smooth surface morphology across the entire
wafer. Moreover, the presence of the Coulomb interaction at the CrTe2/Al2O3
interface serves as an effective tuning parameter to tailor the anomalous Hall
response, and the structural optimization of the CrTe2-based spin-orbit torque
device leads to a substantial switching power reduction by 54%. Our results may
lay out a general framework for the design of energy-efficient spintronics
based on configurable vdW FMs.",2207.05944v1
2022-07-17,Field-induced compensation of magnetic exchange as the possible origin of reentrant superconductivity in UTe$_2$,"The potential spin-triplet heavy-fermion superconductor UTe$_2$ exhibits
signatures of multiple distinct superconducting phases. For field aligned along
the $b$ axis, a metamagnetic transition occurs at $\mu_0
H_\mathrm{m}\approx35\,$T. It is associated with magnetic fluctuations that may
be beneficial for the field-reinforced superconductivity surviving up to
$H_\mathrm{m}$. Once the field is tilted away from the $b$ towards the $c$
axis, a reentrant superconducting phase emerges just above $H_\mathrm{m}$. In
order to better understand this remarkably field-resistant superconducting
phase, we conducted magnetic-torque and magnetotransport measurements in pulsed
magnetic fields. We determine the record-breaking upper critical field of
$\mu_0 H_\mathrm{c2}\approx 73\,$T and its evolution with angle. Furthermore,
the normal-state Hall effect experiences a drastic suppression indicative of a
reduced band polarization above $H_\mathrm{m}$ in the angular range around
$30^\circ$ caused by a partial compensation between the applied field and an
exchange field. This promotes the Jaccarino-Peter effect as a likely mechanism
for the reentrant superconductivity above $H_\mathrm{m}$.",2207.08261v3
2022-09-22,Biskyrmion-based artificial neuron with refractory period,"Magnetic skyrmions are nanoscale magnetic whirls that are highly stable and
can be moved by currents which has led to the prediction of a skyrmion-based
artificial neuron device with leak-integrate-fire functionality. However, so
far, these devices lack a refractory process, estimated to be crucial for
neuronal dynamics. Here we demonstrate that a biskyrmion-based artificial
neuron overcomes this insufficiency. When driven by spin-orbit torques, a
single biskyrmion splits into two subskyrmions that move towards a designated
location and can be detected electrically, resembling the excitation process of
a neuron that fires ultimately. The attractive interaction of the two skyrmions
leads to a unique trajectory: Once they reach the detector area, they
automatically return to the center to reform the biskyrmion but on a different
path. During this reset period, the neuron cannot fire again. Our suggested
device resembles a biological neuron with the leak, integrate, fire and
refractory characteristics better than all existing artificial devices so far.",2209.11017v2
2022-10-04,Diode Like Attributes in Magnetic Domain Wall Devices via Geometrical Pinning for Neuromorphic Computing,"Neuromorphic computing (NC) is considered as a potential vehicle for
implementing energy-efficient artificial intelligence (AI). To realize NC,
several materials systems are being investigated. Among them, the spin-orbit
torque (SOT) -driven domain wall (DW) devices are one of the potential
candidates. To implement these devices as neurons and synapses, the building
blocks of NC, researchers have proposed different device designs. However, the
experimental realization of DW device-based NC is only at the primeval stage.
In this study, we have proposed and investigated pine-tree-shaped DW devices,
based on the Laplace force on the elastic DWs, for achieving the synaptic
functionalities. We have successfully observed multiple magnetization states
when the DW was driven by the SOT current. The key observation is the
asymmetric pinning strength of the device when DW moves in two opposite
directions (defined as, xhard and xeasy). This shows the potential of these DW
devices as DW diodes. We have used micromagnetic simulations to understand the
experimental findings and to estimate the Laplace pressure for various design
parameters. The study leads to the path of device fabrication, where synaptic
properties are achieved with asymmetric pinning potential.",2210.01385v1
2023-01-03,Strong correlation effects observed by an ANN-MFT encoder trained on $α$-RuCl$_3$ high magnetic field data,"$\alpha$-RuCl3 is a magnetic insulator exhibiting quantum spin liquid phases
possibly found in the Kitaev honeycomb model. Much of the effort towards
determining Hamiltonian parameters has focused on low magnetic field ordered
phases. We study this problem in the high magnetic field limit where mean-field
theory is better justified. We do so by machine-learning model parameters from
over 200,000 low dimensional data points by combining available magnetization,
torque, and torsion data sets. Our machine, an artificial neural
network-mean-field theory (ANN-MFT) encoder, maps thermodynamic conditions
(temperature and field vector) to model parameters via a fully connected
time-reversal covariant (equivariant) neural network and then predicts
observable values using mean-field theory. To train the machine, we use PyTorch
to enable backpropagation through mean-field theory with a pure PyTorch
implementation of the Newton-Raphson method. The results at $20$ K and $34.5$ T
are consistent with other parameter inference studies in the literature at low
magnetic field but strikingly have magnitudes that scale with temperature from
1.3 K up to 80 K in the $34.5-60$ T range. We conclude that the data presents
physics beyond the scope of the mean-field theory and that strong interactions
dominate the physics of $\alpha$-RuCl$_3$ up to field strengths of at least 60
Tesla.",2301.01301v1
2023-01-27,Field-free switching of perpendicular magnetization in an ultrathin epitaxial magnetic insulator,"For energy efficient and fast magnetic memories, switching of perpendicular
magnetization by the spin-orbit torque (SOT) appears as a very promising
solution, even more using magnetic insulators that suppress electrical
shunting. This SOT switching generally requires the assistance of an in-plane
magnetic field to break the symmetry. Here, we present experiments
demonstrating the field-free SOT switching of perpendicularly magnetized layers
of the thulium iron garnet (Tm_{3}Fe_{5}O_{12}) magnetic insulator. The
polarity of the switching loops, clockwise (CW) or counter-clockwise (CCW), is
determined by the direction of the initial current pulses, in contrast with
field-assisted switchings in which this polarity is controlled by the direction
of the field. After an independent determination of Dzyaloshinskii-Moriya
interaction (DMI), we relate the field free switching to the interplay of SOT
and DMI and the polarity of the loops to the imprint of a N\'eel domain wall
induced by the first pulse, in agreement with Kerr imaging. Our observation and
interpretation of field-free electrical switching of a magnetic insulator is an
important milestone for future low power spintronic devices.",2301.11469v1
2023-02-02,Controlling the Skyrmion Density and Size for Quantized Convolutional Neural Networks,"Skyrmion devices show energy efficient and high integration data storage and
computing capabilities. Herein, we present the results of experimental and
micromagnetic investigations of the creation and stability of magnetic
skyrmions in the Ta/IrMn/CoFeB/MgO thin film system. We investigate the
magnetic-field dependence of the skyrmion density and size using polar magneto
optical Kerr effect MOKE microscopy supported by a micromagnetic study. The
evolution of the topological charge with time under a magnetic field is
investigated, and the transformation dynamics are explained. Furthermore,
considering the voltage control of these skyrmion devices, we evaluate the
dependence of the skyrmion size and density on the Dzyaloshinskii Moriya
interaction and the magnetic anisotropy. We furthermore propose a skyrmion
based synaptic device based on the results of the MOKE and micromagnetic
investigations. We demonstrate the spin-orbit torque controlled discrete
topological resistance states with high linearity and uniformity in the device.
The discrete nature of the topological resistance makes it a good candidate to
realize hardware implementation of weight quantization in a quantized neural
network (QNN). The neural network is trained and tested on the CIFAR10 dataset,
where the devices act as synapses to achieve a recognition accuracy of 87%,
which is comparable to the result of ideal software-based methods.",2302.01390v1
2023-02-28,Inertial migration of a neutrally buoyant spheroid in plane Poiseuille flow,"We study the cross-stream inertial migration of a torque-free neutrally
buoyant spheroid, of an arbitrary aspect ratio $\kappa$, in wall-bounded plane
Poiseuille flow for small particle Reynolds numbers\,($Re_p\ll1$) and
confinement ratios\,($\lambda\ll1$), with the channel Reynolds number, $Re_c =
Re_p/\lambda^2$, assumed to be arbitrary; here, $\lambda=L/H$ where $L$ is the
semi-major axis of the spheroid and $H$ denotes the separation between the
channel walls. In the Stokes limit\,($Re_p =0)$ and for $\lambda \ll 1$, a
spheroid rotates along any of an infinite number of Jeffery orbits
parameterized by an orbit constant $C$, while translating with a time dependent
speed along a given ambient streamline. Weak inertial effects stabilize either
the spinning\,($C=0$) or the tumbling orbit\,($C=\infty$), or both, depending
on $\kappa$. The separation of the Jeffery-rotation and orbital drift time
scales, from that associated with cross-stream migration, implies that the
latter occurs due to a Jeffery-averaged lift velocity. Although the magnitude
of this averaged lift velocity depends on $\kappa$ and $C$, the shape of the
lift profiles are identical to those for a sphere, regardless of $Re_c$. In
particular, the equilibrium positions for a spheroid remain identical to the
classical Segre-Silberberg ones for a sphere, starting off at a distance of
about $0.6(H/2)$ from the channel centerline for small $Re_c$, and migrating
wallward with increasing $Re_c$. For spheroids with $\kappa \sim O(1)$, the
Jeffery-averaged analysis is valid for $Re_p\ll1$; for extreme aspect ratio
spheroids, the regime of validity becomes more restrictive being given by
$Re_p\,\kappa/\ln \kappa \ll 1$ and $Re_p/\kappa^2 \ll 1$ for $\kappa
\rightarrow \infty$\,(slender fibers) and $\kappa \rightarrow 0$\,(flat disks),
respectively.",2303.00037v1
2023-03-25,Odd symmetry planar Hall effect: A method of detecting current-induced in-plane magnetization switching,"Type-x device attracts considerable interest in the field of spintronics due
to its robust spin-orbit torque (SOT) induced magnetization switching, and easy
deposition technique. However, universally applicable and straightforward
detection of type-X magnetization reversal is still elusive, unlike type-Z
switching, which employs DC-based anomalous Hall effect measurement. Here, we,
demonstrated that the odd planar Hall signal (O-PHV) exhibits an odd symmetry
with the application of an external magnetic field which motivates us to
develop a reading mechanism for detecting magnetization switching of in-plane
magnetized type-X devices. We verified our DC-based reading mechanism in the
Pt/Co/NiFe/Pt stack where a thin Co layer is inserted to create dissimilar
interfaces about the NiFe layer. Remarkably, the current-induced in-plane
fields are found to be significantly large in Pt/Co/NiFe/Pt stack. Further, we
successfully employed the O-PHV method to detect the current-induced
magnetization switching. The pure DC nature of the writing and reading
mechanism of our proposed type-X detection technique through O-PHV makes it the
easiest in-plane magnetization detection technique. Moreover, the high
repeatability and easy detection of our proposed method will open new avenues
toward in-plane SOT switching based memory devices and sensors.",2303.14431v1
2023-05-18,Terminal Velocity Motion Model Used to Analyze the Mutual Phase-locking of STNOs,"Using Legendre transformation, a standard theoretical approach extensively
used in classical mechanics as well as thermal dynamics, two-dimensional
non-linear auto-oscillators including spin torque nano-oscillators (STNOs) can
be equivalently expressed either in phase space or in configuration space where
all of them can be modeled by terminal velocity motion (TVM) particles. The
transformation completely preserves the dynamic information about the canonical
momenta, leading to very precise analytical predictions about the phase-locking
of a coupled pair of perpendicular to plane STNOs (PERP-STNOs) including
dynamical phase diagrams, (un)phase-locked frequencies, phase-locked angles,
and transient evolutions, which are all solved based on Newton mechanics.
Notably, the TVM model successfully solves the difficulty of the generalized
pendulum-like model [Chen \textit{et al}. \textbf{J. Appl. Phys. 130}, 043904
(2021)] failing to make precise predictions for the higher range of current in
serial connection. Additionally, how to simply search for the critical currents
for phase-locked (PL) and asynchronized (AS) states by numerically simulating
the macrospin as well as TVM model, which gets inspired through analyzing the
excitations of a forced pendulum, is also supplied here. Therefore, we believe
that the TVM model can bring a more intuitive and precise way to explore all
types of two-dimensional non-linear auto-oscillators.",2305.11020v1
2023-05-30,Aging and passivation of magnetic properties in Co/Gd bilayers,"Synthetic ferrimagnets based on Co and Gd bear promise for directly bridging
the gap between volatile information in the photonic domain and non-volatile
information in the magnetic domain, without the need for any intermediary
electronic conversion. Specifically, these systems exhibit strong spin-orbit
torque effects, fast domain wall motion and single-pulse all-optical switching
of the magnetization. An important open challenge to bring these materials to
the brink of applications is to achieve long-term stability of their magnetic
properties. In this work, we address the time-evolution of the magnetic moment
and compensation temperature of magnetron sputter grown Pt/Co/Gd trilayers with
various capping layers. Over the course of three months, the net magnetic
moment and compensation temperature change significantly, which we attribute to
quenching of the Gd magnetization. We identify that intermixing of the capping
layer and Gd is primarily responsible for this effect, which can be alleviated
by choosing nitrides for capping as long as reduction of nitride to oxide is
properly addressed. In short, this work provides an overview of the relevant
aging effects that should be taken into account when designing synthetic
ferrimagnets based on Co and Gd for spintronic applications.",2305.18984v1
2023-08-10,Spintronics for image recognition: performance benchmarking via ultrafast data-driven simulations,"We present a demonstration of image classification using an echo-state
network (ESN) relying on a single simulated spintronic nanostructure known as
the vortex-based spin-torque oscillator (STVO) delayed in time. We employ an
ultrafast data-driven simulation framework called the data-driven Thiele
equation approach (DD-TEA) to simulate the STVO dynamics. This allows us to
avoid the challenges associated with repeated experimental manipulation of such
a nanostructured system. We showcase the versatility of our solution by
successfully applying it to solve classification challenges with the MNIST,
EMNIST-letters and Fashion MNIST datasets. Through our simulations, we
determine that within an ESN with numerous learnable parameters the results
obtained using the STVO dynamics as an activation function are comparable to
the ones obtained with other conventional nonlinear activation functions like
the reLU and the sigmoid. While achieving state-of-the-art accuracy levels on
the MNIST dataset, our model's performance on EMNIST-letters and Fashion MNIST
is lower due to the relative simplicity of the system architecture and the
increased complexity of the tasks. We expect that the DD-TEA framework will
enable the exploration of deeper architectures, ultimately leading to improved
classification accuracy.",2308.05810v3
2023-08-18,Physical modelling of near-Earth asteroid (23187) 2000 PN9 with ground-based optical and radar observations,"We present a physical model and spin-state analysis of the potentially
hazardous asteroid (23187) 2000 PN9. As part of a long-term campaign to make
direct detections of the YORP effect, we collected optical lightcurves of the
asteroid between 2006 and 2020. These observations were combined with planetary
radar data to develop a detailed shape model which was used to search for YORP
acceleration. We report that 2000 PN9 is a relatively large top-shaped body
with a sidereal rotation period of 2.53216$\pm$0.00015 h. Although we find no
evidence for rotational acceleration, YORP torques smaller than
$\sim$10$^{-8}$$\,\rm rad/day^{2}$ cannot be ruled out. It is likely that 2000
PN9 is a YORP-evolved object, and may be an example of YORP equilibrium or self
limitation.",2308.09630v1
2023-09-01,Multilayer Ferromagnetic Spintronic Devices for Neuromorphic Computing Applications,"Spintronics has gone through substantial progress due to its applications in
energy-efficient memory, logic and unconventional computing paradigms.
Multilayer ferromagnetic thin films are extensively studied for understanding
the domain wall and skyrmion dynamics. However, most of these studies are
confined to the materials and domain wall/skyrmion physics. In this paper, we
present the experimental and micromagnetic realization of a multilayer
ferromagnetic spintronic device for neuromorphic computing applications. The
device exhibits multilevel resistance states and the number of resistance
states increases with lowering temperature. This is supported by the multilevel
magnetization behavior observed in the micromagnetic simulations. Furthermore,
the evolution of resistance states with spin-orbit torque is also explored in
experiments and simulations. Using the multi-level resistance states of the
device, we propose its applications as a synaptic device in hardware neural
networks and study the linearity performance of the synaptic devices. The
neural network based on these devices is trained and tested on the MNIST
dataset using a supervised learning algorithm. The devices at the chip level
achieve 90\% accuracy. Thus, proving its applications in neuromorphic
computing. Furthermore, we lastly discuss the possible application of the
device in cryogenic memory electronics for quantum computers.",2309.00476v1
2023-09-12,Quantized Non-Volatile Nanomagnetic Synapse based Autoencoder for Efficient Unsupervised Network Anomaly Detection,"In the autoencoder based anomaly detection paradigm, implementing the
autoencoder in edge devices capable of learning in real-time is exceedingly
challenging due to limited hardware, energy, and computational resources. We
show that these limitations can be addressed by designing an autoencoder with
low-resolution non-volatile memory-based synapses and employing an effective
quantized neural network learning algorithm. We propose a ferromagnetic
racetrack with engineered notches hosting a magnetic domain wall (DW) as the
autoencoder synapses, where limited state (5-state) synaptic weights are
manipulated by spin orbit torque (SOT) current pulses. The performance of
anomaly detection of the proposed autoencoder model is evaluated on the NSL-KDD
dataset. Limited resolution and DW device stochasticity aware training of the
autoencoder is performed, which yields comparable anomaly detection performance
to the autoencoder having floating-point precision weights. While the limited
number of quantized states and the inherent stochastic nature of DW synaptic
weights in nanoscale devices are known to negatively impact the performance,
our hardware-aware training algorithm is shown to leverage these imperfect
device characteristics to generate an improvement in anomaly detection accuracy
(90.98%) compared to accuracy obtained with floating-point trained weights.
Furthermore, our DW-based approach demonstrates a remarkable reduction of at
least three orders of magnitude in weight updates during training compared to
the floating-point approach, implying substantial energy savings for our
method. This work could stimulate the development of extremely energy efficient
non-volatile multi-state synapse-based processors that can perform real-time
training and inference on the edge with unsupervised data.",2309.06449v1
2023-10-12,Unconventional Magnetic Oscillations in Kagome Mott Insulators,"We apply a strong magnetic field to a kagome Mott insulator with
antiferromagnetic interactions which does not show magnetic ordering down to
low temperatures. We observe a plateau at magnetization 1/9 Bohr magneton per
magnetic ion (Cu). Furthermore, in the vicinity of this plateau we observe sets
of strong oscillations in the magnetic torque, reminiscent of quantum
oscillations in metals. Such oscillations have never been seen in a wide gap
insulator and point to an exotic origin. While the temperature dependence of
these oscillations follows Fermi-liquid-theory predictions, they are
approximately periodic in the magnetic field $H$, as opposed to $1/H$ in
conventional metals. Furthermore, a strong angular dependence is observed for
the period, which indicates an orbital origin for this effect. We show that the
1/9 plateau and the associated oscillations are consistent with the appearance
of a quantum-spin-liquid state whose excitations are fermionic spinons that
obey a Dirac spectrum. The oscillations are in response to an emergent gauge
field. Our results provide strong evidence that fractionalized particles
coupled to the elusive emergent gauge field have been observed.",2310.07989v1
2023-10-28,"Reduced sensitivity to process, voltage and temperature variations in activated perpendicular magnetic tunnel junctions based stochastic devices","True random number generators (TRNGs) are fundamental building blocks for
many applications, such as cryptography, Monte Carlo simulations, neuromorphic
computing, and probabilistic computing. While perpendicular magnetic tunnel
junctions (pMTJs) based on low-barrier magnets (LBMs) are natural sources of
TRNGs, they tend to suffer from device-to-device variability, low speed, and
temperature sensitivity. Instead, medium-barrier magnets (MBMs) operated with
nanosecond pulses - denoted, stochastic magnetic actuated random transducer
(SMART) devices - are potentially superior candidates for such applications. We
present a systematic analysis of spin-torque-driven switching of MBM-based
pMTJs (Eb ~ 20 - 40 kBT) as a function of pulse duration (1 ps to 1 ms), by
numerically solving their macrospin dynamics using a 1-D Fokker-Planck
equation. We investigate the impact of voltage, temperature, and process
variations (MTJ dimensions and material parameters) on the switching
probability of the device. Our findings indicate SMART devices activated by
short-duration pulses (< 1 ns) are much less sensitive to
process-voltage-temperature (PVT) variations while consuming lower energy (~
fJ) than the same devices operated with longer pulses. Our results show a path
toward building fast, energy-efficient, and robust TRNG hardware units for
solving optimization problems.",2310.18781v1
2024-02-15,Lense-Thirring Precession after a Supermassive Black Hole Disrupts a Star,"An accretion disk formed around a supermassive black hole (SMBH) after it
disrupts a star is expected to be initially misaligned with respect to the
black hole's equatorial plane. This misalignment induces relativistic torques
(the Lense-Thirring effect) on the disk, causing the disk to precess at early
times, while at late times the disk aligns with the black hole and precession
terminates. Here, using high-cadence X-ray monitoring observations of a TDE, we
report the discovery of strong, quasi-periodic X-ray flux and temperature
modulations from a TDE. These X-ray modulations are separated by
17.0$^{+1.2}_{-2.4}$ days and persist for roughly 130 days during the early
phase of the TDE. Lense-Thirring precession of the accretion flow can produce
this X-ray variability, but other physical mechanisms, such as the
radiation-pressure instability, cannot be ruled out. Assuming typical TDE
parameters, i.e., a solar-like star with the resulting disk extending at-most
to so-called circularization radius, and that the disk precesses as a rigid
body, we constrain the disrupting black hole's dimensionless spin parameter to
be 0.05<|a|<0.5.",2402.09689v1
2024-03-12,A Novel Method to Constrain Tidal Quality Factor from A Non-synchronized Exoplanetary System,"We propose a novel method to constrain the tidal quality factor, $Q'$, from a
non-synchronized star-planet system consisting of a slowly rotating low-mass
star and a close-in Jovian planet, taking into account the tidal interaction
and the magnetic braking. On the basis of dynamical system theory, the track of
the co-evolution of angular momentum for such a system exhibits the existence
of a forbidden region in the $\Omega_\mathrm{orb}$ -- $\Omega_\mathrm{spin}$
plane , where $\Omega_\mathrm{spin}$ and $\Omega_\mathrm{orb}$ denote the
angular velocity of the stellar spin and planetary orbit, respectively. The
forbidden region is determined primarily by the strength of the tidal
interaction. By comparing ($\Omega_\mathrm{orb},\Omega_\mathrm{spin}$) of a
single star-planet system to the forbidden region, we can constrain the tidal
quality factor regardless of the evolutionary history of the system. The
application of this method to the star-planet system, NGTS-10 -- NGTS-10 b,
gives $Q' \gtrsim 10^8$, leading to an tight upper bound on the tidal torque.
Since this cannot be explained by previous theoretical predictions for
non-synchronized star-planet systems, our result requires mechanisms that
suppress the tidal interaction in such systems.",2403.07375v1
2024-04-05,Early evolution of spin direction in dark matter halos and the effect of the surrounding large-scale tidal field,"It is usually assumed that the angular momentum (AM) of dark matter halos
arises during the linear stages of structure formation, as a consequence of the
coupling between the proto-haloes' shape and the tidal field produced by their
surrounding density perturbations. This approach, known as linear tidal torque
theory (TTT), has been shown to make fairly good predictions about the mean
evolution of both the AM amplitude and orientation up to approximately the time
when the proto-haloes collapse. After this point, proto-haloes are increasingly
affected by non-linear processes that are not taken into account by the model.
However, it has been seen in numerical simulations that, even at very early
stages, the AM of proto-haloes is systematically reoriented towards
perpendicularity with respect to the forming cosmic filaments, in contradiction
with the fixed direction expected from the TTT. In this work we present a novel
analytical approach that introduces an anisotropic scaling factor to the
standard TTT equations, which allows the AM orientation to change in time, even
during the linear regime. The amplitude and direction of this shift depend on
the large scale tidal field around the forming proto-haloes. Our results
significantly improve the predictions for the AM direction up to the time of
protohalo collapse and, in some cases, even further in time.",2404.04223v1
2016-02-16,Hamiltonian engineering for robust quantum state transfer and qubit readout in cavity QED,"Quantum state transfer into a memory, state shuttling over long distances via
a quantum bus, and high-fidelity readout are important tasks for quantum
technology. Realizing these tasks is challenging in the presence of realistic
couplings to an environment. Here, we introduce and assess protocols that can
be used in cavity QED to perform high-fidelity quantum state transfer and fast
quantum nondemolition qubit readout through Hamiltonian engineering. We show
that high-fidelity state transfer between a cavity and a single qubit can be
performed, even in the limit of strong dephasing due to inhomogeneous
broadening. We generalize this result to state transfer between a cavity and a
logical qubit encoded in a collective mode of a large ensemble of $N$ physical
qubits. Under a decoupling sequence, we show that inhomogeneity in the ensemble
couples two collective bright states to only two other collective modes,
leaving the remaining $N-3$ single-excitation states dark. Moreover, we show
that large signal-to-noise and high single-shot fidelity can be achieved in a
cavity-based qubit readout, even in the weak-coupling limit. These ideas may be
important for novel systems coupling single spins to a microwave cavity.",1602.05090v3
2019-09-07,Universal transfer and stacking technique of van der Waals heterostructures for spintronics,"The key to achieving high-quality van der Waals heterostructure devices made
from various two-dimensional (2D) materials lies in the control over clean and
flexible interfaces. However, existing transfer methods based on different
mediators possess insufficiencies including the presence of residues, the
unavailability of flexible interface engineering, and the selectivity towards
materials and substrates since their adhesions differ considerably with the
various preparation conditions, from chemical vapor deposition (CVD) growth to
mechanical exfoliation. In this paper, we introduce a more universal method
using a prefabricated polyvinyl alcohol (PVA) film to transfer and stack 2D
materials, whether they are prepared by CVD or exfoliation. This peel-off and
drop-off technique promises an ideal interface of the materials without
introducing contamination. In addition, the method exhibits a micron-scale
spatial transfer accuracy and meets special experimental conditions such as the
preparation of twisted graphene and the 2D/metal heterostructure construction.
We illustrate the superiority of this method with a WSe2 vertical spin valve
device, whose performance verifies the applicability and advantages of such a
method for spintronics. Our PVA-assisted transfer process will promote the
development of high-performance 2D-material-based devices.",1909.03271v1
2022-08-16,Why Ortho- and Para-Hydroxy Metabolites Can Scavenge Free Radicals that the Parent Atorvastatin Cannot? Important Pharmacologic Insight from Quantum Chemistry,"The pharmaceutical success of atorvastatin (ATV), a widely employed drug
against the ""bad"" cholesterol (LDL) and cardiovascular diseases, traces back to
its ability to scavenge free radicals. Unfortunately, information on its
antioxidant properties is missing or unreliable. Here, we report detailed
quantum chemical results for ATV and its ortho- and para-hydroxy metabolites
(o-ATV, p-ATV) in the methanolic phase. They comprise global reactivity
indices, bond order indices, and spin densities as well as all relevant
enthalpies of reaction (bond dissociation BDE, ionization IP and electron
attachment EA, proton detachment PDE and proton affinity PA, and electron
transfer ETE). With these properties in hand, we can provide the first
theoretical explanation of the experimental finding that, due to their free
radical scavenging activity, ATV hydroxy metabolites rather than the parent
ATV, have substantial inhibitory effect on LDL and the like. Surprisingly
(because it is contrary to the most cases currently known), we unambiguously
found that HAT (direct hydrogen atom transfer) rather than SPLET (sequential
proton loss electron transfer) or SET-PT (stepwise electron transfer proton
transfer) is the thermodynamically preferred pathway by which o-ATV and p-ATV
in methanolic phase can scavenge DPPH$^\bullet$ (1,1-diphenyl-2-picrylhydrazyl)
radicals. From a quantum chemical perspective, the ATV's species investigated
are surprising because of the nontrivial correlations between bond dissociation
energies, bond lengths, bond order indices and pertaining stretching
frequencies, which do not fit the framework of naive chemical intuition.",2208.07987v1
2023-07-10,Mass-stream trajectories with non-synchronously rotating donors,"Mass-transfer interactions in binary stars can lead to accretion disk
formation, mass loss from the system and spin-up of the accretor. To determine
the trajectory of the mass-transfer stream, and whether it directly impacts the
accretor, or forms an accretion disk, requires numerical simulations. The
mass-transfer stream is approximately ballistic, and analytic approximations
based on such trajectories are used in many binary population synthesis codes
as well as in detailed stellar evolution codes. We use binary population
synthesis to explore the conditions under which mass transfer takes place. We
then solve the reduced three-body equations to compute the trajectory of a
particle in the stream for systems with varying system mass ratio, donor
synchronicity and initial stream velocity. Our results show that on average
both more mass and more time is spent during mass transfer from a
sub-synchronous donor than from a synchronous donor. Moreover, we find that at
low initial stream velocity the asynchronous rotation of the donor leads to
self-accretion over a large range of mass ratios, especially for
super-synchronous donors. The stream (self-)intersects in a narrow region of
parameter space where it transitions between accreting onto the donor or the
accretor. Increasing the initial stream velocity leads to larger areas of the
parameter space where the stream accretes onto the accretor, but also more
(self-)intersection. The radii of closest approach generally increase, but the
range of specific angular momenta that these trajectories carry at the radius
of closest approach gets broader. Our results are made publicly available.",2307.04600v2
2003-01-28,Stopping inward planetary migration by a toroidal magnetic field,"We calculate the linear torque exerted by a planet on a circular orbit on a
disc containing a toroidal magnetic field. All fluid perturbations are singular
at the so--called magnetic resonances, where the Doppler shifted frequency of
the perturbation matches that of a slow MHD wave propagating along the field
line. These lie on both sides of the corotation radius. Waves propagate outside
the Lindblad resonances, and also in a restricted region around the magnetic
resonances. The magnetic resonances contribute to a significant global torque
which, like the Lindblad torque, is negative (positive) inside (outside) the
planet's orbit. Since these resonances are closer to the planet than the
Lindblad resonances, the torque they contribute dominates over the Lindblad
torque if the magnetic field is large enough. In addition, if beta=c^2/v_A^2
increases fast enough with radius, the outer magnetic resonance becomes less
important and the total torque is then negative, dominated by the inner
magnetic resonance. This leads to outward migration of the planet. Even for
beta=100 at corotation, a negative torque may be obtained. A planet migrating
inward through a nonmagnetized region of a disc would then stall when reaching
a magnetized region. It would then be able to grow to become a terrestrial
planet or the core of a giant planet. In a turbulent magnetized disc in which
the large scale field structure changes sufficiently slowly, a planet may
alternate between inward and outward migration, depending on the gradients of
the field encountered. Its migration could then become diffusive, or be limited
only to small scales.",0301556v1
2004-07-19,On the saturation of corotation resonances: a numerical study,"[Abridged] The torque exerted by an external potential on a two-dimensional
gaseous disk at non-co-orbital corotation resonances is studied by means of
numerical simulations. The degree of saturation of these resonances is
important in determining whether an eccentric giant planet embedded in a
protoplanetary disk experiences an eccentricity excitation or damping. We
perform calculations restricted to one or two resonances to investigate the
properties of two neighboring corotation resonances, as well as the properties
of a corotation resonance that overlaps a Lindblad resonance. We find that
these properties hardly differ from the case of an isolated corotation
resonance. In particular, although the torque of two neighboring corotation
resonances may differ from the sum of the torques of the corresponding
resonances considered as isolated, it never exceeds the sum of the fully
unsaturated isolated corotation resonances, and it saturates in a fashion
similar to an isolated resonance. Similarly, the presence of an underlying
Lindblad resonance hardly affects the corotation torque, even if that resonance
implies a torque strong enough to significantly redistribute the azimuthally
averaged surface density profile, in which case the corotation torque scales
with the resulting vortensity gradient. This set of numerical experiments thus
essentially validates previous analytic studies. As a side result, we show that
corotation libration islands misrepresented by a mesh of too low resolution can
lead to a strongly overestimated corotation torque. This may be an explanation
why the eccentricity of embedded Jupiter-sized planets was never observed to
undergo an excitation in the numerical simulations performed so far.",0407403v1
2007-09-17,On the corotation torque in a radiatively inefficient disk,"We consider the angular momentum exchange at the corotation resonance between
a two-dimensional gaseous disk and a uniformly rotating external potential,
assuming that the disk flow is adiabatic. We first consider the linear case for
an isolated resonance, for which we give an expression of the corotation torque
that involves the pressure perturbation, and which reduces to the usual
dependence on the vortensity gradient in the limit of a cold disk. Although
this expression requires the solution of the hydrodynamic equations, it
provides some insight into the dynamics of the corotation region. In the
general case, we find an additional dependence on the entropy gradient at
corotation. This dependence is associated to the advection of entropy
perturbations. These are not associated to pressure perturbations. They remain
confined to the corotation region, where they yield a singular contribution to
the corotation torque. In a second part, we check our torque expression by
means of customized two-dimensional hydrodynamical simulations. In a third
part, we contemplate the case of a planet embedded in a Keplerian disk, assumed
to be adiabatic. We find an excess of corotation torque that scales with the
entropy gradient, and we check that the contribution of the entropy
perturbation to the torque is in agreement with the expression obtained from
the linear analysis. We finally discuss some implications of the corotation
torque expression for the migration of low mass planets in the regions of
protoplanetary disks where the flow is radiatively inefficient on the timescale
of the horseshoe U-turns.",0709.2617v1
2009-11-11,An Observational Estimate for the Mean Secular Evolution Rate in Spiral Galaxies,"We have observationally quantified the effect of gravitational torques on
stars in disk galaxies due to the stellar distribution itself and explored
whether these torques are efficient at transporting angular momentum within a
Hubble Time. We derive instantaneous torque maps for a sample of 24 spiral
galaxies, based on stellar mass maps that were derived using the pixel-by-pixel
mass-to-light estimator by Zibetti, Rix and Charlot. In conjunction with an
estimate of the rotation velocity, the mass maps allow us to determine the
torque-induced instantaneous angular momentum flow across different radii,
resulting from the overall stellar distributions for each galaxy in the sample.
By stacking the sample, which effectively replaces a time average by an
ensemble average, we find that the torques due to the stellar disk act to
transport angular momentum outward over much of the disk (within 3 disk scale
lengths). The strength of the ensemble-averaged gravitational torques within
one disk scale length have a timescale of ~ 4 Gyr for angular momentum
redistribution. This study is the first to observationally determine the
strength of torque-driven angular momentum flow of stars for a sample of spiral
galaxies, providing an important empirical constraint on secular evolution.
(abridged)",0911.2231v2
2010-09-21,Three-dimensional Disk-Planet Torques in a Locally Isothermal Disk,"We determine an expression for the Type I planet migration torque involving a
locally isothermal disk, with moderate turbulent viscosity (~0.0005 < alpha <
~0.05), based on three-dimensional nonlinear hydrodynamical simulations. The
radial gradients (in a dimensionless logarithmic form) of density and
temperature are assumed to be constant near the planet. We find that the torque
is roughly equally sensitive to the surface density and temperature radial
gradients. Both gradients contribute to inward migration when they are
negative. Our results indicate that two-dimensional calculations with a
smoothed planet potential, used to account for the effects of the third
dimension, do not accurately determine the effects of density and temperature
gradients on the three-dimensional torque. The results suggest that
substantially slowing or stopping planet migration by means of changes in disk
opacity or shadowing is difficult and appears unlikely for a disk that is
locally isothermal. The scalings of the torque and torque density with planet
mass and gas sound speed follow the expectations of linear theory. We also
determine an improved formula for the torque density distribution that can be
used in one-dimensional long-term evolution studies of planets embedded in
locally isothermal disks. This formula can be also applied in the presence of
mildly varying radial gradients and of planets that open gaps. We illustrate
its use in the case of migrating super-Earths and determine some conditions
sufficient for survival.",1009.4148v2
2010-11-15,Torqued fireballs in relativistic heavy-ion collisions,"We show that the fluctuations in the wounded-nucleon model of the initial
stage of relativistic heavy-ion collisions, together with the natural
assumption that the forward (backward) moving wounded nucleons emit particles
preferably in the forward (backward) direction, lead to an event-by-event
torqued fireball. The principal axes associated with the transverse shape are
rotated in the forward region in the opposite direction than in the backward
region. On the average, the standard deviation of the relative torque angle
between the forward and backward rapidity regions is about 20deg for the
central and 10deg for the mid-peripheral collisions. The hydrodynamic expansion
of a torqued fireball leads to a torqued collective flow, yielding, in turn,
torqued principal axes of the transverse-momentum distributions at different
rapidities. We propose experimental measures, based on cumulants involving
particles in different rapidity regions, which should allow for a quantitative
determination of the effect from the data. To estimate the non-flow
contributions from resonance decays we run Monte Carlo simulations with
THERMINATOR. If the event-by-event torque effect is found in the data, it will
support the assumptions concerning the fluctuations in the early stage of the
fireball formation, as well as the hypothesis of the asymmetric rapidity shape
of the emission functions of the moving sources in the nucleus-nucleus
collisions.",1011.3354v2
2011-08-30,Force and torque acting on particles in a transitionally rough open channel flow,"Direct numerical simulation of open channel flow over a geometrically rough
wall has been performed at a bulk Reynolds number of approximately 2900. The
wall consisted of a layer of spheres in a square arrangement. Two cases have
been considered. In the first case the spheres are small (with diameter
equivalent to 10.7 wall units) and the limit of the hydraulically smooth flow
regime is approached. In the second case the spheres are more than three times
larger (49.3 wall units) and the flow is in the transitionally rough flow
regime. Special emphasis is given on the characterisation of the force and
torque acting on a particle due to the turbulent flow. It is found that in both
cases the mean drag, lift and spanwise torque are to a large extent produced at
the top region of the particle surface. The intensity of the particle force
fluctuations is significantly larger in the large-sphere case, while the trend
differs for the fluctuations of the individual components of the torque. A
simplified model is used to show that the torque fluctuations might be
explained by the spheres acting as a filter with respect to the size of the
flow scales which can effectively generate torque fluctuations. Fluctuations of
both force and torque are found to exhibit strongly non-Gaussian probability
density functions with particularly long tails, an effect which is more
pronounced in the small-sphere case. Some implications of the present results
for sediment erosion are briefly discussed.",1108.5924v1
2012-03-09,Photon orbital angular momentum and torque metrics for single telescopes and interferometers,"Context. Photon orbital angular momentum (POAM) is normally invoked in a
quantum mechanical context. It can, however, also be adapted to the classical
regime, which includes observational astronomy.
  Aims. I explain why POAM quantities are excellent metrics for describing the
end-to-end behavior of astronomical systems. To demonstrate their utility, I
calculate POAM probabilities and torques from holography measurements of EVLA
antenna surfaces.
  Methods. With previously defined concepts and calculi, I present generic
expressions for POAM spectra, total POAM, torque spectra, and total torque in
the image plane. I extend these functional forms to describe the specific POAM
behavior of single telescopes and interferometers.
  Results. POAM probabilities of spatially uncorrelated astronomical sources
are symmetric in quantum number. Such objects have zero intrinsic total POAM on
the celestial sphere, which means that the total POAM in the image plane is
identical to the total torque induced by aberrations within propagation media &
instrumentation. The total torque can be divided into source- independent and
dependent components, and the latter can be written in terms of three
illustrative forms. For interferometers, complications arise from discrete
sampling of synthesized apertures, but they can be overcome. POAM also
manifests itself in the apodization of each telescope in an array. Holography
of EVLA antennas observing a point source indicate that ~ 10% of photons in the
n = 0 state are torqued to n != 0 states.
  Conclusions. POAM quantities represent excellent metrics for characterizing
instruments because they are used to simultaneously describe amplitude and
phase aberrations. In contrast, Zernike polynomials are just solutions of a
differential equation that happen to ~ correspond to specific types of
aberrations and are typically employed to fit only phases.",1203.2133v1
2013-10-01,On the corotation torque for low-mass eccentric planets,"We present the results of high resolution 2D simulations of low mass planets
on fixed eccentric orbits embedded in protoplanetary discs. The aim of this
study is to determine how the strength of the sustained, non-linear corotation
torque experienced by embedded planets varies as a function of orbital
eccentricity, disc parameters, and planetary mass. In agreement with previous
work we find that the corotation torque diminishes as orbital eccentricity,
$e$, increases. Analysis of the time-averaged streamlines in the disc
demonstrates that the width of the horseshoe region narrows as the eccentricity
increases, and we suggest that this narrowing largely explains the observed
decrease in the corotation torque. We employ three distinct methods for
estimating the strength of the unsaturated corotation torque from our
simulations, and provide an empirical fit to these results. We find that a
simple model where the corotation torque, $\Gamma_C$, decreases exponentially
with increasing eccentricity (i.e. $\Gamma_C \propto \exp{(-e/e_f)}$) provides
a good global fit to the data with an e-folding eccentricity, $e_f$, that
scales linearly with the disc scale height at the planet location. We confirm
that this model provides a good fit for planet masses of 5 and 10 $\Me$ in our
simulations. The formation of planetary systems is likely to involve
significant planet-planet interactions that will excite eccentric orbits, and
this is likely to influence disc-driven planetary migration through
modification of the corotation torque. Our results suggest that high fidelity
models of planetary formation should account for these effects.",1310.0351v1
2015-01-13,Mechanics of torque generation in the bacterial flagellar motor,"The bacterial flagellar motor (BFM) is responsible for driving bacterial
locomotion and chemotaxis, fundamental processes in pathogenesis and biofilm
formation. In the BFM, torque is generated at the interface between
transmembrane proteins (stators) and a rotor. It is well-established that the
passage of ions down a transmembrane gradient through the stator complex
provides the energy needed for torque generation. However, the physics involved
in this energy conversion remain poorly understood. Here we propose a
mechanically specific model for torque generation in the BFM. In particular, we
identify two fundamental forces involved in torque generation: electrostatic
and steric. We propose that electrostatic forces serve to position the stator,
while steric forces comprise the actual 'power stroke'. Specifically, we
predict that ion-induced conformational changes about a proline 'hinge' residue
in an $\alpha$-helix of the stator are directly responsible for generating the
power stroke. Our model predictions fit well with recent experiments on a
single-stator motor. Furthermore, we propose several experiments to elucidate
the torque-speed relationship in motors where the number of stators may not be
constant. The proposed model provides a mechanical explanation for several
fundamental features of the flagellar motor, including: torque-speed and
speed-ion motive force relationships, backstepping, variation in step sizes,
and the puzzle of swarming experiments.",1501.02883v1
2018-01-05,Precise measurements of torque in von Karman swirling flow driven by a bladed disk,"Scrupulous measurements and detailed data analysis of the torque in a
swirling turbulent flow driven by counter-rotating bladed disks reveals an
apparent breaking of the law of similarity. Potentially, such breakdown could
arise from several possible factors, including dependence on dimensionless
numbers other that $Re$ or velocity coupling to other fields such as
temperature. However, careful redesign and calibration of the experiment showed
that this unexpected result was due to background errorscaused by minute
misalignments which lead to a noisy and irreproducible torque signal at low
rotation speeds and prevented correct background subtraction normally ascribed
to frictional losses. An important lesson to be learnt is that multiple minute
misalignments can nonlinearly couple to the torque signal and provide a dc
offset that cannot be removed by averaging. That offset can cause the observed
divergence of the friction coefficient C_f from its constant value observed in
the turbulent regime. To minimize the friction and misalignments, we
significantly modified the experimental setup and carried out the experiment
with one bladed disk where the disk, torque meter and motor shaft axes can be
aligned with significantly smaller error, close to the torque meter resolution.
As a result we made precise measurements with high resolution and sensitivity
of the small torques produced for low rotation speeds for several
water-glycerin solutions of different viscosities and confirmed the similarity
law in a wide range of Re in particular in low viscosity fluids.",1801.01845v1
2018-02-18,Center-of-Mass-Based Grasp Pose Adaptation Using 3D Range and Force/Torque Sensing,"Lifting objects, whose mass may produce high wrist torques that exceed the
hardware strength limits, could lead to unstable grasps or serious robot
damage. This work introduces a new Center-of-Mass (CoM)-based grasp pose
adaptation method, for picking up objects using a combination of exteroceptive
3D perception and proprioceptive force/torque sensor feedback. The method works
in two iterative stages to provide reliable and wrist torque efficient grasps.
Initially, a geometric object CoM is estimated from the input range data. In
the first stage, a set of hand-size handle grasps are localized on the object
and the closest to its CoM is selected for grasping. In the second stage, the
object is lifted using a single arm, while the force and torque readings from
the sensor on the wrist are monitored. Based on these readings, a displacement
to the new CoM estimation is calculated. The object is released and the process
is repeated until the wrist torque effort is minimized. The advantage of our
method is the blending of both exteroceptive (3D range) and proprioceptive
(force/torque) sensing for finding the grasp location that minimizes the wrist
effort, potentially improving the reliability of the grasping and the
subsequent manipulation task. We experimentally validate the proposed method by
executing a number of tests on a set of objects that include handles, using the
humanoid robot WALK-MAN.",1802.06392v1
2018-04-06,"Low mass planet migration in magnetically torqued dead zones - II. Flow-locked and runaway migration, and a torque prescription","We examine the migration of low mass planets in laminar protoplanetary discs,
threaded by large scale magnetic fields in the dead zone that drive radial gas
flows. As shown in Paper I, a dynamical corotation torque arises due to the
flow-induced asymmetric distortion of the corotation region and the evolving
vortensity contrast between the librating horseshoe material and background
disc flow. Using simulations of laminar torqued discs containing migrating
planets, we demonstrate the existence of the four distinct migration regimes
predicted in Paper I. In two regimes, the migration is approximately locked to
the inward or outward radial gas flow, and in the other regimes the planet
undergoes outward runaway migration that eventually settles to fast steady
migration. In addition, we demonstrate torque and migration reversals induced
by midplane magnetic stresses, with a bifurcation dependent on the disc surface
density. We develop a model for fast migration, and show why the outward
runaway saturates to a steady speed, and examine phenomenologically its
termination due to changing local disc conditions. We also develop an
analytical model for the corotation torque at late times that includes
viscosity, for application to discs that sustain modest turbulence. Finally, we
use the simulation results to develop torque prescriptions for inclusion in
population synthesis models of planet formation.",1804.02290v1
2019-01-30,Light with a self-torque: extreme-ultraviolet beams with time-varying orbital angular momentum,"Twisted light fields carrying orbital angular momentum (OAM) provide powerful
capabilities for applications in optical communications, microscopy, quantum
optics and microparticle rotation. Here we introduce and experimentally
validate a new class of light beams, whose unique property is associated with a
temporal OAM variation along a pulse: the self-torque of light. Self-torque is
a phenomenon that can arise from matter-field interactions in electrodynamics
and general relativity, but to date, there has been no optical analog. In
particular, the self-torque of light is an inherent property, which is
distinguished from the mechanical torque exerted by OAM beams when interacting
with physical systems. We demonstrate that self-torqued beams in the
extreme-ultraviolet (EUV) naturally arise as a necessary consequence of angular
momentum conservation in non-perturbative high-order harmonic generation when
driven by time-delayed pulses with different OAM. In addition, the
time-dependent OAM naturally induces an azimuthal frequency chirp, which
provides a signature for monitoring the self-torque of high-harmonic EUV beams.
Such self-torqued EUV beams can serve as unique tools for imaging magnetic and
topological excitations, for launching selective excitation of quantum matter,
and for manipulating molecules and nanostructures on unprecedented time and
length scales.",1901.10942v1
2020-05-07,Local Simulations of Heating Torques on a Luminous Body in an Accretion Disk,"A luminous body embedded in an accretion disk can generate asymmetric density
perturbations that lead to a net torque and thus orbital migration of the body.
Linear theory has shown that this heating torque gives rise to a migration term
linear in the body's mass that can oppose or even reverse that arising from the
sum of gravitational Lindblad and co-orbital torques. We use high-resolution
local simulations in an unstratified disk to assess the accuracy and domain of
applicability of the linear theory. We find agreement between analytic and
simulation results to better than 10\% in the appropriate regime (low
luminosity, low thermal conductivity), but measure deviations in the non-linear
(high luminosity) regime and in the high thermal conductivity regime. In the
non-linear regime, linear theory overpredicts the acceleration due to the
heating torque, which we find to be due to the neglect of non-linear terms in
the heat flux. In the high thermal conductivity regime linear theory
underpredicts the acceleration, although here both non-linear and computational
constraints play a role. We discuss the impact of the heating torque for the
evolution of low-mass planets in protoplanetary disks, and for massive stars or
accreting compact objects embedded in AGN disks. For the latter case, we show
that the thermal torque is likely to be the dominant physical effect at disk
radii where the optical depth drops below a critical value.",2005.03785v2
2021-01-23,Black hole fueling in galaxy mergers: A high-resolution analysis,"Using parsec scale resolution hydrodynamical adaptive mesh refinement
simulations we have studied the mass transport process throughout a galactic
merger. The aim of such study is to connect both the peaks of mass accretion
rate onto the BHs and star formation bursts with both gravitational and
hydrodynamic torques acting on the galactic gaseous component. Our merger
initial conditions were chosen to mimic a realistic system.
  The simulations include gas cooling, star formation, supernovae feedback, and
AGN feedback. Gravitational and hydrodynamic torques near pericenter passes
trigger gas funneling to the nuclei which is associated with bursts of star
formation and black hole growth. Such episodes are intimately related with both
kinds of torques acting on the galactic gas. Pericenters trigger both star
formation and mass accretion rates of $\sim$ few $(1-10)$ $M_\odot$/yr. Such
episodes last $\sim$ $(50-75)$ Myrs. Close passes also can produce black hole
accretion that approaches and reaches the Eddington rate, lasting $\sim$ few
Myrs. Our simulation shows that both gravitational and hydrodynamic torques are
enhanced at pericenter passes with gravitational torques tending to have higher
values than the hydrodynamic torques throughout the merger. We also find that
in the closest encounters, hydrodynamic and gravitational torques can be
comparable in their effect on the gas, the two helping in the redistribution of
both angular momentum and mass in the galactic disc. Such phenomena allow
inward mass transport onto the BH influence radius, fueling the compact object
and lighting up the galactic nuclei.",2101.09407v1
2021-03-24,Hydrodynamic torque on a steadily rotating slender cylinder,"Using fully-resolved simulations, we investigate the torque experienced by a
finite-length circular cylinder rotating steadily perpendicularly to its
symmetry axis. The aspect ratio $\chi$, i.e. the ratio of the length of the
cylinder to its diameter, is varied from 1 to 15. In the creeping-flow regime,
we employ the slender-body theory to derive the expression of the torque up to
order 4 with respect to the small parameter $1/\ln(2\chi)$. Numerical results
agree well with the corresponding predictions for $\chi\gtrsim3$. We introduce
an \textit{ad hoc} modification in the theoretical prediction to fit the
numerical results obtained with shorter cylinders, and a second modification to
account for the increase of the torque resulting from finite inertial effects.
In strongly inertial regimes, a prominent wake pattern made of two pairs of
counter-rotating vortices takes place. Nevertheless the flow remains stationary
and exhibits two distinct symmetries, one of which implies that the
contributions to the torque arising from the two cylinder ends are identical.
We build separate empirical formulas for the contributions of pressure and
viscous stress to the torque provided by the lateral surface and the cylinder
ends. We show that, in each contribution, the dominant scaling law may be
inferred from simple physical arguments. This approach eventually results in an
empirical formula for the rotation-induced torque valid throughout the range of
inertial regimes and aspect ratios considered in the simulations.",2103.13097v1
2022-08-02,Inertialess Gyrating Engines,"A typical model for a gyrating engine consists of an inertial wheel powered
by an energy source that generates an angle-dependent torque. Examples of such
engines include a pendulum with an externally applied torque, Stirling engines,
and the Brownian gyrating engine. Variations in the torque are averaged out by
the inertia of the system to produce limit cycle oscillations. While torque
generating mechanisms are also ubiquitous in the biological world, where they
typically feed on chemical gradients, inertia is not a property that one
naturally associates with such processes. In the present work, seeking ways to
dispense of the need for inertial effects, we study an inertia-less concept
where the combined effect of coupled torque-producing components averages out
variations in the ambient potential and helps overcome dissipative forces to
allow sustained operation for vanishingly small inertia. We exemplify this
inertia-less concept through analysis of two of the aforementioned engines, the
Stirling engine and the Brownian gyrating engine. An analogous principle may be
sought in biomolecular processes as well as in modern-day technological
engines, where for the latter, the coupled torque-producing components reduce
vibrations that stem from the variability of the generated torque.",2208.01292v1
2022-09-19,Effect of excess charge carriers and fluid medium on the magnitude and the sign of the Casimir-Lifshitz torque,"Last year, we reported a perturbative theory of the Casimir-Lifshitz torque
between planar biaxially anisotropic materials in the retarded limit [Phys.
Rev. Lett. {\bf 120}, 131601 (2018)], which is applied here to study the change
of sign and magnitude of the torque with separation distance in biaxial black
phosphorus having excess charge carriers. The study is carried out both in
vacuum as well as in a background fluid medium. The presence of extra charge
carriers and that of an intervening fluid medium are both found to promote
enhancement of the magnitude of the torque between identical slabs. The degree
of enhancement of the magnitude of torque increases not only with an increased
carrier concentration but also with separation distance. In the non-identical
case when different planes of anisotropic black phosphorus face each other,
owing to the non-monotonic characteristic of the sign-reversal effect of the
torque, the enhancement by carrier addition and intervening medium also becomes
non-monotonic with distance. In the presence of a background medium, the
non-monotonic degree of enhancement of the torque with distance is observed
even between identical slabs.",2209.08846v1
2000-12-04,On the pre-RLO spin-orbit couplings in LMXBs,"We investigate the effect of orbital decay caused by nuclear expansion of a
(sub)giant star in synchronous binary system. We compare this effect with the
presence of a magnetic stellar wind and show that the additional transfer of
orbital angular momentum into spin angular momentum is relatively important --
especially since it has been shown that the effect of magnetic braking
saturates at short orbital periods.",0012077v1
1994-08-31,Hyperuniversality of Fully Anisotropic Three-Dimensional Ising Model,"For the fully anisotropic simple-cubic Ising lattice, the critical
finite-size scaling amplitudes of both the spin-spin and energy-energy inverse
correlation lengths and the singular part of the reduced free-energy density
are calculated by the transfer-matrix method and a finite-size scaling for
cyclic L x L x oo clusters with L=3 and 4. Analysis of the data obtained shows
that the ratios and the directional geometric means of above amplitudes are
universal.",9408099v1
1995-08-31,Long-Range Order of the Site-Random Spin Glass Model,"The site-random Ising spin glass model is investigated. We find a rigorous
symmetry for the SG correlation and the free energy, which provides some
restrictions in the phase diagram. Using the defect energies calculated by the
numerical transfer matrix method, we obtain evidence for the existence of the
SG phase in the two-dimensional Ising system. We suggest that the transitions
from the FM and the AF phases in the ground state in this model can be
explained by the percolated-cluster picture, which is quite different from the
frustration picture in the conventional $\pm J$ model.",9508143v1
1996-06-10,Surface Magnetisation and Surface Correlations in Aperiodic Ising Models,"We consider the surface critical behaviour of diagonally layered Ising models
on the square lattice where the inter-layer couplings follow some aperiodic
sequence. The surface magnetisation is analytically evaluated from a simple
formula derived by the diagonal transfer matrix method, while the surface
spin-spin correlations are obtained numerically by a recursion method, based on
the star-triangle transformation. The surface critical behaviour of different
aperiodic Ising models are found in accordance with the corresponding
relevance-irrelevance criterion. For marginal sequences the critical exponents
are continuously varying with the strength of aperiodicity and generally the
systems follow anisotropic scaling at the critical point.",9606058v1
1996-11-04,Spin excitations in the integrable open quantum group invariant supersymmetric t-J model,"The integrable quantum group $spl_q(2,1)$-invariant supersymmetric t-J model
with open boundaries is studied via an analytic treatment of the Bethe
equations. An $su(2)$ feature is seen to hold for states at or close to
half-filling. For these states the eigenvalues of the transfer matrix of the
t-J model satisfy a set of $su(2)$ functional relations. The finite-size
corrections to the relevant eigenvalues, and thus the surface effect on the
spin excitations, have been calculated analytically by solving the functional
relations.",9611013v1
1998-03-10,Thermodynamics of frustrated quantum spin chains,"We apply the transfer matrix DMRG to frustrated quantum spin chains, going
down to T=0.025 while being in the thermodynamic limit. The incommensurability
problem of exact diagonalization and the negative sign problem of quantum Monte
Carlo vanish completely. To illustrate the method, we give results for chains
with next-nearest neighbor frustration and the delta chain, which has been a
testbed for many thermodynamic methods. By comparison, the DMRG proves to be an
extremely powerful method for the old problem of the thermodynamics of
frustrated systems.",9803122v1
1998-07-06,Spinons in Magnetic Chains of Arbitrary Spins at Finite Temperatures,"The thermodynamics of solvable isotropic chains with arbitrary spins is
addressed by the recently developed quantum transfer matrix (QTM) approach. The
set of nonlinear equations which exactly characterize the free energy is
derived by respecting the physical excitations at T=0, spinons and RSOS kinks.
We argue the implication of the present formulation to spinon character formula
of level k=2S SU(2) WZWN model .",9807076v2
1998-10-13,Spin-3/2 models on the Cayley tree -- optimum ground state approach,"We present a class of optimum ground states for spin-3/2 models on the Cayley
tree with coordination number 3. The interaction is restricted to nearest
neighbours and contains 5 continuous parameters. For all values of these
parameters the Hamiltonian has parity invariance, spin-flip invariance, and
rotational symmetry in the xy-plane of spin space. The global ground states are
constructed in terms of a 1-parametric vertex state model, which is a direct
generalization of the well-known matrix product ground state approach. By using
recursion relations and the transfer matrix technique we derive exact
analytical expressions for local fluctuations and longitudinal and transversal
two-point correlation functions.",9810147v1
1999-04-02,Exact Solution of a Vertex Model with Unlimited Number of States Per Bond,"The exact solution is obtained for the eigenvalues and eigenvectors of the
row-to-row transfer matrix of a two-dimensional vertex model with unlimited
number of states per bond. This model is a classical counterpart of a quantum
spin chain with an unlimited value of spin. This quantum chain is studied using
general predictions of conformal field theory. The long-distance behaviour of
some ground-state correlation functions is derived from a finite-size analysis
of the gapless excitations.",9904040v1
1999-09-10,Advanced Dynamic Algorithms for the Decay of Metastable Phases in Discrete Spin Models: Bridging Disparate Time Scales,"An overview of advanced dynamical algorithms capable of spanning the widely
disparate time scales that govern the decay of metastable phases in discrete
spin models is presented. The algorithms discussed include constrained
transfer-matrix, Monte Carlo with Absorbing Markov Chains (MCAMC), and
projective dynamics (PD) methods. The strengths and weaknesses of each of these
algorithms are discussed, with particular emphasis on identifying the parameter
regimes (system size, temperature, and field) in which each algorithm works
best.",9909158v1
2000-03-02,Spinning up and down a Boltzmann gas,"Using the average method, we derive a close set of linear equations that
describes the spinning up of an harmonically trapped gas by a rotating
anisotropy. We find explicit expressions for the needed to transfer angular
momentum as well as the decay time induced by a static residual anisotropy.
These different time scales are compared with the measured nucleation time and
lifetime of vortices by the ENS group. We find a good agreement that may
emphasize the role played by the non-condensed component in thoses experiments.",0003024v1
2000-03-21,Stripe orders in the extended Hubbard model,"We study stripe orders of charge and spin density waves in the extended
Hubbard model with the nearest-neighbor Coulomb repulsion V within the mean
field approximation. We obtain V vs. T(temperature) phase diagram for the
on-site Coulomb interaction U/t=8.0 and the filling n=0.8, here t is a
nearest-neighbor transfer energy. Our result shows that the diagonal stripe
spin density wave state (SDW) is stable for small V, but for large V the most
stable state changes to a charge density wave-antiferromagnetic (CDW-AF) state.
Especially we find at low temperature and for a certain range of value of V, a
vertical stripe CDW-AF state becomes stable.",0003347v1
2000-09-13,Oscillations of the superconducting order parameter in a ferromagnet,"Planar tunneling spectroscopy reveals damped oscillations of the
superconducting order parameter induced into a ferromagnetic thin film by the
proximity effect. The oscillations are due to the finite momentum transfer
provided to Cooper pairs by the splitting of the spin up and down bands in the
ferromagnet. As a consequence, for negative values of the superconducting order
parameter the tunneling spectra are capsized (""$\pi$-state""). The oscillations'
damping and period are set by the same length scale, which depends on the spin
polarization.",0009192v1
2000-11-13,Spin Fluctuation and Persistent Current in a Mesoscopic Ring Coupled to a Quantum Dot,"We investigate the persistent current influenced by the spin fluctuations in
a mesoscopic ring weakly coupled to a quantum dot. It is shown that the Kondo
effect gives rise to some unusual features of the persistent current in the
limit where the charge transfer between two subsystems is suppressed. Various
aspects of the crossover from a delocalized to a localized dot limit are
discussed in relation with the effect of the coherent response of the Kondo
cloud to the Aharonov-Bohm flux.",0011215v1
2001-10-11,Enhanced Gilbert Damping in Thin Ferromagnetic Films,"Using a scattering matrix approach, the precession of the magnetization of a
ferromagnet is shown to transfer spins into adjacent normal metal layers. This
``pumping'' of spins slows down the precession corresponding to an enhanced
Gilbert damping factor in the Landau-Lifshitz equation. The damping is
expressed in terms of the scattering matrix of the ferromagnet-normal metal
interface, which is accessible to model and first-principles calculations. Our
estimates for permalloy thin films explain the trends observed in recent
experiments.",0110247v2
2002-01-30,Spectroscopic signatures of spin-charge separation in the quasi-one-dimensional organic conductor TTF-TCNQ,"The electronic structure of the quasi-one-dimensional organic conductor
TTF-TCNQ is studied by angle-resolved photoelectron spectroscopy (ARPES). The
experimental spectra reveal significant discrepancies to band theory. We
demonstrate that the measured dispersions can be consistently mapped onto the
one-dimensional Hubbard model at finite doping. This interpretation is further
supported by a remarkable transfer of spectral weight as function of
temperature. The ARPES data thus show spectroscopic signatures of spin-charge
separation on an energy scale of the conduction band width.",0201561v1
2002-07-16,Ferromagnetic Luttinger Liquids,"We study weak itinerant ferromagnetism in one-dimensional Fermi systems using
perturbation theory and bosonization. We find that longitudinal spin
fluctuations propagate ballistically with velocity v_m << v_F, where v_F is the
Fermi velocity. This leads to a large anomalous dimension in the spin-channel
and strong algebraic singularities in the single-particle spectral function and
in the transverse structure factor for momentum transfers q ~ 2 Delta/v_F,
where 2 Delta is the exchange splitting.",0207383v1
2002-10-28,Polarization dependence of spin excitations in BaCu2Si2O7,"The polarization dependence of magnetic excitations in the quasi
one-dimensional antiferromagnet BaCu2Si2O7 is studied as a function of momentum
and energy transfer. The results of inelastic neutron scattering measurements
are directly compared to semi-analytical calculations based on the chain-Mean
Field and Random Phase approximations. A quantitative agreement between
theoretically calculated and experimentally measured dynamic structure factors
of transverse spin fluctuations is obtained. In contrast, substantial
discrepancies are found for longitudinal polarization. This behavior is
attributed to intrinsic limitations of the RPA that ignores correlation
effects.",0210586v1
2003-02-11,Monte Carlo Study of Four-Spinon Dynamic Structure Function in Antiferromagnetic Heisenberg Model,"Using Monte Carlo integration methods, we describe the behavior of the exact
four-spinon dynamic structure function $S_{4}$ in the antiferromagnetic spin
1/2 Heisenberg quantum spin chain as a function of the neutron energy $\omega$
and momentum transfer $k$. We also determine the four-spinon continuum, the
extent of the region in the $(k,\omega)$ plane outside which $S_{4}$ is
identically zero. In each case, the behavior of $S_{4}$ is shown to be
consistent with the four-spinon continuum and compared to the one of the exact
two-spinon dynamic structure function $S_{2}$. Overall shape similarity is
noted.",0302219v1
2003-07-10,Transfer-matrix description of heterostructures involving superconductors and ferromagnets,"Based on the technique of quasiclassical Green's functions, we construct a
theoretical framework for describing heterostructures consisting of
superconductors and/or spin-polarized materials. The necessary boundary
conditions at the interfaces separating different metals are formulated in
terms of hopping amplitudes in a t-matrix approximation. The theory is
applicable for an interface with arbitrary transmission and exhibiting
scattering with arbitrary spin dependence. Also, it can be used in describing
both ballistic and diffusive systems. We establish the connection between the
standard scattering-matrix approach and the existing boundary conditions, and
demonstrate the advantages offered by the t-matrix description.",0307239v1
2004-04-01,Temperature dependence of spin-transfer-induced switching of nanomagnets,"We measure the temperature, magnetic-field, and current dependence for the
switching of nanomagnets by a spin-polarized current. Depending on current
bias, switching can occur between either two static magnetic states or a static
state and a current-driven precessional mode. In both cases, the switching is
thermally activated and governed by the sample temperature, not a higher
effective magnetic temperature. The activation barriers for switching between
static states depend linearly on current, with a weaker dependence for dynamic
to static switching.",0404003v1
2004-05-20,A spin-boson thermal rectifier,"Rectification of heat transfer in nanodevices can be realized by combining
the system inherent anharmonicity with structural asymmetry. we analyze this
phenomenon within the simplest anharmonic system -a spin-boson nanojunction
model. We consider two variants of the model that yield, for the first time,
analytical solutions: a linear separable model in which the heat reservoirs
contribute additively, and a non-separable model suitable for a stronger
system-bath interaction. Both models show asymmetric (rectifying) heat
conduction when the couplings to the heat reservoirs are different.",0405472v1
2004-05-24,Replica symmetry breaking in the `small world' spin glass,"We apply the cavity method to a spin glass model on a `small world' lattice,
a random bond graph super-imposed upon a 1-dimensional ferromagnetic ring. We
show the correspondence with a replicated transfer matrix approach, up to the
level of one step replica symmetry breaking (1RSB). Using the scheme developed
by M\'ezard & Parisi for the Bethe lattice, we evaluate observables for a model
with fixed connectivity and $\pm J$ long range bonds. Our results agree with
numerical simulations significantly better than the replica symmetric (RS)
theory.",0405563v1
2005-09-18,Adiabatic Pumping in Interacting Systems,"A dc current can be pumped through an interacting system by periodically
varying two independent parameters such as magnetic field and a gate potential.
We present a formula for the adiabatic pumping current in general interacting
systems, in terms of instantaneous properties of the system, and find the
limits for its applicability. This formula generalizes the scattering approach
for noninteracting pumps. We study the pumped spin in a system that exhibits
the two-channel Kondo effect as an application of the adiabatic pumping
formula. We find that a quantized spin of $\hbar$ is transferred between the
two channels as the temperature approaches zero, and discuss the non-Fermi
liquid features of this system at finite temperatures.",0509467v1
2006-11-01,Scaling of dynamic spin correlations in BaCu2SiGeO7,"The magnetic dynamic structure factor of the one-dimensional S = 1/2 chain
system BaCu2(Si0.5Ge0.5)2O7 is studied in a wide range of energy transfers and
temperatures. Contrary to previous erroneous reports [T. Masuda et al., Phys.
Rev. Lett. 93, 077206 (2004)], the scaling properties observed in the range
0.5-25 meV are found to be fully consistent with expectations for a Luttinger
spin liquid. At higher energies, a breakdown of scaling laws is observed and
attributed to lattice effects. The results are complementary to those found in
literature for other S = 1/2-chain compounds, such as KCuF3 and Cu-benzoate.",0611030v1
2006-12-28,Charge density wave in the spin ladder of Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$,"We consider a multiband charge transfer model for a single spin ladder
describing the holes in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$. Using Hartree-Fock
approximation we show how the charge density wave, with its periodicity
dependent on doping as recently observed in the experiment, can be stabilized
by purely electronic many-body interactions.",0612669v1
2007-03-15,Effective Field Theory of Triangular-Lattice Three-Spin Interaction Model,"We discuss an effective field theory of a triangular-lattice three-spin
interaction model defined by the ${\mathbb Z}_p$ variables. Based on the
symmetry properties and the ideal-state graph concept, we show that the vector
dual sine-Gordon model describes the long-distance properties for $p\ge5$; we
then compare its predictions with the previous argument. To provide the
evidences, we numerically analyze the eigenvalue structure of the transfer
matrix for $p=6$, and we check the criticality with the central charge $c=2$ of
the intermediate phase and the quantization condition of the vector charges.",0703391v2
2007-03-27,Critical Scattering and Dynamical Scaling in an Heisenberg Ferromagnet Neutron Spin Echo versus Renormalization Group Theory,"High resolution Neutron Spin Echo (NSE) spectroscopy was used to investigate
the dynamics of an 3D Heisenberg ferromagnet in the exchange-controlled regime
over a broad range of temperatures and momentum transfer. These results allow
for the first time an extensive comparison between the experimental dynamical
critical behavior and the predictions of the Renormalization Group (RG) theory.
The agreement is exhaustive and surprising as the RG theory accounts not only
for the critical relaxation but also for the shape crossover towards an
exponential diffusive relaxation when moving from the critical to the
hydrodynamic regime above $T_C$.",0703702v1
1997-05-27,Evolution of Gluon Spin in the Nucleon,"We examine the $Q^2$ evolution of gluon polarization in polarized nucleons.
As is well known, the evolution of $\alpha_s \Delta G(Q^2)$ is negligible for
typical momentum transfer variations found in experimental deep inelastic
scattering. As $\alpha_s$ increases, however, the leading nonzero term in the
evolution equation for the singlet first moment reduces the magnitude of the
gluon spin. At low $Q^2$ the term $\alpha_s \Delta G$ can vanish, and
ultimately become negative. Thus, low energy model calculations yielding
negative $\Delta G$ are not necessarily in conflict with experimental evidence
for positive gluon polarization at high $Q^2$.",9705443v1
1998-05-13,The Spin Structure of a Polarized Photon,"We show that the first moment of the spin-dependent structure function
$g_1^{\gamma}(x,Q^2)$ of a real photon vanishes independent of the momentum
transfer $Q^2$ it is probed with. This result is non-perturbative: it holds to
all orders in perturbation theory in abelian and non-abelian gauge theory and
at every twist.",9805316v1
1998-07-29,Spin effects in high-energy proton-proton scattering within a diquark model,"We study $pp$ scattering at high energies and moderately large momentum
transfer, using a model in which the proton is viewed as being composed of a
quark and a diquark. We show that this model leads to single and double spin
transverse asymmetries which are neither small nor vanish at high energies.",9807529v2
2002-09-16,Impact Parameter Dependent Parton Distributions and Transverse Single Spin Asymmetries,"Generalized parton distributions (GPDs) with purely transverse momentum
transfer can be interpreted as Fourier transforms of the distribution of
partons in impact parameter space. The helicity-flip GPD $E(x,0,-\Dps)$ is
related to the distortion of parton distribution functions in impact parameter
space if the target is not a helicity eigenstate, but has some transverse
polarization. This transverse distortion can be used to develop an intuitive
explanation for various transverse single spin asymmetries.",0209179v2
1995-04-17,"Analytical Bethe Ansatz for $A^{(2)}_{2n-1}, B^{(1)}_n, C^{(1)}_n, D^{(1)}_n$ quantum-algebra-invariant open spin chains","We determine the eigenvalues of the transfer matrices for integrable open
quantum spin chains which are associated with the affine Lie algebras
$A^{(2)}_{2n-1}, B^{(1)}_n, C^{(1)}_n, D^{(1)}_n$, and which have the
quantum-algebra invariance U_q(C_n), U_q(B_n), U_q(C_n), U_q(D_n)$,
respectively.",9504085v2
1998-07-09,Duality and quantum-algebra symmetry of the A_{N-1}^(1) open spin chain with diagonal boundary fields,"We show that the transfer matrix of the A_{N-1}^(1) open spin chain with
diagonal boundary fields has the symmetry U_q (SU(L)) x U_q (SU(N-L)) x U(1),
as well as a ``duality'' symmetry which interchanges L and N - L. We exploit
these symmetries to compute exact boundary S matrices in the regime with q
real.",9807065v1
2001-04-09,"""New"" boundary conditions in integrable lattice models","We consider the case of an integrable quantum spin chain with ``soliton
non-preserving'' boundary conditions. This is the first time that such boundary
conditions have been considered in the spin chain framework. We construct the
transfer matrix of the model, we study its symmetry and we find explicit
expressions for its eigenvalues. Moreover, we derive a new set of Bethe ansatz
equations by means of the analytical Bethe ansatz method.",0104083v1
2001-10-09,Bethe Ansatz solution of the open XX spin chain with nondiagonal boundary terms,"We consider the integrable open XX quantum spin chain with nondiagonal
boundary terms. We derive an exact inversion identity, using which we obtain
the eigenvalues of the transfer matrix and the Bethe Ansatz equations. For
generic values of the boundary parameters, the Bethe Ansatz solution is
formulated in terms of Jacobian elliptic functions.",0110081v1
2006-05-22,Exact solution of the open XXZ chain with general integrable boundary terms at roots of unity,"We propose a Bethe-Ansatz-type solution of the open spin-1/2 integrable XXZ
quantum spin chain with general integrable boundary terms and bulk anisotropy
values i \pi/(p+1), where p is a positive integer. All six boundary parameters
are arbitrary, and need not satisfy any constraint. The solution is in terms of
generalized T - Q equations, having more than one Q function. We find numerical
evidence that this solution gives the complete set of 2^N transfer matrix
eigenvalues, where N is the number of spins.",0605223v1
1998-11-30,Vertex Models with Alternating Spins,"The diagonalisation of the transfer matrices of solvable vertex models with
alternating spins is given. The crystal structure of (semi-)infinite tensor
products of finite-dimensional $U_q(\hat{sl}_2)$ crystals with alternating
dimensions is determined. Upon this basis the vertex models are formulated and
then solved by means of $U_q(\hat{sl}_2)$ intertwiners.",9811175v3
2002-09-13,Integral equations for thermodynamics of the osp(1|2s) integrable spin chain,"We propose a system of nonlinear integral equations (NLIE), which gives the
free energy of the osp(1|2s) integrable spin chain at finite temperatures. In
contrast with usual thermodynamic Bethe ansatz equations, our new NLIE contain
only a finite number of unknown functions. On deriving NLIE, we use our
osp(1|2s) version of the T-system and the quantum transfer matrix method. Based
on our NLIE, we also calculate the high temperature expansion of the free
energy and the specific heat.",0209024v1
2006-04-10,Baxter operators for the quantum sl(3) invariant spin chain,"The noncompact homogeneous sl(3) invariant spin chains are considered. We
show that the transfer matrix with generic auxiliary space is factorized into
the product of three sl(3) invariant commuting operators. These operators
satisfy the finite difference equations in the spectral parameters which follow
from the structure of the reducible sl(3) modules.",0604018v2
1998-12-22,Pion Exchange Effects in Elastic Backward Proton-Deuteron Scattering,"The elastic backward proton-deuteron scattering is analyzed within a
covariant approach based on the Bethe-Salpeter equation with realistic
meson-exchange interaction. Contributions of the one-nucleon and one-pion
exchange mechanisms to the cross section and polarization observables are
investigated in explicit form. Results of numerical calculations for the cross
section, tensor analyzing power and spin transfers are presented. The one-pion
exchange contribution is essential for describing the spin averaged cross
section, while in polarization observables it is found to be less important.",9812064v1
2002-02-19,Laser Spinning of Nanotubes: A path to fast-rotating microdevices,"We show that circularly polarized light can spin nanotubes with GHz
frequencies. In this method, angular moments of infrared photons are resonantly
transferred to nanotube phonons and passed to the tube body by ""umklapp""
scattering. We investigate experimental realization of this ultrafast rotation
in carbon nanotubes, levitating in an optical trap and undergoing mechanical
vibrations, and discuss possible applications to rotating microdevices.",0202050v1
1999-12-01,Novel Scheme for Universal Quantum Computation,"A scenario for realization of a quantum computer is proposed consisting of
spatially distributed q-bits fabricated in a host structure where nuclear
spin-spin coupling is mediated by laser pulse controlled electron-nuclear
transferred hyperfine (superhyperfine) Fermi contact interaction. Operations
illustrating entanglement, nonlocality, and quantum control logic operations
are presented and discussed. The notion of universality of quantum computation
is introduced and the irreducible conditions are presented. It is demonstrated
that the proposed generic scenario for realization of a quantum computer
fulfills these conditions.",9912003v1
2001-01-05,NMR Simulation of an Eight-State Quantum System,"The propagation of excitation along a one-dimensional chain of atoms is
simulated by means of NMR. The physical system used as an analog quantum
computer is a nucleus of 133-Cs (spin 7/2) in a liquid crystalline matrix. The
Hamiltonian of migration is simulated by using a special 7-frequency pulse, and
the dynamics is monitored by following the transfer of population from one of
the 8 spin energy levels to the other.",0101029v1
2002-09-03,Atomic squeezing in a Lambda system,"Using a quantum theory for an ensemble of three-level atoms (lambda) placed
in an optical cavity abd driven by electromagnetic fields, we show that the
long-lived spin associated with the ground state sublevels can be squeezed. Two
kinds of squeezing are obtained: self-spin squeezing, when the input fields are
coherent states and the atomic ensemble exhibit a large non-linearity;
squeezing transfer, when one of the incoming fields is squeezed.",0209023v1
2004-11-07,Efficient multiple-quantum transition processes in an n-qubit spin system,"The whole Hilbert state space of an n-qubit spin system can be divided into
(n+1) state subspaces according to the angular momentum theory of quantum
mechanics. Here it is shown that any unknown state in such a state subspace,
whose dimensional size is proportional to either a polynomial or exponential
function of the qubit number n, can be transferred efficiently into a larger
subspace with a dimensional size generally proportional to an exponential
function of the qubit number by the multiple-quantum unitary transformation
with a subspace-selective multiple-quantum unitary operator. The efficient
quantum circuits for the subspace-selective multiple-quantum unitary operators
are really constructed.",0411046v2
2005-10-14,Quantum state swapping via qubit network with Hubbard interaction,"We study the quantum state transfer (QST) in a class of qubit network with
on-site interaction, which is described by the generalized Hubbard model with
engineered couplings. It is proved that the system of two electrons with
opposite spins in this quantum network of $N$ sites can be rigorously reduced
into $N$ one dimensional engineered single Bloch electron models with central
potential barrier. With this observation we find that such system can perform a
perfect QST, the quantum swapping between two distant electrons with opposite
spins. Numerical results show such QST and the resonant-tunnelling for the
optimal on-site interaction strengths.",0510109v1
2007-05-14,Photoproduction of phi meson off deuteron near threshold,"We discuss coherent and incoherent $\phi$ meson photoproduction off the
deuteron at low energy and small momentum transfer with the aim to check
whether the recent experimental data need for their interpretation the
inclusion of exotic channels. Our analysis of the differential cross section
and spin-density matrix elements shows that the existing data may be understood
on the base of conventional dynamics. For a firm conclusion about a possible
manifestation of exotic channels one has to improve the resolution of the data
with providing additional information on channels with spin- and double-spin
flip transitions being sensitive to the properties of the photoproduction
amplitude in $\gamma p$ and $\gamma D$ reactions.",0705.2010v1
2007-08-27,Spin matrix elements in 2D Ising model on the finite lattice,"We present explicit formulas for all spin matrix elements in the 2D Ising
model with the nearest neighbor interaction on the finite periodic square
lattice. These expressions generalize the known results [Phys. Rev. D19,
(1979), 2477--2479; hep-th/0107117; hep-th/0112167] (coincide with them in the
appropriate limits) and fulfill the test of straightforward transfer matrix
calculations for finite $N$.",0708.3625v1
2007-12-28,Entanglement propagation through spin chains in the presence of a staggered magnetic field,"We study the dynamics of entanglement in the XY spin chain subject to a
staggered magnetic field and contrast it to the previously studied uniform
field case. We find that, depending on parameter values, a staggered field can
provide better conditions for a perfect entanglement transfer, while even a
modest amount of exchange anisotropy appears to have a strong detrimental
effect. We also study interactions between different waves of entanglement and
assess the possibility of simultaneous transmission of multiple bits of quantum
information.",0712.4349v1
2008-03-11,A Protocol for Quantum Energy Distribution,"A new protocol, quantum energy distribution (QED), is proposed in which
multiple parties can simultaneously extract positive energy from spin chains by
common secret keys shared by an energy supplier. QED is robust against
impersonation; an adversary, who does not have a common secret key and attempts
to get energy, will instead give energy to the spin chains. The total amount of
energy transfer gives a lower bound of the residual energy of any local cooling
process by the energy supplier.",0803.1512v4
2008-06-16,Two-Photon Exchange Contribution to Proton Form Factors in Time-Like region,"We estimate two-photon exchange contribution to the process $e^+ +e^- \to p +
\bar{p}$. The two-photon exchange corrections to double spin polarization
observables and form factors in the time-like region are calculated. The
corrections are found to be small in magnitude, but with a strong angular
dependence at fixed momentum transfer. These two features are the same as those
in the space-like region. In the view of experiment, the double spin
polarization observable $P_z$ deserves to be considered.",0806.2489v1
2008-10-19,Making vortices in dipolar spinor condensates via rapid adiabatic passage,"We propose to the create vortices in spin-1 condensates via magnetic
dipole-dipole interaction. Starting with a polarized condensate prepared under
large axial magnetic field, we show that by gradually inverting the field,
population transfer among different spin states can be realized in a controlled
manner. Under optimal condition, we generate a doubly quantized vortex state
containing nearly all atoms in the condensate. The resulting vortex state is a
direct manifestation of the dipole-dipole interaction and spin textures in
spinor condensates. We also point out that the whole process can be
qualitatively described by a simple rapid adiabatic passage model.",0810.3379v1
2008-10-28,Analytical Bethe ansatz for the open AdS/CFT SU(1|1) spin chain,"We prove an inversion identity for the open AdS/CFT SU(1|1) quantum spin
chain which is exact for finite size. We use this identity, together with an
analytic ansatz, to determine the eigenvalues of the transfer matrix and the
corresponding Bethe ansatz equations. We also solve the closed chain by
algebraic Bethe ansatz.",0810.5015v3
2008-11-30,Phase diagrams of the Ising-Heisenberg chain with S=1/2 triangular XXZ clusters,"The one dimensional spin system consisted of triangular $S=1/2$ $XXZ$
Heisenberg clusters alternating with single Ising spins is considered.
Partition function of the system is calculated exactly within the
transfer--matrix formalism. T=0 ground state phase diagrams, corresponding to
different regions of the values of system parameters are obtained.",0812.0127v1
2008-12-10,The Quantum No-Stretching: A geometrical interpretation of the no-cloning theorem,"We consider the ideal situation in which a space rotation is transferred from
a quantum spin j to a quantum spin l different from j. Quantum-information
theoretical considerations lead to the conclusion that such operation is
possible only for lj. For l>j the optimal stretching transformation is derived.
We show that for qubits the present no-stretching theorem is equivalent to the
usual no-cloning theorem.",0812.1985v2
2009-05-14,(De)confinement of supercurrent in Z_2 Topological Insulators,"It is shown that the electric supercurrent flows in a Z_2 topological
insulator with U_em(1) X U_z(1) (electromagnetic and spin) gauge symmetries.
When U_z(1) is broken, a dissipationless electric current is still possible to
flow locally but net charge transfer is absent, i.e., current is confined. In
the Kane-Mele model for graphene, this confining-deconfining (superconducting)
transition is driven by the Rashba spin-orbit interaction, which breaks U_z(1).",0905.2296v3
2009-09-05,Phase transitions in self-dual generalizations of the Baxter-Wu model,"We study two types of generalized Baxter-Wu models, by means of
transfer-matrix and Monte Carlo techniques. The first generalization allows for
different couplings in the up- and down triangles, and the second
generalization is to a $q$-state spin model with three-spin interactions. Both
generalizations lead to self-dual models, so that the probable locations of the
phase transitions follow. Our numerical analysis confirms that phase
transitions occur at the self-dual points. For both generalizations of the
Baxter-Wu model, the phase transitions appear to be discontinuous.",0909.0994v1
2010-03-22,Granger causality and the inverse Ising problem,"We study Ising models for describing data and show that autoregressive
methods may be used to learn their connections, also in the case of asymmetric
connections and for multi-spin interactions. For each link the linear Granger
causality is two times the corresponding transfer entropy (i.e. the information
flow on that link) in the weak coupling limit. For sparse connections and a low
number of samples, the L1 regularized least squares method is used to detect
the interacting pairs of spins. Nonlinear Granger causality is related to
multispin interactions.",1003.4217v2
2010-07-02,Spin-polarizing properties of heterostructures with magnetic nano elements,"The problem of electron resonant and non-resonant scatterings on two
magnetized barriers is studied in the one-dimension. The transfer-matrix is
built up to exactly calculate the coefficient of the electron transmittance
through the system of two magnetic barriers with non-collinear magnetizations.
The polarization of the transmitted electron wave for resonance and
non-resonance transmittances is calculated. The transmittance coefficient and
spin polarization can be drastically enhanced and controlled by the angle
between the barrier magnetizations",1007.0421v1
2010-07-16,Exclusive pion electroproduction and transversity,"In this talk it is reported on an analysis of hard exclusive pion
electroproduction within the handbag approach. Particular emphasis is laid on
single-spin asymmetries. It is argued that a recent HERMES measurement of
asymmetries measured with a transversely polarized target clearly indicate the
occurrence of strong contributions from transversely polarized photons. Within
the handbag approach such gamma_T --> pion transitions are described by the
transversity GPDs accompanied by a twist-3 pion wave function. It is shown that
this approach leads to results on cross sections and single-spin asymmetries in
fair agreement with experiment.",1007.2717v1
2010-08-04,Density-functional studies of spin-orbit splitting in graphene on metals,"Spin-orbit splitting in graphene on Ni, Au, or Ag (111) substrates was
examined on the basis of density-functional theory. Graphene grown on the three
metals was found to have Rashba splitting of a few or several tens of meV. The
strong splitting obtained on Au or Ag substrates was mainly ascribed to
effective hybridization of graphene $p_{z}$ state with Au or Ag $d_{z^{2}}$
states, rather than charge transfer as previously proposed. Our work provides
theoretical understandings of the metal-induced Rashba effect in graphene.",1008.0696v1
2010-08-18,Single Transverse-Spin Asymmetry in Hard-Exclusive Meson Electroproduction in the Backward Region,"We discuss the relevance of studying single transverse-spin asymmetry in
hard-exclusive meson electroproduction in the backward region. Such an
asymmetry could help us discriminate between contributions from a soft baryon
exchange in the u-channel and a hard parton-induced scattering.",1008.3119v1
2010-12-08,Optically erasing disorder in semiconductor microcavities with dynamic nuclear polarization,"The mean squared value of the photonic disorder is found to be reduced by a
factor of 100 in a typical GaAs based microcavity, when exposed to a circularly
polarized continuous wave optical pump without any special spatial patterning.
Resonant excitation of the cavity mode excites a spatially non-uniform
distribution of spin-polarized electrons, which depends on the photonic
disorder profile. Electrons transfer spin to nuclei via the hyperfine contact
interaction, inducing a long-living Overhauser magnetic field able to modify
the potential of exciton-polaritons.",1012.1732v2
2011-11-21,Magnetic Compton profiles of Fe and Ni corrected by dynamical electron correlations,"Magnetic Compton profiles (MCPs) of Ni and Fe along [111] direction have been
calculated using a combined Density Functional and many-body theory approach.
At the level of the local spin density approximation the theoretical MCPs does
not describe correctly the experimental results around the zero momentum
transfer. In this work we demonstrate that inclusion of electronic correlations
as captured by Dynamical Mean Field Theory (DMFT) improves significantly the
agreement between the theoretical and the experimental MCPs. In particular, an
energy decomposition of Ni MCPs gives indication of spin polarization and
intrinsic nature of Ni 6 eV satellite, a genuine many-body feature.",1111.4848v1
2012-02-01,Spin state of negative charge-transfer material SrCoO3,"We employ the combination of the density functional and the dynamical
mean-field theory (LDA+DMFT) to investigate the electronic structure and
magnetic properties of SrCoO3, monocrystal of which were prepared recently. Our
calculations lead to a ferromagnetic metal in agreement with experiment. We
find that, contrary to some suggestions, the local moment in SrCoO3 does not
arise from intermediate spin state, but is a result of coherent superposition
of many different atomic states. We discuss how attribution of magnetic
response to different atomic states in solids with local moments can be
quantified.",1202.0110v2
2012-02-22,A description of odd mass W-isotopes in the Interacting 2 Boson-Fermion Model,"The negative and positive parity low-spin states of the even-odd Tungsten
isotopes, 183,185,187W are studied in the frame work of the Interacting
Boson-Fermion Approximation (IBFA) model. The fermion that is coupled to the
system of bosons is taken to be in the negative parity 2f_7|2, 2f_5\2, 3p_3\2,
3p_1\2 and in the positive parity 1i_13\2 single-particle orbits. The
calculated energies of low-spin energy levels of the odd isotopes are found to
agree well with the experimental data. Also B(E2) values and spectroscopic
factors for single-neutron transfer are calculated and found to be in good
agreement with experimental data.",1202.4987v1
2012-02-24,Phase locking dynamics of dipolarly coupled vortex-based spin transfer oscillators,"Phase locking dynamics of dipolarly coupled vortices excited by
spin-polarized current in two identical nanopillars is studied as a function of
the interpillar distance L. Numerical study and analytical model have proved
the remarkable efficiency of magneto-static interaction to achieve phase
locking. Investigating the dynamics in the transient regime towards phase
locking, we extract the evolution of the locking time \tau, the coupling
strength {\mu} and the interaction energy W. Finally, we compare this coupling
energy with the one obtained by simple model.",1202.5499v1
2012-07-25,Transport of Quantum Correlations across a spin chain,"Some of the recent developments concerning the propagation of quantum
correlations across spin channels are reviewed. In particular, we focus on the
improvement of the transport efficiency obtained by the manipulation of few
energy parameters (either end-bond strengths or local magnetic fields) near the
sending and receiving sites. We give a physically insightful description of
various such schemes and discuss the transfer of both entanglement and of
quantum discord.",1207.6048v1
2012-12-07,On Baxter's Q operator of the higher spin XXZ chain at the Razumov-Stroganov point,"Based on the conjecture for the exact eigenvalue of the transfer matrix of
the higher half-integer spin XXZ chain at the Razumov-Stroganov point, we
evaluate the corresponding Baxter's Q operator in closed form by solving the TQ
equation. The combination of the Q operators on the ""right side"" and the ""wrong
side"" is shown to produce the hierarchy of functional relations.",1212.1575v2
2013-01-15,Manipulation of Ferromagnets via the Spin-Selective Optical Stark Effect,"We investigate the non-resonant all-optical switching of magnetization. We
treat the inverse Faraday effect (IFE) theoretically in terms of the
spin-selective optical Stark effect for linearly or circularly polarized light.
In the dilute magnetic semiconductors (Ga,Mn)As, strong laser pulses below the
band gap induce effective magnetic fields of several teslas in a direction
which depends on the magnetization and light wave vectors. Our theory
demonstrates that the polarized light catalyzes the angular momentum transfer
between lattice and the magnetization.",1301.3481v2
2013-05-20,Antiferromagnetic Ising model saturation field entropies: ladders and kagome lattice,"Saturation field entropies of antiferromagnetic Ising models on quasi
one-dimensional lattices (ladders) and the kagome lattice are calculated. The
former is evaluated exactly by constructing the corresponding transfer
matrices, while the latter calculation uses Binder's algorithm for efficiently
and exactly computing the partition function of over 1300 spins to give, in
Boltzmann's units, S = 0.393589(6). We comment on the relation of the kagome
lattice to the experimental situation in the spin-ice compound dysprosium
titanium oxide.",1305.4606v2
2013-06-07,Off-diagonal Bethe ansatz solution of the XXX spin-chain with arbitrary boundary conditions,"With the off-diagonal Bethe ansatz method proposed recently by the present
authors, we exactly diagonalize the $XXX$ spin chain with arbitrary boundary
fields. By constructing a functional relation between the eigenvalues of the
transfer matrix and the quantum determinant, the associated $T-Q$ relation and
the Bethe ansatz equations are derived.",1306.1742v3
2013-07-18,Inhomogeneous T-Q equation for the open XXX chain with general boundary terms: completeness and arbitrary spin,"An inhomogeneous T-Q equation has recently been proposed by Cao, Yang, Shi
and Wang for the open spin-1/2 XXX chain with general (nondiagonal) boundary
terms. We argue that a simplified version of this equation describes all the
eigenvalues of the transfer matrix of this model. We also propose a generating
function for the inhomogeneous T-Q equations of arbitrary spin.",1307.5049v2
2013-09-21,Photovoltaic effect in BiFeO3/TiO2 heterostructures tuned with epitaxial strain and an electric field,"The photovoltaic effect in the BiFeO3/TiO2 heterostructures can be tuned by
epitaxial strain and an electric field in the visible-light region which is
manifested by the enhancement of absorption activity in the heterojunction
under tensile strain and an electric field based on the first-principles
calculations. It is suggested that there are coupling between photon, spin
carrier, charge, orbital, and lattice in the interface of the bilayer film
which makes the heterojunction an intriguing candidate towards fabricating the
multifunctional photoelectric devices based on spintronics. The microscopic
mechanism involved in the heterostruces is related deeply with the spin
transfer and charge rearrangement between the Fe 3d and O 2p orbitals in the
vicinity of the interface.",1309.5432v1
2013-10-01,Magnetocaloric effect in the spin-1/2 Ising-Heisenberg diamond chain with the four-spin interaction,"The magnetocaloric effect in the symmetric spin-1/2 Ising-Heisenberg diamond
chain with the Ising four-spin interaction is investigated using the
generalized decoration-iteration mapping transformation and the transfer-matrix
technique. The entropy and the Gruneisen parameter, which closely relate to the
magnetocaloric effect, are exactly calculated to compare the capability of the
system to cool in the vicinity of different field-induced ground-state phase
transitions during the adiabatic demagnetization.",1310.0277v2
2013-10-31,Magnetization Transfer by a Quantum Ring Device,"We show that a tight-binding model device consisting of a laterally connected
ring at half filling in a tangent time-dependent magnetic field can in
principle be designed to pump a purely spin current. The process exploits the
spin-orbit interaction in the ring. This behavior is understood analytically
and found to be robust with respect to temperature and small deviations from
half filling.",1310.8454v3
2014-01-29,Quantum magnetism of ultracold atoms with a dynamical pseudospin degree of freedom,"We consider bosons in a Hubbard lattice with an SU($\cal N$) pseudospin
degree of freedom which is made dynamical via a coherent transfer term. It is
shown that, in the basis which diagonalizes the pseudospin coupling, a generic
hopping process affects the spin state, similar to a spin-orbit coupling. This
results, for the system in the Mott phase, in a ferromagnetic phase with
variable quantization axis. In extreme cases, it can even give rise to
antiferromagnetic order.",1401.7608v1
2014-08-26,Solid state optical interconnect between distant superconducting quantum chips,"We propose a design for a quantum interface exploiting the electron spins in
crystals to swap the quantum states between the optical and microwave. Using
sideband driving of a superconducting flux qubit and a combined
cavity/solid-state spin ensemble Raman transition, we demonstrate how a
stimulated Raman adiabatic passage (STIRAP)-type operation can swap the quantum
state between a superconducting flux qubit and an optical cavity mode with a
fidelity higher than $90\%$. We further consider two distant superconducting
qubits with their respective interfaces joined by an optical fiber and show a
quantum transfer fidelity exceeding $90\%$ between the two distant qubits.",1408.5972v1
2014-10-20,Isospin transfer modes in exotic nuclei,"This work presents an approach to nuclear spin-isospin response, which is
capable of describing the overall strength distribution up to high excitation
energies, including the fine structure of the low-lying strength, and resolving
the long-standing quenching problem. The model is a covariant realization of
the nuclear field theory and based on the self-consistent extensions of the
covariant energy density functional (CEDF) theory. Results of the recent
calculations for spin-isospin response of ordinary and exotic medium-mass
nuclei are presented and discussed.",1410.5441v1
2014-11-11,The scalar product of XXZ spin chain revisited. Application to the ground state at $Δ=-1/2$,"For the scalar product $S_n$ of the XXZ $s=1/2$ spin chain we derive a new
determinant expression which is symmetric in the Bethe roots. We consider an
application of this formula to the inhomogeneous groundstate of the model with
$\Delta=-1/2$ with twisted periodic boundary conditions. At this point the
ground state eigenvalue $\tau_n$ of the transfer matrix is known and has a
simple form that does not contain the Bethe roots. We use the knowledge of
$\tau_n(\mu)$ to obtain a closed expression for the scalar product. The result
is written in terms of Schur functions. The computations of the normalization
of the ground state and the expectation value of $\sigma^z$ are also presented.",1411.2938v1
2015-02-17,Direct Exchange versus the indirect Exchange of the t-J Hamiltonian in HTSC Cuprates,"The direct exchange integral and the transfer integral are calculated for the
anti-bonding wave-function of the HTSC cuprates. The direct exchange integral
yields a value three times larger than the indirect exchange of the t-J
Hamiltonian. It also predicts positive exchange energy for neighboring parallel
spins, contrary to the prediction of zero energy by the t-J Hamiltonian. A
modified t-J Hamiltonian is proposed, and the implications of the results are
discussed.",1502.05353v3
2015-04-22,Fork stamping of pristine carbon nanotubes onto ferromagnetic contacts for spin-valve devices,"We present a fabrication scheme called 'fork stamping' optimized for the dry
transfer of individual pristine carbon nanotubes (CNTs) onto ferromagnetic
contact electrodes fabricated by standard lithography. We demonstrate the
detailed recipes for a residue-free device fabrication and in-situ current
annealing on suspended CNT spin-valve devices with ferromagnetic Permalloy (Py)
contacts and report preliminary transport characterization and
magnetoresistance experiments at cryogenic temperatures. This scheme can
directly be used to implement more complex device structures, including
multiple gates or superconducting contacts.",1504.05693v1
2015-09-11,Non-Markovian Effects in the Spin Transfer Dynamics in Diluted Magnetic Semiconductors due to Excitation in Proximity to the Band Edge,"The non-Markovian effects in the spin dynamics in diluted magnetic
semiconductors found in quantum kinetic calculations can be reproduced very
well by a much simpler effective single electron theory, if a finite memory is
accounted for. The resulting integro-differential equation can be solved by a
differential transform method, yielding the Taylor series of the solution. From
the comparison of both theories it can be concluded that the non-Markovian
effects are due to the spectral proximity of the excited electrons to the band
edge.",1509.03487v1
2016-01-20,Quantum Transport of Dirac fermions in graphene with a spatially varying Rashba spin-orbit coupling,"We theoretically study electronic transport through a region with
inhomogeneous Rashba spin-orbit (RSO) coupling placed between two normal
regions in a monolayer graphene. The inhomogeneous RSO region is characterized
by linearly varying RSO strength within its borders and constant RSO strength
in the central region. We calculate the transmission properties within the
transfer matrix approach. It is shown that the amplitude of conductance
oscillations reduces and at the same time the magnitude of conductance
increases with increasing border thickness. We also investigate how the Fano
factor can be modified by the border thickness of RSO region.",1601.05276v1
2016-12-14,Quantum Speed Limits for Quantum Information Processing Tasks,"We derive algebraic bounds on achievable rates for quantum state transfer and
entanglement generation in general quantum systems. We apply these bounds to
graph-based models of local quantum spin systems to obtain speed limits on
these tasks. A comparison to numerical optimal control results for spin chains
suggests that unexplored regions of the dynamical landscape may support
enhanced performance of key quantum information processing tasks.",1612.04767v2
2017-01-25,Remote Parameter Estimation in a Quantum Spin Chain Enhanced by Local Control,"We study the interplay of control and parameter estimation on a quantum spin
chain. A single qubit probe is attached to one end of the chain, while we wish
to estimate a parameter on the other end. We find that control on the probe
qubit can substantially improve the estimation performance and discover some
interesting connections to quantum state transfer.",1701.07399v1
2017-02-02,Magnon Condensation and Spin Superfluidity,"We consider the phenomenon of Bose-Einstein condensation of quasi-equilibrium
magnons which leads to a spin superfluidity, the coherent quantum transfer of
magnetization in magnetic materials. These phenomena are beyond the classical
Landau-Lifshitz-Gilbert paradigm. The critical conditions for excited magnon
density for ferro- and antiferromagnets, bulk and thin films are estimated and
discussed. The BEC should occur in the antiferromagnetic hematite at much lower
excited magnon density compared to the ferromagnetic YIG.",1702.00846v2
2017-02-10,Periodically driven random quantum spin chains : Real-Space Renormalization for Floquet localized phases,"When random quantum spin chains are submitted to some periodic Floquet
driving, the eigenstates of the time-evolution operator over one period can be
localized in real space. For the case of periodic quenches between two
Hamiltonians (or periodic kicks), where the time-evolution operator over one
period reduces to the product of two simple transfer matrices, we propose a
Block-self-dual renormalization procedure to construct the localized
eigenstates of the Floquet dynamics. We also discuss the corresponding Strong
Disorder Renormalization procedure, that generalizes the RSRG-X procedure to
construct the localized eigenstates of time-independent Hamiltonians.",1702.03165v2
2017-11-06,Spin Dependence of Small-Angle Proton-Nucleus Scattering,"We study the single-spin asymmetry, $A_N(t)$, arising from Coulomb-nuclear
interference (CNI) at small 4-momentum transfer squared, $-t=q^2$, aiming at
explanation of the recent data from the PHENIX experiment at RHIC on polarized
proton-nucleus scattering, exposing a nontrivial $t$-dependence of $A_N$. We
found that the failure of previous theoretical attempts to explain these data,
was due to lack of absorptive corrections in the Coulomb amplitude of $pA$
elastic scattering. Our prominent observation is that the main contribution to
$A_N(t)$ comes from interference of the amplitudes of ultra-peripheral and
central collisions.",1711.01969v2
2018-04-12,Spinon-orbiton repulsion and attraction mediated by Hund's rule,"We study the impact of Hund's-rule coupling on orbital excitations, as e.g.
measured in inelastic resonant x-ray scattering. We find that the
interpretation in terms of spin-orbit separation, which has been derived for
one-dimensional systems without Hund's rule, remains robust in its presence.
Depending on whether or not the orbital excitation includes a spin excitation,
Hund's rule leads to an attractive or repulsive interaction between spinon and
orbiton. Attraction and repulsion leave clear signatures through a transfer of
spectral weight to the lower resp. upper edge of the spectrum.",1804.04462v1
2019-04-26,The equilibrium landscape of the Heisenberg spin chain,"We characterise the equilibrium landscape, the entire manifold of local
equilibrium states, of an interacting integrable quantum model. Focusing on the
isotropic Heisenberg spin chain, we describe in full generality two
complementary frameworks for addressing equilibrium ensembles: the functional
integral Thermodynamic Bethe Ansatz approach, and the lattice regularisation
transfer matrix approach. We demonstrate the equivalence between the two, and
in doing so clarify several subtle features of generic equilibrium states. In
particular we explain the breakdown of the canonical Y-system, which reflects a
hidden structure in the parametrisation of equilibrium ensembles.",1904.11975v3
2019-05-09,Convolutional Neural Networks Utilizing Multifunctional Spin-Hall MTJ Neurons,"We propose a new network architecture for standard spin-Hall magnetic tunnel
junction-based spintronic neurons that allows them to compute multiple critical
convolutional neural network functionalities simultaneously and in parallel,
saving space and time. An approximation to the Rectified Linear Unit transfer
function and the local pooling function are computed simultaneously with the
convolution operation itself. A proof-of-concept simulation is performed on the
MNIST dataset, achieving up to 98% accuracy at a cost of less than 1 nJ for all
convolution, activation and pooling operations combined. The simulations are
remarkably robust to thermal noise, performing well even with very small
magnetic layers.",1905.03812v1
2019-07-22,Polarization in $Ξ_c^0$ decays,"Measurements on the weak decay asymmetry parameters of charmed baryon, say
$\Xi_c$, provide more information on the $W$-emission and $W$-exchange
mechanisms controlled by the strong and weak interactions. Taking advantage of
the spin polarization in the charmed baryon decays, we investigate the
possibility to measure the weak decay asymmetry parameters in the
$e^{+}e^{-}\to \Xi_c^0\bar\Xi_c^0$ process. We analyze the transverse
polarization spontaneously produced in this process and spin transfer in the
subsequent $\Xi_c$ decays. The sensitivity to measure the asymmetry parameters
are estimated for the decay $\Xi_c\to\Xi \pi$.",1907.09135v2
2020-01-21,Bound states in ultrastrong waveguide QED,"We discuss the properties of bound states in finite-bandwidth waveguide QED
beyond the Rotating Wave Approximation or excitation number conserving
light-matter coupling models. Therefore, we extend the \emph{standard}
calculations to a broader range of light-matter strengths, in particular, in
the so-called ultrastrong coupling regime. We do this using the Polaron
technique. Our main results are as follows. We compute the spontaneous emission
rate, which is renormalized as compared to the Fermi Golden Rule formula. We
generalise the existence criteria for bound states, their properties and their
role in the qubits thermalization. We discuss effective spin-spin interactions
through both vacuum fluctuations and bound states. Finally, we sketch a perfect
state-transfer protocol among distant emitters.",2001.07643v1
2020-06-02,"Hardware Security in Spin-Based Computing-In-Memory: Analysis, Exploits, and Mitigation Techniques","Computing-in-memory (CIM) is proposed to alleviate the processor-memory data
transfer bottleneck in traditional Von-Neumann architectures, and
spintronics-based magnetic memory has demonstrated many facilitation in
implementing CIM paradigm. Since hardware security has become one of the major
concerns in circuit designs, this paper, for the first time, investigates
spin-based computing-in-memory (SpinCIM) from a security perspective. We focus
on two fundamental questions: 1) how the new SpinCIM computing paradigm can be
exploited to enhance hardware security? 2) what security concerns has this new
SpinCIM computing paradigm incurred?",2006.01425v1
2020-10-22,Froissaron and Maximal Odderon with spin-flip in $pp$ and $\bar pp$ high energy elastic scattering,"We assume that the scattering amplitude is represented by Froissaron, Maximal
Odderon as well as by standard Regge poles. From the fit to the data of $pp$
and $\bar pp$ scattering at high energy and not too large momentum transfers we
found that this model taking into account the spin is available to describe not
only the differential, total cross section and $\rho$, but also the existing
experimental data on polarization.",2010.11987v2
2021-04-16,Controlling the RKKY interaction and heat transport in a Kitaev spin liquid via $Z_2$ flux walls,"Kitaev spin liquids (KSLs) contain both itinerant Majorana fermions and
localized $Z_2$ flux excitations. The mobile fermions transport energy, while
the fluxes hinder heat flow. By controlling the flux configuration, one can
separate a KSL into different domains via $Z_2$ flux walls. We show that at low
temperatures, the wall significantly suppresses the Majorana-mediated
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction and blocks the heat transfer
between domains.",2104.08071v1
2021-04-28,Optimal Control of the Operating Regime of a Single Electron Double Quantum Dot,"The double quantum dot device benefits from the advantages of both the spin
and charge qubits, while offering ways to mitigate their drawbacks. Careful
gate voltage modulation can grant greater spinlike or chargelike dynamics to
the device, yielding long coherence times with the former and high electrical
susceptibility with the latter for electrically driven spin rotations or
coherent interactions with microwave photons. We show that optimal control
pulses generated using the GRadient Ascent Pulse Engineering (GRAPE) algorithm
can yield higher-fidelity operating regime transfers than can be achieved using
linear methods.",2104.13571v4
2021-05-11,Spin chains with boundary inhomogeneities,"We investigate the effect of introducing a boundary inhomogeneity in the
transfer matrix of an integrable open quantum spin chain. We find that it is
possible to construct a local Hamiltonian, and to have quantum group symmetry.
The boundary inhomogeneity has a profound effect on the Bethe ansatz solution.",2105.04982v2
2021-07-15,Translational-Rotational Coupling during the Scattering of a Frictional Sphere from a Flat Surface,"At a macroscopic level, concepts such as top spin, back spin and rolling are
commonly used to describe the collision of balls and surfaces. Each term refers
to an aspect of the coupling of rotational motion during the collision of a
spherical particle with a planar surface. In this paper we explore the
mechanisms of energy transfer involving the collision of a rotating sphere and
a surface using a model of frictional interactions developed for granular
material. We present explicit analytical treatments for the scattering and
derive expressions for two important limiting classes: energy conserving
collisions and collisions subject to rapid transverse dissipation.",2107.07159v1
2021-11-15,Arbitrary length XX spin chains boundary-driven by non-Markovian environments,"In this work we provide a recursive method of calculating the wavefunction of
a XX spin chain coupled at both ends to non-Markovian reservoirs with arbitrary
spectral density. The method is based on the appropriate handling of the
time-dependent Schrodinger's equations of motion in Laplace space and leads to
closed form solutions of the transformed amplitudes, for arbitrary chain
lengths as well as arbitrary initial conditions, within the single-excitation
subspace. Results on the dynamical as well as state transfer properties of the
system for various combinations of parameters are also presented. In
particular, detailed quantitative comparisons for Lorentzian and Ohmic
reservoirs are illustrated.",2111.07859v2
2022-03-04,Dissipation in spin chains using quantized nonequilibrium thermodynamics,"We investigate the open dynamics of a chain of interacting spins using the
quantized version of the GENERIC equation from classical out-of-equilibrium
thermodynamics. We focus on both equilibrium and nonequilibrium scenarios for
chains of different sizes. While in the equilibrium case we demonstrate thermal
equilibration to the correct many-body Gibbs density matrix, in the
nonequilibrium dynamics we show a ballistic-to-diffusive transition in the
steady-state energy current and a scaling that is consistent with Fourier's law
of heat transfer.",2203.02174v2
2022-06-18,Frustrations on decorated planar lattices in Ising model,"We study the frustration properties of the Ising model on several decorated
lattices with arbitrary numbers of decorating spins on all bonds of the lattice
within an exact analytical approach based on the Kramers--Wannier
transfer-matrix technique. The existence of magnetic frustrations in such
situations and their influence on the behavior of the thermodynamic functions
of systems is shown. The most important result of our study is related to the
description of the possible coexistence of frustrations and long-range magnetic
order in partially ordered spin systems.",2206.09176v1
2022-07-14,Sub-MHz AC magnetometry with a double-dressed spin qubit in diamond,"We experimentally demonstrate a protocol that effectively suppresses the
qubit-bath interaction in diamond and enables detection of weak AC signals
(below 1 MHz) with enhanced signal-to-noise ratio (SNR) up to SNR = 17. The
method is based on AC magnetometry with single- and double-dressed states that
are adiabatically transferred from the initial qubit states using concatenated
continuous dynamical decoupling. This work paves a way toward sensitive
detection of weakly coupled nuclear spins in low-field NMR experiments.",2207.06611v1
2022-07-28,The Bethe ansatz for a new integrable open quantum system,"In this paper we apply the nested algebraic Bethe ansatz to compute the
eigenvalues and the Bethe equations of the transfer matrix of the new
integrable Lindbladian found in [1]. We show that it can be written as an
integrable spin chain consisting of two interacting XXZ spin chains. We
numerically compute the Liouville gap and its dependence on the parameters in
the system such as scaling with the system length and interaction strength.",2207.14193v1
2022-08-01,Calculation of magnon drag force induced by an electric current in ferromagnetic metals,"Magnon drag effect induced by an applied electric field in ferromagnetic
metals is theoretically studied by a microscopic calculation of the force on
magnons arising from magnon emission/absorption and scattering due to driven
electrons. It is shown that magnon scattering contribution dominates over the
emission/absorption one in a wide temperature regime in good metals with long
elastic lifetime $\taue$, as the latter has a relative suppression factor of
$(\Deltasd\taue)^{-2}$ due to the electron spin flip by the magnon, where
$\Deltasd$ is the $sd$ exchange interaction energy. Spin-transfer efficiency is
discussed including the magnon drag effect.",2208.00622v1
2022-12-24,The exact susceptibility of the spin-S transverse Ising chain with next-nearest-neighbor interactions,"The zero-field susceptibility of the spin-S transverse Ising chain with
next-nearest-neighbor interactions is obtained exactly. The susceptibility is
given in an explicit form for S=1/2, and expressed in terms of the eigenvectors
of the transfer matrix for general spin S. It is found that the low-temperature
limit is independent of spin S, and is divergent at the transition point.",2212.12693v2
2023-07-27,Quantum Phase Transition of Organic Spin Liquid Tuned by Mixing Counterions,"We found a plateau in the magnitude of the isolated magnetic moments as a
function of the anisotropy of the transfer integral (t'/t) in the gapless
quantum spin liquid (QSL) phase of an S=1/2 triangular lattice molecular solid
X[Pd(dmit)2]2 (dmit = 1,3-dithiole-2-thione-4,5-dithiolate), accomplished by a
fine-tuning of t'/t through the mixing of cations, X. In contrast, the magnetic
susceptibility at the lowest temperature in the QSL phase parametrized by t'/t
evinces an unconventional suppression approaching the quantum phase transition,
implying significant critical fluctuations.",2307.14563v2
2023-09-05,Acceleration of a polarized neutron by its weak nuclear self-interaction,"It is proven that the rotation of the spin of a polarized neutron is
accompanied by a net nuclear force upon it. This force arises from the weak
nuclear self-interaction of its constituent quarks, whose chiral nature induces
the transfer of a net momentum to the fields of Z and W-bosons. This effect is
linear in Fermi's constant. As a result, it is estimated that along the
spin-flip of a polarized neutron its velocity undergoes a variation of the
order of meters per second.",2309.02293v1
2023-10-27,Open boundary conditions of the $D^{(2)}_3$ spin chain and sectors of conformal field theories,"We study open boundary conditions for the $D^{(2)}_3$ spin chain, which
shares connections with the six-vertex model, under staggering, and also to the
antiferromagnetic Potts model. By formulating a suitable transfer matrix, we
obtain an integrable, open Hamiltonian, hence allowing for us to classify
different regions of the underlying conformal field theory from eigenvalues of
the Hamiltonian.",2310.18499v2
2023-12-03,Universal Control of Symmetric States Using Spin Squeezing,"The manipulation of quantum many-body systems is a frontier challenge in
quantum science. Entangled quantum states that are symmetric to permutation
between qubits are of growing interest. Yet, the creation and control of
symmetric states has remained a challenge. Here, we find a way to universally
control symmetric states, proposing a scheme that relies solely on coherent
rotations and spin squeezing. We present protocols for the creation of
different symmetric states including Schrodinger cat and
Gottesman-Kitaev-Preskill states. The obtained symmetric states can be
transferred to traveling photonic states via spontaneous emission, providing a
powerful mechanism for the creation of desired quantum light states.",2312.01506v1
2024-03-13,Compton scattering from superstrings,"We propose a candidate Compton amplitude which is valid for any (integer)
quantum spin and free from any spurious poles. We consider the cases of
electromagnetism and gravity. We obtain such amplitudes by calculating the
corresponding ones from superstring theory involving states on the leading
Regge trajectory. To extract the associated field-theory amplitudes a few
considerations in the form of simple physical constraints are required, such
as: Soft momentum transfer, compactification of polarizations and consistent
factorization in the physical channels. We believe the present exploration will
be significantly relevant for the physics of compact binary systems with spin.",2403.08899v1
2018-10-31,Dark Matter Bars in Spinning Halos,"We study nonlinear response of spinning dark matter (DM) halos to dynamic and
secular evolution of stellar bars in the embedded galactic disks, using
high-resolution numerical simulations. For a sequence of halos with the
cosmological spin parameter lambda=0-0.09, and a representative angular
momentum distribution, we analyze evolution of induced DM bars amplitude and
quantify parameters of the response as well as trapping of DM orbits and
angular momentum transfer by the main and secondary resonances. We find that
(1) maximal amplitude of DM bars depends strongly on `lambda', while that of
the stellar bars is indifferent to `lambda'; (2) Efficiency of resonance
trapping of DM orbits by the bar increases with `lambda', and so is the mass
and the volume of DM bars; (3) Contribution of resonance transfer of angular
momentum to the DM halo increases with `lambda', and for larger spin, the DM
halo `talks' to itself, by moving the angular momentum to larger radii --- this
process is maintained by resonances; (4) Prograde and retrograde DM orbits play
different roles in angular momentum transfer. The `active' part of the halo
extends well beyond the bar region, up to few times the bar length in
equatorial plane and away from this plane. (5) We model evolution of diskless
DM halos and halos with frozen disks, and found them to be perfectly stable to
any Fourier modes. Finally, further studies adopting a range of mass and
specific angular momentum distributions of the DM halo will generalize the
dependence of DM response on the halo spin and important implications for
direct detection of DM and that of the associated stellar tracers, such as
streamers.",1811.00033v2
2004-06-13,"Condensation, excitation, pairing, and superfluid density in high-$T_{c}$ superconductors: magnetic resonance mode as a roton analogue and a possible spin-mediated pairing","To find out a primary determing factor of $T_{c}$ and a pairing mechanism in
high-$T_{c}$ cuprates, we combine the muon spin relaxation results on
$n_{s}/m^{*}$ (superconducting carrier density / effective mass), accumulated
over the last 15 years, with the results from neutron and Raman scattering,
STM, specific heat, Nernst effect and ARPES measurements. We identify the
neutron magnetic resonance mode as an analogue of roton minimum in the
superfluid $^{4}$He, and argue that $n_{s}/m^{*}$ and the resonance mode energy
$\hbar\omega_{res}$ play a primary role in determining $T_{c}$ in the
underdoped region. We propose a picture that roton-like excitations in the
cuprates appear as a coupled mode, which has the resonance mode for spin and
charge responses at different momentum transfers but the same energy transfers,
as detected respectively, by the neutron S=1 mode and the Raman S=0 A1$_{g}$
mode. We shall call this as the ``hybrid spin/charge roton''. After discussing
the role of dimensionality in condensation, we propose a generic phase diagram
of the cuprates with spatial phase separation in the overdoped region as a
special case of the BE-BCS crossover conjecture where the superconducting
coupling is lost rapidly in the overdoped region. Using a microscopic model of
charge motion resonating with antiferomagnetic spin fluctuations, we propose a
possibility that the hybrid spin/charge roton and higher-energy spin
fluctuations mediate the superconducting pairing. In this model, the resonance
modes can be viewed as a meson-analogue and the ``dome'' shape of the phase
diagram can be understood as a natural consequence of departure from the
competing Mott insulator ground state via carrier doping.",0406301v1
2018-04-19,Phenomenological Three-Orbital Spin-Fermion Model for Cuprates,"A spin-fermion model that captures the charge-transfer properties of Cu-based
high critical temperature superconductors is introduced and studied via Monte
Carlo simulations. The strong Coulomb repulsion among $d$-electrons in the Cu
orbitals is phenomenologically replaced by an exchange coupling between the
spins of the itinerant electrons and localized spins at the Cu sites, formally
similar to double-exchange models for manganites. This interaction induces a
charge-transfer insulator gap in the undoped case (five electrons per unit
cell). Adding a small antiferromagnetic Heisenberg coupling between localized
spins reinforces the global tendency towards antiferromagnetic order. To
perform numerical calculations the localized spins are considered classical, as
in previous related efforts. In this first study, undoped and doped $8\times 8$
clusters are analyzed in a wide range of temperatures. The numerical results
reproduce experimental features in the one-particle spectral function and the
density-of-states such as $(i)$ the formation of a Zhang-Rice-like band with a
dispersion of order $\sim 0.5$ eV and with rotational symmetry about wavevector
$(\pi/2,\pi/2)$ at the top of the band, and $(ii)$ the opening of a pseudogap
at the chemical potential upon doping. We also observed incipient tendencies
towards spin incommensurability. This simple model offers a formalism
intermediate between standard mean-field approximations, that fail at finite
temperatures in regimes with short-range order, and sophisticated many-body
techniques such as Quantum Monte Carlo, that suffer sign problems.",1804.07191v1
2019-01-10,Half-filled Stripes in a Hole-Doped Three-Orbital Spin-Fermion Model for Cuprates,"Using Monte Carlo techniques, we study a three-orbital CuO$_2$ spin-fermion
model for copper-based high critical temperature superconductors that captures
the charge-transfer properties of these compounds. Our studies reveal the
presence of spin order in the parent compound and, more importantly, stripe
spin and charge order under hole doping. Due to the $p$-$d$ orbital hybridizati
on, the added holes are approximately equally distributed among the two $p$
orbitals of the oxygen atoms and the $d$ orbital of the copper atoms in the
unit cell. In rectangular clusters of dimension $16\times 4$ %that break the
$\pi/2$ lattice rotational symmetry, {\it half-filled} stripes are observed
upon hole doping, namely when $N_h=2n$ holes are introduced in the system then
$n$ stripes of length 4 are formed along the short direction. The original
antiferromagnetic order observed in the parent compound develops a $\pi-$shift
across each stripe and the magnetic structure factor has a peak at wavevector
${\bf k}=(\pi-\delta,\pi)$ with $\delta=2\pi N_h/N=\pi N_h/2L$, where $L=16$.
The electronic charge is also modulated and the charge structure factor is
maximized at ${\bf k}=(2\delta,0)$. As electrons are removed from the system,
intracell orbital nematicity with $\langle n_{p_x}\rangle-\langle
n_{p_y}\rangle\ne 0$ dev elops in the oxygen sector, as well as intercell
magnetic nematicity with $\langle S^z_{{\bf i},d}(S^z_{{\bf i}+{\bf
x},d}-S^z_{{\bf i}+{\ bf y},d})\rangle\ne 0$ in the spin copper sector, in the
standard notation. This occurs not only in rectangular but also in square
8$\times$8 lattices. Overall, our results suggest that the essence of the
stripe spin and charge distribution experimentally observed in hole-doped
cuprates are captured by unbiased Monte Carlo studies of a simple hole-doped
charge-transfer insulator CuO$_2$ spin-fermion model.",1901.03320v1
2019-08-01,Spin-Orbit Excitons in CoO,"CoO has an odd number of electrons in its unit cell, and therefore is
expected to be metallic. Yet, CoO is strongly insulating owing to significant
electronic correlations, thus classifying it as a Mott insulator. We
investigate the magnetic fluctuations in CoO using neutron spectroscopy. The
strong and spatially far-reaching exchange constants reported in [Sarte et al.
Phys. Rev. B 98 024415 (2018)], combined with the single-ion spin-orbit
coupling of similar magnitude [Cowley et al. Phys. Rev. B 88, 205117 (2013)]
results in significant mixing between $j_{eff}$ spin-orbit levels in the low
temperature magnetically ordered phase. The high degree of entanglement,
combined with the structural domains originating from the Jahn-Teller
structural distortion at $\sim$ 300 K, make the magnetic excitation spectrum
highly structured in both energy and momentum. We extend previous theoretical
work on PrTl$_{3}$ [Buyers et al. Phys. Rev. B 11, 266 (1975)] to construct a
mean-field and multi-level spin exciton model employing the aforementioned spin
exchange and spin-orbit coupling parameters for coupled Co$^{2+}$ ions on a
rocksalt lattice. This parameterization, based on a tetragonally distorted
type-II antiferromagnetic unit cell, captures both the sharp low energy
excitations at the magnetic zone center, and the energy broadened peaks at the
zone boundary. However, the model fails to describe the momentum dependence of
the excitations at high energy transfers, where the neutron response decays
faster with momentum than the Co$^{2+}$ form factor. We discuss such a failure
in terms of a possible breakdown of localized spin-orbit excitons at high
energy transfers.",1908.00459v2
2021-03-17,Ab initio Derivation of Low-Energy Hamiltonians for Systems with Strong Spin-Orbit Interaction and Its Application to Ca5Ir3O12,"We present an ab initio derivation method for effective low-energy
Hamiltonians of material with strong spin-orbit interactions. The effective
Hamiltonian is described in terms of the Wannier function in the spinor form,
and effective interactions are derived with the constrained random phase
approximation (cRPA) method. Based on this formalism and the developed code, we
derive an effective Hamiltonian of a strong spin-orbit interaction material
Ca5Ir3O12. This system consists of three edge-shared IrO6 octahedral chains
arranged along the c axis, and the three Ir atoms in the ab plane compose a
triangular lattice. For such a complicated structure, we need to set up the
Wannier spinor function under the local coordinate system. We found that a
density-functional band structure near the Fermi level is formed by local dxy
and dyz orbitals. Then, we constructed the ab initio dxy/dyz model. The
estimated nearest neighbor transfer t is close to 0.2 eV, and the cRPA onsite U
and neighboring V electronic interactions are found to be 2.4-2.5 eV and 1 eV,
respectively. The resulting characteristic correlation strength defined by
(U-V)/t is above 7, and thus this material is classified as a strongly
correlated electron system. The onsite transfer integral involved in the
spin-orbit interaction is 0.2 eV, which is comparable to the onsite exchange
integrals near 0.2 eV, indicating that the spin-orbit-interaction physics would
compete with the Hund physics. Based on these calculated results, we discuss
possible rich ground-state low-energy electronic structures of spin, charge and
orbitals with competing Hund, spin-orbit and strong correlation physics.",2103.09539v1
2005-02-17,Non-LTE Spectra of Accretion Disks Around Intermediate-Mass Black Holes,"We have calculated the structures and the emergent spectra of stationary,
geometrically thin accretion disks around 100 and 1000 M_sun black holes in
both the Schwarzschild and extreme Kerr metrics. Equations of radiative
transfer, hydrostatic equilibrium, energy balance, ionization equilibrium, and
statistical equilibrium are solved simultaneously and consistently. The six
most astrophysically abundant elements (H, He, C, N, O, and Fe) are included,
as well as energy transfer by Comptonization. The observed spectrum as a
function of viewing angle is computed incorporating all general relativistic
effects. We find that, in contrast with the predictions of the commonly-used
multi-color disk (MCD) model, opacity associated with photoionization of heavy
elements can significantly alter the spectrum near its peak. These ionization
edges can create spectral breaks visible in the spectra of slowly-spinning
black holes viewed from almost all angles and in the spectra of
rapidly-spinning black holes seen approximately pole-on. For fixed mass and
accretion rate relative to Eddington, both the black hole spin and the viewing
angle can significantly shift the observed peak energy of the spectrum,
particularly for rapid spin viewed obliquely or edge-on. We present a detailed
test of the approximations made in various forms of the MCD model. Linear
limb-darkening is confirmed to be a reasonable approximation for the integrated
flux, but not for many specific frequencies of interest.",0502355v1
2003-06-19,The $sl_2$ loop algebra symmetry of the twisted transfer matrix of the six vertex model at roots of unity,"We discuss a family of operators which commute or anti-commute with the
twisted transfer matrix of the six-vertex model at $q$ being roots of unity:
$q^{2N}=1$. The operators commute with the Hamiltonian of the XXZ spin chain
under the twisted boundary conditions, and they are valid also for the
inhomogeneous case. For the case of the anti-periodic boundary conditions, we
show explicitly that the operators generate the $sl_2$ loop algebra in the
sector of the total spin operator $S^Z \equiv N/2 ({\rm mod} N)$. The
infinite-dimensional symmetry leads to exponentially-large spectral
degeneracies, as shown for the periodic boundary conditions \cite{DFM}.
Furthermore, we derive explicitly the $sl_2$ loop algebra symmetry for the
periodic XXZ spin chain with an odd number of sites in the sector $S^Z \equiv
N/2 ({\rm mod} N)$ when $q$ is a primitive $N$ th root of unity with $N$ odd.
Interestingly, in the case of N=3, various conjectures of combinatorial
formulas for the XXZ spin chain with odd-sites have been given
\cite{Odd,Razumov,BGN,GBNM}. We also note a connection to the spectral
degeneracies of the eight-vertex model.",0306498v2
2002-12-17,Measurement of Inclusive Spin Structure Functions of the Deuteron,"We report the results of a new measurement of spin structure functions of the
deuteron in the region of moderate momentum transfer ($Q^2$ = 0.27 -- 1.3
(GeV/c)$^2$) and final hadronic state mass in the nucleon resonance region ($W$
= 1.08 -- 2.0 GeV). We scattered a 2.5 GeV polarized continuous electron beam
at Jefferson Lab off a dynamically polarized cryogenic solid state target
($^{15}$ND$_3$) and detected the scattered electrons with the CEBAF Large
Acceptance Spectrometer (CLAS). From our data, we extract the longitudinal
double spin asymmetry $A_{||}$ and the spin structure function $g_1^d$. Our
data are generally in reasonable agreement with existing data from SLAC where
they overlap, and they represent a substantial improvement in statistical
precision. We compare our results with expectations for resonance asymmetries
and extrapolated deep inelastic scaling results. Finally, we evaluate the first
moment of the structure function $g_1^d$ and study its approach to both the
deep inelastic limit at large $Q^2$ and to the Gerasimov-Drell-Hearn sum rule
at the real photon limit ($Q^2 \to 0$). We find that the first moment varies
rapidly in the $Q^2$ range of our experiment and crosses zero at $Q^2$ between
0.5 and 0.8 (GeV/c)$^2$, indicating the importance of the $\Delta$ resonance at
these momentum transfers.",0212044v2
2002-02-14,"Polarization transfer in the $^{16}$O$(p,p')$ reaction at forward angles and structure of the spin-dipole resonances","Cross sections and polarization transfer observables in the $^{16}$O$(p,p')$
reactions at 392 MeV were measured at several angles between $\theta_{lab}=$
0$^\circ$ and 14$^\circ$. The non-spin-flip (${\Delta}S=0$) and spin-flip
(${\Delta}S=1$) strengths in transitions to several discrete states and broad
resonances in $^{16}$O were extracted using a model-independent method. The
giant resonances in the energy region of $E_x=19-$27 MeV were found to be
predominantly excited by ${\Delta}L=1$ transitions. The strength distribution
of spin-dipole transitions with ${\Delta}S=1$ and ${\Delta}L=1$ were deduced.
The obtained distribution was compared with a recent shell model calculation.
Experimental results are reasonably explained by distorted-wave impulse
approximation calculations with the shell model wave functions.",0202015v2
2002-02-08,Describing mixed spin-space entanglement of pure states of indistinguishable particles using an occupation number basis,"Quantum mechanical entanglement is a resource for quantum computation,
quantum teleportation, and quantum cryptography. The ability to quantify this
resource correctly has thus become of great interest to those working in the
field of quantum information theory. In this paper, we show that all existing
entanglement measures but one fail important tests of fitness when applied to n
particle, m site states of indistinguishable particles, where n,m>=2. The
accepted method of measuring the entanglement of a bipartite system of
distinguishable particles is to use the von Neumann entropy of the reduced
density matrix of one half of the system. We show that expressing the full
density matrix using a site-spin occupation number basis, and reducing with
respect to that basis, gives an entanglement which meets all currently known
fitness criteria for systems composed of either distinguishable or
indistinguishable particles.
  We consider an output state from a previously published thought experiment, a
state which is entangled in both spin and spatial degrees of freedom, and show
that the site entropy measure gives the correct total entanglement. We also
show how the spin-space entanglement transfer occurring within the apparatus
can be understood in terms of the transfer of probability from single-occupancy
to double-occupancy sectors of the density matrix.",0202051v2
2012-03-13,Electronic and magnetic properties of molecule-metal interfaces: transition metal phthalocyanines adsorbed on Ag(100),"We present a systematic investigation of molecule-metal interactions for
transition-metal phthalocyanines (TMPc, with TM = Fe, Co, Ni, Cu) adsorbed on
Ag(100). Scanning tunneling spectroscopy and density functional theory provide
insight into the charge transfer and hybridization mechanisms of TMPc as a
function of increasing occupancy of the 3d metal states. We show that all four
TMPc receive approximately one electron from the substrate. Charge transfer
occurs from the substrate to the molecules, inducing a charge reorganization in
FePc and CoPc, while adding one electron to ligand \pi-orbitals in NiPc and
CuPc. This has opposite consequences on the molecular magnetic moment: in FePc
and CoPc the interaction with the substrate tends to reduce the TM spin,
whereas in NiPc and CuPc an additional spin is induced on the aromatic Pc
ligand, leaving the TM spin unperturbed. In CuPc, the presence of both TM and
ligand spins leads to a triplet ground state arising from intramolecular
exchange coupling between d and \pi electrons. In FePc and CoPc the magnetic
moment of C and N atoms is antiparallel to that of the TM. The different
character and symmetry of the frontier orbitals in the TMPc series leads to
varying degrees of hybridization and correlation effects, ranging from the
mixed-valence (FePc, CoPc) to the Kondo regime (NiPc, CuPc). Coherent coupling
between Kondo and inelastic excitations induces finite-bias Kondo resonances
involving vibrational transitions in both NiPc and CuPc and triplet-singlet
transitions in CuPc.",1203.2747v1
2012-05-31,Quantum Logic between Remote Quantum Registers,"We analyze two approaches to quantum state transfer in solid-state spin
systems. First, we consider unpolarized spin-chains and extend previous
analysis to various experimentally relevant imperfections, including quenched
disorder, dynamical decoherence, and uncompensated long range coupling. In
finite-length chains, the interplay between disorder-induced localization and
decoherence yields a natural optimal channel fidelity, which we calculate.
Long-range dipolar couplings induce a finite intrinsic lifetime for the
mediating eigenmode; extensive numerical simulations of dipolar chains of
lengths up to L=12 show remarkably high fidelity despite these decay processes.
We further consider the extension of the protocol to bosonic systems of coupled
oscillators. Second, we introduce a quantum mirror based architecture for
universal quantum computing which exploits all of the spins in the system as
potential qubits. While this dramatically increases the number of qubits
available, the composite operations required to manipulate ""dark"" spin qubits
significantly raise the error threshold for robust operation. Finally, as an
example, we demonstrate that eigenmode-mediated state transfer can enable
robust long-range logic between spatially separated Nitrogen-Vacancy registers
in diamond; numerical simulations confirm that high fidelity gates are
achievable even in the presence of moderate disorder.",1206.0014v1
2013-10-25,Spectrum of Quantum Transfer Matrices via Classical Many-Body Systems,"In this paper we clarify the relationship between inhomogeneous quantum spin
chains and classical integrable many-body systems. It provides an alternative
(to the nested Bethe ansatz) method for computation of spectra of the spin
chains. Namely, the spectrum of the quantum transfer matrix for the
inhomogeneous ${\mathfrak g}{\mathfrak l}_n$-invariant XXX spin chain on $N$
sites with twisted boundary conditions can be found in terms of velocities of
particles in the rational $N$-body Ruijsenaars-Schneider model. The possible
values of the velocities are to be found from intersection points of two
Lagrangian submanifolds in the phase space of the classical model. One of them
is the Lagrangian hyperplane corresponding to fixed coordinates of all $N$
particles and the other one is an $N$-dimensional Lagrangian submanifold
obtained by fixing levels of $N$ classical Hamiltonians in involution. The
latter are determined by eigenvalues of the twist matrix. To support this
picture, we give a direct proof that the eigenvalues of the Lax matrix for the
classical Ruijsenaars-Schneider model, where velocities of particles are
substituted by eigenvalues of the spin chain Hamiltonians, calculated through
the Bethe equations, coincide with eigenvalues of the twist matrix, with
certain multiplicities. We also prove a similar statement for the ${\mathfrak
g}{\mathfrak l}_n$ Gaudin model with $N$ marked points (on the quantum side)
and the Calogero-Moser system with $N$ particles (on the classical side). The
realization of the results obtained in terms of branes and supersymmetric gauge
theories is also discussed.",1310.6958v2
2013-11-19,"An Argument for Weakly-Magnetized, Slowly-Rotating Progenitors of Long Gamma-Ray Bursts","Using binary evolution with Case-C mass transfer, the spins of several black
holes (BHs) in X$-$ray binaries (XBs) have been predicted and confirmed (three
cases) by observations. The rotational energy of these BHs is sufficient to
power up long gamma$-$ray bursts and hypernovae (GRBs/HNe) and still leave a
Kerr BH behind. However, strong magnetic fields and/or dynamo effects in the
interior of such stars deplete their cores from angular momentum preventing the
formation of collapsars. Thus, even though binaries can produce Kerr BHs, most
of their rotation is acquired from the stellar mantle, with a long delay
between BH formation and spin up. Such binaries would not form GRBs. We study
whether the conditions required to produce GRBs can be met by the progenitors
of such BHs. Tidal-synchronization and Alfv\'en timescales are compared for
magnetic fields of different intensities threading He stars. A search is made
for a magnetic field range which allows tidal spin up all the way in to the
stellar core but prevents its slow down during differential rotation phases.
The energetics for producing a strong magnetic field during core collapse,
which may allow for a GRB central engine, are also estimated. An
observationally-reasonable choice of parameters is found ($B \lesssim10^2$ G
threading a slowly-rotating He star) which allows Fe cores to retain
substantial angular momentum. Thus, the Case-C-mass-transfer binary channel is
capable of explaining long GRBs. However, the progenitors must have low initial
spin and low internal magnetic field throughout their H-burning and He-burning
phases.",1311.4876v1
2014-01-14,Photon echoes retrieved from semiconductor spins: access to basis for long-term optical memories,"The possibility to store optical information is important for classical and
quantum communication. Atoms or ions as well as color centers in crystals offer
suitable two-level systems for absorbing incoming photons. To obtain a reliable
transfer of coherence, strong enough light-matter interaction is required,
which may enforce use of ensembles of absorbers, but has the disadvantage of
unavoidable inhomogeneities leading to fast dephasing. This obstacle can be
overcome by echo techniques that allow recovery of the information as long as
the coherence is preserved. Albeit semiconductor quantum structures appear
appealing for information storage due to the large oscillator strength of
optical transitions, inhomogeneity typically is even more pronounced for them
and most importantly the optical coherence is limited to nanoseconds or
shorter. Here we show that by transferring the information to electron spins
the storage times for the optical coherence can be extended by orders of
magnitude up to the spin relaxation time. From the spin reservoir it can be
retrieved on purpose by inducing a stimulated photon echo. We demonstrate this
for an n-doped CdTe/(Cd,Mg)Te quantum well for which the storage time thereby
could be increased by more than three orders of magnitude from the
picosecond-range up to tens of nanoseconds.",1401.3377v1
2015-03-23,Spin alignment and differential accretion in merging black hole binaries,"Interactions between a supermassive black hole binary and the surrounding
accretion disc can both assist the binary inspiral and align the black hole
spins to the disc angular momentum. While binary migration is due to
angular-momentum transfer within the circumbinary disc, the spin-alignment
process is driven by the mass accreting on to each black hole. Mass transfer
between different disc components thus couples the inspiral and the alignment
process together. Mass is expected to leak through the cavity cleared by the
binary, and preferentially accretes on to the lighter (secondary) black hole
which orbits closer to the disc edge. Low accretion rate on to the heavier
(primary) black hole slows the alignment process down. We revisit the problem
and develop a semi-analytical model to describe the coupling between gas-driven
inspiral and spin alignment, finding that binaries with mass ratio q<~0.2
approach the gravitational-wave driven inspiral in differential misalignment:
light secondaries prevent primaries from aligning. Binary black holes with
misaligned primaries are ideal candidates for precession effects in the
strong-gravity regime and may suffer from moderately large (~1500 km/s) recoil
velocities.",1503.06807v2
2017-08-22,HD 49798: Its History of Binary Interaction and Future Evolution,"The bright subdwarf-O star (sdO), HD 49798, is in a 1.55 day orbit with a
compact companion that is spinning at 13.2 seconds. Using the measurements of
the effective temperature ($T_{\rm eff}$), surface gravity ($\log g$), and
surface abundances of the sdO, we construct models to study the evolution of
this binary system using Modules for Experiments in Stellar Astrophysics
($\texttt{MESA}$). Previous studies of the compact companion have disagreed on
whether it is a white dwarf (WD) or a neutron star (NS). From the published
measurements of the companion's spin and spin-up rate, we agree with Mereghetti
and collaborators that a NS companion is more likely. However, since there
remains the possibility of a WD companion, we use our constructed
$\texttt{MESA}$ models to run simulations with both WD and NS companions that
help us constrain the past and future evolution of this system. If it presently
contains a NS, the immediate mass transfer evolution upon Roche lobe (RL)
filling will lead to mass transfer rates comparable to that implied in
ultraluminous X-ray sources (ULXs). Depending on the rate of angular momentum
extraction via a wind, the fate of this system is either a wide ($P_{\rm
orb}{\approx} 3$ day) intermediate mass binary pulsar (IMPB) with a relatively
rapidly spinning NS (${\approx} 0.3$ s) and a high mass WD (${\approx} 0.9
M_\odot$), or a solitary millisecond pulsar (MSP).",1708.06798v2
2018-01-13,Lattice-Mediated Magnetic Order Melting in TbMnO3,"Recent ultrafast magnetic-sensitive measurements [Phys. Rev. B 92, 184429
(2015) and Phys. Rev. B 96, 184414 (2017)] have revealed a delayed melting of
the long-range cycloid spin-order in TbMnO$_3$ following photoexcitation across
the fundamental Mott-Hubbard gap. The microscopic mechanism behind this slow
transfer of energy from the photoexcited carriers to the spin degrees of
freedom is still elusive and not understood. Here, we address this problem by
combining spectroscopic ellipsometry, ultrafast broadband optical spectroscopy
and ab initio calculations. Upon photoexcitation, we observe the emergence of a
complex collective response, which is due to high-energy coherent optical
phonons coupled to the out-of-equilibrium charge density. This response
precedes the magnetic order melting and is interpreted as the fingerprint of
the formation of anti-Jahn Teller polarons. We propose that the charge
localization in a long-lived self-trapped state hinders the emission of magnons
and other spin-flip mechanisms, causing the energy transfer from the charge to
the spin system to be mediated by the reorganization of the lattice.
Furthermore, we provide evidence for the coherent excitation of a phonon mode
associated with the ferroelectric phase transition.",1801.04368v1
2019-06-11,Coherent transfer of quantum information in silicon using resonant SWAP gates,"Solid state quantum processors based on spins in silicon quantum dots are
emerging as a powerful platform for quantum information processing. High
fidelity single- and two-qubit gates have recently been demonstrated and large
extendable qubit arrays are now routinely fabricated. However, two-qubit gates
are mediated through nearest-neighbor exchange interactions, which require
direct wavefunction overlap. This limits the overall connectivity of these
devices and is a major hurdle to realizing error correction, quantum random
access memory, and multi-qubit quantum algorithms. To extend the connectivity,
qubits can be shuttled around a device using quantum SWAP gates, but phase
coherent SWAPs have not yet been realized in silicon devices. Here, we
demonstrate a new single-step resonant SWAP gate. We first use the gate to
efficiently initialize and readout our double quantum dot. We then show that
the gate can move spin eigenstates in 100 ns with average fidelity
$\bar{F}_{SWAP}^p$ = 98%. Finally, the transfer of arbitrary two-qubit product
states is benchmarked using state tomography and Clifford randomized
benchmarking, yielding an average fidelity of $\bar{F}_{SWAP}^c$ = 84% for gate
operation times of ~300 ns. Through coherent spin transport, our resonant SWAP
gate enables the coupling of non-adjacent qubits, thus paving the way to large
scale experiments using silicon spin qubits.",1906.04512v1
2020-02-18,On the Absence of Triplet Exciton Loss Pathways in Non-Fullerene Acceptor based Organic Solar Cells,"We investigate the viability of highly efficient organic solar cells (OSCs)
based on non-fullerene acceptors (NFA) by taking into consideration efficiency
loss channels and stability issues caused by triplet excitons (TE) formation.
OSCs based on a blend of the conjugated donor polymer PBDB-T and ITIC as
acceptor were fabricated and investigated with electrical, optical and
spin-sensitive methods. The spin-Hamiltonian parameters of molecular TEs and
charge transfer TEs in ITIC e.g., zero-field splitting and charge distribution,
were calculated by Density Functional Theory (DFT) modelling. In addition, the
energetic model describing the photophysical processes in the donor-acceptor
blend was derived. Spin-sensitive photoluminescence measurements prove the
formation of charge transfer (CT) states in the blend and the formation of TEs
in the pure materials and the blend. However, no molecular TE signal is
observed in the completed devices under working conditions by spin-sensitive
electrical measurements. The absence of a molecular triplet state population
allows to eliminate a charge carrier loss channel and irreversible
photooxidation facilitated by long-lived triplet states. These results
correlate well with the high power conversion efficiency of the
PBDB-T:ITIC-based OSCs and their high stability.",2002.07531v2
2021-01-21,Kinetic processes in Fermi-Luttinger liquids,"In this work we discuss extensions of the pioneering analysis by
Dzyaloshinskii and Larkin of correlation functions for one-dimensional Fermi
systems, focusing on the effects of quasiparticle relaxation enabled by a
nonlinear dispersion. Throughout the work we employ both, the weakly
interacting Fermi gas picture and nonlinear Luttinger liquid theory to describe
attenuation of excitations and explore the fermion-boson duality between both
approaches. Special attention is devoted to the role of spin-exchange
processes, effects of interaction screening, and integrability. Thermalization
rates for electron- and hole-like quasiparticles, as well as the decay rate of
collective plasmon excitations and the momentum space mobility of spin
excitations are calculated for various temperature regimes. The phenomenon of
spin-charge drag is considered and the corresponding momentum transfer rate is
determined. We further discuss how momentum relaxation due to several competing
mechanisms, viz. triple electron collisions, electron-phonon scattering, and
long-range inhomogeneities affect transport properties, and highlight energy
transfer facilitated by plasmons from the perspective of the inhomogeneous
Luttinger liquid model. Finally, we derive the full matrix of thermoelectric
coefficients at the quantum critical point of the first conductance plateau
transition, and address magnetoconductance in ballistic semiconductor nanowires
with strong Rashba spin-orbit coupling.",2101.08737v2
2023-01-20,Unconstrained quantitative magnetization transfer imaging: disentangling T1 of the free and semi-solid spin pools,"Since the inception of magnetization transfer (MT) imaging, it has been
widely assumed that Henkelman's two spin pools have similar longitudinal
relaxation times, which motivated many researchers to constrain them to each
other. However, several recent publications reported a $T_1^s$ of the
semi-solid spin pool that is much shorter than $T_1^f$ of the free pool. While
these studies tailored experiments for robust proofs-of-concept, we here aim to
quantify the disentangled relaxation processes on a voxel-by-voxel basis in a
clinical imaging setting, i.e., with an effective resolution of 1.24mm
isotropic and full brain coverage in 12min. To this end, we optimized a
hybrid-state pulse sequence for mapping the parameters of an unconstrained MT
model. We scanned four people with relapsing-remitting multiple sclerosis (MS)
and four healthy controls with this pulse sequence and estimated $T_1^f \approx
1.84$s and $T_1^s \approx 0.34$s in healthy white matter. Our results confirm
the reports that $T_1^s \ll T_1^f$ and we argue that this finding identifies MT
as an inherent driver of longitudinal relaxation in brain tissue. Moreover, we
estimated a fractional size of the semi-solid spin pool of $m_0^s \approx
0.212$, which is larger than previously assumed. An analysis of $T_1^f$ in
normal-appearing white matter revealed statistically significant differences
between individuals with MS and controls.",2301.08394v3
2024-01-04,Symmetry of the coupling between surface acoustic waves and spin waves in synthetic antiferromagnets,"Synthetic antiferromagnets host spin waves that are highly tunable. It is of
practical interest to analyze the symmetry of their coupling to surface
acoustic waves with the design of hybrid devices in view. For this we calculate
the layer-resolved susceptibility tensor of a synthetic antiferromagnet, the
effective magneto-elastic and magneto-rotation fields associated to a
travelling elastic wave, and the power irreversibly transferred by the elastic
wave to the magnetic layers. We consider Rayleigh-type surface acoustic waves:
(a) that travel in an elastically isotropic, non-piezoelectric substrate, or
(b) that propagate along the X direction at the surface of a Z-cut LiNbO$_3$
substrate, or (c) that are guided in a thin Z-cut LiNbO$_3$ film grown on a
sapphire substrate. In particular, we show that the complementary angular
dependencies of the acoustic and optical spin wave modes in synthetic
antiferromagnets makes it possible to excite spin waves for any relative
orientation of magnetization and acoustic wavevector. In addition, we discuss
the symmetries of the driving fields and of the energy transferred to the
magnetic degree of freedom. We evidence new interaction channels coupling the
magnetization eigenmodes when elastic anisotropy and piezoelectricity of the
substrate are considered.",2401.02263v1
2013-12-10,Parallel family trees for transfer matrices in the Potts model,"The computational cost of transfer matrix methods for the Potts model is
directly related to the problem of \textit{into how many ways can two adjacent
blocks of a lattice be connected}. Answering this question leads to the
generation of a combinatorial set of lattice configurations. This set defines
the \textit{configuration space} of the problem, and the smaller it is, the
faster the transfer matrix method can be. The configuration space of generic
transfer matrix methods for strip lattices in the Potts model is in the order
of the Catalan numbers, leading to an asymptotic cost of $O(4^m)$ with $m$
being the width of the strip. Transfer matrix methods with a smaller
configuration space indeed exist but they make assumptions on the temperature,
number of spin states, or restrict the topology of the lattice in order to
work. In this paper we propose a general and parallel transfer matrix method,
based on family trees, that uses a sub-Catalan configuration space of size
$O(3^m)$. The improvement is achieved by grouping the original set of Catalan
configurations into a forest of family trees, in such a way that the solution
to the problem is now computed by just solving the root node of each family. As
a result, the algorithm becomes exponentially faster and highly parallel. An
additional advantage is that the final matrix ends up being compressed, not
only saving space but also making numerical evaluation on $(q,v)$ faster than
in a non-compressed scenario. Experimental results for different sizes of strip
lattices show that the \textit{Parallel family trees (PFT)} strategy indeed
runs exponentially faster than the \textit{Catalan Parallel Method (CPM)},
specially when dealing with dense transfer matrices. We can confirm that a
parallel implementation of the PFT algorithm is highly effective and efficient
for large problem sizes...",1312.2664v2
2023-04-27,The three kingdoms - Photoinduced electron transfer cascades controlled by electronic couplings,"Excited states are the key species in photocatalysis, while the critical
parameters that govern their applications are: i) excitation energy, ii)
accessibility, and iii) lifetime. However, in molecular transition metal-based
photosensitizers there is a design tension between the creation of long-lived
excited (triplet), e.g., metal-to-ligand charge transfer (3MLCT) states and the
population of such states. Long-lived triplet states have low spin-orbit
coupling (SOC) and hence their population is low. Thus, a long-lived triplet
state can be populated but inefficiently. If the SOC is increased, the triplet
state population efficiency is improved - coming at the cost of decreasing the
lifetime. A promising strategy to isolate the triplet excited state away from
the metal after intersystem crossing (ISC) involves the combination of the
transition metal complex and an organic donor/acceptor group. Here we elucidate
the excited-state branching processes in a series of Ru(II)-terpyridyl
push-pull triads by means of quantum chemical simulations. Scalar-relativistic
time-dependent density theory simulations reveal that efficient ISC takes place
along 1/3MLCT-gateway states. Subsequently, competitive electron transfer
pathways involving the organic chromophore, i.e., 10-methylphenothiazinyl and
the terpyridyl ligands are available. The kinetics of the underlying electron
transfer processes were investigated within the semi-classical Marcus picture.
The electron transfer kinetics were described along efficient internal reaction
coordinates that connect the respective photoredox intermediates. The key
parameter that governs the population transfer away from the metal either
towards the organic chromophore either by means of ligand-to-ligand (3LLCT;
weakly coupled) or intra-ligand charge transfer (3ILCT; strongly coupled)
states was determined to be the magnitude of the involved electronic coupling.",2304.14261v1
2014-10-05,Measurement of Spin Correlations in $t\bar{t}$ Events from $pp$ Collisions at $\sqrt{s}$ = 7 TeV in the Lepton + Jets Final State with the ATLAS Detector,"The top quark decays before it hadronises. Before its spin state can be
changed in a process of strong interaction, it is directly transferred to the
top quark decay products. The top quark spin can be deduced by studying angular
distributions of the decay products. The Standard Model predicts the
top/anti-top quark ($t\bar{t}$) pairs to have correlated spins. The degree is
sensitive to the spin and the production mechanisms of the top quark. Measuring
the spin correlation allows to test the predictions. New physics effects can be
reflected in deviations from the prediction. In this thesis the spin
correlation of $t\bar{t}$ pairs, produced at a centre-of-mass energy of
$\sqrt{s} = 7\,$TeV and reconstructed with the ATLAS detector, is measured. The
dataset corresponds to an integrated luminosity of $4.6~\text{fb}^{-1}$.
$t\bar{t}$ pairs are reconstructed in the $\ell$+jets channel using a kinematic
likelihood fit offering the identification of light up- and down-type quarks
from the $t \rightarrow bW \rightarrow bq\bar{q}'$ decay. The spin correlation
is measured via the distribution of the azimuthal angle $\Delta\phi$ between
two top quark spin analyzers in the laboratory frame. It is expressed as the
degree of $t\bar{t}$ spin correlation predicted by the Standard Model,
$f_{\text{SM}}$. The results of \begin{align*} &f_{\text{SM}}(
\Delta\phi(\text{charged lepton, down-type quark} )) &= 1.53 \pm
0.14\,\text{(stat.)} \pm 0.32\,\text{(syst.)}, \\ &f_{\text{SM}} (
\Delta\phi(\text{charged lepton, b-quark} )) &= 0.53 \pm 0.18\,\text{(stat.)}
\pm 0.49\,\text{(syst.)}, \\ &f_{\text{SM}} ( \Delta\phi(\text{combined})) &=
1.12 \pm 0.11\,\text{(stat.)} \pm 0.22\,\text{(syst.)}, \end{align*} are
consistent with the Standard Model prediction of $f_{\text{SM}}= 1.0$.",1410.1791v1
2016-01-27,Dynamic nuclear polarization in a magnetic resonance force microscope experiment,"We report achieving enhanced nuclear magnetization in a magnetic resonance
force microscope experiment at 0.6 tesla and 4.2 kelvin using the dynamic
nuclear polarization (DNP) effect. In our experiments a microwire coplanar
waveguide delivered radiowaves to excite nuclear spins and microwaves to excite
electron spins in a 250 nm thick nitroxide-doped polystyrene sample. Both
electron and proton spin resonance were observed as a change in the mechanical
resonance frequency of a nearby cantilever having a micron-scale nickel tip.
NMR signal, not observable from Curie-law magnetization at 0.6 tesla, became
observable when microwave irradiation was applied to saturate the electron
spins. The resulting NMR signal's size, buildup time, dependence on microwave
power, and dependence on irradiation frequency was consistent with a transfer
of magnetization from electron spins to nuclear spins. Due to the presence of
an inhomogenous magnetic field introduced by the cantilever's magnetic tip, the
electron spins in the sample were saturated in a microwave-resonant slice 10's
of nm thick. The spatial distribution of the nuclear polarization enhancement
factor $\epsilon$ was mapped by varying the frequency of the applied
radiowaves. The observed enhancement factor was zero for spins in the center of
the resonant slice, was $\epsilon = +10$ to $+20$ for spins proximal to the
magnet, and was $\epsilon = -10$ to $-20$ for spins distal to the magnet. We
show that this bipolar nuclear magnetization profile is consistent with
cross-effect DNP in a $\sim \! 10^{5} \: \mathrm{T} \: \mathrm{m}^{-1}$
magnetic field gradient. Potential challenges associated with generating and
using DNP-enhanced nuclear magnetization in a nanometer-resolution magnetic
resonance imaging experiment are elucidated and discussed.",1601.07253v2
2020-10-29,Atomic spin-wave control and spin-dependent kicks with shaped subnanosecond pulses,"The absorption of traveling photons resonant with electric dipole transitions
of an atomic gas naturally leads to electric dipole spin wave excitations. For
a number of applications, it would be highly desirable to shape and coherently
control the spatial waveform of the spin waves before spontaneous emission can
occur. This paper details a recently developed optical control technique to
achieve this goal, where counter-propagating, shaped sub-nanosecond pulses
impart sub-wavelength geometric phases to the spin waves by cyclically driving
an auxiliary transition. In particular, we apply this technique to reversibly
shift the wave vector of a spin wave on the $D2$ line of laser-cooled $^{87}$Rb
atoms, by driving an auxiliary $D1$ transition with shape-optimized pulses, so
as to shut off and recall superradiance on demand. We investigate a
spin-dependent momentum transfer during the spin-wave control process, which
leads to a transient optical force as large as $\sim 1\hbar k$/ns, and study
the limitations to the achieved $70\sim 75\%$ spin wave control efficiency by
jointly characterizing the spin-wave control and matterwave acceleration. Aided
by numerical modeling, we project potential future improvements of the control
fidelity to the $99\%$ level when the atomic states are better prepared and by
equipping a faster and more powerful pulse shaper. Our technique also enables a
background-free measurement of the superradiant emission to unveil the precise
scaling of the emission intensity and decay rate with optical depth.",2010.16066v2
2021-04-15,Supernova Fallback as Origin of Neutron Star Spins and Spin-kick Alignment,"Natal kicks and spins are characteristic properties of neutron stars (NSs)
and black holes (BHs). Both offer valuable clues to dynamical processes during
stellar core collapse and explosion. Moreover, they influence the evolution of
stellar multiple systems and the gravitational-wave signals from their inspiral
and merger. Observational evidence of possibly generic spin-kick alignment has
been interpreted as indication that NS spins are either induced with the NS
kicks or inherited from progenitor rotation, which thus might play a
dynamically important role during stellar collapse. Current three-dimensional
supernova simulations suggest that NS kicks are transferred in the first
seconds of the explosion, mainly by anisotropic mass ejection and, on a
secondary level, anisotropic neutrino emission. In contrast, the NS spins are
only determined minutes to hours later by angular momentum associated with
fallback of matter that does not become gravitationally unbound in the
supernova. Here, we propose a novel scenario to explain spin-kick alignment as
a consequence of tangential vortex flows in the fallback matter that is
accreted mostly from the direction of the NS's motion. For this effect the
initial NS kick is crucial, because it produces a growing offset of the NS away
from the explosion center, thus promoting onesided accretion. In this new
scenario conclusions based on traditional concepts are reversed. For example,
pre-kick NS spins are not required, and rapid progenitor-core rotation can
hamper spin-kick alignment. We also discuss implications for natal BH kicks and
the possibility of tossing the BH's spin axis during its formation.",2104.07493v2
2023-08-11,A first-principles study of bilayer 1T'-WTe2/CrI3: A candidate topological spin filter,"The ability to manipulate electronic spin channels in 2D materials is crucial
for realizing next-generation spintronics. Spin filters are spintronic
components that polarize spins using external fields or material properties
like magnetism. Recently, topological protection from backscattering has
emerged as an enticing feature through which to enhance the robustness of 2D
spin filters. In this work, we propose and then characterize one of the first
2D topological spin filters: bilayer CrI3/1T'-WTe2 (BLCW). To do so, we use a
combination of DFT, maximally localized Wannier functions, and quantum
transport simulations to demonstrate that the BLCW satisfies the principal
criteria for being a topological spin filter; namely that it is gapless,
exhibits spin-polarized charge transfer (SPCT) from WTe2 to CrI3 that renders
the BLCW metallic, and has a topological boundary which retains the edge
conductance of monolayer (ML) 1T'-WTe2. We observe that the atomic magnetic
moments on Cr from DFT are approximately 3.2 mB/Cr in the BL compared to 2.9
mB/Cr with small negative ferromagnetic (FM) moments induced on the W atoms in
freestanding ML CrI3. Subtracting the charge/spin densities of the constituent
ML's from those of the BLCW further reveals SOC-enhanced SPCT from WTe2 to
CrI3. We find that the BLCW is topologically trivial by showing that its Chern
number is zero. Lastly, we show that interfacial scattering at the boundary
between the terraced materials does not remove WTe2's edge conductance. This
evidence indicates that BLCW is gapless, magnetic, and topologically trivial,
meaning that a terraced WTe2/CrI3 BL heterostructure in which only a portion of
a WTe2 ML is topped with CrI3 is a promising candidate for a 2D topological
spin filter. Our results further suggest that 1D chiral edge states may be
realized by stacking FM ML's, like CrI3, atop 2D nonmagnetic Weyl semimetals
like 1T'-WTe2.",2308.06415v2
2020-02-19,The role of disc torques in forming resonant planetary systems,"The most accurate method for modelling planetary migration and hence the
formation of resonant systems is using hydrodynamical simulations. Usually, the
force (torque) acting on a planet is calculated using the forces from the gas
disc and the star, while the gas accelerations are computed using the pressure
gradient, the star, and the planet's gravity, ignoring its own gravity. For the
non-migrating the neglect of the disc gravity results in a consistent torque
calculation while for the migrating case it is inconsistent. We aim to study
how much this inconsistent torque calculation can affect the final
configuration of a two-planet system. Our focus will be on low-mass planets
because most of the multi-planetary systems, discovered by the Kepler survey,
have masses around 10 Earth masses. Performing hydrodynamical simulations of
planet-disc interaction, we measure the torques on non-migrating and migrating
planets for various disc masses as well as density and temperature slopes with
and without considering the disc self-gravity. Using this data, we find a
relation that quantifies the inconsistency, use it in an N-body code, and
perform an extended parameter study modelling the migration of a planetary
system with different planet mass ratios and disc surface densities, in order
to investigate the impact of the torque inconsistency on the architecture of
the planetary system. Not considering disc self-gravity produces an
artificially larger torque on the migrating planet that can result in tighter
planetary systems. The deviation of this torque from the correct value is
larger in discs with steeper surface density profiles. In hydrodynamical
modelling of multi-planetary systems, it is crucial to account for the torque
correction, otherwise the results favour more packed systems.",2002.08077v1
1997-12-12,DMRG study of the spin gap in a one dimensional Hubbard model: effect of the distant transfer and exchange coupling,"The spin gap of a one-dimensional repulsive Hubbard model is numerically
calculated with the density matrix renormalization group, with a special
emphasis on the effect of a next-nearest neighbor hopping (t') and the
nearest-neighbor ferromagnetic exchange (J) interaction. At half-filling, a
significant spin gap opens if |t'| \simeq |t| and J=0, in agreement with the
weak coupling theory, while the gap is strongly suppressed by the introduction
of J. On the other hand, the quarter-filled system has very small spin gaps
regardless of the values of t' and J. Implications for the CuO_2 chain in
Sr_{14}Cu_{24}O_{41} and related materials are discussed.",9712134v1
1997-12-30,Thermodynamic properties of the one-dimensional Kondo insulators studied by the density matrix renormalization group method,"Thermodynamic properties of the one-dimensional Kondo lattice model at
half-filling are studied by the density matrix renormalization group method
applied to the quantum transfer matrix. Spin susceptibility, charge
susceptibility, and specific heat are calculated down to T=0.1t for various
exchange constants. The obtained results clearly show crossover behavior from
the high temperature regime of nearly independent localized spins and
conduction electrons to the low temperature regime where the two degrees of
freedom couple strongly. The low temperature energy scales of the charge and
spin susceptibilities are determined and shown to be equal to the quasiparticle
gap and the spin gap, respectively, for weak exchange couplings.",9712315v1
1998-07-20,Zeroes in the Complex Beta Plane Of 2D Ising Block Spin Boltzmannians,"Effective Boltzmannians in the sense of the block spin renormalization group
are computed for the 2D Ising model. The blocking is done with majority and
Kadanoff rules for blocks of size 2 by 2. Transfer matrix techniques allow the
determination of the effective Boltzmannians as polynomials in u=exp(4 Beta)
for lattices of up to 4 by 4 blocks. The zeroes of these polynomials are
computed for all non-equivalent block spin configurations. Their distribution
in the complex Beta plane reflects the regularity structure of the block spin
transformation. In the case of the Kadanoff rule spurious zeroes approach the
positive real Beta axis at large values of Beta. They might be related to the
renormalization group pathologies discussed in the literature.",9807274v1
1998-10-28,"Interplay of Chemical Bonding and Magnetism in Fe_4N, Fe_3N, Fe_2N","Using spin density functional theory we have carried out a comparative study
of chemical bonding and magnetism in Fe_4N, Fe_3N and Fe_2N. All of these
compounds form close packed Fe lattices, while N occupies octahedral
interstitial positions. High spin fcc Fe and hypothetical FeN with rock salt
structure have been included in our study as reference systems. We find strong,
covalent Fe-N bonds as a result of a substantial \sigma-type p-d hybridisation,
with some charge transfer to N. Those Fe d orbitals which contribute to the p-d
bonds, do no longer participate in the exchange splitting of the Fe d bands.
Because of the large exchange fields, the majority spin d bands are always
fully occupied, while the minority spin d bands are close to half-filling, thus
optimizing the Fe d-d covalent bonding. As a consequence, in good approximation
the individual Fe moments decrease in steps of 0.5 \mu_B from fcc iron (2.7
\mu_B) via Fe_4N (2.7 and 1.97 mu_B}), \chem{Fe_3N} (1.99 \mu_B) to \zeta -
Fe_2N (1.43 \mu_B).",9810383v1
1999-11-15,Universality and multifractal behaviour of spin-spin correlation functions in disordered Potts models,"We report a transfer matrix study of the random bond $q-$state Potts model in
the vicinity of the Ising model $q=2$. We draw attention to a precise
determination of magnetic scaling dimensions in order to compare with
perturbative results. Universality is checked by the computation of the
spin-spin correlation function decay exponent obtained with different types of
probability distributions of the coupling strengths. Our numerical data,
compared to perturbative results for the second moment of the correlation
function, obtained with both replica symmetry and replica symmetry breaking
schemes, are conclusively in favour of the replica symmetric calculations. The
multifractal behaviour of higher moments as well as that of typical correlation
functions are also investigated and a comparison is made with the perturbative
expansions. Finally, the shape of the correlation function probability
distribution is analyzed.",9911221v2
2000-02-16,"Luther-Emery Stripes, RVB Spin Liquid Background and High Tc Superconductivity","The stripe phase in high Tc cuprates is modeled as a single stripe coupled to
the RVB spin liquid background by the single particle hopping process. In
normal state, the strong pairing correlation inherent in RVB state is thus
transfered into the Luttinger stripe and drives it toward spin-gap formation
described by Luther-Emery Model. The establishment of global phase coherence in
superconducting state contributes to a more relevant coupling to
  Luther-Emery Stripe and leads to gap opening in both spin and charge sectors.
Physical consequences of the present picture are discussed, and emphasis is put
on the unification of different energy scales relevant to cuprates, and good
agreement is found with the available experimental results, especially in
ARPES.",0002233v1
2002-06-11,Switching the magnetic configuration of a spin valve by current induced domain wall motion,"We present experimental results on the displacement of a domain wall by
injection of a dc current through the wall. The samples are 1 micron wide long
stripes of a CoO/Co/Cu/NiFe classical spin valve structure.
  The stripes have been patterned by electron beam lithography. A neck has been
defined at 1/3 of the total length of the stripe and is a pinning center for
the domain walls, as shown by the steps of the giant magnetoresistance curves
at intermediate levels (1/3 or 2/3) between the resistances corresponding to
the parallel and antiparallel configurations. We show by electric transport
measurements that, once a wall is trapped, it can be moved by injecting a dc
current higher than a threshold current of the order of magnitude of 10^7
A/cm^2. We discuss the different possible origins of this effect, i.e. local
magnetic field created by the current and/or spin transfer from spin polarized
current.",0206182v1
2002-06-27,Magnon-Mediated Superconductivity in Itinerant Ferromagnets,"The present paper discusses magnon-mediated superconductivity in
ferromagnetic metals. The mechanism explains in a natural way the fact that the
superconductivity in UGe_2, ZrZn_2 and URhGe is apparently confined to the
ferromagnetic phase.The order parameter is a spin anti-parallel component ofa
spin-1 triplet with zero spin projection. The transverse spinfluctuations are
pair forming and the longitudinal ones are pair breaking.The competition
between magnons and paramagnons explains the existence of two successive
quantum phase transitions in UGe_2, from ferromagnetism to ferromagnetic
superconductivity, and at higher pressure to paramagnetism. The maximum T_{SC}
results from the suppression of the paramagnon contribution. To form a Cooper
pair an electron transfers from one Fermi surface to the other. As a result,
the onset of superconductivity leads to the appearance of two Fermi surfaces in
each of the spin up and spin down momentum distribution functions. This fact
explains the linear temperaturedependence at low temperature of the specific
heat, and the experimental results for UGe_2.",0206534v2
2002-12-19,The Wave Functions for the Free-Fermion Part of the Spectrum of the $SU_q(N)$ Quantum Spin Models,"We conjecture that the free-fermion part of the eigenspectrum observed
recently for the $SU_q(N)$ Perk-Schultz spin chain Hamiltonian in a finite
lattice with $q=\exp (i\pi (N-1)/N)$ is a consequence of the existence of a
special simple eigenvalue for the transfer matrix of the auxiliary
inhomogeneous $SU_q(N-1)$ vertex model which appears in the nested Bethe ansatz
approach. We prove that this conjecture is valid for the case of the SU(3) spin
chain with periodic boundary condition. In this case we obtain a formula for
the components of the eigenvector of the auxiliary inhomogeneous 6-vertex model
($q=\exp (2 i \pi/3)$), which permit us to find one by one all components of
this eigenvector and consequently to find the eigenvectors of the free-fermion
part of the eigenspectrum of the SU(3) spin chain. Similarly as in the known
case of the $SU_q(2)$ case at $q=\exp(i2\pi/3)$ our numerical and analytical
studies induce some conjectures for special rates of correlation functions.",0212475v1
2003-03-29,Superconductivity in Sr$_2$RuO$_4$ Mediated by Coulomb Scattering,"We investigate the superconductivity in Sr$_2$RuO$_4$ on the basis of the
three-dimensional three-band Hubbard model. We propose a model with Coulomb
interactions among the electrons on the nearest-neighbor Ru sites. In our model
the intersite Coulomb repulsion and exchange coupling can work as the effective
interaction for the spin-triplet paring. This effective interaction is enhanced
by the band hybridization, which is mediated by the interlayer transfers. We
investigate the possibility of this mechanism in the ground state and find that
the orbital dependent spin-triplet superconductivity is more stable than the
spin-singlet one for realistic parameters. This spin-triplet superconducting
state has horizontal line nodes on the Fermi surface.",0303620v1
2003-08-20,Response functions of an artificial Anderson atom in the atomic limit,"We consider the spin and pseudospin (charge) response functions of the
exactly soluble Anderson atom model. We demonstrate, in particular, that a
deviation from the magnetic Curie-law behaviour, appropriate for a free spin
one-half, increases with increasing asymmetry and temperature. In general,
oscillator strength is transferred from the spin degrees of freedom to the
pseudospin modes. We also consider the negative-U Anderson atom and demonstrate
that the pseudospin modes are the relevant low-energy excitations in this case.
Especially, the roles of the spin and charge excitations are interchanged upon
reversal of the intrasite Coulomb repulsion, U.",0308400v1
2004-04-27,An Effective Reduction of Critical Current for Current-Induced Magnetization Switching by a Ru Layer Insertion in an Exchange-Biased Spin-Valve,"Recently it has been predicted that a spin-polarized electrical current
perpendicular-to-plane (CPP) directly flowing through a magnetic element can
induce magnetization switching through spin-momentum transfer. In this letter,
the first observation of current-induced magnetization switching (CIMS) in
exchange-biased spin-valves (ESPVs) at room temperature is reported. The ESPVs
show the CIMS behavior under a sweeping dc current with a very high critical
current density. It is demonstrated that a thin Ruthenium (Ru) layer inserted
between a free layer and a top electrode effectively reduces the critical
current densities for the CIMS. An ""inverse"" CIMS behavior is also observed
when the thickness of the free layer increases.",0404634v1
2004-06-17,Re-entrant Behavior and Gigantic Response in Disordered Spin-Peierls System,"Effects of disorder and external field on the competing spin-Peierls and
antiferromagnetic states are studied theoretically in terms of the numerical
transfer matrix method applied to a quasi one-dimensional spin 1/2 Heisenberg
model coupled to the lattice degree of freedom. We show that, at temperatures
above the impurity-induced antiferromagnetic phase, inhomogeneous spin-Peierls
lattice distortions remain to exist showing a re-entrant behavior. This feature
can be drastically altered by very weak perturbations, e.g., the staggered
magnetic field or the change in interchain exchange coupling $J_\perp$, leading
to a huge response, which is analogous to the colossal magnetoresistance
phenomenon in perovskite manganese oxides.",0406386v1
2004-12-21,Spin dependent transport of ``nonmagnetic metal/zigzag nanotube encapsulating magnetic atoms/nonmagnetic metal'' junctions,"Towards a novel magnetoresistance (MR) device with a carbon nanotube, we
propose ``nonmagnetic metal/zigzag nanotube encapsulating magnetic
atoms/nonmagnetic metal'' junctions. We theoretically investigate how
spin-polarized edges of the nanotube and the encapsulated magnetic atoms
influence on transport. When the on-site Coulomb energy divided by the
magnitude of transfer integral, $U/|t|$, is larger than 0.8, large MR effect
due to the direction of spins of magnetic atoms, which has the magnitude of the
MR ratio of about 100%, appears reflecting such spin-polarized edges.",0412587v1
2005-10-20,Charge and Spin Ordering in Insulating Na$_{0.5}$CoO$_2$: Effects of Correlation and Symmetry,"Ab initio band theory including correlations due to intra-atomic repulsion is
applied to study charge disproportionation and charge- and spin-ordering in
insulating Na$_{0.5}$CoO$_2$. Various ordering patterns (zigzag and two
striped) for four-Co supercells are analyzed before focusing on the observed
""out-of-phase stripe"" pattern of antiferromagnetic Co$^{4+}$ spins along
charge-ordered stripes. This pattern relieves frustration and shows distinct
analogies with the cuprate layers: a bipartite lattice of antialigned spins,
with axes at 90 degree angles. Substantial distinctions with cuprates are also
discussed, including the tiny gap of a new variant of ""charge transfer"" type
within the Co 3d system.",0510555v2
2006-09-15,Nuclear Spin Switch in Semiconductor Quantum Dots,"We show that by illuminating an InGaAs/GaAs self-assembled quantum dot with
circularly polarized light, the nuclei of atoms constituting the dot can be
driven into a bistable regime, in which either a threshold-like enhancement or
reduction of the local nuclear field by up to 3 Tesla can be generated by
varying the intensity of light. The excitation power threshold for such a
nuclear spin ""switch"" is found to depend on both external magnetic and electric
fields. The switch is shown to arise from the strong feedback of the nuclear
spin polarization on the dynamics of spin transfer from electrons to the nuclei
of the dot.",0609371v1
2002-06-19,The PP2PP Experiment at RHIC,"The PP2PP experiment is devoted to the proton-proton elastic scattering
measurement at the Relativistic Heavy Ion Collider at the centre-of-mass
energies between 50 and 500 GeV and the four-momentum transfer $0.0004 \leq |t|
\leq 1.3$ Gev$^2$. The option of polarized proton beams offers a unique
possibility to investigate the spin dependence of the proton elastic scattering
in a systematic way. The energy dependence of the total and elastic cross
section, the ratio of the real to the imaginary part of the forward scattering
amplitude, and the nuclear slope parameter will be studied. In the medium $|t|$
region ($|t| \leq 1.3$ Gev$^2$) the energy dependence of the dip structure in
the elastic differential cross section will be measured. With polarized beams
the measurement of spin dependent observables: the difference of the total
cross sections as function of the of initial transverse spin states, the
analyzing power and the double spin asymmetries will be used to map the $s$ and
$t$ dependence of the proton helicity amplitudes.",0206044v1
1997-08-01,Proton-Proton Spin Correlations at Charm Threshold and Quarkonium Bound to Nuclei,"The anomalous behavior of the spin-spin correlation at large momentum
transfer in pp elastic scattering is described in terms of the degrees of
freedom associated with the onset of the charm threshold. A non-perturbative
analysis based on the symmetries of QCD is used to extract the relevant
dynamics of the charmonium-proton interaction. The enhancement to pp amplitudes
and their phase follow from analyticity and unitarity, giving a plausible
explanation of the spin anomaly. The interaction between charmonium and light
quarks in nuclei may form a distinct kind of nuclear matter, nuclear bound
quarkonium.",9708202v2
1998-10-26,The Generalized Gerasimov-Drell-Hearn Integral and the Spin Structure of the Nucleon,"The spin structure functions g1 and g2 have been calculated in the resonance
region and for small and intermediate momentum transfer. The calculation is
based on a gauge-invariant and unitary model for one-pion photo- and
electroproduction. The predictions of the model agree with the asymmetries and
the spin sturcture functions recently measured at SLAC, and the first moments
of the calculated spin structure functions fullfil the Gerasimov-Drell-Hearn
and Burkhardt-Cottingham sum rules within an error of typically 5-10 %.",9810480v2
2002-01-08,Spin-spin correlation functions of the XXZ-1/2 Heisenberg chain in a magnetic field,"Using algebraic Bethe ansatz and the solution of the quantum inverse
scattering problem, we compute compact representations of the spin-spin
correlation functions of the XXZ-1/2 Heisenberg chain in a magnetic field. At
lattice distance m, they are typically given as the sum of m terms. Each term n
of this sum, n = 1,...,m is represented in the thermodynamic limit as a
multiple integral of order 2n+1; the integrand depends on the distance as the
power m of some simple function. The root of these results is the derivation of
a compact formula for the multiple action on a general quantum state of the
chain of transfer matrix operators for arbitrary values of their spectral
parameters.",0201045v1
2005-03-12,Generalized Number Theoretic Spin Chain-Connections to Dynamical Systems and Expectation Values,"We generalize the number theoretic spin chain, a one-dimensional statistical
model based on the Farey fractions, by introducing a new parameter x>=0. This
allows us to write recursion relations in the length of the chain. These
relations are closely related to the Lewis three-term equation, which is useful
in the study of the Selberg \zeta-function. We then make use of these relations
and spin orientation transformations. We find a simple connection with the
transfer operator of a model of intermittency in dynamical systems. In
addition, we are able to calculate certain spin expectation values explicitly
in terms of the free energy or correlation length. Some of these expectation
values appear to be directly connected with the mechanism of the phase
transition.",0503030v1
2005-04-25,Evaluation of excitation energy and spin from light charged particles multiplicities in heavy-ion collisions,"A simple procedure for evaluating the excitation energy and the spin transfer
in heavy-ion dissipative collisions is proposed. It is based on a prediction of
the GEMINI evaporation code : for a nucleus with a given excitation energy, the
average number of emitted protons decreases with increasing spin, whereas the
average number of alpha particles increases. Using that procedure for the
reaction 107Ag+58Ni at 52 MeV/nucleon, the excitation energy and spin of
quasi-projectiles have been evaluated. The results obtained in this way have
been compared with the predictions of a model describing the primary dynamic
stage of heavy-ion collisions.",0504025v1
2004-02-11,Single-spin readout for buried dopant semiconductor qubits,"In the design of quantum computer architectures that take advantage of the
long coherence times of dopant nuclear and electron spins in the solid-state,
single-spin detection for readout remains a crucial unsolved problem. Schemes
based on adiabatically induced spin-dependent electron tunnelling between
individual donor atoms, detected using a single electron transistor (SET) as an
ultra-sensitive electrometer, are thought to be problematic because of the low
ionisaton energy of the final D- state. In this paper we analyse the adiabatic
scheme in detail. We find that despite significant stabilization due to the
presence of the D+, the field strengths required for the transition lead to a
shortened dwell-time placing severe constraints on the SET measurement time. We
therefore investigate a new method based on resonant electron transfer, which
operates with much reduced field strengths. Various issues in the
implementation of this method are also discussed.",0402077v1
2007-04-08,Measurements of Single and Double Spin Asymmetry in \textit{pp} Elastic Scattering in the CNI Region with Polarized Hydrogen Gas Jet Target,"Precise measurements of the single spin asymmetry, $A_N$ and the double spin
asymmetry, $A_{NN}$, in proton-proton (\textit{pp}) elastic scattering in the
region of four-momentum transfer squared $0.001 < -t < 0.032 ({\rm GeV}/c)^2$
have been performed using a polarized atomic hydrogen gas jet target and the
RHIC polarized proton beam at 24 GeV/$c$ and 100 GeV/$c$. The polarized gaseous
proton target allowed us to achieve the measurement of $A_{NN}$ in the CNI
region for the first time. Our results of $A_N$ and $A_{NN}$ provide
significant constraints to determine the magnitude of poorly known hadronic
single and double spin-flip amplitudes at this energy.",0704.1031v1
2007-05-22,Eigenvectors of Baxter-Bazhanov-Stroganov τ^{(2)}(t_q) model with fixed-spin boundary conditions,"The aim of this contribution is to give the explicit formulas for the
eigenvectors of the transfer-matrix of Baxter-Bazhanov-Stroganov (BBS) model
(N-state spin model) with fixed-spin boundary conditions. These formulas are
obtained by a limiting procedure from the formulas for the eigenvectors of
periodic BBS model. The latter formulas were derived in the framework of the
Sklyanin's method of separation of variables. In the case of fixed-spin
boundaries the corresponding T-Q Baxter equations for the functions of
separated variables are solved explicitly. As a particular case we obtain the
eigenvectors of the Hamiltonian of Ising-like Z_N quantum chain model.",0705.3236v2
2007-10-01,Polar kicks and the spin period - eccentricity relation in double neutron stars,"We present results of a population synthesis study aimed at examining the
role of spin-kick alignment in producing a correlation between the spin period
of the first-born neutron star and the orbital eccentricity of observed double
neutron star binaries in the Galactic disk. We find spin-kick alignment to be
compatible with the observed correlation, but not to alleviate the requirements
for low kick velocities suggested in previous population synthesis studies. Our
results furthermore suggest low- and high-eccentricity systems may form through
two distinct formation channels distinguished by the presence or absence of a
stable mass transfer phase before the formation of the second neutron star. The
presence of highly eccentric systems in the observed sample of double neutron
stars may furthermore support the notion that neutron stars accrete matter when
moving through the envelope of a giant companion.",0710.0345v1
2007-10-02,Microscopic mechanisms of spin-dependent electric polarization in 3d oxides,"We address a systematic microscopic theory of spin-dependent electric
polarization in 3d oxides starting with a generic three-site two-hole cluster.
A perturbation scheme realistic for 3d oxides is applied which implies the
quenching of orbital moments by low-symmetry crystal field, strong intra-atomic
correlations, the dp-transfer effects, and rather small spin-orbital coupling.
An effective spin operator of the electric dipole moment is deduced
incorporating both nonrelativistic and relativistic terms. The nonrelativistic
electronic polarization mechanism related with the effects of the
redistribution of the local on-site charge density due to $pd$ covalency and
exchange coupling is believed to govern the multiferroic behaviour in 3d
oxides. The relativistic exchange-dipole moment is mainly stems from the
nonrelativistic one due to the perturbation effect of Dzyaloshinsky-Moriya
coupling and is estimated to be a weak contributor to the electric polarization
observed in the most of 3d multiferroics.",0710.0496v1
2007-10-17,Infrared catastrophe in two-quasiparticle collision integral,"Relaxation of a non-equilibrium state in a disordered metal with a
spin-dependent electron energy distribution is considered. The collision
integral due to the electron-electron interaction is computed within the
approximation of a two-quasiparticle scattering. We show that the spin-flip
scattering processes with a small energy transfer may lead to the divergence of
the collision integral for a quasi one-dimensional wire. This divergence is
present only for a spin-dependent electron energy distribution which
corresponds to the total electron spin magnetization M=0 and only for non-zero
interaction in the triplet channel. In this case a non-perturbative treatment
of the electron-electron interaction is needed to provide an effective infrared
cut-off.",0710.3222v1
2008-05-15,Monovacancy-induced magnetism in graphene bilayers,"Vacancy-induced magnetism in graphene bilayers is investigated using
spin-polarized density functional theory calculations. One of two graphene
layers has a monovacancy. Two atomic configurations for bilayers are considered
with respect to the position of the monovacancy. We find that spin magnetic
moments localized at the vacancy site decreases by ~10 % for our two
configurations, compared with the graphene monolayer with a monovacancy. The
reduction of the spin magnetic moment in the graphene bilayers is attributed to
the interlayer charge transfer from the adjacent layer to the layer with the
monovacancy, compensating for spin magnetic moments originating from
quasilocalized defect state.",0805.2213v1
2008-05-28,Dynamic nuclear polarization with simultaneous excitation of electronic and nuclear transitions,"Dynamic nuclear polarization transfers spin polarization from electrons to
nuclei. We have achieved this by a new method, simultaneously exciting
transitions of electronic and nuclear spins. The efficiency of this technique
improves with increasing magnetic field. Experimental results are shown for
N@C60 with continuous-wave microwaves, which can be expected to produce even
higher polarization than the corresponding pulsed techniques for electron spins
greater than 1/2. The degree of nuclear polarization in this case can be easily
monitored through the intensities of the well resolved hyperfine components in
the EPR spectrum. The nuclear spin-lattice relaxation time is orders of
magnitude longer than that of the electrons.",0805.4357v1
2008-06-27,Observation of Spin Fluctuations in a High-Tc Parent Compound Using Resonant Inelastic X-ray Scattering,"We report the first observation of soft-x-ray scattering from spin
fluctuations in a high-Tc parent compound. An antiferromagnetic charge transfer
insulator, CaCuO2, was irradiated by Cu M-edge soft x-rays. Ultra-high
resolution measurements of scattered intensity revealed magnon-magnon
excitations, due to spin exchange scattering, as low-energy loss features. The
process is analogous to optical Raman scattering. The spectra provide the first
measurement of the two-magnon excitation energy and the antiferromagnetic
exchange parameter in infinite-layer CaCuO2. The results reveal resonant
inelastic soft x-ray scattering as a novel probe of the spin dynamics in
cuprates.",0806.4432v1
2008-11-04,Chiral odd GPDs in transverse and longitudinal impact parameter spaces,"We investigate the chiral odd generalized parton distributions (GPDs) for
non-zero skewness $\zeta$ in transverse and longitudinal position spaces by
taking Fourier transform with respect to the transverse and longitudinal
momentum transfer respectively. We present overlap formulas for the chiral-odd
GPDs in terms of light-front wave functions (LFWFs) of the proton both in the
ERBL and DGLAP regions. We calculate them in a field theory inspired model of a
relativistic spin 1/2 composite state with the correct correlation between the
different LFWFs in Fock space, namely that of the quantum fluctuations of an
electron in a generalized form of QED. We show the spin-orbit correlation
effect of the two-particle LFWF as well as the correlation between the
constituent spin and the transverse spin of the target.",0811.0521v2
2008-12-24,Effective field theory for spinor dipolar Bose Einstein condensates,"We show that the effective theory of long wavelength low energy behavior of a
dipolar Bose-Einstein condensate(BEC) with large dipole moments (treated as a
classical spin) can be modeled using an extended Non-linear sigma model (NLSM)
like energy functional with an additional non-local term that represents long
ranged anisotropic dipole-dipole interaction. Minimizing this effective energy
functional we calculate the density and spin-profile of the dipolar
Bose-Einstein condensate in the mean-field regime for various trapping
geometries. The resulting configurations show strong intertwining between the
spin and mass density of the condensate, transfer between spin and orbital
angular momentum in the form of Einstein-de Hass effect, and novel topological
properties. We have also described the theoretical framework in which the
collective excitations around these mean field solutions can be studied and
discuss some examples qualitatively.",0812.4558v1
2009-02-24,On locations and properties of the multicritical point of Gaussian and +/-J Ising spin glasses,"We use transfer-matrix and finite-size scaling methods to investigate the
location and properties of the multicritical point of two-dimensional Ising
spin glasses on square, triangular and honeycomb lattices, with both binary and
Gaussian disorder distributions. For square and triangular lattices with binary
disorder, the estimated position of the multicritical point is in numerical
agreement with recent conjectures regarding its exact location. For the
remaining four cases, our results indicate disagreement with the respective
versions of the conjecture, though by very small amounts, never exceeding 0.2%.
Our results for: (i) the correlation-length exponent $\nu$ governing the
ferro-paramagnetic transition; (ii) the critical domain-wall energy amplitude
$\eta$; (iii) the conformal anomaly $c$; (iv) the finite-size susceptibility
exponent $\gamma/\nu$; and (v) the set of multifractal exponents $\{\eta_k \}$
associated to the moments of the probability distribution of spin-spin
correlation functions at the multicritical point, are consistent with
universality as regards lattice structure and disorder distribution, and in
good agreement with existing estimates.",0902.4153v1
2009-06-09,Influence of laser-excited electron distributions on the x-ray magnetic circular dichroism spectra: Implications for femtosecond demagnetization in Ni,"In pump-probe experiments an intensive laser pulse creates non-equilibrium
excited electron distributions in the first few hundred femtoseconds after the
pulse. The influence of non-equilibrium electron distributions caused by a pump
laser on the apparent X-ray magnetic circular dichroism (XMCD) signal of Ni is
investigated theoretically here for the first time, considering electron
distributions immediately after the pulse as well as thermalized ones, that are
not in equilibrium with the lattice or spin systems. The XMCD signal is shown
not to be simply proportional to the spin momentum in these situations. The
computed spectra are compared to recent pump-probe XMCD experiments on Ni. We
find that the majority of experimentally observed features considered to be a
proof of ultrafast spin momentum transfer to the lattice can alternatively be
attributed to non-equilibrium electron distributions. Furthermore, we find the
XMCD sum rules for the atomic spin and orbital magnetic moment to remain valid,
even for the laser induced non-equilibrium electron distributions.",0906.1700v1
2009-06-13,Degradation of superconductivity and spin fluctuations by electron over-doping in LaFeAsO$_{1-x}$F$_{x}$,"Low energy spin fluctuations are studied for the electron-doped Fe-based
superconductor LaFeAsO(1-x)F(x) by inelastic neutron scattering up to the
energy transfer of w = 15 meV using polycrystalline samples. Superconducting
samples (x=0.057, Tc=25 K and x=0.082, Tc=29 K) show dynamical spin
susceptibility chi""(w) almost comparable with the parent sample's. However
chi""(w) is almost vanished in the x=0.158 sample where the superconductivity is
highly suppressed. These results are compatible with the theoretical
suggestions that the spin fluctuation plays an important role for the
superconductivity.",0906.2453v3
2009-06-28,Exclusive rho-0 electroproduction on transversely polarized protons,"The exclusive electroproduction of rho-0 mesons was studied with the HERMES
spectrometer at the DESY laboratory by scattering 27.6 GeV positron and
electron beams off a transversely polarized hydrogen target. Spin density
matrix elements for this process were determined from the measured production-
and decay-angle distributions of the produced rho-0 mesons. These matrix
elements embody information on helicity transfer and the validity of s-channel
helicity conservation in the case of a transversely polarized target. From the
spin density matrix elements, the leading-twist term in the single-spin
asymmetry was calculated separately for longitudinally and transversely
polarized rho-0 mesons. Neglecting s-channel helicity changing matrix elements,
results for the former can be compared to calculations based on generalized
parton distributions, which are sensitive to the contribution of the total
angular momentum of the quarks to the proton spin.",0906.5160v1
2009-07-22,Contrasting Spin Dynamics Between Underdoped and Overdoped Ba(Fe[1-x]Co[x])2As2,"We report the first NMR investigation of spin dynamics in the overdoped
non-superconducting regime of Ba(Fe[1-x]Co[x])2As2 up to x =0.26. We
demonstrate that the absence of inter-band transitions with large momentum
transfer Q(AF) ~ (pi, 0) between the hole and electron Fermi surfaces results
in complete suppression of antiferromagnetic spin fluctuations for x > 0.15.
Our experimental results provide direct evidence for a correlation between Tc
and the strength of Q(AF) antiferromagnetic spin fluctuations.",0907.3875v3
2009-08-13,Predicted band structures of III-V semiconductors in wurtzite phase,"While non-nitride III-V semiconductors typically have a zincblende structure,
they may also form wurtzite crystals under pressure or when grown as
nanowhiskers. This makes electronic structure calculation difficult since the
band structures of wurtzite III-V semiconductors are poorly characterized. We
have calculated the electronic band structure for nine III-V semiconductors in
the wurtzite phase using transferable empirical pseudopotentials including
spin-orbit coupling. We find that all the materials have direct gaps. Our
results differ significantly from earlier {\it ab initio} calculations, and
where experimental results are available (InP, InAs and GaAs) our calculated
band gaps are in good agreement. We tabulate energies, effective masses, and
linear and cubic Dresselhaus zero-field spin-splitting coefficients for the
zone-center states. The large zero-field spin-splitting coefficients we find
may lead to new functionalities for designing devices that manipulate spin
degrees of freedom.",0908.1984v1
2010-05-04,Disorder-induced freezing of dynamical spin fluctuations in underdoped cuprates,"We study the dynamical spin susceptibility of a correlated d-wave
superconductor (dSC) in the presence of disorder, using an unrestricted
Hartree-Fock approach. This model provides a concrete realization of the notion
that disorder slows down spin fluctuations, which eventually ""freeze out"". The
evolution of disorder-induced spectral weight transfer agrees qualitatively
with experimental observations on underdoped cuprate superconductors. For
sufficiently large disorder concentrations, static spin density wave (SDW)
order is created when droplets of magnetism nucleated by impurities overlap. We
also study the disordered stripe state coexisting with a dSC and compare its
magnetic fluctuation spectrum to that of the disorder-generated SDW phase.",1005.0520v2
2010-05-26,Spin- and energy-dependent tunneling through a single molecule with intramolecular spatial resolution,"We investigate the spin- and energy dependent tunneling through a single
organic molecule (CoPc) adsorbed on a ferromagnetic Fe thin film, spatially
resolved by low-temperature spin-polarized scanning tunneling microscopy.
Interestingly, the metal ion as well as the organic ligand show a significant
spin-dependence of tunneling current flow. State-of-the-art ab initio
calculations including also van-der-Waals interactions reveal a strong
hybridization of molecular orbitals and surface 3d states. The molecule is
anionic due to a transfer of one electron, resulting in a non-magnetic (S= 0)
state. Nevertheless, tunneling through the molecule exhibits a pronounced
spin-dependence due to spin-split molecule-surface hybrid states.",1005.4745v1
2010-07-02,External field control of collective spin excitations in an optical lattice of $^2Σ$ molecules,"We show that an ensemble of $^2\Sigma$ molecules in the rotationally ground
state trapped on an optical lattice exhibits collective spin excitations that
can be controlled by applying superimposed electric and magnetic fields. In
particular, we show that the lowest energy excitation of the molecular ensemble
at certain combinations of electric and magnetic fields leads to the formation
of a magnetic Frenkel exciton. The exciton bandwidth can be tuned by varying
the electric or magnetic fields. We show that the exciton states can be
localized by creating vacancies in the optical lattice. The localization
patterns of the magnetic exciton states are sensitive to the number and
distribution of vacancies, which can be exploited for engineering many-body
entangled spin states. We consider the dynamics of magnetic exciton wavepackets
and show that the spin excitation transfer between molecules in an optical
lattice can be accelerated or slowed down by tuning an external magnetic or
electric field.",1007.0458v1
2010-07-29,Spin correlations in nonperturbative electron-positron pair creation by petawatt laser pulses colliding with a TeV proton beam,"The influence of the electron spin degree of freedom on nonperturbative
electron-positron pair production by high-energy proton impact on an intense
laser field of circular polarization is analyzed. Predictions from the Dirac
and Klein-Gordon theories are compared and a spin-resolved calculation is
performed. We show that the various spin configurations possess very different
production probabilities and discuss the transfer of helicity in this highly
nonlinear process. Our predictions could be tested by combining the few-TeV
proton beam at CERN-LHC with an intense laser pulse from a table-top petawatt
laser source.",1007.5176v1
2010-08-20,Charge-induced spin polarization in non-magnetic organic molecule Alq$_{3}$,"Electrical injection in organic semiconductors is a key prerequisite for the
realization of organic spintronics. Using density-functional theory
calculations we report the effect of electron transfer into the organic
molecule Alq$_3$. Our first-principles simulations show that electron injection
spontaneously spin-polarizes non-magnetic Alq$_3$ with a magnetic moment
linearly increasing with induced charge. An asymmetry of the Al--N bond lengths
leads to an asymmetric distribution of injected charge over the molecule. The
spin-polarization arises from a filling of dominantly the nitrogen $p_z$
orbitals in the molecule's LUMO together with ferromagnetic coupling of the
spins on the quinoline rings.",1008.3525v2
2011-04-29,Doping dependence of magnetic excitations of 1D cuprates as probed by Resonant Inelastic x-ray Scattering,"We study the dynamical, momentum dependent two- and four-spin response
functions in doped and undoped 1D cuprates, as probed by resonant inelastic
x-ray scattering, using an exact numerical diagonalization procedure. In the
undoped $t-J$ system the four-spin response vanishes at $\pi$, whereas the
two-spin correlator is peaked around $\pi/2$, with generally larger spectral
weight. Upon doping spectra tend to soften and broaden, with a transfer of
spectral weight towards higher energy. However, the total spectral weight and
average peak position of either response are only weakly affected by doping up
to a concentration of 1/8. Only the two-spin response at $\pi$ changes
strongly, with a large reduction of spectral weight and enhancement of
excitation energy. At other momenta the higher-energy, generic features of the
magnetic response are robust against doping. It signals the presence of strong
short-range antiferromagnetic correlations, even after doping mobile holes into
the system. We expect this to hold also in higher dimensions.",1104.5588v1
2011-06-29,Highly spin-polarized conducting state at the interface between non-magnetic band insulators: LaAlO3/FeS2 (001),"First-principles density functional calculations demonstrate that a
spin-polarized two-dimensional conducting state can be realized at the
interface between two non-magnetic band insulators. The (001) surface of the
diamagnetic insulator FeS2 (pyrite) supports a localized surface state deriving
from Fe d-orbitals near the conduction band minimum. The deposition of a few
unit cells of the polar perovskite oxide LaAlO3 leads to electron transfer into
these surface bands, thereby creating a conducting interface. The occupation of
these narrow bands leads to an exchange splitting between the spin sub-bands,
yielding a highly spin-polarized conducting state distinct from the rest of the
non-magnetic, insulating bulk. Such an interface presents intriguing
possibilities for spintronics applications.",1106.6010v1
2011-11-12,Unrestricted Hartree-Fock Analysis of Sr$_{3-x}$Ca$_x$Ru$_2$O$_7$,"We investigated the electronic and magnetic structure of
Sr$_{3-x}$Ca$_x$Ru$_2$O$_7$ ($0 \leq x \leq 3$) on the basis of the
double-layered three-dimensional multiband Hubbard model with spin-orbit
interaction. In our model, lattice distortion is implemented as the modulation
of transfer integrals or a crystal field. The most stable states are estimated
within the unrestricted Hartree-Fock approximation, in which the colinear spin
configurations with five different spin-quantization axes are adopted as
candidates. The obtained spin structures for some particular lattice
distortions are consistent with the neutron diffraction results for
Ca$_3$Ru$_2$O$_7$. Also, some magnetic phase transitions can occur due to
changes in lattice distortion. These results facilitate the comprehensive
understanding of the phase diagram of Sr$_{3-x}$Ca$_x$Ru$_2$O$_7$.",1111.2891v1
2012-02-09,Interlayer magnetic frustration driven quantum spin disorder in honeycomb compound In$_{3}$Cu$_{2}$VO$_{9}$,"We present electronic and magnetic properties of a honeycomb compound
In$_{3}$Cu$_{2}$VO$_{9}$ in this paper. We find that the parent phase is a
charge transfer insulator with an energy gap of about 1.5 eV. Singly occupied
d$_{3z^{2}-r^{2}}$ electrons of copper ions contribute an $S$ = 1/2 spin, while
vanadium ions show nonmagnetism. Oxygen 2$p$ orbitals hybridizing with a small
fraction of Cu 3$d$ orbitals dominate the density of states near $E_{F}$. The
planar nearest-neighbor, next-nearest-neighbor and interplane superexchange
couplings of Cu spins are $J_{1}$ $\approx$ 16.2 meV, $J_{2}$ $\approx$ 0.3 meV
and $J_{z}$ $\approx$ 1.2 meV, suggesting a low-dimensional antiferromagnet
\cite{Sondhi10}. We propose that the magnetic frustration along the c-axis
leads to a quantum spin disorder in In$_{3}$Cu$_{2}$VO$_{9}$, in accordance
with the recent experiments. {abstract}",1202.1861v3
2012-03-25,First Principles Calculation of Helical Spin Order in Iron Perovskite SrFeO3 and BaFeO3,"Motivated by recent discovery of ferromagnetism in cubic perovskite BaFeO3
under small magnetic field, we investigate spin order in BaFeO3 and
isostructual SrFeO3 by the first principles calculation. The on-site Coulomb
and exchange interactions are necessary for the helical spin order consistent
with experiments. SrFeO3 exhibits stable G-type helical order, while A- and
G-type helical orders in BaFeO3 are almost degenerate at short propagating
vector with tiny energetic barrier with respect to ferromagnetic spin order,
explaining ferromagnetism under small field. The results are consistent with
model calculation where negative charge-transfer energy is explicitly taken
into account.",1203.5470v1
2012-04-17,Thermodynamics of spin chains of Haldane-Shastry type and one-dimensional vertex models,"We study the thermodynamic properties of spin chains of Haldane-Shastry type
associated with the A_{N-1} root system in the presence of a uniform external
magnetic field. To this end, we exactly compute the partition function of these
models for an arbitrary finite number of spins. We then show that these chains
are equivalent to a suitable inhomogeneous classical Ising model in a spatially
dependent magnetic field, generalizing the results of Basu-Mallick et al. for
thezero magnetic field case. Using the standard transfer matrix approach, we
are able to compute in closed form the free energy per site in the
thermodynamic limit. We perform a detailed analysis of the chains'
thermodynamics in a unified way, with special emphasis on the zero field and
zero temperature limits. Finally, we provide a novel interpretation of the
thermodynamic quantities of spin chains of Haldane-Shastry type as weighted
averages of the analogous quantities over an ensemble of classical Ising
models.",1204.3805v1
2012-05-29,Spin Response and Neutrino Emissivity of Dense Neutron Matter,"We study the spin response of cold dense neutron matter in the limit of zero
momentum transfer, and show that the frequency dependence of the
long-wavelength spin response is well constrained by sum-rules and the
asymptotic behavior of the two-particle response at high frequency. The
sum-rules are calculated using Auxiliary Field Diffusion Monte Carlo technique
and the high frequency two-particle response is calculated for several
nucleon-nucleon potentials. At nuclear saturation density, the sum-rules
suggest that the strength of the spin response peaks at $\omega \simeq$ 40--60
MeV, decays rapidly for $\omega \geq $100 MeV, and has a sizable strength below
40 MeV. This strength at relatively low energy may lead to enhanced neutrino
production rates in dense neutron-rich matter at temperatures of relevance to
core-collapse supernova.",1205.6499v2
2012-07-31,Sub-10 nm colloidal lithography for integrated spin-photo-electronic devices,"Colloidal lithography [1] is how patterns are reproduced in a variety of
natural systems and is used more and more as an efficient fabrication tool in
bio-, opto-, and nano-technology. Nanoparticles in the colloid are made to form
a mask on a given material surface, which can then be transferred via etching
into nano-structures of various sizes, shapes, and patterns [2,3]. Such
nanostructures can be used in biology for detecting proteins [4] and DNA [5,6],
for producing artificial crystals in photonics [7,8] and GHz oscillators in
spin-electronics [9-14]. Scaling of colloidal patterning down to 10-nm and
below, dimensions comparable or smaller than the main relaxation lengths in the
relevant materials, including metals, is expected to enable a variety of new
ballistic transport and photonic devices, such as spin-flip THz lasers [15]. In
this work we extend the practice of colloidal lithography to producing
large-area, near-ballistic-injection, sub-10 nm point-contact arrays and
demonstrate their integration in to spin-photo-electronic devices.",1207.7356v2
2012-10-31,Room-temperature high-speed nuclear-spin quantum memory in diamond,"Quantum memories provide intermediate storage of quantum information until it
is needed for the next step of a quantum algorithm or a quantum communication
process. Relevant figures of merit are therefore the fidelity with which the
information can be written and retrieved, the storage time, and also the speed
of the read-write process. Here, we present experimental data on a quantum
memory consisting of a single $^{13}$C nuclear spin that is strongly coupled to
the electron spin of a nitrogen-vacancy (NV) center in diamond. The strong
hyperfine interaction of the nearest-neighbor carbon results in transfer times
of 300 ns between the register qubit and the memory qubit, with an overall
fidelity of 88 % for the write - storage - read cycle. The observed storage
times of 3.3 ms appear to be limited by the T$_1$ relaxation of the electron
spin. We discuss a possible scheme that may extend the storage time beyond this
limit.",1210.8278v2
2012-11-30,Correlation functions in one-dimensional spin lattices with Ising and Heisenberg bonds,"A general technique of exact calculation of any correlation functions for the
special class of one-dimensional spin models containing small clusters of
quantum spins assembled to a chain by alternating with the single Ising spins
is proposed. The technique is a natural generalization of that in the models
solved by a classical transfer matrix. The general expressions for
corresponding matrix operators which are the key components of the technique
are obtained. As it is clear from the general principles, the decay of the
correlation functions of various types is explicitly shown to be governed by a
single correlation length. The technique is illustrated by two examples:
symmetric diamond chain and asymmetric sawtooth chain.",1211.7358v2
2013-06-30,Form factors of spin 1 analogue of the eight-vertex model,"The twenty-one-vertex model, the spin $1$ analogue of the eight-vertex model
is considered on the basis of free field representations of vertex operators in
the $2\times 2$-fold fusion SOS model and vertex-face transformation. The tail
operators, which translate corner transfer matrices of the twenty-one-vertex
model into those of the fusion SOS model, are constructed by using free bosons
and fermions for both diagonal and off-diagonal matrix elements with respect to
the ground state sectors. Form factors of any local operators are therefore
obtained in terms of multiple integral formulae, in principle. As the simplest
example, the two-particle form factor of the spin operator is calculated
explicitly.",1307.0198v8
2013-07-23,Microscopic origin of spin-orbital separation in Sr2CuO3,"Recently performed resonant inelastic x-ray scattering experiment (RIXS) at
the copper L3 edge in the quasi-1D Mott insulator Sr2CuO3 has revealed a
significant dispersion of a single orbital excitation (orbiton). This large and
unexpected orbiton dispersion has been explained using the concept of
spin-orbital fractionalization in which orbiton, which is intrinsically coupled
to the spinon in this material, liberates itself from the spinon due to the
strictly 1D nature of its motion. Here we investigate this mechanism in detail
by: (i) deriving the microscopic spin-orbital superexchange model from the
charge transfer model for the CuO3 chains in Sr2CuO3, (ii) mapping the orbiton
motion in the obtained spin-orbital model into a problem of a single hole
moving in an effective half-filled antiferromagnetic chain t-J model, and (iii)
solving the latter model using the exact diagonalization and obtaining the
orbiton spectral function. Finally, the RIXS cross section is calculated based
on the obtained orbiton spectral function and compared with the RIXS
experiment.",1307.6180v3
2013-08-14,On the formation of the peculiar low-mass X-ray binary IGR J17480$-$2446 in Terzan 5,"IGR J17480$-$2446 is an accreting X-ray pulsar in a low-mass X-ray binary
harbored in the Galactic globular cluster Terzan 5. Compared with other
accreting millisecond pulsars, IGR J17480$-$2446 is peculiar in its low spin
frequency (11 Hz), which suggests that it might be a mildly recycled neutron
star at the very early phase of mass transfer. However, this model seems to be
in contrast with the low field strength deduced from the kiloHertz
quasi-periodic oscillations observed in IGR J17480$-$2446. Here we suggest an
alternative interpretation, assuming that the current binary system was formed
during an exchange encounter either between a binary (which contains a recycled
neutron star) and the current donor, or between a binary and an isolated,
recycled neutron star. In the resulting binary, the spin axis of the neutron
star could be parallel or anti-parallel with the orbital axis. In the later
case, the abnormally low frequency of IGR J17480$-$2446 may result from the
spin-down to spin-up evolution of the neutron star. We also briefly discuss the
possible observational implications of the pulsar in this scenario.",1308.3008v1
2013-11-04,Spin-Resolved Self-Doping Tunes the Intrinsic Half-Metallicity of AlN Nanoribbons,"We present a first-principles theoretical study of electric field-and
strain-controlled intrinsic half-metallic properties of zigzagged aluminium
nitride (AlN) nanoribbons. We show that the half-metallic property of AlN
ribbons can undergo a transition into fully-metallic or semiconducting behavior
with application of an electric field or uniaxial strain. An external
transverse electric field induces a full charge screening that renders the
material semiconducting. In contrast, as uniaxial strain varies from
compressive to tensile, a spin-resolved selective self-doping increases the
half-metallic character of the ribbons. The relevant strain-induced changes in
electronic properties arise from band structure modifications at the Fermi
level as a consequence of a spin-polarized charge transfer between pi-orbitals
of the N and Al edge atoms in a spin-resolved self-doping process. This band
structure tunability indicates the possibility ofdesigning magnetic nanoribbons
with tunable electronic structure by deriving edge states from elements with
sufficiently different localization properties. Finite temperature molecular
dynamics reveal a thermally stable half-metallic nanoribbon up to room
temperature.",1311.0895v1
2014-01-07,Evolution of Accreting Binary Systems on the Spin-up Line,"The measured characteristics of binary pulsars provide valuable insights into
the evolution of these systems. We study the aspects of binary evolution
particularly relevant to binary Millisecond Pulsars (MSPs), and the formation
of close binaries involving degenerate stars through a spin-evolution diagram
(spin-up line). For this task, we use a wide variety of binaries, including
those with compact components that observed in different energy bands, which we
analyze them according to the spin-up line. Their formation and evolution over
timescales of binary evolution models are investigated in order to grab any
constraint on their evolution, and to estimate the masses of neutron stars with
different mass-transfer histories.",1401.1528v2
2014-02-24,Spin-dependent recombination involving oxygen-vacancy complexes in silicon,"Spin-dependent relaxation and recombination processes in $\gamma$-irradiated
$n$-type Czochralski-grown silicon are studied using continuous wave (cw) and
pulsed electrically detected magnetic resonance (EDMR). Two processes involving
the SL1 center, the neutral excited triplet state of the oxygen-vacancy
complex, are observed which can be separated by their different dynamics. One
of the processes is the relaxation of the excited SL1 state to the ground state
of the oxygen-vacancy complex, the other a charge transfer between $^{31}$P
donors and SL1 centers forming close pairs, as indicated by electrically
detected electron double resonance. For both processes, the recombination
dynamics are studied with pulsed EDMR techniques. We demonstrate the
feasibility of true zero-field cw and pulsed EDMR for spin 1 systems and use
this to measure the lifetimes of the different spin states of SL1 also at
vanishing external magnetic field.",1402.5957v2
2014-03-01,Spin filtering in a magnetic barrier structure: in-plane spin orientation,"We investigate ballistic spin transport in a two dimensional electron gas
system through magnetic barriers of various geometries using the transfer
matrix method. While most of the previous studies have focused on the effect of
magnetic barriers perpendicular to the two dimensional electron gas plane, we
concentrate on the case of magnetic barriers parallel to the plane. We show
that resonant oscillation occurs in the transmission probability without
electrostatic potential modulation which is an essential ingredient in the case
of ordinary out-of-plane magnetic barriers. Transmission probability of the
in-plane magnetic barrier structure changes drastically according to the number
of barriers and also according to the electrostatic potential modulation
applied in the magnetic barrier region. Using a hybrid model consisting of a
superconductor, ferromagnets, and a two dimensional electron gas plane, we show
that it can serve as a good in-plane oriented spin selector which can be
operated thoroughly by electrical modulation without any magnetic control.",1403.0067v1
2014-04-16,Unconditional quantum teleportation between distant solid-state qubits,"Realizing robust quantum information transfer between long-lived qubit
registers is a key challenge for quantum information science and technology.
Here we demonstrate unconditional teleportation of arbitrary quantum states
between diamond spin qubits separated by 3 meters. We prepare the teleporter
through photon-mediated heralded entanglement between two distant electron
spins and subsequently encode the source qubit in a single nuclear spin. By
realizing a fully deterministic Bell-state measurement combined with real-time
feed-forward we achieve teleportation in each attempt while obtaining an
average state fidelity exceeding the classical limit. These results establish
diamond spin qubits as a prime candidate for the realization of quantum
networks for quantum communication and network-based quantum computing.",1404.4369v3
2014-08-05,Coherent Excitation Transfer in a Spin Chain of Three Rydberg Atoms,"We study coherent excitation hopping in a spin chain realized using highly
excited individually addressable Rydberg atoms. The dynamics are fully
described in terms of an XY spin Hamiltonian with a long range resonant
dipole-dipole coupling that scales as the inverse third power of the lattice
spacing, $C_3/R^3$. The experimental data demonstrate the importance of next
neighbor interactions which are manifest as revivals in the excitation
dynamics. The results suggest that arrays of Rydberg atoms are ideally suited
to large scale, high-fidelity quantum simulation of spin dynamics.",1408.1055v2
2014-08-14,Engineering the Dynamics of Effective Spin-Chain Models for Strongly Interacting Atomic Gases,"We consider a one-dimensional gas of cold atoms with strong contact
interactions and construct an effective spin-chain Hamiltonian for a
two-component system. The resulting Heisenberg spin model can be engineered by
manipulating the shape of the external confining potential of the atomic gas.
We find that bosonic atoms offer more flexibility for tuning independently the
parameters of the spin Hamiltonian through interatomic (intra-species)
interaction which is absent for fermions due to the Pauli exclusion principle.
Our formalism can have important implications for control and manipulation of
the dynamics of few- and many-body quantum systems; as an illustrative example
relevant to quantum computation and communication, we consider state transfer
in the simplest non-trivial system of four particles representing
exchange-coupled qubits.",1408.3414v2
2014-09-13,A spin-boson theory for charge photogeneration in organic molecules: Role of quantum coherence,"The charge photogeneration process in organic molecules is investigated by a
quantum heat engine model, in which two molecules are modeled by a two-spin
system sandwiched between two bosonic baths at their own temperatures. The two
baths represent the photon emission source and the phonon environment,
respectively. We utilize the time-dependent density matrix renormalization
group algorithm to investigate the ultrafast quantum thermodynamical processes
of the model. We find that the transient energy flow through the two spins
behaves a two-stage effect: The first stage shows a coherent dynamics which
represents the ultrafast delocalization and dissociation of the charge-transfer
state, and in the second stage a steady current is establish. The
photo-to-charge conversion is highly efficient with the maximum efficiency
being $93\%$ with optimized model parameters. The survival entanglement between
the two spins is found to be mostly responsible for the hyper efficiency.",1409.3916v1
2014-11-26,Bose-Einstein condensates with localized spin-orbit coupling: soliton complexes and spinor dynamics,"Spin-orbit (SO) coupling can be introduced in a Bose--Einstein condensate
(BEC) as a gauge potential acting only in a localized spatial domain. Effect of
such a SO ""defect"" can be understood by transforming the system to the
integrable vector model. The properties of the SO-BEC change drastically if the
SO defect is accompanied by the Zeeman splitting. In such a non-integrable
system, the SO defect qualitatively changes the character of soliton
interactions and allows for formation of stable nearly scalar soliton complexes
with almost all atoms concentrated in only one dark state. These solitons exist
only if the number of particles exceeds a threshold value. We also report on
the possibility of transmission and reflection of a soliton upon its scattering
on the SO defect. Scattering strongly affects the pseudo-spin polarization and
can induce pseudo-spin precession. The scattering can also result in almost
complete atomic transfer between the dark states.",1411.7322v1
2014-12-08,Supersymmetric quantum spin chains and classical integrable systems,"For integrable inhomogeneous supersymmetric spin chains (generalized graded
magnets) constructed employing Y(gl(N|M))-invariant R-matrices in
finite-dimensional representations we introduce the master T-operator which is
a sort of generating function for the family of commuting quantum transfer
matrices. Any eigenvalue of the master T-operator is the tau-function of the
classical mKP hierarchy. It is a polynomial in the spectral parameter which is
identified with the 0-th time of the hierarchy. This implies a remarkable
relation between the quantum supersymmetric spin chains and classical many-body
integrable systems of particles of the Ruijsenaars-Schneider type. As an
outcome, we obtain a system of algebraic equations for the spectrum of the spin
chain Hamiltonians.",1412.2586v2
2015-01-28,Manipulation of a single magnetic atom using polarized single electron transport in a double quantum dot,"We consider theoretically a magnetic impurity spin driven by polarized
electrons tunneling through a double quantum dot system. Spin blockade effect
and spin conservation in the system make the magnetic impurity sufficiently
interact with each transferring electron. As a results, a single collected
electron carries information about spin change of the magnetic impurity. The
scheme may develop all electrical manipulation of magnetic atoms by means of
single electrons, which is significant for the implementation of scalable
logical gates in information processing systems.",1501.07189v5
2015-02-16,Study of luminosity and spin-up relation in X-ray binary pulsars with long-term monitoring by MAXI/GSC and Fermi/GBM,"We study the relation between luminosity and spin-period change in X-ray
binary pulsars using long-term light curve obtained by the MAXI/GSC all-sky
survey and pulse period data from the Fermi/GBM pulsar project. X-ray binaries,
consisting of a highly magnetized neutron star and a stellar companion,
originate X-ray emission according to the energy of the accretion matter onto
the neutron star. The accretion matter also transfers the angular momentum at
the Alfven radius, and then spin up the neutron star. Therefore, the X-ray
luminosity and the spin-up rate are supposed to be well correlated. We analyzed
the luminosity and period-change relation using the data taken by continuous
monitoring of MAXI/GSC and Fermi/GBM for Be/X-ray binaries, GX 304$-$1, A
0535$+$26, GRO J1008$-$57, KS 1947$+$300, and 2S 1417$-$624, which occurred
large outbursts in the last four years. We discuss the results comparing the
obtained observed relation with that of the theoretical model by Ghosh \& Lamb
(1979).",1502.04461v1
2015-03-04,Gate induced enhancement of spin-orbit coupling in dilute fluorinated graphene,"We analyze the origin of spin-orbit coupling (SOC) in fluorinated graphene
using Density Functional Theory (DFT) and a tight-binding model for the
relevant orbitals. As it turns out, the dominant source of SOC is the atomic
spin-orbit of fluorine adatoms and not the impurity induced SOC based on the
distortion of the graphene plane as in hydrogenated graphene. More
interestingly, our DFT calculations show that SOC is strongly affected by both
the type and concentrations of the graphene's carriers, being enhanced by
electron doping and reduced by hole doping. This effect is due to the charge
transfer to the fluorine adatom and the consequent change in the
fluorine-carbon bonding. Our simple tight-binding model, that includes the SOC
of the $2p$ orbitals of F and effective parameters based on maximally localized
Wannier functions, is able to account for the effect. The strong enhancement of
the SOC induced by graphene doping opens the possibility to tune the spin
relaxation in this material.",1503.01395v1
2015-03-19,On the spin-statistics connection in curved spacetimes,"The connection between spin and statistics is examined in the context of
locally covariant quantum field theory. A generalization is proposed in which
locally covariant theories are defined as functors from a category of framed
spacetimes to a category of $*$-algebras. This allows for a more operational
description of theories with spin, and for the derivation of a more general
version of the spin-statistics connection in curved spacetimes than previously
available. The proof involves a ""rigidity argument"" that is also applied in the
standard setting of locally covariant quantum field theory to show how
properties such as Einstein causality can be transferred from Minkowski
spacetime to general curved spacetimes.",1503.05797v1
2015-03-22,DMFT+NRG study of spin-orbital separation in a three-band Hund's metal,"We show that the numerical renormalization group (NRG) is a viable multi-band
impurity solver for Dynamical Mean Field Theory (DMFT), offering unprecedent
real-frequency spectral resolution at arbitrarily low energies and
temperatures. We use it to obtain a numerically exact DMFT solution to the
Hund's metal problem for a three-orbital model with filling factor $n_d=2$. The
ground state is a Fermi liquid. The one-particle spectral function has a strong
particle-hole asymmetry, with a clear apparent power law for positive
frequencies only. With increasing temperature it shows a coherence-incoherence
crossover with spectral weight transfered from low to high energies and evolves
qualitatively differently from a doped Mott insulator. The spin and orbital
spectral functions show ""spin-orbital separation"": spin screening occurs at
much lower energies than orbital screening. The renormalization group flows
clearly reveal the relevant physics at all energy scales.",1503.06467v1
2016-01-26,Topological Defects on the Lattice I: The Ising model,"In this paper and its sequel, we construct topologically invariant defects in
two-dimensional classical lattice models and quantum spin chains. We show how
defect lines commute with the transfer matrix/Hamiltonian when they obey the
defect commutation relations, cousins of the Yang-Baxter equation. These
relations and their solutions can be extended to allow defect lines to branch
and fuse, again with properties depending only on topology. In this part I, we
focus on the simplest example, the Ising model. We define lattice spin-flip and
duality defects and their branching, and prove they are topological. One useful
consequence is a simple implementation of Kramers-Wannier duality on the torus
and higher genus surfaces by using the fusion of duality defects. We use these
topological defects to do simple calculations that yield exact properties of
the conformal field theory describing the continuum limit. For example, the
shift in momentum quantization with duality-twisted boundary conditions yields
the conformal spin 1/16 of the chiral spin field. Even more strikingly, we
derive the modular transformation matrices explicitly and exactly.",1601.07185v1
2016-05-14,Coherent perfect absorption mediated enhancement of transverse spin in a gap plasmon guide,"We consider a symmetric gap plasmon guide (a folded Kretschmann
configuration) supporting both symmeric and antisymmetric coupled surface
plasmons. We calculate the transverse spin under illumination from both the
sides like in coherent perfect absorption (CPA), whereby all the incident light
can be absorbed to excite one of the modes of the structure. Significant
enhancement in the transverse spin is shown to be possible when the CPA dip and
the mode excitation are at the same frequency. The enhancement results from
CPA-mediated total transfer of the incident light to either of the coupled
modes and the associated large local fields. The transverse spin is localized
in the structure since in the ambient dielectric there are only incident plane
waves lacking any structure.",1605.04401v5
2016-07-07,Black holes in stellar-mass binary systems: expiating original spin?,"We investigate systematically whether accreting black hole systems are likely
to reach global alignment of the black hole spin and its accretion disc with
the binary plane. In low-mass X-ray binaries (LMXBs) there is only a modest
tendency to reach such global alignment, and it is difficult to achieve fully:
except for special initial conditions we expect misalignment of the spin and
orbital planes by ~1 radian for most of the LMXB lifetime. The same is expected
in high-mass X-ray binaries (HMXBs). A fairly close approach to global
alignment is likely in most stellar-mass ultraluminous X-ray binary systems
(ULXs) where the companion star fills its Roche lobe and transfers on a thermal
timescale to a black hole of lower mass. These systems are unlikely to show
orbital eclipses, as their emission cones are close to the hole's spin axis.
This offers a potential observational test, as models for ULXs invoking
intermediate-mass black holes do predict eclipses for ensembles of > ~10
systems. Recent observational work shows that eclipses are either absent or
extremely rare in ULXs, supporting the picture that most ULXs are stellar-mass
binaries with companion stars more massive than the accretor.",1607.02144v1
2016-09-05,Ground-state and magnetocaloric properties of a coupled spin-electron double-tetrahedral chain (exact study at the half filling),"Ground-state and magnetocaloric properties of a double-tetrahedral chain, in
which nodal lattice sites occupied by the localized Ising spins regularly
alternate with triangular clusters half filled with mobile electrons, are
exactly investigated by using the transfer-matrix method in combination with
the construction of the $N$th tensor power of the discrete Fourier
transformation. It is shown that the ground state of the model is formed by two
non-chiral phases with the zero residual entropy and two chiral phases with the
finite residual entropy $S = Nk_{\rm B}\ln 2$. Depending on the character of
the exchange interaction between the localized Ising spins and mobile
electrons, one or three magnetization plateaus can be observed in the
magnetization process. Their heights basically depend on the values of Land\'e
$g$-factors of the Ising spins and mobile electrons. It is also evidenced that
the system exhibits both the conventional and inverse magnetocaloric effect
depending on values of the applied magnetic field and temperature.",1609.01052v1
2016-09-06,Tailoring Spin Chain Dynamics for Fractional Revivals,"The production of quantum states required for use in quantum protocols &
technologies is studied by developing the tools to re-engineer a perfect state
transfer spin chain so that a separable input excitation is output over
multiple sites. We concentrate in particular on cases where the excitation is
superposed over a small subset of the qubits on the spin chain, known as
fractional revivals, demonstrating that spin chains are capable of producing a
far greater range of fractional revivals than previously known, at high speed.
We also provide a numerical technique for generating chains that produce
arbitrary single-excitation states, such as the W state.",1609.01397v5
2016-09-06,Correlation Effects on Charge Order and Zero-Gap State in the Organic Conductor α-(BEDT-TTF)2I3,"The effects of electron correlation in the quasi-two-dimensional organic
conductor \alpha-(BEDT-TTF)2I3 are investigated theoretically by using an
extended Hubbard model with on-site and nearest-neighbor Coulomb interactions.
A variational Monte Carlo method is applied to study its ground-state
properties. We show that there appears a nonmagnetic horizontal-stripe charge
order in which nearest-neighbor correlation functions indicate a tendency
toward a spin-singlet formation on the bonds with large transfer integrals
along the charge-rich stripe. Under uniaxial pressure, a first-order transition
from the nonmagnetic charge order to a zero-gap state occurs. Our results on a
spin correlation length in the charge-ordered state suggest that a spin gap is
almost unaffected by the uniaxial pressure in spite of the suppression of the
charge disproportionation. The relevance of these contrasting behaviors in spin
and charge degrees of freedom to recent experimental observations is discussed.",1609.01433v1
2016-11-18,Signatures of Dirac cones in a DMRG study of the Kagome Heisenberg model,"The antiferromagnetic spin-$1/2$ Heisenberg model on a kagome lattice is one
of the most paradigmatic models in the context of spin liquids, yet the precise
nature of its ground state is not understood. We use large scale density matrix
normalization group simulations (DMRG) on infinitely long cylinders and find
indications for the formation of a gapless Dirac spin liquid. First, we use
adiabatic flux insertion to demonstrate that the spin gap is much smaller than
estimated from previous DMRG simulation. Second, we find that the momentum
dependent excitation spectrum, as extracted from the DMRG transfer matrix,
exhibits Dirac cones that match those of a $\pi$-flux free fermion model (the
parton mean-field ansatz of a $U(1)$ Dirac spin liquid)",1611.06238v1
2016-12-21,Superconducting grid-bus surface code architecture for hole-spin qubits,"We present a scalable hybrid architecture for the 2D surface code combining
superconducting resonators and hole-spin qubits in nanowires with tunable
direct Rashba spin-orbit coupling. The back-bone of this architecture is a
square lattice of capacitively coupled coplanar waveguide resonators each of
which hosts a nanowire hole-spin qubit. Both the frequency of the qubits and
their coupling to the microwave field are tunable by a static electric field
applied via the resonator center pin. In the dispersive regime, an entangling
two-qubit gate can be realized via a third order process, whereby a virtual
photon in one resonator is created by a first qubit, coherently transferred to
a neighboring resonator, and absorbed by a second qubit in that resonator.
Numerical simulations with state-of-the-art coherence times yield gate
fidelities approaching the $99\%$ fault tolerance threshold.",1612.07292v1
2017-01-10,Temperature dependence of the non-local spin Seebeck effect in YIG/Pt nanostructures,"We study the transport of thermally excited non-equilibrium magnons through
the ferrimagnetic insulator YIG using two electrically isolated Pt strips as
injector and detector. The diffusing magnons induce a non- local inverse spin
Hall voltage in the detector corresponding to the so-called non-local spin
Seebeck effect (SSE). We measure the non-local SSE as a function of temperature
and strip separation. In experiments at room temperature we observe a sign
change of the non-local SSE voltage at a characteristic strip separation d0, in
agreement with previous investigations. At lower temperatures however, we find
a strong temperature dependence of d0. This suggests that both the angular
momentum transfer across the YIG/Pt interface as well as the transport
mechanism of the magnons in YIG as a function of temperature must be taken into
account to describe the non-local spin Seebeck effect.",1701.02635v1
2017-03-06,"Spindynamics in the antiferromagnetic phases of the Dirac metals $A$MnBi$_2$ ($A=$ Sr, Ca)","The square Bi layers in $A$MnBi$_2$ ($A =$ Sr, Ca) host Dirac fermions which
coexist with antiferromagnetic order on the Mn sublattice below $T_\mathrm{N} =
290\,$K (Sr) and $270\,$K (Ca). We have measured the spin-wave dispersion in
these materials by triple-axis neutron spectroscopy. The spectra show
pronounced spin gaps of 10.2(2)$\,$meV (Sr) and 8.3(8)$\,$meV (Ca) and extend
to a maximum energy transfer of 61 - 63$\,$meV. The observed spectra can be
accurately reproduced by linear spin-wave theory from an Heisenberg effective
spin Hamiltonian. Detailed global fits of the full magnon dispersion are used
to determine the in-plane and inter-layer exchange parameters as well as on the
magnetocrystalline anisotropy constant. To within experimental error we find no
evidence that the magnetic dynamics are influenced by the Dirac fermions.",1703.01849v1
2017-03-23,Off-forward gluonic structure of vector mesons,"The spin-independent and transversity generalised form factors (GFFs) of the
$\phi$ meson are studied using lattice QCD calculations with light quark masses
corresponding to a pion mass $m_\pi\sim450(5)$ MeV. One transversity and three
spin-independent GFFs related to the lowest moments of leading-twist
spin-independent and transversity gluon distributions are obtained at six
non-zero values of the momentum transfer up to 1.2 GeV$^2$. These quantities
are compared with the analogous spin-independent quark GFFs and the
electromagnetic form factors determined on the same lattice ensemble. The
results show quantitative distinction between the spatial distribution of
transversely polarised gluons, unpolarised gluons, and quarks, and point the
way towards further investigations of the gluon structure of nucleons and
nuclei.",1703.08220v2
2017-04-07,Non-scalar operators for the Potts model in arbitrary dimension,"We investigate the operator content of the Q-state Potts model in arbitrary
dimension, using the representation theory of the symmetric group. In
particular we construct all possible tensors acting on N spins, corresponding
to given symmetries under $S_Q$ and $S_N$, in terms of representations
involving any Young diagram. These operators transform non-trivially under the
group of spatial rotations, with a definite conformal spin. The two-point
correlation functions are then computed, and their physical interpretation is
given in terms of Fortuin-Kasteleyn clusters propagating between two
neighbourhoods of each N spins. In two dimensions, we obtain analytically the
critical exponent corresponding to each operator. In the simplest and
physically most relevant cases, we confirm the values of the critical exponent
and the conformal spin by numerical measurements, using both Monte Carlo
simulations and transfer matrix diagonalisations. Our classification partially
provides the structure of Jordan cells of the dilatation operator in arbitrary
dimensions, which in turn gives rise to logarithmic correlation functions.",1704.02186v1
2017-04-18,Spin-polarized quasi 1D state with finite bandgap on the Bi/InSb(001) surface,"One-dimensional (1D) electronic states were discovered on 1D surface atomic
structure of Bi fabricated on semiconductor InSb(001) substrates by
angle-resolved photoelectron spectroscopy (ARPES). The 1D state showed steep,
Dirac-cone-like dispersion along the 1D atomic structure with a finite direct
bandgap opening as large as 150 meV. Moreover, spin-resolved ARPES revealed the
spin polarization of the 1D unoccupied states as well as that of the occupied
states, the orientation of which inverted depending on the wave vector
direction parallel to the 1D array on the surface. These results reveal that a
spin-polarized quasi-1D carrier was realized on the surface of 1D Bi with
highly efficient backscattering suppression, showing promise for use in future
spintronic and energy-saving devices.",1704.05258v2
2017-04-26,Transfer of magnetic order and anisotropy through epitaxial integration of 3$d$ and 4$f$ spin systems,"Resonant x-ray scattering at the Dy $M_5$ and Ni $L_3$ absorption edges was
used to probe the temperature and magnetic field dependence of magnetic order
in epitaxial LaNiO$_3$-DyScO$_3$ superlattices. For superlattices with 2 unit
cell thick LaNiO$_3$ layers, a commensurate spiral state develops in the Ni
spin system below 100 K. Upon cooling below $T_{ind} = 18$ K, Dy-Ni exchange
interactions across the LaNiO$_3$-DyScO$_3$ interfaces induce collinear
magnetic order of interfacial Dy moments as well as a reorientation of the Ni
spins to a direction dictated by the strong magneto-crystalline anisotropy of
Dy. This transition is reversible by an external magnetic field of 3 T.
Tailored exchange interactions between rare-earth and transition-metal ions
thus open up new perspectives for the manipulation of spin structures in
metal-oxide heterostructures and devices.",1704.07967v1
2017-08-02,Optically-pumped dynamic nuclear hyperpolarization in $^{13}$C enriched diamond,"We investigate nuclear spin hyperpolarization from nitrogen vacancy centers
in isotopically enriched diamonds with $^{13}$C concentrations up to 100%.
$^{13}$C enrichment leads to hyperfine structure of the nitrogen vacancy
electron spin resonance spectrum and as a result the spectrum of dynamic
nuclear polarization. We show that strongly-coupled $^{13}$C spins in the first
shell surrounding a nitrogen vacancy center generate resolved hyperfine
splittings, but do not act as an intermediary in the transfer of
hyperpolarization of bulk nuclear spins. High levels of $^{13}$C enrichment are
desirable to increase the efficiency of hyperpolarizaiton for magnetic
resonance signal enhancement, imaging contrast agents, and as a platform for
quantum sensing and many-body physics.",1708.00561v1
2017-08-27,Electronic and spin dynamics in the insulating iron pnictide NaFe$_{0.5}$Cu$_{0.5}$As,"NaFe$_{0.5}$Cu$_{0.5}$As represents a rare exception in the metallic iron
pnictide family, in which a small insulating gap is opened. Based on
first-principles study, we provide a comprehensive theoretical characterization
of this insulating compound. The Fe$^{3+} $spin degree of freedom is quantified
as a quasi-1D $S=\frac{5}{2}$ Heisenberg model. The itinerant As hole state is
downfolded to a $p_{xy}$-orbital hopping model on a square lattice. A unique
orbital-dependent Hund's coupling between the spin and the hole is revealed.
Several important material properties are analyzed, including (a) factors
affecting the small $p-d$ charge-transfer gap; (b) role of the extra interchain
Fe; and (c) the quasi-1D spin excitation in the Fe chains. The experimental
manifestations of these properties are discussed.",1708.08065v1
2017-09-27,Magnetization processes and existence of reentrant phase transitions in coupled spin-electron model on doubly decorated planar lattices,"An alternative model for a description of magnetization processes in coupled
2D spin-electron systems has been introduced and rigorously examined using the
generalized decoration-iteration transformation and the corner transfer matrix
renormalization group method. The model consists of localized Ising spins
placed on nodal lattice sites and mobile electrons delocalized over the pairs
of decorating sites. It takes into account a hopping term for mobile electrons,
the Ising coupling between mobile electrons and localized spins as well as the
Zeeman term acting on both types of particles. The ground-state and
finite-temperature phase diagrams were established and comprehensively
analyzed. It was found that the ground-state phase diagrams are very rich
depending on the electron hopping and applied magnetic field. The diversity of
magnetization curves can be related to intermediate magnetization plateaus,
which may be continuously tuned through the density of mobile electrons. In
addition, the existence of several types of reentrant phase transitions driven
either by temperature or magnetic field was proven.",1709.09341v1
2017-10-25,Co- and contra-directional vertical coupling between ferromagnetic layers with grating for short-wavelength spin wave generation,"The possibility to generate short spin waves is of great interest in the
field of magnonics nowadays. We present an effective and technically affordable
way of conversion of long spin waves, which may be generated by conventional
microwave antenna, to the short, sub-micrometer waves. It is achieved by
grating-assisted resonant dynamic dipolar interaction between two ferromagnetic
layers separated by some distance. We analyze criteria for the optimal
conversion giving a semi-analytical approach for the coupling coefficient. We
show by the numerical calculations the efficient energy transfer between layers
which may be either of co-directional or contra-directional type. Such a system
may operate either as a short spin wave generator or a frequency filter, moving
foreward possible application of magnonics.",1710.09138v1
2017-12-14,Quantum simulation of ferromagnetic Heisenberg model,"Large quantum simulators, with sufficiently many qubits to be impossible to
simulate classically, become hard to experimentally validate. We propose two
tests of a quantum simulator with Heisenberg interaction in a linear chain of
spins. In the first, we propagate half of a singlet state through a chain of
spin with a ferromagnetic interaction and subsequently recover the state with
an antiferromagnetic interaction. The antiferromagnetic interaction is
intrinsic to the system while the ferromagnetic one can be simulated by a
sequence of time-dependent controls of the antiferromagnetic interaction and
Suzuki-Trotter approximations. In the second test, we use the same technique to
transfer a spin singlet state from one end of a spin chain to the other. We
show that the tests are robust against parametric errors in operation of the
simulator and may be applicable even without error correction.",1712.05282v1
2017-12-28,Helical liquid in carbon nanotubes wrapped with DNA molecules,"The measured electric resistance of carbon nanotubes wrapped with DNA
molecules depends strongly on the spin of the injected electrons. Motivated by
these experiments, we study the effect of helix-shaped potentials on the
electronic spectrum of carbon nanotubes. We find that in combination with the
curvature-induced spin-orbit coupling inherent to nanotubes, such a
perturbation opens helicity-dependent gaps. Within these partial gaps,
left-moving electrons carry a fixed spin-projection that is reversed for
right-moving electrons, and the probability of electrons to transfer through
the nanotube correlates with their helicity. We explain the origin of this
effect and show that it can alternatively be induced by twisting the nanotube.
Our findings suggest that carbon nanotubes hold great potential for
implementing spin filters and may form an ideal platform to study the physical
properties of one-dimensional helical liquids.",1712.09950v1
2018-02-20,Wavelength convertible quantum memory satisfying ultralong photon storage and near perfect retrieval efficiency,"Quantum coherence control is presented for wavelength convertible quantum
memory in a double-lambda-type solid ensemble whose spin states are
inhomogeneously broadened. Unlike typical atomic media whose spin decay is
homogeneous, a spin inhomogeneously broadened solid ensemble requires a
counter-intuitive access in the quantum coherence control to avoid spontaneous
emission-caused quantum noises. Such quantum coherence control in a solid
ensemble results in a near perfect retrieval efficiency and is applicable to
ultralong photon storage up to the spin phase relaxation time. Here, the basic
physics of the counter-intuitive quantum coherence control is presented not
only for two-photon (Raman) coherent transients, but also for a detailed
coherence transfer mechanism resulting in frequency up-/down-conversion. This
work sheds light on potential applications of quantum optical memories
satisfying noise free, near perfect, ultralong, and multimode photon storage,
where quantum repeaters, scalable entangled qubits, and magnetometry would be
imminent beneficiaries.",1802.06996v1
2018-04-27,Observation of Floquet Raman transition in a driven solid-state spin system,"We experimentally observe Floquet Raman transitions in the weakly driven
solid state spin system of nitrogen-vacancy center in diamond. The periodically
driven spin system simulates a two-band Wannier-Stark ladder model, and allows
us to observe coherent spin state transfer arising from Raman transition
mediated by Floquet synthetic levels. It also leads to the prediction of analog
photon-assisted Floquet Raman transition and dynamical localisation in a driven
two-level quantum system. The demonstrated rich Floquet dynamics offers new
capabilities to achieve effective Floquet coherent control of a quantum system
with potential applications in various types of quantum technologies based on
driven quantum dynamics. In particular, the Floquet-Raman system may be used as
a quantum simulator for the physics of periodically driven systems.",1804.10492v2
2018-08-27,The spin Drude weight of the XXZ chain and generalized hydrodynamics,"Based on a generalized free energy we derive exact thermodynamic Bethe ansatz
formulas for the expectation value of the spin current, the spin
current-charge, charge-charge correlators, and consequently the Drude weight.
These formulas agree with recent conjectures within the generalized
hydrodynamics formalism. They follow, however, directly from a proper treatment
of the operator expression of the spin current. The result for the Drude weight
is identical to the one obtained 20 years ago based on the Kohn formula and
TBA. We numerically evaluate the Drude weight for anisotropies
$\Delta=\cos(\gamma)$ with $\gamma = n\pi/m$, $n\leq m$ integer and coprime. We
prove, furthermore, that the high-temperature asymptotics for general
$\gamma=\pi n/m$---obtained by analysis of the quantum transfer matrix
eigenvalues---agrees with the bound which has been obtained by the construction
of quasi-local charges.",1808.09033v2
2018-10-02,Microwave preparation of two-dimensional fermionic spin mixtures,"We present a method for preparing a single two-dimensional sample of a
two-spin mixture of fermionic potassium in a single antinode of an optical
lattice, in a quantum-gas microscope apparatus. Our technique relies on
spatially-selective microwave transitions in a magnetic field gradient.
Adiabatic transfer pulses were optimized for high efficiency and minimal atom
loss and heating due to spin-changing collisions. We have measured the dynamics
of those loss processes, which are more pronounced in the presence of a spin
mixture. As the efficient preparation of atoms in a single antinode requires a
homogeneous transverse magnetic field, we developed a method to image and
minimize the magnetic field gradients in the focal plane of the microscope.",1810.01434v2
2019-01-03,Novel Chern insulators with half-metallic edge states,"The central target of spintronics research is to achieve flexible control of
highly efficient and spin-polarized electronic currents. Based on
first-principles calculations and k-p models, we demonstrate that Cu2S/MnSe
heterostructures are a novel type of Chern insulators with half-metallic chiral
edge states and a very high Fermi velocity (0.87 * 10^6 m/s). The full
spin-polarization of the edge states is found to be robust against the tuning
of the chemical potential. Unlike the mechanisms reported previously, this
heterostructure has quadratic bands with a normal band order, that is, the
p/d-like band is below the s-like band. Charge transfer between the Cu2S moiety
and the substrate results in variation in the occupied bands, which together
with spin-orbit coupling, triggers the appearance of the topological state in
the system. These results imply that numerous ordinary semiconductors with
normal band order may convert into Chern insulators with half-metallic chiral
edge states through this mechanism, providing a strategy to find a rich variety
of materials for dissipationless, 100% spin-polarized and high-speed spintronic
devices.",1901.00629v1
2019-01-13,Studying Neutral Current Elastic Scattering and the Strange Axial Form Factor in MicroBooNE,"One of the least constrained contributions to the neutral current (NC)
elastic neutrino-proton cross section is the strange axial form factor, which
represents the strange quark spin contribution to the spin structure of the
proton. This becomes the net strange spin contribution, $\Delta s$, in the
limit when the negative four-momentum transfer squared ($Q^2$) is zero. The
strange axial form factor can be determined by studying NC elastic scattering
events in the MicroBooNE detector. MicroBooNE's unique ability to detect
low-energy protons is expected to allow the reconstruction of these events with
a $Q^2$ as low as 0.10 GeV$^2$ and to determine the strange axial form factor
in a model-independent approach. We present a selection of neutral current
elastic events in a subset of MicroBooNE neutrino data, as well as our plan to
extract the strange part of the axial form factor and $\Delta s$ from this
selection in the full data set.",1901.04071v1
2019-02-27,Propagating spin excitations along skyrmion strings,"Magnetic skyrmions, topological solitons characterized by a two-dimensional
swirling spin texture, have recently attracted attention as stable
particle-like objects. In a three-dimensional system, a skyrmion can extend in
the third dimension forming a robust and flexible string structure, whose
unique topology and symmetry are anticipated to host nontrivial functional
responses. Here, we experimentally demonstrate the coherent propagation of spin
excitations along skyrmion strings for the chiral-lattice magnet Cu2OSeO3. We
find that this propagation is directionally non-reciprocal, and the degree of
non-reciprocity, as well as the associated group velocity and decay length, are
strongly dependent on the character of the excitation modes. Our theoretical
calculation establishes the corresponding dispersion relationship, which well
reproduces the experimentally observed features. Notably, these spin
excitations can propagate over a distance exceeding 10^3 times the skyrmion
diameter, demonstrating the excellent long-range nature of the excitation
propagation on the skyrmion strings. Our combined experimental and theoretical
results offer a comprehensive account of the propagation dynamics of
skyrmion-string excitations, and suggest the possibility of unidirectional
information transfer along such topologically-protected strings.",1902.10302v1
2019-04-01,Quantum bath control with nuclear spin state selectivity via pulse-adjusted dynamical decoupling,"Dynamical decoupling (DD) is a powerful method for controlling arbitrary open
quantum systems. In quantum spin control, DD generally involves a sequence of
timed spin flips ($\pi$ rotations) arranged to average out or selectively
enhance coupling to the environment. Experimentally, errors in the spin flips
are inevitably introduced, motivating efforts to optimise error-robust DD. Here
we invert this paradigm: by introducing particular control ""errors"" in standard
DD, namely a small constant deviation from perfect $\pi$ rotations (pulse
adjustments), we show we obtain protocols that retain the advantages of DD
while introducing the capabilities of quantum state readout and polarisation
transfer. We exploit this nuclear quantum state selectivity on an ensemble of
nitrogen-vacancy centres in diamond to efficiently polarise the $^{13}$C
quantum bath. The underlying physical mechanism is generic and paves the way to
systematic engineering of pulse-adjusted protocols with nuclear state
selectivity for quantum control applications.",1904.00893v1
2019-04-25,Collective quantum memory activated by a driven central spin,"Coupling a qubit coherently to an ensemble is the basis for collective
quantum memories. A driven quantum dot can deterministically excite low-energy
collective modes of a nuclear spin ensemble in the presence of lattice strain.
We propose to gate a quantum state transfer between this central electron and
these low-energy excitations -- spin waves -- in the presence of a strong
magnetic field, where the nuclear coherence time is long. We develop a
microscopic theory capable of calculating the exact time evolution of the
strained electron-nuclear system. With this, we evaluate the operation of
quantum state storage and show that fidelities up to 90% can be reached with a
modest nuclear polarisation of only 50%. These findings demonstrate that
strain-enabled nuclear spin waves are a highly suitable candidate for quantum
memory.",1904.11180v2
2019-05-20,Quantum Transport of Rydberg Excitons with Synthetic Spin-Exchange Interactions,"We present a scheme for engineering quantum transport dynamics of spin
excitations in a chain of laser-dressed Rydberg atoms, mediated by synthetic
spin-exchange arising from diagonal van der Waals interaction. The dynamic
tunability and long-range interaction feature of our scheme allows for the
exploration of transport physics unattainable in conventional spin systems. As
two concrete examples, we first demonstrate a topological exciton pumping
protocol that facilitates quantized entanglement transfer, and secondly we
discuss a highly nonlocal correlated transport phenomenon which persists even
in the presence of dephasing. Unlike previous schemes, our proposal requires
neither resonant dipole-dipole interaction nor off-diagonal van der Waals
interaction. It can be readily implemented in existing experimental systems.",1905.08280v2
2019-05-28,Poincaré constraints on the gravitational form factors for massive states with arbitrary spin,"In this work we analyse the constraints imposed by Poincar\'e symmetry on the
gravitational form factors appearing in the Lorentz decomposition of the
energy-momentum tensor matrix elements for massive states with arbitrary spin.
By adopting a distributional approach, we prove for the first time
non-perturbatively that the zero momentum transfer limit of the leading two
form factors in the decomposition are completely independent of the spin of the
states. It turns out that these constraints arise due to the general Poincar\'e
transformation and on-shell properties of the states, as opposed to the
specific characteristics of the individual Poincar\'e generators themselves. By
expressing these leading form factors in terms of generalised parton
distributions, we subsequently derive the linear and angular momentum sum rules
for states with arbitrary spin.",1905.11969v1
2019-05-29,Antiferromagnetic Kitaev Interactions in Polar Spin-Orbit Mott Insulators,"A bond-directional anisotropic exchange interaction, called the Kitaev
interaction, is a promising route to realize quantum spin liquids. The Kitaev
interactions were found in Mott insulators with the strong spin-orbit coupling,
in the presence of quantum interference between indirect electron transfers.
Here we theoretically propose a different scenario by introducing a polar
structural asymmetry that unbalances the quantum interference. We show that the
imbalance activates additional exchange processes and gives rise to a dominant
antiferromagnetic Kitaev interaction, in stark contrast to the conventional
ferromagnetic ones. We demonstrate by ab initio calculations that polar Ru
trihalides with multiple anions, $\alpha$-RuH$_{3/2}X_{3/2}$ ($X$=Cl and Br),
exhibit the antiferromagnetic Kitaev interaction whose magnitude is several
times larger compared to existing candidates. Our proposal opens the way for
materializing the Kitaev spin liquids in unexplored parameter regions.",1905.12139v1
2019-10-21,Prospects of forming high-spin polar molecules from ultracold atoms,"We have investigated Feshbach resonances in collisions of high-spin atoms
such as Er and Dy with closed-shell atoms such as Sr and Yb, using
coupled-channel scattering and bound-state calculations. We consider both
low-anisotropy and high-anisotropy limits. In both regimes we find many
resonances with a wide variety of widths. The wider resonances are suitable for
tuning interatomic interactions, while some of the narrower resonances are
highly suitable for magnetoassociation to form high-spin molecules. These
molecules might be transferred to short-range states, where they would have
large magnetic moments and electric dipole moments that can be induced with
very low electric fields. The results offer the opportunity to study mixed
quantum gases where one species is dipolar and the other is not, and open up
important prospects for a new field of ultracold high-spin polar molecules.",1910.09641v4
2020-01-06,Simulation of topological phases with color center arrays in phononic crystals,"We propose an efficient scheme for simulating the topological phases of
matter based on silicon-vacancy (SiV) center arrays in phononic crystals. This
phononic band gap structure allows for long-range spin-spin interactions with a
tunable profile. Under a particular periodic microwave driving, the band-gap
mediated spin-spin interaction can be further designed with the form of the
Su-Schrieffer-Heeger (SSH) Hamiltonian. In momentum space, we investigate the
topological characters of the SSH model, and show that the topological
nontrivial phase can be obtained through modulating the periodic driving
fields. Furthermore, we explore the zero-energy topological edge states at the
boundary of the color center arrays, and study the robust quantum information
transfer via the topological edge states. This setup provides a scalable and
promising platform for studying topological quantum physics and quantum
information processing with color centers and phononic crystals.",2001.01397v1
2020-02-03,Theory of Spin-Dependent Electron Transfer Dynamics at Ar/Co(0001) and Ar/Fe(110) Interfaces,"Recent core-hole-clock experiments [Phys. Rev. Lett. $\textbf{112}$, 086801
(2014)] showed that the spin dependence of electron injection times at
Ar/Co(0001) and Ar/Fe(110) interfaces is at variance with the expectations
based on previous calculations for related systems. Here we reconcile theory
and experiment, and demonstrate that the observed dependence is rooted in the
details of the spin-split surface band structures. Our ab initio calculations
back that minority electrons are injected significantly faster than majority
electrons in line with the experimentally reported ultrashort injection times.
The dynamics is particularly sensitive to the size (in reciprocal-space) of the
projected band gaps around $\overline{\Gamma}$ for both substrates at the
resonance energies. A simple tunneling model incorporating the spin-dependent
gap sizes further supports these findings.",2002.01042v1
2020-02-27,"Separation of variables for rational gl(n) spin chains in any compact representation, via fusion, embedding morphism and Backlund flow","We propose a way to separate variables in a rational integrable
$\mathfrak{gl}(n)$ spin chain with an arbitrary finite-dimensional irreducible
representation at each site and with generic twisted periodic boundary
conditions. Firstly, we construct a basis that diagonalises a higher-rank
version of the Sklyanin B-operator; the construction is based on recursive
usage of an embedding of a $\mathfrak{gl}(k)$ spin chain into a
$\mathfrak{gl}(k+1)$ spin chain which is induced from a Yangian homomorphism
and controlled by dual diagonals of Gelfand-Tsetlin patterns. Then, we show
that the same basis can be equivalently constructed by action of
Backlund-transformed fused transfer matricies, whence the Bethe wave functions
factorise into a product of ascending Slater determinants in Baxter
Q-functions. Finally, we construct raising and lowering operators -- the
conjugate momenta -- as normal-ordered Wronskian expressions in Baxter
Q-operators evaluated at zeros of B -- the separated variables. It is an
immediate consequence of the proposed construction that the Bethe algebra
comprises the maximal possible number of mutually commuting charges -- a
necessary property for Bethe equations to be complete.",2002.12341v2
2020-04-07,Observation of a neutron spin resonance in the bilayered superconductor CsCa2Fe4As4F2,"We report inelastic neutron scattering (INS) investigations on the bilayer
Fe-based superconductor CsCa2Fe4As4F4 above and below its superconducting
transition temperature Tc = 28.9 K to investigate the presence of a neutron
spin resonance. This compound crystallises in a body-centred tetragonal lattice
containing asymmetric double layers of Fe2As2 separated by insulating CaF2
layers and is known to be highly anisotropic. Our INS study clearly reveals the
presence of a neutron spin resonance that exhibits higher intensity at lower
momentum transfer (Q) at 5K compared to 54 K, at an energy of 15 meV. The
energy ER of the observed spin resonance is broadly consistent with the
relationship E_R = 4.9 k_B T_c, but is slightly enhanced compared to the values
observed in other Fe-based superconductors. We discuss the nature of the
electron pairing symmetry by comparing the value of E_R with that deduced from
the total superconducting gap value integrated over the Fermi surface.",2004.03567v1
2020-05-07,Ultrafast All Optical Magnetization Control for Broadband Terahertz Spin Wave Generation,"Terahertz spin waves could be generated on-demand via all-optical
manipulation of magnetization by femtosecond laser pulse. Here, we present an
energy balance model, which explains the energy transfer rates from laser pulse
to electron bath coupled with phonon, spin, and magnetization of five different
magnetic metallic thin films: Iron, Cobalt, Nickel, Gadolinium and Ni$_{2}$MnSn
Heusler alloy. Two types of transient magnetization dynamics emerge in metallic
magnetic thin films based on their Curie temperatures (T$_{C}$): type I (Fe,
Co, and Ni with T$_{C}$ > room temperature, RT) and type II films (Gd and
Ni$_{2}$MnSn with T$_{C}$ $\approx$ RT). We study the effect of laser fluence
and pulse width for single Gaussian laser pulses and the effect of metal film
thickness on magnetization dynamics. Spectral dynamics show that broadband spin
waves up to 24 THz could be generated by all-optical manipulation of
magnetization in these nanofilms.",2005.03493v1
2020-05-17,Spin-orbital liquid in Ba$_3$CuSb$_2$O$_9$ stabilized by oxygen holes,"Both the Jahn-Teller distortion of Cu$^{2+}$O$_6$ octahedra and magnetic
ordering are absent in hexagonal Ba$_3$CuSb$_2$O$_9$ suggesting a Cu 3$d$
spin-orbital liquid state. Here, by means of resonant x-ray scattering and
absorption experiment, we show that oxygen 2$p$ holes play crucial role in
stabilizing this spin-orbital liquid state. These oxygen holes appear due to
the ""reaction"" Sb$^{5+}$$\rightarrow$Sb$^{3+}$ $+$ two oxygen holes, with these
holes being able to attach to Cu ions. The hexagonal phase with oxygen 2$p$
holes exhibits also a novel charge-orbital dynamics which is absent in the
orthorhombic phase of Ba$_3$CuSb$_2$O$_9$ with Jahn-Teller distortion and Cu
3$d$ orbital order. The present work opens up a new avenue towards
spin-charge-orbital entangled liquid state in transition-metal oxides with
small or negative charge transfer energy.",2005.08200v1
2020-06-14,Hypersonic heat-induced flows of magnons induced by femtosecond laser pulses,"In this work, we present evidence for the existence of a magnonic current on
the sub-picosecond time-scale in a ferrimagnetic bilayer and its effect on
ultrafast spin dynamics. The ferrimagnet, GdFeCo, is a material known to
undergo ultrafast switching within 1-2ps after excitation with femtosecond
laser pulses. Here, we show that the strong thermal gradients induced by
applying femtosecond laser pulses and the presence of chemical inhomogeneities
lead to local imbalances in the effective temperatures of the spins that
produces a rapid transfer of spin angular momentum, which we interpret as an
ultrafast spin Seebeck effect. We have quantified the typical magnon
propagation in such a system. The results show ballistic magnon propagation
with 30nm/ps velocities. The characteristic time scale of such magnon
propagation indicates that this magnon transport can play an important role in
switching, a crucial piece of understanding towards realising next generation
data processing devices that operate at much higher frequencies.",2006.07935v1
2020-07-07,Magnetization control by angular momentum transfer from surface acoustic wave to ferromagnetic spin moments,"The angular momentum interconversion between electron spin and other type of
angular momenta is useful to develop new spintronic functionalities. The
conversions from the angular momentum of photon and mechanical rotation to
ferromagnetic spin moment have been well studied. While the recent studies
theoretically suggested circular vibration of atoms works as angular momentum
of phonon, the direct experimental demonstration of conversion to spin moments
remains to be performed. Here we demonstrate that the phonon angular momentum
of surface acoustic wave can control the magnetization of a ferromagnetic Ni
film by means of the phononic-to-electronic conversion of angular momentum in
Ni/LiNbO$_3$ hybrid device. This result clearly shows the phonon angular
momentum is useful to further fictionalize spintronic devices.",2007.03192v1
2020-08-08,Post-growth annealing effects on charge and spin excitations in Nd$_{2-x}$Ce$_x$CuO$_4$,"We report a Cu K- and L$_3$-edge resonant inelastic x-ray scattering study of
charge and spin excitations of bulk Nd$_{2-x}$Ce$_x$CuO$_4$, with focus on
post-growth annealing effects. For the parent compound Nd$_2$CuO$_4$ ($x = 0$),
a clear charge-transfer gap is observed in the as-grown state, whereas the
charge excitation spectra indicate that electrons are doped in the annealed
state. This is consistent with the observation that annealed thin-film and
polycrystalline samples of RE$_2$CuO$_4$ (RE = rare earth) can become metallic
and superconducting at sufficiently high electron concentrations without Ce
doping. For $x = 0.16$, a Ce concentration for which it is known that oxygen
reduction destroys long-range antiferromagnetic order and induces
superconductivity, we find that the high-energy spin excitations of
non-superconducting as-grown and superconducting annealed crystals are nearly
identical. This finding is in stark contrast to the significant changes in the
low-energy spin excitations previously observed via neutron scattering.",2008.03420v1
2020-11-12,Inverse Tides in Pulsating Binary Stars,"In close binary stars, the tidal excitation of pulsations typically
dissipates energy, causing the system to evolve towards a circular orbit with
aligned and synchronized stellar spins. However, for stars with self-excited
pulsations, we demonstrate that tidal interaction with unstable pulsation modes
can transfer energy in the opposite direction, forcing the spins of the stars
away from synchronicity, and potentially pumping the eccentricity and
spin-orbit misalignment angle. This ""inverse"" tidal process only occurs when
the tidally forced mode amplitude is comparable to the mode's saturation
amplitude, and it is thus most likely to occur in main sequence gravity mode
pulsators with orbital periods of a few days. We examine the long-term
evolution of inverse tidal action, finding the stellar rotation rate can
potentially be driven to a very large or very small value, while maintaining a
large spin-orbit misalignment angle. Several recent asteroseismic analyses of
pulsating stars in close binaries have revealed extremely slow core rotation
periods, which we attribute to the action of inverse tides.",2011.06613v1
2020-12-10,Optical Detection of Paramagnetic Defects in a CVD-grown Diamond,"The electronic spins of the nitrogen-vacancy centers (NV centers) in
Chemical-Vapor-Deposition (CVD) grown diamonds form ideal probes of magnetic
fields and temperature, as well as promising qu-bits for quantum information
processing. Studying and controlling the magnetic environment of NV centers in
such high purity crystals is thus essential for these applications. We
demonstrate optical detection of paramagnetic species, such as hydrogen-related
complexes, in a CVD-grown diamond. The resonant transfer of the NV centers'
polarized electronic spins to the electronic spins of these species generates
conspicuous features in the NV photoluminescence by employing magnetic field
scans along the [100] crystal direction. Our results offer prospects for more
detailed studies of CVD-grown processes as well as for coherent control of the
spin of novel classes of hyper-polarized paramagnetic species.",2012.05791v1
2021-01-12,Room-temperature control and electrical readout of individual nitrogen-vacancy nuclear spins,"Nuclear spins in semiconductors are leading candidates for quantum
technologies, including quantum computation, communication, and sensing.
Nuclear spins in diamond are particularly attractive due to their extremely
long coherence lifetime. With the nitrogen-vacancy (NV) centre, such nuclear
qubits benefit from an auxiliary electronic qubit, which has enabled
entanglement mediated by photonic links. The transport of quantum information
by the electron itself, via controlled transfer to an adjacent centre or via
the dipolar interaction, would enable even faster and smaller processors, but
optical readout of arrays of such nodes presents daunting challenges due to the
required sub-diffraction inter-site distances. Here, we demonstrate the
electrical readout of a basic unit of such systems - a single 14N nuclear spin
coupled to the NV electron. Our results provide the key ingredients for quantum
gate operations and electrical readout of nuclear qubit registers, in a manner
compatible with nanoscale electrode structures. This demonstration is therefore
a milestone towards large-scale diamond quantum devices with semiconductor
scalability.",2101.04769v1
2021-03-25,Ground State Microwave-Stimulated Raman Transitions and Adiabatic Spin Transfer in the $^{15}$Nitrogen-Vacancy Center,"Microwave pulse sequences are the basis of coherent manipulation of the
electronic spin ground state in nitrogen-vacancy (NV) centers. In this work we
demonstrate stimulated Raman transitions (SRT) and stimulated Raman adiabatic
passage (STIRAP), two ways to drive the dipole-forbidden transition between two
spin sublevels in the electronic triplet ground state of the NV center. This is
achieved by a multitone Raman microwave pulse which simultaneously drives two
detuned transitions via a virtual level for SRT or via two adiabatic and
partially overlapping resonant microwave pulses for STIRAP. We lay the
theoretical framework of SRT and STIRAP dynamics and verify experimentally the
theoretical predictions of population inversion by observing the
dipole-forbidden transition in the ground state of a single NV center. A
comparison of the two schemes showed a better robustness and success of the
spin swap for STIRAP as compared to SRT.",2103.13788v1
2021-04-08,Probing the interplay between lattice dynamics and short-range magnetic correlations in CuGeO3 with femtosecond RIXS,"Investigations of magnetically ordered phases on the femtosecond timescale
have provided significant insights into the influence of charge and lattice
degrees of freedom on the magnetic sub-system. However, short-range magnetic
correlations occurring in the absence of long-range order, for example in
spin-frustrated systems, are inaccessible to many ultrafast techniques. Here,
we show how time-resolved resonant inelastic X-ray scattering (trRIXS) is
capable of probing such short-ranged magnetic dynamics in a charge-transfer
insulator through the detection of a Zhang-Rice singlet exciton. Utilizing
trRIXS measurements at the O K-edge, and in combination with model
calculations, we probe the short-range spin-correlations in the frustrated spin
chain material CuGeO3 following photo-excitation, revealing a strong coupling
between the local lattice and spin sub-systems.",2104.03557v1
2021-05-01,Towards Kitaev Spin Liquid in 3d Transition Metal Compounds,"This paper reviews the current progress on searching the Kitaev spin liquid
state in 3d electron systems. Honeycomb cobaltates were recently proposed as
promising candidates to realize the Kitaev spin liquid state, due to the more
localized wave functions of 3d ions compared with that of 4d and 5d ions, and
also the easy tunability of the exchange Hamiltonian in favor of Kitaev
interaction. Several key parameters that have large impacts on the exchange
constants, such as the charge-transfer gap and the trigonal crystal field, are
identified and discussed. Specifically, tuning crystal field effect by means of
strain or pressure is emphasized as an efficient phase control method driving
the magnetically ordered cobaltates into the spin liquid state. Experimental
results suggesting the existence of strong Kitaev interactions in layered
honeycomb cobaltates are discussed. Finally, the future research directions are
briefly outlined.",2105.00168v3
2021-07-07,The Ponzano-Regge cylinder and Propagator for 3d quantum gravity,"We investigate the propagator of 3d quantum gravity, formulated as a discrete
topological path integral. We define it as the Ponzano-Regge amplitude of the
solid cylinder swept by a 2d disk evolving in time. Quantum states for a 2d
disk live in the tensor products of N spins, where N is the number of holonomy
insertions connecting to the disk boundary. We formulate the cylindric
amplitude in terms of a transfer matrix and identify its eigen-modes in terms
of spin recoupling. We show that the propagator distinguishes the subspaces
with different total spin and may select the vanishing total spin sector at
late time depending on the chosen cylinder boundary data. We discuss
applications to quantum circuits and the possibility of experimental
simulations of this 3d quantum gravity propagator.",2107.03264v2
2021-09-07,"Quasiparticle band structures, spontaneous polarization, and spin-splitting in noncentrosymmetric few-layer and bulk $γ$-GeSe","Group-IV monochalcogenides have attracted much attention due to their
potential of ferroelectric and multiferroic properties. Recently,
centrosymmetric gamma-phase GeSe in a double-layer honeycomb lattice has been
theoretically predicted, but the synthesized gamma-phase GeSe showed a
noncentrosymmetric atomic structure, leading to the possibility of
ferroelectricity and spin-splitting. Here, we study the quasiparticle band
structures, spontaneous polarization, and spin-splitting in noncentrosymmetric
gamma-GeSe using density functional theory and GW calculations. Our results
show that noncentrosymmetric few-layer and bulk gamma-GeSe have semiconducting
band structures with indirect band gaps, which depend almost linearly on the
reciprocal of the number of layers. Spontaneous polarization occurs due to a
small charge transfer between the layers, which increases with compressive
strain, and ferroelectric switching can be achieved by an interlayer
translation with a small energy barrier. Spin-splitting is found to be more
significant at the highest valence band than at the lowest conduction band. Our
results provide insights into the fundamental electronic properties of a
layered ferroelectric semiconductor applicable to devices with
ferroelectric/nonferroelectric junctions.",2109.03226v1
2021-10-19,"Ab initio Calculations in Atoms, Molecules, and Solids, Treating Spin-Orbit Coupling and Electron Interaction on Equal Footing","We incorporate explicit, non-perturbative treatment of spin-orbit coupling
into ab initio auxiliary-field quantum Monte Carlo (AFQMC) calculations. The
approach allows a general computational framework for molecular and bulk
systems in which materials specificity, electron correlation, and spin-orbit
coupling effects can be captured accurately and on equal footing, with
favorable computational scaling versus system size. We adopt relativistic
effective-core potentials which have been obtained by fitting to fully
relativistic data and which have demonstrated a high degree of reliability and
transferability in molecular systems. This results in a 2-component
spin-coupled Hamiltonian, which is then treated by generalizing the ab initio
AFQMC approach. We demonstrate the method by computing the electron affinity in
Pb, the bond dissociation energy in Br$_2$ and I$_2$, and solid Bi.",2110.10201v1
2022-03-02,Intrinsic spin-valley locking for conducting electrons in metal-semiconductor-metal lateral hetero-structures of $1H$-transition-metal dichalcogenides,"Lateral-hetero structures of atomic layered materials alter the electronic
properties of pristine crystals and provide a possibility to produce useful
monolayer materials. We reveal that metal-semiconductor-metal lateral-hetero
junctions of $1H$-transition-metal dichalcogenides intrinsically possess
conducting channels of electrons with spin-valley locking, e.g., gate
electrode. We theoretically investigate the electronic structure and transport
properties of the lateral-hetero junctions and show that the hetero-structure
produces conducting channels through the $K$ and $K'$ valleys in the
semiconducting transition-metal dichalcogenide and restricts the spin of the
conducting electrons in each valley due to the valley dependent charge transfer
effect. Moreover, the theoretical investigation shows that the hetero-junction
of WSe$_2$ realizes a high transmission probability for valley-spin locked
electrons even in a long semiconducting region. The hetero-junction also
provides a useful electronic transport property, a step-like I-V
characteristic.",2203.01377v1
2022-06-25,Orbital Angular Momenta and Geometric Phase Characteristics of Spin-polarized Components of a General Paraxial Beam-field,"We explore a subtle and fundamental nature of spin-orbit interaction (SOI) in
a general paraxial beam-field by mathematically characterizing the orbital
angular momentum (OAM) flux densities of the spin-polarized component fields
via Barnett's flux determination formalism. We show the application of our
formalism by considering the special case of a Brewster-reflected paraxial
beam, for which we explore specific details such as non-canonical vortex phase
structures and single-photon interpretation of the field function. The phases
of the spin-component fields are interpreted as geometric phases; and we devise
an experimental method of direct measurement of these phases by transferring
the spatial phase information to the polarization domain -- thus demonstrating
a classical analog von Neumann measurement. Our complete mathematical
characterization of SOI and its relevance to the direct measurement of
geometric phase can find potential application in future methods exploring OAM
and geometric phase characteristics in other general optical systems.",2206.12684v1
2022-08-09,Accurate thermochemistry of covalent and ionic solids from spin-component-scaled MP2,"We study the performance of spin-component-scaled second-order
M{\o}ller-Plesset perturbation theory (SCS-MP2) for the prediction of the
lattice constant, bulk modulus, and cohesive energy of 12 simple,
three-dimensional, covalent and ionic semiconductors and insulators. We find
that SCS-MP2 and the simpler scaled opposite-spin MP2 (SOS-MP2) yield
predictions that are significantly improved over the already good performance
of MP2. Specifically, when compared to experimental values with zero-point
vibrational corrections, SCS-MP2 (SOS-MP2) yields mean absolute errors of 0.015
(0.017) {\AA} for the lattice constant, 3.8 (3.7) GPa for the bulk modulus, and
0.06 (0.08) eV for the cohesive energy, which are smaller than those of leading
density functionals by about a factor of two or more. We consider a
reparameterization of the spin scaling parameters and find that the optimal
parameters for these solids are very similar to those already in common use in
molecular quantum chemistry, suggesting good transferability and reliable
future applications to surface chemistry on insulators.",2208.04865v1
2022-12-30,Local independence in mean-field spin glasses,"We present a new approach to local independence in spin glasses, i.e. the
phenomenon that any fixed subset of coordinates is asymptotically independent
in the thermodynamic limit. The approach generalizes the rigorous cavity method
from Talagrand by considering multiple cavity sites. Under replica-symmetric
conditions of thin-shell and overlap concentration, the cavity fields are
revealed to be asymptotically independent, conditionally on the disorder, which
in turn leads to local independence. Conversely, it is shown that local
independence implies those replica-symmetric properties. The framework is
general enough to encompass the classical and soft spin ($[-1,1]$)
Sherrington-Kirkpatrick models, as well as the Gardner spin glasses.",2212.14851v2
2023-01-26,Partial and complete qubit estimation using a single observable: optimization and quantum simulation,"Quantum state estimation is an important task of many quantum information
protocols. We consider two families of unitary evolution operators, one with a
one-parameter and the other with a two-parameter, which enable the estimation
of a single spin component and all spin components, respectively, of a
two-level quantum system. To evaluate the tomographic performance, we use the
quantum tomographic transfer function (qTTF), which is calculated as the
average over all pure states of the trace of the inverse of the Fisher
information matrix. Our goal is to optimize the qTTF for both estimation
models. We find that the minimum qTTF for the one-parameter model is achieved
when the entangling power of the corresponding unitary operator is at its
maximum. The models were implemented on an IBM quantum processing unit, and
while the estimation of a single-spin component was successful, the whole spin
estimation displayed relatively large errors due to the depth of the associated
circuit. To address this issue, we propose a new scalable circuit design that
improves qubit state tomography when run on an IBM quantum processing unit.",2301.11121v1
2023-05-04,Axial-vector charges of the spin $\frac{1}{2}^+$ and spin $\frac{3}{2}^+$ light and charmed baryons in the SU(4) chiral quark constituent model,"Following the first clear evidence of the presence of intrinsic charm
contribution in the proton, the axial-vector charges of the light and charmed
baryons are investigated in the framework of $SU(4)$ chiral constituent quark
model after including the explicit contributions from the $u\bar u $, $d\bar d
$, $s\bar s $ and $c\bar c $ fluctuations. The axial-vector charges having
physical significance correspond to the generators of the $SU(4)$ group with
flavor singlet $\lambda^0$, flavor isovector $\lambda^3$, flavor hypercharge
$\lambda^8$ and flavor charmed $\lambda^{15}$ combinations of axial-vector
current at zero momentum transfer. In contemplation to further understand the
$Q^2$ dependence of these charges, we have used the conventionally established
dipole form of parametrization. The baryons considered here are the spin
$\frac{1}{2}^+$ and spin $\frac{3}{2}^+$ multiplets decomposed further
depending on the charm content of baryons.",2305.02630v1
2023-06-20,Spinning primordial black holes formed during a matter-dominated era,"We study the formation of spinning primordial black holes during an early
matter-dominated era. Using non-linear 3+1D general relativistic simulations,
we compute the efficiency of mass and angular momentum transfer in the process
-- which we find to be $\mathcal{O}(10\%)$ and $\mathcal{O}(5\%)$,
respectively. We show that subsequent evolution is important due to the seed
PBH accreting non-rotating matter from the background, which decreases the
dimensionless spin. Unless the matter era is short, we argue that the final
dimensionless spin will be negligible.",2306.11810v2
2023-09-01,Spin-fluctuation glue disfavors high-critical temperature of superconductivity?,"Antiferromagnetic fluctuations are believed to be a promising glue to drive
high-temperature superconductivity especially in cuprates. Here, we perform a
close inspection of the superconducting mechanism from spin fluctuations in the
Eliashberg framework by employing a typical one-band model on a square lattice.
While spin fluctuations can eventually drive superconductivity as is well
established, we find that the superconducting tendency is suppressed
substantially by a seemingly negligible contribution from a small momentum
transfer far away from (pi,pi). This suppression comes from phase frustration
of the pairing gap and is expected to be a general feature due to the repulsive
pairing interaction of spin fluctuations. Furthermore, we find that the
momentum dependence of the pairing gap largely deviates from the functional
form of cos kx - cos ky, although this form is well established in cuprate
superconductors. We argue that an instantaneous magnetic interaction plays the
important role to understand high-critical temperature of superconductivity as
well as the momentum dependence of the pairing gap.",2309.00679v1
2023-12-18,Detecting Quantum Anomalies in Open Systems,"Symmetries and quantum anomalies serve as powerful tools for constraining
complicated quantum many-body systems, offering valuable insights into
low-energy characteristics based on their ultraviolet structure. Nevertheless,
their applicability has traditionally been confined to closed quantum systems,
rendering them largely unexplored for open quantum systems described by density
matrices. In this work, we introduce a novel and experimentally feasible
approach to detect quantum anomalies in open systems. Specifically, we claim
that, when coupled with an external environment, the mixed 't Hooft anomaly
between spin rotation symmetry and lattice translation symmetry gives
distinctive characteristics for half-integer and integer spin chains in
measurements of $\exp(\rm{i}\theta S^z_{\rm tot})$ as a function of $\theta$.
Notably, the half-integer spin chain manifests a topological phenomenon akin to
the ``level crossing"" observed in closed systems. To substantiate our
assertion, we develop a lattice-level spacetime rotation to analyze the
aforementioned measurements. Based on the matrix product density operator and
transfer matrix formalism, we analytically establish and numerically
demonstrate the unavoidable singular behavior of $\exp(\rm{i}\theta S^z_{\rm
tot})$ for half-integer spin chains. Conceptually, our work demonstrates a way
to discuss notions like ``spectral flow'' and ``flux threading'' in open
systems not necessarily with a Hamiltonian.",2312.11188v1
2024-01-30,Chirality-Induced Selectivity of Phonon Angular Momenta in Chiral Quartz Crystals,"A generation, propagation, and transfer of phonon angular momenta are
examined on thermal transport in chiral insulative and diamagnetic crystals of
$\alpha$-quartz. We found that thermally-driven phonons carry
chirality-dependent angular momenta in the quartz crystals and they could be
extracted from the quartz as a spin signal. Namely, chirality-induced
selectivity of phonon angular momenta is realized in the chiral quartz. We
argue that chiral phonons available in chiral materials could be a key element
in triggering or enhancing chirality-induced spin selectivity with robust spin
polarization and long-range spin transport found in various chiral materials.",2401.17158v1
2024-02-21,Time-reversal in a dipolar quantum many-body spin system,"Time reversal in a macroscopic system is contradicting daily experience. It
is practically impossible to restore a shattered cup to its original state by
just time reversing the microscopic dynamics that led to its breakage. Yet,
with the precise control capabilities provided by modern quantum technology,
the unitary evolution of a quantum system can be reversed in time. Here, we
implement a time-reversal protocol in a dipolar interacting, isolated many-body
spin system represented by Rydberg states in an atomic gas. By changing the
states encoding the spin, we flip the sign of the interaction Hamiltonian, and
demonstrate the reversal of the relaxation dynamics of the magnetization by
letting a demagnetized many-body state evolve back-in-time into a magnetized
state. We elucidate the role of atomic motion using the concept of a Loschmidt
echo. Finally, by combining the approach with Floquet engineering, we
demonstrate time reversal for a large family of spin models with different
symmetries. Our method of state transfer is applicable across a wide range of
quantum simulation platforms and has applications far beyond quantum many-body
physics, reaching from quantum-enhanced sensing to quantum information
scrambling.",2402.13873v1
2024-03-29,Quadratic optical response of CrSBr controlled by spin-selective interlayer coupling,"The optical properties of the layered magnet CrSBr are dominated by
intralayer excitons: the antiferromagnetic order between the layers makes
layer-to-layer charge hopping, and therefore interlayer excitons,
spin-forbidden. An external magnetic field, however, continuously drives the
magnetic order towards layer-to-layer ferromagnetic, which opens spin-allowed
charge-transfer channels between the layers. Here we elaborate how their
admixture changes the composition and nature of the excitons, leading to an
extension over many layers, and causes a quadratic red-shift with respect to
the external magnetic field. We address these effects by ab-initio $GW$-BSE
calculations as a function of magnetic field and cast the data into a minimal
four-band model to elucidate the interplay between the various interaction and
coupling mechanisms. Our findings should be generally valid for
antiferromagnetic layered magnets with and without external magnetic fields,
and moreover for any couple of layers with different spin directions. Our
insights help to systematically address excitons and predict their optical
signatures in such systems.",2403.20174v1
1995-01-31,MEASURING SPIRAL ARM TORQUES: RESULTS FOR M100,"Spiral arms, if they are massive, exert gravitational torques that transport
angular momentum radially within galactic disks. These torques depend not on
the pattern speed or permanence of the arms but only on the nonaxisymmetric
mass distribution. Hence the torques can be measured from photometry. We
demonstrate this using $gri$ CCD data for M100 (NGC 4321). Since we find
consistency among the three bands, we believe that dust and young stars in the
arms do not seriously bias our results. If the present epoch is representative,
the timescale for redistribution of angular momentum in M100 is $5-10$ Gyr, the
main uncertainty being the mass-to-light ratio of the disk.",9501112v1
2001-08-30,Instability of an accretion disk with a magnetically driven wind,"We present a linear analysis of the stability of accretion disks in which
angular momentum is removed by the magnetic torque exerted by a centrifugally
driven wind. The effects of the dependence of the wind torque on field strength
and inclination, the sub-Keplerian rotation due to magnetic forces, and the
compression of the disk by the field are included. A WKB dispersion relation is
derived for the stability problem. We find that the disk is always unstable if
the wind torque is strong. At lower wind torques instability also occurs
provided the rotation is close to Keplerian. The growth time scale of the
instability can be as short as the orbital time scale. The instability is
mainly the result of the sensitivity of the mass flux to changes in the
inclination of the field at the disk surface. Magnetic diffusion in the disk
stabilizes if the wind torque is small.",0108484v1
2002-11-11,The radiation properties of an accretion disk with a non-zero torque on its inner edge,"The structure of the inner edge of the accretion disk around a black hole can
be altered, if the matter inside the marginally stable orbit is magnetically
connected to the disk. In this case, a non-zero torque is exerted on its inner
edge, and the accretion efficiency $\epsilon$ can be much higher than that in
the standard accretion disk model. We explore the radiation properties of an
accretion disk at its sonic point around a black hole with a time-steady torque
exerted on the inner edge of the disk. The local structure of the accretion
flow at the sonic point is investigated in the frame of general relativity. It
is found that the accretion flow will be optically thin at its sonic point for
most cases, if the additional accretion efficiency $\delta\epsilon$ caused by
the torque is as high as $\sim$10 %. The results imply that the variable torque
may trigger transitions of the flow between different accretion types.",0211220v1
2002-11-14,Radiative Torques on Interstellar Grains. III. Dynamics with Thermal Relaxation,"In the previous papers in this series, we found that radiative torques can
play a major role in the alignment of grains with the interstellar magnetic
field. Since the radiative torques can drive the grains to suprathermal
rotational speeds, in previous work we made the simplifying assumption that the
grain principal axis of greatest moment of inertia is always parallel to the
grain angular momentum. This enabled us to describe many of the features of the
grain dynamics. However, this assumption fails when the grains enter periods of
thermal rotation, which occur naturally in the radiative torque alignment
scenario. In the present paper, we relax this assumption and explore the
consequences for the grain dynamics. We develop a treatment to follow the grain
dynamics including thermal fluctuations and ``thermal flipping'', and show
results for one illustrative example. By comparing with a treatment without
thermal fluctuations, we see that inclusion of thermal fluctuations can lead to
qualitative changes in the grain dynamics. In a future installment in this
series, we will use the more complete dynamical treatment developed here to
perform a systematic study of grain alignment by radiative torques.",0211342v1
2006-04-17,Angular Dependent Torque Measurements on CeCoIn$_5$ Single Crystals,"Angular dependent torque measurements were performed on single crystals of
CeCoIn$_5$, a heavy fermion superconductor ($T_{c0}$ = 2.3 K), in the
temperature, $T$, range 1.9 K $\leq T \leq $ 20 K and magnetic fields $H$ up to
14 T. A large paramagnetic effect is found in the normal state. Torque
measurements in the mixed state were also performed. The torque curves show
sharp hysteresis peaks at $\theta = 90^{o}$ ($\theta$ is the angle between $H$
and the $c-$axis of the crystal), a result of intrinsic pinning of vortices.
The anisotropy $\gamma \equiv \sqrt{m_{c}/m_{a}}$ in the mixed state was
determined from the reversible part of the vortex contribution to the torque
signal using Kogan's model [Phys. Rev. B \textbf{38}, 7049 (1988)]. The
anisotropy $\gamma$ decreases with increasing magnetic field and temperature.
The fact that $\gamma$ is not a constant points towards a multiband scenario in
this heavy fermion material.",0604399v1
2007-02-12,On the stress and torque tensors in fluid membranes,"We derive the membrane elastic stress and torque tensors using the standard
Helfrich model and a direct variational method in which the edges of a membrane
are infinitesimally translated and rotated. We give simple expressions of the
stress and torque tensors both in the local tangent frame and in projection
onto a fixed frame. We recover and extend the results of Capovilla and Guven
[J. Phys. A, 2002, \textbf{35}, 6233], which were obtained using covariant
geometry and Noether's theorem: we show that the Gaussian rigidity contributes
to the torque tensor and we include the effect of a surface potential in the
stress tensor. Many interesting situations may be investigated directly using
force and torque balances instead of full energy minimization. As examples, we
consider the force exerted at the end of a membrane tubule, membrane adhesion
and domain contact conditions.",0702279v1
2006-02-23,Orientation of optically trapped nonspherical birefringent particles,"While the alignment and rotation of microparticles in optical traps have
received increased attention recently, one of the earliest examples has been
almost totally neglected the alignment of particles relative to the beam axis,
as opposed to about the beam axis. However, since the alignment torques
determine how particles align in a trap, they are directly relevant to
practical applications. Lysozyme crystals are an ideal model system to study
factors determining the orientation of nonspherical birefringent particles in a
trap. Both their size and their aspect ratio can be controlled by the growth
parameters, and their regular shape makes computational modeling feasible. We
show that both external shape and internal birefringence anisotropy contribute
to the alignment torque. Three-dimensionally trapped elongated objects either
align with their long axis parallel or perpendicular to the beam axis depending
on their size. The shape-dependent torque can exceed the torque due to
birefringence, and can align negative uniaxial particles with their optic axis
parallel to the electric field, allowing an application of optical torque about
the beam axis.",0602156v1
2006-06-20,Trouton-Noble paradox revisited,"An apparent paradox is obtained in all previous treatments of the
Trouton-Noble experiment; there is a three-dimensional torque in an inertial
frame S in which a thin parallel-plate capacitor is moving, but there is no 3D
torque in S', the rest frame of the capacitor. In this paper instead of using
3D quantities and their ``apparent'' transformations we deal with 4D geometric
quantities their Lorentz transformations and equations with them. We introduce
a new decomposition of the torque N (bivector) into 1-vectors N_{s} and N_{t}.
It is shown that in the frame of ``fiducial'' observers, in which the observers
who measure N_{s} and N_{t} are at rest, and in the standard basis, only the
spatial components N_{s}^{i} and N_{t}^{i} remain, which can be associated with
components of two 3D torques. In such treatment with 4D geometric quantities
the mentioned paradox does not appear. The presented explanation is in a
complete agreement with the principle of relativity and with the Trouton-Noble
experiment without the introduction of any additional torque.",0606176v1
2007-10-10,A turbulent model of torque in von Karman swirling flow,"A stochastic model is derived to predict the turbulent torque produced by a
swirling flow. It is a simple Langevin process, with a colored noise. Using the
unified colored noise approximation, we derive analytically the PDF of the
fluctuations of injected power in two forcing regimes: constant angular
velocity or constant applied torque. In the limit of small velocity
fluctuations and vanishing inertia, we predict that the injected power
fluctuates twice less in the case of constant torque than in the case of
constant angular velocity forcing. The model is further tested against
experimental data in a von Karman device filled with water. It is shown to
allow for a parameter-free prediction of the PDF of power fluctuations in the
case where the forcing is made at constant torque. A physical interpretation of
our model is finally given, using a quasi-linear model of turbulence.",0710.1993v1
2008-10-29,Torque anomalies at magnetization plateaux in quantum magnets with Dzyaloshinskii-Moriya interactions,"We investigate the effect of Dzyaloshinskii-Moriya (DM) interactions on
torque measurements of quantum magnets with magnetization plateaux in the
context of a frustrated spin-1/2 ladder. Using extensive DMRG simulations, we
show that the DM contribution to the torque is peaked at the critical fields,
and that the total torque is non-monotonous if the DM interaction is large
enough compared to the g-tensor anisotropy. More remarkably, if the DM vectors
point in a principal direction of the g-tensor, torque measurements close to
this direction will show well defined peaks even for small DM interaction,
leading to a very sensitive way to detect the critical fields. We propose to
test this effect in the two-dimensional plateau system SrCu$_2$(BO$_3$)$_2$.",0810.5329v2
2010-08-03,Self-Similar Spherical Collapse with Tidal Torque,"N-body simulations have revealed a wealth of information about dark matter
halos however their results are largely empirical. Using analytic means, we
attempt to shed light on simulation results by generalizing the self-similar
secondary infall model to include tidal torque. In this first of two papers, we
describe our halo formation model and compare our results to empirical mass
profiles inspired by N-body simulations. Each halo is determined by four
parameters. One parameter sets the mass scale and the other three define how
particles within a mass shell are torqued throughout evolution. We choose
torque parameters motivated by tidal torque theory and N-body simulations and
analytically calculate the structure of the halo in different radial regimes.
We find that angular momentum plays an important role in determining the
density profile at small radii. For cosmological initial conditions, the
density profile on small scales is set by the time rate of change of the
angular momentum of particles as well as the halo mass. On intermediate scales,
however, $\rho\propto r^{-2}$, while $\rho\propto r^{-3}$ close to the virial
radius.",1008.0639v2
2010-10-01,Type I Migration in Radiatively Efficient Discs,"We study Type I migration of a planet in a radiatively efficient disk using
global two dimensional hydrodynamic simulations. The large positive corotation
torque is exerted on a planet by an adiabatic disk at early times when the disk
has the steep negative entropy gradient. The gas on the horseshoe orbit of the
planet is compressed adiabatically during the change of the orbit from the slow
orbit to the fast orbit, increasing its density and exerting the positive
torque on the planet. The planet would migrate outward in the adiabatic disk
before saturation sets in. We further study the effect of energy dissipation by
radiation on Type I migration of the planet. The corotation torque decreases
when the energy dissipates effectively because the density of the gas on the
horseshoe orbit does not increase by the compression compared with the gas of
the adiabatic disk. The total torque is mainly determined by the negative
Lindblad torque and becomes negative. The planet migrates inward toward the
central star in the radiatively efficient disk. The migration velocity is
dependent on the radiative efficiency and greatly reduced if the radiative
cooling works inefficiently.",1010.0176v1
2012-09-19,Planet-Disk interaction in 3D: the importance of buoyancy waves,"We carry out local three dimensional (3D) hydrodynamic simulations of
planet-disk interaction in stratified disks with varied thermodynamic
properties. We find that whenever the Brunt-Vaisala frequency (N) in the disk
is nonzero, the planet exerts a strong torque on the disk in the vicinity of
the planet, with a reduction in the traditional ""torque cutoff"". In particular,
this is true for adiabatic perturbations in disks with isothermal density
structure, as should be typical for centrally irradiated protoplanetary disks.
We identify this torque with buoyancy waves, which are excited (when N is
non-zero) close to the planet, within one disk scale height from its orbit.
These waves give rise to density perturbations with a characteristic 3D spatial
pattern which is in close agreement with the linear dispersion relation for
buoyancy waves. The torque due to these waves can amount to as much as several
tens of per cent of the total planetary torque, which is not expected based on
analytical calculations limited to axisymmetric or low-m modes. Buoyancy waves
should be ubiquitous around planets in the inner, dense regions of
protoplanetary disks, where they might possibly affect planet migration.",1209.4358v1
2012-10-11,DNA as a one-dimensional chiral material. II. Dynamics of the structural transition between B form and Z form,"We analyze the dynamics of structural transitions between normal right-handed
B form and unusual left-handed Z form for a linear DNA molecule. The dynamics
under the external torque in physiological buffer is modeled by a Langevin
equation, with the potential term given by the authors previously [Phys. Rev. E
84, 021926 (2011)]. With this model, we first simulate the relaxation processes
around B-form structure after sudden changes of the external torques, where
slow relaxation $\sim t^{-1/2}$ as a function of the elapsed time $t$ is
observed. Then, the dynamics of structural transition from Z form to B form is
computed under various external torque strength. For small external torques,
the transition proceeds via nucleation and the growth, while for higher
torques, Z-form structure becomes unstable, and the transition mechanism is
switched to a spinodal-like process. These numerical results are qualitatively
understood by simple phenomenological arguments.",1210.3155v1
2013-02-11,Convergence zones for Type I migration: an inward shift for multiple planet systems,"Earth-mass planets embedded in gaseous protoplanetary disks undergo Type I
orbital migration. In radiative disks an additional component of the corotation
torque scaling with the entropy gradient across the horseshoe region can
counteract the general inward migration, Type I migration can then be directed
either inward or outward depending on the local disk properties. Thus, special
locations exist in the disk toward which planets migrate in a convergent way.
  Here we present N-body simulations of the convergent migration of systems of
low-mass (M=1-10 m_earth) planets. We show that planets do not actually
converge in convergence zones. Rather, they become trapped in chains of mean
motion resonances (MMRs). This causes the planets' eccentricities to increase
to high enough values to affect the structure of the horseshoe region and
weaken the positive corotation torque. The zero-torque equilibrium point of the
resonant chain of planets is determined by the sum of the attenuated corotation
torques and unattenuated differential Lindblad torques acting on each planet.
  The effective convergence zone is shifted inward. Systems with several
planets can experience stochastic migration as a whole due to continuous
perturbations from planets entering and leaving resonances.",1302.2627v1
2013-05-28,Estimation of anthropometrical and inertial body parameters using double integration of residual torques and forces during squat jump,"The inertial (IP) and anthropometrical (AP) parameters of human body are
mostly estimated from coefficients issue from cadaver measurements. These
parameters could involve errors in the calculation of joint torques during
explosive movements. The purpose of this study was to optimize the IP and AP in
order to minimize the residual torque and force during squat jumping. Three
methods of determination have been presented: method A: optimizing AP and IP of
each body part, method B: optimizing trunk AP and IP, assuming that the AP and
IP of the lower limbs were known, method C: using Winter AP and IP. For each
method, the value (degree 0), the integral (degree 1) and the double integral
(degree 2) of the residual moment were also used. The method B with degree 2
was the most accurate to determine trunk AP and IP by minimizing of the
residual force and torque, by providing a linear least squares system. Instead
of minimizing the residual force and torque, by classical way, the double
integral of the latter provided more accurate results.",1305.6426v1
2014-08-22,The Effect of Dissipation on the Torque and Force Experienced by Nanoparticles in an AC Field,"We discuss the force and torque acting on spherical particles in an ensemble
in the presence of a uniform AC electric field. We show that for a torque
causing particle rotation to appear the particle must be absorptive. Our proof
includes all electromagnetic excitations, which in the case of two or more
particles gives rise to one or more resonances in the spectrum of force and
torque depending on interparticle distance. Several peaks are found in the
force and torque between two spheres at small interparticle distances, which
coalesce to just one as the separation grows beyond three particle radii. We
also show that in the presence of dissipation the force on each particle is non
conservative and may not be derived from the classical interaction potential
energy as has been done in the past.",1408.5408v1
2014-10-03,In Situ Calibration of Six-Axes Force Torque Sensors using Accelerometer Measurements,"This paper proposes techniques to calibrate six-axis force-torque sensors
that can be performed in situ, i.e., without removing the sensor from the
hosting system. We assume that the force-torque sensor is attached to a rigid
body equipped with an accelerometer. Then, the proposed calibration technique
uses the measurements of the accelerometer, but requires neither the knowledge
of the inertial parameters nor the orientation of the rigid body. The proposed
method exploits the geometry induced by the model between the raw measurements
of the sensor and the corresponding force-torque. The validation of the
approach is performed by calibrating two six-axis force-torque sensors of the
iCub humanoid robot.",1410.0885v2
2014-10-15,Acoustic interaction forces and torques acting on suspended spheres in an ideal fluid,"In this paper, the acoustic interaction forces and torques exerted by an
arbitrary time-harmonic wave on a set of N spheres suspended in an inviscid
fluid are theoretically analyzed. In so doing, we utilize the partial-wave
expansion method to solve the related multiple scattering problem. The acoustic
interaction force and torque are computed for a sphere using the farfield
radiation force and torque formulas. To exemplify the method, we calculate the
interaction forces exerted by an external traveling and standing plane wave on
an arrangement of two and three olive-oil droplets in water. The droplets radii
are comparable to the wavelength (i.e. Mie scattering regime). The results show
that the radiation force may considerably deviates from that exerted solely by
the external incident wave. In addition, we find that acoustic interaction
torques arise on the droplets when a nonsymmetric effective incident wave
interacts with the droplets.",1410.4162v1
2016-05-12,Fundamental Limits of Optical Force and Torque,"Optical force and torque provide unprecedented control on the spatial motion
of small particles. A valid scientific question, that has many practical
implications, concerns the existence of fundamental upper bounds for the
achievable force and torque exerted by a plane wave illumination with a given
intensity. Here, while studying isotropic particles, we show that different
light-matter interaction channels contribute to the exerted force and torque;
and analytically derive upper bounds for each of the contributions. Specific
examples for particles that achieve those upper bounds are provided. We study
how and to which extent different contributions can add up to result in the
maximum optical force and torque. Our insights are important for applications
ranging from molecular sorting, particle manipulation, nanorobotics up to
ambitious projects such as laser-propelled spaceships.",1605.03945v2
2017-07-05,Improved Selective Harmonic Elimination for Reducing Torque Harmonics of Induction Motors in Wide DC Bus Voltage Variations,"Conventionally, Selective Harmonic Elimination (SHE) method in 2-level
inverters, finds best switching angles to reach first voltage harmonic to
reference level and eliminate other harmonics, simultaneously. Considering
Induction Motor (IM) as the inverter load, and wide DC bus voltage variations,
the inverter must operate in both over-modulation and linear modulation region.
Main objective of the modified SHE is to reduce harmonic torques through
finding the best switching angles. In this paper, optimization is based on
optimizing phasor equations in which harmonic torques are calculated. The
procedure of this method is that, first, the ratio of the same torque harmonics
is estimated, secondly, by using that estimation, the ratio of voltage
harmonics that generates homogeneous torques is calculated. For the estimation
and the calculation of the ratios motor parameter, mechanical speed of the
rotor, the applied frequency, and the concept of slip are used. The advantage
of this approach is highlighted when mechanical load and DC bus voltage
variations are taken into consideration. Simulation results are presented under
a wide range of working conditions in an induction motor to demonstrate the
effectiveness of the proposed method.",1707.01777v1
2017-08-04,Implementation of Torque Controller for Brushless Motors on the Omni-directional Wheeled Mobile Robot,"The major issue for the wheeled mobile robot is the low level controller
gains tuning up especially in the robot competition. The floor surface can be
damaged by the robot wheels during the competition, therefore the surface
coefficient can be changed over time. PI gains have to be tuned before every
match along the competition. In this research, the torque controller is defined
and implemented in order to solve this problem. Torque controller consists of a
PI controller for the robot wheel's angular velocity and a dynamic equation of
brushless motor. The motor dynamics can be derived from the energy conservation
law. Three different carpets, which have the different friction coefficients,
are used in the experiments. The robot wheel's angular velocity profiles are
generated from the robot kinematics with different initial conditions. The
output paths of the robot with the torque controller are compared with the
output paths of the robot with regular PI controller when the same wheel
angular velocity profiles are applied. The results show that the torque
controller can provide a better robot path than the normal PI controller.",1708.02271v1
2018-06-11,Transmission of torque at the nanoscale,"In macroscopic mechanical devices torque is transmitted through gearwheels
and clutches. In the construction of devices at the nanoscale, torque and its
transmission through soft materials will be a key component. However, this
regime is dominated by thermal fluctuations leading to dissipation. Here we
demonstrate the principle of torque transmission for a disc-like colloidal
assembly exhibiting clutch-like behaviour, driven by $27$ particles in optical
traps. These are translated on a circular path to form a rotating boundary that
transmits torque to additional particles confined to the interior. We
investigate this transmission and find that it is determined by solid-like or
fluid-like behaviour of the device and a stick-slip mechanism reminiscent of
macroscopic gearwheels slipping. The transmission behaviour is predominantly
governed by the rotation rate of the boundary and the density of the confined
system. We determine the efficiency of our device and thus optimise conditions
to maximise power output.",1806.03984v1
2018-06-25,Computing the motor torque of Escherichia coli,"The rotary motor of bacteria is a natural nano-technological marvel that
enables cell locomotion by powering the rotation of semi-rigid helical
flagellar filaments in fluid environments. It is well known that the motor
operates essentially at constant torque in counter-clockwise direction but past
work have reported a large range of values of this torque. Focusing on
Escherichia coli cells that are swimming and cells that are stuck on a glass
surface for which all geometrical and environmental parameters are known
(Darnton et al., J. Bacteriology, 2007, 189, 1756-1764), we use two validated
numerical methods to compute the value of the motor torque consistent with
experiments. Specifically, we use (and compare) a numerical method based on the
boundary integral representation of Stokes flow and also develop a hybrid
method combining boundary element and slender body theory to model the cell
body and flagellar filament, respectively. Using measured rotation speed of the
motor, our computations predict a value of the motor torque in the range 440
pNnm to 829 pNnm, depending critically on the distance between the flagellar
filaments and the nearby surface.",1806.09694v1
2018-09-04,Opto Propeller Effect on Chiral Micro-Rotors,"Manipulating mega biomolecules and micro-devices with light is highly
appealing. Opto driving torque can propel micro-rotors to translational motion
in viscous liquid, and then separate microsystems according to their
handedness. We study the torque of dielectric loss generated by circular
polarized lasers. The unwanted axial force which causes the handedness
independent translational motion is cancelled by the counter propagating
reflection beams. The propelling efficiency and the friction torque of water
are obtained by solving the Navier-Stokes equation. In the interesting range of
parameters, the numerical friction torque is found to be linear in the angular
velocity with a slope depending on the radius or rotor as $r^3$. The
time-dependent distribution of angular velocity is obtained as a solution of
the Fokker-Planck equation, with which the thermal fluctuation is accounted.
The results shed light on the micro-torque measurement and suggest a
controllable micro-carrier.",1809.01032v1
2019-06-12,Identification of Motor Parameters on Coupled Joints,"The estimation of the motor torque and friction parameters are crucial for
implementing an efficient low level joint torque control. In a set of coupled
joints, the actuators torques are mapped to the output joint torques through a
coupling matrix, such that the motor torque and friction parameters appear
entangled from the point of view of the joints. As a result, their
identification is problematic when using the same methodology as for single
joints. This paper proposes an identification method with an improved accuracy
with respect to classical closed loop methods on coupled joints. The method
stands out through the following key points: it is a direct open loop
identification; it addresses separately each motor in the coupling; it accounts
for the static friction in the actuation elements. The identified parameters
should significantly improve the contribution of the feed-forward terms in the
low level control of coupled joints with static friction.",1906.05070v1
2019-12-03,Safe rendering of high impedance on a series-elastic actuator with disturbance observer-based torque control,"An important performance metric for series-elastic actuators is the range of
impedance which they can safely render. Advanced torque control, using
techniques such as the disturbance observer, improve torque tracking bandwidth
and accuracy, but their impact on safe impedance range is not established.
However, to define a safe impedance range requires a practical coupled
stability condition. Here, passivity-based conditions are proposed for two
variants of DOB torque control, and validated experimentally in a
high-stiffness environment. While high-gain PD torque control has been shown to
reduce Z-width, it is here shown that a DOB reduces the need for high-gain PD
feedback and allows a higher rendered impedance. A dynamic feedforward
compensator is proposed which increases the maximum safe impedance of the DOB,
validated in experimentally in collision with high-stiffness environments and
manual excitation.",1912.01355v1
2020-04-03,Pressure torque of torsional Alfvén modes acting on an ellipsoidal mantle,"We investigate the pressure torque between the fluid core and the solid
mantle arising from magnetohydrodynamic modes in a rapidly rotating planetary
core. A two-dimensional reduced model of the core fluid dynamics is developed
to account for the non-spherical core-mantle boundary. The simplification of
such a quasi-geostrophic model rests on the assumption of invariance of the
equatorial components of the fluid velocity along the rotation axis. We use
this model to investigate and quantify the axial torques of linear modes,
focusing on the torsional Alfv\'en modes (TM) in an ellipsoid. We verify that
the periods of these modes do not depend on the rotation frequency.
Furthermore, they possess angular momentum resulting in a net pressure torque
acting on the mantle. This torque scales linearly with the equatorial
ellipticity. We estimate that for the TM calculated here topographic coupling
to the mantle is too weak to account for the variations in the Earth's
length-of-day.",2004.01597v2
2020-04-27,Clustering via torque balance with mass and distance,"Grouping similar objects is a fundamental tool of scientific analysis,
ubiquitous in disciplines from biology and chemistry to astronomy and pattern
recognition. Inspired by the torque balance that exists in gravitational
interactions when galaxies merge, we propose a novel clustering method based on
two natural properties of the universe: mass and distance. The concept of
torque describing the interactions of mass and distance forms the basis of the
proposed parameter-free clustering algorithm, which harnesses torque balance to
recognize any cluster, regardless of shape, size, or density. The gravitational
interactions govern the merger process, while the concept of torque balance
reveals partitions that do not conform to the natural order for removal.
Experiments on benchmark data sets show the enormous versatility of the
proposed algorithm.",2004.13160v1
2020-05-12,Inertial torque on a small spheroid in a stationary uniform flow,"How anisotropic particles rotate and orient in a flow depends on the
hydrodynamic torque they experience. Here we compute the torque acting on a
small spheroid in a uniform flow by numerically solving the Navier-Stokes
equations. Particle shape is varied from oblate (aspect ratio $\lambda = 1/6$)
to prolate ($\lambda = 6$), and we consider low and moderate particle Reynolds
numbers (${\rm Re} \le 50$). We demonstrate that the angular dependence of the
torque, predicted theoretically for small particle Reynolds numbers remains
qualitatively correct for Reynolds numbers up to ${\rm Re} \sim 10$. The
amplitude of the torque, however, is smaller than the theoretical prediction,
the more so as ${\rm Re}$ increases. For Re larger than $10$, the flow past
oblate spheroids acquires a more complicated structure, resulting in systematic
deviations from the theoretical predictions. Overall, our numerical results
provide a justification of recent theories for the orientation statistics of
ice-crystals settling in a turbulent flow.",2005.05634v3
2020-07-06,Stokes flow due to point torques and sources in a spherical geometry,"Solutions to the Stokes equations written in terms of a small number of
hydrodynamic image singularities have been a useful tool in theoretical and
numerical computations for nearly fifty years. In this article, we extend the
catalogue of known solutions by deriving the flow expressions due to a general
point torque and point source in the presence of a stationary sphere with
either a no-slip or a stress-free (no shear) boundary condition. For an
axisymmetric point torque and a no-slip sphere the image system simplifies to a
single image point torque, reminiscent of the solution for a point charge
outside an equipotential sphere in electrostatics. By symmetry, this also gives
a simple representation of the solution due to an axisymmetric point torque
inside a rigid spherical shell. In all remaining cases, the solution can be
described by a collection of physically intuitive point and line singularities.
Our results will be useful for the theoretical modelling of the propulsion of
microswimmers and efficient numerical implementation of far-field hydrodynamic
interactions in this geometry.",2007.02897v1
2020-08-25,Electromagnetic radiation and the self torque of an oscillating magnetic dipole,"A uniformly-charged spherical shell of radius $R$, mass $m$, and total
electrical charge $q$, having an oscillatory angular velocity $\Omega(t)$
around a fixed axis, is a model for a magnetic dipole that radiates an
electromagnetic field into its surrounding free space at a fixed oscillation
frequency $\omega$. An exact solution of the Maxwell-Lorentz equations of
classical electrodynamics yields the self-torque of radiation resistance acting
on the spherical shell as a function of $R$, $q$, and $\omega$. Invoking the
Newtonian equation of motion for the shell, we relate its angular velocity
$\Omega(t)$ to an externally applied torque, and proceed to examine the
response of the magnetic dipole to an impulsive torque applied at a given
instant of time, say, $t=0$. The impulse response of the dipole is found to be
causal down to extremely small values of $R$ (i.e., as $R \to 0$) so long as
the exact expression of the self-torque is used in the dynamical equation of
motion of the spherical shell.",2008.11264v1
2020-12-07,Estimation of Gas Turbine Shaft Torque and Fuel Flow of a CODLAG Propulsion System Using Genetic Programming Algorithm,"In this paper, the publicly available dataset of condition based maintenance
of combined diesel-electric and gas (CODLAG) propulsion system for ships has
been utilized to obtain symbolic expressions which could estimate gas turbine
shaft torque and fuel flow using genetic programming (GP) algorithm. The entire
dataset consists of 11934 samples that was divided into training and testing
portions of dataset in an 80:20 ratio. The training dataset used to train the
GP algorithm to obtain symbolic expressions for gas turbine shaft torque and
fuel flow estimation consisted of 9548 samples. The best symbolic expressions
obtained for gas turbine shaft torque and fuel flow estimation were obtained
based on their $R^2$ score generated as a result of the application of the
testing portion of the dataset on the aforementioned symbolic expressions. The
testing portion of the dataset consisted of 2386 samples. The three best
symbolic expressions obtained for gas turbine shaft torque estimation generated
$R^2$ scores of 0.999201, 0.999296, and 0.999374, respectively. The three best
symbolic expressions obtained for fuel flow estimation generated $R^2$ scores
of 0.995495, 0.996465, and 0.996487, respectively.",2012.03527v1
2021-01-06,Collision-induced torque mediates transition of chiral dynamic patterns formed by active particles,"It is still challenging to control dynamic self-organization patterns of
self-propelled particles. Although varieties of patterns associated with
chirality have been observed, essential control factors determining patterns
remain unclear. Here, we explore numerically how torque upon particle collision
affects dynamic self-organization. Based on the particle-based model with both
collision-induced torque and torque in self-propulsion, we find that
introducing collision-induced torque turns homogeneous bi-polar orientation
templated by bi-directional alignment into rotating mono-polar flocks.",2101.02130v3
2021-02-04,Equivalence between angular spectrum-based and multipole expansion-based formulas of the acoustic radiation force and torque,"Two main methods have been proposed to derive the acoustical radiation force
and torque applied by an arbitrary acoustic field on a particle: The first one
relies on the plane wave angular spectrum decomposition of the incident field
(see [Sapozhnikov and Bailey, J. Acoust. Soc. Am. 133, 661 (2013)] for the
force and [Gong and Baudoin, J. Acoust. Soc. Am. 148, 3131 (2020)] for the
torque), while the second one relies on the decomposition of the incident field
into a sum of spherical waves, the so-called multipole expansion (see [Silva,
J. Acoust. Soc. Am. 130, 3541 (2011)] and [Baresh et al., J. Acoust. Soc. Am.
133, 25 (2013)] for the force, and [Silva et al., EPL 97, 54003 (2012)] and
[Gong et al., Phys. Rev. Applied 11, 064022 (2019)] for the torque). In this
paper, we formally establish the equivalence between the expressions obtained
with these two methods for both the force and torque.",2102.02678v1
2021-04-22,Nonlinear Statistical Mechanics Drives Intrinsic Electrostriction and Volumetric Torque in Polymer Networks,"Statistical mechanics is an important tool for understanding polymer
electroelasticity because the elasticity of polymers is primarily due to
entropy. However, a common approach for the statistical mechanics of polymer
chains, the Gaussian chain approximation, misses key physics. By considering
the nonlinearities of the problem, we show a strong coupling between the
deformation of a polymer chain and its dielectric response; that is, its net
dipole. When chains with this coupling are cross-linked in an elastomer network
and an electric field is applied, the field breaks the symmetry of the
elastomer's elastic properties, and, combined with electrostatic torque and
incompressibility, leads to intrinsic electrostriction. Conversely, deformation
can break the symmetry of the dielectric response leading to volumetric torque
(i.e., a couple stress or torque per unit volume) and asymmetric actuation.
Both phenomena have important implications for designing high-efficiency soft
actuators and soft electroactive materials; and the presence of mechanisms for
volumetric torque, in particular, can be used to develop higher degree of
freedom actuators and to achieve bioinspired locomotion.",2104.11278v2
2021-06-03,Rotor Thermal Monitoring Scheme for Direct-Torque-Controlled Interior Permanent Magnet Synchronous Machines via High-Frequency Rotating Flux or Torque Injection,"Interior permanent magnet synchronous machine drives are widely employed in
electric traction systems and various industrial processes. However, prolonged
exposure to high temperatures while operating can demagnetize the permanent
magnets to the point of irreversible demagnetization. In addition, direct
measurements with infrared sensors or contact-type sensors with wireless
communication can be expensive and intrusive to the motor drive systems. This
paper thus proposes a nonintrusive thermal monitoring scheme for the permanent
magnets inside the direct-torque-controlled interior permanent magnet
synchronous machines. By applying an external high-frequency rotating flux or
torque signal to the hysteresis torque controller in the motor drive, the
high-frequency currents can be injected into the stator windings. The permanent
magnet temperature can thus be monitored based on the induced high-frequency
resistance. The nonintrusive nature of the method is indicated by the
elimination of the extra sensors and no hardware change to the existing system.
Finally, the effectiveness of the proposed method is validated with
experimental results.",2106.02116v3
2021-09-23,Energy Efficient Control of Electric Motors,"This paper presents development of an optimal feedback linearization control
(OFLC) for interior permanent magnet (PM) synchronous machines operating in a
non steady-sate operating point, i.e., varying torque and speed, to achieve
precision tracking performance and energy saving by minimizing the copper loss.
An isomorphism mapping between the dq-axes phase voltages and two auxiliary
control inputs over full ranges of torque and speed is established by the
linearization controller using the notion of orthogonal projection. The
auxiliary control inputs are defined to be exclusively responsible for torque
generation and power consumption. Subsequently, an analytical solution for the
optimal-linearization control is derived in a closed-form by applying the
Hamiltonian of optimal control theory in conjunction with the Pontryagin's
minimum principle. The optimal controller takes the maximum voltage limit and
torque tracking constraint into account while maximizing machine efficiency for
non-constant operational load torque and speed. Unlike the convectional
quadratic regulator-based control of electric motors, the proposed control
approach does not rely on steady-state operation conditions and hence it is
suitable for such applications as electric vehicles and robotics.",2109.11113v1
2021-12-06,Engineering of Intrinsic Chiral Torques in Magnetic Thin Films Based on the Dzyaloshinskii-Moriya Interaction,"The establishment of chiral coupling in thin magnetic films with
inhomogeneous anisotropy has led to the development of artificial systems of
fundamental and technological interest. The chiral coupling itself is enabled
by the Dzyaloshinskii-Moriya interaction (DMI) enforced by the patterned
noncollinear magnetization. Here, we create a domain wall track with
out-of-plane magnetization coupled on each side to a narrow parallel strip with
in-plane magnetization. With this we show that the chiral torques emerging from
the DMI at the boundary between the regions of noncollinear magnetization in a
single magnetic layer can be used to bias the domain wall velocity. To tune the
chiral torques, the design of the magnetic racetracks can be modified by
varying the width of the tracks or the width of the transition region between
noncollinear magnetizations, reaching effective chiral magnetic fields of up to
7.8 mT. Furthermore, we show how the magnitude of the chiral torques can be
estimated by measuring asymmetric domain wall velocities, and demonstrate
spontaneous domain wall motion propelled by intrinsic torques even in the
absence of any external driving force.",2112.03017v1
2022-03-08,Optical force and torque on small particles induced by polarization singularities,"Optical forces in the near fields have important applications in on-chip
optical manipulations of small particles and molecules. Here, we report a study
of optical force and torque on small particles induced by the optical
polarization singularities of a gold cylinder. We show that the scattering of
the cylinder generates both electric and magnetic C lines (i.e., lines of
polarization singularities) in the near fields, and the C lines can induce
complex force and torque on a dielectric/magnetic particle. The force and
torque manifest dramatic spatial variations with interesting symmetry
properties, providing rich degrees of freedom for near-field optical
manipulations. The study, for the first time to our knowledge, uncovers the
effect of optical polarization singularities on light-induced force and torque
on small particles. The results contribute to the understanding of chiral
light-matter interactions and can find applications in on-chip optical
manipulations and optical sensing.",2203.04175v1
2023-09-08,Proprioceptive External Torque Learning for Floating Base Robot and its Applications to Humanoid Locomotion,"The estimation of external joint torque and contact wrench is essential for
achieving stable locomotion of humanoids and safety-oriented robots. Although
the contact wrench on the foot of humanoids can be measured using a
force-torque sensor (FTS), FTS increases the cost, inertia, complexity, and
failure possibility of the system. This paper introduces a method for learning
external joint torque solely using proprioceptive sensors (encoders and IMUs)
for a floating base robot. For learning, the GRU network is used and random
walking data is collected. Real robot experiments demonstrate that the network
can estimate the external torque and contact wrench with significantly smaller
errors compared to the model-based method, momentum observer (MOB) with
friction modeling. The study also validates that the estimated contact wrench
can be utilized for zero moment point (ZMP) feedback control, enabling stable
walking. Moreover, even when the robot's feet and the inertia of the upper body
are changed, the trained network shows consistent performance with a
model-based calibration. This result demonstrates the possibility of removing
FTS on the robot, which reduces the disadvantages of hardware sensors. The
summary video is available at https://youtu.be/gT1D4tOiKpo.",2309.04138v1
2024-02-28,Direct measure of DNA bending by quantum magnetic imaging of a nano-mechanical torque-balance,"DNA flexibility is a key determinant of biological function, from nucleosome
positioning to transcriptional regulation, motivating a direct measurement of
the bend-torque response of individual DNA molecules. In this work, DNA bending
is detected using a nano-mechanical torque balance formed by tethering a
ferromagnetic nanoparticle probe by an individual DNA molecule to a diamond
magnetic field imager. The torque exerted by the DNA in response to bending
caused by an applied magnetic torque is measured using wide-field imaging of
quantum defects near the surface of the diamond. Qualitative measurements of
differences in DNA bio-mechanical binding configuration are demonstrated, and
as a proof-of-principle, a quantitative measurement of the bend response is
made for individual DNA molecules. This quantum-enabled measurement approach
could be applied to characterize the bend response of biophysically relevant
short DNA molecules as well as the sequence dependence of DNA bending energy.",2402.17964v1
2024-03-11,Human-Exoskeleton Interaction Portrait,"Human-robot physical interaction contains crucial information for optimizing
user experience, enhancing robot performance, and objectively assessing user
adaptation. This study introduces a new method to evaluate human-robot
co-adaptation in lower limb exoskeletons by analyzing muscle activity and
interaction torque as a two-dimensional random variable. We introduce the
Interaction Portrait (IP), which visualizes this variable's distribution in
polar coordinates. We applied this metric to compare a recent torque controller
(HTC) based on kinematic state feedback and a novel feedforward controller
(AMTC) with online learning, proposed herein, against a time-based controller
(TBC) during treadmill walking at varying speeds. Compared to TBC, both HTC and
AMTC significantly lower users' normalized oxygen uptake, suggesting enhanced
user-exoskeleton coordination. IP analysis reveals this improvement stems from
two distinct co-adaptation strategies, unidentifiable by traditional muscle
activity or interaction torque analyses alone. HTC encourages users to yield
control to the exoskeleton, decreasing muscular effort but increasing
interaction torque, as the exoskeleton compensates for user dynamics.
Conversely, AMTC promotes user engagement through increased muscular effort and
reduced interaction torques, aligning it more closely with rehabilitation and
gait training applications. IP phase evolution provides insight into each
user's interaction strategy development, showcasing IP analysis's potential in
comparing and designing novel controllers to optimize human-robot interaction
in wearable robots.",2403.06851v1
2006-03-29,Unipolar Inductor Model coupled to GW emission: energy budget and model application to RX J0806+15 and RX J1914+24,"We further discuss the Unipolar Inductor Model (UIM) coupled to GW emission
(Dall'Osso et al. 2005) and compare it to observed properties of the two
candidate ultrashort period binaries RX J0806+15 and RX J1914+24 . We consider
the measured orbital periods, period derivatives and inferred X-ray
luminosities of these two sources and find constraints on system parameters in
order for the model to account for them. We find that these properties point to
the two sources being in different regimes of the UIM, with the requirement of
low magnetic moment primaries ($\sim 10^{30} G cm^3$) for both. Given this weak
magnetization, RX J0806+15 has a sufficiently low luminosity that it can be
interpreted as having a primary spin almost synchronous to and just slightly
slower than the orbital motion. Its measured orbital spin-up is only slightly
affected by spin-orbit coupling and is mostly due to GW emission. RX J1914+24,
on the other hand, is too bright in X-rays and has too slow an orbital spin-up
for the same regime to apply. We suggest that this binary system may be
emitting GWs at a significantly higher rate than implied by its measured
$\dot{\omega}_o = 6 \times 10^{-17} rad s^{-2}$. The latter is explained, in
this framework, by the primary spin being slightly faster than the orbital
motion ($\alpha <or= 1.1$). In this case, the associated spin-orbit coupling
transfers to the orbit a significant amount of angular momentum, thus partially
balancing that lost to GW emission. All expectations can be tested in the near
future to confirm the viability of the model.",0603795v1
2007-02-02,Newborn Magnetars as sources of Gravitational Radiation: constraints from High Energy observations of Magnetar Candidates,"Soft Gamma Repeaters and the Anomalous X-ray Pulsars are believed to contain
slowly spinning ""magnetars"". The enormous energy liberated in the 2004 Dece 27
giant flare from SGR 1806-20, together with the likely recurrence time of such
events, points to an internal magnetic field strength ~ 10^{16} G. Such strong
fields are expected to be generated by a coherent alpha-Omega dynamo in the
early seconds after the Neutron Star formation, if its spin period is of a few
milliseconds at most. A substantial deformation of the NS is caused by such
fields and a newborn millisecond-spinning magnetar would thus radiate for a few
days a strong gravitational wave signal. Such a signal may be detected with
Advanced LIGO-class detectors up to the distance of the Virgo cluster, where ~
1 magnetar per year are expected to form. Recent X-ray observations reveal that
SNRs around magnetar candidates do not show evidence for a larger energy
content than standard SNRs (Vink & Kuiper 2006). This is at variance with what
would be expected if the spin energy of the young, millisecond NS were radiated
away as electromagnetic radiation andd/or relativistic particle winds and,
thus, transferred quickly to the expanding gas shell. We show here that these
recent findings can be reconciled with the idea of magnetars being formed with
fast spins, if most of their initial spin energy is radiated thorugh GWs. In
particular, we find that this occurs for essentially the same parameter range
that would make such objects detectable by Advanced LIGO-class detectors up to
the Virgo Cluster.",0702075v1
2004-04-20,Spin Susceptibility of Ga-Stabilized delta-Pu Probed by {69}^Ga NMR,"Spin susceptibility of stabilized \delta phase in the Pu-Ga alloy is studied
by measuring {69,71}^Ga NMR spectra and nuclear spin-lattice relaxation rate
{69}T_{1}^{-1} in the temperature range 5 - 350 K. The shift ({69}^K) of the
{69,71}^Ga NMR line and {69}^T_{1}^{-1} are controlled correspondingly by the
static and the fluctuating in time parts of local magnetic field arisen at
nonmagnetic gallium due to transferred hyperfine coupling with the nearest f
electron environment of the more magnetic Pu. The nonmonotonic with a maximum
around 150 K behavior of {69}^K(T) \chi_{s,5f}(T) is attributed to the
peculiarities in temperature dependence of the f electron spin susceptibility
\chi_{s,5f}(T) in \delta phase of plutonium. The temperature reversibility
being observed in {69}^K(T) data provides strong evidence for an electronic
instability developed with T in f electron bands near the Fermi energy and
accompanied with a pseudogap-like decrease of \chi_{s,5f}(T) at T<150 K. The
NMR data at high temperature are in favor of the mainly localized character of
5f electrons in \delta phase of the alloy with characteristic spin-fluctuation
energy \Gamma(T) T^{0.35(5)}, which is close to $\Gamma(T) T^{0.5} predicted by
Cox et al. [J. Appl. Phys. 57, 3166 (1985)] for 3D Kondo-system above T_Kondo}.
The dynamic spin correlations of 5f electrons become essential to consider for
{69}^T_{1}^{-1}(T) only at T<100 K. However, no NMR evidences favoring
formation of the static magnetic order in \delta-Pu were revealed down to 5K .",0404460v1
2004-09-20,Spontaneous symmetry breaking and response functions,"We study the quantum phase transition occurring in an infinite homogeneous
system of spin 1/2 fermions in a non-relativistic context. As an example we
consider neutrons interacting through a simple spin-spin Heisenberg force. The
two critical values of the coupling strength -- signaling the onset into the
system of a finite magnetization and of the total magnetization, respectively
-- are found and their dependence upon the range of the interaction is
explored. The spin response function of the system in the region where the
spin-rotational symmetry is spontaneously broken is also studied. For a
ferromagnetic interaction the spin response along the direction of the
spontaneous magnetization occurs in the particle-hole continuum and displays,
for not too large momentum transfers, two distinct peaks. The response along
the direction orthogonal to the spontaneous magnetization displays instead,
beyond a softened and depleted particle-hole continuum, a collective mode to be
identified with a Goldstone boson of type II. Notably, the random phase
approximation on a Hartree-Fock basis accounts for it, in particular for its
quadratic -- close to the origin -- dispersion relation. It is shown that the
Goldstone boson contributes to the saturation of the energy-weighted sum rule
for ~25% when the system becomes fully magnetized (that is in correspondence of
the upper critical value of the interaction strength) and continues to grow as
the interaction strength increases.",0409039v1
2004-09-27,Quantum information processing by NMR using a 5-qubit system formed by dipolar coupled spins in an oriented molecule,"Quantum Information processing by NMR with small number of qubits is well
established. Scaling to higher number of qubits is hindered by two major
requirements (i) mutual coupling among qubits and (ii) qubit addressability. It
has been demonstrated that mutual coupling can be increased by using residual
dipolar couplings among spins by orienting the spin system in a liquid
crystalline matrix. In such a case, the heteronuclear spins are weakly coupled
but the homonuclear spins become strongly coupled. In such circumstances, the
strongly coupled spins can no longer be treated as qubits. However, it has been
demonstrated elsewhere, that the $2^N$ energy levels of a strongly coupled N
spin-1/2 system can be treated as an N-qubit system. For this purpose the
various transitions have to be identified to well defined energy levels. This
paper consists of two parts. In the first part, the energy level diagram of a
heteronuclear 5-spin system is obtained by using a newly developed
heteronuclear z-cosy (HET-Z-COSY) experiment. In the second part,
implementation of logic gates, preparation of pseudopure states, creation of
entanglement and entanglement transfer is demonstrated, validating the use of
such systems for quantum information processing.",0409186v1
2007-06-08,Measuring the spin polarization and Zeeman energy of a spin-polarized electron gas: Comparison between Raman scattering and photoluminescence,"We compare resonant electronic Raman scattering and photoluminescence
measurements for the characterization of a spin-polarized two-dimensional
electron gas embedded in $\text{Cd}_{1-x}\text{Mn}_x\text{Te}$ single quantum
wells. From Raman scattering by single-particle excitations in a zero magnetic
field, we measure the Fermi velocity and then obtain the Fermi energy (as well
as the electron density), which is comparable to that extracted from
photoluminescence for moderate electron densities, assuming a bare band-edge
mass. At large electron densities, the Fermi energies derived from Raman
scattering and photoluminescence differ. For an applied in-plane magnetic field
and zero wave vector transferred to the electron gas, Raman scattering spectra
show peaks at both the Zeeman energy $Z$, resulting from collective excitations
of the spin-polarized electron gas, and the one electron spin-flip energy
$Z^*$. Magneto-photoluminescence spectra show conduction band splitting that
are equivalent to $Z$, suggesting that collective effects are present in the
photoluminescence spectra. Assuming (as before) an uncorrected mass, the degree
of spin polarization $\zeta$ determined from the magneto-photoluminescence
lineshape is found to differ from that derived from the magnetic field
dependent Raman scattering measurements for large electron densities. We
attribute the discrepancy in measuring $\zeta$ and the Fermi energy to the
renormalized mass resulting from many-body electron-electron interactions.",0706.1255v1
2008-12-11,Classical spin systems and the quantum stabilizer formalism: general mappings and applications,"We present general mappings between classical spin systems and quantum
physics. More precisely, we show how to express partition functions and
correlation functions of arbitrary classical spin models as inner products
between quantum stabilizer states and product states, thereby generalizing
mappings for some specific models established in [Phys. Rev. Lett. 98, 117207
(2007)]. For Ising- and Potts-type models with and without external magnetic
field, we show how the entanglement features of the corresponding stabilizer
states are related to the interaction pattern of the classical model, while the
choice of product states encodes the details of interaction. These mappings
establish a link between the fields of classical statistical mechanics and
quantum information theory, which we utilize to transfer techniques and methods
developed in one field to gain insight into the other. For example, we use
quantum information techniques to recover well known duality relations and
local symmetries of classical models in a simple way, and provide new classical
simulation methods to simulate certain types of classical spin models. We show
that in this way all inhomogeneous models of q-dimensional spins with pairwise
interaction pattern specified by a graph of bounded tree-width can be simulated
efficiently. Finally, we show relations between classical spin models and
measurement-based quantum computation.",0812.2127v2
2009-03-10,Interfacing nuclear spins in quantum dots to cavity or traveling-wave fields,"We show how to realize a quantum interface between optical fields and the
polarized nuclear spins in a singly charged quantum dot, which is strongly
coupled to a high-finesse optical cavity. An effective direct coupling between
cavity and nuclear spins is obtained by adiabatically eliminating the (far
detuned) excitonic and electronic states. The requirements needed to map qubit
and continuous variable states of cavity or traveling-wave fields to the
collective nuclear spin are investigated: For cavity fields, we consider
adiabatic passage processes to transfer the states. It is seen that a
significant improvement in cavity lifetimes beyond present-day technology would
be required for a quantum interface. We then turn to a scheme which couples the
nuclei to the output field of the cavity and can tolerate significantly shorter
cavity lifetimes. We show that the lifetimes reported in the literature and the
recently achieved nuclear polarization of ~90% allow both high-fidelity
read-out and write-in of quantum information between the nuclear spins and the
output field. We discuss the performance of the scheme and provide a convenient
description of the dipolar dynamics of the nuclei for highly polarized spins,
demonstrating that this process does not affect the performance of our
protocol.",0903.1727v2
2009-11-03,Two-step stabilization of orbital order and the dynamical frustration of spin in the model charge-transfer insulator KCuF3,"We report a combined experimental and theoretical study of KCuF3, which
offers - because of this material's relatively simple lattice structure and
valence configuration (d9, i.e., one hole in the d-shell) - a particularly
clear view of the essential role of the orbital degree of freedom in governing
the dynamical coupling between the spin and lattice degrees of freedom. We
present Raman and x-ray scattering evidence that the phase behaviour of KCuF3
is dominated above the Neel temperature (T_N = 40 K) by coupled orbital/lattice
fluctuations that are likely associated with rotations of the CuF6 octahedra,
and we show that these orbital fluctuations are interrupted by a static
structural distortion that occurs just above T_N. A detailed model of the
orbital and magnetic phases of KCuF3 reveals that these orbital fluctuations -
and the related frustration of in-plane spin-order-are associated with the
presence of nearly degenerate low-energy spin-orbital states that are highly
susceptible to thermal fluctuations over a wide range of temperatures. A
striking implication of these results is that the ground state of KCuF3 at
ambient pressure lies near a quantum critical point associated with an
orbital/spin liquid phase that is obscured by emergent Neel ordering of the
spins; this exotic liquid phase might be accessible via pressure studies.",0911.0619v1
2010-07-29,Looking into the inner black hole accretion disc with relativistic models of iron line,"We discuss black hole spin measurements employing the relativistic iron line
profiles in the X-ray domain. We investigate the iron line band for two
representative sources -- MCG -6-30-15 (active galaxy) and GX 339-4 (X-ray
binary). We compare two models of the broad iron line, LAOR and KYRLINE. We
realise that the spin is currently determined entirely from the position of the
marginally stable orbit while the effect of the spin on the overall line shape
would be resolvable with higher resolution X-ray missions. We show that the
precision of the spin measurements depends on an unknown angular distribution
of the disc emission. We study how sensitive the spin determination is to the
assumptions about the intrinsic angular distribution of the emitted photons. We
find that the uncertainty of the directional emission distribution translates
to 20% uncertainty in the determination of the radius of marginally stable
orbit. We perform radiation transfer computations of an X-ray irradiated disc
atmosphere (NOAR code) to determine the directionality of outgoing X-rays in
the 2-10 keV energy band. Based on these computations, we find that from the
simple formulae for the directionality, the isotropic case reproduces the
simulated data with the best accuracy. The most frequently used limb-darkening
law favours higher values of spin and, in addition, a steeper radial emissivity
profile. Furthermore, we present a spectral analysis of an XMM-Newton
observation of a Seyfert 1.5 galaxy IRAS 05078+1626 being the first X-ray
spectroscopic study of this source. The lack of the significant relativistic
blurring of the reflection model component suggests the accretion disc to be
truncated at a farther radius.",1007.5196v2
2012-06-28,Ferrimagnetic spin-1/2 chain of alternating Ising and Heisenberg spins in arbitrarily oriented magnetic field,"The ferrimagnetic spin-1/2 chain composed of alternating Ising and Heisenberg
spins in an arbitrarily oriented magnetic field is exactly solved using the
spin-rotation transformation and the transfer-matrix method. It is shown that
the low-temperature magnetization process depends basically on a spatial
orientation of the magnetic field. A sharp stepwise magnetization curve with a
marked intermediate plateau, which emerges for the magnetic field applied along
the easy-axis direction of the Ising spins, becomes smoother and the
intermediate plateau shrinks if the external field is tilted from the easy-axis
direction. The magnetization curve of a polycrystalline system is also
calculated by performing powder averaging of the derived magnetization formula.
The proposed spin-chain model brings an insight into high-field magnetization
data of 3d-4f bimetallic polymeric compound Dy(NO_3)(DMSO)_2Cu(opba)(DMSO)_2,
which provides an interesting experimental realization of the ferrimagnetic
chain composed of two different but regularly alternating spin-1/2 magnetic
ions Dy^{3+} and Cu^{2+} that are reasonably approximated by the notion of
Ising and Heisenberg spins, respectively.",1206.6656v2
2012-09-06,One dimensional Potts model with many-body interactions and the Generalized Model of Polypeptide Chain for the helix-coil transition,"Helix-coil transition in polypeptides is an example of a spin model with a
preferred spin direction, in the sense that a theoretical formulation of this
problem requires to assign a preferred value of spin to the helical
conformation in order to account for different symmetries of the helical {\sl
vs.} the coil states. This leads to the spin Hamiltonian of the {\sl
Generalized Model of Polypeptide Chain} (GMPC) variety as opposed to the Potts
model variety, both with many-body interactions. We compare the explicit
solution of the Potts model and the solution of the GMPC within the
transfer-matrix formalism. Comparison of both secular equations reveals that
the largest eigenvalue of the Potts model with $\Delta$ many-body interactions
is identical to the largest eigenvalue of the GMPC model with $\Delta-1$
many-body interactions, indicating the equivalence of both free energies. In
distinction, the second largest eigenvalues do not coincide, leading to
different thermal behavior of the spatial correlation length, related to the
helix-coil transition interval. Spin models with built-in spin anisotropy thus
engender different physical properties in the thermodynamic limit that we
explore in detail.",1209.1281v1
2012-11-08,Interplay between spin frustration and thermal entanglement in the exactly solved Ising-Heisenberg tetrahedral chain,"The spin-1/2 Ising-Heisenberg tetrahedral chain is exactly solved using its
local gauge symmetry, which enables one to establish a rigorous mapping with
the corresponding chain of composite Ising spins tractable within the
transfer-matrix approach. Exact results derived for spin-spin correlation
functions are employed to obtain the frustration temperature, at which a
product of correlation functions along an elementary triangular plaquette
becomes negative and the relevant spins experience a spin frustration. In
addition, we have exactly calculated a concurrence quantifying thermal
entanglement along with a threshold temperature, above which concurrence as a
measure of thermal entanglement vanishes. It is shown that the frustration and
threshold temperature coincide at sufficiently low temperatures, while they
exhibit a very different behavior in the high-temperature region when tending
towards completely different asymptotic limits. The threshold temperature
additionally shows a notable reentrant behavior when it extends over a narrow
temperature region above the classical ground state without any quantum
correlations. It is demonstrated that the specific heat may display temperature
dependence with or without an anomalous low-temperature peak for a relatively
strong or weak Heisenberg interaction, respectively.",1211.1810v2
2015-01-13,Room-Temperature in situ Nuclear Spin Hyperpolarization from Optically-Pumped Nitrogen Vacancy Centers in Diamond,"We report bulk, room-temperature hyperpolarization of 13C nuclear spins
observed via high-field nuclear magnetic resonance (NMR). The hyperpolarization
is achieved by optical pumping (OP) of nitrogen vacancy defect centers in
diamond accompanied by dynamic nuclear polarization (DNP). The technique
harnesses the large optically-induced spin polarization of NV- centers at room
temperature, which is many orders of magnitude greater than thermal equilibrium
polarization and typically achievable only at sub-Kelvin temperatures. Transfer
of the spin polarization to the 13C nuclear spins is accomplished via a
combination of OP and microwave irradiation. The OP/DNP is performed at 420 mT,
where inductive detection of NMR is feasible, in contrast to the typically
exploited level anticrossing regimes at 100 mT and 50 mT. Here, we report a
bulk nuclear spin polarization of 6%. This polarization was generated in situ
and detected with a standard, inductive NMR probe without the need for sample
shuttling or precise crystal orientation. Hyperpolarization via OP/DNP should
operate at arbitrary magnetic fields, enabling orders of magnitude sensitivity
enhancement for NMR of solids and liquids at ambient conditions.",1501.02897v1
2015-03-03,Charge dynamics and spin blockade in a hybrid double quantum dot in silicon,"Electron spin qubits in silicon, whether in quantum dots or in donor atoms,
have long been considered attractive qubits for the implementation of a quantum
computer due to the semiconductor vacuum character of silicon and its
compatibility with the microelectronics industry. While donor electron spins in
silicon provide extremely long coherence times and access to the nuclear spin
via the hyperfine interaction, quantum dots have the complementary advantages
of fast electrical operations, tunability and scalability. Here we present an
approach to a novel hybrid double quantum dot by coupling a donor to a
lithographically patterned artificial atom. Using gate-based rf reflectometry,
we probe the charge stability of this double quantum dot system and the
variation of quantum capacitance at the interdot charge transition. Using
microwave spectroscopy, we find a tunnel coupling of 2.7 GHz and characterise
the charge dynamics, which reveals a charge T2* of 200 ps and a relaxation time
T1 of 100 ns. Additionally, we demonstrate spin blockade at the inderdot
transition, opening up the possibility to operate this coupled system as a
singlet-triplet qubit or to transfer a coherent spin state between the quantum
dot and the donor electron and nucleus.",1503.01049v2
2015-03-05,Reduced spin-down rate of PSR J0738-4042 explained as due to an asteroid disruption event,"Long term observations by Brook et al. reveal that the derivative of
rotational frequency of PSR J0738-4042 changed abruptly in 2005. Originally,
the spin-down rate was relatively stable, with the rotational frequency
derivative of $-1.14 \times 10^{-14}~\rm s^{-2}$. After September 2005, the
derivative began to rise up. About 1000 days later, it arrived at another
relatively stable value of about $-0.98 \times 10^{-14}~\rm s^{-2}$, indicating
that the pulsar is spinning-down relatively slowly. To explain the observed
spin-down rate change, we resort to an asteroid disrupted by PSR J0738-4042. In
our model, the orbital angular momentum of the asteroid is assumed to be
parallel to that of the rotating pulsar, so that the pronounced reduction in
the spin-down rate can be naturally explained as due to the transfer of the
angular momentum from the disrupted material to the central pulsar. The derived
magnetospheric radius is about $4.0 \times 10^{9}$ cm, which is smaller than
the tidal disruption radius ($4.9 \times 10^{10}$ cm). Our model is
self-consistent. It is shown that the variability of the spin-down rate of PSR
J0738-4042 can be quantitatively accounted for by the accretion from the
asteroid disrupted by the central pulsar.",1503.01571v1
2016-01-27,Spin Chains and Electron Transfer at Stepped Silicon Surfaces,"High-index surfaces of silicon with adsorbed gold can reconstruct to form
highly ordered linear step arrays. These steps take the form of a narrow strip
of graphitic silicon. In some cases - specifically, for Si(553)-Au and
Si(557)-Au - a large fraction of the silicon atoms at the exposed edge of this
strip are known to be spin-polarized and charge-ordered along the edge. The
periodicity of this charge ordering is always commensurate with the structural
periodicity along the step edge and hence leads to highly ordered arrays of
local magnetic moments that can be regarded as ""spin chains"". Here, we
demonstrate theoretically as well as experimentally that the closely related
Si(775)-Au surface has - despite its very similar overall structure - zero spin
polarization at its step edge. Using a combination of density-functional theory
and scanning tunneling microscopy, we propose an electron-counting model that
accounts for these differences. The model also predicts that unintentional
defects and intentional dopants can create local spin moments at Si(hhk)-Au
step edges. We analyze in detail one of these predictions and verify it
experimentally. This finding opens the door to using techniques of surface
chemistry and atom manipulation to create and control silicon spin chains.",1601.07489v2
2016-02-02,Non-Markovian Dynamics in Chiral Quantum Networks with Spins and Photons,"We study the dynamics of chiral quantum networks consisting of nodes coupled
by unidirectional or asymmetric bidirectional quantum channels. In contrast to
familiar photonic networks where driven two-level atoms exchange photons via 1D
photonic nanostructures, we propose and study a setup where interactions
between the atoms are mediated by spin excitations (magnons) in 1D $XX$ spin
chains representing spin waveguides. While Markovian quantum network theory
eliminates quantum channels as structureless reservoirs in a Born-Markov
approximation to obtain a master equation for the nodes, we are interested in
non-Markovian dynamics. This arises from the nonlinear character of the
dispersion with band-edge effects, and from finite spin propagation velocities
leading to time delays in interactions. To account for the non-Markovian
dynamics we treat the quantum degrees of freedom of the nodes and connecting
channels as a composite spin system with the surrounding of the quantum network
as a Markovian bath, allowing for an efficient solution with time-dependent
density matrix renormalization group techniques. We illustrate our approach
showing non-Markovian effects in the driven-dissipative formation of quantum
dimers, and we present examples for quantum information protocols involving
quantum state transfer with engineered elements as basic building blocks of
quantum spintronic circuits.",1602.00926v2
2016-04-19,Ion Polarization Scheme for MEIC,"The choice of a figure 8 shape for the booster and collider rings of MEIC
opens wide possibilities for preservation of the ion polarization during beam
acceleration as well as for control of the polarization at the collider's
interaction points. As in the case of accelerators with Siberian snakes, the
spin tune is energy independent but is equal to zero instead of one half. The
figure-8 topology eliminates the effect of arcs on the spin motion. There
appears a unique opportunity to control the polarization of any particle
species including deuterons, using longitudinal fields of small integrated
strength (weak solenoids). Contrary to existing schemes, using weak solenoids
in figure-8 colliders, one can control the polarization at the interaction
points without essentially any effect on the beam's orbital characteristics. A
universal scheme for control of the polarization using weak solenoids provides
an elegant solution to the problem of ion acceleration completely eliminating
resonant beam depolarization. It allows one to easily adjust the polarization
in any direction at any orbital location, which becomes necessary when
transferring the beam from one ring into another or when measuring the
polarization by polarimeters. It also allows for an easy manipulation of the
spin direction at an interaction point during an experiment. The latter feature
allows one to set up a spin-flipping system with a spin reversal time of less
than a second. By compensating the coherent part of the zero-integer spin
resonance strength, which arises due to errors in alignment of the magnetic
element of the lattice, one can reduce the field integrals of the control
solenoids by a few orders of magnitude.",1604.05632v1
2016-06-06,Advanced broad-band solid-state supermirror polarizers for cold neutrons,"An ideal solid-state supermirror (SM) neutron polarizer assumes total
reflection of neutrons from the SM coating for one spin-component and total
absorption for the other, thus providing a perfectly polarized neutron beam at
the exit. However, in practice, the substrate's neutron-nucleai optical
potential does not match perfectly that for spin-down neutrons in the SM. For a
positive step in the optical potential (as in a Fe/SiN(x) SM on Si substrate),
this mismatch results in spin-independent total reflection for neutrons with
small momentum transfer Q, limiting the useful neutron bandwidth in the low-Q
region. To overcome this limitation, we propose to replace Si single-crystal
substrates by media with higher optical potential than that for spin-down
neutrons in the SM ferromagnetic layers. We found single-crystal sapphire and
single-crystal quartz as good candidates for solid-state Fe/SiN(x) SM
polarizers. To verify this idea, we coated a thick plate of single-crystal
sapphire with a m=2.4 Fe/SiN(x) SM. At the T3 instrument at the ILL, we
measured the spin-up and spin-down reflectivity curves with 7.5 A neutrons
incident from the substrate to the interface between the substrate and the SM
coating. The results of this experimental test were in excellent agreement with
our expectations: the bandwidth of high polarizing power extended significantly
into the low-Q region. This finding, together with the possibility to apply a
strong magnetizing field, opens a new road to produce high-efficient
solid-state SM polarizers with an extended neutron wavelength bandwidth and
near-to-perfect polarizing power.",1606.01960v2
2016-06-15,Coupling a single electron spin to a microwave resonator: Controlling transverse and longitudinal couplings,"Microwave-frequency superconducting resonators are ideally suited to perform
dispersive qubit readout, to mediate two-qubit gates, and to shuttle states
between distant quantum systems. A prerequisite for these applications is a
strong qubit-resonator coupling. Strong coupling between an electron-spin qubit
and a microwave resonator can be achieved by correlating spin- and orbital
degrees of freedom. This correlation can be achieved through the Zeeman
coupling of a single electron in a double quantum dot to a spatially
inhomogeneous magnetic field generated by a nearby nanomagnet. In this paper,
we consider such a device and estimate spin-resonator couplings of order ~ 1
MHz with realistic parameters. Further, through realistic simulations, we show
that precise placement of the double dot relative to the nanomagnet allows to
select between a purely longitudinal coupling (commuting with the bare spin
Hamiltonian) and a purely transverse (spin non-conserving) coupling.
Additionally, we suggest methods to mitigate dephasing and relaxation channels
that are introduced in this coupling scheme. This analysis gives a clear route
toward the realization of coherent state transfer between a microwave resonator
and a single electron spin in a GaAs double quantum dot with a fidelity above
90%. Improved dynamical decoupling sequences, low-noise environments, and
longer-lived microwave cavity modes may lead to substantially higher fidelities
in the near future.",1606.04736v3
2016-11-11,Rashba-Dirac cones at the tungsten surface: Insights from a tight-binding model and thin film subband structure,"A tight-binding model of bcc tungsten that includes spin-orbit coupling is
developed and applied to the surface states of (110) tungsten thin films. The
model describes accurately the anisotropic Dirac cone-like dispersion and
Rashba-like spin polarization of the surface states, including the crucial
effect of the relaxation of the surface atomic layer of the tungsten towards
the bulk. It is shown that the surface relaxation affects the tungsten surface
states because it results in increased overlaps between atomic orbitals of the
surface atomic layer and nearby layers whereas electric fields that are due to
charge transfer between the tungsten and the vacuum near the surface or between
the bulk and surface layers do not significantly affect the Rashba-Dirac
surface states. It is found that hybridization with bulk modes has differing
strengths for thin film surface states belonging to the upper and lower
Rashba-Dirac cones and results in $reversal$ of the directions of travel of
spin $\uparrow$ and $\downarrow$ electrons in most of the upper Rashba-Dirac
cone relative to those expected from phenomenology. It is also shown that
intrasite (not intersite) matrix elements of the spin-orbit Hamiltonian are
primarily responsible for the formation of the Rashba-Dirac cones, and their
spin polarization. This finding should be considered when modeling topological
insulators, the spin Hall effect and related phenomena.",1611.03582v1
2017-04-08,Unravelling local spin polarization of Zhang-Rice singlet in lightly hole-doped cuprates using high-energy optical conductivity,"Unrevealing local magnetic and electronic correlations in the vicinity of
charge carriers is crucial in order to understand rich physical properties in
correlated electron systems. Here, using high-energy optical conductivity (up
to 35 eV) as a function of temperature and polarization, we observe a
surprisingly strong spin polarization of the local spin singlet with enhanced
ferromagnetic correlations between Cu spins near the doped holes in lightly
hole-doped La$_{1.95}$Sr$_{0.05}$Cu$_{0.95}$Zn$_{0.05}$O$_{4}$. The changes of
the local spin polarization manifest strongly in the temperature-dependent
optical conductivity at ~7.2 eV, with an anomaly at the magnetic stripe phase
(~25 K), accompanied by anomalous spectral-weight transfer in a broad energy
range. Supported by theoretical calculations, we also assign high-energy
optical transitions and their corresponding temperature dependence,
particularly at ~2.5 ~8.7, ~9.7, ~11.3 and ~21.8 eV. Our result shows the
importance of a strong mixture of spin singlet and triplet states in hole-doped
cuprates and demonstrates a new strategy to probe local magnetic correlations
using high- energy optical conductivity in correlated electron systems.",1704.02452v1
2017-04-20,Coupled mode theory for the acoustic wave and spin wave interaction in the magphonic crystals: Propagating magnetoelastic waves,"We have investigated co-directional and contra-directional couplings between
spin wave and acoustic wave in one-dimensional periodic structure (magphonic
crystal). The system consists of two ferromagnetic layers alternating in space.
We have taken into consideration materials commonly used in magnonics: yttrium
iron garnet, CoFeB, permalloy, and cobalt. The coupled mode theory (CMT)
formalism have been successfully implemented to describe magnetoelastic
interaction as a periodic perturbation in the magphonic crystal. The results of
CMT calculations have been verified by more rigorous simulations by
frequency-domain plane wave method and time-domain finite element method. The
presented resonant coupling in the magphonic crystal is an active in-space
mechanism which spatially transfers energy between propagating spin and
acoustic modes, thus creating propagating magnetoelastic wave. We have shown,
that CMT analysis of the magnetoelastic coupling is an useful tool to optimize
and design a spin wave - acoustic wave transducer based on a magphonic
crystals. The effect of spin wave damping has been included to the model to
discuss the efficiency of such a device. Our model shows that it is possible to
obtain forward conversion of the acoustic wave to the spin wave in case of
co-directional coupling and backward conversion in case of contra-directional
coupling.",1704.06118v1
2017-08-01,Spin States Protected from Intrinsic Electron-Phonon-Coupling Reaching 100 ns Lifetime at Room Temperature in MoSe$_2$,"We present time-resolved Kerr rotation measurements, showing spin lifetimes
of over 100 ns at room temperature in monolayer MoSe$_2$. These long lifetimes
are accompanied by an intriguing temperature dependence of the Kerr amplitude,
which increases with temperature up to 50 K and then abruptly switches sign.
Using ab initio simulations we explain the latter behavior in terms of the
intrinsic electron-phonon coupling and the activation of transitions to
secondary valleys. The phonon-assisted scattering of the photo-excited
electron-hole pairs prepares a valley spin polarization within the first few ps
after laser excitation. The sign of the total valley magnetization, and thus
the Kerr amplitude, switches as a function of temperature, as conduction and
valence band states exhibit different phonon-mediated inter-valley scattering
rates. However, the electron-phonon scattering on the ps time scale does not
provide an explanation for the long spin lifetimes. Hence, we deduce that the
initial spin polarization must be transferred into spin states which are
protected from the intrinsic electron-phonon coupling, and are most likely
resident charge carriers which are not part of the itinerant valence or
conduction band states.",1708.00228v2
2017-11-28,Electron paramagnetic resonance spectroscopy using a single artificial atom,"Electron paramagnetic resonance (EPR) spectroscopy is an important technology
in physics, chemistry, materials science, and biology. Sensitive detection with
a small sample volume is a key objective in these areas, because it is crucial,
for example, for the readout of a highly packed spin based quantum memory or
the detection of unlabeled metalloproteins in a single cell. In conventional
EPR spectrometers, the energy transfer from the spins to the cavity at a
Purcell enhanced rate plays an essential role and requires the spins to be
resonant with the cavity, however the size of the cavity (limited by the
wavelength) makes it difficult to improve the spatial resolution. Here, we
demonstrate a novel EPR spectrometer using a single artificial atom as a
sensitive detector of spin magnetization. The artificial atom, a
superconducting flux qubit, provides advantages both in terms of its quantum
properties and its much stronger coupling with magnetic fields. We have
achieved a sensitivity of $\sim$400 spins/$\sqrt{\mathrm{Hz}}$ with a magnetic
sensing volume around $10^{-14} \lambda^3$ (50 femto-liters). This corresponds
to an improvement of two-order of magnitude in the magnetic sensing volume
compared with the best cavity based spectrometers while maintaining a similar
sensitivity as those spectrometers . Our artificial atom is suitable for
scaling down and thus paves the way for measuring single spins on the nanometer
scale.",1711.10148v1
2017-12-20,Disentangling magnetic hardening and molecular spin chain contributions to exchange bias in ferromagnet/molecule bilayers,"We performed SQUID and FMR magnetometry experiments to clarify the
relationship between two reported magnetic exchange effects arising from
interfacial spin-polarized charge transfer within ferromagnetic metal
(FM)/molecule bilayers: the magnetic hardening effect, and
spinterface-stabilized molecular spin chains. To disentangle these effects,
both of which can affect the FM magnetization reversal, we tuned the metal
phthalocyanine molecule central site's magnetic moment to selectively enhance
or suppress the formation of spin chains within the molecular film. We find
that both effects are distinct, and additive. In the process, we 1) extended
the list of FM/molecule candidate pairs that are known to generate magnetic
exchange effects, 2) experimentally confirmed the predicted increase in
anisotropy upon molecular adsorption; and 3) showed that spin chains within the
molecular film can enhance magnetic exchange. This magnetic ordering within the
organic layer implies a structural ordering. Thus, by distengangling the
magnetic hardening and exchange bias contributions, our results confirm, as an
echo to progress regarding inorganic spintronic tunnelling, that the milestone
of spintronic tunnelling across structurally ordered organic barriers has been
reached through previous magnetotransport experiments. This paves the way for
solid-state devices studies that exploit the quantum physical properties of
spin chains, notably through external stimuli.",1712.07450v1
2018-05-10,"Angular momenta, helicity, and other properties of dielectric-fiber and metallic-wire modes","Spin and orbital angular momenta (AM) of light are well studied for
free-space electromagnetic fields, even nonparaxial. One of the important
applications of these concepts is the information transfer using AM modes,
often via optical fibers and other guiding systems. However, the
self-consistent description of the spin and orbital AM of light in optical
media (including dispersive and metallic cases) was provided only recently
[K.Y. Bliokh et al., Phys. Rev. Lett. 119, 073901 (2017)]. Here we present the
first accurate calculations, both analytical and numerical, of the spin and
orbital AM, as well as the helicity and other properties, for the full-vector
eigenmodes of cylindrical dielectric and metallic (nanowire) waveguides. We
find remarkable fundamental relations, such as the quantization of the
canonical total AM of cylindrical guided modes in the general nonparaxial case.
This quantization, as well as the noninteger values of the spin and orbital AM,
are determined by the generalized geometric and dynamical phases in the mode
fields. Moreover, we show that the spin AM of metallic-wire modes is
determined, in the geometrical-optics approximation, by the transverse spin of
surface plasmon-polaritons propagating along helical trajectories on the wire
surface. Our work provides a solid platform for future studies and applications
of the AM and helicity properties of guided optical and plasmonic waves.",1805.03820v2
2018-06-14,The specific heat and magnetic properties of a spin-1/2 ladder including butterfly-shaped unit blocks,"The specific heat, structural characterization, and magnetic property studies
of a new spin ladder with the geometry of butterfly-shaped configuration are
reported. The model introduced here is an infinite spin ladder-type including
spin-1/2 particle for which unit blocks consist of two butterflies connected
together through their bodies (Body-Body bridges). Localized spins on the wings
of butterflies have XXZ Heisenberg interaction with two extra spin-1/2
particles assumed in the center of each cage (unit block), while they have pure
Ising-type interaction with those spins that are localized on the bodies.
Hence, there are six interstitial spins and four nodal spins (Body-Body
interaction) per block. To obtain the partition function of this model, we use
the transfer matrix approach, then we examine the magnetization process, as
well as, the specific heat of the model. Interestingly, we see a wide plateau
at $\frac{5}{6}$ of the saturation magnetization that is strongly dependent on
the magnetic field and anisotropy variations. Moreover, some unexpected
phenomena are observed in the low-temperature limit, such as anomalous
triple-peak in the specific heat function which gradually turns to a
double-peak upon increasing the magnetic field and/or anisotropic Heisenberg
coupling, due to the ferromagnetic phase predomination.",1806.05391v2
2019-06-24,"Itinerancy-dependent non-collinear spin textures in SrFeO3, CaFeO3, and CaFeO3/SrFeO3 heterostructures probed via resonant x-ray scattering","Non-collinear, multi-q spin textures can give rise to exotic, topologically
protected spin structures such as skyrmions, but the reason for their formation
over simple single-q structures is not well understood. While lattice
frustration and the Dzyaloshinskii-Moriya interaction are known to produce
non-collinear spin textures, the role of electron itinerancy in multi-q
formation is much less studied. Here we investigated the non-collinear, helical
spin structures in epitaxial films of the perovskite oxides SrFeO3 and CaFeO3
using magnetotransport and resonant soft x-ray magnetic diffraction. Metallic
SrFeO3 exhibits features in its magnetoresistance that are consistent with its
recently proposed multi-q structure. Additionally, the magnetic Bragg peak of
SrFeO3 measured at the Fe L edge resonance energy asymmetrically broadens with
decreasing temperature in its multi-q state. In contrast, insulating CaFeO3 has
a symmetric scattering peak with an intensity 10x weaker than SrFeO3. Enhanced
magnetic scattering at O K edge prepeak energies demonstrates the role of a
negative charge transfer energy and the resulting oxygen ligand holes in the
magnetic ordering of these ferrates. By measuring magnetic diffraction of
CaFeO3/SrFeO3 superlattices with thick CaFeO3 layers, we find that the CaFeO3
helical ordering is coherent across 1 unit cell-thick SrFeO3 layers but not 6
unit cell-thick layers. We conclude that insulating CaFeO3 supports only a
simple single-q helical structure in contrast to metallic SrFeO3 that hosts
multi-q structures. Our results provide important insight into the role of
electron itinerancy in the formation of multi-q spin structures.",1906.09998v1
2019-09-18,Dzyaloshinskii-Moriya coupling in 3d insulators,"We present an overview of the microscopic theory of the Dzyaloshinskii-Moriya
(DM) coupling in strongly correlated 3d compounds. Most attention in the paper
centers around the derivation of the Dzyaloshinskii vector, its value,
orientation, and sense (sign) under different types of the (super)exchange
interaction and crystal field. We consider both the Moriya mechanism of the
antisymmetric interaction and novel contributions, in particular, that of
spin-orbital coupling on the intermediate ligand ions. We have predicted a
novel magnetic phenomenon, {\it weak ferrimagnetism} in mixed weak ferromagnets
with competing signs of the Dzyaloshinskii vectors.
  We revisit a problem of the DM coupling for a single bond in cuprates
specifying the local spin-orbital contributions to Dzyaloshinskii vector
focusing on the oxygen term. We predict a novel puzzling effect of the on-site
staggered spin polarization to be a result of the on-site spin-orbital coupling
and the the cation-ligand spin density transfer. The intermediate ligand NMR
measurements are shown to be an effective tool to inspect the effects of the DM
coupling in an external magnetic field. We predict the effect of a $strong$
oxygen weak antiferromagnetism in edge-shared CuO$_2$ chains due to
uncompensated oxygen Dzyaloshinskii vectors. We revisit the effects of
symmetric spin anisotropy directly induced by the DM coupling. A critical
analysis will be given of different approaches to exchange-relativistic
coupling based on the cluster and the DFT based calculations. Theoretical
results are applied to different classes of 3d compounds from conventional weak
ferromagnets ($\alpha$-Fe$_2$O$_3$, FeBO$_3$, FeF$_3$, RFeO$_3$, RCrO$_3$,.. )
to unconventional systems such as weak ferrimagnets (e.g.,
RFe$_{1-x}$Cr$_x$O$_3$), helimagnets (e.g., CsCuCl$_3$), and parent cuprates
(La$_2$CuO$_4$,...).",1909.08342v1
2019-10-04,Spin-wave directional anisotropies in antiferromagnetic Ba$_{3}$NbFe$_{3}$Si$_{2}$O$_{14}$,"Ba$_{3}$NbFe$_{3}$Si$_{2}$O$_{14}$ (langasite) is structurally and
magnetically single domain chiral with the magnetic helicity induced through
competing symmetric exchange interactions. Using neutron scattering, we show
that the spin-waves in antiferromagnetic langasite display directional
anisotropy. On applying a time reversal symmetry breaking magnetic field along
the $c$-axis, the spin wave energies differ when the sign is reversed for
either the momentum transfer $\pm$ $\vec{Q}$ or applied magnetic field $\pm$
$\mu_{0}$H. When the field is applied within the crystallographic $ab$-plane,
the spin wave dispersion is directionally \textit{isotropic} and symmetric in
$\pm$ $\mu_{0}$H. However, a directional anisotropy is observed in the spin
wave intensity. We discuss this directional anisotropy in the dispersion in
langasite in terms of a field induced precession of the dynamic unit cell
staggered magnetization. Directional anisotropy, or often referred to as non
reciprocal responses, can occur in antiferromagnetic phases in the absence of
the Dzyaloshinskii-Moriya interaction or other effects resulting from
spin-orbit coupling.",1910.01977v2
2020-01-03,The spin rates of O stars in WR + O Magellanic Cloud binaries,"Some massive, merging black holes (BH) may be descendants of binary O stars.
The evolution and mass transfer between these O stars determines the spins of
their progeny BH. These will be measurable with future gravitational wave
detectors, incentivizing the measurement of the spins of O stars in binaries.
We previously measured the spins of O stars in Galactic Wolf-Rayet (WR) + O
binaries. Here we measure the vsini of four LMC and two SMC O stars in WR + O
binaries to determine whether lower metallicity might affect the spin rates. We
find that the O stars in Galactic and Magellanic WR + O binaries display
average vsini = 258 +/- 18 km/s and 270 +/- 15 km/s, respectively. Two LMC O
stars measured on successive nights show significant line width variability,
possibly due to differing orbital phases exhibiting different parts of the O
stars illuminated differently by their WR companions. Despite this variability,
the vsini are highly super-synchronous but distinctly subcritical for the O
stars in all these binaries; thus we conclude that an efficient mechanism for
shedding angular momentum from O stars in WR + O binaries must exist. This
mechanism, probably related to Roche lobe overflow-created dynamo magnetic
fields, prevents nearly 100% breakup spin rates, as expected when RLOF
operates, as it must, in these stars. A Spruit-Tayler dynamo and O star wind
might be that mechanism.",2001.01012v1
2020-01-07,Coherent multi-spin exchange coupling in a quantum-dot spin chain,"Heisenberg exchange coupling between neighboring electron spins in
semiconductor quantum dots provides a powerful tool for quantum information
processing and simulation. Although so far unrealized, extended Heisenberg spin
chains can enable long-distance quantum information transfer and the generation
of non-equilibrium quantum states. In this work, we implement simultaneous,
coherent exchange coupling between all nearest-neighbor pairs of spins in a
quadruple quantum dot. The main challenge in implementing simultaneous exchange
couplings is the nonlinear and nonlocal dependence of the exchange couplings on
gate voltages. Through a combination of electrostatic simulation and
theoretical modeling, we show that this challenge arises primarily due to
lateral shifts of the quantum dots during gate pulses. Building on this
insight, we develop two models, which can be used to predict the confinement
gate voltages for a desired set of exchange couplings. Although the model
parameters depend on the number of exchange couplings desired (suggesting that
effects in addition to lateral wavefunction shifts are important), the models
are sufficient to enable simultaneous and independent control of all three
exchange couplings in a quadruple quantum dot. We demonstrate two-, three-, and
four-spin exchange oscillations, and our data agree with simulations.",2001.02277v2
2020-08-12,Mean-field spin-oscillation dynamics beyond the single-mode approximation for a harmonically trapped spin-1 Bose-Einstein condensate,"Compared to single-component Bose-Einstein condensates, spinor Bose-Einstein
condensates display much richer dynamics. In addition to density oscillations,
spinor Bose-Einstein condensates exhibit intriguing spin dynamics that is
associated with population transfer between different hyperfine components.
This work analyzes the validity of the widely employed single-mode
approximation when describing the spin dynamics in response to a quench of the
system Hamiltonian. The single-mode approximation assumes that the different
hyperfine states all share the same time-independent spatial mode. This implies
that the resulting spin Hamiltonian only depends on the spin interaction
strength and not on the density interaction strength. Taking the spinor sodium
Bose-Einstein condensate in the $f=1$ hyperfine manifold as an example and
working within the mean-field theory framework, it is found numerically that
the single-mode approximation misses, in some parameter regimes, intricate
details of the spin and spatial dynamics. We develop a physical picture that
explains the observed phenomenon. Moreover, using that the population
oscillations described by the single-mode approximation enter into the
effective potential felt by the mean-field spinor, we derive a
semi-quantitative condition for when dynamical mean-field induced corrections
to the single-mode approximation are relevant. Our mean-field results have
implications for a variety of published and planned experimental studies.",2008.05118v2
2020-12-31,Dispersively probed microwave spectroscopy of a silicon hole double quantum dot,"Owing to ever increasing gate fidelities and to a potential transferability
to industrial CMOS technology, silicon spin qubits have become a compelling
option in the strive for quantum computation. In a scalable architecture, each
spin qubit will have to be finely tuned and its operating conditions accurately
determined. In this prospect, spectroscopic tools compatible with a scalable
device layout are of primary importance. Here we report a two-tone spectroscopy
technique providing access to the spin-dependent energy-level spectrum of a
hole double quantum dot defined in a split-gate silicon device. A first
GHz-frequency tone drives electric-dipole spin resonance enabled by the
valence-band spin-orbit coupling. A second lower-frequency tone (approximately
500 MHz) allows for dispersive readout via rf-gate reflectometry. We compare
the measured dispersive response to the linear response calculated in an
extended Jaynes-Cummings model and we obtain characteristic parameters such as
g-factors and tunnel/spin-orbit couplings for both even and odd occupation.",2012.15588v2
2021-02-22,Spin Photovoltaic Effect in Magnetic van der Waals Heterostructures,"The development of van der Waals (vdW) crystals and their heterostructures
has created a fascinating platform for exploring optoelectronic properties in
the two-dimensional (2D) limit. With the recent discovery of 2D magnets, the
control of the spin degree of freedom can be integrated to realize 2D
spin-optoelectronics with spontaneous time-reversal symmetry breaking. Here, we
report spin photovoltaic effects in vdW heterostructures of atomically thin
magnet chromium triiodide (CrI3) sandwiched by graphene contacts. In the
absence of a magnetic field, the photocurrent displays a distinct dependence on
light helicity, which can be tuned by varying the magnetic states and photon
energy. Circular polarization-resolved absorption measurements reveal that
these observations originate from magnetic-order-coupled and thus
helicity-dependent charge-transfer exciton states. The photocurrent displays
multiple plateaus as the magnetic field is swept, which are associated with
different spin configurations enabled by the layered antiferromagnetism and
spin-flip transitions in CrI3. Remarkably, giant photo-magnetocurrent is
observed, which tends to infinity for a small applied bias. Our results pave
the way to explore emergent photo-spintronics by engineering magnetic vdW
heterostructures.",2102.10818v1
2021-04-08,Spin-orbit coupling induced ultra-high harmonic generation from magnetic dynamics,"The recent boost in data transfer rates puts a daring strain on information
technology. Sustaining such a growth rate requires the development of sources,
detectors and systems working in the so-called TeraHertz (THz) gap covering the
frequency window from 0.1 to 10 THz (1 THz = 10$^{12}$~Hz). This gap represents
a challenge for conventional electronic devices due to carrier transit delays
($\sim$1-10ps), as well as for photonic devices due to thermal fluctuations
(300K$\sim$6THz). Nonetheless, designing efficient, room-temperature THz
sources would constitute a key enabler to applications spanning from
high-resolution imaging to extreme wide band wireless communication. Whereas
high-harmonic generation in solid is usually limited to less than ten
harmonics, broadband THz emission has been demonstrated using laser-induced
superdiffusive spin currents in magnetic bilayers composed of a ferromagnet
deposited on top of a noble metal. While promising, this technique presents the
major disadvantage of necessitating optical pumping and hence lacks
scalability. Here, we demonstrate that extremely high harmonic emission can be
achieved by exploiting conventional spin pumping, without the need of optical
excitation. We show that when the spin-orbit coupling strength is close to the
s-d exchange energy, a strongly non linear regime resulting from resonant spin
flip scattering occurs leading to the generation of a thousand of harmonics at
realistic antiferromagnetic precession frequencies, thereby enhancing both spin
and charge dynamics by two orders of magnitude, and allowing for an emission at
frequencies above 300 THz.",2104.04001v1
2021-09-22,Optically- and thermally-driven huge lattice orbital and spin angular momenta from spinning fullerenes,"Lattice vibration in solids may carry angular momentum. But unlike the
intrinsic spin of electrons, the lattice vibration is rarely rotational. To
induce angular momentum, one needs to find a material that can accommodate a
twisted normal mode, two orthogonal modes or excitation of magnons. If
excitation is too strong, one may exceed the Lindemann limit, so the material
melts. Therefore these methods are not ideal. Here, we theoretically propose a
new route to phonon angular momentum in a molecular crystal $\rm C_{60}$. We
find that a single laser pulse is able to inject a significant amount of
angular momentum to $\rm C_{60}$, and the momentum transfer is
helicity-dependent. Changing from right-circularly polarized light to
left-circularly polarized light switches the direction of phonon angular
momentum. On the ultrafast time scale, the orbital angular momentum change
closely resembles the displacive excitation of coherent phonons, with a
cosine-function dependence on time, different from the spin counterpart. Atomic
displacements, even under strong laser excitation, remain far below the
Lindemann criterion. Under thermal excitation, spinning $\rm C_{60}$ even at
room temperature generates a huge angular momentum close to several hundred
$\hbar$. Our finding opens the door to a large group of fullerenes, from $\rm
C_{60}$, C$_{70}$ to their endohedral derivatives, where angular momentum can
be generated through light or temperature. This paves the way to the phononic
control electronic spin and harvesting thermal energy through phonon angular
momentum.",2109.11055v1
2022-02-05,"Unitary Design of Quantum Spin Networks for Robust Routing, Entanglement Generation, and Phase Sensing","Spin chains can be used to describe a wide range of platforms for quantum
computation and quantum information. They enable the understanding,
demonstration, and modeling of numerous useful phenomena, such as high fidelity
transfer of quantum states, creation and distribution of entanglement, and
creation of resources for measurement-based quantum processing. In this paper,
a more complex spin system, a 2D spin network (SN) engineered by applying
suitable unitaries to two uncoupled spin chains, is studied. Considering only
the single-excitation subspace of the SN, it is demonstrated that the system
can be operated as a router, directing information through the SN. It is also
shown that it can serve to generate maximally entangled states between two
sites. Furthermore, it is illustrated that this SN system can be used as a
sensor device able to determine an unknown phase applied to a system spin. A
detailed modeling investigation of the effects of static disorder in the system
shows that this system is robust against different types of disorder.",2202.02632v3
2022-07-25,Control of dephasing in spin qubits during coherent transport in silicon,"One of the key pathways towards scalability of spin-based quantum computing
systems lies in achieving long-range interactions between electrons and
increasing their inter-connectivity. Coherent spin transport is one of the most
promising strategies to achieve this architectural advantage. Experimental
results have previously demonstrated high fidelity transportation of spin
qubits between two quantum dots in silicon and identified possible sources of
error. In this theoretical study, we investigate these errors and analyze the
impact of tunnel coupling, magnetic field and spin-orbit effects on the spin
transfer process. The interplay between these effects gives rise to double dot
configurations that include regimes of enhanced decoherence that should be
avoided for quantum information processing. These conclusions permit us to
extrapolate previous experimental conclusions and rationalize the future design
of large scale quantum processors.",2207.11865v2
2022-12-07,Surfing in the phase space of spin-orbit coupling in binary asteroid systems,"For a satellite with an irregular shape, which is the common shape among
asteroids, the well-known spin-orbit resonance problem could be changed to a
spin-orbit coupling problem since a decoupled model does not accurately capture
the dynamics of the system. In this paper, having provided a definition for
close binary asteroid systems, we explore the structure of the phase space in a
classical Hamiltonian model for spin-orbit coupling in a binary system. To map
out the geography of resonances analytically and the cartography of resonances
numerically, we reformulate a fourth-order gravitational potential function, in
Poincare variables, via Stokes coefficients. For a binary system with a
near-circular orbit, isolating the Hamiltonian near each resonance yields the
pendulum model. Analysis of the results shows the geographical information,
including the location and width of resonances, is modified due to the
prominent role of the semi-major axis in the spin-orbit coupling model but not
structurally altered. However, this resulted in modified Chirikov criterion to
predict onset of large-scale chaos. For a binary system with arbitrary closed
orbit, we thoroughly surf in the phase space via cartography of resonances
created by fast Lyapunov indicator (FLI) maps. The numerical study confirms the
analytical results, provides insight into the spin-orbit coupling, and shows
some bifurcations in the secondary resonances which can occur due to material
transfer. Also, we take the (65803) Didymos binary asteroid as a case to show
analytical and numerical results.",2212.03837v1
2023-02-17,Symmetry of the Hyperfine and Quadrupole Interactions of Boron Vacancies in a Hexagonal Boron Nitride,"The concept of optically addressable spin states of deep level defects in
wide band gap materials is successfully applied for the development of quantum
technologies. Recently discovered negatively charged boron vacancy defects (VB)
in hexagonal boron nitride (hBN) potentially allow a transfer of this concept
onto atomic thin layers due to the van der Waals nature of the defect host.
Here, we experimentally explore all terms of the VB spin Hamiltonian reflecting
interactions with the three nearest nitrogen atoms by means of conventional
electron spin resonance and high frequency (94 GHz) electron-nuclear double
resonance. We establish symmetry, anisotropy, and principal values of the
corresponding hyperfine interaction (HFI) and nuclear quadrupole interaction
(NQI). The HFI can be expressed in the axially symmetric form as Aperp = 45.5
MHz and Apar = 87 MHz, while the NQI is characterized by quadrupole coupling
constant Cq = 1.96 MHz with slight rhombisity parameter n = (Pxx - Pyy)/Pzz =
-0.070. Utilizing a conventional approach based on a linear combination of
atomic orbitals and HFI values measured here, we reveal that almost all spin
density (84 %) of the VB electron spin is localized on the three nearest
nitrogen atoms. Our findings serve as valuable spectroscopic data and direct
experimental demonstration of the VB spin localization in a single two
dimensional BN layer.",2302.08831v1
2023-03-03,Detecting spin bath polarization with quantum quench phase shifts of single spins in diamond,"Single-qubit sensing protocols can be used to measure qubit-bath coupling
parameters. However, for sufficiently large coupling, the sensing protocol
itself perturbs the bath, which is predicted to result in a characteristic
response in the sensing measurements. Here, we observe this bath perturbation,
also known as a quantum quench, by preparing the nuclear spin bath of a
nitrogen-vacancy (NV) center in polarized initial states and performing
phase-resolved spin echo measurements on the NV electron spin. These
measurements reveal a time-dependent phase determined by the initial state of
the bath. We derive the relationship between sensor phase and Gaussian spin
bath polarization, and apply it to reconstruct both the axial and transverse
polarization components. Using this insight, we optimize the transfer
efficiency of our dynamic nuclear polarization sequence. This technique for
directly measuring bath polarization may assist in preparing high-fidelity
quantum memory states, improving nanoscale NMR methods, and investigating
non-Gaussian quantum baths.",2303.02233v1
2023-11-14,Generation of electric current and electromotive force by an antiferromagnetic domain wall,"Dynamic magnetic textures may transfer the angular moment from the varying in
time antiferromagnetic order to spins of conduction electrons. Due to the spin
orbit coupling (SOC) these spin excitations can induce the electric current of
conduction electrons. We calculated the electric current and the electromotive
force (EMF) which are produced by a domain wall (DW) moving parallel to the
magnetically compensated interface between an antiferromagnetic insulator
(AFMI) and a two-dimensional spin orbit coupled metal. Spins of conduction
electrons interact with localized spins of a collinear AFMI through the
interface exchange interaction. The Keldysh formalism of nonequilibrium Green
functions was applied for the analysis of this system. It is shown that a Bloch
DW generates the current perpendicular to the DW motion direction. At the same
time a N\'{e}el DW creates the electric potential which builds up across the
wall. The total charge which is pumped by a Bloch DW can be expressed in terms
of a topologically invariant charge quantum. The latter does not depend on
variations of DW's velocity and shape. These effects increase dramatically when
the Fermi energy approaches the van Hove singularity of the Fermi surface. The
obtained results are important for the electrical detection and control of
dynamic magnetic textures in antiferromagnets.",2311.08067v1
2023-11-22,Quantum spin dynamics due to strong Kitaev interactions in the triangular-lattice antiferromagnet CsCeSe$_2$,"The extraordinary properties of the Kitaev model have motivated an intense
search for new physics in materials that combine geometrical and bond
frustration. In this work, we employ inelastic neutron scattering, spin wave
theory, and exact diagonalization to study the spin dynamics in the perfect
triangular-lattice antiferromagnet (TLAF) CsCeSe$_2$. This material orders into
a stripe phase, which is demonstrated to arise as a consequence of the
off-diagonal bond-dependent terms in the spin Hamiltonian. By studying the spin
dynamics at intermediate fields, we identify an interaction between the
single-magnon state and the two-magnon continuum that causes decay of coherent
magnon excitations, level repulsion, and transfer of spectral weight to the
continuum that are controlled by the strength of the magnetic field. Our
results provide a microscopic mechanism for the stabilization of the stripe
phase in TLAF and show how complex many-body physics can be present in the spin
dynamics in a magnet with strong Kitaev coupling even in an ordered ground
state.",2311.13146v2
2024-02-29,Resonant generation of propagating second-harmonic spin waves in nano-waveguides,"Generation of second-harmonic waves is one of the universal nonlinear
phenomena that have found numerous technical applications in many modern
technologies, in particular, in photonics. This phenomenon also has great
potential in the field of magnonics, which considers the use of spin waves in
magnetic nanostructures to implement wave-based signal processing and
computing. However, due to the strong frequency dependence of the phase
velocity of spin waves, resonant phase-matched generation of second-harmonic
spin waves has not yet been achieved in practice. Here, we show experimentally
that such a process can be realized using a combination of different modes of
nano-sized spin-wave waveguides based on low-damping magnetic insulators. We
demonstrate that our approach enables efficient spatially-extended energy
transfer between interacting waves, which can be controlled by the intensity of
the initial wave and the static magnetic field. The demonstrated approach can
be used for the generation of short-wavelength spin waves that are difficult to
excite directly, as well as for the implementation of novel devices for
magnonic logic and unconventional computing.",2402.18964v1
2024-03-05,Novel Dipole-Lattice coupling in the Quantum-Spin-Liquid Material $κ$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$,"A family of molecular Mott insulators on triangular lattice provided a few
S=1/2 triangular quantum spin liquid candidates, with
$\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ being the most studied material of this
group. The large number experimental works present a conflicting set of
evidence, with some suggesting spin liquid behavior, while others point towards
a valence bond solid with orphan spins. In this work we use Raman scattering
spectroscopy to probe both local charge on molecular sites and lattice phonons
as a function of temperature down to 6~K. Based on the analysis of the line
shape of the BEDT-TTF charge sensitive vibration $\nu_2$ on cooling below 40 K,
we suggest a development of disordered fluctuating charge disproportionation on
(BEDT-TTF)$_2$ dimers of amplitude as small as 0.06$e$. The lattice phonons
show strong anomalous broadening on cooling only in the (c,c) scattering
channel, associated with the developing charge disproportionation. We suggest
an interpretation, where the coupling of disordered charge dipoles on dimers to
the lattice results in anisotropic modulation of charge transfer integrals
between dimer lattice sites. Such fluctuations would result in modulation of
magnetic coupling between spins which can produce fluctuating charge ordered
spin-singlet pairs.",2403.02676v2
1996-02-15,"Transfer-Matrix Monte Carlo Estimates of Critical Points in the Simple Cubic Ising, Planar and Heisenberg Models","The principle and the efficiency of the Monte Carlo transfer-matrix algorithm
are discussed. Enhancements of this algorithm are illustrated by applications
to several phase transitions in lattice spin models. We demonstrate how the
statistical noise can be reduced considerably by a similarity transformation of
the transfer matrix using a variational estimate of its leading eigenvector, in
analogy with a common practice in various quantum Monte Carlo techniques. Here
we take the two-dimensional coupled $XY$-Ising model as an example.
Furthermore, we calculate interface free energies of finite three-dimensional
O($n$) models, for the three cases $n=1$, 2 and 3. Application of finite-size
scaling to the numerical results yields estimates of the critical points of
these three models. The statistical precision of the estimates is satisfactory
for the modest amount of computer time spent.",9602089v1
1999-06-04,Electron transfer in the nonadiabatic regime: Crossover from quantum-mechanical to classical behaviour,"We study nonadiabatic electron transfer within the biased spin-boson model.
We calculate the incoherent transfer rate in analytic form at all temperatures
for a power law form of the spectral density of the solvent coupling. In the
Ohmic case, we present the exact low temperature corrections to the zero
temperature rate for arbitrarily large bias energies between the two redox
sites. Both for Ohmic and non-Ohmic coupling, we give the rate in the entire
regime extending from zero temperature, where the rate depends significantly on
the detailed spectral behaviour, via the crossover region, up to the classical
regime. For low temperatures, the rate shows characteristic quantum features,
in particular the shift of the rate maximum to a bias value below the
reorganization energy, and the asymmetry of the rate around the maximum. We
study in detail the gradual extinction of the quantum features as temperature
is increased.",9906061v1
2006-01-17,Collective excitations in unconventional charge-density wave systems,"The excitation spectrum of the t-J model is studied on a square lattice in
the large $N$ limit in a doping range where a $d$-$density$-$wave$ (DDW) forms
below a transition temperature $T^\star$. Characteristic features of the DDW
ground state are circulating currents which fluctuate above and condense into a
staggered flux state below $T^\star$ and density fluctuations where the
electron and the hole are localized at different sites. General expressions for
the density response are given both above and below $T^\star$ and applied to
Raman, X-ray, and neutron scattering. Numerical results show that the density
response is mainly collective in nature consisting of broad, dispersive
structures which transform into well-defined peaks mainly at small momentum
transfers. One way to detect these excitations is by inelastic neutron
scattering at small momentum transfers where the cross section (typically a few
per cents of that for spin scattering) is substantially enhanced, exhibits a
strong dependence on the direction of the transferred momentum and a
well-pronounced peak somewhat below twice the DDW gap. Scattering from the
DDW-induced Bragg peak is found to be weaker by two orders of magnitude
compared with the momentum-integrated inelastic part.",0601382v1
2006-02-09,Measurement of the Charge Transfer Efficiency of Electrons Clocked on Superfluid Helium,"Electrons floating on the surface of liquid helium are possible qubits for
quantum information processing. Varying electric potentials do not modify spin
states, which allows their transport on helium using a charge-coupled device
(CCD)-like array of underlying gates. This scheme depends upon efficient
inter-gate electron transfer and on the absence of electron traps. We will
present a measurement of the charge transfer efficiency (CTE) of electrons
clocked back and forth above a short CCD-like structure. The CTE obtained at
low clocking frequencies is 0.999 with an electron density of about 4 electrons
per square micrometer. We find no evidence for deep electron trapping.",0602228v2
2006-09-04,Resonant Einstein-de Haas effect in a rubidium condensate,"We numerically investigate a condensate of $^{87}$Rb atoms in an F=1
hyperfine state confined in an optical dipole trap. Assuming the magnetic
moments of all atoms are initially aligned along the magnetic field we observe,
after the field's direction is reversed, a transfer of atoms to other Zeeman
states. Such transfer is allowed by the dipolar interaction which couples the
spin and the orbital degrees of freedom. Therefore, the atoms in $m_F=0,-1$
states acquire an orbital angular momentum and start to circulate around the
center of the trap. This is a realization of the Einstein-de Haas effect in
systems of cold gases. We find resonances which amplify this phenomenon making
it observable even in very weak dipolar systems. The resonances occur when the
Zeeman energy on transfer of atoms to $m_F=0$ state is fully converted to the
rotational kinetic energy.",0609061v2
2006-10-25,The density-matrix renormalization group applied to transfer matrices: Static and dynamical properties of one-dimensional quantum systems at finite temperature,"The density-matrix renormalization group (DMRG) applied to transfer matrices
allows it to calculate static as well as dynamical properties of
one-dimensional quantum systems at finite temperature in the thermodynamic
limit. To this end the quantum system is mapped onto a two-dimensional
classical system by a Trotter-Suzuki decomposition. Here we discuss two
different mappings: The standard mapping onto a two-dimensional lattice with
checkerboard structure as well as an alternative mapping introduced by two of
us. For the classical system an appropriate quantum transfer matrix is defined
which is then treated using a DMRG scheme. As applications, the calculation of
thermodynamic properties for a spin-1/2 Heisenberg chain in a staggered
magnetic field and the calculation of boundary contributions for open spin
chains are discussed. Finally, we show how to obtain real time dynamics from a
classical system with complex Boltzmann weights and present results for the
autocorrelation function of the XXZ-chain.",0610689v1
2003-11-18,Rescattering and finite formation time effects in electro-disintegration of the deuteron in the cumulative region,"The role of rescattering due to the final state interaction (FSI) and the
influence of the finite formation time (FFT) on the inclusive $D(e,e')X$ and
exclusive $D(e,e'p)n$ electro-disintegration of the deuteron are studied in the
cumulative kinematical region $x>1$ and moderate values of the 4-momentum
transfer $Q^2=2\div 10$ (GeV/c)$^2$. The spins are averaged out. It is found
that in the inclusive process the relative magnitude of rescattering steadily
grows with $x$ and that at $x=1.7$ it has the same order as the plane wave
impulse approximation (PWIA) contribution, with the finite formation time
effects decreasing the rescattering contribution by $\sim 30$%. In the
exclusive process, with increasing momentum transfer, FFT substantially reduces
the effects from FSI, although the latter are still appreciable in the region
of momentum transfer investigated.",0311060v1
2005-04-23,Perfect transfer of many-particle quantum state via high-dimensional systems with spectrum-matched symmetry,"The quantum state transmission (QST) through the medium of high-dimensional
many-particle system is studied with a symmetry analysis. We discover that, if
the spectrum matches the symmetry of a fermion or boson system in a certain
fashion, a perfect quantum state transfer can be implemented without any
operation on the medium. Based on this observation the well-established results
for the QST via quantum spin chains can be generalized to the high-dimensional
many-particle systems with pre-engineered nearest neighbor (NN) hopping
constants. By investigating a simple but realistic near half-filled
tight-binding fermion system with uniform NN hopping integral, we show that an
arbitrary many-particle state near the fermi surface can be perfectly
transferred to its translational counterpart.",0504175v1
2005-05-23,Wave packet transmission of Bloch electron manipulated by magnetic field,"We study the phenomenon of wave packet revivals of Bloch electrons and
explore how to control them by a magnetic field for quantum information
transfer. It is showed that the single electron system can be modulated into a
linear dispersion regime by the ""quantized"" flux and then an electronic wave
packet with the components localized in this regime can be transferred without
spreading. This feature can be utilized to perform the high-fidelity transfer
of quantum information encoded in the polarization of the spin. Beyond the
linear approximation, the re-localization and self-interference occur as the
novel phenomena of quantum coherence.",0505169v2
2006-01-04,Composite Dipolar Recoupling: Anisotropy Compensated Coherence Transfer in Solid-State NMR,"The efficiency of dipole-dipole coupling driven coherence transfer
experiments in solid-state NMR spectroscopy of powder samples is limited by
dispersion of the orientation of the internuclear vectors relative to the
external magnetic field. Here we introduce general design principles and
resulting pulse sequences that approach full polarization transfer efficiency
for all crystallite orientations in a powder in magic-angle-spinning
experiments. The methods compensate for the defocusing of coherence due to
orientation dependent dipolar coupling interactions and inhomogeneous
radio-frequency fields. The compensation scheme is very simple to implement as
a scaffold (comb) of compensating pulses in which the pulse sequence to be
improved may be inserted. The degree of compensation can be adjusted and should
be balanced as a compromise between efficiency and length of the overall pulse
sequence. We show by numerical and experimental data that the presented
compensation protocol significantly improves the efficiency of known dipolar
recoupling solid-state NMR experiment.",0601022v1
2006-08-06,Excitation and Entanglement Transfer Near Quantum Critical Points,"Recently, there has been growing interest in employing condensed matter
systems such as quantum spin or harmonic chains as quantum channels for short
distance communication. Many properties of such chains are determined by the
spectral gap between their ground and excited states. In particular this gap
vanishes at critical points of quantum phase transitions. In this article we
study the relation between the transfer speed and quality of such a system and
the size of its spectral gap. We find that the transfer is almost perfect but
slow for large spectral gaps and fast but rather inefficient for small gaps.",0608051v1
2007-03-22,Qubit Teleportation and Transfer across Antiferromagnetic Spin Chains,"We explore the capability of spin-1/2 chains to act as quantum channels for
both teleportation and transfer of qubits. Exploiting the emergence of
long-distance entanglement in low-dimensional systems [Phys. Rev. Lett. 96,
247206 (2006)], here we show how to obtain high communication fidelities
between distant parties. An investigation of protocols of teleportation and
state transfer is presented, in the realistic situation where temperature is
included. Basing our setup on antiferromagnetic rotationally invariant systems,
both protocols are represented by pure depolarizing channels. We propose a
scheme where channel fidelity close to one can be achieved on very long chains
at moderately small temperature.",0703202v2
2007-08-29,Cruising through molecular bound state manifolds with radio frequency,"The emerging field of ultracold molecules with their rich internal structure
is currently attracting a lot of interest. Various methods have been developed
to produce ultracold molecules in pre-set quantum states. For future
experiments it will be important to efficiently transfer these molecules from
their initial quantum state to other quantum states of interest. Optical Raman
schemes are excellent tools for transfer, but can be involved in terms of
equipment, laser stabilization and finding the right transitions. Here we
demonstrate a very general and simple way for transfer of molecules from one
quantum state to a neighboring quantum state with better than 99% efficiency.
The scheme is based on Zeeman tuning the molecular state to avoided level
crossings where radio-frequency transitions can then be carried out. By
repeating this process at different crossings, molecules can be successively
transported through a large manifold of quantum states. As an important
spin-off of our experiments, we demonstrate a high-precision spectroscopy
method for investigating level crossings.",0708.3958v1
2008-02-16,"Complete set of polarization transfer coefficients for the ${}^{3}{\rm He}(p,n)$ reaction at 346 MeV and 0 degrees","We report measurements of the cross-section and a complete set of
polarization transfer coefficients for the ${}^{3}{\rm He}(p,n)$ reaction at a
bombarding energy $T_p$ = 346 MeV and a reaction angle $\theta_{\rm lab}$ =
$0^{\circ}$.
  The data are compared with the corresponding free nucleon-nucleon values on
the basis of the predominance of quasi-elastic scattering processes.
  Significant discrepancies have been observed in the polarization transfer
$D_{LL}(0^{\circ})$, which are presumably the result of the three-proton $T$ =
3/2 resonance.
  The spin--parity of the resonance is estimated to be $1/2^-$, and the
distribution is consistent with previous results obtained for the same reaction
at $T_p$ = 48.8 MeV.",0802.2328v2
2008-02-22,Breakdown of Fermi Liquid Theory in Doped Mott Insulators by Dynamical Spectral Weight Transfer,"We show that doped Mott insulators exhibit a collective degree of freedom,
not made out of the elemental excitations, because the number of
single-particle addition states at low energy per electron per spin is greater
than one. The presence of such a collective degree of freedom which is not a
consequence of proximity to a phase transition is a consequence of dynamical
spectral weight transfer from high to low energies. This physics is captured by
the charge $2e$ boson that emerges by explicitly integrating out the
high-energy scale in the Hubbard model. The charge $2e$ boson binds to a hole,
thereby mediating new charge $e$ states at low energy. It is the presence of
such charge $e$ states which have no counterpart in the non-interacting system
that provides the general mechanism for the breakdown of Fermi liquid theory in
doped Mott insulators. The relationship between the charge $2e$ boson
formulation and the standard perturbative treatment is explained.",0802.3405v3
2008-03-16,Perfect transference of a d-level quantum state over pseudo-distance-regular networks,"Following the prescription of Ref. \cite{PST} in which perfect state
transference (PST) of a qubit over distance regular spin networks was
discussed, in this paper PST of an arbitrary $d$-level quantum state (qudit)
over antipodes of more general networks called pseudo distance-regular
networks, is investigated. In fact, the spectral analysis techniques used in
the previous work \cite{PST}, and algebraic structures of pseudo
distance-regular graphs are employed to give an explicit formula for suitable
coupling constants in the Hamiltonians so that the state of a particular qudit
initially encoded on one site will evolve freely to the opposite site without
any dynamical control, i.e., we show that how to derive the parameters of the
system so that PST can be achieved.
  Keywords:Perfect state transfer, $d$-level quantum state, Stratification,
Pseudo-distance-regular network
  PACs Index: 01.55.+b, 02.10.Yn",0803.2334v1
2008-11-29,Chiral effective field theory calculations of neutrino processes in dense matter,"We calculate neutrino processes involving two nucleons at subnuclear
densities using chiral effective field theory. Shorter-range noncentral forces
reduce the neutrino rates significantly compared with the one-pion exchange
approximation currently used in supernova simulations. For densities rho <
10^{14} g cm^{-3}, we find that neutrino rates are well constrained by nuclear
interactions and nucleon-nucleon scattering data. As an application, we
calculate the mean-square energy transfer in scattering of a neutrino from
nucleons and find that collision processes and spin-dependent mean-field
effects dominate over the energy transfer due to nucleon recoil.",0812.0102v2
2009-11-29,Algorithmic approach to simulate Hamiltonian dynamics and an NMR simulation of Quantum State Transfer,"We propose an iterative algorithm to simulate the dynamics generated by any
$n$-qubit Hamiltonian. The simulation entails decomposing the unitary time
evolution operator $U$ (unitary) into a product of different time-step
unitaries. The algorithm product-decomposes $U$ in a chosen operator basis by
identifying a certain symmetry of $U$ that is intimately related to the number
of gates in the decomposition. We illustrate the algorithm by first obtaining a
polynomial decomposition in the Pauli basis of the $n$-qubit Quantum State
Transfer unitary by Di Franco et. al. (Phys. Rev. Lett. 101, 230502 (2008))
that transports quantum information from one end of a spin chain to the other;
and then implement it in Nuclear Magnetic Resonance to demonstrate that the
decomposition is experimentally viable and well-scaled. We furthur
experimentally test the resilience of the state transfer to static errors in
the coupling parameters of the simulated Hamiltonian. This is done by
decomposing and simulating the corresponding imperfect unitaries.",0911.5467v3
2010-05-12,Transfer of optical spectral weight in magnetically ordered superconductors,"We show that, in antiferromagnetic superconductors, the optical spectral
weight transferred to low frequencies below the superconducting transition
temperature originates from energies that can be much larger than twice the
superconducting gap $\Delta$. This contrasts to non-magnetic superconductors,
where the optical spectrum is suppressed only for frequencies below $2\Delta$.
In particular, we demonstrate that the superfluid condensate of the
magnetically ordered superconductor is not only due to states of the
magnetically reconstructed Fermi surface, but is enhanced by transfer of
spectral weight from the mid infrared peak generated by the spin density wave
gap. We apply our results to the iron arsenide superconductors, addressing the
decrease of the zero-temperature superfluid density in the doping regime where
magnetism coexists with unconventional superconductivity.",1005.2174v3
2010-06-18,Vibration-enhanced energy transfer in living molecules,"The conversion of an absorbed photon from the exciton energy into the
reaction centre in the photosynthetic complex has a near unit efficiency. It is
becoming clear that any classical model, where the exciton hopping is modeled
by a classical stochastic diffusion equation, cannot explain such a high degree
of efficiency. A number of different quantum models have been proposed, ranging
from a purely unitary model with long range exciton interactions to a
noise-aided stochastic resonance models. Here we propose a very simple
spin-boson model that captures all the features of the efficient part of energy
transfer. We show how this model describes a scenario where a donor-acceptor
system can be brought into resonance by a narrow band of vibrational modes so
that the excitation transfer between the two can be made arbitrarily high. This
is then extended to a seven exciton system such as the widely-studied FMO
photosynthetic complex to show that a high efficiency is also achievable
therein. Our model encodes a number of readily testable predictions and we
discuss its generalisations to include the localisation in the reaction centre.",1006.3775v1
2011-02-10,Finite-lattice form factors in free-fermion models,"We consider the general $\mathbb{Z}_2$-symmetric free-fermion model on the
finite periodic lattice, which includes as special cases the Ising model on the
square and triangular lattices and $\mathbb{Z}_n$-symmetric BBS
$\tau^{(2)}$-model with $n=2$. Translating Kaufman's fermionic approach to
diagonalization of Ising-like transfer matrices into the language of Grassmann
integrals, we determine the transfer matrix eigenvectors and observe that they
coincide with the eigenvectors of a square lattice Ising transfer matrix. This
allows to find exact finite-lattice form factors of spin operators for the
statistical model and the associated finite-length quantum chains, of which the
most general is equivalent to the XY chain in a transverse field.",1102.2145v2
2011-03-02,Signatures of electronic polarons in La$_{1-x}$Sr$_{1+x}$MnO$_4$ observed by electron energy-loss spectroscopy,"The dielectric properties of La$_{1-x}$Sr$_{1+x}$MnO$_4$ single crystals with
x = 0, 0.125, 0.25, and 0.5 were studied by means of electron energy-loss
spectroscopy as a function of temperature and momentum transfer. A clear
signature of the doped holes is observed around 1.65 eV energy loss, where
spectral weight emerges with increasing x. For all $x \neq 0$, this
doping-induced excitation can propagate within the ab-plane, as revealed by a
clear upward dispersion of the corresponding loss peak with increasing momentum
transfer. The hole-induced excitation also shifts to higher energies with the
onset of magnetic correlations for x = 0.5, implying a strong coupling of
charge and spin dynamics. We conclude that (i) the loss feature at 1.65 eV is a
signature of electronic polarons, which are created around doped holes, and
that (ii) this low-energy excitation involves the charge transfer between
manganese and oxygen. The finite dispersion of these excitations further
indicates significant polaron-polaron interactions.",1103.0428v1
2011-07-28,Direct Detection of Photoinduced Charge Transfer Complexes in Polymer:Fullerene Blends,"We report transient electron paramagnetic resonance (trEPR) measurements with
sub-microsecond time resolution performed on a P3HT:PCBM blend at low
temperature. The trEPR spectrum immediately following photoexcitation reveals
signatures of spin-correlated polaron pairs. The pair partners (positive
polarons in P3HT and negative polarons in PCBM) can be identified by their
characteristic g-values. The fact that the polaron pair states exhibit strong
non-Boltzmann population unambiguously shows that the constituents of each pair
are geminate, i.e. originate from one exciton. We demonstrate that coupled
polaron pairs are present even several microseconds after charge transfer and
suggest that they embody the intermediate charge transfer complexes which form
at the donor/acceptor interface and mediate the conversion from excitons into
free charge carriers.",1107.5649v2
2012-03-24,"Transfer Learning, Soft Distance-Based Bias, and the Hierarchical BOA","An automated technique has recently been proposed to transfer learning in the
hierarchical Bayesian optimization algorithm (hBOA) based on distance-based
statistics. The technique enables practitioners to improve hBOA efficiency by
collecting statistics from probabilistic models obtained in previous hBOA runs
and using the obtained statistics to bias future hBOA runs on similar problems.
The purpose of this paper is threefold: (1) test the technique on several
classes of NP-complete problems, including MAXSAT, spin glasses and minimum
vertex cover; (2) demonstrate that the technique is effective even when
previous runs were done on problems of different size; (3) provide empirical
evidence that combining transfer learning with other efficiency enhancement
techniques can often yield nearly multiplicative speedups.",1203.5443v2
2012-04-12,Confined bulk states as a long-range sensor for impurities and a transfer channel for quantum information,"We show that confinement of bulk electrons can be observed at low-dimensional
surface structures and can serve as a long-range sensor for the magnetism and
electronic properties of single impurities or as a quantum information transfer
channel with large coherence lengths. Our ab initio calculations reveal
oscillations of electron density in magnetic chains on metallic surfaces and
help to unambiguously identify the electrons involved as bulk electrons. We
furthermore discuss the possibility of utilizing bulk state confinement to
transfer quantum information, encoded in an atom's species or spin, across
distances of several nanometers with high efficiency.",1204.2670v1
2012-07-10,Transfer of arbitrary quantum emitter states to near-field photon superpositions in nanocavities,"We present a method to analyze the suitability of particular photonic cavity
designs for information exchange between arbitrary superposition states of a
quantum emitter and the near-field photonic cavity mode. As an illustrative
example, we consider whether quantum dot emitters embedded in ""L3"" and ""H1""
photonic crystal cavities are able to transfer a spin superposition state to a
confined photonic superposition state for use in quantum information transfer.
Using an established dyadic Green's function (DGF) analysis, we describe
methods to calculate coupling to arbitrary quantum emitter positions and
orientations using the modified local density of states (LDOS) calculated using
numerical finite-difference time-domain (FDTD) simulations. We find that while
superposition states are not supported in L3 cavities, the double degeneracy of
the H1 cavities supports superposition states of the two orthogonal modes that
may be described as states on a Poincar\'{e}-like sphere. Methods are developed
to comprehensively analyze the confined superposition state generated from an
arbitrary emitter position and emitter dipole orientation.",1207.2410v3
2013-02-03,Cation Dependence of the Electronic States in Molecular Triangular Lattice System β'-X[Pd(dmit)_2]_2: A First-principles study,"The electronic structure of an isostructural series of molecular conductors,
{\beta}'-X[Pd(dmit)_2]_2 is systematically studied by a first-principles method
based on the density-functional theory. The calculated band structures are
fitted to the tight-binding model based on Pd(dmit)_2 dimers on the triangular
lattice. We find systematic variation in the anisotropy of the transfer
integrals along the three directions of the triangular lattice taking different
values. The transfer integral along the face-to-face stacking direction of
Pd(dmit)_2 dimers is always the largest. Around the quantum spin liquid, X =
EtMe_3Sb, the other two transfer integrals become comparable. We also report
sensible differences in the distribution of wavefunctions near the Fermi level
between the two dmit ligands of the Pd(dmit)_2 molecule.",1302.0477v2
2013-05-15,Multi-channel modeling and two photon coherent transfer paths in NaK,"We explore possible pathways for the creation of ultracold polar NaK
molecules in their absolute electronic and rovibrational ground state starting
from ultracold Feshbach molecules. In particular, we present a multi-channel
analysis of the electronic ground and K(4p)+Na(3s) excited state manifold of
NaK, analyze the spin character of both the Feshbach molecular state and the
electronically excited intermediate states and discuss possible coherent
two-photon transfer paths from Feshbach molecules to rovibronic ground state
molecules. The theoretical study is complemented by the demonstration of STIRAP
transfer from the X^1\Sigma^+ (v=0) state to the a^3\Sigma^+ manifold on a
molecular beam experiment.",1305.3419v1
2013-12-20,Experimental protocol for high-fidelity heralded photon-to-atom quantum state transfer,"A quantum network combines the benefits of quantum systems regarding secure
information transmission and calculational speed-up by employing quantum
coherence and entanglement to store, transmit, and process information. A
promising platform for implementing such a network are atom-based quantum
memories and processors, interconnected by photonic quantum channels. A crucial
building block in this scenario is the conversion of quantum states between
single photons and single atoms through controlled emission and absorption.
Here we present an experimental protocol for photon-to-atom quantum state
conversion, whereby the polarization state of an absorbed photon is mapped onto
the spin state of a single absorbing atom with >95% fidelity, while successful
conversion is heralded by a single emitted photon. Heralded high-fidelity
conversion without affecting the converted state is a main experimental
challenge, in order to make the transferred information reliably available for
further operations. We record >80/s successful state transfer events out of
18,000/s repetitions.",1312.5995v2
2014-01-20,Open spin chains with generic integrable boundaries: Baxter equation and Bethe ansatz completeness from SOV,"We solve the longstanding problem to define a functional characterization of
the spectrum of the transfer matrix associated to the most general spin-1/2
representations of the 6-vertex reflection algebra for general inhomogeneous
chains. The corresponding homogeneous limit reproduces the spectrum of the
Hamiltonian of the spin-1/2 open XXZ and XXX quantum chains with the most
general integrable boundaries. The spectrum is characterized by a second order
finite difference functional equation of Baxter type with an inhomogeneous term
which vanishes only for some special but yet interesting non-diagonal boundary
conditions. This functional equation is shown to be equivalent to the known
separation of variable (SOV) representation hence proving that it defines a
complete characterization of the transfer matrix spectrum. The polynomial
character of the Q-function allows us then to show that a finite system of
equations of generalized Bethe type can be similarly used to describe the
complete transfer matrix spectrum.",1401.4901v1
2014-02-13,$γ^\ast N \to N(1710)$ transition at high momentum transfer,"In a relativistic quark model we study the structure of the $N(1710)$
resonance, and the $\gamma^\ast N \to N(1710)$ reaction focusing on the high
momentum transfer region, where the valence quark degrees of freedom are
expected to be dominant. The $N(1710)$ resonance, a state with spin 1/2 and
positive parity ($J^P = \frac{1}{2}^+$), can possibly be interpreted as the
second radial excitation of the nucleon, after the Roper, $N(1440)$. We
calculate the $\gamma^\ast N \to N(1710)$ helicity amplitudes, and predict that
they are almost identical to those of the $\gamma^\ast N \to N(1440)$ reaction
in the high momentum transfer region. Thus, future measurement of the helicity
amplitudes for the $\gamma^\ast N \to N(1710)$ reaction can give a significant
hint on the internal structure of the $N(1710)$ state.",1402.3234v2
2014-11-05,Adiabatic many-body state preparation and information transfer in quantum dot arrays,"Quantum simulation of many-body systems are one of the most interesting tasks
of quantum technology. Among them is the preparation of a many-body system in
its ground state when the vanishing energy gap makes the cooling mechanisms
ineffective. Adiabatic theorem, as an alternative to cooling, can be exploited
for driving the many-body system to its ground state. In this paper, we study
two most common disorders in quantum dot arrays, namely exchange coupling
fluctuations and hyperfine interaction, in adiabatically preparation of ground
state in such systems. We show that the adiabatic ground state preparation is
highly robust against those disorder effects making it good analog simulator.
Moreover, we also study the adiabatic classical information transfer, using
singlet-triplet states, across a spin chain. In contrast to ground state
preparation the transfer mechanism is highly affected by disorder and in
particular, the hyperfine interaction is very destructive for the performance.
This suggests that for communication tasks across such arrays adiabatic
evolution is not as effective and quantum quenches could be preferable.",1411.1270v2
2014-12-18,Diffusive Transfer of Polarized 3He Gas through Depolarizing Magnetic Gradients,"Transfer of polarized 3He gas across spatially varying magnetic fields will
facilitate a new source of polarized 3He ions for particle accelerators. In
this context, depolarization of atoms as they pass through regions of
significant transverse field gradients is a major concern. To understand these
depolarization effects, we have built a system consisting of a Helmholtz coil
pair and a solenoid, both with central magnetic fields of order 30 gauss. The
atoms are polarized via metastability exchange optical pumping in the Helmholtz
coil and are in diffusive contact via a glass tube with a second test cell in
the solenoid. We have carried out measurements of the spin relaxation during
transfer of polarization in 3He at 1 torr by diffusion. We explore the use of
measurements of the loss of polarization taken in one cell to infer the
polarization in the other cell.",1412.6167v1
2015-08-27,Many-body localization protected quantum state transfer,"In thermal phases, the quantum coherence of individual degrees of freedom is
rapidly lost to the environment. Many-body localized (MBL) phases limit the
spread of this coherence and appear promising for quantum information
applications. However, such applications require not just long coherence times
but also a means to transport and manipulate information. We demonstrate that
this can be done in a one dimensional model of interacting spins at infinite
temperature. Our protocol utilizes protected qubits which emerge at the
boundary between topological and trivial phases. State transfer occurs via
dynamic shifts of this boundary and is shown to preserve quantum information.
As an example, we discuss the implementation of a universal, two-qubit gate
based upon MBL-protected quantum state transfer.",1508.06995v1
2017-05-16,Analysis of the non-Markovianity for electron transfer reactions in an oligothiophene-fullerene heterojunction,"The non-Markovianity of the electron transfer in an oligothiophene-fullerene
heterojunction described by a spin-boson model is analyzed using the time
dependent decoherence canonical rates and the volume of accessible states in
the Bloch sphere. The dynamical map of the reduced electronic system is
computed by the hierarchical equations of motion methodology (HEOM) providing
an exact dynamics. Transitory witness of non-Markovianity is linked to the bath
dynamics analyzed from the HEOM auxiliary matrices. The signature of the
collective bath mode detected from HEOM in each electronic state is compared
with predictions of the effective mode extracted from the spectral density. We
show that including this main reaction coordinate in a one-dimensional vibronic
system coupled to a residual bath satisfactorily describes the electron
transfer by a simple Markovian Redfield equation. Non-Markovianity is computed
for three inter fragment distances and compared with a priori criterion based
on the system and bath characteristic timescales.",1705.05898v2
2017-07-24,How to Suppress Dark States in Quantum Networks and Bio-Engineered Structures,"Transport across quantum networks underlies many problems, from state
transfer on a spin network to energy transport in photosynthetic complexes.
However, networks can contain dark subspaces that block the transportation, and
various methods used to enhance transfer on quantum networks can be viewed as
equivalently avoiding, modifying, or destroying the dark subspace. Here, we
exploit graph theoretical tools to identify the dark subspaces and show that
asymptotically almost surely they do not exist for large networks, while for
small ones they can be suppressed by properly perturbing the coupling rates
between the network nodes. More specifically, we apply these results to
describe the recently experimentally observed and robust transport behaviour of
the electronic excitation travelling on a genetically-engineered
light-harvesting cylinder (M13 virus) structure. We believe that these mainly
topological tools may allow us to better infer which network structures and
dynamics are more favourable to enhance transfer of energy and information
towards novel quantum technologies.",1707.07482v1
2017-08-05,High-fidelity state transfer through long-range correlated disordered quantum channels,"We study quantum-state transfer in $XX$ spin-$1/2$ chains where both
communicating spins are weakly coupled to a channel featuring disordered
on-site magnetic fields. Fluctuations are modelled by long-range correlated
sequences with self-similar profile obeying a power-law spectrum. We show that
the channel is able to perform an almost perfect quantum-state transfer in most
of the samples even in the presence of significant amounts of disorder provided
the degree of those correlations is strong enough. In that case, we also show
that the lack of mirror symmetry does not affect much the likelihood of having
high-quality outcomes. Our results advance a further step in designing robust
devices for quantum communication protocols.",1708.01823v1
2017-08-13,First-order transitions and thermodynamic properties in the 2D Blume-Capel model: the transfer-matrix method revisited,"We investigate the first-order transition in the spin-1 two-dimensional
Blume-Capel model in square lattices by revisiting the transfer-matrix method.
With large strip widths increased up to the size of 18 sites, we construct the
detailed phase coexistence curve which shows excellent quantitative agreement
with the recent advanced Monte Carlo results. In the deep first-order area, we
observe the exponential system-size scaling of the spectral gap of the transfer
matrix from which linearly increasing interfacial tension is deduced with
decreasing temperature. We find that the first-order signature at low
temperatures is strongly pronounced with much suppressed finite-size influence
in the examined thermodynamic properties of entropy, non-zero spin population,
and specific heat. It turns out that the jump at the transition becomes
increasingly sharp as it goes deep into the first-order area, which is in
contrast to the Wang-Landau results where finite-size smoothing gets more
severe at lower temperatures.",1708.03927v2
2017-12-05,Establishing and storing of deterministic quantum entanglement among three distant atomic ensembles,"It is crucial for physical realization of quantum information networks to
first establish entanglement among multiple space-separated quantum memories
and then at a user-controlled moment to transfer the stored entanglement to
quantum channels for distribution and conveyance of information. Here we
present an experimental demonstration on generation, storage and transfer of
deterministic quantum entanglement among three spatially separated atomic
ensembles. The off-line prepared multipartite entanglement of optical modes is
mapped into three distant atomic ensembles to establish entanglement of atomic
spin waves via electromagnetically-induced-transparency light-matter
interaction. Then the stored atomic entanglement is transferred into a
tripartite quadrature entangled state of light, which is space-separated and
can be dynamically allocated to three quantum channels for conveying quantum
information. The existence of entanglement among released three optical modes
verifies that the system has capacity of preserving multipartite entanglement.
The presented protocol can be directly extended to larger quantum networks with
more nodes.",1712.01470v1
2018-02-05,Quantum many-body dynamics of the Einstein-de Haas effect,"In 1915, Einstein and de Haas and Barnett demonstrated that changing the
magnetization of a magnetic material results in mechanical rotation, and vice
versa. At the microscopic level, this effect governs the transfer between
electron spin and orbital angular momentum, and lattice degrees of freedom,
understanding which is key for molecular magnets, nano-magneto-mechanics,
spintronics, and ultrafast magnetism. Until now, the timescales of
electron-to-lattice angular momentum transfer remain unclear, since modeling
this process on a microscopic level requires addition of an infinite amount of
quantum angular momenta. We show that this problem can be solved by
reformulating it in terms of the recently discovered angulon quasiparticles,
which results in a rotationally invariant quantum many-body theory. In
particular, we demonstrate that non-perturbative effects take place even if the
electron--phonon coupling is weak and give rise to angular momentum transfer on
femtosecond timescales.",1802.01638v2
2018-05-24,New D_{n+1}^(2) K-matrices with quantum group symmetry,"We find new families of solutions of the $D_{n+1}^{(2)}$ boundary Yang-Baxter
equation. The open spin-chain transfer matrices constructed with these
K-matrices have quantum group symmetry corresponding to removing one node from
the $D_{n+1}^{(2)}$ Dynkin diagram, namely, $U_{q}(B_{n-p}) \otimes
U_{q}(B_{p})$, where $p=0, \ldots, n$. These transfer matrices also have a $p
\leftrightarrow n-p$ duality symmetry. These symmetries help to account for the
degeneracies in the spectrum of the transfer matrix.",1805.10144v2
2018-11-26,Open and closed spin chains as multiprocessor wires: optimal engineering and reachability,"We consider the perfect transfer of a state between arbitrary nodes of
one-dimensional spin-1/2 chain with optimally engineered couplings. Motivated
by the fact that such a system could be used as a data bus for connecting
multiple quantum processors, we derive two necessary and sufficient conditions
that have to be met in order to perfectly transfer a state between any two
nodes and we employ them to examine both open and closed geometries. Analytical
calculations and numerical optimizations are performed for both cases in order
to determine the reachability of certain target states and to provide optimal
values for the couplings which ensure perfect fidelity. An important finding is
that even-sized closed chains allow for perfect transfer between any pair of
sites and therefore are a promising platform for the implementation of data bus
protocols.",1811.10346v1
2018-12-10,Exact solution of the $sp(4)$ integrable spin chain with generic boundaries,"The off-diagonal Bethe ansatz method is generalized to the integrable model
associated with the $sp(4)$ (or $C_2$) Lie algebra. By using the fusion
technique, we obtain the complete operator product identities among the fused
transfer matrices. These relations, together with some asymptotic behaviors and
values of the transfer matrices at certain points, enable us to determine the
eigenvalues of the transfer matrices completely. For the periodic boundary
condition case, we recover the same $T-Q$ relations obtained via conventional
Bethe ansatz methods previously, while for the off-diagonal boundary condition
case, the eigenvalues are given in terms of inhomogeneous $T-Q$ relations,
which could not be obtained by the conventional Bethe ansatz methods. The
method developed in this paper can be directly generalized to generic $sp(2n)$
(i.e., $C_n$) integrable model.",1812.03618v2
2018-12-16,Charge-transfer effect in hard x-ray 1$s$ and 2$p$ photoemission spectra: LDA+DMFT and cluster-model analysis,"We study $1s$ and $2p$ hard x-ray photoemission spectra (XPS) in a series of
late transition metal oxides: Fe$_2$O$_3$ (3$d^{5}$), FeTiO$_3$ (3$d^{6}$), CoO
(3$d^{7}$) and NiO (3$d^{8}$). The experimental spectra are analyzed with two
theoretical approaches: the MO$_6$ cluster model and the local density
approximation (LDA) + dynamical mean-field theory (DMFT). Owing to the absence
of the core-valence multiplets and spin-orbit coupling, 1$s$ XPS is found to be
a sensitive probe of chemical bonding and nonlocal charge-transfer screening,
providing complementary information to 2$p$ XPS. The 1$s$ XPS spectra are used
to assess the accuracy of the $ab$-initio LDA+DMFT approach, developed recently
to study the material-specific charge-transfer effects in core-level XPS.",1812.06432v2
2020-06-03,Population transfer via a finite temperature state,"We study quantum population transfer via a common intermediate state
initially in thermal equilibrium with a finite temperature $T$, exhibiting a
multi-level Stimulated Raman adiabatic passage structure. We consider two
situations for the common intermediate state, namely a discrete two-level spin
and a bosonic continuum. In both cases we show that the finite temperature
strongly affects the efficiency of the population transfer. We also show in the
discrete case that strong coupling with the intermediate state, or a longer
duration of the controlled pulse would suppress the effect of finite
temperature. In the continuous case, we adapt the thermofield-based
chain-mapping matrix product states algorithm to study the time evolution of
the system plus the continuum under time-dependent controlled pulses, which
shows a great potential to be used to solve open quantum system problems in
quantum optics.",2006.02583v1
2020-09-09,Atom Tunneling in the Hydroxylation Process of Taurine/$α$-Ketoglutarate Dioxygenase Identified by Quantum Mechanics/Molecular Mechanics Simulations,"TauD dioxygenase is one of the most studied $\alpha$-ketoglutarate dependent
dioxygenases ($\alpha$KGDs), involved in several biotechnological applications.
We investigated the key step in the catalytic cycle of the $\alpha$KGDs, the
hydrogen transfer process, by a QM/MM approach (B3LYP/CHARMM22). Analysis of
the charge and spin densities during the reaction demonstrates that a concerted
mechanism takes place, where the H atom transfer happens simultaneously with
the electron transfer from taurine to the Fe=O cofactor. We found quantum
tunneling of the hydrogen atom to increase the rate constant by a factor of 40
at 5\textcelsius{}. As a consequence a quite high KIE value of close to 60 is
obtained, which is consistent with the experimental value.",2009.05441v1
2020-11-11,On scalar products and form factors by Separation of Variables: the antiperiodic XXZ model,"We consider the XXZ spin-1/2 Heisenberg chain with antiperiodic boundary
conditions. The inhomogeneous version of this model can be solved by Separation
of Variables (SoV), and the eigenstates can be constructed in terms of
Q-functions, solution of a Baxter TQ-equation, which have double periodicity
compared to the periodic case. We compute in this framework the scalar products
of a particular class of separate states which notably includes the eigenstates
of the transfer matrix. We also compute the form factors of local spin
operators, i.e. their matrix elements between two eigenstates of the transfer
matrix. We show that these quantities admit determinant representations with
rows and columns labelled by the roots of the Q-functions of the corresponding
separate states, as in the periodic case, although the form of the determinant
are here slightly different. We also propose alternative types of determinant
representations written directly in terms of the transfer matrix eigenvalues.",2011.06109v2
2020-12-21,Many-body delocalisation as symmetry breaking,"We present a framework in which the transition between a many-body localised
(MBL) phase and an ergodic one is symmetry breaking. We consider random Floquet
spin chains, expressing their averaged spectral form factor (SFF) as a function
of time in terms of a transfer matrix that acts in the space direction. The SFF
is determined by the leading eigenvalues of this transfer matrix. In the MBL
phase the leading eigenvalue is unique, as in a symmetry-unbroken phase, while
in the ergodic phase and at late times the leading eigenvalues are
asymptotically degenerate, as in a system with degenerate symmetry-breaking
phases. We identify the broken symmetry of the transfer matrix, introduce a
local order parameter for the transition, and show that the associated
correlation functions are long-ranged only in the ergodic phase.",2012.11580v2
2021-03-09,Experimental study of intruder components in light neutron-rich nuclei via single-nucleon transfer reaction,"With the development of radioactive beam facilities, studies concerning the
shell evolution of unstable nuclei have recently gained prominence. Intruder
components, particularly s-wave intrusion, in the low-lying states of light
neutron-rich nuclei near N=8 are of importance in the study of shell evolution.
The use of single-nucleon transfer reactions in inverse kinematics has been a
sensitive tool that can be used to quantitatively investigate the
single-particle orbital component of selectively populated states. The
spin-parity, spectroscopic factor (or single-particle strength), and effective
single-particle energy can all be extracted from such reactions. These
observables are often useful to explain the nature of shell evolution, and to
constrain, check, and test the parameters used in nuclear structure models. In
this article, the experimental studies of the intruder components in low-lying
states of neutron-rich nuclei of He, Li, Be, B, and C isotopes using various
single-nucleon transfer reactions are reviewed. The focus is laid on the
precise determination of the intruder s-wave strength in low-lying states.",2103.05357v1
2021-05-30,Modelling Chromatic Emittance Growth in Staged Plasma Wakefield Acceleration to 1 TeV using Nonlinear Transfer Matrices,"A framework for integrating transfer matrices with particle-in-cell
simulations is developed for TeV staging of plasma wakefield accelerators.
Using nonlinear transfer matrices in terms up to ninth order in normalized
energy spread $\sqrt{\langle\delta\gamma^2\rangle}$ and deriving a compact
expression for the chromatic emittance growth in terms of the nonlinear matrix,
plasma wakefield accelerating stages simulated using the three-dimensional
particle-in-cell framework OSIRIS 4.0 were combined to model acceleration of an
electron beam from 10 GeV to 1 TeV in 85 plasma stages of meter scale-length
with long density ramps and connected by simple focusing lenses. In this
calculation, we find that for initial relative energy spreads below $10^{-3}$,
energy-spread growth below $10^{-5}$ of the energy gain per stage and
normalized emittance below mm-mrad, the chromatic emittance growth can be
minimal. The technique developed here may be useful for plasma collider design,
and potentially could be expanded to encompass non-linear wake structures and
include other degrees of freedom such as lepton spin.",2105.14481v2
2021-06-18,Efficient conversion of closed-channel dominated Feshbach molecules of $^{23}$Na$^{40}$K to their absolute ground state,"We demonstrate the transfer of $^{23}$Na$^{40}$K molecules from a
closed-channel dominated Feshbach-molecule state to the absolute ground state.
The Feshbach molecules are initially created from a gas of sodium and potassium
atoms via adiabatic ramping over a Feshbach resonance at 78.3$\,$G. The
molecules are then transferred to the absolute ground state using stimulated
Raman adiabatic passage with an intermediate state in the spin-orbit-coupled
complex $|c^3 \Sigma^+, v=35, J=1 \rangle \sim |B^1\Pi, v=12, J=1\rangle$. Our
measurements show that the pump transition dipole moment linearly increases
with the closed-channel fraction. Thus, the pump-beam intensity can be two
orders of magnitude lower than is necessary with open-channel dominated
Feshbach molecules. We also demonstrate that the phase noise of the Raman
lasers can be reduced by filter cavities, significantly improving the transfer
efficiency.",2106.10089v2
2021-06-22,A Simple XY Model for Cascade Transfer,"We propose a modified XY model in which cascade transfer emerges from
spatially local interactions, where the spin corresponds to the ""velocity"" of a
turbulent field. For this model, we theoretically calculate the scale-to-scale
energy flux and the equal time correlation function in $d$ dimensions. The
result indicates an inverse energy cascade with the non-Kolmogorov energy
spectrum proportional to $k^{-3}$. We also numerically confirm the result for
the cases $d=2$ and $d=3$. We thus conclude that the cascade transfer in our
model represents a different universality class from standard fluid turbulence.",2106.11670v3
2021-09-28,Singlet and triplet to doublet energy transfer: improving organic light-emitting diodes with radicals,"Organic light-emitting diodes (OLEDs) must be engineered to circumvent the
efficiency limit imposed by the 3:1 ratio of triplet to singlet exciton
formation following electron-hole capture. Here we show the spin nature of
luminescent radicals such as TTM-3PCz allows direct energy harvesting from both
singlet and triplet excitons through energy transfer, with subsequent rapid and
efficient light emission from the doublet excitons. This is demonstrated with a
model Thermally-Activated Delayed Fluorescence (TADF) organic semiconductor,
4CzIPN, where reverse intersystem crossing from triplets is characteristically
slow (50% emission by 1 microsecond). The radical:TADF combination shows much
faster emission via the doublet channel (80% emission by 100 ns) than the
comparable TADF-only system, and sustains higher electroluminescent efficiency
with increasing current density than a radical-only device. By unlocking energy
transfer channels between singlet, triplet and doublet excitons, further
technology opportunities are enabled for optoelectronics using organic
radicals.",2109.13522v1
2021-10-22,Charge and energy transfer in ac-driven Coulomb-coupled double quantum dots,"We study the dynamics of charge and energy currents in a Coulomb-coupled
double quantum dot system, when only one of the two dots is adiabatically
driven by a time-periodic gate that modulates its energy level. Although the
Coulomb coupling does not allow for electron transfer between the dots, it
enables an exchange of energy between them which induces a time variation of
charge in the undriven dot. We describe the effect of electron interactions at
low temperature using a time-dependent slave-spin 1 formulation within
mean-field that efficiently captures the main effects of the strong
correlations as well as the dynamical nature of the driving. We find that the
currents induced in the undriven dot due to the mutual friction between
inter-dot electrons are same order than those generated in the adiabatically
driven dot. Interestingly, up to 43$\%$ percent of the energy injected by the
ac sources can be transferred from the driven dot to the undriven one. We
complete our analysis by studying the impact of the Coulomb interaction on the
resistance of the quantum dot that is driven by the gate.",2110.11667v2
2021-11-11,$60^{\circ}$ and $120^{\circ}$ Domain Walls in Epitaxial BaTiO$_{3}$(111)/Co Multiferroic Heterostructures,"We report on domain pattern transfer from a ferroelectric
BaTiO$_{\mathrm{3}}$ substrate with a $(111)$-orientation of the surface to an
epitaxial Co film grown on a Pd buffer layer. Spatially modulated interfacial
strain transfer from ferroelectric/ferroelastic domains and inverse
magnetostriction in the ferromagnetic film induce stripe regions with a
modulation of the in-plane uniaxial magnetic anisotropy direction. Using
spin-polarized low energy electron microscopy, we observe the formation of two
distinct anisotropy configurations between stripe regions. Moreover, through
application of a magnetic field parallel or perpendicular to these stripes,
head-to-head or head-to-tail magnetization configurations are initialized. This
results in four distinct magnetic domain wall types associated with different
energies and widths, which in turn affects whether domain pattern transfer can
be achieved.",2111.06191v1
2021-11-30,Competition Between Exchange and Magnetostatic Energies in Domain Pattern Transfer from BaTiO$_3$(111) to Ni Thin Film,"We use spin polarized low energy electron microscopy to investigate domain
pattern transfer in a multiferroic heterostructure consisting of a
$(111)$-oriented BaTiO$_{\mathrm{3}}$ substrate and an epitaxial Ni film. After
in-situ thin film deposition and annealing through the ferroelectric phase
transition, interfacial strain transfer from ferroelastic domains in the
substrate and inverse magnetostriction in the magnetic thin film introduce a
uniaxial in-plane magnetic anisotropy that rotates by $60^{\circ}$ between
alternating stripe regions. We show that two types of magnetic domain wall can
be initialized in principle. Combining experimental results with micromagnetic
simulations we show that a competition between the exchange and magnetostatic
energies in these domain walls have a strong influence on the magnetic domain
configuration.",2111.15381v1
2022-05-05,Indirect optical manipulation of the antiferromagnetic order of insulating NiO by ultrafast interfacial energy transfer,"We report the ultrafast, (sub)picosecond reduction of the antiferromagnetic
order of the insulating NiO thin film in a Pt/NiO bilayer. This reduction of
the antiferromagnetic order is not present in pure NiO thin films after a
strong optical excitation. This ultrafast phenomenon is attributed to an
ultrafast and highly efficient energy transfer from the optically excited
electron system of the Pt layer into the NiO spin system. We propose that this
energy transfer is mediated by a stochastic exchange scattering of hot Pt
electrons at the Pt/NiO interface.",2205.02686v1
2022-06-03,Efficient electron transfer in quantum dot chains controlled by a cubic detuning profile via shortcuts to adiabaticity,"Long-distance fast and precise transfer of charge in semiconductor
nanostructures is one of the goals for scalable electronic devices. We study
theoretically the control of shuttling of an electron along a linear chain of
semiconductor electrostatically-defined quantum dots by an electric field pulse
with nonlinear time-dependent profile. We show that this essential nonlinearity
along with shortcuts to adiabaticity techniques speed up the electron transfer
with high fidelity, while still holding great robustness under spin-flip
interactions and inhomogeneities in the couplings of the chain. A given
fidelity can be set experimentally by controlling the maximum sweep energy and
duration of the control pulse",2206.01805v1
2022-12-27,Angular Dependence of the Polarization Transfer to the Proton in the $e \vec p \to e \vec p$ Process,"The dependence of the longitudinal polarization transfer to the proton in the
$ e \vec p \to e \vec p$ process on the proton scattering angle has been
numerically analyzed for the case where the initial (at rest) proton is
partially polarized along the direction of motion of the detected recoil
proton. The analysis is based on the results of JLab polarization experiments
on measuring the ratio of the Sachs form factors in the $\vec e p \to e \vec p$
process using the Kelly (2004) and Qattan (2015) parameterizations for their
ratio, in the kinematics of the SANE Collaboration experiment (2020) on
measuring the double spin asymmetry in the $\vec e \vec p \to e p$ process. It
is shown that the violation of the scaling of the Sachs form factors leads to a
significant increase in the magnitude of the polarization transfer to the
proton in comparison with the case of dipole dependence.",2212.13431v1
2023-02-23,Efficient Pathway to NaCs Ground State Molecules,"We present a study of two-photon pathways for the transfer of NaCs molecules
to their rovibrational ground state. Starting from NaCs Feshbach molecules, we
perform bound-bound excited state spectroscopy in the wavelength range from
900~nm to 940~nm, covering more than 30 vibrational states of the $c \,
^3\Sigma^+$, $b \, ^3\Pi$, and $B \, ^1\Pi$ electronic states. Analyzing the
rotational substructure, we identify the highly mixed $c \, ^3\Sigma^+_1 \,
|v=22 \rangle \sim b \, ^3\Pi_1 \, | v=54\rangle$ state as an efficient bridge
for stimulated Raman adiabatic passage (STIRAP). We demonstrate transfer into
the NaCs ground state with an efficiency of up to 88(4)\%. Highly efficient
transfer is critical for the realization of many-body quantum phases of
strongly dipolar NaCs molecules and high fidelity detection of single
molecules, for example, in spin physics experiments in optical lattices and
quantum information experiments in optical tweezer arrays.",2302.12293v1
2023-04-11,A Deep Analysis of Transfer Learning Based Breast Cancer Detection Using Histopathology Images,"Breast cancer is one of the most common and dangerous cancers in women, while
it can also afflict men. Breast cancer treatment and detection are greatly
aided by the use of histopathological images since they contain sufficient
phenotypic data. A Deep Neural Network (DNN) is commonly employed to improve
accuracy and breast cancer detection. In our research, we have analyzed
pre-trained deep transfer learning models such as ResNet50, ResNet101, VGG16,
and VGG19 for detecting breast cancer using the 2453 histopathology images
dataset. Images in the dataset were separated into two categories: those with
invasive ductal carcinoma (IDC) and those without IDC. After analyzing the
transfer learning model, we found that ResNet50 outperformed other models,
achieving accuracy rates of 90.2%, Area under Curve (AUC) rates of 90.0%,
recall rates of 94.7%, and a marginal loss of 3.5%.",2304.05022v1
2023-04-21,Optimized control for high-fidelity state transmission in open systems,"Quantum state transfer (QST) through spin chains has been extensively
investigated. Two schemes, the coupling set for perfect state transfer (PST) or
adding a leakage elimination operator (LEO) Hamiltonian have been proposed to
boost the transmission fidelity. However, these ideal schemes are only suitable
for closed systems and will lose their effectiveness in open ones. In this
work, we invoke a well explored optimization algorithm, Adam, to expand the
applicable range of PST couplings and LEO to the open systems. Our results show
that although the transmission fidelity decreases with increasing system-bath
coupling strength, Markovianity and temperature for both ideal and optimized
cases, the fidelities obtained by the optimized schemes always outweigh the
ideal cases. The enhancement becomes more bigger for a stronger bath,
indicating a stronger bath provides more space for the Adam to optimize. This
method will be useful for the realization of high-fidelity information transfer
in the presence of environment.",2304.10748v1
2023-06-26,Nonlocality of Majorana bound states revealed by electron waiting times in a topological Andreev interferometer,"The analysis of waiting times of electron transfers has recently become
experimentally accessible owing to advances in noninvasive probes working in
the short-time regime. We study electron waiting times in a topological Andreev
interferometer: a superconducting loop with controllable phase difference
connected to a quantum spin Hall edge, where the edge state helicity enables
the transfer of electrons and holes into separate leads, with transmission
controlled by the loop's phase difference $\phi$. This setup features gapless
Majorana bound states at $\phi=\pi$. The waiting times for electron transfers
across the junction are sensitive to the presence of the gapless states, but
are uncorrelated for all $\phi$. By contrast, at $\phi=\pi$ the waiting times
of Andreev-scattered holes show a strong correlation and the crossed
(hole-electron) distributions feature a unique behavior. Both effects
exclusively result from the nonlocal properties of Majorana bound states.
Consequently, electron waiting times and their correlations could circumvent
some of the challenges for detecting topological superconductivity and Majorana
states beyond conductance signatures.",2306.14964v2
2023-12-20,Accelerated adiabatic passage of a single electron spin qubit in quantum dots,"Adiabatic processes can keep the quantum system in its instantaneous
eigenstate, which is robust to noises and dissipation. However, it is limited
by sufficiently slow evolution. Here, we experimentally demonstrate the
transitionless quantum driving (TLQD) of the shortcuts to adiabaticity in
gate-defined semiconductor quantum dots (QDs) to greatly accelerate the
conventional adiabatic passage for the first time. For a given efficiency of
quantum state transfer, the acceleration can be more than twofold. The dynamic
properties also prove that the TLQD can guarantee fast and high-fidelity
quantum state transfer. In order to compensate for the diabatic errors caused
by dephasing noises, the modified TLQD is proposed and demonstrated in
experiment by enlarging the width of the counter-diabatic drivings. The
benchmarking shows that the state transfer fidelity of 97.8% can be achieved.
This work will greatly promote researches and applications about quantum
simulations and adiabatic quantum computation based on the gate-defined QDs.",2312.13135v2
1993-05-29,Exclusive Many-Particle Diffusion in Disordered Media and Correlation Functions for Random Vertex Models,"We consider systems of particles hopping stochastically on $d$-dimensional
lattices with space-dependent probabilities. We map the master equation onto an
evolution equation in a Fock space where the dynamics are given by a quantum
Hamiltonian (continuous time) or a transfer matrix resp. (discrete time). We
show that under certain conditions the time-dependent two-point density
correlation function in the $N$-particle steady state can be computed from the
probability distribution of a single particle moving in the same environment.
Focussing on exclusion models where each lattice site can be occupied by at
most one particle we discuss as an example for such a stochastic process a
generalized Heisenberg antiferromagnet where the strength of the spin-spin
coupling is space-dependent. In discrete time one obtains for one-dimensional
systems the diagonal-to-diagonal transfer matrix of the two-dimensional
six-vertex model with space-dependent vertex weights. For a random distribution
of the vertex weights one obtains a version of the random barrier model
describing diffusion of particles in disordered media. We derive exact
expressions for the averaged two-point density correlation functions in the
presence of weak, correlated disorder.",9305040v1
1995-11-16,Surface Free Energies and Surface Critical Behaviour of the ABF Models with Fixed Boundaries,"In a previous paper, we introduced reflection equations for
interaction-round-a-face (IRF) models and used these to construct commuting
double-row transfer matrices for solvable lattice spin models with fixed
boundary conditions. In particular, for the Andrews-Baxter-Forrester (ABF)
models, we derived special functional equations satisfied by the eigenvalues of
the commuting double-row transfer matrices. Here we introduce a generalized
inversion relation method to solve these functional equations for the surface
free energies. Although the surface free energies depend on the boundary spins
we find that the associated surface critical exponent $\alpha_s=(7-L)/4$ is
independent of the choice of boundary.",9511081v1
1999-06-25,Direct exchange in the edge-sharing spin-1/2 compound MgVO_3,"Bandstructure calculations with different spin arrangement for the spin-chain
compound MgVO_3 have been performed, and paramagnetic as well as magnetic
solutions with ferro- and antiferromagnetically ordered chains are found, the
magnetic solutions being by 0.22 eV per formula unit lower than the
paramagnetic one. The orbital analysis of the narrow band crossing the Fermi
level in the paramagnetic solution reveals that the band has almost pure
vanadium 3d character, the lobes of the relevant d-orbitals at the neighboring
in-chain sites being directed towards each other, which suggests direct
exchange. The tight-binding analysis of the band confirms the strong exchange
transfer between neighboring in-chain V-ions. Besides, some additional
superexchange transfer terms are found, which give rise both to in-plane
coupling between the chains and to frustration, the dominant frustration
occuring due to the interchain interaction.",9906385v1
2002-02-20,Magnetic field effects in energy relaxation mediated by Kondo impurities,"We study the energy distribution function of quasiparticles in voltage biased
mesoscopic wires in presence of magnetic impurities and applied magnetic field.
The system is described by a Boltzmann equation where the collision integral is
determined by coupling to spin 1/2 impurities. We derive an effective coupling
to a dissipative spin system which is valid well above Kondo temperature in
equilibrium or for sufficiently smeared distribution functions in
non-equilibrium. For low magnetic field an enhancement of energy relaxation is
found whereas for larger magnetic fields the energy relaxation decreases again
meeting qualitatively the experimental findings by Anthore et al.
(cond-mat/0109297). This gives a strong indication that magnetic impurities are
in fact responsible for the enhanced energy relaxation in copper wires. The
quantitative comparison, however, shows strong deviations for energy relaxation
with small energy transfer whereas the large energy transfer regime is in
agreement with our findings.",0202353v1
2004-05-21,Spin-controlled Mott-Hubbard bands in LaMnO_3 probed by optical ellipsometry,"Spectral ellipsometry has been used to determine the dielectric function of
an untwinned crystal of LaMnO_3 in the spectral range 0.5-5.6 eV at
temperatures 50 K < T < 300 K. A pronounced redistribution of spectral weight
is found at the Neel temperature T_N = 140 K. The anisotropy of the spectral
weight transfer matches the magnetic ordering pattern. A superexchange model
quantitatively describes spectral weight transfer induced by spin correlations.
This analysis implies that the lowest-energy transitions around 2 eV are
intersite d-d transitions, and that LaMnO_3 is a Mott-Hubbard insulator.",0405509v2
2004-07-12,Multi-criticality of the three-dimensional Ising model with plaquette interactions: An extension of Novotny's transfer-matrix formalism,"Three-dimensional Ising model with the plaquette-type (next-nearest-neighbor
and four-spin) interactions is investigated numerically. This extended Ising
model, the so-called gonihedric model, was introduced by Savvidy and Wegner as
a discretized version of the interacting (closed) surfaces without surface
tension. The gonihedric model is notorious for its slow relaxation to the
thermal equilibrium (glassy behavior), which deteriorate the efficiency of the
Monte Carlo sampling. We employ the transfer-matrix (TM) method, implementing
Novotny's idea, which enables us to treat arbitrary number of spins $N$ for one
TM slice even in three dimensions. This arbitrariness admits systematic
finite-size-scaling analyses. Accepting the extended parameter space by Cirillo
and co-worker, we analyzed the (multi) criticality of the gonihedric model for
N \le 13. Thereby, we found that, as first noted by Cirillo and co-worker
analytically (cluster-variation method), the data are well described by the
multi-critical (crossover) scaling theory. That is, the previously reported
nonstandard criticality for the gonihedric model is reconciled with a crossover
exponent and the ordinary three-dimensional-Ising universality class. We
estimate the crossover exponent and the correlation-length critical exponent at
the multi-critical point as \phi=0.6(2) and \nu=0.45(15), respectively.",0407284v1
2005-10-24,Spin-3 Chromium Bose-Einstein Condensates,"We analyze the physics of spin-3 Bose-Einstein condensates, and in particular
the new physics expected in on-going experiments with condensates of Chromium
atoms. We first discuss the ground-state properties, which, depending on still
unknown Chromium parameters, and for low magnetic fields can present various
types of phases. We also discuss the spinor-dynamics in Chromium spinor
condensates, which present significant qualitative differences when compared to
other spinor condensates. In particular, dipole-induced spin relaxation may
lead for low magnetic fields to transfer of spin into angular momentum similar
to the well-known Einstein-de Haas effect. Additionally, a rapid large
transference of population between distant magnetic states becomes also
possible.",0510634v3
2005-11-28,Time- and Polarization-Resolved Optical Spectroscopy of Colloidal CdSe Nanocrystal Quantum Dots in High Magnetic Fields,"In an effort to elucidate the spin (rather than charge) degrees of freedom in
colloidal semiconductor nanocrystal quantum dots, we report on a series of
static and time-resolved photoluminescence measurements of colloidal CdSe
quantum dots in ultra-high magnetic fields up to 45 Tesla. At low temperatures
(1.5 K - 40 K), the steady-state photoluminescence (PL) develops a high degree
of circular polarization with applied magnetic field, indicating the presence
of spin-polarized excitons. Time-resolved PL studies reveal a marked decrease
in radiative exciton lifetime with increasing magnetic field and temperature.
Except for an initial burst of unpolarized PL immediately following
photoexcitation, high-field time-resolved PL measurements reveal a constant
degree of circular polarization throughout the entire exciton lifetime, even in
the presence of pronounced exciton transfer via Forster energy transfer
processes.",0511676v1
1994-12-01,Polyakov loop and spin correlators on finite lattices A study beyond the mass gap,"We derive an analytic expression for point-to-point correlation functions of
the Polyakov loop based on the transfer matrix formalism. For the $2d$ Ising
model we show that the results deduced from point-point spin correlators are
coinciding with those from zero momentum correlators. We investigate the
contributions from eigenvalues of the transfer matrix beyond the mass gap and
discuss the limitations and possibilities of such an analysis. The finite size
behaviour of the obtained $2d$ Ising model matrix elements is examined. The
point-to-point correlator formula is then applied to Polyakov loop data in
finite temperature $SU(2)$ gauge theory. The leading matrix element shows all
expected scaling properties. Just above the critical point we find a Debye
screening mass $~\mu_D/T\approx4~$, independent of the volume.",9412003v1
1997-12-15,Central pseudoscalar production in pp scattering and the gluon contribution to the proton spin,"Central pseudoscalar production in $pp$ scattering is suppressed at small
values of $Q_\perp$, where $Q$ is defined as the difference between the momenta
transferred from the two protons. Such a behaviour is expected if the
production occurs through the fusion of two vectors. Photon exchange could
provide the dominant contribution at low transferred momenta, but we argue that
an extension of the experiment could probe the gluon contribution to the proton
spin.",9712387v2
2001-06-16,Hyperon polarization in semi-inclusive deeply inelastic lepton-nucleon scattering at high energy,"We calculate the polarizations for different octet hyperons produced in the
current fragmentation regions of the deeply inelastic lepton-nucleon
scatterings $\mu^-N \to \mu^- HX$ and $\nu_{\mu} N \to \mu^- HX$ at high energy
using different models for spin transfer in fragmentation processes. The
results show that measurements of those hyperon polarizations should provide
useful information to distinguish between different models in particular the
SU(6) and the DIS pictures used frequently in the literature. We found, in
particular, that measuring the polarization of $\Sigma^+$ produced in these
processes can give a better test to the validity of the different spin transfer
models.",0106184v1
2001-07-13,Spin Transfers for Baryon Production in Polarized pp Collisions at RHIC-BNL,"We consider the inclusive production of longitudinally polarized baryons in
${\vec p}p$ collisions at RHIC-BNL, with one longitudinally polarized proton.
We study the spin transfer between the initial proton and the produced baryon
as a function of its rapidity and we elucidate its sensitivity to the quark
helicity distributions of the proton and to the polarized fragmentation
functions of the quark into the baryon. We make predictions using an SU(6)
quark spectator model and a perturbative QCD (pQCD) based model. We discuss
these different predictions, and what can be learned from them, in view of the
forthcoming experiments at RHIC-BNL.",0107157v2
2002-11-11,Exact conserved quantities on the cylinder I: conformal case,"The nonlinear integral equations describing the spectra of the left and right
(continuous) quantum KdV equations on the cylinder are derived from integrable
lattice field theories, which turn out to allow the Bethe Ansatz equations of a
twisted ``spin -1/2'' chain. A very useful mapping to the more common nonlinear
integral equation of the twisted continuous spin $+1/2$ chain is found. The
diagonalization of the transfer matrix is performed. The vacua sector is
analysed in detail detecting the primary states of the minimal conformal models
and giving integral expressions for the eigenvalues of the transfer matrix.
Contact with the seminal papers \cite{BLZ, BLZ2} by Bazhanov, Lukyanov and
Zamolodchikov is realised. General expressions for the eigenvalues of the
infinite-dimensional abelian algebra of local integrals of motion are given and
explicitly calculated at the free fermion point.",0211094v3
2006-11-21,Polarization of Hyperons in Elementary Photoproduction,"Recent measurements using the CLAS detector at Jefferson Lab of the reactions
$\vec\gamma + p \to K^+ + \vec\Lambda$ and $\vec\gamma + p \to K^+ +
\vec\Sigma^0$ have been used to extract the spin transfer coefficients $C_x$
and $C_z$ for the first time. These observables quantify the degree of the
photon circular polarization that is transferred to the recoiling hyperons in
the scattering plane. The unexpected result is that $\Lambda$ hyperons are
produced ``100% polarized'' as seen when combining $C_x$ and $C_z$ with the
induced transverse polarization, $P$. Furthermore, $C_x$ and $C_z$ seem to be
linearly related. This paper discusses the experimental results and offers a
hypothesis which can explain these observations. We show how the produced
strange quark can be subject to a pure spin-orbit type of interaction which
preserves its state of polarization throughout the hadronization process.",0611035v2
1997-09-16,"Pion Excess, Nuclear Correlations, and the Interpretation of ($\vec p, \vec n$) Spin Transfer Experiments","Conventional theories of nuclear interactions predict a net increase in the
distribution of virtual pions in nuclei relative to free nucleons. Analysis of
data from several nuclear experiments has led to claims of evidence against
such a pion excess. These conclusions are usually based on a collective theory
(RPA) of the pions, which may be inadequate. The issue is the energy dependence
of the nuclear response, which differs for theories with strong NN correlations
from the RPA predictions. In the present paper, information about the energy
dependence is extracted from sum rules, which are calculated for such a
correlated, noncollective nuclear theory. The results lead to much reduced
sensitivity of nuclear reactions to the correlations that are responsible for
the pion excess. The primary example is $(\vec p,\vec n)$ spin transfer, for
which the expected effects are found to be smaller than the experimental
uncertainties. The analysis has consequences for Deep Inelastic Scattering
(DIS) experiments as well.",9709033v1
1998-10-09,Structure of the ^3He in Backward Elastic p ^3He-Scattering,"Backward elastic $p ^3He$-scattering at incident proton kinetic energies
$T_p>1$ GeV is investigated in the framework of the np-pair transfer mechanism
and triangular diagram of one-pion exchange with a subprocess $pd\to ^3He\pi^0$
using a realistic three-body wave function of the $^3He$ nucleus.
  It is found that the $np-$pair transfer mechanism dominates owing to a rich
high momentum component of the $^3He$ wave function.
  We show that the experimental cross section of this process is defined mainly
by the values of the Faddeev component of the $^3He$ wave function, $\phi
^{23}({\bf q}_{23}, {\bf p}_1)$, at high relative momenta $q_{23}> 0.6 GeV/c$
of the NN-pair in the $^1S_0$-state and at low spectator momenta $p_1\leq 0.1$
GeV/c. The spin-spin correlation parameter is calculated in the framework of
the dominating mechanism for the case of polarized target and beam.
Rescatterings in the initial and final states are taken into account.
Comparison with the $pd\to dp$ process is performed.",9810028v2
2003-02-14,Spin effects and relative momentum spectrum of two protons in deuteron charge-exchange breakup,"The relation between the differential cross section of the charge-exchange
breakup of a fast deuteron d+p -> (pp)+n and the differential cross section of
the charge transfer process n+p -> p+n is discussed taking into account the
effects of the proton identity and of the Coulomb and strong interactions of
protons in the final state. The distribution of the relative momenta of the
protons is found in the framework of the impulse approach. It is shown that the
use of polarized initial deuterons and protons allows one to separate two
spin-dependent terms in the amplitude of the charge transfer reaction n+p ->
p+n at zero angle and to determine their phase difference. The influence of the
deuteron d-wave state is investigated.",0302036v1
2004-08-24,Quantum state transfer via the ferromagnetic chain in a spatially modulated field,"We show that a perfect quantum state transmission can be realized through a
spin chain possessing a commensurate structure of energy spectrum, which is
matched with the corresponding parity. As an exposition of the mirror inversion
symmetry discovered by Albanese et. al (quant-ph/0405029), the parity matched
the commensurability of energy spectra help us to present the novel
pre-engineered spin systems for quantum information transmission. Based on the
these theoretical analysis, we propose a protocol of near-perfect quantum state
transfer by using a ferromagnetic Heisenberg chain with uniform coupling
constant, but an external parabolic magnetic field. The numerical results shows
that the initial Gaussian wave packet in this system with optimal field
distribution can be reshaped near-perfectly over a longer distance.",0408152v1
2006-01-30,Cooperative spin decoherence and population transfer,"An ensemble of multilevel atoms is a good candidate for a quantum information
storage device. The information is encrypted in the collective ground state
atomic coherence, which, in the absence of external excitation, is decoupled
from the vacuum and therefore decoherence free. However, in the process of
manipulation of atoms with light pulses (writing, reading), one inadvertently
introduces a coupling to the environment, i.e. a source of decoherence. The
dissipation process is often treated as an independent process for each atom in
the ensemble, an approach which fails at large atomic optical depths where
cooperative effects must be taken into account. In this paper, the cooperative
behavior of spin decoherence and population transfer for a system of two,
driven multilevel-atoms is studied. Not surprisingly, an enhancement in the
decoherence rate is found, when the atoms are separated by a distance that is
small compared to an optical wavelength; however, it is found that this rate
increases even further for somewhat larger separations for atoms aligned along
the direction of the driving field's propagation vector. A treatment of the
cooperative modification of optical pumping rates and an effect of polarization
swapping between atoms is also discussed, lending additional insight into the
origin of the collective decay.",0601204v1
2006-03-21,Quantum Speed Limit for Perfect State Transfer in One Dimension,"The basic idea of spin chain engineering for perfect quantum state transfer
(QST) is to find a set of coupling constants in the Hamiltonian, such that a
particular state initially encoded on one site will evolve freely to the
opposite site without any dynamical controls. The minimal possible evolution
time represents a speed limit for QST. We prove that the optimal solution is
the one simulating the precession of a spin in a static magnetic field. We also
argue that, at least for solid-state systems where interactions are local, it
is more realistic to characterize the computation power by the couplings than
the initial energy.",0603179v2
2008-06-14,"Multiparameter statistical models from $N^2\times N^2$ braid matrices: Explicit eigenvalues of transfer matrices ${\bf T}^{(r)}$, spin chains, factorizable scatterings for all $N$","For a class of multiparameter statistical models based on $N^2\times N^2$
braid matrices the eigenvalues of the transfer matrix ${\bf T}^{(r)}$ are
obtained explicitly for all $(r,N)$. Our formalism yields them as solutions of
sets of linear equations with simple constant coefficients. The role of
zero-sum multiplets constituted in terms of roots of unity is pointed out and
their origin is traced to circular permutations of the indices in the tensor
products of basis states induced by our class of ${\bf T}^{(r)}$ matrices. The
role of free parameters, increasing as $N^2$ with $N$, is emphasized
throughout. Spin chain Hamiltonians are constructed and studied for all $N$.
Inverse Cayley transforms of Yang-Baxter matrices corresponding to our braid
matrices are obtained for all $N$. They provide potentials for factorizable
$S$-matrices. Main results are summarized and perspectives are indicated in the
concluding remarks.",0806.2371v3
2008-09-11,Factorization of R-matrix and Baxter Q-operators for generic sl(N) spin chains,"We develop an approach for constructing the Baxter Q-operators for generic
sl(N) spin chains. The key element of our approach is the possibility to
represent a solution of the the Yang Baxter equation in the factorized form. We
prove that such a representation holds for a generic sl(N) invariant R-operator
and find the explicit expression for the factorizing operators. Taking trace of
monodromy matrices constructed of the factorizing operators one defines a
family of commuting (Baxter) operators on the quantum space of the model. We
show that a generic transfer matrix factorizes into the product of N Baxter
Q-operators and discuss an application of this representation for a derivation
of functional relations for transfer matrices.",0809.2050v2
2009-03-09,Bethe ansatz equations for open spin chains from giant gravitons,"We investigate the open spin chain describing the scalar sector of the Y=0
giant graviton brane at weak coupling. We provide a direct proof of
integrability in the SU(2) and SU(3) sectors by constructing the transfer
matrices. We determine the eigenvalues of these transfer matrices in terms of
roots of the corresponding Bethe ansatz equations (BAEs). Based on these
results, we propose BAEs for the full SO(6) sector. We find that, in the
weak-coupling limit, the recently-proposed all-loop BAEs essentially agree with
those proposed in the present work.",0903.1646v3
2010-03-22,Magnetic excitations of spin and orbital moments in cobalt oxide,"Magnetic and phonon excitations in the antiferromagnet CoO with an unquenched
orbital angular momentum are studied by neutron scattering. Results of energy
scans in several Brillouin zones in the (HHL) plane for energy transfers up to
16 THz are presented. The measurements were performed in the antiferromagnetic
ordered state at 6 K (well below TN~290 K) as well as in the paramagnetic state
at 450 K. Several magnetic excitation modes are identified from the dependence
of their intensity on wavevector and temperature. Within a Hund's rule model
the excitations correspond to fluctuations of coupled orbital and spin degrees
of freedom whose bandwidth is controlled by interionic superexchange. The
different <111> ordering domains give rise to several magnetic peaks at each
wavevector transfer.",1003.4166v1
2010-06-09,Origin of the ESR spectrum in the Prussian Blue analogue RbMn[Fe(CN)6]*H2O,"We present an ESR study at excitation frequencies of 9.4 GHz and 222.4 GHz of
powders and single crystals of a Prussian Blue analogue (PBA),
RbMn[Fe(CN)6]*H2O in which Fe and Mn undergoes a charge transfer transition
between 175 and 300 K. The ESR of PBA powders, also reported by Pregelj et al.
(JMMM, 316, E680 (2007)) is assigned to cubic magnetic clusters of Mn2+ ions
surrounding Fe(CN)6 vacancies. The clusters are well isolated from the bulk and
are superparamagnetic below 50 K. In single crystals various defects with lower
symmetry are also observed. Spin-lattice relaxation broadens the bulk ESR
beyond observability. This strong spin relaxation is unexpected above the
charge transfer transition and is attributed to a mixing of the Mn3+ - Fe2+
state into the prevalent Mn2+ - Fe3+ state.",1006.1777v1
2010-06-22,Opto-mechanical transducers for long-distance quantum communication,"We describe a new scheme to interconvert stationary and photonic qubits which
is based on indirect qubit-light interactions mediated by a mechanical
resonator. This approach does not rely on the specific optical response of the
qubit and thereby enables optical quantum interfaces for a wide range of solid
state spin and charge based systems. We discuss the implementation of quantum
state transfer protocols between distant nodes of a large scale network and
evaluate the effect of the main noise sources on the resulting state transfer
fidelities. For the specific examples of electronic spin qubits and
superconducting charge qubits we show that high fidelity quantum communication
protocols can be implemented under realistic experimental conditions.",1006.4361v2
2010-07-06,Corrections to scaling for block entanglement in massive spin-chains,"We consider the Renyi entropies S_n in one-dimensional massive integrable
models diagonalizable by means of corner transfer matrices (as Heisenberg and
Ising spin chains). By means of explicit examples and using the relation of
corner transfer matrix with the Virasoro algebra, we show that close to a
conformal invariant critical point, when the correlation length xi is finite
but large, the corrections to the scaling are of the unusual form xi^(-x/n),
with x the dimension of a relevant operator in the conformal theory. This is
reminiscent of the results for gapless chains and should be valid for any
massive one-dimensional model close to a conformal critical point.",1007.0881v2
2010-09-21,Phase locking of vortex based spin transfer oscillators to a microwave current,"Phase locking experiments on vortex based spin transfer oscillators with an
external microwave current are performed. We present clear evidence of phase
locking, frequency pulling, as well as fractional synchronization in this
system, with a minimum peak linewidth of only 3 kHz in the locked state. We
find that locking ranges of the order of 1/3 of the oscillator frequency are
easily achievable because of the large tunability $\partial f/\partial I_{dc}$
observed in our vortex based systems. Such large locking ranges allow us to
demonstrate the simultaneous phase locking of two independent oscillators
connected in series with the external source.",1009.4076v1
2010-10-03,Entanglement Transfer via XXZ Heisenberg chain with DM Interaction,"The role of spin-orbit interaction, arises from the Dzyaloshinski-Moriya
anisotropic antisymmetric interaction, on the entanglement transfer via an
antiferromagnetic XXZ Heisenberg chain is investigated. From symmetrical point
of view, the XXZ Hamiltonian with Dzyaloshinski-Moriya interaction can be
replaced by a modified XXZ Hamiltonian which is defined by a new exchange
coupling constant and rotated Pauli operators. The modified coupling constant
and the angle of rotations are depend on the strength of Dzyaloshinski-Moriya
interaction. In this paper we study the dynamical behavior of the entanglement
propagation through a system which is consist of a pair of maximally entangled
spins coupled to one end of the chain. The calculations are performed for the
ground state and the thermal state of the chain, separately. In both cases the
presence of this anisotropic interaction make our channel more efficient, such
that the speed of transmission and the amount of the entanglement are improved
as this interaction is switched on. We show that for large values of the
strength of this interaction a large family of XXZ chains becomes efficient
quantum channels, for whole values of an isotropy parameter in the region $-2
\leq \Delta \leq 2$.",1010.0387v1
2011-10-17,Tuning the magnetic dimensionality by charge ordering in the molecular TMTTF salts,"We theoretically investigate the interplay between charge ordering and
magnetic states in quasi-one-dimensional molecular conductors TMTTF$_2X$,
motivated by the observation of a complex variation of competing and/or
coexisting phases. We show that the ferroelectric-type charge order increases
two-dimensional antiferromagnetic spin correlation, whereas in the
one-dimensional regime two different spin-Peierls states are stabilized. By
using first-principles band calculations for the estimation for the transfer
integrals and comparing our results with the experiments, we identify the
controlling parameters in the experimental phase diagram to be not only the
interchain transfer integrals but also the amplitude of the charge order.",1110.3573v2
2011-10-28,How to construct spin chains with perfect state transfer,"It is shown how to systematically construct the $XX$ quantum spin chains with
nearest-neighbor interactions that allow perfect state transfer (PST). Sets of
orthogonal polynomials (OPs) are in correspondence with such systems. The key
observation is that for any admissible one-excitation energy spectrum, the
weight function of the associated OPs is uniquely prescribed. This entails the
complete characterization of these PST models with the mirror symmetry property
arising as a corollary. A simple and efficient algorithm to obtain the
corresponding Hamiltonians is presented. A new model connected to a special
case of the symmetric $q$-Racah polynomials is offered. It is also explained
how additional models with PST can be derived from a parent system by removing
energy levels from the one-excitation spectrum of the latter. This is achieved
through Christoffel transformations and is also completely constructive in
regards to the Hamiltonians.",1110.6474v2
2011-12-12,Theory of laser-induced demagnetization at high temperatures,"Laser-induced demagnetization is theoretically studied by explicitly taking
into account interactions among electrons, spins and lattice. Assuming that the
demagnetization processes take place during the thermalization of the
sub-systems, the temperature dynamics is given by the energy transfer between
the thermalized interacting baths. These energy transfers are accounted for
explicitly through electron-magnons and electron-phonons interaction, which
govern the demagnetization time scale. By properly treating the spin system in
a self-consistent random phase approximation, we derive magnetization dynamic
equations for a broad range of temperature. The dependence of demagnetization
on the temperature and pumping laser intensity is calculated in detail. In
particular, we show several salient features for understanding magnetization
dynamics near the Curie temperature. While the critical slowdown in dynamics
occurs, we find that an external magnetic field can restore the fast dynamics.
We discuss the implication of the fast dynamics in the application of heat
assisted magnetic recording.",1112.2428v1
2012-08-21,Optimized production of ultracold ground-state molecules: Stabilization employing potentials with ion-pair character and strong spin-orbit coupling,"We discuss the production of ultracold molecules in their electronic ground
state by photoassociation employing electronically excited states with ion-pair
character and strong spin-orbit interaction. A short photoassociation laser
pulse drives a non-resonant three-photon transition for alkali atoms colliding
in their lowest triplet state. The excited state wave packet is transferred to
the ground electronic state by a second laser pulse, driving a resonant
two-photon transition. After analyzing the transition matrix elements governing
the stabilization step, we discuss the efficiency of population transfer using
transform-limited and linearly chirped laser pulses. Finally, we employ optimal
control theory to find the most efficient stabilization pathways. We find that
the stabilization efficiency can be increased by one and two orders of
magnitude for linearly chirped and optimally shaped laser pulses, respectively.",1208.4331v2
2012-08-31,Electron Transfer Reactions: Generalized Spin-Boson Approach,"We introduce a mathematically rigorous analysis of a generalized spin-boson
system for the treatment of a donor-acceptor (reactant-product) quantum system
coupled to a thermal quantum noise. The donor/acceptor probability dynamics
describes transport reactions in chemical processes in presence of a noisy
environment -- such as the electron transfer in a photosynthetic reaction
center. Besides being rigorous, our analysis has the advantages over previous
ones that (1) we include a general, non energy-conserving system-environment
interaction, and that (2) we allow for the donor or acceptor to consist of
multiple energy levels lying closely together. We establish explicit
expressions for the rates and the efficiency (final donor-acceptor population
difference) of the reaction. In particular, we show that the rate increases for
a multi-level acceptor, but the efficiency does not.",1208.6499v2
2012-09-04,A few-electron quadruple quantum dot in a closed loop,"We report the realization of a quadruple quantum dot device in a square-like
configuration where a single electron can be transferred on a closed path free
of other electrons. By studying the stability diagrams of this system, we
demonstrate that we are able to reach the few-electron regime and to control
the electronic population of each quantum dot with gate voltages. This allows
us to control the transfer of a single electron on a closed path inside the
quadruple dot system. This work opens the route towards electron spin
manipulation using spin-orbit interaction by moving an electron on complex
paths free of electrons",1209.0733v1
2013-02-26,Spin transfer nano-oscillators,"The use of spin transfer nano-oscillators (STNOs) to generate microwave
signal in nanoscale devices have aroused tremendous and continuous research
interest in recent years. Their key features are frequency tunability,
nanoscale size, broad working temperature, and easy integration with standard
silicon technology. In this feature article, we give an overview of recent
developments and breakthroughs in the materials, geometry design and properties
of STNOs. We focus in more depth on our latest advances in STNOs with
perpendicular anisotropy showing a way to improve the output power of STNO
towards the {\mu}W range. Challenges and perspectives of the STNOs that might
be productive topics for future research were also briefly discussed.",1302.6467v1
2013-03-26,Proposal for a loophole-free Bell test based on spin-photon interactions in cavities,"We present a scheme to demonstrate loophole-free Bell inequality violation
where the entanglement between photon pairs is transferred to solid state
(spin) qubits mediated by cavity QED interactions. As this transfer can be
achieved in a heralded way, our scheme is basically insensitive to losses on
the channel. This makes it appealing for the implementation of quantum
information protocols based on nonlocality, such as device-independent quantum
key distribution. We consider potential experimental realisations of our scheme
using single atom, colour centre and quantum dot cavity systems.",1303.6522v2
2013-04-16,A description of odd mass Xe and Te isotopes in the Interacting Boson-Fermion Model,"Recent interest in spectroscopic factors for single-neutron transfer in
low-spin states of the even-odd Xenon $^{125,127,129.131}$Xe and even-odd
Tellurium, $^{123,125,127,129,131}$Te isotopes stimulated us to study these
isotopes within the frame work of the Interacting Boson-Fermion Model. The
fermion that is coupled to the system of bosons is taken to be in the positive
parity $3s_{1/2}$, $2d_{3/2}$, $2d_{5/2}$, $1g_{7/2}$ and in the negative
$1h_{11/2}$ single-particle orbits, the complete 50-82 major shell. The
calculated energies of low-spin energy levels of the odd isotopes are found to
agree well with the experimental data. Also B(E2), B(M1) values and
spectroscopic factors for single-neutron transfer are calculated and compared
with experimental data.",1304.4364v1
2014-06-29,Xclaim: a graphical interface for the calculation of core-hole spectroscopies,"Xclaim (x-ray core level atomic multiplets) is a graphical interface for the
calculation of core-hole spectroscopy and ground state properties within a
charge-transfer multiplet model taking into account a many-body hamiltonian
with Coulomb, spin-orbit, crystal-field, and hybridization interactions. Using
Hartree-Fock estimates for the Coulomb and spin-orbit interactions and ligand
field parameters (crystal-field, hybridization and charge-transfer energy) the
program can calculate x-ray absorption spectroscopy (XAS), x-ray photoemission
spectroscopy (XPS), photoemission spectrospcy (PES) and inverse photoemission
(IPES) for d- and f-valence metals and different absorption edges. The program
runs in Linux, Windows and MacOS platforms.",1406.7532v4
2014-07-25,Nonlinear behavior and mode coupling in spin transfer nano-oscillators,"By investigating thoroughly the tunable behavior of coupled modes, we
highlight how it provides new means to handle the properties of spin transfer
nano-oscillators. We first demonstrate that the main features of the microwave
signal associated with coupled vortex dynamics i.e. frequency, spectral
coherence, critical current, mode localization, depends drastically on the
relative vortex core polarities. Secondly we report a large reduction of the
nonlinear linewidth broadening obtained by changing the effective damping
through the control of the core configuration. Such a level of control on the
nonlinear behavior reinforces our choice to exploit the microwave properties of
collective modes for applications of spintronic devices in novel generation of
integrated telecommunication devices.",1407.6901v1
2014-09-18,On the complete-spectrum characterization of quantum integrable spin chains via the inhomogeneous T-Q relation,"With the XXZ spin chains as examples, we prove two theorems: (1) the
functional relations derived from the off-diagonal Bethe Ansatz scheme are the
sufficient and necessary conditions to characterize the complete spectrum of
the corresponding transfer matrix; (2) each eigenvalue of the transfer matrix
can be parameterized by a minimal inhomogeneous T-Q relation. These statements
hold for both with and without inhomogeneity. The proof can be generalized to
other finite-dimensional quantum integrable models.",1409.5303v3
2014-11-08,Spin light of relativistic electrons in neutrino fluxes,"A new mechanism of electromagnetic radiation by electrons under the influence
of a dense neutrino flux, termed ""the spin light of electron"" in neutrino flux
($SLe_\nu$), is considered. It is shown that in the case when electrons are
moving against the neutrino flux with relativistic energy there is a reasonable
increase of the efficiency of the energy transfer from the neutrino flux to the
electromagnetic radiation by the $SLe_\nu$ mechanism. The proposed radiation
process is applied to an astrophysical environment with characteristics
peculiar to supernovae. It is shown that a reasonable portion of energy of the
neutrino flux can be transferred by the $SLe_\nu$ to gamma-rays .",1502.05346v1
2016-02-05,Exact solution of the trigonometric SU(3) spin chain with generic off-diagonal boundary reflections,"The nested off-diagonal Bethe ansatz is generalized to study the quantum spin
chain associated with the $SU_q(3)$ R-matrix and generic integrable
non-diagonal boundary conditions. By using the fusion technique, certain closed
operator identities among the fused transfer matrices at the inhomogeneous
points are derived. The corresponding asymptotic behaviors of the transfer
matrices and their values at some special points are given in detail. Based on
the functional analysis, a nested inhomogeneous T-Q relations and Bethe ansatz
equations of the system are obtained. These results can be naturally
generalized to cases related to the $SU_q(n)$ algebra.",1602.02042v3
2016-04-01,On-chip storage of broadband photonic qubits in a cavity-protected rare-earth ensemble,"Ensembles of solid-state optical emitters enable broadband quantum storage
and transduction of photonic qubits, with applications in high-rate optical
quantum networks for secure communications, global time-keeping, and
interconnecting future quantum computers. To realize coherent quantum
information transfer using ensembles, spin rephasing techniques are currently
used to mitigate fast decoherence resulting from inhomogeneous broadening. Here
we use a dense ensemble of neodymium rare-earth ions strongly coupled to a
nanophotonic resonator to demonstrate that decoherence of a single photon
excitation is near-completely suppressed via cavity protection- a new technique
for accessing the decoherence-free subspace of collective coupling. The
protected Rabi oscillations between the cavity field and the atomic
superradiant state thereby enable ultra-fast transfer of photonic frequency
qubits (~50 GHz bandwidth) into the ions, followed by retrieval with 98.7%
fidelity. By coupling the superradiant excitation to other long-lived
rare-earth spin states, this technology will enable broadband, always-ready
quantum memories and fast optical-to-microwave transducers.",1604.00143v2
2016-06-02,Exact solution of the $D_3$ non-Abelian anyon chain,"Commuting transfer matrices for linear chains of interacting non-Abelian
anyons from the two-dimensional irreducible representation of the dihedral
group $D_3$ (or, equivalently, the integer sector of the $su(2)_4$ spin-$1$
chain) are constructed using the spin-anyon correspondence to a $D_3$-symmetric
formulation of the XXZ Heisenberg spin chain. The spectral problem is solved
using discrete inversion identities satisfied by these transfer matrices and
functional Bethe ansatz methods. The resulting spectrum can be related to that
of the XXZ spin-$1/2$ Heisenberg chain with boundary conditions depending on
the topological sector of the anyon chain. The properties of this model in the
critical regime are studied by finite size analysis of the spectrum. In
particular, points in the phase diagram where the anyon chain realizes some of
the rational $\mathbb{Z}_2$ orbifold theories are identified.",1606.00793v1
2016-07-20,The chiral anomaly in real space,"The chiral anomaly is based on a non-conserved chiral charge and can happen
in Dirac fermion systems under the influence of external electromagnetic
fields. In this case, the spectral flow leads to a transfer of right- to
left-moving excitations or vice versa. The corresponding transfer of chiral
particles happens in momentum space. We here describe an intriguing way to
introduce the chiral anomaly into real space. Our system consists of two
quantum dots that are formed at the helical edge of a quantum spin Hall
insulator on the basis of three magnetic impurities. Such a setup gives rise to
fractional charges which we show to be sharp quantum numbers for large barrier
strength. Interestingly, it is possible to map the system onto a quantum spin
Hall ring in the presence of a flux pierced through the ring where the relative
angle between the magnetization directions of the impurities takes the role of
the flux. The chiral anomaly in this system is then directly related to the
excess occupation of particles in the two quantum dots. This analogy allows us
to predict an observable consequence of the chiral anomaly in real space.",1607.05982v1
2016-10-11,Quantum state transfer with ultracold atoms in optical lattices,"Ultracold atoms can be used to perform quantum simulations of a variety of
condensed matter systems, including spin systems. These progresses point to the
implementation of the manipulation of quantum states and to observe and exploit
the effect of quantum correlations. A natural direction along this line is
provided by the possibility to perform quantum state transfer (QST). After
presenting a brief discussion of the simulation of quantum spin chains with
ultracold gases and reminding the basic facts of QST, we discuss how to
potentially use the tools of present-day ultracold technology to implement the
QST between two regions of the atomic system (the sender and the receiver). The
fidelity and the typical timescale of the QST are discussed, together with
possible limitations and applications of the presented results.",1610.03248v1
2017-01-13,Experimental and theoretical investigations of quantum state transfer and decoherence processes in quasi-one-dimensional systems in multiple-quantum NMR experiments,"Multiple quantum (MQ) NMR methods \cite{Baum} are applied to the analysis of
various problems of quantum information processing.
  It is shown that the two-spin/two-quantum Hamiltonian \cite{Baum} describing
MQ NMR dynamics is related to the flip-flop Hamiltonian of a one-dimensional
spin system in the approximation of the nearest neighbor interactions.
  As a result, it is possible to organize quantum state transfer along a linear
chain.
  MQ NMR experiments are performed on quasi-one-dimensional chains of
\BPChem{\^{19}F} nuclei in calcium fluorapatite \BPChem{Ca\_5(PO\_4)\_3F}.
Relaxation of the MQ NMR coherences is considered as the simplest model of
decoherence processes. A theory of the dipolar relaxation of the MQ NMR
coherences in one-dimensional systems is developed. A good agreement of the
theoretical predictions and the experimental data is obtained.",1701.03588v1
2017-02-24,The X-ray Pulsar 2A 1822-371 as a Super Eddington source,"The low mass X-ray binary 2A 1822-371 is an eclipsing system with an
accretion disc corona and with an orbital period of 5.57 hr. The primary is an
0.59 s X-ray pulsar with a proposed strong magnetic field of 10^10-10^12 G. In
this paper we study the spin evolution of the pulsar and constrain the geometry
of the system. We find that, contrary to previous claims, a thick corona is not
required, and that the system characteristics could be best explained by a thin
accretion outflow due to a super-Eddington mass transfer rate and a
geometrically thick inner accretion flow. The orbital, spectral and timing
observations can be reconciled in this scenario under the assumption that the
mass transfer proceeds on a thermal timescale which would make 2A 1822-371, a
mildly super-Eddington source viewed at high inclination angles. The timing
analysis on 13 years of RXTE data show a remarkably stable spin-up that implies
that 2A 1822-371, might quickly turn into a millisecond pulsar in the next few
thousand years.",1702.07524v1
2017-05-05,Algebraic Bethe ansatz for the XXZ Heisenberg spin chain with triangular boundaries and the corresponding Gaudin model,"The implementation of the algebraic Bethe ansatz for the XXZ Heisenberg spin
chain, of arbitrary spin-$s$, in the case, when both reflection matrices have
the upper-triangular form is analyzed. The general form of the Bethe vectors is
studied. In the particular form, Bethe vectors admit the recurrent procedure,
with an appropriate modification, used previously in the case of the XXX
Heisenberg chain. As expected, these Bethe vectors yield the strikingly simple
expression for the off-shell action of the transfer matrix of the chain as well
as the spectrum of the transfer matrix and the corresponding Bethe equations.
As in the XXX case, the so-called quasi-classical limit gives the off-shell
action of the generating function of the corresponding trigonometric Gaudin
Hamiltonians with boundary terms.",1705.02235v2
2017-06-05,The spectrum of a vertex model and related spin one chain sitting in a genus five curve,"We derive the transfer matrix eigenvalues of a three-state vertex model whose
weights are based on a $\mathrm{R}$-matrix not of difference form with spectral
parameters lying on a genus five curve. We have shown that the basic building
blocks for both the transfer matrix eigenvalues and Bethe equations can be
expressed in terms of meromorphic functions on an elliptic curve. We discuss
the properties of an underlying spin one chain originated from a particular
choice of the $\mathrm{R}$-matrix second spectral parameter. We present
numerical and analytical evidences that the respective low-energy excitations
can be gapped or massless depending on the strength of the interaction
coupling. In the massive phase we provide analytical and numerical evidences in
favor of an exact expression for the lowest energy gap. We point out that the
critical point separating these two distinct physical regimes coincides with
the one in which the weights geometry degenerate into union of genus one
curves.",1706.01525v1
2018-03-06,Coherent dynamics in stochastic systems revealed by full counting statistics,"Stochastic systems feature, in general, both coherent dynamics and incoherent
transitions between different states. We propose a method to identify the
coherent part in the full counting statistics for the transitions. The proposal
is illustrated for electron transfer through a quantum-dot spin valve, which
combines quantum-coherent spin precession with electron tunneling. We show that
by counting the number of transferred electrons as a function of time, it is
possible to distill out the coherent dynamics from the counting statistics even
in transport regimes, in which other tools such as the frequency-dependent
current noise and the waiting-time distribution fail.",1803.02175v2
2018-06-16,Signature of the $s$-wave regime high above ultralow temperatures,"Physical processes involving charge transfer, spin exchange, or excitation
exchange often occur in conditions of resonant scattering. We show that the
$s$-wave contribution can be used to obtain a good approximation for the full
cross section. This approximation is found to be valid for a wide range of
scattering energies, including high above the Wigner regime, where many partial
waves contribute. We derive an analytical expression for the exchange cross
section and demonstrate its relationship to the Langevin cross section. We give
examples for resonant charge transfer as well as spin-flip and excitation
exchange. Our approximation can be used to gain information about the $s$-wave
regime from data obtained at much higher temperatures, which would be
advantageous for systems where the ultracold quantum regime is not easily
reachable.",1806.06162v1
2018-10-09,Ice Rule Fragility via Topological Charge Transfer in Artificial Colloidal Ice,"Artificial particle ices are model systems of constrained, interacting
particles. They have been introduced theoretically to study ice-manifolds
emergent from frustration, along with domain wall and grain boundary dynamics,
doping, pinning-depinning, controlled transport of topological defects,
avalanches, and memory effects. Recently such particle-based ices have been
experimentally realized with vortices in nano-patterned superconductors or
gravitationally trapped colloids. Here we demonstrate that, although these ices
are generally considered equivalent to magnetic spin ices, they can access a
novel spectrum of phenomenologies that are inaccessible to the latter. With
experiments, theory and simulations we demonstrate that in mixed coordination
geometries, entropy-driven negative monopoles spontaneously appear at a density
determined by the vertex-mixture ratio. Unlike its spin-based analogue, the
colloidal system displays a ""fragile ice"" manifold, where local energetics
oppose the ice rule, which is instead enforced through conservation of the
global topological charge. The fragile colloidal ice, stabilized by topology,
can be spontaneously broken by topological charge transfer.",1810.04225v1
2018-12-13,Ultra-luminous X-ray sources as neutron stars propelling and accreting at super-critical rates in high-mass X-ray binaries,"Ultra-luminous X-ray sources (ULXs) are off-nuclear point sources in nearby
galaxies with luminosities well exceeding the Eddington limit for stellar-mass
objects. It has been recognized after the discovery of pulsating ULXs (PULXs)
that a fraction of these sources could be accreting neutron stars in high-mass
X-ray binaries (HMXBs) though the majority of ULXs are lacking in coherent
pulsations. The earliest stage of some HMXBs may harbor rapidly rotating
neutron stars propelling out the matter transferred by the massive companion.
The spin-down power transferred by the neutron-star magnetosphere to the
accretion disk at this stage can well exceed the Eddington luminosities and the
system appears as a non-pulsating ULX. In this picture, PULXs appear as
super-critical mass-accreting descendants of non-pulsating ULXs. We present
this evolutionary scenario within a self-consistent model of magnetosphere-disk
interaction and discuss the implications of our results on the spin and
magnetic field of the neutron star.",1812.05294v1
2019-03-12,Perfect State Transfer in a Spin Chain without Mirror Symmetry,"We introduce an analytical $XX$ spin chain with asymmetrical transport
properties. It has an even number $N+1$ of sites labeled by $n=0,\cdots N$. It
does not exhibit perfect state transfer (PST) from end-to-end but rather from
the first site to the next to last one. In fact, PST of one-excitation states
takes place between the even sites: $n\leftrightarrow N-n-1$, $n=0,2,\cdots,
N-1$; while states localized at a single odd site undergo fractional revival
(FR) over odd sites only. Perfect return is witnessed at double the PST/FR
time. The couplings and local magnetic fields are related to the recurrence
coefficients of the dual -1 Hahn polynomials.",1903.04707v2
2019-04-05,Theory of triangular lattice quasi-one-dimensional charge-transfer solids,"Recent investigations of the magnetic properties and the discovery of
superconductivity in quasi-one-dimensional triangular lattice organic
charge-transfer solids have indicated the severe limitations of the effective
1/2-filled band Hubbard model for these and related systems. Our computational
studies of these materials within a 1/4-filled band Hubbard model in which the
organic monomer molecules, and not their dimers, constitute the sites of the
Hamiltonian are able to reproduce the experimental results. We ascribe the spin
gap transition in kappa-(BEDT-TTF)_2B(CN)_4 to the formation of a
two-dimensional paired-electron crystal and make the testable prediction that
the spin gap will be accompanied by charge-ordering and period doubling in two
directions. We find enhancement of the long-range component of superconducting
pairing correlations by the Hubbard repulsive interaction for band parameters
corresponding to kappa-(BEDT-TTF)_2CF_3SO_3. The overall results strongly
support a valence bond theory of superconductivity we have proposed recently.",1904.03067v2
2019-07-12,Spin Seebeck effect and phonon energy transfer in heterostructures containing layers of a normal metal and a ferromagnetic insulator,"In the framework of the kinetic approach based on the Boltzmann equation for
the phonon distribution function, we analyze phonon heat transfer in a
heterostructure containing a layer of a normal metal ($ N $) and a layer of a
ferromagnetic insulator ($ F $). Two realistic methods for creating a
temperature gradient in such a heterostructure are considered: by heating of
the $N$-layer by an electric current and by placing the $N/F$-bilayer between
massive dielectrics with different temperatures. The electron temperature $ T_e
$ in the $ N $-layer and the magnon temperature $ T_m $ in the $ F $-layer are
calculated. The difference in these temperatures determines the voltage $
V_{ISHE} $ on the $ N $-layer in the Seebeck spin effect regime. The dependence
of $ V_{ISHE} $ on the bath temperature and on the thickness of the $ N $ and $
F $ layers is compared with the available experimental data.",1907.05739v1
2019-09-17,Direct determination of momentum resolved electron transfer in the photo-excited MoS2/WS2 van der Waals heterobilayer by TR-ARPES,"Photo-induced charge separation in transition metal dichalcogenide
heterobilayers is being explored for moir\'e excitons, spin-valley
polarization, and quantum phases of excitons/electrons. While different
momentum spaces may be critically involved in charge separation dynamics,
little is known directly from experiments. Here we determine momentum-resolved
electron dynamics in the WS2/MoS2 heterobilayer using time and angle resolved
photoemission spectroscopy (TR-ARPES). Upon photoexcitation in the K valleys,
we detect electrons in M/2, M, and Q valleys/points on time scales as short as
~70 fs, followed by dynamic equilibration in K and Q valleys in ~400 fs. The
interlayer charge transfer is accompanied by momentum-specific band
renormalization. These findings reveal the essential role of phonon scattering,
the coexistence of direct and indirect interlayer excitons, and constraints on
spin-valley polarization.",1909.07759v2
2019-10-11,Completing the solution for the $OSp(1|2)$ spin chain,"The periodic $OSp(1|2)$ quantum spin chain has both a graded and a non-graded
version. Naively, the Bethe ansatz solution for the non-graded version does not
account for the complete spectrum of the transfer matrix, and we propose a
simple mechanism for achieving completeness. In contrast, for the graded
version, this issue does not arise. We also clarify the symmetries of both
versions of the model, and we show how these symmetries are manifested in the
degeneracies and multiplicities of the transfer-matrix spectrum. While the
graded version has $OSp(1|2)$ symmetry, the non-graded version has only $SU(2)$
symmetry. Moreover, we obtain conditions for selecting the physical singular
solutions of the Bethe equations. This analysis solves a lasting controversy
over signs in the Bethe equations.",1910.05127v2
2019-10-29,On the supersymmetric XXX spin chains associated to $\mathfrak{gl}_{1|1}$,"We study the $\mathfrak{gl}_{1|1}$ supersymmetric XXX spin chains. We give an
explicit description of the algebra of Hamiltonians acting on any cyclic tensor
products of polynomial evaluation $\mathfrak{gl}_{1|1}$ Yangian modules. It
follows that there exists a bijection between common eigenvectors (up to
proportionality) of the algebra of Hamiltonians and monic divisors of an
explicit polynomial written in terms of the Drinfeld polynomials. In particular
our result implies that each common eigenspace of the algebra of Hamiltonians
has dimension one. We also give dimensions of the generalized eigenspaces. We
show that when the tensor product is irreducible, then all eigenvectors can be
constructed using Bethe ansatz. We express the transfer matrices associated to
symmetrizers and anti-symmetrizers of vector representations in terms of the
first transfer matrix and the center of the Yangian.",1910.13360v1
2019-11-21,Symmetry resolved entanglement in gapped integrable systems: a corner transfer matrix approach,"We study the symmetry resolved entanglement entropies in gapped integrable
lattice models. We use the corner transfer matrix to investigate two
prototypical gapped systems with a U(1) symmetry: the complex harmonic chain
and the XXZ spin-chain. While the former is a free bosonic system, the latter
is genuinely interacting. We focus on a subsystem being half of an infinitely
long chain. In both models, we obtain exact expressions for the charged moments
and for the symmetry resolved entropies. While for the spin chain we found
exact equipartition of entanglement (i.e. all the symmetry resolved entropies
are the same), this is not the case for the harmonic system where equipartition
is effectively recovered only in some limits. Exploiting the gaussianity of the
harmonic chain, we also develop an exact correlation matrix approach to the
symmetry resolved entanglement that allows us to test numerically our analytic
results.",1911.09588v3
2020-06-20,First-principles study of the effective Hamiltonian for Dirac fermions with spin-orbit coupling in two-dimensional molecular conductor $α$-(BETS)$_2$I$_3$,"We employed first-principles density-functional theory (DFT) calculations to
characterize Dirac electrons in quasi-two-dimensional molecular conductor
$\alpha$-(BETS)$_2$I$_3$ [= $\alpha$-(BEDT-TSeF)$_2$I$_3$] at a low temperature
of 30K. We provide a tight-binding model with intermolecular transfer energies
evaluated from maximally localized Wannier functions, where the number of
relevant transfer integrals is relatively large due to the delocalized
character of Se $p$ orbitals. The spin-orbit coupling gives rise to an exotic
insulating state with an indirect band gap of about 2 meV. We analyzed the
energy spectrum with a Dirac cone close to the Fermi level to develop an
effective Hamiltonian with site-potentials, which reproduces the spectrum
obtained by the DFT band structure.",2006.11455v3
2021-02-26,1D Spin-Crossover Molecular Chain with Degenerate States,"A study of the one-dimensional molecular chain (MC) with two single-particle
degenerate states is presented. We establish connection of the MC with the
Ising model with phononic interactions and investigate properties of the model
using a transfer matrix method. The transfer matrix method offers a promising
pathway for simulating such materials properties. The role of degeneracy of
states and phononic interaction being made explicit. We analyze regimes of the
system and parameters of the occurring crossover. Here, we present exact
results for the magnetization per spin, the correlation function and the
effective volume of the system. We demonstrate possibility of existence of two
peaks in the specific heat capacity thermal behavior.",2102.13627v2
2021-04-28,Simulation of three-spin evolution under XX Hamiltonian on quantum processor of IBM-Quantum Experience,"We simulate the evolution of three-node spin chain on the quantum processor
of IBM Quantum Experience using the diagonalization of $XX$-Hamiltonian and
representing the evolution operator in terms of CNOT operations and one-qubit
rotations. We study the single excitation transfer from the first to the third
node and show the significant difference between calculated and theoretical
values of state transfer probability. Then we propose a method reducing this
difference by applying the two-parameter transformation including the shift and
scale of the calculated probabilities. { We demonstrate the universality of
this transformation inside of the class of three-node evolutionary systems
governed by the $XX$-Hamiltonian.",2104.13769v2
2021-05-05,Assessing the nature of chiral-induced spin-selectivity by magnetic resonance,"Understanding chiral induced spin-selectivity (CISS), resulting from charge
transport through helical systems, has recently inspired many experimental and
theoretical efforts, but is still object of intense debate. In order to assess
the nature of CISS, we propose to focus on electron-transfer processes
occurring at the single-molecule level. We design simple magnetic resonance
experiments, exploiting a qubit as a highly sensitive and coherent magnetic
sensor, to provide clear signatures of the acceptor polarization. Moreover, we
show that information could even be obtained from time-resolved electron
paramagnetic resonance experiments on a randomly-oriented solution of
molecules. The proposed experiments will unveil the role of chiral linkers in
electron-transfer and could also be exploited for quantum computing
applications.",2105.02350v1
2021-05-06,Positionally precise functionalization of shallow luminescent centers through Forster Resonant Energy Transfer (FRET) driven surface photochemistry,"Paramagnetic luminescent impurities in solids such as Nitrogen-Vacancy (NV)
centers in diamond represent a promising and versatile platform for the
development of a wide range of chemical and biological sensors. This goal can
be accomplished by the placement of chemically active, spin (electron or
nuclear) labeled moiety on the surface in the close vicinity of a shallow
single paramagnetic center. In this paper, we demonstrate that the Forster
Resonant Excitation Transfer driven process where luminescent center plays a
role of excitation donor can accomplish such a goal with high chemical
efficiency, positionally precise and a scalable manner. We obtain the
probability distribution function of the sensing group position relative to the
luminescent center (NV center) and demonstrate that the functionalization
position uncertainty is equal to the luminescent center deposition depth. The
efficiency of the FRET process is analyzed as a function of the luminescent
center deposition depth and the density of the excitation acceptor sites.
Employing the geometric information of the surface-functionalized sensing
groups, we obtain the probability distribution function of the energy gap in
the spectrum of a spin-based detection system. This information allows us to
estimate the single-molecule detection capabilities of the proposed system.",2105.02870v1
2021-09-23,Tunable and Transferable Diamond Membranes for Integrated Quantum Technologies,"Color centers in diamond are widely explored as qubits in quantum
technologies. However, challenges remain in the effective and efficient
integration of these diamond-hosted qubits in device heterostructures. Here,
nanoscale-thick uniform diamond membranes are synthesized via ""smart-cut"" and
isotopically (12C) purified overgrowth. These membranes have tunable
thicknesses (demonstrated 50 nm to 250 nm), are deterministically transferable,
have bilaterally atomically flat surfaces (Rq <= 0.3 nm), and bulk-diamond-like
crystallinity. Color centers are synthesized via both implantation and in-situ
overgrowth incorporation. Within 110 nm thick membranes, individual
germanium-vacancy (GeV-) centers exhibit stable photoluminescence at 5.4 K and
average optical transition linewidths as low as 125 MHz. The room temperature
spin coherence of individual nitrogen-vacancy (NV-) centers shows Ramsey spin
dephasing times (T2*) and Hahn echo times (T2) as long as 150 us and 400 us,
respectively. This platform enables the straightforward integration of diamond
membranes that host coherent color centers into quantum technologies.",2109.11507v1
2021-09-28,Charge glass in an extended dimer Hubbard model,"The charge degrees of freedom in several different organic charge transfer
salts display slow or glassy dynamics. In order to gain insight into this
behaviour, we obtain the low energy theory for an extended dimer Hubbard model,
taking into account the occupations of sites on neighbouring dimers. We take a
classical limit of the resulting effective model of coupled spins and dimers
and study it using classical Monte Carlo simulations. We find that frustration
induced by intra- and inter-dimer interactions leads to glassiness in the
charge degress of freedom in the absence of ordering of the spin degrees of
freedom. Our results may have relevance to experimental observations of relaxor
ferroelectric behaviour in the dynamics of organic charge transfer salts.",2109.14101v1
2021-10-25,Spin dependent charge transfer in MoSe2/hBN/Ni hybrid structures,"We present magneto-photoluminescence measurements in a hybrid 2D
semiconductor/ferromagnetic structure consisting of MoSe2/hBN/Ni. When the
Nickel layer is magnetized, we observe circularly polarized photoluminescence
of the trion peak in MoSe2 monolayer under linearly polarized excitation. This
build-up of circular polarization can reach a measured value of about 4% when
the magnetization of Ni is saturated perpendicularly to the sample plane, and
changes its sign when the magnetization is reversed. The circular polarization
decreases when the hBN barrier thickness increases. These results are
interpreted in terms of a spin-dependent charge transfer between the MoSe2
monolayer and the Nickel film. The build-up of circular polarization is
observed up to 120 K, mainly limited by the trion emission that vanishes with
temperature.",2110.13007v1
2022-05-12,Anti-glitches in accreting pulsars from superfluid vortex avalanches,"Three sudden spin-down events, termed `anti-glitches', were recently
discovered in the accreting pulsar NGC 300 ULX-1 by the \textit{Neutron Star
Interior Composition Explorer} (NICER) mission. Unlike previous anti-glitches
detected in decelerating magnetars, these are the first anti-glitches recorded
in an accelerating pulsar. One standard theory is that pulsar spin-up glitches
are caused by avalanches of collectively unpinning vortices that transfer
angular momentum from the superfluid interior to the crust of a neutron star.
Here we test whether vortex avalanches are also consistent with the
anti-glitches in NGC 300 ULX-1, with the angular momentum transfer reversed. We
perform $N$-body simulations of up to $5 \times 10^{3}$ pinned vortices in two
dimensions in secularly accelerating and decelerating containers. Vortex
avalanches routinely occur in both scenarios, propagating inwards and outwards
respectively. The implications for observables, such as size and waiting time
statistics, are considered briefly.",2205.05896v1
2022-10-25,Comprehensive $ab$ $initio$ investigation of the phase diagram of quasi-one-dimensional molecular solids,"An $ab$ $initio$ investigation of the family of molecular compounds TM$_2$$X$
is conducted, where TM is either TMTSF or TMTTF and $X$ takes centrosymmetric
monovalent anions. By deriving the extended Hubbard-type Hamiltonians from
first-principles band calculations and evaluating not only the intermolecular
transfer integrals but also the Coulomb parameters, we discuss their material
dependence in the unified phase diagram. Furthermore, we apply the
many-variable variational Monte Carlo method to accurately determine the
symmetry-breaking phase transitions, and show the development of the charge and
spin orderings. We show that the material-dependent parameter can be taken as
the correlation effect, represented by the value of the screened on-site
Coulomb interaction $U$ relative to the intrachain transfer integrals, for the
comprehensive understanding of the spin and charge ordering in this system.",2210.13726v2
2023-04-06,Essential Tools of Linear Algebra for Calculating Nuclear Spin Dynamics of Chemically Exchanging Systems,"In this work, we describe essential tools of linear algebra necessary for
calculating the effect of chemical exchange on spin dynamics and polarization
transfer in various nuclear magnetic resonance (NMR) experiments. We show how
to construct Hamiltonian, relaxation, and chemical exchange superoperators in
the Liouville space, as well as demonstrate corresponding code in Python.
Examples of applying the code are given for problems involving chemical
exchange between NH3 and NH4+ at zero and high magnetic field and polarization
transfer from parahydrogen relevant in SABRE (signal amplification by
reversible exchange) at low magnetic field (0-20 mT). The presented methodology
finds utility for describing the effect of chemical exchange on NMR spectra and
can be extended further by taking into account non-linearities in the master
equation.",2304.03139v2
2023-06-09,Dynamic structure factor of two-dimensional Fermi superfluid with Rashba spin-orbit coupling,"We theoretically calculate the dynamic structure factor of two-dimensional
Rashba-type spinorbit coupled (SOC) Fermi superfluid with random phase
approximation, and analyse the main characters of dynamical excitation sh own
by both density and spin dynamic structure factor during a continuous phase
transition between Bardeen-Cooper-Schrieffer superfluid and topological
superfluid. Generally we find three different excitations, including collective
phonon excitation, two-atom molecular and atomic excitations, and pair-breaking
excitations due to two-branch structure of quasi-particle spectrum. It should
be emphasized that collective phonon excitation is overlapped with a gapless DD
type pair-breaking excitation at the critical Zeeman field hc, and is imparted
a finite width to phonon peak when transferred momentum q is around Fermi
vector kF. At a much larger transferred momentum (q = 4kF ), the pair-breaking
excitation happens earlier than two-atom molecular excitation, which is
different from the conventional Fermi superfluid without SOC effect.",2306.05868v2
2023-08-04,Efficient near-infrared organic light-emitting diodes with emission from spin doublet excitons,"The development of luminescent organic radicals has resulted in materials
with excellent optical properties for near-infrared (NIR) emission.
Applications of light generation in this range span from bioimaging to
surveillance. Whilst the unpaired electron arrangements of radicals enable
efficient radiative transitions within the doublet-spin manifold in organic
light-emitting diodes (OLEDs), their performance is limited by non-radiative
pathways introduced in electroluminescence. Here, we present a host:guest
design for OLEDs that exploits energy transfer with demonstration of up to 9.6%
external quantum efficiency (EQE) for 800 nm emission. The
tris(2,4,6-trichlorophenyl)methyl-triphenylamine (TTM-TPA) radical guest is
energy-matched to the triplet state in a charge-transporting
anthracene-derivative host. We show from optical spectroscopy and
quantum-chemical modelling that reversible host-guest triplet-doublet energy
transfer allows efficient harvesting of host triplet excitons.",2308.02355v1
2023-09-20,Tidal Dissipation in Satellites Prevents Hill Sphere Escape,"The transit method is a promising means to detect exomoons, but few
candidates have been identified. For planets close to their stars, the
dynamical interaction between a satellite's orbit and the star must be
important in their evolution. Satellites beyond synchronous orbit spiral out
due to the tide raised on their planet, and it has been assumed that they would
likely escape the Hill sphere. Here we follow the evolution with a three-body
code that accounts for tidal dissipation within both the planet and the
satellite. We show that tidal dissipation in satellites often keeps them bound
to their planet, making exomoons more observable than previously thought. The
probability of escape depends on the ratio of tidal quality factors of the
planet and satellite; when this ratio exceeds 0.5, escape is usually avoided.
Instead, the satellite moves to an equilibrium in which the spin angular
momentum of the planet is not transferred into the orbit of the satellite, but
is transferred into the orbit of the planet itself. While the planet continues
spinning faster than the satellite orbits, the satellite maintains a semi-major
axis of approximately 0.41 Hill radii. These states are accompanied with modest
satellite eccentricity near 0.1 and are found to be stable over long
timescales.",2309.11609v2
2023-09-21,A new generation of effective core potentials: selected Lanthanides and heavy elements,"We construct correlation-consistent effective core potentials (ccECPs) for a
selected set of heavy atoms and f-elements that are of significant current
interest in materials and chemical applications, including Y, Zr, Nb, Rh, Ta,
Re, Pt, Gd, and Tb. As customary, ccECPs consist of spin-orbit averaged
relativistic effective potential (AREP) and effective spin-orbit (SO) terms.
For the AREP part, our constructions are carried out within a relativistic
coupled-cluster framework while also taking into objective function
one-particle characteristics for improved convergence in optimizations. The
transferability is adjusted using binding curves of hydride and oxide
molecules. We address the difficulties encountered with f-elements, such as the
presence of large cores and multiple near-degeneracies of excited levels. For
these elements, we construct ccECPs with core-valence partitioning that
includes 4f-subshell in the valence space. The developed ccECPs achieve an
excellent balance between accuracy, size of the valence space, and
transferability and are also suitable to be used in plane wave codes with
reasonable energy cutoffs.",2309.12145v1
2024-02-06,The open XYZ spin 1/2 chain: Separation of Variables and scalar products for boundary fields related by a constraint,"We consider the open XYZ spin chain with boundary fields. We solve the model
by the new Separation of Variables approach introduced in arXiv:1904.00852. In
this framework, the transfer matrix eigenstates are obtained as a particular
sub-class of the class of so-called separate states. We consider the problem of
computing scalar products of such separate states. As usual, they can be
represented as determinants with rows labelled by the inhomogeneity parameters
of the model. We notably focus on the special case in which the boundary
parameters parametrising the two boundary fields satisfy one constraint, hence
enabling for the description of part of the transfer matrix spectrum and
eigenstates in terms of some elliptic polynomial Q-solution of a usual
TQ-equation. In this case, we show how to transform the aforementioned
determinant for the scalar product into some more convenient form for the
consideration of the homogeneous and thermodynamic limits: as in the open XXX
or XXZ cases, our result can be expressed as some generalisation of the
so-called Slavnov determinant.",2402.04112v1
2024-03-20,Nonequilibrium quantum heat transport between structured environments,"We apply the hierarchical equations of motion technique to analyzing
nonequilibrium heat transport in a spin-boson type model, whereby heat transfer
through a central spin is mediated by an intermediate pair of coupled harmonic
oscillators. The coupling between each pair of oscillators is shown to
introduce a localized gap into the effective spectral densities characterizing
the system-oscillator-reservoir interactions. Compared to the case of a single
mediating oscillator, we find the heat current to be drastically modified at
weak system-bath coupling. In particular, a second-order treatment fails to
capture the correct steady-state behavior in this regime, which stems from the
$\lambda^4$-scaling of the energy transfer rate to lowest order in the coupling
strength $\lambda$. This leads naturally to a strong suppression in the
steady-state current in the asymptotically weak coupling limit. On the other
hand, the current noise follows the same scaling as in the single oscillator
case in accordance with the fluctuation-dissipation theorem. Additionally, we
find the heat current to be consistent with Fourier's law even at large
temperature bias. Our analysis highlights a novel mechanism for controlling
heat transport in nanoscale systems based on tailoring the spectral properties
of thermal environments.",2403.13904v1
2024-03-29,Electric field enhancement of the superconducting spin-valve effect via strain-transfer across a ferromagnetic/ferroelectric interface,"In a ferromagnet/superconductor/ferromagnet (F/S/F) superconducting
spin-valve (SSV), a change of the magnetization alignment of the two F layers
modulates the critical temperature (Tc) of the S layer. The Tc-switching (the
SSV effect) is based on the interplay between superconductivity and magnetism.
Fast and large resistive switching associated with the Tc-switching is suitable
for nonvolatile cryogenic memory applications. However, external magnetic
field-based operation of SSVs is hindering their miniaturization, and
therefore, electric field control of the SSV effect is desired. Here, we report
epitaxial growth of a La0.67Ca0.33MnO3/YBa2Cu3O7/La0.67Ca0.33MnO3 SSV on a
piezo-electric [Pb(Mg0.33Nb0.67)O3]0.7-[PbTiO3]0.3 (001) substrate and
demonstrate electric field control of the SSV effect. Electric field-induced
strain-transfer from the piezo-electric substrate increases the magnetization
and Tc of the SSV, and leads to an enhancement of the magnitude of
Tc-switching. The results are promising for the development of
magnetic-field-free superconducting spintronic devices, in which the S/F
interaction is not only sensitive to the magnetization alignment but also to an
applied electric field.",2403.20210v1
2007-08-26,First-principles study of a single-molecule magnet Mn_{12} monolayer on the Au(111) surface,"The electronic structure of a monolayer of single-molecule magnets Mn$_{12}$
on a Au(111) surface is studied using spin-polarized density-functional theory.
The Mn$_{12}$ molecules are oriented such that the magnetic easy axis is normal
to the surface, and the terminating ligands in the Mn$_{12}$ are replaced by
thiol groups (-SH) where the H atoms are lost upon adsorption onto the surface.
This sulfur-terminated Mn$_{12}$ molecule has a total magnetic moment of 18
$\mu_B$ in the ground state, in contrast to 20$\mu_B$ for the standard
Mn$_{12}$. The Mn$_{12}$ molecular orbitals broaden due to the interaction of
the molecule with the gold surface and the broadening is of the order of 0.1
eV. It is an order of magnitude less than the single-electron charging energy
of the molecule so the molecule is weakly bonded to the surface. Only electrons
with majority spin can be transferred from the surface to the sulfur-terminated
Mn$_{12}$ since the gold Fermi level is well above the majority lowest
unoccupied molecular orbital (LUMO) but below the minority LUMO. The amount of
the charge transfer is calculated to be 1.23 electrons, dominated by the tail
in the electronic distribution of the gold surface. A calculation of level
shift upon charging provides 0.28 electrons being transferred. The majority of
the charge transfer occurs at the S, C, and O atoms close to the surface. The
total magnetic moment also changes from 18 $\mu_B$ to 20 $\mu_B$, due to
rearrangements of the magnetic moments on the S and Mn atoms upon adsorption
onto the surface. The magnetic anisotropy barrier is computed including
spin-orbit interaction self-consistently in density-functional theory. The
barrier for the Mn$_{12}$ on the gold surface decreases by 6 K in comparison to
that for an isolated Mn$_{12}$ molecule.",0708.3460v1
2015-06-06,"Enhancement of electron correlation due to the molecular dimerization in organic superconductors $β$-(BDA-TTP)$_{2}X$ ($X$=I$_3$, SbF$_6$)","We perform a first principles band calculation for quasi-two-dimensional
organic superconductors $\beta$-(BDA-TTP)$_{2}$I$_{3}$ and
$\beta$-(BDA-TTP)$_{2}$SbF$_{6}$. The first principles band structures between
the I$_{3}$ and SbF$_{6}$ salts are apparently different. We construct a
tight-binding model for each material which accurately reproduces the first
principles band structure. The obtained transfer energies give the differences
such as (i) larger dimerization in the I$_{3}$ salt than the SbF$_{6}$ salt,
and (ii) different signs and directions of the inter-stacking transfer
energies. To decompose the origin of the difference into the dimerization and
the inter-stacking transfer energies, we adopt a simplified model by
eliminating the dimerization effect and extract the difference caused by the
inter-stacking transfer energies. From the analysis using the simplified model,
we find that the difference of the band structure comes mainly from the
strength of dimerization. To compare the strength of the electron correlation
having roots in the band structure, we calculate the physical properties
originated from the effect of the electron correlation such as the spin
susceptibility applying two particle self-consistent (TPSC) method. We find
that the maximum value of the spin susceptibility of the I$_{3}$ salt is larger
than that of the SbF$_{6}$ salt. Hypothetically decreasing the dimerization
within the model of the I$_{3}$ salt, the spin susceptibility takes almost the
same value as that of the SbF$_6$ salt for the same magnitude of the
dimerization. We expect that the different ground state between the I$_{3}$ and
SbF$_{6}$ salt mainly comes from the strength of the dimerization which is
apparently masked in the band calculation along a particular $k$-path.",1506.02114v1
2022-10-25,Ingredients for Generalized Models of $κ$-Phase Organic Charge-Transfer Salts: A Review,"The families of organic charge-transfer salts $\kappa$-(BEDT-TTF)$_2X$ and
$\kappa$-(BETS)$_2X$ have proven to serve as a powerful playground for the
investigation of the physics of frustrated Mott insulators. These materials
have been ascribed model character, since dimerization of the organic molecules
allows to map these materials onto a single band Hubbard model, in which the
dimers reside on an anisotropic triangular lattice. By changing the inorganic
unit $X$ or applying physical pressure, the correlation strength and anisotropy
of the triangular lattice can be varied. This has lead to the discovery of a
variety of exotic phenomena, including quantum spin liquid states, a plethora
of long-range magnetic orders in proximity to a Mott metal-insulator
transition, and unconventional superconductivity. While many of these phenomena
can be described within this effective one-band Hubbard model on a triangular
lattice, it became evident in recent years that this simplified description is
insufficient to capture all observed magnetic and electronic properties. The
ingredients for generalized models that are relevant include, but are not
limited to, spin-orbit coupling, intra-dimer charge and spin degrees of
freedom, electron-lattice coupling, as well as disorder effects. Here, we
review selected theoretical and experimental discoveries that clearly
demonstrate the relevance thereof. At the same time, we outline that these
aspects are not only relevant to this class of organic charge-transfer salts,
but are also receiving increasing attention in other classes of inorganic
strongly correlated electron systems. This reinforces the model character that
the $\kappa$-phase organic charge-transfer salts have for understanding and
discovering novel phenomena in strongly correlated electron systems from a
theoretical and experimental point of view.",2210.14251v2
2002-03-07,Timing analysis of the isolated neutron star RX J0720.4-3125,"We present a combined analysis of XMM-Newton, Chandra and Rosat observations
of the isolated neutron star RXJ0720.4-3125, spanning a total period of \sim 7
years. We develop a maximum likelihood periodogramme for our analysis based on
the \Delta C-statistic and the maximum likelihood method, which are appropriate
for the treatment of sparse event lists. Our results have been checked ""a
posteriori"" by folding a further BeppoSAX dataset with the period predicted at
the time of that observation: the phase is found to be consistent. The study of
the spin history and the measure of the spin-down rate is of extreme importance
in discriminating between the possible mechanisms suggested for the nature of
the X-ray emission. The value of \dot P, here measured for the first time, is
\approx 10^{-14} s/s. This value can not be explained in terms of torque from a
fossil disk. When interpreted in terms of dipolar losses, it gives a magnetic
field of B \approx 10^{13} G, making also implausible that the source is
accreting from the underdense surroundings. On the other hand, we also find
unlikely that the field decayed from a much larger value (B\approx 10^{15} G,
as expected for a magnetar powered by dissipation of a superstrong field) since
this scenario predicts a source age of \approx 10^4 yrs, too young to match the
observed X-ray luminosity. The observed properties are more compatible with a
scenario in which the source is \approx 10^6 yrs old, and its magnetic field
has not changed substantially over the lifetime.",0203105v1
2006-07-08,Transitions between turbulent and laminar superfluid vorticity states in the outer core of a neutron star,"We investigate the global transition from a turbulent state of superfluid
vorticity to a laminar state, and vice versa, in the outer core of a neutron
star. By solving numerically the hydrodynamic Hall-Vinen-Bekarevich-Khalatnikov
equations for a rotating superfluid in a differentially rotating spherical
shell, we find that the meridional counterflow driven by Ekman pumping exceeds
the Donnelly-Glaberson threshold throughout most of the outer core, exciting
unstable Kelvin waves which disrupt the rectilinear vortex array, creating a
vortex tangle. In the turbulent state, the torque exerted on the crust
oscillates, and the crust-core coupling is weaker than in the laminar state.
This leads to a new scenario for the rotational glitches observed in radio
pulsars: a vortex tangle is sustained in the differentially rotating outer core
by the meridional counterflow, a sudden spin-up event brings the crust and core
into corotation, the vortex tangle relaxes back to a rectilinear vortex array,
then the crust spins down electromagnetically until enough meridional
counterflow builds up to reform a vortex tangle. The turbulent-laminar
transition can occur uniformly or in patches; the associated time-scales are
estimated from vortex filament theory. We calculate numerically the global
structure of the flow with and without an inviscid superfluid component, for
Hall-Vinen and Gorter-Mellink forms of the mutual friction. We also calculate
the post-glitch evolution of the angular velocity of the crust and its time
derivative, and compare the results with radio pulse timing data, predicting a
correlation between glitch activity and Reynolds number.",0607161v1
2007-05-28,Is the Bardeen-Petterson effect responsible for the warping and precession in NGC 4258?,"Strong evidence for the presence of a warped Keplerian accretion disc in
NGC4258 (M 106) has been inferred from the kinematics of water masers detected
at sub-parsec scales. Assuming a power-law accretion disc and using constraints
on the disc parameters derived from observational data, we have analyzed the
relativistic Bardeen-Petterson effect driven by a Kerr black hole as the
potential physical mechanism responsible for the disc warping. We found that
the Bardeen-Petterson radius is comparable to or smaller than the inner radius
of the maser disc (independent of the allowed value for the black hole spin
parameter). Numerical simulations for a wide range of physical conditions have
shown that the evolution of a misaligned disc due to the Bardeen-Petterson
torques usually produces an inner flat disc and a warped transition region with
a smooth gradient in the tilt and twist angles. Since this structure is similar
to that seen in NGC 4258, we propose that the Bardeen-Petterson effect may be
responsible for the disc warping in this galaxy. We estimated the time-scale
necessary for the disc inside of the Bardeen-Petterson radius to align with the
black hole's equator, as a function of the black hole spin. Our results show
that the Bardeen-Petterson effect can align the disc within a few billion years
in the case of NGC 4258. Finally, we show that if the observed curvature of the
outer anomalous arms in the galactic disc of NGC 4258 is associated with the
precession of its radio jet/counterjet, then the Bardeen-Petterson effect can
provide the required precession period.",0705.4035v1
2009-12-11,Vacuum Electromagnetic Counterparts of Binary Black-Hole Mergers,"As one step towards a systematic modeling of the electromagnetic (EM)
emission from an inspiralling black hole binary we consider a simple scenario
in which the binary moves in a uniform magnetic field anchored to a distant
circumbinary disc. We study this system by solving the Einstein-Maxwell
equations in which the EM fields are chosen with astrophysically consistent
strengths. We consider binaries with spins aligned or anti-aligned with the
orbital angular momentum and study the dependence of gravitational and EM
signals with these spin configurations. Overall we find that the EM radiation
in the lowest l=2, m=2 multipole accurately reflects the gravitational one,
with identical phase evolutions and amplitudes that differ only by a scaling
factor. We also compute the efficiency of the energy emission in EM waves and
find that it is given by E^rad_EM/M ~ 10^-15 (M/10^8 M_Sun)^2 (B/10^4 G)^2,
hence 13 orders of magnitude smaller than the gravitational energy for
realistic magnetic fields. The corresponding luminosity is much smaller than
the accretion luminosity if the system is accreting at near the Eddington rate.
Most importantly, this EM emission is at frequencies of 10^-4 (10^8 M_Sun/M)
Hz, well outside those accessible to astronomical radio observations. As a
result, it is unlikely that the EM emission discussed here can be detected
directly and simultaneously with the gravitational-wave one. However, indirect
processes, driven by changes in the EM fields behavior could yield observable
events. In particular if the accretion rate of the circumbinary disc is small
and sufficiently stable over the timescale of the final inspiral, then the EM
emission may be observable indirectly as it will alter the accretion rate
through the magnetic torques exerted by the distorted magnetic field lines.",0912.2330v1
2010-11-15,Accretion Discs with an Inner Spiral Density Wave,"In Montgomery (2009a), we show that accretion discs in binary systems could
retrogradely precess by tidal torques like the Moon and the Sun on a tilted,
spinning, non-spherical Earth. In addition, we show that the state of matter
and the geometrical shape of the celestial object could significantly affect
the precessional value. For example, a Cataclysmic Variable (CV) Dwarf Novae
(DN) non-magnetic system that shows negative superhumps in its light curve can
be described by a retrogradely precessing, differentially rotating, tilted
disc. Because the disc is a fluid and because the gas stream overflows the
tilted disc and particles can migrate into inner disc annuli, coupled to the
disc could be a retrogradely precessing inner ring that is located near the
innermost annuli of the disc. However, numerical simulations by Bisikalo et al.
(2003, 2004) and this work show that an inner spiral density wave can be
generated instead of an inner ring. Therefore, we show that retrograde
precession in non-magnetic, spinning, tilted CV DN systems can equally be
described by a retrogradely precessing and differentially rotating disc with an
attached retrogradely precessing inner spiral density wave so long as the wave
appears at the same radius as the ring and within the plane of the tilted disc.
We find that the theoretical results generated in this work agree well with the
theoretical results presented in Montgomery (2009a) and thus with the numerical
simulations and select CV DN systems in Montgomery (2009b) that may have a main
sequence secondary. Therefore, pressure effects do need to be considered in CV
DN systems that exhibit negative superhumps if the accretion discs are tilted
and have an inner spiral density wave that is in the plane of the disc.",1011.3446v1
2012-01-07,Interaction of Close-in Planets with the Magnetosphere of their Host Stars. II. Super-Earths as Unipolar Inductors and their Orbital Evolution,"Planets with several Earth masses and a few day orbital periods have been
discovered through radial velocity and transit surveys. Regardless of their
formation mechanism, a key evolution issue is the efficiency of their retention
near their host stars. If these planets attained their present-day orbits
during or shortly after the T Tauri phase of their host stars, a large fraction
would have encountered intense stellar magnetic field. Since these planets have
a higher conductivity than the atmosphere of their stars, the magnetic flux
tube connecting the planet and host star would slip though the envelope of the
star faster than across the planet. The induced electro-motive force across the
planet's diameter leads to a potential drop which propagates along a flux tube
away from the planet with an Alfven speed. The foot of the flux tube sweeps
across the stellar surface and the potential drop drives a DC current analogous
to that proposed for the Io-Jupiter electrodynamic interaction. The ohmic
dissipation of this current produces potentially observable hot spots in the
star envelope. The current heats the planet and leads to a Lorrentz torque
which drives the planet's orbit to evolve toward circularization and
synchronization with the star's spin. The net effect is the damping of the
planet's orbital eccentricity. Around slowly (rapidly) spinning stars, this
process also causes rocky planets with periods less than a few days to undergo
orbital decay (expansion/stagnation) within a few Myr. In principle, this
effect can determine the retention efficiency of short-period hot Earths. We
also estimate the ohmic dissipation in these planets and show that it can lead
to severe structure evolution and potential loss of volatile material. However,
these effects may be significantly weakened by the reconnection of the induced
field [Slightly shortened abstract].",1201.1584v1
2012-03-19,"The pulse profile and spin evolution of the accreting pulsar in Terzan 5, IGR J17480-2446, during its 2010 outburst","(abridged) We analyse the spectral and pulse properties of the 11 Hz
transient accreting pulsar, IGR J17480-2446, in the globular cluster Terzan 5,
considering all the available RXTE, Swift and INTEGRAL observations performed
between October and November, 2010.
  By measuring the pulse phase evolution we conclude that the NS spun up at an
average rate of <nu_dot>=1.48(2)E-12 Hz/s, compatible with the accretion of the
Keplerian angular momentum of matter at the inner disc boundary. Similar to
other accreting pulsars, the stability of the pulse phases determined by using
the second harmonic component is higher than that of the phases based on the
fundamental frequency. Under the assumption that the second harmonic is a good
tracer of the neutron star spin frequency, we successfully model its evolution
in terms of a luminosity dependent accretion torque. If the NS accretes the
specific Keplerian angular momentum of the in-flowing matter, we estimate the
inner disc radius to lie between 47 and 93 km when the luminosity attains its
peak value. Smaller values are obtained if the interaction between the magnetic
field lines and the plasma in the disc is considered.
  The phase-averaged spectrum is described by thermal Comptonization of photons
with energy of ~1 keV. A hard to soft state transition is observed during the
outburst rise. The Comptonized spectrum evolves from a Comptonizing cloud at an
electron temperature of ~20 keV towards an optically denser cloud at kT_e~3
keV. At the same time, the pulse amplitude decreases from 27% to few per cent
and becomes strongly energy dependent. We discuss various possibilities to
explain such a behaviour, proposing that at large accretion luminosities a
significant fraction of the in-falling matter is not channelled towards the
magnetic poles, but rather accretes more evenly onto the NS surface.",1203.4096v1
2012-07-24,Alignment of the stellar spin with the orbits of a three-planet system,"The Sun's equator and the planets' orbital planes are nearly aligned, which
is presumably a consequence of their formation from a single spinning gaseous
disk. For exoplanetary systems this well-aligned configuration is not
guaranteed: dynamical interactions may tilt planetary orbits, or stars may be
misaligned with the protoplanetary disk through chaotic accretion, magnetic
interactions or torques from neighbouring stars. Indeed, isolated 'hot
Jupiters' are often misaligned and even orbiting retrograde. Here we report an
analysis of transits of planets over starspots on the Sun-like star Kepler-30,
and show that the orbits of its three planets are aligned with the stellar
equator. Furthermore, the orbits are aligned with one another to within a few
degrees. This configuration is similar to that of our Solar System, and
contrasts with the isolated hot Jupiters. The orderly alignment seen in the
Kepler-30 system suggests that high obliquities are confined to systems that
experienced disruptive dynamical interactions. Should this be corroborated by
observations of other coplanar multi-planet systems, then star-disk
misalignments would be ruled out as the explanation for the high obliquities of
hot Jupiters, and dynamical interactions would be implicated as the origin of
hot Jupiters.",1207.5804v1
2012-10-08,"Analysis of the rotation period of asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger - search for the YORP effect","The spin state of small asteroids can change on a long timescale by the
Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, the net torque that arises
from anisotropically scattered sunlight and proper thermal radiation from an
irregularly-shaped asteroid. The secular change in the rotation period caused
by the YORP effect can be detected by analysis of asteroid photometric
lightcurves. We analyzed photometric lightcurves of near-Earth asteroids (1865)
Cerberus, (2100) Ra-Shalom, and (3103) Eger with the aim to detect possible
deviations from the constant rotation caused by the YORP effect. We carried out
new photometric observations of the three asteroids, combined the new
lightcurves with archived data, and used the lightcurve inversion method to
model the asteroid shape, pole direction, and rotation rate. The YORP effect
was modeled as a linear change in the rotation rate in time d\omega /dt. Values
of d\omega/ dt derived from observations were compared with the values
predicted by theory. We derived physical models for all three asteroids. We had
to model Eger as a nonconvex body because the convex model failed to fit the
lightcurves observed at high phase angles. We probably detected the
acceleration of the rotation rate of Eger d\omega / dt = (1.4 +/- 0.6) x
10^{-8} rad/d (3\sigma error), which corresponds to a decrease in the rotation
period by 4.2 ms/yr. The photometry of Cerberus and Ra-Shalom was consistent
with a constant-period model, and no secular change in the spin rate was
detected. We could only constrain maximum values of |d\omega / dt| < 8 x
10^{-9} rad/d for Cerberus, and |d\omega / dt| < 3 x 10^{-8} rad/d for
Ra-Shalom.",1210.2219v1
2012-11-06,Tidal resonance locks in inspiraling white dwarf binaries,"We calculate the tidal response of helium and carbon/oxygen (C/O) white dwarf
(WD) binaries inspiraling due to gravitational wave emission. We show that
resonance locks, previously considered in binaries with an early-type star,
occur universally in WD binaries. In a resonance lock, the orbital and spin
frequencies evolve in lockstep, so that the tidal forcing frequency is
approximately constant and a particular normal mode remains resonant, producing
efficient tidal dissipation and nearly synchronous rotation. We show that
analogous locks between the spin and orbital frequencies can occur not only
with global standing modes, but even when damping is so efficient that the
resonant tidal response becomes a traveling wave. We derive simple analytic
formulas for the tidal quality factor Q and tidal heating rate during a g-mode
resonance lock, and verify our results numerically. We find that Q ~ 10^7 for
orbital periods ~ 1 - 2 hr in C/O WDs, and Q ~ 10^9 for P_orb ~ 3 - 10 hr in
helium WDs. Typically tidal heating occurs sufficiently close to the surface
that the energy should be observable as surface emission. Moreover, near an
orbital period of ~ 10 min, the tidal heating rate reaches ~ 10^{-2} L_\sun,
rivaling the luminosities of our fiducial WD models. Recent observations of the
13-minute double-WD binary J0651 are roughly consistent with our theoretical
predictions. Tides naturally tend to generate differential rotation; however,
we show that the fossil magnetic field strength of a typical WD can maintain
solid-body rotation down to at least P_orb ~ 10 min even in the presence of a
tidal torque concentrated near the WD surface.",1211.1393v4
2013-10-16,Stellar Spin-Orbit Misalignment in a Multiplanet System,"Stars hosting hot Jupiters are often observed to have high obliquities,
whereas stars with multiple co-planar planets have been seen to have low
obliquities. This has been interpreted as evidence that hot-Jupiter formation
is linked to dynamical disruption, as opposed to planet migration through a
protoplanetary disk. We used asteroseismology to measure a large obliquity for
Kepler-56, a red giant star hosting two transiting co-planar planets. These
observations show that spin-orbit misalignments are not confined to hot-Jupiter
systems. Misalignments in a broader class of systems had been predicted as a
consequence of torques from wide-orbiting companions, and indeed
radial-velocity measurements revealed a third companion in a wide orbit in the
Kepler-56 system.",1310.4503v2
2014-10-23,The 2014 Magnetism Roadmap,"Magnetism is a very fascinating and dynamic field. Especially in the last 30
years it has experienced many major advances in the full range from novel
fundamental phenomena to new products. Applications such as hard disk drives
and magnetic sensors are part of our daily life, and new applications, such as
in non-volatile computer random access memory, are expected to surface shortly.
Thus it is timely for describing the current status, and current and future
challenges in the form of a Roadmap article. This 2014 Magnetism Roadmap
provides a view on several selected, currently very active innovative
developments. It consists of 12 sections, each written by an expert in the
field and addressing a specific subject, with strong emphasize on future
potential. This Roadmap cannot cover the entire field. We have selected several
highly relevant areas without attempting to provide a full review - a future
update will have room for more topics. The scope covers mostly nano-magnetic
phenomena and applications, where surfaces and interfaces provide additional
functionality. New developments in fundamental topics such as interacting
nano-elements, novel magnon-based spintronics concepts, spin-orbit torques and
spin-caloric phenomena are addressed. New materials, such as organic magnetic
materials and permanent magnets are covered. New applications are presented
such as nano-magnetic logic, non-local and domain-wall based devices,
heat-assisted magnetic recording, magnetic random access memory, and
applications in biotechnology. May the Roadmap serve as a guideline for future
emerging research directions in modern magnetism.",1410.6404v1
2016-02-02,Measuring the neutron star equation of state using X-ray timing,"One of the primary science goals of the next generation of hard X-ray timing
instruments is to determine the equation of state of the matter at supranuclear
densities inside neutron stars, by measuring the radius of neutron stars with
different masses to accuracies of a few percent. Three main techniques can be
used to achieve this goal. The first involves waveform modelling. The flux we
observe from a hotspot on the neutron star surface offset from the rotational
pole will be modulated by the star's rotation, giving rise to a pulsation.
Information about mass and radius is encoded into the pulse profile via
relativistic effects, and tight constraints on mass and radius can be obtained.
The second technique involves characterising the spin distribution of accreting
neutron stars. The most rapidly rotating stars provide a very clean constraint,
since the mass-shedding limit is a function of mass and radius. However the
overall spin distribution also provides a guide to the torque mechanisms in
operation and the moment of inertia, both of which can depend sensitively on
dense matter physics. The third technique is to search for quasi-periodic
oscillations in X-ray flux associated with global seismic vibrations of
magnetars (the most highly magnetized neutron stars), triggered by magnetic
explosions. The vibrational frequencies depend on stellar parameters including
the dense matter equation of state. We illustrate how these complementary X-ray
timing techniques can be used to constrain the dense matter equation of state,
and discuss the results that might be expected from a 10m$^2$ instrument. We
also discuss how the results from such a facility would compare to other
astronomical investigations of neutron star properties. [Modified for arXiv]",1602.01081v1
2016-02-13,Edwards Statistical Mechanics for Jammed Granular Matter,"In 1989, Sir Sam Edwards made the visionary proposition to treat jammed
granular materials using a volume ensemble of equiprobable jammed states in
analogy to thermal equilibrium statistical mechanics, despite their inherent
athermal features. Since then, the statistical mechanics approach for jammed
matter has garnered an extraordinary amount of attention by both theorists and
experimentalists. Here, we review a systematic approach to jammed matter based
on the Edwards statistical mechanical ensemble. We discuss the construction of
microcanonical and canonical ensembles based on the volume function, which
replaces the Hamiltonian in jammed systems. The importance of approximation
schemes at various levels is emphasized leading to quantitative predictions for
ensemble averaged quantities such as packing fractions and contact force
distributions. An overview of the phenomenology of jammed states and
experiments, simulations, and theoretical models scrutinizing the strong
assumptions underlying Edwards' approach is given including recent results
suggesting the validity of Edwards ergodic hypothesis for jammed states. A
theoretical framework for packings whose constitutive particles range from
spherical to non-spherical shapes like dimers, polymers, ellipsoids,
spherocylinders or tetrahedra, hard and soft, frictional, frictionless and
adhesive, monodisperse and polydisperse particles in any dimensions is
discussed providing insight into an unifying phase diagram for all jammed
matter. Furthermore, the connection between the Edwards' ensemble of metastable
jammed states and metastability in spin-glasses is established. This highlights
that the packing problem can be understood as a constraint satisfaction problem
for excluded volume and force and torque balance leading to a unifying
framework between the Edwards ensemble of equiprobable jammed states and
out-of-equilibrium spin-glasses.",1602.04369v4
2016-10-26,On the stability of a space vehicle riding on an intense laser beam,"The Breakthrough Starshot Initiative is suggested to develop the concept of
propelling a nano-scale spacecraft by the radiation pressure of an intense
laser beam. If such a nanocraft could be accelerated to 20 percent of light
speed, it could reach the vicinity of our nearest potentially habitable
exoplanet within our life time and capture its images and obtain other
scientific data. In this project the nanocraft is a gram-scale robotic
spacecraft comprising two main parts: StarChip and Lightsail.
  To achieve the goal of the project it is necessary to solve a number of
outstanding scientific problems. One of these tasks is to make sure that the
nanocraft position and orientation inside the intense laser beam column is
stable. The nanocraft driven by intense laser beam pressure acting on its
Lightsail is sensitive to the torques and lateral forces reacting on the
surface of the sail. These forces influence the orientation and lateral
displacement of the spacecraft, thus affecting its dynamics. If unstable the
nanocraft might be expelled from the area of laser beam. In choosing the models
for nanocraft stability studies we are using several assumptions: 1.
configuration of nanocraft is treated as rigid body (applicability of Euler
equations); 2. flat or concave shape of circular sail; 3. mirror reflection of
laser beam from surface of the Lightsail. We found conditions of position
stability for spherical and conical shape of the sail. The simplest stable
configurations require the StarChip to be removed from the sail to make the
distance to the center of mass of nanocraft bigger than curvature radius of the
sail. Stability criteria do not require the spinning of the nanocraft. A flat
sail is never stable (even with spinning).",1610.08043v4
2016-11-30,Measuring alignments between galaxies and the cosmic web at $z \sim 2-3$ using IGM tomography,"Many galaxy formation models predict alignments between galaxy spin and the
cosmic web (i.e. the directions of filaments and sheets), leading to intrinsic
alignment between galaxies that creates a systematic error in weak lensing
measurements. These effects are often predicted to be stronger at
high-redshifts ($z\gtrsim1$) that are inaccessible to massive galaxy surveys on
foreseeable instrumentation, but IGM tomography of the Ly$\alpha$ forest from
closely-spaced quasars and galaxies is starting to measure the $z\sim2-3$
cosmic web with the requisite fidelity. Using mock surveys from hydrodynamical
simulations, we examine the utility of this technique, in conjunction with
coeval galaxy samples, to measure alignment between galaxies and the cosmic web
at $z\sim2.5$. We show that IGM tomography surveys with $\lesssim5$ $h^{-1}$
Mpc sightline spacing can accurately recover the eigenvectors of the tidal
tensor, which we use to define the directions of the cosmic web. For galaxy
spins and shapes, we use a model parametrized by the alignment strength,
$\Delta\langle\cos\theta\rangle$, with respect to the tidal tensor eigenvectors
from the underlying density field, and also consider observational effects such
as errors in the galaxy position angle, inclination, and redshift. Measurements
using the upcoming $\sim1\,\mathrm{deg}^2$ CLAMATO tomographic survey and 600
coeval zCOSMOS-Deep galaxies should place $3\sigma$ limits on extreme alignment
models with $\Delta\langle\cos\theta\rangle\sim0.1$, but much larger surveys
encompassing $>10,000$ galaxies, such as Subaru PFS, will be required to
constrain models with $\Delta\langle\cos\theta\rangle\sim0.03$. These
measurements will constrain models of galaxy-cosmic web alignment and test
tidal torque theory at $z\sim2$, improving our understanding of the redshift
dependence of galaxy-cosmic web alignment and the physics of intrinsic
alignments.",1612.00067v1
2017-07-04,Changes in orientation and shape of protoplanetary discs moving through an ambient medium,"Misalignments between the orbital planes of planets and the equatorial planes
of their host stars have been observed in our solar system, in transiting
exoplanets, and in the orbital planes of debris discs. We present a mechanism
that causes such a spin-orbit misalignment for a protoplanetary disc due to its
movement through an ambient medium. Our physical explanation of the mechanism
is based on the theoretical solutions to the Stark problem. We test this idea
by performing self-consistent hydrodynamical simulations and simplified
gravitational $N$-body simulations. The $N$-body model reduces the mechanism to
the relevant physical processes. The hydrodynamical simulations show the
mechanism in its full extent, including gas-dynamical and viscous processes in
the disc which are not included in the theoretical framework. We find that a
protoplanetary disc embedded in a flow changes its orientation as its angular
momentum vector tends to align parallel to the relative velocity vector. Due to
the force exerted by the flow, orbits in the disc become eccentric, which
produces a net torque and consequentially changes the orbital inclination. The
tilting of the disc causes it to contract. Apart from becoming lopsided, the
gaseous disc also forms a spiral arm even if the inclination does not change
substantially. The process is most effective at high velocities and
observational signatures are therefore mostly expected in massive star-forming
regions and around winds or supernova ejecta. Our $N$-body model indicates that
the interaction with supernova ejecta is a viable explanation for the observed
spin-orbit misalignment in our solar system.",1707.01096v1
2017-08-15,Ultra-luminous X-ray sources as super-critical propellers,"We study the evolution of newborn neutron stars in high-mass X-ray binaries
interacting with a wind-fed super-Eddington disk. The inner disk is regularized
to a radiation-dominated quasi-spherical configuration for which we calculate
the inner radius of the disk, the total luminosity of the system and the torque
acting on the neutron star accordingly, following the evolution of the system
through the ejector and early propeller stages. We find that the systems with
$B \gtrsim 10^{13}$ G pass through a short ($\sim 20\,{\rm yr}$) ejector stage
appearing as supernova impostors followed by a propeller stage lasting $\sim
10^3\,{\rm yr}$. In the super-critical propeller stage the system is still
bright ($L\sim 10^{40}\,{\rm erg\, s^{-1}}$) due to the spindown power and
therefore appears as an ultra-luminous X-ray source (ULX). The system evolves
into pulsating ULX (PULX) when the neutron star spins down to a period ($P\sim
1$ s) allowing for accretion onto its surface to commence. Systems with lower
magnetic fields, $B \sim 10^{11}$ G, pass through a long ($10^5\,{\rm yr}$)
super-critical propeller stage with luminosities similar to those of the
ultra-luminous super-soft sources (ULS), $L \lesssim 10^{40}\,{\rm erg\,
s^{-1}}$. The equilibrium periods of these systems in the accretion stage is
about $10\,{\rm ms}$, which is much smaller than the typical period range of
PULX observed to date. Such systems could have a larger population, but their
pulsations would be elusive due to the smaller size of the magnetosphere. Our
results suggest that the ULS and some nonpulsating ULX are rapidly spinning and
highly magnetized young neutron stars at the super-critical propeller stage.",1708.04502v5
2017-08-25,"The Young Substellar Companion ROXs 12 B: Near-Infrared Spectrum, System Architecture, and Spin-Orbit Misalignment","ROXs 12 (2MASS J16262803-2526477) is a young star hosting a directly imaged
companion near the deuterium-burning limit. We present a suite of
spectroscopic, imaging, and time-series observations to characterize the
physical and environmental properties of this system. Moderate-resolution
near-infrared spectroscopy of ROXs 12 B from Gemini-North/NIFS and Keck/OSIRIS
reveals signatures of low surface gravity including weak alkali absorption
lines and a triangular $H$-band pseudo-continuum shape. No signs of Pa$\beta$
emission are evident. As a population, however, we find that about half (46
$\pm$ 14\%) of young ($\lesssim$15 Myr) companions with masses $\lesssim$20
$M_\mathrm{Jup}$ possess actively accreting subdisks detected via Pa$\beta$
line emission, which represents a lower limit on the prevalence of
circumplanetary disks in general as some are expected to be in a quiescent
phase of accretion. The bolometric luminosity of the companion and age of the
host star (6$^{+4}_{-2}$ Myr) imply a mass of 17.5 $\pm$ 1.5 $M_\mathrm{Jup}$
for ROXs 12 B based on hot-start evolutionary models. We identify a wide (5100
AU) tertiary companion to this system, 2MASS J16262774-2527247, which is
heavily accreting and exhibits stochastic variability in its $K2$ light curve.
By combining $v$sin$i_*$ measurements with rotation periods from $K2$, we
constrain the line-of-sight inclinations of ROXs 12 A and 2MASS
J16262774-2527247 and find that they are misaligned by
60$^{+7}_{-11}$$^{\circ}$. In addition, the orbital axis of ROXs 12 B is likely
misaligned from the spin axis of its host star ROXs 12 A, suggesting that ROXs
12 B formed akin to fragmenting binary stars or in an equatorial disk that was
torqued by the wide stellar tertiary.",1708.07611v1
2018-07-03,Electrically switchable Berry curvature dipole in the monolayer topological insulator WTe2,"Recent experimental evidence for the quantum spin Hall (QSH) state in
monolayer WTe$_2$ has bridged two of the most active fields of condensed matter
physics, 2D materials and topological physics. This 2D topological crystal also
displays unconventional spin-torque and gate-tunable superconductivity. While
the realization of QSH has demonstrated the nontrivial topology of the electron
wavefunctions of monolayer WTe$_2$, the geometrical properties of the
wavefunction, such as the Berry curvature, remain unstudied. On the other hand,
it has been increasingly recognized that the Berry curvature plays an important
role in multiple areas of condensed matter physics including nonreciprocal
electron transport, enantioselective optical responses, chiral polaritons and
even unconventional superconductivity. Here we utilize mid-infrared
optoelectronic microscopy to investigate the Berry curvature in monolayer
WTe$_2$. By optically exciting electrons across the inverted QSH gap, we
observe an in-plane circular photogalvanic current even under normal incidence.
The application of an out-of-plane displacement field further systematically
controls the direction and magnitude of the photocurrent. Our observed
photocurrent reveals a novel Berry curvature dipole that arises from the
nontrivial wavefunctions near the inverted gap edge. These previously
unrealized Berry curvature dipole and strong electric field effect are uniquely
enabled by the inverted band structure and tilted crystal lattice of monolayer
WTe$_2$. Such an electrically switchable Berry curvature dipole opens the door
to the observation of a wide range of quantum geometrical phenomena, such as
quantum nonlinear Hall, orbital-Edelstein and chiral polaritonic effects.",1807.01259v1
2020-05-20,Alfvén-wave driven magnetic rotator winds from low-mass stars I: rotation dependences of magnetic braking and mass-loss rate,"Observations of stellar rotation show that low-mass stars lose angular
momentum during the main sequence. We simulate the winds of Sun-like stars with
a range of rotation rates, covering the fast and slow magneto-rotator regimes,
including the transition between the two. We generalize an Alfv\'en-wave driven
solar wind model that builds on previous works by including the
magneto-centrifugal force explicitly. In this model, the surface-averaged open
magnetic flux is assumed to scale as $B_\ast f^{\rm open}_\ast \propto {\rm
Ro}^{-1.2}$, where $f^{\rm open}_\ast$ and ${\rm Ro}$ are the surface open-flux
filling factor and Rossby number, respectively. We find that, 1. the angular
momentum loss rate (torque) of the wind is described as $\tau_w \approx 2.59
\times 10^{30} {\rm \ erg} \ \left( \Omega_\ast / \Omega_\odot \right)^{2.82}$,
yielding a spin-down law $\Omega_\ast \propto t^{-0.55}$. 2. the mass-loss rate
saturates at $\dot{M}_w \sim 3.4 \times 10^{-14} M_\odot {\rm \ yr^{-1}}$, due
to the strong reflection and dissipation of Alfv\'en waves in the chromosphere.
This indicates that the chromosphere has a strong impact in connecting the
stellar surface and stellar wind. Meanwhile, the wind ram pressure scales as
$P_w \propto \Omega_\ast^{0.57}$, which is able to explain the lower-envelope
of the observed stellar winds by Wood et al. 3. the location of the Alfv\'en
radius is shown to scale in a way that is consistent with 1D analytic theory.
Additionally, the precise scaling of the Alfv\'en radius matches previous works
which used thermally-driven winds. Our results suggest that the Alfv\'en-wave
driven magnetic rotator wind plays a dominant role in the stellar spin-down
during the main-sequence.",2005.09817v2
2021-01-15,"Realization of the Chern insulator and Axion insulator phases in antiferromagnetic $MnTe$-$Bi_2(Se, Te)_3$-$MnTe$ heterostructures","Breaking time-reversal symmetry in three-dimensional topological insulator
thin films can lead to different topological quantum phases, such as the Chern
insulator (CI) phase, and the axion insulator (AI) phase. Using
first-principles density functional theory methods, we investigate the onset of
these two topological phases in a tri-layer heterostructure consisting of a
Bi$_2$Se$_3$ (Bi$_2$Te$_3$) TI thin film sandwiched between two
antiferromagnetic MnTe layers. We find that an orthogonal exchange field from
the MnTe layers, stabilized by a small anisotropy barrier, opens an energy gap
of the order of 10 meV at the Dirac point of the TI film. A topological
analysis demonstrates that, depending on the relative orientation of the
exchange field at the two interfaces, the total Chern number of the system is
either ${\cal C} = 1$ or ${\cal C} = 0$, characteristic of the CI and the AI
phase, respectively. Non-topological surface states inside the energy-gap
region, caused by the interface potential, complicate this identification.
Remarkably though, the calculation of the anomalous Hall conductivity shows
that such non-topological surface states do not affect the topology-induced
transport properties. Given the size of the exchange gap, we estimate that
gapless chiral edge states, leading to the quantum anomalous Hall effect,
should emerge on the sidewalls of these heterostructures in the CI phase for
widths $\ge 200$ nm. We also discuss the possibility of inducing transitions
between the CI and the AI phases by means of the spin-orbit torque caused by
the spin Hall effect in an adjacent conducting layer.",2101.06259v4
2021-01-29,Improved gravitational radiation time-scales II: spin-orbit contributions and environmental perturbations,"Peters' formula is an analytical estimate of the time-scale of gravitational
wave (GW)-induced coalescence of binary systems. It is used in countless
applications, where the convenience of a simple formula outweighs the need for
precision. However, many promising sources of the Laser Interferometer Space
Antenna (LISA), such as supermassive black hole binaries and extreme mass-ratio
inspirals (EMRIs), are expected to enter the LISA band with highly eccentric
($e \gtrsim$ 0.9) and highly relativistic orbits. These are exactly the two
limits in which Peters' estimate performs the worst. In this work, we expand
upon previous results and give simple analytical fits to quantify how the
inspiral time-scale is affected by the relative 1.5 post-Newtonian (PN)
hereditary fluxes and spin-orbit couplings. We discuss several cases that
demand a more accurate GW time-scale. We show how this can have a major
influence on quantities that are relevant for LISA event-rate estimates, such
as the EMRI critical semi-major axis. We further discuss two types of
environmental perturbations that can play a role in the inspiral phase: the
gravitational interaction with a third massive body and the energy loss due to
dynamical friction and torques from a surrounding gas medium ubiquitous in
galactic nuclei. With the aid of PN corrections to the time-scale in vacuum, we
find simple analytical expressions for the regions of phase space in which
environmental perturbations are of comparable strength to the effects of any
particular PN order, being able to qualitatively reproduce the results of much
more sophisticated analyses.",2102.00015v2
2021-05-07,Long Period Jovian Tilts the Orbits of Two sub-Neptunes Relative to Stellar Spin Axis in Kepler-129,"We present the discovery of Kepler-129 d ($P_{d}=7.2^{+0.4}_{-0.3}$ yr,
$m\sin i_{d}=8.3^{+1.1}_{-0.7}\ \rm M_{Jup}$, $ e_{d}=0.15^{+0.07}_{-0.05} $)
based on six years of radial velocity (RV) observations from Keck/HIRES.
Kepler-129 also hosts two transiting sub-Neptunes: Kepler-129 b ($P_{b}=15.79$
days, $r_{b}=2.40\pm{0.04}\ \rm{R_{\oplus}}$) and Kepler-129 c ($P_{c}=82.20$
days, $r_{c}=2.52\pm{0.07}\ \rm{R_{\oplus}}$) for which we measure masses of
$m_{b}<20\ \rm{M_{\oplus}}$ and $m_{c}=43^{+13}_{-12}\ \rm{M_{\oplus}}$.
Kepler-129 is an hierarchical system consisting of two tightly-packed inner
planets and an external companion whose mass is close to the deuterium burning
limit. In such a system, two inner planets precess around the orbital normal of
the outer companion, causing their inclinations to oscillate with time. Based
on an asteroseismic analysis of Kepler data, we find tentative evidence that
Kepler-129 b and c are misaligned with stellar spin axis by $\gtrsim 38$ deg,
which could be torqued by Kepler-129 d if it is inclined by $\gtrsim 19$ deg
relative to inner planets. Using N-body simulations, we provide additional
constraints on the mutual inclination between Kepler-129 d and inner planets by
estimating the fraction of time during which two inner planets both transit.
The probability that two planets both transit decreases as their misalignment
with Kepler-129 d increases. We also find a more massive Kepler-129 c enables
the two inner planets to become strongly coupled and more resistant to
perturbations from Kepler-129 d. The unusually high mass of Kepler-129 c
provides a valuable benchmark for both planetary dynamics and interior
structure, since the best-fit mass is consistent with this $\rm{2.5\
R_{\oplus}}$ planet having a rocky surface.",2105.03446v1
2021-07-30,Timing and spectral analysis of 2S 1417$-$624 during its 2018 outburst,"We investigate timing and spectral characteristics of the transient X-ray
pulsar 2S 1417$-$624 during its 2018 outburst with \emph{NICER} follow up
observations. We describe the spectra with high-energy cut-off and partial
covering fraction absorption (PCFA) model and present flux-dependent spectral
changes of the source during the 2018 outburst. Utilizing the correlation-mode
switching of the spectral model parameters, we confirm the previously reported
sub-critical to critical regime transitions and we argue that secondary
transition from the gas-dominated to the radiation pressure-dominated disc do
not lead to significant spectral changes below 12 keV. Using the existing
accretion theories, we model the spin frequency evolution of 2S 1417$-$624 and
investigate the noise processes of a transient X-ray pulsar for the first time
using both polynomial and luminosity-dependent models for the spin frequency
evolution. For the first model, the power density spectrum of the torque
fluctuations indicate that the source exhibits red noise component ($\Gamma
\sim -2$) within the timescales of outburst duration which is typical for
disc-fed systems. On the other hand, the noise spectrum tends to be white on
longer timescales with high timing noise level that indicates an ongoing
accretion process in between outburst episodes. For the second model, most of
the red noise component is eliminated and the noise spectrum is found to be
consistent with a white noise structure observed in wind-fed systems.",2107.14492v2
2021-11-01,"Supercurrent Diode Effect, Spin Torques, and Robust Zero-Energy Peak in Planar Half-Metallic Trilayers","We consider a Josephson junction with ${\rm F_1 F_2 F_3}$ ferromagnetic
trilayers in the ballistic regime, where the magnetization in each ferromagnet
${\rm F}_i (i=1,2,3)$, can have arbitrary orientations and magnetization
strengths. The trilayers are sandwiched between two $s$-wave superconductors
with a macroscopic phase difference $\Delta \varphi$. A broad range of
magnetization strengths of the central $\rm F_2$ layer are considered, from an
unpolarized normal metal (N) to a half-metallic phase, supporting only one spin
species. Our results reveal that when the magnetization configuration in ${\rm
F_1 F_2 F_3}$ has three orthogonal components, a supercurrent can flow at
$\Delta \varphi=0$, and a strong second harmonic in the current-phase relation
appears. Upon increasing the magnetization strength in the central ferromagnet
layer up to the half-metallic limit, the self-biased current and second
harmonic component become dramatically enhanced, and the critical supercurrent
reaches its maximum value. The higher harmonics in the current-phase relations
can be controlled by the relative magnetization orientations, with negligible
current damping compared to the corresponding ${\rm F_1 N F_3}$ counterparts.
For a broad range of exchange field strengths in the central ferromagnet ${\rm
F}_2$, the ground state of the system can be tuned to an arbitrary phase
difference $\varphi_0$ by rotating the magnetization in the outer ferromagnet
$\rm F_3$. For intermediate exchange field strengths in ${\rm F}_2$, a
$\varphi_0$ state can arise that creates a superconducting diode effect,
whereby $\Delta\varphi$ can be tuned to create a one-way dissipationless
current flow. The density of states demonstrates the emergence of zero energy
peaks for the mutually orthogonal magnetization configurations, which is
strongest in the half-metallic phase.",2111.01242v1
2022-06-23,Dynamics of asteroid systems post rotational fission,"Asteroid binaries found amongst the Near-Earth objects are believed to have
formed from rotational fission. In this paper, we aim to study the dynamical
evolution of asteroid systems the moment after fission. The initial condition
is modelled as a contact binary, similar to that of Boldrin et al. (2016). Both
bodies are modelled as ellipsoids, and the secondary is given an initial
rotation angle about its body-fixed $y$-axis. Moreover, we consider six
different cases, three where the density of the secondary varies, and three
where we vary its shape. The simulations consider 45 different initial tilt
angles of the secondary, each with 37 different mass ratios. We start the
dynamical simulations at the moment the contact binary reaches a spin fission
limit, and our model ensures that the closest distance between the surfaces of
the two bodies is always kept at 1 cm. The forces, torques and gravitational
potential between the two bodies are modelled using a newly developed surface
integration scheme, giving exact results for two ellipsoids. We find that more
than 80% of the simulations end with the two bodies impacting, and collisions
between the bodies are more common when the density of the secondary is lower,
or when it becomes more elongated. When comparing with data on asteroid pairs
from Pravec et al. (2019) we find that variations in density and shape of the
secondary can account for some of the spread seen in the rotation period for
observed pairs. Furthermore, the secondary may also reach a spin limit for
surface disruption, creating a ternary/multiple system. We find that secondary
fission typically occurs within the first five hours after the contact binary
separates, and is more common when the secondary is less dense or more
elongated.",2206.11570v1
2022-10-18,"Nozzle Shocks, Disk Tearing and Streamers Drive Rapid Accretion in 3D GRMHD Simulations of Warped Thin Disks","The angular momentum of gas feeding a black hole (BH) is typically misaligned
with respect to the BH spin, resulting in a tilted accretion disk. Rotation of
the BH drags the surrounding space-time, manifesting as Lense-Thirring torques
that lead to disk precession and warping. We study these processes by
simulating a thin ($H/r=0.02$), highly tilted ($\mathcal{T}=65^\circ$)
accretion disk around a rapidly rotating ($a=0.9375$) BH at extremely high
resolutions, which we performed using the general-relativistic
magnetohydrodynamic (GRMHD) code H-AMR. The disk becomes significantly warped
and continuously tears into two individually precessing sub-disks. We find that
mass accretion rates far exceed the standard $\alpha$-viscosity expectations.
We identify two novel dissipation mechanisms specific to warped disks that are
the main drivers of accretion, distinct from the local turbulent stresses that
are usually thought to drive accretion. In particular, we identify extreme
scale height oscillations that occur twice an orbit throughout our disk. When
the scale height compresses, `nozzle' shocks form, dissipating orbital energy
and driving accretion. Separate from this phenomenon, there is also extreme
dissipation at the location of the tear. This leads to the formation of
low-angular momentum `streamers' that rain down onto the inner sub-disk,
shocking it. The addition of low angular momentum gas to the inner sub-disk
causes it to rapidly accrete, even when it is transiently aligned with the BH
spin and thus unwarped. These mechanisms, if general, significantly modify the
standard accretion paradigm. Additionally, they may drive structural changes on
much shorter timescales than expected in $\alpha$-disks, potentially explaining
some of the extreme variability observed in active galactic nuclei.",2210.10053v2
2022-11-22,Deep X-ray and radio observations of the first outburst of the young magnetar Swift J1818.0-1607,"Swift J1818.0-1607 is a radio-loud magnetar with a spin period of 1.36 s and
a dipolar magnetic field strength of B~3E14 G, which is very young compared to
the Galactic pulsar population. We report here on the long-term X-ray
monitoring campaign of this young magnetar using XMM-Newton, NuSTAR, and Swift
from the activation of its first outburst in March 2020 until October 2021, as
well as INTEGRAL upper limits on its hard X-ray emission. The 1-10 keV magnetar
spectrum is well modeled by an absorbed blackbody with a temperature of
kT_BB~1.1 keV, and apparent reduction in the radius of the emitting region from
~0.6 to ~0.2 km. We also confirm the bright diffuse X-ray emission around the
source extending between ~50'' and ~110''. A timing analysis revealed large
torque variability, with an average spin-down rate nudot~-2.3E-11 Hz^2 that
appears to decrease in magnitude over time. We also observed Swift J1818.0-1607
with the Karl G. Jansky Very Large Array (VLA) on 2021 March 22. We detected
the radio counterpart to Swift J1818.0-1607 measuring a flux density of S_v =
4.38+/-0.05 mJy at 3 GHz, and a half ring-like structure of bright diffuse
radio emission located at ~90'' to the west of the magnetar. We tentatively
suggest that the diffuse X-ray emission is due to a dust scattering halo and
that the radio structure may be associated with the supernova remnant of this
young pulsar, based on its morphology.",2211.12391v1
2023-10-19,The Three-Phase Evolution of the Milky Way,"We illustrate the formation and evolution of the Milky Way over cosmic time,
utilizing a sample of 10 million red giant stars with full chemodynamical
information, including metallicities and $\alpha$-abundances from
low-resolution Gaia XP spectra. The evolution of angular momentum as a function
of metallicity - a rough proxy for stellar age, particularly for
high-[$\alpha$/Fe] stars - displays three distinct phases: the disordered and
chaotic protogalaxy, the kinematically-hot old disk, and the kinematically-cold
young disk. The old high-$\alpha$ disk starts at [Fe/H] $\approx -1.0$,
'spinning up' from the nascent protogalaxy, and then exhibits a smooth
'cooldown' toward more ordered and circular orbits at higher metallicities. The
young low-$\alpha$ disk is kinematically cold throughout its metallicity range,
with its observed properties modulated by a strong radial gradient. We
interpret these trends using Milky Way analogs from the TNG50 cosmological
simulation, identifying one that closely matches the kinematic evolution of our
Galaxy. This halo's protogalaxy spins up into a relatively thin and misaligned
high-$\alpha$ disk at early times, which is subsequently heated and torqued by
a major gas-rich merger. The merger contributes a large amount of
low-metallicity gas and angular momentum, from which the kinematically cold
low-$\alpha$ stellar disk is subsequently born. This simulated history
parallels several observed features of the Milky Way, particularly the decisive
'GSE' merger that likely occurred at $z \approx 2$. Our results provide an
all-sky perspective on the emerging picture of our Galaxy's three-phase
formation, impelled by the three physical mechanisms of spinup, merger, and
cooldown.",2310.13050v1
2023-10-23,Simulating the tidal disruption of stars by stellar-mass black holes using moving-mesh hydrodynamics,"In the centers of dense star clusters, close encounters between stars and
compact objects are likely to occur. We study tidal disruption events of
main-sequence (MS) stars by stellar-mass black holes (termed $\mu$TDEs), which
can shed light on the processes occurring in these clusters, including being an
avenue in the mass growth of stellar-mass BHs. Using the moving-mesh
hydrodynamics code \texttt{AREPO}, we perform a suite of hydrodynamics
simulations of partial $\mu$TDEs of realistic, \texttt{MESA}-generated MS stars
by varying the initial mass of the star ($0.5\,{\rm M}_{\rm \odot}$ and
$1\,{\rm M}_{\rm \odot}$), the age of the star (zero-age, middle-age and
terminal-age), the mass of the black hole ($10\,{\rm M}_{\rm \odot}$ and
$40\,{\rm M}_{\rm \odot}$) and the impact parameter (yielding almost no mass
loss to full disruption). We then examine the dependence of the masses, spins,
and orbital parameters of the partially disrupted remnant on the initial
encounter parameters. We find that the mass lost from a star decreases
exponentially with increasing distance of approach and that a $1\,{\rm M}_{\rm
\odot}$ star loses lesser mass than a $0.5\,{\rm M}_{\rm \odot}$. Moreover, a
more evolved star is less susceptible to mass loss. Tidal torques at the
closest approach spin up the remnant by factors of $10^2$--$10^4$ depending on
the impact parameter. The remnant star can be bound (eccentric) or unbound
(hyperbolic) to the black hole: hyperbolic orbits occur when the star's central
density concentration is relatively low and the black hole-star mass ratio is
high, which is the case for the disruption of a $0.5\,{\rm M}_{\rm \odot}$
star. Finally, we provide best-fit analytical formulae for a range of
parameters that can be incorporated into cluster codes to model star-black hole
interaction more accurately.",2310.14852v2
2023-11-13,Multipole expansion of the gravitational field in a general class of fourth-order theories of gravity and the application in gyroscopic precession,"A viable weak-field and slow-motion approximation method is constructed in
$F(R,R_{\mu\nu}R^{\mu\nu}, R_{\mu\nu\rho\sigma}R^{\mu\nu\rho\sigma})$ gravity,
a general class of fourth-order theories of gravity. By applying this method,
the metric, presented in the form of the multipole expansion, outside a
spatially compact source up to $1/c^3$ order is provided, and the closed-form
expressions for the source multipole moments are all presented explicitly. The
metric consists of the massless tensor part, the massive scalar part, and the
massive tensor part, where the former is exactly the metric in General
Relativity, and the latter two are the corrections to it. It is shown that the
corrections bear the Yukawa-like dependence on the two massive parameters and
predict the appearance of six additional sets of source multipole moments,
which indicates that up to $1/c^3$ order, there exist six degrees of freedom
beyond General Relativity within $F(R,R_{\mu\nu}R^{\mu\nu},
R_{\mu\nu\rho\sigma}R^{\mu\nu\rho\sigma})$ gravity. By means of the metric, for
a gyroscope moving around the source without experiencing any torque, the
multipole expansions of its spin's angular velocities of the Thomas precession,
the geodetic precession, and the Lense-Thirring precession are derived, and
from them, the corrections to the angular velocities of the three types of
precession in General Relativity can be read off. These results indicate that
differently from $f(R)$ or $f(R,\mathcal{G})$ gravity, the most salient feature
of the general $F(R,R_{\mu\nu}R^{\mu\nu},
R_{\mu\nu\rho\sigma}R^{\mu\nu\rho\sigma})$ gravity is that it gives the
nonvanishing correction to the gyroscopic spin's angular velocity of the
Lense-Thirring precession in General Relativity.",2311.07246v4
2023-11-29,A phenomenological gravitational waveform model of binary black holes incorporating horizon fluxes,"Subjected to the tidal field of its companion, each component of a coalescing
binary suffers a slow change in its mass (tidal heating) and spin (tidal
torquing) during the inspiral and merger. For black holes, these changes are
associated with their absorption of energy and angular momentum fluxes. This
effect modifies the inspiral rate of the binary, and consequently, the phase
and amplitude of its gravitational waveform. Numerical relativity waveforms
contain these effects inherently, whereas analytical approximants for the early
inspiral phase have to include them manually in the energy balance equation. In
this work, we construct a frequency-domain gravitational waveform model that
incorporates the effects of tidal heating of black holes. This is achieved by
recalibrating the inspiral phase of the waveform model IMRPhenomD to
incorporate the phase corrections for tidal heating. We also include
corrections to the amplitude, but add them directly to the inspiral amplitude
model of IMRPhenomD. We show that the new model is faithful, with less than 1%
mismatch, against a set of hybrid waveforms, except for one outlier that barely
breaches this limit. The recalibrated model shows mismatches of up to $\sim
16\%$ with IMRPhenomD for high mass ratios and spins. Amplitude corrections
become less significant for higher mass ratios, whereas the phase corrections
leave more impact - suggesting that the former is practically irrelevant for
gravitational wave data analysis in Advanced LIGO (aLIGO), Virgo and KAGRA.
Comparing with a set of 219 numerical relativity waveforms, we find that the
median of mismatches decreases by $\sim 4\%$ in aLIGO zero-detuned high power
noise curve, and by $\sim 2\%$ with a flat noise curve. This implies a modest
but notable improvement in waveform accuracy.",2311.17554v2
2023-11-30,Anomalous Hall effect with plateaus observed in a magnetic Weyl semimetal NdAlGe at low temperatures,"In the $R$Al(Si,Ge) ($R$: lanthanides) family, both spatial inversion and
time-reversal symmetries are broken. This may offer opportunities to study
Weyl-fermion physics in nontrivial spin structures emerging from a
noncentrosymmetric crystal structure. In this study, we investigated the
anomalous Hall effect (AHE) in NdAlGe via magnetotransport, magnetization, and
magnetic torque measurements down to 40 mK (0.4 K for magnetization). The
single crystals grown by a laser-heated floating-zone method exhibit a single
magnetic phase transition at $T_{\rm M}$ = 13.5 K, where the $T_{\rm M}$ is the
transition temperature. With the magnetic field parallel to the easy
$\lbrack$001$\rbrack$ axis, the AHE gradually evolves as the temperature
decreases below $T_{\rm M}$. The anomalous Hall conductivity (AHC) reaches
$\sim$320 $\Omega^{-1}$cm$^{-1}$ at 40 mK in the magnetically saturated state.
Except in low-temperature low-field plateau phases, the AHC and magnetization
are proportional, and their ratio agrees with the ratios for conventional
ferromagnets, suggesting that the intrinsic AHE occurs by the Karplus-Luttinger
mechanism. Below $\sim$0.6 K, the curves of Hall resistivity against the field
exhibit plateaus at low fields below $\sim$0.5 T, correlating with the plateaus
in the magnetization curve. For the first plateau, the magnetization is one
order of magnitude smaller than the magnetically saturated state, whereas the
AHE is more than half that in the saturated state. This finding under well
below $T_{\rm M}$ suggests that the AHE at the first plateau is not governed by
the magnetization and may be interpreted based on a multipole or spin
chirality.",2312.00222v2
2022-01-21,Neutron transfer reactions on the ground state and isomeric state of a 130Sn beam,"The structure of nuclei around the neutron-rich nucleus 132Sn is of
particular interest due to the vicinity of the Z = 50 and N = 82 shell closures
and the r-process nucleosynthetic path. Four states in 131Sn with a strong
single-particle-like component have previously been studied via the (d,p)
reaction, with limited excitation energy resolution. The 130Sn(9Be,8Be)131Sn
and 130Sn(13C,12C)131Sn single-neutron transfer reactions were performed in
inverse kinematics at the Holifield Radioactive Ion Beam Facility using
particle-gamma coincidence spectroscopy. The uncertainties in the energies of
the single-particle-like states have been reduced by more than an order of
magnitude using the energies of gamma rays. The previous tentative Jpi values
have been confirmed. Decays from high-spin states in 131Sn have been observed
following transfer on the isomeric component of the 130Sn beam. The improved
energies and confirmed spin-parities of the p-wave states important to the
r-process lead to direct-semidirect cross-sections for neutron capture on the
ground state of 130Sn at 30 keV that are in agreement with previous analyses. A
similar assessment of the impact of neutron-transfer on the isomer would
require significant nuclear structure and reaction theory input. There are few
measurements of transfer reaction on isomers, and this is the first on an
isomer in the 132Sn region.",2201.08890v1
2020-10-05,When Do Stalled Stars Resume Spinning Down? Advancing Gyrochronology with Ruprecht 147,"Recent measurements of rotation periods ($P_\text{rot}$) in the benchmark
open clusters Praesepe (670 Myr), NGC 6811 (1 Gyr), and NGC 752 (1.4 Gyr)
demonstrate that, after converging onto a tight sequence of slowly rotating
stars in mass$-$period space, stars temporarily stop spinning down. These data
also show that the duration of this epoch of stalled spin-down increases toward
lower masses. To determine when stalled stars resume spinning down, we use data
from the $K2$ mission and the Palomar Transient Factory to measure
$P_\text{rot}$ for 58 dwarf members of the 2.7-Gyr-old cluster Ruprecht 147, 39
of which satisfy our criteria designed to remove short-period or
near-equal-mass binaries. Combined with the $Kepler$ $P_\text{rot}$ data for
the approximately coeval cluster NGC 6819 (30 stars with $M_\star > 0.85$
M$_\odot$), our new measurements more than double the number of $\approx$2.5
Gyr benchmark rotators and extend this sample down to $\approx$0.55 M$_\odot$.
The slowly rotating sequence for this joint sample appears relatively flat (22
$\pm$ 2 days) compared to sequences for younger clusters. This sequence also
intersects the $Kepler$ intermediate period gap, demonstrating that this gap
was not created by a lull in star formation. We calculate the time at which
stars resume spinning down, and find that 0.55 M$_\odot$ stars remain stalled
for at least 1.3 Gyr. To accurately age-date low-mass stars in the field,
gyrochronology formulae must be modified to account for this stalling
timescale. Empirically tuning a core$-$envelope coupling model with open
cluster data can account for most of the apparent stalling effect. However,
alternative explanations, e.g., a temporary reduction in the magnetic braking
torque, cannot yet be ruled out.",2010.02272v1
2003-03-03,Transfer of energy and angular momentum in magnetic coupling process,"The transfer of energy and angular momentum in the magnetic coupling (MC) of
a rotating black hole (BH) with its surrounding accretion disc is discussed
based on a mapping relation derived by considering the conservation of magnetic
flux with two basic assumptions: (i)the magnetic field on the horizon is
constant, (ii) the magnetic field on the disc surface varies as a power law
with the radial coordinate of the disc. The following results are obtained: (i)
the transfer direction of energy and angular momentum between the BH and the
disc depends on the position of a co-rotation radius relative to the MC region
on the disc, which is eventually determined by the BH spin; (ii) the evolution
characteristics of a rotating BH in the MC process without disc accretion are
depicted in a parameter space, and a series of values of the BH spin are given
to indicate the evolution characteristics; (iii) the efficiency of converting
accreted mass into radiation energy of a BH-disc system is discussed by
considering coexistence of disc accretion and the MC process; (iv) the MC
effects on disc radiation and emissivity index are discussed and it is
concluded that they are consistent with the recent XMM-Newton observation of
the nearby bright Seyfert 1 galaxy MCG-6-30-15 with reference to a variety of
parameters of the BH-disc system.",0303050v3
2005-07-29,Charge states of strongly correlated 3d oxides: from typical insulator to unconventional electron-hole Bose liquid,"We develop a model approach to describe charge fluctuations and different
charge phases in strongly correlated 3d oxides. As a generic model system one
considers that of centers each with three possible valence states described in
frames of pseudo-spin (isospin) formalism by an effective anisotropic
non-Heisenberg Hamiltonian. Simple uniform mean-field phases include an
insulating monovalent phase, mixed-valence binary disproportionated phase, and
mixed-valence ternary under-disproportionated phase. We consider two first
phases in more details focusing on the problem of electron/hole states and
different types of excitons in monovalent phase and formation of electron-hole
Bose liquid in disproportionated phase. Pseudo-spin formalism provides a useful
framework for revealing and describing different topological charge
fluctuations, in particular, like domain walls or bubble domains in
antiferromagnets. All the insulating systems such as monovalent phase may be
subdivided to two classes: stable and unstable ones with regard to the
formation of self-trapped charge transfer (CT) excitons. The latter systems
appear to be unstable with regard to the formation of CT exciton clusters, or
droplets of the electron-hole Bose liquid. The model approach suggested is
believed to be applied to describe a physics of strongly correlated oxides with
charge transfer excitonic instability and a mixed valence. We shortly discuss
an unconventional scenario of the essential physics of cuprates and manganites
that implies their instability with regard to the self-trapping of charge
transfer excitons and the formation of electron-hole Bose liquid.",0507705v1
2006-10-27,Gauge symmetry and non-abelian topological sectors in a geometrically constrained model on the honeycomb lattice,"We study a constrained statistical-mechanical model in two dimensions that
has three useful descriptions. They are 1) the Ising model on the honeycomb
lattice, constrained to have three up spins and three down spins on every
hexagon, 2) the three-color/fully-packed-loop model on the links of the
honeycomb lattice, with loops around a single hexagon forbidden, and 3) three
Ising models on interleaved triangular lattices, with domain walls of the
different Ising models not allowed to cross. Unlike the three-color model, the
configuration space on the sphere or plane is connected under local moves. On
higher-genus surfaces there are infinitely many dynamical sectors, labeled by a
noncontractible set of nonintersecting loops. We demonstrate that at infinite
temperature the transfer matrix admits an unusual structure related to a gauge
symmetry for the same model on an anisotropic lattice. This enables us to
diagonalize the original transfer matrix for up to 36 sites, finding an entropy
per plaquette ~ 0.3661 and substantial evidence that the model is not critical.
We also find the striking property that the eigenvalues of the transfer matrix
on an anisotropic lattice are given in terms of Fibonacci numbers. We comment
on the possibility of a topological phase, with infinite topological
degeneracy, in an associated two-dimensional quantum model.",0610754v2
2000-03-29,Electroproduction of pseudoscalar mesons on the deuteron,"A general analysis of polarization phenomena for coherent meson
electroproduction on deuterons, $e+ d\to e+ d +P^0$, where $P^0$ is a
pseudoscalar $\pi ^0$ or $\eta$-meson, is presented. The spin structure of the
electromagnetic current for $P^0$-production at threshold is parametrized in
terms of specific (inelastic) threshold electromagnetic form factors which
depend on the momentum transfer squared and the effective mass of the produced
hadronic system. We give expressions for the structure functions of the
reaction $e+\vec{d}\to e +d+ P^0$ (where the deuteron target is polarized) in
terms of these threshold form factors. The spin and isospin structures of the
$\gamma ^{*}+d\to d+P^0$ amplitudes (where $\gamma ^*$ is a virtual photon) is
established in the framework of the impulse approximation and relationships
between meson electroproduction on deuterons and on nucleons are given. The
reaction of $\pi^0$ electroproduction on deuterons is investigated in detail
both at threshold and in the region of $\Delta $-isobar excitation, using the
effective Lagrangian approach for the calculation of the amplitudes of the
elementary process $\gamma^*+N\to N+\pi$. Special attention is devoted to the
analysis of all standard contributions to the exclusive cross section for
$d(e,e\pi^0)d$, which are functions of the momentum transfer square, $k^2$, of
the excitation energy of the produced hadrons and of the pion production angle,
in a region of relatively large momentum transfer. The sensitivity of these
contributions to different parametrizations of the $\gamma^*\pi\omega$ form
factor as well as to the choice of $NN-$potential is discussed.",0003280v1
1999-06-23,Spin Transfer in Exclusive Lambda Production from pp Collisions at 3.67 GeV/c,"We report the first polarization transfer measurements for exclusive hyperon
production reactions. The normal spin transfer coefficient DNN for pp -> p K+
Lambda is large and negative for forward Lambda production at a beam momentum
of 3.67 GeV/c, a result qualitatively consistent with expectations for a
mechanism dominated by kaon-exchange and rescattering. The sign of DNN is
opposite to that observed in the fragmentation regime for inclusive Lambda
production at much higher energies.",9906011v1
2008-03-24,Correlation functions for a di-neutron condensate in asymmetric nuclear matter,"Recent calculations with an effective isospin dependent contact interaction
show the possibility of the crossover from superfluidity of neutron Cooper
pairs in $^1S_0$ pairing channel to Bose-Einstein condensation (BEC) of
di-neutron bound states in dilute nuclear matter. The density and spin
correlation functions are calculated for a di-neutron condensate in asymmetric
nuclear matter with the aim to find the possible features of the BCS-BEC
crossover. It is shown that the zero-momentum transfer spin correlation
function satisfies the sum rule at zero temperature. In symmetric nuclear
matter, the density correlation function changes sign at low momentum transfer
across the BCS-BEC transition and this feature can be considered as a signature
of the crossover. At finite isospin asymmetry, this criterion gives too large
value for the critical asymmetry $\alpha_c^d\sim0.9$, at which the BEC state is
quenched. Therefore, it can be trusted for the description of the
density-driven BCS-BEC crossover of neutron pairs only at small isospin
asymmetry.
  This result generalizes the conclusion of the study in Phys. Rev. Lett. {\bf
95}, 090402 (2005), where the change of sign of the density correlation
function at low momentum transfer in two-component quantum fermionic atomic gas
with the balanced populations of fermions of different species was considered
as an unambiguous signature of the BCS-BEC transition.",0803.3362v2
2011-07-26,Interplay between magnetism and superconductivity in EuFe(2-x)Co(x)As2 studied by 57Fe and 151Eu Mössbauer spectroscopy,"The compound EuFe(2-x)Co(x)As2 was investigated by means of the 57Fe and
151Eu Moessbauer spectroscopy versus temperature (4.2 - 300 K) for x=0
(parent), x=0.34 - 0.39 (superconductor) and x=0.58 (overdoped). It was found
that spin density wave (SDW) is suppressed by Co-substitution, however it
survives in the region of superconductivity, but iron spectra exhibit some
non-magnetic component in the superconducting region. Europium orders
anti-ferromagnetically regardless of the Co concentration with the spin
re-orientation from the a-axis in the parent compound toward c-axis with the
increasing replacement of iron by cobalt. The re-orientation takes place close
to the a-c plane. Some trivalent europium appears in EuFe(2-x)Co(x)As2 versus
substitution due to the chemical pressure induced by Co-atoms and it
experiences some transferred hyperfine field from Eu2+. Iron experiences some
transferred field due to the europium ordering for substituted samples in the
SDW and non-magnetic state both, while the transferred field is undetectable in
the parent compound. Superconductivity coexists with the 4f-europium magnetic
order within the same volume. It seems that superconductivity has some
filamentary character in EuFe(2-x)Co(x)As2 and it is confined to the
non-magnetic component seen by the iron Moessbauer spectroscopy.",1107.5271v2
2013-05-16,Pulsed Laser Interactions with Space Debris: Target Shape Effects,"Among the approaches to the proposed mitigation and remediation of the space
debris problem is the de-orbiting of objects in low Earth orbit through
irradiation by ground-based high-intensity pulsed lasers. Laser ablation of a
thin surface layer causes target recoil, resulting in the depletion of orbital
angular momentum and accelerated atmospheric re-entry. However, both the
magnitude and direction of the recoil are shape dependent, a feature of the
laser-based remediation concept that has received little attention. Since the
development of a predictive capability is desirable, we have investigated the
dynamical response to ablation of objects comprising a variety of shapes. We
derive and demonstrate a simple analytical technique for calculating the
ablation-driven transfer of linear momentum, emphasizing cases for which the
recoil is not exclusively parallel to the incident beam. For the purposes of
comparison and contrast, we examine one case of momentum transfer in the
low-intensity regime, where photon pressure is the dominant momentum transfer
mechanism, showing that shape and orientation effects influence the target
response in a similar, but not identical, manner. We address the related
problem of target spin and, by way of a few simple examples, show how ablation
can alter the spin state of a target, which often has a pronounced effect on
the recoil dynamics.",1305.3659v1
2014-11-24,Antiperiodic XXZ chains with arbitrary spins: Complete eigenstate construction by functional equations in separation of variables,"Generic inhomogeneous integrable XXZ chains with arbitrary spins are studied
by means of the quantum separation of variables (SOV) method. Within this
framework, a complete description of the spectrum (eigenvalues and eigenstates)
of the antiperiodic transfer matrix is derived in terms of discrete systems of
equations involving the inhomogeneity parameters of the model. We show here
that one can reformulate this discrete SOV characterization of the spectrum in
terms of functional T-Q equations of Baxter's type, hence proving the
completeness of the solutions to the associated systems of Bethe-type
equations. More precisely, we consider here two such reformulations. The first
one is given in terms of Q-solutions, in the form of trigonometric polynomials
of a given degree $N_s$, of a one-parameter family of T-Q functional equations
with an extra inhomogeneous term. The second one is given in terms of
Q-solutions, again in the form of trigonometric polynomials of degree $N_s$ but
with double period, of Baxter's usual (i.e. without extra term) T-Q functional
equation. In both cases, we prove the precise equivalence of the discrete SOV
characterization of the transfer matrix spectrum with the characterization
following from the consideration of the particular class of Q-solutions of the
functional T-Q equation: to each transfer matrix eigenvalue corresponds exactly
one such Q-solution and vice versa, and this Q-solution can be used to
construct the corresponding eigenstate.",1411.6488v1
2015-11-23,Excitation of an Atomic Transition with a Vortex Laser Beam,"Photons carry one unit of angular momentum associated with their
spin~\cite{Beth1936}. Structured vortex beams carry additional orbital angular
momentum which can also be transferred to matter~\cite{Allen1992}. This extra
twist has been used for example to drive motion of microscopic particles in
optical tweezers as well as to create vortices in degenerate quantum
gases~\cite{He1995,Andersen2006}. Here we demonstrate the transfer of optical
orbital angular momentum from the transverse spatial structure of the beam to
the internal (electronic) degrees of freedom of an atom. Probing a quadrupole
transition of a single trapped $^{40}$Ca$^+$ ion localized at the center of the
vortex, we observe strongly modified selection rules, accounting for both the
photon spin and the vorticity of the field. In particular, we show that an atom
can absorb two quanta of angular momentum from a single photon even when
rotational symmetry is conserved. In contrast to previous
findings~\cite{Araoka2005,Loeffler2011a,Mathevet2013}, our experiment allows
for conditions where the vorticity of the laser beam determines the optical
excitation, contributing to the long-standing discussion on whether the orbital
angular momentum of photons can be transferred to atomic internal degrees of
freedom~\cite{VanEnk1994,Babiker2002,Jauregui2004, Schmiegelow2012, Mondal2014,
Scholz-Marggraf2014} and paves the way for its use to tailor light-matter
interactions.",1511.07206v1
2016-02-26,Coulomb enhancement of superconducting pair-pair correlations in a $\frac{3}{4}$-filled model for $κ$-(BEDT-TTF)$_2$X,"We present the results of precise correlated-electron calculations on the
monomer lattices of the organic charge-transfer solids $\kappa$-(BEDT-TTF)$_2$X
for 32 and 64 molecular sites. Our calculations are for band parameters
corresponding to X = Cu[N(CN)$_2$]Cl and Cu$_2$(CN)$_3$, which are
semiconducting antiferromagnetic and quantum spin liquid, respectively, at
ambient pressure. We have performed our calculations for variable electron
densities $\rho$ per BEDT-TTF molecule, with $\rho$ ranging from 1 to 2. We
find that $d$-wave superconducting pair-pair correlations are enhanced by
electron-electron interactions only for a narrow carrier concentration about
$\rho=1.5$, which is precisely the carrier concentration where
superconductivity in the charge-transfer solids occurs. Our results indicate
that the enhancement in pair-pair correlations is not related to
antiferromagnetic order, but to a proximate hidden spin-singlet state that
manifests itself as a charge-ordered state in other charge-transfer solids.
Long-range superconducting order does not appear to be present in the purely
electronic model, suggesting that electron-phonon interactions also must play a
role in a complete theory of superconductivity.",1602.08480v1
2016-11-18,From the Quantum Transfer Matrix to the Quench Action: The Loschmidt echo in $XXZ$ Heisenberg spin chains,"We consider the computation of the Loschmidt echo after quantum quenches in
the interacting $XXZ$ Heisenberg spin chain both for real and imaginary times.
We study two-site product initial states, focusing in particular on the N\'eel
and tilted N\'eel states. We apply the Quantum Transfer Matrix (QTM) approach
to derive generalized TBA equations, which follow from the fusion hierarchy of
the appropriate QTM's. Our formulas are valid for arbitrary imaginary time and
for real times at least up to a time $t_0$, after which the integral equations
have to be modified. In some regimes, $t_0$ is seen to be either very large or
infinite, allowing to explore in detail the post-quench dynamics of the system.
As an important part of our work, we show that for the N\'eel state our
imaginary time results can be recovered by means of the quench action approach,
unveiling a direct connection with the quantum transfer matrix formalism. In
particular, we show that in the zero-time limit, the study of our TBA equations
allows for a simple alternative derivation of the recently obtained Bethe
ansatz distribution functions for the N\'eel, tilted N\'eel and tilted
ferromagnet states.",1611.06126v2
2019-12-08,Stable and charge-switchable quantum batteries,"A fully operational loss-free quantum battery requires an inherent control
over the energy transfer process, with the ability of keeping the energy
retained with no leakage. Moreover, it also requires a stable discharge
mechanism, which entails that no energy revivals occur as the device starts its
energy distribution. Here, we provide a scalable solution for both
requirements. To this aim, we propose a general design for a quantum battery
based on an {\it{energy current}} (EC) observable quantifying the energy
transfer rate to a consumption hub. More specifically, we introduce an
instantaneous EC operator describing the energy transfer process driven by an
arbitrary interaction Hamiltonian. The EC observable is shown to be the root
for two main applications: (i) a trapping energy mechanism based on a common
eigenstate between the EC operator and the interaction Hamiltonian, in which
the battery can indefinitely retain its energy even if it is coupled to the
consumption hub; (ii) an asymptotically stable discharge mechanism, which is
achieved through an adiabatic evolution eventually yielding vanishing EC. These
two independent but complementary applications are illustrated in quantum spin
chains, where the trapping energy control is realized through Bell pairwise
entanglement and the stability arises as a general consequence of the adiabatic
spin dynamics.",1912.03675v2
2022-05-02,Detailed Study of Quark-Hadron Duality in Spin Structure Functions of the Proton and Neutron,"In this paper, we present for the first time comprehensive and detailed
results on the correspondence between the extrapolated deep inelastic structure
function $g_1$ of both the proton and the neutron with the same quantity
measured in the nucleon resonance region. We use a QCD parameterization of the
world data on DIS spin structure functions, extrapolated into the nucleon
resonance region and averaged over various intervals in the scaling variable
$x$. We compare the results with the large data set collected in the
quark-hadron transition region by the CLAS collaboration, averaged over the
same intervals. We present this comparison as a function of the momentum
transfer $Q^2$. We find that, depending on the averaging interval and the
minimum momentum transfer chosen, a clear transition to quark-hadron duality
can be observed in both nucleon species. Furthermore, we show, for the first
time, the scaling behavior of $g_1$ measured in the resonance region at
sufficiently high momentum transfer. Our results can be used to quantify the
deviations from the applicability of pQCD for data taken at moderate energies,
and help with extraction of quark distribution functions from such data.",2205.01218v3
2022-12-10,Influence of Defects on the Valley Polarization Properties of Monolayer MoS$_{2}$ Grown by Chemical Vapor Deposition,"Here, the underlying mechanisms behind valley de-polarization is investigated
in chemical vapor deposited 1L-MoS$_{2}$. Temperature dependent polarization
resolved photoluminescence spectroscopy was carried out on as-grown,
transferred and capped samples. It has been found that the momentum scattering
of the excitons due to the sulfur-vacancies attached with air-molecule defects
has a strong influence on the valley de-polarization process. Our study reveals
that at sufficiently low densities of such defects and temperatures, long range
electron-hole exchange mediated intervalley transfer due to momentum scattering
via Maialle-Silva-Sham (MSS) mechanism of excitons is indeed the most dominant
spin-flip process as suggested by T. Yu et al. The rate of momentum scattering
of the excitons due to these defects is found to be proportional to the cube
root of the density of the defects. Intervalley transfer process of excitons
involving $\Gamma$-valley also has significance in the valley de-polarization
process specially when the layer has tensile strain or high density of $V_S$
defects as these perturbations reduce $K$ to $\Gamma$-energy separation.
Band-structural calculations carried out within the density functional theory
framework validate this finding. Experimental results further suggest that
exchange interactions with the physisorbed air molecules can also result in the
intervalley spin-flip scattering of the excitons, and this process gives an
important contribution to valley depolarization, specially at the strong
scattering regime.",2212.05247v1
2014-10-31,Spin-orbit coupling in fluorinated graphene,"We report on theoretical investigations of the spin-orbit coupling effects in
fluorinated graphene. First-principles density functional calculations are
performed for the dense and dilute adatom coverage limits. The dense limit is
represented by the single-side semifluorinated graphene, which is a metal with
spin-orbit splittings of about 10 meV. To simulate the effects of a single
adatom, we also calculate the electronic structure of a $10 \times 10$
supercell, with one fluorine atom in the top position. Since this dilute limit
is useful to study spin transport and spin relaxation, we also introduce a
realistic effective hopping Hamiltonian, based on symmetry considerations,
which describes the supercell bands around the Fermi level. We provide the
Hamiltonian parameters which are best fits to the first-principles data. We
demonstrate that, unlike for the case of hydrogen adatoms, fluorine's own
spin-orbit coupling is the principal cause of the giant induced local
spin-orbit coupling in graphene. The $sp^3$ hybridization induced transfer of
spin-orbit coupling from graphene's $\sigma$ bonds, important for hydrogenated
graphene, contributes much less. Furthermore, the magnitude of the induced
spin-orbit coupling due to fluorine adatoms is about $1000$ times more than
that of pristine graphene, and 10 times more than that of hydrogenated
graphene. Also unlike hydrogen, the fluorine adatom is not a narrow resonant
scatterer at the Dirac point. The resonant peak in the density of states of
fluorinated graphene in the dilute limit lies 260 meV below the Dirac point.
The peak is rather broad, about 300 meV, making the fluorine adatom only a
weakly resonant scatterer.",1411.0016v2
2020-08-08,Spin-dependent electron transport along hairpin-like DNA molecules,"The chirality-induced spin selectivity (CISS), demonstrated in diverse chiral
molecules by numerous experimental and theoretical groups, has been attracting
extensive and ongoing interest in recent years. As the secondary structure of
DNA, the charge transfer along DNA hairpins has been widely studied for more
than two decades, finding that DNA hairpins exhibit spin-related effects as
reported in recent experiments. Here, we propose a setup to demonstrate
directly the CISS effect in DNA hairpins contacted by two nonmagnetic leads at
both ends of the stem. Our results indicate that DNA hairpins present
pronounced CISS effect and the spin polarization could be enhanced by using
conducting molecules as the loop. In particular, DNA hairpins show several
intriguing features, which are different from other chiral molecules. First,
the local spin currents can flow circularly and assemble into a number of
vortex clusters when the electron energy locates in the left/right electronic
band of the stem. The chirality of vortex clusters in each band is the same and
will be reversed by switching the electron energy from the left band to the
right one, inducing the sign reversal of the spin polarization. Interestingly,
the local spin currents can be greater than the corresponding spin component of
the source-drain current. Second, both the conductance and the spin
polarization can increase with molecular length as well as dephasing strength,
contrary to the physical intuition that the transmission ability of molecular
wires should be poorer when suffering from stronger scattering. Third, we
unveil the optimal contact configuration of efficient electron transport and
that of the CISS effect, which are distinct from each other and can be
controlled by dephasing strength. The underlying physical mechanism is
illustrated.",2008.03484v1
2020-12-29,Coherent single-spin electron resonance spectroscopy manifested at an exceptional-point singularity in a doped polyacetylene,"Spin-dependent charge transfer decay in an alkali atom doped polyacetylene is
studied in terms of the complex spectral analysis, revealing the single-spin
Zeeman splitting influenced by the spin-orbit interaction. Nonhermitian
effective Hamiltonian has been derived from the total system hermitian
Hamiltonian using Brillouin-Wigner-Feshbach projection method, where the
microscopic spin-dependent dissipation effect is correctly incorporated in the
energy-dependent self-energy. Since the present method maintains the dynamical
and chiral symmetries of the total system, we discovered two types of
exceptional point (EP) singularities in a unified perspective: the EP surface
and EP ring are attributed to the dynamical and chiral symmetry breaking,
respectively. We have revealed that the coherent single-spin electron resonance
(SSESR) spectrum reflects the complex eigenenergy spectrum of the system. We
have formulated the SSESR spectrum in terms of the nonlinear response function
in the Liouville-space pathway approach, where we have constructed the
Liouville space basis using the complex eigenstates of the total Hamiltonian.
We have calculated the one- and two-dimensional Fourier transform SSESR (1DFT
and 2DFT) spectra reflecting the spin-relaxation dynamics at the donor site.
While the 1DFT SSESR spectrum reflects the complex eigenenergy spectrum, the
2DFT gives detailed information on the quantum coherence in the spin-relaxation
dynamics as a cross-correlation between the two frequencies. We found a giant
response of the coherent SSESR around the EP ring singularity due to the
vanishing normalization factors at the EP ring and the resonance effect. We
have discovered that the giant response is much larger in magnitudes in the
2DFT spectrum than in the 1DFT spectrum, which promises the 2DFT SSESR a useful
tool to observe the single-spin response in a molecule.",2012.14655v1
2022-11-09,A group-theoretic approach to the origin of chirality-induced spin selectivity in non-magnetic molecular junctions,"Spin-orbit coupling gives rise to a range of spin-charge interconversion
phenomena in non-magnetic systems where certain spatial symmetries are reduced
or absent. Chirality-induced spin selectivity (CISS), a term that generically
refers to a spin-dependent electron transfer in non-magnetic chiral systems, is
one such case, appearing in a variety of seemingly unrelated situations ranging
from inorganic materials to molecular devices. In particular, the origin of
CISS in molecular junctions is a matter of an intense current debate. Here we
derive a set of geometrical conditions for this effect to appear, hinting at
the fundamental role of symmetries beyond otherwise relevant quantitative
issues. Our approach, which draws on the use of point-group symmetries within
the scattering formalism for transport, shows that electrode symmetries are as
important as those of the molecule when it comes to the emergence of a
spin-polarization and, by extension, to the possible appearance of CISS. It
turns out that standalone metallic nanocontacts can exhibit spin-polarization
when relative rotations which reduce the symmetry are introduced. As a
corollary, molecular junctions with $\textbf{achiral}$ molecules can also
exhibit spin-polarization along the direction of transport, provided that the
whole junction is chiral in a specific way. This formalism also allows the
prediction of qualitative changes of the spin-polarization upon substitution of
a chiral molecule in the junction with its enantiomeric partner. Quantum
transport calculations based on density functional theory corroborate all of
our predictions and provide further quantitative insight within the
single-particle framework.",2211.04830v2
2018-12-19,Field-induced quantum magnetism in the verdazyl-based charge-transfer salt $[$$o$-MePy-V-($p$-Br)$_2]$FeCl$_4$,"We successfully synthesized a verdazyl-based charge-transfer salt
$[$$o$-MePy-V-($p$-Br)$_2]$FeCl$_4$, which has an $S_{\rm{V}}$=1/2 on the
radical $o$-MePy-V-($p$-Br)$_2$ and an $S_{\rm{Fe}}$=5/2 on the FeCl$_4$ anion.
$Ab$ $initio$ molecular orbital calculations indicate the formation of an
$S_{\rm{V}}$=1/2 honeycomb lattice composed of three types of exchange
interaction with two types of inequivalent site. Further, the $S_{\rm{V}}$=1/2
at one site is sandwiched by $S_{\rm{Fe}}$=5/2 spins through antiferromagnetic
(AF) interactions. The magnetic properties indicate that the dominant AF
interactions between the $S_{\rm{V}}$ = 1/2 spins form a gapped singlet state,
and the remaining $S_{\rm{Fe}}$ = 5/2 spins cause an AF order. The
magnetization curve exhibits a linear increase up to approximately 7 T, and an
unconventional 5/6 magnetization plateau appears between 7 T and 40 T. We
discuss the differences between the effective interactions associated with the
magnetic properties of the present compound and ($o$-MePy-V)FeCl$_4$. We
explain the low-field linear magnetization curve through a mean-field
approximation of an $S_{\rm{Fe}}$ = 5/2 spin model. At higher field regions,
the 5/6 magnetization plateau and subsequent nonlinear increase are reproduced
by the $S_{\rm{V}}$ = 1/2 AF dimer, in which a particular internal field is
applied to one of the spin sites. The ESR resonance signals in the
low-temperature and low-field regime are explained by conventional
two-sublattice AF resonance modes with easy-axis anisotropy. These results
demonstrate that exchange interactions between $S_{\rm{V}}$ = 1/2 and
$S_{\rm{Fe}}$ = 5/2 spins in $[$$o$-MePy-V-($p$-Br)$_2]$FeCl$_4$ realize
unconventional magnetic properties with low-field classical behavior and
field-induced quantum behavior.",1812.08334v1
2020-08-16,"Light-Activated Nuclear Spin Polarization in Dilute Ferromagnetic (Ga,Mn)As","We study light-induced nuclear spin-polarization in a thin film of Ga1-xMnxAs
(x 0.04), a dilute ferromagnetic semiconductor, grown on a GaAs substrate.
High-field inductively-detected Ga-71 NMR was performed with samples immersed
in superfluid He to investigate the effects of continuous-wave near band-edge
optical illumination on lattice nuclear spins in the ferromagnetic phase. The
photon energy dependence of the light-induced NMR signals for GaAs and the
GaMnAs film samples were recorded using circularly polarized light.
Interpretation of the data was guided by electronic band structure calculations
using the k.p method in the presence of an external magnetic field using the
modified 8-band Pidgeon-Brown model. The photon energy dependence of the NMR
transition intensity exhibited a shift of the absorption band edge; invariance
with respect to the sense of helicity of the exciting light; and an absence of
oscillations in the photon energy dependence, all of which are consistent with
theoretical predictions. The dynamics of the optically activated NMR
experiments was investigated by variable optical intensity studies and
light/dark modulated optical pumping experiments. This is because doping with
Mn (a p-type dopant) can push the Fermi level deep into the valence bands and
block the optical transitions (Burstein-Moss effect) needed to create spin
polarized electrons. Additionally, the calculated enhancement of the conduction
electron g-factor by over two orders of magnitude is expected to quench the
electron-nuclear spin angular moment transfer, which impedes the
hyperpolarization of lattice nuclei. Experiments with variable light intensity
and optical gating reveal a mechanism consistent with light-induced quadrupolar
relaxation, a process that will certainly interfere with the optical transfer
and storage of quantum information in the lattice nuclear spin states in this
material.",2008.06945v2
2021-10-19,Electronic reconstruction and charge transfer in strained Sr$_2$CoIrO$_6$ double perovskite,"The electronic, magnetic and optical properties of the double perovskite
Sr$_2$CoIrO$_6$ (SCIO) under biaxial strain are explored in the framework of
density functional theory (DFT) including a Hubbard $U$ term and spin-orbit
coupling (SOC) in combination with absorption spectroscopy measurements on
epitaxial thin films. While the end member SrIrO$_3$ is a semimetal with a
quenched spin and orbital moment and bulk SrCoO$_3$ is a ferromagnetic (FM)
metal with spin and orbital moment of 2.50 and 0.13 $\mu_{B}$, respectively,
the double perovskite SCIO emerges as an antiferromagnetic Mott insulator with
antiparallel alignment of Co, Ir planes along the [110]-direction. Co exhibits
a spin and enhanced orbital moment of $\sim 2.35-2.45$ and $0.31-$0.45
$\mu_{B}$, respectively. Most remarkably, Ir acquires a significant spin and
orbital moment of 1.21-1.25 and 0.13 $\mu_{B}$, respectively. Analysis of the
orbital occupation indicates an electronic reconstruction due to a substantial
charge transfer from minority to majority spin states in Ir and from Ir to Co,
signaling an Ir$^{4+\delta}$, Co$^{4-\delta}$ configuration. Biaxial strain,
varied from -1.02% ($a_{\rm NdGaO_3}$) through 0% ($a_{\rm SrTiO_3}$) to 1.53%
($a_{\rm GdScO_3}$), influences in partcular the orbital polarization of the
$t_{2g}$ states and leads to a nonmonotonic change of the band gap between 163
and 235 meV. The absorption coefficient reveals a two plateau fearure due to
transitions from the valence to the lower lying narrow $t_{2g}$ and the higher
lying broader $e_{g}$ bands. Inclusion of many body effects, in particular,
excitonic effects by solving the Bethe-Salpeter equation (BSE), increases the
band gap by $\sim0.2$ and improves the agreement with the measured spectrum
concerning the position of the second peak at $\sim 2.6$ eV.",2110.09810v1
2022-10-15,Non-local magnon transconductance in extended magnetic insulating films.\\ Part I: spin diode effect,"This review provides a comprehensive study of the nonlinear transport
properties of magnons, which are electrically emitted or absorbed inside
extended YIG films by spin transfer effects via a YIG$\vert$Pt interface. Our
purpose is to experimentally elucidate the pertinent picture behind the
asymmetric electrical variation of the magnon transconductance analogous to an
electric diode. The feature is rooted in the variation of the density of
low-lying spin excitations via an electrical shift of the magnon chemical
potential. As the intensity of the spin transfer increases in the forward
direction (regime of magnon emission), the transport properties of low-energy
magnon go through 3 distinct regimes: \textit{i)} at low currents, where the
spin current is a linear function of the electrical current, the spin transport
is ballistic and set by the film thickness; \textit{ii)} for amplitudes of the
order of the damping compensation threshold, it switches to a highly correlated
regime limited by magnon-magnon relaxation process and marked by a saturation
of the magnon transconductance. Here the main bias, that controls the magnon
density, are thermal fluctuations beneath the emitter. \textit{iii)} As the
temperature under the emitter approaches the Curie temperature, scattering with
high-energy magnons dominates, leading to diffusive transport. We note that
such sequence of transport regimes bears analogy with electron hydrodynamic
transport in ultra-pure media predicted by Radii Gurzhi. This study restricted
to low energy part of the magnon manifold complements part II of this
review\cite{kohno_2F}, which concentrates instead on the whole spectrum of
propagating magnons.",2210.08304v2
2002-06-10,Measurement of Spin Transfer Observables in Antiproton-Proton -> Antilambda-Lambda at 1.637 GeV/c,"Spin transfer observables for the strangeness-production reaction
Antiproton-Proton -> Antilambda-Lambda have been measured by the PS185
collaboration using a transversely-polarized frozen-spin target with an
antiproton beam momentum of 1.637 GeV/c at the Low Energy Antiproton Ring at
CERN. This measurement investigates observables for which current models of the
reaction near threshold make significantly differing predictions. Those models
are in good agreement with existing measurements performed with unpolarized
particles in the initial state. Theoretical attention has focused on the fact
that these models produce conflicting predictions for the spin-transfer
observables D_{nn} and K_{nn}, which are measurable only with polarized target
or beam. Results presented here for D_{nn} and K_{nn} are found to be in
disagreement with predictions from existing models. These results also
underscore the importance of singlet-state production at backward angles, while
current models predict complete or near-complete triplet-state dominance.",0206005v1
2014-04-25,"Ultracold, radiative charge transfer in hybrid Yb ion - Rb atom traps","Ultracold hybrid ion-atom traps offer the possibility of microscopic
manipulation of quantum coherences in the gas using the ion as a probe.
However, inelastic processes, particularly charge transfer can be a significant
process of ion loss and has been measured experimentally for the Yb$^{+}$ ion
immersed in a Rb vapour. We use first-principles quantum chemistry codes to
obtain the potential energy curves and dipole moments for the lowest-lying
energy states of this complex. Calculations for the radiative decay processes
cross sections and rate coefficients are presented for the total decay
processes. Comparing the semi-classical Langevin approximation with the quantum
approach, we find it provides a very good estimate of the background at higher
energies. The results demonstrate that radiative decay mechanisms are important
over the energy and temperature region considered. In fact, the Langevin
process of ion-atom collisions dominates cold ion-atom collisions. For spin
dependent processes \cite{kohl13} the anisotropic magnetic dipole-dipole
interaction and the second-order spin-orbit coupling can play important roles,
inducing couplingbetween the spin and the orbital motion. They measured the
spin-relaxing collision rate to be approximately 5 orders of magnitude higher
than the charge-exchange collision rate \cite{kohl13}. Regarding the measured
radiative charge transfer collision rate, we find that our calculation is in
very good agreement with experiment and with previous calculations.
Nonetheless, we find no broad resonances features that might underly a strong
isotope effect. In conclusion, we find, in agreement with previous theory that
the isotope anomaly observed in experiment remains an open question.",1404.6579v1
2017-06-20,On the timing properties of SAX J1808.4-3658 during its 2015 outburst,"We present a timing analysis of the 2015 outburst of the accreting
millisecond X-ray pulsar SAX J1808.4-3658, using non-simultaneous XMM-Newton
and NuStar observations. We estimate the pulsar spin frequency and update the
system orbital solution. Combining the average spin frequency from the previous
observed, we confirm the long-term spin down at an average rate
$\dot{\nu}_{\text{SD}}=1.5(2)\times 10^{-15}$ Hz s$^{-1}$. We also discuss
possible corrections to the spin down rate accounting for mass accretion onto
the compact object when the system is X-ray active. Finally, combining the
updated ephemerides with those of the previous outbursts, we find a long-term
orbital evolution compatible with a binary expansion at a mean rate
$\dot{P}_{orb}=3.6(4)\times 10^{-12}$ s s$^{-1}$, in agreement with previously
reported values. This fast evolution is incompatible with an evolution driven
by angular momentum losses caused by gravitational radiation under the
hypothesis of conservative mass transfer. We discuss the observed orbital
expansion in terms of non-conservative mass transfer and gravitational
quadrupole coupling mechanism. We find that the latter can explain, under
certain conditions, small fluctuations (of the order of few seconds) of the
orbital period around a global parabolic trend. At the same time, a
non-conservative mass transfer is required to explain the observed fast orbital
evolution, which likely reflects ejection of a large fraction of mass from the
inner Lagrangian point caused by the irradiation of the donor by the
magneto-dipole rotator during quiescence (radio-ejection model). This strong
outflow may power tidal dissipation in the companion star and be responsible of
the gravitational quadrupole change oscillations.",1706.06554v1
2000-01-25,Hydrodynamic Simulations of the Bardeen-Petterson Effect,"We present SPH simulations of accretion discs in orbit about rotating compact
objects such as black holes and neutron stars, and study the structure of
warped discs produced by the Bardeen-Petterson effect. We calculate the
transition radius out to which the disc specific angular momentum vector is
aligned with that of the black hole. We focus on the parameter regime where the
warp dynamics are controlled by bending wave propagation, but also consider
models in which warps are subject to diffusion rather than wave transport, and
are able to consider the fully nonlinear regime. Because of hydrodynamic or
pressure effects, for the parameter range investigated, the transition radius
is always found to be much smaller than that obtained by Bardeen & Petterson
(1975). For discs with midplane Mach numbers of about 10, the transition occurs
between 10 - 16 gravitational radii, whereas for a Mach number of about 30 it
occurs at around 30 gravitational radii. A thicker disc with a Mach number of 5
is found to produce no discernible warped structure. The rate of black hole -
disc alignment is found to be consistent with the ideas of Ress (1978), with
the alignment torque behaving as if it arises from the accreted material
transferring its misaligned component of angular momentum at the larger
transition radius of Bardeen & Petterson (1975). The inclusion of Einstein
precession in the calculations modified both the warped disc structure and,
consistent with linear analysis, produced an increased alignment rate by up to
a factor of 4 because of the effect that a non Keplerian potential has on the
propagation of warps.",0001439v1
2001-08-29,The Role of Tidal Interactions in Star Formation,"Nearly all of the initial angular momentum of the matter that goes into each
forming star must somehow be removed or redistributed during the formation
process. The possible transport mechanisms and the possible fates of the excess
angular momentum are discussed, and it is argued that transport processes in
disks are probably not sufficient by themselves to solve the angular momentum
problem, while tidal interactions with other stars in forming binary or
multiple systems are likely to be of very general importance in redistributing
angular momentum during the star formation process. Most, if not all, stars
probably form in binary or multiple systems, and tidal torques in these systems
can transfer much of the angular momentum from the gas around each forming star
to the orbital motions of the companion stars. Tidally generated waves in
circumstellar disks may contribute to the overall redistribution of angular
momentum. Stars may gain much of their mass by tidally triggered bursts of
rapid accretion, and these bursts could account for some of the most energetic
phenomena of the earliest stages of stellar evolution, such as jet-like
outflows. If tidal interactions are indeed of general importance,
planet-forming disks may often have a more chaotic and violent early evolution
than in standard models, and shock heating events may be common. Interactions
in a hierarchy of subgroups may play a role in building up massive stars in
clusters and in determining the form of the upper IMF. Many of the processes
discussed here have analogs on galactic scales, and there may be similarities
between the formation of massive stars by interaction-driven accretion
processes in clusters and the buildup of massive black holes in galactic
nuclei.",0108471v3
2003-06-26,Momentum transfer across shear flows in Smoothed Particle Hydrodynamic simulations of galaxy formation,"We investigate the evolution of angular momentum in SPH simulations of galaxy
formation, paying particular attention to artificial numerical effects. We find
that a cold gas disc forming in an ambient hot gas halo receives a strong
hydrodynamic torque from the hot gas. By splitting the hydrodynamic force into
artificial viscosity and pressure gradients, we find that the angular momentum
transport is caused not by the artificial viscosity but by the pressure
gradients. Using simple test simulations of shear flows, we conclude that the
pressure gradient-based viscosity can be divided into two components: one due
to the noisiness of SPH and the other to ram pressure. The former is
problematic even with very high resolution because increasing resolution does
not reduce the noisiness. On the other hand, the ram pressure effect appears
only when a cold gas disc or sheet does not contain enough particles. In such a
case, holes form in the disc or sheet, and then ram pressure from intra-hole
hot gas, causes significant deceleration. In simulations of galactic disc
formation, star formation usually decreases the number of cold gas particles,
and hole formation leads to the fragmentation of the disc. To circumvent these
problem, we modify the SPH algorithm, decoupling the cold from the hot gas
phases, i.e. inhibiting the hydrodynamic interaction between cold and hot
particles. This, a crude modelling of a multi-phase fluid in SPH cosmological
simulations, leads to the formation of smooth extended cold gas discs and to
better numerical convergence. The decoupling is applicable in so far as the
self-gravitating gas disc with negligible external pressure is a good
approximation for a cold gas disc. (abridged)",0306568v1
2004-07-28,Turbulence and galactic structure,"Interstellar turbulence is driven over a wide range of scales by processes
including spiral arm instabilities and supernovae, and it affects the rate and
morphology of star formation, energy dissipation, and angular momentum transfer
in galaxy disks. Star formation is initiated on large scales by gravitational
instabilities which control the overall rate through the long dynamical time
corresponding to the average ISM density. Stars form at much higher densities
than average, however, and at much faster rates locally, so the slow average
rate arises because the fraction of the gas mass that forms stars at any one
time is low, ~10^{-4}. This low fraction is determined by turbulence
compression, and is apparently independent of specific cloud formation
processes which all operate at lower densities. Turbulence compression also
accounts for the formation of most stars in clusters, along with the cluster
mass spectrum, and it gives a hierarchical distribution to the positions of
these clusters and to star-forming regions in general. Turbulent motions appear
to be very fast in irregular galaxies at high redshift, possibly having speeds
equal to several tenths of the rotation speed in view of the morphology of
chain galaxies and their face-on counterparts. The origin of this turbulence is
not evident, but some of it could come from accretion onto the disk. Such high
turbulence could help drive an early epoch of gas inflow through viscous
torques in galaxies where spiral arms and bars are weak. Such evolution may
lead to bulge or bar formation, or to bar re-formation if a previous bar
dissolved. We show evidence that the bar fraction is about constant with
redshift out to z~1, and model the formation and destruction rates of bars
required to achieve this constancy.",0407582v1
2006-09-14,Fourier Dissection of Early-Type Galaxy Bars,"This paper reports on a near-infrared survey of early-type galaxies designed
to provide information on bar strengths, bulges, disks, and bar parameters in a
statistically well-defined sample of S0-Sa galaxies. Early-type galaxies have
the advantage that their bars are relatively free of the effects of dust, star
formation, and spiral structure that complicate bar studies in later type
galaxies. We describe the survey and present results on detailed analysis of
the relative Fourier intensity amplitudes of bars in 26 early-type galaxies. We
also evaluate the symmetry assumption of these amplitudes with radius, used
recently for bar-spiral separation in later-type galaxies.
  The results show a wide variety of radial Fourier profiles of bars, ranging
from simple symmetric profiles that can be represented in terms of a single
gaussian component, to both symmetric and asymmetric profiles that can be
represented by two overlapping gaussian components. More complicated profiles
than these are also found, often due to multiple bar-like features including
extended ovals or lenses. Based on the gravitational bar torque indicator Q_b,
double-gaussian bars are stronger on average than single-gaussian bars, at
least for our small sample. We show that published numerical simulations where
the bar transfers a large amount of angular momentum to the halo can account
for many of the observed profiles. The range of possibilities encountered in
models seems well-represented in the observed systems.",0609406v1
2009-07-18,On the evolution of anomalous X-ray pulsars and soft gamma ray repeaters with fallback disks,"We show that the period clustering of anomalous X-ray pulsars (AXPs) and soft
gamma-ray repeaters (SGRs), their X-ray luminosities, ages and statistics can
be explained with fallback disks with large initial specific angular momentum.
The disk evolution models are developed by comparison to self-similar
analytical models. The initial disk mass and angular momentum set the viscous
timescale. An efficient torque, with (1 - w^2) dependence on the fastness
parameter w leads to period clustering in the observed AXP-SGR period range
under a wide range of initial conditions. The timescale t_0 for the early
evolution of the fallback disk, and the final stages of fallback disk
evolution, when the disk becomes passive, are the crucial determinants of the
evolution. The disk becomes passive at temperatures around 100 K, which
provides a natural cutoff for the X-ray luminosity and defines the end of
evolution in the observable AXP and SGR phase. This low value for the minimum
temperature for active disk turbulence indicates that the fallback disks are
active up to a large radius greater than ~10^{12} cm. We find that transient
AXPs and SGRs are likely to be older than their persistent cousins. A fallback
disk with mass transfer rates corresponding to the low quiescent X-ray
luminosities of the transient sources in early evolutionary phases would have a
relatively lower initial mass, such that the mass-flow rate in the disk is not
sufficient for the inner disk to penetrate into the light cylinder of the young
neutron star, making mass accretion onto the neutron star impossible. The
transient AXP phase therefore must start later. The model results imply that
the transient AXP/SGRs, although older, are likely to be similar in number to
persistent sources (abridged).",0907.3222v1
2012-02-24,Formation and evolution of primordial protostellar systems,"We investigate the formation of the first stars at the end of the cosmic dark
ages with a suite of three-dimensional, moving mesh simulations that directly
resolve the collapse of the gas beyond the formation of the first protostar at
the centre of a dark matter minihalo. The simulations cover more than 25 orders
of magnitude in density and have a maximum spatial resolution of 0.05 R_sun,
which extends well below the radius of individual protostars and captures their
interaction with the surrounding gas. In analogy to previous studies that
employed sink particles, we find that the Keplerian disc around the primary
protostar fragments into a number of secondary protostars, which is facilitated
by H2 collisional dissociation cooling and collision-induced emission. The
further evolution of the protostellar system is characterized by strong
gravitational torques that transfer angular momentum between the secondary
protostars formed in the disc and the surrounding gas. This leads to the
migration of about half of the secondary protostars to the centre of the cloud
in a free-fall time, where they merge with the primary protostar and enhance
its growth to about five times the mass of the second most massive protostar.
By the same token, a fraction of the protostars obtain angular momentum from
other protostars via N-body interactions and migrate to higher orbits. On
average, only every third protostar survives until the end of the simulation.
However, the number of protostars present at any given time increases
monotonically, suggesting that the system will continue to grow beyond the
limited period of time simulated here.",1202.5552v2
2012-03-06,How to distinguish starbursts and quiescently star-forming galaxies: The `bimodal' submillimetre galaxy population as a case study,"In recent work (arXiv:1101.0002) we have suggested that the high-redshift (z
~ 2-4) bright submillimetre galaxy (SMG) population is heterogeneous, with
major mergers contributing both at early stages, where quiescently star-forming
discs are blended into one submm source (`galaxy-pair SMGs'), and late stages,
where mutual tidal torques drive gas inflows and cause strong starbursts. Here
we combine hydrodynamic simulations of major mergers with 3-D dust radiative
transfer calculations to determine observational diagnostics that can
distinguish between quiescently star-forming SMGs and starburst SMGs via
integrated data alone. We fit the far-IR SEDs of the simulated galaxies with
the optically thin single-temperature modified blackbody, the full form of the
single-temperature modified blackbody, and a power-law temperature-distribution
model. The effective dust temperature, T_dust, and power-law index of the dust
emissivity in the far-IR, \beta, derived can significantly depend on the
fitting form used, and the intrinsic \beta\ of the dust is not recovered.
However, for all forms used here, there is a T_dust above which almost all
simulated galaxies are starbursts, so a T_dust cut is very effective at
selecting starbursts. Simulated merger-induced starbursts also have higher
L_IR/M_gas and L_IR/L_FUV than quiescently star-forming galaxies and lie above
the star formation rate-stellar mass relation. These diagnostics can be used to
test our claim that the SMG population is heterogeneous and to observationally
determine what star formation mode dominates a given galaxy population. We
comment on applicability of these diagnostics to ULIRGs that would not be
selected as SMGs. These `hot-dust ULIRGs' are typically starburst galaxies
lower in mass than SMGs, but they can also simply be SMGs observed from a
different viewing angle.",1203.1318v2
2012-03-12,"Evolution of Galactic Discs: Multiple Patterns, Radial Migration and Disc Outskirts","We investigate the evolution of galactic disks in N-body Tree-SPH
simulations. We find that disks, initially truncated at three scale-lengths,
can triple their radial extent, solely driven by secular evolution. Both Type I
(single exponential) and Type II (down-turning) observed disk
surface-brightness profiles can be explained by our findings. We relate these
results to the strong angular momentum outward transfer, resulting from torques
and radial migration associated with multiple patterns, such as central bars
and spiral waves of different multiplicity. We show that even for stars ending
up on cold orbits, the changes in angular momentum exhibit complex structure as
a function of radius, unlike the expected effect of transient spirals alone.
Focussing on one of our models, we find evidence for non-linear coupling among
m=1, 2, 3 and 4 density waves, where m is the pattern multiplicity. We suggest
that the naturally occurring larger resonance widths at galactic radii beyond
four scale-lengths may have profound consequences on the formation and location
of breaks in disk density profiles, provided spirals are present at such large
distances. We also consider the effect of gas inflow and show that when
in-plane smooth gas accretion of ~5 M_sun/yr is included, the outer disks
become more unstable, leading to a strong increase in the stellar velocity
dispersion. This, in turn, causes the formation of a Type III (up-turning)
profile in the old stellar population. We propose that observations of Type III
surface brightness profiles, combined with an up-turn in the stellar velocity
dispersions beyond the disk break, could be a signature of ongoing
gas-accretion. The results of this study suggest that disk outskirts comprised
of stars migrated from the inner disk would have relatively large radial
velocity dispersions, and significant thickness when seen edge-on. [Abridged]",1203.2621v2
2012-05-01,The Radius of Baryonic Collapse in Disc Galaxy Formation,"In the standard picture of disc galaxy formation, baryons and dark matter
receive the same tidal torques, and therefore approximately the same initial
specific angular momentum. However, observations indicate that disc galaxies
typically have only about half as much specific angular momentum as their dark
matter haloes. We argue this does not necessarily imply that baryons lose this
much specific angular momentum as they form galaxies. It may instead indicate
that galaxies are most directly related to the inner regions of their host
haloes, as may be expected in a scenario where baryons in the inner parts of
haloes collapse first. A limiting case is examined under the idealised
assumption of perfect angular momentum conservation. Namely, we determine the
density contrast Delta, with respect to the critical density of the Universe,
by which dark matter haloes need to be defined in order to have the same
average specific angular momentum as the galaxies they host. Under the
assumption that galaxies are related to haloes via their characteristic
rotation velocities, the necessary Delta is ~600. This Delta corresponds to an
average halo radius and mass which are ~60% and ~75%, respectively, of the
virial values (i.e., for Delta = 200). We refer to this radius as the radius of
baryonic collapse R_BC, since if specific angular momentum is conserved
perfectly, baryons would come from within it. It is not likely a simple step
function due to the complex gastrophysics involved, therefore we regard it as
an effective radius. In summary, the difference between the predicted initial
and the observed final specific angular momentum of galaxies, which is
conventionally attributed solely to angular momentum loss, can more naturally
be explained by a preference for collapse of baryons within R_BC, with possibly
some later angular momentum transfer.",1205.0253v1
2013-04-04,Supermassive Black Hole Formation at High Redshifts via Direct Collapse: Physical Processes in the Early Stage,"We use numerical simulations to explore whether direct collapse can lead to
the formation of SMBH seeds at high-z. We follow the evolution of gas within DM
halos of 2 x 10^8 Mo and 1 kpc. We adopt cosmological density profiles and
j-distributions. Our goal is to understand how the collapsing flow overcomes
the centrifugal barrier and whether it is subject to fragmentation. We find
that the collapse leads either to a central runaway or to off-center
fragmentation. A disk-like configuration is formed inside the centrifugal
barrier. For more cuspy DM distribution, the gas collapses more and experiences
a bar-like perturbation and a central runaway. We have followed this inflow
down to ~10^{-4} pc. The flow remains isothermal and the specific angular
momentum is efficiently transferred by gravitational torques in a cascade of
nested bars. This cascade supports a self-similar, disk-like collapse. In the
collapsing phase, virial supersonic turbulence develops and fragmentation is
damped. For larger initial DM cores the timescales become longer. In models
with more organized initial rotation, a torus forms and appears to be supported
by turbulent motions. The evolution depends on the competition between two
timescales, corresponding to the onset of the central runaway and off-center
fragmentation. For less organized rotation, the torus is greatly weakened, the
central accretion timescale is shortened, and off-center fragmentation is
suppressed --- triggering the central runaway even in previously `stable'
models. The resulting SMBH masses lie in the range 2 x 10^4 Mo - 2 x 10^6 Mo,
much higher than for Population III remnants. We argue that the above upper
limit appears to be more realistic mass. Corollaries of this model include a
possible correlation between SMBH and DM halo masses, and similarity between
the SMBH and halo mass functions, at time of formation.",1304.1369v2
2014-12-08,Supermassive Black Hole Formation at High Redshifts via Direct Collapse in a Cosmological Context,"We study the early stage of the formation of seed supermassive black holes
via direct collapse in dark matter (DM) halos, in the cosmological context. We
perform high-resolution zoom-in simulations of such collapse at high-$z$. Using
the adaptive mesh refinement code ENZO, we resolve the formation and growth of
a DM halo, until its virial temperature reaches $\sim 10^4$K, atomic cooling
turns on, and collapse ensues. We demonstrate that direct collapse proceeds in
two stages, although they are not well separated. The first stage is triggered
by the onset of atomic cooling, and leads to rapidly increasing accretion rate
with radius, from $\dot M\sim 0.1\,M_\odot {\rm yr^{-1}}$ at the halo virial
radius to few $M_\odot \,{\rm yr^{-1}}$, around the scale radius $R_{\rm s}\sim
30$pc of the NFW DM density profile. The second stage of the collapse commences
when the gas density takes precedence over the DM density. This is associated
with the gas decoupling from the DM gravitational potential. The ensuing
collapse approximates that of an isothermal sphere with $\dot M ( r )\sim
$const. We confirm that the gas loses its angular momentum through
non-axisymmetric perturbations and gravitational torques, to overcome the
centrifugal barrier. During the course of the collapse, this angular momentum
transfer process happens on nearly all spatial scales, and the angular momentum
vector of the gas varies with position and time. Collapsing gas also exhibits
supersonic turbulent motions which suppress gas fragmentation, and are
characterized by density PDF consisting of a lognormal part and a high-density
power law tail.",1412.2761v3
2015-07-01,Global vs local energy dissipation: the energy cycle of the turbulent von Kármán flow,"In this paper, we investigate the relations between global and local energy
transfers in a turbulent von K\'arm\'an flow. The goal is to understand how and
where energy is dissipated in such a flow and to reconstruct the energy cycle
in an experimental device where local as well as global quantities can be
measured. We use PIV measurements and we model the Reynolds stress tensor to
take subgrid scales into account. This procedure involves a free parameter that
is calibrated using angular momentum balance. We then estimate the local and
global mean injected and dissipated power for several types of impellers, for
various Reynolds numbers and for various flow topologies. These PIV estimates
are then compared with direct injected power estimates provided by torque
measurements at the impellers. The agreement between PIV estimates and direct
measurements depends on the flow topology. In symmetric situations, we are able
to capture up to 90% of the actual global energy dissipation rate. However, our
results become increasingly inaccurate as the shear layer responsible for most
of the dissipation approaches one of the impellers, and cannot be resolved by
our PIV set-up. Finally, we show that a very good agreement between PIV
estimates and direct measurements is obtained using a new method based on the
work of Duchon and Robert which generalizes the K\'arm\'an-Howarth equation to
nonisotropic, nonhomogeneous flows. This method provides parameter-free
estimates of the energy dissipation rate as long as the smallest resolved scale
lies in the inertial range. These results are used to evidence a well-defined
stationary energy cycle within the flow in which most of the energy is injected
at the top and bottom impellers, and dissipated within the shear layer. The
influence of the mean flow geometry and the Reynolds number on this energy
cycle is studied for a wide range of parameters.",1507.00277v2
2016-01-27,Tidally induced bars of galaxies in clusters,"Using N-body simulations we study the formation and evolution of tidally
induced bars in disky galaxies in clusters. Our progenitor is a massive,
late-type galaxy similar to the Milky Way, composed of an exponential disk and
an NFW dark matter halo. We place the galaxy on four different orbits in a
Virgo-like cluster and evolve it for 10 Gyr. As a reference case we also evolve
the same model in isolation. Tidally induced bars form on all orbits soon after
the first pericenter passage and survive until the end of the evolution. They
appear earlier, are stronger, longer and have lower pattern speeds for tighter
orbits. Only for the tightest orbit the properties of the bar are controlled by
the orientation of the tidal torque from the cluster at pericenters. The
mechanism behind the formation of the bars is the angular momentum transfer
from the galaxy stellar component to its halo. All bars undergo extended
periods of buckling instability that occur earlier and lead to more pronounced
boxy/peanut shapes when the tidal forces are stronger. Using all simulation
outputs of galaxies at different evolutionary stages we construct a toy model
of the galaxy population in the cluster and measure the average bar strength
and bar fraction as a function of clustercentric radius. Both are found to be
mildly decreasing functions of radius. We conclude that tidal forces can
trigger bar formation in cluster cores, but not in the outskirts, and thus
cause larger concentrations of barred galaxies towards cluster center.",1601.07433v3
2018-03-09,Active Galactic Nuclei Feedback in an Elliptical Galaxy with the Most Updated AGN Physics (II): High-Angular Momentum Case,"This is the second paper of our series of works of studying the effects of
active galactic nuclei (AGN) feedback on the cosmological evolution of an
isolated elliptical galaxy by performing two-dimensional high-resolution
hydrodynamical numerical simulations. In these simulations, the inner boundary
is chosen so that the Bondi radius is resolved. Physical processes like star
formation, SNe Ia and II are taken into account. Compared to previous works,
the main improvements is that we adopt the most updated AGN physics, which is
described in detail in the first paper of this series (Yuan et al. 2018, Paper
I). These improvements include the discrimination of the two accretion modes of
the central AGN and the most updated descriptions of the wind and radiation in
the two modes. In Paper I, we consider the case that the specific angular
momentum of the gas in the galaxy is very low. In this paper, we consider the
case that the specific angular momentum of the gas is high. In the galactic
scale, we adopt the gravitational torques raised due to non-axisymmetric
structure in the galaxy as the mechanism of the transfer of angular momentum of
gas, as proposed in some recent works. Since our simulations are axisymmetric,
we make use of a parameterized prescription to mimic this mechanism. Same as
Paper I, we investigate the AGN light curve, typical AGN lifetime, growth of
the black hole mass, AGN duty-cycle, star formation, and the X-ray surface
brightness of the galaxy. Special attention is paid to the effects of specific
angular momentum of the galaxy on these properties. We find that some results
are qualitatively similar to those shown in Paper I, while some results such as
star formation and black hole growth do show a significant difference due to
the mass concentration in the galactic disk as a consequence of galactic
rotation.",1803.03675v2
2018-04-26,SILCC-Zoom: Polarisation and depolarisation in molecular clouds,"We present synthetic dust polarisation maps of 3D magneto-hydrodynamical
simulations of molecular clouds before the onset of stellar feedback. The
clouds are modelled within the SILCC-Zoom project and are embedded in their
galactic environment. The radiative transfer is carried out with POLARIS for
wavelengths from 70 $\mu$m to 3 mm at a resolution of 0.12 pc, and includes
self-consistently calculated alignment efficiencies for radiative torque
alignment. We explore the reason of the observed depolarisation in the center
of molecular clouds: We find that dust grains remain well aligned even at high
densities ($n$ $>$ 10$^3$ cm$^{-3}$) and visual extinctions ($A_\text{V}$ $>$
1). The depolarisation is rather caused by strong variations of the magnetic
field direction along the LOS due to turbulent motions. The observed magnetic
field structure thus resembles best the mass-weighted, line-of-sight averaged
field structure. Furthermore, it differs by only a few 1$^\circ$ for different
wavelengths and is little affected by the spatial resolution of the synthetic
observations. Noise effects can be reduced by convolving the image. Doing so,
for $\lambda$ $\gtrsim$ 160 $\mu$m the observed magnetic field traces reliably
the underlying field in regions with intensities $I$ $\gtrsim$ 2 times the
noise level and column densities above 1 M$_\text{sun}$ pc$^{-2}$. Here,
typical deviations are $\lesssim$ 10$^\circ$. The observed structure is less
reliable in regions with low polarisation degrees and possibly in regions with
large column density gradients. Finally, we show that a simplified and widely
used method without self-consistent dust alignment efficiencies can provide a
good representation of the observable polarisation structure with deviations
below 5$^\circ$.",1804.10157v2
2018-09-24,Turbulent and wind-driven accretion in dwarf novae threaded by a large scale magnetic field,"Dwarf novae (DNe) are accreting white dwarfs that show eruptions due to a
thermal-viscous instability in the accretion disk. The outburst timescales
constrain $\alpha$, the ratio of the viscous stress to the thermal pressure,
and so the mechanism of angular momentum transport. The eruptive state has
$\alpha\approx0.1$ while the quiescent state has $\alpha\approx0.03$. Turbulent
transport due to the magneto-rotational instability (MRI) is generally
considered to be the source of angular momentum transport in DNe. Here, we
perform 3D local magnetohydrodynamic (MHD) shearing box simulations including
vertical stratification, radiative transfer and a net constant vertical
magnetic flux to investigate how transport changes between the outburst and
quiescent states of DNe. We find that a constant $B_z$ provides a higher
$\alpha$ in quiescence than in outburst, in opposition to what is expected.
Including resistivity quenches MRI turbulence in quiescence, suppressing
transport, unless the magnetic field is high enough, which again leads to
$\alpha\approx0.1$. A major difference between simulations with a net poloidal
flux and simulations without is that angular momentum transport in the former
is shared between turbulent and wind-driven transport. We find that wind-driven
transport dominates in quiescence even for low magnetic fields $\sim 1$ G. This
can have a major impact on observational signatures since wind-driven transport
does not heat the disk. Furthermore, wind transport cannot be reduced to an
$\alpha$ prescription. We provide fits for $\alpha$ and the wind torque with
$\beta$, ratio of thermal to magnetic pressure. We conclude that the evolution
of the thermal-viscous instability, and its consequences on the outburst cycles
of CVs, needs to be seriously revised to take into account that most of the
accretion energy may be carried away by a wind instead of being locally
dissipated.",1809.09131v2
2019-08-09,Synthetic observations of dust emission and polarisation of Galactic cold clumps,"The Planck Catalogue of Galactic Cold Clumps (PGCC) contains over 13000
sources detected based on their cold dust signature. They are believed to
consist of a mixture of quiescent, pre-stellar, and already star-forming
objects. We extracted PGCC-type objects from cloud simulations and examined
their physical and polarisation properties. The comparison with the PGCC
catalogue helps to characterise the PGCC sample and provides valuable tests for
numerical simulations of interstellar medium.
  We used several MHD snapshots to define the density field of our models.
Sub-millimetre images of the surface brightness and polarisation were obtained
with radiative transfer calculations. We examined the statistics of synthetic
cold clump catalogues and examined the variations of the clump polarisation
fraction p. The clump sizes, aspect ratios, and temperatures in the synthetic
catalogue are similar to the PGCC. The fluxes and column densities are smaller
by a factor of a few. Rather than with an increased dust opacity, this could be
explained by increasing the average column density of the models by a factor of
two to three, close to N(H2)= 10^22 cm-2. When the line of sight is parallel to
the mean magnetic field, the polarisation fraction tends to increase towards
the clump centres, contrary to observations. When the field is perpendicular,
the polarisation fraction tends to decrease towards the clumps, but the drop in
$p$ is small (e.g. from p~8% to p~7%).
  Magnetic field geometry reduces the polarisation fraction in the simulated
clumps by only \Delta p~1% on average. The larger drop seen towards the actual
PGCC clumps suggests some loss of grain alignment in the dense medium, such as
predicted by the radiative torque mechanism. The statistical study is not able
to quantify dust opacity changes at the scale of the PGCC clumps.",1908.03421v1
2019-09-22,MaLTESE: Large-Scale Simulation-Driven Machine Learning for Transient Driving Cycles,"Optimal engine operation during a transient driving cycle is the key to
achieving greater fuel economy, engine efficiency, and reduced emissions. In
order to achieve continuously optimal engine operation, engine calibration
methods use a combination of static correlations obtained from dynamometer
tests for steady-state operating points and road and/or track performance data.
As the parameter space of control variables, design variable constraints, and
objective functions increases, the cost and duration for optimal calibration
become prohibitively large. In order to reduce the number of dynamometer tests
required for calibrating modern engines, a large-scale simulation-driven
machine learning approach is presented in this work. A parallel, fast, robust,
physics-based reduced-order engine simulator is used to obtain performance and
emission characteristics of engines over a wide range of control parameters
under various transient driving conditions (drive cycles). We scale the
simulation up to 3,906 nodes of the Theta supercomputer at the Argonne
Leadership Computing Facility to generate data required to train a machine
learning model. The trained model is then used to predict various engine
parameters of interest. Our results show that a deep-neural-network-based
surrogate model achieves high accuracy for various engine parameters such as
exhaust temperature, exhaust pressure, nitric oxide, and engine torque. Once
trained, the deep-neural-network-based surrogate model is fast for inference:
it requires about 16 micro sec for predicting the engine performance and
emissions for a single design configuration compared with about 0.5 s per
configuration with the engine simulator. Moreover, we demonstrate that transfer
learning and retraining can be leveraged to incrementally retrain the surrogate
model to cope with new configurations that fall outside the training data
space.",1909.09929v1
2019-10-10,Circumbinary Accretion from Finite and Infinite Disks,"We carry out 2D viscous hydrodynamics simulations of circumbinary disk (CBD)
accretion using {\footnotesize AREPO}. We resolve the accretion flow from a
large-scale CBD down to the streamers and disks around individual binary
components. Extending our recent studies \citep{mun19}, we consider circular
binaries with various mass ratios ($0.1\leq q_{\rm{b}}\leq1$) and study
accretion from ``infinite'', steady-supply disks and from finite-sized,
viscously spreading tori. For ``infinite'' disks, a global steady state can be
reached, and the accretion variability has a dominant frequency
${\sim}0.2\Omega_{\rm{b}}$ for $q_{\rm{b}}>0.5$ and $\Omega_{\rm{b}}$ for
$q_{\rm{b}}<0.5$, ($\Omega_{\rm{b}}$ is the binary angular frequency). We find
that the accretion ``eigenvalue'' $l_0$ -- the net angular momentum transfer
from the disk to the binary per unit accreted mass -- is always positive and
falls in the range ($0.65$-$0.85)a_{\rm b}^2\Omega_{\rm{b}}$ (with $a_{\rm{b}}$
the binary separation), depending weakly on the mass ratio and viscosity. This
leads to binary expansion when $q_{\rm{b}}\gtrsim0.3$. Accretion from a finite
torus can be separated into two phases: an initial transient phase,
corresponding to the filling of the binary cavity, followed by a viscous
pseudo-stationary phase, during which the torus viscously spreads and accretes
onto the binary. In the viscous phase, the net torque on the binary per unit
accreted mass is close to $l_0$, the value derived for ``infinite'' disks. We
conclude that similar-mass binaries accreting from CBDs gain angular momentum
and expand over long time scales. This result significantly impacts the
coalescence of supermassive binary black holes and newly formed binary stars.
We offer a word of caution against conclusions drawn from simulations of
transient accretion onto empty circumbinary cavities.",1910.04763v2
2019-12-23,Mass accretion toward black holes in the final phase of galaxy mergers,"We studied the final phases of galactic mergers, focusing on interactions
between supermassive black holes (SMBHs) and the interstellar medium in a
central sub-kpc region, using an N-body/hydrodynamics code. This numerical
experiment aims to understand the fate of the gas supplied by mergers of two or
more galaxies with SMBHs, whose masses are $10^7 M_\odot$. We observed that the
mass accretion rate to one SMBH exceeds the Eddington accretion rate when the
distance between two black holes (BHs) rapidly decreases. However, this rapid
accretion phase does not last for more than $10^7$ yrs, and it drops to $\sim$
10% of the Eddington rate in the quasi-steady accretion phase. The rapid
accretion is caused by the angular momentum transfer from the gas to the
stellar component, and the moderate accretion in the quasi-steady phase is
caused {by turbulent viscosity and gravitational torque in the disk. The second
merger event enhances the mass accretion to the BHs; however, this phase takes
place on a similar timescale to the first merger event. We also found that the
AGN feedback and the mass accretion to BHs can coexist in the central region of
merged galaxies, if the amount of feedback energy is given as $(2 \times
10^{-4} - 2 \times 10^{-3} )\dot{M} c^2$, where $\dot{M}$ is the accretion rate
to $r= 1$ pc. The accretion rate is suppressed by $\sim$ 1/50 in the
quasi-steady accretion phase for $0.02 \dot{M} c^2$. The fraction of the gas
that finally falls to each BH is approximately 5-7% of the supplied total gas
mass ($10^8 M_\odot$), and 15-20% of the gas forms a circumnuclear gas inside
100 pc. This remnant gas heavily obscures the luminous phase of the active
galactic nuclei (AGN) during merger events, and the moderate AGN feedback does
not alter this property.",1912.10621v1
2020-02-28,From parallel to perpendicular -- On the orientation of magnetic fields in molecular clouds,"We present synthetic dust polarization maps of simulated molecular clouds
(MCs) with the goal to systematically explore the origin of the relative
orientation of the magnetic field ($\bf{B}$) with respect to the MC
sub-structures identified in density ($n$; 3D) and column density ($N$; 2D).
The polarization maps are generated with the radiative transfer code POLARIS,
including self-consistently calculated efficiencies for radiative torque
alignment. The MCs are formed in two sets of 3D MHD simulations: in (i)
colliding flows (CF), and (ii) the SILCC-Zoom simulations. In 3D, for the CF
simulations with an initial field strength below $\sim$5 $\mu$G, $\bf{B}$ is
oriented parallel or randomly with respect to the $n$-structures. For CF runs
with stronger initial fields and all SILCC-Zoom simulations, which have an
initial field strength of 3 $\mu$G, a flip from parallel to perpendicular
orientation occurs at high densities of $n_\text{trans}$ $\simeq$ 10$^2$ -
10$^3$ cm$^{-3}$. We suggest that this flip happens if the MC's mass-to-flux
ratio, $\mu$, is close to or below the critical value of 1. This corresponds to
a field strength around 3 - 5 $\mu$G. In 2D, we use the Projected Rayleigh
Statistics (PRS) to study the orientation of $\bf{B}$. If present, the flip in
orientation occurs at $N_\text{trans}$ $\simeq$ 10$^{21 - 21.5}$ cm$^{-2}$,
similar to the observed transition value from sub- to supercritical magnetic
fields in the ISM. However, projection effects can reduce the power of the PRS
method: Depending on the MC or LOS, the projected maps of the SILCC-Zoom
simulations do not always show the flip, although expected from the 3D
morphology. Such projection effects can explain the variety of recently
observed field configurations, in particular within a single MC. Finally, we do
not find a correlation between the observed orientation of $\bf{B}$ and the
$N$-PDF.",2003.00017v4
2020-04-20,VV 655 and NGC 4418: Implications of an interaction for the evolution of a LIRG,"VV 655, a dwarf irregular galaxy with HI tidal debris, is a companion to the
lenticular luminous infrared galaxy (LIRG) NGC 4418. NGC 4418 stands out among
nearby LIRGs due to its dense central concentration of molecular gas and the
dusty, bi-polar structures along its minor axis suggestive of a wind driven by
a central starburst and possible nuclear activity. We seek to understand the
consequences of the ongoing minor interaction between VV 655 and NGC 4418 for
the evolution of the LIRG, including the origin of the gas supply responsible
for its unusual nuclear properties. We investigate the structural, kinematic,
and chemical properties of VV 655 and NGC 4418 by analyzing archival imaging
data and optical spectroscopic observations from the SDSS-III and new spectra
from SALT-RSS. We characterize their gas-phase metal abundances and spatially
resolved, ionized gas kinematics, and demonstrate that the gas-phase
metallicity in NGC 4418 significantly exceeds that in VV 655. No kinematic
disturbances in the ionized gas are observed along the minor axis of NGC 4418,
but we see evidence for ionized gas outflows from VV 655 that may increase the
cross-section for gas stripping in grazing collisions. A faint, asymmetric
outer arm is detected in NGC 4418 of the type normally associated with
galaxy-galaxy interactions. The simplest model suggests that the minor
interaction between VV 655 and NGC 4418 produced the unusual nuclear properties
of the LIRG via tidal torquing of the interstellar medium of NGC 4418 rather
than through a significant gas transfer event. In addition to inducing a
central concentration of gas in NGC 4418, this interaction also produced an
enhanced star formation rate and an outer tidal arm in the LIRG. The VV 655-NGC
4418 system offers an example of the potential for minor collisions to alter
the evolutionary pathways of giant galaxies.",2004.09534v1
2020-06-01,Linear dust polarization during the embedded phase of protostar formation,"Measuring polarization from thermal dust emission can provide constraints on
the magnetic field structure around embedded protostars. However, interpreting
the observations is challenging without models that consistently account for
both the complexity of the protostellar birth environment and polarization
mechanisms. We aim to provide a better understanding with a focus on
bridge-like structures such as that observed towards the protostellar multiple
IRAS 16293--2422 by comparing synthetic polarization maps of thermal reemission
with observations. We analyze the magnetic field properties associated with the
formation of a protostellar multiple based on ideal MHD 3D zoom-in simulations
carried out with the RAMSES code. To compare with observations, we post-process
a snapshot of a bridge-like structure that is associated with a forming triple
star system with the radiative transfer code POLARIS and produce
multi-wavelength dust polarization maps. In the most prominent bridge of our
sample, the typical density is about 10^(-16) g cm^(-3), and the magnetic field
strength is about 1 to 2 mG. The magnetic field structure has an elongated
toroidal morphology and the dust polarization maps trace the complex
morphology. In contrast, the magnetic field strength associated with the
launching of asymmetric bipolar outflows is significantly more magnetized (~100
mG). At {\lambda}=1.3 mm, the orientation of grains in the bridge is similar
for the case accounting for radiative alignment torques (RATs) compared to
perfect alignment with magnetic field lines. However, the polarization fraction
in the bridge is three times smaller for the RAT scenario compared to assuming
perfect alignment. At shorter wavelengths ({\lambda} < 200 {\mu}m), dust
polarization does not trace the magnetic field because other effects such as
self-scattering and dichroic extinction dominate the orientation of the
polarization.",2006.01297v2
2020-07-22,On the orbital evolution of binaries with circumbinary discs,"Circumbinary discs are generally thought to take up angular momentum and
energy from the binary orbit over time through gravitational torques mediated
by orbital resonances. This process leads to the shrinkage of the binary orbit
over time, and is important in a variety of astrophysical contexts including
the orbital evolution of stellar binaries, the migration of planets in
protoplanetary discs, and the evolution of black hole binaries (stellar and
supermassive). The merger of compact object binaries provides a source of
gravitational waves in the Universe. Recently, several groups have reported
numerical simulations of circumbinary discs that yield the opposite result,
finding that the binary expands with time. Here we argue that this result is
primarily due to the choice of simulation parameters, made for numerical
reasons, which differ from realistic disc parameters in many cases. We provide
physical arguments, and then demonstrate with 3D hydrodynamical simulations,
that thick (high pressure, high viscosity) discs drive sufficient accretion of
high angular momentum material to force binary expansion, while in the more
realistic case of thin (low pressure, low viscosity) discs there is less
accretion and the binary shrinks. In the latter case, tides, which generally
transfer angular momentum and energy from the more rapidly rotating object (the
binary) to the less rapidly rotating object (the disc), are the dominant driver
of disc-binary evolution. This causes the binary to shrink. We therefore
conclude that for common circumbinary disc parameters, binaries with
non-extreme mass ratios are expected to shrink over time. Expansion of the
binary can occur if the disc viscosity is unusually high, which may occur in
the very thick discs encountered in e.g. circumplanetary discs, super-Eddington
AGN, or the outer regions of passive protostellar discs that are heated by the
... (abridged).",2007.11592v1
2020-12-10,Constraining the magnetic field properties of Bok globule B335 using SOFIA/HAWC+,"Thanks to their well-defined shape and mostly isolated locations, Bok
globules are suitable objects for studying the physics of low-mass star
formation. To study the magnetic field of the prototypical Bok globule B335, we
obtained a spatially resolved polarization map with SOFIA/HAWC+ at a wavelength
of 214$\,\mu$m. For the first time, these observations reveal that polarization
holes in Bok globules, that is, the decrease in polarization degree towards
their dense centers, also occur in the far-infrared wavelength regime. The
observed polarization pattern is uniform with a mean polarization angle of
48$^\circ\pm $26$^\circ$ and a magnetic field strength of $\sim$ 142$\,\mu$G.
Moreover, we use complementary polarimetic data for B335 obtained at
near-infrared to millimeter wavelengths to analyze and constrain the magnetic
field across different scales. By applying the 3D Monte-Carlo radiative
transfer code POLARIS (Reissl et al. 2016), we developed a model for the
density and magnetic field structure as well as for the dust properties of this
globule. We conclude that the column density towards the center of B335 is too
low to cause the observed polarization hole in B335 via dichroic absorption
(Brauer et al. 2016). Furthermore, we conclude that the effect of
self-scattering has no significant impact on the observed polarization.
Adopting dust-grain alignment via the radiative torque mechanism, a combination
of the interstellar radiation field and the central star as radiation sources
is consistent with the decrease in polarization degree at the outer regions of
B335 ($\approx\,$10$^4\,$au from the core). However, the model fails to explain
the low polarization degree within the inner 5000 au.",2012.05889v1
2021-05-25,From Motor Control to Team Play in Simulated Humanoid Football,"Intelligent behaviour in the physical world exhibits structure at multiple
spatial and temporal scales. Although movements are ultimately executed at the
level of instantaneous muscle tensions or joint torques, they must be selected
to serve goals defined on much longer timescales, and in terms of relations
that extend far beyond the body itself, ultimately involving coordination with
other agents. Recent research in artificial intelligence has shown the promise
of learning-based approaches to the respective problems of complex movement,
longer-term planning and multi-agent coordination. However, there is limited
research aimed at their integration. We study this problem by training teams of
physically simulated humanoid avatars to play football in a realistic virtual
environment. We develop a method that combines imitation learning, single- and
multi-agent reinforcement learning and population-based training, and makes use
of transferable representations of behaviour for decision making at different
levels of abstraction. In a sequence of stages, players first learn to control
a fully articulated body to perform realistic, human-like movements such as
running and turning; they then acquire mid-level football skills such as
dribbling and shooting; finally, they develop awareness of others and play as a
team, bridging the gap between low-level motor control at a timescale of
milliseconds, and coordinated goal-directed behaviour as a team at the
timescale of tens of seconds. We investigate the emergence of behaviours at
different levels of abstraction, as well as the representations that underlie
these behaviours using several analysis techniques, including statistics from
real-world sports analytics. Our work constitutes a complete demonstration of
integrated decision-making at multiple scales in a physically embodied
multi-agent setting. See project video at https://youtu.be/KHMwq9pv7mg.",2105.12196v1
2021-07-29,Mapping Human Muscle Force to Supernumerary Robotics Device for Overhead Task Assistance,"Supernumerary Robotics Device (SRD) is an ideal solution to provide robotic
assistance in overhead manual manipulation. Since two arms are occupied for the
overhead task, it is desired to have additional arms to assist us in achieving
other subtasks such as supporting the far end of a long plate and pushing it
upward to fit in the ceiling. In this study, a method that maps human muscle
force to SRD for overhead task assistance is proposed. Our methodology is to
utilize redundant DoFs such as the idle muscles in the leg to control the
supporting force of the SRD. A sEMG device is worn on the operator's shank
where muscle signals are measured, parsed, and transmitted to SRD for control.
In the control aspect, we adopted stiffness control in the task space based on
torque control at the joint level. We are motivated by the fact that humans can
achieve daily manipulation merely through simple inherent compliance property
in joint driven by muscles. We explore to estimate the force of some particular
muscles in humans and control the SRD to imitate the behaviors of muscle and
output supporting forces to accomplish the subtasks such as overhead
supporting. The sEMG signals detected from human muscles are extracted,
filtered, rectified, and parsed to estimate the muscle force. We use this force
information as the intent of the operator for proper overhead supporting force.
As one of the well-known compliance control methods, stiffness control is easy
to achieve using a few of straightforward parameters such as stiffness and
equilibrium point. Through tuning the stiffness and equilibrium point, the
supporting force of SRD in task space can be easily controlled. The muscle
force estimated by sEMG is mapped to the desired force in the task space of the
SRD. The desired force is transferred into stiffness or equilibrium point to
output the corresponding supporting force.",2107.13799v2
2022-02-11,The Role of Disk Tearing and Precession in the Observed Variability of Pleione,"We acquired H$\alpha$ spectroscopic observations from 2005 to 2019 showing
Pleione has transitioned from a Be phase to a Be-shell phase during this
period. Using the radiative transfer code \hdust\ we created a grid of
$\sim100,000$ disk models for Pleione. We successfully reproduced the observed
transition with a disk model that varies in inclination while maintaining an
equatorial density of $\rho_0(r) = 3\times 10^{-11}
(r/R_{eq})^{-2.7}~\rm{g~cm^{-3}}$, and an H$\alpha$ emitting region extending
to $15~\rm{R_{eq}}$. We use a precessing disk model to extrapolate the changing
disk inclination over $120$ years and follow the variability in archival
observations. The best-fit disk model precesses over a line of sight
inclination between $\sim25\rm{^{\circ}}$ and $\sim144\rm{^{\circ}}$ with a
precessional period of $\sim80.5$ years. Our precessing models match some of
the observed variability but fail to reproduce all of the historical data
available. Therefore, we propose an ad-hoc model based on our precessing disk
model inspired by recent SPH simulations of similar systems, where the disk
tears due to the tidal influence of a companion star. In this model, a single
disk is slowly tilted to an angle of $30^{\circ}$ from the stellar equator over
$34$ years. Then, the disk is torn by the companion's tidal torque, with the
outer region separating from the innermost disk. The small inner disk returns
to the stellar equator as mass injection remains constant. The outer disk
precesses for $\sim15$ years before gradually dissipating. The process repeats
every $34$ years and reproduces all trends in Pleione's variability.",2202.05900v1
2024-02-14,Textural properties of dense granular pastes produced by kneading,"The efficiency of supported catalysts depends on the porous microstructure of
their solid support, which regulates mass transfer, exposure to the active
phase, and mechanical strength. Here, we focus on the manufacturing of a
specific type of catalytic support, $\gamma$-alumina extrudates, by a
kneading-extrusion process. In this process, a paste is initially formed by
blending and subsequently kneading a boehmite powder, an aluminum oxide
hydroxide precursor of $\gamma$-alumina, with various liquids before undergoing
extrusion. The crucial step in this process is the kneading step, which allows
control over the textural and mechanical properties of the extrudate. The
present experimental study aims to measure the impact of the kneading step on
boehmite pastes prepared using a pilot kneader. The pastes are obtained by
mixing boehmite powder with an acid and a basic solution in a two-step process
known as peptization and neutralization. In this study, kneading is conducted
at various mixing speeds and durations while monitoring the torque exerted by
the boehmite paste on the kneader blades. Moreover, samples are extracted from
the pilot kneader at various stages of the kneading process, and their textural
properties are determined by both nitrogen sorption and mercury intrusion
porosimetry. Our findings show that, at fixed composition, the textural
properties of boehmite pastes are controlled by the overall deformation
accumulated during kneading. Conversely, for a fixed accumulated deformation,
the pH sets the textural properties. Finally, we identify an empirical control
parameter that captures the combined effects of pH and accumulated deformation
on the key textural attributes of boehmite pastes. These results set the stage
for a systematic design approach of boehmite-based catalyst supports.",2402.09220v1
2002-02-25,Entropic torque,"Quantitative predictions are presented of a depletion-induced torque and
force acting on a single colloidal hard rod immersed in a solvent of hard
spheres close to a planar hard wall. This torque and force, which are entirely
of entropic origin, may play an important role for the key-lock principle,
where a biological macromolecule (the key) is only functional in a particular
orientation with respect to a cavity (the lock).",0202443v1
2002-03-01,Defect structures and torque on an elongated colloidal particle immersed in a liquid crystal host,"Combining molecular dynamics and Monte Carlo simulation we study defect
structures around an elongated colloidal particle embedded in a nematic liquid
crystal host. By studying nematic ordering near the particle and the
disclination core region we are able to examine the defect core structure and
the difference between two simulation techniques. In addition, we also study
the torque on a particle tilted with respect to the director, and modification
of this torque when the particle is close to the cell wall.",0203018v2
2005-02-15,Coupling between static friction force and torque,"We show that the static friction force which must be overcome to render a
sticking contact sliding is reduced if an external torque is also exerted. As a
test system we study a planar disk lying on horizontal flat surface. We perform
experiments and compare with analytical results to find that the coupling
between static friction force and torque is nontrivial: It is not determined by
the Coulomb friction laws alone, instead it depends on the microscopic details
of friction. Hence, we conclude that the macroscopic experiment presented here
reveals details about the microscopic processes lying behind friction.",0502358v1
2005-11-07,Casimir torque,"We develop a formalism for the calculation of the flow of angular momentum
carried by the fluctuating electromagnetic field within a cavity bounded by two
flat anisotropic materials. By generalizing a procedure employed recently for
the calculation of the Casimir force between arbitrary materials, we obtain an
expression for the torque between anisotropic plates in terms of their
reflection amplitude matrices. We evaluate the torque in 1D for ideal and
realistic model materials.",0511064v1
2008-12-03,Grain Alignment by Radiative Torques,"Grain alignment is a notoriously difficult problem, that is extremely rich in
underlying physics. The long history of attempts theoretical handling of the
problem resulted in rather sceptical approach to the theory on the part of some
polarimetry practitioners. However, recently the theory has been very
successful in accounting for the observational data. In view of that, I present
a very concise discussion of the most promising mechanism of grain alignment,
namely, radiative torque alignment. In particular, I discuss a new analytical
model which excellently reproduces properties of radiative torques, as well as
the application of the model to predicting the degree of alignment.",0812.0816v1
2009-03-11,Accretion disk warping by resonant relaxation: The case of maser disk NGC4258,"The maser disk around the massive black hole (MBH) in active galaxy NGC 4258
exhibits an O(10 deg) warp on the O(0.1 pc) scale. The physics driving the warp
are still debated. Suggested mechanisms include torquing by relativistic frame
dragging or by radiation pressure. We propose here a new warping mechanism:
resonant torquing of the disk by stars in the dense cusp around the MBH. We
show that resonant torquing can induce such a warp over a wide range of
observed and deduced physical parameters of the maser disk.",0903.2051v2
2009-10-05,"Modeling torque versus speed, shot noise, and rotational diffusion of the bacterial flagellar motor","We present a minimal physical model for the flagellar motor that enables
bacteria to swim. Our model explains the experimentally measured torque-speed
relationship of the proton-driven E. coli motor at various pH and temperature
conditions. In particular, the dramatic drop of torque at high rotation speeds
(the ""knee"") is shown to arise from saturation of the proton flux. Moreover, we
show that shot noise in the proton current dominates the diffusion of motor
rotation at low loads. This suggests a new way to probe the discreteness of the
energy source, analogous to measurements of charge quantization in
superconducting tunnel junctions.",0910.0835v1
2010-04-14,Thermal torque in rotating gas,"Molecular motion in combination with rotation causes a torque in gas when
seen from a coordinate system fixed in the rotating system. The torque is
caused by Coriolis forces.",1004.2421v7
2011-02-07,Hamilton-Poisson formulation for the rotational motion of a rigid body in the presence of an axisymmetric force field and a gyroscopic torque,"We give sufficient conditions for the rigid body in the presence of an
axisymmetric force field and a gyroscopic torque to admit a Hamilton-Poisson
formulation. Even if by adding a gyroscopic torque we initially lose one of the
conserved Casimirs, we recover another conservation law as a Casimir function
for a modified Poisson structure. We apply this frame to several well known
results in the literature.",1102.1274v1
2011-10-24,The role of Hall diffusion in the magnetically threaded thin accretion discs,"We study role of the Hall diffusion in the magnetic star-disc interaction. In
a simplified steady state configuration, the total torque is calculated in
terms of the fastness parameter and a new term because of the Hall diffusion.
We show the total torque reduces as the Hall term becomes more significant.
Also, the critical fastness parameter (at which the total torque is zero)
reduces because of the Hall diffusion.",1110.5142v1
2012-05-23,Resolution of the Mansuripur Paradox,"The interaction of a magnetic dipole with a point charge leads to an apparent
paradox when analyzed using the 3-vector formulation of the Lorentz force.
Specifically, the dipole is subject to a torque in some frames and not in
others. We show that when analyzed according to the covariant 4-vector
formulation the paradox disappears. The torque that arises in certain frames is
connected to the time-space components of the torque in the rest frame, giving
rise to ""hidden"" momentum.",1205.5451v2
2012-06-20,Torques without Rotation: the Right-Angle Lever,"An extended body subject to external forces which exert zero net force and
zero total torque in the rest frame, may experience a nonzero torque in another
inertial frame, and nonetheless does not rotate. Long known as the
Trouton-Noble or right-angle lever paradox, there has been extensive discussion
and indeed controversy, but a clear understanding comes from a suitable
treatment of angular momentum and simultaneity.",1206.4487v1
2012-10-22,Intermittent boundary layers and torque maxima in Taylor-Couette flow,"Turbulent Taylor-Couette flow between counter-rotating cylinders develops
intermittently fluctuating boundary layers for sufficient counter-rotation. We
demonstrate the phenomenon in direct numerical simulations for radius ratios
\eta=0.5 and 0.71 and propose a theoretical model for the critical value in the
rotation ratio. Numerical results as well as experiments show that the onset of
this intermittency coincides with the maximum in torque. The variations in
torque correlate with the variations in mean Taylor vortex flow which is first
enhanced for weak counter-rotation, and then reduced as intermittency sets in.
To support the model, we compare to numerical results, experiments at higher
Reynolds numbers, and to Wendt's data.",1210.6075v1
2012-12-27,On the confinement of semiflexible chains under torsion,"The effect of a finite torque on semiflexible polymers in a confined
environment is investigated. It is shown how a new lengthscale appears in the
strongly confined limit. The influence of a torque on the extension of
biopolymers in nanochannels is also touched upon and it is argued that the
presence of a torque has a strong influence on the dimensions of nanochannels
needed to prevent hairpins.",1212.6294v1
2013-07-11,"Efficient Computation of Power, Force, and Torque in BEM Scattering Calculations","We present concise, computationally efficient formulas for several quantities
of interest -- including absorbed and scattered power, optical force (radiation
pressure), and torque -- in scattering calculations performed using the
boundary-element method (BEM) [also known as the method of moments (MOM)]. Our
formulas compute the quantities of interest \textit{directly} from the BEM
surface currents with no need ever to compute the scattered electromagnetic
fields. We derive our new formulas and demonstrate their effectiveness by
computing power, force, and torque in a number of example geometries. Free,
open-source software implementations of our formulas are available for download
online.",1307.2966v1
2014-11-08,On the anomalous torque applied to a rotating magnetized sphere in a vacuum,"We analyze the torque applied to a rotating magnetized sphere in a vacuum. It
is shown that for the correct determination of one of the torque's component
the angular momentum of the electromagnetic field within the body should be
taken into account.",1411.2107v2
2015-08-24,Effect of reorientation statistics on torque response of self propelled particles,"We consider the dynamics of self-propelled particles subject to external
torques. Two models for the reorientation of self-propulsion are considered,
run-and-tumble particles, and active Brownian particles. Using the standard
tools of non-equilibrium statistical mechanics we show that the run and tumble
particles have a more robust response to torques. This macroscopic signature of
the underlying reorientation statistics can be used to differentiate between
the two types of self propelled particles. Further this result might indicate
that run and tumble motion is indeed the evolutionarily stable dynamics for
bacteria.",1508.05887v1
2016-01-08,An Efficient Algorithm for Periodic Riccati Equation for Spacecraft Attitude Control Using Magnetic Torques,"Spacecraft attitude control using only magnetic torques is a periodic
time-varying system as the Earth magnetic field in the spacecraft body frame
changes periodically while the spacecraft circles around the Earth. The optimal
controller design therefore involves the solutions of the periodic Riccati
differential or algebraic equations. This paper proposes an efficient algorithm
for the periodic discrete-time Riccati equation arising from a linear periodic
time-varying system $(\A,\B)$, which explores and utilizes the fact that $\A$
is time-invariant and only $\B$ is time-varying in the system, a special
properties associated with the problem of spacecraft attitude control using
only magnetic torques.",1601.01990v1
2018-03-09,Exploiting Friction in Torque Controlled Humanoid Robots,"A common architecture for torque controlled humanoid robots consists in two
nested loops. The outer loop generates desired joint/motor torques, and the
inner loop stabilises these desired values. In doing so, the inner loop usually
compensates for joint friction phenomena, thus removing their inherent
stabilising property that may be also beneficial for high level control
objectives. This paper shows how to exploit friction for joint and task space
control of humanoid robots. Experiments are carried out using the humanoid
robot iCub.",1803.04266v3
2019-03-23,Maxwell Eigenmode approach to the Casimir-Lifshitz Torque,"More than forty years ago, Barash published a calculation of the full
retarded Casimir-Lifshitz torque for planar birefringent media with arbitrary
degrees of anisotropy. An independent theoretical confirmation has been lacking
since. We report a systematic and transparent derivation of the torque between
two media with both electric and magnetic birefringence. Our approach, based on
an eigenmode decomposition of Maxwell's equations, generalizes Barash's result
for electrically birefringent materials, and can be generalized to a wide range
of anisotropic materials and finite thickness effects.",1903.09765v2
2021-12-10,On torque computation in electric machine simulation by harmonic mortar methods,"The use of trigonometric polynomials as Lagrange multipliers in the harmonic
mortar method enables an efficient and elegant treatment of relative motion in
the stator-rotor coupling of electric machine simulation. Explicit formulas for
the torque computation are derived by energetic considerations, and their
realization by harmonic mortar finite element and isogemetric analysis
discretizations is discussed. Numerical tests are presented to illustrate the
theoretical results and demonstrate the potential of harmonic mortar methods
for the evaluation of torque ripples.",2112.05572v2
2023-11-20,Non-conservation of the orbital moment of Bloch electrons in an electric field,"The orbital moment (OM) of Bloch electrons has witnessed a surge in interest
in out-of--equilibrium systems. Here, by developing a quantum kinetic theory,
we show that the OM is in general not conserved in an electric field. The force
moment produces a torque on the OM, which is determined by the quantum
geometric tensor and the group velocities of Bloch bands. The torque vanishes
in two-band systems with particle-hole symmetry, but is nonzero otherwise. For
tilted massive Dirac fermions the torque is determined by the magnitude and
direction of the tilt.",2311.12108v1
1997-01-02,Cold Dark Matter in SUSY Theories. The Role of Nuclear Form Factors and the Folding with the LSP Velocity,"The momentum transfer dependence of the total cross section for elastic
scattering of cold dark matter candidates, i.e. lightest supersymmetric
particle (LSP), with nuclei is examined. The presented calculations of the
event rates refer to a number of representative nuclear targets throughout the
periodic table and have been obtained in a relatively wide phenomenologically
allowed SUSY parameter space. For the coherent cross sections it is shown that,
since the momentum transfer can be quite big for large mass of the LSP and
heavy nuclei even though the energy transfer is small ($\le 100 KeV$), the
total cross section can in such instances be reduced by a factor of about five.
For the spin induced cross section of odd-A nuclear targets, as is the case of
$^{207}Pb$ studied in this work, we found that the reduction is less
pronounced, since the high multipoles tend to enhance the cross section as the
momentum transfer increases (for LSP $mass < 200 GeV$) and partially cancell
the momentum retardation. The effect of the Earth's revolution around the sun
on these event rates is also studied by folding with a Maxwellian LSP-velocity
distribution which is consistent with its density in the halos. We thus found
that the convoluted event rates do not appreciably change compared to those
obtained with an average velocity. The event rates increase with A and, in the
SUSY parameter space considered, they can reach values up to 140
$y^{-1}Kg^{-1}$ for Pb. The modulation effect, however, was found to be small
(less than $\pm 5%$).",9701205v1
2002-08-16,Perspectives on Exclusive Processes in QCD,"Hard hadronic exclusive processes are now at the forefront of QCD studies,
particularly because of their role in the interpretation of exclusive hadronic
B decays. Perturbative QCD and its factorization properties at high momentum
transfer provide an essential guide to the phenomenology of exclusive
amplitudes at large momentum transfer--the leading power fall-off of form
factors and fixed-angle cross sections, the dominant helicity structures, and
their color transparency properties. The hard scattering subprocess amplitude
T_H controlling the leading-twist amplitude is evaluated in the perturbative
domain where the propagator virtualities are above the separation scale. A
critical question is the momentum transfer required such that leading-twist
perturbative QCD contributions dominate. I review some of the contentious
theoretical issues and empirical challenges to Perturbative QCD based analyses,
such as the magnitude of the leading-twist contributions, the role of soft and
higher twist QCD mechanisms, the effects of non-zero orbital angular momentum,
the possibility of single-spin asymmetries in deeply virtual Compton
scattering, the role of hidden color in nuclear wavefunctions, the behavior of
the ratio of Pauli and Dirac nucleon form factors, the apparent breakdown of
color transparency in quasi-elastic proton-proton scattering, and the
measurement of hadron and photon wavefunctions in diffractive dijet production.",0208158v2
2011-10-28,The VLT-FLAMES survey of massive stars: NGC346-013 as a test case for massive close binary evolution,"NGC346-013 is a peculiar double-lined eclipsing binary in the Small
Magellanic Cloud discovered by the VLT-FLAMES survey of massive stars. Spectra
obtained with VLT-FLAMES are used to construct a radial velocity curve and
photometry obtained with the Faulkes Telescope South is then used to derive
orbital parameters, while spectra of the secondary are compared with synthetic
spectra from TLUSTY model atmospheres. The orbital period is found to be
4.20381(12) days, with masses of 19.1+/-1.0 and 11.9+/-0.6 Msun. The primary is
a rapidly rotating late-O dwarf while the secondary, an early-B giant, displays
near-synchronous rotation and has filled its Roche lobe, implying that it was
originally the more massive component with recent mass transfer `spinning up'
the primary to near-critical rotation. Comparison with synthetic spectra finds
temperatures of 34.5kK and 24.5kK for the primary and secondary respectively,
with the nitrogen abundance of the secondary enhanced compared to baseline
values for the SMC, consistent with the predictions of models of interacting
binaries. NGC346-013 likely evolved via non-conservative mass transfer in a
system with initial masses ~22+15Msun, with the well-constrained orbital
solution and atmospheric parameters making it an excellent candidate for
tailored modelling with binary evolution codes. This system will form a
cornerstone in constraining the physics of thermal timescale mass transfer, and
the associated mass transfer efficiency, in massive close binary systems.",1110.6325v1
2012-06-04,Non-diagonal open spin-1/2 XXZ quantum chains by separation of variables: Complete spectrum and matrix elements of some quasi-local operators,"The integrable quantum models, associated to the transfer matrices of the
6-vertex reflection algebra for spin 1/2 representations, are studied in this
paper. In the framework of Sklyanin's quantum separation of variables (SOV), we
provide the complete characterization of the eigenvalues and eigenstates of the
transfer matrix and the proof of the simplicity of the transfer matrix
spectrum. Moreover, we use these integrable quantum models as further key
examples for which to develop a method in the SOV framework to compute matrix
elements of local operators. This method has been introduced first in [1] and
then used also in [2], it is based on the resolution of the quantum inverse
problem (i.e. the reconstruction of all local operators in terms of the quantum
separate variables) plus the computation of the action of separate covectors on
separate vectors. In particular, for these integrable quantum models, which in
the homogeneous limit reproduce the open spin-1/2 XXZ quantum chains with
non-diagonal boundary conditions, we have obtained the SOV-reconstructions for
a class of quasi-local operators and determinant formulae for the
covector-vector actions. As consequence of these findings we provide one
determinant formulae for the matrix elements of this class of reconstructed
quasi-local operators on transfer matrix eigenstates.",1206.0646v2
2014-06-17,Scale-estimation of quantum coherent energy transport in multiple-minima systems,"A generic and intuitive model for coherent energy transport in multiple
minima systems coupled to a quantum mechanical bath is shown. Using a simple
spin-boson system, we illustrate how a generic donor-acceptor system can be
brought into resonance using a narrow band of vibrational modes, such that the
transfer efficiency of an electron-hole pair (exciton) is made arbitrarily
high. Coherent transport phenomena in nature are of renewed interest since the
discovery that a photon captured by the light-harvesting complex (LHC) in
photosynthetic organisms can be conveyed to a chemical reaction centre with
near-perfect efficiency. Classical explanations of the transfer use stochastic
diffusion to model the hopping motion of a photo-excited exciton. This accounts
inadequately for the speed and efficiency of the energy transfer measured in a
series of recent landmark experiments. Taking a quantum mechanical perspective
can help capture the salient features of the efficient part of that transfer.
To show the versatility of the model, we extend it to a multiple minima system
comprising seven-sites, reminiscent of the widely studied Fenna-Matthews-Olson
(FMO) light-harvesting complex. We show that an idealised transport model for
multiple minima coupled to a narrow-band phonon can transport energy with
arbitrarily high efficiency.",1406.5530v1
2016-12-15,Control of Intramolecular Electron Transfer in Perylene Dihydrazides and Perylene Diimides: A Comparative Study by Time-Resolved Spectroscopy,"Electron transfer (ET) in molecular donor-acceptor dye systems is crucial for
charge transport in organic semiconductors. Classically, ET rates should
decrease with increasing donor-acceptor distance while the microscopic
mechanism is more complex and shows intricate dependencies on the excitation
conditions. In this paper, we introduce highly soluble N,N'-dialkyl perylene
dihydrazides (PDH) - perylene dyes with a dialkylamino -NR$_2$ donor
functionality directly bonded to both of their imide nitrogen atoms. We compare
the PDH electron-transfer dynamics with a group of classical
N,N'-bisalkylperylene diimides (PDI) equipped with a -NR$_2$ donor linked to
the PDI acceptor core via a varying number of alkylene -(CH$_2$)- spacer
groups, thus at distinctively different distance. Special physicochemical
design features of our study objects include: i) amine moieties as donor group
to minimize spin-orbit coupling; ii) substitution solely at both imide
positions to avoid major impact on HOMO and LUMO levels and distortions of the
PDI backbone; iii) control of donor-acceptor separation by non-conjugated
alkylene groups to exclude any additional effects due to delocalized $\pi$
electron systems. All materials show non-single-exponential photoluminescence
decay dynamics. A rate equation analysis supported by electrochemical and
absolute photoluminescence efficiency measurements yields evidence for
efficient intersystem-crossing without heavy elements and reveals that the
charge-transfer efficiency across the intramolecular interface strongly depends
on the surplus excitation energy.",1612.05046v1
2017-01-16,On the Thermodynamic Formalism for the Farey Map,"The chaotic phenomenon of intermittency is modeled by a simple map of the
unit interval, the Farey map. The long term dynamical behaviour of a point
under iteration of the map is translated into a spin system via symbolic
dynamics. Methods from dynamical systems theory and statistical mechanics may
then be used to analyse the map, respectively the zeta function and the
transfer operator. Intermittency is seen to be problematic to analyze due to
the presence of an `indifferent fixed point'. Points under iteration of the map
move away from this point extremely slowly creating pathological convergence
times for calculations. This difficulty is removed by going to an appropriate
induced subsystem, which also leads to an induced zeta function and an induced
transfer operator. Results obtained there can be transferred back to the
original system. The main work is then divided into two sections. The first
demonstrates a connection between the induced versions of the zeta function and
the transfer operator providing useful results regarding the analyticity of the
zeta function. The second section contains a detailed analysis of the pressure
function for the induced system and hence the original by considering bounds on
the radius of convergence of the induced zeta function. In particular, the
asymptotic behaviour of the pressure function in the limit $\beta$, the inverse
of `temperature', tends to negative infinity is determined and the existence
and nature of a phase transition at $\beta=1$ is also discussed.",1701.04486v1
2017-08-29,Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces,"At interfaces between conventional materials, band bending and alignment are
classically controlled by differences in electrochemical potential. Applying
this concept to oxides in which interfaces can be polar and cations may adopt a
mixed valence has led to the discovery of novel two-dimensional states between
simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a
more complex electronic structure, with charge, orbital and/or spin orders
arising from correlations between transition metal and oxygen ions. Strong
correlations thus offer a rich playground to engineer functional interfaces but
their compatibility with the classical band alignment picture remains an open
question. Here we show that beyond differences in electron affinities and polar
effects, a key parameter determining charge transfer at correlated oxide
interfaces is the energy required to alter the covalence of the metaloxygen
bond. Using the perovskite nickelate (RNiO3) family as a template, we probe
charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray
absorption spectroscopy shows that the charge transfer is thwarted by
hybridization effects tuned by the rare-earth (R) size. Charge transfer results
in an induced ferromagnetic-like state in the nickelate, exemplifying the
potential of correlated interfaces to design novel phases. Further, our work
clarifies strategies to engineer two-dimensional systems through the control of
both doping and covalence.",1708.08823v1
2018-02-19,Role of quantum coherence in the thermodynamics of energy transfer,"Recent research on the thermodynamic arrow of time, at the microscopic scale,
has questioned the universality of its direction. Theoretical studies showed
that quantum correlations can be used to revert the natural heat flow (from the
hot body to the cold one), posing an apparent challenge to the second law of
thermodynamics. Such an ""anomalous"" heat current was observed in a recent
experiment (arXiv:1711.03323), by employing two spin systems initially quantum
correlated. Nevertheless, the precise relationship between this intriguing
phenomenon and the initial conditions that allow it is not fully evident. Here,
we address energy transfer in a wider perspective, identifying a nonclassical
contribution that applies to the reversion of the heat flow as well as to more
general forms of energy exchange. We derive three theorems that describe the
energy transfer between two microscopic systems, for arbitrary initial
bipartite states. Using these theorems, we obtain an analytical bound showing
that certain type of quantum coherence can optimize such a process,
outperforming incoherent states. This genuine quantum advantage is corroborated
through a characterization of the energy transfer between two qubits. For this
system, it is shown that a large enough amount of coherence is necessary and
sufficient to revert the thermodynamic arrow of time. As a second crucial
consequence of the presented theorems, we introduce a class of nonequilibrium
states that only allow unidirectional energy flow. In this way, we broaden the
set where the standard Clausius statement of the second law applies.",1802.06758v2
2019-08-20,Interactions and charge transfer dynamics of an Al$^+$ ion immersed in ultracold Rb and Sr atoms,"Atomic clocks based on an Al$^+$ ion sympathetically cooled by a laser-cooled
alkaline-earth ion have achieved unprecedented accuracy. Here, we investigate
theoretically interactions and charge transfer dynamics of an Al$^+$ ion
immersed in an ultracold gas of Rb and Sr atoms. We calculate potential energy
curves and transition electric dipole moments for the (Al+Rb)$^+$ and
(Al+Sr)$^+$ ion-atom systems using coupled cluster and multireference
configuration interaction methods with scalar relativistic effects included
within the small-core energy-consistent pseudopotentials in Rb and Sr atoms.
The long-range interaction coefficients are also reported. We use the
electronic structure data to investigate cold collisions and charge transfer
dynamics. Scattering of an Al$^+$ ion with alkali-metal or alkaline-earth-metal
atom is governed by one potential energy curve whereas charge transfer can lead
to several electronic states mixed by the relativistic spin-orbit coupling. We
examine the branching ratios resulting from the interplay of the short- and
long-range effects, as well as the prospects for the laser-field control and
formation of molecular ions. We propose to employ the atomic clock transition
in an Al$^+$ ion to monitor ion-atom scattering dynamics via quantum logic
spectroscopy. The presented results pave the way for the application of atomic
ions other than alkali-metal and alkaline-earth-metal ones in the field of cold
hybrid ion-atom experiments.",1908.07492v2
2020-12-18,On the Q operator and the spectrum of the XXZ model at root of unity,"The spin-1/2 Heisenberg XXZ chain is a paradigmatic quantum integrable model.
Although it can be solved exactly via Bethe ansatz techniques, there are still
open issues regarding the spectrum at root of unity values of the anisotropy.
We construct Baxter's Q operator at arbitrary anisotropy from a two-parameter
transfer matrix associated to a complex-spin auxiliary space. A decomposition
of this transfer matrix provides a simple proof of the transfer matrix fusion
and Wronskian relations. At root of unity a truncation allows us to construct
the Q operator explicitly in terms of finite-dimensional matrices. From its
decomposition we derive truncated fusion and Wronskian relations as well as an
interpolation-type formula that has been conjectured previously. We elucidate
the Fabricius-McCoy (FM) strings and exponential degeneracies in the spectrum
of the six-vertex transfer matrix at root of unity. Using a semicyclic
auxiliary representation we give a conjecture for creation and annihilation
operators of FM strings for all roots of unity. We connect our findings with
the 'string-charge duality' in the thermodynamic limit, leading to a conjecture
for the imaginary part of the FM string centres with potential applications to
out-of-equilibrium physics.",2012.10224v3
2021-03-05,Interplay between Zhang-Rice singlets and high-spin states in a model for doped NiO$_2$ planes,"Superconductivity found in doped NdNiO$_2$ is puzzling as two local
symmetries of doped NiO$_2$ layers compete, with presumably far-reaching
implications for the involved mechanism: a cuprate-like regime with Zhang-Rice
singlets {\cblue is replaced by local triplet states at realistic values of
charge-transfer energy, which would suggest a rather different
superconductivity scenario from high-$T_c$ cuprates}. We address this
competition by investigating Ni$_4$O$_8$ clusters with periodic boundary
conditions in the parameter range relevant for the superconducting nickelates.
With increasing value of charge-transfer energy we observe upon hole doping the
expected crossover from the cuprate regime dominated by Zhang-Rice singlets to
the local triplet states. We find that smaller charge-transfer energy $\Delta$
is able to drive this change of the ground state character when realistic
values for nickel-oxygen repulsion $U_{dp}$ are taken into account. For large
values of the charge-transfer energy, oxygen orbitals are less important than
in superconducting cuprates as their spectral weight is found only at rather
high excitation energies. However, a second Ni($3d$) orbital can easily become
relevant, with either the $xy$ or the $3z^2-r^2$ orbitals contributing in
addition to the $x^2-y^2$ orbital {\cblue to the formation of triplet states.
In addition,} our result that $U_{dp}$ (acting between Ni and O) favors onsite
triplets implies that correlation effects beyond purely onsite interactions
should be taken into account when obtaining effective two-band models.",2103.03737v1
2021-06-20,Representations and Strategies for Transferable Machine Learning Models in Chemical Discovery,"Strategies for machine-learning(ML)-accelerated discovery that are general
across materials composition spaces are essential, but demonstrations of ML
have been primarily limited to narrow composition variations. By addressing the
scarcity of data in promising regions of chemical space for challenging targets
like open-shell transition-metal complexes, general representations and
transferable ML models that leverage known relationships in existing data will
accelerate discovery. Over a large set (ca. 1000) of isovalent transition-metal
complexes, we quantify evident relationships for different properties (i.e.,
spin-splitting and ligand dissociation) between rows of the periodic table
(i.e., 3d/4d metals and 2p/3p ligands). We demonstrate an extension to
graph-based revised autocorrelation (RAC) representation (i.e., eRAC) that
incorporates the effective nuclear charge alongside the nuclear charge
heuristic that otherwise overestimates dissimilarity of isovalent complexes. To
address the common challenge of discovery in a new space where data is limited,
we introduce a transfer learning approach in which we seed models trained on a
large amount of data from one row of the periodic table with a small number of
data points from the additional row. We demonstrate the synergistic value of
the eRACs alongside this transfer learning strategy to consistently improve
model performance. Analysis of these models highlights how the approach
succeeds by reordering the distances between complexes to be more consistent
with the periodic table, a property we expect to be broadly useful for other
materials domains.",2106.10768v1
2022-06-03,Energy Transfer into Period-Tripled States in Coupled Electromechanical Modes at Internal Resonance,"Efficient energy transfer often occurs between oscillation modes in a
resonator when they are tuned to internal resonance. We design the
eigenfrequencies of two vibrational modes of an electromechanical resonator to
be close to a ratio of 3:1 and demonstrate that the energy supplied to the
upper mode can be controllably transferred to the lower mode. With the lower
mode vibrating with a period tripled that of the upper mode, the discrete
time-translation symmetry imposed by the periodic drive is broken. The lower
mode settles into one of three stable period-tripled states with different
phases. This channel for energy transfer from the upper mode can be turned on
or off without changing system parameters. When the upper mode itself becomes
multistable under strong resonant or parametric drive, additional sets of
coexisting period-tripled states emerge in the lower mode. In the latter case,
we measure a total of 6 coexisting vibration states with identical amplitude
but phases differing by $\pi$/3. Excitation of coexisting states with three
different phases could open new opportunities in designing mechanical memory
based on ternary logic. Coupled resonators with period-tripled states can also
be used to model complex interacting systems with spin equals one.",2206.01630v3
2022-10-19,"Entering the Era of Measuring Sub-Galactic Dark Matter Structure: Accurate Transfer Functions for Axino, Gravitino & Sterile Neutrino Thermal Warm Dark Matter","We examine thermal warm dark matter (WDM) models that are being probed by
current constraints, and the relationship between the particle dark matter spin
and commensurate thermal history. We find significant corrections to the linear
matter power spectrum for given thermal WDM particle masses. Two primary
classes are examined: spin-1/2 particles (e.g., thermalized sterile neutrinos,
axinos) and thermal spin-3/2 particles (e.g., gravitinos or non-supersymmetric
particles). We present new transfer function fits for thermal WDM candidates in
particle mass regimes beyond the range of previous work, and at the scales of
current and upcoming constraints. Importantly, we find that the standard,
predominantly used, spin-1/2, thermal WDM particle produces a colder transfer
function than that determined in previous work. We also analyze the entropy
requirements for these WDM models to successfully produce observed dark matter
densities. We explore the early Universe physics of gravitinos as either
partially thermalized or fully thermalized species, which considerably changes
the particle dark matter candidates' thermalization history and effects on
structure formation. For the first time, we also calculate the transfer
function for thermal spin-3/2 WDM.",2210.10753v2
2019-04-27,Dry release transfer of graphene and few-layer h-BN by utilizing thermoplasticity of polypropylene carbonate for fabricating edge-contact-free van der Waals heterostructures,"The dry release transfer of two-dimensional (2D) materials such as graphene,
h-BN, and TMDs is a versatile method for fabricating high-quality van der Waals
heterostructures. Up until now, polydimethylpolysiloxane (PDMS) sheets have
been widely used for the dry release transfer of TMD materials. However, this
method has been known to have limitations that make it difficult to transfer
few-layer-thick graphene and h-BN because of the difficulty to fabricate these
materials on PDMS. As an alternative method, we demonstrate the dry release
transfer of single- and bi-layer graphene and few-layer h-BN in this study by
utilizing poly(propylene) carbonate (PPC) films. Because of the strong adhesion
between PPC and 2D materials around room temperature, we demonstrate that
single- to few-layer graphene, as well as few-layer h-BN, can be fabricated on
a spin-coated PPC film/290-nm-thick SiO2/Si substrate via the mechanical
exfoliation method. In addition, we show that these few-layer crystals are
clearly distinguishable using an optical microscope with the help of optical
interference. Because of the thermoplastic properties of PPC film, the adhesion
force between the 2D materials and PPC significantly decreases at about 70
{\deg}C. Therefore, we demonstrate that single- to few-layer graphene, as well
as few-layer h-BN flakes, on PPC can be easily dry-transferred onto another
h-BN substrate. This method enables a multilayer van der Waals heterostructure
to be constructed with a minimum amount of polymer contamination. We
demonstrate the fabrication of encapsulated h-BN/graphene/h-BN devices and
graphene/few-layer h-BN/graphene vertical-tunnel-junction devices using this
method. Since devices fabricated by this method do not require an edge-contact
scheme, our finding provide a simples method for constructing high-quality
graphene and h-BN-based van der Waals heterostructures.",1904.12170v1
2021-04-21,Neutron-proton pairing in the N=Z radioactive fp-shell nuclei 56Ni and 52Fe probed by pair transfer,"The isovector and isoscalar components of neutron-proton pairing are
investigated in the N=Z unstable nuclei of the \textit{fp}-shell through the
two-nucleon transfer reaction (p,$^3$He) in inverse kinematics. The combination
of particle and gamma-ray detection with radioactive beams of $^{56}$Ni and
$^{52}$Fe, produced by fragmentation at the GANIL/LISE facility, made it
possible to carry out this study for the first time in a closed and an
open-shell nucleus in the \textit{fp}-shell. The transfer cross-sections for
ground-state to ground-state (J=0$^+$,T=1) and to the first (J=1$^+$,T=0) state
were extracted for both cases together with the transfer cross-section ratios
$\sigma$(0$^+$,T=1) /$\sigma$(1$^+$,T=0). They are compared with second-order
distorted-wave born approximation (DWBA) calculations. The enhancement of the
ground-state to ground-state pair transfer cross-section close to mid-shell, in
$^{52}$Fe, points towards a superfluid phase in the isovector channel. For the
""deuteron-like"" transfer, very low cross-sections to the first (J=1$^+$,T=0)
state were observed both for \Ni\phe\, and \Fe\phe\, and are related to a
strong hindrance of this channel due to spin-orbit effect. No evidence for an
isoscalar deuteron-like condensate is observed.",2104.10708v1
2024-04-16,Nature of excitons and their ligand-mediated delocalization in nickel dihalide charge-transfer insulators,"The fundamental optical excitations of correlated transition-metal compounds
are typically identified with multielectronic transitions localized at the
transition-metal site, such as $dd$ transitions. In this vein, intense interest
has surrounded the appearance of sharp, below band-gap optical transitions,
i.e. excitons, within the magnetic phase of correlated Ni$^{2+}$ van der Waals
magnets. The interplay of magnetic and charge-transfer insulating ground states
in Ni$^{2+}$ systems raises intriguing questions on the roles of long-range
magnetic order and of metal-ligand charge transfer in the exciton nature, which
inspired microscopic descriptions beyond typical $dd$ excitations. Here we
study the impact of charge-transfer and magnetic order on the excitation
spectrum of the nickel dihalides (NiX$_2$, X $=$ Cl, Br, and I) using Ni-$L_3$
resonant inelastic x-ray scattering (RIXS). In all compounds, we detect sharp
excitations, analogous to the recently reported excitons, and assign them to
spin-singlet multiplets of octahedrally-coordinated Ni$^{2+}$ stabilized by
intra-atomic Hund's exchange. Additionally, we demonstrate that these excitons
are dispersive using momentum resolved RIXS. Our data evidence a
ligand-mediated multiplet dispersion, which is tuned by the charge-transfer gap
and independent of the presence of long-range magnetic order. This reveals the
mechanisms governing non-local interactions of on-site $dd$ excitations with
the surrounding crystal/magnetic structure, in analogy to ground state
superexchange. These measurements thus establish the roles of magnetic order,
self-doped ligand holes, and intersite coupling mechanisms for the properties
of $dd$ excitations in charge-transfer insulators.",2404.10818v1
2006-05-04,The effect of planetary migration on the corotation resonance,"The migration of a planet through a gaseous disc causes the locations of
their resonant interactions to drift and can alter the torques exerted between
the planet and the disc. We analyse the time-dependent dynamics of a
non-coorbital corotation resonance under these circumstances. The ratio of the
resonant torque in a steady state to the value given by Goldreich & Tremaine
(1979) depends essentially on two dimensionless quantities: a dimensionless
turbulent diffusion time-scale and a dimensionless radial drift speed. When the
drift speed is comparable to the libration speed and the viscosity is small,
the torque can become much larger than the unsaturated value in the absence of
migration, but is still proportional to the large-scale vortensity gradient in
the disc. Fluid that is trapped in the resonance and drifts with it acquires a
vortensity anomaly relative to its surroundings. If the anomaly is limited by
viscous diffusion in a steady state, the resulting torque is inversely
proportional to the viscosity, although a long time may be required to achieve
this state. A further, viscosity-independent, contribution to the torque comes
from fluid that streams through the resonant region. In other cases, torque
oscillations occur before the steady value is achieved. We discuss the
significance of these results for the evolution of eccentricity in
protoplanetary systems. We also describe the possible application of these
findings to the coorbital region and the concept of runaway (or type III)
migration. [Abridged]",0605138v1
2007-10-25,Explorando Sistemas Hamiltonianos II: A Natureza de Pontos de Equilibrio Degenerados,"Neste segundo artigo sobre sistemas Hamiltonianos, apresentamos o metodo da
explosao para a determinacao da natureza de pontos fixos (pontos de equilibrio
degenerados. Aplicamos o metodo a dois modelos hamiltonianos com um e dois
graus de liberdade, respectivamente. Primeiramente, analisamos um sistema
formado por um pendulo simples submetido a um torque externo constante T. Em
seguida, consideramos um sistema formado por um pendulo duplo com segmentos de
comprimentos e massas iguais, tambem submetidos a torques externos constantes e
nao nulos. A presenca de pontos de equilibrio degenerados nos casos dos
pendulos simples e duplo ocorre para certos valores dos torques externos.
  In this second article on Hamiltonian systems, we present the blow-up method
for the determination of the nature of degenerate fixed points (equilibrium
points). We apply the method to two hamiltonian models with one and two degrees
of freedom, respectively. Firstly we study a system formed by a simple pendulum
submitted to a constant external torque T. Then we consider a system formed by
a double pendulum of segments with equal lengths and masses, also submitted to
non-vanishing constant external torques. The presence of degenerate equilibrium
points in both cases of simple and double pendulums occurs for some values of
the external torques.",0710.4970v1
2008-05-29,Proton transport and torque generation in rotary biomotors,"We analyze the dynamics of rotary biomotors within a simple
nano-electromechanical model, consisting of a stator part and a ring-shaped
rotor having twelve proton-binding sites. This model is closely related to the
membrane-embedded F$_0$ motor of adenosine triphosphate (ATP) synthase, which
converts the energy of the transmembrane electrochemical gradient of protons
into mechanical motion of the rotor. It is shown that the Coulomb coupling
between the negative charge of the empty rotor site and the positive stator
charge, located near the periplasmic proton-conducting channel (proton source),
plays a dominant role in the torque-generating process. When approaching the
source outlet, the rotor site has a proton energy level higher than the energy
level of the site, located near the cytoplasmic channel (proton drain). In the
first stage of this torque-generating process, the energy of the
electrochemical potential is converted into potential energy of the
proton-binding sites on the rotor. Afterwards, the tangential component of the
Coulomb force produces a mechanical torque. We demonstrate that, at low
temperatures, the loaded motor works in the shuttling regime where the energy
of the electrochemical potential is consumed without producing any
unidirectional rotation. The motor switches to the torque-generating regime at
high temperatures, when the Brownian ratchet mechanism turns on. In the
presence of a significant external torque, created by ATP hydrolysis, the
system operates as a proton pump, which translocates protons against the
transmembrane potential gradient. Here we focus on the F$_0$ motor, even though
our analysis is applicable to the bacterial flagellar motor.",0805.4544v1
2010-09-23,A new closed-loop output error method for parameter identification of robot dynamics,"Off-line robot dynamic identification methods are mostly based on the use of
the inverse dynamic model, which is linear with respect to the dynamic
parameters. This model is sampled while the robot is tracking reference
trajectories that excite the system dynamics. This allows using linear
least-squares techniques to estimate the parameters. The efficiency of this
method has been proved through the experimental identification of many
prototypes and industrial robots. However, this method requires the joint
force/torque and position measurements and the estimate of the joint velocity
and acceleration, through the bandpass filtering of the joint position at high
sampling rates. The proposed new method requires only the joint force/torque
measurement. It is a closed-loop output error method where the usual joint
position output is replaced by the joint force/torque. It is based on a
closed-loop simulation of the robot using the direct dynamic model, the same
structure of the control law, and the same reference trajectory for both the
actual and the simulated robot. The optimal parameters minimize the 2-norm of
the error between the actual force/torque and the simulated force/torque. This
is a non-linear least-squares problem which is dramatically simplified using
the inverse dynamic model to obtain an analytical expression of the simulated
force/torque, linear in the parameters. A validation experiment on a 2
degree-of-freedom direct drive robot shows that the new method is efficient.",1009.4556v1
2011-06-01,Coupling between switching regulation and torque generation in bacterial flagellar motor,"The bacterial flagellar motor plays a crucial role in both bacterial
locomotion and chemotaxis. Recent experiments reveal that the switching
dynamics of the motor depends on the motor rotation speed, and thus the motor
torque, non-monotonically. Here we present a unified mathematical model which
models motor torque generation based on experimental torque-speed curves and
torque-dependent switching based on the conformational spread model. The model
successfully reproduces the observed switching rate as a function of the
rotation speed, and provides a generic physical explanation independent of most
details. A stator affects the switching dynamics through two mechanisms:
accelerating the conformation flipping rates of individual rotor switching
units, which favours slower motor speed and thus increasing torque; and
affecting more switching units within unit time, which favours faster speed.
Consequently, the switching rate shows a maximum at intermediate speed. Our
model predicts that a motor switches more often with more stators. The
load-switching relation may serve as a mechanism for sensing the physical
environment, similar to the chemotaxis system for sensing the chemical
environment. It may also coordinate the switch dynamics of motors within a
cell.",1106.0176v2
2011-10-10,Forward-backward flow correlations in relativistic heavy-ion collisions,"We discuss the torque effect in the initial fireball formed in relativistic
heavy-ion collisions, manifesting itself, on the event-by-event basis, in a
relative angle between the principal axes of the transverse momentum
distributions in the forward and backward rapidity regions. The torque follows
from two natural features: 1) the sources of particles (e.g. wounded nucleons)
emit predominantly in their forward hemispheres, and 2) there exist
fluctuations in the transverse distribution of sources from the two colliding
nuclei. On the average, the standard event-by-event deviation of the relative
torque angle is about 20 degrees for the central and 10 degrees for the
mid-peripheral collisions. The hydrodynamic expansion of a torqued fireball
leads to a torqued collective flow of the fluid, which, in turn, yields torqued
principal axes of the transverse-momentumdistributions at different rapidities.
We discuss experimental measures based on cumulants involving particles in
different rapidity regions, which allow for a quantitative extraction of the
effect from the experimental data. We estimate the non-flow contributions from
resonance decays with the help of THERMINATOR.",1110.2140v2
2012-07-30,Migration rates of planets due to scattering of planetesimals,"Planets migrate due to the recoil they experience from scattering solid
(planetesimal) bodies. To first order, the torques exerted by the interior and
exterior disks cancel, analogous to the cancellation of the torques from the
gravitational interaction with the gas (type I migration). Assuming the
dispersion-dominated regime and power-laws characterized by indices {\alpha}
and {\beta} for the surface density and eccentricity profiles, we calculate the
net torque on the planet. We consider both distant encounters and close
(orbit-crossing) encounters. We find that the close and distant encounter
torques have opposite signs with respect to their {\alpha} and {\beta}
dependences; and that the torque is especially sensitive to the eccentricity
gradient ({\beta}). Compared to type-I migration due to excitation of density
waves, the planetesimal-driven migration rate is generally lower due to the
lower surface density of solids in gas-rich disk, although this may be
partially or fully offset when their eccentricity and inclination are small.
Allowing for the feedback of the planet on the planetesimal disk through
viscous stirring, we find that under certain conditions a self-regulated
migration scenario emerges, in which the planet migrates at a steady pace that
approaches the rate corresponding to the one-sided torque. If the local
planetesimal disk mass to planet mass ratio is low, however, migration stalls.
We quantify the boundaries separating the three migration regimes.",1207.7104v1
2013-05-28,Electric Field Driven Torque in ATP Synthase,"Fo-ATP synthase (Fo) is a rotary motor that converts potential energy from
ions, usually protons, moving from high- to low-potential sides of a membrane
into torque and rotary motion. Here we propose a mechanism whereby electric
fields emanating from the proton entry and exit channels act on asymmetric
charge distributions in the c-ring, due to protonated and deprotonated sites,
and drive it to rotate. The model predicts a scaling between time-averaged
torque and proton motive force, which can be hindered by mutations that
adversely affect the channels. The torque created by the c-ring of Fo drives
the gamma-subunit to rotate within the ATP-producing complex (F1) overcoming,
with the aid of thermal fluctuations, an opposing torque that rises and falls
with angular position. Using the analogy with thermal Brownian motion of a
particle in a tilted washboard potential, we compute ATP production rates vs.
proton motive force. The latter shows a minimum, needed to drive ATP
production, which scales inversely with the number of proton binding sites on
the c-ring.",1305.6590v5
2013-06-04,"Investigations of the torque anomaly in an annular sector. I. Global calculations, scalar case","In an attempt to understand a recently discovered torque anomaly in quantum
field theory with boundaries, we calculate the Casimir energy and torque of a
scalar field subject to Dirichlet boundary conditions on an annular sector
defined by two coaxial cylinders intercut by two planes through the axis. In
this model the particularly troublesome divergence at the cylinder axis does
not appear, but new divergences associated with the curved boundaries are
introduced. All the divergences associated with the volume, the surface area,
the corners, and the curvature are regulated by point separation either in the
direction of the axis of the cylinder or in the (Euclidean) time; the full
divergence structure is isolated, and the remaining finite energy and torque
are extracted. Formally, only the regulator based on axis splitting yields the
expected balance between energy and torque. Because of the logarithmic
curvature divergences, there is an ambiguity in the linear dependence of the
energy on the wedge angle; if the terms constant and linear in this angle are
removed by a process of renormalization, the expected torque-energy balance is
preserved.",1306.0866v1
2013-11-17,Gravity gradient torque of spacecraft orbiting asteroids,"Purpose: This paper presents a full fourth-order model of the gravity
gradient torque of spacecraft around asteroids by taking into consideration of
the inertia integrals of the spacecraft up to the fourth order, which is an
improvement of the previous fourth-order model of the gravity gradient torque.
Design, methodology and approach: The fourth-order gravitational potential of
the spacecraft is derived based on Taylor expansion. Then the expression of the
gravity gradient torque in terms of gravitational potential derivatives is
derived. By using the formulation of the gravitational potential, explicit
formulations of the full fourth-order gravity gradient torque are obtained.
Then a numerical simulation is carried out to verify our model. Findings: We
find that our model is more sound and precise than the previous fourth-order
model due to the consideration of higher-order inertia integrals of the
spacecraft. Numerical simulation results show that the motion of the previous
fourth-order model is quite different from the exact motion, while our full
fourth-order model fits the exact motion very well. Our full fourth-order model
is precise enough for high-precision attitude dynamics and control around
asteroids. Practical implications: This high-precision model is of importance
for the future asteroids missions for scientific explorations and near-Earth
objects mitigation. Originality and value: In comparison with the previous
model, a gravity gradient torque model around asteroids that is more sound and
precise is established. This model is valuable for high-precision attitude
dynamics and control around asteroids.",1311.4127v1
2014-03-18,Equilibria of a charged artificial satellite subject to gravitational and Lorentz torques,"Attitude Dynamics of a rigid artificial satellite subject to gravity gradient
and Lorentz torques in a circular orbit is considered. Lorentz torque is
developed on the basis of the electrodynamic effects of the Lorentz force
acting on the charged satellite's surface. We assume that the satellite is
moving in Low Earth Orbit (LEO) in the geomagnetic field which is considered as
a dipole model. Our model of the torque due to the Lorentz force is developed
for a general shape of artificial satellite, and the nonlinear differential
equations of Euler are used to describe its attitude orientation. All
equilibrium positions are determined and {their} existence conditions are
obtained. The numerical results show that the charge $q$ and radius $\rho_0$ of
the charged center of satellite provide a certain type of semi passive control
for the attitude of satellite. The technique for such kind of control would be
to increase or decrease the electrostatic radiation screening of the satellite.
The results {obtained} confirm that the change in charge can effect the
magnitude of the Lorentz torque, which may affect the satellite's control.
Moreover, the relation between the magnitude of the Lorentz torque and
inclination of the orbits is investigated.",1405.3542v1
2015-08-31,Fast migration of low-mass planets in radiative discs,"Low-mass planets are known to undergo Type I migration and this process must
have played a key role during the evolution of planetary systems. Analytical
formulae for the disc torque have been derived assuming that the planet evolves
on a fixed circular orbit. However, recent work has shown that in isothermal
discs, a migrating protoplanet may also experience dynamical corotation torques
that scale with the planet drift rate. The aim of this study is to examine
whether dynamical corotation torques can also affect the migration of low-mass
planets in non-isothermal discs. We performed 2D radiative hydrodynamical
simulations to examine the orbital evolution outcome of migrating protoplanets
as a function of disc mass. We find that a protoplanet can enter a fast
migration regime when it migrates in the direction set by the entropy-related
horseshoe drag and when the Toomre stability parameter is less than a threshold
value below which the horseshoe region contracts into a tadpole-like region. In
that case, an underdense trapped region appears near the planet, with an
entropy excess compared to the ambient disc. If the viscosity and thermal
diffusivity are small enough so that the entropy excess is conserved during
migration, the planet then experiences strong corotation torques arising from
the material flowing across the planet orbit. During fast migration, we observe
that a protoplanet can pass through the zero-torque line predicted by static
torques. We also find that fast migration may help in disrupting the
mean-motion resonances that are formed by convergent migration of embryos.",1508.07817v1
2015-10-06,Direct numerical simulation of Taylor-Couette flow with grooved walls: torque scaling and flow structure,"We present direct numerical simulations of Taylor-Couette flow with grooved
walls at a fixed radius ratio $\eta=r_i/r_o=0.714$ with inner cylinder Reynolds
number up to $Re_i=3.76\times10^4$, corresponding to Taylor number up to
$Ta=2.15\times10^9$. The grooves are axisymmetric V-shaped obstacles attached
to the wall with a tip angle of $90^\circ$. Results are compared to the smooth
wall case in order to investigate the effects of grooves on Taylor-Couette
flow. We focus on the effective scaling laws for the torque, flow structures,
and boundary layers. It is found that, when the groove height is smaller than
the boundary layer thickness, the torque is the same as that of the smooth wall
cases. With increasing $Ta$, the boundary layer thickness becomes smaller than
the groove height. Plumes are ejected from the tips of the grooves and
secondary circulations between the latter are formed. This is associated to a
sharp increase of the torque and thus the effective scaling law for the torque
vs. $Ta$ becomes much steeper. Further increasing $Ta$ does not result in an
additional slope increase. Instead, the effective scaling law saturates to the
""ultimate"" regime effective exponents seen for smooth walls. It is found that
even though after saturation the slope is the same as for the smooth wall case,
the absolute value of torque is increased, and the more the larger size of the
grooves.",1510.01608v2
2016-03-31,Disentangling the origins of torque enhancement through wall roughness in Taylor-Couette turbulence,"Direct numerical simulations (DNSs) are performed to analyze the global
transport properties of turbulent Taylor-Couette flow with inner rough wall up
to Taylor number $Ta=10^{10}$. The dimensionless torque $Nu_\omega$ shows an
effective scaling of $Nu_\omega \propto Ta^{0.42\pm0.01}$, which is steeper
than the ultimate regime effective scaling $Nu_\omega \propto Ta^{0.38}$ seen
for smooth inner and outer walls. It is found that at the inner rough wall, the
dominant contribution to the torque comes from the pressure forces on the
radial faces of the rough elements; while viscous shear stresses on the rough
surfaces contribute little to $Nu_\omega$. Thus, the log layer close to the
rough wall depends on the roughness length scale, rather than on the viscous
length scale. We then separate the torque contributed from the smooth inner
wall and the rough outer wall. It is found that the smooth wall torque scaling
follows $Nu_s \propto Ta_s^{0.38\pm0.01}$, in excellent agreement with the case
where both walls are smooth. In contrast, the rough wall torque scaling follows
$Nu_r \propto Ta_r^{0.47\pm0.03}$, very close to the pure ultimate regime
scaling $Nu_\omega \propto Ta^{1/2}$. The energy dissipation rate at the wall
of inner rough cylinder decreases significantly as a consequence of the wall
shear stress reduction caused by the flow separation at the rough elements. On
the other hand, the latter shed vortices in the bulk that are transported
towards the outer cylinder and dissipated. Compared to the purely smooth case,
the inner wall roughness renders the system more bulk dominated and thus
increases the effective scaling exponent.",1603.09605v2
2016-05-08,Extended Transiting Disks and Rings Around Planets and Brown Dwarfs: Theoretical Constraints,"Newly formed planets (or brown dwarfs) may possess disks or rings that occupy
an appreciable fraction of the planet's Hill sphere and extend beyond the
Laplace radius, where the tidal torque from the host star dominates over the
torque from the oblate planet. Such a disk/ring can exhibit unique, detectable
transit signatures, provided that the disk/ring is significantly misaligned
with the orbital plane of the planet. There exists tentative evidence for an
extended ring system around the young K5 star 1 SWASP J140747-354542. We
present a general theoretical study of the inclination (warp) profile of
circumplanetary disks under the combined influences of the tidal torque from
the central star, the torque from the oblate planet and the self-gravity of the
disk. We calculate the steady-state warp profile (""generalized Laplace
Surface"") and investigate the condition for coherent precession of the disk. We
find that to maintain non-negligible misalignment between the extended outer
disk and the planet's orbital plane, and to ensure coherent disk precession,
the disk surface density must be sufficiently large so that the self-gravity
torque overcomes the tidal torque from the central star. Our analysis and
quantitative results can be used to constrain the parameters of transiting
circumplanetary disks that may be detected in the future.",1605.02365v2
2016-10-27,Precession-torque-driven domain-wall motion in out-of-plane materials,"Domain-wall (DW) motion in magnetic nanostrips is intensively studied, in
particular because of the possible applications in data storage. In this work,
we will investigate a novel method of DW motion using magnetic field pulses,
with the precession torque as the driving mechanism. We use a one dimensional
(1D) model to show that it is possible to drive DWs in out-of-plane materials
using the precession torque, and we identify the key parameters that influence
this motion. Because the DW moves back to its initial position at the end of
the field pulse, thereby severely complicating direct detection of the DW
motion, depinning experiments are used to indirectly observe the effect of the
precession torque. The 1D model is extended to include an energy landscape in
order to predict the influence of the precession torque in the depinning
experiments. Although preliminary experiments did not yet show an effect of the
precession torque, our calculations indicate that depinning experiments can be
used to demonstrate this novel method of DW motion in out-of-plane materials,
which even allows for coherent motion of multiple domains when the
Dzyaloshinskii-Moriya interaction is taken into account.",1610.08852v2
2017-04-07,Alignment of Irregular Grains by Mechanical Torques,"We study the alignment of irregular dust grains by mechanical torques due to
the drift of grains through the ambient gas. We first calculate mechanical
torques (MATs) resulting from specular reflection of gas atoms for seven
irregular shapes: one shape of mirror symmetry, three highly irregular shapes
(HIS), and three weakly irregular shapes (WIS). We find that the grain with
mirror symmetry experiences negligible MATs due to its mirror-symmetry
geometry. Three highly irregular shapes can produce strong MATs which exhibit
some generic properties as radiative torques, while three weakly irregular
shapes produce less efficient MATs. We then study grain alignment by MATs for
the different angles between the drift velocity and the ambient magnetic field,
for paramagnetic and superparamagnetic grains assuming efficient internal
relaxation. We find that for HIS grains, MATs can align subsonically drifting
grains in the same way as radiative torques, with low-J and high-J attractors.
For supersonic drift, MATs can align grains with low-J and high-J attractors,
analogous to radiative alignment by anisotropic radiation. We also show that
the joint action of MATs and magnetic torques in grains with iron inclusions
can lead to perfect MAT alignment. Our results point out the potential
importance of MAT alignment for HIS grains predicted by the analytical model of
Lazarian \& Hoang (2007b), although more theoretical and observational studies
are required due to uncertainty in the shape of interstellar grains. We outline
astrophysical environments where MAT alignment is potentially important.",1704.02256v2
2018-01-24,Torques Induced by Scattered Pebble-flow in Protoplanetary Disks,"Fast inward migration of planetary cores is a common problem in the current
planet formation paradigm. Even though dust is ubiquitous in protoplanetary
disks, its dynamical role in the migration history of planetary embryos has not
been assessed. In this Letter, we show that the scattered pebble-flow induced
by a low-mass planetary embryo leads to an asymmetric dust-density distribution
that is able to exert a net torque. By analyzing a large suite of multifluid
hydrodynamical simulations addressing the interaction between the disk and a
low-mass planet on a fixed circular orbit, and neglecting dust feedback onto
the gas, we identify two different regimes, gas- and gravity-dominated, where
the scattered pebble-flow results in almost all cases in positive torques. We
collect our measurements in a first torque map for dusty disks, which will
enable the incorporation of the effect of dust dynamics on migration into
population synthesis models. Depending on the dust drift speed, the dust-to-gas
mass ratio/distribution and the embryo mass, the dust-induced torque has the
potential to halt inward migration or even induce fast outward migration of
planetary cores. We thus anticipate that dust-driven migration could play a
dominant role during the formation history of planets. Because dust torques
scale with disk metallicity, we propose that dust-driven outward migration may
enhance the occurrence of distant giant planets in higher-metallicity systems.",1801.07913v2
2018-04-26,The Sublimative Torques of Jupiter Family Comets and Mass Wasting Events on Their Nuclei,"Sublimative outgassing of comets produces torques that alter the rotation
state of their nuclei. Recently, parameterized sublimative torque models have
been developed to study rotation state changes of individual comet nuclei and
populations of cometary bodies. However, these models simplify the interactions
between the escaping gas and cometary surface into only a few parameters that
hide the details of these complex interactions. Here we directly compare the
X-parameter model (Samarasinha & Mueller, 2013) with the SYORP model (Steckloff
& Jacobson, 2016) to tease out insights into the details of the gas-surface
interactions driving sublimative torques. We find that, for both of these
models to accurately model sublimative torques, the number of sublimating
molecules that contribute to the net torque is largely independent of the
detailed shape and activity of the nucleus, but rather depends primarily on the
size of the nucleus and the effective heliocentric distance of the comet. We
suggest that cometary activity must be largely restricted to regions of steep
gravitational surface slopes (above the angle of repose), where mass wasting
can refresh activity by shedding mantles of refractory materials and exposing
fresh volatiles. We propose a new classification scheme for comets based on the
frequency of this mass-wasting process (relative to the timescale of activity
fading): quasi-equilibrium, episodic, quasi-dormant, and extinct.",1804.10232v1
2018-07-17,Optical torque on a two-level system near a strongly nonreciprocal medium,"We investigate the quantum optical torque on an atom interacting with an
inhomogeneous electromagnetic environment described by the most general linear
constitutive relations. The atom is modeled as a two-level system prepared in
an arbitrary initial energy state. Using the Heisenberg equation of motion
(HEM) and under the Markov approximation, we show that the optical torque has a
resonant and non-resonant part, associated respectively with a
spontaneous-emission process and Casimir-type interactions with the quantum
vacuum, which can both be written explicitly in terms of the system Green
function. Our formulation is valid for any inhomogeneous, dissipative,
dispersive, nonreciprocal, and bianisotropic structure. We apply this general
theory to a scenario in which the atom interacts with a material characterized
by strong nonreciprocity and modal unidirectionality. In this case, the main
decay channel of the atom energy is represented by the unidirectional surface
waves launched at the nonreciprocal material-vacuum interface. To provide
relevant physical insight into the role of these unidirectional surface waves
in the emergence of non-trivial optical torque, we derive closed-form
expressions for the induced torque under the quasi-static approximation.
Finally, we investigate the equilibrium states of the atom polarization, along
which the atom spontaneously tends to align due to the action of the torque.
Our theoretical predictions may be experimentally tested with cold Rydberg
atoms and superconducting qubits near a nonreciprocal material. We believe that
our general theory may find broad application in the context of nano-mechanical
and bio-mechanical systems.",1807.06643v2
2019-04-16,Importance of fluid inertia for the orientation of spheroids settling in turbulent flow,"How non-spherical particles orient as they settle in a flow has important
practical implications in a number of scientific and engineering problems. In a
quiescent fluid, a slowly settling particle orients so that it settles with its
broad side first. This is an effect of the torque due to convective inertia of
the fluid set in motion by the settling particle, which maximises the drag
experienced by the particle. Turbulent flows tend to randomise the particle
orientation. Recently the settling of non-spherical particles in turbulence was
analysed neglecting the effect of convective fluid inertia, but taking into
account the effect of the turbulent fluid-velocity gradients on the particle
orientation. These studies reached the opposite conclusion, namely that a rod
settles preferentially with its tip first, wheras a disk settles with its edge
first, therefore minimizing the drag on the particle. Here, we consider both
effects, the convective inertial torque as well as the torque due to
fluctuating velocity gradients, and ask under which circumstances either one or
the other dominate. To this end we estimate the ratio of the magnitudes of the
two torques. Our estimates suggest that the fluid-inertia torque prevails in
high-Reynolds number flows. In this case non-spherical particles are expected
to settle with a maximal drag. But when the Reynolds number is small then the
torque due to fluid-velocity gradients may dominate, causing the particle to
settle with its broad side first.",1904.07575v2
2019-04-29,Oscillatory migration of accreting protoplanets driven by a 3D distortion of the gas flow,"Context. The dynamics of a low-mass protoplanet accreting solids is
influenced by the heating torque, which was found to suppress inward migration
in protoplanetary disks with constant opacities.
  Aims. We investigate the differences of the heating torque between disks with
constant and temperature-dependent opacities.
  Methods. Interactions of a super-Earth-sized protoplanet with the gas disk
are explored using 3D radiation hydrodynamic simulations.
  Results. Accretion heating of the protoplanet creates a hot underdense region
in the surrounding gas, leading to misalignment of the local density and
pressure gradients. As a result, the 3D gas flow is perturbed and some of the
streamlines form a retrograde spiral rising above the protoplanet. In the
constant-opacity disk, the perturbed flow reaches a steady state and the
underdense gas responsible for the heating torque remains distributed in
accordance with previous studies. If the opacity is non-uniform, however, the
differences in the disk structure can lead to more vigorous streamline
distortion and eventually to a flow instability. The underdense gas develops a
one-sided asymmetry which circulates around the protoplanet in a retrograde
fashion. The heating torque thus strongly oscillates in time and does not on
average counteract inward migration.
  Conclusions. The torque variations make the radial drift of the protoplanet
oscillatory, consisting of short intervals of alternating rapid inward and
outward migration. We speculate that transitions between the positive and
oscillatory heating torque may occur in specific disk regions susceptible to
vertical convection, resulting in the convergent migration of multiple
planetary embryos.",1904.12497v1
2019-07-23,When Cold Radial Migration is Hot: Constraints from Resonant Overlap,"It is widely accepted that stars in a spiral disk, like the Milky Way's, can
radially migrate on order a scale length over the disk's lifetime. With the
exception of cold torquing, also known as ""churning,"" processes that contribute
to the radial migration of stars are necessarily associated with kinematic
heating. Additionally, it is an open question whether or not an episode of cold
torquing is kinemically cold over long radial distances. This study uses a
suite of analytically based simulations to investigate the dynamical response
when stars are subject to cold torquing and are also resonant with an
ultraharmonic. Model results demonstrate that these populations are
kinematically heated and have RMS changes in orbital angular momentum around
corotation that can exceed those of populations that do not experience resonant
overlap. Thus, kinematic heating can occur during episodes of cold torquing. In
a case study of a Milky Way-like disk with an exponential surface density
profile and flat rotation curve, up to 40% of cold torqued stars in the solar
cylinder experience resonant overlap. This fraction increases toward the
galactic center. To first approximation, the maximum radial excursions from
cold torquing depend only on the strength of the spiral pattern and the
underlying rotation curve. This work places an upper limit to these excursions
to be the distance between the ultraharmonics, otherwise radial migration near
corotation can kinematically heat. The diffusion rate for kinematically cold
radial migration is thus constrained by limiting the step size in the random
walk approximation.",1907.10100v1
2019-11-08,Optimal Torque Control of Permanent Magnet Synchronous Motors Using Adaptive Dynamic Programming,"In this study, a new approach based on adaptive dynamic programming (ADP) is
proposed to control permanent magnet synchronous motors (PMSMs). The objective
of this paper is to control the torque and consequently the speed of a PMSM
when an unknown load torque is applied to it. The proposed controller achieves
a fast transient response, low ripples and small steady-state error. The
control algorithm uses two neural networks, called critic and actor. The former
is utilized to evaluate the cost and the latter is used to generate control
signals. The training is done once offline and the calculated optimal weights
of actor network are used in online control to achieve fast and accurate torque
control of PMSMs. This algorithm is compared with field oriented control (FOC)
and direct torque control based on space vector modulation (DTC-SVM).
Simulations and experimental results show that the proposed algorithm provides
desirable results under both accurate and uncertain modeled dynamics. Although
the performance of FOC method is comparable with ADP under nominal conditions,
the torque and speed response of ADP is better than FOC under realistic
scenarios, that is, when parameter uncertainties exist.",1911.03534v4
2020-06-17,Flame- and flow-conditioned vorticity transport in premixed swirl combustion,"This paper presents an experimental analysis of flame-induced enstrophy
transport in premixed swirl combustion at Karlovitz numbers between 20-50. Such
flames posses a large-scale pressure field that -- in addition to the pressure
fields associated with small-scale turbulent vortices -- can interact with
density gradients to produce baroclinic torque. Simultaneous tomographic
particle image velocimetry and formaldehyde planar laser induced fluorescence
measurements are used to obtain high-resolution velocity and progress-variable
fields. This allows statistical evaluation of the various terms in the
enstrophy transport equation. The impact of small- and large-scale pressure
gradients is assessed by conditioning the baroclinic torque on the position of
the fluid within the instantaneous flame front, within the flame brush, and
axially within the combustor. At all conditions studied, the baroclinic torque
was a significant contributor to enstrophy transport, with a comparable
magnitude to vortex stretching and viscous diffusion. Enstrophy attenuation and
production by baroclinic torque tended to occur towards the reactant and
product sides of the instantaneous flame surface, respectively. However, the
value of the baroclinic torque also depended equally strongly on the position
in the combustor. Hence, both small- and large-scale pressure fields can result
in significant enstrophy changes through baroclinic torque. This is evidence
both that flame-induced vorticity dynamics are significant in swirl combustion,
and that large-scale geometry-dependent flow fields can impact flame-generated
turbulence.",2006.09940v1
2020-11-20,Perturbation analysis of baroclinic torque in low-Mach-number flows,"In this paper, we propse a series expansion of the baroclinic torque in
low-Mach-number flows, so that the accuracy and universality of any buoyancy
term could be examined analytically, and new types of buoyancy terms could be
constructed and validated. We first demonstrate that the purpose of introducing
a buoyancy term is to approximate the baroclinic torque, and straightforwardly
the accuracy of any buoyancy term could be measured by the deviation of its
curl from the baroclinic torque. Then a regular perturbation method is
introduced for the elliptic equation of the hydrodynamic pressure in
low-Mach-number flows, resulting in a sequence of Poisson equations, whose
solutions lead to the series representation of the baroclinic torque and the
new types of buoyancy terms. With the error definition of buoyancy terms and
the series representation of the baroclinic torque, the classical gravitational
and centrifugal buoyancy term, as well as some other previously proposed
buoyancy terms are revisited. Finally, numerical simulations confirm that, with
a decreasing density variation or an increasing order of our newly proposed
buoyancy term, the simplified equations with one of the new types of buoyancy
terms can converge to the original low-Mach-number equations.",2011.10246v3
2021-01-01,Design and Actuator Optimization of Lightweight and Compliant Knee Exoskeleton for Mobility Assistance of Children with Crouch Gait,"Pediatric exoskeletons offer great promise to increase mobility for children
with crouch gait caused by cerebral palsy. A lightweight, compliant and
user-specific actuator is critical for maximizing the benefits of an
exoskeleton to users. To date, pediatric exoskeletons generally use the same
actuators as adult exoskeletons, which are heavy and resistive to natural
movement. There is yet no easy way for robotic exoskeletons to accommodate the
changes in design requirements that occur as a child ages. We developed a
lightweight (1.65 kg unilateral mass) and compliant pediatric knee exoskeleton
with a bandwidth of 22.6 Hz that can provide torque assistance to children with
crouch gait using high torque density motor. Experimental results demonstrated
that the robot exhibited low mechanical impedance (1.79 Nm average backdrive
torque) under the unpowered condition and 0.32 Nm with zero-torque tracking
control. Root mean square (RMS) error of torque tracking result is less than
0.73 Nm (5.7% with respect to 12 Nm torque). To achieve optimal age-specific
performance, we proposed the first optimization framework that considered both
motor and transmission of the actuator system that can produce optimal settings
for children between 3 and 18 years old. The optimization generated an optimal
motor air gap radius that monotonically increases with age from 0.011 to 0.033
meters, and optimal gear ratio varies from 2.6 to 11.6 (3-13 years old) and
11.6 to 10.2 (13-18 years old), leading to actuators of minimal mass.",2101.00289v1
2021-03-27,Self-adaptive Torque Vectoring Controller Using Reinforcement Learning,"Continuous direct yaw moment control systems such as torque-vectoring
controller are an essential part for vehicle stabilization. This controller has
been extensively researched with the central objective of maintaining the
vehicle stability by providing consistent stable cornering response. The
ability of careful tuning of the parameters in a torque-vectoring controller
can significantly enhance vehicle's performance and stability. However, without
any re-tuning of the parameters, especially in extreme driving conditions e.g.
low friction surface or high velocity, the vehicle fails to maintain the
stability. In this paper, the utility of Reinforcement Learning (RL) based on
Deep Deterministic Policy Gradient (DDPG) as a parameter tuning algorithm for
torque-vectoring controller is presented. It is shown that, torque-vectoring
controller with parameter tuning via reinforcement learning performs well on a
range of different driving environment e.g., wide range of friction conditions
and different velocities, which highlight the advantages of reinforcement
learning as an adaptive algorithm for parameter tuning. Moreover, the
robustness of DDPG algorithm are validated under scenarios which are beyond the
training environment of the reinforcement learning algorithm. The simulation
has been carried out using a four wheels vehicle model with nonlinear tire
characteristics. We compare our DDPG based parameter tuning against a genetic
algorithm and a conventional trial-and-error tunning of the torque vectoring
controller, and the results demonstrated that the reinforcement learning based
parameter tuning significantly improves the stability of the vehicle.",2103.14892v1
2021-07-05,Acoustic radiation force and radiation torque beyond particles: Effects of non-spherical shape and Willis coupling,"Acoustophoresis deals with the manipulation of sub-wavelength scatterers in
an incident acoustic field. The geometric details of manipulated particles are
often neglected by replacing them with equivalent symmetric geometries such as
spheres, spheroids, cylinders or disks. It has been demonstrated that geometric
asymmetry, represented by Willis coupling terms, can strongly affect the
scattering of a small object, hence neglecting these terms may miss important
force contributions. In this work, we present a generalized formalism of
acoustic radiation force and radiation torque based on the polarizability
tensor, where Willis coupling terms are included to account for geometric
asymmetry. Following Gorkov's approach, the effects of geometric asymmetry are
explicitly formulated as additional terms in the radiation force and torque
expressions. By breaking the symmetry of a sphere along one axis using
intrusion and protrusion, we characterize the changes in the force and torque
in terms of partial components, associated with the direct and Willis Coupling
coefficients of the polarizability tensor. We investigate in detail the cases
of standing and travelling plane waves, showing how the equilibrium positions
and angles are shifted by these additional terms. We show that while the
contributions of asymmetry to the force are often negligible for small
particles, these terms greatly affect the radiation torque. Our presented
theory, providing a way of calculating radiation force and torque directly from
polarizability coefficients, shows that in general it is essential to account
for shape of objects undergoing acoustophoretic manipulation, and this may have
important implications for applications such as the manipulation of biological
cells.",2107.01775v1
2021-10-04,Willis coupling-induced acoustic radiation force and torque reversal,"Acoustic meta-atoms serve as the building blocks of metamaterials, with
linear properties designed to achieve functions such as beam steering, cloaking
and focusing. They have also been used to shape the characteristics of incident
acoustic fields, which led to the manipulation of acoustic radiation force and
torque for development of acoustic tweezers with improved spatial resolution.
However, acoustic radiation force and torque also depend on the shape of the
object, which strongly affects its scattering properties. We show that by
designing linear properties of an object using metamaterial concepts, the
nonlinear acoustic effects of radiation force and torque can be controlled.
Trapped objects are typically small compared to the wavelength, and are
described as particles, inducing monopole and dipole scattering. We extend such
models to a polarizability tensor including Willis coupling terms, as a measure
of asymmetry, capturing the significance of geometrical features. We apply our
model to a three-dimensional, sub-wavelength meta-atom with maximal Willis
coupling, demonstrating that the force and the torque can be reversed relative
to an equivalent symmetrical particle. By considering shape asymmetry in the
acoustic radiation force and torque, Gorkov's fundamental theory of
acoustophoresis is thereby extended. Asymmetrical shapes influence the acoustic
fields by shifting the stable trapping location, highlighting a potential for
tunable, shape-dependent particle sorting.",2110.01354v2
2021-12-30,A Test Bench For Evaluating Exoskeletons For Upper Limb Rehabilitation,"The potential of wearable robotics technology is undeniable. However,
quantifying its value is difficult. Various types of exoskeleton robots have
already been developed and tested for upper limb rehabilitation but,
evaluations are not standardized, particularly in pediatric rehabilitation.
This paper proposes a methodology for the quantitative evaluation of upper limb
exoskeletons that, like a test bench, would serve for replicable testing. We
determined the range of motion (ROM) and joint torques using both kinematic
modeling and experimental measurements (using sensors integrated into Dynamixel
actuators). The proposed test bench can provide an accurate range of motion
(ROM) and joint torques during the pronation-supination (PS) task. The range of
motion obtained with the physical prototype was approximately 156.26 +-
4.71{\deg} during the PS task, while it was approximately 146.84 +- 14.32{\deg}
for the multibody model. The results show that the average range of
experimental torques (0.28 +- 0.06 N.m) was overestimated by 40% and just 3.4%,
respectively, when compared to the average range of simulated torques (0.2 +-
0.05 N.m) and to the highest range of simulated torques (0.29 N.m). For the
experimental measurements, test-retest reliability was excellent (0.96-0.98)
within sessions and excellent (0.93) or good (0.81-0.86) between sessions.
Finally, the suggested approach provides a ROM close to the normal ROM
necessary during PS tasks. These results validate the measurements' accuracy
and underline the proposed methodology's relevance. The proposed test bench
could become a reference standard for evaluating exoskeletons. This study also
addresses a methodological aspect on the accurate assessment of joint torques
that can serve in applications such as the sizing of actuators in exoskeletons
or the non-invasive evaluation of muscle forces in the human body.",2112.14885v1
2022-01-03,Convectively driven decadal zonal accelerations in Earth's fluid core,"Azimuthal accelerations of cylindrical surfaces co-axial with the rotation
axis have been inferred to exist in Earth's fluid core on the basis of magnetic
field observations and changes in the length-of-day. These accelerations have a
typical timescale of decades. However, the physical mechanism causing the
accelerations is not well understood. Scaling arguments suggest that the
leading order torque averaged over cylindrical surfaces should arise from the
Lorentz force. Decadal fluctuations in the magnetic field inside the core,
driven by convective flows, could then force decadal changes in the Lorentz
torque and generate zonal accelerations. We test this hypothesis by
constructing a quasi-geostrophic model of magnetoconvection, with
thermally-driven flows perturbing a steady, imposed background magnetic field.
We show that when the Alfv\'{e}n number in our model is similar to that in
Earth's fluid core, temporal fluctuations in the torque balance are dominated
by the Lorentz torque, with the latter generating mean zonal accelerations. Our
model reproduces both fast, free Alfv\'{e}n waves and slow, forced
accelerations, with ratios of relative strength and relative timescale similar
to those inferred for the Earth's core. The temporal changes in the magnetic
field which drive the time-varying Lorentz torque are produced by the
underlying convective flows, shearing and advecting the magnetic field on a
timescale associated with convective eddies. Our results support the hypothesis
that temporal changes in the magnetic field deep inside Earth's fluid core
drive the observed decadal zonal accelerations of cylindrical surfaces through
the Lorentz torque.",2201.00846v1
2022-01-14,Evaluating Muscle Synergies with EMG Data and Physics Simulation in the Neurorobotics Platform,"Although we can measure muscle activity and analyze their activation
patterns, we understand little about how individual muscles affect the joint
torque generated. It is known that they are controlled by circuits in the
spinal cord, a system much less well understood than the cortex. Knowing the
contribution of the muscles towards a joint torque would improve our
understanding of human limb control. We present a novel framework to examine
the control of biomechanics using physics simulations informed by
electromyography (EMG) data. These signals drive a virtual musculoskeletal
model in the Neurorobotics Platform (NRP), which we then use to evaluate
resulting joint torques. We use our framework to analyze raw EMG data collected
during an isometric knee extension study to identify synergies that drive a
musculoskeletal lower limb model. The resulting knee torques are used as a
reference for genetic algorithms (GA) to generate new simulated activation
patterns. On the platform the GA finds solutions that generate torques matching
those observed. Possible solutions include synergies that are similar to those
extracted from the human study. In addition, the GA finds activation patterns
that are different from the the biological ones while still producing the same
knee torque. The NRP forms a highly modular integrated simulation platform
allowing these in silico experiments. We argue that our framework allows for
research of the neurobiomechanical control of muscles during tasks, which would
otherwise not be possible.",2201.05496v1
2022-01-31,An efficient procedure to predict the acoustophoresis of axisymmetric irregular particles above ultrasound transducer array,"Acoustic radiation force and torque arising from wave scattering are able to
translate and rotate matter without contact. However, the existing research
mainly focused on manipulating simple symmetrical geometries, neglecting the
significance of geometric features. For the non-spherical geometries, the shape
of the object strongly affects its scattering properties, and thus the
radiation force and torque as well as the acoustophoretic process. Here, we
develop a semi-analytical framework to calculate the radiation force and torque
exerted on the axisymmetric particles excited by a user-customized transducer
array based on a conformal transformation approach, capturing the significance
of the geometric features. The derivation framework is established under the
computation coordinate system (CCS), whereas the particle is assumed to be
static. For the dynamic processes, the rotation of particle is converted as the
opposite rotation of transducer array, achieved by employing a rotation
transformation to tune the incident driving field in the CCS. Later, the
obtained radiation force and torque in the CCS should be transformed back to
the observation coordinate system (OCS) for force and torque analysis. The
radiation force and torque exerted on particles with different orientations are
validated by comparing the full three-dimensional numerical solution in
different phase distributions. It is found that the proposed method presents
superior computational accuracy, high geometric adaptivity, and good robustness
to various geometric features, while the computational efficiency is more than
100 times higher than that of the full numerical method. Furthermore, it is
found that the dynamic trajectories of particles with different geometric
features are completely different, indicating that the geometric features can
be a potential degree of freedom to tune acoustophoretic process.",2201.13042v1
2022-08-03,Learning Fast and Precise Pixel-to-Torque Control,"In the field, robots often need to operate in unknown and unstructured
environments, where accurate sensing and state estimation (SE) becomes a major
challenge. Cameras have been used to great success in mapping and planning in
such environments, as well as complex but quasi-static tasks such as grasping,
but are rarely integrated into the control loop for unstable systems. Learning
pixel-to-torque control promises to allow robots to flexibly handle a wider
variety of tasks. Although they do not present additional theoretical
obstacles, learning pixel-to-torque control for unstable systems that that
require precise and high bandwidth control still poses a significant practical
challenge, and best practices have not yet been established. To help drive
reproducible research on the practical aspects of learning pixel-to-torque
control, we propose a platform that can flexibly represent the entire process,
from lab to deployment, for learning pixel-to-torque control on a robot with
fast, unstable dynamics: the vision-based Furuta pendulum. The platform can be
reproduced with either off-the-shelf or custom-built hardware. We expect that
this platform will allow researchers to quickly and systematically test
different approaches, as well as reproduce and benchmark case studies from
other labs. We also present a first case study on this system using DNNs which,
to the best of our knowledge, is the first demonstration of learning
pixel-to-torque control on an unstable system with update rates faster than 100
Hz. A video synopsis can be found online at https://youtu.be/S2llScfG-8E, and
in the supplementary material.",2208.02315v1
2023-01-23,How Ram Pressure Drives Radial Gas Motions in the Surviving Disk,"Galaxy evolution can be dramatically affected by the environment, especially
by the dense environment of a galaxy cluster. Recent observational studies show
that massive galaxies undergoing strong ram pressure stripping (RPS) also show
an enhanced frequency of nuclear activity. Here, we investigate this topic
using a suite of wind-tunnel hydrodynamical simulations of an individual
massive $M_\text{star} = 10^{11} M_\odot$ disk galaxy with 39 pc resolution and
including star formation and stellar feedback. We find that RPS increases the
inflow of gas to the galaxy centre regardless of the wind impact angle. This
increase is driven by the mixing of interstellar and non-rotating intracluster
media at all wind angles, and by increased torque on the inner disk gas, mainly
from local pressure gradients when the ICM wind has an edge-on component. In
turn, the increase in pressure torques is driven by rising gradient of ram
pressure. We estimate the black hole (BH) accretion using Bondi-Hoyle and
torque models, and compare it with the mass flux in the central 140 pc region.
We find that the torque model estimates much less accretion onto the BH of a
RPS galaxy than the Bondi-Hoyle estimator. However, we argue that both models
are incomplete because the commonly used torque model does not account for
torques caused by the gas distribution or local pressure gradients and the
Bondi-Hoyle estimator depends on the the sound speed of the hot gas, which
includes the ICM in stripped galaxies, thus a new estimator would be required.",2301.09652v2
2023-05-03,Quantifying the Impact of the Dust Torque on the Migration of Low-mass Planets,"Disk solids are critical in many planet formation processes, however, their
effect on planet migration remains largely unexplored. Here we assess for the
first time this important issue by building on the systematic measurements of
dust torques on an embedded planet by Benitez-Llambay & Pessah (2018). Adopting
standard models for the gaseous disk and its solid content, we quantify the
impact of the dust torque for a wide range of conditions describing the
disk/planet system. We show that the total torque can be positive and revert
inward planet migration for planetary cores with $M_{\rm p} \lesssim 10
M_\oplus$. We compute formation tracks for low-mass embryos for conditions
usually invoked when modeling planet formation processes. Our most important
conclusion is that dust torques can have a significant impact on the migration
and formation history of planetary embryos. The most important implications of
our findings are: $\it{i})$ For nominal dust-to-gas mass ratios $\epsilon
\simeq 0.01$, low-mass planets migrate outwards beyond the water ice-line if
most of the mass in solids is in particles with Stokes numbers St $\simeq 0.1$.
$\it{ii})$. For $\epsilon \gtrsim 0.02-0.05$, solids with small Stokes numbers,
St $\simeq 0.01$, can play a dominant role if most of the mass is in those
particles. $\it{iii})$ Dust torques have the potential to enable low-mass
planetary cores formed in the inner disk to migrate outwards and act as the
seed for massive planets at distances of tens of au.",2305.02140v1
2023-05-05,Physics-informed neural network for modelling force and torque fluctuations in a random array of bidisperse spheres,"We present a physics-informed neural network (PINN) model to predict the
hydrodynamic force and torque fluctuations in a random array of stationary
bidisperse spheres. The PINN model is formulated based on two hypotheses: (i)
pairwise interaction assumption that approximates the total force/torque
exerted on a target sphere by linear superposition of individual contributions
from a finite number of influential neighbors; (i) unified function
representation that suggests a single functional form to describe the
contribution from different neighbors based on the observation of probability
distribution maps obtained with various binary interaction modes in bidisperse
particle-laden flows. We accordingly establish a compact PINN architecture to
evaluate individual force/torque contribution of influential neighbors through
the same neural network block which tremendously reduces the number of unknown
parameters, and ultimately compute the total force/torque exerted on target
sphere by their weighted sum. We compare the model predictions to PR-DNS data
of eight different cases in a range of Reynolds number $1\leq Re\leq100$, solid
volume fraction $10\%\leq\phi\leq40\%$, sphere diameter ratio $1.5\leq
d_l^*/d_s^*\leq2.5$ and volume ratio $1\leq V_l^*/V_s^*\leq 4$, which
demonstrates excellent performance with an optimal $R^2\approx0.9$ for both
force and torque predictions. We establish a universal model that is applicable
within the aforementioned input space, and examine its interpolation capability
to the unseen data with multiple additional datasets. Finally, we extract the
interpretable information of our PINN model in binary and trinary interactions,
and discuss its potential extensions to other particle-laden flow problems with
more complicated scenarios and Eulerian-Lagrangian simulations as a superior
alternative to the classic average drag laws.",2305.03326v1
2023-09-25,Quantum Torque on a Non-Reciprocal Body out of Thermal Equilibrium and Induced by a Magnetic Field of Arbitrary Strength,"A stationary body that is out of thermal equilibrium with its environment,
and for which the electric susceptibility is non-reciprocal, experiences a
quantum torque. This arises from the spatially non-symmetric electrical
response of the body to its interaction with the non-equilibrium thermal
fluctuations of the electromagnetic field: the non-equilibrium nature of the
thermal field fluctuations results in a net energy flow through the body, and
the spatially non-symmetric nature of the electrical response of the body to
its interaction with these field fluctuations causes that energy flow to be
transformed into a rotational motion. We establish an exact, closed-form,
analytical expression for this torque in the case that the environment is the
vacuum and the material of the body is described by a damped oscillator model,
where the non-reciprocal nature of the electric susceptibility is induced by an
external magnetic field, as for magneto-optical media. We also generalise this
expression to the context in which the body is slowly rotating. By exploring
the high-temperature expansion of the torque, we are able to identify the
separate contributions from the continuous spectral distribution of the
non-reciprocal electric susceptibility, and from the resonance modes. In
particular, we find that the torque persists in the limiting case of zero
damping parameter, due to the contribution of the resonance modes. We also
consider the low-temperature expansion of the torque. This work extends our
previous consideration of this model to an external magnetic field of arbitrary
strength, thereby including non-linear magnetic field effects.",2309.14190v1
2023-09-27,Mean-Motion Resonances With Interfering Density Waves,"In this work, we study the dynamics of two less massive objects moving around
a central massive object, which are all embedded within a thin accretion disc.
In addition to the gravitational interaction between these objects, the
disc-object interaction is also crucial for describing the long-term dynamics
of the multi-body system, especially in the regime of mean-motion resonances.
We point out that near the resonance the density waves generated by the two
moving objects generally coherently interfere with each other, giving rise to
extra angular momentum fluxes. The resulting backreaction on the objects is
derived within the thin-disc scenario, which explicitly depends on the resonant
angle and sensitively depends on the smoothing scheme used in the
two-dimensional theory. We have performed hydrodynamical simulations with
planets embedded within a thin accretion disc and have found qualitatively
agreement on the signatures of interfering density waves by measuring the
torques on the embedded objects. By including in interference torque and the
migration torques in the evolution of a pair of planets, we show that the
chance of resonance trapping depends on the sign of the interference torque.
For negative torques the pairs are more likely located at off-resonance
regimes. The negative torques may also explain the $1\%-2\%$ offset (for the
period ratios) from the exact resonance values as observed in {\it Kepler}
multi-planet systems.",2309.15694v2
2023-10-09,DecAP: Decaying Action Priors for Accelerated Learning of Torque-Based Legged Locomotion Policies,"Optimal Control for legged robots has gone through a paradigm shift from
position-based to torque-based control, owing to the latter's compliant and
robust nature. In parallel to this shift, the community has also turned to Deep
Reinforcement Learning (DRL) as a promising approach to directly learn
locomotion policies for complex real-life tasks. However, most end-to-end DRL
approaches still operate in position space, mainly because learning in torque
space is often sample-inefficient and does not consistently converge to natural
gaits. To address these challenges, we propose a two-stage framework. In the
first stage, we generate our own imitation data by training a position-based
policy, eliminating the need for expert knowledge to design optimal
controllers. The second stage incorporates decaying action priors, a novel
method to enhance the exploration of torque-based policies aided by imitation
rewards. We show that our approach consistently outperforms imitation learning
alone and is robust to scaling these rewards from 0.1x to 10x. We further
validate the benefits of torque control by comparing the robustness of a
position-based policy to a position-assisted torque-based policy on a quadruped
(Unitree Go1) without any domain randomization in the form of external
disturbances during training.",2310.05714v2
2023-12-08,Manipulator control of the Robotized TMS System with Incurved TMS Coil Case,"Objective: This study shows the force/torque control strategy for the
robotized TMS system whose TMS coil's floor is incurved. The strategy
considered the adhesion and friction between the coil and the subject's head.
Methods: Hybrid position/force control and proportional torque were used for
the strategy. The force magnitude applied for the force control was scheduled
by the error between the coil's current position and the target point. Results:
The larger desired force for the force controller makes the error quickly. By
scheduling the force magnitude applied for the force control, the low error
between the coil's current and target positions is maintained with the
relatively small force after the larger force is applied for around 10 seconds.
The proportional torque made the adhesion better by locating the contact area
between the coil and the head close to the coil. I was shown by checking the
${\tau}_c/F_c$ value from the experimental results. While the head slowly moved
away from the coil during the TMS treatment, the coil still interacted with the
head. Using that characteristic, the coil could locate the new target point
using the force/torque strategy without any trajectory planning. Conclusion:
The proposed force/torque controller enhanced the adhesion between the incurved
TMS coil and the subject's head. It also reduced the error quickly by
scheduling the magnitude of the force applied. Significance: This study
proposes the robotized TMS system's force/torque control strategy considering
the physical characteristics from the contact between the incurved TMS coil
case and the subject's head.",2312.04868v1
2001-03-08,Electronic structure and magnetism in slightly doped SrB_6,"Spin-polarized band calculations for supercells of SrB$_{6}$, where a La-,
In- or Al- impurity or a vacancy is replacing one Sr, are performed within the
local spin density approximation. Moderately large cells with 8 formula units
(56 atoms) are studied for all dopings and large ones with 27 formula units
(189 atoms) for the case of La-doping. The undoped system has a vanishing
density-of-states (DOS) at the Fermi energy (E$_F$), while the additional La-d
band makes E$_F$ to enter the bands above the gap. An Al (or In) impurity has
the opposite effect, with a rigid-band like shift of E_F to below the gap. In
the former case, the addition of a d-electron makes a local, impurity-like
modification of the electronic structure close to the La atom. As has been
shown in a previous publication, it can lead to a weak ferromagnetic state.
This result is shown to persist at even lower doping, by the 189-atom cell
calculations, with a moment of the order 0.1 $\mu_B$ per La impurity. An
addition of a p-electron, by an In-impurity, makes no similar effect. The
magnetic state can be understood from a charge transfer and an additional gain
in potential energy, as a spin-splitting is imposed. Different models with
modified localization of the La-band are made in order to show the correlation
between charge transfer and the size of the magnetic moment.",0103180v1
2007-03-05,Sub-ns spin-transfer switching: compared benefits of free layer biasing and pinned layer biasing,"We analyze the statistical distribution of switching durations in
spin-transfer switching induced by current steps, and discuss biasing
strategies to enhance the reproducibility of switching durations. We use a
macrospin approximation and model the effect of finite temperature as a
Boltzmann distribution of initial magnetization states (adiabatic limit). We
compare three model spin-valves: a spin-valve with a free layer whose easy axis
is parallel to the pinned layer magnetization (standard geometry), a pinned
layer with magnetization tilted with respect to the free layer easy axis
(pinned layer biasing), and a free layer whose magnetization is pulled away
from easy axis by a hard axis bias (free layer biasing). In the conventional
geometry, the switching durations follow a broad regular distribution, with an
extended long tail comprising very long switching events. For the two biasing
strategies, the switching durations follow a multiply-stepped distribution,
reflecting the precessional nature of the switching, and the statistical number
of precession cycles needed for reversal. We derive analytical criteria to
avoid switching events lasting much longer than the average switching duration,
in order to achieve the highest reproducibilities. Depending on the current
amplitude and the biasing strength, the width of the switching time
distribution can be substantially reduced, the best reproducibility being
achieved for free layer biasing at overdrive current of a few times unity.",0703124v1
2007-05-10,Antiferromagnetic Spin Fluctuations in the Metallic Phase of Quasi-Two-Dimensional Organic Superconductors,"We give a quantitative analysis of the previously published nuclear magnetic
resonance (NMR) experiments in the k-(ET)2X family of organic charge transfer
salts by using the phenomenological spin fluctuation model of Moriya, and
Millis, Monien and Pines (M-MMP). For temperatures above T_nmr ~ 50 K, the
model gives a good quantitative description of the data in the metallic phases
of several k-(ET)2X materials. These materials display antiferromagnetic
correlation lengths which increase with decreasing temperature and grow to
several lattice constants by T_nmr. It is shown that the fact that the
dimensionless Korringa ratio is much larger than unity is inconsistent with a
broad class of theoretical models (such as dynamical mean-field theory) which
neglects spatial correlations and/or vertex corrections. For materials close to
the Mott insulating phase the nuclear spin relaxation rate, the Knight shift
and the Korringa ratio all decrease significantly with decreasing temperature
below T_nmr. This cannot be described by the M-MMP model and the most natural
explanation is that a pseudogap, similar to that observed in the underdoped
cuprate superconductors, opens up in the density of states below T_nmr. Such a
pseudogap has recently been predicted to occur in the dimerised organic charge
transfer salts materials by the resonating valence bond (RVB) theory. We
propose specific new experiments on organic superconductors to elucidate these
issues. For example, measurements to see if high magnetic fields or high
pressures can be used to close the pseudogap would be extremely valuable.",0705.1382v1
2010-11-30,Light-Meson Spectroscopy with COMPASS,"COMPASS is a multi-purpose fixed-target experiment at the CERN Super Proton
Synchrotron investigating the structure and spectrum of hadrons. One primary
goal is the search for new hadronic states, in particular spin-exotic mesons
and glueballs.
  After a short pilot run in 2004 with a 190 GeV/c $\pi^-$ beam on a Pb target,
which showed a significant spin-exotic $J^{PC} = 1^{-+}$ resonance consistent
with the controversial $\pi_1(1600)$, COMPASS collected large data samples with
negative and positive hadron beams on H$_2$, Ni, W, and Pb targets in 2008 and
2009.
  We present results from a partial-wave analysis of diffractive dissociation
of 190 GeV/c $\pi^-$ into $\pi^-\pi^+\pi^-$ final states on Pb and H$_2$
targets with squared four-momentum transfer in the range 0.1 < t' < 1
(GeV/c)^2. This reaction provides clean access to the light-quark meson
spectrum up to masses of 2.5 GeV/c^2. A first comparison of the data from Pb
and H$_2$ target shows a strong target dependence of the production strength of
states with spin projections $M = 0$ and 1 relative to the $a_2(1320)$.
  The 2004 Pb data were also analyzed in the region of small squared
four-momentum transfer t' < 10^{-2} (GeV/c)^2, where we observe interference of
diffractive production and photoproduction in the Coulomb-field of the Pb
nucleus.",1011.6615v2
2012-03-09,Exchange-dependent relaxation in the rotating frame for slow and intermediate exchange - modeling off-resonant spin-lock and chemical exchange saturation transfer,"Chemical exchange observed by NMR saturation transfer (CEST) and spin-lock
(SL) experiments provide an MRI contrast by indirect detection of exchanging
protons. The determination of the relative concentrations and exchange rates is
commonly achieved by numerical integration of the Bloch-McConnell equations. We
derive an analytical solution of the Bloch-McConnell equations that describes
the magnetization of coupled spin populations under radiofrequency
irradiation.As CEST and off-resonant SL are equivalent, their steady-state
magnetization and dynamics can be predicted by the same single eigenvalue: the
longitudinal relaxation rate in the rotating frame R1rho. For the case of
slowly exchanging systems, e.g. amide protons, the saturation of the small
proton pool is affected by transverse relaxation (R2b). It turns out, that R2b
is also significant for intermediate exchange, such as amine- or
hydroxyl-exchange or paramagnetic CEST agents, if pools are only partially
saturated. We propose a solution for R1rho that includes R2 of the exchanging
pool by extending existing approaches, and verify it by numerical simulations.
With the appropriate projection factors, we obtain an analytical solution for
CEST and SL for nonzero R2 of the exchanging pool, whilst considering the
dilution by direct water saturation across the entire Z-spectra. This allows
the optimization of irradiation parameters and the quantification of
pH-dependent exchange rates and metabolite concentrations. In addition, we
propose evaluation methods that correct for concomitant direct saturation
effects. It is shown that existing theoretical treatments for CEST are special
cases of this approach.",1203.2067v2
2012-06-25,Helicity and Angular Momentum. A Symmetry based framework for the study of Light-Matter Interactions,"We propose a new theoretical and practical framework for the study of
light-matter interactions and the angular momentum of light. Our proposal is
based on helicity, total angular momentum, and the use of symmetries. We
compare the new framework to the current treatment, which is based on
separately considering spin angular momentum and orbital angular momentum and
using the transfer between the two in physical explanations. In our proposal,
the fundamental problem of spin and orbital angular momentum separability is
avoided, predictions are made based on the symmetries of the systems, and the
practical application of the concepts is straightforward. Finally, the
framework is used to show that the concept of spin to orbit transfer applied to
focusing and scattering is masking two completely different physical phenomena
related to the breaking of different fundamental symmetries: transverse
translational symmetry in focusing and electromagnetic duality symmetry in
scattering.",1206.5563v4
2012-12-19,Phase transition in Pr0.5Ca0.5CoO3 and related cobaltites,"We present an extensive investigation (magnetic, electric and thermal
measurements and X-ray absorption spectroscopy) of the Pr0.5Ca0.5CoO3 and
(Pr1-yYy)0.7Ca0.3CoO3 (y=0.0625-0.15) perovskites, in which a peculiar
metal-insulator (M-I) transition, accompanied with pronounced structural and
magnetic anomalies, occurs at 76 K and 40-132 K, respectively. The inspection
of the M-I transition using the XANES data of Pr L3-edge and Co K-edge proofs
the presence of Pr4+ ions at low temperatures and indicates simultaneously the
intermediate spin to low spin crossover of Co species on lowering the
temperature. The study thus definitively confirms the synchronicity of the
electron transfer between Pr3+ ions and Co^(3+/4+)O3 subsystem and the
transition to the low-spin, less electrically conducting phase. The large
extent of the transfer is evidenced by the good quantitative agreement of the
determined amount of the Pr4+ species, obtained either from the temperature
dependence of the XANES spectra or via integration of the magnetic entropy
change over the Pr4+ related Schottky peak in the low-temperature specific
heat. These results show that the average valence of Pr3+/Pr4+ ions increases
(in concomitance with the decrease of the formal Co valence) below TMI for
(Pr0.925Y0.075)0.7Ca0.3CoO3 up to 3.16+ (the doping level of the CoO3 subsystem
decreases from 3.30+ to 3.20+), for (Pr0.85Y0.15)0.7Ca0.3CoO3 up to 3.28+ (the
decrease of doping level from 3.30+ to 3.13+) and for Pr0.5Ca0.5CoO3 up to
3.46+ (the decrease of doping level from 3.50+ to 3.27+).",1212.4822v1
2013-05-24,Quantum Energy Teleportation between Spin Particles in a Gibbs State,"Energy in a multipartite quantum system appears from an operational
perspective to be distributed to some extent non-locally because of
correlations extant among the system's components. This non-locality allows
users to transfer, in effect, locally accessible energy between sites of
different system components by LOCC (local operations and classical
communication). Quantum energy teleportation is a three-step LOCC protocol,
accomplished without an external energy carrier, for effectively transferring
energy between two physically separated, but correlated, sites. We apply this
LOCC teleportation protocol to a model Heisenberg spin particle pair initially
in a quantum thermal Gibbs state, making temperature an explicit parameter. We
find in this setting that energy teleportation is possible at any temperature,
even at temperatures above the threshold where the particles' entanglement
vanishes. This shows for Gibbs spin states that entanglement is not
fundamentally necessary for energy teleportation; correlation other than
entanglement can suffice. Dissonance---quantum correlation in separable
states---is in this regard shown to be a quantum resource for energy
teleportation, more dissonance being consistently associated with greater
energy yield. We compare energy teleportation from particle A to B in Gibbs
states with direct local energy extraction by a general quantum operation on B
and find a temperature threshold below which energy extraction by a local
operation is impossible. This threshold delineates essentially two regimes: a
high temperature regime where entanglement vanishes and the teleportation
generated by other quantum correlations yields only vanishingly little energy
relative to local extraction and a second low-temperature teleportation regime
where energy is available at B only by teleportation.",1305.5853v2
2014-12-30,Local and bulk 13C hyperpolarization in NV-centered diamonds at variable fields and orientations,"Polarizing nuclear spins is of fundamental importance in biology, chemistry
and physics. Methods for hyperpolarizing 13C nuclei from free electrons in
bulk, usually demand operation at cryogenic temperatures. Room-temperature
approaches targeting diamonds with nitrogen-vacancy (NV) centers could
alleviate this need, but hitherto proposed strategies lack generality as they
demand stringent conditions on the strength and/or alignment of the magnetic
field. We report here an approach for achieving efficient electron->13C spin
alignment transfers, compatible with a broad range of magnetic field strengths
and field orientations with respect to the diamond crystal. This versatility
results from combining coherent microwave- and incoherent laser-induced
transitions between selected energy states of the coupled electron-nuclear spin
manifold. 13C-detected Nuclear Magnetic Resonance (NMR) experiments demonstrate
that this hyperpolarization can be transferred via first-shell or via distant
13Cs, throughout the nuclear bulk ensemble. This method opens new perspectives
for applications of diamond NV centers in NMR, and in quantum information
processing.",1412.8635v1
2015-04-03,Matrix product solutions of boundary driven quantum chains,"We review recent progress on constructing non-equilibrium steady state
density operators of boundary driven locally interacting quantum chains, where
driving is implemented via Markovian dissipation channels attached to the
chain's ends. We discuss explicit solutions in three different classes of
quantum chains, specifically, the paradigmatic (anisotropic) Heisenberg
spin-1/2 chain, the Fermi-Hubbard chain, and the Lai-Sutherland spin-1 chain,
and discuss universal concepts which characterize these solutions, such as
matrix product ansatz and a more structured walking graph state ansatz. The
central theme is the connection between the matrix product form of
nonequilibrium states and the integrability structures of the bulk Hamiltonian,
such as the Lax operators and the Yang-Baxter equation.
  However, there is a remarkable distinction with respect to the conventional
quantum inverse scattering method, namely addressing nonequilibrium steady
state density operators requires non-unitary irreducible representations of
Yang-Baxter algebra which are typically of infinite dimensionality. Such
constructions result in non-Hermitian, and often also non-diagonalisable
families of commuting transfer operators which in turn result in novel
conservation laws of the integrable bulk Hamiltonians. For example, in the case
of anisotropic Heisenberg model, quasi-local conserved operators which are odd
under spin reversal (or spin flip) can be constructed, whereas the conserved
operators stemming from orthodox Hermitian transfer operators (via logarithmic
differentiation) are all even under spin reversal.",1504.00783v3
2015-05-08,Generalized spin-dependent WIMP-nucleus interactions and the DAMA modulation effect,"Guided by non-relativistic Effective Field Theory (EFT) we classify the most
general spin-dependent interactions between a fermionic Weakly Interacting
Massive Particle (WIMP) and nuclei, and within this class of models we discuss
the viability of an interpretation of the DAMA modulation result in terms of a
signal from WIMP elastic scatterings using a halo-independent approach. We find
that, although several relativistic EFT's can lead to a spin-dependent cross
section, in some cases with an explicit, non-negligible dependence on the WIMP
incoming velocity, three main scenarios can be singled out in the
non-relativistic limit which approximately encompass them all, and that only
differ by their dependence on the transferred momentum. For two of them
compatibility between DAMA and other constraints is possible for a WIMP mass
below 30 GeV, but only for a WIMP velocity distribution in the halo of our
Galaxy which departs from a Maxwellian. This is achieved by combining a
suppression of the WIMP effective coupling to neutrons (to evade constraints
from xenon and germanium detectors) to an explicit quadratic or quartic
dependence of the cross section on the transferred momentum (that leads to a
relative enhancement of the expected rate off sodium in DAMA compared to that
off fluorine in droplet detectors and bubble chambers). For larger WIMP masses
the same scenarios are excluded by scatterings off iodine in COUPP.",1505.01926v1
2016-11-18,"Description of the $^{11}$Li$(p,d){^{10}}$Li transfer reaction using structure overlaps from a full three-body model","Recent data on the differential angular distribution for the transfer
reaction $^{11}$Li(p,d)$^{10}$Li at $E/A=5.7$ MeV in inverse kinematics are
analysed within the DWBA reaction framework, using the overlap functions
calculated within a three-body model of $^{11}$Li. The weight of the different
$^{10}$Li configurations in the system's ground state is obtained from the
structure calculations unambiguously. The effect of the $^{9}$Li spin in the
calculated observables is also investigated. We find that, although all the
considered models succeed in reproducing the shape of the data, the magnitude
is very sensitive to the content of $p_{1/2}$ wave in the $^{11}$Li
ground-state wave function. Among the considered models, the best agreement
with the data is obtained when the $^{11}$Li ground state contains a $\sim$31\%
of $p_{1/2}$ wave in the $n$-$^9$Li subsystem. Although this model takes into
account explicitly the splitting of the $1^+$ and $2^+$ resonances due to the
coupling of the $p_{1/2}$ wave to the $3/2^-$ spin of the core, a similar
degree of agreement can be achieved with a model in which the $^{9}$Li spin is
ignored, provided that it contains a similar p-wave content.",1611.06000v3
2016-12-08,Jonckheere-Terpstra test for nonclassical error versus log-sensitivity relationship of quantum spin network controllers,"Selective information transfer in spin ring networks by energy landscape
shaping control has the property that the error 1-prob, where prob is the
transfer success probability, and the sensitivity of the error to spin coupling
uncertainties are statistically increasing across a family of controllers of
increasing error. The need for a statistical Hypothesis Testing of a concordant
trend is made necessary by the noisy behavior of the sensitivity versus the
error as a consequence of the optimization of the controllers in a challenging
error landscape. Here, we examine the concordant trend between the error and
another measure of performance - the logarithmic sensitivity - used in robust
control to formulate a well known fundamental limitation. Contrary to error
versus sensitivity, the error versus logarithmic sensitivity trend is less
obvious, because of the amplification of the noise due to the logarithmic
normalization. This results in the Kendall {\tau} test for rank correlation
between the error and the log sensitivity to be somewhat pessimistic with
marginal significance level. Here it is shown that the Jonckheere-Terpstra
test, because it tests the Alternative Hypothesis of an ordering of the medians
of some groups of log sensitivity data, alleviates this statistical problem.
This identifies cases of concordant trend between the error and the logarithmic
sensitivity, a highly anti-classical features that goes against the well know
sensitivity versus complementary sensitivity limitation.",1612.02784v2
2016-12-16,Observation of Ultralong Valley Lifetime in WSe2/MoS2 Heterostructures,"The valley degree of freedom in two-dimensional (2D) crystals recently
emerged as a novel information carrier in addition to spin and charge. The
intrinsic valley lifetime in 2D transition metal dichalcoginides (TMD) is
expected to be remarkably long due to the unique spin-valley locking behavior,
where the inter-valley scattering of electron requires simultaneously a large
momentum transfer to the opposite valley and a flip of the electron spin. The
experimentally observed valley lifetime in 2D TMDs, however, has been limited
to tens of nanoseconds so far. Here we report efficient generation of
microsecond-long lived valley polarization in WSe2/MoS2 heterostructures by
exploiting the ultrafast charge transfer processes in the heterostructure that
efficiently creates resident holes in the WSe2 layer. These valley-polarized
holes exhibit near unity valley polarization and ultralong valley lifetime: we
observe a valley-polarized hole population lifetime of over 1 us, and a valley
depolarization lifetime (i.e. inter-valley scattering lifetime) over 40 us at
10 Kelvin. The near-perfect generation of valley-polarized holes in TMD
heterostructures with ultralong valley lifetime, orders of magnitude longer
than previous results, opens up new opportunities for novel valleytronics and
spintronics applications.",1612.05359v1
2017-02-19,Predicting Electronic Structure Properties of Transition Metal Complexes with Neural Networks,"High-throughput computational screening has emerged as a critical component
of materials discovery. Direct density functional theory (DFT) simulation of
inorganic materials and molecular transition metal complexes is often used to
describe subtle trends in inorganic bonding and spin-state ordering, but these
calculations are computationally costly and properties are sensitive to the
exchange-correlation functional employed. To begin to overcome these
challenges, we trained artificial neural networks (ANNs) to predict
quantum-mechanically-derived properties, including spin-state ordering,
sensitivity to Hartree-Fock exchange, and spin- state specific bond lengths in
transition metal complexes. Our ANN is trained on a small set of
inorganic-chemistry-appropriate empirical inputs that are both maximally
transferable and do not require precise three-dimensional structural
information for prediction. Using these descriptors, our ANN predicts
spin-state splittings of single-site transition metal complexes (i.e., Cr-Ni)
at arbitrary amounts of Hartree-Fock exchange to within 3 kcal/mol accuracy of
DFT calculations. Our exchange-sensitivity ANN enables improved predictions on
a diverse test set of experimentally-characterized transition metal complexes
by extrapolation from semi-local DFT to hybrid DFT. The ANN also outperforms
other machine learning models (i.e., support vector regression and kernel ridge
regression), demonstrating particularly improved performance in
transferability, as measured by prediction errors on the diverse test set. We
establish the value of new uncertainty quantification tools to estimate ANN
prediction uncertainty in computational chemistry, and we provide additional
heuristics for identification of when a compound of interest is likely to be
poorly predicted by the ANN.",1702.05771v1
2017-11-10,Transverse acoustic phonon anomalies at intermediate wavevectors in MgV$_{2}$O$_{4}$,"Magnetic spinels (with chemical formula $AX_{2}$O$_{4}$, with $X$ a 3$d$
transition metal ion) that also have an orbital degeneracy are Jahn-Teller
active and hence possess a coupling between spin and lattice degrees of
freedom. At high temperatures, MgV$_{2}$O$_{4}$ is a cubic spinel based on
V$^{3+}$ ions with a spin $S$=1 and a triply degenerate orbital ground state. A
structural transition occurs at T$_{OO}$=63 K to an orbitally ordered phase
with a tetragonal unit cell followed by an antiferromagnetic transition of
T$_{N}$=42 K on cooling. We apply neutron spectroscopy in single crystals of
MgV$_{2}$O$_{4}$ to show an anomaly for intermediate wavevectors at T$_{OO}$
associated with the acoustic phonon sensitive to the shear elastic modulus
$\left(C_{11}-C_{12}\right)/2$. On warming, the shear mode softens for momentum
transfers near close to half the Brillouin zone boundary, but recovers near the
zone centre. High resolution spin-echo measurements further illustrate a
temporal broadening with increased temperature over this intermediate range of
wavevectors, indicative of a reduction in phonon lifetime. A subtle shift in
phonon frequencies over the same range of momentum transfers is observed with
magnetic fields. We discuss this acoustic anomaly in context of coupling to
orbital and charge fluctuations.",1711.03791v1
2020-07-05,Configurational Mean-Field Reduced Transfer Matrix Method for Ising Systems,"A mean-field method for the hypercubic nearest-neighbor Ising system is
introduced and applications to the method are demonstrated. The main idea of
this work is to combine the Kadanoff's mean-field approach with the model
presented by one of us previously. The mean-field approximation is introduced
with the replacement of the central spin in Ising Hamiltonian with an average
value of particular spin configuration, i.e, the approximation is taken into
account within each configuration. This approximation is used in two different
mean-field-type approaches. The first consideration is a pure-mean-field-type
treatment in which all the neighboring spins are replaced with the assumed
configurational average. The second consideration is introduced by the reduced
transfer matrix method. The estimations of critical coupling values of the
systems are evaluated both numerically and also analytically by the using of
saddle point approximation. The analytical estimation of critical values in the
first and second considerations are $ K_{c}=\frac{1}{z} $ and $ (z-2)
K_{c}e^{2K_{c}} =1 $ respectively. Obviously, both of the considerations have
some significant deviation from the exact treatment. In this work, we conclude
that the method introduced here is more appropriate physical picture than
self-consistent mean-field-type models, because the method introduced here does
not presume the presence of the phase transition from the outset. Consequently,
the introduced approach potentially makes our research very valuable
mean-field-type picture for phase transition treatment.",2007.02386v1
2021-07-20,Electric and Magnetic Responses of Two-dimensional Dirac Electrons in Organic Conductor $α$-(BETS)$_2$I$_3$,"Effect of spin-orbit coupling (SOC) on Dirac electrons in the organic
conductor $\alpha$-(BETS)$_2$I$_3$ [BETS =
bis(ethylenedithio)tetraselenafulvalene] has been examined by calculating
electric conductivity and spin magnetic susceptibility. A tight-binding (TB)
model with real and imaginary transfer energies is derived using
first-principles density-functional theory method. The conductivity without the
SOC depends on both anisotropies of the velocity of the Dirac cone and the
tiling of the cone. Such conductivity is suppressed by the SOC, which gives
rise to the imaginary part of the transfer energy. Due to the SOC, we find at
low temperatures that the reduction of the conductivity becomes large and that
the anisotropy of the conductivity is reduced. A nearly constant conductivity
at high temperatures is obtained by an electron--phonon (e--p) scattering.
Further, the property of the Dirac cone is examined for the spin
susceptibility, which is mainly determined by the density of states (DOS). The
result is compared with the case of the organic conductor
$\alpha$-(BEDT-TTF)$_2$I$_3$ [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene],
which provides the Dirac cone without the SOC. The relevance to experiments is
discussed.",2107.09297v2
2021-07-22,Evolution of accretor stars in massive binaries: broader implications from modeling ζ Ophiuchi,"Most massive stars are born in binaries close enough for mass transfer
episodes. These modify the appearance, structure, and future evolution of both
stars. We compute the evolution of a 100-day period binary consisting initially
of a 25 M star and a 17 M star, which experiences stable mass transfer. We
focus on the impact of mass accretion on the surface composition, internal
rotation, and structure of the accretor. To anchor our models, we show that our
accretor broadly reproduces the properties of {\zeta} Ophiuchi, which has long
been proposed to have accreted mass before being ejected as a runaway star when
the companion exploded. We compare our accretor to models of single rotating
stars and find that the later and stronger spin-up provided by mass accretion
produces significant differences. Specifically, the core of the accretor
retains higher spin at the end of the main sequence, and a convective layer
develops that changes its density profile. Moreover, the surface of the
accretor star is polluted by CNO-processed material donated by the companion.
Our models show effects of mass accretion in binaries that are not captured in
single rotating stellar models. This possibly impacts the further evolution
(either in a binary or as single stars), the final collapse, and the resulting
spin of the compact object.",2107.10933v2
2021-11-23,Towards rationalizing photoswitchable behavior of Cu$^{\mathrm{II}}_{2}$Mo$^{\mathrm{IV}}$ cyanido-bridged molecule,"[Cu$^{\mathrm{II}}$(enpnen)]$_{2}$[Mo$^{\mathrm{IV}}$(CN)$_{8}$]$\cdot$7H$_{2}$O
(enpnen = N,N$^\prime$-bis(2-aminoethyl)-1,3-propane-diamine) molecular cluster
compound was subject to a series of irradiations with the light of 405 nm. On
irradiation isothermal magnetization at 1.8 and 5 K in the field range 0-70 kOe
as well as magnetic susceptibility in the temperature range of 2-300 K were
subsequently detected. Both types of magnetic signals were next analyzed
assuming that the irradiation triggers two independent processes: the metal to
metal charge transfer (MMCT) leading to a state with the Arrhenius-type
relaxation and the spin crossover (SC) transition ending in a state whose
relaxation displays a threshold behavior. The first mechanism leads to an
electron from the spinless Mo(IV) configuration being transferred to one of the
Cu(II) ions transforming the trimer into the state Cu(II)-N-C-Mo(V)-C-N-Cu(I),
with spin 1/2 on the Mo(V) ion and the spinless Cu(I) ion. The other mechanism
gives rise to an excited paramagnetic Mo(IV)$^{*}$ linked to two paramagnetic
Cu(II) centers with a possible superexchange interaction. The spin of the
excited Mo(IV)$^{*}$ species is equal to 1 and associated to a disruption of
the 5s-electronic pair. A reasonable result of simultaneous fitting the full
series of susceptibility and magnetization data to the model taking into
account both mechanisms corroborates their presence.",2111.11822v1
2021-12-26,Quark spin-orbit correlations in the proton,"Generalized transverse momentum-dependent parton distributions (GTMDs)
provide a comprehensive framework for imaging the internal structure of the
proton. In particular, by encoding the simultaneous distribution of quark
transverse positions and momenta, they allow one to directly access
longitudinal quark orbital angular momentum, and, moreover, to correlate it
with the quark helicity. The relevant GTMD is evaluated through a lattice
calculation of a proton matrix element of a quark bilocal operator (the
separation in which is Fourier conjugate to the quark momentum) featuring a
momentum transfer (which is Fourier conjugate to the quark position), as well
as the Dirac structure appropriate for capturing the quark helicity. The
weighting by quark transverse position requires a derivative with respect to
momentum transfer, which is obtained in unbiased fashion using a direct
derivative method. The lattice calculation is performed directly at the
physical pion mass, using domain wall fermions to mitigate operator mixing
effects. Both the Jaffe-Manohar as well as the Ji quark spin-orbit correlations
are extracted, yielding evidence for a strong quark spin-orbit coupling in the
proton.",2112.13464v1
2022-01-12,Electrically tunable magnetism and unique intralayer charge transfer in Janus monolayer MnSSe for spintronics applications,"Controlling magnetism and electronic properties of two-dimensional (2D)
materials by purely electrical means is crucial and highly sought for
high-efficiency spintronics devices since electric field can be easily applied
locally compared with magnetic field. The recently discover 2D Janus crystals
has provide a new platform for nanoscale electronics and spintronics due to
their broken inversion symmetry nature. The intrinsic ferromagnetic Jauns
monolayer, and hence the tunable physical properties, is therefore of great
interest. Here, through comprehensive density functional theory calculations
and Monte Carlo simulations, we unveil that single-layer MnSSe is an intrinsic
ferromagnetic half-metal with a direct band gap of 1.14 eV in spin-down channel
and a Curie temperature of about 72 K. The exchange coupling can be
significantly enhanced or quenched by hole and electron doping, respectively.
In particular, a small amount of hole doping MnSSe can tune its magnetization
easy axis in between out-of-plane and in-plane directions, which is conducive
to designing 2D spin field-effect transistor for spin-dependent transport. We
also find a reversible longitudinal interlayer charge transfer between S and Se
layers for the first time that is highly sensitive to the applied external
electric field. Interestingly, the directions of charge flow and the applied
field are the same. The behavior originates from the coexistence and/or the
competition of external and built-in fields. These findings, together with the
excellent stability and large in-plane stiffness, can greatly facilitate the
development of nanoscale electronics and spintronics devices based on 2D MnSSe
crystal.",2201.04334v1
2022-02-25,Correlation functions for open XXZ spin 1/2 quantum chains with unparallel boundary magnetic fields,"In this paper we continue our derivation of the correlation functions of open
quantum spin 1/2 chains with unparallel magnetic fields on the edges; this time
for the more involved case of the XXZ spin 1/2 chains. We develop our study in
the framework of the quantum Separation of Variables (SoV), which gives us both
the complete spectrum characterization and simple scalar product formulae for
separate states, including transfer matrix eigenstates. Here, we leave the
boundary magnetic field in the first site of the chain completely arbitrary,
and we fix the boundary field in the last site $N$ of the chain to be a
specific value along the $z$-direction. This is a natural first choice for the
unparallel boundary magnetic fields. We prove that under these special boundary
conditions, on the one side, we have a simple enough complete spectrum
description in terms of homogeneous Baxter like $TQ$-equation. On the other
side, we prove a simple enough description of the action of a basis of local
operators on transfer matrix eigenstates as linear combinations of separate
states. Thanks to these results, we achieve our main goal to derive correlation
functions for a set of local operators both for the finite and half-infinite
chains, with multiple integral formulae in this last case.",2202.12870v1
2022-03-14,"Generalized fast quasi-adiabatic population transfer for improved qubit readout, shuttling, and noise mitigation","Population-transfer schemes are commonly used to convert information robustly
stored in some quantum system for manipulation and memory into more macroscopic
degrees of freedom for measurement. These schemes may include, e.g.,
spin-to-charge conversion for spins in quantum dots, detuning of charge qubits
between a noise-insensitive operating point and a measurement point, spatial
shuttling of qubits encoded in spins or ions, and parity-to-charge conversion
schemes for qubits based on Majorana zero modes. A common strategy is to use a
slow (adiabatic) conversion. However, in an adiabatic scheme, the adiabaticity
conditions, on the one hand, and accumulation of errors through dephasing,
leakage, and energy relaxation processes on the other hand, limit the fidelity
that can be achieved. Here, we give explicit fast quasiadiabatic (fast-QUAD)
conversion strategies (pulse shapes) beyond the adiabatic approximation that
allow for optimal state conversion. In contrast with many other approaches,
here we account for noise in combination with pulse shaping. Although we
restrict to noise sources that can be modeled by a classical fluctuating
parameter, we allow generally for anisotropic nonGaussian noise that is
nevertheless sufficiently weak to lead to a small error. Inspired by analytic
methods that have been developed for dynamical decoupling theory, we provide a
general framework for unique noise mitigation strategies that can be tailored
to the system and environment of interest.",2203.07517v2
2022-05-22,An Ising-type formulation of the six-vertex model,"We show that the celebrated six-vertex model of statistical mechanics (along
with its multistate generalizations) can be reformulated as an Ising-type model
with only a two-spin interaction. Such a reformulation unravels remarkable
factorization properties for row to row transfer matrices, allowing one to
uniformly derive all functional relations for their eigenvalues and present the
coordinate Bethe ansatz for the eigenvectors for all higher spin
generalizations of the six-vertex model. The possibility of the Ising-type
formulation of these models raises questions about the precedence of the
traditional quantum group description of the vertex models. Indeed, the role of
a primary integrability condition is now played by the star-triangle relation,
which is not entirely natural in the standard quantum group setting, but
implies the vertex-type Yang-Baxter equation and commutativity of transfer
matrices as simple corollaries. As a mathematical identity the emerging
star-triangle relation is equivalent to the Pfaff-Saalschuetz-Jackson summation
formula, originally discovered by J.~F.~Pfaff in 1797. Plausibly, all vertex
models associated with quantized affine Lie algebras and superalgebras can be
reformulated as Ising-type models with only two-spin interactions.",2205.10708v3
2022-05-22,Exact surface energy of the $D^{(1)}_2$ spin chain with generic non-diagonal boundary reflections,"The exact solution of the $D^{(1)}_2$ quantum spin chain with generic
non-diagonal boundary reflections is obtained. It is found that the generating
functional of conserved quantities of the system can be factorized as the
product of transfer matrices of two anisotropic $XXZ$ spin chains with open
boundary conditions. By using the factorization identities and the fusion
technique, the eigenvalues and the Bethe ansatz equations of the model are
obtained. The eigenvalues are also parameterized by the zero roots of the
transfer matrix, and the patterns of root distributions are obtained. Based on
them, ground states energy and the surface energies induced by the twisted
boundary magnetic fields in the thermodynamic limit are obtained. These results
are checked by the numerical calculations. The corresponding isotropic limit is
also discussed. The results given in this paper are the foundation to study the
exact physical properties of high rank $D^{(1)}_{n}$ model by using the nested
processes.",2205.10818v2
2022-06-09,Exchange interactions in $d^{5}$ Kitaev materials: From Na$_2$IrO$_3$ to $α$-RuCl$_3$,"We present an analytical study of the exchange interactions between
pseudospin one-half $d^{5}$ ions in honeycomb lattices with edge-shared
octahedra. Various exchange channels involving Hubbard U, charge-transfer
excitations, and cyclic exchange are considered. Hoppings within $t_{2g}$
orbitals as well as between $t_{2g}$ and $e_g$ orbitals are included. Special
attention is paid to the trigonal crystal field $\Delta$ effects on the
exchange parameters. The obtained exchange Hamiltonian is dominated by
ferromagnetic Kitaev interaction K within a wide range of $\Delta$. It is found
that a parameter region close to the charge-transfer insulator regime and with
a small $\Delta$ is most promising to realize the Kitaev spin liquid phase. Two
representative honeycomb materials Na$_2$IrO$_3$ and $\alpha$-RuCl$_3$ are
discussed based on our theory. We have found that both materials share dominant
ferromagnetic K and positive non-diagonal $\Gamma$ values. However, their
Heisenberg J terms have opposite signs: AFM J>0 in Na$_2$IrO$_3$ and FM J<0 in
$\alpha$-RuCl$_3$. This brings different magnetic fluctuations and results in
their different magnetization behaviors and spin excitation spectra. Proximity
to FM state due to the large FM J is emphasized in $\alpha$-RuCl$_3$. The
differences between the exchange couplings of these two materials originate
from the opposite $\Delta$ values, indicating that the crystal field can serve
as an efficient control parameter to tune the magnetic properties of $d^{5}$
spin-orbit Mott insulators.",2206.04326v1
2022-06-28,Exact solution of a family of staggered Heisenberg chains with conclusive pretty good quantum state transfer,"We construct the exact solution for a family of one-half spin chains
explicitly. The spin chains Hamiltonian corresponds to an isotropic Heisenberg
Hamiltonian, with staggered exchange couplings that take only two different
values. We work out the exact solutions in the one-excitation subspace.
Regarding the problem of quantum state transfer, we use the solution and some
theorems concerning the approximation of irrational numbers, to show the
appearance of conclusive pretty good transmission for chains with particular
lengths. We present numerical evidence that pretty good transmission is
achieved by chains whose length is not a power of two. The set of spin chains
that shows pretty good transmission is a subset of the family with an exact
solution. Using perturbation theory, we thoroughly analyze the case when one of
the exchange coupling strengths is orders of magnitude larger than the other.
This strong coupling limit allows us to study, in a simple way, the appearance
of pretty good transmission. The use of analytical closed expressions for the
eigenvalues, eigenvectors, and transmission probabilities allows us to obtain
the precise asymptotic behavior of the time where the pretty good transmission
is observed. Moreover, we show that this time scales as a power law whose
exponent is an increasing function of the chain length. We also discuss the
crossover behavior obtained for the pretty good transmission time between the
regimes of strong coupling limit and the one observed when the exchange
couplings are of the same order of magnitude.",2206.14230v1
2022-07-03,Chiral surface spin textures in Cu$_2$OSeO$_3$ unveiled by soft x-ray scattering in specular reflection geometry,"Resonant elastic soft x-ray magnetic scattering (XRMS) is a powerful tool to
explore long-periodic spin textures in single crystals. However, due to the
limited momentum transfer range imposed by long wavelengths of photons in the
soft x-ray region, Bragg diffraction is restricted to crystals with the large
lattice parameters. Alternatively, small angle x-ray scattering has been
involved in the soft energy x-ray range which, however, brings in difficulties
with the sample preparation that involves focused ion beam milling to thin down
the crystal to below a few hundred nm thickness. We show how to circumvent
these restrictions by using XRMS in specular reflection from a sub-nanometer
smooth crystal surface. The method allows observing diffraction peaks from the
helical and conical spin modulations at the surface of a Cu$_2$OSeO$_3$ single
crystal and probing their corresponding chirality as contributions to the
dichroic scattered intensity. The results suggest a promising way to carry out
XRMS studies on plethora of noncentrosymmetric systems hitherto unexplored with
soft x-rays due to the absence of the commensurate Bragg peaks in the available
momentum transfer range.",2207.01120v1
2023-07-22,Quantum parametric amplifiation of phonon-mediated magnon-spin interaction,"The recently developed hybrid magnonics provides new opportunities for
advances in both the study of magnetism and the development of quantum
information processing. However, engineering coherent quantum state transfer
between magnons and specific information carriers, in particular, mechanical
oscillators and solid-state spins, remains challenging due to the intrinsically
weak interactions and the frequency mismatch between diffrent components. Here,
we show how to strongly couple the magnon modes in a nanomagnet to the
quantized mechanical motion (phonons) of a micromechanical cantilever in a
hybrid tripartite system. The coherent and enhanced magnon-phonon coupling is
engineered by introducing the quantum parametric amplifiation of the mechanical
motion. With experimentally feasible parameters, we show that the mechanical
parametric drive can be adjusted to drive the system into the strong-coupling
regime and even the ultrastrong-coupling regime. Furthermore, we show the
coherent state transfer between the nanomagnet and a nitrogen-vacancy center in
the dispersive-coupling regime, with the magnon-spin interaction mediated by
the virtually-excited squeezed phonons. The amplifid mechanical noise can
hardly interrupt the coherent dynamics of the system even for low mechanical
quality factors, which removes the requirement of applying additional
engineered-reservoir techniques. Our work opens up prospects for developing
novel quantum transducers, quantum memories and high-precision measurements.",2307.11961v1
2024-01-29,Superexchange interactions and magnetic anisotropy in MnPSe$_3$ monolayer,"Two-dimensional van der Waals magnetic materials are of great current
interest for their promising applications in spintronics. In this work, using
density functional theory calculations in combination with the maximally
localized Wannier functions method and the magnetic anisotropy analyses, we
study the electronic and magnetic properties of MnPSe$_3$ monolayer. Our
results show that it is a charge transfer antiferromagnetic (AF) insulator. For
this Mn$^{2+}$ $3d^5$ system, although it seems straightforward to explain the
AF ground state using the direct exchange, we find that the near 90$^\circ$
Mn-Se-Mn charge transfer type superexchange plays a dominant role in
stabilizing the AF ground state. Moreover, our results indicate that although
the shape anisotropy favors an out-of-plane spin orientation, the spin-orbit
coupling (SOC) leads to the experimentally observed in-plane spin orientation.
We prove that the actual dominant contribution to the magnetic anisotropy comes
from the second-order perturbation of the SOC, by analyzing its distribution
over the reciprocal space. Using the AF exchange and anisotropy parameters
obtained from our calculations, our Monte Carlo simulations give the N\'eel
temperature $T_{\rm N}=47$ K for MnPSe$_3$ monolayer, which agrees with the
experimental 40 K. Furthermore, our calculations show that under a uniaxial
tensile (compressive) strain, N\'eel vector would be parallel (perpendicular)
to the strain direction, which well reproduces the recent experiments. We also
predict that $T_{\rm N}$ would be increased by a compressive strain.",2401.16154v1
2001-06-01,The gravitational torque of bars in optically unbarred and barred galaxies,"The relative bar torques for 45 galaxies observed at $K$- band with the 4.2m
William Herschel Telescope are determined by transforming the light
distributions into potentials and deriving the maximum ratios of the tangential
forces relative to the radial forces. The results are combined with the bar
torques for 30 other galaxies determined from our previous $K$-band survey
(Buta & Block 2001). Relative bar torques determine the degree of spiral arm
forcing, gas accretion, and bar evolution. They differ from other measures of
bar strength, such as the relative amplitude of the bar determined
photometrically, because they include the bulge and other disk light that
contributes to the radial component of the total force. If the bulge is strong
and the radial forcing large, then even a prominent bar can have a relatively
weak influence on the azimuthal motions in the disk. Here we find that the
relative bar torque correlates only weakly with the optical bar type listed in
the Revised Shapley-Ames and de Vaucouleurs systems. In fact, some classically
barred galaxies have weaker relative bar torques than classically unbarred
galaxies. The optical class is a poor measure of azimuthal disk forcing for two
reasons: some infrared bars are not seen optically, and some bars with strong
bulges have their azimuthal forces so strongly diluted by the average radial
force that they exert only small torques on their disks. The Hubble
classification scheme poorly recognizes the gravitational influence of bars.
Applications of our bar torque method to the high-redshift universe are briefly
discussed.",0106019v1
2005-07-04,Molecular Gas in NUclei of GAlaxies (NUGA): IV. Gravitational Torques and AGN Feeding,"We discuss the efficiency of stellar gravity torques as a mechanism to
account for the feeding of the central engines of four low luminosity AGN:
NGC4321, NGC4826, NGC4579 and NGC6951. These galaxies have been observed as
part of the NUGA CO project, aimed at the study of AGN fueling mechanisms. Our
calculations allow us to derive the characteristic time-scales for gas flows
and discuss whether torques from the stellar potentials are efficient enough to
drain the gas angular momentum in the inner 1 kpc of these galaxies. Results
indicate paradoxically that feeding should be thwarted close to the AGN: in the
four cases analyzed, gravity torques are mostly positive inside r~200pc,
resulting in no inflow on these scales. As a possible solution for the paradox,
we speculate that the agent responsible for driving inflow to still smaller
radii is transient and thus presently absent in the stellar potential.
Alternatively, the gravity torque barrier associated with the ILR of the bars
in these galaxies could be overcome by other mechanisms that become competitive
in due time against gravity torques. We find that viscosity can counteract
moderate--to--low gravity torques on the gas if it acts on a nuclear ring of
high gas surface density contrast and a few 100pc size. We propose an
evolutionary scenario in which gravity torques and viscosity act in concert to
produce recurrent episodes of activity during the typical lifetime of any
galaxy. In this scenario the recurrence of activity in galaxies is indirectly
related to that of the bar instabilities.",0507070v1
2005-05-05,"Comment on ``Torque or no torque? Simple charged particle motion observed in different inertial frames,'' by J. D. Jackson [Am. J. Phys. 72 (12), 1484-1487 (2004)]","In this paper it is shown that the real cause of the apparent electrodynamic
paradox discussed by Jackson [J. D. Jackson, Am. J. Phys. 72, 1484 (2004)] is
the use of three-dimensional (3D) quantities E, B, F, L, N, .. . When 4D
geometric quantities are used then there is no paradox and the principle of
relativity is naturally satisfied.",0505038v1
2007-10-19,The Brownian gyrator: a minimal heat engine on the nano-scale,"A Brownian particle moving in the vicinity of a generic potential minimum
under the influence of dissipation and thermal noise from two different heat
baths is shown to act as a minimal heat engine, generating a systematic torque
onto the physical object at the origin of the potential and an opposite torque
onto the medium generating the dissipation.",0710.3735v1
2009-05-23,Influence of a Transport Current on Magnetic Anisotropy in Gyrotropic Ferromagnets,"Current-induced torques are commonly used to manipulate non-collinear
magnetization configurations. In this article we discuss current-induced
torques present in a certain class of collinear magnetic systems, relating them
to current-induced changes in magnetic anisotropy energy. We present a
quantitative estimate of their characteristics in uniform strained
ferromagnetic (Ga,Mn)As.",0905.3856v1
2011-01-27,Thermomechanics of DNA,"A theory for thermomechanical behavior of homogeneous DNA at thermal
equilibrium predicts critical temperatures for denaturation under torque and
stretch, phase diagrams for stable B--DNA, supercoiling, optimally stable
torque, and the overstretching transition as force-induced DNA melting.
Agreement with available single molecule manipulation experiments is excellent.",1101.5182v2
2011-08-31,Stability problem for the torque-free gyrostat by using algebraic methods,"We apply an algebraic method for studying the stability with respect to a set
of conserved quantities for the problem of torque-free gyrostat. If the
conditions of this algebraic method are not fulfilled then the Lyapunov
stability cannot be decided using the specified set of conserved quantities.",1108.6148v1
2012-04-16,Exact Analytic Solutions for the Rotation of an Axially Symmetric Rigid Body Subjected to a Constant Torque,"New exact analytic solutions are introduced for the rotational motion of a
rigid body having two equal principal moments of inertia and subjected to an
external torque which is constant in magnitude. In particular, the solutions
are obtained for the following cases: (1) Torque parallel to the symmetry axis
and arbitrary initial angular velocity; (2) Torque perpendicular to the
symmetry axis and such that the torque is rotating at a constant rate about the
symmetry axis, and arbitrary initial angular velocity; (3) Torque and initial
angular velocity perpendicular to the symmetry axis, with the torque being
fixed with the body. In addition to the solutions for these three forced cases,
an original solution is introduced for the case of torque-free motion, which is
simpler than the classical solution as regards its derivation and uses the
rotation matrix in order to describe the body orientation. This paper builds
upon the recently discovered exact solution for the motion of a rigid body with
a spherical ellipsoid of inertia. In particular, by following Hestenes' theory,
the rotational motion of an axially symmetric rigid body is seen at any instant
in time as the combination of the motion of a ""virtual"" spherical body with
respect to the inertial frame and the motion of the axially symmetric body with
respect to this ""virtual"" body. The kinematic solutions are presented in terms
of the rotation matrix. The newly found exact analytic solutions are valid for
any motion time length and rotation amplitude. The present paper adds further
elements to the small set of special cases for which an exact solution of the
rotational motion of a rigid body exists.",1204.3419v1
2013-02-06,A note on the torque anomaly,"I reproduce, in the case of a conical geometry, the torque anomaly recently
noted by Fulling, Mera and Trendafilova for the wedge. The expected
conservation equation is obtained by a variational method and a mathematical
cancellation of the anomaly is exhibited, motivated by the process of
truncating the cone at some inner radius.",1302.1445v1
2013-08-21,The torque on a dipole in uniform motion,"We calculate the torque on an ideal (point) dipole moving with constant
velocity through uniform electric and magnetic fields.",1308.4569v3
2013-12-10,To the Origin of Anomalous Torque Acting on a Rotating Magnetized Ball in Vacuum,"The magnitude of the anomalous torque acting on a rotating magnetized ball in
vacuum is specified. Its value is shown to depend on the magnetic field
structure inside the body.",1312.2691v1
2014-12-01,Modeling Grain Alignment by Radiative Torques and Hydrogen Formation Torques in Reflection Nebula,"Reflection nebulae--dense cores--illuminated by surrounding stars offer a
unique opportunity to directly test our quantitative model of grain alignment
based on radiative torques (RATs) and to explore new effects arising from
additional torques. In this paper, we first perform detailed modeling of grain
alignment by RATs for the IC 63 reflection nebula illuminated both by a nearby
$\gamma$ Cas star and the diffuse interstellar radiation field. We calculate
linear polarization $p_{\lambda}$ of background stars by radiatively aligned
grains and explore the variation of fractional polarization ($p_{\lambda}/A_V$)
with visual extinction $A_{V}$ across the cloud. Our results show that the
variation of $p_{V}/A_{V}$ versus $A_{V}$ from the dayside of IC 63 to its
center can be represented by a power-law ($p_{V}/A_{V}\propto A_{V}^{\eta}$)
with different slopes depending on $A_{V}$. We find a shallow slope $\eta \sim-
0.1$ for $A_{V}< 3$ and a very steep slope $\eta\sim -2$ for $A_{V}> 4$. We
then consider the effects of additional torques due to H$_{2}$ formation and
model grain alignment by joint action of RATs and H$_2$ torques. We find that
$p_{V}/A_{V}$ tends to increase with an increasing magnitude of H$_{2}$
torques. In particular, the theoretical predictions obtained for $p_{V}/A_{V}$
and peak wavelength $\lambda_{\max}$ in this case show an improved agreement
with the observational data. Our results reinforce the predictive power of the
RAT alignment mechanism in a broad range of environmental conditions and show
the effect of pinwheel torques in environments with efficient H$_2$ formation.
Physical parameters involved in H$_2$ formation may be constrained using
detailed modeling of grain alignment combined with observational data. In
addition, we discuss implications of our modeling for interpreting latest
observational data by {\it Planck} and other ground-based instruments.",1412.0424v2
2015-07-24,Controllability of Spacecraft Using Only Magnetic Torques,"Spacecraft attitude control using only magnetic torques is a time-varying
system. Many designs were proposed using LQR and H-infinity formulations. The
existence of the solutions depends on the controllability of the linear
time-varying systems which has not been established. In this paper, we will
derive the conditions of the controllability for this linear time-varying
systems.",1507.06963v1
2022-04-13,Repulsive torques alone trigger crystallization of constant speed active particles,"We investigate the possibility for self-propelled particles to crystallize
without reducing their intrinsic speed. We illuminate how, in the absence of
any force, the competition between self-propulsion and repulsive torques
determine the macroscopic phases of constant-speed active particles. This
minimal model expands upon existing approaches for an improved understanding of
crystallization of active matter.",2204.06468v1
2023-01-16,Haptic Transparency and Interaction Force Control for a Lower-Limb Exoskeleton,"Controlling the interaction forces between a human and an exoskeleton is
crucial for providing transparency or adjusting assistance or resistance
levels. However, it is an open problem to control the interaction forces of
lower-limb exoskeletons designed for unrestricted overground walking. For these
types of exoskeletons, it is challenging to implement force/torque sensors at
every contact between the user and the exoskeleton for direct force
measurement. Moreover, it is important to compensate for the exoskeleton's
whole-body gravitational and dynamical forces, especially for heavy lower-limb
exoskeletons. Previous works either simplified the dynamic model by treating
the legs as independent double pendulums, or they did not close the loop with
interaction force feedback.
  The proposed whole-exoskeleton closed-loop compensation (WECC) method
calculates the interaction torques during the complete gait cycle by using
whole-body dynamics and joint torque measurements on a hip-knee exoskeleton.
Furthermore, it uses a constrained optimization scheme to track desired
interaction torques in a closed loop while considering physical and safety
constraints. We evaluated the haptic transparency and dynamic interaction
torque tracking of WECC control on three subjects. We also compared the
performance of WECC with a controller based on a simplified dynamic model and a
passive version of the exoskeleton. The WECC controller results in a
consistently low absolute interaction torque error during the whole gait cycle
for both zero and nonzero desired interaction torques. In contrast, the
simplified controller yields poor performance in tracking desired interaction
torques during the stance phase.",2301.06244v3
2023-09-24,Control Performance Analysis of Power Steering System Electromechanical Dynamics,"Modern power steering systems employ an electric motor drive system to
provide torque assistance to the driver. The closed-loop mechanical system
dynamics that impact stability, performance and steering feel are significantly
impacted by the electrical dynamics of the actuator depending on the structure
and tuning of the motor torque controller. This paper presents an integrated
approach to the analysis of this electromechanical dynamic control interaction
through mathematical modeling which is confirmed with simulations.",2309.13623v1
2023-10-10,Circulating Current Induced Electromagnetic Torque Generation in Electric Machines with Delta Windings,"This paper explains the phenomenon of current circulation and the resulting
electromagnetic torque generation in electric machines employing delta
windings. The description entails a systematic assessment of the electrical and
magnetic behavior of the machine to develop mathematical models, followed by
intuitive explanations of the derived analytical forms. The modeling is
thoroughly validated through simulation and experimental results on a prototype
machine.",2310.06469v1
2002-01-11,"Towards a Resolution of the Galactic Spin Crisis: Mergers, Feedback, and Spin Segregation","We model in simple terms the angular-momentum problems of galaxy formation in
CDM cosmologies, and identify the key elements of a scenario that may solve
them. The buildup of angular momentum is modeled via dynamical friction and
tidal stripping in a sequence of mergers. We demonstrate how over-cooling in
incoming halos leads to a transfer of angular momentum from the baryons to the
dark matter, in conflict with observations. By incorporating a simple recipe of
supernova feedback, we are able to solve the problems of angular momentum in
disk formation. Gas removal from the numerous small incoming halos, which merge
to become the low specific angular momentum (j) component of the product,
eliminates the low-j baryons. Heating and puffing-up of the gas in larger
incoming halos, combined with efficient tidal stripping, reduces the angular
momentum loss of baryons due to dynamical friction. Dependence of the feedback
effects on the progenitor halo mass implies that the spin of baryons is
typically higher for lower mass halos. The observed low baryonic fraction in
dwarf galaxies is used to calibrate the characteristic velocity associated with
supernova feedback, yielding ~100 km/s, within the range of theoretical
expectations. We then find that the model naturally produces the observed
distribution of the spin parameter among dwarf and bright disk galaxies, as
well as the j profile inside these galaxies. This suggests that the model
indeed captures the main features of a full scenario for resolving the spin
crisis.",0201187v1
1998-05-19,A numerical study of multi-soliton configurations in a doped antiferromagnetic Mott insulator,"We evaluate from first principles the self-consistent Hartree-Fock energies
for multi-soliton configurations in a doped, spin-1/2, antiferromagnetic Mott
insulator on a two-dimensional square lattice. We find that nearest-neighbor
Coulomb repulsion stabilizes a regime of charged meron-antimeron vortex soliton
pairs over a region of doping from 0.05 to 0.4 holes per site for intermediate
coupling 3 < U/t <8. This stabilization is mediated through the generation of
``spin-flux'' in the mean-field antiferromagnetic (AFM) background. Holes
cloaked by a meron-vortex in the spin-flux AFM background are charged bosons.
Our static Hartree-Fock calculations provide an upper bound on the energy of a
finite density of charged vortices. This upper bound is lower than the energy
of the corresponding charged stripe configurations. A finite density of charge
carrying vortices is shown to produce a large number of unoccupied electronic
levels in the Mott-Hubbard charge transfer gap. These levels lead to
significant band tailing and a broad mid-infrared band in the optical
absorption spectrum as observed experimentally. At very low doping (below 0.05)
the doping charges create extremely tightly bound meron-antimeron pairs or even
isolated conventional spin-polarons, whereas for very high doping (above 0.4)
the spin background itself becomes unstable to formation of a conventional
Fermi liquid and the spin-flux mean-field is energetically unfavorable. Our
results point to the predominance of a quantum liquid of charged, bosonic,
vortex solitons at intermediate coupling and intermediate doping
concentrations.",9805229v2
2000-01-28,"Equation of motion approach for the Hubbard model: improved decoupling scheme, charge fluctuations, and the metal-insulator transition","A new decoupling scheme is developed for the Hubbard model which provides a
unified description of the spin-symmetric (paramagnetic metallic and
insulating) phases as well as the broken-symmetry AFI phase. Independent of
magnetic ordering, the scheme yields, in the lowest order, the correct
strong-coupling bandwidth of order J (for the NN hopping model) and band gap of
order U, a non-zero critical interaction strength (above which the band gap
opens) only if same sublattice hopping (e.g., NNN hopping) is also present, and
the correct integrated spectral weights (1/2 per spin) in each band for the
half-filled model. The effects of charge and spin fluctuations, including spin
twisting due to finite spin correlation length, are investigated with a static,
random approximation. A self-consistent evaluation of the disorder-averaged
self energy within the CPA is carried out numerically. Fluctuations activate
the hopping term at first order resulting in band broadening, and the
consequent decrease in the band gap with fluctuation strength is obtained for
several U values in two and three dimensions. We find that the band gap shrinks
to zero continuously, and subsequently the density of states N(0) between the
bands grows continuously, leading to a continuous metal-insulator transition.
For finite doping there is transfer of spectral weight between the Hubbard
bands, and a qualitative change in the nature of the quasiparticle band
dispersion, with an effective doping-induced hopping strength and bandwidth of
order xt.",0001413v1
2001-10-18,Damping of spin waves and singularity of the longitudinal modes in the dipolar critical regime of the Heisenberg-ferromagnet EuS,"By inelastic scattering of polarized neutrons near the (200)-Bragg
reflection, the susceptibilities and linewidths of the spin waves and the
longitudinal spin fluctuations were determined separately. By aligning the
momentum transfers q perpendicular to both \delta S_sw and the spontaneous
magnetization M_s, we explored the statics and dynamics of these modes with
transverse polarizations with respect to q. In the dipolar critical regime,
where the inverse correlation length kappa_z(T) and q are smaller than the
dipolar wavenumber q_d, we observe:(i) the static susceptibility of \delta
S_sw^T(q) displays the Goldstone divergence while for \delta S_z^T(q) the
Ornstein-Zernicke shape fits the data with a possible indication of a
thermal(mass-)renormalization at the smallest q-values, i.e. we find
indications for the predicted 1/q divergence of the longitudinal
susceptibility; (ii) the spin wave dispersion as predicted by the
Holstein-Primakoff theory revealing q_d=0.23(1)\AA^{-1}in good agreement with
previous work in the paramagnetic and ferromagnetic regime of EuS; (iii) within
experimental error, the (Lorentzian) linewidths of both modes turn out to be
identical with respect to the q^2-variation, the temperature independence and
the absolute magnitude. Due to the linear dispersion of the spin waves they
remain underdamped for q<q_d. These central results differ significantly from
the well known exchange dominated critical dynamics, but are quantitatively
explained in terms of dynamical scaling and existing data for T>=T_C. The
available mode-mode coupling theory, which takes the dipolar interactions fully
into account, describes the gross features of the linewidths but not all
details of the T- and q-dependencies. PACS: 68.35.Rh, 75.40.Gb",0110371v1
2003-05-01,Non-analytic corrections to the Fermi-liquid behavior,"The issue of non-analytic corrections to the Fermi-liquid behavior is
revisited. Previous studies have indicated that the corrections to the
Fermi-liquid forms of the specific heat and the static spin susceptibility
scale as $T^{D}$ and $T^{D-1}$, respectively (with extra logarithms for
$D=1,3$). In addition, the non-uniform spin susceptibility is expected to
depend on the bosonic momentum $Q$ in a non-analytic way, i.e., as $Q^{D-1}$
(again with extra logarithms for $D=1,3$). It is shown that these non-analytic
corrections originate from the universal singularities in the dynamical bosonic
response functions of a generic Fermi liquid. In contrast to the leading,
Fermi-liquid forms which depend on the interaction averaged over the Fermi
surface, the non-analytic corrections are parameterized by only two coupling
constants, which are the components of the interaction potential at momentum
transfers $q=0$ and $q=2k_F$. For 3D systems, a recent result of Belitz,
Kirkpatrick and Vojta for the spin susceptibility is reproduced and the issue
why a non-analytic momentum dependence of the non-uniform spin susceptibility
($Q^{2}\ln |Q|$) is \emph{not}paralleled by a non-analyticity in the $T-$
dependence ($T^2$) is clarified. For the case of a 2D system with a
finite-range interaction, explicit forms of the corrections to the specific
heat ($\propto T^2$), uniform ($\propto T$) and non-uniform ($\propto |Q|$)
spin susceptibilities are obtained. It is shown that previous calculations of
the temperature dependences of these quantities in 2D were incomplete. Some of
the results and conclusions of this paper have recently been announced in a
short communication [A. V. Chubukov and D. L. Maslov, cond-mat/0304381].",0305022v1
2004-05-03,A Novel Long Range Spin Chain and Planar N=4 Super Yang-Mills,"We probe the long-range spin chain approach to planar N=4 gauge theory at
high loop order. A recently employed hyperbolic spin chain invented by
Inozemtsev is suitable for the SU(2) subsector of the state space up to three
loops, but ceases to exhibit the conjectured thermodynamic scaling properties
at higher orders. We indicate how this may be bypassed while nevertheless
preserving integrability, and suggest the corresponding all-loop asymptotic
Bethe ansatz. We also propose the local part of the all-loop gauge transfer
matrix, leading to conjectures for the asymptotically exact formulae for all
local commuting charges. The ansatz is finally shown to be related to a
standard inhomogeneous spin chain. A comparison of our ansatz to semi-classical
string theory uncovers a detailed, non-perturbative agreement between the
corresponding expressions for the infinite tower of local charge densities.
However, the respective Bethe equations differ slightly, and we end by refining
and elaborating a previously proposed possible explanation for this
disagreement.",0405001v3
2001-09-21,Spin-Momentum Correlations in Quasi-Elastic Electron Scattering from Deuterium,"We report on a measurement of spin-momentum correlations in quasi-elastic
scattering of longitudinally polarized electrons with an energy of 720 MeV from
vector-polarized deuterium. The spin correlation parameter $A^V_{ed}$ was
measured for the $^2 \vec{\rm H}(\vec e,e^\prime p)n$ reaction for missing
momenta up to 350 MeV/$c$ at a four-momentum transfer squared of 0.21
(GeV/c)$^2$. The data give detailed information about the spin structure of the
deuteron, and are in good agreement with the predictions of microscopic
calculations based on realistic nucleon-nucleon potentials and including
various spin-dependent reaction mechanism effects. The experiment demonstrates
in a most direct manner the effects of the D-state in the deuteron ground-state
wave function and shows the importance of isobar configurations for this
reaction.",0109015v1
2008-01-11,Spin alignment measurements of the $K^{*0}(892)$ and $φ(1020)$ vector mesons at RHIC,"We present the first spin alignment measurements for the $K^{*0}(892)$ and
$\phi(1020)$ vector mesons produced at mid-rapidity with transverse momenta up
to 5 GeV/c at $\sqrt{s_{NN}}$ = 200 GeV at RHIC. The diagonal spin density
matrix elements with respect to the reaction plane in Au+Au collisions are
$\rho_{00}$ = 0.32 $\pm$ 0.04 (stat) $\pm$ 0.09 (syst) for the $K^{*0}$
($0.8<p_T<5.0$ GeV/c) and $\rho_{00}$ = 0.34 $\pm$ 0.02 (stat) $\pm$ 0.03
(syst) for the $\phi$ ($0.4<p_T<5.0$ GeV/c), and are constant with transverse
momentum and collision centrality. The data are consistent with the unpolarized
expectation of 1/3 and thus no evidence is found for the transfer of the
orbital angular momentum of the colliding system to the vector meson spins.
Spin alignments for $K^{*0}$ and $\phi$ in Au+Au collisions were also measured
with respect to the particle's production plane. The $\phi$ result, $\rho_{00}$
= 0.41 $\pm$ 0.02 (stat) $\pm$ 0.04 (syst), is consistent with that in p+p
collisions, $\rho_{00}$ = 0.39 $\pm$ 0.03 (stat) $\pm$ 0.06 (syst), also
measured in this work. The measurements thus constrain the possible size of
polarization phenomena in the production dynamics of vector mesons.",0801.1729v2
2009-03-12,Structural and spin transitions in Fe$_{2}$O$_{3}$,"First principles density functional calculations for Fe$_{2}$O$_{3}$ has been
performed over a wide range of pressures. The ground state is corundum-type
hematite and is an antiferromagnetic insulator. This is in good agreement with
experiment and other theoretical studies. On increasing pressure, the
ground-state high-spin magnetic phase transforms to low spin via the closure of
the charge transfer gap. The system also evolves to a new orthorhombic
structure. Distorted corundum or Rh$_{2}$O$_{3}$(II) type structure with Pbcn
symmetry and Pbnm type perovskite structure are two known competitive
candidates for this structural phase, based on {\it single}--cationic type and
{\it two}--cationic type picture, respectively. In our calculations, at about
38 GPa, Rh$_{2}$O$_{3}$(II) type structure becomes more stable with respect to
the ground state hematite. Relative stability of Pbnm type perovskite is ruled
out by our calculations in this pressure regime. The Rh$_{2}$O$_{3}$(II) type
structure remains in its low spin state, with 1 $\mu_{B}/$Fe atom, up to about
120 GPa. At this pressure the nonmagnetic solution in Rh$_{2}$O$_{3}$(II) type
structure becomes more favorable with respect to the low spin one. By further
increasing the pressure at about 330 GPa, the system evolves to yet another new
structural phase. This new orthorhombic structural phase is nonmagnetic and has
Pmc2$_{1}$ symmetry, a subgroup of Cmcm. Surprisingly, on furthering rising the
pressure, a Pbnm type nonmagnetic solution becomes competitive with the
Pmc2$_{1}$ type structure and finally becomes stable at about 880 GPa.",0903.2104v1
2009-09-24,Quantum control and measurement of atomic spins in polarization spectroscopy,"Quantum control and measurement are two sides of the same coin. To affect a
dynamical map, well-designed time-dependent control fields must be applied to
the system of interest. To read out the quantum state, information about the
system must be transferred to a probe field. We study a particular example of
this dual action in the context of quantum control and measurement of atomic
spins through the light-shift interaction with an off-resonant optical probe.
By introducing an irreducible tensor decomposition, we identify the coupling of
the Stokes vector of the light field with moments of the atomic spin state.
This shows how polarization spectroscopy can be used for continuous weak
measurement of atomic observables that evolve as a function of time.
Simultaneously, the state-dependent light shift induced by the probe field can
drive nonlinear dynamics of the spin, and can be used to generate arbitrary
unitary transformations on the atoms. We revisit the derivation of the master
equation in order to give a unified description of spin dynamics in the
presence of both nonlinear dynamics and photon scattering. Based on this
formalism, we review applications to quantum control, including the design of
state-to-state mappings, and quantum-state reconstruction via continuous weak
measurement on a dynamically controlled ensemble.",0909.4506v1
2009-11-17,Limits on spin determination from disc spectral fitting in GX 339-4,"We attempt to constrain the black hole spin in GX 339-4 from spectral fitting
of disc dominated data using RXTE spectra from the three most recent outbursts.
We use the best current models for the disc emission, including full radiative
transfer through the photosphere rather than assuming that the intrinsic
emission from each radius has a (colour temperature corrected) blackbody
spectrum. The results strongly depend on the poorly known binary system
parameters, but we find a strict upper limit of a<0.9 for any distance greater
than 6 kpc, assuming that the orbital inclination is the same as that of the
inner disc. By contrast, the higher spin of 0.935 +/- 0.01 (statistical)
+/-0.01 (systematic) claimed from fitting the iron line profile in this object
requires that the inner disc is misaligned by over 20 degrees from the orbital
inclination. While some of these datasets are distorted by instrumental pileup,
the same spin/inclination constraints are derived from data which are not piled
up, so there is a real conflict between the two techniques to measure spin. We
argue that the disc spectral fits are more likely to be robust hence that there
are still issues to be understood in the iron line profile.",0911.3281v2
2010-06-04,"Magnetism and thermodynamics of spin-(1/2,1) decorated Heisenberg chain with spin-1 pendants","The magnetic and thermodynamic properties of a new ferrimagnetic decorated
spin-(1/2,1) Heisenberg chain with spin-1 pendant spins are investigated for
three cases: (A) J1,J2>0; (B) J1>0, J2<0; and (C) J1<0, J2>0, where J1 and J2
are the exchange couplings between spins in the chain and along the rung,
respectively. The low-lying and magnetic properties are explored jointly by the
real-space renormalization group, spin wave, and density-matrix renormalization
group methods, while the transfer-matrix renormalization group method is
invoked to study the thermodynamics. It is found that the magnon spectra
consist of a gapless and two gapped branches. Two branches in case (C) have
intersections. The coupling dependence of low-energy gaps are analyzed. In a
magnetic field, an m=3/2 (m is the magnetization per unit cell) plateau is
observed for case (A), while two plateaux at m=1/2 and 3/2 are observed for
cases (B) and (C). Between the two plateaux in cases (B) and (C), the
sublattice magnetizations for the spins coupled by ferromagnetic interactions
have novel decreasing regions with increasing the magnetic field. At finite
temperature, the zero-field susceptibility temperature product chi*T and
specific heat exhibit distinct exotic features with varying the couplings and
temperature for different cases. chi*T is found to converge as T approaches
zero, which is different from the divergent behavior in the spin-(1/2,1)
mixed-spin chain without pendants. The observed thermodynamic behaviors are
also discussed with the help of their low-lying excitations.",1006.0794v1
2010-07-29,Spectral analysis for the iron-based superconductors: Anisotropic spin fluctuations and fully gapped s^{\pm}-wave superconductivity,"Spin fluctuations are considered to be one of the candidates that drive a
sign-reversed s^{\pm} superconducting state in the iron pnictides. In the
magnetic scenario, whether the spin fluctuation spectrum exhibits certain
unique fine structures is an interesting aspect for theoretical study in order
to understand experimental observations. We investigate the detailed momentum
dependence of the short-range spin fluctuations using a 2-orbital model in the
self-consistent fluctuation exchange approximation and find that a common
feature of those fluctuations that are capable of inducing a fully gapped
s^{\pm} state is the momentum anisotropy with lengthened span along the
direction transverse to the antiferromagnetic momentum transfer. Performing a
qualitative analysis based on the orbital character and the deviation from
perfect nesting of the electronic structure for the 2-orbital and a more
complete 5-orbital model, we gain the insight that this type of anisotropic
spin fluctuations favor superconductivity due to their enhancement of
intra-orbital, but inter-band, pair scattering processes. The momentum
anisotropy leads to elliptically shaped magnetic responses which have been
observed in inelastic neutron scattering measurements. Meanwhile, our detailed
study on the magnetic and the electronic spectrum shows that the dispersion of
the magnetic resonance mode in the nearly isotropic s^{\pm} superconducting
state exhibits anisotropic propagating behavior in an upward pattern and the
coupling of the resonance mode to fermions leads to a dip feature in the
spectral function.",1007.5321v3
2010-10-08,Bulk and boundary critical behaviour of thin and thick domain walls in the two-dimensional Potts model,"The geometrical critical behaviour of the two-dimensional Q-state Potts model
is usually studied in terms of the Fortuin-Kasteleyn (FK) clusters, or their
surrounding loops. In this paper we study a quite different geometrical object:
the spin clusters, defined as connected domains where the spin takes a constant
value. Unlike the usual loops, the domain walls separating different spin
clusters can cross and branch. Moreover, they come in two versions, ""thin"" or
""thick"", depending on whether they separate spin clusters of different or
identical colours. For these reasons their critical behaviour is different
from, and richer than, those of FK clusters. We develop a transfer matrix
technique enabling the formulation and numerical study of spin clusters even
when Q is not an integer. We further identify geometrically the crossing events
which give rise to conformal correlation functions. We study the critical
behaviour both in the bulk, and at a boundary with free, fixed, or mixed
boundary conditions. This leads to infinite series of fundamental critical
exponents, h_{l_1-l_2,2 l_1} in the bulk and h_{1+2(l_1-l_2),1+4 l_1} at the
boundary, valid for 0 <= Q <= 4, that describe the insertion of l_1 thin and
l_2 thick domain walls. We argue that these exponents imply that the domain
walls are `thin' and `thick' also in the continuum limit. A special case of the
bulk exponents is derived analytically from a massless scattering approach.",1010.1700v1
2010-11-29,A scheme for the extraction of WIMP-nucleon scattering cross sections from total event rates,"We propose a scheme that allows to analytically determine the three
elementary cross sections and connect the solutions to the relative sign
between the proton and the neutron spin scattering amplitudes once the
measurements of total event rate from three appropriate targets become
available. In this way it is thus possible to extract the maximum information
on the supersymmetric parameter space obtainable from direct detection
experiments, in the case that the dark matter particle is the lightest
neutralino. Our scheme is based on suitably normalized form of the isospin
momentum dependent structure functions entering in the spin-dependent elastic
neutralino-nucleus cross section. We compare these functions with the commonly
used ones and discuss their advantages: in particular, these allow in the
spin-dependent cross section to factorize the particle physics degrees of
freedom from the momentum transfer dependent nuclear structure functions as it
happens in the spin-independent cross section with the nuclear form factor.",1011.6108v3
2011-08-22,On the formalism and upper limits for spin-dependent cross sections in dark matter elastic scattering with nuclei,"We revise the spin-dependent neutralino-nucleus elastic scattering comparing
the formalisms and approximations found in literature for the momentum transfer
dependent structure functions. We argue that one of the normalized structure
functions of Divari, Kosmas, Vergados and Skouras is all that one needs to
correctly take into account the detailed nuclear physics information provided
by shell-model calculations. The factorization of the particle physics degrees
of freedom from the nuclear physics momentum dependent structure functions
implied by this formalism allows for a better understanding of the so-called
model independent method for setting upper limits. We further discuss the
possibility of experiments with spin-dependent sensitivity like COUPP to test
or set limits on the proton spin-dependent cross section in the framework of
the stau co-annihilation region of the constrained minimal supersymmetric
standard model. For this model with $A_0 =0$, we provide a fitting formula by
which it is possible to convert an upper limit on the spin-independent cross
section as a function of the neutralino mass directly into an exclusion plot in
the ($m_{1/2}$, $\tan\beta$) plane.",1108.4337v2
2013-05-29,An Anti-Glitch in a Magnetar,"Magnetars are neutron stars showing dramatic X-ray and soft $\gamma$-ray
outbursting behaviour that is thought to be powered by intense internal
magnetic fields. Like conventional young neutron stars in the form of radio
pulsars, magnetars exhibit ""glitches"" during which angular momentum is believed
to be transferred between the solid outer crust and the superfluid component of
the inner crust. Hitherto, the several hundred observed glitches in radio
pulsars and magnetars have involved a sudden spin-up of the star, due
presumably to the interior superfluid rotating faster than the crust. Here we
report on X-ray timing observations of the magnetar 1E 2259+586 which we show
exhibited a clear ""anti-glitch"" -- a sudden spin down. We show that this event,
like some previous magnetar spin-up glitches, was accompanied by multiple X-ray
radiative changes and a significant spin-down rate change. This event, if of
origin internal to the star, is unpredicted in models of neutron star spin-down
and is suggestive of differential rotation in the neutron star, further
supporting the need for a rethinking of glitch theory for all neutron stars.",1305.6894v1
2013-08-08,Imprints of spin-orbit density wave in the hidden order state of URu2Si2,"The mysterious second order quantum phase transition, commonly attributed to
the `hidden-order' (HO) state, in heavy-fermion metal URu2Si2 exhibits a number
of paradoxical electronic and magnetic properties which cannot be associated
with any conventional order parameter. We characterize and reconcile these
exotic properties of the HO state based on a spin-orbit density wave order
(SODW), constructed on the basis of a realistic density-functional theory (DFT)
band structure. We quantify the nature of the gapped electronic and magnetic
excitation spectrum, in agreement with measurements, while the magnetic moment
is calculated to be zero owing to the spin-orbit coupling induced time-reversal
invariance. Furthermore, a new collective mode in the spin-1 excitation
spectrum is predicted to localize at zero momentum transfer in the HO state
which can be visualized, for example, by electron spin resonance (ESR) at zero
magnetic field or polarized inelastic neutron scattering measurements. The
results demonstrate that the concomitant broken and invariant symmetries
protected SODW order not only provides insights into numerous nontrivial
hidden-order phenomena, but also offers a parallel laboratory to the formation
of a topologically protected quantum state beyond the quantum spin-Hall state
and Weyl semimetals.",1308.1992v2
2013-10-10,"Magnetization non-rational quasi-plateau and spatially modulated spin order in the model of the single-chain magnet, [{(CuL)_2 Dy}{Mo(CN)_8}] 2CH_3CN H_2O","Using the exact solution in terms of the generalized classical transfer
matrix method we presented a detailed analysis of the magnetic properties and
ground state structure of the simplified model of the single-chain magnet,
trimetallic coordination polymer compound, [{(CuL)_2 Dy}{Mo(CN)_8}] 2CH_3CN
H_2O is N,N'-propylenebis(3-methoxysalicylideneiminato). Due to appearance of
highly anisotropic Dy3+ ion this material is an unique example of the
one-dimensional magnets with Ising and Heisenberg bonds, allowing exact
statistical-mechanical treatment. We found two zero-temperature ground states
corresponding to different part of the magnetization curve of the material. The
zero-filed ground state is shown to be an antiferromagnetic configuration with
spatial modulation of the local Dy3+(which is proven to posses well defined
Ising like properties due two large anisotropy of g-factors) and composite
S=1/2 spin of the quantum spin trimer Cu-Mo-Cu in the form
""up""-""down""-""down""-""up"". Another important feature of this compound is the
appearance of the quasi-plateau at non rational value of magnetization due to
difference of the g-factors of the Cu- and Mo-ion in quantum spin trimers. The
quasi-plateau is an almost horizontal part of the magnetization curve where the
corresponding zero-temperature ground state of the chain demonstrate slow but
monotonous dependence of the magnetization on the external magnetic field,
while the $z$-projection of the total spin is constant.",1310.2811v2
2013-10-12,Anti-glitch induced by collision of a solid body with the magnetar 1E 2259+586,"Glitches have been frequently observed in neutron stars. Previously these
glitches unexceptionally manifest as sudden spin-ups that can be explained as
due to impulsive transfer of angular momentum from the interior superfluid
component to the outer solid crust. Alternatively, such spin-up glitches may
also be due to large-scale crust-cracking events. However, an unprecedented
anti-glitch was recently reported for the magnetar 1E 2259+586. In this case,
the magnetar clearly exhibited a sudden spin-down, strongly challenging
previous glitch theories. Here we show that the anti-glitch can be well
explained by the collision of a small solid body with the magnetar. The
intruder has a mass of about $1.1 \times 10^{21}$ g. Its orbital angular
momentum is assumed to be antiparallel to that of the spinning magnetar, so
that the sudden spin-down can be naturally accounted for. The observed hard
X-ray burst and decaying softer X-ray emission associated with the anti-glitch
can also be reasonably explained. Our study indicates that a completely
different type of glitches as due to collisions between small bodies and
neutron stars should exist and may have already been observed previously. It
also hints a new way for studying the capture events by neutron stars: through
accurate timing observations of pulsars.",1310.3324v3
2014-07-17,Anisotropic neutrino effect on magnetar spin: constraint on inner toroidal field,"The ultra-strong magnetic field of magnetars modifies the neutrino cross
section due to the parity violation of the weak interaction and can induce
asymmetric propagation of neutrinos. Such an anisotropic neutrino radiation
transfers not only the linear momentum of a neutron star but also the angular
momentum, if a strong toroidal field is embedded inside the stellar interior.
As such, the hidden toroidal field implied by recent observations potentially
affects the rotational spin evolution of new-born magnetars. We analytically
solve the transport equation for neutrinos and evaluate the degree of
anisotropy that causes the magnetar to spin-up or spin-down during the early
neutrino cooling phase. Supposing that after the neutrino cooling phase the
dominant process causing the magnetar spin-down is the canonical magnetic
dipole radiation, we compare the solution with the observed present rotational
periods of anomalous X-ray pulsars 1E 1841-045 and 1E 2259+586, whose poloidal
(dipole) fields are $\sim 10^{15}$ G and $10^{14}$ G, respectively. Combining
with the supernova remnant age associated with these magnetars, the present
evaluation implies a rough constraint of global (average) toroidal field
strength at $B^\phi\lesssim 10^{15}$ G.",1407.4653v1
2014-07-23,Preferential antiferromagnetic coupling of vacancies in graphene on SiO_2: Electron spin resonance and scanning tunneling spectroscopy,"Monolayer graphene grown by chemical vapor deposition and transferred to
SiO_2 is used to introduce vacancies by Ar^+ ion bombardment at a kinetic
energy of 50 eV. The density of defects visible in scanning tunneling
microscopy (STM) is considerably lower than the ion fluence implying that most
of the defects are single vacancies. The vacancies are characterized by
scanning tunneling spectroscopy (STS) on graphene and HOPG exhibiting a peak
close to the Fermi level. The peak persists after air exposure up to 180 min,
albeit getting broader. After air exposure for less than 60 min, electron spin
resonance (ESR) at 9.6 GHz is performed. For an ion flux of 10/nm^2, we find a
signal corresponding to a g-factor of 2.001-2.003 and a spin density of 1-2
spins/nm^2. The ESR signal consists of a mixture of a Gaussian and a Lorentzian
of equal weight exhibiting a width down to 0.17 mT, which, however, depends on
details of the sample preparation. The g-factor anisotropy is about 0.02%.
Temperature dependent measurements reveal antiferromagnetic correlations with a
Curie-Weiss temperature of -10 K. Albeit the electrical conductivity of
graphene is significantly reduced by ion bombardment, the spin resonance
induced change in conductivity is below 10^{-5}.",1407.6280v2
2014-11-30,Spin and charge dynamics of a quasi-one-dimensional antiferromagnetic metal,"We use quantum Monte Carlo simulations to study a finite-temperature
dimensional-crossover-driven evolution of spin and charge dynamics in weakly
coupled Hubbard chains with a half-filled band. The low-temperature behavior of
the charge gap indicates a crossover between two distinct energy scales: a
high-energy one-dimensional (1D) Mott gap due to the umklapp process and a
low-energy gap which stems from long-range antiferromagnetic (AF) fluctuations.
Away from the 1D regime and at temperature scales above the charge gap, the
emergence of a zero-frequency Drude-like feature in the interchain optical
conductivity $\sigma_{\perp}(\omega)$ implies the onset of a higher-dimensional
metal. In this metallic phase, enhanced quasiparticle scattering off
finite-range AF fluctuations results in incoherent single-particle dynamics.
The coupling between spin and charge fluctuations is also seen in the spin
dynamical structure factor $S({\pmb q},\omega)$ displaying damped spin
excitations (paramagnons) close to the AF wave-vector ${\pmb q}=(\pi,\pi)$ and
particle-hole continua near 1D momentum transfers spanning quasiparticles at
the Fermi surface. We relate our results to the charge deconfinement in
quasi-1D organic Bechgaard-Fabre salts.",1412.0287v2
2015-08-20,Spin-noise-based magnetometry of an $n$-doped GaAs microcavity in the field of elliptically polarized light,"Recently reported optical nuclear orientation in the $n$-doped GaAs
microcavity under pumping in nominal transparency region of the crystal [Appl.
Phys. Lett. $\mathbf{106}$, 242405 (2015)] has arisen a number of questions,
the main of them concerning mechanisms of angular momentum transfer from the
light to the nuclear spin system and the nature of the light-related magnetic
fields accompanying the optical nuclear polarization. In this paper, we use the
spin noise spectroscopy for magnetometric purposes, particularly, to study
effective fields acting upon electron spin system of an $n$-GaAs layer inside a
high-Q microcavity in the presence of elliptically polarized probe beam. In
addition to the external magnetic field applied to the sample in the Voigt
geometry and the Overhauser field created by optically oriented nuclei, the
spin noise spectrum reveals an additional effective, ""optical,"" magnetic field
produced by elliptically polarized probe itself. This field is directed along
the light propagation axis, with its sign being determined by the sign of the
probe helicity and its magnitude depending on degree of circular polarization
and intensity of the probe beam. We analyze properties of this optical magnetic
field and suggest that it results from the optical Stark effect in the field of
the elliptically polarized electromagnetic wave.",1508.04968v1
2016-02-08,Collective couplings: rectification and supertransmittance,"We investigate heat transport between two thermal reservoirs that are coupled
via a large spin composed of N identical two level systems. One coupling
implements the dissipative Dicke super- radiance. The other coupling is locally
of the pure-dephasing type and requires to go beyond the standard weak-coupling
limit by employing a Bogoliubov mapping in the corresponding reservoir. After
the mapping, the large spin is coupled to a collective mode with the original
pure-dephasing interaction, but the collective mode is dissipatively coupled to
the residual oscillators. Treating the large spin and the collective mode as
the system, a standard master equation approach is now able to capture the
energy transfer between the two reservoirs. Assuming fast relaxation of the
collective mode, we derive a coarse-grained rate equation for the large spin
only and discuss how the original Dicke superradiance is affected by the
presence of the additional reservoir. Our main finding is a cooperatively
enhanced rectification effect due to the interplay of supertransmittant heat
currents (scaling quadratically with $N$) and the asymmetric coupling to both
reservoirs. For large $N$, the system can thus significantly amplify current
asymmetries under bias reversal, functioning as a heat diode. We also briefly
discuss the case when the couplings of the collective spin are locally
dissipative, showing that the heat-diode effect is still present.",1602.02502v2
2016-03-09,Suppression of spin-exciton state in hole overdoped iron-based superconductors,"The mechanism of Cooper pair formation in iron-based superconductors remains
a controversial topic. The main question is whether spin or orbital
fluctuations are responsible for the pairing mechanism. To solve this problem,
a crucial clue can be obtained by examining the remarkable enhancement of
magnetic neutron scattering signals appearing in a superconducting phase. The
enhancement is called spin resonance for a spin fluctuation model, in which
their energy is restricted below twice the superconducting gap value (2Ds),
whereas larger energies are possible in other models such as an orbital
fluctuation model. Here we report the doping dependence of low-energy magnetic
excitation spectra in Ba1-xKxFe2As2 for 0.5<x<0.84 studied by inelastic neutron
scattering. We find that the behavior of the spin resonance dramatically
changes from optimum to overdoped regions. Strong resonance peaks are observed
clearly below 2Ds in the optimum doping region, while they are absent in the
overdoped region. Instead, there is a transfer of spectral weight from energies
below 2Ds to higher energies, peaking at values of 3Ds for x = 0.84. These
results suggest a reduced impact of magnetism on Cooper pair formation in the
overdoped region.",1603.02762v1
2016-05-11,Retrieving the ground state of spin glasses using thermal noise: Performance of quantum annealing at finite temperatures,"We study the problem to infer the ground state of a spin-glass Hamiltonian
using data from another Hamiltonian with interactions disturbed by noise from
the original Hamiltonian, motivated by the ground-state inference in quantum
annealing on a noisy device. It is shown that the average Hamming distance
between the inferred spin configuration and the true ground state is minimized
when the temperature of the noisy system is kept at a finite value, and not at
zero temperature. We present a spin-glass generalization of a well-established
result that the ground state of a purely ferromagnetic Hamiltonian is best
inferred at a finite temperature in the sense of smallest Hamming distance when
the original ferromagnetic interactions are disturbed by noise. We use the
numerical transfer-matrix method to establish the existence of an optimal
finite temperature in one- and two-dimensional systems. Our numerical results
are supported by mean-field calculations, which give an explicit expression of
the optimal temperature to infer the spin-glass ground state as a function of
variances of the distributions of the original interactions and the noise. The
mean-field prediction is in qualitative agreement with numerical data.
Implications on postprocessing of quantum annealing on a noisy device are
discussed.",1605.03303v2
2017-04-05,Influence of the nuclear Zeeman effect on mode locking in pulsed semiconductor quantum dots,"The coherence of the electron spin in a semiconductor quantum dot is strongly
enhanced by mode locking through nuclear focusing, where the synchronization of
the electron spin to periodic pulsing is slowly transferred to the nuclear
spins of the semiconductor material, mediated by the hyperfine interaction
between these. The external magnetic field that drives the Larmor oscillations
of the electron spin also subjects the nuclear spins to a Zeeman-like coupling,
albeit a much weaker one. For typical magnetic fields used in experiments, the
energy scale of the nuclear Zeeman effect is comparable to that of the
hyperfine interaction, so that it is not negligible. In this work, we analyze
the influence of the nuclear Zeeman effect on mode locking quantitatively.
Within a perturbative framework, we calculate the Overhauser-field distribution
after a prolonged period of pulsing. We find that the nuclear Zeeman effect can
exchange resonant and non-resonant frequencies. We distinguish between models
with a single type and with multiple types of nuclei. For the latter case, the
positions of the resonances depend on the individual $g$ factors, rather than
on the average value.",1704.01468v2
2017-06-14,The sensitivity of a radical pair compass magnetoreceptor can be significantly amplified by radical scavengers,"Birds have a remarkable ability to obtain navigational information from the
Earth's magnetic field. The primary detection mechanism of this compass sense
is uncertain but appears to involve the quantum spin dynamics of radical pairs
formed transiently in cryptochrome proteins. We propose here a new version of
the current model in which spin-selective recombination of the radical pair is
not essential. One of the two radicals is imagined to react with a paramagnetic
scavenger via spin-selective electron transfer. By means of simulations of the
spin dynamics of cryptochrome-inspired radical pairs, we show that the new
scheme offers two clear and important benefits. The sensitivity to a 50 {\mu}T
magnetic field is greatly enhanced and, unlike the current model, the radicals
can be more than 2 nm apart in the magnetoreceptor protein. The latter means
that animal cryptochromes that have a tetrad (rather than a triad) of
tryptophan electron donors can still be expected to be viable as magnetic
compass sensors. Lifting the restriction on the rate of the spin-selective
recombination reaction also means that the detrimental effects of inter-radical
exchange and dipolar interactions can be minimised by placing the radicals much
further apart than in the current model.",1706.04564v3
2017-12-15,Quantum entanglement in the neighborhood of pseudo-transition for a spin-1/2 Ising-XYZ diamond chain,"Recently has been observed for some one-dimensional models that exhibit
unexpected pseudo-transitions and quasi-phases. This pseudo-transition
resembles a first- and second-order phase transition simultaneously. One of
those models is the spin-1/2 Ising-XYZ diamond chain, composed of Ising spin
particles at the nodal sites and the Heisenberg spin particles at the
interstitial sites. Where we assume Ising-type interaction between the nodal
and interstitial sites, the Heisenberg-type interaction between interstitial
sites, and with an external magnetic field applied along the z-axis. This model
presents an exact analytical solution applying the transfer matrix technique,
which shows 3 phases at zero temperature in the vicinity of pseudo-transition.
The pseudo-transition separates quasi-phases, these quasi-phases still hold at
a finite temperature most of the pattern configurations of a true phase at zero
temperature. Here we study the quantum entanglement of pair spin particles in
the quasi-phase regions, which can be measured through the concurrence. Then we
observe an unexpected behavior in the concurrence, that is below
pseudo-critical temperature the concurrence remains almost constant up to
pseudo-critical temperature, but above the pseudo-critical temperature, the
concurrence behaves as for the standard one-dimensional spin models. Further,
we consider the entropy behavior of the system, below pseudo-critical
temperature the entropy becomes almost null, while above pseudo-critical
temperature the system exhibits standard behavior as for ordinary
one-dimensional spin models.",1712.05621v3
2018-06-21,Quark spins and Anomalous Ward Identity,"We calculate the intrinsic quark spin contribution to the total proton spin
using overlap valence quarks on three ensembles of $2+1$-flavor RBC/UKQCD
domain-wall configurations with different lattice spacings. The lowest pion
mass of the ensembles is around 171 MeV which is close to the physical point.
With overlap fermions and topological charge derived from the overlap operator,
we verify the anomalous Ward identity between nucleon states with momentum
transfer. Both the connected and disconnected insertions of the axial-vector
current are calculated. For the disconnected-insertion part, the
cluster-decomposition error reduction (CDER) technique is utilized for the
lattice with the largest volume and the error can be reduced by $10\%\sim40\%$.
Nonperturbative renormalization is carried out and the final results are all
reported in the $\overline{{\rm MS}}$ scheme at 2 GeV. We determine the total
quark spin contribution to the nucleon spin to be $\Delta\Sigma=0.401(25)(37)$,
which is consistent with the recent global fitting result of experimental data.
The isovector axial coupling we obtain in this study is $g_A^3=1.256(16)(30)$,
which agrees well with the experimental value of 1.2723(23).",1806.08366v2
2018-09-21,Tailored single-atom collisions at ultra-low energies,"We employ collisions of individual atomic cesium (Cs) impurities with an
ultracold rubidium (Rb) gas to probe atomic interaction with hyperfine- and
Zeeman-state sensitivity. Controlling the Rb bath's internal state yields
access to novel phenomena observed in inter-atomic spin-exchange. These can be
tailored at ultra-low energies, owing to the excellent experimental control
over all relevant energy scales. First, detecting spin-exchange dynamics in the
Cs hyperfine state manifold, we resolve a series of previously unreported
Feshbach resonances at magnetic fields below 300 mG, separated by energies as
low as $h\times 15$ kHz. The series originates from a coupling to molecular
states with binding energies below $h\times 1$ kHz and wave function extensions
in the micrometer range. Second, at magnetic fields below $\approx 100\,$mG, we
observe the emergence of a new reaction path for alkali atoms, where in a
single, direct collision between two atoms two quanta of angular momentum can
be transferred. This path originates from the hyperfine-analogue of dipolar
spin-spin relaxation. Our work yields control of subtle ultra-low-energy
features of atomic collision dynamics, opening new routes for advanced
state-to-state chemistry, for controlling spin-exchange in quantum many-body
systems for solid state simulations, or for determination of high-precision
molecular potentials.",1809.08165v2
2018-10-05,Spin-Dependent Electron Transmission Model for Chiral Molecules in Mesoscopic Devices,"Various device-based experiments have indicated that electron transfer in
certain chiral molecules may be spin-dependent, a phenomenon known as the
Chiral Induced Spin Selectivity (CISS) effect. However, due to the complexity
of these devices and a lack of theoretical understanding, it is not always
clear to what extent the chiral character of the molecules actually contributes
to the magnetic-field-dependent signals in these experiments. To address this
issue, we report here an electron transmission model that evaluates the role of
the CISS effect in two-terminal and multi-terminal linear-regime electron
transport experiments. Our model reveals that for the CISS effect, the
chirality-dependent spin transmission is accompanied by a spin-flip electron
reflection process. Furthermore, we show that more than two terminals are
required in order to probe the CISS effect in the linear regime. In addition,
we propose two types of multi-terminal nonlocal transport measurements that can
distinguish the CISS effect from other magnetic-field-dependent signals. Our
model provides an effective tool to review and design CISS-related transport
experiments, and to enlighten the mechanism of the CISS effect itself.",1810.02662v2
2018-10-11,Accretion in a dynamical spacetime and spinning up of the black hole in the gamma ray burst central engine,"We compute the evolution of a quasi-spherical, slowly rotating accretion flow
around a black hole, whose mass and spin evolve adequately to the mass-energy
transfer through the horizon. Our model is relevant for the central engine
driving a long gamma ray burst, that originates from the collapse of a massive
star. The computations of a GRB engine in a dynamically evolving spacetime
metric are important specifically due to the transient nature of the event, in
which a huge amount of mass is accreted and changes the fundamental black hole
parameters, its mass and spin, during the process. We discuss the results in
the context of angular momentum magnitude of the collapsing star. We also study
the possible formation and evolution of shocks in the envelope, which may
temporarily affect accretion. Our results are important for the limitations on
the mass and spin range of black holes detected independently by
electromagnetic observations of GRBs and gravitational waves. We speculate on
the possible constraints for the final masses and spins of these astrophysical
black holes. It is shown that the most massive BHs were rahter not formed in a
powerful GRB explosion, if the cores of their progenitors were only weakly
rotating.",1810.05261v1
2018-11-30,Double bit in-plane magnetic skyrmions on a track,"A magnetic skyrmion isusually refers to a twisted spin texture surrounded by
uniformly aligned out-of-plane spinsin the background of a uniformly magnetized
state. The invariance of the magnetic skyrmion conserves its topological charge
under any continuous transformations of the spin textures, leads to which
represents the robustness of a magnetic skyrmion their texture against external
perturbations, making it ideal to use skyrmions as . Such a behaviour is
required for an ideal information carriers. To date, most magnetic skyrmion
studies have been performedfocused on in perpendicularly magnetized systems,
where the skyrmion topological number is determined by the relative orientation
between the core and /outer perpendicular magnetization directions of the
skyrmion is either up/down or down/up. Here we show that there also exists a
new type of magnetic skyrmion with surrounding spins to be uniformly aligned to
the in-plane direction. By continuous transformation and relaxation of the spin
textures of out-of-plane skyrmions, we showed that an in-plane skyrmion, where
the background magnetization is in the in-plane direction, is also possible.
Different from the conventional perpendicular magnetic skyrmionsContrary to the
skyrmions in a perpendicularly magnetized state, the in-plane magnetic
skyrmions with opposite signs of topological charges can inherentlycharges can
inherently coexist in the in-plane magnetization system coexist. Moreover, the
iIn-plane skyrmions of opposite charge can move together by an electric current
and exhibit with an opposite spin Hall effect. These findings showdemonstrate
the inherent possibility of a double-bit transfer in a single magnetic wire
that is not possible in a perpendicularly magnetized system.",1811.12552v1
2019-01-28,Spin Hall magnetoresistance in heterostructures consisting of noncrystalline paramagnetic YIG and Pt,"The spin Hall magnetoresistance (SMR) effect arises from spin-transfer
processes across the interface between a spin Hall active metal and an
insulating magnet. While the SMR response of ferrimagnetic and
antiferromagnetic insulators has been studied extensively, the SMR of a
paramagnetic spin ensemble is not well established. Thus, we investigate herein
the magnetoresistive response of as-deposited yttrium iron garnet/platinum thin
film bilayers as a function of the orientation and the amplitude of an
externally applied magnetic field. Structural and magnetic characterization
show no evidence for crystalline order or spontaneous magnetization in the
yttrium iron garnet layer. Nevertheless, we observe a clear magnetoresistance
response with a dependence on the magnetic field orientation characteristic for
the SMR. We propose two models for the origin of the SMR response in
paramagnetic insulator/Pt heterostructures. The first model describes the SMR
of an ensemble of non-interacting paramagnetic moments, while the second model
describes the magnetoresistance arising by considering the total net moment.
Interestingly, our experimental data are consistently described by the net
moment picture, in contrast to the situation in compensated ferrimagnets or
antiferromagnets.",1901.09986v1
2019-04-05,Circuit-Model Analysis for Spintronic Devices with Chiral Molecules as Spin Injectors,"Recent research discovered that charge transfer processes in chiral molecules
can be spin selective and named the effect chiral-induced spin selectivity
(CISS). Follow-up work studied hybrid spintronic devices with conventional
electronic materials and chiral (bio)molecules. However, a theoretical
foundation for the CISS effect is still in development and the spintronic
signals were not evaluated quantitatively. We present a circuit-model approach
that can provide quantitative evaluations. Our analysis assumes the scheme of a
recent experiment that used photosystem~I (PSI) as spin injectors, for which we
find that the experimentally observed signals are, under any reasonable
assumptions on relevant PSI time scales, too high to be fully due to the CISS
effect. We also show that the CISS effect can in principle be detected using
the same type of solid-state device, and by replacing silver with graphene, the
signals due to spin generation can be enlarged four orders of magnitude. Our
approach thus provides a generic framework for analyzing this type of
experiments and advancing the understanding of the CISS effect.",1904.03142v2
2019-06-13,Impact of electromagnetic fields and heat on spin transport signals in Y$_{3}$Fe$_{5}$O$_{12}$,"Exploring new strategies to perform magnon logic is a key requirement for the
further development of magnon-based spintronics. In this work, we realize a
three-terminal magnon transport device to study the possibility of manipulating
magnonic spin information transfer in a magnetic insulator via localized
magnetic fields and heat generation. The device comprises two parallel Pt wires
as well as a Cu center wire that are deposited on the ferrimagnetic insulator
Y$_{3}$Fe$_{5}$O$_{12}$. While the Pt wires act as spin current injector and
detector, the Cu wire is used to create local magnetostatic fields and
additional heat, which impact both the magnetic configuration and the magnons
within the Y$_{3}$Fe$_{5}$O$_{12}$ below. We show that these factors can create
a non-local signal that shows similar features as compared to an electrically
induced magnon flow. Furthermore, a modulation of the spin transport signal
between the Pt wires is observed, which can be partly explained by thermally
excited spin currents of different polarization. Our results indicate a
potential way towards the manipulation of non-local magnon signals, which could
be useful for magnon logic.",1906.05631v2
2020-01-06,Susceptibility of the one-dimensional Ising model: is the singularity at T = 0 an essential one?,"The zero-field isothermal susceptibility of the one-dimensional Ising model
with nearest-neighbor interactions and a finite number of spins is shown to
have a relatively simple singularity as the temperature approaches zero,
proportional only to the inverse temperature. This is in contrast to what is
seen throughout the literature for the inifinite chain: an essential
singularity that includes an exponential dependence on the inverse temperature.
Assuming an arbitrary (but finite) number of spins and retaining terms that are
usually considered ignorable in the thermodynamic limit, the analysis involves
nothing beyond straightforward series expansions, starting either from the
partition function for a closed chain in a magnetic field, obtained using the
transfer-matrix approach; or from the expression for the zero-field
susceptibility found via the fluctuation-dissipation theorem. In both cases,
the exponential singularity is exactly removed. In addition, the susceptibility
per spin is found to increase with the number of spins (except in the case of
noninteracting spins), a result which is also at variance with what is normally
reported for an infinite chain.",2001.01693v4
2020-01-29,Theoretical and Computational Framework for the Analysis of the Relaxation Properties of Arbitrary Spin Systems. Application to High-Resolution Relaxometry,"A wide variety of nuclear magnetic resonance experiments rely on the
prediction and analysis of relaxation processes. Recently, innovative
approaches have been introduced where the sample travels through a broad range
of magnetic fields in the course of the experiment, such as dissolution dynamic
nuclear polarization or high-resolution relaxometry. Understanding the
relaxation properties of nuclear spin systems over orders of magnitude of
magnetic fields is essential to rationalize the results of these experiments.
For example, during a high-resolution relaxometry experiment, the absence of
control of nuclear spin relaxation pathways during the sample transfers and
relaxation delays leads to systematic deviations of polarization decays from an
ideal mono-exponential decay with the pure longitudinal relaxation rate. These
deviations have to be taken into account to describe quantitatively the
dynamics of the system. Here, we present computational tools to (1) calculate
analytical expressions of relaxation rates for a broad variety of spin systems
and (2) use these analytical expressions to correct the deviations arising in
high-resolution relaxometry experiments. These tools lead to a better
understanding of nuclear spin relaxation, which is required to improve the
sensitivity of many pulse sequences, and to better characterize motions in
macromolecules.",2001.10775v2
2020-04-05,Spin wave based tunable switch between superconducting flux qubits,"Quantum computing hardware has received world-wide attention and made
considerable progress recently. YIG thin film have spin wave (magnon) modes
with low dissipation and reliable control for quantum information processing.
However, the coherent coupling between a quantum device and YIG thin film has
yet been demonstrated. Here, we propose a scheme to achieve strong coupling
between superconducting flux qubits and magnon modes in YIG thin film. Unlike
the direct $\sqrt{N}$ enhancement factor in coupling to the Kittel mode or
other spin ensembles, with N the total number of spins, an additional spatial
dependent phase factor needs to be considered when the qubits are magnetically
coupled with the magnon modes of finite wavelength. To avoid undesirable
cancelation of coupling caused by the symmetrical boundary condition, a CoFeB
thin layer is added to one side of the YIG thin film to break the symmetry. Our
numerical simulation demonstrates avoided crossing and coherent transfer of
quantum information between the flux qubits and the standing spin waves in YIG
thin films. We show that the YIG thin film can be used as a tunable switch
between two flux qubits, which have modified shape with small direct inductive
coupling between them. Our results manifest that it is possible to couple flux
qubits while suppressing undesirable cross-talk.",2004.02156v1
2020-05-20,Fluorine Intercalated Graphene: Formation of a 2D Spin Lattice through Pseudoatomization,"A suspended layer made up of ferromagnetically ordered spins could be created
between two mono/multilayer graphene through intercalation. Stability and
electronic structure studies show that, when fluorine molecules are
intercalated between two mono/multilayer graphene, their bonds get stretched
enough ($\sim$ 1.9$-$2.0 {\AA}) to weaken their molecular singlet eigenstate.
Geometrically, these stretched molecules form a pseudoatomized fluorine layer
by maintaining a van der Waals separation of $\sim$ 2.6 {\AA} from the adjacent
carbon layers. As there is a significant charge transfer from the adjacent
carbon layers to the fluorine layers, a mixture of triplet and doublet states
stabilize to induce local spin-moments at each fluorine sites and in turn form
a suspended 2D spin lattice. The spins of this lattice align ferromagnetically
with nearest neighbour coupling strength as large as $\sim$ 100 meV. Our finite
temperature \textit {ab initio} molecular dynamics study reveals that the
intercalated system can be stabilized up to a temperature of 100 K with an
average magnetic moment of $\sim$ 0.6 $\mu_{B}$/F. However, if the graphene
layers can be held fixed, the room temperature stability of such a system is
feasible.",2005.09888v1
2020-10-09,From hard spheres to hard-core spins,"A system of hard spheres exhibits physics that is controlled only by their
density. This comes about because the interaction energy is either infinite or
zero, so all allowed configurations have exactly the same energy. The low
density phase is liquid, while the high density phase is crystalline, an
example of ""order by disorder"" as it is driven purely by entropic
considerations. Here we study a family of hard spin models, which we call
hardcore spin models, where we replace the translational degrees of freedom of
hard spheres with the orientational degrees of freedom of lattice spins. Their
hardcore interaction serves analogously to divide configurations of the many
spin system into allowed and disallowed sectors. We present detailed results on
the square lattice in $d=2$ for a set of models with $\mathbb{Z}_n$ symmetry,
which generalize Potts models, and their $U(1)$ limits, for ferromagnetic and
antiferromagnetic senses of the interaction, which we refer to as exclusion and
inclusion models. As the exclusion/inclusion angles are varied, we find a
Kosterlitz-Thouless phase transition between a disordered phase and an ordered
phase with quasi-long-ranged order, which is the form order by disorder takes
in these systems. These results follow from a set of height representations, an
ergodic cluster algorithm, and transfer matrix calculations.",2010.04714v2
2020-10-26,Pressure-induced phase transition in the $J_1$-$J_2$ square lattice antiferromagnet RbMoOPO$_4$Cl,"We report results of magnetization and $^{31}$P NMR measurements under high
pressure up to 6.4~GPa on RbMoOPO$_4$Cl, which is a frustrated square-lattice
antiferromagnet with competing nearest-neighbor and next-nearest-neighbor
interactions. Anomalies in the pressure dependences of the NMR shift and the
transferred hyperfine coupling constants indicate a structural phase transition
at 2.6~GPa, which is likely to break mirror symmetry and triggers significant
change of the exchange interactions. In fact, the NMR spectra in magnetically
ordered states reveal a change from the columnar antiferromagnetic (CAF) order
below 3.3~GPa to the N\'{e}el antiferromagnetic (NAF) order above 3.9~GPa. The
spin lattice relaxation rate $1/T_1$ also indicates a change of dominant
magnetic fluctuations from CAF-type to NAF-type with pressure. Although the NMR
spectra in the intermediate pressure region between 3.3 and 3.9 GPa show
coexistence of the CAF and NAF phases, a certain component of $1/T_1$ shows
paramagnetic behavior with persistent spin fluctuations, leaving possibility
for a quantum disordered phase. The easy-plane anisotropy of spin fluctuations
with unusual nonmonotonic temperature dependence at ambient pressure gets
reversed to the Ising anisotropy at high pressures. This unexpected anisotropic
behavior for a spin 1/2 system may be ascribed to the strong spin-orbit
coupling of Mo-4$d$ electrons.",2010.13538v2
2020-12-07,Topological chiral spin liquids and competing states in triangular lattice SU($N$) Mott insulators,"SU($N$) Mott insulators have been proposed and/or realized in solid-state
materials and with ultracold atoms on optical lattices. We study the
two-dimensional SU($N$) antiferromagnets on the triangular lattice. Starting
from an SU($N$) Heisenberg model with the fundamental representation on each
site in the large-$N$ limit, we perform a self-consistent calculation and find
a variety of ground states including the valence cluster states, stripe ordered
states with a doubled unit-cell and topological chiral spin liquids. The system
favors a cluster or ordered ground state when the number of flavors $N$ is less
than 6. It is shown that, increasing the number of flavors enhances quantum
fluctuations and eventually transfer the clusterized ground states into a
topological chiral spin liquids. This chiral spin liquid ground state has an
equivalent for the square lattice SU($N$) magnets. We further identify the
corresponding lowest competing states that represent another distinct type of
chiral spin liquid states. We conclude with a discussion about the relevant
systems and the experimental probes.",2012.03444v3
2021-03-02,Spin state and moment of inertia of Venus,"Fundamental properties of the planet Venus, such as its internal mass
distribution and variations in length of day, have remained unknown. We used
Earth-based observations of radar speckles tied to the rotation of Venus
obtained in 2006-2020 to measure its spin axis orientation, spin precession
rate, moment of inertia, and length-of-day variations. Venus is tilted by
2.6392 $\pm$ 0.0008 degrees ($1\sigma$) with respect to its orbital plane. The
spin axis precesses at a rate of 44.58 $\pm$ 3.3 arcseconds per year
($1\sigma$), which gives a normalized moment of inertia of 0.337 $\pm$ 0.024
and yields a rough estimate of the size of the core. The average sidereal day
on Venus in the 2006-2020 interval is 243.0226 $\pm$ 0.0013 Earth days
($1\sigma$). The spin period of the solid planet exhibits variations of 61 ppm
($\sim$20 minutes) with a possible diurnal or semidiurnal forcing. The
length-of-day variations imply that changes in atmospheric angular momentum of
at least $\sim$4% are transferred to the solid planet.",2103.01504v2
2021-08-16,Neutron Scattering Signature of Phonon Renormalization in Nickel (II) Oxide,"The physics of mutual interaction of phonon quasiparticles with electronic
spin degrees of freedom, leading to unusual transport phenomena of spin and
heat, has been a subject of continuing interests for decades. Despite its
pivotal role in transport processes, the effect of spin-phonon coupling on the
phonon system, especially acoustic phonon properties, has so far been elusive.
By means of inelastic neutron scattering and first-principles calculations,
anomalous scattering spectral intensity from acoustic phonons was identified in
the exemplary collinear antiferromagnetic nickel (II) oxide, unveiling strong
spin-lattice correlations that renormalize the polarization of acoustic phonon.
In particular, a clear magnetic scattering signature of the measured neutron
scattering intensity from acoustic phonons is demonstrated by its momentum
transfer and temperature dependences. The anomalous scattering intensity is
successfully modeled with a modified magneto-vibrational scattering cross
section, suggesting the presence of spin precession driven by phonon. The
renormalization of phonon eigenvector is indicated by the observed
""geometry-forbidden"" neutron scattering intensity from transverse acoustic
phonon. Importantly, the eigenvector renormalization cannot be explained by
magnetostriction but instead, it could result from the coupling between phonon
and local magnetization of ions.",2108.07363v3
2021-09-15,Bi-Hamiltonian structure of Sutherland models coupled to two ${\mathfrak u}(n)^*$-valued spins from Poisson reduction,"We introduce a bi-Hamiltonian hierarchy on the cotangent bundle of the real
Lie group ${\mathrm{GL}}(n,{\mathbb{C}})$, and study its Poisson reduction with
respect to the action of the product group ${{\mathrm U}(n)} \times {{\mathrm
U}(n)}$ arising from left- and right-multiplications. One of the pertinent
Poisson structures is the canonical one, while the other is suitably
transferred from the real Heisenberg double of ${\mathrm{GL}}(n,{\mathbb{C}})$.
When taking the quotient of $T^*{\mathrm{GL}}(n,{\mathbb{C}})$ we focus on the
dense open subset of ${\mathrm{GL}}(n,{\mathbb{C}})$ whose elements have
pairwise distinct singular values. We develop a convenient description of the
Poisson algebras of the ${{\mathrm U}(n)} \times {{\mathrm U}(n)}$ invariant
functions, and show that one of the Hamiltonians of the reduced bi-Hamiltonian
hierarchy yields a hyperbolic Sutherland model coupled to two ${\mathfrak
u}(n)^*$-valued spins. Thus we obtain a new bi-Hamiltonian interpretation of
this model, which represents a special case of Sutherland models coupled to two
spins obtained earlier from reductions of cotangent bundles of reductive Lie
groups equipped with their canonical Poisson structure. Upon setting one of the
spins to zero, we recover the bi-Hamiltonian structure of the standard
hyperbolic spin Sutherland model that was derived recently by a different
method.",2109.07391v2
2021-12-06,First principles theory for the magnetic and charge instabilities in AV$_3$Sb$_5$ systems,"Vanadium-based materials AV$_3$Sb$_5$ (A=K, Rb, Cs) with layered kagome
lattice structures have drawn great attention recently due to the discoveries
of topologically nontrivial band structures, charge density wave states, giant
anomalous Hall effect, as well as unusual superconducting phase at low
temperatures. In this work, we theoretically study the magnetic and charge
instabilities for this class of materials based on first principles
calculations. We develop a method to calculate the generalized susceptibility
tensor defined in the sublattice-orbital-spin space, with the effects of
Coulomb interactions treated by generalized random phase approximation (RPA).
The RPA susceptibility calculations indicate that there are three leading
ferromagnetic instability modes at $\Gamma$ point, which are further verified
by unrestricted self-consistent Hartree-Fock calculations including both the
on-site and inter-site Coulomb interactions. The inclusion of inter-site
interactions tend to suppress the spin ferromagnetism due to charge transfer
from the V to Sb sites, leading to weak spin magnetic moments $\sim
0.1\mu_{\textrm{B}}$ per V atom with small intrinsic anomalous Hall
conductivity. Current loops can be generated in such weak spin ferromagnetic
states as a result of spin-orbit coupling effects. The electronic structures in
the ferromagnetic states are significantly reconstructed which have nearly
compensated electron and hole carriers from two bands. On the other hand, we do
not find any diverging instability mode at $M$ point driven by
electron-electron Coulomb interactions. First principles phonon calculations
indicate that there are unstable phonon modes which tend to drive the system
into an inverse star-of-David structure. Our results indicate that there may be
separate phase transitions in the magnetic and charge channels in the system.",2112.02808v1
2022-02-09,A new generation of effective core potentials from correlated and spin-orbit calculations: selected heavy elements,"We introduce new correlation consistent effective core potentials (ccECPs)
for the elements I, Te, Bi, Ag, Au, Pd, Ir, Mo, and W with $4d$, $5d$, $6s$ and
$6p$ valence spaces. These ccECPs are given as a sum of spin-orbit averaged
relativistic effective potential (AREP) and effective spin-orbit (SO) terms.
The construction involves several steps with increasing refinements from more
simple to fully correlated methods. The optimizations are carried out with
objective functions that include weighted many-body atomic spectra,
norm-conservation criteria, and spin-orbit splittings. Transferability tests
involve molecular binding curves of corresponding hydride and oxide dimers. The
constructed ccECPs are systematically better and in a few cases on par with
previous effective core potential (ECP) tables on all tested criteria and
provide a significant increase in accuracy for valence-only calculations with
these elements. Our study confirms the importance of the AREP part in
determining the overall quality of the ECP even in the presence of sizable
spin-orbit effects. The subsequent quantum Monte Carlo (QMC) calculations point
out the importance of accurate trial wave functions which in some cases (mid
series transition elements) require treatment well beyond single-reference.",2202.04747v2
2022-07-24,Wigner-molecularization-enabled dynamic nuclear field programming,"Multielectron semiconductor quantum dots (QDs) provide a novel platform to
study the role of Coulomb correlations in finite quantum systems and their
impact on many-body energy spectra. An example is the formation of
interaction-driven, spatially localized electron states of Wigner molecules
(WMs). Although Wigner molecularization has been confirmed by real-space
imaging and coherent spectroscopy, the open system dynamics of the
strongly-correlated states with the environment are not yet well understood.
Here, we demonstrate efficient control of spin transfer between an artificial
three-electron WM and the nuclear environment in a GaAs double QD. A
Landau-Zener sweep-based polarization sequence and low-lying anti-crossings of
spin multiplet states enabled by Wigner molecularization are utilized. An
efficient polarization rate of 2.58 $h \cdotp kHz \cdotp (g^* \cdotp
\mu_B)^{-1}$ per electron spin flip and, consequently, programmable nuclear
polarization by controlled single-electron tunneling are achieved. Combined
with coherent control of spin states, we achieve control of magnitude,
polarity, and site dependence of the nuclear field. It is demonstrated that the
same level of control cannot be achieved in the non-interacting regime. Thus,
we confirm the multiplet spin structure of a WM, paving the way for active
control of newly emerging correlated electron states for application in
mesoscopic environment engineering.",2207.11655v1
2022-10-06,Random Max-CSPs Inherit Algorithmic Hardness from Spin Glasses,"We study random constraint satisfaction problems (CSPs) in the unsatisfiable
regime. We relate the structure of near-optimal solutions for any Max-CSP to
that for an associated spin glass on the hypercube, using the Guerra-Toninelli
interpolation from statistical physics. The noise stability polynomial of the
CSP's predicate is, up to a constant, the mixture polynomial of the associated
spin glass. We prove two main consequences:
  1) We relate the maximum fraction of constraints that can be satisfied in a
random Max-CSP to the ground state energy density of the corresponding spin
glass. Since the latter value can be computed with the Parisi formula, we
provide numerical values for some popular CSPs.
  2) We prove that a Max-CSP possesses generalized versions of the overlap gap
property if and only if the same holds for the corresponding spin glass. We
transfer results from Huang et al. [arXiv:2110.07847, 2021] to obstruct
algorithms with overlap concentration on a large class of Max-CSPs. This
immediately includes local classical and local quantum algorithms.",2210.03006v2
2023-04-21,Exploiting the close-to-Dirac point shift of Fermi level in Sb2Te3/Bi2Te3 topological insulator heterostructure for spin-charge conversion,"Properly tuning the Fermi level position in topological insulators is of
vital importance to tailor their spin-polarized electronic transport and to
improve the efficiency of any functional device based on them. Here we report
the full in situ Metal Organic Chemical Vapor Deposition (MOCVD) and study of a
highly crystalline Bi2Te3/Sb2Te3 topological insulator heterostructure on top
of large area (4'') Si(111) substrates. The bottom Sb2Te3 layer serves as an
ideal seed layer for the growth of highly crystalline Bi2Te3 on top, also
inducing a remarkable shift of the Fermi level to place it very close to the
Dirac point, as visualized by angle-resolved photoemission spectroscopy. In
order to exploit such ideal topologically-protected surface states, we
fabricate the simple spin-charge converter Si(111)/Sb2Te3/Bi2Te3/Au/Co/Au and
spin-charge conversion (SCC) is probed by spin pumping ferromagnetic resonance.
A large SCC is measured at room temperature, which is interpreted within the
inverse Edelstein effect (IEE), thus resulting in a conversion efficiency
lambda_IEE of 0.44 nm. Our results demonstrate the successful tuning of the
surface Fermi level of Bi2Te3 when grown on top of Sb2Te3 with a full in situ
MOCVD process, which is highly interesting in view of its future technology
transfer.",2304.10841v1
2023-08-29,Relativistic and Spin-Orbit Dynamics at Non-Relativistic Intensities in Strong-Field Ionization,"Spin-orbit dynamics and relativistic corrections to the kinetic energy in
strong-field dynamics, have long been ignored for near- and mid-IR fields with
intensities $10^{13}$--$10^{14}$ W/cm$^2$, as the final photoelectron energies
are considered too low for these effects to play a role. However, using a
precise and flexible path-integral formalism, we include all correction terms
from the fine-structure, Breit-Pauli Hamiltonian. This enables a treatment of
spin, through coherent spin-states, which is the first model to use this
approach in strong-field physics. We are able to show that the most
energetically rescattered wavepackets, undergo huge momentum transfer and
briefly reach relativistic velocities, which warrants relativistic kinetic
energy corrections. We probe these effects and show that they yield notable
differences for a $1600$ nm wavelength laser field on the dynamics and the
photoelectron spectra. Furthermore, we find that the dynamical spin-orbit
coupling is strongly overestimated if relativistic corrections to kinetic
energy are not considered. Finally, we derive a new condition that demonstrates
that relativistic effects begin to play a role at intensities orders of
magnitude lower than expected. Our findings may have important implication for
imaging processes such as laser-induced electron diffraction, which includes
high-energy photoelectron recollisions.",2308.15374v1
2023-09-11,Unified tensor network theory for frustrated classical spin models in two dimensions,"Frustration is a ubiquitous phenomenon in many-body physics that influences
the nature of the system in a profound way with exotic emergent behavior.
Despite its long research history, the analytical or numerical investigations
on frustrated spin models remain a formidable challenge due to their extensive
ground state degeneracy. In this work, we propose a unified tensor network
theory to numerically solve the frustrated classical spin models on various
two-dimensional (2D) lattice geometry with high efficiency. We show that the
appropriate encoding of emergent degrees of freedom in each local tensor is of
crucial importance in the construction of the infinite tensor network
representation of the partition function. The frustrations are thus relieved
through the effective interactions between emergent local degrees of freedom.
Then the partition function is written as a product of a one-dimensional (1D)
transfer operator, whose eigen-equation can be solved by the standard algorithm
of matrix product states rigorously, and various phase transitions can be
accurately determined from the singularities of the entanglement entropy of the
1D quantum correspondence. We demonstrated the power of our unified theory by
numerically solving 2D fully frustrated XY spin models on the kagome, square
and triangular lattices, giving rise to a variety of thermal phase transitions
from infinite-order Brezinskii-Kosterlitz-Thouless transitions, second-order
transitions, to first-order phase transitions. Our approach holds the potential
application to other types of frustrated classical systems like Heisenberg spin
antiferromagnets.",2309.05321v1
2023-12-03,Raman fingerprints of spin-phonon coupling and magnetic transition in an organic molecule intercalated Cr2Ge2Te6,"The manipulation of spin-phonon coupling in both formations and explorations
of magnetism in two-dimensional van der Waals ferromagnetic semiconductors
facilitates unprecedented prospects for spintronics devices. The interlayer
engineering tunes spin-phonon coupling significantly and holds the promise for
controllable magnetism via organic cation intercalation. Here, we present
spectroscopic evidence to reveal the intercalation effect on intrinsic magnetic
and electronic transitions in quasi-two-dimensional Cr2Ge2Te6 using tetrabutyl
ammonium as the intercalant. The temperature-evolution of Raman modes E_g^3 and
A_g^1, along with the magnetization measurements, unambiguously captures the
enhancement of the ferromagnetic Curie temperature in the intercalated
heterostructure. Moreover, the E_g^4 mode highlighted the increased effect of
spin-phonon interaction in magnetic order-induced lattice distortion. Combined
with the first-principle calculations, we observed a substantial number of
electrons transferred from TBA+ to Cr through the interface. These results
provide the interplay between spin-phonon coupling and magnetic ordering in van
der Waals magnets where Raman fingerprints would be highly beneficial for
further understanding the manipulation of magnetism in layered
heterostructures.",2312.01270v1
2024-01-12,FeS2 monolayer: a high valence and high-$T_{\rm C}$ Ising ferromagnet,"Two-dimensional (2D) magnetic materials are of current great interest for
their promising applications in spintronics. Strong magnetic coupling and
anisotropy are both highly desirable for the achievement of a high temperature
magnetic order. Here we propose the unusual high valent FeS$_2$ hexagonal
monolayer as such a candidate for a strong Ising 2D ferromagnet (FM), by
spin-orbital state analyses, first-principles calculations, and the
renormalized spin-wave theory (RSWT). We find that very importantly, the high
valent Fe$^{4+}$ ion is in the low-spin state ($t_{2g}^{4}$, $S$=1) with
degenerate $t_{2g}$ orbitals rather than the high-spin state
($t_{2g}^{3}e_g^{1}$, $S$=2). It is the low-spin state that allows to carry a
large perpendicular orbital moment and then produces a huge single ion
anisotropy (SIA) of 25 meV/Fe. Moreover, the negative charge transfer character
associated with the unusual high valence, strong Fe $3d$-S $3p$ hybridization,
wide bands, and a small band gap all help to establish a strong superexchange.
Indeed, our first-principles calculations confirm the strong FM superexchange
and the huge perpendicular SIA, both of which are further enhanced by a
compressive strain. Then, our RSWT calculations predict that the FM $T_{\rm C}$
is 261 K for the pristine FeS$_2$ monolayer and could be increased to 409 K
under the compressive --5\% strain. The high $T_{\rm C}$ is also reproduced by
our Monte Carlo (MC) simulations. Therefore, it is worth exploring the
high-$T_{\rm C}$ Ising FMs in the high valent 2D magnetic materials with
degenerate orbitals.",2401.06357v1
2024-01-19,Microwave single-photon detection using a hybrid spin-optomechanical quantum interface,"While infrared and optical single-photon detectors exist at high quantum
efficiencies, detecting single microwave photons has been an ongoing challenge.
Specifically, microwave photon detection is challenging compared to its optical
counterpart as its energy scale is four to five orders of magnitude smaller,
necessitating lower operating temperatures. Here, we propose a hybrid
spin-optomechanical interface to detect single microwave photons. The microwave
photons are coupled to a phononic resonator via piezoelectric actuation. This
phononic cavity also acts as a photonic cavity with an embedded Silicon-Vacancy
(SiV) center in diamond. Phonons mediate the quantum state transfer of the
microwave cavity to the SiV spin, in order to allow for high spin-mechanical
coupling at the single quantum level. From this, the optical cavity is used to
perform a cavity-enhanced single-shot readout of the spin-state. Here, starting
with a set of experimentally realizable parameters, we simulate the complete
protocol and estimate an overall detection success probability $P_s^0$ of
$0.972$, Shannon's mutual information $I^{0}(X;Y)$ of $0.82\ln(2)$, and a total
detection time of $\sim2$ $\mu s$. We also talk about the experimental regimes
in which $P_s^0$ tends to near unity and $I^{0}(X;Y)$ tends to $\ln(2)$
indicating exactly one bit of information retrieval about the presence or
absence of a microwave photon.",2401.10455v1
2024-02-05,Understanding voltage-controlled magnetic anisotropy effect for the manipulation of dipolar-dominated propagating spin waves,"Spin waves, known for their ability to propagate without the involvement of
moving charges, hold immense promise for on-chip information transfer and
processing, offering a path toward post-CMOS computing technologies. This study
investigates the potential synergy between propagating Damon-Eshbach spin waves
and voltage-controlled magnetization in the pursuit of environmentally
sustainable computing solutions. Employing micromagnetic simulations, we assess
the feasibility of utilizing spin waves in DE mode in conjunction with
localized voltage-induced alterations in surface anisotropy to enable
low-energy logic operations. Our findings underscore the critical importance of
selecting an optimal excitation frequency and gate width, which significantly
influence the efficiency of the phase shift induced in propagating spin waves.
Notably, we demonstrate that a realistic phase shift of 2.5$\left[ \pi \
\text{mrad}\right]$ can be achieved at a Co(5nm)/MgO material system via the
VCMA effect. Moreover, by tuning the excitation frequency, Co layer thickness,
gate width, and the use of a GdO\textsubscript{x} dielectric, we illustrate the
potential to enhance the phase shift by a factor of 200 when compared to MgO
dielectrics. This research contributes valuable insights towards developing
next-generation computing technologies with reduced energy consumption.",2402.03033v1
2024-02-23,Constraining the quark and gluon helicity at STAR,"How quarks and gluons conspire to provide the total spin of proton is a
long-standing puzzle in quantum chromodynamics (QCD). The unique capability of
RHIC, that can provide longitudinally polarized $p+p$ collisions at both
$\sqrt{s} = 200$ GeV and $\sqrt{s} = 510$ GeV, opened new territory to
constrain the helicity structure of the proton with unprecedented depth and
precision.
  Results from various STAR spin measurements have contributed significantly to
our understanding of the quark and gluon helicity distributions inside the
proton. The longitudinal double-spin asymmetry, $A_{LL}$, from the STAR 2009
inclusive jet measurement, provides the first indication of the positive gluon
polarization with partonic momentum fraction $x$ greater than 0.05 inside the
proton. More precise measurements using the $p+p$ data collected in 2012, 2013
and 2015 at both $\sqrt{s}$ = 510 and 200 GeV confirm the previous findings and
provide additional constraints in the largely unexplored region of $x < 0.05$.
Compared to the inclusive jet observables, analyses of dijet production
extending to higher pseudorapidity (up to $\eta \sim 1.8$) provide better
constraints on the $x$ dependent behavior of $\Delta g(x)$. Moreover, the
reconstruction of $W^{\pm}$ in longitudinally polarized proton-proton
collisions provides significant constraints on the flavor separation of the
light sea quark helicity distributions inside the proton, while the
longitudinal spin transfer to $\Lambda$ and $\bar \Lambda$ hyperons provides
access to the helicity of strange and anti-strange quarks in the proton.
  In this proceeding, an overview of dijet measurements from longitudinally
polarized proton-proton collisions at STAR is presented.",2402.15035v1
2024-04-06,Insights on induced magnetic moments and spin textures in synthetic ferrimagnetic Pt/Co/Gd heterolayers,"To develop new devices based on synthetic ferrimagnetic (S-FiM)
heterostructures, understanding the material's physical properties is pivotal.
Here, the induced magnetic moment (IMM), magnetic exchange-coupling, and spin
textures were investigated at room-temperature in Pt/Co/Gd multilayers using a
multiscale approach. The magnitude and direction of the IMM were interpreted
experimentally and theoretically in the framework of both X-ray magnetic
circular dichroism (XMCD) and density functional theory (DFT). The results
demonstrate that the IMM transferred by Co across the Gd paramagnetic (PM)
thickness leads to a flipped spin state (FSS) within the Gd layers, in which
their magnetic moments couple antiparallel/parallel with the ferromagnetic (FM)
Co near/far from the Co/Gd interface, respectively. For the Pt, in both Pt/Co
and Gd/Pt interfaces the IMM follows the same direction as the Co magnetic
moment, with negligible IMM in the Gd/Pt interface. Additionally, zero-field
spin spirals were imaged using scanning transmission X-ray microscopy (STXM),
while micromagnetic simulations employed to unfold the interactions stabilizing
the FiM configurations, where the existence of a sizable Dzyaloshinskii-Moriya
interaction is demonstrated to be crucial for the formation of those spin
textures. Our outcomes may add fundamental physical and technological aspects
for using FiM films in antiferromagnetic spintronic devices.",2404.04655v1
2015-11-04,"Neutron $2p$ and $1f$ spin--orbit splittings in $^{40}$Ca, $^{36}$S, and $^{34}$Si $N=20$ isotones: tensor--induced and pure spin--orbit effects","Neutron $2p$ and $1f$ spin--orbit splittings were recently measured in the
isotones $^{37}$S and $^{35}$Si by $(d,p)$ transfer reactions. Values were
reported by using the major fragments of the states. An important reduction of
the $p$ splitting was observed, from $^{37}$S to $^{35}$Si, associated to a
strong modification of the spin--orbit potential in the central region of the
nucleus $^{35}$Si. We analyze $2p$ and $1f$ neutron spin--orbit splittings in
the $N=20$ isotones $^{40}$Ca, $^{36}$S, and $^{34}$Si. We employ several
Skyrme and Gogny interactions, to reliably isolate pure spin--orbit and
tensor--induced contributions, within the mean--field approximation. We use
interactions (i) without the tensor force; (ii) with the tensor force and with
tensor parameters adjusted on top of existing parametrizations; (iii) with the
tensor force and with tensor and spin--orbit parameters adjusted simultaneously
on top of existing parametrizations. We predict in cases (ii) and (iii) a non
negligible reduction of both $p$ and $f$ splittings, associated to
neutron--proton tensor effects, from $^{40}$Ca to $^{36}$S. The two splittings
are further decreased for the three types of interactions, going from $^{36}$S
to $^{34}$Si. This reduction is produced by the spin--orbit force and is not
affected by tensor--induced contributions. For both reductions, from $^{40}$Ca
to $^{36}$S and from $^{36}$S to $^{34}$Si, we predict in all cases that the
modification is more pronounced for $p$ than for $f$ splittings. The
measurement of the centroids for neutron $2p$ and $1f$ states in the nuclei
$^{36}$S and $^{34}$Si would be interesting to validate this prediction
experimentally. We show the importance of using interactions of type (iii),
because they provide $p$ and $f$ splittings in the nucleus $^{40}$Ca which are
in agreement with the corresponding experimental values.",1511.01265v1
2017-01-02,Proximity band structure and spin textures on both sides of topological-insulator/ferromagnetic-metal interface and their transport probes,"The control of recently observed spintronic effects in
topological-insulator/ferromagnetic-metal (TI/FM) heterostructures is thwarted
by the lack of understanding of band structure and spin texture around their
interfaces. Here we combine density functional theory with Green's function
techniques to obtain the spectral function at any plane passing through atoms
of Bi$_2$Se$_3$ and Co or Cu layers comprising the interface. In contrast to
widely assumed but thinly tested Dirac cone gapped by the proximity exchange
field, we find that the Rashba ferromagnetic model describes the spectral
function on the surface of Bi$_2$Se$_3$ in contact with Co near the Fermi level
$E_F^0$, where circular and snowflake-like constant energy contours coexist
around which spin locks to momentum. The remnant of the Dirac cone is
hybridized with evanescent wave functions injected by metallic layers and
pushed, due to charge transfer from Co or Cu layers, few tenths of eV below
$E_F^0$ for both Bi$_2$Se$_3$/Co and Bi$_2$Se$_3$/Cu interfaces while hosting
distorted helical spin texture wounding around a single circle. These features
explain recent observation [K. Kondou {\em et al.}, Nat. Phys. {\bf 12}, 1027
(2016)] of sensitivity of spin-to-charge conversion signal at TI/Cu interface
to tuning of $E_F^0$. Interestingly, three monolayers of Co adjacent to
Bi$_2$Se$_3$ host spectral functions very different from the bulk metal, as
well as in-plane spin textures signifying the spin-orbit proximity effect. We
predict that out-of-plane tunneling anisotropic magnetoresistance in vertical
heterostructure Cu/Bi$_2$Se$_3$/Co, where current flowing perpendicular to its
interfaces is modulated by rotating magnetization from parallel to orthogonal
to current flow, can serve as a sensitive probe of spin texture residing at
$E_F^0$.",1701.00462v2
2023-03-27,Spin of protoplanets generated by pebble accretion: Influences of protoplanet-induced gas flow,"We investigate the spin state of a protoplanet during the pebble accretion
influenced by the gas flow in the gravitational potential of the protoplanet
and how it depends on the planetary mass, the headwind speed, the distance from
the host star, and the pebble size. We perform nonisothermal three-dimensional
hydrodynamical simulations in a local frame to obtain the gas flow around the
planet. We then numerically integrate three-dimensional orbits of pebbles under
the obtained gas flow. Finally, assuming uniform spatial distribution of
incoming pebbles, we calculate net spin by summing up specific angular momentum
that individual pebbles transfer to the protoplanet at impacts. We find that a
protoplanet with the envelope acquires prograde net spin rotation regardless of
the planetary mass, the pebble size, and the headwind speed of the gas. This is
because accreting pebbles are dragged by the envelope that commonly has
prograde rotation. As the planetary mass or orbital radius increases, the
envelope is thicker and the prograde rotation is faster, resulting in faster
net prograde spin. When the dimensionless thermal mass of the planet, $m =
R_{\mathrm{Bondi}} / H$, where $R_{\mathrm{Bondi}}$ and $H$ are the Bondi
radius and the disk gas scale height, is larger than a certain critical mass
($m \gtrsim 0.3$ at $0.1 \, \mathrm{au}$ or $m \gtrsim 0.1$ at $1 \,
\mathrm{au}$), the spin rotation exceeds the breakup one. The predicted spin
frequency reaches the breakup one at the planetary mass $m_{\mathrm{iso,rot}}
\sim 0.1 \, (a / 1 \, \mathrm{au})^{-1/2}$ (where $a$ is the orbital radius),
suggesting that the protoplanet cannot grow beyond $m_{\mathrm{iso,rot}}$. It
is consistent with the Earth's current mass and could help the formation of the
Moon by a giant impact on fast-spinning proto-Earth.",2303.15098v1
2023-07-07,Magnetization plateaus and enhanced magnetocaloric effect of a spin-1/2 Ising-Heisenberg and Heisenberg double sawtooth ladder with four-spin interaction,"The ground state, the entropy and the magnetic Gr\""uneisen parameter of the
antiferromagnetic spin-1/2 Ising-Heisenberg model on a double sawtooth ladder
are rigorously investigated using the classical transfer-matrix technique. The
model includes the XXZ interaction between the interstitial Heisenberg dimers,
the Ising coupling between nearest-neighbor spins of the legs and rungs, and
additional cyclic four-spin Ising term in each square plaquette. For a
particular value of the cyclic four-spin exchange we found in the ground-state
phase diagram of the Ising Heisenberg ladder a quadruple point, at which four
different ground states coexist together. During an adiabatic demagnetization
process a fast cooling accompanied with an enhanced magnetocaloric effect can
be detected nearby this quadruple point. The ground-state phase diagram of the
Ising-Heisenberg ladder is confronted with the zero-temperature magnetization
process of the purely quantum Heisenberg ladder, which is calculated by using
exact diagonalization (ED) based on the Lanczos algorithm for a finite-size
ladder of 24 spins and the density-matrix renormalization group (DMRG)
simulations for a finite-size ladder with up to 96 spins. Some indications of
existence of intermediate magnetization plateaus in the magnetization process
of the full Heisenberg model for a small but non-zero four-spin Ising coupling
were found. The DMRG results reveal that the quantum Heisenberg double sawtooth
ladder exhibits a quantum Luttinger spin-liquid phase that is absent in the
Ising-Heisenberg counterpart model. Except this difference the magnetic
behavior of the full Heisenberg model is quite analogous to its simplified
Ising-Heisenberg counterpart and hence, one may bring insight into the fully
quantum Heisenberg model from rigorous results for the Ising-Heisenberg model.",2307.03855v1
2021-10-13,"Rotation acceleration of asteroids (10115) 1992 SK, (1685) Toro, and (1620) Geographos due to the YORP effect","The rotation state of small asteroids is affected by the
Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, which is a net torque
caused by solar radiation directly reflected and thermally reemitted from the
surface. Due to this effect, the rotation period slowly changes, which can be
most easily measured in light curves because the shift in the rotation phase
accumulates over time quadratically. We collected archived light curves and
carried out new photometric observations for asteroids (10115) 1992 SK, (1620)
Geographos, and (1685) Toro. We applied the method of light curve inversion to
fit observations with a convex shape model. The YORP effect was modeled as a
linear change of the rotation frequency $\upsilon \equiv \mathrm{d}\omega /
\mathrm{d}t$ and optimized together with other spin and shape parameters. We
detected the acceleration $\upsilon = (8.3 \pm 0.6) \times
10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$ of the rotation for asteroid (10115)
1992 SK. This observed value agrees well with the theoretical value of
YORP-induced spin-up computed for our shape and spin model. For (1685) Toro, we
obtained $\upsilon = (3.3 \pm 0.3) \times
10^{-9}\,\mathrm{rad}\,\mathrm{d}^{-2}$, which confirms an earlier tentative
YORP detection. For (1620) Geographos, we confirmed the previously detected
YORP acceleration and derived an updated value of $\upsilon$ with a smaller
uncertainty. We also included the effect of solar precession into our inversion
algorithm, and we show that there are hints of this effect in Geographos' data.
The detected change of the spin rate of (10115) 1992 SK has increased the total
number of asteroids with YORP detection to ten. In all ten cases, the
$\mathrm{d}\omega / \mathrm{d}t$ value is positive, so the rotation of these
asteroids is accelerated. It is unlikely to be just a statistical fluke, but it
is probably a real feature that needs to be explained.",2110.06548v1
2001-04-10,Where Have All the Submillisecond Pulsars Gone?,"The existence of pulsars with spin period below one millisecond is expected,
though they have not been detected up to now. Their formation depends on the
quantity of matter accreted from the companion which, in turn, is limited by
the mechanism of mass ejection from the binary. Mass ejection must be
efficient, at least in some cases, in order to produce the observed population
of moderately fast spinning millisecond pulsars. First we demonstrate, in the
framework of the widely accepted recycling scenario, using a population
synthesis approach, that a significant number of pulsars with spin period below
one millisecond is expected. Then we propose that significant variations in the
mass-transfer rate may cause, in systems with orbital periods larger than 1 hr,
the switch-on of a radio pulsar whose radiation pressure is capable of ejecting
out of the system most of the matter transferred by the companion and prevent
any further accretion. We show how this mechanism could dramatically alter the
binary evolution since the mechanism that drives mass overflow from the inner
Lagrangian point is still active while the accretion is inhibited. Moreover we
demonstrate that the persistency of this ``radio ejection'' phase depends on
the binary orbital period, demonstrating that close systems (orbital periods
lower than 1 hr) are the only possible hosts for ultra fast spinning neutron
stars. This could explain why submillisecond pulsars have not been detected so
far, as current radio surveys are hampered by computational limitations with
respect to the detection of very short spin period pulsars in short orbital
period binaries.",0104170v1
2019-06-11,Transfer matrix theory of surface spin echo experiments with molecules,"${}^3$He beam spin-echo experiments have been used to study surface
morphology, molecular and atomic surface diffusion, phonon dispersions, phason
dispersions and phase transitions of ionic liquids. However, the interactions
between ${}^3$He atoms and surfaces or their adsorbates are typically isotropic
and weak. To overcome these limitations, one can use molecules instead of
${}^3$He in surface spin-echo experiments. The molecular degrees of freedom,
such as rotation, may be exploited to provide additional insight into surfaces
and the behaviour of their adsorbates. Indeed, a recent experiment has shown
that $\textit{ortho}$-hydrogen can be used as a probe that is sensitive to the
orientation of a Cu(115) surface [Godsi et al., Nat. Comm. $\textbf{8}$, 15357
(2017)]. However, the additional degrees of freedom offered by molecules also
pose a theoretical challenge: a large manifold of molecular states and magnetic
field-induced couplings between internal states. Here, we present a fully
quantum mechanical approach to model molecular surface spin-echo experiments
and connect the experimental signal to the elements of the time-independent
molecule-surface scattering matrix. We present a one-dimensional transfer
matrix method that includes the molecular hyperfine degrees of freedom and
accounts for the spatial separation of the molecular wavepackets due to the
magnetic control fields. We apply the method to the case of
$\textit{ortho}$-hydrogen, show that the calculated experimental signal is
sensitive to the scattering matrix elements, and perform a preliminary
comparison to experiment. This work sets the stage for Bayesian optimization to
determine the scattering matrix elements from experimental measurements and for
a framework that describes molecular surface spin-echo experiments to study
dynamic surfaces.",1906.04846v2
2020-06-28,Avoided quasiparticle decay and enhanced excitation continuum in the spin-1/2 near-Heisenberg triangular antiferromagnet Ba3CoSb2O9,"We explore the magnetic excitations of the spin-1/2 triangular
antiferromagnet Ba3CoSb2O9 in its 120 degree ordered phase using single-crystal
high-resolution inelastic neutron scattering. Sharp magnons with no decay are
observed throughout reciprocal space, with a strongly renormalized dispersion
and multiple soft modes compared to linear spin wave theory. We propose an
empirical parametrization that can quantitatively capture the complete
dispersions in the three-dimensional Brillouin zone and explicitly show that
the dispersion renormalizations have the direct consequence that one to two
magnon decays are avoided throughout reciprocal space, whereas such decays
would be allowed for the unrenormalized dispersions. At higher energies, we
observe a very strong continuum of excitations with highly-structured intensity
modulations extending up at least 4x the maximum one-magnon energy. The
one-magnon intensities decrease much faster upon increasing energy than
predicted by linear spin wave theory and the higher-energy continuum contains
much more intensity than can be accounted for by a two-magnon cross-section,
suggesting a significant transfer of spectral weight from the high-energy
magnons into the higher-energy continuum states. We attribute the strong
dispersion renormalizations and substantial transfer of spectral weight to
continuum states to the effect of quantum fluctuations and interactions beyond
the spin wave approximation, and make connections to theoretical approaches
that might capture such effects. Finally, through measurements in a strong
applied magnetic field, we find evidence for magnetic domains with opposite
senses for the spin rotation in the 120 degree ordered ground state, as
expected in the absence of Dzyaloshinskii-Moriya interactions, when the sense
of spin rotation is selected via spontaneous symmetry breaking.",2006.15554v1
2022-03-17,Distinct universality classes of diffusive transport from full counting statistics,"The hydrodynamic transport of local conserved densities furnishes an
effective coarse-grained description of the dynamics of a many-body quantum
system. However, the full quantum dynamics contains much more structure beyond
the simplified hydrodynamic description. Here we show that systems with the
same hydrodynamics can nevertheless belong to distinct dynamical universality
classes, as revealed by new classes of experimental observables accessible in
synthetic quantum systems, which can, for instance, measure simultaneous
site-resolved snapshots of all of the particles in a system. Specifically, we
study the full counting statistics of spin transport, whose first moment is
related to linear-response transport, but the higher moments go beyond. We
present an analytic theory of the full counting statistics of spin transport in
various integrable and non-integrable anisotropic one-dimensional spin models,
including the XXZ spin chain. We find that spin transport, while diffusive on
average, is governed by a distinct non-Gaussian dynamical universality class in
the models considered. We consider a setup in which the left and right half of
the chain are initially created at different magnetization densities, and
consider the probability distribution of the magnetization transferred between
the two half-chains. We derive a closed-form expression for the probability
distribution of the magnetization transfer, in terms of random walks on the
half-line. We show that this distribution strongly violates the large-deviation
form expected for diffusive chaotic systems, and explain the physical origin of
this violation. We discuss the crossovers that occur as the initial state is
brought closer to global equilibrium. Our predictions can directly be tested in
experiments using quantum gas microscopes or superconducting qubit arrays.",2203.09526v3
1996-08-20,On weak vs. strong universality in the two-dimensional random-bond Ising ferromagnet,"We address the issue of universality in two-dimensional disordered Ising
systems, by considering long, finite-width strips of ferromagnetic Ising spins
with randomly distributed couplings. We calculate the free energy and spin-spin
correlation functions (from which averaged correlation lengths, $\xi^{ave}$,
are computed) by transfer-matrix methods. An {\it ansatz} for the
size-dependence of logarithmic corrections to $\xi^{ave}$ is proposed. Data for
both random-bond and site-diluted systems show that pure system behaviour (with
$\nu=1$) is recovered if these corrections are incorporated, discarding the
weak--universality scenario.",9608083v1
1997-07-11,Tunneling in quantum wires II: A new line of IR fixed points,"In a previous paper, we showed that the problem of tunneling in quantum wires
was integrable in the isotropic case $g_\sigma=2$. In the present work, we
continue the exploration of the general phase diagram by looking for other
integrable cases. Specifically, we discuss in details the manifold
$g_\rho+g_\sigma=2$, where the associated ``double sine-Gordon'' model is
integrable. Transport properties are exactly computed. Surprisingly, the IR
fixed points, while having complete reflection of charge and spin currents, do
not correspond to two separate leads. Their main characteristic is that they
are approached along irrelevant operators of dimension $1+{1\over g_\rho}$ and
$1+{1\over g_\sigma}$, corresponding to transfer of one electron charge but no
spin, or one spin 1/2 but no charge.",9707131v1
1997-11-06,"Raman, infrared and optical spectra of the spin-Peierls compound NaV_2O_5","We have measured polarized spectra of Raman scattering, infrared and optical
transmission of NaV_2O_5 single crystals above the temperature of the
spin-Peierls transition Tsp=35 K. Some of the far-infrared (FIR) phonon lines
are strongly asymmetric, due to the spin-phonon interaction. In addition to the
phonon lines, a broad band was observed in the c(aa)c Raman spectrum and in the
E||a FIR transmission spectrum. A possible origin of these bands is discussed.
The absorption band at 10000 cm-1 1.25 eV is attributed to vanadium d-d
electronic transitions while the absorption edge above 3 eV is supposed to
correspond to the onset of charge-transfer transitions.",9711048v1
1997-12-16,Spin dynamics of strongly-doped La_{1-x}Sr_xMnO_3,"Cold neutron triple-axis measurements have been used to investigate the
nature of the long-wavelength spin dynamics in strongly-doped
La$_{1-x}$Sr$_{x}$MnO$_3$ single crystals with $x$=0.2 and 0.3. Both systems
behave like isotropic ferromagnets at low T, with a gapless ($E_0 < 0.02$ meV)
quadratic dispersion relation $E = E_0 + Dq^2$. The values of the spin-wave
stiffness constant $D$ are large ($D_{T=0}$ = 166.77 meV$ \AA^2$ for $x$=0.2
and D$_{T=0}$ = 175.87 meV$ \AA^2$ for $x$=0.3), which directly shows that the
electron transfer energy for the $d$ band is large. $D$ exhibits a power law
behavior as a function of temperature, and appears to collapse as T -> T_C.
Nevertheless, an anomalously strong quasielastic central component develops and
dominates the fluctuation spectrum as T -> T_C. Bragg scattering indicates that
the magnetization near $T_C$ exhibits power law behavior, with $\beta \simeq
0.30$ for both systems, as expected for a three-dimensional ferromagnet.",9712191v1
1998-03-27,Network Model for a 2D Disordered Electron System with Spin-Orbit Scattering,"We introduce a network model to describe two-dimensional disordered electron
systems with spin-orbit scattering. The network model is defined by a discrete
unitary time evolution operator. We establish by numerical transfer matrix
calculations that the model exhibits a localization-delocalization transition.
We determine the corresponding phase diagram in the parameter space of disorder
scattering strength and spin-orbit scattering strength. Near the critical point
we determine by statistical analysis a one-parameter scaling function and the
critical exponent of the localization length to be $\nu=2.51\pm 0.18$. Based on
a conformal mapping we also calculate the scaling exponent of the typical local
density of states $\alpha_0=2.174 \pm 0.003$.",9803342v1
1998-04-06,Theory of Excitons in Insulating Cu-Oxide Plane,"We use a local model to study the formation and the structure of the low
energy charge transfer excitations in the insulating Cu-O$_2$ plane. The
elementary excitation is a bound exciton of spin singlet, consisting of a
Cu$^+$ and a neighboring spin singlet of Cu-O holes. The exciton can move
through the lattice freely without disturbing the antiferromagnetic spin
background, in contrast to the single hole motion. There are four eigen-modes
of excitons with different symmetry. The p-wave-like exciton has a large
dispersion width. The s-wave-like exciton mixes with p-state at finite
momentum, and its dipole transition intensity is strongly anisotropic. The
model is in excellent agreement with the electron energy loss spectra in the
insulating Sr$_2$CuO$_2$Cl$_2$.",9804072v1
1998-06-14,Incommensurate Charge and Spin Fluctuations in d-wave Superconductors,"We show analytic results for the irreducible charge and spin
susceptibilities, $\chi_0 (\omega, {\bf Q})$, where ${\bf Q}$ is the momentum
transfer between the nodes in d-wave superconductors. Using the BCS theory and
a circular Fermi surface, we find that the singular behavior of the irreducible
charge susceptibility leads to the dynamic incommensurate charge collective
modes. The peaks in the charge structure factor occur at a set of wave vectors
which form an ellipse around ${\bf Q}_{\pi}=(\pi,\pi)$ and ${\bf Q}_0=(0,0)$ in
momentum space with momentum dependent spectral weight. It is also found that,
due to the non-singular irreducible spin susceptibility, an extremely strong
interaction via random phase approximation is required to support the magnetic
peaks near ${\bf Q}_{\pi}$. Under certain conditions, the peaks in the magnetic
structure factor occur near ${\bf Q}=(\pi,\pi (1 \pm \delta))$ and $(\pi (1 \pm
\delta),\pi)$.",9806170v2
1999-01-21,Influence of finite Hund rules and charge transfer on properties of Haldane systems,"We consider the Kondo-Hubbard model with ferromagnetic exchange coupling $%
J_{H}$, showing that it is an approximate effective model for late transition
metal-O linear systems. We study the dependence of the charge and spin gaps
$\Delta_{C}$, $\Delta_{S}$, and several spin-spin correlation functions,
including the hidden order parameter $Z(\pi)$, as functions of $J_{H}/t$ and
$U/t$, by numerical diagonalization of finite systems. Except for $Z(\pi)$, all
properties converge slowly to the strong-coupling limit. When $J_{H}/t\sim 2$
and $U/t\sim 7$ (the effective parameters that we obtain for Y_2BaNiO_5),
$\Delta_{S}$ is roughly half of the value expected from a strong-coupling
expansion.",9901220v1
1999-03-25,Spin Fluctuation-Induced Superconductivity in κ-BEDT-TTF Compounds,"Spin fluctuation-induced superconductivity in quasi-two dimensional organic
compounds, \kappa-BEDT-TTF salts, is investigated within a fluctuation exchange
(FLEX) approximation using a half-filled Hubbard model with a right-angled
isosceles triangular lattice (transfer matrices -\tau, -\tau^\prime), extending
a previous work above T_c. An energy gap of A_2 or (x^2-y^2)-type develops with
decreasing temperature below T_c more rapidly than in the BCS model. The
calculated dynamical susceptibilities enough below T_c show sharp resonance
peaks like those in certain cuprates superconductors. The calculated nuclear
spin-lattice relaxation rate 1/T_1 shows a T^3 behavior below T_c in accordance
with experiment. Estimated values of 1/T_1 are roughly consistent with
experimental results. A prediction is made for the doping concentration
dependence of T_c and the antiferromagnetic and superconductive instability
points are calculated in the U/\tau vs. \tau^\prime/\tau plane.",9903374v1
1999-07-12,Magnetic reconstruction at (001) CaMnO$_3$ surface,"The Mn-terminated (001) surface of the stable anti-ferromagnetic insulating
phase of cubic perovskite CaMnO$_3$ is found to undergo a magnetic
reconstruction consisting on a spin-flip process at surface: each Mn spin at
the surface flips to pair with that of Mn in the subsurface layer. In spite of
very little Mn-O charge transfer at surface, the surface behavior is driven by
the $e_g$ states due to $d_{xy}$ $\to$ $d_{z^2}$ charge redistribution. These
results, based on local spin density theory, give a double exchange like
coupling that is driven by $e_g$ character, not additional charge, and may have
relevance to CMR materials.",9907173v2
1999-09-29,"Effects of dilute nonmagnetic impurities on the Q=(pi,pi) spin-fluctuation spectrum in YBa2Cu3O7","The effects of nonmagnetic impurities on the Q=(pi,pi) spin-fluctuation
spectral weight Im chi(Q,omega) are studied within the framework of the
two-dimensional Hubbard model using the random phase approximation. In the
first part of the paper, the effects of the nonmagnetic impurities on the
magnetic susceptibility of the noninteracting (U=0) system, chi_0(Q,omega), are
calculated with the self-energy and the vertex corrections using various forms
of the effective electron-impurity interaction. Here, the range and the
strength of the impurity potential are varied as well as the concentration of
the impurities. It is shown that the main effect of dilute impurities on
chi_0(Q,omega) is to cause a weak smearing. In the second part, Im chi(Q,omega)
is calculated for the interacting system. Here, the calculations are
concentrated on the processes which involve the impurity scattering of the spin
fluctuations with finite momentum transfers. In order to make comparisons with
the experimental data on the frequency dependence of Im chi(Q,omega) in Zn
substituted YBa2Cu3O7, results are given for various values of the model
parameters.",9909437v1
1999-11-09,Nanoconstriction Microscopy of the Giant Magnetoresistance in Cobalt/Copper Spin Valves,"We use nanometer-sized point contacts to a Co/Cu spin valve to study the
giant magnetoresistance (GMR) of only a few Co domains. The measured data show
strong device-to-device differences of the GMR curve, which we attribute to the
absence of averaging over many domains. The GMR ratio decreases with increasing
bias current. For one particular device, this is accompanied by the development
of two distinct GMR plateaus, the plateau level depending on bias polarity and
sweep direction of the magnetic field. We attribute the observed behavior to
current-induced changes of the magnetization, involving spin transfer due to
incoherent emission of magnons and self-field effects.",9911133v1
1999-11-12,4f spin density in the reentrant ferromagnet SmMn2Ge2,"The spin contribution to the magnetic moment in SmMn2Ge2 has been measured by
magnetic Compton scattering in both the low and high temperature ferromagnetic
phases. At low temperature, the Sm site is shown to possess a large 4f spin
moment of 3.4 +/- 0.1 Bohr magnetons, aligned antiparallel to the total
magnetic moment. At high temperature, the data show conclusively that ordered
magnetic moments are present on the samarium site.",9911199v4
2000-03-20,Positive Muon Knight Shift Measurements in U_{0.965}Th_{0.035}Be_{13} Single Crystals,"Muon spin rotation measurements of the temperature dependence of the Knight
shift in single crystals of U_{0.965}Th_{0.035}Be_{13} have been used to study
the static spin susceptibility below the transition temperatures T_{c1} and
T_{c2}. While an abrupt reduction of the susceptibility with decreasing
temperature is observed below T_{c1}, the susceptibility does not change below
T_{c2} and remains at a value below the normal-state susceptibility. In the
normal state we find an anomalous anisotropic temperature dependence of the
transferred hyperfine coupling between the muon spin and the U 5f-electrons.",0003334v2
2000-11-11,Griffiths effects and quantum critical points in dirty superconductors without spin-rotation invariance: One-dimensional examples,"We introduce a strong-disorder renormalization group (RG) approach suitable
for investigating the quasiparticle excitations of disordered superconductors
in which the quasiparticle spin is not conserved. We analyze one-dimensional
models with this RG and with elementary transfer matrix methods. We find that
such models with broken spin rotation invariance {\it generically} lie in one
of two topologically distinct localized phases. Close enough to the critical
point separating the two phases, the system has a power-law divergent
low-energy density of states (with a non-universal continuously varying
power-law) in either phase, due to quantum Griffiths singularities. This
critical point belongs to the same infinite-disorder universality class as the
one dimensional particle-hole symmetric Anderson localization problem, while
the Griffiths phases in the vicinity of the transition are controlled by lines
of strong (but not infinite) disorder fixed points terminating in the critical
point.",0011200v1
2000-11-13,Magnetization reversal triggered by spin injection in magnetic nanowires,"It is shown that a pulsed current driven through Ni nanowires provokes an
irreversible magnetization reversal at a field distant from the spontaneous
switching field $H_{sw}$ by $\Delta H$ of as much as 40 % of $H_{sw}$. The
state of the magnetization is assessed by magnetoresistive measurements carried
out on single, isolated nanowires. The reversible part of the magnetization
follows that of a uniform rotation. The switching occurs between the two states
accessible otherwise by normal field ramping. $\Delta H$ is studied as a
function of the angle between the applied field and the wire, and also of the
direction of the pulsed current. The results are interpreted in terms of
spin-flip transfer from the spin-polarized current to the magnetization, while
the switching is approximated by a curling reversal mode.",0011228v1
2001-06-27,Statistical Mechanics and Capacity-Approaching Error-Correcting Codes,"I will show that there is a deep relation between error-correction codes and
certain mathematical models of spin glasses.
  In particular minimum error probability decoding is equivalent to finding the
ground state of the corresponding spin system. The most probable value of a
symbol is related to the magnetization at a different temperature.
Convolutional codes correspond to one-dimensional spin systems and Viterbi's
decoding algorithm to the transfer matrix algorithm of Statistical Mechanics.
  I will also show how the recently discovered (or rediscovered) capacity
approaching codes (turbo codes and low density parity check codes) can be
analysed using statistical mechanics. It is possible to show, using statistical
mechanics, that these codes allow error-free communication for signal to noise
ratio above a certain threshold. This threshold depends on the particular code,
and can be computed analytically in many cases.",0106570v1
2001-08-01,Quenched bond dilution in two-dimensional Potts models,"We report a numerical study of the bond-diluted 2-dimensional Potts model
using transfer matrix calculations. For different numbers of states per spin,
we show that the critical exponents at the random fixed point are the same as
in self-dual random-bond cases. In addition, we determine the multifractal
spectrum associated with the scaling dimensions of the moments of the spin-spin
correlation function in the cylinder geometry. We show that the behaviour is
fully compatible with the one observed in the random bond case, confirming the
general picture according to which a unique fixed point describes the critical
properties of different classes of disorder: dilution, self-dual binary
random-bond, self-dual continuous random bond.",0108014v1
2002-10-11,Dynamics of spin-2 Bose condensate driven by external magnetic fields,"Dynamic response of the F=2 spinor Bose-Einstein condensate (BEC) under the
influence of external magnetic fields is studied. A general formula is given
for the oscillation period to describe population transfer from the initial
polar state to other spin states. We show that when the frequency and the
reduced amplitude of the longitudinal magnetic field are related in a specific
manner, the population of the initial spin-0 state will be dynamically
localized during time evolution. The effects of external noise and nonlinear
spin exchange interaction on the dynamics of the spinor BEC are studied. We
show that while the external noise may eventually destroy the Rabi oscillations
and dynamic spin localization, these coherent phenomena are robust against the
nonlinear atomic interaction.",0210252v1
2003-01-10,Quantum Spin Chains with Nonlocally-Correlated Random Exchange Coupling and Random-Mass Dirac Fermions,"S=1/2 quantum spin chains and ladders with random exchange coupling are
studied by using an effective low-energy field theory and transfer matrix
methods. Effects of the nonlocal correlations of exchange couplings are
investigated numerically. In particular we calculate localization length of
magnons, density of states, correlation functions and multifractal exponents as
a function of the correlation length of the exchange couplings. As the
correlation length increases, there occurs a ""phase transition"" and the above
quantities exhibit different behaviors in two phases. This suggests that the
strong-randomness fixed point of the random spin chains and random-singlet
state get unstable by the long-range correlations of the random exchange
couplings.",0301139v2
2003-01-26,Local Magnetic Susceptibility of the Positive Muon in the Quasi 1D S=1/2 Antiferromagnet dichlorobis (pyridine) copper (II),"We report muon spin rotation measurements of the local magnetic
susceptibility around a positive muon in the paramagnetic state of the quasi
one-dimensional spin 1/2 antiferromagnet dichlorobis (pyridine) copper (II).
Signals from three distinct sites are resolved and have a temperature dependent
frequency shift which is significantly different than the magnetic
susceptibility. This difference is attributed to a muon induced perturbation of
the spin 1/2 chain. The obtained frequency shifts are compared with Transfer
Matrix DMRG numerical simulations.",0301507v2
2003-06-04,Magnetization reversal and two level fluctuations by spin-injection in a ferromagnetic metallic layer,"Slow magnetic relaxation and two level fluctuations measurements under high
current injection is performed in single-contacted ferromagnetic
nanostructures. The magnetic configurations of the samples are described by two
metastable states of the uniform magnetization. The current-dependent effective
energy barrier due to spin-transfer from the current to the magnetic layer is
measured. The comparison between the results obtained with Ni nanowires of 6
$\mu $m length and 60 nm diameter, and Co (10 nm)/Cu (10 nm)/Co(30 nm)
nanometric pillars of about 40 nm in diameter refined the characterization of
this effect. It is shown that all observed features cannot be reduced to the
action of a current dependent effective field. Instead, all measurements can be
described in terms of an effective temperature, which depends on the current
amplitude and direction. The system is then analogous to an unstable open
system. The effect of current induced magnetization reversal is interpreted as
the balance of spin injection between both interfaces of the ferromagnetic
layer.",0306103v1
2003-08-12,Topological doping of repulsive Hubbard models,"The spin configuration induced by single holes and hole pairs doped into
stoichiometric, antiferromagnetic cuprates is considered. Unrestricted
Hartree-Fock calculations for the three-band Hubbard model are employed to
study spin-polaron and vortex-like (meron) solutions. Meron solutions for a
single hole are found to be metastable with higher energy than spin polarons.
We observe that the meron solution shifts from site-centered to bond-centered
as the interaction is increased. Meron-antimeron solutions for hole pairs are
found to be unstable. The results are in agreement with earlier findings for
the one-band Hubbard model. However, we find that the Hubbard interaction of
the one-band model has to be chosen similar to the one of the three-band model
to obtain comparable results, not of the order of the charge-transfer gap, as
previously expected.",0308228v1
2004-04-29,A Density Functional Study of O2 Adsorption on (100) Surface of gamma-Uranium,"We have studied the chemisorption processes of O2 on the (100) surface of
uranium using generalized gradient approximation to density functional theory.
Dissociative adsorptions of O2 are significantly favored compared to molecular
adsorptions. We found interstitial adsorption of molecular oxygen to be less
probable, as no bound states were found in this case. Upon oxygen adsorption, O
2p orbitals is found to hybridize with U 5f bands, and part of the U 5f
electrons become more localized. Also there is a significant charge transfer
from the first layer of the uranium surface to the oxygen atoms, which made the
bonding partly ionic. For the most favored site the dissociative chemisorption
energy is approximately 9.5 eV, which indicates a strong reaction of uranium
surface with oxygen. Spin polarization does not have a considerable effect on
the chemisorption process. For most of the sites and approaches, chemisorption
configurations are almost same at both spin-polarized and non-spin-polarized
cases. For the most favored chemisorption sites of oxygen on uranium,
paramagnetic adsorption is slightly stronger, by 0.304 eV, than the magnetic
adsorption.",0404697v1
2004-05-13,Quantum phase transitions and magnetization of an integrable spin ladder with new parameters in bridging to real compounds,"We study the field-induced quantum phase transitions (QPT) and the relevant
magnetic properties of a spin-1/2 two-leg integrable spin ladder (ISL), of
which the system parameters in bridging to the real compounds are determined by
setting the extra interactions in the Hamiltonian of the ISL relative to the
Heisenberg spin ladder to vanish in the expectation in the ground state (GS).
Such an ISL analytically has the correct leading terms of both the critical
fields of the two QPT's as in the real strongly-coupled compounds: g\mu
_BH_{c1}=J_{\perp}-J_{\parallel} and g\mu_BH_{c2}=J_{\perp}+2J_{\parallel} in
terms of the experimental leg (J_{\parallel}) and rung (J_{\perp})
interactions. The symmetric magnetization inflection point is located at g\mu
_BH_{IP}=J_{\perp}+J_{\parallel}/2. The magnetizations for the GS and at finite
temperatures, as well as the susceptibility, show good agreements in various
comparisons with the finite-site exact diagonalization, the transfer-matrix
renormalization group numerical result, the perturbation theory, and the
compounds (5IAP)_2CuBr_4\cdot 2H_2O, Cu_2(C_5H_{12}N_2)_2Cl_4 and
(C_5H_{12}N)_2CuBr_4.",0405274v1
2004-07-02,Coulomb and Spin blockade of two few-electrons quantum dots in series in the co-tunneling regime,"We present Coulomb Blockade measurements of two few-electron quantum dots in
series which are configured such that the electrochemical potential of one of
the two dots is aligned with spin-selective leads. The charge transfer through
the system requires co-tunneling through the second dot which is $not$ in
resonance with the leads. The observed amplitude modulation of the resulting
current is found to reflect spin blockade events occurring through either of
the two dots. We also confirm that charge redistribution events occurring in
the off-resonance dot are detected indirectly via changes in the
electrochemical potential of the aligned dot.",0407071v1
2004-07-08,Bipolar High Field Excitations in Co/Cu/Co Nanopillars,"Current-induced magnetic excitations in Co/Cu/Co bilayer nanopillars
($\sim$50 nm in diameter) have been studied experimentally at low temperatures
for large applied fields perpendicular to the layers. At sufficiently high
current densities excitations, which lead to a decrease in differential
resistance, are observed for both current polarities. Such bipolar excitations
are not expected in a single domain model of spin-transfer. We propose that at
high current densities strong asymmetries in the longitudinal spin accumulation
cause spin-wave instabilities transverse to the current direction in bilayer
samples, similar to those we have reported for single magnetic layer junctions.",0407210v1
2005-02-03,Density and spin response functions in ultracold fermionic atom gases,"We propose a new method of detecting the onset of superfluidity in a
two-component ultracold fermionic gas of atoms governed by an attractive
short-range interaction. By studying the two-body correlation functions we find
that a measurement of the momentum distribution of the density and spin
response functions allows one to access separately the normal and anomalous
densities. The change in sign at low momentum transfer of the density response
function signals the transition between a BEC and a BCS regimes, characterized
by small and large pairs, respectively. This change in sign of the density
response function represents an unambiguous signature of the BEC to BCS
crossover. Also, we predict spin rotational symmetry-breaking in this system.",0502110v1
2005-06-03,Magnetic excitations in weakly coupled spin dimers and chains material Cu2Fe2Ge4O13,"Magnetic excitations in a weakly coupled spin dimers and chains compound
Cu2Fe2Ge4O13 are measured by inelastic neutron scattering. Both structure
factors and dispersion of low energy excitations up to 10 meV energy transfer
are well described by a semiclassical spin wave theory involving interacting
Fe$^{3+}$ ($S = 5/2$) chains. Additional dispersionless excitations are
observed at higher energies, at $\hbar \omega = 24$ meV, and associated with
singlet-triplet transitions within Cu$^{2+}$-dimers. Both types of excitations
can be understood by treating weak interactions between the Cu$^{2+}$ and
Fe$^{3+}$ subsystems at the level of the Mean Field/ Random Phase
Approximation. However, this simple model fails to account for the measured
temperature dependence of the 24 meV mode.",0506070v1
2005-09-01,Spin-transfer-induced excitations in bilayer magnetic nanopillars at high fields: The effects of contact layers,"Current-induced excitations in bilayer magnetic nanopillars have been studied
with large magnetic fields applied perpendicular to the layers at low
temperature. Junctions investigated all have Cu/Co/Cu/Co/Cu as core layer
stacks. Two types of such junctions are compared, one with the core stack
sandwiched between Pt layers (type A), the other with Pt only on one side of
the stack (type B). Transport measurements show that these two types of
junctions have similar magnetoresistance and slope of critical current with
respect to field, while A samples have higher resistance. The high-field
bipolar excitation, as was previously reported [Oezyilmaz et al., Phys. Rev. B
71, 140403(R) (2005)], is present in B samples only. This illustrates the
importance of contact layers to spin-current-induced phenomena. This also
confirms a recent prediction on such spin-wave excitations in bilayers.",0509034v2
2005-10-06,New light on magnetic excitations: indirect resonant inelastic X-ray scattering on magnons,"Recent experiments show that indirect resonant inelastic X-ray scattering
(RIXS) is a new probe of spin dynamics. Here I derive the cross-section for
magnetic RIXS and determine the momentum dependent four-spin correlation
function that it measures. These results show that this technique offers
information on spin dynamics that is complementary to e.g. neutron scattering.
The RIXS spectrum of Heisenberg antiferromagnets is calculated. It turns out
that only scattering processes that involve at least two magnons are allowed.
Other selection rules imply that the scattering intensity vanishes for specific
transferred momenta ${\bf q}$, in particular for ${\bf q}=0$. The calculated
spectra agree very well with the experimental data.",0510140v3
2005-10-08,Full Counting Statistics of Non-Commuting Variables: the Case of Spin Counts,"We discuss the Full Counting Statistics of non-commuting variables with the
measurement of successive spin counts in non-collinear directions taken as an
example. We show that owing to an irreducible detector back-action, the FCS in
this case may be sensitive to the dynamics of the detectors, and may differ
from the predictions obtained with using a naive version of the Projection
Postulate. We present here a general model of detector dynamics and
path-integral approach to the evaluation of FCS. We concentrate further on a
simple ""diffusive"" model of the detector dynamics where the FCS can be
evaluated with transfer-matrix method. The resulting probability distribution
of spin counts is characterized by anomalously large higher cumulants and
substantially deviates from Gaussian Statistics.",0510215v1
2006-01-11,Electronic Structure of Charge- and Spin-controlled Sr_{1-(x+y)}La_{x+y}Ti_{1-x}Cr_{x}O_{3},"We present the electronic structure of
Sr_{1-(x+y)}La_{x+y}Ti_{1-x}Cr_{x}O_{3} investigated by high-resolution
photoemission spectroscopy. In the vicinity of Fermi level, it was found that
the electronic structure were composed of a Cr 3d local state with the
t_{2g}^{3} configuration and a Ti 3d itinerant state. The energy levels of
these Cr and Ti 3d states are well interpreted by the difference of the
charge-transfer energy of both ions. The spectral weight of the Cr 3d state is
completely proportional to the spin concentration x irrespective of the carrier
concentration y, indicating that the spin density can be controlled by x as
desired. In contrast, the spectral weight of the Ti 3d state is not
proportional to y, depending on the amount of Cr doping.",0601214v1
2006-03-02,Anomalous dynamics in two- and three- dimensional Heisenberg-Mattis spin glasses,"We investigate the spectral and localization properties of unmagnetized
Heisenberg-Mattis spin glasses, in space dimensionalities $d=2$ and 3, at T=0.
We use numerical transfer-matrix methods combined with finite-size scaling to
calculate Lyapunov exponents, and eigenvalue-counting theorems, coupled with
Gaussian elimination algorithms, to evaluate densities of states. In $d=2$ we
find that all states are localized, with the localization length diverging as
$\omega^{-1}$, as energy $\omega \to 0$. Logarithmic corrections to density of
states behave in accordance with theoretical predictions. In $d=3$ the
density-of-states dependence on energy is the same as for spin waves in pure
antiferromagnets, again in agreement with theoretical predictions, though the
corresponding amplitudes differ.",0603043v1
2006-06-01,Broken parity and a chiral ground state in the frustrated magnet CdCr2O4,"We present a model describing the lattice distortion and incommensurate
magnetic order in the spinel CdCr2O4, a good realization of the Heisenberg
""pyrochlore"" antiferromagnet. The magnetic frustration is relieved through the
spin-Peierls distortion of the lattice involving a phonon doublet with odd
parity. The distortion stablizes a collinear magnetic order with the
propagation wavevector q=2\pi(0,0,1). The lack of inversion symmetry makes the
crystal structure chiral. The handedness is transferred to magnetic order by
the relativistic spin-orbit coupling: the collinear state is twisted into a
long spiral with the spins in the ac plane and q shifted to 2\pi(0,\delta,1).",0606039v2
2006-11-06,Dynamic $0-π$ transition induced by pumping mechanism,"Using Nambu$\otimes $spin space Keldysh Green's function approach, we present
a nonequilibrium charge and spin pumping theory of a quantum dot in the
mico-cavity coupled to two superconducting leads. It is found that the charge
currents include two parts: The dissipationless supercurrent standing for the
transfer of coherent Cooper pairs and the pumped quasi-particle current. The
supercurrent exhibits a dynamic $0-\pi $ transition induced by the frequency
and strength of the $\sigma_{-}$ polarized laser field. This dynamic transition
is not affected by the strong Coulomb interaction. Especially, the spin current
appears and is an even function of the phase difference between two
superconductors when the frequency of the polarized laser field is larger than
two times superconducting energy gap. Our theory serves as an extension to
non-superconducting spintronics.",0611134v2
2006-11-25,Quantum Tunneling of Magnetization in Single Molecular Magnets Coupled to Ferromagnetic Reservoirs,"The role of spin polarized reservoirs in quantum tunneling of magnetization
and relaxation processes in a single molecular magnet (SMM) is investigated
theoretically. The SMM is exchange-coupled to the reservoirs and also subjected
to a magnetic field varying in time, which enables the quantum tunneling of
magnetization (QTM). The spin relaxation times are calculated from the Fermi
golden rule. The exchange interaction with tunneling electrons is shown to
affect the spin reversal due to QTM. Furthermore, it is shown that the
switching is associated with transfer of a certain charge between the leads.",0611644v3
2007-03-24,Spectral properties and magneto-optical excitations in semiconductor double-rings under Rashba spin-orbit interaction,"We have numerically solved the Hamiltonian of an electron in a semiconductor
double ring subjected to the magnetic flux and Rashba spin-orbit interaction.
It is found that the Aharonov-Bohm energy spectrum reveals multi-zigzag
periodic structures. The investigations of spin-dependent electron dynamics via
Rabi oscillations in two-level and three-level systems demonstrate the
possibility of manipulating quantum states. Our results show that the optimal
control of photon-assisted inter-ring transitions can be achieved by employing
cascade-type and $\Lambda$-type transition mechanisms. Under chirped pulse
impulsions, a robust and complete transfer of an electron to the final state is
shown to coincide with the estimation of the Landau-Zener formula.",0703638v1
2007-03-26,Origin of charge density wave in the coupled spin ladders in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$,"We formulate a d-p multiband charge transfer model for Cu$_2$O$_5$ coupled
spin ladders, relevant for Cu$_2$O$_3$ plane of
Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$, and solve it using Hartree-Fock
approximation. The results explain that (i) the charge density wave (CDW) with
its periodicity dependent on doping is stabilized by purely electronic
many-body interactions in a single spin ladder and (ii) the inclusion of the
interladder interactions favors (disfavors) the stability of the CDW with odd
(even) periodicity, respectively. This stays in agreement with recent
experimental results and suggests the structure of the minimal microscopic
model which should be considered in future more sophisticated studies.",0703669v2
2005-10-11,Results from PP2PP Experiment at RHIC,"We report on the first measurement of the single spin analyzing power
($A\_N$) at $\sqrt{s}=200$ GeV, obtained by the pp2pp experiment using
polarized proton beams at the Relativistic Heavy Ion Collider (RHIC). Data
points were measured in the four momentum transfer $t$ range $0.01 \leq |t|
\leq 0.03$ $\GeVcSq$. Our result is about one standard deviation above the
calculation, which uses interference between electromagnetic spin-flip
amplitude and hadronic non-flip amplitude, the source of $A\_N$. The difference
could be explained by an additional contribution of a hadronic spin-flip
amplitude to $A\_N$.",0510032v2
2006-02-06,Transversity Physics at Compass,"Transverse spin physics is an important part of the scientific programme of
the COMPASS experiment at CERN, which started taking data in 2002, scattering
160 GeV/c muon beam on a polarized $^6$LiD target. The analysis of the data
taken with the target polarized orthogonally to the muon beam direction has
allowed to measure for the first time the Collins and Sivers asymmetries of the
deuteron. Both for the positive and the negative hadrons produced in
semi-inclusive DIS the measured asymmetries are small and, within errors,
compatible with zero: results on part of the accumulated statistics have
already been published. Two-hadron asymmetries and $\Lambda$ polarization
transfered from the struck quark are also being investigated, and preliminary
results on the data collected in the years 2002 and 2003 are given.",0602013v1
2006-08-08,STAR results on longitudinal spin dynamics,"We present preliminary results on the double longitudinal spin asymmetries
A_LL in inclusive jet production and the longitudinal spin transfer asymmetries
D_LL in inclusive Lambda and anti-Lambda hyperon production. The data amount to
about 0.5 pb-1 collected at RHIC in 2003 and 2004 with beam polarizations up to
45 %. The jet A_LL asymmetries, measured over 5 < pT < 17 GeV/c, are consistent
with evaluations based on deep-inelastic scattering parametrizations for the
gluon polarization in the nucleon, and disfavor large positive values of gluon
polarization in the nucleon. The Lambda and anti-Lambda D_LL, measured at
midrapidity and at low average transverse momentum of 1.5 GeV/c, are consistent
with zero within their dominant statistical uncertainties.",0608022v1
2006-11-28,"Strange Quark Contribution to the Proton Spin, from Elastic $\vec{e}p$ and $νp$ Scattering","The strangeness contribution to the vector and axial form factors of the
proton is presented for momentum transfers in the range 0.45 < $Q^2$ < 1.0
GeV$^2$. The results are obtained via a combined analysis of forward-scattering
parity-violating elastic $\vec{e}p$ asymmetry data from the G0 and HAPPEx
experiments at Jefferson Lab, and elastic $\nu p$ and $\bar{\nu}p$ scattering
data from Experiment 734 at Brookhaven National Laboratory. The combination of
the two data sets allows for the simultaneous extraction of $G_E^s$, $G_M^s$,
and $G_A^s$ over a significant range of $Q^2$ for the very first time.
Determination of the strange axial form factor $G_A^s$ is vital to an
understanding of the strange quark contribution to the proton spin.",0611053v1
1999-05-26,A New Mechanism for Single Spin Asymmetries in Strong Interactions,"It is shown that the contribution of the instantons to the fragmentation of
quarks leads to the appearance of a imaginary part in diagrams of quark-quark
scattering at large transfer momentum. The imaginary part comes from the
analytical continuation of the instanton amplitudes from Euclidean to Minkowsky
space-time and reflects quasiclassical origin of instanton solution of QCD
equations of motion. This phenomenon and instanton--induced quark spin-flip
give a new nonperturbative mechanism for the observed anomalous single-spin
asymmetries in hadron-hadron and lepton-hadron interactions.",9905497v5
1999-11-01,Nucleon Spin Content from Elastic Form Factor Data,"I use the formalism of skewed parton distributions (SPD) to describe elastic
form factors of the nucleon. The results are consistent with approximate dipole
behavior of $G_{Mp}(Q^2)$ and recent JLab data for the ratio of the proton form
factors $G_{Ep}/G_{Mp}$ at $Q^2\leq 3.5$ GeV$^2$. Using the Angular Momentum
Sum Rule, I obtain a numerical estimate for the valence quark contributions to
the nucleon spin at the level of 50%, with their orbital angular momentum {\it
included}. When combined with polarized DIS measurements, this result indicated
that the orbital angular momentum of quarks contributes about 25% to the
nucleon spin.",9910565v1
2001-10-22,The non-forward BFKL amplitude and rapidity gap physics,"We discuss the BFKL approach to processes with large momentum transferred
through a rapidity gap. The Mueller and Tang scheme to the BFKL non-forward
parton-parton elastic scattering amplitude at large $t$, is extended to include
higher conformal spins. The new contributions are found to decrease with
increasing energy, as follows from the gluon reggeisation phenomenon, and to
vanish for asymptotically high energies. However, at moderate energies and high
$|t|$, the higher conformal spins dominate the amplitude. We illustrate the
effects by studying the production of two high $E_T$ jets separated by a
rapidity gap at HERA energies. In a simplified framework, we find excellent
agreement with the HERA photoproduction data once we incorporate the rapidity
gap survival probability against soft rescattering effects. We emphasize that
measurements of the analogous process in electroproduction may probe different
summations over conformal spins.",0110273v2
2002-09-30,Real and Virtual Compton Scattering in a Regge Approach,"We study Real and Deeply Virtual Compton Scattering in a model based on Regge
trajectories and two-gluon exchange. In the kinematic regime of current
experiments, the hadronic component of the outgoing real photon plays a major
role. We analyze the spin structure of Compton scattering at large momentum
transfer and give predictions for several spin asymmetries. In the DVCS
channel, a fairly good agreement is obtained for the recently measured beam
spin and charge asymmetries.",0209362v2
2004-07-09,On the determination of the parity of the $Θ^+$,"We critically examine the possibility of determining the parity of the
$\Theta^+(1540)$ from the reactions $NN\to \Theta^+Y$ ($Y$ = $\Lambda$,
$\Sigma$) recently discussed in the literature. Specifically, we study the
energy dependence of those observables that were suggested to be the most
promising ones to unravel the parity of the $\Theta^+$, namely the spin
correlation coefficient $A_{xx}$, and the spin transfer coefficient $D_{xx}$.
We show that the energy dependence of $\sigma_0(1+A_{xx})$, corresponding to
the spin-triplet production cross section, guarantees unambiguous information
on the parity of the $\Theta^+$. Here, $\sigma_0$ denotes the unpolarized cross
section. Also, the possibility to determine the parity of the $\Theta^+$
through the energy dependence of $\sigma_0D_{xx}$ is discussed.",0407107v1
2005-12-08,Is there exist a hadron spin-flip contribution in the Coulomb-hadron interference at small transfer momenta and high energies,"The analysing power $A_N$ is examined in the range of the Coulomb-hadron
interferenceon on the basis of the experimental data from p_L = 6 GeV/c up to
200 GeV/c taking account of a phenomenological analysis at p_L = 6 GeV/c and a
dynamic high-energy spin model. The results are compared with the new RHIC data
at p_L = 100 GeV/c. The new experimental data obtained at RHIC indicate the
small contributions of the hadrons spin-flip amplitude.",0512092v2
2006-12-05,The explicit procedures for reconstruction of full set of helicity amplitudes in elastic proton-proton and proton-antiproton collisions,"The explicit procedures are described for reconstruction of the full set of
helicity amplitudes in proton-proton and proton-antiproton elastic scattering.
The procedures are based on the derivative relations for the helicity
amplitudes in s-channel, on the explicit parametrization of the leading spin
non flip amplitudes and crossing - symmetry relations. Asymptotic theorems are
used for definition of free parameters in derivative relations. We also study
the Odderon influence on the helicity amplitude reconstruction. Reconstruction
procedures are valid at extremely wide energy domain and broad range of
momentum transfer. These procedures might be useful in studying the spin
phenomena in proton-proton and proton-antiproton elastic scattering.",0612045v2
1991-10-17,Analytical Bethe Ansatz for Quantum-Algebra-Invariant Spin Chains,"We have recently constructed a large class of open quantum spin chains which
have quantum-algebra symmetry and which are integrable. We show here that these
models can be exactly solved using a generalization of the analytical Bethe
Ansatz (BA) method. In particular, we determine in this way the spectrum of the
transfer matrices of the $U_q [(su(2)]$-invariant spin chains associated with
$A^{(1)}_1$ and $A^{(2)}_2$ in the fundamental representation. The
quantum-algebra invariance of these models plays an essential role in obtaining
these results. The BA equations for these open chains are ``doubled'' with
respect to the BA equations for the corresponding closed chains.",9110050v1
1992-08-27,Quantum affine symmetry in vertex models,"We study the higher spin anologs of the six vertex model on the basis of its
symmetry under the quantum affine algebra $U_q(\slth)$. Using the method
developed recently for the XXZ spin chain, we formulate the space of states,
transfer matrix, vacuum, creation/annihilation operators of particles, and
local operators, purely in the language of representation theory. We find that,
regardless of the level of the representation involved, the particles have spin
$1/2$, and that the $n$-particle space has an RSOS-type structure rather than a
simple tensor product of the $1$-particle space. This agrees with the picture
proposed earlier by Reshetikhin.",9208066v1
1993-04-20,Exact Solution of the general Non Intersecting String Model,"We present a thorough analysis of the Non Intersecting String (NIS) model and
its exact solution. This is an integrable $q$-states vertex model describing
configurations of non-intersecting polygons on the lattice. The exact
eigenvalues of the transfer matrix are found by analytic Bethe Ansatz. The
Bethe Ansatz equations thus found are shown to be equivalent to those for a
mixed spin model involving both 1/2 and infinite spin. This indicates that the
NIS model provides a representation of the quantum group $SU(2)_{\hat q}$
($|\hat q|\not= 1$) corresponding to spins $s=1/2$ and $s=\infty$. The
partition function and the excitations in the thermodynamic limit are computed.",9304085v1
1995-02-10,Difference Equations in Spin Chains with a Boundary,"Correlation functions and form factors in vertex models or spin chains are
known to satisfy certain difference equations called the quantum
Knizhnik-Zamolodchikov equations. We find similar difference equations for the
case of semi-infinite spin chain systems with integrable boundary conditions.
We derive these equations using the properties of the vertex operators and the
boundary vacuum state, or alternatively through corner transfer matrix
arguments for the 8-vertex model with a boundary. The spontaneous boundary
magnetization is found by solving such difference equations. The boundary
$S$-matrix is also proposed and compared, in the sine-Gordon limit, with
Ghoshal--Zamolodchikov's result. The axioms satisfied by the form factors in
the boundary theory are formulated.",9502060v1
2002-05-27,Orbiting strings in AdS black holes and N=4 SYM at finite temperature,"Following Gubser, Klebanov and Polyakov [hep-th/0204051], we study strings in
AdS black hole backgrounds. With respect to the pure AdS case, rotating strings
are replaced by orbiting strings. We interpret these orbiting strings as CFT
states of large spin similar to glueballs propagating through a gluon plasma.
The energy and the spin of the orbiting string configurations are associated
with the energy and the spin of states in the dual finite temperature N=4 SYM
theory. We analyse in particular the limiting cases of short and long strings.
Moreover, we perform a thermodynamic study of the angular momentum transfer
from the glueball to the plasma by considering string orbits around rotating
AdS black holes. We find that standard expectations, such as the complete
thermal dissociation of the glueball, are borne out after subtle properties of
rotating AdS black holes are taken into account.",0205280v3
2005-02-21,Conservation of Helicity and SU(2) Symmetry in First Order Scattering,"The structure of the spin interaction operator (SI) (the interaction that
remains after space variables are integrated out) in the first order S-matrix
element of the elastic scattering of a Dirac particle in a general
helicity-conserving vector potential is investigated.It is shown that the
conservation of helicity dictates a specific form of the SI regardless of the
explicit form of the vector potential. This SI closes the SU(2) algebra with
other two operators in the spin space of the particle. The directions of the
momentum transfer vector and the vector bisecting the scattering angle seem to
define some sort of ""intrinsic"" axes at this order that act as some symmetry
axes for the whole spin dynamics . The conservation of helicity at this order
can be formulated as the invariance of the component of the helicity of the
particle along the bisector of the scattering angle in the transition.",0502177v1
2005-07-06,A deformed analogue of Onsager's symmetry in the XXZ open spin chain,"The XXZ open spin chain with general integrable boundary conditions is shown
to possess a q-deformed analogue of the Onsager's algebra as fundamental
non-abelian symmetry which ensures the integrability of the model. This
symmetry implies the existence of a finite set of independent mutually
commuting nonlocal operators which form an abelian subalgebra. The transfer
matrix and local conserved quantities, for instance the Hamiltonian, are
expressed in terms of these nonlocal operators. It follows that Onsager's
original approach of the planar Ising model can be extended to the XXZ open
spin chain.",0507053v3
2005-10-22,Integrable Spin Chains on the Conformal Moose,"We consider N=1, D=4 superconformal U(N)^{pq} Yang-Mills theories dual to
AdS_5xS^5/Z_pxZ_q orbifolds. We construct the dilatation operator of this
superconformal gauge theory at one-loop planar level. We demonstrate that a
specific sector of this dilatation operator can be thought of as the transfer
matrix for a two-dimensional statistical mechanical system, related to an
integrable SU(3) anti-ferromagnetic spin chain system, which in turn is
equivalent to a 2+1-dimensional string theory where the spatial slices are
discretized on a triangular lattice. This is an extension of the SO(6) spin
chain picture of N=4 super Yang-Mills theory. We comment on the integrability
of this N=1 gauge theory and hence the corresponding three-dimensional
statistical mechanical system, its connection to three-dimensional lattice
gauge theories, extensions to six-dimensional string theories, AdS/CFT type
dualities and finally their construction via orbifolds and brane-box models. In
the process we discover a new class of almost-BPS BMN type operators with large
engineering dimensions but controllably small anomalous corrections.",0510189v2
2007-03-15,Supersymmetric Bethe Ansatz and Baxter Equations from Discrete Hirota Dynamics,"We show that eigenvalues of the family of Baxter Q-operators for
supersymmetric integrable spin chains constructed with the gl(K|M)-invariant
$R$-matrix obey the Hirota bilinear difference equation. The nested Bethe
ansatz for super spin chains, with any choice of simple root system, is then
treated as a discrete dynamical system for zeros of polynomial solutions to the
Hirota equation. Our basic tool is a chain of Backlund transformations for the
Hirota equation connecting quantum transfer matrices. This approach also
provides a systematic way to derive the complete set of generalized Baxter
equations for super spin chains.",0703147v2
2004-12-22,Measurement of the analyzing power of proton-carbon elastic scattering in the CNI region at RHIC,"The single transverse spin asymmetry, A_N, of the p-carbon elastic scattering
process in the Coulomb Nuclear Interference (CNI) region was measured using an
ultra thin carbon target and polarized proton beam in the Relativistic Heavy
Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). In 2004, data were
collected to calibrate the p-carbon process at two RHIC energies (24 GeV, 100
GeV). A_N was obtained as a function of momentum transfer -t. The results were
fit with theoretical models which allow us to assess the contribution from a
hadronic spin flip amplitude.",0412053v1
2005-07-25,First Measurement of A_N at sqrt(s)=200 GeV in Polarized Proton-Proton Elastic Scattering at RHIC,"We report on the first measurement of the single spin analyzing power (A_N)
at sqrt(s)=200GeV, obtained by the pp2pp experiment using polarized proton
beams at the Relativistic Heavy Ion Collider (RHIC). Data points were measured
in the four momentum transfer t range 0.01 < |t| < 0.03 (GeV/c)^2. Our result,
averaged over the whole t-interval is about one standard deviation above the
calculation, which uses interference between electromagnetic spin-flip
amplitude and hadronic non-flip amplitude, the source of A_N. The difference
could be explained by an additional contribution of a hadronic spin-flip
amplitude to A_N.",0507030v4
2006-12-18,Absolute Polarization Measurements at RHIC in the Coulomb Nuclear Interference Region,"The Relativistic Heavy Ion Collider at Brookhaven National Laboratory
provides polarized proton beams for the investigation of the nucleon spin
structure. For polarimetry, carbon-proton and proton-proton scattering is used
in the Coulomb nuclear interference region at small momentum transfer ($-t$).
Fast polarization measurements of each beam are carried out with carbon fiber
targets at several times during an accelerator store. A polarized hydrogen gas
jet target is needed for absolute normalization over multiple stores, while the
target polarization is constantly monitored in a Breit-Rabi polarimeter. In
2005, the jet polarimeter has been used with both RHIC beams. We present
results from the jet polarimeter including a detailed analysis of background
contributions to asymmetries and to the beam polarization.",0612020v1
1996-09-12,Triplet np Final State Interactions at Large Momentum Transfers,"Using the simple relation between the np scattering and bound state wave
functions, the spin-triplet contributions to the pp -> pi+ (pn) and backward dp
-> p(pn) reactions are estimated for low np excitation energies. The good
agreement with the pion production data at 400 and 450 MeV over a range of
angles shows that spin-singlet final states cannot be more than of the order of
10%. On the other hand it is seen that the spin-singlet states must provide
about 30% of the strength in pion production at 1 GeV as well as
deuteron-proton backward scattering at 1.6 GeV.",9609032v1
2005-04-08,Bimodality as a signal of Liquid-Gas phase transition in nuclei?,"We use the HIPSE (Heavy-Ion Phase-Space Exploration) Model to discuss the
origin of the bimodality in charge asymmetry observed in nuclear reactions
around the Fermi energy. We show that it may be related to the important
angular momentum (spin) transferred into the quasi-projectile before secondary
decay. As the spin overcomes the critical value, a sudden opening of decay
channels is induced and leads to a bimodal distribution for the charge
asymmetry. In the model, it is not assigned to a liquid-gas phase transition
but to specific instabilities in nuclei with high spin. Therefore, we propose
to use these reactions to study instabilities in rotating nuclear droplets.",0504027v2
2004-05-26,Pure spin-angular momentum coefficients for non-scalar one-particle operators in jj-coupling,"A revised program for generating the spin-angular coefficients in
relativistic atomic structure calculations is presented. When compared with our
previous version [G.Gaigalas, S.Fritzsche and I.P.Grant, CPC 139 (2001) 263],
the new version of the Anco program now provides these coefficients for both,
scalar as well as non-scalar one-particle operators as they arise frequently in
the study of transition probabilities, photoionization and electron capture
processes, the alignment transfer through excited atomic states, collision
strengths, and in many other investigations.
  The program is based on a recently developed formalism [G.Gaigalas,
Z.Rudzikas, and C.F.Fischer, J. Phys. B 30 (1997) 3747], which combines
techniques from second quantization in coupled tensorial form, the theory of
quasispin, and the use of reduced coefficients of fractional parentage, in
order to derive the spin-angular coefficients for complex atomic shell
structures more efficiently. By making this approach now available also for
non-scalar interactions, therefore, studies on a whole field of new properties
and processes are likely to become possible even for atoms and ions with a
complex structure.",0405136v2
2006-09-04,Large atom number Bose-Einstein condensate of sodium,"We describe the setup to create a large Bose-Einstein condensate containing
more than 120x10^6 atoms. In the experiment a thermal beam is slowed by a
Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical
dark-spot MOT in our experiments contains 2.0x10^10 atoms with a temperature of
320 microK and a density of about 1.0x10^11 atoms/cm^3. The sample is spin
polarized in a high magnetic field, before the atoms are loaded in the magnetic
trap. Spin polarizing in a high magnetic field results in an increase in the
transfer efficiency by a factor of 2 compared to experiments without spin
polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s by
evaporative cooling. To suppress the 3-body losses at the end of the
evaporation the magnetic trap is decompressed in the axial direction.",0609028v1
2006-02-01,Quantum correlations in successive spin measurements,"In this paper we present a new approach for testing QM against the realism
aspect of hidden variable theory (HVT). We consider successive measurements of
non-commuting operators on a input spin $s$ state. The key point is that,
although these operators are non-commuting, they act on different states so
that the joint probabilities for the outputs of successive measurements are
well defined. We show that, in this scenario HVT leads to Bell type
inequalities for the correlation between the outputs of successive
measurements. We account for the maximum violation of these inequalities by
quantum correlations by varying spin value and the number of successive
measurements. Our approach can be used to obtain a measure of the deviation of
QM from realism say in terms of the amount of information needed to be
transferred between successive measurements in order to classically simulate
the quantum correlations.",0602005v3
2006-03-16,Quantum Communication in Spin Systems With Long-Range Interactions,"We calculate the fidelity of transmission of a single qubit between distant
sites on semi-infinite and finite chains of spins coupled via the magnetic
dipole interaction. We show that such systems often perform better than their
Heisenberg nearest-neighbour coupled counterparts, and that fidelities closely
approaching unity can be attained between the ends of finite chains without any
special engineering of the system, although state transfer becomes slow in long
chains. We discuss possible optimization methods, and find that, for any
length, the best compromise between the quality and the speed of the
communication is obtained in a nearly uniform chain of 4 spins.",0603148v6
2007-04-26,Polynomial solutions of qKZ equation and ground state of XXZ spin chain at Delta = -1/2,"Integral formulae for polynomial solutions of the quantum
Knizhnik-Zamolodchikov equations associated with the R-matrix of the six-vertex
model are considered. It is proved that when the deformation parameter q is
equal to e^{+- 2 pi i/3} and the number of vertical lines of the lattice is
odd, the solution under consideration is an eigenvector of the inhomogeneous
transfer matrix of the six-vertex model. In the homogeneous limit it is a
ground state eigenvector of the antiferromagnetic XXZ spin chain with the
anisotropy parameter Delta equal to -1/2 and odd number of sites. The obtained
integral representations for the components of this eigenvector allow to prove
some conjectures on its properties formulated earlier. A new statement relating
the ground state components of XXZ spin chains and Temperley-Lieb loop models
is formulated and proved.",0704.3542v3
2007-06-15,Spin Polarized Transport Through a Single-Molecule Magnet: Current-Induced Magnetic Switching,"Magnetic switching of a single-molecule magnet (SMM) due to spin-polarized
current is investigated theoretically. The charge transfer between the
electrodes takes place via the lowest unoccupied molecular orbital (LUMO) of
the SMM. Generally, the double occupancy of the LUMO level, and a finite
on-site Coulomb repulsion, is taken into account. Owing to the exchange
interaction between electrons in the LUMO level and the SMM's spin, the latter
can be reversed. The perturbation approach (Fermi golden rule) is applied to
calculate current-voltage characteristics. The influence of Coulomb
interactions on the switching process is also analyzed.",0706.2315v2
2007-09-27,Quark helicity flip and the transverse spin dependence of inclusive DIS,"Inclusive DIS with unpolarized beam exhibits a subtle dependence on the
transverse target spin, arising from the interference of one-photon and
two-photon exchange amplitudes in the cross section. We argue that this
observable probes mainly the quark helicity-flip amplitudes induced by the
non-perturbative vacuum structure of QCD (spontaneous chiral symmetry
breaking). This conjecture is based on (a) the absence of significant Sudakov
suppression of the helicity-flip process if soft gluon emission in the quark
subprocess is limited by the chiral symmetry-breaking scale mu_chiral^2 >>
Lambda_QCD^2; (b) the expectation that the quark helicity-conserving twist-3
contribution is small. The normal target spin asymmetry is estimated to be of
the order 10^{-4} in the kinematics of the planned Jefferson Lab Hall A
experiment.",0709.4293v1
2007-10-04,Entanglement: A myth introducing non-locality in any quantum theory,"The purposes of the present article are: a) To show that non-locality leads
to the transfer of certain amounts of energy and angular momentum at very long
distances, in an absolutely strange and unnatural manner, in any model
reproducing the quantum mechanical results. b) To prove that non-locality is
the result only of the zero spin state assumption for distant particles, which
explains its presence in any quantum mechanical model. c) To reintroduce
locality, simply by denying the existence of the zero spin state in nature (the
so-called highly correlated, or EPR singlet state) for particles
non-interacting with any known field. d) To propose a realizable experiment to
clarify if two remote (and thus non-interacting with a known field) particles,
supposed to be correlated as in Bell-type experiments, are actually in zero
spin state.",0710.1008v1
2007-10-15,"Structural anomalies, spin transitions and charge disproportionation in LnCoO3","The diamagnetic-paramagnetic and insulator-metal transitions in LnCoO3
perovskites (Ln = La, Y, rare earths) are reinterpreted and modeled as a
two-level excitation process. In distinction to previous models, the present
approach can be characterized as a LS-HS-IS (low-high-intermediate spin)
scenario. The first level is the local excitation of HS Co3+ species in the LS
ground state. The second excitation is based on the interatomic electron
transfer between the LS/HS pairs, leading finally to a stabilization of the
metallic phase based on IS Co3+. The model parameters have been quantified for
Ln = La, Pr and Nd samples using the powder neutron diffraction on the thermal
expansion of Co-O bonds, that is associated with the two successive spin
transitions. The same model is applied to interpret the magnetic susceptibility
of LaCoO3 and YCoO3.",0710.2759v1
2007-12-21,Thermodynamics of antiferromagnetic alternating spin chains,"We consider integrable quantum spin chains with alternating spins (S_1,S_2).
We derive a finite set of non-linear integral equations for the thermodynamics
of these models by use of the quantum transfer matrix approach. Numerical
solutions of the integral equations are provided for quantities like specific
heat, magnetic susceptibility and in the case S_1=S_2 for the thermal Drude
weight. At low temperatures one class of models shows finite magnetization and
the other class presents antiferromagnetic behaviour. The thermal Drude weight
behaves linearly on T at low temperatures and is proportional to the central
charge c of the system. Quite generally, we observe residual entropy for
S_1\neq S_2.",0712.3765v1
2007-12-25,Distribution of Lee-Yang zeros and Griffiths singularities in the $\pm J$ model of spin glasses,"We investigate the distribution of zeros of the partition function of the
two- and three-dimensional symmetric $\pm J$ Ising spin glasses on the complex
field plane. We use the method to analytically implement the idea of numerical
transfer matrix which provides us with the exact expression of the partition
function as a polynomial of fugacity. The results show that zeros are
distributed in a wide region in the complex field plane. Nevertheless we
observe that zeros on the imaginary axis play dominant roles in the critical
behaviour since zeros on the imaginary axis are in closer proximity to the real
axis. We estimate the density of zeros on the imaginary axis by an
importance-sampling Monte Carlo algorithm, which enables us to sample very rare
events. Our result suggests that the density has an essential singularity at
the origin. This observation is consistent with the existence of Griffiths
singularities in the present systems. This is the first evidence for Griffiths
singularities in spin glass systems in equilibrium.",0712.4063v2
2008-03-11,Many body effects and cluster state quantum computation in strongly interacting systems of photons,"We discuss the basic properties of a recently proposed hybrid light-matter
system of strongly interacting photons in an array of coupled cavities each
doped with a single two level system. Using the non-linearity generated from
the photon blockade effect, we predict strong correlations between the hopping
photons in the array, and show the possibility of observing a phase transition
from a polaritonic insulator to a superfluid of photons. In the Mott phase,
this interaction can be mapped to an array of spins. We show how the remaining
Hamiltonian, in conjunction with individual spin manipulation, can thus be used
for simulating spin chains (useful for state transfer protocols) and cluster
state quantum computation.",0803.1665v1
2008-10-14,Spin and Charge Fluctuations and Lattice Effects on Charge Orders in α-(BEDT-TTF)_2I_3,"The effects of spin and charge fluctuations and electron-phonon couplings on
charge ordering in \alpha-(BEDT-TTF)_2I_3
(BEDT-TTF=bis(ethylenedithio)-tetrathiafulvalence) are investigated
theoretically for an anisotropic triangular lattice at 3/4 filling. By the
exact-diagonalization method, we have calculated the hole density distributions
and the modulations of transfer integrals from high-temperature values as a
function of electron-phonon coupling strength. The results clearly show that
the lattice effect on \alpha-(BEDT-TTF)_2I_3 is weak compared with that on
\theta-(BEDT-TTF)_2RbZn(SCN)_4, as previously found by experiments. This
finding, which is also consistent with recent mean-field results, is
systematically explained by strong-coupling perturbation theory; the effects of
spin fluctuations are partially canceled by charge fluctuations in
\alpha-(BEDT-TTF)_2I_3.",0810.2536v1
2008-12-03,Quantum communication through anisotropic Heisenberg XY spin chains,"We study quantum communication through an anisotropic Heisenberg XY chain in
a transverse magnetic field. We find that for some time $t$ and anisotropy
parameter $\gamma$, one can transfer a state with a relatively high fidelity.
In the strong-field regime, the anisotropy does not significantly affect the
fidelity while in the weak-field regime the affect is quite pronounced. The
most interesting case is the the intermediate regime where the oscillation of
the fidelity with time is low and the high-fidelity peaks are relatively broad.
This would, in principle, allow for quantum communication in realistic
circumstances. Moreover, we calculate the purity, or tangle, as a measure of
the entanglement between one spin and all the other spins in the chain and find
that the stronger the anisotropy and exchange interaction, the more
entanglement will be generated for a given time.",0812.0645v2
2009-04-13,Thermal entanglement of one-dimensional Heisenberg quantum spin chains in magnetic fields,"The thermal pairwise entanglement (TE) of the S=1/2 XY chain in a transverse
magnetic field is exactly resolved by means of the Jordan-Wigner
transformation. It is found that the TE vanishes at a common temperature
Tc~0.4843J, which is irrelevant to the field. A thermal quantity is proposed to
witness the entangled state. Furthermore, the TE of the S=1/2
antiferromagnetic-ferromagnetic (AF-F) Heisenberg chain is studied by the
transfer-matrix renormalization group method.The TEs of the spins coupled by AF
and F interactions are found to behave distinctively. The vanishing temperature
of the field-induced TE of the spins coupled by F interactions is observed to
change with the magnetic field. The results are further confirmed and analyzed
by the mean-field theory.",0904.1946v3
2009-07-29,Experimental band structure of the nearly half-metallic CuCr$_2$Se$_4$: An optical and magneto-optical study,"Diagonal and off-diagonal optical conductivity spectra have been determined
form the measured reflectivity and magneto-optical Kerr effect (MOKE) over a
broad range of photon energy in the itinerant ferromagnetic phase of
CuCr$_2$Se$_4$ at various temperatures down to T=10 K. Besides the low-energy
metallic contribution and the lower-lying charge transfer transition at
$E$$\approx$2 eV, a sharp and distinct optical transition was observed in the
mid-infrared region around $E$$=$0.5 eV with huge magneto-optical activity.
This excitation is attributed to a parity allowed transition through the Se-Cr
hybridization-induced gap in the majority spin channel. The large off-diagonal
conductivity is explained by the high spin polarization in the vicinity of the
Fermi level and the strong spin-orbit interaction for the related charge
carriers. The results are discussed in connection with band structure
calculations.",0907.5087v1
2009-08-24,Momentum Dependent Dark Matter Scattering,"It is usually assumed that WIMPs interact through spin-independent and
spin-dependent interactions. Interactions which carry additional powers of the
momentum transfer, q^2, are assumed to be too small to be relevant. In theories
with new particles at the ~ GeV scale, however, these q^2-dependent
interactions can be large, and, in some cases dominate over the standard
interactions. This leads to new phenomenology in direct detection experiments.
Recoil spectra peak at non-zero energies, and the relative strengths of
different experiments can be significantly altered. We present a simple
parameterization for models of this type which captures much of the interesting
phenomenology and allows a comparison between experiments. As an application,
we find that dark matter with momentum dependent interactions coupling to the
spin of the proton can reconcile the DAMA annual modulation result with other
experiments.",0908.3192v2
2009-09-21,Half-metallicity in NiMnSb: a Variational Cluster Approach with ab-initio parameters,"Electron correlation effects in the half-metallic ferromagnet NiMnSb are
investigated within a combined density functional and many-body approach.
Starting from a realistic multi-orbital Hubbard-model including Mn and Ni-d
orbitals, the many-body problem is addressed via the Variational Cluster
Approach. The density of states obtained in the calculation shows a strong
spectral weight transfer towards the Fermi level in the occupied conducting
majority spin channel with respect to the uncorrelated case, as well as states
with vanishing quasiparticle weight in the minority spin gap. Although the two
features produce competing effects, the overall outcome is a strong reduction
of the spin polarisation at the Fermi level with respect to the uncorrelated
case. This result emphasizes the importance of correlation in this material.",0909.3807v1
2009-10-08,Convergence and coupling for spin glasses and hard spheres,"We discuss convergence and coupling of Markov chains, and present general
relations between the transfer matrices describing these two processes. We then
analyze a recently developed local-patch algorithm, which computes rigorous
upper bound for the coupling time of a Markov chain for non-trivial
statistical-mechanics models. Using the coupling from the past protocol, this
allows one to exactly sample the underlying equilibrium distribution. For spin
glasses in two and three spatial dimensions, the local-patch algorithm works at
lower temperatures than previous exact-sampling methods. We discuss variants of
the algorithm which might allow one to reach, in three dimensions, the
spin-glass transition temperature. The algorithm can be adapted to hard-sphere
models. For two-dimensional hard disks, the algorithm allows us to draw exact
samples at higher densities than previously possible.",0910.1530v1
2009-10-20,Correlated band theory of spin and orbital contributions to Dzyaloshinskii-Moriya interactions,"A new approach for calculations of Dzyaloshinskii-Moriya interactions in
molecules and crystals is proposed. It is based on the exact perturbation
expansion of total energy of weak ferromagnets in the canting angle with the
only assumption of local Hubbard-type interactions. This scheme leads to a
simple and transparent analytical expression for Dzyaloshinskii-Moriya vector
with a natural separation into spin and orbital contributions. The main problem
was transferred to calculations of effective tight-binding parameters in the
properly chosen basis including spin-orbit coupling. Test calculations for
La$_2$CuO$_4$ give the value of canting angle in a good agreement with
experimental data.",0910.3748v2
2009-11-09,Review of quasi-elastic charge-exchange data in the nucleon-deuteron breakup reaction,"The available data on the forward charge exchange of nucleons on the deuteron
up to 2GeV per nucleon are reviewed. The value of the inclusive nd->pnn/np->pn
cross section ratio is sensitive to the fraction of spin-independent
neutron-proton backward scattering. The measurements of the polarisation
transfer in d(\vec{n},\vec{p})nn or the deuteron analysing power in
p(\vec{d},pp)n in high resolution experiments, where the final nn or pp pair
emerge at low excitation energy, depend upon the longitudinal and transverse
spin-spin np amplitudes. The relation between these types of experiments is
discussed and the results compared with predictions of the impulse
approximation model in order to see what new constraints they can bring to the
neutron-proton database.",0911.1699v1
2009-11-12,Logical XOR gate response in a quantum interferometer: A spin dependent transport,"We examine spin dependent transport in a quantum interferometer composed of
magnetic atomic sites based on transfer matrix formalism. The interferometer,
threaded by a magnetic flux $\phi$, is symmetrically attached to two
semi-infinite one-dimensional (1D) non-magnetic electrodes, namely, source and
drain. A simple tight-binding model is used to describe the bridge system, and,
here we address numerically the conductance-energy and current-voltage
characteristics as functions of the interferometer-to-electrode coupling
strength, magnetic flux and the orientation of local the magnetic moments
associated with each atomic site. Quite interestingly it is observed that, for
$\phi=\phi_0/2$ ($\phi_0=ch/e$, the elementary flux-quantum) a logical XOR gate
like response is observed, depending on the orientation of the local magnetic
moments associated with the magnetic atoms in the upper and lower arms of the
interferometer, and it can be changed by an externally applied gate magnetic
field. This aspect may be utilized in designing a spin based electronic logic
gate.",0911.2349v3
2009-11-16,$^{235}$U nuclear relaxation rates in an itinerant antiferromagnet USb$_2$,"$^{235}$U nuclear spin-lattice ($T_1^{-1}$) and spin-spin ($T_2^{-1}$)
relaxation rates in the itinerant antiferromagnet USb$_2$ are reported as a
function of temperature in zero field. The heating effect from the intense rf
pulses that are necessary for the $^{235}$U NMR results in unusual complex
thermal recovery of the nuclear magnetization which does not allow measuring
$T_1^{-1}$ directly. By implementing an indirect method, however, we
successfully extracted $T_1^{-1}$ of the $^{235}$U. We find that the
temperature dependence of $T_1^{-1}$ for both $^{235}$U and $^{121}$Sb follows
the power law ($\propto T^n$) with the small exponent $n=0.3$ suggesting that
the same relaxation mechanism dominates the on-site and the ligand nuclei, but
an anomaly at 5 K was observed, possibly due to the change in the transferred
hyperfine coupling on the Sb site.",0911.3068v2
2009-12-11,Zero field spin splitting in AlSb/InAs/AlSb quantum wells induced by surface proximity effects,"InAs quantum well heterostructures are of considerable interest for
mesoscopic device applications such as scanning probe and magnetic recording
sensors, which require the channel to be close to the surface. Here we report
on magnetotransport measurements of AlSb/InAs/AlSb Hall bars at a shallow depth
of 20 nm. Analysis of the observed Shubnikov-de Haas oscillations and modeling
show that spin splitting energies in excess of 2.3 meV occur at zero magnetic
field. We conclude that the spin-splitting results from the Rashba effect due
to the band bending in the quantum well. This is caused by substantial electron
transfer from the surface to the quantum well and becomes significant when the
quantum well is located near the surface.",0912.2143v1
2010-01-29,Strong correlation and massive spectral-weight redistribution induced spin density wave in a-Fe1.06Te,"The electronic structure of a-Fe1.06Te is studied with angle-resolved
photoemission spectroscopy. We show that there is substantial spectral weight
around Gamma and X, and lineshapes are intrinsically incoherent in the
paramagnetic state. The magnetic transition is characterized by a massive
spectral-weight transfer over an energy range as large as the band width, which
even exhibits a hysteresis loop that marks the strong first order transition.
Coherent quasiparticles emerge in the magnetically ordered state due to
decreased spin fluctuations, which account for the change of transport
properties from insulating behavior to metallic behavior. Our observation
demonstrates that Fe1.06Te distinguishes itself from other iron-based systems
with more local characters and much stronger interactions among different
degrees of freedom, and how a spin density wave is formed in the presence of
strong correlation.",1001.5327v1
2010-07-05,Quantum correlation and classical correlation dynamics in the spin-boson model,"We study the quantum correlation and classical correlation dynamics in a
spin-boson model. For two different forms of spectral density, we obtain
analytical results and show that the evolutions of both correlations depend
closely on the form of the initial state. At the end of evolution, all
correlations initially stored in the spin system transfer to reservoirs. It is
found that for a large family of initial states, quantum correlation remains
equal to the classical correlation during the course of evolution. In addition,
there is no increase in the correlations during the course of evolution.",1007.0669v1
2010-08-06,Critical exponents of domain walls in the two-dimensional Potts model,"We address the geometrical critical behavior of the two-dimensional Q-state
Potts model in terms of the spin clusters (i.e., connected domains where the
spin takes a constant value). These clusters are different from the usual
Fortuin-Kasteleyn clusters, and are separated by domain walls that can cross
and branch. We develop a transfer matrix technique enabling the formulation and
numerical study of spin clusters even when Q is not an integer. We further
identify geometrically the crossing events which give rise to conformal
correlation functions. This leads to an infinite series of fundamental critical
exponents h_{l_1-l_2,2 l_1}, valid for 0 </- Q </- 4, that describe the
insertion of l_1 thin and l_2 thick domain walls.",1008.1216v1
2010-08-13,Spin Wave Storage using Chirped Control Fields in Atomic Frequency Comb based Quantum Memory,"It has been shown that an inhomogeneously broadened optical transition shaped
into an atomic frequency comb can store a large number of temporal modes of the
electromagnetic field at the single photon level without the need to increase
the optical depth of the storage material. The readout of light modes is made
efficient thanks to the rephasing of the optical-wavelength coherence similarly
to photon echo-type techniques and the re-emission time is given by the comb
structure. For on-demand readout and long storage times, two control fields are
used to transfer back and forth the optical coherence into a spin wave. Here,
we present a detailed analysis of the spin wave storage based on chirped
adiabatic control fields. In particular, we verify that chirped fields require
significantly weaker intensities than $\pi$-pulses. The price to pay is a
reduction of the multimode storage capacity that we quantify for realistic
material parameters associated with solids doped with rare-earth-metal ions.",1008.2284v1
2010-08-27,Theory of the beta-type Organic Superconductivity under Uniaxial Compression,"We study theoretically the shift of the superconducting transition
temperature (Tc) under uniaxial compression in beta-type organic
superconductors, beta-(BEDT-TTF)2I3 and beta-(BDA-TTP)2X[X=SbF6,AsF6], in order
to clarify the electron correlation, the spin frustration and the effect of
dimerization. The transfer integrals are calculated by the extended Huckel
method assuming the uniaxial strain and the superconducting state mediated by
the spin fluctuation is solved using Eliashberg's equation with the
fluctuation-exchange approximation. The calculation is carried out on both the
dimerized (one-band) and nondimerized (two-band) Hubbard models. We have found
that (i) the behavior of Tc in beta-(BEDT-TTF)2I3 with a stronger dimerization
is well reproduced by the dimer model, while that in weakly dimerized
beta-BDA-TTP salts is rather well reproduced by the two-band model, and (ii)
the competition between the spin frustration and the effect induced by the
fluctuation is important in these materials, which causes nonmonotonic shift of
Tc against uniaxial compression.",1008.4647v2
2010-09-17,Nucleon spin structure at low momentum transfers,"The generalized Gerasimov-Drell-Hearn (GDH) sum rule is known to be very
sensitive to QCD radiative and power corrections. We improve the previously
developed QCD-inspired model for the $Q^2$-dependence of the GDH sum rule. We
take into account higher order radiative and higher twist power corrections
extracted from precise Jefferson Lab data on the lowest moment of the
spin-dependent proton structure function $\Gamma_1^{p}(Q^2)$ and on the Bjorken
sum rule $\Gamma_1^{p-n}(Q^2)$. By using the singularity-free analytic
perturbation theory we demonstrate that the matching point between chiral-like
positive-$Q^2$ expansion and QCD operator product $1/Q^2$-expansion for the
nucleon spin sum rules can be shifted down to rather low $Q\simeq\Lambda_{QCD}$
leading to a good description of recent proton, neutron, deuteron and Bjorken
sum rule data at all accessible $Q^2$.",1009.3355v1
2010-09-20,Emergent Ising degrees of freedom in frustrated two-leg ladder and bilayer $s=1/2$ Heisenberg antiferromagnets,"Based on exact diagonalization data for finite quantum Heisenberg
antiferromagnets on two frustrated lattices (two-leg ladder and bilayer) and
analytical arguments we map low-energy degrees of freedom of the spin models in
a magnetic field on classical lattice-gas models. Further we use
transfer-matrix calculations and classical Monte Carlo simulations to give a
quantitative description of low-temperature thermodynamics of the quantum spin
models. The classical lattice-gas model yields an excellent description of the
quantum spin models up to quite large temperatures. The main peculiarity of the
considered frustrated bilayer is a phase transition which occurs at low
temperatures for a wide range of magnetic fields below the saturation magnetic
field and belongs to the two-dimensional Ising model universality class.",1009.3828v1
2010-10-06,Role of charge fluctuation in Q1D organic superconductor (TMTSF)2ClO4,"We have theoretically investigated the spin and charge fluctuations in the
quasi-one dimensional organic superconductor (TMTSF)2ClO4. Using the extended
multi-site Hubbard model, which contains four sites in a unit cell and the
transfer energies obtained by the extended H\""uckel method, we calculate the
linearized gap equation with the random phase approximation, to find novel
order parameters of superconductivity due to several kinds of charge
fluctuations induced by the anisotropic intersite repulsive interactions. For
the singlet state, the order parameter with line nodes appears in the case of
the strong charge fluctuation, while the order parameter with anisotropic gap
suggested by Shimahara is reproduced in the spin fluctuation. The triplet state
is also obtained for the wide parameter range of repulsive interactions due to
a cooperation between charge and spin fluctuations.",1010.1084v2
2010-11-11,All-electrical coherent control of the exciton states in a single quantum dot,"We demonstrate high-fidelity reversible transfer of quantum information from
the polarisation of photons into the spin-state of an electron-hole pair in a
semiconductor quantum dot. Moreover, spins are electrically manipulated on a
sub-nanosecond timescale, allowing us to coherently control their evolution. By
varying the area of the electrical pulse, we demonstrate phase-shift and
spin-flip gate operations with near-unity fidelities. Our system constitutes a
controllable quantum interface between flying and stationary qubits, an
enabling technology for quantum logic in the solid-state.",1011.2641v1
2010-12-14,Strange Quark Contribution to the Nucleon Spin from Electroweak Elastic Scattering Data,"The total contribution of strange quarks to the intrinsic spin of the nucleon
can be determined from a measurement of the strange-quark contribution to the
nucleon's elastic axial form factor. We have studied the strangeness
contribution to the elastic vector and axial form factors of the nucleon, using
all available elastic electroweak scattering data. Specifically, we combine
elastic $\nu p$ and $\bar{\nu} p$ scattering cross section data from the
Brookhaven E734 experiment with elastic $ep$ and quasi-elastic $ed$ and
$e$-$^4$He scattering parity-violating asymmetry data from the SAMPLE, HAPPEx,
G0 and PVA4 experiments. We have not only determined these form factors at
individual values of momentum-transfer ($Q^2$), as has been done recently, but
also have fit the $Q^2$-dependence of these form factors using simple
functional forms. We present the results of these fits using existing data,
along with some expectations of how our knowledge of these form factors can be
improved with data from the MicroBooNE experiment planned at Fermilab.",1012.2991v1
2010-12-22,Probing photo-induced melting of antiferromagnetic order in La0.5Sr1.5MnO4 by ultrafast resonant soft X-ray diffraction,"Photo-excitation in complex oxides1 transfers charge across semicovalent
bonds, drastically perturbing spin and orbital orders2. Light may then be used
in compounds like magnetoresistive manganites to control magnetism on nanometre
lengthscales and ultrafast timescales. Here, we show how ultrafast resonant
soft x-ray diffraction can separately probe the photo-induced dynamics of spin
and orbital orders in La0.5Sr1.5MnO4. Ultrafast melting of CE antiferromagnetic
spin order is evidenced by the disappearance of a (1/4,1/4,1/2) diffraction
peak. On the other hand the (1/4,1/4,0) peak, reflecting orbital order, is only
partially reduced. Cluster calculations aid our interpretation by considering
different magnetically ordered states accessible after photo-excitation.
Nonthermal coupling between light and magnetism emerges as a primary aspect of
photo-induced phase transitions in manganites.",1012.4960v2
2010-12-29,Linear and nonlinear Stark effect in triangular molecule,"We analyze changes of the electronic structure of a triangular molecule under
the influence of an electric field (i.e., the Stark effect). The effects of the
field are shown to be anisotropic and include both a linear and a nonlinear
part. For strong electron correlations, we explicitly derive exchange couplings
in an effective spin Hamiltonian. For some conditions one can find a dark spin
state, for which one of the spins is decoupled from the others. The model is
also applied for studying electronic transport through a system of three
coherently coupled quantum dots. Since electron transfer rates are anisotropic,
the current characteristics are anisotropic as well, differing for small and
large electric field.",1012.5924v2
2011-01-19,Superconducting to spin glass state transformation in ß-pyrochlore KxOs2O6,"{\ss}-pyrochore KOs2O6, which shows superconductivity below ~ 9.7K, has been
converted into KxOs2O6 (x < 2/3 - 1/2) electrochemically to show spin
glass-like behavior below ~ 6.1K. Room temperature sample surface potential
versus charge transfer scan indicates that there are at least two two-phase
regions for x between 1 and 0.5. Rattling model of superconductivity for the
title compound has been examined using electrochemical potassium
de-intercalation. The significant reduction of superconducting volume fraction
due to minor potassium reduction suggests the importance of defect and phase
coherence in the rattling model. Magnetic susceptibility, resistivity, and
specific heat measurement results have been compared between the
superconducting and spin glass-like samples.",1101.3639v1
2011-05-18,Exciton-spin memory with a semiconductor quantum dot molecule,"We report on a single photon and spin storage device based on a semiconductor
quantum dot molecule. Optically excited single electron-hole pairs are trapped
within the molecule and their recombination rate is electrically controlled
over three orders of magnitude. Single photons are stored up to 1 microsecond
and read out on a sub-nanosecond timescale. Using resonant excitation, the
circular polarisation of individual photons is transferred into the spin state
of electron-hole pairs with a fidelity above 80%, which does not degrade for
storage times up to the 12.5ns repetition period of the experiment.",1105.3737v1
2011-07-24,Distinguishing Spontaneous Quantum Hall States in Graphene Bilayers,"Chirally stacked N-layer graphene with N>=2 is susceptible to a variety of
distinct broken symmetry states in which each spin-valley flavor spontaneously
transfers charge between layers. In mean-field theory the neutral bilayer
ground state is a layer antiferromagnet (LAF) state that has opposite
spin-polarizations in opposite layers. In this Letter we analyze how the LAF
and other competing states are influenced by Zeeman fields that couple to spin
and by interlayer electric fields that couple to layer pseudospin, and comment
on the possibility of using response and edge state signatures to identify the
character of the bilayer ground state experimentally.",1107.4727v1
2011-09-02,Angle-resolved NMR: quantitative theory of 75As T1 relaxation rate in BaFe2As2,"While NMR measurements of nuclear energy spectra are routinely used to
characterize the static properties of quantum magnets, the dynamical
information locked in NMR 1/T1 relaxation rates remains notoriously difficult
to interpret. The difficulty arises from the fact that information about all
possible low-energy spin excitations of the electrons, and their coupling to
the nuclear moments, is folded into a single number, 1/T1. Here we develop a
quantitative theory of the NMR 1/T1 relaxation rate in a collinear
antiferromagnet, focusing on the specific example of BaFe2As2. One of the most
striking features of magnetism in BaFe2As2 is a strong dependence of 1/T1 on
the orientation of the applied magnetic field. By careful analysis of the
coupling between the nuclear and electronic moments, we show how this
anisotropy arises from the ""filtering"" of spin fluctuations by the form-factor
for transferred hyperfine interactions. This allows us to make convincing,
quantitative, fits to experimental 1/T1 data for BaFe2As2, for different field
orientations. We go on to show how a quantitative, angle-dependent theory for
the relaxation rate leads to new ways of measuring the dynamical parameters of
magnetic systems, in particular the spin wave velocities.",1109.0384v2
2011-11-14,Spin interfaces in the Ashkin-Teller model and SLE,"We investigate the scaling properties of the spin interfaces in the
Ashkin-Teller model. These interfaces are a very simple instance of lattice
curves coexisting with a fluctuating degree of freedom, which renders the
analytical determination of their exponents very difficult. One of our main
findings is the construction of boundary conditions which ensure that the
interface still satisfies the Markov property in this case. Then, using a novel
technique based on the transfer matrix, we compute numerically the left-passage
probability, and our results confirm that the spin interface is described by an
SLE in the scaling limit. Moreover, at a particular point of the critical line,
we describe a mapping of Ashkin-Teller model onto an integrable 19-vertex
model, which, in turn, relates to an integrable dilute Brauer model.",1111.3197v1
2012-01-09,Coupling of an erbium spin ensemble to a superconducting resonator,"A quantum coherent interface between optical and microwave photons can be
used as a basic building block within a future quantum information network. The
interface is envisioned as an ensemble of rare-earth ions coupled to a
superconducting resonator, allowing for coherent transfer between optical and
microwave photons. Towards this end, we have realized a hybrid device coupling
a Er$^{3+}$ doped Y$_2$SiO$_5$ crystal in a superconducting coplanar waveguide
cavity. We observe a collective spin coupling of 4 MHz and a spin linewdith of
down to 75 MHz.",1201.1718v2
2012-03-22,Determination of spin Hamiltonian in the Ni$_4$ magnetic molecule,"Magnetic excitations in a Ni$_4$ magnetic molecule were investigated by
inelastic neutron scattering and bulk susceptibility ($\chi_\text{bulk}$)
techniques. The magnetic excitation spectrum obtained from the inelastic
neutron scattering experiments exhibits three modes at energy transfers of
$\hbar\omega=0.5$, 1.35, and 1.6 meV. We show that the energy, momentum, and
temperature dependences of the inelastic neutron scattering data and
$\chi_\text{bulk}$ can be well reproduced by an effective spin Hamiltonian
consisted of intra-molecule exchange interactions, a single-ionic anisotropy,
biquadratic interactions, and Zeeman term. Under a hydrostatic pressure, the
bulk magnetization decreases with increasing pressure, which along with the
biquadratic term indicates spin-lattice coupling present in this system.",1203.5091v1
2012-04-05,Mixed-state quantum transport in correlated spin networks,"Quantum spin networks can be used to transport information between separated
registers in a quantum information processor. To find a practical
implementation, the strict requirements of ideal models for perfect state
transfer need to be relaxed, allowing for complex coupling topologies and
general initial states. Here we analyze transport in complex quantum spin
networks in the maximally mixed state and derive explicit conditions that
should be satisfied by propagators for perfect state transport. Using a
description of the transport process as a quantum walk over the network, we
show that it is necessary to phase correlate the transport processes occurring
along all the possible paths in the network. We provide a Hamiltonian that
achieves this correlation, and use it in a constructive method to derive
engineered couplings for perfect transport in complicated network topologies.",1204.1363v1
2012-05-31,Spin squeezing and Schrödinger cat generation in atomic samples with Rydberg blockade,"A scheme is proposed to prepare squeezed states and Schr\""{o}dinger cat-like
states of the collective spin degrees of freedom associated with a pair of
ground states in an atomic ensemble. The scheme uses an effective
Jaynes-Cummings interaction which can be provided by excitation of the atoms to
Rydberg states and an effective J_x interaction implemented by a resonant Raman
coupling between the atomic ground states. Both dynamical evolution with a
constant Hamiltonian and with adiabatic variation of the two interaction terms
are studied. We show that by the application of further resonant laser fields,
we can suppress non-adiabatic transfer under the time varying Hamiltonian and
significantly speed up the evolution towards a maximally squeezed, J_z=0,
collective spin state.",1205.6985v1
2012-08-06,Spin-dependent WIMP scattering off nuclei,"Chiral effective field theory (EFT) provides a systematic expansion for the
coupling of WIMPs to nucleons at the momentum transfers relevant to direct cold
dark matter detection. We derive the currents for spin-dependent WIMP
scattering off nuclei at the one-body level and include the leading long-range
two-body currents, which are predicted in chiral EFT. As an application, we
calculate the structure factor for spin-dependent WIMP scattering off 129,131Xe
nuclei, using nuclear interactions that have been developed to study nuclear
structure and double-beta decays in this region. We provide theoretical error
bands due to the nuclear uncertainties of WIMP currents in nuclei.",1208.1094v2
2012-08-10,Effects of charge doping and constrained magnetization on the electronic structure of an FeSe monolayer,"The electronic structural properties in the presence of constrained
magnetization and a charged background are studied for a monolayer of FeSe in
non-magnetic, checkerboard-, and striped-antiferromagnetic (AFM) spin
configurations. First principles techniques based on the pseudopotential
density functional approach and the local spin density approximation are
utilized. Our findings show that the experimentally observed shape of the Fermi
surface is best described by the checkerboard AFM spin pattern. To explore the
underlying pairing mechanism, we study the evolution of the non-magnetic to the
AFM-ordered structures under constrained magnetization. We estimate the
strength of electronic coupling to magnetic excitations involving an increase
in local moment and, separately, a partial moment transfer from one Fe atom to
another. We also show that the charge doping in the FeSe can lead to an
increase in the density of states at the Fermi level and possibly produce
higher superconducting transition temperatures.",1208.2260v2
2012-08-23,A coherent and passive one dimensional quantum memory,"We show that the state of a flying qubit may be transferred to a chain of
identical, (near) ferromagnetically polarised, but non-interacting, static
spin-1/2 particles in a passive way. During this process the flying qubit is
coherently polarised, emerging in the direction of the majority static spins.
We also show that this process is reversible for at least two flying qubits
injected sequentially and thus has the potential to be exploited as a passive
quantum memory to encode the flying qubits without the necessity of resetting
between successive encoding operations. We show that the quantum information
may be spread over many static spins in the memory chain, making the mechanism
resistent to spin decoherence and other imperfections. Among some potential
architectures, we discuss implementing the memory in a photonic waveguide
embedded with quantum dots, which is resilient to various possible errors.",1208.4828v2
2012-11-19,The $D(D_{3})$-anyon chain: integrable boundary conditions and excitation spectra,"Chains of interacting non-Abelian anyons with local interactions invariant
under the action of the Drinfeld double of the dihedral group $D_3$ are
constructed. Formulated as a spin chain the Hamiltonians are generated from
commuting transfer matrices of an integrable vertex model for periodic and
braided as well as open boundaries. A different anyonic model with the same
local Hamiltonian is obtained within the fusion path formulation. This model is
shown to be related to an integrable fusion interaction round the face model.
Bulk and surface properties of the anyon chain are computed from the Bethe
equations for the spin chain. The low energy effective theories and operator
content of the models (in both the spin chain and fusion path formulation) are
identified from analytical and numerical studies of the finite size spectra.
For all boundary conditions considered the continuum theory is found to be a
product of two conformal field theories. Depending on the coupling constants
the factors can be a $Z_4$ parafermion or a $\mathcal{M}_{(5,6)}$ minimal
model.",1211.4449v2
2012-12-24,Giant Spin Hall Effect in Single Photon Plasmonics,"We show the existence of a very large spin Hall effect of light (SHEL) in
single photon plasmonics based on spontaneous emission and the dipole-dipole
interaction initiated energy transfer (FRET) on plasmonic platforms. The spin
orbit coupling inherent in Maxwell equations is seen in the conversion of sigma
+ photon to sigma - photon. The FRET is mediated by the resonant surface
plasmons and hence we find very large SHEL. We present explicit results for
SHEL on both graphene and metal films. We also study how the splitting of the
surface plasmon on a metal film affects the SHEL. In contrast to most other
works which deal with SHEL as correction to the paraxial results, we consider
SHEL in the near field of dipoles which are far from paraxial.",1212.5953v1
2013-01-24,"Superconductivity, Antiferromagnetism, and Neutron Scattering","High-temperature superconductivity in both the copper-oxide and the
iron-pnictide/chalcogenide systems occurs in close proximity to
antiferromagnetically ordered states. Neutron scattering has been an essential
technique for characterizing the spin correlations in the antiferromagnetic
phases and for demonstrating how the spin fluctuations persist in the
superconductors. While the nature of the spin correlations in the
superconductors remains controversial, the neutron scattering measurements of
magnetic excitations over broad ranges of energy and momentum transfer provide
important constraints on the theoretical options. We present an overview of the
neutron scattering work on high-temperature superconductors and discuss some of
the outstanding issues.",1301.5888v1
2013-02-08,Abrupt barrier contribution to the electron spin splitting in asymmetric coupled double quantum wells,"We have studied the behavior of the electronic energy spin-splitting of
InGaAs-InAlAs based double quantum wells (narrow gap structures) under in-plane
magnetic and transverse electric fields. We have developed an improved 8x8
version of the Transfer Matrix Approach that consider contributions from abrupt
interfaces and external fields when tunneling through central barrier exists.
We have included the Land\'e g-factor dependence on the external applied field.
Also, we have calculated electron density of states and photoluminescence
excitation. Variations of the electron spin-splitting energy lead to marked
peculiarities in the density of states. Because the density of states is
directly related to photoluminescence excitation, these peculiarities are
observable by this technique.",1302.2012v3
2013-02-10,Quark Transverse Momentum Distributions inside a nucleon : a Light-Front Hamiltonian Dynamics study,"Through an impulse approximation analysis of single spin Sivers and Collins
asymmetries in the Bjorken limit, the possibility to extract the quark
transverse-momentum distributions in the neutron from semi-inclusive deep
inelastic electron scattering off polarized 3He is illustrated. The analysis is
generalized to finite momentum transfers in a light-front Poincare' covariant
framework, defining the light-front spin-dependent spectral function of a J=1/2
system. The definition of the light-front spin-dependent spectral function for
constituent quarks in the nucleon allows us to show that, within the
light-front dynamics, only three of the six leading twist T-even
transverse-momentum distributions are independent.",1302.2344v1
2013-02-19,Thermal Contact. II. A Solvable Toy Model,"A diathermal wall between two heat baths at different temperatures can be
mimicked by a layer of independent spin pairs with some internal energy and
where each spin $\sigma_a$ is flipped by thermostat $a$ ($a=1,2$). The
transition rates are determined from the modified detailed balance discussed in
Ref.[1]. Generalized heat capacities, excess heats, the housekeeping entropy
flow and the thermal conductivity in the steady state are calculated. The joint
probability distribution of the heat cumulated exchanges at any time is
computed explicitly. We obtain the large deviation function of heat transfer
via a variety of approaches. In particular, by a saddle-point method performed
accurately, we obtain the explicit expressions not only of the large deviation
function, but also of the amplitude prefactor, in the long-time probability
density for the heat current. The following physical properties are discussed :
the effects of typical time scales of the mesoscopic dynamics which do not
appear in equilibrium statistical averages and the limit of strict energy
dissipation towards a thermostat when its temperature goes to zero. We also
derive some properties of the fluctuations in the two-spin system viewed as a
thermal machine performing cycles.",1302.4540v2
2013-05-31,Off-diagonal Bethe ansatz and exact solution of a topological spin ring,"A general method is proposed for constructing the Bethe ansatz equations of
integrable models without U(1) symmetry. As an example, the exact spectrum of
the XXZ spin ring with M{\"" o}bius like topological boundary condition is
derived by constructing a modified T-Q relation based on the functional
connection between the eigenvalues of the transfer matrix and the quantum
determinant of the monodromy matrix. With the exact solution, the elementary
excitations of the topological XX spin ring is discussed in detail. It is found
that the excitation spectrum indeed shows a nontrivial topological nature.",1305.7328v4
2013-07-19,Simulation of mirror inversion of quantum states in an XY spin chain using NMR,"We report an experimental quantum simulation of unitary dynamics of an XY
spin chain with pre-engineered couplings. Using this simulation, we demonstrate
the mirror inversion of quantum states, proposed by Albanese et al. [Phys. Rev.
Lett. 93, 230502 (2004)]. The experiment is performed with a 5-qubit dipolar
coupled spin system using nuclear magnetic resonance techniques. To perform
quantum simulation we make use of the recently proposed unitary operator
decomposition algorithm of Ajoy et al. [Phys. Rev. A 85, 030303 (2012)] along
with numerical pulse optimization techniques. Further, using mirror inversion,
we demonstrate that entangled states can be transferred from one end of the
chain to the other end. The simulations are implemented with high experimental
fidelity, which implies that these kind of simulations may be possible in
larger systems.",1307.5220v1
2013-07-29,Signatures of the collapse and revival of a spin Schrödinger cat state in a continuously monitored field mode,"We study the effects of continuous measurement of the field mode during the
collapse and revival of spin Schr\""{o}dinger cat states in the Tavis-Cummings
model of N qubits (two-level quantum systems) coupled to a field mode. We show
that a compromise between relatively weak and relatively strong continuous
measurement will not completely destroy the collapse and revival dynamics while
still providing enough signal-to-noise resolution to identify the signatures of
the process in the measurement record. This type of measurement would in
principle allow the verification of the occurrence of the collapse and revival
of a spin Schr\""{o}dinger cat state.",1307.7637v1
2013-08-21,Importance of anisotropy in the spin-liquid candidate Me3EtSb[Pd(dmit)2]2,"Organic charge transfer salts based on the molecule Pd(dmit)2 display strong
electronic correlations and geometrical frustration, leading to spin liquid,
valence bond solid, and superconducting states, amongst other interesting
phases. The low energy electronic degrees of freedom of these materials are
often described by a single band model; a triangular lattice with a molecular
orbital representing a Pd(dmit)2 dimer on each site. We use ab initio
electronic structure calculations to construct and parametrize low energy
effective model Hamiltonians for a class of Me(4-n) EtnX[Pd(dmit)2]2
(X=As,P,N,Sb) salts and investigate how best to model these systems by using
variational Monte Carlo (VMC) simulations. Our findings suggest that the
prevailing model of these systems as a t-t' triangular lattice is incomplete,
and that a fully anisotropic triangular lattice (FATL) description produces
importantly different results, including a significant lowering of the critical
U of the spin-liquid phase.",1308.4507v2
2013-09-19,Exact spectral function for hole-magnon coupling in the ferromagnetic CuO$_3$-like chain,"We present the exact spectral function for a single oxygen hole with spin
opposite to ferromagnetic order within a one-dimensional CuO$_{3}$-like spin
chain. We find that local Kondo-like exchange interaction generates five
different states in the strong coupling regime. It stabilizes a spin polaron
which is a bound state of a moving charge dressed by magnon excitations, with
essentially the same dispersion as predicted by mean field theory. We then
examine in detail the evolution of the spectral function for increasing
strength of the hole-magnon interaction. We also demonstrate that the $s$ and
$p$ symmetry of orbital states in the conduction band are essentially
equivalent to each other and find that the simplified models do not suffice to
reproduce subtle aspects of hole-magnon coupling in the charge-transfer model.",1309.5054v1
2013-09-28,Enhanced topological phase and spin Hall shifts in an optical trap,"The spin orbit interaction (SOI) of light has been in the focus in recent
times because of fundamental consequences and potential applications in diverse
systems ranging from inhomogeneous anisotropic media to engineered plasmonics
and metamaterial strutures. Here we demonstrate perhaps one of the simplest
means to realize SOI and the Spin Hall Shift (SHS) using a standard Gaussian
TEM$_{00}$ beam in an optical trap. Our system exploits the versatility and
interference generated in a stratified medium to control and manipulate SOI and
transfer the resulting angular momentum to optically trapped micro-particles.
We show that even such a simple setup can lead to an order of magnitude
enhancement in the SHS compared to the sub-wavelength shifts typically
obtained. Importantly, this leads to controlled rotation of mesoscopic
particles using a fundamental Gaussian beam lacking any intrinsic angular
momentum.",1309.7488v1
2013-11-13,Spin polarized induction of quantum correlations-entanglement using a 2 MeV proton beam channeling,"In solid_state hybrid electron_nuclear spin systems quantum entanglement
plays vital role in allowing accessible transfer of information between
subatomic particles, regardless of the host lattice coordination spatial
geometry, revealing the powerful resource for nuclear quantum states
engineering. Here we present study of 2 MeV superfocused channeled proton (SCP)
beam induced polarization of atom_photon correlated states, established in
isotopically purified silicon nanocrystal. Two level entangling interaction
which couples an initial quantum state to two possible light_matter states via
silicon nanocrystal interface is presented. The anisotropic hyperfine coupling
is demonstrated by strong mixing of quantum states within the control mechanism
of the coherent proton pulse sequence. Obtained results reveal the mutual
predictable correlation of particles of energy_matter, by using the fully
broadcastable and precise hybrid electron_nuclear spin qubit manipulations
which can be exploited for the speed_superior communication channels keeping at
the same time the maximum degree of data preservation.",1311.3234v2
2013-11-23,Nonunital non-Markovian dynamics induced by a spin bath and interplay of quantum Fisher information,"We explore the nonunital non-Markovian dynamics of a qubit immersed in a spin
bath. The nonunital environmental effects on the precisions of quantum
parameter estimation are investigated. The time-dependent transfer matrix and
inhomogeneity vector are obtained for the description of the open dynamical
process. The evolution of the coherent vectors for a qubit is studied so as to
geometrically demonstrate the nonunital non-Markovian effects. The revivals of
angles for the fidelity between a maximal mixed state and an arbitrary
trajectory state are presented in the nonunital non-Markovian dynamics. The
degree for the nonunitality is controllable with the changes of the local
magnetic field for a qubit and spin bath temperature. It is found out that the
increase of quantum Fisher information for composite states is connected with
the nonunital non-Markovian effects, which is helpful for the improvement of
quantum metrology.",1311.5952v1
2013-12-18,Long-range spin transfer in triple quantum dots,"Tunneling in a quantum coherent structure is not restricted to only nearest
neighbours. Hopping between distant sites is possible via the virtual
occupation of otherwise avoided intermediate states. Here we report the
observation of long range transitions in the transport through three quantum
dots coupled in series. A single electron is delocalized between the left and
right quantum dots while the centre one remains always empty. Superpositions
are formed and both charge and spin are exchanged between the outermost dots.
Detection of the process is achieved via the observation of narrow resonances,
insensitive to the transport Pauli spin blockade.",1312.5060v2
2013-12-18,Anomalous Quark Chromomagnetic Moment and Dynamics of Elastic Scattering,"We estimate the contribution of nonperturbative quark-gluon chromomagnetic
interaction to the high energy elastic proton-proton cross section at large
momentum transfer. It is shown that this contribution is very large in the
accessible kinematic region of the present experiments.
  We argue that Odderon which is the $P=C=-1$ partner of Pomeron, is governed
by the spin-flip component related to the nonperturbative three-gluon exchange
induced by the anomalous quark chromomagnetic moment. We discuss the possible
spin effects in the elastic proton-proton and proton-antiproton scattering
coming from the interference of spin-flip nonperturbative Odderon and
nonspin-flip Pomeron exchanges.",1312.5094v3
2014-02-20,Turbulent Black Holes,"We show that rapidly-spinning black holes can display turbulent gravitational
behavior which is mediated by a new type of parametric instability. This
instability transfers energy from higher temporal and azimuthal spatial
frequencies to lower frequencies--- a phenomenon reminiscent of the inverse
energy cascade displayed by 2+1-dimensional turbulent fluids. Our finding
reveals a path towards gravitational turbulence for perturbations of
rapidly-spinning black holes, and provides the first evidence for gravitational
turbulence in an asymptotically flat spacetime. Interestingly, this finding
predicts observable gravitational wave signatures from such phenomena in black
hole binaries with high spins and gives a gravitational description of
turbulence relevant to the fluid-gravity duality.",1402.4859v2
2014-03-10,Orbit Maneuver of Spinning Tether via Tidal Force,"Recently, the spinning tethered system is regarded as a typical and
fundamental space structure attracting great interest of the aerospace
engineers, and has been discussed primarily for specific space missions in past
decades, including on-orbit capture and propellantless orbit transfer etc. The
present work studies the dynamical behaviours of a fast spinning tethered
binary system under central gravitational field, and derives principles of the
basic laws of orbital maneuver. Considering the characteristics of coupled
librational and orbital motions, an averaging method is introduced to deal with
the slow-fast system equation, thus a definite equivalent model is derived. The
general orbit motion is completely determined analytically, including the orbit
geometry, periodicity, conversations and moving region etc. Since the
possibility of orbit control using tether reaction has been proved by previous
studies, special attention is paid to the transportation mode of angular
momentum and mechanical energy between the orbit and libration. The effect of
tether length change on the orbit shape is verified both in the averaged model
and original model. The results show the orbit angular momentum and mechanical
energy can be controlled independently, and the operating principles of tether
reactions are derived for special modification of orbit shape.",1403.2221v1
2014-03-16,Measurement induced dynamics for spin chain quantum communication and its application for optical lattices,"We present a protocol for quantum state transfer and remote state preparation
across spin chains which operate in their anti-ferromagnetic mode. The proposed
mechanism harnesses the inherent entanglement of the ground state of the
strongly correlated many-body systems which naturally exists for free. The
uniform Hamiltonian of the system does not need any engineering and, during the
whole process, remains intact while a single qubit measurement followed by a
single-qubit rotation are employed for both encoding and inducing dynamics in
the system. This, in fact, has been inspired by recent progress in observing
spin waves in optical lattice experiments, in which manipulation of the
Hamiltonian is hard and instead local rotations and measurements have become
viable. The attainable average fidelity stays above the classical threshold for
chains up to length $~50$ and the system shows very good robustness against
various sources of imperfection.",1403.3903v2
2014-03-23,Magnon dispersion and Single hole motion in 2D frustrated antiferromagnets with four-sublattice structures,"We study a two dimensional spin-$\frac{1}{2}$ $J_1-J_2$ antiferromagnet in a
square lattice using the linearized spin wave theory recognizing the
4-sublattice nature of the underlying magnetic lattice. Multiple magnon modes
with optical and acoustic branches about the stable Neel ordered and double
acoustic branches about the columnar reference states are obtained for small
and large values of $\lambda(=J_2/J_1)$ respectively. An additional uniaxial
anisotropy, for large $\lambda$, can lead to distinct spin gaps in such
systems, as also witnessed experimentally. The single hole spectral behavior in
a 2D $t-J_1-J_2$ model, for small frustration, is then calculated within the
non-crossing approximation. Our results match fairly well with exact
diagonalization results from a $4\times4$ cluster. Hole spectral features and
their evolution with $\lambda$ resulting in ""water-fall""-like smooth spectral
weight transfer are discussed. Hole energy bands are identified and the
corresponding energy-shift and reduction in width with spin-frustration are
indicated.",1403.5742v3
2014-03-23,Non-collinear Andreev reflections in semiconductor nanowires,"We show that noncollinear Andreev reflections can be induced at interfaces of
semiconductor nanowires with spin-orbit coupling, Zeeman splitting and
proximity-induced superconductivity. In a noncollinear local Andreev
reflection, the spin polarizations of the injected and the retro-reflected
carriers are typically at an angle which is tunable via system parameters.
While in a nonlocal transport, this noncollinearity enables us to identify and
block, at different voltage configurations, the noncollinear cross Andreev
reflection and the direct charge transfer processes. We demonstrate that the
intriguing noncollinearity originates from the spin-dependent coupling between
carriers in the lead and the lowest discrete states in the wire, which, for a
topological superconducting nanowire, are related to the overlap-induced
hybridization of Majorana edge states in a finite system. These interesting
phenomena can be observed in semiconductor nanowires of experimentally relevant
lengths, and are potentially useful for spintronics.",1403.5756v3
2014-04-14,Optimal Quench for Distance-Independent Entanglement and Maximal Block Entropy,"We optimize a quantum walk of multiple fermions following a quench in a spin
chain to generate near ideal resources for quantum networking. We first prove
an useful theorem mapping the correlations evolved from specific quenches to
the apparently unrelated problem of quantum state transfer between distinct
spins. This mapping is then exploited to optimize the dynamics and produce
large amounts of entanglement distributed in very special ways. Two
applications are considered: the simultaneous generation of many Bell states
between pairs of distant spins (maximal block entropy), or high entanglement
between the ends of an arbitrarily long chain (distance-independent
entanglement). Thanks to the generality of the result, we study its
implementation in different experimental setups using present technology: NMR,
ion traps and ultracold atoms in optical lattices.",1404.3634v2
2014-06-19,A criterion of the non-existence of surface states in a semi-infinite crystal,"An infinite crystal can be constructed by an infinite number of parallel
two-dimensional (hkl) crystal planes coupled to each other. For crystals with
negligible spin-orbit coupling, we report a rigorous proof of a criterion on
the non-existence of surface states in a semi-infinite crystal with the crystal
symmetry. The forward transfer to be the same as the backward one, called as
F-B dynamical symmetry, is key to realize the criterion. Based on lattice model
Hamiltonian with coupling between the nearest neighbor crystal planes only, we
prove that a cut crystal will not be able to accommodate any surface states if
the original infinite crystal has reflection symmetry about every crystal plane
which results in F-B symmetry. The criterion provide a platform to simply
conclude whether surface states exist or not in a cut crystal. For any such
crystals, the non-existence or existence of surface states depends on the cut
direction of the crystal plane. Since the spin-orbit coupling breaks the chiral
symmetry, resulting in the F-B asymmetry, surface states can emerge in the
(hkl) cut crystal with spin-orbit coupling.",1406.5010v2
2014-06-19,Dumping Topological Charges on Neighbors: Ice Manifolds for Colloids and Vortices,"We investigate the recently reported analogies between pinned vortices in
nano-structured superconductors or colloids in optical traps, and spin ice
materials. The frustration of colloids and vortices differs essentially from
spin ice. However, their effective energetics is made identical by the
contribution of an emergent field associated to the topological charge, thus
leading to a (quasi) ice manifold for lattices of even (odd) coordination. The
equivalence extends to the local low-energy dynamics of the ice manifold, where
the effect of geometric hard constraints can be subsumed into the spatial
modulation of the emergent field, which mediates an entropic interaction
between topological charges. There, as in spin ice materials, genuine ice
manifolds enter a Coulomb phase, whereas quasi-ice manifolds posses a well
defined screening length, provided by a plasma of embedded topological charges.
The equivalence between the two systems breaks down in lattices of mixed
coordination because of topological charge transfer between sub-latices. We
discuss extensions to social and economical networks.",1406.5201v1
2014-09-11,Transient Exchange Interaction in a Helical Antiferromagnet,"We have performed time-resolved resonant x-ray scattering studies in the
Lanthanide metal Dy to reveal the dynamic response of the helical order
exchange coupling to injection of unpolarized spins. The observed spin dynamics
are significantly slower than that exhibited by the ferromagnetic phase in
Lanthanide metals and are strongly dependent on temperature and excitation
fluence. This unique behavior results from transient changes in the shape of
the conduction electron Fermi surface and subsequent scattering events that
transfer the excitation to the core spin.",1409.3614v1
2014-11-27,Quantum Energy Teleportation across a three-spin Ising chain in a Gibbs State,"In general, it is important to identify what is the informational resource
for quantum tasks. Quantum energy teleportation (QET) is a quantum task, which
attains energy transfer in an operational meaning by local operations and
classical communication, and is expected to play a role in future development
of nano scale smart grids. We consider QET protocols in a three-element Ising
spin system with non periodic boundary conditions coupled to a thermal bath.
The open chain is the minimal model of QET between two edge spins that allows
the measurement and operation steps of the QET protocol to be optimized without
restriction. It is possible to analyze how two-body correlations of the system,
like mutual information, entanglement and quantum discord, can be resources of
this QET at each temperature. In particular, we stress that quantum discord is
not the QET resource in some cases even if arbitrary measurements and
operations are available.",1411.7495v2
2015-01-14,Hydrodynamic spin fluctuations in the antiferromagnetic Heisenberg chain,"We study the finite temperature, low energy, long wave-length spectrum of the
dynamic structure factor of the spin-$1/2$ antiferromagnetic Heisenberg chain
in the presence of exchange anisotropy and external magnetic fields. Using
imaginary-time quantum Monte-Carlo we extract parameters, relevant to
characterize a {\it renormalized} Luttinger liquid. For small momentum our
results are consistent with a change from propagating spinon density waves to
spin diffusion, described by a finite-frequency spin-current relaxation rate.
Results for this relaxation rate as well as other Luttinger liquid parameters
are presented versus temperature, momentum, magnetic field, and anisotropy,
including finite-size analysis, and checks for anomalous diffusion. Our results
are consistent with exact diagonalization and Bethe Ansatz, where available,
and with corroborate findings of other previous studies using bosonization,
transfer matrix renormalization group, and quantum Monte-Carlo.",1501.03447v1
2015-01-14,Dispersionless spin waves in Gadolinium Gallium Garnet,"We report the results of neutron scattering on a powder sample of Gd3Ga5O12
at high magnetic fields. We find that in high fields (B>1.8 T) the system is
not fully polarized, but has a small canting of the moments induced by the
dipolar interaction. We show that the degree of canting is accurately predicted
by the standard Hamiltonian which includes the dipolar interaction. The
inelastic scattering is dominated at large momentum transfers by a band of
almost dispersionless excitations. We show that these correspond to the spin
waves localized on ten site rings, expected for a system described by a nearest
neighbor interaction, and that the spectrum at high fields B>1.8 T is
well-described by a spin wave theory. The phase for fields <1.8 T is
characterized by an antiferromagnetic Bragg peak at (210) and an incommensurate
peak.",1501.03493v1
2015-02-11,Measurement-Assisted Quantum Communication in Spin Channels with Dephasing,"We propose a protocol for countering the effects of dephasing in quantum
state transfer over a noisy spin channel weakly coupled to the sender and
receiver qubits. Our protocol, based on performing regular global measurements
on the channel, significantly suppresses the nocuous environmental effects and
offers much higher fidelities than the traditional no-measurement approach. Our
proposal can also operate as a robust two-qubit entangling gate over distant
spins. Our scheme counters any source of dephasing, including those for which
the well established dynamical decoupling approach fails. Our protocol is
probabilistic, given the intrinsic randomness in quantum measurements, but its
success probability can be maximized by adequately tuning the rate of the
measurements.",1502.03468v2
2015-02-16,Control of optical spin Hall shift in phase-discontinuity metasurface by weak value measurement post-selection,"Optical spin Hall (OSH) shift has been observed by weak measurement
amplification in a refraction beam passing through air-glass interface, the
refractive index gradient $\vec{\nabla} n$ being normal to the interface.
Phase-discontinuity metasurface (PMS) possesses $\vec{\nabla} n$ tangential to
the metasurface, and depending on the incidence angle either positive or
negative refraction takes place satisfying the generalized Snell's law. Rapid
phase-change over subwavelength distance at PMS leads to a large $\vec{\nabla}
n$, enabling a direct observation of OSH shift. Here, we identify that the
relative OSH shift between optical beams with spins $\pm 1$ depends on
incidence and refraction angles at PMS, and construct a measurement of OSH
effect with a variable phase retardance in the post-selection to demonstrate a
control of transverse shift. and demonstrate a control of OSH shift by
constructing a weak value measurement with a variable phase retardance in the
post-selection. Capability of OSH shift control permits a tunable precision
metrology applicable to nanoscale photonics such as angular momentum transfer
and sensing.",1502.04546v1
2015-03-16,Quantum Cloning using Protective Measurement,"Here we show that, in principle it is possible to clone (measure) a single
arbitrary unknown quantum state of a spin-$\frac{1}{2}$ particle (an electron)
with arbitrary precision and with success probability tending to one, using
protective measurement. We first transfer the information from spin to spatial
degree of freedom (d.o.f) of system electron, then trap it in a double well
potential, and finally measure it protectively using a probe electron (which
donot get entangled with system electron, but still extracts expectation value
of an observable from a single quantum system (system electron)) to obtain
information about the unknown spin polarization. Nonorthogonal state
discrimination being a subclass of cloning, part of the paper (till finding out
$\theta_{m}$, polar angle corresponding to the unknown spin polarization) is
sufficient for discrimination.",1503.04547v2
2015-03-31,One-dimensional extended Hubbard model with spin-triplet pairing ground states,"We show that the one-dimensional extended Hubbard model has saturated
ferromagnetic ground states with the spin-triplet electron pair condensation in
a certain range of parameters. The ground state wave functions with fixed
electron numbers are explicitly obtained. We also construct two ground states
in which both the spin-rotation and the gauge symmetries are broken, and show
that these states are transferred from one to the other by applying the edge
operators. The edge operators are reduced to the Majorana fermions in a special
case. These symmetry breaking ground states are shown to be stabilized by a
superconducting mean field Hamiltonian which is related to the Kitaev chain
with the charge-charge interaction.",1503.08998v4
2015-04-08,Magnetocaloric effect in the symmetric spin-1/2 diamond chain with different Landé g-factors of Ising and Heisenberg spins,"The symmetric spin-1/2 Ising-Heisenberg diamond chain with different Land\'e
g-factors of Ising and Heisenberg spins is exactly solved by combining the
generalized decoration-iteration transformation and transfer-matrix method. The
ground state of the system and magnetocaloric effect during the adiabatic
(de)magnetization are particularly examined. It is evidenced that the
considered mixed-spin diamond chain exhibits an enhanced magnetocaloric effect
during the adiabatic (de)magnetization in the vicinity of field-induced phase
transitions as well as in the zero-field limit if the frustrated phase
constitutes the zero-field ground state, but the cooling efficiency depends on
whether the system is macroscopically degenerate in these parameter regions or
not.",1504.02036v3
2015-04-20,Chiral topological spin liquids with projected entangled pair states,"Topological chiral phases are ubiquitous in the physics of the Fractional
Quantum Hall Effect. Non-chiral topological spin liquids are also well known.
Here, using the framework of projected entangled pair states (PEPS), we
construct a family of chiral spin liquids on the square lattice which are
generalized spin-1/2 Resonating Valence Bond (RVB) states obtained from
deformed local tensors with $d+i\, d$ symmetry. On a cylinder, we construct
four topological sectors with even or odd number of spinons on the boundary and
even or odd number of ($\mathbb{Z}_2$) fluxes penetrating the cylinder which,
we argue, remain orthogonal in the limit of infinite perimeter. The analysis of
the transfer matrix provides evidence of short-range (long-range) triplet
(singlet) correlations as for the critical (non-chiral) RVB state. The
Entanglement Spectrum exhibits chiral edge modes, which we confront to
predictions of Conformal Field Theory, and the corresponding Entanglement
Hamiltonian is shown to be long ranged.",1504.05236v3
2015-04-27,Optical orientation of electron spins and valence band spectroscopy in germanium,"We have investigated optical orientation in the vicinity of the direct gap of
bulk germanium. The electron spin polarization is studied via
polarization-resolved photoluminescence excitation spectroscopy unfolding the
interplay between doping and ultrafast electron transfer from the center of the
Brillouin zone towards its edge. As a result, the direct-gap photoluminescence
circular polarisation can vary from 30% to -60% when the excitation laser
energy increases. This study provides also simultaneous access to the resonant
electronic Raman scattering due to inter-valence band excitations of
spin-polarized holes, yielding a fast and versatile spectroscopic approach for
the determination of the energy spectrum of holes in semiconducting materials.",1504.07013v1
2015-05-20,Spin-dependent transport in a multiferroic tunnel junction: Theory for Co/PbTiO$_{3}$/Co,"Spin-dependent electronic transport through multiferroic Co/PbTiO$_{3}$/Co
tunnel junctions is studied theoretically. Conductances calculated within the
Landauer-B\""uttiker formalism yield both a large tunnel magnetoresistance (TMR)
and a large tunnel electroresistance (TER). On top of this, we establish a
four-conductance state. The conductances depend crucially on the details of the
electronic structure at the interfaces. In particular, the spin polarization of
the tunneling electronic states is affected by the hybridization of orbitals
and the associated charge transfer at both interfaces. Digital doping of the
PbTiO$_{3}$ barrier with Zr impurities at the TiO$_{2}$/Co$_{2}$ interface
significantly enhances the TMR\@. In addition, it removes the metalization of
the barrier.",1505.05420v1
2015-07-09,Demonstration of Open Quantum System Optimal Control in Dynamic Nuclear Polarization,"Dynamic nuclear polarization (DNP) is used in nuclear magnetic resonance
(NMR) to transfer polarization from electron spins to nuclear spins. The
resulting nuclear polarization enhancement can, in theory, be two or three
orders of magnitude depending on the sample. In solid state systems, however,
there are competing mechanisms of DNP, which, when occurring simultaneously,
reduce the net polarization enhancement of the nuclear spin. We present a
simple quantum description of DNP and apply optimal control theory (OCT) with
an open quantum system framework to design pulses that select one DNP process
and suppress the others. We demonstrate experimentally an order of magnitude
improvement in the DNP enhancement using OCT pulses.",1507.02610v2
2015-07-15,Self assembled Wigner crystals as mediators of spin currents and quantum information,"Technological applications of many-body structures that emerge in gated
devices under minimal control are largely unexplored. Here we show how emergent
Wigner crystals in a semiconductor quantum wire can facilitate a pivotal
requirement for a scalable quantum computer, namely transmitting quantum
information encoded in spins faithfully over a distance of micrometers. The
fidelity of the transmission is remarkably high, faster than the relevant
decohering effects, independent of the details of the spatial charge
configuration in the wire, and realizable in dilution refrigerator
temperatures. The transfer can evidence near unitary many-body nonequilibrium
dynamics hitherto unseen in a solid-state device. It could also be useful in
spintronics as a method for pure spin current over a distance without charge
movement.",1507.04138v2
2015-08-28,Rigorous determination of the ground-state phases and thermodynamics in an Ising-type multiferroic Ca3CoMnO6 chain,"To understand the collinear-magnetism-driven ferroelectricity in multiferroic
Ca3CoMnO6 compound, we have established an elastic diatomic Ising spin-chain
model with axial-next-nearest-neighbor interaction to describe its
magnetoelectric properties. By employing magneto-phonon decoupling and
transfer-matrix method, the possible ground-state configurations and
thermodynamic behaviors of the system have been exactly determined. From the
perspective of the ground-state configuration, we analyze the computational
results and make a detail comparison with experimental data. The parameter
relation for the appearance of electric polarization has been discussed. Our
data indicate that the magnetic coupling between nearest-neighbor spin pair is
antiferromagnetic rather than ferromagnetic. The system under the driven of
external magnetic field undergoes a different series of transitions from the
up-up-down-down spin configuration to the up-down-up state with peculiar 1/3
magnetization plateau, then to the up-up-up-down state, and finally saturated
at up-up-up-up state.",1508.07072v1
2015-09-15,Nanoscale Mach-Zehnder interferometer with spin-resolved quantum Hall edge states,"We realize a nanoscale-area Mach-Zehnder interferometer with co-propagating
quantum Hall spin-resolved edge states and demonstrate the persistence of
gate-controlled quantum interference oscillations, as a function of an applied
magnetic field, at relatively large temperatures. Arrays of top-gate magnetic
nanofingers are used to induce a resonant charge transfer between the pair of
spin-resolved edge states. To account for the pattern of oscillations measured
as a function of magnetic field and gate voltage, we have developed a simple
theoretical model which satisfactorily reproduces the data.",1509.04437v2
2015-09-17,Spin-orbital excitation continuum and anomalous electron-phonon interaction in the Mott insulator LaTiO$_3$,"Raman scattering experiments on stoichiometric, Mott-insulating LaTiO$_3$
over a wide range of excitation energies reveal a broad electronic continuum
which is featureless in the paramagnetic state, but develops a gap of $\sim
800$ cm$^{-1}$ upon cooling below the N\'eel temperature $T_N = 146$ K. In the
antiferromagnetic state, the spectral weight below the gap is transferred to
well-defined spectral features due to spin and orbital excitations. Low-energy
phonons exhibit pronounced Fano anomalies indicative of strong interaction with
the electron system for $T > T_N$, but become sharp and symmetric for $T <
T_N$. The electronic continuum and the marked renormalization of the phonon
lifetime by the onset of magnetic order are highly unusual for Mott insulators
and indicate liquid-like correlations between spins and orbitals.",1509.05280v1
2015-10-12,Resonance-inclined optical nuclear spin polarization of liquids in diamond structures,"Dynamic nuclear polarization (DNP) of molecules in a solution at room
temperature has potential to revolutionize nuclear magnetic resonance
spectroscopy and imaging. The prevalent methods for achieving DNP in solutions
are typically most effective in the regime of small interaction correlation
times between the electron and nuclear spins, limiting the size of accessible
molecules. To solve this limitation, we design a mechanism for DNP in the
liquid phase that is applicable for large interaction correlation times.
Importantly, while this mechanism makes use of a resonance condition similar to
solid-state DNP, the polarization transfer is robust to a relatively large
detuning from the resonance due to molecular motion. We combine this scheme
with optically polarized nitrogen vacancy (NV) center spins in nanodiamonds to
design a setup that employs optical pumping and is therefore not limited by
room temperature electron thermal polarisation. We illustrate numerically the
effectiveness of the model in a flow cell containing nanodiamonds immobilized
in a hydrogel, polarising flowing water molecules 4700-fold above thermal
polarisation in a magnetic field of 0.35 T, in volumes detectable by current
NMR scanners.",1510.03256v1
2015-10-25,Counterdiabatic driving in spin squeezing and Dicke state preparation,"A method is presented to transfer a system of two-level atoms from a spin
coherent state to a maximally spin squeezed Dicke state, relevant for quantum
metrology and quantum information processing. The initial state is the ground
state of an initial linear Hamiltonian which is gradually turned into a final
quadratic Hamiltonian whose ground state is the selected Dicke state. We use
compensating operators to suppress diabatic transitions to unwanted states that
would occur if the change were not slow. We discuss the possibilities of
constructing the compensating operators by sequential application of quadratic
Hamiltonians available in experiments.",1510.07261v2
2015-10-26,Trigonometric version of quantum-classical duality in integrable systems,"We extend the quantum-classical duality to the trigonometric (hyperbolic)
case. The duality establishes an explicit relationship between the classical
N-body trigonometric Ruijsenaars-Schneider model and the inhomogeneous twisted
XXZ spin chain on N sites. Similarly to the rational version, the spin chain
data fixes a certain Lagrangian submanifold in the phase space of the classical
integrable system. The inhomogeneity parameters are equal to the coordinates of
particles while the velocities of classical particles are proportional to the
eigenvalues of the spin chain Hamiltonians (residues of the properly normalized
transfer matrix). In the rational version of the duality, the action variables
of the Ruijsenaars-Schneider model are equal to the twist parameters with some
multiplicities defined by quantum (occupation) numbers. In contrast to the
rational version, in the trigonometric case there is a splitting of the
spectrum of action variables (eigenvalues of the classical Lax matrix). The
limit corresponding to the classical Calogero-Sutherland system and quantum
trigonometric Gaudin model is also described as well as the XX limit to free
fermions.",1510.07509v1
2015-12-06,Absence of Localization in Disordered Two Dimensional Electron Gas at Weak Magnetic Field and Strong Spin-Orbit Coupling,"The one-parameter scaling theory of localization predicts that all states in
a disordered two-dimensional system with broken time reversal symmetry are
localized even in the presence of strong spin-orbit coupling. While at constant
strong magnetic fields this paradigm fails (recall quantum Hall effect), it is
believed to hold at weak magnetic fields. Here we explore the nature of quantum
states at weak magnetic field and strongly fluctuating spin-orbit coupling,
employing highly accurate numerical procedure based on level spacing
distribution and transfer matrix technique combined with finite-size
one-parameter scaling hypothesis. Remarkably, the metallic phase, (known to
exist at zero magnetic field), persists also at finite (albeit weak) magnetic
fields, and eventually crosses over into a critical phase, which has already
been confirmed at high magnetic fields. A schematic phase diagram drawn in the
energy-magnetic field plane elucidates the occurrence of localized, metallic
and critical phases. In addition, it is shown that nearest-level statistics is
determined solely by the symmetry parameter $\beta$ and follows the Wigner
surmise irrespective of whether states are metallic or critical.",1512.01733v1
2015-12-16,Exactly solvable spin-1 Ising-Heisenberg diamond chain with the second-neighbor interaction between nodal spins,"The spin-1 Ising-Heisenberg diamond chain with the second-neighbor
interaction between the nodal spins is rigorously solved using the
transfer-matrix method. Exact results for the ground state, magnetization
process and specific heat are presented and discussed in particular. It is
shown that the further-neighbor interaction between the nodal spins gives rise
to three novel ground states with a translationally broken symmetry, but at the
same time, it does not increases the total number of intermediate plateaus in a
zero-temperature magnetization curve compared with the simplified model without
this interaction term. The zero-field specific heat displays interesting
thermal dependencies with a single- or double-peak structure.",1512.05150v1
2015-12-19,Spin-orbit-angular-momentum coupling in a spin-1 Bose-Einstein condensate,"We propose a simple model with spin and orbit angular momentum coupling in a
spin-1 Bose- Einstein condensate, where three internal atomic states are Raman
coupled by a pair of co- propagating Laguerre-Gaussian beams. The resulting
Raman transition imposes a transfer of orbital angular momentum between photons
and the condensate in a spin-dependent way. Focusing on a regime where the
single-particle ground state is nearly three-fold degenerate, we show that the
weak interatomic interaction in the condensate produces a rich phase diagram,
and that a many-body Rabi oscillation between two quantum phases can be induced
by a sudden quench of the quadratic Zeeman shift. We carried out our
calculations using both a variational method and a full numerical method, and
found excellent agreement.",1512.06276v1
2016-01-13,Populating Low-Spin States in Radioactive Nuclei to Measure Magnetic Moments Using the Transient Field Technique,"The experimental study of magnetic moments for nuclear states near the ground
state, $I \ge 2$, provides a powerful tool to test nuclear structure models.
The study of magnetic moments in nuclei far away from the stability line is the
next frontier in such studies. Two techniques have been utilized to populated
low-spin states in radioactive nuclei: coulomb excitation reactions using
radioactive nuclei, and the transfer of $\alpha$ particles to stable beams to
populate low spin states in radioactive nuclei. A presentations of these two
techniques, along with the experimental challenges presented for future uses
with nuclei far away from the stability line, will be presented.",1601.03602v1
2016-01-26,Electron Beam Single-Spin Asymmetries in the Resonance Region with Final Hadrons Observed,"We study beam-transverse and normal single-spin asymmetry for electron-proton
inelastic scattering in the resonance region for the case where a pion is
observed in the final state. There is no beam single-spin asymmetry if the
observed particle has single-photon exchange as its only interaction, but this
is naturally circumvented when one observes a strongly interacting final state
particle. The asymmetries are not large as there is an electron mass divided by
momentum transfer suppression. We present results for the cases where the final
electron and a pion are both observed, with asymmetries of order tens of ppm,
and where only a final pion is observed, with asymmetries of order one ppm.",1601.07199v1
2016-07-27,The Role of Multilevel Landau-Zener Interference in Extreme Harmonic Generation,"Motivated by the observation of multiphoton electric dipole spin resonance
processes in InAs nanowires, we theoretically study the transport dynamics of a
periodically driven five-level system, modeling the level structure of a
two-electron double quantum dot. We show that the observed multiphoton
resonances, which are dominant near interdot charge transitions, are due to
multilevel Landau-Zener-Stuckelberg-Majorana interference. Here a third energy
level serves as a shuttle that transfers population between the two resonant
spin states. By numerically integrating the master equation we replicate the
main features observed in the experiments: multiphoton resonances (as large as
8 photons), a robust odd-even dependence, and oscillations in the electric
dipole spin resonance signal as a function of energy level detuning.",1607.08207v1
2016-12-01,"A fast spinning magnetic white dwarf in the double-degenerate, super-Chandrasekhar system NLTT 12758","We present an analysis of the close double degenerate NLTT 12758, which is
comprised of a magnetic white dwarf with a field of about 3.1 MG and an
apparently non-magnetic white dwarf. We measured an orbital period of 1.154
days and found that the magnetic white dwarf is spinning around its axis with a
period of 23 minutes. An analysis of the atmospheric parameters has revealed
that the cooling ages of the two white dwarfs are comparable, suggesting that
they formed within a short period of time from each other. Our modelling
indicates that the non-magnetic white dwarf is more massive (M=0.83 M_sun) than
its magnetic companion (M=0.69 M_sun) and that the total mass of the system is
higher than the Chandrasekhar mass. Although the stars will not come into
contact over a Hubble time, when they do come into contact, dynamically
unstable mass transfer will take place leading to either an accretion induced
collapse into a rapidly spinning neutron star or a Type Ia supernova.",1612.00325v1
2016-12-03,Energy current and its statistics in the nonequilibrium spin-boson model: Majorana fermion representation,"We study the statistics of thermal energy transfer in the nonequilibrium
(two-bath) spin-boson model. This quantum many-body impurity system serves as a
canonical model for quantum energy transport. Our method makes use of the
Majorana fermion representation for the spin operators, in combination with the
Keldysh nonequilibrium Green's function approach. We derive an analytical
expression for the cumulant generating function of the model in the steady
state limit, and show that it satisfies the Gallavotti-Cohen fluctuation
symmetry. We obtain analytical expressions for the heat current and its noise,
valid beyond the sequential and the co-tunnelling regimes. Our results satisfy
the quantum mechanical bound for heat current in interacting nanojunctions.
Results are compared with other approximate theories, as well as with a
non-interacting model, a fully harmonic thermal junction.",1612.01008v1
2016-12-07,Hunting the Gluon Orbital Angular Momentum at the Electron-Ion Collider,"Applying the connection between the parton Wigner distribution and orbital
angular momentum (OAM), we investigate the probe of the gluon OAM in hard
scattering processes at the planned electron-ion collider. We show that the
single longitudinal target-spin asymmetry in the hard diffractive dijet
production is very sensitive to the gluon OAM distribution. The associated spin
asymmetry leads to a characteristic azimuthal angular correlation of
$\sin(\phi_q -\phi_\Delta)$, where $\phi_\Delta$ and $\phi_q$ are the azimuthal
angles of the proton momentum transfer and the relative transverse momentum
between the quark-antiquark pair. This study will enable a first measurement of
the gluon OAM in the proton spin sum rule.",1612.02438v1
2016-12-09,Dynamic RKKY interaction between magnetic moments in graphene nanoribbons,"Graphene has been identified as a promising material with numerous
applications, particularly in spintronics. In this paper we investigate the
peculiar features of spin excitations of magnetic units deposited on graphene
nanoribbons and how they can couple through a dynamical interaction mediated by
spin currents. We examine in detail the spin lifetimes and identify a pattern
caused by vanishing density of states sites in pristine ribbons with armchair
borders. Impurities located on these sites become practically invisible to the
interaction, but can be made accessible by a gate voltage or doping. We also
demonstrate that the coupling between impurities can be turned on or off using
this characteristic, which may be used to control the transfer of information
in transistor-like devices.",1612.02971v1
2017-02-23,Chiral Vortical Effect for Bosons,"The thermal contribution to the chiral vortical effect is believed to be
related to the axial anomaly in external gravitational fields. We use the
universality of the spin-gravity interaction to extend this idea to a wider set
of phenomena. We consider the Kubo formula at weak coupling for the spin
current of a vector field and derive a novel anomalous effect caused by the
medium rotation: the chiral vortical effect for bosons. The effect consists in
a spin current of vector bosons along the angular velocity of the medium. We
argue that it has the same anomalous nature as in the fermionic case and show
that this effect provides a mechanism for helicity transfer, from flow helicity
to magnetic helicity.",1702.07340v3
2017-03-23,Finite-temperature time-dependent variation with multiple Davydov states,"The Dirac-Frenkel time-dependent variational approach with Davydov Ans\""atze
is a sophisticated, yet efficient technique to obtain an acuurate solution to
many-body Schr\""odinger equations for energy and charge transfer dy- namics in
molecular aggregates and light-harvesting complexes. We extend this variational
approach to finite temperatures dynamics of the spin-boson model by adopting a
Monte Carlo importance sampling method. In or- der to demonstrate the
applicability of this approach, we compare real-time quantum dynamics of the
spin-boson model calculated with that from numerically exact iterative
quasiadiabatic propagator path integral (QUAPI) technique. The comparison shows
that our variational approach with the single Davydov Ans\""atze is in excellent
agreement with the QUAPI method at high temperatures, while the two differ at
low temperatures. Accuracy in dynamics calculations employing a multitude of
Davydov trial states is found to improve substantially over the single Davydov
Ansatz, especially at low temperatures. At a moderate computational cost, our
variational approach with the multiple Davydov Ansatz is shown to provide
accurate spin-boson dynamics over a wide range of temperatures and bath
spectral densities.",1703.08010v1
2017-03-23,Magnon activation by hot electrons via non-quasiparticle states,"We consider the situation when a femtosecond laser pulse creates a hot
electron state in half-metallic ferromagnet (e. g. ferromagnetic semiconductor)
on a picosecond timescale but do not act directly on localized spin system. We
show that the energy and magnetic moment transfer from hot itinerant electrons
to localized spins is facilitated by the so-called non-quasiparticle states,
which are the scattering states of a magnon and spin-majority electron. The
magnon distribution is described by a quantum kinetic equation that we derive
using the Keldysh diagram technique. In a typical ferromagnetic semiconductor
such as EuO magnons remain essentially in non-equilibrium on a scale of the
order of microsecond after the laser pulse.",1703.08106v1
2017-04-11,Spin-orbit coupling and rovibrational structure in the iododiacetylene radical cation by PFI-ZEKE photoelectron spectroscopy,"The photoelectron spectrum of the $\textrm{X}^{+}\,{}^{2}\Pi \leftarrow
\textrm{X}\,{}^{1}\Sigma^{+}$ photoionising transition in iododiacetylene,
HC$_4$I, has been recorded using pulsed-field-ionisation zero-kinetic-energy
(PFI-ZEKE) photoelectron spectroscopy with partial resolution of the rotational
structure. The first adiabatic ionisation energy of HC$_4$I and the spin-orbit
splitting of the X$^{+}\,{}^{2}\Pi$ state of HC$_4$I$^+$ are determined as
$E^{\textrm{ad}}_{\textrm{I}}/(hc) = 74470.7(2)$ cm$^{-1}$ and
$\Delta\tilde{\nu}_{\textrm{so}} = 1916.7(4)$ cm$^{-1}$, respectively. Several
vibrational levels of the X$^{+}\,{}^{2}\Pi$ electronic ground state of the
HC$_4$I$^+$ cation have been observed. The experimental data are discussed in
the realm of a simple three-state charge-transfer model without adjustable
parameters which allows for a qualitative description of the electronic
structure and spin-orbit coupling in HC$_4$I$^+$ and of the change in bond
lengths upon ionisation of HC$_4$I.",1704.03280v1
2017-05-10,Decrease of d-wave pairing strength in spite of the persistence of magnetic excitations in the overdoped Hubbard model,"Evidence for the presence of high energy magnetic excitations in overdoped
La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) has raised questions regarding the role of
spin-fluctuations in the pairing mechanism. If they remain present in overdoped
LSCO, why does $T_c$ decrease in this doping regime? Here, using results for
the dynamic spin susceptibility ${\rm Im}\chi(q,\omega)$ obtained from a
determinantal quantum Monte Carlo (DQMC) calculation for the Hubbard model we
address this question. We find that while high energy magnetic excitations
persist in the overdoped regime, they lack the momentum to scatter pairs
between the anti-nodal regions. It is the decrease in the spectral weight at
large momentum transfer, not observed by resonant inelastic X-ray scattering
(RIXS), which leads to a reduction in the $d$-wave spin-fluctuation pairing
strength.",1705.03949v1
2017-06-19,Magnetic Excitations and Continuum of a Field-Induced Quantum Spin Liquid in $α$-RuCl$_3$,"We report on terahertz spectroscopy of quantum spin dynamics in
$\alpha$-RuCl$_3$, a system proximate to the Kitaev honeycomb model, as a
function of temperature and magnetic field. An extended magnetic continuum
develops below the structural phase transition at $T_{s2}=62$K. With the onset
of a long-range magnetic order at $T_N=6.5$K, spectral weight is transferred to
a well-defined magnetic excitation at $\hbar \omega_1 = 2.48$meV, which is
accompanied by a higher-energy band at $\hbar \omega_2 = 6.48$meV. Both
excitations soften in magnetic field, signaling a quantum phase transition at
$B_c=7$T where we find a broad continuum dominating the dynamical response.
Above $B_c$, the long-range order is suppressed, and on top of the continuum,
various emergent magnetic excitations evolve. These excitations follow clear
selection rules and exhibit distinct field dependencies, characterizing the
dynamical properties of the field-induced quantum spin liquid.",1706.06157v1
2017-09-08,Ultrafast carbon monoxide photolysis and heme spin-crossover in myoglobin via nonadiabatic quantum dynamics,"Light absorption of myoglobin triggers diatomic ligand photolysis and spin
crossover transition of iron(II) that initiate protein conformational change.
The photolysis and spin crossover reactions happen concurrently on a
femtosecond timescale. The microscopic origin of these reactions remains
controversial. Here, we apply quantum wavepacket dynamics to elucidate the
ultrafast photochemical mechanism for a heme--carbon monoxide (heme--CO)
complex. We observe coherent oscillations of the Fe-CO bond distance with a
period of 42 fs and an amplitude of $\sim$1 \AA{}. These nuclear motions induce
pronounced geometric reorganization, which makes the CO dissociation
irreversible. The reaction is initially dominated by symmetry breaking
vibrations inducing an electron transfer from porphyrin to iron. Subsequently,
the wavepacket relaxes to the triplet manifold in $\sim$75 fs and to the
quintet manifold in $\sim$430 fs. Our results highlight the central role of
nuclear vibrations at the origin of the ultrafast photodynamics of
organometallic complexes.",1709.03402v4
2017-09-13,Magnetic excitations of the Cu$^{2+}$ quantum spin chain in Sr$_3$CuPtO$_6$,"We report the magnetic excitation spectrum as measured by inelastic neutron
scattering for a polycrystalline sample of Sr$_3$CuPtO$_6$. Modeling the data
by the 2+4 spinon contributions to the dynamical susceptibility within the
chains, and with interchain coupling treated in the random phase approximation,
accounts for the major features of the powder-averaged structure factor. The
magnetic excitations broaden considerably as temperature is raised, persisting
up to above 100 K and displaying a broad transition as previously seen in the
susceptibility data. No spin gap is observed in the dispersive spin excitations
at low momentum transfer, which is consistent with the gapless spinon continuum
expected from the coordinate Bethe ansatz. However, the temperature dependence
of the excitation spectrum gives evidence of some very weak interchain
coupling.",1709.04100v2
2017-10-11,Weak ferromagnetism and glassy state in kappa-(BEDT-TTF)2Hg(SCN)2Br,"Since the first observation of weak ferromagnetism in the charge-transfer
salt kappa-(BEDT-TTF)2-Cu[N(CN)2]Cl [U. Welp et al., Phys. Rev. Lett. 69, 840
(1992)], no further evidence of ferromagnetism in this class of organic
materials has been reported. Here we present static and dynamic spin
susceptibility measurements on kappa-(BEDT-TTF)2Hg(SCN)2Br revealing weak
ferromagnetism below about TWF = 20 K. We suggest that frustrated spins in the
molecular dimers suppress long-range order, forming a spin-glass ground state
in the insulating phase.",1710.04028v3
2017-10-25,System information propagation for spin structures,"We study in details decoherence process of a spin register, coupled to a spin
environment. We use recently developed methods of information transfer study in
open quantum systems to analyze information flow between the register and its
environment. We show that there are regimes when not only the register
decoheres effectively to a classical bit string, but this bit string is
redundantly encoded in the environment, making it available to multiple
observations. This process is more subtle than in a case of a single qubit due
to possible presence of protected subspaces: Decoherence free subspaces and, so
called, orthogonalization free subspaces. We show that this leads to a rich
structure of coherence loss/protection in the asymptotic state of the register
and a part of its environment. We formulate a series of examples illustrating
these structures.",1710.09410v2
2017-12-13,Spin-optomechanical coupling between light and a nanofiber torsional mode,"Light that carries linear or angular momentum can interact with a mechanical
object giving rise to optomechanical effects. In particular, a photon transfers
its intrinsic angular momentum to an object when the object either absorbs the
photon or changes the photon polarization, as in an action/reaction force pair.
Here, we present the implementation of light-induced selective resonant driving
of the torsional mechanical modes of a single-mode tapered optical nanofiber.
The nanofiber torsional mode spectrum is characterized by polarimetry, showing
narrow natural resonances (Q$\approx$2,000). By sending amplitude modulated
light through the nanofiber, we resonantly drive individual torsional modes as
a function of the light polarization. By varying the input polarization to the
fiber, we find the largest amplification of a mechanical oscillation (>35 dB)
is observed when driving the system with light containing longitudinal spin on
the nanofiber waist. These results present optical nanofibers as a platform
suitable for quantum spin-optomechanics experiments.",1712.04605v1
2018-02-02,Stochastic model for quantum spin dynamics in magnetic nanostructures,"We develop a numerical model that reproduces the thermal equilibrium and the
spin transfer mechanisms in magnetic nanomaterials. We analyze the coherent
two-particle spin exchange interaction and the electron-electron collisions.
Our study is based on a quantum atomistic approach and the particle dynamics is
performed by using a Monte Carlo technique. The coherent quantum evolution of
the atoms is interrupted by instantaneous collisions with itinerant electrons.
The collision processes are associated to the quantum collapse of the local
atomic wave function. We show that particle-particle interactions beyond the
molecular field approximation can be included in this framework. Our model is
able to reproduce the thermal equilibrium and strongly out-of-equilibrium
phenomena such as the ultrafast dynamics of the magnetization in nanomatrials.",1802.00663v1
2018-02-12,Quantum spin transistors in superconducting circuits,"Transistors play a vital role in classical computers, and their quantum
mechanical counterparts could potentially be as important in quantum computers.
Where a classical transistor is operated as a switch that either blocks or
allows an electric current, the quantum transistor should operate on quantum
information. In terms of a spin model the in-going quantum information is an
arbitrary qubit state (spin-1/2 state). In this paper, we derive a model of
four qubits with Heisenberg interactions that works as a quantum spin
transistor, i.e. a system with perfect state transfer or perfect blockade
depending on the state of two gate qubits. When the system is initialized the
dynamics complete the gate operation, hence our protocol requires minimal
external control. We propose a concrete implementation of the model using
state-of-the-art superconducting circuits. Finally, we demonstrate that our
proposal operates with high-fidelity under realistic decoherence.",1802.04292v2
2018-02-28,Spin-one bilinear-biquadratic model on a star lattice,"We study the ground-state phase diagram of the $S=1$ bilinear-biquadratic
model\,(BLBQ) on the star lattice with the state-of-art tensor network
algorithms. The system has five phases: the ferromagnetic, anti-ferromagnetic,
ferroquadrupolar, and spin-liquid phases. The phases and their phase boundaries
are determined by examining various local observables, correlation functions
and transfer matrices exhaustively. The spin liquid phase, which is the first
quantum disordered phase found in two-dimensional BLBQ model, is gapped and
devoid of any conventional long-range order. It is also characterized by
fixed-parity virtual bonds in the tensor network formalism, analogous to the
Haldane phase, while the parity varies depending on the location of the bond.",1802.10281v4
2018-03-10,Optical control of competing exchange interactions and coherent spin-charge coupling in two-orbital Mott insulators,"In order to have a better understanding of ultrafast electrical control of
exchange interactions in multi-orbital systems, we study a two-orbital Hubbard
model at half filling under the action of a time-periodic electric field. Using
suitable projection operators and a generalized time-dependent canonical
transformation, we derive an effective Hamiltonian which describes two
different regimes. First, for a wide range of non-resonant frequencies, we find
a change of the bilinear Heisenberg exchange $J_{\textrm{ex}}$ that is
analogous to the single-orbital case. Moreover we demonstrate that also the
additional biquadratic exchange interaction $B_{\textrm{ex}}$ can be enhanced,
reduced and even change sign depending on the electric field. Second, for
special driving frequencies, we demonstrate a novel spin-charge coupling
phenomenon enabling coherent transfer between spin and charge degrees of
freedom of doubly ionized states. These results are confirmed by an exact
time-evolution of the full two-orbital Mott-Hubbard Hamiltonian.",1803.03796v2
2018-03-18,Controllability of Symmetric Spin Networks,"We consider a network of n spin 1/2 systems which are pairwise interacting
via Ising interaction and are controlled by the same electro-magnetic control
field. Such a system presents symmetries since the Hamiltonian is unchanged if
we permute two spins. This prevents full (operator) controllability in that not
every unitary evolution can be obtained. We prove however that controllability
is verified if we restrict ourselves to unitary evolutions which preserve the
above permutation invariance. For low dimensional cases, n=2 and n=3, we
provide an analysis of the Lie group of available evolutions and give explicit
control laws to transfer between any two permutation invariant states. This
class of states includes highly entangled states such as GHZ states and W
states, which are of interest in quantum information.",1803.06689v1
2018-04-17,Schwarzian correction to quantum correlation in SYK model,"We study a class of SYK-type models in large N limit from the gravity dual
side in terms of Schwarzian action analytically. The quantum correction to two
point correlation function due to the Schwarzian action produces transfer of
degree of freedom from the quasiparticle peak to Hubbard band in density of
states (DOS), a signature strong correlation. In Schwinger-Keldysh (SK)
formalism, we calculate higher point thermal out-of-time order correlation
(OTOC) functions, which indicate quantum chaos by having Lyapunov exponent.
Higher order local spin-spin correlations are also calculated, which can be
related to the dynamical local susceptibility of quantum liquids such as spin
glasses, disordered metals.",1804.06164v1
2018-05-03,Electron configuration of the [FeO](2+) group in the H-abstraction from methane: oxyl versus ferryl,"This account presents author's opinion on the mechanism of the H-abstraction
from methane by the [FeO](2+) group. In the course of reaction with hydrogen,
the Fe-O bond in the ferryl configuration becomes elongated causing transfer of
the spin-up electron from one of doubly occupied bonding orbitals leaving
behind single spin-down electron on oxygen. This oxygen in so-formed oxyl
configuration of the [FeO](2+) moiety then easily accept the spin-up hydrogen
atom from methane in the same way as the radical-localized oxygen does. This
mechanism is compared with the scheme in which the hydrogen is accepted by
low-lying unoccupied antibonding orbital in the ferryl configuration.",1805.01778v1
2018-07-15,Calculation of the four-spin cyclic exchange in cuprates,"Starting from the three-band Hubbard model for the cuprates, we calculate
analytically the four-spin cyclic exchange in the limit of infinite on-site
Coulomb repulsion and zero O-O hopping $t_{pp}$ using two methods: i)
perturbation theory in $t_{pd}/\Delta$, where $t_{pd}$ is the Cu-O hopping and
$\Delta$ the Cu-O charge transfer energy and ii) exact solution of a
Cu$_4$O$_4$ plaquette. The latter method coincides with the first to order
eight in $t_{pd}$ and permits to extend the results to $t_{pd}/\Delta$ of order
one. The results are relevant to recent experimental and theoretical research
that relate the splitting of certain spin excitations with $\Delta$ and the
superconducting critical temperature.",1807.05545v2
2018-08-03,Robustness of energy landscape control for spin networks under decoherence,"Quantum spin networks form a generic system to describe a range of quantum
devices for quantum information processing and sensing applications.
Understanding how to control them is essential to achieve devices with
practical functionalities. Energy landscape shaping is a novel control paradigm
to achieve selective transfer of excitations in a spin network with
surprisingly strong robustness towards uncertainties in the Hamiltonians. Here
we study the effect of decoherence, specifically generic pure dephasing, on the
robustness of these controllers. Results indicate that while the effectiveness
of the controllers is reduced by decoherence, certain controllers remain
sufficiently effective, indicating potential to find highly effective
controllers without exact knowledge of the decoherence processes.",1808.01256v1
2018-10-24,Electronic landscape of the P-cluster of nitrogenase as revealed through many-electron quantum wavefunctions,"The electronic structure of the nitrogenase metal cofactors is central to
nitrogen fixation. However, the P-cluster and iron molybdenum cofactor, each
containing eight irons, have resisted detailed characterization of their
electronic properties. Through exhaustive many-electron wavefunction
simulations enabled by new theoretical methods, we report on the low-energy
electronic states of the P-cluster in three oxidation states. The energy scales
of orbital and spin excitations overlap, yielding a dense spectrum with
features we trace to the underlying atomic states and recouplings. The clusters
exist in superpositions of spin configurations with non-classical spin
correlations, complicating interpretation of magnetic spectroscopies, while the
charges are mostly localized from reorganization of the cluster and its
surroundings. Upon oxidation, the opening of the P-cluster significantly
increases the density of states, which is intriguing given its proposed role in
electron transfer. These results demonstrate that many-electron simulations
stand to provide new insights into the electronic structure of the nitrogenase
cofactors.",1810.10196v2
2018-10-25,Separated variables and wave functions for rational gl(N) spin chains in the companion twist frame,"We propose a basis for rational gl(N) spin chains in an arbitrary rectangular
representation $(S^A)$ that factorises the Bethe vectors into products of
Slater determinants in Baxter Q-functions. This basis is constructed by
repeated action of fused transfer matrices on a suitable reference state. We
prove that it diagonalises the so-called B-operator, hence the operatorial
roots of the latter are the separated variables. The spectrum of the separated
variables is also explicitly computed and it turns out to be labelled by
Gelfand-Tsetlin patterns. Our approach utilises a special choice of the spin
chain twist which substantially simplifies derivations.",1810.10996v2
2018-11-06,Superconductivity at an antiferromagnetic quantum critical point: the role of energy fluctuations,"Motivated by recent experiments reporting superconductivity only at very low
temperature in a class of heavy fermion compounds, we study the impact of
energy fluctuations with small momentum transfer on the pairing instability
near an antiferromagnetic quantum critical point. While these fluctuations,
formed by composite spin fluctuations, were proposed to explain the
thermodynamic and transport properties near the quantum critical point of
compounds such as YbRh$_{2}$Si$_{2}$ and CeCu$_{6-x}$Au$_{x}$ at $x\approx0.1$,
here they are found to strongly suppress $T_{c}$ of the $d$-wave pairing of the
hot quasiparticles promoted by the spin fluctuations. Interestingly, if energy
fluctuations are strong enough, they can induce triplet pairing involving the
quasiparticles of the cold regions of the Fermi surface. Overall, the opposing
effects of energy and spin fluctuations lead to a suppression of $T_{c}$.",1811.02170v1
2018-11-14,Microscopic Theory of Ultrafast Out-of-Equilibrium Dynamics in Magnetic Insulators. Unraveling the Magnon-Phonon Coupling,"The interaction between lattice and spins is at the heart of an extremely
intriguing ultrafast dynamics in magnetic materials. In this work we formulate
a general non-equilibrium theory that disentangles the complex interplay
between them in a THz laser-excited antiferromagnetic insulator. The theory
provides a quantitative description of the transient energy flow between the
spin and lattice sub-systems, subject to magnon-phonon and phonon-phonon
scatterings, giving rise to finite life-times of the quasiparticles and to the
equilibration time of the system. We predict a novel kind of scattering process
where two magnons of opposite polarizations decay into a phonon, previously
omitted in the literature. The theory is combined with first-principle
calculations and then applied to simulate a realistic dynamics of NiO. The main
relaxation channels and hot spots in the reciprocal space, giving the strongest
contribution to the energy transfer between phonons and magnons are identified.
The diverse interaction strengths lead to distinct coupled dynamics of the
lattice and spin systems and subsequently to different equilibration
timescales.",1811.05841v1
2018-12-05,Spectral Properties and Quantum Phase Transitions in Superconducting Junctions with a Ferromagnetic Link,"We study theoretically the spectral and transport properties of a
superconducting wire with a magnetic defect. We start by modelling the system
as a one dimensional magnetic Josephson junction and derive the equation
determining the full subgap spectrum in terms of the normal-state transfer
matrix for arbitrary length and exchange field of the magnetic region. We
demonstrate that the quantum phase transition predicted for a short-range
magnetic impurity, and associated with a change of the total spin of the
system, also occurs in junctions of finite length. Specifically, we find that
the total spin changes discontinuously by integer jumps when bounds states
cross the Fermi level. The spin can be calculated by using a generalization of
Friedel sum rule for the superconducting state, which we also derive. With
these tools, we analyze the subgap spectrum of a junction with the length of
the magnetic region smaller than the superconducting coherence length and
demonstrate how phase transitions also manifest as change of the sign of the
supercurrent.",1812.01977v3
2018-12-12,Exact solution of a percolation analogue for the many-body localisation transition,"We construct and solve a classical percolation model with a phase transition
that we argue acts as a proxy for the quantum many-body localisation
transition. The classical model is defined on a graph in the Fock space of a
disordered, interacting quantum spin chain, using a convenient choice of basis.
Edges of the graph represent matrix elements of the spin Hamiltonian between
pairs of basis states that are expected to hybridise strongly. At weak
disorder, all nodes are connected, forming a single cluster. Many separate
clusters appear above a critical disorder strength, each typically having a
size that is exponentially large in the number of spins but a vanishing
fraction of the Fock-space dimension. We formulate a transfer matrix approach
that yields an exact value $\nu=2$ for the localisation length exponent, and
also use complete enumeration of clusters to study the transition numerically
in finite-sized systems.",1812.05115v1
2018-12-17,Domain wall-based spin-Hall nano-oscillators,"In the last decade, two revolutionary concepts in nano magnetism emerged from
research for storage technologies and advanced information processing. The
first suggests the use of magnetic domain walls (DWs) in ferromagnetic
nanowires to permanently store information in DW racetrack memories. The second
proposes a hardware realisation of neuromorphic computing in nanomagnets using
nonlinear magnetic oscillations in the GHz range. Both ideas originate from the
transfer of angular momentum from conduction electrons to localised spins in
ferromagnets, either to push data encoded in DWs along nanowires or to sustain
magnetic oscillations in artificial neurones. Even though both concepts share a
common ground, they live on very different time scales which rendered them
incompatible so far. Here, we bridge both ideas by demonstrating the excitation
of magnetic auto-oscillations inside nano-scale DWs using pure spin currents.",1812.06702v2
2019-01-17,Magnonic band structure in a Co/Pd stripe domain system investigated by Brillouin light scattering and micromagnetic simulations,"By combining Brillouin Light Scattering and micromagnetic simulations we
studied the spin-wave dynamics of a Co/Pd thin film multilayer, features a
stripe domain structure at remanence. The periodic up and down domains are
separated by cork-screw type domain walls. The existence of these domains
causes a scattering of the otherwise bulk and surface spin-wave modes, which
form mode families, similar to a one dimensional magnonic crystal. The
dispersion relation and mode profiles of spin waves are measured for
transferred wave vector parallel and perpendicular to the domain axis.",1901.05985v1
2019-02-24,Off-diagonal Bethe Ansatz on the $so(5)$ spin chain,"The $so(5)$ (i.e., $B_2$) quantum integrable spin chains with both periodic
and non-diagonal boundaries are studied via the off-diagonal Bethe Ansatz
method. By using the fusion technique, sufficient operator product identities
(comparing to those in [1]) to determine the spectrum of the transfer matrices
are derived. For the periodic case, we recover the results obtained in
\cite{NYReshetikhin1}, while for the non-diagonal boundary case, a new
inhomogeneous $T-Q$ relation is constructed. The present method can be directly
generalized to deal with the $so(2n+1)$ (i.e., $B_n$) quantum integrable spin
chains with general boundaries.",1902.08891v2
2019-03-07,Current-induced motion of twisted skyrmions,"Twisted skyrmions, whose helicity angles are different from that of Bloch
skyrmions and N\'eel skyrmions, have already been demonstrated in experiments
recently. In this work, we first contrast the magnetic structure and origin of
the twisted skyrmion with other three types of skyrmion including Bloch
skyrmion, N\'eel skyrmion and antiskyrmion. Following, we investigate the
dynamics of twisted skyrmions driven by the spin transfer toque (STT) and the
spin Hall effect (SHE) by using micromagnetic simulations. It is found that the
spin Hall angle of the twisted skyrmion is related to the dissipative force
tensor and the Gilbert damping both for the motions induced by the STT and the
SHE, especially for the SHE induced motion, the skyrmion Hall angle depends
substantially on the skyrmion helicity. At last, we demonstrate that the
trajectory of the twisted skyrmion can be controlled in a two dimensional plane
with a Gilbert damping gradient. Our results provide the understanding of
current-induced motion of twisted skyrmions, which may contribute to the
applications of skyrmion-based racetrack memories.",1903.02812v1
2019-04-12,Magnetic Field Effect on Strained Graphene Junctions,"We investigate the spin-dependent transport properties of a
ferromagnetic/strained/normal graphene junctions with central region subjected
to a magnetic field $B$. An analytical approach, based on Dirac equation, is
implemented to obtain the eigenstates and eigenvalues of the charge carrier in
three regions. Using the transfer matrix method, we determine the
spin-dependent transmission in the presence of an applied strain along the
armchair and zigzag directions of the graphene sample. We find that the strain
remarkably modifies the Landau levels (LLs) originating from the applied $B$.
It is shown that the spin up/down energy bands, in the first region, are
shifted by the exchange $H_{ex}$ and left the whole spectrum linear as in the
case of pristine graphene. In the central region, the position of the Dirac
point changes due to the uniaxial strain and $B$. It is also found that the
uniaxial strain in graphene induces a contraction of the LLs spectra. Moreover,
the strain and $B$ modify the shape and position of some peaks in the
transmission probabilities.",1904.06388v1
2019-04-16,Multiple magnon modes in the Co$_3$Sn$_2$S$_2$ Weyl semimetal candidate,"We experimentally investigate electron transport in kagome-lattice
ferromagnet Co$_3$Sn$_2$S$_2$, which is regarded as a time-reversal symmetry
broken Weyl semimetal candidate. We demonstrate $dV/dI(I)$ curves with
pronounced asymmetric $dV/dI$ spikes, similar to those attributed to
current-induced spin-wave excitations in ferromagnetic multilayers. In contrast
to multilayers, we observe several $dV/dI$ spikes' sequences at low,
$\approx$10$^4$ A/cm$^2$, current densities for a thick single-crystal
Co$_3$Sn$_2$S$_2$ flake in the regime of fully spin-polarized bulk. The spikes
at low current densities can be attributed to novel magnon branches in magnetic
Weyl semimetals, which are predicted due to the coupling between two magnetic
moments mediated by Weyl fermions. Presence of spin-transfer effects at low
current densities in Co$_3$Sn$_2$S$_2$ makes the material attractive for
applications in spintronics.",1904.07762v2
2019-04-25,The spin Drude weight of the spin-1/2 $XXZ$ chain: An analytic finite size study,"The Drude weight for the spin transport of the spin-1/2 $XXZ$ Heisenberg
chain in the critical regime is evaluated exactly for finite temperatures. We
combine the thermodynamic Bethe ansatz with the functional relations of type
$Y$-system satisfied by the row-to-row transfer matrices. This makes it
possible to evaluate the asymptotic behavior of the finite temperature spin
Drude weight with respect to the system size. As a result, the Drude weight
converges to the results obtained by Zotos (Phys. Rev. Lett. 82, 1764 (1999)),
however with very slow convergence upon increase of the system size. This
strong size dependence may explain that extrapolations from various numerical
approaches yield conflicting results.",1904.11253v1
2019-05-04,Identification and time-resolved study of YIG spin wave modes in a MW cavity in strong coupling regime,"Recently, the hybridization of microwave-frequency cavity modes with
collective spin excitations attracted large interest for the implementation of
quantum computation protocols, which exploit the transfer of information among
these two physical systems. Here, we investigate the interaction among the
magnetization precession modes of a small YIG sphere and the MW electromagnetic
modes, resonating in a tridimensional aluminum cavity. In the strong coupling
regime, anti-crossing features were observed in correspondence of various
magnetostatic modes, which were excited in a magnetically saturated sample.
Time-resolved studies show evidence of Rabi oscillations, demonstrating
coherent exchange of energy among photons and magnons modes. To facilitate the
analysis of the standing spin-wave patterns, we propose here a new procedure,
based on the introduction of a novel functional variable. The resulting easier
identification of magnetostatic modes can be exploited to investigate, control
and compare many-levels hybrid systems in cavity- and opto-magnonics research.",1905.01522v2
2019-05-21,Entanglement between a diamond spin qubit and a photonic time-bin qubit at telecom wavelength,"We report on the realization and verification of quantum entanglement between
an NV electron spin qubit and a telecom-band photonic qubit. First we generate
entanglement between the spin qubit and a 637 nm photonic time-bin qubit,
followed by photonic quantum frequency conversion that transfers the
entanglement to a 1588 nm photon. We characterize the resulting state by
correlation measurements in different bases and find a lower bound to the Bell
state fidelity of F = 0.77 +/- 0.03. This result presents an important step
towards extending quantum networks via optical fiber infrastructure.",1905.08676v1
2019-05-23,Dirac Spin Liquid on the Spin-1/2 Triangular Heisenberg Antiferromagnet,"We study the spin liquid candidate of the spin-$1/2$ $J_1$-$J_2$ Heisenberg
antiferromagnet on the triangular lattice by means of density matrix
renormalization group (DMRG) simulations. By applying an external Aharonov-Bohm
flux insertion in an infinitely long cylinder, we find unambiguous evidence for
gapless $U(1)$ Dirac spin liquid behavior. The flux insertion overcomes the
finite size restriction for energy gaps and clearly shows gapless behavior at
the expected wave-vectors. Using the DMRG transfer matrix, the low-lying
excitation spectrum can be extracted, which shows characteristic Dirac cone
structures of both spinon-bilinear and monopole excitations. Finally, we
confirm that the entanglement entropy follows the predicted universal response
under the flux insertion.",1905.09837v3
2019-06-18,Lattice SUSY for the DiSSEP at $λ^2=1$ (and $λ^2 = -3 $),"We investigate whether the dynamical lattice supersymmetry discussed for
various Hamiltonians, including one-dimensional quantum spin chains, by Fendley
et.al. and Hagendorf et.al. might also exist for the Markov matrices of any
one-dimensional exclusion processes, since these can be related by conjugation
to quantum spin chain Hamiltonians. We find that the DiSSEP (Dissipative
Symmetric Simple Exclusion Process), introduced by Crampe et.al. provides one
such example for suitably chosen parameters. The DiSSEP Markov matrix admits
the supersymmetry in these cases because it is conjugate to spin chain
Hamiltonians which also possess the supersymmetry. We note that the
length-changing supersymmetry relation for the DiSSEP Markov matrix and the
supercharge is reminiscent of a ""transfer matrix"" symmetry that has been
observed in other exclusion processes and discuss the similarity.",1906.07765v1
2019-07-20,Polarized ultrashort brilliant multi-GeV $γ$-rays via single-shot laser-electron interaction,"Generation of circularly-polarized (CP) and linearly-polarized (LP)
$\gamma$-rays via the single-shot interaction of an ultraintense laser pulse
with a spin-polarized counterpropagating ultrarelativistic electron beam has
been investigated in nonlinear Compton scattering in the quantum
radiation-dominated regime. For the process simulation a Monte Carlo method is
developed which employs the electron-spin-resolved probabilities for polarized
photon emissions. We show efficient ways for the transfer of the electron
polarization to the high-energy photon polarization. In particular, multi-GeV
CP (LP) $\gamma$-rays with polarization of up to about 95\% can be generated by
a longitudinally (transversely) spin-polarized electron beam, with a photon
flux at a single shot meeting the requirements of recent proposals for the
vacuum birefringence measurement in ultrastrong laser fields. Such high-energy,
high-brilliance, high-polarization $\gamma$-rays are also beneficial for other
applications in high-energy physics, nuclear physics, and laboratory
astrophysics.",1907.08877v2
2019-09-24,"Magnetism of (LaCoO$_3$)$_n$+(LaTiO$_3$)$_n$ superlattices with $n=1,2$","LaCoO$_3$ provides a poignant example of a transition metal oxide where the
cobalt cations display multiple spin states and spin transitions and which
continues to garner substantial attention. In this work, we describe first
principles studies, based on DFT+$U$ theory, of superlattices containing
LaCoO$_3$, specifically (LaCoO$_3$)$_n$+(LaTiO$_3$)$_n$ for $n=1,2$. The
superlattices show strong electron transfer from Ti to Co resulting in
Co$^{2+}$, significant structural distortions and a robust orbital polarization
of Co$^{2+}$. We predict high-spin Co$^{2+}$ and a checkerboard or G-type
antiferromagnetic (AFM) ground state. We provide a detailed analysis of the
magnetic interactions and phases in the superlattices. We predict that
ferromagnetic order on the Co${2+}$ can be stabilized by hole doping (e.g.,
replacing La by Sr) which is rather unusual for Co$^{2+}$ cations.",1909.11007v1
2019-12-05,Quasiparticle conductance in Spin Valve Josephson Structures,"We study the quasiparticle current in clean ferromagnetic Josephson
structures of the form $S_1/F_1/N/F_2/S_2$, where $S$, $F$, and $N$ denote
superconducting, ferromagnetic or normal layers respectively. Our focus is on
the structure of the conductance $G$ as a function of bias $V$, emphasizing the
subgap region. We use a fully self consistent numerical method, coupled to a
transfer matrix procedure to extract $G(V)$. We choose material parameters
appropriate to experimentally realized Co Cu Nb structures. We find a resonance
peak structure as a function of the intermediate layer thickness and of the
misalignement angle $\phi$ between $F$ layers. To understand this resonance
structure, we develop an approximate analytic method. For experimentally
relevant thicknesses, the conductance has multiple subgap peaks which oscillate
in position between low and critical bias positions. These oscillations occur
in both $\phi$ and the layer thicknesses. We compare our results with those
obtained for the spin valve structures $(F_1/N/F_2/S_2)$ and discuss the
implications of our results for the fabrication of spin Josephson devices.",1912.02715v1
2019-12-07,Simultaneous multiple-users quantum communication across a spin chain channel,"The time evolution of spin chains has been extensively studied for
transferring quantum states between different registers of a quantum computer.
Nonetheless, in most of these protocols only one pair of sender-receivers can
share the channel at each time. This significantly limits the rate of
communication in a network of many users as they can only communicate through
their common data-bus sequentially and not all at the same time. Here, we
propose a protocol in which multiple users can share a spin chain channel
simultaneously without having crosstalk between different parties. This is
achieved by properly tuning the local parameters of the Hamiltonian to mediate
an effective interaction between each pair of users via a distinct set of
energy eigenstates of the system. We introduce three strategies with different
levels of Hamiltonian tuning, each might be suitable for a different physical
platform. All the three strategies provide very high transmission fidelities
with vanishingly small crosstalks. We specifically show that our protocol can
be experimentally realized on currently available superconducting quantum
simulators.",1912.03475v2
2019-12-11,Electronic and magnetic properties of new binary uranium-boron compounds with 2D and 3D boron networks: A revisit of the U:B system,"Based on crystal chemistry rationale and calculations within the density
functional theory DFT, the U:B system is complemented with additional binary
compounds UB3, U2B6, and UB6 possessing two-dimensional 2D and 3D boron
substructures. Observations are supported quantitatively with the trends of
cohesive energies, charge transfers onto the boron sub-lattice and geometry
optimized structures. The results point out to a structure crossover from
hexagonal (layer B network) to 3D boron network at compositions above UB3 found
to be connected with a threshold amount of charge onto boron which is ~0.46.
From the energy-volume of states EOS considering spin degenerate and
spin-polarized configurations, hexagonal UB3, and cubic UB6 were found in a
stable ferromagnetic ground state with 1.47 and 2.40Bohr Magnetons spin-only
moments. The volume variations of magnetization show respectively a smooth and
abrupt evolution for UB3 and UB6.",1912.05224v1
2020-02-29,Nonreciprocal Emergence of Hybridized Magnons in magnetic thin Films,"We investigate the transfer and control of nonreciprocity through magnons
themselves in permalloy thin films deposited on surface oxide silicon
substrate. Evidences of nonreciprocal emergence of hybridized dipole exchange
magnons (spin waves) at two permalloy surfaces are provided by studying magnon
transmission and asymmetry, via Brillouin light scattering measurements. The
dipole dominated spin wave and exchange dominated spin wave are found to be
localized near the top and bottom surfaces, respectively, and traveling along
opposite directions. The nonreciprocity and the localization are intertwined
and ca n be tuned by an in plane magnetic field. The effects are well explained
by the magnetostatic theory and can be quantitatively reproduced by the
micromagnetic simulations. Our findings provide a simple and flexible approach
to nonreciprocal all magnon logi c devices with highly compatible with silicon
based integrated circuit technology.",2003.00230v4
2020-03-09,Breaking Anti-$\mathcal{PT}$ Symmetry by Spinning a Resonator,"Non-Hermitian systems, with symmetric or antisymmetric Hamiltonians under the
parity-time ($\mathcal{PT}$) operations, can have entirely real eigenvalues.
This fact has led to surprising discoveries such as loss-induced lasing and
topological energy transfer. A merit of anti-$\mathcal{PT}$ systems is free of
gain, but in recent efforts on making anti-$\mathcal{PT}$ devices, nonlinearity
is still required. Here, counterintuitively, we show how to achieve
anti-$\mathcal{PT}$ symmetry and its spontaneous breaking in a linear device by
spinning a lossy resonator. Compared with a Hermitian spinning device,
significantly enhanced optical isolation and ultrasensitive nanoparticle
sensing are achievable in the anti-$\mathcal{PT}$-broken phase. In a broader
view, our work provides a new tool to study anti-$\mathcal{PT}$ physics, with
such a wide range of applications as anti-$\mathcal{PT}$ lasers,
anti-$\mathcal{PT}$ gyroscopes, and anti-$\mathcal{PT}$ topological photonics
or optomechanics.",2003.04246v2
2020-04-20,Dynamic crystallization in a quantum Ising chain,"The topological degeneracy of ground states in transverse field Ising chain
cannot be removed by local perturbation and allows it to be a promising
candidate for topological computation. We study the dynamic processes of
crystallization and dissolution for the gapped ground states in an Ising chain.
For this purpose, the real-space renormalization method is employed to build an
effective Hamiltonian that captures the low-energy physics of a given system.
We show that the ground state and the first-excited state of an $ \left(
N+1\right) $-site chain can be generated from that of the $N$-site one by
adding a spin adiabatically and vice versa. Numerical simulation shows that the
robust quasidegenerate ground states of finite-size chain can be prepared with
high fidelity from a set of noninteracting spins by a quasiadiabatic process.
As an application, we propose a scheme for entanglement transfer between a pair
of spins and two separable Ising chains as macroscopic topological qubits.",2004.09021v2
2020-06-10,Hyperfine components of all rovibrational quadrupole transitions in the H$_{2}$ and D$_{2}$ molecules,"We report results of a theoretical investigation of hyperfine interactions in
two homonuclear isotopologues of the hydrogen molecule: H$_{2}$ and D$_{2}$. We
present a set of hyperfine coupling constants: spin-rotation, spin-spin dipole
and, in the case of the D$_{2}$ molecule, electric quadrupole coupling
constants for all bound states of the two isotopologues in their ground
electronic $X^{1}\Sigma^{+}_{g}$ state. We provide a list of positions and
intensities of 220 997 hyperfine components of 16 079 rovibrational quadrupole
transitions of the O, Q and S branches. The positions and intensities of the
hyperfine components are necessary for a reliable interpretation of accurate
measurements of rovibrational transition frequencies in H$_{2}$ and D$_{2}$,
which are used for tests of the quantum electrodynamics of molecules and
searches for new physics beyond the Standard Model.",2006.05717v1
2020-06-12,"Enhanced magnetocaloric effect in a mixed spin-(1/2, 1) Ising-Heisenberg two-leg ladder with strong-rung interaction","The magnetic and magnetocaloric properties of the mixed spin-(1/2,1)
Ising-Heisenberg model on a two-leg ladder with dimer-rung alternation are
exactly examined under an adiabatic demagnetization process using the
transfer-matrix formalism. We notify that the magnetization curve of the model
exhibits plateaux as a function of the applied magnetic field and cyclic
four-spin Ising interaction at certain rational fractions of the saturation
value. We precisely investigate the ability of cooling/heating of the model
nearby the critical points at which discontinuous ground-state phase transition
occurs. It is evidenced that the model manifests an enhanced magnetocaloric
effect in a proximity of the magnetization steps and jumps, accompanying with
the plateaux and jumps of correlation function of the dimer spins. We conclude
that not only the cooling/heating capability of the model could be pleasantly
demonstrated by the applied magnetic field variations, but also a typical
cyclic four-spin Ising interaction plays essential role to determine an
efficiency of the magnetocaloric effect of the model.",2006.07208v2
2020-09-08,Topological Gaps in Quasi-Periodic Spin Chains: A Numerical and K-Theoretic Analysis,"Topological phases supported by quasi-periodic spin-chain models and their
bulk-boundary principles are investigated by numerical and K-theoretic methods.
We show that, for both the un-correlated and correlated phases, the operator
algebras that generate the Hamiltonians are non-commutative tori, hence the
quasi-periodic chains display physics akin to the quantum Hall effect in two
and higher dimensions. The robust topological edge modes are found to be
strongly shaped by the interaction and, generically, they have hybrid
edge-localized and chain-delocalized structures. Our findings lay the
foundations for topological spin pumping using the phason of a quasi-periodic
pattern as an adiabatic parameter, where selectively chosen quantized bits of
magnetization can be transferred from one edge of the chain to the other.",2009.03752v2
2020-09-23,Correlators on the wall and $\mathfrak{sl}_n$ spin chain,"We study algebras and correlation functions of local operators at half-BPS
interfaces engineered by the stacks of D5 or NS5 branes in the 4d
$\mathcal{N}=4$ super Yang-Mills. The operator algebra in this sector is
isomorphic to a truncation of the Yangian $\mathcal{Y}(\mathfrak{gl}_n)$. The
correlators, encoded in a trace on the Yangian, are controlled by the
inhomogeneous $\mathfrak{sl}_n$ spin chain, where $n$ is the number of
fivebranes: they are given in terms of matrix elements of transfer matrices
associated to Verma modules, or equivalently of products of Baxter's
Q-operators. This can be viewed as a novel connection between the
$\mathcal{N}=4$ super Yang-Mills and integrable spin chains. We also remark on
analogous constructions involving half-BPS Wilson lines.",2009.11198v2
2020-11-10,Ultrafast high-harmonic nanoscopy of magnetization dynamics,"Light-induced magnetization changes, such as all-optical switching, skyrmion
nucleation, and intersite spin transfer, unfold on temporal and spatial scales
down to femtoseconds and nanometers, respectively. Pump-probe spectroscopy and
diffraction studies indicate that spatio-temporal dynamics may drastically
affect the non-equilibrium magnetic evolution. Yet, direct real-space magnetic
imaging on the relevant timescale has remained challenging. Here, we
demonstrate ultrafast high-harmonic nanoscopy employing circularly polarized
high-harmonic radiation for real-space imaging of femtosecond magnetization
dynamics. We observe the reversible and irreversible evolution of nanoscale
spin textures following femtosecond laser excitation. Specifically, we map
quenched magnetic domains and localized spin structures in Co/Pd multilayers
with a sub-wavelength spatial resolution down to 16 nm, and strobosocopically
trace the local magnetization dynamics with 40 fs temporal resolution. Our
approach enables the highest spatio-temporal resolution of magneto-optical
imaging to date. Facilitating ultrafast imaging with an extreme sensitivity to
various microscopic degrees of freedom expressed in chiral and linear
dichroism, we envisage a wide range of applications spanning magnetism, phase
transitions, and carrier dynamics.",2011.05450v1
2020-11-29,Dynamical generation of solitons in one-dimensional Fermi superfluids with and without spin-orbit coupling,"We theoretically generalize a systematic language to describe the
phase-imprinting technique to investigate the dynamical generation of solitons
in a one-dimensional Raman-type spin-orbit-coupled Fermi superfluid. We check
our method with the simulation of time-dependent Bogoliubov-de Gennes equations
and find that our method not only can generate stable dark and even gray
solitons in a conventional Fermi superfluid by controlling the transferred
phase jump but also is feasible to create a stable dark soliton in both BCS and
topological states of a spin-orbit-coupled Fermi superfluid. We also discuss
the physical implication of our method.",2011.14245v3
2020-12-16,Adiabatic Sensing Technique for Optimal Temperature Estimation using Trapped Ions,"We propose an adiabatic method for optimal phonon temperature estimation
using trapped ions which can be operated beyond the Lamb-Dicke regime. The
quantum sensing technique relies on a time-dependent red-sideband transition of
phonon modes, described by the non-linear Jaynes-Cummings model in general. A
unique feature of our sensing technique is that the relevant information of the
phonon thermal distributions can be transferred to the collective spin-degree
of freedom. We show that each of the thermal state probabilities is
adiabatically mapped onto the respective collective spin-excitation
configuration and thus the temperature estimation is carried out simply by
performing a spin-dependent laser fluorescence measurement at the end of the
adiabatic transition. We characterize the temperature uncertainty in terms of
the Fisher information and show that the state projection measurement saturates
the fundamental quantum Cram\'er-Rao bound for quantum oscillator at thermal
equilibrium.",2012.08915v1
2020-12-23,Effect of Fullerene on domain size and relaxation in a perpendicularly magnetized Pt/Co/C60/Pt system,"Buckminsterfullerene (C60) can exhibit ferromagnetism at the interface
(called as a spinterface) when it is placed next to a ferromagnet (FM).
Formation of such spinterface happens due to orbital hybridization and spin
polarized charge transfer at the interface. The spinterface can influence the
domain size and dynamics of the organic/ferromagnetic heterostructure. Here, we
have performed magnetic domain imaging and studied the relaxation dynamics in
Pt/Co/C60/Pt system with perpendicular anisotropy. We have compared the results
with its parent Pt/Co/Pt system. It is observed that presence of C60 in the
Pt/Co/Pt system increases the anisotropy and a decrease in the bubble domain
size. Further the switching time of Pt/Co/C60/Pt system is almost two times
faster than Pt/Co/Pt system. We have also performed the spin polarized density
functional theory (DFT) calculations to understand the underneath mechanism.
DFT results show formation of a spin polarized spinterface which leads to an
enhancement in anisotropy.",2012.12777v3
2021-04-02,Spotlighting quantum phase transition in spin-1/2 Ising-Heisenberg diamond chain employing Measurement-Induced Nonlocality,"We examine thermal quantum correlations characterized by Measurement-Induced
Nonlocality (MIN) in an infinite spin-1/2 Ising-Heisenberg spin chain with
Dzyaloshinskii-Moriya (DM) interaction. We evaluate MIN analytically in the
thermodynamic limit using the transfer matrix approach and show that the MIN
and its first-order derivative may spotlight the quantum criticality and
quantum phase transition (QPT). We observe that the DM interaction reduces the
role of anisotropy parameter in initiating QPT. Further, the DM interaction
also induces the nonlocality in the system if the spins are unentangled and
greatly enhances the quantum correlations if the spins are correlated. The
impact of the magnetic field and temperature on quantum correlations is also
brought out at a critical point.",2104.00884v1
2021-04-03,MIEZE Neutron Spin-Echo Spectroscopy of Strongly Correlated Electron Systems,"Recent progress in neutron spin-echo spectroscopy by means of longitudinal
Modulation of IntEnsity with Zero Effort (MIEZE) is reviewed. Key technical
characteristics are summarized which highlight that the parameter range
accessible in momentum and energy, as well as its limitations, are extremely
well understood and controlled. Typical experimental data comprising
quasi-elastic and inelastic scattering are presented, featuring magneto-elastic
coupling and crystal field excitations in Ho2Ti2O7, the skyrmion lattice to
paramagnetic transition under applied magnetic field in MnSi, ferromagnetic
criticality and spin waves in Fe. In addition bench marking studies of the
molecular dynamics in H2O are reported. Taken together, the advantages of MIEZE
spectroscopy in studies at small and intermediate momentum transfers comprise
an exceptionally wide dynamic range of over seven orders of magnitude, the
capability to perform straight forward studies on depolarizing samples or under
depolarizing sample environments, as well as on incoherently scattering
materials.",2104.01389v1
2021-05-05,Nucleon electroweak form factors using spin-improved holographic light-front wavefunctions,"We construct spin-improved holographic light front wavefunctions for the
nucleons (viewed as quark-diquark systems) and use them to successfully predict
their electromagnetic Sachs form factors, their electromagnetic charge radii,
as well as the axial form factor, charge and radius of the proton. The
confinement scale is the universal mass scale of light-front holography,
previously extracted from spectroscopic data for light hadrons. With the Dirac
and Pauli form factors normalized using the quark counting rules and the
measured anomalous magnetic moments respectively, the masses of the quark and
diquark are the only remaining adjustable parameters. We fix them using the
data set for the proton's Dirac-to-Pauli form factor ratio, and then predict
all other data without any further adjustments of parameters. Agreement with
data at low momentum-transfer is excellent. Our findings support the idea that
light (pseudoscalar and vector) mesons and the nucleons share a nonperturbative
universal holographic light-front wavefunction which is modified differently by
their spin structures.",2105.02213v2
2021-05-23,Multifunctional operation of the double-layer ferromagnetic structure coupled by a rectangular nanoresonator,"The use of spin waves as a signal carrier requires developing the functional
elements allowing for multiplexing and demultiplexing information coded at
different wavelengths. For this purpose, we propose a system of thin
ferromagnetic layers dynamically coupled by a rectangular ferromagnetic
resonator. We show that a single and double, clockwise and counter-clockwise,
circulating modes of the resonator offer a wide possibility of control of
propagating waves. Particularly, at frequency related to the double-clockwise
circulating spin-wave mode of the resonator, the spin wave excited in one layer
is transferred to the second one where it propagates in the backward direction.
Interestingly, the wave excited in the second layer propagates in the forward
direction only in that layer. This demonstrates add-drop filtering, as well as
circulator functionality. Thus, the proposed system can become an important
part of future magnonic technology for signal routing.",2105.10875v1
2021-06-01,Chiral photonic circuits for deterministic spin transfer,"Chiral quantum optics has attracted considerable interest in the field of
quantum information science. Exploiting the spin-polarization properties of
quantum emitters and engineering rational photonic nanostructures has made it
possible to transform information from spin to path encoding. Here, compact
chiral photonic circuits with deterministic circularly polarized chiral routing
and beamsplitting are demonstrated using two laterally adjacent waveguides
coupled with quantum dots. Chiral routing arises from the electromagnetic field
chirality in waveguide, and beamsplitting is obtained via the evanescent field
coupling. The spin- and position-dependent directional spontaneous emission are
achieved by spatially selective micro-photoluminescence measurements, with a
chiral contrast of up to 0.84 in the chiral photonic circuits. This makes a
significant advancement for broadening the application scenarios of chiral
quantum optics and developing scalable quantum photonic networks.",2106.00325v1
2021-08-17,Asymmetric Transport in Long-Range Interacting Chiral Spin Chains,"Harnessing power-law interactions ($1/r^\alpha$) in a large variety of
physical systems are increasing. We study the dynamics of chiral spin chains as
a possible multi-directional quantum channel. This arises from the nonlinear
character of the dispersion with complex quantum interference effects. Using
complementary numerical and analytical techniques, we propose a model to guide
quantum states to a desired direction. We illustrate our approach using the
long-range XXZ model modulated by Dzyaloshinskii-Moriya (DM) interaction. By
exploring non-equilibrium dynamics after a local quantum quench, we identify
the interplay of interaction range $\alpha$ and Dzyaloshinskii-Moriya coupling
giving rise to an appreciable asymmetric spin excitations transport. This could
be interesting for quantum information protocols to transfer quantum states,
and it may be testable with current trapped-ion experiments. We further explore
the growth of block entanglement entropy in these systems, and an order of
magnitude reduction is distinguished.",2108.07738v2
2021-08-24,Radiative recombination of twisted electrons with hydrogen-like heavy ions: Linear polarization of emitted photons,"We present a theoretical investigation of the radiative recombination of
twisted Bessel electrons with initially hydrogen-like (finally helium-like)
heavy ions. In our study, we focus especially on the linear polarization of
x-ray photons emitted in the electron capture into the ground $1s^2_{1/2}$
ionic state. Particular emphasis is placed on the question of how this
polarization is affected if incident hydrogen-like ions are themselves
spin-polarized. To explore such a ""polarization transfer"" we apply the density
matrix theory and derive the Stokes parameters of recombination x-rays for the
realistic case of collisions between macroscopic electron and ion beams. Based
on the developed general approach two scenarios are discussed that are of
interest for the planned experiments at ion storage rings. First, we
demonstrate how the use of twisted electrons can empower the known method for
the diagnostics of spin-polarized ion beams, based on the rotation of the
linear polarization of recombination light. In the second scenario we show how
the internal structure of ions beams with inhomogeneous intensity and spin
patterns can be probed by the capture of Bessel electrons, carrying different
values of angular momentum.",2108.10649v1
2021-08-30,Enhancing $d$-wave superconductivity with nearest-neighbor attraction of extended Hubbard model,"Motivated by the recent discovery of the anomalously nearest-neighbor
attraction arising from the electron-phonon coupling, we quantitatively
investigate the enhancing effects of this additional attractive channel on the
$d$-wave SC based on dynamic cluster quantum Monte Carlo calculations of doped
two-dimensional extended Hubbard model with nearest-neighbor attraction $-V$.
Focusing on the range of $0<-V/t \le 2$, our simulations indicate that the
dynamics of $d$-wave projected pairing interaction is attractive at all
frequencies and increases with $|V|$. Moreover, turning on $-V$ attraction
enhances the $(\pi,\pi)$ spin fluctuations but only enhances (suppresses) the
charge fluctuations for small (large) momentum transfer. Thus, at $V/t=-1$
relevant to ``holon folding branch'', the charge fluctuations are insufficient
to compete with $d$-wave pairing interaction strengthened by enhanced spin
fluctuations. Our work suggest the underlying rich interplay between the spin
and charge fluctuations in giving rise to the superconducting properties.",2108.12950v2
2021-10-12,Exact ground state and elementary excitations of a competing spin chain with twisted boundary condition,"A novel Bethe ansatz scheme is proposed to investigate the exact physical
properties of an integrable anisotropic quantum spin chain with competing
interactions among the nearest, next nearest neighbor and chiral three spin
couplings, where the boundary condition is the twisted one. The eigenvalue of
the transfer matrix is characterized by its zero roots instead of the
traditional Bethe roots. Based on the exact solution, the conserved momentum
and charge operators of this U(1)-symmetry broken system are obtained. The
ground state energy and density of rapidities are calculated. It is found that
there exist three kinds of elementary excitations and the corresponding
dispersion relations are obtained, which gives a different picture from that
with periodic boundary condition.",2110.05736v2
2021-10-28,Optical dynamic nuclear polarization of $^{13}$C spins in diamond at a low field with multi-tone microwave irradiation,"Most of dynamic nuclear polarization (DNP) has been requiring helium
cryogenics and strong magnetic fields for a high degree of polarization. In
this work, we instead demonstrate an optical hyperpolarization of naturally
abundant $^{13}$C nuclei in a diamond crystal at a low magnetic field and an
ambient temperature. It exploits continuous irradiations of pump laser for
polarizing electron spins of nitrogen vacancy centers and microwave for
transferring the induced polarization to $^{13}$C nuclear spins. Triplet
structures corresponding to $^{14}$N hyperfine splitting were clearly observed
in the spectrum of $^{13}$C polarization. The powers of microwave irradiation
and pump laser were optimized. By simultaneously irradiating three microwave
frequencies matching to the peaks of the triplet, we achieved a $^{13}$C bulk
polarization of 0.113 %, leading to an enhancement of about a factor of 90,000
over the thermal polarization at 17.6 mT. We believe that the multi-tone
irradiation can be universally adopted to further enhance the $^{13}$C
polarization at a low magnetic field.",2110.14850v1
2021-11-26,A modal approach to modelling spin wave scattering,"Efficient numerical methods are required for the design of optimised devices.
In magnonics, the primary computational tool is micromagnetic simulations,
which solve the Landau-Lifshitz equation discretised in time and space.
However, their computational cost is high, and the complexity of their output
hinders insight into the physics of the simulated system, especially in the
case of multimode propagating wave-based devices. We propose a finite-element
modal method allowing an efficient solution of the scattering problem for
dipole-exchange spin waves propagating perpendicularly to the magnetisation
direction. The method gives direct access to the scattering matrix of the whole
system and its components. We extend the formula for the power carried by a
magnetostatic mode in the Damon-Eshbach configuration to the case with
exchange, allowing the scattering coefficients to be normalised to represent
the fraction of the input power transferred to each output channel. We apply
the method to the analysis of spin-wave scattering on a basic functional block
of magnonic circuits, consisting of a resonator dynamically coupled to a thin
film. The results and the method are validated by comparison with micromagnetic
simulations.",2111.13448v2
2021-12-13,Direct Detection of Spin-Dependent Sub-GeV Dark Matter via Migdal Effect,"Motivated by the current strong constraints on the spin-independent dark
matter (DM)-nucleus scattering, we investigate the spin-dependent (SD)
interactions of the light Majorana DM with the nucleus mediated by an
axial-vector boson. Due to the small nucleus recoil energy, the ionization
signals have now been used to probe the light dark matter particles in direct
detection experiments. With the existing ionization data, we derive the
exclusion limits on the SD DM-nucleus scattering through Migdal effect in the
MeV-GeV DM mass range. It is found that the lower limit of the DM mass can
reach about several MeVs. Due to the momentum transfer correction induced by
the light mediator, the bounds on the SD DM-nucleus scattering cross sections
can be weakened in comparison with the heavy mediator.",2112.06492v2
2021-12-31,Understanding the propagation of excitations in quantum spin chains with different kind of interactions,"The dynamical behaviour of the quantum state of different quantum spin
chains, with designed site dependent interaction strengths, is analyzed when
the initial state belongs to the one excitation subspace. It is shown that the
inhomogeneous chains are able to transfer excitations with near perfect
fidelity. This behaviour is found for two very different spin chain
Hamiltonians. The first one is the ferromagnetic Heisenberg Hamiltonian with
nearest neighbor interactions, the second one describes a chain with long range
anisotropic interactions which are ferromagnetic in the $z$ direction and
antiferromagnetic in the $(x,y)$ plane. It is shown that both designed chains
have in common a partially ordered spectrum and well localized eigenvectors.
This physical trait unifies the description of both kind of systems.",2112.15512v1
2022-02-14,Spectrum of the quantum integrable $D^{(2)}_2$ spin chain with generic boundary fields,"Exact solution of the quantum integrable $D^{(2)}_2$ spin chain with generic
integrable boundary fields is constructed. It is found that the transfer matrix
of this model can be factorized as the product of those of two open staggered
anisotropic XXZ spin chains. Based on this identity, the eigenvalues and Bethe
ansatz equations of the $D^{(2)}_2$ model are derived via off-diagonal Bethe
ansatz.",2202.06531v2
2022-02-18,Exceptional Spectral Phase in a Dissipative Collective Spin Model,"We study a model of a quantum collective spin weakly coupled to a
spin-polarized Markovian environment and find that the spectrum is divided into
two regions that we name normal and exceptional Liouvillian spectral phases. In
the thermodynamic limit, the exceptional spectral phase displays the unique
property of being made up exclusively of second order exceptional points. As a
consequence, the evolution of any initial density matrix populating this region
is slowed down and cannot be described by a linear combination of exponential
decays. This phase is separated from the normal one by a critical line in which
the density of Liouvillian eigenvalues diverges, a phenomenon analogous to that
of excited-state quantum phase transitions observed in some closed quantum
systems. In the limit of no bath polarization, this criticality is transferred
onto the steady state, implying a dissipative quantum phase transition and the
formation of a boundary time crystal.",2202.09337v2
2022-03-07,Ultrafast optical observation of spin-pumping induced dynamic exchange coupling in ferromagnetic semiconductor/metal bilayer,"Spin angular momentum transfer in magnetic bilayers offers the possibility of
ultrafast and low-loss operation for next-generation spintronic devices. We
report the field- and temperature- dependent measurements on the magnetization
precessions in Co$_2$FeAl/(Ga,Mn)As by time-resolved magneto-optical Kerr
effect (TRMOKE). Analysis of the effective Gilbert damping and phase shift
indicates a clear signature of an enhanced dynamic exchange coupling between
the two ferromagnetic (FM) layers due to the reinforced spin pumping at
resonance. The temperature dependence of the dynamic exchange-coupling reveals
a primary contribution from the ferromagnetism in (Ga,Mn)As.",2203.03225v2
2022-04-27,SXP 15.6 -- an accreting pulsar close to spin equilibrium?,"SXP 15.6 is a recently established Be star X-ray binary system (BeXRB) in the
Small Magellanic Cloud (SMC). Like many such systems the variable X-ray
emission is driven by the underlying behaviour of the mass donor Be star. It is
shown here that the neutron star in this system is exceptionally close to spin
equilibrium averaged over several years, with the angular momentum gain from
mass transfer being almost exactly balanced by radiative losses. This makes SXP
15.6 exceptional compared to all other known members of its class in the SMC,
all of whom exhibit much higher spin period changes. In this paper we report on
X-ray observations of the brightest known outburst from this system. These
observations are supported by contemporaneous optical and radio observations,
as well as several years of historical data.",2204.12960v1
2022-05-09,High-Resolution NMR Spectroscopy at Large Fields with Nitrogen Vacancy Centers,"Ensembles of nitrogen-vacancy (NV) centers are used as sensors to detect NMR
signals from micron-sized samples at room temperature. In this scenario, the
regime of large magnetic fields is especially interesting as it leads to a
large nuclear thermal polarisation -- thus, to a strong sensor response even in
low concentration samples -- while chemical shifts and J-couplings become more
accessible. Nevertheless, this regime remains largely unexplored owing to the
difficulties to couple NV-based sensors with high-frequency nuclear signals. In
this work, we circumvent this problem with a method that maps the relevant
energy shifts in the amplitude of an induced nuclear spin signal that is
subsequently transferred to the sensor. This stage is interspersed with
free-precession periods of the sample nuclear spins where the sensor does not
participate. Thus, our method leads to high spectral resolutions ultimately
limited by the coherence of the nuclear spin signal.",2205.04150v2
2022-05-11,Ag(II) as spin super-polarizer in metal fluoride clusters,"Using quantum mechanical calculations, we examine magnetic (super)exchange
interactions in hypothetical, chemically reasonable molecular coordination
clusters containing fluoride bridged late transition metals or selected
lanthanides, as well as Ag(II). By referencing to analogous species comprising
closed shell Cd(II) we provide theoretical evidence that the presence of Ag(II)
may modify the magnetic properties of such systems (including metal metal
superexchange) to a surprising degree, specifically both coupling sign and
strength may markedly change. Remarkably, this happens in spite of the fact
that the fluoride ligand is the least susceptible to spin polarization among
all monoatomic ligands known in chemistry. In an extreme case of a oxo bridged
Ni(II)2 complex, the presence of Ag(II) leads to a nearly 17 fold increase of
magnetic superexchange and switching from antiferro- to ferromagnetic coupling.
Ag(II), with one hole in its d shell that may be shared with or transferred to
ligands, effectively acts as spin superpolarizer, and this feature could be
exploited in spintronics and diverse molecular devices.",2205.05501v2
2022-07-19,Topological Superconductivity From Forward Phonon Scatterings,"We propose a new Rashba-free mechanism to realize topological
superconductivity with electron-phonon interaction. In the presence of a
magnetic field, electron-phonon interaction with small momentum transfer is
found to favor spin-triplet Cooper pairing. This process facilitates the
formation of chiral topological superconductivity even when Rashba spin-orbital
coupling is absent. As a proof of concept, we propose an experimentally
feasible heterostructure to systematically study the entangled relationship
among forward-phonon scatterings, Rashba spin-orbital couplings, pairing
symmetries, and superconducting topology. Our theory sheds light on the
important role of electron-phonon coupled materials in the pursuit of
non-Abelian Majorana quasiparticles.",2207.09443v2
2022-09-07,Wideband Brillouin light scattering analysis of spin waves excited by a white-noise RF generator,"Spin waves are studied intensively for their intriguing properties and
potential use in future technology platforms for the transfer and processing of
information and microwave signals. The development of devices and materials for
spin-wave systems requires a lot of measurement time and effort, and thus
increasing the measurement throughput by extending the instrumentation
capabilities is of the essence. In this letter, we report on a new and
straightforward approach to increase the measurement throughput by fully
exploiting the wideband detection nature of the Brillouin light scattering
technique in single-shot experiments using a white-noise RF generator.",2209.03035v1
2022-09-14,Optimization of the Femtosecond Laser Impulse for Excitation and the Spin-Orbit Mediated Dissociation in the NaRb Dimer,"We study the dynamics of multiple coupled states under the influence of an
arbitrary time-dependent external field to investigate the femtosecond
laser-driven excitation and the spin-orbit mediated dissociation in the NaRb
dimer. In this process, the dimer is excited from the ground triplet state
$1^3\Sigma^+$ to the $1^3\Pi$ state using the femtosecond laser impulse and the
spin-orbit coupling between the $1^3\Pi$ and $2^1\Sigma^+$ states results in
the singlet-triplet transition. The laser impulse parameters are optimised to
obtain maximum yield in electronic states correlating with the first excited
atomic asymptote. We observe the detailed population statistics and power-law
decay of these states. Finally, the analysis of the population oscillations
allows us to determine the optimal time delay for dumping the molecule to its
absolute ground state.",2209.06863v3
2022-10-12,Time-dependent exchange creates the time-frustrated state of matter,"Magnetic systems governed by exchange interactions between magnetic moments
harbor frustration that leads to ground state degeneracy and results in the new
topological state often referred to as a frustrated state of matter (FSM). The
frustration in the commonly discussed magnetic systems has a spatial origin.
Here we demonstrate that an array of nanomagnets coupled by the real retarded
exchange interactions develops a new state of matter, time frustrated matter
(TFM). In a spin system with the time-dependent retarded exchange interaction,
a single spin-flip influences other spins not instantly but after some delay.
This implies that the sign of the exchange interaction changes, leading to
either ferro- or antiferromagnetic interaction, depends on time. As a result,
the system's temporal evolution is essentially non-Markovian. The emerging
competition between different magnetic orders leads to a new kind of time-core
frustration. To establish this paradigmatic shift, we focus on the exemplary
system, a granular multiferroic, where the exchange transferring medium has a
pronounced frequency dispersion and hence develops the TFM.",2210.06308v1
2022-11-10,Elementary excitations in an integrable twisted J1-J2 spin chain in the thermodynamic limit,"The exact elementary excitations in a typical U(1) symmetry broken quantum
integrable system, that is the twisted J1-J2 spin chain with nearest-neighbor,
next nearest neighbor and chiral three spin interactions, are studied. The main
technique is that we quantify the energy spectrum of the system by the zero
roots of transfer matrix instead of the traditional Bethe roots. From the
numerical calculation and singularity analysis, we obtain the patterns of zero
roots. Based on them, we analytically obtain the ground state energy and the
elementary excitations in the thermodynamic limit. We find that the system also
exhibits the nearly degenerate states in the regime of $\eta\in \mathbb{R}$,
where the nearest-neighbor couplings among the z-direction are ferromagnetic.
More careful study shows that the competing of interactions can induce the
gapless low-lying excitations and quantum phase transition in the
antiferromagnetic regime with $\eta\in \mathbb{R}+i\pi$.",2211.05549v3
2022-11-21,Tracking locality in time evolution of disordered systems,"Using local density correlation functions for a one-dimensional spin system,
we introduce a correlation function difference (CFD) which compares
correlations on a given site between a full system of size $L$ and its
restriction to $\ell<L$ sites. We show that CFD provides useful information on
transfer of information in quantum many-body systems by considering the
examples of ergodic, Anderson, and many-body localized regimes in disordered
XXZ spin chain. In the ergodic phase, we find that the propagation of CFD is
asymptotically faster than the spin transport but slower than the ballistic
propagation implied by the Lieb-Robinson bound. In contrast, in the localized
cases, we unravel an exponentially slow relaxation of CFD. Connections between
CFD and other observables detecting non-local correlations in the system are
discussed.",2211.11480v2
2022-11-30,Modelling of Spintronic Terahertz Emitters as a function of spin generation and diffusion geometry,"Spintronic THz emitters (STE) are efficient THz sources constructed using
thin heavy-metal (HM) and ferromagnetic-metal (FM) layers. To improve the
performance of the STE, different structuring methods (trilayers, stacked
bilayers) have been experimentally applied. A theoretical description of the
overall THz emission process is necessary to optimize the efficiency of STE. In
particular, geometry, composition, pump laser frequency, and spin diffusion
will be significant in understanding the pathways for further research
developments. This work will apply a generalized model based on a modified
Transfer Matrix Method (TMM). We will consider the spin generation and
diffusion in the FM and HM layers and explain the spintronic THz emission
process. This model is suitable for calculating emitted THz signal as a
function of FM and HM thicknesses for different geometrical configurations. We
will investigate a bilayer geometry as a test case, but the extension to a
multi-layer configuration is straightforward. We will show how the different
configurations of the sample will influence the THz emission amplitude.",2211.16783v1
2023-01-10,A Q-operator for open spin chains II: boundary factorization,"One of the features of Baxter's Q-operators for many closed spin chain models
is that all transfer matrices arise as products of two Q-operators with shifts
in the spectral parameter. In the representation-theoretical approach to
Q-operators, underlying this is a factorization formula for L-operators
(solutions of the Yang-Baxter equation associated to particular
infinite-dimensional representations). To have such a formalism to open spin
chains, one needs a factorization identity for solutions of the reflection
equation (boundary Yang-Baxter equation) associated to these representations.
In the case of quantum affine $\mathfrak{sl}_2$ and diagonal K-matrices, we
derive such an identity using the recently formulated theory of universal
K-matrices for quantum affine algebras.",2301.03997v3
2023-03-28,Database of semiconductor point-defect properties for applications in quantum technologies,"Solid-state point defects are attracting increasing attention in the field of
quantum information science, because their localized states can act as a
spin-photon interface in devices that store and transfer quantum information,
which have been used for applications in quantum computing, sensing, and
networking. In this work we have performed high-throughput calculations of over
50,000 point defects in various semiconductors including diamond, silicon
carbide, and silicon. Focusing on quantum applications, we characterize the
relevant optical and electronic properties of these defects, including
formation energies, spin characteristics, transition dipole moments,
zero-phonon lines. We find 2331 composite defects which are stable in intrinsic
silicon, which are then filtered to identify many new optically bright telecom
spin qubit candidates and single-photon sources. All computed results and
relaxed defect structures are made publicly available online at
quantumdefects.com, a living database of defect characteristics which will be
continually expanded with new defects and properties, and will enable
researchers to select defects tailored to their applications.",2303.16283v1
2023-05-24,Dirac half-semimetallicity and antiferromagnetism in graphene nanoribbon/hexagonal boron nitride heterojunctions,"Half-metals have been envisioned as active components in spintronic devices
by virtue of their completely spin-polarized electrical currents. Actual
materials hosting half-metallic phases, however, remain scarce. Here, we
predict that recently fabricated heterojunctions of zigzag nanoribbons embedded
in two-dimensional hexagonal boron nitride are half-semimetallic, featuring
fully spin-polarized Dirac points at the Fermi level. The half-semimetallicity
originates from the transfer of charges from hexagonal boron nitride to the
embedded graphene nanoribbon. These charges give rise to opposite energy shifts
of the states residing at the two edges while preserving their intrinsic
antiferromagnetic exchange coupling. Upon doping, an
antiferromagnetic-to-ferrimagnetic phase transition occurs in these
heterojunctions, with the sign of the excess charge controlling the spatial
localization of the net magnetic moments. Our findings demonstrate that such
heterojunctions realize tunable one-dimensional conducting channels of
spin-polarized Dirac fermions that are seamlessly integrated into a
two-dimensional insulator, thus holding promise for the development of
carbon-based spintronics.",2305.15214v1
2023-07-14,Critical charge and spin instabilities in superconducting La$_3$Ni$_2$O$_7$,"Motivated by the recent discovery of superconductivity in La$_3$Ni$_2$O$_7$
under high pressure, we explore its potential charge and spin instabilities
through combined model analysis and first-principles calculations. Taking into
account the negative charge-transfer nature of high valence nickel, a fully
correlated two-cluster model identifies a lattice-coupled rocksalt-type charge
instability characterized by substantial fluctuations of oxygen holes. This
instability is corroborated by density-functional-theory plus $U$ calculations
that also reveal a strong tendency towards concurrent antiferromagnetic
ordering. The charge, spin, and associated lattice instabilities are
significantly suppressed with increasing external pressure, contributing to the
emergence of superconductivity in pressurized La$_3$Ni$_2$O$_7$. Carrier doping
is found to effectively suppress these instabilities, suggesting a viable
strategy to stabilize a superconducting phase under ambient pressure.",2307.07154v1
2023-08-15,A Spin Field Effect Transistor Based on a Strained Two Dimensional Layer of a Weyl Semimetal,"Spin field effect transistors (SpinFET) are an iconic class of spintronic
devices that exploit gate tuned spin-orbit interaction in semiconductor
channels interposed between ferromagnetic source and drain contacts to elicit
transistor functionality. Recently, a new type of SpinFET based on gate tuned
strain in quantum materials (e.g. topological insulators) has been proposed and
may have interesting analog applications, such as in frequency multiplication,
by virtue of its unusual oscillatory transfer characteristic. Here, we propose
and analyze yet another type of SpinFET in this class, which may have a
different application. It is based on a Weyl semimetal. Because the operating
principle is non-classical, the channel conductance shows oscillatory
dependence on the channel length at zero gate voltage. Furthermore, the
transconductance can switch sign if the channel length is varied. This latter
feature can be exploited to implement a complementary device like CMOS by
connecting two such SpinFETs of slightly different channel lengths in series.
These unusual properties may have niche applications.",2308.07986v1
2023-12-06,Structural Chirality and Electronic Chirality in Quantum Materials,"In chemistry and biochemistry, chirality represents the structural asymmetry
characterized by non-superimposable mirror images for a material like DNA. In
physics, however, chirality commonly refers to the spin-momentum locking of a
particle or quasiparticle in the momentum space. While seemingly disconnected,
structural chirality in molecules and crystals can drive electronic chirality
through orbital-momentum locking, i.e. chirality can be transferred from the
atomic geometry to electronic orbitals. Electronic chirality provides an
insightful understanding of the chirality-induced spin selectivity (CISS), in
which electrons exhibit salient spin polarization after going through a chiral
material, and electric magnetochiral anisotropy (EMCA), which is characterized
by the diode-like transport. It further gives rise to new phenomena, such as
anomalous circularly polarized light emission (ACPLE), in which the light
handedness relies on the emission direction. These chirality-driven effects
will generate broad impacts in fundamental science and technology applications
in spintronics, optoelectronics, and biochemistry.",2312.03902v1
2023-12-11,Comparison of time-of-flight with MIEZE spectroscopy of H$_2$O: Necessity to go beyond the spin-echo approximation,"Here, we discuss the comparability of data acquisitioned with the Modulation
of IntEnsity with Zero Effort data, a neutron spin-echo (NSE) technique to
neutron Time-of-Flight (ToF) spectroscopy data. As a NSE technique MIEZE
records the intermediate scattering function $\mathcal{I}(Q, \tau)$ making it
necessary to perform a Fourier transform to directly compare it to $S(Q, E)$,
measured by ToF spectroscopy. Transforming either data set into the
complementary parameter space requires detailed knowledge of detector
efficiency, instrumental resolution, and background. We discuss these aspects
by comparing measurements on pure water performed on the spectrometers RESEDA
and TOFTOF under the same experimental conditions. Additionally, we discuss the
data evaluation of spin-echo data beyond the SE approximation, which limits
these techniques to small energy transfers.",2312.06449v1
2024-01-18,Semi-inclusive production of spin-3/2 hadrons in deep inelastic scattering,"We investigate the production of spin-3/2 hadrons in semi-inclusive deep
inelastic lepton-nucleon scatterings. The complete differential cross section
is derived through the kinematic analysis and expressed in terms of 288
structure functions, corresponding to all polarization configurations and
azimuthal modulations. For an unpolarized lepton beam, half of the 192
structure functions have nonzero leading order contributions in the parton
model, among which 42 are from rank-3 tensor polarized fragmentation functions
of the hadron. For a polarized lepton beam, one third of the 96 structure
functions contribute at the leading order and 14 of them are from rank-3 tensor
polarized fragmentation functions. In addition to the formalism, we perform a
model estimation of the spin transfer to a $S_{hLLL}$ polarized hadron and
sizable asymmetry is expected. Therefore, these newly defined observables for
the production of a spin-3/2 hadron in a deep inelastic scattering process can
be explored in future experiments to understand nucleon spin structures and
spin-dependent fragmentation functions.",2401.10031v2
2024-01-19,Coupling Dynamics and Linear Polarization Phenomena in Codirectional Polariton Waveguide Couplers,"In this work, we explore the potential of spin-based integrated devices using
polariton waveguides that form codirectional couplers. For suitable coupler
parameters, a transfer of condensates between the arms of the coupler, occurs
leading to the observation of Josephson-like oscillations. The ability to tune
the periodicity of these oscillations opens the way to the design of
polaritonic circuits in which the directionality of the signal towards the
output terminals can be controlled. We also investigate the response of the
devices to linearly polarized excitation, delving into the dynamics of linear
polarization at the output terminals of long couplers, providing valuable
insights into the potential applications of spin-based polariton devices,
including polariton switches and logic gates with efficient operation. Our
results are supported by numerical simulations based on generalized
Gross-Pitaevskii equation describing the dynamics of coherent polaritons in
spatially non-uniform system. We show, how the coupling and the controllable
spin degree of freedom in polariton couplers opens avenues for innovative
optical architectures and functionalities.",2401.10742v1
2024-01-19,Anti-Jahn-Teller disproportionation and prospects for spin-triplet superconductivity in d-element compounds,"We argue that the unusual properties of a wide class of materials based on
Jahn-Teller 3d and 4d ions with different crystal and electronic structures,
from quasi-two-dimensional unconventional superconductors (cuprates,
nickelates, ferropnictides/chalcogenides, ruthenate SrRuO4), manganites with
local superconductivity to 3D ferrates (CaSr)FeO3, nickelates RNiO3 and silver
oxide AgO with unusual charge and magnetic order can be explained within a
single scenario. The properties of these materials are related to the
instability of their highly symmetric Jahn-Teller ""progenitors"" with the ground
orbital E-state to charge transfer with anti-Jahn-Teller disproportionation and
the formation of a system of effective local composite spin-singlet or
spin-triplet, electronic or hole bosons moving in a non-magnetic or magnetic
lattice. These unusual systems are characterized by an extremely rich variety
of phase states from non-magnetic and magnetic insulators to unusual metallic
and superconducting states.",2401.11028v1
2024-03-04,Charge and spin fluctuations in superconductors with intersublattice and interorbital interactions,"Multiband superconductors have featured one of the main challenges to achieve
a comprehensive understanding of unconventional superconductivity. Here, the
multiband character is studied separately as orbital and sublattice degrees of
freedom, as they have different effects for the superconducting and magnetic or
charge orders. We build on the framework of the matrix random-phase
approximation (RPA), which accounts for the RPA Feynman diagrams and also
vertex corrections, to treat the electron-electron interactions in an off-site
degenerate Hubbard model. As a result, systems without a sublattice degree of
freedom tend to be dominated by spin fluctuations, while systems with multiple
sublattice sites and orbitals have the charge fluctuations favored. Finally, we
explicitly demonstrate that the known suppression of the superconducting
pairing strength $\lambda$ by spin fluctuations from repulsive interactions at
zero momentum transfer $\boldsymbol{q}$ is countered by the
finite-$\boldsymbol{q}$ pairing, which always improves $\lambda$.",2403.02453v1
2024-04-10,14N Hyperfine and nuclear interactions of axial and basal NV centers in 4H-SiC: A high frequency (94 GHz) ENDOR study,"The nitrogen-vacancy (NV) centers (NCVSi) - in 4H silicon carbide (SiC)
constitute an ensemble of spin S = 1 solid state qubits interacting with the
surrounding 14N and 29Si nuclei. As quantum applications based on a
polarization transfer from the electron spin to the nuclei require the
knowledge of the electron-nuclear interaction parameters, we have used
high-frequency (94 GHz) electron-nuclear double resonance spectroscopy combined
with first-principles density functional theory to investigate the hyperfine
and nuclear quadrupole interactions of the basal and axial NV centers. We
observed that the four inequivalent NV configurations (hk, kh, hh, and kk)
exhibit different electron-nuclear interaction parameters, suggesting that each
NV center may act as a separate optically addressable qubit. Finally, we
rationalized the observed differences in terms of distinctions in the local
atomic structures of the NV configurations. Thus, our results provide the basic
knowledge for an extension of quantum protocols involving the 14N nuclear spin.",2404.06933v1
2022-02-03,The exact solution of the Axial Next-Nearest-Neighbor Ising model on width 2 spin chains,"Using the transfer matrix method for Axial Next-Nearest Neighbor Ising model
without an external field on a closed chain of spins of width 2 in the
direction of interaction of only nearest neighbors and length L in the
direction of interaction of nearest neighbors and next nearest neighbors, we
found exact values of the partition function in a finite strip of length L ,
free energy, internal energy per node, heat capacity in a finite strip of
length L and in the thermodynamic limit. The entire spectrum of the 16x16
transfer matrix and the structure of all transfer matrix eigenvectors are
found. The problem of finding the spectrum of the transfer matrix is reduced to
finding the spectrum of two matrixes of size 8x8. The characteristic polynomial
of the first matrix is decomposed into two linear polynomials of multiplicity
two and two square trinomials. The characteristic polynomial of the second
matrix is decomposed into two polynomials of the fourth degree, the roots of
which are found by the Ferrari method. The free energy in the thermodynamic
limit has a very simple form and is expressed in terms of the logarithm of the
root of the quadratic equation. Two theorems on the physical characteristics of
the ANNNI model in a finite closed strip of length L and in the thermodynamic
limit are formulated and proved. An example of calculation is given for some
values of the model parameters in the thermodynamic limit, heat capacity graphs
are plotted. A comparative analysis of the heat capacity for the
double-stranded ANNNI model and the ANNNI model on the entire flat lattice is
given. The closest connection and similarity of the physical characteristics of
the two-chain model and the model on the entire flat lattice is shown.",2202.01834v2
2022-05-20,Tracking the Electron Transfer Cascade in European Robin Cryptochrome 4 Mutants,"The primary step in the elusive ability of migratory birds to sense weak
Earth-strength magnetic fields is supposedly the light-induced formation of a
long-lived, magnetically sensitive radical pair inside a cryptochrome
flavoprotein located in the retina of these birds. Blue light absorption by a
flavin chromophore triggers a series of sequential electron transfer steps
across a tetradic tryptophan chain towards the flavin acceptor. The recent
ability to express cryptochrome 4 from the night-migratory European robin
(Erithacus rubecula), ErCry4, and to replace the tryptophan residues
individually by a redox-inactive phenylalanine offers the prospect of exploring
the role of each of the tryptophan residues in the electron transfer chain.
Here, we compare ultrafast transient absorption spectroscopy of wild type
ErCry4 and four of its mutants having phenylalanine residues in different
positions of the chain. In the mutants we observe that each of the first three
tryptophan residues in the chain adds a distinct relaxation component (time
constants 0.5, 30 and 150 ps) to the transient absorption data. The dynamics in
the mutant with a terminal phenylalanine residue are very similar to those in
wild type ErCry4, excepted for a reduced concentration of long-lived radical
pairs. The experimental results are evaluated and discussed in connection with
Marcus-Hopfield theory, providing a complete microscopic insight into the
sequential electron transfers across the tryptophan chain. Our results offer a
path to studying spin transport and dynamical spin correlations in flavoprotein
radical pairs.",2205.10393v1
2015-12-23,"Isovector spin-singlet (T=1, S=0) and isoscalar spin-triplet (T=0, S=1) pairing interactions and spin-isospin response","We review several experimental and theoretical advances that emphasise common
aspects of the study of T=1 and T=0 pairing correlations in nuclei. We first
discuss several empirical evidences of the special role played by the T=1
pairing interaction. In particular, we show the peculiar features of the
nuclear pairing interaction in the low density regime, and possible outcomes
such as the BCS-BEC crossover in nuclear matter and, in an analogous way, in
loosely bound nuclei. We then move to the competition between T=1 and T=0
pairing correlations. The effect of such competition on the low-lying spectra
is studied in N=Z odd-odd nuclei by using a three-body model; it is shown that
the inversion of the 0+ and 1+ states near the ground state, and the strong
magnetic dipole transitions between them, can be considered as a clear
manifestation of strong T=0 pairing correlations in these nuclei. The effect of
T=0 pairing correlations is also quite evident if one studies charge-changing
transitions. The Gamow-Teller (GT) states in N=Z+2 nuclei are studied here by
using self-consistent HFB+QRPA calculations in which the T=0 pairing
interaction is taken into account. Strong GT states are found, near the ground
state of daughter nuclei; these are compared with available experimental data
from charge-exchange reactions, and such comparison can pinpoint the value of
the strength of the T=0 interaction. Pair transfer reactions are eventually
discussed: while two-neutron transfer has been long proposed as a tool to
measure the T=1 superfluidity in the nuclear ground states, the study of
deuteron transfer is still in its infancy, despite its potential interest in
revealing effects coming from both T=1 and T=0 interactions.",1512.07589v1
2018-07-12,Efficient population transfer via non-ergodic extended states in quantum spin glass,"We analyze a new computational role of coherent multi-qubit quantum tunneling
that gives rise to bands of non-ergodic extended (NEE) quantum states each
formed by a superposition of a large number of computational states (deep local
minima of the energy landscape) with similar energies. NEE provide a mechanism
for population transfer (PT) between computational states and therefore can
serve as a new quantum subroutine for quantum search, quantum parallel
tempering and reverse annealing optimization algorithms. We study PT in a
quantum n-spin system subject to a transverse field where the energy function
$E(z)$ encodes a classical optimization problem over the set of spin
configurations $z$. Given an initial spin configuration with low energy, PT
protocol searches for other bitstrings at energies within a narrow window
around the initial one. We provide an analytical solution for PT in a simple
yet nontrivial model: $M$ randomly chosen marked bit-strings are assigned
energies $E(z)$ within a narrow strip $[-n -W/2, n + W/2]$, while the rest of
the states are assigned energy 0. We find that the scaling of a typical PT
runtime with n and L is the same as that in the multi-target Grover's quantum
search algorithm, except for a factor that is equal to $\exp(n /(2B^2))$ for
finite transverse field $B\gg1$. Unlike the Hamiltonians used in analog quantum
unstructured search algorithms known so far, the model we consider is
non-integrable and population transfer is not exponentially sensitive in n to
the weight of the driver Hamiltonian. We study numerically the PT subroutine as
a part of quantum parallel tempering algorithm for a number of examples of
binary optimization problems on fully connected graphs.",1807.04792v1
2022-02-10,Self-organized Kagome-lattice in a metal-organic monolayer,"We report on the successful on-surface synthesis of metal-organic covalent
coordination networks with a dense Kagome lattice of metallic centers. In the
case of Mn centers ab-initio calculations show that the adsorbed monolayer on
Ag(111) has all the characteristic features of a strictly two-dimensional (2D)
ferromagnetic Kagome metal. Tetrahydroxyquinone (THQ) and metal atoms (M=Cu or
Mn) are co-deposited on the Ag(111) substrate to build well-ordered 2D lattices
M$_3$C$_6$O$_6$. The surface is studied by scanning tunneling microscopy (STM),
low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy
(XPS) to optimize the growth conditions like fluxes and temperatures. The
details of the atomic, electronic and magnetic structures are clarified by
density functional theory (DFT) calculations. XPS and DFT reveal a Cu$^+$
charge state and no local magnetic moments for the Cu-organic network. For the
Mn-organic network, we find the charge state Mn$^{2+}$ and a local spin S=5/2.
Charge transfer stabilizes the Cu$^+$ and Mn$^{2+}$ charge states. We find two
different modifications of the M$_3$C$_6$O$_6$ lattice. DFT calculations which
neglect the small spin-orbit coupling show a Dirac point, i.e. a band crossing
with linear electron dispersion at the K-point of the Brillouin zone. This
Dirac point is at the Fermi level if there is no charge transfer but drops by
100 meV if electron doping of Cu$_3$C$_6$O$_6$ on Ag(111) surface is
acknowledged. We predict the magnetic couplings of an isolated M$_3$C$_6$O$_6$
monolayer to be short range and antiferromagnetic leading to high frustration
at the Kagome lattice and a tendency towards a spin-liquid ground state. In the
case of hole transfer from the substrates ferromagnetic ordering is introduced,
making M$_3$C$_6$O$_6$ an interesting candidate for the quantum anomalous Hall
effect.",2202.04867v1
2024-01-20,Tracing the evolution of short-period binaries with super-synchronous fast rotators,"The initial distribution of rotational velocities of stars is still poorly
known, and how the stellar spin evolves from birth to the various end points of
stellar evolution is an actively debated topic. Binary interactions are often
invoked to explain the existence of extremely fast-rotating stars ($v\sin\,i$
$\gtrsim$ 200 $km\,s^{-1}$). The primary mechanisms through which binaries can
spin up stars are tidal interactions, mass transfer, and possibly mergers. To
evaluate these scenarios, we investigated in detail the evolution of three
known fast-rotating stars in short-period spectroscopic and eclipsing binaries,
namely HD 25631, HD 191495, and HD 46485, with primaries of masses of 7, 15,
and 24 $M_{\odot}$, respectively, with companions of $\sim1\,M_\odot$ and
orbital periods of less than 7 days. These systems belong to a recently
identified class of binaries with extreme mass ratios, whose evolutionary
origin is still poorly understood. We evaluated in detail three scenarios that
could explain the fast rotation observed in these binaries: it could be
primordial, a product of mass transfer, or the result of a merger within an
originally triple system. We computed grids of single and binary MESA models
varying tidal forces and initial binary architectures to investigate the
evolution and reproduce observational properties of these systems. We find
that, because of the extreme mass-ratio between binary components, tides have a
limited impact, regardless of the prescription used, and that the observed
short orbital periods are at odds with post-mass-transfer scenarios. The most
likely scenario to form such young, rapidly rotating, and short-period binaries
is primordial rotation, implying that the observed binaries are pre-interaction
ones. These binaries show that the initial spin distribution of massive stars
can have a wide range of rotational velocities.",2401.11304v1
2004-08-10,Spin-Orbit Evolution Of Short-Period Planets,"The negligible eccentricity of all extra solar planets with periods less than
six days can be accounted for by dissipation of tidal disturbances within their
envelopes which are induced by their host stars. In the period range of 7-21
days, planets with circular orbits coexist with planets with eccentric orbits.
These will be referred to as the borderline planets. We propose that this
discrepancy can be attributed to the variation in spin-down rates of young
stars. In particular, prior to spin-down, dissipation of a planet's tidal
disturbance within the envelope of a sufficiently rapidly spinning star can
excite eccentricity growth, and for a more slowly spinning star, at least
reduce the eccentricity damping rate. In contrast, tidal dissipation within the
envelope of a slowly spinning low-mass mature star can enhance the eccentricity
damping process. Based on these results, we suggest that short-period planets
around relatively young stars may have a much larger dispersion in eccentricity
than those around mature stars. We also suggest that because the rate of
angular momentum loss from G and K dwarfs via stellar winds is much faster than
the tidal transfer of angular momentum between themselves and their very-short
(3-4 days) period planets, they cannot establish a dynamical configuration in
which the stellar and planetary spins are approximately parallel and
synchronous with the orbital frequency. In principle, however, such
configurations may be established for planets (around G and K dwarfs) with
orbital periods of up to several weeks. In contrast to G and K dwarfs, the
angular momentum loss due to stellar winds is much weaker in F dwarfs. It is
therefore possible for synchronized short-period planets to exist around such
stars. The planet around Tau Boo is one such example.",0408191v1
2005-09-01,Shot noise and spin-orbit coherent control of entangled and spin polarized electrons,"We extend our previous work on shot noise for entangled and spin polarized
electrons in a beam-splitter geometry with spin-orbit (\textit{s-o})
interaction in one of the incoming leads (lead 1). Besides accounting for both
the Dresselhaus and the Rashba spin-orbit terms, we present general formulas
for the shot noise of singlet and triplets states derived within the scattering
approach. We determine the full scattering matrix of the system for the case of
leads with \textit{two} orbital channels coupled via weak \textit{s-o}
interactions inducing channel anticrossings. We show that this interband
coupling coherently transfers electrons between the channels and gives rise to
an additional modulation angle -- dependent on both the Rashba and Dresselhaus
interaction strengths -- which allows for further independent coherent control
of the electrons traversing the incoming leads. We derive explicit shot noise
formulas for a variety of correlated pairs (e.g., Bell states) and lead spin
polarizations. Interestingly, the singlet and \textit{each} of the triplets
defined along the quantization axis perpendicular to lead 1 (with the local
\textit{s-o} interaction) and in the plane of the beam splitter display
distinctive shot noise for injection energies near the channel anticrossings;
hence, one can tell apart all the triplets, in addition to the singlet, through
noise measurements. We also find that spin-orbit induced backscattering within
lead 1 reduces the visibility of the noise oscillations, due to the additional
partition noise in this lead. Finally, we consider injection of two-particle
wavepackets into leads with multiple discrete states and find that two-particle
entanglement can still be observed via noise bunching and antibunching.",0509038v1
2010-05-17,Spin-resolved spectroscopy of the intermediate polar DQ Her,"We present high-speed spectroscopic observations of the intermediate polar DQ
Herculis. Doppler tomography of two He I lines reveals a spiral density
structure in the accretion disc around the white dwarf primary. The spirals
look very similar to the spirals seen in dwarf novae during outburst. DQ Her is
the first well established intermediate polar in which spirals are seen, that
are in addition likely persistent because of the system's high mass transfer
rate. Spiral structures give an alternative explanation for sidebands of the WD
spin frequency that are found in IP light curves. The Doppler tomogram of He II
4686 indicates that a large part of the emission is not disc-like. Spin trails
of spectra reveal a pulsation in the He II 4686 emission that is believed to
result from reprocessing of X-rays from the white dwarf's magnetic poles in the
accretion flow close to the WD. We confirm the previous finding that the
pulsation is only visible in the red-shifted part of the line when the beam
points to the back side of the disc. The absence of reprocessed light from the
front side of the disc can be explained by obscuration by the front rim of the
disc, but the absence of extra emission from the blue-shifted back side of the
disc is puzzling. Reprocessing in accretion curtains can be an answer to the
problem and can also explain the highly non-Keplerian velocity components that
are found in the He II 4686 line. Our spin trails can form a strong test for
future accretion curtain models, with the possibility of distinguishing between
a spin period of 71s or 142s. Spin trails of data taken at selected orbital
phases show little evidence for a significant contribution of the bright spot
to the pulsations and allow us to exclude a recent suggestion that 71s is the
beat period and 70.8s the spin period.",1005.2997v1
2010-07-30,Quantum frustration in organic Mott insulators: from spin liquids to unconventional superconductors,"We review the interplay of frustration and strong electronic correlations in
quasi-two-dimensional organic charge transfer salts, such as k-(BEDT-TTF)_2X
and Et_nMe_{4-n}Pn[Pd(dmit)2]2. These two forces drive a range of exotic phases
including spin liquids, valence bond crystals, pseudogapped metals, and
unconventional superconductivity. Of particular interest is that in several
materials there is a direct transition as a function of pressure from a spin
liquid Mott insulating state to a superconducting state. Experiments on these
materials raise a number of profound questions about the quantum behaviour of
frustrated systems, particularly the intimate connection between spin liquids
and superconductivity. Insights into these questions have come from a wide
range of theoretical techniques including first principles electronic
structure, quantum many-body theory and quantum field theory. In this review we
introduce the basic ideas of the field by discussing a simple frustrated
Heisenberg model with four spins. We then describe the key experimental
results, emphasizing that for two materials, k-(BEDT-TTF)_2Cu_2(CN)_3 and
EtMe_3Sb[Pd(dmit)_2]_2, there is strong evidence for a spin liquid ground
state, and for EtMe_3P[Pd(dmit)_2]_2, a valence bond solid ground state. We
review theoretical attempts to explain these phenomena, arguing that this can
be captured by a Hubbard model on the anisotropic triangular lattice at half
filling, and that resonating valence bond wavefunctions can capture most of the
essential physics. We review evidence that this model can have a spin liquid
ground state for a range of parameters that are realistic for the relevant
materials. We conclude by summarising the progress made thus far and
identifying some of the key questions still to be answered.",1007.5381v2
2013-09-18,The spin-state crossover and low-temperature magnetic state in yttrium doped Pr$_{0.7}$Ca$_{0.3}$CoO$_3$,"The structural and magnetic properties of two mixed-valence cobaltites with
formal population of 0.30 Co$^{4+}$ ions per f.u.,
(Pr$_{1-y}$Y$_{y}$)$_{0.7}$Ca$_{0.3}$CoO$_3$ ($y=0$ and 0.15), have been
studied down to very low temperatures by means of the high-resolution neutron
diffraction, SQUID magnetometry and heat capacity measurements. The results are
interpreted within the scenario of the spin-state crossover from a
room-temperature mixture of the intermediate spin Co$^{3+}$ and low spin
Co$^{4+}$ (IS/LS) at the to the LS/LS mixture in the sample ground states. In
contrast to the yttrium free $y=0$ that retains the metallic-like character and
exhibits ferromagnetic ordering below 55 K, the doped system $y=0.15$ undergoes
a first-order metal-insulator transition at 132 K, during which not only the
crossover to low spin states but also a partial electron transfer from
Pr$^{3+}$ 4f to cobalt 3d states take place simultaneously. Taking into account
the non-magnetic character of LS Co$^{3+}$, such valence shift electronic
transition causes a magnetic dilution, formally to 0.12 LS Co$^{4+}$ or 0.12
$t_{2g}$ hole spins per f.u., which is the reason for an insulating, highly
non-uniform magnetic ground state without long-range order. Nevertheless, even
in that case there exists a relatively strong molecular field distributed over
all the crystal lattice. It is argued that the spontaneous FM order in $y=0$
and the existence of strong FM correlations in $y=0.15$ apparently contradict
the single $t_{2g}$ band character of LS/LS phase. The explanation we suggest
relies on a model of the defect induced, itinerant hole mediated magnetism,
where the defects are identified with the magnetic high-spin Co$^{3+}$ species
stabilized near oxygen vacancies.",1309.4812v1
2014-11-17,Spin mixing mechanism in amplitude analysis of pi(-)p->pi(-)pi(+)n and a new view of dark matter,"We present the first amplitude analysis of the CERN data on
pi(-)p->pi(-)pi(+)n on polarized target at 17.2 GeV/c for dipion masses
580-1080 MeV at low momentum transfer using spin mixing mechanism. The analysis
of the S- and P-wave subsystem determines a unique solution for the spin mixing
transversity amplitudes S_tau, L_tau, the corresponding S-matrix amplitudes
S^0_tau, L^0_tau and the rho^0(770)-f_0(980) spin mixing parameters. The spin
mixing mechanism allows to extract D-wave observables from the CERN data.
Analysis of the full D-wave subsystem for transversity tau=u reveals rho^0(770)
mixing in the amplitudes |D^U_u|^2 and |D^N_u|^2 and a violation of a cosine
condition by the amplitudes D^2U_u and D^2N_u. We determine spin mixing and
S-matrix helicity amplitudes from which we calculate pipi phase-shifts
delta^0_S and delta_P below KKbar threshold. The spin mixing and the violation
of the cosine condition arise from a non-standard pure dephasing interaction of
the produced final S-matrix state rho_f(S) with a quantum state rho(E) of a
quantum environment to produce the observed state rho_f(O). Our analysis
determines that the number of interacting degrees of freedom of the environment
is M=4. We identify the four eigenstates |e_k> that define the density matrix
rho(E) with the four neutrino mass eigenstates |m_k> with m_4 due to light
sterile neutrino. We call the quantum states rho(E) dark neutrinos and propose
to identify them with the particles of a distinct component of dark matter.
Dephasing interactions are not rare events but they require high statistics
experiments with polarized targets for their detection. Our amplitude analysis
illustrates this new kind of search for dark matter.",1411.4468v3
2015-11-10,"A brief account of the Ising and Ising-like models: Mean-field, effective-field and exact results","The article provides a tutorial review on how to treat Ising models within
mean-field (MF), effective-field (EF) and exact methods. MF solutions of the
spin-1 Blume-Capel (BC) model and the mixed-spin Ising model demonstrate a
change of continuous phase transitions to discontinuous ones at a tricritical
point. A quantum phase transition of the spin-S Ising model driven by a
transverse field is explored within MF method. EF theory is elaborated within a
single- and two-spin cluster approach to demonstrate an efficiency of this
approximate method. The long-standing problem of this method concerned with a
self-consistent determination of the free energy is addressed. EF theory is
adapted for the spin-1/2 Ising model, the spin-S BC model and the transverse
Ising model. The particular attention is paid to continuous and discontinuous
transitions. Exact results for the spin-1/2 Ising chain, spin-1 BC chain and
mixed-spin Ising chain are obtained using the transfer-matrix method, the
crucial steps of which are reviewed for a spin-1/2 Ising square lattice.
Critical points of the spin-1/2 Ising model on several lattices are rigorously
obtained with the help of dual, star-triangle and decoration-iteration
transformations. Mapping transformations are adapted to obtain exact results
for the mixed-spin Ising model on planar lattices. An increase in the
coordination number of the mixed-spin Ising model on decorated planar lattices
gives rise to reentrant transitions, while the critical temperature of the
mixed-spin Ising model on a regular honeycomb lattice is always greater than
that of two semi-regular archimedean lattices. The effect of selective site
dilution of the mixed-spin Ising model on a honeycomb lattice upon phase
diagrams is examined. The review affords a brief account of the Ising models
solved within MF, EF and exact methods along with a few comments on their
future applicability.",1511.03031v2
2016-04-09,Reduced radiative conductivity of high and low spin FeO6 octahedra in the Earth's lower mantle,"The ability of Earths mantle to conduct heat by radiation is determined by
optical properties of mantle phases. Optical properties of mantle minerals at
high pressure are accessible through diamond anvil cell experiments, but
because of the extensive thermal radiation at T above 1000 K such studies are
limited to lower temperatures. Particularly uncertain is the
temperature-dependence of optical properties of lower mantle minerals across
the spin transition as the spin state itself is a strong function of
temperature. Here we use laser-heated DACs combined with a pulsed bright
supercontinuum laser probe and a synchronized time-gated detector to examine
optical properties of high and low spin ferrous iron at 45-73 GPa and to 1600 K
in FeO6, one of the most abundant building blocks in the mantle. Siderite
(FeCO3) is used as a model for FeO6-octahedra as it contains no ferric iron and
exhibits a sharp optically apparent spin transition at 44 GPa, simplifying data
interpretation. We find that the optical absorbance of low spin FeO6 is
substantially increased at 1000-1200 K due to the partially lifted Laporte
selection rule. The temperature-induced low to high spin transition, however,
results in a dramatic drop in absorbance of the FeO6-unit. The absorption edge
(Fe-O charge transfer) red-shifts (~ 1 cm-1/K) with increasing temperature and
at T above 1600 K becomes the dominant absorption mechanism in the visible
range, suppressing radiative conductivity. This implies that the radiative
conductivity of analogous FeO6-bearing minerals such as ferropericlase, the
second most abundant mineral in the Earths lower mantle, is substantially
reduced approaching the core-mantle boundary conditions. Finally, our results
emphasize that optical properties of mantle minerals probed at room temperature
are insufficient to model radiative thermal conductivity of planetary
interiors.",1604.02613v1
2016-06-08,Effect of ferromagnetic exchange field on band-gap and spin-polarization of graphene on a TMD substrate,"We calculate the electronic band dispersion of graphene monolayer on a two
dimensional transition metal dichalcogenide substrate (GTMD) (viz., XY2 , X =
Mo, W; Y = S, Se) around K and K prime points taking into account the interplay
of the exchange field due to the ferromagnetic impurities and the substrate
induced, sub-lattice-resolved, strongly enhanced intrinsic spin-orbit
couplings(SOC). There are extrinsic Rashba spin-orbit coupling(RSOC) and the
orbital gap related to the transfer of the electronic charge from graphene to
XY2 as well. The former allows for external tuning of the band gap in GTMD and
connects the nearest neighbors with spin-flip. On account of the strong SOC,
the system acts as a quantum spin Hall insulator. We introduce the exchange
field (M) in the Hamiltonian to take into account the deposition of Fe atoms on
the graphene surface. The cavalcade of the perturbations yield particle-hole
symmetric bands with an effective Zeeman field due to the interplay of the
substrate induced interactions with RSOC as the prime player. Our graphical
analysis with extremely low-lying states strongly suggests the following: The
GTMDs like WY2 exhibit band gap narrowing/widening (Moss-Burs-tein(MB)gap
shift)including the spin-polarization inversion(SPI) at finite but low
temperature (T = 1 K) due to the increase in the exchange field (M) at the
Dirac point K. For graphene on MoY2, on the other hand, the occurrence of the
MB-shift and the SPI at higher temperature (T = 10 K) take place as M is
increased at the Dirac point K prime. Finally, there is anti-crossing of
non-parabolic bands with opposite spins around Dirac points. A direct electric
field control of magnetism at the nano-scale is needed here. The magnetic
multi-ferroics, like BiFeO3 (BFO), are useful for this purpose due to the
coupling between the magnetic and electric order parameters.",1606.02413v2
2022-11-23,"Electronic structure, magnetic properties, spin orientation, and doping effect in Mn$_3$Si$_2$Te$_6$","The layered material Mn$_3$Si$_2$Te$_6$, with alternating stacking honeycomb
and triangular layers, is attracting considerable attention due to its rich
physical properties. Here, using density functional theory and classical Monte
Carlo (MC) methods, we systematically study this system. Near the Fermi level,
the states are mainly contributed by Te $5p$ orbitals hybridized with Mn $3d$
orbitals, resembling a charge transfer system. Furthermore, the spin
orientations of the ferrimagnetic (FiM) ground state display different
conductive behaviors when along the $ab$ plane or out-of-plane directions:
insulating vs. metallic states. The energy difference between the FiM [110]
insulating and FiM [001] metallic phases is very small($ \sim 0.71$ meV/Mn).
Changing the angle $\theta$ of spin orientation from in-plane to out-of-plane
directions, the band gaps of this system are gradually reduced, leading to an
insulator-metal transition, resulting in an enhanced electrical conductivity,
related to the colossal angular magnetoresistance (MR) effect. In addition, we
also constructed the magnetic phase diagram using the classical $XY$ spin model
studied with the MC method. Three magnetic phases were obtained including
antiferromagnetic order, noncollinear spin patterns, and FiM order. Moreover,
we also investigated the Se- and Ge- doping into the Mn$_3$Si$_2$Te$_6$ system:
the FiM state has the lowest energy among the magnetic candidates for both Se-
or Ge- doped cases. The magnetic anisotropy energy (MAE) decreases in the
Se-doped case because the Mn orbital moment is reduced as the doping $x$
increases. Due to the small spin-orbital coupling effect of Se, the
insulator-metal transition caused by the spin orientation disappears in the
Se-doped case, resulting in an insulating phase in the FiM [001] phase. This
causes a reduced colossal angular MR.",2211.13321v2
2023-07-20,Enhanced photo-excitation and angular-momentum imprint of gray excitons in WSe$_{2}$ monolayers by spin-orbit-coupled vector vortex beams,"A light beam can be spatially structured in the complex amplitude to possess
orbital angular momentum (OAM), which introduces a new degree of freedom
alongside the intrinsic spin angular momentum (SAM) associated with circular
polarization. Moreover, super-imposing two twisted lights with distinct SAM and
OAM produces a vector vortex beam (VVB) in non-separable states where not only
complex amplitude but also polarization are spatially structured and entangled
with each other. In addition to the non-separability, the SAM and OAM in a VVB
are intrinsically coupled by the optical spin-orbit interaction and constitute
the profound spin-orbit physics in photonics. In this work, we present a
comprehensive theoretical investigation, implemented on the first-principles
base, of the intriguing light-matter interaction between VVBs and WSe$_{2}$
monolayers (WSe$_{2}$-MLs), one of the best-known and promising two-dimensional
(2D) materials in optoelectronics dictated by excitons, encompassing bright
exciton (BX) as well as various dark excitons (DXs). One of the key findings of
our study is the substantial enhancement of the photo-excitation of gray
excitons (GXs), a type of spin-forbidden dark exciton, in a WSe$_2$-ML through
the utilization of a twisted light that possesses a longitudinal field
associated with the optical spin-orbit interaction. Our research demonstrates
that a spin-orbit-coupled VVB surprisingly allows for the imprinting of the
carried optical information onto gray excitons in 2D materials, which is robust
against the decoherence mechanisms in materials. This observation suggests a
promising method for deciphering the transferred angular momentum from
structured lights to excitons.",2307.10916v1
2023-10-10,A SWAP Gate for Spin Qubits in Silicon,"With one- and two-qubit gate fidelities approaching the fault-tolerance
threshold for spin qubits in silicon, how to scale up the architecture and make
large arrays of spin qubits become the more pressing challenges. In a scaled-up
structure, qubit-to-qubit connectivity has crucial impact on gate counts of
quantum error correction and general quantum algorithms. In our toolbox of
quantum gates for spin qubits, SWAP gate is quite versatile: it can help solve
the connectivity problem by realizing both short- and long-range spin state
transfer, and act as a basic two-qubit gate, which can reduce quantum circuit
depth when combined with other two-qubit gates. However, for spin qubits in
silicon quantum dots, high fidelity SWAP gates have not been demonstrated due
to the requirements of large circuit bandwidth and a highly adjustable ratio
between the strength of the exchange coupling J and the Zeeman energy
difference Delta E_z. Here we demonstrate a fast SWAP gate with a duration of
~25 ns based on quantum dots in isotopically enriched silicon, with a highly
adjustable ratio between J and Delta E_z, for over two orders of magnitude in
our device. We are also able to calibrate the single-qubit local phases during
the SWAP gate by incorporating single-qubit gates in our circuit. By
independently reading out the qubits, we probe the anti-correlations between
the two spins, estimate the operation fidelity and analyze the dominant error
sources for our SWAP gate. These results pave the way for high fidelity SWAP
gates, and processes based on them, such as quantum communication on chip and
quantum simulation by engineering the Heisenberg Hamiltonian in silicon.",2310.06700v1
2000-11-01,A universal angular momentum profile for galactic halos,"[Abridged] We study the angular-momentum profiles of a statistical sample of
halos drawn from a high-resolution N-body simulation of the LCDM cosmology. We
find that the cumulative mass distribution of specific angular momentum, j, in
a halo of mass Mv is well fit by a universal function, M(<j) = Mv \mu
j/(j_0+j). This profile is defined by one shape parameter (\mu or j_0) in
addition to the global spin parameter \lambda. It follows a power-law over most
of the mass, and flattens at large j, with the flattening more pronounced for
small values of \mu. Compared to a uniform sphere in solid-body rotation, most
halos have a higher fraction of their mass in the low- and high-j tails of the
distribution. The spatial distribution of angular momentum in halos tends to be
cylindrical and is well-aligned within each halo for ~80% of the halos. We
investigate two ideas for the origin of this profile. The first is based on a
revised version of linear tidal-torque theory combined with extended
Press-Schechter mass accretion, and the second focuses on j transport in minor
mergers. Finally, we briefly explore implications of the M(<j) profile on the
formation of galactic disks assuming that j is conserved during an adiabatic
baryonic infall. The implied gas density profile deviates from an exponential
disk, with a higher density at small radii and a tail extending to large radii.
The steep central density profiles may imply disk scale lengths that are
smaller than observed. This is reminiscent of the ""angular-momentum problem""
seen in hydrodynamic simulations, even though we have assumed perfect j
conservation. A possible solution is to associate the central excesses with
bulge components and the outer regions with extended gaseous disks.",0011001v2
2001-10-31,Electrodynamics of Magnetars: Implications for the Persistent X-ray Emission and Spindown of the Soft Gamma Repeaters and Anomalous X-ray Pulsars,"(ABBREVIATED) We consider the structure of neutron star magnetospheres
threaded by large-scale electrical currents, and the effect of resonant Compton
scattering by the charge carriers (both electrons and ions) on the emergent
X-ray spectra and pulse profiles. In the magnetar model for the SGRs and AXPs,
these currents are maintained by magnetic stresses acting deep inside the star.
We construct self-similar, force-free equilibria of the current-carrying
magnetosphere with a power-law dependence of magnetic field on radius, B ~
r^(-2-p), and show that a large-scale twist softens the radial dependence to p
< 1. The spindown torque acting on the star is thereby increased in comparison
with a vacuum dipole. We comment on the strength of the surface magnetic field
in the SGR and AXP sources, and the implications of this model for the narrow
measured distribution of spin periods. A magnetosphere with a strong twist,
B_\phi/B_\theta = O(1) at the equator, has an optical depth ~ 1 to resonant
cyclotron scattering, independent of frequency (radius), surface magnetic field
strength, or charge/mass ratio of the scattering charge. When electrons and
ions supply the current, the stellar surface is also heated by the impacting
charges at a rate comparable to the observed X-ray output of the SGR and AXP
sources, if B_{dipole} ~ 10^{14} G. Redistribution of the emerging X-ray flux
at the ion and electron cyclotron resonances will significantly modify the
emerging pulse profile and, through the Doppler effect, generate a non-thermal
tail to the X-ray spectrum. The sudden change in the pulse profile of SGR
1900+14 after the 27 August 1998 giant flare is related to an enhanced optical
depth to electron cyclotron scattering, resulting from a sudden twist imparted
to the external magnetic field.",0110677v2
2002-01-21,Dark halo properties from rotation curves,"We study a large set of high spatial resolution optical rotation curves of
galaxies with the goal of determining the model parameters for a disk embedded
within a CDM halo that we model either with a NFW profile or pseudo-isothermal
profile. We show that parameter degeneracies present in lower resolution data
are lifted at these higher resolutions. 34% of the galaxies do not have a
meaningful fit when using the NFW profile and 32% when using the
pseudoisothermal profile, however only 14% do not have a meaningful fit in
either model. In both models we find correlations between the disk baryon
fraction $f_d$ and the spin parameter of the halo $\lambda'$, between $f_d$ and
the dark halo mass $M_{200}$, and between $M_{200}$ and the concentration
parameter $c$. We show that the distribution of the concentration parameters
$c$, for a NFW halo, is in good agreement with CDM predictions; no significant
galaxy population is found with very low values of $c$. The overall
distribution of $\lambda'$ is in good agreement with theoretical predictions
from hierarchical tidal torque theory. The whole sample is also well fitted by
a pseudo-isothermal dark halo with a core, but the size of the core is rather
small (for 70% of the sample the core size is less than 2 kpc). Thus we
conclude that the profile of dark matter is steep ($r^{-1}$ or steeper) down to
this radius; large dark matter cores (and therefore very low dark matter
central densities) seem to be excluded. LSBs tend to have higher values of
$\lambda'$ for a given $f_d$ and lower values of $c$ for a given mass than
HSBs. In an appendix we give some useful formula for pseudo-isothermal profile
halos and discuss in detail the issue of parameter degeneracies.",0201352v1
2004-01-22,A Frequency Glitch in an Accreting Pulsar,"Frequency glitches have been observed so far only in radio pulsars and
anomalous X-ray pulsars. Here we present evidence of a glitch in a neutron star
accreting from a Be companion. The transient KS 1947+300 reappeared in 2000
October as a moderately strong X-ray source that exhibited 18.7 s pulsations,
leading to an identification with the BATSE source GRO J1948+32, last detected
in 1994. We have analyzed Rossi X-ray Timing Explorer observations taken during
the 2000-01 outburst, as well as additional observations taken during a smaller
outburst in July 2002. Orbital Doppler shifts are apparent in the temporal
variation of the pulse frequency. A joint fit of the RXTE data together with
BATSE measurements from an outburst in 1994 yields the orbital period P_orb =
40.415+/-0.010 d, the projected orbital radius a_x sin i = 137+/-3 lt-s, and
the eccentricity e = 0.033+/-0.013. This degree of eccentricity is unexpectedly
low for such a wide orbit. Pulse timing results also show that the intrinsic
pulse frequency increased from 53.30 to 53.47 mHz at a rate approximately
proportional to the X-ray flux. This is about the degree of spin up expected
from the accretion torques that must be present when the X-ray luminosity
reaches ~10^38 ergs/s. On one occasion during the 2000-01 outburst, the pulse
frequency increased by ~1.8x10^-6 Hz in less than approximately 10 hr over and
above the mean trend seen around that time, without any indication of a
correspondingly large increase in X-ray flux. The fractional change in
frequency of 3.7x10^-5 during this event is significantly larger than the
values observed in the glitches in radio pulsars and anomalous X-ray pulsars.
We discuss other similarities and differences between these events.",0401476v2
2005-12-12,The Impact of Box Size on the Properties of Dark Matter Haloes in Cosmological Simulations,"We investigate the impact finite simulation box size has on the structural
and kinematic properties of Cold Dark Matter haloes forming in cosmological
simulations. Our approach involves generating a single realisation of the
initial power spectrum of density perturbations and studying how truncation of
this power spectrum on scales larger than L_cut affects the structure of dark
matter haloes at z=0. In particular, we have examined the cases of L_cut =
f_cut L_box with f_cut=1 (i.e. no truncation), 1/2, 1/3 and 1/4. In common with
previous studies, we find that the suppression of long wavelength perturbations
reduces the strength of clustering, as measured by a suppression of the 2-point
correlation function xi(r), and reduces the numbers of the most massive haloes,
as reflected in the depletion of the high mass end of the mass function n(M).
Interestingly, we find that truncation has little impact on the internal
properties of haloes. The masses of high mass haloes decrease in a systematic
manner as L_cut is reduced, but the distribution of concentrations is
unaffected. On the other hand, the median spin parameter is ~50% lower in runs
with f_cut<1. We argue that this is an imprint of the linear growth phase of
the halo's angular momentum by tidal torquing, and that the absence of any
measurable trend in concentration and the weak trend observed in halo shape
reflect the importance of virialisation and complex mass accretion histories
for these quantities. These results are of interest for studies that require
high mass resolution and statistical samples of simulated haloes, such as
simulations of the population of first stars. Our analysis shows that
large-scale tidal fields have relatively little effect on the internal
properties of Cold Dark Matter haloes and hence may be ignored in such studies.",0512281v1
2006-01-31,How galaxies lose their angular momentum,"The processes are investigated by which gas loses its angular momentum during
the protogalactic collapse phase, leading to disk galaxies that are too compact
with respect to the observations. High-resolution N-body/SPH simulations in a
cosmological context are presented including cold gas and dark matter. A halo
with quiet merging activity since z~3.8 and with a high spin parameter is
analysed that should be an ideal candidate for the formation of an extended
galactic disk. We show that the gas and the dark matter have similar specific
angular momenta until a merger event occurs at z~2 with a mass ratio of 5:1.
All the gas involved in the merger loses a substantial fraction of its specific
angular momentum due to tidal torques and falls quickly into the center.
Dynamical friction plays a minor role,in contrast to previous claims. In fact,
after this event a new extended disk begins to form from gas that was not
involved in the 5:1 merger event and that falls in subsequently. We argue that
the angular momentum problem of disk galaxy formation is a merger problem: in
cold dark matter cosmology substantial mergers with mass ratios of 1:1 to 6:1
are expected to occur in almost all galaxies. We suggest that energetic
feedback processes could in principle solve this problem, however only if the
heating occurs at the time or shortly before the last substantial merger event.
Good candidates for such a coordinated feedback would be a merger-triggered
star burst or central black hole heating. If a large fraction of the low
angular momentum gas would be ejected as a result of these processes, late-type
galaxies could form with a dominant extended disk component, resulting from
late infall, a small bulge-to-disk ratio and a low baryon fraction, in
agreement with observations.",0602005v1
2006-08-31,Self-induced conversion in dense neutrino gases: Pendulum in flavour space,"Neutrino-neutrino interactions can lead to collective flavour conversion
effects in supernovae and in the early universe. We demonstrate that the case
of ""bipolar"" oscillations, where a dense gas of neutrinos and antineutrinos in
equal numbers completely converts from one flavour to another even if the
mixing angle is small, is equivalent to a pendulum in flavour space. Bipolar
flavour conversion corresponds to the swinging of the pendulum, which begins in
an unstable upright position (the initial flavour), and passes through
momentarily the vertically downward position (the other flavour) in the course
of its motion. The time scale to complete one cycle of oscillation depends
logarithmically on the vacuum mixing angle. Likewise, the presence of an
ordinary medium can be shown analytically to contribute to a logarithmic
increase in the bipolar conversion period. We further find that a more complex
(and realistic) system of unequal numbers of neutrinos and antineutrinos is
analogous to a spinning top subject to a torque. This analogy easily explains
how such a system can oscillate in both the bipolar and the synchronised mode,
depending on the neutrino density and the size of the neutrino-antineutrino
asymmetry. Our simple model applies strictly only to isotropic neutrino gasses.
In more general cases, and especially for neutrinos streaming from a supernova
core, different modes couple to each other with unequal strength, an effect
that can lead to kinematical decoherence in flavour space rather than
collective oscillations. The exact circumstances under which collective
oscillations occur in non-isotropic media remain to be understood.",0608695v3
2006-11-27,High-resolution X-ray spectroscopy of the ultracompact LMXB pulsar 4U 1626-67,"[abridged] We report results from four recent observations of the
ultracompact LMXB pulsar 4U 1626-67. All the observations obtained
high-resolution X-ray spectra of the system, two from the Chandra X-ray
Observatory using the HETGS, and two from the XMM-Newton Observatory using the
RGS as well as the EPIC PN and MOS. These data allow us to study in detail the
prominent Ne and O emission line complexes which make 4U 1626-67 unique among
LMXBs. The observations were spaced over a period of 3 years for a total
observing time of 238 ks, allowing us to monitor the line regions as well as
the overall source flux, continuum spectrum, and timing properties. The
structure of the emission lines and the ratios of the components of the
helium-like Ne IX and O VII triplets support the hypothesis that they are
formed in the high-density environment of the accretion disk. We do not find
any significant changes in the line widths or ratios over this time period,
though we note that the line equivalent widths decrease. We are able to place
constraints on the strengths of the Ne K, Fe L, and O K photoelectric
absorption edges, and find that the data do not require an overabundance of Ne
or O in the system relative to the expected ISM values. We find that the pulsar
is still spinning down, and note that the pulse profile has changed
significantly from what was found prior to the torque reversal in 1990,
suggesting that this event may be linked to a change in the geometry of the
accretion column. The flux of 4U 1626-67 continues to decrease, in keeping with
the trend of the last approximately 30 years over which it has been observed.
Taking into consideration current theory on disk stability, we expect that 4U
1626-67 will enter a period of quiescence in 2-15 years.",0611823v1
2007-04-12,Nanodevices and Maxwell's Demon,"In the last twenty years there has been significant progress in our
understanding of quantum transport far from equilibrium and a conceptual
framework has emerged through a combination of the Landauer approach with the
non-equilibrium Green function (NEGF) method, which is now being widely used in
the analysis and design of nanoscale devices. It provides a unified description
for all kinds of devices from molecular conductors to carbon nanotubes to
silicon transistors covering different transport regimes from the ballistic to
the diffusive limit. In this talk I use a simple version of this model to
analyze a specially designed device that could be called an electronic
Maxwell's demon, one that lets electrons go preferentially in one direction
over another. My objective is to illustrate the fundamental role of contacts
and demons in transport and energy conversion. The discussion is kept at an
academic level steering clear of real world details, but the illustrative
devices we use are very much within the capabilities of present-day technology.
For example, recent experiments on thermoelectric effects in molecular
conductors agree well with the predictions from our model. The Maxwell's demon
device itself is very similar to the pentalayer spin-torque device which has
been studied by a number of groups though we are not aware of any discussion of
the possibility of using the device as a nanoscale heat engine or as a
refrigerator as proposed here. However, my objective is not to evaluate
possible practical applications. Rather it is to introduce a simple transparent
model showing how out-of-equibrium demons suitably incorporated into
nanodevices can achieve energy conversion.",0704.1623v2
2007-07-13,X-ray and Near-IR Variability of the Anomalous X-ray Pulsar 1E 1048.1-5937: From Quiescence Back to Activity,"(Abridged) We report on new and archival X-ray and near-infrared observations
of the anomalous X-ray pulsar 1E 1048.1-5937 performed between 2001-2007 with
RXTE, CXO, Swift, HST, and VLT. During its ~2001-2004 active period, 1E
1048.-5937 exhibited two large, long-term X-ray pulsed-flux flares as well as
short bursts, and large (>10x) torque changes. Monitoring with RXTE revealed
that the source entered a phase of timing stability in 2004; at the same time,
a series of four simultaneous observations with CXO and HST in 2006 showed that
its X-ray flux and spectrum and near-IR flux, all variable prior to 2005,
stabilized. The near-IR flux, when detected by HST (H~22.7 mag) and VLT
(K_S~21.0 mag), was considerably fainter than previously measured. Recently, in
2007 March, this newfound quiescence was interrupted by a sudden flux
enhancement, X-ray spectral changes and a pulse morphology change, simultaneous
with a large spin-up glitch and near-IR enhancement. Our RXTE observations
revealed a sudden pulsed flux increase by a factor of ~3 in the 2-10 keV band.
In observations with CXO and Swift, we found that the total X-ray flux
increased much more than the pulsed flux, reaching a peak value of >7 times the
quiescent value (2-10 keV). With these recent data, we find a strong
anti-correlation between X-ray flux and pulsed fraction, and a correlation
between X-ray spectral hardness and flux. Simultaneously with the radiative and
timing changes, we observed a significant X-ray pulse morphology change such
that the profile went from nearly sinusoidal to having multiple peaks. We
compare these remarkable events with other AXP outbursts and discuss
implications in the context of the magnetar model and other models of AXP
emission.",0707.2093v2
2009-06-25,Spitzer Space Telescope Observations of the Nucleus of Comet 103P/Hartley 2,"We have used the Spitzer 22-um peakup array to observe thermal emission from
the nucleus and trail of comet 103P/Hartley 2, the target of NASA's Deep Impact
Extended mission. The comet was observed on UT 2008 August 12 and 13, while the
comet was 5.5 AU from the Sun. We obtained two 200-frame sets of photometric
imaging over a 2.7-hour period. To within the errors of the measurement, we
find no detection of any temporal variation between the two images. The comet
showed extended emission beyond a point source in the form of a faint trail
directed along the comet's anti-velocity vector. After modeling and removing
the trail emission, a NEATM model for the nuclear emission with beaming
parameter of 0.95 +/- 0.20 indicates a small effective radius for the nucleus
of 0.57 +/- 0.08 km and low geometric albedo 0.028 +/- 0.009 (1 sigma). With
this nucleus size and a water production rate of 3 x 10^28 molecules s-1 at
perihelion (A'Hearn et al. 1995) we estimate that ~100% of the surface area is
actively emitting volatile material at perihelion. Reports of emission activity
out to ~5 AU (Lowry et al. 2001, Snodgrass et al. 2008) support our finding of
a highly active nuclear surface. Compared to Deep Impact's first target, comet
9P/Tempel 1, Hartley 2's nucleus is one-fifth as wide (and about one-hundredth
the mass) while producing a similar amount of outgassing at perihelion with
about 13 times the active surface fraction. Unlike Tempel 1, it should be
highly susceptible to jet driven spin-up torques, and so could be rotating at a
much higher frequency. Barring a catastrophic breakup or major fragmentation
event, the comet should be able to survive up to another 100 apparitions (~700
yrs) at its current rate of mass loss.",0906.4733v1
2009-08-01,Continuous monitoring of pulse period variations in Her X-1 using Swift/BAT,"Context: Monitoring of pulse period variations in accreting binary pulsars is
an important tool to study the interaction between the magnetosphere of the
neutron star and the accretion disk. While the X-ray flux of the brightest
X-ray pulsars have been successfully monitored over many years (e.g. with
RXTE/ASM, CGRO/BATSE, Swift/BAT), the possibility to monitor their pulse timing
properties continuously has so far been very limited. Aims: In our work we show
that the Swift/BAT observations can be used to monitor coherent pulsations of
bright X-ray sources and use the Swift archival data to study one of the most
enigmatic X-ray pulsars, Hercules X-1. A quasi-continuous monitoring of the
pulse period and the pulse period derivative of an X-ray pulsar, here Her X-1,
is achieved over a long time (<~ 4 yrs). We compare our observational results
with predictions of accretion theory and use them to test different aspects of
the physical model of the system. Methods: In our analysis we use the data
accumulated with Swift/BAT starting from the beginning of 2005 (shortly after
launch) until the present time. To search for pulsations and for their
subsequent analysis we used the count rate measured by the BAT detector in the
entire field of view. Results: The slope of the correlation between the locally
determined spin-up rate and the X-ray luminosity is measured for Her X-1 and
found to be in agreement with predictions of basic accretion torque theory. The
observed behaviour of the pulse period together with the previously measured
secular decrease of the system's orbital period is discussed in the frame of a
model assuming ejection of matter close to the inner boundary of the accretion
disk.",0908.0053v1
2009-11-24,Tidal and Magnetic Interactions between a Hot Jupiter and its Host Star in the Magnetospheric Cavity of a Protoplanetary Disk,"We present a simplified model to study the orbital evolution of a young hot
Jupiter inside the magnetospheric cavity of a proto-planetary disk. The model
takes into account the disk locking of stellar spin as well as the tidal and
magnetic interactions between the star and the planet. We focus on the orbital
evolution starting from the orbit in the 2:1 resonance with the inner edge of
the disk, followed by the inward and then outward orbital migration driven by
the tidal and magnetic torques as well as the Roche-lobe overflow of the
tidally inflated planet. The goal in this paper is to study how the orbital
evolution inside the magnetospheric cavity depends on the cavity size, planet
mass, and orbital eccentricity. In the present work, we only target the mass
range from 0.7 to 2 Jupiter masses. In the case of the large cavity
corresponding to the rotational period ~ 7 days, the planet of mass >1 Jupiter
mass with moderate initial eccentricities (>~ 0.3) can move to the region <
0.03 AU from its central star in 10^7 years, while the planet of mass <1
Jupiter mass cannot. We estimate the critical eccentricity beyond which the
planet of a given mass will overflow its Roche radius and finally lose all of
its gas onto the star due to runaway mass loss. In the case of the small cavity
corresponding to the rotational period ~ 3 days, all of the simulated planets
lose all of their gas even in circular orbits. Our results for the orbital
evolution of young hot Jupiters may have the potential to explain the absence
of low-mass giant planets inside ~ 0.03 AU from their dwarf stars revealed by
transit surveys.",0911.4532v1
2009-12-09,Global 3D Simulations of Disc Accretion onto the classical T Tauri Star V2129 Oph,"The magnetic field of the classical T Tauri star V2129 Oph can be modeled
approximately by superposing slightly tilted dipole and octupole moments, with
polar magnetic field strengths of 0.35kG and 1.2kG respectively (Donati et al.
2007). Here we construct a numerical model of V2129 Oph incorporating this
result and simulate accretion onto the star. Simulations show that the disk is
truncated by the dipole component and matter flows towards the star in two
funnel streams. Closer to the star, the flow is redirected by the octupolar
component, with some of the matter flowing towards the high-latitude poles, and
the rest into the octupolar belts. The shape and position of the spots differ
from those in a pure dipole case, where crescent-shaped spots are observed at
the intermediate latitudes. Simulations show that if the disk is truncated at
the distance of 6.2 R_* which is comparable with the co-rotation radius, 6.8
R_*, then the high-latitude polar spots dominate, but the accretion rate
obtained from the simulations is about an order of magnitude lower than the
observed one. The accretion rate matches the observed one if the disk is
disrupted much closer to the star, at 3.4 R_*. However, the octupolar belt
spots strongly dominate. Better match has been obtained in experiments with a
dipole field twice as strong. The torque on the star from the
disk-magnetosphere interaction is small, and the time-scale of spin evolution,
2 x10^7-10^9 years is longer than the 2x10^6 years age of V2129 Oph. The
external magnetic flux of the star is strongly influenced by the disk: the
field lines connecting the disk and the star inflate and form magnetic towers
above and below the disk. The potential (vacuum) approximation is still valid
inside the Alfv\'en (magnetospheric) surface where the magnetic stress
dominates over the matter stress.",0912.1681v2
2011-02-04,Three-dimensional simulations of internal wave breaking and the fate of planets around solar-type stars,"We study the fate of internal gravity waves approaching the centre of a
non-rotating solar-type star, by performing 3D numerical simulations using a
Boussinesq-type model. These waves are excited at the top of the radiation zone
by the tidal forcing of a short-period planet on a circular, coplanar orbit.
This extends previous work done in 2D by Barker & Ogilvie. We first derive a
linear wave solution, which is not exact in 3D; however, the reflection of
ingoing waves from the centre is close to perfect for moderate amplitude waves.
Waves with sufficient amplitude to cause isentropic overturning break, and
deposit their angular momentum near the centre. This forms a critical layer, at
which the angular velocity of the flow matches the orbital angular frequency of
the planet. This efficiently absorbs ingoing waves, and spins up the star from
the inside out, while the planet spirals into the star. We also perform
numerical integrations to determine the linearised adiabatic tidal response
throughout the star, for solar-type stellar models with masses in the range 0.5
< m_star/M_sun < 1.1, throughout their main sequence lifetimes. The aim is to
study the launching region for these waves at the top of the radiation zone in
more detail, and to determine the accuracy of a semi-analytic approximation for
the tidal torque on the star, that was derived under the assumption that all
ingoing wave angular momentum is absorbed in a critical layer. The main
conclusions are that this nonlinear mechanism of tidal dissipation could
provide an explanation for the survival of all short-period extrasolar planets
observed around FGK stars, while it predicts the destruction of more massive
planets. This work provides further support for the model outlined in a
previous paper by Barker & Ogilvie, and makes predictions that will be tested
by ongoing observational studies, such as WASP and Kepler.",1102.0857v1
2011-06-07,Angular Momentum and Vortex Formation in Bose-Einstein-Condensed Cold Dark Matter Haloes,"(Abridged) Extensions of the standard model of particle physics predict very
light bosons, ranging from about 10^{-5} eV for the QCD axion to 10^{-33} eV
for ultra-light particles, which could be the cold dark matter (CDM) in the
Universe. If so, their phase-space density must be high enough to form a
Bose-Einstein condensate (BEC). The fluid-like nature of BEC-CDM dynamics
differs from that of standard collisionless CDM (sCDM), so observations of
galactic haloes may distinguish them. sCDM has problems with galaxy
observations on small scales, which BEC-CDM may overcome for a large range of
particle mass m and self-interaction strength g. For quantum-coherence on
galactic scales of radius R and mass M, either the de-Broglie wavelength
lambda_deB <~ R, requiring m >~ m_H \cong 10^{-25}(R/100 kpc)^{-1/2}(M/10^{12}
M_solar)^{-1/2} eV, or else lambda_deB << R but self-interaction balances
gravity, requiring m >> m_H and g >> g_H \cong 2 x 10^{-64} (R/100
kpc)(M/10^{12} M_solar)^{-1} eV cm^3. Here we study the largely-neglected
effects of angular momentum. Spin parameters lambda \cong 0.05 are expected
from tidal-torquing by large-scale structure, just as for sCDM. Since lab BECs
develop quantum vortices if rotated rapidly enough, we ask if this angular
momentum is sufficient to form vortices in BEC haloes, affecting their
structure with potentially observable consequences. The minimum angular
momentum for this, L_{QM} = $\hbar M/m$, requires m >= 9.5 m_H for lambda =
0.05, close to the particle mass required to influence structure on galactic
scales. We study the equilibrium of self-gravitating, rotating BEC haloes which
satisfy the Gross-Pitaevskii-Poisson equations, to calculate if and when
vortices are energetically favoured. Vortices form as long as self-interaction
is strong enough, which includes a large part of the range of m and g of
interest for BEC-CDM haloes.",1106.1256v4
2012-05-16,Obliquity of the Galilean satellites: The influence of a global internal liquid layer,"The obliquity of the Galilean satellites is small but not yet observed.
Studies of cycloidal lineaments and strike-slip fault patterns on Europa
suggest that Europa's obliquity is about 1 deg, although theoretical models of
the obliquity predict the obliquity to be one order of magnitude smaller for an
entirely solid Europa. Here, we investigate the influence of a global liquid
layer on the obliquity of the Galilean satellites. Io most likely has a fully
liquid core, while Europa, Ganymede, and Callisto are thought to have an
internal global liquid water ocean beneath an external ice shell. We use a
model for the obliquity based on a Cassini state model extended to the presence
of an internal liquid layer and the internal gravitational and pressure torques
induced by the presence of this layer. We find that the obliquity of Io only
weakly depends on the different internal structure models considered, because
of the weak influence of the liquid core which is therefore almost impossible
to detect through observations of the obliquity. The obliquity of Europa is
almost constant in time and its mean value is smaller (0.033-0.044 deg) with an
ocean than without (0.055 deg). An accuracy of 0.004 deg (about 100 m on the
spin pole location at the surface) would allow detecting the internal ocean.
The obliquity of Ganymede and Callisto depends more on their interior structure
because of the possibility of resonant amplifications for some periodic terms
of the solution. Their ocean may be easily detected if, at the measuring time,
the actual internal structure model lead to a very different value of the
obliquity than in the solid case. A long-term monitoring of their shell
obliquity would be more helpful to infer information on the shell thickness.",1205.3628v1
2012-08-18,"Rotation, activity, and lithium abundance in cool binary stars","We have used two robotic telescopes to obtain time-series high-resolution
spectroscopy and V I and/or by photometry for a sample of 60 active stars.
Orbital solutions are presented for 26 SB2 and 19 SB1 systems with
unprecedented phase coverage and accuracy. The total of 6,609 R=55,000 echelle
spectra are also used to systematically determine effective temperatures,
gravities, metallicities, rotational velocities, lithium abundances and
absolute H{\alpha}-core fluxes as a function of time. The photometry is used to
infer unspotted brightness, V - I and/or b - y colors, spot-induced brightness
amplitudes and precise rotation periods. Our data are complemented by
literature data and are used to determine rotation-temperature-activity
relations for active binary components. We also relate lithium abundance to
rotation and surface temperature. We find that 74% of all known
rapidly-rotating active binary stars are synchronized and in circular orbits
but 26% are rotating asynchronously of which half have Prot > Porb and e > 0.
Because rotational synchronization is predicted to occur before orbital
circularization active binaries should undergo an extra spin-down besides tidal
dissipation. We suspect this to be due to a magnetically channeled wind with
its subsequent braking torque. We find a steep increase of rotation period with
decreasing effective temperature for active stars. For inactive, single giants
with Prot > 100 d, the relation is much weaker. Our data also indicate a
period-activity relation for H{\alpha} of the form RH{\alpha} \propto P - 0.24
for binaries and RH{\alpha} \propto P -0.14 for singles. Lithium abundances in
our sample increase with effective temperature. On average, binaries of
comparable effective temperature appear to exhibit 0.25 dex less surface
lithium than singles. We also find a trend of increased Li abundance with
rotational period of form log n(Li) \propto - 0.6 log Prot.",1208.3741v1
2014-09-03,Progenitor neutron stars of the lightest and heaviest millisecond pulsars,"The recent mass measurements of two binary millisecond pulsars, PSR
J1614-2230 and PSR J0751+1807 with a mass M=1.97+/-0.04 Msun and M= 1.26 +/-
0.14 Msun, respectively, indicate a wide range of masses for such objects and
possibly also a broad spectrum of masses of neutron stars born in core-collapse
supernovae.
  Starting from the zero-age main sequence binary stage, we aim at inferring
the birth masses of PSR J1614-2230 and PSR J0751+1807 by taking the differences
in the evolutionary stages preceding their formation into account.
  Using simulations for the evolution of binary stars, we reconstruct the
evolutionary tracks leading to the formation of PSR J1614-2230 and PSR
J0751+1807. We analyze in detail the spin evolution due to the accretion of
matter from a disk in the intermediate-mass/low-mass X-ray binary. We consider
two equations of state of dense matter, one for purely nucleonic matter and the
other one including a high-density softening due to the appearance of hyperons.
Stationary and axisymmetric stellar configurations in general relativity are
used, together with a recent magnetic torque model and
observationally-motivated laws for the decay of magnetic field.
  The estimated birth mass of the neutron stars PSR J0751+1807 and PSR
J1614-2230 could be as low as 1.0 Msun and as high as 1.9 Msun, respectively.
These values depend weakly on the equation of state and the assumed model for
the magnetic field and its accretion-induced decay.
  The masses of progenitor neutron stars of recycled pulsars span a broad
interval from 1.0 Msun to 1.9 Msun. Including the effect of a slow Roche-lobe
detachment phase, which could be relevant for PSR J0751+1807, would make the
lower mass limit even lower. A realistic theory for core-collapse supernovae
should account for this wide range of mass.",1409.1120v2
2014-10-14,Simulations of an offshore wind farm using large eddy simulation and a torque-controlled actuator disc model,"We present here a computational fluid dynamics (CFD) simulation of Lillgrund
offshore wind farm, which is located in the Oresund Strait between Sweden and
Denmark. The simulation combines a dynamic representation of wind turbines
embedded within a Large-Eddy Simulation CFD solver, and uses hr-adaptive
meshing to increase or decrease mesh resolution where required. This allows the
resolution of both large scale flow structures around the wind farm, and local
flow conditions at individual turbines; consequently, the response of each
turbine to local conditions can be modelled, as well as the resulting evolution
of the turbine wakes. This paper provides a detailed description of the turbine
model which simulates interactions between the wind, turbine rotors, and
turbine generators by calculating the forces on the rotor, the body forces on
the air, and instantaneous power output. This model was used to investigate a
selection of key wind speeds and directions, investigating cases where a row of
turbines would be aligned with the wind or at specific angles to the wind.
Results shown include presentations of the spin-up of turbines, the observation
of eddies moving through the turbine array, meandering turbine wakes, and an
extensive wind farm wake several kilometres in length. The key measurement
available for cross-validation with operational wind farm data is the power
output from the individual turbines, where the effect of unsteady turbine wakes
on the performance of downstream turbines was a point of interest. The results
from simulations were compared to performance measurements from the real wind
farm to provide a firm quantitative validation of this methodology. Having
achieved good agreement between the model and actual wind farm measurements,
the potential of the methodology to provide a tool for further investigations
of engineering and atmospheric science problems is outlined.",1410.3650v3
2015-01-28,Rotation of Giant Stars,"The internal rotation of post-main sequence stars is investigated, in
response to the convective pumping of angular momentum toward the stellar core,
combined with a tight magnetic coupling between core and envelope. The spin
evolution is calculated using model stars of initial mass 1, 1.5 and
$5\,M_\odot$, taking into account mass loss on the giant branches. We also
include the deposition of orbital angular momentum from a sub-stellar
companion, as influenced by tidal drag along with the excitation of orbital
eccentricity by a fluctuating gravitational quadrupole moment. A range of
angular velocity profiles $\Omega(r)$ is considered in the envelope, extending
from solid rotation to constant specific angular momentum. We focus on the back
reaction of the Coriolis force, and the threshold for dynamo action in the
inner envelope. Quantitative agreement with measurements of core rotation in
subgiants and post-He core flash stars by Kepler is obtained with a two-layer
angular velocity profile: uniform specific angular momentum where the Coriolis
parameter ${\rm Co} \equiv \Omega \tau_{\rm con} \lesssim 1$ (here $\tau_{\rm
con}$ is the convective time); and $\Omega(r) \propto r^{-1}$ where ${\rm Co}
\gtrsim 1$. The inner profile is interpreted in terms of a balance between the
Coriolis force and angular pressure gradients driven by radially extended
convective plumes. Inward angular momentum pumping reduces the surface rotation
of subgiants, and the need for a rejuvenated magnetic wind torque. The
co-evolution of internal magnetic fields and rotation is considered in Kissin &
Thompson, along with the breaking of the rotational coupling between core and
envelope due to heavy mass loss.",1501.07217v3
2015-02-27,Blowing Magnetic Skyrmion Bubbles,"Soap bubbles form when blowing air through a suspended thin film of soapy
water and this phenomenon entertains children and adults alike. The formation
of soap bubbles from thin films is accompanied by topological transitions, and
thus the natural question arises whether this concept is applicable to the
generation of other topological states. Here we show how a magnetic topological
structure, namely a skyrmion bubble, can be generated in a solid state system
in a similar manner. Beyond enabling the investigation of complex
surface-tension driven dynamics in a novel physical system, this observation
has also practical implications, since the topological charge of magnetic
skyrmions has been envisioned as an information carrier for new data processing
technologies. A main goal towards this end is the experimental creation and
manipulation of individual mobile skyrmions at room temperature. By utilizing
an inhomogeneous in-plane current in a system with broken inversion asymmetry,
we experimentally blow magnetic skyrmion bubbles through a geometrical
constriction. The presence of a spatially divergent spin-orbit torque gives
rise to instabilities of the magnetic domain structures that are reminiscent of
Rayleigh-Plateau instabilities in fluid flows. Experimentally we can determine
the electric current versus magnetic field phase diagram for skyrmion formation
and we reveal the efficient manipulation of these dynamically created
skyrmions, including depinning and motion. The demonstrated current-driven
transformation from stripe domains to magnetic skyrmion bubbles could provide
additional avenues for implementing skyrmion-based spintronics.",1502.08028v1
2015-04-22,Model-Based Cross-Correlation Search for Gravitational Waves from Scorpius X-1,"We consider the cross-correlation search for periodic GWs and its potential
application to the LMXB Sco X-1. This method coherently combines data from
different detectors at the same time, as well as different times from the same
or different detectors. By adjusting the maximum time offset between a pair of
data segments to be coherently combined, one can tune the method to trade off
sensitivity and computing costs. In particular, the detectable signal amplitude
scales as the inverse fourth root of this coherence time. The improvement in
amplitude sensitivity for a search with a coherence time of 1hr, compared with
a directed stochastic background search with 0.25Hz wide bins is about a factor
of 5.4. We show that a search of 1yr of data from Advanced LIGO and Advanced
Virgo with a coherence time of 1hr would be able to detect GWs from Sco X-1 at
the level predicted by torque balance over a range of signal frequencies from
30-300Hz; if the coherence time could be increased to 10hr, the range would be
20-500Hz. In addition, we consider several technical aspects of the
cross-correlation method: We quantify the effects of spectral leakage and show
that nearly rectangular windows still lead to the most sensitive search. We
produce an explicit parameter-space metric for the cross-correlation search in
general and as applied to a neutron star in a circular binary system. We
consider the effects of using a signal template averaged over unknown amplitude
parameters: the search is sensitive to a combination of the intrinsic signal
amplitude and the inclination of the neutron star rotation axis, and the peak
of the expected detection statistic is systematically offset from the true
signal parameters. Finally, we describe the potential loss of SNR due to
unmodelled effects such as signal phase acceleration within the Fourier
transform timescale and gradual evolution of the spin frequency.",1504.05890v2
2016-07-15,Solving the stochastic Landau-Lifshitz-Gilbert-Slonczewski equation for monodomain nanomagnets : A survey and analysis of numerical techniques,"The stochastic Landau-Lifshitz-Gilbert-Slonczewski (s-LLGS) equation is
widely used to study the temporal evolution of the macrospin subject to spin
torque and thermal noise. The numerical simulation of the s-LLGS equation
requires an appropriate choice of stochastic calculus and numerical integration
scheme. In this paper, we comprehensively evaluate the accuracy and complexity
of various numerical techniques to solve the s-LLGS equation. We focus on
implicit midpoint, Heun, and Euler-Heun methods that converge to the
Stratonovich solution of the s-LLGS equation. By performing numerical tests for
both strong (path-wise) and weak (statistical) convergence, we quantify the
accuracy of various numerical schemes used to solve the s-LLGS equation. We
demonstrate a new method intended to solve Stochastic Differential Equations
(SDEs) with small noise (RK4-Heun), and test its capability to handle the
s-LLGS equation. We also discuss the circuit implementation of nanomagnets for
large-scale SPICE-based simulations. We evaluate the efficacy of SPICE in
handling the stochastic dynamics of the multiplicative noise in the s-LLGS
equation. Numerical schemes such as Euler and Gear, typically used by
SPICE-based circuit simulators do not yield the expected outcome when solving
the Stratonovich s-LLGS equation. While the trapezoidal method in SPICE does
solve for the Stratonovich solution, its accuracy is limited by the minimum
time step of integration in SPICE. We implement the s-LLGS equation in both its
cartesian and spherical coordinates form in SPICE and compare the stability and
accuracy of the two implementations. The results in this paper will serve as
guidelines for researchers to understand the tradeoffs between accuracy and
complexity of various numerical methods and the choice of appropriate calculus
to solve the s-LLGS equation.",1607.04596v4
2017-08-07,Motion of a rod pushed at one point in a weightless environment in space,"We analyze the motion of a rod floating in a weightless environment in space
when a force is applied at some point on the rod in a direction perpendicular
to its length. If the force applied is at the centre of mass, then the rod gets
a linear motion perpendicular to its length. However, if the same force is
applied at a point other than the centre of mass, say, near one end of the rod,
thereby giving rise to a torque, then there will also be a rotation of the rod
about its centre of mass, in addition to the motion of the centre of mass
itself. If the force applied is for a very short duration, but imparting
nevertheless a finite impulse, like in a sudden (quick) hit at one end of the
rod, then the centre of mass will move with a constant linear speed and
superimposed on it will be a rotation of the rod with constant angular speed
about the centre of mass. However, if force is applied continuously, say by
strapping a tiny rocket at one end of the rod, then the rod will spin faster
and faster about the centre of mass, with angular speed increasing linearly
with time. As the direction of the applied force, as seen by an external
(inertial) observer, will be changing continuously with the rotation of the
rod, the acceleration of the centre of mass would also be not in one fixed
direction. However, it turns out that the locus of the velocity vector of the
centre of mass will describe a Cornu spiral, with the velocity vector reaching
a final constant value with time. The mean motion of the centre of mass will be
in a straight line, with superposed initial oscillations that soon die down.",1708.05062v3
2017-10-31,"The Sleeping Monster: NuSTAR observations of SGR 1806-20, 11 years after the Giant Flare","We report the analysis of 5 NuSTAR observations of SGR 1806-20 spread over a
year from April 2015 to April 2016, more than 11 years following its Giant
Flare (GF) of 2004. The source spin frequency during the NuSTAR observations
follows a linear trend with a frequency derivative
$\dot{\nu}=(-1.25\pm0.03)\times10^{-12}$ Hz s$^{-1}$, implying a surface dipole
equatorial magnetic field $B\approx7.7\times10^{14}$ G. Thus, SGR 1806-20 has
finally returned to its historical minimum torque level measured between 1993
and 1998. The source showed strong timing noise for at least 12 years starting
in 2000, with $\dot{\nu}$ increasing one order of magnitude between 2005 and
2011, following its 2004 major bursting episode and GF. SGR 1806-20 has not
shown strong transient activity since 2009 and we do not find short bursts in
the NuSTAR data. The pulse profile is complex with a pulsed fraction of
$\sim8\%$ with no indication of energy dependence. The NuSTAR spectra are well
fit with an absorbed blackbody, $kT=0.62\pm0.06$ keV, plus a power-law,
$\Gamma=1.33\pm0.03$. We find no evidence for variability among the 5
observations, indicating that SGR 1806-20 has reached a persistent and
potentially its quiescent X-ray flux level after its 2004 major bursting
episode. Extrapolating the NuSTAR model to lower energies, we find that the
0.5-10 keV flux decay follows an exponential form with a characteristic
timescale $\tau=543\pm75$ days. Interestingly, the NuSTAR flux in this energy
range is a factor of $\sim2$ weaker than the long-term average measured between
1993 and 2003, a behavior also exhibited in SGR $1900+14$. We discuss our
findings in the context of the magnetar model.",1711.00034v2
2017-11-16,"YORP and Yarkovsky effects in asteroids (1685) Toro, (2100) Ra-Shalom, (3103) Eger, and (161989) Cacus","The rotation states of small asteroids are affected by a net torque arising
from an anisotropic sunlight reflection and thermal radiation from the
asteroids' surfaces. On long timescales, this so-called YORP effect can change
asteroid spin directions and their rotation periods. We analyzed lightcurves of
four selected near-Earth asteroids with the aim of detecting secular changes in
their rotation rates that are caused by YORP. We use the lightcurve inversion
method to model the observed lightcurves and include the change in the rotation
rate $\mathrm{d} \omega / \mathrm{d} t$ as a free parameter of optimization. We
collected more than 70 new lightcurves. For asteroids Toro and Cacus, we used
thermal infrared data from the WISE spacecraft and estimated their size and
thermal inertia. We also used the currently available optical and radar
astrometry of Toro, Ra-Shalom, and Cacus to infer the Yarkovsky effect. We
detected a YORP acceleration of $\mathrm{d}\omega / \mathrm{d} t = (1.9 \pm
0.3) \times 10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$ for asteroid Cacus. For
Toro, we have a tentative ($2\sigma$) detection of YORP from a significant
improvement of the lightcurve fit for a nonzero value of $\mathrm{d}\omega /
\mathrm{d} t = 3.0 \times 10^{-9}\,\mathrm{rad}\,\mathrm{d}^{-2}$. For asteroid
Eger, we confirmed the previously published YORP detection with more data and
updated the YORP value to $(1.1 \pm 0.5) \times
10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$. We also updated the shape model of
asteroid Ra-Shalom and put an upper limit for the change of the rotation rate
to $|\mathrm{d}\omega / \mathrm{d} t| \lesssim 1.5 \times
10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$. Ra-Shalom has a greater than $3\sigma$
Yarkovsky detection with a theoretical value consistent with observations
assuming its size and/or density is slightly larger than the nominally expected
values.",1711.05987v1
2019-03-12,On the Anomalous Acceleration of 1I/2017 U1 `Oumuamua,"We show that the $P\sim8\,{\rm h}$ photometric period and the astrometrically
measured $A_{\rm ng}\sim2.5\times10^{-4}\,{\rm cm\,s^{-2}}$ non-gravitational
acceleration (at $r\sim1.4\,{\rm AU}$) of the interstellar object 1I/2017
(`Oumuamua) can be explained by a nozzle-like venting of volatiles whose
activity migrated to track the sub-solar location on the object's surface.
Adopting the assumption that `Oumuamua was an elongated $a\times b \times c$
ellipsoid, this model produces a pendulum-like rotation of the body and implies
a long semi-axis $a\sim 5A_{\rm ng}P^2/4\pi^2 \sim 260\,{\rm m}$. This scale
agrees with the independent estimates of `Oumuamua's size that stem from its
measured brightness, assuming an albedo of $p\sim0.1$, appropriate to ices that
have undergone long-duration exposure to the interstellar cosmic ray flux.
Using ray-tracing, we generate light curves for ellipsoidal bodies that are
subject to both physically consistent sub-solar torques and to the time-varying
geometry of the Sun-Earth-`Oumuamua configuration. Our synthetic light curves
display variations from chaotic tumbling and changing cross-sectional
illumination that are consistent with the observations, while avoiding
significant secular changes in the photometric periodicity. If our model is
correct, `Oumuamua experienced mass loss that wasted $\sim 10\%$ of its total
mass during the $\sim 100\,{\rm d}$ span of its encounter with the inner Solar
System and had an icy composition with a very low $[{\rm C}/{\rm O}]\lesssim
0.003$. Our interpretation of `Oumuamua's behavior is consistent with the
hypothesis that it was ejected from either the outer regions of a planetesimal
disk after an encounter with an embedded $M_{\rm p} \sim M_{\rm Nep}$ planet or
from an exo-Oort cloud.",1903.04723v1
2019-04-15,Episodically Active Asteroid 6478 Gault,"We present imaging and spectroscopic observations of 6478 Gault, a 6 km
diameter inner main-belt asteroid currently exhibiting strong, comet-like
characteristics. Three distinct tails indicate that ultra-slow dust (ejection
speed 0.15+/-0.05 m/s) was emitted from Gault in separate episodes beginning UT
2018 October 28+/-5 (Tail A), UT 2018 December 31+/-5 (Tail B), and UT 2019
February 10+/-7, with durations of 10 to 20 days. With a mean particle radius
100 micron, the estimated masses of the tails are M_A = 2e7 kg, M_B = 3e6 kg
and M_C = 3e5 kg, respectively, and the mass loss rates from the nucleus are 10
to 20 kg/s for Tail A, 2 to 3 kg/s for Tail B and about 0.2 kg/s for Tail C. In
its optical colors Gault is more similar to C-type asteroids than to S-types,
even though the latter are numerically dominant in the inner asteroid belt. A
spectroscopic upper limit to the production of gas is set at 1 kg/s. Discrete
emission in three protracted episodes effectively rules out an impact origin
for the observed activity. Sublimation driven activity is unlikely given the
inner belt orbit and the absence of detectable gas. In any case, sublimation
would not easily account for the observed multiple ejections. The closest
similarity is between Gault and active asteroid 311P/(2013 P5), an object
showing repeated but aperiodic ejections of dust over a 9 month period. While
Gault is 10 times larger than 311P/(2013 P5), and the spin-up time to radiation
torques is 100 times longer, its properties are likewise most consistent with
episodic emission from a body rotating near breakup.",1904.07100v2
2019-12-09,The Young Planet DS Tuc Ab has a Low Obliquity,"The abundance of short-period planetary systems with high orbital obliquities
relative to the spin of their host stars is often taken as evidence that
scattering processes play important roles in the formation and evolution of
these systems. More recent studies have suggested that wide binary companions
can tilt protoplanetary disks, inducing a high stellar obliquity that form
through smooth processes like disk migration. DS Tuc Ab, a transiting planet
with an 8.138 day period in the 40 Myr Tucana-Horologium association, likely
orbits in the same plane as its now-dissipated protoplanetary disk, enabling us
to test these theories of disk physics. Here, we report on Rossiter-McLaughlin
observations of one transit of DS Tuc Ab with the Planet Finder Spectrograph on
the Magellan Clay Telescope at Las Campanas Observatory. We confirm the
previously detected planet by modeling the planet transit and stellar activity
signals simultaneously. We test multiple models to describe the stellar
activity-induced radial velocity variations over the night of the transit,
finding the obliquity to be low: $\lambda = 12 \pm 13$ degrees, suggesting that
this planet likely formed through smooth disk processes and its protoplanetary
disk was not significantly torqued by DS Tuc B. The specific stellar activity
model chosen affects the results at the $\approx 5$ degree level. This is the
youngest planet to be observed using this technique; we provide a discussion on
best practices to accurately measure the observed signal of similar young
planets.",1912.03794v2
2020-11-20,Blandford-Znajek jets in galaxy formation simulations: method and implementation,"Jets launched by active galactic nuclei (AGN) are believed to play a
significant role in shaping the properties of galaxies and provide an
energetically viable mechanism through which galaxies can become quenched. Here
we present a novel AGN feedback model, which we have incorporated into the
AREPO code, that evolves the black hole mass and spin as the accretion flow
proceeds through a thin $\alpha$-disc which we self-consistently couple to a
Blandford-Znajek jet. We apply our model to the central region of a typical
radio-loud Seyfert galaxy embedded in a hot circumgalactic medium (CGM). We
find that jets launched into high pressure environments thermalise efficiently
due to the formation of recollimation shocks and the vigorous instabilities
that these shocks excite increase the efficiency of the mixing of CGM and jet
material. The beams of more overpressured jets, however, are not as readily
disrupted by instabilities so the majority of the momentum flux at the jet base
is retained out to the head, where the jet terminates in a reverse shock. All
jets entrain a significant amount of cold circumnuclear disc material which,
while energetically insignificant, dominates the lobe mass together with the
hot, entrained CGM material. The jet power evolves significantly due to
effective self-regulation by the black hole, fed by secularly-driven,
intermittent mass flows. The direction of jets launched directly into the
circumnuclear disc changes considerably due to effective Bardeen-Petterson
torquing. Interestingly, these jets obliterate the innermost regions of the
disc and drive large-scale, multi-phase, turbulent, bipolar outflows.",2011.10580v2
2021-01-04,Stellar Rotation in the Gaia Era: Revised Open Clusters Sequences,"The period versus mass diagrams (i.e., rotational sequences) of open clusters
provide crucial constraints for angular momentum evolution studies. However,
their memberships are often heavily contaminated by field stars, which could
potentially bias the interpretations. In this paper, we use data from Gaia DR2
to re-assess the memberships of seven open clusters with ground- and
space-based rotational data, and present an updated view of stellar rotation as
a function of mass and age. We use the Gaia astrometry to identify the cluster
members in phase-space, and the photometry to derive revised ages and place the
stars on a consistent mass scale. Applying our membership analysis to the
rotational sequences reveals that: 1) the contamination in clusters observed
from the ground can reach up to $\sim 35\%$; 2) the overall fraction of
rotational outliers decreases substantially when the field contaminants are
removed, but some outliers persist; 3) there is a sharp upper edge in the
rotation periods at young ages; 4) at young ages, stars in the 1.0-0.6 Msun
range inhabit a global maximum of rotation periods, potentially providing an
optimal window for habitable planets. Additionally, we see clear evidence for a
strongly mass-dependent spin-down process. In the regime where rapid rotators
are leaving the saturated domain, the rotational distributions broaden (in
contradiction with popular models), which we interpret as evidence that the
torque must be lower for rapid rotators than for intermediate ones. The cleaned
rotational sequences from ground-based observations can be as constraining as
those obtained from space.",2101.01183v2
2021-02-19,Pseudo-synchronous solutions for dissipative non-autonomous systems,"In the framework of KAM theory, the persistence of invariant tori in
quasi-integrable systems is proved by assuming a non-resonance condition on the
frequencies, such as the standard Diophantine condition or the milder Bryuno
condition. In the presence of dissipation, most of the quasi-periodic solutions
disappear and one expects, at most, only a few of them to survive together with
the periodic attractors. However, to prove that a quasi-periodic solution
really exists, usually one assumes that the frequencies still satisfy a
Diophantine condition and, furthermore, that some external parameters of the
system are suitably tuned with them. In this paper we consider a class of
systems on the one-dimensional torus, subject to a periodic perturbation and in
the presence of dissipation, and show that, however small the dissipation, if
the perturbation is a trigonometric polynomial in the angles and the
unperturbed frequencies satisfy a non-resonance condition of finite order,
depending on the size of the dissipation, then a quasi-periodic solution exists
with slightly perturbed frequencies provided the size of the perturbation is
small enough. If on the one hand the maximal size of the perturbation is not
uniform in the degree of the trigonometric polynomial, on the other hand all
but finitely many frequencies are allowed and there is no restriction arising
from the tuning of the external parameters. A physically relevant case, where
the result applies, is the spin-orbit model, which describes the rotation of a
satellite around its own axis, while revolving on a Keplerian orbit around a
planet, in the case in which the dissipation is taken into account through the
MacDonald torque.",2102.09868v1
2021-08-02,Magnetic and Rotational Evolution of $ρ$ CrB from Asteroseismology with TESS,"During the first half of main-sequence lifetimes, the evolution of rotation
and magnetic activity in solar-type stars appears to be strongly coupled.
Recent observations suggest that rotation rates evolve much more slowly beyond
middle-age, while stellar activity continues to decline. We aim to characterize
this mid-life transition by combining archival stellar activity data from the
Mount Wilson Observatory with asteroseismology from the Transiting Exoplanet
Survey Satellite (TESS). For two stars on opposite sides of the transition (88
Leo and $\rho$ CrB), we independently assess the mean activity levels and
rotation periods previously reported in the literature. For the less active
star ($\rho$ CrB), we detect solar-like oscillations from TESS photometry, and
we obtain precise stellar properties from asteroseismic modeling. We derive
updated X-ray luminosities for both stars to estimate their mass-loss rates,
and we use previously published constraints on magnetic morphology to model the
evolutionary change in magnetic braking torque. We then attempt to match the
observations with rotational evolution models, assuming either standard
spin-down or weakened magnetic braking. We conclude that the asteroseismic age
of $\rho$ CrB is consistent with the expected evolution of its mean activity
level, and that weakened braking models can more readily explain its relatively
fast rotation rate. Future spectropolarimetric observations across a range of
spectral types promise to further characterize the shift in magnetic morphology
that apparently drives this mid-life transition in solar-type stars.",2108.01088v2
2021-08-30,Detection of the YORP Effect on the contact-binary (68346) 2001 KZ66 from combined radar and optical observations,"The YORP effect is a small thermal-radiation torque experienced by small
asteroids, and is considered to be crucial in their physical and dynamical
evolution. It is important to understand this effect by providing measurements
of YORP for a range of asteroid types to facilitate the development of a
theoretical framework. We are conducting a long-term observational study on a
selection of near-Earth asteroids to support this. We focus here on (68346)
2001 KZ66, for which we obtained both optical and radar observations spanning a
decade. This allowed us to perform a comprehensive analysis of the asteroid's
rotational evolution. Furthermore, radar observations from the Arecibo
Observatory enabled us to generate a detailed shape model. We determined that
(68346) is a retrograde rotator with its pole near the southern ecliptic pole,
within a $ 15^\circ$ radius of longitude $ 170^\circ$ and latitude $
-85^\circ$. By combining our radar-derived shape model with the optical light
curves we developed a refined solution to fit all available data, which
required a YORP strength of $ (8.43\pm0.69)\times10^{-8} \rm~rad ~day^{-2} $.
(68346) has a distinct bifurcated shape comprising a large ellipsoidal
component joined by a sharp neckline to a smaller non-ellipsoidal component.
This object likely formed from either the gentle merging of a binary system, or
from the deformation of a rubble pile due to YORP spin-up. The shape exists in
a stable configuration close to its minimum in topographic variation, where
regolith is unlikely to migrate from areas of higher potential.",2108.13494v1
2021-11-22,Shape-Dependent Multi-Weight Magnetic Artificial Synapses for Neuromorphic Computing,"In neuromorphic computing, artificial synapses provide a multi-weight
conductance state that is set based on inputs from neurons, analogous to the
brain. Additional properties of the synapse beyond multiple weights can be
needed, and can depend on the application, requiring the need for generating
different synapse behaviors from the same materials. Here, we measure
artificial synapses based on magnetic materials that use a magnetic tunnel
junction and a magnetic domain wall. By fabricating lithographic notches in a
domain wall track underneath a single magnetic tunnel junction, we achieve 4-5
stable resistance states that can be repeatably controlled electrically using
spin orbit torque. We analyze the effect of geometry on the synapse behavior,
showing that a trapezoidal device has asymmetric weight updates with high
controllability, while a straight device has higher stochasticity, but with
stable resistance levels. The device data is input into neuromorphic computing
simulators to show the usefulness of application-specific synaptic functions.
Implementing an artificial neural network applied on streamed Fashion-MNIST
data, we show that the trapezoidal magnetic synapse can be used as a
metaplastic function for efficient online learning. Implementing a
convolutional neural network for CIFAR-100 image recognition, we show that the
straight magnetic synapse achieves near-ideal inference accuracy, due to the
stability of its resistance levels. This work shows multi-weight magnetic
synapses are a feasible technology for neuromorphic computing and provides
design guidelines for emerging artificial synapse technologies.",2111.11516v2
2022-07-21,Adaptive phototaxis of Chlamydomonas and the evolutionary transition to multicellularity in Volvocine green algae,"A fundamental issue in biology is the nature of evolutionary transitions from
unicellular to multicellular organisms. Volvocine algae are models for this
transition, as they span from the unicellular biflagellate Chlamydomonas to
multicellular species of Volvox with up to 50,000 Chlamydomonas-like cells on
the surface of a spherical extracellular matrix. The mechanism of phototaxis in
these species is of particular interest since they lack a nervous system and
intercellular connections; steering is a consequence of the response of
individual cells to light. Studies of Volvox and Gonium, a 16-cell organism
with a plate-like structure, have shown that the flagellar response to changing
illumination of the cellular photosensor is adaptive, with a recovery time
tuned to the rotation period of the colony around its primary axis. Here,
combining high-resolution studies of the flagellar photoresponse with 3D
tracking of freely-swimming cells, we show that such tuning also underlies
phototaxis of Chlamydomonas. A mathematical model is developed based on the
rotations around an axis perpendicular to the flagellar beat plane that occur
through the adaptive response to oscillating light levels as the organism
spins. Exploiting a separation of time scales between the flagellar
photoresponse and phototurning, we develop an equation of motion that
accurately describes the observed photoalignment. In showing that the adaptive
time scale is tuned to the organisms' rotational period across three orders of
magnitude in cell number, our results suggest a unified picture of phototaxis
in green algae in which the asymmetry in torques that produce phototurns arise
from the individual flagella of Chlamydomonas, the flagellated edges of Gonium
and the flagellated hemispheres of Volvox.",2207.10405v1
2022-10-03,The SAMI Galaxy Survey: Physical drivers of stellar-gas kinematic misalignments in the nearby Universe,"Misalignments between the rotation axis of stars and gas are an indication of
external processes shaping galaxies throughout their evolution. Using
observations of 3068 galaxies from the SAMI Galaxy Survey, we compute global
kinematic position angles for 1445 objects with reliable kinematics and
identify 169 (12%) galaxies which show stellar-gas misalignments. Kinematically
decoupled features are more prevalent in early-type/passive galaxies compared
to late-type/star-forming systems. Star formation is the main source of gas
ionisation in only 22% of misaligned galaxies; 17% are Seyfert objects, while
61% show Low-Ionisation Nuclear Emission-line Region features. We identify the
most probable physical cause of the kinematic decoupling and find that, while
accretion-driven cases are dominant, for up to 8% of our sample, the
misalignment may be tracing outflowing gas. When considering only misalignments
driven by accretion, the acquired gas is feeding active star formation in only
$\sim$1/4 of cases. As a population, misaligned galaxies have higher S\'ersic
indices and lower stellar spin & specific star formation rates than
appropriately matched samples of aligned systems. These results suggest that
both morphology and star formation/gas content are significantly correlated
with the prevalence and timescales of misalignments. Specifically, torques on
misaligned gas discs are smaller for more centrally concentrated galaxies,
while the newly accreted gas feels lower viscous drag forces in more gas-poor
objects. Marginal evidence of star formation not being correlated with
misalignment likelihood for late-type galaxies suggests that such morphologies
in the nearby Universe might be the result of preferentially aligned accretion
at higher redshifts.",2210.01147v1
2022-10-04,Domain Wall Propagation and Pinning Induced by Current Pulses in Cylindrical Modulated Nanowires,"The future developments of three-dimensional magnetic nanotechnology require
the control of domain wall dynamics by means of current pulses. While this has
been extensively studied in planar magnetic strips (planar nanowires), few
reports exist in cylindrical geometry, where Bloch point domain walls are
expected to have intriguing properties. Here we report this investigation in
cylindrical magnetic Ni nanowires with geometrical notches. Experimental work
based on synchrotron X-ray magnetic circular dichroism (XMCD) combined with
photoemission electron microscopy (PEEM) indicates that large current densities
induce domain wall nucleation while smaller currents move domain walls
preferably against the current direction. In the region where no pinning
centers are present we found domain wall velocity of about 1 km/s. The domain
wall motion along current was also detected in the vicinity of the notch
region. Pinning of domain walls has been observed not only at geometrical
constrictions but also outside of them. Thermal modelling indicates that large
current densities temporarily raise the temperature in the nanowire above the
Curie temperature leading to nucleation of domain walls during the system
cooling. Micromagnetic modelling with spin-torque effect shows that for
intermediate current densities Bloch point domain walls with chirality parallel
to the Oersted field propagate antiparallel to the current direction. In other
cases, domain walls can be bounced from the notches and/or get pinned outside
their positions. We thus find that current is not only responsible for the
domain wall propagation but is also a source of pinning due to the Oersted
field action.",2210.01480v1
2023-01-26,Neuromorphic spintronics accelerated by an unconventional data-driven Thiele equation approach,"We design a neural network based on a single spin-torque vortex
nano-oscillator (STVO) multiplexed in time. The behavior of the STVO is
simulated with an improved ultra-fast and quantitative model based on the
Thiele equation approach. Different mathematical and numerical adaptations are
brought to the model in order to increase the accuracy and the speed of the
simulations. We demonstrate the high added value and adaptability of such a
neural network through the resolution of three standard machine learning tasks
in the framework of reservoir computing. The first one is a task of waveform
(sines and squares) classification. We show the ability of the system to
effectively classify waveforms with high accuracy and low root-mean-square
error thanks to the intrinsic short-term memory of the device. Given the high
throughput of the simulations, two innovative parametric studies on the
intensity of the input signal and the level of noise in the system are
performed to demonstrate the value of our new models. The efficiency of our
system is then tested during a speech recognition task on the TI-46 dataset and
shows the agreement between the new models and the corresponding experimental
measurements. Finally, we use our STVO-based neural network to perform image
recognition on the MNIST dataset. State-of-the-art performances are
demonstrated, and the interest of using the STVO dynamics as an activation
function is highlighted. These results support and facilitate the future
development of neuromorphic STVO-based hardware for energy-efficient machine
learning.",2301.11025v2
2023-01-30,The rotational disruption of porous dust aggregates from ab-initio kinematic calculations,"Context: The sizes of dust in the interstellar medium follows a distribution
where most of the dust mass is in smaller grains. However, the re-distribution
from larger grains towards smaller sizes especially by means of rotational
disruption is poorly understood. Aims: We aim to study the dynamics of porous
grain aggregates under accelerated ration. Especially, we determine the
deformation of the grains and the maximal angular velocity up to the rotational
disruption event by caused by centrifugal forces. Methods: We pre-calculate
aggregates my means of ballistic aggregation analogous to the interstellar dust
as input for subsequent numerical simulations. In detail, we perform
three-dimensional N-body simulations mimicking the radiative torque spin-up
process up to the point where the grain aggregates become rotationally
disrupted. Results: Our simulations results are in agreement with theoretical
models predicting a characteristic angular velocity $\omega_{\mathrm{disr}}$ of
the order of ${ 10^8 - 10^9\ \mathrm{rad\ s^{-1}} }$, where grains become
rotationally disrupted. In contrast to theoretical predictions, we show that
for large porous aggregates ($< 300\ \mathrm{nm}$) $\omega_{\mathrm{disr}}$
reaches a lower asymptotic value. Hence, such grains can withstand an
accelerated ration more efficiently up to a factor of 10 because the
displacement of mass by centrifugal forces and the subsequent mechanical
deformation supports the buildup of new connections within the aggregate.
Furthermore, we report that the rapid rotation of grains deforms an ensemble
with initially 50:50 prolate and oblate shapes, respectively, preferentially
into oblate shapes. Finally, we present a best fit formula to predict the
average rotational disruption of an ensemble of porous dust aggregates
dependent on internal grain structure, total number of monomers, and applied
material properties.",2301.12889v1
2023-09-26,A Global 3-D Simulation of Magnetospheric Accretion: I. Magnetically Disrupted Disks and Surface Accretion,"We present a 3-D ideal MHD simulation of magnetospheric accretion onto a
non-rotating star. The accretion process unfolds with intricate 3-D structures
driven by various mechanisms. First, the disc develops filaments at the
magnetospheric truncation radius ($R_T$) due to magnetic interchange
instability. These filaments penetrate deep into the magnetosphere, form
multiple accretion columns, and eventually impact the star at $\sim$30$^o$ from
the poles at nearly the free-fall speed. Over 50% (90%) of accretion occurs on
just 5% (20%) of the stellar surface. Second, the disc region outside $R_T$
develops large-scale magnetically dominated bubbles, again due to magnetic
interchange instability. These bubbles orbit at a sub-Keplerian speed,
persisting for a few orbits while leading to asymmetric mass ejection. The disc
outflow is overall weak because of mostly closed field lines. Third,
magnetically-supported surface accretion regions appear above the disc,
resembling a magnetized disc threaded by net vertical fields, a departure from
traditional magnetospheric accretion models. Stellar fields are efficiently
transported into the disc region due to above instabilities, contrasting with
the ``X-wind'' model. The accretion rate onto the star remains relatively
steady with a 23% standard deviation. The periodogram reveals variability
occurring at around 0.2 times the Keplerian frequency at $R_T$, linked to the
large-scale magnetic bubbles. The ratio of the spin-up torque to
$\dot{M}(GM_*R_T)^{1/2}$ is around 0.8. Finally, after scaling the simulation,
we investigate planet migration in the inner protoplanetary disc. The disc
driven migration is slow in the MHD turbulent disc beyond $R_T$, while
aerodynamic drag plays a significant role in migration within $R_T$.",2309.15318v2
2023-12-28,Chaotic Capture of a Retrograde Moon by Venus and the Reversal of Its Spin,"(Abridged) Planets are surrounded by fractal surfaces (traditionally called
Hill spheres), separating the inner zones of long-term stable orbital motion of
their satellites from the outer space where the gravitational pull from the Sun
takes over. Through this surface, external minor bodies in trajectories loosely
co-orbital to a planet can be stochastically captured by the planet without any
assistance from external perturbative forces, and can become moons chaotically
orbiting the planet for extended periods of time. Using state-of-the-art
orbital integrators, we simulate such capture events for Venus, resulting in
long-term attachment phases by reversing the forward integration of a moon
initially attached to the planet and escaping it after an extended period of
time. Although the probability of a long-term chaotic capture from a single
encounter is generally low, the high density of co-orbital bodies in the
primordial protoplanetary disk makes this outcome possible, if not probable.
The early Venus was surrounded by a dusty gaseous disk of its own, which,
coupled with the tidal dissipation of the kinetic energy in the moon and the
planet, could shrink the initial orbit and stabilize the captured body within
the Hill surface. The tidal torque from the moon, for which we use the
historical name Neith, gradually brakes the prograde rotation of Venus, and
then reverses it, while the orbit continues to decay. Neith eventually reaches
the Roche radius and disintegrates, probably depositing most of its material on
Venus' surface. Our calculations show that surface density values of about 0.06
kg m$^{-2}$ for the debris disk may be sufficient to stabilize the initial
chaotic orbit of Neith and to bring it down within several radii of Venus,
where tidal dissipation becomes more efficient.",2312.17049v1
1999-09-08,Formation of millisecond pulsars. I. Evolution of low-mass X-ray binaries with P > 2 days,"We have performed detailed numerical calculations of the non-conservative
evolution of close binary systems with low-mass (1.0-2.0 M_sun) donor stars and
a 1.3 M_sun accreting neutron star. Rather than using analytical expressions
for simple polytropes, we calculated the thermal response of the donor star to
mass loss, in order to determine the stability and follow the evolution of the
mass transfer. Tidal spin-orbit interactions and Reimers wind mass-loss were
also taken into account. We have re-calculated the correlation between orbital
period and white dwarf mass in wide binary radio pulsar systems. Furthermore,
we find an anti-correlation between orbital period and neutron star mass under
the assumption of the ""isotropic re-emission"" model and compare this result
with observations. We conclude that the accretion efficiency of neutron stars
is rather low and that they eject a substantial fraction of the transferred
material even when accreting at a sub-Eddington level. The mass-transfer rate
is a strongly increasing function of initial orbital period and donor star
mass. For relatively close systems with light donors (P < 10 days and M_2 < 1.3
M_sun) the mass-transfer rate is sub-Eddington, whereas it can be highly
super-Eddington by a factor of 10^4 for wide systems with relatively heavy
donor stars (1.6 - 2.0 M_sun) as a result of their deep convective envelopes.
We briefly discuss the evolution of X-ray binaries with donor stars in excess
of 2 M_sun.
  Based on our calculations we present evidence that PSR J1603-7202 evolved
through a phase with unstable mass transfer from a relatively heavy donor star
and therefore is likely to host a CO white dwarf companion.",9909147v2
2008-03-13,Is irradiation important for the secular evolution of low-mass X-ray binaries?,"It is argued that irradiation in low-mass X-ray binaries (LMXBs) caused by
accretion-generated X-rays can not only change the optical appearance of LMXBs
but also their outburst properties and possibly also their long-term evolution.
Irradiation during an outburst of the outer parts of the accretion disc in a
transient LMXB leads to drastic changes in the outburst properties. As far as
the secular evolution of such systems is concerned, these changes can result in
enhanced loss of mass and angular momentum from the system and, most important,
in neutron star LMXBs in a much less efficient use of the transferred matter to
spin up the neutron star to a ms-pulsar. Irradiation of the donor star can
destabilize mass transfer and lead to irradiation-driven mass transfer cycles,
i.e. to a secular evolution which differs drastically from an evolution in
which irradiation is ignored. It is argued that irradiation-driven mass
transfer cycles cannot occur in systems which are transient because of disc
instabilities, i.e. in particular in long-period LMXBs with a giant donor. It
is furthermore shown that for irradiating either the disc or the donor star,
direct irradiation alone is insufficient. Rather, indirect irradiation via
scattered accretion luminosity must play an important role in transient LMXBs
and is, in fact, necessary to destabilize mass transfer in short-period systems
by irradiating the donor star. Whether and to what extent irradiation in LMXBs
does change their secular evolution depends on a number of unsolved problems
which are briefly discussed at the end of this article.",0803.1970v2
2018-07-30,On quantum separation of variables,"We present a new approach to construct the separate variables basis leading
to the full characterization of the transfer matrix spectrum of quantum
integrable lattice models. The basis is generated by the repeated action of the
transfer matrix itself on a generically chosen state of the Hilbert space. The
fusion relations for the transfer matrix, stemming from the Yang-Baxter algebra
properties, provide the necessary closure relations to define the action of the
transfer matrix on such a basis in terms of elementary local shifts, leading to
a separate transfer matrix spectral problem. Hence our scheme extends to the
quantum case a key feature of Liouville-Arnold classical integrability
framework where the complete set of conserved charges defines both the level
manifold and the flows on it leading to the construction of action-angle
variables. We work in the framework of the quantum inverse scattering method.
As a first example of our approach, we give the construction of such a basis
for models associated to Y(gln) and argue how it extends to their trigonometric
and elliptic versions. Then we show how our general scheme applies concretely
to fundamental models associated to the Y(gl2) and Y(gl3) R-matrices leading to
the full characterization of their spectrum. For Y(gl2) and its trigonometric
deformation a particular case of our method reproduces Sklyanin's construction
of separate variables. For Y(gl3) it gives new results, in particular through
the proper identification of the shifts acting on the separate basis. We stress
that our method also leads to the full characterization of the spectrum of
other known quantum integrable lattice models, including in particular
trigonometric and elliptic spin chains, open chains with general integrable
boundaries, and further higher rank cases that we will describe in forthcoming
publications.",1807.11572v2
2019-03-15,On quantum separation of variables beyond fundamental representations,"We describe the extension, beyond fundamental representations of the
Yang-Baxter algebra, of our new construction of separation of variables bases
for quantum integrable lattice models. The key idea underlying our approach is
to use the commuting conserved charges of the quantum integrable models to
generate bases in which their spectral problem is separated, i.e. in which the
wave functions are factorized in terms of specific solutions of a functional
equation. For the so-called ""non-fundamental"" models we construct two different
types of SoV bases. The first is given from the fundamental quantum Lax
operator having isomorphic auxiliary and quantum spaces and that can be
obtained by fusion of the original quantum Lax operator. The construction
essentially follows the one we used previously for fundamental models and
allows us to derive the simplicity and diagonalizability of the transfer matrix
spectrum. Then, starting from the original quantum Lax operator and using the
full tower of the fused transfer matrices, we introduce a second type of SoV
bases for which the proof of the separation of the transfer matrix spectrum is
naturally derived. We show that, under some special choice, this second type of
SoV bases coincides with the one associated to Sklyanin's approach. Moreover,
we derive the finite difference type (quantum spectral curve) functional
equation and the set of its solutions defining the complete transfer matrix
spectrum. This is explicitly implemented for the integrable quantum models
associated to the higher spin representations of the general quasi-periodic
Y(gl2) Yang-Baxter algebra. Our SoV approach also leads to the construction of
a Q-operator in terms of the fused transfer matrices. Finally, we show that the
Q-operator family can be equivalently used as the family of commuting conserved
charges enabling to construct our SoV bases.",1903.06618v2
2019-08-06,Study of kaon structure using the light-cone quark model,"We investigate the various distributions explaining multi-dimensional
structure of kaon at the level of its constituents ($u$ and $\bar{s}$) using
the light-cone quark model. The overlap form of wavefunctions associated with
the light-cone quark model is adopted for the calculations. The generalized
parton distributions(GPDs)of $u$ and $\bar{s}$ quarks are presented for the
case when the momentum transfer in the longitudinal direction is non-zero. The
dependence of kaon GPDs is studied in terms of variation of quark longitudinal
momentum fraction, momentum transfer in longitudinal direction and total
momentum transfer to the final state of hadron. The transverse impact-parameter
dependent GPDs are also studied by taking the Fourier transformation of general
GPDs. Further, the quantum phase-space distributions; Wigner distributions are
studied for the case of unpolarized, longitudinally-polarized and
transversely-polarized parton in an unpolarized kaon. The Wigner distributions
are analysed in the transverse impact-parameter plane, the transverse momentum
plane and the mixed plane. Further, to get a complete picture of kaon in terms
of its valence quarks, the variation of longitudinal momentum fraction carried
by quark and antiquark in the generalized transverse momentum-dependent parton
distributions (GTMDs) is studied for different values of transverse quark and
antiquark momentum $({\bf k}_\perp)$ as well as for different values of
momentum transferred to the kaon in transverse direction $({\bf
\Delta}_\perp)$. This has been done for zero as well as non-zero skewedness
representing respectively the absence and presence of momentum transfer to the
final state of kaon in longitudinal direction. Furthermore, the possible
spin-orbit correlation for $u$ and $\bar{s}$ in kaon is elaborated in context
of Wigner distributions and GTMDs.",1908.01939v2
1999-11-25,"Magnetized accretion-ejection structures IV. Magnetically-driven jets from resistive, viscous, Keplerian discs","We present steady-state calculations of self-similar magnetized accretion
discs driving cold, adiabatic, non-relativistic jets. For the first time, both
the magnetic torque due to the jets and a turbulent ""viscous"" torque are taken
into account. This latter torque allows a dissipation of the accretion power as
radiation at the disc surfaces, while the former predominantly provides jets
with power.
  The parameter space of these structures has been explored. It is
characterized by four free parameters, namely the disc aspect ratio and three
MHD turbulence parameters, related to the anomalous magnetic diffusivities and
viscosity. It turns out that launching cold jets from thin, dissipative discs
implies anisotropic turbulent dissipation. Jets that asymptotically reach a
high Alfvenic Mach number are only produced by weakly dissipative discs.
  We obtained general analytical relations between disc and jet quantities that
must be fulfilled by any steady-state model of cold jets, launched from a large
radial extension of thin discs. We also show that such discs cannot have a
dominant viscous torque. This is because of the chosen geometry, imposing the
locus of the Alfven surface.
  Some observational consequences of these cold magnetized accretion-ejection
structures are also briefly discussed.",9911471v1
2002-02-22,Geometrically Thin Disk Accreting Into a Black Hole,"A numerical model of a steady state, thin accretion disk with a constant
effective speed of sound is presented. We demonstrate that `zero torque' inner
boundary condition is a reasonable approximation provided that the disk
thickness, including the thickness of the torquing magnetic fields, is small
everywhere. It is likely that this conclusion is correct also for non-steady
disks, as long as the total thickness at the sonic point, H_c, is much smaller
than the radius there, r_c ~ r_{ms}. The very existence of thin disks is not
proved or disproved in this work, but such disks are believed to exist for
moderate accretion rates.
  Within our model there is a small torque at r_{ms}, which may increase disk
luminosity by several percent. An important result of our analysis is that the
physically acceptable steady state solutions in our toy model exist only for
\alpha < 0.14 (100 v_s/c)^{1/3}.
  A significant torque may be applied to a thin disk if there is a large scale
magnetic field, like in a modified Blandford-Znajek mechanism.",0202409v3
1998-11-25,Quantum Oscillations and Overcritical Torque Interaction in Sr2RuO4,"Sr2RuO4 is the only known layered perovskite oxide superconductor without
copper; there is strong evidence for an unconventional (""p-wave"") pairing
mechanism, and it has recently been shown to possess a cylindrical,
""quasi-two-dimensional"" Fermi surface. Using Sr2RuO4 as a test case for the
detection of quantum oscillations with piezoresistive microcantilevers, the
piezolever torque magnetometry technique was successfully implemented on a
dilution refrigerator. It was possible to reproduce the quantum-oscillatory
magnetization data on all three Fermi surface sheets, in a crystal of microgram
mass. Moreover, an absolute estimate of the amplitude of the oscillation is
provided. We also investigated the phenomenon of torque interaction which
distorts the magnetization signal and introduces harmonics and sidebands to the
dHvA spectrum. As the torque interaction effect grows in strength,
overcriticality is shown to lead to discrete magnetization jumps and to a
near-asymptotically damped ""sproing"" effect.",9811364v1
1999-12-03,Torque magnetometry on single-crystal high temperature superconductors near the critical temperature: a scaling approach,"Angular-dependent magnetic torque measurements performed near the critical
temperature on single crystals of HgBa_{2}CuO_{4+y}, La_{2-x}Sr{x}CuO_{4}, and
YBa_{2}Cu_{3}O_{6.93} are scaled, following the 3D XY model, in order to
determine the scaling function dG^{\pm}(z)/dz which describes the universal
critical properties near T_{c}. A systematic shift of the scaling function with
increasing effective mass anisotropy \gamma = (m_{ab}*/m_{c}*)^{1/2} is
observed, which may be understood in terms of a 3D-2D crossover. Further
evidence for a 3D-2D crossover is found from temperature-dependent torque
measurements carried out in different magnetic fields at different field
orientations \delta, which show a quasi 2D ""crossing region'' (M*,T*). The
occurrence of this ""crossing phenomenon'' is explained in a phenomenological
way from the weak z dependence of the scaling function around a value z = z*.
The ""crossing'' temperature T* is found to be angular-dependent. Torque
measurements above T_{c} reveal that fluctuations are strongly enhanced in the
underdoped regime where the anisotropy is large, whereas they are less
important in the overdoped regime.",9912052v1
2004-08-25,"Indeterminacy, Memory, and Motion in a Simple Granular Packing","We apply two theoretical and two numerical methods to the problem of a disk
placed in a groove and subjected to gravity and a torque. Methods assuming
rigid particles are indeterminate -- certain combinations of forces cannot be
calculated, but only constrained by inequalities. In methods assuming
deformable particles, these combinations of forces are determined by the
history of the packing. Thus indeterminacy in rigid particles becomes memory in
deformable ones. Furthermore, the torque needed to rotate the particle was
calculated. Two different paths to motion were identified. In the first,
contact forces change slowly, and the indeterminacy decreases continuously to
zero, and vanishes precisely at the onset of motion, and the torque needed to
rotate the disk is independent of method and packing history. In the second
way, this torque depends on method and on the history of the packing, and the
forces jump discontinuously at the onset of motion.",0408534v1
2005-02-11,Coupling between static friction force and torque for a tripod,"If a body is resting on a flat surface, the maximal static friction force
before motion sets in is reduced if an external torque is also applied. The
coupling between the static friction force and static friction torque is
nontrivial as our studies for a tripod lying on horizontal flat surface show.
In this article we report on a series of experiments we performed on a tripod
and compare these with analytical and numerical solutions. It turns out that
the coupling between force and torque reveals information about the microscopic
properties at the onset to sliding.",0502293v1
2007-02-14,Balancing torques in membrane-mediated interactions: Exact results and numerical illustrations,"Torques on interfaces can be described by a divergence-free tensor which is
fully encoded in the geometry. This tensor consists of two terms, one
originating in the couple of the stress, the other capturing an intrinsic
contribution due to curvature. In analogy to the description of forces in terms
of a stress tensor, the torque on a particle can be expressed as a line
integral along any contour surrounding the particle. Interactions between
particles mediated by a fluid membrane are studied within this framework. In
particular, torque balance places a strong constraint on the shape of the
membrane. Symmetric two-particle configurations admit simple analytical
expressions which are valid in the fully nonlinear regime; in particular, the
problem may be solved exactly in the case of two membrane-bound parallel
cylinders. This apparently simple system provides some flavor of the remarkably
subtle nonlinear behavior associated with membrane-mediated interactions.",0702340v2
2000-09-30,Torque Ripple Minimization in a Switched Reluctance Drive by Neuro-Fuzzy Compensation,"Simple power electronic drive circuit and fault tolerance of converter are
specific advantages of SRM drives, but excessive torque ripple has limited its
use to special applications. It is well known that controlling the current
shape adequately can minimize the torque ripple. This paper presents a new
method for shaping the motor currents to minimize the torque ripple, using a
neuro-fuzzy compensator. In the proposed method, a compensating signal is added
to the output of a PI controller, in a current-regulated speed control loop.
Numerical results are presented in this paper, with an analysis of the effects
of changing the form of the membership function of the neuro-fuzzy compensator.",0010003v1
2003-08-28,Optical measurement of microscopic torques,"In recent years there has been an explosive development of interest in the
measurement of forces at the microscopic level, such as within living cells, as
well as the properties of fluids and suspensions on this scale, using optically
trapped particles as probes. The next step would be to measure torques and
associated rotational motion. This would allow measurement on very small scales
since no translational motion is needed. It could also provide an absolute
measurement of the forces holding a stationary non-rotating particle in place.
The laser-induced torque acting on an optically trapped microscopic
birefringent particle can be used for these measurements. Here we present a new
method for simple, robust, accurate, simultaneous measurement of the rotation
speed of a laser trapped birefringent particle, and the optical torque acting
on it, by measuring the change in angular momentum of the light from passing
through the particle. This method does not depend on the size or shape of the
particle or the laser beam geometry, nor does it depend on the properties of
the surrounding medium. This could allow accurate measurement of viscosity on a
microscopic scale.",0308103v1
2006-10-04,Vacuum induced torque between corrugated metallic plates,"We study the torque arising between two corrugated metallic plates due to the
interaction with electromagnetic vacuum. This Casimir torque can be measured
with torsion pendulum techniques for separation distances as large as 1$\mu$m.
It allows one to probe the nontrivial geometry dependence of the Casimir energy
in a configuration which can be evaluated theoretically with accuracy. In the
optimal experimental configuration, the commonly used proximity force
approximation turns out to overestimate the torque by a factor 2 or larger.",0610026v3
2007-10-30,Casimir torque between corrugated metallic plates,"We consider two parallel corrugated plates and show that a Casimir torque
arises when the corrugation directions are not aligned. We follow the
scattering approach and calculate the Casimir energy up to second order in the
corrugation amplitudes, taking into account nonspecular reflections,
polarization mixing and the finite conductivity of the metals. We compare our
results with the proximity force approximation, which overestimates the torque
by a factor 2 when taking the conditions that optimize the effect. We argue
that the Casimir torque could be measured for separation distances as large as
1 $\mu{\rm m}.$",0710.5679v1
2008-01-01,Alignment of Dust with Magnetic Inclusions: Radiative Torques and Superparamagnetic Barnett and Nuclear Relaxation,"We consider grains with superparamagnetic inclusions and report two new
condensed matter effects that can enhance the internal relaxation of the energy
of a wobbling grain, namely, superparamagnetic Barnett relaxation, as well as,
an increase of frequencies for which nuclear relaxation becomes important. This
findings extends the range of grain sizes for which grains are thermally
trapped, i.e. rotate thermally, in spite of the presence of uncompensated
pinwheel torques. In addition, we show that the alignment of dust grains by
radiative torques gets modified for superparamagnetic grains, with grains
obtaining perfect alignment with respect to magnetic fields as soon as the
grain gaseous randomization time gets larger than that of paramagnetic
relaxation. The same conclusion is valid for the mechanical alignment of
helical grains. If observations confirm that the degrees of alignment are
higher than radiative torques can produce alone, this may be a proof of the
presence of superparamagentic inclusions.",0801.0265v2
2009-04-02,Steps in the bacterial flagellar motor,"The bacterial flagellar motor is a highly efficient rotary machine used by
many bacteria to propel themselves. It has recently been shown that at low
speeds its rotation proceeds in steps [Sowa et al. (2005) Nature 437,
916--919]. Here we propose a simple physical model that accounts for this
stepping behavior as a random walk in a tilted corrugated potential that
combines torque and contact forces. We argue that the absolute angular position
of the rotor is crucial for understanding step properties, and show this
hypothesis to be consistent with the available data, in particular the
observation that backward steps are smaller on average than forward steps. Our
model also predicts a sublinear torque-speed relationship at low torque, and a
peak in rotor diffusion as a function of torque.",0904.0438v1
2009-12-14,Characterization of the Drag Force in an Air-Moderated Granular Bed,"We measure the torque acting on a rod rotated perpendicular to its axis in a
granular bed, through which an upflow of gas is utilized to tune the
hydrostatic loading between grains. At low rotation rates the torque is
independent of speed, but scales quadratically with rod-length and linearly
with depth; the proportionality approaches zero linearly as the upflow of gas
is increased towards a critical value above which the grains are fluidized. At
high rotation rates the torque exhibits quadratic rate- dependence and scales
as the rod's length to the 4th power. The torque has no dependence on either
depth or airflow at these higher rates. A model used to describe the stopping
force experienced by a projectile impacting a granular bed can be shown to
predict these behaviors for our system's geometry, indicating that the same
mechanics dictate both steady-state and transient drag forces in granular
systems, regardless of geometry or material properties of the grains.",0912.2373v1
2010-05-24,Reduction in iron losses in Indirect Vector-Controlled IM Drive using FLC,"This paper describes the use of fuzzy logic controller for efficiency
optimization control of a drive while keeping good dynamic response. At
steady-state light-load condition, the fuzzy controller adaptively adjusts the
excitation current with respect to the torque current to give the minimum total
copper and iron loss. The measured input power such that, for a given load
torque and speed, the drive settles down to the minimum input power, i.e.,
operates at maximum efficiency. The low-frequency pulsating torque due to
decrementation of flux is compensated in a feed forward manner. If the load
torque or speed commands changes, the efficiency search algorithm is abandoned
and the rated flux is established to get the best dynamic response. The drive
system with the proposed efficiency optimization controller has been simulated
with lossy models of converter and machine, and its performance has been
thoroughly investigated.",1005.4265v1
2011-03-05,Torque Theory of Anisotropic Superconductors with No Phenomenological Parameter in determining Vortex Core Size,"The contribution of vortex core has been taken into account properly in
constructing a torque theory for multiband superconductors. We employ the
prescription of describing internal magnetic field in the vortex lattice by Hao
{\it et al.} and by Yaouanc {\it et al.} to derive a torque formula as a
natural extension of a preceding London theory. In marked contrast with the
preceding model, our novel formula does not contain a phenomenological
parameter $\eta$, which prevents us from obtaining a {\it true} upper critical
field $H_{\rm c2}$ by analyzing an experimental torque curve. The parameter
$\eta$ was originally introduced to take care of the uncertainty in determining
the vortex core size $\xi_v$. Furthermore, we reveal that the $\eta$ value is
universally scaled by anisotropy $\gamma$, magnetic field $B$, and $H_{\rm c2}$
due to field dependence of $\xi_v$. This may revitalize the single-band Kogan
model in combination with a universal function $\eta(\gamma, B, H_{\rm c2})$
instead of a constant $\eta$.",1103.1037v1
2011-06-08,Momentum transport and torque scaling in Taylor-Couette flow from an analogy with turbulent convection,"We generalize an analogy between rotating and stratified shear flows. This
analogy is summarized in Table 1. We use this analogy in the unstable case
(centrifugally unstable flow v.s. convection) to compute the torque in
Taylor-Couette configuration, as a function of the Reynolds number. At low
Reynolds numbers, when most of the dissipation comes from the mean flow, we
predict that the non-dimensional torque $G=T/\nu^2L$, where $L$ is the cylinder
length, scales with Reynolds number $R$ and gap width $\eta$, $G=1.46
\eta^{3/2} (1-\eta)^{-7/4}R^{3/2}$. At larger Reynolds number, velocity
fluctuations become non-negligible in the dissipation. In these regimes, there
is no exact power law dependence the torque versus Reynolds. Instead, we obtain
logarithmic corrections to the classical ultra-hard (exponent 2) regimes: $$
G=0.50\frac{\eta^{2}}{(1-\eta)^{3/2}}\frac{R^{2}}{\ln[\eta^2(1-\eta)R^
2/10^4]^{3/2}}.$$ These predictions are found to be in excellent agreement with
available experimental data. Predictions for scaling of velocity fluctuations
are also provided.",1106.1541v1
2012-07-19,"Comment on ""Trouble with the Lorentz Law of Force: Incompatibility with Special Relativity and Momentum Conservation""","In a recent Letter [arXiv:1205.0096], Mansuripur considers a magnetic dipole
positioned at a fixed location from a point charge. Performing a Lorentz
transformation to a laboratory frame where the charge distribution moves he
finds that `a net torque acts on the dipole pair'. He then argues that `this
torque in the (lab) frame in the absence of a corresponding torque in the
(rest) frame is sufficient proof of the inadequacy of the Lorentz (force) law'.
  In this comment we demonstrate that the presence of a torque is not
incompatible with special relativity: it is required by the conservation laws
that apply to the total momentum of the system (including the particles). We
furthermore stress that classical electrodynamics needs a consistent dynamical
description of the particles that involves coupled equations for the
electromagnetic fields and the trajectories [M. Brachet and E. Tirapegui, Nuovo
Cimento Soc. Ital. Fis. A 47, 210 (1978)] and any conserved quantity will then
contain contributions from both the field and the particles.",1207.4613v1
2012-07-21,Stator flux optimization on direct torque control with fuzzy logic,"The Direct Torque Control (DTC) is well known as an effective control
technique for high performance drives in a wide variety of industrial
applications and conventional DTC technique uses two constant reference value:
torque and stator flux. In this paper, fuzzy logic based stator flux
optimization technique for DTC drives that has been proposed. The proposed
fuzzy logic based stator flux optimizer self-regulates the stator flux
reference using induction motor load situation without need of any motor
parameters. Simulation studies have been carried out with Matlab/Simulink to
compare the proposed system behaviors at vary load conditions. Simulation
results show that the performance of the proposed DTC technique has been
improved and especially at low-load conditions torque ripple are greatly
reduced with respect to the conventional DTC.",1207.5152v1
2012-12-01,Fuzzy Based Stator Flux Optimizer Design For Direct Torque Control,"Direct Torque Control (DTC) is well known as an effective control technique
for high performance drives in a wide variety of industrial applications and
conventional DTC technique uses two constant reference value: torque and stator
flux. In this paper, a new fuzzy based stator flux optimizer has been proposed
for DTC controlled induction motor drivers and simulation studies have been
carried out with Matlab/Simulink to compare the proposed system behaviours at
vary load conditions. The most important feature of the proposed fuzzy logic
based stator flux optimizer that it self-regulates the stator flux reference
value using the motor load situation without need of any motor parameters.
Simulation results show that the performance of the proposed DTC technique has
been improved and especially at low-load conditions torque ripples are greatly
reduced with respect to the conventional DTC.",1212.0160v1
2013-08-31,Casimir torque in weak coupling,"In this paper, dedicated to Johan H{\o}ye on the occasion of his 70th
birthday, we examine manifestations of Casimir torque in the weak-coupling
approximation, which allows exact calculations so that comparison with the
universally applicable, but generally uncontrolled, proximity force
approximation may be made. In particular, we examine Casimir energies between
planar objects characterized by $\delta$-function potentials, and consider the
torque that arises when angles between the objects are changed. The results
agree very well with the proximity force approximation when the separation
distance between the objects is small compared with their sizes. In the
opposite limit, where the size of one object is comparable to the separation
distance, the shape dependence starts becoming irrelevant. These calculations
are illustrative of what to expect for the torques between, for example,
conducting planar objects, which eventually should be amenable to both improved
theoretical calculation and experimental verification.",1309.0130v1
2013-10-04,Casimir Torque in Inhomogeneous Dielectric Plates,"In this work, we consider a torque caused by the well known quantum
mechanical Casimir effect arising from quantized field fluctuations between
plates with inhomogeneous, sharply discontinuous, dielectric properties. While
the Casimir effect is a relatively well understood phenomenon, systems
resulting in lateral or rotational forces are far less developed; to our
knowledge, a theoretical study of discontinuous dielectric variants of such
systems has not been attempted. We utilize a Proximity Force Approximation in
conjunction with the Lifshitz dielectric formula to perform theoretical
analyses of resultant torques in systems with bisected and quadrisected
dielectric regions. We also develop a high precision Monte Carlo type numerical
integrator to approximate our derived expressions. Our calculations of an
energy density linear with the alignment angle result in a constant torque and
have implications in NEMS (nano electromechanical systems) and MEMS (micro
electromechanical systems), including a postulated nanoscale oscillating drive
mechanism powered by quantum field interactions.",1310.1421v3
2014-01-15,Critical Analysis of a Hypothesis of the Planetary Tidal Influence on Solar Activity,"The present work is a critical revision of the hypothesis of the planetary
tidal influence on solar activity published by Abreu et al. (Astron. Astrophys.
548, A88, 2012; called A12 here). A12 describes a hypothesis that planets can
have an impact on the solar tachocline and therefore on solar activity. We
checked the procedure and results of A12, namely the algorithm of planetary
tidal torque calculation and the wavelet coherence between torque and
heliospheric modulation potential. We found that the claimed peaks in
long-period range of the torque spectrum are artefacts caused by the
calculation algorithm. Also the statistical significance of the results of the
wavelet coherence is found to be overestimated by an incorrect choice of the
background assumption of red noise. Using a more conservative non-parametric
random phase method, we found that the long-period coherence between planetary
torque and heliospheric modulation potential becomes insignificant. Thus we
conclude that the considered hypothesis of planetary tidal influence on solar
activity is not based on a solid ground.",1401.3547v1
2014-02-04,Negative Optical Torque,"Maxwell noted that light carries angular momentum, and as such it can exert
torques on material objects. This was subsequently proved by Beth in 1936.
Applications of these opto-mechanical effects were limited initially due to
their smallness in magnitude, but later enabled by the invention of laser.
Novel and practical approaches for harvesting light for particle rotation have
been demonstrated, where the structure is subjected to a positive optical
torque along a certain axis21 if the incident angular momentum has a positive
projection on the same axis. We report here a counter-intuitive phenomenon of
negative optical torque, meaning that incoming photons carrying angular
momentum rotate an object in the opposite sense. Surprisingly this can be
realized quite straightforwardly in simple planar structures. Field retardation
is a necessary condition. The optimal conditions are explored and explained.",1402.0621v1
2014-09-05,"Analysis of the magnetic field, force, and torque for two-dimensional Halbach cylinders","The Halbach cylinder is a construction of permanent magnets used in
applications such as nuclear magnetic resonance apparatus, accelerator magnets
and magnetic cooling devices. In this paper the analytical expression for the
magnetic vector potential, magnetic flux density and magnetic field for a two
dimensional Halbach cylinder are derived. The remanent flux density of a
Halbach magnet is characterized by the integer $p$. For a number of
applications the force and torque between two concentric Halbach cylinders are
important. These quantities are calculated and the force is shown to be zero
except for the case where $p$ for the inner magnet is one minus $p$ for the
outer magnet. Also the force is shown never to be balancing. The torque is
shown to be zero unless the inner magnet $p$ is equal to minus the outer magnet
$p$. Thus there can never be a force and a torque in the same system.",1409.1712v1
2015-01-15,Dynamics and performance of clock pendulums,"We analyze the dynamics of a driven, damped pendulum as used in mechanical
clocks. We derive equations for the amplitude and phase of the oscillation, on
time scales longer than the pendulum period. The equations are first order ODEs
and permit fast simulations of the joint effects of circular and escapement
errors, friction, and other disturbances for long times. The equations contain
two averages of the driving torque over a period, so that the results are not
very sensitive to the fine structure of the driving. We adopt a constant-torque
escapement and study the stationary pendulum rate as a function of driving
torque and friction. We also study the reaction of the pendulum to a sudden
change in the driving torque, and to stationary noisy driving. The equations
for the amplitude and phase are shown to describe the pendulum dynamics quite
well on time scales of one period and longer. Our emphasis is on a clear
exposition of the physics.",1501.03673v1
2015-02-18,Performance Estimation for Two-Dimensional Brownian Rotary Ratchet Systems,"Within the context of the Brownian ratchet model, a molecular rotary system
was studied that can perform unidirectional rotations induced by linearly
polarized ac fields, and produce positive work under loads. The model is based
on the Langevin equation for a particle in a two-dimensional (2D) three-tooth
ratchet potential of threefold symmetry. The performance of the system is
characterized by the coercive torque, i.e., the strength of the load competing
with the torque induced by the ac driving field, and the energy efficiency in
force conversion from the driving field to torque. We propose a master equation
for coarse-grained states, which takes into account boundary motion between
states, and develop a kinetic description to estimate mean angular momentum
(MAM) and powers relevant to the energy balance equation. The framework of
analysis incorporates several 2D characteristics, and is applicable to a wide
class of models of smooth 2D ratchet potential. We confirm that the obtained
expressions for MAM, power, and efficiency of the model can predict qualitative
behaviors. We also discuss the usefulness of the torque/power relationship for
experimental analyses, and propose a characteristic for 2D ratchet systems.",1502.05210v1
2015-04-02,The thermal emission from boulders on (25143) Itokawa and general implications for the YORP effect,"Infrared radiation emitted from an asteroid surface causes a torque that can
significantly affect rotational state of the asteroid. The influence of small
topographic features on this phenomenon, called the YORP effect, seems to be of
utmost importance. In this work, we show that a lateral heat diffusion in
boulders of suitable sizes leads to an emergence of a local YORP effect which
magnitude is comparable to the YORP effect due to the global shape. We solve a
three-dimensional heat diffusion equation in a boulder and its surroundings by
the finite element method, using the FreeFem++ code. The contribution to the
total torque is inferred from the computed temperature distribution. Our
general approach allows us to compute the torque induced by a realistic
irregular boulder. For an idealized boulder, our result is consistent with an
existing one-dimensional model. We also estimated (and extrapolated) a size
distribution of boulders on (25143) Itokawa from close-up images of its
surface. We realized that topographic features on Itokawa can potentially
induce a torque corresponding to a rotational acceleration of the order 10^-7
rad day^-2 and can therefore explain the observed phase shift in light curves.",1504.00566v1
2015-04-06,Rotation of a liquid crystal by the Casimir torque,"We present a calculation of the Casimir torque acting on a liquid crystal
near a birefringent crystal. In this system, a liquid crystal bulk is uniformly
aligned at one surface and is twisted at the other surface by a birefringent
crystal, e.g. barium titanate. The liquid crystal is separated from the solid
crystal by an isotropic, transparent material such as SiO$_2$. By varying the
thickness of the deposited layer, we can observe the effect of retardation on
the torque (which differentiates it from the close-range van der Waals torque).
We find that a barium titanate slab would cause 5CB
(4-cyano-4$'$-pentylbiphenyl) liquid crystal to rotate by 10$^\circ$ through
its bulk when separated by 35 nm of SiO$_2$. The optical technique for
measuring this twist is also outlined.",1504.01297v1
2015-07-24,Magnetic torque anomaly in the quantum limit of the Weyl semi-metal NbAs,"Electrons in materials with linear dispersion behave as massless Weyl- or
Dirac-quasiparticles, and continue to intrigue physicists due to their close
resemblance to elusive ultra-relativistic particles as well as their potential
for future electronics. Yet the experimental signatures of Weyl-fermions are
often subtle and indirect, in particular if they coexist with conventional,
massive quasiparticles. Here we report a large anomaly in the magnetic torque
of the Weyl semi-metal NbAs upon entering the ""quantum limit"" state in high
magnetic fields, where topological corrections to the energy spectrum become
dominant. The quantum limit torque displays a striking change in sign,
signaling a reversal of the magnetic anisotropy that can be directly attributed
to the topological properties of the Weyl semi-metal. Our results establish
that anomalous quantum limit torque measurements provide a simple experimental
method to identify Weyl- and Dirac- semi-metals.",1507.06981v1
2015-08-08,Acoustic radiation force and torque exerted on a small viscoelastic particle in an ideal fluid,"We provide a detailed analysis on the acoustic radiation force and torque
exerted on a homogeneous viscoelastic particle in the long-wave limit (the
particle radius is much smaller than the incident wavelength) by an arbitrary
wave. We assume that the particle behaves as a linear viscoelastic solid, which
obeys the fractional Kelvin-Voigt model. Simple analytical expressions for the
radiation force and torque are obtained considering the low- and high-frequency
approximation in the viscoelastic model. The developed theory is used to
describe the interaction of acoustic waves (traveling and standing plane waves,
and zero- and first-order Bessel beams) with a low- and high-density
polyethylene particle chosen as examples. Negative axial radiation force and
torque are predicted when the ratio of the longitudinal to shear relaxation
times is smaller than a constant that depends on the speed of sound in the
particle. In addition, a full 3D tractor Bessel vortex beam acting on the
high-density polyethylene is depicted. These predictions may enable new
possibilities of particle handling in acoustophoretic techniques.",1508.01908v2
2015-10-12,Gravitational torques imply molecular gas inflow towards the nucleus of M51,"The transport of gas towards the centre of galaxies is critical for black
hole feeding and, indirectly, it can control active galactic nucleus (AGN)
feedback. We have quantified the molecular gas inflow in the central R<1kpc of
M51 to be 1 Msun/yr, using a new gravitational torque map and the molecular gas
traced by the PdBI Arcsecond Whirlpool Survey (PAWS). The nuclear stellar bar
is responsible for this gas inflow. We have also used torque profiles to
estimate the location of dynamical resonances, suggesting a corotation for the
bar at R~20"", and a corotation for the spiral at R~100"". We demonstrate how
important it is to correct 3.6um images for dust emission in order to compute
gravitational torques, and we carefully examine further sources of uncertainty.
Our observational measurement of gas inflow can be compared with nuclear
molecular outflow rates and provide useful constraints for numerical
simulations.",1510.03440v2
2016-01-18,The Image Torque Operator for Contour Processing,"Contours are salient features for image description, but the detection and
localization of boundary contours is still considered a challenging problem.
This paper introduces a new tool for edge processing implementing the
Gestaltism idea of edge grouping. This tool is a mid-level image operator,
called the Torque operator, that is designed to help detect closed contours in
images. The torque operator takes as input the raw image and creates an image
map by computing from the image gradients within regions of multiple sizes a
measure of how well the edges are aligned to form closed convex contours.
Fundamental properties of the torque are explored and illustrated through
examples. Then it is applied in pure bottom-up processing in a variety of
applications, including edge detection, visual attention and segmentation and
experimentally demonstrated a useful tool that can improve existing techniques.
Finally, its extension as a more general grouping mechanism and application in
object recognition is discussed.",1601.04669v1
2016-02-13,Distribution of dislocations in twisted bars,"An asymptotically exact continuum dislocation theory of single crystal bars
under torsion is proposed. The dislocation distribution minimizing energy of
the bar with zero torque is shown to be uniform. If the applied torque is
non-zero, the minimizer exhibits a dislocation-free zone at the outer ring of
the bar's cross-section. The non-uniform distribution of dislocations in
equilibrium as well as the twist angle per unit length are found in terms of
the given torque. With the energy dissipation being taken into account, there
exists an elastic core region, while dislocation are concentrated in a ring
between two dislocation-free zones. This leads to the change of the stress
distribution increasing the critical threshold of the torque.",1602.04289v1
2016-03-22,Real-time Adaptive Prediction Method for Smooth Haptic Rendering,"In this paper, we propose a real-time adaptive prediction method to calculate
smooth and accurate haptic feedback in complex scenarios. Smooth haptic
feedback is an important task for haptic rendering with complex virtual
objects. However, commonly the update rate of the haptic rendering may drop
down during multi-point contact in complex scenarios because high computational
cost is required for collision detection and physically-based dynamic
simulation. If the haptic rendering is done at a lower update rate, it may
cause discontinuous or instable force/torque feedback. Therefore, to implement
smooth and accurate haptic rendering, the update rate of force/torque
calculation should be kept in a high and constant frequency. In the proposed
method, the auto-regressive model with real-time coefficients update is
proposed to predict interactive forces/torques during the physical simulation.
In addition, we introduce a spline function to dynamically interpolate smooth
forces/torques in haptic display according to the update rate of physical
simulation. In the experiments, we show the feasibility of the proposed method
and compare its performance with other methods and algorithms. The result shows
that the proposed method can provide smooth and accurate haptic force feedback
at a high update rate for complex scenarios.",1603.06674v1
2016-09-29,Numerical and analytical solutions of Neutrino-Dominated Accretion Flows with a Non-Zero Torque Boundary Condition and its applications in Gamma-ray Bursts,"A stellar mass black hole (BH) surrounded by a neutrino-dominated accretion
flow (NDAF) has been discussed in a number of works as the central engine of
gamma-ray bursts (GRBs). It is widely believed that NDAF cannot liberate enough
energy for bright GRBs. However, these works have been based on the assumption
of ""no torque"" boundary condition, which is invalid when the disk is
magnetized. In this paper, we present both numerical and analytical solutions
for NDAFs with non-zero boundary stresses, and reexamine their properties. We
find that NDAF with such boundary torque can be powerful enough to account for
those bright short GRBs, energetic long GRBs and ultra-long GRBs. The disk
becomes viscously unstable, which makes it possible to interpret the
variability of GRB prompt emission and the steep decay phase in the early X-ray
afterglow. Finally, we study the gravitational waves radiated from a processing
BH-NDAF. We find that the effects of the boundary torque on the strength of the
gravitational waves can be ignored.",1609.09183v1
2016-12-26,Optical alignment of oval graphene flakes,"Patterned graphene, as an atomically thin layer, supports localized surface
plasmon-polaritons (LSPPs) at mid-infrared or far-infrared frequencies. This
provides a pronounced optical force/torque in addition to large optical cross
sections and will make it an ideal candidate for optical manipulation. Here, we
study the optical force and torque exerted by a linearly polarized plane wave
on circular and oval graphene flakes. Whereas the torque vanishes for circular
flakes, the finite torque allows rotating and orienting oval flakes relative to
the electric field polarization. Depending on the wavelength, the alignment is
either perpendicular or parallel. In our contribution, we rely on full-wave
numerical simulation but also on an analytical model that treats the graphene
flakes in dipole approximation. The presented results reveal a good level of
control on the spatial alignment of graphene flakes subjected to far-infrared
illumination.",1612.08418v2
2017-01-26,Non-intuitive Computational Optimization of Illumination Patterns for Maximum Optical Force and Torque,"This paper aims to maximize optical force and torque on arbitrary micro- and
nano-scale objects using numerically optimized structured illumination. By
developing a numerical framework for computer-automated design of 3d
vector-field illumination, we demonstrate a 20-fold enhancement in optical
torque per intensity over circularly polarized plane wave on a model plasmonic
particle. The nonconvex optimization is efficiently performed by combining a
compact cylindrical Bessel basis representation with a fast boundary element
method and a standard derivative-free, local optimization algorithm. We analyze
the optimization results for 2000 random initial configurations, discuss the
tradeoff between robustness and enhancement, and compare the different effects
of multipolar plasmon resonances on enhancing force and torque. All results are
obtained using open-source computational software available online.",1701.07891v1
2017-02-14,A New self-propelled magnetic bearing with helical windings,"In this work a design is proposed for an active, permanent magnet based,
self-propelled magnetic bearing i.e. levitating motor having the following
features : (a) simple winding structure, (b) high load supporting capacity, (c)
no eccentricity sensors, (d) stable confinement in all translational
dimensions, (e) stable confinement in all rotational dimensions and (f) high
efficiency. This design uses an architecture consisting of a helically wound
three-phase stator, and a rotor with the magnets also arranged in a helical
manner. Active control is used to excite the rotor at a torque angle lying in
the second quadrant. This torque angle is independent of the rotor's position
inside the stator cavity hence the control algorithm is similar to that of a
conventional permanent magnet synchronous motor. It is motivated through a
physical argument that the bearing rotor develops a lift force proportional to
the output torque and that it remains stably confined in space. These
assertions are then proved rigorously through a calculation of the magnetic
fields, forces and torques. The stiffness matrix of the system is presented and
a discussion of stable and unstable operating regions is given.",1702.04261v1
2017-03-23,New method for torque magnetometry using a commercially available membrane-type surface-stress sensor,"We present a new method for torque magnetometry by using a commercially
available membrane-type surface-stress sensor (MSS). This sensor has a silicon
membrane supported by four beams in which piezoresistive paths are integrated.
Although originally developed as a gas sensor, it can be used for torque
measurement by modifying its on-chip wiring. We demonstrate the magnetic-torque
measurement of submillimeter-sized crystals at a low temperature and in strong
magnetic fields. This MSS can observe de-Haas-van-Alphen oscillation, which
confirms that it can be an alternative tool for self-sensitive
microcantilevers.",1703.07935v2
2017-07-24,Optimized Body Deformation in Dragonfly Maneuvers,"Tail bending associated with maneuvering flight of insects is a known
phenomenon although there are only a few studies which analyze and quantify the
effects and benefits of body configuration changes. We hypothesized that these
configuration changes help reduce the energy expenditure in flight. This is
quantified by the magnitude of the aerodynamic torque generated by the insect
during the maneuver. To test our hypothesis, a dragonfly body model was
constructed with the ability to bend at the joint between the thorax and the
tail. An optimization problem was defined to find the dynamic body
configuration which minimizes the total pitch and yaw torque. The magnitude of
the tail deflection was found to be directly correlated with the yaw velocity
of the body. Most importantly, our results indicate that for executing the same
aerial maneuver, an insect with a flexible body was found to require
substantially smaller flight torque when compared to an insect with identical
morphology but possessing a rigid body. In addition, changes in the
instantaneous mass distribution of the body had the most substantial effect on
reducing the flight torque, while the inertial term due to the tail movement
had a smaller effect.",1707.07704v1
2017-09-29,Non-local Gilbert damping tensor within the torque-torque correlation model,"An essential property of magnetic devices is the relaxation rate in magnetic
switching which depends strongly on the damping in the magnetisation dynamics.
It was recently measured that damping depends on the magnetic texture and,
consequently, is a non-local quantity. The damping enters the
Landau-Lifshitz-Gilbert equation as the phenomenological Gilbert damping
parameter $\alpha$, that does not, in a straight forward formulation, account
for non-locality. Efforts were spent recently to obtain Gilbert damping from
first principles for magnons of wave vector $\mathbf{q}$. However, to the best
of our knowledge, there is no report about real space non-local Gilbert damping
$\alpha_{ij}$. Here, a torque-torque correlation model based on a tight binding
approach is applied to the bulk elemental itinerant magnets and it predicts
significant off-site Gilbert damping contributions, that could be also
negative. Supported by atomistic magnetisation dynamics simulations we reveal
the importance of the non-local Gilbert damping in atomistic magnetisation
dynamics. This study gives a deeper understanding of the dynamics of the
magnetic moments and dissipation processes in real magnetic materials. Ways of
manipulating non-local damping are explored, either by temperature, material's
doping or strain.",1709.10365v1
2017-12-19,Probabilistic Learning of Torque Controllers from Kinematic and Force Constraints,"When learning skills from demonstrations, one is often required to think in
advance about the appropriate task representation (usually in either
operational or configuration space). We here propose a probabilistic approach
for simultaneously learning and synthesizing torque control commands which take
into account task space, joint space and force constraints. We treat the
problem by considering different torque controllers acting on the robot, whose
relevance is learned probabilistically from demonstrations. This information is
used to combine the controllers by exploiting the properties of Gaussian
distributions, generating new torque commands that satisfy the important
features of the task. We validate the approach in two experimental scenarios
using 7-DoF torquecontrolled manipulators, with tasks that require the
consideration of different controllers to be properly executed.",1712.07249v2
2018-03-03,Inducing and controlling rotation on small objects using photonic topological materials,"Photonic topological insulator plates violate Lorentz reciprocity which leads
to a directionality of surface-guided modes. This in-plane directionality can
be imprinted via an applied magnetic field. On the basis of macroscopic quantum
electrodynamics in nonreciprocal media, we show that two photonic topological
insulator surfaces are subject to a tuneable, magnetic-field dependent Casimir
torque. Due to the directionality, this torque exhibits a unique $2\pi$
periodicity, in contradistinction to the Casimir torques encountered for
reciprocal uniaxial birefringent media or corrugated surfaces which are
$\pi$-periodic. Remarkably, the torque direction and strength can be externally
driven in situ by simply applying a magnetic field on the system, and we show
that this can be exploited to induce a control the rotation of small objects.
Our predictions can be relevant for nano-opto-mechanical experiments and
devices.",1803.01144v1
2018-05-29,"Optimal nanoparticle forces, torques, and illumination fields","A universal property of resonant subwavelength scatterers is that their
optical cross-sections are proportional to a square wavelength, $\lambda^2$,
regardless of whether they are plasmonic nanoparticles, two-level quantum
systems, or RF antennas. The maximum cross-section is an intrinsic property of
the \emph{incident field}: plane waves, with infinite power, can be decomposed
into multipolar orders with finite powers proportional to $\lambda^2$. In this
Article, we identify $\lambda^2/c$ and $\lambda^3/c$ as analogous force and
torque constants, derived within a more general quadratic scattering-channel
framework for upper bounds to optical force and torque for any illumination
field. This framework also solves the reverse problem: computing globally
optimal ""holographic"" incident beams, for a fixed collection of scatterers. We
analyze structures and incident fields that approach the bounds, which for
wavelength-scale bodies show a rich interplay between scattering channels, and
we show that spherically symmetric structures are forbidden from reaching the
plane-wave force/torque bounds. This framework should enable optimal mechanical
control of nanoparticles with light.",1805.11471v2
2018-06-18,Low mass planet migration in Hall-affected disks,"Recent developments in non-ideal magnetohydrodynamic simulations of
protoplanetary disks suggest that instead of being traditional turbulent
(viscous) accretion disks, they have a largely laminar flow with accretion
driven by large-scale wind torques. These disks are possibly threaded by
Hall-effect generated large-scale horizontal magnetic fields. We have examined
the dynamics of the corotation region of a low mass planet embedded in such a
disk and the evolution of the associated migration torque. These disks lack
strong turbulence and associated turbulent diffusion, and the presence of a
magnetic field and radial gas flow presents a situation outside the
applicability of previous corotation torque theory. We summarize the analytical
analysis of the corotation torque, give details on the numerical methods used,
and in particular the relative merits of different numerical schemes for the
inviscid problem.",1806.06960v1
2018-11-30,Superconducting fluctuation in FeSe investigated by precise torque magnetometry,"We investigated the superconducting fluctuation in FeSe, which is assumed to
be located in the BCS--BEC crossover region, via magnetic torque measurements.
In our method, the absolute cantilever displacement is measured by detecting
the interference intensity of the Fabry--Perot cavity formed between the
cantilever and optical fiber. Our findings are totally different from the
results of the previous torque magnetometry using a piezoresistive cantilever;
the ""giant"" fluctuation diamagnetism related to the BCS--BEC crossover does not
exist. Instead, a considerably smaller fluctuation signal originating from the
vortex liquid was observed that showed a qualitatively similar behavior to
those in cuprate superconductors. We also discuss the inconsistency between our
torque data and the existence of a pseudogap proposed by an NMR experiment.",1811.12778v2
2019-04-01,Giant Casimir torque between rotated gratings and the $θ=0$ anomaly,"We study the Casimir torque between two metallic one-dimensional gratings
rotated by an angle $\theta$ with respect to each other. We find that, for
infinitely extended gratings, the Casimir energy is anomalously discontinuous
at $\theta=0$, due to a critical zero-order geometric transition between a 2D-
and a 1D-periodic system. This transition is a peculiarity of the grating
geometry and does not exist for intrinsically anisotropic materials. As a
remarkable practical consequence, for finite-size gratings, the torque per area
can reach extremely large values, increasing without bounds with the size of
the system. We show that for finite gratings with only 10 period repetitions,
the maximum torque is already 60 times larger than the one predicted in the
case of infinite gratings. These findings pave the way to the design of a
contactless quantum vacuum torsional spring, with possible relevance to micro-
and nano-mechanical devices.",1904.00961v1
2019-07-07,"Modeling, Analysis, and Control of Mechanical Systems under Power Constraints","Significant improvements have been achieved in motion control systems with
the availability of high speed power switches and microcomputers on the market.
Even though motor drivers are able to provide high torque control bandwidth
under nominal conditions, they suffer from various physical constraints which
degrade both output amplitude and bandwidth of torque control loop. In this
context, peak power limit of a power source, as one of those constraints, has
not been fully explored from the control perspective so far. A conventional and
practical way of considering peak power limit in control systems is to model it
as a trivial torque saturation derived from the allowable torque at maximum
speed satisfying the constraint. However, this model is overly conservative
leading to poor closed loop performance when actuators operate below their
maximum speed. In this paper, novel ways of incorporating peak power limits
into both classical and optimal controllers are presented upon a theoretical
analysis revealing its effects on stability and performance.",1907.03279v1
2020-05-28,Low-Cost Fiducial-based 6-Axis Force-Torque Sensor,"Commercial six-axis force-torque sensors suffer from being some combination
of expensive, fragile, and hard-to-use. We propose a new fiducial-based design
which addresses all three points. The sensor uses an inexpensive webcam and can
be fabricated using a consumer-grade 3D printer. Open-source software is used
to estimate the 3D pose of the fiducials on the sensor, which is then used to
calculate the applied force-torque. A browser-based (installation free)
interface demonstrates ease-of-use. The sensor is very light and can be dropped
or thrown with little concern. We characterize our prototype in dynamic
conditions under compound loading, finding a mean $R^2$ of over 0.99 for the
$F_x, F_y, M_x$, and $M_y$ axes, and over 0.87 and 0.90 for the $F_z$ and $M_z$
axes respectively. The open source design files allow the sensor to be adapted
for diverse applications ranging from robot fingers to human-computer
interfaces, while the sdesign principle allows for quick changes with minimal
technical expertise. This approach promises to bring six-axis force-torque
sensing to new applications where the precision, cost, and fragility of
traditional strain-gauge based sensors are not appropriate. The open-source
sensor design can be viewed at
http://sites.google.com/view/fiducialforcesensor.",2005.14250v1
2020-08-17,Transverse optical binding for a dual dipolar dielectric nanoparticle dimer,"The physical origins of the transverse optical binding force and torque
beyond the Rayleigh approximation have not been clearly expressed to date.
Here, we present analytical expressions of the force and torque for a dual
dipolar dielectric dimer illuminated by a plane wave propagating
perpendicularly to the dimer axis. Using this analytical model, we explore the
roles of the hybridized electric dipolar, magnetic dipolar, and
electric-magnetic dipolar coupling interactions in the total force and torque
on the particles. We find significant departures from the predictions of the
Rayleigh approximation, particularly for high-refractive-index particles, where
the force is dominated by the magnetic interaction. This results in an
enhancement of the dimer stability by one to four orders of magnitude compared
to the predictions of the Rayleigh approximation. For the case of torque, this
is dominated by the coupling interaction and increases by an order of
magnitude. Our results will help to guide future experimental work in optical
binding of high-refractive-index dielectric particles.",2008.07243v1
2020-09-18,Acoustic radiation force and torque on spheroidal particles in an ideal cylindrical chamber,"We theoretically investigate how the acoustic radiation force and torque
arise on a small spheroidal particle immersed in a nonviscous fluid inside an
ideal cylindrical chamber. The ideal chamber comprises a hard top and bottom
(rigid boundary condition), and a soft or hard lateral wall. By assuming the
particle is much smaller than the acoustic wavelength, we present analytical
expressions of the radiation force and torque caused by an acoustic wave of
arbitrary shape. Unlike previous results, these expressions are given relative
to a fixed laboratory frame. Our model is showcased for analyzing the behavior
of an elongated metallic microspheroid (with a 10 : 1 aspect ratio) in a
half-wavelength acoustofluidic chamber with a few millimeters diameter. The
results show the radiation torque aligns the microspheroid along the nodal
plane, and the radiation force causes a translational motion with a speed of up
to one body length per second. At last, we discuss the implications of this
study to propelled nanorods by ultrasound.",2009.08808v1
2020-11-20,Fluid inertial torque is an effective gyrotactic mechanism for settling elongated micro-swimmers,"Marine plankton are usually modeled as settling elongated micro-swimmers. For
the first time, we consider the torque induced by fluid inertia on such
swimmers, and we discover that they spontaneously swim in the direction
opposite to gravity. We analyze the equilibrium orientation of swimmers in
quiescent fluid and the mean orientation in turbulent flows using direct
numerical simulations. Similar to well-known gyrotaxis mechanisms, the effect
of fluid inertial torque can be quantified by an effective reorientation time
scale. We show that the orientation of swimmers strongly depends on the
reorientation time scale, and swimmers exhibit strong preferential alignment in
upward direction when the time scale is of the same order of Kolmogorov time
scale. Our findings suggest that the fluid inertial torque is a new mechanism
of gyrotaxis that stabilizes the upward orientation of micro-swimmers such as
plankton.",2011.10253v3
2020-12-02,Multimodal Contact Detection using Auditory and Force Features for Reliable Object Placing in Household Environments,"Typical contact detection is based on the monitoring of a threshold value in
the force and torque signals. The selection of a threshold is challenging for
robots operating in unstructured or highly dynamic environments, such in a
household setting, due to the variability of the characteristics of the objects
that might be encountered. We propose a multimodal contact detection approach
using time and frequency domain features which model the distinctive
characteristics of contact events in the auditory and haptic modalities. In our
approach the monitoring of force and torque thresholds is not necessary as
detection is based on the characteristics of force and torque signals in the
frequency domain together with the impact sound generated by the manipulation
task. We evaluated our approach with a typical glass placing task in a
household setting. Our experimental results show that robust contact detection
(99.94% mean cross-validation accuracy) is possible independent of force/torque
threshold values and suitable of being implemented for operation in highly
dynamic scenarios.",2012.01583v1
2020-12-28,Observation of radiation torque shot noise on an optically levitated nanodumbbell,"According to quantum theory, measurement and backaction are inextricably
linked. In optical position measurements, this backaction is known as radiation
pressure shot noise. In analogy, a measurement of the orientation of a
mechanical rotor must disturb its angular momentum by radiation torque shot
noise. In this work, we observe the shot-noise torque fluctuations arising in a
measurement of the angular orientation of an optically levitated nanodumbbell.
We feedback cool the dumbbell's rotational motion and investigate its reheating
behavior when released from feedback. In high vacuum, the heating rate due to
radiation torque shot noise dominates over the thermal and technical heating
rates in the system.",2012.14231v2
2021-03-23,Why do we use constants of motion while studying the motion of a heavy symmetric top?,"While studying the motion of a heavy symmetric top, in general, constants of
motion are used. Some students may want to understand the motion in terms of
torque, which can lie on their routine based on the usage of Newton's second
law. However, this is not easy, and examples of this work will illustrate this
situation.
  In this work, first, we will show the equivalence of torque-angular momentum
relation and Euler equations for a heavy symmetric top which give the
description of the motion in terms of torque. Then, we will study some simple
motions of a heavy symmetric top in terms of torque, angular momentum, angular
velocities and accelerations, which can help students in understanding rigid
body rotations and the necessity of considering the motion of a heavy symmetric
top in terms of constants. We will also study Perry's historical observational
principle on the relation between precession and the rise of the top.",2103.13984v3
2021-04-02,HaptiStylus: A Novel Stylus Capable of Displaying Movement and Rotational Torque Effects,"With the emergence of pen-enabled tablets and mobile devices, stylus-based
interaction has been receiving increasing attention. Unfortunately, styluses
available in the market today are all passive instruments that are primarily
used for writing and pointing. In this paper, we describe a novel stylus
capable of displaying certain vibro-tactile and inertial haptic effects to the
user. Our stylus is equipped with two vibration actuators at the ends, which
are used to create a tactile sensation of up and down movement along the
stylus. The stylus is also embedded with a DC motor, which is used to create a
sense of bidirectional rotational torque about the long axis of the pen.
Through two psychophysical experiments, we show that, when driven with
carefully selected timing and actuation patterns, our haptic stylus can convey
movement and rotational torque information to the user. Results from a further
psychophysical experiment provide insight on how the shape of the actuation
patterns effects the perception of rotational torque effect. Finally,
experimental results from our interactive pen-based game show that our haptic
stylus is effective in practical settings",2104.01088v1
2021-06-30,Qualitative chirality effects on the Casimir-Lifshitz torque with liquid crystals,"We model a cholesteric liquid crystal as a planar uniaxial multilayer system,
where the orientation of each layer differs slightly from that of the adjacent
one. This allows us to analytically simplify the otherwise acutely complicated
calculation of the Casimir-Lifshitz torque. Numerical results differ
appreciably from the case of nematic liquid crystals, which can be treated like
bloc birefringent media. In particular, we find that the torque deviates
considerably from its usual sinusoidal behavior as a function of the
misalignment angle. In the case of a birefringent crystal faced with a
cholesteric liquid one, the Casimir-Lifshitz torque decreases more slowly as a
function of distance than in the nematic case. In the case of two cholesteric
liquid crystals, either in the homochiral or in the heterochiral configuration,
the angular dependence changes qualitatively as a function of distance. In all
considered cases, finite pitch length effects are most pronounced at distances
of about 10 nm.",2106.15855v1
2021-07-13,Experimental validation of fluid inertia models for a cylinder settling in a quiescent flow,"The precise description of the motion of anisotropic particles in a flow
rests on the understanding of the force and torque acting on them. Here, we
study experimentally small, very elongated particles settling in a fluid at
small Reynolds number. In our experiments, we can, to a very good
approximation, relate the rate of rotation of cylindrical tungsten rods, of
aspect ratios \beta = 8 and \beta = 16, settling in pure glycerol to the torque
they are experiencing. This allows us to compare the measured torque with
expressions obtained either in the slender-rod limit, or in the case of
spheroids. Both theories predict a simple angle dependence for the torque,
which is found to capture very well the experimental results. Surprisingly, the
slender-rod approximation predicts much better the results for \beta = 8, than
for \beta = 16. In the latter case, the expression obtained for a spheroid
provides a better approximation. The translational dynamics is shown to be in
qualitative agreement with the slender-rod and spheroid models, the former one
being found to represent better the experimental data.",2107.05918v1
2021-08-06,Electromagnetic force and torque derived from a Lagrangian in conjunction with the Maxwell-Lorentz equations,"Electromagnetic force and torque are typically derived from a stress tensor
in conjunction with Maxwell's equations of classical electrodynamics. In some
instances, the Principle of Least Action (built around a Lagrangian) can be
used to arrive at the same mathematical expressions of force and torque as
those derived from a stress tensor. This paper describes some of the underlying
arguments for the existence of a Lagrangian in the case of certain simple
physical systems. While some formulations of electromagnetic force and torque
admit a Lagrangian, there are other formulations for which a Lagrangian may not
exist.",2108.02896v1
2021-11-29,Ankle Torque During Mid-Stance Does Not Lower Energy Requirements of Steady Gaits,"In this paper, we investigate whether applying ankle torques during
mid-stance can be a more effective way to reduce energetic cost of locomotion
than actuating leg length alone. Ankles are useful in human gaits for many
reasons including static balancing. In this work, we specifically avoid the
heel-strike and toe-off benefits to investigate whether the progression of the
center of pressure from heel-to-toe during mid-stance, or some other approach,
is beneficial in and of itself. We use an ""Ankle Actuated Spring Loaded
Inverted Pendulum"" model to simulate the shifting center of pressure dynamics,
and trajectory optimization is applied to find limit cycles that minimize cost
of transport. The results show that, for the vast majority of gaits, ankle
torques do not affect cost of transport. Ankles reduce the cost of transport
during a narrow band of gaits at the transition from grounded running to aerial
running. This suggests that applying ankle torque during mid-stance of a steady
gait is not a directly beneficial strategy, but is most likely a path between
beneficial heel-strikes and toe-offs.",2111.14987v1
2022-02-06,Soundiation: A multi-functional GUI-based software in evaluation of the acoustophoresis by the acoustic radiation force and torque on arbitrary axisymmetric objects,"Acoustic radiation force and torque arising from wave scattering are commonly
used to manipulate micro-objects without contact. We applied the partial wave
expansion series and the conformal transformation approach to estimate the
radiation force and torque exerted on an axisymmetric particle. Meanwhile,
translational and rotational transformations are required to keep the
coordinate system consistent [1]. Although these theoretical derivations have
been well established, coding the required systems, including generation of the
wave function, implementation of the transformations, calculations between
modules, etc., is non-trivial and time-consuming. Here, a new open-source,
MATLAB-based software, called Soundiation, is provided to address the radiation
force and torque while supporting the dynamic prediction of non-spherical
particles. The implementation is basically generic, and its applicability is
demonstrated through the validation of numerical methods. Furthermore, a
graphical user interface is provided so that it can be used and extended
easily.",2202.04526v1
2022-06-08,Design of electrostatic feedback for an experiment to measure $G$,"The torsion pendulum at the heart of the apparatus to measure the
gravitational constant, $G$ at the Bureau International des Poids et Mesures
(BIPM) is used to measure the gravitational torque between source and test-mass
assemblies with two methods. In the Cavendish method, the pendulum moves
freely. In the electrostatic-servo method, the pendulum is maintained at a
constant angle by applying an electrostatic torque equal and opposite to any
gravitational torque on the pendulum. The electrostatic torque is generated by
a servo. This article describes the design and implementation of this servo at
the National Institute of Standards and Technology. We use a digital servo loop
with a Kalman filter to achieve measurement performance comparable to the one
in an open loop. We show that it is possible to achieve small measurement
uncertainty with an experiment that uses three electrodes for feedback control.",2206.04173v1
2022-07-14,Precision Attitude Stabilization with Intermittent External Torque,"The attitude stabilization of a micro-satellite employing a
variable-amplitude cold gas thruster which reflects as a time varying gain on
the control input is considered. Existing literature uses a persistence filter
based approach that typically leads to large control gains and torque inputs
during specific time intervals corresponding to the 'on' phase of the external
actuation. This work aims at reducing the transient spikes placed upon the
torque commands by the judicious introduction of an additional time varying
scaling signal as part of the control law. The time update mechanism for the
new scaling factor and overall closed-loop stability are established through a
Lyapunov-like analysis. Numerical simulations highlight the various features of
this new control algorithm for spacecraft attitude stabilization subject to
torque intermittence.",2207.06987v1
2022-07-18,Dynamics of certain Euler-Bernoulli rods and rings from a minimal coupling quantum isomorphism,"In some parameter and solution regimes, a minimally coupled nonrelativistic
quantum particle in 1d is isomorphic to a much heavier, vibrating, very thin
Euler-Bernoulli rod in 3d, with ratio of bending modulus to linear density
$(\hbar/2m)^2$. For $m=m_e$, this quantity is comparable to that of a
microtubule. Axial forces and torques applied to the rod play the role of
scalar and vector potentials, respectively, and rod inextensibility plays the
role of normalization. We show how an uncertainty principle $\Delta x\Delta
p_x\gtrsim\hbar$ governs transverse deformations propagating down the
inextensible, force and torque-free rod, and how orbital angular momentum
quantized in units of $\hbar$ or $\hbar/2$ (depending on calculation method)
emerges when the force and torque-free inextensible rod is formed into a ring.
For torqued rings with large wavenumbers, a ``twist quantum'' appears that is
somewhat analogous to the magnetic flux quantum. These and other results are
obtained from a purely classical treatment of the rod, i.e., without quantizing
any classical fields.",2207.08801v2
2022-07-18,"Point-particle drag, lift, and torque closure models using machine learning: hierarchical approach and interpretability","Developing deterministic neighborhood-informed point-particle closure models
using machine learning has garnered interest in recent times from dispersed
multiphase flow community. The robustness of neural models for this complex
multi-body problem is hindered by the availability of particle-resolved data.
The present work addresses this unavoidable limitation of data paucity by
implementing two strategies: (i) by using a rotation and reflection equivariant
neural network and (ii) by pursuing a physics-based hierarchical machine
learning approach. The resulting machine learned models are observed to achieve
a maximum accuracy of 85% and 96% in the prediction of neighbor-induced force
and torque fluctuations, respectively, for a wide range of Reynolds number and
volume fraction conditions considered. Furthermore, we pursue force and torque
network architectures that provide universal prediction spanning a wide range
of Reynolds number ($0.25 \leq Re \leq 250$) and particle volume fraction ($0
\leq \phi \leq 0.4$). The hierarchical nature of the approach enables improved
prediction of quantities such as streamwise torque, by going beyond binary
interactions to include trinary interactions.",2207.08888v1
2023-01-06,Nematic Torques in Scalar Active Matter: when Fluctuations Favor Polar Order and Persistence,"We study the impact of nematic alignment on scalar active matter in the
disordered phase. We show that nematic torques control the emergent physics of
particles interacting via pairwise forces and can either induce or prevent
phase separation. The underlying mechanism is a fluctuation-induced
renormalization of the mass of the polar field that generically arises from
nematic torques. The correlations between the fluctuations of the polar and
nematic fields indeed conspire to increase the particle persistence length,
contrary to what phenomenological computations predict. This effect is generic
and our theory also quantitatively accounts for how nematic torques enhance
particle accumulation along confining boundaries and opposes demixing in
mixtures of active and passive particles.",2301.02568v1
2023-01-25,Near-field GHz rotation and sensing with an optically levitated nanodumbbell,"A levitated non-spherical nanoparticle in a vacuum is ideal for studying
quantum rotations and is an extremely sensitive torque and force detector. It
has been proposed to probe fundamental particle-surface interactions such as
the Casimir torque and the rotational quantum vacuum friction, which require it
to be driven to rotate near a surface at sub-micrometer separations. Here, we
optically levitate a silica nanodumbbell in a vacuum at about 430 nm away from
a sapphire surface and drive it to rotate at GHz frequencies. The relative
linear speed between the tip of the nanodumbbell and the surface reaches 1.4
km/s at a sub-micrometer separation. The rotating nanodumbbell near the surface
demonstrates a torque sensitivity of $(5.0 \pm 1.1) \times 10^{-26} {\rm
NmHz}^{-1/2}$ at room temperature. Moreover, we levitate a nanodumbbell near a
gold nanograting and use it to probe the near-field intensity distribution
beyond the optical diffraction limit. Our numerical simulation shows it is
promising to detect the Casimir torque between a nanodumbbell and a
nanograting.",2301.10868v1
2023-09-20,Energetics of twisted elastic filament pairs,"We investigate the elastic energy stored in a filament pair as a function of
applied twist by measuring torque under prescribed end-to-end separation
conditions. We show that the torque increases rapidly to a peak with applied
twist when the filaments are initially separate, then decreases to a minimum as
the filaments cross and come into contact. The torque then increases again
while the filaments form a double helix with increasing twist. A nonlinear
elasto-geometric model that combines the effect of geometrical nonlinearities
with large stretching and self-twist is shown to capture the evolution of the
helical geometry, the torque profile, and the stored energy with twist. We find
that a large fraction of the total energy is stored in stretching the
filaments, which increases with separation distance and applied tension. We
find that only a small fraction of energy is stored in the form of bending
energy, and that the contribution due to contact energy is negligible. Our
study highlights the consequences of stretchablility on filament twisting which
is a fundamental topological transformation relevant to making ropes, tying
shoelaces, actuating robots, and the physical properties of entangled polymers.",2309.11344v3
2023-09-29,Nonlinear Bayesian Identification for Motor Commutation: Applied to Switched Reluctance Motors,"Switched Reluctance Motors (SRMs) enable power-efficient actuation with
mechanically simple designs. This paper aims to identify the nonlinear
relationship between torque, rotor angle, and currents, to design commutation
functions that minimize torque ripple in SRMs. This is achieved by conducting
specific closed-loop experiments using purposely imperfect commutation
functions and identifying the nonlinear dynamics via Bayesian estimation. A
simulation example shows that the presented method is robust to
position-dependent disturbances, and experiments suggest that the
identification method enables the design of commutation functions that
significantly increase performance. The developed approach enables accurate
identification of the torque-current-angle relationship in SRMs, without the
need for torque sensors, an accurate linear model, or an accurate model of
position-dependent disturbances, making it easy to implement in production.",2309.17099v1
2023-10-10,Acoustic Lateral Recoil Force and Stable Lift of Anisotropic Particles,"Acoustic forces and torques are of immense importance for manipulation of
particles, in particular in biomedical applications. While such forces and
torques are well understood for small spherical particles with lowest-order
monopole and dipole responses, the higher-order effects for larger anisotropic
particles have not been properly investigated. Here we examine the acoustic
force and torque on an anisotropic (ellipsoid) particle and reveal two novel
phenomena. First, we describe the lateral recoil force, orthogonal to the
direction of the incident wave and determined by the tilted orientation of the
particle. Second, we find conditions for the stable acoustic lift, where the
balanced torque and force produce a stable lateral drift of the tilted
particle. We argue that these phenomena can bring about new functionalities in
acoustic manipulation and sorting of anisotropic particles including biological
objects such as blood cells.",2310.06524v1
2023-10-17,Assessment of the Electromagnetic Behaviour of Servovalve Torque Motor Using Reluctance Network Models,"The torque motor is the most common technology used in electrohydraulic
two-stage servovalves to drive the hydraulic pilot stage. As it is a key
component in these valves, its performance considerably affects the overall
performance of servovalve systems. Modeling accurately the magnetic behavior of
the torque motor will help to get a more realistic performance of the
servovalve at different operating conditions during the product design and
development stage. In this paper, an advanced model of the torque motor is
presented. The aim is to integrate it into the overall multiphysics model of
the servovalve through a multi-variable function obtained using the proposed
modeling tool. The advanced reluctance network model has been developed by
progressively considering various magnetic phenomena, including flux leaks
between different parts and variations in magnetic induction. This model allows
rapid assessment of the magnetic performance at various operating temperatures
or using different ferromagnetic materials, without the need for additional
analysis in 3D finite element software.",2310.11076v1
2023-12-19,Johnsen-Rahbek Capstan Clutch: A High Torque Electrostatic Clutch,"In many robotic systems, the holding state consumes power, limits operating
time, and increases operating costs. Electrostatic clutches have the potential
to improve robotic performance by generating holding torques with low power
consumption. A key limitation of electrostatic clutches has been their low
specific shear stresses which restrict generated holding torque, limiting many
applications. Here we show how combining the Johnsen-Rahbek (JR) effect with
the exponential tension scaling capstan effect can produce clutches with the
highest specific shear stress in the literature. Our system generated 31.3
N/cm^2 sheer stress and a total holding torque of 7.1 Nm while consuming only
2.5 mW/cm^2 at 500 V. We demonstrate a theoretical model of an electrostatic
adhesive capstan clutch and demonstrate how large angle (theta > 2pi) designs
increase efficiency over planar or small angle (theta < pi) clutch designs. We
also report the first unfilled polymeric material, polybenzimidazole (PBI), to
exhibit the JR-effect.",2312.12566v2
2024-02-02,Robust Commutation Design: Applied to Switched Reluctance Motors,"Switched Reluctance Motors (SRMs) are cost-effective electric actuators that
utilize magnetic reluctance to generate torque, with torque ripple arising from
unaccounted manufacturing defects in the rotor tooth geometry. This paper aims
to design a versatile, resource-efficient commutation function for accurate
control of a range of SRMs, mitigating torque ripple despite manufacturing
variations across SRMs and individual rotor teeth. The developed commutation
function optimally distributes current between coils by leveraging the variance
in the torque-current-angle model and is designed with few parameters for easy
integration on affordable hardware. Monte Carlo simulations and experimental
results show a tracking error reduction of up to 31% and 11%, respectively. The
developed approach is beneficial for applications using a single driver for
multiple systems and those constrained by memory or modeling effort, providing
an economical solution for improved tracking performance and reduced acoustic
noise.",2402.01216v2
2004-11-25,The dependence of protoplanet migration rates on coorbital torques,"We investigate the migration rates of high-mass protoplanets embedded in
accretion discs via two and three-dimensional hydrodynamical simulations. The
simulations follow the planet's radial motion and employ a nested-grid code
that allows for high resolution close to the planet. We concentrate on the
possible role of the coorbital torques in affecting migration rates. We analyse
two cases: (a) a Jupiter-mass planet in a low-mass disc and (b) a Saturn-mass
planet in a high-mass disc. Planet migration in case (b) is much more
susceptible to coorbital torques than in case (a). We find that the coorbital
torques in both cases do not depend sensitively on whether the planet is
allowed to migrate through the disc or is held on a fixed orbit. We also
examine the dependence of the planet's migration rate on the numerical
resolution near the planet. For case (a), numerical convergence is relatively
easy to obtain, even when including torques arising from deep within the
planet's Hill sphere. The migration rate in this case is numerically on order
of the Type II migration rate and much smaller than the Type I rate, if the
disc has 0.01 solar-masses inside 26 AU. Torques from within the Hill sphere
provide a substantial opposing contribution to the migration rate. In case (b),
the gas mass within the Hill sphere is larger than the planet's mass and
convergence is more difficult to obtain. If the torques within the Hill sphere
are ignored, convergence is more easily achieved but the migration rate is
artificially large. At our highest resolution, the migration rate for case (b)
is much less than the Type I rate, but somewhat larger than the Type II rate.",0411705v1
2009-04-04,Dynamics of the Sharp Edges of Broad Planetary Rings,"(Abridged) The following describes a model of a broad planetary ring whose
sharp edge is confined by a satellite's m^th Lindblad resonance (LR). This
model uses a streamline formalism to calculate the ring's internal forces,
namely, ring gravity, pressure, viscosity, as well as a hypothetical drag
force. The model calculates the streamlines' forced orbit elements and surface
density throughout the perturbed ring. The model is then applied to the outer
edge of Saturn's B ring, which is maintained by an m=2 inner LR with the
satellite Mimas. Ring models are used to illustrate how a ring's perturbed
state depends on the ring's physical properties: surface density, viscosity,
dispersion velocity, and the hypothetical drag force. A comparison of models to
the observed outer B ring suggests that the ring's surface density there is
between 10 and 280 gm/cm^2. The ring's edge also indicates where the viscous
torque counterbalances the perturbing satellite's gravitational torque on the
ring. But an examination of seemingly conventional viscous B ring models shows
that they all fail to balance these torques at the ring's edge. This is due
ring self-gravity and the fact that a viscous ring tends to be nearly
peri-aligned with the satellite, which reduces the satellite's torque on the
ring and makes the ring's edge more difficult to maintain. Nonetheless, the
following shows that a torque balance can still be achieved in a viscous B
ring, but only in an extreme case where the ratio of the ring's bulk/shear
viscosities satisfy ~10^4. However, if the dissipation of the ring's forced
motions is instead dominated by a weak drag force, then the satellite can exert
a much stronger torque that can counterbalance the ring's viscous torque.",0904.0743v1
2010-08-13,"The Effects of Stator Compliance, Backs Steps, Temperature, and Clockwise Rotation on the Torque-Speed Curve of Bacterial Flagellar Motor","Rotation of a single bacterial flagellar motor is powered by multiple stators
tethered to the cell wall. In a ""power-stroke"" model the observed independence
of the speed at low load on the number of stators is explained by a
torque-dependent stepping mechanism independent of the strength of the stator
tethering spring. On the other hand, in models that depend solely on the stator
spring to explain the observed behavior, exceedingly small stator spring
constants are required. To study the dynamics of the motor driven by external
forces (such as those exerted by an optical tweezer), back-stepping is
introduced when stators are driven far out of equilibrium. Our model with
back-stepping reproduces the observed absence of a barrier to backward
rotation, as well the behaviors in the high-speed negative-torque regime.
Recently measured temperature dependence of the motor speed near zero load
(Yuan & Berg 2010 Biophys J) is explained quantitatively by the thermally
activated stepping rates in our model. Finally, we suggest that the general
mechanical properties of all molecular motors (linear and rotary),
characterized by their force(torque)-speed curve, can be determined by their
power-stroke potentials and the dependence of the stepping rates on the
mechanical state of the motor (force or speed). The torque-speed curve for the
clockwise rotating flagellar motor has been observed for the first time
recently (Yuan et al. 2010 PNAS). Its quasi-linear behavior is quantitatively
reproduced by our model. In particular, we show that concave and convex shapes
of the torque-speed curve can be achieved by changing the interaction potential
from linear to quadratic form. We also show that reversing the stepping rate
dependence on force (torque) can lead to non-monotonicity in the speed-load
dependency.",1008.2335v1
2012-08-29,Protoplanetary migration in non-isothermal discs with turbulence driven by stochastic forcing,"Low-mass objects embedded in isothermal protoplanetary discs are known to
suffer rapid inward Type I migration. In non-isothermal discs, recent work has
shown that a decreasing radial profile of the disc entropy can lead to a strong
positive corotation torque which can significantly slow down or reverse Type I
migration in laminar viscous disc models. It is not clear however how this
picture changes in turbulent disc models. The aim of this study is to examine
the impact of turbulence on the torque experienced by a low-mass planet
embedded in a non-isothermal protoplanetary disc. We particularly focus on the
role of turbulence on the corotation torque whose amplitude depends on the
efficiency of diffusion processes in the planet's horseshoe region. We
performed 2D numerical simulations using a grid-based hydrodynamical code in
which turbulence is modelled as stochastic forcing. In order to provide
estimations for the viscous and thermal diffusion coefficients as a function of
the amplitude of turbulence, we first set up non-isothermal disc models for
different values of the amplitude of the turbulent forcing. We then include a
low-mass planet and determine the evolution of its running time-averaged
torque. We show that in non-isothermal discs, the entropy-related corotation
torque can indeed remain unsaturated in the presence of turbulence. For
turbulence amplitudes that do not strongly affect the disc temperature profile,
we find that the running time-averaged torque experienced by an embedded
protoplanet is in fairly good agreement with laminar disc models with
appropriate values for the thermal and viscous diffusion coefficients. In discs
with turbulence driven by stochastic forcing, the corotation torque therefore
behaves similarly as in laminar viscous discs and can be responsible for
significantly slowing down or reversing Type I migration.",1208.5943v1
2017-03-17,Rotation and Neoclassical Ripple Transport in ITER,"Neoclassical transport in the presence of non-axisymmetric magnetic fields
causes a toroidal torque known as neoclassical toroidal viscosity (NTV). The
toroidal symmetry of ITER will be broken by the finite number of toroidal field
coils and by test blanket modules (TBMs). The addition of ferritic inserts
(FIs) will decrease the magnitude of the toroidal field ripple. 3D magnetic
equilibria with toroidal field ripple and ferromagnetic structures are
calculated for an ITER steady-state scenario using the Variational Moments
Equilibrium Code (VMEC). Neoclassical transport quantities in the presence of
these error fields are calculated using the Stellarator Fokker-Planck Iterative
Neoclassical Conservative Solver (SFINCS). These calculations fully account for
$E_r$, flux surface shaping, multiple species, magnitude of ripple, and
collisionality rather than applying approximate analytic NTV formulae. As NTV
is a complicated nonlinear function of $E_r$, we study its behavior over a
plausible range of $E_r$. We estimate the toroidal flow, and hence $E_r$, using
a semi-analytic turbulent intrinsic rotation model and NUBEAM calculations of
neutral beam torque. The NTV from the $\rvert n \rvert = 18$ ripple dominates
that from lower $n$ perturbations of the TBMs. With the inclusion of FIs, the
magnitude of NTV torque is reduced by about 75% near the edge. We present
comparisons of several models of tangential magnetic drifts, finding
appreciable differences only for superbanana-plateau transport at small $E_r$.
We find the scaling of calculated NTV torque with ripple magnitude to indicate
that ripple-trapping may be a significant mechanism for NTV in ITER. The
computed NTV torque without ferritic components is comparable in magnitude to
the NBI and intrinsic turbulent torques and will likely damp rotation, but the
NTV torque is significantly reduced by the planned ferritic inserts.",1703.06129v2
2018-02-23,Orienting lipid-coated graphitic micro-particles in solution using AC electric fields: A new theoretical dual-ellipsoid Laplace model for electro-orientation,"Graphitic micro-particles coated with thin layers in solution are
technologically interesting as they can be manipulated with electric fields.
Modeling the electrical manipulation of submerged layered micro-particles
analytically or numerically is not straight forward. In particular, the
generation of reliable quantitative torque predictions for electro-orientation
experiments has been elusive. The traditional Laplace model approximates the
coated particle by an ellipsoid with a confocal ellipsoidal layer and solves
Laplace's equation to produce convenient analytical predictions. However, due
to the non-uniformity of the layer thickness around the ellipsoid, this method
can lead to incorrect torque predictions. Here we present a new theoretical
dual-ellipsoid Laplace model that corrects the effect of the non-uniform layer
thickness by calculating two layered ellipsoids, each accounting for the
correct layer thickness along each relevant direction for the torque. Our model
describes the electro-orientation of submerged lipid-coated graphitic
micro-particles in the presence of an alternating current (AC) electric field
and is valid for ellipsoids with moderate aspect ratios and coated with thin
shells. It is one of the first models to generate correct quantitative electric
torque predictions. We present model results for the torque versus frequency
and compare them to our measurements for lipid-coated highly ordered pyrolytic
graphite (HOPG) micro-flakes in aqueous NaCl solution at MHz frequencies. The
results show how the lipid shell changes the overall electrical properties of
the micro-flakes so that the torque is low at low frequencies and increases at
higher frequencies into the MHz regime. The torque depends critically on the
lipid-shell thickness, the solution conductivity and the shape of the particle,
all of which can be used as handles to control the response of the particles.",1802.08523v1
2019-03-23,"The Effect of Magnetic Variability on Stellar Angular Momentum Loss II: The Sun, 61 Cygni A, $ε$ Eridani, $ξ$ Bootis A and $τ$ Bootis A","The magnetic fields of low-mass stars are observed to be variable on decadal
timescales, ranging in behaviour from cyclic to stochastic. The changing
strength and geometry of the magnetic field should modify the efficiency of
angular momentum loss by stellar winds, but this has not been well quantified.
In Finley et al. (2018) we investigated the variability of the Sun, and
calculated the time-varying angular momentum loss rate in the solar wind. In
this work, we focus on four low-mass stars that have all had their surface
magnetic fields mapped for multiple epochs. Using mass loss rates determined
from astrospheric Lyman-$\alpha$ absorption, in conjunction with scaling
relations from the MHD simulations of Finley & Matt (2018), we calculate the
torque applied to each star by their magnetised stellar winds. The variability
of the braking torque can be significant. For example, the largest torque for
$\epsilon$ Eri is twice its decadal averaged value. This variation is
comparable to that observed in the solar wind, when sparsely sampled. On
average, the torques in our sample range from 0.5-1.5 times their average
value. We compare these results to the torques of Matt et al. (2015), which use
observed stellar rotation rates to infer the long-time averaged torque on
stars. We find that our stellar wind torques are systematically lower than the
long-time average values, by a factor of ~3-30. Stellar wind variability
appears unable to resolve this discrepancy, implying that there remain some
problems with observed wind parameters, stellar wind models, or the long-term
evolution models, which have yet to be understood.",1903.09871v1
2019-04-30,Synthesis of Biologically Realistic Human Motion Using Joint Torque Actuation,"Using joint actuators to drive the skeletal movements is a common practice in
character animation, but the resultant torque patterns are often unnatural or
infeasible for real humans to achieve. On the other hand, physiologically-based
models explicitly simulate muscles and tendons and thus produce more human-like
movements and torque patterns. This paper introduces a technique to transform
an optimal control problem formulated in the muscle-actuation space to an
equivalent problem in the joint-actuation space, such that the solutions to
both problems have the same optimal value. By solving the equivalent problem in
the joint-actuation space, we can generate human-like motions comparable to
those generated by musculotendon models, while retaining the benefit of simple
modeling and fast computation offered by joint-actuation models. Our method
transforms constant bounds on muscle activations to nonlinear, state-dependent
torque limits in the joint-actuation space. In addition, the metabolic energy
function on muscle activations is transformed to a nonlinear function of joint
torques, joint configuration and joint velocity. Our technique can also benefit
policy optimization using deep reinforcement learning approach, by providing a
more anatomically realistic action space for the agent to explore during the
learning process. We take the advantage of the physiologically-based simulator,
OpenSim, to provide training data for learning the torque limits and the
metabolic energy function. Once trained, the same torque limits and the energy
function can be applied to drastically different motor tasks formulated as
either trajectory optimization or policy learning. Codebase:
https://github.com/jyf588/lrle and https://github.com/jyf588/lrle-rl-examples",1904.13041v2
2023-04-20,"Drag, lift and torque correlations for axi-symmetric non-spherical particles in locally non-uniform flows","This paper derives new correlations to predict the drag, lift and torque
coefficients of axi-symmetric non-spherical rod-like particles for several
fluid flow regimes and velocity profiles. The fluid velocity profiles
considered are locally uniform flow and locally linear shear flow. The novel
correlations for the drag, lift and torque coefficients depend on the particle
Reynolds number \Rep, the orientation of the particle with respect to the main
fluid direction $\theta$, the aspect ratio of the rod-like particle $\alpha$,
and the dimensionless local shear rate $\tilde{G}$. The effect of the linear
shear flow on the hydrodynamic forces is modeled as an additional component for
the resultant of forces acting on a particle in a locally uniform flow, hence
the independent expressions for the drag, lift and torque coefficients of
axi-symmetric particles in a locally uniform flow are also provided in this
work. The data provided to fit the coefficient in the new correlation are
generated using available analytical expressions in the viscous regime, and
performing direct numerical simulations (DNS) of the flow past the
axi-symmetric particles at finite particle Reynolds number. The DNS are
performed using the direct-forcing immersed boundary method. The coefficients
in the proposed drag, lift and torque correlations are determined with a high
degree of accuracy, where the mean error in the prediction lies below $2\%$ for
the locally uniform flow correlations, and below $1.67\%$, $5.35\%$, $6.78\%$
for the correlations accounting for the change in the drag, lift, and torque
coefficients in case of a linear shear flow, respectively. The proposed
correlations for the drag, lift and torque coefficients can be used in
large-scale simulations performed in the Eulerian-Lagrangian framework with
locally uniform and non-uniform flows.",2304.10357v2
2000-10-04,The Role of Clustering of Sub-Clumps in Bright Elliptical Galaxy Formation from a Low-Spin Seed Galaxy,"We reveal the role of clustering of sub-clumps, which is expected in the cold
dark matter (CDM) universe, in forming a bright elliptical galaxy (BEG) from a
low-spin seed galaxy.
  This can be done by comparing the evolution of a low-spin seed galaxy
including small-scale density fluctuations expected in the CDM universe
  (Model 1) with that of a completely uniform one (Model 2), using numerical
experiments.
  We show that Model 2 cannot reproduce the properties of BEGs and forms a disk
which is too compact and too bright due to the conservation of the
initial-small angular momentum.
  In Model 1 clustering of the sub-clumps caused by initial small-scale density
fluctuations leads to angular momentum transfer from the baryon component to
the dark matter and consequently a nearly spherical system supported by random
motions is formed.
  Moreover the collisionless property of the stars formed in the sub-clumps
prevents the dissipative contraction of the system, leading to a large measured
half-light radius.
  As a result, the end-product is quite well reproduces the observed properties
of BEGs, such as the de Vaucouleurs light-profile, typical color and
metallicity gradients, the large half-light radius, the small ratio of the
rotational velocity to the velocity dispersion (V/\sigma). We conclude that the
clustering of sub-clumps, i.e., the hierarchical clustering, plays a crucial
role in the formation of BEGs from a low-spin seed galaxy.",0010088v1
2002-01-19,Resolving the Spin Crisis: Mergers and Feedback,"We model in simple terms the angular momentum (J) problem of galaxy formation
in CDM, and identify the key elements of a scenario that can solve it. The
buildup of J is modeled via dynamical friction and tidal stripping in mergers.
This reveals how over-cooling in incoming halos leads to transfer of J from
baryons to dark matter (DM), in conflict with observations. By incorporating a
simple recipe of supernova feedback, we match the observed J distribution in
disks. Gas removal from small incoming halos, which make the low-J component of
the product, eliminates the low-J baryons. Partial heating and puffing-up of
the gas in larger incoming halos, combined with tidal stripping, reduces the J
loss of baryons. This implies a higher baryonic spin for lower mass halos. The
observed low baryonic fraction in dwarf galaxies is used to calibrate the
characteristic velocity associated with supernova feedback, yielding v_fb sim
100 km/s, within the range of theoretical expectations. The model then
reproduces the observed distribution of spin parameter among dwarf and bright
galaxies, as well as the J distribution inside these galaxies. This suggests
that the model captures the main features of a full scenario for resolving the
spin crisis.",0201331v1
1993-07-19,Evolution of Magnetic Properties of Lightly Doped Copper Oxides,"We study how doping destroys the AF order in the layered cuprates within the
framework of the charge--transfer insulator concept. We use the criterion of
stability of the AF background to show that the stability problem is one of the
main issues in any correspondence between results for the $t-J$ model and, say,
the three--band model for the lightly--doped layered oxides. Provided a
phenomenological conduction band is chosen to satisfy the criterion of
stability, a detailed picture of how dopants influence the spin wave spectrum
at $T=0$ is presented. The critical concentration $x_c$ for the destruction of
the AF long range order is due to the Cherenkov effect when the Fermi velocity
first exceeds the spin wave velocity. We then discuss the overall spectrum of
spin excitations and find that the spin wave attenuation for $x < x_c$, $T=0$
due to Landau damping appears in the range of magnon momenta $k(x) = 2 m^* s
\pm \alpha \sqrt{x}$. We also argue that in the presence of superconductivity,
the Cherenkov effect is eliminated due to the gap in the spectrum. This may
restore the role of the AF fluctuations as the main source of dissipation at
the lowest temperatures.",9307040v1
1996-09-10,Exact results for the optical absorption of strongly correlated electrons in a half-filled Peierls-distorted chain,"In this second of three articles on the optical absorption of electrons in a
half-filled Peierls-distorted chain we present exact results for strongly
correlated tight-binding electrons. In the limit of a strong on-site
interaction $U$ we map the Hubbard model onto the Harris-Lange model which can
be solved exactly in one dimension in terms of spinless fermions for the charge
excitations. The exact solution allows for an interpretation of the charge
dynamics in terms of parallel Hubbard bands with a free-electron dispersion of
band-width $W$, separated by the Hubbard interaction $U$. The spin degrees of
freedom enter the expressions for the optical absorption only via a momentum
dependent but static ground state expectation value. The remaining spin problem
can be traced out exactly since the eigenstates of the Harris-Lange model are
spin-degenerate. This corresponds to the Hubbard model at temperatures large
compared to the spin exchange energy. Explicit results are given for the
optical absorption in the presence of a lattice distortion $\delta$ and a
nearest-neighbor interaction $V$. We find that the optical absorption for $V=0$
is dominated by a peak at $\omega=U$ and broad but weak absorption bands for $|
\omega -U | \leq W$. For an appreciable nearest-neighbor interaction, $V>W/2$,
almost all spectral weight is transferred to Simpson's exciton band which is
eventually Peierls-split.",9609090v1
2000-10-10,A Microscopic Model for D-Wave Pairing in the Cuprates: What Happens when Electrons Somersault?,"We present a microscopic model for a strongly repulsive electron gas on a 2D
square lattice. We suggest that nearest neighbor Coulomb repulsion stabilizes a
state in which electrons undergo a ""somersault"" in their internal spin-space
(spin-flux). When this spin-1/2 antiferromagnetic (AFM) insulator is doped, the
charge carriers nucleate mobile, charged, bosonic vortex solitons accompanied
by unoccupied states deep inside the Mott-Hubbard charge-transfer gap. This
model provides a unified microscopic basis for (i) non-Fermi-liquid transport
properties, (ii) mid-infrared optical absorption, (iii) destruction of AFM long
range order with doping, (iv) angled resolved spectroscopy (ARPES), and (v)
d-wave preformed charged carrier pairs. We use the Configuration Interaction
(CI) method to study the quantum translational and rotational properties of
such pairs. The CI method systematically describes fluctuation and quantum
tunneling corrections to the Hartree-Fock approximation and recaptures
essential features of the (Bethe ansatz) exact solution of the Hubbard model in
1D. For a single hole in the 2D AFM plane, we find a precursor to spin-charge
separation. The CI ground state consists of a bound vortex-antivortex pair, one
vortex carrying the charge and the other one carrying the spin of the doping
hole.",0010151v1
2001-05-16,"Correlation functions, free energies and magnetizations in the two-dimensional random-field Ising model","Transfer-matrix methods are used to calculate spin-spin correlation functions
($G$), Helmholtz free energies ($f$) and magnetizations ($m$) in the
two-dimensional random-field Ising model close to the zero-field bulk critical
temperature $T_{c 0}$, on long strips of width $L = 3 - 18$ sites, for binary
field distributions. Analysis of the probability distributions of $G$ for
varying spin-spin distances $R$ shows that describing the decay of their
averaged values by effective correlation lengths is a valid procedure only for
not very large $R$. Connections between field-- and correlation function
distributions at high temperatures are established, yielding approximate
analytical expressions for the latter, which are used for computation of the
corresponding structure factor. It is shown that, for fixed $R/L$, the
fractional widths of correlation-function distributions saturate asymptotically
with $L^{-2.2}$. Considering an added uniform applied field $h$, a connection
between $f(h)$, $m(h)$, the Gibbs free energy $g(m)$ and the distribution
function for the uniform magnetization in zero uniform field, $P_0(m)$, is
derived and first illustrated for pure systems, and then applied for non-zero
random field. From finite-size scaling and crossover arguments, coupled with
numerical data, it is found that the width of $P_0(m)$ varies against
(non-vanishing, but small) random-field intensity $H_0$ as $H_0^{-3/7}$.",0105326v1
2001-10-23,Coupled CDW and SDW Fluctuations as an Origin of Anomalous Properties of Ferromagnetic Superconductor UGe_2,"It is shown that anomalous properties of UGe_2 can be understood in a unified
way on the basis of a single assumption that the superconductivity is mediated
by the coupled SDW and CDW fluctuations induced by the imperfect nesting of the
Fermi surface with majority spins at T=T_x(P) deep in the ferromagnetic phase.
Excess growth of uniform magnetization is shown to develop in the temperature
range T<T_x(P) as a mode-coupling effect of coupled growth of SDW and CDW
orderings, which has been observed by two different types of experiments. The
coupled CDW and SDW fluctuations are shown to be essentially ferromagnetic spin
fluctuations which induce a spin-triplet p-wave attraction. These fluctuations
consist of two modes, spin and charge fluctuations with large momentum transfer
of the nesting vector. An anomalous temperature dependence of the upper
critical field H_c2(T) such as crossing of H_c2(T) at P=11.4 kbar and P=13.5
kbar, can be understood by the strong-coupling-superconductivity formalism.
Temperature dependence of the lattice specific heat including a large shoulder
near T_x is also explained quite well as an effect of a kind of Kohn anomaly
associated with coupled SDW-CDW transition.",0110492v3
2004-06-13,Green's-function theory of the Heisenberg ferromagnet in a magnetic field,"We present a second-order Green's-function theory of the one- and
two-dimensional S=1/2 ferromagnet in a magnetic field based on a decoupling of
three-spin operator products, where vertex parameters are introduced and
determined by exact relations. The transverse and longitudinal spin correlation
functions and thermodynamic properties (magnetization, isothermal magnetic
susceptibility, specific heat) are calculated self-consistently at arbitrary
temperatures and fields. In addition, exact diagonalizations on finite lattices
and, in the one-dimensional case, exact calculations by the Bethe-ansatz method
for the quantum transfer matrix are performed. A good agreement of the
Green's-function theory with the exact data, with recent quantum Monte Carlo
results, and with the spin polarization of a $\nu=1$ quantum Hall ferromagnet
is obtained. The field dependences of the position and height of the maximum in
the temperature dependence of the susceptibility are found to fit well to power
laws, which are critically analyzed in relation to the recently discussed
behavior in Landau's theory. As revealed by the spin correlation functions and
the specific heat at low fields, our theory provides an improved description of
magnetic short-range order as compared with the random phase approximation. In
one dimension and at very low fields, two maxima in the temperature dependence
of the specific heat are found. The Bethe-ansatz data for the field dependences
of the position and height of the low-temperature maximum are described by
power laws. At higher fields in one and two dimensions, the temperature of the
specific heat maximum linearly increases with the field.",0406302v1
2006-04-16,"Gapless quantum spin liquid, stripe and antiferromagnetic phases in frustrated Hubbard models in two dimensions","Unique features of non-magnetic insulator phase are shown, and phase diagram
for t-t' Hubbard model on square lattice is presented. Using the path-integral
renormalization group method, we find antiferromagnetic phase for small
next-nearest neighbor transfer t' and stripe (or collinear) phase for large t'
in the Mott insulating region of strong on site interaction U. For intermediate
t'/t~ 0.7 at large U/t>7, we find longer-period antiferromagnetic insulator
phase with 2*4 structure. In the Mott insulating region, we also find quantum
spin liquid (in other words, non-magnetic insulator) phase near the Mott
transition to paramagnetic metals. Correlated electrons often crystallize to
the Mott insulator usually with some magnetic orders, whereas the ""quantum spin
liquid"" has been a long-sought issue. We report numerical evidences that a
nonmagnetic insulating (NMI) phase gets stabilized near the Mott transition
with remarkable properties: The 2D Mott insulators on geometrically frustrated
lattices contain a phase with gapless spin excitations and degeneracy of the
ground state in the whole Brillouin zone of the total momentum. It has an
interpretation for an unexplored type of a quantum liquid. The present concept
is useful in analyzing a variety of experimental results in frustrated magnets
including organic BEDT-TTF compounds and 3He atoms adsorbed on graphite.",0604389v3
1999-06-17,Flavor and Spin Structure of $Λ$-Baryon at Large x,"It is shown that a perturbative QCD (pQCD) based analysis and the SU(6)
quark-diquark model give significant different predictions concerning the
flavor and spin structure for the quark distributions of the $\Lambda$-baryon
near $x=1$. Detailed predictions for the ratios $u(x)/s(x)$ of unpolarized
quark distributions, $\Delta s(x)/s(x)$ of valence strange quark, and $\Delta
u(x)/u(x)$ of valence up and down quarks of the $\Lambda$ are given from the
quark-diquark model and from a pQCD based model. It is found that the up and
down quarks are positively polarized at large $x$, even though their net spin
contributions to the $\Lambda$ might be zero or negative. The significant
difference for $u(x)/s(x)$ between the two different approaches are predicted.
The prediction of positively polarized up and down quarks inside the $\Lambda$
at large $x$ has been supported by the available data of $\Lambda$-polarization
in $Z$ decays and also by the most recent HERMES result of spin transfer to the
$\Lambda$ in deep elastic scattering of polarized lepton on the nucleon target.",9906424v2
2004-07-08,Accessing Sivers gluon distribution via transverse single spin asymmetries in p(transv. polarized) p --> D X processes at RHIC,"The production of D mesons in the scattering of transversely polarized
protons off unpolarized protons at RHIC offers a clear opportunity to gain
information on the Sivers gluon distribution function. D production at
intermediate rapidity values is dominated by the elementary g g --> c cbar
channel; contributions from q qbar --> c cbar s-channel become important only
at very large values of x_F. In both processes there is no single spin
transfer, so that the final c or cbar quarks are not polarized. Therefore, any
transverse single spin asymmetry observed for D's produced in p(transv.
polarized) p interactions cannot originate from the Collins fragmentation
mechanism, but only from the Sivers effect in the distribution functions. In
particular, any sizeable spin asymmetry measured in p(transv. polarized) p -->
D X at mid-rapidity values will be a direct indication of a non zero Sivers
gluon distribution function. We study the p(transv. polarized) p --> D X
process including intrinsic transverse motion in the parton distribution and
fragmentation functions and in the elementary dynamics, and show how results
from RHIC could allow a measurement of the Sivers gluon distribution function.",0407100v1
2005-03-02,On quantum group symmetry and Bethe ansatz for the asymmetric twin spin chain with integrable boundary,"Motivated by a study of the crossing symmetry of the `gemini' representation
of the affine Hecke algebra we give a construction for crossing tensor space
representations of ordinary Hecke algebras. These representations build
solutions to the Yang--Baxter equation satisfying the crossing condition (that
is, integrable quantum spin chains). We show that every crossing representation
of the Temperley--Lieb algebra appears in this construction, and in particular
that this construction builds new representations. We extend these to new
representations of the blob algebra, which build new solutions to the Boundary
Yang--Baxter equation (i.e. open spin chains with integrable boundary
conditions).
  We prove that the open spin chain Hamiltonian derived from Sklyanin's
commuting transfer matrix using such a solution can always be expressed as the
representation of an element of the blob algebra, and determine this element.
We determine the representation theory (irreducible content) of the new
representations and hence show that all such Hamiltonians have the same
spectrum up to multiplicity, for any given value of the algebraic boundary
parameter. (A corollary is that our models have the same spectrum as the open
XXZ chain with nondiagonal boundary -- despite differing from this model in
having reference states.) Using this multiplicity data, and other ideas, we
investigate the underlying quantum group symmetry of the new Hamiltonians. We
derive the form of the spectrum and the Bethe ansatz equations.",0503019v1
2004-09-22,From affine Hecke algebras to boundary symmetries,"Motivated by earlier works we employ appropriate realizations of the affine
Hecke algebra and we recover previously known non-diagonal solutions of the
reflection equation for the $U_{q}(\hat{gl_n})$ case. The corresponding $N$
site spin chain with open boundary conditions is then constructed and boundary
non-local charges associated to the non-diagonal solutions of the reflection
equation are derived, as coproduct realizations of the reflection algebra. With
the help of linear intertwining relations involving the aforementioned
solutions of the reflection equation, the symmetry of the open spin chain with
the corresponding boundary conditions is exhibited, being essentially a remnant
of the $U_{q}(\hat{gl_{n}})$ algebra. More specifically, we show that
representations of certain boundary non-local charges commute with the
generators of the affine Hecke algebra and with the local Hamiltonian of the
open spin chain for a particular choice of boundary conditions. Furthermore, we
are able to show that the transfer matrix of the open spin chain commutes with
a certain number of boundary non-local charges, depending on the choice of
boundary conditions.",0409060v4
1997-04-23,"Nuclear medium modifications of the NN interaction via quasielastic ($\vec p,\vec p '$) and ($\vec{p},\vec{n}$) scattering","Within the relativistic PWIA, spin observables have been recalculated for
quasielastic ($\vec p,\vec p '$) and ($\vec p,\vec n$) reactions on a $^{40}$Ca
target. The incident proton energy ranges from 135 to 300 MeV while the
transferred momentum is kept fixed at 1.97 fm^{-1}. In the present
calculations, new Horowitz-Love--Franey relativistic NN amplitudes have been
generated in order to yield improved and more quantitative spin observable
values than before. The sensitivities of the various spin observables to the NN
interaction parameters, such as (1) the presence of the surrounding nuclear
medium, (2) a pseudoscalar versus a pseudovector interaction term, and (3)
exchange effects, point to spin observables which should preferably be measured
at certain laboratory proton energies, in order to test current nuclear models.
This study also shows that nuclear medium effects become more important at
lower proton energies ($\leq$ 200 MeV). A comparison to the limited available
data indicates that the relativistic parametrization of the NN scattering
amplitudes in terms of only the five Fermi invariants (the SVPAT form) is
questionable.",9704049v1
2007-04-20,Evidence for decay of spin-waves above the pseudogap in underdoped YBa2Cu3O6.35,"The magnetic spectrum at high-energies in heavily underdoped
YBa$_{2}$Cu$_{3}$O$_{6.35}$ (T$_{c}$=18 K) has been determined throughout the
Brillouin zone. At low-energy the scattering forms a cone of spin excitations
emanating from the antiferromagnetic (0.5, 0.5) wave vector with an acoustic
velocity similar to that of insulating cuprates. At high energy transfers,
below the maximum energy of 270 meV at (0.5, 0), we observe zone boundary
dispersion much larger and spectral weight loss more extensive than in
insulating antiferromagnets. Moreover we report phenomena not found in
insulators, an overall lowering of the zone-boundary energies and a large
damping of $\sim$ 100 meV of the spin excitations at high-energies. The energy
above which the damping occurs coincides approximately with the gap determined
from transport measurements. We propose that as the energy is raised the spin
excitations encounter an extra channel of decay into particle-hole pairs of a
continuum that we associate with the pseudogap.",0704.2739v1
2007-05-02,Magnetic Excitations in La2CuO4 probed by Indirect Resonant Inelastic X-ray Scattering,"Recent experiments on La$_2$CuO$_4$ suggest that indirect resonant inelastic
X-ray scattering (RIXS) might provide a probe for transversal spin dynamics. We
present in detail a systematic expansion of the relevant magnetic RIXS cross
section by using the ultrashort core-hole lifetime (UCL) approximation. We
compute the scattering intensity and its momentum dependence in leading order
of the UCL expansion. The scattering is due to two-magnon processes and is
calculated within a linear spin-wave expansion of the Heisenberg spin model for
this compound, including longer range and cyclic spin interactions. We observe
that the latter terms in the Hamiltonian enhance the first moment of the
spectrum if they strengthen the antiferromagnetic ordering. The theoretical
spectra agree very well with experimental data, including the observation that
scattering intensity vanishes for the transferred momenta ${\bf q} = (0,0)$ and
${\bf q} = (\pi,\pi)$. We show that at finite temperature there is an
additional single-magnon contribution to the scattering with a spectral weight
proportional to $T^3$. We also compute the leading corrections to the UCL
approximation and find them to be small, putting the UCL results on a solid
basis. All this univocally points to the conclusion that the observed low
temperature RIXS intensity in La$_2$CuO$_4$ is due to two-magnon scattering.",0705.0263v4
2007-05-24,Graph state generation with noisy mirror-inverting spin chains,"We investigate the influence of noise on a graph state generation scheme
which exploits a mirror inverting spin chain. Within this scheme the spin chain
is used repeatedly as an entanglement bus (EB) to create multi-partite
entanglement. The noise model we consider comprises of each spin of this EB
being exposed to independent local noise which degrades the capabilities of the
EB. Here we concentrate on quantifying its performance as a single-qubit
channel and as a mediator of a two-qubit entangling gate, since these are basic
operations necessary for graph state generation using the EB. In particular,
for the single-qubit case we numerically calculate the average channel fidelity
and whether the channel becomes entanglement breaking, i.e., expunges any
entanglement the transferred qubit may have with other external qubits. We find
that neither local decay nor dephasing noise cause entanglement breaking. This
is in contrast to local thermal and depolarizing noise where we determine a
critical length and critical noise coupling, respectively, at which
entanglement breaking occurs. The critical noise coupling for local
depolarizing noise is found to exhibit a power-law dependence on the chain
length. For two qubits we similarly compute the average gate fidelity and
whether the ability for this gate to create entanglement is maintained. The
concatenation of these noisy gates for the construction of a five qubit linear
cluster state and a Greenberger-Horne-Zeilinger state indicates that the level
of noise that can be tolerated for graph state generation is tightly
constrained.",0705.3584v1
2008-04-15,d-wave superconductivity in Hubbard model on the square lattice perturbed by weak 3D uniaxial anisotropy,"The Hubbard model on a square lattice is one of the most studied
condensed-matter quantum problems.Here we find evidence that for intermediate
$U/4t$ values and a hole-concentration range $x\in (x_c,x_*)$ the ground state
of the Hubbard model on the square lattice perturbed by weak three-dimensional
(3D) uniaxial anisotropy has long-range d-wave superconducting order. Here $t$
is the effective nearest-neighbor transfer integral and $U$ the effective
on-site repulsion. The lower critical concentration $x_c$ involves the Ginzburg
number Gi and is approximately given by $x_c\approx {\rm Gi}+x_0\approx 0.05$.
Here $x_0<{\rm Gi}$ is a small critical hole concentration that marks a sharp
quantum phase transition from a Mott-Hubbard insulator with long-range
antiferromagnetic order for $x<x_0$ to an Anderson insulator with short-range
incommensurate spiral spin order for $x\in (x_0,x_c)$. The value of the
critical hole concentration $x_*$ depends on $U/4t$ and is given by $x_*\approx
0.27$ for $U/4t\approx 1.525$. The long-range d-wave superconducting order
emerges below a critical temperature $T_c$ for a hole concentration range
centered at $x_{op}= (x_c+x_*)/2\approx 0.16$. It results from the effects of
the residual interactions of the charge $c$ and spin-neutral two-spinon $s1$
fermions of Ref. \cite{companion2}, as a by-product of the short-range spin
correlations. The spin subsystem provides through such interactions the energy
needed for the effective pairing coupling between the $c$ fermions of the
virtual-electron pair configurations.",0804.2388v3
2008-05-02,Possible Method for Measuring the Proton Form Factors in Processes with and without Proton Spin Flip,"The ratio of the squares of the electric and magnetic proton form factors is
shown to be proportional to the ratio of the cross sections for the elastic
scattering of an unpolarized electron on a partially polarized proton with and
without proton spin flip. The initial proton at rest should be polarized along
the direction of the motion of the final proton. Similar results are valid for
both radiative $ep$ scattering and the photoproduction of pairs on a proton in
the Bethe--Heitler kinematics. When the initial proton is fully polarized in
the direction of the motion of the final proton, the cross section for the $ep
\to ep$ process, as well as for the $ep \to ep \gamma$ and $\gamma p \to e \bar
e p$ processes, without (with) proton spin flip is expressed only in terms of
the square of the electric (magnetic) proton form factor. Such an experiment on
the measurement of the cross sections without and with proton spin flip would
make it possible to acquire new independent data on the behavior of
$G_E^2(Q^2)$ and $G_M^2(Q^2)$, which are necessary for resolving the
contradictions appearing after the experiment of the JLab collaboration on the
measurement of the proton form factors with the method of polarization transfer
from the initial electron to the final proton.",0805.0233v2
2010-01-17,Paramagnetic Spin Correlations in CaFe2As2 Single Crystals,"Magnetic correlations in the paramagnetic phase of CaFe2As2 (T_N=172 K) have
been examined by means of inelastic neutron scattering from 180 K (~ 1.05 T_N)
up to 300 K (~1.8 T_N). Despite the first-order nature of the magnetic
ordering, strong but short-range antiferromagnetic (AFM) correlations are
clearly observed. These correlations, which consist of quasi-elastic scattering
centered at the wavevector Q_{AFM} of the low-temperature AFM structure, are
observed up to the highest measured temperature of 300 K and at high energy
transfer (E> 60 meV). The L dependence of the scattering implies rather weak
interlayer coupling in the tetragonal c-direction corresponding to nearly
two-dimensional fluctuations in the (ab) plane. The spin correlation lengths
within the Fe layer are found to be anisotropic, consistent with underlying
fluctuations of the AFM stripe structure. Similar to the cobalt doped
superconducting BaFe2As2 compounds, these experimental features can be
adequately reproduced by a scattering model that describes short-range
anisotropic spin correlations with overdamped spin dynamics.",1001.2804v2
2010-02-02,Observational Testability of Kerr bound in X-ray Spectrum of Black-Hole Candidates,"The specific angular momentum of a Kerr black hole must not be larger than
its mass. The observational confirmation of this bound which we call a Kerr
bound directly suggests the existence of a black hole. In order to investigate
observational testability of this bound by using the X-ray energy spectrum of
black hole candidates, we calculate energy spectra for a super-spinning object
(or a naked singularity) which is described by a Kerr metric but whose specific
angular momentum is larger than its mass, and then compare the spectra of this
object with those of a black hole. We assume an optically thick and
geometrically thin disc around the super-spinning object and calculate its
thermal energy spectrum seen by a distant observer by solving general
relativistic radiative transfer equations including usual special and general
relativistic effects such as Doppler boosting, gravitational redshift, light
bending and frame-dragging. Surprisingly, for a given black hole, we can always
find its super-spinning counterpart with its spin $a_*$ in the range
$5/3<a_*<8\sqrt{6}/3$ whose observed spectrum is very similar to and
practically indistinguishable from that of the black hole. As a result, we
conclude that to confirm the Kerr bound we need more than the X-ray thermal
spectrum of the black hole candidates.",1002.0421v1
2010-04-25,Studies on regge behaviour and spin-independent and spin-dependent structure functions,"Deep Inelastic Scattering (DIS) experiments have provided important
information on the structure of hadrons and ultimately the structure of matter
and on the nature of interactions between leptons and hadrons, since the
discovery of partons. Various high energy deep inelastic interactions lead to
different evolution equations from which we obtain various structure functions
giving information about the partons i.e. quarks and gluons involved in
different scattering processes. Actually structure function is a mathematical
picture of the hadron structure in the high energy region. Understanding the
behaviour of the structure functions of the nucleon at low-x, where x is the
Bjorken variable, is interesting both theoretically and phenomenologically.
Structure functions are important inputs in many high energy processes and also
important for examination of perturbative quantum chromodynamics (PQCD), the
underlying dynamics of quarks and gluons. In PQCD, for high-Q2, where Q2 is the
four momentum transfer in a DIS process, the Q2-evolutions of these densities
(at fixed-x) are given by mainly Dokshitzer-Gribov-Lipatov-Altarelli-Parisi
(DGLAP) Evolution Equations. In this thesis, we solved both spin-independent
and spin-dependent DGLAP evolution equations applying Regge behaviour of
structure functions at low-x up-to next-next-to-leading order (NNLO) and have
got the respective approximate analytical solutions of structure functions.",1004.4330v1
2010-11-04,"Magnetic order, metamagnetic transitions, and low-temperature spin freezing in Ca3Co2O6: an NMR study","We report on a 59Co NMR investigation of the trigonal cobaltate Ca3Co2O6
carried out on a single crystal, providing precise determinations of the
electric field gradient and chemical shift tensors, and of the internal
magnetic fields at the non-magnetic Co I sites, unavailable from former studies
on powders. The magnetic field-induced ferri- and ferromagnetic phases at
intermediate temperature (e.g. 10 K) are identified by distinct internal
fields, well accounted for by purely dipolar interactions. The vanishing
transferred hyperfine field at the Co I site indicates that the Co3+(I)
orbitals do not participate in the intra-chain superexchange, in disagreement
with a previous theoretical model. The strong Ising character of the system is
confirmed experimentally by the field dependence of the resonance lines,
indicating that local moments are saturated even at the phase boundaries. In
the vicinity of the critical fields, nuclear spin-spin relaxations detect the
spin reversal dynamics of large magnetic assemblies, either Ising chain
fragments or finite size domains, which drive the metamagnetic transitions.
Such collective excitations exhibit a glassy behavior, slowing down to
subacoustic frequencies and freezing at low temperature. The relevance of such
slow fluctuation modes for the low-temperature multi-step behavior reported in
the magnetization is discussed.",1011.1142v2
2011-06-20,Controlled coupling of spin-resolved quantum Hall edge states,"Topologically-protected edge states are dissipationless conducting surface
states immune to impurity scattering and geometrical defects that occur in
electronic systems characterized by a bulk insulating gap. One example can be
found in a two-dimensional electron gas (2DEG) under high magnetic field in the
quantum Hall regime. Based on the coherent control of the coupling between
these protected states, several theoretical proposals for the implementation of
information processing architectures were proposed. Here we introduce and
experimentally demonstrate a new method that allows us to controllably couple
co-propagating spin-resolved edge states of a QH insulator. The scheme exploits
a spatially-periodic in-plane magnetic field that is created by an array of
Cobalt nano-magnets placed at the boundary of the 2DEG. A maximum charge/spin
transfer of about 28% is achieved at 250 mK. This result may open the way to
the realization of scalable quantum-information architectures exploiting the
spin degree of freedom of topologically-protected states.",1106.3965v3
2012-01-20,"Non-magnetic and magnetic thiolate-protected Au25 superatoms on Cu(111), Ag(111) and Au(111) surfaces","Geometry, electronic structure, and magnetic properties of
methylthiolate-stabilized Au$_{25}$L$_{18}$ and MnAu$_{24}$L$_{18}$ (L =
SCH$_3$) clusters adsorbed on noble-metal (111) surfaces have been investigated
by using spin-polarized density functional theory computations. The interaction
between the cluster and the surface is found to be mediated by charge transfer
mainly from or into the ligand monolayer. The electronic properties of the
13-atom metal core remain in all cases rather undisturbed as compared to the
isolated clusters in gas phase. The Au$_{25}$L$_{18}$ cluster retains a clear
HOMO - LUMO energy gap in the range of 0.7 eV to 1.0 eV depending on the
surface. The ligand layer is able to decouple the electronic structure of the
magnetic MnAu$_{24}$L$_{18}$ cluster from Au(111) surface, retaning a high
local spin moment of close to 5 $\mu_{B}$ arising from the spin-polarized
Mn(3d) electrons. These computations imply that the thiolate
monolayer-protected gold clusters may be used as promising building blocks with
tunable energy gaps, tunneling barriers, and magnetic moments for applications
in the area of electron and/or spin transport.",1201.4269v1
2012-03-12,Multi-mode solitons in the classical Dicke-Jaynes-Cummings-Gaudin Model,"We present a detailed analysis of the classical Dicke-Jaynes-Cummings-Gaudin
integrable model, which describes a system of $n$ spins coupled to a single
harmonic oscillator. We focus on the singularities of the vector-valued moment
map whose components are the $n+1$ mutually commuting conserved Hamiltonians.
The level sets of the moment map corresponding to singular values may be viewed
as degenerate and often singular Arnold-Liouville torii. A particularly
interesting example of singularity corresponds to unstable equilibrium points
where the rank of the moment map is zero, or singular lines where the rank is
one. The corresponding level sets can be described as a reunion of smooth
strata of various dimensions. Using the Lax representation, the associated
spectral curve and the separated variables, we show how to construct
explicitely these level sets. A main difficulty in this task is to select,
among possible complex solutions, the physically admissible family for which
all the spin components are real. We obtain explicit solutions to this problem
in the rank zero and one cases. Remarkably this corresponds exactly to
solutions obtained previously by Yuzbashyan and whose geometrical meaning is
therefore revealed. These solutions can be described as multi-mode solitons
which can live on strata of arbitrary large dimension. In these solitons, the
energy initially stored in some excited spins (or atoms) is transferred at
finite times to the oscillator mode (photon) and eventually comes back into the
spin subsystem. But their multi-mode character is reflected by a large
diversity in their shape, which is controlled by the choice of the initial
condition on the stratum.",1203.2488v1
2012-07-12,Formation of Millisecond Pulsars from Intermediate- and Low-Mass X-ray Binaries,"We present a systematic study of the evolution of intermediate- and low-mass
X-ray binaries consisting of an accreting neutron star of mass $1.0-1.8
M_{\odot}$ and a donor star of mass $1.0-6.0 M_{\odot}$. In our calculations we
take into account physical processes such as unstable disk accretion, radio
ejection, bump-induced detachment, and outflow from the $L_{2}$ point.
Comparing the calculated results with the observations of binary radio pulsars,
we report the following results. (1) The allowed parameter space for forming
binary pulsars in the initial orbital period - donor mass plane increases with
increasing neutron star mass. This may help explain why some MSPs with orbital
periods longer than $\sim 60$ days seem to have less massive white dwarfs than
expected. Alternatively, some of these wide binary pulsars may be formed
through mass transfer driven by planet/brown dwarf-involved common envelope
evolution. (2) Some of the pulsars in compact binaries might have evolved from
intermediate-mass X-ray binaries with anomalous magnetic braking. (3) The
equilibrium spin periods of neutron stars in low-mass X-ray binaries are in
general shorter than the observed spin periods of binary pulsars by more than
one order of magnitude, suggesting that either the simple equilibrium spin
model does not apply, or there are other mechanisms/processes spinning down the
neutron stars.",1207.2833v1
2012-09-12,Spin Evolution of Millisecond Magnetars with Hyperaccreting Fallback Disks: Implications for Early Afterglows of Gamma-Ray Bursts,"The shallow decay phase or plateau phase of early afterglows of gamma-ray
bursts (GRBs), discovered by Swift, is currently understood as being due to
energy injection to a relativistic blast wave. One natural scenario for energy
injection invokes a millisecond magnetar as the central engine of GRBs, because
the conventional model of a pulsar predicts a nearly constant
magnetic-dipole-radiation luminosity within the spin-down timescale. However,
we note that significant brightening occurs in some early afterglows, which
apparently conflicts with the above scenario. Here we propose a new model to
explain this significant brightening phenomena by considering a hyperaccreting
fallback disk around a newborn millisecond magnetar. We show that for typical
values of the model parameters, sufficient angular momentum of the accreted
matter is transferred to the magnetar and spins it up. It is this spin-up that
leads to a dramatic increase of the magnetic dipole radiation luminosity with
time and thus significant brightening of an early afterglow. Based on this
model, we carry out numerical calculations and fit well early afterglows of 12
GRBs assuming sufficiently strong fallback accretion. If the accretion is very
weak, our model turns out to be the conventional energy-injection scenario of a
pulsar. Therefore, our model can provide a unified explanation for the shallow
decay phase, plateaus, and significant brightening of early afterglows.",1209.2479v1
2013-05-08,High-bandwidth quantum memory protocol for storing single photons in rare-earth doped crystals,"We present a detailed analysis of a high-bandwidth quantum memory protocol
for storing single photons in a rare-earth-ion doped crystal. The basic idea is
to benefit from a coherent free-induced decay type re-emission which occurs
naturally when a photon with a broadband spectrum is absorbed by a narrow
atomic transition in an optically dense ensemble. This allows for a
high-bandwidth memory for realistic material parameters. Long storage time and
on-demand readout are obtained by means of spins states in a lambda-type
configuration, through the transfer of the optical coherence to a spin
coherence (so-called spin-wave storage). We give explicit formulas and show
numerical results which make it possible to gain insight into the dependence of
the memory efficiency on the optical depth and on the width and the shape of
stored photons. We present a feasibility study in rare-earth doped crystals and
show that high efficiencies and high bandwidth can be obtained with realistic
parameters. High-bandwidth memories using spin-wave storage offers the
possibility of very high time-bandwidth products, which is important for
experiment where high repetition rates are needed.",1305.1863v2
2013-10-23,Neutron scattering measurements of $dd$ and spin-orbit excitations below the Mott-Hubbard gap in CoO,"Neutron scattering is used to investigate the single-ion spin and orbital
excitations below the Mott-Hubbard gap in CoO. Three excitations are reported
at 0.870 $\pm$ 0.009 eV, 1.84 $\pm$ 0.03, and 2.30 $\pm$ 0.15 eV. These were
parameterized within a weak crystal field scheme with an intra-orbital exchange
of $J(dd)$=1.3 $\pm$ 0.2 eV and a crystal field splitting 10Dq=0.94 $\pm$ 0.10
eV. A reduced spin-orbit coupling of \lambda=-0.016 $\pm$ 0.003 eV is derived
from dilute samples of Mg$_{0.97}$Co$_{0.03}$O, measured to remove
complications due to spin exchange and structural distortion parameters which
split the cubic phase degeneracy of the orbital excitations complicating the
inelastic spectrum. The 1.84 eV, while reported using resonant x-ray and
optical techniques, was absent or weak for non resonant x-ray experiments and
overlaps with the expected position of a $^{4}A_{2}$ level. This transition is
absent in the dipolar approximation but expected to have a finite quadrupolar
matrix element that can be observed with neutron scattering techniques at
larger momentum transfers. Our results agree with a crystal field analysis (in
terms of Racah parameters and Tanabe-Sugano diagrams) and with previous
calculations performed using local-density band theory for Mott insulating
transition metal oxides. The results also demonstrate the use of neutron
scattering for measuring dipole forbidden transitions in transition metal oxide
systems.",1310.6207v1
2014-02-06,Secular Damping of Stellar Bars in Spinning Dark Matter Halos,"We demonstrate that growth of stellar bars in spinning dark matter halos is
heavily suppressed in the secular phase of evolution, using numerical
simulations of isolated galaxies. In a representative set of models, we show
that for values of the cosmological spin parameter lambda > 0.03, bar growth
(in strength and size) becomes increasingly quenched. Furthermore, slowdown of
bar pattern speed weakens substantially with increasing `lambda,' until it
ceases completely. The terminal structure of bars is affected as well,
including extent and shape of their boxy/peanut bulges. The essence of this
effect lies in the modified angular momentum exchange between the disk and the
halo facilitated by the bar. For the first time we have demonstrated that a
dark matter halo can emit and not purely absorb angular momentum. Although the
halo as a whole is not found to emit, the net transfer of angular momentum from
the disk to the halo is significantly reduced or completely eliminated. The
paradigm shift implies that the accepted view that disks serve as sources of
angular momentum and halos serve as sinks, must be revised. Halos with lambda >
0.03 are expected to form a substantial fraction, based on lognormal
distribution of lambda. Dependence of secular bar evolution on halo spin,
therefore, implies profound corollaries for the cosmological evolution of
galactic disks.",1402.1491v2
2014-09-12,The dynamics of a doped hole in cuprates is not controlled by spin fluctuations,"Twenty seven years after the discovery of high-temperature superconductivity
\cite{BedMu}, consensus on its theoretical explanation is still absent. To a
good extent, this is due to the difficulty of studying strongly correlated
systems near half-filling, needed to understand the behaviour of one or few
holes doped into a CuO$_2$ layer. To simplify this task it is customary to
replace three-band models \cite{Emery} describing the doping holes as entering
the O $2p$ orbitals of these charge-transfer insulators \cite{ZSA} with much
simpler one-band Hubbard or $tJ$ models \cite{rev1,rev2}. Here we challenge
this approach, showing that not only is the dynamics of a doped hole easier to
understand in models that explicitly include the O orbitals, but also that our
solution contradicts the long-held belief that the quantum spin fluctuations of
the antiferromagnetic (AFM) background play a key role in determining this
dynamics. Indeed, we show that the correct, experimentally observed dispersion
is generically obtained for a hole moving on the O sublattice, and coupled to a
N\'eel lattice of spins without spin fluctuations. This marks a significant
conceptual change in our understanding of the relevant phenomenology and opens
the way to studying few-holes dynamics without finite-size effect issues
\cite{BayoB}, to understand the actual strength of the ""magnetic glue"".",1409.3647v1
2015-04-08,Signature of a spin-up magnetar from multi-band afterglow rebrightening of GRB 100814A,"In recent years, more and more gamma-ray bursts with late rebrightenings in
multi-band afterglows unveil the late-time activities of the central engines.
GRB 100814A is a special one among the well-sampled events, with complex
temporal and spectral evolution. The single power-law shallow decay index of
the optical light curve observed by GROND between 640 s and 10 ks is
$\alpha_{\rm opt} = 0.57 \pm 0.02$, which apparently conflicts with the simple
external shock model expectation. Especially, there is a remarkable
rebrightening in the optical to near infrared bands at late time, challenging
the external shock model with synchrotron emission coming from the interaction
of the blast wave with the surrounding interstellar medium. In this paper, we
invoke a magnetar with spin evolution to explain the complex multi-band
afterglow emission of GRB 100814A. The initial shallow decay phase in optical
bands and the plateau in X-ray can be explained as due to energy injection from
a spin-down magnetar. At late time, with the falling of materials from the
fall-back disk onto the central object of the burster, angular momentum of the
accreted materials is transferred to the magnetar, which leads to a spin-up
process. As a result, the magnetic dipole radiation luminosity will increase,
resulting in the significant rebrightening of the optical afterglow. It is
shown that the observed multi-band afterglow emission can be well reproduced by
the model.",1504.01824v1
2015-08-18,Bogoliubov quasiparticles coupled to the antiferromagnetic spin mode in a vortex core,"In copper- and iron-based unconventional superconductors, the Bogoliubov
quasiparticles interact with a spin resonance at momentum $(\pi,\pi)$. This
interaction is revealed by specific signatures in the quasiparticle
spectroscopies, like kinks in photoemission and dips in tunneling. We study
these signatures, as they appear inside and around a vortex core in the local
density of states (LDOS), a property accessible experimentally by scanning
tunneling spectroscopy. Our model retains the whole nonlocal structure of the
self-energy in space and time and is therefore not amenable to a Hamiltonian
treatment using Bogoliubov-de Gennes equations. The interaction with the spin
resonance does not suppress the zero-bias peak at the vortex center, although
it reduces its spectral weight; neither does it smear out the vortex LDOS, but
rather it adds structure to it. Some of the signatures we find may have been
already measured in FeSe, but remained unnoticed. We compare the LDOS as a
function of both energy and position with and without coupling to the spin
resonance and observe, in particular, that the quasiparticle interference
patterns around the vortex are strongly damped by the coupling. We study in
detail the transfer of spectral weight induced both locally and globally by the
interaction and also by the formation of the vortex. Finally, we introduce a
new way of imaging the quasiparticles in real space, which combines locality
and momentum-space sensitivity. This approach allows one to access
quasiparticle properties that are not contained in the LDOS.",1508.04225v2
2015-11-11,Non-local polarization feedback in a fractional quantum Hall ferromagnet,"In a quantum Hall ferromagnet, the spin polarization of the two-dimensional
electron system can be dynamically transferred to nuclear spins in its vicinity
through the hyperfine interaction. The resulting nuclear field typically acts
back locally, modifying the local electronic Zeeman energy. Here we report a
non-local effect arising from the interplay between nuclear polarization and
the spatial structure of electronic domains in a $\nu=2/3$ fractional quantum
Hall state. In our experiments, we use a quantum point contact to locally
control and probe the domain structure of different spin configurations
emerging at the spin phase transition. Feedback between nuclear and electronic
degrees of freedom gives rise to memristive behavior, where electronic
transport through the quantum point contact depends on the history of current
flow. We propose a model for this effect which suggests a novel route to
studying edge states in fractional quantum Hall systems and may account for
so-far unexplained oscillatory electronic-transport features observed in
previous studies.",1511.03593v2
2016-05-12,Intertwined Lattice Deformation and Magnetism in Monovacancy Graphene,"Using density functional calculations we have investigated the local spin
moment formation and lattice deformation in graphene when an isolated vacancy
is created. We predict two competing equilibrium structures: a ground state
planar configuration with a saturated local moment of 1.5 $\mu_B$, and a
metastable non-planar configuration with a vanishing magnetic moment, at a
modest energy expense of ~50 meV. Though non-planarity relieves the lattice of
vacancy-induced strain, the planar state is energetically favored due to
maximally localized defect states (v$\sigma$, v$\pi$). In the planar
configuration, charge transfer from itinerant (Dirac) states weakens the
spin-polarization of v$\pi$ yielding a fractional moment, which is aligned
parallel to the unpaired v$\sigma$ electron through Hund's coupling. In the
non-planar configuration, the absence of orthogonal symmetry allows interaction
between v$\sigma$ and local d$\pi$ states, to form a hybridized
v$\sigma^\prime$ state. The non-orthogonality also destabilizes the Hund's
coupling, and an antiparallel alignment between v$\sigma$ and v$\pi$ lowers the
energy. The gradual spin reversal of v$\pi$ with increasing non-planarity opens
up the possibility of an intermediate structure with balanced v$\pi$ spin
population. If such a structure is realized under external perturbations,
diluted vacancy concentration may lead to v$\sigma$ based spin-1/2
paramagnetism.",1605.03921v1
2017-01-25,Hybrid nanodiamond-YIG systems for efficient quantum information processing and nanoscale sensing,"The nitrogen-vacancy (NV) center in diamond has been extensively studied in
recent years for its remarkable quantum coherence properties that make it an
ideal candidate for room temperature quantum computing and quantum sensing
schemes. However, these schemes rely on spin-spin dipolar interactions, which
require the NV centers to be within a few nanometers from each other while
still separately addressable, or to be in close proximity of the diamond
surface, where their coherence properties significantly degrade. Here we
demonstrate a method for overcoming these limitations using a hybrid yttrium
iron garnet (YIG)-nanodiamond quantum system constructed with the help of
directed assembly and transfer printing techniques. We show that YIG spin-waves
can amplify the oscillating field of a microwave source by more than two orders
of magnitude and efficiently mediate its coherent interactions with an NV
center ensemble. These results demonstrate that spin-waves in ferromagnets can
be used as quantum buses for enhanced, long-range qubit interactions, paving
the way to ultra-efficient manipulation and coupling of solid state defects in
hybrid quantum networks and sensing devices.",1701.07401v1
2017-03-16,Spin alignment of stars in old open clusters,"Stellar clusters form by gravitational collapse of turbulent molecular
clouds, with up to several thousand stars per cluster. They are thought to be
the birthplace of most stars and therefore play an important role in our
understanding of star formation, a fundamental problem in astrophysics. The
initial conditions of the molecular cloud establish its dynamical history until
the stellar cluster is born. However, the evolution of the cloud's angular
momentum during cluster formation is not well understood. Current observations
have suggested that turbulence scrambles the angular momentum of the
cluster-forming cloud, preventing spin alignment amongst stars within a
cluster. Here we use asteroseismology to measure the inclination angles of spin
axes in 48 stars from the two old open clusters NGC~6791 and NGC~6819. The
stars within each cluster show strong alignment. Three-dimensional
hydrodynamical simulations of proto-cluster formation show that at least 50 %
of the initial proto-cluster kinetic energy has to be rotational in order to
obtain strong stellar-spin alignment within a cluster. Our result indicates
that the global angular momentum of the cluster-forming clouds was efficiently
transferred to each star and that its imprint has survived after several
gigayears since the clusters formed.",1703.05588v2
2017-03-22,Level structure of deeply bound levels of the $c^3Σ_g^+$ state of $^{87}\text{Rb}_2$,"We spectroscopically investigate the hyperfine, rotational and Zeeman
structure of the vibrational levels $\text{v}'=0$, $7$, $13$ within the
electronically excited $c^3\Sigma_g^+$ state of $^{87}\text{Rb}_2$ for magnetic
fields of up to $1000\,\text{G}$. As spectroscopic methods we use short-range
photoassociation of ultracold Rb atoms as well as photoexcitation of ultracold
molecules which have been previously prepared in several well-defined quantum
states of the $a^3\Sigma_u^+$ potential. As a byproduct, we present optical
two-photon transfer of weakly bound Feshbach molecules into $a^3\Sigma_u^+$,
$\text{v}=0$ levels featuring different nuclear spin quantum numbers. A simple
model reproduces well the molecular level structures of the $c^3\Sigma_g^+$
vibrational states and provides a consistent assignment of the measured
resonance lines. Furthermore, the model can be used to predict the relative
transition strengths of the lines. From fits to the data we extract for each
vibrational level the rotational constant, the effective spin-spin interaction
constant, as well as the Fermi contact parameter and (for the first time) the
anisotropic hyperfine constant. In an alternative approach, we perform
coupled-channel calculations where we fit the relevant potential energy curves,
spin-orbit interactions and hyperfine functions. The calculations reproduce the
measured hyperfine level term frequencies with an average uncertainty of
$\pm9\:$MHz, similar as for the simple model. From these fits we obtain a
section of the potential energy curve for the $c^3\Sigma_g^+$ state which can
be used for predicting the level structure for the vibrational manifold
$\text{v}'=0$ to $13$ of this electronic state.",1703.07752v1
2017-07-11,Strong electron-hole symmetric Rashba spin-orbit coupling in graphene/monolayer transition metal dichalcogenide heterostructures,"Despite its extremely weak intrinsic spin-orbit coupling (SOC), graphene has
been shown to acquire considerable SOC by proximity coupling with exfoliated
transition metal dichalcogenides (TMDs). Here we demonstrate strong induced
Rashba SOC in graphene that is proximity coupled to a monolayer TMD film, MoS2
or WSe2, grown by chemical vapor deposition with drastically different Fermi
level positions. Graphene/TMD heterostructures are fabricated with a
pickup-transfer technique utilizing hexagonal boron nitride, which serves as a
flat template to promote intimate contact and therefore a strong interfacial
interaction between TMD and graphene as evidenced by quenching of the TMD
photoluminescence. We observe strong induced graphene SOC that manifests itself
in a pronounced weak anti-localization (WAL) effect in the graphene
magnetoconductance. The spin relaxation rate extracted from the WAL analysis
varies linearly with the momentum scattering time and is independent of the
carrier type. This indicates a dominantly Dyakonov-Perel spin relaxation
mechanism caused by the induced Rashba SOC. Our analysis yields a Rashba SOC
energy of ~1.5 meV in graphene/WSe2 and ~0.9 meV in graphene/MoS2,
respectively. The nearly electron-hole symmetric nature of the induced Rashba
SOC provides a clue to possible underlying SOC mechanisms.",1707.03434v1
2017-07-22,Understanding the magnetic resonance spectrum of nitrogen vacancy centers in an ensemble of randomly-oriented nanodiamonds,"Nanodiamonds containing nitrogen vacancy (NV-) centers show promise for a
number of emerging applications including targeted in vivo imaging and
generating nuclear spin hyperpolarization for enhanced NMR spectroscopy and
imaging. Here, we develop a detailed understanding of the magnetic resonance
behavior of NV- centers in an ensemble of nanodiamonds with random crystal
orientations. Two-dimensional optically detected magnetic resonance
spectroscopy reveals the distribution of energy levels, spin populations, and
transition probabilities that give rise to a complex spectrum. We identify
overtone transitions that are inherently insensitive to crystal orientation and
give well-defined transition frequencies that access the entire nanodiamond
ensemble. These transitions may be harnessed for high-resolution imaging and
generation of nuclear spin hyperpolarization. The data are well described by
numerical simulations from the zero- to high-field regimes, including the
intermediate regime of maximum complexity. We evaluate the prospects of
nanodiamond ensembles specifically for nuclear hyperpolarization and show that
frequency-swept dynamic nuclear polarization may transfer a large amount of the
NV- center's hyperpolarization to nuclear spins by sweeping over a small region
of its spectrum.",1707.07205v1
2017-12-19,Li doping kagome spin liquid compounds,"Herbertsmithite and Zn-doped barlowite are two compounds for experimental
realization of twodimensional gapped kagome spin liquid. Theoretically, it has
been proposed that charge doping a quantum spin liquid gives rise to exotic
metallic states, such as high-temperature superconductivity. However, one
recent experiment about herbertsmithite with successful Li-doping shows
surprisingly the insulating state even under the heavy doped scenario, which
can hardly be explained by many-body physics. Using first-principles
calculation, we performed a comprehensive study about the Li intercalated
doping effect of these two compounds. For the Li-doped herbertsmithite, we
identified the optimized Li position at the Cl-(OH)$_3$-Cl pentahedron site
instead of previously speculated Cl-(OH)$_3$ tetrahedral site. With the
increase of Li doping concentration, the saturation magnetization decreases
linearly due to the charge transfer from Li to Cu ions. Moreover, we found that
Li forms chemical bonds with the nearby (OH)$^-$ and Cl$^-$ ions, which lowers
the surrounding chemical potential and traps the electron, as evidenced by the
localized charge distribution, explaining the insulating behavior measured
experimentally. Though with different structure from herbertsmithite, Zn-doped
Barlowite shows the same features upon Li doping. We conclude that Li doping
this family of kagome spin liquid cannot realize exotic metallic states, other
methods should be further explored, such as element substitution with different
valence electrons.",1712.06791v2
2017-12-20,Spatial and spin symmetry breaking in semidefinite-programming-based Hartree-Fock theory,"The Hartree-Fock problem was recently recast as a semidefinite optimization
over the space of rank-constrained two-body reduced-density matrices (RDMs)
[Phys. Rev. A 89, 010502(R) (2014)]. This formulation of the problem transfers
the non-convexity of the Hartree-Fock energy functional to the rank constraint
on the two-body RDM. We consider an equivalent optimization over the space of
positive semidefinite one-electron RDMs (1-RDMs) that retains the non-convexity
of the Hartree-Fock energy expression. The optimized 1-RDM satisfies ensemble
$N$-representability conditions, and ensemble spin-state conditions may be
imposed as well. The spin-state conditions place additional linear and
nonlinear constraints on the 1-RDM. We apply this RDM-based approach to several
molecular systems and explore its spatial (point group) and spin ($S^2$ and
$S_3$) symmetry breaking properties. When imposing $S^2$ and $S_3$ symmetry but
relaxing point group symmetry, the procedure often locates
spatial-symmetry-broken solutions that are difficult to identify using standard
algorithms. For example, the RDM-based approach yields a smooth,
spatial-symmetry-broken potential energy curve for the well-known Be--H$_2$
insertion pathway. We also demonstrate numerically that, upon relaxation of
$S^2$ and $S_3$ symmetry constraints, the RDM-based approach is equivalent to
real-valued generalized Hartree-Fock theory.",1712.07680v3
2018-03-22,Doping evolution of charge and spin excitations in two-leg Hubbard ladders: comparing DMRG and RPA+FLEX results,"We study the magnetic and charge dynamical response of a Hubbard model in a
two-leg ladder geometry using the density matrix renormalization group (DMRG)
method and the random phase approximation within the fluctuation-exchange
approximation (RPA+FLEX). Our calculations reveal that RPA+FLEX can capture the
main features of the magnetic response from weak up to intermediate Hubbard
repulsion for doped ladders, when compared with the numerically exact DMRG
results. However, while at weak Hubbard repulsion both the spin and charge
spectra can be understood in terms of weakly-interacting electron-hole
excitations across the Fermi surface, at intermediate coupling DMRG shows
gapped spin excitations at large momentum transfer that remain gapless within
the RPA+FLEX approximation. For the charge response, RPA+FLEX can only
reproduce the main features of the DMRG spectra at weak coupling and high
doping levels, while it shows an incoherent character away from this limit.
Overall, our analysis shows that RPA+FLEX works surprisingly well for spin
excitations at weak and intermediate Hubbard $U$ values even in the difficult
low-dimensional geometry such as a two-leg ladder. Finally, we discuss the
implications of our results for neutron scattering and resonant inelastic x-ray
scattering experiments on two-leg ladder cuprate compounds.",1803.08597v1
2018-06-26,Core and crust contributions in pulsar glitches: constraints from the slow rise of the largest glitch observed in the Crab pulsar,"Pulsar glitches are attributed to the sudden re-coupling of very weakly
coupled large scale superfluid components in the neutron star interior. This
process leads to rapid exchange of angular momentum and an increase in spin
frequency. The transfer of angular momentum is regulated by a dissipative
mutual friction, whose strength defines the spin-up timescale of a glitch.
Hence, observations of glitch rises can be used to shed light on the dominant
microphysical interactions at work in the high density interior of the star. We
present a simple analytical model, complemented with more detailed numerical
simulations, which produces a fast spin-up followed by a more gradual rise.
Such features are observed in some large glitches of the Crab pulsar, including
the largest recent glitch of 2017. We also use observations to constrain the
mutual friction coefficient of the glitch-driving region for two possible
locations: the inner crust and outer core of the star. We find that the
features of Crab glitches require smaller values of the mutual friction
coefficient than those needed to explain the much faster Vela spin-ups. This
suggests a crustal origin for the former but an outer core contribution for the
latter.",1806.10168v1
2018-12-18,Petahertz Spintronics,"The enigmatic coupling between electronic and magnetic phenomena was one of
the riddles propelling the development of modern electromagnetism. Today, the
fully controlled electric field evolution of ultrashort laser pulses permits
the direct and ultrafast control of electronic properties of matter and is the
cornerstone of light-wave electronics. In sharp contrast, because there is no
first order interaction between light and spins, the magnetic properties of
matter can only be affected indirectly on the much slower tens-of-femtosecond
timescale in a sequence of optical excitation followed by the rearrangement of
the spin structure. Here we record an orders of magnitude faster magnetic
switching with sub-femtosecond response time by initiating optical excitations
with near-single-cycle laser pulses in a ferromagnetic layer stack. The
unfolding dynamics are tracked in real-time by a novel attosecond time-resolved
magnetic circular dichroism (atto-MCD) detection scheme revealing optically
induced spin and orbital momentum transfer (OISTR) in synchrony with light
field driven charge relocation. In tandem with ab-initio quantum dynamical
modelling, we show how this mechanism provides simultaneous control over
electronic and magnetic properties that are at the heart of spintronic
functionality. This first incarnation of attomagnetism observes light field
coherent control of spin-dynamics in the initial non-dissipative temporal
regime and paves the way towards coherent spintronic applications with
Petahertz clock rates.",1812.07420v1
2019-02-14,Polarization resolved Cu $L_3$-edge resonant inelastic x-ray scattering of orbital and spin excitations in NdBa$_{2}$Cu$_{3}$O$_{7-δ}$,"High resolution resonant inelastic x-ray scattering (RIXS) has proven
particularly effective in the determination of crystal field and spin
excitations in cuprates. Its strength lies in the large Cu $L_{3}$ resonance
and in the fact that the scattering cross section follows quite closely the
single-ion model predictions, both in the insulating parent compounds and in
the superconducting doped materials. However, the spectra become increasingly
broader with (hole) doping, hence resolving and assigning spectral features has
proven challenging even with the highest energy resolution experimentally
achievable. Here we have overcome this limitation by measuring the complete
polarization dependence of the RIXS spectra as function of momentum transfer
and doping in thin films of NdBa$_{2}$Cu$_{3}$O$_{7-\delta}$. Besides
confirming the previous assignment of $dd$ and spin excitations (magnon,
bimagnon) in the antiferromagnetic insulating parent compound, we unequivocally
single out the actual spin-flip contribution at all dopings. We also
demonstrate that the softening of $dd$ excitations is mainly attributed to the
shift of the $xy$ peak to lower energy loss. These results provide a definitive
assessment of the RIXS spectra of cuprates and demonstrate that RIXS
measurements with full polarization control are practically feasible and highly
informative.",1902.05471v1
2019-02-18,Dynamics of frequency-swept nuclear spin optical pumping in powdered diamond at low magnetic fields,"A broad effort is underway to improve the sensitivity of nuclear magnetic
resonance through the use of dynamic nuclear polarization. Nitrogen-vacancy
(NV) centers in diamond offer an appealing platform because these paramagnetic
defects can be optically polarized efficiently at room temperature. However,
work thus far has been mainly limited to single crystals because most
polarization transfer protocols are sensitive to misalignment between the NV
and magnetic field axes. Here we study the spin dynamics of NV-13C pairs in the
simultaneous presence of optical excitation and microwave frequency sweeps at
low magnetic fields. We show that a subtle interplay between illumination
intensity, frequency sweep rate, and hyperfine coupling strength leads to
efficient, sweep-direction-dependent 13C spin polarization over a broad range
of orientations of the magnetic field. In particular, our results strongly
suggest that finely-tuned, moderately coupled nuclear spins are key to the
hyperpolarization process, which makes this mechanism distinct from other known
dynamic polarization channels. These findings pave the route to applications
where powders are intrinsically advantageous, including the hyper-polarization
of target fluids in contact with the diamond surface or the use of
hyperpolarized particles as contrast agents for in-vivo imaging.",1902.06805v1
2019-04-04,Topological-chiral magnetic interactions driven by emergent orbital magnetism,"Two hundred years ago, Andr\'e-Marie Amp\`ere discovered that electric loops
in which currents of electrons are generated by a penetrating magnetic field
can interact with each other. Here we show that Amp\`ere's observation can be
transferred to the quantum realm of interactions between triangular plaquettes
of spins on a lattice, where the electrical currents at the atomic scale are
associated with a peculiar type of the orbital motion of electrons in response
to the non-coplanarity of neighbouring spins playing the role of a magnetic
field. The resulting topological orbital moment underlies the relation of the
orbital dynamics with the topology of the spin structure. We demonstrate that
the interactions of the topological orbital moments with each other and with
the spins of the underlying lattice give rise to a new class of magnetic
interactions $-$ topological chiral interactions $-$ which can dominate over
the celebrated Dzyaloshinskii-Moriya interaction, thus opening a path for the
realization of new classes of chiral magnetic materials with three-dimensional
magnetization textures such as magnetic hopfions.",1904.02369v3
2019-05-23,Spin-orbit coupling and crystal-field distortions for a low-spin $3d^5$ state in BaCoO$_{3}$,"We have studied the electronic structure of BaCoO$_3$ using soft x-ray
absorption spectroscopy at the Co-$L_{2,3}$ and O-$K$ edges, magnetic circular
dichroism at the Co-$L_{2,3}$ edges, as well as valence band hard x-ray
photoelectron spectroscopy. The quantitative analysis of the spectra
established that the Co ions are in the formal low-spin tetravalent 3$d^5$
state and that the system is a negative charge transfer Mott insulator. The
spin-orbit coupling plays also an important role for the magnetism of the
system. At the same time, a trigonal crystal field is present with sufficient
strength to bring the 3$d^5$ ion away from the $J_{eff} = 1/2$ state. The sign
of this crystal field is such that the $a_{1g}$ orbital is doubly occupied,
explaining the absence of a Peierl's transition in this system which consists
of chains of face-sharing CoO$_6$ octahedra. Moreover, with one hole residing
in the $e_g^{\pi}$, the presence of an orbital moment and strong
magneto-crystalline anisotropy can be understood. Yet, we also infer that
crystal fields with lower symmetry must be present to reproduce the measured
orbital moment quantitatively, thereby suggesting the possibility for orbital
ordering to occur in BaCoO$_3$.",1905.09549v1
2020-04-08,Interplay between spin proximity effect and charge-dependent exciton dynamics in MoSe$_2$ / CrBr$_3$ van der Waals heterostructures,"Semiconducting ferromagnet-nonmagnet interfaces in van der Waals
heterostructures present a unique opportunity to investigate magnetic proximity
interactions dependent upon a multitude of phenomena including valley and layer
pseudospins, moir\'e periodicity, or exceptionally strong Coulomb binding.
Here, we report a charge-state dependency of the magnetic proximity effects
between MoSe$_2$ and CrBr$_3$ in photoluminescence, whereby the valley
polarization of the MoSe$_2$ trion state conforms closely to the local CrBr$_3$
magnetization, while the neutral exciton state remains insensitive to the
ferromagnet. We attribute this to spin-dependent interlayer charge transfer
occurring on timescales between the exciton and trion radiative lifetimes.
Going further, we uncover by both the magneto-optical Kerr effect and
photoluminescence a domain-like spatial topography of contrasting valley
polarization, which we infer to be labyrinthine or otherwise highly intricate,
with features smaller than 400 nm corresponding to our optical resolution. Our
findings offer a unique insight into the interplay between short-lived valley
excitons and spin-dependent interlayer tunnelling, while also highlighting
MoSe$_2$ as a promising candidate to optically interface with exotic spin
textures in van der Waals structures.",2004.04073v2
2020-04-20,Operando direct observation of spin states correlated with device performance in perovskite solar cells,"Perovskite solar cells are one of the most attracting cells because of
remarkably improved power conversion efficiency (PCE) recently. Toward their
practical application, it is important not only to increase the PCE but also to
elucidate the deterioration mechanism. Here, we present operando direct
observation of spin states in the cells using electron spin resonance (ESR)
spectroscopy in order to investigate the operation and deterioration mechanisms
from a microscopic viewpoint. By simultaneous measurements of solar-cell and
ESR characteristics of the same cell, the spin states in the hole-transport
material (HTM) spiro-OMeTAD are demonstrated to be changed at the molecular
level, which varies the device performance under device operation. These
variations are ascribed to the change of hole transport by charge-carrier
scatterings and filling of deep trapping levels in the HTM, and to interfacial
electric dipole layers formed at the HTM interfaces. In addition, reverse
electron transfer from TiO2 layer to the HTM layer is directly demonstrated at
the molecular level under ultraviolet light irradiation, which causes the
decrease in the HTM doping effect. Thus, conducting such operando microscopic
investigation on the internal states in the cells would be useful to obtain a
new further guideline for improving the device performance and durability.",2004.09070v1
2020-05-22,Coexistence of Two Components in Magnetic Excitations of La$_{2-x}$Sr$_x$CuO$_4$ ($x$ = 0.10 and 0.16),"To elucidate the spin dynamics of La$_{2-x}$Sr$_x$CuO$_4$, which couples with
the charge degree of freedom, the spin excitations spanning the characteristic
energy ($E_{\rm cross}$ $\sim$35-40 meV) are investigated for underdoped $x$ =
0.10 and optimally doped (OP) $x$ = 0.16 through inelastic neutron scattering
measurements. Analysis based on a two-component picture of high-quality data
clarified the possible coexistence of uprightly standing incommensurate (IC)
excitations with gapless commensurate (C) excitations in the energy-momentum
space. The IC component weakens the intensity toward $E_{\rm cross}$ with
increasing energy transfer ($\hbar\omega$), whereas the C component strengthens
at high-$\hbar\omega$ regions. The analysis results imply that the
superposition of two components with a particular intensity balance forms an
hourglass-shaped excitation in appearance. Furthermore, the temperature
dependence of the intensity of each component exhibits different behaviors; the
IC component disappears near the pseudo-gap temperature ($T$*) upon warming,
whereas the C component is robust against temperature. These results suggest
the itinerant electron spin nature and the localized magnetism of the parent
La$_2$CuO$_4$ in IC and C excitations, respectively, similar to the spin
excitations in the OP YBa$_2$Cu$_3$O$_{6+\delta}$ and HgBa$_2$CuO$_{4+\delta}$
with higher superconducting-transition temperatures.",2005.11025v1
2020-06-19,X-ray detection of ultrashort spin current pulses in synthetic antiferromagnets,"We explore the ultrafast generation of spin currents in magnetic multilayer
samples by applying fs laser pulses to one layer and measuring the magnetic
response in the other layer by element-resolved x-ray spectroscopy. In
Ni(5~nm)/Ru(2~nm)/Fe(4~nm), the Ni and Fe magnetization directions couple
antiferromagnetically due to the RKKY interaction, but may be oriented parallel
through an applied magnetic field. After exciting the top Ni layer with a fs
laser pulse, we find that also the Fe layer underneath demagnetizes, with a
$4.1 \pm 1.9$\% amplitude difference between parallel and antiparallel
orientation of the Ni and Fe magnetizations. We attribute this difference to
the influence of a spin current generated by the fs laser pulse that transfers
angular momentum from the Ni into the Fe layer. Our results confirm that
superdiffusive spin transport plays a role in determining the sub-ps
demagnetization dynamics of synthetic antiferromagnetic layers, but also
evidence large depolarization effects due to hot electron dynamics, which are
independent of the relative alignment of the magnetization in Ni and Fe.",2006.11030v1
2020-07-24,Thermal and orbital evolution of low-mass exoplanets,"Thermal, orbital, and rotational dynamics of tidally loaded exoplanets are
interconnected by intricate feedback. The rheological structure of the planet
determines its susceptibility to tidal deformation and, as a consequence,
participates in shaping its orbit. The orbital parameters and the spin state,
conversely, control the rate of tidal dissipation and may lead to substantial
changes of the interior. We investigate the coupled thermal-orbital evolution
of differentiated rocky exoplanets governed by the Andrade viscoelastic
rheology. The coupled evolution is treated by a semi-analytical model, 1d
parametrized heat transfer and self-consistently calculated tidal dissipation.
First, we conduct several parametric studies, exploring the effect of the
rheological properties, the planet's size, and the orbital eccentricity on the
tidal locking and dissipation. These tests show that the role of tidal locking
into high spin-orbit resonances is most prominent on low eccentric orbits,
where it results in substantially higher tidal heating than the synchronous
rotation. Second, we calculate the long-term evolution of three currently known
low-mass exoplanets with nonzero orbital eccentricity and absent or yet unknown
eccentricity forcing (namely GJ 625 b, GJ 411 b, and Proxima Centauri b). The
tidal model incorporates the formation of a stable magma ocean and a
consistently evolving spin rate. We find that the thermal state is strongly
affected by the evolution of eccentricity and spin state and proceeds as a
sequence of thermal equilibria. Final despinning into synchronous rotation
slows down the orbital evolution and helps to maintain long-term stable orbital
eccentricity.",2007.12459v1
2020-08-12,The effective theory of nuclear scattering for a WIMP of arbitrary spin,"We introduce a systematic approach to characterize the most general
non-relativistic WIMP-nucleus interaction allowed by Galilean invariance for a
WIMP of arbitrary spin $j_\chi$ in the approximation of one-nucleon currents.
Five nucleon currents arise from the nonrelativistic limit of the free nucleon
Dirac bilinears. Our procedure consists in (1) organizing the WIMP currents
according to the rank of the $2 j_\chi+1$ irreducible operator products of up
to $2 j_\chi$ WIMP spin vectors, and (2) coupling each of the WIMP currents to
each of the five nucleon currents. The transferred momentum $q$ appears to a
power fixed by rotational invariance. For a WIMP of spin $j_\chi$ we find a
basis of 4+20$j_\chi$ independent operators that exhaust all the possible
operators that drive elastic WIMP-nucleus scattering in the approximation of
one-nucleon currents. By comparing our operator basis, which is complete, to
the operators already introduced in the literature we show that some of the
latter for $j_\chi=1$ were not independent and some were missing. We provide
explicit formulas for the squared scattering amplitudes in terms of the nuclear
response functions, which are available in the literature for most of the
targets used in WIMP direct detection experiments.",2008.05120v1
2020-10-12,Hyperon--anti-hyperon polarization asymmetry in relativistic heavy-ion collisions as an interplay between chiral and helical vortical effects,"We argue that the enhancement in the spin polarization of anti-hyperons
compared to the polarization of the hyperons in noncentral relativistic
heavy-ion collisions arises as a result of an interplay between the chiral and
helical vortical effects. The chiral vortical effect generates the axial
current of quarks along the vorticity axis while the recently found helical
vortical effect generates the helicity flow -- the projection of the quark's
polarization vector onto its momentum -- along the same axis. For massless
fermions, the helical charge corresponds to a difference in the contributions
of particles and anti-particles to the axial charge. Assuming that the spin of
light quarks transfers to the strange quarks via the vector kaon states (""the
spin-vector dominance""), we are able to describe the ratio of the (anti)hyperon
spin polarizations, obtained by the STAR group, without fitting parameters. We
also argue that the helical vortical effect dominates over the chiral vortical
effect and the chiral magnetic effect in the generation of the electric
current.",2010.05831v2
2020-12-07,Double-Exchange Enhanced Magnetic Blue-Shift of Mott Gaps,"A substantial energy gap of charge excitations induced by strong correlations
is the characteristic feature of Mott insulators. We study how the Mott gap is
affected by long-range antiferromagnetic order. Our key finding is that the
Mott gap is increased by the magnetic ordering: a magnetic blue-shift (MBS)
occurs. Thus, the effect is proportional to the exchange coupling in the
leading order in the Hubbard model. In systems with additional localized spins
the double-exchange mechanism induces an additional contribution to the MBS
which is proportional to the hopping in the leading order. The coupling between
spin and charge degrees of freedom bears the potential to enable spin-to-charge
conversion in Mott systems on extreme time scales determined by hopping and
exchange only, since a spin-orbit mediated transfer of angular momentum is not
involved in the process. In view of spintronic and magnonic applications, it is
highly promising to observe that several entire classes of compounds show
exchange and double-exchange effects. Exemplarily, we show that the magnetic
contribution to the band-gap blue-shift observed in the optical conductivity of
$\alpha$-MnTe is correctly interpreted as the MBS of a Mott gap.",2012.04018v2
2020-12-14,Free fermions behind the disguise,"An invaluable method for probing the physics of a quantum many-body spin
system is a mapping to noninteracting effective fermions. We find such mappings
using only the frustration graph $G$ of a Hamiltonian $H$, i.e., the network of
anticommutation relations between the Pauli terms in $H$ in a given basis.
Specifically, when $G$ is (even-hole, claw)-free, we construct an explicit
free-fermion solution for $H$ using only this structure of $G$, even when no
Jordan-Wigner transformation exists. The solution method is generic in that it
applies for any values of the couplings. This mapping generalizes both the
classic Lieb-Schultz-Mattis solution of the XY model and an exact solution of a
spin chain recently given by Fendley, dubbed ""free fermions in disguise."" Like
Fendley's original example, the free-fermion operators that solve the model are
generally highly nonlinear and nonlocal, but can nonetheless be found
explicitly using a transfer operator defined in terms of the independent sets
of $G$. The associated single-particle energies are calculated using the roots
of the independence polynomial of $G$, which are guaranteed to be real by a
result of Chudnovsky and Seymour. Furthermore, recognizing (even-hole,
claw)-free graphs can be done in polynomial time, so recognizing when a spin
model is solvable in this way is efficient. We give several example families of
solvable models for which no Jordan-Wigner solution exists, and we give a
detailed analysis of such a spin chain having 4-body couplings using this
method.",2012.07857v2
2021-03-02,Conformal quantum mechanics & the integrable spinning Fishnet,"In this paper we consider systems of quantum particles in the $4d$ Euclidean
space which enjoy conformal symmetry. The algebraic relations for
conformal-invariant combinations of positions and momenta are used to construct
a solution of the Yang-Baxter equation in the unitary irreducibile
representations of the principal series $\Delta=2+i\nu$ for any left/right
spins $\ell,\dot{\ell}$ of the particles. Such relations are interpreted in the
language of Feynman diagrams as integral \emph{star-triangle} identites between
propagators of a conformal field theory. We prove the quantum integrability of
a spin chain whose $k$-th site hosts a particle in the representation
$(\Delta_k,\ell_k, \dot{ \ell}_k)$ of the conformal group, realizing a spinning
and inhomogeneous version of the quantum magnet used to describe the spectrum
of the bi-scalar Fishnet theories. For the special choice of particles in the
scalar $(1,0,0)$ and fermionic $(3/2,1,0)$ representation the transfer matrices
of the model are Bethe-Salpeter kernels for the double-scaling limit of
specific two-point correlators in the $\gamma$-deformed $\mathcal{N}=4$ and
$\mathcal{N}=2$ supersymmetric theories.",2103.01940v4
2021-03-11,Electric-field-tunable valley Zeeman effect in bilayer graphene heterostructures: Realization of the spin-orbit valve effect,"We report the discovery of electric-field-induced transition from a
topologically trivial to a topologically nontrivial band structure in an
atomically sharp heterostructure of bilayer graphene (BLG) and single-layer
WSe2 per the theoretical predictions of Gmitra and Fabian [Phys. Rev. Lett.
119, 146401 (2017)]. Through detailed studies of the quantum correction to the
conductance in the BLG, we establish that the band-structure evolution arises
from an interplay between proximity-induced strong spin-orbit interaction (SOI)
and the layer polarizability in BLG. The low-energy carriers in the BLG
experience an effective valley Zeeman SOI that is completely gate tunable to
the extent that it can be switched on or off by applying a transverse
displacement field or can be controllably transferred between the valence and
the conduction band. We demonstrate that this results in the evolution from
weak localization to weak antilocalization at a constant electronic density as
the net displacement field is tuned from a positive to a negative value with a
concomitant SOI-induced splitting of the low-energy bands of the BLG near the K
(K') valley, which is a unique signature of the theoretically predicted
spin-orbit valve effect. Our analysis shows that quantum correction to the
Drude conductance in Dirac materials with strong induced SOI can only be
explained satisfactorily by a theory that accounts for the SOI-induced spin
splitting of the BLG low-energy bands. Our results demonstrate the potential
for achieving highly tunable devices based on the valley Zeeman effect in
dual-gated two-dimensional materials.",2103.06529v1
2021-03-23,The longitudinal neutron resonant spin echo spectrometer RESEDA,"The instrumental layout and technical realisation of the neutron resonant
spin echo (NRSE) spectrometer RESEDA at the Heinz Maier-Leibnitz Zentrum (MLZ)
in Garching, Germany, is presented. RESEDA is based on a longitudinal field
configuration, boosting both dynamic range and maximum resolution of the
spectrometer compared to the conventional transverse layout. The resonant
neutron spin echo technique enables the realisation of two complementary
implementations: A longitudinal NRSE (LNRSE) option comparable to the classical
neutron spin echo (NSE) method for highest energy resolution and large momentum
transfers as well as a Modulation of Intensity with Zero Effort (MIEZE) option
for depolarising samples or sample environments such as high magnetic fields,
and strong incoherent scattering samples. With their outstanding dynamic range,
exceeding nominally seven orders of magnitude, both options cover new fields
for ultra-high resolution neutron spectroscopy in hard and soft condensed
matter systems. In this paper the concept of RESEDA as well as the technical
realisation along with reference measurements are reported.",2103.12836v1
2021-04-30,Generation of arbitrarily polarized GeV lepton beams via nonlinear Breit-Wheeler process,"Generation of arbitrarily spin-polarized lepton (here refer in particular to
electron and positron) beams has been investigated in the single-shot
interaction of high-energy polarized $\gamma$ photons with an ultraintense
asymmetric laser pulse via nonlinear Breit-Wheeler (BW) pair production. We
develop a fully spin-resolved semi-classical Monte Carlo method to describe the
pair creation and polarization in the local constant field approximation. In
nonlinear BW process the polarization of created pairs is simultaneously
determined by the polarization of parent $\gamma$ photons, the polarization and
asymmetry of scattering laser field, due to the spin angular momentum transfer
and the asymmetric spin-dependent pair production probabilities, respectively.
In considered all-optical method, dense GeV lepton beams with average
polarization degree up to about $80\%$ (adjustable between the transverse and
longitudinal components) can be obtained with currently achievable laser
facilities, which could be used as injectors of the polarized $e^{+}e^{-}$
collider to search for new physics beyond the Standard Model.",2104.14864v1
2021-05-26,Atoms in a spin dependent optical potential: ground state topology and magnetization,"We investigate a Bose-Einstein condensate of $F= 1$ $^{87}$Rb atoms in a 2D
spin-dependent optical lattice generated by intersecting laser beams with a
superposition of polarizations. For $^{87}$Rb the effective interaction of an
atom with the electromagnetic field contains a scalar and a vector (called as
fictitious magnetic field, $B_{fic}$) potentials. The Rb atoms behave as a
quantum rotor (QR) with angular momentum given by the sum of the atomic
rotational motion angular momentum and the hyperfine spin. The ground state of
the QR is affected upon applying an external magnetic field, $B_{ext}$,
perpendicular to the plane of QR motion and a sudden change of its topology
occurs as the ratio $B_{ext}/B_{fic}$ exceeds critical value. It is shown that
the change of topology of the QR ground state is a result of combined action of
Zeeman and Einstein-de Haas effects. The first transfers atoms to the largest
hyperfine component to polarize the sample along the field as the external
magnetic field is increased. The second sweeps spin to rotational angular
momentum, modifying the kinetic energy of the atoms.",2105.12650v3
2021-08-06,Mechanism of the insulator-to-metal transition and superconductivity in the spin liquid candidate NaYbSe$_2$ under pressure,"The quantum spin liquid candidate NaYbSe$_2$ was recently reported to exhibit
a Mott transition under pressure. Superconductivity was observed in the
high-pressure metallic phase, raising the question concerning its relation with
the low-pressure quantum spin liquid ground state. Here we combine the density
functional theory and the dynamical mean-field theory to explore the underlying
mechanism of the insulator-to-metal transition and superconductivity and
establish an overall picture of its electronic phases under pressure. Our
results suggest that NaYbSe$_2$ is a charge-transfer insulator at ambient
pressure. Upon increasing pressure, however, the system first enters a
semi-metallic state with incoherent Kondo scattering against coexisting
localized Yb-$4f$ moments, and then turns into a heavy fermion metal. In
between, there may exist a delocalization quantum critical point responsible
for the observed non-Fermi liquid region with linear-in-$T$ resistivity. The
insulator-to-metal transition is therefore a two-stage process.
Superconductivity emerges in the heavy fermion phase with well-nested Yb-4$f$
Fermi surfaces, suggesting that spin fluctuations may play a role in the Cooper
pairing. NaYbSe$_2$ might therefore be the 3rd Yb-based heavy-fermion
superconductor with a very ""high"" $T_c$ than most heavy fermion
superconductors.",2108.03218v1
2021-10-13,"Electron-to-nuclear spectral mapping via ""Galton board"" dynamic nuclear polarization","We report on a strategy to indirectly readout the spectrum of an electronic
spin via polarization transfer to nuclear spins in its local environment. The
nuclear spins are far more abundant and have longer lifetimes, allowing
repeated polarization accumulation in them. Subsequent nuclear interrogation
can reveal information about the electronic spectral density of states. We
experimentally demonstrate the method for reading out the ESR spectrum of
Nitrogen Vacancy center electrons in diamond via readout of lattice 13C nuclei.
Spin-lock control on the 13C nuclei yields significantly enhanced
signal-to-noise for the nuclear readout. Spectrally mapped readout presents
operational advantages in being background-free and immune to crystal
orientation and optical scattering. We harness these advantages to demonstrate
applications in underwater magnetometry. The physical basis for the
""one-to-many"" spectral map is itself intriguing. To uncover its origin, we
develop a theoretical model that maps the system dynamics, involving traversal
of a cascaded structure of Landau-Zener anti-crossings, to the operation of a
tilted ""Galton board"". This work points to new opportunities for ""ESR-via-NMR""
in dilute electronic systems, and in hybrid electron-nuclear quantum memories
and sensors.",2110.06826v2
2021-12-22,Dominant Kitaev interactions in the honeycomb materials Na$_3$Co$_2$SbO$_6$ and Na$_2$Co$_2$TeO$_6$,"Cobaltates with 3$d$ based layered honeycomb structure were recently proposed
as Kitaev magnets and putative candidates to host the long-sought Kitaev spin
liquid. Here we present inelastic neutron scattering results down to 50 mK for
powder samples of Na$_3$Co$_2$SbO$_6$ and Na$_2$Co$_2$TeO$_6$, with high
resolution in regions of low momentum and energy transfers. We compare the
experimental data below the antiferromagnetic zigzag ordering temperature with
dynamical structure factors obtained within spin wave theory. We search the
wide parameter range of a $K$-$J_1$-$\Gamma$-$\Gamma^{\prime}$-$J_3$ spin 1/2
model and identify the best fits to constant momentum cuts of the inelastic
neutron data. The powder average limits the selection of a unique parameter set
for each material, but we see clear trends towards ferromagnetic Kitaev
exchange in both compounds, and ratios $|K/J_1|$ could be as large as $5\ldots
25$; in contrast, antiferromagnetic Kitaev exchange cannot be ruled out, but
requires a fine-tuning of all involved spin exchange couplings with only
moderate ratio $|K/J_1| \sim 1$. Our experimental data are incompatible with a
purely isotropic Heisenberg model.",2112.12254v2
2022-02-20,Spinor matterwave control with nanosecond spin-dependent kicks,"Significant aspects of advanced quantum technology today rely on rapid
control of atomic matterwaves with hyperfine Raman transitions. Unfortunately,
efficient Raman excitations are usually accompanied by uncompensated dynamic
phases and coherent spin-leakages, preventing accurate and repetitive transfer
of recoil momentum to large samples. We provide systematic study to demonstrate
that the limitations can be substantially overcame by dynamically programming
an adiabatic pulse sequence. Experimentally, counter-propagating
frequency-chirped pulses are programmed on an optical delay line to parallelly
drive five $\Delta m=0$ hyperfine Raman transitions of $^{85}$Rb atoms for
spin-dependent kick (SDK) within $\tau=40$~nanoseconds, with an $f_{\rm
SDK}\approx 97.6\%$ inferred fidelity. Aided by numerical modeling, we
demonstrate that by alternating the chirps of successive pulses in a balanced
fashion, accumulation of non-adiabatic errors including the spin-leakages can
be managed, while the dynamic phases can be robustly cancelled. Operating on a
phase-stable delay line, the method supports precise, fast, and flexible
control of spinor matterwave with efficient Raman excitations.",2202.09709v4
2022-02-24,Correlation between spin-phonon coupling and magneto-electric effects in CoFe2O4/PMN-PT nanocomposite: Raman Spectroscopy and XMCD study,"We have investigated the coupling of lattice with spin via strain
interactions in the CoFe2O4/PMN-PT composite system. X-ray diffraction and
Raman spectroscopic studies illustrate a remarkable modification in
CoFe2O4lattice across Curie temperature (450 K) of PMN-PT. Subsequently,
CoFe2O4/PMN-PT composite reveals a sudden drop in magnetic moment across Tc of
PMN-PT (450 K). However,theindependent CoFe2O4phasedisplaystypical
ferromagnetic behaviour across this temperature. These findings establish
spin-lattice coupling owing to th interfacial strain transfer between CoFe2O4
and PMN-PT in composite. The strain intractions leads to magneto-electric
coupling, evidenced by measuring magentization and magneto-electric coefficient
for the electric field poled and unploed CoFe2O4/PMN-PT composite samples.
X-ray magnetic circular dichroism (XMCD) analysis establishes that the cation
(Fe3+/Co2+) redistribution occurs on tetrahedral and octahedral site in the
electrically poled CoFe2O4/PMN-PT composite, confirming the coupling between
magnetic and electric ordering in the composite. The magneto-electric coupling
coefficient alpha vs dc magnetic field curves revealed hysteretic behavior and
enhanced {\alpha} values after electric poling, which originates from the
strain induced modifications in the magnetic domains configuration of composite
in the poled samples. These findings suggest that the existence of spin lattice
coupling may leads to the mechanism of strong magneto-electric effects via
strain interactions in CoFe2O4/PMN-PT composite.",2202.11986v1
2022-07-16,Estimation of the on-site Coulomb potential 1 and covalent state in La2CuO4 by muon spin rotation 2 and density functional theory calculations,"The on-site Coulomb potential, U, and the covalent state of electronic
orbitals play key roles for the Cooper pair symmetry and exotic electromagnetic
properties of high-Tc superconducting cuprates. In this paper, we demonstrate a
way to determine the value of U and present the whole picture of the covalent
state of Cu spins in the mother system of the La-based high-Tc superconducting
cuprate, La2CuO4, by combining the muon spin rotation ({\mu}SR) and the density
functional theory (DFT) calculation. We reveal local deformations of the CuO6
octahedron followed by changes in Cu-spin distributions caused by the injected
muon. Adjusting the DFT and muSR results, U and the minimum charge-transfer
energy between the upper Hubbard band and the O 2p band were optimized to be
4.87(4) and 1.24(1) eV, respectively.",2207.07926v1
2022-08-19,Electrically tunable spin-orbit interaction in an InAs nanosheet,"We report on an experimental study of the spin-orbit interaction (SOI) in an
epitaxially grown free-standing InAs nanosheet in a dual-gate field-effect
device. Gate-transfer characteristic measurements show that independent tunings
of the carrier density in the nanosheet and the potential difference across the
nanosheet can be efficiently achieved with use of the dual gate. The quantum
transport characteristics of the InAs nanosheet are investigated by
magnetoconductance measurements at low temperatures. It is shown that the
electron transport in the nanosheet can be tuned from the weak antilocalization
to the weak localization and then back to the weak antilocalization regime with
a voltage applied over the dual gate without a change in carrier density. The
spin-orbit length extracted from the magnetoconductance measurements at a
constant carrier density exhibits a peak value at which the SOI of the Rashba
type is suppressed and the spin relaxation due to the presence of an SOI of the
Dresselhaus type in the nanosheet can be revealed. Energy band diagram
simulations have also been carried out for the device at the experimental
conditions and the physical insights into the experimental observations have
been discussed in light of the results of simulations.",2208.09395v1
2022-11-15,Drag resistance mediated by quantum spin liquids,"Recent advances in material synthesis made it possible to realize
two-dimensional monolayers of candidate materials for a quantum spin liquid
(QSL) such as $\alpha$-RuCl$_3$,1T-TaSe$_2$ and 1T-TaS$_2$. In this work, we
propose an experimental setup that exploits nonlocal electrical probes to gain
information on the transport properties of a gapless QSL. The proposed setup is
a spinon-mediated drag experiment: a current is injected in one of the two
layers and a voltage is measured on the second metallic film. The overall
momentum transfer mechanism is a two-step process mediated by Kondo interaction
between the local moments in the quantum spin liquid and the spins of the
electrons. In the limit of negligible momentum relaxed within the QSL layer, we
calculate the drag relaxation rate for Kitaev, $\mathbb{Z}_2$, and U(1) QSLs
using Aslamazov-Larkin diagrams. We find, however, that the case of dominant
momentum relaxation within the QSL layer is far more relevant and thus develop
a model based on the Boltzmann kinetic equation to describe the proposed setup.
Within this framework we calculate the low temperature scaling behavior of the
drag resistivity, both for U(1) and $\mathbb{Z}_2$ QSLs with Fermi surfaces. In
some regimes we find a crossover in the temperature scaling that is different
between the $\mathbb{Z}_2$ and U(1) QSL both because of the non-Fermi liquid
nature of the U(1) QSL, and because of the qualitatively different momentum
relaxation mechanism within the QSL layer. Our findings suggest that parameters
of the system can be tuned to make the spinon-mediated drag a significant
fraction of the total transresistance.",2211.08421v1
2023-04-11,Syntropic spin alignment at the interface between ferromagnetic and superconducting nitrides,"The magnetic correlations at the superconductor/ferromagnet (S/F) interfaces
play a crucial role in realizing dissipation-less spin-based logic and memory
technologies, such as triplet-supercurrent spin-valves and ""{\pi}"" Josephson
junctions. Here we report the coexistence of an induced large magnetic moment
and a crypto ferromagnetic state at high-quality nitride S/F interfaces. Using
polarized neutron reflectometry and d. c. SQUID measurements, we quantitatively
determined the magnetization profile of S/F bilayer and confirmed the induced
magnetic moment in the adjacent superconductor only exists below TC.
Interestingly, the direction of the induced moment in the superconductors was
unexpectedly parallel to that in the ferromagnet, which contrasts with earlier
findings in S/F heterostructures based on metals or oxides. The
first-principles calculations verify the observed unusual interfacial spin
texture is caused by the Heisenberg direct exchange coupling through d orbital
overlapping and severe charge transfer across the interfaces. Our work
establishes an incisive experimental probe for understanding the magnetic
proximity behavior at S/F interfaces and provides a prototype epitaxial
building block for superconducting spintronics.",2304.05234v1
2023-08-02,Impulsive Fermi magnon-phonon resonance in antiferromagnetic $CoF_{2}$,"Understanding spin-lattice interactions in antiferromagnets is one of the
most fundamental issues at the core of the recently emerging and booming fields
of antiferromagnetic spintronics and magnonics. Recently, coherent nonlinear
spin-lattice coupling was discovered in an antiferromagnet which opened the
possibility to control the nonlinear coupling strength and thus showing a novel
pathway to coherently control magnon-phonon dynamics. Here, utilizing intense
narrow band terahertz (THz) pulses and tunable magnetic fields up to 7 T, we
experimentally realize the conditions of the Fermi magnon-phonon resonance in
antiferromagnetic $CoF_{2}$. These conditions imply that both the spin and the
lattice anharmonicities harvest energy transfer between the subsystems, if the
magnon eigenfrequency $f_{m}$ is twice lower than the frequency of the phonon
$2f_{m}=f_{ph}$. Performing THz pump-infrared probe spectroscopy in conjunction
with simulations, we explore the coupled magnon-phonon dynamics in the vicinity
of the Fermi-resonance and reveal the corresponding fingerprints of an
impulsive THz-induced response. This study focuses on the role of nonlinearity
in spin-lattice interactions, providing insights into the control of coherent
magnon-phonon energy exchange.",2308.01052v1
2023-09-11,Revisiting UV/optical continuum time lags in AGN,"In this paper, we present an updated version of our model (KYNXiltr) which
considers thermal reverberation of a standard Novikov-Thorne accretion disc
illuminated by an X-ray point-like source. Previously, the model considered
only two cases of black hole spins, and assumed a colour correction factor
$f_{\rm col} = 2.4$. Now, we extend the model to any spin value and colour
correction. In addition, we consider two scenarios of powering the X-ray
corona, either via accretion, or external to the accretion disc. We use
KYNXiltr to fit the observed time lags obtained from intense monitoring of four
local Seyfert galaxies (NGC 5548, NGC 4395, Mrk 817, and Fairall 9). We
consider various combinations of black hole spin, colour correction, corona
height, and fraction of accretion power transferred to the corona. The model
fits well the overall time-lags spectrum in these sources (for a large
parameter space). For NGC 4593 only, we detect a significant excess of delays
in the U-band. The contribution of the diffuse BLR emission in the time-lags
spectrum of this source is significant. It is possible to reduce the large
best-fitting parameter space by combining the results with additional
information, such as the observed Eddington ratio and average X-ray luminosity.
We also provide an update to the analytic expression provided by Kammoun et
al., for an X-ray source that is not powered by the accretion process, which
can be used for any value of colour correction, and for two values of the black
hole spin (0 and 0.998).",2309.05392v2
2023-11-16,Future Prospects for Constraining Black-Hole Spacetime: Horizon-scale Variability of Astrophysical Jet,"The Event Horizon Telescope (EHT) Collaboration has recently published the
first horizon-scale images of the supermassive black holes M87* and Sgr A* and
provided some first information on the physical conditions in their vicinity.
The comparison between the observations and the three-dimensional
general-relativistic magnetohydrodynamic (GRMHD) simulations has enabled the
EHT to set initial constraints on the properties of these black-hole
spacetimes. However, accurately distinguishing the properties of the accretion
flow from those of the spacetime, most notably, the black-hole mass and spin,
remains challenging because of the degeneracies the emitted radiation suffers
when varying the properties of the plasma and those of the spacetime. The
next-generation EHT (ngEHT) observations are expected to remove some of these
degeneracies by exploring the complex interplay between the disk-jet dynamics,
which represents one of the most promising tools for extracting information on
the black-hole spin. By using GRMHD simulations of magnetically arrested disks
(MADs) and general-relativistic radiative-transfer (GRRT) calculations of the
emitted radiation, we have studied the properties of the jet and the
accretion-disk dynamics on spatial scales that are comparable with the horizon.
In this way, we are able to highlight that the radial and azimuthal dynamics of
the jet are well correlated with the black-hole spin. Based on the resolution
and image reconstruction capabilities of the ngEHT observations of M87*, we can
assess the detectability and associated uncertainty of this correlation.
Overall, our results serve to assess what are the prospects for constraining
the black-hole spin with future EHT observations.",2311.10141v1
2023-11-21,Local control of a single nitrogen-vacancy center by nanoscale engineered magnetic domain wall motions,"Effective control and readout of qubits form the technical foundation of
next-generation, transformative quantum information sciences and technologies.
The nitrogen-vacancy (NV) center, an intrinsic three-level spin system, is
naturally relevant in this context due to its excellent quantum coherence, high
fidelity of operations, and remarkable functionality over a broad range of
experimental conditions. It is an active contender for the development and
implementation of cutting-edge quantum technologies. Here, we report magnetic
domain wall motion driven local control and measurements of NV spin properties.
By engineering the local magnetic field environment of an NV center via
nanoscale reconfigurable domain wall motions, we show that NV
photoluminescence, spin level energies, and coherence time can be reliably
controlled and correlated to the magneto-transport response of a magnetic
device. Our results highlight the electrically tunable dipole interaction
between NV centers and nanoscale magnetic structures, providing an attractive
platform to realize interactive information transfer between spin qubits and
non-volatile magnetic memory in hybrid quantum spintronic systems.",2311.12256v1
2023-12-29,Spin-glass states generated in van der Waals magnet Cr$_2$Ge$_2$Te$_6$ by alkali-ion intercalation,"Tuning magnetic properties in layered van der Waals (vdW) materials has
captured a significant attention due to the efficient control of ground-states
by heterostructuring and external stimuli. Electron doping by electrostatic
gating, interfacial charge transfer and intercalation is particularly effective
in manipulating the exchange and spin-orbit properties, resulting in a control
of Curie temperature ($T_{\text{C}}$) and magnetic anisotropy. Here, we
discover an uncharted role of intercalation to generate magnetic frustration.
As a model study, we intercalate Na atoms into the vdW gaps of pristine
Cr$_2$Ge$_2$Te$_6$ (CGT) where generated magnetic frustration leads to emerging
spin-glass states coexisting with a ferromagnetic order. A series of dynamic
magnetic susceptibility measurements/analysis confirms the formation of
magnetic clusters representing slow dynamics with a distribution of relaxation
times. The intercalation also modifies other macroscopic physical parameters
including the significant enhancement of $T_{\text{C}}$ from 66K\, to 240\,K
and the switching of magnetic easy-hard axis direction. Our study identifies
intercalation as a unique route to generate emerging frustrated spin states in
simple vdW crystals.",2312.17554v2
2024-03-12,Characterizing the diffuse continuum excitations in the classical spin liquid $h$-YMnO$_3$,"We extend previous inelastic neutron scattering results on the geometrically
frustrated antiferromagnet hexagonal-YMnO$_3$, which has been suggested to
belong to the class of classical spin liquids. We extend the energy transfer
coverage of the diffuse signal up to 6.9 meV within a wide temperature range
around the ordering temperature, $T_\mathrm{N}$. The two distinct diffuse
signals in the a-b plane, the signal localized at $\Gamma$' and the scattering
intensity connecting $\Gamma$' points over the M', are shown to be only weakly
energy dependent. In addition, an external magnetic field of up to 10.5 T
applied along c is shown to have no effect on the diffuse signal. In the
orthogonal scattering plane, the signals are shown to be dependent on l only
through the magnetic form factor, showing that the correlations are purely
two-dimensional, and supporting its origin to be the frustrated Mn$^{3+}$
triangles. This result is corroborated by atomistic spin dynamics simulations
showing similar scattering vector and temperature behaviours. Lastly, data for
the spin wave scattering in the (h, 0, l) plane allow for a discussion of the
magnetic ground state where better agreement is found between the data and an
ordered structure of the $\Gamma_1$ or $\Gamma_3$ symmetry, albeit crystal
electric field arguments dismisses the $\Gamma_1$ as possibility.",2403.07671v1
2024-03-20,Topological Dipole Insulator,"We expand the concept of two-dimensional topological insulators to encompass
a novel category known as topological dipole insulators (TDIs), characterized
by conserved dipole moments along the $x$-direction in addition to charge
conservation. By generalizing Laughlin's flux insertion argument, we prove a
no-go theorem and predict possible edge patterns and anomalies in a TDI with
both charge $U^e(1)$ and dipole $U^d(1)$ symmetries. The edge of a TDI is
characterized as a quadrupolar channel that displays a dipole $U^d(1)$ anomaly.
A quantized amount of dipole gets transferred between the edges under the
dipolar flux insertion, manifesting as `quantized quadrupolar Hall effect' in
TDIs. A microscopic coupled-wire Hamiltonian realizing the TDI is constructed
by introducing a mutually commuting pair-hopping terms between wires to gap out
all the bulk modes while preserving the dipole moment. The effective action at
the quadrupolar edge can be derived from the wire model, with the corresponding
bulk dipolar Chern-Simons response theory delineating the topological
electromagnetic response in TDIs. Finally, we enrich our exploration of
topological dipole insulators to the spinful case and construct a dipolar
version of the quantum spin Hall effect, whose boundary evidences a mixed
anomaly between spin and dipole symmetry. Effective bulk and the edge action
for the dipolar quantum spin Hall insulator are constructed as well.",2403.13880v1
1997-09-26,Generation of Pulsar Glitches: A Superfluid Core Model,"We show that the neutron star's crust-core interface acts as a potential
barrier on the peripheral neutron vortices approaching this interface and thus
prevents their continuous decay on it in the course of equilibrium state
deceleration. The barrier arises due to the interaction of vortex magnetic flux
with the Meissner currents set up by the crustal magnetic field at the
interface. When the non-balanced part of the Magnus force reaches the value at
which the vortices are able to annihilate at the interface, the rapid transfer
of angular momentum from the superfluid spins-up the observable crust on short
dynamical coupling times.",9709277v2
1999-07-14,Late evolution of cataclysmic variables: the loss of AM Her systems,"The white dwarf in AM Her systems is strongly magnetic and keeps in
synchronous rotation with the orbit by magnetic coupling to the secondary star.
As the latter evolves through mass loss to a cool, degenerate brown dwarf it
can no longer sustain its own magnetic field and coupling is lost. Angular
momentum accreted then spins up the white dwarf and the system no longer
appears as an AM Her system. Possible consequences are run-away mass transfer
and mass ejection from the system. Some of the unusual cataclysmic variable
systems at low orbital periods may be the outcome of this evolution.",9907190v1
2000-03-13,Extracting Energy from Accretion into Kerr Black Hole,"The highest efficiency of converting rest mass into energy by accreting
matter into a Kerr black hole is ~ 31% (Thorne 1974). We propose a new process
in which periods of accretion from a thin disk, and the associated spin-up of
the black hole, alternate with the periods of no accretion and magnetic
transfer of energy from the black hole to the disk. These cycles can repeat
indefinitely, at least in principle, with the black hole mass increasing by ~
66% per cycle, and up to ~ 43% of accreted rest mass radiated away by the disk.",0003187v1
1993-06-09,The class of universality of integrable and isotropic GL(N) mixed magnets,"We discuss a class of transfer matrix built by a particular combination of
isomorphic and non-isomorphic GL(N) invariant vertex operators. We construct a
conformally invariant magnet constituted of an alternating mixture of GL(N)
``spins'' operators at different order of representation. The corresponding
central charge is calculated by analysing the low temperature behaviour of the
associated free energy. We also comment on possible extensions of our results
for more general classes of mixed systems.",9306028v1
1994-01-03,Quantum Measurement in Electric Circuit,"We study fluctuations of electric current in a quantum resistor and derive a
general quantum-mechanical formula for the distribution of transmitted charge.
For that we introduce a scheme of current measurement that involves a spin
$1/2$ coupled to the current so that it precesses at the rate proportional to
the current. Our approach allows the study of charge transfer without breaking
the circuit. We analyze a single channel conductor and derive electron counting
statistics for arbitrary relation between temperature and voltage. For a
perfectly transmitting channel the counting distribution is gaussian, both for
zero-point fluctuations and at finite temperature. At constant voltage and low
temperature the distribution is binomial, i.e., it arises from Bernoulli
statistics.",9401004v1
1995-05-02,The Anomalous Hall Effect in YBa$_2$Cu$_3$O$_7$,"The temperature dependence of the normal state Hall effect and
magnetoresistance in YBa$_2$Cu$_3$O$_7$ is investigated using the Nearly
Antiferromagnetic Fermi Liquid description of planar quasiparticles. We find
that highly anisotropic scattering at different regions of the Fermi surface
gives rise to the measured anomalous temperature dependence of the resistivity
and Hall coefficient while yielding the universal temperature dependence of the
Hall angle observed for both clean and dirty samples. This universality is
shown to arise from the limited momentum transfers available for the anomalous,
spin fluctuation scattering and is preserved for any system with strong
antiferromagnetic correlations.",9505005v1
1995-09-13,Numerical Study of a Mixed Ising Ferrimagnetic System,"We present a study of a classical ferrimagnetic model on a square lattice in
which the two interpenetrating square sublattices have spins one-half and one.
This model is relevant for understanding bimetallic molecular ferrimagnets that
are currently being synthesized by several experimental groups. We perform
exact ground-state calculations for the model and employ Monte Carlo and
numerical transfer-matrix techniques to obtain the finite-temperature phase
diagram for both the transition and compensation temperatures. When only
nearest-neighbor interactions are included, our nonperturbative results
indicate no compensation point or tricritical point at finite temperature,
which contradicts earlier results obtained with mean-field analysis.",9509076v1
1996-01-10,Temperature dependence of the electron chemical potential in YBa2Cu3O,"We study the behaviour of the electronic chemical potential in YBa2Cu3O near
the superconducting transition using the spin-wave exchange theory of pairing.
We find that the experimental value of the jump in the temperature derivative
of the chemical potential is inconsistent with the theoretical value calculated
under the assumption of constant hole concentration. It is suggested that
charge transfer between chains and planes takes place and corresponding
calculations are done.",9601031v3
1996-04-08,Spectral Properties of Statistical Mechanics Models,"The full spectrum of transfer matrices of the general eight-vertex model on a
square lattice is obtained by numerical diagonalization. The eigenvalue spacing
distribution and the spectral rigidity are analyzed. In non-integrable regimes
we have found eigenvalue repulsion as for the Gaussian orthogonal ensemble in
random matrix theory. By contrast, in integrable regimes we have found
eigenvalue independence leading to a Poissonian behavior, and, for some points,
level clustering. These first examples from classical statistical mechanics
suggest that the conjecture of integrability successfully applied to quantum
spin systems also holds for classical systems.",9604042v1
1996-06-25,Exact calculation of thermodynamical quantities of the integrable t-J model,"The specific heat and the compressibility for the integrable t-J model are
calculated showing Luttinger liquid behavior for low temperatures. A
Trotter-Suzuki mapping and the quantum transfer matrix approach are utilized.
Using an algebraic Bethe ansatz this method permits the exact calculation of
the free energy and related quantities. A set of just two non-linear integral
equations determining these quantities is studied for various particle
densities and temperatures. The structure of the specific heat is discussed in
terms of the elementary charge as well as spin excitations.",9606192v1
1997-05-13,Spin-Peierls vs. Peierls distortions in a family of conjugated Polymers,"Distortions in a family of conjugated polymers are studied within two
complementary approaches, i.e. within a many-body Valence Bond (VB) approach
using a transfer matrix technique to treat the Heisenberg model of the systems,
and also in terms of the tight-binding band-theoretic model with interactions
limited to nearest neighbors. The computations indicate that both methods
predict the presence or absence of the same distortions in most of the polymers
studied.",9705121v1
1997-08-26,Vortex coupler for atomic Bose-Einstein condensates,"A coherent coupler is proposed to spin a Bose-Einstein condensate composed of
ultracold alkali atoms into a vortex state (VS). The proposal is based on a
Raman transition induced by two copropagating $\sigma^+$ and $\sigma^-$
polarized Laguerre-Gaussian laser beams with different frequencies. We show
that the transfer of angular momentum of photons to the condensed atoms through
a Raman transition leads to a coherent coupling of the ground-state condensate
to a rotating condensate in a VS. The detection of such a VS is discussed.",9708198v1
1998-05-28,"Thermodynamics of the (1,1/2) Ferrimagnet in Finite Magnetic Fields","We investigate the specific heat and magnetisation of a ferrimagnet with gS=1
and S=1/2 spins in a finite magnetic field using the transfer matrix DMRG down
to T=0.025J. Ferromagnetic gapless and antiferromagnetic gapped excitations for
H=0 lead to rich thermodynamics for H > 0. While the specific heat is
characterized by a generic double peak structure, magnetisation reveals two
critical fields, Hc1=1.76(1) and Hc2=3.00(1) with square-root behaviour in the
T=0 magnetisation. Simple analytical arguments allow to understand these
experimentally accessible findings.",9805376v1
1998-05-31,Polarizability and single particle spectra of two-dimensional s- and d-wave superconductors,"We present analytic results for the polarizabilities, $\chi({\bf Q},\omega)$,
in the charge, spin, and current channels for two-dimensional s- and d-wave
superconductors for large momentum transfer. A collective mode in the charge
channel is predicted to exist for extremum vectors of the Fermi-surface with
energy below twice the maximum superconducting gap. Such modes are directly
observable through inelastic x-ray or electron scattering. Scattering of single
particle excitations by these collective modes leads to several unusual
features in the single particle spectrum in the superconducting state which are
seen in angle resolved photoemission experiments.",9806006v1
1998-12-01,Temperature dependent spatial oscillations in the correlations of the XXZ spin chain,"We study the correlation $<\sigma^z_0\sigma^z_n>$ for the XXZ chain in the
massless attractive (ferromagnetic) region at positive temperatures by means of
a numerical study of the quantum transfer matrix. We find that there is a range
of temperature where the behavior of the correlation for large separations is
oscillatory with an incommensurate period which depends on temperature.",9812012v1
1999-01-27,Essential finite-size effect in the 2D XY model,"The thermodynamics of the 2D XY model is formulated by a transfer matrix
method and analyzed by a density matrix renormalization group. The finite-size
scaling and the beta function of the model are studied by the Roomany-Wyld
renormalization group theory. It is found that the 2D XY model has an essential
finite-size effect and the Berezinskii-Kosterlitz-Thouless transition with the
critical temperature TBKT = 0.892 appears in a finite system of 2000 - 3000
spins as a massless to massive transition with the effective critical
temperature Tc = 1.07 "" 0.01.",9901314v2
1999-01-29,Theory of optical conductivity in doped manganites,"The frequency and temperature dependence of the optical conductivity of
ferromagnetic manganites is explained within the framework of the bipolaron
theory. As these materials are cooled below the Curie temperature, the colossal
magnetoressitance (CMR) is accompanied by a massive transfer of the spectral
weight of the optical conductivity to lower frequencies. As with the CMR
itself, this change in the optical conductivity is explained by the
dissociation of bipolarons into small polarons by exchange interaction with the
localized Mn spins during the transition to the low temperature ferromagnetic
phase.",9901340v2
1999-02-03,Ising spins on the labyrinth,"We consider a zero-field Ising model defined on a quasiperiodic graph, the
so-called Labyrinth tiling. Exact information about the critical behaviour is
obtained from duality arguments and the subclass of models which yield
commuting transfer matrices. For the latter, the magnetization is independent
of the position and the phase transition between ordered and disordered phase
belongs to the Onsager universality class. In order to obtain information about
the generic case, we calculate the magnetization for a series of couplings by
standard Monte-Carlo methods.",9902051v1
1999-08-18,Inelastic neutron scattering peak in Zn substituted YBa2Cu3O7,"The effects of nonmagnetic impurities on the neutron scattering intensity are
studied for a model of the copper oxide layers in the normal state. The
contribution to the Q=(pi,pi) neutron scattering intensity from processes
involving the scattering of the spin fluctuations from an impurity with large
momentum transfers are calculated within the random phase approximation. It is
shown that this type of scatterings could lead to a peak in the neutron
scattering intensity in the normal state.",9908266v1
1999-12-28,Correlation Functions of Multisite Interaction Spin-S models on the Bethe-like Lattices,"Multisite interaction spin-S models in an external magnetic field are studied
recursively on the Bethe-like lattices. The transfer-matrix method is extended
to calculate exactly the two-spin correlation functions. The exact expressions
for the correlation length and magnetic susceptibility are derived for spin-1/2
models. The singularity of the correlation length with critical index $\nu =1$
and the proportionality of magnetic susceptibility to correlation length in the
second order phase transition region of spin-1/2 ferromagnetic models on the
Bethe-like lattices are established analytically.",9912463v2
2000-02-04,Dielectric response of charge induced correlated state in the quasi-one-dimensional conductor (TMTTF)2PF6,"Conductivity and permittivity of the quasi-one-dimensionsional organic
transfer salt (TMTTF)2PF6 have been measured at low frequencies (10^3-10^7 Hz)
between room temperature down to below the temperature of transition into the
spin-Peierls state. We interpret the huge real part of the dielectric
permittivity (up to 10^6) in the localized state as the realization in this
compound of a charge ordered state of Wigner crystal type due to long range
Coulomb interaction.",0002068v1
2000-02-11,Canonical solution of a system of long-range interacting rotators on a lattice,"The canonical partition function of a system of rotators (classical X-Y
spins) on a lattice, coupled by terms decaying as the inverse of their distance
to the power alpha, is analytically computed. It is also shown how to compute a
rescaling function that allows to reduce the model, for any d-dimensional
lattice and for any alpha<d, to the mean field (alpha=0) model.",0002168v2
2000-03-07,Thermodynamics of the bilinear-biquadratic spin one Heisenberg chain,"The magnetic susceptibility and specific heat of the one-dimensional S=1
bilinear-biquadratic Heisenberg model are calculated using the transfer matrix
renormalization group. By comparing the results with the experimental data of
${\rm LiVGe_2O_6}$ measured by Millet et al. (Phys. Rev. Lett. {\bf 83}, 4176
(1999)), we find that the susceptibility data of this material, after
subtracting the impurity contribution, can be quantitatively explained with
this model. The biquadratic exchange interaction in this material is found to
be ferromagnetic, i.e. with a positive coupling constant.",0003102v3
2000-11-15,Eigen-functional bosonization and Eikonal-type equations in one-dimensional strongly correlated electron system,"With the eigen-functional bosonization method, we study one-dimensional
strongly correlated electron systems with large momentum ($2k_{F}$ and/or
$4k_{F}$) transfer term(s), and demonstrate that this kind of problems ends in
to solve the Eikonal-type equations, and these equations are universal, and
independent of whether or not the system is integrable. In contrast to usual
perturbation theory, this method is valid not only for weak electron
interaction, but also for strong electron interaction. Comparing with exact
solution of some integrable models, it can give correct results in one-loop
approximation. This method can also be used to study electron-phonon
interaction systems, and two coupled spin chain or quantum wire systems.",0011253v1
2002-01-16,Why ferromagnetic semiconductors?,"Rapid development of information technologies originates from the exponential
increase in the density of information that can be processed, stored, and
transfer by the unit area of relevant devices. There is, however, a growing
amount of evidences that the progress achieved in this way approaches its
limits. Various novel ideas put forward to circumvent barriers ahead are
described. Particular attention is paid to those concepts which propose to
exploit electron or nuclear spins as the information carriers. Here,
ferromagnetic semiconductors of III-V or II-VI compounds containing a sizable
concentration of transition metals appear as outstanding spintronic materials.",0201279v1
2002-02-21,Interlayer Exchange Coupling in Semiconductor Magnetic/Nonmagnetic Superlattices,"The interlayer spin correlations in the magnetic/non-magnetic semiconductor
superlattices are reviewed. The experimental evidences of interlayer exchange
coupling in different all-semiconductor structures, based on neutronographic
and magnetic studies, are presented. A tight-binding model is used to explain
interaction transfer across the non-magnetic block without the assistance of
carriers in ferromagnetic EuS/PbS and antiferromagnetic EuTe/PbTe systems.",0202377v1
2002-06-22,Andreev Bound States at the Interface of Antiferromagnets and d-wave Superconductors,"We set up a simple transfer matrix formalism to study the existence of bound
states at interfaces and in junctions between antiferromagnets and d-wave
superconductors. The well-studied zero energy mode at the {110} interface
between an insulator and a d-wave superconductor is spin split when the
insulator is an antiferromagnet. This has as a consequence that any competing
interface induced superconducting order parameter that breaks the time reversal
symmetry needs to exceed a critical value before a charge current is induced
along the interface.",0206422v1
2002-07-08,New Developments in the Eight Vertex Model,"We demonstrate that the Q matrix introduced in Baxter's 1972 solution of the
eight vertex model has some eigenvectors which are not eigenvectors of the spin
reflection operator and conjecture a new functional equation for Q(v) which
both contains the Bethe equation that gives the eigenvalues of the transfer
matrix and computes the degeneracies of these eigenvalues.",0207177v3
2002-08-19,Manganese nanoclusters and nanowires on GaAs surfaces,"We have computed the local magnetic moments of manganese and neighboring
arsenic for various cluster configurations on the (001) surface of GaAs bulk
crystal using a cluster of 512 atoms. We obtained for manganese a substantial
local magnetic moment of 3.66 Bohr magnetons for all cases considered. The
induced magnetic moment of arsenic is less than that of manganese by two orders
of magnitude and falls off drastically beyond nearest neighbor distance. A
small amount of charge is transferred from the manganese to arsenic. The
possibility of a spin polarized wire channel on the arsenic layer below the
surface is suggested.",0208370v1
2002-09-17,The ubiquitous 1100 charge ordering in organic charge-transfer solids,"Charge and spin-orderings in the 1/4-filled organic CT solids are of strong
interest, especially in view of their possible relations to organic
superconductivity. We show that the charge order (CO) in both 1D and 2D CT
solids is of the ...1100... type, in contradiction to mean field prediction of
>...1010... CO. We present detailed computations for metal-insulator and
magnetic insulator-insulator transitions in the theta-ET materials. Complete
agreement with experiments in several theta systems is found. Similar
comparisons between theory and experiments in TCNQ, TMTTF, TMTSF, and ET
materials prove the ubiquity of this phenomenon.",0209410v1
2002-12-16,Temperature driven crossover phenomena in the correlation lengths of the one-dimensional t-J model,"We describe a modified transfer matrix renormalization group (TMRG) algorithm
and apply it to calculate thermodynamic properties of the one-dimensional t-J
model. At the supersymmetric point we compare with Bethe ansatz results and
make direct connection to conformal field theory (CFT). In particular we study
the crossover from the non-universal high T lattice into the quantum critical
regime by calculating various correlation lengths and static correlation
functions. Finally, the existence of a spin-gap phase is confirmed.",0212369v1
2003-01-17,Long-lived memory for mesoscopic quantum bits,"We describe a technique to create long-lived quantum memory for quantum bits
in mesoscopic systems. Specifically we show that electronic spin coherence can
be reversibly mapped onto the collective state of the surrounding nuclei. The
coherent transfer can be efficient and fast and it can be used, when combined
with standard resonance techniques, to reversibly store coherent superpositions
on the time scale of seconds. This method can also allow for ``engineering''
entangled states of nuclear ensembles and efficiently manipulating the stored
states. We investigate the feasibility of this method through a detailed
analysis of the coherence properties of the system.",0301323v1
2003-07-27,Anisotropy of the incommensurate fluctuations in Sr2RuO4: a study with polarized neutrons,"The anisotropy of the magnetic incommensurate fluctuations in Sr2RuO4 has
been studied by inelastic neutron scattering with polarized neutrons. We find a
sizeable enhancement of the out of plane component by a factor of two for
intermediate energy transfer which appears to decrease for higher energies. Our
results qualitatively confirm calculations of the spin-orbit coupling, but the
experimental anisotropy and its energy dependence are weaker than predicted.",0307662v1
2003-11-01,Quantum-number projection in the path-integral renormalization group method,"We present a quantum-number projection technique which enables us to exactly
treat spin, momentum and other symmetries embedded in the Hubbard model. By
combining this projection technique, we extend the path-integral
renormalization group method to improve the efficiency of numerical
computations. By taking numerical calculations for the standard Hubbard model
and the Hubbard model with next nearest neighbor transfer, we show that the
present extended method can extremely enhance numerical accuracy and that it
can handle excited states, in addition to the ground state.",0311005v1
2004-04-20,"Optical properties of (Pr,Ce)2CuO4","We studied the optical conductivity of electron doped Pr{1-x)Ce(x)CuO(4) from
the underdoped to the overdoped regime. The observation of low to high
frequency spectral weight transfer reveals the presence of a gap, except in the
overdoped regime. A Drude peak at all temperatures shows the partial nature of
this gap. The close proximity of the doping at which the gap vanishes to the
antiferromagnetic phase boundary leads us to assign this partial gap to a spin
density wave.",0404466v1
2004-08-09,Joint effect of lattice interaction and potential fluctuation in colossal magnetoresistive manganites,"Taking into account both the Jahn-Teller lattice distortion and the on-site
electronic potential fluctuations in the orbital-degenerated double-exchange
model, in which both the core-spin and the lattice distortion are treated
classically, we investigate theoretically the metal-insulator transition (MIT)
in manganites by considering the electronic localization effect. An inverse
matrix method is developed for calculation in which we use the inverse of the
transfer matrix to obtain the localization length. We find that within
reasonable range of parameters, both the lattice effect and the potential
fluctuation are responsible to the occurrence of the MIT. The role of the
orbital configuration is also discussed.",0408189v1
2004-08-27,Study of ortho-to-paraexciton conversion in Cu$_2$O by excitonic Lyman spectroscopy,"Using time-resolved $1s$-$2p$ excitonic Lyman spectroscopy, we study the
orthoexciton-to-paraexcitons transfer, following the creation of a high density
population of ultracold $1s$ orthoexcitons by resonant two-photon excitation
with femtosecond pulses.
  An observed fast exciton-density dependent conversion rate is attributed to
spin exchange between pairs of orthoexcitons.
  Implication of these results on the feasibility of BEC of paraexcitons in
Cu$_2$O is discussed.",0408605v2
2004-09-15,A way to solve BCS-type pairing model,"We propose a way to solve BCS-type pairing model by to exactly solve its
spin-analogy in the subspace. The advantages of our method are to avoid to
directly deal with the approximate procedure and to transfer an exponentially
complicated problem to a polynomial problem. Moreover, it builds the
theoretical foundation of quantum simulation of pairing model and can be used
to check the precision of quantum simulation. It is also helpful to understand
the many-body quantum theory.",0409400v4
2004-10-01,Current-spin coupling for ferromagnetic domain walls in fine wires,"The coupling between a current and a domain wall is examined. In the presence
of a finite current and the absence of a potential which breaks the
translational symmetry, there is a perfect transfer of angular momentum from
the conduction electrons to the wall. As a result, the ground state is in
uniform motion. This remains the case when relaxation is accounted for. This is
described by, appropriately modified, Landau-Lifshitz-Gilbert equations.",0410035v1
2004-10-03,Phase determination in spin-polarized neutron specular reflectometry by using a magnetic substrate,"The scattering length density profile for a thin film structure can be
determined uniquely if both modulus and phase of the reflection coefficient is
known. Here, we describe a method for recovering the phase information which
utilize a magnetic substrate and based on polarization analysis of the
reflected beam. The method is derived in the formalism of transfer matrix so it
is applicable for any unknown real scattering length density of nonmagnetic
films (i.e. in the case where there is no effective absorption).",0410052v1
2004-10-08,Quasiparticle excitations in frustrated antiferromagnets,"We have computed the quasiparticle wave function corresponding to a hole
injected in a triangular antiferromagnet. We have taken into account
multi-magnon contributions within the self consistent Born approximation. We
have found qualitative differences, under sign reversal of the integral
transfer t, regarding the multi-magnon components and the own existence of the
quasiparticle excitations. Such differences are due to the subtle interplay
between magnon-assisted and free hopping mechanisms. We conclude that the
conventional quasiparticle picture can be broken by geometrical frustration
without invoking spin liquid phases.",0410209v1
2004-11-01,Pairing and superconductivity driven by strong quasiparticle renormalization in two-dimensional organic charge transfer salts,"We introduce and analyze a variational wave function for quasi
two-dimensional kappa-ET organic salts containing strong local and nonlocal
correlation effects. We find an unconventional superconducting ground state for
intermediate charge carrier interaction, sandwiched between a conventional
metal at weak coupling and a spin liquid at larger coupling. Most remarkably,
the excitation spectrum is dramatically renormalized and is found to be the
driving force for the formation of the unusual superconducting state.",0411044v1
2005-07-07,Magnetic plateaus in the 1D antiferromagnetic spin-3/2 and spin-2 Ising chains with single-ion anisotropy,"In this study, we have employed the classical transfer matrix technique to
investigate the magnetization plateaus, phase diagrams and other
thermodynamical properties of the one-dimensional antiferromagnetic spin-3/2
and spin-2 Ising chains with single-ion anisotropy in the presence of an
external magnetic field at very low temperature. We have showed that single
ion-anisotropy is one of the indispensable ingredients for an energy gap which
leads to magnetic plateau mechanism in one-dimensional antiferromagnetic Ising
spin chains. Other thermodynamical predictions seem to be provide this
argument.",0507177v1
2005-08-10,Dynamic rewiring in small world networks,"We investigate equilibrium properties of small world networks, in which both
connectivity and spin variables are dynamic, using replicated transfer matrices
within the replica symmetric approximation. Population dynamics techniques
allow us to examine order parameters of our system at total equilibrium,
probing both spin- and graph-statistics. Of these, interestingly, the degree
distribution is found to acquire a Poisson-like form (both within and outside
the ordered phase). Comparison with Glauber simulations confirms our results
satisfactorily.",0508250v1
2005-08-16,Surface free energy for systems with integrable boundary conditions,"The surface free energy is the difference between the free energies for a
system with open boundary conditions and the same system with periodic boundary
conditions. We use the quantum transfer matrix formalism to express the surface
free energy in the thermodynamic limit of systems with integrable boundary
conditions as a matrix element of certain projection operators. Specializing to
the XXZ spin 1/2 chain we introduce a novel `finite temperature boundary
operator' which characterizes the thermodynamical properties of surfaces
related to integrable boundary conditions.",0508377v1
2005-08-29,Interlayer Transport in Bilayer Quantum Hall Systems,"Bilayer quantum Hall systems have a broken symmetry ground state at filling
factor $\nu=1$ which can be viewed either as an excitonic superfluid or as a
pseudospin ferromagnet. We present a theory of inter-layer transport in quantum
Hall bilayers that highlights remarkable similarities and critical differences
between transport in Josephson junction and ferromagnetic metal spin-transfer
devices. Our theory is able to explain the size of the large but finite low
bias interlayer conductance and the voltage width of this collective transport
anomaly.",0508702v2
2005-10-05,Finite Temperature Density Matrix Renormalization using an enlarged Hilbert space,"We apply a generalization of the time-dependent DMRG to study finite
temperature properties of several quantum spin chains, including the frustrated
$J_1-J_2$ model. We discuss several practical issues with the method, including
use of quantum numbers and finite size effects. We compare with transfer-matrix
DMRG, finding that both methods produce excellent results.",0510124v2
2005-10-07,Metastable Bose-Einstein Condensate in a Linear Potential,"We have created a Bose-Einstein condensate whose spin orientation is
metastable. Condensates were transferred into a quadrupole magnetic trap, where
Majorana transitions limited the lifetime to a few hundred milliseconds, about
30 times the trapping period. Atoms held in the trap frequently displayed a
ring-shaped time-of-flight distribution. We speculate that such a ring could be
either a quantized vortex or a feature of the Majorana loss dynamics in the
quantum regime.",0510165v2
2005-12-02,Molecular signatures in the structure factor of an interacting Fermi gas,"The static and dynamic structure factors of an interacting Fermi gas along
the BCS-BEC crossover are calculated at momentum transfer $\hbar{\bf k}$ higher
than the Fermi momentum. The spin structure factor is found to be very
sensitive to the correlations associated with the formation of molecules. On
the BEC side of the crossover, even close to unitarity, clear evidence is found
for a molecular excitation at $\hbar^2 k^2 /4m$, where $m$ is the atomic mass.
Both quantum Monte Carlo and dynamic mean-field results are presented.",0512048v1
2006-03-15,Quantum Stochastic Synchronization,"We study within the spin-boson dynamics the synchronization of quantum
tunneling with an external periodic driving signal. As a main result we find
that at a sufficiently large system-bath coupling strength (Kondo parameter
a>1) the thermal noise plays a constructive role in yielding both a frequency
and a phase synchronization in a symmetric two-level system. Such riveting
synchronization occurs when the driving frequency supersedes the zero
temperature tunneling rate. As an application evidencing the effect, we
consider a charge transfer dynamics in molecular complexes.",0603400v1
2006-05-16,Bose-Einstein condensates in RF-dressed adiabatic potentials,"Bose-Einstein condensates of $^{87}$Rb atoms are transferred into
radio-frequency (RF) induced adiabatic potentials and the properties of the
corresponding dressed states are explored. We report on measurements of the
spin composition of dressed condensates. We also show that adiabatic potentials
can be used to trap atom gases in novel geometries, including suspending a
cigar-shaped cloud above a curved sheet of atoms.",0605393v2
2006-08-03,Structural (B1 to B8) Phase Transition in MnO under Pressure: Comparison of All-electron and Pseudopotential Approaches,"We employ the density functional theory to study a structural transition of
MnO from B1 (rocksalt) to B8 (NiAs) structures that was observed experimentally
at pressures around 100 GPa. We utilize all-electron description as well as
norm-conserving pseudopotentials and demonstrate that these two approaches can
significantly differ in quantitative predictions. We explicitly show that even
small-core pseudopotentials exhibit transferability inaccuracies for quantities
sensitive to the energy differences between high- and low-spin polarizations of
valence electrons.",0608101v2
2007-02-15,Optical Control of Topological Quantum Transport in Semiconductors,"Intense coherent laser radiation red-detuned from absorption edge can
reactively activate sizable Hall type charge and spin transport in n-doped
paramagnetic semiconductors as a consequence of k-space Berry curvature
transferred from valence band to photon-dressed conduction band. In the
presence of disorder, the optically induced Hall conductance can change sign
with laser intensity.",0702346v2
1999-08-18,Improved Transfer-Matrix Schemes of Phenomenological Renormalization,"Different phenomenological RG transformations based on scaling relations for
the derivatives of the inverse correlation length and singular part of the
free-energy density are considered. These transformations are tested on the 2D
square Ising and Potts models as well as on the 3D simple-cubic Ising model.
Variants of RG equations yielding more accurate results than Nightingale's RG
scheme are obtained. In the 2D case the finite-size equations which give the
{\it exact} values of the critical point or the critical exponent are found.",9908019v1
1992-06-11,Effective Heavy Quark Theory,"We show how heavy quark effective theory, including 1/M corrections, may be
matched onto dynamical quark models by making a specific choice of K,m and v in
the p=mv+K expansion. We note that Wigner rotations of heavy quark spins arise
at $O(p^2/m^2)$ in non-relativistic models but at $O(\Lambda_{QCD}/M_Q)$ or
O(velocity-transfer) in HQET and so are necessary for a consistent treatment.",9206217v1
1993-03-16,Rotational covariance and light-front current matrix elements,"Light-front current matrix elements for elastic scattering from hadrons with
spin~1 or greater must satisfy a nontrivial constraint associated with the
requirement of rotational covariance for the current operator. Using a model
$\rho$ meson as a prototype for hadronic quark models, this constraint and its
implications are studied at both low and high momentum transfers. In the
kinematic region appropriate for asymptotic QCD, helicity rules, together with
the rotational covariance condition, yield an additional relation between the
light-front current matrix elements.",9303264v1
1993-12-19,What Can be Learnt from the New Ua4/2 Data,"A careful analysis of the new data of the UA4/2 collaboration reveals that
these data give an essentially large value of the $\rho = Re T(s,t)/Im(s,t)$
that does not contradict the early UA4 experiment. There is the reason to think
also that this experiment reveals for the first time a real possibility of the
existence of the spin-flip amplitude at superhigh energies in the range of
small transfer momenta.",9312305v1
1997-01-02,Cold Dark Matter Detection via the LSP-Nucleus Elastic Scattering,"The momentum transfer dependence of the LSP-nucleus elastic scattering cross
sections is studied. New imput SUSY parameters obtained in a phenomenologically
allowed parameter space are used to calculate the coherent rate for various
nuclear systems and the spin matrix elements for the proposed $^{207}Pb$
target. The results are compared to those obtained from other cold dark matter
detection targets.",9701204v1
2000-10-16,Lambda and Lambda-bar polarization as a measurement of distribution and fragmentation functions,"A combined analysis of the polarization vector of the Lambda baryons produced
in DIS processes may give a relevant insight of the hadronization process which
governs the transition from partons to physical hadrons and precise indications
on the mechanisms of $spin$ transfer from partons to hadrons. We give here a
short review of some interesting results.",0010166v1
2000-12-07,Polarized Proton Nucleus Scattering,"We show that, to a very good approximation, the ratio of the spin-flip to the
non-flip parts of the elastic proton-nucleus amplitude is the same as for
proton-nucleon scattering at very high energy. The result is used to do a
realistic calculation of the analyzing power A_N for pC scattering in the
Coulomb-nuclear interference (CNI) region of momentum transfer.",0012091v2
2000-12-29,Single-spin asymmetry in DVCS: fragmentation region of polarised lepton,"For the kinematical region when a hard photon is emitted predominantly close
to the direction of motion of a longitudinally polarized initial electron and
relatively small momentum transfer to a proton we calculate the azimuthal
asymmetry of photon emission. It arises from the interference of the
Bethe-Heitler amplitude and those which are described by a heavy photon impact
factor. Azimuthal asymmetry does not decrease in the limit of infinite cms
energy. Lowest order expression for the impact factor of a heavy photon is
presented.",0012380v2
2002-03-29,Chiral structure of nucleon gravitational form factors,"We study the low momentum behavior of nucleon gravitational form factors in
the framework of the heavy baryon chiral perturbation theory. At zero recoil
they determine the momentum and spin apportion between nucleon constituents.
Our result provides an insight into the response of the nucleon's pion cloud to
an external weak gravitational field and establishes a theoretical framework
for extrapolation of experimental and lattice data on the nucleon form factors
to zero momentum transfer. We also discuss form factors corresponding to
higher-rank tensor currents related to the moments of generalized parton
distributions.",0203276v2
2003-08-12,Exclusive electromagnetic production of strangeness on the nucleon : review of recent data in a Regge approach,"In view of the numerous experimental results recently released, we provide in
this letter an update on the performance of our simple Regge model for
strangeness electroproduction on the nucleon. Without refitting any parameters,
a decent description of all measured observables and channels is achieved. We
also give predictions for spin transfer observables, recently measured at
Jefferson Lab which have high sensitivity to discriminate between different
theoretical approaches.",0308131v2
2004-01-22,Possible methods for the determination of the $P$-parity of the $Θ^+$-pentaquark in NN-collisions,"We present two possibilities to determine the P-parity of the pentaquark
$\Theta^+$, in a model independent way, via the measurement of polarization
observables in $p+p\to \Theta^+ +\Sigma^+$, or $n+p\to \Theta^+ +\Lambda^0$, in
the near threshold region. Besides the measurement of the spin correlation
coefficient, $A_{xx}=A_{yy}$, (in collisions of transversally polarized
nucleons), the coefficient $D_{xx}$ of polarization transfer from the initial
proton to the final $ \Sigma^+(\Lambda^0)$ hyperon is also unambiguously
related to the $\Theta^+$ parity.",0401162v1
2004-07-28,Diffractive photoproduction of vector mesons at large momentum transfer,"Diffractive photoproduction of rho, phi and J/psi was studied in the BFKL
approach to hard colour singlet exchange. Differential cross sections, the
energy dependence and spin density matrix elements were calculated and compared
to data from HERA. The overall description of data is reasonably good, except
of the single flip amplitude which has the wrong sign. Importance of chiral odd
components of the photon is stressed.",0407328v1
2006-11-30,Diffraction Patterns in Deeply Virtual Compton Scattering,"We report on a calculation to show that the Fourier transform of the Deeply
Virtual Compton Scattering (DVCS) amplitude with respect to the skewness
variable \zeta at fixed invariant momentum transfer squared t gives results
that are analogous to the diffractive scattering of a wave in optics. As a
specific example, we utilize the quantum fluctuations of a fermion state at one
loop in QED to obtain the behavior of the DVCS amplitude for electron-photon
scattering. We then simulate the wavefunctions for a hadron by differentiating
the above LFWFs with respect to M^2 and study the corresponding DVCS amplitudes
in light-front longitudinal space.",0611381v1
2007-01-09,Baryon semileptonic decays: the Mexican contribution,"We give a detailed account of the techniques to compute radiative corrections
in baryon semileptonic decays developed over the years by Mexican
collaborations. We explain how the method works by obtaining an expression for
the Dalitz plot of semileptonic decays of polarized baryons including radiative
corrections to order ${\mathcal O}(\alpha q/\pi M_1)$, where $q$ is the
four-momentum transfer and $M_1$ is the mass of the decaying baryon. From here
we compute the totally integrated spin angular asymmetry coefficient of the
emitted baryon and compare its value with other results.",0701067v1
2007-02-23,On Polarization Of The Beam Extracted With The Bent Crystal,"Particles scattered off the nuclear target acquire a polarization if the
nuclei have a non zero analyzing power. This effect is enhanced when particles
traverse a bent crystal. Such enhancement under certain assumptions allows one
to measure the analyzing power at the level of 10^-4 at the square of transfer
momentum |t| < 10^-5 (GeV/c)2. If it happens that the analyzing power is big
enough, then one can get the beam polarization more than 50% after extraction
of the primary beam with the bent crystal.",0702237v1
1993-06-09,The class of universality of integrable and isotropic GL(N) mixed magnets,"We discuss a class of transfer matrix built by a particular combination of
isomorphic and non-isomorphic GL(N) invariant vertex operators. We construct a
conformally invariant magnet co nstituted of an alternating mixture of GL(N)
``spins'' operators at different order of represent ation. The corresponding
central charge is calculated by analysing the low temperature beha viour of the
associated free energy. We also comment on possible extensions of our results
for more general classes of mixed systems.",9306049v1
1995-04-24,"Modified tetrahedron equation and related 3D integrable models,II","This work is a continuation of paper (hep-th/9407146) where the Boltzmann
weights for the N-state integrable spin model on the cubic lattice has been
obtained only numerically. In this paper we present the analytical formulae for
this model in a particular case. Here the Boltzmann weights depend on six free
parameters including the elliptic modulus. The obtained solution allows to
construct a two-parametric family of the commuting two-layer transfer matrices.
Presented model is expected to be simpler for a further investigation in
comparison with a more general model mentioned above.",9504119v1
1998-07-29,Bethe Ansatze for 19-vertex Models,"The nineteen-vertex models of Zamolodchikov-Fateev, Izergin-Korepin and the
supersymmetric osp(1|2) with periodic boundary conditions are studied. We find
the spectrum of these quantum spin chains using the Coordinate Bethe Ansatz.
The approche is a suitable parametrization of their wavefunctions. We also
applied the Algebraic Bethe Ansatz in order to obtain the eigenvalues and
eigenvectors of the corresponding transfer matrices.",9807219v2
2002-03-08,Generalized Heisenberg Model,"We consider the XXZ model for a chain of particles whose spins are arbitrary
with the anisotropy parameter equal to the root of minus one and generalized
periodic boundary conditions. The conditions for the truncation of the
functional fusion relations of the transfer matrices are obtained. The
truncation results in a closed system of equations whose solution allows
obtaining the energy spectrum.",0203075v1
2003-11-07,3D Lorentzian Quantum Gravity from the asymmetric ABAB matrix model,"The asymmetric ABAB-matrix model describes the transfer matrix of
three-dimensional Lorentzian quantum gravity. We study perturbatively the
scaling of the ABAB-matrix model in the neighbourhood of its symmetric solution
and deduce the associated renormalization of three-dimensional Lorentzian
quantum gravity.",0311072v2
2005-07-14,Generalized T-Q relations and the open XXZ chain,"We propose a generalization of the Baxter T-Q relation which involves more
than one independent Q(u). We argue that the eigenvalues of the transfer matrix
of the open XXZ quantum spin chain are given by such generalized T-Q relations,
for the case that at most two of the boundary parameters {\alpha_-, \alpha_+,
\beta_-, \beta_+} are nonzero, and the bulk anisotropy parameter has values
\eta = i \pi/2, i\pi/4, ...",0507139v1
2005-10-11,Bethe Ansatz for the open XXZ chain from functional relations at roots of unity,"We briefly review Bethe Ansatz solutions of the integrable open spin-1/2 XXZ
quantum spin chain derived from functional relations obeyed by the transfer
matrix at roots of unity.",0510086v1
2003-06-02,On Bethe vectors in the XXZ model at roots of unity,"We give a construction of creation operators responsible for appearance of
Bethe vectors with the same eigenvalues of the transfer-matrix for the
inhomogeneous arbitrary spin XXZ model at roots of unity with particular
quasiperiodic boundary conditions. This construction generalizes the similar
one, recently obtained by K.Fabricius and B.M.McCoy, for the homogeneous
six-vertex model with periodic boundary conditions. Even in the last case, the
given proof for the main formulae are simpler than the original one.",0306032v1
2003-09-30,On the partition function of the six-vertex model with domain wall boundary conditions,"The six-vertex model on an $N\times N$ square lattice with domain wall
boundary conditions is considered. A Fredholm determinant representation for
the partition function of the model is given. The kernel of the corresponding
integral operator is of the so-called integrable type, and involves classical
orthogonal polynomials. From this representation, a ``reconstruction'' formula
is proposed, which expresses the partition function as the trace of a suitably
chosen quantum operator, in the spirit of corner transfer matrix and vertex
operator approaches to integrable spin models.",0309064v2
2003-09-07,Nonlinear optical beams carrying phase dislocations,"We describe different types of self-trapped optical beams carrying phase
dislocations, including vortex solitons and ring-like soliton clusters. We
demonstrate numerically how to create such nonlinear singular beams by the
interaction of several fundamental optical solitons. Mutual trapping of several
solitons can be regarded as a synthesis of `soliton molecules', and it
corresponds to a transfer of an initial orbital angular momentum of a system of
solitons to a spin momentum of an optical vortex.",0309025v1
2005-12-21,Integrable Vertex Models with General Twists,"We review recent progress towards the solution of exactly solved isotropic
vertex models with arbitrary toroidal boundary conditions. Quantum space
transformations make it possible the diagonalization of the corresponding
transfer matrices by means of the quantum inverse scattering method. Explicit
expressions for the eigenvalues and Bethe ansatz equations of the twisted
isotropic spin chains based on the $B_n$, $D_n$ and $C_n$ Lie algebras are
presented. The applicability of this approach to the eight vertex model with
non-diagonal twists is also discussed.",0512063v1
1994-03-03,Polarizing Stored Beams by Interaction with Polarized Electrons,"A polarized, internal electron target gradually polarizes a proton beam in a
storage ring. Here, we derive the spin-transfer cross section for $\vec
e\,(p,\vec p\, )e$\ scattering. A recent measurement of the polarizing effect
of a polarized atomic hydrogen target is explained when the effect of the
atomic electrons is included. We also consider the interaction of a stored beam
with a pure electron target which can be realized either by a comoving electron
beam or by trapping of electrons in a potential well. In the future, this could
provide a practical way to polarize antiprotons.",9403004v1
1997-09-30,Elastic Proton-Deuteron Backward Scattering: Relativistic Effects and Polarization Observables,"The elastic proton-deuteron backward reaction is analyzed within a covariant
approach based on the Bethe-Salpeter equation with realistic meson-exchange
interaction. Lorentz boost and other relativistic effects in the cross section
and spin correlation observables, like tensor analyzing power and polarization
transfer etc., are investigated in explicit form. Results of numerical
calculations for a complete set of polarization observables are presented.",9709071v1
2000-02-09,Quark Substructure and Isobar Effects on Deuteron Form-Factors,"Elastic ed scattering, with deuteron polarization, up to high momentum
transfer provides detailed information on the deuteron wave function. This
determines the range dependence of the orbital and spin components of the one-
and two-body currents, restricting contributions of isobar and meson-exchange
currents and of quark/gluon degrees of freedom, as well as the nucleon
component. The R-matrix boundary condition model combines all these effects,
predicting nucleon-nucleon reactions and the deuteron form-factors
simultaneously. A brief description of the model is followed by a comparison of
its results with data, emphasizing the restrictions placed on the model by ed
elastic form-factors.",0002026v1
2004-09-25,Geodesics and distance in classical physics,"We formulate geodesics on a manifold in terms of a parallel transfer of a
particle state vector transformed by local Lorentz and Yang-Mills symmetry
groups. This formulation leads to an introduction of a canonical one-form the
eigenvalues of which define distance on a manifold. We suggest an action based
on the canonical distance form and apply it to describe classical particles
with spin. Arguments are presented in favour of scaling distance in the
space-time with a scalar field.",0409134v2
2004-11-24,Probing Dynamics at Interfaces: Options for Neutron and X-ray Spectroscopy,"Inelastic neutron and X-ray scattering experiments on surfaces and interfaces
are a challenging topic in modern physics. Particular interest arises regarding
surfaces and interfaces of soft matter and biological systems. We review both
neutron and x-ray spectroscopic techniques with view at their applicability to
these samples. We discuss the different methods, namely neutron triple-axis,
backscattering and spin-echo spectroscopy as well as x-ray photon correlation
spectroscopy, in the context of planar lipid membrane models as an example. By
the combination of the different methods, a large range in momentum and energy
transfer is accessible.",0411220v1
2006-06-16,Diffuse light scattering dynamics under conditions of electromagnetically induced transparency,"We show that, under conditions of electromagnetically induced transparency
(EIT), a significant portion of the incident probe pulse can be transferred
into Rayleigh and Raman scattering channels. The light scattered into the
Rayleigh channel emerges from the sample with an EIT time delay. We show that a
proper description of the probe light propagation in the sample should include,
in the diffusion dynamics, a spin polariton generated by the two-photon EIT
process. The results have important implications for studies of weak light
localization, and for manipulation of single and few photon states in ultracold
atomic gases.",0606150v1
1996-06-16,Quantum logic as a sum over classical logic gates,"It is shown that certain natural quantum logic gates, {\it i.e.} unitary time
evolution matrices for spin-\frac{1}{2} quantum spins, can be represented as
sums, with appropriate phases, over classical logic gates, in a direct analogy
with the Feynman path integral representation of quantum mechanics. On the
other hand, it is shown that a natural quantum gate obtained by analytically
continuing the transfer matrix of the anisotropic nearest-neighbour Ising model
to imaginary time, does not admit such a representation.",9606018v1
2001-06-23,Notions of controllability for quantum mechanical systems,"In this paper, we define four different notions of controllability of
physical interest for multilevel quantum mechanical systems. These notions
involve the possibility of driving the evolution operator as well as the state
of the system. We establish the connections among these different notions as
well as methods to verify controllability.
  The paper also contains results on the relation between the controllability
in arbitrary small time of a system varying on a compact transformation Lie
group and the corresponding system on the associated homogeneous space. As an
application, we prove that, for the system of two interacting spin 1/2
particles, not every state transfer can be obtained in arbitrary small time.",0106128v2
2004-08-26,Control Theoretical Approach to Quantum Control,"We derive the quantum stochastic master equation for bosonic systems without
measurement theory but control theory. It is shown that the quantum effect of
the measurement can be represented as the correlation between dynamical and
measurement noise. The transfer function representation allows us to analyze a
dynamical uncertainty relation which imposes strong constraints on the dynamics
of the linear quantum systems. In particular, quantum systems preserving the
minimum uncertainty are uniquely determined. For large spin systems, it is
shown that local dynamics are equivalent to bosonic systems. Considering global
behavior, we find quantum effects to which there is no classical counterparts.
A control problem of producing maximal entanglement is discussed as the
stabilization of a filtering process.",0408160v1
2004-10-15,Atomic quantum memory: cavity vs single pass schemes,"This paper presents a quantum mechanical treatment for both atomic and field
fluctuations of an atomic ensemble interacting with propagating fields, either
in Electromagnetically Induced Transparency or in a Raman situation. The atomic
spin noise spectra and the outgoing field spectra are calculated in both
situations. For suitable parameters both EIT and Raman schemes efficiently
preserve the quantum state of the incident probe field in the transfer process
with the atoms, although a single pass scheme is shown to be intrinsically less
efficient than a cavity scheme.",0410125v1
2005-01-05,Greenberger-Horne-Zeilinger correlation and Bell-type inequality seen from moving frame,"The relativistic version of the Greenberger-Horne-Zeilinger experiment with
massive particles is proposed. We point out that, in the moving frame, GHZ
correlations of spins in original directions transfer to different directions
due to the Wigner rotation. Its effect on the degree of violation of Bell-type
inequality is also discussed.",0501019v1
2005-06-17,Quantum storage and information transfer with superconducting qubits,"We design theoretically a new device to realize the general quantum storage
based on dcSQUID charge qubits. The distinct advantages of our scheme are
analyzed in comparison with existing storage scenarios. More arrestingly, the
controllable XY-model spin interaction has been realized for the first time in
superconducting qubits, which may have more potential applications besides
those in quantum information processing. The experimental feasibility is also
elaborated.",0506144v1
2006-08-18,Useful entanglement from the Pauli principle,"We address the question whether identical-particle entanglement is a useful
resource for quantum information processing. We answer this question positively
by reporting a scheme to create entanglement using semiconductor quantum wells.
The Pauli exclusion principle forces quantum correlations between the spins of
two independent fermions in the conduction band. Selective electron-hole
recombination then transfers this entanglement to the polarization of emitted
photons, which can subsequently be used for quantum information tasks.",0608141v2
2007-04-30,Alpha decay chains from element 113,"Theoretical estimates of $\alpha$-decay half lives of several nuclei in the
decay from element 113 are presented. Calculations in a WKB framework using
DDM3Y interaction and experimental Q-values are in good agreement with the
experimental data. Half life calculations are found to be quite sensitive to
the Q-values and angular momenta transfers. Calculated decay lifetime
decreases, owing to more penetrability as well as thinner barrier, as Q-value
increases. Deviations to this predominant behaviour observed in some recent
experimental data may be attributed to non zero spin-parities in some cases.",0704.3927v1
2007-05-24,A note on the spin-1/2 XXZ chain concerning its relation to the Bose gas,"By considering the one-particle and two-particle scattering data of the
spin-1/2 Heisenberg chain at T=0 we derive a continuum limit relating the spin
chain to the 1D Bose gas. Applying this limit to the quantum transfer matrix
approach of the Heisenberg chain we obtain expressions for the correlation
functions of the Bose gas at arbitrary temperatures.",0705.3569v3
2007-05-28,Backlund transformations for difference Hirota equation and supersymmetric Bethe ansatz,"We consider GL(K|M)-invariant integrable supersymmetric spin chains with
twisted boundary conditions and elucidate the role of Backlund transformations
in solving the difference Hirota equation for eigenvalues of their transfer
matrices. The nested Bethe ansatz technique is shown to be equivalent to a
chain of successive Backlund transformations ""undressing"" the original problem
to a trivial one.",0705.4006v1
2007-06-19,Astrophysical Violations of the Kerr Bound as a Possible Signature of String Theory,"In 4D general relativity, the angular momentum of a black hole is limited by
the Kerr bound. We suggest that in string theory, this bound can be breached
and compact black-hole-like objects can spin faster. Near such ""superspinars,""
the efficiency of energy transfer from the accreting matter to radiation can
reach 100%, compared to the maximum efficiency of 42% of the extremal Kerr (or
6% of the Schwarzschild) black hole. Finding such superspinning objects as
active galactic nuclei, GBHCs, or sources of gamma ray bursts, could be viewed
as experimental support for string theory.",0706.2873v1
2007-07-24,Singular point characterization in microscopic flows,"We suggest an approach to microrheology based on optical traps in order to
measure fluid fluxes around singular points of fluid flows. We experimentally
demonstrate this technique, applying it to the characterization of controlled
flows produced by a set of birefringent spheres spinning due to the transfer of
light angular momentum. Unlike the previous techniques, this method is able to
distinguish between a singular point in a complex flow and the absence of flow
at all; furthermore it permits us to characterize the stability of the singular
point.",0707.3546v1
2007-08-30,Specific heat of the mixed spin-1/2 and spin-S Ising model with a rope ladder structure,"The mixed spin-1/2 and spin-S (S>1/2) Ising model on a rope ladder is
examined by combining two exact analytical methods. By the decoration-iteration
mapping transformation, this mixed-spin system is firstly transformed to a
simple spin-1/2 Ising model on the two-leg ladder, which is then exactly solved
by the standard transfer-matrix method. The thermal variations of the
zero-field specific heat are discussed in particular.",0708.4100v1
2007-09-25,Circuit theory for crossed Andreev reflection and nonlocal conductance,"Nonlocal currents, in devices where two normal metal terminals are contacted
to a superconductor, are determined using the circuit theory of mesoscopic
superconductivity. We calculate the conductance associated with crossed Andreev
reflection and electron transfer between the two normal metal terminals, in
addition to the conductance from direct Andreev reflection and quasiparticle
tunneling. Dephasing and proximity effect are taken into account.",0709.4020v1
2007-10-30,Current-driven vortex oscillations in metallic nanocontacts,"We present experimental evidence of sub-GHz spin-transfer oscillations in
metallic nano-contacts that are due to the translational motion of a magnetic
vortex. The vortex is shown to execute large-amplitude orbital motion outside
the contact region. Good agreement with analytical theory and micromagnetics
simulations is found.",0710.5680v1
2007-11-05,Deeply Virtual Compton Scattering with CLAS,"The beam spin asymmetries of the reaction ep -> epg in the Bjorken regime
were measured over a wide kinematical domain using the CLAS detector and a new
lead-tungstate calorimeter. Through the interference of the Bethe-Heitler
process with Deeply Virtual Compton Scattering, those asymmetries provide
constraints for the nucleon Generalized Parton Distributions models. The
observed shapes are in agreement with twist-2 dominance predictions.",0711.0755v2
2007-11-14,Elastic proton-proton and proton-antiproton scattering: analysis of complete set of helicity amplitudes,"The differential cross-sections are calculated for proton-proton and
proton-antiproton elastic scattering using the phenomenological model based on
the analytic parameterizations for global scattering parameters (total
cross-section and $\rho$ - parameter), crossing symmetry and derivative
relations. We confront our model predictions with experimental data in wide
range of energy and momentum transfer. The suggested method may be useful for
PAX Program (GSI) as well as for high-energy experiments at RHIC and LHC.",0711.2231v1
2007-11-23,Small-world hypergraphs on a bond-disordered Bethe lattice,"We study the thermodynamic properties of spin systems with bond-disorder on
small-world hypergraphs, obtained by superimposing a one-dimensional Ising
chain onto a random Bethe graph with p-spin interactions. Using transfer-matrix
techniques, we derive fixed-point equations describing the relevant order
parameters and the free energy, both in the replica symmetric and one step
replica symmetry breaking approximation. We determine the static and dynamic
ferromagnetic transition and the spinglass transition within replica symmetry
for all temperatures, and demonstrate corrections to these results when one
step replica symmetry breaking is taken into account. The results obtained are
in agreement with Monte-Carlo simulations.",0711.3757v1
2007-12-10,Induced quantum dots and wires: electron storage and delivery,"We show that quantum dots and quantum wires are formed underneath metal
electrodes deposited on a planar semiconductor heterostructure containing a
quantum well. The confinement is due to the self-focusing mechanism of an
electron wave packet interacting with the charge induced on the metal surface.
Induced quantum wires guide the transfer of electrons along metal paths and
induced quantum dots store the electrons in specific locations of the
nanostructure. Induced dots and wires can be useful for devices operating on
the electron spin.",0712.1422v1
2007-12-19,"Spin-transfer physics and the model of ferromagnetism in (Ga,Mn)As","We describe recent progress and open questions in the physics of
current-induced domain-wall displacement and creep in (Ga,Mn)As. Furthermore,
the reasons are recalled why, despite strong disorder and localization, the p-d
Zener model is suitable for the description of this system.",0712.3247v1
2008-03-24,Measuring complete quantum states with a single observable,"Experimental determination of an unknown quantum state usually requires
several incompatible measurements. However, it is also possible to determine
the full quantum state from a single, repeated measurement. For this purpose,
the quantum system whose state is to be determined is first coupled to a second
quantum system (the ""assistant"") in such a way that part of the information in
the quantum state is transferred to the assistant. The actual measurement is
then performed on the enlarged system including the original system and the
assistant. We discuss in detail the requirements of this procedure and
experimentally implement it on a simple quantum system consisting of nuclear
spins.",0803.3398v1
2008-06-29,Interacting atoms in optical lattices,"We propose an easy to use model to solve for interacting atoms in an optical
lattice. This model allows for the whole range of weakly to strongly
interacting atoms, and it includes the coupling between relative and
center-of-mass motion via anharmonic lattice terms. We apply this model to a
high-precision spin dynamics experiment, and we discuss the corrections due to
atomic interactions and the anharmonic coupling. Under suitable experimental
conditions, energy can be transferred between the relative and center-of-mass
motion, and this allows for creation of Feshbach molecules in excited lattice
bands.",0806.4784v1
2008-08-16,Descent Construction for Gspin Groups: Main Results and Applications,"The purpose of this note is to announce an extension of the descent method of
Ginzburg, Rallis and Soudry to the setting of essentially self dual
representations. This extension of the descent construction provides a
complement to recent work of Asgari and Shahidi on the generic transfer for
general Spin groups as well as to the work of Asgari and Raghuram on
cuspidality of the exterior square lift for representations of GL4. Complete
proofs of the results announced in the present note will appear in our
forthcoming articles.",0808.2269v2
2008-09-02,Heisenberg chains cannot mirror a state,"Faithful exchange of quantum information can in future become a key part of
many computational algorithms. Some Authors suggest to use chains of mutually
coupled spins as channels for quantum communication. One can divide these
proposals into the groups of assisted protocols, which require some additional
action from the users, and natural ones, based on the concept of state
mirroring. We show that mirror is fundamentally not the feature chains of
spins-1/2 coupled by the Heisenberg interaction, but without local magnetic
fields. This fact has certain consequences in terms of the natural state
transfer.",0809.0356v3
2008-10-23,"New possibility for further measurements of nucleon form factors at large momentum transfer in time-like region: $\bar{p}+{p}\to \ell^+ +\ell^-$, $\ell=e$ or $μ$","We briefly summarize the status with electromagnetic nucleon form factors,
and give in this framework, arguments to study the angular dependence of the
differential cross section and single-spin polarization phenomena (polarized
target or polarized beam) in $\bar{p}+{p}\to \ell^++\ell^-$, in view of the
availability of future antiproton beams.",0810.4245v1
2009-01-22,Bethe ansatz of the open spin-s XXZ chain with nondiagonal boundary terms,"We consider the open spin-s XXZ quantum spin chain with nondiagonal boundary
terms. By exploiting certain functional relations at roots of unity, we propose
the Bethe ansatz solution for the transfer matrix eigenvalues for cases where
atmost two of the boundary parameters are set to be arbitrary and the bulk
anisotropy parameter has values \eta = i \pi/3, i \pi/5,... We present
numerical evidence to demonstrate completeness of the Bethe ansatz solutions
derived for s = 1/2 and s = 1.",0901.3558v3
2009-05-29,Antiferromagnetic sawtooth chain with Heisenberg and Ising bonds,"The sawtooth chain with pairs of $S=1/2$ spins interacting with
$XXZ$-interactions placed on each second tooth is considered. All other
interaction bonds are taken to be of Ising type. Exact statistical mechanical
solution of the model within the direct transfer-matrix technique is obtained.
The solution allows one to obtain exact analytic expressions for all
thermodynamic functions of the model. Ground stated properties are also
investigated, the corresponding ground state phase diagram is presented.",0905.4776v4
2009-07-07,Electro-spinon in one-dimensional Mott insulator,"The low-energy dynamical optical response of dimerized and undimerized spin
liquid states in a one-dimensional charge transfer Mott insulator is
theoretically studied. An exact analysis is given for the low-energy asymptotic
behavior using conformal field theory for the undimerized state. In the
dimerized state, the infrared absorption due to the bound state of two
solitons, i.e, the breather mode, is predicted with an accurate estimate for
its oscillator strength, offering a way to detect experimentally the excited
singlet state. Effects of external magnetic fields are also discussed.",0907.1135v2
2009-07-09,A Tuneable Few Electron Triple Quantum Dot,"In this paper we report on a tuneable few electron lateral triple quantum dot
design. The quantum dot potentials are arranged in series. The device is aimed
at studies of triple quantum dot properties where knowing the exact number of
electrons is important as well as quantum information applications involving
electron spin qubits. We demonstrate tuning strategies for achieving required
resonant conditions such as quadruple points where all three quantum dots are
on resonance. We find that in such a device resonant conditions at specific
configurations are accompanied by novel charge transfer behaviour.",0907.1322v1
2009-08-16,Limitations on dispersion relations for Generalized Parton Distributions,"Deeply Virtual Compton Scattering and electroproduction of mesons involve
amplitudes that are analytic in energy. Analyticity enables Dispersion
Relations (DR's) for such amplitudes, relating real and imaginary parts. Lately
it has been suggested that DR's be applied to the integrated Generalized Parton
Distributions that embody the spin-dependent soft, but factorizable part of the
scattering. However, at non-zero momentum transfer, DRs require integration
over unphysical regions of the variables. We show that the relevant unphysical
region of the non-forward DRs is considerable, vitiating efforts to avoid the
actual measurement of the real parts more directly.",0908.2215v1
2009-09-30,Electron-hole pair creation by atoms incident on a metal surface,"Electron-hole pair creation by an adsorbate incident on a metal surface is
described using \textit{ab initio} methods. The approach starts with standard
first principles electronic structure theory, and proceeds to combine
classical, quantum oscillator and time dependent density functional methods to
provide a consistent description of the non-adiabatic energy transfer from
adsorbate to substrate. Of particular interest is the conservation of the total
energy at each level of approximation, and the importance of a spin transition
as a function of the adsorbate/surface separation. Results are presented and
discussed for H and D atoms incident on the Cu(111) surface.",0909.5501v1
2009-10-14,Bipolaron Density-Wave Driven By Antiferromagnetic Correlations and Frustration in Organic Superconductors,"We describe the Paired Electron Crystal (PEC) which occurs in the interacting
frustrated two-dimensional 1/4-filled band. The PEC is a charge-ordered state
with nearest-neighbor spin singlets separated by pairs of vacant sites, and can
be thought of as a bipolaron density wave. The PEC has been experimentally
observed in the insulating state proximate to superconductivity in the organic
charge-transfer solids. Increased frustration drives a PEC-to-superconductor
transition in these systems.",0910.2728v1
2009-12-14,Ultralong Photon Echo Storage Using Optical Locking,"An ultralong photon storage with more than 50% retrieval efficiency is
presented in the three-pulse photon echoes by using a pair of control pulses,
where the control pulses play to freeze atoms dephasing process conditionally
by transferring excited atoms to an auxiliary state and returning them back
later. The observed photon echo decay time much longer than the spin
homogeneous decay time is potential for long distance quantum communications.",0912.2756v2
2009-12-24,A resonance model with magnetic connection for 3:2 HFQPO pairs in black hole binaries,"We apply epicyclic resonances to the magnetic connection (MC) of a black hole
(BH) with a relativistic accretion disc, interpreting the high frequency
quasi-periodic oscillations (HFQPOs) with 3:2 pairs observed in three BH X-ray
binaries. It turns out that the 3:2 HFQPO pairs are associated with the steep
power-law states, and the severe damping can be overcome by transferring energy
and angular momentum from a spinning BH to the inner disc in the MC process.",0912.4776v1
2010-01-04,Influence of Thermal Fluctuations of Spin Density Wave Order Parameter on the Quasiparticle Spectral Function,"The two-dimensional model of itinerant electrons coupled to an
anti-ferromagnetic order parameter is considered. In the mean field solution
the Fermi surface undergoes reconstruction, and breaks into disconnected
``pockets''. We have studied the effect of the thermal fluctuations of the
order parameter on the spectral density in such system. These fluctuations lead
to a finite width of the spectral line scaling linearly with temperature. Due
to the thermal fluctuations the quasi-particle spectral weight is transfered
into a magnetic Brillouin zone. This can be interpreted as restoration of
``arcs'' of the non-interacting Fermi surface.",1001.0590v1
2010-02-01,Relativistic and spin effects in elastic backward p-d scattering,"The elastic backward proton-deuteron scattering is analyzed including
relativistic effects in the deuteron and the mechanism of this reaction which
includes the graphs corresponding to the emission, rescattering and absorption
of the virtual pion by a deuteron nucleon in addition to the one-nucleon
exchange graph. It allows one to obtain a rather satisfactory description of
all the experimental data on the differential cross section, tensor analyzing
power of the deuteron and transfer polarization in this reaction.",1002.0249v1
2010-02-12,The longitudinal polarization of hyperons in the forward region in polarized $pp$ collisions,"We study the longitudinal polarization of hyperons and anti-hyperons at
forward pseudorapidity, $2.5<\eta<4$, in singly polarized $pp$ collisions at
RHIC energies by using different parameterizations of the polarized parton
densities and different models for the polarized fragmentation functions. The
results show that the $\Sigma^+$ polarization is able to distinguish different
pictures on spin transfer in high energy fragmentation processes; and the
polarization of $\Lambda$ and $\bar\Lambda$ hyperons can provide sensitivity to
the helicity distribution of strange sea quarks. The influence from beam
remnant to hyperon polarization in the forward region is also discussed.",1002.2468v1
2010-02-19,Strong Three-magnon Scattering in Cuprates by Resonant X-rays,"We show that Resonant Inelastic X-ray scattering (RIXS) is sensitive to
three-magnon excitations in cuprates. Even if it requires three electrons to
simultaneously flip their spin, the RIXS tri-magnon scattering amplitude is not
small. At the Cu $L$-edge its intensity is generally larger than the bi-magnon
one and at low transferred momentum even larger than the single-magnon
intensity. At the copper $M$-edge the situation is yet more extreme: in this
case three-magnon scattering is dominating over all other magnetic channels.",1002.3773v1
2010-03-22,The transverse spin structure of the pion at short distances,"We study the form factors of the quark tensor currents in the pion at large
squared momentum transfer Q^2. It turns out that certain form factors can be
evaluated using collinear factorization, whereas others receive important
contributions from the end-point regions of the longitudinal quark momenta in
the pion. We derive simple analytic expressions for the dominant terms at high
Q^2 and illustrate them numerically.",1003.4171v2
2010-04-20,Parallel exact diagonalization solver for quantum-electron models,"We present a parallel computation scheme based on the Arnoldi algorithm for
exact diagonalization of quantum-electron models. It contains a selective data
transferring method and distributed storage format for efficient computing of
the matrix-vector product on distributed computing systems. The performed
numerical experiments demonstrated good performance and scalability of our
eigenvalue solver. The developed technique has been applied to investigate the
electronic properties of Sr2RuO4 at experimental temperatures. The role of the
spin-flip term in the electronic Hamiltonian was analyzed.",1004.3354v1
2010-07-12,Vibrational stabilization of ultracold KRb molecules. A comparative study,"The transfer of weakly bound KRb molecules from levels just below the
dissociation threshold into the vibrational ground state with shaped laser
pulses is studied. Optimal control theory is employed to calculate the pulses.
The complexity of modelling the molecular structure is successively increased
in order to study the effects of the long-range behavior of the excited state
potential, resonant spin-orbit coupling and singlet-triplet mixing.",1007.1898v2
2010-07-21,Spectral Properties near the Mott Transition in the One-Dimensional Hubbard Model,"Single-particle spectral properties near the Mott transition in the
one-dimensional Hubbard model are investigated by using the dynamical
density-matrix renormalization group method and the Bethe ansatz. The
pseudogap, hole-pocket behavior, spectral-weight transfer, and upper Hubbard
band are explained in terms of spinons, holons, antiholons, and doublons. The
Mott transition is characterized by the emergence of a gapless mode whose
dispersion relation extends up to the order of hopping t (spin exchange J) in
the weak (strong) interaction regime caused by infinitesimal doping.",1007.3547v2
2010-08-03,Studies of TMDs at COMPASS,"Transverse spin and transverse momentum distribution functions of the
constituents of the nucleon are a crucial input for a complete description of
the nucleon. COMPASS measured such for longitudinally and transversely
polarized deuterons and protons. In the following we will focus on recent
results from the 2007 transverse proton data and on the results for unpolarized
deuterons.",1008.0438v1
2010-08-23,Vortex states in hole-doped iron-pnictide superconductors,"Based on a phenomenological model with competing spin-density-wave (SDW) and
extended $s-$wave superconductivity, the vortex states in
Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ are investigated by solving Bogoliubov-de
Gennes equations. Our result for the optimally doped compound without induced
SDW is in qualitative agreement with recent scanning tunneling microscopy
experiment. We also propose that the main effect of the SDW on the vortex
states is to reduce the intensity of the in-gap peak in the local density of
states and transfer the spectral weight to form additional peaks outside the
gap.",1008.3885v1
2010-09-22,Magnetocaloric effect in integrable spin-s chains,"We study the magnetocaloric effect for the integrable antiferromagnetic
high-spin chain. We present an exact computation of the Gr\""uneisen parameter,
which is closely related to the magnetocaloric effect, for the quantum spin-s
chain on the thermodynamical limit by means of Bethe ansatz techniques and the
quantum transfer matrix approach. We have also calculated the entropy S and the
isentropes in the (H,T) plane. We have been able to identify the quantum
critical points H_c^{(s)}=2/(s+1/2) looking at the isentropes and/or the
characteristic behaviour of the Gr\""uneisen parameter.",1009.4411v1
2010-09-22,Ruelle-Lanford functions for quantum spin systems,"We prove a large deviation principle for the expectation of macroscopic
observables in quantum (and classical) Gibbs states. Our proof is based on
Ruelle-Lanford functions and direct subadditivity arguments, as in the
classical case, instead of relying on G\""artner-Ellis theorem, and cluster
expansion or transfer operators as done in the quantum case. In this approach
we recover, expand, and unify quantum (and classical) large deviation results
for lattice Gibbs states. In the companion paper \cite{OR} we discuss the
characterization of rate functions in terms of relative entropies.",1009.4491v1
2010-09-24,Parametric excitation of a magnetic nanocontact by a microwave field,"We demonstrate that magnetic oscillations of a current-biased magnetic
nanocontact can be parametrically excited by a microwave field applied at twice
the resonant frequency of the oscillation. The threshold microwave amplitude
for the onset of the oscillation decreases with increasing bias current, and
vanishes at the transition to the auto-oscillation regime. The parametrically
excited oscillation mode is the same as the one in the auto-oscillation regime,
enabling studies of both the passive and the active dynamics of the oscillator.
Theoretical analysis shows that measurements of parametric excitation provide
quantitative information about the relaxation rate, the spin transfer
efficiency, and the nonlinearity of the nanomagnetic system.",1009.4837v1
2010-11-02,Uniform Matrix Product State in the Thermodynamic Limit,"We study a uniform matrix product state as a variational state for classical
and quantum spin chains in the thermodynamic limit. Under a careful treatment
of the translational symmetry, eigen values of the transfer matrix defined in
the calculation of expectation values can reflect the periodicity of the ground
state and indicate optimum periodicity of the matrix product state. We discuss
the relation between the periodicity and accuracy of magnetization curves. This
approach is free from the error due to finite system size, which works well
especially for the magnetic plateau problem.",1011.0576v1
2011-03-03,Inelastic neutron and x-ray scattering as probes of the sign structure of the Fe-pnictide superconducting gap,"Neutron spin-flip scattering observations of a resonance in the
superconducting state is often taken as evidence of an unconventional
superconducting state in which the gap changes sign $\Delta(k+Q)=-\Delta(k)$
for momentum transfers $Q$ which play an important role in the pairing.
Recently questions regarding this identification for the Fe-pnictide
superconductors have been raised and it has been suggested that
$\Delta(k+Q)=\Delta(k)$. Here we propose that inelastic neutron or x-ray
scattering measurements of the spectral weight of a phonon of momentum $Q$ can
distinguish between these two pairing scenarios.",1103.0688v1
2011-03-18,Hybrid superconducting quantum magnetometer,"A superconducting quantum magnetometer based on magnetic flux-driven
modulation of the density of states of a proximized metallic nanowire is
theoretically analyzed. With optimized geometrical and material parameters
transfer functions up to a few mV/Phi_0 and intrinsic flux noise ~10^{-9}Phi_0
Hz^{-1/2} below 1 K are achievable. The opportunity to access single-spin
detection joined with limited dissipation (of the order of ~ 10^{-14} W) make
this magnetometer interesting for the investigation of the switching dynamics
of molecules or individual magnetic nanoparticles.",1103.3598v2
2011-03-31,Efficient Thermodynamic Description of Multi-Component One-Dimensional Bose Gases,"We present a new method of obtaining nonlinear integral equations
characterizing the thermodynamics of one-dimensional multi-component gases
interacting via a delta-function potential. In the case of the repulsive
two-component Bose gas we obtain a simple system of two NLIE allowing for an
efficient numerical implementation in contrast with the infinite number of
coupled equations obtained by employing the Thermodynamic Bethe Ansatz. Our
technique makes use of the Quantum Transfer Matrix and the fact that in a
certain continuum limit multi-component gases can be obtained from appropriate
anisotropic spin chains.",1103.6152v2
2011-06-16,Thermomagnonic spin transfer and Peltier effects in insulating magnets,"We study the coupled magnon energy transport and collective magnetization
dynamics in ferromagnets with magnetic textures. By constructing a
phenomenological theory based on irreversible thermodynamics, we describe
motion of domain walls by thermal gradients and generation of heat flows by
magnetization dynamics. From microscopic description based on magnon kinetics,
we estimate the transport coefficients and analyze the feasibility of
energy-related applications in insulating ferromagnets, such as yttrium iron
garnet and europium oxide.",1106.3135v2
2011-07-22,Tensor form factors of nucleon in QCD,"We extract the isovector tensor nucleon form factors, which play an important
role in understanding the transverse spin structure of the nucleon when related
to the quark helicity-flip generalized parton distributions via their first
moments. We employ the light-cone QCD sum rules to leading order in QCD and
include distribution amplitudes up to twist 6 in order to calculate the three
tensor form factors $H_T$, $E_T$ and $\tilde{H}_T$. Our results agree well with
those from other approaches in the low and high momentum-transfer regions.",1107.4584v2
2011-09-19,The eight-vertex model and lattice supersymmetry,"We show that the XYZ spin chain along the special line of couplings
J_xJ_y+J_xJ_z+J_yJ_z=0 possesses a hidden N=(2,2) supersymmetry. This lattice
supersymmetry is non-local and changes the number of sites. It extends to the
full transfer matrix of the corresponding eight-vertex model. In particular, it
is shown how to derive the supercharges from Baxter's Bethe ansatz. This
analysis leads to new conjectures concerning the ground state for chains of odd
length. We also discuss a correspondence between the spectrum of this XYZ chain
and that of a manifestly supersymmetric staggered fermion chain.",1109.4090v1
2011-10-30,Neutral Current Elastic Interactions in MiniBooNE,"Neutral Current Elastic (NCE) interactions in MiniBooNE are discussed. In the
neutrino mode MiniBooNE reported: the flux averaged NCE differential cross
section as a function of four-momentum transferred squared, an axial mass M_{A}
measurement, and a measurement of the strange quark spin content of the
nucleon, \Delta s. In the antineutrino mode we present the
background-subtracted data which is compared with the Monte Carlo predictions.",1110.6574v1
2011-11-24,Veneziano like amplitude as a test for AdS/QCD models,"The high energy asymptotics of QCD correlation functions is often used as a
test for bottom-up holographic models. Since QCD is not strongly coupled in the
ultraviolet domain, such a test may look questionable. We propose that the sum
over resonance poles emerging in correlators of a bottom-up model should
reproduce the structure of a Veneziano like amplitude at zero momentum transfer
assuming equivalence of spin and radial states in the latter. This requires a
five-dimensional background that suppresses the ultraviolet part in the
effective action of a model. We give examples of emerging low-energy
holographic models.",1111.5835v1
2012-02-20,Sum rule for the eight-vertex model on its combinatorial line,"We investigate the conjectured ground state eigenvector of the 8-vertex model
inhomogeneous transfer matrix on its combinatorial line, i.e., at $\eta=\pi/3$,
where it acquires a particularly simple form. We compute the partition function
of the model on an infinite cylinder with certain restrictions on the
inhomogeneities, and taking the homogeneous limit, we obtain an expression for
the squared norm of the ground state of the XYZ spin chain as a solution of a
differential recurrence relation.",1202.4420v2
2012-09-19,Algebraic Bethe ansatz for open XXX model with triangular boundary matrices,"We consider open XXX spins chain with two general boundary matrices submitted
to one constraint, which is equivalent to the possibility to put the two
matrices in a triangular form. We construct Bethe vectors from a generalized
algebraic Bethe ansatz. As usual, the method also provides Bethe equations and
transfer matrix eigenvalues.",1209.4269v2
2012-09-24,Control of the magnetism and magnetic anisotropy of a single-molecule magnet with an electric field,"Through systematics density functional calculations, the mechanism of the
substrate induced spin reorientation transition in FePc/O-Cu(110) was explained
in terms of charge transfer and rearrangement of Fe-d orbitals. Moreover, we
found giant magnetoelectric effects in this system, manifested by the sensitive
dependences of its magnetic moment and magnetic anisotropy energy on external
electric field. In particular, the direction of magnetization of FePc/O-Cu(110)
is switchable between in-plane and perpendicular axes, simply by applying an
external electric field of 0.5 eV/{\AA} along the surface normal.",1209.5453v3
2012-11-19,Superradiant Superconductivity,"We suggest possibility of Dicke superradiance in superconductors. The
necessary 2-level atoms are identified with Anderson pseudo spins in k-space,
seeing a k-dependent self consistent mean field. A way to couple these 2-level
bose atoms to a macroscopically excited coherent boson mode and create a novel
nonequilibrium superradiant superconductivity (SRSC) is suggested. Our
coherence transfer mechanism offers a hope to realize transient
superconductivity, even at room temperatures, in the pseudo gap phase of
certain underdoped cuprates. Recent experiments are briefly discussed in the
light of our theory. Quantum entanglement, QCP and superfluorescence properties
follow.",1211.4567v1
2012-11-20,Conductance enhancement due to atomic potential fluctuations in graphene,"We solve the Dirac equation, which describes charge massless chiral
relativistic carriers in a two-dimensional graphene. We have identified and
analysed a novel pseudospin-dependent scattering effect. We compute the
tunneling conductance and generalize the analytical result in the presence of
the tunable atomic potential of a graphene strip. The absence of back
scattering in graphene is shown to be due to Berry's phase which corresponds to
a sign change of the wave function under a spin rotation of a particle. We use
the transfer matrix approach and find that the electric conductance of doped
graphene increases due to atomic potential fluctuations.",1211.4780v1
2013-01-07,Mesoscopic fluctuations of conductance of a helical edge contaminated by magnetic impurities,"Elastic backscattering of electrons moving along the helical edge is
prohibited by time-reversal symmetry (TRS). We demonstrate, however, that an
ensemble of magnetic impurities may cause TRS-preserving quasi-elastic
backscattering, resulting in interference effects in the conductance. The
characteristic energy transferred in a backscattering event is suppressed due
to the RKKY interaction of localized spins (the suppression is exponential in
the total number of magnetic impurities). We predict the statistics of
conductance fluctuations to differ from those in the conventional case of a
one-dimensional system with quenched disorder.",1301.1185v1
2013-05-03,Organic superconductors: the need to go beyond effective 1/2-filled band models,"A frustrated, effective 1/2-filled band Hubbard-Heisenberg model has been
proposed to describe the strongly dimerized charge-transfer solid families
kappa-(ET)_2X and Z[Pd(dmit)_2]_2. In addition to unconventional
superconductivity these materials also exhibit antiferromagnetism, candidate
spin-liquid phases, and in the case of Z=EtMe_3P, a so-called valence-bond
solid phase. We show that neither superconductivity nor the valence-bond solid
phase occurs within the Hubbard-Heisenberg model, indicating that the effective
1/2-filled band model is unsuitable for these materials.",1305.0843v1
2013-05-08,On boundary fusion and functional relations in the Baxterized affine Hecke algebra,"We construct boundary type operators satisfying fused reflection equation for
arbitrary representations of the Baxterized affine Hecke algebra. These
operators are analogues of the fused reflection matrices in solvable half-line
spin chain models. We show that these operators lead to a family of commuting
transfer matrices of Sklyanin type. We derive fusion type functional relations
for these operators for two families of representations.",1305.1941v2
2013-09-04,Novel Giant Magnetoresistance Model using Multiple Barrier Potential,"This paper proposes a new model for Giant Magnetoresistance (GMR) and
calculates its typical graph qualitatively. The model foundation is the
microscopic mechanism in GMR, where the GMR effect can be explained by
intrinsic and extrinsic potential. The potentials are spin-dependent. The
potentials determine the transmission probability then it will give conductance
value. Here, the multiple barrier potential model is proposed as the new GMR
model. The transmission probability is determined using transfer matrix method.
It was found that this model is fit qualitatively with the typical GMR graph.",1309.1006v2
2013-12-13,Analytical expression of geometrical pumping for a quantum dot based on quantum master equation,"We analytically investigate a non-equilibrium quantum pumping for a single
quantum dot connected to external leads on the basis of the quantum master
equation (QME). We show that the Coulomb interaction associated with the spin
effect in the dot induces the Berry-like phase in the parameter space and this
phase results in the excess charge transfer for the cyclic modulation of
parameters in leads. We obtain an analytical expression of the curvature of the
phase and that for the pumped currents.",1312.3772v1
2013-12-24,Twisted Heisenberg chain and the six-vertex model with DWBC,"In this work we establish a relation between the six-vertex model with Domain
Wall Boundary Conditions (DWBC) and the $XXZ$ spin chain with anti-periodic
twisted boundaries. More precisely, we demonstrate a formal relation between
the zeroes of the partition function of the six-vertex model with DWBC and the
zeroes of the transfer matrix eigenvalues associated with the six-vertex model
with a particular non-diagonal boundary twist.",1312.6817v3
2014-02-05,Towards an improved description of SiDIS by a polarized 3He target,"The possibility of improving the description of the semi-inclusive deep
inelastic electron scattering off polarized 3He, that provides information on
the neutron single spin asymmetries, is illustrated. In particular, the
analysis at finite momentum transfers in a Poincare' covariant framework is
outlined and a generalized eikonal approach to include final state interaction
is presented.",1402.1068v1
2014-02-19,Hierarchy of stochastic pure states for open quantum system dynamics,"We derive a hierarchy of stochastic evolution equations for pure states
(quantum trajectories) to efficiently solve open quantum system dynamics with
non-Markovian structured environments. From this hierarchy of pure states
(HOPS) the exact reduced density operator is obtained as an ensemble average.
We demonstrate the power of HOPS by applying it to the Spin-Boson model, the
calculation of absorption spectra of molecular aggregates and energy transfer
in a photosynthetic pigment-protein complex.",1402.4647v1
2014-02-17,Photon Polarization Precession Spectroscopy for High-Resolution Studies of Spinwaves,"A new type of spectroscopy for high-resolution studies of spin waves that
relies on resonant scattering of hard x-rays is introduced. The energy transfer
in the scattering process is encoded in the precession of the polarization
vector of the scattered photons. Thus, the energy resolution of such a
spectroscopy is independent of the bandwidth of the probing radiation. The
measured quantity resembles the intermediate scattering function of the
magnetic excitations in the sample. At pulsed x-ray sources, especially x-ray
lasers, the proposed technique allows to take single-shot spectra of the
magnetic dynamics. The method opens new avenues to study low-energy
non-equilibrium magnetic processes in a pump-probe setup.",1402.4795v1
2014-04-01,Stamping single wall nanotubes for circuit quantum electrodynamics,"We report on a dry transfer technique for single wall carbon nanotube devices
which allows to embed them in high finesse microwave cavity. We demonstrate the
ground state charge readout and a quality factor of about 3000 down to the
single photon regime. This technique allows to make devices such as double
quantum dots which could be instrumental for achieving the strong spin photon
coupling. It can easily be extended to generic carbon nanotube based microwave
devices.",1404.0162v1
2014-06-04,Magnetization plateaus of an exactly solvable spin-1 Ising-Heisenberg diamond chain,"The spin-1 Ising-Heisenberg diamond chain in a magnetic field is exactly
solved by a rigorous treatment based on the transfer-matrix method. An exact
ground-state phase diagram includes in total three unconventional quantum
ground states with a quantum entanglement of the decorating spin-1 Heisenberg
dimers apart from two ground states with a classical spin arrangement. It is
evidenced that all three values of the magnetization allowed for the spin-1
diamond chain without translationally broken symmetry by the
Oshikawa-Yamanaka-Affleck criterion can become evident in an outstanding
stepwise magnetization curve with three intermediate plateaus at zero,
one-third, and two-thirds of the saturation magnetization.",1406.0999v1
2014-08-22,Integrable approach to simple exclusion processes with boundaries. Review and progress,"We study the matrix ansatz in the quantum group framework, applying
integrable systems techniques to statistical physics models. We start by
reviewing the two approaches, and then show how one can use the former to get
new insight on the latter. We illustrate our method by solving a model of
reaction-diffusion. An eigenvector for the transfer matrix for the XXZ spin
chain with non-diagonal boundary is also obtained using a matrix ansatz.",1408.5357v2
2014-09-01,Calculation of multichannel reactions in the four-nucleon system above breakup threshold,"Exact four-body equations of Alt, Grassberger and Sandhas are solved for
neutron-${}^3\mathrm{He}$ and proton-${}^3\mathrm{H}$ scattering in the energy
regime above the four-nucleon breakup threshold. Cross sections and spin
observables for elastic, transfer, charge-exchange, and breakup reactions are
calculated using realistic nucleon-nucleon interaction models, including the
one with effective many-nucleon forces due to explicit $\Delta$-isobar
excitation. The experimental data are described reasonably well with only few
exceptions such as vector analyzing powers.",1409.0337v1
2014-09-07,Exact solution of Ising model of an alternating delta spin chain,"The Ising model on an alternating triangular lattice with the
nearest-neighbor interaction in a magnetic field is presented. Exact solution
of this model is found. The thermodynamic quantities, like free energy,
specific heat a finite temperature and function correlaction, are calculated by
treatment based on the transfer matrix method. Our results show that the model
proposed does not have phase transition to a finite temperature, but the curve
of specific heat presented a Schottky anomaly.",1409.2127v3
2014-09-12,The gravitational time delay in the field of a slowly moving body with arbitrary multipoles,"We calculate the time delay of light in the gravitational field of a slowly
moving body with arbitrary multipoles (mass and spin multipole moments) by the
Time-Transfer-Function (TTF) formalism. The parameters we use, first introduced
by Kopeikin for a gravitational source at rest, make the integration of the TTF
very elegant and simple. Results completely coincide with expressions from the
literature. The results for a moving body (with constant velocity) with
complete multipole-structure are new, according to our knowledge.",1409.3743v2
2014-10-13,Impact parameter space and transverse distortion,"We investigate the GPDs in impact parameter space using the explicit light
front wave functions (LFWFs) for the two-particle Fock state of the electron in
QED. The Fourier transform (FT) of the GPDs gives the distribution of quarks in
the transverse plane for zero longitudinal momentum transfer ($\zeta=0$). We
study the relationship of the spin flip GPD with the distortion of unpolarized
quark distribution in the transverse plane when the target nucleon is
transversely polarized and also determine the sign of distortion from the sign
of anomalous magnetic moment.",1410.3225v2
2015-02-07,Sound emission from the gas of molecular superrotors,"We use an optical centrifuge to deposit a controllable amount of rotational
energy into dense molecular ensembles. Subsequent rotation-translation energy
transfer, mediated by thermal collisions, results in the localized heating of
the gas and generates strong sound wave, clearly audible to the unaided ear.
For the first time, the amplitude of the sound signal is analyzed as a function
of the experimentally measured rotational energy. The proportionality between
the two experimental observables confirms that rotational excitation is the
main source of the detected sound wave. As virtually all molecules, including
the main constituents of the atmosphere, are amenable to laser spinning by the
centrifuge, we anticipate this work to stimulate further development in the
area of photo-acoustic control and spectroscopy.",1502.02654v1
2015-03-26,On relations between one-dimensional quantum and two-dimensional classical spin systems,"We exploit mappings between quantum and classical systems in order to obtain
a class of two-dimensional classical systems with critical properties
equivalent to those of the class of one-dimensional quantum systems discussed
in a companion paper (J. Hutchinson, J. P. Keating, and F. Mezzadri,
arXiv:1503.05732). In particular, we use three approaches: the Trotter-Suzuki
mapping; the method of coherent states; and a calculation based on commuting
the quantum Hamiltonian with the transfer matrix of a classical system. This
enables us to establish universality of certain critical phenomena by extension
from the results in our previous article for the classical systems identified.",1503.07712v1
2015-05-08,Thermal vector potential theory of magnon-driven magnetization dynamics,"Thermal vector potential formulation is applied to study thermal dynamics of
magnetic structures in insulating ferromagnets. By separating variables of the
magnetic structure and magnons, the equation of motion for the structure
including spin-transfer effect due to thermal magnons is derived in the case of
a domain wall and a vortex. The magnon current is evaluated based on a linear
response theory with respect to the thermal vector potential representing the
temperature gradient. It is shown that the velocity of a domain wall when
driven by thermal magnon has a strong temperature dependence unlike the case of
an electrically-driven domain wall in metals.",1505.01908v1
2015-07-31,Longitudinal vector form factors in weak decays of nuclei,"The longitudinal form factors of the weak vector current of particles with
spin $ J = 1/2 $ and isospin $ I = 1/2 $ are determined by the mass difference
and the charge radii of members of the isotopic doublets. The most promising
reactions to measure these form factors are the reactions with large momentum
transfers involving the spin-1/2 isotopic doublets with a maximum mass
splitting. Numerical estimates of longitudinal form factors are given for
nucleons and eight nuclear spin-1/2 isotopic doublets.",1507.08823v1
2015-09-04,Plasmonic lateral forces on chiral spheres,"We show that the optical force exerted on a finite size chiral sphere by a
surface plasmon mode has a component along a direction perpendicular to the
plasmon linear momentum. We reveal how this chiral lateral force, pointing in
opposite directions for opposite enantiomers, stems from an angular-to-linear
crossed momentum transfer involving the plasmon transverse spin angular
momentum density and mediated by the chirality of the sphere. Our multipolar
approach allows us discussing the inclusion of the recoil term in the force on
a small sphere taken in the dipolar limit and observing sign inversions of the
lateral chiral force when the size of the sphere increases.",1509.01573v1
2015-09-11,Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide,"We investigate the micromechanical exfoliation and van der Waals (vdW)
assembly of ferromagnetic layered dichalcogenide Fe0.25TaS2. The vdW interlayer
coupling at the Fe-intercalated plane of Fe0.25TaS2 allows exfoliation of
flakes. A vdW junction between the cleaved crystal surfaces is constructed by
dry transfer method. We observe tunnel magnetoresistance in the resulting
junction under an external magnetic field applied perpendicular to the plane,
demonstrating spin-polarized tunneling between the ferromagnetic layered
material through the vdW junction.",1509.03525v1
2015-10-29,"Pieri rules, vertex operators and Baxter Q-matrix","We use the Pieri rules to recover the q-boson model and show it is equivalent
to a discretized version of the relativistic Toda chain. We identify its semi
infinite transfer matrix and the corresponding Baxter Q-matrix with half vertex
operators related by an {\omega}-duality transformation. We observe that the
scalar product of two higher spin XXZ wave functions can be expressed with a
Gaudin determinant.",1510.08709v2
2015-11-20,Offset-corrected $Δ$-Kohn-Sham scheme for the prediction of X-ray photoelectron spectra of molecules and solids,"Absolute binding energies of core electrons in molecules and bulk materials
can be efficiently calculated by spin paired density-function theory employing
a $\Delta$ Kohn-Sham ($\Delta$KS) scheme corrected by offsets that are highly
transferable. These offsets depend on core level and atomic species and can be
determined by comparing $\Delta$KS energies to experimental molecular X-ray
photoelectron spectra. We demonstrate the correct prediction of absolute and
relative binding energies on a wide range of molecules, metals and insulators.",1511.06610v2
2015-12-15,Vector Laguerre-Gauss beams with polarization-OAM entanglement in a graded-index medium,"It is shown that the vector-vortex Laguerre-Gauss modes with
polarization-orbital angular momentum (OAM) entanglement are the vector
solutions of the Maxwell equations in a graded-index medium. Focusing of
linearly and circularly polarized vortex light beams with nonzero azimuthal and
radial indices in a cylindrical graded-index medium is investigated. The wave
shape variation with distance taking into account the spin-orbit and
nonparaxial effects is analyzed. Effect of long-term periodical revival of wave
packets due to mode interference in a graded-index cylindrical optical
waveguide is demonstrated. High efficiency transfer of a strongly focused spot
through an optical waveguide over large distances takes place with a period of
revival.",1512.04712v1
2015-12-24,Spontaneous Chiral Symmetry Breaking in Bilayer Graphene,"Bilayer graphene and its thicker cousins with Rhombohedral stacking have
attracted considerable attention because of their susceptibility to a variety
of broken chiral symmetry states. Due to large density-of-states and quantized
Berry phases near their gapless band touching points, each spin-valley flavor
spontaneously transfers charge between layers to yield opening of energy gaps
in quasiparticle spectra and spreading of momentum-space Berry curvatures. In
this article we review the development of theories that predicted such chiral
symmetry breaking and classified the possible topological many-body ground
states, and the observations in recent experiments that are in reasonable
agreement with these theories.",1512.07772v1
2016-03-01,The 3He spectral function in light-front dynamics,"A distorted spin-dependent spectral function for 3He is considered for the
extraction of the transverse-momentum dependent parton distributions in the
neutron from semi-inclusive deep inelastic electron scattering off polarized
3He at finite momentum transfers, where final state interactions are taken into
account. The generalization of the analysis to a Poincar\'e covariant framework
within the light-front dynamics is outlined.",1603.00366v1
2016-04-28,A TBA description of thermal transport in the XXZ Heisenberg model,"It is shown that the Bethe ansatz formulation of the easy-plane 1D Heisenberg
model thermodynamics (TBA) by Takahashi and Suzuki and the subsequent analysis
of the spin Drude weight, also reproduces the thermal Drude weight and
magnetothermal coefficient obtained by the Quantum Transfer Matrix method
(QTM). It can also be extended to study the far-out of equilibrium energy
current generated at the interface between two semi-infinite chains held at
different temperatures.",1604.08434v1
2016-12-02,O(3) model with Nienhuis action,"We study the O(3) sigma model in $D=2$ on the lattice with a Boltzmann weight
linearized in $\beta$ on each link. While the spin formulation now suffers from
a sign-problem the equivalent loop model remains positive and becomes
particularly simple. By studying the transfer matrix and by performing Monte
Carlo simulations in the loop form we study the mass gap coupling in a step
scaling analysis. The question addressed is, whether or not such a simplified
action still has the right universal continuum limit. If the answer is
affirmative this would be helpful in widening the applicability of worm
algorithm methods.",1612.00621v1
2016-12-20,Fermions as generalized Ising models,"We establish a general map between Grassmann functionals for fermions and
probability or weight distributions for Ising spins. The equivalence between
the two formulations is based on identical transfer matrices and expectation
values of products of observables. The map preserves locality properties and
can be realized for arbitrary dimensions. We present a simple example where a
quantum field theory for free massless Dirac fermions in two-dimensional
Minkowski space is represented by an asymmetric Ising model on a euclidean
square lattice.",1612.06695v2
2017-08-19,Entangled quantum Otto heat engines based on two-spin systems with the Dzyaloshinski-Moriya interaction,"We construct an entangled quantum Otto engine based on spin-1/2 systems
undergoing Dzyaloshinski-Moriya (DM) interaction within a varying magnetic
field. We investigate the influence of the DM interaction on basic
thermodynamic quantities, including heat transfer, work done, and efficiency
and find that the DM interaction importantly influences the engine's
thermodynamics. We obtain an expression for engine efficiency, finding it to
yield the same efficiency for antiferromagnetic and ferromagnetic coupling. A
new upper bound, nontrivially consistent with the second law of thermodynamics,
is derived for engine efficiency in the case of non-zero DM interaction.",1708.05804v1
2017-08-24,Effective simulation of state distribution in qubit chains,"This work recollects a non-universal set of quantum gates described by
higher-dimensional Spin groups. They are also directly related with matchgates
in theory of quantum computations and complexity. Various processes of quantum
state distribution along a chain such as perfect state transfer and different
types of quantum walks can be effectively modeled on classical computer using
such approach.",1708.07439v5
2017-09-14,Quantum microwave-optical interface with nitrogen-vacancy centers in diamond,"We propose an efficient scheme for a coherent quantum interface between
microwave and optical photons using nitrogen-vacancy (NV) centers in diamond.
In this setup, an NV center ensemble is simultaneously coupled to an optical
and a microwave cavity. We show that, by using the collective spin excitation
modes as an intermediary, quantum states can be transferred between the
microwave cavity and the optical cavity through either a double-swap scheme or
a dark-state protocol. This hybrid quantum interface may provide interesting
applications in single microwave photon detections or quantum information
processing.",1709.04852v1
2017-11-10,Towards macroscopic spin and mechanical superposition via Rydberg interaction,"This paper is a proposal for the generation of many-body entangled state in
atomic and mechanical systems. Application of strong Rydberg dressing
interaction and fast bifurcation scheme in an ultra-stable Cs lattice clock in
this proposal results to a breakthrough in the formation of large cat states.
By detailed study of the de-coherence effects using Quantum Jump Monte Carlo
approach and considering obstacles in dense ensembles namely level mixing,
molecule formation and collective decoherence this proposal predicts the
formation of 700 atoms cat state. Dipole coupling between Rydberg atoms and
charged cantilevers is proposed for the transfer of the generated superposition
to far separated mechanical oscillators.",1711.03821v2
2017-12-02,Magnetic susceptibility of optimally doped HgBa$_{2}$CuO$_{4+δ}$,"The magnitude of the powder spin susceptibility of an optimally doped
superconductor HgBa$_2$CuO$_{4+\delta}$ (Hg1201) in the normal state is found
to be nearly the same as that of La$_{2-x}$Sr$_{x}$CuO$_{4}$ near the optimally
doped level. The Stoner enhancement factor of Hg1201 is larger than that of
La$_{2-x}$Sr$_{x}$CuO$_{4}$. The magnitude correlation of the Stoner
enhancement factor is inconsistent with the effect of the recent theoretical
Coulomb repulsion between 3$d$ electrons and that of the superexchange
intereraction of a charge transfer type.",1712.00652v1
2018-02-26,Vector Meson Photoproduction with a Linearly Polarized Beam,"We propose a model based on Regge theory to describe photoproduction of light
vector mesons. We fit the SLAC data and make predictions for the energy and
momentum transfer dependence of the spin-density matrix elements in
photoproduction of $\omega$, $\rho^0$ and $\phi$ mesons at $E_\gamma \sim 8.5$
GeV, which are soon to be measured at Jefferson Lab.",1802.09403v1
2018-06-14,Revealing attractive electron-electron interaction in a quantum dot by full counting statistics,"Recent experiments [Nature 521, 196 (2015) and Nat. Commun. 8, 395 (2017)]
have presented evidence for electron pairing in a quantum dot beyond the
superconducting regime. Here, we show that the impact of an attractive
electron-electron interaction on the full counting statistics of electron
transfer through a quantum dot is qualitatively different from the case of a
repulsive interaction. In particular, the sign of higher-order (generalized)
factorial cumulants reveals more pronounced correlations, which even survive in
the limit of fast spin relaxation.",1806.05518v2
2018-07-10,Type B Gaussian Statistics as Noncommutative Central Limits,"We show that the noncommutative central limit theorem of Speicher can be
adapted to produce the Gaussian statistics associated to Coxeter groups of type
B, in the sense of Bo\.zejko, Ejsmont, and Hasebe. Specifically, we show how
type B Gaussian statistics naturally arise in systems of 'mixed spins',
providing a new application of Speicher's argument and paving the way for the
transfer of known results from the bosonic/fermionic settings to such broader
contexts.",1807.03580v2
2018-08-21,A Hubbard model with integrable impurity,"We construct an integrable Hubbard model with impurity site containing spin
and charge degrees of freedom. The Bethe ansatz equations for the Hamiltonian
are derived and two alternative sets of equations for the thermodynamical
properties. For this study, the thermodynamical Bethe ansatz and the quantum
transfer matrix approach are used. The latter approach allows for a consistent
treatment by use of a finite set of non-linear integral equations. In both
cases, TBA and QTM, the contribution of the impurity to the thermodynamical
potential is given by integral expressions.",1808.06993v2
2018-09-24,Superefficient cascade multiresonator quantum memory,"We propose a cascade scheme of a superefficient broadband quantum memory
consisting of four high-Q ring resonators forming a controllable frequency comb
and interacting with long-lived spin systems and with a common waveguide. Using
the transfer function giving extended matching conditions, the optimization of
all spectroscopic parameters of the system for quantum memory in the resonator
is carried out. It was shown that our quantum memory scheme does not impose
large restrictions on the parameters of losses in resonators and allows to
achieve super high efficiency 99.99 % in a wide frequency range.",1809.08759v2
2018-12-20,Switching behaviour of stilbene molecular device: a first-principles study,"The switching behaviour of stilbene molecular system (SMS) device is
investigated with the help of non-equilibrium Green's function (NEGF) approach
using first principles calculation. The transmission spectrum of cis-isomers
confirmed that more electrons are transferred across the SMS-device using
optical excitation by the spin of C$=$C bond by torsion angle
$(\theta=180^\circ)$. The current-voltage characteristics show the lower
magnitude of current for trans-stilbene and higher magnitude of current for
cis-stilbene for an externally applied bias voltage. The outcome of the
proposed work suggests that cis and trans-stilbene molecular device can be used
as a switch.",1812.08532v1
2019-06-17,Scalar Products in Twisted XXX Spin Chain. Determinant Representation,"We consider XXX spin-$1/2$ Heisenberg chain with non-diagonal boundary
conditions. We obtain a compact determinant representation for the scalar
product of on-shell and off-shell Bethe vectors. In the particular case when
both Bethe vectors are on shell, we obtain a determinant representation for the
norm of on-shell Bethe vector and prove orthogonality of the on-shell vectors
corresponding to the different eigenvalues of the transfer matrix.",1906.06897v2
2019-08-07,Universality of the Poincaré gravitational form factor constraints,"Relativistic spin states are convention dependent. In this work we prove that
the zero momentum-transfer limits of the leading two form factors in the
decomposition of the energy-momentum tensor matrix elements are independent of
this choice. In particular, we demonstrate that these constraints are
insensitive to whether the corresponding states are massive or not, and that
they arise purely due to the Poincar\'e covariance of the states.",1908.02567v2
2020-02-08,Atomic diffusion in alpha-iron across the Curie point: an effcient and transferable ab-initio-based modelling approach,"An accurate prediction of atomic diffusion in Fe alloys is challenging due to
thermal magnetic excitations and magnetic transitions. We propose an effcient
approach to address these properties via Monte Carlo simulation, using
ab-initio based effective interaction models. The temperature evolution of
self- and Cu diffusion coeffcients in alpha-iron are successfully predicted,
particularly the diffusion acceleration around the Curie point, which requires
a quantum treatment of spins. We point out a dominance of magnetic disorder
over chemical effects on diffusion in the very dilute systems.",2002.03126v2
2020-04-22,Experimental realization of Lieb-Mattis plateau in a quantum spin chain,"We present a mixed spin-(1/2, 5/2) chain composed of a charge-transfer salt
(4-Br-$o$-MePy-V)FeCl$_4$. We observe the entire magnetization curve up to
saturation, which exhibits a clear Lieb-Mattis magnetization plateau and
subsequent quantum phase transition towards the gapless Luttinger-liquid phase.
The observed magnetic behavior is quantitatively explained by a mixed
spin-(1/2, 5/2) chain model. The present results demonstrate a quantum
many-body effect based on quantum topology and provide a new stage in the
search for topological properties in condensed matter physics.",2004.10416v1
2020-07-30,Jacobi-Trudi identity and Drinfeld functor for super Yangian,"We show that the quantum Berezinian which gives a generating function of the
integrals of motions of XXX spin chains associated to super Yangian
$\mathrm{Y}(\mathfrak{gl}_{m|n})$ can be written as a ratio of two difference
operators of orders $m$ and $n$ whose coefficients are ratios of transfer
matrices corresponding to explicit skew Young diagrams.
  In the process, we develop several missing parts of the representation theory
of $\mathrm{Y}(\mathfrak{gl}_{m|n})$ such as $q$-character theory, Jacobi-Trudi
identity, Drinfeld functor, extended T-systems, Harish-Chandra map.",2007.15573v2
2020-09-13,Spin-polarized fermions with $p$-wave interactions,"We study quantum degenerate Fermi gases of ${^6}$Li atoms at high densities
($10^{15}$ cm$^{-3}$) and observe elastic and inelastic $p$-wave collisions far
away from any Feshbach resonance. $P$-wave evaporation reaches temperatures of
$T/T_F=0.42$ partially limited by the slow transfer of energy from high to low
velocities through $p$-wave collisions. Via cross-dimensional thermalization,
the $p$-wave background scattering volume is determined to be $\lvert V_p
\rvert =(39^{+1.3}_{-1.6}a_0)^3$. $P$-wave dipolar relaxation creates a
metastable mixture of the lowest and highest hyperfine states.",2009.05913v1
2021-07-28,Band structure and energy level alignment of chiral graphene nanoribbons on silver surfaces,"Chiral graphene nanoribbons are extremely interesting structures due to their
low bandgaps and potential development of spin-polarized edge states. Here, we
study their band structure on low work function silver surfaces and assess the
effect of charge transfer on their properties.",2107.13276v1
2022-05-20,Symmetry-induced decoherence-free subspaces,"Preservation of coherence is a fundamental yet subtle phenomenon in open
systems. We uncover its relation to symmetries respected by the system
Hamiltonian and its coupling to the environment. We discriminate between local
and global classes of decoherence-free subspaces for many-body systems through
the introduction of ""ghost variables"". The latter are orthogonal to the
symmetry and the coupling to the environment does not depend on them.
Constructing them is facilitated in classical phase space and can be
transferred to quantum mechanics through the equivalent role that Poisson and
Lie algebras play for symmetries in classical and quantum mechanics,
respectively. Examples are given for an interacting spin system.",2205.10057v1
2022-08-10,Fractional revival on abelian Cayley graphs,"Fractional revival, known as a quantum transport phenomenon, is essential for
entanglement generation in quantum spin networks. The concept of fractional
revival is a generalization of perfect state transfer and periodicity on
graphs. In this paper, we propose a sufficient and necessary condition for
abelian Cayley graphs having fractional revival between any two distinct
vertices. With this characterization, two general constructions of abelian
Cayley graphs having fractional revival is presented. Meanwhile, we establish
several new families of abelian Cayley graphs admitting fractional revival.",2208.05107v1
2023-01-14,QED corrections to elastic electron-nucleus scattering beyond the first-order Born approximation,"A potential for the vertex and self-energy correction is derived from the
first-order Born theory. The inclusion of this potential in the Dirac equation,
together with the Uehling potential for vacuum polarization, allows for a
nonperturbative treatment of these QED effects within the phase-shift analysis.
Investigating the 12C and 208Pb targets, a considerable deviation of the
respective cross-section change from the Born results is found, which becomes
larger with increasing momentum transfer. Estimates for the correction to the
beam-normal spin asymmetry are also provided. For the 12C nucleus, dispersion
effects are considered as well.",2301.05883v2
2023-01-27,Classical Monte Carlo algorithm for simulation of a pseudospin model for cuprates,"A classical Monte Carlo algorithm based on the quasi-classical approximation
is applied to the pseudospin Hamiltonian of the model cuprate. The model takes
into account both local and non-local correlations, Heisenberg spin-exchange
interaction, single-particle and correlated two-particle transfer. We define
the state selection rule that gives both the uniform distribution of states in
the phase space and the doped charge conservation. The simulation results show
a qualitative agreement of a phase diagrams with the experimental ones.",2301.11708v1
2023-06-17,All regular $4 \times 4$ solutions of the Yang-Baxter equation,"We complete the classification of $4\times 4$ regular solutions of the
Yang-Baxter equation. Apart from previously known models, we find four new
models of non-difference form. All the new models give rise to Hamiltonians and
transfer matrices that have a non-trivial Jordan block structure. One model
corresponds to a non-diagonalisable integrable deformation of the XXX spin
chain.",2306.10423v3
2023-10-01,Exact Entanglement Propagation Dynamics in Integrable Heisenberg Chains,"The exact single-magnon entanglement evolution in Heisenberg chains is
obtained using the Quantum Correlation Transfer Function (QCTF) formulation.
The individual spins' entanglement is given by a hypergeometric function, and
its transient behavior is described via a Bessel function of the first kind.
The presented characterization through the lens of QCTF allowed for calculating
the ballistic single-magnon entanglement edge velocity in Heisenberg chains,
which has not been achieved before. Our results can be extended to the
multi-magnon regime, therefore opening up the means to explain equilibration
dynamics and thermodynamics in Heisenberg chains.",2310.00717v2
2023-10-26,On classical orthogonal polynomials on bi-lattices,"In [J. Phys. A: Math. Theor. 45 (2012)], while looking for spin chains that
admit perfect state transfer, Vinet and Zhedanov found an apparently new
sequence of orthogonal polynomials, that they called para-Krawtchouk
polynomials, defined on a bilinear lattice. In this note we present necessary
and sufficient conditions for the regularity of solutions of the corresponding
functional equation. Moreover, the functional Rodrigues formula and a closed
formula for the recurrence coefficients are presented. As a consequence, we
characterize all solutions of the functional equation, including as very
particular cases the Meixner, Charlier, Krawtchouk, Hahn, and para-Krawtchouk
polynomials.",2311.05636v1
2023-11-28,Space-like asymptotics of the thermal two-point functions of the XXZ spin-1/2 chain,"This work proposes a closed formula for the leading term of the long-distance
and large-time asymptotics in a cone of the space-like regime for the
transverse dynamical two-point functions of the XXZ spin 1/2 chain at finite
temperatures. The result follows from a simple analysis of the thermal form
factor series for dynamical correlation functions. The leading asymptotics we
obtain are driven by the Bethe Ansatz data associated with the first
sub-leading Eigenvalue of the quantum transfer matrix.",2311.17196v2
2023-12-26,Large-bipolaron-liquids in cuprate superconductors,"Large bipolarons' self-trapped holes occupy superoxygens, each comprising
four oxygens circumscribed by four coppers in a CuO2 plane, formed as oxygens
relax inward and coppers relax outward. Critically, concomitant oxygen to
copper electron transfer eliminates copper spins. The d symmetry of
superoxygens' groundstate molecular orbital tracks the superoxygens'
predominant zeropoint radial vibrations. These large bipolarons' distinctive
charge transport, absorption, magnetism, local atomic vibrations, condensation
into a liquid and subsequent superconductivity are consistent with cuprate
superconductors' long-established unusual properties.",2312.16130v5
2009-07-29,Low-energy Mott-Hubbard excitations in LaMnO_3 probed by optical ellipsometry,"We present a comprehensive ellipsometric study of an untwinned, nearly
stoichiometric LaMnO_3 crystal in the spectral range 1.2-6.0 eV at temperatures
20 K < T < 300 K. The complex dielectric response along the b and c axes of the
Pbnm orthorhombic unit cell, \epsilon^b(\nu) and \epsilon^c(\nu), is highly
anisotropic over the spectral range covered in the experiment. The difference
between \epsilon^b(\nu) and \epsilon^c(\nu) increases with decreasing
temperature, and the gradual evolution observed in the paramagnetic state is
strongly enhanced by the onset of A-type antiferromagnetic long-range order at
T_N = 139.6 K. In addition to the temperature changes in the lowest-energy gap
excitation at 2 eV, there are opposite changes observed at higher energy at 4 -
5 eV, appearing on a broad-band background due to the strongly dipole-allowed O
2p -- Mn 3d transition around the charge-transfer energy 4.7 eV. Based on the
observation of a pronounced spectral-weight transfer between low- and
high-energy features upon magnetic ordering, they are assigned to high-spin and
low-spin intersite d^4d^4 - d^3d^5 transitions by Mn electrons. The anisotropy
of the lowest-energy optical band and the spectral weight shifts induced by
antiferromagnetic spin correlations are quantitatively described by an
effective spin-orbital superexchange model. An analysis of the multiplet
structure of the intersite transitions by Mn e_g electrons allowed us to
estimate the effective intra-atomic Coulomb interaction, the Hund exchange
coupling, and the Jahn-Teller splitting energy between e_g orbitals in LaMnO_3.
This study identifies the lowest-energy optical transition at 2 eV as an
intersite d-d transition, whose energy is substantially reduced compared to
that obtained from the bare intra-atomic Coulomb interaction.",0907.5098v1
2016-05-25,Doppler shifts on the spin period of the intermediate polar FO Aqr with K2,"We analyse the K2 short cadence data of the intermediate polar FO Aqr and
provide accurate and updated orbital and spin periodicities. We additionally
find small spin period changes as a function of orbital phase of ~0.02 seconds
translating to velocities of ~ a few km/s. The obtained orbital-folded velocity
profile displays two clear maxima and minima, and cannot be explained by the
radial velocity of the orbiting white dwarf. Instead we propose that the
observed velocities are the sum of the radial velocities of both the white
dwarf and of the stellar surface facing the white dwarf which reprocesses the
WD spin pulses. This combination can explain the observed low velocities in FO
Aqr. However asymmetries in the orbital configuration are required to explain
the double peaked velocity profile. One possible scenario would invoke binary
eccentricity. We thus developed a simple binary model to explain and fit our
observations, and find a small binary eccentricity of e=0.03. Although small,
persistent eccentricity in a close interacting binary would induce enhanced
mass transfer occurring preferentially at periastron passages. We thus discuss
alternative scenarios where other asymmetries might explain our observations
assuming circular orbits. Since FO Aqr is the first system where the combined
radial velocities of both the WD and secondary surface have been measured, it
is possible that other mass-transferring binaries also display similar velocity
curves when observed with Kepler. These will provide additional valuable tests
to either confirm or rule out small eccentricities in similar systems.",1605.08030v2
2017-03-24,"Linking structure and dynamics in $(p,pn)$ reactions with Borromean nuclei: the $^{11}$Li$(p,pn){^{10}}$Li case","One-neutron removal $(p,pn)$ reactions induced by two-neutron Borromean
nuclei are studied within a Transfer-to-the-Continuum (TC) reaction framework,
which incorporates the three-body character of the incident nucleus. The
relative energy distribution of the residual unbound two-body subsystem, which
is assumed to retain information on the structure of the original three-body
projectile, is computed by evaluating the transition amplitude for different
neutron-core final states in the continuum. These transition amplitudes depend
on the overlaps between the original three-body ground-state wave function and
the two-body continuum states populated in the reaction, thus ensuring a
consistent description of the incident and final nuclei. By comparing different
$^{11}$Li three-body models, it is found that the $^{11}$Li$(p,pn){^{10}}$Li
relative energy spectrum is very sensitive to the position of the $p_{1/2}$ and
$s_{1/2}$ states in $^{10}$Li and to the partial wave content of these
configurations within the $^{11}$Li ground-state wave function. The possible
presence of a low-lying $d_{5/2}$ resonance is discussed. The coupling of the
single particle configurations with the non-zero spin of the $^{9}$Li core,
which produces a spin-spin splitting of the states, is also studied. Among the
considered models, the best agreement with the available data is obtained with
a $^{11}$Li model that incorporates the actual spin of the core and contains
$\sim$31\% of $p_{1/2}$-wave content in the $n$-$^9$Li subsystem, in accord
with our previous findings for the $^{11}$Li(p,d)$^{10}$Li transfer reaction,
and a near-threshold virtual state.",1703.08320v1
2023-04-25,Tensor network variational optimizations for real-time dynamics: application to the time-evolution of spin liquids,"Within the Projected Entangled Pair State (PEPS) tensor network formalism, a
simple update (SU) method has been used to investigate the time evolution of a
two-dimensional U(1) critical spin-1/2 spin liquid under Hamiltonian quench
[Phys. Rev. B 106, 195132 (2022)]. Here we introduce two different variational
frameworks to describe the time dynamics of SU(2)-symmetric
translationally-invariant PEPS, aiming to improve the accuracy. In one
approach, after using a Trotter-Suzuki decomposition of the time evolution
operator in term of two-site elementary gates, one considers a single bond
embedded in an environment approximated by a Corner Transfer Matrix
Renormalization Group (CTMRG). A variational update of the two tensors on the
bond is performed under the application of the elementary gate and then, after
symmetrization of the site tensors, the environment is updated. In the second
approach, a cluster optimization is performed on a finite (periodic) cluster,
maximizing the overlap of the exact time-evolved state with a symmetric
finite-size PEPS ansatz. Observables are then computed on the infinite lattice
contracting the infinite-PEPS (iPEPS) by CTMRG. We show that the variational
schemes outperform the SU method and remain accurate over a significant time
interval before hitting the entanglement barrier. Studying the spectrum of the
transfer matrix, we find that the asymptotic correlations are very well
preserved under time evolution, including the critical nature of the singlet
correlations, as expected from the Lieb-Robinson (LR) bound theorem.
Consistently, the system (asymptotic) boundary is found to bedescribed by the
same Conformal Field Theory of central charge c = 1 during time evolution. We
also compute the time-evolution of the short distance spin-spin correlations
and estimate the LR velocity.",2304.13184v3
2001-07-20,Penetrating the Mask: The Gravitational Torque of Bars,"The Hubble classification scheme of galaxies is based on blue-light
appearance. Atlases reveal the rich variety of responses of the Population I
component (the ""mask"") of gas and dust to the underlying, older, stellar
population. However, the Population I component may only constitute 5 percent
of the dynamical mass of the galaxy; furthermore, dusty masks are highly
effective in hiding bars. In the 1960s, Ken Freeman presented a meticulous
study of the dynamics of bars at a time when nonbarred galaxies were called
""normal"" spirals and barred galaxies were regarded as curiosities. Now we know
that it is more ""normal"" for a galaxy to be barred than to be nonbarred. What
is the range for gravitational torques of bars? We describe here a recently
developed method for deriving relative bar torques by using gravitational
potentials inferred from near-infrared light distributions. We incorporate a
bar torque class into the Block/Puerari dust-penetrated galaxy classification
system. We find a huge overlap in relative bar torque between Hubble (Sa, Sb,
  ...) and (SBa, SBb, ...) classifications. Application of the method to the
high redshift universe is briefly discussed.",0107407v1
2005-11-02,On the width and shape of gaps in protoplanetary disks,"Although it is well known that a massive planet opens a gap in a
proto-planetary gaseous disk, there is no analytic description of the surface
density profile in and near the gap. The simplest approach, which is based upon
the balance between the torques due to the viscosity and the gravity of the
planet and assumes local damping, leads to gaps with overestimated width,
especially at low viscosity. Here, we take into account the fraction of the
gravity torque that is evacuated by pressure supported waves. With a novel
approach, which consists of following the fluid elements along their
trajectories, we show that the flux of angular momentum carried by the waves
corresponds to a pressure torque. The equilibrium profile of the disk is then
set by the balance between gravity, viscous and pressure torques. We check that
this balance is satisfied in numerical simulations, with a planet on a fixed
circular orbit. We then use a reference numerical simulation to get an ansatz
for the pressure torque, that yields gap profiles for any value of the disk
viscosity, pressure scale height and planet to primary mass ratio. Those are in
good agreement with profiles obtained in numerical simulations over a wide
range of parameters. Finally, we provide a gap opening criterion that
simultaneously involves the planet mass, the disk viscosity and the aspect
ratio.",0511082v1
2008-04-29,On disc protoplanet interactions in a non-barotropic disc with thermal diffusion,"We study the disc planet interactions of low-mass protoplanets embedded in a
circumstellar disc. We extend the standard theory of planet migration from the
usual locally isothermal assumption to include non-barotropic effects, focusing
on the validity of linear theory. We compared solutions of the linear equations
with results from non-linear hydrodynamic simulations, where in both cases we
adopted a background entropy gradient and solved the energy equation. We show
that the migration behavior of embedded planets depends critically on the
background radial entropy gradient in the disc. The presence of such a gradient
not only changes the corotation torque on the planet, but also always
guarantees a departure from linear behavior, which gives a singular density
response at corotation, in the absence of thermal or viscous diffusion. A
negative entropy gradient tends to give rise to positive, non-linear corotation
torques apparently produced as material executes horseshoe turns at
approximately constant entropy. These torques have no counterpart in linear
theory, but can be strong enough to push the planet outwards until saturation
starts to occur after a horseshoe libration period. Increased thermal diffusion
acts to reduce these non-linear torques, but, at the same time, it can help to
prevent their saturation. In combination with a small kinematic viscosity that
is able to maintain a smooth density profile the positive torque could be
sustained.",0804.4547v1
2009-03-05,Quantitative Theory of Grain Alignment: Probing Grain Environment and Grain Composition,"While the problem of grain alignment was posed more than 60 years ago the
quantitative model of grain alignment that can account for the observed
polarization arising from aligned grains has been formulated only recently. The
quantitative predictions of the radiative torque mechanism, which is currently
accepted as the dominant mechanism of grain alignment, open avenues to tracing
magnetic fields in various astrophysical environments, including diffuse and
dense interstellar gas, molecular clouds, circumstellar environments, accretion
disks, comet tails, Zodiacal dust etc. At the same time, measurements of the
absolute value of polarization and its variations can, in addition, provide
unique information about the dust composition and dust environment. In the
review I describe the analytical model describing well radiative torques acting
on irregular grains and discuss how the alignment induced by radiative torques
varies in the presence of superparamagnetic inclusions and pinwheel torques,
e.g. arising from the molecular hydrogen formation over grain surface. I also
describe observations that can establish whether grains are superparamagnetic
and whether recoils from molecular hydrogen formations are powerful enough to
give rise to substantial uncompensated torques. Answering to these questions
should allow for reliable modeling of astrophysical polarization with numerous
important applications, from accounting for dust contribution in Cosmic
Microwave Background polarization studies to obtaining magnetic field strength
using Chandrasekhar-Fermi technique.",0903.1100v1
2011-12-12,The origin of the negative torque density in disk-satellite interaction,"Tidal interaction between a gaseous disk and a massive orbiting perturber is
known to result in angular momentum exchange between them. Understanding
astrophysical manifestations of this coupling such as gap opening by planets in
protoplanetary disks or clearing of gas by binary supermassive black holes
(SMBHs) embedded in accretion disks requires knowledge of the spatial
distribution of the torque exerted on the disk by a perturber. Recent
hydrodynamical simulations by Dong et al (2011) have shown evidence for the
tidal torque density produced in a uniform disk to change sign at the radial
separation of $\approx 3.2$ scale heights from the perturber's orbit, in clear
conflict with the previous studies. To clarify this issue we carry out a linear
calculation of the disk-satellite interaction putting special emphasis on
understanding the behavior of the perturbed fluid variables in physical space.
Using analytical as well as numerical methods we confirm the reality of the
negative torque density phenomenon and trace its origin to the overlap of
Lindblad resonances in the vicinity of the perturber's orbit - an effect not
accounted for in previous studies. These results suggest that calculations of
the gap and cavity opening in disks by planets and binary SMBHs should rely on
more realistic torque density prescriptions than the ones used at present.",1112.2717v1
2012-02-09,Orbital migration of interacting low-mass planets in evolutionary radiative turbulent models,"The torques exerted by a locally isothermal disk on an embedded planet lead
to rapid inward migration. Recent work has shown that modeling the
thermodynamics without the assumption of local isothermality reveals regions
where the net torque on an embedded planet is positive, leading to outward
migration of the planet. When a region with negative torque lies directly
exterior to this, planets in the inner region migrate outwards and planets in
the outer region migrate inwards, converging where the torque is zero. We
incorporate the torques from an evolving non-isothermal disk into an N-body
simulation to examine the behavior of planets or planetary embryos interacting
in the convergence zone. We find that mutual interactions do not eject objects
from the convergence zone. Small numbers of objects in a laminar disk settle
into near resonant orbits that remain stable over the 10 Myr periods that we
examine. However, either or both increasing the number of planets or including
a correlated, stochastic force to represent turbulence drives orbit crossings
and mergers in the convergence zone. These processes can build gas giant cores
with masses of order ten Earth masses from sub-Earth mass embryos in 2-3 Myr.",1202.1868v2
2012-05-28,Type I migration in optically thick accretion discs,"We study the torque acting on a planet embedded in an optically thick
accretion disc, using global two-dimensional hydrodynamic simulations. The
temperature of an optically thick accretion disc is determined by the energy
balance between the viscous heating and the radiative cooling. The radiative
cooling rate depends on the opacity of the disc. The opacity is expressed as a
function of the temperature. We find the disc is divided into three regions
that have different temperature distributions. The slope of the entropy
distribution becomes steep in the inner region of the disc with the high
temperature and the outer region of the disc with the low temperature, while it
becomes shallow in the middle region with the intermediate temperature. Planets
in the inner and outer regions move outward owing to the large positive
corotation torque exerted on the planet by an adiabatic disc, on the other
hand, a planet in the middle region moves inward toward the central star.
Planets are expected to accumulate at the boundary between the inner and middle
regions of the adiabatic disc. The positive corotation torque decreases with an
increase in the viscosity of the disc. We find that the positive corotation
torque acting on the planet in the inner region becomes too small to cancel the
negative Lindblad torque when we include the large viscosity, which destroys
the enhancement of the density in the horseshoe orbit of the planet. This leads
to the inward migration of the planet in the inner region of the disc. A planet
with 5 Earth masses in the inner region can move outward in a disc with the
surface density of 100 g/cm^2 at 1 AU when the accretion rate of a disc is
smaller than 2x10^{-8} solar mass/yr.",1205.6013v1
2014-10-16,Inertial Parameter Identification Including Friction and Motor Dynamics,"Identification of inertial parameters is fundamental for the implementation
of torque-based control in humanoids. At the same time, good models of friction
and actuator dynamics are critical for the low-level control of joint torques.
We propose a novel method to identify inertial, friction and motor parameters
in a single procedure. The identification exploits the measurements of the PWM
of the DC motors and a 6-axis force/torque sensor mounted inside the kinematic
chain. The partial least-square (PLS) method is used to perform the regression.
We identified the inertial, friction and motor parameters of the right arm of
the iCub humanoid robot. We verified that the identified model can accurately
predict the force/torque sensor measurements and the motor voltages. Moreover,
we compared the identified parameters against the CAD parameters, in the
prediction of the force/torque sensor measurements. Finally, we showed that the
estimated model can effectively detect external contacts, comparing it against
a tactile-based contact detection. The presented approach offers some
advantages with respect to other state-of-the-art methods, because of its
completeness (i.e. it identifies inertial, friction and motor parameters) and
simplicity (only one data collection, with no particular requirements).",1410.4410v1
2014-12-24,Tidal Torques on Misaligned Disks in Binary Systems,"We extend previous studies of the tidal truncation of coplanar disks in
binary systems to the more general case of noncoplanar disks. As in the
prograde coplanar case, Lindblad resonances play a key role in tidal
truncation. We analyze the tidal torque acting on a misaligned nearly circular
disk in a circular orbit binary system. We concentrate on the 2:1 inner
Lindblad resonance associated with the m=2 tidal forcing (for azimuthal
wavenumber m) that plays a major role in the usual coplanar case. We determine
the inclination dependence of this torque, which is approximately cos^8(i/2)
for misalignment angle i. Compared to the prograde coplanar case (i=0), this
torque decreases by a factor of about 2 for i = pi/6 and by a factor of about
20 for i=pi/2. The Lindblad torque decreases to zero for a tilt angle of pi
(counter-rotation), consistent with previous investigations. The effects of
higher order resonances associated with m>2 tidal forcing may contribute
somewhat, but are much more limited than in the i=0 case. These results suggest
that misaligned disks in binary systems can be significantly extended compared
to their coplanar counterparts. In cases where a disk is sufficiently inclined
and viscous, it can overrun all Lindblad resonances and overflow the Roche lobe
of the disk central object.",1412.7741v1
2016-04-25,Generalized Similarity for Accretion/Decretion Disks,"Decretion (or external) disks are gas disks freely expanding to large radii
due to their internal stresses. They are expected to naturally arise in tidal
disruption events, around Be stars, in mass-losing post main sequence binaries,
as a result of supernova fallback, etc. Their evolution is theoretically
understood in two regimes: when the central object does not exert torque on the
disk (a standard assumption for conventional accretion disks) or when no mass
inflow (or outflow) occurs at the disk center. However, many astrophysical
objects - circumbinary disks, Be stars, neutron stars accreting in a propeller
regime, etc. - feature non-zero torque simultaneously with the non-zero
accretion (or ejection of mass) at the disk center. We provide a general
description for the evolution of such disks (both linear and non-linear) in the
self-similar regime, to which the disk should asymptotically converge with
time. We identify a similarity parameter $\lambda$, which is uniquely related
to the degree, to which the central mass accretion is suppressed by the
non-zero central torque. The known decretion disk solutions correspond to the
two discrete values of $\lambda$, while our new solutions cover a continuum of
its physically allowed values, corresponding to either accretion or mass
ejection by the central object. A direct relationship between $\lambda$ and
central $\dot M$ and torque is also established. We describe the time evolution
of the various disk characteristics for different $\lambda$, and show that the
observable properties (spectrum and luminosity evolution) of the decretion
disks are in general different from the standard accretion disks with no
central torque.",1604.07439v1
2017-10-03,Magnetic braking of Sun-like and low-mass stars: Dependence on coronal temperature,"Sun-like and low-mass stars possess high temperature coronae and lose mass in
the form of stellar winds, driven by thermal pressure and complex
magnetohydrodynamic processes. These magnetized outflows probably do not
significantly affect the star's structural evolution on the Main Sequence, but
they brake the stellar rotation by removing angular momentum, a mechanism known
as magnetic braking. Previous studies have shown how the braking torque depends
on magnetic field strength and geometry, stellar mass and radius, mass-loss
rate, and the rotation rate of the star, assuming a fixed coronal temperature.
For this study we explore how different coronal temperatures can influence the
stellar torque. We employ 2.5D, axisymmetric, magnetohydrodynamic simulations,
computed with the PLUTO code, to obtain steady-state wind solutions from
rotating stars with dipolar magnetic fields. Our parameter study includes 30
simulations with variations in coronal temperature and surface-magnetic-field
strength. We consider a Parker-like (i.e. thermal-pressure-driven) wind, and
therefore coronal temperature is the key parameter determining the velocity and
acceleration profile of the flow. Since the mass loss rates for these types of
stars are not well constrained, we determine how torque scales for a vast range
of stellar mass loss rates. Hotter winds lead to a faster acceleration, and we
show that (for a given magnetic field strength and mass-loss rate) a hotter
outflow leads to a weaker torque on the star. We derive new predictive torque
formulae for each temperature, which quantifies this effect over a range of
possible wind acceleration profiles.",1710.01340v1
2017-10-23,What confines the rings of Saturn?,"The viscous spreading of planetary rings is believed to be counteracted by
satellite torques, either through an individual resonance or through
overlapping resonances. For the A ring of Saturn, it has been commonly believed
that the satellite Janus alone can prevent the ring from spreading via its 7:6
Lindblad resonance. We discuss this common misconception and show that, in
reality, the A ring is confined by the contributions from the group of
satellites Pan, Atlas, Prometheus, Pandora, Janus, Epimetheus, and Mimas, whose
cumulative torques from various resonances gradually decrease the angular
momentum flux transported outward through the ring via density and bending
waves. We further argue that this decrease in angular momentum flux occurs
through 'flux reversal'.
  Furthermore, we use the magnitude of the satellites' resonance torques to
estimate the effective viscosity profile across the A ring, showing that it
decreases with radius from ~50 cm2 s-1 to less than ~10 cm2 s-1. The gradual
estimated decrease of the angular momentum flux and effective viscosity are
roughly consistent with results obtained by balancing the shepherding torques
from Pan and Daphnis with the viscous torque at the edges of the Encke and
Keeler gaps, as well as the edge of the A ring.
  On the other hand, the Mimas 2:1 Lindblad resonance alone seems to be capable
of confining the edge of the B ring, and contrary to the situation in the A
ring, we show that the effective viscosity across the B ring is relatively
constant at ~24-30 cm2 s-1.",1710.08462v1
2018-07-01,Metriplectic torque for rotation control of a rigid body,"Metriplectic dynamics couple a Poisson bracket of the Hamiltonian description
with a kind of metric bracket, for describing systems with both Hamiltonian and
dissipative components. The construction builds in asymptotic convergence to a
preselected equilibrium state. Phenomena such as friction, electric
resistivity, thermal conductivity and collisions in kinetic theories all fit
within this framework. In this paper an application of metriplectic dynamics is
presented that is of interest for the theory of control: a suitably chosen
torque, expressed through a metriplectic extension of its ""natural"" Poisson
algebra, an algebra obtained by reduction of a canonical Hamiltonian system, is
applied to a free rigid body. On a practical ground, the effect is to drive the
body to align its angular velocity to rotation about a stable principal axis of
inertia, while conserving its kinetic energy in the process. On theoretical
grounds, this example provides a class of non-Hamiltonian torques that can be
added to the canonical Hamiltonian description of the free rigid body and
reduce to metriplectic dissipation. In the canonical description these torques
provide convergence to a higher dimensional attractor. The method of
construction of such torques can be extended to other dynamical systems
describing ""machines"" with non-Hamiltonian motion having attractors.",1807.01168v1
2018-09-30,Stalling of Globular Cluster Orbits in Dwarf Galaxies,"We apply the Tremaine-Weinberg theory of dynamical friction to compute the
orbital decay of a globular cluster (GC), on an initially circular orbit inside
a cored spherical galaxy with isotropic stellar velocities. The retarding
torque on the GC, T(rp) < 0 , is a function of its orbital radius rp . The
torque is exerted by stars whose orbits are resonant with the GC's orbit, and
given as a sum over the infinitely many possible resonances by the Lynden-Bell
Kalnajs (LBK) formula. We calculate the LBK torque T(rp) and determine rp(t),
for a GC of mass Mp = 2 x 10^5 M_sun and an Isochrone galaxy of core mass Mc =
4 x 10^8 M_sun and core radius b = 1000pc. (i) When rp > 300 pc many strong
resonances are active and, as expected, T = T_C , the classical Chandrasekhar
torque. (ii) For rp < 300 pc, T comes mostly from stars nearly co-rotating with
the GC, trailing or leading it slightly; Trailing resonances exert stronger
torques. (iii) As rp decreases the number and strength of resonances drop, so
|T| also decreases, with |T| < 10^{-2} |T_C| at rp = r* = (Mp/Mc)^{1/5} b = 220
pc , a characteristic `filtering' radius. (iv) Many resonances cease to exist
inside r* ; this includes all Leading and low-order Trailing ones. (v) The
higher-order Trailing resonances inside r* are very weak, with |T| < 10^{-4}
|T_C| at rp = 150 pc. (vi) Inspiral times for rp(t) to decay from 300 pc to r*
far exceed 10 Gyr.",1810.00369v2
2018-11-28,Three Dynamical Evolution Regimes for Coupled Ring-Satellite Systems and Implications for the Formation of the Uranian Satellite Miranda,"In coupled ring-satellite systems, satellites exchange angular momentum with
both the primary through tides and with the ring through Lindblad torques, and
may exchange material with the ring through accretion and tidal disruption.
Here we show that these coupled ring-satellite systems fall into three distinct
dynamical regimes, which we refer to as `Boomerang,' `Slingshot,' and
`Torque-Dependent.' These regimes are determined by the relative locations of
the Fluid Roche Limit, the synchronous orbit, and the location of the maximum
orbit that Lindblad torques can perturb a satellite. Satellites that accrete
from rings in the Boomerang regime remain interior to the synchronous orbit,
and may be driven back toward the primary by tides. Satellites that accrete
from rings in the Slingshot regime form exterior to the synchronous orbit, and
are always driven away from the primary. Satellites that accrete from rings in
the Torque-Dependent regime may exhibit either Boomerang or Slingshot behavior,
depending on ring and satellite masses. We consider both known and hypothesized
ring/satellite systems in the solar system, and identify which of these three
regimes they fall into. We determine that Uranus exists within the
Torque-Dependent regime. Using the RING-MOONS code, which models the dynamical
evolution of coupled ring-satellite systems, we show that the Uranian satellite
Miranda may have accreted from a massive ancient Roche-interior ring and
followed a Slingshot-like dynamical path to its present orbit beyond the
synchronous orbit, while satellites that accreted after Miranda followed
Boomerang-like evolution paths and remained interior to the synchronous orbit.",1811.11884v1
2019-06-09,Modeling the light curve of `Oumuamua: evidence for torque and disc-like shape,"We present the first attempt to fit the light curve of the interstellar
visitor `Oumuamua using a physical model which includes optional torque. We
consider both conventional (Lommel-Seeliger triaxial ellipsoid) and alternative
(""black-and-white ball"", ""solar sail"") brightness models. With all the
brightness models, some torque is required to explain the timings of the most
conspicuous features -- deep minima -- of the asteroid's light curve. Our
best-fitting models are a thin disc (aspect ratio 1:6) and a thin cigar (aspect
ratio 1:8) which are very close to being axially symmetric. Both models are
tumbling and require some torque which has the same amplitude in relation to
`Oumuamua's linear non-gravitational acceleration as in Solar System comets
which dynamics is affected by outgassing. Assuming random orientation of the
angular momentum vector, we compute probabilities for our best-fitting models.
We show that cigar-shaped models suffer from a fine-tuning problem and have
only 16 per cent probability to produce light curve minima as deep as the ones
present in `Oumuamua's light curve. Disc-shaped models, on the other hand, are
very likely (at 91 per cent) to produce minima of the required depth. From our
analysis, the most likely model for `Oumuamua is a thin disc (slab)
experiencing moderate torque from outgassing.",1906.03696v3
2019-07-04,Design and Evaluation of Torque Compensation Controllers for a Lower Extremity Exoskeleton,"In this paper, we present an integrated human-in-the-loop simulation paradigm
for the design and evaluation of a lower extremity exoskeleton that is
elastically strapped onto human lower limbs. The exoskeleton has 3 rotational
DOFs on each side and weighs 23kg. Two torque compensation controllers of the
exoskeleton are introduced, aiming to minimize interference and maximize
assistance to human motions, respectively. Their effects on the wearer's
biomechanical loadings are studied with a running motion and predicted ground
reaction forces. It is found that the added weight of the passive exoskeleton
substantially increases the wearer's musculoskeletal loadings. The maximizing
assistance controller reduces the knee joint torque by almost a half when
compared to the passive exoskeleton and the resultant torque is only 72% of
that from the normal running without exoskeleton. When compared to the normal
running, this controller also reduces the hip flexion and extension torques by
31% and 38%, respectively. As a result, the peak activations of the biceps
short head, gluteus maximus, and rectus femoris muscles are reduced by more
than a half. Nonetheless, the axial knee joint reaction force increases for all
exoskeleton cases due to the added weight and higher GRFs. In summary, the
results provide sound evidence of the efficacy of these two controllers on
reducing the wearer's musculoskeletal loadings when compared to the passive
exoskeleton. And it is shown the human-in-the-loop simulation paradigm
presented here can be used for virtual design and evaluation of powered
exoskeletons and pave the way for building optimized exoskeleton prototypes for
experimental evaluation.",1907.02200v2
2020-02-11,Emergent collective dynamics of bottom-heavy squirmers under gravity,"We present the results of hydrodynamic simulations using the method of
multi-particle collision dynamics for a system of squirmer microswimmers moving
under the influence of gravity at low Reynolds numbers. In addition, the
squirmers are bottom-heavy so that they experience a torque which aligns them
along the vertical. The squirmers interact hydrodynamically by the flow fields
of a stokeslet and rotlet, which are initiated by the acting gravitational
force and torque, respectively, and by their own flow fields. By varying the
ratio of swimming to bulk sedimentation velocity and the torque, we determine
state diagrams for the emergent collective dynamics of neutral squirmers as
well as strong pushers and pullers. For low swimming velocity and torque we
observe conventional sedimentation, while the sedimentation profile becomes
inverted when their values are increased. For neutral squirmers we discover
convective rolls of circulating squirmers between both sedimentation states,
which sit at the bottom of the system and are fed by plumes made of
collectively sinking squirmers. At larger torques porous clusters occur that
spawn single squirmers. The two latter states can also occur transiently
starting from a uniform squirmer distribution and then disappear in the
long-time limit. For strong pushers and pullers only weak plume formation is
observed.",2002.04323v2
2020-04-01,Quasi-Direct Drive Actuation for a Lightweight Hip Exoskeleton with High Backdrivability and High Bandwidth,"High-performance actuators are crucial to enable mechanical versatility of
lower-limb wearable robots, which are required to be lightweight, highly
backdrivable, and with high bandwidth. State-of-the-art actuators, e.g., series
elastic actuators (SEAs), have to compromise bandwidth to improve compliance
(i.e., backdrivability). In this paper, we describe the design and human-robot
interaction modeling of a portable hip exoskeleton based on our custom
quasi-direct drive (QDD) actuation (i.e., a high torque density motor with low
ratio gear). We also present a model-based performance benchmark comparison of
representative actuators in terms of torque capability, control bandwidth,
backdrivability, and force tracking accuracy. This paper aims to corroborate
the underlying philosophy of ""design for control"", namely meticulous robot
design can simplify control algorithms while ensuring high performance.
Following this idea, we create a lightweight bilateral hip exoskeleton (overall
mass is 3.4 kg) to reduce joint loadings during normal activities, including
walking and squatting. Experimental results indicate that the exoskeleton is
able to produce high nominal torque (17.5 Nm), high backdrivability (0.4 Nm
backdrive torque), high bandwidth (62.4 Hz), and high control accuracy (1.09 Nm
root mean square tracking error, i.e., 5.4% of the desired peak torque). Its
controller is versatile to assist walking at different speeds (0.8-1.4 m/s) and
squatting at 2 s cadence. This work demonstrates significant improvement in
backdrivability and control bandwidth compared with state-of-the-art
exoskeletons powered by the conventional actuation or SEA.",2004.00467v1
2020-10-17,Modeling and Implementation of Quadcopter Autonomous Flight Based on Alternative Methods to Determine Propeller Parameters,"To properly simulate and implement a quadcopter flight control for intended
load and flight conditions, the quadcopter model must have parameters on
various relationships including propeller thrust-torque, thrust-PWM, and
thrust--angular speed to a certain level of accuracy. Thrust-torque modeling
requires an expensive reaction torque measurement sensor. In the absence of
sophisticated equipment, the study comes up with alternative methods to
complete the quadcopter model. The study also presents a method of modeling the
rotational aerodynamic drag on the quadcopter. Although the resulting model of
the reaction torque generated by the quadcopter's propellers and the model of
the drag torque acting on the quadcopter body that are derived using the
methods in this study may not yield the true values of these quantities, the
experimental modeling techniques presented in this work ensure that the derived
dynamic model for the quadcopter will nevertheless behave identically with the
true model for the quadcopter. The derived dynamic model is validated by basic
flight controller simulation and actual flight implementation. The model is
used as basis for a quadcopter design, which eventually is used for test
purposes of basic flight control. This study serves as a baseline for fail-safe
control of a quadcopter experiencing an unexpected motor failure.",2010.08806v1
2020-10-24,Controlling secondary flows in Taylor-Couette flow using stress-free boundary conditions,"Taylor-Couette (TC) flow, the flow between two independently rotating and
co-axial cylinders is commonly used as a canonical model for shear flows.
Unlike plane Couette, pinned secondary flows can be found in TC flow. These are
known as Taylor rolls and drastically affect the flow behaviour. We study the
possibility of modifying these secondary structures using patterns of
stress-free and no-slip boundary conditions on the inner cylinder. For this, we
perform direct numerical simulations of narrow-gap TC flow with pure inner
cylinder rotation at four different shear Reynolds numbers up to $Re_s=3\times
10^4$. We find that one-dimensional azimuthal patterns do not have a
significant effect on the flow topology, and that the resulting torque is a
large fraction ($\sim80-90\%$) of torque in the fully no-slip case.
One-dimensional axial patterns decrease the torque more, and for certain
pattern frequency disrupt the rolls by interfering with the existing Reynolds
stresses that generate secondary structures. For $Re\geq 10^4$, this disruption
leads to a smaller torque than what would be expected from simple boundary
layer effects and the resulting effective slip length and slip velocity. We
find that two-dimensional checkerboard patterns have similar behaviour to
azimuthal patterns and do not affect the flow or the torque substantially, but
two-dimensional spiral inhomogeneities can move around the pinned secondary
flows as they induce persistent axial velocities. We quantify the roll's
movement for various angles and the widths of the spiral pattern, and find a
non-monotonic behaviour as a function of pattern angle and pattern frequency.",2010.12853v3
2020-12-08,Be star discs: powered by a non-zero central torque,"Be stars are rapidly rotating B stars with Balmer emission lines that
indicate the presence of a Keplerian, rotationally supported, circumstellar gas
disc. Current disc models, referred to as ""decretion discs"", make use of the
zero torque inner boundary condition typically applied to accretion discs, with
the 'decretion' modelled by adding mass to the disc at a radius of about two
per cent larger than the inner disc boundary. We point out that, in this model,
the rates at which mass and energy need to be added to the disc are implausibly
large. What is required is that the disc has not only a source of mass but also
a continuing source of angular momentum. We argue that the disc evolution may
be more physically modelled by application of the non-zero torque inner
boundary condition of Nixon & Pringle (2020), which determines the torque
applied at the boundary as a fraction of the advected angular momentum flux
there and approaches the accretion and decretion disc cases in the appropriate
limits. We provide supporting arguments for the suggestion that the origin of
the disc material is small-scale magnetic flaring events on the stellar
surface, which, when combined with rapid rotation, can provide sufficient mass
to form, and sufficient angular momentum to maintain, a Keplerian Be star disc.
We discuss the origin of such small-scale magnetic fields in radiative stars
with differential rotation. We conclude that small-scale magnetic fields on the
stellar surface, may be able to provide the necessary mass flux and the
necessary time-dependent torque on the disc inner regions to drive the observed
disc evolution.",2012.04657v1
2021-03-08,"A Self-Consistent, Time-Dependent Treatment of Dynamical Friction: New Insights regarding Core Stalling and Dynamical Buoyancy","Dynamical friction is typically regarded a secular process, in which the
subject ('perturber') evolves very slowly (secular approximation), and has been
introduced to the host over a long time (adiabatic approximation). These
assumptions imply that dynamical friction arises from the LBK torque with
non-zero contribution only from pure resonance orbits. However, dynamical
friction is only of astrophysical interest if its timescale is shorter than the
age of the Universe. In this paper we therefore relax the adiabatic and secular
approximations. We first derive a generalized LBK torque, which reduces to the
LBK torque in the adiabatic limit, and show that it gives rise to transient
oscillations due to non-resonant orbits that slowly damp out, giving way to the
LBK torque. This is analogous to how a forced, damped oscillator undergoes
transients before settling to a steady state, except that here the damping is
due to phase mixing rather than dissipation. Next, we present a self-consistent
treatment, that properly accounts for time-dependence of the perturber
potential and circular frequency (memory effect), which we use to examine
orbital decay in a cored galaxy. We find that the memory effect results in a
phase of accelerated, super-Chandrasekhar friction before the perturber stalls
at a critical radius, $R_{\mathrm{crit}}$, in the core (core-stalling). Inside
of $R_{\mathrm{crit}}$ the torque flips sign, giving rise to dynamical
buoyancy, which counteracts friction and causes the perturber to stall. This
phenomenology is consistent with $N$-body simulations, but has thus far eluded
proper explanation.",2103.05004v1
2021-11-08,Analysis of Rotational Motion based on Rolling Friction Torque,"In the problem of cylinder rolling without slipping on a horizontal floor,
both the cylinder and floor are generally treated as rigid bodies in normal
textbooks. When the air resistance is ignored, the equation of motion has a
solution with a constant velocity. However, in the real world, permanent motion
does not occur. The difficulty cannot be solved only by the horizontal force,
because a horizontal force opposite the translational direction increases the
angular velocity of rotation around the center. Therefore other mechanisms need
to be examined. There are two main reasons for this result. 1) Both a cylinder
and a floor are not perfect circle and perfect plane, but have uneven surfaces.
The micro bumps on the surface yield small collisions in the direction
perpendicular to the floor. The collisions generate a rolling friction torque
around the center. 2) A strong force acts on the contact part which is
deformed. The high-speed deformation produces a history effect on the
relationship between stress and strain, because the compressed wave in the
contact part diffuses to the outside at the speed of sound. Therefore a rolling
friction torque is also generated. Both torques are caused by forces
perpendicular to the floor. The rolling friction torque eliminates the
discrepancy between the textbook results and reality by solving the
simultaneous differential equations of rotation and translation. This method is
useful for studying rolling systems such as trains and cars.",2111.06258v1
2022-02-17,"Mechanical response to tension and torque of molecular chains via statistically interacting particles associated with extension, contraction, twist, and supercoiling","A methodology for the statistical mechanical analysis of polymeric chains
under tension introduced previously is extended to include torque. The response
of individual bonds between monomers or of entire groups of monomers to a
combination of tension and torque involves, in the framework of this method of
analysis, the (thermal or mechanical) activation of a specific mix of
statistically interacting particles carrying quanta of extension or contraction
and quanta of twist or supercoiling. The methodology, which is elucidated in
applications of increasing complexity, is capable of describing the conversion
between twist chirality and plectonemic chirality in quasistatic processes. The
control variables are force or extension and torque or linkage (a combination
of twist and writhe). The versatility of this approach is demonstrated in two
applications relevant and promising for double-stranded DNA under controlled
tension and torque. One application describes conformational transformations
between (native) B-DNA, (underwound) S-DNA, and (overwound) P-DNA in accord
with experimental data. The other application describes how the conversion
between a twisted chain and a supercoiled chain accommodates variations of
linkage and excess length in a buckling transition.",2202.08912v1
2022-04-25,Microscopic field theory for structure formation in systems of self-propelled particles with generic torques,"We derive a dynamical field theory for self-propelled particles subjected to
generic torques and forces by explicitly coarse-graining their microscopic
dynamics, described by a many-body Fokker-Planck equation. The model includes
both intrinsic torques inducing self-rotation, as well as interparticle torques
leading to, for instance, the local alignment of particles' orientations.
Within this approach, although the functional form of the pairwise interactions
does not need to be specified, one can directly map the parameters of the field
theory onto the parameters of particle-based models. We perform a linear
stability analysis of the homogeneous solution of the field equations and find
both long-wavelength and short-wavelength instabilities. The former signals the
emergence of a macroscopic structure, which we associate with motility-induced
phase separation, while the second one signals the growth of a finite structure
with a characteristic size. Intrinsic torques hinder phase separation, pushing
the onset of the long-wavelength instability to higher activities. Further,
they generate finite-sized structures with a characteristic size proportional
to both the self-propulsion velocity and the inverse of the self-rotation
frequency. Our results show that a general mechanism might explain why
chirality tends to suppress motility-induced phase separation but instead
promotes the formation of non-equilibrium patterns.",2204.11571v1
2023-10-18,Direct numerical simulation of Taylor-Couette flow with vertical asymmetric rough walls,"Direct numerical simulations are performed to explore the effects of rotating
direction of the vertical asymmetric rough wall on the transport properties of
Taylor-Couette (TC) flow up to a Taylor number of $\textit{Ta} = 2.39 \times
10^7$. It is shown that compared to the smooth wall, the rough wall with
vertical asymmetric strips can enhance the dimensionless torque
\textit{Nu}$_\omega$, and more importantly, at high \textit{Ta} clockwise
rotation of the inner rough wall (the fluid is sheared by the steeper slope
side of the strips) results in a significantly bigger torque enhancement as
compared to the counter-clockwise rotation (the fluid is sheared by the smaller
slope side of the strips) due to the larger convective contribution to the
angular velocity flux, although the rotating direction has a negligible effect
on the torque at low \textit{Ta}. The larger torque enhancement caused by the
clockwise rotation of vertical asymmetric rough wall at high \textit{Ta} is
then explained by the stronger coupling between the rough wall and the bulk due
to the larger biased azimuthal velocity towards the rough wall at the mid-gap
of TC system, the increased intensity of turbulence manifesting by larger
Reynolds stress and thinner boundary layer, and the more significant
contribution of the pressure force on the surface of rough wall to the torque.",2310.11642v2
2023-11-27,Exponential Auto-Tuning Fault-Tolerant Control of N Degrees-of-Freedom Manipulators Subject to Torque Constraints,"This paper presents a novel auto-tuning subsystem-based fault-tolerant
control (SBFC) system designed for robotic manipulator systems with n degrees
of freedom (DoF). It initially proposes a novel model for joint torques,
incorporating an actuator fault correction model to account for potential
faults and a mathematical saturation function to mitigate issues related to
unforeseen excessive torque. This model is designed to prevent the generation
of excessive torques even by faulty actuators. Subsequently, a robust
subsystem-based adaptive control strategy is proposed to force system states
closely along desired trajectories, while tolerating various actuator faults,
excessive torques, and unknown modeling errors. Furthermore, optimal SBFC gains
are determined by tailoring the JAYA algorithm (JA), a high-performance swarm
intelligence technique, standing out for its capacity to optimize without the
need for meticulous tuning of algorithm-specific parameters, relying instead on
its intrinsic principles. Notably, this control framework ensures uniform
exponential stability (UES). The enhancement of accuracy and tracking time for
reference trajectories, along with the validation of theoretical assertions, is
demonstrated through the presentation of simulation outcomes.",2311.15852v3
2024-01-11,Nanoalignment by Critical Casimir Torques,"The manipulation of microscopic objects requires precise and controllable
forces and torques. Recent advances have led to the use of critical Casimir
forces as a powerful tool, which can be finely tuned through the temperature of
the environment and the chemical properties of the involved objects. For
example, these forces have been used to self-organize ensembles of particles
and to counteract stiction caused by Casimir-Liftshitz forces. However, until
now, the potential of critical Casimir torques has been largely unexplored.
Here, we demonstrate that critical Casimir torques can efficiently control the
alignment of microscopic objects on nanopatterned substrates. We show
experimentally and corroborate with theoretical calculations and Monte Carlo
simulations that circular patterns on a substrate can stabilize the position
and orientation of microscopic disks. By making the patterns elliptical, such
microdisks can be subject to a torque which flips them upright while
simultaneously allowing for more accurate control of the microdisk position.
More complex patterns can selectively trap 2D-chiral particles and generate
particle motion similar to non-equilibrium Brownian ratchets. These findings
provide new opportunities for nanotechnological applications requiring precise
positioning and orientation of microscopic objects.",2401.06260v2
2024-01-31,Self-Aligning Active Agents with Inertia and Active Torque,"We extend the study of the inertial effects on the dynamics of active agents
to the case where self-alignment is present. In contrast with the most common
models of active particles, we find that self-alignment, which couples the
rotational dynamics to the translational one, produces unexpected and
non-trivial dynamics, already at the deterministic level. Examining first the
motion of a free particle, we contrast the role of inertia depending on the
sign of the self-aligning torque. When positive, inertia does not alter the
steady-state linear motion of an a-chiral self-propelled particle. On the
contrary, for a negative self-aligning torque, inertia leads to the
destabilization of the linear motion into a spontaneously broken chiral
symmetry orbiting dynamics. Adding an active torque, or bias, to the angular
dynamics the bifurcation becomes imperfect in favor of the chiral orientation
selected by the bias. In the case of a positive self-alignment, the interplay
of the active torque and inertia leads to the emergence, out of a saddle-node
bifurcation, of truly new solutions, which coexist with the simply biased
linear motion. In the context of a free particle, the rotational inertia leaves
unchanged the families of steady-state solutions but can modify their stability
properties. The situation is radically different when considering the case of a
collision with a wall, where a very singular oscillating dynamics takes place
which can only be captured if both translational and rotational inertia are
present.",2401.17798v1
2024-03-12,Crystal design of altermagnetism,"Symmetry plays a fundamental role in condensed matter. The unique
entanglement between magnetic sublattices and alternating crystal environment
in altermagnets provides a unique opportunity for designing magnetic space
symmetry. There have been extensive experimental efforts concentrated on tuning
the Neel vector to reconstruct altermagnetic symmetry. However, it remains
challenging to modulate the altermagnetic symmetry through the crystal aspect.
Here, the crystal design of altermagnetism is successfully realized, by
breaking glide mirrors and magnetic mirrors of the (0001) crystallographic
plane in CrSb films via crystal distortion. We establish a locking relationship
between altermagnetic symmetry and the emergent Dzyaloshinskii-Moriya (DM)
vectors in different CrSb films, realizing unprecedentedly room-temperature
spontaneous anomalous Hall effect in an altermagnetic metal. The concept of
exchange-coupling torques is broadened to include both antiferromagnetic
exchange-coupling torque and DM torque. Their relationship is designable,
determining electrical manipulation modes, e.g., field-assisted switching for
CrSb(1-100)/Pt and field-free switching for W/CrSb(11-20). Particularly, the
unprecedentedly field-free 100-percent switching of Neel vectors is realized by
making these two torques parallel or antiparallel, dependent on Neel vector
orientation. Besides unravelling the rich mechanisms for electrical
manipulation of altermagnetism rooted in broadened concept of exchange-coupling
torques, we list other material candidates and propose that crystal design of
altermagnetism would bring rich designability to magnonics, topology, etc.",2403.07396v1
2002-02-20,Rapid rotation of ultra-Li-depleted halo stars and their association with blue stragglers,"Observations of eighteen halo main-sequence-turnoff stars, four of which are
extremely deficient in Li, show that three of the Li-poor ones have substantial
line broadening. We attribute this to stellar rotation. Despite the great ages
of halo stars, for G202-65, BD+51:1817 and Wolf 550 we infer vsini = 8.3 +/-
0.4, 7.6 +/- 0.3, and 5.5 +/- 0.6 km/s respectively. The stated errors are
3sigma. For CD-31:19466 we derive a 3sigma upper limit vsini < 2.2 km/s. The
three rotating stars are known spectroscopic binaries. We explain the high
rotation velocities in terms of mass and angular momentum transfer onto the
surface of the turnoff star from an initially more-massive donor. Estimates of
the specific angular momentum of accreted material indicate that quite small
transfer masses could have been involved, though the unknown subsequent
spin-down of the accretor prevents us from assigning definitive values for each
star. The accretor is now seen as an ultra-Li-deficient star whose origin makes
it a low-mass counterpart of field blue stragglers. The Li could have been
destroyed before or during the mass-transfer episode. Such objects must be
avoided in studies of the primordial Li abundance and in investigations into
the way normal single stars process their initial Li.",0202369v1
2003-07-22,Heat Transfer in Turbulent Rayleigh-Benard Convection below the Ultimate Regime,"A Rayleigh-B\'enard cell has been designed to explore the Prandtl (Pr)
dependence of turbulent convection in the cross-over range $0.7<Pr<21$ and for
the full range of soft and hard turbulences, up to Rayleigh number $Ra\simeq
10^{11}$. The set-up benefits from the favourable characteristics of cryogenic
helium-4 in fluid mechanics, in-situ fluid property measurements, and special
care on thermometry and calorimetric instrumentation. The cell is cylindrical
with $diameter/height=0.5$. The effective heat transfer $Nu(Ra,Pr)$ has been
measured with unprecedented accuracy for cryogenic turbulent convection
experiments in this range of Rayleigh numbers. Spin-off of this study include
improved fits of helium thermodynamics and viscosity properties. Three main
results were found. First the $Nu(Ra)$ dependence exhibits a bimodality of the
flow with $4-7 %$ difference in $Nu$ for given $Ra$ and $Pr$. Second, a
systematic study of the side-wall influence reveals a measurable effect on the
heat transfer. Third, the $Nu(Pr)$ dependence is very small or null : the
absolute value of the average logarithmic slope $(dlnNu/dlnPr)_{Ra}$ is smaller
than 0.03 in our range of $Pr$, which allows to disciminate between
contradictory experiments [Ashkenazi \textit{et al.}, Phys. Rev.Lett. 83:3641
(1999)][Ahlers \textit{et al.}, Phys.Rev.Lett. 86:3320 (2001)].",0307518v3
2002-04-02,Time transfer and frequency shift to the order 1/c^4 in the field of an axisymmetric rotating body,"Within the weak-field, post-Newtonian approximation of the metric theories of
gravity, we determine the one-way time transfer up to the order 1/c^4, the
unperturbed term being of order 1/c, and the frequency shift up to the order
1/c^4. We adapt the method of the world-function developed by Synge to the
Nordtvedt-Will PPN formalism. We get an integral expression for the
world-function up to the order 1/c^3 and we apply this result to the field of
an isolated, axisymmetric rotating body. We give a new procedure enabling to
calculate the influence of the mass and spin multipole moments of the body on
the time transfer and the frequency shift up to the order 1/c^4. We obtain
explicit formulas for the contributions of the mass, of the quadrupole moment
and of the intrinsic angular momentum. In the case where the only PPN
parameters different from zero are beta and gamma, we deduce from these results
the complete expression of the frequency shift up to the order 1/c^4. We
briefly discuss the influence of the quadrupole moment and of the rotation of
the Earth on the frequency shifts in the ACES mission.",0204009v2
2001-10-18,Experimental Results on the Diffractive Production of Light Vector Mesons at HERA,"We discuss results on the diffractive production of the vector mesons rho,
phi and omega reported by the H1 and ZEUS collaborations at HERA. Unique to
such studies is the experimental accessibility to the polarization of the
vector mesons and hence to the spin-density matrix elements arising in
vacuum-exchange processes. We emphasize the relation between the observed
dependence on momentum transfer and the polarization state of the vector meson.
The diffractive nature of the production mechanism is investigated via
extraction of the Pomeron trajectory at high Q^2. Flavor symmetry is observed
in the phi/rho ratios in the same region of momentum transfer where the
power-law scaling becomes similar. The multivariable helicity analyses impose
stringent constraints on models for the vacuum-exchange production mechanism.
Semi-exclusive photoproduction of transverse rho and phi mesons at momentum
transfers far exceeding their mass scale exhibit a hard scaling behavior which
appears to violate the QCD helicity selection rules in a two-gluon exchange
model.",0110040v1
2001-11-06,The dynamical zeta function and transfer operators for the Kac-Baker model,"The Kac-Baker model describes a 1-dim. classical lattice spin system with
exponentially fast decaying two body interaction. The model was introduced by
M. Kac and G. Baker to investigate the phenomenon of phase transition in
systems with weak long-range interactions like van der Waals gas. Ruelle's
dynamical zeta function for this model can be expressed in terms of Fredholm
determinants of two transfer operators and hence is a meromorphic function. One
of the two operators, found by M. Kac, is an integral operator with symmetric
kernel acting in the Hilbert space of square integrable functions on the line.
The other one is Ruelle's transfer operator acting in some Banach space of
holomorphic observables of the system. In this paper we show how the Kac
operator can be explicitly related basically through the Segal-Bargmann
transform to the Ruelle operator restricted to a certain Segal-Bargmann space
of entire functions in the complex plane. This allows us to show that Ruelle's
zeta function for the Kac-Baker model has infinitely many ""non-trivial"" zeros
on the real axis. In a special case we can show the existence of also
infinitely many ""trivial"" zeros on the line Re s = ln 2 in the complex s-plane.
Hence some kind of Riemann hypothesis seems to hold for this dynamical zeta
function.",0111063v1
2002-05-02,Pair term in the Electromagnetic Current within the Front-Form Dynamics: Spin-0 Case,"The frame and scale dependence of the pair-term contribution to the
electromagnetic form factor of a spin-zero composite system of two-fermions is
studied within the Light Front. The form factor is evaluated from the
plus-component of the current in the Breit frame, using for the first time a
nonconstant, symmetric ansatz for the Bethe-Salpeter amplitude. The frame
dependence is analyzed by allowing a nonvanishing plus component of the
momentum transfer, while the dynamical scale is set by the masses of the
constituents and by mass and size of the composite system. A transverse
momentum distribution, associated with the Bethe-Salpeter amplitude, is
introduced which allows to define strongly and weakly relativistic systems. In
particular, for strongly relativistic systems, the pair term vanishes for the
Drell-Yan condition, while is dominant for momentum transfer along the
light-front direction. For a weakly relativistic system, fitted to the deuteron
scale, the pair term is negligible up to momentum transfers of 1(GeV/c)$^2$. A
comparison with results obtained within the Front-Form Hamiltonian dynamics
with a fixed number of constituents is also presented.",0205010v1
2006-08-18,Entanglement versus energy in the entanglement transfer problem,"We study the relation between energy and entanglement in an entanglement
transfer problem. We first analyze the general setup of two entangled qubits (a
and b) exchanging this entanglement with two other independent qubits (A and
B). Qubit a (b) interacts with qubit A (B) via a spin exchange-like unitary
evolution. A physical realization of this scenario could be the problem of
two-level atoms transferring entanglement to resonant cavities via independent
Jaynes-Cummings interactions. We study the dynamics of entanglement and energy
for the second pair of qubits (tracing out the originally entangled ones) and
show that these quantities are closely related. For example, the allowed
quantum states occupy a restricted area in a phase diagram entanglement vs.
energy. Moreover the curve which bounds this area is exactly the one followed
if both interactions are equal and the entire four qubit system is isolated. We
also consider the case when the target pair of qubits is subjected to losses
and can spontaneously decay.",0608139v2
2008-10-17,Entanglement evolution of two remote and non-identical Jaynes-Cummings atoms,"A detailed treatment of the entanglement dynamics of two distant but
non-identical systems is presented. We study the entanglement evolution of two
remote atoms interacting independently with a cavity field, as in the double
Jaynes-Cummings (JC) model. The four-qubit pairwise concurrences are studied,
allowing for asymmetric atom-cavity couplings and off-resonant ineractions.
Counter to intuition, imperfect matching can prove advantageous to entanglement
creation and evolution. For two types of initial entanglement, corresponding to
spin correlated and anti-correlated Bell states \Phi and \Psi, a full, periodic
and directed transfer of entanglement into a specific qubit pair is possible,
for resonant interactions, depending on the choice of relative couplings.
Furthermore, entanglement transfer and sudden death (ESD) can be prevented
using off-resonant interactions, although for some initial states, detunings
will trigger an otherwise frozen entanglement, to allow a full entanglement
transfer. We confirm a conservation rule governing the pairwise entanglement
between the non-interacting systems, that for the initial state \Psi the sum of
the square of these concurrences (SSC) is conserved. For \Phi, the total SSC is
reduced periodically, even to zero in some cases, to reveal a complete and
abrupt loss of all non-local pairwise entanglement.",0810.3050v2
2008-12-04,Real space first-principles derived semiempirical pseudopotentials applied to tunneling magnetoresistance,"In this letter we present a real space density functional theory (DFT)
localized basis set semi-empirical pseudopotential (SEP) approach. The method
is applied to iron and magnesium oxide, where bulk SEP and local spin density
approximation (LSDA) band structure calculations are shown to agree within
approximately 0.1 eV. Subsequently we investigate the qualitative
transferability of bulk derived SEPs to Fe/MgO/Fe tunnel junctions. We find
that the SEP method is particularly well suited to address the tight binding
transferability problem because the transferability error at the interface can
be characterized not only in orbital space (via the interface local density of
states) but also in real space (via the system potential). To achieve a
quantitative parameterization, we introduce the notion of ghost semi-empirical
pseudopotentials extracted from the first-principles calculated Fe/MgO bonding
interface. Such interface corrections are shown to be particularly necessary
for barrier widths in the range of 1 nm, where interface states on opposite
sides of the barrier couple effectively and play a important role in the
transmission characteristics. In general the results underscore the need for
separate tight binding interface and bulk parameter sets when modeling
conduction through thin heterojunctions on the nanoscale.",0812.0974v1
2009-01-28,Perfect state transfer of a qudit over underlying networks of group association schemes,"As generalizations of results of Christandl et al.\cite{8,9""""} and Facer et
al.\cite{Facer}, Bernasconi et al.\cite{godsil,godsil1} studied perfect state
transfer (PST) between two particles in quantum networks modeled by a large
class of cubelike graphs (e.g., the hypercube) which are the Cayley graphs of
the elementary abelian group $Z_2^n$. In Refs. \cite{PST,psd}, respectively,
PST of a qubit over distance regular spin networks and optimal state transfer
(ST) of a $d$-level quantum state (qudit) over pseudo distance regular networks
were discussed, where the networks considered there were not in general related
with a certain finite group. In this paper, PST of a qudit over antipodes of
more general networks called underlying networks of association schemes, is
investigated. In particular, we consider the underlying networks of group
association schemes in order to employ the group properties (such as
irreducible characters) and use the algebraic structure of these networks (such
as Bose-Mesner algebra) in order to give an explicit analytical formula for
coupling constants in the Hamiltonians so that the state of a particular qudit
initially encoded on one site will perfectly evolve to the opposite site
without any dynamical control. It is shown that the only necessary condition in
order to PST over these networks be achieved is that the centers of the
corresponding groups be non-trivial. Therefore, PST over the underlying
networks of the group association schemes over all the groups with non-trivial
centers such as the abelian groups, the dihedral group $D_{2n}$ with even $n$,
the Clifford group CL(n) and all of the $p$-groups can be achieved.",0901.4504v2
2009-03-06,Atomistic simulations of adiabatic coherent electron transport in triple donor systems,"A solid-state analogue of Stimulated Raman Adiabatic Passage can be
implemented in a triple well solid-state system to coherently transport an
electron across the wells with exponentially suppressed occupation in the
central well at any point of time. Termed coherent tunneling adiabatic passage
(CTAP), this method provides a robust way to transfer quantum information
encoded in the electronic spin across a chain of quantum dots or donors. Using
large scale atomistic tight-binding simulations involving over 3.5 million
atoms, we verify the existence of a CTAP pathway in a realistic solid-state
system: gated triple donors in silicon. Realistic gate profiles from commercial
tools were combined with tight-binding methods to simulate gate control of the
donor to donor tunnel barriers in the presence of cross-talk. As CTAP is an
adiabatic protocol, it can be analyzed by solving the time independent problem
at various stages of the pulse - justifying the use of time-independent
tight-binding methods to this problem. Our results show that a three donor CTAP
transfer, with inter-donor spacing of 15 nm can occur on timescales greater
than 23 ps, well within experimentally accessible regimes. The method not only
provides a tool to guide future CTAP experiments, but also illuminates the
possibility of system engineering to enhance control and transfer times.",0903.1142v1
2009-10-09,Single-nucleon experiments,"We discuss the Jefferson Lab low momentum transfer data on moments of the
nucleon spin structure functions $g_1$ and $g_2$ and on single charged pion
electroproduction off polarized proton and polarized neutron. A wealth of data
is now available, while more is being analyzed or expected to be taken in the
upcoming years. Given the low momentum transfer selected by the experiments,
these data can be compared to calculations from Chiral Perturbation theory, the
effective theory of strong force that should describe it at low momentum
transfer. The data on various moments and the respective calculations do not
consistently agree. In particular, experimental data for higher moments
disagree with the calculations.The absence of contribution from the $\Delta$
resonance in the various observables was expected to facilitate the
calculations and hence make the theory predictions either more robust or valid
over a larger $Q^2$ range. Such expectation is verified only for the Bjorken
sum, but not for other observables in which the $\Delta$ is suppressed.
Preliminary results on pion electroproduction off polarized nucleons are also
presented and compared to phenomenological models for which contributions from
different resonances are varied. Chiral Perturbation calculations of these
observables, while not yet available, would be valuable and, together with
these data, would provide an extensive test of the effective theory.",0910.1751v1
2010-07-01,Exactly solvable mixed-spin Ising-Heisenberg diamond chain with the biquadratic interactions and single-ion anisotropy,"An exactly solvable variant of mixed spin-(1/2,1) Ising-Heisenberg diamond
chain is considered. Vertical spin-1 dimers are taken as quantum ones with
Heisenberg bilinear and biquadratic interactions and with single-ion
anisotropy, while all interactions between spin-1 and spin-1/2 residing on the
intermediate sites are taken in the Ising form. The detailed analysis of the
$T=0$ ground state phase diagram is presented. The phase diagrams have shown to
be rather rich, demonstrating large variety of ground states: saturated one,
three ferrimagnetic with magnetization equal to 3/5 and another four
ferrimagnetic ground states with magnetization equal to 1/5. There are also two
frustrated macroscopically degenerated ground states which could exist at zero
magnetic filed.
  Solving the model exactly within classical transfer-matrix formalism we
obtain an exact expressions for all thermodynamic function of the system. The
thermodynamic properties of the model have been described exactly by exact
calculation of partition function within the direct classical transfer-matrix
formalism, the entries of transfer matrix, in their turn, contain the
information about quantum states of vertical spin-1 XXZ dimer (eigenvalues of
local hamiltonian for vertical link).",1007.0098v2
2012-08-14,Extracting generalized neutron parton distributions from 3He data,"An impulse approximation analysis is described of the generalized parton
distributions (GPDs) H and E of the 3He nucleus, quantities which are
accessible in hard exclusive processes, such as coherent deeply virtual Compton
scattering (DVCS). The calculation is based on the Av18 interaction. The
electromagnetic form factors are correctly recovered in the proper limits. The
sum of the GPDs H and E of 3He, at low momentum transfer, is largely dominated
by the neutron contribution, thanks to the unique spin structure of 3He. This
nucleus is therefore very promising for the extraction of the neutron
information. By increasing the momentum transfer, however, this conclusion is
somehow hindered by the the fast growing proton contribution. Besides, even
when the neutron contribution to the GPDs of 3He is largely dominating, the
procedure of extracting the neutron GPDs from it could be, in principle,
nontrivial. A technique is therefore proposed, independent on both the nuclear
potential and the nucleon model used in the calculation, able to take into
account the nuclear effects included in the IA analysis and to safely extract
the neutron information at values of the momentum transfer large enough to
allow the measurements. Thanks to this observation, coherent DVCS should be
considered a key experiment to access the neutron GPDs and, in turn, the
orbital angular momentum of the partons in the neutron.",1208.2831v2
2012-08-31,Polarized line transfer with F-state interference in a non-magnetic medium: Partial frequency redistribution effects in the collisionless regime,"Quantum interference phenomena manifests itself in several ways in the
polarized solar spectrum formed due to coherent scattering processes. One such
effect arises due to interference between the fine structure (J) states giving
rise to multiplets. Another effect is that which arises due to interference
between the hyperfine structure (F) states. We extend the redistribution matrix
derived for the J-state interference to the case of F-state interference. We
then incorporate it into the polarized radiative transfer equation and solve it
for isothermal constant property slab atmospheres. The relevant transfer
equation is solved using a polarized approximate lambda iteration (PALI)
technique based on operator perturbation. An alternative method derived from
the Neumann series expansion is also proposed and is found to be relatively
more efficient than the PALI method. The effects of PRD and the F-state
interference on the shapes of the linearly polarized Stokes profiles are
discussed. The emergent Stokes profiles are computed for hypothetical line
transitions arising due to hyperfine structure splitting (HFS) of the upper
J=3/2 and lower J=1/2 levels of a two-level atom model with nuclear spin
I_s=3/2. We confine our attention to the non-magnetic scattering in the
collisionless regime.",1208.6369v1
2013-07-24,First Measurement of the Electromagnetic Form Factor of the Neutral Kaon at a Large Momentum Transfer and the Effect of $SU(3)$ Breaking,"At large momentum transfers the photon interacts with the charges and spins
of the constituent partons in a hadron. It is expected that the neutral kaon
can acquire finite electromagnetic form factors because its wave function is
affected by the order of magnitude difference between the mass of the strange
quark and that of the down quark, or flavor $SU(3)$ breaking. We report on the
first measurement of the form factor of neutral kaons at the large timelike
momentum transfer of $|Q^2|=17.4$ GeV$^2$ by measuring the cross section for
$e^+e^-\to K_SK_L$ at $\sqrt{s}=4.17$ GeV using CLEO-c data with an integrated
luminosity of 586 pb$^{-1}$. We obtain
$F_{K_SK_L}(17.4~\textrm{GeV}^2)=5.3\times10^{-3}$, with a 90% C.L. interval of
$(2.9-8.2)\times10^{-3}$. This is nearly an order of magnitude smaller than
$F_{K^+K^-}(17.4~\textrm{GeV}^2)=(44\pm1)\times10^{-3}$, and indicates that the
effect of $SU(3)$ breaking is small. In turn, this makes it unlikely that the
recently observed strong violation of the pQCD prediction,
$F_{\pi^+\pi^-}(|Q^2|)/F_{K^+K^-}(|Q^2|)=f_\pi^2/f_K^2$, which is based on the
assumption of similar wave functions for the pions and kaons, can be attributed
to $SU(3)$ breaking alone.",1307.6587v2
2014-09-10,From dissipative dynamics to studies of heat transfer at the nanoscale,"We study in a unified manner the dissipative dynamics and the transfer of
heat in the two-bath spin-boson model. We use the Bloch-Redfield (BR)
formalism, valid in the very weak system-bath coupling limit, the
noninteracting-blip approximation (NIBA), applicable in the non-adiabatic
limit, and iterative, numerically-exact path integral tools. These
methodologies were originally developed for the description of the dissipative
dynamics of a quantum system, and here they are applied to explore the problem
of quantum energy transport in a non-equilibrium setting. Specifically, we
study the weak-to-intermediate system-bath coupling regime at high temperatures
$k_BT/\hbar>\epsilon$, with $\epsilon$ as the characteristic frequency of the
two-state system. The BR formalism and NIBA can lead to close results for the
dynamics of the reduced density matrix (RDM) in a certain range of parameters.
However, relatively small deviations in the RDM dynamics propagate into
significant qualitative discrepancies in the transport behavior. Similarly,
beyond the strict non-adiabatic limit NIBA's prediction for the heat current is
qualitatively incorrect: It fails to capture the turnover behavior of the
current with tunneling energy and temperature. Thus, techniques that proved
meaningful for describing the RDM dynamics, to some extent even beyond their
rigorous range of validity, should be used with great caution in heat transfer
calculations, since qualitative-serious failures develop once parameters are
mildly stretched beyond the techniques' working assumptions.",1409.3201v1
2014-12-22,Systematic Dimensionality Reduction for Quantum Walks: Optimal Spatial Search and Transport on Non-Regular Graphs,"Continuous time quantum walks provide an important framework for designing
new algorithms and modelling quantum transport and state transfer problems.
Often, the graph representing the structure of a problem contains certain
symmetries that confine the dynamics to a smaller subspace of the full Hilbert
space. In this work, we use invariant subspace methods, that can be computed
systematically using Lanczos algorithm, to obtain the reduced set of states
that encompass the dynamics of the problem at hand without the specific
knowledge of underlying symmetries. First, we apply this method to obtain new
instances of graphs where the spatial quantum search algorithm is optimal:
complete graphs with broken links and complete bipartite graphs, in particular,
the star graph. These examples show that regularity and high-connectivity are
not needed to achieve optimal spatial search. We also show that this method
considerably simplifies the calculation of quantum transport efficiencies.
Furthermore, we observe improved efficiencies by removing a few links from
highly symmetric graphs. Finally, we show that this reduction method also
allows us to obtain an upper bound for the fidelity of a single qubit transfer
on an XY spin network.",1412.7209v2
2015-02-21,Long-term evolution of double white dwarf binaries accreting through direct impact,"We calculate the long-term evolution of angular momentum in double white
dwarf binaries undergoing direct impact accretion over a broad range of
parameter space. We allow the rotation rate of both components to vary, and
account for the exchange of angular momentum between the spins of the white
dwarfs and the orbit, while conserving the total angular momentum. We include
gravitational, tidal, and mass transfer effects in the orbital evolution, and
allow the Roche radius of the donor star to vary with both the stellar mass and
the rotation rate. We examine the long-term stability of these systems,
focusing in particular on those systems that may be progenitors of AM CVn or
Type Ia Supernovae. We find that our analysis yields an increase in the
predicted number of stable systems compared to that in previous studies.
Additionally, we find that by properly accounting for the effects of
asynchronism between the donor and the orbit on the Roche-lobe size, we
eliminate oscillations in the orbital parameters which are found in previous
studies. Removing these oscillations can reduce the peak mass transfer rate in
some systems, keeping them from entering an unstable mass transfer phase.",1502.06147v2
2015-04-26,Charge transfer model for the electronic structure of layered ruthenates,"Motivated by the earlier experimental results and \textit{ab initio} studies
on the electronic structure of layered ruthenates (Sr$_2$RuO$_4$ and
Ca$_2$RuO$_4$) we introduce and investigate the multiband $d-p$ charge transfer
model describing a single RuO$_4$ layer, similar to the charge transfer model
for a single CuO$_2$ plane including apical oxygen orbitals in high $T_c$
cuprates. The present model takes into account nearest-neighbor anisotropic
ruthenium-oxygen $d-p$ and oxygen-oxygen $p-p$ hopping elements, crystal-field
splittings and spin-orbit coupling. The intraorbital Coulomb repulsion and
Hund's exchange are defined not only at ruthenium but also at oxygen ions. Our
results demonstrate that the RuO$_4$ layer cannot be regarded to be a pure
ruthenium $t_{2g}$ system. We examine a different scenario in which ruthenium
$e_g$ orbitals are partly occupied and highlight the significance of oxygen
orbitals. We point out that the predictions of an idealized model based on
ionic configuration (with $n_0=4+4\times 6=28$ electrons per RuO$_4$ unit) do
not agree with the experimental facts for Sr$_2$RuO$_4$ which support our
finding that the electron number in the $d-p$ states is significantly smaller.
In fact, we find the electron occupation of $d$ and $p$ orbitals for a single
RuO$_4$ unit $n=28-x$, being smaller by at least 1--1.5 electrons from that in
the ionic model and corresponding to self-doping with $x\simeq 1.5$.",1504.06850v1
2015-09-17,"Ultracold magnetically tunable interactions without radiative charge transfer losses between Ca$^+$, Sr$^+$, Ba$^+$, and Yb$^+$ ions and Cr atoms","The Ca$^+$, Sr$^+$, Ba$^+$, and Yb$^+$ ions immersed in an ultracold gas of
the Cr atoms are proposed as experimentally feasible heteronuclear systems in
which ion-atom interactions at ultralow temperatures can be controlled with
magnetically tunable Feshbach resonances without charge transfer and radiative
losses. \textit{Ab initio} techniques are applied to investigate
electronic-ground-state properties of the (CaCr)$^+$, (SrCr)$^+$, (BaCr)$^+$,
and (YbCr)$^+$ molecular ions. The potential energy curves, permanent electric
dipole moments, and static electric dipole polarizabilities are computed. The
spin restricted open-shell coupled cluster method restricted to single, double,
and noniterative triple excitations, RCCSD(T), and the multireference
configuration interaction method restricted to single and double excitations,
MRCISD, are employed. The scalar relativistic effects are included within the
small-core energy-consistent pseudopotentials. The leading long-range induction
and dispersion interaction coefficients are also reported. Finally, magnetic
Feshbach resonances between the Ca$^+$, Sr$^+$, Ba$^+$, and Yb$^+$ ions
interacting with the Cr atoms are analyzed. The present proposal opens the way
towards robust quantum simulations and computations with ultracold ion-atom
systems free of radiative charge transfer losses.",1509.05390v2
2016-01-09,Odyssey: A Public GPU-Based Code for General-Relativistic Radiative Transfer in Kerr Spacetime,"General-relativistic radiative transfer (GRRT) calculations coupled with the
calculation of geodesics in the Kerr spacetime are an essential tool for
determining the images, spectra and light curves from matter in the vicinity of
black holes. Such studies are especially important for ongoing and upcoming
millimeter/submillimeter (mm/sub-mm) Very Long Baseline Interferometry (VLBI)
observations of the supermassive black holes at the centres of Sgr A^{*} and
M87. To this end we introduce Odyssey, a Graphics Processing Unit(GPU)-based
code for ray tracing and radiative transfer in the Kerr spacetime. On a single
GPU, the performance of Odyssey can exceed 1 nanosecond per photon, per
Runge-Kutta integration step. Odyssey is publicly available, fast, accurate,
and flexible enough to be modified to suit the specific needs of new users.
Along with a Graphical User Interface (GUI) powered by a video-accelerated
display architecture, we also present an educational software tool,
Odyssey_Edu, for showing in real time how null geodesics around a Kerr black
hole vary as a function of black hole spin and angle of incidence onto the
black hole.",1601.02063v2
2016-11-18,Anisotropic conjugated polymer chain conformation tailors the energy migration in nanofibers,"Conjugated polymers are complex multi-chromophore systems, with emission
properties strongly dependent on the electronic energy transfer through active
sub-units. Although the packing of the conjugated chains in the solid state is
known to be a key factor to tailor the electronic energy transfer and the
resulting optical properties, most of the current solution-based processing
methods do not allow for effectively controlling the molecular order, thus
making the full unveiling of energy transfer mechanisms very complex. Here we
report on conjugated polymer fibers with tailored internal molecular order,
leading to a significant enhancement of the emission quantum yield. Steady
state and femtosecond time-resolved polarized spectroscopies evidence that
excitation is directed toward those chromophores oriented along the fiber axis,
on a typical timescale of picoseconds. These aligned and more extended
chromophores, resulting from the high stretching rate and electric field
applied during the fiber spinning process, lead to improved emission
properties. Conjugated polymer fibers are relevant to develop optoelectronic
plastic devices with enhanced and anisotropic properties.",1611.06052v1
2017-01-12,Magnetic field enhancement of organic photovoltaic cells performance,"Charge separation is a critical process for achieving high efficiencies in
organic photovoltaic cells. The initial tightly bound excitonic electron-hole
pair has to dissociate fast enough in order to avoid photocurrent generation
and thus power conversion efficiency loss via geminate recombination. Such
process takes place assisted by transitional states that lie between the
initial exciton and the free charge state. Due to spin conservation rules these
intermediate charge transfer states typically have singlet character. Here we
propose a donor-acceptor model for a generic organic photovoltaic cell in which
the process of charge separation is modulated by a magnetic field which tunes
the energy levels. The impact of a magnetic field is to intensify the
generation of charge transfer states with triplet character via inter-system
crossing. As the ground state of the system has singlet character, triplet
states are recombination-protected, thus leading to a higher probability of
successful charge separation. Using the open quantum systems formalism we
demonstrate that not only the population of triplet charge transfer states
grows in the presence of a magnetic field, but also how the power outcome of an
organic photovoltaic cell is in that way increased.",1702.05130v1
2018-01-26,Enhancing silicon solar cells with singlet fission: the case for Foerster resonant energy transfer using a quantum dot intermediate,"One way for solar cell efficiencies to overcome the Shockley-Queisser limit
is downconversion of high-energy photons using singlet fission (SF) in
polyacenes like tetracene (Tc). SF enables generation of multiple excitons from
the high-energy photons which can be harvested in combination with Si. In this
work we investigate the use of lead sulfide quantum dots (PbS QDs) with a band
gap close to Si as an interlayer that allows Foerster Resonant Energy Transfer
(FRET) from Tc to Si, a process that would be spin-forbidden without the
intermediate QD step. We investigate how the conventional FRET model, most
commonly applied to the description of molecular interactions, can be modified
to describe the geometry of QDs between Tc and Si and how the distance between
QD and Si, and the QD bandgap affects the FRET efficiency. By extending the
acceptor dipole in the FRET model to a 2D plane, and to the bulk, we see a
relaxation of the distance dependence of transfer. Our results indicate that
FRET efficiencies from PbS QDs to Si well above 50 % are be possible at very
short, but possibly realistic distances of around 1 nm, even for quantum dots
with relatively low photoluminescence quantum yield.",1801.09765v1
2018-06-19,Evolutionary paths of binaries with a neutron star. I. The case of SAX J1808.4-3658,"The evolutionary status of the low mass X-ray binary SAX J1808.4-3658 is
simulated by following the binary evolution of its possible progenitor system
through mass transfer, starting at a period of $\sim$6.6 hr. The evolution
includes angular momentum losses via magnetic braking and gravitational
radiation. It also takes into account the effects of illumination of the donor
by both the X-ray emission and the spin down luminosity of the pulsar. The
system goes through stages of mass transfer and stages during which it is
detached, where only the rotationally powered pulsar irradiates the donor. We
show that the pulsar irradiation is a necessary ingredient to reach SAX
J1808.4-3658 orbital period when the donor mass is reduced to 0.04 - 0.06
M$_\odot$. We also show that the models reproduce important properties of the
system, including the orbital period derivative, which is shown to be directly
linked to the evolution through mass transfer cycles. Moreover we find that the
effects of the irradiation on the internal structure of the donor are non
negligible, causing the companion star to be non completely convective at the
values of mass observed for the system and significantly altering its long term
evolution, as the magnetic braking remains active along the whole evolution.",1806.08225v1
2018-07-13,Photonic quantum state transfer between a cold atomic gas and a crystal,"Interfacing fundamentally different quantum systems is key to build future
hybrid quantum networks. Such heterogeneous networks offer superior
capabilities compared to their homogeneous counterparts as they merge
individual advantages of disparate quantum nodes in a single network
architecture. However, only very few investigations on optical
hybrid-interconnections have been carried out due to the high fundamental and
technological challenges, which involve e.g. wavelength and bandwidth matching
of the interfacing photons. Here we report the first optical quantum
interconnection between two disparate matter quantum systems with photon
storage capabilities. We show that a quantum state can be faithfully
transferred between a cold atomic ensemble and a rare-earth doped crystal via a
single photon at telecommunication wavelength, using cascaded quantum frequency
conversion. We first demonstrate that quantum correlations between a photon and
a single collective spin excitation in the cold atomic ensemble can be
transferred onto the solid-state system. We also show that single-photon
time-bin qubits generated in the cold atomic ensemble can be converted, stored
and retrieved from the crystal with a conditional qubit fidelity of more than
$85\%$. Our results open prospects to optically connect quantum nodes with
different capabilities and represent an important step towards the realization
of large-scale hybrid quantum networks.",1807.05173v1
2018-12-03,Heat transfer statistics in mixed quantum-classical systems,"The modelling of quantum heat transfer processes at the nanoscale is crucial
for the development of energy harvesting and molecular electronics devices.
Herein, we adopt a mixed quantum-classical description of a device, in which
the open subsystem of interest is treated quantum mechanically and the
surrounding heat baths are treated in a classical-like fashion. By introducing
such a mixed quantum-classical description of the composite system, one is able
to study the heat transfer between the subsystem and bath from a closed system
point of view, thereby avoiding simplifying assumptions related to the bath
time scale and subsystem-bath coupling strength. In particular, we adopt the
full counting statistics approach to derive a general expression for the moment
generating function of heat in systems whose dynamics are described by the
quantum-classical Liouville equation (QCLE). From this expression, one can
deduce expressions for the dynamics of the average heat and heat current, which
may be evaluated using numerical simulations. Due to the approximate nature of
the QCLE, we also find that the steady state fluctuation symmetry holds up to
order $\hbar$ for systems whose subsystembath couplings and baths go beyond
bilinear and harmonic, respectively. To demonstrate the approach, we consider
the nonequilibrium spin boson model and simulate its time-dependent average
heat and heat current under various conditions.",1812.01064v1
2018-12-11,"Invariant-mass spectroscopy of $^{18}$Ne, $^{16}$O, and $^{10}$C excited states formed in neutron transfer reactions","Neutron transfer reactions with fast secondary beams of $^{17}$Ne, $^{15}$O,
and $^9$C have been studied with the HiRA and CAESAR arrays. Excited states of
$^{18}$Ne, $^{16}$O, and $^{10}$C in the continuum have been identified using
invariant-mass spectroscopy. The best experimental resolution of these states
is achieved by selecting events where the decay fragments are emitted
transverse to the beam direction. We have confirmed a number of spin
assignments made in previous works for the negative-parity states of $^{18}$Ne.
In addition we have found new higher-lying excited states in $^{16}$O and
$^{18}$Ne, some of which fission into two ground-state $^8$Be fragments.
Finally for $^{10}$C, a new excited state was observed. These transfer
reactions were found to leave the remnant of the $^9$Be target nuclei at very
high excitation energies and maybe associated with the pickup of a deeply-bound
$^9$Be neutron.",1812.04559v1
2018-12-17,Charge-Stripe Crystal Phase in an Insulating Cuprate,"High-Tc superconductivity in cuprates is generally believed to arise from
carrier doping an antiferromagnetic Mott (AFM) insulator. Theoretical proposals
and emerging experimental evidence suggest that this process leads to the
formation of intriguing electronic liquid crystal phases. These phases are
characterized by ordered charge and/or spin density modulations, and thought to
be intimately tied to the subsequent emergence of superconductivity. The most
elusive, insulating charge-stripe crystal phase is predicted to occur when a
small density of holes is doped into the charge-transfer insulator state, and
would provide a missing link between the undoped parent AFM phase and the
mysterious, metallic pseudogap. However, due to experimental challenges, it has
been difficult to observe this phase. Here, we use surface annealing to extend
the accessible doping range in Bi-based cuprates and achieve the lightly-doped
charge-transfer insulating state of a cuprate Bi2Sr2CaCu2O8+x. In this
insulating state with a charge transfer gap at the order of ~1 eV, using
spectroscopic-imaging scanning tunneling microscopy, we discover a
unidirectional charge-stripe order with a commensurate 4a0 period along the
Cu-O-Cu bond. Importantly, this insulating charge-stripe crystal phase develops
before the onset of the pseudogap and the formation of the Fermi surface. Our
work provides new insights into the microscopic origin of electronic
inhomogeneity in high-Tc cuprates.",1812.07013v1
2019-06-11,Van der Waals epitaxy of Mn-doped MoSe$_2$ on mica,"The magnetic order associated with the degree of freedom of spin in
two-dimensional (2D) materials is subjected to intense investigation because of
its potential application in 2D spintronics and valley-related magnetic
phenomena. We report here a bottom-up strategy using molecular beam epitaxy to
grow and dope large-area (cm$^2$) few-layer MoSe$_2$ with Mn as a magnetic
dopant. High-quality Mn-doped MoSe$_2$ layers are obtained for Mn content of
less than 5 % (atomic). When increasing the Mn content above 5 % we observe a
clear transition from layer-by-layer to cluster growth. Magnetic measurements
involving a transfer process of the cm$^2$-large doped layers on
100-micron-thick silicon substrate, show plausible proof of high-temperature
ferromagnetism of 1 % and 10 % Mn-doped MoSe$_2$. Although we could not point
to a correlation between magnetic and electrical properties, we demonstrate
that the transfer process described in this report permits to achieve
conventional electrical and magnetic measurements on the doped layers
transferred on any substrate. Therefore, this study provides a promising route
to characterize stable ferromagnetic 2D layers, which is broadening the current
start-of-the-art of 2D materials-based applications.",1906.04801v1
2019-09-15,"Comprehending robust quantum effects in organic semiconductors: Charge-transfer excitons, aggregate phonons and fractons","In organic semiconductors working under ambient circumstance, there are
remarkable quantum effects lack of comprehensive understanding, and an exotic
composite particle named charge transfer (CT) exciton is normally regarded as
the key ingredient. Another essential substance is the phonons stemming from
intra- and inter-molecular vibrations, and the relevant diagonal
electron-phonon couplings give rise to spatial localization and the
off-diagonal couplings refer to the dispersion of electron wavefunctions. In
this work, we first propose a toy model based upon the fracton physics to
phenomenologically unveil the coherent motion of CT excitons followed by
resonant phonons in the aggregates. Based on this model, a generic scenario of
hierarchical quantum effects is described in various material systems. To
examine whether the fracton model can be applicable in practice, we calculate
the out-of-time-ordered correlator (OTOC), a quantum dynamic measurement of the
entanglement entropy, of CT excitons by the adaptive time-dependent density
matrix renormalization group algorithm. On the basis of three commonly-used
realistic models in organic materials with two competing interactions taking
into account, we investigate the irreducible roles of CT excitons and aggregate
phonons in the ultrafast charge transfer, the coherent polaron hopping, and the
dissociation of triplet pairs, respectively. Our theory unifies the charge,
exciton, spin and phonons into a single framework, which may help clarify the
complicated and diverse quantum effects in organic semiconductors.",1909.06742v2
2019-09-21,On the calculation of quantum mechanical electron transfer rates,"We present a simple interpolation formula for the rate of an electron
transfer reaction as a function of the electronic coupling strength. The
formula only requires the calculation of Fermi Golden Rule and Born-Oppenheimer
rates and so can be combined with any methods that are able to calculate these
rates. We first demonstrate the accuracy of the formula by applying it to a one
dimensional scattering problem for which the exact quantum mechanical, Fermi
Golden Rule, and Born-Oppenheimer rates are readily calculated. We then
describe how the formula can be combined with the Wolynes theory approximation
to the Golden Rule rate, and the ring polymer molecular dynamics (RPMD)
approximation to the Born-Oppenheimer rate, and used to capture the effects of
nuclear tunnelling, zero point energy, and solvent friction on condensed phase
electron transfer reactions. Comparison with exact hierarchical equations of
motion (HEOM) results for a demanding set of spin-boson models shows that the
interpolation formula has an error comparable to that of RPMD rate theory in
the adiabatic limit, and that of Wolynes theory in non-adiabatic limit, and is
therefore as accurate as any method could possibly be that attempts to
generalise these methods to arbitrary electronic coupling strengths.",1909.09882v1
2020-07-07,A discrete memory-kernel for multi-time correlations in non-Markovian quantum processes,"Efficient simulations of the dynamics of open systems is of wide importance
for quantum science and tech-nology. Here, we introduce a generalization of the
transfer-tensor, or discrete-time memory kernel, formalism to multi-time
measurement scenarios. The transfer-tensor method sets out to compute the state
of an open few-body quantum system at long times, given that only short-time
system trajectories are available. Here, we showthat the transfer-tensor method
can be extended to processes which include multiple interrogations (e.g.
measurements) of the open system dynamics as it evolves, allowing us to
propagate high order short-time correlation functions to later times, without
further recourse to the underlying system-environment evolution. Our approach
exploits the process-tensor description of open quantum processes to represent
and propagate the dynamics in terms of an object from which any multi-time
correlation can be extracted. As an illustration of the utility of the method,
we study the build-up of system-environment correlations in the paradigmatic
spin-boson model, and compute steady-state emission spectra, taking fully into
account system-environment correlations present in the steady state.",2007.03234v2
2020-10-27,Bandgap renormalization in monolayer MoS_2 on CsPbBr_3 quantum dot via charge transfer at room temperature,"Many-body effect and strong Coulomb interaction in monolayer transition metal
dichalcogenides lead to shrink the intrinsic bandgap, originating from the
renormalization of electrical/optical bandgap, exciton binding energy, and
spin-orbit splitting. This renormalization phenomenon has been commonly
observed at low temperature and requires high photon excitation density. Here,
we present the augmented bandgap renormalization in monolayer MoS_2 anchored on
CsPbBr_3 perovskite quantum dots at room temperature via charge transfer. The
amount of electrons significantly transferred from perovskite gives rise to the
large plasma screening in MoS_2. The bandgap in heterostructure is red-shifted
by 84 meV with minimal pump fluence, the highest bandgap renormalization in
monolayer MoS_2 at room temperature, which saturates with further increase of
pump fluence. We further find that the magnitude of bandgap renormalization
inversely relates to Thomas-Fermi screening length. This provides plenty of
room to explore the bandgap renormalization within existing vast libraries of
large bandgap van der Waals heterostructure towards practical devices such as
solar cells, photodetectors and light-emitting-diodes.",2010.14015v1
2020-11-20,Mass transfer to freely suspended particles at high Péclet number,"In a theoretical analysis, we generalise well known asymptotic results to
obtain expressions for the rate of transfer of material from the surface of an
arbitrary, rigid particle suspended in an open pathline flow at large P\'eclet
number, $\textrm{Pe}$. The flow may be steady or periodic in time. We apply
this result to numerically evaluate expressions for the surface flux to a
freely suspended, axisymmetric ellipsoid (spheroid) in Stokes flow driven by a
steady linear shear. We complement these analytical predictions with numerical
simulations conducted over a range of $\textrm{Pe} = 10^1 - 10^4$ and confirm
good agreement at large P\'eclet number. Our results allow us to examine the
influence of particle shape upon the surface flux for a broad class of flows.
When the background flow is irrotational, the surface flux is steady and is
prescribed by three parameters only: the P\'eclet number, the particle aspect
ratio and the strain topology. We observe that slender prolate spheroids tend
to experience a higher surface flux compared to oblate spheroids with
equivalent surface area. For rotational flows, particles may begin to spin or
tumble, which may suppress or augment the convective transfer due to a
realignment of the particle with respect to the strain field.",2011.10551v1
2021-07-27,Interacting Stellar EMRIs as Sources of Quasi-Periodic Eruptions in Galactic Nuclei,"A star that approaches a supermassive black hole (SMBH) on a circular extreme
mass ratio inspiral (EMRI) can undergo Roche lobe overflow (RLOF), resulting in
a phase of long-lived mass-transfer onto the SMBH. If the interval separating
consecutive EMRIs is less than the mass-transfer timescale driven by
gravitational wave emission (typically ~1-10 Myr), the semi-major axes of the
two stars will approach each another on scales of <~ hundreds to thousands of
gravitational radii. Close flybys tidally strip gas from one or both RLOFing
stars, briefly enhancing the mass-transfer rate onto the SMBH and giving rise
to a flare of transient X-ray emission. If both stars reside in an common
orbital plane, these close interactions will repeat on a timescale as short as
hours, generating a periodic series of flares with properties (amplitudes,
timescales, sources lifetimes) remarkably similar to the ""quasi-periodic
eruptions"" (QPEs) recently observed from galactic nuclei hosting low-mass
SMBHs. A cessation of QPE activity is predicted on a timescale of months to
years, due to nodal precession of the EMRI orbits out of alignment by the SMBH
spin. Channels for generating the requisite coplanar EMRIs include the tidal
separation of binaries (Hills mechanism) or Type I inwards migration through a
gaseous AGN disk. Alternative scenarios for QPEs, that invoke single stellar
EMRIs on an eccentric orbit undergoing a runaway sequence of RLOF events, are
strongly disfavored by formation rate constraints.",2107.13015v2
2022-01-11,Two Wrongs Can Make a Right: A Transfer Learning Approach for Chemical Discovery with Chemical Accuracy,"Appropriately identifying and treating molecules and materials with
significant multi-reference (MR) character is crucial for achieving high data
fidelity in virtual high throughput screening (VHTS). Nevertheless, most VHTS
is carried out with approximate density functional theory (DFT) using a single
functional. Despite development of numerous MR diagnostics, the extent to which
a single value of such a diagnostic indicates MR effect on chemical property
prediction is not well established. We evaluate MR diagnostics of over 10,000
transition metal complexes (TMCs) and compare to those in organic molecules. We
reveal that only some MR diagnostics are transferable across these materials
spaces. By studying the influence of MR character on chemical properties (i.e.,
MR effect) that involves multiple potential energy surfaces (i.e., adiabatic
spin splitting, $\Delta E_\mathrm{H-L}$, and ionization potential, IP), we
observe that cancellation in MR effect outweighs accumulation. Differences in
MR character are more important than the total degree of MR character in
predicting MR effect in property prediction. Motivated by this observation, we
build transfer learning models to directly predict CCSD(T)-level adiabatic
$\Delta E_\mathrm{H-L}$ and IP from lower levels of theory. By combining these
models with uncertainty quantification and multi-level modeling, we introduce a
multi-pronged strategy that accelerates data acquisition by at least a factor
of three while achieving chemical accuracy (i.e., 1 kcal/mol) for robust VHTS.",2201.04243v1
2022-11-10,Vortex $γ$ photon generation via spin-to-orbital angular momentum transfer in nonlinear Compton scattering,"Vortex $\gamma$ photons with intrinsic orbital angular momenta (OAM) possess
a wealth of applications in various fields, e.g.-strong-laser physics, nuclear
physics, particle physics and astrophysics-yet their generation remains
unsettled. In this work, we investigate the generation of vortex $\gamma$
photons via nonlinear Compton scattering of ultrarelativistic electrons in a
circularly polarized laser pulse. We develop a quantum electrodynamics
scattering theory that explicitly addresses the multiphoton absorption and the
angular momentum transfer mechanism. In pulsed laser fields, we unveil the
vortex phase structure of the scattering matrix element, discuss how the vortex
phase could be transferred to the radiated photon, and derive the radiation
rate of the vortex $\gamma$ photon. We numerically examine the energy spectra
and beam characteristics of the radiation, while also investigating the
influence of finite laser pulses on the angular momentum and energy
distribution of the emitted vortex $\gamma$ photons.",2211.05467v4
2022-12-13,Frontier Orbital Degeneracy: A new Concept for Tailoring the Magnetic State in Organic Semiconductor Adsorbates,"Kondo resonances in molecular adsorbates are an important building block for
applications in the field of molecular spintronics. Here, we introduce the
novel concept of using frontier orbital degeneracy for tailoring the magnetic
state, which is demonstrated for the case of the organic semiconductor
1,4,5,8,9,11-Hexaazatriphenylenehexacarbonitrile (HATCN, C18N12) on Ag(111).
Low-temperature scanning tunneling microscopy/spectroscopy (LT-STM/STS)
measurements reveal the existence of two types of adsorbed HATCN molecules with
distinctly different appearances and magnetic states, as evident from the
presence or absence of an Abrikosov-Suhl-Kondo resonance. Our DFT results show
that HATCN on Ag(111) supports two almost isoenergetic states, both with one
excess electron transferred from the Ag surface, but with magnetic moments of
either 0 or 0.65 uB. Therefore, even though all molecules undergo charge
transfer of one electron from the Ag substrate, they exist in two different
molecular magnetic states that resemble a free doublet or an entangled spin
state. We explain how the origin of this behavior lies in the twofold
degeneracy of the lowest unoccupied molecular orbitals of gas phase HATCN,
lifted upon adsorption and charge-transfer from Ag(111). Our combined STM and
DFT study introduces a new pathway to tailoring the magnetic state of molecular
adsorbates on surfaces, with significant potential for spintronics and quantum
information science.",2212.06943v2
2023-04-14,Controlled catalyst transfer polymerization in graphene nanoribbon synthesis,"Exercising direct control over the unusual electronic structures arising from
quantum confinement effects in graphene nanoribbons (GNRs) - atomically defined
quasi one-dimensional (1D) strips of graphene - is intimately linked to
geometric boundary conditions imposed by the bonding within the ribbon. Besides
composition and position of substitutional dopant atoms, the symmetry of the
unit cell, the width, length, and termination of a GNR are integral factors
that collectively can give rise to highly tuneable semiconductors, innate
metallicity arising from topological zero-mode engineering, or magnetic
ordering in spin-polarized lattices. Here we present a rational design that
integrates each of these interdependent variables within a modular bottom-up
synthesis. Our hybrid chemical approach relies on a catalyst transfer
polymerization (CTP) that establishes uniform control over length, width, and
end-groups. Complemented by a surface-assisted cyclodehydrogenation step,
uniquely enabled by matrix-assisted direct (MAD) transfer protocols, geometry
and functional handles encoded in a polymer template are faithfully mapped onto
the structure of the corresponding GNR. Bond-resolved scanning tunnelling
microscopy (BRSTM) and spectroscopy (STS) validate the robust correlation
between polymer template design and GNR electronic structure and provide a
universal and modular platform for the systematic exploration and seamless
integration of functional GNRs with integrated circuit architectures.",2304.07394v1
2023-04-26,The Gravitational Wave Forms of Galactic Compact Binaries with Mass-Transfer Correction,"In this paper, we focus on the effect of mass-transfer between compact
binaries like neutron-star-neutron-star (NS-NS) systems and
neutron-star-white-dwarf (NS-WD) systems on gravitational waves (GWs). We adopt
the mass quadrupole formula with 2.5 order Post-Newtonian (2.5 PN)
approximation to calculate the GW radiation and the orbital evolution. After a
reasonable discussion of astrophysical processes concerning our scenario, two
kinds of mass-transfer models are applied here. One is the mass overflow of the
atmosphere, where the companion star orbits into the primary's Roche limit and
its atmosphere overflows into the common envelope. The other one is the tidal
disruption of the core, which is viewed as incompressible fluid towards the
primary star, and in the near region branches into an accretion disc (AD) and
direct accretion flow. Viewing this envelope and as a background, the GW of its
spin can be calculated as a rotating non-spherically symmetric star. We
eventually obtained the corrected gravitational waveform (GWF) templates for
different initial states in the inspiral phase.",2304.13581v7
2023-12-19,Optical properties and exciton transfer between N-heterocyclic carbene iridium (III) complexes for blue light-emitting diode applications from first principles,"N-heterocyclic carbene (NHC) iridium (III) complexes are considered as
promising candidates for blue emitters in organic light-emitting diodes. They
can play the roles of the emitter as well as of electron and hole transporters
in the same emission layer. We investigate optical transitions in such
complexes with account of geometry and electronic structure changes upon
excitation or charging and exciton transfer between the complexes from first
principles. It is shown that excitation of NHC iridium complexes is accompanied
by a large reorganization energy $\sim$0.7 eV and a significant loss in the
oscillator strength, which should lead to low exciton diffusion. Calculations
with account of spin-orbit coupling reveal a small singlet-triplet splitting
$\sim$0.1 eV, whereas the oscillator strength for triplet excitations is found
to be an order of magnitude smaller than for the singlet ones. The
contributions of the F\""orster and Dexter mechanisms are analyzed via the
explicit integration of transition densities. It is shown that for typical
distances between emitter complexes in the emission layer, the contribution of
the Dexter mechanism should be negligible compared to the F\""orster mechanism.
On the other hand, the ideal dipole approximation, although gives the correct
order of the exciton coupling, fails to reproduce the result taking into
account spatial distribution of the transition density. For charged NHC
complexes, we find a number of optical transitions close to the emission peak
of the blue emitter with high exciton transfer rates that can be responsible
for exciton-polaron quenching. The nature of these transitions is analyzed.",2312.12160v2
2024-01-25,Atomic multiplet and charge-transfer screening effects in 1$s$ and 2$p$ core-level X-ray photoelectron spectra of early 3$d$ transition-metal oxides,"We present a comparative analysis of 1$s$ and 2$p$ core-level hard X-ray
photoelectron spectroscopy (HAXPES) spectra in metallic VO$_2$ and CrO$_2$.
Even though the V 1$s$ and 2$p$ spectra in VO$_2$ display similar line shapes
except the absence or presence of a spin-orbit coupling splitting, the Cr 1$s$
and 2$p$ spectra exhibit distinct main-line shapes. The experimental HAXPES
spectra are analyzed by the Anderson impurity model based on the density
functional theory + dynamical mean-field theory and a conventional MO$_6$
cluster model. We elucidate the complex interplay between formation of the
intra-atomic multiplet and charge transfer effect on the chemical bonding
followed by the 1$s$ and 2$p$ core electron excitations. We demonstrate the
advantage of the 1$s$ excitations to the routinely-employed 2$p$ excitations
for distinguishing between metal-ligand and metal-metal charge transfer
contributions in early 3$d$ transition-metal oxides.",2401.13951v2
1994-12-07,The Effects of High-Velocity Supernova Kicks on the Orbital Properties and Sky Distributions of Neutron Star Binaries,"We systematically investigate the effects of high supernova kick velocities
on the orbital parameters of post-supernova neutron-star binaries. Using Monte-
Carlo simulations, we determine the post-supernova distributions of orbital
parameters for progeneitors of HMXBs and LMXBs. With the recent distribution of
pulsar birth velocities by Lyne & Lorimer (1994), only about 27% of massive
systems remain bound after the supernova, of which about 26% immediately
experience dynamical mass transfer and possibly merge to become Thorne-Zytkow
objects. The correlations between various orbital parameters can be compared
with observational samples to yield information about supernova kick velocities
and pre-supernova orbital-period distributions. After the supernova, the spins
of most stars in massive systems have large inclinations with respect to their
orbital axes, and a significant fraction of systems (about 20%) contain stars
with retrograde spins. In the case of low-mass companions, we find that about
19% of systems remain bound after the supernova, of which about 57% experience
immediate dynamical mass transfer. There is a tight correlation between the
eccentricity and the post-supernova orbital period in LMXB progeneitors. All
LMXBs with post-supernova periods longer than a few days initially have large
eccentricities (e.g. Cir X-1 is discussed in this context). We use the results
of these calculations to simulate the sky distributions of HMXBs and LMXBs. The
simulated distributions agree with observed samples. Most importantly, the
distribution of Galactic LMXBs is consistent with an ordinary Galactic disk
population which has been widened because of large supernova kicks and does not
require a special population of progenitors.",9412023v1
1999-01-03,Disk-Anchored Magnetic Propellers - A Cure for the SW Sex Syndrome,"In AE Aqr, magnetic fields transfer energy and angular momentum from a
rapidly spinning white dwarf to material in the gas stream from the companion
star, with the effect of spinning down the white dwarf while flinging the gas
stream material out of the binary system. This magnetic propeller produces a
host of observable signatures, chief among which are broad single-peaked
flaring emission lines with phase-shifted orbital kinematics. SW Sex stars have
accretion disks, but also broad single-peaked phase-shifted emission lines
similar to those seen in AE Aqr. We propose that a magnetic propeller similar
to that which operates in AE Aqr is also at work in SW Sex stars -- and to some
extent in all nova-like systems. The propeller is anchored in the inner
accretion disk, rather than or in addition to the white dwarf. Energy and
angular momentum are thereby extracted from the inner disk and transferred to
gas stream material flowing above the disk, which is consequently pitched out
of the system. This provides a non-local dissipationless angular momentum
extraction mechanism, which should result in cool inner disks with temperature
profiles flatter than $T\propto R^{-3/4}$, as observed in eclipse mapping
studies of nova-like variables. The disk-anchored magnetic propeller model
appears to explain qualitatively most if not all of the peculiar features of
the SW Sex syndrome.",9901007v1
2003-09-19,"A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate","Using the HST Fine Guidance Sensor, we have measured a high precision
astrometric parallax of the cataclysmic variable EX Hydrae, pi=15.50+-0.29mas.
  From the wavelength-integrated accretion-induced energy flux, we derive a
quiescent accretion luminosity for EX Hya of Lacc = (2.6+-0.6)x10e32 erg. The
quiescent accretion rate then is Mdot=(6.2\+-1.5)x10e-11
(M1/0.5Msun)^(-1.61})Msun/yr. The time-averaged accretion rate, which includes
a small correction for the rare outbursts, is 6% higher. We discuss the system
parameters of EX Hya and deduce M1=0.4-0.7Msun, M2=0.07-0.10Msun, and
i=76.0deg-77.6deg, using recent radial velocity measurements of both components
and restrictions imposed by other observational and theoretical constraints. We
conclude that the secondary is undermassive, overluminous, and expanded over a
ZAMS star of the same mass. Near the upper limit to M1, the accretion rate of
the white dwarf coincides with that due to near-equilibrium angular momentum
loss by gravitational radiation and angular momentum transfer from the orbit
into the spin-up of the white dwarf. Near the lower mass limit, the
correspondingly higher accretion rate requires that either an additional
angular momentum loss process is acting besides gravitational radiation or that
accretion occurs on a near-adiabatic time scale. The latter possibility would
imply that EX Hya is in a transient phase of high mass transfer and the
associated spin-up of the white dwarf.",0309530v1
1996-09-19,Exchange Instabilities in Semiconductor Double Quantum Well Systems,"We consider various exchange-driven electronic instabilities in semiconductor
double-layer systems in the absence of any external magnetic field. We
establish that there is no exchange-driven bilayer to monolayer charge transfer
instability in the double-layer systems. We show that, within the unrestricted
Hartree-Fock approximation, the low density stable phase (even in the absence
of any interlayer tunneling) is a quantum ``pseudospin rotated'' spontaneous
interlayer phase coherent spin-polarized symmetric state rather than the
classical Ising-like charge-transfer phase. The U(1) symmetry of the double
quantum well system is broken spontaneously at this low density quantum phase
transition, and the layer density develops quantum fluctuations even in the
absence of any interlayer tunneling. The phase diagram for the double quantum
well system is calculated in the carrier density--layer separation space, and
the possibility of experimentally observing various quantum phases is
discussed. The situation in the presence of an external electric field is
investigated in some detail using the
spin-polarized-local-density-approximation-based self-consistent technique and
good agreement with existing experimental results is obtained.",9609180v2
2004-11-18,Role of Electron--Electron Interactions on Spin Effects in Electron--Hole Recombination in Organic Light Emitting Diodes,"We extend our theory of electron--hole recombination in organic light
emitting diodes to investigate the possibility that high energy singlet and
triplet excited states with large electron--hole separations are generated in
such processes, over and above the lowest singlet and triplet excitons. Our
approach involves a time-dependent calculation of the interchain /
intermolecular charge--transfer within model Hamiltonians that explicitly
include electron-electron interactions between the $\pi$-electrons. We show
that the electron--hole recombination reaction can be viewed as a tunneling
process whose cross section depends on both the matrix element of the
interchain part of Hamiltonian and the energy difference between the initial
polaron--pair state and the final neutral states. There occurs a bifurcation of
the electron--hole recombination path in each of the two spin channels that
leads to the generation of both the lowest energy exciton and a specific high
energy charge-transfer state, with the matrix elements favoring the lowest
energy exciton and the energy difference factor favoring the higher energy
state. The overall effect of the electron--electron interactions is to enhance
the singlet:triplet yield ratio over the value of 0.25 predicted from
statistical considerations that are valid only within noninteracting models.",0411466v1
2006-09-18,Cooling of radiative quantum-dot excitons by terahertz radiation: A spin-resolved Monte Carlo carrier dynamics model,"We have developed a theoretical model to analyze the anomalous cooling of
radiative quantum dot (QD) excitons by THz radiation reported by Yusa et al
[Proc. 24th ICPS, 1083 (1998)]. We have made three-dimensional (3D) modeling of
the strain and the piezoelectric field and calculated the 3D density of states
of strain induced quantum dots. On the basis of this analysis we have developed
a spin dependent Monte Carlo model, which describes the carrier dynamics in
QD's when the intraband relaxation is modulated by THz radiation. We show that
THz radiation causes resonance transfer of holes from dark to radiative states
in strain-induced QD's. The transition includes a spatial transfer of holes
from the piezoelectric potential mimima to the deformation potential minimum.
This phenomenon strongly enhances the QD ground state luminescence at the
expense of the luminescence from higher states. Our model also reproduces the
delayed flash of QD ground state luminescence, activated by THz radiation even
$\sim1$ s after the carrier generation. Our simulations suggest a more general
possibility to cool the radiative exciton subsystem in optoelectronic devices.",0609419v2
2001-03-13,Helicity and Transversity Distribution of Nucleon and $Λ$-Hyperon from $Λ$ Fragmentation,"It is shown that $\Lambda$-hyperon fragmentation in charged lepton deep
inelastic scattering (DIS) on a polarized nucleon target can provide sensitive
information concerning the quark helicity and transversity distributions for
both nucleon and $\Lambda$-hyperon at large $x$. Numerical predictions are
given for the spin transfers of the produced $\Lambda$, when the target nucleon
is polarized either longitudinally or transversely, and with the nucleon and
$\Lambda$ quark distributions evaluated both in an SU(6)
quark-spectator-diquark model and in a perturbative QCD (pQCD) based model. It
is also shown that the predicted spin transfers have different behaviors for
proton and neutron targets, and this can provide sensitive tests of different
predictions for the quark helicity and transversity distributions of the $d$
valence quark of the proton at large $x$.",0103136v4
2003-02-03,Auxiliary matrices for the six-vertex model at roots of 1 and a geometric interpretation of its symmetries,"The construction of auxiliary matrices for the six-vertex model at a root of
unity is investigated from a quantum group theoretic point of view. Employing
the concept of intertwiners associated with the quantum loop algebra
$U_q(\tilde{sl}_2)$ at $q^N=1$ a three parameter family of auxiliary matrices
is constructed. The elements of this family satisfy a functional relation with
the transfer matrix allowing one to solve the eigenvalue problem of the model
and to derive the Bethe ansatz equations. This functional relation is obtained
from the decomposition of a tensor product of evaluation representations and
involves auxiliary matrices with different parameters. Because of this
dependence on additional parameters the auxiliary matrices break in general the
finite symmetries of the six-vertex model, such as spin-reversal or spin
conservation. More importantly, they also lift the extra degeneracies of the
transfer matrix due to the loop symmetry present at rational coupling values.
The extra parameters in the auxiliary matrices are shown to be directly related
to the elements in the enlarged center of the quantum loop algebra
$U_q(\tilde{sl}_2)$ at $q^N=1$. This connection provides a geometric
interpretation of the enhanced symmetry of the six-vertex model at rational
coupling. The parameters labelling the auxiliary matrices can be interpreted as
coordinates on a three-dimensional complex hypersurface which remains invariant
under the action of an infinite-dimensional group of analytic transformations,
called the quantum coadjoint action.",0302002v2
2005-09-15,Ammoniated electron as a solvent stabilized multimer radical anion,"The excess electron in liquid ammonia (""ammoniated electron"") is commonly
viewed as a cavity electron in which the s-type wave function fills the
interstitial void between 6-9 ammonia molecules. Here we examine an alternative
model in which the ammoniated electron is regarded as a solvent stabilized
multimer radical anion, as was originally suggested by Symons [Chem. Soc. Rev.
1976, 5, 337]. In this model, most of the excess electron density resides in
the frontier orbitals of N atoms in the ammonia molecules forming the solvation
cavity; a fraction of this spin density is transferred to the molecules in the
second solvation shell. The cavity is formed due to the repulsion between
negatively charged solvent molecules. Using density functional theory
calculations for small ammonia cluster anions in the gas phase, it is
demonstrated that such core anions would semi-quantitatively account for the
observed pattern of Knight shifts for 1-H and 14-N nuclei observed by NMR
spectroscopy and the downshifted stretching and bending modes observed by
infrared spectroscopy. It is speculated that the excess electrons in other
aprotic solvents (but not in water and alcohols) might be, in this respect,
analogous to the ammoniated electron, with substantial transfer of the spin
density into the frontier N and C orbitals of methyl, amino, and amide groups
forming the solvation cavity.",0509137v2
2009-05-04,Magnetization Plateaux in the Antiferromagnetic Ising Chain with Single-Ion Anisotropy,"Two one-dimensional spin-1 antiferromagnetic Ising models with a single-ion
anisotropy under external magnetic field at low temperatures are exactly
investigated by the transfer-matrix technique. The magnetization per spin ($m$)
is obtained for the two types of models (denoted by model 1 and 2) as an
explicit function of the magnetic field ($H$%) and of the anisotropy parameter
($D$). Model 1 is an extension of the recently one treated by Ohanyan and
Ananikian [\emph{Phys. Lett. A} \textbf{% 307} (2003) 76]: we have generalized
their model to the spin-1 case and a single-ion anisotropy term have been
included. In the limit of positive (or null) anisotropy ($D\geq 0$) and strong
antiferromagnetic coupling ($\alpha =J_{A}/J_{F}\geq 3$) the $m \times H$
curves are qualitatively the same as for the spin $S=1/2$ case, with the
presence of only one plateau at $m/m_{sat}=1/3$. On the other hand, for
negative anisotropy ($D<0$) we observe more plateaux ($m=1/6$ and 2/3), which
depend on the values of $D$ and $% \alpha $. The second model (model 2) is the
same as the one recently studied by Chen et al. [\emph{J. Mag. Mag. Mat.
}\textbf{262} (2003) 258)] using Monte Carlo simulation; here, the model is
treated within an exact transfer-matrix framework.",0905.0505v1
2010-01-26,Storing Quantum Information via Atomic Dark Resonances,"In this thesis, after a brief review of some concepts of Quantum Optics, we
analyze a three-level atomic system in the conditions of electromagnetically
induced transparency (EIT), and we investigate the propagation of a gaussian
pulse along a cigar-shaped cloud of both cold and hot atoms in EIT regime. In
particular, we show that it is possible to amplify a slow propagating pulse
without population inversion. We also analyze the regime of anomalous light
propagation showing that it is possible to observe superluminal energy
propagation. In these conditions, it is possible to imprint reversibly
('write') the information carried by the photons onto the atoms, specifically
as a coherent pattern of atomic spins, and later the information stored in the
atomic spins can be transferred back ('read') to the light field, implementing
in this way a quantum memory. Besides, we analyze the propagation of a quantum
field in an EIT medium sustaining dark state polaritons (DSP) in a
quasi-particle picture. Here, the decoherence effects in this quantum memory
for photons, by analyzing the fidelity of the quantum state transfer, and the
emergence of parastatistics in the quasi-particle picture in gain medium are
discussed. Finally, we introduce a polarization quantum memory for photons by
using a tripod atomic configuration in which two ideal EIT windows appear and
the two DSPs, scattering each other, show a solitonic behavior.",1001.4660v1
2010-09-06,Functional Bethe ansatz methods for the open XXX chain,"We study the spectrum of the integrable open XXX Heisenberg spin chain
subject to non-diagonal boundary magnetic fields. The spectral problem for this
model can be formulated in terms of functional equations obtained by separation
of variables or, equivalently, from the fusion of transfer matrices. For
generic boundary conditions the eigenvalues cannot be obtained from the
solution of finitely many algebraic Bethe equations. Based on careful finite
size studies of the analytic properties of the underlying hierarchy of transfer
matrices we devise two approaches to analyze the functional equations. First we
introduce a truncation method leading to Bethe type equations determining the
energy spectrum of the spin chain. In a second approach the hierarchy of
functional equations is mapped to an infinite system of non-linear integral
equations of TBA type. The two schemes have complementary ranges of
applicability and facilitate an efficient numerical analysis for a wide range
of boundary parameters. Some data are presented on the finite size corrections
to the energy of the state which evolves into the antiferromagnetic ground
state in the limit of parallel boundary fields.",1009.1081v2
2011-05-05,He star evolutionary channel to intermediate-mass binary pulsar PSR J1802-2124,"The intermediate-mass binary pulsars (IMBPs) are characterized by relatively
long spin periods (10 - 200 ms) and massive ($\ga 0.4 M_{\odot}$) white dwarf
(WD) companions. Recently, precise mass measurements have been performed for
the pulsar and the WD in the IMBP PSR J1802-2124. Some observed properties,
such as the low mass of the pulsar, the high mass of the WD, the moderately
long spin period, and the tight orbit, imply that this system has undergone a
peculiar formation mechanism. In this work, we attempt to simulate the detailed
evolutionary history of PSR J1802-2124. We propose that a binary system
consisting of a neutron star (NS, of mass $1.3 M_{\odot}$) and an He star (of
mass $1.0 M_{\odot}$), and with an initial orbital period of 0.5 d, may have
been the progenitor of PSR J1802-2124. Once the He star overflows its Roche
lobe, He-rich material is transferred onto the NS at a relatively high rate of
$\sim 10^{-7}-10^{-6} M_{\odot}\,\rm yr^{-1}$, which is significantly higher
than the Eddington accretion rate. A large amount of the transferred material
is ejected from the vicinity of the NS by radiation pressure and results in the
birth of a mildly recycled pulsar. Our simulated results are consistent with
the observed parameters of PSR J1802-2124. Therefore, we argue that the NS + He
star evolutionary channel may be responsible for the formation of most IMBPs
with orbital periods $\la 3 \rm d$.",1105.1046v2
2011-05-13,Biorthonormal Matrix-Product-State Analysis for Non-Hermitian Transfer-Matrix Renormalization-Group in the Thermodynamic Limit,"We give a thorough Biorthonormal Matrix-Product-State (BMPS) analysis of the
Transfer-Matrix Renormalization-Group (TMRG) for non-Hermitian matrices in the
thermodynamic limit. The BMPS is built on a dual series of reduced
biorthonormal bases for the left and right Perron states of a non-Hermitian
matrix. We propose two alternative infinite-size Biorthonormal TMRG (iBTMRG)
algorithms and compare their numerical performance in both finite and infinite
systems. We show that both iBTMRGs produce a dual infinite-BMPS (iBMPS) which
are translationally invariant in the thermodynamic limit. We also develop an
efficient wave function transformation of the iBTMRG, an analogy of McCulloch
in the infinite-DMRG [arXiv:0804.2509 (2008)], to predict the wave function as
the lattice size is increased. The resulting iBMPS allows for probing bulk
properties of the system in the thermodynamic limit without boundary effects
and allows for reducing the computational cost to be independent of the lattice
size, which are illustrated by calculating the magnetization as a function of
the temperature and the critical spin-spin correlation in the thermodynamic
limit for a 2D classical Ising model.",1105.2596v5
2011-09-05,Structural Evolution of One-dimensional Spin Ladder Compounds Sr14-xCaxCu24O41 with Ca doping and Related Hole Redistribution Evidence,"Incommensurate crystal structures of spin ladder series Sr14-xCaxCu24O41
(x=3, 7, 11, 12.2) were characterized by powder neutron scattering method and
refined using the superspace group Xmmm(00{\gamma})ss0 (equivalent to
superspace group Fmmm(0,0,1+{\gamma})ss0); X stands for non-standard centering
(0,0,0,0), (0,1/2,1/2,1/2), (1/2,1/2,0,0), (1/2,0,1/2,1/2)) with a modulated
structure model. The Ca doping effects on the lattice parameters, atomic
displacement, Cu-O distances, Cu-O bond angles and Cu bond valence sum were
characterized. The refined results show that the CuO4 planar units in both
chain and ladder sublattices become closer to square shape with an increase of
Ca doping. The Cu bond valence sum calculation provided new evidence for the
charge transfer from the chains to ladders (approximately 0.16 holes per Cu
from x=0 to 12.2). The charge transfer was attributed to two different
mechanisms: (a) the Cu-O bond distance shrinkage on the ladder; (b) increase of
the interaction between two sublattices, resulting in Cu-O bonding between the
chains and ladders. The low temperature structural refinement resulted in the
similar conclusion, with a slight charge backflow to the chains.",1109.0868v1
2013-04-03,Tuning the Electronic and Optical properties of Graphene and Boron-Nitride Quantum Dots through Molecular Charge-transfer Interactions,"Spin-polarized first-principles calculations have been performed to tune the
electronic and optical properties of graphene (G) and boron-nitride (BN)
quantum dots (QDs) through molecular charge-transfer using
Tetracyanoquinodimethane (TCNQ) and Tetrathiafulvalene (TTF) as dopants. From
our calculations, we find that the nature of interaction between the dopants
and QDs is similar to the interaction between the dopants and their
two-dimensional counter parts of the QDs, namely, graphene and hexagonal
boron-nitride sheets. Based on the values of formation energy and distance
between QDs and dopants, we find that both the dopants are physisorbed on the
QDs. Also, we find that GQDs interact strongly with the dopants compared to the
BNQDS. Interestingly, though the dopants are physisorbed on QDs, their
interaction lead to a decrement in the HOMO-LUMO gap of QDs by more than half
of their original value. We have also observed a spin-polarized HOMO-LUMO gap
in certain QD-dopant complexes. Mulliken population analysis, Density of states
(DOS), projected DOS (pDOS) plots and optical conductivity calculations have
been performed to support and understand the reasons behind the above mentioned
findings.",1304.0972v1
2013-10-18,Origin of spectral purity and tuning sensitivity in a vortex-based spin transfer nano-oscillator,"We investigate the microwave characteristics of a spin transfer
nano-oscillator (STNO) based on coupled vortices as a function of the
perpendicular magnetic field $H_\perp$. While the generation linewidth displays
strong variations on $H_\perp$ (from 40 kHz to 1 MHz), the frequency tunability
in current remains almost constant (~7 MHz/mA). We demonstrate that our
vortex-based oscillator is quasi-isochronous independently of $H_\perp$, so
that the severe nonlinear broadening usually observed in STNOs does not exist.
Interestingly, this does not imply a loss of frequency tunability, which is
here governed by the current induced Oersted field. Nevertheless this is not
sufficient to achieve the highest spectral purity in the full range of
$H_\perp$ either: we show that the observed linewidth broadenings are due to
the excited mode interacting with a lower energy overdamped mode, which occurs
at the successive crossings between harmonics of these two modes. These
findings open new possibilities for the design of STNOs and the optimization of
their performance.",1310.4913v1
2014-04-30,Real-time imaging of spin-to-orbital angular momentum quantum state teleportation,"Quantum teleportation is a process in which an unknown quantum state is
transferred between two spatially separated subspaces of a bipartite quantum
system which share an entangled state and communicate classically. In the case
of photonic states, this process is probabilistic due to the impossibility of
performing a two-particle complete Bell state analysis with linear optics. In
order to achieve a deterministic teleportation scheme, harnessing other degrees
of freedom of a single particle, rather than a third particle, has been
proposed. Indeed, this leads to a novel type of deterministic teleportation
scheme, the so-called hybrid teleportation. Here we report the first
realization of photonic hybrid quantum teleportation from spin-to-orbital
angular momentum degrees of freedom. In our scheme, the polarization state of
photon A is transferred to orbital angular momentum of photon B. The teleported
states are visualized in real-time by means of an intensified CCD camera. The
quality of teleported states is verified by performing quantum state
tomography, which confirms an average fidelity higher than 99.4%. We believe
this experiment paves the route towards a novel way of quantum communication in
which encryption and decryption are carried out in naturally different Hilbert
spaces, and therefore may provide means of enhancing security.",1404.7573v1
2015-06-22,Exchange scattering as the driving force for ultrafast all-optical and bias-controlled reversal in ferrimagnetic metallic structures,"Experimentally observed ultrafast all-optical magnetization reversal in
ferrimagnetic metals and heterostructures based on antiferromagnetically
coupled ferromagnetic $d-$ and $f-$metallic layers relies on intricate energy
and angular momentum flow between electrons, phonons and spins. Here we treat
the problem of angular momentum transfer in the course of ultrafast
laser-induced dynamics in a ferrimagnetic metallic system using microscopical
approach based on the system of rate equations. We show that the magnetization
reversal is supported by a coupling of $d-$ and $f-$ subsystems to delocalized
$s-$ or $p-$ electrons. The latter can transfer spin between the two subsystems
in an incoherent way owing to the $(s;p)-(d;f)$ exchange scattering. Since the
effect of the external excitation in this process is reduced to the transient
heating of the mobile electron subsystem, we also discuss possibility to
trigger the magnetization reversal by applying a voltage bias pulse to
antiferromagnetically coupled metallic ferromagnetic layers embedded in point
contact or tunneling structures. We argue that such devices allow controlling
reversal with high accuracy. We also suggest to use the anomalous Hall effect
to register the reversal, thus playing a role of reading probes.",1506.06585v3
2016-08-19,Optical observation of spin-density-wave fluctuations in Ba122 iron-based superconductors,"In iron-based superconductors, a spin-density-wave (SDW) magnetic order is
suppressed with doping and unconventional superconductivity appears in close
proximity to the SDW instability. The optical response of the SDW order shows
clear gap features: substantial suppression in the low-frequency optical
conductivity, alongside a spectral weight transfer from low to high
frequencies. Here, we study the detailed temperature dependence of the optical
response in three different series of the Ba122 system
[Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$, Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ and
BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$]. Intriguingly, we found that the
suppression of the low-frequency optical conductivity and spectral weight
transfer appear at a temperature $T^{\ast}$ much higher than the SDW transition
temperature $T_{SDW}$. Since this behavior has the same optical feature and
energy scale as the SDW order, we attribute it to SDW fluctuations.
Furthermore, $T^{\ast}$ is suppressed with doping, closely following the doping
dependence of the nematic fluctuations detected by other techniques. These
results suggest that the magnetic and nematic orders have an intimate
relationship, in favor of the magnetic-fluctuation-driven nematicity scenario
in iron-based superconductors.",1608.05474v1
2016-08-24,Dynamic Stimulation of Superconductivity With Resonant Terahertz Ultrasonic Waves,"An experiment is proposed to stimulate a superconducting thin film with
terahertz (THz) acoustic waves, which is a regime not previously tested. For a
thin film on a piezoelectric substrate, this can be achieved by coupling the
substrate to a tunable coherent THz electromagnetic source. Suggested materials
for initial tests are a niobium film on a quartz substrate, with a BSCCO
intrinsic Josephson junction (IJJ) stack. This will create acoustic standing
waves on the nm scale in the thin film. A properly tuned standing wave will
enable electron diffraction across the Fermi surface, leading to electron
localization perpendicular to the substrate. This is expected to reduce the
effective dimensionality, and enhance the tendency for superconducting order
parallel to the substrate, even well above the superconducting critical
temperature. This enhancement can be observed by measuring the in-plane
critical current and the perpendicular tunneling gap. A similar experiment may
be carried out for a cuprate thin film, although the conduction electrons might
be more responsive to spin waves than to acoustic waves. These experiments
address a novel regime of large momentum transfer to the electrons, which
should be quite distinct from the more traditional regime of large energy
transfer obtained from direct electromagnetic stimulation. The experiments are
also motivated in part by novel theories of the superconducting state involving
dynamic charge-density waves and spin-density waves. Potential device
applications are discussed.",1609.02003v1
2016-12-20,Magnetism of PrFeAsO parent compound for iron-based superconductors: Mössbauer spectroscopy study,"Moessbauer spectroscopy measurements were performed for the temperature range
between 4.2 K and 300 K in a transmission geometry applying 14.41-keV resonant
line in 57Fe for PrFeAsO the latter being a parent compound of the iron-based
superconductors belonging to the '1111' family. It was found that an itinerant
3d magnetic order develops at about 165 K and it is accompanied by an
orthorhombic distortion of the chemical unit cell. A complete longitudinal 3d
incommensurate spin density wave (SDW) order develops at about 140 K.
Transferred hyperfine magnetic field generated by the praseodymium magnetic
order on iron nuclei is seen at 12.8 K and below, i.e., below magnetic order of
praseodymium magnetic moments. It is oriented perpendicular to the field of SDW
on iron nuclei. The shape of SDW is almost rectangular at low temperatures and
it transforms into roughly triangular form around 'nematic' transition at about
140 K. Praseodymium magnetic order leads to the substantial enhancement of SDW
due to the large orbital contribution to the magnetic moment of praseodymium. A
transferred field indicates presence of strong magnetic susceptibility
anisotropy in the [b-c] plane while following rotation of praseodymium magnetic
moments in this plane with lowering temperature. It was found that 'nematic'
phase region is a region of incoherent spin density wavelets typical for a
critical region.",1612.06776v3
2017-01-17,Signature of non-Markovianity in time-resolved energy transfer,"We explore signatures of the non-Markovianity in the time-resolved energy
transfer processes for quantum open systems. Focusing on typical systems such
as the exact solvable damped Jaynes-Cummings model and the general spin-boson
model, we establish quantitative links between the time-resolved energy current
and the symmetric logarithmic derivative quantum Fisher information (SLD-QFI)
flow, one of measures quantifying the non-Markovianity, within the framework of
non-Markovian master equations in time-local forms. From the relationships, we
find in the damped Jaynes-Cummings model that the SLD-QFI backflow from the
reservoir to the system always correlates with an energy backflow, thus we can
directly witness the non-Markovianity from the dynamics of the energy current.
In the spin-boson model, the relation is built on the rotating-wave
approximation, calibrated against exact numerical results, and proven reliable
in the weak coupling regime. We demonstrate that whether the non-Markovianity
guarantees the occurrence of an energy backflow depends on the bath spectral
function. For the Ohmic and sub-Ohmic cases, we show that no energy backflow
occurs and the energy current always flow out of the system even in the
non-Markovian regime. While in the super-Ohmic case, we observe that the
non-Markovian dynamics can induce an energy backflow.",1701.04570v2
2018-05-15,Uniform doping of graphene close to the charge neutrality point by polymer-assisted spontaneous assembly of molecular dopants,"Tuning the charge carrier density of two-dimensional (2D) materials by
incorporating dopants into the crystal lattice is a challenging task. An
attractive alternative is the surface transfer doping by adsorption of
molecules on 2D crystals, which can lead to ordered molecular arrays. However,
such systems, demonstrated in ultra-high vacuum conditions (UHV), are often
unstable in ambient conditions. Here we show that air-stable doping of
epitaxial graphene on SiC - achieved by spin-coating deposition of
2,3,5,6-tetrafluoro-tetracyano-quino-dimethane (F4TCNQ) incorporated in poly
(methyl-methacrylate) - proceeds via the spontaneous accumulation of dopants at
the graphene-polymer interface and by the formation of a charge-transfer
complex that yields low-disorder, charge-neutral graphene with carrier
mobilities ~70,000 cm2/Vs at cryogenic temperatures. The assembly of dopants on
2D materials assisted by a polymer matrix, demonstrated by spin coating
wafer-scale substrates in ambient conditions, opens up a scalable technological
route towards expanding the functionality of 2D materials.",1805.05644v1
2019-03-08,Substrate-induced half-metallic property in epitaxial silicene,"For most practical applications in electronic devices, two-dimensional
materials should be transferred onto semiconducting or insulating substrates,
since they are usually generated on metallic substrates. However, the transfer
often leads to wrinkles, damages, contaminations and so on which would destroy
the intrinsic properties of samples. Thus, generating two-dimensional materials
directly on nonmetallic substrates has been a desirable goal for a long time.
Here, via a swarm structure search method and density functional theory, we
employed an insulating N-terminated cubic boron nitride(111) surface as a
substrate for the generation of silicene. The result shows that the silicene
behaves as a ferromagnetic half-metal because of the strong interaction between
silicon and surface nitrogen atoms. The magnetic moments are mainly located on
surface nitrogen sites without bonding silicon atoms and the value is about
0.12 uB. In spin-up channel, it behaves as a direct band gap semiconductor with
a gap of around 1.35 eV, while it exhibits metallic characteristic in spin-down
channel, and the half-metallic band gap is about 0.11 eV. Besides, both the
magnetic and electronic properties are not sensitive to the external
compressive strain. This work maybe open a way for the utility of silicene in
spintronic field.",1903.03230v2
2019-06-15,Investigation of the quasi-free domain in deuteron-deuteron break-up using spin observables,"Precision measurements of vector and tensor analyzing powers of the $^{2}{\rm
H}(\vec d,dp){n}$ break-up process for configurations in the vicinity of the
quasi-free scattering regime with the neutron as spectator, are presented.
These measurements are performed with a polarized deuteron-beam with an energy
of 65 MeV/nucleon impinging on a liquid-deuterium target. The experiment was
conducted at the AGOR facility at KVI using the BINA 4$\pi$-detection system.
Events for which the final-state deuteron and proton are coplanar have been
analyzed and the data have been sorted for various momenta of the missing
neutron. In the limit of vanishing neutron momentum and at large
deuteron-proton momentum transfer, the data agree well with the measured and
theoretically predicted spin observables of the elastic deuteron-proton
scattering process. The agreement deteriorates rapidly with increasing neutron
momentum and/or decreasing momentum transfer from the deuteron beam to the
outgoing proton. This study reveals the presence of a significant contribution
of final-state interactions even at very small neutron momenta.",1906.06525v3
2019-09-27,Numerical approach to the semiclassical method of radiation emission for arbitrary electron spin and photon polarization,"We show how the semiclassical formulas for radiation emission of Baier,
Katkov and Strakhovenko for arbitrary initial and final spins of the electron
and arbitrary polarization of the emitted photon can be rewritten in a form
which numerically converges quickly. We directly compare the method in the case
of a background plane wave with the result obtained by using the Volkov state
solution of the Dirac equation, and confirm that we obtain the same result. We
then investigate the interaction of a circularly polarized short laser pulse
scattering with GeV electrons and see that the finite duration of the pulse
leads to a lower transfer of circular polarization than that predicted by the
known formulas in the monochromatic case. We also see how the transfer of
circular polarization from the laser beam to the gamma ray beam is gradually
deteriorated as the laser intensity increases, entering the nonlinear regime.
However, this is shown to be recovered if the scattered photon beam is
collimated to only allow for passage of photons emitted with angles smaller
than $1/\gamma$ with respect to the initial electron direction, where $\gamma$
is the approximately constant Lorentz factor of the electron. The obtained
formulas also allow us to answer questions regarding radiative polarization of
the emitting particles. In this respect we briefly discuss an application of
the present approach to the case of a bent crystal and high-energy positrons.",1909.12899v1
2019-12-20,Revisiting nuclear tunnelling in the aqueous ferrous-ferric electron transfer,"The aqueous ferrous-ferric system provides a classic example of an
electron-transfer process in solution. There has been a long standing argument
spanning more than three decades around the importance of nuclear tunnelling in
this system, with estimates based on Wolynes theory suggesting a quantum
correction factor of 65, while estimates based on a related spin-boson model
suggest a smaller factor of 7-36. Recently, we have shown that Wolynes theory
can break down for systems with multiple transition states leading to an
overestimation of the rate, and we suggest that a liquid system such as the one
investigated here may be particularly prone to this. We re-investigate this old
yet interesting system with the first application of the recently developed
golden-rule quantum transition-state theory (GR-QTST). We find that GR-QTST can
be applied to this complex system without apparent difficulties and that it
gives a prediction for the quantum rate 6 times smaller than that from Wolynes
theory. The fact that these theories give different results suggests that
although it is well known that the system can be treated using linear response
and therefore resembles a spin-boson model in the classical limit, this
approximation is questionable in the quantum case. It also intriguingly
suggests the possibility that the previous predictions were overestimating the
rate due to a break down of Wolynes theory.",1912.09811v2
2020-01-19,Oscillator realisations associated to the D-type Yangian: Towards the operatorial Q-system of orthogonal spin chains,"We present a family of novel Lax operators corresponding to representations
of the RTT-realisation of the Yangian associated with $D$-type Lie algebras.
These Lax operators are of oscillator type, i.e. one space of the operators is
infinite-dimensional while the other is in the first fundamental representation
of $\mathfrak{so}(2r)$. We use the isomorphism between the first fundamental
representation of $D_3$ and the $\mathbf{6}$ of $A_3$, for which the degenerate
oscillator type Lax matrices are known, to derive the Lax operators for $r=3$.
The results are used to generalise the Lax matrices to arbitrary rank for
representations corresponding to the extremal nodes of the simply laced Dynkin
diagram of $D_r$. The multiplicity of independent solutions at each extremal
node is given by the dimension of the fundamental representation. We further
derive certain factorisation formulas among these solutions and build transfer
matrices with oscillators in the auxiliary space from the introduced degenerate
Lax matrices. Finally, we provide some evidence that the constructed transfer
matrices are Baxter Q-operators for $\mathfrak{so}(2r)$ spin chains by
verifying certain QQ-relations for $D_4$ at low lengths.",2001.06825v3
2020-06-01,Doming and spin cascade in Ferric Haems: Femtosecond X-ray Absorption and X-ray Emission Studies,"The structure-function relationship is at the heart of biology and major
protein deformations are correlated to specific functions. In the case of heme
proteins, doming is associated with the respiratory function in hemoglobin and
myoglobin, while ruffling has been correlated with electron transfer processes,
such as in the case of Cytochrome c (Cyt c). The latter has indeed evolved to
become an important electron transfer protein in humans. In its ferrous form,
it undergoes ligand release and doming upon photoexcitation, but its ferric
form does not release the distal ligand, while the return to the ground state
has been attributed to thermal relaxation. Here, by combining femtosecond Fe
K-edge X-ray absorption near-edge structure (XANES) studies and femtosecond Fe
Kalpha and Kbeta X-ray emission spectroscopy (XES), we demonstrate that the
photocycle of ferric Cyt c is entirely due to a cascade among excited spin
states of the Iron ion, causing the ferric heme to undergo doming, which we
identify for the first time. We also argue that this pattern is common to all
ferric haems, raising the question of the biological relevance of doming in
such proteins.",2006.01234v1
2021-02-15,Exchange-Mediated Mutual Correlation and Dephasing in Free-Electron and Light Interactions,"The quantum world distinguishes itself from the classical world by being
governed by probability amplitudes rather than probabilities. On a
single-particle level, quantum phases can be manipulated leading to observable
interference patterns that can be used as a probe e.g. in matter wave
microscopy. But the quantum world bears even more fascinating effects when it
comes to the interplay between more than one particle. Correlations between
quantum particles such as entanglement can be exploited to speed up
computational algorithms or enable secure cryptography. Here, we propose and
numerically explore a thought experiment to address the question whether
quantum correlations between particles can be used in matter wave microscopy.
Specifically, we address the following questions: How can information be
transferred between two mutually spin-correlated free-electron wavepackets? Can
Coulomb and exchange correlations be linked to the decoherence mechanism of
matter waves? Using a time-dependent Hartree-Fock algorithm, we will show that
the exchange term has a substantial role in transferring the information
between two mutually spin-correlated electrons, whereas the Hartree potential
(or mean-field Coulomb potential) dominates the dephasing on a single-particle
level. Our findings might facilitate fermionic matter-wave interferometry
experiments in which it is possible to retrieve information about non-classical
correlations and the mechanism of decoherence in open versus closed quantum
systems.",2102.07439v2
2022-03-25,Tidal star-planet interaction and its observed impact on stellar activity in planet-hosting wide binary systems,"Tidal interaction between an exoplanet and its host star is a possible
pathway to transfer angular momentum between the planetary orbit and the
stellar spin. In cases where the planetary orbital period is shorter than the
stellar rotation period, this may lead to angular momentum being transferred
into the star's rotation, possibly counteracting the intrinsic stellar
spin-down induced by magnetic braking. Observationally, detecting altered
rotational states of single, cool field stars is challenging, as precise ages
for such stars are rarely available. Here we present an empirical investigation
of the rotation and magnetic activity of a sample of planet-hosting stars that
are accompanied by wide stellar companions. Without needing knowledge about the
absolute ages of the stars, we test for relative differences in activity and
rotation of the planet hosts and their co-eval companions, using X-ray
observations to measure the stellar activity levels. Employing three different
tidal interaction models, we find that host stars with planets that are
expected to tidally interact display elevated activity levels compared to their
companion stars. We also find that those activity levels agree with the
observed rotational periods for the host stars along the usual
rotation-activity relationships, implying that the effect is indeed caused by a
tidal interaction and not a purely magnetic interaction which would be expected
to affect the stellar activity, but not necessarily the rotation. We conclude
that massive, close-in planets have an impact on the stellar rotational
evolution, while the smaller, more distant planets do not have a significant
influence.",2203.13637v1
2022-05-22,Ferrocene as an iconic redox marker: from solution chemistry to molecular electronic devices,"Ferrocene, since its discovery in 1951, has been extensively exploited as a
redox probe in a variety of processes ranging from solution chemistry,
medicinal chemistry, supramolecular chemistry, surface chemistry to solid-state
molecular electronic and spintronic circuit elements to unravel electrochemical
charge-transfer dynamics. Ferrocene represents an extremely chemically and
thermally stable, and highly reproducible redox probe that undergoes reversible
one-electron oxidation and reduction occurring at the interfaces of
electrode/ferrocene solution in response to applied anodic and cathodic
potentials, respectively. It has been almost 70 years after its discovery and
has become one of the most widely studied and model organometallic compounds
not only for probing electrochemical charge-transfer process but also as
molecular building blocks for the synthesis of chiral organometallic catalysts,
potential drug candidates, polymeric compounds, electrochemical sensors, to
name a few. Ferrocene and its derivatives have been a breakthrough in many
aspects due to its versatile reactivity, fascinating chemical structures,
unconventional metal-ligand coordination, and the magic number of electrons (18
e-). The present review discusses the recent progress made towards
ferrocene-containing molecular systems exploited for redox reactions, surface
attachment, spin-dependent electrochemical process to probe spin polarization,
photo-electrochemistry, and integration into prototype molecular electronic
devices. Overall, the present reviews demonstrate a piece of collective
information about the recent advancements made towards the ferrocene and its
derivatives that have been utilized as iconic redox markers.",2205.10829v1
2022-06-06,The open Haldane-Shastry chain: thermodynamics and criticality,"We study the thermodynamics and criticality of the su($m|n$) Haldane-Shastry
chain of $BC_N$ type with a general chemical potential term. We first derive a
complete description of the spectrum of this model in terms of $BC_N$-type
motifs, from which we deduce a representation for the partition function as the
trace of a product of site-dependent transfer matrices. In the thermodynamic
limit, this formula yields a simple expression for the free energy per spin in
terms of the Perron-Frobenius eigenvalue of the continuum limit of the transfer
matrix. Evaluating this eigenvalue we obtain closed-form expressions for the
thermodynamic functions of the chains with $m,n\le2$. Using the motif-based
description of the spectrum derived here, we study in detail the ground state
of these models and their low energy excitations. In this way we identify the
critical intervals in chemical potential space and compute their corresponding
Fermi velocities. By contrast with previously studied models of this type, we
find in some cases two types of low energy excitations with linear
energy-quasimomentum relation. Finally, we determine the central charge of all
the critical phases by analyzing the low-temperature behavior of the expression
for the free energy per spin.",2206.02651v1
2022-06-10,Coherent transfer of the transverse momentum of an optical vortex beam to the motion of a single trapped ion,"We demonstrate the excitation, using a structured light beam carrying orbital
angular momentum, of the center of mass motion of a single atom in the
transverse direction to the beam's propagation. This interaction is achieved
with a vortex beam carrying one unit of orbital angular momentum and one unit
of spin/polarization angular momentum. Using a singly charged $^{40}$Ca$^+$
ion, cooled near the ground state of motion in the 3D harmonic potential of a
Paul trap, we probe the narrow S$_{1/2}$ to D$_{5/2}$ transition near
$729\,\mathrm{nm}$ on its motional sidebands to quantify the momentum transfer.
Exchange of quanta in the perpendicular direction to the beam's wave vector
$\mathbf{k}$ is observed in case of the vortex shaped beam, in strong contrast
to the absence of this spin-motion coupling for the case of a Gaussian beam. We
characterize the coherent interaction by an effective transverse Lamb-Dicke
factor $\eta^\mathrm{exp}_{\perp}=0.0062(5)$ which is in agreement with our
theoretical prediction $\eta^\mathrm{theo}_{\perp}=0.0057(1)$",2206.04894v1
2022-07-01,Valence Transition Theory of the Pressure-Induced Dimensionality Crossover in Superconducting Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$,"More than three decades after the discovery of superconductivity (SC) in the
cuprates, the nature of the ""normal"" state and the mechanism of SC remain
mysterious. One popular theoretical approach has been to treat the CuO$_2$
layer as coupled two-leg one-band Hubbard ladders. In the undoped two-leg
ladder spin-singlets occupy ladder rungs, and doped ladders are characterized
by superconducting correlations with quasi-long range order (quasi-LRO).
Pressure-induced SC in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ (SCCO) has long been
explained within one-band ladder theories. The dramatic pressure-driven
crossover from quasi one-to-two dimensional (1D-to-2D) transport and the
simultaneous vanishing of the spin gap due to ladder singlets in the metallic
state preceding SC however lie outside the scope of ladder-based theories.
Recent demonstration of rapid decay of superconducting correlations with
distance within a realistic multiband model of the cuprate ladder gives
additional credence to this viewpoint. Here we show that the assumption of
pressure-driven increase in hole concentration in the ladders cannot explain
the dimensionality crossover. The dimensionality crossover is due to discrete
change in Cu-ion ionicity accompanied by transfer of holes from the Cu to
O-ions, leading to ""negative charge-transfer gap"". Our theory of valence
transition driven dimensionality crossover in SCCO provides a generic
explanation of the very large increase in charge carrier density at critical
doping concentrations in both hole and electron doped layered cuprates We
propose a falsifiable experimental test of our theory.",2207.00628v2
2022-11-10,"Dynamics of ethylene groups and hyperfine interactions between donor and anion molecules in $λ$-type organic conductors studied by $^{69,71}$Ga-NMR spectroscopy","We present the results of $^{69,71}$Ga-NMR measurements on an organic
antiferromagnet $\lambda$-(BEDSe-TTF)$_2$GaCl$_4$
[BEDSe-TTF=bis(ethylenediseleno)tetrathiafulvalene], with comparison to reports
on $\lambda$-(BETS)$_2$GaCl$_4$ [BETS=bis(ethylenedithio)tetraselenafulvalene]
[T. Kobayashi et al., Phys. Rev. B 102, 235131 (2020)]. We found that the
dynamics of two crystallographically independent ethylene groups induce two
types of quadrupolar relaxation in the high-temperature region. As the ethylene
motion freezes, hyperfine (HF) interactions develop between $\pi$ spin and Ga
nuclear spin below 100 K, and thereby magnetic fluctuations of the $\pi$-spin
system are detected even from the Ga site. The HF interaction in
$\lambda$-(BETS)$_2$GaCl$_4$ was more than twice as large as in
$\lambda$-(BEDSe-TTF)$_2$GaCl$_4$, implying that the short contacts between Cl
atoms and the chalcogens of fulvalene part are essential for the transferred HF
interaction. We propose that NMR using nuclei in anion layers is useful for
studying interlayer interactions in organic conductors, which have not been
studied experimentally. In addition, because the mechanism of the transferred
HF interaction is considered to be the same as $\pi$-$d$ interaction in
isostructural Fe-containing $\lambda$-type salts, our findings aid in the
understanding of their physical properties.",2211.05877v1
2023-03-16,Analyzing and Unifying Robustness Measures for Excitation Transfer Control in Spin Networks,"Recent achievements in quantum control have resulted in advanced techniques
for designing controllers for applications in quantum communication, computing,
and sensing. However, the susceptibility of such systems to noise and
uncertainties necessitates robust controllers that perform effectively under
these conditions to realize the full potential of quantum devices. The
time-domain log-sensitivity and a recently introduced robustness infidelity
measure (RIM) are two means to quantify controller robustness in quantum
systems. The former can be found analytically, while the latter requires
Monte-Carlo sampling. In this work, the correlation between the log-sensitivity
and the RIM for evaluating the robustness of single excitation transfer
fidelity in spin chains and rings in the presence of dephasing is investigated.
We show that the expected differential sensitivity of the error agrees with the
differential sensitivity of the RIM, where the expectation is over the error
probability distribution. Statistical analysis also demonstrates that the
log-sensitivity and the RIM are linked via the differential sensitivity, and
that the differential sensitivity and RIM are highly concordant. This
unification of two means (one analytic and one via sampling) to assess
controller robustness in a variety of realistic scenarios provides a first step
in unifying various tools to model and assess robustness of quantum
controllers.",2303.09518v2
2023-06-16,Accretion spin-up of the massive component in the neutron star stripping model for short gamma-ray bursts,"In this paper, we use analytical methods to study the last stages of the
double neutron star (NS) system evolution. Depending on the initial masses of
the components, this evolution can occur either in the framework of the merging
scenario or in the NS stripping model. The main new ingredient of this work,
compared with the previous calculations, is accounting for accretion spin-up of
the massive component. This effect leads to a significant decrease in the
duration of the stable mass transfer of matter in the stripping mechanism.
Within the framework of the Newtonian approximation, we determine the mass
boundary between the merging and stripping scenarios. It is shown that this
boundary weakly depends on the total mass of the system and the specific form
of the NS equation of state and is determined mainly by the initial mass ratio
of the components. The stripping scenario is realized at M2/M1<0.8, so it
should make a large contribution to the population of close to us gravitational
wave events from NS-NS coalescing binaries and accompanying short gamma-ray
bursts. Nevertheless, the value obtained requires further clarification, taking
into account relativistic effects, possible non-conservative mass transfer,
etc.",2306.10088v2
2023-12-21,"Formation Pathways of the Spin-Correlated, Spatially Separated $^{1}$(T...T) State in the Singlet Fission Process of Perylene Diimide Stacks","For the theoretical screening of Singlet Fission (SF) rates in molecular
aggregates, commonly dimer model systems are employed. However, there is
experimental evidence, that the SF process proceeds from the $^{1}$(TT) state
via an triplet-triplet energy transfer process to a further intermediate: a
$^{1}$(T...T) state with two non-adjacent, spin-correlated triplets, which
cannot be captured by the dimer models. In this work, we extend Michl's
diabatic frontier orbital model to trimer systems, for which we automatically
generate the diabatic two and three-center couplings using symbolic algebra. We
apply this method to study the packing dependence of the $^{1}$(T...T)
formation in the perylene diimide (PDI) trimer stack. We find that efficient
triplet-triplet energy transfer is facilitated by structural motifs for which
also significant excimer character can be observed. Furthermore, the coupling
shows a local maximum for the structural motif that has been assigned to
efficient $^{1}$(TT) population. Employing second order perturbation theory, we
study the interference of the individual electronic pathways that arise in the
PDI trimer system, allowing us to reproduce the packing dependence of the SF
rates derived from the Redfield simulations in the work by Mirjani et. al.
(Phys. Chem. C 2014, 118, 26, 14192-14199).",2312.13966v1
2023-12-27,Optimal STIRAP shortcuts using the spin to spring mapping,"We derive shortcuts to adiabaticity maximizing population transfer in a
three-level $\Lambda$ quantum system, using the spin to spring mapping to
formulate the corresponding optimal control problem on the simpler system of a
classical driven dissipative harmonic oscillator. We solve the spring optimal
control problem and obtain analytical expressions for the impulses, the
durations of the zero control intervals and the singular control, which are the
elements composing the optimal pulse sequence. We also derive suboptimal
solutions for the spring problem, one with less impulses than the optimal and
others with smoother polynomial controls. We then apply the solutions derived
for the spring system to the original system, and compare the population
transfer efficiency with that obtained for the original system using numerical
optimal control. For all dissipation rates used, the efficiency of the optimal
spring control approaches that of the numerical optimal solution for longer
durations, with the approach accomplished earlier for smaller decay rates. The
efficiency achieved with the suboptimal spring control with less impulses is
very close to that of the optimal spring control in all cases, while that
obtained with polynomial controls lies below, and this is the price paid for
not using impulses, which can quickly build a nonzero population in the
intermediate state. The analysis of the optimal solution for the classical
driven dissipative oscillator is not restricted to the system at hand but can
also be applied in the transport of a coherent state trapped in a moving
harmonic potential and the transport of a mesoscopic object in stochastic
thermodynamics.",2312.16643v1
2024-01-02,Unraveling the mechanisms of triplet state formation in a heavy-atom free photosensitizer,"Triplet excited state generation plays a pivotal role in photosensitizers,
however the reliance on transition metals and heavy atoms can limit the utility
of these systems. In this study, we demonstrate that an interplay of competing
quantum effects control the high triplet quantum yield in a prototypical boron
dipyrromethene-anthracene (BD-An) donor-acceptor dyad photosensitizer, which is
only captured by an accurate treatment of both inner and outer sphere
reorganization energies. Our ab initio-derived model provides excellent
agreement with experimentally measured spectra, triplet yields and excited
state kinetic data, including the triplet lifetime. We find that rapid triplet
state formation occurs primarily via high-energy triplet states through both
spin-orbit coupled charge transfer and El-Sayed's rule breaking intersystem
crossing, rather than direct spin-orbit coupled charge transfer to the lowest
lying triplet state. Our calculations also reveal that competing effects of
nuclear tunneling, electronic state recrossing, and electronic polarizability
dictate the rate of non-productive ground state recombination. This study sheds
light on the quantum effects driving efficient triplet formation in the BD-An
system, and offers a promising simulation methodology for diverse photochemical
systems.",2401.01463v3
2001-10-20,Stellar Exotica produced from Stellar Encounters,"The importance of stellar encounters in producing stellar exotica in dense
stellar clusters is reviewed. We discuss how collisions between main-sequence
stars may be responsible for the production of blue stragglers in globular
clusters. We also discuss the possible pathways to the production of X-ray
binaries, cataclysmic variables, and millisecond pulsars in globular clusters.
Neutron stars in globular clusters are likely to exchange into binaries
containing moderate-mass main-sequence stars, replacing the lower-mass
components of the original systems. These binaries will become
intermediate-mass X-ray binaries (IMXBs), once the moderate-mass star evolves
off the main-sequence, as mass is transferred onto the neutron star possibly
spinning it up in the process. Such systems may be responsible for the
population of millisecond pulsars (MSPs) that has been observed in globular
clusters. Additionally, the period of mass-transfer (and thus X-ray visibility)
in the vast majority of such systems will have occurred 5 - 10 Gyr ago thus
explaining the observed relative paucity of X-ray binaries today, given the
large MSP population.",0110466v1
2004-12-05,Metal-poor Field Blue Stragglers: More Evidence for Mass Transfer,"We report radial velocity studies of five candidate metal-poor field blue
stragglers, all known to be deficient in lithium. Four of the five stars are
single-lined spectroscopic binaries, with periods ranging from 302 to 840 days,
and low orbital eccentricities, in agreement with similar behavior found for
other blue straggler candidates by Preston & Sneden (2000) and Carney et al.
(2001). The limited data available for lithium abundances indicate that all
blue straggler candidates have depleted lithium abundances. Our results show
higher values of v(rot) sin i for the binary stars than comparable temperature
constant-velocity stars. The orbital periods are too long for tidal effects to
now be important, implying that spin-up during mass transfer when the orbital
separations and periods were smaller is that cause of the enhanced rotation.",0412110v1
2005-05-26,Kelvin Helmholtz Instability and Circulation Transfer at an Isotropic-Anisotropic Superfluid Interface in a Neutron Star,"A recent laboratory experiment (Blaauwgeers et al. 2003) suggests that a
Kelvin-Helmholtz (KH) instability at the interface between two superfluids, one
rotating and anisotropic, the other stationary and isotropic, may trigger
sudden spin-up of the stationary superfluid. This result suggests that a KH
instability at the crust-core ($^1S_0$-$^3P_2$-superfluid) boundary of a
neutron star may provide a trigger mechanism for pulsar glitches. We calculate
the dispersion relation of the KH instability involving two different
superfluids including the normal fluid components and their effects on
stability, particularly entropy transport. We show that an entropy difference
between the core and crust superfluids reduces the threshold differential shear
velocity and threshold crust-core density ratio. We evaluate the wavelength of
maximum growth of the instability for neutron star parameters and find the
resultant circulation transfer to be within the range observed in pulsar
glitches.",0505529v1
2006-02-22,"A Grid of Relativistic, non-LTE Accretion Disk Models for Spectral Fitting of Black Hole Binaries","Self-consistent vertical structure models together with non-LTE radiative
transfer should produce spectra from accretion disks around black holes which
differ from multitemperature blackbodies at levels which may be observed. High
resolution, high signal-to-noise observations warrant spectral modeling which
both accounts for relativistic effects, and treats the physics of radiative
transfer in detail. In Davis et al. (2005) we presented spectral models which
accounted for non-LTE effects, Compton scattering, and the opacities due to
ions of abundant metals. Using a modification of this method, we have tabulated
spectra for black hole masses typical of Galactic binaries. We make them
publicly available for spectral fitting as an Xspec model. These models
represent the most complete realization of standard accretion disk theory to
date. Thus, they are well suited for both testing the theory's applicability to
observed systems and for constraining properties of the black holes, including
their spins.",0602499v1
1996-06-01,Enhancement of Persistent Current on Multichannel Ring,"We describe a ""train"" effect which may exist in small metallic and
semiconductor rings and might be associated with the long-standing problem of
the persistent current enhancement. The current is associated with the
cooperative motion of N electrons constituing the N-electron ""train"". The train
arises via an excitation or a backflow of spin waves or of interchannel charge
density sound modes. The impurities and defects have a little effect on the
""train"" current. The reason is that the ""train"" current is associated with a
small momentum transfer, which is much smaller than the momentum transfer of
the free electron current equal to 2 pi/L. For an illustration of the ""train""
effect we have calculated the persistent current in the framework of the Bethe
ansatz solutions for Hubbard model. The fractional M/N periodicities of the
persistent current serve as an indication of the electron ""train""",9605202v1
1996-12-31,"Electronic States of doped spin ladders (Sr,Ca)14Cu24O41","We examine the electronic states of Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ by the
ionic and cluster model approach. It is found that self-doped holes are likely
to stay on the chain at $x=0$ and the Ca substitution drives the holes to move
to the ladder. This feature is caused by the change of the positions of (Sr,Ca)
layers, which enhances the electrostatic potentials in the chain. The optical
conductivity is calculated applying the exact diagonalization method to small
Cu-O clusters. It is shown that the excitations below 2 eV are governed by the
ladder, giving rise to the spectral weight transfer from the charge-transfer
excitation around 2 eV to low energy Drude excitation, while the contribution
from the chain mainly emerges in higher energy region showing large weight
around 3 eV. These provide consistent explanation to recent experiment.",9612252v1
1998-12-08,Autocorrelations from the transfer matrix DMRG method,"Extending the transfer matrix DMRG algorithm, we are able to calculate
imaginary time spin autocorrelations with high accuracy (absolute error
$<10^{-6}$) over a wide temperature range ($0<\beta J<20$). After analytic
continuation using the rules of probability theory along with the entropic
prior (MaxEnt), we obtain real frequency spectra for the XY model, the
isotropic Heisenberg and the gaped Heisenberg-Ising model. Available exact
results in some limits allow for a critical evaluation of the quality of
answers expected from this procedure. We find that high precision data are
still insufficient for resolving specific lineshapes such as low frequency
divergences. However, the method is appropriate for identifying low temperature
gaps and peak positions.",9812117v1
1999-01-17,Numerical Renormalization Approach to Two-Dimensional Quantum Antiferromagnets with Valence-Bond-Solid Type Ground State,"We study the ground-state properties of the two-dimensional quantum spin
systems having the valence-bond-solid (VBS) type ground states. The
``product-of-tensors'' form of the ground-state wavefunction of the system is
utilized to associate it with an equivalent classical lattice statistical model
which can be treated by the transfer-matrix method. For diagonalization of the
transfer matrix, we employ the product-wavefunction renormalization group
method which is a variant of the density-matrix renormalization group method.
We obtain the correlation length and the sublattice magnetization accurately.
For the anisotropically ``deformed'' S=3/2 VBS model on the honeycomb lattice,
we find that the correlation length as a function of the deformation parameter
behaves very much alike as that in the S=3/2 VBS chain.",9901155v1
1999-04-01,Output coupling of a Bose-Einstein condensate formed in a TOP trap,"Two distinct mechanisms are investigated for transferring a pure 87Rb
Bose-Einstein condensate in the F = 2, mF = 2 state into a mixture of
condensates in all the mF states within the F = 2 manifold. Some of these
condensates remain trapped whilst others are output coupled in the form of an
elementary pulsed atom laser. Here we present details of the condensate
preparation and results of the two condensate output coupling schemes. The
first scheme is a radio frequency technique which allows controllable transfer
into available mF states, and the second makes use of Majorana spin flips to
equally populate all the manifold sub-states.",9904007v1
2000-10-24,Electron energy relaxation in the presence of magnetic impurities,"We study inelastic electron-electron scattering mediated by the exchange
interaction of electrons with magnetic impurities, and find the kernel of the
corresponding two-particle collision integral. In a wide region of parameters,
the kernel K is proportional to the inverse square of the transferred energy,
$K\propto J^4/E^2$. The exchange constant J is renormalized due to the Kondo
effect, yielding an additional weak dependence of K on the energies of the
colliding electrons. At small energy transfers, the $1/E^2$ divergence is cut
off; the cut-off energy is determined by the dynamics of the impurity spins.
The obtained results may provide a quantitative explanation of the experiments
of Pothier et al. [Phys. Rev. Lett. 79, 3490 (1997)] on anomalously strong
energy relaxation in short metallic wires.",0010379v2
2001-06-25,A supersymmetric U_{q}[osp(2|2)]-extended Hubbard model with boundary fields,"A strongly correlated electron system associated with the quantum
superalgebra ${U}_q[{osp}(2|2)]$ is studied in the framework of the quantum
inverse scattering method. By solving the graded reflection equation, two
classes of boundary-reflection $K$-matrices leading to four kinds of possible
boundary interaction terms are found. Performing the algebraic Bethe ansatz, we
diagonalize the two-level transfer matrices which characterize the charge and
the spin degrees of freedom, respectively. The Bethe-ansatz equations, the
eigenvalues of the transfer matrices and the energy spectrum are presented
explicitly. We also construct two impurities coupled to the boundaries. In the
thermodynamic limit, the ground state properties and impurity effects are
discussed.",0106511v1
2001-10-06,The 8V CSOS model and the $sl_2$ loop algebra symmetry of the six-vertex model at roots of unity,"We review an algebraic method for constructing degenerate eigenvectors of the
transfer matrix of the eight-vertex Cyclic Solid-on-Solid lattice model (8V
CSOS model), where the degeneracy increases exponentially with respect to the
system size.
  We consider the elliptic quantum group $E_{\tau, \eta}(sl_2)$ at the discrete
coupling constants: $2N \eta = m_1 + i m_2 \tau$, where $N, m_1$ and $m_2$ are
integers. Then we show that degenerate eigenvectors of the transfer matrix of
the six-vertex model at roots of unity in the sector $S^Z \equiv 0$ (mod $N$)
are derived from those of the 8V CSOS model, through the trigonometric limit.
They are associated with the complete $N$ strings. From the result we see that
the dimension of a given degenerate eigenspace in the sector $S^Z \equiv 0$
(mod $N$) of the six-vertex model at $N$th roots of unity is given by
$2^{2S_{max}^Z/N}$, where $S_{max}^Z$ is the maximal value of the total spin
operator $S^Z$ in the degenerate eigenspace.",0110121v1
2003-11-23,Double exchange mechanisms for Mn doped III-V ferromagnetic semiconductors,"A microscopic model of indirect exchange interaction between transition metal
impurities in dilute magnetic semiconductors (DMS) is proposed. The
hybridization of the impurity d-electrons with the heavy hole band states is
largely responsible for the transfer of electrons between the impurities,
whereas Hund rule for the electron occupation of the impurity d-shells makes
the transfer spin selective. The model is applied to such systems as $n-$type
GaN:Mn and $p-$type (Ga,Mn)As, $p-$type (Ga,Mn)P. In $n-$type DMS with
Mn$^{2+/3+}$ impurities the exchange mechanisms is rather close to the
kinematic exchange proposed by Zener for mixed-valence Mn ions. In $p-$type DMS
ferromagnetism is governed by the kinematic mechanism involving the kinetic
energy gain of heavy hole carriers caused by their hybridization with 3d
electrons of Mn$^{2+}$ impurities. Using the molecular field approximation the
Curie temperatures $T_C$ are calculated for several systems as functions of the
impurity and hole concentrations. Comparison with the available experimental
data shows a good agreement.",0311525v1
2003-12-16,Characterization of low-energy magnetic excitations in chromium,"The low-energy excitations of Cr, i.e. the Fincher-Burke (FB) modes, have
been investigated in the transversely polarized spin-density-wave phase by
inelastic neutron scattering using a single-(Q+-) crystal with a propagation
vector (Q+-) parallel to [0,0,1]. The constant-momentum-transfer scans show
that the energy spectra consist of two components, namely dispersive FB modes
and an almost energy-independent cross section. Most remarkably, we find that
the spectrum of the FB modes exhibits one peak at 140 K near Q = (0,0,0.98) and
two peaks near Q = (0,0,1.02), respectively. This is surprising because Cr
crystallizes in a centro-symmetric bcc structure. The asymmetry of those energy
spectra decreases with increasing temperature. In addition, the observed
magnetic peak intensity is independent of Q suggesting a transfer of
spectral-weight between the upper and lower FB modes. The energy-independent
cross section is localized only between the incommensurate peaks and develops
rapidly with increasing temperature.",0312383v1
2005-07-26,Fourier-Transformed Local Density of States and Tunneling into a $D$-Wave Superconductor with Bosonic Modes,"We analyze the effects of the electronic coupling to bosonic modes in a
d-wave superconductor. The role of the scattering due to boson on the momentum
transfer between electronic states in the Brilloine zone is addressed. We
consider specific examples of $B_{1g}$ phonon, breathing mode phonon and spin
resonance at $(\pi,\pi)$. The Fourier spectrum of the energy derivative local
density of states (LDOS) is calculated. To properly calibrate the effects of
different modes we fix the quasipartilce renormalization at specific momentum
points. It is found that the $B_{1g}$ mode with highly anisotropic
momentum-dependent coupling matrix element gives rise to well definded features
in the Fourier spectrum, at the energy of mode plus gap, with a momentum
transfer along the Cu-O bond direction of cuprates. This result is in a
striking contrast to the cases of the coupling to other modes and also to the
case of no mode coupling. The origin of this difference is explored in detail.
A comparison with the recent STM experiments is briefly discussed.",0507610v1
2006-01-11,Temperature dependence of spectral functions for the one-dimensional Hubbard model: comparison with experiments,"We study the temperature dependence of the single particle spectral function
as well as of the dynamical spin and charge structure factors for the
one-dimensional Hubbard model using the finite temperature auxiliary field
quantum Monte Carlo algorithm. The parameters of our simulations are chosen so
to at best describe the low temperature photoemission spectra of the organic
conductor TTF-TCNQ. Defining a magnetic energy scale, T_J, which marks the
onset of short ranged 2k_f magnetic fluctuations, we conclude that for
temperatures T < T_J the ground state features of the single particle spectral
function are apparent in the finite temperature data. Above T_J spectral weight
transfer over a scale set by the hopping t is observed. In contrast,
photoemission data points to a lower energy scale below which spectral weight
transfer occurs. Discrepancies between Hubbard model calculations and
experiments are discussed.",0601222v1
2006-02-17,On the Degenerate Multiplicity of the $sl_2$ Loop Algebra for the 6V Transfer Matrix at Roots of Unity,"We review the main result of cond-mat/0503564. The Hamiltonian of the XXZ
spin chain and the transfer matrix of the six-vertex model has the $sl_2$ loop
algebra symmetry if the $q$ parameter is given by a root of unity,
$q_0^{2N}=1$, for an integer $N$. We discuss the dimensions of the degenerate
eigenspace generated by a regular Bethe state in some sectors, rigorously as
follows: We show that every regular Bethe ansatz eigenvector in the sectors is
a highest weight vector and derive the highest weight ${\bar d}_k^{\pm}$, which
leads to evaluation parameters $a_j$. If the evaluation parameters are
distinct, we obtain the dimensions of the highest weight representation
generated by the regular Bethe state.",0602427v1
1999-10-19,Measurement of diffractive photoproduction of vector mesons at large momentum transfer at HERA,"Elastic and proton-dissociative photoproduction of $\rho^0$, $\phi$ and
$J/\psi$ vector mesons ($\gamma p\to Vp$, $\gamma p\to VN$, respectively) have
been measured in e^+p interactions at HERA up to -t=3 GeV$^2$, where t is the
four-momentum transfer squared at the photon-vector meson vertex. The analysis
is based on a data sample in which photoproduction reactions were tagged by
detection of the scattered positron in a special-purpose calorimeter. This
limits the photon virtuality, Q^2, to values less than 0.01 GeV$^2$, and
selects a $\gamma p$ average center-of-mass energy of <W> = 94 GeV. Results for
the differential cross sections, d$\sigma$/d$t$, for $\rho^0$, $\phi$ and
$J/\psi$ mesons are presented and compared to the results of recent QCD
calculations. Results are also presented for the t-dependence of the pion-pair
invariant-mass distribution in the $\rho^0$ mass region and of the spin-density
matrix elements determined from the decay-angle distributions. The Pomeron
trajectory has been derived from measurements of the W dependence of the
elastic differential cross sections d$\sigma$/d$t$ for both $\rho^0$ and $\phi$
mesons.",9910038v1
2002-12-06,First Measurement of Transferred Polarization in the Exclusive e p --> e' K+ Lambda Reaction,"The first measurements of the transferred polarization for the exclusive ep
--> e'K+ Lambda reaction have been performed in Hall B at the Thomas Jefferson
National Accelerator Facility using the CLAS spectrometer. A 2.567 GeV electron
beam was used to measure the hyperon polarization over a range of Q2 from 0.3
to 1.5 (GeV/c)2, W from 1.6 to 2.15 GeV, and over the full center-of-mass
angular range of the K+ meson. Comparison with predictions of hadrodynamic
models indicates strong sensitivity to the underlying resonance contributions.
A non-relativistic quark model interpretation of our data suggests that the
s-sbar quark pair is produced with spins predominantly anti-aligned.
Implications for the validity of the widely used 3P0 quark-pair creation
operator are discussed.",0212014v1
2006-03-20,Diffractive Photoproduction of Rho Mesons with Large Momentum Transfer at HERA,"The diffractive photoproduction of rho mesons, e p \to e rho Y, with large
momentum transfer squared at the proton vertex, |t|, is studied with the H1
detector at HERA using an integrated luminosity of 20.1 pb^{-1}. The
photon-proton centre of mass energy spans the range 75 < W < 95 GeV, the photon
virtuality is restricted to Q^2 < 0.01 GeV^2 and the mass M_Y of the proton
remnant is below 5 GeV. The t dependence of the cross section is measured for
the range 1.5 < |t| < 10.0 GeV^2 and is well described by a power law, dsigma/
d|t| \propto |t|^{-n}. The spin density matrix elements, which provide
information on the helicity structure of the interaction, are extracted using
measurements of angular distributions of the rho decay products. The data
indicate a violation of s-channel helicity conservation, with contributions
from both single and double helicity-flip being observed. The results are
compared to the predictions of perturbative QCD models.",0603038v1
1993-11-29,The analysis of Polyakov loop and spin correlators in finite volumes,"We derive an analytic expression for point to point correlation functions of
the Polyakov loop based on the transfer matrix formalism. The contributions
from the eigenvalues of the transfer matrix including and beyond the mass gap
are investigated both for the $2d$ Ising model and in finite temperature
$SU(2)$ gauge theory. We find that the leading matrix element shows similar
scaling properties in both models. Just above the critical point we obtain for
$SU(2)$ a Debye screening mass $~\mu_D/T\approx4~$, independent of the volume.
Sorry, figures are not included and can be sent by ordinary mail.",9311055v1
2000-10-02,Bounds in proton-proton elastic scattering at low momentum transfer,"We present a bound on the imaginary part of the single helicity-flip
amplitude for spin 1/2-spin 1/2 scattering at small momentum transfer. The
variational method of Lagrange multipliers is employed to optimize the
single-flip amplitude using the values of the total cross section, the elastic
cross section and diffraction slope as equality constraints in addition to the
inequality constraints resulting from unitarity. Such bounds provide important
information related to the determination of polarization of a proton beam. In
the case of elastic proton collisions the analyzing power at small scattering
angles inside the Coulomb Nuclear Interference region offers a method of
measuring the polarization of a proton beam, the accuracy of the polarization
measurement depending on the single helicity-flip amplitude. The bound obtained
on the imaginary part of the single helicity-flip amplitude indicates that the
analyzing power for proton-proton collisions in the Coulomb nuclear
interference region should take positive nonzero values at high energies.",0010014v1
2001-03-01,On a possible manifestation of f_1 trajectory in J/psi photoproduction,"We analyze a possible manifestation of f_1-trajectory in elastic J/psi
photoproduction at high energy and large momentum transfer. Inspite of the
small contribution of f_1-trajectory in total cross sections, it becomes
significant in various spin observables. In particular, we show that the
crucial test for f_1-exchange can be made by measuring the single beam- and
double parity- and beam-target asymmetries at large momentum transfers, where a
strong deviation from the exchange of conventional Pomerons is expected. This
effect is caused by the interference of natural (Pomeron) and unnatural (f_1)
parity exchange parts of amplitude in the region where their contributions
become comparable to each other and might be interesting to observe in
forthcoming experiments, if feasible. .",0103004v1
2001-04-06,Evidence for the flavor singlet axial anomaly related effects in $φ$ meson electromagnetic production at large momentum transfers,"The gluonic contributions to the conventional PCAC formulas due to flavor
singlet axial anomaly have been instrumental in explaining the mass of the
$\eta^{\prime}$ and providing a plausible explanation for solving the spin
crisis. We show that they also play an important role in the description of
photo- and electroproduction of vector mesons at low energy and high momentum
transfers. We calculate the contributions of this type to $\phi$ meson
electromagnetic production in a model, which contains also a soft pomeron, and
find agreement with recent CLAS data.",0104070v3
1995-12-13,On the combinatorics of row and corner transfer matrices of the $A_{n-1}^{(1)}$ restricted face models,"We establish a weight-preserving bijection between the index sets of the
spectral data of row-to-row and corner transfer matrices for
$U_q\widehat{sl(n)}$ restricted interaction round a face (IRF) models. The
evaluation of momenta by adding Takahashi integers in the spin chain language
is shown to directly correspond to the computation of the energy of a path on
the weight lattice in the two-dimensional model. As a consequence we derive
fermionic forms of polynomial analogues of branching functions for the cosets
${(A^{(1)}_{n-1})_{\ell -1}\otimes (A^{(1)}_{n-1})_{1}} \over
(A^{(1)}_{n-1})_{\ell}$, and establish a bosonic-fermionic polynomial identity.",9512095v2
2001-04-12,Loop symmetry of integrable vertex models at roots of unity,"It has been recently discovered in the context of the six vertex or XXZ model
in the fundamental representation that new symmetries arise when the anisotropy
parameter $(q+q^{-1})/2$ is evaluated at roots of unity $q^{N}=1$. These new
symmetries have been linked to an $U(A^{(1)}_1)$ invariance of the transfer
matrix and the corresponding spin-chain Hamiltonian.In this paper these results
are generalized for odd primitive roots of unity to all vertex models
associated with trigonometric solutions of the Yang-Baxter equation by invoking
representation independent methods which only take the algebraic structure of
the underlying quantum groups $U_q(\hat g)$ into account. Here $\hat g$ is an
arbitrary Kac-Moody algebra. Employing the notion of the boost operator it is
then found that the Hamiltonian and the transfer matrix of the integrable model
are invariant under the action of $U(\hat{g})$. For the simplest case $\hat
g=A_1^{(1)}$ the discussion is also extended to even primitive roots of unity.",0104120v2
2005-04-13,Bethe Ansatz derived from the functional relations of the open XXZ chain for new special cases,"The transfer matrix of the general integrable open XXZ quantum spin chain
obeys certain functional relations at roots of unity. By exploiting these
functional relations, we determine the Bethe Ansatz solution for the transfer
matrix eigenvalues for the special cases that all but one of the boundary
parameters are zero, and the bulk anisotropy parameter is \eta = i\pi/3, i\pi/5
,... In an Addendum, these results are extended to the cases that any two of
the boundary parameters {\alpha_-, \alpha_+,\beta_-, \beta_+} are arbitrary and
the remaining boundary parameters are either \eta or i \pi/2.",0504124v4
2005-11-12,Q-operator and T-Q relation from the fusion hierarchy,"We propose that the Baxter $Q$-operator for the spin-1/2 XXZ quantum spin
chain is given by the $j\to \infty$ limit of the transfer matrix with spin-$j$
(i.e., $(2j+1)$-dimensional) auxiliary space. Applying this observation to the
open chain with general (nondiagonal) integrable boundary terms, we obtain from
the fusion hierarchy the $T$-$Q$ relation for {\it generic} values (i.e. not
roots of unity) of the bulk anisotropy parameter. We use this relation to
determine the Bethe Ansatz solution of the eigenvalues of the fundamental
transfer matrix. This approach is complementary to the one used recently to
solve the same model for the roots of unity case.",0511134v2
2005-12-14,$T$-$Q$ relation and exact solution for the XYZ chain with general nondiagonal boundary terms,"We propose that the Baxter's $Q$-operator for the XYZ quantum spin chain with
open boundary conditions is given by the $j\to \infty$ limit of the
corresponding transfer matrix with spin-$j$ (i.e., $(2j+1)$-dimensional)
auxiliary space. The associated $T$-$Q$ relation is derived from the fusion
hierarchy of the model. We use this relation to determine the Bethe Ansatz
solution of the eigenvalues of the fundamental transfer matrix. This solution
yields the complete spectrum of the Hamiltonian.",0512154v3
2006-09-16,Bethe Ansatz and boundary energy of the open spin-1/2 XXZ chain,"We review recent results on the Bethe Ansatz solutions for the eigenvalues of
the transfer matrix of an integrable open XXZ quantum spin chain using
functional relations which the transfer matrix obeys at roots of unity. First,
we consider a case where at most two of the boundary parameters
{{$\alpha_-$,$\alpha_+$,$\beta_-$,$\beta_+$}} are nonzero. A generalization of
the Baxter $T-Q$ equation that involves more than one independent $Q$ is
described. We use this solution to compute the boundary energy of the chain in
the thermodynamic limit. We conclude the paper with a review of some results
for the general integrable boundary terms, where all six boundary parameters
are arbitrary.",0609114v2
2006-10-09,The Analytic Bethe Ansatz for a Chain with Centrally Extended su(2|2) Symmetry,"We investigate the integrable structure of spin chain models with centrally
extended su(2|2) and psu(2,2|4) symmetry. These chains have their origin in the
planar AdS/CFT correspondence, but they also contain the one-dimensional
Hubbard model as a special case. We begin with an overview of the
representation theory of centrally extended su(2|2). These results are applied
in the construction and investigation of an interesting S-matrix with su(2|2)
symmetry. In particular, they enable a remarkably simple proof of the
Yang-Baxter relation. We also show the equivalence of the S-matrix to Shastry's
R-matrix and thus uncover a hidden supersymmetry in the integrable structure of
the Hubbard model. We then construct eigenvalues of the corresponding transfer
matrix in order to formulate an analytic Bethe ansatz. Finally, the form of
transfer matrix eigenvalues for models with psu(2,2|4) symmetry is sketched.",0610017v2
2006-11-21,First Measurement of Beam-Recoil Observables Cx and Cz in Hyperon Photoproduction,"Spin transfer from circularly polarized real photons to recoiling hyperons
has been measured for the reactions $\vec\gamma + p \to K^+ + \vec\Lambda$ and
$\vec\gamma + p \to K^+ + \vec\Sigma^0$. The data were obtained using the CLAS
detector at Jefferson Lab for center-of-mass energies $W$ between 1.6 and 2.53
GeV, and for $-0.85<\cos\theta_{K^+}^{c.m.}< +0.95$. For the $\Lambda$, the
polarization transfer coefficient along the photon momentum axis, $C_z$, was
found to be near unity for a wide range of energy and kaon production angles.
The associated transverse polarization coefficient, $C_x$, is smaller than
$C_z$ by a roughly constant difference of unity. Most significantly, the {\it
total} $\Lambda$ polarization vector, including the induced polarization $P$,
has magnitude consistent with unity at all measured energies and production
angles when the beam is fully polarized. For the $\Sigma^0$ this simple
phenomenology does not hold. All existing hadrodynamic models are in poor
agreement with these results.",0611034v1
1999-11-15,Reaction mechanism and characteristics of T_{20} in d + ^3He backward elastic scattering at intermediate energies,"For backward elastic scattering of deuterons by ^3He, cross sections \sigma
and tensor analyzing power T_{20} are measured at E_d=140-270 MeV. The data are
analyzed by the PWIA and by the general formula which includes virtual
excitations of other channels, with the assumption of the proton transfer from
^3He to the deuteron. Using ^3He wave functions calculated by the Faddeev
equation, the PWIA describes global features of the experimental data, while
the virtual excitation effects are important for quantitative fits to the
T_{20} data. Theoretical predictions on T_{20}, K_y^y (polarization transfer
coefficient) and C_{yy} (spin correlation coefficient) are provided up to GeV
energies.",9911044v1
2002-01-03,"RPWIA analysis of dynamical relativistic contributions in $^{16}O(\vec{e},e'\vec{p})$ reactions","Coincidence scattering of polarized electrons from nuclei with polarization
transfer to outgoing nucleons is studied within the context of relativistic
mean field theory. Effects introduced by the dynamical enhancement of the lower
components of the bound nucleon wave function are analyzed for the polarized
response functions and transferred polarization asymmetries assuming the
relativistic plane-wave impulse approximation (RPWIA). Results obtained by
projecting out the negative-energy components are compared with the
fully-relativistic calculation for proton knockout from $p_{1/2}$ and $p_{3/2}$
shells in $^{16}O$ for a variety of kinematic situations. The crucial role
played by the relativistic dynamics in some spin-dependent observables is
clearly manifested even for low/medium values of the missing momentum. The
degree to which knowledge about nucleon form factors can be extracted from
analyses of this type of process is also discussed.",0201005v2
2002-01-16,Relativistic vs. Non-relativistic Nuclear Models,"Both the relativistic and non-relativistic model explain very well low-energy
nuclear phenomena, but in a physically different way from each other. There
seems to be no low-energy phenomenon to answer which model is more reasonable.
In order to explore a difference between two models, high momentum transfer
phenomena are investigated. First it is shown that the neutron spin-orbit
charge density in the relativistic model reproduces very well experimental data
on elastic electron scattering which have not been explained in the
non-relativistic model. Next it is predicted that the relativistic Coulomb sum
value is strongly quenched, compared with the non-relativistic one. This
quenching is owing to the anti-nucleon degrees of freedom, which make the
nucleon size larger and equivalently the vector-meson mass smaller in nuclear
medium. New experiment on the Coulomb sum values around the momentum transfer
1GeV is expected to distinguish the relativistic from the non-relativistic
model.",0201035v1
2002-11-07,Relativity in polarized electron scattering observables,"Coincidence scattering of polarized electrons from nuclei with polarization
transfer to outgoing nucleons is studied within the context of relativistic
mean field theory. Effects introduced by the dynamical enhancement of the lower
components of the bound and scattered nucleon wave functions are analyzed for
the polarized response functions and transferred polarization asymmetries.
Results obtained by projecting out the negative-energy components are compared
with the fully-relativistic calculation. The crucial role played by the
relativistic dynamics in some spin-dependent observables is clearly manifested
even for low/medium values of the missing momentum. Kinematical relativistic
effects are also analyzed. A discussion of the factorization approach and the
mechanism for its breakdown is also briefly presented.",0211019v2
2004-11-17,Deuteron-proton charge exchange reaction at small transfer momentum,"The charge-exchange reaction pd -> npp at 1 GeV projectile proton energy is
studied. This reaction is considered in a special kinematics, when the transfer
momentum from the beam proton to fast outgoing neutron is close to zero. Our
approach is based on the Alt-Grassberger-Sandhas formulation of the
multiple-scattering theory for the three-nucleon system. The matrix inversion
method has been applied to take account of the final state interaction (FSI)
contributions. The differential cross section, tensor analyzing power
$C_{0,yy}$, vector-vector $C_{y,y}$ and vector-tensor $C_{y,xz}$ spin
correlation parameters of the initial particles are presented. It is shown,
that the FSI effects play a very important role under such kinematical
conditions. The high sensitivity of the considered observables to the
elementary nucleon-nucleon amplitudes has been obtained.",0411067v1
2006-08-24,Cooling and trapping of ultra-cold strontium isotopic mixtures,"We present the simultaneous cooling and trapping of an isotopic mixture in a
magneto-optical trap and we describe the transfer of the mixture into a
conservative, far-off resonant dipole trap. The mixture is prepared with a new
technique that applies to intermediate and heavy alkaline earth like atoms. In
this work, 88Sr and 86Sr are simultaneously loaded first into the
magneto-optical trap operated on the 1S0-3P1 spin-forbidden line at 689 nm, and
then transferred into the dipole trap. We observe fast inter-species
thermalization in the dipole trap which allows one to set a lower bound on the
88Sr-86Sr elastic cross section.",0608233v1
2003-02-08,Boundary of Quantum Evolution under Decoherence,"Relaxation effects impose fundamental limitations on our ability to
coherently control quantum mechanical phenomena. In this letter, we establish
physical limits on how closely can a quantum mechanical system be steered to a
desired target state in the presence of relaxation. In particular, we
explicitly compute the maximum coherence or polarization that can be
transferred between coupled nuclear spins in the presence of very general
decoherence mechanisms that include cross-correlated relaxation. We give
analytical expressions for the control laws (pulse sequences) which achieve
these physical limits and provide supporting experimental evidence.
Exploitation of cross-correlation effects has recently led to the development
of powerful methods in NMR spectroscopy to study very large biomolecules in
solution. We demonstrate with experiments that the optimal pulse sequences
provide significant gains over these state of the art methods, opening new
avenues for spectroscopy of much larger proteins. Surprisingly, in spite of
very large relaxation rates, optimal control can transfer coherence without any
loss when cross-correlated relaxation rates are tuned to auto-correlated
relaxation rates.",0302060v1
2004-07-05,High efficiency transfer of quantum information and multi-particle entanglement generation in translation invariant quantum chains,"We demonstrate that a translation invariant chain of interacting quantum
systems can be used for high efficiency transfer of quantum entanglement and
the generation of multi-particle entanglement over large distances and between
arbitrary sites without the requirement of precise spatial or temporal control.
The scheme is largely insensitive to disorder and random coupling strengths in
the chain. We discuss harmonic oscillator systems both in the case of arbitrary
Gaussian states and in situations when at most one excitation is in the system.
The latter case which we prove to be equivalent to an xy-spin chain may be used
to generate genuine multi particle entanglement. Such a 'quantum data bus' may
prove useful in future solid state architectures for quantum information
processing.",0407034v2
2005-11-02,Entanglement of remote atomic qubits,"We report observations of entanglement of two remote atomic qubits, achieved
by generating an entangled state of an atomic qubit and a single photon at Site
A, transmitting the photon to Site B in an adjacent laboratory through an
optical fiber, and converting the photon into an atomic qubit. Entanglement of
the two remote atomic qubits is inferred by performing, locally, quantum state
transfer of each of the atomic qubits onto a photonic qubit and subsequent
measurement of polarization correlations in violation of the Bell inequality
|S| <2. We experimentally determine S =2.16 +/- 0.03. Entanglement of two
remote atomic qubits, each qubit consisting of two independent spin wave
excitations, and reversible, coherent transfer of entanglement between matter
and light, represent important advances in quantum information science.",0511012v1
2007-05-16,Charge-Transfer Excitations in One-Dimensional Dimerized Mott Insulators,"We investigate the optical properties of one-dimensional (1D) dimerized Mott
insulators using the 1D dimerized extended Hubbard model. Numerical
calculations and a perturbative analysis from the decoupled-dimer limit clarify
that there are three relevant classes of charge-transfer (CT) states generated
by photoexcitation: interdimer CT unbound states, interdimer CT exciton states,
and intradimer CT exciton states. This classification is applied to
understanding the optical properties of an organic molecular material,
1,3,5-trithia-2,4,6-triazapentalenyl (TTTA), which is known for its
photoinduced transition from the dimerized spin-singlet phase to the regular
paramagnetic phase. We conclude that the lowest photoexcited state of TTTA is
the interdimer CT exciton state and the second lowest state is the intradimer
CT exciton state.",0705.2303v1
2007-06-14,Exactly solvable interacting vertex models,"We introduce and solvev a special family of integrable interacting vertex
models that generalizes the well known six-vertex model. In addition to the
usual nearest-neighbor interactions among the vertices, there exist extra
hard-core interactions among pair of vertices at larger distances.The
associated row-to-row transfer matrices are diagonalized by using the recently
introduced matrix product {\it ansatz}. Similarly as the relation of the
six-vertex model with the XXZ quantum chain, the row-to-row transfer matrices
of these new models are also the generating functions of an infinite set of
commuting conserved charges. Among these charges we identify the integrable
generalization of the XXZ chain that contains hard-core exclusion interactions
among the spins. These quantum chains already appeared in the literature. The
present paper explains their integrability.",0706.2178v1
2007-12-01,Extension of a Borel subalgebra symmetry into the sl(2) loop algebra symmetry for the twisted XXZ spin chain at roots of unity and the Onsager algebra,"We discuss a conjecture that the twisted transfer matrix of the six-vertex
model at roots of unity with some discrete twist angles should have the sl(2)
loop algebra symmetry. As an evidence of this conjecture, we show the following
mathematical result on a subalgebra of the sl(2) loop algebra, which we call a
Borel subalgebra: any given finite-dimensional highest weight representation of
the Borel subalgebra is extended into that of the sl(2) loop algebra, if the
parameters associated with it are nonzero. Thus, if operators commuting or
anti-commuting with the twisted transfer matrix of the six-vertex model at
roots of unity generate the Borel subalgebra, then they also generate the sl(2)
loop algebra. The result should be useful for studying the connection of the
sl(2) loop algebra symmetry to the Onsager algebra symmetry of the
superintegrable chiral Potts model.",0712.0066v1
2008-01-16,"A new eight vertex model and higher dimensional, multiparameter generalizations","We study statistical models, specifically transfer matrices corresponding to
a multiparameter hierarchy of braid matrices of $(2n)^2\times(2n)^2$ dimensions
with $2n^2$ free parameters $(n=1,2,3,...)$. The simplest, $4\times 4$ case is
treated in detail. Powerful recursion relations are constructed giving the
dependence on the spectral parameter $\theta$ of the eigenvalues of the
transfer matrix explicitly at each level of coproduct sequence. A brief study
of higher dimensional cases ($n\geq 2$) is presented pointing out features of
particular interest. Spin chain Hamiltonians are also briefly presented for the
hierarchy. In a long final section basic results are recapitulated with
systematic analysis of their contents. Our eight vertex $4\times 4$ case is
compared to standard six vertex and eight vertex models.",0801.2548v3
2008-02-26,Alignment Timescale of the Microquasar GRO J1655-40,"The microquasar GRO J1655-40 has a black hole with spin angular momentum
apparently misaligned to the orbital plane of its companion star. We
analytically model the system with a steady state disc warped by Lense-Thirring
precession and find the timescale for the alignment of the black hole with the
binary orbit. We make detailed stellar evolution models so as to estimate the
accretion rate and the lifetime of the system in this state. The secondary can
be evolving at the end of the main sequence or across the Hertzsprung gap. The
mass-transfer rate is typically fifty times higher in the latter case but we
find that, in both cases, the lifetime of the mass transfer state is at most a
few times the alignment timescale. The fact that the black hole has not yet
aligned with the orbital plane is therefore consistent with either model. We
conclude that the system may or may not have been counter-aligned after its
supernova kick but that it is most likely to be close to alignment rather than
counteralignment now.",0802.3912v1
2008-04-16,Single-band tight-binding parameters for Fe-MgO-Fe magnetic heterostructures,"We present a computationally efficient transferable single-band tight-binding
model (SBTB) for spin polarized transport in heterostructures with an effort to
capture the band structure effects. As an example, we apply it to study
transport through Fe-MgO-Fe(100) magnetic tunnel junction devices. We propose a
novel approach to extract suitable tight-binding parameters for a material by
using the energy resolved transmission as the benchmark, which inherently has
the bandstructure effects over the two dimensional transverse Brillouin zone.
The SBTB parameters for each of the four symmetry bands for bcc Fe(100) are
first proposed which are complemented with the transferable tight-binding
parameters for the MgO tunnel barrier for the Delta_1 and Delta_5 bands. The
non-equilibrium Green's function formalism is then used to calculate the
transport. Features like I-V characteristics, voltage dependence and the
barrier width dependence of the tunnel magnetoresistance ratio are captured
quantitatively and the trends match well with the ones observed by ab initio
methods.",0804.2557v5
2008-10-29,Fluctuations of current-driven domain walls in the non-adiabatic regime,"We outline a general framework to determine the effect of non-equilibrium
fluctuations on driven collective coordinates, and apply it to a current-driven
domain wall in a nanocontact. In this case the collective coordinates are the
domain-wall position and its chirality, that give rise to momentum transfer and
spin transfer, respectively. We determine the current-induced fluctuations
corresponding to these processes and show that at small frequencies they can be
incorporated by two separate effective temperatures. As an application, the
average time to depin the domain wall is calculated and found to be lowered by
current-induced fluctuations. It is shown that current-induced fluctuations
play an important role for narrow domain walls, especially at low temperatures.",0810.5232v3
2008-11-13,Radiative transfer in black hole systems,"We present a convariant formulation for radiative transfer in curved space
time and demonstrate some applications in the black-hole systems. We calculate
the emission from semi-transparent accretion tori around black holes, for
opacity provided by the Fe K lines and for opacity dominated by electron
scattering. We also calculate the emission from radiative inefficient accretion
flow in black holes with opacity provided by electron-positron annihilation
lines. Finally we show shadows cast by accreting black holes with different
spins and with different distribution of warm material around them.",0811.2060v1
2009-01-12,Maximal Information Transfer and Behavior Diversity in Random Threshold Networks,"Random Threshold Networks (RTNs) are an idealized model of diluted, non
symmetric spin glasses, neural networks or gene regulatory networks. RTNs also
serve as an interesting general example of any coordinated causal system. Here
we study the conditions for maximal information transfer and behavior diversity
in RTNs. These conditions are likely to play a major role in physical and
biological systems, perhaps serving as important selective traits in biological
systems. We show that the pairwise mutual information is maximized in
dynamically critical networks. Also, we show that the correlated behavior
diversity is maximized for slightly chaotic networks, close to the critical
region. Importantly, critical networks maximize coordinated, diverse dynamical
behavior across the network and across time: the information transmission
between source and receiver nodes and the diversity of dynamical behaviors,
when measured with a time delay between the source and receiver, are maximized
for critical networks.",0901.1675v1
2009-02-18,Scale-free antiferromagnetic fluctuations in the S=1/2 kagome antiferromagnet herbertsmithite,"Neutron spectroscopy and diffuse neutron scattering on herbertsmithite [ZnCu3
(OH)6Cl2], a near-ideal realisation of the s = 1/2 kagome antiferromagnet,
reveal the hallmark property of a quantum spin liquid; instantaneous
short-ranged antiferromagnetic correlations in the absence of a time-averaged
ordered moment. These dynamic antiferromagnetic correlations are only very
weakly dependent of neutron-energy transfer and temperature, and persist up to
25 meV and 120 K. At low energy transfers a shift of the magnetic scattering to
low Q is observed with increasing temperature, providing evidence of gapless
spinons. It is argued that these observations provide important evidence in
favour of RVB theories of (doped) Mott insulators.",0902.3194v4
2009-03-12,Universal Existence of Exact Quantum State Transmissions in Interacting Media,"We consider an exact state transmission, where a density matrix in one
information processor A at time $t=0$ is exactly equal to that in another
processor B at a later time. We demonstrate that there always exists a complete
set of orthogonal states, which can be employed to perform the exact state
transmission. Our result is very general in the sense that it holds for
arbitrary media between the two processors and for any time interval. We
illustrate our results in terms of models of spin, fermionic and bosonic
chains. This complete set can be used as bases to study the perfect state
transfer, which is associated with degenerated subspaces of this set of states.
Interestingly, this formalism leads to a proposal of perfect state transfer via
adiabatic passage, which does not depend on the specific form of the driving
Hamiltonian.",0903.2154v1
2009-04-02,Revision of model parameters for kappa-type charge transfer salts: an ab initio study,"Intense experimental and theoretical studies have demonstrated that the
anisotropic triangular lattice as realized in the kappa-(BEDT-TTF)2X family of
organic charge transfer (CT) salts yields a complex phase diagram with
magnetic, superconducting, Mott insulating and even spin liquid phases. With
extensive density functional theory (DFT) calculations we refresh the link
between manybody theory and experiment by determining hopping parameters of the
underlying Hubbard model. This leads us to revise the widely used semiempirical
parameters in the direction of less frustrated, more anisotropic triangular
lattices. The implications of these results on the systems' description are
discussed.",0904.0302v2
2009-04-22,Electronic and magnetic properties of the ionic Hubbard model on the striped triangular lattice at 3/4 filling,"We report a detailed study of a model Hamiltonian which exhibits a rich
interplay of geometrical spin frustration, strong electronic correlations, and
charge ordering. The character of the insulating phase depends on the magnitude
of Delta/|t| and on the sign of t. We find a Mott insulator for Delta >> U >>
|t|; a charge transfer insulator for U >> \Delta >> |t|; and a correlated
covalent insulator for U >> \Delta ~ |t|. The charge transfer insulating state
is investigated using a strong coupling expansion. The frustration of the
triangular lattice can lead to antiferromagnetism or ferromagnetism depending
on the sign of the hopping matrix element, t. We identify the ""ring"" exchange
process around a triangular plaquette which determines the sign of the magnetic
interactions. Exact diagonalization calculations are performed on the model for
a wide range of parameters and compared to the strong coupling expansion. The
regime U >> \Delta ~ |t| and t<0 is relevant to Na05CoO2. The calculated
optical conductivity and the spectral density are discussed in the light of
recent experiments on Na05CoO2.",0904.3402v1
2009-05-25,Nonlinear quantum heat transfer in hybrid structures: Sufficient conditions for thermal rectification,"We present a unified description of heat flow in two-terminal hybrid quantum
systems. Using simple models, we analytically study nonlinear aspects of heat
transfer between various reservoirs: metals, solids, and spin baths, mediated
by the excitation/relaxation of a central (subsystem) mode. We demonstrate rich
nonlinear current-temperature characteristics, originating from either the
molecular anharmonicity, or the reservoirs (complex) energy spectra. In
particular, we establish sufficient conditions for thermal rectification in
two-terminal junctions. We identify two classes of rectifiers. In type-A
rectifiers the density of states of the reservoirs are dissimilar. In type-B
rectifiers the baths are identical, but include particles whose statistics
differ from that of the subsystem, to which they asymmetrically couple.
Nonlinear heat flow, and specifically thermal rectification, are thus
ubiquitous effects that could be observed in a variety of systems, phononic,
electronic, and photonic.",0905.4015v1
2009-06-01,Superdense coding using the quantum superposition principle,"By sending a classical two-level system, one can transfer information about
only \emph{two} distinguishable outcomes. Here we show that in quantum
mechanics, using both the spin and path degrees of freedom of a spin-1/2
particle, and a Mach-Zehnder type interferometric arrangement with two suitable
Stern-Gerlach detectors, it is possible to transfer information about
\emph{four} distinguishable outcomes. This procedure does \emph{not} require
using quantum entanglement as a resource as in the well-known protocol of dense
coding, but instead hinges entirely on the quantum superposition principle. We
also study probabilistic dense coding using our set-up and show that the dense
coding scheme using quantum superposition cannot be optimized any further by
extending the interferometric arrangement with more beam splitters.",0906.0270v1
2009-08-24,Nitrogen clusters inside C60 cage and new nanoscale energetic materials,"We explore the possibility to trap polynitrogen clusters inside C60 fullerene
cage, opening a new direction of developing nitrogen-rich high energy
materials. We found that a maximum of 13 nitrogen atoms can be encapsulated in
a C60 cage. The nitrogen clusters in confinement exhibit unique stable
structures in polymeric form which possess a large component of (~ 70-80%)
single bond character. The Nn@C60 molecules retain their structure at 300K for
n<12. The Mulliken charge analysis shows very small charge transfer in N@C60,
consistent with the quartet spin state of N. However, for 2<n<10, charge
transfer take place from cage surface to Nn compounds and inverse polarization
thereafter. These nitrogen clusters when allowed to relax to N2 molecules which
are triply bonded are capable of releasing a large amount of energy.",0908.3412v1
2009-12-30,Entanglement manipulation via dynamics in multiple quantum spin systems,"We study manipulation of entanglement between two identical networks of
quantum mechanical particles. Firstly, we reduce the problem of entanglement
transfer to the problem of quantum state transfer. Then, we consider
entanglement concentration and purification based on free dynamics on the
networks and local measurements on the vertices. By introducing an appropriate
measure of efficiency, we characterize the performance of the protocol. We give
evidence that such a measure does not depend on the network topology, and we
estimate the contribution given by the number of entangled pairs initially
shared by the two networks.",0912.5499v3
2010-05-14,Spin State Transfer in Laterally Coupled Quantum Dot Chains with Disorders,"Quantum dot arrays are a promising media for transferring quantum information
between two distant points without resorting to mobile qubits. Here we study
two most common disorders namely, hyperfine interaction and exchange coupling
fluctuations, in quantum dot arrays and their effects on quantum communication
through these chains. Our results show that the hyperfine interaction is more
destructive than the exchange coupling fluctuations. The average optimal time
for communication is not affected by any disorder in the system and our
simulations show that anti-ferromagnetic chains are much more resistive than
the ferromagnetic ones against both kind of disorders. Even when time
modulation of a coupling and optimal control is employed to improve the
transmission, the anti-ferromagnetic chain performs much better. We have
assumed the quasi-static approximation for hyperfine interaction and time
dependent fluctuations in the exchange couplings. Particularly, for studying
exchange coupling fluctuations we have considered the static disorder, white
noise and $1/f$ noise.",1005.2571v2
2010-07-19,An analytical approach for calculating transfer integrals in superexchange coupled dimers,"An analytical expression for the transfer integral HAB between the localized
magnetic orbitals in superexchange-coupled dimers as a function of the type of
atoms and geometry of the molecule has been derived by explicitly including
orbital interactions. It is shown that HAB plays the key role for the magnetic
coupling constant J in understanding magneto-structural correlations. The
reliability and capability of this approach is confirmed by comparison with
numerical electronic structure calculations in the local spin-density
approximation on singly and doubly bridged Cu(II)-dimers with fluorine ligands.
All results can be calculated and understood within the analytical formalism
representing, therefore, a powerful tool for understanding the
magneto-structural correlations and also for constructing magnetic orbitals
analytically.",1007.3107v3
2010-07-27,General relativistic polarized radiative transfer: building a dynamics-observations interface,"The rising amount of polarized observations of relativistic sources requires
the correct theory for proper model fitting. The equations for general
relativistic (GR) polarized radiative transfer are derived starting from the
Boltzmann equation and basic ideas of general relativity. The derivation is
aimed at providing a practical guide to reproducing the synchrotron part of
radio & sub-mm emission from low luminosity active galactic nuclei (LLAGNs), in
particular Sgr A*, and jets. The recipe for fast exact calculation of
cyclo-synchrotron emissivities, absorptivities, Faraday rotation and conversion
coefficients is given for isotropic particle distributions. The multitude of
physical effects influencing simulated spectrum is discussed. The application
of the prescribed technique is necessary to determine the black hole (BH) spin
in LLAGNs, constraining it with all observations of total flux, linear and
circular polarization fractions, and electric vector position angle as
functions of the observed frequency.",1007.4831v2
2010-10-31,Linearized Tensor Renormalization Group Algorithm for Thermodynamics of Quantum Lattice Models,"A linearized tensor renormalization group (LTRG) algorithm is proposed to
calculate the thermodynamic properties of one-dimensional quantum lattice
models, that is incorporated with the infinite time-evolving block decimation
technique, and allows for treating directly the two-dimensional transfer-matrix
tensor network. To illustrate its feasibility, the thermodynamic quantities of
the quantum XY spin chain are calculated accurately by the LTRG, and the
precision is shown to be comparable with (even better than) the transfer matrix
renormalization group (TMRG) method. Unlike the TMRG scheme that can only deal
with the infinite chains, the present LTRG algorithm could treat both finite
and infinite systems, and may be readily extended to boson and fermion quantum
lattice models.",1011.0155v2
2010-11-24,Quantum Entanglement transfer between spin-pairs,"We investigate the transfer of entanglement from source particles (SP) to
target particles (TP) in the Heisenberg interaction $ H=\vec s_{1} \cdot \vec
s_{2}$. In our research, TP are two qubits and SP are two qubits or qutrits.
When TP are two qubits, we find that no matter what state the TP is initially
prepared in, at the specific time $t=\pi$, the entanglement of TP can attain to
1 after interaction with SP which stay on the maximally entangled state. For
the TP are two qutrits, we find that the maximal entanglement of TP after
interaction is relative to the initial state of TP and always cannot attain to
1 to almost all of initial states of TP. But we discuss an iterated operation
which can make the TP to the maximal entangled state.",1011.5352v2
2011-01-05,"Non-thermal laser induced precession of magnetization in ferromagnetic semiconductor (Ga,Mn)As","Non-thermal laser induced spin excitations, recently discovered in
conventional oxide and metal ferromagnets, open unprecedented opportunities for
research and applications of ultrafast optical manipulation of magnetic
systems. Ferromagnetic semiconductors, and (Ga,Mn)As in particular, should
represent ideal systems for exploring this new field. Remarkably, the presence
of non-thermal effects has remained one of the outstanding unresolved problems
in the research of ferromagnetic semiconductors to date. Here we demonstrate
that coherent magnetization dynamics can be excited in (Ga,Mn)As non-thermally
by a transfer of angular momentum from circularly polarized femtosecond laser
pulses and by a combination of non-thermal and thermal effects due to a
transfer of energy from laser pulses. The thermal effects can be completely
suppressed in piezo-electrically controlled samples. Our work is based on
pump-and-probe measurements in a large set of (Ga,Mn)As epilayers and on
systematic analysis of circular and linear magneto-optical coefficients. We
provide microscopic theoretical interpretation of the experimental results.",1101.1049v1
2011-03-08,Ultrafast magnetization dynamics of Gd(0001): Bulk vs. surface,"Ultrafast laser-induced demagnetization of Gd(0001) has been investigated by
magneto-induced optical second harmonic generation and the magneto-optical Kerr
effect which facilitate a comparison of surface and bulk dynamics. We observe
pronounced differences in the transient changes of the surface and bulk
sensitive magneto-optical signals which we attribute to transfer of optically
excited, spin-polarized carriers between surface and bulk states of the
Gd(0001) film. A fluence dependent analysis of the bulk magnetization dynamics
results in a weak variation of the demagnetization time constant, which starts
at about 700 fs and increases by 10% within a fluence variation up to 1 mJ/cm2.
We compare these results with fluence dependent changes in the transient energy
density calculated by the two temperature model. The determined characteristic
times of excess energy transfer from the electron system to the lattice, which
is mediated by e-ph scattering, range from 0.2 - 0.6 ps. Such a more pronounced
fluence dependent change in the characteristic time compared to the observed
rather weakly varying demagnetization times suggests a more advanced
description of the optically excited state than by the two-temperature model.",1103.1512v1
2011-04-29,Optical vortices of slow light using tripod scheme,"We consider propagation, storing and retrieval of slow light (probe beam) in
a resonant atomic medium illuminated by two control laser beams of larger
intensity. The probe and two control beams act on atoms in a tripod
configuration of the light-matter coupling. The first control beam is allowed
to have an orbital angular momentum (OAM). Application of the second
vortex-free control laser ensures the adiabatic (lossles) propagation of the
probe beam at the vortex core where the intensity of the first control laser
goes to zero. Storing and release of the probe beam is accomplished by
switching off and on the control laser beams leading to the transfer of the
optical vortex from the first control beam to the regenerated probe field. A
part of the stored probe beam remains frozen in the medium in the form of
atomic spin excitations, the number of which increases with increasing the
intensity of the second control laser. We analyse such losses in the
regenerated probe beam and provide conditions for the optical vortex of the
control beam to be transferred efficiently to the restored probe beam.",1104.5536v1
2011-05-09,Full Counting Statistics in the Resonant-Level Model,"We derive the large deviation function, which provides the large-time full
counting statistics for the charge transfer, in the non-equilibrium steady
state of the resonant-level model. The general form of this function in free
fermion models, in terms of transmission coefficients, was proposed by Levitov
and Lesovik in 1993 using a particular measurement set-up involving an
interacting spin. It was later suggested to hold as well for a proper quantum
mechanical measurement of the transferred charge. We give a precise proof of
both statements in the resonant-level model. We first give a full description
of the model and its steady state. That is, we explain how the decoupled system
prepared with a charge differential evolves, with the impurity coupling,
towards the Hershfield non-equilibrium density matrix, in the sense of averages
of finitely-supported operators. We describe how this holds both for the usual
resonant-level model with a point-like impurity, and for a regularised model
with an impurity spread on a finite region, shedding light on subtleties
associated to the point-like impurity. We then prove Levitov-Lesovik formula by
recasting the problem into calculating averages of finitely-supported
operators.",1105.1695v1
2011-06-23,Perfect State Transfer in Two and Three Dimensional Structures,"We introduce a scheme for perfect state transfer in regular two and three
dimensional structures. The interactions on the lattices are of XX spin type
with uniform couplings. In two dimensions the structure is a hexagonal lattice
and in three dimensions it consists of hexagonal planes joined to each other at
arbitrary points. We will show that compared to other schemes, i) much less
control is needed for routing, ii) the algebra of global control is quite
simple, iii) the same kind of control can upload and download qubit states to
or from built-in Read-Write (RW) heads. Pivotal use is made of a quantum switch
which we introduce and call it Hadamard switch, since its operation depends on
the existence of a Hadamard matrix in four dimensions.",1106.4829v2
2011-08-24,On Pulsar-Driven Mass Ejection in Low-Mass X-ray Binaries,"There is accumulating evidence for mass ejection in low-mass X-ray binaries
(LMXBs) driven by radio pulsar activity during X-ray quiescence. In this paper
we consider the condition for mass ejection by comparing the radiation pressure
from a millisecond pulsar, and the gas pressure at the inner Lagrange point or
at the surrounding accretion disk. We calculate the critical spin period of the
pulsar below which mass ejection is allowed. Combining with the evolution of
the mass transfer rate, we present constraints on the orbital periods of the
systems. We show that mass ejection could happen in both wide and compact
LMXBs. It may be caused by transient accretion due to thermal instability in
the accretion disks in the former, and irradiation-driven mass-transfer cycles
in the latter.",1108.4742v1
2011-10-02,Spatial distribution of electrons on a superfluid helium charge-coupled device,"Electrons floating on the surface of superfluid helium have been suggested as
promising mobile spin qubits. Three micron wide channels fabricated with
standard silicon processing are filled with superfluid helium by capillary
action. Photoemitted electrons are held by voltages applied to underlying
gates. The gates are connected as a 3-phase charge-coupled device (CCD).
Starting with approximately one electron per channel, no detectable transfer
errors occur while clocking $10^9$ pixels. One channel with its associated
gates is perpendicular to the other 120, providing a CCD which can transfer
electrons between the others. This perpendicular channel has not only shown
efficient electron transport but also serves as a way to measure the uniformity
of the electron occupancy in the 120 parallel channels.",1110.0193v1
2012-02-27,Speed limits for quantum gates in multi-qubit systems,"We use analytical and numerical calculations to obtain speed limits for
various unitary quantum operations in multiqubit systems under typical
experimental conditions. The operations that we consider include single-, two-,
and three-qubit gates, as well as quantum-state transfer in a chain of qubits.
We find in particular that simple methods for implementing two-qubit gates
generally provide the fastest possible implementations of these gates. We also
find that the three-qubit Toffoli gate time varies greatly depending on the
type of interactions and the system's geometry, taking only slightly longer
than a two-qubit controlled-NOT (CNOT) gate for a triangle geometry. The speed
limit for quantum-state transfer across a qubit chain is set by the maximum
spin-wave speed in the chain.",1202.5872v2
2012-02-28,Controlling the quantum state of a single photon emitted from a single polariton,"We investigate in detail the optimal conditions for a high fidelity transfer
from a single-polariton state to a single-photon state and subsequent homodyne
detection of the single photon. We assume that, using various possible
techniques, the single polariton has initially been stored as a spin-wave
grating in a cloud of cold atoms inside a low-finesse cavity. This state is
then transferred to a single-photon optical pulse using an auxiliary beam. We
optimize the retrieval efficiency and determine the mode of the local
oscillator that maximizes the homodyne efficiency of such a photon. We find
that both efficiencies can have values close to one in a large region of
experimental parameters.",1202.6195v1
2012-03-31,CCD Photometric Investigation of A W UMa-Type Binary GSC 0763-0572,"A photometric solution of an A-type W UMa binary, GSC 0763-0572 is examined
with a revised orbital period. The overcontact degree is found to be $f$ =
40.66%, with a low mass ratio of $q$ = 0.2554. The result demonstrates an
unambiguous increase in the orbital period with a relative period change of
$\Delta P\slash P = +5.69\times10^{-7} $d yr$^{-1}$. This indicates that GSC
0763-0572 is undergoing a process of mass transfer from the secondary component
to the primary one with a rate of relative mass change of
$\Delta$$m_1$$\slash$$m$ $=+5.18\times10^{-8}$ yr$^{-1}$, for a conservative
model of mass transfer. We find that GSC 0763-0572 might transform into a
rapidly rotating star, if total spin angular momentum increases until it is
greater than one-third of the orbital angular momentum, without breaking the
contact configuration.",1204.0122v3
2013-01-29,Scalable universal holonomic quantum computation realized with an adiabatic quantum data bus and potential implementation using superconducting flux qubits,"In this paper we examine the use of an adiabatic quantum data transfer
protocol to build a universal quantum computer. Single qubit gates are realized
by using a bus protocol to transfer qubits of information down a spin chain
with a unitary twist. This twist arises from altered couplings on the chain
corresponding to unitary rotations performed on one region of the chain. We
show how a controlled NOT gate can be realized by using a control qubit with
Ising type coupling. The method discussed here can be extended to non-adiabatic
quantum bus protocols. We also examine the potential of realizing such a
quantum computer by using superconducting flux qubits.",1301.7100v3
2013-02-15,Information transfer of an Ising model on a brain network,"We implement the Ising model on a structural connectivity matrix describing
the brain at a coarse scale. Tuning the model temperature to its critical
value, i.e. at the susceptibility peak, we find a maximal amount of total
information transfer between the spin variables. At this point the amount of
information that can be redistributed by some nodes reaches a limit and the net
dynamics exhibits signature of the law of diminishing marginal returns, a
fundamental principle connected to saturated levels of production. Our results
extend the recent analysis of dynamical oscillators models on the connectome
structure, taking into account lagged and directional influences, focusing only
on the nodes that are more prone to became bottlenecks of information. The
ratio between the outgoing and the incoming information at each node is related
to the number of incoming links.",1302.3869v4
2013-03-19,Magnetic field-induced giant enhancement of electron-phonon energy transfer in strongly disordered conductors,"Relaxation of soft modes (e.g. charge density in gated semiconductor
heterostructures, spin density in the presence of magnetic field) slowed down
by disorder may lead to giant enhancement of energy transfer (cooling power)
between overheated electrons and phonons at low bath temperature. We show that
in strongly disordered systems with time-reversal symmetry broken by external
or intrinsic exchange magnetic field the cooling power can be greatly enhanced.
The enhancement factor as large as $10^{2}$ at magnetic field $B \sim 10$ Tesla
in 2D {\rm InSb} films is predicted. A similar enhancement is found for the
ultrasound attenuation.",1303.4936v2
2013-04-04,Electronic excitations from a linear-response range-separated hybrid scheme,"We study linear-response time-dependent density-functional theory (DFT) based
on the single-determinant range-separated hybrid (RSH) scheme, i.e. combining a
long-range Hartree-Fock exchange kernel with a short-range DFT
exchange-correlation kernel, for calculating electronic excitation energies of
molecular systems. It is an alternative to the long-range correction (LC)
scheme which has a standard full-range DFT correlation kernel instead of only a
short-range one. We discuss the local-density approximation (LDA) to the
short-range exchange-correlation kernel, and assess the performance of the
linear-response RSH scheme for singlet-singlet and singlet-triplet valence and
Rydberg excitations in the N2, CO, H2CO, C2H4, and C6H6 molecules, and for the
first charge-transfer excitation in the C2H4-C2F4 dimer. The introduction of
long-range HF exchange corrects the underestimation of charge-transfer and
high-lying Rydberg excitation energies obtained with standard (semi)local
density-functional approximations, but also leads to underestimated excitation
energies to low-lying spin-triplet valence states which can be cured by the
Tamm-Dancoff approximation. This work thus suggests that the present
linear-response RSH scheme is a reasonable starting approximation for
describing electronic excitation energies, even before adding an explicit
treatment of long-range correlation.",1304.1322v1
2013-05-23,From Gamma-Ray Bursts/Hypernovae To Black-Hole Binaries,"In this work I summarize a model of binary stellar evolution involving Case C
mass transfer followed by a common envelope that strips away the hydrogen from
the core of the primary star at the cost of shrinking the orbital separation
and then, through tidal interaction, spins it up. This model is then used to
produce the possible progenitors of long gamma-ray burst / hypernova (GRB/HN)
explosions. As the core collapses with the newly supplied angular momentum it
produces a Kerr black hole surrounded by an accretion disk. Energy is extracted
from the rotation of the black hole (BH) through the Blandford-Znajek (BZ)
mechanism to power both, the long gamma-ray burst and the accompanying
hypernova (supernova type Ic broad line). If the binary survives the asymmetric
mass loss its remnant is a black-hole binary that may eventually be observed as
a soft X-ray transient (SXT) when the companion evolves and starts to transfer
mass back to the black hole. A comparison with a sample of black-hole binaries
where the masses and orbital periods are well constrained is performed.",1305.5543v1
2013-06-04,Exciton dynamics in emergent Rydberg lattices,"The dynamics of excitons in a one-dimensional ensemble with partial spatial
order are studied. During optical excitation, cold Rydberg atoms spontaneously
organize into regular spatial arrangements due to their mutual interactions.
This emergent lattice is used as the starting point to study resonant energy
transfer triggered by driving a $nS$ to $n^\prime P$ transition using a
microwave field. The dynamics are probed by detecting the survival probability
of atoms in the $nS$ Rydberg state. Experimental data qualitatively agree with
our theoretical predictions including the mapping onto XXZ spin model in the
strong-driving limit. Our results suggest that emergent Rydberg lattices
provide an ideal platform to study coherent energy transfer in structured media
without the need for externally imposed potentials.",1306.0869v2
2013-09-06,Photoexcitation of graphene with twisted light,"We study theoretically the interaction of twisted light with graphene. The
light-matter interaction matrix elements between the tight-binding states of
electrons in graphene are determined near the Dirac points. We examine the
dynamics of the photoexcitation process by posing the equations of motion of
the density matrix and working up to second order in the field. The time
evolution of the angular momentum of the photoexcited electrons and their
associated photocurrents are examined in order to elucidate the mechanisms of
angular momentum transfer. We find that the transfer of spin and orbital
angular momentum from light to the electrons is more akin here to the case of
intraband than of interband transitions in semiconductors, due to the fact that
the two relevant energy bands of graphene originate from the same atomic
orbitals.",1309.1708v1
2013-12-11,Angular Momentum Exchange Between Light and Material Media Deduced from the Doppler Shift,"Electromagnetic waves carry energy as well as linear and angular momenta.
When a light pulse is reflected from, transmitted through, or absorbed by a
material medium, energy and momentum (both linear and angular) are generally
exchanged, while the total amount of each entity remains intact. The extent of
such exchanges between light and matter can be deduced, among other methods,
with the aid of the Doppler shift phenomenon. The main focus of the present
paper is on the transfer of angular momentum from a monochromatic light pulse
to spinning objects such as a mirror, an absorptive dielectric, or a
birefringent plate. The fact that individual photons of frequency omega carry
energy in the amount of h_bar*omega, where h_bar is Planck's reduced constant,
enables one to relate the Doppler shift to the amount of energy exchanged.
Under certain circumstances, the knowledge of exchanged energy leads directly
to a determination of the momentum transferred from the photon to the material
body, or vice versa.",1312.3271v1
2014-07-15,Proximity induced topological state in graphene,"The appearance of topologically protected states at the surface of an
ordinary insulator is a rare occurrence and to date only a handful of materials
are known for having this property. An intriguing question concerns the
possibility of forming topologically protected interfaces between different
materials. Here we propose that a topological phase can be transferred to
graphene by proximity with the three-dimensional topological insulator
Bi$_2$Se$_3$. By using density functional and transport theory we prove that,
at the verge of the chemical bond formation, a hybrid state forms at the
graphene/Bi$_2$Se$_3$ interface. The state has Dirac-cone-like dispersion at
the $\Gamma$ point and a well-defined helical spin-texture, indicating its
topologically protected nature. This demonstrates that proximity can transfer
the topological phase from Bi$_2$Se$_3$ to graphene.",1407.4008v1
2014-08-06,Integrable anyon chains: from fusion rules to face models to effective field theories,"Starting from the fusion rules for the algebra $SO(5)_2$ we construct
one-dimensional lattice models of interacting anyons with commuting transfer
matrices of `interactions round the face' (IRF) type. The conserved topological
charges of the anyon chain are recovered from the transfer matrices in the
limit of large spectral parameter. The properties of the models in the
thermodynamic limit and the low energy excitations are studied using Bethe
ansatz methods. Two of the anyon models are critical at zero temperature. From
the analysis of the finite size spectrum we find that they are effectively
described by rational conformal field theories invariant under extensions of
the Virasoro algebra, namely $\mathcal{W}B_2$ and $\mathcal{W}D_5$,
respectively. The latter contains primaries with half and quarter spin. The
modular partition function and fusion rules are derived and found to be
consistent with the results for the lattice model.",1408.1282v2
2014-08-26,"3D full-band, Atomistic Quantum transport in n-Si Junction less Nanowire field-effect transistors","In the present work, we have investigated the quantum transport in n Si
junction less nanowire field effect transistors using 3 D, full band atomistic
sp3d5s spin orbital coupled tight binding method. We have investigated the IDS
VGS transfer characteristics, IDS VDS output characteristics, ON current, OFF
current leakage, subthreshold swing and energy position resolved electron
density spectrum Gn x, E in n Si junction less nanowire field effect
transistors. We also study IDS VGS transfer characteristics with variation of
High K gate materials. Quantum mechanical simulation is performed on the basis
of Non Equilibrium Green Function formalism to solve coupled Poisson Schr
""odinger equation self consistently for potentials and local density of state
in n Si junction less nanowire field effect transistors.",1408.6003v1
2014-10-14,Isolating electrons on superfluid helium,"Electrons floating on the surface of superfluid helium have been suggested as
promising mobile spin quantum bits (qubits). Transferring electrons extremely
efficiently in a narrow channel structure with underlying gates has been
demonstrated, showing no transfer error while clocking $10^9$ pixels in a
3-phase charge coupled device (CCD). While on average, one electron per channel
was clocked, it is desirable to reliably obtain a single electron per channel.
We have designed an electron turnstile consisting of a narrow (0.8$\mu$m)
channel and narrow underlying gates (0.5$\mu$m) operating across seventy-eight
parallel channels. Initially, we find that more than one electron can be held
above the small gates. Underlying gates in the turnstile region allow us to
repeatedly split these electron packets. Results show a plateau in the electron
signal as a function of the applied gate voltages, indicating quantization of
the number of electrons per pixel, simultaneously across the seventy-eight
parallel channels.",1410.3792v1
2014-11-03,Direct photonic coupling of a semiconductor quantum dot and a trapped ion,"Coupling individual quantum systems lies at the heart of building scalable
quantum networks. Here, we report the first direct photonic coupling between a
semiconductor quantum dot and a trapped ion and we demonstrate that single
photons generated by a quantum dot controllably change the internal state of an
$\textrm{Yb}^+$ ion. We ameliorate the effect of the sixty-fold mismatch of the
radiative linewidths with coherent photon generation and a high-finesse
fiber-based optical cavity enhancing the coupling between the single photon and
the ion. The transfer of information presented here via the classical
correlations between the $\sigma_z$-projection of the quantum-dot spin and the
internal state of the ion provides a promising step towards quantum
state-transfer in a hybrid photonic network.",1411.0738v1
2014-12-09,Interaction potential of FePt with the MgO(001) surface,"By means of density functional theory we have undertaken a structural,
electronic and magnetic survey of the adsorption of the Fe_xPt_y(x,y=<4)
clusters on MgO (001) surface under the generalized gradient approximation. We
have tested different atomic adsorption geometries with the aim of scan a wider
range of adsorption sites in order to determine the preferential surface
covering. Our main conclusion in this respect is that the FePt wets the
surface. The intracluster (before and after the adsorption) and
cluster-to-surface binding mechanisms were investigated via the adsorption
energy, charge transfer, density of states and hybridization analysis. The
adsorption energy values increased for those geometries in which keeping the Fe
or Pt atom @top-O, the outermost species was moved to cover the surface. In
general the unsupported clusters present higher intracluster energies than the
adsorbed ones being the average difference of 1.5 eV. In this regard there was
a small reduction in the net magnetic moment of the supported clusters due to
an internal and external rearrangement of the spin-up/-down charge.
Furthermore, a complex and subtle charge transfer between different species
takes place having an increasing the Pt and O population at the expense of the
lost Fe charge.",1412.2920v1
2015-02-24,Engineered Mott ground state in LaTiO$_{3+δ}$/LaNiO$_3$ heterostructure,"In pursuit of creating cuprate-like electronic and orbital structures,
artificial heterostructures based on LaNiO$_3$ have inspired a wealth of
exciting experimental and theoretical results. However, to date there is a very
limited experimental understanding of the electronic and orbital states
emerging after interfacial charge-transfer and their connections to the
modified band structure at the interface. Towards this goal, we have
synthesized a prototypical superlattice composed of correlated metal LaNiO$_3$
and doped Mott insulator LaTiO$_{3+\delta}$, and investigated its electronic
structure by resonant X-ray absorption spectroscopy combined with X-ray
photoemission spectroscopy, electrical transport and theory calculations. The
heterostructure exhibits interfacial charge-transfer from Ti to Ni sites giving
rise to an insulating ground state with orbital polarization and $e_\textrm{g}$
orbital band splitting. Our findings demonstrate how the control over charge at
the interface can be effectively used to create exotic electronic, orbital and
spin states.",1502.06920v3
2015-03-20,Direct Observation of Long Electron-Hole Diffusion Distance in CH3NH3PbI3 Perovskite Thin Film,"In high performance perovskite based solar cells, CH3NH3PbI3 is the key
material. We carried out a study on charge diffusion in spin-coated CH3NH3PbI3
perovskite thin film by transient fluorescent spectroscopy. A
thickness-dependent fluorescent lifetime was found. By coating the film with an
electron or hole transfer layer, [6,6]-phenyl-C61-butyric acid methyl ester
(PCBM) or 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene
(Spiro-OMeTAD) respectively, we observed the charge transfer directly through
the fluorescence quenching. One-dimensional diffusion model was applied to
obtain long charge diffusion distances in thick films, which is ~1.7 um for
electrons and up to ~6.3 um for holes. Short diffusion distance of few hundreds
of nanosecond was also observed in thin films. This thickness dependent charge
diffusion explained the formerly reported short charge diffusion distance (~100
nm) in films and resolved its confliction to thick working layer (300-500 nm)
in real devices. This study presents direct support to the high performance
perovskite solar cells and will benefit the devices design.",1503.05984v2
2015-05-13,State-Transfer Simulation in Integrated Waveguide Circuits,"Spin-chain models have been widely studied in terms of quantum information
processes, for instance for the faithful transmission of quantum states. Here,
we investigate the limitations of mapping this process to an equivalent one
through a bosonic chain. In particular, we keep in mind experimental
implementations, which the progress in integrated waveguide circuits could make
possible in the very near future. We consider the feasibility of exploiting the
higher dimensionality of the Hilbert space of the chain elements for the
transmission of a larger amount of information, and the effects of unwanted
excitations during the process. Finally, we exploit the information-flux method
to provide bounds to the transfer fidelity.",1505.03486v2
2015-06-16,Inhomogeneous discrete-time exclusion processes,"We study discrete time Markov processes with periodic or open boundary
conditions and with inhomogeneous rates in the bulk. The Markov matrices are
given by the inhomogeneous transfer matrices introduced previously to prove the
integrability of quantum spin chains. We show that these processes have a
simple graphical interpretation and correspond to a sequential update. We
compute their stationary state using a matrix ansatz and express their
normalization factors as Schur polynomials. A connection between Bethe roots
and Lee-Yang zeros is also pointed out.",1506.04874v2
2015-07-31,Bethe ansatz for an AdS/CFT open spin chain with non-diagonal boundaries,"We consider the integrable open-chain transfer matrix corresponding to a Y=0
brane at one boundary, and a Y_theta=0 brane (rotated with the respect to the
former by an angle theta) at the other boundary. We determine the exact
eigenvalues of this transfer matrix in terms of solutions of a corresponding
set of Bethe equations.",1507.08866v3
2015-08-01,Theory of Primary Photoexcitations in Donor-Acceptor Copolymers,"We present a generic theory of primary photoexcitations in low band gap
donor-acceptor conjugated copolymers. Because of the combined effects of strong
electron correlations and broken symmetry, there is considerable mixing between
a charge-transfer exciton and an energetically proximate triplet-triplet state
with an overall spin singlet. The triplet-triplet state, optically forbidden in
homopolymers, is allowed in donor-acceptor copolymers. For an intermediate
difference in electron affinities of the donor and the acceptor, the
triplet-triplet state can have stronger oscillator strength than the
charge-transfer exciton. We discuss the possibility of intramolecular singlet
fission from the triplet-triplet state, and how such fission can be detected
experimentally.",1508.00071v2
2015-08-05,Many-body theory of ultrafast demagnetization and angular momentum transfer in ferromagnetic transition metals,"Exact calculated time evolutions in the framework of a many-electron model of
itinerant magnetism provide new insights into the laser-induced ultrafast
demagnetization observed in ferromagnetic (FM) transition metal thin films. The
interplay between local spin-orbit interactions and interatomic hopping is
shown to be at the origin of the observed post-excitation breakdown of FM
correlations between highly stable local magnetic moments. The mechanism behind
spin- and angular-momentum transfer is revealed from a microscopic perspective
by rigorously complying with all fundamental conservation laws. An
energy-resolved analysis of the time evolution shows that the efficiency of the
demagnetization process reaches almost 100% in the excited states.",1508.00983v2
2015-08-31,"Elastic proton scattering at intermediate energies as a probe of the $^{6,8}$He nuclear matter densities","The Glauber model analysis of the elastic $^{6,8}$He+$p$ scattering data at
energies around 700 MeV/nucleon, measured in two separate experiments at
GSI-Darmstadt, has been done using several phenomenological parametrizations of
the nuclear matter density. By taking into account the new data points measured
at the high momentum transfer, the nuclear matter radii of $^{6,8}$He were
accurately determined from the Glauber model analysis of the data, with the
spin-orbital interaction explicitly taken into account. The well-known geometry
for the core and dineutron halo has been used with the new parametrizations of
the $^{6}$He density to extract the detailed information on the structure of
$^{6}$He in terms of the core and dineutron halo radii. An enhanced sensitivity
of the data measured at the high momentum transfer to the core part of the
$^{6,8}$He densities has been found.",1508.07679v1
2015-09-15,Entanglement Entropy from Corner Transfer Matrix in Forrester Baxter non-unitary RSOS models,"Using a Corner Transfer Matrix approach, we compute the bipartite
entanglement R\'enyi entropy in the off-critical perturbations of non-unitary
conformal minimal models realised by lattice spin chains Hamiltonians related
to the Forrester Baxter RSOS models in regime III. This allows to show on a set
of explicit examples that the R\'enyi entropies for non-unitary theories
rescale near criticality as the logarithm of the correlation length with a
coefficient proportional to the effective central charge. This complements a
similar result, recently established for the size rescaling at the critical
point, showing the expected agreement of the two behaviours. We also compute
the first subleading unusual correction to the scaling behaviour, showing that
it is expressible in terms of expansions of various fractional powers of the
correlation length, related to the differences $\Delta-\Delta_{\min}$ between
the conformal dimensions of fields in the theory and the minimal conformal
dimension. Finally, a few observations on the limit leading to the off-critical
logarithmic minimal models of Pearce and Seaton are put forward.",1509.04601v1
2015-09-23,Spin-orbit mode transfer via a classical analog of quantum teleportation,"We translate the quantum teleportation protocol into a sequence of coherent
operations involving three degrees of freedom of a classical laser beam. The
protocol, which we demonstrate experimentally, transfers the polarisation state
of the input beam to the transverse mode of the output beam. The role of
quantum entanglement is played by a non-separable mode describing the path and
transverse degrees of freedom. Our protocol illustrates the possibility of new
optical applications based on this intriguing classical analogue of quantum
entanglement.",1509.06826v3
2015-10-14,STIRAP in sodium vapor with picosecond laser pulses,"Experimental measurements and calculations of STIRAP transfer efficiencies
were made on a sodium gas starting from the $3^2{\rm S}_{1/2}$ electronic
ground state, passing through the $3^2{\rm P}_{1/2}$ and/or the $3^2{\rm
P}_{3/2}$ to the $5^2{\rm S}_{1/2}$ state. The lasers used in the experiments
had a pulse width of several picoseconds and were close to the Fourier
transform limit. Although the linewidth of the laser was much smaller than the
spin orbit splitting between the $3^2{\rm P}_{1/2}$ and $3^2{\rm P}_{3/2}$
states, Experiments and calculations reveal that both 3p states play a role in
the transfer efficiency when the lasers are tuned to resonance through the
$3^2{\rm P}_{1/2}$ state, revealing evidence for quantum interference between
the competing pathways.",1510.04334v4
2015-11-16,Giant edge state splitting at atomically precise zigzag edges,"Zigzag edges of graphene nanostructures host localized electronic states that
are predicted to be spin-polarized. However, these edge states are highly
susceptible to edge roughness and interaction with a supporting substrate,
complicating the study of their intrinsic electronic and magnetic structure.
Here, we focus on atomically precise graphene nanoribbons whose two short
zigzag edges host exactly one localized electron each. Using the tip of a
scanning tunneling microscope, the graphene nanoribbons are transferred from
the metallic growth substrate onto insulating islands of NaCl in order to
decouple their electronic structure from the metal. The absence of charge
transfer and hybridization with the substrate is confirmed by scanning
tunneling spectroscopy (STS), which reveals a pair of occupied / unoccupied
edge states. Their large energy splitting of 1.9 eV is in accordance with ab
initio many-body perturbation theory calculations and reflects the dominant
role of electron-electron interactions in these localized states.",1511.04940v1
2015-12-14,Dynamics of a Chlorophyll Dimer in Collective and Local Thermal Environments,"We present a theoretical analysis of exciton transfer and decoherence effects
in a photosynthetic dimer interacting with collective (correlated) and local
(uncorrelated) protein-solvent environments. Our approach is based on the
framework of the spin-boson model. We derive explicitly the thermal relaxation
and decoherence rates of the exciton transfer process, valid for arbitrary
temperatures and for arbitrary (in particular, large) interaction constants
between the dimer and the environments. We establish a generalization of the
Marcus formula, giving reaction rates for dimer levels possibly individually
and asymmetrically coupled to environments. We identify rigorously parameter
regimes for the validity of the generalized Marcus formula.
  The existence of long living quantum coherences at ambient temperatures
emerges naturally from our approach.",1512.08810v1
2016-05-24,Generation of Gamma-ray Beam with Orbital Angular Momentum in the QED Regime,"We propose a scheme to generate gamma-ray photons with an orbital angular
momentum (OAM) and high energy simultaneously from laser-plasma interactions by
irradiating a circularly polarized Laguerre-Gaussian laser on a thin plasma
target. The spin angular momentum and OAM are first transferred to electrons
from the driving laser photons, and then the OAM is transferred to the
gamma-ray photons from the electrons through quantum radiation. This scheme has
been demonstrated using three-dimensional quantum electrodynamics
particle-in-cell simulation. The topological charge, chirality and
carrier-envelope phase of the short ultra-intense vortex laser can be revealed
according to the pattern feature of the energy density of radiated photons.",1605.07463v1
2016-06-29,Physics of ultrathin films and heterostructures of rare earth nickelates,"The electronic structure of transition metal oxides featuring correlated
electrons can be rationalized within the Zaanen-Sawatzky-Allen framework.
Following a brief description of the present paradigms of electronic behavior,
we focus on the physics of rare earth nickelates as an archetype of complexity
emerging within the charge transfer regime. The intriguing prospect of
realizing the physics of high $T_c$ cuprates through heterostructuring resulted
in a massive endeavor to epitaxially stabilize these materials in ultra-thin
form. A plethora of new phenomena unfolded in such artificial structures due to
the effect of epitaxial strain, quantum confinement, and interfacial charge
transfer. Here we review the present status of artificial rare-earth nickelates
in an effort to uncover the interconnection between the electronic and magnetic
behavior and the underlying crystal structure. We conclude by discussing future
directions to disentangle the puzzle regarding the origin of the
metal-insulator transition, the role of oxygen holes, and the true nature of
the antiferromagnetic spin configuration in the ultra-thin limit.",1606.09291v1
2016-09-07,A Note on the Speed of Perfect State Transfer,"In Phys. Rev. A 74, 030303 (2006), Yung showed that for a one-dimensional
spin chain of length $N$ and maximum coupling strength $J_{\max}$, the time
$t_0$ for a quantum state to transfer from one end of the chain to another is
bounded by $J_{\max} t_0\geq\pi N/4$ (even $N$) and $J_{\max}
t_0\geq\pi\sqrt{N^2-1}/4$ (odd $N$). The proof for even $N$ was elegant, but
the proof for odd $N$ was less so. This note provides a proof for the odd $N$
case that is simpler, and more in keeping with the proof for the even case.",1609.01854v5
2016-10-04,A study of the gamma* - f0(980) transition form factors,"The spin wave function of the f0(980)-meson is constructed under the
assumption that the meson is dominantly a quark-antiquark state. This wave
function is used in a calculation of the gamma* - f0 transition form factors.
In the real-photon limit the results for the transverse form factor are
compared to the large momentum transfer data measured by the BELLE
collaboration recently. It turns out that, for the momentum-transfer range
explored by BELLE, the collinear approximation does not suffer, power
corrections to it, modeled as quark transverse moment effects, seem to be
needed. Mixing of the f0 with the sigma(500) is also briefly discussed.",1610.01020v2
2016-11-03,Complex spectrum of spin models for finite-density QCD,"We consider the spectrum of transfer matrix eigenvalues associated with
Polyakov loops in lattice QCD at strong coupling. The transfer matrix at finite
density is non-Hermitian, and its eigenvalues become complex as a manifestation
of the sign problem. We show that the symmetry under charge conjugation and
complex conjugation ensures that the eigenvalues are either real or part of a
complex conjugate pair, and the complex pairs lead to damped oscillatory
behavior in Polyakov loop correlation functions, which also appeared in our
previous phenomenological models using complex saddle points. We argue that
this effect should be observable in lattice simulations of QCD at finite
density.",1611.01180v1
2016-12-29,Soft modes in the proton-neutron pairing channel as precursors of deuteron condensate in N=Z nuclei,"Relativistic nuclear response theory is formulated for the proton-neutron
pairing, or deuteron transfer, channel. The approach is based on the
meson-nucleon Lagrangian of Quantum Hadrodynamics (QHD) and advances the
relativistic field theory to connect consistently the high-energy scale of
heavy mesons, the medium-energy range of the pion and the low-energy domain of
emergent collective vibrations (phonons) in a parameter-free way. Mesons and
phonons build up the in-medium nucleon-nucleon interaction in spin-isospin
transfer channels, in particular, the phonon-exchange part takes care of the
leading-order retardation effects. In this framework, we explore $J^{\pi} =
0^+$ and $J^{\pi} = 1^+$ channels of the nuclear response to the proton-neutron
pair removal and addition in $^{56}$Ni and $^{100}$Sn with a special focus on
the lowest (soft) modes as precursors of deuteron condensate and candidates for
being the mediators of the proton-neutron pairing interaction.",1612.09182v4
2017-01-19,Einstein-de Haas Effect in a Dipolar Fermi Gas,"We show that an analogue to the classical Einstein-de Haas effect can appear
in ultracold dipolar Fermi gases. The anisotropic nature of dipole-dipole
interactions can lead to a transfer of magnetization into orbital angular
momentum. Remarkably, distinct from a Bose-Einstein condensate, this transfer
is accompanied by twisting motion, where individual spin components rotate in
opposite directions with larger orbital angular momenta than the full system,
possibly leading to easier experimental observation of the effect. This feature
is induced by the deformation of the Fermi surface and the direction of the
twisting motion can be controlled by an s-wave scattering length or external
magnetic field, possibly providing a method of measuring scattering lengths of
strongly dipolar atomic species.",1701.05446v2
2017-02-03,"Four-body calculation of ${}^2\mathrm{H}(d,p){}^3\mathrm{H}$ and ${}^2\mathrm{H}(d,n){}^3\mathrm{He}$ reactions above breakup threshold","Nucleon transfer reactions in deuteron-deuteron collisions at energies above
the three- and four-body breakup threshold are described using exact four-body
equations for transition operators that are solved in the momentum-space
framework. Differential cross sections, analyzing powers, polarizations, and
spin transfer coefficients are obtained using realistic two-nucleon potentials
and including the Coulomb repulsion between protons. Overall good agreement
between predictions and experimental data is found. Most remarkable
discrepancies are seen around the minima of the differential cross section at
higher energies and in the outgoing nucleon polarization at lower energies.",1702.01034v1
2017-02-09,Electron paramagnetic resonance and photochromism of $\mathrm{N}_{3}\mathrm{V}^{0}$ in diamond,"The defect in diamond formed by a vacancy surrounded by three
nearest-neighbor nitrogen atoms and one carbon atom,
$\mathrm{N}_{3}\mathrm{V}$, is found in $\approx98\%$ of natural diamonds.
Despite $\mathrm{N}_{3}\mathrm{V}^{0}$ being the earliest electron paramagnetic
resonance spectrum observed in diamond, to date no satisfactory simulation of
the spectrum for an arbitrary magnetic field direction has been produced due to
its complexity. In this work, $\mathrm{N}_{3}\mathrm{V}^{0}$ is identified in
$^{15}\mathrm{N}$-doped synthetic diamond following irradiation and annealing.
The $\mathrm{^{15}N}_{3}\mathrm{V}^{0}$ spin Hamiltonian parameters are revised
and used to refine the parameters for $\mathrm{^{14}N}_{3}\mathrm{V}^{0}$,
enabling the latter to be accurately simulated and fitted for an arbitrary
magnetic field direction. Study of $\mathrm{^{15}N}_{3}\mathrm{V}^{0}$ under
excitation with green light indicates charge transfer between
$\mathrm{N}_{3}\mathrm{V}$ and $\mathrm{N_s}$. It is argued that this charge
transfer is facilitated by direct ionization of $\mathrm{N}_{3}\mathrm{V}^{-}$,
an as-yet unobserved charge state of $\mathrm{N}_{3}\mathrm{V}$.",1702.02959v1
2017-06-06,Correlated electron-hole mechanism for molecular doping in organic semiconductors,"The electronic and optical properties of the paradigmatic F4TCNQ-doped
pentacene in the low-doping limit are investigated by a combination of
state-of-the-art many-body \emph{ab initio} methods accounting for
environmental screening effects, and a carefully parametrized model
Hamiltonian. We demonstrate that while the acceptor level lies very deep in the
gap, the inclusion of electron-hole interactions strongly stabilizes
dopant-semiconductor charge transfer states and, together with spin statistics
and structural relaxation effects, rationalize the possibility for
room-temperature dopant ionization. Our findings reconcile available
experimental data, shedding light on the partial vs. full charge transfer
scenario discussed in the literature, and question the relevance of the
standard classification in shallow or deep impurity levels prevailing for
inorganic semiconductors.",1706.01853v2
2017-06-10,Structured singular value analysis for spintronics network information transfer control,"Control laws for selective transfer of information encoded in excitations of
a quantum network, based on shaping the energy landscape using time-invariant,
spatially-varying bias fields, can be successfully designed using numerical
optimization. Such control laws, already departing from classicality by
replacing closed-loop asymptotic stability with alternative notions of
localization, have the intriguing property that for all practical purposes they
achieve the upper bound on the fidelity, yet the (logarithmic) sensitivity of
the fidelity to such structured perturbation as spin coupling errors and bias
field leakages is nearly vanishing. Here, these differential sensitivity
results are extended to large structured variations using $\mu$-design tools to
reveal a crossover region in the space of controllers where objectives usually
thought to be conflicting are actually concordant.",1706.03247v1
2017-08-03,Coherence evolution and transfer supplemented by state-restoring,"The evolution of quantum coherences comes with a set of conservation laws
provided that the Hamiltonian governing this evolution conserves the
spin-excitation number. At that, coherences do not intertwist during the
evolution. Using the transmission line and the receiver in the initial ground
state we can transfer the coherences to the receiver without interaction
between them, { although the matrix elements contributing to each particular
coherence intertwist in the receiver's state. } Therefore we propose a tool
based on the unitary transformation at the receiver side to { untwist these
elements and thus} restore (at least partially) the structure of the sender's
initial density matrix. A communication line with two-qubit sender and receiver
is considered as an example of implementation of this technique.",1708.01132v1
2017-08-08,Towards hyperpolarization of oil molecules via nitrogen-vacancy centers in diamond,"Efficient polarization of organic molecules is of extraordinary relevance
when performing nuclear magnetic resonance (NMR) and imaging. Commercially
available routes to dynamical nuclear polarization (DNP) work at extremely
low-temperatures, thus bringing the molecules out of their ambient thermal
conditions and relying on the solidification of organic samples. In this work
we investigate polarization transfer from optically-pumped nitrogen vacancy
centers in diamond to external molecules at room temperature. This polarization
transfer is described by both an extensive analytical analysis and numerical
simulations based on spin bath bosonization and is supported by experimental
data in excellent agreement. These results set the route to hyperpolarization
of diffusive molecules in different scenarios and consequently, due to
increased signal, to high-resolution NMR.",1708.02427v1
2017-08-10,Perfect quantum state transfer in weighted paths with potentials (loops) using orthogonal polynomials,"A simple method for transmitting quantum states within a quantum computer is
via a quantum spin chain---that is, a path on $n$ vertices. Unweighted paths
are of limited use, and so a natural generalization is to consider weighted
paths; this has been further generalized to allow for loops (\emph{potentials}
in the physics literature). We study the particularly important situation of
perfect state transfer with respect to the corresponding adjacency matrix or
Laplacian through the use of orthogonal polynomials. Low-dimensional examples
are given in detail. Our main result is that PST with respect to the Laplacian
matrix cannot occur for weighted paths on $n\geq 3$ vertices nor can it occur
for certain symmetric weighted trees. The methods used lead us to a conjecture
directly linking the rationality of the weights of weighted paths on $n>3$
vertices, with or without loops, with the capacity for PST between the end
vertices with respect to the adjacency matrix.",1708.03283v2
2017-08-17,"Discovery of a Detached, Eclipsing 40 min Period Double White Dwarf Binary and a Friend: Implications for He+CO White Dwarf Mergers","We report the discovery of two detached double white dwarf (WD) binaries,
SDSS J082239.546+304857.19 and SDSS J104336.275+055149.90, with orbital periods
of 40 and 46 min, respectively. The 40 min system is eclipsing; it is composed
of a 0.30 Msun and a 0.52 Msun WD. The 46 min system is a likely LISA
verification binary. The short 20 Myr and ~34 Myr gravitational wave merger
times of the two binaries imply that many more such systems have formed and
merged over the age of the Milky Way. We update the estimated Milky Way He+CO
WD binary merger rate and affirm our previously published result: He+CO WD
binaries merge at a rate at least 40 times greater than the formation rate of
stable mass-transfer AM~CVn binaries, and so the majority must have unstable
mass-transfer. The implication is that spin-orbit coupling in He+CO WD mergers
is weak, or perhaps nova-like outbursts drive He+CO WDs into merger as proposed
by Shen.",1708.05287v1
2017-08-22,Effects of tunnelling and asymmetry for system-bath models of electron transfer,"We apply the newly derived nonadiabatic golden-rule instanton theory to
asymmetric models describing electron-transfer in solution. The models go
beyond the usual spin-boson description and have anharmonic free-energy
surfaces with different values for the reactant and product reorganization
energies. The instanton method gives an excellent description of the behaviour
of the rate constant with respect to asymmetry for the whole range studied. We
derive a general formula for an asymmetric version of Marcus theory based on
the classical limit of the instanton and find that this gives significant
corrections to the standard Marcus theory. A scheme is given to compute this
rate based only on equilibrium simulations. We also compare the rate constants
obtained by the instanton method with its classical limit to study the effect
of tunnelling and other quantum nuclear effects. These quantum effects can
increase the rate constant by orders of magnitude.",1708.06702v1
2017-09-28,Blandford-Znajek process in vacuo and its holographic dual,"Blandford and Znajek discovered a process by which a spinning black hole can
transfer rotational energy to a plasma, offering a mechanism for energy and jet
emissions from quasars. Here we describe a version of this mechanism that
operates with only vacuum electromagnetic fields outside the black hole. The
setting, which is not astrophysically realistic, involves either a cylindrical
black hole or one that lives in 2+1 spacetime dimensions, and the field is
given in simple, closed form for a wide class of metrics. For asymptotically
Anti-de Sitter black holes in 2+1 dimensions the holographic dual of this
mechanism is the transfer of angular momentum and energy, via a resistive
coupling, from a rotating thermal state containing an electric field to an
external charge density rotating more slowly than the thermal state. In
particular, the entropy increase of the thermal state due to Joule heating
matches the Bekenstein-Hawking entropy increase of the black hole.",1709.10090v2
2017-10-21,Imaging state-to-state reactive scattering in the Ar+ + H2 charge transfer reaction,"The charge transfer reaction of Ar+ with H2 and D2 has been investigated in
an experiment combining crossed beams with three-dimensional velocity map
imaging. Angle-differential cross sections for two collision energies have been
obtained for both neutral species. We find that the product ions are highly
internally excited. In the reaction with H2 the spin-orbit excited Ar+ state's
coupling to the 'resonant' vibrationally excited product H2+(v=2) dominates for
both investigated energies, in line with previous investigations. The observed
angular distributions, however, show significantly less back-scattering than
was found previously. Furthermore, we discovered that the product ions are
highly rotationally excited. In the case of Ar+ reacting with D2 the
energetically closest lying vibrational levels are not strictly preferred and
higher-lying vibrational levels are also populated. For both species the
backward-scattered products show higher internal excitation.",1710.07790v1
2017-11-01,Steady state current fluctuations and dynamical control in a nonequilibrium single-site Bose-Hubbard system,"We investigate nonequilibrium energy transfer in a single-site Bose-Hubbard
model coupled to two thermal baths. By including a quantum kinetic equation
combined with full counting statistics, we investigate the steady state energy
flux and noise power. The influence of the nonlinear Bose-Hubbard interaction
on the transfer behaviors is analyzed, and the nonmonotonic features are
clearly exhibited. Particularly, in the strong on-site repulsion limit, the
results become identical with the nonequilibrium spin-boson model. We also
extend the quantum kinetic equation to study the geometric-phase-induced energy
pump. An interesting reversal behavior is unraveled by enhancing the
Bose-Hubbard repulsion strength.",1711.00206v1
2017-11-22,Momentum transfer dependence of the hadron GPDs and Compton form factors,"The generalized parton distributions (GPDs) of the meson and nucleon at small
and large values of the momentum transfer were determined on the basis of the
comparative analysis of different sets of experimental data of electromagnetic
form factors of the proton and neutron, using the different sets of the parton
distribution functions (PDFs). As a result, different form factors of the
nucleons and meson were calculated. The t-dependence of these form factors was
checked up in the description of the nucleon-nucleon and meson-nucleon elastic
scattering and the differential cross sections of the real Compton scattering.",1711.08205v1
2018-03-02,Improved Charge Transfer Multiplet Method to Simulate M- and L-Edge X-ray Absorption Spectra of Metal-Centered Excited States,"Charge transfer multiplet (CTM) theory is a computationally undemanding and
highly mature method for simulating the soft X-ray spectra of first-row
transition metal complexes. However, CTM theory has seldom been applied to the
simulation of excited state spectra. In this article, we extend the CTM4XAS
software package to simulate M2,3- and L2,3-edge spectra of excited states of
first-row transition metals and to interpret CTM eigenfunctions in terms of
Russell-Saunders term symbols. We use these new programs to reinterpret the
recently reported excited state M2,3-edge difference spectra of photogenerated
ferrocenium cations and propose alternative assignments for the electronic
state of the photogenerated ferrocenium cations supported by CTM theory
simulations. We also use these new programs to model the L2,3-edge spectra of
FeII compounds during nuclear relaxation following photoinduced spin crossover,
and propose spectroscopic signatures for their vibrationally hot states",1803.01067v1
2018-04-17,Emergent Magnetism at the 3$d$-5$d$ Interface: SrMnO$_3/$SrIrO$_3$,"Recent experiments have found new magnetic behaviors, which are different
from the parent bulk materials, at the interfaces between 3$d$ and 5$d$ oxides
such as SrMnO$_3$ (SMO) and SrIrO$_3$ (SIO). The system is of considerable
interest due to the strong spin-orbit coupling in the 5$d$ materials on one
hand and the double exchange physics in SMO on the other, which belongs to the
class of the colossal magnetoresistive (CMR) manganites. In order to gain
insight into the physics of the system, we have performed density-functional
studies on a selected interface structure, viz., the (SMO)$_1$(SIO)$_1$
superlattice, which has been experimentally grown and studied. Our
density-functional results show that the interfacial magnetism is controlled by
a net charge transfer at the interface from the SIO to the SMO side, turning
both of them into ferromagnetic metal from the original antiferromagnetic
insulating state in the bulk. The transferred electrons to the SMO side make it
ferromagnetic through the Anderson-Hasegawa double exchange interaction, while
the SIO part becomes ferromagnetic due to the doping of the half-filled
Mott-Hubbard insulator as suggested by the Nagaoka Theorem. Our results are
discussed in the context of the experiments for the same structure.",1804.06381v1
2018-05-14,Charge-transfer insulation in twisted bilayer graphene,"We studied the real space structure of states in twisted bilayer graphene at
the `magic angle' $\theta = 1.08^\circ$. The flat bands close to charge
neutrality are composed of a mix of `ring' and `center' orbitals around the AA
stacking region. An effective model with localized orbitals is constructed,
which necessarily includes more than just the four flat bands. Long-range
Coulomb interaction causes a charge-transfer at half-filling of the flat bands
from the `center' to the `ring' orbitals. Consequently, the Mott phase is a
featureless spin-singlet paramagnet. We estimate the effective Heisenberg
coupling that favors the singlet coupling to be $J = 3.3$ K, consistent with
experimental values. The superconducting state depends on the nature of the
dopants: hole-doping yields $p+ip$-wave whereas electron-doping yields
$d+id$-wave pairing symmetry.",1805.05294v2
2019-01-16,Landau-Zener topological quantum state transfer,"Fast and robust quantum state transfer (QST) is a major requirement in
quantum control and in scalable quantum information processing. Topological
protection has emerged as a promising route for the realization of QST robust
against sizable imperfections in the network. Here we present a scheme for
robust QST of topologically protected edge states in a dimeric
Su-Schrieffer-Heeger spin chain assisted by Landau-Zener tunneling. As compared
to topological QST protocols based on Rabi flopping proposed in recent works,
our method is more advantageous in terms of robustness against both diagonal
and off-diagonal disorder in the chain, without a substantial increase of the
interaction time.",1901.05157v1
2019-05-04,Interface-engineered hole doping in Sr2IrO4/LaNiO3 heterostructure,"The relativistic Mott insulator Sr2IrO4 driven by large spin-orbit
interaction is known for the Jeff = 1/2 antiferromagnetic state which closely
resembles the electronic structure of parent compounds of superconducting
cuprates. Here, we report the realization of hole-doped Sr2IrO4 by means of
interfacial charge transfer in Sr2IrO4/LaNiO3 heterostructures. X-ray
photoelectron spectroscopy on Ir 4f edge along with the X-ray absorption
spectroscopy at Ni L2 edge confirmed that 5d electrons from Ir sites are
transferred onto Ni sites, leading to markedly electronic reconstruction at the
interface. Although the Sr2IrO4/LaNiO3 heterostructure remains non-metallic, we
reveal that the transport behavior is no longer described by the Mott variable
range hopping mode, but by the Efros-Shklovskii model. These findings highlight
a powerful utility of interfaces to realize emerging electronic states of the
Ruddlesden-Popper phases of Ir-based oxides.",1905.01550v1
2019-07-19,A scaling hypothesis for matrix product states,"We revisit the question of describing critical spin systems and field
theories using matrix product states, and formulate a scaling hypothesis in
terms of operators, eigenvalues of the transfer matrix, and lattice spacing in
the case of field theories. Critical exponents and central charge are
determined by optimizing the exponents such as to obtain a data collapse. We
benchmark this method by studying critical Ising and Potts models, where we
also obtain a scaling ansatz for the correlation length and entanglement
entropy. The formulation of those scaling functions turns out to be crucial for
studying critical quantum field theories on the lattice. For the case of
$\lambda\phi^4$ with mass $\mu^2$ and lattice spacing $a$, we demonstrate a
double data collapse for the correlation length $ \delta
\xi(\mu,\lambda,D)=\tilde{\xi}
\left((\alpha-\alpha_c)(\delta/a)^{-1/\nu}\right)$ with $D$ the bond dimension,
$\delta$ the gap between eigenvalues of the transfer matrix, and
$\alpha_c=\mu_R^2/\lambda$ the parameter which fixes the critical quantum field
theory.",1907.08603v1
2019-07-23,Effects of Ca substitution on quasi-acoustic sliding modes in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$,"The low energy lattice dynamics of the quasi-periodic spin-ladder cuprate
Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ are investigated using terahertz frequency
synchrotron radiation. A high density of low-lying optical excitations are
present in the 1-3 THz energy range, while at least two highly absorbing
excitations stemming from rigid acoustic oscillations of the incommensurate
chain and ladder sublattices, are observed at sub-terahertz frequencies. The
effects of Ca substitution on the sub-terahertz quasi-acoustic sliding mode
gaps is investigated using coherent synchrotron radiation. Analysis of the
results suggest increasing substitution of Sr for Ca is accompanied by a
transfer of spectral weight between sliding modes associated with different
chain-ladder dynamics. The observation is consistent with a transfer of hole
charges from the chains to the ladders and modification of the sublattice
dimensions following Ca substitution. The results are discussed in context to
the significance of low-lying vibrational dynamics and electron-phonon coupling
in the superconducting state of certain quasi-periodic systems.",1907.09739v1
2019-09-21,Can Thermodynamic Behavior of Alice's Particle Affect Bob's Particle?,"We propose an experiment to investigate the possibility of long-distance
thermodynamic relationships between two entangled particles. We consider a pair
of spin 1/2 particles prepared in an entangled singlet state in which one
particle is sent to Alice and the other to her distant mate Bob, who are
spatially separated. Our proposed experiment consists of three different
setups: First, both particles are coupled to two heat baths with various
temperatures. In the second setup, only Alice's particle is coupled to a heat
bath and finally, in the last setup, only Bob's particle is coupled to a heat
bath. We study the evolution of an open quantum system using the first law of
thermodynamics based on the concepts of ergotropy, adiabatic work, and
operational heat, in a quantum fashion. We analyze and compare ergotropy and
heat transfer in three setups. Our results show that the heat transfer for each
entangled particle is not independent of the thermalization process that occurs
for the other one. We prove that the existence of quantum correlations affects
the thermodynamic behavior of distant particles in an entangled state.",1909.10512v2
2019-12-25,A re-formulization of the transfer matrix method for calculating wave-functions in higher dimensional disordered open systems,"We present a numerically stable re-formulization of the transfer matrix
method (TMM). The iteration form of the traditional TMM is transformed into
solving a set of linear equations. Our method gains the new ability of
calculating accurate wave-functions of higher dimensional disordered systems.
It also shows higher efficiency than the traditional TMM when treating finite
systems. In contrast to the diagonalization method, our method not only
provides a new route for calculating the wave-function corresponding to the
boundary conditions of open systems in realistic transport experiments, but
also has advantages that the calculating wave energy/frequency can be tuned
continuously and the efficiency is much higher. Our new method is further used
to identify the necklace state in the two dimensional disordered Anderson
model, where it shows advantage in cooperating the wave-functions with the
continuous transmission spectrum of open systems. The new formulization is very
simple to implement and can be readily generalized to various systems such as
spin-orbit coupling systems or optical systems.",1912.11672v1
2020-01-18,"Diabatic States,Couplings and Potential Energy Surfaces through the Block Localized Excitation Method","We propose a new block localized excitation (BLE) method to directly
construct diabatic excited states without the need to first compute the
adiabatic states. The new method is capable to keep any electrons, spins, and
excitations localized in any divided blocks of intermolecular and
intramolecular systems. At the same time, the electrostatic, exchange, and
polarization interactions between different blocks can be fully taken account
of. To achieve this, a new delta-SCF project method and the maximum
wavefunction overlap method are employed to obtain localized excited states
with orbitals relaxation, and the coupling between them are obtained using
approaches similar to the multistate DFT (MSDFT) method. Numerical results show
that the new BLE method is accurate in calculating the electronic couplings of
the singlet excitation energy transfer (SEET) and triplet energy excitation
transfer (TEET) processes, as well as the excited-state intermolecular
potential energy surface.",2001.06634v1
2020-03-17,The role of silanol nests in the activation of the [Fe=O]2+ group in the reaction of hydrogen atom transfer from methane,"Silanol nests can play the role of places into which positively charged
groups, such as, [FeO]2+, can invade. In the framework of this work, the
influence of such structures on the activity of the [FeO]2+ group in the
reaction of detachment of a hydrogen atom from methane was considered. Two ways
of the reaction of hydrogen atom transfer (HAT) from methane were found: the
so-called ferryl and oxyl routes. It was shown that the reaction of the
detachment of a hydrogen atom from methane, which is a limiting stage of the
oxidation of methane to methanol at the alpha center, proceeds through the
formation of the so-called oxidation state [Fe(III)-O(-)]2+, and fingerprint of
this state is negative spin density on oxo moiety.",2003.07565v1
2020-07-08,Transfer of angular spectrum in parametric down-conversion with structured light,"We develop the formal approach to the angular spectrum transfer in parametric
down-conversion that allows pumping with a structured beam. The scheme is based
on an entangled photon source pumped by a laser beam structured with a
vector-vortex polarization profile. This creates a two-photon quantum state
exhibiting polarization-dependent transverse correlations that can be accessed
through coincidence measurements on the spatially separated photons. The
calculated correlations are shown to present a spin-orbit profile typical of
vector beams, however, distributed on separate measurement regions. Our
approach allows the design of the pump beam vector spatial structure and
measurement strategies for potential applications of these entangled states,
such as in quantum communication.",2007.03883v2
2020-08-08,All magnetic field values cancelling $D_1$ line transitions of alkali metal atoms,"In this work, $\pi$, $\sigma^+$ and $\sigma^-$ transitions between magnetic
sublevels of the $D_1$ line of all alkali atoms are considered analytically.
General block Hamiltonian matrices in presence of a magnetic field for the
ground and excited states are built in order to describe all the transitions.
Eigenvalues and eigenkets describing ground and excited levels are calculated,
""modified"" and unperturbed transfer coefficients as a function of the nuclear
spin $I$, the magnetic quantum number $m$ and the magnetic field magnitude $B$
are defined. Transition cancellations are observed only for some $\pi$
transitions of each isotope. The main result is that we obtain one single
formula which expresses the magnetic field values cancelling these transitions.
These values also correspond to the case when some of other transitions
intensity have their maximum. In addition, we examine the derivative of $\pi$
transition ""modified"" transfer coefficients in order to find the magnetic field
values which correspond to the intensities maximum. The accuracy of the
magnetic field $B$ values is only limited by the uncertainty of the involved
physical quantities.",2008.03581v2
2020-08-21,Integration and characterization of micron-sized YIG structures with very low Gilbert damping on arbitrary substrates,"We present a novel process that allows the transfer of monocrystalline
yttrium-iron-garnet microstructures onto virtually any kind of substrate. The
process is based on a recently developed method that allows the fabrication of
freestanding monocrystalline YIG bridges on gadolinium-gallium-garnet. Here the
bridges' spans are detached from the substrate by a dry etching process and
immersed in a watery solution. Using drop casting the immersed YIG platelets
can be transferred onto the substrate of choice, where the structures finally
can be reattached and thus be integrated into complex devices or experimental
geometries. Using time resolved scanning Kerr microscopy and inductively
measured ferromagnetic resonance we can demonstrate that the structures retain
their excellent magnetic quality. At room temperature we find a ferromagnetic
resonance linewidth of $\mu_0\Delta H_{HWHM}\approx 195\,\mu T$ and we were
even able to inductively measure magnon spectra on a single micron-sized
yttrium-iron-garnet platelet at a temperature of 5 K. The process is flexible
in terms of substrate material and shape of the structure. In the future this
approach will allow for new types of spin dynamics experiments up to now
unthinkable.",2008.09390v1
2020-09-01,Exploring neural network training strategies to determine phase transitions in frustrated magnetic models,"The transfer learning of a neural network is one of its most outstanding
aspects and has given supervised learning with neural networks a prominent
place in data science. Here we explore this feature in the context of strongly
interacting many-body systems. Through case studies, we test the potential of
this deep learning technique to detect phases and their transitions in
frustrated spin systems, using fully-connected and convolutional neural
networks. In addition, we explore a recently-introduced technique, which is at
the middle point of supervised and unsupervised learning. It consists in
evaluating the performance of a neural network that has been deliberately
""confused"" during its training. To properly demonstrate the capability of the
""confusion"" and transfer learning techniques, we apply them to a paradigmatic
model of frustrated magnetism in two dimensions, to determine its phase diagram
and compare it with high-performance Monte Carlo simulations.",2009.00661v2
2020-11-05,Exact solutions of the $C_n$ quantum spin chain,"We study the exact solutions of quantum integrable model associated with the
$C_n$ Lie algebra, with either a periodic or an open one with off-diagonal
boundary reflections, by generalizing the nested off-diagonal Bethe ansatz
method. Taking the $C_3$ as an example we demonstrate how the generalized
method works. We give the fusion structures of the model and provide a way to
close fusion processes. Based on the resulted operator product identities among
fused transfer matrices and some necessary additional constraints such as
asymptotic behaviors and relations at some special points, we obtain the
eigenvalues of transfer matrices and parameterize them as homogeneous $T-Q$
relations in the periodic case or inhomogeneous ones in the open case. We also
give the exact solutions of the $C_n$ model with an off-diagonal open boundary
condition. The method and results in this paper can be generalized to other
high rank integrable models associated with other Lie algebras.",2011.02746v2
2020-11-25,A thermal form factor series for the longitudinal two-point function of the Heisenberg-Ising chain in the antiferromagnetic massive regime,"We consider the longitudinal dynamical two-point function of the XXZ quantum
spin chain in the antiferromagnetic massive regime. It has a series
representation based on the form factors of the quantum transfer matrix of the
model. The $n$th summand of the series is a multiple integral accounting for
all $n$-particle $n$-hole excitations of the quantum transfer matrix. In
previous works the expressions for the form factor amplitudes appearing under
the integrals were either again represented as multiple integrals or in terms
of Fredholm determinants. Here we obtain a representation which reduces, in the
zero-temperature limit, essentially to a product of two determinants of finite
matrices whose entries are known special functions. This will facilitate the
further analysis of the correlation function.",2011.12752v3
2020-12-07,Dynamic structure factors of a strongly interacting Fermi superfluid near an orbital Feshbach resonance across the phase transition from BCS to Sarma superfluid,"We theoretically investigate dynamic structure factors of a strongly
interacting Fermi superfluid near an orbital Feshbach resonance with random
phase approximation, and find their dynamical characters during the phase
transition between a balanced conventional Bardeen-Cooper-Schrieffer superfluid
and a polarized Sarma superfluid by continuously varying the chemical potential
difference of two spin components. In a BEC-like regime of the BCS superfluid,
dynamic structure factors can do help to distinguish the in-phase ground state
from the out-of-phase metastable state by the relative location of molecular
excitation and Leggett mode, or the minimum energy to break a Cooper pair. In
the phase transition between BCS and Sarma superfluid, we find the dynamic
structure factor of Sarma superfluid has its own specific gapless excitation at
a small transferred momentum which is mixed with the collective phonon
excitation, and also a relatively strong atomic excitation at a large
transferred momentum because of the existence of unpaired Fermi atoms, these
signals can be used to differentiate Sarma superfluid from BCS superfluid.",2012.03497v1
2020-12-07,Parahydrogen-induced polarization relayed via proton exchange,"The sensitivity of NMR and MRI can be boosted via hyperpolarization of
nuclear spins. However, current methods are costly, polarization is relatively
low, or applicability is limited. Here, we report a new hyperpolarization
method combining the low-cost, high polarization of hydrogenative
parahydrogen-induced polarization (PHIP) with the flexibility of polarization
transfer via proton exchange. The new method can be used to polarize various
molecules, including alcohols, water, lactate, and pyruvate. On average, only
$\approx$3 mM of a hyperpolarized transfer agent was sufficient to
significantly enhance the signal of $\approx$100 mM of target molecules via
proton exchange. Thus, hydrogenative parahydrogen-induced hyperpolarization
with proton exchange (PHIP-X) provides a new avenue for NMR applications beyond
the limits imposed by thermal polarization.",2012.03626v1
2020-12-11,From one- to two-magnon excitations in the S=3/2 magnet $β$-CaCr$_2$O$_4$,"We apply neutron spectroscopy to measure the magnetic dynamics in the S=3/2
magnet $\beta$-CaCr$_2$O$_4$ (T$_N$=21 K). The low-energy fluctuations, in the
ordered state, resemble large-S linear spin-waves from the incommensurate
ground state. However, at higher energy transfers, these semi-classical and
harmonic dynamics are replaced by an energy and momentum broadened continuum of
excitations. Applying kinematic constraints required for energy and momentum
conservation, sum rules of neutron scattering, and comparison against exact
diagonalization calculations, we show that the dynamics at high-energy
transfers resemble low-S one-dimensional quantum fluctuations.
$\beta$-CaCr$_2$O$_4$ represents an example of a magnet at the border between
classical N\'eel and quantum phases, displaying dual characteristics.",2012.06314v2
2021-03-04,A paradigm system for strong correlation and charge transfer competition,"In chemistry and condensed matter physics the solution of simple paradigm
systems, such as the hydrogen atom and the uniform electron gas, plays a
critical role in understanding electron behaviors and developing electronic
structure methods. The H$_2$ molecule is a paradigm system for strong
correlation with a spin-singlet ground state that localizes the two electrons
onto opposite protons at dissociation. We extend H$_2$ to a new paradigm system
by using fractional nuclear charges to break the left-right nuclear symmetry,
thereby enabling the competition between strong correlation and charge transfer
that drives the exotic properties of many materials. This modification lays a
foundation for improving practical electronic structure theories and provides
an extendable playground for analyzing how the competition appears and evolves.",2103.03178v1
2021-04-06,All-Optical Control of Magnetization in Quantum-Confined Ultrathin Magnetic Metals,"All-optical control dynamics of magnetization in sub-10 nm metallic thin
films are investigated, as these films with quantum confinement undergo unique
interactions with femtosecond laser pulses. Our theoretical derivations based
on the free electron model show that the density of states at Fermi level
(DOS_F) and electron-phonon coupling coefficients (G_ep) in ultrathin metals
have very high sensitivity to film thickness within a few Angstroms. As DOS_F
and G_ep depend on thickness, we show that completely different magnetization
dynamics characteristics emerge compared with bulk metals. Our model suggests
highly-efficient energy transfer from fs laser photons to spin waves due to
minimal energy absorption by phonon. This sensitivity to thickness and
efficient energy transfer offers an opportunity to obtain ultrafast on-chip
magnetization dynamics.",2104.02608v1
2021-08-19,Transfer Matrix description of heterostructured spintronics Terahertz emission,"In this work we developed an extension to the Transfer Matrix method (TMM) to
include a current source term, with the aim of describing both the transmission
and emission of THz pulses in spintronics THz emitters. The TMM with source is
derived from the Maxwell equations with a volume free current term. This
extension to the TMM allows for the study of realistic spintronics THz emitters
as multilayers of different materials with different thicknesses. We use this
to prove that, in spite of a common misconception, the drop rate of the THz
emission amplitude at higher heavy metal layer thicknesses is not related and
does not provide information about the spin diffusion length. It is instead the
effect of the increase in the parasitic absorption of the generated radiation
by the conducting parts of the spintronics THz emitter itself.",2108.08472v1
2021-09-12,Concurrent J-Evolving Refocusing Pulses,"Conventional refocusing pulses are optimised for a single spin without
considering any type of coupling. However, despite the fact that most couplings
will result in undesired distortions, refocusing in delay-pulse-delay-type
sequences with desired heteronuclear coherence transfer might be enhanced
considerably by including coupling evolution into pulse design. We provide a
proof of principle study for a Hydrogen-Carbon refocusing pulse sandwich with
inherent J-evolution following the previously reported ICEBERG-principle with
improved performance in terms of refocusing performance and/or overall
effective coherence transfer time. Pulses are optimised using optimal control
theory with a newly derived quality factor and z-controls as an efficient tool
to speed up calculations. Pulses are characterised in detail and compared to
conventional concurrent refocusing pulses, clearly showing an improvement for
the J-evolving pulse sandwich. As a side-product, also efficient J-compensated
refocusing pulse sandwiches -- termed BUBU pulses following the nomenclature of
previous J-compensated BUBI and BEBE(tr) pulse sandwiches -- have been
optimised.",2109.05453v1
2021-09-14,A bosonic perspective on the classical mapping of fermionic quantum dynamics,"We consider the application of the original Meyer-Miller (MM) Hamiltonian to
mapping fermionic quantum dynamics to classical equations of motion.
Non-interacting fermionic and bosonic systems share the same one-body density
dynamics when evolving from the same initial many-body state. The MM classical
mapping is exact for non-interacting bosons, and therefore it yields the exact
time-dependent one-body density for non-interacting fermions as well. Starting
from this observation, the MM mapping is compared to different mappings
specific for fermionic systems, namely the spin mapping (SM) with and without
including a Jordan-Wigner transformation, and the Li-Miller mapping (LMM). For
non-interacting systems, the inclusion of fermionic anti-symmetry through the
Jordan-Wigner transform does not lead to any improvement in the performance of
the mappings and instead it worsens the classical description. For an
interacting impurity model and for models of excitonic energy transfer, the MM
and LMM mappings perform similarly, and in some cases the former outperforms
the latter when compared to a full quantum description. The classical mappings
are able to capture interference effects, both constructive and destructive,
that originate from equivalent energy transfer pathways in the models.",2109.06563v1
2021-09-24,Partial Charge Transfer and Absence of Induced Magnetization in EuS(111)/Bi$_2$Se$_3$ Heterostructures,"Heterostructures made from topological and magnetic insulators promise to
form excellent platforms for new electronic and spintronic functionalities
mediated by interfacial effects. We report the results of a first-principles
density functional theory study of the geometric, electronic structure, and
magnetic properties of EuS(111)/Bi$_2$Se$_3$ interface, including van der Waals
and relativistic spin-orbit effects. In contrast to previous theoretical
studies, we find no appreciable magnetic anisotropy in such a heterostructure.
We also do not see additional induced magnetization at the interface or the
magnetic proximity effect on the topological states. This is due to the
localized nature of Eu moments, and because of a partial charge transfer of
$\sim$0.5 electron from Eu to Se. The formation of the surface dipole shifts
the Dirac cone about 0.4~eV below the chemical potential, and the associated
electrostatic screening moves the topological state from the first to the
second quintuple layer of Bi$_2$Se$_3$.",2109.11991v1
2021-11-08,Newly born extragalactic millisecond pulsars as efficient emitters of PeV neutrinos,"The origins of the diffuse flux of cosmogenic PeV neutrinos detected in the
IceCube experiment during 2010 - 2017 remain unidentified. A population of
extragalactic newly born fast spinning pulsars are investigated as possible
candidates for generating the PeV energy scale neutrinos. A two-step mechanism
of particle acceleration is adopted for transferring energy from star rotation
to high energy electrons. Electrons might be boosted up to $\approx 0.01$ EeV
energies and above, and produce ultra-high-energy (UHE) neutrinos and gamma
rays when these electrons interact with low energy positrons and soft
radiations in the acceleration zone. The theoretically derived extragalactic
diffuse muon neutrino flux in the energy range [1-10] PeV is found consistent
with the IceCube level if only a fraction ($\eta_{k} \approx 0.31\%$) of the
total bolometric luminosity of pulsars are transferred to power the PeV
neutrinos. Using the above value of the cosmic ray electron loading parameter
$\eta_{k}$, the diffuse gamma ray flux from inverse Compton scattering off UHE
electrons in the soft radiation field might be predicted from the model.",2111.04656v1
2021-11-09,Real time phase imaging with an asymmetric transfer function metasurface,"The conversion of phase variations in an optical wavefield into intensity
information is of fundamental importance for optical imaging technology
including microscopy of biological cells. While conventional approaches to
phase-imaging commonly rely on bulky optical components or computational post
processing, meta-optical devices have recently demonstrated all-optical,
ultracompact image processing methods. Here we describe a metasurface that
exploits photonic spin-orbit coupling to create an asymmetric optical transfer
function for real time phase-imaging. The effect of the asymmetry on
transmission through the device is demonstrated experimentally with the
generation of high contrast pseudo-3D intensity images of phase variations in
an optical wavefield without the need for post-processing. This
non-interferometric method has potential applications in biological live cell
imaging and real-time wavefront sensing.",2111.05404v1
2022-01-03,Single Phonon Detection for Dark Matter via Quantum Evaporation and Sensing of $^3$Helium,"Dark matter is five times more abundant than ordinary visible matter in our
Universe. While laboratory searches hunting for dark matter have traditionally
focused on the electroweak scale, theories of low mass hidden sectors motivate
new detection techniques. Extending these searches to lower mass ranges, well
below 1 GeV/c$^2$, poses new challenges as rare interactions with standard
model matter transfer progressively less energy to electrons and nuclei in
detectors. Here, we propose an approach based on phonon-assisted quantum
evaporation combined with quantum sensors for detection of desorption events
via tracking of spin coherence. The intent of our proposed dark matter sensors
is to extend the parameter space to energy transfers in rare interactions to as
low as a few meV for detection of dark matter particles in the keV/c$^2$ mass
range.",2201.00738v3
2022-01-04,Spectrum of the transfer matrices of the spin chains associated with the $A^{(2)}_3$ Lie algebra,"We study the exact solution of quantum integrable system associated with the
$A^{(2)}_3$ twist Lie algebra, where the boundary reflection matrices have
non-diagonal elements thus the $U(1)$ symmetry is broken. With the help of the
fusion technique, we obtain the closed recursive relations of the fused
transfer matrices. Based on them, together with the asymptotic behaviors and
the values at special points, we obtain the eigenvalues and Bethe ansatz
equations of the system. We also show that the method is universal and valid
for the periodic boundary condition where the $U(1)$ symmetry is reserved. The
results in this paper can be applied to studying the exact solution of the
$A^{(2)}_n$-related integrable models with arbitrary $n$.",2201.00963v2
2022-03-31,Variational corner transfer matrix renormalization group method for classical statistical models,"In the context of tensor network states, we for the first time reformulate
the corner transfer matrix renormalization group (CTMRG) method into a
variational bilevel optimization algorithm. The solution of the optimization
problem corresponds to the fixed-point environment pursued in the conventional
CTMRG method, from which the partition function of a classical statistical
model, represented by an infinite tensor network, can be efficiently evaluated.
The validity of this variational idea is demonstrated by the high-precision
calculation of the residual entropy of the dimer model, and is further verified
by investigating several typical phase transitions in classical spin models,
where the obtained critical points and critical exponents all agree with the
best known results in literature. Its extension to three-dimensional tensor
networks or quantum lattice models is straightforward, as also discussed
briefly.",2203.17098v1
2022-04-06,Power transfer in magnetoelectric resonators,"We derive an analytical model for the power transfer in a magnetoelectric
film bulk acoustic resonator consisting of a piezoelectric--magnetostrictive
bilayer. The model describes the dynamic magnetostrictive influence on the
elastodynamics via an effective frequency-dependent stiffness constant. This
allows for the calculation of both the magnetic and elastic power absorption in
the resonator as well as of its energy efficiency when such a resonator is
considered as a magnetic transducer. The model is then applied to example
systems consisting of piezoelectric ScAlN and magnetostrictive CoFeB, Ni, or
Terfenol-D layers.",2204.03072v2
2022-08-07,Discrimination of Chiral and Helical Contributions to Raman Scattering of Liquid Crystals using Vortex Beams,"We use vortex photon fields with orbital and spin angular momentum to probe
chiral fluctuations within liquid crystals. In the regime of iridescence with a
well-defined pitch length of chirality, we find low energy Raman scattering
that can be decomposed into helical and chiral components depending on the
scattering vector and the topological charge of the incident photon field.
Based on the observation of an anomalous dispersion we attribute quasi-elastic
scattering to a transfer of angular momenta to roton-like quasiparticles. The
latter are due to a competition of short-range repulsive and long-range dipolar
interactions. Our approach using a transfer of orbital angular momentum opens
up an avenue for the advanced characterization of chiral and optically active
devices and materials.",2208.03793v2
2022-12-17,Multi-point correlation functions in the boundary XXZ chain at finite temperature,"We consider multi-point correlation functions in the open XXZ chain with
longitudinal boundary fields and in a uniform external magnetic field. We show
that, at finite temperature, these correlation functions can be written in the
quantum transfer matrix framework as sums over thermal form factors. More
precisely, and quite remarkably, each term of the sum is given by a simple
product of usual matrix elements of the quantum transfer matrix multiplied by a
unique factor containing the whole information about the boundary fields. As an
example, we provide a detailed expression for the longitudinal spin one-point
functions at distance $m$ from the boundary. This work thus solves the
long-standing problem of setting up form factor expansions in integrable models
subject to open boundary conditions.",2212.08824v2
2023-05-24,Quantum turnstiles for robust measurement of full counting statistics,"We present a scalable protocol for measuring full counting statistics (FCS)
in experiments or tensor-network simulations. In this method, an ancilla in the
middle of the system acts as a turnstile, with its phase keeping track of the
time-integrated particle flux. Unlike quantum gas microscopy, the turnstile
protocol faithfully captures FCS starting from number-indefinite initial states
or in the presence of noisy dynamics. In addition, by mapping the FCS onto a
single-body observable, it allows for stable numerical calculations of FCS
using approximate tensor-network methods. We demonstrate the wide-ranging
utility of this approach by computing the FCS of the transferred magnetization
in a Floquet Heisenberg spin chain, as studied in a recent experiment with
superconducting qubits, as well as the FCS of charge transfer in random
circuits.",2305.15464v1
2023-07-04,Two-photon-transition superadiabatic passage in an nitrogen-vacancy center in diamond,"Reaching a given target quantum state with high fidelity and fast operation
speed close to the quantum limit represents an important goal in quantum
information science. Here, we experimentally demonstrate superadiabatic quantum
driving to achieve population transfer in a three-level solid-state spin
system. Starting from traditional stimulated Raman adiabatic passage (STIRAP),
our approach implements superadiabatic corrections to the STIRAP Hamiltonians
with several paradigmatic pulse shapes. It requires no need of intense
microwave pulses or long transfer times and shows enhanced robustness over
pulse imperfections. These results might provide a useful tool for quantum
information processing and coherent manipulations of quantum systems.",2307.01675v1
2023-08-10,"Wannier functions, minimal model and charge transfer in Pb$_9$CuP$_6$O$_{25}$","Recent preprints claimed that the copper doped lead apatite
Pb$_9$CuP$_6$O$_{25}$ (LK99) might be a high-temperature superconductor because
of its strong diamagnetism and transport properties. Motivated by the strongly
correlated effects that can arise from a triangular lattice of Cu atoms with
narrow bandwidth, we calculated the maximally projected Wannier functions from
density functional theory simulations, and constructed a minimal two-orbital
triangular model with Cu ($3d_{xz},3d_{yz}$) basis, and a four-orbital buckled
honeycomb model with Cu ($3d_{xz},3d_{yz}$), O ($2p_x,2p_y$). Since the Coulomb
interaction Ud is much larger than potential energy difference between Cu and
O, charge transfer will occur for hole filling fraction $n_h > 1$. We further
calculate the interaction parameters, and discuss the possible insulating state
and corresponding spin exchange coupling.",2308.05528v1
2023-09-27,Detecting quantum phase transitions in a frustrated spin chain via transfer learning of a quantum classifier algorithm,"The classification of phases and the detection of phase transitions are
central and challenging tasks in diverse fields. Within physics, it relies on
the identification of order parameters and the analysis of singularities in the
free energy and its derivatives. Here, we propose an alternative framework to
identify quantum phase transitions. Using the axial next-nearest neighbor Ising
(ANNNI) model as a benchmark, we show how machine learning can detect three
phases (ferromagnetic, paramagnetic, and a cluster of the antiphase with the
floating phase). Employing supervised learning, we demonstrate the feasibility
of transfer learning. Specifically, a machine trained only with
nearest-neighbor interactions can learn to identify a new type of phase
occurring when next-nearest-neighbor interactions are introduced. We also
compare the performance of common classical machine learning methods with a
version of the quantum nearest neighbors (QNN) algorithm.",2309.15339v1
2023-09-28,Folding QQ-relations and transfer matrix eigenvalues: towards a unified approach to Bethe ansatz for super spin chains,"Extending the method proposed in [arXiv:1109.5524], we derive QQ-relations
(functional relations among Baxter Q-functions) and T-functions (eigenvalues of
transfer matrices) for fusion vertex models associated with the twisted quantum
affine superalgebras $U_{q}(gl(2r+1|2s)^{(2)})$, $U_{q}(gl(2r|2s+1)^{(2)})$,
$U_{q}(gl(2r|2s)^{(2)})$, $U_{q}(osp(2r|2s)^{(2)})$ and the non-twisted quantum
affine orthosymplectic superalgebras $U_{q}(osp(2r+1|2s)^{(1)})$ and
$U_{q}(osp(2r|2s)^{(1)})$ (and their Yangian counterparts, $Y(osp(2r+1|2s))$
and $Y(osp(2r|2s))$) as reductions (a kind of folding) of those for associated
with $U_{q}(gl(M|N)^{(1)})$. In particular, we reproduce previously proposed
generating functions (difference operators) of the T-functions for the
symmetric or anti-symmetric representations, and tableau sum expressions for
more general representations for orthosymplectic superalgebras
[arXiv:0911.5393,arXiv:0911.5390], and obtain Wronskian-type expressions
(analogues of Weyl-type character formulas) for them. T-functions for spinorial
representations are related to reductions of those for asymptotic limits of
typical representations of $U_{q}(gl(M|N)^{(1)})$.",2309.16660v3
2023-10-22,Pion gravitational form factors at large momentum transfer in the instant-form relativistic impulse approximation approach,"We extend our relativistic theory of gravitational structure of composite
hadrons to obtain the pion gravitational form factors at large momentum
transfers. The approach was used in the case of intermediate region of the
variable in our preceding works arXiv:2010.11640 and arXiv:2201.04991. The
calculation is carried out in the framework of a relativistic
composite-particle model complemented by the special relativistic form of
impulse approximation. It is found that in the limit of massless and pointlike
quarks, the obtained asymptotic expansion coincides with the predictions of
perturbative QCD for gravitational pion form factors. The principal
contribution to the asymptotics, coinciding with the predictions of QCD, is
given by the relativistic effect of spin rotation. In particular, the
asymptotics of the D form factor is completely determined by this kinematic
effect. Several constraints on the allowed form of gravitational form factors
of quarks are derived.",2310.14287v2
2023-11-02,Polarization effects in elastic deuteron-electron scattering,"The differential cross section and polarization observables for the elastic
reaction induced by deuteron scattering off electrons at rest are calculated in
the one-photon-exchange (Born) approximation. Specific attention is given to
the kinematical conditions, that is, to the specific range of incident energy
and transferred momentum. The specific interest of this reaction is to access
very small transferred momenta. Numerical estimates are given for polarization
observables that describe the of single- and double-spin effects, provided that
the polarization components (both, vector and tensor) of each particle in the
reaction are determined in the rest frame of the electron target.",2311.01102v2
2023-12-07,Off-diagonal approach to the exact solution of quantum integrable systems,"We investigate the $t$-$W$ scheme for the anti-ferromagnetic XXX spin chain
under both periodic and open boundary conditions. We propose a new
parametrization of the eigenvalues of transfer matrix. Based on it, we obtain
the exact solution of the system. By analyzing the distribution of zero roots
at the ground state, we obtain the explicit expressions of the eigenfunctions
of the transfer matrix and the associated $\mathbb{W}$ operator (see (2.8) and
(3.20)) in the thermodynamic limit. We find that the ratio of the quantum
determinant with the eigenvalue of $\mathbb{W}$ operator for the ground state
exhibits exponential decay behavior. Thus this fact ensures that the so-called
inversion relation (the $t-W$ relation without the $W$-term) can be used to
study the ground state properties of quantum integrable systems with/without
$U(1)$-symmetry in the thermodynamic limit.",2312.04153v1
2023-12-13,Non-relativistic nuclear reduction for tensor couplings in dark matter direct detection and $μ\to e$ conversion,"In recent years, the non-relativistic effective theory (NRET) has been widely
used for direct detection of dark matter and $\mu \to e$ conversion.
Nevertheless, existing literature has not fully considered tensor interactions,
introducing a critical gap in our understanding. This study addresses this
omission by integrating tensor amplitudes into the NRET framework, employing a
novel approach for decomposing antisymmetric tensor-type interactions. This
work establishes the connection between the tensor amplitudes and the
non-relativistic Galilean-invariant operators. Specifically, it explores this
relationship up to the leading order in momentum transfer, stemming from the
exchange of spin-half particles in dark matter scenarios, and extends the
analysis to the lepton-velocities orders for $\mu \to e$ conversion cases. To
facilitate further research and experimental analyses, comprehensive tables
containing the requisite tensor matrix elements at finite momentum transfer are
furnished, encompassing all possible Lorentz-invariant terms. These tensor
terms are crucial to the analysis of ongoing experiments of dark matter
detection through scattering off nuclei, as well as charged-lepton flavor
violation in the $\mu \to e$ conversion. Upon successful detection, they will
contribute significantly to the comprehension of the nature of these new
physics interactions.",2312.08339v1
2024-01-20,Charge transfer transitions and circular magnetooptics in ferrites,"The concept of charge-transfer (CT) transitions in ferrites is based on the
cluster approach and takes into account the relevant interactions as the
low-symmetry crystal field, spin-orbital, Zeeman, exchange and
exchange-relativistic interactions. For all its simplicity, this concept yield
a reliable qualitative and quantitative microscopic explanation of spectral,
concentration, temperature, and field dependences of optic and magneto-optic
properties ranging from the isotropic absorption as well as the optic
anisotropy to the circular magneto-optics. In this review paper, starting with
a critical analysis of the fundamental shortcomings of the ""first-principles""
DFT-based band theory we present the main ideas and techniques of the cluster
theory of the CT transitions to be main contributors to circular magneto-optics
of ferrites.",2401.11267v1
2024-02-16,Generation of heralded vector-polarized single photons in remotely controlled topological classes,"We demonstrate an experimental protocol for the preparation and control of
heralded single photons in inhomogeneously polarized states, such as Vector
Vortex and Full Poincar\'e beam states. A laser beam is shaped by a
voltage-controlled spin-to-orbital angular momentum converter q-plate device
which eliminates the need for an interferometer for the robust preparation of
high-quality inhomogeneously polarized beams. Such a beam is then used as pump
in a spontaneous parametric downconversion (SPDC) photon-pair source. We
demonstrate the full pump to heralded single photon transfer of the
intensity/phase distributions, as well as of the vector polarization structure.
Additionally, we show that by controlling the polarization to which the
heralding idler photon is projected before detection, we can toggle between the
direct and basis-switched pump-single photon transfer. We show that this
non-local control of the heralded single photon pertains also to the
topological class of the resulting heralded single photon. We believe that our
work will lead to new opportunities in photons-based quantum information
processing science.",2402.11046v1
1994-11-02,Exact Diagonalization Study of Strongly Correlated Electron Models: Hole pockets and shadow bands in the doped t-J model,"A detailed exact-diagonalization study is made for the doping dependence of
the single-particle spectral function $A({\bf k},\omega)$ and momentum
distribution function $n({\bf k})$ of the two-dimensional $t$$-$$J$ model as a
representative model for doped Mott insulators. The results for $A({\bf
k},\omega)$ show unambiguously that the rigid-band behavior is realized in the
small-cluster $t$$-$$J$ model: upon doping, the uppermost states of the
quasiparticle band observed at half filling simply cross the Fermi level and
reappear as the lowermost states of the inverse photoemission spectrum, while
the photoemission side of the band remains essentially unaffected. We discuss
problems in directly determining the Fermi surface from $n({\bf k})$ and make a
situation where they are largely avoided; we then find clear signatures of a
Fermi surface which takes the form of small hole pockets. The identical scaling
with $t/J$ of the quasiparticle weight $Z_h$ and difference in $n({\bf k})$
between neighboring ${\bf k}$-points suggests the existence of such a Fermi
surface in the physical regime of parameters. We construct spin-bag operators
which describe the holes dressed by the antiferromagnetic spin fluctuations and
find that elementary electronic excitations of the system can be described well
in terms of weakly-interacting spin-1/2 Fermionic quasiparticles corresponding
to the doped holes. We make a comparison with other numerical calculations and
recent angle-resolved photoemission experiment and argue that, adopting this
rather conventional Fermi-liquid scenario with non-Luttinger Fermi surface, one
would explain many quasiparticle-relating properties of doped cuprates in a
very simple and natural way. We also show that the dynamical spin and charge
excitations deviate from the particle-hole excitations of this Fermi liquid:
e.g., the dominant low-energy spin excitation at momentum transfer $(\pi,\pi)$
reflects excitations of the incoherent spin background and is identified as a
collective mode comparable to spin waves in the Heisenberg antiferromagnet.",9411010v1
2005-08-01,Heavy Hyperon--Antihyperon Production,"Based on the experience from the production of anti-Lambda Lambda and
anti-Sigma Sigma pairs at LEAR (experiment PS185) it is suggested to continue
the investigations towards the heavier antihyperon--hyperon pairs anti-Xi Xi
and anti-Omega Omega in view of: (1) the production dynamics of the heavier
antihyperon--hyperon out of the anti-p p annihilation (2) a comparison of the
(3s 3anti-s quark system) anti-Omega Omega to the (3 (anti-s s)) 3 phi meson
production, where both systems have similar masses (3.345 and 3.057,
respectively) and identical valence quark content. A systematic study of the
antihyperon--hyperon production with increasing strangeness content is
interesting for the following reasons: The anti-Omega Omega production is the
creation of two spin 3/2 objects out of the two spin 1/2 anti-p p particles.
Results of the PS185 experiments prove a clear dominance of the spin triplet
anti-s s dissociation. In the Omega anti-Omega the three s-quarks (three anti-s
quarks) are aligned to spin 3/2 each. If the three anti-s s pairs are now all
in spin triplet configurations when created out of the gluonic interaction they
should have spin parity quantum number as 3^- as long as Omega anti-Omega is
created with relative L=0 angular momentum. The comparison of the Omega
anti-Omega baryon pair to the phi phi phi three meson production (where the
three anti-s s quark pairs might not but can be produced without relative
correlation) would provide a unique determination of the intermediate matter
state. Measurements of excitation functions and polarization transfers should
be used to examine these gluon rich anti-p p --> anti-Omega Omega and anti-p p
--> phi phi phi reaction channels. Such experiments should be performed at the
PANDA detector at the FAIR facility of the GSI.",0508006v1
2012-09-05,Hubbard-model description of the high-energy spin-spectral-weight distribution in La(2)CuO(4),"The spectral-weight distribution in recent neutron scattering experiments on
the parent compound La$_2$CuO$_4$ (LCO), which are limited in energy range to
about 450\,meV, is studied in the framework of the Hubbard model on the square
lattice with effective nearest-neighbor transfer integral $t$ and on-site
repulsion $U$. Our study combines a number of numerical and theoretical
approaches, including, in addition to standard treatments, density matrix
renormalization group calculations for Hubbard cylinders and a suitable spinon
approach for the spin excitations. Our results confirm that the $U/8t$
magnitude suitable to LCO corresponds to intermediate $U$ values smaller than
the bandwidth $8t$, which we estimate to be $8t \approx 2.36$ eV for
$U/8t\approx 0.76$. This confirms the unsuitability of the conventional linear
spin-wave theory. Our theoretical studies provide evidence for the occurrence
of ground-state d-wave spinon pairing in the half-filled Hubbard model on the
square lattice. This pairing applies only to the rotated-electron spin degrees
of freedom, but it could play a role in a possible electron d-wave pairing
formation upon hole doping. We find that the higher-energy spin spectral weight
extends to about 566 meV and is located at and near the momentum $[\pi,\pi]$.
The continuum weight energy-integrated intensity vanishes or is extremely small
at momentum $[\pi,0]$. This behavior of this intensity is consistent with that
of the spin waves observed in recent high-energy neutron scattering
experiments, which are damped at the momentum $[\pi,0]$. We suggest that future
LCO neutron scattering experiments scan the energies between 450 meV and 566
meV and momenta around $[\pi,\pi]$.",1209.1010v1
2013-02-03,Settling accretion onto slowly rotating X-ray pulsars,"Quasi-spherical subsonic accretion onto slowly rotating magnetized NS is
considered, when the accreting matter settles down subsonically onto the
rotating magnetosphere, forming an extended quasi-static shell. The shell
mediates the angular momentum transfer to/from the rotating NS magnetosphere by
large-scale convective motions, which lead to an almost iso-angular-momentum
rotation law inside the shell. The accretion rate through the shell is
determined by the ability of the plasma to enter the magnetosphere due to
Rayleigh-Taylor instability while taking cooling into account. The settling
regime of accretion is possible for moderate X-ray luminosities L <4 10^36
erg/s. At higher luminosities a free-fall gap above the NS magnetosphere
appears due to rapid Compton cooling, and accretion becomes highly
non-stationary. From observations of spin-up/spin-down rates of wind accreting
equilibrium XPSRs with known orbital periods (GX 301-2, Vela X-1), the main
dimensionless parameters of the model and be determined and the NS magnetic
field can be estimated. For equilibrium pulsars with independent measurements
of the magnetic field the velocity of the stellar wind can be estimated without
the use of complicated spectroscopic measurements. For non-equilibrium pulsars,
a maximum possible value of the spin-down rate of the accreting neutron star
exists. From observations of the spin-down rate and the X-ray luminosity in
such pulsars (e. g. GX 1+4, SXP 1062 and 4U 2206+54) a lower limit on the
neutron star magnetic field is obtained, which in all cases turns out to be
close to the standard 10^12-10^13 G value, in agreement with cyclotron line
measurements. The model explains both the spin-up/spin-down of the pulsar
frequency on large time-scales and the irregular short-term frequency
fluctuations, which may correlate or anti-correlate with the X-ray luminosity
fluctuations.",1302.0500v1
2013-03-12,Kinetic Control of Recombination in Organic Photovoltaics: The Role of Spin,"In photovoltaic diodes recombination of photogenerated electrons and holes is
a major loss process. Biological light harvesting complexes (LHCs) prevent
recombination via the use of cascade structures, which lead to spatial
separation of charge-carriers1. In contrast, the nanoscale morphology and high
charge densities in organic photovoltaic cells (OPVs) give a high rate of
electron-hole encounters, which should result in the formation of spin triplet
excitons, as in organic light emitting diodes (OLEDs)2. OPVs would have poor
quantum efficiencies if every encounter lead to recombination, but
state-of-the-art OPVs demonstrate near-unity quantum efficiency3. Here we show
that this suppression of recombination can be engineered through the interplay
between spin, energetics and delocalisation of electronic excitations in
organic semiconductors. We use time-resolved spectroscopy to study a series of
model, high efficiency polymer-fullerene systems in which the lowest lying
molecular triplet exciton (T1) (on the polymer) lies below the intermolecular
charge transfer state (CT). We observe the formation of T1 states following
bimolecular recombination, indicating that encounters of spin-uncorrelated
electrons and holes generate CT states with both spin singlet (1CT) and spin
triplet (3CT) characters. We show that triplet exciton formation can be the
major loss mechanism in OPVs. However, we find that even when energetically
favoured, the relaxation of 3CT to T1 can be strongly suppressed, via control
over wavefunction delocalisation, allowing for the dissociation of 3CT back to
free changes, thereby reducing recombination and enhancing device performance.
Our results point towards new design rules for artificial photo-conversion
systems, enabling the suppression of electron-hole recombination, and also for
OLEDs, avoiding the formation of triplet states and enhancing fluorescence
efficiency.",1303.2821v1
2015-06-23,Semi-phenomenological analysis of neutron scattering results for quasi-two dimensional quantum anti-ferromagnet,"The available results from the inelastic neutron scattering experiment
performed on the quasi-two dimensional spin $\frac{1}{2}$ anti-ferromagnetic
material $La_2 Cu O_4$ have been analysed theoretically. The formalism of ours
is based on a semi-classical like treatment involving a model of an ideal gas
of mobile vortices and anti-vortices built on the background of the
N$\acute{e}$el state, using the bipartite classical spin configuration
corresponding to an XY- anisotropic Heisenberg anti-ferromagnet on a square
lattice. The results for the integrated intensities for our spin $\frac{1}{2}$
model corresponding to different temperatures, show occurrence of vigorous
unphysical oscillations, when convoluted with a realistic spectral window
function. These results indicate failure of the conventional semi-classical
theoretical model of ideal vortex/anti-vortex gas arising in the
Berezinskii-Kosterlitz-Thouless theory for the low spin magnetic systems. A
full fledged quantum mechanical formalism and calculations seem crucial for the
understanding of topological excitations in such low spin systems. Furthermore,
a severe disagreement is found to occur at finite values of energy transfer
between the integrated intensities obtained theoretically from the conventional
formalism and those obtained experimentally. This further suggests strongly
that the full quantum treatment should also incorporate the interaction between
the fragile-magnons and the topological excitations. This is quite plausible in
view of the recent work establishing such a process in XXZ quantum ferromagnet
on 2D lattice. The high spin XXZ quasi-two dimensional antiferromagnet like
$MnPS_3$ however follows the conventional theory quite well",1506.06856v3
2016-10-19,Beam-target double spin asymmetry in quasi-elastic electron scattering off the deuteron with CLAS,"Quasi-elastic electron scattering on the deuteron is a benchmark reaction to
test our understanding of deuteron structure and the properties and
interactions of the two nucleons bound in the deuteron. The experimental data
presented here can be used to test state-of-the-art models of the deuteron and
the two-nucleon interaction in the final state after two-body breakup of the
deuteron. Focusing on polarization degrees of freedom, we gain information on
spin-momentum correlations in the deuteron ground state (due to the D-state
admixture) and on the limits of the Impulse Approximation (IA) picture as it
applies to measurements of spin-dependent observables like spin structure
functions for bound nucleons. We measured the beam-target double spin asymmetry
for quasi-elastic electron scattering off the deuteron at several beam energies
using the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson
National Accelerator Facility. The deuterons were polarized along (or opposite
to) the beam direction. The double spin asymmetries were measured as a function
of photon virtuality , missing momentum, and the angle between the (inferred)
""spectator"" neutron and the momentum transfer direction. The results are
compared with a recent model that includes Final State Interactions (FSI) using
a complete parameterization of nucleon-nucleon scattering, as well as a
simplified model using the Plane Wave Impulse Approximation (PWIA). We find
overall good agreement with both the PWIA and FSI expectations at low to medium
missing momenta, including the change of the asymmetry due to the contribution
of the deuteron D-state at higher momenta. At the highest missing momenta, our
data clearly agree better with the calculations including FSI.",1610.06109v1
2017-06-13,Integrability of Conformal Fishnet Theory,"We study integrability of fishnet-type Feynman graphs arising in planar
four-dimensional bi-scalar chiral theory recently proposed in arXiv:1512.06704
as a special double scaling limit of gamma-deformed $\mathcal{N}=4$ SYM theory.
We show that the transfer matrix ""building"" the fishnet graphs emerges from the
$R-$matrix of non-compact conformal $SU(2,2)$ Heisenberg spin chain with spins
belonging to principal series representations of the four-dimensional conformal
group. We demonstrate explicitly a relationship between this integrable spin
chain and the Quantum Spectral Curve (QSC) of $\mathcal{N}=4$ SYM. Using QSC
and spin chain methods, we construct Baxter equation for $Q-$functions of the
conformal spin chain needed for computation of the anomalous dimensions of
operators of the type $\text{tr}(\phi_1^J)$ where $\phi_1$ is one of the two
scalars of the theory. For $J=3$ we derive from QSC a quantization condition
that fixes the relevant solution of Baxter equation. The scaling dimensions of
the operators only receive contributions from wheel-like graphs. We develop
integrability techniques to compute the divergent part of these graphs and use
it to present the weak coupling expansion of dimensions to very high orders.
Then we apply our exact equations to calculate the anomalous dimensions with
$J=3$ to practically unlimited precision at any coupling. These equations also
describe an infinite tower of local conformal operators all carrying the same
charge $J=3$. The method should be applicable for any $J$ and, in principle, to
any local operators of bi-scalar theory. We show that at strong coupling the
scaling dimensions can be derived from semiclassical quantization of finite gap
solutions describing an integrable system of noncompact $SU(2,2)$ spins. This
bears similarities with the classical strings arising in the strongly coupled
limit of $\mathcal{N}=4$ SYM.",1706.04167v2
2018-09-25,"Single-beam resonant spin amplification of electrons interacting with nuclei in a GaAs/(Al,Ga)As quantum well","The dynamic polarization of nuclear spins interacting with resident electrons
under resonant excitation of trions is studied in a nominally undoped
GaAs/(Al,Ga)As quantum well. Unlike in common time-resolved pump-probe
techniques, we used a single beam approach where the excitation light is
modulated between the circular and linear polarization states. The
time-integrated intensity of the excitation laser reflected from the sample
surface, proportional to the optical generation rate and changes due to the
pumping of the resident electrons, is detected. Polarized electrons on the
other hand transfer their spin to the lattice nuclei via the hyperfine
interaction. Exciting the sample with a train of pulses in an external magnetic
field leads to resonant spin amplification observed when the Larmor precession
frequency is synchronized with the laser pulse repetition rate. Build-up of the
nuclear spin polarization causes a shifting of the RSA peaks since the
resulting nuclear field alters the strength of the external magnetic field
experienced by the electrons. It was established that the nuclear spin
polarization time $T_1$ is temperature dependent and owing to the electron
localization at lower temperatures becomes shorter. ""Locking"" of the nuclear
field manifested as the limited by the strength of the external field growth of
the nuclear field, that is related to the anisotropy of the electron
$g$-factor, was observed. The $g$-factor ratio between the in plane
$g_{\parallel}$ and out-of-plane $g_{\bot}$ components was estimated to be
$g_{\bot}/g_{\parallel}=1.3$.",1809.09556v1
2020-02-19,"Sr$_2$RuO$_4$, like doped cuprates and barium bismuthate, is a negative charge-transfer gap even parity superconductor with $\frac{3}{4}$-filled oxygen band","A comprehensive theory of superconductivity in Sr$_2$RuO$_4$ must explain
experiments that suggest even parity superconducting order and others that
suggest broken time reversal symmetry. Completeness further requires that the
theory applies to Ca$_2$RuO$_4$, a Mott-Hubbard semiconductor that exhibits an
unprecedented insulator-to-metal transition driven by very small electric
field, and also by doping with very small concentration of electrons, leading
to a metallic state proximate to ferromagnetism. A valence transition model,
previously proposed for superconducting cuprates [Phys. Rev. B {\bf 98},
205153] is extended to Sr$_2$RuO$_4$ and Ca$_2$RuO$_4$. The insulator to metal
transition is distinct from that expected from the simple melting of the
Mott-Hubbard semiconductor. Rather, the Ru ions occur as low spin Ru$^{4+}$ in
the semiconductor, and as high spin Ru$^{3+}$ in the metal, the driving force
behind the valence transition being the strong spin-charge coupling and
consequent large ionizaton energy in the low charge state. Metallic and
superconducting ruthenates are two-component systems in which the half-filled
high spin Ru$^{3+}$ ions determine the magnetic behavior but not transport,
while the charge carriers are entirely on on the layer oxygen ions, which have
an average charge -1.5. Spin singlet superconductivity evolves from the
correlated lattice frustrated 3/4 filled band of layer oxygen ions alone, in
agreement with quantum many body calculations that have demonstrated
enhancement by electron-electron interactions of superconducting pair-pair
correlations tions uniquely at or very close to this filling [Phys. Rev. B {\bf
93}, 165110 and {\bf 93}, 205111]. Several model specific experimental
predictions are made, including that spin susceptibility due to Ru ions will
remain unchanged as Sr$_2$RuO$_4$ is taken through superconducting Tc.",2002.08451v2
2020-08-10,"Transverse Single-Spin Asymmetries of Midrapidity Direct Photons, Neutral Pions, and Eta Mesons in 200 GeV Polarized Proton-Proton Collisions at PHENIX","Experimental observations of strikingly large transverse single-spin
asymmetries (TSSAs) opened a window into quark and gluon dynamics present in
hadronic collisions, revealing large spin-momentum correlations within nucleons
and in the process of forming hadrons. Though originally measured in lower
energy fixed target experiments, they have been found to persist in collisions
with momentum transfer well into the perturbative regime of quantum
chromodynamics (QCD) and yet their origin remains poorly understood. TSSA
measurements have allowed for the development of both transverse momentum
dependent and collinear twist-3 descriptions of nonperturbative spin-momentum
correlations for both initial- and final-state effects. Results are presented
for the TSSAs of direct photons, neutral pions, and eta mesons in the
pseudorapidity range $|\eta|<0.35$ from $p^\uparrow+p$ collisions with
$\sqrt{s} = 200$ GeV at PHENIX. As hadrons, $\pi^0$ and $\eta$ mesons are
sensitive to both initial- and final-state effects. At midrapidity, $\pi^0$ and
$\eta$ measurements are sensitive to the dynamics of gluons along with a mix of
quark flavors. These results are a factor of three increase in statistical
precision and extend to higher transverse momentum when compared with previous
PHENIX measurements in this kinematic region. Because direct photon production
does not include hadronization, the direct photon TSSA is only sensitive to
spin-momentum correlations in the proton. The kinematics of this result in
particular make the direct photon TSSA a clean probe of gluon dynamics in the
transversely polarized proton. All three of these asymmetries will help
constrain the twist-3 trigluon collinear correlation function as well as the
gluon Sivers function, improving our knowledge of spin-dependent gluon dynamics
in QCD.",2008.04283v2
2021-05-24,Spin Canting in Exchange Coupled Bi-Magnetic Nanoparticles: Interfacial Effects and Hard / Soft Layer Ordering,"We investigate the spatial distribution of spin orientation in magnetic
nanoparticles consisting of hard and soft magnetic layers. The nanoparticles
are synthesized in a core / shell spherical morphology where the magnetically
hard, high anisotropy layer is CoFe$_2$O$_4$ (CFO) while the lower anisotropy
material is Fe$_3$O$_4$ (FO). The nanoparticles have a mean diameter of
$\sim$9.2 - 9.6 nm and are synthesized as two variants: a conventional hard /
soft core / shell structure with a CFO core / FO shell (CFO@FO) and the
inverted structure FO core / CFO shell (FO@CFO). High resolution electron
microscopy confirms the coherent spinel structure across the core / shell
boundary in both variants while magnetometry indicates the nanoparticles are
superparamagnetic at 300 K and develop a considerable anisotropy at reduced
temperatures. Low temperature \textit{M vs. H} loops suggest a multi-step
reversal process. Temperature dependent small angle neutron scattering (SANS)
with full polarization analysis reveals a strong perpendicular plane alignment
of the spins near zero field, indicative of spin canting, but the perpendicular
alignment quickly disappears upon application of a weak field and little spin
ordering parallel to the field until the coercive field is reached. Above the
coercive field of the sample, spins orient predominantly along the field
direction. At both zero field and near saturation, the parallel magnetic SANS
peak coincides with the structural peak, indicating the magnetization is
uniform throughout the nanoparticle volume, while near the coercive field the
parallel scattering peak shifts to higher momentum transfer (Q), suggesting
that the coherent scattering volume is smaller and likely originates in the
softer Fe$_3$O$_4$ portion of the nanoparticle.",2105.11501v1
2023-11-14,Nuclear spin ratios of deuterated ammonia in prestellar cores. LAsMA observations of H-MM1 and Oph D,"We determine the ortho/para ratios of NH2D and NHD2 in two dense, starless
cores, where their formation is supposed to be dominated by gas-phase
reactions, which, in turn, is predicted to result in deviations from the
statistical spin ratios. The Large APEX sub-Millimeter Array (LAsMA) multibeam
receiver of the Atacama Pathfinder EXperiment (APEX) telescope was used to
observe the prestellar cores H-MM1 and Oph D in Ophiuchus in the ground-state
lines of ortho and para NH2D and NHD2. The fractional abundances of these
molecules were derived employing 3D radiative transfer modelling, using
different assumptions about the abundance profiles as functions of density. We
also ran gas-grain chemistry models with different scenarios concerning proton
or deuteron exchanges and chemical desorption from grains to find out if one of
these models can reproduce the observed spin ratios. The observationally
deduced ortho/para ratios of NH2D and NHD2 are in both cores within 10% of
their statistical values 3 and 2, respectively, and taking 3-sigma limits,
deviations from these of about 20% are allowed. Of the chemistry models tested
here, the model that assumes proton hop (as opposed to full scrambling) in
reactions contributing to ammonia formation, and a constant efficiency of
chemical desorption, comes nearest to the observed abundances and spin ratios.
The nuclear spin ratios derived here are in contrast with spin-state chemistry
models that assume full scrambling in proton donation and hydrogen abstraction
reactions leading to deuterated ammonia. The efficiency of chemical desorption
influences strongly the predicted abundances of NH3, NH2D, and NHD2, but has a
lesser effect on their ortho/para ratios. For these the proton exchange
scenario in the gas is decisive. We suggest that this is because of rapid
re-processing of ammonia and related cations by gas-phase ion-molecule
reactions.",2311.08006v1
2024-01-31,A Channel to Form Fast-spinning Black Hole-Neutron Star Binary Mergers as Multimessenger Sources. II. Accretion-induced Spin-up,"In this work, we investigate an alternative channel for the formation of
fast-spinning black hole-neutron star (BHNS) binaries, in which super-Eddington
accretion is expected to occur in accreting BHs during the stable mass transfer
phase within BH-stripped helium (BH--He-rich) star binary systems. We evolve
intensive \texttt{MESA} grids of close-orbit BH--He-rich star systems to
systematically explore the projected aligned spins of BHs in BHNS binaries, as
well as the impact of different accretion limits on the tidal disruption
probability and electromagnetic (EM) signature of BHNS mergers. Most of the BHs
in BHNS mergers cannot be effectively spun up through accretion, if the
accretion rate is limited to $\lesssim10\,\dot{M}_{\rm Edd}$, where
$\dot{M}_{\rm Edd}$ is the standard Eddington accretion limit. In order to
reach high spins (e.g., $\chi_{\rm BH} \gtrsim 0.5$), the BHs are required to
be born less massive (e.g., $\lesssim3.0\,M_\odot$) in binary systems with
initial periods of $\lesssim0.2-0.3\,{\rm days}$ and accrete material at
$\sim100\,\dot{M}_{\rm Edd}$. However, even under this high accretion limit,
$\gtrsim6\,M_\odot$ BHs are typically challenging to significantly spin up and
generate detectable associated EM signals. Our population simulations suggest
that different accretion limits have a slight impact on the ratio of tidal
disruption events. However, as the accretion limit increases, the EM
counterparts from the cosmological BHNS population can become bright overall.",2401.17558v2
2001-12-14,The pattern of the charge ordering in quasi-one- and two-dimensional organic charge transfer solids,"We examine critically two different recently proposed models of charge
ordering in the nominally 1/4-filled organic charge transfer solids (CTS). In
one dimension, the two models are characterized by site charge densities of the
form ...1010... and ...1100..., respectively. We establish the following
theoretical results: 1) there exists a critical nearest-neighbor Coulomb
interaction (V_c > 2|t|) only above which does the ...1010... state become the
ground state; 2) Hartree-Fock mean field theory predicts V_c incorrectly; 3)
accurate quantum Monte Carlo calculations indicate that V_c increases with
decreasing U; 4) for sufficiently strong e-ph interactions, the ...1010...
state can undergo a spin-Peierls (SP) transition; 5) for V < V_c, in the
presence of e-ph interactions, the ...1100... CO state is the ground state and
also undergoes a SP transition. We show that experimental observations clearly
indicate the ...1100... CO in the 1:2 anionic CTS and the (TMTSF)_2X class of
materials, while the results for (TMTTF)_2X with narrower one-electron
bandwidths are more ambiguous. In two dimensions, we focus on the
theta-(BEDT-TTF)_2X materials, and establish that the CO pattern there
corresponds to the so-called horizontal stripe structure, with ...1100... CO
along the two directions with larger electron hopping. We give precise
explanations of the observed spontaneous bond distortions in the c-direction of
theta-(BEDT-TTF)_2X at the metal-insulator transition and also show that the
appearance of the spin gap at lower temperatures is a true two-dimensional
effect different from the usual SP transition. Superconductivity in the charge
transfer solids appears to be limited to the class of materials which exhibits
the ...1100... CO in the insulating phase.",0112278v2
2007-09-24,Mott-Hubbard versus charge-transfer behavior in LaSrMnO4 studied via optical conductivity,"Using spectroscopic ellipsometry, we study the optical conductivity
sigma(omega) of insulating LaSrMnO4 in the energy range of 0.75-5.8 eV from 15
to 330 K. The layered structure gives rise to a pronounced anisotropy. A
multipeak structure is observed in sigma_1^a(omega) (2, 3.5, 4.5, 4.9, and 5.5
eV), while only one peak is present at 5.6 eV in sigma_1^c(omega). We employ a
local multiplet calculation and obtain (i) an excellent description of the
optical data, (ii) a detailed peak assignment in terms of the multiplet
splitting of Mott-Hubbard and charge-transfer absorption bands, and (iii)
effective parameters of the electronic structure, e.g., the on-site Coulomb
repulsion U_eff=2.2 eV, the in-plane charge-transfer energy Delta_a=4.5 eV, and
the crystal-field parameters for the d^4 configuration (10 Dq=1.2 eV,
Delta_eg=1.4 eV, and Delta_t2g=0.2 eV). The spectral weight of the lowest
absorption feature (at 1-2 eV) changes by a factor of 2 as a function of
temperature, which can be attributed to the change of the nearest-neighbor
spin-spin correlation function across the Neel temperature. Interpreting
LaSrMnO4 effectively as a Mott-Hubbard insulator naturally explains this strong
temperature dependence, the relative weight of the different absorption peaks,
and the pronounced anisotropy. By means of transmittance measurements, we
determine the onset of the optical gap Delta^a_opt=0.4-0.45 eV at 15 K and
0.1-0.2 eV at 300 K. Our data show that the crystal-field splitting is too
large to explain the anomalous temperature dependence of the c-axis lattice
parameter by thermal occupation of excited crystal-field levels. Alternatively,
we propose that a thermal population of the upper Hubbard band gives rise to
the shrinkage of the c-axis lattice parameter.",0709.3711v2
2008-04-08,Spin-up and hot spots can drive mass out of a binary,"The observed distribution of periods and mass ratios of Algols with a B type
primary at birth was updated. Conservative evolution fails to produce the large
fraction with a high mass ratio: i.e. q in [0.4-0.6]. Interacting binaries thus
have to lose mass before or during Algolism. During RLOF mass is transferred
continuously from donor to gainer. The gainer spins up; sometimes up to
critical velocity. Equatorial material on the gainer is therefore less bound to
the system. The material coming from the donor through the first Langrangian
point impinges violently on the surface of the gainer or the edge of the
accretion disc, creating a hot spot in the area of impact. The sum of
rotational energy (fast rotation) and radiative energy (hot spot) depends on
the mass-loss rate. The sum of both energies on a test mass located in the
impact area equals exactly its binding energy at some critical value. As long
as the mass transfer rate is smaller than this value the gainer accepts all the
mass coming from the donor: RLOF happens conservatively. But as soon as the
critical rate is exceeded the gainer will acquire no more than the critical
value and RLOF runs into its liberal era. Low mass binaries never achieve
mass-loss rates larger than the critical value. Intermediate mass binaries
evolve mainly conservatively but mass will be blown away from the system during
the short era of rapid mass transfer soon after RLOF-ignition. Binaries with
9+5.4 solar masses (P in [2-4] d) evolve almost always conservatively. Only
during some 20,000 years the gainer is not capable of grasping all the material
that comes from the donor. During this short lapse of time a significant
fraction of the mass of the system is blown into interstellar space. The mass
ratio bin [0.4-0.6] is now much better represented.",0804.1215v2
2014-05-13,A VLT/FLAMES survey for massive binaries in Westerlund 1. IV. Wd1-5 - binary product and a pre-supernova companion for the magnetar CXOU J1647-45?,"The first soft gamma-ray repeater was discovered over three decades ago, and
subsequently identified as a magnetar. However there is currently no consenus
on the formation channel(s) of these objects. The presence of a magnetar in the
starburst cluster Westerlund 1 implies a >40Msun progenitor, favouring
formation in a binary that was disrupted at supernova. To test this hypothesis
we searched for the putative pre-SN companion via a radial velocity survey to
identify high-velocity runaways, with subsequent atmospheric analysis of the
resultant candidate, Wd1-5. Wd1-5 appears overluminous for its spectroscopic
mass and we find evidence of He- and N-enrichment, O-depletion, and critically
C-enrichment, a combination of properties that is difficult to explain for a
single star. We infer a pre-SN history for Wd1-5 which supposes an initial
close binary comprising two stars of comparable (~41Msun+35Msun) masses.
Efficient mass transfer from the initially more massive component leads to the
mass-gainer evolving more rapidly, initiating luminous blue variable/common
envelope evolution. Reverse, wind-driven mass transfer during its subsequent WC
Wolf-Rayet phase leads to the carbon pollution of Wd1-5, before a type Ibc
supernova disrupts the binary system. Under the assumption of a physical
association between Wd1-5 and J1647-45, the secondary is identified as the
magnetar progenitor; its common envelope evolutionary phase prevents spin-down
of its core prior to SN and the seed magnetic field for the magnetar forms
either in this phase or during the earlier episode of mass transfer in which it
was spun-up. Our results suggest that binarity is a key ingredient in the
formation of at least a subset of magnetars by preventing spin-down via
core-coupling and potentially generating a seed magnetic field.",1405.3109v1
2017-11-27,Electronic and magnetic properties of the graphene densely decorated with 3d metallic adatoms,"The electronic properties of graphene decorated with Ni, Co, Cu and Zn
adatoms is studied with the density functional theory approach. Within the
analysis the spin-orbit interaction is taken into account. We focus on the case
when the indicated $3d$ metallic adatoms form a perfect, close-packed
single-atomic layer above the graphene surface. The two configurations are
examined, namely the adatoms in the on-top, and the hollow positions on
graphene. First, we verify that the metallic adatoms in the close-packed
structure do not form a covalent bonds with the graphene substrate. However,
due to the proximity of the metallic adatoms to the graphene, the charge
transfer from the adatom layer to the graphene takes place, and in consequence
the graphene becomes $n$-doped. The observed charge transfer results from the
arising hybridization between the graphene $2p$ and transition metal $3d$
orbitals. The proximity of metallic adatoms modifies the magnetic state of the
graphene. This effect is especially pronounced for the decoration with magnetic
atoms, when the magnetic moments on the graphene sublattices are induced. The
analysis of the band structure demonstrates that the charge transfer, as well
as the induced magnetism on graphene, modify the graphene electronic properties
near high symmetry points, especially the Dirac cones. The presence of the
metallic adatoms breaks graphene $K-K^{'}$ symmetry and splits the bands due to
the exchange coupling. We show that for the hollow configuration the gap
opening arises at the $K(K^{'})$-point due to the Rashba-like spin-orbit
interaction, while in the case of the on-top configuration the energy gap opens
mainly due to the staggered potential. We also mapped the parameters of an
effective Hamiltonian on the results obtained with the density functional
theory approach.",1711.09828v1
2018-10-10,"Non-local interactions in the $(d,p)$ surrogate method for $(n,γ)$ reactions","Single-neutron transfer reactions populating states in the continuum are
interesting both for structure and astrophysics. In their description often
global optical potentials are used for the nucleon-target interactions, and
these interactions are typically local. In our work, we study the effects of
nonlocality in $(d,p)$ reactions populating continuum states. This work is
similar to that of [1] but now for transfer to the continuum. A theory for
computing cross sections for inclusive processes $A (d,p) X$ was explored in
[2]. Therein, local optical potentials were used to describe the nucleon-target
effective interaction. The goal of the present work is to extend the theory
developed in [2] to investigate the effects of including nonlocality in the
effective interaction on the relevant reaction observables. We implement the
R--matrix method to solve the non--local equations both for the nucleon
wavefunctions and the propagator. We then apply the method to systematically
study the inclusive process of $(d,p)$ on $^{16}$O, $^{40}$Ca, $^{48}$Ca and
$^{208}$Pb at 10, 20 and 50 MeV. We compare the results obtained when
non--local interactions are used with those obtained when local equivalent
interactions are included. We find that nonlocality affects different pieces of
the model in complex ways. Depending on the beam energy and the target, the
non-elastic breakup can either increase or decrease. While the non-elastic
transfer cross section for each final spin state can change considerably, the
main prediction of the model [2], namely the shape of the spin distributions,
remains largely unaltered by nonlocality.
  [1] L. J. Titus and F. M. Nunes. Testing the Perey effect. Phys. Rev. C,
89:034609, Mar 2014.
  [2] G. Potel, F. M. Nunes, and I. J. Thompson. Establishing a theory for
deuteron-induced surrogate reactions. Phys. Rev. C, 92:034611, Sep 2015.",1810.04751v2
2019-01-16,Synergy as a warning sign of transitions: the case of the two-dimensional Ising model,"We consider the formalism of information decomposition of target effects from
multi-source interactions, i.e. the problem of defining redundant and
synergistic components of the information that a set of source variables
provides about a target, and apply it to the two-dimensional Ising model as a
paradigm of a critically transitioning system. Intuitively, synergy is the
information about the target variable that is uniquely obtained taking the
sources together, but not considering them alone; redundancy is the information
which is shared by the sources. To disentangle the components of the
information both at the static level and at the dynamical one, the
decomposition is applied respectively to the mutual information and to the
transfer entropy between a given spin, the target, and a pair of neighbouring
spins (taken as the drivers). We show that a key signature of an impending
phase transition (approached from the disordered size) is the fact that the
synergy peaks in the disordered phase, both in the static and in the dynamic
case: the synergy can thus be considered a precursor of the transition. The
redundancy, instead, reaches its maximum at the critical temperature. The peak
of the synergy of the transfer entropy is far more pronounced than those of the
static mutual information. We show that these results are robust w.r.t. the
details of the information decomposition approach, as we find the same results
using two different methods; moreover, w.r.t. previous literature rooted on the
notion of Global Transfer Entropy, our results demonstrate that considering as
few as three variables is sufficient to construct a precursor of the
transition, and provide a paradigm for the investigation of a variety of
systems prone to crisis, like financial markets, social media, or epileptic
seizures.",1901.05405v2
2024-02-18,"Combined X-ray diffraction, electrical resistivity, and $ab$ $initio$ study of (TMTTF)$_2$PF$_6$ under pressure: implications to the unified phase diagram","We present a combined experimental and theoretical study on the
quasi-one-dimensional organic conductor (TMTTF)$_2$PF$_6$, and elucidate the
variation of its physical properties under pressure. We fully resolve the
crystal structure by single crystal x-ray diffraction measurements using a
diamond anvil cell up to 8 GPa, and based on the structural data, we perform
first-principles density-functional theory calculations and derive the $ab$
$initio$ extended Hubbard-type Hamiltonians. Furthermore, we compare the
behavior of the resistivity measured up to 3 GPa using a BeCu clamp-type cell
and the ground state properties of the obtained model numerically calculated by
the many-variable variational Monte Carlo method. Our main findings are as
follows: i) The crystal was rapidly compressed up to about 3 GPa where the
volume drops to 80% and gradually varies down to 70% at 8 GPa. The transfer
integrals increase following such behavior whereas the screened Coulomb
interactions decrease, resulting in a drastic reduction of correlation effect.
ii) The degree of dimerization in the intrachain transfer integrals, as the
result of the decrease in structural dimerization together with the change in
the intermolecular configuration, almost disappears above 4 GPa; the interchain
transfer integrals also show characteristic variations under pressure. iii) The
results of identifying the characteristic temperatures in the resistivity and
the charge and spin orderings in the calculations show an overall agreement:
The charge ordering sensitively becomes unstable above 1 GPa, while the spin
ordering survives up to higher pressures. These results shed light on the
similarities and differences between applying external pressure and
substituting the chemical species (chemical pressure).",2403.13816v1
1995-07-07,Nucleon Spin Fluctuations and the Supernova Emission of Neutrinos and Axions,"In the hot and dense medium of a supernova (SN) core, the nucleon spins
fluctuate so fast that the axial-vector neutrino opacity and the axion
emissivity are expected to be significantly modified. Axions with
$m_a\alt10^{-2}\,{\rm eV}$ are not excluded by SN~1987A. A substantial transfer
of energy in neutrino-nucleon ($\nu N$) collisions is enabled which may alter
the spectra of SN neutrinos relative to calculations where energy-conserving
$\nu N$ collisions had been assumed near the neutrinosphere.",9507023v2
1998-01-11,The Effects of Correlations on Neutrino Opacities in Nuclear Matter,"Including nucleon-nucleon correlations due to both Fermi statistics and
nuclear forces, we have developed a general formalism for calculating the
neutral-current neutrino-nucleon opacities in nuclear matter. We derive
corrections to the dynamic structure factors due to both density and spin
correlations and find that neutrino-nucleon cross sections are suppressed by
large factors around and above nuclear density. In addition, we find that the
spectrum of energy transfers in neutrino scattering is considerably broadened
by the interactions in the medium. An identifiable component of this broadening
comes from the absorption and emission of quanta of collective modes akin to
the Gamow-Teller and Giant Dipole resonances in nuclei (zero-sound; spin
waves), with \v{C}erenkov kinematics. Under the assumption that both the
charged-current and the neutral-current cross sections are decreased by
many-body effects, we calculate a set of ad hoc protoneutron star cooling
models to gauge the potential importance of the new opacities to the supernova
itself. We find that after many hundreds of milliseconds to seconds the driving
neutrino luminosities might be increased by from 10% to 100%. However, the
actual consequences, if any, of these new neutrino opacities remain to be
determined.",9801082v1
1998-03-31,PSR J2019+2425: A Unique Testing Ground for Binary Evolution,"If the theoretical relationship between white dwarf mass and orbital period
for wide-orbit binary radio pulsars is assumed to be correct, then the neutron
star mass of PSR J2019+2425 is shown to be ~1.20 M_sun. Hence the mass of the
neutron star in this system prior to the mass transfer phase is expected to
have been < 1.1 M_sun. Alternatively this system descends from the accretion
induced collapse (AIC) of a massive white dwarf. We estimate the magnetic
inclination angles of all the observed wide-orbit low-mass binary pulsars in
the Galactic disk using the core-mass period relation and assuming that the
spin axis of an accreting neutron star aligns with the orbital angular momentum
vector in the recycling process of the pulsar. The large estimated magnetic
inclination angle of PSR J2019+2425, in combination with its old age, gives for
this system evidence against alignment of the magnetic field axis with the
rotational spin axis. However, in the majority of the similar systems the
distribution of magnetic inclination angles is concentrated toward low values
(if the core-mass period relation is correct) and suggests that alignment has
taken place.",9803337v1
2000-03-28,Possible evidence of quark matter in neutron star X-ray binaries,"We study the spin evolution of X-ray neutron stars in binary systems, which
are being spun up by mass transfer from accretion disks. Our investigation
reveals that a quark phase transition resulting from the changing central
density induced by the changing spin, can lead to a pronounced peak in the
frequency distribution of X-ray neutron stars. This finding provides one of
several possible explanations available in the literature, or at least a
contributor to part of the observed anomalous frequency distribution of neutron
stars in low-mass X-ray binaries (LMXBs), which lie in a narrow band centered
at about 300 Hz, as found by the Rossi Explorer (RXTE).",0003426v2
2002-10-22,Are pulsar glitches triggered by a superfluid two-stream instability?,"Mature neutron stars are expected to have several superfluid components.
Strong evidence for this is provided by the glitches that have been observed in
dozens of pulsars. The underlying idea behind most glitch models is that, as
the neutron star crust spins down due to the emission of electromagnetic
radiation, the superfluid component lags behind until a critical point is
reached and angular momentum is transferred from the superfluid to the crust,
leading to the spin-up associated with the glitch. In this Letter we describe a
superfluid analogue of the two-stream instability that is well known in plasma
physics, and provide evidence that this instability is likely to be relevant
for neutron stars. This is a new physical mechanism which may play a key role
in explaining the glitch mechanism and which could also prove to be relevant in
laboratory experiments on superfluid Helium.",0210486v1
2003-02-12,Binary evolution models with rotation,"We discuss the first available binary evolution models which include
up-to-date rotational physics for both components, as well as angular momentum
accretion and spin-orbit coupling. These models allow a self-consistent
computation of the mass transfer efficiency during Roche-lobe overflow phases,
and a determination of the transition from quasi-conservative to
non-conservative evolution. Applications to massive binary systems lead to
predictions for the spin rates of compact objects in binaries, and for the
occurrence of gamma-ray bursts from collapsars in binaries. Rotational effects
in accreting white dwarfs are found to stabilise the shell burning and decrease
the carbon abundance in progenitor models for Chandrasekhar-mass Type Ia
supernovae, and to potentially avoid a detonation of the white dwarf within the
sub-Chandrasekhar mass scenario.",0302232v1
2003-05-24,An analytic model of rotating hot spot and kHz QPOs in X-ray binaries,"An analytic model of rotating hot spot is proposed to explain kilohertz
quasi-periodic oscillations (kHz QPO) in X-ray binaries, which is based on the
magnetic coupling (MC) of a rotating black hole (BH) with its surrounding
accretion disc. The hot spot in the inner region of the disc is produced by
energy transferred from a spinning BH with non-axisymmetric magnetic field. The
frequency and energy band of the hot spot turns out to be related to six
parameters, by which the strength and the azimuthal angular region of the
bulging magnetic field on the BH horizon, the mass and spin of the BH, and the
power-law index of the magnetic field varying with the radial coordinate on the
disc are described. In addition, the correlation of the fluctuation of the
bulging magnetic field with the widths of QPO frequency is discussed.",0305478v1
2004-10-08,A Toy Model for Gamma-Ray Bursts in Type Ib/C Supernovae,"A toy model for gamma-ray burst-supernovae (GRB-SN) is discussed by
considering the coexistence of baryon poor outflows from black holes (BHs) and
a powerful spin-connection to surrounding disk, giving rise to consistent
calorimetry as described by van Putten (2001a) in a variant of the
Blandford-Znajek process (BZ, 1977). In this model the half-opening angle of
the magnetic flux tube on the horizon is determined by the mapping relation
between the angular coordinate on the BH horizon and the radial coordinate on
the surrounding accretion disk. The GRB is powered by the baryon poor outflows
in the BZ process, and the associated SN is powered by very small fraction of
the spin energy transferred from the BH to the disk in the magnetic coupling
(MC) process. The timescale of the GRB is fitted by the duration of the open
magnetic flux on the horizon. It turns out that the data of several GRB-SNe are
well fitted with our model.",0410219v1
2005-07-27,The spin period - eccentricity relation of double neutron stars: evidence for weak supernova kicks?,"Double neutron stars (DNSs), binary systems consisting of a radio pulsar and
a generally undetected second neutron star (NS), have proven to be excellent
laboratories for testing the theory of general relativity. The seven systems
discovered in our Galaxy exhibit a remarkably well-defined relation between the
pulsar spin period and the orbital eccentricity. Here we show, using a simple
model where the pulsar is spun up by mass transfer from a helium-star
companion, that this relation can only be produced if the second neutron star
received a kick that is substantially smaller (with a velocity dispersion of
less than 50 km/s) than the standard kick received by a single radio pulsar.
This demonstrates that the kick mechanism depends on the evolutionary history
of the NS progenitor and that the orbital parameters of DNSs are completely
determined by the evolution in the preceding helium star - neutron star phase.
This has important implications for estimating the rates of NS-NS mergers, one
of the major potential astrophysical sources for the direct detection of
gravitational waves, and for short-period gamma-ray bursts.",0507628v1
2007-01-18,Effects of Magnetic Coupling on Radiation from Accretion Disc around a Kerr Black Hole,"The effects of magnetic coupling (MC) process on the inner edge of the disc
are discussed in detail. It is shown that the inner edge can deviate from the
innermost stable circular orbit (ISCO) due to the magnetic transfer of energy
and angular momentum between a Kerr black hole (BH) and its surrounding
accretion disc. It turns out that the inner edge could move inward and outward
for the BH spin $a_{*}$ being greater and less than 0.3594, respectively. The
MC effects on disc radiation are discussed based on the displaced inner edge. A
very steep emissivity can be provided by the MC process, which is consistent
with the observation of MCG-6-30-15. In addition, the BH spins of GRO J1655-40
and GRS 1915+105 are detected by X-ray continuum fitting based on this model.",0701532v1
1994-11-09,Low-temperature dynamical simulation of spin-boson systems,"The dynamics of spin-boson systems at very low temperatures has been studied
using a real-time path-integral simulation technique which combines a
stochastic Monte Carlo sampling over the quantum fluctuations with an exact
treatment of the quasiclassical degrees of freedoms. To a large degree, this
special technique circumvents the dynamical sign problem and allows the
dynamics to be studied directly up to long real times in a numerically exact
manner. This method has been applied to two important problems: (1) crossover
from nonadiabatic to adiabatic behavior in electron transfer reactions, (2) the
zero-temperature dynamics in the antiferromagnetic Kondo region 1/2<K<1 where K
is Kondo's parameter.",9411006v1
1994-10-31,Directed Paths in Random Media,"Contents:
  A. Introduction
  B. High Temperature Expansions for the Ising Model
  C. Characteristic Functions and Cumulants
  D. The One Dimensional Chain
  E. Directed Paths and the Transfer Matrix
  F. Moments of the Correlation Function
  G. The Probability Distribution in Two Dimensions
  H. Higher Dimensions
  I. Random Signs
  J. Other Realizations of DPRM
  K. Quantum Interference of Strongly Localized Electrons
  L. The Locator Expansion and Forward Scattering Paths
  M. Magnetic Field Response
  N. Unitary Propagation
  O. Unitary Averages
  P. Summing all Paths in High Dimensions
  Q. The Ising Model on a Square Lattice
  R. Singular Behavior
  S. The Two Dimensional Spin Glass
  T. Results for the Two Dimensional Spin Glass",9411022v1
1996-01-10,Exact Ground-State Energy of the Ising Spin Glass on Strips,"We propose a new method for exact analytical calculation of the ground-state
energy of the Ising spin glass on strips. An outstanding advantage of this
method over the numerical transfer matrix technique is that the energy is
obtained for complex values of the probability describing quenched randomness.
We study the $\pm J$ and the site-random models using this method for strips of
various sizes up to $5\times\infty$. The ground-state energy of these models is
found to have singular points in the complex-probability plane, reminiscent of
Lee-Yang zeros in the complex-field plane for the Ising ferromagnet. The $\pm
J$ Ising model has a series of singularities which may approach a limiting
point around $p \sim 0.9$ on the real axis in the limit of infinite width.",9601033v2
1996-09-03,Quantum Interference Phenomena in the Local Polarization Dynamics of Mesoscopic Systems: An NMR Observation,"It was predicted that local spin polarization in a ring of five dipolar
coupled spins should present a particular fingerprint of quantum interferences
reflecting both the discrete and finite nature of the system [Phys. Rev. Lett.
75 (1995) 4310]. We report its observation for the proton system of a
(C$_5$H$_5$)$_2$Fe molecule using a rare $^{13}$C as {\it local probe}. Novel
high frequency ($\simeq 60k$Hz) polarization oscillations appear because
incomplete $^{13}$C-$^1$H cross-polarization transfer {\it splits} the
polarization state, in a portion that wanders in the proton system and one that
remains in the $^{13}$ C. They interfere with each other after rejoining.",9609036v1
1995-03-20,Critical Finite-Size-Scaling Amplitudes of a Fully Anisotropic Three-Dimensional Ising Model,"A fully anisotropic simple-cubic Ising lattice in the geometry of periodic
cylinders $n\times n\times\infty$ is investigated by the transfer-matrix
finite-size scaling method. In addition to the previously obtained critical
amplitudes of the inverse correlation lengths and singular part of the free
energy [M. A. Yurishchev, Phys. Rev. B 50, 13 533 (1994)], the amplitudes of
the usual (``linear'') and nonlinear susceptibilities and the amplitude of the
second derivative of the spin-spin inverse correlation length with respect to
the external field are calculated. The behavior of critical amplitude
combinations (which, in accordance with the Privman-Fisher equations, do not
contain in their composition the nonuniversal metric coefficients and geometry
prefactor) are studied as a function of the interaction anisotropy parameters.",9612219v1
1997-02-05,Phase diagrams of the S=1/2 quantum antiferromagnetic XY model on the triangular lattice in magnetic fields,"We study the S=1/2 quantum antiferromagnetic XY model on finite triangular
lattices with N sites in both longitudinal and transverse magnetic fields. We
calculate physical quantities in the ground state using a diagonalization for
spins $N \leq 27$, and those at finite temperatures using a quantum transfer
Monte Carlo method for $N \leq 24$. In the longitudinal magnetic field, the
long-range chiral order parameter seems to have a finite, nonzero value at low
temperatures suggesting the occurrence of a classical umbrella-type phase. In
the transverse magnetic field, the 1/3-plateau of the magnetization curve
appears even at low temperatures, in contrast with the classical model. The
magnetic field dependences of the order parameters suggest that the
chiral-ordered, the ferrimagnetic, and the spin flop phases appear successively
as the magnetic field is increased. The transition temperatures are estimated
from the peak position of the specific heat, and the phase diagrams are
predicted in both longitudinal and transverse magnetic fields.",9702046v1
1997-11-28,The Hubbard chain at finite temperatures: ab initio calculations of Tomonaga-Luttinger liquid properties,"We present a novel treatment of finite temperature properties of the
one-dimensional Hubbard model. Our approach is based on a Trotter-Suzuki
mapping utilizing Shastry's classical model and a subsequent investigation of
the quantum transfer matrix. We derive non-linear integral equations for three
auxiliary functions which have a clear physical interpretation of elementary
excitations of spin type and charge excitations in lower and upper Hubbard
bands. This allows for a transparent analytical study of certain limiting cases
as well as for precise numerical investigations. We present data for the
specific heat, magnetic and charge susceptibilities for various particle
densities and coupling strengths U. The structure exposed by these curves is
discussed in terms of the elementary charge and spin excitations. Special
emphasis is placed on the study of the low-temperature behavior within our ab
initio approach confirming the scaling predictions by Tomonaga-Luttinger liquid
theory. In addition we make contact with the ``dressed energy'' formalism
established for the analysis of ground state properties.",9711310v1
1998-01-27,NaV_2O_5 as a quarter-filled ladder compound,"A new X-ray diffraction study of the one-dimensional spin-Peierls compound
\alpha-NaV_2O_5 reveals a centrosymmetric (Pmmn) crystal structure with one
type of V site, contrary to the previously postulated non-centrosymmetric
P2_1mn structure with two types of V sites (V^{+4} and V^{+5}). Density
functional calculations indicate that NaV_2O_5 is a quarter-filled ladder
compound with the spins carried by V-O-V molecular orbitals on the rungs of the
ladder. Estimates of the charge-transfer gap and the exchange coupling agree
well with experiment and explain the insulating behavior of NaV_2O_5 and its
magnetic properties.",9801276v2
1998-02-25,Exact four-spinon dynamical correlation function in isotropic Heisenberg model,"We discuss some properties of the exact four-spinon dynamical correlation
function $S_4$ in the antiferromagnetic spin 1/2 $XXX$-model, the expression of
which we derived recently. We show that the region in which it is not
identically zero is different from and larger than the spin-wave continuum. We
describe its behavior as a function of the neutron momentum transfer $k$ for
fixed values of the neutron energy $\omega$ and compare it to the one
corresponding to the exact two-spinon dynamical correlation function $S_2$. We
show that the overall shapes are quite similar, even though the expression of
$S_4$ is much more involved than that of $S_2$. We finish with concluding
remarks.",9802271v3
1998-06-22,Manifestation of spin-charge separation in the dynamic dielectric response of one--dimensional Sr2CuO3,"We have determined the dynamical dielectric response of a one-dimensional,
correlated insulator by carrying out electron energy-loss spectroscopy on
Sr2CuO3 single crystals. The observed momentum and energy dependence of the
low-energy features, which correspond to collective transitions across the gap,
are well described by an extended one-band Hubbard model with moderate nearest
neighbor Coulomb interaction strength. An exciton-like peak appears with
increasing momentum transfer. These observations provide experimental evidence
for spin-charge separation in the relevant excitations of this compound, as
theoretically expected for the one-dimensional Hubbard model.",9806257v1
1998-07-18,Two Magnetic Impurities in a Spin Chain,"In this letter, the Kondo magnetic effect is studied for the $XXZ$ spin chain
where the impurities are coupled to the edges of the system. The Hamiltonian of
our model can be constructed from the transfer matrix. It is exactly solvable
and the exchange constants between the bulk and the boundary impurities are
arbitrary. The finite size corrections to the ground state energy are obtained
for the magnetic impurities and the boundary condition. The specific heat and
the susceptibility contributed by the impurities are derived and the Kondo
temperature is given explicitly by the use of the Luttinger-Fermi liquid
picture and the Bethe ansatz method.",9807263v1
1998-07-24,Spin Fluctuation-Induced Superconductivity in Organic Compounds,"Spin fluctuation-induced superconductivity in two-dimensional organic
compounds such as \kappa-(ET)_2-X is investigated by using a simplified dimer
Hubbard model with right-angled isosceles triangular lattice (transfer matrices
-\tau, -\tau^\prime). The dynamical susceptiblity and the self-energy are
calculated self-consistently within the fluctuation exchange approximation and
the value for T_c as obtained by solving the linearized Eliashberg-type
equations is in good agreement with experiment. The pairing symmetry is of
d_{x^2-y^2} type. The calculated (U/\tau)-dependence of T_c compares
qualitatively well with the observed pressure dependence of T_c. Varying the
value for \tau^\prime/\tau from 0 to 1 we interpolate between the square
lattice and the regular triangular lattice and find firstly that values of T_c
for \kappa-(ET)_2-X and cuprates scale well and secondly that T_c tends to
decrease with increasing \tau^\prime/\tau and no superconductivity is found for
\tau^\prime/\tau=1, the regular triangular lattice.",9807322v2
1999-02-06,Effects of Disorder on the Competition between Antiferromagnetism and Superconductivity,"Motivated by the observation of unusual magnetism in Ce_xCu_2Si_2 ($x\sim
1$), we study the effect of disorder, such as Ce vacancy, on the competition
between superconductivity (SC) and antiferromagnetism (AF) on the basis of the
phenomenological Ginzburg-Landau theory. Assuming that the AF-SC transition is
of first order in clean system, we show that a single impurity in the SC state
can induce staggered magnetization by suppressing the SC around it. For finite
concentration of impurities, the first-order AF-SC boundary in the clean case
is replaced by a finite region where the SC and the induced AF moments coexist
microscopically with spatially varying order parameters. We argue that spin
excitation spectrum in the coexistent state has a dual structure of SC gapped
mode and the low-energy spin-wave mode. In accordance with the emergence of AF
out of SC ground state, the spectral weight will be transferred from the former
mode to the latter, keeping the structure of both modes basically unchanged.",9902089v1
1999-06-25,Magnetic field effects on two-leg Heisenberg antiferromagnetic ladders: Thermodynamic properties,"Using the recently developed transfer-matrix renormalization group method, we
have studied the thermodynamic properties of two-leg antiferromagnetic ladders
in the magnetic field. Based on different behavior of magnetization, we found
disordered spin liquid, Luttinger liquid, spin-polarized phases and a classical
regime depending on magnetic field and temperature. Our calculations in
Luttinger liquid regime suggest that both the divergence of the NMR relaxation
rate and the anomalous specific heat behavior observed on
Cu$_2$(C$_5$H$_{12}$N$_2$)$_2$Cl$_4$}are due to quasi-one-dimensional effect
rather than three-dimensional ordering.",9906399v4
1999-09-02,Origin of Superconductivity in 2D-Organic Compounds and High-T_c Cuprates,"A phase diagram is drawn in a parameter space of the nearly half-filled
single band two-dimensional Hubbard model with U/t, t'/t and n as the
parameters, U, t, t' and n being the on-site interaction, the nearest and
second nearest neighbor transfer matrices and the number of electrons per site,
respectively. The parameter space is chosen so as to include the models for the
high-T_c cuprates as well as 2D-organic superconductors. The superconducting
and antiferromagnetic instability surfaces are drawn from the results of
calculations by using the spin fluctuation theory within the fluctuation
exchange approximation. The metal-insulator transition surface is also
indicated in the diagram. From this phase diagram we discuss the possibility of
the spin fluctuation mechanism being the common origin of the superconductivity
in the high-T_c cuprates and 2D-organic compounds.",9909024v1
2000-04-11,Antiferromagnetic Zigzag Spin Chain in Magnetic Fields at Finite Temperatures,"We study thermodynamic behaviors of the antiferromagnetic zigzag spin chain
in magnetic fields, using the density-matrix renormalization group method for
the quantum transfer matrix. We focus on the thermodynamics of the system near
the critical fields in the ground-state magnetization process($M$-$H$ curve):
the saturation field, the lower critical field associated with excitation gap,
and the field at the middle-field cusp singularity. We calculate magnetization,
susceptibility and specific heat of the zigzag chain in magnetic fields at
finite temperatures, and then discuss how the calculated quantities reflect the
low-lying excitations of the system related with the critical behaviors in the
$M$-$H$ curve.",0004159v2
2000-10-10,Nishimori point in the 2D +/- J random-bond Ising model,"We study the universality class of the Nishimori point in the 2D +/- J
random-bond Ising model by means of the numerical transfer-matrix method. Using
the domain-wall free-energy, we locate the position of the fixed point along
the Nishimori line at the critical concentration value p_c = 0.1094 +/- 0.0002
and estimate nu = 1.33 +/- 0.03. Then, we obtain the exponents for the moments
of the spin-spin correlation functions as well as the value for the central
charge c = 0.464 +/- 0.004. The main qualitative result is the fact that
percolation is now excluded as a candidate for describing the universality
class of this fixed point.",0010143v2
2001-05-16,Critical behaviour of fully-frustrated Potts models,"A numerical transfer matrix calculation is presented for two fully-frustrated
three-state Potts models on the square lattice: the Potts piled-up-domino model
and the Potts zig-zag model. The ground state entropies and phase diagrams are
found. The Potts piled-up-domino model displays a finite-temperature transition
when the frustration effects are maximal, and displays reentrant behaviour, in
contrast to the Ising model equivalent. The ground-state entropy per spin is
larger than in the Ising equivalent. The Potts zig-zag model displays the same
qualitative behaviour as its Ising counterpart, and the ground-state entropy
per spin is the same in the Potts and Ising cases.",0105320v1
2001-06-19,Redistribution of Spectral Weight in Spin-1/2-Doped Haldane Chains,"We study the evolution of the dynamical spin structure factor in a spin-1
antiferromagnetic Heisenberg chain which is randomly doped with spin-1/2
moments. Using stochastic series expansion Quantum Monte Carlo simulations
combined with the Maximum Entropy method, we monitor the crossover from the
spin-1 chain, dominated by a single resonance at the Haldane energy, to the
spin-1/2 chain with a continuum of spinon states which diverges at
zero-frequency. Upon increasing the doping level, spectral weight is rapidly
transferred from the Haldane peak to lower energies. If the exchange couplings
between the spin-1/2 substituents and the spin-1 sites of the host are
sufficiently small, finite-frequency bound states are observed below the spin
gap for small doping concentrations.",0106385v1
2002-01-31,Correlation Effect on Peierls Transition,"The effect of correlation on Peierls transition, which is accompanied by a
dimerization, t_d, of a bond alternation for transfer energy, has been examined
for a half-filled one-dimensional electron system with on-site repulsive
interaction (U). By applying the renormalization group method to the
interaction of the bosonized Hamiltonian, the dimerization has been calculated
variationally and self-consistently with a fixed electron-phonon coupling
constant (\lambda) and it is shown that t_d takes a maximum as a function of U.
The result is examined in terms of charge gap and spin gap and is compared with
that of the numerical simulation by Hirsch [Phys. Rev. Lett 51 (1983) 296].
Relevance to the spin Peierls transition in organic conductors is discussed.",0201570v1
2002-04-01,Superconductivity and Antiferromagnetism in Three-Dimensional Hubbard model,"Interplay between antiferromagnetism and superconductivity is studied by
using the 3-dimensional nearly half-filled Hubbard model with anisotropic
transfer matrices $t_{\rm z}$ and $t_{\perp}$. The phase diagrams are
calculated for varying values of the ratio $r_{\rm z}=t_{\rm z}/t_{\perp}$
using the spin fluctuation theory within the fluctuation-exchange
approximation. The antiferromagnetic phase around the half-filled electron
density expands while the neighboring phase of the anisotropic
$d_{x^{2}-y^{2}}$-wave superconductivity shrinks with increasing $r_{\rm z}$.
For small $r_{\rm z}$ $T_{\rm c}$ decreases slowly with increasing $r_{\rm z}$.
For moderate values of $r_{\rm z}$ we find the second order transition, with
lowering temperature, from the $d_{x^{2}-y^{2}}$-wave superconducting phase to
a phase where incommensurate SDW coexists with $d_{x^{2}-y^{2}}$-wave
superconductivity. Resonance peaks as were discussed previously for 2D
superconductors are shown to survive in the $d_{x^{2}-y^{2}}$-wave
superconducting phase of 3D systems. Soft components of the incommensurate SDW
spin fluctuation mode grow as the coexistent phase is approached.",0204024v1
2002-07-10,Adiabatic Transfer of Electrons in Coupled Quantum Dots,"We investigate the influence of dissipation on one- and two-qubit rotations
in coupled semiconductor quantum dots, using a (pseudo) spin-boson model with
adiabatically varying parameters. For weak dissipation, we solve a master
equation, compare with direct perturbation theory, and derive an expression for
the `fidelity loss' during a simple operation that adiabatically moves an
electron between two coupled dots. We discuss the possibility of visualizing
coherent quantum oscillations in electron `pump' currents, combining quantum
adiabaticity and Coulomb blockade. In two-qubit spin-swap operations where the
role of intermediate charge states has been discussed recently, we apply our
formalism to calculate the fidelity loss due to charge tunneling between two
dots.",0207257v1
2002-12-18,Thermodynamics and Crossover Phenomena in the Correlation Lengths of the One-Dimensional t-J Model,"We investigate the thermodynamics of the one-dimensional t-J model using
transfer matrix renormalization group (TMRG) algorithms and present results for
quantities like particle number, specific heat, spin susceptibility and
compressibility. Based on these results we confirm a phase diagram consisting
of a Tomonaga-Luttinger liquid (TLL) phase for small J/t and a phase separated
state for J/t large. Close to phase separation we find a spin-gap
(Luther-Emery) phase at low densities consistent with predictions by other
studies. At the supersymmetric point we compare our results with exact results
from the Bethe ansatz and find excellent agreement. In particular we focus on
the calculation of correlation lengths and static correlation functions and
study the crossover from the non-universal high T lattice into the quantum
critical regime. At the supersymmetric point we compare in detail with
predictions by conformal field theory (CFT) and TLL theory and show the
importance of logarithmic corrections.",0212437v1
2003-01-21,Stochastic gene expression as a many body problem,"Gene expression has a stochastic component owing to the single molecule
nature of the gene and the small number of copies of individual DNA binding
proteins in the cell. We show how the statistics of such systems can be mapped
on to quantum many body problems. The dynamics of a single gene switch
resembles the spin boson model of a two site polaron or an electron transfer
reaction. Networks of switches can be approximately described as quantum spin
systems by using an appropriate variational principle. In this way the concept
of frustration for magnetic systems can be taken over into gene networks. The
landscape of stable attractors depends on the degree and style of frustration,
much as for neural networks. We show the number of attractors, which may
represent cell types, is much smaller for appropriately designed, weakly
frustrated stochastic networks than for randomly connected networks.",0301365v1
2003-04-21,Q-dependence of the inelastic neutron scattering cross section for molecular spin clusters with high molecular symmetry,"For powder samples of polynuclear metal complexes the dependence of the
inelastic neutron scattering intensity on the momentum transfer Q is known to
be described by a combination of so called interference terms. They reflect the
interplay between the geometrical structure of the compound and the spatial
properties of the wave functions involved in the transition. In this work, it
is shown that the Q-dependence is strongly interrelated with the molecular
symmetry of molecular nanomagnets, and, if the molecular symmetry is high
enough, is actually completely determined by it. A general formalism connecting
spatial symmetry and interference terms is developed. The arguments are
detailed for cyclic spin clusters, as experimentally realized by e.g. the
octanuclear molecular wheel Cr8, and the star like tetranuclear cluster Fe4.",0304463v1
2003-08-19,"Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors","We describe a theory of Mn local-moment magnetization relaxation due to p-d
kinetic-exchange coupling with the itinerant-spin subsystem in the
ferromagnetic semiconductor (Ga,Mn)As alloy. The theoretical Gilbert damping
coefficient implied by this mechanism is calculated as a function of Mn moment
density, hole concentration, and quasiparticle lifetime. Comparison with
experimental ferromagnetic resonance data suggests that in annealed strongly
metallic samples, p-d coupling contributes significantly to the damping rate of
the magnetization precession at low temperatures. By combining the theoretical
Gilbert coefficient with the values of the magnetic anisotropy energy, we
estimate that the typical critical current for spin-transfer magnetization
switching in all-semiconductor trilayer devices can be as low as $\sim 10^{5}
{\rm A cm}^{-2}$.",0308386v3
2003-12-11,Spin-dependent transport in phase-separated manganites,"Starting from the assumption that ferromagnetically correlated regions exist
in manganites even in the absence of long-range magnetic order, we construct a
model of charge transfer due to the spin-dependent tunnelling of charge
carriers between such regions. This model allows us to analyze the temperature
and magnetic field dependence of resistivity, magnetoresistance, and magnetic
susceptibility of phase-separated manganites in the temperature range
corresponding to non-metallic behavior. The comparison of theoretical and
experimental results reveals the main characteristics of the phase-separated
state.",0312294v1
2004-01-23,Spin-boson models for quantum decoherence of electronic excitations of biomolecules and quantum dots in a solvent,"We give a theoretical treatment of the interaction of electronic excitations
(excitons) in biomolecules and quantum dots with the surrounding polar solvent.
Significant quantum decoherence occurs due to the interaction of the electric
dipole moment of the solute with the fluctuating electric dipole moments of the
individual molecules in the solvent. We introduce spin boson models which could
be used to describe the effects of decoherence on the quantum dynamics of
biomolecules which undergo light-induced conformational change and on
biomolecules or quantum dots which are coupled by Forster resonant energy
transfer.",0401444v3
2004-01-30,Superconductivity in Organic Compounds with Pseudo-Triangular Lattice,"We study spin fluctuation (SF) mediated superconductivity (SC) in a
half-filled square lattice Hubbard model with the transfer matrices -t between
nearest neighbor sites and -t' between a half of next nearest neighbor sites
neighboring along only one of the <1,1> directions, considering application of
this model to organic kappa-(BEDT-TTF)2X compounds. Varying the t'/t value from
0 to 1, one can interpolate between a square and an equilateral triangular
lattice, the latter giving frustration to antiferromagnetically (AF) coupled
spin systems. Within the fluctuation exchange (FLEX) approximation, we
calculate chi(q,omega), Tc and the SC order parameter for various model
parameter values and find that both AF and SC are suppressed as one approaches
the frustration geometry or |(t'/t)-1| \to 0. The SC phase, however, extends
beyond the AF phase boundary fairly close to t'/t=1 for realistic U/t values.
The order parameter is of x2-y2-type for t'/t<1 and of xy-type for t'/t>1.",0401623v1
2004-02-15,Dependence of spin susceptibility of a two-dimensional electron system on the valley degree of freedom,"We report measurements of the spin susceptibility, $\chi\propto g_v g^*m^*$,
in an AlAs two-dimensional electron system where, via the application of
in-plane stress, we transfer electrons from one conduction-band valley to
another ($g_v$ is the valley degeneracy, and $m^*$ and $g^*$ are the electron
effective mass and g-factor). At a given density, when the two valleys are
equally populated ($g_v=2$), the measured $g^*m^*$ is smaller than when only
one valley is occupied ($g_v=1$). This observation counters the common
assumption that a two-valley two-dimensional system is effectively more dilute
than a single-valley system because of its smaller Fermi energy.",0402399v1
2004-02-27,Thermodynamic properties and thermal correlation lengths of a Hubbard model with bond-charge interaction,"We investigate the thermodynamics of a one-dimensional Hubbard model with
bond-charge interaction X using the transfer matrix renormalization group
method (TMRG). Numerical results for various quantities like spin and charge
susceptibilities, particle densities, specific heat and thermal correlation
lengths are presented and discussed. We compare our data also to results for
the exactly solvable case X/t=1 as well as to bosonisation results for weak
coupling X/t << 1, which shows excellent agreement. We confirm the existence of
a Tomonaga-Luttinger and a Luther-Emery liquid phase, in agreement with
previous studies at zero temperature. Thermal singlet-pair correlation lengths
are shown to dominate density and spin correlations for finite temperatures in
certain parameter regimes.",0402679v1
2004-10-08,Electronic structure of the $Sr_{0.4}Ca_{13.6}Cu_{24}O_{41}$ incommensurate compound,"We extracted, from strongly-correlated ab-initio calculations, a complete
model for the chain subsystem of the $Sr_{0.4}Ca_{13.6}Cu_{24}O_{41}$
incommensurate compound. A second neighbor $t-J+V$ model has been determined as
a function of the fourth crystallographic parameter $\tau$, for both low and
room temperature crystallographic structures. The analysis of the obtained
model shows the crucial importance of the structural modulations on the
electronic structure through the on-site energies and the magnetic
interactions. The structural distortions are characterized by their long range
effect on the cited parameters that hinder the reliability of analyses such as
BVS. One of the most striking results is the existence of antiferromagnetic
nearest-neighbor interactions for metal-ligand-metal angles of $90^\circ$. A
detailed analysis of the electron localization and spin arrangement is
presented as a function of the chain to ladder hole transfer and of the
temperature. The obtained spin arrangement is in agreement with
antiferromagnetic correlations in the chain direction at low temperature.",0410204v2
2004-11-22,"PES and XAS Study on Electronic Structures of Multiferroic RMnO$_3$ (R=Y, Er)","Electronic structures of multiferroic RMnO$_3$ (R=Y, Er) have been
investigated by employing photoemission spectroscopy (PES) and x-ray absorption
spectroscopy (XAS). We have found that Mn ions in RMnO$_3$ are in the trivalent
high-spin state with the total spin of S=2. The occupied Mn ($d_{xz} - d_{yz}$)
states lie deep below $\rm E_F$, while the occupied Mn ($d_{xy} - d_{x^2
-y^2}$) states overlap very much with the O $2p$ states. It is observed that
the PES spectral intensity of Mn 3d states is negligible above the occupied O
$2p$ bands, suggesting that YMnO$_3$ is likely to be a charge-transfer
insulator. The Mn $d_{3z^2 -r^2}$ state is mostly unoccupied in the
ferroelectric phase of YMnO$_3$.",0411561v1
2004-12-10,Thermodynamic properties of tetrameric bond-alternating spin chains,"Thermodynamic properties of a tetrameric bond-alternating Heisenberg spin
chain with ferromagnetic-ferromagnetic-antiferromagnetic-antiferromagnetic
exchange interactions are studied using the transfer-matrix renormalization
group and compared to experimental measurements. The temperature dependence of
the uniform susceptibility exhibits typical ferrimagnetic features. Both the
uniform and staggered magnetic susceptibilities diverge in the limit $T\to 0$,
indicating that the ground state has both ferromagnetic and antiferromagnetic
long-range orders. A double-peak structure appears in the temperature
dependence of the specific heat. Our numerical calculation gives a good account
for the temperature and field dependence of the susceptibility, the
magnetization, and the specific heat for Cu(3-Clpy)$_{2}$(N$_{3}$)$_{2}$
(3-Clpy=3-Chloroyridine).",0412275v2
2005-01-06,Ground State Properties of one-dimensional Antiferromagnetic Spin-1 Chain with Single-ion Anisotropy,"In this study, we have investigated ground state properties of
one-dimensional antiferromagnetic spin-1 chain with single-ion anisotropy at
very low temperatures using the Transfer Matrix method. Magnetic plateaus,
phase diagram, specific heat, susceptibility of the spin chain have been
evaluated numerically from the free energy. Results are in good agreement with
the experimental data for the spin-1 compounds
[Ni$_2$(Medpt)$_2$($\mu$-ox)(H$_2$O)$_2$](ClO$_4$)$_2$2H$_2$O,
[Ni$_{2}$(Medpt)$_{2}$($\mu$-ox)($\mu$-N$_{3}$)](ClO$_{4}$)0.5H$_{2}$O,
Ni(C$_2$H$_8$N$_2$)Ni(CN)$_4$ and Ni(C$_{10}$H$_8$N$_2$)$_2$Ni(CN)$_4$.H$_2$O.
However, spin-Peierls transition have not been observed in the temperature
dependence of specific heat and magnetic susceptibility.",0501111v2
2005-02-03,Leading interactions in the $β$-$Sr V_6 O_{15}$ compound,"The present study shows that the electronic structure of the
$\beta$-$AV\_6O\_{15}$ family of compounds ($A = Sr, Ca, Na ...$) is based on
weakly interacting two-leg ladders, in contrast with the zig-zag chain model
one could expect from their crystal structure. Spin dimer analysis, based on
extended H\""{u}ckel tight-binding calculations, was performed to determine the
structure of the dominant transfer and magnetic interactions in the room
temperature $\beta$-$SrV\_6O\_{15}$ phase. Two different two-legs ladders,
associated with different charge/spin orders are proposed to describe these
one-dimensional $\beta$-type systems. The antiferromagnetic ladders are packed
in an 'IPN' geometry and coupled to each other through weak antiferromagnetic
interactions. This arrangement of the dominant interactions explains the
otherwise surprising similarities of the optical conductivity and Raman spectra
for the one-dimensional $\beta$-type phases and the two-dimensional
$\alpha$-type ones such as the well-known $\alpha^\prime$-$NaV\_2O\_5$ system.",0502107v1
2005-12-16,Logarithmic corrections to correlation decay in two-dimensional random-bond Ising systems,"The statistics of critical spin-spin correlation functions in Ising systems
with non-frustrated disorder are investigated on a strip geometry, via
numerical transfer-matrix techniques. Conformal invariance concepts are used,
in order to test for logarithmic corrections to pure power-law decay against
distance. Fits of our data to conformal-invariance expressions, specific to
logarithmic corrections to correlations on strips, give results with the
correct sign, for the moments of order $n=0-4$ of the correlation-function
distribution. We find an interval of disorder strength along which corrections
to pure-system behavior can be decomposed into the product of a known
$n$-dependent factor and an approximately $n$-independent one, in accordance
with predictions. A phenomenological fitting procedure is proposed, which takes
partial account of subdominant terms of correlation-function decay on strips.
In the low-disorder limit, it gives results in fairly good agreement with
theoretical predictions, provided that an additional assumption is made.",0512407v3
2006-03-24,Single-crystalline nanopillars for spin-transfer measurements,"We report on current-induced magnetization switching (CIMS) in single-
crystalline nanopillars. Fe(14 nm)/Cr(0.9 nm)/Fe(10 nm)/Ag(6 nm)/Fe(2 nm)
multilayers are deposited by molecular-beam epitaxy. The central Fe layer is
coupled to the thick one by interlayer exchange coupling over Cr. The topmost
Fe layer is decoupled (free layer). Nanopillars with 150 nm diameter are
prepared by optical and e-beam lithography. The opposite spin scattering
asymmetries of Fe/Cr and Fe/Ag interfaces enable us to observe CIMS at small
magnetic fields and opposite current polarity in a single device. At high
magnetic fields, step-like resistance changes are measured at positive currents
and are attributed to current-driven magnetic excitations.",0603662v1
2006-03-29,Electronic Structure and Linear Optical Properties of Sr$_{2}$CuO$_{2}$Cl$_{2}$ Studied from the First Principles Calculation,"First-principles calculations with the full-potential linearized augmented
plane-wave (FP-LAPW) method have been performed to investigate detailed
electronic and linear optical properties of Sr$_{2}$CuO$_{2}$Cl$_{2}$, which is
a classical low-dimensional antiferromagnet (AFM) charge transfer ({\it CT})
insulator. Within the local-spin-density approximation (LSDA) plus the on-site
Coulomb interaction $U$ (LADA+$U$) added on Cu 3d orbitals, our calculated band
gap and spin moments are well consistent with the experimental and other
theoretical values. The energy dispersion relation agrees well with the angle
resolved photoemission measurements. Its linear optical properties are
calculated within the electric-dipole approximation. The absorption spectrum is
found to agree well with the experimental result.",0603776v1
2006-05-11,Possible phases of two coupled n-component fermionic chains,"A two-leg ladder with $n$-component fermionic fields in the chains has been
considered using an analytic renormalization group method. The fixed points and
possible phases have been determined for generic filling as well as for a
half-filled system and for the case when one of the subbands is half filled. A
weak-coupling Luttinger-liquid phase and several strong-coupling gapped phases
have been found. In the Luttinger liquid phase, for the most general spin
dependence of the couplings, all $2n$ modes have different velocities if the
interband scattering processes are scaled out, while $n$ doubly degenerate
modes appear if the interband scattering processes remain finite. The role of
backward-scattering, charge-transfer and umklapp processes has been analysed
using their bosonic form and the possible phases are characterized by the
number of gapless modes. As a special case the SU($n$) symmetric Hubbard ladder
has been investigated numerically. It was found that this model does not scale
to the Luttinger liquid fixed point. Even for generic filling gaps open up in
the spectrum of the spin or charge modes, and the system is always insulator in
the presence of umklapp processes.",0605300v1
2006-05-22,Localization in a quantum spin Hall system,"Localization problem of electronic states in a two-dimensional quantum spin
Hall system (QSH - a symplectic model with a non-trivial topological structure)
is studied by the transfer matrix method. The phase diagram in the plane of
energy and disorder strength is exposed, and demonstrates ""levitation"" and
""pair-annihilation"" of the domains of extended states analogous to that of the
integer quantum Hall system. The critical exponent $\nu$ for the divergence of
the localization length is estimated as $\nu \cong 1.6$ which is distinct from
both exponents pertaining to the conventional symplectic and the unitary
quantum Hall systems. This strongly suggests a different universality class
related to the non-trivial topology of the QSH system.",0605510v2
2006-05-22,Thermodynamics of spin systems on small-world hypergraphs,"We study the thermodynamic properties of spin systems on small-world
hypergraphs, obtained by superimposing sparse Poisson random graphs with p-spin
interactions onto a one-dimensional Ising chain with nearest-neighbor
interactions. We use replica-symmetric transfer-matrix techniques to derive a
set of fixed-point equations describing the relevant order parameters and free
energy, and solve them employing population dynamics. In the special case where
the number of connections per site is of the order of the system size we are
able to solve the model analytically. In the more general case where the number
of connections is finite we determine the static and dynamic
ferromagnetic-paramagnetic transitions using population dynamics. The results
are tested against Monte-Carlo simulations.",0605527v2
2006-06-15,Valency Configuration of Transition Metal Impurities in ZnO,"We use the self-interaction corrected local spin-density approximation to
investigate the ground state valency configuration of transition metal (TM =
Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn1-xTMxO, the
localized TM2+ configuration is energetically favored over the itinerant
d-electron configuration of the local spin density (LSD) picture. Our
calculations indicate furthermore that the (+/0) donor level is situated in the
ZnO gap. Consequently, for n-type conditions, with the Fermi energy eF close to
the conduction band minimum, TM remains in the 2+ charge state, while for
p-type conditions, with eF close to the valence band maximum, the 3+ charge
state is energetically preferred. In the latter scenario, modeled here by
co-doping with N, the additional delocalized d-electron charge transfers into
the entire states at the top of the valence band, and hole carriers will only
exist, if the N concentration exceeds the TM impurity concentration.",0606417v1
2006-06-23,Magnetic fullerenes inside single-wall carbon nanotubes,"C59N magnetic fullerenes were formed inside single-wall carbon nanotubes by
vacuum annealing functionalized C59N molecules encapsulated inside the tubes. A
hindered, anisotropic rotation of C59N was deduced from the temperature
dependence of the electron spin resonance spectra near room temperature.
Shortening of spin-lattice relaxation time, T_1, of C59N indicates a reversible
charge transfer toward the host nanotubes above $\sim 350$ K. Bound C59N-C60
heterodimers are formed at lower temperatures when C60 is co-encapsulated with
the functionalized C59N. In the 10-300 K range, T_1 of the heterodimer shows a
relaxation dominated by the conduction electrons on the nanotubes.",0606597v1
2006-09-27,The influence of photon angular momentum on ultrafast spin dynamics in Nickel,"The role of photon angular momentum in laser-induced demagnetization of
Nickel thin films is investigated by means of pump-probe time-resolved
magneto-optical Kerr effect in the polar geometry. The recorded data display a
strong dependency on pump helicity during pump-probe temporal overlap, which is
shown to be of non-magnetic origin. By accurately fitting the demagnetization
curves we also show that demagnetization time and electron-phonon equilibration
time are not affected by pump-helicity. Thereby our results do not support
direct transfer of angular momentum between photons and spins to be relevant
for the demagnetization process. This suggests, in agreement with the
microscopic model that we recently presented, that the source of angular
momentum could be phonons or impurities rather than laser photons as required
in the microscopic model proposed by Zhang and Huebner.",0609698v1
2006-10-04,Evolution of the Spin Susceptibility of High-$T_c$ Superconductors,"We demonstrate that a new tool, a model independent numerical Eliashberg
inversion of the optical self-energy, based on maximum entropy considerations
can be used to extract the magnetic excitation spectra of
high-transition-temperature superconductors. In Bi-2212 we explicitly show that
the magnetic mode that dominates the self-energy at low temperatures directly
evolves out of a smooth transfer of spectral weight to the mode from the
continuum just above it. This redistribution starts already at 200 K in
optimally doped materials but is much weaker in overdoped samples. This
provides evidence for the magnetic origin of the superconductivity and presents
a challenge to theories of the spin susceptibility and to neutron scattering
experiments in high-temperature superconductors.",0610127v1
2006-12-07,Interplay of electromagnetic noise and Kondo effect in quantum dots,"We investigate the influence of an electromagnetic environment, characterized
by a finite impedance $Z(\omega)$, on the Kondo effect in quantum dots. The
circuit voltage fluctuations couple to charge fluctuations in the dot and
influence the spin exchange processes transferring charge between the
electrodes. We discuss how the low-energy properties of a Kondo quantum dot
subject to dynamical Coulomb blockade resemble those of Kondo impurities in
Luttinger liquids. Using previous knowledge based on the bosonization of
quantum impurity models, we show that low-voltage conductance anomalies appear
at zero temperature. The conductance can vanish at low temperatures even in
presence of a screened impurity spin. Moreover, the quantitative determination
of the corresponding Kondo temperature depends on the full frequency-dependent
impedance of the circuit. This is demonstrated by a weak-coupling calculation
in the Kondo interaction, taking into account the full distribution $P(E)$ of
excited environmental modes.",0612175v3
2006-12-07,Metal-ligand interplay in strongly-correlated oxides: a parametrized phase diagram for pressure induced spin transitions,"We investigate the magnetic properties of archetypal transition-metal oxides
MnO, FeO, CoO and NiO under very high pressure by x-ray emission spectroscopy
at the K\beta line. We observe a strong modification of the magnetism in the
megabar range in all the samples except NiO. The results are analyzed within a
multiplet approach including charge-transfer effects. The pressure dependence
of the emission line is well accounted for by changes of the ligand field
acting on the d electrons and allows us to extract parameters like local
d-hybridization strength, O-2p bandwidth and ionic crystal field across the
magnetic transition. This approach allows a first-hand insight into the
mechanism of the pressure induced spin transition.",0612179v1
2007-02-13,Centipede ladder at quarter filling,"We study the ground state and excitation spectrum of a quasi one-dimensional
nanostructure consisting of a pole and rungs oriented in the opposite
directions (""centipede ladder"", CL) at quarter filling. The spin and charge
excitation spectra are found in the limits of small and large longitudinal
hopping $t_\|$ compared to the on-rung hopping rate $t_\perp$ and exchange
coupling $I_\perp$. At small $t_\|$ the system with ferromagnetic on-rung
exchange demonstrates instability against dimerization. Coherent propagation of
charge transfer excitons is possible in this limit. At large $t_\|$ CL behaves
like two-orbital Hubbard chain, but the gap opens in the charge excitation
spectrum thus reducing the symmetry from SU(4) to SU(2). The spin excitations
are always gapless and their dispersion changes from quadratic magnon-like for
ferromagnetic on-rung exchange to linear spinon-like for antiferromagnetic
on-rung exchange in weak longitudinal hopping limit.",0702307v1
2007-03-16,Distribution of local Lyapunov exponents in spin-glass dynamics,"We investigate the statistical properties of local Lyapunov exponents which
characterize magnon localization in the $d=1$ Heisenberg-Mattis spin glass
(HMSG) at zero temperature, by means of a connection to a suitable version of
the Fokker-Planck (F-P) equation. We consider the local Lyapunov exponents
(LLE), in particular the case of {\em instantaneous} LLE. We establish a
connection between the transfer-matrix recursion relation for the problem, and
an F-P equation governing the evolution of the probability distribution of the
instantaneous LLE. The closed-form (stationary) solutions to the F-P equation
are in excellent accord with numerical simulations, for both the unmagnetized
and magnetized versions of the HMSG. Scaling properties for non-stationary
conditions are derived from the F-P equation in a special limit (in which
diffusive effects tend to vanish), and also shown to provide a close
description to the corresponding numerical-simulation data.",0703444v2
1997-12-17,Gravity and Parity Violation in Spin Gauge Theory,"Within a spin-gauge theory of gravity unified with the electroweak
interaction we start with totally symmetric left- and right-handed fermions and
explain the parity violation by symmetry breaking in such a way that the
$W^{\pm}$-bosons couple only to the left-handed leptons. Right-handed neutrinos
exist and couple as the right-handed electrons only to the Z-bosons (and to
gravity). The mass of the neutrinos comes out to be necessarily zero. Therefore
this procedure cannot be transferred to the quarks, because then the u-quark
would become massless too; for this reason parity violation with respect to the
quarks is avoided. On the other hand concerning gravity the u-quark couples
only with u-quarks and the d-quark only with d-quarks, however with the same
strength, so that isotopic effects appear regarding the equivalence principle
in such a way, that the macroscopic gravitational constant depends on the
isotopic composition of the material.",9712074v1
1999-08-06,Measurement of the Spin-Density Matrix Elements in Exclusive Electroproduction of rho^0 Mesons at HERA,"Exclusive electroproduction of rho^0 mesons has been measured using the ZEUS
detector at HERA in two Q^2 ranges, 0.25<Q^2<0.85 GeV^2 and 3<Q^2<30 GeV^2. The
low-Q^2 data span the range 20<W<90 GeV; the high-Q^2 data cover the 40<W<120
GeV interval. Both samples extend up to four-momentum transfers of |t|=0.6
GeV^2. The distribution in the azimuthal angle between the positron scattering
plane and the rho^0 production plane shows a small but significant violation of
s-channel helicity conservation, corresponding to the production of
longitudinally polarised (i.e. helicity zero) rho^0 mesons from transverse
photons. Measurements of the 15 combinations of spin-density matrix elements
which completely define the angular distributions are presented and discussed.",9908026v2
2001-11-23,First Measurement of the Double Spin Asymmetry in $\vec{e}\vec{p}\to e' π^+ n$ in the Resonance Region,"The double spin asymmetry in the $\vec{e}\vec{p}\to e' \pi^+ n$ reaction has
been measured for the first time in the resonance region for four-momentum
transfer $Q^2=0.35-1.5$ GeV$^2$. Data were taken at Jefferson Lab with the CLAS
detector using a 2.6 GeV polarized electron beam incident on a polarized solid
NH$_3$ target. Comparison with predictions of phenomenological models shows
strong sensitivity to resonance contributions. Helicity-1/2 transitions are
found to be dominant in the second and third resonance regions. The measured
asymmetry is consistent with a faster rise with $Q^2$ of the helicity asymmetry
$A_1$ for the $F_{15}(1680)$ resonance than expected from the analysis of the
unpolarized data.",0111074v2
2001-12-17,Single-spin azimuthal asymmetry in exclusive electroproduction of pi^+ mesons,"A single-spin asymmetry in the distribution of exclusively produced pi^+
mesons azimuthally around the virtual photon direction relative to the lepton
scattering plane has been measured for the first time in deep-inelastic
scattering of positrons off longitudinally polarized protons. Integrated over
the experimental acceptance, the sin \phi moment of the polarization asymmetry
of the cross section is measured to be -0.18 +/- 0.05 (stat.) +/- 0.02 (syst.).
The asymmetry is also studied as a function of the relevant kinematic
variables, and its magnitude is found to grow with decreasing x and increasing
-t and vanish at t -> t_min (where x is the Bjorken scaling variable and t is
the squared four-momentum transferred to the nucleon).",0112022v4
2002-03-14,A measurement of the t dependence of the helicity structure of diffractive rho meson electroproduction at HERA,"The helicity structure of the diffractive electroproduction of rho mesons, e
+ p -> e + rho + Y, is studied in a previously unexplored region of large
four-momentum transfer squared at the proton vertex, t: 0 < t' < 3 GeV^2, where
t' = |t| - |t|_min. The data used are collected with the H1 detector at HERA in
the kinematic domain 2.5 < Q^2 < 60 GeV^2, 40 < W < 120 GeV. No t dependence of
the r^04_00 spin density matrix element is found. A significant t dependent
helicity non-conservation from the virtual photon to the rho meson is observed
for the spin density matrix element combinations r^5_00+2r^5_11 and
r^1_00+2r^1_11. These t dependences are consistently described by a
perturbative QCD model based on the exchange of two gluons.",0203022v1
1994-12-02,Spin Chains and Chiral Lattice Fermions,"The generalization of Lorentz invariance to solvable two-dimensional lattice
fermion models has been formulated in terms of Baxter's corner transfer matrix.
In these models, the lattice Hamiltonian and boost operator are given by
fermionized nearest-neighbor Heisenberg spin chain operators. The
transformation properties of the local lattice fermion operators under a boost
provide a natural and precise way of generalizing the chiral structure of a
continuum Dirac field to the lattice. The resulting formulation differs from
both the Wilson and staggered (Kogut-Susskind) prescriptions. In particular, an
axial $Q_5$ rotation is sitewise local, while the vector charge rotation mixes
nearest neighbors on even and odd sublattices.",9412019v1
1996-04-02,QCD Selection Rules in Polarized Hadron Collisions,"Plans are underway to measure spin asymmetries at large momentum transfer in
hadron hadron collisions at RHIC and elsewhere. Proposals have focused on
measuring quark transversity and quark and gluon helicity distributions in the
nucleon. These experiments will also provide a strong and simple test of
perturbative QCD, namely that ${\cal A}_{TT}/{\cal A}_{LL}\ll 1$ in
$pp\rightarrow 2\, {\rm jets} +X$ and several related processes, whereas ${\cal
A}_{TT}/{\cal A}_{LL}\sim 1$ in Drell-Yan production of muon pairs. The
prediction tests the helicity, twist and chirality selection rules of
perturbative QCD that form the foundation for the analysis of spin dependent
hard processes. We estimate the ratio ${\cal A}_{TT}/{\cal A}_{LL}$ numerically
for polarized protons at RHIC.",9604220v1
1997-03-03,Neutrinos with Magnetic Moment: Depolarization Rate in Plasma,"Neutrinos with a magnetic moment $\mu$ change their helicity when interacting
with an electromagnetic field. Various aspects of this effect have been
described as spin precession, spin-flip scattering, and magnetic Cherenkov
radiation. These perspectives are unified in an expression for the
$\nu_L\to\nu_R$ transition rate which involves the correlators of the
electromagnetic field distribution. Our general formula corrects a previous
result and generalizes it to the case where the fields cannot be viewed as
classical and where the momentum transfers need not be small. We evaluate our
result explicitly for a relativistic QED plasma and determine the
depolarization rate to leading order in the fine structure constant. Assuming
that big-bang nucleosynthesis constraints do not allow a right-handed neutrino
in equilibrium we derive the limit $\mu<6.2\EE{-11}\mu_B$ on the neutrino
magnetic moment. Bounds on $\mu$ from a possible large scale magnetic fields
are found to be more stringent even for very weak fields",9703214v2
1999-08-24,Spin Dependence of Diffractive Vector Meson Production,"I review the recent progress in the theory of s-channel helicity
nonconservation (SCHNC) effects in diffractive DIS. SCHNC in diffractive vector
meson production is an unique probe of the spin-orbit coupling and Fermi motion
of quarks in vector mesons. Photo- and electroproduction of the $\phi$ and its
radial and angular excitations at Jlab is perfectly posed to probe SCHNC in QCD
pomeron exchange. I also discuss the unitarity driven demise of the
Burkhardt-Cottingham sum rule and large & scaling departure from the
Wandzura-Wilczek relation.",9908453v2
2000-06-23,Radiative corrections to the semileptonic Dalitz plot with angular correlation between polarized decaying hyperons and emitted charged leptons,"We obtain a model-independent expression for the Dalitz plot of semileptonic
decays of polarized hyperons including radiative corrections to order alpha and
neglecting terms of order (alpha q)/(pi M_1), where q is the four-momentum
transfer and M_1 is the mass of the decaying hyperon. We specialize our results
to exhibit the correlation between the charged-lepton momentum and the spin of
the decaying hyperon. We present results for the three-body region of the
Dalitz plot and for the complete Dalitz plot (which includes the four-body
region). From these results we also obtain the corresponding radiative
corrections to the integrated lepton spin-asymmetry coefficient. Our formulas
are valid for charged as well as for neutral decaying hyperons and are
appropriate for model-independent experimental analysis whether the real photon
is discriminated or not.",0006279v1
2000-12-29,Neutralino-Nucleus Elastic Cross Section in the Minimal Supersymmetric Standard Model with Explicit CP Violation,"We study the elastic scattering of the lightest neutralino with a nucleus in
the framework of the minimal supersymmetric standard model (MSSM) with explicit
flavor preserving CP violation, including the one-loop CP-violating neutral
Higgs-boson mixing effects induced dominantly by the CP phases in the top and
bottom (s)quark sectors. We construct the most general form of the effective
Lagrangian for the neutralino-nucleus scattering in the limit of vanishing
momentum transfers and then we perform a comprehensive analysis of the effects
of the complex CP phases on the mass spectra of the lightest neutralino,
neutral Higgs bosons and top squarks, and on the the spin-dependent and
spin-independent neutralino-nucleus scattering cross section for three neucleus
targets F, Si and Ge. The CP phases can reduce or enhance the
neutralino-nucleus cross sections significantly, depending on the values of the
real parameters in the MSSM.",0012370v1
2001-01-29,Measurement of Lambda polarization in muon neutrino charged current interactions in NOMAD,"The Lambda polarization in muon neutrino charged current interactions has
been measured in the NOMAD experiment. We observe negative polarization along
the W - boson direction which is enhanced in the target fragmentation region:
  Px (xF < 0) = -0.21 +/- 0.04(stat) +/- 0.02(sys). In the current
fragmentation region we find: Px (xF > 0) = -0.09 +/- 0.06(stat) +/- 0.03(sys).
These results provide a test of different models describing the nucleon spin
composition and the spin transfer mechanisms. A significant transverse
polarization (in the direction orthogonal to the Lambda production plane) has
been observed for the first time in a neutrino experiment: Py = -0.22 +/-
0.03(stat) +/- 0.01(sys). The dependence of the absolute value of Py on the
Lambda transverse momentum with respect to the hadronic jet direction is in
qualitative agreement with the results from unpolarized hadron-hadron
experiments.",0101325v1
2001-05-03,Radiative Corrections to Polarized Inelastic Scattering in Coincidence,"The coplete analysis of the model-independent leading radiative corrections
to cross-section and polarization observables in semi-inclusive deep-inelastic
electron-nucleus scattering with detection of a proton and scattered electron
in coincidence has been performed. The basis of the calculations consists of
the Drell-Yan like representation in electrodynamics for both spin-independent
and spin-dependent parts of the cross-section in terms of the electron
structure functions. The applications to the polarization transfer effect from
longitudinally polarized electron beam to detected proton as well as to
scattering by the polarized target are considered.",0105032v1
2001-11-09,Radiative corrections to the semileptonic Dalitz plot with angular correlation between polarized decaying and emitted hyperons: effects of the four-body region,"We obtain a model-independent expression for the complete Dalitz plot of
semileptonic decays of polarized hyperons, which includes both the three-body
and the four-body regions. We calculate radiative corrections to order alpha,
neglecting terms of order alpha q/(pi M_1), where q is the four-momentum
transfer and M_1 is the mass of the decaying hyperon. Our results exhibit
explicitly the correlation between the emitted hyperon three-momentum and the
spin of the decaying hyperon. This allows us to obtain the corresponding
radiative corrections to the integrated emitted hyperon spin-asymmetry
coefficient. Our formulas are valid for charged as well as for neutral decaying
hyperons and are appropriate for model-independent experimental analysis
whether the real photon is discriminated or not.",0111117v1
2001-11-28,$q \to Λ$ Fragmentation Function and Nucleon Transversity Distribution in a Diquark Model,"Based on a simple quark-diquark model, we propose a set of unpolarized,
longitudinally polarized and transversely polarized fragmentation functions for
the $\Lambda$ by fitting the unpolarized $\Lambda$ production data in $e^+ e ^-
$ annihilation. It is found that the helicity structure of the obtained
$\Lambda$ fragmentation functions is supported by the all available
experimental data on the longitudinal $\Lambda$ polarization. Within the same
framework of the diquark model, the nucleon transversity distributions are
presented and consistent descriptions of the available HERMES data on the
azimuthal spin asymmetries in pion electroproduction are obtained. Furthermore,
the spin transfers to the transversely polarized $\Lambda$ in the charged
lepton DIS on a transversely polarized nucleon target are predicted for future
experiments.",0111382v1
2003-11-10,How to extract the $ΛN$ scattering length from production reactions,"A dispersion integral is derived that allows one to relate directly (spin
dependent) $\Lambda N$ invariant mass spectra, measured in a large-momentum
transfer reaction such as $pp\to K^+p\Lambda$ or $\gamma d\to K^+n\Lambda$, to
the scattering length for elastic $\Lambda N$ scattering. The involved
systematic uncertainties are estimated to be smaller than 0.3 fm. This estimate
is confirmed by comparing results of the proposed formalism with those of
microscopic model calculations. We also show, for the specific reaction $pp\to
K^+\Lambda p$, how polarization observables can be used to separate the two
spin states of the $\Lambda N$ system.",0311116v1
2003-12-20,Evaluation of the Higher Twist Contribution to the Moments of Proton Structure Functions F2 and g1,"We performed the measurement of the inclusive electron scattering off the
proton in the resonance region (W<2.5 GeV) at momentum transfer Q2 below 4.5
(GeV/c)^2 with the CLAS detector. The large acceptance of CLAS provided an
access to a large, continuous two-dimensional kinematic domain in Q2 and x,
allowing therefore an integration of the data at fixed Q2 over x-interval. The
covered x-interval at each measured Q2 value is sufficient for an evaluation of
the higher moments (n>2). From these data we extracted the structure function
F2 and, by including other world data, we studied the Q2 evolution of its
moments, Mn(Q2), in order to estimate the higher twist contributions. A similar
experiment with polarized proton target is completed at CLAS. These new data
allow an accurate determination of higher moments of the proton structure
function g1. A preliminary phenomenological analysis indicates an excess of the
higher twist contribution in the spin-dependent structure function with respect
to the spin-independent one.",0312288v2
2004-06-10,Large Logarithms in the Beam Normal Spin Asymmetry of Elastic Electron--Proton Scattering,"We study a parity-conserving single-spin beam asymmetry of elastic
electron-proton scattering induced by an absorptive part of the two-photon
exchange amplitude. It is demonstrated that excitation of inelastic hadronic
intermediate states by the consecutive exchange of two photons leads to
logarithmic and double-logarithmic enhancement due to contributions of hard
collinear quasi-real photons. The asymmetry at small electron scattering angles
is expressed in terms of the total photoproduction cross section on the proton,
and is predicted to reach the magnitude of 20-30 parts per million. At these
conditions and fixed 4-momentum transfers, the asymmetry is rising
logarithmically with increasing electron beam energy, following the high-energy
diffractive behavior of total photoproduction cross section on the proton.",0406127v2
2005-11-03,Masses and electroweak properties of light mesons in the relativistic quark model,"The masses, pseudoscalar and vector weak decay constants and electromagnetic
form factors of light S-wave mesons are studied in the framework of the
relativistic quark model based on the quasipotential approach. We use the same
model assumptions and parameters as in our previous investigations of heavy
meson and baryon properties. The masses and wave functions of the ground state
and radially excited pi, rho, K, K* and phi mesons, obtained by solving
numerically the relativistic Schroedinger-like equation with the complete
relativistic q bar q potential including both spin-independent and
spin-dependent terms, are presented. Novel relativistic expressions for the
weak decay constants of the pseudoscalar and vector mesons are derived. It is
shown that the intermediate negative-energy quark states give significant
contributions which essentially decrease the decay constants bringing them in
agreement with experimental data. The electromagnetic form factors of the pion,
charged and neutral kaon are calculated in a broad range of the space-like
momentum transfer. The corresponding charge radii are determined. All results
agree well with available experimental data.",0511029v2
2007-01-31,Two-Photon Physics in Hadronic Processes,"Two-photon exchange contributions to elastic electron-scattering are
reviewed. The apparent discrepancy in the extraction of elastic nucleon form
factors between unpolarized Rosenbluth and polarization transfer experiments is
discussed, as well as the understanding of this puzzle in terms of two-photon
exchange corrections. Calculations of such corrections both within partonic and
hadronic frameworks are reviewed. In view of recent spin-dependent electron
scattering data, the relation of the two-photon exchange process to the
hyperfine splitting in hydrogen is critically examined. The imaginary part of
the two-photon exchange amplitude as can be accessed from the beam normal spin
asymmetry in elastic electron-nucleon scattering is reviewed. Further
extensions and open issues in this field are outlined.",0701272v1
1995-05-08,Interactions of a $j=1$ boson in the $2(2j+1)$ component theory,"The amplitudes for boson-boson and fermion-boson interactions are calculated
in the second order of perturbation theory in the Lobachevsky space. An
essential ingredient of the used model is the Weinberg's $2(2j+1)$ component
formalism for describing a particle of spin $j$, recently developed
substantially. The boson-boson amplitude is then compared with the two-fermion
amplitude obtained long ago by Skachkov on the ground of the hamiltonian
formulation of quantum field theory on the mass hyperboloid, $p_0^2 -{\bf
p}^2=M^2$, proposed by Kadyshevsky. The parametrization of the amplitudes by
means of the momentum transfer in the Lobachevsky space leads to same spin
structures in the expressions of $T$ matrices for the fermion and the boson
cases. However, certain differences are found. Possible physical applications
are discussed.",9505044v1
1995-10-31,Fermion-Fermion and Boson-Boson Amplitudes: Surprising Similarities,"Amplitudes for boson-boson and fermion-boson interactions are calculated in
the second order of perturbation theory in the Lobachevsky space. An essential
ingredient of the used model is the Weinberg's $2(2j+1)$ component formalism
for describing a particle of spin $j$, recently developed substantially. The
boson-boson amplitude is then compared with the two-fermion amplitude obtained
by Skachkov long ago on the ground of the hamiltonian formulation of quantum
field theory on the mass hyperboloid, $p_0^2 -{\vec p}^{2}=M^2$, proposed by
Kadyshevsky. The parametrization of the amplitudes by means of the momentum
transfer in the Lobachevsky space leads to same spin structures in the
expressions of $T$ matrices for the fermion and the boson cases. However,
certain differences are found. Possible physical applications are discussed.",9510238v1
2004-04-20,Gyrating Strings: A new instability of black strings?,"A thermodynamic argument is presented suggesting that near-extremal spinning
D1-D5-P black strings become unstable when their angular momentum exceeds
$J_{crit} = {3Q_1Q_5}/2\sqrt{2}$. In contrast, the dimensionally reduced black
holes are thermodynamically stable. The proposed instability involves a phase
in which the spin angular momentum above $J_{crit}$ is transferred to gyration
of the string in space; i.e., to orbital angular momentum of parts of the
string about the mean location in space. Thus the string becomes a rotating
helical coil. We note that an instability of this form would yield a
counter-example to the Gubser-Mitra conjecture, which proposes a particular
link between dynamic black string instabilities and the thermodynamics of black
strings. There may also be other instabilities associated with radiation modes
of various fields. Our arguments also apply to the D-brane bound states
associated with these black strings in weakly coupled string theory.",0404139v3
2004-05-10,Topological-charge anomalies in supersymmetric theories with domain walls,"Domain walls in 1+2 dimensions are studied to clarify some general features
of topological-charge anomalies in supersymmetric theories, by extensive use of
a superfield supercurrent. For domain walls quantum modifications of the
supercharge algebra arise not only from the short-distance anomaly but also
from another source of long-distance origin, induced spin in the domain-wall
background, and the latter dominates in the sum. A close look into the
supersymmetric trace identity, which naturally accommodates the central-charge
anomaly and its superpartners, shows an interesting consequence of the
improvement of the supercurrent: Via an improvement the anomaly in the central
charge can be transferred from induced spin in the fermion sector to an induced
potential in the boson sector. This fact reveals a dual character, both
fermionic and bosonic, of the central-charge anomaly, which reflects the
underlying supersymmetry. The one-loop superfield effective action is also
constructed to verify the anomaly and BPS saturation of the domain-wall
spectrum.",0405073v1
1999-12-17,Thermodynamic Bethe ansatz equation from fusion hierarchy of osp(1|2) integrable spin chain,"The thermodynamic Bethe ansatz (TBA) and the excited state TBA equations for
an integrable spin chain related to the Lie superalgebra osp(1|2) are proposed
by the quantum transfer matrix (QTM) method. We introduce the fusion hierarchy
of the QTM and derive the functional relations among them (T-system) and their
certain combinations (Y-system). Their analytical property leads to the
non-linear integral equations which describe the free energy and the
correlation length at any finite temperatures. With regard to the free energy,
they coincide with the TBA equation (math-ph/9911010, Mod. Phys. Lett. A, 14,
2427 (1999)) based on the string hypothesis.",9912014v3
2002-03-23,The Phase Transition in Statistical Models Defined on Farey Fractions,"We consider several statistical models defined on the Farey fractions. Two of
these models may be regarded as ""spin chains"", with long-range interactions,
while another arises in the study of multifractals associated with chaotic maps
exhibiting intermittency. We prove that these models all have the same free
energy. Their thermodynamic behavior is determined by the spectrum of the
transfer operator (Ruelle-Perron-Frobenius operator), which is defined using
the maps (presentation functions) generating the Farey ""tree"". The spectrum of
this operator was completely determined by Prellberg. It follows that these
models have a second-order phase transition with a specific heat divergence of
the form [t (ln t)^2]^(-1). The spin chain models are also rigorously known to
have a discontinuity in the magnetization at the phase transition.",0203048v3
2004-11-30,Unified Analysis of Spin Isospin Responses of Nuclei,"We investigated the Gamow-Teller (GT) strength distribution, especially the
quenching with respect to the GT sum rule, and the enhancement of the pionic
responses in the quasielasic scattering region, in the same theoretical
framework. That is the continuum random phase approximation with the pi+rho+g'
model interaction, incorporated with distorted wave impulse approximation and
two-step calculations. From this analysis we searched the Landau-Migdal
parameters, g'NN and g'ND, through the comparison with the experimental data of
the GT strength distribution obtained at 300 MeV and the spin-longitudinal
(pionic) cross sections IDq of (p,n) at 350 and 500 MeV. This comprehensive and
sophisticated study gave a common set of g'NN=0.6-0.7 and g'ND=0.2-0.4, for
both low and high momentum transfers.",0411055v1
1998-03-26,Toroidal collective motions in the atomic nucleus,"The work deals with one of the topics of collective motion. In the frame of
Nuclear Fluid Dynamics, a model which portrays the nuclear matter as a quantum
elastic body, the torus-like motions and their associated energies are computed
using the thirteen moment approximation. The spin-dependent collective
excitations, with toroidal electromagnetic structure, are studied by means of
the Generalized Goldhaber-Teller model, with emphasize on the 1$^{-}$ spin-flip
mode and its excitation in spherical nuclei by inelastic electron scattering.
We discuss the importance of toroidal contributions in the inclusive electron
scattering $(e, e')$ and exclusive coincidence electron scattering $(e,
e'\gamma)$. In order to extract the toroidal multipole, we use the
backscattering angles in the first mentioned reaction, and the separation of
the longitudinal/transverse interference in the second case. The introduction
of a quantity which accounts for the deviations from the Siegert theorem, shows
the importance of toroidal quadrupole transitions at high-momentum transfer.",9803051v1
2001-11-15,Irreducible pionic effects in nucleon-deuteron scattering below 20 MeV,"The consequences of a recently introduced irreducible pionic effect in low
energy nucleon-deuteron scattering are analyzed. Differential cross-sections,
nucleon (vector) and deuteron (vector and tensor) analyzing powers, and four
different polarization transfer coefficients have been considered. This
3NF-like effect is generated by the pion-exchange diagram in presence of a
two-nucleon correlation and is partially cancelled by meson-retardation
contributions. Indications are provided that such type of effects are capable
to selectively increase the vector (nucleon and deuteron) analyzing powers,
while in the considered energy range they are almost negligible on the
differential cross sections. These indications, observed with different
realistic nucleon-nucleon interactions, provide additional evidences that such
3NF-like effects have indeed the potential to solve the puzzle of the vector
analyzing powers. Smaller but non negligible effects are observed for the other
spin observables. In some cases, we find that the modifications introduced by
such pionic effects on these spin observables (other than the vector analyzing
powers) are significant and interesting and could be observed by experiments.",0111045v1
2003-12-17,Sensitivity of exclusive proton knockout spin observables to different Lorentz invariant representations of the NN interaction,"Within the framework of the relativistic plane wave impulse approximation, we
study the observable consequences of employing a complete Lorentz invariant
representation of the NN scattering matrix in terms of 44 independent
amplitudes, as opposed to the previously-employed, but ambiguous, five-term
Lorentz invariant parametrization of the NN scattering matrix, for the
prediction of complete sets of exclusive ($\vec{p},2 \vec{p} $) polarization
transfer observables. Two kinematic conditions are considered, namely proton
knockout from the $3s_{1/2}$ state of $^{208}$Pb at an incident energy of 202
MeV for coplanar scattering angles ($28.0^{\circ}, -54.6^{\circ}$), as well as
an incident energy of 392 MeV for the angle pair ($32.5^{\circ},
-80.0^{\circ}$). The results indicate that certain spin observables are ideal
for discriminating between the two representations.",0312066v1
2004-09-08,Spin asymmetry and GDH sum rule for real and virtual photons for the deuteron,"An explicit evaluation of the spin asymmetry of the deuteron and the
associated GDH sum rule is presented which includes disintegration, single and
double pion and eta production. For the GDH integral a large cancellation is
found between the disintegration channel and the meson production channels.
Furthermore, first results for the contribution of the disintegration channel
to the generalized GDH integral at constant four-momentum transfer reveal a
dominance of the isovector M1 transition to the $^1$S$_0$-state near threshold
resulting in a negative contribution with a minimum around $Q^2\approx 0.2$
fm$^{-2}$ which is driven by the nucleon anomalous isovector magnetic moment.",0409015v1
2002-12-02,Theory of adiabatic Hexaamminecobalt-Self-Exchange,"We have reexamined the thermally induced Co(NH_3)_6^{2+/3+} [Co(II/III)]
redox reaction using the first principles density-functional-theory method,
semiclassical Marcus theory, and known charge transfer parameters. We confirm a
previously suggested mechanism involving excited state (^2E_g) of Co(II) which
becomes lower than the ground state (^4T_1g) in the transition state region.
This lowers the transition state barrier considerably by about 6.9 kcal/mol and
leads to a spin-allowed and adiabatic electron exchange process. Our
calculations are consistent with previous experimental results regarding the
spin-excitation energy (^3T_1g) of Co(III), and the fact that an optical
absorption peak (^2E_g) of the Co(II) species could not be found
experimentally. Our rate is of order 6 10^{-3} 1/Ms and hence 2 orders of
magnitude faster than determined previously by experiments.",0212010v1
1996-09-27,Einstein-Podolsky-Rosen-Bohm experiment with relativistic massive particles,"The EPRB experiment with massive partcles can be formulated if one defines
spin in a relativistic way. Two versions are discussed: The one using the spin
operator defined via the relativistic center-of-mass operator, and the one
using the Pauli-Lubanski vector. Both are shown to lead to the SAME prediction
for the EPRB experiment: The degree of violation of the Bell inequality
DECREASES with growing velocity of the EPR pair of spin-1/2 particles. The
phenomenon can be physically understood as a combined effect of the Lorentz
contraction and the Moller shift of the relativistic center of mass. The effect
is therefore stronger than standard relativistic phenomena such as the Lorentz
contraction or time dilatation. The fact that the Bell inequality is in general
less violated than in the nonrelativistic case will have to be taken into
account in tests for eavesdropping if massive particles will be used for a key
transfer.",9609022v2
2000-09-15,"The Topological AC and HMW Effects, and the Dual Current in 2+1 Dimensions","We study the Aharonov-Casher (AC) effect and the related He-McKellar-Wilkens
(HMW) effect in 2+1 dimensions. In this restricted space these effects are the
result of the interaction of the electromagnetic field tensor with the dual of
a current. Transferring the dual operation from the current to the field tensor
shows that this interaction may be reinterpreted as due to the interaction of
an effective vector potential and a current, and the AC and HMW effects follow
immediately. A general proof of this for particles with an arbitrary spin is
provided.
  The restriction to 2+1 dimensions, with this interpretation, provides a
unified way of treating the AC and HMW effects for an arbitrary spin. Perhaps
more interestingly the treatment shows that a spin-0 particle can show AC and
HMW effects, although it has no magnetic or electric dipole moment in the usual
sense.",0009065v1
2002-05-19,Entanglement generation by adiabatic navigation in the space of symmetric multi-particle states,"We propose a technique for robust and efficient navigation in the Hilbert
space of entangled symmetric states of a multiparticle system with externally
controllable linear and nonlinear collective interactions. A linearly changing
external field applied along the quantization axis creates a network of well
separated level crossings in the energy diagram of the collective states. One
or more transverse pulsed fields applied at the times of specific level
crossings induce adiabatic passage between these states. By choosing the timing
of the pulsed field appropriately, one can transfer an initial product state of
all N spins into (i) any symmetric state with n spin excitations and (ii) the
N-particle analog of the Greenberger-Horne-Zeilinger state. This technique,
unlike techniques using pulses of specific area, does not require precise
knowledge of the number of particles and is robust against variations in the
interaction parameters. We discuss potential applications in two-component Bose
condensates and ion-trap systems.",0205118v1
2002-08-07,Optimal Control of Spin Dynamics in the Presence of Relaxation,"Experiments in coherent spectroscopy correspond to control of quantum
mechanical ensembles guiding them from initial to final target states. The
control inputs (pulse sequences) that accomplish these transformations should
be designed to minimize the effects of relaxation and to optimize the
sensitivity of the experiments. For example in nuclear magnetic resonance (NMR)
spectroscopy, a question of fundamental importance is what is the maximum
efficiency of coherence or polarization transfer between two spins in the
presence of relaxation. Furthermore, what is the optimal pulse sequence which
achieves this efficiency? In this letter, we initiate the study of a class of
control systems, which leads to analytical answers to the above questions.
Unexpected gains in sensitivity are reported for the most commonly used
experiments in NMR spectroscopy.",0208050v1
2004-05-28,Entanglement Witness Derived from NMR Superdense Coding,"We show that it is possible to transfer two-bit information via encoding a
single qubit in a conventional nuclear magnetic resonance (NMR) experiment with
two very weakly polarized nuclear spins. Nevertheless, the experiment can not
be regarded as a demonstration of superdense coding by means of NMR because it
is based on the large number of molecules being involved in the ensemble state
rather than the entanglement of the NMR states. Following the discussions, an
entanglement witness, particularly applicable for NMR, is introduced based on
separate and simultaneous measurement of the individual nuclear spin
magnetizations.",0405175v4
2004-07-07,Theory of control of spin/photon interface for quantum networks,"A cavity coupling a charged nanodot and a fiber can act as a quantum
interface, through which a stationary spin qubit and a flying photon qubit can
be inter-converted via cavity-assisted Raman process. This Raman process can be
controlled to generate or annihilate an arbitrarily shaped single-photon
wavepacket by pulse-shaping the controlling laser field. This quantum interface
forms the basis for many essential functions of a quantum network, including
sending, receiving, transferring, swapping, and entangling qubits at
distributed quantum nodes as well as a deterministic source and an efficient
detector of a single photon wavepacket with arbitrarily specified shape and
average photon number. Numerical study of noise effects on the operations shows
high fidelity.",0407060v1
2004-07-08,Optical Quantum Computation with Perpetually Coupled Spins,"The possibility of using strongly and continuously interacting spins for
quantum computation has recently been discussed. Here we present a simple
optical scheme that achieves this goal while avoiding the drawbacks of earlier
proposals. We employ a third state, accessed by a classical laser field, to
create an effective barrier to information transfer. The mechanism proves to be
highly efficient both for continuous and pulsed laser modes; moreover it is
very robust, tolerating high decay rates for the excited states. The approach
is applicable to a broad range of systems, in particular dense structures such
as solid state self-assembled (e.g., molecular) devices. Importantly, there are
existing structures upon which `first step' experiments could be immediately
performed.",0407063v2
2005-05-09,Quantum Computing with Spin Qubits Interacting Through Delocalized Excitons: Overcoming Hole Mixing,"As a candidate scheme for controllably coupled qubits, we consider two
quantum dots, each doped with a single electron. The spin of the electron
defines our qubit basis and trion states can be created by using polarized
light; we show that the form of the excited trion depends on the state of the
qubit. By using the Luttinger-Kohn Hamiltonian we calculate the form of these
trion states in the presence of light-heavy hole mixing, and show that they can
interact through both the F\""orster transfer and static dipole-dipole
interactions. Finally, we demonstrate that by using chirped laser pulses, it is
possible to perform a two-qubit gate in this system by adiabatically following
the eigenstates as a function of laser detuning. These gates are robust in that
they operate with any realistic degree of hole mixing, and for either type of
trion-trion coupling.",0505055v3
2007-05-28,Information-flux approach to multiple-spin dynamics,"We introduce and formalize the concept of information flux in a many-body
register as the influence that the dynamics of a specific element receive from
any other element of the register. By quantifying the information flux in a
protocol, we can design the most appropriate initial state of the system and,
noticeably, the distribution of coupling strengths among the parts of the
register itself. The intuitive nature of this tool and its flexibility, which
allow for easily manageable numerical approaches when analytic expressions are
not straightforward, are greatly useful in interacting many-body systems such
as quantum spin chains. We illustrate the use of this concept in quantum
cloning and quantum state transfer and we also sketch its extension to
non-unitary dynamics.",0705.4076v2
2007-06-13,Neutron Transfer Reactions for Deformed Nuclei Using Sturmian Basis,"We study the spin-parity distribution P(J$^{\pi}$,E) of $^{156}$Gd excited
states above the neutron separation energy that are expected to be populated
via the neutron pickup reaction $^{157}$Gd($^{3}$He,$^{4}$He)$^{156}$Gd. In
general, modeling of the spin-parity distribution is important for the
applicability of the surrogate reaction technique as a method of deducing
reaction cross sections. We model excited states in $^{156}$Gd as rotational
states built on intrinsic states consisting of a hole in the core where the
hole represents neutron removal form a deformed single particle state. The
reaction cross section to each excited state is calculated using standard
reaction code that uses spherical reaction form-factor input. The spectroscopic
factor associated with each form-factor is the expansion coefficient of the
deformed neutron state in a spherical Sturmian basis consisting of the
spherical reaction form-factors.",0706.2002v1
2007-06-28,Entanglement Transfer Through an Antiferromagnetic Spin Chain,"We study the possibility of using an uniformly coupled finite
antiferromagnetic spin-1/2 Heisenberg chain as a channel for transmitting
entanglement. One member of a pair of maximally entangled spins is initially
appended to one end of a chain in its ground state and the dynamical
propagation of this entanglement to the other end is calculated. We show that
compared to the analogous scheme with a ferromagnetic chain in its ground
state, here the entanglement is transmitted faster, with less decay, with a
much higher purity and as a narrow pulse form rising non-analytically from
zero. Here non-zero temperatures and depolarizing environments are both found
to be less destructive in comparison to the ferromagnetic case. The
entanglement is found to propagate through the chain in a peculiar fashion
whereby it hops to skip alternate sites.",0706.4176v4
2007-08-09,Will Zigzag Graphene Nanoribbon Turn to Half Metal under Electric Field?,"At B3LYP level of theory, we predict that the half-metallicity in zigzag edge
graphene nanoribbon (ZGNR) can be realized when an external electric field is
applied across the ribbon. The critical electric field to induce the
half-metallicity decreases with the increase of the ribbon width. Both the spin
polarization and half-metallicity are removed when the edge state electrons
fully transferred from one side to the other under very strong electric field.
The electric field range under which ZGNR remain half-metallic increases with
the ribbon width. Our study demonstrates a rich field-induced spin polarization
behavior, which may leads to some important applications in spinstronics.",0708.1213v1
2007-08-28,Trapping radioactive ^{82}Rb in an optical dipole trap and evidence of spontaneous spin polarization,"Optical trapping of selected species of radioactive atoms has great potential
in precision measurements for testing fundamental physics such as EDM, PNC and
parity violating beta-decay asymmetry correlation coefficients. We report
trapping of 10^4 radioactive ^{82}Rb atoms (t_{1/2}=75 s) with a trap lifetime
of ~55 seconds in an optical dipole trap. Transfer efficiency from the
magneto-optical trap was ~14%. We further report the evidence of spontaneous
spin polarization of the atoms in optical dipole trap loading. This advancement
is an important step towards a new generation of precision J-beta correlations
measurements with polarized ^{82}Rb atoms.",0708.3826v2
2007-09-13,Selfconsistent gauge-invariant theory of in-plane infrared response of high-Tc cuprate superconductors involving spin fluctuations,"We report on results of our theoretical study of the in-plane infrared
conductivity of the high-Tc cuprate superconductors using the model where
charged planar quasiparticles are coupled to spin fluctuations. The
computations include both the renormalization of the quasiparticles and the
corresponding modification of the current-current vertex function (vertex
correction), which ensures gauge invariance of the theory and local charge
conservation in the system. The incorporation of the vertex corrections leads
to an increase of the total intraband optical spectral weight (SW) at finite
frequencies, a SW transfer from far infrared to mid infrared, a significant
reduction of the SW of the superconducting condensate, and an amplification of
characteristic features in the superconducting state spectra of the inverse
scattering rate 1/tau. We also discuss the role of selfconsistency and propose
a new interpretation of a kink occurring in the experimental low temperature
spectra of 1/tau around 1000cm^{-1}.",0709.2014v1
2007-09-18,Trapped Rydberg Ions: From Spin Chains to Fast Quantum Gates,"We study the dynamics of Rydberg ions trapped in a linear Paul trap, and
discuss the properties of ionic Rydberg states in the presence of the static
and time-dependent electric fields constituting the trap. The interactions in a
system of many ions are investigated and coupled equations of the internal
electronic states and the external oscillator modes of a linear ion chain are
derived. We show that strong dipole-dipole interactions among the ions can be
achieved by microwave dressing fields. Using low-angular momentum states with
large quantum defect the internal dynamics can be mapped onto an effective spin
model of a pair of dressed Rydberg states that describes the dynamics of
Rydberg excitations in the ion crystal. We demonstrate that excitation transfer
through the ion chain can be achieved on a nanosecond timescale and discuss the
implementation of a fast two-qubit gate in the ion chain.",0709.2849v4
2007-10-12,Slonczewski windmill with dissipation and asymmetry,"J. Slonczewski invented spin-transfer effect in layered systems in 1996.
Among his first predictions was the regime of ``windmill motion'' of a
perfectly symmetric spin valve where the magnetizations of the layers rotate in
a fixed plane keeping the angle between them constant. Since ``windmill'' was
predicted to happen in the case of zero magnetic anisotropy, while in most
experimental setups the anisotropy is significant, the phenomenon was not a
subject of much research. However, the behavior of the magnetically isotropic
device is related to the interesting question of current induced ferromagnetism
and is worth more attention. Here we study the windmill regime in the presence
of dissipation, exchange interaction, and layer asymmetry. It is shown that the
windmill rotation is almost always destroyed by those effects, except for a
single special value of electric current, determined by the parameters of the
device.",0710.2564v1
2007-10-24,Magnetic tight-binding and the iron-chromium enthalpy anomaly,"We describe a self consistent magnetic tight-binding theory based in an
expansion of the Hohenberg-Kohn density functional to second order, about a non
spin polarised reference density. We show how a first order expansion about a
density having a trial input magnetic moment leads to the Stoner--Slater rigid
band model. We employ a simple set of tight-binding parameters that accurately
describes electronic structure and energetics, and show these to be
transferable between first row transition metals and their alloys. We make a
number of calculations of the electronic structure of dilute Cr impurities in
Fe which we compare with results using the local spin density approximation.
The rigid band model provides a powerful means for interpreting complex
magnetic configurations in alloys; using this approach we are able to advance a
simple and readily understood explanation for the observed anomaly in the
enthalpy of mixing.",0710.4399v1
2007-11-10,SU(2) Symmetry and Conservation of Helicity for a Dirac Particle in a Static Magnetic Field at First Order,"We investigate the spin dynamics and the conservation of helicity in the
first order $S-$matrix of a Dirac particle in any static magnetic field. We
express the dynamical quantities using a coordinate system defined by the three
mutually orthogonal vectors; the total momentum
$\mathbf{k}=\mathbf{p_f}+\mathbf{p_i}$, the momentum transfer
$\mathbf{q}=\mathbf{p_f-p_i}$, and $\mathbf{l}=\mathbf{k\times q}$. We show
that this leads to an alternative symmetric description of the conservation of
helicity in a static magnetic field at first order. In particular, we show that
helicity conservation in the transition can be viewed as the invariance of the
component of the spin along $\mathbf{k}$, and the flipping of its component
along $\mathbf{q}$, just as what happens to the momentum vector of a ball
bouncing off a wall. We also derive a ""plug and play"" formula for the
transition matrix element where the only reference to the specific field
configuration, and the incident and outgoing momenta is through the kinematical
factors multiplying a general matrix element that is independent of the
specific vector potential present.",0711.1583v2
2007-11-14,Fermion-fermion and boson-boson amplitudes: surprising similarities,"Amplitudes for fermion-fermion, boson-boson and fermion-boson interactions
are calculated in the second order of perturbation theory in the Lobachevsky
space. An essential ingredient of the model is the Weinberg's 2(2j+1)-component
formalism for describing a particle of spin j. The boson-boson amplitude is
then compared with the two-fermion amplitude obtained long ago by Skachkov on
the basis of the Hamiltonian formulation of quantum field theory on the mass
hyperboloid, p_0^2 - p^2=M^2, proposed by Kadyshevsky. The parametrization of
the amplitudes by means of the momentum transfer in the Lobachevsky space leads
to same spin structures in the expressions of T-matrices for the fermion case
and the boson case. However, certain differences are found. Possible physical
applications are discussed.",0711.2276v1
2007-11-28,Quantum transport and spin dynamics on shearless tori,"We investigate for quantum dynamics in phase-space regions containing
``shearless tori''. We show that the properties of these peculiar classical
phase-space structures -- important to the dynamics of tokamaks -- may be
exploited for quantum information applications. In particular we show that
shearless tori permit the non-dispersive transmission of localized wavepackets.
The quantum many-body Hamiltonian of a Heisenberg ferromagnetic spin chain,
subjected to an oscillating magnetic field, can be reduced to a classical
one-body ``image'' dynamical system which is the well-studied Harper map. The
Harper map belongs to a class of Hamiltonian systems (non-twist maps) which
contain shearless tori. We show that a variant with sinusoidal time driving
``driven Harper model'' produces shearless tori which are especially suitable
for quantum state transfer. The behavior of the concurrence is investigated as
an example.",0711.4395v3
2007-12-07,Spin effects in elastic backward P-D scattering,"The elastic backward proton-deuteron scattering is analyzed including both
relativistic effects in the deuteron and the reaction mechanism. It is shown
that inclusion of the graphs corresponding to the emission, rescattering and
absorption of the virtual pion by a deuteron nucleon in addition to the
one-nucleon exchange graph allows a rather satisfactory description of all the
experimental data on the differential cross section, tensor analyzing power of
the deuteron and transfer polarization in this reaction.",0712.1161v2
2007-12-18,Coherent adiabatic theory of two-electron quantum dot molecules in external spin baths,"We derive an accurate molecular orbital based expression for the coherent
time evolution of a two-electron wave function in a quantum dot molecule where
the electrons interact with each other, with external time dependent
electromagnetic fields and with a surrounding nuclear spin reservoir. The
theory allows for direct numerical modeling of the decoherence in quantum dots
due to hyperfine interactions. Calculations result in good agreement with
recent singlet-triplet dephasing experiments by Laird et. al. [Phys. Rev. Lett.
97, 056801 (2006)], as well as analytical model calculations. Furthermore, it
is shown that using a much faster electric switch than applied in these
experiments will transfer the initial state to excited states where the
hyperfine singlet-triplet mixing is negligible.",0712.2925v1
2008-01-18,Quantum Spin Hall Effect in Inverted Type II Semiconductors,"The quantum spin Hall (QSH) state is a topologically non-trivial state of
quantum matter which preserves time-reversal symmetry; it has an energy gap in
the bulk, but topologically robust gapless states at the edge. Recently, this
novel effect has been predicted and observed in HgTe quantum wells. In this
work we predict a similar effect arising in Type-II semiconductor quantum wells
made from InAs/GaSb/AlSb. Because of a rare band alignment the quantum well
band structure exhibits an ""inverted"" phase similar to CdTe/HgTe quantum wells,
which is a QSH state when the Fermi level lies inside the gap. Due to the
asymmetric structure of this quantum well, the effects of inversion symmetry
breaking and inter-layer charge transfer are essential. By standard
self-consistent calculations, we show that the QSH state persists when these
corrections are included, and a quantum phase transition between the normal
insulator and the QSH phase can be electrically tuned by the gate voltage.",0801.2831v1
2008-03-21,Critical intermediate phase and phase transitions in a triangular-lattice three-spin interaction model: Level-spectroscopy approach,"We investigate infinite-order phase transitions like the
Berezinskii-Kosterlitz-Thouless transition observed in a triangular-lattice
three-spin interaction model. Based on a field theoretical description and the
operator-production-expansion technique, we perform the renormalization-group
analysis, and then clarify properties of marginal operators near the phase
transition points. The results are utilized to establish criteria to determine
the transition points and some universal relations among excitation levels to
characterize the transitions. We verify these predictions via the numerical
analysis on eigenvalue structures of the transfer matrix. Also, we discuss an
enhancement of symmetry at the end points of a critical intermediate phase in
connection with a transition observed in the ground state of the
bilinear-biquadratic spin-1 chain.",0803.3114v2
2008-06-05,Extraction of finite-energy contributions to the Sivers asymmetry from the analysis of exclusive proton-proton scattering,"I study the effect of scalar and spin-orbit rescattering terms, in the
production of a nonzero Sivers-like asymmetry in proton-proton collisions
(nclusive production and Drell-Yan) at moderate center of mass energies
$\sqrt{s}$ $<$ 15 GeV and transverse momentum up to 3 GeV/c. An
ultrarelativistic generalization of the Glauber formalism is here used to (i)
fit the scalar and spin-orbit interaction terms on proton-proton elastic
scattering data, including analyzing power, (ii) transfer such information to
inclusive proton-proton scattering. It is shown that the phenomenological
interactions responsible for the nonzero analyzing power in proton-proton
elastic scattering produce a relevant nonzero analyzing power in inclusive
processes associated with proton-proton collisions. This could represent a
relevant (possibly higher-twist) contribution to the Sivers asymmetry.",0806.0943v2
2008-09-19,Doping a Mott insulator with orbital degrees of freedom,"We study the effects of hole doping on one-dimensional Mott insulators with
orbital degrees of freedom. We describe the system in terms of a generalized
t-J model. At a specific point in parameter space the model becomes integrable
in analogy to the one-band supersymmetric t-J model. We use the Bethe ansatz to
derive a set of nonlinear integral equations which allow us to study the
thermodynamics exactly. Moving away from this special point in parameter space
we use the density-matrix renormalization group applied to transfer matrices to
study the evolution of various phases of the undoped system with doping and
temperature. Finally, we study a one-dimensional version of a realistic model
for cubic titanates which includes the anisotropy of the orbital sector due to
Hund's coupling. We find a transition from a phase with antiferromagnetically
correlated spins to a phase where the spins are fully ferromagnetically
polarized, a strong tendency towards phase separation at large Hund's coupling,
as well as the possibility of an instability towards triplet superconductivity.",0809.3427v1
2008-09-23,Critical interfaces in the random-bond Potts model,"We study geometrical properties of interfaces in the random-temperature
q-states Potts model as an example of a conformal field theory weakly perturbed
by quenched disorder. Using conformal perturbation theory in q-2 we compute the
fractal dimension of Fortuin Kasteleyn domain walls. We also compute it
numerically both via the Wolff cluster algorithm for q=3 and via
transfer-matrix evaluations. We obtain numerical results for the fractal
dimension of spin cluster interfaces for q=3. These are found numerically
consistent with the duality kappa(spin) * kappa(FK)= 16 as expressed in
putative SLE parameters.",0809.3985v1
2008-09-26,Critical behavior at edge singularities in one dimensional spin models,"In ferromagnetic spin models above the critical temperature ($T > T_{cr}$)
the partition function zeros accumulate at complex values of the magnetic field
($H_E$) with a universal behavior for the density of zeros $\rho (H) \sim | H -
H_E |^{\sg}$. The critical exponent $\sg$ is believed to be universal at each
space dimension and it is related to the magnetic scaling exponent $y_h$ via
$\sg = (d-y_h)/y_h$. In two dimensions we have $y_h=12/5 (\sg = -1/6)$ while
$y_h=2 (\sg=-1/2)$ in $d=1$. For the one dimensional Blume-Capel and
Blume-Emery-Griffiths models we show here, for different temperatures, that a
new value $y_h=3 (\sg =-2/3)$ can emerge if we have a triple degeneracy of the
transfer matrix eigenvalues.",0809.4510v1
2008-10-02,Doubly excited ferromagnetic spin-chain as a pair of coupled kicked rotors,"We show that the dynamics of a doubly-excited 1D Heisenberg ferromagnetic
chain, subject to short pulses from a parabolic magnetic field may be analyzed
as a pair of quantum kicked rotors. By focusing on the two-magnon dynamics in
the kicked XXZ model we investigate how the anisotropy parameter - which
controls the strength of the magnon-magnon interaction - changes the nature of
the coupling between the two ""image"" coupled Kicked Rotors. We investigate
quantum state transfer possibilities and show that one may control whether the
spin excitations are transmitted together, or separate from each other.",0810.0454v3
2009-01-12,Kondo effect in the helical edge liquid of the quantum spin Hall state,"Following the recent observation of the quantum spin Hall (QSH) effect in
HgTe quantum wells, an important issue is to understand the effect of
impurities on transport in the QSH regime. Using linear response and
renormalization group methods, we calculate the edge conductance of a QSH
insulator as a function of temperature in the presence of a magnetic impurity.
At high temperatures, Kondo and/or two-particle scattering give rise to a
logarithmic temperature dependence. At low temperatures, for weak Coulomb
interactions in the edge liquid the conductance is restored to unitarity with
unusual power-laws characteristic of a `local helical liquid', while for strong
interactions transport proceeds by weak tunneling through the impurity where
only half an electron charge is transferred in each tunneling event.",0901.1685v3
2009-02-03,Neutron scattering evidence for isolated spin-1/2 ladders in (C$_5$D$_{12}$N)$_2$CuBr$_4$,"Inelastic neutron scattering was used to determine the spin Hamiltonian for
the singlet ground state system of fully deuterated BPCB,
(C$_{5}$D$_{12}$N)$_{2}$CuBr$_{4}$. A 2-leg spin-1/2 ladder model, with $J_\bot
= (1.09 \pm 0.01)$ meV and $J_\| = (0.296 \pm 0.005)$ meV, accurately describes
the data. The experimental limit on the effective inter-ladder exchange
constant is $|J_{\rm int}^{\rm eff}|\lesssim 0.006$ meV, and the limit on total
diagonal, intra-ladder exchange is $|J_F+J_{F'}|\leq 0.1$ meV. Including the
effects of copper to bromide covalent spin transfer on the magnetic
form-factor, the experimental ratios of intra-ladder bond energies are
consistent with the predictions of continuous unitary transformation.",0902.0599v3
2009-03-26,Exact solution of the mixed spin-1/2 and spin-S Ising-Heisenberg diamond chain,"The geometric frustration in a class of the mixed spin-1/2 and spin-S
Ising-Heisenberg diamond chains is investigated by combining three exact
analytical techniques: Kambe projection method, decoration-iteration
transformation and transfer-matrix method. The ground state, the magnetization
process and the specific heat as a function of the external magnetic field are
particularly examined for different strengths of the geometric frustration. It
is shown that the increase of the Heisenberg spin value S raises the number of
intermediate magnetization plateaux, which emerge in magnetization curves
provided that the ground state is highly degenerate on behalf of a sufficiently
strong geometric frustration. On the other hand, all intermediate magnetization
plateaux merge into a linear magnetization versus magnetic field dependence in
the limit of classical Heisenberg spin S -> infinity. The enhanced
magnetocaloric effect with cooling rate exceeding the one of paramagnetic salts
is also detected when the disordered frustrated phase constitutes the ground
state and the external magnetic field is small enough.",0903.4566v1
2009-11-02,The role of black hole spin and magnetic field threading the unstable neutrino disk in Gamma Ray Bursts,"We report on the third phase of our study of the neutrino-cooled
hyperaccreting torus around a black hole that powers the jet in Gamma Ray
Bursts. We focus on the influence of the black hole spin on the properties of
the torus. The structure of a stationary torus around the Kerr black hole is
solved numerically. We take into account the detailed treatment of the
microphysics in the nuclear equation of state that includes the neutrino
trapping effect. We find, that in the case of rapidly rotating black holes, the
thermal instability discussed in our previous work is enhanced and develops for
much lower accretion rates. We also find the important role of the energy
transfer from the rotating black hole to the torus, via the magnetic coupling.",0911.0395v2
2009-11-16,The transverse shape of the electron,"We study the charge density, form factors and spin distributions of the
electron induced by its |e \gamma> light-front Fock state in impact parameter
space. Only transversally compact Fock states contribute to the leading
behavior of the Dirac and Pauli form factors as the momentum transfer tends to
infinity. Power suppressed contributions are not compact, and distributions
weighted by the transverse size have end-point contributions. The Fock state
conserves the spin of the parent electron locally, but the separate
contributions of the electron, photon and orbital angular momentum depend on
longitudinal momentum and impact parameter. The sign of the anomalous magnetic
moment of the electron may be understood intuitively from the density
distribution, addressing a challenge by Feynman.",0911.3011v1
2009-11-29,Nested algebraic Bethe ansatz for open GL(N) spin chains with projected K-matrices,"We consider an open spin chain model with GL(N) bulk symmetry that is broken
to GL(M) x GL(N-M) by the boundary, which is a generalization of a model
arising in string/gauge theory. We prove the integrability of this model by
constructing the corresponding commuting transfer matrix. This construction
uses operator-valued ""projected"" K-matrices. We solve this model for general
values of N and M using the nested algebraic Bethe ansatz approach, despite the
fact that the K-matrices are not diagonal. The key to obtaining this solution
is an identity based on a certain factorization property of the reduced
K-matrices into products of R-matrices. Numerical evidence suggests that the
solution is complete.",0911.5494v3
2009-12-03,Antiferromagnetic fluctuations in the normal state of LiFeAs,"We present a detailed study of 75As NMR Knight shift and spin-lattice
relaxation rate in the normal state of stoichiometric polycrystalline LiFeAs.
Our analysis of the Korringa relation suggests that LiFeAs exhibits strong
antiferromagnetic fluctuations, if transferred hyperfine coupling is a dominant
interaction between 75As nuclei and Fe electronic spins, whereas for an on-site
hyperfine coupling scenario, these are weaker, but still present to account for
our experimental observations. Density-functional calculations of electric
field gradient correctly reproduce the experimental values for both 75As and
7Li sites.",0912.0692v2
2009-12-11,Constraining the Accretion Flow in Sgr A* by GR Dynamical and Radiative Modeling,"We present the combination of dynamical accretion model based on 3D GRMHD
simulations and general relativistic (GR) polarized radiative transfer. We
write down the formalism of and perform the GR ray-tracing of cyclo-synchrotron
radiation through the model of accretion flow in Sagittarius A*. GR
polarimetric imaging is presented as well as the results for spectrum for a
probable set of spins and orientations. Precise fitting formulae for Faraday
rotation and Faraday conversion coefficients are employed for thermal plasma.
The axisymmetic flow pattern and the magnetic field geometry correspond to
averaged 3D GRMHD simulations near the black hole, whereas the analytic model
was used far from the black hole. The density scaling is found by fitting the
sub-mm flux. Spin $a=0.7$ and inclination angle $\theta=0.6$ produce the best
fit to sub-mm flux and linear polarization fraction.",0912.2106v1
2010-02-05,Numerical Models of Sgr A*,"We review results from general relativistic axisymmetric magnetohydrodynamic
simulations of accretion in Sgr A*. We use general relativistic radiative
transfer methods and to produce a broad band (from millimeter to gamma-rays)
spectrum. Using a ray tracing scheme we also model images of Sgr A* and compare
the size of image to the VLBI observations at 230 GHz. We perform a parameter
survey and study radiative properties of the flow models for various black hole
spins, ion to electron temperature ratios, and inclinations. We scale our
models to reconstruct the flux and the spectral slope around 230 GHz. The
combination of Monte Carlo spectral energy distribution calculations and 230
GHz image modeling constrains the parameter space of the numerical models. Our
models suggest rather high black hole spin ($a_*\approx 0.9$), electron
temperatures close to the ion temperature ($T_i/T_e \sim 3$) and high
inclination angles ($i \approx 90 \deg$).",1002.1261v1
2010-03-24,Ultrafast Electron Dynamics Theory of Photo-excited Ruthenium Complexes,"An explanation is provided for the ultrafast photo-excited electron dynamics
in low-spin Ruthenium (II) organic complexes. The experimentally-observed
singlet to triplet decay in the metal-to-ligand charge-transfer (MLCT) states
contradicts the expectation that the system should oscillate between the
singlet and triplet states in the presence of a large spin-orbit coupling and
the absence of a significance change in metal-ligand bond length. This dilemma
is solved with a novel quantum decay mechanism that causes a singlet to triplet
decay in about 300 femtoseconds. The decay is mediated by the triplet
metal-centered state ($^3$MC) state even though there is no direct coupling
between the $^1$MLCT and $^3$MC states. The coupling between the $^3$MLCT and
$^3$MC via excited phonon states leads to vibrational cooling that allows the
local system to dissipate the excess energy. In the relaxed state, the
population of the $^3$MC state is low and the metal-ligand bond length is
almost unchanged with respect to the initial photoexcited state, in agreement
with experiment.",1003.4752v1
2010-04-01,Valence evaluation of LiMnO2 and related battery materials by x-ray absorption spectroscopy,"We present an x-ray absorption study of the oxidation states of
transition-metal-ions of LiMnO2 and its related materials, widely used as
cathodes in Li-ion batteries. The comparison between the obtained spectrum and
the configuration-interaction cluster-model calculations showed that the Mn3+
in LiMnO2 is a mixture of the high-spin and low-spin states. We found that Li
deficiencies occur in the case of Cr substitution, whereas there are no Li
deficiencies in the case of Ni substitution. We conclude that the substitution
of charge-transfer-type Ni or Cu is effective for LiMnO2 battery materials.",1004.0185v1
2010-04-20,Communication at the quantum speed limit along a spin chain,"Spin chains have long been considered as candidates for quantum channels to
facilitate quantum communication. We consider the transfer of a single
excitation along a spin-1/2 chain governed by Heisenberg-type interactions. We
build on the work of Balachandran and Gong [1], and show that by applying
optimal control to an external parabolic magnetic field, one can drastically
increase the propagation rate by two orders of magnitude. In particular, we
show that the theoretical maximum propagation rate can be reached, where the
propagation of the excitation takes the form of a dispersed wave. We conclude
that optimal control is not only a useful tool for experimental application,
but also for theoretical enquiry into the physical limits and dynamics of
many-body quantum systems.",1004.3445v1
2010-04-27,Ultrafast Cascading Theory in Intersystem Crossings in Transition-Metal Complexes,"We investigate the cascade decay mechanism for ultrafast intersystem crossing
mediated by the spin-orbit coupling in transition-metal complexes. A
quantum-mechanical description of the cascading process that occurs after
photoexcitation is presented. The conditions for ultrafast cascading are given,
which relate the energy difference between the levels in the cascading process
to the electron-phonon self energy. These limitations aid in the determination
of the cascade path. For $Fe^{2+}$ spin-crossover complexes, this leads to the
conclusion that the ultrafast decay primarily occurs in the manifold of
antibonding metal-to-ligand charge-transfer states. We also give an
interpretation why some intermediate states are bypassed.",1004.4823v2
2010-05-31,Separation of variables for integrable spin-boson models,"We formulate the functional Bethe ansatz for bosonic (infinite dimensional)
representations of the Yang-Baxter algebra. The main deviation from the
standard approach consists in a half infinite 'Sklyanin lattice' made of the
eigenvalues of the operator zeros of the Bethe annihilation operator. By a
separation of variables, functional TQ equations are obtained for this half
infinite lattice. They provide valuable information about the spectrum of a
given Hamiltonian model. We apply this procedure to integrable spin-boson
models subject to both twisted and open boundary conditions. In the case of
general twisted and certain open boundary conditions polynomial solutions to
these TQ equations are found and we compute the spectrum of both the full
transfer matrix and its quasi-classical limit. For generic open boundaries we
present a two-parameter family of Bethe equations, derived from TQ equations
that are compatible with polynomial solutions for Q. A connection of these
parameters to the boundary fields is still missing.",1005.5681v3
2010-09-02,"Spin transition in Gd$_3$N@C$_{80}$, detected by low-temperature on-chip SQUID technique","We present a magnetic study of the Gd$_3$N@C$_{80}$ molecule, consisting of a
Gd-trimer via a Nitrogen atom, encapsulated in a C$_{80}$ cage. This molecular
system can be an efficient contrast agent for Magnetic Resonance Imaging (MRI)
applications. We used a low-temperature technique able to detect small magnetic
signals by placing the sample in the vicinity of an on-chip SQUID. The
technique implemented at NHMFL has the particularity to operate in high
magnetic fields of up to 7 T. The Gd$_3$N@C$_{80}$ shows a paramagnetic
behavior and we find a spin transition of the Gd$_3$N structure at 1.2 K. We
perform quantum mechanical simulations, which indicate that one of the Gd ions
changes from a $^8S_{7/2}$ state ($L=0, S=7/2$) to a $^7F_{6}$ state ($L=S=3,
J=6$), likely due to a charge transfer between the C$_{80}$ cage and the ion.",1009.0440v1
2010-11-20,Electromagnetic properties of non-Dirac particles with rest spin 1/2,"We resolve a number of questions related to an analytic description of
electromagnetic form factors of non-Dirac particles with the rest spin 1/2. We
find the general structure of a matrix antisymmetric tensor operator. We obtain
two recurrence relations for matrix elements of finite transformations of the
proper Lorentz group and explicit formulas for a certain set of such elements.
Within the theory of fields with double symmetry, we discuss writing the
components of wave vectors of particles in the form of infinite continued
fractions. We show that for $Q^{2} \leq 0.5$ (GeV/c)$^{2}$, where $Q^{2}$ is
the transferred momentum squared, electromagnetic form factors that decrease as
$Q^{2}$ increases and are close to those experimentally observed in the proton
can be obtained without explicitly introducing an internal particle structure.",1011.4574v1
2010-12-13,Ising correlations and elliptic determinants,"Correlation functions of the two-dimensional Ising model on the periodic
lattice can be expressed in terms of form factors - matrix elements of the spin
operator in the basis of common eigenstates of the transfer matrix and
translation operator. Free-fermion structure of the model implies that any
multiparticle form factor is given by the pfaffian of a matrix constructed from
the two-particle ones. Crossed two-particle form factors can be obtained by
inverting a block of the matrix of linear transformation induced on fermions by
the spin conjugation. We show that the corresponding matrix is of elliptic
Cauchy type and use this observation to solve the inversion problem explicitly.
Non-crossed two-particle form factors are then obtained using theta functional
interpolation formulas. This gives a new simple proof of the factorized
formulas for periodic Ising form factors, conjectured by A. Bugrij and one of
the authors.",1012.2856v2
2010-12-17,Electrically detected magnetic resonance of neutral donors interacting with a two-dimensional electron gas,"We have measured the electrically detected magnetic resonance of
channel-implanted donors in silicon field-effect transistors in resonant X-
($9.7\:$GHz) and W-band ($94\:$GHz) microwave cavities, with corresponding
Zeeman fields of $0.35\:$T and $3.36\:$T, respectively. It is found that the
conduction electron resonance signal increases by two orders of magnitude from
X- to W-band, while the hyperfine-split donor resonance signals are enhanced by
over one order of magnitude. We rule out a bolometric origin of the resonance
signals, and find that direct spin-dependent scattering between the
two-dimensional electron gas and neutral donors is inconsistent with the
experimental observations. We propose a new polarization transfer model from
the donor to the conduction electrons as the main contributer to the spin
resonance signals observed.",1012.3811v1
2011-05-09,Properties of magnetic nanodots with perpendicular anisotropy,"Nanodots with magnetic vortices have many potential applications, such as
magnetic memories (VRAMs) and spin transfer nano-oscillators (STNOs). Adding a
perpendicular anisotropy term to the magnetic energy of the nanodot it becomes
possible to tune the vortex core properties. This can be obtained, e.g., in Co
nanodots by varying the thickness of the Co layer in a Co/Pt stack. Here we
discuss the spin configuration of circular and elliptical nanodots for
different perpendicular anisotropies; we show for nanodisks that micromagnetic
simulations and analytical results agree. Increasing the perpendicular
anisotropy, the vortex core radii increase, the phase diagrams are modified and
new configurations appear; the knowledge of these phase diagrams is relevant
for the choice of optimum nanodot dimensions for applications. MFM measurements
on Co/Pt multilayers confirm the trend of the vortex core diameters with
varying Co layer thicknesses.",1105.1813v1
2011-05-24,The spin-orbit potential and Poincaré invariance in finite temperature pNRQCD,"Heavy quarkonium at finite temperature has been the subject of intense
theoretical studies, for it provides a potentially clean probe of the
quark-gluon plasma. Recent studies have made use of effective field theories to
exploit in a systematic manner the hierarchy of energy scales that characterize
the system. In the case of a quarkonium in a medium whose temperature is
smaller than the typical momentum transfer in the bound state but larger than
its energy, the suitable effective field theory is pNRQCD_HTL, where degrees of
freedom with energy or momentum larger than the binding energy have been
integrated out. Thermal effects are expected to break Poincar\'e invariance,
which, at zero temperature, manifests itself in a set of exact relations
between the matching coefficients of the effective field theory. In the paper,
we evaluate the leading-order thermal corrections to the spin-orbit potentials
of pNRQCD_HTL and show that Poincar\'e invariance is indeed violated.",1105.4807v2
2011-05-31,Universal and non-universal amplitude ratios for scaling corrections on Ising strips,"We consider strips of Ising spins at criticality. For strips of width $N$
sites, subdominant (additive) finite-size corrections to scaling are assumed to
be of the form $a_k/N^k$ for the free energy, and $b_k/N^k$ for inverse
correlation length, with integer values of $k$. We investigate the set
$\{a_k,b_k\}$ ($k \geq 2$) by exact evaluation and numerical transfer-matrix
diagonalization techniques, and their changes upon varying anisotropy of
couplings, spin quantum number $S$, and (finite) interaction range, in all
cases for both periodic (PBC) and free (FBC) boundary conditions across the
strip. We find that the coefficient ratios $b_k/a_k$ remain constant upon
varying coupling anisotropy for $S=1/2$ and first-neighbor couplings, for both
PBC and FBC (albeit at distinct values in either case). Such universal behavior
is not maintained upon changes in $S$ or interaction range.",1105.6248v2
2011-06-07,Critical temperatures of the three- and four-state Potts models on the kagome lattice,"The value of the internal energy per spin is independent of the strip width
for a certain class of spin systems on two dimensional infinite strips. It is
verified that the Ising model on the kagome lattice belongs to this class
through an exact transfer-matrix calculation of the internal energy for the two
smallest widths. More generally, one can suggest an upper bound for the
critical coupling strength $K_c(q)$ for the $q$-state Potts model from exact
calculations of the internal energy for the two smallest strip widths.
Combining this with the corresponding calculation for the dual lattice and
using an exact duality relation enables us to conjecture the critical coupling
strengths for the three- and four-state Potts models on the kagome lattice. The
values are $K_c(q=3)=1.056~509~426~929~0$ and $K_c(q=4) = 1.149~360~587~229~2$,
and the values can, in principle, be obtained to an arbitrary precision. We
discuss the fact that these values are in the middle of earlier approximate
results and furthermore differ from earlier conjectures for the exact values.",1106.1296v1
2011-06-15,Exact nonequilibrium steady state of a strongly driven open XXZ chain,"An exact and explicit ladder-tensor-network ansatz is presented for the
non-equilibrium steady state of an anisotropic Heisenberg XXZ spin-1/2 chain
which is driven far from equilibrium with a pair of Lindblad operators acting
on the edges of the chain only. We show that the steady-state density operator
of a finite system of size n is - apart from a normalization constant - a
polynomial of degree 2n-2 in the coupling constant. Efficient computation of
physical observables is faciliated in terms of a transfer operator reminiscent
of a classical Markov process. In the isotropic case we find cosine spin
profiles, 1/n^2 scaling of the spin current, and long-range correlations in the
steady state. This is a fully nonperturbative extension of a recent result
[Phys. Rev. Lett. 106, 217206 (2011)].",1106.2978v2
2011-06-24,Baxter operators for arbitrary spin,"We construct Baxter operators for the homogeneous closed $\mathrm{XXX}$ spin
chain with the quantum space carrying infinite or finite dimensional $s\ell_2$
representations. All algebraic relations of Baxter operators and transfer
matrices are deduced uniformly from Yang-Baxter relations of the local building
blocks of these operators. This results in a systematic and very transparent
approach where the cases of finite and infinite dimensional representations are
treated in analogy. Simple relations between the Baxter operators of both cases
are obtained. We represent the quantum spaces by polynomials and build the
operators from elementary differentiation and multiplication operators. We
present compact explicit formulae for the action of Baxter operators on
polynomials.",1106.4991v3
2011-07-08,Large Scales - Long Times: Adding High Energy Resolution to SANS,"The Neutron Spin Echo (NSE) variant MIEZE (Modulation of IntEnsity by Zero
Effort), where all beam manipulations are performed before the sample position,
offers the possibility to perform low background SANS measurements in strong
magnetic fields and depolarising samples. However, MIEZE is sensitive to
differences \DeltaL in the length of neutron flight paths through the
instrument and the sample. In this article, we discuss the major influence of
\DeltaL on contrast reduction of MIEZE measurements and its minimisation.
Finally we present a design case for enhancing a small-angle neutron scattering
(SANS) instrument at the planned European Spallation Source (ESS) in Lund,
Sweden, using a combination of MIEZE and other TOF options, such as TISANE
offering time windows from ns to minutes. The proposed instrument allows
studying fluctuations in depolarizing samples, samples exposed to strong
magnetic fields, and spin-incoherently scattering samples in a straightforward
way up to time scales of \mus at momentum transfers up to 0.01 {\AA}-1, while
keeping the instrumental effort and costs low.",1107.1568v1
2011-09-17,Establishing spin-network topologies by repeated projective measurements,"It has been recently shown that in quantum systems, the complex time
evolution typical of many-bodied coupled networks can be transformed into a
simple, relaxation-like dynamics, by relying on periodic dephasings of the
off-diagonal density matrix elements. This represents a case of ""quantum Zeno
effects"", where unitary evolutions are inhibited by projective measurements. We
present here a novel exploitation of these effects, by showing that a
relaxation-like behaviour is endowed to the polarization transfers occurring
within a N-spin coupled network. Experimental implementations and coupling
constant determinations for complex spin-coupling topologies, are thus
demonstrated within the field of liquid-state nuclear magnetic resonance (NMR).",1109.3796v1
2011-11-08,Charge dynamics in half-filled Hubbard chains with finite on-site interaction,"We study the charge dynamic structure factor of the one-dimensional Hubbard
model with finite on-site repulsion U at half filling. Numerical results from
the time-dependent density matrix renormalization group are analyzed by
comparison with the exact spectrum of the model. The evolution of the line
shape as a function of U is explained in terms of a relative transfer of
spectral weight between the two-holon continuum that dominates in the limit
U\to \infty and a subset of the two-holon-two-spinon continuum that
reconstructs the electron-hole continuum in the limit U\to 0. Power-law
singularities along boundary lines of the spectrum are described by effective
impurity models that are explicitly invariant under spin and \eta-spin SU(2)
rotations. The Mott-Hubbard metal-insulator transition is reflected in a
discontinuous change of the exponents of edge singularities at U=0. The sharp
feature observed in the spectrum for momenta near the zone boundary is
attributed to a Van Hove singularity that persists as a consequence of
integrability.",1111.2009v2
2012-01-18,Investigation of Some Physical Properties of Accretion Induced Collapse in Producing Millisecond Pulsars,"We investigate some physical characteristics of Millisecond Pulsar (MSP) such
as magnetic fields, spin periods and masses, that are produced by Accretion
Induced Collapse (AIC) of an accreting white dwarf (WD) in stellar binary
systems. We also investigate the changes of these characteristics during the
mass-transfer phase of the system in its way to become a MSP. Our approach
allows us to follow the changes in magnetic fields and spin periods during the
conversion of WDs to MSPs via AIC process. We focus our attention mainly on the
massive binary WDs (M > 1.0Msun) forming cataclysmic variables, that could
potentially evolve to reach Chandrasekhar limit, thereafter they collapse and
become MSPs. Knowledge about these parameters might be useful for further
modeling of the observed features of AIC.",1201.3779v2
2012-02-02,Topological invariants of edge states for periodic two-dimensional models,"Transfer matrix methods and intersection theory are used to calculate the
bands of edge states for a wide class of periodic two-dimensional tight-binding
models including a sublattice and spin degree of freedom. This allows to define
topological invariants by considering the associated Bott-Maslov indices which
can be easily calculated numerically. For time-reversal symmetric systems in
the symplectic universality class this leads to a Z_2-invariant for the edge
states. It is shown that the edge state invariants are related to Chern numbers
of the bulk systems and also to (spin) edge currents, in the spirit of the
theory of topological insulators.",1202.0537v2
2012-05-31,Time-Resolved Magnetic Relaxation of a Nanomagnet on Subnanosecond Time Scales,"We present a two-current-pulse temporal correlation experiment to study the
intrinsic subnanosecond nonequilibrium magnetic dynamics of a nanomagnet during
and following a pulse excitation. This method is applied to a model
spin-transfer system, a spin valve nanopillar with perpendicular magnetic
anisotropy. Two-pulses separated by a short delay (< 500 ps) are shown to lead
to the same switching probability as a single pulse with a duration that
depends on the delay. This demonstrates a remarkable symmetry between magnetic
excitation and relaxation and provides a direct measurement of the magnetic
relaxation time. The results are consistent with a simple finite temperature
Fokker-Planck macrospin model of the dynamics, suggesting more coherent
magnetization dynamics in this short time nonequilibrium limit than near
equilibrium.",1205.7034v1
2012-06-27,Boundary information inflow enhances correlation in flocking,"The most conspicuous trait of collective animal behaviour is the emergence of
highly ordered structures. Less obvious to the eye, but perhaps more profound a
signature of self-organization, is the presence of long-range spatial
correlations. Experimental data on starling flocks in 3d show that the exponent
ruling the decay of the velocity correlation function, C(r) ~ 1/r^\gamma, is
extremely small, \gamma << 1. This result can neither be explained by
equilibrium field theory, nor by off-equilibrium theories and simulations of
active systems. Here, by means of numerical simulations and theoretical
calculations, we show that a dynamical field applied to the boundary of a set
of Heisemberg spins on a 3d lattice, gives rise to a vanishing exponent \gamma,
as in starling flocks. The effect of the dynamical field is to create an
information inflow from border to bulk that triggers long range spin wave
modes, thus giving rise to an anomalously long-ranged correlation. The
biological origin of this phenomenon can be either exogenous - information
produced by environmental perturbations is transferred from boundary to bulk of
the flock - or endogenous - the flock keeps itself in a constant state of
dynamical excitation that is beneficial to correlation and collective response.",1206.6314v1
2012-07-03,The effects of the small t properties of hadronic scattering amplitude on the determination its real part,"Taking into account the different forms of the Coulomb-hadron interference
phase and the possible spin-flip contribution the new analysis of the
experimental data of the proton-antiproton elastic scattering at $3.8 < p_L
<6.0 \ $GeV/c and small momentum transfer is carried out. It is shown that the
size of the spin-flip amplitude can be determined from the form of the
differential cross sections at small $t$, and the deviation of $\rho(s,t)$
obtained from the examined experimental data of the $p\bar{p}$ scattering from
the analysis \cite{Kroll}, based on the dispersion relations, is conserved in
all xamined assumptions. The analysis of the proton-proton elastic scattering
at $9 < p_L < 70 \ $GeV/c also shows the impact of the examined effects on the
form of the differential cross sections.",1207.0600v1
2012-08-29,Strange Quark Contribution to the Nucleon Spin from Electroweak Elastic Scattering Data,"The total contribution of strange quarks to the intrinsic spin of the nucleon
can be determined from a measurement of the strange-quark contribution to the
nucleon's elastic axial form factor. We have studied the strangeness
contribution to the elastic vector and axial form factors of the nucleon, using
elastic electroweak scattering data. Specifically, we combine elastic $\nu p$
and $\bar{\nu} p$ scattering cross section data from the Brookhaven E734
experiment with elastic $ep$ and quasi-elastic $ed$ and $e$-$^4$He scattering
parity-violating asymmetry data from the SAMPLE, HAPPEx, G0 and PVA4
experiments. We have not only determined these form factors at individual
values of momentum-transfer ($Q^2$), but also have fit the $Q^2$-dependence of
these form factors using simple functional forms. We present the results of
these fits, along with some expectations of how our knowledge of these form
factors can be improved with data from Fermilab experiments.",1208.5944v1
2012-09-10,Inelastic Electron Tunneling Spectroscopy for Topological Insulators,"Inelastic Electron Tuneling Spectroscopy (IETS) is a powerful spectroscopy
that allows one to investigate the nature of local excitations and energy
transfer in the system of interest. We study IETS for Topological Insulators
(TI) and investigate the role of inelastic scattering on the Dirac node states
on the surface of TIs. Local inelastic scattering is shown to significantly
modify the Dirac node spectrum. In the weak coupling limit, peaks and steps are
induced in second derivative $d^2I/dV^2$. In the strong coupling limit, the
local negative U centers are formed at impurity sites, and the Dirac cone
structure is fully destroyed locally. At intermediate coupling resonance peaks
emerge. We map out the evolution of the resonance peaks from weak to strong
coupling, which interpolate nicely between the two limits. There is a sudden
qualitative change of behavior at intermediate coupling, indicating the
possible existence of a local quantum phase transition. We also find that even
for a simple local phonon mode the inherent coupling of spin and orbital
degrees in TI leads to the spin polarized texture in inelastic Friedel
oscillations induced by local mode.",1209.2055v1
2012-11-18,Correlation lengths of the repulsive one-dimensional Bose gas,"We investigate the large-distance asymptotic behavior of the static
density-density and field-field correlation functions in the one-dimensional
Bose gas at finite temperature. The asymptotic expansions of the Bose gas
correlators are obtained performing a specific continuum limit in the similar
low-temperature expansions of the longitudinal and transversal correlation
functions of the XXZ spin chain. In the lattice system the correlation lengths
are computed as ratios of the largest and next-largest eigenvalues of the XXZ
spin chain quantum transfer matrix. In both cases, lattice and continuum, the
correlation lengths are expressed in terms of solutions of Yang-Yang type [C.N.
Yang and C.P. Yang, J.Math.Phys. 10, 1151 (1969)] non-linear integral equations
which are easily implementable numerically.",1211.4200v4
2012-12-01,Dynamic control of quantum geometric heat flux in a nonequilibrium spin-boson model,"We study the quantum geometric heat flux in the nonequilibrium spin-boson
model. By adopting the noninteracting-blip approximation that is able to
accommodate the strong system-bath coupling, we show that there exists a
nonzero geometric heat flux only when the two-level system is nondegenerate.
Moreover, the pumping, no pumping, and dynamic control of geometric heat flux
are discussed in detail, compared to the results with Redfield weak-coupling
approximation. In particular, the geometric energy transfer induced by
modulation of two system-bath couplings is identified, which is exclusive to
quantum transport in the strong system-bath coupling regime.",1212.0067v2
2013-01-09,Nonlocal Thermoelectric Effects and Nonlocal Onsager Relations in a Three-Terminal Proximity-Coupled Superconductor-Ferromagnet Device,"We study thermal and charge transport in a three-terminal setup consisting of
one superconducting and two ferromagnetic contacts. We predict that the
simultaneous presence of spin filtering and of spin- dependent scattering phase
shifts at each of the two interfaces will lead to very large nonlocal thermo-
electric effects both in clean and in disordered systems. The symmetries of
thermal and electric transport coefficients are related to fundamental
thermodynamic principles by the Onsager reciprocity. Our results show that a
nonlocal version of the Onsager relations for thermoelectric currents holds in
a three-terminal quantum coherent ferromagnet-superconductor heterostructure
including a spin-dependent crossed Andreev reflection and coherent electron
transfer processes.",1301.1840v2
2013-01-17,Topological quantum memory interfacing atomic and superconducting qubits,"We propose a scheme to manipulate a topological spin qubit which is realized
with cold atoms in a one-dimensional optical lattice. In particular, by
introducing a quantum opto-electro-mechanical interface, we are able to first
transfer a superconducting qubit state to an atomic qubit state and then to
store it into the topological spin qubit. In this way, an efficient topological
quantum memory could be constructed for the superconducting qubit. Therefore,
we can consolidate the advantages of both the noise resistance of the
topological qubits and the scalability of the superconducting qubits in this
hybrid architecture.",1301.4139v2
2013-01-29,"On the Universality of the Energy Response Function in the Long-Range Spin Glass Model with Sparse, Modular Couplings","We consider energy relaxation of the long-range spin glass model with sparse
couplings, the so-called dilute Sherrington-Kirkpatrick (SK) model, starting
from a random initial state. We consider the effect that modularity of the
coupling matrix has on this relaxation dynamics. In the absence of finite size
effects, the relaxation dynamics appears independent of modularity. For finite
sizes, a more modular system reaches a less favorable energy at long times. For
small sizes, a more modular system also has a less favorable energy at short
times. For large sizes, modularity appears to lead to slightly more favorable
energies at intermediate times. We discuss these results in the context of
evolutionary theory, where horizontal gene transfer, absent in the Glauber
equilibration dynamics of the SK model studied here, endows modular organisms
with larger response functions at short times.",1301.6841v3
2013-03-13,Melting of the orbital order in LaMnO3 probed by NMR,"The Mn spin correlations were studied near the O'-O phase transition at T{JT}
= 750 K, up to 950 K with 17O and 139La NMR in a stoichiometric LaMnO3
crystalline sample. The measured local hyperfine fields originate from the
electron density transfered from the eg- and t2g-orbitals to the 2s(O) and
6s(La) orbits, respectively. By probing the oxygen nuclei, we show that the
correlations of the Mn spins are ferromagnetic in the ab-plane and robust up to
T{JT} whereas along the c-axis, they are antiferromagnetic and start to melt
below T{JT}, at about 550 K. Above T{JT} the ferromagnetic Mn-Mn exchange
interaction is found isotropic. The room temperature orbital mixing angle,
{\phi}nmr = 109+-1.5{\deg}, of the eg ground state is close to the reported
value which was deduced from structural data on Jahn-Teller distorted MnO6
octahedra. For T > T{JT} LaMnO3 can be described in terms of non-polarized
eg-orbitals since both eg-orbitals are equally occupied.",1303.3112v1
2013-04-19,Generalized Gibbs Ensemble for Heisenberg Spin Chains,"We consider the Generalized Gibbs Ensemble (GGE) in the context of global
quantum quenches in XXZ Heisenberg spin chains. Embedding the GGE into the
Quantum Transfer Matrix formalism we develop an iterative procedure to fix the
Lagrange-multipliers and to calculate predictions for the long-time limit of
short-range correlators. The main idea is to consider truncated GGE's with only
a finite number of charges and to investigate the convergence of the numerical
results as the truncation level is increased. As an example we consider a
quantum quench situation where the system is initially prepared in the N\'eel
state and then evolves with an XXZ Hamiltonian with anisotropy Delta>1. We
provide predictions for short range correlators and gather numerical evidence
that the iterative procedure indeed converges. The results show that the system
retains memory of the initial condition, and there are clear differences
between the numerical values of the correlators as calculated from the purely
thermal and the Generalized Gibbs ensembles.",1304.5374v3
2013-04-23,Correlations and phase structure of Ising models at complex temperature,"We investigate the spin-spin correlation functions of Ising magnets at
complex values of the temperature, T. For one-dimensional chain and ladder
systems, we show the existence of a kind of helimagnetic order in the vicinity
of contours where the leading two eigenvalues of the transfer matrix become
equal in magnitude. We analyse the development of long-range order as the
two-dimensional limit is approached, and find that there is rich structure in
much of the complex-T plane. In particular, and contrary to the work of Fisher
on this problem, the development of long-range order is actually associated
with a proliferation of partition function zeros in a certain finite region of
that plane containing the real-temperature magnetically ordered phase. The
thermodynamic consequences of this are also discussed.",1304.6314v1
2013-10-07,Specific heat of segmented Heisenberg quantum spin chains in (Yb_{1-x}Lu_x)_4As_3,"We report low-temperature specific heat, $C(T)$, measurements on
(Yb$_{1-x}$Lu$_x$)$_4$As$_3$ with $x=0.01$ and $x=0.03$, where nonmagnetic Lu
atoms are randomly distributed on antiferromagnetic $S=1/2$ Heisenberg chains
with $J/k_{\mathrm B}=28$ K. The observed reduction of $C$ below 15 K with
increasing $x$ is accurately described by quantum transfer matrix simulations
without any adjustable parameter, implying that the system is an excellent
experimental realization of segmented quantum spin chains. Finite-size effects
consistent with conformal-field theory predictions are leading to the formation
of an effective low-energy gap. The size of the gap increases with Lu content
and accounts for the impurity driven reduction of the specific heat. For both
concentrations our results verify experimentally the low temperature scaling
behavior established theoretically and also confirm the value of $J$ determined
from pure Yb$_4$As$_3$.",1310.1675v1
2013-10-11,Local moment dynamics and screening effects in doped charge-transfer insulators,"By means of Dynamical Mean-Field Theory we investigate the spin response
function of a model for correlated materials with d- or f-electrons hybridized
with more delocalized ligand orbitals. We point out the existence of two
different processes responsible for the dynamical screening of local moments of
the correlated electrons. Studying the local spin susceptibility we identify
the contribution of the ""direct"" magnetic exchange and of an ""indirect"" one
mediated by the itinerant uncorrelated orbitals. In addition, we characterize
the nature of the dynamical screening processes in terms of different classes
of diagrams in the hybridization-expansion contributing to the density-matrix.
Our analysis suggests possible ways of estimating the relative importance of
these two classes of screening processes in realistic calculations for
correlated materials.",1310.3043v1
2013-10-15,The interfacial effects on the spin density wave in FeSe/SrTiO3 thin film,"Recently, the signs of both superconducting transition temperature (Tc)
beyond 60 K and spin density wave (SDW) have been observed in FeSe thin film on
SrTiO3 (STO) substrate, which suggests a strong interplay between
superconductivity and magnetism. With the first-principles calculations, we
find that the substrate-induced tensile strain tends to stabilize the SDW state
in FeSe thin film by enhancing of the next-nearest-neighbor superexchange
antiferromagnetic interaction bridged through Se atoms. On the other hand, we
find that when there are oxygen vacancies in the substrate, the significant
charge transfer from the substrate to the first FeSe layer would suppress the
magnetic order there, and thus the high-temperature superconductivity could
occur. In addition, the stability of the SDW is lowered when FeSe is on a
defect-free STO substrate due to the redistribution of charges among the Fe
3d-orbitals. Our results provide a comprehensive microscopic explanation for
the recent experimental findings, and build a foundation for the further
exploration of the superconductivity and magnetism in this novel
superconducting interface.",1310.4024v2
2013-11-08,Large Negative Quantum Renormalization of Excitation Energies in the Spin-1/2 Kagome Lattice Antiferromagnet Cs$_2$Cu$_3$SnF$_{12}$,"Magnetic excitations in the spin-$\frac{1}{2}$ distorted kagome lattice
antiferromagnet Cs$_2$Cu$_3$SnF$_{12}$, which has an ordered ground state owing
to the strong Dzyaloshinskii-Moriya interaction, were studied using inelastic
neutron scattering. Although the spin-wave dispersion can be qualitatively
understood in terms of linear spin-wave theory (LSWT), the excitation energies
are renormalized by a factor of approximately 0.6 from those calculated by
LSWT, almost irrespective of the momentum transfer. This inadequacy of LSWT,
which is attributed to quantum fluctuations, provides evidence of negative
quantum renormalization in the spin-$\frac{1}{2}$ kagome lattice
antiferromagnet.",1311.1875v2
2013-11-14,Helical multiferroics for electric field controlled quantum information processing,"Magnetoelectric coupling in helical multiferroics allows to steer spin order
with electric fields. Here we show theoretically that in a helical multiferroic
chain quantum information processing as well as quantum phases are highly
sensitive to electric (E) field. Applying E-field, the quantum state transfer
fidelity can be increased and made directionally dependent.
  We also show that E field transforms the spin-density-wave/nematic or
multipolar phases of frustrated ferromagnetic spin-1/2 chain in chiral phase
with a strong magnetoelectric coupling. We find sharp reorganization of the
entanglement spectrum as well as a large enhancement of fidelity susceptibility
at Ising quantum phase transition from nematic to chiral states driven by
electric field. These findings point to a new tool for quantum information with
low power consumption.",1311.3439v1
2013-12-02,Exact solution of the one-dimensional super-symmetric t-J model with unparallel boundary fields,"The exact solution of the one-dimensional super-symmetric t-J model under
generic integrable boundary conditions is obtained via the Bethe ansatz
methods. With the coordinate Bethe ansatz, the corresponding R-matrix and
K-matrices are derived for the second eigenvalue problem associated with spin
degrees of freedom. It is found that the second eigenvalue problem can be
transformed to that of the transfer matrix of the inhomogeneous XXX spin chain,
which allows us to obtain the spectrum of the Hamiltonian and the associated
Bethe ansatz equations by the off-diagonal Bethe ansatz method.",1312.0376v2
2013-12-11,Multisymplectic effective General Boundary Field Theory,"The transfer matrix in lattice field theory connects the covariant and the
initial data frameworks; in spin foam models, it can be written as a
composition of elementary cellular amplitudes/propagators. We present a
framework for discrete spacetime classical field theory in which solutions to
the field equations over elementary spacetime cells may be amalgamated if they
satisfy simple gluing conditions matching the composition rules of cellular
amplitudes in spin foam models. Furthermore, the formalism is endowed with a
multisymplectic structure responsible for local conservation laws.
  Some models within our framework are effective theories modeling a system at
a given scale. Our framework allows us to study coarse graining and the
continuum limit.",1312.3220v2
2014-01-17,"The $^3$He$(e,e^\prime p)^2$H and $^4$He$(e,e^\prime p)^3$H reactions at high momentum transfer","We present updated calculations for observables in the processes
$^3$He($e,e^\prime p$)$^2$H, $^4$He($e,e^\prime p$)$^3$H, and
$^4$He($\vec{e},e^\prime \vec{p}\,$)$^3$H. This update entails the
implementation of improved nucleon-nucleon ($NN$) amplitudes to describe final
state interactions (FSI) within a Glauber approximation and includes full
spin-isospin dependence in the profile operator. In addition, an optical
potential, which has also been updated since previous work, is utilized to
treat FSI for the $^4$He($e,e^\prime p$)$^3$H and $^4$He($\vec{e},e^\prime
\vec{p}\,$)$^3$H reactions. The calculations are compared with experimental
data and show good agreement between theory and experiment. Comparisons are
made between the various approximations in the Glauber treatment, including
model dependence due to the $NN$ scattering amplitudes, rescattering
contributions, and spin dependence. We also analyze the validity of the Glauber
approximation at the kinematics the data is available, by comparing to the
results obtained with the optical potential.",1401.4399v1
2014-02-09,Enhanced spin-orbit interaction and Kondo scattering in $δ$-doped LaTiO$_3$/SrTiO$_3$ interfaces,"We present a study of delta ($\delta$) doping at LaTiO$_3$/SrTiO$_3$
(LTO/STO) interface with iso-structural antiferromagnetic perovskite LaCrO$_3$
(LCO) that dramatically alters the properties of the two dimensional electron
gas (2-DEG) at the interface. The effects include a reduction in sheet-carrier
density, prominence of the low temperature resistivity minimum, enhancement of
weak antilocalization below 10 K and observation of a strong anisotropic
magnetoresistance (MR). The positive and negative MR for out-of-plane and
in-plane field respectively and the field and temperature dependencies of MR
suggest Kondo scattering by localized Ti$^{3+}$ moments renormalized by
spin-orbit interaction at T $<$ 10 K, with the increased $\delta$-layer
thickness. Electron energy loss spectroscopy and density functional
calculations provide convincing evidence for blocking of electron transfer from
LTO to STO by the $\delta$-layer.",1402.1915v2
2014-05-20,"Spin and orbital magnetic moments of Fe in the $n$-type ferromagnetic semiconductor (In,Fe)As","The electronic and magnetic properties of Fe atoms in the ferromagnetic
semiconductor (In,Fe)As codoped with Be have been studied by x-ray absorption
spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the Fe
$L_{2,3}$ edge. The XAS and XMCD spectra showed simple spectral line shapes
similar to Fe metal, but the ratio of the orbital and spin magnetic moments
($M_\mathrm{orb}$/$M_\mathrm{spin}$) estimated using the XMCD sum rules was
significantly larger than that of Fe metal, indicating a significant orbital
moment of Fe $3d$ electrons in (In,Fe)As:Be. The positive value of
$M_\mathrm{orb}$/$M_\mathrm{spin}$ implies that the Fe $3d$ shell is more than
half-filled, which arises from the hybridization of the Fe$^{3+}$ ($d^5$) state
with the charge-transfer $d^6\underline{L}$ states, where $\underline{L}$ is a
ligand hole in the host valence band. The XMCD intensity as a function of
magnetic field indicated hysteretic behavior of the superparamagnetic-like
component due to discrete ferromagnetic domains.",1405.5130v1
2014-06-12,Electronic structure of spin frustrated magnets: Mn$_3$O$_4$ spinel and postspinel,"Mn$_3$O$_4$ is a spin frustrated magnet that adopts a tetragonally distorted
spinel structure at ambient conditions and a CaMn$_2$O$_4$-type postspinel
structure at high pressure. We conducted both optical measurements and
\emph{ab} \emph{initio} calculations, and systematically studied the electronic
band structures of both the spinel and postspinel Mn$_3$O$_4$ phases. For both
phases, theoretical electronic structures are consistent with the optical
absorption spectra, and display characteristic band-splitting of the conduction
band. The band gap obtained from the absorption spectra is 1.91(6) eV for the
spinel phase, and 0.94(2) eV for the postspinel phase. Both phases are
charge-transfer type insulators. The Mn 3\emph{d} $t_2$$_g$ and O 2\emph{p}
form antibonding orbitals situated at the conduction band with higher energy.",1406.4486v1
2014-06-27,Synchrotron X-ray emission from old pulsars,"We study the synchrotron radiation as the observed non-thermal X-ray emission
from old pulsars ($\gtrsim1-10$Myr) to investigate the particle acceleration in
their magnetospheres. We assume that the power-law component of the observed
X-ray spectra is caused by the synchrotron radiation from electrons and
positrons in the magnetosphere. We consider two pair production mechanisms of
X-ray emitting particles, the magnetic and the photon-photon pair productions.
High-energy photons, which ignite the pair production, are emitted via the
curvature radiation of the accelerated particles. We use the analytical
description for the radiative transfer and estimate the luminosity of the
synchrotron radiation. We find that for pulsars with the spin-down luminosity
$L_{\rm sd}\lesssim10^{33}$ erg s$^{-1}$, the locations of the particle
acceleration and the non-thermal X-ray emission are within $\lesssim10^7$cm
from the centre of the neutron star, where the magnetic pair production occurs.
For pulsars with the spin-down luminosity $L_{\rm sd}\lesssim10^{31}$ erg
s$^{-1}$ such as J0108-1431, the synchrotron radiation is difficult to explain
the observed non-thermal component even if we consider the existence of the
strong and small-scale surface magnetic field structures.",1406.7151v1
2014-08-22,Non-adiabatic effect in quantum pumping for a spin-boson system,"We clarify the role of non-adiabatic effects in a quantum pumping for a
spin-boson system. When we sinusoidally control the temperatures of two
reservoirs with \pi/2 phase difference, we find that the pumping current
strongly depends on the initial condition, and thus, the current deviates from
that predicted by the adiabatic treatment. We also analytically obtain the
contribution of non-adiabatic effects in the pumping current proportional to
\Omega^3 where \Omega is the angular frequency of the temperature control. The
validity of the analytic expression is verified by our numerical calculation.
Moreover, we extend the steady heat fluctuation theorem to the case for slowly
modulated temperatures and large transferred energies.",1408.5182v3
2014-09-07,The Effects of Long Pulse Durations and Radiation Damping in Selective Inversion Recovery Experiments,"Long pulse durations necessary in selective inversion recovery (SIR)
experiments along with radiation damping (RD) introduce difficulties in
quantitative nuclear magnetic resonance measurements, such as those that allow
for the determination of a sample's characteristics, including the rates that
govern magnetization transfer. Because of these influences, the assumption of
perfect inversion is invalid. In this work, we present data that demonstrates
that long pulse durations as well as RD cause difficulties in SIR experiments
performed on simple one-spin systems, indicating that they will be problematic
for multiple-spin systems as well. These results emphasize the importance of
understanding the evolution of magnetization for all time points throughout an
experiment used in quantitative NMR measurements. Furthermore, experimental
parameters must be chosen carefully and understood completely.",1409.2136v2
2014-09-12,Exact solution of the XXZ alternating spin chain with generic non-diagonal boundaries,"The integrable XXZ alternating spin chain with generic non-diagonal boundary
terms specified by the most general non-diagonal K-matrices is studied via the
off-diagonal Bethe Ansatz method. Based on the intrinsic properties of the
fused R-matrices and K-matrices, we obtain certain closed operator identities
and conditions, which allow us to construct an inhomogeneous T-Q relation and
the associated Bethe Ansatz equations accounting for the eigenvalues of the
transfer matrix.",1409.3646v2
2014-09-17,Axial-vector form factors for the low lying octet baryons in the chiral quark constituent model,"We have calculated the axial-vector form factors of the low lying octet
baryons ($N$, $\Sigma$, $\Xi$ and $\Lambda$) in the chiral constituent quark
model ($\chi$CQM). In particular, we have studied the implications of chiral
symmetry breaking and SU(3) symmetry breaking for the singlet ($g^0_{A}$) and
non-singlet ($g^3_{A}$ and $g^8_{A}$) axial-vector coupling constants expressed
as combinations of the spin polarizations at zero momentum transfer. The
conventional dipole form of parametrization has been used to analyse the $Q^2$
dependence of the axial-vector form factors ($G^0_{A}(Q^2)$, $G^3_{A}(Q^2)$ and
$G^8_{A}(Q^2)$). The total strange singlet and non-singlet contents
($G_s^0(Q^2)$, $G_s^3(Q^2)$ and $G_s^8(Q^2)$) of the nucleon determining the
strange quark contribution to the nucleon spin ($\Delta s$) have also been
discussed.",1409.4943v1
2014-10-03,On a family of symmetric rational functions,"This paper is about a family of symmetric rational functions that form a
one-parameter generalization of the classical Hall-Littlewood polynomials. We
introduce two sets of (skew and non-skew) functions that are akin to P and Q
Hall-Littlewood polynomials. We establish (a) a combinatorial formula that
represents our functions as partition functions for certain path ensembles in
the square grid; (b) symmetrization formulas for non-skew functions; (c)
identities of Cauchy and Pieri type; (d) explicit formulas for principal
specializations; (e) two types of orthogonality relations for non-skew
functions.
  Our construction is closely related to the half-infinite volume, finite
magnon sector limit of the higher spin six-vertex (or XXZ) model, with both
sets of functions representing higher spin six-vertex partition functions
and/or transfer-matrices for certain domains.",1410.0976v1
2014-10-10,Silent Flocks,"Experiments find coherent information transfer through biological groups on
length and time scales distinctly below those on which asymptotically correct
hydrodynamic theories apply. We present here a new continuum theory of
collective motion coupling the velocity and density fields of Toner and Tu to
the inertial spin field recently introduced to describe information propagation
in natural flocks of birds. The long-wavelength limit of the new equations
reproduces Toner-Tu theory, while at shorter wavelengths (or, equivalently,
smaller damping), spin fluctuations dominate over density fluctuations and
second sound propagation of the kind observed in real flocks emerges. We study
the dispersion relation of the new theory and find that when the speed of
second sound is large, a gap sharply separates first from second sound modes.
This gap implies the existence of `silent' flocks, namely medium-sized systems
across which neither first nor second sound can propagate.",1410.2868v1
2014-10-30,"First Measurements of Timelike Form Factors of the Hyperons, Lambda0, Sigma0, Sigma+, Xi0, Xi-, and Omega-, and Evidence of Diquark Correlations","Using 805 pb^-1 of e+e- annihilation data taken with the CLEO-c detector at
psi(3770), sqrt{s}=3770 MeV, we report the first measurements of the
electromagnetic form factors of the Lambda0, Sigma0, Sigma+, Xi0, Xi-, and
Omega- hyperons for the large timelike momentum transfer of |Q^2|=14.2 GeV^2.
The form factors for the different hyperons are found to vary by nearly a
factor two. It is found that |G_M(Lambda0)|=1.66(24) x |G_M(Sigma0)|. The
Lambda0 and Sigma0 hyperons have the same uds quark content, but differ in
their isospin, and therefore the spin of the $ud$ quark pair. It is suggested
that the spatial correlation implied by the singlet spin--isospin configuration
in the Lambda0 is an example of strong diquark correlations in the Lambda0, as
anticipated by Jaffe and Wilczek. Improved measurements of the branching
fractions of psi(2S) -> p pbar and hyperon--antihyperon pairs are also
reported.",1410.8356v1
2014-11-14,Modelling Dynamical Fluorescent Micro Thermal Imaging of the Heat Diffusion in the La5Ca9Cu24O41 Spin Ladder Compound,"The dynamical fluorescent microthermal imaging (FMI) experiment has been used
to investigate the phonon-magnon interaction in the 1D Heisenberg
antiferromagnet La5Ca9Cu24O41. This material shows highly anisotropic heat
conductivity due to the efficient magnetic heat transport along the spin
ladders in the compound. To extract information on the phonon-magnon
interaction we modelled the dynamic heat transport experiment using a two
temperature model approach, taking both the crystal as well as the PMMA/EuTTA
fluorescent heat imaging layer into account. The simulations are carried out by
the finite element method using COMSOL Multiphysics Heat Transfer Module. The
results of the numerical calculations are expected to be used for the data
analysis of the experimental studies.",1411.3872v2
2014-11-14,Topologically Massive Spin-1 Particles and Spin-Dependent Potentials,"We investigate the role played by particular field representations of an
intermediate massive spin-1 boson in the context of spin-dependent
interparticle potentials between fermionic sources in the limit of low momentum
transfer. The comparison between the well-known case of the Proca field and
that of an exchanged spin-1 boson (with gauge-invariant mass) described by a
2-form potential mixed with a 4-vector gauge field is established in order to
pursue an analysis of spin- as well as velocity-dependent profiles of the
interparticle potentials. We discuss possible applications and derive an upper
bound on the product of vector and pseudo-tensor coupling constants.",1411.3991v2
2014-11-19,Effect of the Pauli exclusion principle on the singlet exciton yield in conjugated polymers,"Optical devices fabricated using conjugated polymer systems give rise to
singlet exciton yields which are high compared to the statistically predicted
estimate of 25% obtained using simple recombination schemes. In this study we
evaluate the singlet exciton yield in conjugated polymers systems by fitting to
a model that incorporates the Pauli exclusion principle. The rate equations
which describe the exciton dynamics include quantum dynamical components (both
density and spin-dependent) which arise during the spin-allowed conversion of
composite intra-molecular excitons into loosely bound charge-transfer (CT)
electron-hole pairs. Accordingly, a crucial mechanism by which singlet excitons
are increased at the expense of triplet excitons is incorporated in this work.
Non-ideal triplet excitons which form at high densities, are rerouted via the
Pauli exclusion mechanism to form loosely bound CT states which subsequently
convert to singlet excitons. Our derived expression for the yield in singlet
exciton incorporates the purity measure, and provides a realistic description
of the carrier dynamics at high exciton densities.",1411.5185v2
2014-11-27,A Light-Front approach to the $^3$He spectral function,"The analysis of semi-inclusive deep inelastic electron scattering off
polarized $^3$He at finite momentum transfers, aimed at the extraction of the
quark transverse-momentum distributions in the neutron, requires the use of a
distorted spin-dependent spectral function for $^3$He, which takes care of the
final state interaction effects. This quantity is introduced in the
non-relativistic case, and its generalization in a Poincar\'e covariant
framework, in plane wave impulse approximation for the moment being, is
outlined. Studying the light-front spin-dependent spectral function for a J=1/2
system, such as the nucleon, it is found that, within the light-front dynamics
with a fixed number of constituents and in the valence approximation, only
three of the six leading twist T-even transverse-momentum distributions are
independent.",1411.7559v1
2014-12-07,Linear response of homogeneous nuclear matter with energy density functionals,"Response functions of infinite nuclear matter with arbitrary isospin
asymmetry are studied in the framework of the random phase approximation. The
residual interaction is derived from a general nuclear Skyrme energy density
functional. Besides the usual central, spin-orbit and tensor terms it could
also include other components as new density-dependent terms or three-body
terms. Algebraic expressions for the response functions are obtained from the
Bethe-Salpeter equation for the particle-hole propagator. Applications to
symmetric nuclear matter, pure neutron matter and asymmetric nuclear matter are
presented and discussed. Spin-isospin strength functions are analyzed for
varying conditions of density, momentum transfer, isospin asymmetry, and
temperature for some representative Skyrme functionals. Particular attention is
paid to the discussion of instabilities, either real or unphysical, which could
manifest in finite nuclei.",1412.2339v1
2014-12-09,"Lieb-Robinson bounds, Arveson spectrum and Haag-Ruelle scattering theory for gapped quantum spin systems","We consider translation invariant gapped quantum spin systems satisfying the
Lieb-Robinson bound and containing single-particle states in a ground state
representation. Following the Haag-Ruelle approach from relativistic quantum
field theory, we construct states describing collisions of several particles,
and define the corresponding $S$-matrix. We also obtain some general
restrictions on the shape of the energy-momentum spectrum. For the purpose of
our analysis we adapt the concepts of almost local observables and
energy-momentum transfer (or Arveson spectrum) from relativistic QFT to the
lattice setting. The Lieb-Robinson bound, which is the crucial substitute of
strict locality from relativistic QFT, underlies all our constructions. Our
results hold, in particular, in the Ising model in strong transverse magnetic
fields.",1412.2970v2
2014-12-30,Detection of Nonlocal Spin Entanglement by Light Emission from a Superconducting p-n Junction,"We model a superconducting p-n junction in which the n- and the p-sides are
contacted through two optical quantum dots (QDs), each embedded into a photonic
nanocavity. Whenever a Cooper pair is transferred from the n-side to the
p-side, two photons are emitted. When the two electrons of a Cooper pair are
transported through different QDs, polarization-entangled photons are created,
provided that the Cooper pairs retain their spin singlet character while being
spatially separated on the two QDs. We show that a CHSH Bell-type measurement
is able to detect the entanglement of the photons over a broad range of
microscopic parameters, even in the presence of parasitic processes and
imperfections.",1412.8619v1
2015-01-20,Generalized Parton Distributions of proton for non zero skewness in transverse and longitudinal position spaces,"We investigate the Generalized Parton Distributions(GPDs) of proton by
expressing them in terms of overlaps of light front wave functions (LFWFs)
using a simulated model which is able to qualitatively improve the convergence
near the end points of $x$. We study the spin non-flip $H(x, \zeta, t)$ and
spin flip $E(x, \zeta, t)$ part of GPDs for the particle conserving $n
\rightarrow n$ overlap in the DGLAP region $(\zeta<x<1)$. The Fourier transform
(FT) of the GPDs w.r.t. to the transverse momentum transfer as well the FT of
the GPDs w.r.t. $\zeta$ have also been obtained giving the distribution of
partons in the transverse position space and the distribution in the
longitudinal position space respectively. Diffraction pattern is obtained for
both $ \mathcal{H}(x,\sigma,t)$ and $ \mathcal{E}(x,\sigma,t)$ in the
longitudinal position space.",1501.04745v1
2015-01-23,Interfacing microwave qubits and optical photons via spin ensembles,"A protocol is discussed which allows one to realize a transducer for single
photons between the optical and the microwave frequency range. The transducer
is a spin ensemble, where the individual emitters possess both an optical and a
magnetic-dipole transition. Reversible frequency conversion is realized by
combining optical photon storage, by means of EIT, with the controlled
switching of the coupling between the magnetic-dipole transition and a
superconducting qubit, which is realized by means of a microwave cavity. The
efficiency is quantified by the global fidelity for transferring coherently a
qubit excitation between a single optical photon and the superconducting qubit.
We test various strategies and show that the total efficiency is essentially
limited by the optical quantum memory: It can exceed 80% for ensembles of NV
centers and approaches 99% for cold atomic ensembles, assuming state-of-the-art
experimental parameters. This protocol allows one to bridge the gap between the
optical and the microwave regime so to efficiently combine superconducting and
optical components in quantum networks.",1501.05860v1
2015-01-28,Coexistence of charge-density-wave and pair-density-wave orders in underdoped cuprates,"We analyze incommensurate charge-density-wave (CDW) and pair-density-wave
(PDW) orders with transferred momenta $(\pm Q,0)$/$(0,\pm Q)$ in underdoped
cuprates within the spin-fermion model. Both orders appear due to exchange of
spin fluctuations before magnetic order develops.We argue that the ordered
state with the lowest energy has non-zero CDW and PDW components with the same
momentum. Such a state breaks $C_4$ lattice rotational symmetry, time-reversal
symmetry, and mirror symmetries. We argue that the feedback from CDW/PDW order
on fermionic dispersion is consistent with ARPES data. We discuss the interplay
between the CDW/PDW order and $d_{x^2-y^2}$ superconductivity and make specific
predictions for experiments.",1501.07287v2
2015-02-10,The Ising chain constrained to an even or odd number of positive spins,"We investigate the statistical mechanics of the periodic one-dimensional
Ising chain when the number of positive spins is constrained to be either an
even or an odd number. We calculate the partition function using a
generalization of the transfer matrix method. On this basis, we derive the
exact magnetization, susceptibility, internal energy, heat capacity and
correlation function. We show that in general the constraints substantially
slow down convergence to the thermodynamic limit. By taking the thermodynamic
limit together with the limit of zero temperature and zero magnetic field, the
constraints lead to new scaling functions and different probability
distributions for the magnetization. We demonstrate how these results solve a
stochastic version of the one-dimensional voter model.",1502.02883v1
2015-02-24,A Monte Carlo wavefunction method for semiclassical simulations of spin-position entanglement,"We present a Monte Carlo wavefunction method for semiclassically modeling
spin-$\frac12$ systems in a magnetic field gradient in one dimension. Our model
resolves the conflict of determining what classical force an atom should be
subjected to when it is in an arbitrary superposition of internal states.
Spatial degrees of freedom are considered to be an environment, entanglement
with which decoheres the internal states. Atoms follow classical trajectories
through space, punctuated by probabilistic jumps between spin states.
  We modify the conventional Monte Carlo wavefunction method to jump between
states when population transfer occurs, rather than when population is later
discarded via exponential decay. This results in a spinor wavefunction that is
continuous in time, and allows us to model the classical particle trajectories
(evolution of the environment variables) more accurately. The model is not
computationally demanding and it agrees well with simulations of the full
spatial wavefunction of an atom.",1502.06674v1
2015-03-08,In-plane Charge Fluctuations in Bismuth Sulfide Superconductors,"Evidence for local charge fluctuations linked to a charge disproportionation
of the Bi ions in the distorted lattice of superconducting LaO$_{1-x}$F$_{x}$
BiS$_{2}$ is presented. In-plane short-range distortions of sulfur atoms up to
0.3 \AA\ in magnitude break site symmetry and create two distinct environments
around Bi. Out-of-plane motion of apical sulfur brings it closer to the La-O/F
doping layer with increasing $x$ that may lead to a charge transfer conduit
between the doping layers and the superconducting BiS$_{2}$ planes. The
mechanism for superconductivity may arise from the interplay between charge
density fluctuations and an enhanced spin-orbit coupling suggested
theoretically, that induces spin polarization.",1503.02333v1
2015-03-17,Proposal to directly observe the Kondo effect through enhanced photo-induced scattering of cold fermionic and bosonic atoms,"We propose an experimental protocol to directly observe the Kondo effect by
scattering ultracold atoms with spin-dependent interactions. We propose using
an optical Feshbach resonance to engineer Kondo-type spin-dependent
interactions in a system with ultracold $^6$Li and $^{87}$Rb gases. We
calculate the momentum transferred from the $^{87}$Rb gas to the $^6$Li gas in
a scattering experiment and show that it has a logarithmically enhanced
temperature dependence, characteristic of the Kondo effect and analogous to the
resistivity of alloys with magnetic impurities. Experimentally detecting this
enhancement will give a different perspective on the Kondo effect, and allow us
to explore a rich variety of problems such as the Kondo lattice problem and
heavy-fermion systems.",1503.05234v3
2015-03-25,Effect of broken symmetry on resonant inelastic x-ray scattering from undoped cuprates,"We study the magnetic excitation spectra of resonant inelastic x-ray
scattering (RIXS) at the $L$-edge from undoped cuprates beyond the fast
collision approximation. We analyse the effect of the symmetry breaking ground
state on the RIXS process of the Heisenberg model by using a projection
procedure. We derive the expressions of the scattering amplitude in both
one-magnon and two-magnon excitation channels. Each of them consists of the
isotropic and anisotropic contributions. The latter is a new finding and
attributed to the long range order of the ground state. The presence of
anisotropic terms is supported by numerical calculations on a two-dimensional
spin cluster. We express the RIXS spectra in the form of spin-correlation
functions with the coefficients evaluated on the cluster, and calculate the
function in a two dimensional system within the $1/S$ expansion. Due to the
anisotropic terms, the spectral intensities are considerably enhanced around
momentum transfer $\textbf{q}=0$ in both one-magnon and two-magnon excitation
channels. This finding may be experimentally confirmed by examining carefully
the $\textbf{q}$-dependence of the spectra.",1503.07264v1
2015-04-06,Electrical control of exchange spring in antiferromagnetic metals,"Manipulation of antiferromagnetic (AFM) spins by electrical means is on great
demand to develop the AFM spintronics with low power consumption. In spite of
the electrical modulation of insulated AFMs through coupling between their
intrinsic ferroelectricity and antiferromagnetism, direct electrical control of
AFM metals remains challenging due to the screening effect by the surface
charge, and the manipulation is confined to a limited depth of atomic
dimensions, which is insufficient to form a stable AFM exchange spring. In the
present letter we primarily report a reversible electrical control of exchange
spring in AFM metals, using an ionic liquid to exert a substantial
electric-field effect. The exchange spring could transfer the force to the
ferromagnet/antiferromagnet interface, enabling a deeper modulation depth in
AFM metals. The manipulation of AFM moments by gate voltage is demonstrated in
[Co/Pt]/IrMn model system and a single IrMn layer with the IrMn thickness up to
5 nm. Besides the fundamental significance of modulating the spin structures in
metallic AFM via all-electrical fashion, the present finding would advance the
development of low-power-consumption AFM spintronics.",1504.01193v1
2015-04-08,Unidirectional sub-diffraction waveguiding based on optical spin-orbit coupling in subwavelength plasmonic waveguides,"Subwavelength plasmonic waveguides show the unique ability of strongly
localizing (down to the nanoscale) and guiding light. These structures are
intrinsically two-way optical communication channels, providing two opposite
light propagation directions. As a consequence, when light is coupled to these
planar integrated devices directly from the top (or bottom) surface using
strongly focused beams, it is equally shared into the two opposite propagation
directions. Here, we show that symmetry can be broken by using incident
circularly polarized light, on the basis of a spin-orbital angular momentum
transfer directly within waveguide bends. We predict that up to 94 \% of the
incoupled light is directed into a single propagation channel of a gap plasmon
waveguide. Unidirectional propagation of strongly localized optical energy, far
beyond the diffraction limit, becomes switchable by polarization, with no need
of intermediate nano-antennas/scatterers as light directors. This study may
open new perspectives in a large panel of scientific domains, such as
nanophotonic circuitry, routing and sorting, optical nanosensing, nano-optical
trapping and manipulation.",1504.02038v3
2015-04-09,Non-thermal melting of Neel order in the Hubbard model,"We study the unitary time evolution of antiferromagnetic order in the Hubbard
model after a quench starting from the perfect N\'eel state. In this setup,
which is well suited for experiments with cold atoms, one can distinguish
fundamentally different pathways for melting of long-range order at weak and
strong interaction. In the Mott insulating regime, melting of long-range order
occurs due to the ultra-fast transfer of energy from charge excitations to the
spin background, while local magnetic moments and their exchange coupling
persist during the process. The latter can be demonstrated by a local
spin-precession experiment. At weak interaction, local moments decay along with
the long-range order. The dynamics is governed by residual quasiparticles,
which are reflected in oscillations of the off-diagonal components of the
momentum distribution. Such oscillations provide an alternative route to study
the prethermalization phenomenon and its influence on the dynamics away from
the integrable (noninteracting) limit. The Hubbard model is solved within
nonequilibrium dynamical mean-field theory, using the density
matrix-renormalization group as an impurity solver.",1504.02461v1
2015-04-20,Raman scattering as a probe of nematic correlations,"We use the symmetry constrained low energy effective Hamiltonian of iron
based superconductors to study the Raman scattering in the normal state of
underdoped iron-based superconductors. The incoming and scattered Raman photons
couple directly to orbital fluctuations and indirectly to the spin
fluctuations. We computed both couplings within the same low energy model. The
symmetry constrained Hamiltonian yields the coupling between the orbital and
spin fluctuations of only the same symmetry type. Attraction in B2g symmetry
channel was assumed for the system to develop the subleading instability
towards the discrete in-plane rotational symmetry breaking, referred to as
Ising nematic transition. We find that upon approaching this instability, the
Raman spectral function develops a quasi-elastic peak as a function of energy
transferred by photons to the crystal. We attribute this low-energy B2g
scattering to the critical slow-down associated with the build up of nematic
correlations.",1504.05054v2
2015-06-18,Dynamical structure factor of magnetic Bloch oscillations at finite temperatures,"Domain-walls in one-dimensional Ising ferromagnets can undergo Bloch
oscillations when subjected to a skew magnetic field. Such oscillations imply
finite temperature non-dispersive low-frequency peaks in the dynamical
structure factor which can be probed in neutron scattering. We study in detail
the spectral weight of these peaks. Using an analytical approach based on an
approximate treatment of a gas of spin-cluster excitations we give an explicit
expression for the momentum- and temperature-dependence of the spectral
weights. Generally the spectral weights increase with temperature and
approaches the same order of magnitude as the spin-wave spectral weights at
high temperatures. We compare the analytical expression to numerical exact
diagonalizations and find that it can, without any adjustable parameters,
account for the temperature and momentum-transfer dependence of the numerically
obtained spectral weights in the parameter regime where the ratio of magnetic
fields $h_x/h_z \ll 1$ and the temperature is $h_x < T <\sim J_z/2$. We also
carry out numerical calculations pertinent to the material CoNb$_2$O$_6$, and
find qualitatively similar results.",1506.05614v1
2015-07-15,Nonexistence of steady solutions for rotational slender fibre spinning with surface tension,"Reduced one-dimensional equations for the stationary, isothermal rotational
spinning process of slender fibers are considered for the case of large
Reynolds ($\delta=3/\text{Re}\ll 1$) and small Rossby numbers ($\varepsilon \ll
1$). Surface tension is included in the model using the parameter
$\kappa=\sqrt{\pi}/(2 \text{We})$ related to the inverse Weber number. The
inviscid case $\delta=0$ is discussed as a reference case. For the viscous case
$\delta > 0$ numerical simulations indicate, that for a certain parameter
range, no physically relevant solution may exist. Transferring properties of
the inviscid limit to the viscous case, analytical bounds for the initial
viscous stress of the fiber are obtained. A good agreement with the numerical
results is found. These bounds give strong evidence, that for $\delta >
3\varepsilon^2 \left( 1- \frac{3}{2}\kappa +\frac{1}{2}\kappa^2\right)$ no
physical relevant stationary solution can exist.",1507.04200v1
2015-07-22,Quantum Error Correction for State Transfer in Noisy Spin Chains,"Can robustness against experimental imperfections and noise be embedded into
a quantum simulation? In this paper, we report on a special case in which this
is possible. A spin chain can be engineered such that, in the absence of
imperfections and noise, an unknown quantum state is transported from one end
of the chain to the other, due only to the intrinsic dynamics of the system. We
show that an encoding into a standard error correcting code (a
Calderbank-Shor-Steane code) can be embedded into this simulation task such
that a modified error correction procedure on read-out can recover from
sufficiently low rates of noise during transport.",1507.06139v3
2015-09-16,Q-operators for the open Heisenberg spin chain,"We construct Q-operators for the open spin-1/2 XXX Heisenberg spin chain with
diagonal boundary matrices. The Q-operators are defined as traces over an
infinite-dimensional auxiliary space involving novel types of reflection
operators derived from the boundary Yang-Baxter equation. We argue that the
Q-operators defined in this way are polynomials in the spectral parameter and
show that they commute with transfer matrix. Finally, we prove that the
Q-operators satisfy Baxter's TQ-equation and derive the explicit form of their
eigenvalues in terms of the Bethe roots.",1509.04867v3
2015-09-24,Triplet-Polaron Interaction Induced Upconversion from Triplet to Singlet: a New Way to Obtain Highly Efficient OLEDs,"The triplet harvesting is a main challenge in organic light-emitting devices
(OLEDs), due to the radiative decay of triplet is spin-forbidden. Here, we
designed and synthesized two D-A type molecules, TPA-TAZ and TCP. The OLEDs
based on them exhibit deep-blue emission and the singlet formation ratios are
higher than the simple spin-statistics of 25 %. Specially, a TPA-TAZ-based OLED
achieves a maximum EQE of 6.8 %, which is the largest value of the undoped
OLEDs with CIE(y)< 0.06 (the EBU blue standard) up to date. Comprehensive
experiments eliminate the triplet-harvesting processes of thermally activated
delayed fluorescence and triplet-triplet annihilation. Instead, the
triplet-polaron interaction induced upconversion from triplet to singlet
through one-electron transfer mechanism is proposed, and proven by the
magneto-current measurement and quantum chemistry computation. Our results may
offer a new route to break through the 25 % upper limit of IQE of fluorescent
OLEDs, especially, the deep-blue fluorescent OLEDs.",1509.07224v1
2015-10-02,Continuous Compressed Sensing of Inelastic and Quasielastic Helium Atom Scattering Spectra,"Helium atom scattering (HAS) is a well established technique for examining
the surface structure and dynamics of materials at atomic sized resolution. The
HAS technique Helium spin-echo spectroscopy opens up the possibility of
compressing the data acquisition process. Compressed sensing (CS) methods
demonstrating the compressibility of spin-echo spectra are presented. In
addition, wavelet based CS approximations, founded on a new continuous CS
approach, are used to construct continuous spectra that are compatible with
variable transformations to the energy/momentum transfer domain. Moreover,
recent developments on structured multilevel sampling that are empirically and
theoretically shown to substantially improve upon the state of the art CS
techniques are implemented. These techniques are demonstrated on several
examples including phonon spectra from a gold surface.",1510.00555v1
2015-11-24,Interacting quantum fluid in a polariton topological insulator,"We study Bogoliubov excitations of a spinor Bose Einstein condensate in a
honeycomb periodic potential, in the presence of a Zeeman field and of a
spin-orbit coupling specific for photonic systems, which is due to the energy
splitting between TE and TM polarized eigenstates. We also consider
spin-anisotropic interactions typical for cavity polaritons. We show that the
non-trivial topology of the single particle case is also present for the
interacting system. At low condensate density, the topology of the
single-particle bands is transferred to the bogolon dispersion. At a critical
value, the self-induced Zeeman field at the Dirac points of the dispersion
becomes equal to the real Zeeman field and then exceeds it. The gap is thus
closed and then re-opened with inverted Chern numbers. This change of topology
is accompanied by a change of the propagation directions of the one-way edge
modes. This result demonstrates that the chirality of a topological insulator
can be reversed by collective effects in a Bose-Einstein condensate.",1511.07758v1
2015-12-15,Multiferroicity and Magnetoelectric Coupling in TbMnO3 Thin Films,"In this work, we report the growth and functional characterizations of
multiferroic TbMnO3 thin films grown on Nb-doped SrTiO3 (001) substrates using
pulsed laser deposition. By performing detailed magnetic and ferroelectric
properties measurements, we demonstrate that the multiferroicity of spin origin
known in the bulk crystals can be successfully transferred to TbMnO3 thin
films. Meanwhile, anomalous magnetic transition and unusual magnetoelectric
coupling related to Tb moments are observed, suggesting a modified magnetic
configuration of Tb in the films as compared to the bulk counterpart. In
addition, it is found that the magnetoelectric coupling enabled by Tb moments
can even be seen far above the Tb spin ordering temperature, which provides a
larger temperature range for the magnetoelectric control involving Tb moments.",1512.04773v1
2015-12-21,Compton scattering S-matrix and cross section in strong magnetic field,"Compton scattering of polarized radiation in a strong magnetic field is
considered. The recipe for calculation of the scattering matrix elements, the
differential and total cross sections based on quantum electrodynamic (QED)
second order perturbation theory is presented for the case of arbitrary initial
and final Landau level, electron momentum along the field and photon momentum.
Photon polarization and electron spin state are taken into account. The correct
dependence of natural Landau level width on the electron spin state is taken
into account in general case of arbitrary initial photon momentum for the first
time. A number of steps in calculations were simplified analytically making the
presented recipe easy-to-use. The redistribution functions over the photon
energy, momentum and polarization states are presented and discussed. The paper
generalizes already known results and offers a basis for accurate calculation
of radiation transfer in strong $B$-field, for example, in strongly magnetized
neutron stars.",1512.06681v2
2016-01-07,Valley Plasmonics in the Dichalcogenides,"The rich phenomenology of plasmonic excitations in the dichalcogenides is
analyzed as a function of doping. The many-body polarization, the dielectric
response function and electron energy loss spectra are calculated using an ab
initio based model involving material-realistic Coulomb interactions, band
structure and spin-orbit coupling. Focusing on the representative case of
MoS$_2$, a plethora of plasmon bands are observed, originating from scattering
processes within and between the conduction or valence band valleys. We discuss
the resulting square-root and linear collective modes, arising from long-range
versus short-range screening of the Coulomb potential. We show that the
multi-orbital nature of the bands and spin-orbit coupling strongly affects
inter-valley scattering processes by gapping certain two-particle modes at
large momentum transfer.",1601.01707v1
2016-01-12,Oersted field and spin current effects on magnetic domains in [Co/Pd]15 nanowires,"An out-of-plane Oersted field produced from a current-carrying Au wire is
used to induce local domain formation in wires made from [Co/Pd]15 multilayers
with perpendicular anisotropy. A 100 ns pulsed current of 56-110 mA injected
into the Au wire created a reverse domain size of 120-290 nm in a Co/Pd
nanowire on one side of the Au wire. A Biot-Savart model was used to estimate
the position dependence of the Oersted field around the Au wire. The shape,
size and location of the reversed region of Co/Pd was consistent with the
magnitude of the Oersted field and the switching field distribution of the
unpatterned film. A current density of 6.2 x 10^11 A m-2 in the Co/Pd nanowire
did not translate the domain walls due to low spin transfer efficiency, but the
Joule heating promoted domain growth in a field below the coercive field.",1601.02738v1
2016-01-19,Lattice vibrations of the charge-transfer salt $κ$-(BEDT-TTF)$_2$Cu$_2$(CN)$_{3}$: novel interpretation of the electrodynamic response in a spin-liquid compound,"The dimer Mott insulator $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ exhibits
unusual electrodynamic properties. Numerical investigations of the electronic
ground state and the molecular and lattice vibrations reveal the importance of
the Cu$_2$(CN)$_3^-$ anion network coupled to the BEDT-TTF molecules: The
threefold cyanide coordination of copper and linkage isomerism in the anion
structure cause a loss of symmetry, frustration, disorder, and domain
formation. Our findings consistently explain the temperature and
polarization-dependent THz and infrared measurements, reinforce the
understanding of dielectric properties and have important implications for the
quantum spin-liquid state, which should be treated beyond two-dimensional,
purely electronic models.",1601.04926v1
2016-02-20,Time independent quantum circuits with local interactions,"Heisenberg spin chains can act as quantum wires transferring quantum states
either perfectly or with high fidelity. Gaussian packets of excitations passing
through dual rails can encode the two states of a logical qubit, depending on
which rail is empty and which rail is carrying the packet. With extra
interactions in one or between different chains, one can introduce interaction
zones in arrays of such chains, where specific one or two qubit gates act on
any qubit which passes through these interaction zones. Therefore universal
quantum computation is made possible in a static way where no external control
is needed. This scheme will then pave the way for a scalable way of quantum
computation where specific hardwares can be connected to make large quantum
circuits. Our scheme is an improvement of a recent scheme where we have
achieved to borrow an idea from quantum electrodynamics to replace non-local
interactions between spin chains with local interactions mediated by an
ancillary chain.",1602.06362v4
2016-02-17,Jets launched at magnetar birth cannot be ignored,"I question models for powering super energetic supernovae (SESNe) with a
magnetar central engine that do not include jets that are expected to be
launched by the magnetar progenitor. I show that under reasonable assumptions
the outflow that is expected during the formation of a magnetar can carry an
amount of energy that does not fall much below, and even surpasses, the energy
that is stored in the newly born spinning neutron star (NS). The rapidly
spinning NS and the strong magnetic fields attributed to magnetars require that
the accreted mass onto the newly born NS possesses high specific angular
momentum and strong magnetic fields. These ingredients are expected, as in many
other astrophysical objects, to form collimated outflows/jets. I argue that the
bipolar outflow in the pre-magnetar phase transfers a substantial amount of
energy to the supernova (SN) ejecta, and it cannot be ignored in models that
attribute SESNe to magnetars. I conclude that jets launched by accretion disks
and accretion belts are more likely to power SESNe than magnetars are. This
conclusion is compatible with the notion that jets might power all core
collapse SNe (CCSNe).",1602.07343v2
2016-03-17,J$_{eff}$ description of the honeycomb Mott insulator $α$-RuCl$_3$,"Novel ground states might be realized in honeycomb lattices with strong
spin-orbit coupling. Here we study the electronic structure of
${\alpha}$-RuCl$_3$, in which the Ru ions are in a d5 configuration and form a
honeycomb lattice, by angle-resolved photoemission, x-ray photoemission and
electron energy loss spectroscopy supported by density functional theory and
multiplet calculations. We find that ${\alpha}$-RuCl$_3$ is a Mott insulator
with significant spin-orbit coupling, whose low energy electronic structure is
naturally mapped onto Jeff states. This makes ${\alpha}$-RuCl$_3$ a promising
candidate for the realization of Kitaev physics. Relevant electronic parameters
such as the Hubbard energy U, the crystal field splitting 10Dq and the charge
transfer energy are evaluated. Furthermore, we observe significant Cl
photodesorption with time, which must be taken into account when interpreting
photoemission and other surface sensitive experiments.",1603.05507v1
2016-04-20,Nonlinear Dynamics of Dipoles in Microtubules: Pseudo-Spin Model,"We perform a theoretical study of the dynamics of the electric field
excitations in a microtubule by taking into consideration the realistic
cylindrical geometry, dipole-dipole interactions of the tubulin-based protein
heterodimers, the radial electric field produced by the solvent, and a possible
degeneracy of energy states of individual heterodimers. The consideration is
done in the frames of the classical pseudo-spin model. We derive the system of
nonlinear dynamical ordinary differential equations of motion for interacting
dipoles, and the continuum version of these equations. We obtain the solutions
of these equations in the form of snoidal waves, solitons, kinks, and localized
spikes. Our results will help to a better understanding of the functional
properties of microtubules including the motor protein dynamics and the
information transfer processes. Our considerations are based on classical
dynamics. Some speculations on the role of possible quantum effects are also
made.",1604.05971v1
2016-05-23,Theory of storage and retrieval of intense-broadband pulses at room temperature: analytical and numerical solutions,"We analyze the storage and retrieval of intense-broadband pulses with the
added effects of Doppler broadening and detuning in a $\Lambda$ configuration.
We compute analytical solutions via the inverse scattering technique and show
how the signal field is transferred to a spin-wave in the atomic medium and
later retrieved by the interaction of a control pulse. Due to the intensity of
the pulses, the pulse area (as defined for self-induced transparency) plays a
key role in the interaction, as it determines the location of the spin wave
within the medium. Additionally, we compare our results to non-ideal conditions
by considering pulses of finite length and the effect of spontaneous emission.",1605.06870v2
2016-05-30,On Photon Spin and the Electrodynamic Origin of the charge of the Electron,"We recently performed experiments on the transfer of photon spin to electron
orbital angular momentum. For an interpretation of the experimental results we
used a classical electrodynamic model of the photon as a propagating
electromagnetic solitary wave which is developed in detail here. A linearly
polarized monochromatic photon is considered as a propagating solitary
electromagnetic wave of finite energy hf which carries an angular momentum
h/2pi with the frequency f and Plancks constant h. This model has, apart from
being a tool for an interpretation of our experimental results, far reaching
consequences of fundamental relevance and guides us to an outline to a unified
quantum theory of electromagnetism and gravitation including an explanation of
the electrodynamic origin of the quantized charge of an electron.",1606.02251v2
2016-06-28,Periodic driving control of Raman-induced spin-orbit coupling in Bose-Einstein condensates: the heating mechanisms,"We focus on a technique recently implemented for controlling the magnitude of
synthetic spin-orbit coupling (SOC) in ultra-cold atoms in the Raman-coupling
scenario. This technique uses a periodic modulation of the Raman-coupling
amplitude to tune the SOC. Specifically, it has been shown that the effect of a
high-frequency sinusoidal modulation of the Raman-laser intensity can be
incorporated into the undriven Hamiltonian via effective parameters, whose
adiabatic variation can then be used to steer the SOC. Here, we characterize
the heating mechanisms that can be relevant to this method. We identify the
main mechanism responsible for the heating observed in the experiments as
basically rooted in driving-induced transfer of population to excited states.
Characteristics of that process determined by the harmonic trapping, the decay
of the excited states, and the technique used for preparing the system are
discussed. Additional heating, rooted in departures from adiabaticity in the
variation of the effective parameters, is also described. Our analytical study
provides some clues that may be useful in the design of strategies for curbing
the effects of heating on the efficiency of the control methods.",1606.08800v1
2016-07-20,Spin polarized Charge Trapping and Transfer at a HgTe Topological Insulator Quantum Dot,"This work presents theoretical demonstration of a carrier trap unit formed by
dual topological insulator constrictions (TIC) on the HgTe/CdTe quantum well
(QW) with inverted band structures. The sample of HgTe/CdTe QW is patterned
into a Hall bar device and a topological quantum dot is created by adding split
gate electrodes closely on the QW. In sharp contrast to conventional
semiconductor quantum dots, the presence or absence of topological edge states
in the proposed quantum hall bar system leads to distinct
propagating/insulating state of the TICs with large on/off ratio. This
topological quantum dot functions as a carrier trap memory element with near
perfect program/erase efficiency by proper adjusting the voltages applied to
the split gates. For completeness, we also demonstrate that the Rashba spin
orbit interaction in the quantum dot does not destroy the topological edge
states and have negligible impact on the conductance of the quantum hall bar.
The rapid oscillations in conductance can be suppressed when applying a
perpendicular magnetic field in the quantum dot.",1607.05821v2
2016-07-23,Rashba interaction and local magnetic moments in a graphene-Boron Nitride heterostructure by intercalation with Au,"We intercalate a van der Waals heterostructure of graphene and hexagonal
Boron Nitride with Au, by encapsulation, and show that Au at the interface is
two dimensional. A charge transfer upon current annealing indicates
redistribution of Au and induces splitting of the graphene bandstructure. The
effect of in plane magnetic field confirms that splitting is due to
spin-splitting and that spin polarization is in the plane, characteristic of a
Rashba interaction with magnitude approximately 25 meV. Consistent with the
presence of intrinsic interfacial electric field we show that the splitting can
be enhanced by an applied displacement field in dual gated samples. Giant
negative magnetoresistance, up to 75%, and a field induced anomalous Hall
effect at magnetic fields < 1 T are observed. These demonstrate that hybridized
Au has a magnetic moment and suggests the proximity to formation of a
collective magnetic phase. These effects persist close to room temperature.",1607.06893v1
2016-07-26,Anions effects on the electronic structure and electrodynamic properties of the Mott insulator $κ$-(BEDT-TTF)$_2$Ag$_2$(CN)$_{3}$,"The Mott insulator $\kappa$-(BEDT-TTF)$_2$Ag$_2$(CN)$_3$ forms a
highly-frustrated triangular lattice of $S=1/2$ dimers with a possible
quantum-spin-liquid state. Our experimental and numerical studies reveal the
emergence of a slight charge imbalance between crystallographically
inequivalent sites, relaxor dielectric response and hopping dc transport. In a
broader perspective we conclude that the universal properties of
strongly-correlated charge-transfer salts with spin liquid state are an
anion-supported valence band and cyanide-induced quasi-degenerate electronic
configurations in the relaxed state. The generic low-energy excitations are
caused by charged domain walls rather than by fluctuating electric dipoles.
They give rise to glassy dynamics characteristic of dimerized Mott insulators,
including the sibling compound $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$.",1607.07596v1
2016-09-07,Emerging magnetism and anomalous Hall effect in iridate-manganite heterostructures,"Strong Coulomb repulsion and spin-orbit coupling are known to give rise to
exotic physical phenomena in transition metal oxides. Initial attempts to
investigate systems where both of these fundamental interactions are comparably
strong, such as 3d and 5d complex oxide superlattices, have revealed properties
that only slightly differ from the bulk ones of the constituent materials.
Here, we observe that the interfacial coupling between the 3d antiferromagnetic
insulator SrMnO3 and the 5d paramagnetic metal SrIrO3 is enormously strong,
yielding an anomalous Hall response as the result of charge transfer driven
interfacial ferromagnetism. These findings show that low dimensional spin-orbit
entangled 3d-5d interfaces provide an avenue to uncover technologically
relevant physical phenomena unattainable in bulk materials.",1609.01973v1
2016-09-15,WIMP capture by the Sun in the effective theory of dark matter self-interactions,"We study the capture of WIMP dark matter by the Sun in the non-relativistic
effective theory of dark matter self-interactions. The aim is to assess the
impact of self-interactions on the expected neutrino flux from the annihilation
of WIMPs trapped in the Sun in a model independent manner. We consider all
non-relativistic Galilean invariant self-interaction operators that can arise
from the exchange of a heavy particle of spin less than or equal to 1 for WIMPs
of spin equal to 0, 1/2 and 1. We show that for interaction operators depending
at most linearly on the momentum transfer, the WIMP-induced neutrino flux can
be enhanced by several orders of magnitude compared to the same flux in absence
of self-interactions. This is true even for standard values of the thermally
averaged annihilation cross-section. This conclusion impacts the analysis of
present and future observations performed at neutrino telescopes.",1609.04825v1
2016-10-31,Dipolar effects on the critical fluctuations in Fe: Investigation by MIEZE,"Iron is one of the archetypical ferromagnets to study the critical
fluctuations at a continuous phase transition thus serving as a model system
for the application of scaling theory. We report a comprehensive study of the
critical dynamics at the transition from the ferro- to the paramagnetic phase
in Fe, employing the high-resolution neutron spin echo technique MIEZE. The
results show that the dipolar interactions lead to an additional damping of the
critical spin fluctuations at small momentum transfers $\bf q$. The results
agree essentially with scaling theory if the dipolar interactions are taken
into account by means of the mode-coupling equations. However, in contrast to
expectations, the dipolar wavenumber $q_D$ that plays a central role in the
scaling function $f(\kappa/q,q_D/\kappa)$ becomes temperature dependent. In the
limit of small $\bf q$ the critical exponent $z$ crosses over from 2.5 to 2.0.",1610.09755v1
2016-10-31,Competing order in the fermionic Hubbard model on the hexagonal graphene lattice,"We study the phase diagram of the fermionic Hubbard model on the hexagonal
lattice in the space of on-site and nearest neighbor couplings with
Hybrid-Monte-Carlo simulations. With pure on-site repulsion this allows to
determine the critical coupling strength for spin-density wave formation with
the standard approach of introducing a small mass term, explicitly breaking the
sublattice symmetry. The analogous mass term for charge-density wave formation
above a critical nearest-neighbor repulsion, on the other hand, would introduce
a fermion sign problem. The competition between the two and the phase diagram
in the space of the two coouplings can however be studied in simulations
without explicit sublattice symmetry breaking. Our results compare
qualitatively well with the Hartree-Fock phase diagram. We furthermore
demonstrate how spin-symmetry breaking by the Euclidean time discretization can
be avoided also, when using an improved fermion action based on an exponetial
transfer matrix with exact sublattice symmetry.",1610.09855v1
2016-11-06,Quantum critical local spin dynamics near the Mott metal-insulator transition in infinite dimensions,"Finding microscopic models for metallic states that exhibit quantum critical
properties such as $\omega/T$ scaling is a major theoretical challenge. We
calculate the local dynamical spin susceptibility $\chi(T,\omega)$ for a
Hubbard model at half filling using Dynamical Mean-Field Theory, which is exact
in infinite dimensions. Qualitatively distinct behavior is found in the
different regions of the phase diagram: Mott insulator, Fermi liquid metal, bad
metal, and a quantum critical region above the finite temperature critical
point. The signature of the latter is $\omega/T$ scaling where $T$ is the
temperature. Our results are consistent with previous results showing scaling
of the dc electrical conductivity and are relevant to experiments on organic
charge transfer salts.",1611.01822v2
2016-11-16,Nanodiamond-enhanced MRI,"Nanodiamonds are of interest as nontoxic substrates for targeted drug
delivery and as highly biostable fluorescent markers for cellular tracking.
Beyond optical techniques however, options for noninvasive imaging of
nanodiamonds in vivo are severely limited. Here, we demonstrate that the
Overhauser effect, a proton-electron double resonance technique developed to
detect free radicals in vivo, can enable high contrast magnetic resonance
imaging (MRI) of nanodiamonds in water at room temperature and ultra-low
magnetic field. The technique transfers spin polarization from paramagnetic
impurities at nanodiamond surfaces to $^1$H spins in the surrounding water
solution, creating MRI contrast on-demand. We further examine the conditions
required for maximum enhancement as well as the ultimate sensitivity of the
technique. The ability to perform continuous hyperpolarization via the
Overhauser mechanism, in combination with excellent in vivo stability, raises
the possibility of performing noninvasive tracking of nanodiamonds over
indefinitely long periods of time.",1611.05167v1
2016-12-14,"Exactly solved mixed spin-(1,1/2) Ising-Heisenberg distorted diamond chain","The mixed spin-(1,1/2) Ising-Heisenberg model on a distorted diamond chain
with the spin-1 nodal atoms and the spin-1/2 interstitial atoms is exactly
solved by the transfer-matrix method. An influence of the geometric spin
frustration and the parallelogram distortion on the ground state,
magnetization, susceptibility and specific heat of the mixed-spin
Ising-Heisenberg distorted diamond chain are investigated in detail. It is
demonstrated that the zero-temperature magnetization curve may involve
intermediate plateaus just at zero and one-half of the saturation
magnetization. The temperature dependence of the specific heat may have up to
three distinct peaks at zero magnetic field and up to four distinct peaks at a
non-zero magnetic field. The origin of multipeak thermal behavior of the
specific heat is comprehensively studied.",1612.04841v1
2016-12-19,"Metric versus observable operator representation, higher spin models","We elaborate further on the metric representation that is obtained by
transferring the time-dependence from a Hermitian Hamiltonian to the metric
operator in a related non-Hermitian system. We provide further insight into the
procedure on how to employ the time-dependent Dyson relation and the
quasi-Hermiticity relation to solve time-dependent Hermitian Hamiltonian
systems. By solving both equations separately we argue here that it is in
general easier to solve the former. We solve the mutually related
time-dependent Schroedinger equation for a Hermitian and non-Hermitian spin
1/2, 1 and 3/2 model with time-independent and time-dependent metric,
respectively. In all models the overdetermined coupled system of equations for
the Dyson map can be decoupled algebraic manipulations and reduces to simple
linear differential equations and an equation that can be converted into the
nonlinear Ermakov-Pinney equation.",1612.06122v1
2017-01-09,Spin-orbit coupled interferometry with ring-trapped Bose--Einstein condensates,"We propose a method of atom-interferometry using a spinor Bose-Einstein
condensate (BEC) with a time-varying magnetic field acting as a coherent
beam-splitter. Our protocol creates long-lived superpositional counterflow
states, which are of fundamental interest and can be made sensitive to both the
Sagnac effect and magnetic fields on the sub-micro-G scale. We split a
ring-trapped condensate, initially in the $m_f=0$ hyperfine state, into
superpositions of internal $m_f=\pm1$ states and condensate superflow, which
are spin-orbit coupled. After interrogation, relative phase accumulation can be
inferred from a population transfer to the $m_f=\pm1$ states. The counterflow
generation protocol is adiabatically deterministic and does not rely on
coupling to additional optical fields or mechanical stirring techniques. Our
protocol can maximise the classical Fisher information for any rotation,
magnetic field, or interrigation time, and so has the maximum sensitivity
available to uncorrelated particles. Precision can increase with the
interrogation time, and so is limited only by the lifetime of the condensate.",1701.02154v2
2017-01-18,Sensing Floquet-Majorana fermions via heat transfer,"Time periodic modulations of the transverse field in the closed XY spin-1/2
chain generate a very rich dynamical phase diagram, with a hierarchy of
topological phases characterized by differing numbers of Floquet-Majorana
modes. We show that this rich phase diagram survives when the system is coupled
to dissipative end reservoirs. Circumventing the obstacle of preparing and
measuring quasi energy configurations endemic to Floquet-Majorana detection
schemes, we show that stroboscopic heat transport and spin density are robust
observables to detect both the dynamical phase transitions and Majorana modes.
In particular, we find that the derivative of the heat current, with respect to
a control parameter, changes sign at the boundaries separating topological
phases with different numbers of Floquet Majorana modes. We present a simple
scheme to directly count the number of Floquet-Majorana modes in a phase from
the Fourier transform of the local spin density profile. Our results are valid
provided the anisotropies are not strong and can be easily implemented in
quantum engineered systems.",1701.05206v2
2017-02-16,Strong Algorithmic Cooling in Large Star-Topology Quantum Registers,"Cooling the qubit into a pure initial state is crucial for realizing
fault-tolerant quantum information processing. Here we envisage a star-topology
arrangement of reset and computation qubits for this purpose. The reset qubits
cool or purify the computation qubit by transferring its entropy to a heat-bath
with the help of a heat-bath algorithmic cooling procedure. By combining
standard NMR methods with powerful quantum control techniques, we cool central
qubits of two large star topology systems, with 13 and 37 spins respectively.
We obtain polarization enhancements by a factor of over 24, and an associated
reduction in the spin temperature from 298 K down to 12 K. Exploiting the
enhanced polarization of computation qubit, we prepare combination-coherences
of orders up to 15. By benchmarking the decay of these coherences we
investigate the underlying noise process. Further, we also cool a pair of
computation qubits and subsequently prepare them in an effective pure-state.",1702.04992v3
2017-01-30,Ultrafast optical excitation of coherent magnons in antiferromagnetic NiO,"In experiment and theory, we resolve the mechanism of ultrafast optical
magnon excitation in antiferromagnetic NiO. We employ time-resolved optical
two-color pump-probe measurements to study the coherent non-thermal spin
dynamics. Optical pumping and probing with linearly and circularly polarized
light along the optic axis of the NiO crystal scrutinizes the mechanism behind
the ultrafast optical magnon excitation. A phenomenological symmetry-based
theory links these experimental results to expressions for the optically
induced magnetization via the inverse Faraday effect and the inverse
Cotton-Mouton effect. We obtain striking agreement between experiment and
theory that, furthermore, allows us to extract information about the spin
domain distribution. We also find that in NiO the energy transfer into the
magnon mode via the inverse Cotton-Mouton effect is about three orders of
magnitude more efficient than via the inverse Faraday effect.",1702.05666v1
2017-03-21,Influence of magnetic field and ferromagnetic film thickness on domain pattern transfer in multiferroic heterostructures,"Domains in BaTiO$_3$ induces a regular modulation of uniaxial magnetic
anisotropy in CoFeB via an inverse magnetostriction effect. As a result, the
domain structures of the CoFeB wedge film and BaTiO$_3$ substrate correlate
fully and straight ferroelectric domain boundaries in BaTiO$_3$ pin magnetic
domain walls in CoFeB. We use x-ray photoemission electron microscopy and
magneto-optical Kerr effect microscopy to characterize the spin structure of
the pinned domain walls. In a rotating magnetic field, abrupt and reversible
transitions between two domain wall types occur, namely, narrow walls where the
magnetization vectors align head-to-tail and much broader walls with
alternating head-to-head and tail-to-tail magnetization configurations. We
characterize variations of the domain wall spin structure as a function of
magnetic field strength and CoFeB film thickness and compare the experimental
results with micromagnetic simulations.",1703.07227v1
2017-04-16,Superradiant Instability and Backreaction of Massive Vector Fields around Kerr Black Holes,"We study the growth and saturation of the superradiant instability of a
complex, massive vector (Proca) field as it extracts energy and angular
momentum from a spinning black hole, using numerical solutions of the full
Einstein-Proca equations. We concentrate on a rapidly spinning black hole
($a=0.99$) and the dominant $m=1$ azimuthal mode of the Proca field, with real
and imaginary components of the field chosen to yield an axisymmetric
stress-energy tensor and, hence, spacetime. We find that in excess of $9\%$ of
the black hole's mass can be transferred into the field. In all cases studied,
the superradiant instability smoothly saturates when the black hole's horizon
frequency decreases to match the frequency of the Proca cloud that
spontaneously forms around the black hole.",1704.04791v2
2017-06-01,Forbidden coherent transfer observed between two realizations of quasi-harmonic spin system,"The multi-level system $^{55}$Mn$^{2+}$ is used to generate two
pseudo-harmonic level systems, as representations of the same electronic
sextuplet at different nuclear spin projections. The systems are coupled using
a forbidden nuclear transition induced by the crystalline anisotropy. We
demonstrate Rabi oscillations between the two representations in conditions
similar to two coupled quasi-harmonic quantum oscillators. Rabi oscillations
are performed at a detuned pumping frequency which matches energy difference
between electro-nuclear states of different oscillators. We measure a coupling
stronger than the decoherence rate, to indicate the possibility fast
information exchange between the systems.",1706.00193v2
2017-06-11,Absorbing boundary layers for spin wave micromagnetics,"Micromagnetic simulations are used to investigate the effects of different
absorbing boundary layers (ABLs) on spin waves (SWs) reflected from the edges
of a magnetic nano-structure. We define the conditions that a suitable ABL must
fulfill and compare the performance of abrupt, linear, polynomial and tan
hyperbolic damping profiles in the ABL. We first consider normal incidence in a
permalloy stripe and propose a transmission line model to quantify reflections
and calculate the loss introduced into the stripe due to the ABL. We find that
a parabolic damping profile absorbs the SW energy efficiently and has a low
reflection coefficient, thus performing much better than the commonly used
abrupt damping profile. We then investigated SWs that are obliquely incident at
26.6, 45 and 63.4 degrees on the edge of a yttrium-iron-garnet film. The
parabolic damping profile again performs efficiently by showing a high SW
energy transfer to the ABL and a low reflected SW amplitude.",1706.03325v1
2017-07-07,Magnetoelectric antiferromagnets as platforms for the manipulation of solitons,"We study the magnetic dynamics of magnetoelectric antiferromagnetic thin
films, where an unconventional boundary ferromagnetism coexists with the bulk
N\'{e}el phase below the N\'{e}el temperature. The spin exchange between the
two order parameters yields an effective low-energy theory that is formally
equivalent to that of a ferrimagnet. Dynamics of domain walls and skyrmions are
analyzed within the collective variable approach, from which we conclude that
they behave as massive particles moving in a viscous medium subjected to a
gyrotropic force. We find that the film thickness can be used as a control
parameter for the motion of these solitons. In this regard, it is shown that an
external magnetic field can drive the dynamics of domain walls, whose terminal
velocity is tunable with the sample thickness. Furthermore, the classification
of the skyrmion dynamics is sensitive to the spatial modulation of the sample
thickness, which can be easily engineered with the present (thin-film)
deposition techniques. Current-driven spin transfer can trigger drifting orbits
of skyrmions, which can be utilized as racetracks for these magnetic textures.",1707.02374v1
2017-07-12,Long-Lived Ultracold Molecules with Electric and Magnetic Dipole Moments,"We create fermionic dipolar $^{23}$Na$^6$Li molecules in their triplet ground
state from an ultracold mixture of $^{23}$Na and $^6$Li. Using
magneto-association across a narrow Feshbach resonance followed by a two-photon
STIRAP transfer to the triplet ground state, we produce $3\,{\times}\,10^4$
ground state molecules in a spin-polarized state. We observe a lifetime of
$4.6\,\text{s}$ in an isolated molecular sample, approaching the $p$-wave
universal rate limit. Electron spin resonance spectroscopy of the triplet state
was used to determine the hyperfine structure of this previously unobserved
molecular state.",1707.03925v2
2017-08-09,Enormous sample scale-up from nanoliter to microliter in high field liquid state dynamic nuclear polarization,"Dynamic nuclear polarization (DNP) enhances nuclear magnetic resonance (NMR)
signals by transferring electron spin polarization to nuclei. As DNP requires
microwave magnetic fields B1 strong enough to saturate electron spins,
microwave resonators are generally used to achieve a sufficient B1, at the
expense of restricting the sample size. Higher fields improve NMR sensitivity
and resolution. However, resonators at 9 T for example can only hold
nano-liters (nL). Larger volumes are possible by avoiding resonators, but the
higher power needed to reach B1 is likely to evaporate the sample. Here, we
demonstrate a breakthrough in liquid state DNP at 9 T, boosting the sample size
to the microliter range. We could use high-power (70 W) microwaves thanks to a
planar probe designed to alleviate dielectric heating. We enhanced the 1H NMR
signal intensity of 2 uL of liquid water by a factor of 14, while maintaining
the water temperature below 40 degree Celsius.",1708.02800v1
2017-08-21,Fast Hole Tunneling Times in Germanium Hut Wires Probed by Single-Shot Reflectometry,"Heavy holes confined in quantum dots are predicted to be promising candidates
for the realization of spin qubits with long coherence times. Here we focus on
such heavy-hole states confined in Germanium hut wires. By tuning the growth
density of the latter we can realize a T-like structure between two neighboring
wires. Such a structure allows the realization of a charge sensor, which is
electrostatically and tunnel coupled to a quantum dot, with charge-transfer
signals as high as 0.3e. By integrating the T-like structure into a
radio-frequency reflectometry setup, single-shot measurements allowing the
extraction of hole tunneling times are performed. The extracted tunneling times
of less than 10$\mu$s are attributed to the small effective mass of Ge
heavy-hole states and pave the way towards projective spin readout
measurements.",1708.06278v1
2017-10-05,Importance of van der Waals interactions and cation-anion coupling in an organic quantum spin liquid,"The Mott insulator $\beta'$-EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ belongs to a class
of charge transfer solids with highly-frustrated triangular lattice of $S=1/2$
molecular dimers and a quantum-spin-liquid ground state. Our experimental and
ab initio theoretical studies show the fingerprints of strong correlations and
disorder, important role of cation-dimer bonding in charge redistribution, no
sign of intra- and inter-dimer dipoles, and the decisive van der Waals
contribution to inter-dimer interactions and the ground state structure. The
latter consists of quasi-degenerate electronic states related to the different
configurations of cation moieties which permit two different equally probable
orientations. Upon reducing the temperature, the low-energy excitations slow
down, indicating glassy signatures as the cation motion freezes out.",1710.01942v2
2017-11-01,Negative differential thermal conductance and heat amplification in a nonequilibrium triangle-coupled spin-boson system at strong coupling,"We investigate the nonequilibrium quantum heat transfer in a triangle-coupled
spin-boson system within a three-terminal setup. By including the
nonequilibrium noninteracting blip approximation approach combined with the
full counting statistics, we analytically obtain the steady state populations
and heat currents. The negative differential thermal conductance and giant heat
amplification factor are clearly observed at strong qubit-bath coupling. %and
the heat amplification is dramatically suppressed in the moderate coupling
regime. Moreover, the strong interaction between the gating qubit and gating
thermal bath is unraveled to be compulsory to exhibit these far-from
equilibrium features.",1711.00204v1
2017-12-11,Nonstandard Bethe Ansatz equations for open O(N) spin chains,"The double row transfer matrix of the open O(N) spin chain is diagonalized
and the Bethe Ansatz equations are also derived by the algebraic Bethe Ansatz
method including the so far missing case when the residual symmetry is
O(2M+1)$\times$O(2N-2M-1). In this case the boundary breaks the ""rank"" of the
O(2N) symmetry leading to nonstandard Bethe Ansatz equations in which the
number of Bethe roots is less than as it was in the periodic case. Therefore
these cases are similar to soliton-nonpreserving reflections.",1712.03753v2
2017-12-26,Quantum Walks on Graphs of the Ordered Hamming Scheme and Spin Networks,"It is shown that the hopping of a single excitation on certain triangular
spin lattices with non-uniform couplings and local magnetic fields can be
described as the projections of quantum walks on graphs of the ordered Hamming
scheme of depth 2. For some values of the parameters the models exhibit perfect
state transfer between two summits of the lattice. Fractional revival is also
observed in some instances. The bivariate Krawtchouk polynomials of the Tratnik
type that form the eigenvalue matrices of the ordered Hamming scheme of depth 2
give the overlaps between the energy eigenstates and the occupational basis
vectors.",1712.09200v5
2018-01-05,Autonomous quantum Maxwell's demon based on two exchange-coupled quantum dots,"I study an autonomous quantum Maxwell's demon based on two exchange-coupled
quantum dots attached to the spin-polarized leads. The principle of operation
of the demon is based on the coherent oscillations between the spin states of
the system which act as a quantum iSWAP gate. Due to the operation of the iSWAP
gate one of the dots acts as a feedback controller which blocks the transport
with the bias in the other dot, thus inducing the electron pumping against the
bias; this leads to the locally negative entropy production. Operation of the
demon is associated with the information transfer between the dots, which is
studied quantitatively by mapping the analyzed setup onto the thermodynamically
equivalent auxiliary system. The calculated entropy production in a single
subsystem and information flow between the subsystems are shown to obey a local
form of the second law of thermodynamics, similar to the one previously derived
for classical bipartite systems.",1801.01659v1
2018-02-14,Asymptotic Prethermalization in Periodically Driven Classical Spin Chains,"We reveal a continuous dynamical heating transition between a prethermal and
an infinite-temperature stage in a clean, chaotic periodically driven classical
spin chain. The transition time is a steep exponential function of the drive
frequency, showing that the exponentially long-lived prethermal plateau,
originally observed in quantum Floquet systems, survives the classical limit.
Even though there is no straightforward generalization of Floquet's theorem to
nonlinear systems, we present strong evidence that the prethermal physics is
well described by the inverse-frequency expansion. We relate the stability and
robustness of the prethermal plateau to drive-induced synchronization not
captured by the expansion. Our results set the pathway to transfer the ideas of
Floquet engineering to classical many-body systems, and are directly relevant
for photonic crystals and cold atom experiments in the superfluid regime.",1802.04910v2
2018-02-13,"From mean-field localized magnetism to itinerant spin fluctuations in the ""Non-metallic metal"" - FeCrAs","FeCrAs displays an unusual electrical response that is neither metallic in
character nor divergent at low temperatures, as expected for an insulating
response, and therefore it has been termed a ""nonmetal-metal"". We carried out
neutron scattering experiments on powder and single crystal samples to study
the magnetic dynamics and critical fluctuations in FeCrAs. Magnetic neutron
diffraction measurements find Cr3+ magnetic order setting in at 115 K with the
mean-field critical exponent. Neutron spectroscopy, however, observes gapless
stiff magnetic fluctuations emanating from magnetic positions with propagation
wave vector q_0=(1/3,1/3), which persists up to at least 80 meV. The magnetism
in FeCrAs therefore displays a response which resembles that of itinerant
magnets at high energy transfers, such as chromium alloys. We suggest that the
presence of stiff high-energy spin fluctuations is the origin of the unusual
temperature dependence of the resistivity.",1802.05271v2
2018-03-12,Non-analytic behavior of the Loschmidt echo in XXZ spin chains: exact results,"We address the computation of the Loschmidt echo in interacting integrable
spin chains after a quantum quench. We focus on the massless regime of the XXZ
spin-1/2 chain and present exact results for the dynamical free energy
(Loschmidt echo per site) for a special class of integrable initial states. For
the first time we are able to observe and describe points of non-analyticities
using exact methods, by following the Loschmidt echo up to large real times.
The dynamical free energy is computed as the leading eigenvalue of an
appropriate Quantum Transfer Matrix, and the non-analyticities arise from the
level crossings of this matrix. Our exact results are expressed in terms of
""excited-state"" thermodynamic Bethe ansatz equations, whose solutions involve
non-trivial Riemann surfaces. By evaluating our formulas, we provide explicit
numerical results for the quench from the N\'eel state, and we determine the
first few non-analytic points.",1803.04380v1
2018-04-20,Scaling Phononic Quantum Networks of Solid-State Spins with Closed Mechanical Subsystems,"Phononic quantum networks feature distinct advantages over photonic networks
for on-chip quantum communications, providing a promising platform for
developing quantum computers with robust solid-state spin qubits. Large
mechanical networks including one-dimensional chains of trapped ions, however,
have inherent and well-known scaling problems. In addition, chiral phononic
processes, which are necessary for conventional phononic quantum networks, are
difficult to implement in a solid-state system. To overcome these seemingly
unsolvable obstacles, we have developed a new network architecture that breaks
a large mechanical network into small and closed mechanical subsystems. This
architecture is implemented in a diamond phononic nanostructure featuring
alternating phononic crystal waveguides with specially-designed bandgaps. The
implementation also includes nanomechanical resonators coupled to color centers
through phonon-assisted transitions as well as quantum state transfer protocols
that can be robust against the thermal environment.",1804.07862v2
2018-05-15,"Magnetic orders in the hole doped three-band Hubbard model: spin spirals, nematicity, and ferromagnetic domain walls","The Copper-Oxygen planes in cuprates have been at the center of the search
for a theory of high-temperature superconductivity. We conduct an extensive
study of the ground state of the three-band Hubbard (Emery) model in the
underdoped regime. We focus on the magnetic and charge orders, and present
results from generalized Hartree-Fock (GHF) calculations. The ground-state
properties at the thermodynamic limit are challenging to pin down because of
sensitivity to computational details including the shapes and sizes of the
supercells. We employ large-scale computations with various technical
improvements to determine the orders within GHF. The ground state exhibits a
rich phase diagram with hole doping as the charge transfer energy is varied,
including ferromagnetic domain walls embedded in an antiferromagnetic
background, spin spirals, and nematic order.",1805.05969v2
2018-05-18,Band crossings in honeycomb-layered transition metal compounds,"Two-dimensional electron dispersions with peculiar band crossings provide a
platform for realizing topological phases of matter. Here we theoretically show
that the $e_g$-orbital manifold of honeycomb-layered transition metal compounds
accommodates a plethora of peculiar band crossings, such as multiple Dirac
point nodes, quadratic band crossings, and line nodes. From the tight-binding
analysis, we find that the band topology is systematically changed by the
orbital dependent transfer integrals on the honeycomb network of edge-sharing
octahedra, which can be modulated by distortions of the octahedra as well as
chemical substitutions. The band crossings are gapped out by the spin-orbit
coupling, which brings about a variety of topological phases distinguished by
the spin Chern numbers. The results provide a comprehensive understanding of
the previous studies on various honeycomb compounds. We also propose another
candidate materials by ab initio calculations.",1805.07068v2
2018-06-19,Gradient flow approach to local mean-field spin systems,"It is well-known that many diffusion equations can be recast as Wasserstein
gradient flows. Moreover, in recent years, by modifying the Wasserstein
distance appropriately, this technique has been transferred to further
evolution equations and systems. In this paper we establish such a gradient
flow representation for evolution equations that depend on a non-evolving
parameter. These equations are connected to a local mean-field interacting spin
system. We then use this gradient flow representation to prove a large
deviation principle for the empirical process associated to this system. This
is done by using a criterion that was established by Max Fathi in 2016.
Finally, the corresponding hydrodynamic limit is shown by using an approach
that was initiated by Sandier and Serfaty in 2004.",1806.07121v5
2018-07-01,Spin-Boson Model to Demonstrate Quantum Tunneling in Biomolecules using IBM Quantum Computer,"Efficient simulation of quantum mechanical problems can be performed in a
quantum computer where the interactions of qubits lead to the realization of
various problems possessing quantum nature. Spin-Boson Model (SBM) is one of
the striking models in quantum physics that enables to describe the dynamics of
most of the two-level quantum systems through the bath of harmonic oscillators.
Here we simulate the SBM and illustrate its applications in a biological system
by designing appropriate quantum circuits for the Hamiltonian of photosynthetic
reaction centers in IBM's 5-qubit quantum computer. We consider both two-level
and four-level biomolecular quantum systems to observe the effect of quantum
tunnelling in the reaction dynamics. We study the behaviour of tunneling by
changing different parameters in the Hamiltonian of the system. The results of
SBM can be applied to various two-, four- and multi-level quantum systems
explicating electron transfer process.",1807.00323v1
2018-09-21,Phase Slips and Parity Jumps in Quantum Oscillations of Inverted InAs/GaSb Quantum Wells,"We present magnetotransport measurements of a strongly hybridized inverted
InAs/GaSb double quantum well. We find that the spin-orbit interaction leads to
an appreciable spin-splitting of hole-like states, which form distinct Landau
levels in a perpendicular magnetic field. The resulting quantum Hall state is
governed by a periodic even and odd total filling arising due to the
simultaneous occupation of electron-like and hole-like Landau levels of
differing degeneracy. Furthermore, oscillatory charge transfer between all
involved subbands leads to discrete phase slips in the usual sequential filling
of Landau levels, and coincidentally the phase slips are close to $\pi$. These
results shed new insights on the Landau level structure in composite systems
and have consequences for interpreting intercepts obtained from index plots,
which are routinely employed to investigate the presence of Berry's phase.",1809.08068v1
2018-11-06,Topological Frequency Conversion in a Driven Dissipative Quantum Cavity,"Recent work (PRX 7, 041008) has shown that a spin coupled to two externally
supplied circularly-polarized electromagnetic modes can effectuate a
topological, quantized transfer of photons from one mode to the other. Here we
study the effect in the case when only one of the modes is externally provided,
while the other is a dynamical quantum mechanical cavity mode. Focusing on the
signatures and stability under experimentally accessible conditions, we show
that the effect persists down to the few-photon quantum limit and that it can
be used to generate highly entangled ""cat states"" of cavity and spin. By tuning
the strength of the external drive to a ""sweet spot"", the quantized pumping can
arise starting from an empty (zero photon) cavity state. We also find that
inclusion of external noise and dissipation does not suppress but rather
stabilizes the conversion effect, even after multiple cavity modes are taken
into account.",1811.02222v3
2018-11-21,Momentum reconstruction and contact of the one-dimensional Bose-Fermi mixture,"We investigate the one-dimensional mixture of scalar bosons and spin
polarized fermions interacting through a $\delta$-function potential. Using a
thermodynamic description derived by employing a lattice embedding of the
continuum model and the quantum transfer matrix method we perform a detailed
analysis of the contact and quantum critical behaviour. We show that the
compressibility Wilson ratio presents anomalous enhancement at the quantum
critical points and that the boundaries of the quantum critical regions can be
well mapped by the maxima of the specific heat. As a function of the coupling
strength and temperature the contact presents nonmonotonic behavior. In the
strong coupling regime the local minimum exhibited by the contact as a function
of temperature is accompanied by a significant momentum reconstruction at both
low and high momenta. This momentum reconstruction occurs as the system crosses
the boundary between the Tomonaga-Luttinger liquid phase to the spin-incoherent
regime and provides an experimental signature of the transition.",1811.08692v2
2018-11-23,Vertex Models and Spin Chains in Formulas and Pictures,"We systematise and develop a graphical approach to the investigations of
quantum integrable vertex statistical models and the corresponding quantum spin
chains. The graphical forms of the unitarity and various crossing relations are
introduced. Their explicit analytical forms for the case of integrable systems
associated with the quantum loop algebra ${\mathrm U}_q(\mathcal
L(\mathfrak{sl}_{l + 1}))$ are given. The commutativity conditions for the
transfer operators of lattices with a boundary are derived by the graphical
method. Our consideration reveals useful advantages of the graphical approach
for certain problems in the theory of quantum integrable systems.",1811.09401v3
2018-12-09,On Spin II,"Having previously identified the photon field with a (special) linear
Complex, we give a brief account on identifications and reasoning so far. Then,
in order to include spinorial degrees of freedom into the Lagrangean
description, we discuss the mapping of lines to spins based on an old transfer
principle by Lie. This introduces quaternionic reps and relates to our original
group-based approach by SU(4) and SU*(4)~SL(2,H), respectively. Finally, we
discuss some related geometrical aspects in terms of (spatial) projective
geometry which point to a projective construction scheme and algebraic
geometry.",1812.04944v2
2019-03-02,Strong system-bath coupling induces negative differential thermal conductance and heat amplification in nonequilibrium two-qubits systems,"Quantum heat transfer is analyzed in nonequilibrium two-qubits systems by
applying the nonequilibrium polaron-transformed Redfield equation combined with
full counting statistics. Steady state heat currents with weak and strong
qubit-bath couplings are clearly unified. Within the two-terminal setup, the
negative differential thermal conductance is unraveled with strong qubit-bath
coupling and finite qubit splitting energy. The partially strong spin-boson
interaction is sufficient to show the negative differential thermal
conductance. Based on the three-terminal setup, that two-qubits are
asymmetrically coupled to three thermal baths, a giant heat amplification
factor is observed with strong qubit-bath coupling. Moreover, the strong
interaction of either the left or right spin-boson coupling is able to exhibit
the apparent heat amplification effect.",1903.00654v1
2019-03-18,Role of excited states in the dynamics of excitons and their spins in diluted magnetic semiconductors,"We theoretically investigate the impact of excited states on the dynamics of
the exciton ground state in diluted magnetic semiconductor quantum wells.
Exploiting the giant Zeeman shift in these materials, an external magnetic
field is used to bring transitions between the exciton ground state and excited
states close to resonance. It turns out that, when treating the exciton
dynamics in terms of a quantum kinetic theory beyond the Markov approximation,
higher exciton states are populated already well below the critical magnetic
field required to bring the exciton ground state in resonance to an excited
state. This behavior is explained by exciton-impurity correlations that can
bridge energy differences on the order of a few meV and require a quantum
kinetic description beyond the independent-particle picture. Of particular
interest is the significant spin transfer toward states on the optically dark
$2p$ exciton parabola which are protected against radiative decay.",1903.07564v2
2019-04-05,Common universal behaviors of magnetic domain walls driven by spin-polarized electrical current and magnetic field,"We explore universal behaviors of magnetic domain wall driven by the
spin-transfer of an electrical current, in a ferromagnetic (Ga,Mn)(As,P) thin
film with perpendicular magnetic anisotropy. For a current direction transverse
to domain wall, the dynamics of the thermally activated creep regime and the
depinning transition are found to be compatible with a self-consistent
universal description of magnetic field induced domain wall dynamics. This
common universal behavior, characteristic of the so-called quenched
Edwards-Wilkinson universality class, is confirmed by a complementary and
independent analysis of domain wall roughness. However, the tilting of domain
walls and the formation of facets is produced by the directionality of
interaction with the current, which acts as a magnetic field only in the
direction transverse to domain wall.",1904.03047v2
2019-04-23,Empirical case for two pseudogaps in cuprate superconductors,"Superconductivity in cuprates is achieved by doping holes into a correlated
charge-transfer insulator. While the correlated character of the parent
insulator is now understood, there is no accepted theory for the ""normal"" state
of the doped insulator. I present a mostly empirical analysis of a large range
of experimental characterizations, making the case for two pseudogaps: (1) a
large pseudogap resulting from the competition between the energy of
superexchange-coupled local Cu moments and the kinetic energy of doped holes;
(2) a small pseudogap that results from dopant disorder and consequent
variations in local charge density, leading to a distribution of local
superconducting onset temperatures. The large pseudogap closes as hole kinetic
energy dominates at higher doping and the dynamic antiferromagnetic
correlations become overdamped. Establishing spatially-homogeneous $d$-wave
superconductivity is limited by those regions with the weakest superconducting
phase coherence, which tends to be limited by low-energy spin fluctuations. The
magnitude of the small pseudogap is correlated with the doping-dependent energy
$E_{\rm cross}$ associated with the neck of the hour-glass dispersion of spin
excitations. The consequences of this picture are discussed.",1904.10473v1
2019-05-08,Polarization transfer in hyperon decays and its effect in relativistic nuclear collisions,"We calculate the contribution to the polarization of $\Lambda$ hyperons in
relativistic nuclear collisions at high energy from the decays of
$\Sigma^*(1385)$ and $\Sigma^0$, which are the predominant sources of $\Lambda$
production besides the primary component, as a function of the $\Lambda$
momentum. Particularly, we estimate the longitudinal component of the mean spin
vector as a function of the azimuthal angle in the transverse plane, assuming
that primary $\Sigma^*$ and $\Sigma^0$ polarization follow the predictions of
local thermodynamic equilibrium in a relativistic fluid. Provided that the
rapidity dependence around midrapidity of polarization is negligible, we find
that this component of the overall spin vector has a very similar pattern to
the primary one. Therefore, we conclude that the secondary decays cannot
account for the discrepancy in sign between experimental data and hydrodynamic
model predictions of the longitudinal polarization of $\Lambda$ hyperons
recently measured by the STAR experiment at RHIC.",1905.03123v3
2019-05-27,Towards the solution of an integrable $D_2^{(2)}$ spin chain,"Two branches of integrable open quantum-group invariant $D_{n+1}^{(2)}$
quantum spin chains are known. For one branch (epsilon=0), a complete Bethe
ansatz solution has been proposed. However, the other branch (epsilon=1) has so
far resisted solution. In an effort to address this problem, we consider here
the simplest case n=1. We propose a Bethe ansatz solution, which however is not
complete, as it describes only the transfer-matrix eigenvalues with odd
degeneracy. We also consider a proposal for the missing eigenvalues.",1905.11144v2
2019-05-29,The Double Spin Asymmetry of Nitrogen in Elastic and Quasielastic Kinematics from a Solid Ammonia Dynamically Polarized Target,"Solid ammonia (NH$_3$) is commonly used as a dynamically polarized proton
target for electron and muon scattering cross-section asymmetry measurements.
As spin 1$^{+}$ particles, the $^{14}$N nuclei in the target are also polarized
and contribute a non-trivial asymmetry background that should be addressed. We
describe here a method to extract the nitrogen contribution to the asymmetry,
and report the cross-section asymmetries of electron-nitrogen scattering at
beam energies of $E=1.7$ GeV and $E=2.2$ GeV, and momentum transfer of
$Q^{2}=0.023-0.080$ GeV$^{2}$.",1905.12550v3
2019-08-09,Spin-1/2 Ising-Heisenberg Cairo pentagonal model in the presence of an external magnetic field: Effect of Landé g-factors,"In the present paper, a study of the magnetic properties of a spin-1/2
Ising-Heisenberg Cairo pentagonal structure is presented. The model has been
investigated in Ref. [34] in the absence of external magnetic field. Here, we
consider the effects of an external tunable magnetic field. By using the
transfer matrix approach, we investigate the magnetic ground-state phase
transition, the low-temperature magnetization process, and how the magnetic
field influences the various thermodynamic parameters such as entropy, internal
energy and specific heat. It is shown that the model exhibits intermediate
magnetization plateaux accompanied by a double-peak in the specific heat curve
versus temperature. The position of each magnetization jump is in accordance
with the merging and/or separation of the two peaks in the specific heat curve.
Considering different g-factors for the nodal Ising spins and spin dimers also
results in arising different intermediate plateaux and to remarkable
alterations of the thermodynamic properties of the model.",1908.04676v3
2019-09-26,The Fundamentals of the 21-cm Line,"We review some of the fundamental physics necessary for computing the
highly-redshifted spin-flip background. We first discuss the radiative transfer
of the 21-cm line and define the crucial quantities of interest. We then review
the processes that set the spin temperature of the transition, with a
particular focus on Wouthuysen-Field coupling, which is likely to be the most
important process during and after the Cosmic Dawn. Finally, we discuss
processes that heat the intergalactic medium during the Cosmic Dawn, including
the scattering of Lyman-alpha, cosmic microwave background, and X-ray photons.",1909.13740v1
2019-10-02,Magnetic Scattering Chapter,"The present chapter reviews current neutron and x-ray scattering techniques
employed to elucidate the magnetic structures and spin dynamics of magnetic
materials. Both techniques provide measurements as a function of the energy and
the momentum transferred from the spin system to the probe particles, in terms
of five-dimensional data sets as a function of various thermodynamic fields at
the control of the experimenter. These scattering techniques yield fundamental
information about the equal-time correlations such the magnetic configuration
and symmetry, as well as the dynamics that determine the exchange interactions
for prototypical systems that behave as linear, planar, or three-dimensional
systems. Historically, neutron scattering has been the magnetic scattering
technique of choice for such investigations, but the extraordinary advances in
resonant x-ray scattering techniques have enable new types of magnetic
scattering measurements. The type of information obtained with the two
techniques is largely complementary and depends on the interests of the
investigators. We discuss these possibilities and provide numerous examples of
the techniques applied to different classes of magnetic systems.",1910.01218v1
2019-11-08,Core-level x-ray photoemission and Raman spectroscopy studies on electronic structures in Mott-Hubbard type nickelate oxide NdNiO$_2$,"We perform core-level X-ray photoemission spectroscopy (XPS) and electronic
Raman scattering studies of electronic structures and spin fluctuations in the
bulk samples of the nickelate oxide NdNiO$_2$. According to Nd $3d$ and O $1s$
XPS spectra, we conclude that NdNiO$_2$ has a large transfer energy. From the
analysis of the main line of the Ni $2p_{3/2}$ XPS, we confirm the NiO$_2$
planes in NdNiO$_2$ are of Mott-Hubbard type in the Zaanen-Sawatzky-Allen
scheme. The two-magnon peak in the Raman scattering provides direct evidence
for the strong spin-fluctuation in NdNiO$_2$. The peak position determines the
antiferromagnetic exchange $J=25$~meV. Our experimental results agree well with
our previous theoretical results.",1911.03177v2
2020-02-06,Controlling magnetic correlations in a driven Hubbard system far from half-filling,"We propose using ultracold fermionic atoms trapped in a periodically shaken
optical lattice as a quantum simulator of the t-J Hamiltonian, which describes
the dynamics in doped antiferromagnets and is thought to be relevant to the
problem of high-temperature superconductivity in the cuprates. We show
analytically that the effective Hamiltonian describing this system for
off-resonant driving is the t-J model with additional pair hopping terms, whose
parameters can all be controlled by the drive. We then demonstrate numerically
using tensor network methods for a 1D lattice that a slow modification of the
driving strength allows near-adiabatic transfer of the system from the ground
state of the underlying Hubbard model to the ground state of the effective t-J
Hamiltonian. Finally, we report exact diagonalization calculations illustrating
the control achievable on the dynamics of spin-singlet pairs in 2D lattices
utilising this technique with current cold-atom quantum-simulation technology.
These results open new routes to explore the interplay between density and spin
in strongly-correlated fermionic systems through their out-of-equilibrium
dynamics.",2002.02312v2
2020-02-21,Coexistence of localized Gibbs measures and delocalized gradient Gibbs measures on trees,"We study gradient models for spins taking values in the integers (or an
integer lattice), which interact via a general potential depending only on the
differences of the spin values at neighboring sites, located on a regular tree
with d + 1 neighbors. We first provide general conditions in terms of the
relevant p-norms of the associated transfer operator Q which ensure the
existence of a countable family of proper Gibbs measures. Next we prove
existence of delocalized gradient Gibbs measures, under natural conditions on
Q. This implies coexistence of both types of measures for large classes of
models including the SOS-model, and heavy-tailed models arising for instance
for potentials of logarithmic growth.",2002.09363v2
2020-02-24,Metal-free magnetism in chemically doped covalent organic frameworks,"Organic and molecule-based magnets are not easily attainable, because to
introduce stable paramagnetic centers to pure organic systems is challenging.
Crystalline covalent organic frameworks (COFs) with high designability and
chemical diversity constitute ideal platforms to access intriguing magnetic
phenomena of organic materials. In this work, we proposed a general approach to
attain unpaired electron spin and metal-free magnetism in narrow-band COFs by
chemical doping. By using density functional theory calculations, we found that
dopants with energy-matched frontier orbitals to COFs not only inject charges
to them but also further localize the charges through orbital hybridization and
formation of supramolecular charge-transfer complex. The localized states
enable stable paramagnetic centers introduced to nonmagnetic COFs. Based on
this discovery, we designed two new COFs with narrow valence band, which show
prospective magnetism after doping with iodine. Further, we unraveled magnetic
anisotropy in two-dimensional COFs and showed that both spin-conduction and
magnetic interactions can be modulated by manipulating the building blocks of
COFs. Our work highlights a practical scenario to attain magnetism in COFs and
other organic materials, which hold great promise for applications in organic
spintronic devices.",2002.10216v2
2020-03-08,Influence of the velocity barrier on the massive Dirac electron transport in a monolayer MoS$_{2}$ quantum structure,"Using the transfer matrix method, spin- and valley-dependent electron
transport properties modulated by the velocity barrier were studied in the
normal/ferromagnetic/normal monolayer MoS$_{2}$ quantum structure. Based on
Snell's Law in optics, we define the velocity barrier as $\xi=v_{2}/v_{1}$ by
changing the Fermi velocity of the intermediate ferromagnetic region to obtain
a deflection condition during the electron transport process in the structure.
The results show that both the magnitude and the direction of spin- and
valley-dependent electron polarization can be regulated by the velocity
barrier. $-100\%$ polarization of spin- and valley-dependent electron can be
achieved for $\xi>1$, while $100\%$ polarization can be obtained for $\xi<1$.
Furthermore, it is determined that perfect spin and valley transport always
occur at a large incident angle. In addition, the spin- and valley-dependent
electron transport considerably depends on the length $k_{F}L$ and the gate
voltage $U(x)$ of the intermediate ferromagnetic region. These findings provide
an effective method for designing novel spin and valley electronic devices.",2003.03718v1
2020-04-02,Electronic Correlation and Geometrical Frustration in Molecular Solids -- A Systematic ab initio Study of $β^\prime$-$X$[Pd(dmit)$_{2}$]$_{2}$,"We systematically derive low-energy effective Hamiltonians for molecular
solids $\beta^\prime$-$X$[Pd(dmit)$_{2}$]$_{2}$ ($X$ represents a cation) using
ab initio density functional theory calculations and clarify how the cation
controls the inter-dimer transfer integrals and the interaction parameters. The
effective models are solved using the exact diagonalization method and the
antiferromagnetic ordered moment is shown to be significantly suppressed around
the spin-liquid candidate of $X$=EtMe$_{3}$Sb, which is reported in
experiments. We also show that both the geometrical frustration and the
off-site interactions play essential roles in the suppression of
antiferromagnetic ordering. This systematic derivation and analysis of the
low-energy effective Hamiltonians offer a firm basis to clarify the nature of
the quantum spin liquid found in
$\beta^\prime$-EtMe$_{3}$Sb[Pd(dmit)$_{2}$]$_{2}$.",2004.00970v2
2020-04-03,"Real-time ab initio simulation of inelastic electron scattering using the exact, density functional, and alternative approaches","To investigate inelastic electron scattering, which is ubiquitous in various
fields of study, we carry out ab initio study of the real-time dynamics of a
one-dimensional electron wave packet scattered by a hydrogen atom using
different methods: the exact solution, the solution provided by time-dependent
density functional theory (TDDFT), and the solutions given by alternative
approaches. This research not only sheds light on inelastic scattering
processes but also verifies the capability of TDDFT in describing inelastic
electron scattering. We revisit the adiabatic local-density approximation
(ALDA) in describing the excitation of the target during the scattering process
along with a self-interaction correction and spin-polarized calculations. Our
results reveal that the ALDA severely underestimates the energy transferred in
the regime of low incident energy particularly for a spin-singlet system. After
demonstrating alternative approaches, we propose a hybrid ab initio method to
deal with the kinetic correlation alongside TDDFT. This hybrid method would
facilitate first-principles studies of systems in which the correlation of a
few electrons among many others is of interest.",2004.01802v1
2020-04-14,Probing photo-induced rearrangements in the NdNiO$_{3}$ magnetic spiral with polarization-sensitive ultrafast resonant soft x-ray scattering,"We use resonant soft X-ray diffraction to track the photo-induced dynamics of
the antiferromagnetic structure in a NdNiO$_{3}$ thin film. Femtosecond laser
pulses with a photon energy of 0.61 eV, resonant with electron transfer between
long-bond and short-bond nickel sites, are used to excite the material and
drive an ultrafast insulator-metal transition. Polarization sensitive soft
X-ray diffraction, resonant to the nickel L$_{3}$-edge, then probes the
evolution of the underlying magnetic spiral as a function of time delay with 80
picosecond time resolution. By modelling the azimuthal dependence of the
scattered intensity for different linear X-ray polarizations, we benchmark the
changes of the local magnetic moments and the spin alignment. The measured
changes are consistent with a reduction of the long-bond site magnetic moments
and an alignment of the spins towards a more collinear structure at early time
delays.",2004.06752v2
2020-06-25,Entanglement dynamics and fractional quantum state transport in the spin-$\frac{1}{2}$ triangular plaquette,"The dramatic growth of research areas within the province of quantum state
transmission (QST) is rapidly accelerating. An important insight to understand
the process of QST can be fulfilled by considering the dynamical behavior of
its entanglement content. One well-established approach to continuously
transfer quantum states is utilizing spin structures. Here, from the view of
entanglement propagation, we disclose the signature of fractional QST
possibilities. In the present work, we proposed a form of spin-$\frac{1}{2}$
triangular plaquette whose Hamiltonian entails the spin-orbit coupling on the
rungs and exchange interaction over the legs. The feature of such a system is
that the time instants of QST emerge in a discrete fashion, thereby the values
of exchange interactions associated with these moments behave fractionally.
Importantly, it is found that for special values of magnetic interaction, QST
has singularity i.e., the entanglement propagation is forbidden. In addition,
the finite-size nature of this system makes it possible for us to read the
nexus between time crystallinity and symmetry breaking. The development of our
knowledge about time crystalline symmetry and its breaking helps us to
understand the defined concept and fundamental physics of this phenomenon.",2006.14187v1
2020-08-05,Effects of Sr-doping on the electronic and spin-state properties of infinite-layer nickelates,"The recent discovery of high-T$_{c}$ superconductivity (HTS) in Sr-doped
NdNiO$_2$ has sparked a renewed interest in investigating nickelates as cuprate
counterparts. Parent cuprates [Cu$^{2+}$: d$^9$] are antiferromagnetic
charge-transfer insulators with the involvement of a single d$_{x^2-y^2}$ band
around the Fermi level and strong $p-d$ hybridization. In contrast,
isoelectronic NdNiO$_2$ [Ni$^+$: d$^9$] is metallic with a d$_{x^2-y^2}$ band
self-doped by Nd-d states. Using first-principles calculations, we study the
effect of Sr-doping in the electronic and magnetic properties of infinite-layer
nickelates as well as the nature of the holes. We find that hole doping tends
to make the material more cuprate-like as it minimizes the self-doping effect,
it enhances the $p-d$ hybridization, and it produces low-spin (S=0,
non-magnetic) Ni$^{2+}$ dopants in analogy with the S=0 Zhang-Rice singlets
that appear in cuprates.",2008.02237v1
2020-08-14,Magnetic and charge orders in the ground state of the Emery model -- accurate numerical results,"We perform extensive auxiliary-field quantum Monte Carlo (AFQMC) calculations
for the three-band Hubbard (Emery) model in order to study the ground-state
properties of Copper-Oxygen planes in the cuprates. Employing cutting-edge
AFQMC techniques with a self-consistent gauge constraint in auxiliary-field
space to control the sign problem, we reach supercells containing around 500
atoms to capture collective modes in the charge and spin orders and
characterize the behavior in the thermodynamic limit. The self-consistency
scheme interfacing with generalized Hartree-Fock calculations allows high
accuracy in AFQMC to resolve small energy scales, which is crucial for
determining the complex candidate orders in such a system. We present detailed
information on the charge order, spin order, momentum distribution, and
localization properties as a function of charge-transfer energy for the the
under-doped regime. In contrast with the stripe and spiral orders under
hole-doping, we find that the corresponding 1/8 electron-doped system exhibits
purely antiferromagnetic order in the three-band model, consistent with the
asymmetry between electron and hole-doping in the phase diagram of cuprates.",2008.06527v1
2020-08-26,Extensive Rényi entropies in matrix product states,"We prove that all R\'enyi entanglement entropies of spin-chains described by
generic (gapped), translational invariant matrix product states (MPS) are
extensive for disconnected sub-systems: All R\'enyi entanglement entropy
densities of the sub-system consisting of every k-th spin are non-zero in the
thermodynamic limit if and only if the state does not converge to a product
state in the thermodynamic limit. Furthermore, we provide explicit lower bounds
to the entanglement entropy in terms of the expansion coefficient of the
transfer operator of the MPS and spectral properties of its fixed point in
canonical form. As side-result we obtain a lower bound for the expansion
coefficient and singular value distribution of a primitve quantum channel in
terms of its Kraus-rank and entropic properties of its fixed-point. For unital
quantum channels this yields a very simple lower bound on the distribution of
singular values and the expansion coefficient in terms of the Kraus-rank.
Physically, our results are motivated by questions about equilibration in
many-body localized systems, which we review.",2008.11764v2
2020-09-01,Radical pairs may play a role in xenon-induced general anesthesia,"Understanding the mechanisms underlying general anesthesia would be a key
step towards understanding consciousness. The process of xenon-induced general
anesthesia has been shown to involve electron transfer, and the potency of
xenon as a general anesthetic exhibits isotopic dependence. We propose that
these observations can be explained by a mechanism in which the xenon nuclear
spin influences the recombination dynamics of a naturally occurring radical
pair of electrons. We develop a simple model inspired by the body of work on
the radical-pair mechanism in cryptochrome in the context of avian
magnetoreception, and we show that our model can reproduce the observed
isotopic dependence of the general anesthetic potency of xenon in mice. Our
results are consistent with the idea that radical pairs of electrons with
entangled spins could be important for consciousness.",2009.01661v2
2020-09-04,Magnon-induced Giant Anomalous Nernst Effect in Single Crystal MnBi,"Thermoelectric modules are a promising approach to energy harvesting and
efficient cooling. In addition to the longitudinal Seebeck effect, recently
transverse devices utilizing the anomalous Nernst effect (ANE) have attracted
interest. For high conversion efficiency, it is required that the material
should have a large ANE thermoelectric power and low electrical resistance, the
product of which is the ANE conductivity. ANE is usually explained in terms of
intrinsic contributions from Berry curvature. Our observations suggest that
extrinsic contributions also matter. Studying single-crystal MnBi, we find a
very high ANE thermopower (~10 $\mu$V/K) under 0.6 T at 80 K, and a transverse
thermoelectric conductivity of over 40 A/Km. With insight from theoretical
calculations, we attribute this large ANE predominantly to a new advective
magnon contribution arising from magnon-electron spin-angular momentum
transfer. We propose that introducing large spin-orbit coupling into
ferromagnetic materials may enhance the ANE through the extrinsic contribution
of magnons.",2009.02211v3
2020-09-14,Incidence of Quantum Confinement on Dark Triplet Excitons in Carbon Nanotubes,"Photophysics of single-wall carbon nanotubes (SWCNTs) is intensively studied
due to their potential application in light harvesting and optoelectronics.
Excited states of SWCNTs form strongly bound electron-hole pairs, excitons, of
which only singlet excitons participate in application relevant optical
transitions. Long-living spin-triplet states hinder applications but they
emerge as candidates for quantum information storage. Therefore knowledge of
the triplet exciton energy structure, in particular in a SWCNT chirality
dependent manner, is greatly desired. We report the observation of light
emission from triplet state recombination, i.e. phosphorescence, for several
SWCNT chiralities using a purpose-built spectrometer. This yields the
singlet-triplet gap as a function of SWCNT diameter and it follows predictions
based on quantum confinement effects. Saturation under high microwave power (up
to 10 W) irradiation allows to determine the spin-relaxation time for triplet
states. Our study sensitively discriminates whether the lowest optically active
state is populated from an excited state on the same nanotube or through
F\""orster exciton energy transfer from a neighboring nanotube.",2009.06314v1
2020-09-23,An endoreversible quantum heat engine driven by atomic collisions,"Quantum heat engines are subjected to quantum fluctuations related to their
discrete energy spectra. Such fluctuations question the reliable operation of
quantum engines in the microscopic realm. We here realize an endoreversible
quantum Otto cycle in the large quasi-spin states of Cesium impurities immersed
in an ultracold Rubidium bath. Endoreversible machines are internally
reversible and irreversible losses only occur via thermal contact. We employ
quantum control over both machine and bath to suppress internal dissipation and
regulate the direction of heat transfer that occurs via inelastic spin-exchange
collisions. We additionally use full-counting statistics of individual atoms to
monitor heat exchange between engine and bath at the level of single quanta,
and evaluate average and variance of the power output. We optimize the
performance as well as the stability of the quantum engine, achieving high
efficiency, large power output and small power output fluctuations.",2009.10946v1
2020-10-08,Chiral Hinge Magnons in Second-Order Topological Magnon Insulators,"When interacting spins in condensed matter order ferromagnetically, their
ground state wave function is topologically trivial. Nonetheless, in two
dimensions, the ferromagnetic state can support spin excitations with
nontrivial topology, an exotic state known as topological magnon insulator
(TMI). Here, we theoretically unveil and numerically confirm a novel
ferromagnetic state in three dimensions dubbed second-order TMI, whose
hallmarks are excitations at its hinges, where facets intersect. Since
ferromagnetism naturally comes with broken time-reversal symmetry, the hinge
magnons are chiral, rendering backscattering impossible. Hence, they trace out
a three-dimensional path about the sample unimpeded by defects and are
topologically protected by the spectral gap. They are remarkably robust against
disorder and simultaneously highly tunable by atomic-level engineering of the
sample termination. Our findings empower magnonics with the tools of
higher-order topology, a promising route to combine low-energy information
transfer free of Joule heating with three-dimensional vertical integration.",2010.04142v1
2020-11-11,Hybrid Berezinskii-Kosterlitz-Thouless and Ising topological phase transition in the generalized two-dimensional XY model using tensor networks,"In tensor network representation, the partition function of a generalized
two-dimensional XY spin model with topological integer and half-integer vortex
excitations is mapped to a tensor product of one-dimensional quantum transfer
operator, whose eigen-equation can be solved by an algorithm of variational
uniform matrix product states. Using the singularities of the entanglement
entropy, we accurately determine the complete phase diagram of this model. Both
the integer vortex-antivortex binding and half-integer vortex-antivortex
binding phases are separated from the disordered phase by the usual
Berezinskii-Kosterlitz-Thouless (BKT) transitions, while a continuous
topological phase transition exists between two different vortex binding
phases, exhibiting a logarithmic divergence of the specific heat and
exponential divergence of the spin correlation length. A new hybrid BKT and
Ising universality class of topological phase transition is thus established.
We further prove that three phase transition lines meets at a multi-critical
point, from which a deconfinement crossover line extends into the disordered
phase.",2011.05682v2
2020-12-17,Entangling nuclear spins in distant quantum dots via an electron bus,"We propose a protocol for the deterministic generation of entanglement
between two ensembles of nuclear spins surrounding two distant quantum dots.
The protocol relies on the injection of electrons with definite polarization in
each quantum dot and the coherent transfer of electrons from one quantum dot to
the other. Computing the exact dynamics for small systems, and using an
effective master equation and approximate non-linear equations of motion for
larger systems, we are able to confirm that our protocol indeed produces
entanglement for both homogeneous and inhomogeneous systems. Last, we analyze
the feasibility of our protocol in several current experimental platforms.",2012.09507v2
2020-12-29,Topological turbulence in spin-orbit-coupled driven-dissipative quantum fluids of light generates high angular momentum states,"We demonstrate the formation of a high angular momentum turbulent state in an
exciton-polariton quantum fluid with TE-TM Spin-Orbit Coupling (SOC). The
transfer of particles from quasi-resonantly cw pumped \spl component to \sm
component is accompanied with the generation of a turbulent gas of quantum
vortices by inhomogeneities. We show that this system is unstable with respect
to the formation of bogolons at a finite wave vector, controlled by the laser
detuning. In a finite-size cavity, the domains with this wave vector form a
ring-like structure along the border of a cavity, with a gas of mostly
same-sign vortices in the center. The total angular momentum is imposed by the
sign of TE-TM SOC, the wave vector of instability, and the cavity size. This
effect can be detected experimentally via local dispersion measurements or by
interference. The proposed configuration thus allows simultaneous experimental
studies of quantum turbulence and high-angular momentum states in
continuously-pumped exciton-polariton condensates.",2012.14814v1
2021-02-10,Star-topology Registers: NMR and Quantum Information Perspectives,"Quantum control of large spin registers is crucial for many applications
ranging from spectroscopy to quantum information. A key factor that determines
the efficiency of a register for implementing a given information processing
task is its network topology. One particular type, called star-topology,
involves a central qubit uniformly interacting with a set of ancillary qubits.
A particular advantage of the star-topology quantum registers is in the
efficient preparation of large entangled states, called NOON states, and their
generalized variants. Thanks to the robust generation of such correlated
states, spectral simplicity, ease of polarization transfer from ancillary
qubits to the central qubit, as well as the availability of large
spin-clusters, the star-topology registers have been utilized for several
interesting applications over the last few years. Here we review some recent
progress with the star-topology registers, particularly via nuclear magnetic
resonance methods.",2102.05203v1
2021-02-10,Optical control of the density and spin spatial profiles of a planar Bose gas,"We demonstrate the arbitrary control of the density profile of a
two-dimensional Bose gas by shaping the optical potential applied to the atoms.
We use a digital micromirror device (DMD) directly imaged onto the atomic cloud
through a high resolution imaging system. Our approach relies on averaging the
response of many pixels of the DMD over the diffraction spot of the imaging
system, which allows us to create an optical potential with arbitrary grey
levels and with micron-scale resolution. The obtained density distribution is
optimized with a feedback loop based on the measured absorption images of the
cloud. Using the same device, we also engineer arbitrary spin distributions
thanks to a two-photon Raman transfer between internal ground states.",2102.05492v1
2021-02-18,"On the failure of effective-field theory in predicting a spurious spontaneous ordering and phase transition of Ising nanoparticles, nanoislands, nanotubes and nanowires","The present work clarifies a failure of the effective-field theory in
predicting a false spontaneous long-range order and phase transition of Ising
nanoparticles, nanoislands, nanotubes and nanowires with either zero- or
one-dimensional magnetic dimensionality. It is conjectured that the standard
formulation of the effective-field theory due to Honmura and Kaneyoshi
generally predicts for the Ising spin systems a spurious spontaneous long-range
order with nonzero critical temperature regardless of their magnetic
dimensionality whenever at least one Ising spin has coordination number greater
than two. The failure of the effective-field theory is exemplified on a few
paradigmatic exactly solved examples of zero- and one-dimensional Ising
nanosystems: star, cube, decorated hexagon, star of David, branched chain,
sawtooth chain, two-leg and hexagonal ladders. The presented exact solutions
illustrate eligibility of a few rigorous analytical methods for exact treatment
of the Ising nanosystems: exact enumeration, graph-theoretical approach,
transfer-matrix method and decoration-iteration transformation. The paper also
provides a substantial survey of the scientific literature, in which the
effective-field theory led to a false prediction of the spontaneous long-range
ordering and phase transition.",2102.09296v1
2021-03-02,Tests of collectivity in $^{98}$Zr by absolute transition rates,"Lifetimes of low-spin excited states in $^{98}$Zr were measured using the
recoil-distance Doppler-shift technique and the Doppler-shift attenuation
method. The nucleus of interest was populated in a
$^{96}$Zr($^{18}$O,$^{16}$O)$^{98}$Zr two-neutron transfer reaction at the
Cologne FN Tandem accelerator. Lifetimes of six low-spin excited states, of
which four are unknown, were measured. The deduced $B(E2)$ values were compared
with Monte Carlo shell model and interacting boson model with configuration
mixing calculations. Both approaches reproduce well most of the data but leave
challenging questions regarding the structure of some low lying states.",2103.01642v1
2021-03-04,Origin of the different electronic structure of Rh- and Ru-doped Sr2IrO4,"One way to induce insulator to metal transitions in the spin-orbit Mott
insulator Sr2IrO4 is to substitute iridium with transition metals (Ru, Rh).
However, this creates intriguing inhomogeneous metallic states, which cannot be
described by a simple doping effect. We detail the electronic structure of the
Ru-doped case with angle-resolved photoemission and show that, contrary to Rh,
it cannot be connected to the undoped case by a rigid shift. We further
identify bands below $E_F$ coexisting with the metallic ones that we assign to
non-bonding Ir sites. We rationalize the differences between Rh and Ru by a
different hybridization with oxygen, which mediates the coupling to Ir and
sensitively affects the effective doping. We argue that the spin-orbit coupling
does not control neither the charge transfer nor the transition threshold.",2103.03056v1
2021-01-18,"Spacetime geometry of spin, polarization, and wavefunction collapse","To incorporate quantum nonlocality into general relativity, we propose that
the preparation and measurement of a quantum system are simultaneous events. To
make progress in realizing this proposal, we introduce a spacetime geometry
that is endowed with particles which have no distinct points in their
worldlines; we call these particles 'pointons'. This new geometry recently
arose in nonnoetherian algebraic geometry. We show that on such a spacetime,
metrics are degenerate and tangent spaces have variable dimension. This
variability then implies that pointons are spin-$\tfrac 12$ fermions that
satisfy the Born rule, where a projective measurement of spin corresponds to an
actual projection of tangent spaces of different dimensions. Furthermore, the
$4$-velocities of pointons are necessarily replaced by their Hodge duals, and
this transfer from vector to pseudo-tensor introduces a free choice of
orientation that we identify with electric charge. Finally, a simple composite
model of electrons and photons results from the metric degeneracy, and from
this we obtain a new ontological model of photon polarization.",2103.03743v2
2021-03-23,Long-term coherent timing of the accreting millisecond pulsar IGR J17062-6143,"We report on a coherent timing analysis of the 163 Hz accreting millisecond
X-ray pulsar IGR J17062-6143. Using data collected with the Neutron Star
Interior Composition Explorer and XMM-Newton, we investigated the pulsar
evolution over a timespan of four years. We obtained a unique phase-coherent
timing solution for the stellar spin, finding the source to be spinning up at a
rate of $(3.77\pm0.09)\times 10^{-15}$ Hz/s. We further find that the $0.4-6$
keV pulse fraction varies gradually between 0.5% and 2.5% following a
sinusoidal oscillation with a $1210\pm40$ day period. Finally, we supplemented
this analysis with an archival Rossi X-ray Timing Explorer observation, and
obtained a phase coherent model for the binary orbit spanning 12 years,
yielding an orbital period derivative measurement of $(8.4\pm2.0) \times
10^{-12}$ s/s. This large orbital period derivative is inconsistent with a
binary evolution that is dominated by gravitational wave emission, and is
suggestive of highly non-conservative mass transfer in the binary system.",2103.12556v1
2021-04-30,An atomic bright vector soliton as an active particle,"Solitons in general are configurations of extended fields which move like
isolated particles. Vector bright solitons can occur in a two-component
self-attractive Bose-Einstein condensate. If the components of the condensate
have different chemical potentials, the total spin of the soliton can serve as
an internal energy depot that makes the soliton into an \emph{active} particle,
able to move against an external force using energy carried within the particle
-- if there is a dynamical mechanism for steadily transferring energy from
soliton spin into soliton motion. Here we present such a dynamical mechanism,
embed it in an experimentally feasible way within the larger system of a spinor
condensate mean field, and show how the mechanism works to realize a solitonic
active particle. In what can be considered a toy model for the project of going
beyond toy models for active particles, we test the robustness of the activity
mechanism by exploring a range of deformations to the simplest model for
embedding the nonlinear mechanism in the condensate system.",2104.15089v1
2021-04-30,Carbon-enhanced stars with short orbital and spin periods,"Many characteristics of dwarf carbon stars are broadly consistent with a
binary origin, including mass transfer from an evolved companion. While the
population overall appears to have old-disc or halo kinematics, roughly
2$\,$per cent of these stars exhibit H$\alpha$ emission, which in low-mass
main-sequence stars is generally associated with rotation and relative youth.
Its presence in an older population therefore suggests either irradiation or
spin-up. This study presents time-series analyses of photometric and
radial-velocity data for seven dwarf carbon stars with H$\alpha$ emission. All
are shown to have photometric periods in the range 0.2--5.2$\,$d, and orbital
periods of similar length, consistent with tidal synchronisation. It is
hypothesised that dwarf carbon stars with emission lines are the result of
close-binary evolution, indicating that low-mass, metal-weak or metal-poor
stars can accrete substantial material prior to entering a common-envelope
phase.",2105.00036v3
2021-05-04,T-W relation and free energy of the Heisenberg chain at a finite temperature,"A new nonlinear integral equation (NLIE) describing the thermodynamics of the
Heisenberg spin chain is derived based on the t-W relation of the quantum
transfer matrices. The free energy of the system in a magnetic field is thus
obtained by solving the NLIE. This method can be generalized to other lattice
quantum integrable models. Taking the SU(3)-invariant quantum spin chain as an
example, we construct the corresponding NLIEs and compute the free energy. The
present results coincide exactly with those obtained via other methods
previously.",2105.01352v2
2021-07-10,Excitation spectrum of spin-1 Kitaev spin liquids,"We study the excitation spectrum of the spin-1 Kitaev model using the
symmetric tensor network. By evaluating the virtual order parameters defined on
the virtual Hilbert space in the tensor network formalism, we confirm the
ground state is in a $\mathbb{Z}_2$ spin liquid phase. Using the correspondence
between the transfer matrix spectrum and low-lying excitations, we find that
contrary to the dispersive Majorana excitation in the spin-1/2 case, the
isotropic spin-1 Kitaev model has a dispersive charge anyon excitation. Bottom
of the gapped single-particle charge excitations are found at $\mathbf{K},
\mathbf{K}'=(\pm2\pi/3, \mp 2\pi/3)$, with a corresponding correlation length
of $\xi \approx 6.7$ unit cells. The lower edge of the two-particle continuum,
which is closely related to the dynamical structure factor measured in
inelastic neutron scattering experiments, is obtained by extracting the
excitations in the vacuum superselection sector in the anyon theory language",2107.04730v1
2021-07-21,Gluon gravitational structure of hadrons of different spin,"The gravitational form factors (GFFs) of hadrons encode the matrix elements
of the energy momentum tensor of QCD. These quantities describe how energy,
spin, and various mechanical properties of hadrons are carried by their quark
and gluon constituents. We present the gluon GFFs of the pion, nucleon, $\rho$
meson, and $\Delta$ baryon as functions of the squared momentum transfer $t$ in
the region $0 \leq -t < 2 \; \text{GeV}^2$, as determined in a lattice QCD
study with pion mass $m_{\pi} = 450(5) \; \text{MeV}$. By fitting the extracted
GFFs using multipole and z-parameter expansion functional forms, we extract
various gluon contributions to the energy, pressure, and shear force
distributions of the hadrons in the 3D and 2D Breit frames as well as in the
infinite momentum frame. We also obtain estimates for the corresponding gluon
mechanical and mass radii, as well as the forward-limit gluon contributions to
the momentum fraction and angular momentum of the hadrons.",2107.10368v4
2021-07-27,Hexagonalization of Fishnet integrals I: mirror excitations,"In this paper we consider a conformal invariant chain of $L$ sites in the
unitary irreducible representations of the group $SO(1,5)$. The $k$-th site of
the chain is defined by a scaling dimension $\Delta_k$ and spin numbers
$\frac{\ell_k}{2}$, $\frac{\dot{\ell}_k}{2}$. The model with open and fixed
boundaries is shown to be integrable at the quantum level and its spectrum and
eigenfunctions are obtained by separation of variables. The transfer matrices
of the chain are graph-builder operators for the spinning and inhomogeneous
generalization of squared-lattice ""fishnet"" integrals on the disk. As such,
their eigenfunctions are used to diagonalize the mirror channel of the the
Feynman diagrams of Fishnet conformal field theories. The separated variables
are interpreted as momentum and bound-state index of the $\textit{mirror
excitations}$ of the lattice: particles with $SO(4)$ internal symmetry that
scatter according to an integrable factorized $\mathcal{S}$-matrix in $(1+1)$
dimensions.",2107.13035v2
2021-07-16,Acoustic Geometric-Phase Meta-Array,"Metasurfaces based on geometric phase acquired from the conversion of the
optical spin states provide a robust control over the wavefront of light, and
have been widely employed for construction of various types of functional
metasurface devices. However, this powerful approach cannot be readily
transferred to the manipulation of acoustic waves because acoustic waves do not
possess the spin degree of freedom. Here, we propose the concept of acoustic
geometric-phase meta-array by leveraging the conversion of orbital angular
momentum of acoustic waves, where well-defined geometric-phases can be attained
through versatile topological charge conversion processes. This work extends
the concept of geometric-phase metasurface from optics to acoustics, and
provides a new route for acoustic wave control.",2108.04688v1
2021-08-17,Relativistic quantum-mechanical versus classical magnetic resonant scattering cross sections,"Radiative transfer calculations in strong (few $\times 10^{12}$ G) magnetic
fields, observed in X-ray pulsars, require accurate resonant differential
scattering cross sections. Such cross sections exist, but they are quite
cumbersome. Here we compare the classical (non-relativistic) with the
quantum-mechanical (relativistic) resonant differential scattering cross
sections and offer a prescription for the use of the much simpler classical
expressions with impressively accurate results. We have expanded the
quantum-mechanical differential cross sections and kept terms up to first order
in $\epsilon \equiv E/m_ec^2$ and $B \equiv {\cal B}/{\cal B}_{cr}$, where $E$
is the photon energy and ${\cal B}_{cr}$ is the critical magnetic field, and
recovered the classical differential cross sections plus terms that are due to
spin flip, which is a pure quantum-mechanical phenomenon. Adding by hand the
spin-flip terms to the polarization-dependent classical differential cross
sections, we find that they are in excellent agreement with the quantum
mechanical ones for all energies near resonance and all angles. We have plotted
both of them and the agreement is impressive. We give a prescription for the
use of the classical differential cross sections that guarantees very accurate
results.",2108.07568v1
2021-08-18,Root patterns and energy spectra of quantum integrable systems without $U(1)$ symmetry: antiperiodic $XXZ$ spin chain,"Finding out root patterns of quantum integrable models is an important step
to study their physical properties in the thermodynamic limit. Especially for
models without $U(1)$ symmetry, their spectra are usually given by
inhomogeneous $T-Q$ relations and the Bethe root patterns are still unclear. In
this paper with the antiperiodic $XXZ$ spin chain as an example, an analytic
method to derive both the Bethe root patterns and the transfer-matrix root
patterns in the thermodynamic limit is proposed. Based on them the ground state
energy and elementary excitations in the gapped regime are derived. The present
method provides an universal procedure to compute physical properties of
quantum integrable models in the thermodynamic limit.",2108.08060v2
2021-08-27,Reservoir-assisted energy migration through multiple spin-domains,"The transfer of energy through a network of nodes is fundamental to both how
nature and current technology operates. Traditionally we think of the nodes in
a network being coupled to channels that connect them and then energy is passed
from node to channel to node until it reaches its targeted site. Here we
introduce an alternate approach to this where our channels are replaced by
collective environments (or actually reservoirs) which interact with pairs of
nodes. We show how energy initially located at a specific node can arrive at a
target node - even though that environment may be at zero temperate. Further we
show that such a migration occurs on much faster time scales than the damping
rate associated with a single spin coupled to the reservoir. Our approach shows
the power of being able to tailor both the system & environment and the
symmetries associated with them to provide new directions for future quantum
technologies.",2108.12119v1
2021-09-06,Generation of relativistic positrons carrying intrinsic orbital angular momentum,"High energy positrons can be efficiently created through high-energy photons
splitting into electron-positron pairs under the influence of the Coulomb
field. Here we show that a new degree of freedom-the intrinsic orbital angular
momentum (OAM) can be introduced into relativistic positrons when the incident
photons are twisted. We developed the full-twisted scattering theory to
describe the transfer of angular momentum before and after the interaction. It
is found that the total angular momentum (TAM) of the photon is equally
distributed among the positron and electron. For each photon TAM value, the
generated leptons gain higher average OAM number when the photon spin is
anti-parallel to its TAM. The impact of photon polarization on the OAM spectrum
profile and the scattering probability is more significant at small photon TAM
numbers, owing to the various interaction channels influenced by flipping the
photon spin. Our work provides the theoretical basis to study OAM physics in
particle scattering and to obtain copious relativistic vortex positrons through
the Beth-Heitler process.",2109.02234v1
2021-09-08,Triplet resonating valence bond theory and transition metal chalcogenides,"We develop a quantum spin liquid theory for quantum magnets with easy-plane
ferromagnetic exchange. These strongly entangled quantum states are obtained by
dimer coverings of 2D lattices with triplet $S = 1, m_z = 0$ bonds, forming a
triplet resonating valence bond (tRVB) state. We discuss the conditions and the
procedure to transfer well-known results from conventional singlet resonating
valence bond theory to tRVB. Additionally, we present mean field theories of
Abrikosov fermions on 2D triangular and square lattices, which can be
controlled in an appropriate large $N$ limit. We also incorporate the effect of
charge doping which stabilizes $p+ip$-wave superconductivity. Beyond the pure
theoretical interest, our study may help to resolve contradictory statements on
certain transition metal chalcogenides, including 1T-TaS$_2$, as a potential
tRVB spin-liquid.",2109.03851v1
2021-12-14,Scattering matrix of elementary excitations in the antiperiodic XXZ spin chain with η=iπ/3,"We study the thermodynamic limit of the antiperiodic XXZ spin chain with the
anisotropic parameter $\eta=\frac{\pi i}{3}$. We parameterize eigenvalues of
the transfer matrix by their zero points instead of Bethe roots. We obtain
patterns of the distribution of zero points. Based on them, we calculate the
ground state energy and the elementary excitations in the thermodynamic limit.
We also obtain the two-body scattering matrix of elementary excitations. Two
types of elementary excitations and three types of scattering processes are
discussed in detailed.",2112.07180v1
2021-12-19,Quantum Approximate Optimization Algorithm applied to the binary perceptron,"We apply digitized Quantum Annealing (QA) and Quantum Approximate
Optimization Algorithm (QAOA) to a paradigmatic task of supervised learning in
artificial neural networks: the optimization of synaptic weights for the binary
perceptron. At variance with the usual QAOA applications to MaxCut, or to
quantum spin-chains ground state preparation, the classical Hamiltonian is
characterized by highly non-local multi-spin interactions. Yet, we provide
evidence for the existence of optimal smooth solutions for the QAOA parameters,
which are transferable among typical instances of the same problem, and we
prove numerically an enhanced performance of QAOA over traditional QA. We also
investigate on the role of the QAOA optimization landscape geometry in this
problem, showing that the detrimental effect of a gap-closing transition
encountered in QA is also negatively affecting the performance of our
implementation of QAOA.",2112.10219v1
2022-01-11,"Experimental Verification of Charge Soliton Excitations in the Ionic Mott-Peierls Ferroelectric, TTF-CA","Strong coupling of charge, spin, and lattice in solids brings about emergent
elementary excitations with their intertwining and, in one dimension, solitons
are known as such. The charge-transferred organic ferroelectric, TTF-CA, has
been argued to host charge solitons; however, the existence of the charge
solitons remains unverified. Here, we demonstrate that the charge-transport gap
in the ionic Mott-Peierls insulating phase of TTF-CA is an order of magnitude
smaller than expected from quasiparticle excitations, however, being entirely
consistent with the charge soliton excitations. We further suggest that charge
and spin solitons move with similar diffusion coefficients in accordance with
their coexistence. These results provide a basis for the thermal excitations of
the emergent solitons.",2201.03889v1
2022-02-18,Phase-locking matter-wave interferometer of vortex states,"Matter-wave interferometer of ultracold atoms with different linear momenta
has been extensively studied in theory and experiment. The vortex matter-wave
interferometer with different angular momenta is applicable as a quantum sensor
for measuring the rotation, interatomic interaction, geometric phase, etc. Here
we report the first experimental realization of a vortex matter-wave
interferometer by coherently transferring the optical angular momentum to an
ultracold Bose condensate. After producing a lossless interferometer with atoms
only populating the two spin states, we demonstrate that the phase difference
between the interferences in the two spin states is locked on $\pi$. We also
demonstrate the robustness of this out-of-phase relation, which is independent
of the angular-momentum difference between the two interfering vortex states,
constituent of Raman optical fields and expansion of the condensate. The
experimental results agree well with the calculation from the unitary evolution
of wave packet in quantum mechanics. This work opens a new way to build a
quantum sensor and measure the atomic correlation in quantum gases.",2202.09001v1
2022-02-28,A Phase-Space Semiclassical Approach for Modeling Nonadiabatic Nuclear Dynamics with Electronic Spin,"Chemical relaxation phenomena, including photochemistry and electron transfer
processes, form a vigorous area of research in which nonadiabatic dynamics
plays a fundamental role. Here, we show that for nonadiabatic dynamics with two
electronic states and a complex-valued Hamiltonian that does not obey
time-reversal symmetry, the optimal semiclassical approach is to run surface
hopping dynamics on a set of phase-space adiabatic surfaces. In order to
generate such phase-adiabats, one must isolate a proper set of diabats and
apply a phase gauge transformation, before eventually diagonalizing the total
Hamiltonian (which is now parameterized by both R and P). The resulting
algorithm is valid in both the adiabatic and nonadiabatic limits, incorporates
all Berry curvature effects, and allows for the study of semiclassical
nonadiabatic dynamics in the presence of spin-orbit coupling and/or external
magnetic fields.",2202.13973v1
2022-03-23,Information conduction and convection in noiseless Vicsek flocks,"Physical interactions generally respect certain symmetries, such as
reciprocity and energy conservation, which survive in coarse grained isothermal
descriptions. Active many-body systems usually break such symmetries
intrinsically, on the particle level, so that their collective behavior is
often more naturally interpreted as a result of information exchange. Here, we
study numerically how information spreads from a ""leader"" particle through an
initially aligned flock, described by the Vicsek model without noise. In the
low-speed limit of a static spin lattice, we find purely conductive spreading,
reminiscent of heat transfer. Swarm motility and heterogeneity can break
reciprocity and spin conservation. But what seems more consequential for the
swarm response is that the dispersion relation acquires a significant
convective contribution along the leader's direction of motion.",2203.12316v2
2022-06-14,Frustration and ordering in Ising chain in an external magnetic field with third-neighbor interactions,"In this paper, the frustration properties of the Ising model on a
one-dimensional monoatomic equidistant lattice in an external magnetic field
are investigated, taking into account the exchange interactions of atomic spins
at the sites of the first, second, and third neighbors. Exact analytical
expressions for the thermodynamic functions of the system are obtained by the
Kramers--Wannier transfer-matrix method. A magnetic phase diagram of the ground
state of such a spin system is constructed and studied thoroughly. The points
and lines of frustrations of the system depending on the values and signs of
exchange interactions and on an external magnetic field are found. The criteria
for the occurrence of magnetic frustrations in the presence of competition
between the energies of exchange interactions and an external magnetic field
are formulated. The peculiar features are investigated and the values of
entropy and magnetization of the ground state of this model are obtained in the
frustration regime and beyond it. Various types of behavior of entropy,
magnetization, and magnetic susceptibility depending on the model parameters
are revealed.",2206.06753v1
2022-06-17,Optimal and robust experiment design for quantum state tomography of star-topology register,"While quantum state tomography plays a vital role in the verification and
benchmarking of quantum systems, it is an intractable task if the
controllability and measurement of quantum registers are constrained. In this
paper, we study the quantum state tomography of star-topology registers, in
which the individual addressability of peripheral spins is infeasible. Based on
the star-symmetry, we decompose the Hilbert space to alleviate the complexity
of tomography and design a compact strategy with minimum number of
measurements. By optimizing the parameterized quantum circuit for information
transfer, the robustness against measurement errors is also improved.
Furthermore, we apply this method to a 10-spin star-topology register and
demonstrate its ability to characterize large-scale systems. Our results can
help future investigations of quantum systems with constrained ability of
quantum control and measurement.",2206.08581v1
2022-09-18,Strong Dzyaloshinskii-Moriya Interaction in Monolayer CrI$_3$ on Metal Substrates,"Dzyaloshinskii-Moriya interaction (DMI) is the primary mechanism for
realizing real-space chiral spin textures, which are regarded as key components
for the next-generation spintronics. However, DMI arises from a perturbation
term of the spin-orbit interaction and is usually weak in pristine magnetic
semiconductors. To date, large DMI and the resulting skyrmions are only
realized in a few materials under stringent conditions. Using first-principles
calculations, we demonstrate that significant DMI occurs between
nearest-neighbor Cr atoms in two-dimensional (2D) magnetic semiconductor
CrI$_3$ on Au or Cu substrates. This exceptionally strong DMI is generated by
the interfacial charge transfer and weak chemical interactions between chromium
halides and metal substrates, which break the spatial inversion symmetry. These
findings highlight the significance of substrate effects in 2D magnets and
expand the inventory of feasible materials with strong DMI.",2209.08444v1
2022-10-06,Stacking order and interlayer coupling tuning the properties of charge density waves in layered 1T-NbSe_2,"Layered transition metal dichalcogenide 1T-NbSe_2 is a good candidate to
explore the charge density wave (CDW) and Mott physics. However, the effects of
stacking orders and interlayer coupling in CDW 1T-NbSe_2 are still less
explored and understood. Using density functional theory calculations, we
present a systematic study of the electronic and magnetic properties of
monolayer and layered CDW 1T-NbSe_2. Our results indicate that monolayer CDW
1T-NbSe_2 is a magnetic insulator with \sqrt13\times\sqrt13 periodic lattice
modulation. Nevertheless, the magnetic properties of bilayer CDWs 1T-NbSe_2 are
found stacking orders dependence. The mechanism is understood by the changes of
local magnetic moments in each layer due to spin charge transfer between
interlayers. Furthermore, the bulk CDW 1T-NbSe_2 opens a band gap with 0.02 eV
in 1\times 1 \times 2 supercell due to the interlayer spin coupling. We also
discover that the electronic structures of layered 1T-NbSe_2 show a strong
dependence on stacking configurations and dimensionality.",2210.02922v1
2022-10-23,Dynamics of direct impact accretion in degenerate binary systems,"We consider the gas dynamics in an accreting binary system of degenerate
stars within the framework of the Newtonian approximation. In such a system,
the accretion stream can impact the surface of a white dwarf (WD) or neutron
star (NS) as a result of the very compact orbit. This causes a loss of angular
momentumfrom the orbit and spin-up of the accretor. We construct approximations
for the specific angular momentum of the accreting matter which goes to spin up
the accretor and some other parameters of the system. It is shown that the
obtained approximation of the specific momentum is qualitatively different from
the widely used Keplerian formula. It should affect the boundary between
scenarios of immediate tidal disruption and slow mass loss of the donor in
WD-WD and NS-NS binaries, as well as the time of stable mass transfer in the
stripping scenario.",2210.12700v2
2022-10-24,"Separation of quadrupole, spin, and charge across the magnetic phases of a one-dimensional interacting spin-1 gas","We study the low-energy collective properties of a 1D spin-1 Bose gas using
bosonization. After giving an overview of the technique, emphasizing the
physical aspects, we apply it to the $S=1$ Bose-Hubbard Hamiltonian and find a
novel separation of the quadrupole-spin-charge sectors, confirmed by time-MPS
numerical simulations. Additionally, through the single particle spectrum, we
show the existence of the superfluid-Mott insulator transition and the point at
which the physics are described by a Heisenberg-like Hamiltonian. The magnetic
phase diagrams are found for both the superfluid and insulating regimes; the
latter is determined by decomposing the complete Heisenberg
bilinear-biquadratic Hamiltonian, which describes the Mott insulator, into
simpler, effective Hamiltonians. This allows us to keep our methods flexible
and transferable to other interesting interacting condensed matter systems.",2210.13586v2
2022-10-24,Switching between Mott-Hubbard and Hund physics in moiré quantum simulators,"Mott-Hubbard and Hund electron correlations have been realized thus far in
separate classes of materials. Here, we show that a single moir\'e homobilayer
encompasses both kinds of physics in a controllable manner. We develop a
microscopic multiband model that we solve by dynamical mean-field theory to
nonperturbatively address the local many-body correlations. We demonstrate how
tuning with twist angle, dielectric screening, and hole density allows us to
switch between Mott-Hubbard and Hund correlated states in a twisted WSe$_2$
bilayer. The underlying mechanism is based on controlling
Coulomb-interaction-driven orbital polarization and the energetics of
concomitant local singlet and triplet spin configurations. From a comparison to
recent experimental transport data, we find signatures of a filling-controlled
transition from a triplet charge-transfer insulator to a Hund-Mott metal. Our
finding establishes twisted transition metal dichalcogenides as a tunable
platform for exotic phases of quantum matter emerging from large local spin
moments.",2210.13652v3
2022-10-25,Microwave-optical double resonance in a erbium-doped whispering-gallery-mode resonator,"We showcase an erbium-doped whispering-gallery-mode resonator with optical
modes that display intrinsic quality factors better than $10^8$ (linewidths
less than 2 MHz), and coupling strengths to collective erbium transitions of up
to 2$\pi\times$1.2 GHz - enough to reach the ensemble strong coupling regime.
Our optical cavity sits inside a microwave resonator, allowing us to probe the
spin transition which is tuned by an external magnetic field. We show a
modified optically detected magnetic resonance measurement that measures
population transfer by a change in coupling strength rather than absorption
coefficient. This modification was enabled by the strong coupling to our modes,
and allows us to optically probe the spin transition detuned by more than the
inhomogeneous linewidth. We contrast this measurement with electron
paramagnetic resonance to experimentally show that our optical modes are
confined in a region of large microwave magnetic field and we explore how such
a geometry could be used for coherent microwave-optical transduction.",2210.13793v1
2022-11-03,Josephson Effect in NbS$_{2}$ van der Waals Junctions,"Van der Waals (vdW) Josephson junctions can possibly accelerate the
development of advanced superconducting device that utilizes the unique
properties of two-dimensional (2D) transition metal dichalcogenide (TMD)
superconductors such as spin-orbit coupling, spin-valley locking. Here, we
fabricate vertically stacked NbS$_{2}$/NbS$_{2}$ Josephson junctions using a
modified all-dry transfer technique and characterize the device performance via
systematic low-temperature transport measurements. The experimental results
show that the superconducting transition temperature of the NbS$_{2}$/NbS$_{2}$
Josephson junction is 5.84 K, and the critical current density reaches 3975
A/cm$^{2}$ at 2K. Moreover, we extract a superconducting energy gap
$\Delta=0.58$ meV, which is considerably smaller than that expected from the
single band s-wave Bardeen-Cooper-Schrieffer (BCS) model ($\Delta=0.89$ meV).",2211.01609v1
2023-01-09,A Quantum Mechanical Description of Photosensitization in Photodynamic Therapy using a Two-Electron Molecule Approximation,"A fundamental, Quantum Mechanical description of photoactivation of a generic
photosensitizer and the ensuing transfer of energy to endogenous oxygen as part
of the Type II pathway to photodamage during photodynamic therapy (PDT) is
presented. The PS and molecular oxygen are approximated as two-electron
molecules. Conservation of energy and of angular momenta of the two molecule
system are abided via selection rules throughout the four-stage process,
including initial states, absorption of a photon by the PS, conversion of the
PS to an excited spin triplet via intersystem crossing (ISC), and the
transition of molecular oxygen to an excited spin singlet state via a
Triplet-Triplet Exchange of electrons with the PS. The provided description of
photosensitization will provide students and researchers with a fundamental
introduction to PDT, while offering the broader population of Quantum Mechanics
and Physical Chemistry students an advanced example of quantum systems in an
applied, medical context.",2301.03653v1
2023-01-20,Quantum Control of Trapped Polyatomic Molecules for eEDM Searches,"Ultracold polyatomic molecules are promising candidates for experiments in
quantum science, quantum sensing, ultracold chemistry, and precision
measurements of physics beyond the Standard Model. A key, yet unrealized,
requirement of these experiments is the ability to achieve full quantum control
over the complex internal structure of the molecules. Here, we establish
coherent control of individual quantum states in a polyatomic molecule, calcium
monohydroxide (CaOH), and use these techniques to demonstrate a method for
searching for the electron electric dipole moment (eEDM). Optically trapped,
ultracold CaOH molecules are prepared in a single quantum state, polarized in
an electric field, and coherently transferred into an eEDM sensitive state
where an electron spin precession measurement is performed. To extend the
coherence time of the measurement, we utilize eEDM sensitive states with
tunable, near-zero magnetic field sensitivity. The spin precession coherence
time is limited by AC Stark shifts and uncontrolled magnetic fields. These
results establish a path for eEDM searches with trapped polyatomic molecules,
towards orders-of-magnitude improved experimental sensitivity to
time-reversal-violating physics.",2301.08656v1
2023-02-22,Magnetic Inclination Evolution of Accreting Neutron Stars in Intermediate/Low-Mass X-ray Binaries,"The magnetic inclination angle $\chi$, namely the angle between the spin and
magnetic axes of a neutron star (NS), plays a vital role in its observational
characteristics. However, there are few systematic investigations on its
long-term evolution, especially for accreting NSs in binary systems. Applying
the model of \citet{2021MNRAS.505.1775B} and the binary evolution code \mesa{},
we simultaneously simulate the evolution of the accretion rate, spin period,
magnetic field, and magnetic inclination angle of accreting NSs in
intermediate/low X-ray binaries (I/LMXBs). We show that the evolution of $\chi$
depends not only on the initial parameters of the binary systems, but also on
the mass transfer history and the efficiency of pulsar loss. Based on the
calculated results we present the characteristic distribution of $\chi$ for
various types of systems including ultracompact X-ray binaries, binary
millisecond pulsars, and ultraluminous X-ray sources, and discuss their
possible observational implications.",2302.11243v1
2023-02-22,Advanced magnon-optic effects with spin-wave leaky modes,"We numerically demonstrate the excitation of leaky spin waves (SWs) guided
along a ferromagnetic stripe by an obliquely incident SW beam on the thin film
edge placed below the stripe. During propagation, leaky waves emit energy back
to the layer in the form of plane waves and several laterally shifted parallel
SW beams. This resonance excitation, combined with interference effects of the
reflected and re-emitted waves, results in the magnonic Woods anomaly and
significant increase of the Goos-Hanchen shift magnitude. Hence, we provide a
unique platform to control SW reflection and to transfer SWs from a 2D platform
into the 1D guiding mode that can be used to form a transdimensional magnonic
router.",2302.11507v3
2023-02-25,Finite-momentum Cooper pairing in proximitized altermagnets,"Finite-momentum Cooper pairing is an unconventional form of superconductivity
that is widely believed to require finite magnetization. Altermagnetism is an
emerging magnetic phase with highly anisotropic spin-splitting of specific
symmetries, but zero net magnetization. Here, we study Cooper pairing in
metallic altermagnets connected to conventional $s$-wave superconductors.
Remarkably, we find that the Cooper pairs induced in the altermagnets acquire a
finite centre-of-mass momentum, despite the \textit{zero} net magnetization in
the system. This anomalous Cooper-pair momentum strongly depends on the
propagation direction and exhibits unusual symmetric patterns. Furthermore, it
yields several unique features: (i) highly orientation-dependent oscillations
in the order parameter, (ii) controllable 0-$\pi$ transitions in the Josephson
supercurrent, (iii) large-oblique-angle Cooper-pair transfer trajectories in
junctions parallel with the direction where spin splitting vanishes, and (iv)
distinct Fraunhofer patterns in junctions oriented along different directions.
Finally, we discuss the implementation of our predictions in candidate
materials such as RuO$_{2}$ and KRu$_{4}$O$_{8}$.",2302.13185v2
2023-03-01,Robustness of Energy Landscape Controllers for Spin Rings under Coherent Excitation Transport,"The design and analysis of controllers to regulate excitation transport in
quantum spin rings presents challenges in the application of classical feedback
control techniques to synthesize effective control, and generates results in
contradiction to the expectations of classical control theory. In this paper,
we examine the robustness of controllers designed to optimize the fidelity of
an excitation transfer to uncertainty in system and control parameters. We use
the logarithmic sensitivity of the fidelity error as the measure of robustness,
drawing on the classical control analog of the sensitivity of the tracking
error. In our analysis we demonstrate that quantum systems optimized for
coherent transport demonstrate significantly different correlation between
error and the log-sensitivity depending on whether the controller is optimized
for readout at an exact time T or over a time-window about T.",2303.00142v3
2023-04-07,Frustrations on decorated triangular lattice in Ising model,"We study the frustration properties of the Ising model on a decorated
triangular lattice with an arbitrary number of decorating spins on all lattice
bonds in the framework of an exact analytical approach based on the
Kramers--Wannier transfer matrix method. Expressions for the entropy, heat
capacity, and spontaneous magnetization of the lattice are obtained, including
the residual (zero-temperature) entropy and residual (zero-temperature)
spontaneous magnetization of the system. The existence of magnetic frustrations
in such a model and their influence on the behavior of the thermodynamic
functions of the system are shown. The new and most important result of our
study is related to the description of the possible coexistence of frustrations
and long-range magnetic order in partially ordered spin systems.",2304.03818v1
2023-04-20,Theory of Singlet Fission in Carotenoid Dimers,"We develop a theory of singlet fission in carotenoid dimers. Following
photoexcitation of the 'bright' state (i.e., a singlet electron-hole pair) in a
single carotenoid, the first step in the singlet fission process is ultrafast
intramolecular conversion into the highly-correlated 'dark' (or 2Ag) state.
This state has both entangled singlet triplet-pair and charge-transfer
character. Our theory is predicated on the assumption that it is the singlet
triplet-pair component of the 'dark' state that undergoes bimolecular singlet
fission. We use valence bond theory to develop a minimal two-chain model of the
triplet-pair states. The single and double chain triplet-pair spectrum is
described, as this helps explain the dynamics and the equilibrated populations.
We simulate the dynamics of the initial entangled pair state using the quantum
Liouville equation, including both spin-conserving and spin-nonconserving
dephasing processes. By computing the intrachain and interchain singlet,
triplet and quintet triplet-pair populations, we show that singlet fission
depends critically on the interchain coupling and the driving potential (that
determines endothermic versus exothermic fission). We also show that the
Horodecki pair-entanglement provides a good metric for singlet fission.",2304.10404v1
2023-04-27,All the matrix elements of covariant tensor currents of massless particles in the covariant formulation,"We present an efficient algorithm for constructing all the matrix elements of
covariant tensor currents of massless particles of arbitrary spins in the
covariant formulation. The construction of matrix elements can be taken simply
by assembling the basic matrix elements which are derived from the basic
three-point vertices. We obtain the selection rules for the decay of an
off-shell massive particle into two identical massless particles which are the
generalization of the Landau-Yang (LY) theorem. After showing how to identify
fully the discontinuity between the matrix elements for the spacelike and
lightlike momentum transfers, we derive all the matrix elements of conserved
tensor currents of massless particles including high spins, from which the
Weinberg and Witten (WW) theorem is automatically extracted with additional
limits on the particles.",2304.14083v3
2023-05-14,Adiabatic manipulation of a system interacting with a spin-bath,"Stimulated Raman Adiabatic Passage, a very efficient technique for
manipulating a quantum system based on the adiabatic theorem, is analyzed in
the case where the manipulated physical system is interacting with a spin bath.
Exploitation of the rotating wave approximation allows for the identification
of a constant of motion which simplifies both the analytical and the numerical
treatment, which allows for evaluating the total unitary evolution of system
and bath. The efficiency of the population transfer process is investigated in
several regimes, including the weak and strong coupling with the environment
and the off-resonance. The formation of appropriate Zeno subspaces explains the
lowering of the efficiency in the strong damping regime.",2305.08209v3
2023-05-29,Dynamics of an Exciton-phonon Triangle under Photoirradiation,"Herein, the dynamics of excitons coupled with optical phonons in a triangular
system is numerically studied. By representing the excitons by quasi-spin
states, the similarity between the chiral spin states and the exciton chiral
states is discussed. In particular, the optical control of excitons is
discussed, where photoirradiation causes the switching of the exciton states on
the ultrafast time scale by Raman scattering. A phase diagram is obtained based
on the ground-state properties of the system determined by the magnitudes of
the exciton-phonon interactions and exciton transfer energy. By varying the
frequency and/or intensity of light, a transition between exciton-phonon
composite states is induced, which suggests the possibility of the coherent
control of the chiral properties of excitonic systems via phonon excitation.",2305.18182v1
2023-06-09,Nonlinear multi-state tunneling dynamics in a spinor Bose-Einstein condensate,"We present an experimental realization of dynamic self-trapping and
non-exponential tunneling in a multi-state system consisting of ultracold
sodium spinor gases confined in moving optical lattices. Taking advantage of
the fact that the tunneling process in the sodium spinor system is resolvable
over a broader dynamic energy scale than previously observed in rubidium scalar
gases, we demonstrate that the tunneling dynamics in the multi-state system
strongly depends on an interaction induced nonlinearity and is influenced by
the spin degree of freedom under certain conditions. We develop a rigorous
multi-state tunneling model to describe the observed dynamics. Combined with
our recent observation of spatially-manipulated spin dynamics, these results
open up prospects for alternative multi-state ramps and state transfer
protocols.",2306.05877v1
2023-06-11,Jahn-Teller magnets,"A wide class of materials with different crystal and electronic structures
from quasi-two-dimensional unconventional superconductors (cuprates,
nickelates, ferropnictides/chalcogenides, ruthenate SrRuO$_4$), 3D systems as
manganites RMnO$_3$, ferrates (CaSr)FeO$_3$, nickelates RNiO$_3$, to silver
oxide AgO are based on Jahn-Teller $3d$ and $4d$ ions. These unusual materials
called Jahn-Teller (JT) magnets are characterized by an extremely rich variety
of phase states from non-magnetic and magnetic insulators to unusual metallic
and superconducting states. The unconventional properties of the JT-magnets can
be related to the instability of their highly symmetric Jahn-Teller
""progenitors"" with the ground orbital $E$-state to charge transfer with
anti-Jahn-Teller $d$-$d$ disproportionation and the formation of a system of
effective local composite spin-singlet or spin-triplet, electronic or hole
$S$-type bosons moving in a non-magnetic or magnetic lattice. We consider
specific features of the anti-JT-disproportionation reaction, properties of the
electron-hole dimers, possible phase states of JT-magnets, effective
Hamiltonians for single- and two-band JT-magnets, and present a short overview
of physical properties for actual JT-magnets.",2306.06612v1
2023-07-05,Frustrating quantum batteries,"We propose to use a quantum spin chain as a device to store and release
energy coherently (namely, a quantum battery) and we investigate the interplay
between its internal correlations and outside decoherence. We employ the
quantum Ising chain in a transverse field, and our charging protocol consists
of a sudden global quantum quench in the external field to take the system out
of equilibrium. Interactions with the environment and decoherence phenomena can
dissipate part of the work that the chain can supply after being charged,
measured by the ergotropy. We find that the system shows overall remarkably
better performances, in terms of resilience, charging time, and energy storage,
when topological frustration is introduced by setting AFM interactions with an
odd number of sites and periodic boundary conditions. Moreover, we show that in
a simple discharging protocol to an external spin, only the frustrated chain
can transfer work and not just heat.",2307.02529v1
2023-07-21,Finite temperature properties of an integrable zigzag ladder chain,"We consider the interaction-round-a-face version of the six-vertex model for
arbitrary anisotropy parameter, which allow us to derive an integrable
one-dimensional quantum Hamiltonian with three-spin interactions. We apply the
quantum transfer matrix approach for the face model version of the six-vertex
model. The integrable quantum Hamiltonian shares some thermodynamical
properties with the Heisenberg XXZ chain, but has different ordering and
critical exponents. Two gapped phases are the dimerized antiferromagnetic order
and the usual antiferromagnetic (N\'eel) order for positive nearest neighbour
Ising coupling. In between these, there is an extended critical region, which
is a quantum spin-liquid with broken parity symmetry inducing an oscillatory
behavior at the long distance $<\sigma_1^z\sigma_{\ell+1}^z>$ correlation. At
finite temperatures, the numerical solution of the non-linear integral
equations allows for the determination of the correlation length as well as for
the momentum of the oscillation.",2307.11279v2
2023-07-25,Lattice structure dependence of laser-induced ultrafast magnetization switching in ferrimagnets,"The experimental discovery of single-pulse ultrafast magnetization switching
in ferrimagnetic alloys, such as GdFeCo and MnRuGa, opened the door to a
promising route toward faster and more energy efficient data storage. A recent
semi-phenomenological theory has proposed that a fast, laser-induced
demagnetization below a threshold value puts the system into a dynamical regime
where angular momentum transfer between sublattices dominates. Notably, this
threshold scales inversely proportional to the number of exchange-coupled
nearest neighbours considered in the model, which in the simplest case is
directly linked to the underlying lattice structure. In this work, we study the
role of the lattice structure on the laser-induced ultrafast magnetization
switching in ferrimagnets by complementing the phenomenological theory with
atomistic spin dynamics computer simulations. We consider a spin model of the
ferrimagnetic GdFeCo alloy with increasing number of exchange-coupled
neighbours. Within this model, we demonstrate that the laser-induced
magnetization dynamics and switching depends on the lattice structure. Further,
we determine that the critical laser energy for switching reduces for
decreasing number of exchange-coupled neighbours.",2307.13522v1
2023-08-22,Pressure Driven Fractionalization of Ionic Spins Results in Cupratelike High-$T_c$ Superconductivity in La$_3$Ni$_2$O$_7$,"Beyond 14GPa of pressure, bi-layered La$_3$Ni$_2$O$_7$ was recently found to
develop strong superconductivity above the liquid nitrogen boiling temperature.
An immediate essential question is the pressure-induced qualitative change of
electronic structure that enables the exciting high-temperature
superconductivity. We investigate this timely question via a numerical
multi-scale derivation of effective many-body physics. At the atomic scale, we
first clarify that the system has a strong charge transfer nature with
itinerant carriers residing mainly in the in-plane oxygen between spin-1
Ni$^{2+}$ ions. We then elucidate in eV- and sub-eV-scale the key physical
effect of the applied pressure: It induces a cupratelike electronic structure
through partially screening the Ni spin from 1 to 1/2. This suggests a
high-temperature superconductivity in La$_3$Ni$_2$O$_7$ with microscopic
mechanism and ($d$-wave) symmetry similar to that in the cuprates.",2308.11614v2
2023-12-07,Spin and orbital dynamics of planets undergoing thermal atmospheric tides using a vectorial approach,"Earth-mass planets are expected to have atmospheres and experience thermal
tides raised by the host star. These tides transfer energy to the planet that
can counter the dissipation from bodily tides. Indeed, even a relatively thin
atmosphere can drive the rotation of these planets away from the synchronous
state. Here we revisit the dynamical evolution of planets undergoing thermal
atmospheric tides. We use a novel approach based on a vectorial formalism,
which is frame independent and valid for any configuration of the system,
including any eccentricity and obliquity values. We provide the secular
equations of motion after averaging over the mean anomaly and the argument of
the pericenter, which are suitable to model the long-term spin and orbital
evolution of the planet.",2312.06672v1
2023-12-29,"A ""Magnetic"" Machine Learning Interatomic Potential for Nickel","Nickel (Ni) is a magnetic transition metal with two allotropic phases, stable
face-centered cubic (FCC) and metastable hexagonal close-packed (HCP), widely
used in structural applications. Magnetism affects many mechanical and defect
properties, but spin-polarized density functional theory (DFT) calculations are
computationally inefficient for studying material behavior requiring large
system sizes and/or long simulation times. Here we develop a ""magnetism-hidden""
machine-learning Deep Potential (DP) model for Ni without a descriptor for
magnetic moments, using training datasets derived from spin-polarized DFT
calculations. The ""magnetism-hidden"" DP-Ni model exhibits high transferability
and representability for a wide-range of FCC and HCP properties, including
(finite-temperature) lattice parameters, elastic constants, phonon spectra, and
many defects. As an example of its applicability, we investigate the Ni FCC-HCP
allotropic phase transition under (high-stress) uniaxial tensile loading. The
DP model for magnetic Ni facilitates accurate large-scale atomistic simulations
for complex mechanical behavior and serves as a foundation for developing
interatomic potentials for Ni-based superalloys and other multi-principal
component alloys.",2312.17596v2
2024-01-16,Active Control of Ballistic Orbital Transport,"Orbital current, defined as the orbital character of Bloch states in solids,
can ballistically travel with larger coherence length through a broader range
of materials than its spin counterpart, facilitating a robust, higher density
and energy efficient information transmission. Hence, active control of orbital
transport plays a pivotal role in propelling the progress of the evolving field
of quantum information technology. Unlike spin angular momentum, orbital
angular momentum (OAM), couples to phonon angular momentum (PAM) efficiently
via orbital-crystal momentum (L-k) coupling, giving us the opportunity to
control orbital transport through crystal field potential mediated angular
momentum transfer. Here, leveraging the orbital dependant efficient L-k
coupling, we have experimentally demonstrated the active control of orbital
current velocity using THz emission spectroscopy. Our findings include the
identification of a critical energy density required to overcome collisions in
orbital transport, enabling a swifter flow of orbital current. The capability
to actively control the ballistic orbital transport lays the groundwork for the
development of ultrafast devices capable of efficiently transmitting
information over extended distance.",2401.08373v1
2024-01-22,Strong zero modes in integrable quantum circuits,"It is a classic result that certain interacting integrable spin chains host
robust edge modes known as strong zero modes (SZMs). In this work, we extend
this result to the Floquet setting of local quantum circuits, focusing on a
prototypical model providing an integrable Trotterization for the evolution of
the XXZ Heisenberg spin chain. By exploiting the algebraic structures of
integrability, we show that an exact SZM operator can be constructed for these
integrable quantum circuits in certain regions of parameter space. Our
construction, which recovers a well-known result by Paul Fendley in the
continuous-time limit, relies on a set of commuting transfer matrices known
from integrability, and allows us to easily prove important properties of the
SZM, including normalizabilty. Our approach is different from previous methods
and could be of independent interest even in the Hamiltonian setting. Our
predictions, which are corroborated by numerical simulations of
infinite-temperature autocorrelation functions, are potentially interesting for
implementations of the XXZ quantum circuit on available quantum platforms.",2401.12305v2
2024-01-30,A universal pairing gap measurement proposal by dynamical excitations in 2D doped attractive Fermi-Hubbard model with spin-orbit coupling,"By calculating dynamical structure factor of two-dimensional doped attractive
Fermi-Hubbard model with Rashba spin-orbit coupling, we not only investigate
collective modes and single-particle excitations of the system during the phase
transition between Bardeen-Cooper-Schrieffer superfluid and topological
superfluid, but also propose a universal method to measure pairing gap
measurement in an optical lattice system. Our numerical results show that the
area of the molecular excitation peak at the transferred momentum ${\bf
q}=\left[\pi,\pi\right]$ is proportional to the square of the pairing gap in
the system with Rashba SOC. In particular, this method is very sensitive to the
pairing gap. This goes on verifying that this method is universal to measure
the pairing gap in a doped optical lattice with Rashba SOC. These theoretical
results are important for experimentally measuring the pairing gap and studying
the topological superfluid in an optical lattice.",2401.17488v1
2024-02-07,A Non-Abelian Gauge Theory for Surface Excitations of $~^3$He-B,"In $~^3$He-B, two atoms pair in an orbital angular momentum $1$ spin triplet
state above the phase transition temperature with $SO(3) \times SO(3)$
symmetry. Below the transition temperature, this symmetry is spontaneously
broken to the diagonal $SO(3)$ due to spin-orbit coupling. Considerations based
on effective potentials and solitons show that $SO(3)$'s gets enhanced to
$SU(3)$'s and the symmetry breaking is that of $G= SU(3) \times SU(3)\times
U(1)$ to $H= SU(3)$. The theory of the resultant Goldtsone modes can be
naturally formulated as a gauge theory of $H$. Its Gauss law is treated here
and shown to lead to surface states in a container with a dynamics governed by
large gauge transformations.
  Observable consequences are pointed. The transference of the analysis to the
chiral model of QCD is pointed out where $SU(3)$ are the left and right chiral
groups, $U(1)$ is the axial $U(1)$ , the surviving symmetry is flavour $SU(3)$
and the Goldstone modes are the pions.",2402.04714v2
2024-02-27,"Novel Ternary AgIICoIIIF5 Fluoride: Synthesis, Structure and Magnetic Characteristics","We present a new compound in the silver cobalt fluoride system, featuring
paramagnetic silver (d9) and high-spin cobalt (d6), synthesized by solid state
method in an autoclave under F2 overpressure. Based on powder X ray
diffraction, we determined that AgIICoIIIF5 crystallizes in a monoclinic system
with space group C2/c. The calculated fundamental band gap falls in the visible
range of the electromagnetic spectrum, and the compound has the character of
charge-transfer insulator. AgCoF5 is a ferrimagnet with one predominant
superexchange magnetic interaction constant between mixed spin cations (Ag ...
Co) of minus 62 meV (SCAN result). Magnetometric measurements conducted on a
powdered sample allowed the identification of a transition at 128 K, which
could indicate magnetic ordering.",2402.17399v1
2024-04-03,Glue in hadrons at medium resolution and the QCD instanton vacuum,"We discuss a general framework for the evaluation of the gluonic form factors
in light hadrons at low momentum transfer, in the QCD instanton vacuum. At
medium resolution of the order of the inverse mean instanton size, the glue is
mostly localized in single or pair of pseudoparticles, and globally constrained
by the fluctuations of their topological charges. These pseudoparticles trap
light quarks, giving rise to emerging multiflavor 't Hooft interactions. We
explicitly evaluate the gluonic scalar, pseudoscalar, energy-momentum tensor
(EMT), and the leading C-odd and C-even three gluons hadronic form factors, at
next to leading order (NLO) in the instanton density, including molecular
clusters of like and unlike instantons. We use the results for the EMT to
address the contribution of the gluons in Ji$^\prime$s mass and spin sum rules,
at low resolution. When evolved, our results for the mass and spin composition
of the nucleon, are shown to be in good agreement with the recently reported
lattice results at higher resolution.",2404.03047v1
2024-04-05,Constraining stellar tidal quality factors from planet-induced stellar spin-up,"The dynamical evolution of tight star-planet systems is influenced by tidal
interactions between the star and the planet, as was shown recently. The rate
at which spins and orbits in such a system evolve depends on the stellar and
planetary tidal dissipation efficiency. Here, we present a method to constrain
the modified tidal quality factor $Q'_*$ of a planet-hosting star whose
rotational evolution has been altered by its planet through angular momentum
transfer from the planetary orbital motion to the rotation of the stellar
convective zone. The altered rotation is estimated from an observed discrepancy
of magnetic activity of the planet-hosting star and a coeval companion star,
i.e. this method is applicable to star-planet systems with wide stellar
companions. We give an example of the planet-hosting wide binary system
HD189733 and find that the planet host's modified tidal quality factor is
constrained to be $Q'_* \leq 2.33 \times 10^7$.",2404.04047v1
2013-05-10,Mathematical structure of three - dimensional (3D) Ising model,"An overview of the mathematical structure of the three-dimensional (3D) Ising
model is given, from the viewpoints of topologic, algebraic and geometric
aspects. By analyzing the relations among transfer matrices of the 3D Ising
model, Reidemeister moves in the knot theory, Yang-Baxter and tetrahedron
equations, the following facts are illustrated for the 3D Ising model: 1) The
complexified quaternion basis constructed for the 3D Ising model represents
naturally the rotation in a (3 + 1) - dimensional space-time, as a relativistic
quantum statistical mechanics model, which is consistent with the 4-fold
integrand of the partition function by taking the time average. 2) A unitary
transformation with a matrix being a spin representation in 2^(nlo)-space
corresponds to a rotation in 2nlo-space, which serves to smooth all the
crossings in the transfer matrices and contributes as the non-trivial topologic
part of the partition function of the 3D Ising model. 3) A tetrahedron relation
would ensure the commutativity of the transfer matrices and the integrability
of the 3D Ising model, and its existence is guaranteed also by the Jordan
algebra and the Jordan-von Neumann-Wigner procedures. 4) The unitary
transformation for smoothing the crossings in the transfer matrices changes the
wave functions by complex phases {\Phi}x, {\Phi}y, and {\Phi}z. The relation
with quantum field and gauge theories, physical significance of weight factors
are discussed in details. The conjectured exact solution is compared with
numerical results, and singularities at/near infinite temperature are
inspected. The analyticity in {\beta} = 1/(kB T) of both the hard-core and
Ising models has been proved for {\beta} > 0, not for {\beta} = 0. Thus the
high-temperature series cannot serve as a standard for judging a putative exact
solution of the 3D Ising model.",1305.2956v1
2014-11-13,Intervalence Charge Transfer luminescence: The anomalous luminescence of Cerium-doped Cs2LiLuCl6 elpasolite,"The existence of intervalence charge transfer (IVCT) luminescence is
reported. It is shown that the so called anomalous luminescence of Ce-doped
elpasolite Cs2LiLuCl6, which is characterized mainly by a very large Stokes
shift and a very large band width, corresponds to an IVCT emission in Ce3+-Ce4+
pairs, from the 5deg orbital of Ce3+ to 4f orbitals of Ce4+. Its Stokes shift
is the sum of the large reorganization energies of the Ce4+ and Ce3+ centers
formed after the fixed-nuclei electron transfer and it is equal to the energy
of the IVCT absorption commonly found in mixed-valence compounds, which is
predicted to exist in this material and to be slightly larger than 10000 cm-1.
The large band width is the consequence of the large offset between the minima
of the Ce3+-Ce4+ and Ce4+-Ce3+ pairs along the electron transfer reaction
coordinate. This offset is approximately 2*sqrt(3) times the difference of
Ce-Cl equilibrium distances in the Ce3+ and Ce4+ centers. It is shown that the
energies of the peaks and the widths of IVCT absorption and emission bands can
be calculated ab initio with reasonable accuracy from diabatic energy surfaces
of the ground and excited states and that these can be obtained, in turn, from
independent calculations on the donor and acceptor active centers. We obtained
the energies of the Ce3+ and Ce4+ active centers of Ce-doped Cs2LiLuCl6 by
means of state-of-the-art wave-function-theory spin-orbit coupling relativistic
calculations on the donor cluster (CeCl6Li6Cs8)11+ and the acceptor cluster
(CeCl6Li6Cs8)12+ embedded in a quantum mechanical embedding potential of the
host. The calculations provide interpretations of unexplained experimental
observations as due to higher energy IVCT absorptions, and allow reinterpreting
others. The existence of another IVCT emission of lower energy, at around
14000-16000 cm-1 less than the 5dt2g emission, is also predicted.",1411.3512v2
2015-06-12,Polarization Transfer in Wide-Angle Compton Scattering and Single-Pion Photoproduction from the Proton,"Wide-angle exclusive Compton scattering and single-pion photoproduction from
the proton have been investigated via measurement of the polarization transfer
from a circularly polarized photon beam to the recoil proton. The wide-angle
Compton scattering polarization transfer was analyzed at an incident photon
energy of 3.7~GeV at a proton scattering angle of \cma$= 70^\circ$. The
longitudinal transfer \KLL, measured to be $0.645 \pm 0.059 \pm 0.048$, where
the first error is statistical and the second is systematic, has the same sign
as predicted for the reaction mechanism in which the photon interacts with a
single quark carrying the spin of the proton. However, the observed value is
$\sim$3~times larger than predicted by the
generalized-parton-distribution-based calculations, which indicates a
significant unknown contribution to the scattering amplitude.",1506.04045v2
2019-06-12,A rapidly-changing jet orientation in the stellar-mass black hole V404 Cygni,"Powerful relativistic jets are one of the main ways in which accreting black
holes provide kinetic feedback to their surroundings. Jets launched from or
redirected by the accretion flow that powers them should be affected by the
dynamics of the flow, which in accreting stellar-mass black holes has shown
increasing evidence for precession due to frame dragging effects that occur
when the black hole spin axis is misaligned with the orbital plane of its
companion star. Recently, theoretical simulations have suggested that the jets
can exert an additional torque on the accretion flow, although the full
interplay between the dynamics of the accretion flow and the launching of the
jets is not yet understood. Here we report a rapidly changing jet orientation
on a timescale of minutes to hours in the black hole X-ray binary V404 Cygni,
detected with very long baseline interferometry during the peak of its 2015
outburst. We show that this can be modelled as Lense-Thirring precession of a
vertically-extended slim disk that arises from the super-Eddington accretion
rate. Our findings suggest that the dynamics of the precessing inner accretion
disk could play a role in either directly launching or redirecting the jets
within the inner few hundred gravitational radii. Similar dynamics should be
expected in any strongly-accreting black hole whose spin is misaligned with the
inflowing gas, both affecting the observational characteristics of the jets,
and distributing the black hole feedback more uniformly over the surrounding
environment.",1906.05400v1
1998-12-16,Warps Caused by Jet-Induced Pressure Gradients in Radio Galaxies,"In radio galaxies such as M84 dust features tend to be nearly perpendicular
to radio jets yet are not aligned with the galaxy isophotes. The timescale for
precession in the galaxy is short suggesting that an alternative mechanism
causes the gas disk to be misaligned with the galaxy. In M84 we estimate the
pressure on the disk required to overcome the torque from the galaxy and find
that it is small compared to the thermal pressure in the hot ambient ISM
estimated from the X-ray emission. We therefore propose that pressure gradients
in a jet associated hot interstellar medium exert a torque on the gas disk in
M84 causing it to be misaligned with the galaxy isophotal major axis. This
mechanism could explain the connection between gas disk angular momentum and
jet axes in nearby radio galaxies.
  By integrating the light of the galaxy through a warped gas and dust disk we
find that the geometry of gas disk in M84 is likely to differ that predicted
from a simple precession model. We find that the morphology of the gas disk in
M84 is consistent with a warped geometry where precession is caused by a
combination of a galactic torque and a larger torque due to pressure gradients
in the ambient X-ray emitting gas. Precession occurs at an axis between the jet
and galaxy major axis, but nearer to the jet axis implying that the pressure
torque is 2-4 times larger than the galactic torque. A better model to the
morphology of the disk is achieved when precession takes place about an
elliptical rather than circular path. This suggests that the isobars in the hot
medium are strongly dependent on angle from the jet axis.",9812312v2
2012-02-27,Evolution of binary black holes in self gravitating discs: dissecting the torques,"We study the interplay between gas accretion and gravity torques in changing
a binary elements and its total angular momentum (L) budget. Especially, we
analyse the physical origin of the gravity torques (T_g) and their location
within the disc. We analyse 3D SPH simulations of the evolution of initially
quasi-circular massive black hole binaries (BHBs) residing in the central
hollow of massive self-gravitating circumbinary discs. We use different
thermodynamics within the cavity and for the numerical size of the black holes
to show that (i) the BHB eccentricity growth found previously is a general
result, independent of the accretion and the adopted thermodynamics; (ii) the
semi-major axis decay depends both on the T_g and on the interplay with the
disc-binary L-transfer due to accretion; (iii) the spectral structure of the
T_g is predominately caused by disc edge overdensities and spiral arms
developing in the body of the disc and, in general, does not reflect directly
the period of the binary; (iv) the net T_g changes sign across the BHB
corotation radius. We quantify the relative importance of the two, which appear
to depend on the thermodynamical properties of the instreaming gas, and which
is crucial in assessing the disc-binary L-transfer; (v) the net torque
manifests as a purely kinematic (non-resonant) effect as it stems from the
cavity, where the material flows in and out in highly eccentric orbits. Both
accretion onto the black holes and the interaction with gas streams inside the
cavity must be taken into account to assess the fate of the BHB. Moreover, the
total torque exerted by the disc affects L(BHB) by changing all the elements
(mass, mass ratio, eccentricity, semimajor axis) of the BHB. Common
prescriptions equating tidal torque to semi-major axis shrinking might
therefore be poor approximations for real astrophysical systems.",1202.6063v2
2015-01-12,Type I Planet Migration in a Magnetized Disk. II. Effect of Vertical Angular Momentum Transport,"We study the effects of a large-scale, ordered magnetic field in
protoplanetary disks on Type I planet migration using a linear perturbation
analysis in the ideal-MHD limit. We focus on wind-driving disks, in which a
magnetic torque $\propto B_{0z} \partial B_{0\varphi}/\partial z$ (where
$B_{0z}$ and $B_{0\varphi}$ are the equilibrium vertical and azimuthal field
components) induces vertical angular momentum transport. We derive the
governing differential equation for the disk response and identify its
resonances and turning points. For a disk containing a slightly subthermal,
pure-$B_{0z}$ field, the total 3D torque is close to its value in the 2D limit
but remains lower than the hydrodynamic torque. In contrast with the 2D
pure-$B_{0\varphi}$ field model considered by Terquem (2003), inward migration
is not reduced in this case when the field amplitude decreases with radius. The
presence of a subdominant $B_{0\varphi}$ component whose amplitude increases
from zero at $z=0$ has little effect on the torque when acting alone, but in
conjunction with a $B_{0z}$ component it gives rise to a strong torque that
speeds up the inward migration by a factor $\gtrsim 200$. This factor could,
however, be reduced in a real disk by dissipation and magnetic diffusivity
effects. Unlike all previously studied disk migration models, in the
$B_{0z}+\partial B_{0\varphi}/\partial z$ case the dominant contributions to
the torque add with the same sign from the two sides of the planet. We
attribute this behavior to a new mode of interaction wherein a planet moves
inward by plugging into the disk's underlying angular momentum transport
mechanism.",1501.02707v1
2016-03-10,Radiation forces and torque on a rigid elliptical cylinder in acoustical plane progressive and (quasi)standing waves with arbitrary incidence,"Analytical expressions for the axial and transverse acoustic radiation forces
as well as the radiation torque per length are derived for a rigid elliptical
cylinder placed arbitrarily in the field of in plane progressive,
quasi-standing or standing waves. The rigid elliptical cylinder case is
important to be considered as a first-order approximation of the behavior of a
fluid particle suspended in air, because of the significant acoustic impedance
mismatch at the particle's boundary. Based on the partial-wave series expansion
method in cylindrical coordinates, non-dimensional acoustic radiation force and
torque functions are derived and defined in terms of the scattering
coefficients of the elliptic cylinder. A coupled system of linear equations is
obtained after applying the Neumann boundary condition for an immovable surface
in a non-viscous fluid, and solved numerically by matrix inversion after
performing a single numerical integration procedure. Computational results for
the non-dimensional force components and torque, showing the transition from
the progressive to the (equi-amplitude) standing wave behavior, are performed
with particular emphasis on the aspect ratio a/b, where a and b are the
semi-axes of the ellipse, the dimensionless size parameter, as well as the
angle of incidence ranging from end-on to broadside incidence. The results show
that the elliptical geometry has a direct influence on the radiation force and
torque, so that the standard theory for circular cylinders (at normal
incidence) leads to significant miscalculations when the cylinder cross-section
becomes non-circular. Moreover, the elliptical cylinder experiences, in
addition to the acoustic radiation force, a radiation torque that vanishes for
the circular cylinder case. The application of the formalism presented here may
be extended to other 2D surfaces of arbitrary shape.",1603.03446v1
2016-05-12,Dynamical Tides Reexpressed,"Zahn (1975) first put forward and calculated in detail the torque experienced
by stars in a close binary systems due to dynamical tides. His widely used
formula for stars with radiative envelopes and convective cores is expressed in
terms of the stellar radius, even though the torque is actually being applied
to the convective core at the core radius. This results in a large prefactor,
which is very sensitive to the global properties of the star, that multiplies
the torque. This large factor is compensated by a very small multiplicative
factor, $E_{2}$. Although this is mathematically accurate, depending on the
application this can lead to significant errors. The problem is even more
severe, since the calculation of $E_{2}$ itself is non-trivial, and different
authors have obtained inconsistent values of $E_{2}$. Moreover, many codes
(e.g. BSE, StarTrack, MESA) interpolate (and sometimes extrapolate) a fit of
$E_{2}$ values to the stellar mass, often in regimes where this is not sound
practice. We express the torque in an alternate form, cast in terms of
parameters at the envelope-core boundary and a dimensionless coefficient,
$\beta_{2}$. Previous attempts to express the torque in such a form are either
missing an important factor, which depends on the density profile of the star,
or are not easy to implement. We show that $\beta_{2}$ is almost independent of
the properties of the star and its value is approximately unity. Our formula
for the torque is simple to implement and avoids the difficulties associated
with the classic expression.",1605.03810v3
2016-08-31,Migration of accreting planets in radiative discs from dynamical torques,"We present the results of hydrodynamical simulations of the orbital evolution
of planets undergoing runaway gas accretion in radiative discs. We consider
accreting disc models with constant mass flux through the disc, and where
radiative cooling balances the effect of viscous heating and stellar
irradiation. We assume that 20-30 $M_\oplus$ giant planet cores are formed in
the region where viscous heating dominates and migrate outward under the action
of a strong corotation torque. In the case where gas accretion is neglected, we
find evidence for strong dynamical torques in accreting discs with accretion
rates ${\dot M}\gtrsim 7\times 10^{-8} \;M_\odot/yr$. Their main effect is to
increase outward migration rates by a factor of $\sim 2$ typically. In the
presence of gas accretion, however, runaway outward migration is observed with
the planet passing through the zero-torque radius and the transition between
the viscous heating and stellar heating dominated regimes. The ability for an
accreting planet to enter a fast migration regime is found to depend strongly
on the planet growth rate, but can occur for values of the mass flux through
the disc of ${\dot M}\gtrsim 5\times 10^{-8} \;M_\odot/yr$. We find that an
episode of runaway outward migration can cause an accreting planet formed in
the 5-10 AU region to temporarily orbit at star-planet separations as large as
$\sim$60-70 AU. However, increase in the amplitude of the Lindblad torque
associated with planet growth plus change in the streamline topology near the
planet systematically cause the direction of migration to be reversed. Our
results indicate that a planet can reach large orbital distances under the
combined effect of dynamical torques and gas accretion, but an alternative
mechanism is required to explain the presence of massive planets on wide
orbits.",1608.08756v1
2017-03-11,On the orbital evolution of supermassive black hole binaries with circumbinary accretion discs,"Gaseous circumbinary accretion discs provide a promising mechanism to
facilitate the mergers of supermassive black holes (SMBHs) in galactic nuclei.
We measure the torques exerted on accreting SMBH binaries, using 2D,
isothermal, moving-mesh, viscous hydrodynamical simulations of circumbinary
accretion discs. Our computational domain includes the entire inner region of
the circumbinary disk with the individual black holes (BHs) included as point
masses on the grid and a sink prescription to model accretion onto each BH. The
BHs each acquire their own well-resolved accretion discs (""minidiscs""). We
explore a range of mass removal rates for the sink prescription removing gas
from the central regions of the minidiscs. We find that the torque exerted on
the binary is primarily gravitational, and dominated by the gas orbiting close
behind and ahead of the individual BHs. The torques from the distorted
circumbinary disc farther out and from the direct accretion of angular momentum
are subdominant. The torques are sensitive to the sink prescription: slower
sinks result in more gas accumulating near the BHs and more negative torques,
driving the binary to merger more rapidly. For faster sinks, the torques are
less negative and eventually turn positive (for unphysically fast sinks). When
the minidiscs are modeled as standard alpha discs, our results are insensitive
to the choice of sink radius. Scaling the simulations to a binary orbital
period tbin = 1yr and background disc accretion rate Mdot = 0.3MEdd in
Eddington units, the binary inspirals on a timescale of 3X10^6 years,
irrespective of the SMBH masses. For binaries with total mass <10^7Msun, this
is shorter than the inspiral time due to gravitational wave (GW) emission
alone, implying that gas discs will have a significant impact on the SMBH
binary population and can affect the GW signal for Pulsar Timing Arrays.",1703.03913v1
2020-05-22,Evolution of gas disc-embedded intermediate mass ratio inspirals in the LISA band,"Among the potential milliHz gravitational wave (GW) sources for the upcoming
space-based interferometer LISA are extreme- or intermediate-mass ratio
inspirals (EMRI/IMRIs). These events involve the coalescence of supermassive
black holes in the mass range $10^5 M_{\odot} \lesssim M \lesssim 10^7
M_{\odot}$ with companion BHs of much lower masses. A subset of E/IMRIs are
expected to occur in the accretion discs of active galactic nuclei (AGN), where
torques exerted by the disc can interfere with the inspiral and cause a phase
shift in the GW waveform. Here we use a suite of two-dimensional hydrodynamical
simulations with the moving-mesh code DISCO to present a systematic study of
disc torques. We measure torques on an inspiraling BH and compute the
corresponding waveform deviations as a function of the binary mass ratio
$q\equiv M_2/M_1$, the disc viscosity ($\alpha$), and gas temperature (or
equivalently Mach number; $\mathcal{M}$). We find that the absolute value of
the gas torques is within an order of magnitude of previously determined
planetary migration torques, but their precise value and sign depends
non-trivially on the combination of these parameters. The gas imprint is
detectable by LISA for binaries embedded in AGN discs with surface densities
above $\Sigma_0\ge10^{4-6} \rm \, g cm^{-2}$, depending on $q$, $\alpha$ and
$\mathcal{M}$. Deviations are most pronounced in discs with higher viscosities,
and for E/IMRIs detected at frequencies where LISA is most sensitive. Torques
in colder discs exhibit a noticeable dependence on the GW-driven inspiral rate
as well as strong fluctuations at late stages of the inspiral. Our results
further suggest that LISA may be able to place constraints on AGN disc
parameters and the physics of disc-satellite interaction.",2005.11333v2
2021-10-16,A New Theory for Estimating Maximum Power from Wind Turbines: A Fundamental Newtonian Approach,"A novel method for calculating power output from wind turbines using
Newtonian mechanics is proposed. This contrasts with current methods based on
interception rates by airfoils of kinetic energy to estimate power output,
governed by the Betz limit of propeller theory. Radial action generates torques
from impulses from air molecules at differing radii on rotor surfaces, both
windward and leeward. Dimensionally, torque is a rate of action. Integration of
the windward torque is achieved numerically using inputs of rotor dimensions,
the angle of incidence of elastic wind impulse on the blade surface, chord and
blade lengths and the tip speed ratio with wind speed. The rate of leeward or
back torque in the plane of rotation is estimated from radial impulses from the
blades rotation on material particles, with magnitude varying with the square
of the blade radius and its angular velocity. The net torque from these rates
of action and reaction is converted to power by its product with the angular
velocity of the turbine rotors, considered as an ideal cycle for wind turbines.
Its design should assist optimization of the aerodynamic elements of turbine
operation. A matter of concern must be predictions for a significant rate of
heat production by wind turbines, represented partly by the magnitude of the
leeward reaction torque but also by a greater release of heat downwind caused
by a turbulent cascade in the wake of air flow following its impacts with the
blades. Given the widespread occurrence of wind farms as sources of renewable
energy and a need to minimize environmental impacts this new method should
promote improved theory and practice regarding wind energy.",2110.15117v1
2021-12-23,Dynamics of irregularly-shaped cometary particles subjected to outflowing gas and solar radiative forces and torques,"The dynamics of irregularly-shaped particles subjected to the combined effect
of gas drag and radiative forces and torques in a cometary environment is
investigated. The equations of motion are integrated over distances from the
nucleus surface up to distances where the gas drag is negligible. The
aerodynamic forces and torques are computed assuming a spherically symmetric
expanding gas. The calculations are limited to particle sizes in the geometric
optics limit, which is the range of validity of our radiative torque
calculations. The dynamical behaviour of irregular particles is quite different
to those exhibited by non-spherical but symmetric particles such as spheroids.
An application of the dynamical model to comet 67P/Churyumov-Gerasimenko, the
target of the Rosetta mission, is made. We found that, for particle sizes
larger than about 10 micrometer, the radiative torques are negligible in
comparison with the gas-driven torques up to a distance of about 100 km from
the nucleus surface. The rotation frequencies of the particles depend on their
size, shape, and the heliocentric distance, while the terminal velocities,
being also dependent on size and heliocentric distance, show only a very weak
dependence on particle shape. The ratio of the sum of the particles projected
areas in the sun-to-comet direction to that of the sum of the particles
projected areas in any direction perpendicular to it is nearly unity,
indicating that the interpretation of the observed u-shaped scattering phase
function by Rosetta/OSIRIS on comet 67P coma cannot be linked to mechanical
alignment of the particles.",2112.12457v1
2022-05-05,Calibrated Gas Accretion and Orbital Migration of Protoplanets in 1D Disc Models,"We aim to develop a simple prescription for migration and accretion in 1D
disc models, calibrated with results of 3D hydrodynamic simulations. Our focus
lies on non-self-gravitating discs, but we also discuss to what degree our
prescription could be applied when the discs are self-gravitating.
  We study migration using torque densities. Our model for the torque density
is based on existing fitting formulas, which we subsequently modify to prevent
premature gap-opening. At higher planetary masses, we also apply torque
densities from hydrodynamic simulations directly to our 1D model. These torque
densities allow modelling the orbital evolution of an initially low-mass planet
that undergoes runaway-accretion to become a massive planet. The two-way
exchange of angular momentum between disc and planet is included. This leads to
a self-consistent treatment of gap formation that only relies on directly
accessible disc parameters. We present a formula for Bondi- and Hill- gas
accretion in the disc-limited regime. This formula is self-consistent in the
sense that mass is removed from the disc in the location from where it is
accreted.
  We find that the resulting evolution in mass and semi-major axis in the 1D
framework is in good agreement with those from 3D hydrodynamical simulations
for a range of parameters.
  Our prescription is valuable for simultaneously modelling migration and
accretion in 1D-models. We conclude that it is appropriate and beneficial to
apply torque densities from hydrodynamic simulations in 1D models, at least in
the parameter space we study here. More work is needed to in order to determine
whether our approach is also applicable in an even wider parameter space and in
situations with more complex disc thermodynamics, or when the disc is
self-gravitating.",2205.02858v2
2023-02-24,Accounting for Differential Rotation in Calculations of the Sun's Angular Momentum-loss Rate,"Sun-like stars shed angular momentum due to the presence of magnetised
stellar winds. Magnetohydrodynamic models have been successful in exploring the
dependence of this ""wind-braking torque"" on various stellar properties, however
the influence of surface differential rotation is largely unexplored. As the
wind-braking torque depends on the rotation rate of the escaping wind, the
inclusion of differential rotation should effectively modulate the angular
momentum-loss rate based on the latitudinal variation of wind source regions.
In order to quantify the influence of surface differential rotation on the
angular momentum-loss rate of the Sun, we exploit the dependence of the
wind-braking torque on the effective rotation rate of the coronal magnetic
field. This quantity is evaluated by tracing field lines through a Potential
Field Source Surface (PFSS) model, driven by ADAPT-GONG magnetograms. The
surface rotation rates of the open magnetic field lines are then used to
construct an open-flux weighted rotation rate, from which the influence on the
wind-braking torque can be estimated. During solar minima, the rotation rate of
the corona decreases with respect to the typical solid-body rate (the
Carrington rotation period is 25.4 days), as the sources of the solar wind
shift towards the slowly-rotating poles. With increasing activity, more solar
wind emerges from the Sun's active latitudes which enforces a Carrington-like
rotation. The effect of differential rotation on the Sun's current wind-braking
torque is found to be small. The wind-braking torque is ~10-15% lower during
solar minimum, than assuming solid body rotation, and a few percent larger
during solar maximum. For more rapidly-rotating Sun-like stars, differential
rotation may play a more significant role, depending on the configuration of
the large-scale magnetic field.",2302.12700v1
2008-08-06,The simulated 21 cm signal during the epoch of reionization : full modeling of the Ly-alpha pumping,"The 21 cm emission of neutral hydrogen is the most promising probe of the
epoch of reionization(EoR). In the next few years, the SKA pathfinders will
provide statistical measurements of this signal. Numerical simulations
predicting these observations are necessary to optimize the design of the
instruments. The main difficulty is the computation of the spin temperature of
neutral hydrogen which depends on the gas kinetic temperature and on the level
of the local Lyman-alpha flux. A T_s >> T_cmb assumption is usual. However,
this assumption does not apply early in the reionization history, or even later
in the history as long as the sources of X-rays are too weak to heat the
intergalactic medium significantly. This work presents the first EoR numerical
simulations including, beside dynamics and ionizing continuum radiative
transfer, a self-consistent treatment of the Ly-alpha radiative transfer. This
allows us to compute the spin temperature more accurately. We use two different
box sizes, 20 Mpc/h and 100 Mpc/h, and a star source model. Using the redshift
dependence of average quantities, maps, and power spectra, we quantify the
effect of using different assumptions to compute the spin temperature and the
influence of the box size. The first effect comes from allowing for a signal in
absorption. The magnitude of this effect depends on the amount of heating by
hydrodynamic shocks and X-rays in the intergalactic medium(IGM). The second
effects comes from using the real, local, Lyman-alpha flux. This effect is
important for an average ionization fraction of less than 10%: it changes the
overall amplitude of the 21 cm signal, and adds its own fluctuations to the
power spectrum.",0808.0925v2
2010-01-29,Magnetic Connection Model for Launching Relativistic Jets from a Kerr Black Hole,"We present a model for launching relativistic jets in active galactic nuclei
(AGN) from an accreting Kerr black hole (BH) as an effect of the rotation of
the space-time, where the gravitational energy of the accretion disc inside the
ergosphere, which can be increased by the BH rotational energy transferred to
the disc via closed magnetic field lines that connect the BH to the disc
(BH-disc magnetic connection), is converted into jet energy. The main role of
the BH-disc magnetic connection is to provide the source of energy for the jets
when the mass accretion rate is very low. We assume that the jets are launched
from the disc inside the BH ergosphere, where the rotational effects of the
space-time become much stronger, being further accelerated by magnetic
processes. The rotation of the space-time channels a fraction of the disc
energy (i.e., the gravitational energy of the disc plus the rotational energy
of the BH which is deposited into the disc by magnetic connection) into a
population of particles that escape from the disc surfaces, carrying away mass,
energy and angular momentum in the form of jets, allowing the remaining disc
gas to accrete. In the limit of the spin-down power regime, the model proposed
here can be regarded as a variant of the Blandford-Znajek mechanism, where the
BH rotational energy is transferred to the disc inside the ergosphere and then
used to drive the jets. We use general-relativistic conservation laws to
calculate the mass flow rate into the jets, the launching power of the jets and
the angular momentum transported by the jets for BHs with a spin parameter $a_*
\geqslant 0.95$. We found that a stationary state of the BH ($a_* = $ const)
can be reached if the mass accretion rate is larger than $\dot{m} \sim 0.001$.
In addition, the maximum AGN lifetime can be much longer than $\sim 10^{7}$ yr
when using the BH spin-down power.",1001.5434v2
2010-06-22,Search for pulsations at high radio frequencies from accreting millisecond X-ray pulsars in quiescence,"It is commonly believed that millisecond radio pulsars have been spun up by
transfer of matter and angular momentum from a low-mass companion during an
X-ray active mass transfer phase. A subclass of low-mass X-ray binaries is that
of the accreting millisecond X-ray pulsars, transient systems that show periods
of X-ray quiescence during which radio emission could switch on. The aim of
this work is to search for millisecond pulsations from three accreting
millisecond X-ray pulsars, XTE J1751-305, XTE J1814-338, and SAX J1808.4-3658,
observed during their quiescent X-ray phases at high radio frequencies (5 - 8
GHz) in order to overcome the problem of the free-free absorption due to the
matter engulfing the system. A positive result would provide definite proof of
the recycling model, providing the direct link between the progenitors and
their evolutionary products. The data analysis methodology has been chosen on
the basis of the precise knowledge of orbital and spin parameters from X-ray
observations. It is subdivided in three steps: we corrected the time series for
the effects of (I) the dispersion due to interstellar medium and (II) of the
orbital motions, and finally (III) folded modulo the spin period to increase
the signal-to-noise ratio. No radio signal with spin and orbital
characteristics matching those of the X-ray sources has been found in our
search, down to very low flux density upper limits. We analysed several
mechanisms that could have prevented the detection of the signal, concluding
that the low luminosity of the sources and the geometric factor are the most
likely reasons for this negative result.",1006.4260v1
2010-07-10,New measurement of orbital and spin period evolution of the Accretion Disk Corona source 4U 1822-37,"4U 1822-37 is a Low Mass X-ray Binary (LMXB) system with an Accretion Disk
Corona. We have obtained 16 new mid-eclipse time measurements of this source
during the last 13 years using X- ray observations made with the RXTE-PCA,
RXTE-ASM, Swift-XRT, XMM-Newton and Chandra observatories. These, along with
the earlier known mid-eclipse times have been used to accurately determine the
timescale for a change in the orbital period of 4U 1822-37. We have derived an
orbital period Porb = 0.23210887(15) d, which is changing at the rate of \cdot
Porb = 1.3(3) x 10-10 d d-1 (at T0 = MJD 45614). The timescale for a change in
the orbital period is Porb/ \cdot Porb of 4.9(1.1) x 106 yr. We also report the
detection of 0.59290132(11) s (at T0 = MJD 51975) X-ray pulsations from the
source with a long term average \cdot Pspin of -2.481(4) x 10-12 s s-1, i.e., a
spin-up time scale (Pspin/ \cdot Pspin) of 7578(13) yr. In view of these
results, we have discussed various mechanisms that could be responsible for the
orbital evolution in this system. Assuming the extreme case of conservative
mass transfer, we have found that the measured \cdot Porb requires a large mass
transfer rate of (4.2 - 5.2) x 10-8 M\odot yr-1 which together with the spin up
rate implies a magnetic field strength in the range of (1-3) x 108 G. Using the
long term RXTE-ASM light curve, we have found that the X-ray intensity of the
source has decreased over the last 13 years by ? 40% and there are long term
fluctuations at time scales of about a year. In addition to the long term
intensity variation, we have also observed significant variation in the
intensity during the eclipse.",1007.1731v1
2015-07-25,"Binary Neutron Stars with Generic Spin, Eccentricity, Mass ratio, and Compactness - Quasi-equilibrium Sequences and First Evolutions","Information about the last stages of a binary neutron star inspiral and the
final merger can be extracted from quasi-equilibrium configurations and
dynamical evolutions. In this article, we construct quasi-equilibrium
configurations for different spins, eccentricities, mass ratios, compactnesses,
and equations of state. For this purpose we employ the SGRID code, which allows
us to construct such data in previously inaccessible regions of the parameter
space. In particular, we consider spinning neutron stars in isolation and in
binary systems; we incorporate new methods to produce highly eccentric and
eccentricity reduced data; we present the possibility of computing data for
significantly unequal-mass binaries; and we create equal-mass binaries with
individual compactness up to 0.23. As a proof of principle, we explore the
dynamical evolution of three new configurations. First, we simulate a $q=2.06$
mass ratio which is the highest mass ratio for a binary neutron star evolved in
numerical relativity to date. We find that mass transfer from the companion
star sets in a few revolutions before merger and a rest mass of
$\sim10^{-2}M_\odot$ is transferred between the two stars. This configuration
also ejects a large amount of material during merger, imparting a substantial
kick to the remnant. Second, we simulate the first merger of a precessing
binary neutron star. We present the dominant modes of the gravitational waves
for the precessing simulation, where a clear imprint of the precession is
visible in the (2,1) mode. Finally, we quantify the effect of an eccentricity
reduction procedure on the gravitational waveform. The procedure improves the
waveform quality and should be employed in future precision studies, but also
other errors, notably truncation errors, need to be reduced in order for the
improvement due to eccentricity reduction to be effective. [abridged]",1507.07100v1
2016-01-28,Models of Kilonova/macronova emission from black hole-neutron star mergers,"Black hole-neutron star mergers are among the promising gravitational-wave
sources for ground-based detectors, and gravitational waves from black
hole-neutron star mergers are expected to be detected in the next few years.
Simultaneous detection of electromagnetic counterparts with gravitational-wave
detection provides rich information about the merger events. Among the possible
electromagnetic counterparts from the black hole-neutron star merger, the
emission powered by the decay of radioactive r-process nuclei, so called
kilonova/macronova, is one of the best targets for follow-up observation. We
derive fitting formulas for the mass and the velocity of ejecta from a generic
black hole-neutron star merger based on recently performed numerical relativity
simulations. We combined these fitting formulas with a new semi-analytic model
for a black hole-neutron star kilonova/macronova lightcurve which reproduces
the results of radiation-transfer simulations. Specifically, the semi-analytic
model reproduces the result of each band magnitude obtained by the radiation
transfer simulations within ~1 mag. By using this semi-analytic model, we found
that, at 400 Mpc, the kilonova/macronova is as bright as 22-24 mag for the
cases with a small chirp mass and a high black hole spin, and >28 mag for a
large chirp mass and a low black hole spin. We also apply our model to
GRB130603B as an illustration, and show that a black hole-neutron star merger
with a rapidly spinning black hole and a large neutron star radius is favored.",1601.07711v3
2017-06-08,Three--Dimensional parton structure of light nuclei,"Two promising directions beyond inclusive deep inelastic scattering
experiments, aimed at unveiling the three dimensional structure of the bound
nucleon, are reviewed, considering in particular the $^3$He nucleus. The 3D
structure in coordinate space can be accessed through deep exclusive processes,
whose non-perturbative part is encoded in generalized parton distributions
(GPDs). In this way, the distribution of partons in the transverse plane can be
obtained. As an example, coherent deeply virtual Compton scattering (DVCS) off
$^3$He nuclei, important to access the neutron GPDs, will be discussed. In
Impulse Approximation (IA), the sum of two GPDs of $^3$He, $H$ and $E$, at low
momentum transfer, turns out to be dominated by the neutron contribution.
Besides, a technique, able to take into account the nuclear effects included in
the Impulse Approximation analysis, has been developed. The spin dependent GPD
$\tilde H$ of $^3$He is also found to be largely dominated, at low momentum
transfer, by the neutron contribution. Semi-inclusive deep inelastic scattering
processes access the momentum space 3D structure parameterized through
transverse momentum dependent parton distributions. A distorted spin-dependent
spectral function has been recently introduced for $^3$He, in a
non-relativistic framework, to take care of the final state interaction between
the observed pion and the remnant in semi-inclusive deep inelastic electron
scattering off transversely polarized $^3$He. The calculation of the Sivers and
Collins single spin asymmetries for $^3$He, and a straightforward procedure to
effectively take into account nuclear dynamics and final state interactions,
will be reviewed. The Light-front dynamics generalization of the analysis is
also addressed.",1706.02626v1
2018-04-19,The Ultrafast Einstein-De Haas Effect,"The original observation of the Einstein-de Haas effect was a landmark
experiment in the early history of modern physics that illustrates the
relationship between magnetism and angular momentum. Today the effect is still
discussed in elementary physics courses to demonstrate that the angular
momentum associated with the aligned electron spins in a ferromagnet can be
converted to mechanical angular momentum by reversing the direction of
magnetisation using an external magnetic field. In recent times, a related
problem in magnetism concerns the time-scale over which this angular momentum
transfer can occur. It is known experimentally for several metallic
ferromagnets that intense photoexcitation leads to a drop in the magnetisation
on a time scale shorter than 100 fs, a phenomenon called ultrafast
demagnetisation. The microscopic mechanism for this process has been hotly
debated, with one key question still unanswered: where does the angular
momentum go on these sub-picosecond time scales? Here we show using femtosecond
time-resolved x-ray diffraction that a large fraction of the angular momentum
lost from the spin system on the laserinduced demagnetisation of ferromagnetic
iron is transferred to the lattice on sub-picosecond timescales, manifesting as
a transverse strain wave that propagates from the surface into the bulk. By
fitting a simple model of the x-ray data to simulations and optical data, we
roughly estimate that the angular momentum occurs on a time scale of 200 fs and
corresponds to 80% of the angular momentum lost from the spin system. Our
results show that interaction with the lattice plays an essential role in the
process of ultrafast demagnetisation in this system.",1804.07159v2
2021-08-13,Hyperpolarized solution-state NMR spectroscopy with optically polarized crystals,"Nuclear spin hyperpolarization provides a promising route to overcome the
challenges imposed by the limited sensitivity of nuclear magnetic resonance.
Here we demonstrate that dissolution of spin-polarized pentacene-doped
naphthalene crystals enables transfer of polarization to target molecules via
intermolecular cross relaxation at room temperature and moderate magnetic
fields (1.45$\,$T). This makes it possible to exploit the high spin
polarization of optically polarized crystals while mitigating the challenges of
its transfer to external nuclei, particularly of the large distances and
prohibitively weak coupling between source and target nuclei across solid-solid
or solid-liquid interfaces. With this method, here we inject the highly
polarized mixture into a benchtop NMR spectrometer and observe the polarization
dynamics for target $^1$H nuclei. Although the spectra are radiation damped due
to the high naphthalene magnetization, we describe a procedure to process the
data in order to obtain more conventional NMR spectra, and extract the target
nuclei polarization. With the entire process occurring on a timescale of one
minute, we observe NMR signals enhanced by factors between -200 and -1730 at
1.45$\,$T for a range of small molecules.",2108.06147v2
2021-08-23,Constraints on compact binary merger evolution from spin-orbit misalignment in gravitational-wave observations,"The identification of the first confirmed neutron star - black hole (NS-BH)
binary mergers by the LIGO, Virgo and KAGRA collaboration provides the
opportunity to investigate the properties of the early sample of confirmed and
candidate events. Here, we focus primarily on the tilt angle of the black
hole's spin relative to the orbital angular momentum vector of the binary, and
the implications for the physical processes that determine this tilt. The
posterior tilt distributions of GW200115 and the candidate events
GW190426_152155 and GW190917_114630 peak at significantly anti-aligned
orientations (though display wide distributions). Producing these tilts through
isolated binary evolution would require stronger natal kicks than are typically
considered (and preferentially-polar kicks would be ruled out), and/or an
additional source of tilt such as stable mass transfer. The early sample of
NS-BH events are less massive than expected for classical formation channels,
and may provide evidence for efficient mass transfer that results in the merger
of more massive NS-BH binaries before their evolution to the compact phase is
complete. We predict that future gravitational-wave detections of NS-BH events
will continue to display total binary masses of $\approx 7$ M$_{\odot}$ and
mass ratios of $q \sim 3$ if this interpretation is correct. Conversely, the
high mass of the candidate GW191219_163120 suggests a dynamical capture origin.
Large tilts in a significant fraction of merging NS-BH systems would weaken the
prospects for electromagnetic detection. However, EM observations, including
non-detections, can significantly tighten the constraints on spin and mass
ratio.",2108.10184v2
2022-09-12,A magnetic valve at L1 revealed in TESS photometry of the asynchronous polar BY Cam,"We present TESS photometry of the asynchronous polar BY Cam, which undergoes
a beat-cycle between the 199.384-min white dwarf (WD) spin period and the
201.244-min orbital period. This results in changes in the flow of matter onto
the WD. The TESS light curve covers 92% of the beat cycle once and 71% of the
beat cycle twice. The strongest photometric signal, at 197.560-min, is ascribed
to a side-band period. During times of light-curve stability, the photometry
modulates at the spin frequency, supporting our WD spin-period identification.
Both one-pole and two-pole accretion configurations repeat from one beat cycle
to the next with clear and repeatable beat-phase dependent intensity
variations. To explain these, we propose the operation of a magnetic valve at
L1. The magnetic valve modulates the mass-transfer rate, as evidenced by a
factor of 5 variation in orbital-averaged intensity, over the course of the
beat cycle in a repeatable manner. The accretion stream threading distance from
the WD is also modulated at the beat-period, because of the variation of the WD
magnetic field with respect to the stream and because of changes in the mass
transfer rate due to the operation of the magnetic valve. Changes in the
threading distance result in significant shifts in the position of accreting
spots around the beat cycle. As a consequence, only the faintest photometric
minima allow for an accurate ephemeris determination. Three regions on the
white dwarf appear to receive most of the accretion flow, suggestive of a
complex WD magnetic field.",2209.05524v1
2023-09-18,From ZAMS to Merger: Detailed Binary Evolution Models of Coalescing Neutron Star-Black Hole Systems at Solar Metallicity,"Neutron star $-$ black hole (NSBH) merger events bring us new opportunities
to constrain theories of stellar and binary evolution, and understand the
nature of compact objects. In this work, we investigate the formation of
merging NSBH binaries at solar metallicity by performing a binary population
synthesis study of merging NSBH binaries with the newly developed code POSYDON.
The latter incorporates extensive grids of detailed single and binary evolution
models, covering the entire evolution of a double compact object progenitor. We
explore the evolution of NSBHs originating from different formation channels,
which in some cases differ from earlier studies performed with rapid binary
population synthesis codes. Then, we present the population properties of
merging NSBH systems and their progenitors such as component masses, orbital
features, and BH spins, and investigate the model uncertainties in our
treatment of common envelope (CE) evolution and core-collapse process. We find
that at solar metallicity, under the default model assumptions, most of the
merging NSBHs have BH masses in a range of $3-11\,M{_\odot}$ and chirp masses
within $1.5-4\,M{_\odot}$. Independently of our model variations, the BH always
forms first with dimensionless spin parameter $\lesssim 0.2$, which is
correlated to the initial binary orbital period. Some BHs can subsequently spin
up moderately ($\chi_{\rm BH} \lesssim 0.4$) due to mass transfer, which we
assume to be Eddington limited. Binaries that experienced CE evolution rarely
demonstrate large tilt angles. Conversely, approximately $40\%$ of the binaries
that undergo only stable mass transfer without CE evolution contain an
anti-aligned BH. Finally, accounting for uncertainties in both the population
modeling and the NS equation of state, we find that $0-18.6\%$ of NSBH mergers
may be accompanied by an electromagnetic counterpart.",2309.09600v1
2024-01-11,First investigation on the isomeric ratio in multinucleon transfer reactions: Entrance channel effects on the spin distribution,"The multinucleon transfer (MNT) reaction approach was successfully employed
for the first time to measure the isomeric ratios (IRs) of $^{211}$Po
(25/2$^+$) isomer and its (9/2$^+$) ground state at the IGISOL facility using a
945 MeV $^{136}$Xe beam impinged on $^{209}$Bi and $^{\rm nat}$Pb targets. The
dominant production of isomers compared to the corresponding ground states was
consistently revealed in the $\alpha$-decay spectra. Deduced IR of $^{211}$Po
populated through the $^{136}$Xe+$^{\rm nat}$Pb reaction was found to enhance
$\approx$1.8-times than observed for $^{136}$Xe+$^{209}$Bi. State-of-the-art
Langevin-type model calculations have been utilized to estimate the spin
distribution of an MNT residue. The computations qualitatively corroborate with
the considerable increase in IRs of $^{211}$Po produced from $^{136}$Xe+$^{\rm
nat}$Pb compared to $^{136}$Xe+$^{209}$Bi. Theoretical investigations indicate
a weak influence of target spin on IRs. The enhancement of the $^{211}$Po
isomer in the $^{136}$Xe+$^{\rm nat}$Pb over $^{136}$Xe+$^{209}$Bi can be
attributed to the different proton ($p$)-transfer production routes.
Estimations demonstrate an increment in the angular momentum transfer,
favorable for isomer production, with increasing projectile energy. Comparative
analysis indicates the two entrance channel parameters, projectile mass and
$p$-transfer channels, strongly influencing the population of the high-spin
isomer of $^{211}$Po (25/2$^+$). This is the first experimental and theoretical
investigation on the IRs of nuclei produced via different channels of MNT
reactions, with the latter quantitatively underestimating the former by a
factor of two.",2401.06206v2
2002-08-01,Radio ejection in the evolution of X-ray binaries: the bridge between low mass X-ray binaries and millisecond pulsars,"We present a scenario for the spin-up and evolution of binary millisecond
pulsars. This can explain the observational properties of the recently
discovered binary millisecond pulsar PSR J1740-5340, with orbital period 32.5
hrs, in the Globular Cluster NGC 6397. The optical counterpart of this system
is a star as luminous as the cluster turnoff stars, but with a lower Teff (a
larger radius) which we model with a star of initial mass compatible with the
masses evolving in the cluster (~0.85 Msun). This star has suffered Roche lobe
overflow while evolving off the main sequence, spinning up the neutron star to
the present period of 3.65 ms. There are evidences that at present, Roche lobe
overflow is still going on. Indeed Roche lobe deformation of the mass losing
component is necessary to be compatible with the optical light curve. The
presence of matter around the system is also consistent with the long lasting
irregular radio eclipses seen in the system. We propose that this system is
presently in a phase of `radio-ejection' mass loss. The radio-ejection phase
can be initiated only if the system is subject to intermittency in the mass
transfer during the spin-up phase. In fact, when the system is detached the
pulsar radio emission is not quenched, and may be able to prevent further mass
accretion due to the action of the pulsar pressure at the inner Lagrangian
point.",0208021v1
2006-09-06,Heating of the Intergalactic Medium by Primordial Miniquasars,"A simple analytical model is used to calculate the X-ray heating of the IGM
for a range of black hole masses. This process is efficient enough to decouple
the spin temperature of the intergalactic medium from the cosmic microwave
background (CMB) temperature and produce a differential brightness temperature
of the order of $\sim 5-20 \mathrm{mK}$ out to distances as large as a few
co-moving Mpc, depending on the redshift, black hole mass and lifetime. We
explore the influence of two types of black holes, those with and without
ionising UV radiation. The results of the simple analytical model are compared
to those of a full spherically symmetric radiative transfer code. Two simple
scenarios are proposed for the formation and evolution of black hole mass
density in the Universe. The first considers an intermediate mass black hole
that form as an end-product of Population III stars, whereas the second
considers super-massive black holes that form directly through the collapse of
massive halos with low spin parameter. These scenarios are shown not to violate
any of the observational constraints, yet produce enough X-ray photons to
decouple the spin-temperature from that of the CMB. This is an important issue
for future high redshift 21 cm observations.",0609151v2
1995-08-21,Magnetism and Structural Distortion in the La0.7Sr0.3MnO3 Metallic Ferromagnet,"Neutron scattering studies on a single crystal of the highly-correlated
electron system, La1-xSrxMnO3 with x~0.3, have been carried out elucidating
both the spin and lattice dynamics of this metallic ferromagnet. We report a
large measured value of the spin wave stiffness constant, which directly shows
that the electron transfer energy of the d band is large. The spin dynamics,
including magnetic critical scattering, demonstrate that this material behaves
similar to other typical metallic ferromagnets such as Fe or Ni. The crystal
structure is rhombohedral, as previously reported, for all temperatures studied
(below ~425K). We have observed new superlattice peaks which show that the
primary rhombohedral lattice distortion arises from oxygen octahedra rotations
resulting in an R-3c structure. The superlattice reflection intensities which
are very sensitive to structural changes are independent of temperature
demonstrating that there is no primary lattice distortion anomaly at the
magnetic transition temperature, Tc = 378.1 K, however there is a lattice
contraction.",9508087v1
1996-04-09,Correlation functions in the two-dimensional random-bond Ising model,"We consider long strips of finite width $L \leq 13$ sites of ferromagnetic
Ising spins with random couplings distributed according to the binary
distribution: $P(J_{ij})= {1 \over 2} ( \delta (J_{ij} -J_0) + \delta (J_{ij}
-rJ_0) ) ,\ 0 < r < 1 $. Spin-spin correlation functions $ <\sigma_{0}
\sigma_{R}>$ along the ``infinite'' direction are computed by transfer-matrix
methods, at the critical temperature of the corresponding two-dimensional
system, and their probability distribution is investigated. We show that,
although in-sample fluctuations do not die out as strip length is increased,
averaged values converge satisfactorily. These latter are very close to the
critical correlation functions of the pure Ising model, in agreement with
recent Monte-Carlo simulations. A scaling approach is formulated, which
provides the essential aspects of the $R$-- and $L$-- dependence of the
probability distribution of $\ln <\sigma_{0} \sigma_{R}>$, including the result
that the appropriate scaling variable is $R/L$. Predictions from scaling theory
are borne out by numerical data, which show the probability distribution of
$\ln <\sigma_{0} \sigma_{R}>$ to be remarkably skewed at short distances,
approaching a Gaussian only as $R/L \gg 1$ .",9604053v1
1997-06-19,Universality and logarithmic corrections in two-dimensional random Ising ferromagnets,"We address the question of weak versus strong universality scenarios for the
random-bond Ising model in two dimensions. A finite-size scaling theory is
proposed, which explicitly incorporates $\ln L$ corrections ($L$ is the linear
finite size of the system) to the temperature derivative of the correlation
length. The predictions are tested by considering long, finite-width strips of
Ising spins with randomly distributed ferromagnetic couplings, along which free
energy, spin-spin correlation functions and specific heats are calculated by
transfer-matrix methods. The ratio $\gamma/\nu$ is calculated and has the same
value as in the pure case; consequently conformal invariance predictions remain
valid for this type of disorder. Semilogarithmic plots of correlation functions
against distance yield average correlation lengths $\xi^{av}$, whose size
dependence agrees very well with the proposed theory. We also examine the size
dependence of the specific heat, which clearly suggestsa divergency in the
thermodynamic limit. Thus our data consistently favour the Dotsenko-Shalaev
picture of logarithmic corrections (enhancements) to pure system singularities,
as opposed to the weak universality scenario.",9706202v1
1999-06-08,"Universality, frustration and conformal invariance in two-dimensional random Ising magnets","We consider long, finite-width strips of Ising spins with randomly
distributed couplings. Frustration is introduced by allowing both ferro- and
antiferromagnetic interactions. Free energy and spin-spin correlation functions
are calculated by transfer-matrix methods. Numerical derivatives and
finite-size scaling concepts allow estimates of the usual critical exponents
$\gamma/\nu$, $\alpha/\nu$ and $\nu$ to be obtained, whenever a second-order
transition is present. Low-temperature ordering persists for suitably small
concentrations of frustrated bonds, with a transition governed by pure--Ising
exponents. Contrary to the unfrustrated case, subdominant terms do not fit a
simple, logarithmic-enhancement form. Our analysis also suggests a vertical
critical line at and below the Nishimori point. Approaching this point along
either the temperature axis or the Nishimori line, one finds non-diverging
specific heats. A percolation-like ratio $\gamma/\nu$ is found upon analysis of
the uniform susceptibility at the Nishimori point. Our data are also consistent
with frustration inducing a breakdown of the relationship between
correlation-length amplitude and critical exponents, predicted by conformal
invariance for pure systems.",9906114v1
2000-04-21,The 1/2-XXZ spin-chain at finite magnetic field: Crossover phenomena driven by temperature,"We investigate the asymptotic behaviour of spin-spin correlation functions
for the integrable Heisenberg chain. To this end we use the Quantum Transfer
Matrix (QTM) technique developed in \cite{AK} which results in a set of
non-linear integral equations (NLIE). In the case of the largest eigenvalue the
solution to these equations yields the free energy and by modifications of the
paths of integration the next-leading eigenvalues and hence the correlation
lengths are obtained. At finite field $h>0$ and sufficiently high temperature
$T$ the next-leading eigenvalue is unique and given by a 1-string solution to
the QTM taking real and negative values thus resulting into exponentially
decaying correlations with antiferromagnetic oscillations. At sufficiently low
temperatures a different behaviour sets in where the next-leading eigenvalues
of QTM are given by a complex conjugate pair of eigenvalues resulting into
incommensurate oscillations.
  The above scenario is the result of analytical and numerical investigations
of the QTM establishing a well defined crossover temperature $T_c(h)$ at which
the 1-string eigenvalue to the QTM gets degenerate with the 2-string solution.
Among other things we find a simple particle-hole picture for the excitations
of the QTM and we make contact with the dressed charge formulation of CFT.",0004379v2
2000-05-04,Optical Properties of the Spin-Ladder Compound Sr_{14}Cu_{24}O_{41},"We report the measurements of the pseudodielectric function, far-infrared
reflectivity and Raman scattering spectra in Sr_{14}Cu_{24}O_{41} single
crystal. We study the lattice and the spin dynamics of the Cu$_2$O$_3$ spin
ladders and CuO$_2$ chains of this compound. The ellipsometric and the optical
reflectivity measurements yield the gap values of 1.4 eV, 1.86 eV, 2.34 eV (2.5
eV) for the ladders (chains) along the {\bf c}-axis and 2.4 eV along the {\bf
a}-axis. The electronic structure of the Cu$_2$O$_3$ ladders is analyzed using
tight-binding approach for the correlated electron systems. The correlation gap
value of 1.4 eV is calculated with the transfer energy (hopping) parameters
$t=t_{0}$=0.26 eV, along and perpendicular to legs, $t_{xy}$=0.026 eV
(interladder hopping) and U=2.1 eV, as a Coulomb repulsion. The optical
parameters of the infrared active phonons and plasmons are obtained by
oscillator fitting procedure of the reflectivity spectra. Raman scattering
spectra are measured at different temperatures using different laser line
energies. The two-magnon peak is observed at about 2880 cm$^{-1}$. At
temperatures below 150 K the new infrared and Raman modes appear due to the
charge ordering.",0005096v1
2001-06-01,"The two-dimensional random-bond Ising model, free fermions and the network model","We develop a recently-proposed mapping of the two-dimensional Ising model
with random exchange (RBIM), via the transfer matrix, to a network model for a
disordered system of non-interacting fermions. The RBIM transforms in this way
to a localisation problem belonging to one of a set of non-standard symmetry
classes, known as class D; the transition between paramagnet and ferromagnet is
equivalent to a delocalisation transition between an insulator and a quantum
Hall conductor. We establish the mapping as an exact and efficient tool for
numerical analysis: using it, the computational effort required to study a
system of width $M$ is proportional to $M^{3}$, and not exponential in $M$ as
with conventional algorithms. We show how the approach may be used to calculate
for the RBIM: the free energy; typical correlation lengths in quasi-one
dimension for both the spin and the disorder operators; even powers of
spin-spin correlation functions and their disorder-averages. We examine in
detail the square-lattice, nearest-neighbour $\pm J$ RBIM, in which bonds are
independently antiferromagnetic with probability $p$, and ferromagnetic with
probability $1-p$. Studying temperatures $T\geq 0.4J$, we obtain precise
coordinates in the $p-T$ plane for points on the phase boundary between
ferromagnet and paramagnet, and for the multicritical (Nishimori) point. We
demonstrate scaling flow towards the pure Ising fixed point at small $p$, and
determine critical exponents at the multicritical point.",0106023v3
2002-05-09,Optical Conductivity $σ(ω)$ and Resistivity $ρ_{dc}$ of a Hole Doped Spin-Fermion Model for Cuprates,"The optical conductivity and Drude weight of a Spin-Fermion model for
cuprates are studied as a function of electronic density and temperature. This
model develops stripes and robust D-wave pairing correlation upon hole doping,
and it has the advantage that it can be numerically simulated without sign
problems. Both static and dynamical information can be obtained. In this work
it was possible to analyze up to 12x12 site clusters at low temperatures
ranging between 0.01t and 0.1t (between 50K and 500K for a hopping amplitude $t
\sim 0.5 eV$). As the temperature is reduced, spectral weight is transferred
from high to low frequencies in agreement with the behavior observed
experimentally. Varying the hole density, the Drude weight has a maximum at the
optimal doping for the model, i.e., at the density where the pairing
correlations are stronger. It was also observed that the inverse of the Drude
weight, roughly proportional to the resistivity, decreases linearly with the
temperature at optimal doping, and it is abruptly reduced when robust pairing
correlations develop upon further reducing the temperature. The behavior and
general form of the optical conductivity are found to be in good agreement with
experimental results for the cuprates. Our results also establish the
Spin-Fermion model for cuprates as a reasonable alternative to the t-J model,
which is much more difficult to study accurately.",0205201v1
2003-08-08,Dynamic Stripes and Resonance in the Superconducting and Normal Phases of YBa2Cu3O6.5 Ortho-II Superconductor,"We describe the relation between spin fluctuations and superconductivity in a
highly-ordered sample of YBaCu3O6.5 using both polarized and unpolarized
neutron inelastic scattering. The spin susceptibility in the superconducting
phase exhibits one-dimensional incommensurate modulations at low-energies,
consistent with hydrodynamic stripes. With increasing energy the susceptibility
curves upward to a commensurate, intense, well-defined and asymmetric resonance
at 33 meV with a precipitous high-energy cutoff. In the normal phase, which we
show is gapless, the resonance remains surprisingly strong and persists clearly
in Q scans and energy scans. Its similar asymmetric spectral form above Tc=59 K
suggests that incoherent superconducting pairing fluctuations are present in
the normal state. On cooling, the resonance and the stripe modulations grow in
well above Tc below a temperature that is comparable to the pseudogap
temperature where suppression occurs in local and low-momentum properties. The
spectral weight that accrues to the resonance is largely acquired by transfer
from suppressed low-energy fluctuations. We find the resonance to be
isotropically polarized, consistent with a triplet carrying ~2.6% of the total
spectral weight of the Cu spins in the planes.",0308168v2